GB2388560A

GB2388560A - Carbon-carbon brake disc with protective outer layer on friction surface

Info

Publication number: GB2388560A
Application number: GB0209565A
Authority: GB
Inventors: Martin John Michael Murphy
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-04-26
Filing date: 2002-04-26
Publication date: 2003-11-19
Also published as: WO2003091588A2; GB0209565D0; WO2003091588A3; AU2003229943A8; AU2003229943A1

Abstract

The invention relates to a component such as a brake disc formed of a carbon-carbon composite with a protective outer layer on the friction surface. The protective outer layer is preferably formed from a ceramic and is selected to provide a friction co-efficient and/or high wear resistance appropriate to the service conditions. The invention allows a wide range of carbon based substrates to be used in brakes allowing cost and technical efficiency to be optimised.

Description

The invention relates to a component such as a brake disc formed of a carbon-carbon composite with a protective outer layer on the friction surfaces.

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. It will also be of advantage to form other components of this material able to withstand similar conditions of use. Such components can be parts used in automotive, aerospace, railways aeronautic, machine fool' construction and like equipment.

It is one object of this invention to provide a component formed of a C/C composite, which component is able to withstand stresses induced in use. e.g. applied frictional and abrasive forces.

Heretofore, in the field of carbon brake discs, such discs have utilized some type of

reinforcement, invariably carbon filaments in some form such as cloth, chopped fibre, woven and the like. The primary purpose of such filaments is to impart high mechanical properties such as strength and rigidity to the discs so that they can withstand the forces encountered during braking in high performance applications.

Such applications are typically but not exclusively automotive and aerospace, for example for use in the braking systems of high performance sports cars and the like.

The fabrication of laminated brake discs containing carbon cloth or filament layers is commonly referred to in the art as a carbon/carbon (C/C) composite. (The term "carbon?' is used in the generic sense and can mean either amorphous carbon or crystalline graphite). Additionally, brake discs have been made utilizing a bulk carbonaceous layer such as bulk graphite in order to reduce the long fabrication time of the C/C composite laminate and to reduce cost. Of course, brake discs have also utilized combinations of the C/C composite and bulk graphite layers In operation these brakes can reach temperatures in excess of 1000 C. Such high temperatures lead to oxidation of the disc (the threshold for oxidation of Carbon is approximately 1010 C) and resulting high wear rates of both the friction and non-

friction areas.

Various patents teach the coating of the non-friction regions of the disc to reduce oxidation and loss of mass from those areas. For example in GB 1544994 it is taught that coatings can be applied to the "non-wear" surface of C/C discs in order to provide an oxidation limiting coating. Significantly none of these patents teaches the application of a coating to the friction or wear surface. Presumably this is because this surface is critical to the operation of the C/C brake and hence it is important that it is free to forth a friction couple with the brake pad (or in the case of a disc stack the neighbouring disc). Patent EP 0 54 196 teaches the application of a ceramic coating

to a metallic substrate, preferably an aluminium MMC, the intention being to improve the temperature capability of the aluminium disc by the formation of a thermal barrier.

The present invention teaches the application of a coating to the surface of a C/C brake disc with the intention of protecting the surface of the disc from oxidation and increasing the wear resistance of the disc. Thus the life of the disc is extended and the cost of the component is significantly reduced. The coating also provides one half of the friction couple formed between disc and pad that previously had been formed between the C/C substrate and the pad.

The resultant disc brake possesses the properties of À 1) a friction coefficient that can be altered to suit the application 2) low weight due to the low density of the C/C composite 3! strength and stiffness at temperature such that the integrity of the disc is retained under severe braking conditions 4) high wear resistance All of these properties are highly desirable in a brake disc.

In another aspect the invention teaches the application of a coating to other types of carbon based brake discs. In this respect it is possible to use alternative materials to the C/C composites used in uncoated brake discs as in the presence of a coating there is no longer the requirement for the carbon based material to have the friction characteristics of a brake material.

According to the invention in one aspect there is provided a brake disc or like component formed of C/C composite, the component having a protective coating on at least one surface thereof characterized in that the protective coating is a ceramic coating selected to provide a combination of properties selected from wear resistance.

thermal capacity, thermal conductivity, friction performance, oxidation resistance and has a thickness of about 0.2 millimetres.

As indicated, one particular component is a bake disc which in use can be worn down by a brake pad during use and in this case the protective coating is selected to protect the surface against an applied abrasive force. In another aspect the applied abrasive force is the passage of hot gases over the combustors and turbine blades in a jet engine. In addition or alternatively the coating may be selected to provide corrosion resistance, hardness, wear resistance, compatibility or other properties. Depending on the intended use, the coating may be selected to have thermal properties, e.g. conductivity. The coating can be applied by any method and can be a combination of several coatings and layers incorporating interlayers designed for example to provide high oxidation andlor abrasion resistance and/or bonding of the upper layer to the substrate. Preferably, the protective coating is applied by electroplating, plasma deposition, magnetron sputtering, dipping or impregnation or a like technique.

