Abstract:
A method and device for improved pressure balancing in a bearing chamber pressurization system for gas turbine engines employ a partition member to substantially separate first and second air-oil seals of the bearing housing.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to gas turbine engines, and more particularly to a bearing chamber pressurization system for gas turbine engines.  
       BACKGROUND OF THE INVENTION  
       [0002]     Bearing chamber pressurization is often provided in gas turbine engines in order to improve the air-oil sealing provided by the seals for the bearing chamber, and thereby enhance the ability to prevent oil from leaking from the bearing chamber. Some leakage may occur in some instances, and in these instances, it is preferable to direct the leakage in a manner which has the minimum adverse impact on the engine and its operation. In bearings located adjacent the compressor, for example, it is desirable to minimize the oil which leaks into bleed air systems, to thereby minimize the possibility of aircraft cabin bleed air contamination with oil. Various pressurization systems are known, but improvements to the weight, cost and size thereof are always desired, and it is an object of the present invention to provide an improved pressurization system.  
       SUMMARY OF THE INVENTION  
       [0003]     One object of the present invention is to provide improved pressure balancing in a bearing chamber pressurization system of a gas turbine engine.  
         [0004]     In accordance with one aspect of the present invention, there is a bearing chamber pressurization system provided for a gas turbine engine, which comprises a bearing housing defining a bearing chamber therein, the housing having first and second air-oil seals. A source of pressurized air is provided, communicating with the air-oil seals along an air flow path. A partition is disposed within the air flow path between the first and second air-oil seals of the bearing housing. The system further includes at least one metering orifice in the air flow path upstream of the second air-oil seal, forming a passage by-passing the first air-oil seal. The orifice is disposed in the partition and adapted to regulate relative pressures of the pressurized air provided to the first and second air-oil seals.  
         [0005]     In accordance with another aspect of the present invention, there is a bearing chamber pressurization system provided for a gas turbine engine, which comprises a bearing housing defining a bearing chamber therein, the housing having first and second air-oil seals. A source of pressurized air is provided, communicating with the air-oil seals along an air flow path. Means are provided for regulating a pressure of the pressurized air. Said means are provided at least partially by a centrifugal compressor heat shield of the engine and adapted to provide a pre-determined pressure difference in the pressurized air provided to the first and second air-oil seals. Said pressure difference is adapted to preferentially direct an oil leak from the housing through the second air-oil seal.  
         [0006]     In accordance with a further aspect of the present invention, there is a method provided for controlling pressurized air delivered to a plurality of air-oil seals of a bearing housing in a gas turbine engine, which comprises steps of: directing an compressor bleed air flow to the bearing housing; dividing the flow into at least two flows; directing a first flow to a first air-oil seal; metering a second flow and thereby creating a step drop in pressure thereof; and directing the pressure dropped second flow to a second air-oil seal, wherein the step drop in pressure is adapted in magnitude to provide a pre-selected pressure differential between air pressures of the first and second flows provided to the first and second air-oil seals.  
         [0007]     These and other aspects of the present invention will be better understood with reference to the following description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a schematic cross-sectional view of a turbofan gas turbine engine which illustrates an exemplary application of the present invention;  
         [0009]      FIG. 2  is a partial cross-sectional view of the gas turbine engine of  FIG. 1 , illustrating a bearing chamber pressurization system according to one embodiment of the present invention;  
         [0010]      FIG. 3  is a partial front elevational view of a bearing housing of  FIG. 2 ; and  
         [0011]      FIG. 4  is a partial cross-sectional view along line  4 - 4  in  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]     Referring to  FIG. 1 , a turbofan gas turbine engine incorporates an embodiment of the present invention, presented as an example of the application of the present invention, and includes a nacelle  10 , a core casing  13 , a low pressure spool assembly seen generally at  12  which includes a fan  14 , low pressure compressor  16  and low pressure turbine  18 , and a high pressure spool assembly seen generally at  20  which includes a high pressure compressor  22 , a centrifugal compressor  23  and a high pressure turbine  24 . A combustor  26  has a plurality of fuel injectors  28 . Each of the low and high pressure spool assemblies  12 ,  20  includes a shaft (not indicated) rotatably supported by a plurality of bearing assemblies  30  (only one of which is shown). A bearing chamber pressurization system provided for supplying pressurized air to seal the bearing assembly  30  will now be described.  
