阅读说明：本技术 带有离合器组件的燃气涡轮发动机 (Gas turbine engine with clutch assembly ) 是由 B·L·德文多夫 于 2020-10-15 设计创作，主要内容包括：提供一种燃气涡轮发动机。该燃气涡轮发动机包括：涡轮机,该涡轮机具有低速转轴和高速转轴；转子组件,该转子组件联接到低速转轴；电机,该电机可与低速转轴旋转,以用于从低速转轴中提取功率,以用于为低速转轴增加功率,或两者；以及转轴间离合器,该转轴间离合器定位在低速转轴与高速转轴之间,以用于将低速转轴选择性地联接到高速转轴。(A gas turbine engine is provided. The gas turbine engine includes: a turbine having a low speed shaft and a high speed shaft; a rotor assembly coupled to the low-speed rotating shaft; a motor rotatable with the low-speed shaft for extracting power from the low-speed shaft, for adding power to the low-speed shaft, or both; and an inter-shaft clutch positioned between the low-speed rotating shaft and the high-speed rotating shaft for selectively coupling the low-speed rotating shaft to the high-speed rotating shaft.)

1. A gas turbine engine, the gas turbine engine comprising:

a turbine comprising a low speed shaft and a high speed shaft;

a rotor assembly coupled to the low speed rotating shaft;

a motor rotatable with the low-speed spool for extracting power from the low-speed spool, for adding power to the low-speed spool, or both; and

an inter-shaft clutch positioned between the low speed rotating shaft and the high speed rotating shaft for selectively coupling the low speed rotating shaft to the high speed rotating shaft.

2. The gas turbine engine of claim 1, wherein the inter-shaft clutch is a one-way clutch.

3. The gas turbine engine of claim 1, wherein the inter-shaft clutch is a sprag clutch.

4. The gas turbine engine of claim 1, wherein the low-speed spool and the high-speed spool are configured to rotate in a first circumferential direction during operation of the gas turbine engine, wherein the inter-spool clutch is configured to passively disengage and disconnect the low-speed spool from the high-speed spool to allow a rotational speed of the high-speed spool to exceed a rotational speed of the low-speed spool in the first circumferential direction.

5. The gas turbine engine of claim 1, wherein the low-speed spool and the high-speed spool are configured to rotate in a first circumferential direction during operation of the gas turbine engine, wherein the inter-spool clutch is configured to passively engage and couple the low-speed spool to the high-speed spool to prevent a rotational speed of the low-speed spool from exceeding a rotational speed of the high-speed spool in the first circumferential direction.

6. The gas turbine engine of claim 1, wherein the turbomachine further comprises a combustion section, and wherein the inter-shaft clutch is aligned with or positioned forward of the combustion section in an axial direction of the gas turbine engine.

7. The gas turbine engine of claim 1, wherein the high speed spool at least partially comprises a high speed compressor, and wherein the inter-spool clutch is aligned with or positioned forward of the high speed compressor in an axial direction of the gas turbine engine.

8. The gas turbine engine of claim 1, wherein the electric machine is configured to rotate the high speed spool to a light-off speed via the inter-spool clutch and the low speed spool during a start operation of the gas turbine engine.

9. The gas turbine engine of claim 1, further comprising:

an accessory gearbox coupled to the low speed spool, and wherein the motor is coupled to the low speed spool through the accessory gearbox.

10. The gas turbine engine of claim 1, wherein the gas turbine engine is configured as a single unducted rotor engine, and wherein the rotor assembly comprises a single stage unducted rotor blade.

Technical Field

This application relates generally to a gas turbine engine configured to be started using an electric machine coupled to a low speed rotating shaft.

Background

Gas turbine engines generally include a turbine and a rotor assembly. In the case of a turbofan engine, the rotor assembly may be configured as a fan assembly. Turbomachines generally include a high speed rotating shaft and a low speed rotating shaft. The combustion section receives pressurized air that is mixed with fuel and combusted within the combustion chamber to generate combustion gases. The combustion gases are first supplied to the high speed turbine of the high speed spool to drive the high speed spool and then to the low speed turbine of the low speed spool to drive the low speed spool. The rotor assembly is typically coupled to a low speed rotating shaft.

Some gas turbine engines also include accessory gearboxes for powering various accessory systems of the gas turbine engine. The accessory gearbox is coupled to the high speed spool. However, as will be appreciated, extracting power from the high speed spool may result in a low response of the high speed spool to engine commands, which in turn may result in a low response of the low speed spool and rotor assembly to engine commands.

The inventors of the present disclosure have discovered that it may be useful to couple an accessory gearbox to a low speed rotating shaft to increase the responsiveness of the high speed rotating shaft. However, the inventors of the present disclosure have also found that such a configuration may make it difficult to start the engine using an electric motor coupled to the accessory gearbox because the electric motor in such a configuration does not have a mechanical connection to the high speed rotating shaft.

