GB2272501A - Friction clutch driven plates with variable hysteresis - Google Patents

Abstract

A friction clutch driven plate having a friction facing carrier 14 mounted on a hub 11 with damping springs 15, 48 operating in two stages to resist rotation of the carrier 14. First stage friction damping means 40 acts, between the carrier 14 and hub 11, during the initial angular relative rotation. To produce variable hysteresis the first stage damping means 40 has raised areas (52, fig 8) on either side plate 41 or side plate 42, both fixed to the carrier 14, which rub across raised areas (62, 63, fig 6) on flange 43 when the flange 43, which is fixed to the hub 11, rotates relative to the side plates 41, 42. The flange 43 is biased into contact with the side plates 41, 42 by a spring washer 27. Deformation of the flange 43, which may be moulded from a flexible resilient material eg nylon, takes place as the flange 43 moves relative to the side plates 41, 42. The first stage damping means is assembled with the main damper as a pre-built unit. <IMAGE>

Description

FRICTION CLUTCH DRIVEN PLATES This invention relates to friction clutch driven plates, and in particular, but not exclusively, to friction clutch driven plates for use on vehicles.

In a typical motor vehicle the engine is connected to the vehicle gearbox via a friction clutch which includes a fly wheel and pressure plate connected to the engine, and between which is sandwiched a driven plate which is connected to the gearbox.

A friction clutch driven plate typically comprises a hub which is splined onto the gearbox input shaft, a co-axial friction facing carrier plate mounted on the hub and capable of limited angular rotation about the hub, and springs housed in aligned apertures in a flange connected to the hub and the carrier plate, to act between the hub and carrier plate to restrain said angular rotation. The facing carrier plate is connected to the vehicle flywheel through the friction facings.

In some vehicles when the engine is idling and there is no torque load passing through the clutch driven plate the irregular impulses from the vehicle engine can be transmitted to the gearbox and cause gearbox idle chatter.

Solutions to overcome this problem have involved the use of multi-stage spring damping in which the movement between the friction facing carrier plate and the hub flange is dampened by main or second stage damping springs and the hub flange is free to rotate through a limited angular movement relative to the hub drive and is restrained in this movement by a very low rate first stage torsional damping spring or springs. The hub flange can oscillate around the hub when the vehicle is idling with only the first stage damping springs operating to suppress any transmission of vibrations to the gearbox.

These very low load impulses passing through the driven plate can also be dampened by use of a low rate friction damping means which is operated only in conjunction with the first stage damping.

Accordingly there is provided a friction clutch driven plate comprising a hub, a friction facing carrier mounted on the hub and capable of limited angular rotation around the hub, and a friction damping means operating between the carrier and the hub for an initial period of angular rotation of the carrier around the hub, said friction damping means comprising a flange means rotationally fast with one of the carrier or hub, and a pair of side plates rotationally fast with the other of said carrier or hub, said flange being biased into frictional engagement with one of the side plates and wherein said one side plate has raised areas thereon which make frictional contact with raised areas on the adjacent surface of the flange means, the hysteresis effect of the frictional contact varying as the raised areas on said one side plate move across the raised areas on the flange means.

The invention will be described by way of example and with reference to the accompanying drawings in which: FIG 1 is an elevation of a clutch driven plate according to the invention, FIG 2 is a section on the line II-II of Fig. 1, FIG 3 is a pre-built first stage damping unit as used in Fig. 1, FIG 4 is a section on the line IV-IV of Fig. 3, FIG 5 is a centre flange from the first stage damping unit viewed from one side, FIG 6 is the centre flange of Fig. 5 viewed from the other side showing the low spots in dark shading, FIG 7 is a graph of torque versus angular displacement for the driven plate, FIG 8 is an elevation of a side plate from the first stage damper unit showing the raised radial ribs, FIG 9 is a section on the line IX-IX of Fig. 8, and FIG 10 is a graph of hysteresis versus angular displacement for the first stage damper unit only.

