GB2343721A

GB2343721A - Friction disc for a clutch or disc brake

Info

Publication number: GB2343721A
Application number: GB9819942A
Authority: GB
Inventors: Lefkos Andrews
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-09-15
Filing date: 1998-09-15
Publication date: 2000-05-17
Also published as: GB9819942D0

Abstract

A friction disc for a clutch or disc brake of a vehicle, has a plurality of bosses 14 arranged around the periphery of carrier disc 10 and projecting in the axial direction thereof. Each boss 14 is spaced from its neighbouring bosses whereby air may flow freely therearound when the friction disc rotates to effect cooling. When used in a disc brake with a brake calliper, the friction material of the calliper engages the end faces 15 of the bosses 14 lying in a radial plane. The carrier disc and bosses may be made in one piece, by a machining operation on on a solid disc or casting of aluminium alloy. Once ground, the end faces 15 are polished and then subjected to a nitriding treatment to give a very hard high quality surface finish.

Description

FRICTION DISC This invention relates to a friction disc. In particular, though not exclusively, this invention relates to a friction disc suitable for use in conjunction with a calliper to form a disc brake for a vehicle, or suitable for use as a clutch disc, though the friction disc may be used in other applications as well.

A well-known and understood problem associated with the use of friction discs in disc brakes for vehicles is the dissipation of heat from the disc, resulting from the application of the brake. The kinetic energy of the vehicle is converted to heat by the gripping of the disc between a pair of opposed brake pads mounted in a calliper, which pads are relatively non-conductive of heat. The greater part of the heat must be directly absorbed by the disc, from which the heat must then be dissipated. If the heat cannot be dissipated quickly enough, the temperature of the disc will rise to an unacceptable level, which can result in disc distortion and also present a fire risk. There can also be so-called brakefade, where the maximum braking effect which can be achieved falls away with increased disc temperature. For small, lightweight vehicles, a simple solid disc may have sufficient thermal capacity for no significant problem to arise, even from repeated braking. With higher performance or heavier vehicles other measures must be taken to prevent the discs overheating and distorting heat. To address these problems,. it is known to provide a ventilated disc, where there are two parallel disc surfaces held spaced apart by vanes, and one of the discs is cut away in the central region whereby generally radial outward air flow may take place between the two disc surfaces, promoted by the vanes on rotation of the disc. Heat is transferred to the air flowing between the disc surfaces, so dissipating the heat generated on applying the brake.

It is also known to provide a brake disc with holes therethrough, parallel to the disc axis. This reduces the overall weight of the disc, but more importantly also promotes air flow through the disc, allowing heat transfer to take place from the disc to the air.

Despite the measures as described above, the problem of over-heating brake discs still arises, particularly if a vehicle is used for competition purposes.

There is thus a need for a disc which is able to demonstrate high heat dissipation, whilst permitting repeated strong brake application without displaying brake fade.

According to one aspect of the present invention, there is provided a friction disc comprising a mounting region and an annular friction region around the mounting region, which friction region has a plurality of bosses upstanding axially from one side of a carrier portion and arranged serially therearound, each boss being spaced from its neighbouring bosses and the end faces of the bosses being disposed in the same radial plane for engagement in use by frictionmaterial.

The disc of this invention differs significantly from the previous disc designs discussed above, in that there is a carrier portion having bosses upstanding from at least one side thereof, which bosses project in a direction parallel to the disc axis with each boss being spaced from its neighbours. The end faces of the bosses remote from the carrier portion are all disposed in the same radial plane, whereby the disc may be used with a calliper, in a disc brake assembly. Experimental tests have shown that this disc is able to dissipate heat particularly effectively while still permitting excellent brake performance even at elevated temperatures. It is presumed that this is on account of the complex air flow currents generated upon rotation of the disc, by virtue of the upstanding and spaced apart bosses. These air currents allow heat to be transferred to the cooler air flowing past and over the bosses. This, together with the increased thermal capacity of the disc as compared to a simple disc having a thickness comparable to that of the carrier itself, allows the enhanced performance.

A preferred form of the disc of this invention has bosses upstanding parallel to the disc axis from the two opposed radial side faces of the carrier portion. In such an arrangement, the bosses upstanding from the two side faces are aligned with one another. Such a friction disc may conveniently be constructed by casting a suitable metal and then finish-machining the casting, or by machining the disc from solid. It also would be possible to provide a generally planar carrier portion with a plurality of apertures therethrough, the bosses being located centrally in the apertures so as to project to both sides of the carrier portion. Whichever way the disc is made, in this preferred design, the bosses upstanding from both sides of the carrier portion should be of substantially the same shape and configuration.

Experiments have shown that it is preferred for each boss to be of a circular configuration, so that a circular face is presented for engagement by friction material, when in use. It is believed this gives advantageous properties for the air flow around the bosses, promoted by rotation of the disc, for the transfer of heat to that air.

Further to improve the disc performance, the outer periphery of the carrier portion may be profile to match the outer edge surfaces of the bosses, but for a part only of the outer edge surface of each boss. Thus, the outer periphery of the carrier portion may comprise a plurality of arcuate sections centred respectively on each boss, and joined together by a further plurality of arcuate sections each of which may be centred on the axis of rotation of the carrier portion. Alternatively, these further arcuate sections could be centred externally of the carrier portion on an extended radius of the carrier portion passing between the respective bosses.

It is preferred for the entire disc to be made of an aluminium alloy material. Such an arrangement allows a relatively lightweight construction as well as giving good thermal conductivity properties. With bosses of an aluminium alloy material, the surfaces of the bosses engaged in use by friction material are preferably subjected to a nitride hardening treatment to minimise wear, in use. The disc could instead be made of steel or other metals.

