Turbofan engine bearing and gearbox arrangement
A turbofan engine ( 300; 600; 700 ) comprising a fan shaft ( 120 ) configured to rotate about an axis ( 500 ) of the engine. A fan drive gear system ( 60 ) is configured to drive the fan shaft. The fan drive gear system has a centerplane ( 540 ). A first spool comprises a high pressure turbine ( 326 ) and a high pressure compressor ( 324 ). A second spool comprises an intermediate pressure turbine ( 328 ), a lower pressure compressor, and a shaft ( 334 ) coupling the intermediate pressure turbine to the lower pressure compressor. A third spool comprises a lower pressure turbine ( 330 ) coupled to the fan drive gear system to drive the fan. The engine has a plurality of main bearings. The turbofan engine has a single stage fan. Of the main bearings, at least one is a shaft-engaging bearing engaging a driving shaft ( 336 ) coupled to the fan drive gear system. A closest ( 340; 640 ) of the shaft-engaging bearings engaging the driving shaft behind the fan drive gear system has a centerplane ( 550 ) and a characteristic radius (R B ). The half angle (θ) of a virtual cone ( 530 ) intersecting the core flowpath inboard boundary at the gear system centerplane ( 540 ) and said closest of the shaft-engaging bearings at the characteristic radius (R B ) is greater than about 32°. A hub-to-tip ratio (H R :F R ) of the fan is less than about 0.38.
1. A turbofan engine ( 300 ; 600 ; 700 ) comprising:
a fan shaft ( 120 ) configured to rotate about an axis ( 500 ) of the engine;
a fan drive gear system ( 60 ) configured to drive the fan shaft, the fan drive gear system having a plurality of gears ( 84 ) carried by a carrier ( 86 ) and having a gear length L G along an externally toothed portion and a centerplane ( 540 ) extending centrally through said externally toothed portion;
a first spool comprising:
a high pressure turbine ( 326 ); and
a high pressure compressor ( 324 );
a second spool comprising:
an intermediate pressure turbine ( 328 );
a lower pressure compressor; and
a shaft ( 334 ) coupling the intermediate pressure turbine to the lower pressure compressor;
a third spool comprising:
a lower pressure turbine ( 330 ) coupled to the fan drive gear system to drive the fan;
a core flowpath ( 506 ); and
a plurality of main bearings,
wherein:
the turbofan engine has a single stage fan;
of the main bearings, at least one is a shaft-engaging bearing engaging a driving shaft ( 336 ) coupled to the fan drive gear system;
a closest ( 340 ; 640 ) of the shaft-engaging bearings engaging the driving shaft behind the fan drive gear system has a centerplane ( 550 ) and a characteristic radius (R B );
the half angle (θ) of a virtual cone ( 530 ) intersecting the core flowpath inboard boundary at the gear system centerplane ( 540 ) and said closest of the shaft-engaging bearings at the characteristic radius (R B ) is greater than 32°; and
a hub-to-tip ratio (H R :F R ) of the fan is less than 0.38.
2. The engine of claim 1 wherein:
a length L D between the centerplane ( 540 ) and a centerplane ( 580 ) of a forward/upstreammost compressor disk is at least one of:
2.0 times or less of a gear width L G of the fan drive gear system;
60% or less of a core flowpath inboard radius R T2 at the forward/upstreammost compressor disk centerplane ( 580 ); and
50% less of a core flowpath inboard radius R T at the centerplane ( 540 ).
3. The engine of claim 2 wherein:
the length L D between the centerplane ( 540 ) and the centerplane ( 580 ) of the forward/upstreammost compressor disk is at least one of:
1.5 times or less of the gear width L G of the fan drive gear system;
50% or less of the core flowpath inboard radius T T2 at the forward/upstreammost compressor disk centerplane ( 580 ); and
40% less of the core flowpath inboard radius R T at the centerplane ( 540 ).
4. The engine of claim 2 wherein:
the length L D between the centerplane ( 540 ) and the centerplane ( 580 ) of the forward/upstreammost compressor disk is all of:
2.0 times or less of the gear width L G of the fan drive gear system;
60% or less of the core flowpath inboard radius T T2 at the forward/upstreammost compressor disk centerplane ( 580 ); and
50% less of the core flowpath inboard radius R T at the centerplane ( 540 ).
5. The engine of claim 1 wherein:
a universal joint ( 202 ) couples the driving shaft to the fan drive gear system.
6. The engine of claim 1 wherein:
a diaphragm coupling ( 702 ) couples the driving shaft to the fan drive gear system.
7. The engine of claim 6 wherein:
the diaphragm coupling ( 702 ) is a Bendix-style coupling.
8. The engine of claim 1 wherein:
a flexure retains a carrier in the fan drive gear system, the flexure having a longitudinal cross section characterized by:
an outboard mounting flange ( 225 );
an inboard portion ( 223 ) engaged to the carrier;
an intermediate portion ( 226 ) extending along a radial span between the outboard portion and the inboard portion.
9. The engine of claim 8 wherein:
the intermediate portion does not depart from radial by more than a longitudinal distance of half of said radial span.
10. The engine of claim 1 wherein one or more of:
a fan bearing is a duplex bearing;
the fan is a single-stage fan;
the case includes a core case and a fan case;
the engine has a bypass ratio of greater than about 6.0.
