Development of a Custom Data Acquisition System for the Study of Vehicle
Dynamics in Longer Combination Vehicles
by
Jameson Colbert
A thesis submitted to the Graduate Faculty of
Auburn University
in partial ful llment of the
requirements for the Degree of
Master of Science
Auburn, Alabama
August 2, 2014
Keywords: Heavy Truck Vehicle Dynamics, Vehicle Simulation, Data Acquisition
Copyright 2014 by Jameson Colbert
Approved by
David Bevly, Chair, Albert J. Smith Jr. Professor of Mechanical Engineering
David Beale, Professor of Mechanical Engineering
Song-yul Choe, Associate Professor of Mechanical Engineering
Thaddeus Roppel, Associate Professor of Electrical and Computer Engineering
Abstract
This thesis details the development, deployment, and veri cation of a custom data
acquisition system for the purpose of studying vehicle dynamics in a triple trailer Longer
Combination Vehicle (LCV). In addition to the data acquisition the thesis details the sim-
ulation e orts that were undertaken to both verify the experimental data as well as assess
the stability of the vehicle itself. The research was part of an e ort to assess the viability of
widening the available roadways that are currently accessible to LCV trailers. This project
undertook the task of fully instrumenting a triple trailer LCV with a package of more than
35 sensors and implementation of a custom Data Acquisition System (DAQ) to log over 200
channels coming from the aforementioned sensors. Once out tted with the sensor package,
the LCV was put through a variety of dynamic tests including lane changes and constant
radius turns in an attempt to capture various dynamic characteristics of the vehicle.
A series of simulations were run to match the maneuvers undertaken during the experi-
mental phase. That data was then compared to ensure that the simulation did indeed agree
with the experimental data. Once in agreement the simulations were expanded to speeds
that were not able to be achieved experimentally due to safety concerns. The last element
of the simulation was a comparison between the LCV triple and a standard double trailer
heavy truck as seen on the highways today.
The LCV under test behaved as expected given the prior research into LCV dynamics.
Additionally the simulation and the experimental data were shown to agree. The simulation
exposed the instability of the vehicle at speeds easily expected on the highways. When
comparing the triple LCV to the double it was shown that at lower speeds the  rst four
units behaved similarly, but as the speeds increased the e ects of the third trailer were
shown in the responses of the second. Finally this thesis shows that there is a need for heavy
ii
precautions before allowing triple LCV to traverse the highway roads. At lower speeds the
vehicle is safe but increasing that speed to that of the standard highway speed shows that
the vehicle will respond with undesirable outputs.
iii
Acknowledgments
There are many people to thank individually that helped me get to this stage in both
my education and my life. The person that is at the top of that list is my wife, Katherine.
She has stood by and endured the long hours, missed deadlines, and setbacks that have
accompanied this process. Without her, I would not be who I am today. Additionally I
would like to thank my father for  rst inspiring me to become an engineer, you taught me to
never take anything at face value and always strive to understand the ?how? with everything
in life. That skill has enabled me to achieve things that I didn?t think I would be able to.
Academically, I would like to speci cally thank Dr. David Bevly for advising my through
this process of graduate school and having faith in me from the beginning when others did
not. Additionally thanks go out to all of my engineering professors, speci cally those in the
Mechanical Engineering Department who taught me how to  nd the answers to the questions
that we face not only in the classroom but in life.
Lastly, I would like to thank the members of the GPS and Vehicle Dynamics Laboratory
for their collaboration and background knowledge that was provided on not only this project
but all projects I worked on during graduate studies. Particular thanks are expressed to Dr.
David Broderick, Ryan Hill, and Eric Broshears for assisting in the design, fabrication,
and construction of the complex data acquisition system that was implemented during this
project.
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Table of Contents
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii
List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvi
1 Introduction & Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Literature Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.1 LCV Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.2 LCV Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2 Test Vehicle Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.1 Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.1.1 Displacement Measurements . . . . . . . . . . . . . . . . . . . . . . . 26
2.1.2 Positioning Measurements . . . . . . . . . . . . . . . . . . . . . . . . 27
2.1.3 Accelerations & Rates Measurements . . . . . . . . . . . . . . . . . . 28
2.2 Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.2.1 CAN Bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.2.2 Sensor Interfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.2.3 Data Logging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2.3 Hardware Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.1 Test Track . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.2 Test Vehicle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.3 Testing Maneuvers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
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3.3.1 Constant Radius Turn . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.3.2 Single Lane Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.3.3 Double Lane Change . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.4 Data Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3.4.1 Data Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3.4.2 Data Formatting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3.4.3 RTK Corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.5 Analysis of Experimental Data . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.5.1 Understeer Characteristics . . . . . . . . . . . . . . . . . . . . . . . 54
3.5.2 Rearward Ampli cation . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.5.3 Roll Behavior of LCV Units During 40 mph Double Lane Change . . 64
3.6 Data Quality Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4 Vehicle Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.1 Vehicle Con guration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.2 Experimental Maneuver Simulation . . . . . . . . . . . . . . . . . . . . . . . 75
4.2.1 Constant Radius Turn . . . . . . . . . . . . . . . . . . . . . . . . . . 75
4.2.2 Single Lane Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
4.2.3 Double Lane Change . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
4.3 Experimental vs. Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
4.4 Double vs. Triple LCV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.4.1 Single Lane Change Comparison . . . . . . . . . . . . . . . . . . . . . 93
4.4.2 Double Lane Change Comparison . . . . . . . . . . . . . . . . . . . . 98
4.4.3 Double vs. Triple Conclusions . . . . . . . . . . . . . . . . . . . . . . 103
4.5 Sources of Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
4.6 Improvements for Future Simulations . . . . . . . . . . . . . . . . . . . . . . 104
5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
5.1 Experimental Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
vi
5.2 Simulation Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
5.3 Final Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
5.4 Future Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
A TruckSima174 Con guration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
A.1 TruckSima174 General Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 113
A.2 Model Formulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
A.2.1 Vehicle Con guration . . . . . . . . . . . . . . . . . . . . . . . . . . 114
A.2.2 Tractor Con guration . . . . . . . . . . . . . . . . . . . . . . . . . . 117
A.2.3 Trailer 1 Con guration . . . . . . . . . . . . . . . . . . . . . . . . . 121
A.2.4 Trailers 2 & 3 Con guration . . . . . . . . . . . . . . . . . . . . . . 126
A.2.5 Con guring the Converter Dollies . . . . . . . . . . . . . . . . . . . . 126
A.3 Model Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
A.4 Maneuver Paths & Con guration . . . . . . . . . . . . . . . . . . . . . . . . 133
A.4.1 The Constant Radius Maneuver . . . . . . . . . . . . . . . . . . . . . 135
A.4.2 The Single Lane Change Maneuver . . . . . . . . . . . . . . . . . . . 136
A.4.3 The Double Lane Change Maneuver . . . . . . . . . . . . . . . . . . . 139
A.4.4 Future Potential Improvements for TruckSima174 Model . . . . . . . . . 140
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List of Figures
1.1 LCV Triple Test Vehicle Maneuvering Highway Corner . . . . . . . . . . . . . . 2
1.2 Map of Approved Highway Routes for LCVs [1] . . . . . . . . . . . . . . . . . . 3
1.3 Typical Tractor & Single Semi-Trailer Combination [2] . . . . . . . . . . . . . . 6
1.4 Typical LCV Double Trailer Con guration . . . . . . . . . . . . . . . . . . . . . 7
1.5 Converter Dolly with Pintle Hitch [3] . . . . . . . . . . . . . . . . . . . . . . . . 8
1.6 Possible LCV Con gurations [4] . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.7 Rearward Ampli cation Response of Double Tank Trailer [5] . . . . . . . . . . . 13
1.8 Rearward Ampli cation Response of Various Vehicle Combinations [3] . . . . . 14
1.9 Low Speed LCV O -Tracking [4] . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.10 High Speed LCV O -Tracking [4] . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.11 Rollover Moment Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.1 Sensor Placement on LCV Triple . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.2 Sketch of Axle De ection Measurements . . . . . . . . . . . . . . . . . . . . . . 27
2.3 Celesco String Potentiometers, SR1A-62 (left) and SP1-25 (right) . . . . . . . . 27
2.4 GPS Receivers Novatel ProPak (left) u-Blox Receiver (right) . . . . . . . . . . . 28
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2.5 Illustration of Triple-Trailer Frame of Reference . . . . . . . . . . . . . . . . . . 29
2.6 MemSense Inertial Measurement Unit . . . . . . . . . . . . . . . . . . . . . . . 30
2.7 MemSense Inertial Measurement Unit . . . . . . . . . . . . . . . . . . . . . . . 31
2.8 Oxford RT Units RT2500 (left) and RT3100 (right) . . . . . . . . . . . . . . . . 32
2.9 Placement of Advantech Industrial PC . . . . . . . . . . . . . . . . . . . . . . . 33
2.10 Wiring Diagram Illustrating the Connections Between the Sensors and the DAQ 34
2.11 Diagram of CAN Bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.12 Inside of a CAN Box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.13 CAN Message Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.14 Illustration of the MOOS Architecture . . . . . . . . . . . . . . . . . . . . . . . 38
2.15 Screen Shot of Asynchronous Log File . . . . . . . . . . . . . . . . . . . . . . . 39
2.16 String Pots Mounted for Axle De ection . . . . . . . . . . . . . . . . . . . . . . 40
2.17 Example of Toolboxes Mounted Underneath Trailers for Sensor Mounting . . . . 40
2.18 Mounted CAN Box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
2.19 String Pots Mounted for Articulation Angle . . . . . . . . . . . . . . . . . . . . 42
2.20 Steer Axle String Pots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.21 String Pot Mounted for Steer Angle . . . . . . . . . . . . . . . . . . . . . . . . . 43
2.22 GPS Antenna Mounted on the Trailer Roof . . . . . . . . . . . . . . . . . . . . 44
ix
3.1 Aerial View of NCAT Test Track . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.2 Single Lane Change Maneuver Diagram . . . . . . . . . . . . . . . . . . . . . . 48
3.3 Double Lane Change Maneuver Diagram . . . . . . . . . . . . . . . . . . . . . . 50
3.4 Zones for separating data recorded on the curves from data recorded on the
straights. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.5 ISO standard frame-of-reference with Y to the left and Z up. . . . . . . . . . . . 52
3.6 Raw vs. Post Processed Angular Rates. . . . . . . . . . . . . . . . . . . . . . . 52
3.7 Constant Radius Maneuver Path Overlay. . . . . . . . . . . . . . . . . . . . . . 55
3.8 Sections of Constant Radius Maneuver. . . . . . . . . . . . . . . . . . . . . . . . 58
3.9 Sections of Constant Radius Maneuver. . . . . . . . . . . . . . . . . . . . . . . . 58
3.10 Tractor 1 Steering Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
3.11 Double Lane Change Steering Input (20 mph) . . . . . . . . . . . . . . . . . . . 63
3.12 Double Lane Change Steering Input (40 mph) . . . . . . . . . . . . . . . . . . . 64
3.13 Steering Axle Body Roll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
3.14 Drive Axle Body Roll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
3.15 Trailer Body Roll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
3.16 LCV Body Roll (Un-Filtered) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
3.17 LCV Body Roll (Filtered) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
3.18 Lever arm mounting for string pots . . . . . . . . . . . . . . . . . . . . . . . . . 69
x
4.1 Screen Shot of TruckSima174 Environment . . . . . . . . . . . . . . . . . . . . . . 72
4.2 Screen Shot of TruckSima174 Steering Path Input for Double Lane Change . . . . 73
4.3 Steering Wheel Response to No Steering Input . . . . . . . . . . . . . . . . . . 74
4.4 Yaw Response to No Steering Input . . . . . . . . . . . . . . . . . . . . . . . . . 74
4.5 Screen Shot of Animation for Constant Radius Turn . . . . . . . . . . . . . . . 76
4.6 Path of LCV During Constant Radius Turn . . . . . . . . . . . . . . . . . . . . 76
4.7 Roll of Each Unit for 25 mph Constant Radius Turn . . . . . . . . . . . . . . . 77
4.8 Roll of Each Unit for 40 mph Constant Radius Turn . . . . . . . . . . . . . . . 77
4.9 Unit O -Tracking During 40 mph Constant Radius Turn . . . . . . . . . . . . . 78
4.10 Path of LCV During 25 mph Single Lane Change . . . . . . . . . . . . . . . . . 79
4.11 Low Speed O -Tracking During 25 mph Single Lane Change . . . . . . . . . . . 79
4.12 Path of LCV During 45 mph Single Lane Change . . . . . . . . . . . . . . . . . 80
4.13 High Speed O -Tracking During 45 mph Single Lane Change . . . . . . . . . . 80
4.14 Lateral Acceleration During 25 mph Single Lane Change . . . . . . . . . . . . . 81
4.15 Lateral Acceleration During 45 mph Single Lane Change . . . . . . . . . . . . . 81
4.16 Unit Yaw During 25 mph Single Lane Change . . . . . . . . . . . . . . . . . . . 82
4.17 Unit Yaw During 45 mph Single Lane Change . . . . . . . . . . . . . . . . . . . 82
4.18 Path of LCV During 25 mph Double Lane Change . . . . . . . . . . . . . . . . 83
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4.19 Path of LCV During 45 mph Double Lane Change . . . . . . . . . . . . . . . . 83
4.20 Low Speed O -Tracking During 25 mph Double Lane Change (1st Lane Change) 84
4.21 High Speed O -Tracking During 45 mph Double Lane Change (1st Lane Change) 84
4.22 Low Speed O -Tracking During 25 mph Double Lane Change (2nd Lane Change) 85
4.23 High Speed O -Tracking During 45 mph Double Lane Change (2nd Lane Change) 85
4.24 Lateral Acceleration During 25 mph Double Lane Change . . . . . . . . . . . . 86
4.25 Lateral Acceleration During 45 mph Double Lane Change . . . . . . . . . . . . 86
4.26 Lateral Acceleration During 60 mph Double Lane Change . . . . . . . . . . . . 87
4.27 Unit Roll During 60 mph Double Lane Change . . . . . . . . . . . . . . . . . . 88
4.28 Steering Input Comparison for Simulation & Experimental Data . . . . . . . . . 89
4.29 Dolly 1 Articulation Angle Comparison for Simulation & Experimental Data . . 90
4.30 Dolly 2 Articulation Angle Comparison for Simulation & Experimental Data . . 90
4.31 Trailer 1 Roll Comparison for Simulation & Experimental Data . . . . . . . . . 91
4.32 Trailer 3 Roll Comparison for Simulation & Experimental Data . . . . . . . . . 92
4.33 45 mph Single Lane Change Double vs. Triple Yaw Comparison . . . . . . . . . 93
4.34 55 mph Single Lane Change Double vs. Triple Yaw Comparison . . . . . . . . . 94
4.35 65 mph Single Lane Change Double vs. Triple Yaw Comparison . . . . . . . . . 94
4.36 45 mph Single Lane Change Double vs. Triple Roll Comparison . . . . . . . . . 95
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4.37 55 mph Single Lane Change Double vs. Triple Roll Comparison . . . . . . . . . 95
4.38 65 mph Single Lane Change Double vs. Triple Roll Comparison . . . . . . . . . 96
4.39 45 mph Single Lane Change Double vs. Triple Lateral Acceleration Comparison 97
4.40 55 mph Single Lane Change Double vs. Triple Lateral Acceleration Comparison 97
4.41 65 mph Single Lane Change Double vs. Triple Lateral Acceleration Comparison 98
4.42 45 mph Double Lane Change Double vs. Triple Yaw Comparison . . . . . . . . 99
4.43 55 mph Double Lane Change Double vs. Triple Yaw Comparison . . . . . . . . 99
4.44 60 mph Double Lane Change Double vs. Triple Yaw Comparison . . . . . . . . 100
4.45 45 mph Double Lane Change Double vs. Triple Roll Comparison . . . . . . . . 100
4.46 55 mph Double Lane Change Double vs. Triple Roll Comparison . . . . . . . . 101
4.47 60 mph Double Lane Change Double vs. Triple Roll Comparison . . . . . . . . 101
4.48 45 mph Double Lane Change Double vs. Triple Lateral Acceleration Comparison 102
4.49 55 mph Double Lane Change Double vs. Triple Lateral Acceleration Comparison 102
4.50 60 mph Double Lane Change Double vs. Triple Lateral Acceleration Comparison 103
5.1 Unit Roll During 55 mph Double Lane Change . . . . . . . . . . . . . . . . . . 107
5.2 Unit Roll During 60 mph Double Lane Change . . . . . . . . . . . . . . . . . . 108
A.1 Screen Shot of Simulation Animation . . . . . . . . . . . . . . . . . . . . . . . . 114
A.2 TruckSim Main Window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
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A.3 TruckSim Vehicle Window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
A.4 TruckSim Custom Second Trailer Con guration . . . . . . . . . . . . . . . . . . 117
A.5 Vehicle Con guration Window . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
A.6 Steer Axle Kinematic Con guration Window . . . . . . . . . . . . . . . . . . . . 120
A.7 Steer Axle Suspension Con guration Window . . . . . . . . . . . . . . . . . . . 121
A.8 Steer Axle Roll Sti ness Con guration Window . . . . . . . . . . . . . . . . . . 122
A.9 Drive Axle Kinematic Con guration Window . . . . . . . . . . . . . . . . . . . 122
A.10 Drive Axle Roll Steer Window . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
A.11 Trailer Main Con guration Window . . . . . . . . . . . . . . . . . . . . . . . . 123
A.12 Trailer 1 Axle Kinematics Window . . . . . . . . . . . . . . . . . . . . . . . . . 125
A.13 Trailer 1 Axle Leaf Suspension Con guration Window . . . . . . . . . . . . . . 125
A.14 Trailer 1 Roll Sti ness Con guration Window . . . . . . . . . . . . . . . . . . . 126
A.15 Trailer 1 Payload Con guration Window . . . . . . . . . . . . . . . . . . . . . . 127
A.16 Converter Dolly Con guration Window . . . . . . . . . . . . . . . . . . . . . . . 129
A.17 Converter Dolly Sprung Mass Con guration Window . . . . . . . . . . . . . . . 130
A.18 Converter Dolly Kinematics Con guration Window . . . . . . . . . . . . . . . . 131
A.19 Converter Dolly Kinematics Con guration Window . . . . . . . . . . . . . . . . 131
A.20 Converter Dolly Roll Sti ness Con guration Window . . . . . . . . . . . . . . . 132
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A.21 Unit Yaw During Open-Loop Maneuver . . . . . . . . . . . . . . . . . . . . . . 133
A.22 Steering Wheel Angle During Open-Loop Maneuver . . . . . . . . . . . . . . . . 134
A.23 Screen Shot of Maneuver Setup Screen . . . . . . . . . . . . . . . . . . . . . . . 134
A.24 Constant Radius Path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
A.25 3D Representation of Gradual Lane Twist . . . . . . . . . . . . . . . . . . . . . 137
A.26 Gradual Lane Twist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
A.27 Single Lane Change Driver Input . . . . . . . . . . . . . . . . . . . . . . . . . . 138
A.28 Single Lane Change Cone Positions . . . . . . . . . . . . . . . . . . . . . . . . . 138
A.29 Double Lane Change Driver Input . . . . . . . . . . . . . . . . . . . . . . . . . 139
A.30 Double Lane Change Cone Positions . . . . . . . . . . . . . . . . . . . . . . . . 140
xv
List of Tables
1.1 E ciency Comparison Single Trailer vs. LCV Triple . . . . . . . . . . . . . . . 4
1.2 Low Speed O -Tracking Results [3] . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.3 Legend for Table 1.2, Table 1.4, and Figure 1.8 [3] . . . . . . . . . . . . . . . . . 17
1.4 High Speed O -Tracking Results [3] . . . . . . . . . . . . . . . . . . . . . . . . 18
1.5 Resulting Dynamics from Understeer/Oversteer Combinations [6] . . . . . . . . 22
2.1 Summary of Measurements and Sensors . . . . . . . . . . . . . . . . . . . . . . 25
2.2 MemSense Performance Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.3 CrossBow Nav 440 Performance Statistics . . . . . . . . . . . . . . . . . . . . . 31
2.4 Oxford RT2500/3100 Performance Statistics . . . . . . . . . . . . . . . . . . . . 32
3.1 Understeer Gradient Calculations for LCV Tractor . . . . . . . . . . . . . . . . 59
3.2 Understeer Gradient Calculations for LCV Trailer 1 . . . . . . . . . . . . . . . . 60
3.3 Understeer Gradient Calculations for LCV Trailer 2 . . . . . . . . . . . . . . . . 61
3.4 Understeer Gradient Calculations for LCV Trailer 3 . . . . . . . . . . . . . . . . 61
3.5 Rearward Ampli cation for LCV during 40 mph Double Lane Change . . . . . . 67
4.1 Simulation Plot Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
A.1 TruckSim Main Set-Up Screen Options . . . . . . . . . . . . . . . . . . . . . . . 115
A.2 TruckSim Vehicle Con guration Options . . . . . . . . . . . . . . . . . . . . . . 116
A.3 TruckSim Custom Solver Options . . . . . . . . . . . . . . . . . . . . . . . . . . 118
A.4 TruckSim Tractor Set-Up Screen Options . . . . . . . . . . . . . . . . . . . . . . 119
A.5 Trailer Con guration Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
A.6 NCAT Vehicle Gross Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
A.7 Trailer Linkage Con guration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
A.8 Converter Dolly Con guration Options . . . . . . . . . . . . . . . . . . . . . . . 129
A.9 TruckSim Maneuver Set-Up Screen Options . . . . . . . . . . . . . . . . . . . . 135
xvi
Chapter 1
Introduction & Background
Highway safety has been and for the foreseeable future will always be a topic of great
concern and research. The most prominent reason for that are auto accident fatalities. In
2011 alone, a total of 32,367 people died as a result of a car accident[7]. Most individuals
 nd themselves weary of driving next to or in the vicinity of large trucks as they fear being
involved in an accident with one. of the 32,367 fatalities, 3,373 people where killed in
accidents in 2011 involving large trucks. Of those 3,373 people, only 16% (553) of those
where occupants of the large truck; the rest being either occupants of another vehicle or
pedestrians[7]. So when discussing the safety and stability of large vehicles the people most
a ected by these results are the individuals driving in the vicinity the large trucks and not
actually the occupants of the large trucks itself. To that e ect there needs to be a good
amount of certainty that a large vehicle is stable before it is permitted on highway systems
in all states. Currently the only large trucks allowed to operate on all highways in the 50
states are single semi-trailer and smaller double trailer units.
