# Patent

## Title
Rotating shaft scavenging scoop

## 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.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application is a divisional of Ser. No. 10/802,830, now U.S. Pat. No. 7,124,857 filed Mar. 18, 2004 and issued on Oct. 24, 2006.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to gas turbine engines and, more particularly, to oil scavenging systems.
2. Description of the Prior Art
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.
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.
Accordingly, there is a need for an efficient scavenge system for a bearing assembly that has a minimal weight.
SUMMARY OF THE INVENTION
It is therefore an aim of the present invention to provide an improved scavenge system for a bearing assembly of a gas turbine engine.
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.
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.
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.
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.
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
Reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment of the invention and in which:
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;
FIG. 2 is a cross-sectional side view showing bearing assemblies supporting a rotating shaft of the gas turbine engine of FIG. 1; and
FIG. 3 is a cross-sectional view of a scavenge system taken along lines B-B of FIG. 2.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
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.
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.
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.
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.
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.
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.
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.
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.
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 exist 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.
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.
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.
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.
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.
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.

## Claims

1. A method of evacuating scavenge air and oil from a bearing assembly supporting a main hollow 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 hollow shaft, b) drawing the scavenge air and oil from said interface radially inwardly into said main hollow shaft, and c) evacuating the oil axially internally through said main hollow shaft.

2. A method as defined in claim 1, wherein step a) comprises the steps of: defining a plurality of circumferentially aligned openings in an annular surface of a bearing compartment, the annular surface being located at the interface between the bearing compartment and the main shaft, and providing fluid communication between the bearing compartment and the openings.

3. A method as defined in claim 2, wherein step b) comprises the steps of: defining a plurality of circumferentially aligned holes in the rotating shaft at the interface, the holes being defined such as to create an interaction between the holes and the openings which draws the air and oil radially inwardly from the openings to the holes upon rotation of the main shaft.

4. A method as defined in claim 3, wherein step c) comprises the steps of: providing fluid communication within the main shaft from the holes to a stationary chamber; and rotating the main shaft so as to produce the interaction between the holes and the openings such that the air and oil are moved from the bearing compartment to the stationary chamber.

5. A method as defined in claim 1, wherein step b) comprises scooping the oil with at least one scoop defined on said hollow shaft.

6. A method as defined in claim 5, comprising directing the oil at a surface closely surrounding the hollow shaft and scooping the oil from the surface as the shaft is rotated.