Study On The Control Of Vehicle Stability System And Four Wheel Steering System And Integrated System

At present, the study on improving vehicle handling stability and safety is paid attention to by the people with the more and more demands for three goals of aotomobile safety, energy saving, environmental protection and fierce competition increasingly in aotomobile industry. Among them, the vehicle stability control as active chassis technology as an important part of the modern automobile technology has developed into one of the most important direction. The integrated control research with four-wheel steering control also begins to get the attention of researchers.Four-wheel steering control used to be a research hotspot of active chassis technology, and it has the advantage of control system of maintaining track and slip angle easily to be realizd. However, four-wheel steering control exists more limitations because of the dependence of transverse force and the slip angle saturated characteristic, the current development direction is the vehicle stability control technology based on the direct yaw moment control (DYC).The vehicle stability control contains two aspects of the problem, maintaining track and stability problem described by the body slip angle and the yaw velocity respectively. With regard to the problem of maintaining track, body slip can be the control target, and as for the stability problem, yaw velocity can be the control target, the coupling also makes the research of vehicle stability control algorithm present a diversified development trend, such as the yaw velocity control or the body slip angle control or the combined control. Because the vehicle slip angle is determined together by the longitudinal force and the lateral force, it is difficult to control the lateral force directly with the braking force, and the tire lateral force control is direct and effective by the four-wheel steering control, thus the study of vehicle stability system and four-wheel steering system integration has the factor of technology driving.The research data shows that the main goal of four-wheel steering system is to improve the steering stability, and it has the advantage of being easy to realize the goal through the slip angle control by the tire lateral force, and also can satisfy the stability requirements under the general driving condition, and the vehicle stability system based on direct yaw moment solves the loss of stability through the regulation of tire longitudinal force when the tire lateral force tends to be saturated condition under the emergency conditions. So, it becomes a new development direction on the vehicle active chassis control to combine the four-wheel steering system and the stability system and to improve the performance of integrated system.Based on the study of vehicle stability control system, this paper explored the integration control method of stability system and four-wheel steering system, which mainly includes the following content: This paper established the linear2DOF four-wheel steering model and the yaw velocity feedback control system. Further considered the influnence of tires and other nonlinear factors, used the four-wheel steering control method based on the neural network theory, designed the mixed control system using the MATLAB neural network toolbox, realized a mixed control of the four-wheel steering based on the yaw velocity feedback and the adaptive neural network.The vehicle stability control target was discussed, the stability control logic based on direct yawing moment was analysed, a kind of stability control system based on the yaw velocity feedback was designed. This system consisted of a four-wheel brake logic controller and a PID controller of monowheel brake force, and used the ABS system with a tire sliding rate control to prevent wheel instability, solved the loss of dynamic stability when the tire lateral force approached adhesion limit or reached saturation. Each of the shortage was analysed as the body slip angle as the control target for the four-wheel steering system, and as the yaw velocity as the control target for the stability system, and the integrated control system was made up of two subsystem. The integrated control system took advantage of both subsystem synthetically, improved the path tracking performance and the steering stability, enhanced the steering maneuverability and sensitivity, improved the transient response quality and the comprehensive performance of integrated control system.The control system co-simulation was based on ADAMS and MATLAB. ADAMS was used to establish the system virtual prototyping model, considered the requirements of integration control of the stability system and the four-wheel steering system, reserved the integration control interface. MATLAB was used to establish the hierarchical integration control system, designed the lower subsystem controller and the upper system management controller, and the upper system management controller monitored the vehicle running state and decided what to do. This kind of layered integration method improved the vehicle comprehensive performance and ensured that the subsystem has a good performance. The vehicle stability system test platform based on LabVIEW was designed and the simulation of hardware in loop was tested, tested the effect of control strategy, developed the controler based on the rapid control prototype and performed the test bench experiment, the experimental results showed that the system runs normally, the control effect is good.