Gas turbine engine with internal electromechanical device

[0001] The application relates generally to gas turbine engines and, more particularly, to electromechanical devices in such an engine.

[0002] A known method of installing an internal starter/generator in a gas turbine engine includes attaching the rotating component of the internal starter/generator cantilevered from the forward end of the high pressure shaft of the engine. This usually results in additional rotating weight on the high pressure shaft and as such may have an adverse effect on the dynamics of the high pressure shaft. As such, the addition of an internal starter/generator to an engine not originally designed to accept one may necessitate a redesign of the high pressure shaft to support the additional loads associated with the starter/generator, displacement of bearing supports to accommodate the starter/generator which may require a redesign of the low pressure shaft, and/or changes in the low pressure shaft support structure requiring retesting the engine for blade-off and bird-ingestion, any of which may result in substantial development costs.

[0003] In one aspect, there is provided a gas turbine engine comprising: a rotatable high pressure shaft in driving engagement with at least one high pressure rotor of the engine and having a shaft gear secured thereto; a low pressure shaft in driving engagement with at least one low pressure rotor of the engine and rotatable independently of the high pressure shaft; an electromechanical device having a rotor and a stator coupled such that the rotor is rotatable with respect to the stator, the rotor having a device gear secured thereto, the device being secured to a support structure in a bearing housing, the bearing housing forming part of a bearing assembly supporting a portion of the low pressure shaft extending in proximity of the high pressure shaft and of the shaft gear; and a coupling idle gear secured for rotation about a stationary gear support mounted in the bearing housing, the idle gear being in toothed engagement with the shaft gear and with the device gear.

[0004] In another aspect, there is provided an electromechanical device assembly for a gas turbine engine, said assembly comprising: a rotor mounted on a rotor support, the rotor support having a device gear secured thereto; a stator mounted on a stator support, the rotor and stator supports being coupled such that the rotor is rotatable about the stator to generate at least one of electrical and mechanical power, the stator support being secured to a bearing support adapted to be part of a bearing assembly of a low pressure shaft of the engine; a shaft gear adapted to be secured to a high pressure shaft of said engine; and a coupling idle gear in toothed engagement with the device gear and with the shaft gear, the coupling gear being adapted to be rotationally supported by a stationary gear support in a bearing housing of the bearing assembly.

[0005] In a further aspect, there is provided a method of operating an electromechanical device of a gas turbine engine, the method comprising: mounting the device in a bearing housing about a low pressure shaft of the engine with a rotor of said device having a device gear connected thereto; securing a shaft gear to a high pressure shaft of the engine; and coupling the device and shaft gears through direct engagement with a coupling idle gear rotationally supported on a stationary gear support mounted in the bearing housing.

[0012] 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 compressor section 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 high pressure shaft 19 drivingly interconnects high pressure rotors of the compressor and turbine sections 14, 18. A low pressure shaft 20 rotatable independently from the high pressure shaft 19 drivingly interconnects the fan 12 and low pressure rotor(s) of the turbine section 18. Although not shown, the low pressure shaft 20 may also support additional low pressure rotor(s) of the compressor section 14. The low pressure shaft 20 is hollow and extends through the high pressure shaft 19 beyond each end thereof. Although the engine 10 is illustrated as a turbofan engine, alternately the engine may be any other adequate type of gas turbine engine, such as for example a turboprop or a turboshaft engine.

[0013] Referring to FIG. 2, the portion of the low pressure shaft 20 protruding from the high pressure shaft 19 is supported by first and second spaced apart bearing assemblies 42, 50 each received in a respective beating cavity 33, 29, the first bearing assembly 42 being located closer to the end of the low pressure shaft 20, and as such further from the high pressure shaft 19, than the second bearing assembly 50. An electromechanical device 21 is described herein and is installed between the two spaced apart bearing assemblies 50, 42 about the low pressure shaft 20 to be driven by the high pressure shaft 19. In a particular embodiment, the electromechanical device is a starter/generator. The electromechanical device 21 is an internal device as it is received radially inwardly with respect to the flowpath of the engine. In a particular embodiment, the internal electromechanical device 21 is received within one or more bearing housings.

