Linear mechanical transmission

Abstract

Described is a linear mechanical transmission (T) comprising a roto-translational element (200), extending along an axis (X) of rotation and comprising a first threaded portion (1a) and a second threaded portion (2a), and a rotary input element (300) provided with a first thread (1b) designed to engage rotatably with the first threaded portion (1a) to define a first threaded connection (C1). The transmission (T) also comprises a fixed guide (400), having a second thread (2b) designed to engage with the second threaded portion (2a) to define a second threaded connection (C2). The transmission (T) also comprises at least one output thrust unit (500), translating along the axis (X), and a transmission stage (S) interposed between the roto-translational element (200) and the at least one output thrust unit (500) and having a third threaded connection (C3) for varying the linear speed between the roto-translational element (200) and the at least one output thrust unit (500).

Description

[0001] DESCRIPTION

[0002] LINEAR MECHANICAL TRANSMISSION

[0003] This invention relates to a rotary mechanical transmission and is used in particular in the aeronautical field in particular in the control of the surfaces of an aircraft. There are prior art linear electro-mechanical actuators comprising an electric motor and a transmission consisting, for example, a screw and a lead nut or a pinion and rack system or alternatively with worm screws.

[0004] In the above-mentioned applications, the need is known of developing particularly high axial forces.

[0005] In that situation, the direct-drive actuators, that is, the actuators having the electric motor directly connected to the nut screw by means of recirculating balls, are not very suitable as they must develop a torque proportional to the pitch of the screw which is higher the higher the axial load is.

[0006] In that situation, the torque required of the motor will also be high, due to the lower speed of rotation of the motor caused by a transmission ratio which cannot be reduced beyond a limit value.

[0007] In other words, since the torque required of the motor is proportional to the pitch of the screw, in the presence of large axial loads the motor operates in a condition of large torque and low speed, that is to say, in low efficiency conditions.

[0008] As is known, reduction systems are often used to reduce the load required of the motor by means of a gear box or epicyclic gear mechanisms which are interposed between the motor and the nut screw.

[0009] Disadvantageously, these transmission systems have some drawbacks in terms of reliability, efficiency and duration.

[0010] Alternatively to the gear box or epicyclic gear mechanisms, there are prior art transmission systems comprising a roto-translational element, connected to a power output unit, and a rotary element connected to a drive unit and rotatably engaged with the roto-translational element in such a way as to define a first connection threaded with a short pitch. These transmission systems also comprise a fixed guide engaged with the roto-translational element in such a way as to define a second threaded connection with a long pitch. The roto-translational element is thus simultaneously coupled to the rotary element and to the fixed guide, respectively, by means of the first and second threaded connections which have different pitches in such a way as to vary the angular speed between the roto- translational element and the rotary element.

[0011] A similar actuator is known from patent application WO2021 / 069994 in the name of the same Applicant as this invention.

[0012] This solution operates in an optimum manner, however the Applicant has found that with increasingly stringent requests in terms of transversal dimensions, dictated by increasingly high level design requirements, there is the need to foresee increasingly greater axial forces, using increasingly reduced transversal dimensions.

[0013] This leads to a technical constraint which requires compromises: the solution known from patent WO2021 / 069994 is, in fact, suitable for increasing axial loads by means of technical features which inevitably increase the radial dimensions.

[0014] In effect, this system is subject to two load lines, one acting on the first threaded connection and one acting on the second threaded connection. Since the first threaded connection is provided with a smaller pitch, it is therefore subjected to a greater load.

[0015] In this situation, an increase in the output thrust, thus of the final transmission ratio, requires that the first threaded connection provided with smaller pitch has increasingly small angles (therefore increasingly smaller pitches), with the consequent need to reduce the overall dimensions of the balls, but the balls cannot be reduced below a limit value dictated by the capacity of the actuator to withstand the axial thrusts.

[0016] Moreover, greater forces require greater drive torques and, therefore, larger motors or with larger diameters, but that contrasts with the need for miniaturization of the actuator.

[0017] The technical purpose of the invention is therefore to provide a mechanical transmission which is able to overcome the drawbacks of the prior art. The aim of the invention is therefore to provide a mechanical transmission which allows high axial thrusts to be achieved whilst guaranteeing limited radial dimensions.

