Gas turbine engine with clutch assembly

Abstract

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 shaft; an electric 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 shaft and the high-speed shaft for selectively coupling the low-speed shaft to the high-speed shaft.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is a nonprovisional application that claims the benefit of priority under 35 USC § 119(e) to U.S. Provisional Application No. 62 / 915,364, filed on October 15, 2019 (which is hereby incorporated by reference in its entirety). Technical Field

[0003] This application generally relates to a gas turbine engine configured to be started using an electric machine coupled to a slow speed rotating shaft. Background Art

[0004] A gas turbine engine generally comprises a turbine and a rotor assembly. In the case of a turbofan engine, the rotor assembly may be configured as a fan assembly. The turbine generally comprises a high-speed rotating shaft and a low-speed rotating shaft. The combustion section receives pressurized air, which is mixed with fuel and combusted in a combustion chamber to generate combustion gases. The combustion gases are first provided to a high-speed turbine of the high-speed rotating shaft to drive the high-speed rotating shaft, and then provided to a low-speed turbine of the low-speed rotating shaft to drive the low-speed rotating shaft. The rotor assembly is typically coupled to the low-speed rotating shaft.

[0005] Some gas turbine engines also include an accessory gearbox for providing power to 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 the high-speed spool being less responsive to engine commands, which in turn may result in the low-speed spool and rotor assembly being less responsive to engine commands.

[0006] The inventors of the present disclosure have discovered that it can be useful to couple an accessory gearbox to a low-speed shaft to increase the responsiveness of the high-speed shaft. However, the inventors of the present disclosure have also discovered that such a configuration can 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 shaft.

[0007] Therefore, 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. Summary of the invention

[0008] 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.

[0009] 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 shaft; an electric 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 shaft and the high-speed shaft for selectively coupling the low-speed shaft to the high-speed shaft.

[0010] 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 present invention and, together with the description, serve to explain the principles of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] A complete and enabling disclosure of the present invention including the best mode thereof to one of ordinary skill in the art is set forth in the specification with reference to the accompanying drawings, in which:

[0012] Figure 1 is a schematic cross-sectional view of a gas turbine engine according to an exemplary aspect of the present disclosure.

[0013] Figure 2 is another schematic cross-sectional view of a gas turbine engine according to another exemplary aspect of the present disclosure.

[0014] Figure 3 is a schematic diagram of a clutch according to an exemplary embodiment of the present disclosure in a first position.

[0015] Figure 4 It is in the second position Figure 3 Schematic diagram of an exemplary clutch.

[0016] Figure 5 It is in the third position Figure 3 Schematic diagram of an exemplary clutch.

[0017] Figure 6 is a view of a clutch between rotating shafts in an axial direction according to an exemplary embodiment of the present disclosure.

[0018] Figure 7 is a flow chart of a method of operating a propulsion system according to an exemplary aspect of the present disclosure. DETAILED DESCRIPTION

[0019] Reference will now be made in detail to embodiments of the present invention, one or more examples of which are shown in the accompanying drawings. The detailed description uses numbers and letters to indicate features in the drawings. Similar or similar numbers in the drawings and description are used to indicate similar or similar parts of the present invention.

[0020] The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other implementations.

[0021] As used herein, the terms “first,” “second,” and “third” are used interchangeably to distinguish one component from another, and are not intended to indicate the position or importance of each component.

[0022] The terms "front" and "rear" refer to relative positions within a gas turbine engine or vehicle and refer to the normal operating attitude of the gas turbine engine or vehicle. For example, with respect to a gas turbine engine, front refers to a position closer to the engine inlet, and rear refers to a position closer to the engine nozzle or exhaust.

[0023] The terms "upstream" and "downstream" refer to relative directions with respect to fluid flow in a fluid pathway. For example, "upstream" refers to the direction from which the fluid flows, and "downstream" refers to the direction to which the fluid flows.

[0024] Unless otherwise specified herein, the terms "coupled," "fixed," "attached to," and the like may refer to both direct coupling, fixing, or attachment as well as indirect coupling, fixing, or attachment through one or more intermediate members or features.

