MXPA98003781A - Spring brake actuator having plast pressure plug assembly - Google Patents

Abstract

The present invention relates to a diaphragm spring-operated brake actuator, which comprises: a housing having a first end wall and at the other end a second end wall defining a push-rod opening; a movable diaphragm in the housing defining a spring chamber and a fluid pressure chamber, the diaphragm adapted to move between a retracted position and an actuating position; a push rod connected to the diaphragm and extending through the opening of the diaphragm; push rod for driving a brake in response to movement of the diaphragm between the retracted position and the driving position, a pressure plate mounted on the diaphragm, away from the push rod, and in the spring chamber, and a compression spring mounted on the housing between the first end wall and the pressure plate, the improvement comprising: that the pressure plate comprises a plastic body ico molded integralmen

Description

SPRING BRAKE ACTUATOR HAVING A PLASTIC PRESSURE PLATE ASSEMBLY BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a spring brake actuator and, more particularly, to a spring brake actuator having a plastic pressure plate assembly. Description of the Related 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 an actuator by means of an actuator assembly operated by the selective application of a fluid , such as compressed air. Conventional air brake actuators have both a service brake actuator for operating the brakes under normal driving conditions by applying compressed air, as well as a spring brake actuator which causes the brakes to be actuated when the brake is applied. released the air pressure. This is often referred to as the spring brake. The spring brake actuator can be installed by itself or in tandem with the service brake actuator. When the full pressure is applied to the spring brake actuator, the air pressure acting against a diaphragm and a pressure plate compresses the spring. A spring brake actuator rod is either integral with the pressure plate and held in a retracted position by air pressure or retracted by a return spring. In the case of a loss of air pressure or an intentional discharge of air from the spring brake actuator, the brake will be activated mechanically by the force of a strong compression spring acting on the spring brake actuator rod which, in turn, acts on a push rod attached to apply the brakes. Examples of known spring brake assemblies include U.S. Patent Nos. 5,107,727, issued to Boer on April 21, 1992; 3,439,585, granted to Herrera on April 22, 1969; and 3,842,716, issued to S ander, Jr. on October 22, 1974. A typical spring brake pressure plate assembly comprises a circular, flat plate made of steel or aluminum having a central tubular portion through which the actuator rod is connected. The pressure plate is typically heavy, made of a strong metal to withstand the intense compressive forces applied to the pressure plate while the compression spring is restricted. It would be desirable to build the pressure plate of a lightweight material to reduce the weight of the spring brake actuator, which, in turn, would reduce the total weight of the truck and even, conceivably, reduce the number of parts. Plastic parts have been used in brake auggers which involve much lower pressures than the spring brake actuators. See U.S. Patents Nos. 5,076,142, issued December 31, 1991, and 4,803,912, issued February 14, 1989. SUMMARY OF THE INVENTION The spring brake actuator according to the invention overcomes the problems of the invention. prior art incorporating a plastic pressure plate that is strong enough to withstand the applied forces of the compression spring. The plastic pressure plate provides a reduction in weight by using plastic as opposed to steel or aluminum, and reduces the number of parts in the brake by incorporating the guide function. A first embodiment of an emergency brake actuating mechanism comprises a cylindrical housing having a closed end and an open end. A brake housing adapter is received in a locked manner at the open end of the housing defining a housing interior with an opening centrally disposed in the housing adapter. An elastomeric bearing diaphragm is suspended within the housing and divides the housing into a spring chamber and a pressure chamber. A pressure plate assembly is received in the spring chamber. The pressure plate assembly is reciprocally movable, in response, in part to the introduction and discharge of pressurized fluid to the pressure chamber. The pressure plate assembly comprises a plate member having a tubular central portion and a radially extending flange. The central