Control of Band/Drum Interface Temperature in Automatic Transmissions and the Impact Upon Friction System Durability

The importance of controlling band/drum interface temperature to maintain friction system durability in an automatic transmission clutch is investigated in this paper. Frictional durability is extremely important to assure smooth, consistent shifts and long transmission life. A statistically designed series of experiments was run in a SAE No. 2 band test machine to determine the parameters which impact interface temperature. Sump level, sump temperature, engagement speed, system inertia, direct lubrication of the drum surface, and engagement time were all examined. The analysis reveals each of these parameters, with the exception of engagement time, directly influences interface temperature under the tested conditions.

Interface temperature was then linked to frictional system stability. This was accomplished through a second series of experiments where interface temperature was varied by changing only one of the previously identified parameters. Based upon these results, a graph is presented relating interface temperature to system durability. This graph may be used in transmission design to ensure consistent shifts and increased durability of band friction systems.