Title of Invention

"A CLUTCH FRICTION WHEEL FOR A DEY FRECTION CLUTCH"

Abstract

A clutch friction wheel for a dry friction clutch, more particularly for a motor vehicle, the friction wheel having two friction crowns, wherein the said friction crowns include means for generating an air pressure force under the effect or rotation of the clutch friction wheel, the said air pressure force generating means comprising grooves formed on the face of each of the friction crowns, which are arranged to make contact with, respectively, a reaction plate and a pressure plate of the clutch of which the friction wheel forms part characterized in that the said grooves comprise a circumferential groove (20) and a plurality of radial grooves (30) open at the inner periphery (13) of the friction crown and in communication with the circumferential groove.

Full Text

The present invention relates to clutch friction wheels for dry friction clutches, that is to say clutches which operate in dry friction, more particularly for motor vehicles. The invention also relates to friction crowns, or annular friction liners, made of friction material and arranged for equipping such a clutch friction wheel. A motor vehicle dry friction clutch generally comprises a clutch friction wheel having two friction crowns, each of which is secured to a support member, or clutch disc, which may be common to both crowns. The support member, or support member, is connected to a splined hub which is in engagement with an inpu: shaft' of the gearbox of the vehicle. Generally, a torsion damper is interposed between the support member or members of the crov/ns on the one hand, and the splined hub on the other. A progressive engagement device is generally placed between the two crowns, and is embodied in the support member or members, which for this purpose are disposed in suitable particular ways; alternatively the progressive engagement device may consist of a suitable additional device. In use, the clutch friction wheel is located between, firstly, a reaction plate which is coupled directly or indirectly to the crankshaft of the engine of the vehicle, and, on the other hand/ a pressure plate of a clutch mechanism. The clutch mechanism includes a cover plate connected to the reaction plate together with an elastic system, which in practice is a springy member in the form of a diaphragm. The diaphragm biases the pressure plate in the axial direction, the pressure plate being coupled in rotation to the cover plate while being able to be displaced axially with respect to the cover plate by a limited amount. In the engaged condition of the clutch, the friction crowns of the clutch friction wheel are gripped under the influence of the above mentioned elastic system between the reaction plate and the pressure plate, so that the torque produced by the engine is transmitted to the input shaft of the gearbox. Declutching means, for example the fingers of the diaphragm, are provided. When axial pressure is applied on the fingers, this eliminates the effect of the elastic system. Due to return means of the pressure plate acting between the pressure plate and the cover plate, the absence of the above mentioned effect of the elastic system causes the pressure plate to be displaced away from the reaction plate, so that the friction crowns of the clutch friction wheel are released from their gripping engagement between these plates. Thus the clutch friction wheel, being mounted for axial movement on the input shaft of the gearbox, is displaced between the reaction plate and the pressure plate, and the effect of this is to interrupt the transmission of the torque from the engine. In order to ensure total interruption of torque transmission, the declutching operation must be total, that is to say the friction crowns must be taken fully out of any contact with the reaction plate and the pressure plate. The Applicant has found that there do exist phenomena which are detrimental to the correct and complete disengagement of the friction crowns from these plates. In this connection, unequal disengagement of the friction crowns from one of the adjacent plates, that is to say the reaction plate or the pressure plate, frequently occurs, or even, sometimes, retention of a friction crown against one of these plates. This makes is difficult to change gear, and it also gives rise to premature wear in the gearbox components. An object of the present invention is to overcome the above mentioned drawbacks. Accordingly, there is provided a clutch friction wheel for a dry friction clutch, more particularly for a motor vehicle, the friction wheel having two friction crowns, wherein the said friction crowns include means for generating an air pressure force under the effect or rotation of the clutch friction wheel, the said air pressure force generating means comprising grooves formed on the face of each of the friction crowns, which are arranged to make contact with, respectively, a reaction plate and a pressure plate of the clutch of which the friction wheel forms part characterized in that the said grooves comprise a circumferential groove (20) and a plurality of radial grooves (30) open at the inner periphery (13) of the friction crown and in communication with the circumferential groove. According to the invention in a first aspect, there is provided a clutch friction wheel for a dry friction clutch, more