A Comparison of Methods for Evaluating Automatic Transmission Fluid Effects on Friction Torque Capacity - A Study by the International Lubricant Standardization and Approval Committee (ILSAC) ATF Subcommittee

As part of the International Lubricant Standardization and Approval Committee's (ILSAC) goal of developing a global automatic transmission fluid (ATF) specification, members have been evaluating test methods that are currently used by various automotive manufacturers for qualifying ATF for use in their respective transmissions. This report deals with comparing test methods used for determining torque capacity in friction systems (shifting clutches). Three test methods were compared, the Plate Friction Test from the General Motors DEXRON^®-III Specification, the Friction Durability Test from the Ford MERCON^® Specification, and the Japanese Automotive Manufacturers Association Friction Test - JASO Method 348-95. Eight different fluids were evaluated. Friction parameters used in the comparison were breakaway friction, dynamic friction torque at midpoint and the end of engagement, and the ratio of end torque to midpoint torque. Correlation among the three test methods was relatively good in the early portions of the test procedures, however as tests progressed correlation deteriorated. A “severity index” was developed that might help explain the deterioration in correlation among the three test methods.