GB2191252A

GB2191252A - Friction clutch

Info

Publication number: GB2191252A
Application number: GB08613384A
Authority: GB
Inventors: David Roger Arrowsmith; John Pius Burke
Original assignee: Automotive Products PLC
Current assignee: Automotive Products PLC
Priority date: 1986-06-03
Filing date: 1986-06-03
Publication date: 1987-12-09
Also published as: GB8613384D0

Abstract

A wet friction clutch assembly has a reaction plate (22) and a pressure plate (25) with a driven plate (38) interposed therebetween, the reaction plate (22) and the pressure plate (25) being drivingly interconnected and free to move axially relative to one another. Application means (50) comprising an annular piston is provided for moving the pressure plate (25) towards the reaction plate (22) to clamp the driven plate (38) therebetween, said application means (50) acting against the pressure plate (25) through resilient means (70) in order to provide a progressive application of a clamping load to the driven plate (38). The means (70) may comprise a Belville spring and this spring may engage an annular spring plate (72) of relatively light spring rate. <IMAGE>

Description

SPECIFICATION Friction clutches The present invention relates to friction clutches and in particular to wet friction clutches.

Conventionally, wet friction clutches include a driven plate with friction material secured to the faces thereof. Said driven plate is sandwiched between a reaction plate and pressure plate which are drivingly interconnected. Normally the reaction plate and pressure plate will have sufficient clearance to permit rotation thereof relative to the driven plate, the friction linings of the driven plate being lubricated by hydraulic fluid such as oil or transmission fluid.

To engage the clutch, the pressure plate may be moved towards the reaction plate, by for example hydraulic means, to clamp the driven plate therebetween, so that drive may be transmitted from the pressure plate/reaction plate assembly to the driven plate.

With this form of clutch, only a small amount of movement of the piston is required to go from a position in which the pressure plate and reaction plate are free to rotate relative to the driven plate to a position in which the driven plate is fully clamped. As a result, engagement of drive upon actuation of the clutch is substantially instantaneous, imposing great stresses on the drive train and producing a violent engagement of drive.

The present invention provides a wet friction clutch which is able to achieve a smooth engagement of drive.

According to one aspect of the present invention, a wet friction clutch assembly comprises; a reaction plate adapted to be mounted for rotation with a driving component; a pressure plate drivingly interconnected and spaced axially of the reaction plate, said pressure plate being movable axially with respect to the reaction plate; a driven plate interposed between the reaction plate and the pressure plate, said driven plate being adapted to be mounted on a driven component in a manner which is capable of transmitting torsional loads while permitting axial movement therebetween; application means arranged to move the pressure plate towards the reaction plate and clamp the driven plate therebetween; and resilient means interposed between the application means and the pressure plate to provide a progressive transmission of load from the application means to the pressure plate.

The resilient means may comprise a single spring element which will give a substantially linear increasing clamping load. Alternatively, two or more spring elements of different spring rate may be used in series, to increase the rate at which the clamping load is increased in two or more stages.

An embodiment of the invention is now described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a part-sectional side elevation of a clutch assembly formed in accordance with the present invention; and Figure 2 is a section along the line ll-ll in Fig. 1.

The clutch illustrated in Figs. 1 and 2 is a multi-plate double clutch by means of which a pair of output shafts 16, 17 may be connected, either separately or together, to a single input shaft 13.

The clutch includes a housing 10 formed from two dished formations 11 and 12. One formation 11 is formed integrally of an input shaft 13, said shaft having a splined formation 14 for engagement by drive means (not shown). The other formation 12 has a central aperture 15 through which extend a pair of coaxial output shafts 16 and 17, the end of the inner shaft 16 engaging a spigot bearing 18 on the formation 11. A bearing formation 19 is provided around the central aperture 15 in formation 12, so that the housing 10 may be supported rotatably on a non-rotational structural element 20.

The two formations 11 and 12 are bolted together by means of a number of angularly spaced bolts 21, an annular reaction plate 22 being interposed between the two formations 11 and 12, so that it is drivingly interconnected therewith and extends radially inwardly of the housing 10.

The components of the clutches interconnecting shafts 16 and 17 to shaft 13 are substantially identical, being positioned on opposite sides of the reaction plate 22. In the accompanying drawings and the following description, the same reference numerals have been used for similar components.

