Patent ID: 12234777

DETAILED DESCRIPTION

The present disclosure is directed to gas-turbine engine systems, e.g., for gas-turbine engine powered vehicles such an aircraft, and techniques for operating the same. For ease of description, examples of the disclosure will be primarily described in the context of aircraft as a gas-turbine engine powered vehicle. However, examples of the disclosure are not limited to aircraft. For instance, aspects of this disclosure may be applicable to gas-turbine powered ground vehicles, watercraft, and the like.

Starting a gas turbine engine may require rotation of a compressor to a speed that provides sufficient pressurized air into combustion chambers of the gas turbine engine. Accordingly, energy for starting the gas turbine engine may be supplied by another source separate from the gas turbine engine, which may be a starter motor. The starter motor may use power from internal combustion, electric power, or other suitable power source to turn a first shaft, which may be mechanically coupled to an accessory gearbox of the gas turbine engine via a clutch assembly to the gas turbine engine, such that shaft work output by the starter motor may be used to start the gas turbine engine by rotating a compressor mechanically fixed to the first shaft, which is turned by the starter motor.

The starter motor may also be used in barring applications. In a barring application, which may occur at the tail end of a gas turbine operation (e.g., a flight) or after an operation of the gas turbine engine, the gas turbine engine may be shut off or powered down. However, to more uniformly cool components of the gas turbine engine, shaft work from the starter motor may cause portions of the gas turbine engine to slowly rotate (e.g., relative to the rotation of the gas turbine engines during propulsion operations) to promote heat transfer from relatively hot portions of the gas turbine engine to relatively cooler portions. As such, the starter motor may provide the dual-purpose of starting the gas turbine engine before a propulsion operation and barring the gas turbine engine at the conclusion of the propulsion operation.

In some examples, the starter motor may be permanently mechanically coupled and be rotationally fixed to the gas turbine engine. In such examples, one or more rotationally fixed shafts may mechanically couple an accessory gearbox of the gas turbine engine and the starter motor, so that the gas turbine engine and the start motor are configured to rotate simultaneously. Such an arrangement may disadvantageously drive rotational motion of the starter motor when the starter motor is not needed for either starting or barring operations. During these time periods, permanent magnets in the starter motor may induce a current in a stator of the starter motor, which may generate heat. Unnecessarily moving parts and excessive heat may cause component fatigue which may shorten the useful life of components, and/or may cause a performance penalty (e.g., increased fuel burn), or may present other failure modes or degraded operation.

For safety and reliability, it may be desired to disengage the starter motor from the accessory gearbox during operations when the starter motor is not needed (e.g., propulsion operations of the gas turbine engine), and to engage or reengage the starter motor during operations when the starter motor is needed (e.g., starting and/or barring applications). In this way, unnecessary rotation of the starter motor and the associated generation of heat may be reduced or minimized. A clutch assembly may be used to disengage a first shaft associated with the starter motor from a second shaft associated with the accessory gearbox of the gas turbine engine. In some examples, the clutch assembly may be an active clutch assembly which uses control circuitry of a controller to send a signal to actuate a clutch mechanism to disengage or engage the clutch. The actuation of the clutch mechanism may be electromagnetic, hydraulic, pneumatic, or the like. Active clutch arrangements may disadvantageously add weight and/or complexity to the mechanical system. Additionally, active clutch arrangements may be prone to failure due to one or more components or processes of the complex systems breaking down.

Clutch assemblies according to the present disclosure may address one or more of the disadvantages associated with conventional clutch systems. For example, clutch assemblies according to the present disclosure may be configured to passively disengage the starter motor from the accessory gearbox of the gas turbine engine. Passive disengagement, as described herein, means that the clutch assembly is configured to mechanically disengage without a signal from control circuitry of a controller when a torque associated with the gas turbine engine exceeds a threshold level. In some examples, the threshold level may be reached when the torque from the gas turbine engine exceeds the torque from the starter motor. The passive clutch assembly may reduce or eliminate components necessary for active disengagement of the clutch, and accordingly may reduce the weight of the clutch assembly.

In some examples, the starter motor may be configured to apply a torque to the first shaft which causes the first shaft to rotate about a first shaft central axis, and the accessory gearbox may be configured to apply a torque to the second shaft which causes the second shaft to rotate about a second shaft central axis. The first clutch member and the second clutch member may be configured to passively disengage from each other when the torque of the second shaft exceeds the torque of the first shaft. In this way, the starter motor may supply the energy necessary to start the gas turbine engine, but may disengage from the gas turbine engine once it has started so that the starter motor does not run in “whirl” mode throughout the entire operation of the gas turbine engine. “Whirl” mode may involve the starter motor spinning without energy input, due to rotation of the second shaft. Running the starter motor in whirl be leaving the starter motor engaged to the gas turbine engine after the gas turbined engine has started may have deleterious effects including efficiency losses, heat generation, or the like.

Clutch assemblies according to the present disclosure may actively reengage the clutch assembly. Active reengagement, as used herein, means that the clutch assembly is configured to reengage the first surface of the first clutch member and the second surface of the second clutch member via a signal from control circuitry of a controller. Engagement of the first surface and the second surface may cause frictional engagement of the first clutch member and the second clutch member such that rotational motion may be transferred between the clutch members. In some examples, the first surface and the second surface may lock together such that there is no relative motion or substantially no relative motion between the first surface and the second surface when the clutch assembly is completely engaged.

