WO2004001252A1

WO2004001252A1 - Drive clutches

Info

Publication number: WO2004001252A1
Application number: PCT/GB2003/002564
Authority: WO
Inventors: Alastair John Young
Original assignee: Automotive Products Driveline Technology Limited
Priority date: 2002-06-19
Filing date: 2003-06-13
Publication date: 2003-12-31
Also published as: AU2003250364A1; GB0214078D0

Abstract

A clutch in which a driving plate (10) clamped against a driven plate (11) by a pressure plate (22) under action of over-centre toggle linkage (23). The toggle linkage includes a clamping member (24) which acts on the pressure plate (22) and reacts against an axially fixed abutment (28) and a link (26) displaceable from an engaged position on one side of the over-centre position (X) of the linkage (23) to a disengaged position on the other side of an over-centre position by an actuating member (27) via a release bearing (36). The reaction force (R) of the clamping member (24) on the abutment (28) applying an axial load (CA) on the linkage which tends to hold the link in the engaged position. A bias means (37) is provided which applies an axial bias force (B) to the linkage (23) which is in opposition to but lower than the axial load (CA) on the linkage resulting from the reaction of the clamping member (24) on the abutment (28) when the clutch is in an unworn condition so that the clutch remains engaged. The reaction force (R) and axial load (CA) decrease as the clutch wears up to a point where the axial bias force (B) exceeds the axial load (CA) at which point the clutch is disengaged by the bias force (B) or some other indication that adjustment of the clutch is required occurs.

Description

DRIVE CLUTCHES

This invention relates to drive clutches and in particular to clutches (hereinafter referred to as being of the type specified) which comprise:-

a driving plate clamped against a driven plate by a pressure plate under action of over- centre toggle linkage,

the toggle linkage including a clamping member which acts on the pressure plate and reacts against an axially fixed abutment and a link displaceable from an engaged position on one side of the over-centre position of the linkage to a disengaged position on the other side of an over-centre position by an actuating member via a release bearing,

the reaction force of the clamping member on the abutment applying an axial load on the linkage which tends to hold the link in the engaged position.

Clutches of the type specified are commonly used in static applications where, for example, a prime mover drives an output shaft via the clutch, the output shaft being connected to a device such as an electrical generator or water pump.

Clutches of the type specified are thus subject to long periods of operation often without supervision and can thus suffer from significant abuse.

One of the main problems is associated with ensuring that the clutch does not operate for any significant amount of time with a significant level of slippage due to wear of the driving plate or driven member. Typically clutches of the type specified include multiple driving plates which are in turn clamped against multiple interleaved driven members by the pressure plate in a so-called clutch pack.

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 bias means is provided which applies an axial bias force to the linkage which is in opposition to but lower than the axial load on the linkage resulting from the reaction of the clamping member on the abutment when the clutch is in an unworn condition so that the clutch remains engaged, the reaction force and axial load decreasing as the clutch wears up to a point where the axial bias force exceeds the axial load at which point the clutch is disengaged by the bias force or some other indication that adjustment of the clutch is required occurs.

In a preferred arrangement the bias means comprises one or more belleville springs which are compressed when the link is in the engaged position to provide the axial bias force.

Typically the toggle linkage may include a first axially displaceable ring member which surrounds an output shaft driven by the clutch and on which are mounted a plurality of generally radially extending links each connected to a respective clamping member, such an arrangement the bias means is conveniently arranged to act axially on the ring member to move the ring member and hence the connected links between their engaged and disengaged positions.

Preferably the axially fixed abutment is adjustable and comprises a second ring member which surrounds and is screw-threaded engagement with an output member to which the output shaft and the or each driven member is rotationally fast, hi such an arrangement the axial position of the abutment can be adjusted by rotating the second ring member about the output member in order to increase the clamp load when the clutch driving plates or driven members wear.

In a preferred arrangement, the first ring member which supports the links contacts the second ring member when the links are in the engaged position and the bias means is sandwiched between the ring members with a pre-determined amount of compression of the bias means. This arrangement is particularly useful when the bias means comprises one or more belleville springs which may not be flat in an axial sense since it enables the fully clamped position of the clutch to be better controlled by the direct contact of the ring members without relying on squashing belleville springs of doubtful axial dimensions.

Although in the arrangements described above the bias means has been arranged to cause automatic disengagement of the clutch when a predetermined amount of wear has occurred resulting in the clamp load falling to a level at which the bias means can move the overcentre linkage from its engaged to its disengaged condition, it will be understood that the bias means could be arranged to additionally or alternatively operate a warning device to alert a supervisor (who may be at a remote location) that the clutch is in need of adjustment.

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

Figure 1 shows an axial section through a drive clutch in accordance with the present invention;

Figure 2 shows the forces acting on the over-centre linkage of the clutch of Figure 1;

Figure 3 shows details of a modified form of the clutch shown in Figure 1 on a larger scale;

Figure 4 shows the effect on the clamping load of the use of the biasing belleville springs, and Figure 5 shows details of a further modified form of the clutch shown in Figure 1.

