Disconnect arrangement with actuation device

Abstract

An electrical machine (100, fig 1), such as a generator, arranged to be driven by a prime mover (2, fig 1) of an aircraft (1, fig 1), comprises a rotor 101, an input shaft assembly 120 with an input s

Description

TECHNICAL FIELD The present invention relates to an electrical machine for use in an aircraft. In particular the invention relates to an electrical machine for use in an aircraft, having a disconnect arrangement with an actuation device for disconnecting the rotational drive of an aircraft engine from a generator driven by the aircraft engine. BACKGROUND 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 electrical generators of aircraft engines. A disconnect device which can mechanically decouple the electrical generator from the engine'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 performance of the aircraft engine may be hindered. Known 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; 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 can be more reliable in service. However, the axial force they can produce is typically limited and will not always be sufficient to guarantee disconnection; 3. Using 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. While the known solutions are useful in a range of situations, there exists a need for an improved disconnect device. SUMMARY OF THE INVENTION According to a first aspect, there is provided an electrical machine arranged to be driven by a prime mover of an aircraft. The electrical machine comprises: a rotor, which is rotatable about a rotational axis A; an input shaft assembly, comprising an input shaft, for receiving a drive input; and a disconnect arrangement, comprising: a drive transfer means, arranged to selectively transfer rotational drive between the input shaft assembly and the rotor; and an actuation device, arranged to actuate the drive transfer means. The disconnect arrangement comprises a braking means for braking the rotor. The actuation device may be arranged to selectively disconnect the drive transfer means from the rotor and to selectively decelerate rotational drive of the rotor of the generator. The disconnect arrangement is configurable in a plurality of operational configurations, including: a connected configuration, in which the drive transfer means is configured to transfer rotational drive between the generator input shaft assembly to the rotor; a braked configuration, in which the actuation device is configured to disconnect the drive transfer means from the rotor and the braking means is activated to hinder rotation of the rotor. In some embodiments, the actuation device comprises a disconnected configuration, in which the actuation device is configured to disconnect the drive transfer means from the rotor. In the disconnected configuration, the rotor is allowed to continue in rotation. This is because the braking means is not activated in the disconnected configuration. Such an arrangement provides an electrical machine which may be disconnected from transferring rotational drive in the event of a fault. Advantageously, the operational configurations provided by the disconnect arrangement also permit the selective disconnection of the rotational drive transfer to the rotor, as well as selective braking once the drive transfer is disconnected. Thus, the selective disconnection of the of the rotational drive transfer to the rotor may be activated independently of the braking. For this function, the actuation device may comprise a separation means, configured to selectively disconnect the drive transfer means from the rotor. The actuation device may comprise the braking means, configured to selectively hinder or brake or stop rotation of the rotor of the generator. Preferably, the actuation device comprises both the separation means and the braking means. This reduces the complexity of manufacture for the overall assembly. This also reduces the complexity of servicing either of the separation means and the braking means. In the present configuration, the functions are co-located in a single part, increasing the ease of manufacture and servicing. The separation means may be configured to selectively disconnect the drive transfer means from the rotor independently of the braking means. This provides an arrangement in which the rotor may be free to rotate when disconnected or, alternatively, may be selectively braked. This can be particularly advantageous for operating the separation means without operating the braking means, and reducing wear and maintenance requirements for the braking means. Two or more of the operational configurations may correspond to different axial positions of the actuation device relative to the rotor. Optionally, each of the operational configurations may correspond to different axial positions of the actuation device relative to the rotor. In preferable embodiments, the actuation device may be at an axially distal position from the rotor in the connected configuration. That is, at the furthest axial extent from the rotor, the actuation device may be in the connected configuration. Therefore, when the actuation device is at the furthest axial extent from the rotor, the drive transfer means may be connected to the rotor such that it is configured to transfer rotational drive thereto. Preferably, the braking means may be configured to selectively hinder or brake or stop rotation of the rotor only when the drive transfer means is disconnected from the rotor. The actuation device may be in an axially proximal position