[0018] The technical purpose indicated and the specified aim are substantially achieved by a mechanical transmission comprising the technical features described in one or more of the accompanying claims 1 to 11.

[0019] Further features and advantages of the invention are more apparent in the nonlimiting description which follows of a non-exclusive embodiment of a mechanical transmission.

[0020] The description is set out below with reference to the accompanying drawings which are provided solely for purposes of illustration without restricting the scope of the invention and in which:

[0021] Figure 1 is a cross section view of a mechanical transmission according to the invention;

[0022] Figures 2 to 4 are respective cross sections of further embodiments of the mechanical transmission according to the invention.

[0023] The accompanying drawings illustrate different embodiments of the invention.

[0024] The accompanying drawings illustrate a linear actuator “A”, that is to say, an actuator which is able to convert rotational motion into a linear motion.

[0025] In accordance with a preferable but non-limiting use, the actuator “A” is used for actuating control surfaces of an aircraft. More specifically, the actuator is suitable for use in situations where the radial dimensions (transversal) are the most stringent requirement, whilst there are no particular restrictions in length.

[0026] The actuator “A” basically comprises an electric motor and a mechanical transmission “T” acting in conjunction with the electric motor.

[0027] Preferably, the electric motor is connected to a rotary input element 300 of the mechanical transmission “T”, as described below.

[0028] Preferably, the motor has a rotor connected or integral with the rotary input element 300. The rotary input element 300 is, in particular, a component (preferably tubular in shape) provided with exclusively rotary movement.

[0029] The transmission “T” comprises a containment structure 100, preferably substantially cylindrical in shape, and a roto-translational element 200 extending along an axis “X” of rotation.

[0030] The roto-translational element 200 is configured to translate along the axis “X” and simultaneously rotate about the axis “X”.

[0031] The roto-translational element 200 comprises a first threaded portion la and a second threaded portion 2a.

[0032] Preferably, the roto-translational element 200 is made in the form of a hollow body.

[0033] Preferably, the first and the second threaded portions la, 2a occupy, on an outer surface of the roto-translational element 200, along the axis “X”, positions separate and consecutive with each other.

[0034] The transmission “T” also comprises the above-mentioned rotary input element 300 connected or connectable to a drive unit “M”, for example to the above- mentioned electric motor, to define a mechanical power input unit.

[0035] According to the embodiments illustrated, the rotary input element 300 is made in a hollow form in such a way as to be able to position itself around the roto- translational element 200, more precisely it is made in the form of a mechanical lead nut with a hollow tubular shape and threaded internally.

[0036] The rotary input element 300 is in effect equipped internally with a first thread lb designed to engage rotatably with the first threaded portion la of the roto- translational element 200 in particular by means of a lead nut and screw or recirculating ball or roller connection in such a way as to define a first threaded connection of the helical type Cl.

[0037] The rotary input element 300 is axially locked thanks to the presence, respectively, of ball bearings and / or roller bearings; this means that the rotary input element 300 is mounted inside the mechanical transmission “T” in such a way as to be axially locked and therefore not able to translate along a direction parallel to the axis “X” but only able to perform a rotational movement about the axis “X”.

[0038] In other words, the rotary input element 300 is positioned about the roto- translational element 200 in such a way that the first thread lb enters rotatably into contact with the first threaded portion la of the roto-translational element 200 positioned in such a way as to create the first threaded connection Cl.

[0039] Preferably, the first threaded connection Cl is defined by a recirculating ball screw.

[0040] The transmission “T” also comprises a fixed guide 400, fixed to the containment structure 100.

[0041] The fixed guide 400 has a second thread 2b designed to engage with the second threaded portion 2a of the roto-translational element 200 in such a way as to define a second threaded connection C2.

[0042] Preferably, the second threaded connection C2 is defined by a recirculating ball screw.

[0043] Even more preferably (and in particular in all the embodiments which will be described), the second threaded connection C2 is defined by a recirculating ball screw wherein the balls are recirculated inside the fixed guide 400.

[0044] The roto-translational element 200 is therefore simultaneously coupled to the rotary input element 300 and to the fixed guide 400, respectively, by means of the first and the second threaded connections Cl, C2.

[0045] Preferably, the first and the second threaded connections Cl, C2 are positioned on an outer surface of the roto-translational element 200 occupying separate and consecutive axial positions.

