Rotary servo for fixed fail actuators

In general, techniques are described regarding a rotary servo for actuators. A servo assembly includes a cylindrical outer sleeve including ports, a cylindrical outer spool annularly disposed within the cylindrical outer sleeve, a stepper motor mechanically coupled to the cylindrical outer spool, and an actuator mechanically coupled to compressor variable geometry that controls compression provided by a compressor. The cylindrical outer spool includes channels configured to provide fluidic interconnection between the ports and a cylindrical inner spool, where the cylindrical inner spool is annularly disposed within the cylindrical outer spool, and the cylindrical inner spool includes grooves configured to provide fluidic interconnection through the channels of the cylindrical outer sleeve. The stepper motor is configured to rotate the cylindrical outer spool within the cylindrical outer sleeve to deliver a fluid to and thereby actuate the actuator to control the compressor variable geometry.

TECHNICAL FIELD

The disclosure relates to gas turbine engines.

BACKGROUND

Gas turbine engines may include an axial compressor that provides compression (e.g., of air) prior to combustion. The axial compressor may include multiple compression stages, each stage including a row of rotating blades (referred to as a rotor) and a row of stationary blades (referred to as a stator). In each adjacent compressor stage, the rotors and stators become smaller to accommodate the increase in pressure across each stage and thereby maintain near constant axial velocity of the air.

To improve fuel efficiency and responsiveness of the compressor in achieving targeted levels of compression during variable conditions (e.g., accelerating, decelerating, etc.), the compressor may include variable geometry, such as in the form of variable stators. Actuators may control the variable geometry, where such actuators are controlled via an electrohydraulic servo assembly that operates with respect to a control signal and a fluid (such as fuel). The actuators may receive, via the electrohydraulic servo assembly, the fuel as a way by which to adjust linear movement of the actuator that then adjusts the position of the variable geometry.

The electrohydraulic servo assembly may include a rotary stepper motor that is electrically controlled via a control signal. The rotary stepper motor is further coupled via a mechanical mechanism (e.g., a rotary to linear translation mechanism coupled to a lever) that is mechanically coupled to a variable geometry feedback link that indicates mechanical movement of the variable geometry. This feedback link adjusts the delivery of the fuel (via the lever) and accompanying activation of the actuator to balance movement of the variable geometry with fuel delivery to the combustor to potentially achieve the improved fuel efficiency and responsiveness of the gas turbine engine.

SUMMARY

In one example, the disclosure is directed to a rotary actuation system of a gas turbine engine comprising: a servo assembly that includes: a cylindrical outer sleeve including multiple ports; a cylindrical outer spool annularly disposed within the cylindrical outer sleeve, wherein: the cylindrical outer spool includes multiple channels configured to provide fluidic interconnection between the multiple ports and a cylindrical inner spool, the cylindrical inner spool is annularly disposed within the cylindrical outer spool, and the cylindrical inner spool includes grooves configured to provide fluidic interconnection through the multiple channels of the cylindrical outer sleeve; and a stepper motor mechanically coupled to the cylindrical outer spool; and an actuator mechanically coupled to compressor variable geometry that controls compression provided by a compressor of the gas turbine engine, wherein the stepper motor is configured to rotate the cylindrical outer spool within the cylindrical outer sleeve to deliver a fluid to and thereby actuate the actuator to control the compressor variable geometry.

In another example, the disclosure is directed to a method comprising: receiving a control signal; and rotating, by a stepper motor of a servo assembly and based on the control signal, a cylindrical outer spool within a cylindrical outer sleeve in which the cylindrical outer spool is annularly displaced within to deliver a fluid to and thereby actuate an actuator to control compressor variable geometry of a gas turbine engine, wherein the cylindrical outer sleeve includes multiple ports, wherein the stepper motor is mechanically coupled to the cylindrical outer spool, wherein the cylindrical outer spool includes multiple channels configured to provide fluidic interconnection between the multiple ports and a cylindrical inner spool, wherein the cylindrical inner spool is annularly displaced within the cylindrical outer spool, the cylindrical inner spool including grooves configured to provide fluidic interconnection through the multiple channels of the cylindrical outer sleeve, and wherein the actuator is mechanically coupled to the compressor variable geometry.

In another example, the disclosure is directed to a gas turbine engine comprising: a combustor; a compressor fluidically upstream of the combustor that includes compressor variable geometry configured to control compression by the compressor; and a rotary actuation system mounted to a body of the gas turbine engine, the rotary actuation system including: a servo assembly that includes: a cylindrical outer sleeve including multiple ports; a stepper motor mechanically coupled to a cylindrical outer spool annularly displaced within the cylindrical outer sleeve; the cylindrical outer spool including multiple channels configured to provide fluidic interconnection between the multiple ports and a cylindrical inner spool; and the cylindrical inner spool annularly displaced within the cylindrical outer spool, the cylindrical inner spool including grooves configured to provide fluidic interconnection through the multiple channels of the cylindrical outer sleeve; and an actuator mechanically coupled to the compressor variable geometry, wherein the stepper motor is configured to rotate the cylindrical outer spool within the cylindrical sleeve to deliver a fluid to and thereby actuate the actuator to control the compressor variable geometry.

