Limited Slip Wet Clutch Transmission Fluid for AWD Differentials; Part 2: Fluid Development and Verification

During the last years several electronically controllable automotive transmission systems, where wet clutches are used as intelligent differentials, have been developed. These applications generally apply high stress on the transmission fluids. The fluids must preserve the desired frictional characteristics at different torque level in an environment where the ambient and system temperature varies over a wide range.

This paper is focused on limited-slip wet clutches in all-wheel-drive systems. Different approaches for transmission fluid development are described. Data from thermal analysis and friction measurements are used to illustrate the influence of system related parameters on frictional characteristics.

The friction characteristics resulting from temperature changes on the surface of the lamella material is presented. It was found that the changes on friction characteristics and the negative trend of the friction curves are dependent on the increase of the temperature at the surface of the lamella material.

The data from a reciprocating friction measurement apparatus was compared to the data from a disc-on-disc clutch equipment. The study shows that the generated information on friction characteristics from these two test equipments is fairly comparable. Different types of fluids applied in this application are compared and discussed.