[0046] The roto-translational element 200 is therefore rotatably connected to the rotary input element 300 by means of the first threaded connection Cl defined by the first threaded portion la of the roto-translational element 200 and by the first thread lb of the rotary input element 300 and is also engaged with the fixed guide 400 by means of the second threaded connection C2, defined by the second threaded portion lb of the roto-translational element 200 and by the second thread 2b of the fixed guide 400.

[0047] Preferably, the pitches of the first and the second threaded connections Cl, C2 have a constant value along the entire axial extension of each threaded portion la, 2a.

[0048] The first and the second threaded connections Cl, C2 have different pitches, that is to say, the pitch of the first threaded connection Cl is different from the pitch of the second threaded connection C2 and in particular less (the first threaded connection is a “short pitch” whilst the second is a “long pitch”).

[0049] Since the first and the second threaded connections Cl, C2 have different pitches to each other, in particular of a different module and / or opposite direction, they allow a variation in the angular speed between the roto-translational element 200 and the rotary input element 300.

[0050] A rotation of the rotary input element 300 therefore corresponds to a roto- translation of the roto-translational element 200 the angular speed of which is different from that of the rotary input element 300 and a function of the values of the pitches of the first and the second threaded connections Cl, C2.

[0051] The transmission “T” also comprises at least one output thrust unit 500 translating along the axis “X” and defining a power output unit.

[0052] The transmission “T” also comprises an anti-rotation mechanism 600 interposed between the containment structure 100 and the at least one output thrust unit 500 for locking the at least one output thrust unit 500 with respect to a rotation movement.

[0053] In other words, the anti-rotation mechanism 600 is configured to prevent a rotation of the at least one output thrust unit 500 about the axis “X” and allow the translation movement along the axis “X”.

[0054] As will in fact be clarified below, unlike the previous patent application WO202 1 / 069994 of the Applicant, the output thrust unit 500 is not simply coupled to the roto-translational element 200 by means of a circular guide such as to receive from the roto-translational element 200 only the thrust component transferred by the latter.

[0055] According to the invention, in fact, the transmission “T” also comprises at least one transmission stage “S” interposed between the roto-translational element 200 and the at least one output thrust unit 500 and having a third threaded connection C3 having a third pitch for varying the linear speed between the roto-translational element 200 and the at least one output thrust unit 500.

[0056] Preferably, the third pitch has a value different from the first pitch and from the second pitch and more preferably has an intermediate value between the first pitch (short pitch) and the second pitch (long pitch).

[0057] In other words, the transmission stage “S” is configured both for transmitting the translating motion of the roto-translational element 200 to the at least one output thrust unit 500 and for causing, by means of the third threaded connection C3, a variation of the linear speed between the roto-translational element 200 and the at least one output thrust unit 500.

[0058] In use, the drive unit “M” rotates the rotary input element 300 with a predetermined angular speed. By means of the first threaded connection Cl, the rotary input element 300 in turn rotates the roto-translational element 200.

[0059] The roto-translational element 200 thus, due to the motion imparted by the rotary input element 300, rotates about the axis “X” but simultaneously also translates along the axis “X” thanks to the presence of the fixed guide 400.

[0060] In this situation, the value of the angular speed of the rotary input element 300 is varied, as a function of the pitches of the first and the second threaded connections Cl, C2, and then transmitted to the roto-translational element 200.

[0061] By means of the action of the transmission stage “S”, only the translating motion of the roto-translational element 200 is transmitted to the at least one output thrust unit 500 but with a further variation of the thrust which, in particular, is a multiplication of thrust. During this transmission of the motion, the linear speed transmitted to the at least one output thrust unit 500 is varied relative to the linear speed of translation of the roto-translational element 200 thanks to the third threaded connection C3.

[0062] The variation between the linear speed of the roto-translational element 200 and that of the at least one output thrust unit 500 is therefore a function of the pitch of the third threaded connection C3.

[0063] According to an aspect of this invention, the first, the second and the third threaded connections C2, C2, C3 are positioned in respective positions which are separate and consecutive with each other along the axis “X”.

[0064] According to an aspect of the invention, the transmission stage “S” comprises an intermediate rotary element 700 provided with only rotational movement and comprising a threaded portion 3 a designed to couple rotatably to a corresponding threaded portion 3b made on the at least one output thrust unit 500 to define the third threaded connection C3.