DETAILED DESCRIPTION

The disclosure describes a gas turbine engine in which a compressor of the gas turbine engine includes a rotary actuator assembly. The rotary actuator assembly may operate rotationally in order to potentially avoid complicated mechanical mechanisms required to translate rotational motion of the stepper motor into linear operation for configuring the servo valve to deliver a fluid (e.g., fuel) to drive the linear motion of the actuator. The rotary actuator assembly may include a rotary servo valve in which a cylindrical outer spool annularly disposed within a cylindrical outer sleeve is mechanically coupled to the rotary stepper motor.

Responsive to receiving a control signal, the rotary stepper motor may rotate the cylindrical outer spool to deliver the fuel to the actuator and thereby actuate the actuator to deliver linear force to control the compressor variable geometry (e.g., stators). In this way, the rotary actuator assembly may reduce the complexity of the complicated mechanical mechanisms to translate rotational motion of the stepper motor into linear operation for configuring the servo valve to deliver the fuel to drive the linear motion of the actuator.

In addition, the actuator may be mounted on a body of the gas turbine engine via a rotary mount that enables the actuator to rotate when actuated. The rotation of the actuator may rotate a mechanical coupling to a cylindrical inner spool of the servo valve, where this cylindrical inner spool is annularly disposed within the cylindrical outer spool. The actuator may rotate about the mechanical coupling to the rotary stepper motor providing feedback representative of movement of the compressor variable geometry, turning the cylindrical inner spool to effectively disable actuation of the actuator (e.g., by stopping delivery of the fuel). In other words, the linear operation of the actuator when moving the variable geometry may result in rotation that provides feedback to the stepper motor via the mechanical coupling (e.g., a link coupled between the actuator and the rotary stepper motor).

This mechanical coupling, being directly coupled to the actuator (meaning there may be little to no intervening mechanical mechanisms to translate between rotational to linear movement), may further simplify the actuator assembly by removing the compressor variable geometry feedback link. Removal of the compressor variable geometry feedback link may allow for easier routing of lines (e.g., servo lines, fuel lines, etc.) and other components (e.g., fuel pumps, etc.) while still potentially achieving accurate feedback.

Removal of the servo translational mechanism and accompanying feedback link may result in more efficient maintenance. For example, the translational mechanism (between rotational and linear movement) may be prone to wear due to the varying stresses applied during operation of the gas turbine engine and the nature of competing forces from the rotary stepper motor and the competing feedback from the feedback link. Given the hydraulic nature of the rotary actuator assembly, this translational mechanism may reside within the fluid and thereby require disassembly of a fluid tight case. Removal of the translational mechanism may thereby allow for more straightforward maintenance, as the wear on the mechanical coupling of the rotary actuator assembly may occur outside of the hydraulic system used to activate the actuator while also reducing part counts that are subject to wear.

FIG.1is a conceptual diagram illustrating an example gas turbine engine that includes a rotatory actuator assembly for control of compressor variable geometry in accordance with various aspects of the techniques described in this disclosure. Gas turbine engine10is a primary propulsion engine that provides shaft horsepower for flight operations of a vehicle, such as an aircraft. In some examples, gas turbine engine10is a two-spool engine having a low pressure (LP) spool24and a high pressure (HP) spool26. In other examples, gas turbine engine10may include a single spool or three or more spools, e.g., may include an intermediate pressure (IP) spool and/or other spools. In some examples, gas turbine engine10may include any suitable turbine powered-engine propulsion system, including but not limited to, a turboprop engine or a turboshaft engine (including rotary wing aircraft).

Gas turbine engine10includes a propulsor12, a compressor14, a combustor18, a high pressure (HP) turbine20, and a low pressure (LP) turbine22, each of which is fluidically disposed in series with respect to one another as shown in the example ofFIG.1. That is, air enters compressor14, which produces first stage compressed air that is directed into combustor18.

Combustor18is fluidically disposed between compressor14and HP turbine20, and as such is in series flow downstream from compressor14. In some examples, combustor18includes a combustion liner (not shown) that encloses a continuous combustion process using the compressed air and fuel. In other examples, combustor18may take other forms, and may be, for example, a wave rotor combustion system, a rotary valve combustion system, a pulse detonation combustion system, or a slinger combustion system, and may employ deflagration and/or detonation combustion processes. Combustor18outputs the result of burning the fuel as hot expanding gases.