Rather than relying on a separate actuation system, the axially offset permanent magnets of the starter motor may combine to provide an axial force for reengagement of the clutch assembly when the starter motor is energized. The misalignment of two axial electrical centers (one on the rotor with its permanent magnets and one on the stator) may cause an axial force sufficient to bring the clutch assembly together for reengagement. This phenomenon may be called the axial attractive force (AAF). In this way, a signal may energize the starter motor, and may cause the first shaft to translate axially from a disengaged position where the first and second clutch members are not in contact to an engaged position where the first and second clutch members contact each other and interface to translate rotational motion between them.

In some examples, the first clutch member may include a plurality of helical splines disposed spirally about the circumference of the first shaft, and the second clutch member may include a hub defining a plurality of helical grooves configured to receive the helical splines, or vice versa. The helical splines may get more engaged (e.g., translate axially further into the hub) as the starter motor provides more torque, and disengage as the starter motor torque diminishes, disengaging when the torque direction reverses (i.e., the torque exerted on the second shaft by the gas turbine engine exceeds the torque exerted on the first shaft by the starter motor). A helical spline/hub arrangement of the first and second clutch members may advantageously provide increased surface area for engagement because the helical splines and grooves may engage each other over an axial length. The increased surface area for engagement may efficiently transfer rotational motion between the clutch members, while reducing material stresses relative to other types of clutch members. Additionally, or alternatively in some examples, the first clutch member and the second clutch member may be opposing lock plates, which may advantageously allow for high stress engagement over a lower axial length. When the distance between the engagement position and disengagement position of the first shaft is less than a threshold distance (e.g., about 5 millimeters), a lock plate arrangement may be desirable.

In some examples, clutch assemblies according to the present disclosure may include a speed matching system that may be activated before or during reengagement of the first clutch member and the second clutch member to reduce the probability of a jam or damage to one or more components. The speed matching system may include a speed sensor on each of the first shaft and the second shaft. The speed matching system may be configured to control the starter motor, while the first clutch member and second clutch member are disengaged, to rotate the first shaft about a first shaft central axis at substantially the same rotational speed that the second shaft is rotating about a second shaft central axis. In this way the first clutch member and the second clutch member may be rotating at substantially the same rotational speed when they actively reengage with each other. Substantially the same speed, as described herein, may be an equal rotational speed or a rotational speed within plus or minus 10 percent. It should also be noted that as used herein, relational terms, such as “first” and “second,” “over” and “under,” “front” and “rear,” and the like, may be used solely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or elements.

FIG.1is a conceptual diagram illustrating an example system100including clutch assembly106. System100may include, for example, a starter motor108(motor108) coupled to a first shaft114, an engine102, a drive shaft112, an accessory gear box104coupled to a second shaft116, a clutch assembly106, and a controller110. As will be described further below, clutch assembly106includes two clutch members109(individually shown as first clutch member122and second clutch member124inFIG.2Afor example). System100may include any suitable mechanical system, mobile or stationary. In some examples, system100may include at least a portion of a mechanical system of a vehicle (e.g., an aircraft, a boat, a truck, etc.) powered by an internal combustion engine. In some examples, system100may include a gas turbine engine, whether the gas turbine engine is stationary and used for industrial purposes or attached to a vehicle. As one specific example, system100may include at least a portion of a mechanical system of an aircraft powered by a gas turbine engine. For instance, system100may form a part of a system that includes an aircraft engine (e.g., turbine engine) that drives a reduction gearbox.

Engine102may be mechanically coupled to accessory gear box104via drive shaft112. Engine102is configured to rotate (e.g., drive) drive shaft112.

Drive shaft112may include any suitable shaft and/or gear system to transfer shaft work from engine102to accessory gear box104. In examples in which engine102includes a gas turbine engine, drive shaft112may include an internal gearbox including a direct drive, a stub shaft drive, an idler shaft drive, or other mechanical coupling configured to drive a radial drive shaft or tower shaft. In some examples, drive shaft112may include an intermediate gearbox.

Accessory gearbox104is configured to transfer shaft work from drive shaft112to second shaft116and vice versa. In some examples, accessory gearbox104may include an accessory drive of a gas turbine engine system. Although illustrated as a single second shaft116, system100may include two or more input shafts driven by drive shaft112via accessory gearbox104. For example, accessory gearbox104may include a plurality of spur gears mechanically coupling drive shaft112to respective input shafts of a plurality of auxiliary gearbox mechanisms such as oil pumps, fuel pumps, alternators, etc (not shown), each at a selected gear ratio.

Starter motor108is configured to rotate (e.g., drive) first shaft114. Starter motor108may include any suitable motor to output shaft work, such as one or more internal combustion engines, fuel cells, electric motors or generators, pneumatic motors, or hydraulic motors. Starter motor108may start gas turbine engine102by driving first shaft114. Starter motor108may include stator111and rotor113. In some examples, In some examples, rotor113may be a “floating” rotor which is allowed to translate axially back and forth along arrow A inFIG.1. Stator111may include one or more permanent magnets configured to generate a magnetic field that causes rotor113to rotate when energy is supplied to starter motor108. Stator111may define an electrical center, which may be positioned at the center of the axial length of the magnetic elements of stator111and labeled ECSinFIG.1.

