SELF-ENERGISING DISC BRAKE

Abstract: In a self-energising disc brake of the spreading type the actuator mechanism (9,10,14,12,13) incorporates a restrictor in the form of a circumferentially extending discontinuous oil-seal (27) which co-operates with radial faces on the two pressure plates (9,10). A secondary or elevated reservoir for liquid is therefore defined between the plates (9,10) by the seal (27). Liquid can escape from this reservoir in order to enhance the cooling of the braking surfaces, defined by engagement of rotatable friction discs (1,3) with end faces (6,7) of a housing (8), pressure plates (9,10), and a planar non-rotatable disc (4). In the brake of Figure 6 two annular members (60,61) act as seals on the ends of the friction discs (1,3).

Description: This invention relates to self-energising disc brakes of the kind in which rotatable friction discs provided with lining of friction material are adapted to be brought into engagement with spaced opposed braking surfaces in a housing by an actuator mechanism comprising a pair of annular pressure plates located between the friction discs and centred by stationary pilot lugs, and balls or rollers located in co-operating oppositely inclined recesses in the adjacent faces of the pressure plates, the application of the brake is initiated by moving the pressure plates angularly in opposite directions, and the pressure plates then move apart, due to the tendency for the balls or rollers to ride up ramps defined by the edges of the recesses, and into engagement with the friction discs which are urged into engagement with the braking surfaces, the pressure plates being carried round with the friction discs until one is arrested by the engagement of a lug on the plate with a drag-taking stop abutment in the housing, and the continued angular movement of the other pressure plate providing a servo action. Self-energising brakes of the kind set forth may be dry or they may be of the liquid cooled type, and such brakes are commonly used in tractors and like vehicles and are hereinafter called brakes of the kind set forth. In brakes of the kind set forth it is known that high temperatures at the braking faces causes degradation of the linings of friction material, especially when non-metallic linings of organic materials are utilised, rather than the more conventional linings of inorganic metallic materials. Such lining failure is particularly evident in those brakes of the kind set forth in which at least two friction discs are disposed between the actuator mechanism and the adjacent braking surface, and a non-rotatable intermediate spacer disc is disposed between the adjacent linings of those discs, the spacer discs comprising a metal plate keyed to the housing for relative sliding movement in an axial direction. When brakes of the kind set forth are of the liquid cooled type they may be cooled by liquid flowing through the gearbox and other transmission parts of tl:e vehicle. To minimise parasitic drag, particularly when the oil is cool, and consequent loss of power, it is preferable to maintain the level of oil in the gearbox at a mininum, rather than at a maximum, level. Since such a volume of oil is often in sufficient to provide adequate cooling of the braking faces, consequent degradation of the linings as discussed above may occur. It is known in brakes of the kind set forth to provide slots or grooves in the friction linings themselves in order to facilitate cooling itself, and in particular when the brake is of the liquid cooled type, the slot or grooves are so chosen as to act as a reservoir for cooling liquid and to control the flow of liquid across the braking faces. According to our invention, in a self energising disc brake of the kind set forth the actuator mechanism is provided with restrictor means to restrict the flow of cooling liquid from between the pressure plates in a radially outwards direction. The space between the pressure plates therefore defines a secondary elevated reservoir from which liquid escapes to the friction discs in order to enhance cooling of the braking surfaces. Conveniently the restrictor means comprises a circumferentially extending member which is disposed within the actuator mechanism for co-operation with radial faces on the two pressure plates and which opens towards the upper end of the brake. The liquid is directed into the secondary reservoir by suitable means, and its release from the secondary reservoir is restricted by the circumferentially extending member. For example the means may comprise a supply nozzle located in an upper region of the housing of the brake, adjacent to the outer peripheral edges of the pressure plates. Alternatively the means may comprise an integral pump disposed within the brake. The circumferentially extending member may comprise a discontinuous ring of elongate section provided at opposite ends with locations, each for co-operation with one of the plates to prevent angular movement of the ring with respect to that plate when the brake is applied, and the liquid is directed between the spaced upper ends of the ring. Two annular members may also be included in the brake construction in such a way as to seal the ends of the rotatable braking members, thereby defining a reservoir inside the brake assembly itself. The running clearances between the plates when the brake is not applied allow the oil to flow away without building up pressure and causing drag on the end plates. Some embodiments of our invention are illustrated in the accompanying drawings in which:- Figure 1 is a longitudinal section through a liquid-cooled brake of the kind set forth; Figure 2 is an end view of the brake of Figure 1; Figure 3 is a section through the pressure plates but showing a modification; Figure 4 is a view similar to Figure 3 but showing another modification; Figure 5 is a view similar to Figure 1 but showing a modification; and Figure 6 is a view similar to Figure 1 but showing yet another modification. The brake illustrated