Accordingly, a gas turbine engine having one or more features for increasing the responsiveness of the gas turbine engine to engine commands would be useful. More particularly, a gas turbine engine having one or more features for increasing the responsiveness of the gas turbine engine to engine commands while still facilitating starting of the gas turbine engine with an electric motor coupled to an accessory gearbox would be useful.

Disclosure of Invention

Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

In one aspect of the present disclosure, a gas turbine engine is provided. The gas turbine engine includes: a turbine having a low speed shaft and a high speed shaft; a rotor assembly coupled to the low-speed rotating shaft; a motor rotatable with the low-speed shaft for extracting power from the low-speed shaft, for adding power to the low-speed shaft, or both; and an inter-shaft clutch positioned between the low-speed rotating shaft and the high-speed rotating shaft for selectively coupling the low-speed rotating shaft to the high-speed rotating shaft.

These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention.

Drawings

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 is a schematic cross-sectional view of a gas turbine engine according to an exemplary aspect of the present disclosure.

FIG. 2 is another schematic cross-sectional view of a gas turbine engine according to another exemplary aspect of the present disclosure.

FIG. 3 is a schematic illustration of a clutch according to an exemplary embodiment of the present disclosure in a first position.

FIG. 4 is a schematic illustration of the example clutch of FIG. 3 in a second position.

FIG. 5 is a schematic illustration of the example clutch of FIG. 3 in a third position.

Fig. 6 is a view of an inter-shaft clutch in an axial direction according to an exemplary embodiment of the present disclosure.

FIG. 7 is a flow chart of a method of operating a propulsion system according to an exemplary aspect of the present disclosure.

Detailed Description

Reference now will be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention.

The word "exemplary" is used herein to mean "serving as an example, instance, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

As used herein, the terms "first," "second," and "third" are used interchangeably to distinguish one element from another, and are not intended to denote the position or importance of the various elements.

The terms "forward" and "aft" refer to relative positions within the gas turbine engine or vehicle and to normal operating attitudes of the gas turbine engine or vehicle. For example, with respect to a gas turbine engine, front means a position closer to the engine inlet, and rear means a position closer to the engine nozzle or exhaust.

The terms "upstream" and "downstream" refer to relative directions with respect to fluid flow in a fluid passageway. For example, "upstream" indicates the direction from which the fluid flows, and "downstream" indicates the direction to which the fluid flows.

Unless otherwise specified herein, the terms "coupled," "fixed," "attached," and the like mean directly coupled, fixed, or attached, as well as indirectly coupled, fixed, or attached through one or more intermediate components or features.

The singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise.

Approximating language, as used herein throughout the specification and claims, is applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as "about", "about" and "approximately", are not to be limited to the precise value specified. In at least some examples, the approximating language may correspond to the precision of an instrument for measuring the value, or the precision of a method or machine for constructing or manufacturing the component and/or system. For example, the approximating language may be represented within a margin of 1, 2, 4, 10, 15, or 20 percent.

Here and throughout the specification and claims, unless the context or language indicates otherwise, range limitations are combined and interchanged, such ranges are equivalent and include all the sub-ranges contained therein. For example, all ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other.

Referring now to the drawings, FIG. 1 illustrates an elevation cross-sectional view of an exemplary embodiment of a gas turbine engine, which may incorporate one or more inventive aspects of the present disclosure. In particular, the exemplary gas turbine engine of FIG. 1 is configured as a single unducted rotor engine 10 defining an axial direction A, a radial direction R and a circumferential direction C1 (see FIGS. 2 and 3, which extends about axial direction A). As can be seen in FIG. 1, the engine 10 takes the form of an open rotor propulsion system and has a rotor assembly 12 that includes an array of airfoils disposed about a central longitudinal axis 14 of the engine 10, and more particularly an array of rotor blades 16 disposed about the central longitudinal axis 14 of the engine 10. Moreover, as will be explained in greater detail below, the engine 10 additionally includes a non-rotating vane assembly 18 positioned aft of the rotor assembly 12 (i.e., non-rotating relative to the central axis 14), which includes an array of airfoils also disposed about the central axis 14, and more particularly an array of vanes 20 disposed about the central axis 14. The rotor blades 16 are arranged in a typical equidistant relationship about the centerline 14, and each has a root 22 and a tip 24 and a span defined therebetween. Similarly, the vanes 20 are also arranged in a typical equidistant relationship about the centerline 14, and each vane has a root 26 and a tip 28 and a span defined therebetween. Rotor assembly 12 also includes a hub 43 forward of the plurality of rotor blades 16.

