Abstract:
An oil spreader for a gearbox includes: an annular body with a central axis, opposed upper and lower ends, an upper portion adjacent the upper end, and a lower portion adjacent the lower end, the lower portion comprising at least two vanes extending between the upper portion and an annular ring disposed at the lower end, the vanes defining slots therebetween.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to gearboxes and more particularly to control of oil flow in gearboxes for gas turbine engines. 
         [0002]    A gas turbine engine usually includes one or more mechanically-driven accessories, such as fuel or oil pumps, generators or alternators, control units, and the like. Such accessories are mounted to an accessory gearbox (“AGB”) which extracts torque from the engine, and drives each accessory at the required rotational speed, using an internal gear train. 
         [0003]    Pressurized oil flow is delivered to the AGB for lubrication and cooling. The spent oil from the AGB drains back to a supply and scavenging system of the engine. Because such engines are often used in aircraft, the engine&#39;s orientation (i.e. its roll and pitch angle) varies significantly during operation. 
         [0004]    Some engine orientations can cause an excessive amount of oil draining from the AGB to flow into a bearing sump of the engine, instead of directly to an oil tank. This excessive oil inflow can exceed the capability of the supply and scavenge system to remove or scavenge oil from the sump. This in turn can cause churning or flooding of oil in the sump, which in turn can cause engine stalls. It is possible to control oil flow with devices such as baffles. However, such devices have a significant size and therefore cannot be installed without extensive disassembly of the gearbox. 
         [0005]    Accordingly, there is a need for a compact device to control oil drain flow within a gearbox. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    This need is addressed by the present invention, which provides a compact rotating oil spreader which can be mounted to a rotating shaft of a gearbox. 
         [0007]    According to one aspect of the invention, an oil spreader for a gearbox comprises: an annular body with a central axis, opposed upper and lower ends, an upper portion adjacent the upper end, and a lower portion adjacent the lower end, the lower portion comprising an array of at least two vanes extending between the upper portion and an annular ring disposed at the lower end, the vanes defining slots therebetween 
         [0008]    According to another aspect of the invention a gearbox comprises: a housing enclosing at least one gear; an input shaft mounted for rotation in the housing, the input shaft having a central axis, and upper and lower ends; an oil spreader attached to and surrounding a portion of the input shaft, the oil spreader comprising: an annular body having a central axis, opposed upper and lower ends, an upper portion adjacent the upper end, and a lower portion adjacent the lower end, the lower portion comprising at least two vanes extending between the upper portion and an annular ring disposed at the lower end, the vanes defining slots therebetween. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
           [0010]      FIG. 1  is a perspective view of a gas turbine engine incorporating an accessory gearbox constructed according to an aspect of the present invention; 
           [0011]      FIG. 2  is a partially-sectioned front elevation view of an accessory gearbox in a first orientation; 
           [0012]      FIG. 3  is a partially-sectioned front elevation view of an accessory gearbox in a second orientation; 
           [0013]      FIG. 4  is a partially-sectioned front elevation view of the gearbox of  FIG. 2  with an oil spreader constructed according to an aspect of the present invention installed therein, showing an upper bearing assembly thereof; 
           [0014]      FIG. 5  is a partially-sectioned front elevation view of the gearbox of  FIG. 2  with an oil spreader constructed according to an aspect of the present invention installed therein, showing a lower bearing assembly thereof; 
           [0015]      FIG. 6  is a top plan view of an oil spreader constructed according to an aspect of the present invention; 
           [0016]      FIG. 7  is a side elevation view of the oil spreader of  FIG. 6 ; 
           [0017]      FIG. 8  is a view taken along lines  8 - 8  of  FIG. 7 ; and 
           [0018]      FIG. 9  is a cross-sectional view of the oil spreader of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIG. 1  depicts an aircraft gas turbine engine  10 . The illustrated example is a turboshaft engine, but the principles of the present invention are applicable to any type of gearbox having a circulating oil supply. The engine  10  has an accessory gearbox (“AGB”)  12  mounted to it. Various shaft-driven engine accessories (shown generally at  14 ), such as oil and fuel pumps, starters, generators, alternators, etc. are mounted to the AGB  12 . Torque from the engine  10  is transferred through a gear train housed within the AGB  12  to drive each of the individual accessories  14 . 