Similarly, rotor113may define an electrical center, which may be positioned at the center of the axial length of the magnetic elements of rotor113. At a rest position when starter motor108is not energized, the electrical center of rotor113, labeled ECRRinFIG.1, may be offset or displaced from the electrical center of stator ECSin an axial direction. When energy is supplied to starter motor108, magnetic attraction, which may be called the axial attractive force and labeled AAF inFIG.1, between magnetic elements in stator111and rotor113may cause axial translation of rotor113such that the electrical center of rotor113when starter motor108is energized translates to the position labeled ECREinFIG.1. Although illustrated as slightly axially separated inFIG.1, in some examples ECSand ECREmay occupy the same axial position.

Rotor113may be mechanically coupled to first shaft114such that rotational motion of rotor113is transferred to first shaft114, causing rotation of first shaft114. Similarly, axial translation of rotor113may be transferred to first shaft114such that first shaft114may translate axially to engage clutch assembly106when power is supplied to starter motor108. The rotational motion of first shaft114may be transferred by clutch assembly106to second shaft116, then through accessory gearbox104into drive shaft112. In this way, while the first and second clutch members122,124(shown inFIG.2A) of clutch assembly106are engaged, system100may be operated such that either starter motor108drives rotation of gas turbine engine102, or vice versa.

For example, to start gas turbine engine102, first shaft114may be selectively coupled to second shaft116via clutch assembly106so that second shaft116is rotationally driven by first shaft114when clutch assembly106is engaged and, conversely, when clutch assembly106is disengaged, second shaft116is not driven by first shaft114. First shaft114may be coupled (e.g., rotationally fixed) to first clutch member122(shown inFIG.2A) of clutch assembly106, and second clutch member124(shown inFIG.2A) of clutch assembly106may be coupled (e.g., rotationally fixed) to second shaft116. Although system100is described herein primarily with first clutch member122being fixed to first shaft114and with second clutch member124being fixed to second shaft116, in other examples, first clutch member122may be fixed to second shaft116and second clutch member124may be fixed to first shaft114.

In some examples, system100may include speed matching system119. Speed matching system119may include at least one of speed sensors115and117. Speed sensors115and117are configured to sense a rotational speed of first shaft114(or a clutch member coupled to first shaft114) and second shaft116(or a clutch member coupled to second shaft116), respectively. For example, speed sensors115and/or117may include one or more of a reflective sensor, an interrupter sensor, an optical encoder, a variable-reluctance sensor, an eddy-current killed oscillator sensor, a Wiegand sensor, or a Hall-effect sensor. In some examples, speed sensors115and/or117may be configured to determine a rotation of first shaft114or second shaft116, respectively, based on sensing a target disposed on input shaft114(or the first clutch member) or second shaft116(or the second clutch member). In some examples, controller110may be configured to receive signals from at least one of speed sensors115or117and control, based on a rotational speed determined based on the signal, power supplied to starter motor108or gas turbine engine102to substantially match the rotational speed to the other shaft, prior to causing engagement of clutch assembly106.

FIG.2Aillustrates a portion of clutch assembly106ofFIG.1. As mentioned above, clutch assembly106includes first clutch member122and second clutch member124. With concurrent reference to bothFIG.1andFIG.2A, first clutch member122and second clutch member124may be configured to passively disengage from each other and actively reengage with each other, as will be further described below. For example, first clutch member122and second clutch member124may be configured to passively disengage from each other mechanically without being controlled by control logic of controller110. In this way, first clutch member122and second clutch member124may automatically disengage after engine102is started and the torque on second shaft116exceeds a threshold torque. In some examples, the threshold torque may be the torque on first shaft by starter motor108.

First clutch member122and second clutch member124may be configured to actively reengage with each other via a signal from control circuitry of controller110. To engage clutch assembly106, controller110may move first clutch member122towards second clutch member124to frictionally engage opposing surfaces of members122,124. Controller110may send a signal causing selective reengagement of clutch assembly106as described herein, e.g., to selectively drive second shaft116via first shaft114, such as in a barring application. For example, as described further below, controller110may control the axial position of first clutch member122relative to second clutch member124as described below. In some examples, to actively reengage first clutch member122and second clutch member124, an electrical center of stator111of starter motor108and an electrical center of rotor113of starter motor108may be offset. For example, the electrical centers may be offset in an axial direction (A inFIG.1). The electrical center of rotor113may be further away in an axial direction from clutch assembly106than the electrical center of stator111. Additionally, rotor113may be mechanically supported in a way that allows for axial translation of rotor113. In this way, when power is supplied to starter motor108, electromagnetic attraction between the electrical centers may cause rotor113to translate towards clutch assembly106(to the left along axis A inFIG.1).