In addition, the engine 10 includes a turbine 30 having a core (or high speed system) 32 and a low speed system. The core 32 generally includes a high-speed compressor 34, a high-speed turbine 36, and a high-speed shaft 38 extending therebetween and connecting the high-speed compressor 34 and the high-speed turbine 36. The high-speed compressor 34 (or at least a rotating component thereof), the high-speed turbine 36 (or at least a rotating component thereof), and the high-speed shaft 38 may collectively be referred to as the high-speed spool 35 of the engine. Further, the combustion section 40 is located between the high speed compressor 34 and the high speed turbine 36. The combustion section 40 may include one or more configurations for receiving a mixture of fuel and air and providing a flow of combustion gases through the high-speed turbine 36 to drive the high-speed spool 35.

The low speed system similarly includes a low speed turbine 42, a low speed compressor or booster 44, and a low speed shaft 46 extending between and connecting the low speed compressor 44 and the low speed turbine 42. The low-speed compressor 44 (or at least a rotating component thereof), the low-speed turbine 42 (or at least a rotating component thereof), and the low-speed shaft 46 may collectively be referred to as a low-speed spool 45 of the engine.

Although engine 10 is depicted with low-speed compressor 44 positioned forward of high-speed compressor 34, in certain embodiments, compressors 34, 44 may be interdigitated. Additionally or alternatively, although engine 10 is depicted with high-speed turbine 36 positioned at low-speed turbine 42, in certain embodiments, turbines 36, 42 may similarly be interdigitated.

Still referring to FIG. 1, the turbine 30 is generally enclosed in a nacelle 48. Further, it will be appreciated that the engine casing 48 at least partially defines an inlet 50 and an exhaust 52, and includes a turbomachine flowpath 54 extending between the inlet 50 and the exhaust 52. For the illustrated embodiment, the inlet 50 is an annular or axisymmetric 360-degree inlet 50 located between the rotor blade assembly 12 and the stationary or stationary vane assembly 18 and provides a path for incoming atmospheric air to enter the turbine flowpath 54 (and compressors 44, 34, combustion section 40, and turbines 36, 42) inboard of the guide vanes 28 in the radial direction R. Such a location may be advantageous for a variety of reasons, including icing performance management and protection of the inlet 50 from various objects and materials that may be encountered in operation.

However, in other embodiments, the inlets 50 may be positioned at any other suitable location, such as aft of the vane assemblies 18, arranged in a non-axisymmetric manner, or the like.

As briefly mentioned above, the engine 10 includes the vane assembly 18. Vane assembly 18 extends from a shroud 48 and is positioned aft of rotor assembly 12. The vanes 20 of the vane assembly 18 may be mounted to a stationary frame or other mounting structure and do not rotate relative to the central axis 14. For reference purposes, fig. 1 also depicts the forward direction with arrow F, which in turn defines the front and rear of the system. As shown in fig. 1, the rotor assembly 12 is located forward of the turbine 30 in a "puller" configuration, and the exhaust port 52 is located aft of the guide vanes 28. As will be appreciated, the vanes 20 of the vane assembly 18 may be configured for straightening the airflow from the rotor assembly 12 (e.g., reducing vortices in the airflow) to increase the efficiency of the engine 10. For example, the vanes 20 may be sized, shaped, and configured to impart a counteracting swirl to the airflow from the rotor blades 16 such that the airflow in the downstream direction of the two rows of airfoils (e.g., blades 16, vanes 20) has a greatly reduced swirl, which may translate into an increased level of induction efficiency.

Still referring to FIG. 1, it may be desirable for the rotor blades 16, vanes 20, or both, to incorporate a pitch mechanism such that the airfoils (e.g., blades 16, vanes 20, etc.) may be rotated relative to a pitch axis of rotation, either individually or in combination with one another. Such pitching may be used to vary thrust and/or vortex effects under various operating conditions, including adjusting the magnitude or direction of thrust generated at the rotor blade 16, or to provide thrust reversal features that may be useful under certain operating conditions, such as at aircraft landing, or desirably adjusting noise generated at least in part by the rotor blade 16, vanes 20, or from aerodynamic interaction of the rotor blade 16 with respect to the vanes 20. More specifically, for the embodiment of FIG. 1, rotor assembly 12 is depicted with a pitch mechanism 58 for rotating rotor blades 16 about their respective pitch axes 60, and vane assembly 18 is depicted with a pitch mechanism 62 for rotating vanes 20 about their respective pitch axes 64.

