WO2021123755A1

WO2021123755A1 - Brake disc, method of manufacturing the same, and an insert

Info

Publication number: WO2021123755A1
Application number: PCT/GB2020/053221
Authority: WO
Inventors: Martin Murphy
Original assignee: Materials I.P. Limited
Priority date: 2019-12-16
Filing date: 2020-12-15
Publication date: 2021-06-24
Also published as: GB2590411A; GB201918550D0

Abstract

A brake disc (100) is provided, comprising two outer plates (12) for receiving a compressive force from brake callipers and at least one inner plate (14). A plurality of bridges (16) extend between each outer plate and the inner plate for spacing the outer plates from the inner plate and providing thermal conduction there between. A plurality of bores (15) are formed, each bore of the plurality of bores extending through the inner plate (14) and at least one of the outer plates (12). Each bore (15) of the plurality of bores is aligned with and extending through a respective bridge (16) of the plurality of bridges.

Description

BRAKE DISC, METHOD OF MANUFACTURING THE SAME, AND AN INSERT

The present invention relates to a high performance brake design with advanced thermal management.

Vehicle brakes operate by the formation of a friction couple between two materials. The performance of that friction couple at any moment determines how the applied braking force, resulting from, for example, hydraulic pressure in a set of pistons is converted into a force that stops the vehicle. The performance of the friction couple, as measured by the friction co-efficient, changes with the operation parameters of the brake, e.g. power density, surface speed, temperature, time and brake diameter. The selection of brake materials and brake design is used to optimise the operation parameters of the friction couple with respect to the requirements of the vehicle braking system. The present invention describes an innovative design for a ventilated disc brake that enables the brake designer to further optimise the effectiveness of the cooling, temperature management, friction couple and brake performance.

Disc brakes comprising a caliper and a disc have been widely adopted, particularly for automotive applications. The disc is squeezed during braking between pads of friction material, mounted in the caliper; and since the disc has a high resistance to compression, and since much of the disc is exposed and so can cool more quickly than for instance the drum of a drum brake, a disc brake is less prone than the drum brake to brake "fade" i.e. to partial loss of braking at high disc and/or pad temperatures, as may occur following intensive brake usage over a short period.

In order to further attempt to reduce the effect of fade designers have adopted various strategies. The most obvious of these is the provision of additional mass in the brake; this raises the thermal capacity of the disc enabling it to absorb more energy for less of an increase in temperature. The major disadvantage of this approach is that the increase in mass is undesirable as it produces poor ride and handling characteristics as well as increased fuel consumption.

An alternative approach to reducing fade is to introduce cooling vents into the disc so that air can circulate between the “friction plates” and heat can be removed by conducting it through the solid parts of the disc and releasing it to cooling air driven or pulled through the vents. The development of the ideal vent structure has been the subject of many studies and has resulted in a number of patents covering the shape, number of vents and the provision and design of entry and exit ports for the cooling air. A recent approach concerning the development of such a disc is described in US 2002/0166738 A1 .

GB 2444 927 A discloses a brake disc which can be formed of three layers separated by vane formations. The vane formations are solid and do not have any bores passing therethrough.

Two ways in which the designer can avoid fade is by making the disc thicker or selecting a brake material with higher thermal conductivity, both these methods improve the rate of heat transfer away from the friction surface.

It can be seen that in most circumstances a friction couple will have an optimum temperature range of operation and the designer of the brake would like to manage the thermal response of a brake system so that the majority of operation of the brake is within that temperature regime. It can thus be seen that methods of controlling heat flow through design of a brake is highly desirable. The present invention provides such a design and the means to manufacture discs using this design philosophy at the same time as keeping the mass to a minimum.

The effectiveness of a vented disc brake can be affected by a number of design factors. During the braking event energy is introduced into a disc through the surface of the disc and is conducted away into the solid parts of the disc. During the cooling cycle the energy is removed from the disc primarily by the conduction of heat through the solid parts of the disc to the support structure of the brake, the free surfaces of the disc and the surface of the vents. The energy is transferred from the free surfaces of the disc and vents by the passage of air over the disc and through the vents.

