GB2372079A

GB2372079A - Constant lift mechanism for wear adjustable clutch

Info

Publication number: GB2372079A
Application number: GB0103574A
Authority: GB
Inventors: Alastair John Young
Original assignee: Automotive Products PLC
Current assignee: Automotive Products PLC
Priority date: 2001-02-13
Filing date: 2001-02-13
Publication date: 2002-08-14
Also published as: GB0103574D0

Abstract

A clutch comprises: cover 12 supporting diaphragm spring 16 on rings 18; ramped 24 automatic adjustor pivot ring 20 with fulcrum 22 for engaging the spring and pressure plate 14 rotationally fixed to the cover by straps 15 and having pivot ring engaging ramps 26. Pivot ring rotation by pawl mechanism 28 responding to wear increases effective pressure plate thickness. Ramped stop segments 38 spring 56 biassed in one circumferential direction are located in pivot ring cutouts 36 positioned corresponding to pressure plate ramps. On clutch disengagement the stop segments are clamped between cover stops (52 Fig. 8) and pressure plate ramps to limit pressure plate lift and relieve spring load from the pivot ring, enabling adjustment rotation. On clutch re-engagement the pivot ring is loaded, releasing the stop segments which advance on ramps 26 under springs 56, maintaining constant lift despite wear.

Description

Automatically Adjusting Friction Clutches

The present invention relates to automatically adjusting friction clutches, and in particular to automatically adjusting friction clutches for use on motor vehicles Known automatically adjusting friction clutches (hereinafter referred to as automatically adjusting clutches of the type defined) comprise a pressure plate connected to a clutch cover so as to be constrained to rotate with the cover whilst being able to move relative to the cover in an axial direction of the clutch, a spring means which acts on the pressure plate so that, in use, an associated driven plate is clamped between the pressure plate and a counter pressure plate, which may be a flywheel of an internal combustion engine, an adjustment means to compensate for wear, in particular of the friction linings of the associated driven plate, and which adjustment device ensures that the spring means provides a substantially constant clamp load, the adjustment means comprising a pivot ring arranged between the pressure plate and the spring means, the pivot ring having a fulcrum for engagement with the spring means when the clutch is engaged, and means to displace the fulcrum axially in a direction towards the spring means in response to wear of the friction linings of the associated driven plate.

In automatically adjusting clutches of the type defined, the pivot ring is clamped between the spring means and the pressure plate when the clutch is engaged so that adjustment can only take place when the clutch is disengaged. It is important in such clutches to ensure that when the clutch is disengaged, the clamp load of the spring means is fully removed from the pivot ring if proper adjustment is to take place This is particularly important

I when the pressure plate is connected to the clutch cover by torque straps which bias the pressure plate away from the counter pressure plate during clutch disengagement.

For this reason it is known to provide an automatically adjusting clutch of the type described with a constant lift device that limits movement of the pressure plate away from the counter pressure plate during clutch disengagement.

It is an objective of the present invention to provide an automatically adjusting clutch of the type described having an improved constant lift device It is a further objective of the present invention to provide an automatically adjusting clutch of the type defined which is easier and cheaper to produce than the known automatically adjusting clutches.

In accordance with the invention, there is provided an automatically adjusting clutch of the type defined comprising a constant lift means for limiting the movement of the pressure plate away from the counter pressure plate to a substantially constant amount over the life of the clutch, the constant lift means comprising one or more stop segments, each segment having a stop for engagement with a corresponding stop on the clutch cover to limit the movement of the pressure plate during clutch disengagement, each segment further comprising a ramp surface for engagement with a corresponding ramp surface on the pressure plate such that circumferential movement of the segment relative to the pressure plate in an adjustment direction causes an axial displacement of the segment stop towards the stop on the clutch cover.

An embodiment of the invention will now be described, by way of example only, with reference to the following drawings in which.

