GB2579198A

GB2579198A - Shaft disconnection

Info

Publication number: GB2579198A
Application number: GB1819063.7A
Authority: GB
Inventors: Muralha Schweikert Farinh Marcelo; P Scothern David
Original assignee: Rolls Royce Deutschland Ltd and Co KG; Rolls Royce PLC
Current assignee: Rolls Royce Deutschland Ltd and Co KG; Rolls Royce PLC
Priority date: 2018-11-23
Filing date: 2018-11-23
Publication date: 2020-06-17
Also published as: GB201819063D0

Abstract

A shaft disconnection mechanism 150, which may be used in a gas turbine engine (10, fig 1) or electric machine (100), comprises a securing member, such as a solenoid 152, comprising a threaded portion (158). A connector shaft 154 is arranged to rotate relative to the securing member 152 and comprises a coupling member, e.g. gear 153, arranged to couple the connector shaft 154 to a drivetrain components, such as electric machine 102 and/or an output shaft 104 of an engine. The connector shaft 154 in a first axial position couples the drivetrain components and in a second axial position decouples the drivetrain component 102, 104. A first shaft portion (154a) has a thread sized to engage the threaded portion (158) of the securing member 152 and an actuator (156) is arranged to move the securing member 152 relative to the connector shaft 154 so as to engage the threaded portion (158) with the first shaft portion (154a), and wherein continued rotation of the connector shaft 154 with the threads (158, 154a) engaged is arranged to move the connector shaft 154 into the second axial position.

Description

SHAFT DISCONNECTION

The present disclosure relates to a shaft disconnection mechanism, and its use in an electric machine, gas turbine engine, or the likes. In particular, the disclosure relates to a mechanism for disconnecting a gearbox, turbine, fan, generator, motor, or the likes from an input (or output) shaft. A generator or fan, or any equipment connected to a drivetrain by a rotating shaft, can thereby be disconnected, stopping power input.

The skilled person will appreciate that motors and generators (or the likes) may need to be disconnected from their output or input, respectively, for safety and/or in order to prevent damage to the motor or generator, for example in the event of a winding fault or a fault in a system being driven by the motor / driving the generator. In particular, permanent magnet motors may need to be physically disconnected in the event of a fault, since they may otherwise continue to generate current in a faulty coil, which may present a hazard. Disconnecting the generator or motor may safely isolate the generator or motor if it, or a drivetrain component, fails, without shutting down the engine or other equipment to which it is connected. It may also be desirable to disconnect a motor from a particular drivetrain whilst still allowing the motor to keep driving one or more other systems, for example if the particular drivetrain has a fault or is not presently wanted.

In particular, the skilled person will appreciate that in an electric propulsion aircraft, an electric motor may drive a propulsive fan. Where a permanent magnet electric machine is used, the electric machine should be physically stopped from rotating in the event of a winding failure, otherwise current may continue to be generated, potentially resulting in large heat loads. However, it may be desirable to allow the fan to continue to rotate to reduce drag. A shaft disconnect system may allow for this.

A shaft disconnect system may equally be used in other contexts where a shaft disconnect (a clutch) is required. Examples include gearbox failure in a geared turbine engine, where disconnection of the gearbox from the fan may be desired. A shaft disconnect system may allow the fan to continue to rotate, potentially reducing drag, if the gearbox is locked due to a failure.

Whilst the disclosure addresses use with electric machines and gas turbine engines in particular, by way of examples, the skilled person will appreciate that such a shaft disconnection mechanism may be used in many different contexts.

The skilled person will appreciate that conventional clutches are generally heavy and unreliable, and can fail to release when required. Such clutches may also slip in use, which may lead to an additional source of failure.

According to a first aspect there is provided a shaft disconnection mechanism comprising: a securing member comprising a threaded portion; a connector shaft arranged to rotate relative to the securing member, the connector shaft comprising: a coupling member arranged to couple the connector shaft to a drivetrain component in a first axial position and to be decoupled from the drivetrain component in a second axial position; and a first shaft portion with a thread sized to engage the threaded portion of the securing member; and an actuator arranged to provide relative movement of the securing member and connector shaft so as to engage the threaded portion of the securing member with the first shaft portion, and wherein the rotation of the connector shaft relative to the securing member with the threads engaged is arranged to cause axial movement of the connector shaft into the second axial positon.

The mechanism therefore includes two threaded bodies, which are arranged to rotate relative to one another when the drivetrain shaft is rotating.

The connector shaft is arranged to rotate relative to the securing member in normal operation -in particular, the connector shaft may rotate and the securing member may not rotate.

Drivetrain components may comprise any component arranged to drive, or to be driven by, rotation of the connector shaft in normal operation.

The drivetrain component may be a drivetrain shaft. The drivetrain shaft may be an input shaft for a generator, or an output shaft for a motor.

The drivetrain component may be a motor, generator, gearbox, engine or the likes. In such embodiments, the connector shaft may be a, or the, drivetrain shaft; for example an input shaft for a generator, or an output shaft for a motor.

In normal operation, the threads are disengaged. In the event of a failure, or a choice to decouple drivetrain components, an actuator moves the threads into engagement (or at least into a position in which engagement is a natural result of continued rotation of the connector shaft). The engagement of the threads then causes relative lateral/axial movement of the threaded bodies as the rotation continues, so disengaging a motor or generator from the drivetrain shaft.

In various embodiments, the two threaded bodies may comprise a nut (the securing means) that is static (with respect to the motor or generator), and a shaft (the connector shaft) that rotates (with respect to the motor or generator and the securing means).

In case of failure of the motor or generator, or of another drivetrain component such as any component coupled to the drivetrain shaft, the connector shaft may be disconnected using the rotation of the shaft itself in various embodiments. This is accomplished by a thread on the connector shaft and a thread on the securing member. By moving a thread of the securing member onto the thread of the connector shaft and holding the securing member such that it cannot rotate with the connector shaft, an axial force is applied on the connector shaft, disconnecting it from the drivetrain.

The skilled person will appreciate that embodiments may effectively incorporate a clutch system into the shaft itself, potentially saving space, weight and/or cost.

The drivetrain component may be a drivetrain shaft. In such embodiments, the connector shaft may be arranged to connect the drivetrain shaft to an engine core, gearbox, motor or generator, or the likes.

In such embodiments, the coupling member may be or comprise a gear arranged to mesh with a gear of the drivetrain shaft in the first axial position and to be disengaged from the gear of the drivetrain shaft in the second axial position. The axial movement of the connector shaft (enabled by the actuator and thread engagement) may be arranged to move the connector shaft from the first axial position into the second axial position.

The drivetrain component may be an engine core, gearbox, motor or generator, or the likes. In such embodiments, the connector shaft may be the drivetrain shaft, or may be coupled to the drivetrain shaft.

In such embodiments, the coupling member may be or comprise a gear arranged to mesh with teeth provided by the engine core, gearbox, motor or generator, or the likes. The coupling member may comprise splines arranged to mesh with splines of the engine core, gearbox, motor or generator, or the likes.

The actuator may be arranged to provide relative axial movement of the securing member and connector shaft, so as to allow the threads to be engaged. Continued rotation of the connector shaft relative to the securing member with the threads engaged may be arranged to cause further relative axial movement, optionally in the same relative direction as the movement provided by the actuator.

In additional or alternative embodiments, the actuator may be arranged to provide relative movement of the securing member and connector shaft in a radial direction.

The actuator may be arranged to move the securing member.

The connector shaft may be arranged to pass through the securing member, or between portions of the securing member.

The securing member may be arranged to surround the connector shaft.

The threaded portion of the securing member may be a threaded hole. In such embodiments, the connector shaft may be arranged to pass through the threaded hole. The connector shaft may comprise a second shaft portion sized not to engage the threaded portion of the securing member. The thread of the first shaft portion may be sized to engage the threaded hole when the first shaft portion is within the threaded hole. The second shaft portion may be sized to pass through the threaded hole without engaging the threaded hole.

The securing member may be or comprise a nut, the nut providing the threaded hole.

The actuator may comprise a solenoid. The securing member may be mounted on a non-rotating support by one or more solenoid pins of the actuator.

In such embodiments, the securing member may be mounted on the non-rotating support by a plurality of solenoid pins, the plurality of solenoid pins optionally being arranged to prevent relative rotation of the securing member and the non-rotating support.

The shaft disconnection mechanism may further comprise a retaining mechanism arranged to limit axial movement of the connector shaft. The continued rotation of the connector shaft once the threads are engaged may be arranged to overcome the retaining mechanism. In alternative or additional embodiments, the actuator may be arranged to overcome the retaining mechanism.