With reference to Fig. 1 and Fig. 2 there is illustratged a friction clutch driven plate for a motor vehicle and which comprises a hub 11 having internal splines 13 for connection with a gearbox input shaft and an annular array of circumferentially spaced teeth 20 extending radially outwards on the outer surface of the hub 11. A coaxial annular flange 12 having spaced annular notches 30 in its inner peripheral margin is mounted on the hub 11 concentrically with the teeth 20 so that the teeth 20 loosely engage with the notches 30 allowing the flange 12 limited angular movement about the hub 11. A coaxial friction facing carrier 14 is also mounted on the hub 11 and is capable of limited angular movement relative to both the flange 12 and the hub 11.A set of main torsion damping springs 15 are housed in aligned apertures 16 and 17 in the hub flange 12 and facing carrier 14 respectively, and act to restrain the angular movement therebetween. Although the number of springs illustrated is a preferred six springs, there is no reason why other number of springs cannot be used, for example between four springs and eight springs. The main torsion damping spring provide a resistance to relative rotation of into 25 da Nm.

The annular facing carrier 14 comprises an annular carrier plate 18 located to one axial side of the flange 12, and an annular retainer plate 19 disposed on the other axial side of the flange 12. The two annular plates 18 and 19 are secured together by three stop pins 21 which pass through co-operating apertures 22 in the outer peripheral margin of the flange 12. The stop pins 21 limit the rotational movement of the facing carrier 14 about the hub 11 and flange 12 by abutment against the radial ends of the apertures 22.

A plurality of segments 23 are arranged in a circular array and are attached to the outer peripheral margin of the carrier plate 18 by any suitable means such as rivets, and a pair of opposed annular friction facings 24 are secured one on each side of the segments 23 by suitable means such as rivets. The segments 23 typically are of spring steel and are shaped to provide resilient axial cushioning between the two friction facings.

The carrier plate 18 and consequently the flange 12 are supported for rotational movement about the hub 11 by a flanged bush 25, preferably of nylon, which is rotationally fast with the carrier plate. A friction damping washer 26 is located axially between the' hub flange 12 and the carrier plate 19 and is biased against the hub flange by a spring washer 27, which acts between the hub flange 12 and the side plate 41 of a first stage torsion damping unit to be described in greater detail later. The bush 25 is made rotationally fast to the facing carrier 14.

The main damping springs 15 are housed in the aligned apertures (sometimes referred to as spring windows) 16, in the hub flange 12, and apertures 17 in the carrier plate 18 and retainer plate 19. The spring windows 16 and 17 have circumferential ends that are contactable with the ends of the springs 15 during the rotational movement of the carrier 14 around. the hub 11 to compress the springs 15.

The teeth 20 on the hub 11 are engaged in the notches 30 on the inner peripheral margin of flange 12 so that the flange 12 is capable of limited angular rotation around the hub 11. The angular rotation of the flange 12 around the hub 11 being limited in both directions of rotation by abutment of teeth 20 with the circumferential ends of the notches 30.

The rotational movement between the flange 12 and the hub 11 is resisted by an initial damping spring sometimes called a first stage damping unit 40 more clearly illustrated in Figs 3 and 4.

The first stage damping unit 40 is pre-built sub-assembly which is an independant rotary coupling in its own right and which is added to the remainder of the driven plate as a pre -tuned and pre-tested unit.

The first stage damping unit is of a similar construction to the main damping unit of the driven plate and comprises a central flange means 43 having lugs 44 on its inner periphery for engagement with splines or slots 45 on the outer surface of the hub 11 so that flange is rotationally fast with the hub 11 and is free to move axially . A pair of side plates 41 and 42 are fastened together by pins 46, preferablly four pins, and are free to rotate relative to the flange means 43. The side plates 41 and 42 are made rotationally fast to the flange 12 by three axial tabs 47 on the plate 4 that engage in slots on the radially inner edge of the hub flange spring windows 16.

Four low rates first stage damping springs 48 are housed in spring apertures or windows 49, 51, in the flange means 43 and side plate 41 and 42 respectively (see ,Figs 5, 6, 8, and 9). These low rate springs 48 provide a resistance to rotation of up to 1 da NM.

The springs 48 may all have the same springs rating or not as is desired and can all be brought into operation simultaneously or may be phased in at different dwell angles, again as is desired. In this case at least two spring an under a pre load condition to return the hub 11 to an at-rest position relative to the hub flange under no load conditions ( no torque loads on the friction facings The side plate 41 which engages the hub flange 12 is shown in greater detail in Figs 8 and 9. The plate 41 on its surface adjacent the flange means 12 has eight raised surface portions in the form of radial ribs 52.

