192 clutches and power-stop control – Clutches – Axially engaging
Reexamination Certificate
1999-08-18
2001-03-20
Marmor, Charles A (Department: 3681)
192 clutches and power-stop control
Clutches
Axially engaging
C192S111400, C192S089230, C192S089240
Reexamination Certificate
active
06202815
ABSTRACT:
The present invention concerns friction clutches with low declutching force, notably for motor vehicles.
DESCRIPTION OF THE RELATED ART
As is known, in a conventional clutch interposed between input shaft and an output shaft, a diaphragm bears on the bottom of a cover, fixed to a flywheel driving in rotation, in order to move a thrust plate in the direction of the said flywheel, forming a reaction plate, in order to grip the friction linings of a clutch friction member between the said thrust and reaction plates.
The driving flywheel is fixed to a first shaft, such as an input shaft, whilst the clutch friction member has at its inner periphery a hub for fixing it, with respect to rotation, to a second shaft, such as an output shaft.
The clutch is therefore normally engaged, or clutched, with transmission of torque between the input and output shafts.
In order to disengage, or declutch, the clutch, it is necessary, by means of a clutch release bearing, to act axially by pushing, in the case of a clutch of the pushed type, on the inner end of the fingers of the diaphragm in order to cause the said diaphragm to pivot and to 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 input shaft to the output shaft since the friction linings are no longer gripped between the thrust and reaction plates fixed to the cover with respect to rotation.
Normally, the cover, the thrust plate and the diaphragm form a unitary assembly referred to as a clutch mechanism which is attached by its cover to the flywheel, elastic tongues connecting the thrust plate to the cover with respect to rotation, with axial mobility.
The diaphragm, as is known, has a central hole and has an outer peripheral part in the form of a Belleville washer extended inwards by a central part divided into radial fingers by slots. This diagram, through its Bellville washer part, bears on the cover and on the thrust plate. Thus the declutching device of the clutch, which makes it possible to counteract the action of the clutching elastic means at will, is formed by the fingers of the diaphragm on the inner end of which the clutch release bearing acts, whilst the Bellville washer of the diaphragm constitutes axially acting clutching elastic means for gripping the friction linings between the thrust and reaction plates and therefore to act axially on the thrust plate in the opposite direction to the bottom of the cover.
In the free state, this diaphragm has a frustoconical form. Once mounted in the clutch, its Bellville washer is mounted under prestressing and is more or less flattened. During the operation of declutching, or disengaging, the clutch, the clonicity of its Bellville washer is modified.
As is known, the characteristic curve of this diaphragm, which represents the force exerted as a function of the movement, for example referred to the level of the inner end of the diaphragm fingers, is determined by the dimensions of its Bellville washer, notably by the ratio between the height of the truncated cone of the Bellville 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 inner end of the diaphragm fingers increases up to a maximum, gradually decreases to a minimum, and then increases once again. The difference between the maximum and minimum can be great. For more information on this characteristic curve, reference should be made for example to the documents FR-A-1 392 569 and WO 97/19 275.
In the document FR-A-1 392 569, an elastic progressive action device was provided to avoid passing through the aforementioned maximum during the declutching travel. This device is mounted in series with the Bellville washer of the diaphragm and has an elastic force appreciably less than that of the Bellville washer. This device has a limited travel between a prestressed position where its force is at a maximum and a stressed position where its force is at a minimum.
With this arrangement, a declutching force is obtained which is increasing overall at the clutch release bearing.
During the declutching travel it is not possible to obtain as great an assistance as desired, the progressive action device reducing the load exerted by the diaphragm on the thrust plate during declutching.
The load curves of the progressive action device, when it is mounted within the friction member, and of the diaphragm, have shapes which do not make it possible to combine them in order to obtain high assistance for declutching, in particular if it is wished to respect declutching travels and forces compatible with the current declutching controls. Moreover, the shape of the curve of the progressive action device changes, notably because of phenomena of encrustation of the friction linings, very rapidly with the life of the clutch, and the higher the assistance level required, the more this cancels out the assistance for declutching. In order to prevent ageing of the curve of the assistance device, it is preferable to place the latter at a point where its stiffness curve will remain stable over time and, in particular, at a point placed outside the progressive action zone of the friction member where the lining contact and the phenomenon of encrustation change and cause the progressive action curve to change.
It can then be considered using an assistance spring.
Thus, in the certificate of addition 86 983 to French patent 1 392 569, it has already been proposed to interpose, between the elastic washer of the diaphragm and the thrust plate, an auxiliary elastic washer, the said two elastic washers being placed in series; the auxiliary elastic washer allows a certain amount of progressiveness in the engagement of the clutch and procures a certain degree of assistance force during its disengagement.
In the document U.S. Pat. No. 5,186,298, a friction clutch including a device for taking up wear and a progressive action device mounted within the friction member has already been proposed; in the document FR-A-2 684 151, a clutch of the same type has already been proposed in which the load curves of the progressive action device and of the diaphragm are combined in order to obtain high assistance on declutching; unfortunately, for the reasons indicated above, such an arrangement is not suitable.
SUMMARY OF THE INVENTION
The object of the present invention is to create, simply and economically, a friction clutch equipped with a device for taking up wear and a progressive action device mounted within the friction member, with a low declutching force, having recourse to springs acting in series without appreciably decreasing, throughout the life of the clutch, the force for gripping the friction linings in the state with the clutch engaged.
Thus, according to the invention, a friction clutch, notably for motor vehicles, has a clutch friction member and a clutching mechanism having a cover with a transversely oriented bottom and fixing means for fixing the clutching mechanism to a flywheel driving in rotation, a thrust plate having at the front a friction face for cooperating with the clutch friction member, elastic tongues for connecting the thrust plate with the cover with respect to rotation, with axial mobility, and, interposed between the back face of the thrust plate and the bottom of the cover, on the one hand axially acting elastic clutching means axially forcing the thrust plate in the opposite direction to the bottom of the cover and on the other hand a declutching device for counteracting the action of the said elastic clutching means as required and moving the thrust plate in the direction of the bottom of the cover over a so-called plate lifting distance, the clutching mechanism being equipped with a device for taking up wear on at least one of the linings of the clutch friction member and elastic assistance means for assisting the declutching force, elastic progressive action means being mounted within the clutch friction member and actin
Bacher Michel
Blard Michel
Dalbiez Andre
Graton Michael
Minereau Hugues
Liniak Berenato Longacre & White
Marmor Charles A
Rodriguez Saul
Valeo
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