The coating is chosen to be compatible with the component, e.g. to have a rate of linear heat expansion substantially the same as that of the composite of the brake disc component to avoid the risk of debonding at service temperature.

A brake disc of the invention can be used with a wide range of brake pads. For certain applications it is possible to use commercially available brake pads without modification. The discs may be used at the front and/or rear of a vehicle, including a racing vehicle.

The invention will be further described by way of example with reference to the accompanying diagrammatic drawing in which: Figure 1 is a crosssectional view of a typical disc for use in a disc brake; and Figure 2 is an enlarged section of a circled portion of Figure I The vehicle brake disc 10 is of generally a "floating" form, with a mounting bell portion 13 adapted to be secured to rotate with a vehicle wheel or axle ( 1 1); in alternative embodiments the disc can be mounted to rotate with the vehicle propshaft and may be ventilated. The bell and disc are held together in known manner, e.g. by bolts and nuts, not shown. Friction pads A,B are movable into engagement with opposed side faces 1 Oa, I Ob of disc 10 to effect braking of the disc. During such engagement if the disc is rotating, high temperatures are generated at the discs surfaces, which may have therefore a frictionally induced temperature exceeding } O00 C.

The disc I O comprises a body portion 12, formed of a C/C composite with a coating applied by a plasma spray technique. The density of the composite is about I.81 gm/cm3. The plasma sprayed coating 20 is applied to a depth sufficient to protect the underlying composite, typically about 0.2 millimetre. In this instance the coating was alumina based. An objective of this particular embodiment of the invention is to provide enhanced wear resistance to the C/C composite. Another objective of this particular embodiment is to provide a friction couple with the brake pad that is similar to that obtained when using the C/C composite without the coating in the same application.

Claims

Claims to be appended - Page 1/1 1. A brake disc or like component fonned of a C/C composite or like material, the component having a protective coating on at least one surface thereof characterized in that the coating is selected to reduce wear of the brake disc in operation and provide an acceptable friction couple with the brake pad. 2. A component according to Clairm 1 where the coating is a ceramic. 3. A component according to either of (:laims I or 2 where the coating contains a predominance of alumina. 4. A component according to any of Clahns 1 to 3 wherein the coating is less than 0.3 mm. 5. A component according to any of Claims I to 4, comprising a brake disc having, the protective coating formed on opposite faces thereof: 6. A component as described in any of Claims 1-5 wherein the coating is composed ot several layers. 7. A component according to any of C laims 1-6 where the non-friction parts of the disc are also coated. 8. A component according to any of Claims 1-7 where the component is part of an automotive brake system used for automotive applications. 9. A component according to any of Claims 1-7 where the component is part of an aerospace brake system used for aerospace applications.

1 O. A component according to any of Claims I - 7 where the component part of a brake used for railway applications.

11. A component according to any of Claims I - 7 where the primary requirement of the component is abrasion, wear or oxidation resistance.

I 9. component according to any of the preceding claims where the bulk material of the disc is formed from a carbon preform infiltrated with Silicon.

Amendments to the claims have been filed as follows -Page 1/! 1. A brake disc or like component fcrmcd of a (2/C composite or like matenal, the component having a protective coating orl at least one surface thereof charactcrizcl in that the coating is selected to rcUuce wear of the braLc disc in operation and provide an acceptable friction couple with the brake pad.

2. A component according to Claim I where the coating is a ceramic.

3. A component according to either of (claims 1 or 2 where the c<:ating contains a predominance of alumina.

4. component according to any of Claims t<' 3 wherein the coating is less than 0.3 mm.

5..N component according to either of claims 1 to 4 where the coating is applied using a plasma coating process.

6. A component according to any of (claims I to 5, comprising a brake disc having the protective coating formed on opposite faces thereof.

7, component as described in any Of (claims I to 6 wherein the.coating is composed of several layers.

8..\ component accorcling to any cuff (,laims 1 to 7 where the nonfnction parts of the disc are also coated.

9. component according to any of Claims 1 to 8 where the component is part of an automotive brake system used for automotive applications.

10. A component according; to any of Claims I to 8 where the component is part of an aerospace brake system used for aerospace applications.

11.:\ component according to any of (claims 1 to 8 where the cormponcnt part of a brake used for railway applications.

12. A component according to any of (claims I to where the primary reqtiremcot of the component is abrasion, wear or oxidation resistance.

13. A component according to any of the preceding claims where the bulk material of the disc is forrocd from a carbon pre{'crm infiltrated with tSilicc>n.