When first clutch member122is in the disengaged position, energy supplied to starter motor108generates an axial force (to the left along axis A inFIG.1) on first shaft114sufficient to reengage first clutch member122and second clutch member124. Advantageously, in some examples, additional electromagnets may be omitted because actuation of the slidable translation of first shaft114to the engagement position may be accomplished by energization of starter motor108. In this way, the permanent magnets of starting motor108may be used to actuate translation of first shaft114to engage clutch assembly106.

Controller110may include, for example, a computing device, a desktop computer, a laptop computer, a workstation, a server, a mainframe, a cloud computing system, a tablet, a smart phone, or the like. Controller110is configured to control operation of system100, including, for example, the power supplied to starter motor108and thus the position of first clutch member122relative to second clutch member124. Controller110may be communicatively coupled to the various component of system100including, e.g., sensors115and/or117, and/or the like using respective communication connections. In some examples, the communication connections may include network links, such as Ethernet, ATM, or other network connections. Such connections may be wireless and/or wired connections. In other examples, the communication connections may include other types of device connections, such as USB, IEEE 1394, or the like. In some examples, controller110may include control circuitry, such as one or more processors, including one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. The term “processor” or “processing circuitry” may generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry. In some examples, controller110may be an Electrical Engine Controller (EEC) or Full Authority Digital Engine Controller (FADEC).

FIG.2Aillustrates first clutch member122and second clutch member124of clutch assembly106ofFIG.1from a perspective view. First clutch member122is positioned proximate first end134of first shaft114. Although illustrated as mounted on first end134of shaft114and extending axially beyond first end134, in some examples first end134of first shaft114may extend axially beyond first clutch member122. Similarly, although second clutch member124is illustrated as mounted proximate to first end136of second shaft116, in some examples shaft116may extend axially beyond second clutch member124. Thus, positioned proximate to a first end of shaft114, when used in this context, means that first clutch member122is positioned closer to first end134than the distal second opposite end.

First shaft114and first clutch member122are configured to rotate about first shaft central axis L1under power from starter motor108(FIG.1), or gas turbine engine102(FIG.1) through accessory gearbox104(FIG.1) when clutch assembly106is engaged. Similarly, second shaft116and second clutch member124are configured to rotate about second shaft central axis L2when under power from gas turbine engine102(FIG.1) through accessory gearbox104(FIG.1) when clutch assembly106is in an engaged state. In some examples, as illustrated, axes L1and L2may be collinear, although other arrangements are considered.

In some examples, as illustrated, first clutch member122and second clutch member124may be arranged such that first clutch member122includes a plurality of helical splines130A,130B (other helical splines not labeled inFIG.2Afor clarity) (collectively, “helical splines130”) disposed spirally about the circumference of first shaft114. Helical splines130are described as wrapping spirally about first shaft114, but need not make a full revolution about a circumference of shaft114. Rather, helical splines130need only to curve about a portion of the circumference of shaft114. Second clutch member124may include hub140. Hub140may define a plurality of helical grooves132A,132B (other helical grooves not illustrated for clarity) (collectively, “helical grooves132”) configured to receive helical splines130. First surface142, which covers first clutch member122, is configured to contact second surface144, the interior surface of hub140, of second clutch member124. Advantageously, first clutch member122may axially translate further into second clutch member124when starter motor108(FIG.1) applies more torque to first shaft114than gas turbine engine102(FIG.1) applies to second shaft116, inducing more surface area contact between surfaces142and144. In this way, first clutch member122may be configured to screw into second clutch member124to axially translate from the disengaged position, where there is no or little contact between surfaces142and144, to an engaged position where there is contact between surfaces142and144along at least a portion of the axial length of first clutch member122.

Helical splines130and/or helical grooves132may include one or more optional modifications configured to reduce material stresses induced by engagement of first clutch member122and second clutch member124, and thus may prolong the life of the components of clutch assembly106. For example, each respective helical spline130A of helical splines130may define spline width WS. Each corresponding helical groove132A of helical groves132may define groove width WG. In some examples, as illustrated, the magnitude of groove width WGis larger than the magnitude of the spline tooth width WS. In some examples, WG/WSmay be at least 1.10, or at least about 1.05, which may advantageously allow for translation of helical splines130into grooves132without excess material stresses. This difference is magnified in the illustration ofFIG.2Afor clarity. Additionally, or alternatively, as shown inFIG.2B, at least one helical spline130A of a plurality of helical splines130may define a bullnose shape at first end146of first clutch member122. The bullnose shape may be a rounded off or angular corner configured to reduces stresses in helical spline130A during engagement with hub140. In some examples, as illustrated the bullnose shape defined by spline130may mean that helical spline130A does not include a sharp edge at first end146, so that damage to hub140may be reduced.

FIGS.3A and3Bare schematic side view diagrams illustrating clutch assembly106ofFIGS.1and2in an engaged position and a disengaged position, respectively. As illustrated, helical splines130are omitted from first clutch member122, and helical grooves are omitted for second clutch member124, for clarity. First shaft114is configured to slidably translate across distance D to transition between the engaged position illustrated inFIG.3A, in which at least a portion of first surface142of first clutch member122is in contact with and opposes second surface144of second clutch member124, and the disengaged position illustrated inFIG.3B, where surfaces142,144, do not oppose.

