Study On Stability Analysis And Integrated Control Of The Key Subsystems Of Vehicle Chassis

In order to further enhance the overall performance of vehicle, active control technology of vehicle chassis through controlling lateral movement, vertical movement, and vertical movement of the vehicle to improve vehicle handling, ride comfort and braking performance is a research focus of vehicle dynamics in recent years. Suspension damping or spring stiffness are adjusted in active suspension system (ASS) according to road conditions to improve vehicle ride comfort; It provide different torque in electric power steering system (EPS) depending on different vehicle speed to improve handling performance; It prevent wheel car lock in anti-lock braking system (ABS) during braking to improve the vehicle braking performance; However, most of the literature focus only on the control characteristics of the active chassis control systems while the stability of the control system itself involves little. In fact, because of nonlinearity or uncertainties caused by the complexity of external environment and time delay of the system itself in EPS, ASS, and ABS, it lead to the control system instability and affect the normal function of the system. Therefore, it should be paid close attention ensuring the stability of the control system while studying the control characteristics of active control systems. Meanwhile, it often meet its different performance indicators in the designing of a single active chassis control system, but in integrated control system the vehicle does not necessarily have good overall performance because of dynamics coupling between systems. Therefore in order to further improve the overall performance of vehicles, it necessary to study integrated control of chassis systems in order to improve chassis dynamics coupling on the basis of studying stability of vehicle chassis control subsystems.In this paper, based on vehicle dynamics theory combined with modern robust control theory vehicle chassis control systems and it's integrated control system has been studied. To ensure a good communication performance and system performance controller area network is carried out to integrated control system. It includes the following specifically:Firstly, in this paper mathematical model is established for electric power steering system (EPS),anti-lock braking system(ABS) and active suspension system(ASS) based on semi-car model respectively, different control methods were adopted for controller design of subsystems, the simulation research was carried out.Secondly, It has been shown that the parameter-dependent stability condition is of less conservativeness than quadratic stability condition which requires a common Lyapunov function for the entire uncertain domain. the control system robust performance was evaluated and conservatism was analyzed for active suspension system. The results show that robustness of vehicle active suspension system was better guaranteed with a smaller conservatism.Thirdly, an integrated chassis control system was designed in two different control structure respectively: (â…°) The mathematical model of vehicle systems was established, then a global optimal control targets is determined, EPS and ASS were centralized to integrate control. (â…±) Take controllers designed for subsystems(EPS\ABS)as bottom controllers, upper coordinated controller was designed based on deeply analyzing the influences among EPS and ABS, upper controller was a decision-making controller, sensor signals were transmitted to upper controller through CAN bus; Simulation results show that vehicle synthesis performance is improved.Finally, Hard in Loop experiment was carried out based on LabVIEW development platform for integrated control system and real vehicle test was carried out based on integrated controllers'development of ABS and EPS using ARM7 and protel software. The result of real vehicle test and HIL(Hard-in-Loop) experiment proves that the integrated control logic we put forward is correct and feasible. It could not only apparently improve the performance of braking stability, but making steering portable as well.