SYSTEM AND METHOD FOR USE WITH GAS TURBINE ENGINE

Abstract

The present disclosure relates to a system for use with a gas turbine engine having a gas turbine shaft and an accessory gearbox drivably coupled to the gas turbine shaft. The system includes an accessory of the accessory gearbox. The system further includes an output shaft drivably coupled between the accessory gearbox and the accessory. The system further includes a sensor configured to generate a sensor signal. The system further includes a controller configured to determine a speed of the output shaft based on the sensor signal. The controller is further configured to determine a speed of the gas turbine shaft based at least on the speed of the output shaft.

Claims

1. A system for use with a gas turbine engine having a gas turbine shaft and an accessory gearbox drivably coupled to the gas turbine shaft, the system comprising: an accessory of the accessory gearbox; an output shaft drivably coupled between the accessory gearbox and the accessory; a sensor configured to generate a sensor signal indicative of a position of the output shaft; and a controller communicably coupled to the sensor, wherein the controller is configured to: determine a speed of the output shaft based on the sensor signal; and determine a speed of the gas turbine shaft based at least on the speed of the output shaft.

2. The system of claim 1, further comprising: a prime mover; a drive shaft drivably coupled to the prime mover; and a clutch configured to selectively drivably engage the drive shaft with the output shaft.

3. The system of claim 2, wherein the controller is further configured to: compare the speed of the gas turbine shaft with a predetermined threshold speed; and control the clutch and/or the prime mover to drivably engage the drive shaft with the output shaft upon determining that the speed of the gas turbine shaft is less than the predetermined threshold speed.

4. The system of claim 3, wherein the controller is further configured to control the clutch and/or the prime mover to keep the drive shaft disengaged from the output shaft upon determining that the speed of the gas turbine shaft is greater than or equal to the predetermined threshold speed.

5. The system of claim 3, wherein the controller is further configured to keep the prime mover in an inactive state upon determining that the speed of the gas turbine shaft is greater than or equal to the predetermined threshold speed.

6. The system of claim 3, wherein the clutch is an active clutch communicably coupled to the controller and configured to be controlled by the controller, and wherein the controller is further configured to control the clutch and activate the prime mover to drivably engage the drive shaft with the output shaft upon determining that the speed of the gas turbine shaft is less than the predetermined threshold speed.

7. The system of claim 6, wherein the controller is further configured to control the clutch to keep the drive shaft disengaged from the output shaft upon determining that the speed of the gas turbine shaft is greater than or equal to the predetermined threshold speed.

8. The system of claim 3, wherein the clutch is an overrunning clutch configured to drivably engage the drive shaft with the output shaft only if a speed of the drive shaft is greater than the speed of the output shaft, and wherein the controller is further configured to activate the prime mover to drivably engage the drive shaft with the output shaft upon determining that the speed of the gas turbine shaft is less than the predetermined threshold speed.

9. The system of claim 3, further comprising an electronic module communicably coupled to the prime mover and the controller, wherein the electronic module is configured to control the prime mover in response to a control signal received from the controller, such that the controller controls the prime mover via the electronic module.

10. The system of claim 3, wherein the predetermined threshold speed is about ten revolutions per minute.

11. The system of claim 2, wherein the accessory is a barring unit, and the prime mover is a barring motor disposed within the barring unit.

12. The system of claim 2, wherein the sensor is disposed on the output shaft between the clutch and the accessory gearbox.

13. The system of claim 1, wherein the sensor is disposed on the output shaft.

14. The system of claim 1, further comprising a converter communicably coupled to the sensor and the controller, wherein the converter is configured to receive the sensor signal from the sensor and convert the sensor signal into an output signal, and wherein the controller is further configured to receive the output signal and determine the speed of the output shaft based on the output signal.

15. The system of claim 1, wherein the sensor is a resolver or an encoder or a rotary variable differential transformer or a hall sensor array.

16. The system of claim 1, wherein controller is configured to determine the speed of the gas turbine shaft based further on a gear ratio of the accessory gearbox.

17. A gas turbine engine comprising: a gas turbine shaft; an accessory gearbox drivably coupled to the gas turbine shaft; and the system of claim 1, wherein the output shaft of the system is drivably coupled between the accessory gearbox and the accessory.

18. A method for use with a gas turbine engine having a gas turbine shaft and an accessory gearbox drivably coupled to the gas turbine shaft, the method comprising: determining a position of an output shaft drivably coupled between the accessory gearbox and an accessory of the accessory gearbox; determining a speed of the output shaft based on the position of the output shaft; and determining a speed of the gas turbine shaft based at least on the speed of the output shaft.

19. The method of claim 18, further comprising: providing a prime mover and a drive shaft drivably coupled to the prime mover; and providing a clutch configured to selectively drivably engage the drive shaft with the output shaft.

20. An apparatus for use with a gas turbine engine having a gas turbine shaft and an accessory gearbox drivably coupled to the gas turbine shaft, the apparatus comprising a controller configured to: determine a position of an output shaft drivably coupled between the accessory gearbox and an accessory of the accessory gearbox; determine a speed of the output shaft based on the position of the output shaft; and determine a speed of the gas turbine shaft based at least on the speed of the output shaft.

