Abstract:
A bearing scavenge system comprises a scavenging passage extending axially through a rotating shaft supported by the bearing assembly. Oil and air are drawn from an oil cavity of the bearing assembly and evacuated through the rotating shaft as the shaft rotates.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention generally relates to gas turbine engines and, more particularly, to oil scavenging systems.  
         [0003]     2. Description of the Prior Art  
         [0004]     Proper scavenging of used oil in bearing assemblies is essential to prevent overheating and premature wear of gas turbine engine mechanical parts. The used oil is usually circulated to an oil treatment system to remove air and particles therefrom before being returned to the bearing assemblies.  
         [0005]     Oil scavenging systems typically rely on a simple pressure imbalance to direct the used oil into collection tubes for transport to a main oil pump of the oil treatment system. More efficient systems have been devised, employing special pumps or spinning vanes to improve the used oil circulation. However, such special pumps and vanes increase the weight of the engine and thus the costs of operation.  
         [0006]     Accordingly, there is a need for an efficient scavenge system for a bearing assembly that has a minimal weight.  
       SUMMARY OF THE INVENTION  
       [0007]     It is therefore an aim of the present invention to provide an improved scavenge system for a bearing assembly of a gas turbine engine.  
         [0008]     Therefore, in accordance with a general feature of the present invention, there is provided a scavenge system for a bearing assembly, the system comprising a scavenging passage extending axially through a rotating shaft supported by the bearing assembly, and at least one scoop provided on the rotating shaft, said at least one scoop impelling oil internally of said rotating shaft into said scavenging passage as said at least one scoop rotates with said rotating shaft.  
         [0009]     In accordance with a further general aspect of the present invention, there is provided a scavenge system for a bearing assembly, the system comprising a scavenging passage extending axially through a rotating shaft supported by the bearing assembly, and means provided on the rotating shaft for drawing oil internally of said rotating shaft into said scavenging passage as said shaft rotates.  
         [0010]     In accordance with a further general aspect of the present invention, there is provided a gas turbine engine comprising a compressor section, a combustor and a turbine section in serial flow communication with one another, a main rotating shaft supported by a bearing assembly, and a scavenge system for the bearing assembly, the scavenge system comprising a scavenging passage extending axially through said main rotating shaft, and at least one inlet hole defined in said main rotating shaft and in flow communication with said scavenging passage, said at least one inlet hole extending at an angle to a radius of the main rotating shaft to thereby cause oil about the rotating shaft to be drawn into said scavenging passage in said main shaft via said at least one inlet hole as said main shaft rotates.  
         [0011]     Also in accordance with another general aspect of the present invention, there is provided a scavenge system for a bearing assembly supporting a rotating shaft in a gas turbine engine, the system comprising first fluid communication means between a lubricant cavity containing the bearing assembly and an annular inner surface closely surrounding an outer surface of the rotating shaft, second fluid communication means within the rotating shaft communicating with a stationary chamber, and third fluid communication means between the outer surface of the rotating shaft and the second fluid communication means, the third fluid communication means being defined such as to communicate with the first fluid communication means during at least a portion of a rotation of the shaft, and such that the rotation of the shaft causes used lubricant coming from the lubricant cavity to be moved from the first fluid communication means to the third fluid communication means so as to deliver the used lubricant to the stationary chamber through the second fluid communication means.  
         [0012]     In accordance with a still further general aspect of the present invention, there is provided a method of evacuating scavenge air and oil from a bearing assembly supporting a main shaft of a gas turbine engine, the method comprising the steps of: a) feeding the scavenge air and oil from the bearing assembly to an interface with said main shaft, b) drawing the scavenge air and oil from said interface into said main shaft, and c) evacuating the oil axially through said main shaft. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     Reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment of the invention and in which:  
         [0014]      FIG. 1  is a schematic side view of a gas turbine engine, in partial cross-section, to which an embodiment of the present invention is applied;  
         [0015]      FIG. 2  is a cross-sectional side view showing bearing assemblies supporting a rotating shaft of the gas turbine engine of  FIG. 1 ; and  
         [0016]      FIG. 3  is a cross-sectional view of a scavenge system taken along lines B-B of  FIG. 2 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]      FIG. 1  illustrates a gas turbine engine  10  of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan  12  through which ambient air is propelled, a multistage compressor  14  for pressurizing the air, a combustor  16  in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section  18  for extracting energy from the combustion gases. A rotating shaft  20  extends within the engine  10  and transfers energy from the turbine section  18  to the compressor  14  and the fan  12 .  
         [0018]     Referring to  FIG. 2 , the rotating shaft  20  is supported by a plurality of annular bearing assemblies  22 , as well known in the art. Each annular bearing assembly  22  comprises a series of roller bearings  24  located in a bearing compartment  26 . The bearing compartment  26  is defined such that each bearing assembly  22  is located within an annular oil cavity  28 . The annular oil cavity  28  contains oil providing adequate lubrication to the bearing assembly  22 .  