Figure 1 is an axial view of a clutch cover assembly of a friction clutch in accordance with the invention ; Figure 2 is an exploded perspective view of the clutch cover assembly of Figure 1 ; Figure 3 is a cross sectional view of part of the clutch cover assembly of Figure 1 taken on the line X-X,

Figure 4 is a perspective view of part of a pivot ring of the friction clutch assembly of Figure 1, showing a stop segment; Figure 5 is a similar view to that of Figure 4, showing the position of the segment relative to the pivot ring after the pivot ring has made an adjustment to compensate for wear ; Figure 6 is an exploded perspective view of the pivot ring and the stop segment ; Figure 7 is a further perspective view of the pivot ring and stop segment viewed from an alternative angle, and Figure 8 is a cross sectional view of part of the clutch cover assembly of Figure 1 taken on the line Y-Y With reference to the Figures, a clutch cover assembly, indicated generally at 10, comprises a clutch cover 12, a pressure plate 14 and a diaphragm spring 16. The pressure plate is connected to the clutch cover by means of a plurality of torque straps 15 in a conventional manner so that the pressure plate 14 is constrained to rotate with the clutch cover whilst being able to move in an axial direction of the clutch to a limited extent.

The clutch cover 12 supports the diaphragm spring 16 via two support rings 18 situated one on each axial side of the diaphragm spring in a manner well known in the art. In use, the clutch cover 12 is fixed rotationally fast, via a flange 12a, with a counter pressure plate (not shown), such as the flywheel of an internal combustion engine, and the diaphragm spring biases the pressure plate 14 towards the flywheel. An associated clutch driven plate (not shown) is situated between the pressure plate 14 and the flywheel and in use is connected to the input shaft of a gear box (not shown). The arrangement so far described is entirely conventional and will be well known to those skilled in the art.

Located between the pressure plate 14 and the diaphragm spring 16 is part of an adjustment means for automatically compensating for wear of the friction linings of the associated driven plate. The adjustment means comprises an annular pivot ring 20 having a fulcrum 22 for engagement with the diaphragm spring 16. The pivot ring is provided with a number of circumferentialy spaced and circumferentialy disposed ramp surfaces

24, for engagement with corresponding ramp surfaces 26 on the pressure plate The arrangement of ramp surfaces 24,26 is such that circumferential movement of the pivot ring 20 relative to the pressure plate 14 in an adjustment direction (as indicated by the arrow A) results in an axial displacement of the fulcrum towards the diaphragm spring 16.

Movement of the pivot ring in the adjustment direction is carried out incrementally by an adjustment mechanism 28 in response to a pre-determined amount of wear of the friction linings of the associated driven plate. In the present embodiment the adjustment mechanism 28 is a pawl mechanism which may be of the type described in the applicant's co-pending patent application WO 00/11365 or as described in the applicant's patent application WO 97/10448. However, it will be understood that the adjustment mechanism 28 need not be a pawl mechanism and that any suitable adjustment mechanism may be used.

The construction and operation of the pawl mechanism 28 will not be described in detail in the present application since it does not form part of the present invention and the reader should refer to the applicant's co-pending application and patent, the disclosures of which are hereby included by reference However, briefly, the pawl mechanism 28 cooperates with a set of adjustment teeth 29 on the pivot ring. Once a pre-determined amount of wear of the friction linings of the driven plate has taken place, a tooth on the pawl will engage behind one of the adjustment teeth 29 during engagement of the clutch.

On a subsequent disengagement of the clutch, the pawl mechanism 28 rotates the pivot ring 20 in the adjustment direction relative to the pressure plate 14. As the pivot ring rotates, the ramp surfaces 24 on the pivot ring ride over the corresponding ramp surfaces 26 on the pressure plate so that the fulcrum is displaced axially towards the diaphragm spring, increasing the effective axial thickness of the pressure plate and pivot ring combination By suitable design of the ramp surfaces 24,26 and the pawl mechanism, it can be arranged that for each adjustment the fulcrum 22 is moved axially towards the diaphragm spring 16 by an amount which is equal to the pre-determined amount of wear required to trigger an adjustment. If the increments between adjustments are small, the effect is to

