WO2000030913A1

WO2000030913A1 - Two-piece pressure plate and method of fabrication

Info

Publication number: WO2000030913A1
Application number: PCT/US1999/026394
Authority: WO
Inventors: Francisco Alvarez
Original assignee: Holland Neway International, Inc.
Priority date: 1998-11-24
Filing date: 1999-11-09
Publication date: 2000-06-02

Abstract

The invention relates to an improved, two-piece pressure plate assembly for a spring brake actuator. The two-piece pressure plate assembly includes a plate (68) and a separate connector (102) secured to the plate (68). The plate is, in the preferred embodiment, a stamped steel disk with a central opening (120) surrounded by an upturned collar (124). The connector (102), in the preferred embodiment, includes a generally cylindrical body (106) with a longitudinal shaft having a keyed opening and internal lands for receiving a caging bolt in a bayonet-style engagement. The exterior of the connector has some structure to aid in securing the connector to the plate, a portion of which will bear against one side of the plate (68) when the connector (102) is inserted in the central opening (120) of the plate (68). The connector (102) can be further secured to the plate (68) by being press fit into the opening (120), staked to the plate, or by embossments in the collar engaging the structure on the exterior of the connector (102).

Description

TWO-PIECE PRESSURE PLATE AND METHOD OF FABRICATION BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to a spring brake actuator. More specifically, the invention relates to a spring brake actuator having a two-piece pressure plate for the spring chamber, and a method for fabricating the pressure plate.

State of the Prior 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 operated by the selective application of a fluid such as compressed air. Conventional air brake actuators have both a service brake actuator for actuating the brakes under normal driving conditions by the application of compressed air and an emergency or spring brake actuator that causes actuation of the brakes when air pressure has been released. The emergency brake actuator includes a strong compression spring that forces application of the brake when air is released. This is often referred to as the spring brake. Typically, the spring brake actuator is disposed in tandem with the service brake actuator.

When full pressure is applied to the spring brake actuator, air pressure acting against a diaphragm and a pressure plate compresses the spring. In many applications, a spring brake actuator rod is held in a retracted position by a relatively small return spring. The spring brake actuator rod thus does not affect the normal operation of the brake. Depressing the brake pedal during normal driving operation introduces compressed air into the service brake actuator which, acting against a diaphragm, causes a service brake push rod to be extended and the brakes to be applied with an application force proportional to the air pressure in the service brake actuator. In the event of a loss of air pressure or an intentional exhaustion of air from the spring brake actuator, the brake will be mechanically activated by the force of the strong compression spring adting on the spring brake adapter push rod which, in turn, acts upon the service brake push rod to apply the brakes. Thus, the spring brake portion serves as both a parking brake and an emergency brake.

A spring brake actuator may include both a spring brake portion and a service brake portion. The service brake portion includes an air chamber partially defined by a flexible diaphragm acting against a service brake push rod and a return spring to assure proper release of the brake when air is exhausted from the air chamber. The spring brake portion also includes an air chamber comprising a spring brake housing and a spring brake adapter push rod abutting a spring brake pressure plate with the spring brake diaphragm therebetween. A strong power spring acts between an end of the spring brake housing and the pressure plate, and tends to urge the adapter push rod out of the air chamber to engage the diaphragm and push rod of the service brake and to cause the brake to be applied. During normal operation, the spring force is counteracted by air pressure inside of the spring brake air chamber, which acts against the diaphragm to compress the power spring, retracting the adapter push rod. When system air pressure is lost, or manually released, the power spring extends to apply the brakes.

Pressure plates are typically die cast from a lightweight material such as aluminum. Die casting the pressure plate, however, is relatively expensive due to its size and shape.

SUMMARY OF THE INVENTION A more cost-effective brake actuating assembly is obtained by the present invention of a two-piece pressure plate assembly comprising a plate mounted to a separate connector. According to the invention, the plate has a central opening and the connector is mounted within the opening and secured to the plate. In one embodiment, the connector is press fit into the central opening in the plate and secured thereto by protrusions formed in the plate and received within channels formed in the connector, the connector further forming a flush face with one side of the plate. A diaphragm is secured between the pressure plate assembly and a push rod adapter. The connector is provided with a centrally disposed bore through a tubular housing, which includes a keyed aperture for receiving a caging bolt and lands defining a bayonet fitting for selectively locking the caging bolt therein. Advantageously, the connector is die cast to specific tolerances and the plate can be stamped, pressed, or otherwise formed to lesser tolerances, thereby eliminating the cost of die casting or otherwise forming the entire pressure plate assembly to within specific tolerances. Accordingly, the fit of the parts of the brake actuating assembly is improved and the cost of producing the parts is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a cross-sectional view of an air-operated brake actuating assembly having a spring brake actuator arrangement in accordance with the principles of this invention;

FIG. 2 is an enlarged fragmentary cross-sectional view of the spring brake actuator arrangement of FIG. 1 ;

FIG. 3 is a cross-sectional view of the two-piece pressure plate assembly of the spring brake actuator arrangement of FIGS. 1 and 2;

FIG. 4 is an exploded perspective view of the two-piece pressure plate assembly of the spring brake actuator arrangement of FIGS. 1 through 3; FIG. 5 is a perspective view of the assembled two-piece pressure plate assembly according to the invention; and

FIG. 6 is a reverse perspective view of the two-piece pressure plate assembly according to the invention.

