| Electric vehicles have incomparable advantage over the traditional vehicles in the aspects of energy saving and environmental protection, which has become one of the main streans of automotive technology research in the future. Meanwhile, with the people’s attention to the issue of the automotive safety, the handling stability research of electric vehicle has gradually become a hot spot in the field.In view of the drive motor system superiority in dynamics control, this thesis takes vehicle stability control system as the research object based on the four-wheel independent drive electric vehicle, and establishes a vehicle stability control strategy that can effectively reflect the driver’s manipulation intention by introducing the driver model, which can characterize as a real driver. The main work of this thesis is as follows:Firstly, a nonlinear vehicle dynamics model with 8 degrees of freedom is built in this thesis to provide an effective model for the vehicle stability control strategy. According to the structure of four wheel independent drive electric vehicle, modular method is used on every subsystem of the vehicle model, including eight degrees of freedom vehicle model, wheel model, Dugoff tire model and driver model. And the model is verified effectively by compared with Carsim, a commercial simulation software.Secondly, the novel vehicle stability control strategy is proposed based on the driver’s preview feature. The control strategy is divided into three parts:(1) the ideal reference model that can precisely provide driving intention for the vehicle stability control strategy. In addition to the traditional vehicle tracking model, the driver model is used to research the characteristic of driver preview to establish the intention correction model, which composes of the ideal reference model that can enhance the driving intention.(2) The design of the vehicle stability controller for calculating the desired yaw moment that the ideal state response needs. The dynamic weighted fuzzy control method is used to design the vehicle stability controller according to the two control objectives of the ideal reference model output. This method can improve the control effect by adjusting the dynamic weighting factor to dynamic control the target.(3) The tire force distribution strategy based on the rules is used to achieve the desired yaw moment. This strategy is designed by axial load ratio based on the change of the vehicle vertical load characteristic. And the proposed vehicle stability control strategy takes a double lane change simulation test. Simulation results show that the proposed vehicle stability control strategy meets the design requirements and has the better ideal vehicle response compared with the ones that used the traditional reference model.Then, the tire force distribution strategy based on optimization theory is designed. The tire force distribution strategy based on the rules does not have enough accuracy and robustness especially in the extreme conditions. Meanwhile, in order to give full play to the advantages of the electric vehicle drive motor system, such as continuously controllable, fast response and high control precision, the tire force distribution strategy is designed to minimize the road adhesion consumption by considering the constraint conditions of each wheel. In addition, the influence of the single wheel driving/braking force on the vehicle yaw motion is studied by applying the driving/braking force to the wheels under the limit conditions, so as to determine the weight coefficient of each wheel attached margin. And the quadratic programming theory is used to solve this optimal problem of the road adhesion consumption. Compared the two different tire force distribution strategies in simulation, the simulation results show that the strategy using the quadratic programming can be more precisely achieved the desired yaw moment and further improve the stability of the vehicle.Finally, this thesis builds the human-vehicle closed loop control system based on the vehicle stability control strategy, and the effectiveness of the proposed control strategy is verified by simulation. The vehicle stability control strategy can still achieve the intention of the driver manipulative under extreme conditions through the double land change and snake simulation conditions. And the simulation tests can further validate the control strategy which can enhance the driving intention of the ideal reference model output and improve the control intervention instant. Meanwhile, this proposed strategy not only improves the accuracy of the road vehicle tracking, but also improve the performance of the vehicle handling and stability. |
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