Study On Non-steady Tire Mechanical Characteristics Considering Inflation Pressure

Tire mechanical properties are the basis of vehicle dynamics.With the continuous development of vehicle control technology,it is necessary to establish a tire model which has higher accuracy and wider scope of application.Vehicle driving mode often changes,and the state of tire is often non-steady,so the description of tire non-steady characteristics is an important part of the description of vehicle dynamics and is of great significance for achieving more accurate and efficient vehicle dynamics control.Tire inflation pressure is one of the most important parameters that affect the tire non-steady mechanical properties,and the problem of influence mechanism and characteristic modeling of pressure is still to be solved.This paper aims to establish a non-steady tire theoretical model,analyze the influence of tire pressure on non-steady tire mechanical properties,and with the guide of theoretical model,establish a non-steady tire model which takes inflation pressure into consideration and is convenient for engineering application.And in this paper,the influence of tire pressure on vehicle handling stability is qualitatively analyzed.To achieve the above objectives,this paper has carried on four aspects of work: Theoretical model;Discrete simulation model;Semi empirical model;Model application.Theoretical model: the coupling effects of tire pressure and vertical load on the tire contact patch and physical parameters are analyzed with the experimental data and the linear steady state model.On this basis,a non-steady theoretical model of tire cornering characteristics considering tire pressure is established,the influence mechanism of tire pressure and vertical load on tire steady and non-steady characteristics is revealed.Discrete simulation model: to analyze the tire non-steady characteristics under large slip ratio input and combined slip condition,the discrete simulation model is established,and the variation law of tire relaxation length with inflation pressure,vertical load and slip ratio is analyzed.The results show that pressure and vertical load have coupling effect on tire relaxation length.Lateral relaxation length of tire increases first and then decreases with the increase of the inflation pressure and vertical load,and with the increase of vertical load(pressure),the peak point of the curve of relaxation length and pressure(load)moves to the side of high pressure(load);Longitudinal relaxation length decreases monotonically with the increase of inflation pressure and increases monotonically with the increase of vertical load.Moreover,lateral and longitudinal relaxation length of tire decrease with the increase of slip ratio.Semi empirical model: based on the approximation of theoretical model,pure lateral and pure longitudinal semi-empirical model for large slip input range are established.To solve the modeling problem of aligning torque,this paper puts forward the ‘reconstruction method' to modelling the pneumatic trail;then a semi-empirical model combined cornering and braking/driving is established.The pure cornering,pure longitudinal and combined tire test are carried out and the semi-empirical model is identified and verified.Model application: the tire non-steady model is applied to the two degree of freedom vehicle model,the effects of tire non-steady mechanical characteristics and tire pressure on vehicle handling stability are analyzed.The results show that the tire non-steady characteristics have obvious effect on vehicle handling stability especially at low speed.Tire inflation pressure affects vehicle dynamic response through changing the lateral stiffness and relaxation length.