The connector shaft may comprise a circumferential groove. The retaining mechanism may comprise a detent. The detent may be mounted on a non-rotating support. The detent may be biased towards the connector shaft and arranged to be received in the groove in the connector shaft.

The detent may be or comprise a spring-mounted ball.

The securing member may be arranged to be mounted on a motor or generator. The connector shaft may be a motor shaft or generator shaft, respectively. The actuator may be arranged to move the securing member with respect to the motor or generator on which it is mounted.

According to a second aspect, there is provided an electric machine comprising: a motor or generator; a drivetrain shaft; and the shaft disconnection mechanism of the first aspect, wherein the connector shaft is connected to the motor or generator, and the coupling member of the connector shaft is arranged to be coupled to the drivetrain shaft in the first axial position and to be decoupled from the drivetrain shaft in the second axial position.

The securing member may be mounted on the motor or generator.

The connector shaft may further comprise a second coupling member. The second coupling member may be arranged to couple the connector shaft to the motor or generator in the first axial position and to be decoupled from the motor or generator in the second axial position.

The first coupling member may be located in a first end region of the connector shaft and the second coupling member may be located in a second end region of the connector shaft, the second end region optionally lying within the motor or generator.

According to a third aspect, there is provided an electric machine comprising: a motor or generator; and the shaft disconnection mechanism of the first aspect, wherein the connector shaft is a drivetrain shaft of the electric machine, and the coupling member of the connector shaft is arranged to be coupled to the motor or generator in the first axial position and to be decoupled from the motor or generator in the second axial position.

The securing member may be mounted on the motor or generator.

The electric machine of the second or third aspect may comprise an electric motor; the drivetrain shaft (which may also be the connector shaft, or may be coupled to the connector shaft) may be an output shaft of the electric motor.

The electric machine of the second or third aspect may comprise a generator; the drivetrain shaft (which may also be the connector shaft, or may be coupled to the connector shaft) may be an input shaft of the generator.

In embodiments in which the drivetrain shaft is separable from the connector shaft, the connector shaft of the third aspect may further comprise a second coupling member. The second coupling member may be arranged to couple the connector shaft to the drivetrain shaft in the first axial position and to be decoupled from the motor or generator in the second axial position. In such embodiments, the electric machine may be or comprise the electric machine of the second embodiment.

The electric machine of the second or third aspect may be an electric motor of an electric propulsion aircraft. In such embodiments, the drivetrain shaft may connect the motor to a fan of the aircraft.

According to a fourth aspect, there is provided a gas turbine engine for an aircraft comprising: an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan comprising a plurality of fan blades; and a gearbox that receives an input from the core shaft and outputs drive to the fan so as to drive the fan at a lower rotational speed than the core shaft; a drivetrain shaft that transmits the drive from the gearbox to the fan so as to drive the fan; and the shaft disconnection mechanism of the first aspect, wherein the coupling member of the connector shaft is arranged to be coupled to the drivetrain shaft, between the drivetrain shaft and the gearbox, in the first axial position and to be decoupled from the drivetrain shaft in the second axial position, such that the gearbox is arranged to be disconnected from the fan by movement of the connector shaft from the first axial position to the second axial position.

The securing member of the shaft disconnection mechanism may be mounted on the gearbox.

According to a fifth aspect, there is provided a gas turbine engine for an aircraft comprising: an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan comprising a plurality of fan blades; and a gearbox that receives an input from the core shaft and outputs drive to the fan so as to drive the fan at a lower rotational speed than the core shaft; and the shaft disconnection mechanism of the first aspect, wherein the connector shaft is a drivetrain shaft that transmits the drive from the gearbox to the fan so as to drive the fan, and the coupling member of the connector shaft is arranged to be coupled to the gearbox in the first axial position and to be decoupled from the gearbox in the second axial position, such that the gearbox is arranged to be disconnected from the fan by movement of the connector shaft from the first axial position to the second axial position.

According to a sixth aspect, there is provided a method of disengaging drivetrain components in a drivetrain comprising a rotating connector shaft, the method comprising: moving a securing member relative to the rotating connector shaft so as to engage a thread of the securing member with a thread of the rotating connector shaft, wherein continued rotation of the connector shaft relative to the securing member with the threads engaged is arranged to cause axial movement of the connector shaft from a first axial position in which the connector shaft is coupled to a drivetrain component into a second axial positon in which the connector shaft is decoupled from the drivetrain component.

The moving the securing member may comprise axial and/or radial movement relative to the connector shaft.

The connector shaft is arranged to rotate relative to the securing member. The securing member may be non-rotating.

The method may further comprise, prior to the moving the securing member, receiving a signal indicating that the securing member should be moved. The step of moving the securing member may be performed in response to the received signal.

The method may be implemented using the apparatus of any preceding aspect.

As noted elsewhere herein, the present disclosure may relate to a gas turbine engine. Such a gas turbine engine may comprise an engine core comprising a turbine, a combustor, a compressor, and a core shaft connecting the turbine to the compressor. Such a gas turbine engine may comprise a fan (having fan blades) located upstream of the engine core.

Arrangements of the present disclosure may be particularly, although not exclusively, beneficial for fans that are driven via a gearbox. Accordingly, the gas turbine engine may comprise a gearbox that receives an input from the core shaft and outputs drive to the fan so as to drive the fan at a lower rotational speed than the core shaft. The input to the gearbox may be directly from the core shaft, or indirectly from the core shaft, for example via a spur shaft and/or gear. The core shaft may rigidly connect the turbine and the compressor, such that the turbine and compressor rotate at the same speed (with the fan rotating at a lower speed).

The gas turbine engine as described and/or claimed herein may have any suitable general architecture. For example, the gas turbine engine may have any desired number of shafts that connect turbines and compressors, for example one, two or three shafts. Purely by way of example, the turbine connected to the core shaft may be a first turbine, the compressor connected to the core shaft may be a first compressor, and the core shaft may be a first core shaft. The engine core may further comprise a second turbine, a second compressor, and a second core shaft connecting the second turbine to the second compressor. The second turbine, second compressor, and second core shaft may be arranged to rotate at a higher rotational speed than the first core shaft.

In such an arrangement, the second compressor may be positioned axially downstream of the first compressor. The second compressor may be arranged to receive (for example directly receive, for example via a generally annular duct) flow from the first compressor.

The gearbox may be arranged to be driven by the core shaft that is configured to rotate (for example in use) at the lowest rotational speed (for example the first core shaft in the example above). For example, the gearbox may be arranged to be driven only by the core shaft that is configured to rotate (for example in use) at the lowest rotational speed (for example only be the first core shaft, and not the second core shaft, in the example above). Alternatively, the gearbox may be arranged to be driven by any one or more shafts, for example the first and/or second shafts in the example above.

In any gas turbine engine as described and/or claimed herein, a combustor may be provided axially downstream of the fan and compressor(s). For example, the combustor may be directly downstream of (for example at the exit of) the second compressor, where a second compressor is provided. By way of further example, the flow at the exit to the combustor may be provided to the inlet of the second turbine, where a second turbine is provided. The combustor may be provided upstream of the turbine(s).

The or each compressor (for example the first compressor and second compressor as described above) may comprise any number of stages, for example multiple stages. Each stage may comprise a row of rotor blades and a row of stator vanes, which may be variable stator vanes (in that their angle of incidence may be variable). The row of rotor blades and the row of stator vanes may be axially offset from each other.

The or each turbine (for example the first turbine and second turbine as described above) may comprise any number of stages, for example multiple stages. Each stage may comprise a row of rotor blades and a row of stator vanes. The row of rotor blades and the row of stator vanes may be axially offset from each other.

Each fan blade may be defined as having a radial span extending from a root (or hub) at a radially inner gas-washed location, or 0% span position, to a tip at a 100% span position. The ratio of the radius of the fan blade at the hub to the radius of the fan blade at the tip may be less than (or on the order of) any of: 0.4, 0.39, 0.38 0.37, 0.36, 0.35, 0.34, 0.33, 0.32, 0.31, 0.3, 0.29, 0.28, 0.27, 0.26, or 0.25. The ratio of the radius of the fan blade at the hub to the radius of the fan blade at the tip may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds). These ratios may commonly be referred to as the hub-to-tip ratio. The radius at the hub and the radius at the tip may both be measured at the leading edge (or axially forwardmost) part of the blade. The hub-to-tip ratio refers, of course, to the gas-washed portion of the fan blade, i.e. the portion radially outside any platform.

