Patent Publication Number: US-2023137247-A1

Title: Generator coupling system

Description:
TECHNICAL FIELD 
     The invention relates to a disconnect device for disconnecting a rotational drive of an aircraft engine from a generator driven by the aircraft engine. 
     BACKGROUND OF THE INVENTION 
     Aircraft engines, such as jet or turbojet engines, can be used to drive electrical generators which generate electricity used by the aircraft during operation. Typically, the electrical generators are driven by a drive shaft which is connected, directly or indirectly (e.g. via a gearbox), to a main turbine of an aircraft engine. 
     As with any mechanical system, mechanical failures can happen in the electrical generators of aircraft engines. A disconnect device which can mechanically decouple the electrical generator from the engine&#39;s turbine must therefore be provided. Even though the loss of electrical generation capacity through disconnection can be serious, if a malfunctioning generator is not disconnected from the turbine, the aircraft engine as a whole may be damaged or its performance hindered. 
     The majority of prior art disconnect devices used in this context provide a means by which an axial force can be applied to the drive shaft, causing the drive shaft to move axially which in turn enables a decoupling mechanism to operate. Known methods exist for providing this axial force in the prior art, each of which has its own disadvantages. These three known methods are:
         1. Extracting mechanical power from the rotating drive shaft to operate a disconnect mechanism. Whilst this enables very high actuating forces and rapid disconnection, the known disconnect mechanisms of this kind typically require very accurate tolerances and thus a selective assembly process and so often prove unreliable in the event of a rotor bearing failure with loss of radial location. Therefore, this method has proved to be less reliable in use than would be preferred to date;   2. Using a large actuator and a mechanical advantage generating mechanism such as a lever arm, or using an actuator to release a large and powerful spring. These methods typically have a more robust assembly process and thus prove to be more reliable in service. However, the axial force they can produce is typically limited and will not always be sufficient to guarantee disconnection. Therefore, this method cannot ensure a successful disconnect in all likely failure scenarios;   3. Using hydraulic pressure from the oil cooling system of an aircraft engine to provide the axial force required for disconnection. Whilst this solution can provide very high disconnecting forces, this method does not work in the event of a failure in the oil cooling system. Therefore, this method also cannot ensure disconnect in all likely failure scenarios.       

     US 2017/0016489 A1 discloses a disconnect mechanism that includes an input shaft defining a drive axis. A disconnect shaft is selectably engaged with the input shaft and driven about the drive axis by the input shaft. When a pawl actuator is translated to engage a ramp, the disconnect ramp shaft axially moves the disconnect shaft from a first axial position to a second axial position. 
     There exists a need for an improved disconnect device. 
     SUMMARY OF THE INVENTION 
     The inventors have identified that improvements can be made to known disconnect devices. These improvements may be best understood with reference to a known disconnect device in which an output from the aircraft engine drives a generator input shaft which is selectably engageable, via a disconnectable drive transfer means, with a disconnect shaft to transfer drive to a rotor of a generator. 
     The inventors have identified several issues with this known system. One issue arises from misalignment between the generator input shaft and the engine output shaft. Such misalignment causes accelerated wear of the drive transfer means which, in addition to decreasing its service life, can impede the movement of the drive transfer means into its disconnected configuration, making the disconnect device less reliable. Furthermore, the inventors have identified that a lack of lubrication of the drive transfer means can further accelerate wear thereof. The invention seeks to address these drawbacks. 
     According to the invention, there is provided a generator input shaft assembly, of a generator arranged to be driven by a prime mover of an aircraft, the generator input shaft assembly comprising:
         a generator input shaft arranged to receive a drive input to the generator; and   a disconnect input shaft arranged to deliver a drive input from the generator input shaft to a disconnectable drive transfer means, the disconnectable drive transfer means being configured to transfer rotational drive from the generator input shaft assembly to a rotor of the generator;   wherein the generator input shaft assembly is configured such that the generator input shaft can: float axially relative to the disconnect input shaft; and/or drive the disconnect input shaft with an axis of rotation of the generator input shaft non-parallel to an axis of rotation of the disconnect input shaft, so as to compensate for a misaligned input to the generator input shaft.       

     The invention provides a solution to the issues identified in known disconnect devices. In particular, the disconnectable drive transfer means does not suffer accelerated wear should there be a misaligned input to the generator input shaft. Instead, misalignment is compensated by the generator input shaft assembly having a generator input shaft that is able to transfer drive even when its axis of rotation is non-parallel to that of the disconnect input shaft. Furthermore, the generator input shaft being able to float axially relative to the disconnect input shaft allows it to transfer drive when there is misalignment as a result of the disconnect input shaft&#39;s position along the axis of the rotor. 
     The generator input shaft may be configured to drive the disconnect input shaft via an axially moveable torque transferring interface. The axially moveable torque transferring interface may comprise intermeshing input teeth. The intermeshing input teeth project radially with respect to the disconnect input shaft. The intermeshing input teeth may comprise a first set of teeth extending from an inner circumferential surface of the disconnect input shaft. The first set of teeth may be arranged to intermesh with a second set of teeth. The second set of teeth may extend from an outer circumferential surface of the generator input shaft. The axially moveable torque transferring interface may comprise a spline arrangement. 
     According to another aspect of the invention, there is provided a generator arranged to be driven by an aircraft engine, comprising the generator input shaft assembly as described hereinabove. The generator may further comprise a fluid circuit configured to deliver a flow of fluid to the axially moveable torque transferring interface. This has the advantage of providing a generator in which the axially moveable torque transferring interface may be sufficiently lubricated to increase its wear resistance to thereby increase its service life and improve the reliability of the disconnect device. 
