Research And Design Of Electric Power Steering

With the electric technique applied to engine, transmission and brake system successfully, EHPS (Electric Hydraulic Power Steering) is going to be replaced by EPS (Electric Power Steering), which is a new technology of automotive power steering. EPS adopts motor to provide assist torque directly, which controlled by ECU according to the torque of the steering wheel and velocity of the vehicle etc. Compared with HPS, EPS is saving energy and protecting environment. The control system of EPS was researched and designed.Based on the ideal power characteristic curve analysis, the mathematic model for the fold line of many segments approaching to the ideal curve was set up. Searching table of EPS control was adopted and the spaces for it in memory were calculated. In order to obtain greater damping in high-speed, the regenerative braking from power motor was replaced by active damping control strategy. In addition, Active aligning control was designed to realize steering angle to zero at the end of the aligning process. Conversion conditions among idle, power control, aligning control and damping control were described.According to the request of the automotive electronic standards, the overall design of EPS was completed, and the key parts such as MCU, motor and torque sensor were selected. The H-Bridge circuit and the restricted monopole control mode were adopted to realize forward/inverse rotation of power assisted motor. To provent intermittent current of motor effectively, the frequency of PWM signal was increased. ECU with self diagnostics provided many fail-safe means were provided by ECU when torque sensor, motor and clutch was abnormal. The multidimensional data table and integral separation incremental PID algorithm were applied to reduce the amount of computation and enhanced the response speed of system.Finally, experimental environment was constructed, on which the experiments of EPS were completed. The results show that the system has good performance.