Study On Evaluation Index And Control System Of Electric Power Steering System

Electric power steering (EPS) system which has advantages such as safety in low temperature, energy saving, environmental friendly, variable assist power, small volume and easy to industry product complied with the inevitable trend of the automotive development. EPS has been widely used in practical application by many foreign automotive enterprises, while this steering system was used rarely and developed slowly in our country. Many enterprises and universities in domestic area have set to develop this kind of steering system.In this thesis, the EPS system was divided into three sub modules:mechanical structure of steering system, motor module and the tire module, the vehicle modeling was built in this thesis. And the force situation of each module was analyzed. According to the dynamic equations of each module, the mathematic model of entire system was established using MATLAB. And choosing the appropriate inputs and outputs signals, the state space equation of EPS was established too.Choosing the steering road feel, relationship between driver’s torque and yaw rate of the vehicle and the steering stability as evaluation indexes to assess the performance of EPS, the impact of system parameters on the EPS’s performance was simulated based on the state space equation of EPS system. Selecting the road feeling as the optimization target, the value of system parameters was optimized which meeting the steering stability requirement and the maximum road feel.The assist curve and the controller were discussed in this thesis. The linear assist curve was designed considering vehicle spin and steering during drive. In the discussion of the controller, firstly the motor was simplified which proved effective through simulation, secondly the quadratic optimal control theory was chosen as the control algorithm of the EPS system, and PID algorithm as a comparison. The quadratic optimal control theory was proved better than PID algorithm. And at last, the design in this thesis was proved effective in assist mode of EPS through the comparison between assist torque and resistance torque, which obtained through simulation.