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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.