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Traction drive continuously variable transmissions (TCVTs) are under active investigation by a number of OEMs and suppliers. Along with advances in control systems and metallurgy, improved traction fluids will be key to successful implementation of this technology. Traction fluids will need to function over a wide range of temperatures and contact pressures. Contact pressures may reach as high as 4 GPa, while temperatures may range from about - 40 C to about 140 C. It is widely recognized that low temperature fluidity at start-up is an issue, since fluids which give high traction coefficients and adequate viscosity under normal operating temperatures generally exhibit high viscosity at low temperatures. However, fe published data are available on traction behavior at temperatures below about 20 C and at contact pressures above about 2 GPa.

The friction behaviors of fresh and aged ATFs and a paper-based wet friction material were characterized using a low velocity friction apparatus (LVFA). Friction tests on 30 ml samples of ATF were used to characterize the friction durability of ATFs aged in test vehicles and in the Ford Aluminum Beaker Oxidation Test (ABOT). Oxidation test data gave stability rankings for the various ATFs which were consistent with limited vehicle experience. The procedure was applied to the analysis of results from a fleet test run with transmissions equipped with a modulated torque converter clutch. The test was aimed at characterizing friction degradation and shudder. Samples obtained from the test fleet were used to construct degradation profiles for two ATFs. The profiles showed no significant difference between the two ATFs in friction stability, consistent with the results of bench oxidation tests. However, an oil to air cooler was seen to provide some improvement.

Torque converter clutch friction interface and automatic transmission fluid (ATF) temperatures, pressure difference across the clutch piston, flow through the friction material grooves, and engine crankshaft dynamic torque were measured for typical operating conditions on a running transmission. The friction coefficient, clutch unit pressure, fraction of heat rejected to ATF flowing through the grooves, and time dependent thermal response were determined. Simplified heat transfer calculations were compared with thermal data. Clutch interface temperatures were assessed as they relate to the process of friction material and ATF degradation. The inductively powered radiotelemetry system was found to be a robust and powerful tool for investigating continuously slipping clutch system performance.