GB2483714A - Gas turbine engine bearing housing sealing - Google Patents

Gas turbine engine bearing housing sealing Download PDF

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Publication number
GB2483714A
GB2483714A GB1015684.2A GB201015684A GB2483714A GB 2483714 A GB2483714 A GB 2483714A GB 201015684 A GB201015684 A GB 201015684A GB 2483714 A GB2483714 A GB 2483714A
Authority
GB
United Kingdom
Prior art keywords
bearing chamber
bearing
pump
turbine engine
air
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB1015684.2A
Other versions
GB201015684D0 (en
Inventor
David Anthony Edwards
Peter Frederick William Foster
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Rolls Royce PLC
Original Assignee
Rolls Royce PLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Rolls Royce PLC filed Critical Rolls Royce PLC
Priority to GB1015684.2A priority Critical patent/GB2483714A/en
Publication of GB201015684D0 publication Critical patent/GB201015684D0/en
Publication of GB2483714A publication Critical patent/GB2483714A/en
Withdrawn legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D25/00—Component parts, details, or accessories, not provided for in, or of interest apart from, other groups
    • F01D25/18—Lubricating arrangements
    • F01D25/20—Lubricating arrangements using lubrication pumps
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D25/00—Component parts, details, or accessories, not provided for in, or of interest apart from, other groups
    • F01D25/18—Lubricating arrangements
    • F01D25/183—Sealing means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02C—GAS-TURBINE PLANTS; AIR INTAKES FOR JET-PROPULSION PLANTS; CONTROLLING FUEL SUPPLY IN AIR-BREATHING JET-PROPULSION PLANTS
    • F02C7/00—Features, components parts, details or accessories, not provided for in, or of interest apart form groups F02C1/00 - F02C6/00; Air intakes for jet-propulsion plants
    • F02C7/06—Arrangements of bearings; Lubricating
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2240/00—Components
    • F05D2240/55—Seals
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2240/00—Components
    • F05D2240/60—Shafts
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2260/00—Function
    • F05D2260/60—Fluid transfer
    • F05D2260/602—Drainage

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Turbine Rotor Nozzle Sealing (AREA)

Abstract

A gas turbine engine comprises a bearing housing 10 for a rotatable shaft 12 of the engine, and an interior of the housing defines a bearing chamber 14. A feed pump 24 supplies lubricating fluid, such as oil, to the bearing chamber. A scavenge pump 26 removes lubricating fluid from the bearing chamber. A centrifugal pump 32 reduces the air pressure of the bearing chamber to below the surrounding air pressure. This causes a positive flow of air into the bearing chamber between the bearing housing and the shaft, thus preventing lubricating fluid from leaking out of the bearing chamber 14. Carbon seals may be provided between the shaft and the bearing chamber. A breather 36 may remove lubricating fluid from the air removed from the bearing chamber.