The radius of the fan may be measured between the engine centreline and the tip of a fan blade at its leading edge. The fan diameter (which may simply be twice the radius of the fan) may be greater than (or on the order of) any of: 250 cm (around 100 inches), 260 cm, 270 cm (around 105 inches), 280 cm (around 110 inches), 290 cm (around 115 inches), 300 cm (around 120 inches), 310 cm, 320 cm (around 125 inches), 330 cm (around 130 inches), 340 cm (around 135 inches), 350cm, 360cm (around 140 inches), 370 cm (around 145 inches), 380 (around 150 inches) cm or 390 cm (around 155 inches). The fan diameter may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds).

The rotational speed of the fan may vary in use. Generally, the rotational speed is lower for fans with a higher diameter. Purely by way of non-limitative example, the rotational speed of the fan at cruise conditions may be less than 2500 rpm, for example less than 2300 rpm. Purely by way of further non-limitative example, the rotational speed of the fan at cruise conditions for an engine having a fan diameter in the range of from 250 cm to 300 cm (for example 250 cm to 280 cm) may be in the range of from 1700 rpm to 2500 rpm, for example in the range of from 1800 rpm to 2300 rpm, for example in the range of from 1900 rpm to 2100 rpm. Purely by way of further non-limitative example, the rotational speed of the fan at cruise conditions for an engine having a fan diameter in the range of from 320 cm to 380 cm may be in the range of from 1200 rpm to 2000 rpm, for example in the range of from 1300 rpm to 1800 rpm, for example in the range of from 1400 rpm to 1600 rpm.

In use of the gas turbine engine, the fan (with associated fan blades) rotates about a rotational axis. This rotation results in the tip of the fan blade moving with a velocity Utip. The work done by the fan blades 13 on the flow results in an enthalpy rise dH of the flow. A fan tip loading may be defined as dH/Utip2, where dH is the enthalpy rise (for example the 1-D average enthalpy rise) across the fan and Utip is the (translational) velocity of the fan tip, for example at the leading edge of the tip (which may be defined as fan tip radius at leading edge multiplied by angular speed). The fan tip loading at cruise conditions may be greater than (or on the order of) any of: 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39 or 0.4 (all units in this paragraph being Jkg-1K-1/(ms-1)2). The fan tip loading may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds).

Gas turbine engines in accordance with the present disclosure may have any desired bypass ratio, where the bypass ratio is defined as the ratio of the mass flow rate of the flow through the bypass duct to the mass flow rate of the flow through the core at cruise conditions. In some arrangements the bypass ratio may be greater than (or on the order of) any of the following: 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, or 17. The bypass ratio may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds). The bypass duct may be substantially annular. The bypass duct may be radially outside the core engine. The radially outer surface of the bypass duct may be defined by a nacelle and/or a fan case.

The overall pressure ratio of a gas turbine engine as described and/or claimed herein may be defined as the ratio of the stagnation pressure upstream of the fan to the stagnation pressure at the exit of the highest pressure compressor (before entry into the combustor). By way of non-limitative example, the overall pressure ratio of a gas turbine engine as described and/or claimed herein at cruise may be greater than (or on the order of) any of the following: 35, 40, 45, 50, 55, 60, 65, 70, 75. The overall pressure ratio may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds).

Specific thrust of an engine may be defined as the net thrust of the engine divided by the total mass flow through the engine. At cruise conditions, the specific thrust of an engine described and/or claimed herein may be less than (or on the order of) any of the following: 110 Nkg-'s, 105 Nkg-ls, 100 Nkg-'s, 95 Nkg-'s, 90 Nkg-ls, 85 Nkg-ls or 80 Nkg-ls. The specific thrust may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds). Such engines may be particularly efficient in comparison with conventional gas turbine engines.

A gas turbine engine as described and/or claimed herein may have any desired maximum thrust. Purely by way of non-limitative example, a gas turbine as described and/or claimed herein may be capable of producing a maximum thrust of at least (or on the order of) any of the following: 160kN, 170kN, 180kN, 190kN, 200kN, 250kN, 300kN, 350kN, 400kN, 450kN, 500kN, or 550kN. The maximum thrust may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds). The thrust referred to above may be the maximum net thrust at standard atmospheric conditions at sea level plus 15 deg C (ambient pressure 101.3kPa, temperature 30 deg C), with the engine static.

In use, the temperature of the flow at the entry to the high pressure turbine may be particularly high. This temperature, which may be referred to as TET, may be measured at the exit to the combustor, for example immediately upstream of the first turbine vane, which itself may be referred to as a nozzle guide vane. At cruise, the TET may be at least (or on the order of) any of the following: 1400K, 1450K, 1500K, 1550K, 1600K or 1650K. The TET at cruise may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds). The maximum TET in use of the engine may be, for example, at least (or on the order of) any of the following: 1700K, 1750K, 1800K, 1850K, 1900K, 1950K or 2000K. The maximum TET may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds). The maximum TET may occur, for example, at a high thrust condition, for example at a maximum take-off (MTO) condition.

A fan blade and/or aerofoil portion of a fan blade described and/or claimed herein may be manufactured from any suitable material or combination of materials. For example at least a part of the fan blade and/or aerofoil may be manufactured at least in part from a composite, for example a metal matrix composite and/or an organic matrix composite, such as carbon fibre. By way of further example at least a part of the fan blade and/or aerofoil may be manufactured at least in part from a metal, such as a titanium based metal or an aluminium based material (such as an alum iniumlithium alloy) or a steel based material. The fan blade may comprise at least two regions manufactured using different materials. For example, the fan blade may have a protective leading edge, which may be manufactured using a material that is better able to resist impact (for example from birds, ice or other material) than the rest of the blade. Such a leading edge may, for example, be manufactured using titanium or a titanium-based alloy. Thus, purely by way of example, the fan blade may have a carbon-fibre or aluminium based body (such as an aluminium lithium alloy) with a titanium leading edge.

A fan as described and/or claimed herein may comprise a central portion, from which the fan blades may extend, for example in a radial direction. The fan blades may be attached to the central portion in any desired manner. For example, each fan blade may comprise a fixture which may engage a corresponding slot in the hub (or disc). Purely by way of example, such a fixture may be in the form of a dovetail that may slot into and/or engage a corresponding slot in the hub/disc in order to fix the fan blade to the hub/disc. By way of further example, the fan blades maybe formed integrally with a central portion. Such an arrangement may be referred to as a blisk or a bling. Any suitable method may be used to manufacture such a blisk or bling. For example, at least a part of the fan blades may be machined from a block and/or at least part of the fan blades may be attached to the hub/disc by welding, such as linear friction welding.

The gas turbine engines described and/or claimed herein may or may not be provided with a variable area nozzle (VAN). Such a variable area nozzle may allow the exit area of the bypass duct to be varied in use. The general principles of the present disclosure may apply to engines with or without a VAN.

The fan of a gas turbine as described and/or claimed herein may have any desired number of fan blades, for example 16, 18, 20, or 22 fan blades.

As used herein, cruise conditions may mean cruise conditions of an aircraft to which the gas turbine engine is attached. Such cruise conditions may be conventionally defined as the conditions at mid-cruise, for example the conditions experienced by the aircraft and/or engine at the midpoint (in terms of time and/or distance) between top of climb and start of decent.

Purely by way of example, the forward speed at the cruise condition may be any point in the range of from Mach 0.7 to 0.9, for example 0.75 to 0.85, for example 0.76 to 0.84, for example 0.77 to 0.83, for example 0.78 to 0.82, for example 0.79 to 0.81, for example on the order of Mach 0.8, on the order of Mach 0.85 or in the range of from 0.8 to 0.85. Any single speed within these ranges may be the cruise 11.

condition. For some aircraft, the cruise conditions may be outside these ranges, for example below Mach 0.7 or above Mach 0.9.

Purely by way of example, the cruise conditions may correspond to standard atmospheric conditions at an altitude that is in the range of from 10000m to 15000m, for example in the range of from 10000m to 12000m, for example in the range of from 10400m to 11600m (around 38000 ft), for example in the range of from 10500m to 11500m, for example in the range of from 10600m to 11400m, for example in the range of from 10700m (around 35000 ft) to 11300m, for example in the range of from 10800m to 11200m, for example in the range of from 10900m to 11100m, for example on the order of 11000m. The cruise conditions may correspond to standard atmospheric conditions at any given altitude in these ranges.

Purely by way of example, the cruise conditions may correspond to: a forward Mach number of 0.8; a pressure of 23000 Pa; and a temperature of -55 deg C. As used anywhere herein, "cruise" or "cruise conditions" may mean the aerodynamic design point. Such an aerodynamic design point (or ADP) may correspond to the conditions (comprising, for example, one or more of the Mach Number, environmental conditions and thrust requirement) for which the fan is designed to operate. This may mean, for example, the conditions at which the fan (or gas turbine engine) is designed to have optimum efficiency.

