GB2024346A - Brake Discs - Google Patents

Abstract

The brake disc 10 comprises two co-axial annular metal (e.g. austenitic ferrous or copper) disc portions 11 and 12, each having a braking surface 13 and 14 respectively, and with opposed inner faces 17 and 18 respectively having undercut axial projections 15 extending between the disc portions 11 and 12 and embedded in and interlocked against axial movement by a core of metal (specifically aluminium) cast between the two disc portions. The aluminium filled circumferential spaces between groups 21, 22, 23 of projections 15 have radial air passageways 33 for cooling air- passageways are separated by webs of which alternate ones extend across the whole radial width and across 50% of this width of the disc 10. The process of forming the disc is disclosed. <IMAGE>

Description

SPECIFICATION Brake discs This invention relates to brake discs for disc brakes.

According to this invention there is provided a brake disc comprising two co-axial annular disc portions each having a braking surface, and with axially opposed inner faces having axial projections thereon extending between the disc portions and embedded in and interlocked against axial movement by a core of metal cast between the two disc portions.

Preferably the metal core is of a metal, such as aluminium, of a high specific heat, high thermal conductivity and low specific gravity.

Conveniently the projections extend from inner face of each annular disc portion to abut against the inner face of the other disc portion. The projections therefore, take the clamping loads on each side of the disc when the brakes are applied.

Also by making the two disc portions interchangeable the number of different parts and therefore cost is kept to a minimum.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings in which: Fig. 1 is a section of a brake disc according to this invention taken on the line I-I of Fig. 2; Fig. 2 is a section through a brake disc taken on the line ll-ll of Fig. 1; Fig. 3 is a section through a brake disc taken on the line Ill-Ill of Fig. 1; and Fig. 4 is a view of a brake disc in the direction of arrow X in Fig. 1.

With reference to Fig. 1 to 4 a brake disc 10 comprises two co-axially spaced annular austenitic ferrous metal disc portions 11 and 12, each having a braking surface 13 and 14 respectively for engaging with a pair of friction pads (not shown) of a disc brake. The two disc portions 11 and 12 have axially opposed inner faces 17 and 18, each face 17 and 18 having axial projections 15 integral therewith which extend from that face to abut against the opposed inner face of the other disc portion 11 and 12.

Each projection 15 is tapered with a 50 angle of taper to form a dove-tail such that the end face of the projection 15 away from its inner surface is of a greater cross-sectional area than its root thus forming an undercut. The projections 15 are arranged on the opposed inner faces 17 and 18 of the disc portions to occur in twelve equiangularly spaced groups each of our projections 15, and each group of four projections is arranged on a radius of the disc such that the axial projections 15 alternate one from each inner face 17 or 18 across the radial width of the disc.

A radial group 21 of projections 15 is shown in section in Fig. 2 and it can be seen that the outer peripheral projection is integral with the disc portion 12 and the adjacent projection radially inwards is integral with the disc portion 11 as described above.

In an adjacent group 22 of projection 15 the outer peripheral projection is integral with the disc portion 11 and the adjacent radially inwards projection is integral with the disc portion 12. A group 23 on the opposite side of the group 22 to the first mentioned group 21 is arranged in the same manner as the group 21 i.e. the radially outer projection is integral with the disc portion 12 followed by the alternating sequence across the radial width of the disc. This alternate arrangement of the groups of projections is continued in sequence around the disc 10. The two disc portions 11 and 12 are therefore identical, the one disc portion 11 being rotated by some 30 so that the projections 15 on the one disc portion intermesh with the projections 15 on the other disc portion 12.

The space 19 formed between the two disc portions 11 and 12 is filled by casting an aluminium alloy core therein. The aluminium core envelopes the projections 15 from each inner face 17 and 18 so as to hold by means of the dove tail reverse 5 taper, the two disc portions 11 and 12 together.

The aluminium filled circumferential spaces between the groups of projections 15 have radial air passageways 33 therein for the flow of cooling air.

The air passageways 33 are separated by radial webs 24 which extend from the outer periphery of the brake disc 10 radially inwards. Alternate webs extend across the whole radial width of the disc and the other webs, located between said alternate webs, only extend approximately 50 across said width, so as not to choke the in flow of air to the inner periphery of the disc.

The aluminium alloy is cast into the space between the austenitic iron discs 11 and 12 using a technique known as the "Alfin" process. The Alfin process is fully described in U.S. Patent 2396730 and U.S. Patent 2455457 and very briefly in this case, involves the following steps: (a) cleaning annular disc 11 and 12 by sand blasting; (b) covering the portions of the discs not to be coated in a stop-off preparation and then immersting the disc in a bath of molten aluminium alloy at about 1525"F-1625"F (830 = 870"C) and forming a thin iron aluminium alloy, forming a molecular bonded layer of aluminium on the inner surface of the disc. This might be described as being equivalent to "tinning" during soldering; (c) immediately transferring the discs coated with the thin film of iron-aluminium alloy to a mould and then casting in the aluminium alloy to form the ventilation passageways and to interlock the two annular disc halves of the brake disc together.

Whilst this process has been described for austenitic ferrous discs it is equally applicable to a copper disc with an aluminium core, (see U.S. 2453772).

The advantages of casting an aluminium core into the brake disc is that it makes a lighter disc, and the aluminium has a higher specific heat and a higher thermal conductivity than the iron annular discs and therefore heat is conducted more rapidly away from the braking surfaces than would be the case for the equivalent all ferrous brake disc. Furthermore aluminium is a easier material to cast and therefore more complicated and delicate cooling vanes and webs are within the brake designers grasp.

Claims (7)

1. A brake disc comprising two co-axial annular metal disc portions each having a braking surface, and with axially opposed inner faces having undercut axial projections thereon extending between the disc portions and embedded in and interlocked against axial movement by a core of a lower melting point metal cast between the two disc portions.

2. A brake disc as claimed in Claim 1, wherein the disc portions are cast ferrous metal and the metal core is of a metal, such as aluminium, of a high specific heat, high thermal conductivity, and low specific gravity.

3. A brake disc as claimed in Claim 1 or Claim 2, wherein the axial projections on each annular disc portion extend from the inner face thereof to abut against the inner face of the other annular disc portion.

4. A brake disc as claimed in any one of Claims 1 to 3, wherein the projections comprise equiangularly spaced sets of radially aligned projections and said aligned projections alternate one from each annular disc portion across the radial width of the brake disc.

5. A brake disc as claimed in any one of Claims 1 to 4, wherein each projection is of a dove tail configuration to provide the interlock with the cast metal core.

6. A brake disc as claimed in any one of Claims 1 to 5, wherein the two annular discs are interchangeable.

7. A brake disc substantially as described herein and as shown in the accompanying drawings.