WO2016069303A1

WO2016069303A1 - Method and system for operating a rotatable machine

Info

Publication number: WO2016069303A1
Application number: PCT/US2015/056141
Authority: WO
Inventors: Dennis Michael DEFREITAS; Scott Brian Wright
Original assignee: Unison Industries, Llc
Priority date: 2014-10-29
Filing date: 2015-10-19
Publication date: 2016-05-06

Abstract

The subject disclosure relates to a method and system for operating a rotatable machine. The innovation includes a turning gear motor, a clutch device configured to mechanically couple the turning gear motor to the rotatable machine, and a turning gear controller configured to receive a set of inputs, and drive the turning gear motor or instruct the clutch device to mechanically couple the turning gear motor to the rotatable machine based at least in part on the inputs. The turning gear motor maintains a rotational speed of a rotor of the rotatable machine to facilitate even cooling during shut down, and reduce or prevent bowing of the rotatable machine or components of the rotatable machine.

Description

METHOD AND SYSTEM FOR OPERATING A ROTATABLE MACHINE

CROSS REFERENCE TO RELATED APPLICATIONS

[00011 This PCX utility application claims priority to and benefit from currently pending provisional application having U.S. Patent Application Serial No.

62/069,901, titled "METHOD AND SYSTEM FOR OPERATING A ROTATABLE; MACHINE" and having filing date October 29, 2014, all of which is incorporated by reference herein.

BACKGROUND

[00Θ2] The present innovations generally pertain to methods and systems for maintaining a. shaft alignment of the rotatable machines during non-operational periods. As one skilled in the art will understand, while various embodiments are described relative to a gas turbine engine, the apparatus, methods and/or systems may also be used in various alternative applications where it is desired to operate a rotatable machine.

[0003] At rated power, aircraft gas turbine engines typically operate in the temperature range of approximately 600 °C at the compressor discharge point and approximately 1260 °C at the turbine inlet area. The temperature typically decreases toward the turbine outlet. After the engine is shut down, various components of the engine may cool at different rates based at least in part on their respective geometries, mass, and locations within the engine. Furthermore, because hot air typically rises, lower sections of the engine cool, and contract in length, at a rate greater than that of components on the upper section of the engine. These differences in cooling rates may result in the engine, or engine components, taking an undesirable deformation during or after the cool down period. This deformation is commonly referred to as "bow" or "bowing". Bowing can occur in many gas turbine aircraft engines to a greater or lesser degree, depending, for example, on their design and operating parameters, and can be most pronounced in the turbine shaft, casing, and stationary seals of the engine. [00Θ4] Once the engine has developed a bow, the compressor and turbine rotors may not maintain concentric alignment with corresponding stationary seals. As a result, if the engine is motored o ver, the rotors may rub during the starting transient. The rubbing cars deteriorate stationary seals in certain clock locations causing an unwanted increase in seal clearance, and hence, a performance ioss.

[0005] In addition, there may also be measureable vibration due to bowing during a starting transient. This mode may gradually disappear as the engine warms up;

however, any form of vibration excitation in an engine is an unwanted characteristic and should be eliminated or held to an absolute minimum. In addition to passenger discomfort, vibrating patterns can influence bearing life along with other parts affected by vibration excitation,

SUMMARY

[0006] In one embodiment, a turning gear system, includes a turning gear motor, a clutch device configured to selectively couple the turning gear motor to a rotatabie machine, and a turning gear controller configured to receive a set of inputs, and drive the turning gear motor based at feast in pari, on the inputs.

[00Θ7] In another embodiment, a method of operating a turbine engine, includes operating the turbine engine at a first operating rotational speed, shutting down the turbine engine, engaging a turning gear when a rotational speed of the turbine is reduced to a predetermined rotational speed, wherein the predetermined rotational speed is greater than zero revolutions per minute, and operating, via the turning gear, the turbine engine at a second turning rotational speed, the second turning rotational speed being greater than zero revolutions per minute and less than the first operating rotational speed.

