Note: Descriptions are shown in the official language in which they were submitted.
20 6 2 0 4 3
HYDRAULIC--PNEUMATIC CUSHIONING ~EVICE
WITH PRESSURE INDICATOR
Field of the Invention
The invention relates to cushioning or shock absorbing devices
of the type having a sealed interior charged with a volume of
hydraulic fluid and a pressurized gas used for automatic return of
a collapsed device to the normal extended position. These devices
may be used to cushion the coupling of railway cars, closing of
presses or the movement of suspensions in large off-road vehicles.
Description of the Prior Art
Conventional hydraulic--pneumatic cushioning devices are
charged with hydraulic fluid and pressurized nitrogen gas. These
devices are highly reliable and often require little, if any,
maintenance. Railway car hydraulic--pneumatic cushioning devices
may have a life-span of ten or more years without leaking or loss
of internal pressure.
However, occasionally cushioning devices leak hydraulic fluid.
through the piston rod seal. When this occurs, the leaked
hydraulic fluid builds up on the outside of the device and commonly
collects dirt on the bottom of the unit and may promote corrosion
of the exterior of the unit and surrounding support members.
However, a loss of hydraulic fluid is not a positive indication
that the performance of the cushioning device is degraded. An
CA 02062043 1999-03-18
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appreciable volume of hydraulic fluid may be lost from modern
hydraulic--pneumatic cushioning devices before the cushioning
capacity of the device is degraded. This means that a visual
inspection of the cushioning device to determine whether it is wet
or dry does not provide a positive indication of whether or not
the cushioning device works and, for example, is capable of
absorbing shocks between adjacent railway cars during coupling.
The operation efficiency of a hydraulic-pneumatic cushioning
device may be determined by measuring the pressure of the
hydraulic fluid in the device. This pressure is proportional to
the volume of hydraulic fluid in the device. If hydraulic fluid
leaks from the device the volume of the remaining hydraulic fluid
is reduced thereby increasing the volume for the pressurized
nitrogen within the unit and, consequently, reducing the pressure
of the nitrogen. If the measured pressure of the hydraulic fluid
is below a threshold level then there is insufficient fluid
remaining within the device to cushion shocks properly. In
practice, substantial hydraulic fluid may leak from the cushioning
device before the cushioning efficiency of the device is degraded.
This means that pressure within a leaking device may fall
considerably below the charging pressure without degrading the
cushioning efficiency of the device.
It is conventional to test the efficiency of a cushioning
unit by determining the pressure of the hydraulic fluid within the
unit. This test is performed by removing a cap covering a check
valve in the unit, threadably attaching a pressure gauge to the
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check valve and then determining the pressure by reading the gauge.
After the test is performed, the gauge must be unthreaded and the
cover cap reattached. This is a time consuming and difficult
operation, particularly when performed on a railway car cushioning
device located within the frame of the car in a recess accessible
only from below the car. In practice, railway inspectors do not
readily perform this test and, as a result, tend not to check the
actual pressure of the hydraulic fluid in cushioning devices to
determine whether the devices are or are not operating properly.
Another conventional way of determining the amount of
hydraulic fluid in a hydraulic-pneumatic cushioning device is to
provide a standpipe within the pressure chamber in the device and
a window for viewing the standpipe from the outside of the
cushioning device. This method has two problems. First, the use
of a window within the pressure wall of the cushioning device
requires reducing the charging pressure in the device to prevent
leaks and, accordingly, the efficiency of the cushioning device.
Secondly, the window tends to become obscured during use of
the device making a visual determination of the level of the
hydraulic fluid in the device difficult at best and sometimes
impossible when the device is mounted in an inaccessible location.
Hydraulic--pneumatic cushioning devices used for coupling railway
cars are mounted in virtually inaccessible locations under the
railway cars.
Because of the difficulty of determining the actual amount of
hydraulic fluid within a hydraulic-pneumatic cushioning device in
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a railway car and the severe consequence in terms of freight damage
resulting from failure to detect a defective hydraulic--pneumatic
cushioning device, the railroads assume all leaking devices do not
work. All of these devices are removed for reconditioning. Removal
of cushioning devices is a difficult procedure requiring burning or
cutting away of bolts and rivets and lowering of the very heavy
units down from the railway car. During removal of the devices and
shipment to a repair facility it is possible that injury may occur
to the devices, particularly to the exposed piston rods. In
practice, it has been found that only about 30 percent of
hydraulic--pneumatic cushioning devices returned for repair are
defective and require repair. The remaining 70 percent of these
devices work properly, despite the observed hydraulic fluid
leakage. The premature removal, shipment, repair, and
reinstallation of properly operating hydraulic--pneumatic
cushioning devices is difficult, time consuming, expensive and
unnecessary.
