CA1180979A

CA1180979A - Piston sealing arrangement

Info

Publication number: CA1180979A
Application number: CA000413933A
Authority: CA
Inventors: Douglas M. Gage
Original assignee: Deere and Co
Current assignee: Deere and Co
Priority date: 1981-10-26
Filing date: 1982-10-21
Publication date: 1985-01-15
Also published as: EP0078031A1; DE3271950D1; JPS5881202A; ES8400553A1; EP0078031B1; ES516793A0

Abstract

PISTON SEALING ARRANGEMENT
Abstract of the Disclosure A cylinder piston as employed in an accumulator having a housing defining a cylinder, a plurality of piston heads positioned generally transversely and slidably in the cylinder, a generally incompressable fluid encapsulated between opposing piston heads and a cylinder wall, and sealing means for providing sealing communication between said pistons and said cylinder wall.

Description

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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~

2 --t79 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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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In an accumulator having a housing defining a generally longitudinal extending cylindrical chamber, piston means slidably mounted in said chamber dividing said chamber into a first and second section, a first end cap fixably and sealably mounted to said housing enclosing said first chamber section and having a valve means extending therethrough, and a second end cap fixably and sealably mounted to said housing enclosing said second chamber section and having a port extending therethrough, wherein the improvement includes, said piston means solely consisting of a plurality of piston heads in longitudinally spaced apart relationship, a generally incompressible fluid encapsulated between adjacent piston heads in conjunction with said cylinder's wall, said piston head immediately adjacent to said first chamber having an endless cavity therearound and having a port extending from said cavity rearward of said first chamber to receive a portion of said encapsulated fluid, said cavity encapsulating said portion of the fluid in conjunction with a portion of said chamber's wall, a sealing ring received in said piston head forward of said cavity and continuously abutting to a portion of said chamber's wall.

2. In an accumulator as claimed in claim 1 wherein piston means, further includes a second sealing ring received rearwardly of said endless cavity in said piston head immediately adjacent to said first chamber in continuous communication with a portion of said chamber's wall.

3. In an accumulator having a housing defining a generally longitudinal extending cylindrical chamber, piston means slidably mounted in said chamber dividing said chamber into a first and second chamber section, a first end cap fixably and sealably mounted to said housing enclosing said first chamber section and having a valve means extending therethrough, and a second end cap fixably and slidably mounted to said housing enclosing said second chamber section and having a port extending therethrough, wherein the improvement includes, said piston means solely consisting of a first piston head, a second piston head in longitudinally spaced apart relationship from said first piston head, a generally incompressible fluid encapsulated between said first and second piston heads in onjunction with said chamber's wall, each of said piston heads includes an endless cavity, a port extending from said endless cavity rearwardly of said first chamber, a first seal received in each of said piston heads forward of said respective cavity extending endlessly around said piston head and in continuous communication with a portion of said chamber's wall and a second seal received in each of said piston head rearwardly of respective said cavity extending endlessly around said piston head in continuous communication with a portion of said cylinder's wall.