Description

DESCRIPTION OF THE DRAWINGS

[0067] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0068] FIG. 1 is a sectional side view of a gas turbine engine;

[0069] FIG. 2 is a close up sectional side view of an upstream portion of a gas turbine engine;

[0070] FIG. 3 is a partially cut-away view of a gearbox for a gas turbine engine;

[0071] FIG. 4 is a schematic block diagram illustrating an accessory gearbox and various accessories of the accessory gearbox of the gas turbine engine of FIG. 1;

[0072] FIG. 5 is a schematic block diagram of a system for use with the gas turbine engine of FIG. 1, according to an embodiment of the present disclosure;

[0073] FIG. 6A is a schematic block diagram of a system for use with the gas turbine engine of FIG. 1, according to another embodiment of the present disclosure;

[0074] FIG. 6B is a schematic block diagram of the system of FIG. 6A in an engaged configuration;

[0075] FIG. 7 is a flowchart for a process implemented by the system of FIGS. 6A and 6B, according to an embodiment of the present disclosure;

[0076] FIG. 8A is a schematic block diagram of a system for use with the gas turbine engine of FIG. 1, according to another embodiment of the present disclosure;

[0077] FIG. 8B is a schematic block diagram of the system of FIG. 8A in an engaged configuration;

[0078] FIG. 9 is a flowchart illustrating a process implemented by the system of FIGS. 8A and 8B, according to an embodiment of the present disclosure;

[0079] FIG. 10 is a graph illustrating a time variation of a speed of a gas turbine shaft of the gas turbine engine of FIG. 1, according to an embodiment of the present disclosure; and

[0080] FIG. 11 is a flowchart illustrating a method for use with the gas turbine engine of FIG. 1, according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

[0081] Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art.

[0082] As used herein, the term “configured to” and like is at least as restrictive as the term “adapted to” and requires actual design intention to perform the specified function rather than mere physical capability of performing such a function.

[0083] As used herein, the term “communicably coupled to” refers to direct coupling between components and/or indirect coupling between components via one or more intervening components. Such components and intervening components may comprise, but are not limited to, junctions, communication paths, wireless networks, components, circuit elements, circuits, functional blocks, and/or devices. As an example of indirect coupling, a signal conveyed from a first component to a second component may be modified by one or more intervening components by modifying the form, nature, or format of information in a signal, while one or more elements of the information in the signal are nevertheless conveyed in a manner than can be recognized by the second component.

[0084] As used herein, the term “signal,” includes, but is not limited to, one or more electrical signals, optical signals, electromagnetic signals, analog and/or digital signals, one or more computer instructions, a bit and/or bit stream, or the like.

[0085] FIG. 1 illustrates a gas turbine engine 10 having a principal rotational axis 9. The gas turbine engine 10 comprises an air intake 12 and a propulsive fan 23 that generates two airflows: a core airflow A and a bypass airflow B. The gas turbine engine 10 comprises a core 11 that receives the core airflow A. The core 11 comprises, in axial flow series, a low pressure compressor 14, a high pressure compressor 15, combustor 16, a high pressure turbine 17, a low pressure turbine 19 and a core exhaust nozzle 20. A nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass exhaust nozzle 18. The bypass airflow B flows through the bypass duct 22. The fan 23 is attached to and driven by the low pressure turbine 19 via an input shaft 26 and an epicyclic gearbox 30. The gas turbine engine 10 further includes a gas turbine shaft 50 and an accessory gearbox 52 drivably coupled to the gas turbine shaft 50. During normal operation of the gas turbine engine 10, the accessory gearbox 52 is powered or driven by the input shaft 26 via the gas turbine shaft 50 and a gear arrangement comprising gears (not shown) and shafts. The accessory gearbox 52 will be discussed later in the description.

[0086] In use, the core airflow A is accelerated and compressed by the low pressure compressor 14 and directed into the high pressure compressor 15 where further compression takes place. The compressed air exhausted from the high pressure compressor 15 is directed into the combustor 16 where it is mixed with fuel and the mixture is combusted. The resultant hot combustion products then expand through, and thereby drive, the high pressure and low pressure turbines 17, 19 before being exhausted through the core exhaust nozzle 20 to provide some propulsive thrust. The high pressure turbine 17 drives the high pressure compressor 15 by a suitable interconnecting shaft 27. In some cases, the accessory gearbox 52 and the gas turbine shaft 50 may be driven by the interconnecting shaft 27. The fan 23 generally provides the majority of the propulsive thrust. The epicyclic gearbox 30 is a reduction gearbox.

[0087] An exemplary arrangement for a geared fan gas turbine engine 10 is shown in FIG. 2. The low pressure turbine 19 (see FIG. 1) drives the input shaft 26, which is coupled to a sun wheel, or sun gear, 28 of the epicyclic gearbox 30. Radially outwardly of the sun gear 28 and intermeshing therewith is a plurality of planet gears 32 that are coupled together by a planet carrier 34. The planet carrier 34 constrains the planet gears 32 to process around the sun gear 28 in synchronicity whilst enabling each planet gear 32 to rotate about its own axis. The planet carrier 34 is coupled via linkages 36 to the fan 23 in order to drive its rotation about the engine axis 9. Radially outwardly of the planet gears 32 and intermeshing therewith is an annulus or ring gear 38 that is coupled, via linkages 40, to a stationary supporting structure 24.

