IMPROVEMENTS IN VEHICLE DISC BRAKES OF THE LIQUID COOLED TYPE

Abstract: A braking member for a brake of the liquid cooled type is provided on at least one side with an annular reservoir (15) for cooling liquid, and passages (10) are arranged to control the release of liquid from the reservoir to braking surfaces in response to centrifugal force.

Description: This invention relates to improvements in vehicle disc brakes of the liquid-cooled type, of the kind in which at least one rotatable friction braking member keyed to a shaft to be braked and having a braking surface is rotatable in a housing containing a cooling liquid for cooling the braking member, and the braking member is adapted to co-operate with a relatively stationary braking surface to apply the brake. Brakes of the kind set forth are commonly used in tractors or the like vehicles, and the cooling liquid usually comprises oil from the gearbox. In order to minimise parasitic drag, particularly when the oil is cool, and conserve consequent power, it is usual for the oil in the gearbox to be maintained substantially at the minimum level only necessary to provide adequate lubrication. This, in turn, creates the problem that such a minimum level represents a volume of oil which is normally inadequate to achieve a degree of cooling of the braking member necessary to sustain a minimum wear life for the lining. We are aware of US Patent No. 3 124 216 which discloses a disc brake of the kind set forth in which each of a pair of complementary disc members or pressure plates are provided with internal annular reservoirs through which cooling liquid is circulated. The reservoirs are completely sealed, both within the disc members or pressure plates, and from co-operating braking surfaces of the brake. We are also aware of GB Published Patent Application No. 2 141 193 A which discloses a liquid cooled disc braking having a rotatable friction braking disc keyed to a shaft to be braked and having opposed surfaces each of which carries a friction lining. Each friction lining is divided into two annular rings by a single annular groove. Radial grooves are provided in the inner ring extending from the inner peripheral edge of the inner ring to the annular groove. The annular groove acts as a reservoir for cooling liquid in the face of the friction disc and its cooling liquid is replenished by the radial grooves in the inner ring which serve as reservoir supply flow grooves. Further radial grooves are usually provided in the outer ring and these help to control the flow of cooling liquid across the braking faces of the friction disc. The aim of the present invention is to provide a brake having a further improved reservoir for cooling liquid for rotatable braking members. According to our invention, in a disc brake of the kind set forth the braking member is provided on at least one side with an annular reservoir for cooling liquid, and passage means are arranged to control the release of liquid from the reservoir to the braking surfaces in response to centrifugal force, characterised in that the braking member comprises a generally planar member and an annular wall axially spaced from the planar member, the reservoir being defined between the annular wall and the adjacent portion of the planar member. The reservoir stores the cooling liquid for supply to the braking surfaces, and the cooling liquid is conserved by arranging for the passage means to release the liquid only at a rate sufficient to affect adequate cooling of the braking surfaces for a given volume of available cooling liquid. This helps alleviate problems of a braking surface having two much or too little cooling liquid and so improves the brake. Preferably the annular wall is secured to, or is otherwise integral with, the planar member at least at the radially innermost end of the wall. The reservoir is adapted to receive cooling liquid, for example by means of a gravity feed, or by means of a pump separate from the braking member, or by means of an impeller constituted at least in part by the braking member itself. The reservoir may have an open mouth at its innermost end, which is particularly suitable for receiving cooling liquid by gravity feed or from a pump separate from the braking member. When the impeller is constituted by a part of the braking member, the reservoir may be closed at its innermost end and may receive liquid from the impeller through transfer openings in the braking member itself. The passage means may comprise angularly spaced exit slots at the radially outermost end of the reservoir. The slots may be disposed in the wall adjacent to the friction member, or the slots may be provided in the thickness of the material of the friction member itself with the inner ends of the slots extending into the projected area of the reservoir. The reservoir may be provided with angularly spaced baffles which act to raise liquid into the reservoir from a sump and/or restrict movement of liquid in the reservoir in circumferential direction. The baffles may extend between the braking member and the wall, and they may be straight. Some embodiments of our invention are illustrated in the accompanying drawings in which:- Figure 1 is an end view of a friction braking member for a disc brake of the liquid-cooled type; Figure 2 is a section on the line 2-2 of Figure 1; Figure 3 is an end view of another friction braking member; Figure 4 is a section on the line 4-4 of Figure 3; Figure 5 is an end view of a portion of another friction braking member; Figure 6 is a side elevation of two friction braking members, each as shown in Figure 5; Figure 7 is an end view of yet another friction braking member; Figure 8 is a section on the line B-B of Figure 7; Figure 9 is an end view of another friction member; Figure 10 is a section on the line 10-10 of Figure 9; Figure 11 is an end view of another friction