1998-10-19

ATF Bulk Oxidative Degradation and Its Effects on LVFA Friction and the Performance of a Modulated Torque Converter Clutch 982668

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. A friction coefficient - speed slope criterion was proposed as an indicator for an ATF prone to cause shudder. ABOT tests were carried out on one fluid at several different temperatures. Samples were withdrawn periodically and run in the LVFA. Time-temperature degradation profiles were constructed from the friction data and used to make quantitative predictions of friction degradation in the test vehicles. The results agreed well, supporting the idea that bulk oxidative degradation of ATF in service is a key factor in friction durability of modulated torque converter clutches.

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