Theoretical And Experimental Research On Vibration And Control Of Automobile Semi-Active Suspension System

With the improvement of people’s requirements for the stability of the car’s driving,people’s demand can’t be satisfied by traditional linear passive control suspension system.The nonlinear semi-active suspension system has become present research focus.In present master’s thesis,the nonlinear semi-active delayed feedback control is applied to control the vibration of the automobile suspension system.A set of mechanics experimental model is designed to simulate and analyze the vibration characteristics of automobile nonlinear suspension system.In chapter 1,the development history of automotive suspension,research status of semi-active suspension and the prospect of time-delay feedback control technology are summarized.In chapter 2,the vehicle suspension system is simplified to a single degree of freedom system,and nonlinear time-delay feedback control is used to control the vertical vibration of the car body.The cubic and quintic stiffness nonlinearities are considered in this model.The effects of the vehicle suspension system parameters,the delay feedback gain coefficient and the time delay on the vertical vibration of the suspension system are analyzed.The larger coefficient of nonlinear stiffness is,the harder characteristics of the spring.The resonance peak shifts to one side due to the existence of nonlinear coefficient,and multiple values of the amplitude frequency response curve of the system occurs.The effects of the two important parameters of the time-delay feedback control(time-delay feedback gain coefficients and time delay)on system vibration are analyzed.For a fixed time-delay feedback gain coefficient,there is a range of time-delay values,which the amplitude of the system is much lower than the passive control system.And there will be a time-delay point in this time delay interval,the amplitude of the system is suppressed to a minimum value.In Chapter 3,a two-degree-of-freedom model is investigated,and stiffness and damping of automotive tires are considered in this model.The model is more realistic and complex than the single degree model.Similarly,in a two-degree-of-freedom system,for a fixed time-delay feedback gain coefficient,there is also a range of time-delay values,which the amplitude of the system can be suppressed compared with the passive one.The influence of time-delay feedback gain coefficients and time delay on the control stability is also analyzed.Higher time-delay feedback gain coefficients together with the optimal time delay is,the better vibration control effect is obtained.However,the vibration suppress interval of time delayed is shrink.The coordination relationship between the optimal time delay feedback gain coefficient and the best time delay point is found out.In chapter 4,an experimental model of a linear two-degree-of-freedom vehicle suspension is designed.The parameters of the model system are obtained by scaling down the 1/4 car body parameters of a general car.The structure of the experimental model and some parameters of the vibration test instrument are introduced.The modal frequency and damping ratio of the model were obtained by modal test and frequency sweep analysis.The results of experiment are compared with the theoretical modal frequencies,and the experimental model is agreed with the designed expectations.In the chapter 5,based on the linear experimental model in chapter 4,the mutual repulsive force of permanent magnets is introduced to as a nonlinear equivalent stiffness.A nonlinear two-degree-of-freedom vehicle suspension model is constructed.The modal frequency and damping ratio of the model are measured by modal test and sweep frequency analysis.The repulsive force between the permanent magnets is measured in the experiment,and the fitting equation of the repulsive force is obtained by curve fitting.The fitting equation contained the cubic terms.The ratio of the first-order to second-order mode is satisfied one to three,it means that a one-to-three internal resonance occurs.The one-to-three internal resonance of the model is verified by the frequency spectrum of the first and second modes of the model.At the same time,time domain map of nonlinear model with fixed-frequency excitation is compared with the linear one.It is found that in the nonlinear model,due to the presence of the third-order nonlinearity in the nonlinear model,the system has internal resonance,making the amplitude of the main system and the isolator of the nonlinear model both larger than that of the linear.In present master’s thesis,the time delay feedback control is employed to control the vibration of the semi-active vehicle suspension system.A new research idea for the control of the semi-active suspension system of the vehicle is presented.Moreover,an experimental model of a two-degree-of-freedom vehicle nonlinear suspension is designed to do experimental research.It provides reference to engineering practice.