A horizontal stabilizer drive with an electromechanical linear drive

Description

TECHNICAL FIELD

[0001] The present invention relates to trim horizontal stabiliser actuators such as for example, trim horizontal stabiliser actuators for use in aircraft controls.BACKGROUND

[0002] The present invention relates to trim horizontal stabilisers comprising electromechanical linear actuators. Such actuators are used to actuate control surfaces and other surfaces in aircraft, for example slats, flaps, thrust reverser doors and so on.

[0003] In some applications such as, for example, in the aerospace industry, there is a need to produce actuators which require as small a space or envelope as possible, particularly with regard to the diameter thereof. There is also a need to produce actuators which are as light as possible and which are reliable.

[0004] US 10,443,696 B1 discloses a stabiliser system comprising a stabiliser that is adjustable relative to aircraft fuselage, a motor and a ballscrew assembly coupled to the motor.

[0005] WO 2005 / 012755 A1 discloses an actuator including an electric motor having a stator and a rotor, in which the rotor defines a bearing surface having a non-circular profile, and a radially flexible annular sleeve defines a facing bearing surface. The flexible sleeve adopts a non-circular shape complimentary to the profile of the bearing surface. The flexible sleeve is restrained against rotation and is in toothed meshing engagement with a circular drive ring at least two contact regions which are equidistantly spaced apart. The drive ring is rotationally engaged with a screw and threaded sleeve assembly, such that rotation of the drive ring drives the screw and sleeve assembly and causes extension or withdrawal of an output portion of the screw and sleeve assembly for actuation. The actuator is operable such that rotation of the rotor causes the flexible sleeve to flex radially at each of the contact regions to generate a rolling wave which causes rotation of the contact regions and of the drive ring, and the drive ring rotates at a reduced rotational velocity as compared to the rotational velocity of the rotor.SUMMARY

[0006] According to the invention, a trim horizontal stabiliser actuator according to claim 1 is provided.

[0007] It will be understood that by providing a harmonic drive gear arrangement extending radially outwardly of and coaxially with the rotary shaft and an electric motor positioned radially outwardly of the harmonic drive gear arrangement, the diameter of the space or envelope required by the electromechanical linear actuator may be reduced compared to some other electromechanical linear actuators.

[0008] In various examples of the invention, the electric motor may comprise a rotor which is coaxial with and extends around the harmonic drive gear arrangement.

[0009] The rotary shaft could take various forms. In various examples however, the rotary shaft may comprise a ball screw and the output component may comprise a ball nut.

[0010] In various examples of the invention, it may be desirable to provide a trim horizontal stabiliser actuator which will not fail in the event of a single component failure. This could be beneficial for example in aerospace applications where a failure of the electromechanical linear actuator could cause a catastrophic failure of the aircraft. In various examples of the invention therefore, the motor may be a fault tolerant motor.

[0011] Various types of fault tolerant motor may be provided. In various examples of the invention however, the fault tolerant motor may comprise a single rotor and two or the fault tolerant motor may comprise a multi-phase fault tolerant motor drive system.

[0012] In any example of the invention, the trim horizontal stabiliser actuator may further comprise a stop for limiting the movement of the output component along the rotary shaft in a first direction.

[0013] In any example of the invention, the trim horizontal stabiliser actuator may further comprise a further stop for limiting the movement of the output component along the rotary shaft in a second direction, opposite to the first direction.

[0014] In some examples of the invention, it may be desirable to limit or stop rotation of the rotary shaft in the event of the electric motor being inactive, for example due to a motor failure or power failure. This may be achieved in a variety of ways. In various examples of the invention, the harmonic drive gear arrangement may be configured to limit, or in some examples to stop, rotation of the rotary shaft when the electric motor is inactive.

[0015] In these or various other examples of the invention, the trim horizontal stabiliser actuator may further comprise a brake configured to limit, or in some examples to stop, rotation of the rotary shaft when the brake is engaged.

[0016] In various examples of the invention, it may be desirable to provide a trim horizontal stabiliser actuator which will not fail in the event of a single component failure. This could be beneficial for example in aerospace applications where a failure of the electromechanical linear actuator could cause a catastrophic failure of the aircraft. In various examples of the invention therefore, the trim horizontal stabiliser actuator may be configured such that the brake will act to limit or stop rotation of the rotary shaft in the event of a failure of the harmonic drive gear arrangement and / or the harmonic drive gear arrangement will act to limit or stop rotation of the rotary shaft in the event of a failure of the brake.

[0017] In various examples of the invention, the brake may be a passive brake.

[0018] According to a further embodiment of the invention, an actuation system may be provided comprising one or more trim horizontal stabiliser actuators and a controller for controlling the one or more trim horizontal stabiliser actuators.

