Research On Temperature Characteristics And Thermal Failure Of Wet Multi-disk Clutch

In recent years,with the development of self-owned brand automatic transmission technology,wet dual clutch transmission has become one of the automatic transmissions competitively developed by transmission enterprises in China.As one of the key parts in wet dual clutch transmission,the thermal reliability of the wet dual clutch has a decisive effect on the starting,gear shifting performance and life of the transmission.The wet dual clutch is generally composed of two sets of wet multi-disk clutches.The two sets of clutches are alternately separated an engaged to realize gear shifting during the operation of dual clutch transmission.During the working process of the wet dual clutch,the friction pairs of each clutch are repeatedly separated and engaged,resulting in a large amount of friction heat on each friction interface.Especially in some extreme work conditions,the friction pair surface generates a large amount of friction heat in a short time,which easily causes thermal failure of friction pair.Aiming at the thermal failure of wet clutch in the development of wet dual clutch transmission in a certain enterprise,this dissertation established the thermal structure coupling analysis model of friction pairs in wet multi-disc clutch and made an intensive research on the temperature characteristics and thermal failure of wet clutch.The results are of great engineering guiding significance to the development and optimization of wet dual clutch transmission.The results of the research show that the structural characteristics of wet clutch have a significant effect on its thermal characteristics.The main contents were as follows.(1)The dynamic friction transmission mechanism in wet clutch engagement was analyzed,and the oil film pressure model,asperity contact model,bearing capacity model and dynamic friction coefficient model in engagement were established.And the variation of engagement pressure,transmission torque,angular velocity difference and dynamic friction coefficient during engagement in wet clutch was analyzed,which provides the theoretical basis for the heat generation mechanism of the subsequent thermal analysis of friction pairs in wet clutch.(2)The heat generation mechanism and heat transfer mechanism of wet clutch were studied.And the thermal boundary condition of heat flux model,heat transfer model and convective heat transfer model in the actual working process of wet clutch were determined.The boundary conditions of the wet clutch structure are established.Combining with the motion constraint boundary conditions of wet clutch,the thermal structure coupled finite element analysis model of wet clutch was established.(3)The influence of the structural characteristics of the piston and thrust ring in wet clutch on the temperature characteristics,stress distribution and axial displacement of the friction pairs were studied on the basis of the finite element analysis model and the direct thermal structure coupling analysis method.(4)The influence of different structural characteristics of piston and thrust ring on thermal failure of friction pairs in wet clutch was analyzed by DOE optimization design method basing on the three indexes of radial temperature difference,maximum equivalent stress and axial displacement of separator.The optimization result of piston and thrust ring assemble was obtained.