As depicted, the rotor assembly 12 is driven by the turbine 30, and more particularly, by the low speed shaft 45. More specifically, the engine 10 in the embodiment shown in FIG. 1 includes a power gearbox 56, and the rotor assembly 12 is driven by the low speed rotating shaft 45 of the turbine 30 across the power gearbox 56. The power gearbox 56 may include a gear set for reducing the rotational speed of the low-speed spool 45 relative to the low-speed turbine 42 such that the rotor assembly 12 may rotate at a slower rotational speed than the low-speed spool 45. In this manner, the rotating rotor blades 16 of the rotor assembly 12 may rotate about the axis 14 and generate thrust to propel the engine 10, and thus the aircraft associated therewith, in the forward direction F.

Still referring to FIG. 1, the exemplary engine 10 includes an accessory gearbox 66 and an electric machine 68, wherein the turbine 30 drives the accessory gearbox 66 and the electric machine 68. For example, in certain exemplary embodiments, the accessory gearbox 66 may be coupled to the low speed spool 45 (e.g., the low speed shaft 46) through a suitable gear train, and the motor 68 may be coupled to the accessory gearbox 66. However, in other exemplary embodiments, the motor 68 may be coupled to the low-speed spool 45 of the turbine 30 independently of the accessory gearbox 66, and the accessory gearbox 66 may be coupled to either the low-speed spool 45 or the high-speed spool 35.

Further, the exemplary turbine 30 depicted in FIG. 1 includes an inter-shaft clutch 72. An inter-axle clutch 72 is positioned between the high-speed spool 35 and the low-speed spool 45 to selectively couple the low-speed spool 45 to the high-speed spool 35 during certain operations, such as a starting operation. This may allow the electric machine 68 to be used to start or assist in starting the turbine 30.

However, it will be appreciated that the exemplary single rotor unducted engine 10 depicted in FIG. 1 is by way of example only, and that in other exemplary embodiments, engine 10 may have any other suitable configuration including, for example, any suitable number of shafts or rotating shafts, turbines, compressors, and the like. Additionally or alternatively, in other exemplary embodiments, any other suitable gas turbine engine may be provided. For example, in other exemplary embodiments, the gas turbine engine may be a ducted turbofan engine, a turboshaft engine, a turboprop engine, a turbojet engine, or the like.

Referring now to FIG. 2, a schematic diagram of a gas turbine engine 10 is depicted, according to an exemplary embodiment of the present disclosure. The exemplary gas turbine engine 10 of FIG. 2 may be configured in a similar manner as the exemplary engine 10 described above with respect to FIG. 1. In particular, for the illustrated embodiment, the engine 10 includes an electric machine 68 mechanically coupled to the low speed spool 45 of the turbine 30 of the engine 10, and more particularly includes an accessory gearbox 66 mechanically coupled to the low speed spool 45 of the engine 10, wherein the electric machine 68 is coupled to the low speed spool 45 through the accessory gearbox 66. More specifically, low-speed spool 45 includes a low-speed shaft 46 and at least partially forms a low-speed compressor 54 and a low-speed turbine 42 (not shown). The accessory gearbox 66 is depicted as being coupled to the low speed shaft 46 of the low speed spool 45.

In this manner, the accessory gearbox 66 may transfer rotational power from the low-speed spool 45 of the engine 10 to one or more accessory systems 70, such as the engine 10 or an aircraft incorporating the engine 10, that are mechanically coupled to the accessory gearbox 66 and the electric machine 68 (which may rotate with the accessory gearbox 66). The engine 10 also includes a rotor assembly 12 and a power gearbox 56, wherein the rotor assembly 12 is driven by the low speed rotating shaft 45 that traverses the power gearbox 56.

As will be appreciated, the various electrical and other accessory systems 70 of the gas turbine engine 10 typically shut down (power off) an accessory gearbox driven by the core 32 of the engine 10 (or more particularly the high speed/high pressure system of the engine 10). With such a configuration, the engine core 32 is generally oversized to allow the accessory systems to operate throughout the flight envelope. It is noteworthy, however, that such a configuration may reduce the responsiveness of engine 10 by virtue of the additional load and inertia on core 32 of engine 10. It will be appreciated that by coupling the accessory gearbox 66 and the electric machine 68 to the low speed spool 45 of the engine 10, rather than the high speed spool 35, the gas turbine engine 10 may have a more responsive core 32. Moreover, while this may in turn result in low responsiveness of the low speed system and rotor assembly 12, inclusion of the motor 68 may offset the responsiveness, as discussed below.

Still referring to FIG. 2, it will be appreciated that the motor 68 is coupled to the low speed spool 45 of the turbine 30 at a connection point 100 of the low speed spool 45. More specifically, for the illustrated embodiment, the accessory gearbox 66 is coupled to the low speed spool 45 at a connection point 100, and the motor 68 is coupled to the low speed spool 45 through the accessory gearbox 66. Further, for the illustrated embodiment, the turbine 30 includes a gear train 102, the gear train 102 being coupled to the low speed spool 45 at a connection point 100 and extending to the accessory gearbox 66. In this manner, the accessory gearbox 66 may transfer rotational power from the low-speed spool 45 of the engine 10 to one or more accessory systems 70, for example, mechanically coupled to the accessory gearbox 66 and the electric machine 68 that may rotate with the accessory gearbox 66.