HP turbine20is fluidically disposed between combustor18and LP turbine22, and as such is in series flow downstream of combustor18. HP turbine20utilizes the hot expanding gases to drive HP spool26, which in turn drives compressor14. The hot expanding gases pass through HP turbine20to LP turbine22, thereby driving LP spool24. LP spool24is coupled to a gearbox, which provides mechanical energy to drive propulsor12(e.g., a propeller). Propulsor12provides thrust, lift, and/or rotational control for the aircraft (such as a helicopter—where such propellers may be referred to as a rotor—or propeller-driven airplanes, including rotary wing aircraft).

Compressor14includes one or more compressor stages. Each compressor stage may include a compressor stator vane row along the axial circumference of gas turbine engine10and a compressor rotor (which may refer to compressor blades attached along an axial circumference of a rotor disc), both of which are not shown for ease of illustration purposes in the example ofFIG.1. The compressor rotors for compressor14are spun between the compressor stator vane rows of compressor14via HP spool26to produce the compressed air. As shown inFIG.1, compressor14may be fluidically upstream from combustor18.

Each of HP turbine20and LP turbine22include one or more turbine stages. Each turbine sage may include a stator vane row along the axial circumference of gas turbine engine10and a turbine rotor (which may refer to turbine blades attached along an axial circumference of a rotor disc), both of which again are not shown in the example ofFIG.1for ease of illustration purposes. The gas emitted by combustor18drives the turbine rotors of HP turbine20and LP turbine22, which spin between the respective stator vane rows of HP turbine20and LP turbine22. The rotation or spinning drives respective HP spool26and LP spool24, which as noted above drive compressor14and propulsor12.

Gas turbine engine10also includes a casing28(which may also be referred to as a “body28”) surrounding or otherwise forming portions of compressor14, combustor18, HP turbine20, LP turbine22and possibly other components of gas turbine engine10that are not shown for ease of illustration in the example ofFIG.1. For example, the above noted compressor stator vane rows may be affixed to casing28. Likewise, the turbine stator vane rows may be affixed to casing28.

To maximize efficiency of gas turbine engine10, the compression stator vanes in each row and the rotor blades are configured to produce a desired compression ratio of input air pressure to output air pressure. Similarly, to maximize efficiency of gas turbine engine10, spacing between turbine stator vanes in each row and the blades of turbine rotors are configured so as to produce a desired ratio of mechanical energy to input energy (in terms of fuel expended).

In addition, the compression stator vanes may have a variable geometry in that the stator vanes may change pitch to potentially optimize the performance (in terms of the ratio of mechanical energy to input energy) of gas turbine engine10across the operating range. In the example ofFIG.1, the variable stator vanes are shown as bands30A-30C (“bands30,” which may also be referred to as “variable geometry30,” “compressor variable geometry30,” “stator vanes30,” and/or “vanes30”). As such, variable geometry30may control compression provided by compressor14of gas turbine engine10. Although shown in the example ofFIG.1as having three vanes30, compressor14may have additional or less vanes30and may includes a number of vanes30equal to the number of compression stages.

Vanes30mechanically couple to a crank shaft32, which may further be mechanically coupled to a linking assembly34. Crank shaft32may also mechanically couple to support links36A and36B (“support links36”) although crank shaft32may be supported by additional or less mechanical support links36than the two support links shown in the example ofFIG.1. Linking assembly34and support links36may include couplings that allow crank shaft32to rotate axially (and possibly be displaced along a perpendicular axis to the center lengthwise axis) and thereby mechanically move vanes30to vary a pitch of vanes30.

As a measure of input energy (e.g., fuel consumed) and thereby adjust vanes30to possibly optimize performance, gas turbine engine10also includes a fuel pump and metering unit (FPMU)38. FPMU38includes a fuel pump (e.g., a fluid pump) and a fuel meter. The fuel meter may measure an amount of fuel39(or possibly other fluid) retrieved from a fuel reservoir by the fuel pump and provided to combustor18.

The fuel pump may output a high pressure fuel via a high pressure fuel line40A in excess of the amount of fuel required for combustion by combustor18. This excess fuel is returned as a low pressure fuel (relative to pressure of the high pressure fuel) via a low pressure fuel line40B. Some of the high pressure fuel is used for activation of the compressor variable geometry, where the actuation process also returns flow back to the low pressure side of the fuel pump (via low pressure fuel line40B). The actuator servo assembly uses the pressure differential across the fuel pump to generate flow and motive force to move actuator54.

