Research On Variable Steering Ratio Control For Four Wheel Independent Drive And Steering Electric Vehicle Steer-by-Wire System With Joystick

The four wheel drive torque and steering angle of four wheel independent drive and steering electric vehicle are independently controllable.The vehicle is an excellent support for new technology research and development.The steer-by-wire system with joystick,which replaces the steering wheel and steering column mechanism,can save the interior space and reduce the risk of secondary injury in accidents.It has been applied in some concept cars.The research group developed the four wheel independent drive and steering electric vehicle,and installed a joystick.The subject takes the four wheel independent drive and steering electric vehicle steer-by-wire system with joystick as the research object,and studies the control method of variable steering ratio,aiming to provide theoretical basis and technical support for the future application of steer-by-wire system with joystick in four wheel independent drive and steering electric vehicle.The paper is based on the general project of the national natural science foundation of China(51675257),the major science and technology platform project of the education department of Liaoning province(JP2017007,JP2016003)and innovation talent project of higher education institutions of Liaoning province(LR2016054).The specific research content of this paper is as follows:(1)Construction of vehicle simulation model.According to the principle of vehicle control,a simulation model of four wheel independent drive and steering electric vehicle with steer-by-wire system with joystick is established.According to the vehicle parameters,the vehicle body model,wheel and tire model,suspension system model,brake model and other parameters in CarSim were modified,and the simulation model is built jointly with Matlab/Simulink.(2)Research on control of variable steering ratio of front wheel steering.The steer-by-wire system with joystick should ensure that the vehicle condition to be able to have enough flexibility in low-speed working condition and lower sensitivity in high speed working condition.According to the different speed divided into low,medium and high speed interval,the constant steering ratio is used at low speed,the variable steering ratio is designed based on constant yaw rate gain in medium speed,the variable steering ratio is designed based on limiting lateral acceleration gain in high speed.The effectiveness of the method is verified by simulation.(3)Research on the control of rear wheel additional steering variable steering ratio is proposed.The subject takes the four wheel independent drive and steering electric vehicle as the research object.The relation between the rear wheel and the front wheel steering in different speed range was studied depend on the advantages of four wheel independent steering.In order to further improve the sensitivity in low speed and the stability in high speed of the vehicle,the variable steering ratio study of the additional steering angle of rear wheel was increased.The reverse steering angle of the additional rear wheel was appended to the low speed control method and the additional coaxial steering angle of the additional rear wheel was appended to the high speed control method.The simulation results show that the latter is better than the former in improving vehicle flexibility and stability.(4)Experimental verification.The variable steering ratio control algorithm of the steer-by-wire system with joystick was experimentally verified by the driving simulator experimental platform,and verified by the four wheel independent drive and steering electric vehicle at low speed operating condition.The results show that the proposed variable steering ratio control method can improve the steering stability of four wheel independent drive and steering electric vehicle,and realize steering sensitivity at low speed and stability control at high speed.