Note: Descriptions are shown in the official language in which they were submitted.
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"IMPROVED GAS SPRING"
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is based on, and claims priority from, U.S.
s provisional application Serial No. 60/149,754, filed August 19, 1999, and
entitled: "Improved Double Stop Dynamic Gas Spring," which provisional
application is incorporated herein, in its entirety, by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an improved gas spring, and more
io particularly, to an improved multiple stop gas spring where the movement of
the gas spring shaft may be selectively stopped at one or more positions,
intermediate and during the shaft's normal stroke of travel, and additionally
or
alternatively, may be decelerated before it comes to its normal, prescribed
mechanical stop at the end of its normal stroke.
~s Gas springs have been used in many fields to facilitate and control the
movement of movable objects with respect to relatively fixed objects. One
field in which gas springs have found widespread utility is the automotive
field
where they have been employed to facilitate and control the movement of
hatches, lids and lift gates. Generally speaking, gas springs include, among
20 other components: a tube or cylinder that defines an internal tubular
cavity
extending between the ends of the tube; a metering piston assembly, which is
reciprocally moveable within and which divides the tubular cavity into
compression and extension working chambers; a shaft connected moveable
with the piston assembly, with one end of the shaft projecting out of an end
of
2s the tubular cavity; and end closures or caps for closing the ends of the
tubular
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cavity, with one of the end closures also including a bushing seal for the
reciprocally moveable shaft as it moves with respect to the tube.
In conventional gas springs, the projecting end of the shaft may extend
or retract at a nominal rate through its normal stroke due to the metering of
s the gas across the piston assembly. In some gas spring applications, the
movement of the gas spring shaft has been decelerated -- during the
extension stroke of the gas spring and before the shaft is extended fully
mechanically stopped by including a higher viscosity fluid in the tubular
cavity.
The inclusion of such fluid causes the piston assembly to slow incrementally
io and provides an end-of-travel "cushioned" stop. This use of the higher
viscosity fluid to achieve end-of-travel damping is, however, orientation
sensitive. The gas spring must be in a shaft-down orientation through its
extension stroke or else the higher viscosity fluid will meter through the
metering piston assembly prematurely, and the end-of-travel damping feature
is is lost.
In many automotive environments (for instance, when gas springs are
used with hatchbacks), this required shaft-down orientation cannot be
maintained. Hence, end-of-travel damping has been unavailable in such "flip
over" automotive environments without significant component additions that
2o cause the price of the gas spring systems to be increased significantly.
In conventional gas springs, the spring, or more particularly the
projecting end of the shaft, extends at a nominal rate for the majority of the
stroke. (This rate is determined, in large part, by the gas metering orifice
in
the piston assembly). The extending movement, as noted above, may be
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decelerated under certain circumstances before coming to a mechanical stop
at the end of the stroke by including a higher viscosity fluid in the tubular
cavity. However, having the shaft make intermediate stops, that is, stopping
the movement of the shaft between the end of a stroke, has not been
attainable without significant external component additions and features that
increase the price of the gas spring system dramatically.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide an improved
gas spring having novel structure that enables the gas spring to be capable of
io having the shaft make an intermediate stops) at one or more positions
during
its stroke between its fully closed and fully opened positions, and
additionally
or alternatively, being capable of decelerating ar slowing incrementally the
movement of the shaft, as the shaft approaches the end of its stroke, so as to
afford a cushioned stop at the end of the stroke.
is Another object of the present invention is to provide an improved gas
spring of the type described where the gas spring includes a tubular cavity
that has one or more sections in which the ID is different from the ID of the
other remaining sections of the tubular cavity, and where the shaft of the gas
spring also includes a novel second piston assembly (called the "stop piston
2o assembly" herein) that cooperates with a different ID section to cause the
shaft to make an intermediate stop and/or, additionally or alternatively, to
achieve an end of travel damping of the shaft movement.
Still another object of the present invention is to provide an improved
gas spring of the type described where shaft movement may continue, after
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an intermediate stop, by applying an external force to the shaft so as to move
the stop piston assembly away from being adjacent to the different ID section.