These radial ribs 52 are angularly spaced so as to engage raised co-operating surfaces on the adjacent surface of the flange means 43.

Now with reference to Figs 5 and 6 the flange means 43 is shown in Fig 5, viewing the side adjacent the side plate 42. There are four angularly spaced spring windows 49 and stop pin apertures 54 to allow for the limited angle rotation of the side plates 41, 42 relative to the flange means 43 against the resistance of the springs 48.

As viewed from its side adjacent the side plate 41, as shown in Fig 6, the flange means 43 has a surface comprising raised surface portions and low surface portions. The low portions are shown as shaded areas.

The raised surface portions comprise a radially inner set of eight raised surface portion 62 which are angularly spaced to be in alignment with the eight raised ribs 52 on the plate 41 in the 'at rest' condition, and a set of eight radially outer raised surface portions 63 which are circumferentially offset from the inner raised portions 62, and are located outwardly of the spring windows 49, and stop pin apertures 54. The flange means 43 is formed from nylon, preferably nylon 66 and all these raised areas can be formed in a single moulding operation.

In the first stage damping unit the plate 41 is biased towards the flange means 43 by a wavy washer 64 located between the flange means 43 and the side plate 42 at the outer peripheral margin thereof.

The pre-built first stage damper unit is arranged in the driven plate in annular space around the hub 11 between the hub flange 12 and the retainer plate 19.

The side plate 42 is arranged to fit concentrically within the centre of the retainer plate and is in axial alignment therewith.

When the pre-built unit is placed into position, the wavy washer 17 is first located on the hub flange 12 and the three tabs 47 on the plate 41 are each located in their respective slot in the radially inner edges of hub flange spring windown 16. Washers or spaces 66 are then placed over the plate 42 and are located between the side plate 41 and the retainer plate 19 and act to transmit the loading from the wavy washer spring 27 via the retainer plate 19 onto the friction washers 26.

The operation of the driven plate will now be explained and for the sake of simplicity the operation of the hysterises control for first stage damper unit will be explained separately.

Now also with reference to Fig. 1 and Fig 7 with the hub 11 held stationary and drive load applied to the friction facing 2, the facing carrier 14 is moved anti-clockwise as shown by arrow A in Fig. 1. Since carrier 14 and flange 12 are held rotationaly fast by the main tension damping springs 15, the flange 12 will move initially relative to the hub 11 to take up the lost motion linkages between the teeth 20 and notches 30. Since the plates 41 and 42 are held fast in the flange 12, and the flange means 43 is held fast to the hub 11, the initial resistance to rotational movement is due to the friction damping generated by the bush 25 on the hub 11 and flange 12, and by the first stage damping unit 40.In the first period of rotation the springs 48 are compressed between the ends of the spring windows 49 and 51 and come on in phased stages A and B as the side plates 41 & 42 rotate relative to the flange means 43.

When the lost motion movement between the teeth 20 on the hub 11 and the notches in the flange has been taken up, point C on Fig. 7, further anit-clockwise movement causes the compression of the main torsion springs 15 between the end of the respective flange spring windows 16 and the opposed friction carried spring windows 17. The movement will contine until the stop pins 21 abut the ends of the hub flange apertures 22 and the torsion drive becomes solid, this shown in portion D of the graph.

As the carrier 14 rotates around the hub 11 and flange 12 some friction hysterises will be generated by the friction washers 26 and the spaces 66.

If the torque drive load is now decreased the facing carrier 14 rotates clockwise releiving the torque springs 15, which are still held in compression. The friction damping generated by the friction washer 26 and spaces 66 still operates, and a reverse movement down the graph takes place. As the driven plate returns to the at rest state the springs 15 become relaxed. However there is some pre-load on the first stage damper springs 48 so as to return the hub 11 to a predetermined position relative to the hub flange. The drive load passes through the origin of the graph as the driven plate goes into an overdrive or overun condition.

