GB2366842A

GB2366842A - A bearing chamber sealing system

Info

Publication number: GB2366842A
Application number: GB0022295A
Authority: GB
Inventors: Nigel Peter Jackson
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2000-09-09
Filing date: 2000-09-09
Publication date: 2002-03-20
Also published as: GB0022295D0

Abstract

An annular bearing chamber 56 surrounds a ball bearing 50. An annular structure 62 encloses the bearing chamber 56 and isolates it from the surrounding environment 68, defining a buffer zone 64. The buffer zone 64 is in fluid communication with a region 72 at a pressure P<SB>5</SB> which is arranged to be lower than the pressure P<SB>4</SB> in the buffer zone 64. This results in an inward air flow 74 through the buffer zone seals 66, so that any lubricant leaking out of the bearing chamber 56 cannot pass out through the buffer zone seals 66 and contaminate the surrounding environment.

Description

<Desc/Clms Page number 1> A BEARING CHAMBER SEALING SYSTEM This invention relates to bearing chamber sealing systems and particularly, though not exclusively, to such systems for use in gas turbine engines.

one of the functions of a bearing chamber sealing system in a gas turbine engine is to prevent the contamination of bleed or core compressor air by oil leaking from a bearing chamber. It is known to enclose the bearing chamber with a buffer zone, which is fed with air at a pressure above that of the surrounding environment. The pressurization of the buffer zone, combined with the action of the oil scavenge pump and often a bearing chamber vent, results in an inward flow of air through the bearing chamber seals, inhibiting oil leakage. The pressure drop across the bearing chamber seals must be large enough to accommodate any front-to-rear pressure imbalance and ensure the air flow is always in the desired direction. Because the buffer zone pressure is higher than the pressure in the surrounding environment, air will also flow outward through the outer seals of the buffer zone.

When "conventional" bearing chamber seals are used, a relatively large air flow is needed to maintain the necessary pressure drop across them, and so the bearing chamber must be vented. Alternatively, "low-flow" seals may be employed, and the oil scavenge pump will then maintain an adequate pressure drop with a lower air flow and without the need for a bearing chamber vent. By "conventional" seals is meant labyrinth seals, or seals of other types in which the leakage flow through the seal, for a given pressure drop across it, is similar to that in a labyrinth seal. By "low-flow" seals is meant carbon seals or brush seals, or seals of other types in which the leakage flow through the seal, for a given pressure drop across it, is

similar to that in a carbon seal or brush seal, and lower than that in a "conventional" seal.

A disadvantage of the arrangement described above is that if changes in the relative pressures inside and outside the bearing chamber allow the air flow through the bearing chamber seals to be reversed (as is possible during certain transient manoeuvres of the engine), oil will leak from the bearing chamber into the buffer zone and will tend to be carried outward through the buffer zone seals and into the surrounding environment. This may contaminate compressor or bleed air, or may affect the engine's performance if oil is deposited on aerofoil surfaces.

It is therefore an object of this invention to provide a bearing chamber sealing system which will, under normal conditions, inhibit the leakage of oil from the bearing chamber; but if any such leakage does occur, will ensure there is no contamination of the air in the surrounding environment.

According to the present invention, a bearing chamber sealing system includes structure defining a buffer zone which surrounds the bearing chamber and isolates it from the surrounding environment, and fluid communication means linking said buffer zone to a region which under normal operating conditions is at a pressure lower than that in said surrounding environment, so that any lubricant leaking from said bearing chamber cannot leak out of said buffer zone into said surrounding environment.

Preferably said fluid communication means are arranged so as also to carry away any lubricant flowing out of said bearing chamber into said buffer zone.

In a preferred embodiment of the invention, said bearing chamber is defined at least in part by a shaft, there being provided first seal means between said bearing chamber and said shaft, said first seal means restricting

fluid flow between said bearing chamber and said buffer zone, and second seal means between said structure defining a buffer zone and said shaft, said second seal means restricting fluid flow between said buffer zone and said surrounding environment. Preferably said first seal means are carbon seals, or brush seals, or any other type of "low-flow" seals. Preferably said second seal means are labyrinth seals, or any other type of "conventional" seals.