particularly for a motor vehicle, the friction wheel having two friction crowns, wherein the said friction crowns include means for generating an air pressure force under the effect of rotation of the clutch friction wheel, the said air pressure force generating means comprising grooves formed on the face of each of the friction crowns, which are arranged to make contact with, respectively, a reaction plate and a pressure plate of the clutch of which the friction wheel forms part, and wherein the said grooves comprise a circumferential groove and a plurality of radial grooves open at the inner periphery of the friction crown and in communication with the circumferential groove. Thus, disengagement of the friction crowns, with tota1 release of the clutch friction wheel from its gripping engagemem between the pressure and reaction plates, is correctly ensured. Any one or more of the following preferred features cf the invention may be incorporated in a clutch friction wheel according to the invention to the extent that they are not technically exclusive from each other:- - the grooves of one friction crown are symmetrical with those of the other about a central plane of the clutch friction wheel, so as to create, when the latter is rotating, air pressure forces on either side of the friction wheel which are substantially equal and opposite to each other; - at least one of the radial grooves has a cross section which increases in width in an outward radial direction of the crown; - the said circumferential groove is isolated from the outer periphery of the friction crown; - the said circumferential groove is in communication with the outer periphery of the friction crown through at least one radial groove having a cross section which increases in width in the outward radial direction of the friction crown; - the said circumferential groove is in communication with the outer periphery of the friction crown through at least one element for creating a loss of energy; - the said element for creating a loss of energy comprises at least one groove of smaller cross section than the said circumferential and/or radial grooves; - the said element for creating a loss of energy comprises at least one groove having a throttling section; - each friction crown has only one said circumferential groove; - the circumferential groove is in a zone lying between one half of the radius of the friction crown and the outer periphery of the latter; - the circumferential groove is on a radius situated between about two thirds of the radius of the friction crown and its outer periphery; - the circumferential groove has a trapezoidal cross section; and/or - the said radial grooves have a trapezoidal cross section. According to the invention in a second aspect, there is provided a friction crown for a clutch friction wheel for operating in dry friction, including grooves formed on a face of the crown, which is adapted to make contact with a pressure or reaction plate of a clutch, wherein the said grooves comprise a circumferential groove and a plurality of radial grooves open at the inner periphery of the friction crown and in communication with the circumferential groove. Any or all of the following preferred features of the invention may be incorporated in a friction crown according to the invention to the extent that they are not technically exclusive:- - each said radial groove has a cross section the width of which increases in the outward radial direction of the crown; - the said circumferential groove is isolated from the outer periphery of the friction crown; - the said circumferential groove is in communication with the outer periphery of the friction crown through at least one radial groove having a cross section the width of which increases in the outward radial direction of the friction crown; - the said circumferential groove is in communication with the outer periphery of the friction crown through an element for creating a loss of energy; - the said element for creating a loss of energy comprises at least one groove of smaller cross section than the said circumferential and/or radial grooves; - the said element for creating a loss of energy comprises at least one groove having a throttling section; - the friction crown has only one said circumferential groove; - the said circumferential groove is in a zone lying between one half of the radius of the friction crown and the outer periphery of the latter; - the said circumferential groove is on a radius situated between about two thirds of the radius of the friction crown and its outer periphery; - the said circumferential groove has a trapezoidal cross section; and/or - the said radial grooves have a trapezoidal cross section. It has been found that, thanks to the invention, an air cushion under pressure is created during the declutching operation. The pressure of this air cushion is of the same value between each friction crown of the clutch friction wheel and the associated plate (reaction or pressure plate) of the clutch. The effect of this is to urge these components apart sharply, so as to give effective and symmetrical disengagement of the friction crowns, and consequently sharp and total declutching. Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of a preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the single Figure of the accompanying drawing, which is a partial front view of a friction crown in accordance with the invention. A clutch friction wheel, or friction disc, operating in dry friction includes, in the usual way, two friction liners in the form of friction crowns, each of which is secured directly or indirectly to a metallic support, not shown. This support may consist of a single support disc common to both crowns. Alternatively, it may consist of two support discs coupled together, with each disc carrying a respective one of the crowns. The support preferably constitutes, or is associated with, a progressive engagement device (not shown). A torsion damper is preferably disposed between the friction crown support or supports and a splined hub which is arranged to be fitted on the input shaft of the gearbox. Each friction crown 10 includes means 20, 30 which generate an air pressure force under the effect of rotation of the clutch friction wheel. These air pressure generating means comprise grooves 20 and 30 which are formed on the face 11 of each of the friction crowns 10. Each crown 10 is intended to make contact with another plate of the clutch, namely a reaction plate in respect of one of the friction crowns, and a pressure plate in respect of the other. The pressure and reaction plates are disposed symmetrically on either side of a centre plane of the clutch friction wheel, so as to set up air pressure forces on either side of the clutch friction wheel when the latter is rotated, these forces being substantially equal and opposite to each other. The provision of grooves in friction crowns per se has been proposed before now, the purpose of these grooves being to collect and evacuate dust resulting from wear in the friction material of the crowns. However, such grooves have no effect on release of the crowns coming unstuck from the reaction and pressure plates; they can even have a detrimental effect in this connection. As can be seen in the drawing, the grooves in a liner according to the invention comprise a circumferential groove 20 which is isolated from the outer periphery 12 of the crown 10, together with a plurality of radial grooves 30 which are open into the circumferential groove 20 at one end of the radial grooves, while the other end of each radial groove is open at the inner periphery 13 of the crown. In another version, not shown, the circumferential grooves are in communication with the outer periphery 12 of the crown, through an interposed element which produces a loss of energy, for example at least one groove which has, over at least part of its length, a section which is narrower than that of the circumferential grooves 20 and/or the radial grooves 30. The circumferential groove 20 is situated in a zone lying between one half of the radius of the friction crown and the outer periphery 12 of the latter, and, in the embodiment shown, the circumferential groove 20 is situated on a radius lying between about two thirds of the radius of the friction crown 10 and its outer periphery 12. The circumferential groove 20 and/or the radial grooves 30 (and preferably all of them) have a trapezoidal cross section. In this connection, the Applicant has found that this form of cross section shifts towards the outside the centre of gravity of the air cushion trapped by the grooves, so that the repulsion force tending to release each crown 10 from the associated reaction or pressure plate is greatly increased. This is a factor in obtaining clean and total declutching. Experimental work has shown that the circumferential groove 20 captures an air cushion under pressure when the clutch is in rotation, and that the radial grooves 30 feed the circumferential groove 20 with air by centrifugal effect. In a further version, not shown, all or part of the radial grooves have a cross section which becomes wider in the outward radial direction. In a further modified version, the circumferential groove is in communication with the outer periphery of the friction crown, through at least one radial groove having a cross section which becomes wider in the outward radial direction of the friction crown. In yet another modified version, the radial grooves 30 are replaced by oblique grooves, but in such a way that, as between one crown and another, when fitted on the support described above and forming part of the clutch friction wheel, the grooves have a symmetry about a central plane of the clutch friction wheel. Finally, in yet another version, a plurality of circumferential grooves are provided, more particularly when the clutch friction wheel has a large diameter, and these circumferential grooves are then in communication with each other through further radial grooves. WE CLAIM: 1. A clutch friction wheel for a dry friction clutch, more particularly for a motor vehicle, the friction wheel having two friction crowns, wherein the said friction crowns include means for generating an air pressure force under the effect or rotation of the clutch friction wheel, the said air pressure force generating means comprising grooves formed on the face of each of the friction crowns, which are arranged to make contact with, respectively, a reaction plate and a pressure plate of the clutch of which the friction wheel forms part characterized in that the said grooves comprise a circumferential groove (20) and a plurality of radial grooves (30) open at the inner periphery (13) of the friction crown and in communication with the circumferential groove. 