With concurrent reference toFIGS.1and3A, as described above, starter motor108is configured to apply a torque to first shaft114, illustrated inFIGS.3A and3Bas force T1. Gas turbine engine102is configured to apply a torque to second shaft116as force T2. In some examples, as illustrated, torque T1exceeds torque T2, as illustrated by the thicker arrow inFIG.3A. In these examples, the energy supplied to starter motor108to drive first shaft114may cause first shaft114to translate axially due to the electrically offset stator111and rotor113, driving first clutch member122and second clutch member124to be engaged in the illustrated engagement position. Therefore, rotational motion of first clutch member122can be transferred to second clutch member124. As such, starter motor108may start gas turbine102or reengage gas turbine engine102for a barring application.

In some examples, as illustrated inFIG.3B, torque T2may exceed torque T1, such as, for example, during a cruise operation where energy is not supplied to starter motor108and gas turbine engine102is in a propulsion operation. Helical splines130(FIG.2A) of first clutch member122may be configured to unthread from helical grooves132(FIG.2) of second clutch member124. Thus, clutch assembly106may be configured to passively disengage without a signal from control circuitry of controller110. The centripetal force from the relative rotation of second shaft116may slidably engage helical splines130and helical grooves132(FIG.2A) to translate first shaft114relative to second shaft116, such that first clutch member122and second clutch member124disengage.

FIGS.4A and4Billustrate system200including clutch assembly206. Clutch assembly206includes first shaft214, first clutch member222.FIGS.4A and4Billustrating clutch assembly206correspond toFIGS.3A and3Billustrating clutch assembly106as described above, where similar reference characters indicate similar elements. In this example, clutch assembly206includes biasing spring250.

Biasing spring250is configured to assist in passively disengaging first clutch member222and second clutch member224by applying spring force F. As illustrated, the mechanism for assisting in passive disengagement of clutch assembly206is a spring, but other suitable mechanisms are considered. For example, additionally, or alternatively, clutch assembly206may include one or more stacking disc springs (e.g., a Belleville washer spring stack), wave springs, spiral spring, centrifugal, or hydraulic pressure systems configured to help push first shaft214towards the disengagement position illustrated inFIG.4Bfrom the engagement position illustrated inFIG.4A. In the example ofFIGS.4A and4B, biasing spring250is illustrated in a compressed state inFIG.4Aand a default/rest position inFIG.4B, such that spring force F is acting on first clutch member222inFIG.4A.

Although illustrated as a single spring in the illustrated example, clutch assembly206may include more than one biasing spring, such as two, three, or four biasing springs. Although illustrated as an expansion force pushing first clutch member122and second clutch member124apart inFIGS.4A and4B, spring force F may be a contraction force in other examples. Spring force F is configured to assist in passively disengaging clutch assembly206by being configured to assist in translating first shaft214from the engagement position to the disengagement position.

Clutch assembly206may overcome spring force F in order to actively reengage first clutch member222and second clutch member224for a barring application. Stated similarly, system200is configured to generate an axial attractive force (AAF,FIG.1) from the offset centers ECS, ECRRof stator111and rotor113, respectively of starter motor108(FIG.1). In some examples, force AAF may be of greater magnitude than spring force F of biasing spring250. Therefore, spring force F should be selected to meet the needs of the application, as the AAF will generally scale with the size of the machine, and may change based on the shape and topology of stator111and rotor113. In some examples, which are not intended to be limiting, the AAF may be in a range of from about 5 Newtons (N) to about 1000 N, such as from about 10 N to about 150 N. The word “about,” as used herein, encompasses values within plus or minus five percent of the stated value.

Biasing spring250may be mechanically supported by one or more spring supports252. Springs supports252may be configured to anchor and/or secure the ends of spring250. Spring supports252may be mounted on first shaft214, second shaft216, both, or on another part of system200.

FIG.5illustrates first lock plate322of example clutch assembly306of system300. Clutch assembly306may be an example of clutch assembly106ofFIG.1, and first lock plate322may be an example of first clutch member122.

In the illustrated example, rather than a splined shaft and hub arrangement as illustrated above with respect to clutch assembly106, first clutch member322and the second clutch member (not illustrated) are opposing lock plates, and first clutch member322may also be referred to as first lock plate322. Although only first lock plate322is shown inFIG.5, the second clutch member (not illustrated) may be a similar lock plate configured to oppose and interface with first clutch member322.

First lock plate322defines a surface342that has a larger diameter D2than diameter D1of first shaft314. Although illustrated and described herein as a circular lock plate having a diameter, it is also considered that lock plate322may define another cross-sectional shape taken along an axial plane, and the shape may have at least one dimension that is larger than diameter D1of first shaft314.

First lock plate322defines a plurality of teeth360A,360B (collectively “teeth360”). At least one tooth360A of teeth360may be asymmetrical, in that a plane passing through tooth360A and central axis L1does not cut the tooth into equal volumes. Rather, tooth360A defines a sloped face362relative to a face cut along a radial cross-section of first lock plate322. The second lock plate (not illustrated) may have teeth configured to intermesh and seat with grooves364between teeth360. As such, the interfacing teeth may be configured to transfer rotational motion between first lock plate322and the second lock plate. Relative to the splined shaft and hub arrangement illustrated and described above, the lock plate arrangement ofFIG.5may provide similar or increased surface area for engagement between the two clutch members over a shorter axial distance, which may be desirable in some instances, and may allow for implementation smaller systems, or in systems with alternative arrangements. For example, a lock plate arrangement may advantageously allow for reduced volume or weight of clutch assembly306.

