Fluid-operated brake actuator with internal valve

Abstract

A fluid-operated brake actuator having a hollow actuator rod between a spring chamber of a spring brake housing and a spring chamber of a service brake housing incorporates a valve within the actuator rod. The valve isolates the two spring chambers from each other in normal operation and releases a vacuum in the spring brake housing spring chamber when the spring brake is activated. A separate one-way check valve mounted in a well of the spring brake housing permits fluid to exhaust from the spring chamber to atmosphere and prevents contaminants in the atmosphere from entering the spring chamber.

Description

BACKGROUND OF THE INVENTION

1. 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.

2. 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.

The spring brake actuator is typically divided into two chambers separated by a rubber diaphragm and pressure plate, with the spring in one of the chambers acting between and end wall of the spring brake housing and the pressure plate. When full pressure is applied to the opposite chamber, air pressure acting against the diaphragm and 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. The service chamber is typically divided into two chambers by a diaphragm. Depressing the brake pedal during normal driving operation introduces compressed air into one of the chambers of the service brake actuator which, acting against the diaphragm, causes a service brake push rod in the opposite chamber 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.

When pressure is released from the spring brake actuator, the spring and diaphragm extend significantly, expanding the volume of the spring brake actuator chamber containing the spring. Means must be provided for allowing air to enter the expanded volume of the chamber. Conversely, when the spring is retracted, and the volume of the chamber contracts, means must be provided for evacuating air from the chamber. In many prior brake actuators, the chamber containing the spring is simply open to atmosphere through ports in the chamber housing. However, this allows dirt, salt, moisture and other unwanted material to enter that chamber through the ports. With the advent of hollow actuator rods containing caging tools, the presence of foreign material within the actuator rod has become an increasing concern of brake designers.

has an abutting surface 74' which extends into the valve chamber open end 128, pushing the valve piston 134 toward the reaction plate 66, so that the radial passageways 166 are no longer aligned with the valve chamber annular groove 140. The radial passageways 166 abut the wall of the valve chamber 124, and the seals 164 prevent air from escaping from the piston interior chamber 144 into the upper portion of the valve chamber 124. The control valve 120 is thus closed and prevents air flow therethrough.

A second condition, when the spring brake is being applied, occurs when neither the second spring chamber portion 63, nor first service chamber portion 26 are pressurized. When pressure is lost in the second spring chamber portion 63, either due to a system failure or manual release, the spring 60 and the actuator rod 56 extend, thus moving the control valve 120 in the end of the actuator rod 56 away from the valve pin 74. This condition is illustrated in FIG. 3. Upon separation of the valve pin 74 from the end wall 146 of the control valve 120, the spring 136 pushes the valve piston 134 into abutment with the radial inward projections 138, putting the radial passageways 166 into alignment with the annular groove 140. The open control valve 120 allows air to flow from the air service port 42, through the control valve 120, through the hollow actuator rod 56 and into the expanding volume of the first spring chamber 62. The spring 158 keeps the float piston 152 in abutment with the inward projections 160, allowing air to freely flow past the float piston 152.

A third condition occurs when the service brake has been applied before activating or releasing the spring brake. In the third condition (detail illustrated in FIG. 6), pressure is lower in the first spring chamber portion 62 than the first service chamber 26 (as when the driver sets the parking brake by depressurizing the second spring chamber 63 while applying the service brake so that the first service chamber portion 26 is pressurized). The resulting pressure differential across the float piston 152 forces the chamfered edge 154 of the float piston 152 into sealing abutment with the conical transition wall 150, preventing flow around the float piston 152.

Any flow passing through the control valve 120 must pass through the small central aperture 156 in the float piston 152. The aperture 156 allows some flow to fill the expanding volume of the first spring chamber portion 62 as when the spring brake is being applied, for example, but restricts excess flow which would otherwise exhaust to atmosphere through the vents 100. Of course, when the service brake is released, thereby removing pressure from the first service chamber portion 26, and relieving the pressure differential across the float piston 152, the float piston 152 reverts to the position shown in FIG. 3.

As previously described with reference to FIG. 2, when the diaphragm 52 and spring 60 are retracted, reducing the volume of the first spring chamber portion 62, the vents 100 allow the excess air therein to exhaust to atmosphere. The one to two psig positive pressure within the first spring chamber portion 62 inhibits introduction of foreign matter from the brake actuator's service environment into the first spring chamber portion 62 through the ports 65.