     The fluid circuit may be configured to deliver a flow of fluid to the disconnectable drive transfer means. The disconnectable drive transfer means may comprise a first disconnect member and a second disconnect member, and an engaging interface therebetween. The fluid circuit may be configured to deliver a flow of fluid to the engaging interface. This has the advantage of providing a generator in which the disconnectable drive transfer means may be sufficiently lubricated to increase its wear resistance to thereby increase its service life. In particular, this has the advantage of increasing the reliability of the disconnect device, especially when operated at high speeds, and of increasing the durability of the disconnect device to allow for a greater number of disconnections before servicing is required. 
     The first disconnect member may be configured to transfer rotational drive to the rotor via an intermeshing rotor interface. The fluid circuit may be configured to deliver a flow of fluid to the intermeshing rotor interface. This has the advantage of providing a generator in which the intermeshing rotor interface may be sufficiently lubricated to increase its wear resistance to thereby increase its service life and improve the reliability of the disconnect device. 
     The rotor may be mounted in a generator housing. The rotor may be journaled by a rotor bearing. The fluid circuit may be configured to deliver a flow of fluid to the rotor bearing. This has the advantage of providing a generator in which the rotor bearing may be sufficiently lubricated to increase its wear resistance to thereby increase its service life and improve the reliability of the generator. 
     The fluid circuit may comprise a first branch, configured to deliver a flow of fluid to the axially moveable torque transferring interface between the generator input shaft and the disconnect input shaft. The first branch may be configured to deliver a flow of fluid to the disconnectable drive transfer means. The fluid circuit may comprise a second branch. The second branch may be configured to deliver a flow of fluid to the rotor bearing. This has the advantage of substantially separating the fluid circuits into two branches such that a blockage or loss of pressure in one branch will have a reduced negative effect on the other branch. Therefore, this provides the advantage of a more reliable disconnect device that is able to continue providing fluid for lubrication to the axially moveable torque transferring interface and to the disconnectable drive transfer means even in a situation of failure of the rotor bearing. Furthermore, this provides the advantage that components will retain their wear resistance even in some situations of failure. 
     According to another aspect of the present invention, there is provided a system comprising the generator as described hereinabove. The system may further comprise an aircraft engine assembly comprising an engine assembly output shaft. The generator may be arranged to be driven by the engine assembly output shaft. The generator input shaft may be configured to be able to float axially relative to the disconnect input shaft and/or to be able to drive the disconnect input shaft when an axis of rotation of the generator input shaft is non-parallel to an axis of rotation of the disconnect input shaft so as to be able to compensate for a misalignment between the engine output shaft and the disconnect input shaft of the generator. 
     The generator input shaft may comprise a distal end facing the aircraft engine and a generator end facing the rotor. The generator input shaft may be configured such that a force generated by a pressure of the fluid circuit of the generator impinging on the generator end is equal to a force generated by a pressure of an engine assembly fluid impinging on the distal end. This has the advantage that the pressure of the fluid circuit from the generator is balanced by the pressure of fluid impinging on the distal end of the generator input shaft, such that the resultant force on the generator input shaft along its axis may be zero. This has the advantage of providing a system in which the generator input shaft does not suffer from a high axial load due to the hydrostatic pressure of the fluid. Therefore, premature wear and damage to the generator input shaft assembly is reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the present invention will become apparent from the following description of embodiments thereof, presented by way of example only, and by reference to the drawings, wherein: 
         FIG.  1    is a schematic diagram illustrating a disconnect device according to one embodiment of the present invention. 
         FIG.  2    is a schematic diagram illustrating the disconnect device of  FIG.  1   . 
         FIG.  3    is a schematic diagram illustrating the disconnect device of  FIG.  1   . 
         FIG.  4    is a schematic diagram illustrating the disconnect device of  FIG.  1   . 
         FIG.  5    is a schematic diagram illustrating an aircraft and an aircraft engine according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Turning to  FIGS.  1  and  5   , there is shown a generator input shaft assembly  129  according to one embodiment. The generator input shaft assembly  129  is shown and described herein in the context of a generator drive disconnect device  100 . The generator drive disconnect device  100  can be comprised in a generator  3 , arranged to be driven by a prime mover of an aircraft such as an aircraft engine  2 , of an aircraft  1 . The generator  3  comprises a rotor  110 , rotatable about a rotor axis A. The generator  3  further comprises a disconnect input shaft  120 , rotatable about the rotor axis A. The generator input shaft assembly  129  transfers drive from the aircraft engine  2  to the disconnect device  100 . The drive from the engine may optionally be provided via an output gearbox, preferably via an output shaft, of the aircraft engine. A system can therefore comprise an aircraft engine assembly, comprising a prime mover and an output shaft, and a generator input shaft assembly  129 . 
