# Patent

## Title
Geared fan with inner counter rotating compressor

## Abstract

A gas turbine engine comprises a fan section including a fan hub supporting a plurality of fan blades for rotation relative to a fan case, a shaft rotatable relative to the fan case about an engine center axis, and a geared architecture driven by the shaft to provide driving output to rotate the fan hub. A compressor is positioned forward of the geared architecture and radially inward of the fan blades, with the compressor being driven by the shaft.

## Background
BACKGROUND OF THE INVENTION
A gas turbine engine includes a fan section, a compressor section, a combustor section, and a turbine section. The fan section drives air along a bypass flowpath while the compressor section drives air along a core flowpath for compression and communication into the combustor section then expansion through the turbine section
The engine typically includes a low speed shaft and a high speed shaft mounted for rotation about an engine central longitudinal axis relative to an engine static structure via several bearing systems. The high speed shaft interconnects a high pressure compressor and high pressure turbine. The low speed shaft interconnects a fan, a low pressure compressor, and a low pressure turbine. In one example, the low speed shaft is connected to the fan through a geared architecture to drive the fan at a lower speed than the low speed shaft. The low pressure compressor is positioned aft or rearward of the geared architecture. An example engine configuration having this low pressure compressor position is found in U.S. Pat. No. 8,176,725.
The core airflow is compressed by the low pressure compressor then the high pressure compressor, mixed and burned with fuel in a combustor, then expanded over the high pressure turbine and low pressure turbine. The turbines rotationally drive the respective low speed and high speed shafts in response to the expansion. This typical arrangement provides a geared turbofan of significant length. In certain applications shorter engine lengths are needed.
SUMMARY OF THE INVENTION
In a featured embodiment, a gas turbine engine has a fan section including a fan hub supporting a plurality of fan blades for rotation relative to a fan case. A shaft is rotatable relative to the fan case about an engine center axis. A geared architecture is driven by the shaft and provides driving output to rotate the fan hub. A compressor is positioned forward of the geared architecture and radially inward of the fan blades, the compressor being driven by the shaft.
In another embodiment according to the previous embodiment, the compressor includes a rotor. The shaft directly drives the rotor.
In another embodiment according to any of the previous embodiments, the compressor comprises a low pressure compressor having a plurality of blades fixed for rotation with the shaft and a plurality of vanes fixed to the fan hub.
In another embodiment according to any of the previous embodiments, the low pressure compressor is comprised of a plurality of stages.
In another embodiment according to any of the previous embodiments, the compressor includes a rotor directly driven by the shaft. The plurality of stages comprises at least a first stage having a first set of blades directly coupled to the shaft and a first set of vanes mounted to the fan hub, and a second stage having a second set of blades mounted to the rotor and a second set of vanes mounted to the fan hub.
In another embodiment according to any of the previous embodiments, the vanes rotate with the fan hub in one direction while the blades rotate with the shaft in an opposite direction.
In another embodiment according to any of the previous embodiments, at least one inter-shaft bearing is mounted between the shaft and a set of vanes to support the vanes for rotation relative to the shaft.
In another embodiment according to any of the previous embodiments, a static structure and at least one fan support bearing supports the fan hub for rotation relative to the static structure. The geared architecture is comprised of a sun gear that is driven by the shaft. A plurality of star gears is supported by a carrier fixed to the static structure and in meshing engagement with the sun gear, and an outer annular gear in meshing engagement with the star gears.
In another embodiment according to any of the previous embodiments, the fan hub includes a plurality of fan drive struts. The outer annular gear provides driving input to the fan drive struts.
In another embodiment according to any of the previous embodiments, the at least one fan support bearing comprises at least a first bearing positioned radially between the fan drive struts and the static structure.
In another embodiment according to any of the previous embodiments, a second bearing is positioned radially between the fan hub and the static structure, and is positioned forward of the first bearing.
In another embodiment according to any of the previous embodiments, the fan section includes a plurality of static vanes extending between the fan case and the static structure.
In another embodiment according to any of the previous embodiments, the compressor includes a rotor that is directly driven by the shaft. The compressor includes a first stage with a first set of blades fixed to a forward end of the shaft and a first set of vanes mounted to the fan hub, a second stage aft of the first stage and including a second set of blades mounted to the rotor and a second set of vanes mounted to the fan hub, and a third stage aft of the second stage and including a third set of blades mounted to the rotor.
In another featured embodiment, a gas turbine engine has a fan section including a fan outer case, a static structure positioned radially inward of the fan outer case, and a fan hub supporting a plurality of fan blades for rotation relative to the static structure. At least one fan support bearing supports the fan hub for rotation relative to the static structure. A shaft is rotatable relative to the static structure about an engine center axis. A geared architecture is driven by the shaft and provides driving output to rotate the fan hub. A low pressure compressor is positioned forward of the geared architecture and radially inward of the fan blades. The compressor is driven directly by the shaft.
In another embodiment according to the previous embodiment, the geared architecture is comprised of a sun gear that is driven by the shaft. A plurality of star gears is supported by a carrier fixed to the static structure and in meshing engagement with the sun gear, and an outer annular gear in meshing engagement with the star gears to drive the fan hub.
In another embodiment according to any of the previous embodiments, the fan hub includes a plurality of fan drive struts. The outer annular gear is drivingly engaged with the fan drive struts.
In another embodiment according to any of the previous embodiments, the at least one fan support bearing comprises at least a first bearing positioned radially between the fan drive struts and the static structure and a second bearing positioned radially between the fan hub and the static structure. The second bearing is located axially forward of the first bearing.
In another embodiment according to any of the previous embodiments, the first bearing comprises a roller bearing and the second bearing comprises a ball bearing.
In another embodiment according to any of the previous embodiments, the low pressure compressor is comprised of at least one stage having a set of blades driven by the shaft and a set of vanes positioned aft of the set of blades. The vanes rotate with the fan hub in one direction while the blades rotate with the shaft in an opposite direction.
In another embodiment according to any of the previous embodiments, at least one inter-shaft bearing is mounted between the shaft and set of vanes to support the vanes for rotation relative to the shaft.
These and other features of this application will be best understood from the following specification and drawings, the following of which is a brief description.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically illustrates a fan section and low pressure compressor of a gas turbine engine.
FIG. 2 schematically illustrates a high pressure compressor, combustor and turbine section of the gas turbine engine.