[0065] Preferably, the third threaded connection C3 is defined by a recirculating ball screw.

[0066] As shown in the embodiments of the accompanying drawings, the intermediate rotary element 700 is hollow.

[0067] Preferably, the intermediate rotary element 700 receives at least partly the at least one output thrust unit 500 in such a way that the third threaded connection C3 is positioned inside the intermediate rotary element 700 and outside the output thrust unit 500.

[0068] In other words, the intermediate rotary element 700 is fitted about the at least one output thrust unit 500 in such a way as to roto-translate relative to it, in particular in such a way as to rotate about the at least one output thrust unit 500 whilst the latter translates along the axis “X”.

[0069] Preferably, the intermediate rotary element 700 is rotatably connected to the containment structure 100 by one or more ball bearings 800 and / or rollers and / or by means of circular guides, preferably ball and / or roller bearings.

[0070] In particular, the bearings and / or circular guides are positioned outside the intermediate rotary element 700 and on an inner surface of the containment structure 100.

[0071] Preferably, the intermediate rotary element 700 is mounted on the containment structure 100 exclusively by means of one or more ball bearings 800 and / or rollers and / or by means of the circular guides.

[0072] The one or more ball bearings 800 or rollers and / or circular guides act as thrust bearing units which are able to absorb the axial load exerted from the outside on the output thrust unit500 so as to lighten the load acting on the components upstream of the intermediate rotary element 700.

[0073] In use, during the roto-translation of the roto-translational element 200, the intermediate rotary element 700, through the third threaded connection C3, transmits to the at least one output thrust unit 500 only the translating motion of the roto-translational element 200 in such a way that the at least one output thrust unit 500 is translated with a linear speed different from the linear speed of the roto-translational element 200.

[0074] This linear speed is a function of the angular speed of the rotary input element 300, of the values of the pitches of the first, second and third threaded connections C1, C2, C3.

[0075] As shown in the embodiments of the accompanying drawings, the roto- translational element 200 is connected to the intermediate rotary element 700 by means of a linear guide 900 parallel to the axis “X” in such a way that the intermediate rotary element 700 is rotatably integral with the roto-translational element 200 and axially independent from the roto-translational element 200.

[0076] In other words, the linear guide 900 is configured to allow the transmission of the rotational motion of the roto-translational element 200 to the intermediate rotary element 700 and to prevent the transmission of the translational motion of the roto-translational element 200 to the intermediate rotary element 700.

[0077] Preferably, the linear guide 900 is defined by a splined or recirculating ball connection.

[0078] According to the embodiment shown in Figures 1 and 2, the linear guide 900 is at least partly superposed on the third threaded connection C3.

[0079] In other words, the third threaded connection C3 is “intersected” by the linear tracks of the linear guide 900.

[0080] Preferably, in this situation, the third threaded connection C3 comprises a recirculating ball screw integrated in the intermediate rotary element 700.

[0081] Alternatively, in accordance with the embodiment shown in Figures 3 and 4, the linear guide 900 is positioned in a position adjacent to the third threaded connection C3 along the axis “X”.

[0082] In other words, the linear guide 900 occupies a position axially spaced and adjacent, along the axis “X”, relative to the third threaded connection C3.

[0083] Preferably, in this situation, the linear guide 900 comprises a recirculating ball screw integrated in the roto-translational element 200.

[0084] As may be noted in all the embodiments illustrated, the arrangement of the threaded connections and the linear guide 900 makes it possible to obtain actuators “A” substantially elongate along the axis “X” but having a diameter particularly reduced and suitable for aeronautical applications.

[0085] Figures 1 and 3 show an actuator “A” of the single-acting type. In this situation, the mechanical transmission “T” comprises a single output thrust unit 500 which protrudes from an end of the containment structure 100 and translates in extraction and retraction relative to it along the axis “X” as described above.

[0086] In the single-acting actuator “A” there is a single transmission stage “S” and a single third threaded connection C3.

[0087] In particular, according to the embodiment of Figure 1, the second threaded connection C2 is at least partly superposed on the linear guide 900 whilst, according to the embodiment of Figure 3, the second threaded connection C2 is positioned in a position adjacent to the linear guide 900 along the axis “X”, in particular the second threaded connection C2 and the linear guide 900 are made on sections of the roto-translational element 200 spaced from each other along the axis “X”.