relative to the rotor in the braked configuration. Specifically, at the proximal axial extent from the rotor, such as when in a position closest to the rotor, the actuation device may be in the braked configuration. In this position, the braking means may be adjacent to, or contiguous with, a surface of the rotor or a surface connected to rotate with the rotor. The term "contiguous," as used herein, refers to a state of being in physical contact and touching at least partially along a surface, boundary, or at a point. This arrangement provides a means by which braking cannot be performed without disconnection having taken place. This prevents the possibility of inadvertent braking with the electric machine connected to a drive source and limits the possibility of braking to scenarios where the electrical machine has been disconnected from any drive input or output. In the disconnected configuration, the actuation device may be at an intermediate axial position, between the axially distal and axially proximal positions. Such a mode provides the option to disconnect the drive transfer means from the rotor but allow the rotor to rotate freely. Braking can subsequently be selectively provided by the braked configuration if it is required. An actuation biasing means may be configured to bias the actuation device to the connected operational mode. To provide this function, the actuation biasing means may be configured to bias the actuation device to the furthest axial extent from the rotor. The biasing means may comprise a spring arrangement. The separation means may comprise at least one rotatable member configured to allow the rotor to continue in rotation. The at least one rotatable member may comprise rollers, bearings, or bushings. The actuation device preferably comprises a piston. In some embodiments, the actuation device comprises an annular piston. The actuation device may comprise a hydraulically-activated piston. The actuation device may comprise a pneumatically- activated piston. The actuation device may provide an axial actuation force P, the axial actuation force P being applied at points which are on laterally opposing sides of the rotational axis A. With such arrangements, a corresponding hydraulic or pneumatic controller may be provided to the aircraft, enabling the selective activation of the separation means. As previously noted, the selective activation of the separation means also provides the option to selectively activate the braking means. According to a further aspect, there is provided an aircraft comprising the electrical machine according to the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS Further features and advantages of the present invention will be further described below, by way of example only, with reference to the accompanying drawings in which: FIGURE 1 is a schematic diagram illustrating an aircraft comprising an electrical machine according to the present invention. FIGURE 2 is a schematic diagram illustrating a disconnect arrangement of the electrical machine depicted in FIGURE 1. FIGURE 3 is a schematic diagram illustrating an actuation device for use in the disconnect arrangement depicted in FIGURE 2. FIGURE 4 is an enlarged schematic diagram illustrating the electrical machine of FIGURE 1 when the actuation device is in a connected configuration. FIGURE 5 is an enlarged schematic diagram illustrating the electrical machine of FIGURE 1 when the actuation device is in a braked configuration. FIGURE 6 is an enlarged schematic diagram illustrating the electrical machine of FIGURE 1 when the actuation device is in a disconnected configuration. DETAILED DESCRIPTION Referring firstly to Figures 1 and 2, there is shown a generator drive disconnect arrangement comprised as part of an electrical machine 100. The generator drive disconnect arrangement can be comprised in said electrical machine 100 which is arranged to be driven by a prime mover of an aircraft such as an aircraft engine 2, of an aircraft 1. The electrical machine 100 comprises a rotor 101, rotatable about rotational axis A, and a stator 102, which may comprise a plurality of stator windings. The stator 102 is typically configured as an annular member comprising a bore within which the typically cylindrical rotor 101 is rotatably mounted. The rotor 101 ordinarily being arranged concentrically within the bore of the stator 102, is generally rotatably mounted on an input-output shaft assembly 120 defining a rotational axis A therethrough. The electrical machine 100 may be configured to operate as a motor. In this configuration, the stator 102 is configured to receive electrical power from a power source 104. The electrical power is provided to the windings of the stator, producing a time-varying magnetic field which causes the rotor 101 to rotate. The rotor 101 in turn rotates the shaft assembly 120 and thus may be used to transfer drive to the prime mover 2. In some arrangements, such as is depicted in the embodiment of FIGS. 1 and 2, the electrical machine 100 may be configured to operate as a generator or a startergenerator. In such configurations, the rotor 101 is generally driven by the prime mover 2 via the shaft assembly 120 in generator mode. As the rotor 101 is rotated about the rotational axis A within the bore of stator 102, an associated magnetic field of the rotor 101 is also rotated. This causes a rotating magnetic field which interacts with the electrical conductors and thus generates a voltage within the windings of the machine 100. This voltage may subsequently be supplied to at least one