In use, a gas turbine engine described and/or claimed herein may operate at the cruise conditions defined elsewhere herein. Such cruise conditions may be determined by the cruise conditions (for example the mid-cruise conditions) of an aircraft to which at least one (for example 2 or 4) gas turbine engine may be mounted in order to provide propulsive thrust.

The skilled person will appreciate that except where mutually exclusive, a feature or parameter described in relation to any one of the above aspects may be applied to any other aspect. Furthermore, except where mutually exclusive, any feature or parameter described herein may be applied to any aspect and/or combined with any other feature or parameter described herein.

Embodiments will now be described by way of example only, with reference to the Figures, in which: Figure 1 is a sectional side view of a gas turbine engine; Figure 2 is a close up sectional side view of an upstream portion of a gas turbine engine; Figure 3 is a partially cut-away view of a gearbox for a gas turbine engine; Figure 4 is a schematic plan view of a shaft disconnection mechanism of an embodiment; Figure 5 is a schematic plan view of a generator drivetrain of an embodiment in a first axial position, including a front view of the securing member; Figure 6 is a schematic plan view of the generator drivetrain of Figure 5 in a second axial position; Figure 7 is a cross-sectional side view of a connector shaft of an embodiment including a biased detent; and Figures 8A and 8B are cross-sectional schematic views illustrating a connector shaft connected to, and disconnected from, a generator, respectively; Figures 9A and 9B are cross-sectional schematic views illustrating a different connector shaft connected to, and disconnected from, a generator, respectively; Figures 10A and 10B are cross-sectional schematic views illustrating the connector shaft of Figures 8A and 8B with a detent; and Figure 11 illustrates a method of an embodiment.

Figure 1 illustrates a gas turbine engine 10 having a principal rotational axis 9. The engine 10 comprises an air intake 12 and a propulsive fan 23 that generates two airflows: a core airflow A and a bypass airflow B. The gas turbine engine 10 comprises a core 11 that receives the core airflow A. The engine core 11 comprises, in axial flow series, a low pressure compressor 14, a high-pressure compressor 15, combustion equipment 16, a high-pressure turbine 17, a low pressure turbine 19 and a core exhaust nozzle 20. A nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass exhaust nozzle 18. The bypass airflow B flows through the bypass duct 22. The fan 23 is attached to and driven by the low pressure turbine 19 via a shaft 26 and an epicyclic gearbox 30.

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

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

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

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

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

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

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

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

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

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

In further arrangements, the disclosure may apply to any system comprising a rotating shaft coupled to one or more other drivetrain components; for example a motor or generator 102. Such arrangements are described first for ease of reference. The skilled person will appreciate that equivalent principles can then be applied to any rotating shaft system, including aircraft engines 10 and the likes.

The electric machine 100 shown in Figure 5 comprises a generator 102 and a drivetrain shaft 104. The drivetrain shaft 104 is arranged to drive the generator 102 and may therefore be described as an input shaft 104. Rotation of the input shaft 104 may be driven directly or indirectly, for example electrically or by another shaft or a steam, water, or air flow, or the likes, or by any other means known in the art.

Whilst the below disclosure is provided primarily as a discussion of a generator 100, 102, the skilled person will appreciate that the principles may equally apply to a motor 102, in which case the drivetrain shaft 104 may be arranged to be driven by the motor 102 and may therefore be described as an output shaft 104, or to any other engine, machine or mechanism comprising a rotating shaft which is intended to be releasably coupled to another drivetrain component.

The electric machine 100 further comprises a shaft disconnection mechanism 150. The shaft disconnection mechanism 150 is arranged to releasably couple drivetrain components together; in this embodiment coupling the drivetrain shaft 104 to the generator 102 (or motor 102 in other embodiments).

In the embodiment shown in Figures 4 and 5, the shaft disconnection mechanism 150 comprises a connector shaft 154. The connector shaft 154 extends between the generator 102 and the drivetrain shaft 104 in the embodiment being described, coupling the generator 102 to the drivetrain shaft 104.

The connector shaft 154 is arranged to transfer torque from the drivetrain (input) shaft 104 to the generator 102 in the embodiment being described. In alternative embodiments in which the generator 102 is replaced with a motor 102, the connector shaft 154 may instead be arranged to transfer torque from the motor 102 to the drivetrain (output) shaft 104. In normal use, the connector shaft 154 therefore rotates whenever the drivetrain shaft 104 is rotating and whenever the generator/motor 102 is active.

In the embodiment being described, the connector shaft 154 is coupled to the drivetrain shaft 104 by a coupling member 153. In the embodiment being described, the coupling member 153 is a gear 153, and the gear 153 is arranged to engage a gear 103 of the drivetrain shaft 104. In alternative or additional embodiments, any suitable coupling member 153 known in the art may be used. In such embodiments, the coupling member 103 of the drivetrain shaft 104 may be replaced or adjusted accordingly.

In the embodiment being described, the gears 103, 153 are of the same size and shape such that the rotation ratio between the two shafts 104, 154 is 1:1, i.e. the two shafts rotate at the same rate. In alternative embodiments, the gears 103, 153 may be arranged to provide a different rotation ratio between the shafts, and/or an intermediate gear may be provided, for example to allow both shafts 104, 154 to rotate in the same direction.

In the embodiments being described, the shafts 104, 154 are parallel to each other. In the embodiments being described, the shafts 104, 154 are offset from each other such that they are not coaxial. In alternative embodiments, the shafts 104, 154 may be differently angled and the coupling members 103, 153 may be adjusted or replaced accordingly.

In the embodiment shown in Figures 4 and 5, the shaft disconnection mechanism 150 comprises a securing member 152. The connector shaft 154 is arranged to rotate relative to the securing member 152.

The securing member 152 is mounted on the generator 102 in the embodiment shown. In the embodiment being described, the securing member 152 is mounted on a body of the generator 102. The body of the generator 102 does not rotate with the connector shaft 154 and may therefore be thought of as a non-rotating support 102 for the securing member 152. In alternative embodiments, the securing member 152 may be mounted to a different non-rotating support such as the ground, a wall of a building, an engine casing or the likes. The skilled person will appreciate that the securing member 152 may still move, e.g. as an engine or the generator 102 moves, but is not free to rotate with the connector shaft 154. The securing member 152 may therefore be described as non-rotating or static.

In the embodiment being described, the securing member 152 is mounted on the generator 102 by means of a plurality of pins 156. In the embodiment being described, four pins 156 are used, although the skilled person will appreciate that any number of pins could be used, and/or that a different or additional mounting means could be used; for example screws or the likes. In the embodiment being described, the securing member 152 comprises four apertures therethrough, each arranged to receive one of the four pins 156.

Use of a plurality of pins 156 rather than a single pin may aid in preventing rotation of the securing member 152 in various embodiments.

In the embodiment being described, the coupling member 153 of the connector shaft 154 is arranged to lie on a far side of the securing member 152 from the generator 102. In the embodiment being described, the coupling member 153 of the connector shaft 154 is located on one end of the connector shaft 154 (the distal end from the generator 102). In alternative embodiments, the connector shaft 154 may extend beyond the coupling member 153. In such embodiments, the securing member 152 may be located on the far side of the coupling member 153 from the generator 102 instead of between the coupling member 153 and the generator 102.

The securing member 152 comprises a threaded portion 158.

In the embodiment being described, the securing member 152 is a nut 152. The nut comprises a threaded aperture 158 therethrough; the threaded aperture 158 provides the threaded portion of the securing member 152. In alternative embodiments, the securing member 152 may be or comprise a plate, block or other body with a threaded aperture 158 therethrough, or may take different forms as discussed below.

In the embodiment being described, the connector shaft 154 is arranged to extend through the securing member 152, and more specifically through the threaded aperture 158 of the securing member 152.

In the embodiment being described, the connector shaft 154 comprises a first portion 154a comprising a thread arranged to fit through the threaded aperture 158 of the securing member 152 and to engage the threaded aperture 158. In the embodiment being described, the first portion 154a is threaded; the thread being arranged to be engagingly received by the thread of the threaded aperture 158.

In the embodiment being described, each thread 158, 154a is arranged to extend for at least one full turn around its axis, and more specifically by a plurality of turns about its axis. In alternative embodiments, one or both threads may only extend by one turn about the axis.

In the embodiment being described, the connector shaft 154 comprises a second portion 154b arranged to fit through the threaded aperture 158 of the securing member 152 without engaging the threaded aperture 158. In the embodiment being described, the second portion 154b is unthreaded. In the embodiment being described, the second portion 154b has a radius smaller than the smallest radius of the threaded aperture 158.

