Bearing structure for gas turbine engine

Abstract

This bearing structure for a gas turbine engine comprises: an engine shaft that extends in the front-rear direction; a compressor, a combustor, and a turbine that are disposed as aligned in the axial direction of the engine shaft; and a plurality of bearings that support the engine shaft. The plurality of bearings are disposed more forward in the axial direction than the combustor.

Description

Gas turbine engine bearing structure

[0001] The present disclosure relates to bearing structures for gas turbine engines.

[0002] As disclosed in Patent Document 1, the gas turbine engine includes a compressor section, a combustion section, a turbine section, and a shaft connecting the compressor section and the turbine section, the shaft being supported by a plurality of bearings.

[0003] Japanese Patent Application Laid-Open No. 2017-194055

[0004] When a gas turbine engine is running, the engine shaft connecting the compressor and turbine rotates, causing the temperature inside the engine to rise, which places a load on the bearings that support the engine shaft, resulting in high temperatures, especially in the combustion section and turbine section.

[0005] Therefore, one aspect of the present disclosure aims to provide a bearing structure for a gas turbine engine that can suppress the load applied to the bearings that support the engine shaft due to the temperature inside the engine and stably support the engine shaft.

[0006] A bearing structure for a gas turbine engine according to one aspect of the present disclosure includes an engine shaft extending in a longitudinal direction, a compressor, a combustor, and a turbine arranged in line in the axial direction of the engine shaft, and a plurality of bearings supporting the engine shaft, the plurality of bearings being arranged forward of the combustor in the axial direction.

[0007] According to one aspect of the present disclosure, it is possible to provide a bearing structure for a gas turbine engine that can suppress the load applied to a bearing that supports an engine shaft due to the temperature inside the engine and stably support the engine shaft.

[0008] Fig. 1 is a schematic diagram of a gas turbine engine according to a first embodiment. Fig. 2 is an enlarged view showing a bearing structure of a gas turbine engine according to a second embodiment.

[0009] Hereinafter, embodiments will be described with reference to the drawings. In the following, "forward" means the upstream side in the air flow direction within the gas turbine engine. "rearward" means the downstream side in the air flow direction. "radial direction" means the direction perpendicular to the rotation axis of the engine shaft. "axial direction" means the axial direction of the engine shaft.

[0010] First Embodiment Fig. 1 is a schematic diagram of a gas turbine engine 1 (hereinafter also simply referred to as "engine 1") according to a first embodiment. The engine 1 is for a vehicle, as an example, but is not limited to this. Specifically, the engine 1 is for an aircraft. The engine 1 includes a bearing structure 2 that supports an engine shaft 7.

[0011] When a gas turbine engine is operating, the engine shaft typically rotates at a high rotation speed, causing the temperature inside the engine to rise. This places a load on bearings disposed in the turbine section of the engine and supporting the engine shaft. As will be described in detail later, the bearing structure 2 of this embodiment includes multiple bearings BR1, BR2 that support the engine shaft 7, and the multiple bearings BR1, BR2 are disposed axially forward of the combustor 5. This prevents the multiple bearings BR1, BR2 from being used in the harsh environment of the engine 1, where the engine rotates at high speeds under high temperatures. In this way, the engine 1 is configured to stably support the engine shaft 7 with the multiple bearings BR1, BR2.

[0012] As an example, the engine 1 is a two-shaft gas turbine engine. The engine 1 includes a fan 3, a compressor 4, a combustor 5, a turbine 6, an engine shaft 7 connecting the compressor 4 and the turbine 6, a generator 8, a casing 9 accommodating at least the compressor 4 and the combustor 5, at least one electric accessory 10, and a cylinder 11. The compressor 4, the combustor 5, and the turbine 6 are arranged side by side in the axial direction of the engine shaft 7.

[0013] The bearing structure 2 of the engine 1 also includes a plurality of bearings BR1, BR2 that rotatably support the engine shaft 7. The plurality of bearings BR1, BR2 are arranged spaced apart in the axial direction. The plurality of bearings BR1, BR2 support the engine shaft 7 at a plurality of locations. As an example, the plurality of bearings BR1, BR2 in this embodiment include different types of bearings. As a specific example, the plurality of bearings BR1, BR2 include ball bearings, roller bearings, or a combination thereof.