electrical accessory or component 104 of the aircraft 1. The rotor 101 of the generator is rotatably mounted in a housing of the generator (not shown) and is journaled by a rotor bearing 105. The rotor 101 further comprises a rotor shaft 106 which is fixedly mounted to the rotor 101. The rotor shaft 106 extends axially from the rotor 101 along the rotational axis A towards the prime mover 2. The generator 100 further comprises a first disconnect member 110. The first disconnect member 110 is configured to transfer rotational drive to the rotor 101. The rotor 101 comprises splines 108 arranged to mesh with splines 118 of the first disconnect member 110. Therefore, the first disconnect member 110 is able to rotate with the rotor 101 via meshed splines 108, 118 and may be translated along rotational axis A relative to the rotor 110. Thus, the first disconnect member 110 may move axially along the rotational axis A. The first disconnect member 110 further comprises a first disconnectable interface 115 which is configured to rotate with the rotor shaft 106, discussed in further detail below. In Figure 2, there is also shown a generator input shaft assembly 120, configured to transfer drive from the aircraft engine 2 to the generator 100, or vice versa when the electrical machine works in starter mode. The generator input shaft assembly 120 comprises a disconnectable transfer shaft 130 which is rotatably mounted in the generator housing (not shown). The disconnectable transfer shaft 130 may be journaled to rotate about rotational axis A by a bearing (not shown). The generator input shaft assembly 120 further comprises an intermediate shaft 140. The intermediate shaft 140 comprises a first end 140a, proximal to the rotor; and a second end 140b, distal to the rotor. The first end 140a of the intermediate shaft 140 is mounted within the disconnectable input shaft 130 by a set of intermeshing splines 131, 141. In operation, an aircraft engine can be connected to the input shaft assembly 120 via splines 142, which are provided at the second end 140b of the intermediate shaft 140. Proximal to the rotor, the input shaft assembly 120 functions as a second disconnect member. To perform this function, the disconnectable input shaft 130 comprises a second disconnectable interface 135. The second disconnectable interface 135 is configured to rotate with the input shaft assembly 120. Although the second disconnectable interface 135 is shown in Figure 2 to be an integral part of the disconnectable input shaft 130, it will be appreciated that this component may otherwise be provided as a separate component to the disconnectable input shaft 130 while still being assembled to rotate therewith. The first and second disconnectable interfaces 115, 135 are configured to provide a drive transfer means 150 between the input shaft assembly 120 and the rotor 101. That is, the drive transfer means 150 comprises the first and second disconnectable interfaces 115, 135. In the illustration of Figure 2, the first and second disconnectable interfaces 115, 135 comprise clutch members which are together configured as a dog clutch and are axially separable along the rotational axis A. It will be appreciated that other suitable forms of drive transfer means 150, such as any separable meshing arrangement, or a friction clutch, may be employed. In this way, the input shaft assembly 120 is configured to selectively transfer rotational drive from the aircraft engine 2 to drive the rotor 101 to rotate about rotational axis A. The rotor 101 may further comprise a rotor shaft biasing means 107. In FIG. 2, the rotor shaft biasing means 107 is shown to be a coiled spring disposed around the rotor shaft 106, but it will be understood that other suitable biasing means may be employed instead of, or in addition to, a spring. The rotor shaft biasing means 107 is arranged to be in compression such that it exerts a force to bias the first disconnectable interface 115 away from the rotor 101. Therefore, the rotor shaft biasing means 107 biases the first disconnectable interface 115 towards the second disconnectable interface 135 to thereby bias the drive transfer means 150 to its connected configuration. The drive transfer means 150 may be connected (engaged), or disconnected (disengaged), selectively. The first disconnect member 110 is moveable along rotational axis A between a first axial position and a second axial position. In the first axial position of the first disconnect member 110, the first disconnectable interface 115 is engaged with the second disconnectable interface 135 such that the drive transfer means 150 is in an engaged configuration. In the second axial position of the first disconnect member 110, the first disconnectable interface 115 is disconnected from the second disconnectable interface 135 such that the drive transfer means 150 is in a disconnected configuration. In Figure 2, the first disconnect member 110 is shown to be positioned in its first axial position, such that the drive transfer means 150 is in the engaged configuration. In the connected configuration of the drive transfer means 150, the first and second disconnectable interfaces 115, 135 cause the rotor shaft 106 and the input shaft assembly 120 to rotate together at the same speed. In the disconnected configuration of the drive transfer means 150, the first and second disconnectable interfaces 115, 135 are separated along the rotational axis A such that the rotor shaft 106 and the input shaft assembly 120 rotate independently of each other. 