| With the increasingly serious environmental protection problem,the pressure of automobile energy saving and emission reduction is increasing day by day.At the same time,with the development of automotive intelligence and the increase of automotive active safety system configuration requirements,a new form of vehicle appears.Four-wheel steering,independent drive electric vehicle(EV)is a kind of vehicle with a new chassis arrangement,which is powered by a drive motor and steered by a steering motor.4WS-4WID electric vehicle has the advantages of energy saving and emission reduction that cannot be surpassed by traditional vehicles and the advantages of comprehensive development and design of active safety control system based on structure.Of course,this advantage can only be realized after the comprehensive design of the control system is completed.This paper mainly studies the steering coordinated control of 4WS-4WID electric vehicles.In this paper,the 4WS system,4WID system and 4WS-4WID coordinated control system are studied respectively in the four wheel steering independent drive electric vehicle driven by hub motor.The purpose is to solve the steering stability problem of4WS-4WID electric vehicles,in which the research on 4WID system is to assist the steering stability of 4WS system,and the main research is as follows:(1)The 8-DOF car body dynamics model,Dugoff tire model,steering system model and the auxiliary calculation model needed for the study of car body dynamics were built.Modified vehicle model data and driveline model in Car Sim.The vehicle model built by Matlab/Simulink is compared with the CARSIM model with modified data and transmission system for simulation verification,which provides a basis for subsequent research.(2)A feedforward and feedback 4WS system controller was designed by using linear quadratic optimal control theory(LQR)through vehicle dynamics analysis to make full use of tire lateral forces.A two-degree-of-freedom lateral dynamics model combined with the ideal reference model was used to design the control rate of the rear wheel Angle.In order to improve the adaptability and control effect of the LQR controller,a parameter regulator based on the vehicle steering state and speed was designed to automatically adjust the parameters of the LQR controller through the fuzzy control logic.The simulation test verified that the variable parameter LQR controller designed in this paper can control the 4WS system well.(3)Starting from making full use of tire longitudinal force to assist 4WS system based on tire lateral force,DYC controller containing upper and lower two layers of controllers is designed.The upper fuzzy sliding mode controller is designed to calculate the additional yaw moment based on the sliding mode control theory and the fuzzy control theory,in which the fuzzy control theory is used to reduce the chattering problem.The lower torque distributor is designed according to the principle of proportional distribution of shaft load.Finally,the effectiveness of DYC controller designed in this paper is verified by simulation.(4)The coordination control strategy between 4WS system and DYC system is studied.The coordination principle of 4WS and DYC and the activation function of DYC auxiliary steering controller were designed,and the additional torque allocation strategy for auxiliary steering was also designed.Finally,the simulation test proves that the 4WS-DYC coordination controller designed in this paper has a good control effect when controlling the steering stability of the vehicle,and also verifies the effectiveness of the control strategy. |
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