tubular portion of the pressure plate is adapted to receive the actuator rod in press fit relationship and the radially extending flange fits into a U-shaped annular guide, which determines the degree of freedom of movement of the pressure plate. The pressure plate has on its lower side a plurality of pins that mate with holes in the bearing diaphragm. Arranged below the diaphragm is a retainer plate, which also has mating holes for the pressure plate pins so that the diaphragm is retained between the pressure plate and the retainer plate. The retaining plate and diaphragm are fastened to the pressure plate by pins that deform ultrasonically below the underside of the retainer plate. Further, according to the invention, a method for making an air operated spring brake actuator comprises the steps of providing a housing having at one end an end wall and at another end an adapter wall defining an opening of push rod, install a movable diaphragm in the housing to define a spring chamber and a fluid pressure chamber so that the diaphragm is adapted to move between a retracted position and a driving position, mount a pressure plate To the diaphragm in the spring chamber, connect a push rod to the pressure plate so that it extends through the push rod opening to actuate a brake in response to movement of the diaphragm between the retracted position and the position of the diaphragm. drive, and install a compression spring in the housing between an end wall and the pressure plate to polarize the diaphragm to the external position loss. According to the invention, the pressure plate is integrally molded from a synthetic plastic material with a plurality of axially extending pins. Further, the step of mounting the pressure plate to the diaphragm comprises the step of placing the pins in openings in the diaphragm and inelastically deforming the pins to lock the pressure plate in the diaphragm. Preferably, the step of mounting the pressure plate to the diaphragm further comprises the step of placing a retaining plate in contact with the diaphragm on a distant side of the pressure plate and placing the pins through holes in the retaining plate and subsequently inelasticly deforming the pins to secure the diaphragm between the retaining plate and the pressure plate. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described with reference to the drawings, in which: Figure 1 is a cross-sectional view of an air operated brake actuator assembly having a plastic pressure plate according to the invention;; Figure 2 is a sectional elevation view of a first embodiment of the pressure plate according to the invention shown in Figure 1; Figure 3 is a bottom plan view of the plastic pressure plate shown in Figure 2; and Figure 4 is a cross-sectional view of an air operated dual-chamber spring brake actuator having a plastic pressure plate according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings and to Figure 1 in particular, a first embodiment of a parking brake 200 for joining an existing braking system on a vehicle (not shown) is shown to provide Emergency brake and parking service. The spring brake actuator 200 comprises a cylindrical head 202 formed of steel and having a cylindrical portion 203, an end wall 204 and an opposite open end 206. An aluminum or forged steel adapter 208 is received within the open end of the head 206. The adapter 208 has an annular outer wall 210 which bears three annular grooves 212, 214 and 216 and a portion of the head 202 is deformed in the two outer outer annular grooves 214 and 216 to permanently secure the head 202 to the adapter 208. The adapter 208 has a tubular central guide 219, which has an internal bore 270. A bearing diaphragm 218 divides the inner chamber of the brake actuator 200 into a pressure chamber 220 and a spring chamber 222. The The shape of the diaphragm 218 is generally tubular, with one end terminating in an annular eye 224. The inner annular end slot 212 receives the annular eyebrow 224 so that the diaphragm 218 is held between the adapter 208 and the head 202 in a sealing relationship. A plastic pressure plate 228 is attached to the diaphragm 218 in the spring chamber 222. A strong compression spring 226 extends between the head end wall 204 and the pressure plate 228, providing a bearing surface for the spring. 