WO2004029473A1

WO2004029473A1 - Disc brake

Info

Publication number: WO2004029473A1
Application number: PCT/GB2003/004070
Authority: WO
Inventors: Peter Campbell Johnston
Original assignee: Federal Mogul Friction Products Ltd
Current assignee: Federal Mogul Friction Products Ltd
Priority date: 2002-09-24
Filing date: 2003-09-23
Publication date: 2004-04-08
Anticipated expiration: 2005-03-24
Also published as: AU2003267598A1; GB0222133D0; GB2393486A

Abstract

A disc brake (10) comprising a disc (12) having oppositely-facing annular braking surfaces (12a, 12b), and two engagement members (14) mounted on opposite sides of the disc. The disc brake also comprises operating means (16) operable to cause the engagement members to move into braking engagement with the disc. The disc (12) comprises a metal support (12c) mounted on the member to be braked and poorly thermally conductive friction material (20b) in the form of a plurality of discrete pads mounted on said support so that the friction material forms said braking surfaces of the disc. The engagement members (14) are formed of material such as steel having relatively good thermal conductivity and being of limited angular extent are less prone to thermal stress deformation and, being at fixed positions in the rotational direction may be provided with simple and/or efficient cooling. The engagement members (14) may be formed of a resin based friction material provided it has a better thermal conductivity than the pads, preferably by a factor of two or more.

Description

DISC BRAKE

This invention is concerned with a disc brake of the spot type. In particular, a disc brake according to this invention is suitable for use on railway vehicles, on industrial machinery, and road vehicles.

A conventional disc brake of the spot type comprises a disc mounted for rotation with a member to be braked. For example, the disc may be mounted on the axle of a railway vehicle's wheel, on the flange of a railway vehicle's wheel, on an axle of an industrial machine such as a conveyor, or on the hub of a road vehicle's wheel. Such a disc has oppositely-facing annular braldng surfaces. Such a conventional disc brake also comprises two engagement members mounted on opposite sides of the disc in opposed relationship with a portion of the braldng surface on that side of the disc. The engagement members are mounted for movement towards said disc, and the disc brake also comprises operating means, such as a pneumatic or hydraulic system or a spring arrangement, operable to cause the engagement members to move into braldng engagement with the disc. Thus, during braking, each of the engagement members engages the disc over a portion of the braldng surface thereof, thereby creating fiictional forces which serve to brake the disc.

hi conventional disc brakes of the spot type, the materials of the disc and of the engagement members are selected so that high frictional forces are generated to ensure efficient braldng, and so that the heat generated during braking is conducted away. Normally, the disc is made from metal which is thermally-conducting and wears only slowly during the service life of the brake. For example, such discs are often made from cast iron as a single casting. The engagement members comprise so-called "friction material" selected to generate high frictional forces in engagement with the disc but not to cause rapid wear of the disc. For example, such friction material may be formed from sintered metal s or ^"from resin-bonded particulate material, especially phenolic resin-bonded. Such friction material is frequently thermally-insulating.

In many conventional disc brakes of the spot type, the disc is subject to an increased risk of damage because of the effects of the heat generated during braking. Where the disc is large and relatively cold, the commencement of braking rapidly heats a portion of the disc, setting up thermal stresses as part of the disc expands before the remainder can heat-up. Also, during severe or frequent braking, some discs become excessively hot and require to be actively cooled. Providing cooling for a disc is often not easy because of the rotation of the disc. For this reason, many discs are of complex construction incorporating ducts through which air is driven by centrifugal forces in order to cool the disc.

The friction material of the engagement members of conventional disc brakes of the spot type is somewhat sacrificial in that it wears much faster than the material of the disc. When wear of the friction material reaches an unacceptable level, it is the relatively easy to replace since the engagement members are relatively small and detachably mounted in holders. Although, as mentioned above, the material of the disc is selected so that it wears only slowly, it eventually wears to an unacceptable level or may be damaged. Thus, in due course, the disc must be replaced and this is often a major undertaking. For example, in the case of a railway carriage, in order to change the disc, it is necessary to drop the bogey of the carriage.

It is known for heavy duty braldng applications, such as landing aircraft and competitive sports, to bralce discs made of other than metal, particularly carbon composites and stationary pads for a complementary carbon composite or sintered material. Such arrangements may provide impressive levels of friction retardation but are not considered suitable for normal operation of road or rail-going vehicles whose brakes are operated only intermittently and required to effect low levels of retardation as well as high levels for which such carbon-based brakes are intended. Furthermore, it is also a requirement for such intermittently braked vehicles to operate in so-called wet conditions when the disc surface, and thus the interface between stationary and rotating surfaces, has a film of water therein prior to application of bralce pressure. It is known in the art that the coefficient of friction available from carbon-carbon brakes in such wet conditions is unsatisfactory, but whereas in the operational circumstances that require high braking levels such wetness is rapidly removed for braking to commence, this is not true of low braking levels that makes such carbon-carbon combination particularly unsuited to widespread use in typical land based transport vehicles.

It is an object of the present invention to provide a disc brake in which the problems caused by generated heat are reduced.

