GB2592973A - Generator shaft mechanical disconnect - Google Patents

Abstract

A generator drive disconnect device comprises a drive transfer means 116 having a connected configuration and a disconnected configuration. The drive transfer means 116 transfers a rotational drive between an input shaft 120 and a rotor 110. The disconnect device further comprises a disconnect actuating member 140 moveable between an activated position and a de-activated position, and a moveable disconnect member 101 rotatable about a rotor axis of the generator. The disconnect actuating member comprises a rolling element bearing 141 and the moveable disconnect member comprises a ramp member 130, configured such that movement of the disconnect actuating member to its activated position causes the disconnect actuating member to engage the ramp member via the rolling element bearing, to axially displace the moveable disconnect member, to move the drive transfer means toward the disconnected configuration. Other aspects of the invention relate to an aircraft engine assembly and an aircraft comprising the generator drive disconnect device.

Description

Generator Shaft Mechanical Disconnect

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'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 Al 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 inventor has 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 there is a disconnect shaft selectably engaged with an input shaft and having a ramp surface, and a pawl actuator configured to interact with the ramp surface to axially displace the disconnect shaft to decouple the disconnect shaft from the input shaft.

The inventor has identified several issues with this known system. One issue arises from direct contact between static and rotating parts, which can lead to wear and the production of swarf in operation, resulting in a high frequency of maintenance operations to clean the system after use. This contact can also result in excessive heat generation due to friction which, particularly at high speeds, can further lead to friction welding of components to one another, resulting in high maintenance costs, or otherwise complex lubrication systems need to be implemented, increasing costs and complexity. The inventor has also identified that the reliability of known disconnect devices can be improved, since the pawl can bounce out of engagement with the ramp surface, such that disconnection might not be achieved on first operation; this risk of the mechanism's failure to properly disengage increases with the speed of rotation of the device. Furthermore, the inventor has identified that known disconnect devices generally only allow for a small number of disconnections before maintenance overhaul is required, resulting in more significant operational downtime and reconditioning or replacement of parts. In certain cases, around 15 disconnections at low speed (i.e. engine idle speed of the aircraft) may be a limit of a device, and only one disconnection may be possible at high speed, i.e. cruising speed of an aircraft, before a full overhaul is required. The invention seeks to address these drawbacks.

According to the invention, there is provided a generator drive disconnect device, of a generator arranged to be driven by a prime mover of an aircraft, the disconnect device comprising: a drive transfer means, configured to transfer a rotational drive between an input shaft and a rotor of the generator, the drive transfer means having a connected configuration and a disconnected configuration; a disconnect actuating member, arranged to be moveable between a de-activated position and an activated position; and a moveable disconnect member, arranged to be rotatable about a rotor-axis of the generator; the disconnect actuating member comprising a rolling element bearing and the moveable disconnect member comprising a ramp member, the disconnect actuating member and the ramp member being configured such that movement of the disconnect actuating member to its activated position causes the disconnect actuating member to engage the ramp member via the rolling element bearing, to axially displace the moveable disconnect member, to move the drive transfer means toward the disconnected configuration.

The invention provides a solution to the issues identified in known disconnect devices. In particular, there is no direct contact between static and rotating parts. Instead, the disconnect actuating member engages the ramp member via the rolling element bearing.

As will be understood by the skilled person, this arrangement prevents the production of swarf and reduces heat generation. Furthermore, the inventor has found that the invention provides a more reliable disconnect device that does not suffer from the disconnect actuating member bouncing out of engagement with the ramp member. In particular, the invention has been shown to operate reliably at high speeds. These advantages provide a more reliable and durable disconnect device capable of allowing for a greater number of disconnections, at low speed (i.e. aircraft engine idle speed) and several disconnections at high speed, that is, at aircraft cruising speed.

The ramp member may be formed as an integral part of the moveable disconnect mechanism. Alternatively, the ramp member may be formed from a component independent from the moveable disconnect member. This has the advantage of providing a disconnect device that facilitates quicker servicing because the ramp member may be removed and replaced without removing the moveable disconnect member.

The ramp member of the disconnect device may comprise a ramp. The ramp may be oriented in a substantially axial direction of the moveable disconnect member. The rolling element bearing may be configured to engage the ramp. This has the advantage of providing a surface against which the disconnect actuating member may impact when the disconnect actuating member is moved to its activated position. This impact may provide the force necessary to move the moveable disconnect member axially to thereby move the drive transfer means into its disconnected configuration. Such an orientation of the ramp provides the advantage of a simple construction of the ramp on the ramp member that allows the ramp to exert the required axial force on the disconnect actuating member.

