Study On EPS Boosting Characteristic Considering Pavement Adhesion Coefficient

Although the traditional control strategy of Electric Power Steering System(EPS)can basically meet the Steering requirements of daily driving,the traditional control strategy of EPS system can not meet the requirements when the road adhesion coefficient changes,especially when the vehicle is driving on the road with low adhesion coefficient.In this paper,an EPS system power control strategy based on BP neural network considering road adhesion coefficient is proposed.An EPS system with better directional performance under different road adhesion coefficient is designed and compared with the traditional EPS system.The joint simulation of CarSim and Simulink proves that the EPS system with road adhesion coefficient has better steering performance.It ensures that the driver can get the convenience of steering and better road feeling under different road adhesion coefficients,and at the same time ensures the safety of vehicle driving.Firstly,the main working principle of EPS system is analyzed,and the overall layout and type selection of EPS are completed.The mechanical analysis of EPS system is carried out.Based on the torsion bar spring model,the mechanical characteristics mathematical model of EPS system and the mathematical model of booster motor are established.Secondly,the influence of road adhesion coefficient on steering system is analyzed,and the shortcomings of traditional EPS control strategy in coping with the change of road adhesion coefficient are introduced.The EPS system boost characteristics considering the change of road adhesion coefficient are proposed,and the basic boost characteristic curve and the boost characteristic curve considering road adhesion coefficient are designed.Based on BP neural network,the prediction model of maximum steering resistance moment is established and its accuracy is verified.The simulation results show that the prediction model of maximum steering resistance moment is more accurate than the traditional table lookup module in predicting the maximum steering resistance moment of different road adhesion coefficients.Thirdly,the control strategy of EPS system is studied,and the traditional control strategy of EPS system and the assistant control strategy of EPS system considering the change of road adhesion coefficient are established respectively.The PID controller of the boost control mode is established and the controller of the return control mode and the damping control mode is proposed.Finally,the joint simulation model of EPS system is established by CarSim and Simulink software.Through steering angle step input test,steering portability test,double line-shifting test and snake-like test,the influence of EPS system boost control strategy on stability and boost performance is analyzed compared with traditional control strategy considering the change of road adhesion coefficient.