Tractor trailers are everywhere, single tractors pulling a single trailer are as common
as a family sedan on today?s highways and interstates. To some degree the same can be
said for a tractor pulling a pair of ?pup trailers? (28 ft semitrailers); this con guration is
referred to as as a double. Both of those combinations are used to transport low-density
freight across the nation as both are permitted on the highways in all 50 states. The topic of
concern and the focus of this thesis will be the assessment of stability of triple-trailer LCVs,
and a comparison of the triple-trailer con guration to the double-trailer con guration using
computer simulations. The term ?LCV? is an acronym for Longer Combination Vehicle and
is used to describe a combination of two or more trailers with a gross weight in excess of
1
80,000 lb. The most common LCV combinations are two trailers where one is longer than
28 ft or a series of three pup trailers. The test vehicle used in this project is that of a single
tractor pulling three pup trailers, it can be seen in Figure 1.1.
Figure 1.1: LCV Triple Test Vehicle Maneuvering Highway Corner
The research done on this project included both experimental results involving the triple-
trailer and computer simulations of the same vehicle. The experimental data was obtained
by instrumenting the vehicle shown in Figure 1.1; which is one of the vehicles used at the
National Center for Asphalt Technologies (NCAT) for asphalt life cycle testing. The vehicle
was then put through a variety of standard dynamic maneuvers during which the vehicle?s
response was recorded. The methodology and results of the experimental phase is described
in Chapter 3. The simulated data was obtained by running numerous simulations in TrukSim,
which is a software package developed by Mechanical Simulation Corporation speci cally for
simulating the response of large vehicles. This data was then to be compared with the
results of the computer simulations in Chapter 4. The research for this thesis was done in
conjunction with a larger e ort to characterize and study LCV dynamics, sponsored by the
National Transportation Research Center Incorporated (NTRCI) and was a collaborative
e ort including both universities and private companies. The report generated from that
e ort can be found in [6].
2
1.1 Background
As mentioned above, both single trailers and combinations of two small trailers are
permitted on all highways throughout the nation. The end goal of this research is to assess
the stability of the triple-trailer LCV in an e ort to help determine whether or not they
should also be allowed throughout this nation?s highway system. Currently only a handful
of states permit LCVs to operate on their highways, and each of those states have di erent
restrictions in place on what type of LCV can be used. The current highways on which LCVs
can operate on in the United States is shown in Figure 1.2; as illustrated the options are
limited for the triple trailer LCV of 100? or greater in length combination. This is of note
since this is the type of LCV that was used in this study and is the form that has the most
push to become legal.
Figure 1.2: Map of Approved Highway Routes for LCVs [1]
3
One of the driving forces for this research is the push to expand the network of highways
and roads that are accessible to LCV?s. The reasoning for this is to increase the e ciency of
the commercial vehicles. For instance, examine the case of a single semitrailer versus a LCV
con gured with three pup trailers. The increased e ciency can be seen in Table 1.1; for this
example the trip length was 15,000 miles and both trucks are assumed to have the same fuel
e ciency of 6.5 mpg and using the average cost of one gallon of diesel being a363.951. This
represents a fuel cost of a369,117.70 for this simulated trip. This cost savings is signi cant
when you think about this on a national scale and not just a single trip, so it is easy to see
why there would be a push to permit the use of LCV on most of the highways in the nation.
Table 1.1: E ciency Comparison Single Trailer vs. LCV Triple
Vehicle Type Height Width Length # of Trailers ft3 Cost per ft3
Single Trailer 10 8 40 1 3,200 a362.85
LCV Triple 10 8 25 3 6,000 a361.52
Di erences: 2,800 a361.34
1.2 Literature Review
There are several di erent classi cations of LCVs, each of them having their own unique
advantages and disadvantages. Though the LCV has been around for some time there
has been little experimental research performed on this family of vehicles. Most of the
experimental research to date has been aimed at characterizing the simple single semitrailer
con guration, which makes sense do to the ubiquitous nature of that vehicle. This section will
go into what has been done in the past to study the LCV as well as establish a fundamental
understanding of what components go into an LCV as well as how they go together to form
the vehicle.
While there was no research found where a triple LCV was instrumented and then un-
derwent experimental testing liken to that described in this thesis there were other e orts
put forth in the characterization of Longer Combination Vehicles. One of the most helpful
4
pieces found was ?An Overview of the Dynamic Performance Properties of Long Truck Com-
binations? [3]. This paper went through and outlined what was to be expected from vehicles
with multiple trailers in combination. it formed a general understanding of the dynamics
using simulation and gathering of current literature at the time of publication. This paper
served as the foundation for what this thesis expanded upon. When searching for a general
understanding of the components found in LCV units ?A Factbook of the Mechanical Prop-
erties of the Components for Single-Unit and Articulated Heavy Trucks? [8] by Paul Francher
et al described each component and what role it played in the dynamics. In addition to the
study of how the LCV?s behave there have been several e orts into exploring how to control
them. One such e ort is described in ?Performance Characteristics for Automated Driving
of Long Heavy Combinations Evaluated in Motion Simulator? [9]. In that publication the
authors describe the e orts of formulating multiple control methods for autonomous driving
of LCV?s. They achieve this by studying the inputs of numerous experienced LCV drivers
given the same vehicle path to drive. This is the path of the future, commercial vehicles are
being explored as one of the leading areas for autonomous driving on the highway systems
both stateside and internationally.
As mentioned the research done for this thesis was done in conjunction with a larger
project put on by the National Transportation Research Center Inc. as such there are
several prior e orts put on by the center that all lead up to the project for which this thesis
is indebted to. The report for the research project that supported this thesis is found in
?U32: Vehicle Stability and Dynamics Longer Combination Vehicles Final Report? [6]. The
aforementioned prior e orts are detailed in [10], [11], and [12]. Those projects performed
similar experimental and simulation testing that was undertaken for this research on other
heavy articulation vehicles. Those e orts lead directly to current research.
5
1.2.1 LCV Overview
The basic components for an LCV are a tractor and an assortment of semitrailers. The
formal de nition of a semitrailer is a trailer that cannot stand on it?s own and has to be
supported by the vehicle which it follows. The most common occurrence of semitrailers is
where only one trailer is being supported by a tractor, this is the typical ?18 Wheeler? or
?semi-truck? illustrated in Figure 1.3.
Figure 1.3: Typical Tractor & Single Semi-Trailer Combination [2]
The other common occurrence is that of two semi-trailers towed by one tractor. The
 rst trailer is supported by the tractor exactly like it would be if it were the only semi-trailer
attached. The di erence here is the second semi-trailer is supported via a converter dolly,
that is also attached to the  rst trailer. The converter dolly is what connects a semi-trailer to
another semi-trailer or anything other than the tractor for that matter. The name converter
dolly comes from the fact that the dolly ?converts? the semi-trailer into a full stand alone
trailer that can then be towed via the pintle hitch at the front of the dolly. An illustration
of the double trailer con guration can be seen in Figure 1.4 and an illustration of a typical
converter dolly is shown in Figure 1.5.
6
Figure 1.4: Typical LCV Double Trailer Con guration
7
Figure 1.5: Converter Dolly with Pintle Hitch [3]
As those two combinations are the most prominent throughout the nation they are the
only combinations most people think possible. There are however  ve other conventional
combinations. These, along with the two most popular are pictured in Figure 1.6. As
mentioned earlier the triple trailer combination is the focus of this research but much of the
same dynamic properties apply to all of these vehicles and are either ampli ed or dampened
depending on the con guration.
8
Figure 1.6: Possible LCV Con gurations [4]
1.2.2 LCV Dynamics
When dealing with any vehicle dynamics project there are always certain behaviors
that are identi ed as crucial. Those behaviors then become the center of attention when
9
out tting the vehicle with a sensor package. With the goal being to capture the behaviors
that have been identi ed the selection and implementation of the sensor package can be found
in Chapter 2. In the case of the triple trailer LCV there are four key areas of concern. Those
are, in no particular order; Rearward Ampli cation, Vehicle O -Tracking, Vehicle Rollover,
and Vehicle Understeer/Oversteer propensity. The two that pose the greatest complexities
in dealing with LCV stability are Vehicle O -Tracking and Rearward Ampli cation. The
rollover phenomena is very similar to that of any other vehicle and as such there are numerous
approaches to limit the rollover propensity of a vehicle, or in this case a trailer. The same
can be said for Oversteer/Understeer; each unit can be examined as a single vehicle typically
would.
Rearward Ampli cation is the act of dynamic responses growing in magnitude the fur-
ther from the the steer axle you are. This is easily visualized with the cracking of a whip;
small rapid inputs results in large outputs at the end of the whip. The formal de nition
of rearward ampli cation is the ratio of a unit?s maximum amplitude in a trailing unit to
its amplitude in the tractor [13]. The most common calculation when considering rearward
ampli cation is the lateral accelerations but in theory, any quantity would work. Vehicle
o -tracking is de ned as the lateral deviation between the path of the center of the front
axle and the path of the centerline of another part of the vehicle [13]. Essentially it is when
a following axle fails to follow the path set by the lead axle, this is not only seen in heavy
vehicles but most individuals who drive light trucks experience it on a daily basis.
Both rearward ampli cation and o -tracking are directly related to trailer length, and
both are large factors is the perceived stability of the LCV. The di cult part is that they
are inversely proportionate to trailer length. So the longer the trailer the less rearward
ampli cation but the more o -tracking and vis versa. When traveling through urban envi-
ronments, shorter trailers are desired as they would give you a smaller turning radius with
less o -tracking. However, longer trailers are desired on the highways to reduce rearward
ampli cation as o -tracking is of little concern on the highways.
10
Rearward Ampli cation
One of the of the most common causes of vehicle crashes is lane departure. In 2011
there were 15,307 fatal roadway departure crashes resulting in 16,948 fatalities, which was
51 percent of the fatal crashes in the United States for that year [14]. When a vehicle begins
to depart a lane the most common reaction from the driver is to rapidly correct in an attempt
to return to the lane. This results in a sudden, high magnitude change in steer angle. This of
course initiates a dynamic maneuver; referred to as an impulse steer response. Additionally
another leading cause of vehicle crashes is obstacle avoidance. This maneuver is simulated
by either a single or double lane change. The vehicle purposefully leaves the lane it was
traveling in and in the case of the double lane change return to the original lane after the
obstacle. All three of these maneuvers result in a rapid change in steering input and at high
speeds the response of the vehicle can become rather violent.
Speed is particularly important when dealing with such maneuvers on LCVs, once the
speed is in excess of 50 mph the phenomena of rearward ampli cation plays a large roll
in the overall dynamics of the LCV [15]. At such speeds mundane and subtle maneuvers
experienced at the tractor can result in a rather large dynamic response towards the end
of the vehicle train. This can lead to very dangerous outcomes including rollover and lane
departure of subsequent units depending on the lateral acceleration and steering input from
the leading vehicle.
Rearward Ampli cation In uences
The largest factor on rearward ampli cation is the length of the trailer. The longer the
trailer, the less susceptible it is to rearward ampli cation. Additionally as the number of
trailers increase, so does the rearward ampli cation with the added trailer. For example,
a triple trailer LCV with trailers measuring 48 ft in length will experience less rearward
ampli cation than a triple with 28 ft trailers. Similarly the triple will have less rearward
ampli cation than a double with 28 ft trailers [3]. If the trailers are of the same length then
11
simply the more trailers that are added the more rearward ampli cation can be expected.
Additionally the magnitude of rearward ampli cation can be in uenced by the frequency of
steering input, location of pintle hitch connections between trailers, and the ratio between
lateral sti ness on the vehicle tires to the weight of the vehicle [3].
As mentioned the frequency of the steering input plays a signi cant role in the rearward
ampli cation characteristics of a vehicle. This correlation is illustrated in Figure 1.7. This
graph was produced using data generated by a double tank trailer simulation. As can be
seen at low frequencies the amplitudes of the three units is identical, i.e. there is no rearward
ampli cation. As the frequency increases there begins to be some separation between the
responses of the three units. As the frequency crosses 1 rad/s (0.16 Hz) the  rst two units
(tractor &  rst trailer) begin to separate themselves from the last two units (dolly & second
trailer). It is at this point that the lateral acceleration of the second trailer is greater than
that of the tractor. Then, at approx 3 rad/s (0.48 Hz) the maximum separation between the
response of the tractor and second trailer is experienced. At this frequency the magnitude of
the lateral acceleration experienced by the second trailer is nearly double that of the tractor.
12
Figure 1.7: Rearward Ampli cation Response of Double Tank Trailer [5]
Though the  gure shows that the lateral acceleration is less that what is generated at
lower steering frequencies, the trend as it pertains to rearward ampli cation remains similar
in more severe maneuvers and raises great concern as a potential cause for rollover. The
danger is that since the driver of the tractor is limited to feeling only the lateral accelerations
of the tractor, he/she may  nd themselves unaware of a potential rollover about to occur.