Summary of the Invention
The invention relates to a hydraulic--pneumatic cushioning
device with a pressure indicator mounted in the front head of the
device where it is readily accessible for tactile inspection by a
worker checking the condition of the device, a pressure indicator
and a related method. The exposed end of the pressure indicator
has a recess and a small pin that extends into the recess from the
body of the cushioning indicator. The inspector feels the end of
the pressure indicator to sense the position of the pin. If the
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pin is withdrawn into the recess, the inspector immediately knows
that the pressure within the cushioning device is below the
threshold level and, as a result, there is an inadequate volume of
hydraulic fluid within the device. The device is known to be
defective and must be removed and repaired.
If the pin extends outwardly into the recess the inspector
pushes on the pin. If the pin cannot be pushed in or is hard to
push in and returns to the extended position when released,
possibly slowly because of friction, the inspector knows that
pressure within the cushioning device is above the threshold
pressure and there is sufficient hydraulic fluid within the device
for proper cushioning. The device can be left in operation.
However, if the pin is out when first sensed and the inspector
can push the pin flush to the bottom of the recess and the pin
stays withdrawn in withdrawn position and does not return into the
recess or when the pin is found already withdrawn from the recess,
the inspector knows that the pressure within the unit is below the
threshold level, there is insufficient volume of hydraulic fluid
and the device needs to be removed and repaired.
As a matter of precaution, the inspector may conduct a conven-
tional pressure check on the installed cushioning device to confirm
the low pressure as determined by the pressure indicator prior to
removal of the cushioning device.
The pressure indicator is highly reliable to assure proper
operation during the long-term useful life of the cushioning
device. Movement of the indicating pin relative to the recess is
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limited by the frictional loading between a pressure seal and pin,
thereby decreasing incidental movement of the pin during operation
of the cushioning device. As a practical matter, high friction
loading assures that once the cushioning device has been charged
with high pressure nitrogen gas, the pressure exerted on the pin by
the hydraulic fluid in the unit holds the pin in the extended
position within the recess until the pressure should drop below the
threshold level sufficiently to allow a spring in the pressure
indicator to overcome the pressure and retract the pin against the
frictional loading exerted by the seal. The seal is highly reliable
and includes a pressure seal which is biased against the pin by the
internal pressure of the hydraulic fluid in the cushioning device
to prevent leakage. This fluid also lubricates the seal when the
pin is shifted.
Other objects and features of the invention will become
apparent as the description proceeds, especially when taken in
conjunction with the accompanying drawings illustrating the
invention, of which there are three sheets and two embodiments.
In the Drawings
Figure 1 is a perspective view of a hydraulic--pneumatic
cushioning device according to the invention;
Figure 2 is a front view of the device, partially broken away;
and
Figures 3 and 4 are sectional views taken along lines 3--3 and
4--4, respectively, of Figure 2; and
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Figure 5 is a top view of a railway car with a cushioning
device according to the invention.
Description of the Preferred Embodiments
Hydraulic--pneumatic cushioning device 10 includes a cylin-
drical body 12 having a front head 14, rear head 16 and tubular
wall 18 extending between the two heads. An inner piston cylinder
20 is confined within the body inwardly of wall 18 and extends
between and is joined to the two heads as shown in Figure 3. A
series of flow control bores 22 are formed through cylinder 20
adjacent the rear head 16. One way check valves 24 are mounted in
the cylinder adjacent front head 14 to permit hydraulic fluid to
flow outwardly through the cylinder.
Piston 26 is fitted within inner piston cylinder 20 and is
connected to a piston rod 28 extending outwardly through a bore
formed in the front head 14. The piston carries suitable seals 30
for forming a tight seal with the inner surface of cylinder 20 and
preventing flow of hydraulic fluid past the piston. Rod seals 32
are provided in front head 14 to prevent leakage of hydraulic fluid
from the interior of device 10.