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. In the present disclosure, the function of separating the disconnectable interfaces 115, 135 along the rotational axis A is performed by an actuation device 200. In Figure 3, there is illustrated an example of the actuation device 200 according to the present invention. The actuation device 200 is generally configured to disconnect the electric machine's rotor from its input shaft and includes both a separation means and a braking means. The provision of both means in a single device is advantageous for meeting the volume constraints of an electrical machine. Such an actuation device 200 also simplifies both assembly and servicing of an electrical machine. The actuation device 200 comprises annular body 210 which projects axially. The annular body 210 may comprise an annular piston. Being annular, the body 210 of actuation device 200 therefore defines a bore 211. With this construction, the actuation device 200 can be fitted concentrically around parts within the generator assembly, such as the disconnectable input shaft 130 and the intermediate shaft 140 of the input shaft assembly 120. Thus, such parts can be accommodated within the bore 201 of the actuation device 200. The actuation device 200 further comprises one or more separation means 220. The one or more separation means 220 may comprise one or more protrusions which project radially inwards from an inner surface of the actuation device 200. In the example of Figure 2, the actuation device 200 comprises a multiple contact-point mechanism 220 which is configured to contact a surface of the first disconnect member 110 to disconnect the drive transfer means. In other examples, not illustrated, a ramped surface may be provided on an inner surface of the actuation device 200 configured to axially move the first disconnectable interface 115 away from the second disconnectable interface 135 to thereby move the drive transfer means 150 to its disconnected configuration. The actuation device 200 may comprise a separation means 220 comprising a pawl which is configured to separate the first and second disconnectable interfaces 115, 135. It will therefore be understood that the separation means 220 may take any appropriate form. The actuation device 200 comprises a braking means in the form of a braking surface 230. It will be understood that the term "braking surface" in this context refers to an interface which is configured to contact an otherwise moveable component (e.g. a rotor), to hinder or prevent it from rotating. Braking by contacting a moveable component of the electrical machine with the braking contact surface of the rotor would prevent the motor from being operated. The braking surface 230 is configured to apply a frictional braking force upon a face of the rotor 101 when contacted therewith. In the present invention, the actuation device 200 is preferably configured to translate along the rotational axis A. Specifically, the actuation device 200 may move in the axial direction, towards and away from the rotor 101. The actuation device 200 may be actuated by hydraulic or pneumatic pressure. Thus, the actuation device 200 may be hydraulically or pneumatically activated. As shown in Figure 2, the actuation device 200 may be accommodated in a piston chamber 250. The piston chamber 250 is preferably annular. The piston chamber 250 may comprise at least one inlet 251. The at least one inlet 251 is in fluid communication with the piston chamber 250 and configured to port pressure, such as hydraulic or pneumatic pressure, to the actuation device 200. Porting pressure to the actuation device 200 may exert an axial actuation force P on the actuation device 200. The actuation force P thereby moves the actuation device 200 in the axial direction. Thus, the actuation device 200 may be translated along the rotational axis A. Figure 4 illustrates the actuation device 200 in a connected configuration. In the connected configuration, the drive transfer means 150 is configured to transfer rotational drive from the generator input shaft assembly to the rotor. Specifically, the first and second disconnectable interfaces 115, 135 are engaged in this operational configuration, and thus the drive transfer means 150 is in the aforementioned connected configuration. As can be seen in the illustration, the electrical machine 100 further comprises an actuation biasing means 240 disposed between the actuation device 200 and a face of the rotor 101. The actuation biasing means 240 is configured to bias the actuation device 200 to a furthermost axial position relative to the rotor 101. In the connected configuration, the actuation device 200 is at a furthest axial extent from the rotor 101. Thus, the first axial position comprises an axially distal position of the actuation device 200 relative to the rotor 101. In the connected configuration, there is no contact between the separation means 220 of the actuation device and the first disconnection member 110 of the rotor 101. Further, in the connected configuration, there is no contact between the braking surface 230 of the actuation device 200 and any face of, or any face connected to, the rotor 101. Figure 5 illustrates the actuation device 200, in a braked configuration. In the braked configuration, the actuation device 200 is configured to disconnect the drive transfer 150 means from the rotor 101, and the braking means 230 is activated to hinder or stop rotational drive of the rotor 101. In the braked configuration, the actuation device 200 is at a proximal axial extent from to the rotor 