So it is easy to see the danger in rearward ampli cation since the lateral accelerations
experienced by the tractor may be well within its limits while the last trailing vehicle may
experience lateral accelerations too great for it to handle, causing rollover.
Taking these results and exploring the outcome of several di erent con gurations yields
Figure 1.8. This plot looks at the ampli cation gain (the ratio of lateral acceleration between
13
the last and  rst vehicle in a LCV) as a function of the same steering input frequency. As
previously illustrated, the ampli cation is minimal at low frequencies and begins to separate
at approximately 1 rad/s (0.16 Hz) with a maximum separation experienced at approximately
3 rad/s (0.48 Hz). Note that the largest gain is experienced by the triple trailer with 28 ft
trailers, which is very similar to the vehicle used in testing for this research. The description
of each con guration in the study can be found in Table 1.3.
Figure 1.8: Rearward Ampli cation Response of Various Vehicle Combinations [3]
Rearward Ampli cation Outcomes
The most severe result of rearward ampli cation is vehicle rollover. This is due to the
increased lateral acceleration in each successive unit which at some point will exceed the
vehicle?s static rollover threshold (SRT). The SRT is de ned as the maximum angle which
a vehicle can withstand before it or any of the successive units experience rollover. As with
any vehicle though, the rollover threshold is e ected by a variety of parameters including
14
but not limited to CG height, suspension components, tire sti ness, track width, and load
distribution.
Vehicle O -Tracking
During low-speed turns, the trailing axle follows a path inside the one set by the lead
axle. The lateral o set from the front axle path is proportionate to the wheelbase of the
vehicle. This same trait is exhibited in LCVs in that the axles of each unit of the combination
track to the inside of the path followed by the preceding axle. This phenomena is what leads
to drivers of semi-trucks to have to ?square the corner? when making turns in low speed urban
environments. An illustration of low speed o -tracking is shown in Figure 1.9. As previously
stated as speed is increased the trailing axle tracks closer to the centerline of the lead axle
and will eventually, at high enough speeds track to the outside of the lead axle path. This
behavior is illustrated in Figure 1.10.
Figure 1.9: Low Speed LCV O -Tracking [4]
15
Figure 1.10: High Speed LCV O -Tracking [4]
The level of o -tracking is e ected by the length between each axle and the number of
articulation points between the units of the vehicle also in uences o -tracking [3]. One of
the key areas of concern is that of on ramps and exit ramps of highways and interstates.
With enough o -tracking the trailing vehicle can end up traveling o the inside edge of
the ramp [3]. In order to better characterize o -tracking a simulation was run with seven
di erent con gurations at low speeds around an exit ramp with a constant radius of 300 ft.
Those results are shown in Table 1.2. The abbreviations for the con gurations are detailed
in Table 1.3.
The ?Swept Path? is the width needed to pass the entire vehicle, assuming a common
width of 102 inches [3]. As discussed above, if a vehicle increases speed through the turn
the amount of o -tracking diminishes to a point where the trailers will actually begin to
track outside of the path set by the lead vehicle. The same simulation was run as above
but with a radius of 600 ft and at a speed of 55 mph, those results are shown in Table 1.4.
Again, refer to Table 1.3 for abbreviation explanations. In the high speed simulation, all of
16
Table 1.2: Low Speed O -Tracking Results [3]
Maximum
O -Tracking Swept Path
m ft m ft
1 Double-28 0.61 3.20 2.0 10.5
2 Triple-28 0.88 3.47 2.9 11.4
3 Tr/Semi 48 0.98 3.57 3.2 11.7
4 RMD-45/28 1.04 3.63 3.4 11.9
5 RMD-48/28 1.16 3.75 3.8 12.3
6 TPD-45/45 1.49 4.08 4.9 13.4
7 TPD-48/48 1.71 4.30 5.6 14.1
Table 1.3: Legend for Table 1.2, Table 1.4, and Figure 1.8 [3]
Semitrailer Semitrailer
Short Name Full Name Lengths (ft) Lengths (m)
Tr/Semi-48 Tractor with 48 ft Semitrailer 48.0 - 14.6 -
Double-28 STAA Double 28.0 28.0 8.5 8.5
RMD 48/28 Rocky Mountain Double 48.0 28.0 14.6 14.6
RMD45/28 Rocky Mountain Double 45.0 28.0 13.7 13.7
TPD 48/48 Turnpike Double 48.0 48.0 14.6 14.6
TPD 45/45 Turnpike Double 45.0 45.0 13.7 13.7
Triple-28 Triple 28.0 28.0 8.5 8.5
the con gurations saw a decrease in o -tracking. Additionally all of the LCV con gurations
saw more o -tracking than the typical trailer/semitrailer combination. While interesting,
there shouldn?t be much weight put on this as the potential for the high speed o -tracking
phenomenon to cause a collision is considered minimal [3].
17
Table 1.4: High Speed O -Tracking Results [3]
O -Tracking
m ft
1 Tr/Semi 48 0.16 0.52
2 TPD-48/48 0.34 1.10
3 TPD-45/45 0.38 1.25
4 RMD-48/28 0.41 1.33
5 Double-28 0.44 1.43
6 RMD-45/28 0.44 1.45
7 Triple-28 0.65 2.13
Vehicle Rollover
When a vehicle undergoes a dynamic maneuver, weight is transferred from the inside
wheel to the outside wheel. If the vehicle has a suspension system then the phenomena of
roll is experienced. The aforementioned weight transfer creates a moment about the roll
center of the vehicle that is referred to as the roll moment. To counteract this moment, force
is transferred from the inner wheels to the outer wheels. This is illustrated in Figure 1.11.
Summing the moment about the center of the outer tire contact patch yields Equation (1.1).
This is using the small angle approximation of sin? = ?;cos? = 1.
18
Figure 1.11: Rollover Moment Diagram
Mayhcg M?hcg +Fzit Mgt2 = 0 (1.1)
where
Fzi = Inner Vertical Tire Force
t = Track Width
M = Vehicle Mass
ay = Lateral Acceleration
hcg = Vertical Height of Center of Gravity (CG)
? = Transverse Slope
It is important to note that there were some assumptions made when deriving Equa-
tion (1.1), those being that you can neglect the e ect of the vehicle frame and suspension
compliance. These neglections are made because rigid chassis behavior is much easier to
19
calculate as you do not need more precise information about the vehicle i.e. suspension
sti ness and roll center. As long as the vehicle stays within its rollover threshold, the e ect
of this assumption is minimal [6].
The phenomena of roll happens in several stages. First the vertical load on the vehicle
is transferred from the inner tires to the outer tires and continues until the vertical load on
the inner tires is equal to zero. This point is refereed to as the stability limit of the vehicle.
The vehicle will not rollover until one of two things happen. One, the location of the center
of gravity (CG) passes outside of the outer tires. Or the stabilizing moment described above
is less than the roll inertia generated by the maneuver. This rarely happens in passenger
vehicle as they experience what is called yaw divergence typically long before rollover. Yaw
divergence is when the tires cannot provide enough lateral force to maintain the maneuver
and the tires begin to slide on the road.
Vehicle Understeer/Oversteer
One of the most common metrics to measure a vehicle?s steering characteristic is by
calculating the understeer gradient. As de ned in Equation (1.2), the understeer gradient is
the ratio of the deviation from the Ackerman steering angle to the lateral acceleration [16].
K =
    L
R
  57:3 
ay (1.2)
where
 = Road Wheel Angle (deg)
L = Tractor Wheel Base Length (steer axle to drive axle center-line)
R = Turn Radius
v2
Rg = Lateral Acceleration ay
K = Understeer Gradient (deg/g)
The factor 57.3 converts from radians to degrees
20
However, when you look to analyze a heavy vehicle with many axles it become much
more complicated; but can be expressed as an equivalent two-axle vehicle [17].
The yaw stability of a vehicle is dependent on whether the understeer gradient, K for
that vehicle is greater than zero, less than zero, or exactly zero. In the case where K is less
than zero the vehicle is said to be understeer. Whereas a positive K characterizes the vehicle
as oversteer; if K is zero then the vehicle is said to exhibit neutral steer characteristics [16].
Passenger cars in today?s market avoid making a vehicle that is oversteer as that is a more
dangerous case for the everyday driver. In the oversteer case it would take less steer angle
to perform a constant radius turn if the driver were to increase speed. It is obvious to see
how that would not be the desired condition for even the most experienced drivers to deal
with on a daily basis.
When dealing with LCV?s, Equation (1.2) can be applied to each unit of the combination
in order to determine each unit?s understeer gradient. This is achieved by using the road
wheel angle of the steer axle to calculate K for the tractor. The articulation angle between
the subsequent trailers and the dolly or tractor to which they are connected is used to
calculate K for the other vehicles in the combination [5]. When studying LCV dynamics it
is important to remember that since each unit has an independent value for K there can be
units that are oversteer at the same time as there are other ones that are understeer and/or
neutral steer. Furthermore, as each unit in the combination is unique in that they are loaded
and constructed di erently; the e ects of vehicle speed and lateral acceleration on the unit?s
understeer gradient are going to be di erent [18, 19].
Being that there are instances where there will be a mixture of understeer and oversteer
units in a LCV, it is important to understand what each combination will mean for the
dynamics of the vehicle. Since it is very rare to see any vehicle exhibit neutral steer we
will only consider the resulting four possible combinations of understeer and oversteer. The
dynamics of each combination is described in Table 1.5.
21
Table 1.5: Resulting Dynamics from Understeer/Oversteer Combinations [6]
Leading Vehicle
Oversteer Understeer
Trailing
Vehicle
Understeer
As speed increases toward the
critical speed, the articulation
gain approaches in nity. This re-
sults in a jackknife. System is un-
stable at high speed.
The vehicle is stable. As speed
increases, the articulation angle
gain (increase in articulation rel-
ative to steering input increase)
will approach the ratio of the two
units? understeer gradients.
Ov
ersteer
Response depends on whether the
ratio of the understeer gradients
is greater or less than the ratio
of the wheelbases, and the articu-
lation gain will go to negative or
positive in nity. This results in a
jackknife or a swing out, though
the di erence will be hard to tell
from the driving perspective. The
vehicle is unstable at high speed.
The articulation gain is initially
positive but becomes negative
and the trailer swings out. This is
an unstable arrangement at high
speed. However, at low speeds,
the articulation gain is positive,
making the vehicle drivable.
22
Chapter 2
Test Vehicle Instrumentation
The aim of this chapter is to detail the process of developing and implementing the data
acquisition system (DAQ) for use on the LCV triple test vehicle. The goal of the DAQ was
to capture those responses outlined earlier in section 1.2.2 at high data rates and store the
data in a manner conducive to analysis. Each section will discuss the process of selecting the
sensor(s) as well as integrating the sensor into the DAQ. The resulting data  les containing
the dynamic measurements will facilitate the analysis and comparison of the response of the
actual vehicle to that of the simulated vehicle. Through a collaborative e ort with other
research partners the following list of responses were chosen to be targeted for measuring:
1. Roll Angle per Lateral Acceleration
2. Yaw Rate per Lateral Acceleration of Tractor and Trailers
3. Path Deviation Error per Trailer Referenced to the Tractor
4. Lateral Acceleration per Steer Angle
5. Yaw Rate per Steer Angle
6. Lateral Acceleration per Trailer
7. Lateral Acceleration of the Tractor
8. Yaw Rate per Trailer
9. Yaw Rate of the Tractor
10. Understeer Gradient of the Tractor and Trailers
23
11. Trailer Motion Damping Time and Distance
The above characteristics can be separated into three measurement groups
1. Position Measurements
2. Inertial Measurements
3. Displacement Measurements
2.1 Sensors
Sensor selection was a critical part of this project. With such a large vehicle it required
a large amount of sensors; luckily this research involved several other research team members
outside of Auburn University that were able to help provide the additional sensors needed
to instrument the triple. This process included many discussions on not only what needed
to be captured but how to capture what was identi ed as the critical responses. In the end
a total of 37 individual sensors were installed on the triple-trailer. These sensors produced a
total of 206 individual channels of data that were to be recorded by the DAQ. That process
is outlined below in Section 2.2. The measurements that were recorded are shown below in
tabular form in Table 2.1 as well as in picture form in Figures 2.1. Note that in Table 2.1
a sensor bracketed by ?()? means that the measurement was attempted but for some reason
not captured.
The channels that are key to characterizing vehicle dynamics were to be recorded at
a nominal sampling rate of 100 Hz. Supplementary channels were sampled at lower rates,
as indicated in the table. Section 2.2 explains how each sensor?s data was transmitted to a
central computer and every single data point was given a time stamp. While the sampling
rate was not exactly 100 Hz and not all channels were sampled simultaneously, an experiment
prior to data collection showed that the method reliably provided data at the time indicated
in each time stamp.
24
Table 2.1: Summary of Measurements and Sensors
Unit Quantity Vehicle
CAN
String
Pot
GPS IMU GPS &
IMU
Tractor
Horizontal and Vertical Dis-
placement of the Steer Axle
SP1-25
Horizontal and Vertical Dis-
placement of the Second
Drive Axle
SP1-25
Steer Input at the Steer Col-
umn
SP1-25
Steer Input, Steer Kingpin SP1-25
Engine Parameters (X)
Three-Axis Accelerations
and Angular Rates
MemSense
Position Novatel
Trailer
1 Horizontal and Vertical Dis-placement of the Axle SP1-25
Three-Axis Accelerations
and Angular Rates
CrossBow
Position Novatel
Trailer
2
Articulation Angle to Lead-
ing Converter Dolly
SR1A-
62
Horizontal and Vertical Dis-
placement of the Axle
SP1-25
Three-Axis Accelerations
and Angular Rates (RT2500)
Position Novatel
Trailer
3
Articulation Angle to Lead-
ing Converter Dolly
SR1A-
62
Horizontal and Vertical Dis-
placement of the Axle
SP1-25
Three-Axis Accelerations
and Angular Rates (RT3200)
Position Novatel
Each unit of the vehicle had two GPS receivers one for the measurement and one for
redundancy. Additionally each unit had an IMU to record accelerations and angular rates,
and string potentiometers to measure displacements within the vehicle. The two GPS and
25
Figure 2.1: Sensor Placement on LCV Triple
IMUs were separate sensors on the Tractor and Trailer 1; whereas the GPS units and the
IMU were integrated on Trailers 2 and 3.
2.1.1 Displacement Measurements
String potentiometers or ?string pots? were used to measure dolly-to-trailer articulation
angles, lateral and vertical displacement of axles, and steering input. Several of the desired
characteristics have to do with vehicle roll and understeer tendencies. In order to fully
capture those characteristics it is necessary to understand what the axle of the vehicle is
doing at the time of the maneuver. To achieve this, the decision was made to use string
pots to measure the linear displacement of each axle in three dimensions. A diagram to
show how this was to be achieved is shown below in Figure 2.2. Combining the string pot
measurements with the IMUs and GPS measurements the desired characteristic values can
be obtained. A total of 27 string pots were used along the vehicle; four were model SR1A-
62 shown to the left in Figure 2.3 used to measure the dolly-to-trailer articulation. These
weatherproof units have a stroke length of 62 inches. All other string pots on the vehicle
were model SP1-25, shown in Figure 2.3 to the right, with a stroke length of 25 inches. They
were installed to measure axle displacement on the test vehicle. The steering input was also
measured with a SP1-25 string pot.
26
Figure 2.2: Sketch of Axle De ection Measurements
Figure 2.3: Celesco String Potentiometers, SR1A-62 (left) and SP1-25 (right)
2.1.2 Positioning Measurements
One of the most crucial measurements for this project is position. If the position mea-
surement is not accurate then the entire analysis can be e ected greatly. GPS receivers range
27
wildly in performance as well as cost. The most costly units being the ones used in missile
guidance and other various high precision environments. The cheapest being the ones placed
in consumer electronics such as cell phones. In an attempt to minimize the error all four
of the units were out tted with a Novatel ProPak GPS receiver that provides acceptable
performance for such a project. In addition the the Novatel receivers, the tractor and the
 rst trailer had a u-Blox GPS receiver for redundancy. The second and third trailer used
the OxfordRT units for redundancy. A picture of the Novatel receiver as well as the u-Blox
receiver can be seen in Figure 2.4, an image of the OxfordRT units is shown below in Section
2.1.3.
Figure 2.4: GPS Receivers Novatel ProPak (left) u-Blox Receiver (right)
2.1.3 Accelerations & Rates Measurements
Inertial measurements use accelerometers and gyroscopes to measure the rate of change
bot laterally and rotationally in anywhere from one to six axes. Inertial Measurement Units
(IMUs) contain three accelerometers and three gyroscopes internally aligned in such a fashion
to measure both the acceleration and rotational rate along three axes. The IMU is referred
to as a six axes since there are two measurements on each axes. When placed near the center
of gravity of a vehicle, the output from the IMU can be translated into the yaw, pitch, and
28
roll of the vehicle. Figure 2.5 shows the three axes that are measured by the IMU and which
axes translates to yaw, pitch, and roll.
Figure 2.5: Illustration of Triple-Trailer Frame of Reference
IMU grades range from tactical, which is used in missiles and other very high precision
environments all the way to hobby level where the sensors are very cheap and precision is
not of the highest priority. Several quality IMUs were borrowed for this project from various
sources. An IMU was mounted on each of the units in the combination. A MemSense IMU
was obtained to be mounted on the tractor. Being much lower in price than the other sensors,
the MemSense o ers exceptional quality for its price. The MemSense is shown in Figure 2.6
along with its technical speci cations in Table 2.2.
29
Table 2.2: MemSense Performance Statistics
Figure 2.6: MemSense Inertial Measurement Unit
The Crossbow NAV 440, shown in Figure 2.7 is a higher-grade IMU. Table 2.3 shows
its technical speci cations.
