Research On AFSM Control Strategy Of Active Front Steering Of Electric Vehicle Based On Variable Steering Ratio

With the rapid development of the vehicle industry,the total number of cars owned by citizens continues to grow.Meanwhile,traffic accidents are also increasing every year,especially in the process of vehicle steering,which often causes side slip and instability.Ultimately and unfortunately,they can cause serious safety risks.In order to effectively improve driving safety and steering comfort of the vehicle,this paper is composed.Taking the in-wheel electric vehicle as the controlled object,this paper conducts in-depth research on the vehicle steering system and proposes an active front-wheel steering control scheme for the in-wheel electric vehicle on the premise of variable steering ratio.Firstly,based on the vehicle dynamics analysis,the vehicle model is established and the active front wheel steering control strategy is designed.The control strategy mainly consists of three parts:(1)Changing the traditional pattern of fixed steering ratio,putting forward the variable steering ratio control scheme according to the yaw angular velocity gain,and optimizing the design to make the curve more in line with the actual driving habits,this scheme can better solve the contradiction between‘light’and‘flexible’and improve the driving comfort for drivers;(2)Aiming at the uncertainty of the model of the active front steering system of electric vehicles,the estimation value of the side slip angle and disturbance were obtained by constructing the observer based on the two degrees of freedom model to provide accurate compensation for the active front steering controller;(3)According to the control objectives of this study,the PI control algorithm and the second order sliding mode control algorithm are proposed to improve the steering performance of the system.Secondly,an adaptive fuzzy sliding mode control algorithm for active front steering system of electric vehicles is designed to solve the problems of time-varying characteristics,low tracking accuracy of PI,and difficulty to overcome chattering caused by traditional sliding mode control,then,the stability of the designed system is analyzed based on the Lyapunov theory.This scheme uses the adaptive algorithm to update the parameters of the fuzzy system in real time,thus effectively reducing the tracking error,not only reducing the chattering problem,but also further improving the robustness of the active front steering system.Finally,the vehicle model was built in Carsim and the active front steering system model was built in Matlab/Simulink to achieve joint simulation.The closed loop and open loop simulation tests were carried out with or without crosswind interference.The results show that the active front steering control strategy proposed in this paper can guarantee the driving safety and stability of the vehicle,and through different comparison and analysis of the simulation results of the front steering controller of the company,it can be found that the active front steering controller based on the adaptive fuzzy sliding mode algorithm has better performance in different working conditions,which not only reduces the high frequency chattering caused by the traditional sliding mode controller,but also improves the tracking accuracy and anti-interference ability of the system.