I maintain the relative axial positions of the diaphragm spring 16 and the fulcrum 22 substantially constant. This maintains the cone angle of the diaphragm spring substantially constant so that the clamp load of the diaphragm spring and the release load required to disengage the clutch also remain substantially constant The pivot ring 20 is formed as a pressed component and has a generally"Z"shaped cross section as can be seen from Figure 3, The fulcrum 22 is formed on the end of an inner limb 30 of the pivot ring by a simple machining process. The ramp surfaces 24 are press formed in the central region 32 of the ring whilst an outer limb 34 extends along the outer circumferential edge of the ramp surfaces 26 to hold the pivot ring in position Three circumferentially, equi-spaced cutouts 36 are provided in the outer limb 34 of the ring.

Each cutout 36 is positioned so as to correspond with the position of one of the ramp surfaces 26 on the pressure plate. Each cutout 36 accommodates a stop segment 38 (see Figure 8 as compared to Figure 3) forming part of a constant lift mechanism as will be described in more detail later It can be seen from Figure 3 in particular, that the diaphragm spring 16 acts on the pressure plate 14 via the pivot ring 20 As a result, the pivot ring is clamped between the diaphragm spring and the pressure plate when the clutch is engaged or partially engaged.

This means that adjustment can only take place when the clutch is disengaged.

Furthermore, it will be understood that in order for the pivot ring 20 to be able to move freely relative to the pressure plate 14 during an adjustment, it is necessary to ensure that the clamp load of the diaphragm spring is fully removed from the pivot ring when the clutch is disengaged. If the clamp load is not fully removed then there is a risk that correct adjustment will not take place Alternatively, it will be necessary to increase the force exerted by the adjustment mechanism on the pivot ring so that any clamp load between the diaphragm spring and the pressure plate is overcome To ensure that the pivot ring is fully released when the clutch is disengaged a constant lift mechanism is provided. As indicated above, the constant lift mechanism comprises three stop segments 38 circumferentially disposed about the pivot ring 20. Each of the segments 38 is received in one of the cutouts 36 in the outer limb 30 of the pivot ring 20.

As can be seen best from Figures 4 to 7, the stop segments 38 each comprise a main body portion 40 which is received in the cutout 36 in the outer wall 30 of the pivot ring. A bridging portion 42 extends radially inwardly from an inner side 44 of the main body 40 The bridging portion 42 extends with an axial clearance over the central region 32 of the pivot ring and through a smaller cut out 46 in the inner limb 30. The clearance between the bridging portions 42 and the central region 32 of the pivot ring is selected such that the pivot ring has sufficient free play to be able to adjust correctly when the clutch is disengaged whilst preventing excessive movement of the pivot ring away from the pressure plate.

An inner retention member 48 is provided on the radially inner end of the bridging portion 42. The inner retention member 48 extends axially towards the pressure plate 14 so as to run around the radially inner edge of the pressure plate ramp surfaces 26 and prevent the stop segments from centrifuging outwards when the clutch is rotating at speed A first axial end face 50 of the main body portion 40 comprises a stop which contacts a corresponding stop 52 on the clutch cover 12 to limit the movement or lift of the pressure plate 14 towards the clutch cover when the clutch is disengaged. The opposite axial end face 54 of the main body portion is formed as a ramp surface and is arranged to contact one of the ramp surfaces 26 on the pressure plate The arrangement is such that circumferential movement of the stop segments 38 relative to the pressure plate 14 in the adjustment direction will cause the ramp surfaces 54 on the segments to ride up the corresponding ramp surfaces 26 on the pressure plate so that the stop surfaces 50 on the segments are moved axially towards the corresponding stop surfaces 52 on the clutch cover A coil spring 56 is located between a first circumferential end 58 of the bridging portion 42 and an opposed surface 60 on the pivot ring. Tangs 62,64 may be provided on the bridging portion 42 and the opposed surface 60 to hold the spring in position. The second circumferential end 66 of the bridging portion 42 comprises an abutment that engages with a corresponding abutment 68 on the pivot ring. In this case the corresponding

abutment 68 is one of the circumferential ends of the cutout 46 in the inner limb 30 of the pivot ring through which the bridging portion 42 extends.