An electrohydraulic servo assembly may operate with respect to an electric control signal and the fuel. The electrohydraulic servo assembly may include a stepper motor configured to rotate based on the electric control signal to interface with a mechanical mechanism that translates the rotational movement of the stepper motor into a linear movement that operates the servo valve outputting various different pressurized fuels. The actuators may receive, via the electrohydraulic servo assembly, the fuel as a way by which to adjust linear movement of the actuator that then adjusts the position of the variable geometry via crank shaft32and the linking assembly34. As such, the servo assembly may include an electrohydraulic servo assembly that receives a fluid as a high pressure fluid and a low pressure fluid.

In addition, the rotational to linear translation mechanism may be coupled to a lever that attaches to a variable geometry feedback link that indicates mechanical movement of the variable geometry, where this variable geometry feedback link is mechanically coupled to crank shaft32. The position of actuator54may, as an example, be scheduled using an engine shaft speed and an air temperature within compressor14. The engine shaft speed and air temperature within compressor14may vary with the flow of combustor18potentially depending on how engine10is being operated (e.g., accelerated, decelerated, altitude, airframe forward speed, day temperature, etc.).

However, the mechanical mechanisms required to translate rotational motion of the stepper motor into linear operation for configuring the servo valve to deliver the fuel to drive the linear motion of the actuator may be mechanically complicated and difficult to maintain. For example, the mechanical mechanism may include a linear ball screw that moves one end of the lever which displaces a servo spool of the servo valve. The servo spool then generates a pressure differential and flow to move the actuator, which then feeds back a position of crank shaft42via the feedback link to the other end of the lever.

This mechanical mechanism may increase component count that increase build costs as well as introduce a detrimental impact on mass (which may be of significant concern for airplanes) and reliability (as more components may increase points of failure). Furthermore, the number of links between the rotating components (e.g., stepper motor and ball screw) and articulating components (e.g., levers, feedback link, etc.) may create opportunities for wear and ingress of contamination. Wear of components may lead to non-linearity (e.g., backlash), which may affect accuracy of position control of the actuator. Contamination of the articulating components may impact friction in the mechanical mechanism, which may lead to detrimental impacts to accuracy of position control while potentially providing a wearout mechanism that affects the life and possibly the cost of ownership of gas turbine engine10.

In accordance with various aspects of the techniques described in this disclosure, compressor14of gas turbine engine10includes a rotary actuator assembly (RAS)50. RAS50may operate rotationally in order to potentially avoid complicated mechanical mechanisms required to translate rotational motion of servo assembly (SA)52into linear operation for configuring the servo valve to deliver the fuel to drive the linear motion of an actuator (ACT)54. SA52may include the rotary stepper motor and a rotary servo valve in which a cylindrical outer spool annularly disposed within a cylindrical outer sleeve is mechanically coupled to the rotary stepper motor. Responsive to receiving a control signal, the rotary stepper motor may rotate the cylindrical outer spool to deliver the fuel to the actuator and thereby actuate the actuator to deliver linear force to linking assembly34to control vanes30.

In operation, RAS50of gas turbine engine10includes SA52and actuator54. SA52represents an electrohydraulic servo assembly that includes a rotary servo valve coupled to a stepper motor. The stepper motor may represent a rotary stepper motor that turns at fixed steps (e.g., angular degrees) to operate the rotary servo value, which may include a cylindrical outer sleeve, a cylindrical outer spool, and a cylindrical inner spool. The cylindrical outer spool is annularly disposed within the cylindrical outer sleeve, which includes multiple ports. The ports interconnect with high pressure fuel line40A and low pressure fuel line40B. The ports also interconnect with actuator control lines60A and60B.

The cylindrical outer spool may include multiple channels configured to provide fluidic interconnection between the multiple ports and the cylindrical inner spool. The cylindrical inner spool is annularly disposed within the cylindrical outer spool and includes grooves configured to provide fluidic interconnection through the multiple channels of the cylindrical outer sleeve.

The stepper motor may mechanically connect to the cylindrical outer spool and rotate the cylindrical outer spool one or more of the fixed steps. The stepper motor may rotate the cylindrical outer spool to align the multiple channels with the ports of the cylindrical outer sleeve and the grooves of the cylindrical inner sleeve to varying degrees of overlap, thereby delivering high pressure fuel from high pressure fuel line40A or low pressure fuel from low pressure fuel line40B. SA52may output this fuel at varying pressures via actuator control lines60A and60B (“actuator control lines60”) to actuate actuator54, which may act as a piston controlled by pressure differentials between actuator control lines60to translate the hydraulic pressure differences into linear force applied to linking assembly34to crank shaft32and thereby control vanes30.

