Note: Descriptions are shown in the official language in which they were submitted.
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COMBINED ~YDROPNEUMATIC BRAKE CYLI~DER/AIR
RESE~OIR DEVICE WITH AUTOMATIC
RRANGEME~T
BACKGROUND OF THE INVENTION
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The present inven~ion is related to hydropneumatic type
actuators~ and more particularly to brake actuators of the
above type, which are suitable for use in .Ereight type railway
bxake systems.
At the present time, railroads typically employ tradi-
tional automatic air brake systems. Each car in a train iæ
normally equipped with auxiliary and emergency reservoirs
which are charged with compressed air from a brake pipe extend-
ing through the train, and a control val~e which responds to
changes in the brake pipe pressure to control the fl~w o~
compressed air to and from the car brake cylinders. Since
the railroad industry has standardized on relatively low
braking pressures, and practical considerations limit the
size of the car brake cylinders, it has become necessary to
employ force-multi.plying linkages between the brake cylinder
and brake shoes in or~er to obtain the high braking forces
required. Such brake rigging arrangements inherentl~ increase
the stroke of the brake cylinder piston required to move the
brake shoes enough to take up the clearance space be~ween the
,
brake shoes and wheel treads. Accordingly, the plston ~troke
required to bring the shoes into wheel contact, must be
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relatively large and thus consumes a considerable amount of
air. This in turn requires relativel~ large air reservoir~,
which are space~consuming and thus impose al further restric-
tion on the arPa needed ~or the force-multiplying brake
rigging.
The gradual acceptance of hydraulic brake system~ in the
rapid transit segment of the railway industry suggests the
possibility o~ using hydraulics as a means of transmittirlg
brake ~orces to the brake shoes in freigh~ type service. Such
an approach would be advantageous in eliminating the need ~or
the cumbersome, mechanical brake rigging presently employed
on ~reight cars to transmit the brake cylinder ~orces to the
brake shoes. Ideally, such an arrangement would require only
a single hydropneumatic actuator de~ice on each car corres-
15 ponding to the brake ylinder in a conventional mechanicalbrake rigging sy~tem. Mechanical ad~antage sufficient to
obtain the desired high brake shoe forces would be obtained
by a high ratio input to output hydropneumatic piston of the
actuator device. Because of this high input to output ratio
and the brake shoe clearance to be taken up, the stroke of
the actuator piston in the pneumatic actuator portion would
be necessarily large, and thus re~uire a considerable amount
o~ air simply to bring the brake shoes into braking engagement
with the wheel treads.
SUMMARY OF THE I~VENTIO~
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The object of the present invention is to pro~ide a
compact, low-cost, yet highly reliable hydropneumatic actuator
device having a -twc-stage pneumatic actuator portion to reduce
the air required to take up the clearance between the brake
shoes and wheel treads of a railway vehicle.
Another objec$ of the invention is to provide a hydro-
pneumatic actuator of the above type, which automatically
comp~nsates fox variations in the clearance between the brake
shoes and wheel treads due to brake shoe wear or replacement,
for example, in order to maintain the desired stroke of the
pneumatic piston su~stantially constant to assure optimum
operation of the two-stage pneumatic actuator portion.
Briefly, the hydropneumatic actuator according to the
present invention converts an input force, such as the pneu-
matic output of an air braka control valve device, intv a
proportionally higher hydraulic pressure. During the first
stage of operation, a relatively small pneumatic piston drives
a hydraulic piston through a distance corresponding to the
nominal brake shoe clearance in order to obtain a ~arge volu-
metric displacement v hydraulic fluid with low air consump~
tion. The pneumatic piston and consequently the hydraulic
piston, which is formed on the end of the pneumatic piston, is
therefore displaced a distance corresponding to the nominal
stroke of the pneumatic/hydraulic piston. FollGwing this, a
second s~age of operation is initiated by venting air from the
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one side of the larger pneumatic piston, which is integral
with the smaller pneumatic piston. This result~ in a hig~er
pneumatic to hydraulic force multiplication being obtained
after the brake shoe ~learance has heen taken up~ but with
less air consumption since in the actuated po~ition of the
larger pneumatic piston, the volume of air existing on the
one side of the piston is reduced to a mini~um.
