Research On Driving Force Distribution Strategy Of Four-Wheel-Independent-Drive EV

Four-wheel-independent-drive EV becomes the trend of future vehicles, because it satisfies the requirements of sustainable development strategy, has flexible layout and independently controlled power, and is easy to realize some functions, such as electric differential control, braking energy feedback, stepless speed changing, and turning fixedly. The driving force distribution control system is one of the most important technologies to improve the dynamic performance, the economical efficiency and the security of four-wheel-independent-drive EV. Therefore, this paper researchs on driving force distribution control strategy of the four wheel independent drive EV.According to the vehicle dynamics, the vehicle body model, the tire model and the basic equation of the vehicle driving force distribution were established. The motion of vehicle body and tire was divided into three directions: the longitudinal direction, the lateral direction and the transverse direction.A driving force distribution control strategy for different driving operations was proposed to avoid the limitations of the existing control method. The nonlinear constraints of each drive wheel were different when the vehicle is moving. According to the load transfer situation, the vehicle driving operations were divided into three modes: and straight line driving mode, accelerating or climbing mode, steering mode.The driving force distribution control system including the torque calculation layer and the driving force distribution layer is designed. The torque calculation layer calculated the expected total demand torque of the vehicle according to the input. The driving force distribution layer was designed to realize the following three functions: recognized the vehicle driving mode in real time, called the corresponding driving force distribution algorithm based on the driving mode, and optimized the distribution of driving force on each driving wheel. The torque calculation layer contained there modules: the driving mode recognition module, driving force distribution module and driving antiskid modules.The driving force distribution control strategies according different driving modes were studied. When a vehicle driving with uniform speed in a straight line, the aim of driving force control was to get the optimal economical efficiency. And in accelerating or climbing mode, the aim was to obtain the optimal dynamic performance. While in steering condition, the aim was to receive the optimal operational stability.Using the AVL CRUSE and MATLAB / Simulink, the co-simulation was carried out to validate the driving force distribution control strategies. The simulation results prove that the control strategy is feasible, and it can improve the vehicle’s dynamic performance and the driving stability effectively.(1) In the straight line accelerating mode, both the changing trends of the front and rear axle drive force, the ratio of rear axle drive force with total drive force were consistent with the changing of acceleration, and the rear axle drive force is greater than that of the front axle.(2) In climbing mode, the valve of maximum slope increased almost by 50%, and at the condition of ignoring driving motor constraints, the largest climbing ability under this control strategy is higher than that under the average driving force distribution.(3) During steering mode, under the controlling of this strategy, the vehicle’s maximum yaw angular velocity decreased by about 40%, stable yaw angular velocity decreased by 10%, the total utilization rate of tyre dropped by 24%, and the driving stability of the vehicle is improved.