GB2165321A

GB2165321A - Friction clutch cover assembly

Info

Publication number: GB2165321A
Application number: GB08519365A
Authority: GB
Inventors: Guy Keith Osborne
Original assignee: Automotive Products PLC
Current assignee: Automotive Products PLC
Priority date: 1984-10-03
Filing date: 1985-08-01
Publication date: 1986-04-09
Also published as: GB8519365D0; GB8424890D0; GB2165321B

Abstract

A diaphragm spring clutch cover assembly 2 for a clutch, which additionally comprises a driven plate 8 and a driving plate 4 formed by a fly-wheel, is provided with a diaphragm spring 40 which acts on a pressure plate 38 through a force amplifier formed by a plurality of hydraulic jacks disposed in annular array about the clutch axis X. Each jack consists of a respective chamber 26 in which small and large pistons 32 and 34 work. <IMAGE>

Description

SPECIFICATION Friction clutch cover assembly This invention concerns a friction clutch cover assembly for a clutch which comprises in combination said cover assembly and a driven friction plate and a rotatably driven driving member so that transmission of driving torque from the driving member to the driven plate can be effected consequent to clamping the driven plate between pressure plate means and the driving member.

The cover assembly concerned may be used in a clutch for a motor vehicle, or in any transmission.

Diaphragm spring friction clutches are known in which the annular driven friction plate is keyed to rotate an input shaft to a gear-box of a motor vehicle, one side of the driven plate being adjacent to a side of the driving member formed, for example, by a flywheel fast with a crank-shaft of an internal combustion engine of the vehicle. The clutch has a cover assembly including a casing secured to the fly-wheel to rotate therewith, an annular pressure plate adjacent to the other side of the driven plate and mounted to rotate with the casing but movable relatively there to axially of the pressure plate, an annular discshaped diaphragm spring held to rotate with the cover and acting adjacent to an outer periphery of the spring on the pressure plate. The spring is constrained between first and second fulcrum rings which are on either side of the spring.The spring is highly stressed to provide (when the clutch is engaged) the necessary loading to cause strong clamping of the driven plate between the pressure plate and fly-wheel to ensure efficient torque transmission to the driven plate. When the clutch is to be disengaged pushing force towards the flywheel is applied to the inner periphery of the spring causing the outer periphery of the spring to swing away from the fly-wheel and so relieve the clamping pressure on the pressure plate. This pushing force must be strong because the spring is highly stressed, and in consequence, via the casing, the fly-wheel experiences a strong pushing force causing undesirable and potentially damaging loading of the crank-shaft. Furthermore since the spring is highly stressed it has a lower life expectancy than a lesser stressed softer spring.

An object of the invention is to provide a clutch cover assembly which can be constructed so that when used in a clutch can achieve strong clamping of the friction plate, when the clutch is engaged, using a less stressed softer spring than would hitherto have been necessary to achieve the same clamping and can reduce the load applied to the driving member when the clutch is disengaged.

According to the invention there is provided a friction clutch cover assembly for a clutch which comprises in combination said cover assembly and a driven friction plate and a rotatably driven driving member so that transmission of driving torque from the driving member to the driven plate can be effected consequent to clamping the driven plate between pressure plate means and the driving member, said cover assembly comprising a cover mounted or for mounting to rotate with the driving member, said cover mounting spring means and pressure plate means movable relatively to the cover and force transmitting means to receive an input force derived from the spring means and in response give an output force for urging the pressure plate means whereby, when the clutch comprising the cover assembly is in use, the driven plate is clampable between the driving member and the urged pressure plate means under a clamping force which is a function of said output force, and said force transmitting means comprising hydraulic jack means providing force amplifying means whereby said output force is greater than said input force.

Since the force amplifying means provides a greater output force than the input force derived from the spring means the same clamping force on the friction plate can be achieved using weaker less stressed spring means than hitherto, with the attendant advantage of less loading on the driving member at clutch disengagement.

The spring means may be a diaphragm spring.

The invention will now be further described, by way of example, with reference to the accompanying drawing which is a fragmentary and diagrammatic cross-sectional view of a friction clutch cover assembly formed in accordance with the invention, and included in a clutch.

In the drawing the clutch cover assembly 2 forms part of a diaphragm spring friction clutch in which the driven driving member is a fly-wheel 4 fast with a crank-shaft (not shown) of an internal combustion engine of a motor vehicle, the fly-wheel being rotated about axis X. Adjacent to annular side face 6 of the fly-wheel is a driven annular friction plate 8, which can be of any construction known per se, provided with facings 10 and 12 of friction material, for example carbon/carbon. The friction plate is secured to a central hub 14 splined at 16 to drivingly engage the vehicle's gear box input shaft (not shown) which also rotates about axis X.

The cover assembly 2 has a cover formed by an end plate 18 and an annular side wall 20 clamped to each other and to the fly-wheel 4 using a circular array of spaced bolts 22.