A slack ad]uster piston in a reference chambar of the
hydraulic portion operates between opposite end stops as the
pneumatic/hydraulic piston is actuated through its nominal
stroke, thereb~ displacirlg a predetermined amount of hyclrau~ic
fluid sufficient to take up the brake shoe clearance.
In the event brake shoe engagement occurs pxematurely,
~ such as during the initial application of the brakes following
lnstallation of new brake shoes~ a high pressure is developed
in the reference chamber due to brake shoe engagement occur-
ring before complete displacement of hydraulic fluid has taken
place. Accordingly, a one-way check val~e between the refex-
ence chamber and a hydraulic reservoir is opened by the
2~ hydraulic pressure buildup, thereby displacing the excess
hydraulic fluid from the reference chamber until the slack
adjuster piston engages its one end stop. During a subsequent
brake release, the braXe shoes will be retracted as the slack
adjuster piston is returned to its original position against
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its other end stop, thereby esta~lishing the desired brake
shoe clearance.
In the event overtravel occurs due to brake shoe wear,
in which case hydraulic fluid in the r~ference chamber is
completely displaced, consequent movement of the slack
adjuster piston into engagement with the one end stop results
in a one-way check valve opening a passageway through the
slack adjuster piston via which passageway any additional
hydraulic fluid necessary to maintain brake shoe engagement
with shoe wear is supplied from the hydraulic cylinder. During
a subsequent brake release, the slack adjuster piston i9
retracted to establish the desi.red brake shoe clearance,
following which continued movement of the pneumatic-hydraulic
piston to release position corresponding to overtravel during
the preceding brake application draws makeup hydraulic fluid
into the hydraulic cylinder from the hydraulic reservoir via
another one-way check valve~
BRIEF DESCRIPTIOM OF THE DRAWING
The foregoing objects and additional advantages and
features of the present invention will become apparent from
the following more detailed explanation of the invention when
taken in conjunction with the a~tendant single Figure drawing
showing a sectional assembly view of a hydropneumatic actuator
device, in which the pneumatic portion embodie~ a combined
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brake cylinder/air reservolr design and the hydraulic portion
provides a double-acting slack adjusterO
DESCRIPTION A3!~D OPERATIO:W
In a preferred embodiment o~ the invention~ there is
shown a hydropneumatic brake actuator including a pneumatic
portion 1 in the form of a combined brake cylinder/air
raservoir device, such as disclosed in U0 S0 Patent ~oO
4055701810 assigned to the assignee of the present invention,
and a hydraulic portion 20 Pneumatic portion 1 comprises a
main cast mg 3 hav mg a partition forming a pressure head 4
with an opening 5 in pressure head 4O A back cover 6 is
bolted to the one end of main casting 3 and an end casting 7
is bolted to the opposite end of maln casting 3. A cylindrical
tube 8 extends longitudinally be~ween pressure head 4 and
back cover 60 thereby o.rming an annular emergency chamber 9
about the outer periphery of ~ube 80 A fluted guide sleeve 10
is disposed within tube 8, such that its opposite ends also
extend between pressure head 4 and back co~er 6. Longitudinal
passageways 11 are formed by t~e fluted sleeve ~0 and tube 80
The guide slee~e 10 is aligned axially concentric with opening
5 and has an inside diameter substantially the same as the
diameter of opening 5. Slidably disposed within guide sleeve
10 is a tubular-shaped positioning piston 12 that forms, in
cooperation with sleeve 10 and back cover 6D a positioning
chamber 13.
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Positioning piston 12 includes a piston head 14 integral
with a tubular~shaped, elongated body lS that projects through
opening 5 and to which i9 attached a p~wer pist~n 16 having
a diameter larger than the diameter of positioning piston 12.