As further shown in the example ofFIG.1, actuator54is coupled to casing28of gas turbine engine10via a rotary mount64such that actuator54rotates around rotary mount64when actuated. Actuator54may couple, at rotary mount, to a mechanical coupling62, which itself is coupled to the cylindrical inner spool of the servo valve of SA52. Mechanical coupling62may provide rotary feedback that rotates the cylindrical inner spool of the rotary servo valve that may effectively disable delivery of the fuel to actuator54(and thereby stop actuation of actuator54). In other words, the linear operation of actuator54when moving vanes30may result in rotation that provides feedback to the stepper motor via mechanical coupling62(e.g., a link coupled between actuator54and the rotary servo valve and/or stepper motor of SA52). The stepper motor may also include a magnetic detent to arrest (or in other words, lock) the stepper motor in the event of electrical failure.

In this way, RAS50may avoid the complicated mechanical mechanisms to translate rotational motion of the stepper motor in SA52into linear operation for configuring the servo valve of SA52to deliver the fuel to drive the linear motion of actuator54. Mechanical coupling62, being directly coupled to actuator54(meaning there may be little to no intervening mechanical mechanisms to translate between rotational to linear movement). In addition, the benefit of potentially only utilizing rotational motion is that servo assembly52may be positioned relatively close to actuator54(and no linear compressor variable geometry feedback link is required.

Removal of the servo translational mechanism and accompanying feedback link may result in more efficient maintenance. For example, the translational mechanism (between rotational and linear movement) may be prone to wear due to the varying stresses applied during operation of gas turbine engine10and the nature of competing forces from the rotary stepper motor and the competing feedback from the feedback link. Given the hydraulic nature of RAS50, this translational mechanism may reside within the fluid and thereby require disassembly of a fluid tight case. Removal of the translational mechanism may thereby allow for more straightforward maintenance, as the wear on the mechanical coupling of RAS50may occur outside of the hydraulic system used to activate actuator54while also reducing part counts that are subject to wear.

FIG.2is a conceptual diagram illustrating the rotatory actuator assembly ofFIG.1in more detail. As shown in the example ofFIG.2, rotary actuator assembly (RAS)50includes servo assembly (SA)52and actuator54, which is mounted on rotary mount64to casing28of gas turbine engine10and mechanically coupled to SA52via mechanical coupling62(which may represent a mechanical link, such as a bar).

As further shown in the example ofFIG.2, SA52includes stepper motor70and servo valve72. Stepper motor70may represent a rotary stepper motor that is configured to rotate in fixed steps of a configurable number of angular degrees. As noted above, stepper motor70may include a magnetic detent that may arrest (or, in other words, lock) stepper motor70responsive to an electrical failure. Stepper motor70may receive a control signal indicative of a direction of rotation and a number of steps.

Servo valve72may represent a rotary servo valve (and hence may be referred to as rotary servo valve72) that is configured to connect high pressure (HP) fuel from HP line40A or low pressure (LP) fuel from LP line40B to actuator54. Rotary servo valve72may include a cylindrical outer sleeve74that includes ports76A-76C (and corresponding ports76D-76F, which are not explicitly shown for ease of illustration purposes and reside opposite to ports76A-76C by approximately 180 degrees around cylindrical outer sleeve74) that couple rotary servo valve72to HP line40A (via ports76B and76E) and LP line40B (via ports76A,76C,76D, and76F).

Cylindrical outer sleeve74also includes ports78A and78B (and corresponding ports78C and78D, which again are not explicitly shown for ease of illustration purposes and reside opposite to ports78A and78B by approximately 180 degrees around cylindrical outer sleeve74). Ports78A (and78C) couple rotary servo valve72to actuator control lines60A, while ports78B (and78D) couple rotary servo valve72to actuator control lines60B.

Rotary servo valve72also includes a cylindrical outer spool80annularly disposed within concentric outer sleeve74. Cylindrical outer spool80includes multiple channels82disposed adjacent to and directly below ports76A-76F (“ports76”) and/or ports78A-78D (“ports78”) to provide a fluidic interconnection with cylindrical outer sleeve74and a cylindrical inner spool84. Channels82may be regularly or irregularly disposed around cylindrical outer spool80and may not necessarily include corresponding channels82that are disposed around cylindrical outer spool80opposite to ports78denoted in the example ofFIG.2at approximately 180 degrees).

Rotary servo valve72may also include cylindrical inner spool84that includes multiple grooves86that are disposed around cylindrical inner spool84at 90 degree intervals. Grooves86may be offset at 90 degree intervals around cylindrical inner spool84to balance delivery of either HP fuel or LP fuel to actuator54, as discussed in more detail below with respect to the example ofFIGS.3A-3C. Grooves86may be disposed below channels82to provide a fluidic interconnection between cylindrical inner spool84and cylindrical outer spool80.

