192 clutches and power-stop control – Clutches – Axially engaging
Patent
1996-02-28
1998-03-24
Pitts, Andrea L.
192 clutches and power-stop control
Clutches
Axially engaging
192 8923, 192 8925, F16D 1344
Patent
active
057302677
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates, in general terms, to clutch mechanisms of the kind comprising, in the form of generally annular components, a cover plate, a pressure plate, and at least one diaphragm interposed operatively between these latter.
This diaphragm has, firstly, a peripheral portion defining a Belleville ring, which engages on the cover plate in the vicinity of one of its peripheries and bears on the pressure plate in the vicinity of its other periphery, and secondly, a central portion divided into radial fingers by slots.
In use, when the clutch mechanism is attached on a reaction plate through its cover plate, with a friction disc between the pressure plate and the reaction plate, the diaphragm biasses the pressure plate towards the reaction plate, so that, the friction disc being duly gripped between these latter by its friction liners, the clutch thus constituted is engaged.
In order to disengage this clutch, it is necessary to exert a certain axial force on the ends of the radial fingers of the diaphragm.
The application of this force is obtained by means of a clutch release bearing, which is mounted for axial movement under the control of the clutch pedal or of an actuator.
However, the characteristic curve for the operating mode of the diaphragm, that is to say the curve which expresses the axial force that must be exerted on the ends of its radial fingers in order to give a predetermined axial travel at this level, starts as a rising curve and then usually passes through a maximum before subsequently becoming a falling, and possibly once again a rising, curve, thus defining a "hump" which depends in practice on the geometrical characteristics of the diaphragm, and in particular on the ratio between, firstly, the height of the frustum of a cone which is defined by its peripheral portion, and secondly its thickness.
As a result, the load at the clutch release bearing decreases beyond a certain travel, before possibly once again increasing, and the same effect occurs at the clutch pedal which is detrimentally felt by the user, and which can indeed be uncomfortable.
2. Description of the Prior Art
It has previously been proposed, in addition, to make use of two diaphragms instead of one for various reasons.
In the document FR-A-1 317 772, for example, two identical diaphragms are disposed in tandem, so as to increase the value of the torque that can be transmitted.
In the document FR-A-2 580 752, the diaphragm is only doubled up by another over a portion of its extent which essentially corresponds to its radial fingers, this being for the purpose of stiffening the latter.
However, in both cases the "hump" problem remains the same.
In the document FR-A-2 189 658, which is not concerned with a clutch mechanism, it has further been proposed, in order to render the said hump uniform, to arrange in tandem two Belleville rings having geometrical characteristics which are equal in absolute values, but which are of opposite senses.
Apart from the high friction that develops in service between these two Belleville rings, the characteristic curve of the assembly still has a hump.
SUMMARY OF THE INVENTION
An object of the invention is to provide a clutch mechanism in which this hump is minimised to advantage, or even eliminated, without at the same time any significant friction being developed.
This clutch mechanism, which is of the kind concerned, and which has two diaphragms, is in general terms characterised in that, in combination, the peripheral portions of the two diaphragms are essentially spaced apart axially from each other, and in that they have different geometrical characteristics in absolute values, and in that along one of their peripheries the peripheral portions of the diaphragms are spaced apart from each other by spacing means.
In practice, these peripheral portions are so selected that the force/travel characteristic curve of the assembly has a substantially flat local portion, instead of having any hump whatsoever.
Thus, after the ri
REFERENCES:
patent: 4737492 (1988-04-01), Ball et al.
patent: 4828092 (1989-05-01), Kohler
patent: 4940126 (1990-07-01), Flotow et al.
patent: 5181594 (1993-01-01), Nash
Pitts Andrea L.
Valeo
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