AU639676B2 - Air brake with integral spring chamber - Google Patents

Description

AUSTRALi3 7J J PATENTS ACT 1952 Form COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Short Title: Int. Cl: Application Number: Lodged: Complete Specification-Lodged: Accepted: Lapsed: Published: Priority: Related Art: TO BE COMPLETED BY APPLICANT Name of Applicant: Address of Applicant: Actual Inventor: ANCHORLOK CORP.

2910 EAST ANA

COMPTON

CALIFORNIA 90221

USA

Address for Service: GR-I-F-P~H-HAC-K-&-G-O., -60-1-St-.-K-i--da-Read, c O.

Me-l-boune-V-ietori-a--004 it x. r *Aust-rl-ia I Complete Specification for the invention entitled: AIR BRAKE WITH INTEGRAL SPRING CHAMBER.

The following stateme:it is a full description of this invention including the best method of performing it known to me:- -1- 1 AIR BRAKE WITH INTEGRAL SPRING CHAMBER BACKGROUND OF THE INVENTION Field of the Invention This invention relates to air-operated combination diaphragm spring brakes of the type used with air-brake systems on vehicles such as trucks. More particularly, the invention relates to an air-operated diaphragm spring brake wherein the spring chamber is secured to the adapter by forming so as to become an integral part of the adapter.

State of the Prior Art Spring brake-applying actuators are ii common use with air-brake systems used on trucks, buses, and towed vehicles. Such actuators are normally provided within a service brake chamber for applying and releasing the brakes in response to delivery and exhaust of compressed air, and a spring brake chamber disposed in tandem with the service brake chamber. A spring brake actuator uses spring force to operate a service brake actuator and apply brakes when the air in the spring brake chamber is reduced below some predetermined level. Air may be reduced in the spring brake chamber to apply the brakes under the control of the operator or automatically as a result of failure of the air system. The service brake chamber and spring brake chamber are separated by an adapter housing which forms a wall between the two chambers.

In a typical spring brake, a barrel-shaped spring is used to store energy and to exert the large force 1equired for braking in the event of air pressure failure. Air pressure acting on a diaphragm is employed to compress the spring and maintain it in its brake release position. When the air is exhausted, the spring acts on the diaphragm, typically a elastomeric diaphragm 3 S or a piston, and through an actuating rod to exert the spring force on the service push rod.to apply the brakes.

-2- The spring brake actuator operates within the spring brake chamber, which is typically formed by clamping an elastomeric diaphragm between a spring housing and the adapter housing by a clamping mechanism such as a clamp band. It is necessary to manually cage the spring prior to any dismantling of the spring brake if service is required. If the clamping band is loosened prior to caging the spring and the safety ears on the chamber are damaged or removed, the stored energy in the barrel-spring may cause the spring housing to disengage the adapter housing with significant force.

SUMMARY OF THE INVENTION According to a first aspect of the invention, a permanent, fluid tight seal is provided ,etween a spring housing and an adapter housing in an air operated combiiation diaphragm spring brake or a fluid operated brake actuator; the spring side of the adapter housing has an annular portion or flange at one end thereof in confronting relationship with an annular rim or shoulder of the spring housing; an elastomeric diaphragm is positioned between the adapter housing and the spring housing with a circumferential edge portion thereof between the annular portion or flange and the annular rim or shoulder; and clamping means in the form of an annular channel clamps the circumferential edge of the diaphragm between the annular portion or flange and the rim or shoulder to form a fluid tight seal.

Preferably, the annular channel extends around the diaphragm, annular flange and the annular shoulder to clamp the annular shoulder to the annular flange and provide a tamper resistant clamp for the joint between the spring housing and the adapter housing.

In. one preferred embodiment, the annular shoulder may be integrally formed with the spring housing. The annular channel may be formed by a conventional mechanical swaging operation, or by an electromagnetic swaging process. In the swaging process, the cicumferential edge portion is interposed between the flange and the shoulder, with a lip portion of the shoulder beirng bent back over the flange substantially JRG:DMW\spc\#613.dl 12 May 1993 A1! I parallel to the shoulder to form the annular channel.