226. A hollow actuator rod 230 is press fit onto the pressure plate 228 and extends out of the pressure chamber 220 through an opening 232 in the adapter 208. The bearing 288 and the O-ring 290 are mounted in an annular groove 217 for guiding and sealing the actuator rod 230 as it passes through an opening 232 to provide an air-tight seal between the actuator rod 230 and the adapter 208. Referring to FIGS. 1-3, the plate of pressure 228 has a flat plate portion 229, a tubular central flange 234 and an inner tubular hub 246, which receives the actuator rod 230. It also has an annular rim 236, which extends axi ally towards the head end wall 204. The flange 236 terminates in an annular guide flange 238, which extends radially outwardly from the flange 236 towards the cylindrical portion 203 of the head 202. As seen in Figure 1, the return flange of pressure plate 236 is spaced radially inward from the cylindrical portion 203 of the head 202 to form a free annular space 266. The guide flange 238 has a series of transverse holes 239 for venting the free annular space 266 The flange 238 bears against the internal cylindrical portion 203 of the head 202 in reciprocal movement. The inner tubular hub 246 defines a first bore 248, which ends in a shoulder 260 and a second bore 250. The outer diameter of the inner tubular hub 246 is slightly smaller in an upper portion forming the bore 250 than in a lower portion which forms the first perforation 248. A plurality of axially extending pins 264 extend from a lower portion of the planar plate portion 229. Squares 268 are integrally formed between the annular rim and an upper portion of the flat plate portion 229 to strengthen the annular rim 236. The actuator rod 230 comprises a proximal end 244 fixed to the pressure plate 288 and a distal end 247 extending from the aperture actuator rod 232. Distant end 247 mounts an annular sleeve 273. The proximal end 244 of the actuator rod is received in the first bore of pressure plate 248. A steel sheave 258 lies against the shoulder 260. The proximal end of the Actuator rod 244 is press fit in the first hole 248, supporting against sheave 258 to keep sheave 258 safely in place. A disc-shaped retaining plate 262 and pressure plate 228 sandwich diaphragm 218 to secure diaphragm 218 to pressure plate 228. Pins 264 (FIG. 3) pass through mating holes (not shown) in the bearing diaphragm 218 and the retaining plate 262 and are ultrasonically strapped to the underside of the retainer plate 262 to lock the pressure plate 228, the bearing diaphragm 218 and the retainer plate 262 together. Alternatively, threaded fasteners can be used to join the pressure plate 228, the bearing diaphragm 218 and the retainer plate 262 together. The compression spring 226 is nested in the pressure plate 228 between the annular rim 236 and the central tubular flange 234. A collar 276 is mounted on the end wall 204 and has a threaded bore into which a cage bolt is screwed. 272. A hexagonal nut 278 is staked on the outer end of the cage bolt 272 for rotation of the bolt 272 by means of a wrench. A head 270 is formed at the inner end of the bolt 276 to engage the sheave 258 and manually retract the diaphragm 218 and the pressure plate 228 to compress the spring 226 to release braking pressure, if desired, when in the operating mode. emergency or parking. During normal operation of the brake actuator 200, the actuator rod 230 will be in the fully retracted position, as seen in Figure 1, by means of compressed air which is maintained in the pressure chamber 220. When the compressed air is discharged, the compression spring 226 expands to force the pressure plate 228 and the actuator rod integrally connected 230 down through the adapter opening 232 to drive a brake (not shown), in emergency or parking mode. The guide flange 238 and the guide 240 guide the movement of the pressure plate 228 when reciprocating inside the head 202. As the pressure plate 228 moves towards the adapter 208, the diaphragm 218 is folded on itself or rolled, As received in the free annular space 266. When the brake is released, compressed air is again introduced into the pressure chamber 220. The force of the compressed air against the bearing diaphragm 218 and the retaining plate 262 overcomes the compression force of the spring 226 and the pressure plate 228 and the actuator rod 230 return to the position observed in figure 1. Referring now to FIG. 4, a second embodiment of the plastic pressure plate is shown in FIG. the context of a conventional air-operated spring brake, with a service brake attached shown in a cross-sectional view of an air operated brake actuator unit 10. Numbers are used similar to identify similar parts. The actuator unit 10 comprises a service brake portion 12 mounted in tandem to a spring brake or emergency brake portion 14. A service brake thrust rod 18 extends from the service brake 12 for reciprocating movement and is provided with an anvil 20 which is adapted for connection to a conventional brake (not shown) in a conventional manner. The reciprocating