Vibration Control For Vehicle Suspension System Based On Variable Structure Theory

The suspension system is an extremely important component of the vehicle and is one of the important indicators to measure the quality of the vehicle. The vehicle is easy to produce the strong vibration during the driving because of changes in travel conditions such as road roughness, speed and direction of movement.This vibration of the vehicle not only reduce economy, but also affect the overall performance of the vehicle chassis,ride comfort and handling stability. Therefore, studying on the vibration and stress of the vehicle suspension system and takeing effective suppression strategy play an important role in improving the ride comfort, guaranteeing the stability of the vehicle and keeping tire contact with the ground.The present dissertation focuses on the control law design for semi-active/active suspension system based on variable structure theory to improve ride comfort and analyze the stability of vehicle.The main contents are summarized as follows:(1) In order to improve vehicle ride comfort and reduce the tire dynamic load, the 2-DOF mathematic model of semi-active suspension system with sky-hook damping was first established. Then the fractional calculus theory was applied to the semi-active suspension,Then the optimal parameters of the fractional order sky-hook damping control were found by using genetic algorithm.(2) With an aim at solving the problem of high frequency chattering in traditional exponent reaching law (TERL) sliding-mode system, a novel variable rate reaching law (VRRL) strategy is proposed for vehicle semi-active suspension system. Taking an ideal-skyhook damping (ISD)suspension system as the reference objective, considering the sliding mode system in the whole dynamic responding robustness and the sliding mode reaching segment features. The fuzzy logic control is used to change the sliding mode reaching rate so as to decrease the system chattering.(3) With an aim at solving the problem of control stability caused by the model uncertainties for the vehicle active suspension system, a novel adaptive fuzzy sliding mode control (AFSMC) strategy is proposed for the nonlinear active suspension system. To improve the vehicle ride comfort and ensure the vehicle safety performance, the nonlinear dynamic model of a quarter vehicle suspensions is first built based on T-S fuzzy model method. Then,the appreciate switching surface function and sliding mode control law are designed through the slidingmode control and adaptive control theory.Finally, the stability analysis of the proposed controller is further conducted based on Lyapunov stability theory.