Also, the shoulder is formed on the spring housing at an acute angle to a longitudinal axis of the spring housing. The mechanical swaging is preferably carried out by forming the lip portion of the spring housing over the annular flange of the adapter by mechanical rollers.

The electromagnetic swaging process is carried out with the lip portion.of, the spring housing conductively shaped by powerful electromagnetic pulses. Accordingly, the spring housing is preferably made of any suitable ferromagnetic material.

A similar clamping means may also be used to provide a tamper resistant joint and fluid tight seal between a service housing and a service side of the adapter housing. r In a secondkembodiment according to the invention, the clamping means comprises an annular channel formed by a separate tube segment having f'rst and second ends. The adapter housing is identi.-al to the adapter housing in the first embodiment, but the spring housing has an annular flange instead of an annular shoulder which is in confronting relationship with the annular flange of the adapter housing. An elastomeric diaphragm is positioned between the adapter housing and the spring housing with a circumferential edge portion thereof interposed between the respective annular flanges. The tube segment is positioned to surround the circumferential edge portion with a first annular end extending beyond the adapter housing annular flange, and a second annular end extending beyond the spring housing annular flange. The first and second ends, respectively, are swaged radially inwardly over each corresponding annular flange to form the clamping channel to provide a tamperresistant clamp for the joint between the adapter housing and the spring housing, and also a fluid-tight seal. The swaging can be accomplished both mechanically and electromagneticily as in the first embodiment.

-4- 1 Accordingly, the tube segment is preferably made of any suitable ferromagnetic material.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described with reference to the accompanying drawings in which: Fig. 1 shows a cross-sectional view of an airoperated combination diaphragm spring brake of the prior art; Fig. 2 shows a cross-sectional view of an airoperated combination diaphragm spring brake with a formed seal according to the invention; Fig. 3 shows an enlarged cross-sectional view of the formed seal on the spring brakehousing illustrated in Fig. 2; Fig. 4 shows a cross-sectional view of an air operated combination diaphram spring brake illustrating a second embodiment of the invention; Fig. 5 shows an enlarged cross-sectional view of the formed seal of Fig. 4; and Fig. 6 shows an end view of the spring brake of Fig.

4 seen along lines 6-6.

DETAILED DESCRIPTION OF THE DRAWINGS Referring now to Fig. 1, there is shown an airoperated combination diaphragm spring brake of the type well known in the art and commonly referred to as an air-operated combination diaphragm spring brake. The brake is adapted to mount to a frame (not shown) of a vehicle and is further adapted to operate a braking system (not shown) through a service push rod 10 which extends to and connects with the braking system of the vehicle.

The air-operated combination diaphragm spring brake comprises a service brake chamber 12 and a spring brake chamber 14 joined together in tandem. The service brake chamber 12 is defined by a cup-shaped service housing 16 and a double cup-shaped adapter housing 18 joined together through a clamp 20 to Corm a hollow interior chamber. A first elastomeric diaphragm 42 (also known 1 as the service brake diaphragm) is clamped in fluid tight engagement between the service housing 16 and the service side of the adapter housing 18. Openings 22 are provided in the service housing 16 for bolts 24 which bolt the service housing 16 to the vehicle. A central opening 26 and side openings 27 are also provided in the service housing 16.

The adapter housing 18 forms a divider wall 28 and has a central opening 30 with one or more O-rings 31 positioned therein. An indentation or angular depression 32 is formed around the opening 30. An aperture 34 is provided in the adapter housing 18 for providing communication between a source of pressure (not shown) and the portion the service brake chamber 12 between the diaphragm 42 and the adapter housing 18 to permit the air to act upon the diaphragm in a manner to be described.

The service push rod 10 is mounted within the service brake chamber 12 for reciprocation within the central opening 26 and mounts a service push rod plate 38 at an'inner end thereof. A service return spring extends between a central portion of the service housing 16 and the service push rod plate 38 to bias the service push rod plate 38 and thus the service push rod 10 to the right as viewed in Fig. 1. The spring biased service push rod plate 38 normally forces the diaphragm 42 against the divider wall 28 on the service side of adapter housing 18 in the brake release position as shown in Fig. 1.