First and second annular pressure plates 25 and 26 are positioned coaxially on both sides of the reaction plate 22. Each of the pressure plates 25 and 26 is connected to the housing 10 by means of three flexible drive straps 27 positioned symmetrically about the periphery of the pressure plate 25, 26. The drive straps 27 are connected between lugs 28 on the periphery of the pressure plates 25, 26 and formations 29 on the housing 10. Apertures 30 are provided in the peripheral wall 31 of the housing 10 to provide a clearance for the lugs 28 and drive straps 27 and also provide the formations 29. The drive straps 27 provide a tangential drive connection between the cover 10 and pressure plates 25 and 26 and also locate the pressure plates 25 and 26 coaxially in spaced relationship to the reaction plate 22 while also permitting limited axial movement therebetween.

Internally splined hubs 35 are mounted on splined portions 36 of the shafts 16 and 17, so that torsional loads may be transmitted to the shafts 16, 17 from the hubs 35, while permitting limited axial movement of the hubs.

Each hub 35 has a radially outwardly extending flange 37. A first annular driven plate 38 is attached to the flange 37 by means of a series of angularly spaced rivets 34, so that it extends radially outwardly from the flange 37 and between the reaction plate 22 and first pressure plate 25. Friction linings 39 are secured on each side of the driven plate 38, to the portion thereof sandwiched between the reaction plate 22 and pressure plate 25.

A radially outwardly extending support member 40 having an axially extending cylindrical flange portion 41 which is disposed radially inwardly of the first and second pressure plates 25 and 26, is also attached to the flange 37 by means of rivets 34. Splined formations 42 are provided externally of the cylindrical flange portion 41. A second annular driven plate 43 with corresponding splined formations 44 on its internal diameter, is mounted on the cylindrical flange portion 41 so that torsional loads may be transmitted to the support member 40 and via hub 35 to shafts 16, 17, while the driven plate 43 is free to move axially relative to the support member 40, hub 35 and the first driven plate 38.The second driven plate 43 extends radially outwardly between the first pressure plate 25 and second pressure plate 26 and friction linings 39 are secured to each side of the driven plate 43, to the portions thereof sandwiched between the first and second pressure plates 25 and 26.

An annular piston 50 is slidingly sealed with respect to and supported on axial formations 51 and 52 on the associated dished formations 11, 12 so as to define a working chamber 53. An inlet 54 is provided to this working chamber 53 by means of which fluid under pressure may be introduced into the working chamber 53 to force the piston 50 away from the end wall of the associated formations 11, 12. Fluid connection is made to the inlet 54, by means of a stationary slip ring arrangement 55 (only one illustrated) which is sealed to the associated rotating components 12, 13 by means of a pairof seals 56 positioned axially of one another on either side of the inlet 54.

An annular support plate 60 is mounted on the axial formation 51 and is retained thereon by circlip 61. An annular bearing 62 is provided around the outer periphery of the support plate 60 and this engages an axial formation 63 on the piston 50, to guide movement of the piston 50 axially of the associated formation 11, 12. A series of angularly spaced compression springs 64 act between the support plate 60 and piston 50 to urge the piston 50 towards the end wall of the associated formations 11, 12, so as to return the piston 50 towards the end wall when fluid pressure in the working chamber 53 is removed. Formations 65 are pressed into the support plate 60 to maintain the springs 64 in position.

Vents 66 are provided in the formation 51 in order to prevent pressure build-up in the space between the piston 50 and support plate 60.

A belville spring 70 engages in a recess 71 in the outer periphery of piston 50, the inner periphery of spring 70 abutting against the piston 50 and its outer periphery being displaced clear of the piston 50 towards the pressure plate 26. This belville spring 70 engages an annular spring plate 72 of relatively light spring rate, which abuts against the second pressure plate 26 and is supported on an axially extending surface 73 on piston 50 so that it is slidable axially with respect to said surface 73.

The clutch assembly described above would be located within, for example a gearbox housing having a wet sump, so that the housing 10 is at least partially immersed in oil or transmission fluid and upon rotation of the housing 10, the reaction plate 22, pressure plates 25 and 26 and driven plates 38 and 43 will be wetted by the oil or transmission fluid.

In operation, the clutches will normally be de-energised, no fluid pressure being applied to the working chambers 53. The springs 64 will thus force pistons 50 back against the end wall of the associated formations 11, 12.