in Figures 1 and 2 of the drawings is of a spreading type in which three rotatable friction discs 1, 2, 3 are splined for sliding movement on a rotatable shaft (not shown). A stationary planar disc 4 is disposed between the friction discs 2, 3 and is keyed to a housing 8. Each rotatable disc 1, 2, 3 is provided on opposite sides with linings 5 of a metallic or non-metallic friction material adapted to be brought into engagement with spaced opposed radial surfaces 6, 7 in the housing 8, and opposite faces of the disc 4, by pressure plates 9, 10 located between an adjacent pair of the discs 1, 2 and centred by three angularly spaced stationary pilots (not shown) of which one comprises a drag-taking pin. Balls 14 are located in co-operating oppositely inclined recesses 12, 13 in the adjacent faces of the pressure plates 9, 10 and which the pressure plates 9, 10 constitute an actuator mechanism. The two pressure plates 9 and 10 are similar in construction. Each plate is generally of annular outline provided with a pair of outwardly extending radial lugs 16 and 17, and a plurality of inwardly extending radial lugs 18. The lug 16 is provided adjacent to its outer end with an opening by which one of a pair of toggle links 20, 21 is coupled in order to initiate application of the brake when the outer ends of the toggle links are withdrawn relatively from the housing 8 by means of a pull-rod. The lug 17 acts to co-operate with the pin to arrest rotation of the plate 10 in the application of the brake. Superimposed pairs of the lugs 18 provide anchorages for opposite ends of tension return springs 24 which urge the pressure plates 9, 10 towards each other with the balls 14 held at the bases of ramps defined by end faces of the recesses 12, 13. The pressure plates 9, 10 are provided at their inner ends with radial sealing faces 25, 26 defined by the bases of superimposed shallow recesses, and an oil seal comprising a flat circumferentially extending discontinuous ring 27 co-operates with the sealing faces so that the part circular space 28 defined between the pressure plates 9, 10 and the ring 27 constitutes a secondary elevated reservoir for liquid, suitably oil. Tags 29 and 30 at opposite ends of on the ring 27 are received in pockets 31, 32 in the plates 9, and 10 respectively to anchor the ring against relative rotation. The pockets 31, 32 are disposed in the pressure plates 9, 10 well above the shaft, and the circumferential lengths of the pockets is sufficient to accommodate relative angular movement between the pressure plates in the application of the brake. The housing defines a main reservoir which contains liquid to a level 40, and the elevated secondary reservoir contains liquid to the depth 33. At least the arcuate lowermost portions of the friction discs and the pressure plates are immersed in the secondary reservoir to the depth 33. In addition superimposed circumferentially extending recesses 34, 35 are provided in adjacent faces of the two pressure plates 9, 10 to define a chamber into which liquid from the main reservoir can be discharged from a nozzle 36 and into the upper end of the secondary or elevated reservoir. In a modification liquid is supplied to the elevated reservoir by means of an integral pump disposed within the brake. The application of the brake is initiated by moving the pressure plates 9, 10 angularly in opposite directions by withdrawing the pull-rod from the housing 8. This causes the pressure plates 9, 10 to move axially relatively away from each other due to the tendency for the balls 14 to ride up the ramps defined by the end faces of the recesses 12, 13. This urges the friction discs l and 3 into engagement with the radial surfaces 6 and 7 on the housing 8. The pressure plates 9 and 10 are then carried round with the discs 1, 2 until one, say the plate 10, is arrested by the engagement of the lug 17 with a drag-taking abutment defined by the pin, whereafter continued angular movement of the other plate 9 provides a servo action. The oil seal 27 acts to restrict flow through the actuator mechanism so as to encourage flow onto the friction discs l, 2 and 3, and especially onto the planar disc 4, whereby to enhance the cooling of the braking surfaces. As illustrated all the discs are provided with angularly spaced oil-circulation holes 38, suitably radial slots, to facilitate the flow onto the linings and braking faces. In the modified construction illustrated in Figure 3 the ring 27 is of arcuate, concave outwardly directed, cross-section so that the ends of the ring co-operate with the adjacent ends of the recesses to enhance the sealing effect of the ring. In the modification shown in Figure 4, the end edges 37 of the ring are deformed outwardly to co-operate with the sealing faces 25 and 26. In the modification shown in Figure 6, two annular members 60, 61 act as seals on the ends of the rotatable braking members 1, 3. As all of the exits apart from the lining groove portion 62 are sealed, a reservoir of oil can be retained inside the brake, and thus a high internal oil level is maintained to feed the lining grooves 62. The running clearances between the plates 2, 3, 4 when the brake is not applied, allow the oil to flow away without building up pressure and causing drag on the end plates. In the brakes described above, when the brakes are applied, the planar disc 4 will be raised to a higher temperature than the discs l, 2 and 3, especially if the discs 1, 2 and 3 are provided with non-metallic linings. The cooling of the planar disc 4 is therefore of paramount importance. The oil circulation holes 38 may therefore be arranged in the friction discs and to encourage oil flow the elevated reservoir towards the planar disc 4. As shown in Figure 5 this may be achieved by omitting the oil circulation holes 38 from the two outermost friction discs 1 and 3. The two discs 1 and 3 are therefore imperforate, and the oil tends to be trapped between them, whereby to concentrate its cooling effect on the planar disc 4.

