Self Adjusting Clutch

Principle of the self-adjusting clutch: load sensor

Figure 1 shows a schematic illustration. The essential difference as compared to a conventional clutch is that the bearing of the (main) diaphragm spring is not riveted fast to the cover but is supported by a so-called sensor diaphragm spring.This sensor diaphragm spring has a sufficiently long range with an almost constant load unlike the strongly degressive main diaphragm spring.

The LuK Self Adjusting Clutch offers two key benefits:

	low release loads which remain constant throughout the clutch life
	increased wear reserve and extended service life due to wear tracking

There is also a series of secondary benefits, for example:

	no servo-systems (in the case of commercial vehicles)
	simpler release systems
	smaller pedal loads and smaller pedal paths
	new opportunities to reduce the clutch diameter
	equal pedal loads throughout entire engine series

smaller release bearing path over service life

The horizontal range of the sensor diaphragm spring is set to somewhat more that the required release load. While the release load is less than the retaining load of the sensor spring the slew bearing of the main diaphragm spring remains in the same place as the clutch is released. If, however, the release frorce is increased due to wear on the linings, the counter-load of the sensor diaphragm spring is exceeded and the slew bearing drifts far enough towards the flywheel that the release load is lowered once more to the sensor load. When the sensor diaphragm spring drifts a gap appears between the slew bearing and the cover. This can be compensated, e.g. by a wedge.

Reference to Figure 2:

The load sensor with the thickness compensated for by wedges is supremely elegant and simple. The picture shows one example. Compared to the conventional clutch, just one sensor spring (red) and a ramp ring (yellow) are added.

Reference to Figure 3:

The picture shows the release load curves for a conventional clutch as new and with worn linings. Note in comparison the far lower release load of the self-adjusting clutch (SAC), whose characteristic curve remains practically unchanged throughout the life of the clutch.

A further benefit is the higher wear-reserve which no longer depends, as with conventional clutches, on the length of the diaphragm spring performance curve but on the ramp height and can be therefore increased to around 4 mm in small clutches and up to around 10 mm in very large clutches. This is a really significant step towards extending the life of clutches.

The sensor diaphragm spring is suspended externally in the cover and forms the bearing for the main diaphragm spring together with its inner fingers. The wedges that perform the readjustment are not mounted radially as in the previous principle diagram but circumferentially due to centrifugal forces. For this purpose a ramp ring with 12 ramps runs on opposite ramps in the cover. The ramp ring is circumferentially pre-tensioned by three small compression springs to ensure that it can fill the gaps between the diaphragm spring bearing and the cover as the sensor diaphragm spring drifts.