member; Figure 12 is a section on the line 12-12 of Figure 11; Figure 13 is a section on the line 13-13 of Figure 12; Figure 14 is an end view of another friction member; and Figure 15 is a section on the line 15-15 of Figure 14. The friction braking member illustrated in Figures 1 and 2 of the accompanying drawings is adapted for use in a brake of the liquid cooled-type having a sump filled with cooling liquid, constituted by oil, to a depth 1 as shown. The friction member comprises a planar metal disc 2 of annular outline which is slidably splined for axial sliding movement on a shaft 3 which extends axially through a housing (not shown). The housing defines the sump. Annular braking surfaces 4, 5 are defined by portions of opposite faces of the disc which terminate at the peripheral edge of the disc. The braking surfaces 4, 5 may carry annular linings of friction material. A wall 6 of dish-shaped outline is mounted on one side of the disc. The wall 6 comprises oppositely directed inner and outer annular flanges 7 and 8 which are interconnected by an circumferentially extending rim 9. The inner flange 7 is of greater radial length than the outer flange 8, and the outer flange 8 is secured to the disc with its outer peripheral edge disposed inwardly of the braking surface 4. The flange 8 and the rim 9 are perforated and/or otherwise deformed to define a plurality of angularly spaced exit ports 10. When the braking member is installed in the housing, it is positioned between members which are provided with braking surfaces similar to the surfaces 4 and 5, and with which the surfaces 4 and 5 are adapted to co-operate. For example, when the braking member is incorporated in brake of the self-energising spreading type, for example as disclosed in G.B. 2 141 193, it may be disposed between the actuating mechanism and a face constituted by one end of the housing. The annular space between the wall 6 and the disc 2 defines a reservoir 15 for cooling liquid. When the disc rotates, the liquid is forced outwardly centrifugally through the exit ports 10 and over the adjacent braking surface 4. The liquid is progressively released from the reservoir during each revolution of the disc. In the friction braking member illustrated in Figures 3 and 4 of the drawings, the braking surfaces 4 and 5 carry annular linings 11 of friction material, and a wall 12 similar to the wall 6 is mounted on the opposite side of the disc to constitute a second reservoir 14, with the wall 12 also provided with a plurality of annularly spaced exit ports 13. Thus, upon rotation of the discs, cooling liquid is supplied to both friction linings 11. Each reservoir 14, 15 may be provided with a plurality of angularly spaced baffles 16 to facilitate the transfer of liquid from the sump and into each reservoir. In addition at least the wall 6 may be provided with a plurality of angularly spaced impellers 17 through which liquid is drawn into the reservoir 15 upon rotation of the disc. The construction and operation of the disc of Figures 3 and 4 is otherwise the same as that of Figures 1 and 2, and corresponding reference numerals have been applied to corresponding parts. As shown schematically in Figures 5 and 6, the cooling liquid may be supplied to a pair of discs 21, 22 each similar in construction to the disc of Figures 3 and 4. In this construction cooling liquid is discharged through the discs from a jet 23. The discs 21, 22 are provided with a plurality of angularly spaced, circumferentially extending, slots 24, with lands 25 defined between adjacent pairs of slots 24. When the discs are arranged in side-by-side relationship in a slack, such as in a disc brake of the multi-plate type, the discs utilise graduated slot: land ratios to allow interrupted liquid jet flow. This, therefore, controls the distribution of liquid across the stack to provided substantially even cooling effects. We arrange for the resistance to flow to increase relatively across the stack with respect to the jet 23. Specifically this is achieved by reducing the arcuate lengths of the slots with consequent increase in the widths of the lands in respect of the discs positioned relatively further from the jet 23. The friction disc illustrated in Figures 7 and 8 of the accompanying drawings is similar to that of Figures 1 and 2, and corresponding reference numerals have been applied to corresponding parts. In this construction, however, the reservoir 15 is sub-divided interiorly into a plurality of angularly spaced chambers 25 of segmental outline by means of eight angularly spaced, straight, baffles 26. In the friction disc illustrated in Figures 9 and 10 of the accompanying drawings the exit ports 10 are omitted, and the disc is provided with a plurality of angularly spaced slots 27, each substantially of Tee-shaped outline, and through which liquid is fed from the reservoir 15 and to the braking faces 4, 5. Specifically the heads of the slots communicate with the reservoir and the stems extend across the braking faces. Liquid is trapped in the slots 27 between the braking faces on opposite sides of the disc, which is lined with linings 11, and flows out through grooves 28 in the linings. In the disc illustrated in Figures 11-13, the baffles 26 are extended radially inwardly of the wall 6 and are inclined with respect to the wall 6 and the disc itself so that the disc acts as an impeller to help fill the reservoir 15, The slots 27 are of L-shaped outline. The wall 6 and the baffles 26 are constructed from two metal pressings 30, 31. The pressing 31 is generally flat with flaps 33 bent up from it, and the pressing 30, which comprises the wall 6, is of generally dish-shaped outline with the free ends of the flaps 33 engaging the inner face of the wall 6. The pressings 30 and 31 are attached to the disc by any suitable means, for example by welding, the use of tags or by