DETAILED DESCRIPTION

Referring now to the FIG. 1 , there is shown an air-operated diaphragm spring brake of the type disclosed in U.S. Pat. No. 3,926,094 and commonly referred to an air-operated spring brake. The brake is typically attached to a mounting bracket 10 on a vehicle and is adapted to operate a braking system through a push rod 36 that extends through the bracket 10 of the vehicle. The air-operated spring brake comprises a service chamber 12 and a spring chamber 14 joined together in tandem. The service chamber 12 comprises a cup-shaped service housing 16 and a doublc-cup-shaped service/spring housing 18 (sometimes called an aperture or flange case) joined together through a clamp 20 and forming a hollow interior chamber. Openings 22 are provided in the service housing 16 for bolts 24 which bolt the service housing 16 to the wall 10. A central opening 26 and side openings 27 are also provided in the service housing 16.

The service/spring housing 18 forms a divider wall 28 and has a central opening 30 with an O-ring 31 positioned therein. An indentation or annular depression 32 is formed around the opening 30. A pressure opening 34 is provided in the housing 18 for providing communication between a source of pressure (not shown) and the interior of the service chamber 12.

A service brake push rod 36 is mounted in the service chamber 12 for reciprocation within the opening 26 and mounts a pressure plate 38 at an inner end thereof. A compression spring 40 extends between a central portion of the service housing 16 and the pressure plate 38 to bias the pressure plate 38 and thus the service brake push rod 36 toward the divider wall 28. A first elastomeric diaphragm 42 (also known as the service brake diaphragm) is mounted within the service chamber 12 and is clamped between the service housing 16 and the service/spring housing 18. The spring-biased pressure plate 38 forces the diaphragm 42 against the divider wall 28 of the service/spring housing 18 as shown in figure 1.

When pressurized air is supplied to the pressure opening 34 as, for example, when the brakes are applied by a vehicle operator, air pressure is increased between the diaphragm 42 and the divider wall 28, thereby forcing the diaphragm 42 toward the central portion of the service housing 16 and against the bias of the spring 40. In this manner, the push rod 36 is extended outwardly from the service housing 16 to apply braking pressure to the vehicle brakes in a conventional fashion.

The spring chamber 14 comprises a side of the service-spring housing 18 and a spring housing 46, which is clamped to the service/spring housing 18 at a joint 50. An opening 44 is provided within the service/spring housing 18 to connect the interior of the spring chamber 14 with a source of pressure (not shown). A second elastomeric diaphragm 48 (known as the spring diaphragm) is clamped between the service/spring housing 18 and the spring housing 46. An adapter push rod 52 is mounted within the spring chamber 14 and has a reaction plate 54 securely fixed to one end and an actuator plate 56 secured to the other end thereof. The adapter push rod 52 extends through the opening 30 and in sealing engagement with the O-ring 31. The actuator plate 56 seats within the annular depression 32 of the divider wall 28. A compression 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 and the reaction plate 54 against the diaphragm 48, as illustrated in the figure.

Referring now to FIG. 2, the interior of the spring housing 46 has in a central portion thereof an annular ridge 60 surrounding a central opening 62 in a circular recess 63. A compression spring 70 is aligned over the annular ridge 60 and is positioned between the spring housing 46 and a pressure plate assembly 100 to bias the pressure plate assembly 100 toward the divider wall 28.

Referring now also to FIGS. 3 through 6, a plate 68 and a connector 102 comprise the pressure plate assembly 100. The plate 68 has a central opening 120 into which the connector 102 is mounted. The connector 102 includes a bore 104 formed through a tubular housing 106, which includes a flanged end 108. The tubular housing 106 includes lands 92 extending radially into the bore 104 and a keyed entry 91 for receiving a release tool 72, as will be described below. As is best shown in FIG. 4, the flanged end 108 includes a series of flanges 1 10 each having an upper shoulder 1 1 1 and being separated by channels 1 12 extending generally axially in the tubular housing 106, partially along an outer face thereof, from the flanged end 108. The channels 1 12 include open proximal ends 1 14 disposed between adjacent flanges 1 10 and closed distal ends 1 16 disposed intermediately in the exterior of the tubular housing 106.

