192 clutches and power-stop control – Clutches – Axially engaging
Patent
1998-12-04
2000-11-28
Marmor, Charles A
192 clutches and power-stop control
Clutches
Axially engaging
192 7027, 192111A, 192 8923, F16D 1354
Patent
active
061522740
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns friction clutches with low disengagement force, notably for motor vehicles, and relates more particularly to the engagement mechanism in such a clutch.
2. Description of Related Art
As is known, in a conventional clutch interposed between a driving shaft and a driven shaft, a diaphragm bears on the base of a cover, fixed to a flywheel for driving in rotation, in order to move a thrust plate in the direction of the flywheel, forming a reaction plate, in order to clamp the friction linings of a clutch friction device between the thrust and reaction plates.
The driving flywheel is fixed with respect to rotation to a first shaft, such as a driving shaft, whilst the clutch friction device has at its internal periphery a hub for fixing it with respect to rotation to a second shaft, such as a driven shaft.
The clutch is therefore normally engaged, with torque transmission between the driving and driven shafts.
In order to disengage, or declutch, the clutch, it is necessary, using a clutch release bearing, to act axially by pushing, in the case of a clutch of the pushed type, on the internal end of the diaphragm fingers in order to pivot the diaphragm and cancel out the force exerted by this diaphragm on the axially movable thrust plate in order to release the friction linings. The torque is then no longer transmitted from the driving shaft to the driven shaft, since the friction linings are no longer clamped between the thrust and reaction plates fixed with respect to rotation to the hollow-shaped cover.
Normally, the cover, thrust plate and diaphragm form a unitary assembly referred to as the clutch mechanism, which is attached by its cover to the flywheel, elastic tongues rotatably connecting, with axial mobility, the thrust plate to the cover.
The diaphragm, as is known, has a central hole and an external peripheral part in the form of a Belleville washer extended inwards by a central part divided into radial fingers by slots. This diaphragm, through its Belleville washer part, bears on the cover and on the thrust plate. Thus the disengagement device of the clutch, which makes it possible to counteract at will the action of the elastic engagement means, consists of the fingers of the diaphragm on the internal end of which the clutch release bearing acts, whilst the Belleville washer of the diaphragm constitutes elastic axially acting engagement means for clamping the friction linings between the thrust and reaction plates and therefore to axially force the thrust plate in the opposite direction to the base of the cover.
In the free state, this diaphragm has a frustoconical shape. Once mounted in the clutch, its Belleville washer is mounted under prestress and is more or less flattened. During the operation of declutching, or disengaging, the clutch, the conicity of its Belleville washer is modified.
As is known, the characteristic curve of this diaphragm, which represents the force exerted according to the disengagement travel, for example returned to the level of the inner end of the diaphragm fingers, is determined by the dimensions of its Belleville washer, notably by the ratio between the height of the truncated cone of the Belleville washer in the free state and the thickness of the diaphragm.
This characteristic curve passes through a maximum.
Thus the force to be exerted on the internal end of the diaphragm fingers, during the disengagement operation, increases up to a maximum, decreases gradually to a minimum, and then increases once again.
The difference between the maximum and the minimum can be great. For more information on this characteristic curve, reference should be made for example to the document FR-A-1 392 569 or to the document WO-97/19 275.
In the document FR-A-1 392 569, provision is made for an elastic progressive-action device for avoiding passing through the aforementioned maximum during the disengagement travel. This device is mounted in series with the Belleville washer of the diaphragm and has an e
REFERENCES:
patent: 4949829 (1990-08-01), Tojima et al.
patent: 5730267 (1998-03-01), Lopez
patent: 5816379 (1998-10-01), De Briel et al.
patent: 5855267 (1999-01-01), Giroire et al.
Blard Michel
Minereau Hugues
Marmor Charles A
Valeo
Waddell Tisha D.
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