Abstract:
A turbine engine includes a shaft, a fan, at least one bearing mounted on the shaft and rotationally supporting the fan, a fan drive gear system coupled to drive the fan, a bearing compartment around the at least one bearing and a source of pressurized air in communication with a region outside of the bearing compartment.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present disclosure is a continuation in part of U.S. patent application Ser. No. 12/708,621, filed Feb. 19, 2010. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates generally to gas turbine engines, and more particularly, to a system for supplying buffer air and ventilation air to the bearing compartments and shaft(s) in gas turbine engines. 
         [0003]    In typical multi-shaft bypass jet turbine engines, one shaft supports the rotors of a low pressure compressor and a low pressure turbine and another shaft supports the rotors of a high pressure compressor and a high pressure turbine. Generally, each of the shafts is supported by bearings, and each bearing is lubricated by a forced lubrication system which circulates lubricating oil fed by a pump. 
         [0004]    In the forced lubricating system, high pressure air is drawn from the high pressure compressor and is conducted to the exterior of the oil seals of the bearing compartments to keep the interior of the bearing compartments at a lower pressure than its immediate surroundings. This pressure differential prevents the lubricating oil from leaking out of the bearing compartments. In particular, high pressure buffer air drawn from the high pressure compressor is utilized because at least one of the bearing compartments is located in a high pressure environment where buffer air from the low pressure compressor would not provide adequate compartment pressurization at low power engine operating conditions. Unfortunately, buffer air drawn from the high pressure compressor is excessively hot and requires cooling at higher power engine operating conditions. Therefore, a dedicated cooler is required to lower the temperature of the buffer air. This cooler adds additional weight to the engine and can be difficult to package especially in smaller engine models. 
       SUMMARY OF THE INVENTION 
       [0005]    A disclosed example turbine engine according to an exemplary embodiment includes a shaft, a fan, at least one bearing mounted on the shaft and rotationally supporting the fan, a fan drive gear system coupled to drive the fan, a bearing compartment around the at least one bearing, and a source of pressurized air in communication with a region outside of the bearing compartment. 
         [0006]    In a further embodiment of the foregoing turbine engine, the fan drive gear system includes an epicyclic gear train. 
         [0007]    In a further embodiment of the foregoing turbine engine, the epicyclic gear train has a gear reduction ratio of greater than or equal to about 2.3. 
         [0008]    In a further embodiment of the foregoing turbine engine, the turbine engine, the epicyclic gear train has a gear reduction ratio of greater than or equal to 2.3. 
         [0009]    In a further embodiment of the foregoing turbine engine the epicyclic gear train has a gear reduction ratio of greater than or equal to about 2.5. 
         [0010]    In a further embodiment of the foregoing turbine engine, the epicyclic gear train has a gear reduction ratio of greater than or equal to 2.5. 
         [0011]    In a further embodiment of the foregoing turbine engine, the fan defines a bypass ratio of greater than about ten (10) with regard to a bypass airflow and a core airflow. 
         [0012]    In a further embodiment of the foregoing turbine engine, the fan defines a bypass ratio of greater than 10.5:1 with regard to a bypass airflow and a core airflow. 
         [0013]    In a further embodiment of the foregoing turbine engine, the fan defines a bypass ratio of greater than ten (10) with regard to a bypass airflow and a core airflow. 
         [0014]    In a further embodiment of the foregoing turbine engine, the fan defines a pressure ratio that is less than about 1.45. 
         [0015]    In a further embodiment of the foregoing turbine engine, the fan defines a pressure ratio that is less than 1.45. 
         [0016]    In a further embodiment of the foregoing turbine engine, a core compressor section is the source of the pressurized air. 
         [0017]    A disclosed method of operating a turbine engine that includes a shaft, a fan, at least one bearing mounted on the shaft and rotationally supporting the fan, a fan drive gear system coupled to drive the fan and a bearing compartment around the at least one bearing according to an exemplary embodiment includes the steps of providing pressurized air to a region outside of the bearing compartment to establish a positive pressure differential between the region outside of the bearing compartment and the interior of the bearing compartment. 
         [0018]    In a further embodiment of the foregoing method the fan drive gear system includes an epicyclic gear train. 
         [0019]    In a further embodiment of the foregoing method, the epicyclic gear train has a gear reduction ratio of greater than or equal to about 2.3. 
         [0020]    In a further embodiment of the foregoing method, including the step of providing the pressurized air from a core compressor section. 
         [0021]    Although different examples have the specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components of another of the examples. 
         [0022]    These and other features disclosed herein can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a schematic partial sectional view of a gas turbine engine with a centrifugal compressor driven by an accessory gearbox. 