[0025] The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0026] As used herein throughout the specification and claims, approximate language is applicable to modify any quantitative representation that is permissible to vary without causing a change in the basic function to which it relates. Therefore, values ​​modified by one or more terms such as "about," "approximately," and "roughly" are not limited to the exact values ​​specified. In at least some instances, approximate language may correspond to the accuracy of an instrument used to measure a value or the accuracy of a method or machine used to construct or manufacture a component and / or system. For example, approximate language may be expressed within a margin of 1, 2, 4, 10, 15, or 20 percent.

[0027] Here and throughout the specification and claims, range limitations are combined and interchangeable unless context or language indicates otherwise, and such ranges are equivalent and include all subranges contained therein. For example, all ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other.

[0028] Now refer to the figure, Figure 1 An elevational cross-sectional view of an exemplary embodiment of a gas turbine engine is shown, which may incorporate one or more inventive aspects of the present disclosure. In particular, Figure 1 The exemplary gas turbine engine is configured to define an axial direction A, a radial direction R and a circumferential direction C1 (see Figure 2 and Figure 3 , which extends about the axial direction A) of a single unducted rotor engine 10. Figure 1 As can be seen, the engine 10 takes the form of an open rotor propulsion system and has a rotor assembly 12 that includes an array of airfoils arranged about a central longitudinal axis 14 of the engine 10, and more particularly includes an array of rotor blades 16 arranged about the central longitudinal axis 14 of the engine 10. Moreover, as will be explained in more detail below, the engine 10 additionally includes a non-rotating vane assembly 18, which is positioned rearward of the rotor assembly 12 (i.e., does not rotate relative to the central axis 14), which includes an array of airfoils also arranged about the central axis 14, and more particularly includes an array of vanes 20 arranged about the central axis 14. The rotor blades 16 are arranged in a typical equidistant relationship about the centerline 14, and each blade 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 located forward of the plurality of rotor blades 16 .

[0029] In addition, the engine 10 includes a turbomachine 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 its rotating components), the high-speed turbine 36 (or at least its rotating components), and the high-speed shaft 38 may be collectively referred to as the high-speed rotating shaft 35 of the engine. In addition, a 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 rotating shaft 35.

[0030] The low-speed system similarly includes a low-speed turbine 42, a low-speed compressor or supercharger 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 its rotating components), the low-speed turbine 42 (or at least its rotating components), and the low-speed shaft 46 may be collectively referred to as the low-speed rotating shaft 45 of the engine.

[0031] 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 arranged in an interdigitated manner. Additionally or alternatively, although engine 10 is depicted with high-speed turbine 36 positioned forward of low-speed turbine 42, in certain embodiments, turbines 36, 42 may similarly be arranged in an interdigitated manner.

[0032] Still refer to Figure 1 , the turbine 30 is generally enclosed in a cowling 48. Further, it will be appreciated that the cowling 48 at least partially defines an inlet 50 and an exhaust port 52, and includes a turbomachinery flow path 54 extending between the inlet 50 and the exhaust port 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 fixed or stationary vane assembly 18, and provides a path for the incoming atmosphere to enter the turbine flow path 54 (and the compressor 44, 34, the combustion section 40, and the turbine 36, 42) inboard of the guide vanes 28 in a radial direction R. Such a location may be advantageous for a variety of reasons, including icing performance management and protecting the inlet 50 from various objects and materials that may be encountered in operation.

[0033] However, in other embodiments, the inlet 50 may be positioned at any other suitable location, such as, for example, aft of the vane assembly 18 , arranged in a non-axisymmetric manner, etc.

[0034] As briefly mentioned above, the engine 10 includes a vane assembly 18. The vane assembly 18 extends from the hood 48 and is positioned aft of the 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, Figure 1 The forward direction is also depicted by arrow F, which in turn defines the front and rear of the system. Figure 1 , the rotor assembly 12 is located in front of the turbine 30 in a "puller" configuration, and the exhaust port 52 is located behind the guide vanes 28. As will be appreciated, the vanes 20 of the vane assembly 18 may be configured to straighten the airflow from the rotor assembly 12 (e.g., reduce swirl 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 degree of swirl, which may translate into an increased level of induction efficiency.