30
Table 2.3: CrossBow Nav 440 Performance Statistics
Figure 2.7: MemSense Inertial Measurement Unit
31
Table 2.4: Oxford RT2500/3100 Performance Statistics
The Oxford RT-2500 Inertial and GPS Navigation System, shown in Figure 2.8, to the
left includes three angular rate sensors (gyroscopes), three servo-grade accelerometers, the
GPS receiver and all the required processing in one very compact box. The internal pro-
cessing includes the strap-down algorithms (using a WGS-84 earth model), Kalman  ltering
and in- ight alignment algorithms. The internal Pentium-class processor runs the QNX real-
time operating system to ensure that the outputs are always delivered on time the technical
speci cations can be seen in Table 2.4. The Oxford RT-3100, shown in Figure 2.8, to the
right is similar to the Oxford RT-2500 model; but promises a little better accuracy in its
measurements. Its technical speci cations can be seen in Table 2.4 as well.
Figure 2.8: Oxford RT Units RT2500 (left) and RT3100 (right)
32
2.2 Data Acquisition
The test vehicle was equipped with numerous sensors that needed to be interfaced
with various communication methods. To facilitate this complex data collection with the
maximum control over the process, a custom data collection system was developed. The
system consisted of an industrial computer with Ubuntu Linux operating system and a
wireless (WiFi) router. The Industrial computer ran without a monitor, keyboard, or mouse
and connected to the Oxford RT units via the router on an Ethernet network connection.
The wireless router allows the data collection process to be monitored and controlled via a
laptop computer in the truck cab. It should be noted that no data was sent over the wireless
link it was only to monitor and control the data acquisition. All data was recorded directly
to the industrial PC and the data acquisition process, and once started was not interrupted
by a loss of communication from the laptop in the cab. The location of the PC can be seen
in Figure 2.9.
Figure 2.9: Placement of Advantech Industrial PC
The Advantech PC was wired to each of the sensors either directly or through an on-
board network i.e. CAN bus. The interfaces of the Advantech are detailed as follows.
a136 Direct UDP/IP communication with the OxfordRT units over CAT6 Ethernet
33
a136 Four Serial (RS-232) ports:
{ Three Novatel GPS Units for Tractor and Trailer 1&2
{ Trailer 1 IMU (Crossbow 440)
a136 Six USB Connections
{ MemSense IMU
{ RS-232 to USB Converter for Novatel GPS Receiver on Tractor
{ Two u-Blox GPS Receivers
{ Two USB-CAN Converters for the Two CAN Buses
The wiring between the sensors and the computer is shown in Figure 2.10.
Figure 2.10: Wiring Diagram Illustrating the Connections Between the Sensors and the DAQ
2.2.1 CAN Bus
Most of the sensors in this project had internal signal conditioning and output a digital
signal. Part of this research required the need to build signal conditioning, including an
analog-to-digital (A/D) converter, for the string pots. The string pots needed to be connected
to an A/D converter, which would convert the signal to digital and then send the message
over a Controller Area Network (CAN) network similar to that which is found on most
34
production vehicles. The main driving force behind this decision as opposed to purchasing
and using a commercial DAQ with A/D converters attached was controllability. Since the
entire system was to be designed and implemented in house, all of the inner workings will be
known making any possible troubleshooting easily accomplished. A diagram of the system
is in Figure 2.11.
Figure 2.11: Diagram of CAN Bus
As mentioned, the CAN network is the same network that is standard on vehicles today
in order for microcontrollers and devices to communicate with each other within a vehicle
without a host computer. The LCV contained two separate CAN buses, one that is already
there from the factory and one that was created for the string pots. The factory installed
CAN network is in accordance with the SAE J1939 standard. Using the SAE J1939 message
list, the vehicle codes were translated and the values were able to be read by the DAQ and
subsequently logged.
The second network created was for use with the string pots and their associated A/D
converters. This path was chosen for multiple reasons; the main two being complete control
over design as well as lowering line noise on the string pots by placing the A/D converter
close to the string pots themselves. The idea of having complete control over the network
is the most critical part of the whole process. This allowed for the creation of a proprietary
message set that could not interfere with any other CAN network. An added bene t is that
it provided extensive knowledge of the system so that in the event something went wrong
35
it took less time to diagnose and resolve the issue. There were a total of six CAN boxes
created, each containing the A/D converter, CAN chip, and circuit board. One of these
boxes can be seen in Figure 2.12.
Figure 2.12: Inside of a CAN Box
Each string pot was connected to the CAN box by a custom DB25 connector that was
wired to provide power and ground to each string pot as well as a line for the message. In
order to collect the measurements from the string pots, each A/D had to be polled over the
network. This was achieved by setting up one of the CAN boxes to send out a message on
the CAN bus at 100 Hz that would trigger each of the A/D converters to poll all of the
connected string pots. The message set used for the string pots is relatively straightforward;
each A/D will send out a status message every second to alert the computer if something is
not working. The message structure for the String Pot CAN-bus can be seen in Figure 2.13.
36
Figure 2.13: CAN Message Structure
2.2.2 Sensor Interfacing
Code had to be written to receive and interpret the data from each sensor. Some of
the code already existed and was used again for this research. The new sensors that had
to be interfaced were the MemSense IMU, the u-blox GPS units, and the Oxford RT units.
The code for all of the sensor interfaces was written in C++ and ran on the embedded
Linux computer on the tractor. The middleware used to communicate all of the sensor data
between processes is called Mission Oriented Operating Suite (MOOS) [20]. This middleware
uses client-server architecture with a centralized database and provides basic tools for Inter-
Process Communication via sockets. This allows for viewing the raw data in real time, and
logging the data in a standard format. Each sensor had a corresponding process running
that interfaced with that sensor, formated its data, and published it as separate channels
to the MOOS database. The MOOS database holds the latest value from each channel on
37
each sensor and allows other processes to access this data. An illustration of this interface
process can be seen in Figure 2.14.
Figure 2.14: Illustration of the MOOS Architecture
2.2.3 Data Logging
Using the laptop in the cab of the truck, the logging was started and stopped via Secure
Shell (SSH). Additionally, the data was monitored using MOOSs uMS utility which shows
the latest values for each of the sensors in a table. The MOOS utility pLogger connects to
the MOOS database and records all changes to all channels to an asynchronous log format.
This preserves the data in its raw form with its original timestamps taken by the sensor
interface process. This is more di cult to process than synchronous data logs, but provides
more accurate timing information. An example of the  le format can be seen in Figure 2.15.
38
Figure 2.15: Screen Shot of Asynchronous Log File
2.3 Hardware Installation
With the three trailers being nearly identical, the mounting boxes and brackets required
were fairly similar. Several sensors needed to be mounted in the tractor?s engine compart-
ment. This included one string pot set up on the steer axle, along with two string pots for
vertical and horizontal displacement of the kingpin, and lastly a string pot for the angular
rotation of the steering shaft. Behind the tractor cab a toolbox with the main CPU was
mounted. This box is where the two CAN buses were connected to the industrial computer
for data acquisition and processing. Figure 2.9 shows the actual toolbox that was on the
tractor along with the location. This box contained the industrial computer, which handled
all of the data acquisition as well as various networking devices used for communication
throughout the vehicle.
As previously stated, string pots were used to measure the vertical and horizontal dis-
placement of the axles. One pair of string pots were mounted directly above the axle and
39
another mounted directly horizontal to the axle. This was done to maximize the displace-
ments and maximize signal to noise. Figure 2.16 shows these brackets mounted on the LCV
with the string pots attached. Note the cable for the string pots is highlighted in red for all
of the following pictures.
Figure 2.16: String Pots Mounted for Axle De ection
Similar to the toolbox mounted directly behind the cab of the tractor. Another toolbox
was mounted under each of the trailers. Figure 2.17 shows how they were mounted; a close-up
shows the power and serial cables going into and coming out of the box.
Figure 2.17: Example of Toolboxes Mounted Underneath Trailers for Sensor Mounting
As described above, each of the string pots were connected to a CAN-box that contained
the A/D converter. These A/D converters could handle six string pot inputs, and they output
40
their data into the CAN bus that run alongside the trailer combination. Figure 2.18 below
shows one of these A/D converter boxes mounted under a trailer.
Figure 2.18: Mounted CAN Box
To calculate the articulation angle, the longer string pots were mounted on the dolly
and attached to the successive trailer. They were crisscrossed in an attempt to get as linear
of a measurement as possible and to maximize the displacement. Figure 2.19 shows the
actual mounting on the LCV.
41
Figure 2.19: String Pots Mounted for Articulation Angle
The tractor?s engine compartment was not only less conducive to taking measurements,
but it also required more of them. The displacement of the kingpin on both sides required
two more string pots to be mounted on the axle. Additionally, measuring the angular
displacement of the steering shaft required a string pot be mounted perpendicular to the
shaft. The axle de ection string pots can be seen in Figure 2.20 and the steering shaft in
Figure 2.21.
Figure 2.20: Steer Axle String Pots
42
Figure 2.21: String Pot Mounted for Steer Angle
Each of the GPS receivers requires antennas to be mounted on top of its respective
trailer. Shown in Figure 2.22 are the patch antenna on the center of the trailer roof for the
u-blox, and the larger antenna on the side of the trailer roof for the Novatel.
43
Figure 2.22: GPS Antenna Mounted on the Trailer Roof
44
Chapter 3
Experimental Results
The scope of this chapter is to outline and describe the experimental testing undertaken
with the LCV triple at the NCAT test track. The goal of the test plan was to expose the
test vehicle to various maneuvers that are designed to incite certain dynamic responses. The
dynamic responses of interest were outlined earlier in Section 1.2.2. The responses to these
maneuvers were to be captured by use of a custom designed data acquisition system (DAQ)
that was detailed in Chapter 2.
3.1 Test Track
All of the experimental testing was conducted at NCAT in Opelika, AL. This facility
is used for advanced asphalt wear testing and uses a  eet of tractor trailer combinations to
wear sections of asphalt at accelerated rates. The track located at the facility is one of a kind
and o ers a very unique platform for both heavy truck research as well as other automotive
research goals that could not be conducted on normal roads and highways. The track is a
1.7 mile long oval comprised of 46 di erent 200-ft. test sections. The two curves the track
has an 8a176 banking and use a spiral-curve-spiral con guration. An aerial view of the track
can be seen in Figure 3.1.
3.2 Test Vehicle
As mentioned, NCAT operates a  eet of tractor trailer combinations, the majority of
which consist of a lead tractor pulling three sleds loaded with steel plates. However, one of
the vehicles was perfectly suited for this research project. It consists of a Freightliner tractor
pulling three standard shipping containers; which are loaded down with concrete barriers.
45
Figure 3.1: Aerial View of NCAT Test Track
The containers are loaded to greater than the legal limit in order to increase the wear rate
of the asphalt. Each container measures 20 ft in length and is riding on a Cheetah container
chassis. The  rst trailer is obviously connected to the tractor with the second and third
trailers being connected via identical silver eagle converter dollies.
3.3 Testing Maneuvers
As mentioned above, the vehicle underwent several di erent maneuvers as a part of this
testing. This section will describe in detail each of those maneuvers as well as what the
maneuver is aimed at achieving with regards to the LCV triple.
3.3.1 Constant Radius Turn
Object of Maneuver
The object of the constant radius maneuver is to asses several of the vehicle?s steady-
state handling characteristics. The main two being the understeer gradient of each trailer as
well as the roll steer of the converter dollies. The maneuver was to be repeated at various
speeds ranging from 20 to 45 mph. The driver was to have  nal say on whether or not each
46
attempt was to be completed. Each speed was to be repeated 10 times to ensure that not
only adequate but complete data was recorded. In order for this maneuver to be successful
in characterizing the vehicle characteristics the conditions of the maneuver needed to meet
most if not all of the following.
a136 Consistent Road Wheel Steer Angle
a136 Consistent Vehicle Speed
a136 Consistent Lateral Acceleration for runs of the same speed
Maneuver Path
The maneuver is to be performed exactly as it sounds. The vehicle is to travel in a
constant radius turn while attempting as best as possible to maintain the conditions listed
above. As mentioned earlier in Section 3.1 the curves at the NCAT test track are not true
curves except for in the middle of the curve. For this reason, the GPS position data that
is recorded during the maneuver will serve to both establish the correct course that the
maneuver is performed on but also will de ne the radius that the vehicle travels.
3.3.2 Single Lane Change
Object of Maneuver
The goal of this test is to capture the response of the vehicle due to obstacle avoidance
style maneuver. The target of the test is to show the transient response of the vehicle due
to the step change in position. The output from this test will allow for the study of path
deviation for all of the units in the vehicle train as well as the settling distances of the
subsequent units due to steering inputs at the tractor. Similarly it will allow for the study
of rearward ampli cation of the units. The critical parameters for the test are each unit?s
lateral acceleration and relative position of each unit to the original path of the tractor.
47
Maneuver Path
The path that the vehicle is to follow is exactly like the name of the maneuver suggests.
The goal is to begin the test with the vehicle in a steady velocity driving straight so that the
transient responses are minimal at the start. Additionally it is desired that the vehicle be in
zero-yaw attitude, meaning that the vehicle is driving straight. The driver is to maneuver the
vehicle through the  rst gate and then steer the vehicle into the targeted lane and through
the second gate within the determined distance. This maneuver had to be attempted in
a portion of road that is as straight and  at as possible as to mitigate any non-accounted
for e ects. The driver?s ability to negotiate the maneuver consistently will help insure that
su cient data will be collected during the test series. The layout of the Single Lane Change
is illustrated below in Figure 3.2.
Figure 3.2: Single Lane Change Maneuver Diagram
48
3.3.3 Double Lane Change
Object of Maneuver
The double lane change is designed to capture the response of the vehicle in an obstacle
avoidance maneuver, much like the single lane change. The main di erence in the two is
that when executing the double lane change, the maneuver is not complete until the vehicle
has returned to the lane that it was originally traveling in. This test is the most dangerous
of the three as it incites the most lateral acceleration of them all and therefor leads to the
most dangerous conditions for large, high center-of-gravity vehicles. The same measurements
are of interest in the double lane change that were critical in the single lane change (path
deviation, lateral acceleration, and settling distances) for each of the units. This maneuver
stands to give the most data towards characterizing the rearward ampli cation as it is not
just a single step change response nor a response in steady state, but instead a response to
consecutive lane changes.
Maneuver Path
The path of the vehicle is approximately two consecutive single lane changes maneuvers.
The vehicle is to start out in the outer lane and once it passes through the  rst gate location.
Change course and move to the inner lane before the next gate location. Once through the
second gate location, there is a brief stretch of distance to be traveled in the inner lane,
the end of this segment is marked by the third gate location. Once through the third gate
location, the vehicle is to maneuver back into the outer lane once again before the fourth
and  nal gate location. Once the entire vehicle has passed through the fourth gate and
has returned to a steady state operation the maneuver is complete. An illustration of the
maneuver can be seen in Figure 3.3.
49
Figure 3.3: Double Lane Change Maneuver Diagram
3.4 Data Processing
Once all data was collected, the raw data  les were downloaded from the DAQ system
and needed to be cleaned up and prepared for analysis. This process was broken down into a
three step process: data handling (3.4.1), data formatting (3.4.2)), and real-time kinematic
(RTK) corrections (3.4.3)).
3.4.1 Data Handling
The computer that was mounted on the test vehicle recorded every run and stored
the data internally. Following testing, all of the data sets were downloaded from the vehicle
computer to a more powerful computer for the post-process work. A backup copy was left on
the vehicle computer and another raw backup was stored in another location for redundancy.
3.4.2 Data Formatting
Data recording was more e cient when the recorder ran continuously as the vehicle went
around the track, with maneuvers on both the north and south straight segments. Data for
each maneuver on the straight or curve were extracted from the larger  le following the tests.
This was accomplished by de ning zones around the track using known GPS coordinates for
the track, as shown in Figure 3.4.
50
Figure 3.4: Zones for separating data recorded on the curves from data recorded on the
straights.
A MATLAB program was written to step through the large  les line-by-line to de-
termine the zone, and then to write all of the corresponding data for each zone to a new
 le. This program was also run against the individual recordings to ensure that all of the
 les representing a certain maneuver started and stopped at the same geographic point.
The speed and maneuver were coded in the individual  le names. An example of this is:
?NTRCI 35mph Dbl Ln Chng R2? which corresponds to the second running of a 56 km/h
(35 mph) double lane change.
The next step was coordinate transformations and unit conversions. The analysts chose
to use the ISO vehicle coordinate system with positive z direction up, as indicated in Figure
3.5.
Another MATLAB program was written to bring in the data from speci c runs and
create an overlay plot so the accelerations of the tractor and three trailers could be compared.
Figure 3.6 is the speci c case of angular rate about the z-axis in a double lane change. The
four IMUs are listed in their order from front to rear in the combination vehicle. The upper
graph is the raw data prior to the coordinate transformation, and the lower is after the
transformation. The lower graph shows the four units of the vehicle yawing in their proper
sequence . The data shown is after being put through a 10th order Butter-worth  lter with
a cut-o frequency of 3 Hz.
51
Figure 3.5: ISO standard frame-of-reference with Y to the left and Z up.
Figure 3.6: Raw vs. Post Processed Angular Rates.
After the necessary transforms were con rmed, a program was written in Python to it-
erate through each  le automatically and perform the rotations on the desired channels. The
52
program additionally converted the latitude and longitude coordinates to Universal Trans-
verse Mercator (UTM) coordinates. This gave a set of rectilinear positioning coordinates
of the tractor and trailers relative to an origin point close to the track. This simpli ed
visualization of the data.
3.4.3 RTK Corrections
In order to obtain global positioning coordinates, two GPS receivers were placed on
each of the units in the combination. Novatel GPS receivers were on each of the units, while
the lower cost alternatives, the u-blox GPS receivers, were on the tractor and  rst trailer.