movement of the push rod 18 by the actuator unit 10 will cause the brake to be applied and released alternately. The service brake portion 12 comprises a pair of cup-shaped housing sections 21, 22 that look, each having an outwardly facing flange edge 25, 26, respectively. The housing sections 21, 22 are gripped together at their flanged edges by a staple 27 to form an internal service brake chamber 30. The peripheral edge of an elastomeric diaphragm 32 is captured between the opposing edges., 26 of the housing 21, 22 and suspended within the internal chamber 30. The service brake pushing rod 18 extends through a central opening 34 in the housing section 21 to the service brake chamber 30 where it ends in a plate 36. A compression spring 40 extends between the plate 36 and the inner surface of the housing section 21. A spring seat 48 is disposed about the central opening 34 to receive the end of the compression spring 40 and hold it in position around the opening 34. The spring 40 urges the plate 36 and the service brake push rod 18 to a fully retracted position, as seen in figure 4. Mounting studs 46 are provided in the housing 21 for mounting the brake actuator unit 10 in an appropriate bracket (not shown). To operate the service brake, compressed air is introduced through an air service gate 38 formed in the housing section 22 to force the diaphragm 32 and the plate 36 against the compression force of the spring 40 to drive the rod. Pushing 18. Vacuum openings 44 are provided in the housing section 21 to allow rapid evacuation of air from the internal chamber 30 when pressurized air is introduced through the air service damper 38. The spring brake 14 comprises a pair of cup-shaped housing sections facing 51, 52 joined at their edges to define an internal chamber 53. The housing section 51 is provided with an outwardly facing circumferential flange edge 54, which is received within a rolled peripheral edge 56 formed in the housing section 52.

The elastomeric diaphragm 58 is suspended within the spring brake chamber 53 and is captured at its peripheral edge between the edges 54, 56 of the opposite housing sections 51, 52. The portion of the chamber 53 between the diaphragm 58 and the housing section 51 forms an air chamber which is filled with compressed air supplied through an air service gate 59 in housing section 51 when the emergency brake is in its normal, released position. An actuator rod 60, aligned with the push rod 18, has an end that extends through a central opening 64 formed in the end wall of the housing section 51. This end of the actuator rod 60 terminates in a housing plate. reaction 62, which is received in a central opening 63 of the end wall of the housing section 22 of the service brake portion 12. The central opening 64 is provided with a bearing 66 having annular recesses to accommodate a torque of O-rings 68. The bearing 66 forms a bearing surface and an air-tight seal for the actuator rod 60. The other end of the actuator rod 60 extends through a centrally disposed opening 81 in the diaphragm 58 and ends in a spring brake pressure plate 228, which connects the spring brake compression spring 72. The spring brake pressure plate 228 is made of plastic and comprises a substantial portion of the spring brake pressure plate. flat planar 229 that links one end of the spring 72 and an inner tubular hub 246 that extends generally axially along the axis of the spring 72. The inner tubular hub 246 is snapped onto an end portion of the actuator rod 60 such that the spring brake pressure plate 228 and the rod 60 form an integral unit. As in the first embodiment, the pressure plate 228 includes pins 264 located in a lower portion of the substantially planar portion 229. To attach the pressure plate to the elastomer diaphragm 58, the pins 264 pass through mating holes ( not shown) in the elastomeric diaphragm and a steel holding plate 262. The pins 264 are then ultrasonically deformed below the underside of the retaining plate 262. The purpose of the steel holding plate 262 is to add structural strength and stiffness to the plastic pressure plate and assisting the retention of the inner diaphragm seal flange 224 in the annular groove 212. Alternatively, the pressure plate 70 can be attached to the elastomeric diaphragm 58 and retaining plate 262 by means of threaded fasteners (not shown) that pass through perforations aligned in the three components. During the normal operation of the brake 10, the actuator rod 60 will be in the fully retracted position, as seen in Figure 4, by means of compressed air which is maintained in the portion of the chamber 53 defined by the diaphragm 58 and the section 51. When the compressed air