Being interconnected, positioning piston 12 and power piston
16 form a dual piston assembly that moves as a unit between a
braXe release position and a brake application position.
stop bwmper 17 is carried by power piston 16 for engagement
with pressure head 4 in the brake release position of the dual
piston assembly, as shown. A cylindrical sleeve 18 i~ bolted
to an inwardly projecting annular sleeve 19 of end casting 7
and carries on its outer periphery a sealing ring 20 with which
the inner perlphery of tubular-shaped body 15 is engageable
during movement of the dual piston assemblyO
An annular cylinder liner 21 is secured to main casting
3 between the main casting and end casting 7 to receive ~ower
piston 16~ m e inside diameter of cylinder liner 21 is sub-
stantially the same as the outside diameter of power piston 16.
By unbolting end cover 7 from main casting 3, the piston
assembly and cylinder liner may be withdrawn from the main
casting and, if different braking power is desired, replaced
with a piston asse~bly having a different sized power pi~ton.
A cylinder liner having a diameter corresponding to the
replacement power piston may then be installed in main casting
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30 as exp].ained above, ~o accommodate the diferent sized
power piston~
T~e end of cylinder liner 21 adjacent power piston 16
is spaced longikudinally ~rom the power pi~3ton when the dual
S piston assembly is in release position, as shown. Until power
piston 16 enters the cylinder liner 21 duri.ng an application
stroka, free air ~low between opposite sides of power piston
16 oc~ur~. When the power piston entars the cylinder liner 21,
an application chamber 22 is formed on one side of the power
piston and a release chamber 23 is formed on the opposite side,
it being understood that the combined volume of chambers 22
and 23 is substantially greater than the maximum volume o~
c~lamber 13. 'rhe volumetric dimension o~ chamber 13 increases
by axial displacement of positioning piston 12 during movement
of the dual piston assembly t~ward brake application posi-
tion and is maximum in the application position. An annular
pressure seal 24 is carried on the periphery of power piston
16 and makes sealing ~ngagement with the cylinder wall of
liner 21 to establish a pressure seal between chambers 22
and 23. In the release position shown, fluid pres~ure com,
munication is established between chambers 22 and 23, by way
of the space between piston 16 and the adjacent end of liner
21. At this point, chambers 22 and 23 are,in effect~ a single
cha~er~ until piston 16 enters into sealing engagemant with
.
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liner 21 during subseguent movement toward ~he brake applica~
tion position.
A ~luid pressure seal ring 25 is carried on pressure head
4 about the central opening 5, so as to engage tha outer peri-
p~ery of the tubular-shaped body 15 of positioning piston 12
and thereby maintain a pressure_tight seal be~ween pressure
chambers 22-23 and chamber 13. The fluid pressure seal ring
20 carried on the outer perip~ery of cylindrical sleeve 18
near its free end maintains a pressure_tight seal between
chambers 22-23 and akmosphere.
A hollow piston rod 27 is connected, as by threads, at
its one end to positioning piston 12 within tubular body 15.
The other end o~ piston rod 27 is ~ixed, as by welding~ to a
~ydraulic piston 28 that projects through a sealed opening 29
formed at the juncture of interconnected sleeves 18 and 19
and into a hydraulic chamber 30. Hydraulic chamber 30 is
contained in a hydraulic cylinder 31 that is integral with
end casting 7 and comprises hydraulic portion 2. A piston
return spring 32 acts between the head 14 of positioning piston
12 and a spring seat 33 that abuts the seal end of sleeve 18
to urge the dual piston assembly toward release position.
A branch pipe 34 is c~nnected between a brake pipe 35
and a mounting boss 36 that receives a control valve device
38, which may be similar to that described in U. S. Patent No.
4,405,182. Mounting boss 36 includes a port 39 leading to
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emergency chamber 9, a port 40 leading to chamber 13 via
fluted passageway 11, and ports 41t 42 leading to the respec-
tive application and release chambers 22, 23.