A further object of the present invention is to provide an improved gas
spring of the type described where the gas spring may be manufactured for
s sale at an acceptable price (particularly in the highly competitive price
conscious auto industry), and is capable of making intermediate stops(s)
and/or end of stroke damping, both without regard to the orientation of the
gas
spring and either during the extension stroke or during the compression stroke
of the shaft.
to A still further object of the present invention is to provide an improved
gas spring of the type described where the gas spring includes a tube or
cylinder that has a first closed end (which is adapted to be connected with
one
of a moveable object or a relatively fixed object), a second end and a tubular
cavity (which extends between the tube's ends and which is adapted to be
is filled with gas under pressure during gas spring usage) and that has at
least
one first axially longitudinally extending section in the tubular cavity, with
this
first section having a preselected ID; a shaft that has a first end and a
second
end {which is adapted to be connected with the other of the moveable object
or relatively fixed object), that is disposed, in part, in the tubular cavity
so that
2o the longitudinal axes of the tube and the shaft are coaxial, so that its
first end
is within and its second end is without the tube, and so that the shaft may
reciprocally move, selectively in a first axial direction or a second axial
direction, through a preselected stroke, and with respect to the tube; a
bushing assembly that provides a gas seal about the shaft as the shaft moves
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with respect to the tube; a metering piston assembly that is connected and
moveable with the shaft in the tubular cavity, and that meters the passage of
gas across the metering piston assembly as the shaft and the metering piston
assembly move in the tubular cavity; and where the tubular cavity has at least
s one second, longitudinally or axially extending section that has a
preselected
ID, which is different than the ID of the first section; and a second or stop
piston assembly that is connected and moves with the shaft in the tubular
cavity and that selectively restricts the passage of gas across the stop
piston
assembly when the shaft is moved in the first direction with respect to the
tube
io and when the stop piston assembly is adjacent a second section of the
tubular
cavity.
A related object of the present invention is to provide an improved gas
spring of the type described where the stop piston assembly is connected with
the shaft a preselected distance longitudinally or axially from the metering
is piston assembly; and where the ID of each first section of the tubular
cavity is
larger than the ID of each second section of the tubular cavity. A still
further
related object of the present invention is to provide a gas spring of the type
described where the longitudinal or axial distance between the metering
piston assembly and the stop piston assembly is selected so that the metering
2o piston assembly remains substantially adjacent to a first section of the
tubular
cavity during movement of the shaft through its preselected stroke
These and other objects, benefits and advantages of the present
invention will be more apparent from the following description of the drawings
and the preferred embodiments of the present invention.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 illustrates the use of an improved gas spring of the present
invention with a hatchback style automobile where the lift gate is in its
fully
open position.
FIGURE 2 is similar to the illustration of FIGURE 1 but where the lift
gate is shown in a less than fully open position due to the gas spring having
stopped in an intermediate position, that is, at a position that is less than
its
fully extended stroke position.
FIGURE 3 is an axial, cross-sectional view of one embodiment of an
io improved gas spring of the present invention.
FIGURE 4 is an enlarged, cross-sectional view of the stop piston
assembly and the metering piston assembly of the gas spring of FIGURE 3
showing the flow path of the gas passing across these assemblies during an
extension stroke of the gas spring and while these assemblies are adjacent to
is a larger, base ID section of the tubular cavity of the gas spring tube.
FIGURE 5 is a cross-sectional view, similar to FIGURE 4, showing the
flow path of gas passing across the stop piston assembly and the metering
piston assembly during a compression stroke of the gas spring and while
these assemblies are adjacent to a larger base ID section of the tubular
cavity
20 of the gas spring tube.
FIGURE 6 is a cross-sectional view, similar to FIGURE 4, showing the
flow path of the gas passing across the stop piston assembly and the
metering piston assembly during an extension stroke of the gas spring and
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while the assemblies are adjacent to a reduced section of the tubular cavity
of
the tube.
