Abstract:
A journal bearing that includes a central body having first and second passageways and a filter. The central body extends axially and is adapted to be supported at each outer end. The first passageway extends generally axially through a portion of the central body. The filter is disposed in the first passageway and is configured to trap debris from a lubricant fluid flowing therethrough. The second passageway extends between both the first passageway and an exterior surface of the central body to allow for delivery of lubricant fluid thereto.

Description:
BACKGROUND 
     The present invention relates to gas turbine engines, and more particularly, to an epicyclic gear system for use in gas turbine engines. 
     Epicyclic gear trains are complex mechanisms for reducing or increasing the rotational speed between two rotating shafts or rotors. The compactness of planetary or star system gear trains makes them appealing for use in aircraft engines. 
     The forces and torque transferred through an epicyclic gear train place tremendous stresses on the gear train components, making them susceptible to breakage and wear. For example, the longitudinal axes of an epicyclic gear train&#39;s sun gear, star gear, and ring gear are ideally parallel with the longitudinal axis of an external shaft that rotates the sun gear. Unfortunately, many components of epicyclic gear trains, particularly an internal journal bearing within each star gear, are difficult to install and to effectively align. Additionally, because a perfect alignment is rare due to numerous factors (including imbalances in rotating hardware, manufacturing imperfections, and transient flexure of shafts and support frames due to aircraft maneuvers), it is necessary to have a proper amount of lubrication (i.e. an adequate film thickness) between each internal journal bearing and each star gear. Proper lubrication is necessary because misalignment (both parallel and angular) imposes moments and forces on the internal journal bearing which will cause it to contact and wear on the star gear it is disposed in. Unfortunately, to deliver adequate lubrication between each journal bearing and corresponding star gear, many prior art epicyclic gear trains require multiple parts which also require lubrication and are themselves susceptible to wear. 
     SUMMARY 
     According to the present invention, a journal bearing includes a central body having first and second passageways and a filter. The central body extends axially and is adapted to be supported at each outer end. The first passageway extends generally axially through a portion of the central body. The filter is disposed in the first passageway and is configured to trap debris from a lubricant fluid flowing therethrough. The second passageway extends between both the first passageway and an exterior surface of the central body to allow for delivery of lubricant fluid thereto. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional side view of a gas turbine engine with an epicyclic gear system. 
         FIG. 2  is a schematic cross-sectional view of the epicyclic gear system of  FIG. 1 . 
         FIG. 3  is a diagrammatic view of the entire epicyclic gear system taken along line  3 - 3  of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     The present application describes an epicyclic gear system with a minimum number of internal passageways and components which allow an adequate amount of lubricating liquid to reach the journal bearings of the epicyclic gear system in a gas turbine engine. The configuration of the internal passageways also allows for effective filtration of the lubricant within each journal bearing immediately adjacent to the bearing/star interface surface. Additionally, each journal bearing is provided with an alignment pin which allows for more effective installation of the journal bearing with respect to the star gear. The alignment pin helps to ensure proper angular orientation of the passageways delivering lubricant such that an adequate film thickness is achieved to react load between the journal bearing and the star gear in a load zone. 
       FIG. 1  is a schematic cross-sectional side view of gas turbine engine  10 . Gas turbine engine  10  includes low pressure unit or spool  12  (which includes low pressure compressor  14  and low pressure turbine  16  connected by low pressure shaft  18 ), high pressure unit or spool  20  (which includes high pressure compressor  22  and high pressure turbine  24  connected by high pressure shaft  26 ), combustor  28 , nacelle  30 , fan  32 , fan shaft  34 , and epicyclic gear system  36 . The epicycle gear system  36  includes star gear  38 , ring gear  40 , and sun gear  42 . The general construction and operation of gas turbine engines is well-known in the art. 
     As shown in  FIG. 1 , low pressure unit  12  is coupled to fan shaft  34  via epicyclic gear system  36 . Sun gear  42  is attached to and rotates with low pressure shaft  18 . Sun gear  42  is rotatably mounted the low pressure shaft  18 . Ring gear  40  is connected to fan shaft  34  which turns at the same speed as fan  32 . Star gear  38  is enmeshed between sun gear  42  and ring gear  40  such that star gear  38  rotates when sun gear  42  rotates. Star gear  38  is rotatably mounted on the stationary gear carrier (not shown) by stationary journal bearing (not shown). When low pressure unit  12  rotates, epicyclic gear system  36  causes fan shaft  34  to rotate at a slower rotational velocity than that of low pressure unit  12 , but in the opposite direction. 
     In an alternative embodiment to the embodiment shown in  FIG. 1 , epicyclic gear system  36  can be configured in a different manner sometimes called a planetary gear system. In this alternative configuration, star or “planet” gear  38  are rotatably mounted on the gear carrier by bearings. Star gear  38  meshes with sun gear  42 . Mechanically grounded, internally toothed ring gear  40  circumscribes and meshes with star gear  38 . Input and output shafts extend from sun gear  42  and the gear carrier respectively. During operation, the input shaft rotatably drives sun gear  42 , rotating star gear  38  about its own axis, and because ring gear  40  is mechanically grounded, causes star gear  38  to orbit sun gear  42  in the manner of a planet. Orbital motion of star gear  38  turns the gear carrier and the output shaft in the same direction as the input shaft, but slower. 
