GB2222640A - A friction clutch cover - Google Patents

Abstract

A friction clutch cover (114) is provided which, in use, houses a clutch driven plate of the maximum desired diameter given the constraints of the pitch circle of the fastener holes (6), fig 4. The cover (114) has an axially extending cylindrical sidewall (5) having at one end a flange (7) with the fastener holes (6) therein whereby the cover (114) is secured to a flywheel. The portion of the sidewall (5) adjacent the flange (7) has circumferentially spaced apertures (115) that align with the fastener holes (6) so that the flange portions (7A) adjacent each aperture (115) are open to the interior of the cover to provide a flat clamping seat (116) for a respective fastener head (B), fig 5, and each clamping seat (116) extends radially inwardly at least to the outer circumference of the sidewall (5). <IMAGE>

Description

A FRICTION CLUTCH COVER This invention relates to covers used in friction clutches and in particular to covers for motor vehicle friction clutches.

A motor vehicle friction clutch generally comprises a driven plate sandwiched between a flywheel and a pressure plate. The flywheel is usually rotationally fast with the vehicle engine crankshaft, and the driven plate is rotationally fast with the vehicle gearbox input shaft. The pressure plate is usually biased by a spring or springs towards the flywheel and in the drive mode, traps the driven plate between itself and the flywheel. To release the driven plate, the pressure plate is moved away from the flywheel against the spring bias. The pressure plate and springs(s) are held within an annular clutch cover which is mounted on the flywheel so that the pressure plate, cover, and flywheel are rotationally fast whilst the pressure plate can move axially relative to the flywheel and cover to release or trap the driven plate as is required.

The overall radial dimensions of the friction clutch cover are constrained by the pitch circle diameter of the screw threaded fastener holes in the vehicle flywheel by which the cover is attached to the flywheel. For a given diameter of flywheel the maximum torque load that can be passed through the driven plate is dependant upon the clamped area of the driven plate and the maximum clamping load available from the clutch spring(s). For a diaphragm spring clutch assembly this is related to the diameter of the diaphragm spring. Therefore it is desirable in certain applications to have a driven plate and spring of the maximum possible diameter within the constraints of the pitch circle diameter of the vehicle flywheel bolt holes.

The applicants have found a means of maximising the available usable volume within a clutch cover for a given pitch center diameter of fastener holes which secure the cover to a flywheel.

Accordingly there is provided a clutch cover for a friction clutch which in use will house a clutch driven plate of a desired diameter, said cover comprising an axially extending annular sidewall having at one end a radially outwardly extending annular flange with a plurality of circumferentially spaced fastener holes therein whereby the cover in use is secured to a flywheel, whereinthe portion of the sidewall adjacent the flange is continuously substantially cylindrical and has a plurality of circumferentially spaced apertures therein, so that the flange portion within the circumferential length of an aperture is open to the interior of the cover, and each fastener hole is in circumferential alignment with a respective one of said apertures, each of said apertures in use accommodating the head of a fastener securing the cover to a flywheel.

Preferably the flange portion surrounding each fastener hole extends radially inwardly of the axially adjacent sidewall portion to provide radially inwardly of the sidewall a portion of a clamping seat for the head of a fastener, said radially inwardly extending portions terminating outwardly of the desired driven plate diameter.

Preferably each sidewall aperture has notches adjacent each circumferential edge thereof which extend into the flange on either side of the respective fastener hole.

The fastener holes may be in the form of radially elongated slots having open ends that are directed into the interior of the cover.

The invention will be described by way of example with reference to the accompanying drawings in which: Figure 1 is a cross-section of a typical prior art friction clutch cover assembly showing the assembly mounted in a vehicle friction clutch, Figure 2 is a plan view of a prior art clutch cover and assembly of the type shown in Figure 1, Figure 3 is an enlargement of the fastener hole area in Figure 2, Figure 4 is a fragmentary plan view of a clutch cover according to this invention, Figure 5 is a section on the line V-V of Fig. 4, Figure 6 is a view of the clamping area around the fastener holes in the flange viewed from arrow A in Figure 5, and Figure 7 is a modification of the cover of Figures 4 and 5.

In the drawings the same reference numerals refer to like or comparable parts.

Figure 1 illustrates a typical motor vehicle friction clutch cover assembly 2, comprising an annular cover4, a pressure plate 22 located coaxially within the cover 4, and a coaxial diaphragm spring 16 located between the cover and the pressure plate to bias the pressure plate 22 towards the open end of the cover 4.

The cover 4 comprises an annular sidewall 5 having a radially outwardly projecting flange 7 at its open end and a radially inwardly projecting flange 8 at the other axial end. The outwardly projecting flange 7 has a plurality of fastener holes 6 (Fig 2) therein whereby the cover is attached by fasteners, preferably bolts B, to a flywheel F on the crankshaft of a vehicle engine. The inwardly projecting flange 8 has a plurality of tabs 26 on its radially inner periphery whereby the diaphragm spring 16 is attached to the cover.

The spring 16 is a frustoconical plate spring coned away from the pressure plate 22 and having a radially outer continuous annular portion 17 with a plurality of spaced radially inwardly extending fingers 18 projecting from the radially inner periphery of the annular portion 17. The spring 16 is attached to the cover 4 by the tabs 26 on the cover, extending though respective apertures 19 (Fig 2) at the base of the fingers 18 and being bent around the continuous portion 17 of the spring to clinch the spring to the cover. A pair of coaxial fulcrum rings 24 and 28 are located one on each side of the diaphragm spring and are located against the radially outer surface of the tabs 26 prior to the tabs being bent around the spring 16. The outer margin 17 of the spring 16 acts against the pressure plate 22.