Operation of the constant lift mechanism will now be described.

Considering first a clutch in which no wear has taken place.

The pivot ring 20 is located on the pressure plate so that the corresponding ramp surfaces 24,26 are at their initial relative positions with a maximum amount of overlap The stop segments 38 are similarly positioned so that the segment ramp surfaces 54 are at their initial positions with respect to the corresponding pressure plate ramp surfaces 26 and the abutment 66 on the bridging portion is held in contact with the corresponding abutment 68 on the pivot ring 20 by the coil spring 54 which has a small pre-tension.

With the clutch engaged, the ramp surfaces 24 on the pivot ring 20 are clamped against the corresponding ramp surfaces 26 on the pressure plate by the diaphragm spring 16 and the pivot ring 20 is thereby prevented from rotating relative to the pressure plate 14. The stop segments 38 are also prevented from moving circumferentially in the adjustment direction because the abutments 66 on the bridging portions are in contact with the abutments 68 on the pivot ring. The pre-tension in the spring 56 prevents the segments from moving in the opposite direction or from rattling around.

When the clutch is disengaged, the pressure plate 14, pivot ring 20 and the stop segments 38 are all moved axially towards the cover 12 due to the bias force of the torque straps 15 This movement will continue until the stop surfaces 50 on the segment stops contact the stops 52 on the clutch cover At this point, further axial movement of the pressure plate 14 towards the clutch cover is prevented and the bias force of the torque straps is taken through the stop segments 38 to the clutch cover.

Further movement of the diaphragm spring in the disengagement direction will fully relieve the pivot ring of any clamp load. However, because no wear has taken place, the adjustment mechanism 28 does not bias the pivot ring 20 to rotate relative to the pressure plate in the adjustment direction. Movement of the pivot ring in the opposite direction is

prevented because of the engagement between the corresponding abutments 66, 68 on the pivot ring and segments It should be noted, that the stop segments 38 are now clamped between the pressure plate 14 and the cover 12 by the bias force of the torque straps and so are prevented from rotating relative to the pressure plate.

When the clutch is re-engaged, the diaphragm spring 16 will once again clamp the pivot ring 20 to the pressure plate 14 and move the pressure plate, pivot ring and stop segments away from the clutch cover 12 towards the flywheel Considering now a clutch in which a predetermined amount of wear has taken place.

When the clutch is engaged, the pawl mechanism 28 will engage behind one of the adjustment teeth 29. During a subsequent clutch disengagement, the pressure plate 14 and pivot ring 20 are moved towards the clutch cover, until the stop surfaces 50 on the segment stops 38 again contact the stops 52 on the cover to limit the axial lift of the pressure plate 14 Further disengagement movement of the diaphragm spring 16 relieves the pivot ring 20 of any clamp load so that the pawl mechanism 28 can rotate the pivot ring in the adjustment direction. As the pivot ring rotates, the ramp surfaces 24 on the ring ride up the corresponding ramp surfaces 26 on the pressure plate, moving the fulcrum 22 axially towards the diaphragm spring to compensate for the wear. However, the stop segments 38, which are clamped between the clutch cover and the pressure plate, are not able to move in the adjustment direction and so a gap B is opened up between the abutments 66 on the bridging portions and the abutments 68 on the pivot ring and the coil springs 56 are compressed (see Figure 5).

When the clutch is next engaged, the diaphragm spring 16 will again clamp the pivot ring 20 to the pressure plate 14 and move the pressure plate, pivot ring and stop segments away from the clutch cover. Once the stop segments 38 have been moved away from the cover stops 52 and are no longer clamped between the pressure plate and the cover, they

are biased by the coil springs 56 in the adjustment direction until the abutments 66 on the bridging portions 42 are brought into contact with the abutments 68 on the pivot ring.

