MXPA99006956A - Spring brake actuator with internal breathing conduit - Google Patents

Abstract

A spring brake actuator (10), with a large-force compression spring (82) in a second spring chamber (78) of the housing, has vent openings (100) in the housing communicating with the second spring chamber (78). A filter assembly (134) covers the vent openings (100). Weep holes (62, 104, 102, and 100) in a sleeve (50) of a push rod (18), in a spring brake actuator rod (84), and in a spring brake housing portion (68) together permit fluid compressed in a first service brake chamber (30) to flow through a conduit defined by these weep holes out of the brake actuator (10) wherein it is filtered by the filter assembly (134).

Description

SPRING BRAKE ACTUATOR WITH INTERNAL BREATHING DUCT Background of the Invention Field of the Invention The invention relates to air operated diaphragm brakes for vehicles, and particularly to assemblies in combination of brake actuator and service. STATE OF THE ART An air brake system for a vehicle, such as a bus, truck, or the like, typically includes a brake shoe and drum assembly that is actuated by means of an actuator assembly operated by the selective application of air compressed. Conventional air brake actuators have both a service brake actuator for operating the brakes under normal driving conditions by application of compressed air, and a spring-type emergency brake actuator which causes the brakes to actuate when The air pressure has been released. The emergency brake actuator includes a strong compression spring, which forces the application of the brake when the air is released. This is often referred to as the spring brake. Normally, the spring brake actuator is arranged in the row with the service brake actuator. When the total pressure is applied to the spring brake actuator, the air pressure acting against a diaphragm compresses the compression spring. A rod of the spring brake actuator is held in a retracted position by a relatively small return spring, thus not affecting brake operation. When the brake is to be applied during the normal driving operation, compressed air is supplied to the service brake actuator, which, acting against a diaphragm, causes the service brake to push the rod to extend, and causes them to apply the brakes with an application force that is proportional to the air pressure applied to the service brake actuator. In the event of a loss of air pressure or intentional depletion of air from the spring brake actuator, the brake will be mechanically activated by the force of the compression spring acting on the spring brake actuator rod, which in turn acts on the push rod of the service brake to apply the brakes. Accordingly, the spring brake portion serves as both a parking brake and an emergency brake. In a typical air brake system of the prior art, the spring brake actuator and the service brake actuator are disposed in a single housing comprising a spring brake portion and a service brake portion. The service brake portion includes an air chamber partially defined by a flexible service diaphragm which acts against a service brake push rod and a return spring to ensure proper release of the brake when air is exhausted from the chamber of air. The spring brake portion includes a spring chamber and an air chamber, both partially defined by a diaphragm of the spring brake acting against a spring pressure plate to compress the compression spring in the spring chamber when it is applied. the air pressure to the diaphragm of the spring brake in the air chamber. An actuator rod extends through the diaphragm of the spring brake to connect integrally with the pressure plate. In operation, it is pushed out from the air chamber through an opening in the housing and a bearing provided with a pneumatic seal to mate with the service diaphragm and the service brake push rod, causing it to be applied from this way the brake. The diaphragm of the spring brake is provided with a centrally disposed opening having an annular edge, and the actuator rod extends through the opening, and engages with the annular edge to form an air-tight seal. The actuator rod is hollow with a central hole, and a brake release cage screw extends into the central hole. An end plate on the screw engages the pressure plate of the spring brake to direct the spring to a compressed state when the spring is caged by the rotation of the screw. The spring chamber on the spring side of the spring brake diaphragm is normally vented to the outside atmosphere to allow air to be drawn from that portion of the housing when the diaphragm is driven in the direction of the spring to compress the compression spring of the spring brake in the spring chamber. When the spring expands, the diaphragm moves in one direction to enlarge the spring chamber, and the external air is directed into the spring chamber. Since the spring chamber is vented to the outside atmosphere beneath the truck chassis, outside air directed into the spring chamber is often accompanied by moisture and corrosive substances, such as road salt. Because the spring wears out as it cycles, and its bare metal becomes exposed as a result of it, the spring tends to corrode due to air pollutants. Also, because the compression spring of the spring brake must exert a substantial force in order to act as an emergency brake, the spring is under great tension when compressed. The durability of the spring is inversely proportional to the amount of corrosion and stress it experiences. In sealed housing, the spring can not be removed from the housing without permanently deforming the housing. In other housings, the actuator must be replaced by a new actuator, and the old actuator must be sent to a rebuilder. In any case, the actuator can not be served by the truck operator. Accordingly, when the compression spring of the spring brake is broken, the entire brake