The plate 68 comprises a substantially flat face 122 engaging one end of the spring 70 and a collar 124 upstanding from the flat face 122 and about the periphery of opening 120. Upon assembly, the collar 124 includes multiple equidistantly spaced protrusions 126 extending radially inwardly of the opening 120. As shown pre-assembly in FIG. 4, the collar 124 does not yet include the protrusions 126, which are formed after the connector 102 is press-fit into the opening 120 in the plate 68. On an opposite face 128 of the plate 68 is formed an annular depression 130, which accommodates the flanged end 108 after the connector 102 is assembled with the plate 68.

To assemble, the plate 68 is secured to the connector 102. Specifically, the connector 102 is received in the opening 120 formed centrally through plate 68. The connector 102 extends generally axially through the opening 120 and is aligned with its central axis such that its flanged end 108 is substantially flush with the face 128 and the shoulders 1 1 1 abut the depression 130 formed in face 128 about the periphery of the opening 120. The protrusions 126 are formed in the collar 124 and extend into the channels 1 12 formed in the connector 102 and abut the closed distal ends 1 16 thereof to prevent dislocation of the connector 102 relative the plate 68 after assembly. The protrusions 126 are formed typically by a punching operation that deforms the material of the collar 124 at discrete points. With the protrusions 126 abutting the distal ends 1 16 of the channels 1 12, the connector 102 is blocked against removal from the opening 120 in the plate 68.

The plate 68 is preferably formed of pressed or stamped steel, whereby the part can be inexpensively made, while the connector 102 is preferably die cast, of a material such as aluminum.

During normal operation of the spring brake, a constant pressure is applied to the spring chamber 14 through the opening, thereby holding the spring 70 in the retracted position of FIG. 1 by the force of diaphragm 48 against the plate 68 and thus against the spring 70. When fully retracted, the spring 70 applies a force of approximately 3,000 pounds against the pressure plate assembly 100. When pressure is released from the chamber 14, the spring 70 extends and presses the adapter push rod 52 into the service chamber 12.

The release tool 72 is provided in association with the pressure plate assembly 100 for mechanically retracting the spring 70 and thus enabling the spring 58 to urge the reaction plate 54 into the position illustrated in the FIG. 1 in the event of air pressure failure within the spring chamber 14. Specifically, the release tool 72 comprises a caging bolt 74 having a nut 76 threaded thereon which bears against the outer surface of the spring housing 46 so that the spring 70 can be manually compressed and the adapter push rod 52 retracted.

The caging bolt 74, which includes opposing projections 80 on an interior end thereof, extends through the central opening 62 of the housing 46 and into the bore 104 of the connector 102. The tubular housing 106 of the connector 102 has a keyed entry aperture 91 for receiving the caging bolt 74 with its projections 80. After the caging bolt 74 is fully received through the keyed entry aperture 91 of the connector 102, the caging bolt 74 is rotated 90° so that the projections 80 engage the lands 92 in a bayonet-type fitting. More specifically, the projections 80 on the end of the caging bolt 74 are selectively engageable with the lands 92 of the tubular housing 106 of the connector 102 upon rotation of the threaded bolt 74 through opening 91 , so that the threaded bolt 74 can engage and draw the pressure plate assembly 100 toward the housing 46. The nut 76 is threaded onto the caging bolt 74 and torque is applied to a predetermined level to fully withdraw or "cage" the spring 70. The position of the caging bolt 74 with respect to the spring housing 46 is controlled by the relative position of the nut 76 and the bolt 74 as the nut 76 bears against the housing 46.

In operation, air pressure is continually supplied to the spring chamber 14 through the opening 44 to maintain the diaphragm 48 essentially in the position illustrated in FIG. 1. In this position, the brake push rod 36 normally will be operated as described above by selective pressurization of the service chamber by introduction of air through the opening 34. However, in the event of failure of the air pressure system, the pressure in the spring chamber will be decreased so that the springs 40 and 58 would no longer be able to overcome the force of the much larger and stronger compression spring 70. Thus, the plate 68 forces the diaphragm 48, and thus the adapter push rod 52, toward the dividing wall 28, thereby also forcing the brake push rod 36 outwardly to apply the braking pressure to the brakes. Typically, diaphragm 48 is axially separable from plate 68, but is kept in contact therewith by air pressure and by the reaction plate 54.

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

Claims

CLAIMSWhat is claimed is:

1. In a spring brake actuator comprising a housing ( 14) having first and second end walls (46, 28) defining a housing interior with an opening (30) disposed in the second end wall (28), an elastomeric diaphragm (48) suspended within the housing (14) and dividing the housing into a first and second chamber, the diaphragm (48) being disposed to cooperatively move a push rod (52) extending through the opening (30), a pressure plate assembly (100) disposed in the first chamber adjacent to the diaphragm (48) and a spring (70) positioned between the pressure plate assembly (100) and the first end wall (46), the improvement in the pressure plate assembly (100) characterized by:

a plate (68) having a central opening (120);

and a connector (102) mounted within the opening (120) and secured to the plate (68).

