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Patent Searching and Data


Title:
FRICTION DEVICE
Document Type and Number:
WIPO Patent Application WO/2006/002471
Kind Code:
A1
Abstract:
A friction device (1) of a brake or clutch assembly, the friction device has at least one support member (4, 5) supporting a heat transfer material (7) and a friction material, the friction material provides at least one friction surface (8, 9) arranged to contact a cooperating at least one friction element of said assembly, and wherein the heat transfer material has a thermal conductivity higher than that of the support member and includes a layer thereof sandwiched between the at least one support member and the friction material. A further portion is formed as a plurality of heat transfer elements extending through the at least one support member, each said element having a portion thereof exposed to atmosphere, and the heat transfer elements are connected together by the layer for dissipating heat to atmosphere generated in said friction material adjacent said layer during operation of said brake or clutch assembly.

Inventors:
HOOPER GREGORY JOHN (AU)
Application Number:
PCT/AU2005/000965
Publication Date:
January 12, 2006
Filing Date:
June 30, 2005
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
HOOPER GREGORY JOHN (AU)
International Classes:
F16D13/72; F16D65/78; F16D69/04; (IPC1-7): F16D13/72; F16D65/78; F16D69/04
Foreign References:
JPH07224868A1995-08-22
DE19754740A11999-03-11
JPH11148525A1999-06-02
JPH06288827A1994-10-18
Attorney, Agent or Firm:
WATERMARK PATENT & TRADEMARK ATTORNEYS (Hawthorn, VIC 3122, AU)
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Claims:
THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:
1. A friction device of a brake or clutch assembly, the friction device having at least one support member supporting a heat transfer material and a friction material, wherein the friction material provides at least one friction surface arranged to contact a cooperating at least one friction element of said assembly, and wherein the heat transfer material has a thermal conductivity higher than that of the support member and includes a layer thereof sandwiched between the at least one support member and the friction material, and a further portion formed as a plurality of heat transfer elements extending through the at least one support member, each said element having a portion thereof exposed to atmosphere, and wherein said heat transfer elements are connected together by said layer for dissipating heat to atmosphere generated in said friction material adjacent said layer during operation of said brake or clutch assembly.
2. The device according to claim 1 , wherein all of the heat transfer elements are connected together by a common layer of the heat transfer material.
3. The device according to claim 1 or 2, wherein the at least one support member includes first and second support members including respective first and second layers of heat transfer material, and wherein the plurality of heat transfer elements extend through the first and second support members to thermally connect together the first and second layers of heat transfer material, and wherein an intermediate portion of each of said heat transfer elements is exposed to the atmosphere.
4. A device according to any one of the preceding claims, wherein the heat transfer material and/or the friction material are/is selected from copper, copper alloy, iron, steel, alloy steel, stainless steel, nickel, nickel alloy, cobalt, cobalt alloy, chrome, chrome alloy, molybdenum, molybdenum alloy, aluminium, aluminium alloy, titanium, titanium alloy, silicon, boron, carbon, or a combination thereof.
5. The device according to ant one of the preceding claims, wherein the heat transfer elements are in the form of plates, tubes or bars extending into the atmosphere through and from a respective said at least one support member.
6. The device according to any one of the preceding claims being a brake rotor or disc for a vehicle.
7. The device according to any one of the preceding claims, wherein the at least one support member is two support members forming disc members disposed laterally adjacent one another and connected together by support means.
8. The device according to claim 7, wherein the support means are plates either cast with the disc rotor or welded in place.
9. The device according to any one of the preceding claims, wherein the heat transfer material is formed by a thermal spray process, cold spray process, impregnated mats, liquid suspension, plate or shim which is cut, rolled or machined to the desired dimensions by an electroplating method.
