~'"~'O 94!25736 PCTILTS9410~737
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~PltIb1(3 CHAMBER I~o~, TA ION B'~iBTEM
T~'OR A ~'LDID-OPERATED BRAKE ?~CTQAT()R
BACKGROUND QF THE ~~1VENTZON
F;pid 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.
Mate of the ~, io~r 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. 6Jhen full
3o pressure is applied to the opposite chamber, air
pressure acting against the diaphragm and pressure
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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
Z0 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
i5 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
20 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
Z5 and an emergency brake.
In tandem actuator assemblies, the spring
brake push rod typically extends from a chamber in the
spring b~cake portion, through an aperture in a wall
separating the spring brake actuator from the service
30 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
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O-rings positioned in annular channels in the wall
around the aperture.
When pressure is released from the sgring
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
i5 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.
Zp Some prior designs have attempted to address
this problem by providing a breather tube between the
push rod chamber of the service brake actuator and the
spring chamber of the spring brake actuator, as in the
U.S. Patent Number 4,960,036 to Gummer et al. In~this
Z5 design, the push rod chamber of the service brake
actuator must be vented to atmosphere for normal
application of the brakes. Venting of the push rod
chamber;occurs"either through a separate vent, or
through the external opening carrying the push rod.
30 Thus, the spring chamber of the spring brake actuator
remains open to atmosphere, and is still exposed to
moisture,~dirt and grime, albeit through a longer
passage than a fully vented spring chamber. This
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longer passage may also prevent the spring chamber from
drying as effectively as a sealed or more fully vented
spring chamber.
SUMMARY O~ THE INVENTION
The brake actuator of the present invention
overcomes these limitations.
A brake actuator for a vehicle comgrises a
service brake housing and a tandem spring brake
housing. A first moveable member, disposed within the
service brake housing, divides the interior thereof
into a first service brake chamber and a second service
brake chamber. The member is reciprocally moveable
therein in response to the delivery and exhaust of
pressurized fluid to the first service brake chamber.
A brake actuator push rod extends from the second
service brake chamber and operably connects to the
first moveable member for actuation of a brake. A
second moveable member, disposed within the spring
brake housing, divides the interior thereof into a
Z0 first spring brake chamber and a second spring brake
chamber. The second member is reciprocally moveable
therein in response to the delivery and exhaust of
pressurized fluid to the second spring brake chamber.
The spring brake housing has an aperture establishing
communication between the first spring brake chamber
and atmosphere. A power spring, disposed in the first
spring brake chamber, moves the second moveable member
upon exhaust of fluid from the second spring brake
chamber. A hollow actuator rod has a proximal end
mounted to and extending through the second movable '
member for reciprocal movement with the second moveable .
member between an extended position and a retracted
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position. A distal end of the actuator rod is disposed
within the first service brake chamber in a position to f
move the first moveable member when the second moveable
f
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member moves.
In accordance with the invention, a one-way
valve is mounted to the spring brake housing at the
aperture so that fluid flow from atmosphere to the
first spring brake chamber is restricted. The actuator
rod is open at its proximal and distal ends so that the
first spring brake chamber is in fluid communication
with the first service brake chamber through the
actuator rod. A control valve mounts within the
actuator rod and has an open mode where the first
spring brake chamber is in open communication with the
i5 first service brake chamber. In a closed mode of the
control valve, the first spring brake chamber is not in
communication with the first service brake chamber.
Closing means places the control valve in the closed
mode when the actuator rod is in the retracted
position. Fluid is delivered to the first spring brake
chamber from the first service brake chamber upon
movement of the actuator rod to the extended position
and the first spring brake chamber is isolated from the
introduction of fluid from atmosphere.
Preferably, the one-way valve comprises a
plug having a shaft disposed within the aperture, and a
head on the shaft larger than the aperture and exterior
of the spring brake housing. Biasing means biases the
head into sealing abutment with the exterior surface of
the spring brake housing at a predetermined force,
whereby when fluid pressure within the first spring
brake chamber exceeds the predetermined force, the head
of the plug will move away from the exterior surface
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and fluid will escape through the aperture to '
atmosphere. The biasing means preferably comprises at .
least one flexible projection, extending from the shaft
at a point within the first spring brake chamber into
~ abutment with~the interior.surface of the spring brake
housing. The flexible projection is deformed so that
. the deformation of the projection tends to urge the
head of the plug into sealing abutment with the spring
housing: Preferably, the predetermined force is one to
l0 wo pounds per square inch of gauge pressure. An
annular ring on the head contacts the spring brake
housing to form the seal..
