Research And Development On Vehicle Electrical Power Steering

The auto industry is becoming one of the most important industries in China.The direction of its development should be save,environmental-friendly and enery-saving.Compare to the big,high-energy consuming and unintelligent hydraulic power steering(HPS) system,electrical power steering(EPS) system is more competitve with the advantages of smaller,more efficient,simple assembling and more intelligent.The thesis analysed the charactors of the EPS system and designed 2 important parts in the system:signal processing and adjusting circuit for non-contact torque sensor and electrical control unit(ECU).The non-contact torque sensor's main function is to transform the torque into voltage signal.After the analysis of the mechanical part,the signal processing circuit was made. Considering the circuit should match the mechanical part with both deviations,an adjusting circuit based on PIC16F676 microcontrol unit(MCU) was designed to adjust the circuit automaticly.Also,the software for this circuit was finished.The ECU,which is designed for signal input,motor control and system control,is the core of EPS.An ECU based on PIC16F877A MCU was made with the following functions:first,deal with(e.g.filter) the output of the sensor's(e.g.torque sensor) using hardware and send them to MCU;then,the MCU decide to use which power assisting rule and how much the assisting force should be after computation and analysis;finally, PWM generated by the MCU drive H-bridge circuit to control the permanent magnet DC motor using fuzzy self-turning PID control algorithm.After the hardware design,the software part was finished according to the modularize idea.These modules are main function,signal collecting part,motor control part and fault diagnosis part.After the design part,a non-contact torque sensor test and an EPS system test (concluding non-contact torque sensor and ECU was made.The results showed that the both part is up to the EPS standard with rapid responding and stability.