[0014] Referring to FIG. 2, there is shown the manner in which the device 21 is supported about the low pressure shaft 20. As herein shown, the device 21 is provided with a stator 22 and a rotational rotor 23 which is rotatable about the stator 22. The stator 22 is housed in a stationary stator support 24 which is secured to a bearing support 25′ of the second bearing assembly 50. The rotor 23 is secured to an arm of a rotor support 25. A ring gear 25″ is secured to an arm of the rotor support 25. The device gear 25″ has a series of circumferential teeth 32. A ring gear 26 is further secured about the end of the high pressure shaft 19 and rotated therewith. The shaft gear 26 has a series of bevelled gear teeth 27 thereabout.

[0015] In order to transfer the drive between the shaft gear 26 and the device gear 25″ to produce electricity by the device 21 when in a generator mode and/or to use the device 21 to drive the high pressure shaft 19 when in a starter mode, these gears have to be coupled. In the embodiment shown, this is achieved by mounting a coupling idle gear 28 in the bearing cavity 29 associated with the second bearing assembly 50. The coupling idle gear 28 has circumferential teeth gear 31 which are in toothed engagement with the bevel gear teeth 27 of the shaft gear 26 and the bevel gear teeth 32 of the device gear 25″. As herein shown, the coupling idle gear 28 has a hub 40 which is configured for rotational displacement in a support assembly 30 secured to stationary components of bearing support 25′. When the high pressure shaft 19 is rotated, it will cause rotation of the coupling idle gear 28 which in turn rotates the device gear 25″ thereby displacing the rotor support 25 and the rotor 23 about the stator 22 of the device to produce electricity. Additionally or alternately, when the rotor 23 is rotated as the device 21 is powered, the device gear 25″ rotates the idle gear 28 which in turn rotates the high pressure shaft 19 through the shaft gear 26. It is pointed out that the rotating components of the device 21 are fully supported independent of other rotating engine components by the same structure as the bearing support 25′ associated with the second bearing assembly 50. In a particular embodiment, replacement of an external starter/generator driven by a power shaft by the device 21 driven by the intermediate coupling idle gear 28 supported in the bearing cavity 29 allows for the bearing support 25′ to remain at the same location so that the shaft dynamics of the low pressure shaft 20 may be maintained, and so that the dynamics of the high pressure shaft 19 may be unaffected by the device installation.

[0016] In summary, the method of operating the device 21 generally comprises the steps of mounting the electromechanical device 21 about the low pressure shaft 20 of a gas turbine engine with the rotor 23 of the device 21 mounted on the rotor support 25, having the device gear 25″ secured thereto, and supported about the low pressure shaft 20 by the bearing support 25′. The method further comprises securing the shaft gear 26 about the high pressure shaft 19. Still further, the method comprises coupling the shaft gear 26 to the device gear 25″ through the coupling idle gear 28 rotationally supported by a stationary gear support immovably mounted in the bearing cavity 29.

[0017] It can be appreciated that the ratio between the number of the bevelled gear teeth of the shaft gear 26, the coupling idle gear 28 and the device gear 25″ determines the rotational speed of the rotor 23 in relation to the high pressure shaft speed. Accordingly, the rotor drive speed can be stepped up or down.

[0018] Referring to FIG. 3, there is shown a further embodiment of a gear coupling ratio between the high pressure shaft 19 and the device gear 25″, allowing for a step-up speed relationship. As herein shown, a shaft ring gear 35 has a conical section 45 rearwardly projecting in the bearing cavity 29. Circumferential teeth 46 are disposed about the larger outer periphery of the conical section 45 and are in toothed engagement with the teeth 31′ of a smaller coupling idle gear 28′. The teeth 31′ of the coupling idle gear 28′ are also in toothed engagement with the teeth 32 of the device gear 25″. Accordingly, it can be seen that by modifying the size of the shaft gears 26, and the coupling idle gear 28, 28′ that the relative rotational speed of the rotor 23 with respect to that of the high pressure shaft 19 can be modified.

