Development of Friction Material and Quantitative Analysis for Hot Spot Phenomenon in Wet Clutch System

In recent years, several new types of automatic transmissions have been developed and launched such as CVT, AMT, DCT and Multi Step AT. The operating condition of wet friction material in automatic transmission has become more severe in order to achieve further improvement of fuel economy and compact size with high power engine. Under higher speed engagement, the sliding interface between friction material and separator plate (steel) must absorb a large amount of energy in a very short time. Recently, there is increasing to focus on the hot spot phenomenon that is appeared as some discoloration and distortion on reaction plate for wet friction material. This hot spot phenomenon is known as a typical failure mode of wet clutch system, because it influences the durability and shift quality in clutch system. [1][2] Hot spots can cause degradation of friction performance during shift change in automatic transmission. And the high thermal stresses developed can also cause friction material damage, wear and permanent deformation of separator plate leading to coning deformation. Therefore, it is very important to prevent the formation of hot spot and to understand the mechanism of hot spot phenomenon. In this paper, we introduce the quantitative analysis and an evaluation technique for the formation of hot spot derived from Thermal Elastic Theory, and the development of anti hot spot friction material in automatic transmission.