Preferably, the control valve is mounted
within the distal end of the actuator rod. A caging
is tool extends into the actuator rod through its proximal
end, and the closing means comprises a valve pin on the
end of the caging tool adapted to push against a
portion of the control valve when the actuator rod is
in the retracted position.
Zo The control valve preferably comprises a
tubular body disposed within the distal end of the
actuator rod. A piston chamber within the body has an
open first end and an open second end. A main piston
is'disposed within the piston chamber for reciprocal
ZS' movement therein. The main piston has an open position
where the first end of the piston chamber communicates
r with the second end of the piston chamber, and a closed
position where''the~pis~ton blocks communication between .
the first end of the piston chamber and the second end
of the piston chamber. The open and closed positions
correspond to the open and closed modes of the valve,
respectively.
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A spring biases the main piston toward its
open position. The main piston has a~coaxial interior
bore with an open distal end and a closed proximal end.
The distal end is oriented toward the first end of the
piston chamber. At least one radial passageway extends
from the interior bore radially outwardly through the
main piston body to an exit opening. The exit opening
is outside of the piston chamber in the open position,
and inside of the piston chamber in the closed a
position. The valve pin extends into the piston
chamber through its second end and holds the main
piston in its closed position when the actuator rod is
in the retracted position. The piston chamber first
end~communicates with the piston chamber second end
i5 through the piston interior bore and the radial
passageway. This communication only occurs when the
open control valve is in the open position.
An overpressure stop valve can be provided.
The stop valve comprises a pressure plate moveable
within the main piston second chamber between an open
position and a restricted position. A pressure plate
biasing means biases the pressure plate toward the open
position. The pressure plate abuts a sealing lip in
the interior chamber to restrict flow through the
Z5 interior chamber in the restricted position. The
pressure plate is away from the sealing lip in the open
position.
Preferably, the pressure plate comprises a
float piston, the biasing means comprises a spring
between the float piston and the closed and of the
interior chamber, and the sealing lip comprises an
ahnular shoulder on the inside surface of the interior
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chamber. The float piston can be provided with a small
restricted flow aperture therethrough.
Alternatively, the pressure plate comprises a
spring metal diaphragm having a flow aperture
therethrough. The sealing~lip comprises an annular lip
on an end of a coaxial stanchion within the interior
chamber. The biasing_means comprises the diaphragm
having a resting shape wherein the diaphragm flow
aperture is away from the annular lip. The diaphragm
also has a deformed shape under a predetermined
pressure gradient across the diaphragm wherein the
diaphragm contacts the annular lip and the diaphragm
flow aperture is restricted by the stanchion.
Preferably, the actuator rod has an exterior
iS face at its distal end having at least one groove
extending radially outwardly from the opening at the
actuator rod distal end to a radial edge thereof. The
first service brake chamber has an air port adapted to
be connected to a source of pressurized air. A channel
in the'service brake housing leads from the air port to
~e groove, so that the opening at the distal end of
the actuator rod remains in communication with the air
port if the first moveable member is in contact with
portions of the spring brake housing between the
ZS opening at the distal end of the actuator rod and the
air port.
BRIEF.DESCRFPTION,~F THE DRAWINGS
FIG. 1 is a cross-sectional view of an air-
operated brake actuator with vents and control valve of
30 an isolation system according to the invention:
FIG. 2 is an enlarged fragmentary cross
sectional view of the vents of FIG. 1: '
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FIG. 3 is an enlarged fragmentary cross
sectional view of the control valve of FIG. 1;
FIG. 4 is a sectional view taken along line
4-4 of FIG. 1; .
FIG. 5 is an enlarged fragmentary cross
sectional view of the control valve of FIG. 3, shown in
the normal operating condition;
FIG. 6 is an enlarged fragmentary cross
sectional view similar to FIG. 3, showing an additional
operating condition of the control valve of FIG. 3;
FIG. 7 is an enlarged fragmentary cross
sectional view of a second embodiment of a control
valve according to the invention;
FIG. 8 is an enlarged fragmentary cross
sectional view of the control valve of FIG. 7 shown in
the normal operating condition: and
FIG. 9 is an enlarged fragmentary cross
sectional view similar to FIG. 3 showing an additional
operating condition of the control valve of FIG. 7;
Z0 FIG. 10 is an enlarged fragmentary cross-
sectional view of a third embodiment of a control valve
according to the invention.
gETAILED DESCRIPTION OF TI3E 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 service brake actuator 14 mounted in tandem
to a spring chamber or emergency brake actuator i6. A
service brake push rod 12 extends from the service
brake actuator 14 for reciprocating movement between a
retracted position and an extended actuating position
relative to the service brake actuator 14, and is
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provided with a clevis 17 which is adapted to connect
to a conventional brake shoe and drum (not shown) in a
standard fashion. Reciprocating motion of the service
brake push rod 12 will cause the brake to be
alternately applied and released.
