Determining Frictional Performance of Automatic Transmission Fluids in a Band Clutch

Frictional characteristics of several automatic transmission fluids (ATF's) were evaluated in an SAE No. 2 Friction Machine adapted to the band clutch from a front-wheel-drive, three-speed automatic transaxle. The bench test apparatus subjects the band clutch to repeated engagements (24 000 in a 100-hour test period) at elevated temperature with representative clutch energy dissipation and lockup time, and with forced aeration of the fluid. Fluid frictional performance is judged from the level and stability of friction torque during the 24 000 clutch engagements. The test is repeatable and readily distinguishes fluids having different frictional characteristics. Fluid frictional behavior in the band machine is shown to reflect fluid effects on shift performance in an engine dynamometer, transaxle cycling test. Also, fluid effects determined in the cycling test are shown to match those obtained in a vehicle. Both shift quality and durability can be inferred from the band friction machine results.