When the cover assembly is mounted on the flywheel F the pressure plate 22 is biased by the spring 16 to clamp a driven plate D between itself and the flywheel F. The hub H of the driven plate D is fitted onto a gearbox input shaft I. To release the driven plate D, a release load L is applied to the radially inner ends of the spring fingers 18, via a clutch release bearing G, to move the inner ends of the fingers towards the flywheel F, causing the outer annular portion 17 of the spring to pivot about the fulcrum rings 24, 28 and move away from the flywheel F. when the clutch is re-engaged the reverse operation takes place.

The pressure plate 22 is made rotationally fast with the cover 4 by three circumferentially spaced drive straps 14 which extend between the cover and lugs 23 on the outer periphery of the plate 22. The drive straps 14 allow for axial movement of the pressure plate 22 relative to the cover 4 whilst holding the two rotationally fast. The drive straps are secured to the cover by rivets 30 which are secured in holes in the flange 7 of the cover.

For a given flywheel F the internal volume of the cover is constrained by the pitch circle diameter of the fastener holes 6 since a sufficient flat clamping area 6A (Fia 3) must be provided around the holes against which the head of the bolt B can act.

As can be seen in Fig 2 and Fig 3 if the cover is coined inwardly to accommodate the head of the bolt this reduces the maximum internal diameter available within the cover envelope from D1 to D2.

Now with reference to Figs. 4 to 6, there is illustrated a clutch cover according to this invention. The same reference numerals will be used for components which are similar to components described with reference to Figs 1 to 3.

A cover 114 has a radially outwardly projecting flange 7 at one end for attachment to a flywheel as previously discussed. The flange 7 has a plurality of fastener holes 6 for attachment to the vehicle flywheel F preferably by bolts B. In the prefered embodiment there are six fastener holes but the number of fastener holes could vary between three and eight.

The portion of the sidewall 5 of the cover 4 adjacent the flange 7 is continuously substantially cylindrical without any radially inwardly coined portions as in the prior art cover, so as to maximise the internal volume available to accomodate a clutch driven plate or a diaphragm spring 16 In the sidewall 5 of the cover there are located a plurality of apertures 115 which are circumferentially spaced around the sidewall 5 so that each fastener hole 6 is in circumferential alignment with an aperture 115. Each aperture 115 extends axially from the flange 7 for a distance of at least half the axial overall length 'L'of the cover, and the flange 7 within the circumferential length of each aperture has its radially inner margin 116 open to the interior of the cover to accomodate the head of a fastener.

The flange portion surrounding each fastener hole 6 has a radially inwardly extending portion 117 that extends radially inwardly of the axially adjacent sidewall portion 118 to provide a clamping area 116 for the head of a bolt B radially within the outer radius of the adjacent portion of the sidewalls. The inwardly extending portions 117 having an internal diameter such that there is approximately a 2 mm clearance between these portions 117 and the largest diameter driven plate D to be accommodated within the cover.

Each aperture 115 in the sidewall 15 has notches 119 adjacent to the circumferential edges 120 thereof that extend into the flange 7 approximately to the pitch centre diameter (PCD) of the fastener holes 6 so that each clamping area 116 is a form of a salient projecting radially inwardly from the respective fastener hole. Each notch 119 is in form of a rounded 'V' or arrow head with the side of the arrow shaped notch being in radial alingment with the repective circumferential edge 120 of the aperture 115.

With reference to Fig 7 there is illustrated a second embodiment of the invention which is the same as the cover described with reference to Figs. 4 to 6 in which the bolt holes 6 in the flange 7 have been formed as a slots 206 which open into the interior of the cover. The clamping area 216 around the fastener slot 206 is shown in dotted outline.

Claims (10)

1. A clutch cover for a friction clutch and which in use will house a clutch driven plate of a desired diameter, said cover comprising an axially extending annular sidewall having at one end a radially outwardly extending annular flange with a plurality of circumferentially spaced fastener holes therein whereby the cover in use is secured to a flywheel, wherein the portion of the sidewall adjacent the flange is continuously substantially cylindrical and has a plurality of circumferentially spaced apertures therein so that the flange portion within the circumferential length of the aperture is open to the interior of the cover, and each fastener hole is in circumferential alignment with a respective one of said apertures, each of said apertures in use accommodating the head of a fastener securing the cover to a flywheel.

2. A clutch cover as claimed in Claim 1 wherein the flange portion surrounding each fastener hole extends radially inwardly of the axially adjacent sidewall portion to provide radially inwardly of the sidewall a portion of a clamping seat for the head of a fastener, said radially inwardly extending portions terminating outwardly of the desired driven plate diameter.

3. A clutch cover as claimed in Claim 1 or Claim 2 wherein each sidewall aperture has notches adjacent each circumferential edge thereof which extend into the flange on either side of the respective fastener hole.

4. A clutch cover as claimed in Claim 3, wherein the notches extend radially outwardly to approximately the pitch centre diameter of the fastener holes.

5. A clutch cover as claimed in Claim 3 or Claim 4 wherein the notches are each in the form of an arrow head with one side of the arrow in radial alignment with the respective circumferential edge of the sidewall aperture.

6. A clutch cover as claimed in any one of claims 1 to 5 wherein the fastener holes are in the form of elongated slots having open ends directed into the interior of the cover.

7. A clutch cover as claimed in any one of Claims 1 to 6 wherein there are between three and eight fastener holes in the flange.

8. A clutch cover for a friction clutch and which is substantially as described herein and with reference to Figs 4 to 6, and Fig 7 of the accompanying drawing.

9. A motor vehicle friction clutch cover assembly having a clutch cover as claimed in any one of Claims 1 to 8.

10. A motor vehicle friction clutch cover assembly as claimed in Claim 9 in which the clutch assembly spring is a diaphragm spring.