Further, as depicted in FIG. 2, the exemplary gas turbine engine 10 includes an engine clutch 104 positioned in the torque path of the low-speed spool 45 at a location forward of the connection point 100 of the low-speed spool 45 (where the accessory gearbox 66 is coupled to the low-speed spool 45 through the gear train 102). In particular, for the illustrated embodiment, the engine clutch 104 is positioned in the torque path of the low speed rotating shaft 45 between the connection point 100 and the rotor assembly 12.

The engine clutch 104 is movable between an engaged position, in which torque may be transmitted across the engine clutch 104 along the low-speed rotating shaft 45 to drive the rotor assembly 12 (or vice versa), and a disengaged position, in which torque may not be transmitted across the engine clutch 104 to the rotor assembly 12 along the low-speed rotating shaft 45. In this manner, the engine clutch 104 may facilitate operation of the engine 10 without rotating the rotor assembly 12. This may be beneficial, particularly during certain ground operations, where it may be desirable to rotate the turbine 30 without generating thrust from the rotor assembly 12.

In at least some exemplary aspects, the engine clutch 104 may be a two-step clutch for transitioning from a disengaged position to an engaged position. For example, referring now to fig. 3 and 4, a sample exemplary embodiment of the engine clutch 104 is depicted in accordance with an exemplary embodiment of the present disclosure. For the illustrated embodiment, the engine clutch 104 includes a first portion 108 and a second portion 110 that are movable relative to each other along the longitudinal direction L. In certain exemplary embodiments, the longitudinal direction L may be aligned with the axial direction a of the engine 10. Further, in certain exemplary embodiments, the first portion 108 may rotate with the rotor assembly 12, and the second portion 110 may rotate with the low speed shaft 45 at the connection point 100 and rearward of the connection point 100.

As shown in fig. 3 and 4, the first portion 108 of the engine clutch 104 includes a first friction plate 112 and a first set of geometric features 114 (depicted in phantom, positioned in an inner surface of the first portion 108). The second portion 110 of the engine clutch 104 includes a second friction plate 116 and a second set of geometric features 118, the second set of geometric features 118 being correspondingly shaped as the first set of geometric features 114. More particularly, for the illustrated embodiment, the first set of geometric features 114 includes a plurality of protrusions extending along the longitudinal direction L, and the second set of geometric features 118 includes a plurality of recesses extending along the longitudinal direction L. The plurality of projections are configured to be slidably received within the plurality of grooves. In this manner, the first geometric feature 114 and the second set of geometric features 118 may be referred to as a spline connection.

As will be appreciated, the low speed rotating shaft 45 may freely rotate relative to the rotor assembly 12 when the engine clutch 104 is in the disengaged position (fig. 3). In contrast, when the engine clutch 104 is in the engaged position (fig. 4), the low-speed rotating shaft 45 rotates with the rotor assembly 12. The friction plates 112, 116 provide a relatively smooth transition from the disengaged position to the engaged position.

More particularly, referring now also to fig. 5, it will be appreciated that the clutch 104 may be moved further to the transition position. In the transition position, the first friction plate 112 and the second friction plate 116 are in contact with each other, but the first set of geometric features 114 and the second set of geometric features 118 are not in contact. This may allow the rotor assembly 12 to slowly accelerate to lock the first and second portions 108, 110 of the clutch 104 together prior to engaging the first and second geometric features 114, 118.

Notably, for the depicted embodiment, as will also be appreciated, the second friction plate 116 is configured to slide in a longitudinal direction between the transitional position and the engaged position. The second friction plate 116 may be biased in a longitudinal direction toward the first friction plate 112 by, for example, one or more spring assemblies (not shown).

Further, after the rotor assembly 12 substantially matches the rotational speed of the low-speed rotating shaft 45, the clutch 104 may be moved in the longitudinal direction L from the transitional position to the engaged position such that the second geometric feature 118 engages the first geometric feature 114 to secure the first and second portions 108, 110 of the engine clutch 104 together.

It will also be appreciated that such a configuration may allow for improved operation of the gas turbine engine 10. For example, such a configuration may allow the core 32 of the gas turbine engine 10 to operate during, for example, idle and post-landing operations without participating in rotating the rotor assembly 12. In this manner, electric machine 68 may be sized to accept 100% of rated engine power such that gas turbine engine 10 may operate at rated engine power (i.e., by moving engine clutch 104 to the disengaged position) without engaging rotor assembly 12, and electric machine 68 converts substantially all such power into electrical energy to be provided to aircraft 248 that incorporates gas turbine engine 10 via electrical bus 120 (see fig. 2), to one or more energy storage units within or in electrical communication with bus 230 to assist in starting additional engines, combinations thereof, and so forth.