In some examples, a distance between the engagement position and the disengagement position of the clutch assembly may be separated by a distance of from about 1 millimeter (mm) to about 10 mm, or from about 3 millimeters (mm) to about 10 mm. In examples nearer to the bottom end of the range, a lock plate arrangement may be desirable.

FIG.6is a flowchart illustrating an example technique for operating a clutch assembly according to the present disclosure. Although primarily described herein with respect to clutch assembly106ofFIGS.1-3B, clutch assembly206ofFIGS.4A and4B, and clutch assembly306ofFIG.5, the illustrated technique may be performed with another clutch assembly, and other clutch assemblies may be used to perform the illustrated technique.

With concurrent reference toFIGS.1-3BandFIG.6, the technique ofFIG.6includes engaging first clutch member122and second clutch member124(400). Step400may occur at a first time, such as, for example, during a starting of gas turbine engine102. First clutch member122is disposed near first end134of first shaft114. First clutch member122defines first surface142. Starter motor108may be coupled to a second end of first shaft114. Second clutch member124may be disposed near first end136of second shaft116. Second clutch member124member may define second surface144opposing first surface142, and accessory gearbox104of gas turbine engine102may be coupled to a second end of second shaft116. When first clutch member122is engaged with second clutch member124, first surface142of first clutch member122engages second surface144of second clutch member124such that rotational motion may be transferred between first clutch member122and second clutch member124.

The technique ofFIG.6also includes passively disengaging first clutch member122and second clutch member124(402). In some examples, passively disengaging first clutch member122and second clutch member124may include disengaging first clutch member122and second clutch member124from each other mechanically without a signal from control circuitry of controller110. In some examples, step402may occur at a second time that is after the first time, such as, for example, at the conclusion of a starting operation of gas turbine engine102or during a cruising operation of gas turbine engine102.

In some examples, starter motor108may to apply a torque T1to first shaft114which causes first shaft114to rotate about first shaft central axis L1. Gas turbine engine102, via accessory gearbox104, may apply torque T2to second shaft116which causes second shaft116to rotate about second shaft central axis L2. In some examples, step402, passively disengaging first clutch member122and second clutch member124may include applying torque T2to second shaft116that exceeds torque T1applied to first shaft114. In some examples, step402, passively disengaging first clutch member122and second clutch member124may include axially translating first shaft114from an engagement position (FIG.3A) where first clutch member122is engaged with second clutch member124to a disengagement position (FIG.3B) where first clutch member122and second clutch member124are disengaged.

With reference toFIG.4A,FIG.4B, andFIG.6, in some examples step402, passively disengaging first clutch member122and second clutch member124, may include applying spring force F from biasing spring250to assist in translating first shaft114from the engagement position (FIG.4A) to the disengagement position (FIG.4B). In some examples, the engagement position and the disengagement position may be separated by a distance of from about 1 mm to about 10 mm, or from about 3 mm to about 10 mm.

The technique ofFIG.6also includes actively reengaging first clutch member122and second clutch member124(404). Step404may occur at a third time, which may be after the second time, such as during a re-start operation or during a barring operation of gas turbine engine102. In some examples, actively engaging first clutch member122and second clutch member124may include delivering a signal from control circuitry of controller110. In some examples, step404, actively reengaging first clutch member122and second clutch member124may include engaging a plurality of helical splines130disposed spirally about the circumference of first shaft114with hub140. Hub140may define a plurality of helical grooves132configured to receive helical splines130. In some examples, each respective helical spline130A of plurality of helical splines130may define spline width WS. Similarly, each helical groove132A of plurality of helical grooves132may define groove width WG. In some examples, the magnitude of groove width WGmay be larger than the magnitude of spline width WS. In some examples, at least one spline130A of splines130may define a bullnose shape (FIG.2B) at first end146of first clutch member122. The bullnose shape may be configured to reduce material stresses induced by engagement with hub140. In some examples, the technique ofFIG.6further includes delivering a signal, via control circuitry of controller110, to actively reengage first clutch member122and second clutch member124with each other.

Referring now toFIGS.5and6, in some examples, first clutch member322may be a first lock plate322. First lock plate322may define diameter D2, which may be larger than diameter D1defined by first shaft114. In some examples, the second clutch member (not pictured inFIG.5) may be a second lock plate that defines a larger diameter than the second shaft. Each of first lock plate322and the second lock plate may define a plurality of teeth360. At least one tooth360A of teeth160defined by first lock plate322may be an asymmetrical tooth which defines a sloped face362disposed at an acute angle relative to a face of first lock plate322. In some examples, each of teeth360may be asymmetrical, and may be configured to intermesh with a corresponding tooth of the second lock plate (not illustrated) such that rotational motion may be transferred.