The second and third trailer both carried an Oxford RT unit, but they did not function as
discussed in Section 3.6.
The accuracy (1 ) of the standard GPS positions that the receivers report are usually
on the order of 1 or 2 meters (3 to 6 ft). This error comes from several factors, including
atmospheric conditions, which is the largest contributor, as well as satellite and receiver
clock biases, and noise in the measurements inside the GPS receiver. As the satellite?s signal
propagates through the ionosphere and troposphere that surround the Earth, the electron
dispersion and humidity can a ect the GPS signal.
When several GPS receivers are operating within close proximity (several kilometers),
these signal errors become highly correlated. Di erential GPS (DGPS) techniques take
advantage of this fact and compensate for the correlated errors. DGPS methods can use the
pseudorange, the carrier noise measurement, or a combination of both. Real-Time Kinematic
(RTK) systems can take a precise carrier phase measurement and calculate global positions
that are equally precise. The RTK system at NCAT uses a static base station with known
coordinates near the track and compares its GPS measurements to those of a roving GPS
receiver in close proximity.
53
3.5 Analysis of Experimental Data
The experimental data was analyzed in order to look at the understeer characteristics
of the LCV along with the body roll of each unit and axle steer. As described below in
Section 3.6, there were some data collection issues that prohibited the accurate collection of
acceleration data for the second and third trailers. However the second and third trailers
there was adequate data collected on position, speed, and suspension de ections. This
data was then compared to the results of the simulation which is described in Chapter 4.
The vehicle characterization parameters mentioned above were obtained in conjunction with
Western Michigan University as part of the collaborative e ort for the NTRCI project for
LCV vehicle dynamics. That report can be found in the appendices of [6].
3.5.1 Understeer Characteristics
As described in Section 1.2.2 the understeer gradient e ects the vehicle?s ability to follow
the path de ned by the steer angle of the steer axle tires or road wheel angle. The portion
of the data that will contribute to the analysis of this characteristic is the data obtained
during the constant radius maneuvers in the banked corners of the track. An overlay of two
separate runs at separate speeds in shown below in Figure 3.7, this is to illustrate that the
data at multiple speeds have the same nominal radii. Using the GPS data taken during the
constant radius turns it was determined that the curve had a nominal radius of 476 ft.
Steering Characteristics of the Tractor
The understeer gradient was calculated using Equation (1.2) at various speeds using the
experimental data. The measurement of the road wheel was taken from the string pot data
and the lateral acceleration was both calculated analytically as well as recorded via IMU
measurements. The equation for the analytical calculation of the lateral acceleration is seen
in Equation (3.1).
54
Figure 3.7: Constant Radius Maneuver Path Overlay.
ay = V
2
Rg (3.1)
where
ay = Lateral Acceleration
V = Vehicle Velocity
R = Turn Radius
g = Gravitational Constant
This equation is for vehicles that undergo constant radius turns on  at surfaces which
is not the case in this application. In order to correct for this, the gravitational contribution
to the lateral acceleration is subtracted from the results from Equation (3.1). As described
in Section 3.1, the corners in which the maneuvers took place had an 8a176 banking. So the
resulting gravitational component of the lateral acceleration is g sin(8) = 4:478fts2 . In
55
addition to the equation for lateral acceleration, Equation (1.2) is listed below again for
reference.
K =
    L
R
  57:3 
ay (1.2)
where
Fzo = Outer Vertical Tire Force
Fzi = Inner Vertical Tire Force
T = Track Width
M = Vehicle Mass
Ay = Lateral Acceleration
hcg = Vertical Height of Center of Gravity (CG)
There other series of equations that is of use are the equations for calculating the steer
angles. Equations (3.2) - (3.4) show the calculations for the steer angle of both the inner
and out wheels as well as the average steer angle, which is de ned as the Ackerman steer
angle[16].
 o = L(R +t=2) (3.2)
 i = L(R t=2) (3.3)
 = LR (3.4)
where
 = Road Wheel Angle (deg)
L = Tractor Wheel Base Length (steer axle to drive axle center-line)
R = Turn Radius
56
These equations are set for low speed cornering where the lateral acceleration is negli-
gible. In order to proceed with the calculations a value for both the road wheel steer angles
and the hand wheel angle needed to be calculated from the measured data. In order to do
this the data was broken down into two separate sections, the  rst being the period the
vehicle was transitioning from the straight-a-ways into the constant radius. This portion of
the data is represented at the beginning and end of the data set. An example of the two
separate sections from data taken at 35 mph can be seen in Figure 3.8. The second portion
is the portion of the turn data that was analyzed as the constant radius section. It was
this data that was  tted with a linear regression to get best  t linear curve, the resulting
equation for the line is shown in Equation (3.5), and as can be seen by the low slope value
of the section of the data is representative of a constant steering angle during the constant
radius maneuver.
y = 0:005x 3:2160 (3.5a)
R2 = 0:00248 (3.5b)
The same plot was generated, shown in Figure 3.9, at lower speeds to illustrate that the
road wheel angle is indeed comparable. The di erences between the two can be attributed
to high speed corrections made by the driver in an attempt to maintain the constant radius.
The results of the calculations can be found in Table 3.1. Of note is that the under-
steer gradient was calculated using only six discrete data sets at the various speeds of the
maneuvers.
57
Figure 3.8: Sections of Constant Radius Maneuver.
Figure 3.9: Sections of Constant Radius Maneuver.
58
Table 3.1: Understeer Gradient Calculations for LCV Tractor
Target Vehicle Speed (mph) 20.0 25.0 30.0 35.0 40.0 45.0
Target Vehicle Speed (m/s) 8.94 11.17 13.41 15.65 17.88 20.12
Calculated Avg. Speed (m/s) 9.1558 11.0530 13.3027 15.1395 17.2976 19.2648
Measured Road Wheel Angle (deg) 2.3960 2.5726 2.6767 2.5444 2.2074 2.1626
Ackerman Angle (deg) 1.9799 1.9799 1.9799 1.9799 1.9799 1.9799
Under/Over Steer (deg) 0.4161 0.5927 0.6968 0.5654 0.2275 0.1827
Calculated ay (g) 0.0589 0.0859 0.1244 0.1611 0.2103 0.2609
ay Corrected for Banking (g) -0.0802 -0.0533 -0.0148 0.0220 0.0712 0.1217
Measured ay (g) -0.0130 0.0024 0.0372 0.0734 0.1289 0.1951
Understeer Gradient (deg/g) 7.0605 6.9006 5.6010 3.5035 1.0815 0.7003
Steering Characteristics of Trailer 1
The same calculations were performed on the data for the  rst trailer in the combination.
Those results are shown in Table 3.2. In the case of the  rst trailer, the steer angle was
measured by subtracting the measured heading of the 1st Trailer from that of the Tractor.
In doing the above subtraction of heading angles the assumption was made that during the
maneuver there was no slip for either of the two units. In other words the assumption is
that the tires are pointed in their direction of travel [16]. This assumption can be made do
to the low road wheel steer angle, should the steer angle increase above say 5 degrees then
the assumption would lead to greater error then acceptable. An example of the output is
shown in Figure 3.10. As illustrated the resulting steering input looks very similar to that
of the Tractor.
Steering Characteristics of Trailer 2
As described in Section 3.6, there were several issues with some of the data for the
second and third trailer. As a result the recorded lateral accelerations were not reliable. For
those purposes there is no value recorded for the measured lateral acceleration for neither
the 2nd nor 3rd trailer. The results from the second trailer can be found in Table 3.3.
59
Figure 3.10: Tractor 1 Steering Input
Table 3.2: Understeer Gradient Calculations for LCV Trailer 1
Target Vehicle Speed (mph) 20.0 25.0 30.0 35.0 40.0 45.0
Target Vehicle Speed (m/s) 8.94 11.17 13.41 15.65 17.88 20.12
Calculated Avg. Speed (m/s) 9.1372 11.0246 13.3071 14.9739 17.0491 18.7962
Measured Road Wheel Angle (deg) 2.4080 2.5350 1.5999 2.8151 2.6588 2.4725
Ackerman Angle (deg) 1.8513 1.8513 1.8513 1.8513 1.8513 1.8513
Under/Over Steer (deg) 0.5566 0.6837 -0.2514 0.9638 0.8075 0.6212
Calculated ay (g) 0.0587 0.0854 0.1245 0.1576 0.2043 0.2484
ay Corrected for Banking (g) -0.0805 -0.0537 -0.0147 0.0185 0.0652 0.1092
Measured ay (g) -0.0885 -0.0883 -0.0347 0.0119 0.0799 0.1367
Understeer Gradient (deg/g) 9.4858 8.0015 6.9825 6.1144 3.9518 2.5013
Steering Characteristics of Trailer 3
Similarly to the 2nd trailer the 3rd trailer also experienced data issues, because of this
the data from the 3rd trailer was processed in the same manner that the 2nd trailer was and
the outcome of the calculations is detailed in Table 3.4.
60
Table 3.3: Understeer Gradient Calculations for LCV Trailer 2
Target Vehicle Speed (mph) 20.0 25.0 30.0 35.0 40.0 45.0
Target Vehicle Speed (m/s) 8.94 11.17 13.41 15.65 17.88 20.12
Calculated Avg. Speed (m/s) 9.1307 11.0151 13.3039 15.1185 17.3635 19.3044
Measured Road Wheel Angle (deg) 1.6651 1.6311 1.5666 1.8866 1.9075 2.5102
Ackerman Angle (deg) 2.0897 2.0897 2.0897 2.0897 2.0897 2.0897
Under/Over Steer (deg) -0.4246 -0.4586 -0.5230 -0.2031 -0.1822 0.4206
Calculated ay (g) 0.0586 0.0853 0.1244 0.1607 0.2120 0.2620
ay Corrected for Banking (g) -0.0806 -0.0539 -0.0147 0.0215 0.0728 0.1228
Measured ay (g) n/a n/a n/a n/a n/a n/a
Understeer Gradient (deg/g) -7.2440 -5.3767 -4.2034 -1.2639 -0.8595 1.6053
Table 3.4: Understeer Gradient Calculations for LCV Trailer 3
Target Vehicle Speed (mph) 20.0 25.0 30.0 35.0 40.0 45.0
Target Vehicle Speed (m/s) 8.94 11.17 13.41 15.65 17.88 20.12
Calculated Avg. Speed (m/s) 9.1372 11.0246 13.3071 14.9739 17.0491 18.7962
Measured Road Wheel Angle (deg) 2.4080 2.5350 1.5999 2.8151 2.6588 2.4725
Ackerman Angle (deg) 1.8513 1.8513 1.8513 1.8513 1.8513 1.8513
Under/Over Steer (deg) 0.5566 0.6837 -0.2514 0.9638 0.8075 0.6212
Calculated ay (g) 0.0587 0.0854 0.1245 0.1576 0.2043 0.2484
ay Corrected for Banking (g) -0.0805 -0.0537 -0.0147 0.0185 0.0652 0.1092
Measured ay (g) n/a n/a n/a n/a n/a n/a
Understeer Gradient (deg/g) 9.4858 8.0015 6.9825 6.1144 3.9518 2.5013
3.5.2 Rearward Ampli cation
As detailed in Section 1.2.2, rearward ampli cation at it?s simplest form it the tendency
of a unit to exaggerate the inputs. In the case of LCV dynamics, this is most clearly
illustrated in path deviation, lateral acceleration, and body roll of the vehicle. The lead
unit for the LCV is the tractor and the inputs came from the driver and as those inputs are
passed through the ?Train? they can grow in amplitude. The magnitude of ampli cation can
be in uenced by several di erent factors. The most prominent ones are trailer length, dolly
con guration, speed, and period of the maneuver [21]. The formal calculation of rearward
ampli cation is de ned in Equation (3.6).
61
Rearward Ampli cation = Amplitude of Measured UnitAmplitude of Lead Unit (3.6)
Should this value be greater than one, then the unit under measurement experiences a
greater response to the inputs of the lead vehicle.There is no set characteristic that must
be used to calculate the rearward ampli cation. Typically the value of lateral acceleration
or yaw rate is used to determine the magnitude of the ampli cation. However, as described
in Section 3.6, there were some complications with obtaining both of those measurements
accurately for the latter half of the LCV. Due to that, the measurement of body roll was
used in it?s place. Body roll was accurately captured for each vehicle with the use of string
potentiometers attached to each unit?s ride axle. In the case of the tractor the potentiometers
were installed both on the steer axle and on the second drive axle. The roll of the  rst drive
axle was assumed to be the same as the second. The input to the system is the hand wheel
input by the driver. It was determined that the steering linkage had a 1=20 steering ratio, a
plot of the input for a double lane change at 20 mph is illustrated in Figure 3.11. In each
plot of the steering input there are eight di erent points of interest during the maneuver;
those points are detailed below.
POI 1 Start of the left turn to enter left lane.
POI 2 Maximum left steer angle for initial lane change into left lane.
POI 3 Point where hand wheel crosses from positive to negative after initial lane change.
POI 4 Maximum right steer input for  rst lane change. This is the corrective steer input
to maintain the vehicle in the right lane after the  rst lane change.
POI 5 Maximum right steer input to return the vehicle to the original (right lane) lane of
travel.
POI 6 Point where the hand wheel crosses from negative to positive during  nal lane change.
62
Figure 3.11: Double Lane Change Steering Input (20 mph)
POI 7 Maximum left steer input for the  nal lane change. This is the same corrective input
that is seen at POI 4 but this is to return the right lane as opposed to enter the left
lane.
POI 8 Steering input returns to zero and maneuver is ended.
Of note is that at higher speeds or shorter gate spacings POIs 4&5 are the same point
on the input curve. At lower speeds or longer gate spacing there is a period of time where
the driver is attempting to straighten out and steady the vehicle in the left lane. This results
in two distinct peaks negative in magnitude which correlate to a right steer input. When the
speeds are higher or spacing shorter there is no time for this correction and the end of the
initial lane change coincides with the start of the second lane change. A plot of such input
63
is shown in Figure 3.12, notice the di erence between Figures 3.11 & 3.12 where there are
two distinct negative peaks versus one.
Figure 3.12: Double Lane Change Steering Input (40 mph)
3.5.3 Roll Behavior of LCV Units During 40 mph Double Lane Change
With the knowledge that the steering input given by the driver is the overall input to
the system the  rst step is to analyze how the closest link responds to the driver?s input.
The  rst axle that responds to the input is the steer axle on the tractor. As it was one of
the axles out tted with string potentiometers the body roll angle relative to the axle was
captured during testing. A plot of the resulting roll for a double lance change at 40 mph
can be seen in Figure 3.13.
As illustrated, the body roll at the steer axle responds almost instantaneously to the
input from the driver. This response of body roll is now the measurement that will be used to
calculate the rearward ampli cation of all the subsequent LCV units. Keeping the analysis
64
Figure 3.13: Steering Axle Body Roll
in the same order as the axles, the  rst axle to investigate is the drive axle of the tractor.
Any delays here would constitute the frame of the tractor was twisting during testing and
causing a delay and /or ampli cation. A plot of the Steer axle roll compared to the drive
axle roll can be seen in Figure 3.14. The same plot was generated for each of the towed
trailers. That plot can be seen in Figure 3.15.
As somewhat evident in the collection on plots in Figure 3.15, a slight delay and am-
pli cation can be seen in the responses of the subsequent trailers. All of the signals were
combined on the same plot and the outcome of that e ort is illustrated in Figure 3.16.
As with some of the previous data sets it was necessary to  lter the data in order to
better analyze it as well as visualize it in plots. The signal for the body roll of all the axes
except the steer axis were subjected to a low pass 10th order Butterworth  lter with a cut-o 
65
Figure 3.14: Drive Axle Body Roll
frequency of 5 Hz. The new  ltered responses were plotted again and produced Figure 3.17.
As clearly shown in Figure 3.17 there is a de nite delay as well as a de nite increase in
magnitude as the input is propagated down the LCV.
In order to calculate an instantaneous value for the rearward ampli cation one point
on the curve during the dynamics had to be chosen. For the following discussions and
table the point that was chosen was the roll response to the highest input steer that was in
right direction, POI 4& 5 in Figure 3.12. Using that point and the de nition of Rearward
Ampli cation Equation (3.6), Table 3.5 was populated with the results from the calculations
as well as the values used to plug into the equation.
66
Figure 3.15: Trailer Body Roll
Table 3.5: Rearward Ampli cation for LCV during 40 mph Double Lane Change
POI 4 Delta Rearward
t  rt r Ampli cation
HandWheel 16.12 -2.1080 n/a n/a n/a
Steer Axle 16.35 -0.7204 0.00 0.00 1.00
Drive Axle 16.84 -0.9271 0.49 -0.21 1.29
Trailer 1 17.08 -1.0980 0.73 -0.38 1.52
Trailer 2 17.60 -1.1510 1.25 -0.43 1.60
Trailer 3 18.05 -1.2310 1.70 -0.51 1.71
3.6 Data Quality Issues
The  rst speci c issue to arise was the attachment point for the string pot used to
measure the horizontal displacement of the steer axle on the right side of the tractor had
broken, so the string pot measured zero for the majority of the test week. Additionally it
67
Figure 3.16: LCV Body Roll (Un-Filtered)
was discovered was that the messages from the engine CAN-bus were not logged. This was
a result of code changing during the  rst few days of the test week and the log statements
that tell the computer which messages to be logged where not in the correct place in the
con guration  les for the DAQ.
Noise was an issue raised for the string pots but this was not a result of anything other
than process noise. Since the string pots were used to measure linear displacement they were
put in a position as to track as much linear movement as possible for the axles; this meant a
string pot was placed directly above and directly horizontal to the axle in its static position,
shown in Figure 3.18.
Due to the nature of the testing, recording noise-free data is not practically feasible.