[0088] Note that the terms “low pressure turbine” and “low pressure compressor” as used herein may be taken to mean the lowest pressure turbine stages and lowest pressure compressor stages (i.e. not including the fan 23) respectively and/or the turbine and compressor stages that are connected together by the input shaft 26 with the lowest rotational speed in the engine (i.e. not including the gearbox output shaft that drives the fan 23). In some literature, the “low pressure turbine” and “low pressure compressor” referred to herein may alternatively be known as the “intermediate pressure turbine” and “intermediate pressure compressor”. Where such alternative nomenclature is used, the fan 23 may be referred to as a first, or lowest pressure, compression stage.

[0089] The epicyclic gearbox 30 is shown by way of example in greater detail in FIG. 3. Each of the sun gear 28, planet gears 32 and ring gear 38 comprise teeth about their periphery to intermesh with the other gears. However, for clarity only exemplary portions of the teeth are illustrated in FIG. 3. There are four planet gears 32 illustrated, although it will be apparent to the skilled reader that more or fewer planet gears 32 may be provided within the scope of the disclosure. Practical applications of a planetary epicyclic gearbox 30 generally comprise at least three planet gears 32.

[0090] The epicyclic gearbox 30 illustrated by way of example in FIGS. 2 and 3 is of the planetary type, in that the planet carrier 34 is coupled to an output shaft via linkages 36, with the ring gear 38 fixed. However, any other suitable type of epicyclic gearbox 30 may be used. By way of further example, the epicyclic gearbox 30 may be a star arrangement, in which the planet carrier 34 is held fixed, with the ring (or annulus) gear 38 allowed to rotate. In such an arrangement the fan 23 is driven by the ring gear 38. By way of further alternative example, the gearbox 30 may be a differential gearbox in which the ring gear 38 and the planet carrier 34 are both allowed to rotate.

[0091] It will be appreciated that the arrangement shown in FIGS. 2 and 3 is by way of example only, and various alternatives are within the scope of the present disclosure. Purely by way of example, any suitable arrangement may be used for locating the gearbox 30 in the gas turbine engine 10 and/or for connecting the gearbox 30 to the gas turbine engine 10. By way of further example, the connections (such as the linkages 36, 40 in the FIG. 2 example) between the gearbox 30 and other parts of the gas turbine engine 10 (such as the input shaft 26, the output shaft and the fixed structure 24) may have any desired degree of stiffness or flexibility. By way of further example, any suitable arrangement of the bearings between rotating and stationary parts of the engine (for example between the input and output shafts from the gearbox and the fixed structures, such as the gearbox casing) may be used, and the disclosure is not limited to the exemplary arrangement of FIG. 2. For example, where the gearbox 30 has a star arrangement (described above), the skilled person would readily understand that the arrangement of output and support linkages and bearing locations would typically be different to that shown by way of example in FIG. 2.

[0092] Accordingly, the present disclosure extends to a gas turbine engine having any arrangement of gearbox styles (for example star or planetary), support structures, input and output shaft arrangement, and bearing locations.

[0093] Optionally, the gearbox may drive additional and/or alternative components (e.g., the intermediate pressure compressor and/or a booster compressor).

[0094] Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of interconnecting shafts. By way of further example, the gas turbine engine shown in FIG. 1 has a split flow nozzle 18, 20 meaning that the flow through the bypass duct 22 has its own nozzle 18 that is separate to and radially outside the core exhaust nozzle 20. However, this is not limiting, and any aspect of the present disclosure may also apply to engines in which the flow through the bypass duct 22 and the flow through the core 11 are mixed, or combined, before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) may have a fixed or variable area. Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example. In some arrangements, the gas turbine engine 10 may not comprise a gearbox 30. In some other arrangements, the gas turbine engine 10 may comprise a direct drive.

[0095] The geometry of the gas turbine engine 10, and components thereof, is defined by a conventional axis system, comprising an axial direction (which is aligned with the rotational axis 9), a radial direction (in the bottom-to-top direction in FIG. 1), and a circumferential direction (perpendicular to the page in the FIG. 1 view). The axial, radial and circumferential directions are mutually perpendicular.

[0096] In addition, the present disclosure is equally applicable to aero gas turbine engines, marine gas turbine engines and land-based gas turbine engines.

[0097] FIG. 4 is a schematic block diagram illustrating the accessory gearbox 52 and various accessories. During operation of the gas turbine engine 10, the accessory gearbox 52 may drive various accessories, such as a fuel pump 54, an oil pump 56, an electric generator 58, and an oil breather 60. In some cases, the accessory gearbox 52 may also drive other accessories as well, such as a fuel flow governor, a starter motor, a tachometer, and so on. The accessory gear box 52 may also be selectively drivably coupled with a barring unit 62. The barring unit 62 may also be considered as an accessory of the accessory gearbox 52.