Referring back toFIGS.1-3B and6, in some examples, actively reengaging first clutch member122and second clutch member124may include generating an axial force on first shaft114by supplying energy to starter motor108. In some examples, generating the axial force may include using the axial attractive force (AAF) by offsetting the electrical centers of stator111and rotor113along axial axis A (FIG.1.).

In some examples, actively reengaging first clutch member122and second clutch member124may include operating speed matching system119. Operating speed matching system119may include rotating first shaft114about first shaft central axis L1at substantially the same rotational speed that second shaft116is rotating about central axis L2, such that first clutch member122and second clutch member124are rotating at substantially the same rotational speed when they actively reengage with each other. In some examples, speed matching system119may include first speed sensor115on first shaft114and second speed sensor117on second shaft116.

In some examples, the technique ofFIG.6may further include operating gas turbine engine102. Operating gas turbine engine102may include engaging first clutch member122and second clutch member124during a starting operation, passively disengaging first clutch member122and second clutch member124during a cruise operation of gas turbine engine102, and actively reengaging first clutch member122and second clutch member124during a barring operation of gas turbine engine102.

Various examples have been described. These and other examples are within the scope of the following clauses and claims.

Clause 1: A clutch assembly includes a first clutch member disposed near a first end of a first shaft, the first clutch member defining a first surface, and a starter motor coupled to a second end of the first shaft; and a second clutch member disposed near a first end of a second shaft, the second clutch member defining a second surface opposing the first surface, and an accessory gearbox of a gas turbine engine coupled to a second end of the second shaft, wherein, when the first clutch member is engaged with the second clutch member, the first surface of the first clutch member engages the second surface of the second clutch member such that rotational motion is transferred between the first clutch member and the second clutch member, and wherein the first clutch member and the second clutch member are configured to passively disengage from each other and actively reengage with each other.

Clause 2: The clutch assembly of clause 1, wherein the first clutch member and the second clutch member are configured to passively disengage from each other mechanically without being controlled by control logic, and wherein the first clutch member and the second clutch member are configured to actively reengage with each other via a signal from control circuitry of a controller.

Clause 3: The clutch assembly of clause 1 or clause 2, wherein the starter motor is configured to apply a torque to the first shaft which causes the first shaft to rotate about a first shaft central axis, the accessory gearbox of the gas turbine engine is configured to apply a torque to the second shaft which causes the second shaft to rotate about a second shaft central axis, and wherein the first clutch member and the second clutch member are configured to passively disengage from each other when the torque of the second shaft exceeds the torque of the first shaft.

Clause 4: The clutch assembly of any of clauses 1-3, wherein the first shaft is configured to translate axially between an engagement position where the first clutch member is engaged with the second clutch member and a disengaged position wherein the first clutch member and the second clutch member are disengaged.

Clause 5: The clutch assembly of any of clauses 4, further comprising a biasing spring configured to assist in translating the first shaft from the engagement position to the disengagement position.

Clause 6: The clutch assembly of clause 4, wherein the engagement position and the disengagement position are separated by a distance of from about 1 millimeters (mm) to about 10 mm.

Clause 7: The clutch assembly of any of clauses 1-6, wherein the first clutch member comprises a plurality of helical splines disposed spirally about the circumference of the first shaft, and wherein the second clutch member comprises a hub defining a plurality of helical grooves configured to receive the helical splines.

Clause 8: The clutch assembly of any of clause 7, wherein each respective helical spline of the plurality of helical splines of the plurality of splines defines a spline width, and wherein each helical groove of the plurality of helical grooves defines a groove width, and wherein magnitude of the groove width is larger than the magnitude of the spline width.

Clause 9: The clutch assembly of any of clauses 7 or 8, wherein at least one spline of the plurality of splines defines a bullnose shape at a first end configured to reduce material stresses induced by engagement with the hub.

Clause 10: The clutch assembly of any of clauses 1-6, wherein the first clutch member is a first lock plate which defines a larger diameter than the first shaft, and wherein the second clutch member is a second lock plate which defines a larger diameter than the second shaft, and wherein each of the first lock plate and the second lock plate define a plurality of teeth.

Clause 11: The clutch assembly of clause 10, wherein at least one tooth of the plurality of teeth defined by the first lock plate is an asymmetrical tooth defining a sloped face disposed at an acute angle relative to a face of the first lock plate.

Clause 12: The clutch assembly of any of clauses 1-11, wherein, to actively reengage the first clutch member and the second clutch member, an electrical center of a stator of the starter motor and an electrical center of a rotor of the starter motor are electrically axially offset when the first clutch member is in the disengaged position, such that energy supplied to the starter motor generates an axial force on the first shaft sufficient to reengage the first clutch member and the second clutch member.

Clause 13: The clutch assembly of any of clauses 1-12, further comprising a speed matching system, wherein the speed matching system is configured to rotate the first shaft about a central axis at substantially the same rotational speed that the second shaft is rotating about a central axis, such that the first clutch member and the second clutch member are rotating at substantially the same rotational speed when they actively reengage with each other.

Clause 14: The clutch assembly of clause 13, wherein the speed matching system comprises a first speed sensor on the first shaft and a second speed sensor on the second shaft.

