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.

The embodiments for which an exclusive property or privilege is claimed are defined as follows: 
     
       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.]. .Iadd.first service brake .Iaddend.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.Iadd.; 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.Iaddend..   
     
     
       2. A brake actuator according to claim 1 wherein the first moveable seal comprises a diaphragm. 
     
     
       3. A brake actuator according to claim .[.2.]. .Iadd.1 .Iaddend.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 .Iadd.associated with the abutting surface and the valve .Iaddend.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 .Iadd.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.Iaddend. the control means comprises a .[.bore wall defining a valve bore in the first valve, a.]. piston .[.slidable.]. .Iadd.disposed .Iaddend.within the valve .[.bore, a channel through the piston and an abutting surface connected to the spring brake housing.]. .Iadd.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,.Iaddend.   wherein the abutting surface abuts the piston and pushes the piston inwardly .Iadd.of the first end .Iaddend.of the valve .[.bore.]. .Iadd.chamber .Iaddend.when the actuator rod is in the first position .[.whereby the bore wall blocks the channel.]. .Iadd.to thereby close the valve.Iaddend..   
     
     
       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.]. .Iadd.an .Iaddend.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;   .Iadd.a central bore extending through the actuator rod;.Iaddend. 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 .Iadd.the central bore of .Iaddend.the actuator rod;   a control valve mounted .[.to.]. .Iadd.within the distal end of .Iaddend.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.[...]..Iadd.; 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,.Iaddend.   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..]..Iadd.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..Iaddend..Iadd.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..Iaddend..Iadd.20.  A brake actuator according to claim 19 wherein the valve is mounted within the distal end of the actuator rod..Iaddend..Iadd.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..Iaddend..Iadd.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..Iaddend..Iadd.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..Iaddend..Iadd.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..Iaddend..Iadd.25. A brake actuator according to claim 1, wherein the predetermined value of fluid pressure is two pounds per square inch of gauge pressure..Iaddend..Iadd.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..Iaddend..Iadd.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..Iaddend..Iadd.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..Iaddend..Iadd.29. A brake actuator according to claim 28, wherein the float piston has a small coaxial aperture therethrough..Iaddend..Iadd.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..Iaddend..Iadd.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..Iaddend.