[0098] FIG. 5 is a schematic block diagram of a system 70 for use with the gas turbine engine 10 (shown in FIG. 1), according to an embodiment of the present disclosure. In some embodiments, the gas turbine engine 10 includes the system 70. In other words, the system 70 may be a part of the gas turbine engine 10. The system 70 includes an accessory 64 of the accessory gearbox 52. The accessory 64 may include any of the accessories illustrated in FIG. 4, such as the barring unit 62, the fuel pump 54, the oil pump 56, the electric generator 58, and the oil breather 60.

[0099] The system 70 further includes an output shaft 106 drivably coupled between the accessory gearbox 52 and the accessory 64 of the accessory gearbox 52. During the normal operation of the gas turbine engine 10 (shown in FIG. 1), the output shaft 106 is driven by the accessory gearbox 52. The system 70 further includes a sensor 110 configured to generate a sensor signal 112 indicative of a position of the output shaft 106. The position of the output shaft 106 may correspond to a rotational position of the output shaft 106. The sensor signal 112 is an electrical signal, either analog or digital. In the illustrated embodiment of FIG. 5, the sensor 110 is disposed on the output shaft 106.

[0100] In some embodiments, the sensor 110 is a resolver or an encoder or a rotary variable differential transformer (RVDT) or a hall sensor array. When used as the resolver or encoder, the sensor 110 is configured to determine the position of the output shaft 106 by measuring degrees of rotation of the output shaft 106. Generally, a resolver includes a rotary angular position sensor, such as a rotating electrical transformer having stator windings and optional rotor windings. A magnitude of the energy through the stator windings and rotor windings varies sinusoidally as the output shaft 106 rotates. Based on relative angular positions of the stator windings and rotor windings, the resolver is configured to output the sensor signal 112 indicative of the position of the output shaft 106.

[0101] The encoder provides an output corresponding to the rotation of the output shaft 106, either in terms of voltage pulses or absolute angular position. In some applications, the encoder may consist of two plates, with one plate fixed and another plate with unique coding attached to the output shaft 106. As the output shaft 106 rotates, these plates rotate relative to each other without making contact. An electric field between these plates is influenced in response to the relative rotation and that variation represents the angular position of the output shaft 106 in the form of the sensor signal 112.

[0102] When used as the RVDT, the sensor 110 is used for determining the angular position of the output shaft 106 by using an electromechanical transducer that outputs an alternating current voltage proportional to the angular displacement of the output shaft 106. While using the sensor 110 as the hall sensor array, the sensor 110 measures a changing voltage when the output shaft 106 is placed in a magnetic field. In other words, once a Hall sensor array detects that it is now in a magnetic field, it can be used to sense the position of objects.

[0103] FIG. 5 further illustrates an apparatus 115 for use with the gas turbine engine 10. The system 70 as well as the apparatus 115 further includes a controller 114 communicably coupled to the sensor 110. In an application, the controller 114 may be a control circuit, a computer, a microprocessor, a microcomputer, a central processing unit, or any suitable device or apparatus. The controller 114 may comprise one or more of a digital processor, an analog processor, a digital circuit designed to process information, an analog circuit designed to process information, a state machine, and/or other mechanisms for electronically processing information. The controller 114 further includes a memory 116. The memory 116 may be configured to store a set of instructions executed by the controller 114.

[0104] The system 70 may further includes a converter 118 communicably coupled to the sensor 110 and the controller 114. The converter 118 is configured to receive the sensor signal 112 from the sensor 110 and convert the sensor signal 112 into an output signal 119. In some embodiments, the converter 118 is an analog to digital converter, the sensor signal 112 is an analog signal, and the output signal 119 is a digital signal. The output signal 119 is indicative of the position of the output shaft 106. The controller 114 is further configured to receive the output signal 119 and determine a speed S1 of the output shaft 106 based on the output signal 119. As the output signal 119 is based on the sensor signal 112, it can be stated that the controller 114 is configured to determine the speed S1 of the output shaft 106 based on the sensor signal 112. In some embodiments, the converter 118 may be a part of the controller 114. The speed S1 of the output shaft 106 is stored in the memory 116. The speed S1 may correspond to a rotational speed of the output shaft 106.

[0105] The controller 114 is further configured to determine a speed S2 of the gas turbine shaft 50 based at least on the speed S1 of the output shaft 106. The speed S2 may correspond to a rotational speed of the gas turbine shaft 50. Specifically, the controller 114 is configured to determine the speed S2 of the gas turbine shaft 50 based further on a gear ratio GR of the accessory gearbox 52. The gear ratio GR of the accessory gearbox 52 is a predetermined ratio of the speed S1 of the output shaft 106 to the speed S2 of the gas turbine shaft 50. Therefore, the controller 114 is configured to determine the speed S2 of the gas turbine shaft 50 based on the speed S1 of the output shaft 106 and the gear ratio GR (S1/S2) of the accessory gearbox. The speed S2 of the gas turbine shaft 50 is stored in the memory 116.

[0106] FIG. 6A is a schematic block diagram of a system 100 for use with the gas turbine engine 10 (shown in FIG. 1), according to an embodiment of the present disclosure. In some embodiments, the gas turbine engine 10 includes the system 100. In other words, the system 100 may be a part of the gas turbine engine 10. The system 100 is substantially similar to the system 70 illustrated in FIG. 5, with common components being referred to by the same reference numerals. However, in the system 100, the accessory 64 is the barring unit 62.