The mounting region of the carrier portion should be adapted to allow the mounting of the disc on a shaft, irrespective of whether the friction disc is to be used as a brake disc or as a clutch disc. At its simplest, the mounting region may comprise a hub adapted to be carried on a shaft extending through a central bore. Alternatively, the mounting region may comprise a plurality of lugs formed around the inner periphery of the annular carrier portion, a plurality of holes being formed on a common pitch circle in said lugs for mounting the disc on a separate hub.

This invention extends to an automotive friction brake comprising in combination a friction disc of this invention as described above and a calliper supporting friction material to each side of the friction region of the disc whereby in use the calliper urges the friction material into engagement with the friction surfaces of the bosses upstanding from the disc.

By way of example only, one specific embodiment of friction disc of this invention, intended for use as a brake disc for a racing go-kart, will now be described in detail, reference being made to the accompanying drawings, in which : Figure 1 is a plan view of the embodiment of disc; Figure 2 is a perspective view of the disc of Figure ; Figure 3 is a diagrammatic view of the disc being used in a disc brake assembly ; and Figure 4 is a diagrammatic view of the disc being used in a clutch assembly.

The friction disc shown in the drawings comprises a carrier 10 of a generally annular shape, and having six inwardly directed lugs 11, each provided with a mounting hole 12. The carrier supports a plurality of cylindrical bosses 14, equi-spaced around the outer periphery of the carrier with gaps 3 between adjacent bosses. The end faces 15 of all of the bosses are accurately aligned in the same radial plane, achieved by grinding the opposed end faces of all of the bosses so as to lie in two precisely parallel radial planes. The carrier and bosses are preferably all made in one piece, by a machining operation on a disc having an initial thickness not less than the required spacing of the opposed end faces 15.

Both the carrier 10 and all of the bosses 14 are made from a hard aluminium alloy material. Once ground, the end faces 15 of all of the bosses are polished and then are subjected to a nitriding treatment, to give a very hard high quality surface finish thereto. In this embodiment, approximately one third of the area of the end face 15 of each boss lies outside the periphery of the carrier 10.

When the disc is to be used as a brake disc for a brake disc assembly, it is mounted on a suitable hub such as that shown at 16, in Figure 3, utilising bolts extending through holes 12 in the carrier and threaded into the hub. The hub 16 itself is carried on a shaft 17 rotatably mounted in a suitable part of a vehicle-and in the case of a go-kart, on the transverse drive shaft extending between the two rear wheels. A calliper 18 is mounted on a fixed component of the kart and has a pair of friction pads (not shown) arranged to engage the opposed end faces of the bosses, when hydraulic fluid is supplie under pressure to the calliper 18.

In the case of a clutch disc, a relatively narrow hub (not shown) is arranged within the central opening of the annular carrier 10, which hub is secured to the carrier by bolts extending through holes 12. The hub has a splined central aperture for sliding engagement on a correspondingly-splined spigot 20, forming part of the drive train from an engine. The friction plate is arranged between a driven disc 21, such as the flywheel of an engine, and a pressure plate 22 secured to the driven disc 21-in Figure 4, the disc 21 is shown separate from the pressure plate 22, for clarity. Clutch operation is performed by a mechanism (also not shown) which bears on the spring fingers 23 of the pressure plate 22.

In use, it is found that the air flow generated by the upstanding bosses of the disc causes significant air currents around the bosses. These currents dissipate heat from the bosses, generated by friction between the friction pads and the end faces of the bosses. The friction disc has a relatively low weight whilst displaying good thermal conductivity, and the nitrided end faces of the bosses allows excellent braking performance with very low wear rates.

Claims

CLAIMS 1. A friction disc comprising a mounting region and an annular friction region around the mounting region, which friction region has a plurality of bosses upstanding axially from one side of a carrier portion and arranged serially therearound, each boss being spaced from its neighbouring bosses and the end faces of the bosses being disposed in the same radial plane for engagement in use by friction material.
2. A friction disc as claimed in claim 1, wherein the annular friction region has bosses upstanding axially from both side faces of the carrier portion.
3. A friction disc as claimed in claim 2, wherein the bosses upstanding from the other side face of the carrier portion are aligned with the bosses upstanding from said one side face of the carrier portion.
4. A friction disc as claimed in claim 2 or claim 3, wherein the bosses upstanding from both sides of the carrier portion are of substantially the same shape and configuration.
5. A friction disc as claimed in any of the preceding claims, wherein each boss is of circular configuration, presenting a circular face for engagement in use by friction material.
6. A friction disc as claimed in any of the preceding claims, wherein the outer periphery of the carrier portion is profile to match the outer edge surfaces of the bosses, for a part only of the outer edge surface of each boss.
7. A friction disc as claimed in any of the preceding claims, wherein each of said bosses is made of an aluminium alloy material.
8. A friction disc as claimed in claim 7, wherein the surfaces of the bosses engaged in use by friction material are subjected to a nitride hardening treatment.
9. A friction disc as claimed in any of the preceding claims, wherein the mounting region is configured to allow attachment of the disc to a rotatable shaft.
10. A friction disc as claimed in any of the preceding claims, wherein the disc is manufactured by a machining operation on one of a solid metal disc or a metal casting.
11. A friction disc as claimed in claim 1 and substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
12. An automotive friction brake comprising in combination a friction disc as claimed in any one of the preceding claims and a calliper supporting friction material to each side of the friction region of the disc and arranged in operation to urge the friction material into engagement with the friction region of the disc.