Research On Straight Line Stability Control Strategy Of Four-Wheel Drive Vehicle With Hub Motors

With the rapid development of new energy vehicle industry, the four-wheel drive vehicle with hub motors is becoming a hot spot of the present research of the universities and the enterprises. The four-wheel drive vehicle with hub motors has an advantage of short transmission chain, fast dynamic response and high energy transfer efficiency. How to make good use of the hub motor, make the four motors working harmoniously, ensure the straight line driving stability become the research focus.Based on the research of Beijing Municipal Commission of education project "The control theory and key technology research of the electric passenger vehicle driven by distributed motors ", the straight line stability characteristics of the four-wheel drive vehicle with hub motors is analyzed.First of all, through the multi-body dynamics software Car Sim, the model of four-wheel vehicle is established with in-wheel motor. According to the vehicle dynamic performance index, the parameters of the in-wheel motor driving system is mached and the in-wheel motor model is established in MATLAB. Through the combination simulation of MATLAB and Car Sim, the straight line ability of the vehicle is verified, which laid a foundation for subsequent vehicle simulation.The effects are analyzed on the straight line driving stability of the high adhesion road,low adhesion road and bisectional road. The simulation results show that the low adhesion road and bisectional road have a great influence on the performance of straight line driving.The vehicle straight line driving stability control strategy is designed based on the influence of different pavement. The control strategy mainly includes the upper controller based on the sliding mode variable structure algorithm and PID algorithm, the substratum controller based on the optimization control allocation method. The upper controller mainly includes the speed tracking based on the sliding mode controller, yawing moment controller of sliding mode, the road recognition module and a slip rates controller by PID.For high adhesion coefficient road, low adhesion coefficient road, bisectional road, the simulations of straight line driving stability of vehicles are carried on. Simulation results show that when the tire-road adhesion coefficient is low, the control strategy not only makes the sliping rates stay near the optimal ratio, through yaw moment adjustment, alsoensures that vehicle yaw angle rates not beyond 0.5deg/ s.The control strategy can effectively ensure the straight line driving stability of vehicle.Finally, the four-wheel drive vehicle with hub motors experiment platform is established based on the RT_LAB, the motor drive code is completed, the CAN bus data acquisition is designed based on Labview software. At last a test of low adhesion coefficient road is carried on: the experiment results show that after 0.5s, the wheel slip rates are controlled near 0.12 and the yaw angular rates below 0.1deg/ s, proving the validity of the proposed control strategy.