is discharged, the compression spring 72, one end of which connects the outer end wall of the housing 52, forces the spring brake pressure plate 228 and the rod 60 integrally bonded in the direction of the brake push rod 18 of the service brake 12. The housing section 22 of the service brake 12 and the housing section 51 of the spring brake 14 are preferably steel ferrules connected together by means of an eyebrow welded circumferentially extending 76 or other suitable joining means or may be an integral aluminum forge. The force of the spring 72 causes the actuator rod 60 to be extended through the central opening 64 and causes the reaction plate 62 to apply a force to the diaphragm 32 and the plate 36 of the service brake. This action causes the service brake thrust rod 18 to be actuated and the brake applied. When the brake is going to be released, compressed air is once again introduced into the space between the housing section 51 and the diaphragm 58. The force of the compressed air against the diaphragm 58 exceeds the compression force of the spring 72 and returns the pressure plate 228 and the rod 60. to the position observed in Figure 1. The actuator rod 60 is a hollow tube or rod provided with a central bore 61 for accommodating a brake release or caging bolt 78. The bolt 78 is adapted to attach an end edge 80. of the tubular portion 74 of the spring brake pressure plate 70 to maintain the spring 72 in a compressed position whenever desired.The pin 78 can be used to manually release the spring brake or to ensure that the spring Compression 72 will remain fully compressed when maintenance functions are carried out on the brake assembly .. Bolt 78 is threaded and links a fixed, threaded opening on a nut 77 fixed by welding or staking to the end wall of the housing section 52. A second nut or head 79 is fixedly attached to the threaded bolt such that the bolt can be rotated in the nut 77 by a common wrench or similar. The plastic pressure plate 228 according to the invention provides a sufficiently strong assembly between the elastomeric diaphragm 58 and the retaining plate 262 while providing a reduction in the overall weight of the spring brake actuator. The plastic pressure plate assembly according to the invention provides significant advantages over conventional plate assemblies. Any reduction of weight in an individual component of a truck is desirable. The spring brake actuator according to the invention provides such weight savings including a pressure plate made of light weight plastic, reinforced with a steel holding plate instead of a steel or aluminum pressure plate only. The steel retaining plate provides sufficient structural rigidity to prevent deformation of the plastic pressure plate. In addition, the plastic pressure plate can be manufactured inexpensively by injection molding. Replaces six parts in a previous design of a bearing lobe brake actuator. Reasonable variations and modifications are possible within the spirit of the foregoing description and the drawings, without departing from the scope of the invention.

Claims (19)

1. CLAIMS 1. In an air operated diaphragm spring brake actuator, comprising: a housing having a first end wall and at the other end a second end wall defining a push rod opening; a movable diaphragm in the housing defining a spring chamber and a fluid pressure chamber, the diaphragm adapted to move between a retracted position and a driving position; a push rod connected to the diaphragm and extending through the push rod opening to drive a brake in response to movement of the diaphragm between the retracted position and the driving position; a pressure plate mounted on the diaphragm, distant from the push rod, and in the spring chamber; and a compression spring mounted in the housing between the first end wall and the pressure plate; the improvement comprising: that the pressure plate comprises an integrally molded plastic body.
2. 2. An air operated diaphragm spring brake actuator according to claim 1, wherein the plastic pressure plate has a flat plate portion with one side in contact with the diaphragm and an opposite side in contact with the diaphragm. to the compression spring; a flange extending towards the spring chamber from the flat plate portion; a central tubular flange extending towards the spring chamber from the flat plate portion; and the compression spring being housed between the central tubular flange and the flange at least when the diaphragm is in the retracted position.
3. 3. An air operated diaphragm spring brake actuator according to claim 2, wherein the pressure plate further has an internal tubular hub that telescopically receives one end of the push rod.