DETAILED DESCRIPTION
FIGS. 1-2 schematically illustrate a gas turbine engine 20. The gas turbine engine 20 is disclosed herein as a two-spool turbofan that generally incorporates a fan section 22, a compressor section 24, a combustor section 26 and a turbine section 28. Alternative engines might include an augmentor section (not shown) among other systems or features. The fan section 22 drives air along a bypass flowpath B while the compressor section 24 drives air along a core flowpath C for compression and communication into the combustor section 26 then expansion through the turbine section 28. Although depicted as a turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures.
The engine 20 generally includes a low speed spool 30 and a high speed spool 32 mounted for rotation about an engine central longitudinal axis A relative to an engine static structure 36 via several bearing systems 38. It should be understood that various bearing systems 38 at various locations may alternatively or additionally be provided.
The low speed spool 30 generally includes an inner shaft 40 that interconnects a low pressure (or first) compressor section 44 and a low pressure (or first) turbine section 46. The fan section 22 includes a fan 42 that is driven by the inner shaft 40 through a geared architecture 48. The high speed spool 32 includes an outer shaft 50 that interconnects a high pressure (or second) compressor section 52 and high pressure (or second) turbine section 54. A combustor 56 is arranged between the high pressure compressor 52 and the high pressure turbine 54. A mid-turbine frame 57 of the engine static structure 36 is arranged generally between the high pressure turbine 54 and the low pressure turbine 46. The mid-turbine frame 57 supports one or more bearing systems 38 in the turbine section 28. The inner shaft 40 and the outer shaft 50 are concentric and rotate via bearing systems 38 about the engine central longitudinal axis A, which is collinear with their longitudinal axes. As used herein, a “high pressure” compressor or turbine experiences a higher pressure than a corresponding “low pressure” compressor or turbine.
The core airflow C is compressed by the low pressure compressor 44 then the high pressure compressor 52, mixed and burned with fuel in the combustor 56, then expanded over the high pressure turbine 54 and low pressure turbine 46. The mid-turbine frame 57 includes airfoils 59 which are in the core airflow path. The turbines 46, 54 rotationally drive the respective low speed spool 30 and high speed spool 32 in response to the expansion.
The engine 20 in one example is a high-bypass geared aircraft engine. In a further example, the engine 20 bypass ratio is greater than about six (6), with an example embodiment being greater than ten (10), the geared architecture 48 is an epicyclic gear train, such as a star gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine 46 has a pressure ratio that is greater than about 5. In one disclosed embodiment, the engine 20 bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor 44, and the low pressure turbine 46 has a pressure ratio that is greater than about 5:1. Low pressure turbine 46 pressure ratio is pressure measured prior to inlet of low pressure turbine 46 as related to the pressure at the outlet of the low pressure turbine 46 prior to an exhaust nozzle. 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.
A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section 22 of the engine 20 is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of lbm of fuel being burned per hour divided by lbf of thrust the engine produces at that minimum point. “Fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. 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.
As shown in FIG. 1, the fan section 22 includes a fan hub 60 supporting a plurality of fan blades 62 for rotation relative to a fan case 64. The geared architecture 48 is driven by the inner shaft 40 and provides driving output to rotate the fan hub 60 such that the fan hub 60 rotates at a slower speed than the inner shaft 40. In one example, the gear ratio between the shaft and the fan is approximately 3:1; however, other ratios could also be used. The low pressure compressor 44 has a rotor 66 that is positioned forward of the geared architecture 48. The rotor 66 receives driving input from the inner shaft 40.
In one example, the inner shaft 40 directly drives the rotor 66, i.e. the rotor 66 is not driven by the shaft via the geared architecture. As such, the rotor 66 of the low pressure compressor 44 is divorced from the fan 42.
In the example shown in FIG. 1, the low pressure compressor 44 is comprised of a plurality of stages 68a, 68b, 68c with each stage of the first 68a and second 68b stages including a set of blades 70 and a set of vanes 72 positioned aft of an associated set of blades 70. In this example, the third stage 68c only includes a set of blades; however, a third set of vanes 72 could also be utilized with the third stage 68c if needed. The set of blades 70 of the first stage 68a are coupled directly to the inner shaft 40. The sets of blades 70 of the second 68b and third 68c stages are fixed for rotation with the rotor 66. In this example, the low pressure compressor 44 has three stages; however, it should be understood that the low pressure compressor 44 could have fewer or additional stages than that which is shown.