10. A method of producing a friction device for a brake or clutch assembly, including the steps of: a) providing a support member having at least one peripheral face and a plurality of heat transfer elements which extend through and from the support member into the atmosphere surrounding the friction device; b) applying a layer of heat transfer material to the support member such that the heat transfer material is in direct or indirect contact with said at least one peripheral face; c) applying a layer of a friction material to said support member such that said friction material is in direct or indirect contact with said at least one peripheral face; d) bonding the heat transfer material and friction material to the support member; wherein, the friction material provides a friction surface of the friction device for contact with a friction element during operation of the assembly, and wherein the heat transfer material and elements have a higher thermal conductivity than the support member or friction material and act to dissipate to atmosphere heat generated in the friction device during operation of the brake or clutch assembly.
11. The method according to claim 1 , wherein the heat transfer material is applied to the peripheral face prior to applying the friction material.
12. The method according to claim 10 or 11 , wherein the heat transfer material and/or the friction material are/is applied by a thermal spray process, cold spray process, or in the form of impregnated mats, liquid suspension, electroplating, or as a plate or shim that is cut, rolled or machined to predetermined dimensions.
13. The method according to any one of claims 10 to 12, wherein the step of applying the heat transfer material and/or the friction material also provides the bonding.
14. The method according to any one of claims 10 to 13, wherein when the friction and heat transfer materials are in the form of impregnated mats, the friction material mat is applied to the peripheral face, with the heat transfer material mat applied on top thereof to form a sandwich, and the bonding step includes allowing the heat transfer material to permeate or infiltrate the friction material such that a layer of heat transfer material bonds to the peripheral face and to the elements, and a layer of friction material is produced to form the friction surface.
15. The method according to any one of claims 10 to 14, wherein the bonding step is by furnace brazing at a temperature high enough to melt the heat transfer material whilst bonding.
16. The method according to any one of claims 10 to 14, wherein the heat transfer material and/or the friction material are applied by thermally or cold spraying onto the support member.
17. The method according to any one of claims 10 to 16, wherein the heat transfer material and friction material are applied in a combined application step by blending two powders together in predetermined proportions, or by mixing during application.
18. The method according to any one of claims 10 to 17, wherein heat transfer material is subjected to a brazing process step to bond the material to the support member.
19. The method according to claim 18, wherein the friction material applied onto the heat transfer material via a laser cladding process.
Description:
FRICTION DEVICE TECHNICAL FIELD The present invention relates to brake and clutch system. In particular, the present invention relates to friction components, such as brake rotor, brake drum or clutch plates for use respectively in brake or clutch systems. BACKGROUND OF THE INVENTION A common problem associated with brake and clutch systems, is the dissipation of heat generated during the translation of rotational energy into heat energy. Thermal stresses subjected to the components of brake or clutch systems can create several problems. For example, steels and irons normally used for such systems may undergo an unwanted volume change and/or display checking or cracking due to the high temperatures generated in operation. In addition, the frictional coefficient of components can decrease leading to a corresponding decrease in operation efficiency. With the ever increasing speed and power of motor vehicles, trains and aircraft, the demands on the brake and clutch systems have also increased. The types of materials currently used in brake and clutch systems have been found to be inadequate where high thermal stresses are present. For example, cast iron, steel and cast steel are often the materials of choice, however, these materials undergo relatively large volume change and tend to store heat generated during operation of the clutch or brake system. Carbon composite materials have been considered as an alternative, particularly where high performance is required, such as, for brake rotors in some aircraft and formula-1 racing vehicles. However, their widespread use has been limited due to their high expense, and for operational efficiency at lower temperatures. Ceramic materials have also been considered, however, these materials are also very expensive and thus, do not find widespread application, and also do not have the efficiency of iron and steel materials at lower operating temperatures. A major problem identified with friction devices used in brake and clutch systems is heat and the need to