Referring to figure 1 the drive clutch comprises a plurality of driving plates 10 which are splined at 11 onto an input member 12 which is bolted at 13 to the flywheel (not shown) of an engine. Interleaved between the driving plates 10 are driven plates 14 with driven plate 14a being formed integrally with an output member in the form of output sleeve 15 onto which driven plates 14b and 14c are splined at 16. Output sleeve 15 is itself keyed at 17 onto output shaft 18 which is supported by bearings 19 in a clutch bell housing 20. Output shaft 18 drives a stationary device such as a water pump or electrical generator etc. via a driving key 21.

Also keyed on output sleeve 15 is a pressure plate 22 which clamps the driving and driven plates 10 and 14 together under the action of an over-centre toggle linkage 23.

The toggle linkage comprises a plurality of circumferentially spaced clamping members 24 which are pivoted at 25 on trunnions 22a on pressure plate 22 and are each pivotally connected at 26a with a respective generally radially extending link 26 which is itself pivoted at 30 on a first ring member 27 which is axially slideable on output shaft 18. Each clamping member 24 reacts on pressure plate 22 via trunnions 22a and pivot 25 and also at a radially inner camming zone 24a on a wear plate 28a supported on a second ring member 28 which forms an axially fixed but adjustable abutment. Second ring member 28 is in screw-threaded engagement at 29 with output sleeve 15 so that by rotating the second ring member about output member 15 the axial position of the second ring member 28 can be adjusted and hence the load which is imparted onto the pressure plate as a result of the reaction of the camming zone 24a of each clamping member on the ring 28 which is represented in figure 1 by the arrow R.

Each toggle linkage 23 has an over-centre position indicated by the plane of dotted line X in figure 1 and the links 26 are displaceable from the engaged position shown in figure 1 in which the pivots 30 of linlcs 26 lie to the left of plane X to a disengaged position in which the pivots 30 lie to the right of plane X. Displacement of the first ring member 27 between the engaged and disengaged position is effected by a lever 31 pivoted at 32 on bell housing 20. This lever in turn operates a fork 33 which engages two diametrically opposite pins 34 formed on an actuating ring 35. Actuating ring 35 displaces first ring member 27 via a release bearing 36.

Figure 2 shows a force diagram of the toggle linkage 23 and in particular the force C applied to abutment ring 28 via wear plate 28a by each clamping member 24 (resisted by the reaction force R). This force C is in turn transmitted to first ring member 27 via each link 26 so that the ring member 27 is subjected to a horizontal clamping component CA and a radial clamping component CR.

hi accordance with the present invention a bias means in the form of belleville springs 37 is positioned between first and second ring members 27 and 28. These belleville springs apply a bias force B to first ring 27 which opposes the axial components CA of the clamping force C exerted by all the clamping members 24.

This spring bias force B is arranged to be less than the axial clamping force CA when the clutch is engaged and the driving and driven members are in an unworn condition. As the clutch wears the clamping force C reduces until the axial component CA becomes less than the bias force B. At this point the bias force displaces the first ring member 27 to the right, as viewed in figure 1, thus moving the link 26 from one side of the over-centre position indicated by plane X to the other. This results in clamping members 24 being rotated sufficiently to disengage the second ring member 28 which acts as the reaction abutment thus disengaging the clutch.

Thus operation of the clutch for a significant period of time with excessive slippage is avoided.

The movement of the toggle linkage 23 from one side of the over-centre position to the other can also be used to trigger the operation of a warning device (visual and/or audible) to warn a supervisor located at a location remote from the clutch that adjustment of the clutch (by rotation of ring member 28 on output member 15) is necessary due to wear of the driving/driven members 10/14.

Figure 3 shows a modified form of the present invention in which the belleville springs 37 are recessed in a cut-out 40 in ring member 28 so that when the clutch is in the engaged position the first ring member 27 contacts the second ring member 28 directly and not via the belleville springs 37.

This arrangement gives accurate control over the engaged position of the clutch in view of the direct contact of ring members 27 and 28 and does not rely in determining the engaged position on the level of squashing of the Belleville springs 37. This gives much better control over the engaged clamp condition of the clutch since belleville spring 37 are frequently not flat in an axial sense (i.e. their level of axial dishing is not constant around their circumference).

Figure 4 shows in graphical form the effect of superimposing the spring load B on the operating load from the lever 31 through the toggle linkage.

Curve A shows the original load applied to the linkage before the introduction of the Belleville springs. The bellevilles are ineffective beyond 6.5mm travel from their flat condition. This curve reaches a maximum at peak Tl at about 9mm travel. The load is zero at the over-centre position indicated by dotted line P and reaches a fairly high negative value in the fully clamped zero travel position at the left hand end of the graph. This relatively high negative load is the end load in the toggle linkage 23 which is reacted by the load R shown in figures 1 and 2. The actual value of this load is dependent on the state of adjustment of the clutch which in turn affects the angle of the radial links 26 and is also dependent on the stiffness on the whole clamped clutch assembly.