101. Thus, the second axial position comprises an axially proximal position of the actuation device 200 relative to the rotor 101. In the braked configuration, there is contact between the separation means 220 of the actuation device 200 and the first disconnection member 110 of the rotor 101. The separation means 220 are substantially contiguous with the first disconnection member 110 in the braked configuration. Further, in the braked configuration, there is contact between the braking surface 230 of the actuation device 200 and any face of the rotor 101, or any face connected to the rotor 101. Thus, at least part of the braking surface 230 may be contiguous with a face of the rotor 101. Preferably, substantially the entire braking surface 230 is contiguous with a face of the rotor 101. This increases the effectiveness of the resulting braking force. The contact between contiguous surfaces is established by pressure exerted on the actuation device 200. The actuation biasing means 240 is configured to bias the actuation device 200 to a second axial position. In the braked configuration, the actuation device 200 is at a proximal axial extent from the rotor 101. Thus, to attain the braked configuration, a force may be exerted on the actuation device 200 in response to an associated control being activated, in order to counteract the actuation biasing means 240. This is discussed further below. Figure 6 illustrates the actuation device 200 in-situ, in a disconnected configuration. In the disconnected configuration, the actuation device 200 is configured to disconnect the drive transfer means from the rotor. However, in the disconnected configuration the braking surface 230 is not activated to hinder rotation of the rotor 101. Thus, the rotor is free to rotate 101 in the disconnected configuration. In the disconnected configuration, the actuation device 200 is at an intermediate axial extent from the rotor 101. Specifically, the actuation device 200 is at an axial position which is between the furthermost axial position associated with the connected configuration and the proximal axial position associated with the braked configuration. Thus, the third axial position comprises an axially intermediate position of the actuation device 200 relative to the rotor 101. In the disconnected configuration, it is maintained that there is no contact between the braking surface 230 of the actuation device 200 and any face of the rotor 101. However, there is contact between the separation means 220 of the actuation device 200 and the first disconnection member 110 of the rotor 101. The separation means of the actuation device 200, may comprise at least one contact member 220, which may be arranged within a radially inner surface of the actuation device 200. The, or each one contact point may be arranged to make contact with the drive transfer means to separate it, and may be configured to permit continued rotation of the drive transfer means with the rotor while applying an axial force component to separate and thus disconnect the drive transfer means. In the example of Figures 2-6, at least one fixed shaft 221 is installed in the body 210 of the actuation device 200. The fixed shaft 221 can be configured such that it does not rotate. The fixed shaft 221 may be installed in the body 210 of the actuation device 200 such that at least part of the fixed shaft 221 is embedded within the body 210 of the actuation device. At least part of the fixed shaft 221 may project radially inwards from an inner surface of the actuation device 200. Optionally, a rotatable member 222 may be mounted upon the fixed shaft 221 and may be free to rotate about a rotational axis B of the fixed shaft 221. The rotatable member 222 may comprise rollers, bearings, or bushings, for example. In the Figures, the rotatable member comprises bearings 222. The or each clutch or contact member 220 provided can be configured to allow free rotation of the rotor 101. When there is contact between the separation means 220 of the actuation device 200 and the first disconnection member 110 of the rotor 101, it is the, or each, contact member 220 which is contiguous with a surface of the first disconnection member 110. When the first disconnection member 110, and thus the first disconnectable interface 115, is separated from the generator input shaft assembly 120, the rotor 101 can continue to rotate freely. The bearings 222 provided on the, or each, contact member 220 being free to rotate enables the continued rotation of the rotor 101 as there is little resistance to the rotation of the rotor. In the example of Figures 2-6, there are provided a plurality such as three contact members 220. The clutch members 220 are preferably arranged on the actuation member 200 at equal angular intervals about the rotational axis A of the rotor 101. It will be appreciated that there may be more than three clutch members 220. Equally, there may be fewer than three clutch members 220 in some embodiments. Similar to the braked configuration, to attain the disconnected configuration an actuation force P may be exerted on the actuation device 200 in order to counteract the actuation biasing means 240. Generally, this actuation force P is exerted in response to an associated control being activated. The actuation force P preferably acts parallel to the rotational axis A, towards the rotor 101. The actuation force P may comprise an hydraulically, electrically or pneumatically exerted force. The actuation force P is generally exerted on the actuation device 200, which subsequently exerts the