It is a further object of the present invention to disc bralce in which the problems associated with disc replacement are reduced.

The invention provides a disc bralce of the spot type comprising a disc mounted for rotation about an axis of rotation with a member to be braked, the disc having oppositely-facing annular braldng surfaces, the disc brake also comprising two engagement members mounted on opposite sides of the disc in opposed relationship with a portion of the braking surface on that side of the disc, the engagement members being mounted for movement towards said disc, such that the engagement members bear on and generate frictional braldng forces and heat at each of said oppositely-facing annular braking surfaces, and the disc bralce also comprising operating means operable to cause the engagement members to move into braldng engagement with the disc, wherein the engagement members are in the form of plates, each of which presents a substantially planar surface to the disc, the disc comprises a metallic support mounted on the member to be braked and friction material mounted on said support so that the friction material forms said braking surfaces of the disc, the friction material on each side of the support being in the form of a plurality of discrete pads of material selected from sintered materials and resin- bonded particulate materials material having a high coefficient of friction and a thermal conductivity lower than the engagement member with each pad occupying an arc of a circle centred on the axis of rotation, the pads together forming a substantially continuous braking surface.

hi a disc brake according to the invention, only the support of the disc is at risk due to thermal stress and this is separated from the surfaces at which heat is generated by the friction material. Where the friction material is thermally- insulating, the protection of the support is increased, and the need for cooling is reduced. Furthermore, wear on the disc occurs on the friction material mounted on the support and the friction material can be pads mounted for replacement when worn without requiring replacement of the support so that the operation is greatly simplified. In the case of a railway carriage, the friction material of the disc can be replaced without dropping the bogey. Since more friction material is present, the need to replace it should occur less frequently. The pads are preferably all of the same shape, that is, each occupies an arc of the same length about the axis of rotation.

The friction pads mounted on the disc have a lower thermal conductivity than each engagement member so that heat generated during braking does not result in deformation or damage to the disc and particularly the support. Heat generated at the interface between disc surface and engagement member, insofar as it is conducted away from the disc surface, is conducted by and into the engagement member and its support rather than through the disc friction material to the disc support.

There are, for various types of vehicles, performance standards to be met and for example, UIC requirements for railway vehicle braking requires that the coefficient of friction should not fall by more than 15% between dry and wet braking conditions, and it is found that carbon-carbon braldng does not meet this requirement in typical operating conditions. The engagement members, as they do not rotate, are easily actively cooled, for example, by circulating cooling fluid, either from a source or by circulating ambient air through fins.

a disc brake according to the invention, the engagement members can be of simpler form than in conventional disc brakes. For example, the engagement members in the form of metal plates each of which presents a substantially planar surface to the disc may be formed of steel. Such plates can be mounted, such as by welding, on plate supports adapted to fit conventional holders on existing vehicles or machines.

It is not essential that the engagement members be of a metal that offers best thermal conduction, and may alternatively be of a friction material, typically a resin- based friction material that offers a higher coefficient of friction than a metal plate, albeit with a somewhat lower thermal conductivity.

Such a friction material suitable for the engagement members may be a resin based formulation having a particularly high metal and/or graphite content in the fillers used. Such a resin-based engagement member should have a thermal conductivity greater than the disc friction pads by a factor of at least two and material maybe used offering thermal conductivity better by a factor of five or more.

As mentioned above, it is usual for a resin-based friction material in rubbing contact with metal to wear at a greater rate than the metal. The use of resin-based friction material for both disc mounted pads and stationary engagement members can result in longer operating lifetimes for the pads or indeed both pads and engagement members compared to when one is metal.

There now follows a detailed description, to be read with reference to the accompanying drawings, of a disc brake which is illustrative of the invention. In the drawings:

Figure 1 is a plan view of a portion of the illustrative disc bralce; and Figure 2 is an elevational view, partially in section, taken in the direction of the arrow π in Figure 1.

The illustrative disc bralce 10 shown in the drawings is of the spot type and comprises a disc 12 mounted for rotation with a member (not shown) to be braked. In this case, the disc brake 10 is for use on a railway vehicle and the member to be braked is a wheel set on which the disc 12 is fixedly mounted to rotate with the wheels and the axle. The disc 12 has oppositely-facing annular braking surfaces 12a and 12b.

The disc bralce 10 also comprises two engagement members 14 which are mounted on opposite sides of the disc 12 for movement towards the disc. Specifically, the members 14 are mounted on a conventional scissors-type mounting 15 so that one member is in opposed relationship with a portion of the braking surface 12a on that side of the disc and the other member 14 is in opposed relationship with a portion of the braking surface 12b on the other side of the disc. The members 14 are constructed so that they engage the braking surface over a segment thereof which, in this case, is along an arc of approximately 90° of the annulus formed by the braldng surface. The members 14 are arranged directly opposite one another on opposite sides of the disc.

The disc brake 10 also comprises operating means 16 (shown diagrammatically in Figure 1) operable to cause the engagement members 14 to move into braking engagement with the disc 12. In this case, the operating means 16 is of conventional construction and operates pneumatically to move the scissors-type mounting 15 so that the members 14 move towards the baking surfaces 12a and 12b.