[0008J In yet another embodiment, a turning gear control system, includes an input component that receives a set of inputs associated with a rotatabie machine, a determination component that determines at least one of a first rotational speed or operational state of the rotatabie machine based at least in part on the set of inputs, a trigger component that determines to mechanically couple a rotatabie member of the rotatabie machine to a turning gear motor to maintain a predetermined turning gear speed, and an output component that at least one of drives a turning gear motor or instructs a clutch device to couple the rotatable member of the rotata ble machine to a turning gear motor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The above-mentioned and other features and advantages of these exemplary embodiments, and the manner of attaining them, will become more apparent and the methods and systems for operating a rotatable machine will be better understood by reference to the following description of embodiments taken in conjunction with the accompanying drawings, wherein;

[0010| FIG. 1 illustrates an example schematic block diagram of a turning gear system for a rotatable machine in accordance with various aspects described herein;

[0011] FIG. 2 illustrates an example turning gear controller in accordance with various aspects described herein;

[0012] FIG. 3 illustrates an example turning gear controller in accordance with various aspects described herein; and

[0013] FIGS. 4-5 are example flow diagrams of respective methods for operating a rotatable machine in accordance with various aspects described herein,

DETAILED DESCRIPTION

[0014J The innovation is now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the subject innovation. It may be evident, however, that the innovation can be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing the innovation.

[0015] As noted in the Background Section, after a rotatable machine (e.g., turbine engine) is shut down, various components of the machine may cool at different rates based at least in part on their respective geometries, mass, and locations within the engine. The non-uniform cooling can l ead to bowing of the rotatable machine or components of the rotatable machine. Accordingly, a non-limiting intent of the disclosed subject matter is to provide analytical and methodical embodiments of managing heat related stresses in rotating machinery in industrial, commercial, and residential applications.

[0016] Referring now the drawings, with reference to FIG. 1, illustrated is an example schematic block diagram of a. turning gear system 100 for a rotatable machine. The rotatable machine can include, but is not limited to, a gas turbine engine 102 that includes one or more rotatable members, for example, a shaft 104. During operation of the gas turbine engine 102, shaft 104 may operate at elevated temperatures compared to temperatures of the shaft 104 experienced during periods of non-operation (e.g., long term shutdown). For example, if permitted to completely stop or come to standstill during a shutdown procedure without continuous rotation, shaft 104 may bow, which could lead to undesirable effects during a. subsequent startup.

[0017] To mitigate such effects, the turning gear system 100 includes a turning gear motor 106. The turning gear motor 106 can include, for example, an electric motor supplied by a power supply 1 10. The power supply 1 10 can include, as a non-limiting example, a 400 Hertz (Hz) alternating current (AC) power source located on a same vehicle (not shown) as the gas turbine engine 102, Additionally or alternatively, the power supply 1 10 can include a. direct current (DC) power source. The turning gear motor 106 can include a shaft 112 that is couplabie to a clutch 1 14. The clutch 1 14 can include, but is not limited to, a centrifugal clutch, an overrunning clutch, or may^¬ be a mechanically or electrically engagable clutch. For example, clutch 114 may be actuated by a solenoid or a pneumatic or hydraulic piston to engage turning gear motor 106 to a downstream load. Additionally or alternatively, a mechanical or fluid drive system may be used to drive the turning gear system 100, particularly for ground or land-based applications.

[0018] As illustrated in FIG. 1, an output shaft 116 of clutch 114 can be coupled to a turning gear gearbox 1 18. Additionally or alternatively, the turning gear gearbox 118 may not be used and the shaft 116 can be coupled directly to a shaft 120 of an accessory gearbox 122. The accessory gearbox 122 is coupled through a shaft 124 to a gear assembly 126 in rotational communication with shaft 104 or a component coupled to shaft 104. Additionally or alternatively, the turning gear box 118 can be located between the turning gear motor 106 and clutch 114 with the clutch 1 14 and shaft 1 16 connecting directly with accessory gearbox 122.

