Modeling On Tire Thermal-mechanical Characteristics

Tire presents the thermal-mechanical characteristics during working.Testing by Michelin indicates that temperature increase would reduce the tire cohesive force by 10% and thus affect vehicle safety.Currently,researchers around the world only focus on the numerical study of thermal-mechanical characteristics under cornering instead of complex conditions with the combined affects by load,speed,pressure,and temperature.This study attempts to solve the above problem by theoretical and experimental method and unveil the mechanism of the coupled mechanical and thermal characteristics of the tire.First,this thesis develops the theoretical tire model,focusing on how the temperature affects the tire characteristics.More specifically,based on the existing studies and the experimental research,the nonlinear theoretical model is developed to describe the correlation between load,pressure and the length of the contact patch as well as the tire stiffness.Accordingly,the combined tire model is derived based on the dynamical friction characteristics between the road and tire.By analyzing the coupled effects caused by load and pressure on the tire longitudinal and lateral stiffness,the coupled mechanism is uncovered without considering the temperature aspect,which thematically paves the way to studying the coupled tire thermal features in the combined conditions.Second,research of the thermal-mechanical features of the tire.This thesis focuses on how the load,speed,and pressure influences the tire temperature in both longitudinal and lateral pure slip condition,and then how the temperature affects the stiffness and friction.By experimentally study of the phenomenon of the temperature increase,the stain energy model is introduced with the load-varying and pressure-varying factors.With the heat-exchange coefficient,which is linearly changing with the temperature,a thermal model related to the load,speed,and pressure is developed.The correlation between the temperature and tire stiffness is analyzed according to how the temperature affects the rubber shear modulus and the mechanical feature of the linear region.Based on the mechanical feature of the nonlinear region,rubber friction testing,and Persson's rubber friction theory,the friction characteristics between the tire and road is studied.Then,in accordance with the ideal gas equations and the correlation between temperature and pressure,the pressure feature model is derived.Combined with the tire mechanical,temperature,rubber material,and pressure characteristics,the theoretical tire thermal-mechancial model is finally obtained.This model can describe the thermal effects on its mechanical features and can also be easily used in the vehicle stability control.Third,develop the high-fidelity semi-empirical tire model with the thermal-mechanical characteristics.With the high fidelity,good prediction ability,and the flexible “Plug-in” dynamical friction feature of the semi-empirical Uni Tire model,the nonlinear equations of the longitudinal and lateral stiffness with the effects by the load,pressure,and the stiffness-decay factor,the feature of the coupled temperature and sliding velocity between the road and tire with the temperature-equivalent factor,the equation of the curvature factor including the effects by the load,pressure,and temperature are introduced,and then the thermal-mechanical based high-fidelity semi-empirical model is developed,which improves the tire model accuracy and extends its application ability.At last,study on the effects of the thermal-mechanical model on vehicle stability.The developed model is firstly connected with the vehicle model in Car Sim,then several typical scenarios are studied to show how it influences the vehicle stability.And then the thermal-mechanical feature can enlarge the effects caused by the load and pressure differences of the front and rear axle,finally influencing the understeering and extreme lateral acceleration.