       FIG.  1    illustrates one embodiment of the disconnect device  100 . A disconnect input shaft  120  is rotatably mounted in a generator housing  150 , journaled to rotate about rotor axis 
     A by a bearing  127 . A generator input shaft  160  is mounted within the disconnect input shaft  120  by a set of intermeshing splines  123 ,  163 . The disconnect input shaft  120  and the generator input shaft  160  are together comprised in an input shaft assembly  129 . In operation, an aircraft engine can be connected to the input shaft assembly via splines  164  provided on the generator input shaft  160 . In this way, the input shaft assembly  129  transfers rotational drive from the aircraft engine to drive the disconnect device  100  to rotate about rotor axis A. The rotor  110  of the generator is rotatably mounted in the housing  150 , journaled by a rotor bearing  117 . The rotor comprises splines  114  arranged to mesh with splines  104  of a first disconnect member  101 . Therefore, the first disconnect member  101  is able to rotate with the rotor  110  via meshed splines  104 ,  114  and can move along rotor axis A relative to the rotor  110 . The disconnect device  100  comprises a disconnectable drive transfer means  116  arranged to transfer rotational drive between the first disconnect member  101  and a second disconnect member  121 . The second disconnect member  121  is arranged to rotate with the disconnect input shaft  120 . Although the second disconnect member  121  is shown in  FIG.  1    to be an integral part of the disconnect input shaft  120 , it will be appreciated that this component may instead be distinct from the disconnect input shaft  120  while still being able to rotate therewith. The first and second disconnect members  101 ,  121  comprise first and second clutch members  105 ,  125 , respectively, that are axially separable from one another. When engaged, the clutch members  105 ,  125  facilitate the transfer of rotational drive in the drive transfer means  116  such that the drive transfer means  116  is in a connected configuration. In the connected configuration, the drive transfer means  116  transfers rotational drive from the disconnect input shaft  120  to the rotor  110 , via the first and second disconnect members  101 ,  121 . When the clutch members  105 ,  125  are axially separated by the relative axial separation of the first and second disconnect members  101 ,  121 , the drive transfer means is in a disconnected configuration. Such separation may be achieved by any suitable disconnect mechanism. For example, a ramp member  130  may be provided, able to rotate with the drive transfer means  116  and comprising a ramp  131 . A disconnect actuating member  140  may be mounted to the housing  150  and can be actuated towards the rotor axis A, that is, towards the ramp member  130 . After actuation of the disconnect actuating member  140 , it engages the ramp  131  to axially move the first disconnect member  101  away from the second disconnect member  121  to thereby move the drive transfer means  116  to its disconnected configuration. 
     The clutch members  105 ,  125  are together configured as a dog clutch and are axially separable along rotor axis A, but it will be appreciated that other suitable forms of drive transfer means, such as a friction clutch, may be employed. The first disconnect member  101  is moveable along rotor axis A between a first axial position and a second axial position. In the first axial position of the first disconnect member  101 , the first clutch member  105  is engaged with the second clutch member  125  such that the drive transfer means  116  is in its connected configuration. In the second axial position of the first disconnect member  101 , the first clutch member  105  is disengaged from the second clutch member  125  such that the drive transfer means  116  is in its disconnected configuration. In  FIG.  1   , the first disconnect member  101  is shown to be positioned in its first axial position such that the drive transfer means  116  is in its connected configuration. In the connected configuration of the drive transfer means  116 , the clutch members  105 ,  125  cause the first disconnect member  101  and the second disconnect member  121  to rotate together at the same speed. In the disconnected configuration of the drive transfer means  116 , the clutch members  105 ,  125  are separated along rotor axis A such that the first disconnect member  101  and the second disconnect member  121  rotate independently of each another. 
     In the arrangement shown in  FIG.  1   , the second disconnect member  121  is not moveable along the rotor axis A relative to the disconnect input shaft  120 . In another arrangement, the second disconnect member  121  may be an independent component to the disconnect input shaft  120  and may be configured to rotate therewith by, for example, a set of meshing teeth. In a further arrangement, the second disconnect member  121  is an independent component to the disconnect input shaft  120  and can, for example by the provision of meshing splines, move along the rotor axis A relative to the disconnect input shaft  120 . Therefore, while the figures referenced herein illustrate an embodiment in which only the first disconnect member  101  is moveable along rotor axis A, it will be understood that modifications to this arrangement could be made such that the second disconnect member  121  were also, or solely, able to move along rotor axis A, in order to move the drive transfer means  116  into and out of the disconnected configuration. 
     The rotor  110  is rotatable within the housing  150 , journaled by a bearing  117 . The rotor  110  comprises a plurality of splines  114  on an inner circumferential surface thereof. These may be provided on a flange  111 . The first disconnect member  101  comprises a plurality of splines  104  disposed around an outer circumferential surface of a second end  107  of the first disconnect member  101 . The splines  104  engage the splines  114  such that rotational drive can be transferred between the first disconnect member  101  and the rotor  110 . The splines  104 ,  114  allow the first disconnect member  101  to translate along the rotor axis A between the first axial position and the second axial position. Therefore, the first disconnect member  101  can rotate with the rotor  110 , relative to the housing  150 , while being axially moveable relative to the rotor  101 . In the connected configuration, rotational drive is transferred from the disconnect input shaft  120  to the rotor  110  via the drive transfer means  116  and the splines  104 ,  114 . The rotor  110  further comprises a rotor shaft  112 , fixedly mounted to the rotor  110 . The rotor shaft  112  extends axially from the rotor  110  along the rotor axis A towards the drive transfer means  116 . 
     The disconnect device  100  may further comprise a biasing means  119 . The biasing means  119  can be arranged to bias the drive transfer means  116  to its connected configuration. In  FIG.  1   , the biasing means is shown to be a coiled spring disposed around the rotor shaft  112  in an annular space  118  around rotor axis A, but it will be understood that other suitable biasing means may be employed instead of, or in addition to, a spring. The biasing means  119  is arranged to be in compression such that it exerts a force to bias the first disconnect member  101  away from the rotor  110 . Therefore, the biasing means  119  biases the first disconnect member  101  towards the second disconnect member  121 , thereby biasing the first clutch member  105  towards engagement with the second clutch member  125 , to thereby bias the drive transfer means  116  to its connected configuration. As such, the biasing means  119  is a connection biasing means. 
