Study On The Control Strategy And Development Of Automobile's Electric Power Steering System

Comparing to the traditional steering system, the electronic power steering system has more advantage and will take the place of the hydraulic power steering in the future. The electric power steering system take advantage of motor to provides the power directly, so it gives attention to facility and road sense, improves the operation stability and realizes the facility at low speed and prompt road sense at high speed.The electric power steering system (EPS) consists of the torque sensor, the speed sensor, the Electronic Control Unit, no brush direct current motor, electromagnetic clutch and deceleration system etc. They perform the function together with the help of the according the software and control arithmetic. The thesis introduces the construction and theory of the EPS, set up the power model on the base of the power characteristic and the force analysis of the EPS, compares the influences that the P control and PD control have on the system power, establishes the control style which is mainly fuzzy PID current closed loop control arithmetic.The EPS must be equipped with adequate bandwidth to fulfill the follow performance of assist motor when the steering wheel turns quickly and should has road sense at the same time. The lag of the signal from the turning sensor and the signal instantaneous aberration reduce the follow performance and the stability of the system. We apply the root locus method to design the dynamic compensator of the turning sensor to improve the dynamic and static characteristic. The results of the simulation and the examination prove that the transient and static characteristic are satisfied, the vibration of the system is reduced apparently after the compensator is equipped. So the compensator is validated. The dynamic compensator has great signification on the application of turning sensor in projects.The thesis analyzes the three different types of the EPS theoretically and discusses the method of establishing the curve power characteristic primarily, on the base of which the thesis set up the EPS simulation model with power characteristic by MATLAB/Simulink, and applies the current control method to the motor electrics model, realized the PID closed loop control of the objective current on the base of the fact that the characteristic of the electromagnetic characteristic of motor transforms the moment type power characteristic to the current type power characteristic. The angle rate signal from motor model is applied to make sure the compensation current of damped control. The simulation proves indicates that the curve power characteristic can satisfy the requirement of turning fixedly, facility at low speed and the road sense at high speed.