Influence of clutch lining frictional characteristics upon cold and hot take-up judder

Clutch take-up judder is a torsional vibration phenomenon induced by stick-slip oscillations at the friction lining interfaces between the clutch friction disc and the flywheel and pressure plate surfaces during the process of clutch engagement. This is short-lived transient phenomenon affected by the clutch lining material’s friction characteristics, topography of the mating-sliding surfaces and operational conditions during engagement such as contact pressure , interfacial slip speed and contact temperature. The phenomenon leads to driver discomfort as well as gradual wear of contacting surfaces, even if short-lived. Its frequency is is usually reported to be in the range 5-20Hz depending on the vehicle type. The friction characteristics alter in a transient manner during engagement and it should be measured under controlled conditions. In this paper the measured interfacial friction characteristics together with clamp load variation (contact pressure) under different surface temperatures are included in a multi-degree of freedom dynamic analysis to obtain torsional vibrations of the system, pertaining to take up judder conditions. Such an in-depth investigation has not hitherto been reported in literature. The paper shows that take up stick-slip judder is omnipresent under all clutch engagement conditions, but its poignancy is most evident at cold surface temperatures. It is also shown that the transient judder response has a broader spectral content that is generally understood.