     The disconnect device  100  further comprises a disconnect mechanism. The disconnect mechanism comprises any suitable mechanism capable of moving the drive transfer means  116  into the disconnected configuration. Such separation may be achieved by moving the first disconnect member  101  axially relative to the second disconnect member  121 . 
     The figures described herein refer to one possible example of a known disconnect mechanism that may be employed in the disconnect device  100 . In this example, the ramp member  130  is disposed around an outer circumferential surface of the first end  106  of the first disconnect member  101 . The ramp member comprises a ramp  131  extending around at least a part of the angular extent of the ramp member  130 . The ramp member  130  comprises an inner flat section  133  that comprises an annular surface disposed around rotor axis A, extending around the full angular extent of the first disconnect member  101 . The ramp member  130  further comprises an outer flat section  132 , disposed at least part way around the rotor axis A, that is, extending around at least a part of the angular extent of the first disconnect member  101 . The ramp  131  and the outer flat section  132  are disposed radially outwards of the inner flat section  133 . The outer flat section  132  is axially offset, along the rotor axis A, from the inner flat section  133 . In this embodiment, the outer flat section  132  is offset from the inner flat section  133  towards the flange  111 , but it will be understood by the skilled person that a different arrangement may be employed in different embodiments, such as in an embodiment in which the ramp member is instead disposed around the second disconnect member  121 . The ramp  131  of the ramp member  130  begins at an axial position of the outer flat section  132  and ramps in a helical manner towards the axial position of the inner flat section  133 , that is, towards the disconnect input shaft  120  in this embodiment. Therefore, the ramp  131  provides a substantially axially-oriented incline extending from the axial position of the outer flat section  132  towards the axial position of the inner flat section  133 . 
     The disconnect mechanism of this example further comprises a disconnect actuating member  140  within an actuation chamber  145  of the housing  150 . In  FIG.  1   , the disconnect actuating member  140  is shown to have a cylindrical portion slideably receivable by an extension  142  of the housing  150 , but it will be appreciated that other suitable means for mounting the disconnect actuating member  140  to the housing may be employed. Furthermore, while the disconnect actuating member is shown in  FIG.  1    to have an axis of motion perpendicular to the rotor axis A, it will be appreciated that the disconnect actuating member  140  may instead be oblique to the rotor axis A. The disconnect actuating member  140  is moveable between a de-activated position and an activated position. A spring  144  is provided between the disconnect actuating member  140  and the housing  150 , but it will be appreciated that other suitable biasing means may be employed. The spring  144  biases the disconnect actuating member  140  towards its activated position, that is, towards the rotor axis A in a direction that may be perpendicular to the rotor axis A. In  FIG.  1   , the disconnect actuating member  140  is in its de-activated position. The disconnect actuating member  140  is maintained in its de-activated position, against the force of the spring  144 , by a retaining means (not shown). It will be understood by the skilled person that any such retaining means capable of enabling the disconnect actuating means  140  to be spring-loaded will be suitable. The retaining means may comprise a mechanical latching mechanism, or any suitable pneumatic, hydraulic or magnetic mechanism capable of holding the disconnect actuating member  140  in its de-activated position, against the force of the spring  144 . It will be understood by the skilled person that upon releasing the retaining mechanism, the disconnect actuating member  140  will be forced, by the spring  144 , towards the rotor axis A into an activated position, in which it can activate the disconnect mechanism. Alternatively, the biasing and retaining means may be replaced or supplemented by an active actuation means (not shown), capable of moving the disconnect actuating member  140  between its de-activated and activated positions. Such an active actuation means may comprise a solenoid, hydraulic or pneumatic arrangement, or any other arrangement capable of actuating the disconnect actuating member  140  towards the ramp member  131  and further towards the rotor axis A. 
     In the de-activated position, the disconnect actuating member  140  of the disconnect mechanism of this example is positioned in proximity to, and radially outward of, the ramp member  130 , but not in contact therewith. Movement of the disconnect actuating member  140  into the activated position, that is, towards the rotor axis A, allows it to engage the ramp member  130 . When the disconnect actuating member  140  engages the ramp  131  on the ramp member  130 , the interaction between the disconnect actuating member  140  and the ramp  131  forces the ramp member  130  along rotor axis A to move the first disconnect member  101  from its first axial position to its second axial position, thereby moving the drive transfer means  116  into its disconnected configuration. 
     As shown in  FIG.  1   , the disconnect actuating member  140  is in its de-activated position. The first disconnect member  101  is held in its first axial position by the biasing means  119 . Therefore, the drive transfer means  116  is in its connected configuration such that rotational drive is transferred from the disconnect input shaft  120  via the drive transfer means  116  to the first disconnect member  101  and to the rotor  110 . As such, the disconnect input shaft  120 , first disconnect member  101 , ramp member  130  and the rotor  110  rotate together with respect to the disconnect actuating member  140 . 