FIGURE 7 is a cross-sectional view, similar to FIGURE 4, showing the
flow path of the gas across the stop piston assembly and the metering piston
assembly during a compression stroke and while the assemblies are adjacent
to a reduced ID section of the tubular cavity of the tube.
FIGURE 8 is an enlarged cross-sectional view of the stop piston
assembly and the metering piston assembly where the stop piston assembly
is connected with the shaft so that an intermediate stops) and/or end-of
travel
~o damping function may be achieved during a compression stroke of the gas
spring.
FIGURE 9 is a cross-sectional view, similar to FIGURE 3, of the
presently most preferred embodiment of a gas spring of the present invention.
FIGURES 10-12 are cross-sectional views of an illustrative tube, a
is flexible stop seal and a backing plate, respectively, that are components
of
the stop piston assembly of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENTS OF THE INVENTION
2o Overview:
Improved gas springs of the present invention have particular utility in
the automotive field because they can be relatively inexpensively
manufactured and provide commercially important features not found in any
previously available gas spring. As illustrated in FIGURES 1 and 2, a gas
2s spring (indicated generally at 20) of the present invention may be employed
to
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hold the lift gate 22 of a hatchback automobile 24 in a fully opened position
(FIGURE 1 ) or in an intermediate or partially opened position (FIGURE 2).
The ability to position the lift gate 22 at an intermediate position, such as
shown in FIGURE 2, is a desirable "selling" feature because, for example, it
s permits persons of shorter stature to be able to easily lift the lift gate
22 to a
position where ready access can be obtained to the rear compartment of the
automobile 24 while not having to strain to reach the lift gate when trying to
close the gate.
The lift gate 22 can be moved from a closed position to the
io intermediate position, as shown in FIGURE 2, by opening the lift gate latch
and pushing, in a normal manner, the lift gate upwardly. The lift gate 22 then
stops at this intermediate position "automatically," that is, without any
further
effort on the part of the person. If for some reason it is a desire to move
the
lift gate from the intermediate position, shown in FIGURE 2, to the fully open
is position, shown in FIGURE 1, the person need only briefly apply external
force to the lift gate, and the gas spring will then move the lift gate 22
from its
intermediate position to its fully open position. Another advantageous feature
of the improved gas spring of the present invention is that the lift gate 22,
whether in its intermediate or fully open position, may be returned to a
closed
2o position in the same manner and using the same force that would be required
if a conventional gas spring had been employed instead.
Gas springs of the present invention are also capable of providing end-
of travel damping or slowing down of the rate of movement of the lift gate 22
as it moves to its fully open position. This, too, is an advantageous
"selling"
a
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feature since it prevents the jarring and shaking of the lift gate as it is
mechanically stopped when the lift gate reaches its fully opened position.
To achieve these commercially important, consumer pleasing
advantages, the improved gas spring of the present invention incorporates a
s tubular cavity that has a variations) in its inside diameter or ID profiles
so as
to provide stopping zones or sections and/or deceleration or damping zones
or sections. In other words, the ID's of one or more sections or zones of the
tubular cavity are varied with respect to the other sections) or zone(s). In
this
regard, the tubular cavity may initially have a uniform, "base" ID, and in
certain
io selected sections, the ID is preferably reduced vis-a-vis the "base" ID.
ID profile variations are formed by expanding or be reducing the tube.
Tube expansion or reduction may be accomplished by the use of several
means, such as form rollers, hydroforming, or expanding mandrells, on the
surface of the tubing so as to reduce or expand the tubular cavity ID by a
is preselected dimension. This cylindricity of the tube is maintained
throughout
the process by incorporating appropriate fixturing which prevents the tube
from deforming outside of the specific ID sections.
A novel piston assembly, called a stop piston assembly herein, is
adapted to cooperate with the reduced tube ID (when the shaft is moving in
20 one direction, normally, its extension direction) section so as to provide
a
necessary sealing action for an intermediate stop and/or for an end-of-travel
damping. A good sealing interface between the stop piston assembly and the
reduced ID section is required whenever and wherever an intermediate stop
or damping is desired.
