WO2003087606A1

WO2003087606A1 - Clutches

Info

Publication number: WO2003087606A1
Application number: PCT/GB2003/001225
Authority: WO
Inventors: Alastair John Young
Original assignee: Automotive Products Group Limited
Priority date: 2002-04-09
Filing date: 2003-03-21
Publication date: 2003-10-23
Also published as: GB2402721B; AU2003219285A1; GB0208137D0; GB0421728D0; GB2402721A

Abstract

A clutch in which a driven plate is clamped between a flywheel or other reaction member and a pressure plate (13) by a first conical diaphragm spring (14) which reacts against a clutch cover (15) which is connected with the flywheel. A second diaphragm spring (20) acts between the cover and the first diaphragm spring to either assist or oppose the disengaging movement of the first diaphragm spring to modify the clamp load characteristic of the first diaphragm spring and thus provide a flatter overall clam characteristic to give a more constant pedal effort throughout the life of the clutch as the driven plate wears. A first periphery (22,22a) of the second diaphragm spring contacts the cover and biases the second diaphragm spring (20) against a fulcrum (16) of the first diaphragm spring (14) when the second diaphragm spring is disengaged from the first diaphragm spring load in order to prevent rattle of the second diaphragm spring.

Description

CLUTCHES

This invention relates to clutches in which a driven plate is clamped between a flywheel or other reaction member and a pressure plate by a first conical diaphragm spring which reacts against a clutch cover which is connected with the flywheel.

It is well known that the clamp load characteristics of such clutches result in an increase in the pedal effort required to release such clutches due to changes in the diaphragm spring attitude (cone angle) as the driven plate wears.

It is also known to use a second diaphragm spring acting between the cover and the first diaphragm spring to either assist or oppose the disengaging movement of the first diaphragm spring to modify the clamp load characteristic of the first diaphragm spring and thus provide a flatter overall clamp characteristic to give a more constant pedal effort throughout the life of the clutch as the driven plate wears. Such a clutch with second diaphragm spring is hereinafter referred to as a clutch of the type specified.

It is an object of the present invention to provide an improved form of clutch of the type specified.

Thus according to the present invention there is provided a clutch of the type specified in which a first periphery of the second diaphragm spring contacts the cover and biases the second diaphragm spring against a fulcrum of the first diaphragm spring when the second diaphragm spring is disengaged from the first diaphragm spring load in order to prevent rattle of the second diaphragm spring.

Typically the first diaphragm spring has one periphery in the form of radially extending fingers and the spring is mounted on the cover via a fulcrum in the form of two fulcrum rings, one on each side of the first diaphragm spring, the rings being held on the cover by a series of circumferentially spaced tabs which extend axially between the fingers of the first diaphragm spring and are bent back towards the cover to secure the first diaphragm spring to the cover between the fulcrum rings.

In such an arrangement the second diaphragm spring is arranged to be biased into contact with the fulcrum ring on the cover side of the first diaphragm spring when the second diaphragm spring disengages the first diaphragm spring.

In a preferred arrangement one periphery of the second diaphragm spring is also provided with a series of circumferentially spaced sets of radially extending fingers, the free ends of these fingers engaging the inside of the cover to bias the second diaphragm spring towards the first diaphragm spring.

Preferably the fingers on the second diaphragm spring extend between the tabs which pivot the first diaphragm ring on the cover and thus prevent circumferential movement of the second diaphragm spring relative to the cover.

In one arrangement, the outer periphery of the second diaphragm spring is biased against the cover and the inner periphery of the second diaphragm spring contacts the first diaphragm spring to assist clutch disengaging movement of the first diaphragm spring.

In such an arrangement some of the fingers on the second diaphragm spring may be radially longer (or inclined at a different cone angle) than the other fingers of the second diaphragm spring in order to lift the remainder, of the second diaphragm clear of the cover and into contact with the fulcrum of the first diaphragm spring as the load on the second diaphragm spring reduces, the longer (or differently inclined) fingers providing an initial lower rate to the operating characteristic of the second diaphragm spring thus smoothing out the combined overall characteristic of the first and second diaphragm springs in the region where the second diaphragm spring begins to become active.