Subsequently, when thrust is desired to be generated with the rotor assembly 12, the engine clutch 104 may be moved from the disengaged position to the transitional position, slowly bringing the rotor assembly 12 to a speed to rotationally lock the rotor assembly 12 to the low-speed rotating shaft 45 before subsequently moving the engine clutch 104 to the engaged position.

It will also be appreciated that with the above configuration, once the engine clutch 104 is moved to the engaged position, the electric machine 68 may be used to accelerate the rotor assembly 12 more quickly during pre-takeoff operation. More specifically, electrical power may be provided to the motor 68 and converted into rotational power provided to the low speed spool 45 through the accessory gearbox 66 to directly assist in accelerating the rotor assembly 12. While the accessory gearbox 66 is mounted to the low-speed spool 45, this ensures that the low-speed spool 45 has the desired responsiveness.

As will also be appreciated, in this manner, the electric machine 68 may also be used to start or assist in starting the engine 10. Referring back to FIG. 2, it will be appreciated that the depicted exemplary engine 10 also includes an inter-shaft clutch 122 positioned between the low speed/low pressure system of the gas turbine engine 10 and the high speed/high pressure system of the gas turbine engine 10. In particular for the illustrated embodiment, the inter-shaft clutch 122 is positioned between the low-speed shaft 45 and the high-speed shaft 35. More specifically, for the illustrated embodiment, inter-spool clutch 122 is positioned between low-speed spool 45 and high-speed spool 35 at a location aligned with combustion section 40 in axial direction a of gas turbine engine 10 or positioned forward of combustion section 40 and aligned with high-speed compressor 34 in axial direction a or aft of the high-pressure compressor. Such a configuration may allow torque balance on the inter-shaft clutch 122 when the inter-shaft clutch 122 couples the low-speed shaft 45 to the high-speed shaft 35.

However, it will be appreciated that in other embodiments, the inter-shaft clutch 122 may be positioned at any other suitable location. For example, in other exemplary embodiments, as depicted in phantom in FIG. 2 (as element 122'), inter-shaft clutch 122 may be positioned at any suitable location forward of combustion section 40, such as aligned with or forward of high speed compressor 34 in axial direction A, such as forward of high speed compressor 34 in axial direction A. Such a configuration may provide a cooler inter-shaft clutch by virtue of the spacing of the inter-shaft clutch 122 from the combustion section 40 to reduce the likelihood of premature wear of the inter-shaft clutch 122.

During operation, inter-spool clutch 122 may ensure that the low-speed/low-pressure system (low-speed spool 45) does not rotate faster in first circumferential direction C1 than the high-speed/high-pressure system (high-speed spool 35) (i.e., the circumferential directions of high-speed spool 35 and low-speed spool 45 are configured to rotate during normal flight operation; see also FIG. 6 discussed below). The inter-shaft clutch 122 may be a one-way clutch configured to be passively engaged and disengaged depending on one or more operating conditions, such as the relative rotational speeds and torques on the high-speed rotating shaft 35 and the low-speed rotating shaft 45. For example, in certain exemplary embodiments, electric machine 68 may operate as a starter motor for gas turbine engine 10. In such exemplary embodiments, during a starting operation, the electric motor 68 may receive electrical power through the electrical power bus 120 and convert such power into mechanical power that is transmitted through the accessory gearbox 66 and the gear train 102 to the low-speed spool 45, causing the low-speed spool 45 to rotate in a first circumferential direction C1. The inter-axle clutch 122 is engageable by such rotation, such that the low-speed spool 45 rotates the high-speed spool 35 correspondingly across the axle clutch 122 in the first circumferential direction C1. Such operation may continue until the gas turbine engine 10 reaches a light-off point. As used herein, the term "light-off point" refers to a rotational speed wherein the high speed spool 45 and/or the low speed spool 35 are sufficient to provide an amount of airflow to the combustion section 40 to allow ignition and sustained combustion in the combustion section 40. At this point, the combustion section 40 may generate combustion gases to drive the high speed spool 35, and the high speed spool 35 may have additional force (from the combustion gases) that urges the high speed spool 35 to rotate faster than the low speed spool 45 in the first circumferential direction C1. The inter-axle clutch 122 may be passively/automatically disengaged at this time, allowing the high speed spool 35 to rotate faster than the low speed spool 45 in the first circumferential direction C1.

