Research On Assist Characteristics And Control Strategy Of Automobile EPS System

With the fast development of technology and the progress of manufacturing capability,the automobile industry has happened enormous transformations in terms of comfort and safety.The electric power steering system(EPS)is an essential part of the steering assist system,which determines the comfort and safety of the vehicle on road.EPS has its unique advantages and wide application area in the either domestic or foreign markets.The technique of EPS has become a hot spot of technological research now.This paper studies the dynamic model of the EPS system,the power-assisted characteristic curve,the basic power-assisted control strategy,and the return damping control strategy.The purpose of this paper is aiming to improve the steering portability and return performance of the EPS.The main work of this paper is introduced in the following sections:(1)The components of the EPS system are introduced in detail,according to the kinematics of each part,the two DOF dynamic model of EPS and a simulation model including monorail wheels are established,which laid the foundation for subsequent modeling.On the basis of the dynamic model,the transfer function of the EPS assist control system is derived,where the motor voltage,driver input torque,ground rolling friction resistance torque,and tire self-alignment torque are determined as the input,and the motor angle,current and boost torque are output.(2)Analyze the superiority and dis superiority of the three commonly used power-assisting characteristics curve and meet the requirements of the power-assisting characteristic curves,and combine the actual situation of the EPS system and the interference of nonlinear factors on the steering system,and use the arbitrary nonlinear approximation characteristics of the BP neural network to discretize Power-assisted characteristic curve,a new power-assisting characteristic curve based on this network is proposed.In the basic assist control strategy,research and comparative analysis based on traditional PID control and BP neural network PID adaptive adjustment control algorithm,and design a power-assisted current controller.(3)Combined with the impact of damping control on the EPS system,the active return performance and return evaluation index under vehicle conditions is analyzed.This paper designs the active return control decision,then studies the active return performance,and proposes an active return strategy based on the steering wheel angle as the control target.In the active return damping control strategy,a PSO optimized BP neural network PID parameter adaptive adjustment algorithm is proposed.Furthermore,the BP neural network PID parameter adaptive adjustment algorithm,fuzzy PID adaptive algorithm,and PID control algorithm itself are compared and analyzed respectively.(4)According to the dynamic model of EPS,Simulink is used to build the overall simulation model of the power-assisting characteristics curve,the assist controller and the active return damping controller.Then the input and output parameters are set in the simulation to ensure the accuracy of the results.Finally,the simulation analyzes the current tracking performance of the motor and the regression performance of the steering wheel angle to verify the effectiveness of the designed model and the proposed control strategy in EPS.