GB2132290A

GB2132290A - Improvements in disc assemblies for vehicle disc brakes

Info

Publication number: GB2132290A
Application number: GB08332513A
Authority: GB
Inventors: John Patrick Bayliss
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1982-12-16
Filing date: 1983-12-06
Publication date: 1984-07-04
Also published as: GB8332513D0; GB2132290B

Abstract

In a disc assembly, a brake disc ring 1 is secured to one face of a rotor 3 by bolts or other fasteners 5 which are passed through openings 7 and 9 in the ring and the rotor and are stressed substantially only in tension and the bolts or other fasteners allow movement between ring and rotor as a result of differential thermal expansion associated with a braking operation: a plug 20 e.g. of malleable or ductile material is located in the outer end of each opening 7 in the ring 1 to modify the level of the strains and associated stresses. The specification discloses a number of embodiments of bolt fasteners and their associated plugs e.g. the plugs 20, 21 in respective openings 7, 9 in rings 1, 2 may be driven into counterbores 11, 13, or plugs are in the form of hollow liners or bushings 40, 41, a head 10 on bolt (5) engaging a shoulder in bushing 40. <IMAGE>

Description

SPECIFICATION Improvements in disc assemblies for vehicle disc brakes This invention relates to disc assemblies for vehicle disc brakes of the kind in which a brake disc ring is secured to a face of a rotor, such as a supporting wheel of a rail vehicle, by bolts or other fasteners which are passed through openings in the rotor and in the disc ring and which are stressed substantially only in tension, and the bolts or other fasteners being so constructed and arranged as to permit relative movement between the disc ring and the wheel as a result of their differential thermal expansion associated with a brake-applying operation in which a friction member is applied to the outer braking face of the disc ring.

It has been found in disc assemblies of the kind set forth that small cracks or crazing sometimes occur in the outer braking faces of the disc ring, in the region of the openings. it is believed that these may be caused by strain in a hoop direction which is set up around the openings as a result of the temperature gradient across the rings or, alternatively, as the result of a stress concentration factor, substantially in the order of 3:1, due to the presence of the openings.

According to our invention in a disc assembly of the kind set forth a plug is located in the outer end of each opening in the brake disc to modify the level of the strains and associated stresses.

This reduces substantially the tendency for cracking or crazing to occur in the region of the openings.

The plug may be of malleable or ductile material, conveniently in the form of a cup which is inserted into the outer end of the opening in a position in which it is flush with, or lies slightly below, the braking face of the disc ring. In such a construction the plug may be of sufficient interference in the opening to achieve positive retention, or the plug may be retained in the opening by a locking engagement with a solid ring which is clamped against a shoulder in the opening by a head on the bolt or other fastener.

Alternatively the plug may comprise a hollow liner or bushing of generally stepped outline which is either pressed into the opening or is cast into the disc ring during its manufacture, a head on the bolt or other fastener engaging with a shoulder comprising a radial flange at the inner end of the liner or bushing.

When each fastener comprises a bolt which projects through the opening in the rotor and is screwed into a nut which, in turn, is operative to clamp a brake disc ring against the opposite face of the rotor, the opening in which the nut is received is provided with a similar plug or the nut itself is enlarged to fill the opening which is of complementary outline, example hexagonal.

When the said similar plug is in the form of a cup it can be retained in position in the opening by the engagement with the nut itself.

In another construction the plug comprises a liner or bushing, which is retained in the opening by the clamp action of the bolt.

In yet another construction the bolt projects through a bushing which, in turn, projects through the openings in the two brake disc rings and the rotor, and plugs are retained in the outer ends of the openings in the disc rings by engagement with a flange on the bushing, with which the head of the bolt co-operates, and the nut itself, respectively.

Some embodiments of our invention are illustrated in the accompanying drawings in which: Figure 1 is a section through a disc assembly for the disc brake of a rail vehicle; Figure 2 is a view on a enlarged scale of the connection between the head of the bolt and one of the brake disc rings in the disc assembly of Figure 1; Figure 3 is a view similar to Figure 2 but showing a modification; Figure 4 is a view similar to Figure 2 but showing another modification; Figure 5 is a view similar to Figure 1 but showing a modification; Figure 6 is a view similar to Figure 1 but showing another construction; Figure 7 is a view similar to Figure 6 but showing a modification; Figure 8 is a modification of the construction shown in Figure 6; and Figure 9 is a plan of Figure 8.

In the disc assembly illustrated in Figures 1 and 2 of the drawings cast iron brake disc rings 1 and 2 of annular outline are clamped against opposite faces of a rotor 3, suitably the wheel of a rail vehicle, by a plurality of angularly spaced fasteners 4.

Each fastener comprises a bolt 5 having a threaded stem 6 which projects through aligned, clearance, openings 7, 8 and 9 in the two rings 1 and 2, and the rotor 3, respectively, and a conical head 10 which is received in a counterbore 11 in the outer, braking face, of the ring 1, and a conical nut 1 2 which is received in a counterbore 13 in the outer, braking face, of the ring 2.

The head 10 acts on a shoulder 1 5 at the base of the counterbore 11 through a solid washer 17, and the nut 12 acts directly on a shoulder 18 at the base of the counterbore 13.

A solid plug 20, suitably of malleable cast iron, is driven into the counterbore 11 to close its outer end, and a similar solid plug 21 is driven into the counterbore 13. Each plug 20 and 21 is provided at its inner end with an annular ring or angularly spaced axially extending fingers 22 which embrace outer conical faces 23, 24 on the washer 1 7 and on the nut 12 respectively when the plugs 20 and 21 are driven into the outer ends of the counterbores 11 and 1 3 into positions in which they lie substantially flush with, or slightly below, the braking faces. The plugs 20 and 21 constitute inserts of generally cup-shaped outline.

