Chaotic Vibration And Chaos Control Of The Vehicle Suspension System With Multi-degrees-of-freedom Under Consecutive Speed Control Humps Excitation

An automobile is a highly integrated nonlinear system in practice because of many nonlinear properties, such as nonlinear stiffness of suspension spring, hydraulic nonlinear damper, hydrodynamic nonlinear damping, and nonlinear stiffness of tire, which consist in suspensions, tires, seat and other components. Therefore, some nonlinear behaviors, such as bifurcations and chaos, may appear when the vehicle moves over the bumpy road. These non-linear phenomena may lead to increase vibration of the vehicle, threaten traffic safety, impact ride comfort and cause undesirable vibrations and road noises. Therefore, it is important to study the nonlinear dynamic phenomena of the vehicle caused by the road surface-speed coupled excitation, and its inhibition method.In order to describe the actual vehicle system realistically, this dissertation studies the chaos vibration and chaotic control of the multi-DOF(degrees of freedom) nonlinear vehicle suspension system by focusing on the 4-DOF nonlinear half vehicle model, the 7-DOF nonlinear full vehicle model and the excitation from the consecutive SCHs(speed control humps)on the highway. This dissertation will analyse the nonlinear dynamics characteristics of the vehicle model under different conditions of excitation and system parameters, reveal the nature and impact of chaotic motion and design the rational chaos control method for better dynamic behavior of the vehicle suspension system. The results will provide the important reference in the design of the vehicle suspension system as well as road pavement design. The main work of this dissertation includes five parts:①Aiming to a kind of special shape of road surface on the highway such as the consecutive SCHs, the dynamic excitation models coupled with vehicle-road-SCH are built. The models simulate the excitation when a vehicle passes over the general road and a series of periodic and aperiodic SCHs with a certain speed.②Based on the 4-DOF nonlinear half vehicle suspension system, the motion equations of 4-DOF nonlinear half vehicle model are first established. Then, the numerical simulation is conducted and the nonlinear dynamic responses of the half vehicle model are investigated when the vehicle moves over the consecutive SCHs at the steady speed and variable speed(including acceleration and deceleration). It reveals that various forms of nonlinear vibrations, the critical condition of chaotic phenomena and the routes leading to chaos.③Based on the 7-DOF nonlinear full vehicle suspension system, the motion equations of 7-DOF nonlinear full vehicle model are first established. Then, the numerical simulation is conducted and the nonlinear dynamic responses of the full vehicle model are investigated when the vehicle passes over the consecutive SCHs at the steady speed and variable speed(including acceleration and deceleration). It shows that various forms of nonlinear vibrations, the critical condition of chaotic phenomena and the routes leading to chaos. Compared with the 4-DOF nonlinear half vehicle model, the more abundant results are obtained based on the 7-DOF nonlinear full vehicle model.④A 11-DOF dynamic model of human-vehicle-road coupled system for ride comfort analysis is built and the numerical simulation based on the model excited by the vehicle-road-SCH coupled incentive model is conducted to analyze the relationship between nonlinear behavior, and vibration amplitude and intensity. The results reveal that quasi-periodic motion and chaos may lead to a significant increase in vehicle vibration amplitude and intensity, and ride comfort is bad. Ride comfort is good at the periodic motion state because vibration amplitude and intensity are low.⑤A 4 DOF nonlinear half vehicle model and a 7 DOF nonlinear full vehicle with active control forces are used to investigate the control of chaotic vibration by direct state variable feedback control method and slide mode variable structure control method, respectively. The simulation results show that vibration amplitude and intensity could be decreased and ride comfort could be improved by means of the suppress of chaotic vibration.