Exploration of the Reliability of Automotive Electronic Power Steering System Using Device Junction Electrothermal Profile Cycle

This paper focuses on the driving steering load cycle stress-strain, shake, and transient temperature profiles in relation to failure in an automotive electric power steering (EPS) system. A compact EPS control system model was applied to construct a lookup table for the device power loss calculations. The lookup table was used to obtain the full electrothermal profile of a vehicle EPS system converter. An accurate thermal model was introduced using FLOTHERM software and compared with the results from EPS device temperature testing. The transient junction temperature profiles of the device were studied based on the operational cycles of the vehicle EPS system. Finally, an efficient rainflow cycle counting method was introduced to obtain the statistic random transient thermal stress cycles. Miner's rule was also explored, and the relationship between the accumulated thermal stress damage and material fatigue was used to predict the converter's reliability.