In an alternative arrangement the inner periphery of the second diaphragm spring may act against the cover and the outer periphery of the second diaphragm spring contacts the first diaphragm spring to oppose clutch disengaging movement of the first diaphragm spring.

hi such an arrangement some of the fingers on the second diaphragm spring are bent towards the cover and some are straight and thus extend closer to the fulcrum of the first diaphragm spring and are arranged to contact the fulcrum as the load on the second diaphragm spring reduces.

Alternatively some of the fingers of the second diaphragm spring are radially longer than the other fingers of the second diaphragm spring in order to lift the remainder of the second diaphragm clear of the cover and into contact with the fulcrum of the first diaphragm spring as the load on the second diaphragm spring reduces, the longer fingers providing an initial lower rate to the operating characteristic of the second diaphragm spring thus smoothing out the combined overall characteristic of the first and second diaphragm springs in the region where the second diaphragm spring begins to become active.

Several embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which :-

Figure 1 is a perspective view of a clutch cover assembly for use in a clutch in accordance with the present invention;

Figure 2 shows a plan view of the cover assembly of Figure 1 ;

Figure 3 shows a section on the line IH - in of Figure 2;

Figure 4 is a perspective sectional view of the assembly of Figure 1;

Figure 5 shows a plan view of a second diaphragm spring used in the cover assembly of Figure 1;

Figure 6 shows the clamp load spring characteristic of the cover assembly of Figure 1; Figure 7 shows a plan view of an alternative form of clutch cover assembly embodying the present invention;

Figure 8 is a section on the line Nut - VIE of figure 7;

Figure 9 is a plan view of a second diaphragm spring used in the cover assembly of Figure 7;

Figure 10 shows the clamp load spring characteristic of the cover assembly of Figure 7, and

Figure 11 is a sectional view of the assembly of Figure 7.

Referring to figures 1 to 5 these show a clutch cover assembly 10 for use in a clutch of the type specified. The cover assembly comprises, in conventional manner a pressure plate 13 mounted on a clutch cover 15 via torque straps 12 and a first diaphragm spring 14 which acts between the cover and the pressure plate. The first diaphragm spring clamps a clutch driven plate (not shown) between a flywheel (not shown) and the pressure plate. As is conventional, the first diaphragm spring 14 is pivoted on the cover plate 15 between two fulcrum rings 16 and 17 positioned one on each side of the spring 14, the rings being held on the cover 15 by a series of circumferentially spaced tabs 18. The tabs 18 extend axially between radially extending fingers 19 provided in the inner periphery of the spring 14 and are bent back towards the cover 15 at 18a to secure spring 14 between the fulcrum rings. In a conventional manner the inner ends 19a of fingers 19 are contacted by a clutch release bearing (not shown) which when moved in the direction A shown in figures 3 and 4 by a suitable clutch release mechanism disengages the clamp load on the driven plate.

In accordance with the present invention a second diaphragm spring 20 is provided whose inner peripheral portion 21 contacts the first diaphragm spring fingers 19 and whose outer periphery is provided with a series of radially extending fingers 22 which contact the insides of cover 15. As can be seen from figure 5, some of the fingers 22 are longer as shown at 22a. The fingers 22 project radially outwardly between the tabs 18 under raised portions 23 of the cover 15.

Figures 3 and 4 show the pressure plate 13 in the fully engaged position with an unworn driven plate. In this condition the second diaphragm spring 20 acts on cover 15 at its outer periphery via the spring fingers 22, 22a to tend to bias the first diaphragm spring in the clutch release direction A via its inner peripheral portion 21. When in this condition the second diaphragm spring 20 is spaced from the inner fulcrum ring 16.

When the clutch is released by movement of the inner ends 19a of the fingers in direction A by the clutch release mechanism (not shown) the fingers 19 tend to move away from the inner peripheral portion 21 of the second diaphragm spring 20 and in the fully released condition of the clutch the second diaphragm spring no longer contacts the first diaphragm spring fingers 19.