[0019] A turning gear controller 128 receives inputs 130, which it uses to generate commands to, for example, the clutch 114 or motor 106. The inputs 130 may be received individually from their respective sources, may be combined into a single enablement signal 132 via a logic circuit 134, or virtually any combination thereof. The inputs 130 can provide data related to the rotatable machine or an associated system to the controller 128. For example, where the rotatable machine includes the turbine engine 102 associated with an aircraft, the inputs 120 can include, for example, a rotational shaft speed signal 136 for the shaft 104, a weight on wheels (WOW) signal 138, a. signal 140 from a manual switch (not shown) located, for example, in the cockpit of an aircraft (not shown), and a control signal 142 from an aircraft and/or engine controller, such as, but, not limited to a full authority digital electronic control (FADEC). The turning gear controller 128 can generate a variable speed control signal 143 to drive the turning gear motor 106 such that turning gear motor 106 is able to operate at a plurality of rotational speeds. Additionally or alternatively, the controller 128 can provide a fixed frequency AC excitation or a fixed DC voltage excitation to drive the turning gear motor 106 for single turning speed operation.

[002Θ] The controller 128 includes a processor 144 and a memory device 146 communicatively coupled together such that instructions stored in memory device 146 are read and executed by processor 144 to facilitate automatic operation of turning gear system 100. Additionally or alternatively, the controller 128 can include a dedicated logic circuit capable of performing the functions described herein, or be integrated with or in communication with the logic circuit 134.

[0021] During operation, the turbine engine 102 may be controlled to operate at a first operating rotational speed providing needed power for, for example, propelling a vehicle or supplying a load, such as a generator or pump. When turbine engine 102 is no longer needed or has tripped due to a malfunction, turbine engine 102 may be commanded to perform a shutdown procedure. The shutdown procedure can include reducing a fuel flow to turbine engine 102 and allowing the shaft 104 to coast to a rotational speed that is less than the first operating rotational speed, for example, a predetermined or selectable turning gear speed. During the coast down period, the controller 128 can monitor (e.g., via the inputs 130) the rotational speed of shaft 104, and when the rotational speed of shaft 104 is approximately equal to the turning gear speed, the turning gear controller 128 can engage the clutch 1 14 and/or energize the turning gear motor 106. Additionally or alternatively, in response to receiving an enablement signal 132 from the logic circuit 134, the turning gear controller 128 can engage the clutch 1 14 and/or energize the turning gear motor 106.

[0022] By engaging turning gear system 100 before a rotational speed of shaft 104 reaches a predetermined threshold or zero rotations per minute (RPM), the turning gear motor 106 can be sized smaller and lighter than if turning gear motor 106 was designed to accelerate shaft 104 from standstill up to a predetermined turning gear speed. For example, the turning gear motor 106 can be sized to provide sufficient torque to keep shaft 104 rotating at the turning gear speed, and does not need to be sized to provide torque sufficient to start rotating the shaft 104 and accelerating the shaft 104 up to the turning gear speed. The turning gear motor 106 can provide sufficient torque to rotate the shaft 104 at the turning gear speed while the engine 102 cools to a predetermined temperature or for a predetermined amount of time. Rotating the shaft 104 while the turbine engine 102 cools enables the turbine engine 102 to cool evenly and reduces the development of bowing in the shaft 104.

[0023] Turning now to FIG. 2, illustrated is an example turning gear controller 128 in accordance with various aspects described herein. As discussed, the turning gear controller 128 can rotate a rotatable member or shaft (e.g., shaft 104) of a rotatable machine (e.g., turbine engine 102) at a turning gear speed during cool down of the rotatable machine to reduce or prevent bowing of the rotatable member. For example, the turning gear controller 128 can energize, command, or otherwise direct a turning gear motor (e.g., turning gear motor 106) to maintain a predetermined turning gear speed of the rotatable member when the rotatable machine is shutdown. The turning gear controller 128 can include an input component 202, a. determination component 204, a trigger component 206, an output component 208, a processor 144, and a memory 146.