dissipate that heat generated during operation. For example, during braking in a brake system, heat generated can cause major problems, such as excessive wear, distortion, bearing failure, brake fade, thermal stress, and even complete system failure. With specific regard to brake systems, previous attempts have been made to dissipate heat generated during operation more quickly by adopting larger discs or rotors, thus providing a greater volume of material to act as a heat sink, ventilated discs and cross drilling to assist in the transfer of heat to the atmosphere to cool the disc or rotor. Other attempts have been to adopt ceramic rotors or even ceramic coatings applied to iron or steel rotors to address the problem of heat generated. However, such an arrangement does — protect the rotor and bearings from excessive heat build-up, rather, many results in the heat generated being transferred to other brake components, such as, brake linings (pads or shoes etc.), callipers or pistons, and brake fluid. An additional problem associated with ceramic coatings is that they are applied via a thermal spray process which relies on a mechanical bonding mechanism of the ceramic coating to a base material. Although the bond strength between the ceramic coating and the underlying base material can be high (approximately 5,000 to 10,000 psi or 34.5 MPa to 70 MPa) they have been known to spall when operating in harsh environments or extreme operating conditions, especially when there are differences in the coefficient of thermal expansion between the ceramic coating and the base material. Traditional materials, such as cast iron, steel and cast steel, used in brake and clutch devices have relatively low thermal conductivity. The thermal conductivity of a material is equivalent to the quantity of heat that passes in unit time through unit area of a plate, when it's opposite faces are subject to unit temperature gradient (e.g., 10C temperature difference across a thickness of one unit). Known values for the thermal conductivity of cast iron, steel and cast steel brake and clutch devices are 30 to 50 Wm"1 K"1. A known prior art device which attempts to alleviate the aforementioned problems known in the art is disclosed in US 3,391 ,763, This document discloses a brake disc having a surface coating of copper, silicon carbide composition, and a number of heat transfer elements which are in thermal contact with the surface coating and which extends through the material of the disc to have an end thereof disposed to the air surrounding the disc to help dissipate heat generated in the surface coating during braking. The heat transfer elements are formed from copper and are generally cylindrical in shape and with a tapered head. The cylindrical body portion of each heat element is received in a bore formed in a respective brake disc. A portion of the cylindrical body extends into an air gap between adjacent discs. Thus, a large number of bores are required in each disc to provide sufficient additional cooling of the disc (see Figures 1 and 2), however, the large number of bores and their corresponding heat transfer elements required in each disc have been found to greatly degrade the structural strength of the disc, particularly in a direction normal to the friction surface, which direction will receive clamping forces from brake pads during braking operations. The reduced structural integrity due to the large number of bores, exacerbated by the difference in coefficient of thermal expansion between the material (copper) of each heat transfer element and the material of the disc (steel or iron), can cause structural failure of the disc. Furthermore, the present Applicant has found that the bond strength and cohesive strength of flame sprayed coatings, such as proposed by US 3,391 ,763 are not sufficient to withstand the cyclic heating and compressive loads produced in friction braking. The Applicant has found that flame sprayed coatings tend to delaminate, thus increasing the risk of the (copper) heat transfer elements falling out of their respective bores, potentially leading to catastrophic failure of the disc. Furthermore, the applicant has found that when copper is applied as a coating via a thermal spray method as proposed by US 3,391 ,763 the porosity and oxides formed in the coating greatly reduce the thermal conductivity of the coating, to the extent that there is no increase in the thermal conductivity of the coating when compared to the base material. In addition, US 3,391 ,763 requires a molybdenum bond layer between the base material of the disc and the silicon carbide copper matrix friction material in order for the flame sprayed friction material to bond to the base material of the disc. With the aforementioned in mind, it is an object of the present invention to provide a rotational friction device of a brake or clutch assembly which exhibits improved heat dissipation characteristics whilst maintaining high structural integrity. SUMMARY OF THE INVENTION With the aforementioned in mind, the present invention provides a friction device of a brake or clutch assembly, the friction device having at least one support member supporting a heat transfer material and a friction material, wherein the friction material provides at least one friction surface