Modeling And Control Of Vehicle Hydraulic Active Suspension Systems

For its advantages in technology and vast field of application, active suspension has been a hot point since it appeared and is called as a kind of technology representing the developing trend of vehicle suspensions. At the same time, there are a lot of challenges in dynamics, control and application of the active suspension systems.This dissertation systematically discusses some issues related to the modeling and control of the vehicle hydraulic active suspensions. These issues include the modeling of active suapension systems based on considering hydraulic actuator dynamics, combining control of the optimal control and the backstepping method, and adaptive control on the problems of uncertainties. What's more, there is a discussion on the passenger-seat dynamics included in active suspension system. The main contributions are as follows:1. The nonlinear models of the vehicle hydraulic active suspension system are built based on hydraulic actuator dynamics analysis. For better evaluating the performance of the active suspension system, we choose two degrees-of-freedom quarter-car model of active suspension, four degrees-of-freedom half-car model of active suspension, seven degrees-of-freedom whole-car model of active suspension, and six degrees-of-freedom half-car model of active suspension including passenger-seat dynamics in the dissertation.2. The control strategy using a combination of the optimal control and the nonlinear backstepping technique is provided for the active suspension system, which is divided into two parts: the linear part (outer loop) and the nonlinear part caused by hydraulic actuator (inner loop). The detailed procedure is also divided into two steps: firstly the linear quadratic optimal controller is designed based on the performance requirements in the outer loop, and then the nonlinear terms are dealt with the backstepping method in the inner loop. Simulation results show the effectiveness of the proposed strategy.3. Considering the variations in the parameters of the active suspension, we study the sensitivity of the control strategy proposed in the third chapter. Aiming at the uncertainty of the time constant, the control law and parameter update law are designed in the inner loop using adaptive backstepping method in this dissertation. The verifying in theory and simulation results demonstrate that the uncertainty can be dealt effectively.4. In order to realize the full potential of active suspensions the controller should have the capability of adapting to changing road environments. We present a gain scheduling control strategy for vehicle suspension design. The control gains of the optimal controller in the outer loop are adapted to the changes of the road input by acceleration feedback. Thus, optimal suspension performance can be obtained in different conditions. Simulations show that the control strategy provides superior passenger comfort over the whole range of road conditions.5. An analytical investigation of the nonlinear half-car model including passenger-seat dynamics is examined. The simulation results demonstrate that the control strategy based on the combination of the optimal control and the backstepping technique, when including passenger acceleration in the performance index, retains both excellent ride comfort and road handling characteristics. Furthermore, the potential improvements through wheelbase preview control are investigated.In conclusion, by analyzing and simulating, it mainly studies the problems in dynamics, modeling and control of the vehicle hydraulic active suspension in the dissertation and proposes some methods on the control design and the practical problems, which can provide ideas for the study of the active suspension in other kinds, and be of some help to the development of active suspensions.