[0024] The input component 202 can obtain, acquire or otherwise receive a set of inputs 210, The set of inputs 210 can provide data related to the rotatable machine or a related system (e.g., vehicle, aircraft, etc.). For example, where the rotatable machine includes an aircraft turbine engine (e.g., turbine engine 102), the set of inputs 210 can include a rotational turbine shaft speed signal (e.g., signal 136), a weight on wheels (WOW) signal (e.g., signal 138), a manual input signal (e.g., signal 140), for example, from an input or control device located in the cockpit of the aircraft, or a control signal 142 from the aircraft or engine controller, such as, but, not limited to a full authority digital electronic control (F.ADEC ). Additionally or alternatively, the set of inputs 210 can include an enablement signal (e.g., enablement signal 132) that notifies, instincts, or otherwise indicates that the turning gear controller 128 can engage a turning gear system ( e.g., system 100).

[0025] The determination component 204 can ascertain, verify or otherwise determine a speed of the rotatable machine and/or an operational state of the rotatable machine based at least in parts on the set of inputs 210, For example, the

determination component 204 can determine that the rotatable machine is operating at a typical operating speed based on the rotational turbine shaft speed signal (e.g., signal 136) included in the set of inputs 210. Additionally or alternatively, the determination component 204 can determine that the rotatable machine has been shut down based on, for example, a manual input signal or enablement signal included in the set of inputs 210.

[0026] The trigger component 206 can compare the speed or operational state of the rotatable machine to a set of predetermined criteria, and based on the comparison, determine whether to mechanically couple a shaft of the rotatable machine to a turning gear motor (e.g., motor 106) to maintain a predetermined turning gear shaft speed. For example, if the determination component 204 determines that the rotatable machine 204 has been shut down, the trigger component 206 can determine to mechanically couple a shaft of the rotatable machine to the turning gear motor when the shaft speed decreases to, or reaches, a predetermined threshold. [0027] The output component 208 can generate a set of outputs 212 to direct, instruct or otherwise command a. turning gear system. For example, the output component 208 can generate a speed control signal (e.g., signal 143) for a turning gear motor (e.g., motor 106). The speed control signal can include, but is not limited to, a variable speed control signal, a fixed frequency AC excitation signal, or a fixed DC voltage excitation signal. In addition, the output component 208 can generate and provide a signal that instructs a clutch (e.g., clutch 1 14) to engage or mechanically couple the turning gear motor with the rotatable machine.

[0028| FIG. 3 illustrates an example turning gear controller 128 in accordance with various aspects described herein. The turning gear controller 128 can include or be associated with an intelligence component 302 that can provide for or aid in various inferences or determinations. In particular, in accordance with or in addition to what has been described supra, with respect to intelligent determination or inferences provided by various components described herein. For example, all or portions of input component 202, determination component 204, trigger component 206, and output component 208 (as well as other components described herein) can be operatively coupled to intelligence component 302. Additionally or alternatively, ail or portions of intelligence component 302 can be included in one or more components described herein. Moreover, intelligence component 302 will typically have access to all or portions of data sets described herein, such as any data in memory 146.

[0029] Accordingly, in order to provide for or aid in the numerous inferences described herein, intelligence component 302 can examine the entirety or a subset of the data available and can provide for reasoning about or infer states of the system, environment, and/or user from a set of observations as captured via. events and/or data. Inference can be employed to identify a specific context or action, or can generate a probability distribution over states, for example. The inference can be probabilistic - that is, the computation of a probability distribution over states of interest based on a consideration of data and events. Inference can also refer to techniques employed for composing higher-level events from a set of events and/or data. [003Θ] Such inference can result in the construction of new events or actions from a set of observed events and/or stored event data, whether or not the events are correlated in close temporal proximity, and whether the events and data come from one or several event and data sources. Various classification (explicitly and/or implicitly trained) schemes and/or systems (e.g., support vector machines, neural networks, expert systems, Bayesian belief networks, fuzzy logic, data fusion engines, , ,) can be employed in connection with performing automatic and/or inferred action in connection with the claimed subject matter.