actuator unit must be replaced at a substantial cost. Attempts have been made to seal the spring chamber, including the provision of breather tubes to direct air from the spring chamber to other portions of the brake actuator and one-way internal valves, to provide a one-way airflow from inside the brake actuator to the atmosphere. For example, U.S. Patent Nos. 5,263,403 and 5,311,809 to Choins i et al. Discloses a brake actuator having a spring brake chamber and a non-pressurized service brake chamber fluidly interconnected by a breather tube mounted on an external surface of the brake actuator. U.S. Patent No. 4,890,540 to Mullins discloses a brake actuator unit having a housing provided with a pair of vent holes, wherein one of the vent holes is capped to prevent contaminants from entering the housing. accommodation. In addition, U.S. Patent No. 3,896,706 to Ne stead et al. Discloses a brake unit having a tubular piston including a vent opening extending inward from a spring housing, which it is in communication with a filter at one end of the spring housing. The solutions of the prior art to the problem that contaminated air enters the spring chamber, have been little functional or expensive and complicated to manufacture. SUMMARY OF THE INVENTION A brake actuator in accordance with the invention solves the problem of preventing contaminants from entering the brake actuator housing by providing an internal breathing conduit connecting a service brake housing with a fluidly connected filter with a spring brake housing. In one embodiment, the brake actuator comprises a spring brake actuator housing and a service brake actuator housingthe spring brake actuator housing having a first movable member disposed therein, which divides its interior into a first spring brake chamber and a second spring brake chamber. The first movable member preferably can reciprocally move therein in response to the supply and withdrawal of pressurized fluid to the first spring brake chamber. A spring is provided in the second spring brake chamber, in a position for forcing the first movable member to a first position, wherein the first spring brake chamber collapses when extracting the pressurized fluid from the first brake chamber of the spring. spring. The service brake actuator housing has a second movable member disposed therein, which divides its interior into a first service brake chamber and a second service brake chamber. The second movable member can preferably move reciprocally therein in response to the supply and withdrawal of pressurized fluid to the second chamber of the service brake. A hollow rod actuating the spring brake is operatively connected to the first movable member, and a service brake actuating rod is operatively connected to the second movable member. The operating brake actuator rod extends through the service brake actuator housing to connect with a brake. The improvement in accordance with the invention is that the service brake actuator housing is sealed, and the spring brake actuator housing is sealed, except for at least one filtered ventilation opening in the second spring brake chamber, the service brake operating rod is hollow with an opening in communication with the first service brake chamber, the spring brake actuating rod is in communication with the second spring brake chamber, and extends through the second member movable to a communication with the service brake actuating rod to vent the fluid from the first service brake chamber through the service brake actuating rod and the spring brake actuating rod when the second brake chamber is pressurized of service. The second movable member preferably has an opening. The actuating rod of the service brake is preferably anchored to the second movable member, and the spring brake actuating rod extends through the opening to the operating brake operating rod. The actuating rod of the service brake is preferably snapped into the second movable member. The second movable member preferably comprises a diaphragm mounted on a peripheral edge thereof with the service brake actuator housing. The second movable member preferably further comprises a pressure plate, and wherein the actuating rod of the service brake is preferably snapped into the pressure plate. Preferably, an O-ring seal is provided between the spring brake actuator rod and the second movable member. The brake actuator preferably further comprises a plug disposed at one end of the operating rod of the service brake. The spring brake actuating rod preferably extends to the service brake actuator rod sufficiently to abut the plug and force the service brake actuator to engage with the brake when the first spring brake chamber is evacuated. The opening in the actuating rod of the service brake is preferably located adjacent to the second movable member. Preferably, at least one drain hole is provided at each end of the spring brake actuator rod, whereby the at least one drain hole at each end of the spring brake actuator rod fluidly connects the interior of the spring brake. actuating rod of the service brake with the second spring brake chamber. Preferably a cage rod is mounted on a first end with the spring brake actuator, and extending inside the spring brake actuator rod. A second end of the cage rod preferably has a plate thereon. The plate on the second end of the cage rod preferably has at least one passage extending therethrough. The at least one passage of the plate preferably is disposed inward from a peripheral edge of the plate. In another embodiment, the brake actuator according to the invention preferably has a second movable member comprising a piston. The piston can mount the service brake actuator rod as described herein. Brief Description of the Drawings Figure 1 is a cross-sectional view of a diaphragm-type spring brake actuator with an internal breathing duct according to the invention.

