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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.

Nissan has developed a practical and available toroidal continuously variable transmission (T-CVT) for passenger vehicles for the first time in the world. This CVT is applicable to engines having an output of torque larger than 400 N-m and makes it possible to use a lock-up clutch at low vehicle speed, resulting in marked improvements in drivability and fuel economy. The authors have developed the T-CVT fluid, which is in this application, having excellent traction coefficient and sufficient capacity as the transmission fluid. This paper mainly describes the traction coefficient measurement procedure and the performance of the newly developed fluid.