[0019] According to a further embodiment of the invention, an aircraft may be provided, the aircraft comprising: a horizontal stabiliser; and a trim horizontal stabiliser actuator or an actuation system wherein the electromechanical linear actuator is configured to move the horizontal stabiliser relative to the aircraft.

[0020] Features described in relation to one embodiment of this invention may of course be applied to the further embodiments thereof. In general, features of any example described herein may be applied wherever appropriate to any other example described herein. Where reference is made to different examples or sets of examples, it should be understood that these are not necessarily distinct but may overlap.BRIEF DESCRIPTION OF DRAWINGS

[0021] Certain examples of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Fig. 1 shows a schematic perspective view of the tail end of an aircraft; Fig. 2 shows a schematic representation of a trim horizontal stabiliser actuator according to an example of the invention; Fig. 3 shows a schematic representation of a trim horizontal stabiliser actuator according to an example of the invention; and Fig. 4 shows an exploded perspective view of a harmonic drive gear arrangement of a trim horizontal stabiliser actuator according to an example of the invention. DETAILED DESCRIPTION

[0022] Fig. 1 shows a schematic perspective view of the tail 2 of an aircraft. The aircraft tail 2 includes a vertical stabiliser 4 extending upwardly from the aircraft fuselage 6 and respective horizontal stabilisers 8a, 8b extending outwardly from the aircraft fuselage 6 on respective sides of the aircraft. One or more rudders 10 are provided at the trailing edge 12 (i.e. the rear face) of the vertical stabiliser 4 and one or more elevators 14 are provided on the trailing edge 16 (i.e. the rear face) of each horizontal stabiliser 8a, 8b. The vertical stabiliser 4, horizontal stabilisers 8a, 8b, rudders 10 and elevators 14 are adapted to be moved by an actuation system (not shown) to control movement of the aircraft.

[0023] The horizontal stabilisers 8a, 8b are connected to the aircraft fuselage 6 and are configured to rotate about a hinge (not shown) in the aircraft such that the tip 18 of a horizontal stabiliser 8a, 8b can be moved both downwardly toward the underside of the plane and upwardly toward the top of the plane depending on whether the horizontal stabiliser 8a, 8b is rotated in a first direction or a second direction. Typically, a horizontal stabiliser 8a, 8b will be rotated downwardly for take-off of an aircraft and will be rotated upwardly for landing of an aircraft. It will be understood however that the rotation of the horizontal stabilisers may be controlled to provide any required movement thereof at any given time during an aircraft take off, flight or landing.

[0024] The actuation system includes a control system (not shown) and a number of actuators provided move the respective vertical stabilisers 4, horizontal stabilisers 8a, 8b, rudders 10 and elevators 14 under the control of the control system.

[0025] The actuators may take a number of different forms depending for example on the type and size of aircraft in which they are used. In one example, one or more electromechanical actuators, more specifically electromechanical linear actuators may be provided in the actuation system. An example of an electromechanical linear actuator which may be used to move the horizontal stabilisers 8a, 8b is a "Trim horizontal stabiliser actuator" (often referred to as a THSA). The electromechanical linear actuator according to various examples of the invention is a THSA for use with horizontal stabilisers as described above.

[0026] Fig. 2 is a schematic representation of a trim horizontal stabiliser actuator THSA of the type described above.

[0027] As shown, the electromechanical linear actuator 100 is made up of a rotary shaft 102 adapted to be driven for rotary movement about a longitudinal axis X-X thereof by a motor 104. A harmonic drive gear arrangement 106 extends around the rotary shaft 102, between the motor 104 and the rotary shaft 102. The rotary shaft 102 is configured to be driven by the motor 104 via the harmonic drive gear arrangement 106.

[0028] An output component 108 is provided on the rotary shaft 102 and is configured to be driven linearly along the rotary shaft 102 when the rotary shaft 102 rotates. Thus, the output component 108 is configured to be driven linearly along the rotary shaft 102 in a first direction D1 when the rotary shaft 102 rotates in one direction and to be driven linearly along the rotary shaft 102 in a second, opposite direction D2 when the rotary shaft 102 rotates in the other, opposite direction. The output component 108 may be annular, a radially inner surface (not shown) thereof being adapted to engage with a radially outer surface r o of the rotary shaft 102. In some examples of the invention, the rotary shaft 102 has a helical thread (not shown) provided on the radially outer surface thereof, the helical thread engaging with a corresponding helical thread (not shown) provided on the radially inner surface of the annular output component 108. In some further examples of the invention, the rotary shaft 102 and the annular output component 108 may be a ball screw and a ball nut.