The string pot data re ects this with all the noise induced by the environment embedded
68
Figure 3.17: LCV Body Roll (Filtered)
Figure 3.18: Lever arm mounting for string pots
in each measurement. The string pots were mounted on 80/20 frames to the undercarriage
of the vehicle in various positions. These axles are the rotation axis for the tires, which
themselves experience a great deal of noise from the surface of the road. Not only does the
69
uneven pavement introduce noise to the measurements, but also the vibration of the test
vehicle as it is driven down the road can be enough to a ect the data.
In addition to the string pot issues, the two Oxford measurement units were used to
record the positional and orientation data needed to fully characterize the motion of the
two rear trailers of the test vehicle. An Oxford RT2500 was positioned on Trailer 2 and
a RT3100 unit was located on Trailer 3 of the LCV. The RT units use both GPS and an
inertial measurement unit (IMU) to measure the motion of the vehicle, and Kalman  ltering
is automatically applied by the RT system to fuse the data from these two types of sensor
for optimal accuracy. Unfortunately, the devices were not con gured/initialized properly for
the measurements and the RT data recorded were discovered to be erroneous. This was not
uncovered until the data was thoroughly analyzed, as described below the initial data looked
to be noisy but correct.
Initially, it was observed that more noise was present in the signals than what had
been expected or previously experienced. Filtering of some of the signals while the testing
was being conducted showed results that were consistent with the expected motions of the
vehicle for the maneuvers performed. As a result of various delays prior to testing and the
resulting pressure to complete all testing within the planned time-frame, the testing had to
be continued without a complete review and validation of the data integrity.
70
Chapter 4
Vehicle Simulation Results
TruckSima174 is a simulation software that is developed by Mechanical Simulation Inc.
The software is highly con gurable to allow for customization of the simulation to best
match that of the desired vehicle. TruckSima174 is geared towards the heavy truck industry.
This includes but is not limited to commercial vehicles, military vehicles, and large buses.
TruckSima174 allows the user to input mass properties as well dynamic characteristics of the
vehicle under test. These characteristics are normally entered as linear coe cients or tables
of data. Once the vehicle has been con gured the user can then run the vehicle through
a in nite number of sceneries. The user can either choose from pre-de ned maneuvers or
can create their own. For this research the maneuvers that were undertaken during the
experimental phase were mirrored in the simulation as closely as possible. Of note is that
as packaged TruckSima174 cannot simulate the NCAT LCV as it can only simulate up to a
double trailer con guration out of the box. In order to resolve this issue, a custom math
package was purchased from Mechanical Simulation Inc. to allow for the simulation of the
NCAT LCV.
Out of the box with the custom solvers installed, TruckSima174 contains generic models
of several di erent types of trailers to be implemented on the LCV. The default model
was used as the starting point for the simulations. The data that was taken during the
LCV characterization phase in conjunction with Western Michigan University was used to
con gure the simulation model in order to more accurately represent that of the test vehicle.
A screen shot of the TruckSima174 environment with the representative model can be seen in
Figure 4.1. The LCV characterization report that was used to set up the model can be found
in the appendices of [6].
71
Figure 4.1: Screen Shot of TruckSima174 Environment
4.1 Vehicle Con guration
As mentioned, the vehicle was con gured using the parameters that were determined
during the characterization e ort, when measurements were not available the standard
TruckSima174 parameters were left alone. The paths for each of the maneuvers described
in Section 3.3 were entered in as closed-loop driver input paths. An example of this for the
maneuver of a Double Lane Change is shown in Figure 4.2. The goal of this is to match the
results of the simulation to that of the experimental in order to con rm that that simulation
data is accurate and can therefore be used to simulate the vehicle in conditions that were
not able to be run experimentally due to safety concerns. Complete details of the set-up of
TruckSima174 can be found in Appendix A.
Since the vehicle is a combination of six independent components it is unreasonable to
expect the LCV to behave as a single vehicle. This means that when traveling in a straight
line one should not expect all of the subsequent components to have zero for steer angles even
if the lead unit does. What this means is that the driver must compensate for the di erent
72
Figure 4.2: Screen Shot of TruckSima174 Steering Path Input for Double Lane Change
steer angles when attempting to drive in a straight line or along a speci ed path. The driver
must constantly correct with slight turns of the steering wheel in order to maintain a straight
path. This is a result of many minor contributions of the LCV components such as steering
misalignment, suspension wear & misalignment, tire variations, and many other e ects. In
an attempt to illustrate this, a simulation was run with the NCAT vehicle with no steering
input at all. What this is indicative of is the driver removing their hands from the steering
wheel and letting the vehicle settle at some steady state. The steering input from the hand
wheel is shown in Figure 4.3.
As shown, the steering input does not stay at zero as the vehicle settles to steady state.
Additionally this is illustrated in the yaw of each of the units, shown in Figure 4.4. While
the magnitude of the di erence is small it still stands to illustrate that the vehicle does not
track perfectly straight. In all of the subsequent plots regarding the TruckSima174 data the
nomenclature for the plots are detailed in Table 4.1.
The response to the zero steering input serves another purpose other than illustrating
the steady state characteristics of the LCV. It also serves to prove that the model is indeed
stable and suitable for continuing the simulations. One crucial result of the simulation is
73
Figure 4.3: Steering Wheel Response to No Steering Input
Figure 4.4: Yaw Response to No Steering Input
the observation that it takes several seconds for each unit to settle after the start of the
maneuver. For that reason extra time was added to the beginning of all the simulations to
ensure that the vehicle was in steady-state prior to performing the maneuver.
74
Axle 1 Tractor Steer Axle
Unit 1 Freightliner Tractor
Axle 3 Rear Drive Axle of Tractor
Unit 2 Trailer 1
Axle 4 Trailer 1 Rear Axle
Unit 3 Converter Dolly Connecting Trailers 1 & 2
Unit 4 Trailer 2
Axle 6 Trailer 2 Rear Axle
Unit 5 Converter Dolly Connecting Trailers 2 & 3
Unit 6 Trailer 3
Axle 8 Trailer 3 Rear Axle
Table 4.1: Simulation Plot Key
4.2 Experimental Maneuver Simulation
In order to simulate the maneuvers that were undertaken on the test track the steering
inputs had to be placed into TruckSim. This was done by  lling in tables of data with desired
positions of the LCV and TruckSim would then steer the vehicle so that it would follow that
path as best as it could. An example of such input is shown above in Figure 4.2. Each of the
maneuvers and subsequent speeds that were undertaken on the test track were duplicated
in the TruckSim environment. However, for the sake of space only the results from two of
the speeds will be presented for each maneuver in this thesis.
4.2.1 Constant Radius Turn
The constant radius maneuver is exactly what it sounds like, the vehicle travels through
a constant radius curve at a constant speed. A screen shot of the animation of the LCV
traveling trough the curve is shown in Figure 4.5. The path the vehicle traveled is shown
in Figure 4.6. This path is the same for all speeds. Figures 4.7 & 4.8 show the roll of the
vehicle at 25 & 40 mph respectively. Of note for the roll  gures is that the roll is less for the
40 mph than the 20, this is due to the vehicle traveling at higher speeds and therefor having
a greater lateral acceleration that counteracts the gravitational forces that are leading the
vehicle to roll in the negative direction. Figure 4.9 illustrates the o -tracking of the LCV
75
during the constant radius turn. You can easily see that none of the units are actually able
to follow the designed path and that each unit tracks to the inside of the previous unit in
the combination.
Figure 4.5: Screen Shot of Animation for Constant Radius Turn
Figure 4.6: Path of LCV During Constant Radius Turn
76
Figure 4.7: Roll of Each Unit for 25 mph Constant Radius Turn
Figure 4.8: Roll of Each Unit for 40 mph Constant Radius Turn
4.2.2 Single Lane Change
The single lane change is simply maneuvering the vehicle from one lane to the other
within the speci ed gate spacing. For this testing the gate spacing was set at 200 ft. The
maneuver isn?t initiated until the vehicle is in a steady-state. The path is illustrated in
Figure 4.10. In the constant radius turn the o -tracking that was evident was each unit
traveling to the inside of the path set by the preceding vehicle. In the case of lane change
77
Figure 4.9: Unit O -Tracking During 40 mph Constant Radius Turn
maneuvers, the same o set direction is seen at lower speeds. Yet as the speed increases
the o set decreases, eventually becoming such that the trailing vehicle tracks outside of the
leading vehicle. This is illustrated in Figures 4.11 & 4.13 where the  rst is a zoomed section
of of the single lane change at 25 mph and the second is a zoomed section of the single lane
change at 45 mph. To illustrate the o -tracking focus should be paid to the rear axles of
each unit, those being axle three and greater. The full version of the 45 mph single lane
change is shown in Figure 4.12.
The fact that the o -tracking switched from inside to out is due to the speed increase
between maneuvers. The speed at which the o -tracking transitions is at 40 mph; below
that the trailing axles track fully inside the lead axle whereas above that speed the axles
begin to track outside the path of the lead axle. The same response can be seen in the
plots of lateral acceleration as well as yaw. In both cases the highest values are that of
the tractor and then decreasing down the LCV. Whereas at high speeds that behavior is
reversed and the further back in the LCV the point of interest is the greater the response.
This is the notion of rearward ampli cation. At lower speeds the rearward ampli cation
is less than one, but after the vehicle crosses the critical speed limit the magnitude of the
ampli cation becomes greater than one. That is to simply say the trailing vehicle exhibits
78
Figure 4.10: Path of LCV During 25 mph Single Lane Change
Figure 4.11: Low Speed O -Tracking During 25 mph Single Lane Change
a greater response than that of the leading vehicle. This is shown in the following  gures;
Figure 4.14 (Lateral Acceleration 25 mph) & Figure 4.15 (Lateral Acceleration 45 mph) &
Figure 4.17 (Unit Yaw 25 mph) & lastly Figure 4.17 (Unit Yaw 45 mph).
79
Figure 4.12: Path of LCV During 45 mph Single Lane Change
Figure 4.13: High Speed O -Tracking During 45 mph Single Lane Change
4.2.3 Double Lane Change
The double lane change (DLC) is an obstacle avoidance simulation maneuver. The
aim is to view the response of the vehicle to two quick subsequent lane changes that would
occur in the case of the lane being suddenly obstructed and the driver having to rapidly
adjust. The maneuver begins in the right lane and once the vehicle is at steady state the
80
Figure 4.14: Lateral Acceleration During 25 mph Single Lane Change
Figure 4.15: Lateral Acceleration During 45 mph Single Lane Change
driver steers the vehicle over to the left lane within a pre-de ned gate spacing. Once in the
left lane the driver then returns to the right lane within the same gate spacing. A more
detailed description of the maneuver was provided previously in Section 3.3. Most of the
same characteristics are looked at for the double lane change that were examined for the
single lane change. The di erences is that the double tends to excite larger ampli cations as
81
Figure 4.16: Unit Yaw During 25 mph Single Lane Change
Figure 4.17: Unit Yaw During 45 mph Single Lane Change
it is the culmination of two rapid lane changes instead of only one. The same gate spacing
of 200 ft was used for the double that was utilized in the single lane change. The path of the
double lane change is shown in Figure 4.18 (25 mph), the plot for 45 mph DLC is shown in
Figure 4.19.
82
Figure 4.18: Path of LCV During 25 mph Double Lane Change
Figure 4.19: Path of LCV During 45 mph Double Lane Change
One of the di erences between the single and double lane changes is that due to the
short distance that is traveled in the left lane prior to performing the 2nd lane change there is
little to no o -tracking shown in the  rst lane change regardless of speed. This is illustrated
in Figures 4.20 & 4.21 which are for 25 and 45 mph respectively.
83
Figure 4.20: Low Speed O -Tracking During 25 mph Double Lane Change (1st Lane Change)
Figure 4.21: High Speed O -Tracking During 45 mph Double Lane Change (1st Lane Change)
However when examining the 2nd lane change you can discern the same experience with
the o -tacking as illustrated in the single lane change. This is explained by understanding
that the initial lane change is never fully completed as the vehicle is not allowed to settle
prior to commencing the return lane change. To examine the o -tracking for the return lane
change see Figures 4.22 & 4.23 again for 25 and 45 mph respectively.
84
Figure 4.22: Low Speed O -Tracking During 25 mph Double Lane Change (2nd Lane Change)
Figure 4.23: High Speed O -Tracking During 45 mph Double Lane Change (2nd Lane
Change)
One of the most informative plots to look at for the double lane change is the lateral
acceleration of each unit in the LCV. From this plot, not only can rearward ampli cation be
examined but also settling time and stability of the units can be assessed. Figures 4.24 &
85
4.25 show the lateral acceleration according to TruckSim for the 25 and 45 mph double lane
changes.
Figure 4.24: Lateral Acceleration During 25 mph Double Lane Change
Figure 4.25: Lateral Acceleration During 45 mph Double Lane Change
As shown in the single lane change, the rearward ampli cation is less than one at the
lower speed of 25 mph and greater than one at the higher speed of 45 mph. The more
interesting element is the settling time of the third trailer as well as the amplitude of the
86
oscillation in the acceleration. At the lower speed of 25 mph the third trailer follows the
acceleration patterns of the rest of the LCV fairly indistinguishably. Yet with an increase of
only 15 mph, the third trailer becomes rather unstable and very oscillatory in it?s response.
This is speci cally evident in the return lane change. This gross increase in lateral accelera-
tion led to the simulation at highway speeds of 60 mph for exploratory purposes. That plot
is shown in Figure 4.26.
Figure 4.26: Lateral Acceleration During 60 mph Double Lane Change
While it may be hard to discern what occurred during the maneuver, it is easily noted
that the behavior of the third trailer is nothing like that of any other unit. The reason for
this is that at the speed of 60 mph the simulation of the double lane change resulted in the
third trailer rolling over in the middle of the return lane change, which is easily illustrated
in the plot of unit roll for the maneuver which is shown in Figure 4.27. The third trailer of
the LCV actually experiences wheel lift-o in the middle of the initial lane change and then
when the tractor tries to navigate back into the original lane the third trailer rolls over and
takes the second converter dolly with it. Another property of the 60 mph double lane change
is how the tractor seems to be uninterrupted by the instability and subsequent crashing of
the third trailer during the maneuver.
87
Figure 4.27: Unit Roll During 60 mph Double Lane Change
4.3 Experimental vs. Simulation
In an attempt to compare the results from the TruckSim simulations and that of the data
taken experimentally, several overlay plots were generated. The following plots represent the
data collected and simulated for a 30 mph double lane change. The  rst plot to examine
is the driver input which is the hand wheel angle. That comparison is illustrated in Figure
4.28.
There are several key di erences between the two data sets. The most noticeable is
the early steer into the left lane in the experimental data. This can be explained by under-
standing that the driver in the experimental phase had a much longer preview time than
the simulation did. That is to say that the driver knew what was coming and started to
turn to the left sooner than he should have. Whereas in the simulation, the computer does
exactly what is laid out in the simulation and does not begin to make the turn until the exact
moment the LCV passes through gate 1. This results in a lower steer input for both the
initial departure from the original lane as well as the return into the original lane. Additional
e ects of this discrepancy will be described shortly.
Another key point of interest is the articulation angle of the two converter dollies. The
experimental data was passed through a low pass  lter to remove some of the noise so that
88
Figure 4.28: Steering Input Comparison for Simulation & Experimental Data
the two data sets could be plotted together. The calculated and measured articulation angles
are presented in Figure 4.29 & 4.30 for the  rst and second dolly respectively for the 30 mph
double lane change.
As shown, the two data sets match up rather well with minimal disagreements. The
early steer input can be seen in both plots as well. This measurement was of some concern as
it was the combination of two di erent string potentiometers placed adjacent to one another
and measuring the linear displacement of the proceeding trailer. That measurement was
then converted to an angle based on the radius of the trailer tongue. This shows that the
methodology and implementation of the articulation measurement was su cient in capturing
the angle. This articulation angle serves as the steer input into the proceeding trailer, hence
why from a dynamic analysis standpoint it is a crucial measurement to get right.
The last set of comparison plots to present are that of unit roll. The roll for the  rst
and last trailers is presented below in Figure 4.31 & 4.32 respectively. While the two do not
agree as much as would be desired the di erences are believed to be because of the longer
89
Figure 4.29: Dolly 1 Articulation Angle Comparison for Simulation & Experimental Data
Figure 4.30: Dolly 2 Articulation Angle Comparison for Simulation & Experimental Data
preview time described above. Since there was a lower steer rate input for the experimental
data than that of the simulation data set it would be expected that the input would not
90
incite as much roll. Of interest is that for the steer input back into the original lane of travel
the  rst trailer comparison appears to match rather well. This is due to the preview time
of the drive being shortened during the middle of the maneuver. In essence by the time the
driver has successfully navigated the vehicle into the left lane, he has to begin his transition
back into the original lane of travel. this causes an increased steer rate than that of the
original lane change and therefore incites a greater roll response from the subsequent units.
Figure 4.31: Trailer 1 Roll Comparison for Simulation & Experimental Data
91
Figure 4.32: Trailer 3 Roll Comparison for Simulation & Experimental Data
4.4 Double vs. Triple LCV
One of the best ways to assess the safety of a triple is to compare it to a standard
that is prominent currently. To that end, several simulations were run using a standard
double semi-trailer con guration. The settings for the vehicle were all left as packaged from
TruckSim with the assumption that they were representative of the average parameters for
the vehicle. Three separate simulations were chosen for comparison, two of which were
double lane change maneuvers and the third a single lane change. The double lane changes
were run at 45, 55, and 60 mph. The single lane changes were compared at 45, 55, and 65
mph. For all of the maneuvers the characteristics of interest where roll, yaw, and lateral
acceleration; each of those values will be plotted for comparison.
