Study Of Dynamic Stability Control And Driver-vehicle Closed Loop System For In-wheel Motor Electric Vehicles Steering

With the aggravation of the global energy crisis and environment pollution, governments and automobile manufacturers are committed to promoting the development of the electric vehicle industry, in order to solve the traditional automobile’s energy and environmental problems. The electric vehicle with electric motor wheel is one form of the electric vehicle(EV), which is driven by four in-wheel motors or hub motors, each of which independently drives one wheel. Meanwhile, compared with the traditional vehicle, this new form EV has more controllable degrees of freedom. Therefore, it is suitable to adopt vehicle chassis integrated control technology to allocate steering, driving and braking system actuator actions to achieve the global optimum of vehicle performance. Therefore, electric motor wheel EV equipped with integrated chassis control technology can be convenient to solve the vehicle stability problem of the electric motor wheel EV, and have good development prospects.In view of the vehicle stability control problem, the integrated control system is recognized to be an effective way. Meanwhile, how to deal with the coordination problems between steering and driving and establish a unified control structure is the key to solve the problem of integrated control. Aimed at the problem, this thesis takes the electric wheel drive vehicle with the four wheel independent steering as the research target, and establishs a vehicle stability control system. Meanwhile, based on the hierarchical control structure, this thesis considers the problem of the steering and driving integrated control, the tyre longitudinal force distribution, and the actuators and sensors/observer delay.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 a simulation platform for the vehicle stability control system. For the convenience of the study, a concise form Dugoff tyre model which reflects tyre nonlinear characteristics is used in tyre modeling part of the vehicle dynamics model.Secondly, the vehicle stability control system based on hierarchical control structure is designed in this thesis. The structure of the control system is divided into three layers. The first layer is called the desired planning layer, designs the reference model which characterizes the intentions of driver handling and stability based on the driver familiar with the linear vehicle characteristics. The second layer is called the coordinated planning layer, designs four wheel steering(4WS) controller and direct yaw moment(DYC) controller using the principle of sliding mode variable structure, and implements the coordinating integration of 4WS and DYC in the process of controller design. The third layer is called the driving force distribution and control layer, designs the tyre longitudinal force dynamic distribution strategy based on the vehicle maneuverability and driving comfort, and also designs the Smith predictor to solve the delay problem of the actuator and sensor/observer. The tyre longitudinal force dynamic distribution strategy can not only use the vehicle steady turning performance to assist vehicle steering, but also can take care of the driver longitudinal intention for reducing the influence of the vehicle longitudinal velocity. The open loop simulation test results of the vehicle stability control system show that the vehicle stability control system in this thesis can meet the design requirements and well realize the handling and stability control of the vehicle.Then, for the human-vehicle closed loop simulation research, this thesis studies the preview and decision-making mechanism of the driver, and designs the direction preview driver model which is used to obtain the driver steering angle in the process of vehicle steering and provide effective driver model for the human-vehicle closed loop simulation research of the vehicle stability control system.Finally, this thesis builds the human-vehicle closed loop control system based on the vehicle stability control system. The closed loop simulation test is carried out to verify the effectiveness of the vehicle stability control system which is designed in this thesis. The closed loop simulation test verifies that the vehicle stability control system can achieve the purpose of the vehicle handling and stability and improve the vehicle’s driving safety in the extreme condition. Under the premise of ensuring the vehicle stability, the vehicle stability control system can better cooperate with the driver to achieve its handling intent.