Description

APPARATUS AND METHOD FOR SEALING A BEARING HOUSING
OF A GAS-TURBINE ENGINE
The present invention relates to an apparatus and method for sealing a bearing housing of a gas-turbine engine, in particular, an apparatus and method using a centrifugal pump.
In gas-turbine engines it is known to support a rotatable shaft within the engine chamber using a number of support structures. Each support structure comprises a bearing housing which comprises a bearing chamber within which a number of bearing elements are located. In order to lubricate the bearing elements, oil is continually fed from an oil tank to the bearing chamber using a feed pump. A scavenge pump is used to continually remove oil from the bearing chamber and return it, after filtering, to the oil tank. This ensures that the bearing chamber is continually provided with cool and clean oil.
It is desirable to prevent oil from leaking out of the bearing chamber. This is because the leakage of oil can, amongst other things create cabin odour in the case of a gas-turbine for a jet engine. Also, it results in oil loss from the oil system which is undesirable.
There are a number of known ways of preventing oil from leaking out of the bearing chamber.
In one previously considered arrangement buffers are provided either side of the bearing housing in the region where the rotating shaft enters and exits the bearing housing. High-pressure air from the compressor is fed into the buffers which ensures a positive flow of air into the bearing chamber. This prevents any oil from leaking out of the bearing chamber. A second scavenge pump is provided to remove air from the bearing chamber.
When the gas-turbine engine is operating at high-power, for example at take-off, the pressure of the air provided by the compressor to the bearing chamber is particularly high. However, the second scavenge pump which removes the air from the bearing chamber cannot remove the air quickly enough. This means that the second scavenge pump acts as a restriction in the system. A result is a transient pressure reversal in which the bearing chamber pressure is higher than the local pressure surrounding the bearing chamber, which can have the effect of causing oil to leak out of the bearing chamber.
It is therefore known to provide a bypass valve that bypasses the second scavenge pump when the gas-turbine engine is operating at high-power, thus avoiding a transient pressure reversal. This requires a solenoid valve and a control circuit. The timing of the switching of the bypass valve is critical. If the bypass valve is not switched at the correct point in time then a transient pressure reversal may occur resulting in oil leaking out of the bearing chamber.
In a second previously considered arrangement carbon seals are used to seal between the rotatable shaft and the bearing housing. These provide a particularly tight seal and therefore buffers may not be required. This means that no, or significantly less, high-pressure air need be directly fed from the compressor into the bearing chamber, which can produce a specific fuel consumption benefit. In order to reduce the bearing chamber pressure so that oil does not flow out of the chamber, a large scavenge pump is used to reduce the air pressure within the bearing chamber. However, this design also suffers from the problem that when the gas-turbine engine is operating at high-power the scavenge pump must be bypassed in order to avoid a transient pressure reversal.
It is also necessary to carefully match the pump capacity to the leakage rate. If the pump capacity is too small then the bearing chamber pressure becomes too high and oil leaks out of the bearing chamber. If the pump capacity is too large then the pump inlet pressure is too low which leads to the danger of pump cavitation. Also, the large scavenge pump has to be run at a high airfoil ratio which means that additional lubrication is required in order to avoid seizure.
Embodiments of the present invention aim to address at least some of the above problems.
According to a first aspect of the present invention there is provided a gas-turbine engine comprising: a bearing housing for a rotatable shaft of the engine, wherein the interior of the bearing housing defines a bearing chamber; a feed pump in fluid communication with the bearing chamber for supplying lubricating fluid to the bearing chamber; a scavenge pump in fluid communication with the bearing chamber for removing lubricating fluid from the bearing chamber; and a centrifugal pump in fluid communication with the bearing chamber for reducing the air pressure within the bearing chamber to below a surrounding air pressure so as to cause a positive flow of air, between the bearing housing and the rotatable shaft, into the bearing chamber.
There may be a seal for at least partially sealing between the rotatable shaft and the bearing chamber. In one embodiment the seal is a carbon seal.
The engine may further comprise a breather that is in fluid communication with an outlet of the centrifugal pump for removing lubricating fluid from air removed from the bearing chamber by the centrifugal pump.
