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Comfort requirements have significantly increased in recent years, even in the commercial vehicle sector. Transmission noise, caused by higher engine excitation (due to emission changes), can be reduced with a new torsional damper in the clutch disc, with a special idle damper. Up until now, free play (sometimes referred to as backlash) in the clutch or transmission helped reduce idle rattle. In many cases this simple solution is no longer adequate. This paper explains dynamic behavior during idling and provides the background for understanding the causes of rattle noise.

The torque transmission capability of a vehicle clutch is significantly influenced by the cover assembly's clamping load and the friction characteristic of the clutch disk's facing material. The clutch facing's frictional value can be drastically reduced as a result of excessively high temperatures (“fading”). Generous safety factors have been integrated into existing clutch systems to prevent any uncontrolled clutch slip. The diaphragm springs in the cover assembly have to be designed to provide high clamping loads. High clamping loads, however, also have disadvantages: the clutch components are heavy and expensive and the elements in the actuating and releaser systems are subjected to severe loads. The slip control presented here should serve to lower clutch system clamping loads and at the same time ensure that the clutch is reliably prevented from suffering any uncontrolled slip.

The torsional damper of a vehicle's clutch is, as part of the drive train, subjected to various dynamic loads. Increasing torques and spatial limitations call for lightweight construction. The design of these components is now increasingly being influenced by the need to consider them from an fatigue strength standpoint. A new testing concept which aims at providing evidence of fatigue strength is introduced here, taking commercial vehicle clutch disks as an example, and touching upon the areas of analysis and evaluation of the load collective characteristic and of control systems for servo-hydraulic test rigs.