Claims: 1. A self-energising disc brake of the liquid cooled type in which rotatable friction discs (1,2,3) provided with linings (5) of friction material are adapted to be brought into engagement with spaced opposed braking surfaces (6,7) in a housing (8), defining a reservoir for liquid, by an actuator mechanism (9,10,12,13,14) comprising a pair of annular pressure plates (9,10) located between the friction discs (1,2) and centred by stationary pilot lugs, and balls (14) or rollers located in co-operating oppositely inclined recesses (12,13) in the adjacent faces of the pressure plates (9,10), application of the brake being initiated by moving the pressure plates (9,10) angularly in opposite directions, such that the pressure plates (9,10) move apart, due to the tendency of the balls (14) or rollers to ride up ramps defined by the edges of the recesses (12,13), and into engagement with the friction discs (1,2) which are urged into engagement with the braking surfaces (6,7), the pressure plates (9,10) being carried round with the friction discs (1,2) until one is arrested by the engagement of a lug (17) on the plate (10) with a drag-taking stop abutment in the housing, the continued angular mouvement of the other pressure plate (9) providing a servo action characterised in that the actuator mechanism is provided with a restrictor means to restrict the flow of cooling liquid from between the pressure plates in a radially outwards direction. 2. A self-energising disc brake according to Claim 1 characterised in that the space between the pressure plates (9,10) defines a secondary elevated reservoir from which liquid escapes to the friction discs (1,2,3) to enhance cooling of the braking surfaces (6,7). 3. A self-energising disc brake according to Claim 2 characterised in that the restrictor means comprises a circumferentially extending member (27) disposed within the actuator mechanism (9,10,12,13,14) for co-operation with the radial faces on the two pressure plates (9,10) and which opens towards the upper end of the brake, the circumferentially extending member (27) restricting the release of liquid from the secondary elevated reservoir. 4. A self-energising disc brake according to Claim 3 characterised in that liquid is directed into the secondary reservoir by a supply nozzle (36) located in an upper region of the housing (8) of the brake adjacent to the outer peripheral edge of the pressure plates (9,10). 5. A self-energising disc brake according to Claim 3 characterised in that liquid is directed into the secondary reservoir by means of an integral pump disposed within the brake. 6. A self-energising disc brake according to Claim 4 or Claim 5 characterised in that the circumferentially extending member (27) comprises a discontinuous ring of elongate section provided at opposite ends with tags (29,30) which are received in pockets (31,32) in the plates (9,10) to prevent angular movement of the ring (27) with respect to that plate when the brake is applied, the liquid being directed between the spaced upper ends of the ring (27). 7. A self-energising disc brake according to Claim 6 characterised in that the discs (1,2,3,4) and a stationary planar disc 4 are provided with angularly spaced liquid circulation holes (38) to facilitate the flow of the liquid onto the linings (5) and the braking surfaces (6,7). 8. A self-energising disc brake according to Claim 7 characterised in that the outermost friction discs (1,3) are imperforate trapping the liquid between them and concentrating its cooling effect on the planar disc(4). 9. A self-energising disc brake according to Claim 6 or Claim 8 characterised in that the ring (27) is of arcuate, concave, outwardly directed, cross-section so that the ends of the ring(27) co-operate with adjacent ends of the recesses (12,13) to enhance the sealing effect of the ring. 10. A self-energising disc brake according to Claim 6 or Claim 8 characterised in that the peripheral edges (37) of the ring (27) are deformed outwardly to co-operate with the sealing faces (25,26) of the pressure plates (9,10). 11. A self-energising disc brake according to Claim 8 characterised in that two annular members (60,61) are included in the brake construction such as to seal the ends of the rotatable braking members (1,3), defining a reservoir inside the brake assembly, the running clearances between the plates (9,10) when the brake is not applied allowing the liquid to flow away without building up pressure and causing drag on the braking faces.

Inventors: CAMPBELL, ROY, GREEN, ANDREW PETER, PARRY, DAVID, PRICE, ANTHONY GEORGE
Applicants: LUCAS INDUSTRIES PUBLIC LIMITED COMPANY
Application year: 1988
Main classification: F16D65
IPC codes: F16D65, F16D55