         [0020]      FIG. 2  is a partially cut-away view of the AGB  12 . The AGB  12  has a stationary housing  16 . A shaft  18 , also referred to as an “A-axis shaft”, is mounted in the housing  16  and extends along a radial axis (labeled “A”) that intersects the longitudinal centerline axis of the engine  10 . The shaft  18  has an inner end  20  and an outer end  22 . The inner end  20  is engaged with a drive gear (not shown) of the engine  10 . The outer end  22  carries a bevel gear  24  which engages another bevel gear  26 . The bevel gear  26  is engaged with other gears (not shown) within the housing  16 . The gears are configured in a known manner to drive multiple output shafts at the speeds and directions needed for the various accessories  14  (shown in  FIG. 1 ). 
         [0021]      FIGS. 4 and 5  show in more detail how the shaft  18  is mounted. Specifically, the shaft  18  rotates in an upper bearing assembly  28  and a lower bearing assembly  30 . It is noted that, as used herein, directional terms applied to certain components (for example, “upper”, “lower”, “inner”, and “outer”) are intended for the purpose of convenient reference and description, and do not imply that any particular orientation of the component is necessary relative to the external environment. 
         [0022]    The upper bearing assembly  28  comprises an outer race  32  received in an upper bore  34  of the housing  16 , an inner race  36  fixedly attached to the shaft  18  (for example by interference fit), and a plurality of rolling elements  38  such as balls or rollers disposed between the inner and outer races  36  and  32 . As used herein, the term “fixedly” means that the two components which are “fixedly attached” to each other do not experience relative movement to each other during normal operation of the AGB  12 . The diameter of the upper bore  34  is selected to be greater than the maximum diameter of the bevel gear  24 . 
         [0023]    The lower bearing assembly  30  (best seen in  FIG. 5 ) comprises an annular outer race  40  fixedly mounted to a lower bore  42  in the housing  16  (for example by interference fit), an annular inner race  44  fixedly mounted to the shaft  18  (for example by interference fit), and a plurality of rolling elements  46  such as balls or rollers disposed between the inner and outer races  44  and  40 . 
         [0024]    Referring back to  FIG. 2 , the interior of the housing  16 , including the upper and lower bearing assemblies  28  and  30 , is provided with a flow of lubricant such as petroleum-based oil for cooling and lubrication. The lubricant flow is provided by a supply and scavenging system of a known type, which is not shown. The spent oil drains vertically downward by gravity. Some of the oil drain flow (shown by arrow “D 1 ”) passes along a first internal flow path which leads to an oil tank  48  (shown schematically in  FIG. 2 ). The remainder of the oil drain flow (shown by arrow “D 2 ”) runs along a second internal flow path, down the exterior of the shaft  18 , and eventually into a bearing sump  50  of the engine (shown schematically in  FIG. 2 ). The oil tank  48  and the bearing sump  50  are both part of the supply and scavenging system.  FIG. 2  corresponds to conditions during level-flight operation of the engine. In this orientation, an arrow “G” representing a vertical or 12:00 o&#39;clock direction of the AGB  12  coincides with an earth-vertical vector “V” shown. In this orientation, the proportion of the oil drain flow passing into the bearing sump  50  is within the design capacity of the supply and scavenging system to remove excess oil from the bearing sump  50 . 