Figure 2 is a cross-sectional view of a cage rod head of the spring brake actuator, taken along lines 2-2 of Figure 1. Figure 3 is a cross-sectional view of an actuator. of piston-type spring brake with an internal breathing duct according to the invention. Detailed Description Figure 1 shows a cross-sectional view of an air-operated brake actuator unit 10, having a general configuration well known in the art, and modified in accordance with the teachings of this invention. The actuator unit 10 comprises a service brake portion 12 mounted in a row with a spring brake or emergency brake portion 14. A push rod or actuator of the service brake 18 extends from the service brake 12, and it adapts to operatively connect with a conventional brake shoe and drum (not shown in the drawing) in a standard form. The reciprocating movement of the push rod 18 will cause the brake to be applied and released in an alternating manner. The service brake 12 comprises a pair of facing cup-shaped housing sections 20 and 22, each having an outwardly facing flange edge 24. The housing sections 20, 22 are fastened together at their flange edges. by means of a clamp 26 to form a first service brake chamber 30 and a second service brake chamber 31 on either side thereof. An elastomeric diaphragm 32 is suspended inside the inner chamber 30, and is compressed on its peripheral edge between the flange edges 24 of the housing sections 20, 22. The housing section 20 is provided with a central opening 34 therein. . The push rod of the service brake 18 extends through the opening 34 in the housing section 20, and to the first chamber of the service brake 30, where it terminates in a pressure plate 36. The pressure plate 36 it includes a cylindrical cylindrical sleeve 38 having a base 40. The push rod guide 42 is arranged around the central opening 34, and comprises a sleeve 44 having a radially extending flange thereon, which forms a seat spring 46. The compression spring 48 extends between the base 40 of the pressure plate 36 and the spring seat 46 of the push rod guide 42. The guide of the push rod 42 acts to center the spring 48 around the opening 34. The push rod of the service brake 18 comprises an elongated cylindrical sleeve 50 having a first end 52 and a second end 54. The first end 52 of the push rod of the service brake 18 is mounted in the base 40 of the pressure plate 36. The second end 54 of the push rod of the service brake 18 is mounted inside the sleeve portion 44 of the push rod guide 42, and extends through the central opening 44. The second end 54 is closed by a plug 56, which mounts a pivotable actuator rod 58, operatively connected with a brake assembly (not shown). The jacket 50 defines an internal chamber 60. The first end 52 further includes several drainage holes 62 disposed adjacent the base 40 of the pressure plate 36. An O-ring 64 is located between the guide of the push rod 42 and the shirt 50, to provide a seal therebetween. The spring 48 thus tends to force the pressure plate 36 and the push rod of the service brake 18 to a fully retracted position shown in Figure 1. The spring brake 14 comprises a pair of shaped housing sections. cup faces 66, 68. The housing sections 66, 68 can be formed from an integral cast part. The housing sections 66 and 68 are each provided with an outwardly facing circumferential flange edge 70, and a curved peripheral edge 72, respectively. The housing sections 66 and 68 are held together by the curved edge 72 of the housing section 68 which engages the edge 70 of the housing section 66. An elastomeric diaphragm 74 is compressed on a peripheral edge 76 between the edges 70, 72 of the housing sections 66, 68, and divides the interior of the spring brake 14 into a first spring brake chamber 76 and a second spring brake chamber 78. The first spring brake chamber 76 it is filled with compressed air normally supplied through an air service hatch 80 in the housing section 66 when the emergency brake is in its normal released position. The second spring brake chamber 78 contains a high force spring brake compression spring 82. An actuator rod 84, aligned with the push rod 18, comprises a cylindrical sleeve having a proximal end 86 and a distal end 88. The proximal and distal ends 86 and 88 are provided with several drain holes 102 and 104, respectively. The proximal end 86 of the actuator rod 84 extends through a centrally disposed aperture 90 in the diaphragm 74, and terminates in a