The service 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 enclosure 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
Z0 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 opening 32 in the cup-
Z~ 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 spring 46 in the second service chamber portion
30 28.
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
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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
i0 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.
35 To operate the service brake, compressed air
is introduced through the air service port 42 into the
first service chamber portion 26 to create a force
against the first elastomeric diaphragm 24 and pressure
plate 44 sufficient to overcome 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
lower service chamber section 23 as the service brake
is actuated. Mounting studs 47 are provided to mount
Z5 the fluid-operated brake actuator 10 onto a vehicle
not' shown ) .
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
30 or spring chamber, 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
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suspended within the spring brake chamber 51, the
peripheral edge thereof secured in fluid tight . ..
enclosure 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 38 in divider wall
35 for reciprocating motion through the central opening
38 between a retracted position and an actuating
position. One or more O-ring seals 37 are provided in
the central opening 38 through which the spring brake
actuator rod 56 reciprocates.
A distal end 55 of the spring brake actuator
rod 56 terminates in a reaction plate 66 in the first
service chamber portion 26, and which is received in an
annular seat 40 when the spring brake actuator rod 56
is in the retracted position as depicted in FIG. 1. An
opposite, proximal end 57 of the actuator rod 56
extends through an opening 53 in the second elastomeric
diaphragm 52 and terminates in a pressure plate 58
which abuts an end of a large force compression spring
60. The pressure plate 58 abuts one end of the
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compression spring 60. A tubular portion 61 of the
pressure plate 58 extends generally axially along the
axis of the compression spring 60. The tubular portion
61 of pressure plate 58 is press-fit into the proximal
end 57 of the spring brake actuator rod 56 such that
the pressure plate 58 and the spring brake actuator rod
56 form an integral unit with the second elastomeric
diaphragm 52 secured therebetween.
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, l,~by means of compressed air which is maintained
in the second spring chamber portion 63. When the
compressed air is exhausted from the second spring
13 chamber portion 63, the compression spring 60, one end
of which abuts the outer end wall of the cylindrical
head 48, forces the integral pressure plate 58 aid
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 38,
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
25 the service brake push rod 12 to be extended toward the
actuating position, thereby applying the brake (not
shownj. When the spring brake actuator 16 is to be
released, compressed air is once 'again introduced into
the second spring chamber portion 63 to a pressure
30 sufficient to overcome the force of the compression
spring 60. Th~ force of the compressed air against the
second elastomeric diaphragm 52 causes the pressure
plate 58, the spring brake actuator rod 56 and the
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compression spring 60 to be returned to the position
depicted in FIG. 1.
In the embodiment shown, the spring brake
actuator rod 56 is a hollow tube or rod provided with a -
central bore 68 to aceommodate a brake release rod or
caging tool 70. The central bore 68 of the spring i
brake actuator rod 56 receives the caging tool 70,
which passes through aligned apertures 69, 73, and 75
in the cylindrical head 48, pressure plate 58 and
19 spring brake actuator rod 56, respectively. The caging
tool 70 comprises a threaded elongated shaft 71, with
one end having an enlarged head portion 72, which
terminates in a valve pin 74. The opposite end of the
caging tool 70 is threaded through a head nut ?6
fixedly mounted to the cylindrical head 48, and has a
hex head nut 78 fixedly secured thereto.
The caging tool 70 primarily serves to enable
manual retraction of the powerful compression spring
60. Rotation of the hex head nut 78, threads the shaft
ZO 71 through the head nut 76, to axially move the caging
tool 70 with respect to the cylindrical head 48. The
head portion 72 slides freely within the bore 68 of the
actuator rod 56, yet is restrained by an inwardly
directed annular flange 80 at the actuator rod proximal
ZS end 57. Thus, withdrawal of the caging tool 70 by
rotation of the hex head nut 78, causes the head
. portion 72 to abut the flange 80, and retract the v
pressure plate 58 and spring 60. For safety, the
spring 60 is typically retracted during r~pairs to the
30 brake actuator 10 and during shipping.