The surface area of the vents can be increased by utilizing “studs” instead of or in combination with solid vanes or pins or introducing surface perturbations onto the surface of the vent, both these features increase the surface area of the vents but do little for the mass flow of air over the surface of the vents. An alternative method is to increase the cross sectional area of the vent thus increasing the mass flow of air through that vent, but not however the mass flow of air in direct contact with the surface of the vent; thus little enhancing cooling. This also undesirably reduces the thermal capacity of the disc if the external dimensions of the disc are maintained constant.

Accordingly, it is desirable to provide an improved disc to tackle at least some of the problems associated with the prior art or, at least, to provide a commercially viable alternative thereto.

JP S60 30836 A discloses a disc vibration preventing part comprising holes formed at unequal intervals in a direction extending orthogonal to the braking surface of a disc which is attached to a coupling plate part of a middle plate for coupling two discs.

DE 20 2018000 728 U discloses a brake disc for use on vehicles, aircraft and other mobility devices, in particular cars, trucks and motorcycles, consisting of a metallic, preferably monolithic core body, also called a base body, and friction rings made of carbon- ceramic and/or other non-metallic composites.

US 2013/092486 A1 discloses a brake disk containing through channels running across primary vanes skewly to the inter-vane space.

EP 1 298342 A2 discloses a brake disk arrangement made from fiber-reinforced ceramic composite materials comprising two disks connected using cross-ribs.

According to a first aspect there is provided a brake disc comprising: two outer plates for contacting brake calipers; at least one inner plate; and a plurality of bridges extending between each outer plate and the inner plate for spacing the outer plates from the inner plate and providing thermal conduction there between.

A brake disc according to the present invention is provided according to claim 1 .

The present invention will now be further described. In the following passages different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous. In order to increase the cooling of the disc it is desirable to both decrease the diffusion distance within the solid parts of the disc and to increase the surface area of the vent and/or increase the mass flow of air carried through the vent. Ideally this is done whilst maintaining a constant heat capacity for the disc.

The present invention however provides a means for increasing the effective mass of air flowing over the vent surface. It also reduces diffusion distances within the disc enhancing the rate of transfer of heat energy from the bulk of the disc to the free surface of the vent. Both these are achieved whilst maintaining the thermal capacity of the disc. This is achieved by removing material from near the surface of the disc and placing it nearer the midpoint between the two friction surfaces. This is achieved by providing a central plate to the disc, thus providing two sets of ventilation channels, as illustrated in figure 1. This is particularly efficacious where the brake disc material used is aluminium alloy which has a low melting point but excellent thermal conductivity.

The present invention relates to a brake disc. However, it is also suitable for use as a clutch disc.

The disc comprises two outer plates. These provide a friction surface for contacting brake calipers in use, in order to retard rotation of the disc and provide a braking force.

The disc comprises at least one inner plate. This provides the structure to the disc and acts as a heat sink for heat from the outer plates. In most embodiments there is only a single inner plate.

The inner plate(s) is connected to the outer plates by a plurality of bridges extending between each outer plate and the inner plate for spacing the outer plates from the inner plate and providing thermal conduction there between. These are described in more detail below.

A plurality of bores is provided, each bore extending through the inner plate and at least one of the outer plates, each bore aligned with and extending through a respective bridge of the plurality of bridges. By a bore being provided, this means that a hole is formed through the plates and bridges. To form the brake disc, the outer plates may be attached to or integral with the inner plate. In the disc (i.e. when the plates are attached to one another), the bores may be unobstructed. That is, there may not be any fastener provided through the bores in order to assemble the disc. The bores may be suitable for allowing airflow through the bores, between the outer plate and inner plate, in the assembled disc.

Each bridge between one of the outer plates and the inner plate may be aligned with another bridge between the other of the outer plates and the inner plate, and each bore may extend between the two outer plates, through the inner plate and each corresponding bridge. This allows the bores to extend from outer plate to outer plate.

For the avoidance of doubt, there may be additional bores formed in the disc and not passing through and/or aligned with the bridges.

The brake disc may further comprise one or more secondary bores not aligned with any bridge of the plurality of bridges, preferably the or each secondary bore extends generally perpendicular to the plurality of bores. Such secondary bores can further be used to control the heat transfer.

