Influence of Temperature Rise on Local Lubrication and Friction Characteristics of Wet Clutch

Aiming at the accelerated failure of wet clutch due to the deterioration of local lubrication conditions, a microscopic lubrication and friction calculation model for wet clutch friction pairs with surface asperity contacts was developed in this paper. In addition, small sample pin-on-disc tests were conducted on Universal Material Tester. The influence of temperature rise on the bearing capacity of lubricating oil film, asperity contact pressure and contact area, load sharing ratio, local temperature rise, and friction coefficient of wet clutch friction pair were analyzed, which helped to reveal the mechanisms of temperature rise influence on the local lubrication and friction characteristics of the wet clutch friction pair. The simulation calculation results and experimental test results showed that, firstly, as the temperature increased from 30 to 90 ℃, due to the decrease of the lubricant viscosity, the fluid dynamic pressure between the friction pair decreased significantly, and the asperity contact pressure increases significantly. The maximum contact pressure increased rapidly from about 0.09 GPa to about 0.32 GPa. When the temperature further increased from 90 to 150 ℃, due to the fact that the viscosity of the lubricating oil was already low and there were already lots of asperity contacts, the increase rate of the maximum contact pressure slowed down, increasing gradually from about 0.32 GPa to about 0.37 GPa. Secondly, the load bearing capacity of the lubricating oil film decreased with the increase of temperature. During the process of temperature rose from 30 to 150 ℃, although the load bearing ratio of lubricating oil film between the friction pairs of the wet clutch decreased gradually from about 97% to about 57%, the lubricating oil film still bore most of the load between the friction pairs of the wet clutch, and the dynamic pressure effect of the fluid could not be ignored. In addition, as the temperature increased, the actual contact area between the friction pairs of wet clutch increased rapidly. During the temperature increased from 30 to 150℃, the actual contact area rate of the friction pair increased rapidly from less than 1% to about 6%. As the temperature increased, the local temperature between the friction pairs increased rapidly with the actual contact area, and the temperature rose at the micro asperity contact position was more significant. Furthermore, during the temperature increased from 30 to 90 ℃, the friction coefficient of the friction pair increased rapidly from less than 0.04 to about 0.07, which was significantly slower than the increase speed of the actual contact area. When the temperature was below 90 ℃, the friction force between the friction pair generated by shearing the lubricating oil film could not be ignored. When the temperature increased from 90 to 150 ℃, the area of the lubricating oil film decreased, and the viscosity of the lubricant decreased. Therefore, the friction coefficient between the friction pair increased gradually from about 0.07 to about 0.11. When the temperature was higher than 90 ℃, the increasing speed of the friction coefficient was basically the same as the increasing speed of the actual contact area.