In additio~ to hydraulic chanber 30, ~hydraulic cylinder
31 also comprises a reference chamber 43 that is axially
aligned with hydraulic cha~ber 30 and a hydraulic reservoir
44. A one-way check valve device 45, such as a conventional
sprin~-biased ball check valve, is provided in a passage 46
be~ween reservoir 44 and chamber 30 via w~ich a source of
hydraulic fluid is connected to the hydraulic system.
Operably disposed in reference chamber 43 i9 a slack
adjuster piston 47 having a predetermined maximum stroke corras
ponding to the desired clearance to be maintained, for example,
between the bxake shoes (not shown) of a railway vehicle and
the tread of the wheel to be braked (not shown). This pre-
determined maximum stroke of slack adjuster piston 47 is estab_
lished by a stop at one end of chamber 43 formed by a shoulder
48 between chambers 30 and 43, and a stop at the other end of
chamber 43 formed by a cover member 49 that closes this other
end of the reference chamber 43. A return spring 50 be~ween
piston 47 and end cover 49 normally maintains the slack
adjuster piston 47 in engagement with shoulder 48. Contained
in a throu~h passage 51 of slack adjuster piston 47 is a one-
way check valve device 52, such as a conventional spring-biased
ball check valve that is arranged ko permit fluid flow in a
directlon from chamber 43 to chamber 30 when the foxce of
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fluid pressure in chal~ber 43 becomes substantially greater than
the force required to open another one_way check valve 53.
This one-way check valve device 53 may also be a conventional
spring-biased ball check valve that is disposed in a passage 54
between chamber 43 and reservoir 44. A pin 55 is set in cover
member 49 so as to project into chaMber 43 ~o engage and unseat
the spring-loaded ball valve o~ one-way check valve 52 when
slack adjuster piston 47 is in engagement with its stop pro-
vided by cover mQmber 49. An outlet 56 is provided in cover
member 49 via which hydraulic fluid is transmitted ~rom chambers
30, 43 to an output device, such as the wheel brake cylinders
(not shown), to which the aforementioned brake shoes may be
attached. A high pressure, annular seal 57 is provided in the
piston bore of chamber 43 between passage 54 and outlet 56 to
isolate these passages when piston 47 is in its extreme right
hand position.
During initial charging of the brake e~uipment, pressure
chambers 9, 22 and 23 are stored with compressed air su~plied
by wa~ of brake pipe 35, branch pip~ 34, control valve de~ice
38, and the respective ports 39, 41 and 42 of main casting 3~
The dual piston assembly comprising positioning piston 12 and
power piston 16 is maintained in release position, as shown,
under the in~luence o~ return spring 32.
In order ~o initiate a service brake application, air in
brake pipe 35 is reduced at a~service rate. During the initial
stage o~ a service brake application, control va}ve 38 is
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operative in rasponse to the brake pipe pressure reduction
to connect com~ressed air from charged chambers 22 ana 23
to the previously evacuated positioning chamber 13. As this
aix pres.sure in positioning chamber 13 builds up in attempting
to equalize with the higher air prassur~ in chambers 22 and
23, a force is developed on positioning piston 12 in a right_
hand direction. When this force exceeds the force of return
spring 32, the dual piston assembly will be forced in a brake
application direction, carrying along piston rod 27. During
this movement of the dual piston assembly, unrestricted flow
of compressed air takes place from release chamber 23 to
application chamber 22 via the space between the power piston
16 and the adjacent end o~ cylinder liner 21 to accommodate
the displacement of power piston 16. A one~way chec~ valve
(not shown) is also provided in control valve device 38 to
accommodate displacement of air from release chamber 23 to
application chamber 22 when piston 16 makes full sealing
engagement with cylinder liner 21, as the dual piston assembly
moves toward full application position.
