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This paper examines the anti-shudder property of automatic transmission fluid (ATF) in terms of evaluation criteria and durability. The anti-shudder property is required for precise slip control around the clutch in that kind of automatic transmission, applications which are currently increasing. To evaluate anti-shudder properties, friction characteristics are measured by modified Low Velocity Friction Apparatus (LVFA), and the data are compared with those from the actual vehicle. The analysis confirms that the occurrence of shudder on the vehicle is closely related to the ratio of the static friction coefficient to the dynamic one measured by modified LVFA.

Based on IAE gear OK load tests and Shell four ball wear tests of oils thickened with several polymers, it was concluded that the effective viscosity* in such concentrated contacts is governed by the partial permanent viscosity loss in the limited area of the contact. The fact that sheared oils, which were designed to have a finished permanent viscosity loss as would occur in such concentrated contacts, showed similar OK loads and wear scar diameters also proved the validity of the above mechanism as proposed in the previous paper(1)**.