[0088] Figures 2 and 4 show, on the other hand, a double-acting actuator “A”.

[0089] Figure 4 shows an embodiment of the double-acting actuator “A” wherein the transmission “T” comprises a single output thrust unit 500 extending along the axis “X” between a first and a second end 500a, 500b protruding from respective ends of the containment structure 100. The output thrust unit 500, in this case, is preferably supported at two separate points, in particular at the opposite ends of the containment structure 100.

[0090] As shown in Figure 4, the output thrust unit 500 is inserted inside the roto- translational element 200 and is connected to the roto-translational element 200 by means of the transmission stage “S”.

[0091] In other words, the output thrust unit 500 is a single body the ends of which define respective power outputs and wherein the transmission “T” comprises a single transmission stage “S”. In this way, when the transmission stage “S” transmits the translating motion of the roto-translational element 200 to the output thrust unit 500 to make it translate along the axis “X”, an extraction of the first end 500a of the output thrust unit 500 from the containment structure 100 corresponds to a retraction of the second end 500b of the output thrust unit 500 inside the containment structure 100 and vice versa.

[0092] According to this embodiment, as shown in Figure 4, the third threaded connection C3 (connecting the output thrust unit 500 with the roto-translational element 200), the linear guide 900, the second threaded connection C2 and the first threaded connection Cl are positioned, in this specific order, in respective positions which are separate and consecutive from each other along the axis “X”. Alternatively, in this order the second threaded connection C2 and the first threaded connection Cl may be reversed.

[0093] Figure 2 shows a different embodiment of the double-acting actuator “A” wherein the transmission “T” comprises a first and a second output thrust unit 501, 502 protruding from opposite ends of the containment structure 100 and each connected to a respective end of the roto-translational element 200 by means of a respective transmission stage “S”.

[0094] According to the embodiment of Figure 2, the first and the second output thrust units 501, 502 are separate from each other and connected to a respective intermediate rotary element 700 by respective third threaded connections C3.

[0095] In other words, according to the embodiment of Figure 1, there is a single roto- translational element 200 connected to two separate transmission stages "S" and, in turn, operatively connected to the first and to the second output thrust units 501, 502 in such a way that the translating motion of the roto-translational element 200 is transmitted, by respective transmission stages "S", to the first and to the second output thrust units 501, 502.

[0096] According to this embodiment, as shown in Figure 2, a third threaded connection C3 (connecting the first output thrust unit 501 with an end of the roto-translational element 200), the first threaded connection Cl, the second threaded connection C2 (superposed on the linear guide 900) and the other third threaded connection C3 (connecting the second output thrust unit 502 with the end of the roto- translational element 200) are positioned in the above-mentioned order in respective positions which are separate and consecutive from each other along the axis “X”.

[0097] However, according to each of the embodiments, the linear guide 900 may have recirculating balls on the roto-translational element 200 (obtaining more robust solutions, with intermediate rotary element 700 provided with linear and axial tracks and the second threaded portion 2a of the roto-translational element 200 separated from them, resulting in a longer actuator “A”) or recirculating balls on the intermediate rotary element 700 (in this case making an actuator “A” shorter but with linear tracks and second threaded portion 2a of the roto-translational element 200 intersecting each other).

[0098] The invention achieves the preset aims eliminating the drawbacks of the prior art. In particular, the transmission “T” is very compact in a transversal direction whilst achieving extremely high thrust values. Moreover, the torque required of the motor is reduced allowing its dimensions to be reduced.

[0099] Moreover, the transmission is extremely robust and provides an intermediate stage of absorbing axial loads, reducing the stresses on the first and second threaded connections, in particular on the short pitch.