As mentioned, the inter-shaft clutch 122 may be configured as a one-way clutch. For example, referring now to FIG. 6, it will be appreciated that, in at least certain exemplary aspects, the inter-shaft clutch 122 may be configured as a sprag clutch. Fig. 6 provides a schematic axial view (i.e., a view in axial direction a) of the exemplary inter-axle clutch 122. The depicted exemplary sprag clutch includes a plurality of sprags 124 positioned between an inner race 126 and an outer race 128. The inner race 126 is fixed to or formed integrally with the low-speed rotating shaft 45, and the outer race 128 is coupled to the high-speed rotating shaft 35. The plurality of sprags 124 generally provide no resistance to such movement when the inner race 126 rotates counterclockwise relative to the outer race 128 (at least for the depicted embodiment views), or when the outer race 128 rotates faster than the inner race 126. In contrast, when the inner race 126 attempts to rotate clockwise relative to the outer race 128 (first circumferential direction C1), the plurality of sprags 124 rotate about their respective axes of rotation 125 and lock the inner race 126 to the outer race 128 such that relative rotation of the inner race 126 in the clockwise direction relative to the outer race 128 is not permitted.

More particularly, it will be appreciated that for the exemplary view depicted in fig. 6, the clockwise direction is the first circumferential direction C1. In this manner, it will be appreciated that the low-speed spool 45 and the high-speed spool 35 are configured to rotate in the first circumferential direction C1 during operation of the gas turbine engine 10. It will also be appreciated that, with such a configuration, the inter-shaft clutch 122 is configured to passively engage and couple the low-speed shaft 45 (inner race 126) to the high-speed shaft 35 (outer race 128) to prevent the rotational speed of the low-speed shaft 45 (inner race 126) from exceeding the rotational speed of the high-speed shaft 35 (outer race 128) in the first circumferential direction C1. In this way, the low-speed rotating shaft 45 may be coupled to the high-speed rotating shaft 35 during a starting operation, so that the motor 68 may start rotation of the high-speed rotating shaft 35 although coupled to the low-speed rotating shaft 45.

Further, it will be appreciated that, with such a configuration, the inter-shaft clutch 122 is configured to passively disengage and disconnect the low-speed shaft 45 (inner race 126) from the high-speed shaft 35 (outer race 128) to allow the rotational speed of the high-speed shaft 35 (outer race 128) to exceed the rotational speed of the low-speed shaft 45 (inner race 126) in the first circumferential direction C1. In this manner, the inter-shaft clutch 122 may allow the high-speed spool 35 to rotate faster than the low-speed spool 45 upon engine start without having to actively actuate the inter-shaft clutch 122.

However, it should be appreciated that in other embodiments, any other suitable inter-shaft clutch 122 may be used. For example, in other exemplary embodiments, the inter-shaft clutch 122 may be an actively actuated two-stage clutch (similar to the engine clutch discussed above), may be any other suitable form of one-way clutch, or the like.

In this way, the motor 68, while coupled to the low-speed rotating shaft 45, may assist in starting the engine 10 by directly rotating the high-speed rotating shaft 35.

However, it will be appreciated that in other exemplary embodiments, the engine may have any other suitable configuration. For example, while for the embodiment depicted in the figures, the motor 68 is spaced from the low-speed spool 45, it will be appreciated that in other exemplary embodiments, the motor 68 may instead be mounted about the low-speed spool 45, sharing a common axis of rotation with the low-speed spool 45. With such a configuration, the rotor of the motor 68 can be mounted around the low-speed shaft of the low-speed rotating shaft 45.

Other configurations are also contemplated.

Referring now to FIG. 7, a flow chart of a method 200 of operating a gas turbine engine is provided. The method 200 may be used to operate a gas turbine engine configured in a manner similar to one or more of the gas turbine engines described above. Accordingly, a gas turbine engine may include a low speed spool, a high speed spool, and an electric machine coupled to the low speed spool.

For the exemplary aspect of fig. 7, the method 200 includes: rotating, at least in part, the low speed spool with the electric machine during a start-up operation of the gas turbine engine at (202). More specifically, for the exemplary aspect of FIG. 7, rotating the low speed spool at least partially with the motor during a start-up operation of the gas turbine engine at (202) includes rotating the high speed spool with the low speed spool across an inter-spool clutch positioned between the low speed spool and the high speed spool during a start-up operation of the gas turbine engine at (204). As discussed above, the inter-shaft clutch may be a one-way clutch.

Further, with the exemplary aspect of FIG. 7, rotating the low speed spool at least partially with the motor during a start-up operation of the gas turbine engine at (202) more particularly includes: rotating the low speed spool with the electric machine only during a start-up operation of the gas turbine engine at (206), rotating the low speed spool with the electric machine across the accessory gearbox at (208), and rotating the low speed spool and the high speed spool with the electric machine to a light-off speed at (210).