actuation force P against the actuation biasing means 240. The or each clutch or contact member 220, being optional, may otherwise be replaced by or combined with at least one protrusion or protruding surface (not shown), which may project radially inwards from an inner surface of the actuation device 200. Such a protrusion or surface may comprise a bezel or chamfered surface, for example. The protrusion or protruded surface may act as a braking means in some embodiments, configured to both disconnect the drive transfer means from the rotor and hinder rotation of the rotor. One or more contact members may therefore be arranged to disconnect the drive transfer means and to brake its rotation. This effect may be achieved by axial movement of the contact member(s) in a direction along axis A. The contact member(s) may have multiple contact points around the axis A to provide an evenly distributed axial disconnection force, to provide even pressure and resulting forces to actuate the disconnect mechanism smoothly in the axial direction without crabbing due to asymmetrical or off-centre forces being applied. As previously described, the braked configuration corresponds to the actuation device 200 being proximal the rotor, the disconnected configuration corresponds to an intermediate axial position of the actuation device 200. The actuation biasing means 240 is configured to bias the actuation device 200 to the connected configuration (i.e., the furthermost axial position relative to the rotor 101). It will therefore be understood that the actuation biasing means 240 necessitates first and second force thresholds Pl, P2 which define the operational configurations. In the following examples, P2 is greater than Pl. When the actuation force P is below the first force threshold Pl, there is no contact between the separation means 220 of the actuation device and the first disconnection member 110 of the rotor 101. Thus, below the first force threshold Pl, the actuation device 200 is in the connected configuration. This is because, below this threshold, the actuation force P is not sufficient to activate disconnection of the drive transfer means 150. When the actuation force P is above the first force threshold Pl, but below the second force threshold P2, there is contact between the separation means 220 of the actuation device and the first disconnection member 110 of the rotor 101. However, there is no contact between the braking surface 230 of the actuation device 200 and any face of the rotor 101. Thus, when the actuation force P is above the first force threshold Pl and below the second force threshold P2, the actuation device 200 is in the disconnected configuration. When the actuation force P is raised above the second force threshold P2, there is both contact between: the separation means 220 of the actuation device and the first disconnection member 110 of the rotor 101; and the braking surface 230 of the actuation device 200 and any face of the rotor 101. Thus, when the actuation force P is above the second force threshold P2, the actuation device 200 is in the braked configuration. The above-described force thresholds Pl, P2 therefore provides a means by which disconnection can take place independently of braking. This can be useful for using the functionality of the separation means 220 without activating the braking means, thereby avoiding unnecessary wear on the braking surface 230. Alternatively, there may be scenario in which it is not essential to brake the rotor once disconnected, so the brake can be preserved in certain disconnect scenarios. In other scenarios, it may be more important to stop rotation of the rotor more quickly to stop electrical current being generated more quickly, and the brake can be beneficial in these circumstances. Further, because of the force thresholds Pl, P2, braking cannot be performed without disconnection having taken place. This removes the possibility of inadvertent braking without the generator 100 having first been disconnected. Thus, there is no scenario in which the generator 100 would be both in use and braked. This is an occurrence which would cause significant wear on the braking surface 230 and apply a significant additional torque to the engine. In some embodiments, the disconnect arrangement may further, or otherwise, comprise a position control means (not shown). The position control means may comprise a position detection device, configured to identify the axial position of the actuation device 200. The position detection device may comprise a sensor, for example. The position control means may further comprise a position control actuator, configured to adjust, or maintain, the axial position of the actuation device 200 in response to conditions detected by the position detection device. The position control means may control the axial actuation force P by applying a pressure to the actuation device 200 in response to conditions detected by the position detection device. In other embodiments, the position control means may further, or otherwise, comprise 5 a mechanical position control means. Such a control means may comprise a fastening, latch, bolt, hook, or clamp mechanism with fixed positions corresponding to the aforementioned axial positions related to the operational configurations. Any mechanical position control means is preferably configured to selectively maintain the axial position of the actuation device 200. Advantageously, this prevents the 10 operational configuration of the disconnection arrangement from being changed inadvertently.

