WO1994021892A1

WO1994021892A1 - Sealed bearing for fluid-operated brake actuator

Info

Publication number: WO1994021892A1
Application number: PCT/US1993/009217
Authority: WO
Inventors: J. Hicks William; C. Pierce William
Original assignee: Nai Anchorlok Inc
Current assignee: Nai Anchorlok Inc
Priority date: 1993-03-25
Filing date: 1993-09-28
Publication date: 1994-09-29
Anticipated expiration: 1995-09-25
Also published as: AU6516794A; WO1994021501A1; AU5349194A

Abstract

An air-operated diaphragm spring brake (10) has a brake actuator (14) in tandem with a spring brake actuator (16), wherein the brake actuator (14) and spring brake actuator (16 ) are separated by a dividing wall (35) in which is formed an annular opening (37). A spring brake actuator rod (56) reciprocates from within the spring brake actuator (16) through the central aperture (37) into the brake actuator (14) where it contacts and actuates a service brake push rod (12) to apply the emergency or parking brakes of a vehicle. The spring brake actuator rod (56) is actuated when the emergency brake or parking brake is applied by exhausting air from the brake actuator. A sealed bearing (38) is located within the central aperture (37) of the divider wall (35) and fluidly seals the spring brake chamber (51) from the service brake chamber (23). The sealed bearing further comprises a polymer ring (80) and an elastomeric sealing member (96). The ring (80) has an annular channel which receives the elastomeric sealing member (96).

Description

SEALED BEARING FOR FLUID-OPERATED BRAKE ACTUATOR

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to fluid-operated brake actuators for vehicles and more particularly to service and spring brake actuators combined in tandem and having a spring brake actuator rod.

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 which is actuated 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 actuating the brakes under normal driving conditions by the application of compressed air and an emergency or spring brake actuator which causes actuation of the brakes when air pressure has been released. The emergency brake actuator includes a strong compression spring which 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. In newer applications, the spring brake actuator rod is integral with the pressure plate and held in a retracted position by the air pressure. In both designs, 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 acting on the spring brake actuator rod which, in turn, acts upon the service brake push rod to apply the brakes. Thus, the spring brake portion serves both as a parking brake and an emergency brake.

In tandem actuator assemblies, the spring brake push rod typically extends from a chamber in the spring brake portion, through an aperture in a wall separating the spring brake actuator from the service brake actuator, and into a chamber in the service brake portion. Because at least one of the adjoining chambers is usually pressurized, a seal is provided at the aperture around the push rod comprising one or more O-rings positioned in annular channels in the wall around the aperture. The wall is typically a cast aluminum part in which the channels are machined. On the other hand, the spring brake actuator rod is typically formed of chromed steel. It sometimes occurs that, as the spring brake actuator rod reciprocates through the aperture, the dissimilar metals of the wall and the push rod will abrade, thereby creating discontinuities in the actuator rod surface as well as loose metal chips. These chips and discontinuities accelerate wear on the O-rings and significantly diminish their durability.

SUMMARY OF THE INVENTION

In accordance with the invention, a fluid-operated brake actuator comprises two internal tandem chambers separated by a wall which has an opening between the two chambers. An actuating rod extends through the opemng and is adapted to reciprocate through the opemng for alternately actuating and releasing a brake. A sealing means seals the chambers from each other. The sealing means comprises a body securely fixed within the opening and having a self-lubricating inner surface. The body at least partially defines an annular channel within the opening. An elastomeric sealing member is disposed within the annular channel so that the actuating rod bears against the inner surface and the elastomeric sealing member as it reciprocates through the opening. Preferably, the body is a ring. In one aspect of the invention, the ring has an outer surface in which there is an annular channel. A second elastomeric sealing member is disposed within the channel in the outer surface of the ring and bears against the wall to form a second seal between the two chambers.

In another aspect of the invention, the wall comprises one or more tabs to secure the body within the opening. The wall can also have an annular shoulder extending into the opening with the ring securely clamped between the shoulder and the tabs. Preferably, the tabs are deformable.