The first portion 154a is axially adjacent the second portion 154b. In the embodiment being described, the second portion 154b is closer to the generator 102 than the first portion 154a in use. In alternative embodiments, this positioning may be reversed -for example, in the embodiment shown in Figures 5 to 8, the connector shaft 154 is arranged to move towards the generator 102 to disengage the coupling members 103, 153 (rightward in the orientation shown) whereas in alternative embodiments the connector shaft 154 may instead be arranged to move away from the generator 102 to disengage the coupling members 103, 153 (leftward in the orientation shown).

In the embodiment being described, the first portion 154a is arranged to lie adjacent to, and disengaged from, the threaded aperture 158 in normal use.

In the embodiment being described, the second portion 154b is arranged to extend through the threaded aperture 158 in normal use.

In normal use, the securing member 152 of the embodiment being described therefore does not make contact with the rotating connector shaft 154 and does not affect the connector shaft 154.

In Figure 4, the gap between the securing member 152 and the adjacent end of the second portion 154b is shown enlarged as compared to the spacing in normal operation. In the embodiments being described, in normal operation a spacing between a forward edge (i.e. the edge furthest from the generator 102/closest to the coupling 153 to the drivetrain shaft 104 in the embodiment shown) of the threaded portion of the securing member 152 and a nearest edge of the threaded portion 154a of the connector shaft 154 may be less than 1 cm, optionally less than 5 mm, and further optionally around 3 mm. The spacing may be between 1 mm and 5 mm in some embodiments.

In alternative embodiments, the connector shaft 154 may be arranged to extend around the securing member 152 -for example, the connector shaft 154 may be hollow, or may comprise a hollow portion, with an inwardly-directed thread and the securing member 152 may comprise a screw extending axially and arranged to be engagingly received by the inwardly-directed thread of the connector shaft 154.

In the embodiment shown in Figures 4 and 5, the securing member 152 is mounted on the generator 102 so as to be axially moveable (i.e. so as to permit movement of the securing member 152 along the length of the connector shaft 154). The shaft disconnection mechanism 150 comprises an actuator 156 arranged to move the securing member 152 axially in response to a received signal.

The relative (in this case, axial) movement of the securing member 152 and the connector shaft 154 caused by the actuator 156 is arranged to move a thread 158 of the securing member 152 into engagement with a thread 154a of the connector shaft. The distance of the movement is arranged to match the spacing between adjacent edges of the threaded portions 154a, 158, so bringing the threads together for engagement.

In alternative embodiments, the relative movement of the securing member 152 and the connector shaft 154 may not be axial. For example, the securing member 152 may comprise a threaded groove, for example having a semi-circular cross-section, rather than a threaded aperture, and may be arranged to move radially towards the connector shaft 154 so as to engage the thread 154a on the connector shaft 154. In some embodiments, multiple threaded grooves may be moved into contact with the connector shaft 154, from different circumferential and/or axial positions. In such embodiments, the only axial motion may be that caused by interaction of continued rotation of the connector shaft 154 once the thread 154a of the (rotating) connector shaft 154 is engaged with the thread of the (non-rotating) securing member 152. In such embodiments, the thread 154a may extend the full length of the connector shaft 154a and/or there may be no second shaft portion 154b.

In alternative or additional embodiments, the shaft disconnection mechanism 150 may comprise an actuator arranged to move the connector shaft 154 in response to a received signal, instead of or as well as the actuator 156 arranged to move the securing member 152. The skilled person will appreciate that relative movement of the connector shaft 154 and the securing member 152 can be obtained by moving either or both of the connector shaft 154 and the securing member 152. In the embodiment being described, the movement provided by the actuator is insufficient to decouple the drivetrain components.

In various embodiments, the relative movement caused by the actuator 156 is arranged to bring the threads 154a, 158 of the connector shaft 154 and the securing member 152 into engagement. In particular, in the embodiment shown, the securing member 152 is moved such that an edge of the first (threaded) portion 154a of the connector shaft 154 enters the threaded aperture 158. The relative movement is arranged to move the threaded portion 158 of the securing member 152 toward the threaded portion 154a of the connector shaft 154. In the embodiment being described, the relative movement is relative axial movement, indicated by arrows A in Figures 4 and 5. The securing member 152 is moved towards the first portion 154a of the connector shaft 154, and, in the embodiment being described, correspondingly towards the coupling member 153. The rotation of the connector shaft 154 then pulls a crest of a thread of the first portion 154a into a groove of the thread of the aperture 158, or vice versa.

In the embodiment being described, the actuator 156 comprises a solenoid. In the embodiment being described, the pins 156 used to mount the securing member 152 are solenoid pins and are arranged to move the securing member 152 axially when the actuator 156 is activated. In the embodiment being described, the solenoid pins 156 are arranged to move the securing member 152 towards the first portion 154a of the connector shaft 154 (and correspondingly away from the generator 102 in the embodiment shown) when the actuator 156 is activated.

In the embodiment being described, the actuator 156 is activated in response to receipt of a signal, such as an electrical signal. In the embodiment being described, the signal is generated and sent in response to a sensor detecting a failure of the generator 102. In alternative embodiments, any other activation mechanism may be used; for example depression of a physical button, flicking of a switch, an entered command to disengage the generator 102, or the likes.

In the embodiment being described, the actuator 156 is arranged to move the securing member 152 axially by only a relatively small distance (1-5 mm, and more particularly around 3 mm, in the embodiment being described); the axial displacement due to the actuator 156 is insufficient to decouple the coupling members 153, 103. In the embodiment shown, in which the coupling members 153, 103 are gears, the teeth of the gears may slide axially relative to each other, so potentially reducing the axial overlap, whilst remaining meshed -the axial displacement due to the actuator 156 is less than the width of the gears 153, 103, which is 1-5 cm, and more particularly around 2 cm, in the embodiment being described. The skilled person will appreciate that a minimum required power for the actuator 156 / force exerted by the actuator 156 may therefore be relatively low and/or only of a relatively brief duration.

The relatively small movement caused by the actuator 156 is however sufficient to engage adjacent ends of the threads 158, 154a.

The threads 158, 154a are arranged to allow the shaft 154 to continue rotating relative to the securing member 152 -the threads 158, 154a are therefore aligned for the direction of rotation in normal operation. Once the threads 158, 154a are engaged, the continued rotation causes axial movement of the connector shaft 154 (and in this embodiment further relative axial movement of the connector shaft 154 and the securing member 152), as one thread 154a is screwed into the second 158. In the embodiment being described, the connector shaft 154 is drawn further through the securing member 152 / towards the generator 102 as the rotation continues. This axial movement is arranged to decouple the coupling members 153, 103. In the embodiment shown, in which the coupling members 153, 103 are gears, the teeth of the gears slide axially relative to each other until they no longer mesh, as is shown in Figure 6.

In the case of failure, the drivetrain shaft 104 is therefore disconnected from the generator 102 by using the rotation of the shaft 104 itself. This is accomplished by a thread 154a on the connector shaft 154 and a thread 158 on the securing member 152. By moving the thread 158 of the securing member 152 onto the thread 154a of the connector shaft 154 and the securing member 152 being arranged such that it cannot rotate with the connector shaft 154 / such that the connector shaft 154 rotates relative to the securing member 152, an axial force is applied to the connector shaft 154 which disconnects it from the drivetrain shaft 104.

The interaction of the threads 154, 158 therefore disengages the coupling members 153, 103.

In embodiments in which the generator 102 is replaced with a motor 102, it may be the rotation of the motor which disconnects the drivetrain shaft 104 from the motor 102. In scenarios in which the motor itself has failed, instead of a downstream system component, angular momentum in the system, and/or e.g. windmilling of a fan 23 of an aircraft engine 10 in flight or the likes may keep the connector shaft 154 rotating for at least long enough to disconnect the drivetrain shaft 104.

In the embodiment being described, the axial movement caused by interaction of the threads 154, 158 as the connector shaft 154 continues to rotate moves the connector shaft 154 by around 1 to 5 cm, and more particularly by around 2 cm so as to disengage it from the drivetrain shaft 104. In various embodiments in which the coupling members 153, 103 are gears, the axial movement may be by a distance substantially equal to, or slightly greater than, the axial width of the gears 153, 103, so moving teeth of the gears out of alignment.

In the embodiment being described, the axial movement caused by interaction of the threads 154, 158 is illustrated by arrow B in Figures 4 and 5.