9
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wo oman~a Pc~rivsoonzss6
Any number of expanded or reduced ID sections may be incorporated
in an improved gas spring of the present invention. The number of such
sections will be determined by the requirements of the application to which
the
gas spring is to be employed.
s As noted, the improved gas springs of the present invention may have
reduced ID sections which will provide for intermediate stopping of the
movement of the shaft and/or will provide end-of travel damping regardless of
orientation of the gas spring. The fatter reduced ID sections causes the shaft
to slow incrementally as the shaft approaches its end-of stroke, that is, is
io about to be mechanically stopped in a conventional manner.
The degree of reduction of the ID in a reduced ID section relates to a
reduction in the velocity of the spring's extension (or compression) rate of
movement through the section. The basic operation of the improved gas
spring of the present invention is identical whether the reduced ID section is
is intended to bring the gas spring to an intermediate stop or to dampen the
movement of the gas spring. Preferably, however, achieving a damping
function requires a smaller pressure differential, that is, requires a smaller
reduction in the ID of the section as compared to the base ID of the tubular
cavity (In practice, the same ID reduction may be used to achieve both the
2o intermediate stop and damping functions).
The damping of the movement of the gas spring shaft does not have to
occur only at or near the end of the stroke of the shaft. Rather this damping
function, like the stopping function, may be located anywhere within the
tubular cavity. In other words, the precise location of a reduced ID section
for
io
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achieving an intermediate stop function or damping function may be readily
accomplished anywhere along the length of the tube (within the travel range),
and thus along the stroke of the shaft, forming different ID profiles for the
appropriate function at the desired locations.
A novel and intentional feature of the stop piston assembly of the
present invention, which cooperates with the reduced ID sections of the
tubular cavity to achieve an intermediate stop andlor damping function(s), is
functional in only one direction. In other words, if the stop piston assembly
is
used to provide these functions during the extension stroke, then the stop
io piston assembly is functionally "invisible" during the dynamic compression
stroke, that is, the assembly does not cooperate with the reduced ID
sections) to provide any damping and/or intermediate stopping function
during the compression stroke. Alternatively, the stop piston assembly may
be used so as to provide an intermediate stop andlor damping functions)
is during the compression stroke of the gas spring, but when so used, is
functionally "invisible" during the extension stroke, that is, the stop piston
assembly does not cooperate with the reduced ID sections) to provide for an
intermediate stop and/or damping function during the extension stroke.
When the stop piston assembly is used to afford an intermediate stop
2o and/or damping function during the compression stroke, the gas spring would
be employed in applications) that would or should require a greater force to
compress the gas spring through a portion of its stroke and then return it to
standard or normal operation. Thus, this gas spring might be used as a semi-
locking device, holding an object up or open and requiring a greater than
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normal force to initiate a closing motion. Additionally, the stop piston
assembly could be made so that it would intentionally have a stopping
function in both directions of travel, such as a bi-direction stopping
function,
would have utility with, for instance, tanning bed covers.
s As will be described in more detail hereinafter, the novel stop piston
assembly may be disposed or positioned adjacent a metering piston
assembly. It is, however, presently most preferred that the stop piston
assembly be spaced longitudinally or axially from the metering piston
assembly, and that the spacing be selected so that, to the extent practical,
the
to metering piston assembly does not ever become adjacent to or in contact
with
a reduced ID section of the tubular cavity. So, separating the two piston
assemblies affords a significant improvement in the number of cycles to
failure. This improvement was achieved, it is believed, because of reduced
side loading on the seals in the gas spring and results in a longer seal life
and
is longer acceptable gas and oil leakage.
More Detailed Description:
Turning now to FIGURES 3-7, an improved gas spring 26 of the
present invention includes a cylindrical tube 28 that has a first end 32 and a
second end 34. The tube 28 includes a tubular cavity 36, which is adapted to
2o be filled with gas under pressure as is conventional in the gas spring art.
