Study On The Handling Stability Of Four-wheel-drive Electric Vehicle

The four-wheel-drive vehicle can gain greater driving force, which improves the vehicle passing ability and cross country performance. The four-wheel-drive electric vehicle also can realize the braking energy recovery, which improves the efficiency of energy utilization. The common scheme of four-wheel-drive electric vehicle includes in-wheel motor drive electric vehicle and dual motor four wheel drive electric vehicle, and so on. The in-wheel motor electric vehicle has larger under spring mass, which leads to the poor comfort performance. The in-wheel motor electric vehicle also needs the electronic differential, and some key technology is still under exploration. The dual motor four-wheel-drive electric vehicle can realize the same energy recovery performance with in-wheel motor electric vehicle, and does not need the electronic differential. The dual-motor dour-wheel-drive electric vehicle has low cost for the appliance of traditional mechanical differential, so it has the better industrial prospect. This paper focuses on the research of handling and stability of dual motor four-wheel-drive electric vehicle, especially the stability with high speed and low adhesion road. The purpose of the research is to improve the vehicle’s active safety, to protect the driver’s life.The movement state of vehicle can be divided into two part, longitudinal movement and lateral movement. For the coupling of longitudinal and the lateral movement, the longitudinal speed needs to be considered during the stability control system development. Electronic stability program introduced by Bosch is aimed improving the vehicle handling stability, and is also the mainstream stability control system. This paper focuses on a dual motor four-wheel-drive electric vehicle, and the stability control system is developed. The main research contents of this paper are as follows:The structural characteristic and the advantages of dual motor four-wheel-drive electric vehicle are analyzed, and the electric vehicle topological model is established at the same time. The transmission system which includes battery model, electric motor model, and differential model is constructed in AVL Cruise. The vehicle dynamics model is constructed in Car Sim, which contains the simulation conditions, such as pavement condition, the driver manipulation and simulation environment etc. The traction controller is developed in Matlab/Simulink. To testify the validation of the electric vehicle model, the constant acceleration test and the constant steering wheel angle test are conducted.The mechanism of vehicle losing stability during ultimate conditions is researched in chapter. First, the nonlinear Burhardt tire model is established. Then, combining the nonlinear tire model, the nonlinear two degree of freedom vehicle simulation model is conducted. At last, the planar motion analysis methodology is adopted to analyze the stability domain. The target yaw rate is revised by the slip angle to gain stability in emergency conditions.The hierarchical control strategy is adopted to develop stability control unit. With this strategy, the upper /underlying structure controller is proposed, in which the nonlinearity of vehicle and tires can be directly taken into consideration. The upper layer controller is motion tracking controller, and the sliding mode control methodology is applied to calculate the desired force and moment. The controller parameters are optimized by genetic algorithm. The quadratic programming methodology is applied for the underlying controller design, the longitudinal forces of tires is determined and optimized by the distribution controller. The double lane change test is used for the validation of the control system under diverse conditions.Combining the d SPACE integrated development environment, the electric vehicle stability control system rapid control prototype is developed. The hardware-in-loop real time test bench based on CAN communication protocol is constructed by the combination of the rapid control prototype and d SPACE DS1006. The stability control system can improve the stability of the electric vehicle through the hardware-in-loop test.The research contents of this dissertation are summarized, and the innovation points and inadequacies are pointed out, which provides the direction of follow-up study.