The interior of the hydraulic--pneumatic cushioning device 10
includes a fluid reservoir divided into three chambers. Chamber 34
is located mainly within the interior of cylinder 20 and is defined
by the cylinder, the piston 26 and rear head 16. Chamber 36 is
likewise located within the interior of cylinder 20 and is defined
by the cylinder, piston 26 and front head 14. An annular chamber
38 surrounds cylinder 20 and is defined by the cylinder, wall 18
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and the front and rear heads 14 and 16. As shown in Figure 3,
bores 22 communicate chambers 34 and 38. Check valves 24 communi-
cate chambers 36 and 38 and permit one-way flow of hydraulic fluid
from chamber 36 to chamber 38. Check valve 40 located in front
5head 14 also communicates chambers 36 and 38 and permits one-way
flow of hydraulic fluid from chamber 38 to chamber 36.
Charge valve 42 is mounted at the bottom of front head 14 in
order to permit charging the interior cavities of device 10 with a
fluid mixture of hydraulic fluid and pressurized nitrogen gas.
10With the piston in the extended position of Figure 3, the interior
cavities 34, 36 and 38 are filled with hydraulic fluid up to the
level of line 44 with the space above the line filled with
pressurized nitrogen gas. The charge pressure of the nitrogen gas
may be as high as 600 psi. During cushioning, the piston rod 28
lSand piston 26 are moved to the left to decrease the total volume of
chambers 34 and 36 by the volume of the piston rod 28 moved into
cylinder 20 thereby further compressing the nitrogen gas and
raising the level of the hydraulic fluid in chamber 38 to a level
indicated generally by line 46. The compression of the gas during
20operation of the cushioning device may increase the pressure of the
gas exerted on the hydraulic fluid to as much as about 3,000 psi.
During collapse of the cushioning device and movement of
piston 26 toward rear head 16, hydraulic fluid flows outwardly from
chamber 34 through bores 22 and past check valve 40 and into
25chamber 36 to cushion the compression force exerted on the piston
rod 28. When the force is released the pressure exerted by the
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compressed nitrogen gas moves the piston toward front wall 14 and
the piston rod 28 is withdrawn from chamber 36 to increase the
total volume of chamber 34 and thereby return the device to the
position shown in Figure 3. During extension of the device,
5 hydraulic fluid in chamber 36 flows back to chamber 34 through
valves 24, chamber 38 and bores 22. Movement of the piston and rod
back and forth in body 12 serves to thoroughly mix and dissolve the
gas into the hydraulic fluid to form a homogeneous froth.
Accordingly, lines 44 and 46 are indicative of the static levels of
the hydraulic fluid when the device has been inactive for a period
of time sufficient to allow separation of the gas from the
hydraulic fluid.
Cushioning devices 10 are conventionally mounted on railway
cars with the end of the piston rod 28 connected to a coupling for
15 joining adjacent railway cars. However, the cushioning device may
be used with other applications as previously mentioned.
Pressure indicator 48 is mounted in the lower portion of front
head 14 adjacent or contiguous charge valve 42. The indicator
includes a body 50 having a hex head 52 facing outwardly of the
20 front head 14 and a cylindrical portion 54 fitted within a bore in
the front head and a step 56 joining the head and portion. An
enlarged recess 58 is formed in the exterior face of head 52.
Threads 60 on portion 54 engage corresponding threads in the front
head 14 to secure the indicator in place with an O-ring 62 confined
25 between step 56 and a corresponding step 64 formed in the front
head to make a fluid tight seal between the indicator and the front
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head. Large diameter bore 66 extends from the end of the
cylindrical portion 54 to bottom 70 located within head 52. A
small diameter pin bore 72 extends from the bottom 70 into recess
58.
Slide or piston 74 is fitted within bores 66 and 72 and
includes a head 76 slidably engaging the larger bore 66 and a
smaller diameter indicating pin 78 slidably engaging bore 72 such
that shifting of the slide to the right from the position shown in
Figure 4 in solid lines to the position shown in dashed lines moves
the end of the pin into the recess 58. As seen in Figure 4, pin 78
extends outward from head 76. The free or outbound end of the pin
or piston rod 78 serves as a tactile indicator means whereby an
operator, by manually contacting the tactile indicator and pressing
inward on the tactile indicator, can ascertain or sense whether
suitable fluid pressure is available in cushioning device 10.