pressure plate 92 which engages the compression spring 82. The pressure plate 92 comprises a portion substantially flat 94 which engages an end of the spring 82, and a tubular or truncoconical rod 96 which extends coaxially with the axis of the spring 82. The rod 96 snaps onto the proximal end 86 of the actuator rod 84, such that the pressure plate 92 and the actuator rod 84 form an integral unit. An annular recess 98 in an end wall of the housing section 68 serves as a seat for the spring 82, and also provides rigidity to the end wall against the force of the spring 72. The annular recess 98 is provided with drainage holes 100 The distal end 88 of the actuator rod 84 extends through a central opening 106 in an end wall of the housing section 66, sealed by an O-ring 108, through the cylindrical cylindrical sleeve 38 of the mounting plate. service pressure 36, and into the internal chamber 60 of the jacket 50. The O-ring 108 seals the second service braking chamber 31 of the first spring brake chamber 76. An O-ring 109 in the sleeve 38 seals the inner chamber 30 of the service brake chamber 31. The distal end 88 of the actuator rod 84 terminates in a reaction plate 110 provided with an annular seat 112 that completely encloses the distal end 88 of the actuator rod 84. The end of the reaction plate 110 abuts the plug 56, when both emergency and service brakes are not engaged. The reaction plate 110 includes spacer tabs 114 defining an annular groove that stops a low friction wear strip 115 made of Teflon, Delrin, or the like, which centers the reaction plate 110, and in turn, the drive rod 84. inside the chamber 60 of the shirt 50 of the push rod actuator 18. In this way an annular recess 116 is def having an internal limit def by the actuator rod 84, and an external limit def by the actuator sleeve 50 of push rod 18. Actuator rod 84 preferably accommodates a brake release cage rod 118 disposed coaxially therein, and having a first end 120 and a second end 122. The first end 120 extends through a coaxial hole in the rod 96 of the pressure plate 92 and through a coaxial opening in an end wall of the housing portion 68 coaxial with the annular recess 98. The second end rowing 122 of the cage rod 118 mounts an enlarged plate 124. The cage rod 118 is used to manually release the spring brake, or to ensure that the compression spring 82 remains compressed (or caged) when performing the functions of maintenance on the brake assembly. As seen in Figure 1, and in greater detail in Figure 2, the plate 124 has an outer diameter that generally corresponds to, or just slightly less than, the internal diameter of the actuator rod 84. The plate 124 also includes several grooves or axial passages 126 disposed at intervals around the plate 124, and extending radially inward from its circumferential edge. It will be understood that the cage rod 118 is preferably a screw or the like screwed into a fixed thread opening, such as the threaded collar 128 mounted, such as by welding, to the end wall of the housing section 68 coaxial with the annular recess 98. A hexagonal head nut 130 is fixedly attached to the first end 120 of the cage rod 118, to facilitate the screwing of the rod 118 in and out of the spring brake 14 by a common wrench or the like. An inwardly directed annular shoulder 132 is provided on the rod 96 of the pressure plate 92, to provide a positive coupling with the proximal end 86 of the actuator rod 84, when actuating rod 84 is actuated, and further serves as a coupling surface for the plate 124 on the second end 122 of the cage rod 118, against which the plate 124 will rest when the cage rod 118 is removed. When removed, the cage rod 118 retains the compression spring 82 in its compressed or caged state. Otherwise, the cage rod 118 extends toward the distal end 88 of the actuator rod 84 by a distance sufficient to allow the actuator rod 84 to extend for its entire length of travel without engagement between the shoulder 132 and the plate 124. of the cage rod 118. Figure 1 further shows a filter assembly 134 mounted on the end wall of the housing section 68., coaxial with the annular recess 98, which covers the drainage holes 100 therein. The filter assembly 134 defines a tortuous air path for entry and egress of the second spring brake chamber 78, which collects particles and other contaminants therein. The filter assembly 134 generally comprises a frame housing a gas permeable filter, and is described in greater