Preferably each outer plate comprises a friction surface for contacting and thereby receiving the compressive force from the brake calipers, the friction surface comprising one or more of: a carbon-ceramic composite material, a ceramic material, a metal.

Preferably, the bores extend through the friction surface.

Preferably the friction surface is provided by an insert held at the surface of the outer plate. The friction surface may be provided by an insert, typically less than 1 mm thick to provide the friction face. These could be made of metal, a carbon-ceramic composite and also ceramic materials. They are there to provide consistent friction behaviour and, in the case of ceramic inserts, an additional thermal barrier.

The inserts are preferably secured to the surface of the outer plate with a low thermal conductivity, high temperature ceramic glue. Such glues are well known in the art. In installing the inserts, preferably recesses are machined into the surface of each outer plate to a depth such that the insert sits proud in the corresponding recess. The recess depth therefore needs to take into account any layer of retaining glue and a thickness of the glue is typically about 0.2mm. The recesses that are produced are part filled with the ceramic glue and the insert is placed in the recess. This method of gluing the insert in also provides a secondary thermal barrier between the insert and the bottom of the recess machined in the outer surface of the disc.

The high temperature ceramic glue is preferably an aqueous composition comprising ceramic powder. Preferably the composition comprises alumina powder, more preferably, from about 40wt% to about 80wt% alumina powder based on the total weight of the composition such as from about 50wt% to about 70wt%. Preferably, the aqueous composition is an acidic aqueous composition comprising aluminium dihydrogen phosphate, preferably wherein the acidic aqueous composition has a pH of from about 0 to about 2.0, more preferably from about 0.6 to about 1.0. Preferably, the pH of the acidic aqueous composition is achieved by the addition of phosphoric acid to the composition. Preferably, the acidic aqueous composition comprises from about 5wt% to about 40wt% aluminium dihydrogen phosphate, more preferably, from about 10wt% to about 30wt% such as about 20wt%. Preferably, the composition consists of water, aluminium dihydrogen phosphate, phosphoric acid and alumina powder.

According to one embodiment a ceramic (thermal) barrier may be provided on the surface of the outer plates in the form of a semi-continuous or continuous layer in combination with the invention. This can be applied by a variety of methods to those skilled in the art for example thermal spraying or analysing and may be composed of ceramic materials.

Preferably the inner plate has a greater thickness than each outer plate. This helps it act as a heatsink.

In one embodiment the inner plate is made of aluminium.

Preferably the bridges take the form of studs or vanes and, preferably, wherein the bridges are hollow. That is, preferably the bridges form a tube from one face of the disc to the other. This provides improved cooling of the plate. The hollow form of the bridges is preferably achieved by drilling through the plate at positions aligned with the bridges to form the additional ventilation channels. Preferably the bridges are:

1) arranged in concentric rings, preferably centred around a centre-point of the brake disc; and/or

2) distributed in radially extending lines along a surface of each plate; and/or

3) arranged in a spiral pattern, preferably centred around a centre-point of the brake disc.

Preferably the inner and outer plates are:

1) concentric rings; and/or

2) parallel; and/or

3) equally spaced.

Preferably the outer plates are spaced from an inner plate by a distance of from 1 to 20mm, preferably 2 to 17mm.

Preferably the outer plates have a thickness of from 1 to 15mm, preferably 2 to 12mm, and/or an outer diameter of from 15 to 60cm, preferably 20 to 25cm.

A further brake disc according to the present invention is provided according to claim 19. This embodiment does not include an inner plate between the two outer plates. For the avoidance of doubt, any features described in relation to the first brake disc (of claim 1) are equally applicable to this further brake disc, with appropriate modification for the lack of an inner plate.

A brake disc assembly according to the present invention is provided according to claim 20, comprising a brake disc according to any of claims 1 to 19 and a brake calliper for engaging the brake disc.

Use of the brake disc according to the present invention is provided according to claim 21 . This use is for Automotive brake discs, for Motorsport brake discs or for Aerospace brake discs.