Step 80 in bore 66 faces away from head 52 and provides a stop
for spring retention washer 82. Spring 84 is confined within the
bore 66 between washer 82 and a flange on slide 74 to bias the
piston or slide 74 to the left as shown in Figure 4. When the
piston or slide is in the full retracted position the spring 84
holds piston head 76 against snap ring 86 mounted in a recess in
bore 66. In this position of the piston 74, pin 78, as shown in
solid lines in Figure 4, is withdrawn completely from recess 58
with the end of the pin lying flush with the bottom of the recess.
Passage 88 in the front head 14 communicates the pressure
indicator bore 66 with chamber 38 of device 10. The pressure
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indicator 48 is located below the level of hydraulic fluid in body
12 so that the pressurized fluid flows into the indicator. A
passage 90 extends from the rear face of head 76 past the head and
opens into bore 66 forward of the head 76. In this way, the
pressurized hydraulic fluid within body 12 flows past the head and
into the bore 66.
A conventional seal washer 92 is seated in the bottom 70 of
bore 66 and includes a rigid annular plastic base 94 and an annular
rubber seal ring 96 mounted on the base. The seal ring faces away
from the recess 58. The seal ring includes inner and outer annular
rubber pressure seals 98 with the inner seal engaging pin 78 and
the outer seal engaging the adjacent wall of bore 66. The high
pressure hydraulic fluid in bore 66 acts on the seals 98 to main-
tain reliable high pressure seals with the pin and bore. The
pressurized hydraulic fluid in bore 66 also provides a lubricant
between the pin and the inner seal 98 to facilitate movement of the
pin without degrading the seal 98.
Bleed passage 100 extends through the thickness of the body 50
a short distance inwardly of step 56. Occasionally, a workman will
start to unthread the pressure indicator 48 from body 12 prior to
relieving the pressure of the hydraulic fluid in the body. During
initial unthreading of the indicator, the step 56 is moved out-
wardly from the adjacent shoulder 64 in the front head thereby
opening the seal previously formed by O-ring 62. The seal at the
shoulder is opened before the pressure indicator 48 is substan-
tially unthreaded from the front head. When the seal is opened,
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CA 02062043 1999-03-18
hydraulic fluid from the interior of the body flows through
passages 88, 90 and 100 and out the opening between the indicator
and the front head. This initial limited flow of pressurized
hydraulic fluid serves as a warning to the worker that the
interior of the cushioning device is highly pressurized and alerts
the worker to rethread the pressure indicator back into the head
to prevent further leakage and possible injury. The flow warns
the worker that proper disassembly of the cushioning device
requires removal of the pressurized hydraulic fluid and gas from
the device using a standard depressurizing procedure through the
port normally closed by charge valve 42.
The metal parts of pressure indicator 48 are preferably made
from stainless steel in order to prevent corrosion and to assure
reliable long-term operation of the indicator.
During normal operation of hydraulic--pneumatic cushioning
device 10 the interior pressure of the hydraulic fluid within the
device is sufficient to move the slide 74 to the dashed line posi-
tion shown in Figure 4 against the force of spring 84, thereby
extending the lead end of indicating pin 78 into the interior of
recess 58. The seal washer 92 has a high friction engagement with
the indicating pin thereby maintaining the pin in the extended
position despite the slight variations in pressure of the
hydraulic fluid. In this position, the spring is collapsed and
the slide piston is bottomed on retention washer 82 and cannot
move further to the right.
2 0 6 2 0 4 3
Hydraulic--pneumatic cushioning devices 10 are highly
reliable. For instance, when used as cushioning devices mounted on
railway cars for absorbing shocks during coupling of cars, the
devices may have useful lives of ten years or longer and may not
require any maintenance during their useful life. This reliability
is desirable because the cushioning devices are mounted within the
railway cars and are relatively inaccessible. The rod seals are
highly reliable and effectively maintain the hydraulic fluid within
the devices without leakage. These units run dry and maintain the
confined nitrogen gas at the original high charging pressure.
Occasionally hydraulic fluid leaks through seals 32 to wet the
underside of the device and attract a build-up of dirt and, on
occasion, form corrosion on surrounding parts. Minimal leakage of
hydraulic fluid from the cushioning device does not affect the
ability of the device to cushion shocks between railway cars. Of
course, if sufficient hydraulic fluid leaks from a cushioning
device the cushioning ability of the device is degraded with the
result that the unit is no longer capable of efficiently absorbing
coupling shocks. In this case, automobiles or other cargo mounted
on the two railway cars being coupled through the cushioning device
may be subjected to undesirably high and potentially damaging
undamped inertial shocks.