Rotary servo valve72may also include a drain86. Drain86may be arranged within a double seal along a rotary drive shaft of the cylindrical inner spool84to allow rotation of actuator54to be transmitted to cylindrical inner spool84. The double seal arrangement with intermediate drain86provides overboard leakage to contain fuel, which may pose a fire risk. Failure of the inner seal (meaning closer to rotary servo valve72compared to the outer seal which is closer to the linking mechanism62) may feed to a controlled drain point (not shown in the example ofFIG.1) on gas turbine engine10rather than a leak overboard to the engine bay.

As also shown in the example ofFIG.2, actuator54includes a housing90, a piston92disposed within housing90, an upper chamber94, a lower chamber96, and a drain98. Housing90may represent a hydraulically sealed housing in which a piston92is disposed that separates housing90into upper chamber94and lower chamber96. Housing90may include a single chamber, in other words, that piston92moves within in response to a fluid being injected via either of actuator control line60A (into upper chamber94) or actuator control line60B (into lower chamber96). Drain98may be intermediately positioned between two seals that allows any of the fuel that escapes the housing90(due to movement of piston92) to flow to drain98, and thereby potentially prevent fuel from entering the engine bay, which again may result in a fire hazard.

As discussed above, stepper motor70may receive a control signal (not shown in the example ofFIG.2for ease of illustration purposes). Responsive to receiving the control signal, stepper motor70may rotate cylindrical outer spool80to fluidly interconnect cylindrical inner spool84to ports78of cylindrical outer sleeve74, and thereby provide fuel via actuator control lines60to actuator54. Depending on whether the fuel is LP fuel or HP fuel, piston92of actuator55may move linearly up or down to move linking assembly34in order to adjust crank shaft32that moves vanes30.

Responsive to activation of piston92of actuator54, actuator54may rotate about rotary mount64that further rotates linking mechanism62that is mechanically coupled to the drive shaft of cylindrical inner spool84, providing a form of feedback by which to measure movement of actuator54(and mechanically linked crank shaft32). Rotation of linking mechanism62may turn cylindrical inner spool84so as to adjust delivery of HP fuel or LP fuel to actuator control lines60via channels82of cylindrical outer spool80(and ports78of cylindrical outer sleeve74).

RAS50may further include a rotary variable differential transformer (RVDT)100configured to produce an electrical signal representative of rotational movement of linking mechanism62between actuator54and cylindrical inner spool84. RVDT100may provide feedback to a controller (that outputs the control signal to control stepper motor70, where such controller is not shown in the example ofFIG.2for ease of illustration purposes). Although shown as being located on the rotary axis of stepper motor70and actuator54, RVDT100may be part of actuator54, SA52, or elsewhere in the actuated mechanism.

FIGS.3A-3Care diagrams illustrating cross-sectional views of the cylindrical outer spool and the cylindrical inner spool at different positions along an axis of the servo valve shown in the example ofFIG.2. In the example ofFIG.3A, cross-sectional view200A shows cylindrical outer spool80and cylindrical inner spool84at an axial location close to the drive shaft and linking mechanism62. Cylindrical inner spool84includes two grooves86A and86C that are used to deliver LP fuel via LP line40B. Groves86A and86C are offset radially by 180 degrees about the circumference of cylindrical inner spool84.

In the example ofFIG.3B, cross-sectional view200B shows cylindrical outer spool80and cylindrical inner spool84at an axial location in the middle of servo valve72. Cylindrical outer spool80includes two channels82that fluidically couple to ports78and thereby allows grooves86to fluidically interconnect through channels82to ports78, thereby providing (in this example) LP fuel from LP line40B to ports78. Cylindrical inner spool84includes four grooves86that are offset 90 degrees radially about the outer surface of cylindrical inner spool84. Grooves86A and86C provide LP fuel while grooves86B and86D provide HP fuel.

In the example ofFIG.3C, cross-sectional view200C shows cylindrical outer spool80and cylindrical inner spool84at an axial location close to stepper motor70. Cylindrical inner spool84includes two grooves86B and86D that are used to deliver HP fuel via HP line40A. Grooves86B and86D are offset radially by 180 degrees about the circumference of cylindrical inner spool84.

Rotation of cylindrical inner spool84(by way of linking mechanism62) relative to cylindrical outer spool80may change the communication between supply pressure (HP fuel) and return pressure (LP fuel) with actuator servo pressure. The second actuator servo line/port is similarly configured but clocked at 90° to the other servo porting such that when one actuator control line60is in communication with supply pressure the other actuator control line60is in communication with return pressure and vice versa.