[00311 A classifier can be a function that maps an input attribute vector, x = (xl , x2, x3, x4, xn), to a confidence that the input belongs to a class, that is, f(x) =

confidence(ciass). Such classification can employ a probabilistic and/or statistical- based analysis (e.g., factoring into the analysis utilities and costs) to prognose or infer an action that a user desires to be automatically performed. A support vector machine (SVM) is an example of a classifier that can be employed. The SVM operates by finding a hyper-surface in the space of possible inputs, where the hyper-surface attempts to split the triggering criteria from the non-triggering events. Intuitively, this makes the classification correct for testing data that is near, but not identical to training data. Other directed and undirected model classification approaches include, e.g., naive Bayes, Bayesian networks, decision trees, neural networks, fuzzy logic models, and probabilistic classification models providing different patterns of independence can be employed. Classification as used herein also is inclusive of statistical regression that is utilized to develop models of priority.

[0032] FIGS, 4-5 illustrate various methodologies in accordance with the disclosed subject matter. While, for purposes of simplicity of explanation, the methodologies are shown and described as a series of acts, it is to be understood and appreciated that the disclosed subject matter is not limited by the order of acts, as some acts may occur in different orders and/ or concurrently with other acts from that shown and described herein. For example, those skilled in the art will understand and appreciate that a methodology can alternatively be represented as a series of interrelated states or events, such as in a state diagram. Moreover, not all illustrated acts may be required to implement a. methodology in accordance with the disclosed subject matter. Additionally, it is to foe further appreciated that the methodologies disclosed hereinafter and throughout this disclosure are capable of being stored on an article of manufacture to facilitate transporting and transferring such methodologies to computers.

[0033] Referring now to FIG. 4, illustrated is an example methodology 400 for operating a turbine engine in accordance with various aspects described herein. At reference numeral 402, a turbine engine (e.g., turbine engine 102) is operated at first operating rotational speed. The first operating rotational speed can be a speed providing needed power for, for example, propelling a vehicle or supplying a load, such as a generator or pump. At reference numeral 404, the turbine engine is shutdown. For example, the turbine engine may be shut down when it is no longer needed or when a fault has occurred requiring shutdown.

[0034] At reference numeral 406, a turning gear is engaged when a rotational speed of the turbine engine is reduced to a predetermined rotational speed. For example, the predetermined rotational speed can be a speed greater than zero (0) rotations per minute (RPMs). By engaging the turning gear system before a rotational shaft speed of the turbine engine reaches zero RPMs, a turning gear motor can be sized smaller and lighter than if turning gear motor was designed to accelerate the turbine engine from standstill to a predetermined turning gear speed.

[0035] At reference numeral 408, the turbine engine is operated, via the turning gear, at the second or turning gear rotational speed. The second rotational speed can be, for example, greater than zero RPMs and less than the first operating rotational speed. The turbine engine can be operated at the second rotational speed while the turbine engine cools, or for a predetermined period of time. Operating the turbine engine at the second rotational speed enables the turbine engine, and its' components, to cool evenly and reduces or prevents the development of bowing in the turbine engine.

[0036] FIG. 5 illustrates an example methodology 500 for operating a turbine engine in accordance with various aspects described herein. At reference numeral 502, a set of inputs (e.g., inputs 210) are received (e.g., via an input component 202). The set of inputs can provide data related to the rotatable machine or a related system (e.g., vehicle, aircraft, etc.). For example, where the rotatable machine includes an aircraft turbine engine (e.g., turbine engine 102), the set of inputs can include a rotational turbine shaft speed signal (e.g., signal 136), a weight on wheels (WOW) signal (e.g., signal 138), a manual input signal (e.g., signal 140), for example, from an input or control device located in the cockpit of the aircraft, or a control signal (e.g., signal 142) from the aircraft or engine controller, such as, but, not limited to a full authority digital electronic control (FADEC), Additionally or alternati ely, the set of inputs can include an enablement signal (e.g., enablement signal 132) that notifies, instructs, or otherwise indicates that the turning gear system (e.g., system 100) can be engaged.