arranged to contact a cooperating at least one friction element of said assembly, and wherein the heat transfer material has a thermal conductivity higher than that of the support member and includes a layer thereof sandwiched between the at least one support member and the friction material, and a further portion formed as a plurality of heat transfer elements extending through the at least one support member, each said element having a portion thereof exposed to atmosphere, and wherein said heat transfer elements are connected together by said layer for dissipating heat to atmosphere generated in said friction material adjacent said layer during operation of said brake or clutch assembly. Thus, advantageously, the present invention provides a friction device of a brake or clutch assembly which is able to more evenly and efficiently dissipate generated heat to the atmosphere during operation by sharing thermal loads between heat transfer elements forming heat sinks due to their interconnection through a common layer of the same heat transfer material. Preferably, all of the heat transfer elements are connected together by a common layer of the heat transfer material. Thus, the entire heat load received by the layer of heat transfer material is shared by all of the heat transfer elements and is thus more regularly dissipated through the friction device to the atmosphere, which helps to alleviate thermal stresses in the friction device which may otherwise be present due to more uneven heat dissipation. Preferably, the at least one support member includes first and second support members including respective first and second layers of heat transfer material, and wherein the plurality of heat transfer elements extend through the first and second support members to thermally connect together the first and second layers of heat transfer material, and wherein an intermediate portion of each of said heat transfer elements is exposed to the atmosphere. Thus, thermal loads present in one support member can be shared and dissipated through connection of the heat transfer elements and further layer of heat transfer material in another support member to assist in overall cooling and reduction of heat. Furthermore, mechanical support provided by the interconnection of heat transfer elements, layers and support members can assist in providing increased structural integrity of the friction device. Preferably, the heat transfer material is copper and/or copper alloy. However, iron, steel, alloy steel, stainless steel, nickel, nickel alloy, cobalt, cobalt alloy, chrome, chrome alloy, molybdenum, molybdenum alloy, aluminium, aluminium alloy, titanium, titanium alloy, silicon, boron, carbon and combination thereof are envisages as heat transfer materials provided the thermal conductivity of the heat transfer material is higher than that of the material of the corresponding support member. Preferably, the friction material includes iron, steel, steel alloy, stainless steel, nickel, nickel alloy, cobalt, cobalt alloy, chrome, chrome alloy, molybdenum, molybdenum alloy, copper, copper alloy, aluminium, aluminium alloy, titanium, titanium alloy, silicon, boron, carbon, ceramics, cermets, carbides, borides, nitrides, oxides or any combination thereof. Preferably, the heat transfer elements are in the form of plates, tubes or bars extending into the atmosphere through and from a respective at least one support member. Preferably, the friction device is a brake rotor or disc for a vehicle, including two support members forming disc members disposed laterally adjacent one another and connected together by support means. Preferably the support means are in the form of plates which may be cast with the disc rotor or welded in place. Preferably the support means are equally spaced between adjacent discs, and the spaces there between may include in some or all whereof one or more of the plurality of heat transfer elements extending between the discs. Thus, the heat transfer elements can provide a number of cooling ventilation plates, preferably made from copper and/or copper alloy, aluminium and/or aluminium alloy, and/or metal matrix composite, and/or carbon fibre reinforced carbon matrix composites to act as heat sinks conducting the heat generated, away from the friction surface of the respective friction material to where it is subjected to the cooling effect of the surrounding air. The number of support means and cooling vents, bar or tubes can vary depending on the strength of thermal dissipation required. Preferably, the heat transfer material is formed as a layer by a thermal spray process, cold spray process, impregnated mats, liquid suspension, electroplating, plate or shim which is cut, rolled or machined to the desired dimensions. Preferably, the layer covers the entire face of the friction material opposite the friction surface thereof. A further aspect of the present invention provides a method of producing a friction device for a brake or clutch assembly, including the steps of: a) providing a support member having at least one peripheral face and a plurality of heat transfer elements which extend through and from the support member into the atmosphere surrounding the friction device; b) applying a layer of heat transfer material to the support member