A FRICTION CLUTCH

Abstract: A motor vehicle multiplate clutch utilises friction facings (14, 16) formed from carbon/carbon compositions. The facings (14, 16) have drive notches (34) on the inner or outer peripheries thereof. In order to improve the wear resistance of the notches (34) the drive surfaces (35, 36) of the notches are coated in a metallic layer (32), which is deposited by electroless plating techniques.

Description: A FRICTION. CLUTCH The present invention relates to friction clutches for motor vehicles, and in particular but not exclusively to multiplate friction clutches. A known multiplate friction clutch comprises a cover having a plurality of friction facings, comprising a plurality of drive plates rotationally fast with the cover and a plurality of driven plates which are rotationally fast with a hub and which are located between the drive plates. The drive plates and driven plates are annular plates formed from a carbon/carbon composition and typically have notches or slots formed in one of the inner and outer peripheries for engaging rotationally fast with either the cover or the hub for rotational movement with the respective cover or hub. The drive surfaces of the notches in the friction facings are subject to wear. *1 Carbon/carbon friction facings are machined to -shape,- and one means of overcoming the problem is to redensify the carbon/carbon facings after machining by CVD techniques (carbon vapour deposition) , and remachine the friction surfaces to obtain the required friction propoerties, whilst leaving the densified drive surfaces. This is an expensive process requiring specialist carbon fibre manufacturing equipment. Accordingly there is provided a motor vehicle clutch annular friction facing formed from a carbon/carbon composition and having drive notches on at least one of its inner and outer peripheries in use for rotational engagement with a clutch member, the drive surfaces of said notches being coated in a metallic layer by plating a layer of metal thereon to provide a wear resistant metallic layer bonded to the carbon/carbon facing to be integral therewith. The metal is preferably a coating of an electroless deposition of metal, preferably electroless nickel, which may or may not include additives such as PTFE, and the electroless nickel may be further plated using electro deposition techniques to apply a further layer of metal, preferably chromium plating, or may be further coated by the deposition of electroless nickel with additives. Also according to the invention there is provided a method of manufacture of a carbon/carbon friction clutch drive plate having drive notches on at least one of the inner or outer peripheries thereof, wherein the drive surfaces of the drive notches are coated in a metallic layer by plating a layer of metal thereon using electroless plating techniques. Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which:- Fig 1 is an elevation of a clutch cover assembly according to the invention; Fig 2 is a section on line II-II of Fig 1. Fig 3 is a plan view of a driven plate for use in multiplate. Fig 4 is a section on line IV-IV of Fig 3^ Fig and Fig 6 are plan views of driven plates for use in a multiplate clutch. A multiplate clutch assembly, particularly of the type used in racing cars, comprises a cover 10 which in use is mounted on a flywheel (not shown) and a hub 12 mounted on a gearbox input shaft (not shown). Four annular drive plates 14 are mounted on the cover 10 such that they can slide axially along it but are rotationally fast with it. Three annular driven plates 16 are mounted on the hub 12 such that they can slide axially along it but are rotationally fast with it. The drive plates 14 and the driven plates 16 overlap such that they can frictionally engage to transmit torque between the cover 10 and hub 12. The plates 14 and 16 are formed from a carbon-carbon composition. A pressure plate 18 engages the drive plate furthest from the flywheel, and at least one diaphragm spring 20 is mounted on the cover such that it reacts between the cover 10 and the pressure plate 18 to urge the drive plates 14 and driven plates 16 towards the flywheel. In this case there are two diaphragm springs mounted one on top of the other. Each diaphragm spring 20 has an outer annular section having radially inwardly projecting spring fingers 21 thereon. There are sixteen spring fingers 21 which are spaced circumferentially apart with apertures between adjacent pairs of spring fingers at the base of the spring fingers. The springs 20 are mounted on the cover 10 between a first fulcrum 22 and a second fulcrum ring 24 which is fixed to the cover by bolts 30. The hub has a plurality of circumferentially spaced radially outwardly extending teeth or spokes 25 that engage in notches 34 on the inner periphery margin 35 of a driven plate 16. A driven plate 16 is shown in Figs 3 and 4 and comprises an annular carbon/carbon disc having a plurality of notches 34 engageable with the teeth or spokes 25 on the hub (as previously described). The notches 34 have drive surfaces 35,36 that engage the hub teeth 25. The surface of each notch 34 including the drive surfaces 35,36 is coated in a metal layer 37 (only three shown for convenience). The plate has radially outer friction surfaces 38 for engagement with the drive plates 1 . A drive plate 14 is shown in Fig 5 which has drive teeth 44 on its outer periphery spaced by notches 45 for engaging the clutch cover 10. Again the d rive surfaces of the notches and teeth are coated in a metallic layer. The plates 14 has a radially inner friction surface 48. An alternative design of drive plate 114 is shown in Fig 6. In this embodiment notches 155 in the outer peripheral margin of the facing are larger and more widely spaced. The drive surfaces 156, 157 are again coated with a metal layer. The carbon/carbon facings 14,16/114, are coated by electroless plating of the whole facing preferably electroless nickel plating but copper plating could be used. If desired the friction faces of the facings could be masked. The electroless nickel . coated facing could be heat treated at about 300-400 degrees centigrade to harden the nickel coating. Alternatively the electroless nickel is coated by chrome plating in the conventional manner by electro deposition. Other coatings such as nickel alloys or electroless nickel containing additives in suspension such as PTFE (polytetra-fluro ethylene) , the so called Niflor (trade mark of Surface Technology pic, Coventry, England) process, could be plated onto the electroless nickel . Because of the pourous nature of the carbon/carbon facings the electroless nickel is absorbed into the surface of the facing especially any exposed radial and circumferential surfaces. The plating or coating is then machined from the friction surfaces of the drive plates and driven plates. Alternatively the areas to be left free of plating can be masked during the plating process.

Claims: CLAIMS 1. A motor vehicle clutch annular friction facing formed from a carbon/carbon composition and having drive notches on at least one of its inner and outer peripheries in use form rotational engagement with a clutch member, the drive surfaces of said notches being coated in a metallic layer by plating a layer of metal thereon to provide a wear resistant metal layer bonded to the carbon/carbon facing to be integral therewith. 2. A friction facing as claimed in Claim 1 wherein a layer of electroless nickel is deposited on the drive surfaces, and the electroless nickel being hardened by heat treatment. 3. A friction facing as claimed in Claim l r wherein the electroless metallic layer has a further metallic layer thereon which is deposited thereon. 4. A friction facing as claimed in Claim 3 wherein the electroless metallic layer comprises electroless nickel and the further metallic layer, deposited thereon by electro chemical deposition techniques. 5. A friction facing as claimed in Claim 3 wherein the electroless metallic layer is electroless nickel and the further metallic layer is a layer of PTFE filled electroless nickel. 6. A method of manufacture of a carbon/carbon friction clutch drive plate having drive notches on at least one of the inner or outer peripheries thereof, wherein the drive surfaces of the drive notches are coated in a metallic layer by plating a layer of metal thereon using electroless plating techniques. 7. A method as claimed in Claim 6, wherein the electroless nickel layer is further coated by a further second metallic layer containing additives which is also deposited thereon using electroless plating techniques.

Inventors: NASH IAN ANTONY, SIMMONDS ROBERT ANTONY, NASH, IAN, ANTONY, SIMMONDS, ROBERT, ANTONY
Applicants: AUTOMOTIVE PRODUCTS PLC, NASH IAN ANTONY, SIMMONDS ROBERT ANTONY
Application year: 1993
Main classification: F16D13
IPC codes: F16D13, F16D69