     Upon release of the retaining mechanism of the disconnect actuating member  140 , the disconnect actuating member  140  is biased by the spring  144  towards its activated position, that is, towards the ramp member  130 . Depending upon the rotational position of the ramp member  130  when the disconnect actuating member  140  is moved to its activated position, the disconnect actuating member  140  will either contact an outer circumferential surface of the ramp  131  or engage the outer flat section  132 . In the former case, the ramp member  130  will rotate with respect to the disconnect actuating member  140  until the outer flat section  132  is brought into rotational alignment with the disconnect actuating member  140 , at which point the spring  144  continues to bias the disconnect actuating member  140  towards rotor axis A and into engagement with the outer flat section  132 . In any case, the disconnect actuating member  140  will engage the outer flat section  132  within one revolution of the ramp member  130  about rotor axis A. 
     As the ramp member  130  continues to rotate with respect to the disconnect actuating member  140 , so too does the outer flat section  132 , until the disconnect actuating member  140  eventually engages the ramp  131 . At this point, continued rotation of the ramp member  130  with respect to the disconnect actuating member  140  forces the ramp member  130  in a axial direction to thereby move the first disconnect member  101  from its first axial position to its second axial position, thereby disengaging the drive transfer means  116 . Once the ramp member  130  has been forced a sufficient distance along rotor axis A, the continued biasing of the disconnect actuating member  140  towards the rotor axis A allows the disconnect actuating member  140  to move radially inwards towards rotor axis A to thereby bring the disconnect actuating member  140  into engagement with the inner flat section  133 . The engagement of the disconnect actuating member  140  with the inner flat section  133  holds the ramp member  130  at an axial position that maintains the first disconnect mechanism  101  at its second axial position, against the action of the biasing means  119 . 
     The generator input shaft assembly  129  comprises the disconnect input shaft  120  and a generator input shaft  160 . The generator input shaft  160  is mounted at least partially within the disconnect input shaft  120  and has an axis of rotation about an input axis C. In  FIG.  1   , the generator input shaft  160  is disposed around rotor axis A; therefore, the input axis C and the rotor axis A are collinear. The generator input shaft  160  comprises splines  163  extending from an outer circumferential surface of a first end  160   a  of the generator input shaft  160 . The disconnect input shaft  120  comprises splines  123  extending from an inner circumferential surface thereof, the splines  123  being arranged to intermesh with the splines  163 . This splined connection  123 ,  163  permits the generator input shaft  160  to transfer rotational drive to the disconnect input shaft  120 . Furthermore, the splined connection  123 ,  163  permits axial movement of the generator input shaft  160  along rotor axis A relative to the disconnect input shaft  120 . Although the figures and the description provided herein specify that the disconnect input shaft  120  and the generator input shaft  160  are connected by a splined engagement, it will be understood that any suitable means for transferring drive rotational drive while permitting relative axial movement may be employed, such as an axially moveable torque transferring interface. Furthermore, the splined engagement  123 ,  163  is arranged such that the generator input shaft  160  can rock about rotor axis A such that input axis C and rotor axis A may become non-parallel. In one embodiment, this is achieved by an arrangement wherein the inner diameter of the disconnect input shaft  120  is sufficiently larger than the largest outer diameter of the splines  163 , thereby permitting the splines  163  to rock relative to the splines  123 . The splined engagement  123 ,  163  may comprise crowned splines to further facilitate such freedom of movement of the generator input shaft  160  relative to the disconnect input shaft  120 . Therefore, the splined engagement  123 ,  163  facilitates the transfer of rotational drive between the generator input shaft  160  and the disconnect input shaft  120 , even in circumstances in which the generator input shaft  160  is moved axially relative to the disconnect input shaft  120  and/or the generator input shaft  160  is non-parallel to the rotor axis A. 
     Optionally, the generator input shaft  160  further comprises a shear neck portion  168 . As is well known in the art, the shear neck portion  168  comprises a portion of reduced thickness of the shaft. Therefore, should the generator input shaft  160  experience a high shear stress resulting from, for example, a lagging generator rotor and a failed disconnect device, then the generator input shaft  160  will fail at the shear neck portion  168  to reduce adverse effects on the gearbox. The generator input shaft  160  further comprises a plurality of splines  164 , provided at a second end  160   b  of the generator input shaft  160 . The splines  164  are shown to be disposed around an outer circumferential surface of the second end  160   b  of the generator input shaft  160 . The splines  164  are provided as a means to connect the generator input shaft  160  to the aircraft engine, as will be described with reference to  FIG.  2   . 
       FIG.  2    illustrates an embodiment of the disconnect device  100  as described hereinabove with reference to  FIG.  1   . The disconnect device  100  is configured to selectably transfer drive from an aircraft engine, of an aircraft in which the disconnect device  100  is installed, to the rotor  110  of the generator. Rotational drive may be transferred to the disconnect device  100  via an aircraft gearbox (not shown). The aircraft gearbox transfers a rotational drive via an aircraft gearbox output shaft  170 . As shown in  FIG.  2   , the gearbox output shaft  170  is rotatably mounted in an aircraft gearbox housing  180 , journaled by bearings  181   a ,  181   b , such that the gearbox output shaft  170  can rotate about a gearbox axis B. The gearbox output shaft  170  comprises splines  174  on an inner circumferential surface thereof. The generator input shaft  160  and gearbox output shaft  170  are arranged such that the splines  164  are able to intermesh with the splines  174 . This splined connection  164 ,  174  permits the gearbox output shaft  170  to transfer rotational drive to the generator input shaft  160 . Furthermore, the splined connection  164 ,  174  permits axial movement of the generator input shaft  160  along rotor axis B relative to the gearbox output shaft  170 . Although the figures and the description provided herein specify that the gearbox output shaft  170  and the generator input shaft  160  are connected by a splined engagement, it will be understood that any suitable means for transferring drive rotational drive while permitting relative axial movement may be employed, such as an axially moveable torque transferring interface. The splined engagement  164 ,  174  between the gearbox output shaft  170  and the generator input shaft  160  may be arranged in a similar manner to the splined engagement  123 ,  163  between the generator input shaft  160  and the disconnect input shaft  170 , such that the splined engagement  164 ,  174  facilitates the transfer of rotational drive between the generator input shaft  160  and the gearbox output shaft  170 , even in circumstances in which the generator input shaft  160  is moved axially relative to the gearbox output shaft  170  and/or the generator input shaft  160  is non-parallel to the gearbox axis B. 