such that the heat transfer material is in direct or indirect contact with said at least one peripheral face; c) applying a layer of a friction material to said support member such that said friction material is in direct or indirect contact with said at least one peripheral face; d) bonding the heat transfer material and friction material to the support member; wherein, the friction material provides a friction surface of the friction device for contact with a friction element during operation of the assembly, and wherein the heat transfer material and elements have a higher thermal conductivity than the support member or friction material and act to dissipate to atmosphere heat generated in the friction device during operation of the brake or clutch assembly. Preferably the heat transfer material may be applied to the peripheral face prior to applying the friction material. For example, the heat transfer material may be applied by a thermal spray process, cold spray process, or in the form of impregnated mats, liquid suspension, electro-plating, or as a plate or shim that is cut, rolled or machined to pre-determined dimensions. Preferably, the step of applying the heat transfer material and/or the friction material also provides the bonding. Whilst it is envisaged that application steps b) and c) may be consecutive steps, alternatively, and particularly in the case of impregnated mats, the friction material and heat transfer material may be applied at the same time. For example, a friction material mat and heat transfer material mat may be first brought together and subsequently applied together on the peripheral face. Alternatively or in addition, the friction material mat may be placed on the peripheral face first, with the heat transfer material mat placed on top thereof. In this form of the invention it will be appreciated that the friction material mat is sandwiched between the peripheral face of the support member and the heat transfer material. Subsequent bonding of the mats to the peripheral face allows the heat transfer material to permeate or infiltrate the friction material such that a layer of heat transfer material bonds to the peripheral face and to a plurality of the elements, and a layer of friction material is produced to form the friction surface. The bonding process may be a furnace brazing process at a temperature high enough to melt the heat transfer material whilst bonding eg metallurgical bonding to the support member. The heat transfer material and/or the friction material may be applied to and/or bonded to other portions of the support member as well as the peripheral face(s). Preferably, the heat transfer material and/or the friction material may be sprayed eg thermally or cold spray technique onto the support member. For example, the heat transfer material may be a copper or copper alloy powder spray applied on the peripheral face and optionally onto further portions of the support member. The friction material may subsequently be thermally sprayed onto and to mechanically bond with the previous layer of heat transfer material. Alternatively, or in addition, the heat transfer material and friction material may be applied in a combined application step, for example, by blending two powders (powdered heat transfer material and friction material) together in predetermined proportions, or by mixing during application e.g. at a spray outlet using two powder feeders. A particular advantage of using twin powder feeders is the ability to change the proportions of friction material to heat transfer material during application. For example, proportions of 9:1 heat transfer material to friction material may initially be applied, with subsequent blending or discrete stepping during the application process to a 1 :9 mix at the outer surface of the friction face. A subsequent brazing process may then be carried out to metallurgicaly bond the layers together and to the support member. Preferably, after the deposition of the heat transfer material, the friction device is subjected to a brazing process to bond the material to the support member and optionally the cooling plates, vanes or vents. The friction material may subsequently be applied via a laser cladding process, which process allows larger particulates eg of oxides, carbides, borides etc to form than can be achieved with thermal spraying techniques. The size and percentage of particulates present in the friction material can be controlled during the laser process to provide a desired coefficient of friction at the friction surface. In the case of the heat transfer material and friction material being preformed plates, shims or similar layers, a suitable braze material may be applied between the material of the support member and the heat transfer material (shim etc), and/or between the heat transfer material and the friction material (shim etc) prior to the (furnace) brazing process. Preferably, the friction device is a brake rotor, brake disc, or drum brake of a motor vehicle, e.g., car, motorbike, truck. However, it is envisaged that the friction device according to one or more forms of the present invention may be in the form of a clutch plate of a clutch assembly. The skilled addressee will appreciate that both brake assemblies and clutch assemblies are devices