[0035] Still refer to Figure 1It may be desirable to incorporate a pitch mechanism into the rotor blades 16, the vanes 20, or both so that the airfoils (e.g., blades 16, vanes 20, etc.) may be rotated independently or in conjunction with one another relative to the pitch axis of rotation. Such pitching may be used to vary thrust and / or swirl effects under various operating conditions, including adjusting the magnitude or direction of thrust generated at the rotor blades 16, or providing a thrust reversal feature that may be useful under certain operating conditions, such as when an aircraft is landing, or to desirably adjust noise generated at least in part by the rotor blades 16, the vanes 20, or from the aerodynamic interaction of the rotor blades 16 relative to the vanes 20. More particularly, for Figure 1 In the embodiment of the present invention, rotor assembly 12 is depicted as having a pitch mechanism 58 for rotating rotor blades 16 about their respective pitch axes 60 , and vane assembly 18 is depicted as having a pitch mechanism 62 for rotating vanes 20 about their respective pitch axes 64 .

[0036] As depicted, rotor assembly 12 is driven by turbine 30, and more particularly, by low speed shaft 45. More particularly, Figure 1 The engine 10 in the embodiment shown in FIG. 5 includes a power gearbox 56, and the rotor assembly 12 is driven by the low-speed 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 shaft 45 relative to the low-speed turbine 42, so that the rotor assembly 12 can rotate at a slower rotational speed than the low-speed shaft 45. In this way, the rotating rotor blades 16 of the rotor assembly 12 can rotate about the axis 14 and generate thrust to propel the engine 10 in a forward direction F, and therefore propel the aircraft associated therewith.

[0037] Still refer to Figure 1 , the exemplary engine 10 includes an accessory gearbox 66 and an electric motor 68, wherein the turbine 30 drives the accessory gearbox 66 and the electric motor 68. For example, in certain exemplary embodiments, the accessory gearbox 66 may be coupled to the low-speed shaft 45 (e.g., the low-speed shaft 46) through a suitable gear train, and the electric motor 68 may be coupled to the accessory gearbox 66. However, in other exemplary embodiments, the electric motor 68 may be coupled to the low-speed shaft 45 of the turbine 30 independently of the accessory gearbox 66, and the accessory gearbox 66 may be coupled to the low-speed shaft 45 or the high-speed shaft 35.

[0038] also, Figure 1 The exemplary turbine 30 depicted in FIG. 6 includes an inter-shaft clutch 72. The inter-shaft clutch 72 is positioned between the high-speed shaft 35 and the low-speed shaft 45 to selectively couple the low-speed shaft 45 to the high-speed shaft 35 during certain operations, such as starting operations. This may allow the electric machine 68 to be used to start or assist in starting the turbine 30.

[0039] However, it will be understood that Figure 1 The exemplary single-rotor un-ducted engine 10 depicted in the drawings is merely an example, and in other exemplary embodiments, the engine 10 may have any other suitable configuration, including, for example, any suitable number of shafts or rotating shafts, turbines, compressors, etc. 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, etc.

[0040] Now refer to Figure 2 , depicts a schematic diagram of a gas turbine engine 10 according to an exemplary embodiment of the present disclosure. Figure 2 The exemplary gas turbine engine 10 may be configured as described above with respect to Figure 1 The exemplary engine 10 described is constructed in a similar manner. In particular, for the illustrated embodiment, the engine 10 includes an electric machine 68 mechanically coupled to the low-speed shaft 45 of the turbine 30 of the engine 10, and more particularly includes an accessory gearbox 66 mechanically coupled to the low-speed shaft 45 of the engine 10, wherein the electric machine 68 is coupled to the low-speed shaft 45 through the accessory gearbox 66. More particularly, the low-speed shaft 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 shaft 45.

[0041] In this manner, the accessory gearbox 66 can transfer rotational power from the low speed shaft 45 of the engine 10 to, for example, one or more accessory systems 70 of the engine 10 or an aircraft incorporating the engine 10, which are mechanically coupled to the accessory gearbox 66 and the motor 68 (which is rotatable 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 shaft 45 across the power gearbox 56.