In another aspect of the invention, the body comprises first and second rings. Preferably, the first and second rings are shaped to form the inner channel when they abut each other axially. The first ring has an elongated depending flange and the second ring has an axial channel into which the depending channel fits. An outer channel can be similarly formed when the first and second rings are coupled. A second elastomeric ring is disposed within the outer channel to form a second fluid seal between the two chambers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an air-operated brake actuator having a sealed bearing according to the invention;

FIG. 2 is an enlarged fragmentary cross sectional view taken from area A in FIG. 1 showing the sealed bearing of FIG. 1; FIG. 3 is an enlarged fragmentary cross sectional view similar to

FIG. 2 showing a second embodiment of a sealed bearing according to the invention; and

FIG. 4 is an enlarged fragmentary cross sectional view similar to FIG. 2 showing a third embodiment of a sealed bearing according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a fluid-operated brake actuator 10 having a general configuration well known in the art. The fluid-operated brake actuator 10 comprises a brake actuator 14 mounted in tandem to a spring chamber or emergency brake actuator 16. A service brake push rod 12 extends from the brake actuator 14 for reciprocating movement between a retracted position and an extended actuating position relative to the brake actuator 14, and is provided with a clevis 17 which is adapted to connect to a conventional brake shoe and drum (not shown in the drawing) in a standard fashion. Reciprocating motion of the service brake push rod 12 will cause the brake to be alternately applied and released. The brake actuator 14 comprises a cup-shaped service housing section 18 and a double cup-shaped adapter housing 20 joined together by a clamp 22 to form a service brake chamber 23. The adapter housing 20 is also sometimes known as a flange case.

A first elastomeric diaphragm 24 (also known as the service brake diaphragm) is suspended within the service brake chamber 23, the peripheral edge thereof secured in fluid tight engagement between the cup- shaped service housing section 18 and the service side of the adapter housing 20 by the clamp 22. The first elastomeric diaphragm 24 thus separates the service brake chamber 23 into two portions: a first service chamber portion 26 and a second service chamber portion 28. The first service chamber portion 26 communicates with a source of pressurized air (not shown) through an air service port 42 in the adapter housing 20. The second service chamber portion 28 is vented to the atmosphere through at least one opemng 32 in the cup-shaped service housing section 18. In FIG. 1, the first service chamber portion 26 is shown evacuated so that the first elastomeric diaphragm 24 is forced against the adapter housing 20 because of the force from compression spring 46.

The service brake push rod 12 extends through a central opening 30 in the cup-shaped service housing section 18 and has a pressure plate 44 at the end thereof within the second service chamber portion 28. The pressure plate 44 bears against the first elastomeric diaphragm 24. A compression spring 46 extends between the pressure plate 44 and the interior surface of the cup-shaped service housing section 18. A push rod guide 34 having an annular seat 40 is disposed within the central opening 30 to guide reciprocal movement of the service brake push rod 12 within the central opening 30 and also to receive the end of the compression spring 46 and retain it in position around the central opening 30. The compression spring 46 thus urges the pressure plate 44 and the service brake push rod 12 to a fully retracted position as depicted in FIG. 1. To operate the service brake, compressed air is introduced through the air service port 42 into the first service chamber portion 26 to force the first elastomeric diaphragm 24 and pressure plate 44 against the force of the compression spring 46, thereby extending the service brake push rod 12 toward the actuating position. The openings 32 permit rapid evacuation of air from the second service chamber portion 28 as the service brake is actuated. Mounting studs 47 are provided to mount the fluid- operated brake actuator 10 onto a vehicle.

The spring chamber or emergency brake actuator 16 is defined by the spring side of the adapter housing 20 and a generally cylindrical head 48 or spring housing, which is clamped to the spring side of the adapter housing 20 by a clamp 50 to form the spring brake chamber 51. A second elastomeric diaphragm 52, known as the spring diaphragm, is suspended within the spring brake chamber 51, the peripheral edge thereof secured in fluid tight engagement between the cylindrical head 48 and the spring side of the adapter housing 20 by the clamp 50. The second elastomeric diaphragm 52 thus separates the spring brake chamber 51 into two portions: a first spring chamber portion 62 and a second spring chamber portion 63. The second spring chamber portion 63 is filled with pressurized air supplied through an air service port 54 in the adapter housing 20 when the emergency brake is in its normal released position as depicted in FIG. 1.