The blades 70 are fixed for rotation with the inner shaft 40 and the vanes 72 are fixed to the fan hub 60. As such, the vanes 72 rotate with the fan hub 60 in one direction while the rotor 66 and blades 70 rotate with the inner shaft 40 in opposite direction. Further, as the fan hub 60 is driven through the geared architecture 48, the vanes 72 and fan hub 60 rotate at a slower speed than the inner shaft 40, rotor 66, and blades 70.
The bearing system 38 includes at least one inter-shaft bearing 74 that is mounted between the inner shaft 40 and one set of the vanes 72 to provide additional support for the vanes 72 as the shaft 40 and vanes 72 rotate relative to each other. In one example, the inter-shaft bearing 74 supports the vanes 72 of the first stage 68a, i.e. the stage that is foremost located within the engine 20. In the example shown, the inter-shaft bearing 74 is radially aligned with the fan blades 62.
The inner shaft 40 has an increased diameter portion 76 at a forward end 78 of the inner shaft 40. The set of blades 70 for the first stage 68a are directly mounted for rotation with the inner shaft 40 at the increased diameter portion 76. The inter-shaft bearing 74 is positioned aft of these blades 70. The rotor 66 that supports the blades 70 for the second 68b and third 68c stages is positioned aft of the inter-shaft bearing 74.
The engine 20 includes a static structure 80 and one or more fan support bearings 82 that support the fan hub 60 for rotation relative to the static structure 80. In one example, the geared architecture 48 is comprised of a sun gear 84 that is driven by the inner shaft 40 and a plurality of star gears 86 that are supported by a carrier that is fixed to the static structure 80. The star gears 86 are in meshing engagement with the sun gear 84 and an outer annular gear 90 is in meshing engagement with the star gears 86. As such, the inner shaft 40 directly drives the sun gear 84 and the outer annular gear 90 provides driving output to the fan hub 60.
In one example, the fan hub 60 includes a plurality of fan drive struts 92. The fan hub 60 includes a forward end 94 and an aft end 96. The fan blades 62 are fixed to the forward end 94 and extend radially outwardly toward the fan case 64. The fan drive struts 92 are fixed to the aft end 96 and extend radially inwardly toward the engine center axis A. The outer annular gear 90 provides direct driving input to the fan drive struts 92.
In one example, the at least one fan support bearing 82 comprises at least a first bearing 82a positioned radially between the fan drive struts 92 and the static structure 80, and a second bearing 82b positioned radially between the fan hub 60 and the static structure 80. The second bearing 82b is positioned forward of the first bearing 82a. In one example, the second bearing 82b is radially aligned with the second stage 68b of the low pressure compressor 44. Further, the second bearing 82b is positioned axially between the inter-shaft bearing 74 and the first bearing 82a. In one example, the first bearing 82a comprises a roller bearing and the second bearing 82b comprises a ball bearing.
The fan section 22 also includes a plurality of static vanes 100 extending between the fan case 64 and the static structure 80. The static vanes 100 are positioned immediately aft of the fan blades 62.
By locating the low pressure compressor 44 forward of the geared architecture 48, the overall length of the geared turbofan engine can be reduced. The low pressure compressor rotor 66 is not geared and thus rotates substantially faster and in the opposite direction of the geared fan 42. As such, the core (inner) flow path C includes a forward located, counter rotating low pressure compressor 44. The low pressure compressor vanes 72 are connected to the fan hub 60 and thus rotate with the geared fan 42 in the opposite direction in which the fan blades 70 rotate. The fan 42 is driven by the struts 92 that comprise part of the low pressure compressor flow path. As a result of the counter-rotating low pressure compressor blades 70 and vanes 72, the amount of compression per stage (blade/vane) is greater than conventional engines in which the vanes are stationary. Further, as a result of the increase in compression per stage, fewer stages are needed in comparison to conventional engines to achieve the same amount of compression. Finally, as a result of the fewer stages needed, the number of engine parts is correspondingly reduced, which enables the engine to be lighter and shorter in overall axial length, as compared to conventional engines.
Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