In this condition, there will be no, or only very light, loading between the pressure plates 25 and 26 and the driven plates 38 and 43 sandwiched therebetween. The reaction plate 22 and pressure plates 25 and 26 will consequently be free to rotate relative to the driven plates 38 and 43, and there will be no transmission of drive from shaft 13 to either of shafts 16 or 1 7. The friction linings 39 are lubricated by the oil or transmission fluid, so that even if they rub against the pressure plates 25 and 26 and reaction plate 22, wear of the friction linings 39 will be minimised.

To engage transmission between the input shaft 13 and one or both of the output shafts 16 and 17, the appropriate one or both of pistons 50 are energised by introduction of fluid under pressure into the working chamber 53. Movement of the pistons 50 away from the end wall of the associated formations 11, 12 is transmitted to the second pressure plate 26 via belville spring 70 and spring plate 72 until the pressure plates 25 and 26 and driven plates 38 and 43 are tightly clamped against the reaction plate 22. As the piston 50 moves away from the end wall of the associated formations 11, 12 the belville spring 70 and spring plate 72 will be gradually deformed, thus providing a progressive increase in the clamping load and producing a smooth engagement of drive. The spring plate 72 being of low spring rate will deform first, giving an initial relatively low rate of increase in clamping load, and only after the spring plate 72 is fully deformed against the second pressure plate 26 will the belville spring 70 begin to deform, giving a higher rate of increase in clamping load. In this manner, the change in clamping load with movement of piston 50 and thus rate of takeup of drive, may be designed as required for the particular application.

Various modifications may be made without departing from the invention. For example, while a multi-plate double clutch is described above, the invention is applicable to any form of wet clutch. Furthermore, application means other than hydraulic pistons may be used to engage the clutch. Alternative forms of spring element may also be used to transmit the clamping load from the application means to the pressure plate.

Claims

1. A wet friction clutch assembly comprising a reaction plate adapted to be mounted for rotation with a driving component; a pressure plate drivingly interconnected and spaced axially of the reaction plate, said pressure plate being movable axially with respect to the reaction plate; a driven plate interposed between the reaction plate and the pressure plate, said driven plate being adapted to be mounted on a driven component in a manner which is capable of transmitting torsional loads while permitting axial movement therebetween; application means arranged to move the pressure plate towards the reaction plate and clamp the driven plate therebetween; and resilient means interposed between the application means and the pressure plate to provide a progressive transmission of load from the application means to the pressure plate.

2. A wet friction clutch according to Claim 1 in which the resilient means comprises a spring element which acts between the application means and the pressure plate.

3. A wet friction clutch assembly according to Claim 1 or 2 in which the resilient means comprises a plurality of spring elements of different spring rate which act in series between the application means and the pressure plate.

4. A wet friction clutch assembly according to Claim 2 or 3 in which the spring element is in the form of a belville spring.

5. A wet friction clutch assembly according to Claim 4 when taken with Claim 3, in which the belville spring acts against an annular spring plate.

6. A wet friction clutch assembly according to Claim 4 or 5 in which the application means comprises an annular piston, the outer periphery of said piston radially overlapping the pressure plate, said belville spring being located in a recess in the outer periphery of the piston, so that in its unstressed condition, the inner periphery of the belville spring abuts against the piston and its outer periphery is displaced clear of the piston towards the pressure plate.

7. A wet friction clutch assembly according to Claim 6 in which an annular spring plate is interposed between the Belleville spring and the pressure plate, said spring plate abutting the pressure plate, its inner periphery being supported on a formation on the piston so that it is

7. A wet friction clutch assembly according to Claim 6 in which an annular spring plate is interposed between the belville spring and the pressure plate, said spring plate abutting the pressure plate, its inner periphery being supported on a formation on the piston so that it is slidable axially with respect to said formation.

8. A wet friction clutch assembly substantially as described herein with reference to, and as shown in, Figs. 1 and 2 of the accompanying drawings.

CLAIMS Claims 4-7 above have been deleted or textually amended.

4. A wet friction clutch assembly according to Claim 2 or 3 in which the spring element is in the form of a Belleville spring.

5. A wet friction clutch assembly according to Claim 4 when taken with Claim 3, in which the Belleville spring acts against an annular spring plate.

6. A wet friction clutch assembly according to Claim 4 or 5 in which the application means comprises an annular piston, the outer periphery of said piston radially overlapping the pressure plate, said Belleville spring being located in a recess in the outer periphery of the piston, so that in its unstressed condition, the inner periphery of the Belleville spring abuts against the piston and its outer periphery is displaced clear of the piston towards the pressure plate.