[0037] At reference numeral 504, an operaiional state of the rotatable machine is determined based at least in part on the set of inputs (e.g., via a determination component 204). The operational state can include a rotational speed at which the rotaiable machine is operating. Additionally or alternatively, the operational state can include a status of the rotatable machine. For instance, the status can include, but is not limited to, non-operational, operating at a typical operating speed, or shutting down.

[0038] At reference numeral 506, a determination is made whether the rotatable machine is shutting down, or has received instructions to shut down, based at least in part on the determined operational state of the rotatable machine. If the rotatable machine is not shutting down (N at reference numeral 506), then the methodology returns to reference numeral 502. If the rotatable machine is shutting down (Y at reference numeral 508), then at reference numeral 508 the turning gear can be triggered. Triggering the turning gear can include instructing a. clutch (e.g., clutch 1 14) to engage, or providing a control signal to a turning gear motor (e.g., motor 106). Based on the triggering, the rotaiable machine can be operated at a predetermined turning speed while the rotatable machine cools, or for a predetermined period of time. Operating the rotaiable machine at the second rotational speed enables the rotatable machine, and its' components, to cool evenly and reduces or prevents the development of bowing in the rotatable machine. [0039] Unless specifically stated otherwise as apparent from the above discussion, it is appreciated that throughout the description, discussions utilizing terms such as "processing" or "computing" or "calculating" or "determining" or "displaying" or "providing" or the like, refer to the action and processes of a computer system, or similar electronic digital or analog computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system memories or registers or other such information storage, transmission or display- devices. Alternately controller 128 electronic controls can be implemented utilizing electronic: amplifiers, comparator's, logic circuits, switches and relays.

[0040] Based on the foregoing specification, the above-discussed embodiments of the disclosure may be implemented using computer programming or engineering techniques including computer software, firmware, hardware or any combination or subset thereof. Any such resulting program, having computer-readable and/or computer-executable instructions, may be embodied or provided within one or more computer-readable media, thereby making a computer program product, i.e., an article of manufacture, according to the discussed embodiments of the disclosure. The computer-readable media may be, for instance, a fixed (hard) drive, diskette, optical disk, magnetic tape, semiconductor memory such as read-only memory (ROM) or flash memory, etc., or any transmitting/receiving medium such as the Internet or other communication network or link. The article of manufacture containing the computer code may be made and/or used by executing the instructions directly from one medium, by copying the code from one medium to another medium, or by- transmitting the code over a network.

[0041] Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as "about" and "substantially", are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.

[0042] The term processor, as used herein, refers to central processing units, microprocessors, microcontrollers, reduced instruction set circuits (RISC), application specific integrated circuits (A SIC), logic circuits, and any other circuit or processor capable of executing the functions described herein.

[0043] As used herein, the terms "software" and "firmware" are interchangeable, and include any computer prograin stored in memory for execution by processor 144 and by devices that include, without limitation, mobile devices, clusters, personal computers, workstations, clients, and servers, including RAM memory, ROM memory, EPROM memory, EEPROM memory, and non-volatile RAM (NVRAM) memory. The above memory types are examples only, and are thus not limiting as to the types of memory usable for storage of a computer program.

[0044] The above-described embodiments of a method and system of maintaining a rotatable member of a rotatable machine rotating during a shutdown provides a cost- effective and reliable means for reducing weight and size of turning gear system components. More specifically, the methods and systems described herein facilitate providing enough torque to the rotatable member to maintain it rotating at a turning gear speed, but not enough torques to start the shaft from a standstill condition. In addition, the above-described methods and systems facilitate automatically engaging the turning gear system after enablement conditions are satisfied. As a result, the methods and systems described herein facilitate managing a cool down of a rotatable machine during a shutdown in a cost-effective and reliable manner.