According to a second aspect of the present invention there is provided a method of supplying lubricating fluid to a bearing housing for a rotatable shaft of a gas-turbine engine, the interior of the bearing housing defining a bearing chamber, the method comprising: supplying lubricating fluid to the bearing chamber; removing lubricating fluid from the bearing chamber; and reducing the air pressure within the bearing chamber to below a surrounding air pressure using a centrifugal pump that is in fluid communication with the bearing chamber so as to cause a positive flow of air, between the bearing housing and the rotatable shaft, into the bearing chamber.
In one embodiment a breather is used to remove lubricating fluid from air removed from the bearing chamber by the centrifugal pump.
According to a further aspect of the present invention there is provided a gas-turbine engine comprising: a bearing housing for a rotatable shaft of the engine, wherein the interior of the bearing housing defines a bearing chamber; a feed pump in fluid communication with the bearing chamber for supplying lubricating fluid to the bearing chamber; a scavenge pump in fluid communication with the bearing chamber for removing lubricating fluid from the bearing chamber; and a pump in fluid communication with the bearing chamber for reducing the air pressure of the bearing chamber to below the pressure of the surrounding air so as to cause a positive flow of air, between the bearing housing and the rotatable shaft, into the bearing chamber, wherein the pump is arranged to generate a substantially constant pressure rise (delta p) between the pump inlet and the pump outlet over the working mass flow rate range of air through the bearing chamber.
This means that the pressure within the bearing housing is kept below the pressure of the surrounding air in all operating conditions, thus reducing the risk of lubricating fluid leaking out of the bearing chamber.
In a preferred arrangement the pump is a centrifugal pump.
The invention may comprise any combination of the features and/or limitations referred to herein, except combinations of such features as are mutually exclusive.
Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 schematically shows a perspective view of a bearing housing; Figure 2 schematically shows a sectional cut through the bearing housing of Figure 1; Figure 3 schematically shows the flow path of fluid through a bearing housing; Figure 4 schematically shows a perspective view of a centrifugal pump with a section cut away; Figure 5 shows a system characteristic when the gas-turbine engine is at idle; and Figure 6 shows the system characteristic when the gas-turbine engine is operating at high-power.
Figure 1 schematically shows a single bearing housing 10 that is used to support a turbine shaft 12 of a gas-turbine engine. As will be readily apparent to one skilled in the art, a plurality of bearing housings 10 may be, and indeed usually are, used to support a turbine shaft 12. At least some of the bearing housings 10 may be located in a compressor region of the gas-turbine engine.
With reference to Figure 2 the bearing housing 10 defines a bearing chamber 14 within which a plurality of bearing elements 16, such as roller bearings, are located. As shown in Figure 3, lubricating fluid such as oil is continually supplied to the bearing chamber 14 from an oil tank 20 via an oil supply line 22. This provides lubrication for the bearing elements 16 and turbine shaft 12. The oil is pumped to the bearing chamber 14 using a feed pump 24. A single feed pump 24 may be used to supply oil to a number of bearing chambers 14. Oil is removed from the bearing chamber 14 using a scavenge pump 26 via a drain line 28 and returned to the oil tank 20. The continuous supply and removal of oil to and from the bearing chamber ensures that the oil within the bearing chamber 14 is both sufficiently cool and clean.
A carbon seal 30 (Figure 1) is provided in between the turbine shaft 12 and the bearing housing 10 in order to reduce the leakages of oil from the bearing chamber 14.
Although the carbon seal 30 produces a relatively tight seal it is not completely fluid-tight. As will be readily apparent to one skilled in the art, other types of seal may be used.
In order to prevent oil from leaking out of the bearing chamber 14 into the gas-turbine engine a positive flow of air is created into the bearing chamber 14. This is done by connecting a centrifugal pump 32, otherwise known as a centrifugal impeller, to a vent line 34 that is in fluid communication with the bearing chamber 14. The centrifugal pump 32 reduces the air pressure within the bearing chamber 14 which causes the higher-pressure air surrounding the bearing housing 10 to be drawn into the bearing chamber 14. The centrifugal pump 32 removes the air drawn into the bearing chamber 14 and discharges it to a breather 36 via a discharge line 38. The breather 36 acts to remove oil from the air extracted by the centrifugal pump 32, thus cleaning the air. The clean air is then discharged to the atmosphere through an overboard line 40 and the oil the breather 36 removed from the air is returned to the oil tank 20 via a drain line 44 using a further scavenge pump 42. Figure 4 shows one example of a centrifugal pump 32 with a section cut away.