As piston rod 27 is moved from release to application
position, hydraulic piston 28 is forced into hydraulic chamber
30, thereby displacing hydraulic ~luid via outlet 56 to force
the vehicle brake shoes into braking ~ngagement, as herein-
after described more fully. Consequently, brake shoe clearance
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is taken up with a low brake force r0quirement during this
initial stage of a ~ervice brake application.
It will be further appreciated that in application posi-
tion of power piston 16, the volume of application chamber 22
is increased and the volume of release chamber 23 is decreased.
In th2 second stage of this service brake application, the air
in the reduced volume of chamber 23 is exhausted by control
valve 38 an amount corresponding to the reduction of ir pres-
sure in brake pipe 380 The resultant reduction of pressure in
release chamber 23 establishes a relatively high di~erential
force across power piston 16 in a brake application direction,
since the pressure in chamber 22 is prevented from equalizing
with the pressure in chamber 23 by seal ring 24. This high
pneu~atic force is transmitted to the brake shoes ~ia the
~ydraulic fluid in the brake circuit, w~ich in effect becomes
a solid link once brake shoe clearance has been taken up.
During a subsequent brake release operation, air in
rel~ase chamber 23 is inikially connected by control valve
device 38 to cha~ber 22 via a release control choke ~not shown)
in control val~e device 38 to assure a controlled release of
braking force. Concurrently, the pressure in positioning
chamber 13 is vented to atmosphere. As the pressures acro~s
power piston 13 become egualized, return spring 25 is efec-
tive to ~orce the dual piston assembly toward the release
position. Once power piston 13 move~ out of engagement with
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cylinder liner 1~, unrestricted flow of air occurs between
chambers 22 and 23 to hasten movement of the dual piston
assembly and the car brake shoes to the xelea~e position. As
the dual piston assembly is retracted, so is hydraulic piston
5 28, which relieves the hydraulic brake pressure to permit the
brake shoes to be retracted from engagement with the wheel
tread braking surface. In this release position, the brake
shoes are spaced~apart from the wheel tread brake surface a
distance correspsnding to tha desired brake shoe clearance,
as maintained by operation of the hydraulic slack adjuster
to be now explained.
It will be appreciated that the two-~tage operatîon o~
the pneumatic portion 1 minimizes air usage by initially taking
up the brake shoe clearance through the use of a relatively
small positioning piston 12 and subsequently obtaining the
desired high braking forces by venting air from one side of
a relatively large power piston 16 that is connectad to the
positioning piston 13. Since only low force is required to
move the brake shoes into engagement with the braking suxfaca
o the wheel treads through the brake shoe clearance, whi~h
; constitutes the entire piston stroke, a reduced air require-
ment is realized, as compared to arrangements employing a
single, large piston. In addition, the high force output
required for obtaining the desired brake force i5 obtained
by ~enting only a minimum of air from the release chamber ~3,
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since in the application position, the volume o~ this chamber
23 has been reduced to a minimum s.ize.
In the present invention, the pneumatic output force
realized is converted into hydraulic pressure through hydraulic
piston 28, which eliminates the need for mechanical brake
rigging to obtain the desired output forces.
In order to maintain maximum efficien~y of the pneumatic
portion 1 with respect to air consumptivn, hydraulic portion 2
is provid~d with a double-actiny slack adjuster arrangement to
maintain the brake shoe clearance at a predetermined value.
During the initial stage of operation of pneumatic portion
1, hydraulic piston 28 advances into hydraulic chamher 30 as
~he dual piston assemhly comprising pistons 12 and 16 advances
toward brake application position. During this stroke of t~e
dual piston assembly, sufficient hydraulic fluid in hydraulic
chamber 30 is displaced to ~orce slack adjuster piston 47
fxom i~s normal or release position against shoulder 48 right-
wardly into engagement with cover member 49. During this
displacement of slack adjuster piston 47, the hydraulic fluid
in re~erence ~hamber 43 is forced to flow to the vehicle brake
clrcult via outlet 56. The volume of hydraulic fluid dis-
placed from referenca chamber 43 is selected such that the
predetermined brake shoe clearance will be taken up by move-
: ment of the brake shoes into brake engagement with the wheel
treads. It will be understood that during takeup of this
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brake shoe clearance, the force buildup in reerence chamber43 is relatively low9 since brak~ shoe/wheel engagement has
not ye-t occurred. This force buildup is less than the force
required to overcome the spring bias o~ on~way chec}c ~alve
5 53, which accoxdingly remains closed to prevent hydraulic
fluid from being forced into reservoir 44. Thus, the hydxau7ic
fluid is forced to flow via outlet 56 to the vehicle brake
circuit.
