Rotary kinetic fluid motors or pumps – Bearing – seal – or liner between shaft or shaft sleeve and... – Seal
Reexamination Certificate
1999-12-20
2001-07-03
Verdier, Christopher (Department: 3745)
Rotary kinetic fluid motors or pumps
Bearing, seal, or liner between shaft or shaft sleeve and...
Seal
C415S174200, C415S174500, C277S355000
Reexamination Certificate
active
06254344
ABSTRACT:
THE FIELD OF THE INVENTION
The present invention relates generally to a seal arrangement and in particular to improvements to brush seals.
BACKGROUND OF THE INVENTION
It is often necessary to effect a fluid tight seal between two components, and in particular between a rotating shaft and a stationary housing. One type of seal that has been used, especially within the gas turbine engine field, is a brush seal. Such seals have been used within gas turbine engines to seal a gap between a rotating shaft, typically rotating at high speed, and a stationary housing where regions of higher pressure and lower pressure air, which may also be at an elevated temperature, respectively exists on each side of the seal.
Brush seals comprise a plurality of densely packed bristles sandwiched between a front plate and a backing plate. The bristles, and front and backing plate, are all attached to either of the stationary housing or the rotating shaft with the bristles extending across the gap between the shaft and housing to a sealing surface on the other of the shaft or housing. The bristles extend further than the backing plate with the free ends of the bristles generally just touching the sealing surface, or being in close proximity to it. The bristles thereby present a physical barrier to the fluid so sealing the gap between the housing and shaft.
The backing plate provides axial support to the bristles and also, since it is a solid member, partially obstructs the gap between the housing and the shaft. Consequently the backing plate is generally arranged to extend across the majority of the gap between the housing and shaft with a clearance being provided between the free end of the backing plate and the sealing surface to prevent interference between the backing plate and the shaft or housing. This clearance being sealed by the bristles that extend beyond the end of the backing plate and which are compliant so as to flex in response to the shaft movement.
Differential thermal growth, centrifugal growth of the shaft, engine manoeuvring, and build tolerances can all reduce the clearance between the backing plate and the seal surface. In the worst case in which the clearance is reduced to zero the backing plate contacts the seal surface causing unacceptable irreversible damage to the backing plate and seal surface. Consequently a sufficiently large clearance is provided between the backing plate and the sealing surface to accommodate the anticipated reduction in the clearance during operation. Unfortunately the provision of such a large clearance reduces the seal performance. Additionally due to the large clearance required the bristles can bend under the backing plate further reducing the seal performance and causing damage to the bristles.
It is therefore desirable to provide a seal arrangement which addresses the above mentioned problems in which the clearance between the backing ring and the sealing surface is minimised whilst ensuring that excessive interference between the backing plate and the sealing surface does no occur. It is also desirable to provide the improvements to such seals generally.
SUMMARY OF THE INVENTION
According to the present invention there is provided an annular seal comprising a mass of bristles packed together in a layer axially adjacent to an annular backing plate, the bristles and backing plate, in use, are arranged to be mounted on and extend from a radially outer member towards and around a cylindrical inner member, the bristles having free ends which extend radially further than the backing plate and which are arranged to operationally co-operate with the inner cylindrical member to form a seal thereagainst, said outer member and inner cylindrical member arranged in use for relative rotational movement about the axis of the cylindrical inner member; characterised in that the seal further comprises an expansion ring disposed radially inwardly of the backing plate and mounted from the backing plate in substantially the same plane as the backing plate via a suitable mounting means which are arranged to permit radial movement of the expansion ring relative to the backing plate and the operational position of the inner cylindrical member.
The expansion ring mounted from the lower portion of the backing plate can move radially. Consequently the expansion ring can move radially away from the inner cylindrical member if, or when, the expansion contacts the inner cylindrical component. This alleviates the risk of damage to the inner cylindrical member and backing plate, by such contact caused by the relative movement of the backing plate and inner cylindrical member. This thereby allows the clearance between the backing member and the seal surface to be minimised during all conditions thereby improving the seal performance.
Preferably the expansion ring is adapted such that, when in use, frictional heating of the expansion ring when the expansion ring is in contact with and the inner cylindrical member causes the expansion ring to expand radially away from the inner cylindrical member.
Furthermore the expansion ring may have a low thermal mass as compared to the backing plate and inner cylindrical member. Preferably the expansion ring is made from a high expansion material.
Since the expansion ring has a low thermal mass when the expansion ring contacts the inner cylindrical component (shaft) the rapid frictional heating which occurs causes the expansion ring to rapidly expand and increase in diameter. Thereby in effect the expansion ring rapidly moves out of contact with tine inner cylindrical member.
The expansion ring may be operationally arranged to initially be in contact with the inner cylindrical member when there is no relative rotational movement.
Preferably the mounting means comprise resilient mounting means. The resilient mounting means may be biased in a radially inward direction. Preferably the mounting means comprise an annular spring with substantially U shaped circumferential cross section. The annular spring may be slotted. An annular shield member may also be provided to obstruct a flow of fluid into the open end of the annular spring.
Preferably the seal is arranged to be used with the inner cylindrical member adapted to rotate within the stationary outer member. Alternatively the annular seal may be arranged to be used with the outer member adapted to rotate about the stationary inner cylindrical member.
Preferably the expansion ring comprises at least two concentric adjacent annular section. The expansion ring may be circumferentially segmented.
A sealing surface on the inner cylindrical member may be adapted to withstand, in operation, contact between expansion ring and inner cylindrical member.
Preferably the seal is adapted to comprise a component part of a gas turbine engine.
REFERENCES:
patent: 3837631 (1974-09-01), Evans et al.
patent: 5106104 (1992-04-01), Atkinson et al.
patent: 5174582 (1992-12-01), Ferguson
patent: 5308088 (1994-05-01), Atkinson et al.
patent: 5351971 (1994-10-01), Short
patent: 5480160 (1996-01-01), Harms
patent: 5568931 (1996-10-01), Tseng et al.
patent: 6079945 (2000-06-01), Wolfe et al.
patent: 1484288 (1977-09-01), None
patent: 1484936 (1977-09-01), None
patent: 2193269 (1988-02-01), None
patent: 0276839 A2 (1988-08-01), None
Allen Steven V
Morgan Jonathan J
Saysell Guy
Wright Christopher
Manelli Denison & Selter PLLC
Rolls-Royce plc
Taltavull W. Warren
Verdier Christopher
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