Figure 5 shows the system characteristic when the gas-turbine engine is idle. The system characteristic for a bearing housing 10 having a normal seal is shown by line A. The system characteristic for a bearing housing 10 having a leaky seal is shown by line B. The characteristic of the centrifugal pump 32 is shown by line C. As a comparative example the characteristic of a conventional positive displacement pump is shown by line D. As can be seen from Figure 5, when the system is idle and the seal of the bearing housing 10 is operating correctly (line A), both the centrifugal pump 32 (line C) and a conventional positive displacement pump (line D) create the same positive pressure head (point Z), hereinafter referred to as delta p. This means that the pressure within the bearing chamber 14 is sufficiently low to ensure that there is a positive air flow into the bearing chamber 14, and oil does not leak out of the bearing chamber 14.
If the seal of the bearing housing 10 is leaky (line B) then the centrifugal pump 32 (line is C) will generate substantially the same delta p as when the seal is normal (point Y).
This means that the centrifugal pump 32 will generate a pressure within the bearing chamber 14 that is sufficiently low to ensure a positive flow of air into the bearing chamber 14, thereby preventing oil from leaking out of the bearing chamber 14.
However, a conventional positive displacement pump will generate a much lower delta p (point X). This means that the pressure within the bearing chamber 14 is higher when compared to using the centrifugal pump 32. This results in the risk of a transient pressure reversal in which the pressure within the bearing chamber 14 is higher than the external surrounding pressure and therefore oil leaks out of the bearing chamber 14.
If the seal is particularly tight (not shown on Figure 5) then the centrifugal pump 32 will generate substantially the same delta p as when the seal is normal. Therefore, the bearing chamber 14 pressure is sufficiently low such that oil leakage is avoided.
However, a conventional positive displacement pump will generate a much higher delta p which means that there may be a very low pressure at the pump inlet, thus causing the risk of pump cavitation.
Figure 6 shows the system characteristic when the gas-turbine engine is operating at high-power, for example at take-off of a gas-turbine jet engine. The system characteristic for a bearing housing 10 having a normal seal is shown by line F. The characteristic of the centrifugal pump 32 is shown by line F. As a comparative example the characteristic of a conventional positive displacement pump is shown by line C. As can be seen from Figure 6, when the gas-turbine engine is operating at high-power then the centrifugal pump 32 (line F) is able to generate a positive delta p (point W).
This means that the pressure within the bearing chamber 14 is lower than the external pressure and hence a positive air flow into the bearing chamber 14 is ensured. This means that oil leakage from the bearing chamber 14 is prevented.
However, if a conventional positive displacement pump (line C) is used then the pump capacity is too low and hence the pump creates a restriction in the system. The pump therefore generates a negative delta p (point V) which results in the bearing chamber 14 pressure being high. This means that there is the risk of a transient pressure reversal in which the pressure within the bearing chamber 14 is higher than the external pressure, thus resulting in the risk of oil leakage from the bearing chamber 14. As discussed previously, it is known to provide a bypass valve in order to bypass the positive displacement pump when operating at high-power. The bypass valve requires a solenoid and a control circuit that is activated when operating at high-power. When the gas-turbine engine is operating at high-power the positive displacement pump is bypassed and therefore does not create a restriction in the system. However, the timing of the switching of the valve is critical in order to ensure that the pressure within the bearing chamber 14 does not exceed the external pressure.
The use of a centrifugal pump 32 means that it is not necessary to have a bypass valve and a control circuit because the pump can generate a positive delta p even when the gas-turbine engine is operating at high-power. This results in a simpler and cheaper arrangement. Additionally, the use of a centrifugal pump 32 generates a lower bearing chamber 14 pressure than is possible with a bypassed positive displacement pump.
This means that the risk of transient pressure reversal and consequent oil leakage is reduced.
It may be possible to use other types of pumps instead of the centrifugal pump 32 to reduce the air pressure of the bearing chamber 14. However, the important characteristic is that the pump must be capable of generating a substantially constant delta p over the working mass flow rate range of the system.

