Research On Return-to-center Control Strategy Of Electric Power Steering System

Electric Power Steering(EPS)system,as an important part of the vehicle,has a direct bearing on the comfort,safety and Steering stability of the vehicle.EPS system can not only ensure that the car has a good portability in steering,but also improve the vehicle's ability to return to normal under different speed conditions.In this paper,the steering performance of the vehicle under different speed conditions is analyzed by studying two control strategies of booster and return-forward.Firstly,the operating principle of EPS system is described,the causes of generating positive torque are analyzed,and then the model of generating positive torque is established.The dynamics of EPS system was analyzed,and the mathematical models of steering wheel,steering column,torque sensor,power motor,and rack and pinion mechanism were established,laying a foundation for the following control model.Secondly,EPS power control strategy was studied.The characteristics of three EPS power characteristic curves were analyzed,and the linear power characteristic curve was designed according to the steering characteristic and related parameter configuration.The power control scheme is designed,and the design method and setting rules of the fuzzy adaptive PID controller are studied.The results show that the designed linear power characteristic curve has good power characteristics,and the PID control adjusted by fuzzy rules can adjust the control parameters in real time,and improve the anti-interference performance in complex working conditions.Then,the research of the return-to-center control strategy is carried out.According to the requirements of the performance of the car is back,to determine the return-to-center performance evaluation index,the back is condition judgment method,designed the back is the logical model,according to the return-to-center control scheme,the steering wheel Angle of zero as return-to-center control objective point of view,based on the steering wheel Angle feedback correction control strategy,according to the requirement under different speed is back to adjust control parameters.In Matlab/Simulink software to complete the EPS system Simulink simulation model,and simplify the model,responsive simulation,verify the feasibility of the model.Finally,the vehicle model was established in Carsim,the required input and output parameters,road environment and simulation conditions were set,and the EPS system model established in Simulink was co-simulated.The results showed that the steering handiness of EPS system with power control was significantly improved,and the powercontrol after fuzzy adaptive setting was more stable and the effect was better.With the addition of the return-control,the steering wheel can return to the middle position more quickly under low-speed operating conditions,and the return-over-control can be effectively avoided under high-speed operating conditions,thus improving the return-over-control performance under different speed operating conditions.