[0014] The compressor 4 compresses air supplied from the front of the engine 1. The combustor 5 burns fuel to generate combustion gas. The combustor 5 has an internal space S in which the combustion gas is generated, and a nozzle N that ejects fuel into the internal space S from behind the internal space S. As an example, the combustor 5 of this embodiment is a reverse flow type in which the internal space S is folded back toward the rear.

[0015] The turbine 6 is supplied with combustion gas generated in the combustor 5. The engine shaft 7 extends in the front-to-rear direction of the engine 1 and rotates about a predetermined rotation axis X. The engine shaft 7 is supported so as to be freely rotatable. The fan 3 is mechanically connected to the engine shaft 7 and rotates together with the engine shaft 7. The compressor 4, combustor 5, and turbine 6 are arranged in this order from front to rear.

[0016] The compressor 4 includes a low-pressure compressor 13 and a high-pressure compressor 14. In this embodiment, the high-pressure compressor 14 is arranged axially rearward of the low-pressure compressor 13. As an example, the low-pressure compressor 13 is an axial compressor. As another example, the high-pressure compressor 14 is an axial compressor or a centrifugal compressor. The high-pressure compressor 14 has an impeller 15 that rotates around a rotation axis X. The turbine 6 is mechanically connected to the engine shaft 7. The turbine 6 includes a low-pressure turbine 16 and a high-pressure turbine 17. The low-pressure turbine 16 is arranged axially rearward of the high-pressure turbine 17. As another example, the engine 1 is equipped with a single high-pressure compressor 14.

[0017] The engine shaft 7 includes a high-pressure shaft 18 and a low-pressure shaft 19. The high-pressure shaft 18 is a hollow member and connects the high-pressure compressor 14 and the high-pressure turbine 17. The high-pressure shaft 18 has an expanded diameter portion 18a that is disposed axially between two adjacent bearings BR1 and BR2 and partially expands the outer diameter of the high-pressure shaft 18. The expanded diameter portion 18a increases the radial thickness of the high-pressure shaft 18, thereby improving the rigidity and mechanical strength of the high-pressure shaft 18. The multiple bearings BR1 and BR2 support the high-pressure shaft 18. For example, the maximum outer diameter of the high-pressure shaft 18 between the adjacent bearings BR1 and BR2 is larger than the maximum outer diameter of the high-pressure shaft 18 rearward of the rearmost bearing BR2 among the multiple bearings BR1 and BR2. For example, the maximum outer diameter of the high-pressure shaft 18 in the region where the low-pressure compressor 13 is disposed is larger than the maximum outer diameter of the high-pressure shaft 18 in the region axially rearward of the aforementioned region. As an example, the maximum outer diameter of the high-pressure shaft 18 in the region where the low-pressure compressor 13 is disposed is the maximum outer diameter of the expanded diameter portion 18a.

[0018] The rear end 18b of the high-pressure shaft 18 is disposed axially forward of the low-pressure turbine 16. The rear end 18b of the high-pressure shaft 18 is also disposed at a position radially overlapping with the combustor 5. As an example, the rear end 18b of the high-pressure shaft 18 in the present embodiment is disposed axially forward of the outlet of the nozzle N.

[0019] The low-pressure shaft 19 connects the low-pressure compressor 13 and the low-pressure turbine 16. The low-pressure shaft 19 is inserted into the high-pressure shaft 18 and rotates about the rotation axis X. When the engine 1 is running, the low-pressure shaft 19 rotates at a slower speed than the high-pressure shaft 18. The low-pressure turbine 16 is connected to the fan 3 via the low-pressure shaft 19.

[0020] In the engine 1, all of the bearings BR1, BR2 that support the high-pressure shaft 18 are disposed axially forward of the combustor 5. Furthermore, of the multiple bearings BR1, BR2, the rearmost bearing BR2 is disposed axially forward of the rear end of the high-pressure compressor 14. As an example, the multiple bearings BR1, BR2 in this embodiment are disposed axially forward of the impeller 15 of the high-pressure compressor 14. As another example, the multiple bearings BR1, BR2 are disposed axially between the front end of the low-pressure compressor 13 and the rear end of the high-pressure compressor 14.