[0042] As will be appreciated, the various electrical and other accessory systems 70 of the gas turbine engine 10 are typically powered off of an accessory gearbox driven by the core 32 of the engine 10 (or more particularly the high speed / high pressure systems of the engine 10). With such a configuration, the engine core 32 is generally oversized to allow these accessory systems to operate throughout the flight envelope. However, it is worth noting that such a configuration may reduce the responsiveness of the engine 10 by virtue of the additional loads and inertia on the core 32 of the engine 10. It will be appreciated that by coupling the accessory gearbox 66 and the motor 68 to the low speed shaft 45 of the engine 10, rather than the high speed shaft 35, the gas turbine engine 10 may have a more responsive core 32. Furthermore, while this may in turn result in less responsiveness of the low speed systems and rotor assembly 12, the inclusion of the motor 68 may compensate for the responsiveness, as discussed below.

[0043] Still refer to Figure 2 , it will be appreciated that the electric machine 68 is coupled to the low speed shaft 45 of the turbine 30 at a connection point 100 to the low speed shaft 45. More specifically, for the illustrated embodiment, the accessory gearbox 66 is coupled to the low speed shaft 45 at the connection point 100, and the electric machine 68 is coupled to the low speed shaft 45 through the accessory gearbox 66. Further, for the illustrated embodiment, the turbine 30 includes a gear train 102 that is coupled to the low speed shaft 45 at the connection point 100 and extends to the accessory gearbox 66. In this manner, the accessory gearbox 66 can transfer rotational power from the low speed shaft 45 of the engine 10 to one or more accessory systems 70, such as the electric machine 68 that is mechanically coupled to the accessory gearbox 66 and that can rotate with the accessory gearbox 66.

[0044] In addition, if Figure 2 , the exemplary gas turbine engine 10 includes an engine clutch 104 positioned in the torque path of the low speed shaft 45 at a location forward of the connection point 100 of the low speed shaft 45 (where the accessory gearbox 66 is coupled to the low speed shaft 45 via the gear train 102). In particular, for the illustrated embodiment, the engine clutch 104 is positioned in the torque path of the low speed shaft 45 between the connection point 100 and the rotor assembly 12.

[0045] The engine clutch 104 may be moved between an engaged position, in which torque may be transferred across the engine clutch 104 along the low-speed shaft 45 to drive the rotor assembly 12 (or vice versa), and a disengaged position, in which torque may not be transferred across the engine clutch 104 along the low-speed shaft 45 to the rotor assembly 12. In this way, 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.

[0046] In at least some exemplary aspects, the engine clutch 104 can be a two-stage clutch for switching from a disengaged position to an engaged position. Figure 3 and Figure 4 , depicting a sample exemplary embodiment of an engine clutch 104 according to 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 a longitudinal direction L. In certain exemplary embodiments, the longitudinal direction L can be aligned with an axial direction A of the engine 10. Further, in certain exemplary embodiments, the first portion 108 can rotate with the rotor assembly 12, and the second portion 110 can rotate with the low speed shaft 45 at and behind the connection point 100.

[0047] like Figure 3 and Figure 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 the 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, which are correspondingly shaped as the first set of geometric features 114. More specifically, 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 grooves extending along the longitudinal direction L. The plurality of protrusions are configured to be slidably received within the plurality of grooves. In this manner, the first geometric features 114 and the second set of geometric features 118 may be referred to as a spline connection.

[0048] As will be appreciated, when the engine clutch 104 is in the disengaged position ( Figure 3 ), the low speed shaft 45 is free to rotate relative to the rotor assembly 12. In contrast, when the engine clutch 104 is in the engaged position ( Figure 4 ), the low speed 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.

[0049] More specifically, now also refer to Figure 5 , it will be appreciated that the clutch 104 may be further moved to a transition position. In the transition position, the first friction plates 112 and the second friction plates 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 be slowly accelerated before engaging the first and second geometric features 114, 118 to lock the first and second portions 108, 110 of the clutch 104 together.

[0050] Notably, for the depicted embodiment, as will also be appreciated, the second friction plate 116 is configured to slide in the longitudinal direction between the transition position and the engagement position. The second friction plate 116 may be biased in the longitudinal direction toward the first friction plate 112 by, for example, one or more spring assemblies (not shown).

[0051] In addition, after the rotor assembly 12 roughly matches the rotational speed of the low-speed shaft 45, the clutch 104 can be moved from the transition position to the engagement position along the longitudinal direction L so that the second geometric feature 118 engages with the first geometric feature 114 to secure the first portion 108 and the second portion 110 of the engine clutch 104 together.