[0029] As seen in Fig. 2, the rotary shaft 102 is fixed to the aircraft, for example to the aircraft fuselage, by a fixing component 110 provided at a first longitudinal end 112 thereof. It will be understood that in other examples of the invention, the fixing component 110 may be provided at a different location on the rotary shaft 102.

[0030] The output component 108 may be fixed to a part which is to be moved by the actuator. In one example therefore, the output component 108 is fixed to a horizontal stabiliser 8a, 8b at a point removed from a pivot point so as to cause the horizontal stabiliser 8a, 8b to pivot as required. In one example as shown in Fig. 3, the output component 108 may be connected to a horizontal stabiliser 8a via a link 20 so as to pivot about point 22 when the output component 108 is moved along the rotary shaft 102 in either the first or the second axial direction D1, D2.

[0031] Respective first and second stops 114 may be provided on the rotary shaft 102 at desired longitudinal positions to limit the possible movement of the output component 108 along the rotary shaft 102 in both the first and second opposite directions D1, D2.

[0032] A secondary braking means such as a passive brake116 (for example a No Back Brake (NBB)) is also provided such that the rotary shaft 102 cannot rotate in either direction when the passive brake 116 is engaged in the event of a motor failure, a power failure or a control failure. Thus, when engaged, the passive brake 116 acts against rotation of the rotary shaft under loads from the output component 108 (reverse rotation). Under normal operating conditions, the passive brake 116 may be redundant as the primary means (the harmonic drive gear arrangement 106) acts against reverse rotation of the rotary shaft 102 as is described in further detail below. By providing both the irreversible harmonic drive gear arrangement 106 and the passive brake 116 however, the actuator may meet safety requirements as used for example in aerospace applications because the passive brake 116 will act to stop reverse rotation of the rotary shaft 102 in the event of a failure of the harmonic drive gear arrangement 106. Similarly, a failure of the passive brake 116 would not result in a malfunction of any part controlled by the actuator (for example, a horizontal stabiliser) as the harmonic drive gear arrangement 106 would still act against reverse rotation of the rotary shaft 102 under the load of the horizontal stabilizer or other loadings. This is advantageous in various applications, including but not limited to aerospace applications, as no single failure of a component within the actuator should cause or be capable of causing a catastrophic event such as might be caused for example by a horizontal stabiliser moving in a manner other than that intended.

[0033] The structure of the harmonic drive gear arrangement 106 is now described in further detail. As seen in Fig. 4, the harmonic drive gear arrangement 106 comprises a radially inner elliptical wave generating part 202. This part is configured to engage with the rotary shaft 102 so as to drive rotation thereof. An annular spline 204 extends around and radially outwardly of the elliptical wave generating part 202 and engages with an outer annular spline 206. The annular spline 204 is made from torsionally stiff yet flexible material and has teeth 208 in the radially outer surface thereof. The teeth 208 engage with corresponding teeth 210 provided on a radially inner surface of the outer annular spline 206. The outer annular spline 206 is driven to rotate by the motor 104, thus driving rotation of the rotary shaft 102 via the harmonic drive gears.

[0034] The ratio of the number of teeth provided on the annular spline 204 to teeth on the outer annular spline 206 may alter the gear ratio between the outer annular spline 206 and the radially inner elliptical wave generating part 202. It will be understood that the ratio of the teeth may be set so as to magnify the output from the motor 104 and thus allow a relatively low torque output from the motor 104 to drive the rotary shaft 102. Due to the gear ratio of the harmonic drive gear arrangement 106, a relatively large force is required to drive rotation of the radially inner elliptical wave generating part 202. Because of this, when no power is provided to the motor 104 in the event of a motor failure, a power failure or a control failure, the rotary shaft 102 is held against rotation in the reverse direction by the harmonic drive gear arrangement 106. Thus, the harmonic drive gear arrangement 106 is irreversible when no power is provided to the motor 104 and so acts as a brake against reverse rotation of the rotary shaft 102 (under the load exerted on the shaft by a horizontal stabiliser for example).

[0035] Because the harmonic drive gear arrangement 106 may act as a brake against reverse rotation of the rotary shaft 102, no other primary means to stop reverse rotation of the rotary shaft 102 in the event of a motor or other failure is required.

[0036] This is in contrast to various known THSA architectures in which one or more brakes (such as Electronic Off Brakes for example) are provided to act as an additional safety mechanism.