The annular side wall 20 is centred on axis X and has a radially inwardly extending rib 24 formed with a plurality of chambers 26 (for example, sixteen) which are disposed in a cir cular array centred on axis X and are substantially equi-angularly spaced apart about the axis. Each chamber 26 is stepped with a substantially cylindrical chamber portion 28 opening to a substantially cylindrical chamber portion 30, wherein transversely to the axis X the chamber portion 30 has a greater crosssectional area than the chamber portion 28. In each chamber two pistons 32 and 34 slide in fluid tight manner in the respective chamber portions 28 and 30, seals being provided at 31 and 33. The chamber space between the pistons is occupied by liquid 35.Thus each chamber 26 and its respective pistons form an hydraulic jack in which the effective piston area of end face 32A of piston 32 is less than the effective piston area of end face 34A of piston 34. The jacks, which are substantially similar, act as a force amplifier in which an input force propelling each piston 32 into the corresponding chamber 26 produces an increased output force propelling the piston 34 outwardly of the chamber.

The wall 20 and pistons 32 and 34 may be of metal, for example aluminium.

Beyond rib 24, the pistons 34 (which can have a recessed or cup-shaped cross-section as shown) abut an annular pressure plate 36 adjacent to the friction facing 12. This pressure plate had a plurality of peripheral notches 38 engaged by lugs (not shown) on the wall 20 to rotate the pressure plate with the cover 18, 20. The pressure plate 36 may be of metal, for example titanium.

The cover assembly has an annular diaphragm spring 40 which can be of a kind known per se in which slots (not shown) radiate from its central opening 42 some distance towards its outer periphery. The diaphragm spring 40 is held on the cover end plate 18 by a circular array of bolts 44. These cooperate with distance sleeves 46 and fulcrum rings 48 and 50 between which the spring 40 is constrained under stress so that in the clutch engaged attitude shown in the drawing the diaphragm spring presses at or adjacent to its outer periphery on narrow end or fulcrum portions 51 on the pistons 32. This input force is amplified by the jacks so that under the effect of the increased output force on pistons 34 pushing the pressure plate 36 the driven plate 8 is clamped between the pressure plate and the fly-wheel 4.

The clutch is disengaged in known manner using a release bearing 52 moved leftward in the drawing to push the inner part of the diaphragm spring 40 causing the outer periphery of the diaphragm to swing rightwards thus relieving the diaphragm spring loading on the pistons 32. Consequently other springs (known per se, but not shown) can move the pressure plate 36 rightwards to clear the driven plate 8.

In a modification the pistons 34 may be formed integrally with the pressure plate 36 or otherwise mounted fast therewith if desired.

The chambers 26 may have any desired cross-sectional shape and naturally the pistons 32 and 34 are appropriately shaped to work in such chambers. For example, instead of the chambers 26 being of substantially circular cross-section each chamber may be elongated in the circumferential direction of the clutch cover assembly so that the chamber may be arcuate in cross-section about the axis X.

In a modification the individual chamber portions 30 can be replaced by a single annular chamber portion encircling the axis X and containing a single annular piston instead of the separate pistons 34 and/or the individual chamber portions 28 can be replaced by a single annular chamber portion containing a single annular piston instead of the separate pistons 32, provided the rib 24 is formed with sufficient material extending radially in the form of circumferentially spaced supporting struts holding the radially inner portion 24A of the rib 24 on the radially outer portion 24B.

Claims

1. A friction clutch cover assembly for a clutch which comprises in combination said cover assembly and a driven friction plate and a rotatably driven driving member so that transmission of driving torque from the driving member to the driven plate can be effected consequent to clamping the driven plate between pressure plate means and the driving member, said cover assembly comprising a cover mounted or for mounting to rotate with the driving member, said cover mounting spring means and pressure plate means movable relatively to the cover and force transmitting means to receive an input force derived from the spring means and in response give an output force for urging the pressure plate means whereby, when the clutch comprising the cover assembly is in use, the driven plate is clampable between the driving member and the urged pressure plate means under a clamping force which is a function of said output force, and said force transmitting means comprising hydraulic jacks means providing force amplifying means whereby said output force is greater than said input force.

2. A cover assembly as claimed in Claim 1, in which the pressure plate means and cover are rotatable about a first axis which when the cover assembly is mounted on the driving element substantially coincides with the axis of rotation of the driving member, said hydraulic jack means being disposed about said first axis.

3. A cover assembly as claimed in Claim 2, in which the hydraulic jack means comprises a plurality of hydraulic jacks arrayed about the first axis, each jack comprises a chamber with first and second piston means movable in the chamber and liquid occupying space in the chamber between the first and second piston means, said first piston means having an effective piston area exposed to said liquid which is less than an effective piston area of the second piston means exposed to the liquid, the first piston means being acted upon by the input force and the second piston means transmitting said output force.

4. A cover assembly as claimed in Claim 3, in which the spring means applies input force directly to the first piston means.

5. A cover assembly as claimed in Claim 3 or Claim 4, in which the pressure plate means is acted on by or is fast or integral with said second piston means.

6. A cover assembly as claimed in any one preceding claim, in which the spring means is a diaphragm spring.

7. A friction clutch cover assembly for a clutch which comprises in combination said cover assembly and a driven friction plate and a rotatably driven driving member so that transmission of driving torque from the driving member to the driven plate can be effected consequent to clamping the driven plate between pressure plate means and the driving member, said cover assembly being substantially as hereinbefore described with reference to the accompanying drawing.

8. A friction clutch comprising a cover assembly as claimed in any one preceding claim in combination with said driving member and pressure plate means.

9. A clutch as claimed in Claim 8, in which the driving member is a fly-wheel.

10. A friction clutch substantially as hereinbefore described with reference to the accompanying drawing.

11. A motor vehicle having a friction clutch as claimed in any one of Claims 8 to 10.