Research On Optimizing Torque Distribution Strategy For Independent 4WD Electric Vehicle

Because of the urgent demand of energy efficiency and environment protection, electric vehicle has become a promising development direction of vehicle industry. The electric vehicle with four independently driven in-wheel motors is one of the hottest research areas, given that the advantages of independently torque control and easiness of integration. This thesis focuses on the wheel torque coordination distribution of four-wheel-independently-drive electric vehicle. The main works are as follows:First of all, based on the multi-body dynamics theory, the 7-DOF dynamic model of four-wheel-independently-drive electric vehicle is established, including the longitudinal, lateral, and yaw movements of vehicle body as well as the spin of four wheels. The tires and motors models are also built such that the research foundation of torque distribution is set up.Secondly, the driving torque distribution method based on the maximal adhesion margin is proposed, considering the influence of road longitudinal and lateral friction coefficients on vehicle driving force. This method is divided into the driving torque distribution layer and the anti-slip driving control layer. On the latter layer, the sliding mode variable structure methodology is adopted; on the former layer, the driving torque is distributed using the least square method to maximize the road adhesion function based on the longitudinal and lateral adhesion abilities.Then, the vehicle lateral stability is analyzed. And the driving torque distribution method based on the lateral stability is proposed. This method is divided into lateral stability control layer and yaw moment distribution layer. On the former layer, the lateral stability is controlled based on the sliding mode variable structure, taking the heading angle and yaw rate as combined control variable; on the latter layer, the yaw moment is distributed based on the recognition of driver’s steering intention and vehicle steering characteristic.Finally, the influence of driving torque distribution on vehicle stability is studied. And the coordination distribution method based on the fuzzy-SQP multi-objective optimization algorithm is proposed, considering the coupling relationship between driving torque and yaw moment. The vehicle power and stability are optimized by fuzzy-SQP multi-objective optimization algorithm with the driver’s vehicle acceleration demand, tire adhesion limit and vehicle’s maximum yaw moment as constraints.In conclusion, through the research on wheel torque coordination distribution of four-wheel-independently-drive electric vehicle, this thesis provides the theoretical basis and technique support of the research on electric-wheel vehicle wheel torque coordination distribution.