which need to dissipate heat generated in converting rotational energy into heat energy. Thus, applications of the present invention are envisaged that are analogous between brake and clutch assemblies. Any combination of the abovementioned processes and arrangements are envisaged, without limitation to the scope of the invention, in order to obtain the final desired result. Further features and advantages of the present invention will be described or become apparent to the skilled addressee in the course of the following details description. BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more clearly understood, the preferred embodiments thereof will now be described in detail by way of example, with references to the accompanying drawings, though without limitation to the scope of the invention, in which: Figure 1 shows a sectional view through part of a ventilated disc rotor according to an embodiment of the present invention. Figure 2 shows a partial sectional view of a ventilated brake disc according to an embodiment of the present invention, including tube type heat transfer elements interspersed between support veins or vents. Figure 3 shows an exploded view of a fabricated brake disc according to an embodiment of the present invention. Figure 4 shows a further exploded view of an alternative fabricated brake disc according to another embodiment of the present invention. Figure 5 shows a perspective view of a brake drum according to a further embodiment of the present invention. Figure 6 shows a partial sectional view through part of the brake drum shown in Figure 5. Figure 7 shows a partial view of a motorcycle brake disc according to a further embodiment of the present invention. DESCRIPTION OF PREFERRED EMBODIMENTS Figure 1 shows a sectional view through part of a ventilated brake disc 1. The disc 1 includes dual friction faces 2, 3, each arranged for frictional contact with a corresponding brake pad of the brake assembly (not shown). Pressure is applied by the opposing brake pads to the surfaces 2, 3 of the disc 1 to effect braking. The disc 1 includes first and second support members 4, 5. The support members 4, 5 are mechanically connected together via number of support webs 6a, 6b, 6c, 6d etc., the first and second support members and the supporting webs are cast together as a single unit. However, it is envisaged that the disc may be fabricated from individual support members and webs, for example, by welding or brazing the webs into place. Each support member 4, 5 provides a disc base upon which is bonded a copper or copper alloy heat transfer material 7. The heat transfer material has a higher thermal conductivity than the underlying base material of each support member. For example, the support members may be formed by casting or fabricating steel or iron. The ventilated disc 1 has outer faces 2, 3 having corresponding outer friction materials forming friction surfaces 8, 9 thereof. The friction surfaces 8, 9 make contact with the brake pad material during braking. When in operation, with the brake pad applying pressure to each of the friction surfaces 8, 9, heat is generated which needs to be dissipated. The copper or copper alloy layers 7 sandwiched between the friction material of each respective friction surface 8, 9 and the respective support member 4, 5 is able to rapidly conduct heat from the friction material and transfer this through direct contact with the heat transfer elements 6a to 6n forming the webs of the same material. As the disc rotates (into the plane of the page) through the atmosphere, heat is given up by the webs 6a to 6n to the air. If thermal loads are higher in one surface (8 say) then the other (9 say), the high conductivity of the heat transfer material and thus of the webs helps to share the heat load, and therefore helps to dissipate the heat more rapidly, than would otherwise be the case if the layers of heat transfer material on respective support members 4, 5 were not connected. Furthermore, due to the layer of heat transfer material on each support member, heat is more readily dissipated within each disc face. Thus, corresponding forms of the present invention are able to increase the thermal conduction of heat generated at the friction surface(s) of such friction devices by materials with high thermal conductivity through the support structure of the friction device where the heat can be dissipated into the surrounding atmosphere. It is also envisaged that one or more of the present invention are able to apply a friction surface that can be tailored for different coefficient of friction requirements and increase the operational life of the friction device dramatically. The friction device may be manufactured (fabricated) or cast from a suitable support material such as steel, iron, stainless steel, nickel, nickel alloy, cobalt, cobalt alloy, aluminium, aluminium alloy, titanium, titanium alloy, copper or copper alloy. Although Figure 1 shows the friction device in the form of a ventilated brake disc, it will be appreciated that solid disc or drum devices can be constructed in accordance with the present invention. The selection of the material to be used depends upon the environment, cost and weight requirements for a particular application and do not limit the scope of the present