[0037] In the example of Fig. 2, the rotor (not shown) of the motor 104 (which comprises an annular component) may be mounted coaxially with and radially externally of the harmonic drive gear arrangement 106. For example, a radially inner surface of the rotor may engage with the outer annular spline 206 so as to drive rotation thereof when the motor 104 is powered on. By providing an arrangement in which the motor 104 is coaxial with and extends around the gear system in this way, the envelope required by an electromechanical linear actuator of this type may be reduced. The diameter of the actuator and the total number of parts required in the actuator may also be reduced, thus reducing the number of parts which may fail and so making the actuator safer as well as lighter and less expensive to manufacture.

[0038] As a further safety mechanism in an electromechanical linear actuator according to examples of the invention, it may be desirable to provide a fault tolerance in the motor 104. This may be achieved in one example by providing a motor (not shown) having a common rotor and two separate stators, the motor being configured such that the first stator drives the rotor or, in the event of a failure of that first stator, the second stator then drives the rotor.

[0039] In an alternative example, a multi-phase fault tolerant motor drive system may be provided. As shown schematically in Fig. 2, in any of the possible fault tolerant motor configurations used in different examples of the invention, the rotor or rotors of the motor 104 may be concentrically mounted with the harmonic drive gear arrangement 106 on the rotary shaft 102 such that the or each rotor is coaxial with and extends around the harmonic drive gear arrangement.

[0040] While the invention has been described in detail in connection with only a limited number of examples, it should be readily understood that the invention is not limited to such disclosed examples. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the scope of the claims.

[0041] Additionally, while various examples of the invention have been described, it is to be understood that aspects of the invention may include only some of the described examples. Accordingly the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims

1. A trim horizontal stabiliser actuator comprising an electromechanical linear actuator (100), the electromechanical linear actuator (100) comprising: a rotary shaft (102); an electric motor (104), wherein the rotary shaft is configured to be driven by the electric motor; and an output component (108) configured to be driven along the rotary shaft in response to rotation thereof, characterised in that the electromechanical linear actuator (100) comprises a harmonic drive gear arrangement (106) extending radially outwardly of and coaxially with the rotary shaft, wherein the electric motor (104) is positioned radially outwardly of the harmonic drive gear arrangement, wherein the rotary shaft is configured to be driven by the electric motor via the harmonic drive gear arrangement.

2. A trim horizontal stabiliser actuator as claimed in claim 1, wherein the electric motor (104) comprises a rotor which is coaxial with and extends around the harmonic drive gear arrangement (106).

3. A trim horizontal stabiliser actuator as claimed in claim 1 or 2, wherein the rotary shaft (102) comprises a ball screw and the output component (108) comprises a ball nut.

4. A trim horizontal stabiliser actuator as claimed in any preceding claim, wherein the electric motor (104) is a fault tolerant motor.

5. A trim horizontal stabiliser actuator as claimed in claim 4, wherein the fault tolerant motor (104) comprises a single rotor and two or more stators.

6. A trim horizontal stabiliser actuator as claimed in claim 4, wherein the fault tolerant motor (104) comprises a multi-phase fault tolerant motor drive system.

7. A trim horizontal stabiliser actuator as claimed in any preceding claim, further comprising a stop (114) for limiting the movement of the output component (108) along the rotary shaft (102) in a first direction (D1).

8. A trim horizontal stabiliser actuator as claimed in claim 7, further comprising a further stop (114) for limiting the movement of the output component (108) along the rotary shaft (102) in a second direction (D2), opposite to the first direction (D1).

9. A trim horizontal stabiliser actuator as claimed in any preceding claim, wherein the harmonic drive gear arrangement (106) is configured to limit, or in some examples to stop, rotation of the rotary shaft when the electric motor (104) is inactive.

10. A trim horizontal stabiliser actuator as claimed in any of claims 1 to 8, further comprising a brake (116) configured to limit, or in some examples to stop, rotation of the rotary shaft when the brake is engaged.

11. A trim horizontal stabiliser actuator as claimed in claim 9, further comprising a brake (116) configured to limit, or in some examples to stop, rotation of the rotary shaft when the brake is engaged, wherein the brake will act to limit or stop rotation of the rotary shaft (102) in the event of a failure of the harmonic drive gear arrangement (106) and / or the harmonic drive gear arrangement will act to limit or stop rotation of the rotary shaft in the event of a failure of the brake.

12. A trim horizontal stabiliser actuator as claimed in claim 10 or 11, wherein the brake (116) is a passive brake.

13. An actuation system comprising one or more trim horizontal stabiliser actuators as claimed in any preceding claim and a controller for controlling the one or more trim horizontal stabiliser actuators.

14. An aircraft (2) comprising: a horizontal stabiliser (8a, 8b); and a trim horizontal stabiliser actuator as claimed in any of claims 1 to 12 or an actuation system as claimed in claim 13, wherein the electromechanical linear actuator is configured to move the horizontal stabiliser relative to the aircraft.