| The suspension system is the key component to achieve ride comfort and drive safety for a vehicle.The semi-active suspension system is currently the focus of suspension research for its superior performance,simple structure and low cost.The two core contents of semi-active suspension research are as follows:Firstly,the development of high-performance adjustable shock absorbers;And secondly,the study of semi-active control strategy.The research of control strategy needs precise models as support.Tire is a system with complex nonlinear character because of its material and structure.At present,most studies ignore the effect of tire damping on the transmission characteristics of suspension system,modeling the tire with a simple spring.This paper aims to build an accurate and efficient tire nonlinear vibration model,and design a sliding mode controller for the semi-active suspension model,which considers the nonlinear damping of the tire.Therefore,this dissertation focuses on the study of tire nonlinear vibration model,the influence of tire damping on the transmission characteristic of suspension system,and the sliding mode control for semi-active suspension.The main contents include:(1)Modeling of tire nonlinear stiffness and damping.According to the mechanical characteristics of the tire,select the appropriate model from previous tire nonlinear model.Do the parameter identification of the selected tire model by test data.(2)Analyze the influence of tire damping on the transmission characteristics of suspension system.compare the simulation results of quarter-car models with and without tire damping,and study the effect of tire damping on the transmission characteristics and the’Invariant Point’ in the frequency domain curve.Simulation results show that with the condition of high velocity or in 4-10Hz frequency considering tire damping will lower the value of sprung mass acceleration,suspension stroke and tire dynamic force.And at the 2nd resonance frequency considering tire damping will couple the motion of sprung and unsprung mass,and the invariant point in the frequency domain curve of sprung mass acceleration will disappear.(3)Designing of controller for semi-active suspension with nonlinear tire damping.A sliding mode controller is designed for the suspension system with nonlinear tire damping.By comparing with the skyhook control and passive system,study the control effect of the sliding mode controller for the nonlinear system.The simulation results show that the sliding mode controller can significantly reduce the sprung mass acceleration and the tire dynamic force in the frequency range of 4-10 Hz.After considering tire nonlinear damping,ride comfort near the second-order resonance frequency can be greatly improved.(4)The HIL test of validating the sliding mode control is carried out.In order to validate the effect of the designed sliding mode controller,impulse,sinusoidal and random road are chosen as the road input.SMC is compared with the skyhook control and the passive system.The results show that sliding mode control can effectively improve the ride comfort and handling stability. |