detail in a request assigned to the assignee hereof, and entitled "Spring Brake Actuator with Filtered Vent Openings", PCT international application / US95 / 02151, filed February 21, 1995. The filter assembly 134 effectively requires that all air entering and leaving the chamber 78 through the drain holes 100, go through the filter assembly 134, while simultaneously protecting the filter contained therein and the openings from dirt, debris, ice buildup, paint, and the like. It will be understood that as air is directed into the chamber 78 when the spring 82 expands, the contaminants in the atmosphere will be trapped by the filter assembly 134. Conversely, as air is expelled from the chamber 78 when the it retracts the pressure plate 92, forces it back through the filter assembly 134, and effectively cleans it, expelling the contaminants into the atmosphere. Therefore, the chamber 78 remains substantially free of contaminants, independent of the operation of the spring brake 14. During normal operation of the brake actuator 10, the actuator rod 84 will be in the fully retracted position, as illustrated in FIG. Figure 1, by means of compressed air, which is introduced through the air gate 80 in the housing section 66, and is maintained in the first spring brake chamber 76. To operate the service brake 12, it is introduces compressed air through an air service hatch in the housing section 22 (not shown), into the second chamber of the service brake 31, to force the diaphragm 32 and the pressure plate 36 against the force of the spring 48, in order to actuate the push rod actuator 18. As the diaphragm 32 is actuated, any fluid in the first service brake chamber 30 is compressed and forced into a through the drainage holes 62 of the jacket 50 of the push rod actuator 18. The compression of the fluid in the first chamber of the service brake 30 causes the fluid flowing through the drain holes 62 in the sleeve 50, pass through the gap 116, further through the drain holes 104 at the distal end 88 of the actuator rod, and up to its interior. Then the fluid flows to the proximal end 86 of the actuator rod 84. If and when the fluid encounters the plate 124 on the second end 122 of the cage rod 118, it passes through the plate 124 through the passages 126. Then the fluid exits the proximal end 86 of the actuator rod 84, and towards the second chamber of the spring brake 78 through the drain holes 102. The fluid exits the second chamber of the spring brake 78 through the drain holes 100 in the annular recess 98, and inwardly of the filter assembly 134. When the compressed air is withdrawn from the first spring brake chamber 76, the compression spring 82 forces the pressure plate 92 and the actuator rod 84, integrally attached to the pressure plate 92, in the direction of the push rod 18 of the service brake 12. The force of the spring 82, when released, causes the actuator rod 84 to extend through the central opening 3. 8, which in turn causes the reaction plate 110 to apply a force to the plug 56. This action causes the push rod of the service brake 18 and the drive rod 58 to be actuated, and the brake applied. When the emergency brake is released, once again compressed fluid is introduced into the first chamber of the spring brake 76. The force of the fluid compressed against the diaphragm 74 forces the pressure plate 92, the actuator rod 84, and the spring 82 towards the retracted position illustrated in Figure 1. When the spring 82 is retracted, fluid flows through the recess 116 in a reverse direction from that described above, as well as outwardly of the filter 134 through the drainage holes 100. It will be understood that poles are provided. 136 to mount the brake actuator unit 10 on a vehicle. Figure 3 shows a cross-sectional view of a second embodiment of an air-operated brake actuator unit 10, having a general configuration well known in the art, and modified in accordance with the teachings of this invention. It will be understood that Figure 3 contains some reference numerals in common with those of Figure 1, to denote similar components or characteristics among the modalities shown in each figure. It will be further understood that the reference numerals of Figure 3 are greater by 200 than those of Figure 1, to denote the components or characteristics of the second embodiment. The second embodiment of the actuator unit 10 comprises a service brake portion 212 mounted in a row with a spring brake or