     In  FIG.  2   , the gearbox axis B is shown to be offset from rotor axis A by a distance, x. Although the gearbox axis B is shown to be parallel to the rotor axis A, it will be understood that the disclosure presented herein is not limited to such an arrangement, and may equally apply to situations in which the gearbox axis B were non-parallel to the rotor axis A, instead of, or as well as, being offset from the rotor axis A.  FIG.  2    illustrates a possible situation in aircraft engine assemblies in which the axis of rotation of the gearbox output shaft  170 , or any other input providing rotational drive to the generator, is non-parallel to and/or offset from the axis of rotation of the rotor of the generator. As such, the input to the generator is misaligned. This may occur as a result of manufacturing tolerances. In other words, the rotor axis A may be non-parallel to, and/or offset from, the gearbox axis B. 
     In certain prior disconnect devices, a gearbox output shaft is connected to a generator input shaft by a splined engagement, with the input shaft being directly connected to a disconnect device, for example, such that rotational drive is transferred directly from the gearbox output shaft to the disconnect device. In these prior disconnect devices, any misalignment between the gearbox output shaft and the generator input shaft would cause the input side of the disconnect device to be non-parallel with an axis of rotation of the rotor of the generator. As such, a drive transfer means, through which rotational drive would be transferred from the disconnect input shaft to the rotor, would be required to transfer drive between two shafts that were misaligned from one another. Such misalignment causes accelerated wear of the drive transfer means. For example, for a drive transfer means comprising a set of intermeshing clutch members, misalignment therebetween would cause accelerated wear of the clutch members, leading to an increased requirement for servicing and a less reliable disconnect device. Furthermore, misalignment in the drive transfer means would make fast disconnection more difficult. 
     The embodiment described herein seeks to solve the problem of accelerated wear of the drive transfer means  116  by employing the generator input shaft assembly  129 , comprising a separate generator input shaft  160  and disconnect input shaft  120  as described hereinabove. In the situation illustrated in  FIG.  2   , gearbox axis B is misaligned with rotor axis A, that is, the gearbox output shaft  170  is misaligned with the rotor  110 . This misalignment causes the input axis C to be non-parallel to the rotor axis A, that is, the misalignment causes the generator input shaft  160  to rotate about an axis that is non-parallel to the rotor  110 . In this illustration, the input axis C is at an angle, δ, to the rotor axis A. In  FIG.  2   , parts of the generator input shaft  160  may appear to impinge on surrounding parts of the gearbox output shaft  170  and the disconnect input shaft  120 ; this is a result of the angle δ being exaggerated for the sake of illustration. The arrangement shown allows the generator input shaft  160  to accommodate for the misalignment by it being able to rotate, and thereby transfer rotational drive, even when its input axis C is non-parallel to the rotor axis A. In particular, this is achieved by the splined engagement  164 ,  174  between the gearbox output shaft and the generator input shaft  160  and the splined engagement  123 ,  163  between the generator input shaft  160  and the disconnect input shaft  120  allowing the generator input shaft  160  to accommodate misalignment between the gearbox output shaft  170  and the rotor axis  11 , to thereby reduce misalignment between the first and second disconnect members  101 ,  121  of the drive transfer means  116 . 
     In addition to the generator input shaft  160  being able to rock about rotor axis A, it is further configured to float axially relative to the disconnect input shaft  120  and relative to the gearbox output shaft  120 . The generator input shaft  160  may be further provided with a first flange  165 , extending from the outer circumferential surface thereof, in proximity to an open end of the disconnect input shaft  120 . The flange  165  provides a means to limit the movement of the generator input shaft  160  towards the drive transfer means  116 , along rotor axis A. The generator input shaft  160  may further comprise a second flange  166 , extending from the outer circumferential surface thereof, in proximity to an open end of the gearbox output shaft  170 . The flange  166  provides a means to limit movement of the generator input shaft  160  towards the gearbox, along rotor axis A. 
       FIG.  3    illustrates an embodiment of the disconnect device  100  as described hereinabove with reference to  FIGS.  1  and  2   . In particular,  FIG.  3    illustrates the flow of a lubricant fluid, such as oil, throughout the disconnect device, which provides lubrication and heat transfer, for cooling purposes, from certain components in use. In certain prior disconnect devices that lack the generator input shaft assembly  129  as described herein, there has been no need to provide a fluid circuit to such an assembly. Therefore, an oil circuit is provided herein that may be employed in an embodiment of the disconnect device  100  and the flow of a suitable cooling/lubrication fluid in use is depicted using dotted areas. Although references to oil are made herein, the skilled person will appreciate that any other suitable fluid, particularly a liquid, capable of providing the required lubrication and/or heat transfer may be suitable. The oil circuit comprises a bore  115  provided in the rotor shaft  112 . The bore  115  is in fluid communication with an inlet port (not shown) provided upstream of the disconnect device, towards the rotor  110 . The bore  115  is pressure regulated upstream using a pressure relief valve (not shown) and facilitates the flow of oil from the rotor  110 , through the rotor shaft  112 , and towards the disconnect device  100 . The rotor shaft  112  comprises a first fluid port  112   a  and a second fluid port  112   b , which may be considered to be sized attenuators to control the oil flow rate. In this way, the flow of oil is maintained and controlled even when the rotor is stationary or is disconnected from the input shaft  160 . 