In alternative or additional embodiments, the connector shaft 154 may be coupled to multiple drivetrain shafts 104 -for example, a motor 102 may be used to drive multiple mechanisms from the same connector shaft 154. In such embodiments, the connector shaft may comprise multiple coupling members 153. In some such embodiments, the coupling members 153 may be gears spaced along the length of the connector shaft 154. Optionally, the gears 153 may have different widths such that drivetrain shafts 104 are disengaged in a particular order (narrower gears first) when the connector shaft 154 moves. In some such embodiments, the connector shaft 154 may have multiple separate, axially spaced, threaded portions 154a arranged such that another activation of the actuator 156, or an activation of a different actuator, is needed to move a further threaded portion of the shaft 154 into engagement with the threaded portion 158 of the securing member 152 once the full extent of the thread of the first portion 154a has passed the securing member 152. Such an arrangement may allow only a subset of the multiple drivetrain shafts 104 to be disengaged if wanted -for example only one drivetrain shaft 104 (e.g. that with the narrowest gear 153, 103).

In the embodiment being described, the movement of the securing member 152 caused by the actuator 156 is in a first direction along the axis (leftward, in the orientation shown), as marked by Arrow A, whereas the axial movement of the connector shaft 154 is in a second direction along the axis, opposed to the first direction (rightward, in the orientation shown), as marked by Arrow B. The relative movement is however in the same direction -the securing member 152 gets closer to the distal end of the first portion 154a (the end of the first portion closest to the coupling member 153 in the embodiments shown) as a result of each movement and the axial movement as a result of the threads 158, 154a interacting may therefore be described as further (relative) axial movement, continuing the relative movement started by the actuator 156. In alternative embodiments, such as embodiments in which the securing member 152 is moved radially by the actuator 156, the (relative) axial movement may be in a different direction from, and optionally perpendicular to, the movement caused by the actuator 156.

The shaft disconnection mechanism 150 may be described as a quill drive 150, as it allows one shaft to change its position relative to its driving shaft, and the connector shaft 154 may therefore be described as a quill shaft 154. The skilled person will appreciate that which shaft 104, 154 drives which may vary between different embodiments -for example between embodiments in which the electric machine 100 comprises a motor 102 and in which the electric machine 100 comprises a generator 102. In alternative embodiments discussed below, a single shaft may perform the function of both the connector shaft 154 and the drivetrain shaft 104.

In the embodiment being described, the shaft disconnection mechanism 150 comprises a retaining mechanism 110, 112 arranged to limit axial movement of the connector shaft 154. The retaining mechanism 110, 112 may reduce the chance of unintentional axial forces, e.g. vibrations, moving the threads 158, 154a into engagement.

In the embodiment being described, and as shown in Figure 7, the retaining mechanism 110, 112 comprises a detent 110 arranged to limit axial movement of the connector shaft 154. Figure 7 illustrates the detent 110 in normal operation; in the first axial position in which the drivetrain components 104, 102 are coupled together by the connector shaft 154.

In the embodiment being described, the detent 110 is mounted within the generator 102. In alternative embodiments, the detent 110 may be mounted elsewhere; for example in a separate support to which the securing member 152 may be mounted, or the likes. The detent 110 of various embodiments is arranged to be mounted in a fixed axial position with respect to the generator 102 and/or the coupling member 103 of the drivetrain shaft 104.

In the embodiment being described, the detent 110 is biased towards the connector shaft 154. In the embodiment being described, the detent 110 is mounted on a spring 112. The spring 112 is arranged to bias the detent 110 towards the connector shaft 154. In alternative embodiments, any suitable biasing means known in the art may be used.

In the embodiment being described, the spring 112 is mounted within a recess 105 of the generator 102. The recess 105 is sized to be able to accommodate at least a portion of the detent 110 if or when the biasing force is overcome, as the connector shaft 154 moves from the first axial position into the second axial position, so causing the spring 112 to retract as the detent 110 moves away from the connector shaft 154/towards the generator 102.

In the embodiment being described, the detent 110 is ball-shaped. The detent 110 may therefore be described as a spring-mounted ball. In alternative embodiments, different shapes may be used. The skilled person will appreciate that detent shape may be selected to reduce or minimise a risk of the detent 110 becoming trapped between the connector shaft 154 and a surface of the generator 102 / of the detent 110 being blocked from moving into the recess 105.

In the embodiment being described, the connector shaft 154 comprises a circumferential groove 157. The circumferential groove 157 is arranged to receive the detent 110. The circumferential groove 157 has a limited axial extent along the connector shaft 154. In the embodiment being described, the circumferential groove 157 has an axial width only 1-2 mm greater than that of the detent 110, so allowing only 1-2 mm of axial movement. The amount of movement allowed by the circumferential groove 157 may be selected to be less than that required to bring the threads 158, 154a into engagement. The interaction of the circumferential groove 157 with the detent 110 may therefore be arranged to prevent inadvertent engagement of the threads 158, 154a.

In the embodiments being described, the sizes of the circumferential groove 157 and of the detent 110 are set such that the axial movement possible with the detent 110 within the grove 157 is less than the required to bring the threads 158, 154a into engagement.

The skilled person will appreciate that the purpose of the detent 110 is to prevent random axial movement (e.g. due to vibration) of the shaft 154 bringing the threads 158, 154a into engagement -any movement that would otherwise be equal to or greater than the necessary axial movement for the securing member 152 to be brought into engagement is resisted by the detent 110.

In the embodiments being described, the detent 110 is inside the generator 102 and has no connection to the securing member 152 or actuator/solenoid pins 156. In the embodiment being described, the actuator 156 is designed to move the securing member 152 relative to the connector shaft and the generator 102 so as to engage the threads, without moving the connector shaft 154. The actuator 156 therefore does not need to be able to overcome the force of the detent 110 as there is no relative movement of the connector shaft 154 and generator 102 / detent 110 until after the threads are engaged. Once the threads are engaged, the rotation of the shaft 154 drives the axial movement and overcomes the retaining force of the detent 110.

In the embodiment being described, the circumferential groove 157 is trapezoidal in cross-section, with its width decreasing radially inwardly into the shaft 154. The axial width may be measured at the narrowest point. The skilled person will appreciate that the sloped sides of the groove 157 may facilitate retraction of the detent 110 into the recess 105 when a sufficient force to overcome the biasing effect of the spring 112 is applied. The circumferential groove 157 may be differently shaped in alternative embodiments, for example optionally having curved sides instead of straight, angled sides.

In the embodiment being described, a single detent 110 is shown. In various embodiments, a plurality of detents 110 may be arranged around the circumference. In the embodiment being described, three detents 110 are present, spaced equally around the circumference. In alternative embodiments, 1, 2, 3, 4, 5, 6 or more detents may be used, and/or the detents 110 may be unevenly spaced around the circumference.

In the embodiment being described, a single detent circumferential groove 157 is provided. In alternative embodiments, there may be two or more circumferential grooves 157 axially spaced from each other, each groove 157 having one or more corresponding detents 110.

In the embodiment being described, the axial force applied to the connector shaft 154 as a result of its rotation combined with the interaction of the threads 158, 154a is sufficient to overcome the retaining mechanism 110, 112, and in particular to overcome the spring force biasing the detent 110 towards the shaft 154. The detent is therefore pushed back into the recess 105 as the connector shaft 154 moves from the first axial position in which the drivetrain shaft 104 is engaged to the second axial position in which the drivetrain shaft 104 is disengaged.

In alternative or additional embodiments, a different detent design may be used. For example, the detent 110 may be mounted on the connector shaft 154 and arranged to be received in a circumferential groove of the generator 102. In alternative embodiments, the detent 110 may be or comprise an axial biasing member -for example a spring extending axially from a forward end of the connector shaft 154 and rotatably connected to a wall of the generator 102 such that the spring restrains axial movement towards or away from the wall. The axial force resulting from rotation of the shaft 154 once the threads 154a, 158 are engaged is arranged to overcome the spring force of the detent 110.

In alternative embodiments, the movement caused by the actuator 156 may be arranged to overcome the detent 110 -e.g., for the embodiment being described with reference to Figures 4 to 6, the detent 110 could instead be mounted on the securing member 152, or in alternative embodiments the actuator 156 may be arranged to move the connector shaft 154. The skilled person would appreciate that a stronger actuator 156 may be needed in such embodiments.

In the embodiments described above, the connector shaft 154 detachably connects a drivetrain shaft 104 to a motor, generator 102 or the likes (e.g. a gearbox 30, or engine core 11) by permitting disconnection of a coupling 103, 153 between the connector shaft 154 and the drivetrain shaft 104.

In alternative or additional embodiments, the connector shaft 154 may detachably connect the drivetrain shaft 104 to the motor, generator 102 or the likes by permitting disconnection of a coupling 109, 159 between the connector shaft 154 and the motor, generator 102 or the likes.

