GB2221966A

GB2221966A - Improvements in vehicle disc brakes of the liquid cooled type

Info

Publication number: GB2221966A
Application number: GB8917595A
Authority: GB
Inventors: Michael Anthony John Genge; Mark Chillery
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1988-08-17
Filing date: 1989-08-01
Publication date: 1990-02-21
Anticipated expiration: 2009-08-01
Also published as: GB8819559D0; IT8921499A0; DE3927119A1; IT1231111B; GB2221966B; GB8917595D0

Description

2221966 1 IMPROVEMENTS IN VEHICLE DISC BRAKES OF THE LIQUID COOLED TYPE

This invention relates to improvements in vehicle disc brakes of the liquid-cooled type, of the kind in which at least one rotor comprising a rotatable friction braking member slidably keyed to a shaft to be braked and provided on opposite sides with braking faces is rotatable in a housing defining a sump for cooling liquid for cooling the braking member, and actuating means have a relatively stationary braking surface for urging the braking member into engagement with a second 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.

In our GB-A-2 141 193 we have disclosed a disc brake of the kind set forth in which the braking member carries a lining of friction material, and the lining of friction material is separated into inner and outer annular rings by a single annular groove, substantially coaxially with the axis of rotation of the rotatable friction braking member, said groove acting as a reservoir for cooling liquid, throttling means are 2 provided for throttling the flow of liquid across the braking faces of the rings, and reservoir supply flow grooves are provided in the inner ring to replenish the cooling liquid of the annular groove.

In some of the specific constructions disclosed in GB-A-2 141 193, the reservoir supply grooves comprise slots which pass through the material of the braking member and the lining and are parallel-sided and elongate radially, the slots extending radially outwards from a position inwardly of the inner edge of the inner ring.

According to our invention in a disc brake of the kind set f orth a stator with which the rotor has an interface is formed below the level of oil in the sump with a void def ined by a slot or recess of which the effective volume decreases in a direction corresponding to the direction of rotation of the co-operating rotor, whereby an hydrodynamic pressure is generated within the liquid at the smaller end of the slot, in turn to generate a flow of liquid in a radially inwards direction.

By incorporating openings in the rotor and/or the stator fluid can be pumped to a separate location, suitably to facilitate cooling of the braking faces, by the positive hydrodynamic pressure so generated.

When the actuating means includes a pair of pressure plates, a void is provided in the outer face of each pressure plate which defines a braking surface when the brake is applied. The liquid may escape from the slot or recess defining the void through passage means provided in the rotor for co-operation with the void. The passage means may comprise one or more slots i 3 passing through the material of the rotor. These slots are preferably spaced angularly, at least at their outermost ends. Alternatively or additionally the passage means in the rotor may comprise a groove, or grooves, which does not pass completely through the material of the rotor. The groove comprising the passage means would be provided in that face of the rotor which is adjacent the pressure plate defining the void. Another way of allowing the cooling liquid to be pumped from the void may be to provide channels in the pressure plates through which the liquid may escape. These channels may be provided in addition to passage means in the rotor, or as an alternative.

one embodiment of our invention is illustrated in the accompanying drawings in which:- Figure 1 is an axial section through a brake of the self-energising spreading type; Figure 2 is a section on the line 2-2 of Figure 1; Figure 3 is a section on the line 3-3 of Figure 1; Figure 4 is a section on the line 4-4 of Figure 3; Figure 5 shows a relatively stationary plate; and Figure 6 is a section on line 6-6 of Figure 5.

The brake illustrated in Figures 1 to 4 ofthe drawings is of the spreading type in which a rotatable 4 shaft 1 extending axially through a housing 2 is adapted to be braked by two stacks of annular braking members 3, 4 each disposed between a brake actuator 5 and a braking surface 6, 7 on an adjacent end of the housing. Each stack of braking members 3, 4 comprises a pair of rotatable friction discs 8, 9 (rotors) which are splined to the shaft 1 for sliding movement and are provided on opposite sides with linings 10, of friction material, and an intermediate stationary plate 12 which is slidably keyed to the housing 2 against relative rotation.

The brake actuator 5 comprises a pair of pressure plates 14, 15 which are disposed between the innermost rotors 9 of the set 3, 4 and are centred by three angularly spaced pilots 20, 21, 22. Balls or rollers 23 are located in co-operating oppositely inclined recesses 24, 25 in adjacent faces of the pressure plates 14, 15, and coupled toggle links 26, 27 connected between the pressure plates 14, 15 adapted to be withdrawn radially from the housing initiate application of the brake. This causes the are to two pressure plates 14, 15 to move angularly relative to each other accompanied by axial separation of the plates due to a tendency for the balls or rollers 23 to ride up ramps defined by the edges of the recesses 24, 25. The plates 14, 15 are then carried round with the rotors 8, 9 until one of the plates is arrested by the engagement with an annular pin which defines the pilot 22. Thereafter the continued angular movement of the other pressure plate provides a servo or self-energising action and enhances the force clamping the braking -members of both sets together and between the actuator 5 and the braking surfaces 6, 7.