The cylindrical head 48 includes one or more
ports 65 therein which establish communication between
the first spring chamber portion 62 and the atmosphere. -
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A one-way vent 100, installed in each port 65, controls
the flow of air through the port.
Turning now to FIG. 2, it can be seen that
the vent 100 comprises a mushroom shaped cap 102
i
S external to the first spring chamber portion 62, a
shaft 104 received within the port 65, and a plurality
of flexible tabs 106 sloping outwardly from the shaft
104, from a point interior of the first spring chamber
62, toward the cap 102. The tabs 106 abut an interior
surface 108 of the cylindrical head 48 and bias the
vent cap 102 against an exterior surface 110 of the
cylindrical head 48.
The vent 100 thus prevents air and
contaminants in the atmosphere from entering the first
spring chamber portion 62 through the port 65. One or
more concentric rings 112 on the cap 102 contact the
exterior surface 110 of the cylindrical head 48 to
enhance the seal formed between the cap 102 and the
cylindrical head 48. Elevated pressure within the
ZO first spring chamber portion 62 will overcome the
biasing force of the tabs 106 and vent cap 102 and
allow air within the first spring chamber portion 62 to
exhaust through the port 65. Preferably, the biasing
force of the tabs 106 will prevent the vent 100 from
Zs opening until the pressure within the first spring
chamber portion exceeds one to two psig, thereby
maintaining a slight positive pressure within the first
spring chamber'portion~'62'. It will be apparent that
when the volume within the first spring chamber portion
62 expands upon release of the spring 60, air flow into
the chamber from atmosphere through the ports 65 will
be blocked by the vents 100.
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Returning to FIG. 1, air flow to the first
spring chamber portion 62, in response to the extension -
of the spring 60, and diaphragm 52, comes through the '
actuator rod 56 and is controlled by a control valve
120 in the distal end 55 of the actuator rod 56. The
control valve 120 controls the flow of air from the
first service chamber portion 26 into the first spring
chamber portion 62 in a manner to be more fully
explained hereinafter.
Turning to FIG. 3, the control valve 120
comprises a cylindrical body 122 integrally formed with
the reaction plate 66, and having a cylindrical valve
chamber 124 therein. The reaction plate 66 forms a~
closed end 126 of the valve chamber: an opposite end
128 is open. The control valve body 122 is press fit
into the distal end 55 of the actuator rod 56, and is
sealed thereto by an o-ring seal 130 in a
circumferential groove 132 about the valve body 122. ;
A main piston 134 is mounted within the valve
chamber 124 for axial reciprocal movement therein. A
spring 136, positioned between.the reaction plate 66
and the main piston 134, biases the main piston 134
away from the reaction plate 66. Outward movement of
the main piston 134 is restrained by a plurality of
radially inwardly directed projections 138 at the valve '
chamber's open end 128. An annular groove 140 is
provided in the wall of the valve chamber 124
immediately adjacent the'projections 138. ' j
The main piston 134 comprises a cylindrical s
body 142, having a first cylindrical interior wall 143
and an end wall 146, forming a cylindrical interior '
chamber 144: and a second cylindrical interior wall 147
forming a larger diameter cylindrical outer chamber '
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148. ~uter chamber 148 opens at one end to the valve
- chamber 124, and at an apposite end to the interior
chamber 144. A conical transition wall 150 separates
- the first interior wall 143 and the second interior
wall 147.
A discoid shaped float piston 152 is disposed
within the outer chamber 148 for reciprocal movement
and comprises a chamfered annular edge 154 adapted to
mate with the conical transition wall 150, and a small,
l0 axially extending, central aperture 156. A spring 158,
positioned between the interior chamber end wall 146
and the float piston 152 biases the float piston 152
away from the end wall 146. A plurality of axially
inwardly directed projections 160 or a snap sing, or a
i5 washer restrain the outward movement of the float
piston 152.