In some embodiments, two disconnection mechanisms 150 may therefore be provided -a first coupling between the connector shaft 154 and the drivetrain shaft 104, and a second coupling between the same connector shaft 154 and the generator 102 or the likes. The first coupling 103, 153 may be located in a first end region of the connector shaft 154. The second coupling 109, 159 may be located in a second end region of the connector shaft 154, the second end region optionally lying within the motor, generator 102 or the likes. In embodiments with two couplings, both couplings may require the same axial movement for disengagement, or one coupling may require a greater axial movement for disengagement than the other, e.g. due to having wider gears providing the coupling, such that one coupling is decoupled before the other.

In alternative embodiments, there may be no separate connector shaft 154 and drivetrain shaft 104. Instead, a drivetrain shaft 104 may be detachably connected to the motor, generator 102 or the likes (e.g. a gearbox 30, engine core 11) directly, so also fulfilling the role of the connector shaft 154. In such embodiments, the coupling 153, 103 between the two shafts 104, 154 of the embodiments described above may be replaced by a coupling 109, 159 between the single shaft 154 and the motor or generator 102.

Detachable connections between the connector shaft 154 (which may or may not itself also be the drivetrain shaft 104) and the motor, generator 102 or the likes are described below with respect to Figures 8 to 10.

In the embodiments being described, a portion of the connector shaft 154 extends into the generator 102, as is shown in Figures 8 to 10.

In the embodiment shown in Figures 9A and 9B, the connector shaft 154 comprises a head 159 arranged to engage a portion 109 of the generator 102. The head 159 of the connector shaft 154 may be described as a coupling member 159; the head 159 is arranged to couple the connector shaft 154 to the generator 102. The head 159 has teeth or splines arranged to engage teeth or splines of the engaging portion 109 of the generator 102 in the embodiment being described. The head 159 may take the form of a gear 159; the gear 159 optionally being integral with the connector shaft 154.

The engaging portion 109 of the generator 102 extends inwardly towards the connector shaft 154 in the embodiment being described. In the embodiment being described, the engaging portion 109 has inwardly-directed teeth arranged to engage the teeth of the head 159.

In the embodiment being described, the head 159 is wider than the rest of the connector shaft 154, or at least wider than the rest of the portion of the connector shaft 154 within the generator 102.

The engaging portion 109 of the generator 102 is arranged to engage the head 159 of the connector shaft 154 such that the connector shaft 154 rotates a rotor of the generator 102, driving the generator, when the connector shaft 154 is in the first axial position. In embodiments in which the generator 102 is replaced with a motor or the likes, the engagement may instead allow the motor or the likes to drive rotation of the connector shaft 154. Engagement of the head 159 and engagement portions 109 allows torque to be transferred between the motor or generator 102 and the connector shaft 154.

In the embodiment being described, a disconnection mechanism 150 as described above is provided, with the coupling of the engagement portions 109, 159 within the generator 102 performing an equivalent function to the coupling 153, 103 to a separate drive shaft 104 described with respect to Figures 4 to 6. The engagement portions may be described as coupling members 109, 159.

In the embodiment being described, an actuator 156 moves a securing member 152 into engagement with a thread 154a on a part 154a of the connector shaft 154 not shown in Figures 8 to 10, and the continued rotation of the connector shaft 154 moves the connector shaft 154 axially until the engaging portions 109, 159 are disconnected.

In the embodiment shown in Figures 9A and 9B, when the connector shaft is moved from the first axial position (Figure 9A) into the second axial position (Figure 9B), the shaft 154 moves further into the generator 102, such that the head 159 moves past the engaging portion 109 and into a wider space in which the head 159 is not engaged. In alternative embodiments, the shaft 154 may instead be moved out of the generator 102. In either case, the connector shaft 154 is moved by a distance equal to or greater than the overlap distance between the head 159 and the engaging portion 109 of the generator 102 so as to fully disconnect the shaft 154 from the generator 102.

The skilled person will appreciate that an overlap length/area of the engaging portions 109, 159 may be chosen to be relatively large to provide a strong and reliable connection. For the design shown in Figures 9A and 9B, a relatively large axial movement of the connector shaft 154 may therefore be needed to disengage the coupling members 109, 159 (and thereby the drivetrain components 154, 102) around 1 to 5 cm in the embodiment shown.

In the embodiment shown in Figures 8A and 8B, the engaging portion 109 of the generator 102 comprises a row of axially spaced protrusions 109 extending inwardly towards the connector shaft 154. The protrusions 109 are arranged to engage corresponding protrusions 159 on the connector shaft 154 such that the connector shaft 154 rotates a rotor of the generator 102, driving the generator. In the embodiment being described, each protrusion 159 on the connector shaft 154 has teeth and may be described as a gear 159. In the embodiment being described, each protrusion 109 of the generator comprises teeth arranged to engage teeth on the corresponding gear 159. In the embodiment being described, the connector shaft 154 and the generator 102 each have four protrusions 159, 109. In alternative embodiments, the number of protrusions may vary, for example being between two and ten, and optionally between three and five, and/or the number of protrusions 109 on the generator 102 may differ from the number of protrusions 159 on the connector shaft 154, for example being larger, so optionally allowing the head 159 to be fully engaged in multiple different positions.

The skilled person will appreciate that, for the same total overlap distance and/or area between the engaging portions 109, 159 (summed over all protrusions), a smaller axial movement of the connector shaft 154 may be sufficient to disengage the components as compared to the embodiment shown in Figure 9, as each protrusion 109 of the generator 102 may be moved to align with a space between protrusions 159 on the shaft 154. In the embodiment being described, the connector shaft 154 is moved by a distance equal to the overlap distance between one protrusion of the head 159/engaging portion 109 of the generator 102 so as to fully disconnect the shaft 154 from the generator 102 rather than the whole overlap distance of the head 159 and engaging portion 109.

The skilled person will appreciate that such embodiments may be beneficial, for example when room for axial movement of the connector shaft 154 is limited. In the embodiment being described, the total movement required to disengage the mechanism 150 of Figures 8 and 10 is around 4-10 mm, as compared to 1-5 cm for the embodiment shown in Figure 9. The skilled person will appreciate that dimensions in various embodiments would depend on system size and configuration.

Figure 10 illustrates the coupling member 109, 159 design of Figure 8 with a detent 110 as described above. In the embodiment shown, the detent 110 is mounted on the generator 102 and biased towards the connector shaft 154. The detent 110 is received within a circumferential groove 157 of the connector shaft 154 in the first axial position (Figure 10A) and forced back towards the generator 102 / into the recess 105 when the connector shaft 154 moves into the second axial position (Figure 10B).

In the embodiment shown in Figure 10, the detent 110 is mounted near an entrance to the generator 102, and between the connector shaft head 159 and the entrance. In alternative embodiments, the detent 110 may be mounted further within the generator 102; for example, the shaft 154 may continue beyond the head 159 and the detent 110 may lie in a circumferential groove 157 on the far side of the head 159 from the entrance.

The skilled person will appreciate that an equivalent mechanism 150 may be used in a gas turbine engine 10, for example in a gas turbine engine 10 of an aircraft. The skilled person will appreciate that it may be beneficial to allow a fan 23 to keep rotating in the event of an engine failure in flight, to reduce drag, and that it may therefore be desirable for the fan 23 to be disconnectable from at least a portion of the gas turbine engine 10, such that the fan 23 can continue to rotate should the engine 10, or an engine component such as a gearbox 30, fail.

The shaft disconnection mechanism 150 may be used to decouple the fan 23 from a core shaft 26 driven by a turbine 19. In some embodiments, for example in non-geared gas turbine engines, the core shaft 26 may be the drivetrain shaft 104 and/or the connector shaft 154 for the shaft disconnection mechanism 150, and the shaft disconnection mechanism 150 may decouple the core shaft 26 directly from the fan 23 and/or from the turbine 19. In other embodiments, for example in geared gas turbine engines 10, the fan 23 may be driven by a drivetrain shaft 36 different from the core shaft 26, and optionally rotating at a different rate from the core shaft 26 for example, the core shaft 26 may drive a gearbox 30 which allows the drivetrain shaft 36 to be rotated at a different rate. The drivetrain shaft 36 may be the drivetrain shaft 104 and/or the connector shaft 154 for the shaft disconnection mechanism 150 of such embodiments. The skilled person will appreciate that the likelihood of a gearbox 30 jamming may be higher than that of the turbine 19 failing, and that it may therefore be desirable to have a decouple-able link between the gearbox 30 and the fan 23.

The skilled person will appreciate that, in normal operation of an aircraft, air passing through the fan 23 in flight is likely to drive the fan 23 to continue rotating even if motive power to the fan 23 fails -this is commonly termed "windmilling" of the fan 23. The windmilling of the fan may therefore keep the drivetrain shaft 104 rotating, so rotating the connector shaft 154 and providing the required force for the decoupling in such embodiments.