A second embodiment of a control valve 200, according to the invention, is illustrated in FIGS. 7 to 9 where like parts are numbered with like numerals. Referring first to FIG. 7, the control valve 200 employs a valve body 122a substantially similar to the valve body 122 previously described with reference to the first embodiment control valve 120. A piston 202, received within the valve body 122a for reciprocal movement, comprises a cylindrical body 204, having a cylindrical interior chamber 206 with an end wall 208 and an open end 210, which opens into the valve chamber 124a. A short conical portion 211 of the interior chamber 206 expands outwardly toward the open end 210. A plurality of radial passageways 216 extend outwardly radially from the interior chamber 206 to exit the piston body 204 at points in alignment with the annular groove 140a when the piston 200 abuts the inward radial projections 138a. A pair of annular grooves 212 about the exterior of the piston on either side of the radial passageways 216 contain annular seals 214. The piston 200 functions similarly to the previously described first embodiment piston 134.

An annular groove 218 in the interior chamber 206 at its open end 210 retains a slightly convex spring metal diaphragm 220, having a central aperture 222. A stanchion 224 extends coaxially in the interior chamber 206 from the end wall 208 towards the metal diaphragm 220. A bore 226 extending coaxially into the free end of the stanchion 224 forms an annular, axially extending lip 228.

Referring to FIG. 1, and to each of FIGS. 7 to 9, operation of the control valve 200 in the three operating conditions of the brake actuator 10 will now be described. When the brake actuator is in the first condition (normal operation, second spring chamber portion 63 pressurized), as shown in FIG. 8, the valve pin 74a of the caging tool 70a forces the piston 202 into the valve body 122a so that the radial passageways 216 and seal 214 are inward of the annular groove 140a. In this position, the piston 202 closes the control valve 200.

When the brake actuator is in the second condition (second spring chamber portion 63, and first service chamber portion 26 both depressurized) as illustrated in FIG. 7, the piston 202 abuts the inward radial projections 138a, so that the interior chamber 206 communicates with the central bore 68a of the actuator rod 56a. The interior chamber 206 is open to the first service chamber portion 26 through the central aperture 222 of the metal diaphragm 220. The metal diaphragm 220 and stanchion 224 perform essentially the same function as the previously described float piston 152. When the brake actuator 10 is in the third condition (second spring chamber portion 63 depressurized and first service chamber portion 26 pressurized), as illustrated in FIG. 9, the pressure differential across the metal diaphragm 220 causes it to deform towards the stanchion 224, engaging the lip 228 thereon. The central aperture 222 of the metal diaphragm 220 aligns with the stanchion bore 226 so that in this position flow through the aperture 222 is greatly reduced. The spring constant of the metal diaphragm 220 is large, so that pressure differentials above approximately 35 psig in the first service chamber portion 26 will cause the metal diaphragm 220 to deform into contact with the stanchion 224.

An alternative means for restraining movement of the main piston 134 or 134a is illustrated in FIG. 10, where like parts are numbered with like numerals. The inwardly directed radial projections 138 or 138a of the first and second embodiments are replaced by a snap ring 300. The snap ring 300 is received within an annular snap ring groove 302 in the annular groove 140b, and projects inwardly radially from the snap ring groove 302 a sufficient distance to abut the end wall 146b of the main piston 134b. When the main piston 134b abuts the snap ring 300, the interior chamber 144b communicates with the annular groove 140b through the radial passageways 166b. An annular groove 304 encircles the exterior of the control valve body 122b, at its uppermost edge. The annular groove 140b remains in constant fluid communication with the central bore 68b of the actuator rod 56b through a plurality of axial passageways 306 leading from the annular groove 140b to the annular groove 304.

Preferably, the valve body 122, reaction plate 66, the main pistons 134, 202, and the float piston 152 are formed of plastic.

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. For instance, the invention is not limited to the flexible plugs 100 described herein, and other means may be provided which pass air from the first spring chamber 62 to atmosphere and block air flow from the operating environment into the first spring chamber, such as a flap valve.

Also, alternate means can be provided in place of the control valves 120 and 200 disclosed herein for preventing flow through the actuator rod 56 when it is in its retracted position. For instance, the actuator rod 56 can be made to seal against the end of the head 48 when the actuator rod 56 is retracted, or the distal end 55 of the actuator rod 56 can be formed with a narrower diameter receiver which receives the head portion 72 of the caging tool 70, so that the head portion 72 effectively seals the actuator rod 56. The invention has been described with reference to a diaphragm style spring brake actuator for illustration purposes only, and it would applicable to piston style brake actuators as well.

