Effects of sliding velocity and clamp load on the coefficient of friction in the study of self-exited vibrations (judder) in automotive clutches abstract

Abstract

Self-exited vibrations or judder aretorsional vibrations of the driveline which occurduring clutch engagement.In dry automotive clutches clutch judder has been attributed to loss of clamp load in hurried clutchengagement and/or falling coefficient of friction with increasing clutch-face slip speed (Centea, 1999). Therefore, themain influential parameter in clutchjudder is the friction liningmaterialcharacteristics with load and sliding speed. It is known that during clutchengagement,COFof theclutchlining canvary with the sliding velocity(i.e. μ-v characteristiccurve)(Centea et al. 1999; Centea et al. 2001).In the currentstudy, an in-house specifically-designedpin-on-disctribometerisused for measuringthe COFof the clutch lining material at different sliding speeds and clamping loads representingin situisothermal clutchconditions (Fig.1). The operating conditions in the tribometer are set to mimic the sliding speed and loading conditions in real clutch applications during the clutch engagement process. A 4-degree of freedomlumped parameter dynamic model is developed to simulate clutch engagement with take-up judder.The experimentally measuredCOFsfrom the testrig under various sliding speeds andclamping loadsareused as input tothe dynamic model.This paper presents a combination of experimental and numericalinvestigations of the dependence friction lining material on clamp load, sliding speedand itstake-up judder performance.