92
4.4.1 Single Lane Change Comparison
The single lane change is a good starting point for assessing the stability of any vehicle.
It is a low risk maneuver as it is not intended to excite large dynamic responses, especially
in the case of the SLC set up for this research with a gate spacing of 200 ft. Figures 4.33 -
4.35 show the varying yaw responses for 45, 55, and 65 mph respectively.
Figure 4.33: 45 mph Single Lane Change Double vs. Triple Yaw Comparison
As illustrated in the  gures, at lower speeds the units tend to behave identical. This is
especially the case with the trailers. As the speeds increase though the responses begin to
vary, most notably with respect to the tractor. Of note is that at the 65 mph speed the triple
LCV experienced rollover of the third trailer, that is why the triple data plots end abruptly.
One interesting characteristic that is illustrated is the lower oscillation of the tractor, this
is a result of the heavier load in the triple. At the lower speeds the heavier load does not
require as much correctional steering as the double. That correctional steering to keep the
vehicle in the lane is the cause of the oscillation in the yaw of the double combination. The
next characteristic to observe is the roll behavior of each vehicle during the same double
93
Figure 4.34: 55 mph Single Lane Change Double vs. Triple Yaw Comparison
Figure 4.35: 65 mph Single Lane Change Double vs. Triple Yaw Comparison
lane change maneuvers. Figures 4.36 - 4.38 show the varying roll responses for 45, 55, and
65 mph respectively.
94
Figure 4.36: 45 mph Single Lane Change Double vs. Triple Roll Comparison
Figure 4.37: 55 mph Single Lane Change Double vs. Triple Roll Comparison
The same heavier load that helped the triple in the yaw comparison hurts it in the roll
comparison. Because of the heavier load, the vehicle experiences much larger roll than that
95
Figure 4.38: 65 mph Single Lane Change Double vs. Triple Roll Comparison
of the double. This also causes the triple to ?rock? after each maneuver and takes some time
to settle out. The roll of the vehicle is the most visual evident characteristic for large trucks
with their innate high center of gravity. Of note is that none of these speeds were even
attempted during the experimental phase as they were all beyond the driver?s comfort level.
The visual of the triple settling out after the lane change is not one that would be comforting
to any motorist. The  nal characteristic that will be explored is the lateral acceleration of
the units in the combinations. Those responses for 45, 55, & 65 mph are plotted below in
Figures 4.39 - 4.41 respectively.
The lateral acceleration response is somewhat a combination of both the Yaw response
and the Roll response. The trailers appear to response identically at the lower speeds, as the
speeds increase the triple begins to experience higher amplitude along with a shorter period
of oscillation for the response. It can be seen in Figure 4.40 that the third trailer on the
triple takes a considerable amount of time to settle after the maneuver. This is an indication
96
Figure 4.39: 45 mph Single Lane Change Double vs. Triple Lateral Acceleration Comparison
Figure 4.40: 55 mph Single Lane Change Double vs. Triple Lateral Acceleration Comparison
that the trailer is approaching it?s stability moment and any increase in speed could lead to
rollover, which is exactly what happens at 60 mph.
97
Figure 4.41: 65 mph Single Lane Change Double vs. Triple Lateral Acceleration Comparison
4.4.2 Double Lane Change Comparison
The next maneuver that was simulated for comparison was the Double Lane Change
(DLC). This maneuver is meant to excite large dynamic responses and that is very evident
at the higher speeds. Figures 4.42 - 4.44 show the varying yaw responses for 45, 55, and 60
mph respectively.
The yaw responses of the vehicles behaves similar to that of the single lane change.
At lower speeds the units, especially the tractors appear almost identical. Then as the
speeds increase the tractor experiences a decrease in amplitude while the trailers appear
to be una ected. That is, until you reach 60 mph at which the third trailer in the triple
combination experiences rollover. The next characteristic to observe is the roll behavior of
each vehicle during the same double lane change maneuvers. Figures 4.45 - 4.47 show the
varying roll responses for 45, 55, and 60 mph respectively.
The roll response of the triple especially does not look ideal at any speed. The third
trailer fails to settle fully in any of the simulations. The responses of the triple truck and
98
Figure 4.42: 45 mph Double Lane Change Double vs. Triple Yaw Comparison
Figure 4.43: 55 mph Double Lane Change Double vs. Triple Yaw Comparison
 rst trailer appear to match that of the double truck and  rst trailer more closely during the
double lane change than the single lane change. This is believed to be because once in the
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Figure 4.44: 60 mph Double Lane Change Double vs. Triple Yaw Comparison
Figure 4.45: 45 mph Double Lane Change Double vs. Triple Roll Comparison
left lane the driver must already begin the maneuver to go back to the right lane, therefor
not allowing any of the units to begin to settle in the left lane. The  nal characteristic that
100
Figure 4.46: 55 mph Double Lane Change Double vs. Triple Roll Comparison
Figure 4.47: 60 mph Double Lane Change Double vs. Triple Roll Comparison
will be explored is the lateral acceleration of the units in the combinations. Those responses
for 45, 55, & 60 mph are plotted below in Figures 4.48 - 4.50 respectively.
101
Figure 4.48: 45 mph Double Lane Change Double vs. Triple Lateral Acceleration Compari-
son
Figure 4.49: 55 mph Double Lane Change Double vs. Triple Lateral Acceleration Compari-
son
102
Figure 4.50: 60 mph Double Lane Change Double vs. Triple Lateral Acceleration Compari-
son
The lateral acceleration of the units for the double lane change is not a good vote for
the legalization of triple trailers on highways across the nation. The lateral acceleration the
triple undergoes in the 45 mph maneuver alone is enough cause for concern. The double
lane change is a maneuver that happens often and any vehicle that is going to be traveling
at highway speeds needs to have the ability to perform such a maneuver in the event of an
emergency. The triple LCV does not show any indication that it would be able to perform
the double lane change at any speed greater than that of residential with any form of safety.
This was also experienced in the experimental phase when it was attempted to perform the
double lane change at 40 mph. After performing the maneuver the driver decided that it
was too fast and only one attempt was made at that speed.
4.4.3 Double vs. Triple Conclusions
After running the simulations and comparing the outputs it was interesting to see that
for the most part the vehicle performed identical at lower speeds. This shows that the trailing
103
vehicles have little e ect on the leading vehicles from a dynamics standpoint at the lower
speeds. However, as the speeds increased it was easy to see that the triple is much less stable
and has a higher propensity for rollover making it unsafe. The triple experiences rollover in
the double lane change maneuver at approximately 58 mph and at approximately 62 mph in
the single lane change, both speeds that are well within the expected operating speed of any
highway vehicle. It would appear that the triple needs much more safety integration before
being suitable for the highway.
4.5 Sources of Error
There were several large sources of error that were encountered in this project. the
mitigation of such sources is key to improving the research and increasing the  delity of
the simulation. The main source of error for this phase of the research was human error
in calculation the LCV characteristics. All of the distance measurements were ascertained
by hand which innately leads to some margin of error. Additionally, material property
assumptions had to be made in order to estimate both mass as well as compliance for the
suspension system. Another source of error is the lack of complete characteristic data for
the LCV as found at NCAT. As described in detail in Appendix A, there were a multitude
of instances that characteristics were left as packaged from TruckSim. These characteristics
might be a representative value of the average tractor and/or trailer they were not speci c
to the NCAT LCV. It is unknown if there were any assumptions made in the creation of the
simulation package for TruckSim that may be violated by the NCAT vehicle, which could
serve as another source of error.
4.6 Improvements for Future Simulations
As with any simulation, there is always room to improve upon it. This simulation is no
di erent as there were several di erent areas in which the model was lacking to some extent.
The most critical area in which the  delity can be improved upon is the tire data. The tires
104
for the simulation were left as packaged from TruckSim. If the model is to be improved, the
 rst step suggested would be to obtain more accurate tire data and insert that data into the
simulation. In addition to the tire data, more knowledge about the suspension kinematics
would help serve the simulation. The data was also limited to what could be obtained
by hand without the use large test equipment speci cally engineered to characterize heavy
trucks. Some examples of such equipment would be a tilt table to better locate the CG of the
units and a Kinematics and Compliance (K&C) measurement machine to better characterize
the suspension.
105
Chapter 5
Conclusions
This project was but a step in the direction of the research that needs to be completed to
fully understand and characterize the dynamics of Longer Combination Vehicles. In conjunc-
ture with experimental testing, an analytical model was developed and simulated through
the use of a computer simulation package. The models created in the simulation phase are
available for improvement and future use in parallel research. The known characteristics of
LCV dynamics were shown to be present in both the experimental and simulation results.
A method for capturing dynamic data on a LCV was both designed as well as tested. If
the e orts were to be summed into one transfer function that would be Equation (5.1). The
characteristic of most concern is that of the roll behavior of the third trailer as it reacts to
the driver input of steer angle. This relationship is the basis for stability and subsequent
safety assessments talked about in this chapter.
TF = ThirdTrailerRollResponseDriverSteerInput (5.1)
5.1 Experimental Conclusions
The experimental data concluded that the measurement of roll angle of the separate
trailers was a reasonable predictor of rearward ampli cation of roll angle between the tractor
and subsequent trailers. Additionally, the tractor and trailers showed understeer gradients
that were expected given the mechanical linkage between the units. The custom designed
DAQ worked adequately for the project, yet had it?s shortcomings. As described lateral
acceleration data was not obtained for half of the LCV and as a result the traditional
method for determining rearward ampli cation wasn?t possible. In future e orts, closer
106
considerations and precautions should be taken to ensure the correct data is being recorded
and that the data recorded is reasonable in magnitude and shape.
5.2 Simulation Conclusions
The simulation environment enabled multiple di erent scenarios being explored and
allowed for the exploration of the behavior at higher speed unattainable during the ex-
perimental phase. Many di erent maneuvers were simulated at many di erent speeds, for
example through the iterative process it was determined that the critical speed for stability
of the LCV during the double lane change was 58 mph. At speeds less than that the LCV
would recover from the extensive dynamic response that was incited via the double lane
change. Whereas at speeds above that, the vehicle would not recover and the third trailer
would roll over during the returning lane change. This threshold is illustrated in Figures 5.1
& 5.2 where the roll of each unit is plotted versus time for 55 mph and 60 mph respectively.
Figure 5.1: Unit Roll During 55 mph Double Lane Change
In comparing the Triple LCV to a standard Double Trailer con guration it was shown
that the triple had a lower stability limit in that it had a higher propensity for rollover at
speeds that are to be expected of a highway vehicle. In addition, given the unsettling feeling
107
Figure 5.2: Unit Roll During 60 mph Double Lane Change
most motorists have towards the double trailers it is hard to envision a triple trailer being
received well if at all.
5.3 Final Conclusions
Several of the dynamic characteristics were con rmed when comparing the experimental
data to the output of the simulation. Measurements of all articulation angles along with vi-
sual observations of the LCV (speci cally the third trailer) were in agreement. The rearward
ampli cation of the unit roll and articulation were successfully measured and compared for
single and double lane change maneuvers. Understeer properties were successfully measured
using a constant radius turn. The combination of the above was adequate for a partial
veri cation of the simulation.
Taking all of this into consideration, the initial conclusions at this stage in the research
is that LCV triples need a large number of safety equipment that is not yet available before
they should be permitted on all highways throughout the US. Some of those improvements
include a robust Electronic Stability Control (ESC) that can implement di erential braking
on all of the units, as well the possibility of inducing torque on the  fth wheel of each
trailer in order to dampen out the oscillatory response seen in the simulations at higher
108
speeds. In order to achieve this, the communications between the trailers will need to be
greatly improved. That improvement can be accomplished via a CAN bus that is common
to the entire LCV. The additions that would be required would be more complete sensor
packages that include but not limited to IMU?s, GPS receivers, and linear displacement
measurements. The combination of the aforementioned sensors could be implemented into
a control algorithm to predict and monitor the safety threshold for the unit and control the
ESC accordingly to prevent any unwanted behavior.
5.4 Future Research
The simulation model can be used to predict the potential impact of any changes in the
con guration of the LCV. This includes changes in payload, dimensions, mechanical prop-
erties, and many others. The vehicle used in this research was chosen because of both it?s
availability and the availability of the testing course. It is to some level indicative of what a
commercial LCV would be but that relationship could be improved upon. Most notably by
payload weight and con guration. In addition the the payloads, the suspension characteris-
tics of the units were assumed to be the same, if this research is to become complete that
assumption has to be thrown out and each individual unit needs to be accurately modeled
and tested.
Perhaps the most in uential modi cation lies underneath the LCV. The tires are how
the LCV interacts with the road, all of the forces that act between the ground and the LCV
go through the tires. Due to this relationship, the tire properties are a crucial improvement in
order to increase the  delity of the model. There are two ways of improving those properties,
either extensive experimental e orts or some propriety agreement with a tire manufacture.
The simulations showed that the vehicle was unstable at highway speeds, a potential
area of interest would be to investigate how to best increase the stable speed of the LCV
through either weight distribution or some other mechanical property adjustment. This could
be achieved  rst in simulation prior to being implemented on any vehicle fro experimental
109
testing. An additional area of interest would be to incorporate the ESC system described
above, or some subset of it in order to asses it?s performance in increasing the stability and
safety of the LCV for the purpose of highway travel.
110
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112
Appendix A
TruckSima174 Con guration
A.1 TruckSima174 General Overview
TruckSim is a software package o ered by Mechanical Simulation. It is speci c to
simulating and analyzing the dynamic behavior of medium to heavy trucks. Mechanical
Simulation also produces CarSim, which is geared towards the more typical vehicle dynamics
of smaller vehicles. The package provides the ability to run modeled vehicles through user-
de ned tests and output the results in forms varying from tabular data, synchronous log  les,
plots, animations, and more. Data characterizing the vehicle to be modeled is entered into
TruckSim in the form of mechanical properties, linear coe cients, or tables. As packaged,
TruckSim cannot simulate an LCV triple; the most trailers that can be attached on the
standard version is two. For that reason, a custom solver was purchased from Mechanical
Simulation to enable to simulation of the LCV triple. Since it is a custom solution the set-up
di ers slightly from the generic. Once the custom solvers were installed, the task of entering
in the vehicle speci c data that represented the NCAT LCV was undertaken. A screen shot
of TruckSim animating a simulation of the NCAT Triple can be seen in Figure A.1.
A.2 Model Formulation
The vehicle was modeled according to the measurements taken in conjuncture with
Western Michigan University as part of an LCV characterization e ort. Where measurements
were not available, the standard parameters in TruckSim were used. The following sections
will describe in detail the steps taken to enter in the kinematic and dynamic properties of
the NCAT LCV. Once installed and launched the  rst screen that the user encounters is the
113
Figure A.1: Screen Shot of Simulation Animation
main screen. That screen is shown in Figure A.2. In this window the user can select which
vehicle con guration to use, which procedure to run, and what output if any they desire for
the results. A description of all the options and why they are set that way is found in Table
A.1.
A.2.1 Vehicle Con guration
Under vehicle con guration the user selects a vehicle class which in the case of the NCAT
triple is S SS + S + dS + S + dS + S, each S represents an axle and each dS represents a
converter dolly. Upon entering the con guration window for the vehicle the user is presented
with the vehicle selection window, which is shown in Figure A.3. It is here that the user will
select which vehicle components that are to be con gured to make up the vehicle under test.
A description of the settings is shown in Table A.2
As seen, there are numerous di erent properties to be set. Of note is that for the NCAT
LCV the second trailer is actually two trailers and a dolly which is why the vehicle type for
114
Figure A.2: TruckSim Main Window
Table A.1: TruckSim Main Set-Up Screen Options
Test Speci cations
Vehicle Con guration
Set the the data set of S SS + S + dS + S + dS + S to represent the custom
solver for triple trailers. The vehicle selected is the custom vehicle built to
match that of the test vehicle at NCAT, that process is detailed in Section
A.2.
Procedure Select which procedure is to be run. The set up for the procedures is detailedin Section A.4.
Run Control
Run Math Model The START button, will run simulation based on the selections made onpage.
Output Variables Can write selected variables to external  les such as .csv  les or MATLAB.mat  les.
Results
Animate Will run the animation and create a video of the simulation. Will not runif output variables are written to  le.
Plot Will plot the de ned plots selected in the procedure set up (Section A.4),can additionally de ne extra plots of interest.
More Options
Screen Options Can overwrite certain parameters de ned in the procedure set-up.
Overlay Animations Can plot other simulations simultaneously as well as animate multiple sim-ulations at once.
115
Figure A.3: TruckSim Vehicle Window
Table A.2: TruckSim Vehicle Con guration Options
Lead Unit
Vehicle Type The Tractor class is S SS as it is a single steer axle with double drive axles.
Vehicle De nition Set to the con guration that resembles the NCAT Tractor, the detailedcon guration for the Tractor is described in section A.4.
Trailer
Trailer Type The selection here is a single axle trailer, which is what the single S repre-sents.
Trailer De nition The Con guration that best represents the  rst trailer in the combinationis selected, that con guration is detailed in Section A.2.3.
Loads in First Trailer The payload is selected that represents the  rst trailer, this too is detailedin Section A.2.3.
Second Trailer
Trailer Type
For the second trailer the type dS + S + dS + S is selected to represent
the remaining two trailers and converter dollies. This is selected as such
because of the custom solvers that had to be installed in order to simulate
a triple trailer.
Trailer De nition The con guration for the Second & Third Trailer is outlined in the followingparagraph and accompanying pictures and tables.
116
Figure A.4: TruckSim Custom Second Trailer Con guration
the second trailer is dS + S + dS + S instead of just dS + S for a typical double trailer
con guration. In order to complete the con guration of the vehicle the user most con gure
the custom solver options that are found once entering the con guration for the custom
second trailer. Upon entering said con guration the screen encountered is shown in Figure
A.4 and the accompanying description of options is outlined in Table A.3.