When air pressure is supplied through the aperture 34 as, for example, when the brakes are applied by a vehicle operator, air pressure is introduced between the diaphragm 42 and the divider wall 28, thereby forcing the diaphragm 42 toward thL central portion of the service housing 16 (to the left as seen in Fig. In this manner, the service push rod 10 is extended to the left as illustrated to apply braking pressure to the vehicle brakes in a conventional fashion.

The spring brake chamber 14 is defined by the spring side of the adapter housing 18 and a spring housing 46 which is clamped to the spring side of the adapter housing 18 through a clamp 50. A safety ear 51 extends laterally outwardly from the spring housing 46 to engage conventional clamping bolts (not shown) which secure the clamp band 50. A second elastomeric diaphragm 48 known as the spring diaphragm is clamped in fluid tight engagement between the spring side of adapter 18 and the 0 spring housing 46.

An aperture 44 is provided within the spring side of the adapter housing 18 to connect the spring brake chamber 14 with a source of pressure (not shown). An adapter push rod 52 j,s mounted within the adapter 18 housing to extend within the spring brake chamber 14 and has a reaction plate 54 rigidly bolted to one end, and a second reaction plate 56 bolted to the other end thereof. The adapter push rod 52 extends through the opening 30 and in sealing engagement with at least one O-ring 31. The reaction plate 56 seats within the angular depression 32 of the divider wall 28. An adapter return spring 58 is mounted within the spring chamber 14 between the divider wall 28 and the reaction plate 54 to bias the adapter push rod 52 into the poSition illustrated in Fig. 1.

The spring housing 46 has in a central portion thereof a cone receptacle 60 which forms a central opening 62. This opening expands in a conical fashion from the entrance end into the interior of the spring brake chamber 14.

A pressure plate 64 has a conical portion 66 with an outer surface which complements the central opening 62 of the cone receptacle 60 and further has a pressure plate bearing surface 68 at an inner portion thereof which bears against the diaphragm 48. A pilot opening with lands 70 (see Fig. 2) is provided in the center of the pressure plate 64. A compression spring 72 is positioned between the pressure plate bearing surface 68 -7- I and the spring housing 46 to bias the pressure plate 64 to the left as viewed in Fig. 1.

The adapter housing 18 and spring housing 46 are typically made of a strong but lightweight metal.

A release tool 74 can be provided within the central opening 62 of the cone receptacle 60 for mechanically drawing the pressure plate 64 back into the position illustrated in Fig. 1 in the event of an air pressure loss within the spring chamber 14, or if there is a need to cage the compression spring 72 in order to dismantle the spring brake for service. To this end, the release tool 74 comprises a threaded rod 76 having a nut 78 threaded on the end thereof and a washer 80 which bears against the outer surface of the spring housing 46.

Projections 82 on the end of the threaded rod 76 are selectively engageable with the lands 70 of the pressure plate 64 when the threaded rod 76 is rotated, so that the threaded rod can engage and draw to the right the pressure plate 64 upon movement of the threaded rod 76 to the right as viewed in Fig. 1. The position of the threaded rod 76 with respect to the spring housing 46 is controlled by the position of the nut 78 on the threaded rod 76 as the nut 78 bears against the washer In operation, air pressure is continually supplied to the spring brake chamber 14 through the aperture 44 to maintain the spring diaphragm 48 essentially in the position illustrated in Fig. 1. In this position, the service push rod 10 normally will be operated as described above by selective pressurization of air into the service brake chamber 12 through the aperture 34. However, in the event of failure of the air pressure system, the pressure in the spring brake chamber 14 will be decreased so that the service return spring 40 and adapter return spring 58 would no longer be able to overcome the pressure of the much larger and stronger compression spring 72. Thus, the pressure plate 64 forces the spring diaphragm 48, and thus the adapter push rod 52 to the left, thereby also forcing the ser- -8- 1 vice push rod 10 to the left to apply braking pressure to the brakes. The reciprocating movement of the pressure plate 64 with respect to the cone receptacle 60 is guided by the complementary conical surfaces of the central opening 62 and the outer surface of the conical portion 66.

