GB1592874A - Clutch assemblies - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO CLUTCH ASSEMBLIES (71) We, GKN TRANSMISSIONS LIMITED, a British Company of Chester Road, Erdington, Birmingham, West Mid.

lands, do hereby declare the invention for which we pray that a patent be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a clutch assembly comprising a recessed cover member, a pressure plate flexible means connecting the cover member and the pressure plate together for torque transmission whilst permitting relative axial movement therebetween (such axis being the axis of rotation of the clutch assembly when in use) and spring means operative between the cover member and pressure plate to bias the pressure plate towards a position corresponding, when the assembly is in use, to the engaged position. Such a clutch assembly will hereinafter be referred to as a clutch assembly of the kind specified.

One form od clutch assembly of the kind specified commonly used has a cover member which is provided with a peripheral flange adapted to be bolted to the fly wheel of an internal combustion engine with which the clutch assembly is to be used. The pressure plate is accommodated within the recess of the cover, the spring means biasing the pressure plate outwardly thereof to engage a driven plate received between it and the flywheel. When the cover member of the assembly is secured to the flywheel, the range of permitted free movement of the pressure plate within the cover is limited because of its engagement with the driven plate, but this constraint is not present when the assembly of the cover and pressure plate is not connected to the flywheel. Whilst movement of the pressure plate into the cover member is restrained by the spring means, movement of the pressure plate outwardly of the cover member is not constrained other than by the flexible means connecting it to the cover member.

This lack of constraint on movement of the pressure plate and the cover member can lead to problems during handling of the clutch assembly. In particular, if the assembly is placed or dropped onto a surface, with the flange of the cover member downwardly, the flange will normally contact the surface first.

The pressure plate will then have to move downwardly within the cover member before it contacts the surface itself, which can give rise to overstressing of the flexible means connecting it to the cover member. The pressure plate typically is a relatively heavy component, which can aggravate the problem since it will then possess appreciable inertia if, for example, the clutch assembly should be dropped or roughly handled. It will be appreciated that the flexible means will, when the clutch assembly is not in use, already be in a relatively highly stressed condition because of the force exerted by the spring means biasing the pressure plate outwardly of the cover.

With the object of overcoming or alleviating this problem, the present invention provides a clutch assembly of the kind specified wherein there is provided abutment means projecting axially from the pressure plate in a direction away from the cover such that when the clutch is placed on a plain surface with the recess directed towards the surface, the abutment means engage the surface and thereby prevent movement of the pressure plate out from the recess to an extent which would over stress the flexible means.

Thus, when a clutch assembly embodying the invention is placed on a surface the abutment means, arranged to contact the surface either simultaneously with the cover member's contacting such surface or after slight movement of the pressure plate, prevents excess travel of the pressure plate.

Conveniently, the abutment means is constituted by extended portions of the fastening means securing the flexible torque transmitting means to the pressure plate. When the flexible means comprises a plurality of straps, and the fastening means therefor com prises rivets, such rivets may be provided with enlarged heads to constitute the abutment means.

The invention will now be described by way of example with reference to the accompanying drawings of which FIGURE 1 is a section through part of one embodiment of clutch assembly according to the invention; FIGURE la is a plan of part of the assembly of Figure 1, FIGURE 2 is a section through a further embodiment of clutch assembly according to the invention.

Referring firstly to Figure 1, there is illustrated a clutch assembly comprising a cover member 10 of recessed annular form, provided with a peripheral flange 11 formed with a plurality of apertures 12 for receiving bolts to secure the cover member to a flywheel, not shown, of an internal combustion engine. Accommodated within the cover member for axial movement relative thereto is an annular pressure plate 13, there being provided a diaphragm spring 14 operative between the cover member and pressure plate for biasing the latter towards the flywheel, i.e. outwardly of the cover member. The diaphragm spring 14 is secured to thc cover member by rivets 1S and a wire ring 16, presses against an annular ridge 17 on the cover member and an annular ridge 18 on the pressure plate, and is provided with radially inwardly extending fingers 19 for engagement by a release mechanism, not shown.

The pressure plate 13 is secured to the cover member for torque transmission while permitting relative axial movement by a plurality of flexible metal straps 20, only one of which is depicted in the drawings at its point of attachment to the pressure plate.

Such straps extend generally tangentially of the clutch assembly as seen in Figure la, each strap being secured to the cover member at its one end and to the pressure plate at its opposite end. The illustrated strap 20 i secured to the pressure plate by a rivet having a shank 21, and heads 22, 23 and to the cover member by a rivet 21a.

The clutch assembly illustrated is depicted in its free condition, i.e. with the spring 14 relaxed. When the assembly is in use, the spring will be nearly planar, but it will be noted that in the illustrated condition there is an axial distance 24 between the plane of the surface 25 of the pressure plate which engages the driven plate when the assembly is in use, and the plane of the surface of the flange 11 on the cover member. In the absence of any means to prevent it, placing the clutch assembly downwardly on a surface would mean that the pressure plate would have to travel through a distance equal to the clearance 24 before it contacted the surface, which could lead to overstressing of the straps 20 securing the pressure plate to the cover.

In order to prevent this occurring, the heads 23 of the rivets securing the straps to the pressure plate are enlarged so that they terminate in or close to the plane of the flange 11. Thus, the rivet heads 23 contact a surface on which the assembly is placed at the same time as or soon after the flange 11, thereby preventing such potentially damaging excess movement ob the pressure plate.

The clutch assembly shown in Figure 2 corresponds to that of Figure 1 with the exception that the straps 20 are secured, by rivets 21, at the opposite side of the pressure plate 13. In this case, the lowermost heads 26 of rivets 21 are enlarged to constitute abutment means preventing overtravel of the pressure plate as above described.

