Turbofan engine bearing and gearbox arrangement
A turbofan engine comprising a fan shaft configured to rotate about an axis of the engine. A fan drive gear system is configured to drive the fan shaft. A first spool comprises a high pressure turbine and a high pressure compressor. A second spool comprises a lower pressure turbine, a lower pressure compressor, and a shaft coupling the lower pressure turbine to the intermediate pressure compressor. The engine has a plurality of main bearings. The lower pressure compressor has a plurality of disks and a forward hub mounted to a forwardmost disk.
1. A turbofan engine comprising:
a fan supported on a fan shaft, the fan shaft configured to rotate about an axis (500) of the engine;
a fan drive gear system configured to drive the fan shaft, the fan drive gear system having a centerplane;
a first spool comprising:
a high pressure turbine; and
a high pressure compressor;
a second spool comprising:
a lower pressure turbine;
a lower pressure compressor; and
a shaft coupling the lower pressure turbine to the lower pressure compressor;
a core flowpath; and
a plurality of main bearings, wherein:
the lower pressure compressor has a plurality of disks;
the lower pressure compressor has a forward hub mounted to a forwardmost disk of the plurality of disks;
of the main bearings, at least one is a shaft-engaging bearing engaging a driving shaft coupled to the fan drive gear system;
a closest of the shaft-engaging bearings engaging the driving shaft behind the fan drive gear system as a centerplane and a characteristic radius (R B ); and
the half angle (θ) of a virtual cone intersecting the core flowpath inboard boundary at the gear system centerplane and said closest of the shaft-engaging bearings at the characteristic radius (R B ) is greater than 32° .
2. The engine of claim 1 wherein:
a hub-to-tip ratio (H R :F R ) of the fan is less than 0.38.
3. The engine of claim 1 wherein a universal joint couples the driving shaft to the fan drive gear system.
4. The engine of claim 1 wherein the angle (θ) is 33° to 68° .
5. The engine of claim 1 wherein the hub-to-tip ratio (H R :F R ) is 0.24 to 0.33.
6. The engine of claim 1 wherein the angle (θ) is greater than 40° .
7. The engine of claim 1 wherein the angle (θ) is greater than 50° .
8. The engine of claim 1 wherein:
the driving shaft is said second spool shaft; and
the closest of the shaft-engaging bearings behind the fan drive gear system is a low spool bearing directly coupling the driving shaft to a case immediately behind the gear system.
9. The engine of claim 1 wherein at least one of said main bearings is a fan bearing engaging the fan shaft forward of the gear system centerplane.
10. The engine of claim 1 wherein the fan drive gear system comprises:
a sun gear;
a ring gear;
a plurality of intermediate gears engaging between the sun gear and the ring gear; and
a carrier holding the intermediate gears circumferentially spaced apart from each other.
11. The engine of claim 10 wherein the sun gear is coupled to the driving shaft.
12. The engine of claim 1 further comprising:
a third spool comprising:
an additional turbine and said driving shaft.
13. The engine of claim 12 wherein:
a bearing support aft of the fan drive gear system has:
a forward portion supporting the driving shaft by said closest of the shaft-engaging bearings; and
an aft portion supporting the second spool shaft by a second bearing of the main bearings.
14. The engine of claim 12 wherein:
a universal joint couples the driving shaft to the fan drive gear system.
15. 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;
an inboard portion engaged to the carrier;
an intermediate portion 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.
16. 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 6.0.
17. The engine of claim 1 wherein:
the fan is a single-stage fan having a centerplane 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.
18. The engine of claim 1 wherein:
the fan is a single-stage fan having a centerplane, a hub radius (H R ) at blade leading edges and a tip radius (F R ); and
a ratio of said hub radius to said tip radius is between 0.24 and 0.33.
19. A turbofan engine comprising:
a fan supported on a fan shaft, the fan shaft configured to rotate about an axis of the engine;
a fan drive gear system configured to drive the fan shaft, the fan drive gear system having a centerplane;
a first spool comprising:
a high pressure turbine; and
a high pressure compressor;
a second spool comprising:
a lower pressure turbine;
a lower pressure compressor; and
a shaft coupling the lower pressure turbine to the lower pressure compressor;
a core flowpath; and
a plurality of main bearings, wherein:
the lower pressure compressor has a plurality of disks;
the lower pressure compressor has a forward hub mounted to a forwardmost disk of the plurality of disks; and
a flexure retains a carrier in the fan drive gear system, the flexure having a longitudinal cross-section characterized by:
an outboard mounting flange;
an inboard portion engaged to the carrier; and
an intermediate portion 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.
20. A turbofan engine comprising:
a fan supported on a fan shaft, the fan shaft configured to rotate about an axis of the engine;
a fan drive gear system configured to drive the fan shaft, the fan drive gear system having a centerplane;
a first spool comprising:
a high pressure turbine; and
a high pressure compressor;
a second spool comprising:
a lower pressure turbine;
a lower pressure compressor; and
a shaft coupling the lower pressure turbine to the lower pressure compressor;
a core flowpath; and
a plurality of main bearings, wherein:
the lower pressure compressor has a plurality of disks;
the lower pressure compressor has a forward hub mounted to a forwardmost disk of the plurality of disks;
the fan is a single-stage fan having a centerplane 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.
21. A turbofan engine comprising:
a fan supported on a fan shaft, the fan shaft configured to rotate about an axis of the engine;
a fan drive gear system configured to drive the fan shaft, the fan drive gear system having a centerplane;
a plurality of main bearings;
a first spool comprising:
a high pressure turbine; and
a high pressure compressor;
a second spool comprising:
a lower pressure turbine;
a lower pressure compressor; and
a shaft coupling the lower pressure turbine to the lower pressure compressor;
a third spool comprising:
an additional turbine and a shaft coupled to the fan drive gear system; and
a core flowpath, wherein;
of the main bearings, at least one is a shaft-engaging bearing engaging the third spool shaft;
a closest of the shaft-engaging bearings engaging the third spool shaft behind the fan drive gear system is a non-thrust bearing;
the lower pressure compressor has a plurality of disks;
the lower pressure compressor has a forward hub mounted to a forwardmost disk of the plurality of disks;
a bearing support aft of the fan drive gear system has;
a forward portion supporting the third spool shaft by said closest of the shaft-engaging bearings; and
an aft portion supporting the second spool shaft by a second bearing of the main bearings;
said second bearing non-thrust bearing;
the second spool shaft engages an additional bearing behind a thrust bearing; and
the third spool shaft engages an additional bearing being a thrust bearing.