The air-oprrated combination diaphragm spring brake described above is a well-known type of air-operated spring brake which has been sold for many years by the Anchorlok Division of Lear Siegler, Inc., of Compton, California. It will be readily understood that a common feature of all such tandem air-operated combination diaphragm spring brakes currently existing in the art is that each of the respective service and spring brake chambers are held together by a clamping mechanism.

A new air-operated combination diaphragm spring brake of the present invention is shown in Figs. 2 and 3. As can readily be seen in Fig. 2, the general configuration of the tandem air spring brake in accordance with the invention is substantially similar to the air-spring brake shown in Fig. i Herein, like numerals are used to identify like parts. However, it can readily be seen that the spring clamp band 50 and safety ears 51 of the prior art have been replaced by a formed seal 84 in accordance with the invention. The formed seal 84 secures the spring housing 46 to the adapter housing 18.

Fig. 3 shows the formed seal 84 in greater detail.

The spring housing 46 is generally cup-shaped and has an annular extended wall portion 86 formed therein at the point at which the spring housing 46 will be secured to the adapter housing 18. Preferably, the extended wall portion 86 will be at an acute angle with respect to the spring housing 46. Also, a circumferential lip portion 88 extends at an acute angle with respect to the extended wall portion 86 axially of the spring housing 46, thus forming an annular shoulder 90. The phantom -9- 1 lines in Fig. 3 show the position of the lip portion 88 prior to forming the seal 84.

The spring-diaphragm 48 typically has a circumferential bead 92 at an outer end thereof. The bead 92 can be flared as shown, or comprise an annular rib or ring extending outwardly from the surface of the diaphragm.

The spring side of the adapter housing 18 has an annular flange 94 which is generally complementary in shape to the bead on the spring diaphragm.

To form the seal, the bead 92 of the spring diaphragm 48 is positioned securely against the annular shoulder 90 of the spring housing 46. The annular flange 94 of the spring side of the adapter housing 18 is then positioned snugly against the bead 92 of the spring diaphragm 48. The bead is thus sandwiched between the annular flange 94 and the annular shoulder The lip portion 88 of the spring housing 46 extends beyond the annular flange 94 as shown by the phantom lines in Fig. 3. The outer end 89 of the lip portion 88 is forced back over the annular flange 94 to compress the bead 92 between the annular flange 94 and the annular shoulder 90 within a circumfezential channel, thus forming a permanent, fluid tight seal 84. The spring diaphragm 48 is thus secured between the spring housing 46 and the spring side of the adapter housing 18. The seal 84 also supplies the means by which the spring diaphragm 48 is suspended within the spring chamber 14.

The seal may be formed by conventional mechanical means. However, it is also possible to use a process of electromagnetically forming or swaging the cooperating pieces in an apparatus such as that described in U. S.

Patent No. 4,531,393 to Wier, issued July 30, 1985 and incorporated hatein by reference. Such a process is commercially known as Magnaforming, developed by Maxwell Laboratories, Inc., in San Diego, California, and forms metallic materials by using a generated magnetic field which allows the material to be formed without having Sany physical contact. Therefore, the spring housing 46 is preferably made of a ferromagnetic material.

Referring again to Fig. 2, it can be seen that the clamp band 20.can be replaced by a formed seal 85 on the service brake chamber 12 in a similar manner and of similar structure to the formed Stal 84 on the spring brake chamber 14. As illustrated, the elements forming the seal 85 are integral with the service housing 16.

It will also be apparent that the forming elements can be integral with the adapter housing 18 on either or both the spring brake side or the service brake side.

A seal plug 96 can be inserted into the central opening 62 of the spring housing 46. The seal plug 96 is removable so that the release tool 74, as described above, can still, be used to retract the compression spring 72, should it ever become necessary to do so.