An insert for a brake disc is provided according to claim 22. This insert can be readily machined, while maintaining the beneficial heat transfer properties of a composite. The insert may be formed by a method comprising:

(i) providing a mixture comprising chopped carbon fibers and at least one phenolic resin;

(ii) providing an aqueous composition comprising aluminium dihydrogen phosphate and, optionally, alumina powder, having a pH of from 0.6 to 1.0;

(iii) introducing the mixture into a mould and compressing the mixture within the mould to form a moulded body;

(iv) heating the moulded body under an inert atmosphere to pyrolyse the at least one phenolic resin to form a porous body;

(v) infiltrating the porous body with the aqueous composition to form an infused porous body; and

(vi) drying and curing the infused porous body to form the composite material.

According to a further aspect there is provided a method of making the brake disc according to claim 25 as described herein, wherein the outer plates are glued to the central plate via the plurality of bridges.

Preferably the plurality of bridges are formed integrally to the inner plate or to each outer plate.

Preferably the glue is a high temperature ceramic glue. These are particularly suitable for use in a brake disc.

The invention will now be described further with reference to the following non-limiting figures, in which:

Figure 1 shows a multi-layered brake disc in accordance with the present invention.

The principle of the design can be used to balance the heat conducted through the bulk of the disc with the energy lost from the vent surface. That is, a balance between the thermal capacity and rate of heating of the disc and the exposed surface area for venting. Thus enabling the disc designer to optimize the design. It provides a disc with the same thermal capacity but much greater cooling compared with current state-of-the-art design due to its short diffusion paths and high mass air flow over the vent surfaces. It is also possible by this method to adapt the behaviour of the disc to allow for a better combination of low and high energy performance. A disc can be designed such that in low energy braking events the surface of the disc heats rapidly boosting the interface temperature into the operating regime resulting in improved performance, particularly when using high performance brake pads. In high energy braking events, heat generated at the surface of the disc that cannot be absorbed entirely within the “surface” plate can be soaked into the inner plates where the energy can be held until it can be dissipated during the cooling cycle. By careful design it is thus practical to manufacture a disc capable of performance over a much greater range of operation than current brakes.

In order to illustrate and describe the invention further an example of a disc 100 manufactured according to the invention is shown in figure 1 . In this instance the disc is constructed with three plates, positioned to rotate about an axis 20 which is coincident with the axis of rotation of the part to be stopped. For example, this axis 20 may be generally coincident with the vehicle axle.

The disc 100 includes two outer plates 12. These two outer plates 12 are positioned so that a caliper can apply a compressive force perpendicular to the plane of these outer plates 12. The disc 100 may further comprise one or more plates (not shown) mounted on the outer plates 12. The plates are arranged to cover the portion of the outer plates 12 that would contact the brake caliper. The brake caliper comprises pads (not shown) which are brought into contact with the surface 18 of the outer plates 12 or the plates. This then provides the retarding force of the brake. In this respect the disc 100, pad and caliper assembly is similar to that which will be well known to those skilled in the art of brake disc design.

According to the invention there is further provided an additional plate 14, positioned between the two outer plates 12. The additional plate 14 is an inner plate and connected to the outer plates 12 on either side by bridges 16. These bridges 16 may be in the form of vanes, studs or pins/studs or pins. The bridges 16 are of a heat conductive material and act to thermally conduct heat from the outer plates 12 towards the inner plate 14.

In another aspect of the invention further inner plates can be positioned between the outer plates 12 in a similar manner such that the disc 100 can consist of 4, 5, 6 or any number of plates dependent on the design requirements for the operation of the disc 100. These multiple inner plates 12 may be connected by additional bridges 16. The disc 100 is connected to the axis of rotation 20 by the provision of a driving bell arrangement as is well known to those skilled in the art. This can be a separate component as in the case of a floating bell disc as commonly used on some high performance vehicles or the driving bell can be incorporated into the discs 100 to form one continuous component as is common on road vehicles. The driving bell can be joined to the disc plates 12, 14 at any location commensurate with operation of the caliper. It is within the spirit of the invention to attach the driving bell to any or all of the plates 12, 14 that make up the disc 100.

Air can flow through the disc 100 via vents 19 in the disc 100. The outside air may pass through either of the surfaces or the driving hub itself or through the inside and/or outside edges of the disc.