[0052] 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 without participating in rotating the rotor assembly 12 during, for example, idle and post-landing operations. In this manner, the electric machine 68 may be sized to accept 100% of the rated engine power, such that the gas turbine engine 10 may be operated at rated engine power (i.e., by moving the engine clutch 104 to the disengaged position) without engaging the rotor assembly 12, and the electric machine 68 converts substantially all of such power into electrical energy to be transmitted via the electrical bus 120 (see FIG. Figure 2 ) provided to an aircraft 248 incorporating a gas turbine engine 10, provided to one or more energy storage units within or electrically connected to the bus 230 to assist in starting additional engines, combinations thereof, and the like.

[0053] Subsequently, when it is desired to generate thrust with the rotor assembly 12 , the engine clutch 104 may be moved from the disengaged position to a transition position, thereby slowly bringing the rotor assembly 12 up to speed before subsequently moving the engine clutch 104 to the engaged position to rotationally lock the rotor assembly 12 to the low speed shaft 45 .

[0054] It will also be appreciated that with the above configuration, once the engine clutch 104 is moved to the engaged position, the motor 68 can be used to more quickly accelerate the rotor assembly 12 during pre-takeoff operations. More specifically, electrical power can be provided to the motor 68 and converted into rotational power that is provided to the low speed shaft 45 through the accessory gearbox 66 to directly assist in accelerating the rotor assembly 12. Although the accessory gearbox 66 is mounted to the low speed shaft 45, this ensures that the low speed shaft 45 has the desired responsiveness.

[0055] 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. Figure 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 particularly, for the illustrated embodiment, the inter-shaft clutch 122 is positioned between the low speed shaft 45 and the high speed shaft 35 at a location aligned with or positioned forward of the combustion section 40 in the axial direction A of the gas turbine engine 10 and aligned with or rearward of the high speed compressor 34 in the axial direction A. Such a configuration may allow for torque balancing on the inter-shaft clutch 122 when the inter-shaft clutch 122 couples the low speed shaft 45 to the high speed shaft 35.

[0056] However, it will be appreciated that in other embodiments, the inter-shaft clutch 122 may be positioned at any other suitable location. Figure 2 As depicted in phantom in FIG. 4 (e.g., element 122'), the inter-shaft clutch 122 may be positioned at any suitable location forward of the combustion section 40, such as aligned with or forward of the high-speed compressor 34 in the axial direction A, such as forward of the high-speed compressor 34 in the 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.

[0057] During operation, the inter-shaft clutch 122 can ensure that the low speed / low pressure system (low speed shaft 45) does not rotate faster than the high speed / high pressure system (high speed shaft 35) in a first circumferential direction C1 (i.e., the circumferential directions of the high speed shaft 35 and the low speed shaft 45 are configured to rotate during normal flight operations; see also the discussion below). Figure 6 ). The inter-shaft clutch 122 may be a one-way clutch configured to passively engage and disengage depending on one or more operating conditions, such as relative rotational speeds and torques on the high-speed shaft 35 and the low-speed shaft 45. For example, in certain exemplary embodiments, the motor 68 may be operated as a starting motor for the gas turbine engine 10. In such exemplary embodiments, during a starting operation, the motor 68 may receive electrical power via the electrical power bus 120 and convert such power into mechanical power that is transmitted to the low-speed shaft 45 via the accessory gearbox 66 and the gear train 102, causing the low-speed shaft 45 to rotate in a first circumferential direction C1. The inter-shaft clutch 122 may be engaged by such rotation, causing the low-speed shaft 45 to cross the shaft clutch 122 to correspondingly rotate the high-speed shaft 35 in the first circumferential direction C1. Such operation may continue until the gas turbine engine 10 reaches a ignition point. As used herein, the term "ignition point" refers to a rotational speed at which the high-speed shaft 45 and / or the low-speed shaft 35 are sufficient to provide a certain amount of airflow to the combustion section 40 to allow the combustion section 40 to be ignited and to continue to burn. At this time, the combustion section 40 may generate combustion gases to drive the high-speed shaft 35, and the high-speed shaft 35 may have additional force (from the combustion gases) that causes the high-speed shaft 35 to rotate faster than the low-speed shaft 45 in the first circumferential direction C1. The inter-shaft clutch 122 may be passively / automatically disengaged at this time, thereby allowing the high-speed shaft 35 to rotate faster than the low-speed shaft 45 in the first circumferential direction C1.