A
conventional end cap 3$ closes and seals the first end of the tube 28.
The gas spring 26 also includes a reciprocally moveable shaft 42. As
is conventional, the shaft is disposed, in part, in the tubular cavity 36 so
that
the longitudinal axes of the shaft and the tubular cavity are coaxial. The
shaft
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has a first end 44, which is adjacent to the first end 32 of the tube 28 and a
second end 46, which projects out of the tube.
A conventional bushing assembly 48 is disposed adjacent the second
end 34 of the tube and surrounds the shaft 42 so as to provide a gas and oil
s seal for the shaft as the shaft reciprocally moves within the tube 28 in a
conventional manner. The bushing assembly 48 includes a front bushing 52,
an O-ring 54, a TeflonC~ washer 56, an annular front seal 58 and an annular
bushing back 62, which may be optional. The bushing 52 is generally cup-
shaped, with an open end of the "cup" facing to the right and the closed base
to of the "cup" facing to the left, as seen in FIGURE 3. The °O" ring
54 seals
between the bushing 52 and the ID of the tubular cavity, adjacent the end 34.
The washer 56 is disposed about the shaft 42 and between the right facing
surface (as seen in FIGURE 3) of the bottom of the "'cup" of bushing 52 and
the front seal 58, which is also disposed about the shaft and within the "cup"
is of bushing 52. The optional bushing back 62 is axially spaced, rightward
(as
seen in FIGURE 3) from the seal 58, is disposed about the shaft, and is
supported in the distal end of the bushing 52 "cup."
Two piston assemblies, that is, a metering piston assembly 64 and a
novel stop piston assembly 66, are both connected with and moveable with
2o the shaft 42. More particularly, and as shown in FIGURE 3, the assembly 64
is connected with the front end 44 of the shaft. The metering piston assembly
64 may be of conventional design and function and serves to divide the
tubular cavity 36 into an extension working chamber, which is between the
assembly 64 (and the assembly 66) and the end 34, and a compression
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working chamber, which is between the assembly 64 and the end 32. The
assembly also functions to meter the flow of gas past the metering piston
assembly as the assembly 64 moves, with the shaft 42, in the tubular cavity
36.
s As shown in FIGURES 3-7, the assembly 64 includes an orifice plate
68 and an O-ring shuttle valve 72. The shuttle valve 72 includes an annular
recess that faces the orifice plate 68 and receives therein an O-ring 74. A
washer 76 is disposed between the O-ring 74 and the facing (left in FIGURE
3) side of the plate 68. The relative dimensions of the orifice in the plate
68,
to valve 72, O-ring 74 and washer 76 determine the rate at which gas can be
metered or passed across the assembly 64.
As noted, the stop piston assembly 66 is of novel design and
construction and serves to permit the gas to pass freely, without significant
metering across the assembly 66 when the assembly is adjacent those
is sections of the tubular cavity 36 which have a "base" 1D, that is, the ID
that
would be present if only the metering piston assembly were connected with
the shaft 42. The base ID is indicated at ID1 in FIGURE 10.
The stop piston assembly 66 includes an annular stop seal shuttle
valve member 78 that abuts a shoulder on the shaft 42 and is adjacent to the
2o end 46 of the shaft. The member 78 includes a radially extending portion
80,
which abuts the shaft shoulder, and a central portion 82 that projects toward
the end 32 of the tube. The OD of the portion 80 is slightly less than the ID
of
any section of the tubular cavity, and the OD of the portion 82 is less than
the
OD of the portion 80. A backing plate 84 is mounted on the shaft adjacent to
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the distal end of the central portion 82, that is, the end closest to the tube
end
32. An annular. resilient stop seal 86 is mounted about the central n~rti~n R2
2o a preselected sections) or zone(s), such as sections 96 and 98 (whose ID's
are indicated by ID2 in FIGURE 10), so that in these sections, 96 and 98, the
lip portion 92 of the stop seal 86 may come into sealing contact with the ID
of
the section so as to cause an intermediate stop (section 96) and/or damping
(section 98) of the movement of the shaft with respect to the tube. In other
or
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base sections of the tubular cavity 36, such as sections 102, shown generally
in FIGURE 10, the ID of the sections 102 (which ID's are indicated at ID1 in
FIGURE 10) is selected so that the lip portion 92 cannot come into sealing
contact with the ID of the section 102. In these latter sections 102, the
s movement of the shaft proceeds as in a conventional gas spring since the
stop piston assembly 66 has no functional effect on the operation of the gas
spring.