invention. Figure 2 shows a portion of a brake disc or rotor 20. In particular, the view shown is a side view of a part of a ventilated brake disc. Thus, it will be appreciated that a similar, but opposite face, view would be apparent if looking from the other side back towards the disc 20. Between each disc plate 21a (21b not shown) extend a number of support vents or veins 22. These vents or veins 22 are either cast or fabricated with the disc plates to connect and support the disc structure. The vents or veins 22 also help to provide air flow and ventilation during rotation of the disc 20. Extending between and through the disc plates 21a, 21b are copper or copper alloy tubes 23. These tubes 23 provide the heat transfer elements which are in contact with a layer of heat transfer material (not shown) within each disc plate. Thus, each disc plate is able to share, heat load and transfer heat load to the copper or copper alloy tubes 23 which are cooled in the air flowing between the vents or veins 22 during rotation of the disc 20. It will be noted that spacing between adjacent vents or veins 22 narrows from the outer edge 24 of the disc 20 towards the inner edge 25 of the disc. As the disc rotates, and under braking where heat is generated, air flow speeds up through the narrowing channel formed by adjacent vents or veins 22, and subsequently provides forced cooling air flow over the spaced copper tubes. It will be appreciated that although the embodiment shown includes copper or copper alloy tubes, these may be solid bars or plates as required for a particular application. Alternatively, a copper or copper alloy honeycomb providing a large surface area is envisaged. Figure 3 shows a fabricated form of a brake disc. The brake disc 30 includes a series of consecutive support vents or veins 31 connected to a pair of parallel disposed support plates 32. Between each support vent or vein 31 is disposed a copper or copper alloy vent or vein plate 33. The support plates 32 are constructed from steel, iron, stainless steel, nickel, nickel alloy, cobalt, cobalt alloy, aluminium, aluminium alloy, titanium, titanium alloy, copper or copper alloy. The support plates are cut, machined to the desired dimensions, thickness, inside diameter and outside diameter may vary depending on the finished size of the friction device required to achieve the desired braking efficiency, strength of thermal dissipation. Slots or holes are cut and/or machined in the support plates equally spaced there around. The number, size, radius, shape and angle of the slots and/or holes can vary depending on the finished size, braking efficiency and thermal dissipation required. Support ventilation vents or veins 31 are constructed to fit into the slots or holes in the two support plates, joining them together as one unit. It will be appreciated that the support vents or veins may be bars or tubes or a combination of plates bars or tubes. A number of cooling ventilation vents or veins 33 are constructed from copper and/or copper alloy, and/or aluminium and/or aluminium alloy, and/or metal matrix composite, and/or carbon fibre reinforced carbon matrix composites, to act as heat sinks to conduct the heat generated away from the friction surfaces to where it is subjected to the cooling effect of the surrounding air. A number of support vents or veins 31 and cooling vents or veins 33 can vary depending on the strength of thermal dissipation of the disc required. The support vents or veins 31 and then welded to the support plates 32. Preferably welding is performed via a low heat input process like lazer welding and/or electron beam welding to minimise distortion and to help achieve full penetration welds for strength purposes. Alternatively, it is envisaged that furnace brazing processes with a requirement of high strength fully brazed joints may be utilised. Alternatively, the disc may be cast with, the support vents or veins 31 integral to the cast, and subsequently accommodation for the cooling vents or veins 33 can be achieved afterwards. A layer of heat conductive material 34 having a high thermal conductivity, preferably a copper and/or copper alloy material, is then applied as a solid shim or plate to the peripheral (outer) face of each support plate 32 and in intimate contact with the cooling heat transfer vanes, plates, tubes or bars 33. Alternatively, this can be achieved by a suitable thermal spray process, cold spray process, impregnated mats, liquid suspension, or by an electro plating method. In the embodiment shown, a plate or shim of friction material 35 is subsequently applied to the shim 34. The entire disc is then brazed to bond the layers 34,35 to the base disc material forming the support plates 32. Thus, the brazing process bonds the shims 34,35 to the disc and thereby also bonds the heat transfer shim 34 to the heat transfer elements 33 (vents, vanes, tubes bars) creating permanent contact between the heat transfer shim 34 and the elements 33 across the surface of the disc which greatly assists in evenly spreading heat throughout the disc which helps to avoid hot spots, thermal stresses and potential disc failure by more efficiently transferring and dissipating heat. The support vents 31 may also be coated with the heat transfer copper material also. Figure 