The disc 12 comprises a support 12c which is fixedly mounted on the member to be braked which is, in this case, the axle of the wheel set. The support 12c is made of cast iron and comprises a central annular portion 12d and two annular friction material-supporting portions 12e arranged on opposite sides of the portion 12d. The portions 12e are co-axial with the portion 12d but have a greater diameter. The portions 12d and 12e are provided by a single casting. As illustrated in Figure 2, the portions 12e are provided with tapped holes into which bolts 18 can be inserted. Specifically, each portion 12e has thirty-two such tapped holes.

The disc 12 also comprises sixteen discrete pads 20 which are detachably mounted on the support 12c by means of the bolts 18. Eight of the pads 20 are mounted on each of the portions 12e of the support 12 and each pad 20 occupies an arc of approximately 45° of the ring provided by one of the portions 12e. Each pad 20 comprises a backing plate 20a made of steel and a block of friction material 20b secured to one surface of the plate 20a. The friction material 20b occupies substantially all of the surface area of one side of the plate 20a so that the friction material 20b of the pads 20 mounted on one of the support portions 12e form a substantially continuous braking surface 12a or 12b.

Each of the engagement members 14 comprises an alloyed steel plate 14a mounted on a support 14b. The support 14b is arranged to fit the mounting 15 and to support the plate 14a which is welded to the support 14b so that it presents a substantially planar surface 14c to the disc 12.

In the operation of the bralce 10, when it is desired to bralce the vehicle, the operating means 16 is utilised to move the plates 14b into engagement with the braking surfaces 12a and 12b formed by the friction material 20 of the pads 20. This creates braldng force on the disc 12. Heat generated during braking is only conducted to the disc's support 12c to a small extent because of the thermally insulating effect of the friction material 20b.

When the friction material 20b becomes worn to an extent that it requires replacement, the bolts 18 are undone and the pads 20 are replaced by new ones also secured by the bolts 18. This operation does not require removal of the entire disc from the vehicle. The engagement members 14 are also replaced when they become worn in the same manner as in conventional disc brakes.

As discussed above, the stationary engagement members may be formed from other than metal plates, by a resin-based friction material that is suited to high temperatures concentrated at the braking 'spot', and to conduct heat away from the pads. Such material should have a high filler content of thermally conductive materials and on such material based upon an available resin having fillers of graphite, copper fibres and large MgO particles for load bearing and thermal tolerance is able to provide a thermal conductivity of approximately five times that of the relatively poorly conductive friction material of the pads. A material having suitable properties is described in GB-A-2282821.

Claims

1. A disc bralce of the spot type comprising a disc mounted for rotation about an axis of rotation with a member to be braked, the disc having oppositely-facing annular braking surfaces, the disc brake also comprising two engagement members mounted on opposite sides of the disc in opposed relationship with a portion of the braking surface on that side of the disc, the engagement members being mounted for movement towards said disc, such that the engagement members bear on and generate frictional braking forces and heat at each of said oppositely-facing annular braldng surfaces, and the disc brake also comprising operating means operable to cause the engagement members to move into braking engagement with the disc, wherein the engagement members are in the form of plates, each of which presents a substantially planar surface to the disc, the disc comprises a metallic support mounted on the member to be braked and friction material mounted on said support so that the friction material forms said braldng surfaces of the disc, the friction material on each side of the support being in the form of a plurality of discrete pads of material selected from sintered materials and resin-bonded particulate materials material having a high coefficient of friction and a thermal conductivity lower than the engagement member, with each pad occupying an arc of a circle centred on the axis of rotation, the pads together forming a substantially continuous braking surface.

2. A disc brake according to claim 1, wherein the friction material pads are detachably mounted on the support.

3. A disc bralce according to claim 1 or claim 2 in which each engagement member comprises a metal plate.

4. A disc brake according to claim 3 in which each engagement member comprises a steel plate.

5. A disc bralce according to claim 4 in which in which the steel is alloyed steel.

6. A disc brake according to any one of claims 3 to 5 in which each engagement member comprises a plate support for said plate welded to the plate.

7. A disc brake according to any one of claims 1 to 6 in which each engagement member is dimensioned to fit a conventional engagement member mounting.

8. A disc brake according to claim 1 or claim 2 in which the engagement member is in the form of a plate of a resin-based friction material having a thermal conductivity better than the friction pads by a factor of two.

9. A disc bralce according to claim 8 in which the engagement member is in the form of a plate of a resin-based friction material having a thermal conductivity better than the friction pads by a factor of five.

10. A disc bralce according to any one of the preceding claims in which at least one of the engagement member and engagement member mounting includes cooling means operable to conduct heat away from the engagement member plate.

11. A disc bralce according to claim 10 in which the cooling means comprises cooling fins.

12. A disc brake according to claim 10 in which the cooling means comprises a source of cooling fluid and means to circulate it in contact with the engagement member or engagement member mounting.

13. A disc brake according to any one of the preceding claims in which each of said discrete pads extends around the axis of rotation through an angle of

. approximately 45 degrees.