GB2135732A - Brake actuators - Google Patents

Abstract

A known brake actuator assembly has a chamber 4 to which compressed air is admitted to act on diaphragm 6 and compress a brake applying spring 12. Release of pressure from chamber 4 allows spring 12 to cause extension of push rods 14, 21 to apply a vehicle wheel brake. With spring 12 compressed the brake may be applied by admission of compressed air to chamber 5 to act on diaphragm 7 and cause push rod 21 to be extended to apply new braking requirements to be met by interposing a mounting ring 28 (Fig. 3) in a fluid pressure tight manner between the housing 2 and diaphragm 7, preferably with a sealing ring 32 bonded to one face 30, the opposite face 31 being extended to engage the rim of the diaphragm 7. <IMAGE>

Description

SPECIFICATION Brake actuators This invention relates to a combined service/ emergency brake actuator assemblyfor causing operation of a vehicle wheel brake.

Such brake actuntor assemblies, operated by compressed air underthe control of the driver of a vehicle, are well known.They are made by a number of manufacturers and include flexible diaphragms which,though slightlydifferentfor individual actuator manufacturers, arefrequently interchangeable between actuator assemblies of different manufacturers.

New and mandatory braking requirements, particu larly a brake fade testrflecessitate an increase in the stroke ofthe standard actuator so as to maintain brake performance when the brake is hot due to repeated applications. This invention is concerned with a method of achieving the increased stroke requirement using existing standard actuator assemblies with a minimum numberofnew partswherebythe cost of modification to meet the new requirements is minimised.

The standard actuator assembly referred to has a housing, first and second flexible diaphragms which together with the housing define first and second fluid chambers, first and second caps which together with the first and second diaphragms define respective third and fourth chambers, first and second clamping means to clamp the respective caps and diaphragms to the housing, first spring means in the first chamber acting between the housing and the first diaphragm to bias said first diaphragm away from the housing, second and third spring means in said third and fourth chambers acting between the respective caps and diaphragms to bias the diaphragms into the housing, means to admit pressure fluid to and to exhaust it from the first and second chambers, and push road means extending from the fourth chamber and acting between the first second andfourth chambers whereby the push rod means is extended to cause operation of a vehicle brake either bythe second diaphragm upon application of pressurefluid to the second chamber or bythe second spring means when the pressure offluid in the first chamber falls below a predetermined value. Such an actuator assembly will hereafter be referred to as an actuator assembly ofthe type described.

According to the present invention in an actuator assembly of the type described a mounting ring is interposed between the housing and the second diaphragm such that fluid pressure tight seals are made between the housing and the mounting ring and between the mounting ring and the second diaphragm whereby the periphery of the second diaphragm is spaced from the housing bythe mounting ring and the available stroke of the push rod means is thereby increased.

The mounting ring may have opposed faces one of which is adapted to make a fluid pressure tight seal with a face of the second diaphragm and the other of which is adapted to make a fluid pressure tight seal with the housing.

The fluid pressure tight seal between the mounting ring and the housing may be effected by a sealing ring, for example an elastomeric sealing ring, or such a sealing ring may conveniently be bonded to, so as to form part of, the mounting ring.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure lisa longitudinal section through an actuator assembly ofthe type described, Figure 2 is a front elevation of a mounting ring and sealing ring fitted thereto, Figure 3 is a section on line X-X of Figure 2 on an enlarged scale, Figure 4 is a front elevation of a mounting ring, Figure 5 is a part section through a diaphragm, and Figure 6 is asectionthrough part ofthe diaphragm of Figure 5 adjacent its periphery on an enlarge scale.

Referring to the drawing Figure 1, an actuator assembly 1 comprises a housing 2 havinga dividing wall 3 and opposed circularflanged openings. First andsecond fluid chambers 4rare defined on opposite sides ofwall 3 bythe housing 2 and first and second flexible diaphragms 6,7 respectively at the opposed openings. Afirst cap 8 has a circular opening corresponding to the first chamber opening of housing 2 and has opposed hooks 9 which engage overthe flange atthat opening. Cap 8 has peripheral flanges (not shown) extending between the hooks 9.

Two half clamps (not shown) engage the flanges of housing.2 and cap 8 and are secured together as by bolts passing through holes 10 in hooks 9to secure cap 8, diaphragm 6 and housing 2 together asan assembly providing afluid pressuretightseal between housing 2 and diaphragm 6.

The cap 8 and diaphragm 6 define a third chamber 11 within which is contained a compression spring 12 which acts between cap 8 and a pressure plate 13 to bias the diaphragm 6 into the housing 2.

The innerwall 3 ofthe housing 2 which separates the first and second chambers 4,5 has a central circular opening within which a first push rod 14 is slidable.

Push rod 14 has a flat plate 15 secured to one end and this is maintained against the diaphragm 6 by one end of a compression spring 16 whose other end.is located by the wall 3. The other end of push rod 14 is within thechamber 5 and has a flat plate 17 secured to it.