In the overdrive condition, the hub 11 is still held stationary and the friction facing continues its relative clockwise movement. Since the teeth 20 are slightly offset relative to the notches 30, the first period of rotation , during which the only resistance to rotation of the carrier 14 around the hub 11 is due to the first stage damping springs 48 and the friction damping caused by rotation of the bush 25 on the hub ll,is of a lesser angular period than for the drive condition . This is shown by the portion E of the graph.

When the teeth 20 abut the ends of the notches 20, at point F the flange 12 is now held stationary relative to the hub 11 and the main torsion spring 15 and friction washer 26 and spacers 66 come into operation. This is the portion G of the graph. This clockwise movement will continue until the stop pin 21 abut the ends of the hub flange apertures 22 and the torque drives goes solid.

If the overdrive torque load is now decreased, the facing carrier 14 moves anti-clockwise relative to the hub relieving the main torque springs 15 and then the first stage damping springs.

It will be appreciated that because the first stage spring damping has a so much smaller resistance load than the main torsion damping that the hysterises generated in first stage damper is insignificant in comparision torque capacity of the driven plate.

The generation of the friction hysterisis in the first stage damping unit will now be explained.

As the plate 41 rotates relative to the flange means 43 the raised ribs 52 on one plate 41 each move across their respective radially inner raised portion 62 which is shaped so that the ribs encounter increasing resistance to the rotational movement. This may also result in some resilient distortion of the nylon flange means 43. This is position S of the graph in Fig. 10.

At the end of a predetermined relative angular movement, the load exerted by the ribs 52 is transfered from the inner raised portions 62, to the outer raised portions 63. At this movement of transfer at point T there is a slight fall off in hysterises but this builds up again as further rotation takes place. Since the friction contact is now radially further out than before the maximum value is increased due to effect of an increased moment of force. This is shown at 'U' in Fig. 10. It is thought possible that the inherent elastic resilience in the flange means 43 also adds to the hysterises effect , as does the relative tangential movement of the ribs 52 across the raised surfaces 62 and 63.

Claims (9)

Claims

1. A clutch driven plate comprising a hub, a friction facing carrier mounted on the hub and capable of limited angular rotation around the hub, and a friction damping means operating between the carrier and the hub for an initial period of angular rotation of the carrier around the hub, said friction clamping means comprising a flange means rotationally fast with one of the carrier or hub, and a pair of side plates rotationally fast with the other of said carrier or hub, said flange means being biased inte frictional engagement with the side plates and wherein said one side plate has raised areas thereon which make frictional contact with raised areas on the adjacent surface of the flange means, the hysteresis effect of the frictional contact varying as the raised areas on said one side plate move across the raised areas on the flange means.

2. A clutch driven plate as claimed in Claim 1 characterised in that the raised areas on the flange means are divided into radially inner raised areas, and radially outer raised arena which are circumferentially off set from the inner raised areas, and the frictional contact changes from the inner areas to the outer areas after a predetermined angular rotation of the carrier to the hub to give two distinct stages of hysteresis.

3. A clutch driven plate as claimed in Claim 1 or Claim 2, wherein the raised area on the one side plate are in the form of angularly spaced radial ribs.

4. A clutch driven plate as claimed in Claim 3 when dependant upon Claim 2 characterised in that the radial ribs are in alignment with the radially inner raised portion in the at rest condition, and as the side plates rotate relative to the flange means the friction contact between the radial ribs and the raised portion changes from contact with the inner raised portion to contact with the outer raised portions to give two distinct stages of hysteresis.

5. A clutch driven plate as Claimed in Claim 4, wherein said flange means has eight radially inner raised surface portions, and four radially outer surface portions and there are eight radial ribs on said one side plate.

6 A clutch driven plate as Claimed in any one of Claims 1 to 5 wherein said flange means is a moulding.

7. A clutch driven plate as claimed in any one of claims 1 to 6 wherein said flange means is formed from a a flexible resilient material that allows the flange means to deform as the side plates move relative to the flange means.

8. A Clutch diven plate as-Claimed in any one of claims 1 to 7 wherein the flange means is rotationally fast with the hub and the side plates are rotationally fast with the friction facing carrier.

9. A clutch driven plate as claimed in any one of Claims lto 8 wherein the falnge means and side plates are part of a first stage torsion damping unit.