     The first fluid port  112   a  is provided by an axial hole through an end wall of the rotor shaft  112 . The first fluid port  112   a  is in fluid communication with both the bore  115  and a disconnect spline chamber  167 , in which the splined engagement  123 ,  163  is provided between the generator input shaft  160  and the disconnect input shaft  120 . Therefore, the first fluid port  112   a  provides a flow path to allow oil to flow from the bore  115  to the disconnect spline chamber  167 . The centrifugal force acting on the oil in the disconnect spline chamber  167 , provided by the rotating input shaft assembly  129  in use, causes the oil to flood the splines  123 ,  163 . In this way, the first fluid port  112   a  provides oil to lubricate the splines  123 ,  163 . An O-ring  122  is provided at an interface between the disconnect input shaft  120  and the generator input shaft  160  to seal the interface and prevent leakage of oil from the disconnect spline chamber  167 . The drive transfer means  116  is in fluid communication with the disconnect spline chamber  167 . Therefore, oil from the disconnect spline chamber  167  can be provided to the drive transfer means  116  to thereby flood the clutch members  105 ,  125  with oil. In this way, the clutch members  105 ,  125  of the drive transfer means  116  are lubricated with oil. An O-ring  135  is provided at an interface between the ramp member  130  and the disconnect input shaft  120  to seal the interface and prevent leakage of oil from the drive transfer means. The first disconnect member  101  comprises a first fluid port  101   a . The ramp member  130  comprises a fluid port  130   a . The fluid ports  101   a ,  130   a  together provide a flow path between the drive transfer means  116  and the actuation chamber  145 . The centrifugal force acting on the oil flooding the drive transfer means  116  forces the oil from the drive transfer means, through the fluid ports  101   a  and  130   a , and into the actuation chamber  145 . In this way, oil is provided to the disconnect actuating member  140  and to any other components in the actuation chamber  145  that may require lubrication and/or cooling, such as the ramp member  130 . 
     The second fluid port  112   b  is provided by a radial hole through the circumferential wall of the rotor shaft  112 . The rotor shaft  112  may also comprise an indentation  112   c , positioned diametrically opposite to the second fluid port  112   b , to substantially mechanically balance the effect of the removed material of the second fluid port  112   b . The second fluid port  112   b  is in fluid communication with both the bore  115  and the annular space  118 , thereby providing an oil flow path therebetween. Therefore, in use, the pressure acting on the oil forces oil out of the bore  115 , through the second fluid port  112   b , and into the annular space  118 . In this way, the annular space  118  can be flooded with oil. An O-ring  109  is provided at an interface between the first disconnect member  101  and the rotor  110 , at an outer circumferential surface of the annular space  118 , to seal the interface and prevent leakage of oil. In addition to the biasing means  119 , the annular space  118  further comprises a spacer  190 . The spacer  190  is an annulus, disposed around the rotor shaft  112  between the first disconnect member  101  and the biasing means  119  in order to maintain the biasing means  119  in a desired axial position. The spacer  190  comprises a plurality of radial holes  190   a . The spacer  190  maintains the position of the biasing means  119  around the rotor shaft  112  while allowing oil to flow within the annular space  118 . The first disconnect member  101  further comprises a second fluid port  101   b . The second fluid port  101   b  provides a flow path between the annular space  118  and a rotor spline chamber  102 , in which the splined engagement  104 ,  114  is provided between the first disconnect member  101  and the rotor  110 . The centrifugal force acting on the oil in the annular space  118  forces oil out of the annular space  118 , through the second fluid port  101   b , and into the rotor spline chamber  102 . Therefore, the second fluid port  101   b  provides oil to the rotor spline chamber  102  to thereby flood the splines  104 ,  114  with oil. In this way, the second fluid port  101   b  provides oil to lubricate the splines  104 ,  114 . Furthermore, the second fluid port  101   b  provides a weir to allow the annular space  118  to be flooded with oil; this ensures the contact faces of the biasing means  119  are lubricated. The rotor  110  comprises a fluid port  110   a . The fluid port  110   a  provides a flow path between the rotor spline chamber  102  and the rotor bearing  117 . The centrifugal force acting on the oil in the rotor spline chamber  102  forces oil out of the rotor spline chamber  102 , through the fluid port  110   a , and toward the rotor bearing  117 . In this way, the fluid port  110   a  provides oil to lubricate the bearing  117 . 
