Hydraulic Solenoid Valve Reliability and Modeling Study
Type of DegreeThesis
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The current work has studied the reliability of a solenoid valve (SV) used in automobile transmissions through a joint theoretical and experimental approach. Based on an extensive literature search, the most common failures seen in solenoid valves appear to be due to either overpowering and eventual overheating of the valves, or wearing out of the valve components. The goal of this work is to use accelerated tests to characterize SV failure and correlate the results to new comprehensive finite element models. A custom test apparatus has been designed and built to simultaneously monitor and actuate up to four SVs using the LabView™ programming language environment and a National Instruments™ Data Acquisition device. The test apparatus is capable of applying a controlled duty cycle, applied voltage and actuation frequency. The SVs are also placed in a thermal chamber so that the ambient temperature can be controlled precisely. The apparatus measures in real-time the temperature, current, and voltage of each SV. A multimeter is used to measure the electrical resistance across each SV. A series of tests have been conducted to produce repeated failures of the SVs. The failure of the SV appears to be caused by overheating and failure of the insulation used in the solenoid coil. The current tests are run at a 100ºC ambient temperature, 16.8V of average peak voltage, 50% duty cycle, and 60 Hz actuation frequency. Upon failure, the solenoid electrical resistance drops to a significantly lower value due to shorting of the solenoid coil. This drop in resistance causes a measurable and noticeable increase in the average current. The insulation also melts and exits the SV. Hence, increasing ambient temperature and current is believed to cause a decrease in SV reliability. In addition, a comprehensive multiphysics theoretical model of the SV is constructed using the commercial finite element software ANSYS™. The multiphysics model includes the coupled effects of electromagnetic, thermodynamics and solid mechanics. The resulting finite element model of the SV provides useful information on the temperature distribution, mechanical and thermal deformations, and stresses. The model is also correlated to the experimental results and can be used as a predictive tool in future solenoid design. Finally, a proposed solution to improve SV reliability is to increase heat conduction and convection away from the SV, or by decreasing the ambient temperature or find an insulation material resistant to high temperatures.