emergency brake portion 14. A push rod of the service brake 218 extends from the service brake 212 to the application of a conventional brake assembly as in the previous modality. In this embodiment, service brake 212 is a piston-type brake comprising a pair of facing cup-shaped housing sections 220 and 222, each having an outwardly facing flange edge 224. Housing sections 220 222 are fastened together on their flange edges 224 by means of a fastener 226 to form a first service brake chamber 230 and a second service brake chamber 331 on either side thereof. A piston 232 is suspended inside the inner chamber 230, and comprises a plate 233 having a wall 235 extending from an outer radial edge of the plate 233, and a rod 238 having a coaxial hole 240 therethrough. Elastomeric sealing members 237 and 239 can be located in the grooves of an outer surface of the wall 235 and an inner surface of the rod 238, to provide a sealing stop against an inner wall of the housing portion 220 and an actuating rod 84. housing section 220 is provided with a central opening 234 therein. The service brake rod of the service brake 218 extends through the opening 234 in the housing section 220, and into the first chamber of the service brake 230, where it ends in the rod 238 of the piston 232. A push rod guide 242 is disposed around the central opening 234, and comprises a sleeve 244 having a radially extending flange thereon, which forms a spring seat 246. A compression spring 248 extends between the rod 238 of the piston 232 and the spring seat 246 of the push rod guide 242. The guide of the push rod 242 acts to center the spring 248 around the opening 234. The push rod of the service brake 218 comprises an elongated cylindrical sleeve 250 having a first end 252 and a second end 254. The first end 252 of the push rod of the service brake 218 extends from the rod 238 of the piston 232. The cam isa 250 can be formed integrally as part of the piston 232. The second end 254 of the service brake push rod 218 is mounted inside the sleeve portion 244 of the push rod guide 242, and extends through of the central opening 234. The second end 254 is closed by a plug 256, which can mount a pivotable actuator rod 258. The actuator rod 258 can be mounted to the brake assembly (not shown). The jacket 250 defines an internal chamber 260. The first end 252 further includes several drainage holes 262 disposed adjacent the rod 238 of the piston 232. An O-ring 264 can be located between the guide of the push rod 242 and the sleeve 250 , to provide a seal between them. The spring 248 in this manner tends to force the piston 232 and the push rod of the service brake 218 to a fully retracted position, as shown in Figure 3. The spring brake 14 is configured and shown with reference numerals identical to those of the first embodiment shown in Figure 1, and is not further described below, except to note that a discussion follows with reference to the reference numerals describing the spring brake 14. During normal operation of the actuator of the brake 10, the actuator rod 84 is in the fully retracted position, as illustrated in Figure 1, by means of compressed air, which is introduced through the air damper 80 into the housing section 66, and is maintained in the first spring brake chamber 76. To operate the service brake 212, compressed air is introduced through an air service gate into the housing section 22 2 (not shown), towards the second chamber of the service brake 231, to force the piston 232 against the force of the spring 248, to drive the push rod actuator 218. In this way, the piston 232 can slide coaxially around of the actuator rod 84. When the piston 232 is actuated, any fluid in the first chamber of the service brake 230 can be compressed and can traverse through the drain holes 262 in the jacket 250 of the push rod actuator 218 The compression of the fluid in the first chamber of the service brake 230 causes fluid flowing through the drain holes 262 in the jacket 250, to pass through the recess 116, and to run out of the brake actuator 10. through the filter assembly 134, as described above. The invention encompasses other variations and modifications not illustrated in the drawings, but clearly evident to one skilled in the art. It will be understood that those skilled in the art can devise other variations and modifications of the above embodiments without departing from the scope of the invention as defined by the appended claims.