[0058] As mentioned, the inter-shaft clutch 122 can be configured as a one-way clutch. Figure 6It will be appreciated that in at least some exemplary aspects, the inter-shaft clutch 122 can be configured as a sprag clutch. Figure 6 A schematic axial view (i.e., a view along the axial direction A) of an exemplary inter-shaft clutch 122 is provided. 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 integrally formed with the low-speed shaft 45, and the outer race 128 is coupled to the high-speed shaft 35. When the inner race 126 rotates counterclockwise relative to the outer race 128 (at least for the depicted view of the embodiment), or when the outer race 128 rotates faster than the inner race 126, the plurality of sprags 124 provide substantially no resistance to such movement. In contrast, when the inner race 126 attempts to rotate clockwise relative to the outer race 128 (a first circumferential direction C1), the plurality of sprags 124 rotate about their respective rotational axes 125 and lock the inner race 126 to the outer race 128, such that relative rotation of the inner race 126 relative to the outer race 128 in the clockwise direction is not permitted.

[0059] More particularly, it will be appreciated that for Figure 6 , the clockwise direction is the first circumferential direction C1. In this way, it will be understood that the low-speed shaft 45 and the high-speed shaft 35 are configured to rotate in the first circumferential direction C1 during operation of the gas turbine engine 10. It will also be understood 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 rotation speed of the low-speed shaft 45 (inner race 126) from exceeding the rotation speed of the high-speed shaft 35 (outer race 128) in the first circumferential direction C1. In this way, the low-speed shaft 45 can be coupled to the high-speed shaft 35 during the starting operation, so that the motor 68 can start the rotation of the high-speed shaft 35 although it is coupled to the low-speed shaft 45.

[0060] In addition, 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 rotation speed of the high-speed shaft 35 (outer race 128) to exceed the rotation speed of the low-speed shaft 45 (inner race 126) in the first circumferential direction C1. In this way, once the engine is started, the inter-shaft clutch 122 can allow the high-speed shaft 35 to rotate faster than the low-speed shaft 45 without actively actuating the inter-shaft clutch 122.

[0061] However, it should be understood 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, etc.

[0062] In this manner, while coupled to the low-speed shaft 45 , the electric machine 68 may assist in starting the engine 10 by directly rotating the high-speed shaft 35 .

[0063] 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 apart from the low speed shaft 45, it will be appreciated that in other exemplary embodiments, the motor 68 may instead be mounted around the low speed shaft 45, sharing a common axis of rotation with the low speed shaft 45. With such a configuration, the rotor of the motor 68 may be mounted around the low speed axis of the low speed shaft 45.

[0064] Other configurations are also contemplated.

[0065] Now refer to Figure 7 , a flow chart of a method 200 for 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. Thus, the gas turbine engine may include a low-speed shaft, a high-speed shaft, and an electric machine coupled to the low-speed shaft.

[0066] for Figure 7 In an exemplary aspect of the present invention, method 200 includes: at (202) rotating a low-speed spool at least partially with an electric motor during a start-up operation of a gas turbine engine. More particularly, for Figure 7 In an exemplary aspect of the invention, at least partially rotating the low-speed shaft with the electric motor during a startup operation of the gas turbine engine at (202) includes rotating the high-speed shaft with the low-speed shaft across an inter-shaft clutch positioned between the low-speed shaft and the high-speed shaft during a startup operation of the gas turbine engine at (204). As discussed above, the inter-shaft clutch may be a one-way clutch.

[0067] In addition, for Figure 7 An exemplary aspect of at least partially rotating the low-speed shaft with an electric motor during a starting operation of a gas turbine engine at (202) more particularly includes: rotating only the low-speed shaft with an electric motor during a starting operation of the gas turbine engine at (206), rotating the low-speed shaft with an electric motor across an accessory gearbox at (208), and rotating the low-speed shaft and the high-speed shaft with an electric motor to a start-up speed at (210).

