This invention concerns a clutch of the type (hereinafter called "the type referred to") comprising a driving plate which is rotatable about an .axis, a cover connected with the driving plate so as to rotate with said driving plate, a pressure plate mounted to rotate with the cover, a driven plate for rotation about said axis being disposed between the driving and pressure plates, and clutch spring means acting between the pressure plate and the cover so that the driven plate can be clamped between the driving and pressure plates under the load of the spring means.

The clutch is engaged by the clamping of the driven plate and is disengaged by the driven plate being released by an axial effort applied to the spring means by, for example, a release bearing.

The driving plate is rotated by a driving input thereto and may be driven by a motor vehicle engine; for example the driving plate may be mounted on a crank-shaft and may be mounted on or be part of a fly-wheel. In well known clutches of the type referred to the driven plate is cushioned in that it comprises a carrier plate having friction facings mounted on cushioning between the facings. But to simplify and cheapen production of driven plates and to reduce inertia thereof, driven plates with reduced or no cushioning

between the friction facings have been proposed in diaphragm spring clutches of the type referred to in which the clutch spring means in a diaphragm spring having a plurality of radially inwardly directed fingers, and the diaphragm spring acts between a first annular fulcrum arrangement on the pressure plate and a second annular fulcrum arrangement on the cover. To compensate for the aforesaid lack of cushioning it has been proposed to incorporate means which provides a degree of axial flexibility or cushioning into one of the annular fulcra in the diaphragm spring clutch. One way of providing cushioning means in the clutch which is simple to manufacture and install and yet provides a subjectively acceptable clutch engagement when mounted in a motor vehicle is disclosed in G.B. 1583403. That patent describes a diaphragm spring clutch further comprising cushioning means in one of the annular fulcra arrangements, the cushioning means being formed by a single wavy ring having undulations which extend parallel to the axis of the diaphragm spring, and the undulations being constituted by a first series and by a second series of said undulations wherein the undulations of the first series have a lower stiffness but greater axial amplitude and wavelength than the undulations of the second series. During re-engagement of the driven plate (after a disengagement) the initial cushioning is by the first series and then by both series.

One object of the invention is to provide a clutch of the type referred to capable of being constructed, as will be understood from the ensuing description with reference to the drawings, in a simple manner to provide cushioning and at the same time the clutch may be used in a motor vehicle in which clutch engagement can be subjectively acceptable.

According to first aspect of the invention a clutch of the type referred to further comprises said cover being capable of axial movement relatively to the driving plate during engagement and disengagement of the clutch, and resilient means acting to resiliently oppose movement of the cover away from said driving plate.

The resilient means may act on a side of the cover remote from the driving plate.

The resilient means may comprise a plurality of spring arrangements disposed about the axis.

The cover may be axially oveable, relatively to the driving plate, on a plurality of guides disposed about the axis. Each guide may be mounted on the driving plate. Each guide can be provided with an abutment for a said spring arrangement which can surround the guide and be disposed between the abutment and the cover.

According to a second aspect of the invention there is provided a clutch cover assembly intended to be used in the formation of a clutch according to the first aspect, the cover assembly comprising the cover intended

to be connected with a said driving plate when the clutch is formed, the pressure plate mounted to rotate with the cover, said clutch spring means acting between the pressure plate and the cover, said cover having holes each receiving a said guide which is to be secured to the driving plate, each guide being surrounded by the . corresponding spring arrangement disposed between the cover and the abutment on the guide, and each guide being held on the cover by retaining means. In a clutch formed according to the first aspect or a clutch cover assembly formed according to the second aspect, the clutch spring means can be a diaphragm spring having a plurality of radially inwardly directed fingers, the diaphragm spring acting between a first annular fulcrum arrangement on the pressure plate and a second annular fulcrum arrangement on the cover.

The invention will now be further described, by way of example, with reference to the accompanying drawings in which:- Fig.l is a half plan view of a diaphragm spring, pull-type clutch formed according to the invention, the driving plate and connection of the cover therewith being omitted;

Fig.2 is a diametral section (with parts absent) on line II - II in Fig.l of the clutch in a fully engaged attitude; the section assuming that the absent half in Fig.l were present in that Fig., and the driving plate

and connection of the cover therewith being shown;

Fig.3 is a fragment of a section similar to Fig.2 showing the clutch disengaged;

Figs.4 and 5 are on enlarged scale diagrammatic sections of details of Figs.2 and 3 respectively.

Figs.6 to 12 are diagrammatic sections comparable with Fig.5, but on smaller scale, of respective modi ications of the clutch in Figs.l to 5;

Fig.13 is a fragmentary section comparable with Fig.3 but of another embodiment of a diaphragm spring clutch (namely a push-to-release clutch) formed according to the invention, and

Fig.14 is a diagrammatic illustration partly in section of a fragment of the clutch cover assembly for the clutch in Figs 1 and 2, showing retaining means when the clutch cover assembly is initially provided in accordance with the second aspect of the invention, and

Fig.15 is a diagrammatic illustration partly in section of a fragment of a modification of the clutch in Figs 1 and 2 showing alternative retaining means when the clutch cover assembly is initially provided in accordance with the second aspect of the invention.

