Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PISTON SEALI~IG ARRANGEMENT
_ck~ d of_the Invention
This invention relates to piston seals and, more
particularly, to piston seals fzlvorably suited for employment in
an accumulator.
An accumulator has two main functions as used in part oE the
hydraulic circuit. The Eirst function is to store a supply of
pressure-influenced hydraulic fluid to be delivered to the
hydraulic circuit should pressure-influenced fluid be needed on
an emergency basis. The second main function of an accumulator
is to absorb pressure spikes in the hydraulic system.
An accumulator is basically comprised of a housing defining
a cylinder closed at each end having a piston slidably mounted
therein dividing the cylinder into first and second chambers.
The first chamber contains a gas precharge. The second chamber
receives hydraulic fluid at system pressure. Should, for some
reason, the system pressure unexpectedly drop, the gas precharge
will bias the piston to force hydraulic fluid frol~ the second
chamber to the system for emergency operations. When the system
pressure is restored, the second chamber receives a
replenishment of hydraulic Eluid to again be biased by the gas
precharge.
It has been found that over a period of time, the gas
precharge pressure can drop due to leakage making the
accumulator incapable of supplying hydraulic fluid at
sufficiently high pressure for emergency operation. One of the
suspected reasons for the loss of gas precharge pressure is due
to leakage or seepage of the gas precharge from the first
chamber to the second chamber around the piston. When the
piston has bottomed out in the second chamber during a prior
use, a pressure imbalance across the piston develops to motivate
gas to seep past the sealing rings of the pistons resulting in a
reduction of precharge pressure when the first chamber is
replenished for subsequent. Also, when accumulators are used in
off-road vehicles operating in a low-temperature environment~ it
is suspected that a decrease in flexibility and possibly some
contraction of the sealing material around the piston allows the
gas to escape from the first chamber to the second, thereby
dropping the precharge pressure.
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1 Sum~ary of !he Invention
It is an objective of the present invention to present a
piston sealing arrangement part:icularly suited for employment in
an accumulator. The accumulator contains a plurality of piston
heads slidably mounted therein iin spaced apart relationship
dividing the accumulator into two chambers. A generally
incompressible fluid is encapsulated between opposing piston
heads and the interior accumulator wall to provide a fluid or
wet seal between the operative chambers of the accumulator.
Each piston head has an endless cavity therearound facing the
interior wall of the accumulator. Each cavity receives fluid
through a port in the respective piston head to provide
additional sealing capacity. It: is observed that this
arrangement creates a pressure balance across the piston head to
suppress leakage.
Brief Description of the Drawings
FIG. 1 is a sectioned side elevational view of a prior art
accumulator~
FIG. 2 is a side sectional view of an accumulator containing
a sealed piston in compliance with the present invention.
D ailed Description of the Preferred Embodiment
Referring to FIG. 1, a prior art accumulator is shown
including a housing 11 defining a cylindrical chamber 12 closed
at the ends by a respective end cap 27 and 29. A piston 13 is
slidably mounted within the chamber 12. The piston contains a
ringed cavity 15 and a port 17 ]eading from the cavity to the
rearward piston face. Sealing means are provided between the
piston 13 and the chamber wall ]2 by packing rings 19 and 21
located to either side of the cavity 15. The piston 13 divides
chamber 12 into two chamber sect:ions 23 and 25, respectively.
The end cap 27 has an oil port 39 to admit hydraulic fluid to
and from the chamber 25. The end cap 29 has a gas valve 41 to
permit gas charging of chamber 23.
As aforementioned, the prior art accumulator as illustrated
in FIG. 1 has exhibited a tendency to lose its gas precharge
under certain extreme conditions. One possible reason for the
loss of gas precharge is occasioned by total ejection of
hydraulic fluid from the second chamber 25 resulting in the
piston 15 bottoming against end cap 27. The pressure imbalance
thereby created across ring 19 will precipitate loss o~
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recharye g~s lnto cavity 15. Another possibility i5 OCCaSiOrled
by placing the accumulator in an extremely low temperature
environment, which reduces the Elexibility of rings 19 and 21,
thereby degrading the seal to again allow gas seepage into
cavity 25 from the precharge chamber 23.
Referring now to FIG. 2, an accumulator in compliance with
the present invention includes a housing 50 defining a cylinder
chamber 51. A double piston generally indicated as 52 is
composed of first piston head 52a and second piston head 52b
slidably mounted within the cylinder chamber 51. Piston 52a and
52b have an endless cavity 54 and 64, respectively, formed in
their side surface, facing the cylinder wall. Piston 52a and
52b have respective ports 56 and 66 extending from respective
cavity 54 and 64 rearward. A first sealing ring stack 58
precedes the ringed cavity 54. A second ring stack 60 follows
the cavity 54. A sealing ring stack 68 precedes the ringed
cavity 64 formed in piston head 52b and a sealing ring stack 70
follows cavity 54. The sealing ring stacks 6B and 70 are
identical to stack 58 and 60, respectively.
The piston heads 52a and 52b divide the accumulator into a
first section 72 for receiving a gas precharge and a second
section 74 for receiving hydrau:Lic fluid. Sandwiched between
the piston heads 52a and 52b and encapsulated therebetween in
conjunction with the cylinder wall is a generally incompressible
fluid of relatively high density. The fluid encapsulated
occupies the entire space between piston heads 52a and 52b to
place the piston heads 52a and 52b in cooperative motion, i~eO,
piston heads 52a and 52b and the hydraulic fluid move
longitudinally in the cylinder chamber 52 as a unit. The fluid
is injected between the piston heads 52a and 52b during
fabrication through a passage sealed thereafter by a stop 78.
The ends of cylinder 51 are enclosed by end caps 80 and 82,
respectively. The end cap 80 is fixably and sealably mounted to
the housing 50 by any conventional means such as welding at 90
to enclose the chamber section 72. End cap 80 has a
conventional gas valve 92 to permit gas charging of chamber
section 72. The end cap 82 is fixably mounted to housing 52 by
snap ring 86 in a conventional manner. A sealing ring stack 84
identical to stack 58 precedes the snap ring 86. A port 83
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Ytend.s thro~gh the end cap ~2 to conduct hydraulic fluid to and
from chamber section 74.
It is observed that iE the gas chamber 72 is pressurized and
hydraulic Eluid is in the second chamber 74, that there is a
pressure balance across the double piston 52 causing the fluid
between piston heads 52a and 52b to act as a we~ seal, thereby
reducing the possibility of charge-gas seepage. It is also
noted that the benefit of using a generally incompressible Eluid
is that it conforms to the shape of the container and thereby
forms a wet seal which under pressure forbids the penetration by
the charged gas contained in chamber 72. Even in low
temperatures, the wet seal will conform to the shape of the
container to maintain the seal's integrity. Also, should the
piston 52b contact the end wall 82 due to the discharge of fluid
from chamber 74, the pressure balance across the pistons 52a and
52b maintain the integrity of the wet seal. There is also a
pressure balance across seals 5~ and 60.
The present invention has been described in its prefered
embodiment which should not be viewed as limiting the scope of
the invention. The full scope of the present invention is
defined by the appended claims.
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