[0068] In addition, the depicted exemplary method 200 also includes, at (212), igniting the combustion section of the gas turbine engine after rotating the low-speed shaft and the high-speed shaft to an ignition speed using an electric motor, and, at (214), rotating the high-speed shaft faster than the low-speed shaft, wherein rotating the high-speed shaft faster than the low-speed shaft includes automatically disengaging a clutch between the shafts.

[0069] Further aspects of the invention are provided by the subject matter of the following clauses:

[0070] A gas turbine engine includes: a turbine including a low-speed shaft and a high-speed shaft; a rotor assembly connected to the low-speed shaft; an electric 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 shaft and the high-speed shaft for selectively coupling the low-speed shaft to the high-speed shaft.

[0071] A gas turbine engine as claimed in one or more of these clauses, wherein the inter-shaft clutch is a one-way clutch.

[0072] A gas turbine engine as claimed in one or more of these clauses, wherein the inter-shaft clutch is a sprag clutch.

[0073] A gas turbine engine of one or more of these clauses, wherein the low-speed shaft and the high-speed shaft are configured to rotate in a first circumferential direction during operation of the gas turbine engine, wherein the inter-shaft clutch is configured to passively disengage and disconnect the low-speed shaft from the high-speed shaft to allow the rotational speed of the high-speed shaft to exceed the rotational speed of the low-speed shaft in the first circumferential direction.

[0074] A gas turbine engine of one or more of these clauses, wherein the low-speed shaft and the high-speed shaft are configured to rotate in a first circumferential direction during operation of the gas turbine engine, wherein the inter-shaft clutch is configured to passively engage and couple the low-speed shaft to the high-speed shaft to prevent the rotational speed of the low-speed shaft from exceeding the rotational speed of the high-speed shaft in the first circumferential direction.

[0075] The gas turbine engine of one or more of these clauses, wherein the turbine further comprises a combustion section, and wherein the inter-shaft clutch is aligned with the combustion section or positioned in front of the combustion section in the axial direction of the gas turbine engine.

[0076] The gas turbine engine of one or more of these clauses, wherein the high-speed shaft at least partially comprises a high-speed compressor, and wherein the inter-shaft clutch is aligned with or positioned in front of the high-speed compressor in an axial direction of the gas turbine engine.

[0077] A 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.

[0078] The gas turbine engine of one or more of these clauses, further comprising: an accessory gearbox coupled to the low-speed shaft, and wherein the electric machine is coupled to the low-speed shaft via the accessory gearbox.

[0079] 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 includes a single stage of unducted rotor blades.

[0080] The gas turbine engine of one or more of these clauses, further comprising: an unducted guide vane stage positioned downstream of the single stage of unducted rotor blades.

[0081] A method for operating a gas turbine engine, the gas turbine engine comprising a low-speed shaft, a high-speed shaft and an electric motor connected to the low-speed shaft, the method comprising: at least partially rotating the low-speed shaft with the electric motor during a starting operation of the gas turbine engine; wherein at least partially rotating the low-speed shaft with the electric motor during a starting operation of the gas turbine engine comprises rotating the high-speed shaft with the low-speed shaft across an inter-shaft clutch positioned between the low-speed shaft and the high-speed shaft during a starting operation of the gas turbine engine.

[0082] The method of one or more of these clauses, wherein at least partially rotating the low speed shaft with the electric machine during a startup operation of the gas turbine engine further comprises rotating the low speed shaft and the high speed shaft with the electric machine to a light-off speed.

[0083] The method of one or more of these clauses further comprises: igniting a combustion section of the gas turbine engine after rotating the low-speed shaft and the high-speed shaft to a light-off speed with the electric motor.

[0084] The method of one or more of these clauses further comprises: rotating the high-speed shaft faster than the low-speed shaft, wherein rotating the high-speed shaft faster than the low-speed shaft comprises automatically disengaging a clutch between the shafts.

[0085] The method of one or more of these clauses, wherein the inter-shaft clutch is a one-way clutch.

[0086] 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 in front of the combustion section in an axial direction of the gas turbine engine.

[0087] The method of one or more of these clauses, wherein rotating the low-speed spool at least partially with the electric machine during a startup operation of the gas turbine engine comprises rotating the low-speed spool only with the electric machine during a startup operation of the gas turbine engine.

[0088] The method of one or more of these clauses, wherein at least partially rotating the low speed shaft with the electric machine during a starting operation of the gas turbine engine includes rotating the low speed shaft with the electric machine across an accessory gearbox.