         [0013]      FIG. 2  depicts the bearing chamber pressurization system according to one preferred embodiment of the present invention. The bearing assembly  30  includes an annular bearing housing  32  having a front side air-oil seal  36  and a rear air-oil side seal  38 . A bearing chamber  34  is defined within the bearing housing  32  for accommodating bearings  40  which rotatably support the shaft (not indicated) of the high pressure spool. The bearing housing  32  is supported within a stationary structure (not indicated) of the engine. Annular heat shields  48 ,  50  are installed to cover the outer wall (not indicated) of the bearing housing  32 . The heat shields  48  and  50  in combination with the outer wall of the bearing housing  32 , define a space (not indicated) therebetween for insulating the bearing chamber from the combustor.  
         [0014]     The stationary structure of the engine defines a plenum  42  surrounding the bearing assembly  30 . The plenum  42  contains pressurized air which enters the bearing chamber  34  of the bearing housing  32  through the front side seal  36  and rear side seal  38 .  
         [0015]     A diffuser heat shield  44  which is preferably an annular metal plate, extends from the stationary structure of the engine radially and inwardly towards the bearing housing  32 . An inner end of the annular diffuser shield  44  abuts an annular ridge  46  such that the diffuser shield  44  in combination with the ridge  46  of the bearing housing  32 , forms a partition between the front and rear seals  36 ,  38  of the bearing housing  32 .  
         [0016]     Referring to  FIGS. 2, 3  and  4 , the ridge  46  includes an axially protruding rim portion  52  preferably having bevelled surfaces (not indicated) and a recessed portion  54  having a substantially radial annular surface  56 . The inner end of the diffuser shield  44  has a wave-like shape to generally correspond with the contour of the annular ridge  46  of the bearing housing  32 . It is preferable to bias the diffuser shield  44  against the ridge such that the diffuser shield  44  forcibly abuts the ridge  46 .  
         [0017]     A plurality of openings, such as grooves  58 , is provided in ridge  46 , as shown in  FIGS. 3 and 4 . The grooves  58  are circumferentially spaced apart from one another and extend radially through the ridge  46 , thereby forming a passage for fluid communication to the plenum  42  so that a portion of bleed air may be provided to the rear side seal  38 , by-passing the front side seal  36 .  
         [0018]     The diffuser shield  44  is typically spaced apart from a back surface  60  of an impeller  62  of the centrifugal compressor  23 , and thus defines a radial passage indicated by numerals  64 ,  66  which permits a compressor bleed air flow to be directed to the bearing housing  32 . The compressor bleed air flow diverges at the inner end of the diffuser shield  44 , with a portion entering the bearing chamber  34  through the front side seal  36  and a portion passing through grooves  58  to enter the plenum  42  and, ultimately, the rear side seal  38 . Preferably, the flow of bleed air flow directed to the rear side seal  38  is less than the flow entering the front side seal  36 , such that any leakage form the chamber  32  will tend to leak towards the turbine rather than the compressor, thereby protecting the bleed air from oil contamination.  
         [0019]     The radial position where the compressor bleed air flow diverges to flow into the plenum  42  (i.e. towards real seal  38 ) is close to the radial position where the flow enters the front side seal  36 . This facilitates providing a higher pressure to front side seal  36 .  
         [0020]     Furthermore, the air pressure at the respective front and rear side seals  36 ,  38  can be balanced (or unbalanced, as the case may be) by control of the number, size and/or shape of the orifices or openings (e.g. grooves  58 ) into plenum  42 , which preferably creates a step drop in pressure, to vary the air flow rate and pressure supplied to the rear seal relative to the front seal. Thus, a pre-selected pressure differential between the air pressures of the respective flows to the front and rear seals can be achieved.  
         [0021]     The grooves  58  or other openings may also be configured to deswirl the compressor bleed air flow entering the plenum  42 .  
         [0022]     The skilled reader will appreciate that changes can be made to the above embodiments without departing from the principles of the present invention taught herein. For example, neither the diffuser heat shield, nor the bearing housing need be used to provide the partition member. Any suitable type of flow/pressure dividing arrangement between the front and rear side seals of the bearing housing  32  can be used. As mentioned, grooves as such are not required, and holes, slits, etc. through the heat shield, bearing housing, casing, or other structure may be provided instead, or additionally. Though described as “front” and “rear” side seals, the present invention may be employed to provide pressure balancing between air-oil seals in any location. The principle of the present invention is applicable to other types of gas turbine engines. Still other modifications will be apparent to those skilled in the art, and thus the foregoing description is intended to be exemplary rather than limiting. The scope of the present invention is therefore intended to be limited solely by the scope of the appended claims.