During this movement, the ramp surfaces 54 on the segments ride up the corresponding ramp surfaces 26 on the pressure plate so that the segment stop surfaces 50 are moved axially closer to the clutch cover stops 52 by an amount which is equal to the predetermined amount of wear It can be seen, therefore, that the arrangement described maintains the relative axial positions between the stops 50 on the segments and the stops 52 on the cover substantially constant Consequently, the axial movement of the pressure plate 14 towards the clutch cover during disengagement is also maintained substantially constant.

Claims

Claims An automatically adjusting clutch of the type defined comprising a constant lift means for limiting movement of the pressure plate away from the counter pressure plate to a substantially constant amount over the life of the clutch, the constant lift means comprising one or more stop segments, each segment having a stop for engagement with a corresponding stop on the clutch cover to limit the movement of the pressure plate during clutch disengagement, each segment further comprising a ramp surface for engagement with a corresponding ramp surface on the pressure plate such that circumferential movement of the segment relative to the pressure plate in an adjustment direction causes an axial displacement of the segment stop towards the stop on the clutch cover
2 An automatically adjusting clutch as claimed in claim 1 in which the adjustment means includes ramp means between the pivot ring and the pressure plate such that circumferential movement of the pivot ring relative to the pressure plate in an adjustment direction displaces the fulcrum axially in the direction of the diaphragm spring.
3 An automatically adjusting clutch as claimed in claim 2 in which each stop segment is moved circumferentially relative to the pressure plate in the adjustment direction in response to movement of the pivot ring in the adjustment direction.
4. An automatically adjusting clutch as claimed in claim 3 in which the pivot ring is moved circumferentially when the clutch is disengaged following a predetermined amount of wear and each stop segment is subsequently moved when the clutch is next engaged.
5. An automatically adjusting clutch as claimed in any previous claim in which movement of each stop segment in the adjustment direction is controlled by abutment between the stop segment and the pivot ring.
6 An automatically adjusting clutch as claimed in claim 1 in which each segment is at least partially housed within a radial cutout in the pivot ring.
7 An automatically adjusting clutch as claimed in any previous claim in which there are three stop segments equi-spaced around the pivot ring.
8 An automatically adjusting clutch as claimed in any previous claim in which each segment has a bridging portion which extends radially over a region of the pivot ring such that the region of the pivot ring is located between the bridging portion and the pressure plate, there being an axial clearance between the bridging portion and the region of the pivot ring.
9. An automatically adjusting clutch as claimed in claim 8 when dependent on claim

5 in which the abutment on each segment is provided on the bridging portion thereof.
10 An automatically adjusting clutch as claimed in any previous claim in which a spring means biases the segment in the adjustment direction.
11 An automatically adjusting clutch as claimed in claim 10 in which the spring means acts between each segment and the pivot ring.
12. An automatically adjusting clutch as claimed in any previous claim when dependent on claim 8 in which a retaining member on the radially inner end of the bridging member engages the radially inner edge of a ramp means on the pressure plate to stop the or each segment centrifuging out when the clutch is rotated at high speed.
13 An automatically adjusting clutch as claimed in any previous claim in which the pivot ring is moved in the adjustment direction by an adjustment mechanism in response to a pre-determined amount of wear of the friction linings of an associated driven plate.
14. An automatically adjusting clutch as claimed in claim 13 in which the adiustment mechanism comprises a pawl mounted to the clutch cover and which co-operates with an array of adjuster teeth on the pivot ring.
15 An automatically adjusting clutch as claimed in any previous claim in which the pivot ring is a pressed annular component having a generally Z shape in cross section.
16 An automatically adjusting clutch as claimed in claim 15 in which the fulcrum is formed on the axial end of one limb of the pivot ring and a plurality of ramp surfaces are formed in a central region of the pivot ring.
17 An automatically adjusting clutch as claimed in any of claims 2 to 16 in which the ramp surfaces on the pressure plate which are engaged by the segments also form part of the ramp means provided between the pivot ring and the pressure plate.
18. An automatically adjusting clutch substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

