Testing Method and Effect of ATF Performance on Degradation of Wet Friction Materials

Degradation of wet friction materials can cause changes in friction characteristics and a reduction of material strength. The former changes may reduce the friction coefficient or result in a μ-V characteristic with a negative slope. It is well known that the blocking of friction material pores substantially affects changes in characteristics. A decline in strength may reduce the thickness of friction materials and lead to delamination in the worst case. This paper presents the results of a study concerning the effect of the automatic transmission fluid (ATF) on friction material pore blockage and reduction of material strength (delamination life). It was found that the high-temperature detergency of ATFs affects the blocking of friction material pores and that ATF compatibility with cellulose fiber affects the reduction of friction material strength. It was also found that the respective degree of influence of the ATF could be evaluated by a hot-tube test and differential thermal analysis.