Research On The Nonlinear Characteristics And Control Strategy Of Vehicle Semi-suspension

Vehicle suspension system is the key component for riding comfort and stability. Semi-active suspension is the development direction of suspension, but also a key research hotspot in recent years. In this paper, random surface model, damping nonlinear modeling, semi-active suspension nonlinear characteristics of semi-active suspension and nonlinear control strategy are studied in theoretical and experimental research and made some progress as follows:A new approach to simulate three-dimensional road spectrum model, which could represent road surface roughness and coherence of wheelpath excitation, was put forward. The model was obtained by the further study on the sinusoid superposition method, based on two-dimensional road surface spectrum model. It was expanded to three-dimensional space, and was studied by numerical simulation. The spectrum characteristics analysis shows that, the new model reconstructed the time domain model of road surface spectrum and included the coherent relationship between wheelpaths of vehicle driving.A modificatory Bouc-Wen parametric model is proposed, aiming at the nonlinear modeling of MRD. The new model can describe the hysteretic loop in low speed exactly, introduces hysteretic characteristics in high speed and contains the bias of damping force caused by accumulator of single-out-rod damper. The force-velocity and force-displacement curves are obtained by indicator experiment on self-designed large scaled MRD. The modificatory Bouc-Wen model parameters are identified with the test data, and correspond to the practical physical quantities. Then excitation current parameter is introduced to the model. The modificatory Bouc-Wen model is verified by experiment data finally.The nonlinear characteristics of semi-active suspension including modificatory Bouc-Wen model are researched. It analyzed the influence on the varible sprung mass, unsprung mass, spring stiffness and dampering to the nonlinear suspension characteristics. Then it judged the vibration forms of nonlinear suspension on various frequency and amplitude, and studied the path of the suspension vibration to chaos with variety of pavement, by phase portrait, Poincare diagram and bifurcate diagram. Finally, the suspension response under stochastic road irregularities is simulated, and analyzes the time series. It proved that the suspension vibration is chaotic motion. The research ultimately indicates the chaotic behavior under variable situations, and provides the basis for the dynamic design of ground vehicle.The semi-active control strategy of nonlinear suspension is studied based on analyzing the nonlinear force component of MRD. The optimal semi-active sky-ground hook hybrid control method is gain by layer progression from ideal sky-hook control method. The semi-active suspension controller is designed by feedback linearization method. The simulation result shows that the optimal semi-active sky-ground hook hybrid control method can inhibit vehicle body acceleration and dynamic tyre load. Then a quarter suspension vehicle lab system is established. And the effect of optimal semi-active sky-ground hook hybrid control method is verified by experiment.