Research On Electronic Differential Control Strategies Of In-wheel Motor Driving Vehicle

With the global energy crisis and a strong demand for low-carbon environmental Protection, countries around the world are seeking environmental friendly, energy-saving and safe new energy vehicles. Wheel hub motor driving vehicle can be independently controlled for each of the driving wheels and has simple structure and so on, so it has great prospects. In this paper, hub motor vehicle driven by four wheels independent was used as research object, the research of electronic differential control strategies were carried on.First of all, a "magic formula" tire model and nine degrees of freedom vehicle model were established.The simulation results show that wheel hub motor vehicle model by established is correct. Secondly, the not easily acquired parameters of vehicle in the actual movement process were estimated. Thirdly, the research of electronic differential control strategies were carried on. In this paper, the strategy of motor speed control was chosen. Turning condition and line conditions were analyzed,respectively. For turning condition, two different differential control methods were designed. One differential control method was based on Ackermann steering model. The target rotation speed of each wheel was calculated when the vehicle is cornering. This goal was achieved by controlling the motor speed. If the wheel appears slip, the slip ratio of wheel would be controlled until reaching the target rotation speed of each wheel. Another differential control method was based on fuzzy control. The sideslip angle and yaw rate were control objectives. The ideal vehicle turning model of linear two degrees of freedom was established. The deviations of sideslip angle and yaw rate were inputs to the fuzzy controller. Fuzzy controller output a speed change. Then outside wheels increased some speed and inside wheels decreased some speed. At the same time, the slip ratio of wheel would also be controlled. For line condition, on low adhesion and butt pavement, the strategy was mainly controlling the slip ratio of wheel. And on bisectional road, firstly the slip ratio of wheels on low adhesion side was controlled. Then reference speed on high adhesion side is wheel heart speed on low adhesion side. This reference speed is achieved by controlling the motor speed for ensuring the vehicle traveling in a straight line on bisectional road.Finally, the above designed electronic differential control strategies were simulated. Simulation results showed that for turning condition when speed was not high two control methods had achieved good control effect,and for line condition when speed was high the control effect based on Ackermann was little and the control effect based on fuzzy control was well. For line condition, wheel slip did not appear on the low adhesion and docking pavement through control, wheel slip did not appear and vehicle can keep straight on bisectional road. It indicated that the above design differential control strategy was effective.