4 shows an alternative form of the present invention wherein impregnated mats 44,45 are used to apply the friction and heat transfer materials at the same time. In particular, this is achieved by using impregnated mats of the friction material 44 which are laid on to the support plate 42 face first with the heat transfer material impregnated mats 45 on top ie on the outside. The friction device with the mats in position is then subjected to a furnace brazing process at a temperature high enough to melt the heat transfer material which infiltrates the friction material whilst at the same time metallurgically bonding to the base support material and the cooling plates, bars or tubes 43. The heat transfer material on the outside is able to permeate the friction material such that a high proportion of the heat transfer material bonds directly to the support plates 42 of the disc and a corresponding high proportion of the friction material translates to the outer surface of the disc to form the friction surface. For example, the friction material 44 may be a carbide mat. Where a thermal spray, or cold spray process is used the high conductivity heat transfer material, preferably a copper or copper alloy powder, is applied to both of the support plate faces so as to mechanically bond to the base material as well as to the cooling vents or veins. The friction material powder can then be thermally sprayed to mechanically bond to the previously deposited layer. The heat transfer material and the friction material can also be applied in one operation by first blending the two powders together in the desired percentages, or by mixing the powders at the thermal spray torch by using two powder feeders. A benefit of using two powder feeders is the ability to change the percentage of friction material to heat transfer material as it is being applied to the support plates. For example, it is possible to start off with say 90% heat transfer material powder and 10% friction material, and alter these proportions to end up with say 10% friction material and 90% heat transfer material at the friction surface. The coated device is then subjected to a furnace brazing process to metallurgically bond all of the layers together as well as to the support plates and to the cooling plates, bar or tubes. An alternative process to achieve the desired result is after deposition of the heat transfer material, the device is subjected to a brazing process to metallurgically bond the heat transfer material to the support plate material and the cooling plates, bars or tubes. The friction material can subsequently be applied by a laser cladding process which allows the addition of larger particulates of oxides, carbides, borides, etc., than can otherwise be achieved with a thermal spray process. The size and percentage of the particulates will greatly affect the coefficient of friction of the applied surface. Where the layers are in the form of a plate or shim, a suitable braze material should be applied between the support plate material and the copper or copper alloy heat transfer layer, and/or between the heat transfer layer and the friction layer, before being subjected to the furnace brazing process. However, combinations of the above processes or arrangements are envisaged. Figure 5 shows an embodiment of the present invention incorporated in a brake drum 50. The drum 50 includes an interior friction surface 51 , a support member 52 providing an outer drum surface, and heat transfer elements 53 extending through the support member 52. It will be appreciated that friction devices, such as brake shoes or pads, will contact the inner drum surface 51 in order to effect braking. Figure 6 shows a partial sectional view through the brake drum of Figure 5. In particular, the inner drum surface 51 includes the friction material 54. Underlying the friction material 54 is the heat transfer material, copper or copper alloy in this form of the invention 55 which is connected to the heat transfer element 53 extending through the support member 52. Figure 7 shows a portion of a brake disc for a motorcycle. This portion includes a single disc plate 70 in the form of an annular disc. Apertures extending through the disc material provide ventilation. Some of the apertures 71 are purely ventilation holes. Other apertures include heat transfer elements 72. The brake disc includes an underlying base material providing a support member which is applied on either side thereof the layer of a heat transfer material which is in contact with a portion of each of the heat transfer elements 72. The faces of the heat transfer material are then coated with the friction material 73. Thus, calliper pressure applied to brake pads either side of the disc generates heat during braking which is transferred through the friction material 73 into the underlying heat transfer material and subsequently transferred by conduction to the copper or copper alloy tube elements of the heat transfer element 72 extending through the disc material. During rotation, heat is given up to the atmosphere by the heat transfer element extending between opposite faces, and therefore opposite layers of the heat transfer material, to help cool the disc and thereby maintain braking efficiency and structural integrity of the disc.