The rolling element bearing may have a rotational axis. The rotational axis may be substantially perpendicular to the axis of the rotor.

The ramp may extend around a part of the angular extent of the moveable disconnect member. The ramp may extend around less than three quarters, preferably less than one half, preferably less than one quarter, preferably less than one eighth, preferably less than one sixteenth, preferably less than one thirty second of the angular extent of the moveable disconnect member. This provides the advantage of providing a disconnect device in which the ramp may be configured to extend around the moveable disconnect member by a desired angular extent to meet the relevant operational requirements. For example, for aircraft engines running at relatively low speed, the impact force between the rolling element bearing and the ramp will be relatively low; therefore, the ramp may need to have a greater angular extent to move the moveable disconnect member sufficiently far along the rotor axis to effect disconnection of the drive transfer means. However, at high speed, the impact force will be relatively high such that the ramp need only extend around a minority of the angular extent of the moveable disconnect member in order to provide the necessary force to move the moveable disconnect member sufficiently far along the rotor axis to effect disconnection.

The ramp member may comprise a radially inner flat section. The radially inner flat section may be at a first axial position on the ramp member. The radially inner flat section provides a surface along which the rolling element bearing can roll once the disconnected configuration has been reached. Therefore, while the disconnect actuating member maintains the moveable disconnect member in its disconnected position, any rotation of the ramp member caused by rotation of the moveable disconnect member will continue to be communicated to the disconnect actuating member via the rolling element bearing.

Therefore, even after disconnection, excessive friction between the disconnect actuating member and the ramp member is prevented.

The ramp member may comprise a radially outer flat section. The radially outer flat section may be at a second axial position on the ramp member. Since the disconnect actuating member may, upon activation, contact an outer circumferential surface of the ramp member, the outer flat section provides the advantage of increasing the likelihood that the disconnect actuating member will engage the ramp within one revolution of the ramp member.

The ramp may be configured to apply a force to the rolling element bearing to move the moveable disconnect member in an axial direction. The rolling element bearing may move from the radially outer flat section toward the radially inner flat section upon rotational contact with the ramp.

The outer flat section may extend around more than one thirty second, preferably more than one sixteenth, preferably more than one eighth, preferably more than one quarter, preferably more than one half, preferably more than three quarters of the angular extent of the movable disconnect member. This provides the advantage of providing a disconnect device in which the outer flat section may be configured to extend around the moveable disconnect member by a desired angular extent to meet the relevant operational requirements. For example, for aircraft engines running at relatively low speed, the disconnect actuating member will have more time to engage the outer flat section such that the outer flat section need only extend around a minority of the angular extent of the moveable disconnect member in order to provide sufficient time for the disconnect actuating member to engage the outer flat section and, subsequently, the ramp.

Furthermore, a longer ramp section provides the advantage of reducing the acceleration of the first disconnect member on impact with the roller bearing, thereby reducing the impact load to the roller bearing and disconnect actuating member. However, at high speed, the disconnect actuating member has less time to engage the outer flat section; therefore, the outer flat section may need to extend around a greater angular extent of the moveable disconnect member in order to provide sufficient time for the disconnect actuating member to engage the outer flat section and, subsequently, the ramp, in order to effect disconnection. While a workaround for extending the outer flat section, as described above, would be to increase the actuating force of the disconnect actuating member, such an increase could make it more difficult to return the disconnect actuating member to its inactivated position, due to the greater force that would need to be overcome.

A plane of the inner flat section may be substantially perpendicular to the axis of the rotor. A plane of the outer flat section may be substantially perpendicular to the axis of the rotor.

The ramp may ramp from the outer flat section to the inner flat section. This provides the advantage that the ramp can exert a force on the disconnect actuating member at several positions along the length of the ramp. In particular, a longer ramp is preferable for use at low speed, when the force on the disconnect actuating member from a single contact with the ramp is insufficient to effect disconnection.

The disconnect device may be configured such that moving the disconnect actuating member to the activated position causes the rolling element bearing to engage the ramp. The disconnect device may be configured such that the rolling element bearing engages the outer flat section before engaging the ramp. The disconnect device may be configured such that the rolling element bearing engages the inner flat section to maintain the drive transfer means in its disconnected configuration.

