Seal for a joint or juncture – Seal between relatively movable parts – Brush seal
Reexamination Certificate
1999-02-11
2001-03-06
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
Brush seal
C277S926000
Reexamination Certificate
active
06196550
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to sealing devices disposed in association with two relatively rotatable members and providing a fluid seal therebetween. More particularly, the present invention relates to an apparatus for achieving sealing between a rotating member and a housing circumscribing the rotating member.
BACKGROUND OF THE INVENTION
Gas turbine engines employ sealing devices in various capacities where it is necessary to restrict the flow of fluid or gases from one portion of the engine to another. A common use is for separating the primary engine flowpath from the secondary flowpath. The primary engine flowpath directs the flow of gases to the compressor and turbine stages, from which the engine derives thrust or power. The secondary flowpath comprises a series of conduits for delivering compressed air throughout the engine for performing a variety of functions. Compressed air is used, for example, to cool individual components, provide a bleed air source, buffer the lubricated bearing cavities, control the ventilation among engine cavities and structures, and affect the thrust balance of the engine. Loss of compressed air from the secondary flowpath through leakage can have a substantial adverse effect on the performance of these functions. In a turbine engine, at least one sealing device typically is required for each turbine and compressor stage of the engine.
Another common use for sealing devices in turbine engines is for separating the secondary flowpath from engine cavities containing fluids such as lubricating oil. In pressurized aircraft, bleed air taken from the secondary flowpath supplies the aircraft environmental control system. Even small amounts of oil in the bleed air can render it unsuitable for this purpose. Further, oil leakage can lead to coking of the seal, and ultimately reduced seal life. To prevent this, buffered sealing devices typically are incorporated adjacent lubricated bearings and engine oil sumps.
Among the sealing devices more recently developed is the finger seal. Finger seals are comprised generally of a plurality of flexible members fixed at one end, the opposite ends sealingly engaging a surface that is rotatable relative thereto. The fingers of a finger seal are an integral part of the seal, usually formed by machining a series of curved slots in a forged ring or a length of sheet stock, the slots being of consistent length and extending from a common edge of the material. A complete seal is usually made up of two or more layers of fingers relatively positioned such that the gaps between fingers in one layer are blocked by the fingers of the next layer.
During engine operation, the fingers deform in a generally radially outward direction due to various factors including centrifugal growth of the rotating surface. In order to maintain an effective seal, it is also necessary for the fingers to restore themselves radially inward as the rotating surface shrinks. Fluid pressure acting on the radially deformed fingers, however, causes the fingers to deform axially often resulting in forceful contact between the fingers and adjacent structures. This axial deformation creates a frictional force that hampers radially inward recovery of the fingers as rotational velocity of the rotatable surface subsides. Consequently, the fingers are unable to re-engage the movable surface as it shrinks. Accordingly, the desired seal therebetween is undermined leading to engine inefficiencies.
Accordingly, a need exists for a seal capable of preventing or reducing the frictional forces between the finger members and adjacent structures such that the seal between the finger members and the movable surface is maintained during the full range of engine operation speed and power levels.
SUMMARY OF THE INVENTION
In accordance with the present invention, an annular sealing apparatus is disclosed for disposition in cooperation with a body defining a bore and a rotating member rotatably received in the bore. The bore and rotating member bound a high fluid pressure region and a relatively lower pressure fluid region therebetween. The sealing apparatus inhibits fluid leakage between the high and low fluid pressure regions.
In a preferred embodiment of the invention, the sealing apparatus is comprised of fore and aft annular cover plates. Disposed between these plates are a fore spacer, a sealing element, and an aft spacer. The sealing element comprises a plurality of comb-like diaphragm members extending radially inward from a continuous, circumferential band portion. Each diaphragm member has a plurality of uniformly spaced integral finger members, the foot portions of which sealingly contact the rotating member. The finger members of each diaphragm member have gaps therebetween. Each successive diaphragm member is positioned so that the finger members of each block the finger member gaps of other contiguous diaphragm members. The band portions have a plurality of circumferentially disposed holes which define an axial passage when the diaphragm members are assembled. The fore spacer has a plurality of radial passages which deliver high pressure fluid to the axial passage in the diaphragm members. From the axial pressure the high pressure fluid flows through radial passages in the aft space to cavities in the aft spacer. Thus, the net axial force or thrust exerted on the sealing element is greatly reduced when compared to the prior art configurations that do not have these pressure balancing passages. With this reduced axial force, the frictional force between aft spacer and the sealing element is reduced which eliminates or greatly reduces binding of sealing element against the aft spacer. The sealing element is now free to expand and contract radially as required to maintain sealing.
REFERENCES:
patent: 5108116 (1992-04-01), Johnson et al.
patent: 5799952 (1998-09-01), Morrison et al.
patent: 5884918 (1999-03-01), Basu et al.
Arora Gulshan K.
Glick Donald L.
Allied-Signal Inc.
Desmond, Esq. Robert
Knight Anthony
Peavey Enoch
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