           [0024]      FIG. 2  is a schematic of the buffer and ventilation air system of the gas turbine engine of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]    The present application describes new pressurization and ventilation systems for bearing compartments and shafts of a gas turbine engine. In particular, the present application describes an assembly and a method for providing buffer and/or ventilation air to bearing compartments and/or shafts of a gas turbine engine. The gas turbine engine described includes a dedicated centrifugal compressor that compresses bleed air from a low pressure compressor section and/or a fan section of the gas turbine engine. The compressed air is delivered to the core of the engine to buffer the bearing compartments and/or ventilate one or more shafts. The centrifugal compressor compresses the bleed air to a higher pressure more efficiently than traditional axial compressor arrays because it avoids the loss of kinetic energy and the throttling losses at the compressor case that are experienced with traditional axial compressor arrays. By utilizing the centrifugal compressor, air is drawn from the fan section and/or the low pressure compressor section and compressed to a desired optimal pressure and temperature, thereby eliminating the need for cooling within a cooler. This arrangement also reduces the likelihood of an inadequately pressurized bearing compartment at low power engine operating conditions, discussed previously. The flow rate and pressure ratio requirements of the centrifugal compressor are low enough to allow for a compact design that can fit within various locations such as the engine core and allow the centrifugal compressor to be integrated as an accessory to be driven by the gearbox. 
         [0026]      FIG. 1  shows a schematic partial cross section of a portion of a gas turbine engine  10 . Gas turbine engine  10  has bearing compartments  12 A and  12 B which house anti-friction bearings that support shafts  14 A and  14 B. Gas turbine engine  10  is defined around an engine centerline CL about which various engine sections rotate. In  FIG. 1 , only a portion of gas turbine engine  10  including a rotor section  16 , a fan section  18 , a low pressure compressor (LPC) section  20 , and a high pressure compressor (HPC) section  22  is illustrated. Gas turbine engine  10  is illustrated as a high bypass ratio turbofan engine with a dual spool arrangement in which fan section  18  and LPC  20  are connected to a low pressure turbine section (not shown) by rotor  16 , fan drive gear system  15 , and shaft  14 A, and high pressure compressor section  22  is connected to a high pressure turbine section (not shown) by second shaft  14 B. The general construction and operation of gas turbine engines, and in particular turbofan engines, is well-known in the art, and therefore, detailed discussion herein is unnecessary. It should be noted, however, that engine  10  is shown in  FIG. 1  merely by way of example and not limitation. The present invention is also applicable to a variety of other gas turbine engine configurations, such as a turbofan engine without fan-drive gear system and a turboprop engine, for example. 
         [0027]    In one example, the gas turbine engine  10  is a high-bypass geared architecture aircraft engine. In one disclosed, non-limiting embodiment, the engine  10  has a bypass ratio that is greater than about six (6) to ten (10), the fan drive gear system  15  is epicyclic gear train and includes a planetary gear system or other gear system with a gear reduction ratio of greater than about 2.3 or greater than about 2.5, and a low pressure turbine of the engine  10  has a pressure ratio that is greater than about 5. In one disclosed embodiment, the engine  10  bypass ratio is greater than about ten (10:1) or greater than about 10.5:1, the a fan rotor  24  diameter is significantly larger than that of the low pressure compressor of the compressor section  20 / 22 , and the low pressure turbine has a pressure ratio that is greater than about 5:1. In one example, the epicyclic gear train has a gear reduction ratio of greater than about 2.3:1 or greater than about 2.5:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans. 
         [0028]    A significant amount of thrust is provided by a bypass flow B due to the high bypass ratio. The fan of the engine  10  is designed for a particular flight condition—typically cruise at about 0.8M and about 35,000 feet. The flight condition of 0.8 M and 35,000 ft, with the engine at its best fuel consumption—also known as “bucket cruise TSFC”—is the industry standard parameter of 1 bm of fuel being burned divided by 1 bf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tambient deg R)/518.7)̂0.5]. The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second. 
         [0029]    In addition to fan section  18 , low pressure compressor section  20 , and high pressure compressor section  22 , gas turbine engine  10  includes a fan rotor  24 , an outer case  26 , a bypass duct  27 , an inner fan case  28 , an intermediate case  30 , an accessory gearbox  32 , a centrifugal compressor  34 , and a radial drive shaft  36 . Inner fan duct  28  and intermediate case  30  define a core compartment  38 . 
         [0030]    Air enters fan section  18  of turbine engine  10  where it is divided into streams of primary air Ar and bypass air AB after passing through the fan  24 . Bypass air AB flows inside outer case  26  and along inner fan case  28  and eventually exits bypass duct  27  and engine  10 . The fan  24  is disposed radially inward of outer case  26  and is rotated by the low pressure turbine (not shown) through the shaft  14  and fan-drive gear system  15  to accelerate the bypass air AB through fan section  18 , thereby producing a significant portion of the thrust output of engine  10 . 
