Automotive clutches are rotary components which transmits the torque from the engine to the transmission. During the engagement, due to the difference in speed of the shafts the friction lining initially slips until it makes a complete engagement. Enormous amount of heat is generated due to the slippage of the friction lining, leading to poor shift quality and clutch failure. Depending on the road & traffic conditions, and frequency of engagement and disengagement of the clutch, it generates transient heating and cooling cycles.
Hill fade test with maximum GVW conditions being the worst case scenario for the clutch. A test was conducted to understand the performance of the clutch, in which clutch burning was observed. The clutch lining got blackened and burning smell was perceived. The friction coefficient drops sharply to a point until it cannot transmit the torque required to encounter the slope. This further worsen clutch slippage and lead to more severe temperature rise. The major reason attributed to the burning was inefficient cooling and less thickness of the flywheel & pressure plate. To address this issue transient CFD simulation is performed. Co-simulation methodology is applied to study how the solid temperature influences the air temperature at different time interval of the cycle. The temperature & convective heat transfer co-efficient data exchange happens across the domains after a fixed time interval mentioned in simulation. The heat generated in the solid components are mapped to the air and cooling effect of the fresh air from the ventilation holes are mapped on the solid. To replicate the exact test scenario varying launch energy, convective heat transfer coefficient and rpm is applied on the frictional discs as compared to the conventional steady state simulation approach where constant heat is applied on the frictional disc neglecting the cyclic variation of heating and cooling.
A physical test on vehicle was conducted for hill fade condition by inserting the thermocouples in the clutch housing close to the friction lining to measure the air temperature. The measured air temperature shows good trend of correlation with the predicted temperature.