The adapter housing 20 includes a divider wall 35 which separates the adjoining service brake chamber 23 and spring brake chamber 51. A spring brake actuator rod 56, aligned with the service brake push rod 12, has one end extending from the spring brake chamber 51 through a central opening 37 in divider wall 35 for reciprocating motion through the central opening 37 between a retracted position and an actuating position. A sealed bearing 38 is provided in the central opening 37 through which the spring brake actuator rod 56 reciprocates. The sealed bearing 38 will be described in greater detail below.

The one end of the spring brake actuator rod 56 terminates in a reaction plate 66 in the first service chamber portion 26. The reaction plate 66 is received in an annular seat 41 when the spring brake actuator rod 56 is in the retracted position as depicted in FIG. 1. The other end of the spring brake actuator rod 56 terminates in a push plate 58. The push plate 58 bears against the second elastomeric diaphragm 52 and a return spring 61 is disposed in the second spring chamber portion 63 between the push plate 58 and the divider wall 35 to bias the push plate 58 against the second elastomeric diaphragm 52. A pressure plate 59 bears against the other side of the second elastomeric diaphragm 52 and a large force compression spring or power spring 60 is disposed in the first spring chamber portion 62 between the pressure plate 59 and the cylindrical head 48.

During normal operation of the fluid-operated brake actuator 10, the spring brake actuator rod 56 will be in the fully retracted position, as depicted in FIG. 1, by means of compressed air which is maintained in the second spring chamber portion 63. When the compressed air is exhausted, the compression spring 60, one end of which engages the outer end wall of the cylindrical head 48, forces the push plate 58 and spring brake actuator rod 56 in the direction of the service brake push rod 12. The force of the compression spring 60 causes the spring brake actuator rod 56 to be extended through the central opening 37, thereby causing the reaction plate 66 to apply a force to the first elastomeric diaphragm 24 and pressure plate 44 of the brake actuator 14. This action causes the service brake push rod 12 to be extended toward the actuating position, thereby applying the brake. When the brake is to be released, compressed air is once again introduced into the second spring chamber portion 63 to a pressure that exerts a force greater than the force of the compression spring 60. The force of the compressed air against the second elastomeric diaphragm 52 causes the pressure plate 59, to be returned to the position depicted in FIG. 1. The force of the return spring 61 causes the spring brake actuator rod 56 to also be retracted.

The pressure plate 59 is adapted to receive a threaded caging bolt 70, which passes through an opening 72 in the cylindrical head 48. A hex head nut 78 is threadably received on the threaded caging bolt 70. To manually release the spring brake or otherwise cage the compression spring 60 in the compressed position shown in FIG. 1, the hex head nut 78 is rotated to bear against the cylindrical head 48, thereby drawing the threaded caging bolt 70 outwardly and the pressure plate 59 toward the cylindrical head 48. When the threaded caging bolt 70 is not installed, a plug 74 is provided to plug the opening 72.