## Claims

1. A gas turbine engine comprising:
a fan section including a fan hub supporting a plurality of fan blades for rotation relative to a fan case;
a shaft rotatable relative to the fan case about an engine center axis;
a geared architecture driven by the shaft and providing driving output to rotate the fan hub, wherein the geared architecture includes a sun gear that is driven by the shaft and a carrier that includes a plurality of gears in meshing engagement with the sun gear, and wherein the carrier is fixed to an engine static structure; and
a compressor positioned forward of the geared architecture and radially inward of the fan blades in an overlapping relationship with the fan blades, the compressor being driven by the shaft, and wherein the compressor includes at least one set of vanes that rotate in a first direction about the engine center axis and at least one set of compressor blades that rotate in a second direction about the engine center axis, wherein the second direction is opposite of the first direction.

2. The gas turbine engine according to claim 1 wherein the compressor includes a rotor, and wherein the shaft directly drives the rotor.

3. The gas turbine engine according to claim 1 wherein the compressor comprises a low pressure compressor having the at least one set of compressor blades fixed for rotation with the shaft and the at least one set of vanes fixed to the fan hub.

4. The gas turbine engine according to claim 3 wherein the low pressure compressor is comprised of a plurality of stages.

5. The gas turbine engine according to claim 4 wherein the compressor includes a rotor directly driven by the shaft, and wherein the plurality of stages comprises at least a first stage and a second stage, and wherein the at least one set of compressor blades comprises at least a first set of blades and a second set of blades, and the at least one set of vanes comprises at least a first set of vanes and a second set of vanes, the first stage having the first set of blades directly coupled to the shaft and the first set of vanes mounted to the fan hub, and the second stage having the second set of blades mounted to the rotor and the second set of vanes mounted to the fan hub.

6. The gas turbine engine according to claim 3 wherein the at least one set of vanes rotate with the fan hub in the first direction while the at least one set of compressor blades rotate with the shaft in the second direction.

7. The gas turbine engine according to claim 6 including at least one inter-shaft bearing mounted between the shaft and the at least one set of vanes to support the vanes for rotation relative to the shaft.

8. The gas turbine engine according to claim 1 including at least one fan support bearing that supports the fan hub for rotation relative to the static structure, and wherein the geared architecture includes an outer annular gear in meshing engagement with the plurality of gears.

9. The gas turbine engine according to claim 8 wherein the fan hub includes a plurality of fan drive struts, and wherein the outer annular gear provides driving input to the fan drive struts.

10. The gas turbine engine according to claim 9 wherein the at least one fan support bearing comprises at least a first bearing positioned radially between the fan drive struts and the static structure.

11. The gas turbine engine according to claim 10 including a second bearing positioned radially between the fan hub and the static structure, the second bearing being positioned forward of the first bearing.

12. The gas turbine engine according to claim 8 wherein the fan section includes a plurality of static vanes extending between the fan case and the static structure.

13. The gas turbine engine according to claim 1 wherein the compressor includes a rotor that is directly driven by the shaft, and wherein the compressor includes at least a first stage, a second stage, and a third stage, and wherein the at least one set of compressor blades comprises at least a first set of blades, a second set of blades, and a third set of blades, and wherein the at least one set of vanes comprises at least a first set of vanes and a second set of vanes, and wherein the first stage includes the first set of blades fixed to a forward end of the shaft and the first set of vanes mounted to the fan hub, the second stage is aft of the first stage and includes the second set of blades mounted to the rotor and the second set of vanes mounted to the fan hub, and the third stage is aft of the second stage and includes the third set of blades mounted to the rotor.

