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Design changes in automatic transmissions have resulted in new requirements for automatic transmission fluids. Electronic controls, for instance, perform best with fluids having better low-temperature properties. Achievement of the target low-temperature properties can be accomplished in different ways. The advantages and disadvantages of each approach are discussed with respect to total fluid performance. Fluid performance properties examined include viscometrics, shear stability, antiwear and stability toward thermal stress and oxidation.

One of the barriers to successful implementation of the continuous slip torque converter clutch (CSTCC) design for automatic transmissions (AT) is transmission shudder. An important factor contributing to shudder is the frictional characteristics of the automatic transmission fluid (ATF). In this paper, we report the development of a test that allows the precise measurement of the frictional characteristics of the ATF at different sliding speeds (μ-v data) using an SAE No. 2 friction machine. A conventional SAE No. 2 machine was modified, by installing a DC static drive motor, to simulate the sliding speeds, surface pressures, and fluid temperatures found in actual vehicle operating conditions. The μ-v data obtained with the machine showed good correlation with the vehicle shudder, i.e., the ATFs showing more negative gradient in the μ-v data caused more severe shudder in the vehicle.