In the event brake shoe/wheel engagement occurs before
the hydraulic fluid in reference chamber 43 is completely dis-
placed; due to premature brake shoe engagement, as would be
the case in applying the brakes ~ollowing instal~ation of new
brake shoes, for example, khe pressure of the remaining
hydraulic fluid in reference chamber 43 will increase ~u~fi-
ciently to o~ercome the spring bias and open ona-way check
valve 53 to allow the excess hydraulic fluid pre~iously
accumulated in the hydxaulic brake circuit during wear-out
of the repla~ed brake shoes to pass into reservoir 44. As
this occurs~ slack adjuster piston 47 will xeach its rightward-
most position abutting cover member 49. It should bs mentionedat this point that the spring bias of one~way check valve 52
in slack adjuster piston 47 is greater than the spring bias
vf one~way check valve 53 to prevent back-~law of hydraulic
fluid from chamber 43 to cha~ber 30 during this time.
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In this rig~tward~most position of slack adjuster piston
47, annular seal 57 engages the skirt of piston 47 tv isolate
any further flow of high pressure hydraulic fluid into reser-
voir 44 via one~way check valve 53. Concurrently, one~way
check valve device 52 carried by piston 47 engages projecting
pin 55 to cause the æprin~-biased ball valve to openO This
allows additional hydraulic fluid to be delivered from hydraulic
chamber 30 to the vahicle hrake circuit via the open one-way
check valve 52 and outlet 56, in the even~ overtravel of the
dual piston assemhly occurs due to braka shoe wear.
During a s~sequent brake release, hydraulic pi~ton 28
is retracted with the dual piston assembly under th~ influence
of return spring 32, t~ereby relieving the high pressure
developed in hydraulic chamber 30 during the preceding brake
1~ application. This permits return ~pring 50 to force slac~
adjuster pi~ton 47 in a leftward direction out o enyagement
with co~er member 49, whereby the ball check valve of one-way
check valve device 52 is closed by its bias spring. As slack
adjuster piston 47 is shifted back to its normal release posi
2n tion into engagement with shoulder 48~ hydraulic fluid in the
braking circuit is drawn back into reference chamber 43,
thereby allowing the brake shoes to be retracted fr~m t~e
wheeL tread braking surfaces. The volume of ~ydraulic fluid
returDed to reference chamber 43 is such that the predeter-
mined ~rake shoe clearance is established.
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The dual piston assembly and hydraulic piston 28 continue
to be retracted toward release position a distance corres-
ponding to any overtravel accumulated during brake application.
Since slack adjuster piston 47 is pre~ented from follow~
ing ~ydraulic piston 28 during this period o~ the release
stro~e, a low pressure is created in chamber 30 sufficient
to open check valve device 45 to admit mak~eup hydraulic fluid
to flow from reservoir 44 to chamber 30 via passageway 46 and
one-way check valve device 45 until complete retraction of the
dual piston assembly occurs, as determined by engagement of
bumpers 17 with pressure head 4. It wi~l be understood at
this point that the spring bias of check valve device 52 is
substantially greater than that of check valve device 45 so
that back-flow o~ hydraulic fluid from chamber 43 to chamb~r
30 cannot occur as this makeup hydraulic fluid is drawn into
chamber 30. Accordingly, brake shoe wear is automatically
aompensated to maintain a predetexmined brake shoe clearance
and thereby assure the optimum operating characteristic o
pneumatic portion 1.
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