2. A clutch friction wheel as claimed in claim 1, wherein the grooves of one friction crown are symmetrical with those of the other about a central plane of the clutch friction wheel, so as to create, when the latter is rotating, air pressure forces on either side of the friction wheel which are equal and opposite to each other. 3. A clutch friction wheel as claimed in claim 1 or claim 2, wherein at least one of the radial grooves has a cross section which increases in width in an outward radial direction of the crown. 4. A clutch friction wheel as claimed in claim 1 or 3, wherein the said circumferential groove is isolated from the outer periphery of the friction crown. 5. A clutch friction wheel as claimed in claim 1 or claim 3, wherein the said circumferential groove is in communication with the outer periphery of the friction crown through at least one radial groove having a cross section which increases in width in the outward radial direction of the friction crown. 6. A clutch friction wheel as claimed in claim 1 or claim 3, wherein the said circumferential groove is in communication with the outer periphery of the friction crown through at least one element for creating a loss of energy. 7. A clutch friction wheel as claimed in claim 6, wherein the said element for creating a loss of energy comprises at least one groove of smaller cross section than the said circumferential and/or radial grooves. 8. A clutch friction wheel as claimed in claim 6, wherein the said element for creating a loss of energy comprises at least one groove having a throttling section. 9. A clutch friction wheel as claimed in any one of the preceding claims, wherein each friction crown has only one said circumferential groove. 10. A clutch friction wheel as claimed in claim 9, wherein the circumferential groove is in a zone lying between one half of the radius of the friction crown and the outer periphery of the latter. 11. A clutch friction wheel as claimed in claim 10, wherein the circumferential groove is on a radius situated between about two thirds of the radius of the friction crown and its outer periphery. 12. A clutch friction wheel as claimed in any one of the preceding claims, wherein the circumferential groove has a trapezoidal cross section. 13. A clutch friction wheel as claimed in any one of the preceding claims, wherein the said radial grooves have a trapezoidal cross section, 14. A friction crown for a clutch friction wheel for operating in dry friction, including grooves formed on a face of the crown, which is adapted to make contact with a pressure or reaction plate of a clutch, wherein the said grooves comprise a circumferential groove and a plurality of radial grooves open at the linner periphery of the friction crown and in communication with the circumferential groove. 15. A friction crown as claimed in claim 14, wherein each said radial groove has a cross section which increases in width in the outward radial direction of the crown. 16. A friction crown as claimed in claim 14 or claim 15, wherein the said circumferential groove is isolated from the outer periphery of the friction crown. 17. A friction crown as claimed in claim 14 or claim 15, wherein the said circumferential groove is in communication with the outer periphery of the friction crown through at least one radial groove having a cross section which increases in width in the outward radial direction of the friction crown. 18. A friction crown as claimed in claim 14 or claim 15, wherein the said circumferential groove is in communication with the outer periphery of the friction crown through an element for creating a loss of energy. 19. A friction crown as claimed in claim 18, wherein the said element for creating a loss of energy comprises at least one groove of smaller cross section than the said circumferential and/or radial grooves. 20. A friction crown as claimed in claim 18, wherein the said element for creating a loss of energy comprises at least one groove having a throttling section. 21. A friction crown as claimed in any one claims 14 to 20, having only one said circumferential groove. 22. A friction crown as claimed in claim 21, wherein the said circumferential groove is in a zone lying between one half of the radius of the friction crown and the outer periphery of the latter. 23. A friction crown as claimed in claim 22, wherein the said circumferential groove is on a radius situated between about two thirds of the radius of the friction crown and its outer periphery. 24. A friction crown as claimed in any one of claims 14 to 23, wherein the said circumferential groove has a trapezoidal cross section. 25. A friction crown as claimed in any one of claims 14 to 24, wherein the said radial grooves have a trapezoidal cross section. 26. A clutch friction wheel for a dry friction clutch substantially as herein described with reference to the accompanying drawings.

Documents:

1666-del-1998-abstract.pdf

1666-del-1998-claims.pdf

1666-del-1998-correspondence-others.pdf

1666-del-1998-correspondence-po.pdf

1666-del-1998-description (complete).pdf

1666-del-1998-drawings.pdf

1666-del-1998-form-1.pdf

1666-del-1998-form-13.pdf

1666-del-1998-form-19.pdf

1666-del-1998-form-2.pdf

1666-del-1998-form-3.pdf

1666-del-1998-form-4.pdf

1666-del-1998-form-6.pdf

1666-del-1998-gpa.pdf

1666-del-1998-petition-137.pdf

1666-del-1998-petition-138.pdf