Looking now more closely at FIG. 2, the sealed bearing 38 is mounted within the central opening 37 of the adapter housing 20 and is in sealing engagement between the adapter housing 20 and the spring brake actuator rod 56. The seal is necessary because pressurization of the first service chamber portion 26 or the adjoining second spring chamber portion 63 must be independent of each other for proper functioning of the fluid- operated brake actuator 10. The sealed bearing 38 comprises a non-metallic body 80 made from a synthetic polymer such as nylon. The non-metallic body 80 thus has a softer, self-lubricating inner surface 82 against which the spring brake actuator rod 56 bears as it reciprocates. This structure significantly reduces the potential for abrasions characteristic of the prior art metal-to- metal contact between the actuator rod and the adapter housing. In the embodiment of FIG. 2, the non-metallic body 80 comprises a first ring 84, T-shaped in cross section, and a second ring 86, U- shaped in cross section. An elongated flange 88 forming the cross-sectional "T" of the first ring 84 is received in a shallower axial channel 90 of the second ring 86, thereby forming an inner annular channel 92 and outer annular channel 94. An inner O-ring 96 is disposed within the inner annular channel 92 and an outer O-ring 98 is disposed within the outer annular channel 94. It will be understood that ring seals having different cross sections are functional equivalents of conventional O-rings, such as ring seals having elliptical or star shaped cross sections. The sealed bearing 38 is securely fixed within the central opening 37 by any of several different means. For example, it can be press fit, snap fit, adhesively bonded, or staked. In FIG. 2, the adapter housing is formed with an annular shoulder 100 on the service side and a plurality of annular tabs 102 on the spring side of the opening. Alternatively, the tabs 102 can be replaced with a continuous ring or flange that can be rolled inwardly. Preferably, the annular shoulder 100 and the annular tabs 102 can be cast with the adapter housing, thereby avoiding unnecessary and costly machining operations. The sealed bearing 38 is received in the central opening 37, one end thereof abutting the annular shoulder 100. The annular tabs 102 are cast so that they extend axially and are then bent inwardly toward the central opening 37 and against the other end of the sealed bearing 38 to securely fix the sealed bearing 38 within the central opening 37. It will be apparent that the inner O-ring 96 establishes a fluid tight seal between the spring brake actuator rod 56 and the non-metallic body 80, even as the spring brake actuator rod 56 reciprocates. Similarly, the outer O-ring 98 establishes a fluid tight seal between the non-metallic body 80 and the adapter housing 20.

FIG. 3 illustrates a second embodiment of a sealed bearing 38' according to the invention. In this and subsequent embodiments, like numerals are used to identify components similar in structure and function to those of the first embodiment. Here, the adapter housing 20' is formed with an annular rib 104 protruding radially into the central opening 37'. Annular tabs 102' are formed on both the service and spring sides of the central opening 37'. The sealed bearing 38' comprises first and second polymer rings

108, 110. The first ring 108 abuts the spring brake side of the annular rib 104 and can be securely fixed in the central opening 37' by the annular tabs 102' in the manner described above. Similarly, the second ring 110 abuts the service brake side of the annular rib 104 and is secured by the annular tabs 102'. The first and second rings 108, 110 are dimensioned radially to be greater than the depth of annular rib 104. Thus, the first and second rings 108, 110 and the annular rib 104 define a channel 112 which receives an O-ring 114. The O- ring 114 simultaneously establishes a fluid tight seal between the spring brake actuator rod 56' and the adapter housing 20', while the rings 108, 110 provide a self-lubricated bearing surface for the spring brake actuator rod 56'. FIG. 4 illustrates a third embodiment of a sealed bearing according to the invention. The adapter housing 20" has annular tabs 102" formed on both sides of the central opening 37" as described above. The sealed bearing 38" comprises a single, molded, polymer annular ring 118 having a radial inner channel 120 and radial outer channel 122. An inner O- ring 124 is received within the radial inner channel 120 and an outer O-ring 126 is received within the radial outer channel 122. The sealed bearing is secured within the central opening 37" by the annular tabs 102". Thus, the inner O-ring 124 will be in sealing engagement with the spring brake actuator rod 56 and the outer O-ring 126 will be in sealing engagement with the adapter housing 20". The annular ring 118 can also be used without the radial outer channel 122 and outer O-ring 126.

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

Claims

CLAIMSThe embodiments for which an exclusive property or privilege is claimed are defined as follows:

1. In a fluid-operated brake actuator comprising two internal tandem chambers separated by a wall, the wall having an opening therein between the two chambers, an actuating rod extending through the opening and adapted to reciprocate through the opening for alternately actuating and releasing a brake, and sealing means to seal the chambers from each other, the improvement in the sealing means comprising: a body securely fixed within the opening and having a self- lubricating inner surface, said body at least partially defining an annular channel within the opening, and an elastomeric sealing member disposed within the annular channel, wherein the actuating rod bears against the inner surface and the elastomeric sealing member as it reciprocates through the opening.

