Design And Development Of Four-wheel Steering Controller For Electric Vehicle With In-wheel Motors

Distributed electric vehicles with in-wheel motors is an important technical research direction in the development of new energy vehicles.Its new chassis citation allows electric vehicles with inwheel motors to not only achieve independent control of the torque and speed of the driving wheels,but also effectively improve their flexibility and stability at low and high speeds by controlling the steering angle of each wheel.But at the same time,the realization of four-wheel steering will increase the design freedom of steering control system.Therefore,how to make the electric vehicle with inwheel motors to achieve stable four-wheel steering on the basis of ensuring the vehicle steering according to the established route,still need to focus on research.In this paper,an electric vehicle with in-wheel motors with four-wheel steering structure was taken as the research object.Based on the establishment of the dynamics model of distributed electric vehicle with in-wheel motors,the control strategy of four-wheel steering is studied and designed.At the same time,the hardware and software of the steering control system were designed,and the fourwheel steering controller of the electric vehicle with in-wheel motors was developed,and the effectiveness of the controller and the feasibility of the proposed four-wheel steering control strategy were verified by experiments.The specific research content of this paper is as follows:(1)Establishment of dynamic model of electric vehicle with in-wheel motors.Taking electric vehicles with in-wheel motors as the research object,the structure of the vehicle was first introduced,and then the dynamics model was established according to the basic structure of electric vehicles with in-wheel motors,including: in-wheel motors model,tire model,steering model,suspension model,etc.According to the structure arrangement scheme of the vehicle,the vehicle dynamics simulation model considering the structure characteristics was established in the multi-body dynamics analysis software Adams/View.In addition,model verification was carried out on the established model to ensure the correctness of the built model,which lays a foundation for the verification of the control strategy in the following paper.(2)Research on four-wheel steering control strategy of electric vehicle with in-wheel motors.In order to improve the four-wheel steering ability of electric vehicles with in-wheel motors,the four-wheel steering control strategy of the electric vehicle with in-wheel motor was studied.The control strategy adopted the proportional feedforward + fuzzy feedback control mode combined with Ackerman steering principle.Firstly,the feedforward control method proportional to the angle of front and rear wheels uses the angle of front wheels and speed information to calculate the angle of rear wheels.The output angle control of rear wheels can ensure that the lateral deflection angle of the vehicle’s center of mass is always close to zero in a short time under any driving conditions.On the basis of proportional feedforward control,fuzzy feedback control with yaw velocity error and its rate of change as input and rear wheel angle compensation as output was added,which can comprehensively control the yaw velocity and centroid of vehicle and improve the efficiency of comprehensive control.At the same time,particle swarm optimization algorithm was used to control the weight coefficient of fuzzy feedback control,which can increase the adaptability of the control strategy under various steering conditions.(3)Simulation analysis of four-wheel steering characteristics.After designing the four-wheel independent steering control mode,it is necessary to adopt effective methods to verify the effect of the control strategy.It will consume a lot of time and material resources if it is tested directly on the real vehicle.In this paper,multi-body system dynamics simulation software Adams combined with Matlab/Simulink was used to build a co-simulation platform,and different speed and different steering conditions were simulated and verified on different road conditions,and the four-wheel steering control strategy designed in this paper was simulated and compared with the vehicle under no control state.And the simulation results are analyzed.(4)Design and development of four-wheel steering controller for electric vehicle with in-wheel motors.The design of four wheel steering controller includes the design of hardware and software of steering motor control system.The controller can obtain vehicle information required for steering control in the process of running,such as wheel steering angle,vehicle speed,etc.,through various sensors.Then the wheel angle information was obtained according to the calculation method of the designed four-wheel steering control strategy,and the steering control signal was sent to each motor controller.The established controller and the 4WS control strategy were tested by hardware in the loop to verify the feasibility.