As is conventional, the stop groove or radially inward projection 104
formed in the tube 28, adjacent the bushing assembly 48. The stop groove
l0 104 has an ID, which is smaller than the ID's of sections 96 and 98, and
which
is indicated by ID3 in FIGURE 10, and serves to mechanically stops the shaft
42, and the end of its stroke, by the contact between the end portion 80 of
the
valve member 78 and the groove 104. By having a damping section 98
adjacent to the groove 104 (that is, to the right of the groove as shown in
is FIGURE 3), the shaft will come to a cushioned stop just as the portion 80
comes into contact with the groove 104.
FIGURES 4 and 5 illustrate how the gas in the tubular cavity 36 may
pass across both the metering piston assembly 64 and the stop piston
assembly 66 when the shaft is moved in the extension direction (FIGURE 4)
zo and in the compression direction (FIGURE 5) while these assemblies are in
or
adjacent a base ID section, such as the section 102. FIGURE fi illustrates
how the reverse stop seal 86 and backing plate 84 cooperate so that the lip
portion 92 will block the passage of the gas across or past the assembly 66
when the shaft 42 is moved in the extension direction, and the stop piston
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assembly fib is adjacent a stop or damping section, such as the sections 96
and 98, respectively. FIGURE 7 illustrates how the gas is able to pass across
both the assemblies 64 and 66 when the shaft 42 is moved in a compression
direction even though the assemblies are disposed in or adjacent to a stop or
s a damping section, such as sections 96 and 98, respectively. In this latter
instance, that is, when the shaft 42 is moved in the compression direction
while the stop piston assembly 66 is adjacent to a section 96 and/or section
98, the stop seal 86 shuttles axially away from contact with the backing plate
84 and into contact with the portion 80 of the member 78 so that gas can pass
~o in the annular space between the ID of the seal 86 and OD of the portion 82
of the member 78.
As noted above, the most preferred embodiment of the present
invention is a gas spring in which the metering piston assembly 64 is
connected with the shaft 42 at or substantially at the end 44 of the shaft 42
Is and in which the stop piston assembly 66 is connected with the shaft 42 an
axial distance from the end 44, toward the end 46 of the shaft. Such a gas
spring 106 is illustrated in FIGURE 9.
The gas spring 106 is structurally and functionally identical to the gas
spring 26, as shown in FIGURES 3-7 (and the stop piston assembly 66 may
2o also be employed as in FIGURE 8), except as noted below and except for the
distance or axial spacing between the assemblies 64 and 66. The backing
plate 84 includes an integral, annular, axially extending portion 108 that
fits
about the shaft 42 and that extends between the plate 84 and shuttle valve
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72. The OD of the portion 108 may be approximately the same as the OD of
the central portion 82 of the valve member 78.
Preferably, the distance or axial spacing between the assemblies 64
and 66 is selected so that, during all or as much as possible, of the stroke,
the
s metering piston assembly 64 will remain adjacent to section 102 (that is, a
section having a base ID). Selecting such a distance or spacing, and thus
reducing the travel of the assembly 64 through reduced ID sections 96 and 98
minimizes the side loading on, and hence wear on the seals. This results in
longer part lives and reduced gas and oil leakage.
io As shown in FIGURE 9, the gas spring 106 includes an alternative,
conventional front bushing assembly 110. Specifically, the assembly 110
includes a front bushing 112, which is adjacent the end 34 of the tube 28, and
a front seal 114, which is disposed adjacent the stop groove 104. A Teflon~
washer 116 is disposed between the bushing 112 and the front seal 114. The
is bushing assembly 110 functions, like the assembly 48, to provide a gas and
oil seal around the shaft 42 and at the end 34 as the shaft reciprocates and
when the shaft is stationary. The assembly 110 may be used interchangeably
with the assembly 48.