4. 4. An air operated diaphragm spring brake actuator according to claim 2, wherein the plastic pressure plate further has a plurality of strengthening squares between the flange and the flat plate portion.
5. 5. An air operated diaphragm spring brake actuator according to claim 2, and further comprising a guide flange at an outer end of the plastic pressure plate, contacting an inner surface of the at least when the diaphragm is in the retracted position to guide the movement of the pressure plate with respect to the housing.
6. 6. An air operated diaphragm spring brake actuator according to claim 5, wherein the inner surface of the housing has a cylindrical wall portion and the guide flange is annular and is in contact with the cylindrical inner surface. of the housing when reciprocating the pressure plate inside the housing.
7. 7. An air operated diaphragm spring brake actuator according to claim 1, wherein the pressure plate has a plurality of pins extending from the flat plate portion through the diaphragm and are inelastically formed for Hold the pressure plate in the diaphragm.
8. 8. An air operated diaphragm spring brake actuator according to claim 7, and further comprising a retainer plate in contact with the diaphragm on a distant side of the pressure plate and the pins extending through of the retainer plate to secure the retention plate to the diaphragm.
9. 9. An air operated diaphragm spring brake actuator according to claim 8, wherein the plastic retainer plate further has a plurality of strengthening brackets between the cylindrical flange and the flat plate portion.
10. A method of making an air operated diaphragm spring brake actuator, comprising the steps of: providing a housing having at one end an end wall and at the other end an adapter wall defining a rod opening push; installing a movable diaphragm in the housing to define a spring chamber and a fluid pressure chamber so that the diaphragm is adapted to move between a retracted position and a driving position; mount a pressure plate to the diaphragm in the spring chamber; connecting a push rod to the pressure plate so as to extend through the push rod opening to drive a brake in response to movement of the diaphragm between the retracted position and the driving position; installing a compression spring in the housing between the end wall and the pressure plate to bias the diaphragm to the extended position; the improvement comprising: integrally molding the pressure plate of a synthetic plastic material with a plurality of axially extending pins; and the step of mounting a pressure plate to the diaphragm comprises the step of placing the pins in apertures in the diaphragm and inelastically deforming the pins to lock the pressure plate to the diaphragm.
11. A method according to claim 10, wherein the step of mounting a pressure plate to the diaphragm further comprises the step of placing a retaining plate in contact with the diaphragm on a distant side of the pressure plate and placing the pins through holes in the retaining plate and subsequently inelasticly deforming the pins to secure the diaphragm between the retaining plate and the pressure plate.
12. 12. An air operated spring brake actuator, comprising: a generally cylindrical housing having at one end a first end wall and at another end a second end wall, the second end wall having a rod opening of push, a plastic pressure unit plate, mounted within the housing for reciprocal movement between a retracted position and a driving position, a push rod operatively connected to the pressure plate and extending through the shaft opening of the pressure plate. thrust to drive the pressure plate towards the driving position, a bearing lobe diaphragm mounted between the pressure plate and the housing, and a compression spring between the first end wall and the pressure plate.
13. 13. An air operated spring brake actuator according to claim 12, wherein the pressure plate has a cup shape with a lip portion.
14. 14. An air operated spring brake actuator according to claim 13, wherein the lip portion has a guide flange in contact with an inner surface of the housing.
15. 15. An air operated spring brake actuator according to claim 12, wherein the pressure plate has an inner hub and an outer wall, and the spring is retained between the inner hub and the outer wall.
16. 16. An air operated spring brake actuator according to claim 15, wherein the push rod is secured to the hub.
17. 17. An air operated spring brake actuator according to claim 12, wherein the diaphragm is mounted on the pressure plate by pins.
18. 18. An air operated spring brake actuator according to claim 17, wherein the pins are inelasticly deformed to secure the diaphragm to the pressure plate.
19. 19. An air operated spring brake actuator according to claim 16, wherein the diaphragm is gripped between the push rod and the hub.