The plates 12, 14 do not have to be identical in outline and can have different diameters and positions as long as they are concentric about the rotating axis 20. The bridges 16 between the discs 12, 14 can be of any design: they can be composed of continuous vanes, studs or pins or any combination thereof. Further, the bridges 16 can incorporate ribs and perturbations for the purposes of increasing surface area or stiffening. They can also be of any shape, for example curved or otherwise aerodynamically shaped. The bridges 16 between any two adjacent plates 12, 14 can be immediately opposite each other or they can be displaced from each other, they can also be of different design. There can be any number of bridges 16. In short it is possible to incorporate any of the known features of vented disc design using two plates into a disc 100 produced with multiple plates 12, 14 according to the invention.

The bridges 16 may be arranged in any suitable pattern for achieving the cooling effect. However, in particular embodiments the bridges 16 may be arranged in a plurality of concentric rings. These concentric rings may be centred around a centre-point of the brake disc. Alternatively; the bridges 16 may be distributed in radially extending lines along a surface of each plate. These lines may extend from a centre-point of the brake disc.

Further alternatively, the bridges 16 may be arranged in a spiral pattern, this spiral pattern may be centred around a centre-point of the brake disc. The brake disc generally defines a circle in plan view and the centre-point is the centre of this circle. A plurality of bores 15 are formed by drilling holes through the outer plates 12 to promote cooling through the disc 100 and help in keeping the brake pads conditioned. The holes, and hence the bores 15, are aligned with the bridges 16 such that the holes are drilled through the plate 12 on one side, the bridge 16 that attach the plates 12 to the central plate 14, and the central plate 14. In particular embodiments, there is a corresponding bridge 16 and the other plate 12 and the central plate 14 and the bore 15 further passes through this other bridge 16 and the other plate 12. This provides a large increase in surface area and promotes cooling from the interior of the disc 100. In other aspects the some or all of the holes do not have to be drilled through the bridge 16, but may be formed by any other suitable method. Each bridge 16 may align with only one bore 15. For example, each bridge 16 may be formed (once the bore 15 is formed) essentially as a hollow tube, such as a hollow circular tube.

In the assembled disc 100, the bores 15 are unobstructed. Particularly, there may not be any fastener provided through the bores 15, such as a screw, bolt or rivet. The bores 15 are suitable for allowing airflow through the bores 15, between the outer plate 12 and inner plate 14, in the assembled disc 100. Alternatively one or more of the bores 15 may contain rivets for securing the assembled disc 100. Thus, there may be a mixture of obstructed and unobstructed bores 15.

In further alternative embodiments, the bridges 16 may be aligned such that bridges 16 extending between a first of the outer plates 12 and the inner plate 14 are not aligned with the bridges 16 extending from the other of the outer plates 12 and the inner plate 14. In such embodiments, the bores 15 extend from the outer plate 12, through the bridge 16 and the inner plate 14 to form a passageway there between.

There may, of course, be secondary bores which may not aligned with any bridges 16. These additional bores pass solely through a single plate 12, 14 to an air gap either side of the plate 12, 14 they pass through. Alternatively, these secondary bores may pass in a generally radial direction, substantially perpendicular to the bores 15 passing through the bridges 16. In particular embodiments, the secondary bores may be provided primarily in the central plate 14 and may extend in a radial direction thereof. That is, these secondary bores may extend along a line extending from a circumference to a center-point of the central plate 14. The secondary bores do not have to necessarily extend from the circumference, or all the way to the center-point, but merely in this direction. Such secondary bores may intersect one or more of the bores 15 passing through the bridges. In this sense, the bores 15 passing through the bridges 16 may be referred to as primary bores.

The disc plates 12, 14 can be made of any material that can be fabricated into the arrangement described. By way of example but not exclusively, they can be made from existing brake materials, for example steel or iron (i.e. ferrous materials), Carbon-carbon composites or variants thereof and other Carbon-ceramic composite materials (for example those infiltrated with Silicon, so as to form Silicon Carbide). They can also be made from other materials such as ceramics or aluminium alloys or metal matrix composites. They can also be made from a combination of materials, for example aluminium alloys and ceramics. Ceramics used in this invention do not have to be made from a single ceramic for example they can be made from combinations of Alumina, Silicon Carbide, Boron Carbide or Silicon Nitride or any of these individually. The materials from which the disc 100 is made can also include those that are reinforced with fibres, whiskers or particulate as is well known to those skilled in the art of the manufacture of Metal or Ceramic or Resin Matrix composites.