bonding In the friction member illustrated in Figures 14 and 15 of the drawings the disc 2 is provided on one side with an annular dish shaped member 50 comprising a cylindrical body part 51 which is secured to the disc 2 surrounding its central opening, and a radial flange 52 which extends outwardly from the outer end of the body 51. An annular chamber 53, which opens outwardly, is defined between the flange 52 and the braking member 2. A plurality of angularly spaced vanes or scoops 54 of arcuate outline extend between the body part 51, the flange 52 and the braking member 2 to raise liquid from the sump 1 when the disc 2 is rotating in a normal forward direction. A plurality of openings 55, each of which is elongate in a circumferential direction, are provided in the disc adjacent to the inner end of the concave side of each vane 54. The opposite side of the disc 1, 2 carries an annular member 56 substantially of U or channel outline which is superimposed at its inner end over the member 50. The member 56 has a cylindrical body part 57, from the outer end of which a radial flange 58 extends in an outwards direction, and the flange 58 is cranked at its intermediate point in its length to form a circumferentially extending axial extension 59 which is spaced at its free end from the friction disc 1, 2 to define an annular gap 60 for the escape of liquid. When the disc is rotating in a normal forward direction, the liquid is raised from the sump at the level 61 by the vanes 54, and passes through the openings 55 into the interior of the member 56 which defines a reservoir 62, and from which it can escape to the braking surfaces through the gap 60. The vanes 54 raise the liquid from the level 61 to an effective level 63 in the reservoir 62. In a reverse direction of rotation, substantially no liquid will be raised from the sump 30. From the foregoing description it will be appreciated that our invention is applicable both to friction member comprising planar metal plates, and to friction members in which the braking faces comprise annular linings of friction material secured to opposite faces of a metal plate.

Claims: 1. A vehicle disc brake of the liquid-cooled type in which at least one rotatable friction braking member keyed to a shaft (3) to be braked and having a braking surface (4,5) is rotatable in a housing containing a cooling liquid for cooling the braking member, and the braking member is adapted to co-operate with a relatively stationary braking surface to apply the brake, the braking member being provided on at least one side with an annular reservoir (15) for cooling liquid, and passage means (10) are arranged to control the release of liquid from the reservoir to the braking surfaces in response to centrifugal force, characterised in that the braking member comprises a generally planar member (2) and an annular wall (6) axially spaced from the planar member, the reservoir (15) being defined between the annular wall (6) and the adjacent portion of the planar member (2). 2. A disc brake according to Claim 1, characterised in that the annular wall (6) is secured to, or otherwise integral with, the planar member (2) at least at the radially innermost end of the wall. 3. A disc brake according to Claim 1 or Claim 2, characterised in that the reservoir (15) is adapted to receive liquid by means of a gravity feed. 4. A disc brake according to Claim 1 or Claim 2, characterised in that a pump (16) supplies liquid to the reservoir (15). 5. A disc brake according to Claim 4, characterised in that the pump (16) is separate from the braking member. 6. A disc brake according to Claim 4, characterised in that the pump (16) comprises an impeller (17) constituted at least in part by the braking member itself. 7. A disc brake according to any preceding claim, characterised in that the reservoir has an open mouth at its innermost end, for receiving cooling liquid. 8. A disc brake according to Claim 6, characterised in that the reservoir (15) is closed at its innermost end and receives liquid from the impeller (17) through transfer openings (24,55) in the braking member itself. 9. A disc brake according to any preceding claim, characterised in that the passage means (10) comprise angularly spaced exit slots at the radially outermost end of the reservoir. 10. A disc brake according to Claim 9, characterised in that the slots are disposed in the wall (6) adjacent to the friction member. 11. A disc brake according to Claim 9, characterised in that the slots (22) are provided in the thickness of the material of the friction member itself with the inner ends of the slots extending into the projected area of the reservoir (15). 12. A disc brake according to any preceding claim, characterised in that the reservoir (15) is provided with angularly spaced baffles (16). 13. A disc brake according to Claim 12, characterised in that the baffles extend between the braking member and the wall (6). 14. A disc brake according to Claim 12 or Claim 13, characterised in that the baffles (16) are straight. 15. A rotatable friction braking member for use in a disc brake as claimed in claim 1, in which the braking member has a braking surface (4, 5) and is provided on at least one side with an annular reservoir (15) for cooling liquid, and passage means (10) are arranged to control in use the release of liquid from the reservoir to the braking surface (4, 5) in response to centrifugal force, characterised in that the braking member comprises a generally planar member (2) and an annular wall (6) axially spaced from the planar member, the reservoir (15) being defined between the annular wall (6) and the adjacent portion of the planar member (2).

Inventors: CAMPBELL, ROY, GREEN, ANDREW PETER, PRICE, ANTHONY GEORGE
Applicants: LUCAS INDUSTRIES PUBLIC LIMITED COMPANY
Application year: 1988
Main classification: F16D65
IPC codes: F16D65, F16D69