Claims (7)

  1. CLAIMS1 A gas-turbine engine comprising: a bearing housing (10) for a rotatable shaft (12) of the engine, wherein the interior of the bearing housing defines a bearing chamber (14); a feed pump (24) in fluid communication with the bearing chamber (14) for supplying lubricating fluid to the bearing chamber; a scavenge pump (26) in fluid communication with the bearing chamber (14) for removing lubricating fluid from the bearing chamber; and a centrifugal pump (32) in fluid communication with the bearing chamber (14) for reducing the air pressure within the bearing chamber to below a surrounding air pressure so as to cause a positive flow of air, between the bearing housing (10) and the rotatable shaft (12), into the bearing chamber.
  2. 2 A gas-turbine engine according to claim 1, further comprising a seal (30) for at least partially sealing between the rotatable shaft (12) and the bearing chamber (10).
  3. 3 A gas-turbine engine according to claim 2, wherein the seal (30) is a carbon seal.
  4. 4 A gas-turbine engine according to any preceding claim, further comprising a breather (36) that is in fluid communication with an outlet of the centrifugal pump (32) for removing lubricating fluid from air removed from the bearing chamber (14) by the centrifugal pump. -11 -
  5. A method of supplying lubricating fluid to a bearing housing (10) for a rotatable shaft (12) of a gas-turbine engine, the interior of the bearing housing defining a bearing chamber (14), the method comprising: supplying lubricating fluid to the bearing chamber (14); removing lubricating fluid from the bearing chamber (14); and reducing the air pressure within bearing chamber (14) to below a surrounding air pressure using a centrifugal pump (32) that is in fluid communication with the bearing chamber (14) so as to cause a positive flow of air, between the bearing housing (10) and the rotatable shaft (12), into the bearing chamber (14).
  6. 6 A gas-turbine engine according to claim 5, using a breather (36) to remove lubricating fluid from air removed from the bearing chamber (14) by the centrifugal pump.
  7. 7 An apparatus or method substantially as described herein with reference to the accompanying drawings.
GB1015684.2A 2010-09-20 2010-09-20 Gas turbine engine bearing housing sealing Withdrawn GB2483714A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB1015684.2A GB2483714A (en) 2010-09-20 2010-09-20 Gas turbine engine bearing housing sealing

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB1015684.2A GB2483714A (en) 2010-09-20 2010-09-20 Gas turbine engine bearing housing sealing

Publications (2)

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GB201015684D0 GB201015684D0 (en) 2010-10-27
GB2483714A true GB2483714A (en) 2012-03-21

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110080883A (en) * 2019-06-04 2019-08-02 中国航空工业集团公司北京长城计量测试技术研究所 A kind of online outer circulation auxiliary device of minute leakage lubricating oil for sealing device

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1398456A (en) * 1972-11-08 1975-06-25 Bbc Sulzer Turbomaschinen Gas turbine engines
GB2130308A (en) * 1982-11-16 1984-05-31 Mtu Muenchen Gmbh Hydraulic system for an aircraft
US5429208A (en) * 1993-05-25 1995-07-04 Societe Nationale D'etude Et De Construction De Moteurs D'aviation "Snecma" Depressurization device for the bearing lubricating chambers of a turbomachine
EP1255024A2 (en) * 2001-04-30 2002-11-06 General Electric Company Methods and systems for preventing gas turbine engine lube oil leakage

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1398456A (en) * 1972-11-08 1975-06-25 Bbc Sulzer Turbomaschinen Gas turbine engines
GB2130308A (en) * 1982-11-16 1984-05-31 Mtu Muenchen Gmbh Hydraulic system for an aircraft
US5429208A (en) * 1993-05-25 1995-07-04 Societe Nationale D'etude Et De Construction De Moteurs D'aviation "Snecma" Depressurization device for the bearing lubricating chambers of a turbomachine
EP1255024A2 (en) * 2001-04-30 2002-11-06 General Electric Company Methods and systems for preventing gas turbine engine lube oil leakage

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110080883A (en) * 2019-06-04 2019-08-02 中国航空工业集团公司北京长城计量测试技术研究所 A kind of online outer circulation auxiliary device of minute leakage lubricating oil for sealing device

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Publication number Publication date
GB201015684D0 (en) 2010-10-27

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