A.2.2 Tractor Con guration
The  rst unit to be con gured is the tractor, upon exiting the custom con guration and
returning to the main vehicle con guration screen (A.3)) the user can enter the con guration
for the tractor. Once in the con guration the user sees the vehicle con guration screen shown
here in Figure A.5. It is here that the mechanical properties of the tractor will be assigned
and other properties de ned. A description of the settings is detailed in Table A.4.
Tractor Sprung Mass Characteristics
For the NCAT LCV the 2A Day Can Sprung Mass was selected as the vehicle type
as that most closely re ects the actual tractor. The aerodynamics, animator shape, tires,
117
Table A.3: TruckSim Custom Solver Options
Dataset Code
This is left as packaged from TruckSim Custom Installation, additionally all of the comments
in the parameter set boxes are untouched.
Link 1
Link Type The selection here is a single axle trailer with a converter dolly, which is rep-resented by dS + S.
Link De nition The Con guration that best represents the second trailer in the combinationis selected, that con guration is detailed in Section A.2.4.
Link 2
Link Type The second link for the custom solver is the payload options of the secondtrailer.
Link De nition The payload for the Second Trailer is de ned in Section A.2.4.
Link 3
Link Type The selection here is a single axle trailer with a converter dolly, which is rep-resented by dS + S.
Link De nition The Con guration that best represents the third trailer in the combination isselected, that con guration is detailed in Section A.2.4.
Link 4
Link Type The fourth and  nal link for the custom solver is the payload options of thethird trailer.
Link De nition The payload for the Third Trailer is de ned in Section A.2.4.
Figure A.5: Vehicle Con guration Window
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Table A.4: TruckSim Tractor Set-Up Screen Options
Sprung Mass
Class & De nition Rigid Spring Mass; 2A Day Cab Sprung Mass. These selections were left aspackaged.
Aerodynamics
De nition Conv. Cab w/o Fairings 4.3 m Ref. Again selection was left as packaged asno information about the aerodynamics was obtained.
Animator Shape
De nition 3A Day Cab, selection was made to aesthetically represent the sprung massselection. Con guration was left as packaged.
Tires
De nition 3000 kg Steer, 3000 kg Drive/Tandem. Selection left as packaged.
Steering Wheel
De nition 1/25 (Typical) - Left as packaged
Powertrain
Class 6 x 4, axles 2 & 3
De nition 330 kW, 18 spd MT, 4WD - selection was left as packaged.
Axle 1
Class Solid Axle (full K & C)
Susp Kin, Con guration made to match that of the kinematics of the steer axle.
Comp Con guration changed to mirror that of the NCAT tractor steer axle.
Brakes Left as packaged
Steering Selection was left as packaged
Axle 2 & 3
Class Solid Axle (full K & C)
Susp Kin, Con guration made to match that of the kinematics of the drive axles.
Comp Con guration changed to mirror that of the NCAT tractor drive axles.
Brakes Left as packaged
Steering No steering on the drive axles
Hitch
De nition 5th Wheel - left as packaged.
Position Dist Back (4760.9 mm) Y (0 mm) Height (1081 mm)
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Figure A.6: Steer Axle Kinematic Con guration Window
and steering wheel torque were left as packaged. The power-train was set at 6x4, axles 2
& 3 with the 330 kW, 18 spd, MT, 4WD transmission selected. The distances placed in
all of the yellow boxes came from the LCV Characterization report. In the lower half of
the window, the user is to select and con gure the suspension properties of the tractor the
 rst axle being the steering axle was con gured  rst. The  rst aspect to con gure was the
suspension kinematics, this window is shown in Figure A.6. Again, the measurements that
are placed in the yellow boxes are either re ective of the LCV Characterization Report or
left as packaged in TruckSim.
Tractor Steer Axle Suspension Characteristics
Once back to the Vehicle Con guration Window, Figure A.5 the next set of properties
to con gure are the suspension characteristics for the steer axle. That window is illustrated
in Figure A.7.
The  rst property to set is the spring characteristics, based o the LCV Characteriza-
tion Report the leaf springs where given a sti ness of 263N/mm at 2000N. The only other
characteristic that wasn?t left as packages is the roll moment for the steer axle. That was
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Figure A.7: Steer Axle Suspension Con guration Window
con gured using data collected during the LCV characterization e ort. That screen is shown
in Figure A.8.
Tractor Drive Axle Suspension Characteristics
The last component of the tractor to be con gured is the drive axles kinematics and
suspension properties. The  rst is the kinematic data, that screen is shown in Figure A.9.
For the drive axles, the data from the characterization report was entered where appli-
cable. In addition to the static data, the roll steer for the drive axle was not a simple linear
coe cient as it was for the steer axle. Upon entering the con guration for the roll steer the
user should see Figure A.10. The data for the roll steer was taken from the characterization
report. This is the completion of the tractor con guration.
A.2.3 Trailer 1 Con guration
Once the con guration of the tractor is complete the next unit to con gure is the  rst
trailer. That screen is represented in Figure A.11, with the description of the  elds in Table
A.5.
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Figure A.8: Steer Axle Roll Sti ness Con guration Window
Figure A.9: Drive Axle Kinematic Con guration Window
122
Figure A.10: Drive Axle Roll Steer Window
Figure A.11: Trailer Main Con guration Window
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Table A.5: Trailer Con guration Options
Sprung Mass
1A Trailer - Since the trailers were permanently loaded, measuring the
sprung mass was not possible. Therefor the mass properties were adjusted
using payload modi cations.
Aerodynamics No Aerodynamics
Animator Shape NCAT Box - Some minor adjustments were made to the default settings forcosmetic reasons, they bared no e ect on the simulation
Dolly There is no dolly on the  rst trailer as it attached to the  fth wheel on thetractor.
Tires Left as packaged as tire data was unavailable.
Axle 1
Kinematics Con gured to match NCAT Trailer.
Compliance Entered characterization report values.
Brakes Left as Packaged
Hitch
Position
De nition
Trailer Kinematic Characteristics
The  rst con guration to complete for the trailer suspension is the kinematic data for the
trailer axle, that con guration can be seen in Figure A.12. As with the other con gurations,
the data was either left as packaged or taken from the LCV characterization report.
Trailer Compliance Characteristics
Next, the leaf springs needed characterization, that screen is shown in Figure A.13. The
additional con guration of the roll moment is illustrated in Figure A.14.
Trailer Payload Con guration
The last step in con guring the  rst trailer is to adjust the payload to match that of
the loaded NCAT Trailer. The screen in which this is done is accessed through the main
vehicle con guration window, Figure A.2, and is captured in Figure A.15. The numbers
that were entered for the payload were taken from the vehicle characterization report and
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Figure A.12: Trailer 1 Axle Kinematics Window
Figure A.13: Trailer 1 Axle Leaf Suspension Con guration Window
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Figure A.14: Trailer 1 Roll Sti ness Con guration Window
were generated during the weighing of the loaded LCV axle by axle. This completes the
con guration of the  rst trailer.
A.2.4 Trailers 2 & 3 Con guration
The suspension of each trailer was con gured the same as that of the  rst trailer since all
of the trailers had identical suspensions and axles. The main di erence in the con guration
of the second and third trailer versus the  rst is the additional step(s) in con guring the dolly
that accompanies the trailer. That process is detailed below in Section A.2.5. Seeing that the
second and third trailers were identical from a kinematics and compliance standpoint, they
were con gured exactly the same minus the variations in payload weight. That variation,
along with the  rst trailer is detailed in Table A.6.
A.2.5 Con guring the Converter Dollies
In order to con gure the converter dollies the user  rst needs to ensure that all of the
trailers are con gured correctly with respect to dollies and pintle hitches. In order for a
trailer to ride on a converter dolly it must be speci ed in the trailer con guration that is
126
Figure A.15: Trailer 1 Payload Con guration Window
Table A.6: NCAT Vehicle Gross Weight
Measured TruckSim Measured TruckSim
Unit kg kg lb lb
Tractor & Trailer 1 32,986 33,029 72,900 72,994
Trailer 2 19,186 13,013 42,400 42,019
Trailer 3 18,552 18,588 41,000 41,080
Whole Vehicle 70,724 70,630 156,300 156,093
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Table A.7: Trailer Linkage Con guration
Dolly Pintle Hitch Fifth Wheel
Unit Y/N Y/N
Dist.
Back
(mm)
Y (mm) Height(mm) Y/N
Dist.
Back
(mm)
Y (mm) Height(mm)
Tractor N/A Yes 4760.9 0 1081
Trailer 1 No Yes 6692.9 0 774.70 No N/A
Dolly 1 N/A Yes 1829 0 1100
Trailer 2 No Yes 6692.9 0 774.70 No N/A
Dolly 2 N/A Yes 1829 0 1100
Trailer 3 Yes No N/A No N/A
to use that dolly. That is to say for the second trailer that rides on the converter dolly
between the  rst and second trailer the dolly must be con gured within the second trailer
con guration. The  rst trailer is di erent because the  fth wheel joint it rides on is part of
the tractor and is included in the tractor con guration. Similarly, for the trailers that are to
attach to a converter dolly (1st & 2nd) the pintle hitch must be de ned for the converter dolly
to attach to. Table A.7 details which settings need to be con gured on each trailer such that
the linkage is correct. All of the distances and heights came from the LCV characterization
report.
Once all of the linkages has been correctly con gured the last step in the model for-
mulation is the con guration of the converter dolly compliance and kinematic data. Upon
entering the dolly con guration screen the user should see Figure A.16. The settings of the
converter dolly are detailed in Table A.8.
Dolly Sprung Mass Characteristics
The sprung mass con guration screen is shown in Figure A.17, the information was
taken from the characterization report.
Dolly Kinematics Characteristics
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Figure A.16: Converter Dolly Con guration Window
Table A.8: Converter Dolly Con guration Options
General Options
Sprung Mass NCAT 1A Dolly
Animator Shape Dolly w/1A
Tires Left as packaged as tire data was unavailable.
Axle 1
X Dist. Back 2100 mm
Kinematics Con gured to match NCAT Dolly.
Compliance Entered characterization report values.
Brakes Left as Packaged
Hitch
Position Dist. (1829 mm) Y (0 mm) H (1100 mm)
De nition 5th Wheel Typical - As Packaged
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Figure A.17: Converter Dolly Sprung Mass Con guration Window
The kinematics con guration screen is shown in Figure A.18, the information was taken
from the characterization report.
Dolly Compliance Characteristics
The suspension compliance con guration screen is shown in Figure A.19. The con gu-
ration screen for the roll sti ness of the converter dollies is shown in Figure A.20. In both
cases the information was taken from the characterization report.
A.3 Model Stability
An LCV should not be expected to move as a single unit in a straight line with zero
steer angles in any of the constituent units. The driver must guide the vehicle straight
with alternating right and left motions of the hand wheel to compensate for disturbance
from wind and road. Tolerances and wear of the vehicle can cause misalignment to occur,
requiring units of the vehicle to maintain a steer angle to keep an apparently steady state
straight motion. This can be due to any minor di erences between the units such as steering
misalignment, steering gear wear, suspension angle misalignment, frame damage, suspension
130
Figure A.18: Converter Dolly Kinematics Con guration Window
Figure A.19: Converter Dolly Kinematics Con guration Window
131
Figure A.20: Converter Dolly Roll Sti ness Con guration Window
wear, tire in ation variation, road crown, or even bearing drag. Measurement o sets can also
be present in the test data as a result of imprecise alignment of sensors, imprecise calibration,
or other systematic errors associated with the instrumentation setup. While it is impossible
to pinpoint a cause for this behavior in the NCAT test vehicle, it was apparent in the
test data. Of concern during analysis, TruckSim demonstrates a starting transient behavior
that can be mitigated but not completely eliminated. This starting instability causes the
simulation to start in a dynamic out-of-line orientation, which settles into a constant angle
of articulation between the units of the LCV. This attitude continues for the duration of the
simulation.FigureA.21 shows the yaw angles of each unit in the LCV during an un-steered
simulation at 72 km/h (45 mph).
This was simulated by setting the model in motion at a constant 72 km/h (45 mph) with
an open loop steer controller having no steer angle de ned, which is as if the driver takes
his hands o the steering wheel while maintaining the constant speed. This simulation was
performed in order to demonstrate the stability of the model, but the results also show some
interesting characteristics that are relevant to the transient maneuvers.. The results show
transient dynamics during the  rst few seconds. Afterwards, the vehicle stabilizes until a
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Figure A.21: Unit Yaw During Open-Loop Maneuver
dynamically neutral attitude is achieved, where the yaw angles of each unit maintain a near
straight trajectory. This initial oscillation is typical of simulations as the masses \settle"
from their initial conditions into equilibrium. Each maneuver begins with a short straight
section during which the vehicle simulation is allowed to stabilize before the primary steering
inputs begin. The steering wheel angle during this open-loop maneuver is plotted below in
Figure A.22.
A.4 Maneuver Paths & Con guration
TruckSim came packaged with a multitude of default maneuvers as well as other inputs
such as speed control pro les. For the sake of this research the speed controller was always
set to constant as that was the goal of the maneuvers during the experimental phase. Each
maneuver was set up as described below, when the user enters into the maneuver pro le
screen they are presented with the screen shot shown in Figure A.23.
The description of each setting and the subsequent selection is described in Table
133
Figure A.22: Steering Wheel Angle During Open-Loop Maneuver
Figure A.23: Screen Shot of Maneuver Setup Screen
134
Table A.9: TruckSim Maneuver Set-Up Screen Options
Driver Controls
Target Speed Set to constant speed based on which maneuver it wasto represent
Braking No braking needs as speed was to be constant
Shifting Set to allow TruckSim to determine shift points usingan 18 speed transmission
Steering Selected the driver input path needed for the desiredmaneuver
Additional Data
3D Road Selected the 3D road con guration that was detailed fordesired maneuver
Start and Stop Conditions
Start Start at 0,0 for time and position on path
Stop Stop at either 120 seconds or 350 m, whichever comes rst
Plot De nitions
De ne which plots that are desired when the data is plotted inside of TruckSim
A.4.1 The Constant Radius Maneuver
The constant radius maneuver was simulated by creating a circular path with two tan-
gent roads that would slowly twist until the correct banking was achieved. The curve of the
constant radius was created using the equation for a circle with a radius of 479 ft. The X-Y
coordinates were calculated for the curve at every degree for the 180a176curve. Once this was
created the points were shifted in order to become tangent with the two tangent road pro les
that were created. A screen shot of the constant radius path is shown below in Figure A.24.
As shown the path is two straight road segments that are tangent to the constant radius
curve, this method was used over a complete circular path due to the orientation in which
TruckSim would begin each maneuver. Many iterations and di ering attempts were used to
get the LCV to orient on the 8a176banking and on the correct heading but none proved correct.
Therefor the solution was reached that the vehicle was to start out on a  at straight road that
would twist from 0a176banking to 8a176banking over a span of 100 m. a graphical representation
135
Figure A.24: Constant Radius Path
of the twist is shown in Figure A.25. The actual data points that were used for the twist are
shown in Figure A.26.
A.4.2 The Single Lane Change Maneuver
TruckSim came pre-packaged with the single lane change maneuver, this was used as the
base point to create the new maneuver. The points were generated to match the intended
path outlined in Section 3.3. The resulting driver input path is shown in Figure A.27. The
aim of the path was to travel down the centerline of the right lane and once through the  rst
gate steer into the left lane.
In parallel with adjusting the default driver input path for the single lane change, the
animation needed to be altered to match the desired path. This was done in a similar fashion
that the driver path was determined. The di erence is that the points needed to represent
the edges of the road instead of the centerline. Four sets of cones where placed to represent
the maneuver, the middle two being the most crucial as the spacing had to match what was
prescribed in Section 3.3. The resulting cone positions along with a graphical representation
of the cones is shown in Figure A.28.
136
Figure A.25: 3D Representation of Gradual Lane Twist
Figure A.26: Gradual Lane Twist
137
Figure A.27: Single Lane Change Driver Input
Figure A.28: Single Lane Change Cone Positions
138
Figure A.29: Double Lane Change Driver Input
A.4.3 The Double Lane Change Maneuver
Similar to the single lane change, TruckSim already had a double lane change maneuver
de ned so again it was modi ed to match the maneuver that was performed during the
experimental phase. As detailed in Section 3.3, the driver was to steer back into the right
lane after traveling through the second gate in the left lane. The same method that was used
for de ning the single lane change path was used for the double lane change. The resulting
driver input path is shown in Figure A.29.
Again, the simulation cone positions had to be adjusted in order to match the newly
de ned maneuver. The same cone positions where used from the single lane change however,
there were two more sets of cones positioned in the right lane to represent the second lane
change in the double lane change maneuver. In the case of the double lane change, the middle
four sets of cones were critical as so to match the desired spacing of the gates outlined in
Section 3.3. The resulting cone positions along with a graphical representation of the cones
is shown in Figure A.30.
139
Figure A.30: Double Lane Change Cone Positions
A.4.4 Future Potential Improvements for TruckSima174 Model
As with any simulation, there is always room to improve upon it. This simulation is no
di erent as there were several di erent areas in which the model was lacking to some extent.
The most critical area in which the  delity can be improved upon is the tire data. The tires
for the simulation were left as packaged from TruckSim. If the model is to be improved, the
 rst step suggested would be to obtain more accurate tire data and insert that data into the
simulation. In addition to the tire data, more knowledge about the suspension kinematics
would help serve the simulation. The data was also limited to what could be obtained
by hand without the use large test equipment speci cally engineered to characterize heavy
trucks. Some examples of such equipment would be a tilt table to better locate the CG of the
units and a Kinematics and Compliance (K&C) measurement machine to better characterize
the suspension.
140