The pressure indicator 48 provides a reliable tactile
indicator of the coupling efficiency of the cushioning device 10.
The coupling efficiency can be determined by the position of the
indicator pin 78 in recess 58. There is no need to observe the
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position of the pin or to determine whether the cushioning device
is wet or dry.
An inspector determines the operating condition of the
cushioning device by feeling the exposed end of the pressure
indicator 48 to determine whether the indicating pin 78 extends
into the recess 58 or is withdrawn. If the pin is withdrawn, the
inspector immediately knows that the pressure within the unit is
below an acceptable level and the device will not function properly
to cushion coupling shocks.
If the pin extends into the recess, the inspector manually
pushes the pin in an attempt to move the pin into the body 50. If
the pin is hard to push in and, when released, returns to the
extended position or shortly after being released returns, the
interior of the unit is known to be under high pressure with suffi-
cient hydraulic fluid to assure proper operation. The return of
the pin may be delayed due to the high friction between the pin and
the seal washer 92. However, if the pin is pushed in and stays in
then there is insufficient pressure within the cushioning device to
overcome the pressure of spring 84 and the high friction between
the pin and the seal washer. In such case pressure has been
decreased by leakage of sufficient hydraulic fluid from the
cushioning device to increase the space occupied by the nitrogen
gas and decrease the pressure of the nitrogen gas. In this
condition, with the low pressure insufficient to return the pin to
the extended position, there is insufficient hydraulic fluid within
the cushioning device to assure proper cushioning operation. The
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cushioning device needs to be removed and reconditioned to restore
operating efficiency.
Finally, the inspector may find upon initial inspection, that
pin 78 is withdrawn from recess 58. This is an indication of
insufficient interior pressure and insufficient hydraulic fluid,
requiring removal and reconditioning of the cushioning device.
While the present invention has been described in connection
with a hydraulic-pneumatic cushioning device as used to couple
railway cars, it is clear that the device 10 may also be used for
other applications including shock absorber applications for road
and off-road vehicles, shock absorbers for presses and other types
of machine tools and in other applications using hydraulic--
pneumatic cushioning devices where it is desirable to readily and
easily determine the condition of the device tactilly.
Pressure indicator 48 is disclosed being mounted directly on
the front head 14 of cushioning device 10. Figure 5 illustrates
that device 10 may be mounted on one end of a railway car with the
piston rod extending from the car for coupling with another railway
car. Alternatively, the pressure indicator may be mounted to a
remote location, such as an accessible location on the side or end
of a railway car and connected to the cushioning device by an
appropriate hydraulic line. Figure 5 illustrates cushioning unit
10 mounted on one end of railway car 102 below the railway car
support surface 104 with piston rod 28 extending beyond car end 106
for coupling with another railway car. As illustrated, the railway
car 102 includes a car end 108 located opposite from car end 106
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and opposed sides 110 and 112. The car is supported by conven-
tional wheels 114 and wheel assemblies (not illustrated). Pressure
indicator 116, identical to pressure indicator 48 as previously
described, is mounted on car side 112 with head 118, like head 52,
in an accessible location. The indicator may be mounted on car end
106, if desired. Hydraulic line 120 connects indicator 116 to the
pressurized reservoir within unit 10. In this way, the pressure of
the hydraulic fluid--gas mixture within the reservoir is directly
communicated to the interior of the pressure indicator 116 through
the line 120 to permit use of the remote indicator 116 in exactly
the same way as previously described. The advantage of a remote
location of the indicator is that the pressure in the cushioning
device can be easily checked without the necessity of reaching
under the railway car, locating the cushioning device and the
pressure indicator directly mounted on the device and then tactilly
sensing the pressure within the device. With a pressure indicator
mounted in an accessible remote location, this operation is easily
and rapidly performed.
A plastic cover (not illustrated) may be mounted on the
exposed end of head 52 to cover the recess and pin and prevent an
accumulation of dirt within the recess. The cover is easily
removed during determination of the pressure within the cushioning
device and then replaced after the test has been conducted.
While I have illustrated and described a preferred embodiment
of my invention, it is understood that this is capable of modifica-
tion, and I therefore do not wish to be limited to the precise
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details set forth, but desire to avail myself of such changes and
alterations as fall within the purview of the following claims.
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