Claims

1. In a brake actuator for a vehicle comprising:

a service brake actuator housing and a spring brake actuator housing each having an interior space;

a first movable seal disposed within the spring brake actuator housing dividing the interior space thereof into a first spring brake actuator chamber and a second spring brake actuator chamber;

a second movable seal disposed within the service brake actuator housing dividing the interior space thereof into a first service brake actuator chamber and a second service brake actuator chamber; and

an actuator rod operably connected to the first movable seal and movable therewith for reciprocation between a first position wherein the actuator rod is essentially within the interior space of the spring brake actuator housing and a second position wherein the actuator rod extends into the interior space of the service brake actuator housing;

the improvement comprising:

an aperture through the spring brake actuator housing at the first spring brake chamber and a one-way check valve at the aperture whereby the check valve allows fluid flow out of the first spring brake chamber and prevents fluid flow into the first spring brake chamber through the aperture;

the actuator rod having a passageway extending therethrough wherein the first spring brake actuator chamber is in communication with the second spring brake first service brake actuator chamber through the actuator rod; and

a first valve at the actuator rod passageway adapted to establish flow of fluid through the passageway only when the actuator rod moves from the first position toward the second position; and

an abutting surface connected to the spring brake housing adapted to abut a portion of the valve when the actuator rod is in the first position.

2. A brake actuator according to claim 1 wherein the first moveable seal comprises a diaphragm.

3. A brake actuator according to claim 2 1 wherein the first valve has an open mode wherein the first valve allows fluid flow through the passageway, a closed mode wherein the first valve inhibits fluid flow through the passageway, and a control means associated with the abutting surface and the valve for placing the first valve into the closed mode when the actuator rod is in the first position and for placing the first valve into the open mode when the actuator rod is away from the first position.

4. A brake actuator according to claim 3 wherein the valve comprises a valve body having a valve chamber therewithin, the valve chamber having an open first end and an open second end; and

the control means comprises a bore wall defining a valve bore in the first valve, a piston slidable disposed within the valve bore, a channel through the piston and an abutting surface connected to the spring brake housing chamber for reciprocal movement therein and having an open position wherein the first end of the valve chamber communicates with the second end of the valve chamber, and a closed position wherein the piston blocks communication between the first end of the valve chamber and the second end of the valve chamber, the open and closed positions corresponding to the open and closed modes, respectively,

wherein the abutting surface abuts the piston and pushes the piston inwardly of the first end of the valve bore chamber when the actuator rod is in the first position whereby the bore wall blocks the channel to thereby close the valve.

5. In a brake actuator for a vehicle, comprising;

a service brake housing having an interior space;

a tandem spring brake housing having an interior space;

a first movable sealing member, disposed within the service brake housing, dividing the interior space thereof into a first service brake chamber and a second service brake chamber;

a second movable sealing member, disposed within the spring brake housing, dividing the interior thereof into a first spring brake chamber and a second spring brake chamber;

a power spring disposed in the first spring brake chamber between the spring brake housing and the second sealing member, the power spring biasing the second sealing member toward the service brake housing; and

a hollow an actuator rod having a distal end and a proximal end, the proximal end extending through the second sealing member for reciprocal movement therewith between an extended position and a retracted position, and the distal end disposed within the first service brake chamber;

a central bore extending through the actuator rod;

the improvement comprising:

the spring brake housing comprising a wall having an exterior surface exposed to atmosphere, an interior surface exposed to the first spring brake chamber, and an aperture therethrough;

a one-way check valve mounted to the wall at the aperture to permit fluid to flow from the first spring brake chamber to atmosphere only when fluid pressure in said first spring brake chamber exceeds a predetermined value;

the actuator rod being open at its proximal and distal ends wherein the first spring brake chamber is in fluid communication with the first service brake chamber through the central bore of the actuator rod;

a control valve mounted to within the distal end of the actuator rod for controlling fluid flow through the actuator rod and having an open mode wherein the first spring brake chamber is in open communication with the first service brake chamber, and a closed mode wherein the flow of fluid between the first spring brake chamber and the first service brake chamber is closed; and

a valve actuator operatively connected to the control valve for placing the control valve in the closed mode when the actuator rod is in the retracted position and for placing the control valve in the open mode as the actuator rod moves from the retracted position toward the extended position.; and

a caging tool extending into the actuator rod through the proximal end, wherein the valve actuator comprises an end of the caging tool adapted to engage a portion of the control valve when the actuator rod is in the retracted position,

whereby fluid is delivered to the first spring brake chamber from the first service brake chamber upon movement of the actuator rod toward the extended position.