[0045] Example methods and apparatus for automatically engaging a turning gear system during a shutdown procedure for a rotatable machine are described above in detail. The apparatus illustrated is not limited to the specific embodiments described herein, but rather, components of each may be utilized independently and separately from other components described herein. Each system component can also be used in combination with other system components. [0046] This written description uses examples to describe the disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims

CLAIMS WHAT IS CLAIMED IS:

1. A turning gear system, comprising:

a turning gear motor;

a clutch, device configured to selectively couple the turning gear motor to a rotatable machine; and

a turning gear controller configured to receive a set of inputs, and drive the turning gear motor based at least in part on the inputs.

2. The turning gear system of claim 1 , wherein the clutch device is configured to selectively couple the turning gear motor to the rotatable machine via a gearbox.

3. The turning gear system of claim 2, wherein the gearbox includes a turning gear gearbox comprising an output shaft configured to couple to a shaft of an aircraft engine accessory gearbox.

4. The turning gear system of claim 1, wherein the turning gear controller drives the turning gear motor by electrically coupling the turning gear motor to a source of electrical power.

5. The turning gear system of claim 1 , wherein the set of inputs include at least one of a rotor speed signal, a weight on wheels signal, a manual input signal, a control signal, or an enablement signal

6. The turning gear system of claim 1, wherein the clutch device is configured to couple the turning gear motor to the rotatable machine at a

predetermined rotational speed of the rotatable machine.

7. The turning gear system of claim 1, wherein the rotatable machine includes an aircraft gas turbine engine.

8. The turning gear system of claim 1 , wherein the turning gear controller is configured to engage the clutch when a rotational speed of the rotatable machine is reduced from a first operating speed to a second turning speed, wherein the first operating speed is greater than the second turning speed.

9. A method of operating a turbine engine, the method comprising:

operating the turbine engine at a first operating rotational speed;

shutting down the turbine engine;

engaging a turning gear when a rotational speed of the turbine is reduced to a. predetermined rotational speed, wherein the predetermined rotational speed is greater than zero revolutions per minute; and

operating, via the turning gear, the turbine engine at a second turning rotational speed, the second turning rotational speed being greater than zero revolutions per minute and less than the first operating rotational speed,

10. The method of claim 9, wherein the engaging the turning gear includes engaging a clutch configured to couple a turning motor to a gearbox coupled to a rotor of the turbine engine.

11. The method of claim 9, wherein the engaging the turning gear includes engaging the turning gear while the turbine is coasting at the predetermined rotational speed.

12. The method of claim 9, wherein the engaging the turning gear comprises supplying power to a turning motor.

13. The method of claim 9, further comprising receiving a set of inputs including at least one of an aircraft weight on wheels signal, a signal trom a manual switch operable by a user, an engine controller permissive signal, a turbine rotor speed switch signal, or an enablement signal.

14. The method of claim 13, wherein the engaging the turning gear is based at least in part on the set of inputs.

15. A turning gear control system, comprising:

an input component that receives a set of inputs associated with a rotatable machine; a determination component that determines at l east one of a first rotational speed or operational state of the rotatable machine based at least in part on the set of inputs;

a trigger component that determines to mechanically couple a rotatable member of the rotatable machine to a turning gear motor to maintain a predetermined turning gear speed; and

an output component that at least one of drives a turning gear motor or instructs a clutch device to couple the rotatable member of the rotatable machine to a turning gear motor,

16. The turning gear control system of claim 15, wherein the set of inputs include at least one of an aircraft weight on wheels signal, a signal from a manual switch operable by a user, an engine controller permissive signal, a turbine rotor speed switch signal, or an enablement signal,

17. The turning gear control system of claim 15, wherein the operational state includes at least one of: operating at a typical operating rotational speed, or shutting down.

18. The turning gear control system of claim 15, wherein the output component drives the turning gear motor by providing at least one of a variable speed control signal, a fixed frequency AC excitation signal, or a fixed DC voltage excitation signal,

19. The turning gear control system of claim 15, wherein the output component drives the turning gear motor to operate the rotatable machine at a second rotational speed that is less than the first rotational speed.

20. The turning gear control system of claim 19, wherein the output component instructs the clutch device to mechanically couple the shaft of the rotatable machine to the turning gear motor when the rotational speed of the shaft satisfies a predetermined threshold.