Coupling Analysis About Thermal Instability And Thermal Wear Of Piston Ring In Vehicle Transmission

The sealing ring is mainly applied to the wet clutch in advanced vehicle transmission.Working at high speed and heavy load condition,local thermal instability phenomenon and wear will appear on sealing ring because of the relative friction between sealing ring and rotating shaft.Then sealing ring will fail,resulting that the operating pressure will not meet the required value,the wet clutch cannot work.Eventually,the vehicle cannot run normally.Therefore,thermal instability problem of composite sealing ring was researched in this paper by theoretical model,simulation analysis and experiments,then we obtained the critical velocity of hot band phenomenon,analyzed the effect factors of the critical velocity.The interaction mechanism between thermal instability and thermal-induced wear was explored.These researches provided basis for avoiding the thermal instability of sealing ring,improving its performance and ensuring the stability of clutch mechanism.Firstly,the theoretical model of thermal instability with hot band was constructed based on perturbation method.Galerkin finite element method was used to construct non-uniform physical models of heat conduction,temperature field disturbance and their coupling relations.By transforming the thermal instability problem into solving matrix determinant problem,a method for calculating the critical speed of hot band phenomena in sealing ring was obtained.The effects of friction coefficient,elastic modulus,thermal conductivity,thermal expansion coefficient and sealing ring size on the critical velocity were analyzed quantitatively.The thermal instability of sealing ring was dynamically researched by finite element software.The heat conduction differential equation and thermal boundary conditions were established.According to the thermal-structural coupling calculation module of the explicit dynamic algorithm,sealing ring was simulated in two conditions,higher than and lower than critical velocity,to obtain the distribution of temperature and contact pressure of friction surface on the sealing ring.The basic characteristics of the sealing ring in thermal instability state were acquired,which provided a reliable and convenient means for studying the thermal instability phenomenon of the sealing ring.Simulation process of cyclic iteration calculation was proposed and simulation of the service rules of composite sealing ring from local material thermal damage to overall wear damage was simulated to research the interaction mechanism between thermal instability and thermal-induced wear of composite sealing ring.The wear of the node on the friction surface of sealing ring was calculated by thermal-structural coupling method and Archard wear model.The surface geometry was updated to reflect the degree of wear in a given time.In the process of circulation,the changes of hot band were observed.The results showed that wear is the driving mechanism of hot band migration.Under complex wear conditions,the hot band will present more complex changes,such as the division and merger.To get the variation between speed and surface temperature of the sealing ring when the sealing friction pair were in sliding process.A comprehensive performance test bench for dynamic seal was built and the test scheme was formulated.According to the calculated critical velocity,the temperature disturbance of sealing ring at the corresponding speed was observed,and the critical velocity of the sealing ring entering the thermal instability state is confirmed.The typical wear characteristics of the seal ring which caused by thermal instability were obtained by scanning electron microscopy.Compared with the experimental results,the practicability and accuracy of the numerical simulation method for thermal instability of composite sealing ring were verified.