Rivets used for securing straps to the pressure plate are supplied with one manufactured head, the other head on the rivet being formed during the riveting process. It is usual for the manufactured heads of the rivets to be disposed on the side of the pressure plate on which the straps are disposed, and thus in the embodiment of Figure 2 the rivets will be supplied with manufactured heads of appropriate thickness. In the embodiment of Figure 1, the heads of the rivets formed during the riveting process would be formed to a suitable thickness by varying the initial length of the rivets used, or by controlling the conditions of the actual riveting process.

WHAT WE CLAIM IS: 1. A clutch assembly of the kind specified wherein there is provided abutment means projecting axially from the presrure plate in a direction away from the cover such that when the clutch is placed on a plain surface with the recess directed towards the surface, the abutment means engage the surface and thereby prevent movement of the pressure plate out from the recess to an extent which would over stress the flexible means.

2. An assembly according to claim 1 wherein the abutment means is constituted by extended portions of fastening means which also secures the flexible torque transmitting means to the pressure plate.

3. An assembly according to claim 2 wherein said flexible means comprises a plurality of generally tangentially extending straps, the fastening means therefor comprises rivets, and such rivets are provided with enlarged heads constituting the abutment means.

4. A clutch assembly substantially as hereinbefore described with reference to and as shown in Figure 1 or Figure 2 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. prises rivets, such rivets may be provided with enlarged heads to constitute the abutment means. The invention will now be described by way of example with reference to the accompanying drawings of which FIGURE 1 is a section through part of one embodiment of clutch assembly according to the invention; FIGURE la is a plan of part of the assembly of Figure 1, FIGURE 2 is a section through a further embodiment of clutch assembly according to the invention. Referring firstly to Figure 1, there is illustrated a clutch assembly comprising a cover member 10 of recessed annular form, provided with a peripheral flange 11 formed with a plurality of apertures 12 for receiving bolts to secure the cover member to a flywheel, not shown, of an internal combustion engine. Accommodated within the cover member for axial movement relative thereto is an annular pressure plate 13, there being provided a diaphragm spring 14 operative between the cover member and pressure plate for biasing the latter towards the flywheel, i.e. outwardly of the cover member. The diaphragm spring 14 is secured to thc cover member by rivets 1S and a wire ring 16, presses against an annular ridge 17 on the cover member and an annular ridge 18 on the pressure plate, and is provided with radially inwardly extending fingers 19 for engagement by a release mechanism, not shown. The pressure plate 13 is secured to the cover member for torque transmission while permitting relative axial movement by a plurality of flexible metal straps 20, only one of which is depicted in the drawings at its point of attachment to the pressure plate. Such straps extend generally tangentially of the clutch assembly as seen in Figure la, each strap being secured to the cover member at its one end and to the pressure plate at its opposite end. The illustrated strap 20 i secured to the pressure plate by a rivet having a shank 21, and heads 22, 23 and to the cover member by a rivet 21a. The clutch assembly illustrated is depicted in its free condition, i.e. with the spring 14 relaxed. When the assembly is in use, the spring will be nearly planar, but it will be noted that in the illustrated condition there is an axial distance 24 between the plane of the surface 25 of the pressure plate which engages the driven plate when the assembly is in use, and the plane of the surface of the flange 11 on the cover member. In the absence of any means to prevent it, placing the clutch assembly downwardly on a surface would mean that the pressure plate would have to travel through a distance equal to the clearance 24 before it contacted the surface, which could lead to overstressing of the straps 20 securing the pressure plate to the cover. In order to prevent this occurring, the heads 23 of the rivets securing the straps to the pressure plate are enlarged so that they terminate in or close to the plane of the flange 11. Thus, the rivet heads 23 contact a surface on which the assembly is placed at the same time as or soon after the flange 11, thereby preventing such potentially damaging excess movement ob the pressure plate. The clutch assembly shown in Figure 2 corresponds to that of Figure 1 with the exception that the straps 20 are secured, by rivets 21, at the opposite side of the pressure plate 13. In this case, the lowermost heads 26 of rivets 21 are enlarged to constitute abutment means preventing overtravel of the pressure plate as above described. Rivets used for securing straps to the pressure plate are supplied with one manufactured head, the other head on the rivet being formed during the riveting process. It is usual for the manufactured heads of the rivets to be disposed on the side of the pressure plate on which the straps are disposed, and thus in the embodiment of Figure 2 the rivets will be supplied with manufactured heads of appropriate thickness. In the embodiment of Figure 1, the heads of the rivets formed during the riveting process would be formed to a suitable thickness by varying the initial length of the rivets used, or by controlling the conditions of the actual riveting process. WHAT WE CLAIM IS:

1. A clutch assembly of the kind specified wherein there is provided abutment means projecting axially from the presrure plate in a direction away from the cover such that when the clutch is placed on a plain surface with the recess directed towards the surface, the abutment means engage the surface and thereby prevent movement of the pressure plate out from the recess to an extent which would over stress the flexible means.

2. An assembly according to claim 1 wherein the abutment means is constituted by extended portions of fastening means which also secures the flexible torque transmitting means to the pressure plate.

3. An assembly according to claim 2 wherein said flexible means comprises a plurality of generally tangentially extending straps, the fastening means therefor comprises rivets, and such rivets are provided with enlarged heads constituting the abutment means.

4. A clutch assembly substantially as hereinbefore described with reference to and as shown in Figure 1 or Figure 2 of the accompanying drawings.