         [0031]    The primary air Ar (also known as gas path air) is directed first through the low pressure compressor section  20  (which is partially bounded by intermediate case  30 ) and then through high pressure compressor section  22 . As illustrated in  FIG. 1 , accessory gearbox  32  is connected to intermediate case  30  and extends radially outward of engine centerline CL away from low pressure compressor section  20 . As is known in the art, the location of accessory gearbox  32  in  FIG. 1  is by way of example and not limitation. In other embodiments, accessory gearbox  32  can be disposed on outer case  26 , inner fan case  28  or in other locations including within the core of the gas turbine engine  10 . Accessory gearbox  32  is connected to and drives centrifugal compressor  34 . More particularly, accessory gearbox  32  transfers torque from radial drive shaft  36  to centrifugal compressor  34 . Radial drive shaft  36  is coupled to accessory gearbox  32  and extends into bearing compartment  12 B (specifically called a high rotor thrust bearing compartment) to couple with and transfer torque from shaft  14 B. 
         [0032]    Accessory gearbox  32  commonly drives various engine accessories including an electrical generator (not shown) and a main engine oil system, which is used to lubricate components of the engine including the bearings. Accessory gearbox  32  is specifically adapted to drive centrifugal compressor  34 , which is disposed within core compartment  38 . Scoops or other known devices bleed air at a lower pressure from fan section  18  and/or low pressure compressor section  20 . This bleed air is directed to centrifugal compressor  34  where it is compressed to a higher pressure. Thus, lower pressure bleed air directed to the centrifugal compressor  34  can comprise either bypass air AB or primary air Ar or a mixture of both. Primary air Ar can be drawn off various stages of the low pressure compressor section  20  as desired. 
         [0033]    Centrifugal compressor  34  operates in a manner known in the art to compress lower pressure bleed air to a higher pressure. Operation of the centrifugal compressor causes a pressure differential that circulates the higher pressure air A to all bearing compartments including forward bearing compartments  12 A and  12 B and more rearward bearing compartments ( FIG. 2 ) to act as buffer air. In addition to or in alternative to being used as buffer air for the bearing compartments, higher pressure air A can be used as ventilation air to ventilate shaft  14  in a manner know in the art. 
         [0034]    A pressure differential between the interior of bearing compartments  12 A and  12 B and higher pressure air A, along with the configuration of the bearing compartment seals, allows higher pressure air A to migrate across bearing compartment seals into the bearing compartments  12 A and  12 B. Migration of higher pressure air A across seals helps to prevent the caustic and flammable lubricating oil from leaking out of bearing compartments  12 A and  12 B. Utilization of centrifugal compressor  34  allows higher pressure A to be compressed to a desired optimal pressure and temperature to provide adequate pressurization to bearing compartments  12 A and  12 B to prevent oil leakage therefrom. Compressing air A to the desired optimal temperature and pressure eliminates the need for the cooling of air A within a cooler, thereby reducing engine  10  weight and providing more design space within engine  10 . 
         [0035]      FIG. 2  shows a schematic view of a system  39  that provides buffer air and ventilation air within gas turbine engine  10 . System  39  includes a lower pressure location  40 , lower pressure external lines or internal passages  42 , higher pressure external lines or internal passages  44 , metering devices  46 , structures  48 A- 48 E, bearing compartments  12 A- 12 D surrounded by seal cavities  13 A- 13 F, and a secondary air flow  50 . 
         [0036]    Accessory gearbox  32  is coupled to and acts to drive centrifugal compressor  34 . Scoops or other known devices bleed air at a lower pressure from lower pressure location  40  within gas turbine engine  10 . In one embodiment, location  40  comprises fan section  18  ( FIG. 1 ) and/or low pressure compressor section  20  ( FIG. 1 ). Bleed air is directed as air flow through lower pressure external lines or internal passages  42  to centrifugal compressor  34 , which operates to compress the lower pressure bleed air to a higher pressure. The higher pressure air that is compressed in centrifugal compressor  34  circulates away from centrifugal compressor  34  through higher pressure external lines and internal passages  44 . Higher pressure air flow branches into several flows that are directed through one or more metering devices  46 , such as valves or orifices, which throttle air flow as desired. In the embodiment illustrated in  FIG. 2 , higher pressure air flow is directed through structures  48 A- 48 E. Structures  48 A- 48 E can variously comprise struts and/or other portions of the front center body, intermediate case, or mid-turbine frame of gas turbine engine  10 . Higher pressure air flow passes through structures  48 A- 48 E to provide buffer air to seal cavities  13 A- 13 F that surround bearing compartments  12 A- 12 D and ventilation air to shaft  14  ( FIG. 1 ). In the embodiment shown, secondary air flow  50  continues from seal cavity  13 C as ventilation air along the inner diameter of shaft  14 A. Secondary air flow  50  also provides buffer air to seal cavity  13 F that buffers bearing compartment  12 D toward the rear of gas turbine engine  10 . 
         [0037]    While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.