CLUTCH SHUDDER CORRELATED TO ATF DEGRADATION THROUGH LOCAL FRICTION VS VELOCITY-MEASUREMENTS BY A SCANNING FORCE MICROSCOPE

Shudder in continuously slipping wet clutch (CSWC) systems is an insta bility that manifests itself as a vibration of the automobile's drive train. Dynamometer experiments imply that the shudder is connected to degradation of the frictional properties of the clutch friction materi al-automatic transmission fluid (ATF) system. The poor friction charac teristics are revealed in negatively sloped torque vs. slip speed curv es which can result in dynamic friction oscillation instabilities. The authors report local measurements of friction vs. velocity with the u se of a scanning force microscope (SFM) on new and glazed wet clutch f riction material with either new or degraded ATF acting as a lubricant . The friction material was a commonly used cellulose/phenolic resin m aterial. Results in the very low-speed dynamic regime indicate that th e fluid condition plays a critical role in determining the slope chara cteristics of the friction vs. velocity curve. ATF degraded in service imparts a flat or negative slope to the friction vs. velocity curve, whether on new or glazed (degraded) friction material. A positive slop e is measured for fresh ATF. The SFM measurements are therefore consis tent with dynamometer and vehicle experiments which measure gross prop erties of the friction clutch system. The ability of the SFM to reprod uce the dynamometer results on a local scale implies that shudder is n ot due to the gross fluid flow or mechanical effects that are present in a complete torque converter. The frictional characteristics of the clutch plate materials and the ATF are paramount. This technique allow s continuous monitoring of ATF fluid degradation in test fleet vehicle s without ATF replenishment since only a few ccs of fluid are necessar y for these tests.