Further, the depicted exemplary method 200 also includes, at (212), igniting a combustion section of the gas turbine engine after rotating the low-speed spool and the high-speed spool with the electric machine to a light-off speed, and at (214), rotating the high-speed spool faster than the low-speed spool, wherein rotating the high-speed spool faster than the low-speed spool includes automatically disengaging an inter-spool clutch.

Further aspects of the invention are provided by the subject matter of the following clauses:

a gas turbine engine comprising: a turbine comprising a low speed shaft and a high speed shaft; a rotor assembly coupled to the low-speed rotating shaft; a motor rotatable with the low-speed shaft for extracting power from the low-speed shaft, for adding power to the low-speed shaft, or both; and an inter-shaft clutch positioned between the low-speed rotating shaft and the high-speed rotating shaft for selectively coupling the low-speed rotating shaft to the high-speed rotating shaft.

The gas turbine engine of one or more of these clauses, wherein the inter-axle clutch is a one-way clutch.

The gas turbine engine of one or more of these clauses, wherein the inter-axle clutch is a sprag clutch.

The gas turbine engine of one or more of these clauses, wherein the low-speed spool and the high-speed spool are configured to rotate in a first circumferential direction during operation of the gas turbine engine, wherein the inter-spool clutch is configured to passively disengage and disconnect the low-speed spool from the high-speed spool to allow a rotational speed of the high-speed spool to exceed a rotational speed of the low-speed spool in the first circumferential direction.

The gas turbine engine of one or more of these clauses, wherein the low-speed spool and the high-speed spool are configured to rotate in a first circumferential direction during operation of the gas turbine engine, wherein the inter-spool clutch is configured to passively engage and couple the low-speed spool to the high-speed spool to prevent a rotational speed of the low-speed spool from exceeding a rotational speed of the high-speed spool in the first circumferential direction.

The gas turbine engine of one or more of these clauses, wherein the turbomachine further comprises a combustion section, and wherein the inter-shaft clutch is aligned with or positioned forward of the combustion section in an axial direction of the gas turbine engine.

The gas turbine engine of one or more of these clauses, wherein the high speed spool at least partially comprises a high speed compressor, and wherein the inter-spool clutch is aligned with or positioned forward of the high speed compressor in an axial direction of the gas turbine engine.

The gas turbine engine of one or more of these clauses, wherein the electric machine is configured to rotate the high speed spool to a light-off speed via the inter-spool clutch and the low speed spool during a starting operation of the gas turbine engine.

The gas turbine engine of one or more of these clauses further comprising: an accessory gearbox coupled to the low speed rotating shaft, and wherein the motor is coupled to the low speed rotating shaft through the accessory gearbox.

The gas turbine engine of one or more of these clauses, wherein the gas turbine engine is configured as a single unducted rotor engine, and wherein the rotor assembly comprises a single pole unducted rotor blade.

The gas turbine engine of one or more of these clauses further comprising: an unducted leading stator vane stage positioned downstream of the single stage unducted rotor blade.

A method of operating a gas turbine engine including a low-speed spool, a high-speed spool, and an electric machine coupled to the low-speed spool, the method comprising: rotating a low speed spool at least partially with a motor during a starting operation of a gas turbine engine; wherein rotating the low-speed spool at least partially with the motor during a start-up operation of the gas turbine engine includes rotating the high-speed spool with the low-speed spool across an inter-spool clutch positioned between the low-speed spool and the high-speed spool during a start-up operation of the gas turbine engine.

The method of one or more of these clauses, wherein rotating the low-speed spool at least partially with the electric machine during a starting operation of the gas turbine engine further comprises rotating the low-speed spool and the high-speed spool with the electric machine to a light-off speed.

The method of one or more of these clauses, further comprising: after the low-speed spool and the high-speed spool are rotated by the motor to a light-off speed, a combustion section of the gas turbine engine is ignited.

The method of one or more of these clauses, further comprising: rotating the high speed spool faster than the low speed spool, wherein rotating the high speed spool faster than the low speed spool includes automatically disengaging an inter-spool clutch.

The method of one or more of these clauses, wherein the inter-shaft clutch is a one-way clutch.

The method of one or more of these clauses, wherein the turbomachine further comprises a combustion section, and wherein the inter-shaft clutch is aligned with or positioned forward of the combustion section in an axial direction of the gas turbine engine.

The method of one or more of these clauses, wherein rotating the low speed spool at least partially with the motor during a starting operation of the gas turbine engine comprises rotating the low speed spool with only the motor during a starting operation of the gas turbine engine.

The method of one or more of these clauses, wherein rotating the low speed spool with the electric machine at least partially during a starting operation of the gas turbine engine comprises rotating the low speed spool with the electric machine across the accessory gearbox.

The method of one or more of these clauses, wherein the gas turbine engine is configured as a single unducted rotor engine, and wherein the rotor assembly comprises a single stage unducted rotor blade.