To balance hydraulic forces from rotary spool ports78, axial grooves86are distributed symmetrically around the periphery of cylindrical outer and inner spools80/84. This symmetrical distribution may minimize asymmetric loading that can create friction between moving parts that would otherwise require more electrical power (from stepper motor70) to overcome. The differential pressure between the ends of each spool80/84may also be minimized to reduce axial loading and remove the necessity for a significant thrust bearing.

An example sequence of operation to move actuator54would be the following. First, power stepper motor70(via a control signal) to rotate stepper motor70to a new position. Cylindrical inner spool84rotates (in response to the new position of stepper motor70and movement of actuator54) allowing communication between one actuator control pressure line60and HP line40A and between the other actuator control pressure line60and LP line40B. Once friction in the actuated mechanism (e.g., crank shaft32) is overcome the linear actuator slews, changing the position of components in the engine actuated mechanism (e.g., vanes30) and also causing actuator54to rotate about rotary mount64. Rotation of actuator54about rotary mount64rotates in turn linking mechanism62, thereby rotating cylindrical inner spool84to reduce the communication between actuator control lines60and HP/LP lines40. Actuator54continues to slew until cylindrical inner spool84has moved far enough to close off (e.g., decouple) fluidic interconnection between HP line40A and actuator control lines60, at which point movement of actuator54ceases.

As another example, the operation of servo assembly52may include instances where power to stepper motor70has been lost. The ability of the controller to maintain position of actuator54in this scenario of lost power may be beneficial. Operation, in this example, would be as described above except that no input from stepper motor70is given, as stepper motor70lacks power. Movement of actuator54through loading or vibration will feed back via the above described mechanisms and produce a corrective force to push actuator54back into position. This functionality is in comparison to normal servo systems that are designed to drift to one end of their stroke when electrical power is lost, rather than stay fixed.

FIG.4is a flowchart illustrating example operation of the rotary actuator assembly ofFIG.2for control of compressor variable geometry in accordance with various aspects of the techniques described in this disclosure. Stepper motor70may initially receive a control signal (300). Stepper motor70may rotate, based on the control signal, cylindrical outer spool80within cylindrical outer sleeve74in which cylindrical outer spool80is annularly displaced within to deliver a fluid to and thereby actuate actuator54to control compressor variable geometry30(shown in the example ofFIG.1) of gas turbine engine10(302).

As noted above, there may be various corrective mechanisms (e.g., RVDT100) that avoid error due to various conditions (such as slippage in stepper motor70). RVDT1000may output a signal that allows the controller to identify an error in position, which thereby enables controller to perform corrective steps with respect to the position of actuator54.

In this way, various aspects of the techniques may enable the following clauses.

Clause 1. A rotary actuation system of a gas turbine engine comprising: a servo assembly that includes: a cylindrical outer sleeve including multiple ports; a cylindrical outer spool annularly disposed within the cylindrical outer sleeve, wherein: the cylindrical outer spool includes multiple channels configured to provide fluidic interconnection between the multiple ports and a cylindrical inner spool, the cylindrical inner spool is annularly disposed within the cylindrical outer spool, and the cylindrical inner spool includes grooves configured to provide fluidic interconnection through the multiple channels of the cylindrical outer sleeve; and a stepper motor mechanically coupled to the cylindrical outer spool; and an actuator mechanically coupled to compressor variable geometry that controls compression provided by a compressor of the gas turbine engine, wherein the stepper motor is configured to rotate the cylindrical outer spool within the cylindrical outer sleeve to deliver a fluid to and thereby actuate the actuator to control the compressor variable geometry.

Clause 2. The rotary actuation system of clause 1, wherein the actuator is coupled to a body of the gas turbine engine via a rotary mount such that the actuator rotates when actuated about a mechanical coupling to the stepper motor.

Clause 3. The rotary actuation system of clause 2, wherein the mechanical coupling between the actuator and the stepper motor rotates the cylindrical inner spool to decouple fluidic interconnection between the grooves and the multiple channels to prevent further actuation of the actuator.

Clause 4. The rotary actuation system of any combination of clauses 2 and 3, further comprising a rotary variable differential transformer configured to produce an electrical signal representative of rotational movement of the mechanical coupling between the actuator and the cylindrical inner spool.

Clause 5. The rotary actuation system of any combination of clauses 1-4, wherein the stepper motor includes a magnetic detent that locks the stepper motor in event of electrical failure to the stepper motor.

Clause 6. The rotary actuation system of any combination of clauses 1-5, wherein the actuator comprises a linear actuator that is mechanically coupled to a crank shaft of the compressor variable geometry.

Clause 7. The rotary actuation system of any combination of clauses 1-6, wherein the compressor variable geometry includes compressor vanes that are mechanically disposed to change pitch in response to actuation of the actuator by the stepper motor.

Clause 8. The rotary actuation system of any combination of clauses 1-7, wherein the fluid comprises fuel used by the gas turbine engine for combustion.