         [0019]     During use, used oil from the oil cavity  28  is circulated to an oil treatment system (not shown) in order to remove unwanted debris and air from the used oil. A scavenge system  40  is used to direct the mixture of air and oil from the oil cavity  28  to the oil treatment system. The scavenge system  40  is illustrated in  FIGS. 2-3  and will be described in the following.  
         [0020]     In the bearing compartment  26 , a series of axial tubes  50  extend along an axial direction of the rotating shaft  20 , and a series of radial tubes  48  extend along a radial direction relative to the rotating shaft  20 . Each axial tube  50  has one end connected to one end of a corresponding radial tube  48 . The opposed end of each axial tube  50  is in fluid communication with the oil cavity  28 . The opposed end of each radial tube  48  defines an opening  51  in an inner annular surface of the bearing assembly  22  which closely surrounds the rotating shaft  20 . The openings  51  are distributed along a circumference of the inner annular surface.  
         [0021]     The combination of each axial tube  50  with the corresponding radial tube  48  forms a conduit going from the oil cavity  28  to an opening  51  at the interface between the bearing compartment  26  and the rotating shaft  20 .  
         [0022]     An annular channel  42  is defined within the rotating shaft  20  and is concentric therewith. A plurality of holes  44  are defined around a circumference of an outer surface of the rotating shaft  20 . The holes  44  are in fluid communication with the annular channel  42 . The holes  44  are preferably perpendicular to the annular channel  42  and defined at a large angle with respect to a radius of the rotating shaft  20 . The holes  44  are machined so that the remaining shaft material between adjacent holes forms a curved scoop  46 . The holes  44  are located in the same diametrical plane as the openings  51 , such that each hole  44  can be aligned in turn with each opening  51  and be in fluid communication therewith during the rotation of the shaft  20 .  
         [0023]     The scoops  46  preferably have a curved section, and are progressively thinner toward the outer surface of the shaft  20 . As such, they have a profile which is similar to an airfoil. The scoops  46  are curved in the direction of rotation of the shaft  20  as depicted by arrow  47  in  FIG. 3 . A space between adjacent scoops  46 , which is curved and thinner toward the center of the shaft  20 , defines the shape of the holes  44 . The shape and angle of the holes  44  and scoops  46  minimizes the effects of the centrifugal forces acting to push the air and oil mixture away from the shaft  20 . Thus, a rotation of the holes  44  and scoops  46  brought by the rotation of the shaft  20  will “pick up” and draw the air and oil mixture coming from the openings  51  to bring it to the annular channel  42  through the holes  44 .  
         [0024]     Because the angle of the holes  44  with respect to the radial direction of the shaft  20  is preferably large, the number of holes  44  and scoops  46  is preferably limited to three. As illustrated in  FIG. 3 , a preferred embodiment of the scavenge system  40  includes three groups having each three radial tubes  48  and axial tubes  50  defined in proximity to one another such as to have a common opening  51  for each group. The holes  44 , scoops  46  and groups of tubes  48 ,  50 , are all equally angularly spaced apart in order to provide a balanced scavenge system  40 .  
         [0025]     Thus, the mixture of air and oil can be transported from the oil cavity  28  to the openings  51  at the interface between the bearing compartment  26  and the rotating shaft  20 , then from the openings  51  to the holes  44 . The mixture then travels along the annular channel  42  to an extremity thereof which extends such as to define an annular exit port at the end of the shaft  20 . This exit port provides fluid communication between the annular channel  42  and a stationary chamber  52  located at the downstream end of the shaft  20 , where the mixture is collected. Pipes  54  provide fluid communication between the chamber  52  and an oil treatment system. A sufficient pressure gradient ensures that the air and oil mixture will circulate adequately from the oil cavity  28  to the oil treatment system following arrow  56 . The following treatment of the air and oil mixture and subsequent return of the cleaned oil to the oil cavity  28  is well known in the art and as such will not be discussed herein.  
         [0026]     In an alternate embodiment, it is contemplated to replace the chamber  52  located at the end of the shaft  20  by an annular stationary chamber located around the rotating shaft  20  and in fluid communication with the channel  42  through a series of radial holes. In this case, the centrifugal forces acting on the used oil propels it from the channel  42  to the annular chamber, where it can be led to the oil treatment system through appropriate piping.  
         [0027]     The scavenge system  40  can also be used with other types of bearing assemblies supporting a rotating shaft, and as such should not be construed as being limited to aircraft engines.  
         [0028]     The scavenge system  40  uses a channel  42  which is directly machine within the shaft, and scoops  46  are preferably formed by removing material from the rotating shaft  20  in order to machine the holes  44 . Thus, these components reduce the weight of the rotating shaft rather than increase the overall engine weight, as added components would. The scavenge system  40  therefore has the advantage of representing a minimal weight increase for the engine.  
         [0029]     It is understood that the present invention applies to any gas turbine engines, and in fact to any rotating machinery in which oil is scavenged.  
         [0030]     The embodiments of the invention described above are intended to be exemplary. Those skilled in the art will therefore appreciate that the forgoing description is illustrative only, and that various alternatives and modifications can be devised without departing from the spirit of the present invention. Accordingly, the present is intended to embrace all such alternatives, modifications and variances which fall within the scope, of the appended claims.