Asecond cap 18 has a circular opening corresponding to the adjacent opening of housing 2 and has a peripheral flange. Two half clamps 19 engage the adjacent flanges of housing 2 and cap 18 and are secured together as by bolts to secure cap 18, diaphragm 7 and housing 2togetheras an assembly providing a fluid presure tight seal between housing 2 and diaphragm 7.

The cap 18 and diaphragm 7 define a fourth chamber 20 within which is slidable a second push rod 21. The push rod 21 has a flat head 22 which is held in engagement with diaphragm 7 by a compression spring 23 which reacts against an end wall of cap 18.

The push rod 21 slides and is guided in a central opening in the end wall of cap 18 and carries a clevis 24 at its outer end for connection to a brake operating mechanism.

The housing 2 has individual fluid pressure ports (notshown)whereby pressure fluid, for example compressed air, can be admitted to or released from each ofthe chambers 4,5. An '0' ring seal in a recess in wall 3 engages with the push rod 14 to isolate chambers 4,5 from one another. Bolts 25 in cap 18 are provided for mounting ofthe actuator assembly.

When the actuator is in use compressed air is admitted to chamber4to cause spring 12 to be compressed (as shown in Figure 1) and allow retraction of the push rods 14,21 by springs 16,23 whereby the vehicle brake is released. lithe pressure is released from, orfalls below a predetermined value in, chamber4the spring 12 extends and appliesthe brake. When chamber4 is maintained pressurised the brake may be applied by admission of compressed air to chamber 5to cause push rod 21 to be extended. The brake is then released by exhausting the compressed airfrom chamber 5.

In accordance with the invention the half clamps 19 are removed. Depending on the amount of increased stroke required from the actuator a replacement diaphragm, as 26 in Figures 5 6, may be required.

This will be substantially identical to the diaphragm 7 exceptthat its depth, shown as dimension A on Figure 5, will be greater two allow for the increased stroke if this increased stroke cannot be accommodated by the standard diaphragm 7. Both faces 27 of the peripheral edge of diaphragm 26 are moulded with grooves for sealing purposes as in the standard diaphragm.

An annular mounting ring 28 of generallyTshaped cross-section, Figures 2,3 and 4, has a flange 29 at its periphery and opposed inclined side faces 30,31 tapering thereto. The ring 28 may, for example, be an aluminium die casting. An elastomeric sealing ring 32 is bonded to face 30 ofthe ring 28 and to the adjacent underside of flange 29. The sealing ring 32 is generally similar in cross-section to the peripheral edge ofthe diaphragm 26 with moulded grooves in one face 33 but the opposite face 34 being flat to mate with face 30 ofthe ring 28.

The mounting ring 28, with its sealing ring 32, is fitted to the housing 2 with face 33 ofthe sealing ring engaging the face oftheflange on the housing. The diaphragm 26 is offered uptotheface31 of ring 28 and then the cap 18 is applied and the assembly is completedwith half clamps as 19. These half clamps, however, need to be wider so asto accommodate the width ofthe mounting ring 28 and sealing ring 32 in addition to the flanges ofthe cap and housing and the diaphragm 26.

As described the sealing ring 32 is conveniently bonded to the mounting ring 28so asto be integral therewith but a separate sealing ring may be used if desired.

By this invention the standard actuator assembly has been modified at minimum costto provide an increased stroke without expensive tooling for a modified housing and with a minimum number of new parts, i.e. the mounting ring, sealing ring and half clamps, and a new diaphragm if so required to accommodate the additional stroke.

Claims (8)

1. A brake actuator assembly of the type described including a mounting ring interposed between the housing and the second diaphragm suchthatfluid pressure tight seals are made between the housing and the mounting ring and between the mounting ring and the second diaphragm whereby the periphery of the second diaphragm is spaced from the housing by the mounting ring and the available stroke of the push rod means is thereby increased.

2. A brake actuator assembly as claimed in Claim 1 wherein the fluid pressure tight seal between the housing and the mounting ring is provided by a sealing ring.

3. A brake actuator assembly as claimed in Claim 2 wherein the sealing ring is of an elastomeric material.

4. A brake actuatorassemblyas claimed in Claim 2 or Claim 3wherein the sealing ring is bonded, or otherwise secured,to the mounting ring.

5. A brake actuator assembly as claimed in any of Claims 2to 4wherein the mounting ing ring is of generally Tshaped cross-section having a stem witch inwardly inclined outwardly extending side faces which join a peripheral flange whereby the mounting ring is adapted to co-operate with and retain the sealing ring on one side and the periphery of the second diaphragm on the other side.

6. Amounting ringfora brakeactuat,prsubstan- tially as described herein with reference to the accompanying drawings.

7. An assemblyofa mounting ring and a sealing ring substantially as described herein with reference to the accompanying drawings.

8. A brake actuator assembly incorporating a mounting ring substantially as described herein with reference to the accompanying drawings.