A Study On Characteristic Of Electric Power Steering

Electric power steering system is the inevitable developing direction for automobile power steering. It has the advantage of smaller volume, lighter weight, simpler structure, easier installation and maintenance, lower consumption, better environmental protection, which is much superior to hydraulic power steering system. The assist torque is provided by motor directly in EPS system, whose value is controlled by ECU. And EPS possesses high-level performance such as ensuring different steering feel owing to adjusting steering assist force according to vehicle speed, which enables it fit for many kinds of vehicle such as car, truck etc. So it is a new high-tech which follows modern vehicle development topic closely.Through the analysis of components of EPS system and the steering system, EPS'dynamics model, full vehicle model with two degrees of freedom and tire model was built. Then the state function of the combination system model was deduced and the model for simulation was built via MATLAB/SIMULINK in this paper.Several performance evaluations such as steering sensitivity and steering feel to evaluate the handling performance of the combination system including EPS system and vehicle handling system were put forward and their expressions were deduced after the integral analysis of vehicle's handling dynamics and EPS'dynamics. Having investigated the effects of several factors such as gear ratio of the assisting mechanisms and moment of inertia of the motor etc. on these indices, a stability criterion was built. Finally, based on the restrictions of stability criterion and maximize the object function of steering feel, an optimization model of EPS system was built and an example was presented and the steering feel is much better after optimization. In the foundation of general consider the effects of several alterable parameters on steering handling performance, good steering handling performance would be gained and the difficulty would be reduced at the same time.In the foundation of the theoretic analysis of the assist characteristic, assist curve to reduce steering force was designed with Ford ZX3's chassis parameter.