The Development Of Electric Power Steering System Controller With Fault Self-diagnosis Function

Electric power steering system (EPS) as a vehicle electronic control system, not onlyneed it to improve vehicle steering portability and return-to-center performance, but alsoneed to have good stability and safety. The purpose of this paper is to develop anElectric Power Steering System Controller which can not only meet the basicrequirements of automobile power steering, but also have a certain fault self-diagnosisand protection function.Firstly, the vehicle differential equation of two degrees of freedom movement,mathematical model of EPS system and boost motor is established. The EPS controlstrategies is analyzed, including PID power control strategy which based on motorcurrent, PI return-to-center control strategy which based on steering wheel angle,damping control strategy and fault self-diagnosis and protection strategy.The EPS system Fault Tree is established, and carried on qualitative analysis.According to the results of qualitative analysis and combined with the importance of thefault tree bottom event, set up the EPS system fault self-diagnosis monitoring targets. Inaddition, each of the EPS failure modes are analyzed, and proposed EPS faultidentification method.According to the function requirement, the hardware circuit is designed, includingmicrocontroller system, motor drive circuit, signal acquisition circuit, fault detectionand protection circuit，and selected MC9S12XS128as the core controller and IR2110Sas the MOFET pre-drive chip.The software program is designed, including the data acquisition and signalprocessing, the judgment of control mode, target current calculation, electrical currentcontrol and fault self-diagnosis and strategy. At the same time, in order to guarantee thestable operation of the software system, we joined the software anti-interferencemeasures.Finally, in order to verify the efficiency of the control system. Motor bench test, EPSbench test and EPS controller vehicle test are carried out. Test results show thatself-designed EPS controller not only meet vehicle power steering requirements, butalso have a certain fault self-diagnosis and protection function.