       FIG. 2  is a cross-sectional view of epicyclic gear system  36  taken through only a single star gear  38 . Epicyclic gear system  36 , however, includes multiple star gears arranged circumferentially around the sun gear  42 . In addition to star gear  38 , ring gear  40 , and sun gear  42 , epicyclic gear system  36  includes journal bearing subassembly  44 , lubricant manifold  46 , carrier  48 , end caps  50  and  51 , alignment pin  52  and bolt  55 . In addition to end caps  50  and  51 , journal bearing subassembly  44  includes central pin  53 , axial passage  54 , cavity  56 , central body pin  57 , filter  58  and radial passages  60 . Radial passages  60  fluidly connect to distribution recess  62 . Lubricant manifold  46  includes fittings  64  and is connected to feed tube  66 . 
     As discussed previously, in one embodiment, low pressure unit  12  ( FIG. 1 ) is coupled to fan shaft  34  via epicyclic gear system  36 . Sun gear  42  is attached to and rotates with low pressure shaft  18  ( FIG. 1 ). Sun gear  42  is rotatably mounted on low pressure shaft  18 . Carrier  48  is stationarily mounted within gas turbine engine  10  ( FIG. 1 ) to the non-rotating engine case walls radially outboard of epicyclic gear system  36 . Carrier  48  has two generally interfacing faces which support the ends of the stationary journal bearing subassembly  44 . Ring gear  40  is connected to fan shaft  34  ( FIG. 1 ) which turns at the same speed as fan  32  ( FIG. 1 ). Star gear  38  (only one is illustrated although epicyclic gear system  36  includes a set of multiple star gears) is enmeshed between sun gear  42  and ring gear  40  such that star gear  38  rotates when sun gear  42  rotates. Star gear  38  is rotatably mounted on the stationary carrier  48  by journal bearing subassembly  44 . When low pressure unit  12  rotates, epicyclic gear system  36  causes fan shaft  34  to rotate at a slower rotational velocity than that of low pressure unit  12 . The operation of similar epicyclic gear systems and lubrication systems for epicycle gear systems are further detailed in U.S. Pat. Nos. 6,223,616 and 5,102,379, which are herein incorporated by reference. 
     In the embodiment shown in  FIG. 2 , stator journal bearing subassembly  44  is positioned inside of rotatable star gear  38 . Lubricant manifold  46  is disposed adjacent to journal bearing subassembly  44  and is fluidically connected thereto. Star gear  38  is rotatably mounted on carrier  48  by journal bearing subassembly  44 . End caps  50  and  51  of journal bearing subassembly  44  are welded to ends of central body pin  57 . End cap  50  has a flange with holes in it for accepting alignment pin  52  and bolt  55  such that journal bearing subassembly  44  can be securely attached and aligned with apertures in carrier  48 . End cap  51  is configured without a flange so that it fits through an aperture in carrier  48  making generally radial contact with the carrier  48  and the central body pin  57 . End caps  50  and  51  are welded or otherwise affixed to journal bearing subassembly  44 . End caps  50  and  51  provide support for journal bearing subassembly  44 . In one embodiment, end caps  50  and  51  are electron beam welded to the ends of central body pin  57  and are press fit into carrier  48 . Alignment pin  52  is fitted into carrier  48  and extends through end cap  50 . Bolt  55  secures journal bearing subassembly  44  to carrier  48 . As discussed subsequently with respect to  FIG. 3 , a plurality of end caps  50  and alignment pins  52  are anti-rotated to align radial passages  60  relative to carrier  48  to ensure proper lubrication distribution between journal bearing subassembly  44  and star gear  38  and to keep journal bearing subassembly  44  from rotating under extreme loads such as those that occur during a touchdown event. 
     Central pin  53  and fitting  64  define axial passage  54  which is fluidly connected to lubricant manifold  46 . Lubricant manifold  46  is fed pressurized lubricant from other components of the gas turbine engine via feed tube  66 . Liquid lubricant from lubricant manifold  46  is supplied through axial passage  54  to cavity  56 . Cavity  56  houses filter  58 . In one embodiment, filter  58  is constructed of wire mesh with stainless steel screen and is rated to trap particulates or debris larger than about 45 microns (.0018 inches) in diameter. Filter  58  is inserted within cavity  56  and is held in place by means of a snap ring which presses into grooves or other features in the walls of the cavity  56 . The close proximity of filter  58  to the surface of journal bearing subassembly  44  allows filter  58  to more effectively trap particulates or debris in the lubricant before the lubricant passes to the surface of bearing  44  (an area of high heat and friction). Filter  58  is an important feature to trap debris since journal bearing subassembly  44  is not tolerant of contamination due to the extremely thin lubricant film it employs during operational load. 