2. A fluid-operated brake actuator according to claim 1 wherein the body comprises a ring.

3. A fluid-operated brake actuator according to claim 2 wherein the ring has an outer surface with an annular channel in which is disposed a second elastomeric sealing member that bears against the wall to form a second seal between the two chambers.

4. A fluid-operated brake actuator according to claim 3 wherein the wall has an annular shoulder extending into the opening and at least one tab extending into the opening spaced axially from the shoulder, with the ring securely clamped within the opening between the shoulder and the at least one tab.

5. A fluid-operated brake actuator according to claim 4 wherein the at least one tab is deformable metal and clamps the ring within the opening by being bent beyond its elastic limit into the opening and against the ring.

6. A fluid-operated brake actuator according to claim 1 wherein the body is formed of a low friction polymer and the elastomeric sealing member comprises an O-ring.

7. A fluid-operated brake actuator according to claim 6 wherein the body is a polymer ring with an inner annular channel and an outer annular channel, said inner annular channel and outer annular channel each having an

8. A fluid-operated brake actuator according to claim 1 wherein the body comprises a first ring and a second ring.

9. A fluid-operated brake actuator according to claim 8 wherein the first ring and second ring are shaped to form the annular channel when they abut each other axially.

10. A fluid-operated brake actuator according to claim 9 wherein the first ring has an elongated depending axial flange and the second ring has an axial channel into which the elongated depending flange fits.

11. A fluid-operated brake actuator according to claim 10 wherein the body has an outer channel formed between the first ring and the second ring and a second elastomeric ring is disposed within the outer channel to form a second seal between the two chambers.

12. A fluid-operated brake actuator according to claim 11 wherein the wall has an annular shoulder extending inwardly at one portion of the opening and at least one tab extending into the opening and spaced axially from the shoulder, with the body securely clamped within the opening between the shoulder and the at least one tab.

13. A fluid-operated brake actuator according to claim 8 wherein the first and second rings are a low friction polymer.

14. A fluid-operated brake actuator according to claim 13 wherein the wall has an annular shoulder extending inwardly at one portion of the opening and at least one tab extending into the opening and spaced axially from the shoulder, with the body securely clamped within the opening between the shoulder and the at least one tab.

15. A fluid-operated brake actuator according to claim 14 wherein the at least one tab is deformable metal and clamps the body within the opemng by being bent beyond its elastic limit into the opening and against the body.

16. A fluid-operated brake actuator according to claim 8 wherein the wall has an annular rib extending inwardly at one portion of the opening and the first ring and second ring abut the rib on opposite sides, each ring having an annular width greater than the annular width of the rib, wherein the annular channel is defined by the first and second rings and the

17. A fluid-operated brake actuator according to claim 16 wherein the wall further comprises at least one tab spaced axially from one side of the rib, and the first ring is clamped within the opening and between the at least one tab and the rib, and at least one other tab spaced axially from the other side of the rib, the second ring being clamped within the opening and between the at least one other tab and the rib to secure the second ring within the opening.

18. A method of sealing adjoining spring and service chambers in a fluid-operated brake actuator, wherein the chambers are separated by a wall having an opening therein between the two chambers and wherein an actuating rod is adapted to extend through the opening and to reciprocate therethrough for alternately actuating and releasing a brake, the method comprising the steps of: securing a body having a central aperture defined by a self- lubricating inner surface within the opening, said body having an annular channel in the inner surface, placing an elastomeric sealing member within the annular channel, and extending the actuating rod through the aperture wherein the actuating rod will bear against the elastomeric sealing member and the inner surface as it reciprocates through the opening.

19. The method of claim 18 wherein the body is secured within the central opening by deforming a portion of the wall over the body.