[0021] The generator 8 generates electricity by being driven by the rotational driving force of the engine shaft 7. The electric power generated by the generator 8 drives the electric accessory 10. The generator 8 may also have a starter function that rotates the engine shaft 7 when starting the engine 1. In this case, in other words, the generator 8 is a motor generator.

[0022] The generator 8 is disposed inside the casing 9. In this embodiment, the generator 8 is housed in the cylindrical body 11 and disposed in front of the high-pressure compressor 14. The generator 8 has a hollow rotating shaft 20 extending in the axial direction, a rotor 21 that rotates integrally with the rotating shaft 20, and a stator 22 that is disposed radially outside the rotor 21. As an example, the rotating shaft 20 and the rotor 21 rotate together with the high-pressure shaft 18.

[0023] The generator 8 is disposed axially forward of the combustor 5. The multiple bearings BR1, BR2 are disposed axially forward and rearward of the generator 8. Of the multiple bearings BR1, BR2, the outer diameter of the portion of the high-pressure shaft 18 supported by the bearing BR1 forward of the generator 8 may be the same as or different from the outer diameter of the portion of the high-pressure shaft 18 supported by the bearing BR2 rearward of the generator 8. In this embodiment, the maximum outer diameter of the high-pressure shaft 18 is larger than the maximum outer diameter of the rotating shaft 20. As an example, the maximum outer diameter of the high-pressure shaft 18 is the maximum outer diameter of the expanded diameter portion 18a.

[0024] The high-pressure shaft 18 and the rotating shaft 20 are restricted from moving relative to each other in the circumferential and axial directions. In other words, the high-pressure shaft 18 and the rotating shaft 20 are fixed to each other. In this embodiment, the high-pressure shaft 18 and the rotating shaft 20 are coupled to each other by, for example, at least one of welding, shrink fitting, and a fixed spline. Here, the term "fixed spline" refers to a structure in which the high-pressure shaft 18 and the rotating shaft 20 are fixed to each other such that relative movement due to the spline structure of the high-pressure shaft 18 and the rotating shaft 20 is prevented by the coupling of the high-pressure shaft 18 and the rotating shaft 20. When the high-pressure shaft 18 and the rotating shaft 20 are shrink fitted, the high-pressure shaft 18 and the rotating shaft 20 include a coupling portion that is coupled to each other by, for example, a curvic coupling.

[0025] The casing 9 is a cylindrical body extending in the axial direction of the rotation axis X. The casing 9 of this embodiment houses the engine shaft 7, the fan 3, the compressor 4, the combustor 5, and the turbine 6. As an example, the casing 9 has an inner shell 25, an outer shell 26, and struts 27. The inner shell 25 houses the compressor 4, the combustor 5, and the turbine 6. The outer shell 26 is arranged concentrically with the inner shell 25 and spaced radially outward from the inner shell 25. A cylindrical bypass passage BP is arranged between the inner shell 25 and the outer shell 26. A portion of the air sucked by the fan 3 flows through the bypass passage BP and is discharged rearward. The electric accessory 10 is attached to the outer peripheral surface of the casing 9. The struts 27 extend radially to connect the inner shell 25 and the outer shell 26.

[0026] The cylindrical body 11 axially connects the low-pressure compressor 13 and the high-pressure compressor 14. The outer diameter and inner diameter of the cylindrical body 11 decrease from the front to the rear. The cylindrical body 11 defines a part of the compressed air flow path R leading from the low-pressure compressor 13 to the high-pressure compressor 14. A generator 8 is disposed inside the cylindrical body 11 of this embodiment.

[0027] In the engine 1, of the multiple bearings BR1, BR2 that support the engine shaft 7, the rearmost bearing BR2 is disposed axially forward of the combustor 5. In the engine 1 of the present embodiment, all of the bearings BR1, BR2 that support the high-pressure shaft 18 are disposed axially forward of the combustor 5.