[0019] Referring now to FIGS. 4 and 5, there will be described the method of assembling the device 21 in a gas turbine engine and about the low pressure shaft 20 thereof and between bearing assemblies 42, 50.

[0020] The method comprises mounting the rotational rotor 23 of the device 21 on the rotor support 25 which is provided with the device gear 25″. The bearings 47 of the rotor support 25 are installed on a support sleeve 48 of the rotor support 25. The stator 22 of the device 21 is secured to the stator support 24. The rotor support 25 of the rotor 23 is coupled to a stator housing 49 to rotate about the stator housing with the stator 22 immovably supported therein. The stator support 24 is then secured to the bearing support 25′ of the second bearing assembly 50. The second bearing assembly 50 is then secured, herein by press-fitting it on the low pressure shaft 20. The stator support 24 and the rotor support 25 of the rotor 23 coupled for rotation thereabout are then installed over the bearing assembly 50 to form a low pressure shaft assembly as shown in FIG. 5.

[0021] As shown in FIG. 4, the bearing support 25′ is provided with an annular flange 51 which is fitted over the second bearing assembly 50 and the bearings 47 supported on the support sleeve 48 of the rotor support 25 are retained in position by a ledge on the surface of the flange 51. This secures the bearings and the support sleeve 48 captive but rotatable on its bearing support. Accordingly, the internal stator generator with its connection to the bearing support 25′ is now mounted on the low pressure shaft 20, as shown in FIG. 5.

[0022] As shown in FIG. 4, the bearing support 25′ is also provided with a connecting portion 52 having a flange 52′ which is immovably connected to a flange 54′ of the bearing housing 54 by a series of bolts 53 thereabout. The bearing housing 55 of the first bearing assembly 42 is also provided with a flange 55′ which is interconnectable with the flanges 52′ and 54′ of the second bearing housing 54 and the connecting portion 52 for connection therewith. This is done by different bolts after the flanges 52′ and 54′ are interconnected.

[0023] Before the first bearing housing 55 is secured over the device 21, the power cable 56 are routed from inside the second bearing housing 54 through the bearing support 25′ and over the stator support 24. The power cable 56 is then secured to cable connectors 57 mounted exteriorly on the front end of the stator support 24. The device gear 25″ may be coupled to the coupling idle gear 28 during the mounting of the bearing support 25′ over the bearings or thereafter. The method therefore also driveably engaging the high pressure shaft 19 and the rotor 23 of the device 21 and in the particular embodiment shown this includes by securing the shaft gear 26 to the high pressure shaft 19, rotationally installing the idle gear 28 on a support 30 in the second bearing cavity 29 or attached to a gear support 60 securable or integrally formed on the outer face of the bearing support 25′ of the second bearing assembly 50, and meshing the idle gear 28 with the shaft gear 26 and the device gear 25″, as shown in FIG. 3.

[0024] In a particular embodiment the idle gear 28 is engaged with the device gear 25″ and assembled with the low pressure shaft assembly (including the device 21 and the bearing support 25′). The shaft gear 26 is assembled to the high pressure shaft 19 before the installation of the low pressure shaft assembly to the second bearing housing 54. Assembly of the low pressure shaft assembly to the second bearing housing 54 engages the teeth of the idle gear 28 and of the shaft gear 26.

[0025] In an alternate embodiment, the idle gear 28, 28′ may be replaced by any other adequate type of member allowing a driving engagement, including but not limited to a lay shaft.

[0026] The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. For example, by modifying the gear ratios, a desired rotor drive speed can be obtained and modified. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.