     Therefore, from a single feed of oil from the bore  115  of the rotor shaft  112 , a number of components of the disconnect device  100  that require lubrication, including the disconnect actuating member  140 , the rotor bearing  117 , the splines  104 ,  114 ,  123 ,  163  and the clutch members  105 ,  125  are provided with oil accordingly. Furthermore, these components are provided with oil using two separate fluid ports  112   a ,  112   b  from the bore  115 . Separating the oil circuit into a first and second branch as shown may be advantageous in that, in the event of disruption of oil flow or pressure loss in the first branch, the negative effect on the second branch will be reduced as compared to a case where a single path circuit is used. Similarly, in the event of disruption of oil flow or pressure loss in the second branch, the negative effect on the first branch will be reduced. One example of where this is can be advantageous is in the event of oil pressure loss from the branch defined by the first fluid port  112   a  due to, for example, rotor disconnection or failure of the rotor bearing  117 ; despite such an event, the drive transfer means  116  and/or the splines at the interface  123  will continue to be flooded with oil and will thereby continue to be lubricated. Therefore, the fluid circuit provided herein complements the generator input shaft assembly  129  by providing the drive transfer means with further wear and failure mode resistance, thereby lengthening its service life. Complementary to the shear neck portion  168  described hereinabove, the generator input shaft  160  optionally comprises an oil plug  169 . As shown in  FIG.  3   , the oil plug  169  is positioned inside the generator input shaft  160  at an axial position between the shear neck portion  168  and the disconnect spline chamber  167 . As such, in the event of failure of the generator input shaft  160  at the shear neck portion  168 , oil in the disconnect spline chamber  167  will be prevented by the oil plug  169  from escaping. 
       FIG.  4    illustrates an embodiment of the disconnect device  100  as described hereinabove with reference to  FIGS.  1  to  3   . In particular,  FIG.  4    illustrates the presence of oil around the generator input shaft  160 . As explained above, the first fluid port  112   a  provides a jet of oil from the bore  115  to the disconnect spline chamber  167 , and the apparent centrifugal force acting on the oil in the disconnect spline chamber  167 , provided by the rotating input shaft assembly  129  in use, causes the oil to flood the splines  123 ,  163 . As will be appreciated by the skilled person, the oil in the disconnect spline chamber  167  will have a certain pressure, P 1 . Furthermore, the oil in the disconnect spline chamber  167  will impinge on the generator input shaft  160  over a certain area, A 1 , in a direction that is towards the gearbox output shaft  170  along input axis C, that is, to the left of  FIG.  4   . Therefore, the oil in the disconnect spline chamber  167  will exert a force, F 1 , on the generator input shaft  160  in the direction of the arrow. The force F 1  will be equal to the product of the pressure P 1  and the area A 1 . As will be understood, the hydrostatic pressure of the oil used to lubricate the splines  123 ,  163  may produce a resultant force and an associated axial load on the generator input shaft  160 . Given that the generator input shaft  160  is configured to float axially relative to the disconnect input shaft  120  and to the gearbox output shaft  170 , such a resultant force would cause the generator input shaft  160  to accelerate towards the gearbox output shaft  170  until the flange  166  were brought into contact with the gearbox output shaft  170 , thereby limiting any further axial movement of the generator input shaft  160 . At this position, the generator input shaft  160  would continue to experience a compressive axial load due to the resultant force from the oil pressure. 
     In order to reduce such an axial load, the embodiment described herein advantageously provides a second force, F 2 , able to balance the first force F 1 . The gearbox output shaft  170 , to which the disconnect device  100  may be connected to in use, may be provided with an oil circuit (not shown). The oil circuit may comprise an inlet port (not shown) in fluid communication with a bore  172  of the gearbox output shaft  170 . The inlet port provides a supply of oil to the gearbox spline chamber  171 , via the bore  172 . The centrifugal force acting on the oil in the gearbox spline chamber  171 , provided by the rotating gearbox output shaft  170  in use, causes the oil to flood the splines  164 ,  174 . In this way, the fluid port  172  provides oil to lubricate the splines  164 ,  174 . An O-ring  173  is provided at an interface between the gearbox output shaft  170  and the generator input shaft  160  to seal the interface and prevent leakage of oil from the gearbox spline chamber  171 . Similarly to that of the disconnect spline chamber  167 , the oil in the gearbox spline chamber  171  will have a certain pressure P 2  and will impinge on the generator input shaft  160  over a certain area, A 2 , in a direction that is towards the disconnect input shaft  120  along input axis C, that is, to the right of  FIG.  4   . Therefore, the oil in the generator spline chamber  171  will exert a force, F 2 , on the generator input shaft  160  in the direction of the arrow. The force F 2  will be equal to the product of the pressure P 2  and the area A 2 . 
     The disconnect device  100  is configured such that F 1 =F 2  so that there is no resultant force along input axis C as a result of the oil pressure on the generator input shaft  160 . Therefore, the disconnect device  100  is configured such that A 1 P 1 =A 2 P 2 . Indeed, this condition may be satisfied even when, for example, P 1 ≠P 2 , by choosing appropriate values for A 1  and/or A 2  accordingly. Likewise, the condition for zero resultant force may be satisfied even when A 1 ≠A 2 , by choosing appropriate vales for P 1  and/or P 2  accordingly. Therefore, this embodiment of the disconnect device  100  advantageously provides flexibility of design while maintaining compatibility with the aircraft engines in which it may be installed. 
       FIG.  5    schematically illustrates an aircraft  1  comprising an aircraft engine  2  and a generator  3 . The aircraft engine  2  is able to transfer drive to the generator  3  via a generator input shaft  160 . The generator input shaft  160  is able to transfer drive to the rotor  110  via a disconnect device  100  as described hereinabove. 
     Various modifications, whether by way of addition, deletion and/or substitution, may be made to all of the above described embodiments to provide further embodiments, any and/or all of which are intended to be encompassed by the appended claims.