Figs. 4, 5 and 6 show a second embodiment of the invention wherein like numerals have been used to designate like parts. The formed seal is identified as 84' in Fig. 4. Fig. 5 shows the formed seal 84' in greater detail. The adapter housing 18' has an annular flange 94'. The spring housing 46, has a similar flange 96. The spring diaphragm 48' typically has a circumferential bead 92' at an outer end thereof. The bead 92' can be flared as in the first embodiment, or comprise an annular rib or ring extending outwardly from one or both surfaces near the outer edge of the diaphragm. The flanges 94', 96 will generally be complementary in shape to the bead on the spring diaphragm.

To form the seal, the bead 92' of the spring diaphragm 48' is positioned securely between the annular flange 94' of the adapter housing 18' and the annular flange 96 of the spring housing 46' and thus suspended within the compartment formed by the adapter housing 18' Lnd the spring housing 46'. A cylindrical tube segment 98 with an interria, radius .,,;,oximately equal to che radius of the spring diaphragm 48' is positioned 11-i I adjacent to and surrounding the edges of the flanges 94', 96 and the bead 92'. Preferably, the radii of the flanges 94' and 96 are approximately equal to the radius of the spring diaphragm 48' and the internal radius of the tube segment 98. Thus positioned, the tube segment 98 has ends 100, 102 which extend beyond the flanges 94', 96, respectively. Each outer end 100, 102 of the tube segment 98 is forced back over its respective aninular flange 94'1, 96 'to compress the bead 92' between the annular flanges and within a circumferential channel thus formed in the tube segment, thereby forming a permanent, fluid-tight seal 84'. The seal may be formed mechanically using conventional rollers, or electromagnetically as |,ereinabove described. Accordingly, the preferred material for the tube segment 98 is any suitable ferromagnetic material such as steel.

As shown in Fig. 4, the seal 85' can also be formed at the junction of the service housing 16 and the service side of the adapter housing 18 in a similar manner. As can readily be seen in Fig. 6, the annular seal formed by the tube segment provides a lower profile than conventional clamping means.

It is thus seen that the invention provides a very economical and practical way of providing a permanent fluid tight seal. The spring brake chamber or service brake chamber thus constructed is secure and tamperresistant.

Reasonable variation and modification are possible within the scope of the foregoing disclosure and drawings without departing from the spirit of the invention, as defined in the accompanying claims.

Claims (10)

1. An air-operated diaphragm spring brake having a first shell with a first-annular flange at an open end thereof; a second shell having a second annular flange in confronting relationship to the first annular flange thereby forming a housing defining a chamber; an elastomeric diaphragm disposed within the chamber and having a circumferential edge portion interposed between the first annular flange and the second annular flange; and means for clamping the circumferential edge portion of the diaphragm between the flanges to form a fluid-tight seal, wherein the clamping means comprises: one of the first shell and the second shell having a wall portion at an acute angle relative to its respective flange; and one of the flanges extending radially outwardly, then axially beyond the other of the flanges, and then radially inwardly to envelop the other of the flanges and the elastomeric diaphragm and to sealingly clamp the elastomeric diaphragm between the first annular flange and the second annular flange thereby providing a tamper-resistant clamp for the joint.

2. An air-operated diaphragm spring brake according to claim 1 wherein the circumferential edge of the diaphragm has 1 a bead. C"13:: ~~V 7 o$> 13

3. An air-operated diaphragm spring brake according to claim 2 wherein at least one of the annular flanges is complementary in shape to the bead.

4. An air-operated diaphragm spring brake according to claim 3 wherein the spring housing is made of a ferromagnetic material.

