A Fully Integrated Sensor Fusion Method Combining a Single Antenna GPS Unit with Electronic Stability Control Sensors
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This work presents a method for incorporating GPS (Global Positioning System) and standard roll stability control (RSC) sensors into the electronic stability control (ESC) and RSC systems. It is an adaptation of the very well known loosely-coupled GPS/INS (Inertial Navigation System) integration strategy which has been modified for the purposes of ESC systems. The first modification is the removal of the pitch rate gyroscope, a sensor which is unavailable on commercial vehicles. The second modification deals with the observability problems of the standard loosely coupled filter by adding heading constraints when the vehicle is not turning. The structure and algorithm of this method is presented. Observability conditions are evaluated, and the convergence of the estimates are analyzed via simulations. The conclusions from these simulations are compared with the expectations from the literature and observability condition checks. An experiment which illustrates the long term performance of the bias estimation was performed, followed by an experiment showing the roll and sideslip estimation performance during dynamic events. It is shown that over the long term the inertial bias estimates will converge if the vehicle experiences adequate dynamics, and that the system is able to accurately estimate sideslip and roll during dynamic maneuvers. The system is also able to estimate slow sideslip buildup, an important capability for ESC systems. The unified system is compared with a less integrated or ''modular'' approach for both experiments. Furthermore, a method for using GPS to detect tire pressure changes is presented based on the hypothesis that the tire effective radius varies according to tire pressure. A technique using GPS and wheel speed signals to estimate the effective radius of the tires is discussed and validated in simulation and experiment. Experiments are given to show how the radius estimate varies according to tire pressure, and a simple pressure loss detection law is discussed. A method to detect steering misalignment is also presented.