18 An automatically adjusting clutch substantially as hereinbefore described with reference to and as shown in the accompanying drawings

Amendments to the claims have been filed as follows so Claims 1. An automatically adjusting clutch of the type defined comprising a constant lift means for limiting movement of the pressure plate away from the counter pressure plate to a substantially constant amount over the life of the clutch, the constant lift means comprising a plurality of stop segments, each segment having a stop for engagement with a corresponding stop on the clutch cover to limit the movement of the pressure plate during clutch disengagement, each segment further comprising a ramp surface for engagement with a corresponding ramp surface on the pressure plate such that circumferential movement of the segment relative to the pressure plate in an adjustment direction causes an axial displacement of the segment stop towards the stop on the clutch cover.

2. An automatically adjusting clutch as claimed in claim 1 in which the adjustment means includes ramp means between the pivot ring and the pressure plate such that circumferential movement of the pivot ring relative to the pressure plate in an adjustment direction displaces the fulcrum axially in the direction of the diaphragm spring.

3. An automatically adjusting clutch as claimed in claim 2 in which each stop segment is moved circumferentially relative to the pressure plate in the adjustment direction in response to movement of the pivot ring in the adjustment direction.

4. An automatically adjusting clutch as claimed in claim 3 in which the pivot ring is moved circumferentially when the clutch is disengaged following a predetermined amount of wear and each stop segment is subsequently moved when the clutch is next engaged.

5. An automatically adjusting clutch as claimed in any previous claim in which movement of each stop segment in the adjustment direction is controlled by abutment between the stop segment and the pivot ring.

6 An automatically adjusting clutch as claimed in claim 1 in which each segment is at least partially housed within a radial cutout in the pivot ring 7 An automatically adjusting clutch as claimed in any previous claim in which there are three stop segments equi-spaced around the pivot ring 8 An automatically adjusting clutch as claimed in any previous claim in which each segment has a bridging portion which extends radially over a region of the pivot ring such that the region of the pivot ring is located between the bridging portion and the pressure plate, there being an axial clearance between the bridging portion and the region of the pivot ring 9 An automatically adjusting clutch as claimed in claim 8 when dependent on claim

5 in which the abutment on each segment is provided on the bridging portion thereof 10. An automatically adjusting clutch as claimed in any previous claim in which a spring means biases the segment in the adjustment direction.

11 An automatically adjusting clutch as claimed in claim 10 in which the spring means acts between each segment and the pivot ring.

12. An automatically adjusting clutch as claimed in any previous claim when dependent on claim 8 in which a retaining member on the radially inner end of the bridging member engages the radially inner edge of a ramp means on the pressure plate to stop the or each segment centrifuging out when the clutch is rotated at high speed 13 An automatically adjusting clutch as claimed in any previous claim in which the pivot ring is moved in the adjustment direction by an adjustment mechanism in response to a pre-determined amount of wear of the friction linings of an associated driven plate.

14. An automatically adjusting clutch as claimed in claim 13 in which the adjustment mechanism comprises a pawl mounted to the clutch cover and which co-operates with an array of adjuster teeth on the pivot ring.

15. An automatically adjusting clutch as claimed in any previous claim in which the pivot ring is a pressed annular component having a generally Z shape in cross section.

16. An automatically adjusting clutch as claimed in claim 15 in which the fulcrum is formed on the axial end of one limb of the pivot ring and a plurality of ramp surfaces are formed in a central region of the pivot ring.

17 An automatically adjusting clutch as claimed in any of claims 2 to 16 in which the ramp surfaces on the pressure plate which are engaged by the segments also form part of the ramp means provided between the pivot ring and the pressure plate.