Figure 11 illustrates a method 200 of an embodiment.

At step 202, a signal is received indicating that a rotating drivetrain shaft 104, 154 should be disconnected, for example disconnected from a motor, generator 102, or gearbox 30. The signal may be an electrical signal.

In response to the signal, relative movement of a securing member 152 and a rotating connector shaft 154 is performed, at step 204, bringing a threaded portion 158 of the securing member 152 into position for engagement with a threaded portion 154a of the connector shaft 154. The connector shaft 154 may be the drivetrain shaft 104 in some embodiments. The connector shaft 154 may be disconnectably coupled to the drivetrain shaft 104 in other embodiments.

The skilled person will appreciate that, whilst the movement 204 may bring the threads 158, 154a into a position in which they can be engaged, in some embodiments (e.g. the embodiment depicted in Figures 4 to 6) it may be the continued rotation of the connector shaft 154 that engages the threads -the movement 204 may simply axially align the threads for engagement.

In alternative embodiments, for example in embodiments in which a securing member 152 is moved radially into contact with the threaded portion 154a of the connector shaft 154, the movement 204 itself may engage the threads 158, 154a without any rotational movement being required for engagement.

In various embodiments, only adjacent end regions of the threaded portions 158, 154a are engaged as a result of the movement of step 204 -the axial overlap between the threaded portions 158, 154a may be minimal.

The moving 204 the securing member 152 relative to the connector shaft 154 may comprise moving either or both of the securing member 152 and the connector shaft 154.

The relative movement 204 of the securing member 152 and the connector shaft 154 may be or comprise axial movement.

An actuator 156 may receive the signal and effect the movement 204 At step 206, continued rotation of the connector shaft 154 causes axial movement of the connector shaft 154 due to the interaction of the threads 154a, 158. The connector shaft 154 is therefore drawn away from its coupling to the drivetrain shaft 104 and/or its coupling to the motor, generator 102, or gearbox 30, disconnecting the drivetrain shaft 104 from the motor, generator 102, or gearbox 30.

In embodiments in which step 204 comprises relative axial movement, the movement in step 206 may be termed further relative axial movement.

It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

Claims

CLAIMS1. A shaft disconnection mechanism (150) comprising: a securing member (152) comprising a threaded portion (158); a connector shaft (154) arranged to rotate relative to the securing member (152), the connector shaft (154) comprising a coupling member (153, 159) arranged to couple the connector shaft (154) to a drivetrain component (102, 104) in a first axial position and to be decoupled from the drivetrain component (102, 104) in a second axial position, and a first shaft portion (154a) with a thread sized to engage the threaded portion (158) of the securing member (152); and an actuator (156) arranged to provide relative movement of the securing member (152) and connector shaft (154) so as to engage the threaded portion (158) of the securing member (152) with the first shaft portion (154a), and wherein the rotation of the connector shaft (154) relative to the securing member (152) with the threads (158, 154a) engaged is arranged to cause axial movement of the connector shaft (154) into the second axial positon.
2. The shaft disconnection mechanism (150) of claim 1, wherein the drivetrain component (104) is a drivetrain shaft (104), and wherein the connector shaft (154) is arranged to connect the drivetrain shaft (104) to an engine core (11), gearbox (30), motor or generator (102).
3. The shaft disconnection mechanism (150) of claim 2, wherein the coupling member (153) is or comprises a gear arranged to mesh with a gear (103) of the drivetrain shaft (104) in the first axial position and to be disengaged from the gear (103) of the drivetrain shaft (104) in the second axial position, the actuator (156) and the axial movement of the connector shaft (154) being arranged to move the connector shaft (154) from the first axial position into the second axial position.
4. The shaft disconnection mechanism (150) of claim 1, wherein the drivetrain component (102) is an engine core (11), gearbox (30), motor or generator (102).
5. The shaft disconnection mechanism (150) of any preceding claim, wherein the actuator (156) is arranged to provide relative axial movement of the securing member (152) and connector shaft (154), optionally by moving the securing member (152) axially.
6. The shaft disconnection mechanism (150) of any preceding claim, wherein the threaded portion (158) of the securing member (152) is a threaded hole (158), and wherein the connector shaft (154) is arranged to pass through the threaded hole (158) and comprises a second shaft portion (154b) sized not to engage the threaded portion (158) of the securing member (152), with the thread (154a) of the first shaft portion (154a) being sized to engage the threaded hole (158) and the second shaft portion (154b) being sized to pass through the threaded hole (158) without engaging the threaded hole (158).
7. The shaft disconnection mechanism (150) of claim 6, wherein the securing member (152) is a nut.
8. The shaft disconnection mechanism (150) of any preceding claim, wherein the actuator (156) comprises a solenoid.
9. The shaft disconnection mechanism (150) of claim 5, wherein the securing member (152) is mounted on a non-rotating support (102) by one or more solenoid pins (156), and wherein optionally the securing member (152) is mounted on the non-rotating support (102) by a plurality of solenoid pins (156), the plurality of solenoid pins (156) being arranged to prevent relative rotation of the securing member (152) and the non-rotating support (102).
10. The shaft disconnection mechanism (150) of any preceding claim, further comprising a retaining mechanism (110, 112) arranged to limit axial movement of the connector shaft (154), and wherein the continued rotation of the connector shaft (154) once the threads (154a, 158) are engaged is arranged to overcome the retaining mechanism (110, 112).
11. The shaft disconnection mechanism (150) of claim 10, wherein the connector shaft (154) comprises a circumferential groove (157), and wherein the retaining mechanism (110, 112) comprises a detent (110) biased towards the connector shaft (154) and arranged to be received in the groove (157) in the connector shaft (154).
12. The shaft disconnection mechanism (150) of claim 11, wherein the detent (110) is or comprises a spring-mounted ball.
13. The shaft disconnection mechanism (150) of any preceding claim, wherein the securing member (152) is arranged to be mounted on a motor or generator (102), and the connector shaft (154) is a motor shaft or generator shaft, respectively.
14. The shaft disconnection mechanism of claim 13, wherein the actuator (156) is arranged to move the securing member (152) with respect to the motor or generator (102) on which it is mounted.
15. An electric machine (100) comprising: a motor or generator (102); a drivetrain shaft (104); and the shaft disconnection mechanism (150) of any preceding claim, wherein the connector shaft (154) is connected to the motor or generator (102), and the coupling member (153) of the connector shaft (154) is arranged to be coupled to the drivetrain shaft (104) in the first axial position and to be decoupled from the drivetrain shaft (104) in the second axial position.
16. The electric machine (100) of claim 15, wherein the connector shaft (154) further comprises a second coupling member (159), the second coupling member (159) being arranged to couple the connector shaft (154) to the motor or generator (102) in the first axial position and to be decoupled from the motor or generator (102) in the second axial position.
17. An electric machine (100) comprising: a motor or generator (102); and the shaft disconnection mechanism (150) of any of claims 1 to 14, wherein the connector shaft (154) is a drivetrain shaft (104) of the electric machine (100), and the coupling member (159) of the connector shaft (154) is arranged to be coupled to the motor or generator (102) in the first axial position and to be decoupled from the motor or generator (102) in the second axial position.
18. The electric machine (100) of any of claims 15 to 17 wherein either: (i) the electric machine (100) comprises an electric motor (102) and the drivetrain shaft (104) is an output shaft of the electric motor (102); or (H) the electric machine (100) comprises a generator (102) and the drivetrain shaft (104) is an input shaft of the generator (102).
19. A gas turbine engine (10) for an aircraft comprising: an engine core (11) comprising a turbine (19), a compressor (14), and a core shaft (26) connecting the turbine to the compressor; a fan (23) located upstream of the engine core (11), the fan (23) comprising a plurality of fan blades; and a gearbox (30) that receives an input from the core shaft (26) and outputs drive to the fan (23) so as to drive the fan (23) at a lower rotational speed than the core shaft (26); a drivetrain shaft (36) that transmits the drive from the gearbox (30) to the fan (23) so as to drive the fan (23); and the shaft disconnection mechanism (150) of any of claims 1 to 12, wherein the coupling member (153) of the connector shaft (154) is arranged to be coupled to the drivetrain shaft (36), between the drivetrain shaft (36) and the gearbox (30), in the first axial position and to be decoupled from the drivetrain shaft (36) in the second axial position, such that the gearbox (30) is arranged to be disconnected from the fan (23) by movement of the connector shaft from the first axial position to the second axial position.
20. The gas turbine engine (10) of claim 19, wherein the securing member (152) is mounted on the gearbox (30).