[0107] The system 100 further includes a prime mover 102. In the illustrated embodiment of FIG. 6A, the prime mover 102 is a barring motor disposed within the barring unit 62. The barring motor is usually an electric motor, which can be selectively connected to and disconnected from the accessory gearbox 52 and/or the gas turbine shaft 50 in response to a request. Generally, the prime mover 102 (e.g., the barring motor) is used to rotate various components (the high pressure turbine 17, the high pressure compressor 15, etc., shown in FIG. 1) at a low speed in order to prevent bowing of the gas turbine shaft 50 during engine shutdown and engine start up conditions. In some cases, the prime mover 102 may be driven by a generator. In some cases, the prime mover 102 (e.g., the barring motor) may be supplied with electrical energy that is converted into a mechanical torque used to assist a starter, an electric starter generator, or other starter, during the engine start up.

[0108] The system 100 further includes a drive shaft 104 drivably coupled to the prime mover 102. The system 100 further includes a clutch 108 configured to selectively drivably engage the drive shaft 104 with the output shaft 106. In the illustrated embodiment of FIG. 6A, the drive shaft 104 is disengaged from the output shaft 106. Further, in the illustrated embodiment of FIG. 6A, the clutch 108 is an overrunning clutch. In general, an overrunning clutch or a freewheel transfers power in only one direction and is adapted to disengage a driveshaft from a driven shaft when the driven shaft rotates faster than the driveshaft.

[0109] In the illustrated embodiment of FIG. 6A, the sensor 110 is disposed on the output shaft 106 between the clutch 108 and the accessory gearbox 52. In some embodiments, the sensor 110 may be disposed on another output shaft (not shown) between the accessory gearbox 52 and an accessory 64 other than the barring unit 62.

[0110] The controller 114 is further configured to compare the speed S2 of the gas turbine shaft 50 with a predetermined threshold speed S3 (stored in the memory 116). The predetermined threshold speed S3 may be selected based on specifications of the gas turbine engine 10 (shown in FIG. 1). In some embodiments, the predetermined threshold speed S3 is about 10 revolutions per minute (rpm) of the gas turbine shaft 50.

[0111] The system 100 may further include an electronic module 120 communicably coupled to the prime mover 102 and the controller 114. The electronic module 120 is configured to control the prime mover 102 in response to a control signal 122 received from the controller 114, such that the controller 114 controls the prime mover 102 via the electronic module 120. The electronic module 120 may include a power electronics unit to control the prime mover 102. The electronic module 120 may include a control circuit for switching the prime mover 102 between an active state and an inactive state. The control circuit can also keep the prime mover 102 in the active state or the inactive state. The electronic module 120 module may further regulate the speed of the drive shaft 104 and a direction of rotation of the drive shaft 104 based on application requirements. In some embodiments, the electronic module 120 may be a part of the controller 114.

[0112] The controller 114 is further configured to keep the prime mover 102 in the inactive state upon determining that the speed S2 of the gas turbine shaft 50 is greater than or equal to the predetermined threshold speed S3 (i.e., S2>S3). In the illustrated embodiment of FIG. 6A, in response to the control signal 122, the electronic module 120 keeps the prime mover 102 in the inactive state to keep the drive shaft 104 disengaged from the output shaft 106 upon determining that the speed S2 of the gas turbine shaft 50 is greater than or equal to the predetermined threshold speed S3. Specifically, upon determining that the speed S2 of the gas turbine shaft 50 is greater than or equal to the predetermined threshold speed S3, the controller 114 sends the control signal 122 to the electronic module 120, such that the electronic module 120 keeps the prime mover 102 in the inactive state to keep the drive shaft 104 disengaged from the output shaft 106.

[0113] With reference to embodiment illustrated in FIG. 6A, the clutch 108 (i.e., the overrunning clutch) is configured to drivably engage the drive shaft 104 with the output shaft 106 only if a speed of the drive shaft 104 is greater than the speed S1 of the output shaft 106. Therefore, as the clutch 108 is the overrunning clutch, the clutch 108 is configured to transfer power from the drive shaft 104 to the output shaft 106, and not vice versa. FIG. 6B is a schematic block diagram of the system 100 wherein the drive shaft 104 is illustrated as drivably engaged with the output shaft 106.

[0114] The controller 114 is further configured to activate the prime mover 102 to drivably engage the drive shaft 104 with the output shaft 106 upon determining that the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3 (i.e., S2<S3). Specifically, with reference to FIG. 6B, upon determining that the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3, the controller 114 sends the control signal 122 to the electronic module 120, such that the electronic module 120 activates the prime mover 102 to drivably engage the drive shaft 104 with the output shaft 106. In other words, the controller 114 is configured to activate the prime mover 102 to drivably engage the prime mover 102 with the gas turbine shaft 50 upon determining that the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3. The clutch 108 drivably engages the drive shaft 104 with the output shaft 106 upon activation of the prime mover 102 as the speed of the drive shaft 104 is greater than the speed of the output shaft 106.