[0028] In this embodiment having the above configuration, the load applied to the bearings BR1 and BR2 that support the engine shaft 7 due to the temperature inside the engine 1 is suppressed, and the engine shaft 7 can be supported stably.

[0029] Furthermore, to reduce the size and weight of a gas turbine engine and improve its drive efficiency, it is necessary to increase the engine's compression ratio and combustion temperature. This increases the engine temperature and may require the engine shaft to rotate at high speeds. Even in such a case, this embodiment can suppress the load on the bearings BR1 and BR2 and stably support the engine shaft 7.

[0030] Furthermore, in this embodiment, of the bearings that support the engine shaft 7, all of the bearings BR1, BR2 that support the high-pressure shaft 18 are disposed axially forward of the combustor 5. This prevents the bearings BR1, BR2 that support the high-pressure shaft 18, which rotates at a higher speed than the low-pressure shaft 19, from being exposed to high temperatures caused by the combustor 5. This can also reduce the number of parts and production costs of the engine 1, and can also reduce the weight of the engine 1.

[0031] Second Embodiment Figure 2 is an enlarged view showing a bearing structure 102 of a gas turbine engine 101 according to a second embodiment. The second embodiment will be described below, focusing on the differences from the first embodiment. As shown in Figure 2, the high-pressure shaft 118 of this embodiment is a single shaft including a first shaft portion 118c connected to the high-pressure compressor 14 and a second shaft portion 118d inserted into the rotor 21 of the generator 108. The bearing structure 102 includes a plurality of bearings BR1, BR2 arranged axially in front and rear of the generator 108. The high-pressure shaft 118 has an expanded diameter portion 118a arranged axially between two adjacent bearings BR1, BR2.

[0032] According to the second embodiment, the generator 108 does not have a hollow rotating shaft extending in the axial direction, and the second shaft portion 118d, which is a part of the high-pressure shaft 118, essentially functions as the rotating shaft of the generator 108. Furthermore, the high-pressure shaft 118 is configured as a single shaft including the first shaft portion 118c and the second shaft portion 118d. Therefore, compared to when the first shaft portion 118c and the second shaft portion 118d are configured separately, the first shaft portion 118c and the second shaft portion 118d can be configured integrally. Therefore, the high-pressure shaft 118 can be stably supported by the multiple bearings BR1 and BR2 of the bearing structure 102 while suppressing vibration of the high-pressure shaft 118 during rotation. Furthermore, the number of parts of the engine 101 can be reduced.

[0033] The low-pressure compressor 13, the high-pressure compressor 14, and the combustor 5 are not limited to the configurations described in the above embodiments. The engine 1, 101 may be for an unmanned aerial vehicle. The engine 1, 101 may also be for an application other than a vehicle. The types of the multiple bearings included in the bearing structure 2, 102 are not limited. The multiple bearings may include three or more bearings.

[0034] When the engine shafts 7, 107 include the low-pressure shaft 19, the plurality of bearings may include at least one bearing that supports the low-pressure shaft 19. The at least one bearing may include, for example, of the bearings BR1, BR2 that support the high-pressure shaft 18, a bearing that is arranged forward of the forward-most bearing BR1 in the axial direction, and a bearing that is arranged rearward of the rearmost bearing BR2.

[0035] (Disclosure Items) Each of the following items discloses a preferred embodiment. [Item 1] A bearing structure for a gas turbine engine, comprising: an engine shaft extending in a front-to-rear direction; a compressor, a combustor, and a turbine arranged side by side in the axial direction of the engine shaft; and a plurality of bearings supporting the engine shaft, the plurality of bearings being arranged forward of the combustor in the axial direction.

[0036] The above configuration can prevent the bearings supporting the engine shaft from being used in the harsh environment of high-temperature, high-speed rotation caused by the combustor. This reduces the load on the bearings supporting the engine shaft due to the temperature inside the gas turbine engine. This makes it possible to provide a bearing structure for a gas turbine engine that can stably support the engine shaft.

