Study Of Steering Feeling Of Electric Of Power Steering System

Compared with the traditional hydraulic power steering system,Electric Power Steering System(EPS)had some advantages such as compact structure,good returnability,easy installation,energy saving and environmental protection,and good low temperature performance.EPS can not only provide steering power,reduce the driver’s handling burden,but also improve the vehicle’s steering performance,driving comfort and vehicle active safety.EPS was based on the pure mechanical steering system,adding torque sensor,motor and reducer.With the rapid response ability of the motor and its precise control ability of the torque,it can realize the accurate adjustment of steering road feeling.At the same time,the increased system components will affect the transmission characteristics of the torque and cause changes in the road feel.The road feeling was the feedback of the steering system to the driver.The driver perceives the road condition and the driving state of the vehicle through the steering system,The road feeling was not only reflected in the size of the steering wheel torque feedback,the size of the vehicle response,and the speed of the steering wheel returning,but also in the corresponding relationship between the steering wheel input and the vehicle response.Based on this,this thesis studies the road feeling of EPS as follows:Firstly,the influence of assist parameters,motor parameters,torque sensor parameters and reducer parameters on road feeling strength was analyzed,dynamic compensation methods to eliminate adverse effects,From the open-loop amplitude-frequency response of the system,the relationship between the assist gain and the rapidity and stability of the system was obtained.Aiming at the lack of system stability margin caused by large gain,the advanced phase correction of torque signal was carried out to improve the stability margin of the system.Then,the EPS model and the vehicle model are established in Simulink and Car Sim respectively,and the co-simulation model was obtained.Based on the road feel preference function,the assist curve with speed was designed.The simulation results show that the nonlinear road feel of high-speed driving was improved after matching EPS.The assist control can reduce the steering dry friction,steering torque and torque gradient,but does not change the returnability.The friction compensation control can reduce the steering dry friction and steering torque,and improve the returnability without changing the torque gradient.But the intervention of power control makes the steering friction sense weaken with the increase of steering angle.The friction sense in the central area was optimized by variable friction compensation,so that the driver can obtain a more consistent steering friction sense.Finally,the yaw rate feedback was used to improve the stability of high-speed driving.For the low-adhesion road surface,the road feel was easily lost,and the steering feel was enhanced by reducing the power.In order to overcome the influence of vehicle speed change on the return performance of the vehicle,the actual return torque was estimated by the lateral acceleration signal,the ideal return torque was determined by the steering wheel angle signal,and the return torque was compensated.Using the co-simulation model,the feasibility of the return algorithm was verified.The simulation results show that the steering wheel can return to the middle position more accurately,the proposed return control algorithm had strong applicability for different initial angles at different speeds.