5. An air-operated diaphragm spring brake having a first shell with a first annular flange at an open end thereof; a second shell having a second annular flange in confronting relationship to the first annular flange thereby forming a housing defining a chamber; an elastomeric diaphragm disposed within the chamber and having a circumferential edge portion interposed between the first annular flange and the second annular flange; and means for clamping the circumferential edge of the diaphragm between the flanges to form a fluid-tight seal, wherein: the circumferential edge portion of the diaphragm has a bead; and one of the flanges extends radially outwardly, then axially beyond the other of the flanges, and then radially inwardly to envelop the other of the flanges and the elastomeric diaphragm and to sealingly clamp the elastomeric diaphragm between the first JRG:DlW\spe\9613.r 12 May 1993

14- annular flange and the second annular flange thereby providing a tamper-resistant clamp for the joint. 6. An air-operated diaphragm spring brake according to claim 5 wht,'ein one of the annular flanges is complementary in shape to the bead. 7. An air-operated diaphragm spring brake according to claim 6 wherein the spring housing is made of a ferromagnetic material. 8. An air-operated diaphragm spring brake having a first shell with a first annular flange at an open end thereof; a second shell having a second annular flange in confronting relationship to the first annular flange thereby forming a first housing defining a chamber; an elastomeric diaphragm disposed within the chamber and having a circumferential edge portion interposed between the first annular flange and the second annular flange; and means for clamping the circumferential edge of the diaphragm between the flanges to form a fluid-tight seal, wherein the clamping means comprises: one of the flanges extending radially outwardly, then axially beyond the other of the flanges, and then radially inwardly to envelop the other of the flanges and the elastomeric diaphragm and to sealingly clamp the elastomeric diaphragm between the first JRG:DMW\spc\#9613.cl 12 May 1993 15 annular flange and the second annular flange thereby providing a tamper-resistant clamp for the joint; and wherein a second housing is disposed in tandem with the first housing, and the second housing is formed of mating shells with annular flanges and an elastomeric diaphragm wherein one of the flanges extends radially outwardly, then axially, and then rad;aly inwardly to envelop the other of the flanges and the elastomeric diaphragm to sealingly clamp the elastomeric diaphragm between the flanges thereby providing a tamper-resistant clamp for the second housing; and one of the mating shells forming the second housing has a wall portion at an acute angle relative to its respective flange. 9. An air-operated diaphragm spring brake according to claim 8 wherein the circumferential edge of the diaphragm associated with the second housing has a bead and the annular flange is complementary in shape to the bead. A method of joining a first shell to a second shell in an air-operated diaphragm spring brake with an elastomeric diaphragm interposed therebetween, each of said shells having an annular flange, and said diaphragm having a circumferential edge portion, comprising the steps of: placing the circumferential edge portion against one of the annular flanges in a circumferentially abutting relationship, JRG:DMW\spe\#9613.c 12 May 1993 -16- placing the other of the annular flanges against the circumferential edge portion in a circumferentially abutting relationship, and electromagnetically swaging one of the annular flanges over the other annular flange to secure the circumferential edge portion between the annular flanges in a sealing engagement. 11. An air-operated diaphragm spring brake having an adapter shell with a first annular flange at an open end thereof; a spring shell having a second annular flange in confronting relationship to the first annular flange forming a housing defining a spring brake chamber; an elastomeric 'diaphragm within the spring brake chamber between the adapter shell and the spring shell with a circumferential edge portion of said elastomeric diaphragm interposed between the first annular flange and the second annular flange; means for clamping said circumferential edge of the diaphragm between the first annular flange and the second annular flange to form a fluid-tight seal, wherein: the circumferential edge of the diaphragm has a bead; and an annular channel is formed by a tube segment having first and second annular ends, the first annular end extending radially inwardly and tightly against the first annular flange, -17- and the second annular end extending radially inwardly and tightly against the second annular flange to provide a tamper- resistant clamp for the joint between the adapter housing and the spring housing. 12. An air-operated diaphragm spring brake according to claim 11 wherein one of the first annular flange and the second annular flange is complementary in shape to the bead. 13. An air-operated diaphragm spring brake according to claim 12 wherein the tube segment is made of a ferromagnetic material. 14. An air-operated diaphragm spring brake according to claim 12 wherein a service brake shell is clamped to a service side of the adapter shell to form a second housing defining a service brake chamber in tandem with the spring brake chamber, the service brake chamber being separated from the spring brake chamber by the adapter shell. A method of joining a first shell to a second shell in an air-operated diaphragm spring brake with an elastomeric diaphragm interposed therebetween, each of said shells having an annular flange at an open end thereof, and said diaphragm having a circumferential edge portion, comprising the steps of: 18 placing the circumferential edge portion against one of the annular flanges in a circumferentially abutting relationship; placing the other o'f the annular flanges against the circumferential edge portion in a circumferentially abutting relationship; surrounding the circumferential edge portion with a tube segment having first and second annular ends; and electromagnetically swaging the first end radially inwardly over one of the annular flanges, and the second annulpr end radially inwardly over the other annular fl~age, and. in clamping relationship thereto to secure the circumferential edge portion between the first annular flange and the second annular flange in a sealing engagement.