[0037] [Item 2] A bearing structure for a gas turbine engine according to Item 1, wherein the compressor includes a high-pressure compressor and a low-pressure compressor arranged forward in the axial direction relative to the high-pressure compressor; the turbine includes a high-pressure turbine and a low-pressure turbine arranged rearward in the axial direction relative to the high-pressure turbine; the engine shaft includes a hollow high-pressure shaft connecting the high-pressure compressor and the high-pressure turbine, and a low-pressure shaft inserted into the high-pressure shaft and connecting the low-pressure compressor and the low-pressure turbine; and the plurality of bearings are arranged to support the high-pressure shaft.

[0038] With the above configuration, it is possible to prevent the bearing supporting the high-pressure shaft from being used in a harsh environment where it rotates at high speed together with the high-pressure shaft at high temperatures generated by the combustor, thereby reducing the load on the bearing supporting the high-pressure shaft due to the temperature inside the gas turbine engine.

[0039] [Item 3] A bearing structure for a gas turbine engine according to Item 2, wherein the high-pressure compressor is an axial compressor or a centrifugal compressor.

[0040] According to the above configuration, by using a high-pressure compressor that is an axial flow compressor or a centrifugal compressor, it is possible to drive the engine with high efficiency even when, for example, the gas turbine engine is downsized. Furthermore, it is possible to suppress the load on the bearing that supports the high-pressure shaft due to the temperature inside the gas turbine engine.

[0041] [Item 4] The bearing structure for a gas turbine engine according to any one of Items 2 to 3, wherein a maximum outer diameter of the high-pressure shaft between adjacent bearings among the plurality of bearings is larger than a maximum outer diameter of the high-pressure shaft rearward of a rearmost bearing among the plurality of bearings.

[0042] With the above configuration, the rigidity and mechanical strength of the portion of the high-pressure shaft between adjacent bearings can be improved. Therefore, when the high-pressure shaft is supported and rotated by the bearings, unnecessary vibration of the high-pressure shaft can be suppressed, and the high-pressure shaft can be stably supported. Furthermore, the load on the bearings supporting the high-pressure shaft due to the temperature inside the gas turbine engine can be suppressed.

[0043] [Item 5] A bearing structure for a gas turbine engine according to any one of Items 2 to 4, wherein a maximum outer diameter of the high-pressure shaft in a region where the low-pressure compressor is located is larger than a maximum outer diameter of the high-pressure shaft in a region rearward in the axial direction from the region where the low-pressure compressor is located.

[0044] According to the above configuration, the rigidity and mechanical strength of the high-pressure shaft can be improved in the region of the high-pressure shaft where the low-pressure compressor is located. Therefore, vibrations during rotation of the high-pressure shaft can be suppressed in the axial direction forward of the high-pressure compressor. This makes it easier to stably support the high-pressure shaft by the multiple bearings arranged in the axial direction forward of the combustor. Furthermore, the load on the bearings supporting the high-pressure shaft due to the temperature inside the gas turbine engine can be suppressed.

[0045] [Item 6] The bearing structure for a gas turbine engine according to any one of Items 2 to 5, wherein the high-pressure compressor has an impeller that rotates around a rotational axis of the engine shaft, and the plurality of bearings are disposed forward of the impeller in the axial direction.

[0046] With the above configuration, it is possible to prevent the use of multiple bearings supporting the high-pressure shaft in the harsh environment of high-temperature, high-speed rotation occurring behind the front end of the impeller of the high-pressure compressor, and therefore the high-pressure shaft can be stably supported by the multiple bearings.

[0047] [Item 7] A bearing structure for a gas turbine engine according to any one of Items 2 to 6, wherein the plurality of bearings are arranged in the axial direction between a front end of the low-pressure compressor and the high-pressure compressor.

[0048] With the above configuration, it is possible to prevent the use of multiple bearings that support the high-pressure shaft in the harsh environment of high-temperature high-speed rotation occurring behind the front end of the high-pressure compressor. Also, the multiple bearings can be efficiently arranged by utilizing the space between the low-pressure compressor and the high-pressure compressor in the axial direction.