Clause 15: The clutch assembly of any of clauses 1-14, further comprising the controller including control circuitry, wherein the controller is configured to deliver a signal to actively reengage the first clutch member and the second clutch member from each other.

Clause 16: The clutch assembly of any of clauses 1-16, further comprising the gas turbine engine, and wherein the first clutch member and second clutch member are configured to be engaged during a starting operation of the gas turbine engine, passively disengaged during a cruise operation of the gas turbine engine, and actively reengaged during a barring operation of the gas turbine engine.

Clause 17: A method of operating a clutch assembly includes engaging, at a first time, a first clutch member and a second clutch member, wherein the first clutch member is disposed near a first end of a first shaft, the first clutch member defines a first surface, and a starter motor is coupled to a second end of the first shaft, wherein the second clutch member is disposed near a first end of a second shaft, the second clutch member defines a second surface opposing the first surface, and an accessory gearbox of a gas turbine engine is coupled to a second end of the second shaft, and wherein, when the first clutch member is engaged with the second clutch member, the first surface of the first clutch member engages the second surface of the second clutch member such that rotational motion is transferred between the first clutch member and the second clutch member; passively disengaging, at a second time that is after the first time, the first clutch member and the second clutch member; and actively reengaging, at a third time that is after the second time, the first clutch member and the second clutch member.

Clause 18: The method of clause 17, wherein passively disengaging the first clutch member and the second clutch member comprises disengaging the first clutch member and the second clutch member from each other mechanically without a signal from control logic.

Clause 19: The method of clause 17 or 18, wherein actively engaging the first clutch member and the second clutch member comprises delivering a signal from control circuitry of a controller.

Clause 20: The method of any of clauses 17-19, wherein the starter motor is configured to apply a torque to the first shaft which causes the first shaft to rotate about a first shaft central axis, the accessory gearbox of the gas turbine engine is configured to apply a torque to the second shaft which causes the second shaft to rotate about a second shaft central axis, and wherein passively disengaging the first clutch member and the second clutch member comprises applying a torque to the second shaft that exceeds a torque applied to the first shaft.

Clause 21: The method of any of clauses 17-20, wherein passively disengaging the first clutch member and the second clutch member comprises axially translating the first shaft from an engagement position where the first clutch member is engaged with the second clutch member to a disengagement position wherein the first clutch member and the second clutch member are disengaged.

Clause 22: The method of clause 21, wherein passively disengaging the first clutch member and the second clutch member comprises applying a spring force from a biasing spring to assist in translating the first shaft from the engagement position to the disengagement position.

Clause 23: The method of clause 22, wherein the engagement position and the disengagement position are separated by a distance of from about 1 millimeters (mm) to about 10 mm.

Clause 24: The method of any of clauses 17-23, wherein actively reengaging the first clutch member and the second clutch member comprises engaging a plurality of helical splines disposed spirally about the circumference of the first shaft with a hub defining a plurality of helical grooves configured to receive the helical splines.

Clause 25: The method of clause 24, wherein each respective helical spline of the plurality of helical splines of the plurality of splines defines a spline width, and wherein each helical groove of the plurality of helical grooves defines a groove width, and wherein magnitude of the groove width is larger than the magnitude of the spline width.

Clause 26: The method of any of clauses 24-25, wherein at least one spline of the plurality of splines defines a bullnose shape at a first end configured to reduce material stresses induced by engagement with the hub.

Clause 27: The method of any of clauses 17-23, wherein the first clutch member is a first lock plate which defines a larger diameter than the first shaft, and wherein the second clutch member is a second lock plate defines a larger diameter than the second shaft, and wherein each of the first lock plate and the second lock plate define a plurality of teeth.

Clause 28: The method of clause 27, wherein at least one tooth of the plurality of teeth defined by the first lock plate is an asymmetrical tooth defining a sloped face disposed at an acute angle relative to a face of the first lock plate.

Clause 29: The method of any of clauses 17-28, wherein actively reengaging the first clutch member and the second clutch member comprises generating an axial force on the first shaft by supplying energy to the starter motor, wherein an electrical center of a stator of the starter motor and an electrical center of a rotor of the starter motor are electrically offset when the first clutch member is in the disengaged position, such that energy supplied to the starter motor generates an axial force on the first shaft sufficient to reengage the first clutch member and the second clutch member.

Clause 30: The method of any of clauses 17-29, actively reengaging the first clutch member and the second clutch member comprises operating a speed matching system which rotates the first shaft about a central axis at substantially the same rotational speed that the second shaft is rotating about a central axis, such that the first clutch member and the second clutch member are rotating at substantially the same rotational speed when they actively reengage with each other.

Clause 31: The method of clause 30, wherein the speed matching system comprises a first speed sensor on the first shaft and a second speed sensor on the second shaft.

Clause 32: The method of any of clauses 17-31, further comprising delivering a signal, via control circuitry of a controller, to actively reengage the first clutch member and the second clutch member from each other.

Clause 33: The method of any of clauses 17-32, further comprising operating the gas turbine engine, and wherein the first clutch member and second clutch member are configured to be engaged during a starting operation of the gas turbine engine, passively disengaged during a cruise operation of the gas turbine engine, and actively reengaged during a barring operation of the gas turbine engine.