The disconnect device may comprise a connection biasing means. The connection biasing means may be configured to bias the drive transfer means to the connected configuration. This provides the advantage that when the disconnect actuating member is in its de-activated position, the drive transfer means is maintained in its connected configuration, thereby preventing the occurrence of unexpected disconnection.

The disconnect device may be configured such that moving the disconnect actuating member from the activated position to the de-activated position causes the connection biasing means to move the drive transfer means to the connected configuration. This provides the advantage that the disconnect device is resettable in that once the disconnect actuating member is returned to its de-activated position, the drive transfer means will automatically return to the connected configuration.

The disconnect actuating member may be moved towards the ramp member by an actuation means. This provides the advantage that the disconnect device may be operated remotely, such as from the aircraft's control panel. The actuation means may comprise a biasing means. The biasing means may be retained by a latch mechanism. This provides the advantage that the potential energy required to effect disconnection is retained in the biasing means such that only a relatively small input is required to release the latch mechanism.

The biasing means may bias the rolling element bearing towards the rotor axis of the generator.

The rolling element bearing may comprise a bearing cover. The bearing cover may be disposed around the circumference of the bearing and may additionally or alternatively be disposed at the base of the bearing, i.e. the side of the bearing facing the ramp member.

According to another aspect of the invention, there is provided an aircraft engine assembly comprising a generator drive disconnect device as described hereinabove.

According to another aspect of the invention, there is provided an aircraft comprising an aircraft engine assembly as described hereinabove.

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: Figure 1 is a schematic diagram illustrating a disconnect device according to one embodiment of the present invention.

Figure 2A is a perspective diagram illustrating the connected configuration of the disconnect device.

Figure 2B is a perspective diagram illustrating the disconnected configuration of the disconnect device.

Figure 3A is a diagram illustrating a first arrangement of a moveable disconnect member for use in embodiments of the present invention.

Figure 35 is a further diagram illustrating the moveable disconnect member of Figure 3A.

Figure 4A is a diagram illustrating a second arrangement of a moveable disconnect member for use in embodiments of the present invention.

Figure 4B is a further diagram illustrating the moveable disconnect member of Figure 4A.

Figure 5 is a schematic diagram illustrating an aircraft and an aircraft engine according to embodiments of the present invention.

Detailed Description

Turning to Figures 1 and 5, there is shown a generator drive disconnect device 100 according to one embodiment. 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. An aircraft engine assembly can therefore comprise a prime mover, a generator and the disconnect device 100. The generator 3 comprises a rotor 110, rotatable about a rotor axis A. The aircraft engine 2 comprises an input shaft 120, rotatable about the rotor axis A. Figure 1 illustrates one embodiment of the disconnect device 100. An input shaft 120 is rotatably mounted in a housing 150 by bearings 127a, 127b, but it will be appreciated that a single bearing may also be sufficient. The input shaft 120 transfers rotational drive from the aircraft engine to the disconnect device 100 about rotor axis A. A rotor 110 of the generator is rotatably mounted in the housing 150 by a 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 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 input shaft 120. Although the second disconnect member 121 is shown in Figure 1 to be an integral part of the input shaft 120, it will be appreciated that this component may instead be distinct from the 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 input shaft 120 to the rotor 110. 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. A ramp member 130 is able to rotate with the drive transfer means 116 and comprises a ramp 131. A disconnect actuating member 140 is mounted to the housing 150 and can be actuated towards the rotor axis A, that is, towards the ramp member 130. The disconnect actuating member 140 comprises a roller bearing 141. After actuation of the disconnect actuating member 140, it engages the ramp 131 via the roller bearing 141 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 drive transfer means 116 comprises a first disconnect member 101 and a second disconnect member 121. The drive transfer means 116 has a connected configuration, in which rotational drive is transferred between the first disconnect member 101 and the second disconnect member 121, and a disconnected configuration, in which drive is not transferred between the first disconnect member 101 and the second disconnect member 121. The first disconnect member 101 comprises a first clutch member 105 at a first end 106 of the first disconnect member 101. The second disconnect member 121 comprises a second clutch member 125 engageable with the first clutch member 105. In this embodiment, 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 Figure 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 permit 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.

The input shaft 120 is rotatable within a housing 150, journaled by bearings 127a, 127b. In Figure 1, the second disconnect member 121 is shown to be an integral part of the input shaft 120 and rotates therewith. In this embodiment, the second disconnect member 121 is not moveable along the rotor axis A relative to the input shaft 120. In another embodiment, the second disconnect member 121 is an independent component to the input shaft 120 and may be configured to rotate therewith by, for example, a set of meshing teeth. In yet another embodiment, the second disconnect member 121 is an independent component to the input shaft 120 and can, by the provision of meshing splines, move along the rotor axis A relative to the 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 flange 111, the flange 111 comprising a plurality of splines 114 on an inner circumferential surface thereof. 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 input shaft 120 to the rotor 110 via the drive transfer means 116 and the splines 104, 114.