Claims (25)

1. CLAIMS 1. In a brake actuator for a vehicle, comprising: a spring brake actuator housing and a service brake actuator housing; the spring brake actuator housing having a first movable member disposed therein, dividing its interior into a first spring brake chamber and a second spring brake chamber and movable reciprocally therein in response to the delivery and discharge of the spring. fluid under pressure to the first spring brake chamber; a spring disposed in the second spring brake chamber in a position for urging the first movable member to a first position where the first spring brake chamber is collapsed upon discharge of the pressurized fluid from the first spring brake chamber; the service brake actuator housing having a second movable member disposed therein, dividing its interior into a first service brake chamber and a second service brake chamber and movable reciprocally therein in response to the delivery and discharge of the service brake. fluid under pressure to the second service brake chamber; a hollow spring brake actuator rod, operatively connected to the first movable member; and a service brake actuator rod operatively connected to the second movable member, and extending through the service brake actuator housing for connecting a brake, the improvement wherein: the service brake actuator housing is sealed and the housing spring brake actuator is sealed, except for at least one filtered vent in the second spring brake chamber, the service brake actuator rod is hollow, with an opening in communication with the first service brake chamber, and the hollow spring brake actuator rod is in communication with the second spring brake chamber and extends through the second movable member toward communication with the service brake actuator rod, thereby venting fluid from the brake. first service brake chamber through the service brake actuator rod and the spring brake actuator stem when the second The service brake chamber is pressurized. The brake actuator of claim 1, wherein the second movable member has an opening, the service brake actuator rod is anchored to the second movable member, and the spring brake actuator rod extends through the opening toward the service brake actuator rod. 3. The brake actuator of claim 2, wherein the service brake actuator rod is press-fitted into the second movable member. The brake actuator of claim 3, wherein the second movable member comprises a diaphragm mounted on a peripheral edge thereof to the service brake actuator housing. The brake actuator of claim 4, wherein the second movable member further comprises a pressure plate, and wherein the service brake actuator rod is pressurized into the pressure plate. 6. The brake actuator of claim 5, and further comprising an O-ring seal disposed between the spring brake actuator rod and the second movable member. The brake actuator of claim 2, and further comprising a plug disposed at one end of the service brake actuator rod. The brake actuator of claim 7, wherein the spring brake actuator rod extends towards the service brake actuator rod far enough to bump into the cap and urges the service brake actuator to engage a brake when evacuates the first spring brake chamber. 9. The brake actuator of claim 2, wherein the opening in the service brake actuator rod is located adjacent to the second movable member. 10. The brake actuator of claim 9, wherein at least one drain hole is disposed at each end of the spring brake actuator rod, whereby the at least one drain hole at each end of the spring brake actuator rod fluidly connects the interior of the brake actuator rod of service with the second spring brake chamber. The brake actuator of claim 10, and further comprising a cage rod mounted on a first end to the spring brake actuator housing and extending within the spring brake actuator rod, a second end of the cage shaft having a plate in it. The brake actuator of claim 11, wherein the plate at the second end of the caging rod has at least one passage extending therethrough. The brake actuator of claim 12, wherein the at least one passage in the plate is disposed inwardly from a peripheral edge of the plate. 14. The brake actuator of claim 1, wherein the service brake actuator rod is pressurized to the second movable member. The brake actuator of claim 1, wherein the second movable member comprises a diaphragm mounted on a peripheral edge thereof to the service brake actuator housing. 16. The brake actuator of claim 1, wherein the second movable member further comprises a pressure plate, and wherein the service brake actuator rod is pressurized into the pressure plate. 17. The brake actuator of claim 1, and further comprising an O-ring seal disposed between the spring brake actuator rod and the second movable member. 18. The brake actuator of claim 1, wherein the second movable member is a piston mounted on the service brake actuator rod. 19. The brake actuator of claim 1, and further comprising a plug disposed at one end of the service brake actuator rod. The brake actuator of claim 19, wherein the service brake actuator rod extends toward the service brake actuator rod far enough to bump into the plug and urges the service brake actuator to engage the brake when evacuates the first spring brake chamber. 21. The brake actuator of claim 1, wherein the opening in the service brake actuator rod is located adjacent the second movable member. 22. The brake actuator of claim 1, wherein at least one drain hole is disposed at each end of the spring brake actuator rod whereby the at least one drain hole at each end of the spring brake actuator rod fluidly connects the interior of the service brake actuator rod with the second spring brake chamber. 23. The brake actuator of claim 1, and further comprising a cage rod mounted on a first end to the spring brake actuator housing and extending within the spring brake actuator rod, a second end of the cage shaft having a plate in it. 24. The brake actuator of claim 23, wherein the plate at the second end of the caging rod has at least one passage extending through the plate. 25. The brake actuator of claim 24, wherein the at least one passage in the plate extends into a peripheral edge of the plate.