As noted above, the stop piston assembly 66 may be disposed on the
2o shaft 42 such that it will function to cause movement of the shaft to stop
or
dampen when the shaft is moved in the compression direction as opposed to
the extension direction. As shown best in FIGURE 8, the assembly 66
contains the same components when it is used to stop or dampen the shaft
moving in the compression direction as when the stop piston assembly 66 is
ig
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used to achieve or use a dampening function in the extension direction. As
illustrated in FIGURE 8, however, the components of the stop piston
assembly 66 are in a reversed (mirror image) arrangement when used to
provide the stop or damping functions when the shaft 42 moves in the
s compression direction.
The stop piston assembly 66 provides an intermediate stop and/or
damping function due to the creation of a prescribed pressure differential
caused by the contact between the lip portion 92 of the seal 86 and the ID of
the tubular cavity in those sections 96 and 98 that have a reduced diameter or
io ID. The desired pressure differential is determined by the geometry of the
stop seal 86, the properties of the stop seal material, and the diameter and
shape of the supporting backing plate 84. By increasing the OD of the
backing plate 84, the lip portion 92 will stand higher pressures before
deforming and bypassing due to a pressure differential. By reducing the OD,
is the lip portion 92 will deflect and bypass at a lower pressure
differential. The
use of the plate 84 with the seal 86 allows those working in this art to
"tailor"
the stop piston assembly 66 for individual gas spring applications.
Also, and as noted above, the intermediate stop position of the gas
seal of the present invention is a function of the location of the reduced ID
2o section, such as sections 96 and 98. Another feature of the improved gas
spring of the present invention and particularly the stop piston assembly 66
is
the shuttling action of the seal 86. This shuttling feature permits the stop
and
damping functions to be "invisible" (to a user) when the shaft is moved in the
direction other than the direction in which those functions are intended to be
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achieved. This shuttling is achieved by utilizing the difference between the
OD of the lip portion 92 and the ID of the reduced ID sections, such as
sections 96 and 98, to "pull" the seal off of the backing plate 84 and thereby
allow a hatch or lid, for example, to be shut quickly and easily without the
s intermediate stop or damping.
As also noted above, once the stop piston assembly 66 is adjacent to
the stop section (such as section 96) so as to cause an intermediate stop in
the shaft movement, an externally extending force (assuming that the stop
piston assembly 66 is being used to function in the shaft extension direction)
io may be applied to the end 46 of the shaft 42 so that the stop piston
assembly
66 is pulled axially beyond the section 96. The gas spring 26 then extends
normally since the gas can once again pass across the stop piston assembly
66 and the assembly 64. The force required to "pull" the stop piston assembly
66 across a stop section 96 is a function of: the length of the stop section
96,
is the net effective force of the gas spring on the application such as the
hatch,
the portion of gas volume on the shaft side of the stop piston assembly 66 vs.
the non-shaft side of the stop piston assembly 66, and the OD of the backing
plate 84.
The seal 86 preferably be made from a material that has a predictable
2o force/pressure balance to counter a differential pressure applied across
it.
Such materials may include EPDM (the presently preferred material),
elastomeric_materiaf, rubber, TPR, etc. Any material used for the seal 86
should provide a near absolute seal in stop sections, such as section 96. A
differential pressure creates a robust stop.
CA 02347498 2001-04-12
WO 01/14764 PCTNS00/22556
While particular elements, embodiments and applications of the
present invention have been shown and described, it will be understood that
the present invention is not limited to these descriptions and showings since
modifications can be made by those skilled in the art, particularly in light
of
teachings herein. It is therefore contemplated that the appended claims will
incorporate all such modifications that fairly come within the spirit and
scope
of the invention.
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