Torque Distribution Control Strategy And Simulation Of On-demand 4WD Vehicle

Electric controlled On-Demand 4WD system has been more and more popular in city SUVs.The study of control strategy for straight line and steering conditions is significant for better vehicle performance.The control strategies are based on the vehicle's demand and the target torque is given according to the vehicle working conditions.First of all,the dynamic model of torque distribution,the 3DOF longitudinal vehicle model and the 3DOF lateral vehicle model have been built in this paper.The torque distribution principle and the influence of On-Demand system have been analyzed based on the dynamic model.The control strategies for performance and economy have been designed for straight line working condition,respectively.The torque management device was controlled by lock or slipping according to the lock schedule of performance control strategy.The torque management device slipping control was based on the feed forward algorithm according to the idea torque distribution theory.Then the feed forward torque was amended by the feed back control of speed difference.The economy strategy was based on the tire spin ratio feedback control and the control torque was adjusted according to tire spin ratio.The performance and economy strategy were selected according to the vehicle working conditions to achieve better performance as well as better fuel saving.The steering control strategy was based on the feed forward and feedback control.The feed forward control algorithm was designed according to the idea torque distribution based on the tire friction circle theory.The torque management device speed difference has been selected as the feedback control variable and the feedback control algorithm was designed to amend the feed forward torque.Finally,the typical working condition simulation has been done based on the Carsim and Simulink model.The results show that the straight line control strategy can satisfy the vehicle acceleration demand as well as the economic demand and the steering strategy can improve the maneuvering and stability of vehicle.