Said structure defining a buffer zone may comprise a i single structure enclosing the whole of said bearing chamber, or may comprise two structures, each enclosing one end of said bearing chamber, said two structures being in fluid communication.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of a prior art bearing chamber sealing system having a buffer zone; Figure 2 is a schematic representation of an t embodiment of a bearing chamber sealing system according to the present invention.

Referring first to Figure 1, there is shown a conventional bearing chamber sealing system having a buffer zone. A shaft 12 is mounted from structure 11 via a ball bearing 10. The shaft 12 is able to rotate about an axis of rotation 14. An annular bearing chamber 16, concentric with the shaft 12, encloses the ball bearing 10. The ball bearing 10 is lubricated by oil, supplied by an oil jet 18. An oil scavenge pump (not shown) removes surplus oil from 1 the bearing chamber 16. Annular bearing chamber seals 22, which are of the labyrinth type, are provided at the axial extents of the bearing chamber 16 to restrict fluid flow into the bearing chamber 16. A bearing chamber vent 20

provides means for creating a pressure drop across the bearing chamber seals 22.

An annular structure 24 is provided, concentric with the shaft 12. This is radially outward of the bearing chamber 16 and encloses it. This annular structure 24, together with the bearing chamber 16, defines a buffer zone 26. Buffer zone seals 28, which are of the labyrinth type, are provided at the axial extents of the annular structure 24 to restrict fluid flow between the buffer zone 26 and the surrounding environment 30.

In operation, the pressure in the surrounding environment 30 is P1. The buffer zone 26 is fed with air 32, via a duct 34, from a region 36 containing air at a pressure P2, which is arranged to be higher than P1. This results in an air flow 38 outward from the buffer zone 26, through the buffer zone seals 28. At the same time, a pressure P3 is maintained within the bearing chamber 16 by the action of the oil scavenge pump (not shown) and the bearing chamber vent 20. P3 is arranged to be lower than PZ under normal operating conditions. This pressure difference results in an air flow 40 from the buffer zone 26 into the bearing chamber 16, through the bearing chamber seals 22. This air flow 40 inhibits leakage of oil from the bearing chamber 16.

It will be apparent that if PZ Or P3 changes so that P3 becomes higher than PZ (as is possible during certain engine manoeuvres) the direction of the air flow 40 will be reversed and oil will be carried out of the bearing chamber 16 and into the buffer zone 26. The air flow 38 will then tend to carry this oil out of the buffer zone 26, leading to contamination of the air in the surrounding environment 30.

Referring now to Figure 2, which shows an embodiment of a bearing chamber sealing system according to the

present invention. A shaft 52 is mounted from structure 51 via a ball bearing 50. The shaft 52 is able to rotate about an axis of rotation 54. An annular bearing chamber 56, concentric with the shaft 52, encloses the ball bearing 50. The ball bearing 50 is lubricated by oil, supplied by an oil jet 58. An oil scavenge pump (not shown) removes surplus oil from the bearing chamber 56.

Although the invention has been described so far with reference to a ball bearing, it is to be understood that it is equally applicable to systems employing any other type of oil-lubricated bearing.

Annular bearing chamber seals 60, which are of carbon type, are provided at the axial extents of the bearing chamber 56 to restrict fluid flow into and out of the bearing chamber 56. It is to be understood that the bearing chamber seals 60, although described here as being of carbon type, could equally well be of any other "low-flow" type.

An annular structure 62 is provided, concentric with the shaft 52. This is radially outward of the bearing chamber 56 and encloses it. This annular structure 62, together with the bearing chamber 56, defines a buffer zone 64. Buffer zone seals 66, which are of labyrinth type, are provided at the axial extents of the annular structure 62 to restrict fluid flow between the buffer zone 64 and the surrounding environment 68. It is to be understood that the buffer zone seals 66, although described here as being of labyrinth type, could equally well be of any other "conventional" type.

