GB2031540A

GB2031540A - Multi-disc brakes

Info

Publication number: GB2031540A
Application number: GB7935569A
Authority: GB
Original assignee: Dunlop Ltd
Current assignee: Dunlop Ltd
Priority date: 1978-10-14
Filing date: 1979-10-12
Publication date: 1980-04-23
Also published as: GB2031540B

Abstract

In a multi-disc brake for a vehicle interleaved, axially displaceable rotor and stator discs, (14 and 16 respectively), are brought into frictional engagement to apply the brake by a plurality of plungers 27 circumferentially spaced around a backing ring 26, which is fixed to one side of a diaphragm 24, when air under pressure is admitted to the other side of the diaphragm. Second, sleeve-like plungers 29 surround the first plungers 27 and are urged by Belleville washers 32 to apply the brake if air pressure in a second chamber 23 is lost, e.g. when a parking brake is applied, each plunger 27 being movable in the brake-applying direction independently of the associated plunger 29 by a lost-motion connection formed by a pin 30 travelling in a slot 31. <IMAGE>

Description

SPECIFICATION Improvements in brakes The present invention relates to improvements in brakes and more particularly to means whereby a brake of the type in which annular rotor and stator discs are displaceable axially into mutual frictional engagement can be satisfactorily operated pneumatically using the source of compressed air which is available as standard equipment on heavy road vehicles.

In an advantageous form of such a brake a plurality of rotor discs which rotate with the wheel are interleaved with a plurality of stator discs which are constrained against rotation, the brake being applied by axially displacing all of the disc toward a reaction member by means of a thrust ring which is in turn acted upon by a plurality of pressurised fluid operated devices spaced circumferentially around the ring. Since hydraulic fluid is available in heavy road vehicles at higher pressure than compressed air it would be preferable that these thrust applying devices should be hydraulic except that the great heat developed by the disc pack, especially under conditions of prolonged braking, will tend to vapou rive the hydraulic fluid.This problem is avoided if the thrust applying devices are pneumatic rather than hydraulic, but conventional heavy road vehicles do not carry as standard equipment air compressors capable of delivering air at a pressure of more than about 100 p.s.i. Isolated pneumatic devices receiving air at this pressure would be unsuitable to operate a brake of the multi-disc type.

A principle object of the present invention is to provide means whereby a multi-disc brake can be operated pneumatically using a source of air at relatively low pressure.

In accordance with the preseht invention there is provided a brake assembly comprising an annular stator disc constrained against rotation while free to move axially and an annular rotor disc keyed to the wheel to be braked for rotation therewith while free to move axially, a reaction member provided on one side of the discs and a thrust ring provided on the other side of the discs axially displaceable toward the reaction member so as to bring the disc into mutual frictional engagement, wherein pneumatically operated thrust applying means is provided which comprises an annular air chamber mountable to be co-axial with the thrust ring, an annular diaphragm spanning the chamber radially and sealed thereto at both peripheries of the diaphragm, means for admitting pressurised air to the chamber on one side of the diaphragm and a plurality of plungers extending between the other side of the diaphragm and the thrust ring in circumferentially spaced relation, the arrangement being such that when air under pressure is admitted to the chamber the diaphragm displaces the plungers, the thrust ring and the disc toward the reaction member.

Preferably the diameter of the air chamber is at least as great as that of the disc pack, and the radial extent of the air chamber is approximately equal to that of the disc pack.

Preferably the plungers extend from one side of an annular backing plate secured to said other side of the diaphragm and of slightly smaller radial extent than the latter.

In a preferred construction there is located between the thrust ring and the first mentioned air chamber a second, annular air chamber co-axial with the first and spanned by a second diaphragm, and extending between the second diaphragm and the thrust ring is a second series of plungers which are spring biassed toward the thrust ring, the arrangement being such that by admitting air under pressure to the side of the second diaphragm nearer the thrust ring the second plungers are displaced away from the thrust ring against the bias of their springs, the arrangement being such that if air pressure is not maintained in the second air chamber the second series of plungers is displaced by the springs toward the thrust ring to apply the brake.

In a preferred construction each of the plungers of the second series is in the form of a sleeve which surrounds a plunger of the first series, there being a lost motion connection between co-axial plungers of the two series so that the brake can be applied by the first diaphragm even when the second diaphragm is in the "brake-off" position.

A preferred embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a sectional elevation in a diametral plane taken through a wheel and axle provided with a brake assembly in accordance with the invention.

Figure 2 is a partial end view of the assembly of Figure 1 viewed from its right-hand end as illustrated, and Figure 3 is a detail of Figure 1 on an enlarged scale.

Illustrated in Figure 1 is an axle 10 on which a wheel 11 is rotatably mounted. Mounted within the rim 12 of the wheel is a multi-disc brake assembly 13 which comprises a plurality of rotor discs 14 keyed to a drum 15 which is fixed to the wheel lithe rotor discs being interleaved with a plurality of stator discs 16 which are keyed to a torque tube 17 fixed relative to the axle 10. The rotor discs engage the drum 15 by keys at their radially outer peripheries which engage in circumferentially spaced, axially elongated slots in the drum and the stator discs 16 engage the torque tube 17 by keys projecting from the radially inner peripheries of the stator discs which engage in axially elongated, circumferentially spaced slots in the toeque tube.By this arrangement the stator and rotor discs can be axially displaced into mutual frictional engagement to apply the brake when a thrust ring 18 at one end of the disc pack, which is keyed to the torque tube in the same manner as the stator discs, is moved toward a reaction flange 19 extending radially from the outboard end of the torque tube 17.