The disconnect device 100 further comprises a biasing means 119. The biasing means 119 is arranged to bias the drive transfer means 116 to its connected configuration. In Figure 1, the biasing means 119 is shown to be a coiled spring disposed 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. A first end 119a of the biasing means 119 abuts a shoulder 108 of the first disconnect member 101. A second end 119b of the biasing means 119 abuts the rotor 110. 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 ramp member 130, arranged to rotate with the first disconnect member 101. In Figure 1, the ramp member 130 is shown to be disposed around an outer circumferential surface of the first end 106 of the first disconnect member 101. The ramp member 130 comprises a ramp 131 extending around at least part of the angular extent of the ramp member 130. Further detail of the ramp member 130 is provided later in the description of the subsequent figures.

In another embodiment, the ramp member 130 is instead disposed around an outer circumferential surface of the second disconnect member 121. This arrangement may facilitate the embodiment described earlier in which the second disconnect member 121 is able to move along the rotor axis A relative to the input shaft 120.

The disconnect device 100 further comprises a disconnect actuating member 140. In Figure 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 Figure 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 Figure 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, for example, a solenoid (or hydraulic or pneumatic, for example) arrangement capable of actuating the disconnect actuating member 140 towards the ramp member 131 and further towards the rotor axis A. The disconnect actuating member 140 comprises a roller bearing 141. The roller bearing 141 comprises an inner race 141a, fixed to a portion of the disconnect actuating member 140, and an outer race 141b, free to rotate about the axis of the disconnect actuating member 140, as will be understood by the skilled person. The roller bearing 141 further comprises a bearing cover 143 disposed around and fixed to at least a portion of the outer circumferential surface of the outer race 141b to rotate therewith. The bearing cover 143 may be an integral part of the outer race 141b by using, for example, a custom-built bearing. The bearing cover 143 may be disposed around an axial face of the roller bearing 141. In Figure 1, the bearing cover 143 is shown to be disposed around a bottom axial face of the roller bearing 141 such that the bearing cover 143 faces the ramp member 130. In the de-activated position, the disconnect actuating member 140 and the roller bearing 141 are positioned such that a first half of the roller bearing 141 (shown in Figure 1 at the right-hand side of the disconnect actuating member 140) is disposed 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, causes the roller bearing 141 to engage the ramp member 130. When the roller bearing 141 engages the ramp 131 on the ramp member 130, the interaction between the roller bearing 141 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. The roller bearing 141 may comprise a ball bearing assembly. The roller bearing 141 may comprise a needle roller bearing assembly, or any other type of bearing assembly suitable for preventing direct contact between static and rotating parts. The roller bearing 141 may comprise a combined needle roller and angular contact ball bearing in order to withstand both radial and axial loads. Using a roller bearing in this way prevents excessive friction between the disconnect actuating member 140 and the ramp member 130 during, and after, disconnection. By reducing friction, the risk of excessive heat and swarf generation is reduced. Therefore, the disconnect mechanism can be more durable and effective, and can withstand more disconnections.

The ramp member 130 will now be described in more detail with reference to the subsequent figures. As shown in Figures 2A and 2B, 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 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.

Figures 3A and 35 illustrate one possible arrangement for a ramp member 330 comprising a ramp 331. Figure 3A illustrates a front view of the ramp member 330 in which the ramp member 330 further comprises an inner flat section 333 that comprises an annulus disposed around and facing in a direction of rotor axis A, and extending around the full angular extent of the first disconnect member (not shown). The ramp member 330 further comprises an outer flat section 332 disposed around approximately half of the angular extent of the first disconnect member and facing in a direction of the rotor axis A. In one example, the outer flat section 332 is disposed around 180° of the rotor axis A. The ramp 331 is disposed around approximately half of the angular extent of the first disconnect member. In one example, the ramp 331 is disposed around approximately 180° of the rotor axis A. The ramp 331 and the outer flat section 332 are disposed radially outwards of the inner flat section 333. Figure 3B illustrates a side view of the ramp member 330 in which approximately half of the angular extent of the ramp member 330 is visible. As shown, the outer flat section 332 is axially offset from the inner flat section 333. The ramp 331 of the ramp member 330 begins at an axial position of the outer flat section 332 and ramps in a helical manner to the axial position of the inner flat section 333. In this embodiment, the ramp ramps in an axial direction between the axial position of the outer flat section 332 and the axial position of the inner flat section 333.