[0049] [Item 8] A bearing structure for a gas turbine engine according to any one of Items 2 to 7, further comprising a generator having a hollow rotating shaft extending in the axial direction and a rotor rotating integrally with the rotating shaft, the generator being disposed forward in the axial direction relative to the combustor, and the plurality of bearings being disposed forward and rearward in the axial direction of the generator.

[0050] According to the above configuration, it is possible to easily arrange a plurality of bearings that support the high-pressure shaft by utilizing the space in front and rear of the generator in the axial direction. Furthermore, for example, the plurality of bearings can stably support the rotating shaft of the generator.

[0051] [Item 9] The bearing structure for a gas turbine engine according to Item 8, wherein the rotating shaft and the rotor rotate together with the high-pressure shaft, and the high-pressure shaft and the rotating shaft are restricted from moving relative to each other in the circumferential direction and the axial direction.

[0052] According to the above configuration, the relative movement between the rotating shaft and the high-pressure shaft is restricted when the engine is running, so that the high-pressure shaft can be stably supported by multiple bearings when the generator rotor rotates together with the high-pressure shaft.

[0053] [Item 10] A bearing structure for a gas turbine engine according to Item 9, wherein the high-pressure shaft and the rotating shaft are coupled to each other by at least one of welding, shrink fitting, and fixed splines.

[0054] According to the above configuration, the high-pressure shaft and the rotating shaft are reliably connected to each other, thereby forming the high-pressure shaft and the rotating shaft as a single unit. This suppresses vibration of the high-pressure shaft and the rotating shaft during rotation, and enables the high-pressure shaft to be stably supported by the multiple bearings.

[0055] [Item 11] A bearing structure for a gas turbine engine according to any one of Items 2 to 7, further comprising a generator having a hollow rotor that rotates integrally with the high-pressure shaft and that is disposed forward of the combustor in the axial direction, wherein the high-pressure shaft is a single shaft that includes a first shaft portion connected to the high-pressure compressor and a second shaft portion that is inserted into the rotor.

[0056] According to the above configuration, the second shaft portion of the high-pressure shaft inserted into the rotor of the generator can function substantially as the rotating shaft of the generator. Furthermore, the high-pressure shaft is configured as a single shaft including the first shaft portion and the second shaft portion. Therefore, compared to when the first shaft portion and the second shaft portion are configured separately, the first shaft portion and the second shaft portion can be configured integrally. Therefore, the high-pressure shaft can be stably supported by multiple bearings. Furthermore, the number of parts in the gas turbine engine can be reduced.

[0057] [Item 12] The bearing structure for a gas turbine engine according to any one of Items 2 to 10, further comprising a generator having a hollow rotating shaft extending in the axial direction and a rotor that rotates integrally with the rotating shaft, the generator being disposed forward in the axial direction relative to the combustor, wherein a maximum outer diameter of the high-pressure shaft is larger than a maximum outer diameter of the rotating shaft.

[0058] According to the above configuration, the maximum outer diameter of the high-pressure shaft is larger than the maximum outer diameter of the rotating shaft, thereby improving the rigidity and mechanical strength of the high-pressure shaft, thereby suppressing vibration of the high-pressure shaft during rotation and enabling the high-pressure shaft to be stably supported by the multiple bearings.

[0059] [Item 13] A bearing structure for a gas turbine engine according to any one of Items 2 to 12, wherein a rear end of the high-pressure shaft is disposed forward of the low-pressure turbine in the axial direction.

[0060] According to the above configuration, the rear end of the high-pressure shaft is positioned axially forward of the low-pressure turbine, thereby shortening the high-pressure shaft. This reduces vibration of the high-pressure shaft during high-speed rotation. Furthermore, it reduces the risk of the bearings supporting the high-pressure shaft being heated by the high heat generated by driving the low-pressure turbine via the high-pressure shaft.