6. A brake actuator according to claim 5, wherein the check valve comprises a plug having a shaft disposed within the aperture, a head on the shaft larger than the aperture and exterior of the spring brake housing, and biasing means connected to the plug for biasing the head into sealing abutment with the exterior surface when fluid pressure within the first spring brake chamber is less than the predetermined value.

7. A brake actuator according to claim 6, wherein the shaft extends into the first spring broke chamber and the biasing means comprises at least one flexible projection extending from the shaft toward and deformably abutting the interior surface of the spring brake housing wherein the deformation of the projection urges the head of the plug into sealing abutment with the spring brake housing.

8. A brake actuator according to claim 6, wherein the predetermined pressure is two pounds per square inch of gauge pressure.

9. A brake actuator according to claim 6 wherein the head has an annular ring which contacts the spring brake housing to form a

seal.

10. A brake actuator according to claim 5 wherein the control valve is mounted within the distal end of the actuator rod.

11. A brake actuator according to claim 10 and further comprising a caging tool extending into the actuator rod through its proximal end, and wherein the valve actuator comprises an end of the caging tool adapted to engage a portion of the control valve when the actuator rod is in the retracted position.

12. A brake actuator according claim 5 wherein the spring brake housing further comprises:

a wall having an exterior surface exposed to atmosphere, an interior surface exposed to the first spring brake chamber, and an aperture therethrough; and

a one-way check valve mounted to the wall at the aperture to permit fluid to flow from the first spring brake chamber to atmosphere only when fluid pressure in said first spring brake chamber exceeds a predetermined

value.

13. A brake actuator according to claim 12, wherein the main piston has a sealing lip at the distal end of the interior bore, and further comprising an overpressure stop valve comprising:

a sealing element movable within the piston chamber between an open position and a restricted position; and

a spring biasing the sealing element toward the open position;

wherein the sealing element abuts the sealing lip to restrict flow through the interior bore in the restricted position, and the sealing element is

spaced from the sealing lip in the open position.

14. A brake actuator according to claim 13 wherein the sealing element comprises a float piston, the spring is mounted between the float piston and the closed proximal end of the interior bore, and the sealing lip comprises an annular shoulder.

15. A brake actuator according to claim 14 wherein the float piston has a small coaxial aperture therethrough.

16. A brake actuator according to claim 14 wherein a stanchion extends coaxially from the proximal end within the interior bore, and the sealing element comprises a spring diaphragm having a flow aperture therethrough, the diaphragm having a resting shape wherein the diaphragm flow aperture is away from the stanchion and deformable under a predetermined pressure gradient across the diaphragm wherein the diaphragm contacts the stanchion so that fluid flow through the diaphragm flow aperture is blocked by the

stanchion.

17. A brake actuator according to claim 5 wherein the actuator rod has an exterior face at its distal end with at least one groove extending radially outwardly from the opening at the actuator rod distal end to a radial edge thereof; and

the first service brake chamber has an air port adapted to be connected to a source of pressurized air and a channel in the service brake housing leading from the air port to the at least one groove, whereby the opening at the distal end of the actuator rod remains in communication with the air port when the first moveable member is in contact with portions of the spring brake housing between the opening at the distal end of the actuator rod and the air port.18. In a brake actuator for a vehicle comprising:

a service brake actuator housing and a spring brake actuator housing each having an interior space;

a first movable seal disposed within the spring brake actuator housing dividing the interior space thereof into a first spring brake actuator chamber and a second spring brake actuator chamber;

a second movable seal disposed within the service brake actuator housing dividing the interior space thereof into a first service brake actuator chamber and a second service brake actuator chamber; and

an actuator rod operably connected to the first movable seal and movable therewith for reciprocation between a first position wherein the actuator rod is essentially within the interior space of the spring brake actuator housing and a second position wherein the actuator rod extends into the interior space of the service brake actuator housing;

the improvement comprising:

the spring brake housing comprises a wall having an exterior surface exposed to atmosphere, an interior surface exposed to the first spring brake chamber, and an aperture extending through the spring brake housing;

a one-way check valve being mounted to the wall at the aperture to permit fluid to flow from the first spring brake chamber to atmosphere through the aperture only when fluid pressure in the first spring brake chamber exceeds a predetermined value and prevents fluid flow into the first spring brake chamber through the aperture;

