Research On Coordinated Control Of All-Wheel Steering And Assisted Steering For Eight-Wheel Independent Drive Vehicle

With the intensification of the fossil energy crisis and environmental protection problems,the electrification of vehicles has become an inevitable trend of the future development of the automotive industry.In-wheel motor-driven electric vehicles have been widely considered as an ideal carrier for researching the optimal dynamic performance of vehicles and the ultimate form of future electric vehicle development due to their advantages of flexible spatial arrangement and independent controllable torque of each wheel.As multi-axle heavy vehicles are more and more widely used,they are also facing more and more problems,such as large steering radius,severe wheel wear,and poor handling stability.Applying all-wheel steering technology to multi-axle heavy vehicles can greatly improve their steering flexibility and handling stability.However,due to the limitation of tire lateral force saturation,relying solely on all-wheel steering control is not sufficient to meet its steering needs on low adhesion road surfaces.In view of these problems,based on the characteristics of independently controllable torque of the wheels of the in-wheel motor-driven electric vehicles,this paper designs an assisted steering control algorithm to improve the steering stability of the vehicle on low adhesion roads.At the same time,in order to solve the coupling relationship between assisted steering and all-wheel steering,a corresponding coordinated control scheme is proposed.This paper can be divided into the following four parts:1.Firstly,based on TruckSim/Simulink,a dynamic model of 8×8 in-wheel motor-driven vehicle with all-wheel steering was built,including vehicle model establishment,power and steering system modification in TruckSim software,what’s more,establishment of a motor model,steering mechanism model and longitudinal driver model in Simulink software,and the definition of the input-output interface between TruckSim and Simulink.Finally,the double lane change test was used to verify it,which laid the foundation for subsequent research and simulation.2.In view of the shortcomings of the traditional zero side-slip angle proportional control strategy for all-wheel steering,this paper designed an optimal controller with zero side-slip angle proportional feedforward and LQR state feedback.The simulation analysis results showed that the optimal controller is more effective than proportional control and traditional front-wheel steering control,which can improve the low-speed steering flexibility and high-speed steering stability.3.In order to improve the vehicle dynamic performance,based on the wheel slip rate,this paper used an adaptive fuzzy PID control algorithm to design the wheel anti-slip controller.In order to identify the optimal slip rate of the current wheels,a road identification module was designed based on fuzzy theory.Finally,the anti-slip control algorithm was simulated and verified by bisectional road test.The results showed that the designed control algorithm could effectively prevent the wheels from severely slipping and ensure the dynamic and stability of the vehicle.Because the control effect of all-wheel steering is limited by the lateral force saturation,based on the characteristic that the torque of each wheel can be controlled independently,this paper designed an assisted steering controller by means of differential driving.At the same time,the influence of vehicle speed and load transfer was considered in the driving force distribution of each wheel.Finally,a typical double lane change test was used for simulation analysis.The results showed that the designed assisted steering control strategy could effectively improve the vehicle’s steering stability under extreme steering conditions such as low adhesion roads.4.Considering that the phase plane can accurately determine the stable state of the vehicle,this paper introduced the β-(?) phase plane for coordinated control.Firstly,a non-linear two degree of freedom vehicle model was established for drawing β-(?) phase plans.Then,based on the phase plane stability domain boundary model,the factors affecting its boundary parameters were analyzed,and a parameter MAP was developed.Finally,a coordinated control strategy for all-wheel steering and assisted steering was designed based on the phase plane.The coordination algorithm was simulated and verified using three typical test conditions.The results showed that the coordination control algorithm established in this paper can effectively improve the vehicle’s path tracking ability and steering stability under extreme conditions.