In the drawings like or comparable parts are identified by the same reference numerals. In Figs.l to 5 there is shown a pull-type clutch

2 which may be used in a motor vehicle. The clutch comprises a driving plate 4 which, as shown, may be

integral with a fly-wheel 6 which may be rotatably driven by an engine of the vehicle. The clutch also comprises a driven plate 8 and a clutch cover assembly 10. Cover assembly 10 comprises a cover pressing 12, an annular pressure plate 14, and a diaphragm spring- 16. The clutch is rotated about axis X. On one side the diaphragm spring 16 acts on an annular fulcrum arrangement 18 on the pressure plate 14 and on the other side the spring acts on an annular fulcrum ring 20 on the cover 12. The diaphragm spring 16 has a plurality of inwardly extending radial fingers 22 spaced by radial slots 24, the inner ends of these fingers being engaged by a pull-type clutch release bearing 26 of any suitable type known per se. Openings 28 in the cover 12 receive lugs 30 on the pressure plate 14, each lug being riveted at 32 to one end of a respective tangential, spring, drive strap 34 riveted at 36 at its other end to the cover.

The driven plate 8 may be of any suitable type known per se. In the drawing the plate 8 comprises a central hub 38 internally axially splined at 40 to engage with axial splines on an output shaft 42, and further comprises torsion damping springs 44 and a carrier plate 46 to which annular facings 43 of friction material are secured. The facings 48 may be riveted to the carrier plate as shown or may be otherwise secured thereto, for example by adhesive bonding. If desired no cushioning

need be provided between the friction facings 48, and the friction facings may be provided by a single annulus the two opposite sides of which respectively engage the driving plate 4 and the pressure plate 14. Cover 12 has a circumferential flange 50 formed with substantially equi-angularly spaced holes 52 each receiving a respective pin 54 in the form of a bolt having a head 56 and a shank comprising a relatively wide, enlarged diameter portion 58 between the head and a shoulder 60 beyond which projects a threaded portion 62 screwed up to the shoulder into a corresponding bore 61 in the fly-wheel 6. The cover 12 is axially slidable on the wider bolt portions 58 each of which is surrounded by a respective Belleville washer 64. These Bellevilles may be fully flattened in the clutch engaged position as shown in Figs.2 and 4 and are coned in the clutch release positions as shown in Figs.3 and 5.

When the clutch is fully engaged (Figs.2 and 4) the cover 12 in flattening the Bellevilles 64 stands off the driving plate 4 by a small distance y (Fig.4) under the urging of the diaphragm spring 16 reacting through the cover 12. When the release bearing 26 is pulled in direction A to release the clutch, the clamping load exerted by the diaphragm spring is reduced by the pull of bearing 26 so the reaction in the cover to the diaphragm spring 16 reduces allowing the Bellevilles 64 to expand axially. When the pull on release bearing 26 is

diminished to allow clutch re-engagement the Bellevilles 64 become progressively flattened under an increasing axial load which is function of the difference between the clamping load exerted by the diaphragm spring 16 and the release load exerted by the release bearing. The effect of compressing the Bellevilles 64 is to provide a cushioning effect during clutch re-engagmenet to give a subjectively acceptable feel.

Because the bolts 54 cannot be inserted in the fly-wheel beyond the shoulders 60, the amount of pre-stressing of the Bellevilles 64 can be controlled by choosing an appropriate axial length for the wide diameter bolt portion 58.

To ensure the cover assembly 10 is provided (for fitting to a fly-wheel) with the desired Bellevilles 64 appropriately orientated, the bolts 54 with the Bellevilles thereon may be fitted in the holes 52 and then retained on the cover by retaining means so that the retained bolts are ready for screwing to the fly-wheel. These retaining means may be sleeves 80 (Fig.14) of, for example, plastics material snugly fitting on the threaded shanks 62 to prevent the bolts 54 from being pulled from the holes 52. The sleeves 80 are removed at the time of mounting the cover assembly 10 (Fig.2) on the fly-wheel. Alternatively the retaining means may be intended to remain permanently on the bolts 54 and can be provided by spring clips 82 (Fig.15), for example cirσlips, of

greater diameter than the holes 52 and each disposed in an annular groove 84 adjacent to the shoulder 60 and formed in bolt shank portion 62. In this case each threaded bore 61 in the fly-wheel 6 to receive a said bolt 54 can have a counter-bored entrance 86 to accept the clip 82.

A plurality or stack of Bellevilles may be mounted on each bolt 54. In Fig.6 Bellevilles 64A and 64B are nested, in Fig.7 Bellevilles 64C and 64D are disposed apex to apex whilst in Fig.8 Bellevilles 64E and 64F are disposed base to base.

In Fig.9 cushioning is provided by a spring wavy washer 64G having radial flutings.

A helical compression spring 64H provides cushioning in Fig.10, whereas a resilient split ring 64J provides cushioning in Fig.11. In Fig.12 cushioning is provided by an annular, resilient pad 64K of elastomeric material.

In the push-to-release clutch 2A in Fig.13 bolts 54 securing the cover 12 to the fly-wheel 6 each have a Belleville washer 64 to provide cushioning. But any of the modifications in Figs.6 to 12 could be used. Clutch release pressure is applied in direction B by a release bearing (not shown) to the inner ends of the fingers 22 of the diaphragm spring 16. The diaphragm spring is constrained between two annular fulcrum rings 66 and 68

retained by tabs 70 axially turned from the cover to pass through the slots 24 between the fingers 22.

The clutch cover assembly 2A can be provided with retaining means such as described with reference to Fig. 14 or Fig. 15. - .