[0061] BR1, BR2 Bearing X Rotation axis 1, 101 Gas turbine engine 2, 102 Bearing structure of gas turbine engine 2 Generator 4 Compressor 5 Combustor 6 Turbine 7 Engine shaft 8 Generator 13 Low-pressure compressor 14 High-pressure compressor 15 Impeller 16 Low-pressure turbine 17 High-pressure turbine 18, 118 High-pressure shaft 18b Rear end of high-pressure shaft 19 Low-pressure shaft 20 Rotating shaft 21 Rotor 118c First shaft portion 118d Second shaft portion

Claims

1. A bearing structure for a gas turbine engine comprising: an engine shaft extending in a fore-and-aft direction; a compressor, a combustor, and a turbine arranged in line in the axial direction of the engine shaft; and a plurality of bearings supporting the engine shaft, the plurality of bearings being arranged forward in the axial direction of the combustor.

2. A bearing structure for a gas turbine engine as described in claim 1, wherein the compressor includes a high-pressure compressor and a low-pressure compressor arranged forward in the axial direction of the high-pressure compressor, the turbine includes a high-pressure turbine and a low-pressure turbine arranged rearward in the axial direction of the high-pressure turbine, the engine shaft includes a hollow high-pressure shaft connecting the high-pressure compressor and the high-pressure turbine, and a low-pressure shaft inserted into the high-pressure shaft and connecting the low-pressure compressor and the low-pressure turbine, and the multiple bearings are arranged to support the high-pressure shaft.

3. A bearing structure for a gas turbine engine according to claim 2, wherein the high-pressure compressor is an axial compressor or a centrifugal compressor.

4. A bearing structure for a gas turbine engine according to any one of claims 2 to 3, wherein the maximum outer diameter of the high-pressure shaft between adjacent bearings among the plurality of bearings is greater than the maximum outer diameter of the high-pressure shaft rearward of the rearmost bearing among the plurality of bearings.

5. A bearing structure for a gas turbine engine according to any one of claims 2 to 4, wherein the maximum outer diameter of the high-pressure shaft in a region in which the low-pressure compressor is located is larger than the maximum outer diameter of the high-pressure shaft in a region axially rearward of said region.

6. A bearing structure for a gas turbine engine according to any one of claims 2 to 5, wherein the high-pressure compressor has an impeller that rotates around the rotational axis of the engine shaft, and the plurality of bearings are disposed forward of the impeller in the axial direction.

7. A bearing structure for a gas turbine engine according to any one of claims 2 to 6, wherein the plurality of bearings are arranged in the axial direction between a front end of the low-pressure compressor and the high-pressure compressor.

8. A bearing structure for a gas turbine engine according to any one of claims 2 to 7, further comprising a generator having a hollow rotating shaft extending in the axial direction and a rotor rotating integrally with the rotating shaft, the generator being disposed forward in the axial direction relative to the combustor, and the plurality of bearings being disposed forward and rearward in the axial direction of the generator.

9. A bearing structure for a gas turbine engine as set forth in claim 8, wherein the rotating shaft and the rotor of the generator rotate together with the high-pressure shaft, and the high-pressure shaft and the rotating shaft are restricted from moving relative to each other in the circumferential direction and the axial direction.

10. A bearing structure for a gas turbine engine according to claim 9, wherein the high-pressure shaft and the rotating shaft are coupled to each other by at least one of welding, shrink fitting, and fixed splines.

11. A bearing structure for a gas turbine engine according to any one of claims 2 to 7, further comprising a generator having a hollow rotor which rotates integrally with said high-pressure shaft and which is located forward of said combustor in the axial direction, said high-pressure shaft being a single shaft including a first shaft portion connected to said high-pressure compressor and a second shaft portion which is inserted into said rotor.

12. A bearing structure for a gas turbine engine according to any one of claims 2 to 10, further comprising a generator having a hollow rotating shaft extending in the axial direction and a rotor rotating integrally with the rotating shaft, the generator being disposed forward in the axial direction relative to the combustor, wherein the maximum outer diameter of the high-pressure shaft is larger than the maximum outer diameter of the rotating shaft.

13. A bearing structure for a gas turbine engine according to any one of claims 2 to 12, wherein a rear end of the high-pressure shaft is disposed forward in the axial direction relative to the low-pressure turbine.

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