[0115] FIG. 7 is a flowchart for a process 600 implemented by the system 100 of FIGS. 6A and 6B, according to an embodiment of the present disclosure. The process 600 is embodied as an algorithm implemented by the system 100 (shown in FIGS. 6A and 6B) including the controller 114. Further, the process 600 may be stored in the memory 116 in the form of instructions executable by the controller 114.

[0116] At step 602, the process 600 begins. Referring to FIGS. 6A, 6B, and 7, at step 604, the sensor 110 generates the sensor signal 112 indicative of the position of the output shaft 106. Thus, at the step 604, the process 600 includes determining the position of the output shaft 106. The process 600 further moves to step 606.

[0117] At the step 606, the controller 114 determines the speed S1 of the output shaft 106 based on the sensor signal 112. The process 600 further moves to step 608. At the step 608, the controller 114 determines the speed S2 of the gas turbine shaft 50 based on the speed S1 of the output shaft 106 and the gear ratio GR of the accessory gearbox 52. The process 600 further moves to step 610. At the step 610, the controller 114 compares the speed S2 of the gas turbine shaft 50 with the predetermined threshold speed S3. The process 600 further moves to step 612.

[0118] At the step 612, the controller 114 determines if the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3. Upon determining that the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3, the process 600 moves to step 614. With reference to FIGS. 6B and 7, at the step 614, the controller 114 activates the prime mover 102 to drivably engage the drive shaft 104 with the output shaft 106. Specifically, the controller 114 sends the control signal 122 to the electronic module 120 to activate the prime mover 102. Once the prime mover 102 is activated and the speed of the drive shaft 104 is greater than the speed S1 of the output shaft 106, the clutch 108 (i.e., the overrunning clutch) drivably engages the drive shaft 104 with the output shaft 106. Therefore, upon determining that the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3, the controller 114 drivably engages the prime mover 102 with the gas turbine shaft 50. The process 600 further moves to step 618 where the process 600 is terminated.

[0119] Upon determining that the speed S2 of the gas turbine shaft 50 is greater than or equal to the predetermined threshold speed S3 at the step 612, the process 600 moves to step 616. With reference to FIGS. 6A and 7, at the step 616, the controller 114 keeps the prime mover 102 in the inactive state. Specifically, the controller 114 sends the control signal 122 to the electronic module 120 to keep the prime mover 102 in the inactive state. As the prime mover 102 is the inactive state, the clutch 108 (i.e., the overrunning clutch) keeps the drive shaft 104 disengaged from the output shaft 106. Therefore, upon determining that the speed S2 of the gas turbine shaft 50 is greater than or equal to the predetermined threshold speed S3, the controller 114 keeps the prime mover 102 disengaged from the gas turbine shaft 50. The process 600 further moves to step 618 where the process 600 is terminated.

[0120] FIG. 8A is a schematic block diagram of a system 200 for use with the gas turbine engine 10 (shown in FIG. 1), according to an embodiment of the present disclosure. In some embodiments, the gas turbine engine 10 includes the system 200. In other words, the system 200 may be a part of the gas turbine engine 10. The system 200 is substantially similar to the system 100 illustrated in FIG. 6A, with common components being referred to by the same reference numerals. However, in the system 200, the clutch 108 is an active clutch communicably coupled to the controller 114 and configured to be controlled by the controller 114.

[0121] In contrast to the overrunning clutch (i.e., the clutch 108 in FIGS. 6A and 6B), the active clutch (i.e., the clutch 108 in FIG. 8A) is configured to transfer power from the drive shaft 104 to the output shaft 106 and vice versa, depending on a position of the clutch 108.

[0122] In some embodiments, the clutch 108 is hydraulically actuated by the controller 114 between a disengaged state and an engaged state. A hydraulic actuating unit (not shown) may be provided to enable the controller 114 to hydraulically actuate the clutch 108.

[0123] With reference to FIG. 8A, in response to the control signal 122, the controller 114 is configured to control the clutch 108 to keep the drive shaft 104 disengaged from the output shaft 106 upon determining that the speed S2 of the gas turbine shaft 50 is greater than or equal to the predetermined threshold speed S3.

[0124] FIG. 8B is a schematic block diagram of the system 200 wherein the drive shaft 104 is illustrated as drivably engaged with the output shaft 106. The controller 114 is further configured to control the clutch 108 and activate the prime mover 102 to drivably engage the drive shaft 104 with the output shaft 106 upon determining that the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3. Specifically, with reference to FIG. 8B, upon determining that the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3, the controller 114 controls the clutch 108 and sends the control signal 122 to the electronic module 120 to activate the prime mover 102, such that the drive shaft 104 is drivably engaged with the output shaft 106. In other words, the controller 114 is configured to control the clutch 108 and activate the prime mover 102 to drivably engage the prime mover 102 with the gas turbine shaft 50 upon determining that the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3.