16. A tamper-resistant fluid operated brake actuator comprising: a spring housing ,of deformable metal; an adapter housing having a first portion extending radially outwardly from the remainder of said adapter housing; a flexible diaphragm disposed between said spring housing and said adapter housing, and having a bead at its circumferential edge; said, spring housing being adapted to mount a power spring' between said spring housing and said diaphragm, an overlying portion of said diaphragm overlying a portion of said first portion of said adapter housing, QT\ I 19 said spring housing further including an integral annular rim extending radially outwardly from the remainder of said spring housing and overlying a portion of said diaphragm; wherein said first portion of said adapter housing and said annular rim on said spring housing diverge as they extend outward from said adapter housing and said spring housing respectively; a securing member for securing said annular rim to said first portion of said adapter housing, said securing member having a portion radially aligned with said overlying portion of said diaphragm and on a side of said diaphragm towards said spring housing, said securing member extending axially beyond both said diaphragm and said first portion of said adapter housing and radially inwardly behind said first portion of said adapter housing, and being inelastically deformed into a generally U-shaped configuration to retain said spring housing in contact with said adapter housing such that said spring housing is rigidly secured to said adapter housing by said securing member, whereby to remove said spriig housing from said adaptor housing said securing member must be deformed beyond its elastic limit. DM h p 96134 12 May 1993 ?4i) 20

17. A tamper-resistant fluid operated brake actuator according to claim 1i wherein the securing member is formed of a ferro-magnetic material.

18. A tamper-resistant fluid operated brake actuator comprising: a spring housing of deformable metal; an adapter housing having a first portion extending s radially outwardly from the remainder of said adapter housing; a flexible diaphragm disposed between said spring housing and said adapter housing, and having a bead at its circumferential edge; said spring housing being adapted to mount a power spring between said spring housing and said diaphragm, an overlying portion of said diaphragm overlying a portion of said first portion of said adapter housing; and said spring housing including an integral annular rim extending radially outwardly from the remainder of said spring housing and overlying a portion of said diaphragm, said annular rim haviog a securing portion for securing said annular rim to said first portion of Oaid adapter housing, said annular rim being radially aligned with said overlying portion of said diaphragm and on a side of said diaphragm towards said spring housing, j l 21 said securing portion then extending axially beyond said diaphragm and said first portion of said adapter housing and inelastically deformed radially inwardly behind said first portion of said adapter housing into a generally U-shaped configuration to retain said spring housing in contact with said adaptor housing such that said spring housing is rigidly secured to said adapter housing by said securing member, whereby to remove said spring housing from said adapter housing said securing member miust be deformed beyond its elastic limit.

19. A tamper-resistant fluid operated brake actuator according to claim 18 wherein said first portion of said spring housing and said annular rim on said adapter housing diverge as they etend outward from said spring housing and said adapter housing respectively. An air-operated diaphragm spring brake substantially as hereinbefore described with reference to one or more of Figures 2 to 6 of the accompanying drawings. DATED: 12 May 1993 CARTER SMITH BEADLE Patent Attorneys for the Applicant: ANCHORLOK CORP IRGMWpc\#9613.d 12 May 1993 V C o£-