Claims

1. An electrical machine arranged to be driven by a prime mover of an aircraft, the electrical machine comprising:a rotor, which is rotatable about a rotational axis A;an input shaft assembly, comprising an input shaft for receiving a drive input; anda disconnect arrangement, comprising:a drive transfer means, arranged to selectively transfer rotational drive between the input shaft assembly and the rotor; andan actuation device, arranged to actuate the drive transfer means; anda braking means for braking the rotor;the disconnect arrangement being configurable in a plurality of operational configurations, including:a connected configuration, in which the drive transfer means is configured to transfer rotational drive between the generator input shaft assembly to the rotor;a braked configuration, in which the actuation device is configured to disconnect the drive transfer means from the rotor, and the braking means is activated to hinder rotation of the rotor.

2. The electrical machine of claim 1, wherein the disconnect arrangement further comprises:a disconnected configuration, in which the actuation device is configured to disconnect the drive transfer means from the rotor and the braking means is not activated and does not hinder rotation of the rotor.

3. The electrical machine of claim 1 or claim 2, wherein two or more of the operational configurations correspond to different axial positions of the actuation device relative to the rotor.

4. The electrical machine of claim 3, wherein, in the connected configuration, the actuation device is at a position axially distal from the rotor, and is at a position axially proximal to the rotor in the braked configuration.

5. The electrical machine of claim 4, wherein, in the disconnected configuration, the actuation device is at located at an intermediate axial position, between the axially distal and axially proximal positions.

6. The electrical machine of any preceding claim, wherein an actuation biasing means is configured to bias the actuation device to the connected position.

7. The electrical machine of any preceding claim, wherein the actuation device comprises a separation means, configured to selectively disconnect the drive transfer means from the rotor while allowing the rotor to continue in rotation.

8. The electrical machine of claim 7, wherein the separation means is configured to selectively disconnect the drive transfer means from the rotor, independently of the braking means.

9. The electrical machine of claim 7 or claim 8, wherein the braking means is configured to selectively hinder rotation of the rotor only when the drive transfer means is disconnected from the rotor.

10. The electrical machine of any of claims 7 to 9, wherein the separation means comprises at least one rotatable member configured to allow the rotor to continue in rotation.

11. The electrical machine of claim 10, wherein the at least one rotatable member comprises rollers, bearings, or bushings.

12. The electrical machine of any preceding claim, wherein the actuation device is configured to provide an axial actuation force P, the axial actuation force P being applied at points which are on laterally opposing sides of the rotational axis A.

13. The electrical machine of any preceding claim, wherein the actuation device comprises a piston, preferably an annular piston.

14. An aircraft comprising the electrical machine of any preceding claim.18

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