Whilst any carbon-ceramic composite material known in the art may be used, a particularly advantageous carbon-ceramic composite material for use in the present invention may be formed by a method comprising:

(vi) drying and curing the infused porous body to form the composite material.

Preferably the composite material produced by the method described herein has a density of from 1.5 g/cm³ to 2 g/cm³. Preferably, the mixture comprises carbon black. Advantageously, including carbon black in the mixture improves the frictional performance of the composite material. Preferably, the aqueous composition comprises from 30wt% to 60wt% aluminium dihydrogen phosphate and/or the pH is achieved by the addition of phosphoric acid. Preferably, the method further comprises repeating the step of infiltrating the porous body to infiltrate the dried and cured porous body with further aqueous composition to form a further infused porous body and drying and curing the further infused porous body to form the composite material.

The carbon-ceramic composite material formed by the method described herein is capable of withstanding high temperatures generated through frictional forces without degradation. Advantageously, the composite material produced by the method described herein also has fewer internal stresses. Therefore, the composite material may be machined, such as cut, turned, chamfered, reamed, milled, and/or drilled, without resulting any distortion in the material.

The plates 12, 14 can be prepared by any manufacturing process or combinations thereof. For example, if the plates 12, 14 are made from metallic materials that are suitable for casting, they can be made using known casting methods. It is also possible, for example to manufacture the discs by machining from bulk materials.

According to a most preferred embodiment at least the inner plate 14 is formed of aluminium and the outer plates 12 have a surface comprising a carbon-ceramic composite material, a ceramic material, optionally provided by inserts retained on the outer plates 12. The inserts may be substantially ring-shaped and extend in a complete circle around the outer surface of the outer plates 12. Alternatively, there may be a plurality of inserts distributed circumferentially around the outer plates 12, preferably with gaps between the inserts. These inserts may be chamfered to reduce noise when operating the brake disc.

In addition, the plurality of bridges 16 extending between each outer plate 12 and the inner plate 14 are through-drilled to provide ventilation through the disc 100 from an outer surface of the first outer plate 12 to an outer surface of the second outer plate 12.

Multiplate discs, designed and manufactured in the manner of the invention, can be used to produce braking systems for use in automotive, motorsport, aerospace and industrial applications. They can also be used for clutches. Brake discs as described above can be manufactured by providing first and second outer plates 12 and at least one inner plate 14. The outer plates 12 being separated from the inner plate 14 by a plurality of bridges 16 extending from the outer plates 12 to the inner plate 14. These bridges 14 may be integral components to either of the plates 12, 14. The plates 12, 14 may be attached to the bridges 16 via an adhesive. Alternatively, the plates 12, 14 may be attached to the bridges 16 via any suitable method, including the bridges 16 being integrally formed with one or more of the plates 12, 14. A plurality of bores are then drilled through the outer plates 12 and inner plate 14, each bore aligned with and extending through a respective bridge 16 of the plurality of bridges 16.

According to a less preferred embodiment there is also described herein a disc 100 comprising only the two outer plates 12, directly attached together with a plurality of bridges 16 as described herein and no inner plate 14. All features disclosed above in relation to the first disc may be applied to this embodiment.

The invention will be further described by means of the following non-limiting example.

Example 1

A disc of 278mm x 25mm thick was produced in LM6 aluminium casting alloy using conventional sand casting techniques. The disc had two outer plates and a thicker centre plate joined together by way of pins. The disc was machined to size and through holes drilled through the centre of each connecting stud pin in a direction perpendicular to the surface of the disc. Pockets were machined into the outer surface of the disc with the smaller inner pocket 0.2mm deeper than the outer large pocket which was 1 mm deep. The pockets were filled to the correct level with low thermal conductivity, high temperature ceramic glue and the carbon-ceramic composite inserts were fitted and riveted in place prior to curing.

Although preferred embodiments of the invention have been described herein in detail, it will be understood by those skilled in the art that variations may be made thereto without departing from the scope of the invention or of the appended claims.

