In recent years, the slip lock-up mechanism has been adopted widely, because of its fuel efficiency and its ability to improve NVH. This necessitates that the automatic transmission fluid (ATF) used in automatic transmissions with slip lock-up clutches requires anti-shudder performance characteristics. The test methods used to evaluate the anti-shudder performance of an ATF can be classified roughly into two types. One is specified to measure whether a μ-V slope of the ATF is positive or negative, the other is the evaluation of the shudder occurrence in the practical vehicle. The former are μ-V property tests from MERCON® V, ATF+4®, and JASO M349-98, the latter is the vehicle test from DEXRON®-III. Additionally, in the evaluation of the μ-V property, there are two tests using the modified SAE No.2 friction machine and the modified low velocity friction apparatus (LVFA). Automobile manufacturers evaluate their ATF's using their own friction material, as such there is currently no globally recognized test procedure to evaluate anti-shudder performance of the slip lock-up ATF.
The members of International Lubricant Standardization and Approval Committee (ILSAC) ATF subcommittee have researched the correlation among the test methods of DEXRON®-III, MERCON® V and JASO.
The μ-V properties of the ATFs that member companies are currently using or previously used as factory fill fluids were compared in tests conducted with the R-H friction apparatus and with the JASO M349-98 test procedure using a modified LVFA. The correlation between the two test procedures was investigated with respect to their validity as a test method for evaluating anti-shudder performance. The results made clear the μ-V characteristics and anti-shudder durability of the ATFs used by the member companies in slip lock-up clutch systems. Through these studies, the evaluation of μ-V characteristics was shown once again to be a valid and effective screening test for assessing anti-shudder performance.