1 The brake is liquid cooled and the housing 2 forms a sump for liquid to a level 30.

The outer faces of the two pressure plates 14, 15 are provided within the depth of liquid in the sump with a slot or recess 40 of which the effective volume reduces progressively in a direction relative to the direction of rotation of the adjacent rotor 9, as shown by the arrow 42 in Figure 3 of the drawings. As illustrated, the slot or recess 40 is substantially of segmental outline having an outwardly directed inlet opening 41 at its end of greater area. Each slot or recess 40 is defined by faces which converge with respect to the direction of rotation.

Each rotor 8, 9 is formed with a plurality of angularly spaced slots 53 which extend through the material of the rotor, and each lining 10 has a central recess or groove 54, which may be concentric with, or eccentric with respect to, the axis of the shaft 1. In addition the groove 54 is traversed by a plurality of grooves 55 which extend chordally across the friction linings.

When the brake is applied the interfaces between the rotors 9 and the pressure plates 14, 15 cause hydrodynamic pressures to be generated in the slots or recesses 40, in turn to generate flows of liquid in a radially inwards direction. Liquid is therefore pumped over the braking faces by passage through the slots 53 in the rotors 8, 9, and over the inner peripheral edges of the stators.

In a modification liquid could be released from the slots or recesses 40 through channels machined in the pressure plates 14 and 15 themselves. Furthermore, 6 the slots 53 may not extend completely through the material of the rotor, being provided as grooves instead.

Figures 5 and 6 show an annular relatively stationary plate 12 provided with a slot or recess 56. Recess 56 has a similar function to recess 40 of the brake of Figures 1 to 4. The recess 56 has a shallower end 57 spaced from a deeper end 58 in the direction of rotation of a friction disc which in use rotates adjacent to the plate 12. The recess 56 has a substantially straight trailing edge 59 and a curved forward edge 60 and extends completely across the braking face of the plate 12. The radially outer end of the recess 56 is below the level 30 of cooling liquid in a sump of a brake.

In use during a braking operation the rotation of a friction disc adjacent the plate 12 induces a hydrodynamic pressure which causes cooling liquid to be pumped from the sump. In the embodiment shown in Figure 6 the cooling liquid flows radially inwards along the recess 56 to the inner peripheral edge of the plate 12 and thereafter onto the braking surfaces of the brake to cool the brake.

The maximum depth of the recess 56 is of the same depth across the full radial width of the plate 12.

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Claims

A disc brake of the kind set forth further comprises a stator with which the rotor has an interface, the stator being formed below the level of oil in the sump with a void defined by a slot or recess of which the effective volume decreases in a direction corresponding to the direction of rotation of the co-operating rotor, whereby an hydrodynamic pressure is generated within the liquid at the smaller end of the slot, in turn to generate a flow of liquid in a radially inwards direction.
2. A disc brake according to claim 1 in which openings are provided in the rotor and/or the stator so as to enable cooling liquid to be pumped by the hydrodynamic pressure from the sump to another location.
3. A disc brake according to claim 1 or claim 2 in which cooling liquid is pumped from the sump to the braking surfaces so as to facilitate cooling of the braking surfaces.
4. A disc brake according to any preceding claim which comprises a pair of internally expanding pressure plates whose outer faces define braking surfaces when the brake is applied, and voids provided in the outer faces of the pressure plates.
5. A disc brake according to any preceding claim in which a recess defines the void, the recesses having a shallow end and a circumferentially spaced deeper end and extending at least at its deeper end to the radially outer peripheral edge of the pressure plate.

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6. A disc brake according to any preceding claim in which the rotor is provided with passage means which communicates with the void at least at some time during the rotation of the rotor and provides a pathway for cooling liquid under pressure to escape from the void.
7. A disc brake according to claim 6 in which the passage means comprises a slot or recesses extending completely through the material of the rotor.
8. A disc brake according to claim 7 in which a plurality of angularly spaced slots or recesses are provided in the rotor.

is
9. A disc brake according to any preceding claim in which the pressure plate, or plates, is provided with channels through which cooling liquid escapes from the void.
10. A disc brake illustrated herein.

substantially as described and 9 j Published 1990 atThe Patent=ce. State House, 6671 MghHolborn. LondonWO1R4TP.Purther copies maybe obtainedfrom The PatentOInceSales Branch. St Mary Cray. Orpingtor. Nei.t BR5 3F.D. Prirwd by Williplex techniques Ita, St Mary Cray, Kent. Con. 1187