the actuator having a passageway extending therethrough wherein the first spring brake actuator chamber is in communication with the first service brake actuator chamber through the actuator rod;

a valve at the actuator rod passageway adapted to establish flow of fluid through the passageway only when the actuator rod moves from the first position toward the second position; and

an abutting surface connected to the spring brake housing adapted to abut a portion of the valve when the actuator rod is in the first

position.19. A brake actuator according to claim 1 wherein the actuator rod has a proximal and distal end, the proximal end connected to the first movable seal and the distal end disposed within the first service brake chamber;

a caging tool extending into the actuator rod through the proximal end, and wherein the abutting surface comprises an end of the caging

tool.20. A brake actuator according to claim 19 wherein the valve is mounted within the distal end of the actuator rod.21. A brake actuator according to claim 5 wherein the control valve comprises:

a valve body disposed within the distal end of the actuator rod and having a valve chamber therewithin, the valve chamber having an open first end and an open second end; and

a main piston disposed within the valve chamber for reciprocal movement therein and having an open position wherein the first end of the valve chamber communicates with the second end of the valve chamber, and a closed position wherein the main piston blocks communication between the first end of the valve chamber and the second end of the valve chamber, the open and closed positions corresponding to the open and closed modes, respectively.22. A brake actuator according to claim 21 and further comprising:

a spring biasing the main piston toward its open position;

the main piston having a coaxial interior bore with an open distal end and a closed proximal end, the distal end being oriented toward the first end of the valve chamber;

an annular groove located in the valve body adjacent to the valve chamber first end, the annular groove being in fluid communication with the central bore of the actuator rod;

at least one radial passageway extending from the piston interior bore outwardly radially through the piston to an exit opening, the exit opening being in fluid communication with the annular groove in the open position, and being blocked from the annular groove in the closed position; and

the caging tool extending into the second end of the valve chamber holding the main piston in its closed position when the actuator rod is in the retracted position;

whereby the valve chamber first end communicates with the valve chamber second end through the piston interior bore and the at least one radial

passageway only in the open position.23. A brake actuator according to claim 1, wherein the check valve comprises a plug having a shaft disposed within the aperture, a head on the shaft larger than the aperture and located exterior of the spring brake housing, and biasing means connected to the plug for biasing the head into sealing abutment with the exterior surface when fluid pressure within the first spring brake chamber is less than the predetermined value.24. A brake actuator according to claim 23, wherein the shaft extends into the first spring brake chamber and the biasing means comprises at least one flexible projection extending from the shaft toward and deformably abutting the interior surface of the spring brake housing wherein the deformation of the projection urges the head of the plug into sealing abutment with the spring brake housing.25. A brake actuator according to claim 1, wherein the predetermined value of fluid pressure is two pounds per square inch of gauge pressure.26. A brake actuator according to claim 23 wherein the head has an annular ring which contacts the spring brake housing to form a seal.27. A brake actuator according to claim 22, wherein the main piston has a sealing lip at the distal end of the piston interior bore, and further comprising an overpressure stop valve comprising:

a sealing element movable within the valve chamber between an open position and a restricted position; and

a spring, biasing the sealing element toward the open position;

wherein the sealing element abuts the sealing lip to restrict flow through the interior bore in the restricted position, and the sealing element is spaced from the sealing lip in the open position.28. A brake actuator according to claim 27, wherein the sealing element comprises a float piston, the spring is mounted between the float piston and the closed proximal end of the piston interior bore, and the sealing lip comprises an annular shoulder.29. A brake actuator according to claim 28, wherein the float piston has a small coaxial aperture therethrough.30. A brake actuator according to claim 27, wherein a stanchion extends coaxially from the proximal end within the piston interior bore, and the sealing element comprises a spring diaphragm having a flow aperture therethrough, the diaphragm having a resting shape wherein the diaphragm flow aperture is away from the stanchion and deformable under a predetermined pressure gradient across the diaphragm wherein the diaphragm contacts the stanchion such that fluid flow through the diaphragm flow aperture is blocked by the stanchion.31. A brake actuator according to claim 27 wherein the actuator rod distal end has an exterior face defined between the valve body second opening and a radial edge of the exterior face;

at least one groove extending radially outwardly along said exterior face from the valve body second opening to the radial edge; and

the first service brake chamber has an air port adapted to be connected to a source of pressurized air and a channel in the service brake housing leading from the air port to the at least one groove, whereby the valve body second opening remains in communication with the air port when the first moveable sealing member is in contact with portions of the spring brake housing between the valve body second end and the air port.