The plugs 20 and 21 act to modify the stresses and strains surrounding the openings 7 and 8 which occur as a result of the temperature gradients across the disc rings 1 and 2 when the brake is in use.

In the modification of Figure 3, the head 10 of the bolt 5 has parallel ends, and the washer 17 is provided with a recess of complementary outline and, in the modification of Figure 4, the thickness of the washer is increased to enhance the grip with the plug 20.

In the construction of Figure 5 the washer 17 is omitted and a bush 30 is a close fit in the openings 7, 8 and 9. The stem 6 extends, with substantial clearance, through the bore 31 of the bush 30, the head 10 engages with a radial flange 32 of the adjacent end of the bush 30, which is equivalent to the washer 17, and the nut 12 includes a central spigot portion 33 which is received in a counterbore 34 in the adjacent end of the bore 31.

The construction of the brake disc of Figure 5 is otherwise the same as that of Figure 1 and 2 and corresponding reference numerals have been applied to corresponding parts.

In the construction illustrated in Figure 6 inserts in the form of hollow liners or bushings 40 and 41, suitably of steel, are pressed into the counterbores 11 and 1 3. Alternatively, the liners or bushings 40 and 41 can be cast into the disc rings 1, 2 during their manufacture. When the liner or bushing 41 is pressed into the disc ring 2 the liner of bushing 41 and at least the complementary counterbore 13, may be of noncircular, suitably hexagonal, outline to prevent the liner or bushing 41 , which is threaded internally to constitute the nut 12, from rotating as the bolt 5 is tightened.

In the modified construction illustrated in Figure 7, the bores 7 and 8 are enlarged and the steel liners or bushings 40 and 41 are pressed into the bores 7 and 8 and the counterbores 11 and 13 with complementary shoulders in engagement to clamp the disc rings 1 and 2 against the rotor 3. In this construction the head 10 has parallel end faces.

In the modified construction illustrated in Figures 8 and 9, the liner or bushing 41 has a recess 50 of hexagonal outline in which a nut 51 is received, and the stem 6 is screwed into the nut 51, which is held against rotation by the wall of the recess 50.

Claims

1. A disc assembly of the kind set forth in which a plug is located in the outer end of each opening in the brake disc to modify the level of the strains and associated stresses.

2. A disc assembly as claimed in Claim 1, in which the plug is of malleable or ductile material.

3. A disc assembly as claimed in Claim 1 or Claim 2, in which the plug is retained in its opening by interference.

4. A disc assembly as claimed in Claim 1 or Claim 2, in which the plug is retained in the opening by the clamp action of the bolt or other fastener.

5. A disc assembly as claimed in Claim 4, in which the plug is of cup-shaped outline having an annular ring or axially extending angularly spaced fingers at its inner end, and the plug is retained in its opening by the locking engagement of the ring or the fingers with a solid ring which is clamped against a shoulder in the opening by a head on the bolt or other fastener.

6. A disc assembly as claimed in Claim 5, in which the solid ring comprises a radial flange at one end of a bushing.

7. A disc assembly as claimed in Claim 6, in which the bushing projects through openings in two brake disc rings and the rotor, and a second plug is retained in the outer end of the opening in the second disc ring on the side of the rotor remote from the radial flange, the bolt or other fastening projecting through the bushing and being screwed into a nut, which nut co-operates with an annular ring or radial fingers at the inner end of the second plug to retain it in the opening by the locking engagement of the nut with the ring or fingers.

8. A disc assembly as claimed in Claim 4, in which the plug comprises a hollow liner or bushing of generally stepped outline and a head on the bolt or other fastener engages with a shoulder comprising a radial flange at the inner end of the liner or bushing.

9. A disc assembly as claimed in Claim 8, in which the liner or bushing is pressed into the opening.

10. A disc assembly as claimed in Claim 8, in which the liner or bushing is cast into the disc ring during its manufacture.

11. A disc assembly as claimed in any of Claims 1 to 6 or 8 to 10, in which each fastener comprises a bolt which projects through an opening in the rotor and is screwed into a nut which, in turn, is operative to clamp a brake disc against the opposite face of the rotor.

12. A disc assembly as claimed in Claim 11, in which the opening in which the nut is received is provided with a plug having annular ring or radial fingers at its inner end to retain it in the opening by the locking engagement of the nut with the ring or fingers.

13. A disc assembly as claimed in Claim 11, in which the nut is enlarged to fill the opening which is of complementary outline.

14. A disc assembly as claimed in Claim 13, in which the nut and the opening are both of hexagonal outline.

15. A disc assembly as claimed in Claim 11, in which the opening in which the nut is received is provided with a plug comprising a hollow liner or bushing of generally stepped outline and the nut engages with a shoulder comprising a radial flange at the inner end of the liner or bushing.

1 6. A disc assembly substantially as described herein with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.

1 7. A disc assembly substantially as described herein with reference to and as illustrated in Figure 3 of the accompanying drawings.

1 8. A disc assembly substantially as described herein with reference to and as illustrated in Figure 4 of the accompanying drawings.

1 9. A disc assembly substantialy as described herein with reference to and as illustrated in Figure 5 of the accompanying drawings.

20. A disc assembly substantially as described herein with reference to and as illustrated in Figure 6 of the accompanying drawings.

21. A disc assembly substantially as described herein with reference to and as illustrated in Figure 7 of the accompanying drawings.

22. A disc assembly substantially as described herein with reference to and as illustrated in Figures 8 and 9 of the accompanying drawings.