Prior to the removal of all load from the second diaphragm spring 20 by disengagement of the clutch, the ends 22a of the longer spring second spring fingers 22 are the only second spring fingers contacting the cover and thus tend to bodily move the second spring away from the cover and into contact with the inner fulcrum ring 16 thus ensuring that when the second diaphragm spring 20 loses contact with the first diaphragm spring 19 the second diaphragm spring has made contact with the inner fulcrum ring 16 under the action of the longer spring fingers 22a and is thus prevented from rattling.

Figure 6 shows the individual and combined spring characteristics of the first and second diaphragm springs of the arrangement shown in Figures 1 to 5. Spring curve X shows the spring characteristics of the first diaphragm spring 40 whilst curve Y shows the spring characteristic of the second diaphragm spring 20 which, as indicated above, tends to assist the disengagement of the clutch. The combined effect of these two curves is shown by curve Z which is the combined characteristic which is felt by the vehicle driver when the associated clutch pedal is depressed. As can be seen this spring characteristic is considerably flatter than would otherwise be felt by the vehicle operator. Spring curve S shows a typical standard spring curve for the clutch design in question from which it can be seen that the capacity of the first diaphragm spring 14 has to be higher than the standard spring shown by characteristic S in order to combat the reduction in clamp load caused by the second diaphragm spring 20. The designed clamp load of the clutch is shown for comparison purposes by the line C in figure 6.

The use of the longer fingers 22a on the second diaphragm spring gives the spring characteristic of the second diaphragm spring a smoother take-up in that zone when only the longer spring fingers 22a are acting and thus providing a lower rate as shown in region L of curve Y in figure 6. This smoothes out the combined overall characteristic of the first and second diaphragm springs in the region where the second diaphragm spring becomes active which is shown in region M of curve Z of figure 6.

A similar effect to that provided by the longer spring 22a can be achieved by arranging for some of the fingers to extend at a different angle to the others and to be bent more towards the cover 15 than the remainder of the fingers. These bent fingers therefore retain their contact with the inside of cover 15 in a similar manner to the longer fingers 22a when the other fingers have already lost contact with the cover to provide the smoothing effect on the coming into action of the second diaphragm spring 20 as described above.

As will be appreciated, as the driven plate wears and therefore reduces in thickness the fully clamped position of the pressure plate 13 moves progressively further away from the clutch cover 15 so that the force applied to the first diaphragm spring by the second diaphragm spring increases in the fully clamped position and greater assistance is therefore provided during release of the clutch by the second diaphragm spring.

Figures 7 to 11 show a further form of the present invention in which a first diaphragm spring 14 is again supported from cover 15 via fulcrum rings 16 and 17 and tabs 18. In this embodiment a second diaphragm spring 40 opposes disengaging movement of the first diaphragm spring 14, so that as the diaphragm spring 14 is moved in direction A to release the clutch, the second diaphragm spring 40 becomes progressively more effective. Again the second diaphragm spring is provided with a series of radially inwardly extending fingers 42 spaced around its inner periphery 41 these fingers extend between the tabs 18 to locate the spring circumferentially. Some of these fingers 42 are bent towards the cover and some of these fingers (shown at 42a) are straight and thus extend closer to the inner fulcrum ring 16.

Figures 8 and 11 show the pressure plate in the fully clamped condition when the associated driven plate is in a new unworn condition. As will be appreciated, as the driven plate wears the angle occupied by the first diaphragm spring 14 when in a fully clamped condition changes as shown at 14' in Figure 11 and thus there is tendency for the second diaphragm spring 40 to eventually not be in contact with the first diaphragm spring 14 when in the fully clamped condition. It is thus necessary for the second diaphragm spring 40 to be biased into contact with the inner fulcrum ring 16 when it is not in contact with the first diaphragm spring 14 and this is ensured by the straight fingers 42a which make contact with inner fulcrum ring 16 in this condition.

As an alternative to the straight fingers 42a some of the bent fingers 42 could be arranged to be longer than the other bent fingers (as at 22a in Figure 5) in order to get the same progressive introduction into operation of spring 40.

As will be appreciated the overall operating characteristic of the clutch is as shown in figure 10 in which the spring characteristic of the first diaphragm spring 14 is shown by curve X. The characteristic of the second diaphragm spring 40 is shown by curve Y and the combined overall characteristic of the system is shown by curve Z.

