Research On Following Control Strategy Of Automatic Steering System

With the continuous development of artificial intelligence technology and network information,intelligent driving and unmanned driving have become the main direction of vehicle development.Automatic steering system is the main part of intelligent vehicle lateral motion control.How to control the vehicle to accurately follow the target path is the key problem of automatic steering system.This paper focuses on the lateral follow-up control of automatic steering system,and studies the path tracking and front wheel angle tracking control,so as to realize the function of vehicle accurately following the target path.The selection of steering actuator is the research basis of automatic steering follow-up control.Through the analysis of the safety and economy of each steering system,the mechanical active steering system is selected as the actuator,the dynamic model of the steering system is established by using the reduced order modeling method,the vehicle and driving environment model are established in Car Sim,and the automatic steering simulation experiment platform is built in combination with Simulink,The joint simulation platform is verified by using PID to control the front wheel angle.In order to realize the automatic steering system to follow the planned path,a double-layer control structure is designed.The upper controller mainly tracks the planned path.The input of the controller is the planned path information and the structural and state parameters of the controlled vehicle,and the output is the target front wheel angle;The lower controller receives the target front wheel angle output by the upper controller,and realizes the steering wheel to follow the target angle by controlling the steering actuator.Considering its calculation amount,tracking ability and stability performance,the upper controller of path tracking adopts the feed-forward linear quadratic regulator(LQR)control method based on vehicle dynamics model.In order to reduce the path tracking error caused by inaccurate modeling,PID control is added on the basis of feed-forward LQR control to compensate the steering angle,so as to improve the system stability and tracking accuracy,The simulation and comparison experiments of feed-forward LQR control and feed-forward LQR + PID compensation control are carried out.The results show that after adding PID compensation,the tracking error of the system under standard double lane change condition is reduced by 0.317 m,the maximum tracking error under urban road right turn condition is reduced by 0.198 m,and the path tracking accuracy is greatly improved.Considering the nonlinear and uncertain characteristics of the steering system,the lower front wheel angle tracking controller designs a double closed-loop control structure to track the front wheel angle.The inner loop uses the classical pi to control the motor current and reduce the influence of the motor on the control system.The outer loop uses the improved non singular fast terminal sliding mode(NFTSM)control method to track the front wheel angle,and designs a fuzzy controller to estimate the sliding mode switching gain in real time,so as to improve the chattering problem of sliding mode control and improve the steering angle tracking accuracy and anti-interference performance.In order to verify the effectiveness of the fuzzy NFTSM outer loop controller,the fuzzy sliding mode front wheel angle control is designed and compared with it,and the simulation comparison experiment is carried out.The experimental results show that compared with the fuzzy sliding mode control,the double closed-loop front wheel angle control of fuzzy NFTSM reduces the maximum tracking error by 0.232 deg under the standard double lane change condition,and the maximum tracking error is reduced by 0.108 deg under the standard Serpentine condition.Finally,combined with path tracking control and front wheel angle tracking control,a joint simulation platform of automatic steering following double-layer controller is established.The control effect of the control strategy is simulated under double lane change conditions of high and low adhesion roads and right turning conditions of urban roads.The experimental results show that the proposed control strategy can have good path following effect,good stability and tracking performance under urban roads,It can meet the requirements of automatic steering follow-up control.