A pair of annular grooves 162 in the outer
surface of the main piston body 142 retain a pair of
O-ring seals 164. A plurality of passageways 166
20 extend radially outwardly from the interior chamber
144, through the first cylindrical wall 143, and exit
the main piston body 142 at points 165 between the
annular seals 164. When the main piston 134 abuts the
projections 138 as shown in FIG. 3, the radial
25 passageways 166 align with the annular groove 140,
putting the central bore 68 of the actuator rod 56 into
fluid communication with the interior chamber 144 of
the main piston 134:'
Regardless of the position of the float
30 piston 152 within the outer chamber 148, the interior
chamber 144 communicates fluidly with the valve chamber
124, and ultimately with the first service chamber
portion 26 (not shown in FIG. 3) through a central
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aperture 168 in the portion of the reaction plate 66
forming the valve chamber closed end 126. When the
chamfered edge 154 of the float piston 152 abuts and
seals against the conical transition wall 150 (see FIG. .
6), fluid flow into the interior chamber 144 through
the outer chamber 148 is possible only through the
small aperture 156. However, when the float piston 152
abuts the inward radial projections 160 as shown in
FIG. 3, flow may also pass around the float piston 152.
i0 Operation of the control valve 120, valve piston 134
and float piston 152 will be more fully described
hereinafter.
Turning now to FIG. 4, a plurality of radial
grooves 170 in the face of the reaction plate 66 lead
from the central aperture 168 to a peripheral edge 172
thereof. A further groove 174 in the face of the wall
35, leads from the annular seat 40 in the adapter
housing 20 to the air service port 42 (Fig. 1). Thus,
even when the first service chamber portion is
evacuated and the first elastomeric diaphragm 24 is
forced against the adapter housing 20, as shown in FIG.
1, the valve chamber 124 remains in fluid communication
with the air service port 42 through the grooves 170,
174.
Returning to FIG. 1, the control valve 120
controls the flow of air into the first spring chamber
62 from the air service port 42, through the central
bore '68of the'' actuator rod ; 56, and apertures 75 and 73
in the proximal end 57 of the actuator rod 56 and
pressure plate 58. The control valve 120 restricts or
blocks flow under some operating conditions and permits
flow under other conditions.
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A normal operating condition where the spring
brake is not actuated is illustrated in FIG. 1 with the
detail of the control valve 120 in this condition shown
in FIG. 5. In this condition, the caging tool 70 is
fully extended into the spring chamber 51. However,
the second spring chamber portion 63 is pressurized so
that the diaphragm 52 and pressure plate 58 keep the
spring 60 and actuator rod 56 retracted. Selective
application of pressurized air to the first service
chamber 26 extends the pushrod 12 to apply the brakes
(not shown) in the normal manner.
Because the spring 60 and diaphragm 52 remain
retracted, the first spring chamber portion 62 is
static and does not require an inflow of air through
the control valve 120. Hence, the control,valve 120 is
in the closed position as shown in FIG. 5. An open
control valve 120 would vent air every time pressurized
air is introduced to the first service chamber portion
26 to apply the brakes (not shown), by exhausting air
through the aperture 168, the control valve 120, the
central bore 68 of the actuator rod 56, into the first
spring chamber portion 62 and out to atmosphere through
the vents 100.
The valve pin 74 on the caging tool 70
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.
WO 94/25736 PCTIUS94102737~ ~.
'!
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
9.5 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
2o 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
25 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
3o chamber portion 26 is pressurized). The resulting
pressure differential across the float piston 152 -
forces the chamfered edge 154 of the float piston 152
'O 94/25736 ~ ~ ~ ~ ~ ' ~ 'g PCT/US94/02737
.21.
into sealing abutment with the conical transition wall
I50, 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,
25 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~~bady 1~22a substantially similar to the
valve body 122 previously described with reference to y
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
WO 94125736 PCTItJS94102737 -~ '
C .:a
-22-
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
i0 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
i5 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
Z0 extending lip 228.
Referring to FIG. 1, and to each of FIGS. ?
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
ZS condition (normal operation, second spring chamber
portion 63 pressurized), as shown in FIG. 8, the valve
pin ?4a of the caging tool ?Oa forces the piston 202
into th~~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
-:"O 94125?36 ~~ ~ ~ ~ ~ ~ ' PCT/IJS94I0273?
-23_
service chamber portion 26 both depressurized) as
illustrated in FIG. 7, the piston 202 abuts the inward
radial projections 138x, 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. ~, 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 defona into contact with the stanchion 224.
An alternative means for restraining movement
Z5 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
WO 94/25736 ~ ~ ~ ~ w,, ; ~ ~ PCT/LTS94/02737 ~
.z t
-24-
134b abuts the snap ring 300, the interior chamber 144b
communicates with the annular groove .l4~Ob 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 l4ob 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
Z0 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
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