[0089] 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 includes a single stage of unducted rotor blades.

Claims

1. A gas turbine engine defining an axial direction, the gas turbine engine comprising: a turbine, the turbine comprising a combustion section, a low-speed rotor shaft and a high-speed rotor shaft; a rotor assembly coupled to the low speed shaft; an electric 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 shaft and the high-speed shaft for selectively coupling the low-speed shaft to the high-speed shaft; Wherein, the high-speed rotating shaft at least partially includes a high-speed compressor, and Wherein, at least a portion of the inter-shaft clutch is positioned in an axial direction aligned with the combustion section or in front of the combustion section and in an axial direction aligned with the high-speed compressor or positioned behind the high-pressure compressor.

2. The gas turbine engine according to claim 1, characterized in that The inter-rotating shaft clutch is a one-way clutch.

3. The gas turbine engine according to claim 1, characterized in that The inter-rotating shaft clutch is a sprag clutch.

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

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

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

7. The gas turbine engine according to claim 1, characterized in that The electric machine is configured to rotate the high-speed shaft to a light-off speed via the inter-shaft clutch and the low-speed shaft during a starting operation of the gas turbine engine.

8. The gas turbine engine according to claim 1, characterized in that The gas turbine engine further comprises: An accessory gearbox is coupled to the low speed shaft, and wherein the electric motor is coupled to the low speed shaft through the accessory gearbox.

9. The gas turbine engine according to claim 1, characterized in that The gas turbine engine is configured as a single unducted rotor engine, and wherein the rotor assembly includes a single stage of unducted rotor blades.

10. The gas turbine engine according to claim 9, characterized in that The gas turbine engine further comprises: An unducted guide vane stage is positioned downstream of the single stage of unducted rotor blades.

11. A method of operating a gas turbine engine defining an axial direction and comprising a combustion section, a low speed shaft, a high speed shaft, and an electric machine coupled to the low speed shaft, the method comprising: rotating the low speed shaft at least partially with the electric machine during a starting operation of the gas turbine engine; wherein at least partially rotating the low-speed shaft with the electric motor during a starting operation of the gas turbine engine includes rotating the high-speed shaft with the low-speed shaft across an inter-shaft clutch positioned between the low-speed shaft and the high-speed shaft during a starting operation of the gas turbine engine; Wherein, the high-speed rotating shaft at least partially includes a high-speed compressor, and Wherein, at least a portion of the inter-shaft clutch is positioned in an axial direction aligned with the combustion section or in front of the combustion section and in an axial direction aligned with the high-speed compressor or positioned behind the high-pressure compressor.

12. The method according to claim 11, characterized in that At least partially rotating the low-speed spool with the electric machine during a startup operation of the gas turbine engine further includes rotating the low-speed spool and the high-speed spool with the electric machine to a light-off speed.

13. The method according to claim 12, characterized in that The method further comprises: After the low-speed shaft and the high-speed shaft are rotated by the electric motor to reach the light-off speed, the combustion section of the gas turbine engine is ignited.

14. The method according to claim 13, characterized in that The method further comprises: The high-speed shaft is caused to rotate faster than the low-speed shaft, wherein causing the high-speed shaft to rotate faster than the low-speed shaft includes automatically disengaging the inter-shaft clutch.

15. The method according to claim 11, characterized in that The inter-rotating shaft clutch is a one-way clutch.

16. The method according to claim 11, characterized in that The gas turbine engine further includes a combustion section, and wherein the inter-shaft clutch is aligned with or positioned in front of the combustion section in an axial direction of the gas turbine engine.

17. The method according to claim 11, characterized in that At least partially rotating the low-speed spool with the electric machine during a startup operation of the gas turbine engine includes rotating the low-speed spool with only the electric machine during a startup operation of the gas turbine engine.

18. The method according to claim 11, characterized in that At least partially rotating the low speed shaft with the electric machine during a starting operation of the gas turbine engine includes rotating the low speed shaft with the electric machine across an accessory gearbox.

19. The method according to claim 11, characterized in that The gas turbine engine is configured as a single unducted rotor engine, and wherein a rotor assembly of the gas turbine engine includes a single stage of unducted rotor blades.

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