When the belleville springs 37 are introduced (their effect shown by curve B) curves A and B are in effect added together to give the final overall curve F. As can be seen this final curve F has a second peak T2 which (depending on the clutch stiffness) is close to the over-centre position shown by the dotted line P. This final curve also passes through zero load much closer to the final clamped position and has a relatively small negative value at the clamped position when the bellevilles are flat (or near flat as per figure 3).

When the clutch wears and goes out of adjustment the clamp load drops and this will result in the end load on the curve A moving closer to zero. This in turn causes the final curve F to rise past zero in the clamped position which signifies a positive load which is then capable of disengaging the clutch automatically (in other words the bias force B now exceeds the axial clamped component CA).

Although the clutch arrangements described above have been described as being operated manually via lever 31 the invention is equally applicable to arrangements in which the ring member 27 is moved axially by any suitable means such as, for example, an electric motor or an hydraulic actuator.

Figure 5 shows a further modified form of the present invention which has fewer interleaved plates 10 and 11 and in which a single belleville spring 37 is located between the first ring member 27 and the second ring member 28. The second ring member 28 includes a steel wear insert 28a which is contacted by clamping member 24. A tube 40 having an attachment flange 41 is secured to second ring member 28 by countersunk screws 42. The outer peripheral portion of belleville spring 37 reacts against the right hand end 43 of tube 40 and belleville 37 is housed in a recess 44 machined in the first ring member 27 which has an entry chamfer 44a.

When the clutch is in the fully engaged clamp condition the left hand end 27a of the first ring member 27 abuts face 41a of attachment flange 41 so that the diaphragm spring 37 is contained in an almost flat condition between the end 43 of tube 40 and the bottom 45 of the recess 44 in first ring member 27. This accurately controls the bias supplied by the belleville spring 37 when the clutch is in the clamped condition. When the clutch is in the fully undamped condition the belleville spring 37 may come clear of the recess 44 and is guided back into the recess by chamfer 44a when the clutch is re- clamped.

If desired two belleville springs may be used in the arrangement shown in figure 5. In such an arrangement the bellevilles will contact each other at their inner periphery and the outer edge of the right hand belleville, as viewed in figure 5, will sit in the top corner of the recess 44 in the first ring member 27.

The arrangement shown in figure 5 is a particularly simple and efficient manner to incorporate the present invention in a drive clutch of the type specified since the only additional components necessary are the flanged tube 40, the screws 42 and the belleville 37.

As shown in figure 5 a series of wire springs 46 are provided which act against the pressure plate 22 and have ends 46a hooked over the clamping members 24 so as to tend to bias the toggle linkage in a direction to disengage the clutch once the linkage has moved through the over centre position in the disengaging direction. These springs 46 are also present in the arrangement of figures 1 and 3 but are not visible in the drawings.

Claims

1. A clutch which comprises:- a driving plate clamped against a driven plate by a pressure plate under action of over-centre toggle linkage,

the reaction force of the clamping member on the abutment applying an axial load on the linkage which tends to hold the link in the engaged position,

the clutch being characterised in that a bias means is provided which applies an axial bias force to the linkage which is in opposition to but lower than the axial load on the linkage resulting from the reaction of the clamping member on the abutment when the clutch is in an unworn condition so that the clutch remains engaged, the reaction force and axial load decreasing as the clutch wears up to a point where the axial bias force exceeds the axial load at which point the clutch is disengaged by the bias force or some other indication that adjustment of the clutch is required occurs.

2. A clutch according to claim 1 in which the bias means comprises one or more belleville springs which are compressed when the link is in the engaged position to provide the axial bias force.

3. A clutch according to claim 1 or 2 in which the toggle linkage includes a first axially displaceable ring member which surrounds an output shaft driven by the clutch and on which are mounted a plurality of generally radially extending links each connected to a respective clamping member, the bias means acting axially on the ring member to move the ring member and hence the connected links between their engaged and disengaged positions.

4. A clutch according to any one of claims 1 to 3 in which the axially fixed abutment is adjustable and comprises a second ring member which surrounds and is in screw- threaded engagement with an output member to which the output shaft and the or each driven member is rotationally fast, the axial position of the abutment being adjusted by rotating the second ring member about the output member in order to increase the clamp load when the clutch driving plates or driven members wear.

5. A clutch according to claim 3 or 4 in which the first ring member which supports the links contacts the second ring member when the links are in the engaged position and the bias means is sandwiched between the ring members with a pre-determined amount of compression of the bias means.

6. A clutch according to claim 3 or 4 in which the first ring member which supports the links contacts a component carried by the second ring member when the links are in the engaged position and the bias means is sandwiched between the component and the first ring member with a predetermined amount of compression of the bias means.

7. A clutch according to any one of claims 1 to 5 in which the bias means additionally or alternatively operates a warning device to alert a supervisor that the clutch is in need of adjustment.

8. A clutch of the type specified constructed and arranged substantially as hereinbefore described with reference to and as shown in figures 1 and 2 or 3 or 5 of the accompanying drawings.