In operation the air pressure in the surrounding environment 68 is P4. The buffer zone 64 is linked by a duct 70 to a region 72 containing air at a pressure P5, which is arranged to be lower than P4. This pressure difference gives rise to an air flow 74 from the surrounding environment 68

into the buffer zone 64, through the buffer zone seals 66. The action of the oil scavenge pump (not shown) maintains a pressure P6 within the bearing chamber 56. P6 is arranged to be lower than P5 in normal operation, so there is an air flow 76 inward through the bearing chamber seals 60 into the bearing chamber 56. This inhibits leakage of oil from the bearing chamber 56.

In a preferred embodiment of the invention, the duct 70 is located so that, in normal operation, it will lie at or near the lowest point in the annular structure 62, so that it will also carry away any oil which does leak out of the bearing chamber 56.

If PS or P6 changes so that P6 becomes higher than P5, the direction of the air flow 76 will be reversed and oil will be carried out of the bearing chamber 56 and into the buffer zone 64. However, because the air flow 74 is still inward through the buffer zone seals 66, no oil will be carried out into the surrounding environment 68.

A further advantage of the invention is that a bearing chamber sealing system according to the present invention is simpler and has fewer components than a bearing chamber sealing system of the type shown in Figure 1 - requiring no supply of pressurized air for the buffer zone, nor a bearing chamber vent - and consequently offers cost and weight benefits over the bearing chamber sealing systems previously known.

Although a single embodiment of the invention has been described above, it will be appreciated that alternative embodiments are possible which still incorporate the essential features of the invention. For example, although the invention has been described with a single annular structure wholly enclosing the bearing chamber, it will be appreciated that the objectives of the invention could equally well be achieved with two separate annular

structures, each enclosing one end of the bearing chamber, and the two structures being in fluid communication.

Also, although the invention has been described with reference to an embodiment in which a bearing is located part-way along a shaft, it will be appreciated that the invention could equally well be applied in a situation where a bearing is located at an end of a shaft, so that the shaft extends out of the bearing chamber only in one axial direction.

Claims

CLAIMS 1. A bearing chamber sealing system in which there is structure defining a buffer zone which surrounds the bearing chamber and isolates it from the surrounding environment, and in which fluid communication means link said buffer zone to a region which under normal operating conditions is at a pressure lower than that in said surrounding environment, so that any lubricant leaking from said bearing chamber cannot leak out of said buffer zone into said surrounding environment.
2. A bearing chamber sealing system as claimed in Claim 1, in which said fluid communication means are arranged so as also to carry away any lubricant flowing out of the bearing chamber into the buffer zone.
3. A bearing chamber sealing system as claimed in Claim 1 or Claim 2, in which the bearing chamber is defined at least in part by a shaft, there being provided first seal means between said bearing chamber and said shaft, said first seal means restricting fluid flow between said bearing chamber and said buffer zone, and second seal means between said said structure defining a buffer zone and said shaft, said second seal means restricting fluid flow between said buffer zone and said surrounding environment.
4. A bearing chamber sealing system as claimed in Claim 3, in which said first seal means are of "low-flow" type.
5. A bearing chamber sealing system as claimed in Claim 3, in which said first seal means are carbon seals.
6. A bearing chamber sealing system as claimed in Claim 3, in which said first seal means are brush seals.
7. A bearing chamber sealing system as claimed in any one of Claims 3, 4, 5 or 6, in which said second seal means are of "conventional" type.

<Desc/Clms Page number 9>
8. A bearing chamber sealing system as claimed in any one of Claims 3, 4, 5 or 6, in which said second seal means are labyrinth seals.
9. A bearing chamber sealing system according to any one of Claims 1 to 8, in which said structure defining a buffer zone comprises a single structure enclosing the whole of said bearing chamber.
10. A bearing chamber sealing system according to any one of Claims 1 to 8, in which said structure defining a buffer zone comprises two structures, each enclosing one end of said bearing chamber, said two structures being in fluid communication.
11. A bearing chamber sealing system substantially as hereinbefore described, with reference to Figure 2 of the accompanying drawings.