Figures 4A and 4B illustrate another possible arrangement for a ramp member 430 comprising a ramp 431. Figure 4A illustrates a front view of the ramp member 430 in which the ramp member 430 further comprises an inner flat section 433 that comprises an annulus disposed around rotor axis A and extending around the full angular extent of the first disconnect member (not shown). The ramp member 430 further comprises an outer flat section 432 disposed around the majority of the angular extent of the first disconnect member. In one example, the outer flat section 432 is disposed around approximately 350° of the rotor axis A. The outer flat section 432 may be disposed around more than one thirty second, preferably more than one sixteenth, preferably more than one eighth, preferably more than one quarter, preferably more than one half, preferably more than three quarters of the angular extent of the first disconnect member. The ramp 431 is disposed around the minority of the angular extent of the first disconnect member. In one example, the ramp 431 is disposed around approximately 10° of the rotor axis A. The ramp 431 may be disposed around less than three quarters, preferably less than one half, preferably less than one quarter, preferably less than one eighth, preferably less than one sixteenth, preferably less than one thirty second of the angular extent of the first disconnect member. The ramp 431 and the outer flat section 432 are disposed radially outward of the inner flat section 433. Figure 4B illustrates a side view of the ramp member 430 in which approximately half of the angular extent of the ramp member 430 is visible.

As shown, the outer flat section 432 is axially offset from the inner flat section 433. The ramp 431 of the ramp member 430 begins at an axial position of the outer flat section 432 and ramps in a helical manner towards the axial position of the inner flat section 433. In this embodiment, the ramp ramps in an axial direction from the axial position of the outer flat section 432 towards the axial position of the inner flat section 433 without reaching the axial position of the inner flat section 433. The ramp is not limited to being a linear ramp and may instead comprise at least a portion that is non-linear. A non-linear ramp provides the advantage of reducing the instantaneous acceleration rate of the first disconnect member 101 upon impact with the bearing 141, thereby reducing the instantaneous impact to the bearing 141 and the disconnect actuating member.

The operation of the disconnect device will now be described with particular reference to Figures 2A and 2B. As shown in Figure 2A, 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 input shaft 120 via the drive transfer means 116 to the first disconnect member 101 and to the rotor 110. As such, the 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. In other arrangements, the disconnect actuating member 140 may be moved towards its activated position by an active actuation mechanism, such as a solenoid, hydraulic or pneumatic actuation system. The activated position of the disconnect actuated member 140 is shown in Figure 2B. Depending upon the rotational position of the ramp member 130 when the disconnect actuating member 140 is moved to its activated position, the roller bearing 141 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 roller bearing 141. While the disconnect actuating member 140 is in contact with the outer circumferential surface of the ramp 131, the bearing cover 143 will rotate as the roller bearing 141 moves along the surface of the ramp member 130. In this way, the bearing cover 143 reduces the friction between the moving parts, even before the bearing 141 engages the ramp. Once the outer flat section 132 is rotationally aligned with the roller bearing 141, 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 roller bearing 141 will engage the outer flat section 132 within one revolution of the ramp member 130 about rotor axis A. Therefore, the disconnect device provides the ability to effect quick disconnection of the generator rotor 110 from the input shaft 120 at a range of speeds while preventing the disadvantages associated with contact between static and rotating parts. Instead, the rolling element bearing provides the means to transfer a high actuating force to the disconnect mechanism without excessive heat and swarf generation. Therefore, not only does this disconnect device function more reliably than previous systems, but it also lasts longer in use and reduces the work required during maintenance of the aircraft engine.

It will be understood by the skilled person that once the roller bearing 141 is brought into engagement with the outer flat section 132, the bearing cover 143 and the outer race 141b will rotate in response to the rotation of the outer flat section 132, thereby reducing friction between the moving parts. 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 roller bearing 141 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 axially (to the right of Figure 2B) 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 roller bearing 141 into engagement with the inner flat section 133. The engagement of the roller bearing 141 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. Once the drive transfer means 116 is in the disconnected configuration, the rotor 110 may continue to rotate in an idle manner. Therefore, the ramp member 130 will continue to rotate, relative to the disconnect actuating member 140, such that rolling contact is provided therebetween by the roller bearing 141 and the inner flat section 133. In particular, rolling contact is provided between the outer race 141b or the cover 143 of the roller bearing 141. Thus, the roller bearing 141 facilitates reduced wear between the disconnect actuating member 140 and the ramp member 130.