[0125] As stated earlier with reference to FIG. 6A, the controller 114 is configured to keep the prime mover 102 in the inactive state upon determining that the speed S2 of the gas turbine shaft 50 is greater than or equal to the predetermined threshold speed S3. Also, as stated above with reference to FIG. 8A, the controller 114 is configured to control the clutch 108 (i.e., the active clutch) to keep the drive shaft 104 disengaged from the output shaft 106 upon determining that the speed S2 of the gas turbine shaft 50 is greater than or equal to the predetermined threshold speed S3. Therefore, with reference to FIGS. 6A and 8A, it can be stated that the controller 114 is configured to control the clutch 108 (i.e., the active clutch in FIG. 8A) and/or the prime mover 102 (inactive state in FIG. 6A) to keep the drive shaft 104 disengaged from the output shaft 106 upon determining that the speed S2 of the gas turbine shaft 50 is greater than or equal to the predetermined threshold speed S3.

[0126] As stated earlier with reference to FIG. 6B, the controller 114 is configured to activate the prime mover 102 to drivably engage the drive shaft 104 with the output shaft 106 upon determining that the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3. Also, as stated above with reference to FIG. 8B, the controller 114 is configured to control the clutch 108 (i.e., the active clutch in FIG. 8B) and activate the prime mover 102 to drivably engage the drive shaft 104 with the output shaft 106 upon determining that the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3. Therefore, with reference to FIGS. 6B and 8B, it can be stated that the controller 114 is configured to control the clutch 108 (i.e., the active clutch in FIG. 8B) and/or the prime mover 102 to drivably engage the drive shaft 104 with the output shaft 106 upon determining that the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3.

[0127] FIG. 9 is a flowchart for a process 800 implemented by the system 200 of FIGS. 8A and 8B, according to an embodiment of the present disclosure. The process 800 is embodied as an algorithm implemented by the system 200 (shown in FIGS. 7A and 7B) including the controller 114. Further, the process 800 may be stored in the memory 116 in the form of instructions executable by the controller 114.

[0128] At step 802, the process 800 begins. In the process 800, steps 804, 806, 808, 810, and 812 are the same as the steps 604, 606, 608, 610, and 612, respectively, of the process 600 of FIG. 6. As already stated above, at the step 812, the controller 114 determines if the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3. Upon determining that the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3, the process 800 moves to step 814.

[0129] With reference to FIGS. 8B and 9, at the step 814, the controller 114 controls the clutch 108 (i.e., the active clutch) and activates the prime mover 102 to drivably engage the drive shaft 104 with the output shaft 106. Specifically, at the step 814, the controller 114 controls the clutch 108 and sends the control signal 122 to the electronic module 120 to activate the prime mover 102, such that the drive shaft 104 is engaged with the output shaft 106. Therefore, upon determining that the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3, the controller 114 drivably engages the prime mover 102 with the gas turbine shaft 50. The process 800 further moves to step 818 where the process 800 is terminated.

[0130] Upon determining that the speed S2 of the gas turbine shaft 50 is greater than or equal to the predetermined threshold speed S3 at the step 812, the process 800 moves to step 816. With reference to FIGS. 8A and 9, at the step 816, the controller 114 controls the clutch 108 (i.e., the active clutch) to keep the drive shaft 104 disengaged from the output shaft 106. The controller 114 may also keep the prime mover 102 in the inactive state. Therefore, upon determining that the speed S2 of the gas turbine shaft 50 is greater than or equal to the predetermined threshold speed S3, the controller 114 keeps the prime mover 102 disengaged from the gas turbine shaft 50 and the prime mover 102 in the inactive state. The process 800 further moves to step 818 where the process 800 is terminated.

[0131] FIG. 10 is a graph 900 illustrating a variation in the speed S2 of the gas turbine shaft 50 (shown in FIGS. 1 and 2) with time, according to an embodiment of the present disclosure. As illustrated in the graph 900, speed is depicted in arbitrary units (a.u.) on the ordinate. Time is depicted on the abscissa.

[0132] Referring to FIGS. 6A, 6B, 8A, 8B, and 9, the graph 900 includes a curve 902 depicting the variation in the speed S2 of the gas turbine shaft 50 with time. Once the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3, the controller 114 controls the clutch 108 and/or the prime mover 102 to drivably engage the drive shaft 104 with the output shaft 106 at time t1. Therefore, once the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3, the controller 114 drivably engages the prime mover 102 with the gas turbine shaft 50 at the time t1.

[0133] With reference to FIGS. 1, 6A, 6B, 8A, and 8B, based on the sensor signal 112 generated by the sensor 110, the controller 114 is configured to determine the speed S2 of the gas turbine shaft 50 and then compare it with the predetermined threshold speed S3. Once the speed S2 of the gas turbine shaft 50 is below the predetermined threshold speed S3, the prime mover 102 drives the drive shaft 104 to drive the output shaft 106, which further drives the gas turbine shaft 50 through the accessory gearbox 52. As the gas turbine shaft 50 is driven by the prime mover 102, components, such as compressors and turbines, of the gas turbine engine 10 may rotate at low speeds during the engine shutdown.