Claims

CLAIMS1. A linear mechanical transmission (T) comprising:- a containment structure (100);- a roto-translational element (200) extending along an axis of rotation (X) and comprising a first threaded portion (la) and a second threaded portion (2a), said roto-translational element (200) being configured to translate along said axis (X) and simultaneously rotate about said axis (X);- a rotary input element (300) connected or connectable to a drive unit (M) to define a mechanical power input unit and equipped with a first thread (lb) designed to engage rotatably with said first threaded portion (la) of said roto- translational element (200), in particular by means of a lead nut and screw or recirculating ball or roller coupling, in such a way as to define a first threaded connection (Cl);- a fixed guide (400), fixed to said containment structure (100), having a second thread (2b) designed to engage with said second threaded portion (2a) of the roto- translational element (200) in such a way as to define a second threaded connection (C2); said roto-translational element (200) being simultaneously coupled to the rotary input element (300) and to the fixed guide (400), respectively, by means of said first and second threaded connections (Cl, C2), and wherein said first and second threaded connections (Cl, C2) have different pitches;- at least one output thrust unit (500) translating along said axis (X) and defining a power output unit, said at least one output thrust unit (500) being connected to the roto-translational element (200) for translating along the axis (X);- an anti-rotation mechanism (600) interposed between the containment structure (100) and the at least one output thrust unit (500) for locking said at least one output thrust unit (500) with respect to a rotation movement; characterised in that it comprises at least one transmission stage (S) interposed between said roto-translational element (200) and said at least one output thrust unit (500) and having a third threaded connection (C3) having a third pitch for varying the linear speed between the roto-translational element (200) and the atleast one output thrust unit (500).

2. The mechanical transmission according to claim 1, wherein the transmission stage (S) comprises an intermediate rotary element (700) equipped with only rotational movement and comprising a threaded portion (3 a) designed to couple rotatably to a corresponding threaded portion (3b) made on said at least one output thrust unit (500) to define said third threaded connection (C3), in particular of the recirculating ball type, preferably said intermediate rotary element (700) being hollow and more preferably receiving at least partly said at least one output thrust unit (500) in such a way that the third threaded connection (C3) is positioned inside the intermediate rotary element (700) and outside the output thrust unit (500).

3. The mechanical transmission according to claim 2, wherein said first, second and third threaded connections (Cl, C2, C3) are positioned in respective positions separate and consecutive with each other along said axis (X).

4. The mechanical transmission according to claim 3, wherein said intermediate rotary element (700) is rotatably connected to the containment structure (100) by one or more ball or roller bearings (800) and / or circular guides preferably of the ball type, in particular positioned outside the intermediate rotary element (700) and on an inner surface of the containment structure (100); preferably, the intermediate rotary element (700) being mounted on the containment structure (100) exclusively by means of said one or more ball or roller bearings (800) and / or circular guides.

5. The mechanical transmission according to any one of claims 2 to 4, wherein said roto-translational element (200) is connected to said intermediate rotary element (700) by a linear guide (900) parallel to said axis (X) in such a way that said intermediate rotary element (700) is rotatably integral with the roto- translational element (200) and axially independent from the roto-translationalelement (200), preferably said linear guide (900) being defined by a splined or recirculating ball connection.

6. The mechanical transmission according to claim 5, wherein said linear guide (900) is at least partly superposed on said third threaded connection (C3), preferably said third threaded connection (C3) comprising a recirculating ball screw integrated in the intermediate rotary element (700).

7. The mechanical transmission according to claim 5, wherein said linear guide (900) is positioned in a position adjacent to said third threaded connection (C3) along the axis (X), preferably said third threaded connection (C3) comprising a recirculating ball screw integrated in the roto-translational element (200) and said intermediate rotary element (700) having internally axial tracks for the balls of the linear guide (900).

8. The mechanical transmission according to any one of the preceding claims, wherein said first and second threaded connections (Cl, C2) are defined by respective recirculating ball screws.

9. The mechanical transmission according to any one of the preceding claims, wherein said transmission (T) comprises a single output thrust unit (500).

10. The mechanical transmission according to any one of claims 1 to 9, comprising a first and a second output thrust unit (501, 502) protruding from opposite ends of said containment structure (100) and each connected to a respective end of the roto-translational element (200) by means of a respective transmission stage (S).

11. The mechanical transmission according to any one of claims 1 to 9, comprising a single output thrust unit (500) extending along said axis (X) between a first and a second end (500a, 500b) protruding from respective ends of saidcontainment structure (100), said output thrust unit (500) being inserted inside the roto-translational element (200) and connected to the roto-translational element (200) by means of said transmission stage (S).

12. A linear actuator (A), comprising a mechanical transmission (T) according to any one of the preceding claims, and an electric motor connected to said rotary input element (300), in particular having a rotor connected to or integral with said rotary input element (300).

13. Use of an actuator (A) according to claim 12 for actuating flaps of control surfaces of an aircraft.

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