In accordance with the present invention means for applying a thrust to the ring 18 in the direction of the reaction flange 19 to apply the brake comprises a housing 20 which is fixed relative to the axle 10 by bolts 21. The housing 20 is made up of three annular metal components with the wheel axle 10 and each of approximately the same radial dimensions as the pack of interleaved discs 14, 16. First and second annular diaphragms 24 and 25 radially span the respective air chambers 22 and 23, each being clamped at both of its peripheries in an air sealing manner between metal components of the housing.

Secured to one side of the diaphragm 24 is a metal backing ring 26 of slightly smaller radial extent than an air chamber 22 in which it is located and from the face of the backing plate 26 remote from the diaphragm 24 a plurality of plungers 27 extend in circumferentially spaced relation into contact with the thrust ring 18. An air inlet 28 can admit air under pressure into the chamber 22 on the side of the diaphragm 24 remote from the backing plate 26 which will displace the diaphragm 24 across the air chamber 22, thus causing the plungers 27 to move the thrust ring 18 toward the reaction flange 19 and compress the pack of interleaved rotor discs 14 and stator discs 16. A suitable slack adjustment mechanism is preferably interposed between each plunger 27 and the thrust ring 18 to compensate for wear of the brake discs.

Surrounding each plunger 27 is a second, sleevelike plunger 29 which is capable of limited axial movement relative to the plunger 27 by a lost motion connection constituted by a pin 30 traversing an axially elongated slot 31 in the plunger 27. Each sleeve 29 is in turn surrounded by a pack of Beliville washers 32 constrained between a circiip 33 at one end of the sleeve 29 and the adjacent end of the housing 20 so that the Bellville washers bias the sleeve 29 toward the thrust ring 18. When air under pressure is admitted to the second air chamber 23 through an inlet 34 the diaphragm 25 is displaced to the right-hand side of the air chamber 23, as viewed, carrying with it the sleeves 29 against the bias of their springs 32.However if air pressure in the chamber 23 drops below a value overcoming the springs 32 the latter will displace the sleeves 29 toward the reaction flange 19 and apply the brake, the sleeves 29 carrying with them the plungers 27 because of the presence of the pins 30 in the slots 31.

By this arrangement the brake is automatically applied if for any reason air under adequate pressure becomes unavailable. For example if the compressor fails or if an air leak develops. The arrangement can be such that air is vented from the second air chamber 23 when the hand brake of the vehicle is put on whereby the springs 32 apply the brake.

It will be appreciated that the diaphragm 24 and plungers 27 are movable to apply the brake under the influence of pressurised air admitted through inlet 28 while the diaphragm 25 and plunger 29 are in the "brake-off" position shown because of the lost motion connection 30, 31 between the plungers.

The plungers 27 are biassed to the "brake-off' position shown by a spring 35 acting on the back plate 26.

To provide an air seal where the sleeves 29 pass out of the housing 20 an 'O'-ring 36 is provided in an annular groove in the housing surrounding each sleeve 29 and another, flexible seal 37 extends between the housing 20 and the plungers 37 to prevent the ingress of dirt or oil to the assembly of plungers and Beliville washers.

Claims

1. A brake assembly comprising an annular stator disc constrained against rotation while free to move axially and an annular rotor disc keyed to the wheel to be braked for rotation therewith while free to move axially, a reaction member provided on one side of the discs and a thrust ring provided on the other side of the discs axially displaceable toward the reaction member so as to bring the discs into mutual frictional engagement, wherein pneumatically operated thrust applying means is provided which comprises an annular air chamber mountable to be co-axial with the thrust ring, an annular diaphragm spanning the chamber radially and sealed thereto at both peripheries of the diaphragm, means for admitting pressurised air to the chamber on one side of the diaphragm and a plurality of plungers extending between the other side of the diaphragm and the thrust ring in circumferentially spaced relation, the arrangement being such that when air under pressure is admitted to the chamber the diaphragm displaces the plungers, the thrust ring and the discs toward the reaction member.

2. A brake assembly as claimed in claim 1, wherein the diameter of the air chamber is at least as great as that of the disc pack, and the radial extent of the air chamber is approximately equal to that of the disc pack.

3. A brake as claimed in either preceding claim, wherein the plungers extend from one side of an annular backing plate secured to said other side of the diaphragm and of slightly smaller radial extent than the latter.

4. A brake assembly as claimed in any one of the preceding claims, wherein there is located between the thrust ring and the first mentioned air chamber a second, annular air chamber co-axial with the first and spanned by a second diaphragm, and extending between the second diaphragm and the thrust ring is a second series of plungers which are spring biassed toward the thrust ring, the arrangement being such that by admitting air under pressure to the side of the second diaphragm nearer the thrust ring the second plungers are displaced away from the thrust ring against the bias of their springs, the arrangement being such that if air pressure is not maintained in the second air chamber the second series of plungers is displaced by the springs toward the thrust ring to apply the brake.

5. A brake assembly as claimed in claim 4, wherein each of the plungers of the second series is in the form of a sleeve which surrounds a plunger of the first series, there being a lost motion connection between co-axial plungers of the two series so that the brake can be applied by the first diaphragm even when the second diaphragm is in the "brake off"position.

6. A brake assembly substantially as herein de scribed with reference to and as shown in the accompanying drawings.