14. The gas turbine engine according to claim 1 wherein the at least one set of vanes is radially aligned with the fan blades.

15. The gas turbine engine according to claim 1 wherein the compressor includes at least a first stage and a second stage, and wherein the at least one set of compressor blades comprises at least a first set of compressor blades and a second set of compressor blades, and the at least one set of vanes comprises at least a first set of vanes and a second set of vanes, and wherein the first stage comprises the first set of compressor blades and the first set of vanes and the second stage comprises the second set of compressor blades and the second set of vanes, and wherein the first and second sets of vanes rotate in the first direction about the engine center axis, and wherein the first and second sets of compressor blades rotate in the second direction about the engine center axis, and wherein the first set of compressor blades is positioned forward of the fan blades, the first set of vanes is radially aligned with the fan blades, and wherein the second set of compressor blades and the seconds set of vanes extend aft of the fan blades.

16. A gas turbine engine comprising:
a fan section including a fan outer case, a static structure positioned radially inward of the fan outer case, and a fan hub supporting a plurality of fan blades for rotation relative to the static structure;
at least one fan support bearing to support the fan hub for rotation relative to the static structure;
a shaft rotatable relative to the static structure about an engine center axis;
a geared architecture driven by the shaft and providing driving output to rotate the fan hub, and wherein in the geared architecture includes a carrier that is fixed to the static structure; and
a low pressure compressor positioned forward of the geared architecture and radially inward of the fan blades in an overlapping relationship with the fan blades, the compressor being driven directly by the shaft, and wherein the low pressure compressor includes at least one set of vanes that rotate in a first direction about the engine center axis and at least one set of compressor blades that rotate in a second direction about the engine center axis, wherein the second direction is opposite of the first direction.

17. The gas turbine engine according to claim 16 wherein the geared architecture is comprised of a sun gear that is driven by the shaft, a plurality of star gears supported by the carrier fixed to the static structure and in meshing engagement with the sun gear, and an outer annular gear in meshing engagement with the star gears to drive the fan hub.

18. The gas turbine engine according to claim 17 wherein the fan hub includes a plurality of fan drive struts, and wherein the outer annular gear is drivingly engaged with the fan drive struts.

19. The gas turbine engine according to claim 18 wherein the at least one fan support bearing comprises at least a first bearing positioned radially between the fan drive struts and the static structure and a second bearing positioned radially between the fan hub and the static structure, and wherein the second bearing is located axially forward of the first bearing.

20. The gas turbine engine according to claim 19 wherein the first bearing comprises a roller bearing and the second bearing comprises a ball bearing.

21. The gas turbine engine according to claim 18 wherein the low pressure compressor is comprised of at least one stage having the at least one set of compressor blades driven by the shaft and the at least one set of vanes positioned aft of the set of the at least one set of compressor blades, and wherein the at least one set of vanes rotate with the fan hub in one direction while the at least one set of compressor blades rotate with the shaft in an opposite direction.

22. The gas turbine engine according to claim 21 including at least one inter-shaft bearing mounted between the shaft and the at least one set of vanes to support the vanes for rotation relative to the shaft.

23. The gas turbine engine according to claim 16 wherein the at least one set of vanes is radially aligned with the fan blades.

24. The gas turbine engine according to claim 16 wherein the low pressure compressor includes at least a first stage and a second stage, and wherein the at least one set of compressor blades comprises at least a first set of compressor blades and a second set of compressor blades, and the at least one set of vanes comprises at least a first set of vanes and a second set of vanes, and wherein the first stage includes the first set of compressor blades and the first set of vanes and the second stage includes the second set of compressor blades and the second set of vanes, and wherein the first and second sets of vanes rotate in a first direction about the engine center axis, and wherein the first and second sets of compressor blades rotate in a second direction about the engine center axis, wherein the second direction is opposite of the first direction.

25. The gas turbine engine according to claim 24 wherein the first set of compressor blades is positioned forward of the fan blades, the first set of vanes is radially aligned with the fan blades, and wherein the second set of compressor blades and the second set of vanes extend aft of the fan blades.

26. The gas turbine engine according to claim 25 wherein the low pressure compressor includes a third stage positioned aft of the second stage and forward of the geared architecture.