11. The engine of claim 1 wherein:
a bearing support ( 344 ) aft of the fan drive gear system has:
a forward portion ( 380 ) supporting the driving shaft by said closest of the shaft-engaging bearings; and
an aft portion ( 382 ) supporting the second spool shaft by a second bearing ( 360 ) of the main bearings.
12. The engine of claim 11 wherein:
said closest of the shaft-engaging bearing ( 640 ) and the second bearing ( 360 ) are non-thrust bearings;
the second spool shaft engages an additional bearing being a thrust bearing; and
the driving shaft engages an additional bearing being a thrust bearing.
13. A turbofan engine ( 200 ; 300 ; 600 ; 700 ) comprising:
a fan supported on a fan shaft ( 120 ), the fan shaft configured to rotate about an axis ( 500 ) of the engine;
a fan drive gear system ( 60 ) configured to drive the fan shaft, the fan drive gear system having a plurality of gears ( 84 ) carried by a carrier ( 86 ) and having a gear length L G along an externally toothed portion and a centerplane ( 540 ) extending centrally through said externally toothed portion;
a first spool comprising:
a high pressure turbine ( 26 ; 326 ); and
a high pressure compressor ( 28 ; 324 );
a second spool comprising:
a lower pressure turbine ( 27 ; 328 );
a lower pressure compressor; and
a shaft ( 25 ; 334 ) coupling the lower pressure turbine to the lower pressure compressor;
a core flowpath ( 506 ); and
a plurality of main bearings,
wherein:
of the main bearings, at least one is a shaft-engaging bearing engaging a driving shaft ( 25 ; 336 ) coupled to the fan drive gear system;
a closest ( 160 ; 340 ; 640 ) of the shaft-engaging bearings engaging the driving shaft behind the fan drive gear system has a centerplane ( 550 ) and a characteristic radius (R B );
the half angle (θ) of a virtual cone ( 530 ) intersecting the core flowpath inboard boundary at the gear system centerplane ( 540 ) and said closest of the shaft-engaging bearings at the characteristic radius (R B ) is greater than 32°;
a hub-to-tip ratio (H R :F R ) of the fan is less than 0.38; and
a universal joint ( 202 ) or a diaphragm coupling ( 702 ) couples the driving shaft to the fan drive gear system.
14. The engine of claim 13 wherein the angle (θ) is 33° to 68°.
15. The engine of claim 13 wherein the hub-to-tip ratio (H R :F R ) is 0.24 to 0.33.
16. The engine of claim 13 wherein the angle (θ) is greater than 40°.
17. The engine of claim 13 wherein the angle (θ) is greater than 50°.
18. The engine of claim 13 wherein the closest of the shaft-engaging bearings behind the fan drive gear system is a low spool bearing directly coupling the shaft ( 25 ) to a case immediately behind the gear system.
19. The engine of claim 13 wherein at least one of said main bearings is a fan bearing ( 148 , 150 ) engaging the fan shaft forward of the gear system centerplane.
20. The engine of claim 13 wherein the fan drive gear system comprises:
a sun gear ( 80 );
a ring gear ( 82 );
a plurality of intermediate gears ( 84 ) engaging between the sun gear and the ring gear; and
a carrier ( 86 ) holding the intermediate gears circumferentially spaced apart from each other.
21. The engine of claim 20 wherein the sun gear is coupled to the driving shaft.
22. The engine of claim 13 further comprising:
a third spool comprising:
an additional turbine ( 330 ) and said driving shaft ( 336 ).
23. The engine of claim 22 wherein:
a bearing support ( 344 ) aft of the fan drive gear system has:
a forward portion ( 380 ) supporting the driving shaft by said closest of the shaft-engaging bearings; and
an aft portion ( 382 ) supporting the second spool shaft by a second bearing ( 360 ) of the main bearings.
24. The engine of claim 23 wherein:
said closest of the shaft-engaging bearing ( 640 ) and the second bearing ( 360 ) are non-thrust bearings;
the second spool shaft engages an additional bearing being a thrust bearing; and
the driving shaft engages an additional bearing being a thrust bearing.
25. The engine of claim 22 wherein:
a universal joint ( 202 ) couples the driving shaft to the fan drive gear system.
26. The engine of claim 22 wherein:
a diaphragm coupling ( 702 ) couples the driving shaft to the fan drive gear system.
27. The engine of claim 26 wherein:
the diaphragm coupling ( 702 ) is a Bendix-style coupling.
28. The engine of claim 13 wherein:
a flexure retains a carrier in the fan drive gear system, the flexure having a longitudinal cross section characterized by:
an outboard mounting flange ( 225 );
an inboard portion ( 223 ) engaged to the carrier;
an intermediate portion ( 226 ) extending along a radial span between the outboard portion and the inboard portion and not departing from radial by more than a longitudinal distance of half of said radial span.
29. The engine of claim 13 wherein one or more of:
a fan bearing is a duplex bearing;
the fan is a single-stage fan;
a case includes a core case and a fan case;
the engine has a bypass ratio of greater than 6.0.
30. The engine of claim 13 wherein:
the fan is a single-stage fan having a centerplane ( 518 ) and a tip radius (F R ); and
a distance (L F ) from the fan centerplane to the gear system centerplane is at least one of less than 3.2 times the gear width (L G ) and less than 0.37 times the tip radius.
31. The engine of claim 13 wherein:
the fan is a single-stage fan having a centerplane ( 518 ), a hub radius (H R ) at blade leading edges ( 106 ), and a tip radius (F R ); and
a ratio of said hub radius to said tip radius is between 0.24 and 0.33.