         [0025]      FIG. 3  corresponds to operation of the engine  10  and AGB  12  in a position rolled away from the vertical orientation. In this orientation, an arrow “G” representing a vertical or 12:00 o&#39;clock direction of the AGB  12  defines a nonzero angle θ with an earth-vertical vector V. In this orientation, a greater proportion of the oil drain flow D 2  passes down along the shaft  18  and into the bearing sump  50  than when then engine  10  is in a vertical orientation. Under some circumstances this flow can exceed the scavenging ability of the bearing sump  50 , leading to oil churning and/or flooding, and possibly causing engine stalls. 
         [0026]    To prevent undesired oil drain flow in to the bearing sump  50 , the AGB is provided with an oil spreader  52  (seen in  FIG. 5 ) which is attached to the shaft  18  just below the lower bearing assembly  30 . 
         [0027]      FIGS. 6-9  illustrate the oil spreader  52  in more detail. The oil spreader has an annular body (generally in the shape of a hollow cylinder) with a central axis “C”, an upper end  54 , and a lower end  56 . As illustrated it is a single integral component made from a metal alloy, but it could be built up from smaller components. It is roughly divided into an upper portion  58  and a lower portion  60 . The interior of the upper portion  58  is provided with female threads  62 , and the exterior may be formed into wrenching flats  64 , i.e. planar surfaces arranged in a hexagon or other shape to facilitate installation and removal of the oil spreader  52  using a wrench, spanner, or other similar tool. The maximum outer diameter of the oil spreader  52  is less than the inside diameter of the outer race  40  of the lower bearing assembly  30 . 
         [0028]    An annular array of circumferentially spaced-apart vanes  66  extend in a generally axial direction between the upper portion  58  and a ring  68  located at the lower end  56 . The ring  68  interconnects the distal ends of the vanes  66 . Open slots  70  are defined between the sidewalls  72  of each pair of adjacent vanes  66 . The vanes  66  are configured so as to function as a centrifugal pump and effectively create a radially outward air flow when the oil spreader  52  rotates about its central axis C. In the illustrated example, each of the vanes  66  is defined in part by two sidewalls  72  oriented at an oblique angle to each other, creating a wedge-shaped in cross-section. The sidewalls  72  of adjacent vanes  66  are aligned parallel to a radial direction, denoted “r” in  FIG. 8 . Depending on the particular application, the vanes  66  may have a different cross-sectional shape or may be turned at a different angle relative to the radial direction r in order to provide an effective air flow. The number and size of the vanes  66  may also be varied to suit a particular application. 
         [0029]    The oil spreader  52  is shown installed in  FIG. 5 . The female threads  62  engage mating male threads  74  of the shaft  18 , and the oil spreader  52  is screwed into position abutting the inner race  44  of the lower bearing assembly  30 . The oil spreader  52  may be installed without disassembling or removing the AGB  12  from the engine  10 . To accomplish this, a cover  76  (seen in  FIG. 4 ) is removed and the shaft  18  is withdrawn from the AGB  12 . The oil spreader  52  is then threaded onto the shaft  18 . The shaft  18  is then reinserted. Because the outer diameter of the oil spreader  52  is less than the inside diameter of the outer race  40 , it is able to pass therethrough without interference. Finally the cover  76  is replaced. 
         [0030]    In operation, the rotating oil spreader  52  generates a radially outward flow of air, in the manner of a centrifugal pump. This flow of air (shown schematically by the block arrows in  FIG. 5 ) entrains oil and directs it away from the shaft  18  and the flowpath to the bearing sump  50 , and towards the oil tank  48  (seen in  FIG. 3 ). This ensures that the flow rate of oil into the bearing sump  50  is not excessive regardless of the orientation of the AGB  12 . 
         [0031]    The oil spreader described herein has several advantages as compared to prior art configurations. It can be both a production component and a field retrofit. It is inexpensive and in the case of a field retrofit, it does not require removal of the AGB  12 , as the shaft  18  can be removed and reinstalled while the AGB  12  remains installed on the engine  10 . This represents a significant savings in time, effort, and cost compared to other means for controlling oil flow. 
         [0032]    The foregoing has described an oil spreader for a gearbox. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation, the invention being defined by the claims.