[0134] Therefore, during the engine shutdown, the prime mover 102 may drive the gas turbine shaft 50 and rotate the high pressure turbine 17 at a low speed only after the speed S2 of the gas turbine shaft 50 drops below the predetermined threshold speed S3. As the prime mover 102 is drivably engaged with the gas turbine shaft 50 only after the speed S2 of the gas turbine shaft 50 drops below the predetermined threshold speed S3, there may be no risk of overturning and damaging the prime mover 102 due to inertia and residual rotational energy of the gas turbine shaft 50. The drivable engagement of the drive shaft 104 with the output shaft 106 of the accessory gearbox 52 after the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3 may provide a safe mechanical engagement of the prime mover 102 with the gas turbine shaft 50. Each of the systems 100, 200 may therefore provide a means for accurate timing of the drivable engagement of the prime mover 102 with the gas turbine shaft 50.

[0135] For precisely determining the timing of the drivable engagement of the prime mover 102 with the gas turbine shaft 50, each of the systems 100, 200 does not use any modelling of the decaying speed S2 of the gas turbine shaft 50 that could have otherwise led to inaccurate timing of the drivable engagement of the prime mover 102 with the gas turbine shaft 50. Moreover, each of the systems 100, 200 uses the sensor 110 and the controller 114 to determine a moment when the drive shaft 104 should be drivably engaged with the output shaft 106 of the accessory gearbox 52. Therefore, each of the systems 100, 200 drivably engages the prime mover 102 with the gas turbine shaft 50 after the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3, and before the speed S2 of the gas turbine shaft 50 reaches zero during the engine shutdown. As the prime mover 102 is drivably engaged with the gas turbine shaft 50 before the speed S2 of the gas turbine shaft 50 reaches zero during the engine shutdown, each of the systems 100, 200 of the present disclosure may not require the prime mover 102 to have a high rated power configuration.

[0136] In contrast to a conventional technique for measuring the speed S2 of the gas turbine shaft 50 by using variable reluctance sensors disposed on the gas turbine shaft 50, each of the systems 100, 200 of the present disclosure is configured to determine the speed S2 of the gas turbine shaft 50 based at least on the speed S1 of the output shaft 106, which is further based on the sensor signal 112 indicative of the position of the output shaft 106. In other words, each of the systems 100, 200 determines the speed S2 of the gas turbine shaft 50 based on the sensor signal 112 generated by the sensor 110 disposed on the output shaft 106. Further, in contrast to the conventional technique comprising use of the variable reluctance sensors disposed on the gas turbine shaft 50, the sensor signal 112 in each of the systems 100, 200 may not drop with the decaying speed S2 of the gas turbine shaft 50 during the engine shutdown. Therefore, even at low speeds of the gas turbine shaft 50, the sensor signal 112 may be processed to determine the speed S1 of the output shaft 106 and eventually, the speed S2 of the gas turbine shaft 50. Hence, during the engine shutdown, each of the systems 100, 200 may provide a safe drivable engagement of the prime mover 102 with the gas turbine shaft 50.

[0137] FIG. 11 is a flowchart illustrating a method 300 for use with the gas turbine engine 10 of FIG. 1, according to an embodiment of the present disclosure. The method 300 may be implemented by the system 100 of FIGS. 6A and 6B. The method 300 may also be implemented by the system 200 of FIGS. 8A and 8B.

[0138] Referring to FIGS. 6A, 6B, 8A, 8B, 10, and 11, at step 302, the method 300 includes determining the position of the output shaft 106 drivably coupled between the accessory gearbox 52 and the accessory 64 of the accessory gearbox 52. At step 304, the method 300 further includes determining the speed S1 of the output shaft 106 based on the position of the output shaft 106. At step 306, the method 300 further includes determining the speed S2 of the gas turbine shaft 50 based at least on the speed S1 of the output shaft 106. Specifically, the controller 114 is configured to determine the speed S2 of the gas turbine shaft 50 based on the speed S1 of the output shaft 106 and the gear ratio GR of the accessory gearbox 52.

[0139] The method 300 may further include providing the prime mover 102 and the drive shaft 104 drivably coupled to the prime mover 102. The method 300 may further include providing the clutch 108 configured to selectively drivably engage the drive shaft 104 with the output shaft 106. The method 300 may include comparing the speed S2 of the gas turbine shaft 50 with the predetermined threshold speed S3. The method 300 may further include drivably engaging the drive shaft 104 with the output shaft 106 upon determining that the speed S2 of the gas turbine shaft 50 is less than the predetermined threshold speed S3.

[0140] In some embodiments, drivably engaging the drive shaft 104 with the output shaft 106 further includes controlling the clutch 108 and/or the prime mover 102 to drivably engage the drive shaft 104 with the output shaft 106. In some embodiments, controlling the clutch 108 and/or the prime mover 102 further includes activating the prime mover 102, such that the clutch 108 drivably engages the drive shaft 104 with the output shaft 106 (in case of the overrunning clutch in FIG. 6B). In some embodiments, controlling the clutch 108 and/or the prime mover 102 further includes activating the prime mover 102 and controlling the clutch 108 (i.e., the active clutch in FIG. 8B) to drivably engage the drive shaft 104 with the output shaft 106.

[0141] In some embodiments, the method 300 further includes keeping the drive shaft 104 disengaged (e.g., via the clutch 108) from the output shaft 106 upon determining that the speed S2 of the gas turbine shaft 50 is greater than or equal to the predetermined threshold speed S3.

[0142] It will be understood that the disclosure is not limited to the embodiments above described and various modifications and improvements can be made departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.