Figure 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 an input shaft 120. The input shaft 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.

Claims (21)

1. Claims 1. A generator drive disconnect device, of a generator arranged to be driven by a prime mover of an aircraft, the disconnect device comprising: a drive transfer means, configured to transfer a rotational drive between an input shaft and a rotor of the generator, the drive transfer means having a connected configuration and a disconnected configuration; a disconnect actuating member, arranged to be moveable between a de-activated position and an activated position; and a moveable disconnect member, arranged to be rotatable about a rotor-axis of the generator; the disconnect actuating member comprising a rolling element bearing and the moveable disconnect member comprising a ramp member, the disconnect actuating member and the ramp member being configured such that movement of the disconnect actuating member to its activated position causes the disconnect actuating member to engage the ramp member via the rolling element bearing, to axially displace the moveable disconnect member, to move the drive transfer means toward the disconnected configuration.
2. 2. A disconnect device according to claim 1, wherein the ramp member has a ramp oriented in a substantially axial direction of the moveable disconnect member.
3. 3. A disconnect device according to claim 2, wherein the rolling element bearing is configured to engage the ramp.
4. 4. A disconnect device according to any preceding claim, wherein the rolling element bearing has a rotational axis, the rotational axis being substantially perpendicular to the axis of the rotor.
5. 5. A disconnect device according to any preceding claim, wherein the ramp extends around a part of the angular extent of the moveable disconnect member.
6. 6. A disconnect device according to any preceding claim, wherein the ramp extends around less than three quarters, preferably less than one half, preferably less than one quarter, preferably less than one eighth, preferably less than one sixteenth, preferably less than one thirty second of the angular extent of the moveable disconnect member.
7. 7. A disconnect device according to any preceding claim, wherein the ramp member comprises a radially inner flat section at a first axial position on the ramp member; and/or a radially outer flat section at a second axial position on the ramp member.
8. 8. A disconnect device according to claim 7, wherein the ramp is configured to apply a force to the rolling element bearing to move the moveable disconnect member in an axial direction, such that the rolling element bearing moves from the radially outer flat section toward the radially inner flat section upon rotational contact with the ramp.
9. 9. A disconnect device according to claim 7 or claim 8, wherein the outer flat section extends around more than one thirty second, preferably more than one sixteenth, preferably more than one eighth, preferably more than one quarter, preferably more than one half, preferably more than three quarters of the angular extent of the movable disconnect member.
10. 10. A disconnect device according to any of claims 7 to 9, wherein a plane of the inner flat section and a plane of the outer flat section are substantially perpendicular to the axis of the rotor.
11. 11. A disconnect device according to any of claims 7 to 10, wherein the ramp ramps from the outer flat section to the inner flat section.
12. 12. A disconnect device according to any of claims 2 to 11, wherein the disconnect device is configured such that moving the disconnect actuating member to the activated position causes the rolling element bearing to engage the ramp.
13. 13. A disconnect device according to any of claims 7 to 12, wherein the disconnect device is configured such that after activation of the disconnect device the rolling element bearing engages the inner flat section to maintain the drive transfer means in its disconnected configuration.
14. 14. A disconnect device according to any preceding claim, wherein the disconnect device further comprises a connection biasing means, configured to bias the drive transfer means to the connected configuration.
15. 15. A disconnect device according to any preceding claim, wherein the disconnect device is configured such that moving the disconnect actuating member from the activated position to the de-activated position causes the connection biasing means to move the drive transfer means to the connected configuration.
16. 16. A disconnect device according to any preceding claim, wherein the disconnect actuating member is moved towards the ramp member by an actuation means.
17. 17. A disconnect device according to claim 16, wherein the actuation means comprises a biasing means.
18. 18. A disconnect device according to claim 17, wherein the biasing means biases the rolling element bearing towards the rotor axis of the generator.
19. 19. A disconnect device according to any preceding claim, wherein the rolling element bearing comprises a bearing cover, the bearing cover being disposed around the circumference of the rolling element bearing and preferably at an axial face of the rolling element bearing.
20. 20. An aircraft engine assembly comprising a generator drive disconnect device in accordance with any of claims 1 to 19.
21. 21. An aircraft comprising an aircraft engine assembly in accordance with claim 20.