Clause 9. The rotary actuation system of any combination of clauses 1-8, wherein the servo assembly comprises an electrohydraulic servo assembly that receives the fluid as a high pressure fluid and a low pressure fluid, wherein the grooves of the cylindrical inner spool are disposed around the cylindrical inner spool at 90 degree intervals, wherein the actuator comprises a hydraulic actuator that drives a piston via varying fluid pressures, and wherein the stepper motor is configured to rotate the cylindrical outer spool to deliver either the high pressure fluid or the low pressure fluid via the channels to the ports in order to actuate the hydraulic actuator to drive the piston mechanically coupled to the compressor variable geometry.

Clause 10. The rotary actuation system of clause 9, wherein the servo assembly is fluidically coupled to a fluid pump that delivers the high pressure fluid and the low pressure fluid to the servo assembly.

Clause 11. A method comprising: receiving a control signal; and rotating, by a stepper motor of a servo assembly and based on the control signal, a cylindrical outer spool within a cylindrical outer sleeve in which the cylindrical outer spool is annularly displaced within to deliver a fluid to and thereby actuate an actuator to control compressor variable geometry of a gas turbine engine, wherein the cylindrical outer sleeve includes multiple ports, wherein the stepper motor is mechanically coupled to the cylindrical outer spool, wherein the cylindrical outer spool includes multiple channels configured to provide fluidic interconnection between the multiple ports and a cylindrical inner spool, wherein the cylindrical inner spool is annularly displaced within the cylindrical outer spool, the cylindrical inner spool including grooves configured to provide fluidic interconnection through the multiple channels of the cylindrical outer sleeve, and wherein the actuator is mechanically coupled to the compressor variable geometry.

Clause 12. A gas turbine engine comprising: a combustor; a compressor fluidically upstream of the combustor that includes compressor variable geometry configured to control compression by the compressor; and a rotary actuation system mounted to a body of the gas turbine engine, the rotary actuation system including: a servo assembly that includes: a cylindrical outer sleeve including multiple ports; a stepper motor mechanically coupled to a cylindrical outer spool annularly displaced within the cylindrical outer sleeve; the cylindrical outer spool including multiple channels configured to provide fluidic interconnection between the multiple ports and a cylindrical inner spool; and the cylindrical inner spool annularly displaced within the cylindrical outer spool, the cylindrical inner spool including grooves configured to provide fluidic interconnection through the multiple channels of the cylindrical outer sleeve; and an actuator mechanically coupled to the compressor variable geometry, wherein the stepper motor is configured to rotate the cylindrical outer spool within the cylindrical sleeve to deliver a fluid to and thereby actuate the actuator to control the compressor variable geometry.

Clause 13. The gas turbine engine of clause 12, wherein the actuator is coupled to a body of the gas turbine engine via a rotary mount such that the actuator rotates when actuated about a mechanical coupling to the stepper motor.

Clause 14. The gas turbine engine of clause 13, wherein the mechanical coupling between the actuator and the stepper motor rotates the cylindrical inner spool to decouple fluidic interconnection between the grooves and the multiple channels to prevent further actuation of the actuator.

Clause 15. The gas turbine engine of any combination of clauses 13 and 14, further comprising a rotary variable differential transformer configured to produce an electrical signal representative of rotational movement of the mechanical coupling between the actuator and the cylindrical inner spool.

Clause 16. The gas turbine engine of any combination of clauses 12-15, wherein the stepper motor includes a magnetic detent that locks the stepper motor in event of electrical failure to the stepper motor.

Clause 17. The gas turbine engine of any combination of clauses 12-16, wherein the actuator comprises a linear actuator that is mechanically coupled to a crank shaft of the compressor variable geometry.

Clause 18. The gas turbine engine of any combination of clauses 12-17, wherein the compressor variable geometry includes compressor vanes that are mechanically disposed to change pitch in response to actuation of the actuator by the stepper motor.

Clause 19. The gas turbine engine of any combination of clauses 12-18, wherein the fluid comprises fuel used by the gas turbine engine for combustion.

Clause 20. The gas turbine engine of any combination of clauses 12-19, wherein the servo assembly comprises an electrohydraulic servo assembly that receives the fluid as a high pressure fluid and a low pressure fluid, wherein the grooves of the cylindrical inner spool are disposed around the cylindrical inner spool at 90 degree intervals, wherein the actuator comprises a hydraulic actuator that drives a piston via varying fluid pressures, and wherein the stepper motor is configured to rotate the cylindrical outer spool to deliver either the high pressure fluid or the low pressure fluid via the channels to the ports in order to actuate the hydraulic actuator to drive the piston mechanically coupled to the compressor variable geometry.