Study On Temperature-pressure Distribution Characteristics On Friction Pairs Of Multi Disc Wet Clutch For Vehicle

Wet multi disk clutch is an important part of the automotive driveline. The process of vehicle's start-up is accomplished by the clutch's sliding and friction. Therefore, the contact state of the friction surface affects the starting process of the vehicle directly.Due to the thermal expansion caused by the temperature rise during the sliding process of wet multi disc clutch, the contact surface pressure is distributed in a non-uniform distribution. The wear of the clutch disc caused by the uneven contact pressure is not uniform, which decreases the performance of the wet clutch, or even causes the surface damage and the failure of the friction element. Therefore, it is very necessary to analyze and study the temperature and the contact pressure of the friction pair in the wet clutch.In this paper, a wet clutch equipped in some vehicle is taken as research object. The surface temperature and the contact pressure of the clutch friction pair are analyzed under two start-up conditions: gentle start-up and rapid acceleration start-up. The contents are as follows:(1) The structure, working principle and characteristics of wet clutch are introduced, and the research status of thermal stress and contact pressure of wet clutch at home and abroad is analyzed. These points out the direction for the research of this paper.(2) As the theoretical basis of the research on the temperature and contact pressure in the friction pairs, the basic theory of heat transfer and thermal stress are briefly described, and the processing method of contact problem in the finite element method is expounded.(3) The power transmission model of wet clutch is established. The rotational speed curve and the engagement pressure curve of different starting conditions are analyzed and compared, and the boundary conditions are calculated based on these. One pair of friction pairs in the wet multi disc clutch is taken to establish a reasonable and simplified model. The friction heat and the contact pressure are calculated by using ANSYS software. The changes of temperature and contact pressure on the surface of the friction pairs are analyzed, and the relationship between the contact pressure and the change of the surface temperature is discussed.(4) Based on the perturbation theory of thermal elastic instability, a two dimensional analytical model of clutch is established. The analytical solution of temperature field and stress field in two dimensional model of the wet clutch is derived based on Fourier's law, and the characteristic equation of the system is derived based on the energy balance equation. According to the system characteristic equation, the relationship between the disturbance growth and the velocity is obtained, and the change of the contact pressure disturbance of the friction contact surface is analyzed under different start-up conditions.Through the study of the surface temperature distribution and the contact pressure distribution of the friction pair, the relationship between the temperature change and the contact pressure change of the contact surface is revealed. This study can provide basis for the structural design of wet clutch, and provide reference for the control strategy of starting process.