Claims

CLAIMS:

1. A brake disc comprising : two outer plates for receiving a compressive force from brake callipers; at least one inner plate; a plurality of bridges extending between each outer plate and the inner plate for spacing the outer plates from the inner plate and providing thermal conduction there between; and a plurality of bores, each bore of the plurality of bores extending through the inner plate and at least one of the outer plates, each bore of the plurality of bores aligned with and extending through a respective bridge of the plurality of bridges.

2. The brake disc according to claim 1 , wherein each bridge between one of the outer plates and the inner plate is aligned with another bridge between the other of the outer plates and the inner plate, and each bore extends between the two outer plates, through the inner plate and each corresponding bridge.

3. The brake disc according to any preceding claim, further comprising one or more secondary bores not aligned with any bridge of the plurality of bridges, preferably the or each secondary bore extends generally perpendicular to the plurality of bores.

4. The brake disc according to any preceding claim, wherein each outer plate comprises a surface for receiving the compressive force from the brake callipers, the surface comprising one or more of: a carbon-ceramic composite material, a ceramic material, or a metal.

5. The brake disc according to claim 4, wherein the surface is provided by an insert held at the surface of the outer plate.

6. The brake disc according to claim 4 or 5, wherein the bores extend through the surface.

7. The brake disc according to any of the preceding claims, wherein the inner plate has a greater thickness than each outer plate.

8. The brake disc according to any of the preceding claims, wherein there is a single inner plate.

9. The brake disc according to any of the preceding claims, wherein the inner plate is made of aluminium.

10. The brake disc according to any of the preceding claims, wherein the bridges take the form of studs or vanes and, preferably, wherein the bridges are hollow.

11 . The brake disc according to any of the preceding claims, wherein the bridges are:

1 ) arranged in concentric rings, preferably centred around a centre-point of the brake disc; and/or

12. The brake disc according to any of the preceding claims, wherein the inner and outer plates are:

1) concentric rings; and/or

2) parallel; and/or

3) equally spaced.

13. The brake disc according to any of the preceding claims, wherein the outer plates are spaced from an inner plate by a distance of from 1 to 20mm.

14. The brake disc according to any of the preceding claims, wherein the outer plates have a thickness of from 1 to 15mm, and/or an outer diameter of from 15 to 60cm.

15. The brake disc according to any of the preceding claims, wherein the outer plates are glued to the central plate via the plurality of bridges.

16. The brake disc according to any of the preceding claims, wherein the plurality of bridges are formed integrally to the inner plate or to each outer plate.

17. The brake disc according to claim 14 or 15, wherein the glue is a ceramic glue.

18. The brake disc according to any of the preceding claims, wherein the inner plate and the outer plates are made of aluminium, wherein each outer plate comprises a surface for contacting brake calipers, wherein the surface is provided by an insert held at the surface of the outer plate and wherein the surface comprises a carbon-ceramic composite material, and wherein the bridges take the form of studs and are hollow, providing an air channel through the brake disc.

19. A brake disc comprising : two outer plates for receiving a compressive force from brake callipers; a plurality of bridges extending between the outer plates for spacing the outer plates and providing thermal conduction there between; a plurality of bores, each bore of the plurality of bores extending through the outer plates, each bore of the plurality of bores aligned with and extending through a respective bridge of the plurality of bridges.

20. A brake disc assembly comprising the brake disc according to any of the preceding claims and a brake calliper for engaging the brake disc.

21. Use of the brake disc according to any of the preceding claims for Automotive brake discs, for Motorsport brake discs or for Aerospace brake discs.

22. An insert for a brake disc, the insert formed of chopped carbon fibers encased in at least one phenolic resin.

23. The insert of claim 22, wherein the insert is formed by a method comprising:

(iv) heating the moulded body under an inert atmosphere to pyrolyse the at least one phenolic resin to form a porous body; (v) infiltrating the porous body with the aqueous composition to form an infused porous body; and

(vi) drying and curing the infused porous body to form the composite material.

24. The brake disc of claim 4 or 5, wherein the insert is according to claim 22 or 23.

25. A method of manufacturing a brake disc, the method comprising the steps of: providing first and second outer plates and at least one inner plate, the outer plates separated from the inner plate by a plurality of bridges extending from the outer plates to the inner plate; and drilling a plurality of bores through the outer plates and inner plate, each bore aligned with and extending through a respective bridge of the plurality of bridges.