The characteristic Y in Figure 10 is for a spring 40 with some longer fingers to give the progressive introduction effect apparent in zone L of curve Y in Figure 10. This progressive effect is also reflected in zone M of the combined characteristic Z of Figure 10.

Claims

A clutch of the type specified characterised in that a first periphery (22,22a) of the second diaphragm spring (20) contacts the cover (15) and biases the second diaphragm spring against a fulcrum (16) of the first diaphragm spring (14) when the second diaphragm spring is disengaged from the first diaphragm spring load in order to prevent rattle of the second diaphragm spring.

A clutch according to claim 1 characterised in that the first diaphragm spring (14) has one periphery in the form of radially extending fingers (19) and the spring is mounted on the cover via a fulcrum in the form of two fulcrum rings (16,17), one on each side of the first diaphragm spring, the rings being held on the cover by a series of circumferentially spaced tabs (18) which extend axially between the fingers of the first diaphragm spring and are bent back towards the cover (15) to secure the first diaphragm spring (14) to the cover between the fulcrum rings, the second diaphragm spring (20) being arranged to be biased into contact with the fulcrum ring (16) on the cover side of the first diaphragm spring when the second diaphragm spring disengages the first diaphragm spring.

A clutch according to claim 2 characterised in that one periphery of the second diaphragm spring (20) is also provided with a series of circumferentially spaced sets of radially extending fingers (22,22a), the free ends of these fingers engaging the inside of the cover (15) to bias the second diaphragm spring (20) towards the first diaphragm spring (14).

A clutch according to claim 3 characterised in that the fingers (22) on the second diaphragm spring (20) extend between the tabs (18) which pivot the first diaphragm spring (14) on the cover (15) and thus prevent circumferential movement of the second diaphragm spring relative to the cover.

5. A clutch according to any one of claims 1 to 4 characterised in that the outer periphery (22,22a) of the second diaphragm spring (20) is biased against the cover and the inner periphery (21) of the second diaphragm spring contacts the first diaphragm spring (14) to assist clutch disengaging movement of the first diaphragm spring.

6. A clutch according to any one of claims 1 to 4 characterised in that the inner periphery (42,42a) of the second diaphragm spring (40) acts against the cover (15) and the outer periphery of the second diaphragm spring contacts the first diaphragm spring (14) to oppose clutch disengaging movement of the first diaphragm spring.

7. A clutch according to claim 5 characterised in that some of the fingers (22a) on the second diaphragm spring (20) are radially longer (or inclined at a different cone angle) than the other fingers of the second diaphragm spring in order to lift the remainder of the second diaphragm clear of the cover (15) and into contact with the fulcrum (16) of the first diaphragm spring (14) as the load on the second diaphragm spring reduces, the longer (or differently inclined) fingers (22a) providing an initial lower rate to the operating characteristic of the second diaphragm spring (20) thus smoothing out the combined overall characteristic (Z) of the first and second diaphragm springs in the region (M) where the second diaphragm spring begins to become active.

8. A clutch according to claim 6 characterised in that some of the fingers (42) on the second diaphragm spring (40) are bent towards the cover (15) and some (42a) are straight and thus extend closer to the fulcrum (16) of the first diaphragm spring (14) and are arranged to contact the fulcrum as the load on the second diaphragm spring (40) reduces.

9. A clutch according to claim 6 characterised in that some of the fingers (42) of the second diaphragm spring (40) are radially longer than the other fingers of the second diaphragm spring in order to lift the remainder of the second diaphragm clear of the cover (15) and into contact with the fulcrum (16) of the first diaphragm spring (14) as the load on the second diaphragm spring reduces, the longer fingers (42) providing an initial lower rate to the operating characteristic of the second diaphragm spring (40) thus smoothing out the combined overall characteristic (Z) of the first and second diaphragm springs in the region (M) where the second diaphragm spring begins to become active.

10. A clutch of the type specified constructed and arranged substantially as hereinbefore described with reference to and as shown in Figures 1 to 6 or 7 to 11 of the accompanying drawings.