     After being filtered, the lubricant flows through radial passages  60  into distribution recess  62  between journal bearing subassembly  44  and star gear  38 . In one embodiment, distribution recess  62  extends in an arch along about 30° of the exterior surface of journal bearing subassembly  44 . The lubricating liquid forms a film of lubrication on journal bearing subassembly  44  in the distribution recess  62 . From distribution recess  62  the film of lubrication spreads circumferentially and axially due to viscous forces between star gear  38  and journal bearing subassembly  44 . The lubricant film helps to support star gear  38  and reduce friction between the interior surface of star gear  38  and the exterior surface of journal bearing subassembly  44  as star gear  38  rotates. To ensure adequate thickness of the lubricant film, the rate the lubricant is fed to the external surface of the journal bearing subassembly  44  varies and is determined by the pressure profile and temperature at the interface between star gears  38  and journal bearings subassembly  44 . In one embodiment, the flow rate of the lubricant provides the external surface of journal bearing subassembly  44  with a minimum lubricant film thickness of between about 0.013 mm (500 micro inches) and 0.051 mm (2000 micro inches) in the load zone (defined subsequently). 
       FIG. 3  shows a schematic view of the entire epicyclic gear system  36  taken along section  3 - 3  of  FIG. 2 . Because  FIG. 3  shows the entire epicycle gear system  36  a plurality of star gears  38  are illustrated. These star gears  38  are mounted on carrier  48  by a plurality of journal bearing subassemblies  44 . In  FIG. 3 , end caps  50  and alignment pins  52  are shown in phantom because they would not be visible to the viewer along section  3 - 3  of  FIG. 2 . In addition to the components previously discussed, the epicyclic gear system  36  includes baffles or spray bars  68 . 
     As discussed previously with reference to  FIG. 2 , lubricant introduced into the journal bearing/star gear interface spreads axially and circumferentially to form a load supporting lubricant film between journal bearing subassembly  44  outer surface and star gear  38  inner surface. Each journal bearing subassembly  44  is connected to end caps  50  and  51  by welding. Alignment pins  52  extend through end caps  50  and connect to carrier  48  (not shown) to act as an anti-rotation feature to keep the assembly from spinning within carrier  48  due to the additional forces epicyclic gear assembly  36  experiences during touchdown or a bird strike. Touchdown/landing or a bird strike exerts extreme forces that can interfere with the spread of lubricant film between the journal bearing subassembly  44  and star gear  38 . Each alignment pin  52  also acts as a locator device by statically affixing the corresponding journal bearing subassembly  44  to a particular location of the carrier  48 . By fixing the angular orientation of each journal bearing subassembly  44  with respect to carrier  48 , each journal radial passage  60  is held in a fixed location with respect to rotating star gear  38 , ring gear  40 , and sun gear  42 , thereby ensuring that radial passages  60  of each journal bearing subassembly  44  are angularly aligned to bearing load. Load zone L (an area of most critical bearing load) is identified using finite element analysis as the region between journal bearing subassembly  44  and star gear  38  requiring at least a minimum lubricant film to react load and avoid excessive friction and wear. Thus, proper angular alignment of radial passages  60  relative to load zone L provides time for lubricant film to spread (in both the axial and circumferential directions) between journal bearing subassembly  44  outer surface and star gear  38  inner surface as star gear  38  rotates relative to stator journal bearing subassembly  44 . Thus, by the time lubricant film has reached load zone L it has achieved a thickness sufficient to react load and avoid excessive friction and wear. In the embodiment shown, proper angular alignment of the radial passages  60  is achieved by positioning the radial passages  60  outside of load zone L. In this embodiment, if radial passages  60  were extended along their radial paths the centerline of the radial passages  60  would intersect with the point of tangential contact between the ring gear  40  and star gear  38 . 
     After forming a film between journal bearing subassembly  44  and star gear  38 , lubricant is discharged from the axial extremities of the bearing interface. Substantially all of the discharged lubricant is directed into the sun/star mesh, partly because of the presence of the nearby baffle  68 . The directed lubricant cools and lubricates the sun and star gear teeth and then is expelled from the sun/star mesh. The adjacent baffle  68  then guides substantially all of the expelled lubricant radially outwardly into the star/ring mesh. The lubricant is then ejected from the star/ring mesh and centrifugally channeled away from the epicyclic gear system  36 . 
     It will be recognized that the present invention provides numerous benefits and advantages. For example, placing filter  58  within each journal bearing subassembly  44  allows filter  58  to act as a last chance screen to trap debris since journal bearings subassembly  44  are not tolerant of contamination due to the extremely thin lubricant film they employ during operational load. Similarly, alignment pin  52  ensures proper angular alignment of radial passages  60  by statically affixing journal bearing subassembly  44  to a particular location in the carrier  48 . By affixing each journal bearing subassembly  44  to carrier  48 , each journal bearing subassembly  44  is held in a fixed location with respect to rotating star gear  38 , ring gear  40 , and sun gear  42 , thereby ensuring that radial passages  60  of each journal bearing subassembly  44  are angularly aligned to bearing load such that adequate lubricant film can spread axially and circumferentially between journal bearing subassembly  44  outer surface and star gear  38  inner surface in critical load zone L. These features, and others, reduce epicyclic gear system wear thereby prolonging service life of the system. 
     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.