2. In the spring brake actuator of claim 1 , the improvement further characterized by a collar (124) around the opening (120) in the plate (68).

3. In the spring brake actuator of claim 2, the improvement further characterized by the connector (102) being press fit in the collar (124).

4. In the spring brake actuator of any one of claims 2 or 3, the improvement further characterized by protrusions (126) projecting inwardly of the collar (124).

5. In the spring brake actuator of any one of claims 2-4, the improvement further characterized by an end (108) of the connector (102) forming a flush face with the plate (68).

6. In the spring brake actuator of any one of claims 2-5, the improvement further characterized by the plate (68) being constructed of a stamped metal.

7. In the spring brake actuator of any one of claims 2-6, the improvement wherein the plate (68) is formed of steel.

8. In the spring brake actuator of any one of claims 2-7, the improvement further characterized by the collar (124) being recessed from a face (128) of the plate (68).

9. In the spring brake actuator of claim 1 , the improvement further characterized by the connector ( 102) having internal lands (92) for receiving projections (80) at an end of a caging bolt (74).

10. In the spring brake actuator of any one of claims 1 or 9, the improvement further characterized by axial grooves (1 12) on an external surface of the connector (102).

1 1. In the spring brake actuator of any one of claims 1 , 9 or 10, the improvement further characterized by the connector ( 102) being cast.

12. In the spring brake actuator of any one of claims 1 or 9- 1 1 , the improvement further characterized by the connector (102) having a keyed bore (91).

13. In the spring brake actuator of claim 1 , the improvement further characterized by the plate (68) being disc-shaped.

14. In the spring brake actuator of claim 1 , the improvement further characterized by the connector (102) having projections (1 1 1) that serve as stops when the connector (102) is received in the opening (120) of the plate (68).

15. In the spring brake actuator of claim 1 , the improvement further characterized by the connector being press fit into the opening (120).

16. In the spring brake actuator of claim 1 , the improvement further characterized by the connector (102) being staked in the opening (120).

17. A pressure plate assembly for use in an air operated diaphragm spring brake actuator comprising a plate (68) having a central opening (120) and a connector (102) mounted within the opening (120) and secured to the plate (68).

18. The pressure plate assembly of claim 18, further characterized by a collar (124) around the opening (120) in the plate (68).

19. The pressure plate assembly of claim 18, further characterized by the connector (102) being press fit in the collar (124).

20. The pressure plate assembly of any one of claims 18 or 19, further characterized by protrusions (126) projecting inwardly of the collar (124).

21. The pressure plate assembly of any one of claims 18-20, further characterized by an end (108) of the connector (102) forming a flush face with the plate (68).

22. The pressure plate assembly of any one of claims 18-21 , further characterized by the plate (68) being constructed of a stamped metal.

23. In the spring brake actuator of any one of claims 18-22, the improvement wherein the plate (68) is formed of steel.

24. The pressure plate assembly of any one of claims 18-23, further characterized by the collar (124) being recessed from a face (128) of the plate (68).

25. The pressure plate assembly of claim 17, further characterized by the connector (102) having internal lands (92) for receiving projections (80) at an end of a caging bolt (74).

26. The pressure plate assembly of any one of claims 17 or 25, further characterized by axial grooves (1 12) on an external surface of the connector (102).

27. The pressure plate assembly of any one of claims 17, 25 or 26, further characterized by the connector (102) being cast.

28. The pressure plate assembly of any one of claims 25-27, further characterized by the connector (102) having a keyed bore (91).

29. The pressure plate assembly of claim 17, further characterized by the plate (68) being disc-shaped.

30. The pressure plate assembly of claim 17, further characterized by the connector (102) having projections (1 1 1) that serve as stops when the i connector (102) is received in the opening (120) of the plate (68).

31. The pressure plate assembly of claim 17, further characterized by the connector being press fit into the opening (120).

32. The pressure plate assembly of claim 17, further characterized by the connector (102) being staked in the opening (120).

33. A method of making a pressure plate assembly ( 100) for an air operated diaphragm spring brake actuator characterized by stamping a plate (68) with an aperture ( 120) and a collar (124) about the aperture (120), casting a connector (102) with a bore (104), inserting the connector (102) into the aperture (120) so that one end (108) of the connector (102) is flush with a flat surface (128) of the plate (68), and securing the connector (102) to the plate (68).

34. The method of claim 34, further characterized by the securing being accomplished by staking.

35. The method of claim 34, further characterized by the securing being accomplished by press fitting.

36. The method of claim 34, further characterized by the securing being accomplished by embossment of protrusions (126) into grooves (112) cast into an exterior surface of the connector (102).