Research On Electronic Differential Control System Based On Wheel Hub Motor

With the increasing situation of shortage of energy resources and air pollution, electric vehicles gradually become one of the important development of the new energy industry. The vehicle drived by electric wheel uses wheel hub motor to drive single wheel directly intead of the traditional mechanical differential component and mechanical transmission mechanism. This structure can simplify the chassis structure and reduce the vehicle quality. It has the advantages of high transmission efficiency, flexible space layout, easy control and so on. And the electric-wheel-drive vehicles also faces an important problem, that is, how to realize the speed coordination among different electric wheels.This paper takes the electric vehicle which has two front steering wheel and two rear hub motor driving wheel as the research object. Firstly, the selection of wheel motor is carried out. The permanent magnet brushless DC motor is selected as direct drive power source of the driving wheel after a detailed comparison among various motors about performance and usage and advantages and disadvantages. The parameter table of the permanent magnet brushless DC motor is matched based on the structure parameters and the dynamic performance index of the electric vehicle. The motor mathematical model is established based on this. Speed and current double closed-loop control method is selected as the control strategy of the motor, which the outer speed loop uses discrete PID control and the layer current loop uses current-hysteresis comparison control. In order to verify the control effect of the motor control scheme, Matalb/Simulink software is used to build simulation model of the system. The results show that the designed motor control scheme can satisfy the performance requirements of the motor.This paper formulates a electronic differential speed strategy scheme which is joint controlled by variable slip ratio and yaw motiont. This scheme is divided into three blocks: variable slip rate control module, the yaw motion control module and differential drive control module. Giving full of the driving force when the vehicle driving in a straight line and ensuring a smooth steering when the vehicle turning are taken as the purpose of variable slip rate control module. The rate of target tracking is formulated based on different driving conditions and road conditions. According to the internal control system, the wheel controlled by the slip rate and the controlled torque are determined. Fuzzy control method is choosen as the way of slip rate tracking control. The yaw motion control system is used for real-time correction to track the ideal model of the moving position of the vehicle and ensuring the safety of the vehicle. Classical PI control algorithm is adopted in the control system. The differential driven allocation algorithm is used for the combined control of the vehicle yaw and wheel slip rate to achieve the reasonable allocation of the two driving wheel torque. In order to state the actual operation of a real car reaction, eight degree of freedom model of electric vehicle is established in this paper. And considering the influence of tire characteristics, the "magic formula" tire model was established. It is used in the electronic differential control system calibration platform. At the same time, the joint control model of vehicle model, tire model and the electronic differential system was built by using Matalb/Simulink software. The three special conditions of open ground, docking and high-speed steering operation stability test were simulated and analyzed. The results show that the designed electronic differential control system can recognise the changes of the external abrupt pavement and driving conditions well. It can realize the moving wheels no slip and make the vehicle travel along the ideal path.