Research Of Wheel Differenrtial Control Strategy For In-Wheel Drive Electric Vehicle

The steering differential problem of the wheel drive electric vehicle which restricts the wheel drive electric vehicle development is mainly solved in this paper. Based on reading literature at home and abroad and further studying the problem of electronic differential wheel drive electric vehicle, four-wheel differential control strategy based on torque control is studied from the perspective of improving vehicle stability.Firstly, the research object is four wheel drive and four wheel steering electric vehicle which the hub motor is the low-speed external rotor motor. The nine degrees of freedom including a front wheel angle, vertical and lateral, yaw, roll and wheel rotation nonlinear vehicle steering vehicle model and tire model based on the "magic formula" are established. Then, two degrees of freedom linear model is got by linearizing the nonlinear model. And on the basis of the analysis the ideal yaw rate calculation formula relative the front wheel steering angle is got.Secondly, in order to pave the way for the subsequent design of electronic differential system, it is need to get the ideal yaw rate numerical value of vehicle. Involving the ideal yaw rate calculation parameters are estimated by using in-vehicle sensors and the corresponding estimation methods. The parameters including longitudinal and lateral speed, side-slip angle, cornering stiffness of front and rear axles, the maximum adhesion coefficient need to be estimated.Again, in the current basis of the wheel speed or torque control electronic differential system, the electronic differential system based on fuzzy PID control has been designed. The system includes two modules: (1) the yaw moment control module which mainly control yaw moment by using the fuzzy PID control algorithm for making the difference between the actual yaw rate and the ideal yaw angular velocity less than 0.05.Thereby, the lateral stability of vehicles is improved when four wheels is in the extreme conditions and the handling and stability of electric vehicles are improved further. (2) fuzzy PID control module based on the relative slip rate which first give each allocation method based on traditional mechanical wheel torque differential speed differential principle and front and rear hub motor power, and then control wheel torque difference between outside wheel and inside wheel by using fuzzy PID so as to make the inner and outer wheel slip ratio less than 0.005.Finally, in order to verify the effectiveness of electronic differential system based on fuzzy PID, the vehicle, tire and electronic differential system simulation model are established in the MATLAB/Simulink software and then the online simulation is carried on. The simulation results show that the fuzzy PID control algorithm can achieve good control target.