FR3079563A1 - ACTUATING DEVICE FOR MOVING A MOBILE HOOD FROM A THRUST INVERTER - Google Patents

Abstract

The invention relates to an actuating device for moving a movable cowl of a thrust reverser, comprising: an actuator comprising a first element, such as a screw, and a second element, such as a nut, co-operating with the first element so that a rotation of the first element causes a translation of the second element, and - a movable locking part between a locked position in which the locking piece prevents the rotation of the first element, and an unlocked position in which the locking member for rotating the first member, wherein the locking member comprises a latch (47) having a convex portion (50) and a planar or substantially concave portion (51) adapted to be selectively positioned facing a tooth (21) integral in rotation of the first element, to prevent or allow the rotation of the first element.

Description

FIELD OF THE INVENTION

The invention relates to an actuating device for moving a movable cover of a thrust reverser.

STATE OF THE ART

Propulsion systems or PPS (Power Plant System) aircraft generally include a nacelle and a turbojet engine attached to a wing pylon or an aircraft fuselage. In the case of a high-dilution turbofan (turbofan), the turbojet includes a gas generator (high pressure body or CoHP), a low pressure body (or CoBP), a blower and nozzles. The blower accelerates a flow of secondary air flowing through a blower air stream, to generate the thrust necessary to propel the aircraft.

Aircraft propulsion systems generally include a Thrust Reverse (TR) system that reverses thrust during landing to improve the braking ability of the aircraft. Such a system includes a set of movable hoods actuated by a set of associated actuators or TR (“Thrust Reverse”) making it possible to temporarily obstruct the air stream and to divert the flow of secondary air outward and towards the 'front of the nacelle, thereby generating a counter-thrust which is added to the braking of the wheels.

In the case of a so-called “door” reverse thrust system, the nacelle is equipped with movable cowls (called “doors”) which pivot relative to the structure of the nacelle between a retracted position in which they allow a circulation of the air flow in the duct towards the outside and towards the rear of the nacelle and a deployed position in which the flaps obstruct the duct and redirect the air flow towards the outside and towards the front of the nacelle.

In the case of a so-called "grid" or "cascade" thrust reversal system, the nacelle is fitted with movable cowls which slide relative to the structure of the nacelle along rails between a retracted position in which they allow a circulation of the secondary flow in the conduit towards the outside and towards the rear of the nacelle and a deployed position in which they discover grids of deflection vanes arranged in the thickness of the nacelle and obstruct the annular conduit by means of flaps, the actuation of which is linked to the movement of the covers.

In general, in either case, the movable covers are actuated by a set of dedicated actuators. Mechanical synchronization of the movement of the actuators is ensured by a synchronization system comprising flexible shafts making it possible to mechanically connect the actuators to one another.

In addition, the thrust reversal systems must include several locking devices to prevent inadvertent deployment of the covers during the flight phase. Among the locking devices fitted to the reverse thrust systems, certain locking systems called "primary" or PLS ("Primary Lock System") act on the flexible shaft to block the flexible shaft in rotation.

Document US Pat. No. 6,786,039 describes a system for actuating a thrust reverser comprising an actuator driven in movement between a retracted configuration and a configuration deployed by means of a drive shaft connected to a flexible shaft. The system includes a locking device that can be controlled to engage or disengage the drive shaft to prevent or allow rotation of the drive shaft. The system further includes a locking inhibitor to maintain the locking device in the disengaged position as long as the actuator is not in the retracted configuration.

The locking device comprises a locking rod movable in translation, a spring for urging the rod towards the engaged position and an electromagnet which can be activated to urge the rod towards the disengaged position.

Such a locking device must be designed so as not to unlock in the event of an impact. In particular, the device must operate despite significant dynamic loads that can occur in the event of the loss of a blade in the aircraft engine (Fan Blade Out), three of these shocks can generate sudden accelerations. The locking device must also be insensitive to other sources of excitation (unbalance, rolling shocks, etc.) which can cause accelerations up to 200 G.

This is why, in locking devices, it is generally necessary to provide a spring having a significant stiffness in order to ensure that the locking rod is not disengaged in the event of an impact. This has the consequence that it is also necessary to provide a solenoid for generating a large unlocking force in order to overcome the force exerted by the spring and disengage the locking rod.

It follows that the locking device necessarily has a large size due to the large dimensions of the spring and the electromagnet which are provided to avoid inadvertent unlocking.

SUMMARY OF THE INVENTION

An object of the invention is to propose an actuation device which has a reduced bulk.

This problem is solved in the context of the present invention by means of an actuating device for moving a movable cover of a thrust reverser, comprising:

an actuator comprising a first element and a second element mounted movable in translation relative to the first element, one of the first element and of the second element being a screw, and the other being a nut suitable for cooperating with the screw, so that a rotation of the first element relative to the second element causes a translation of the second element relative to the first element,

a locking device comprising a locking piece movable between a locked position in which the locking piece prevents the rotation of the first element and an unlocked position in which the locking piece allows the rotation of the first element, and

- an unlocking device comprising a movable unlocking part in rotation between an active position in which the unlocking part urges the locking part towards the unlocked position and a passive position in which the unlocking part authorizes a return of the locking part in the locked position, and a drive member capable of driving the unlocking part in rotation so that the unlocking part moves the locking part towards the unlocked position.

As the unlocking part is movable in rotation (and not in translation), the unlocking device can be designed so that the unlocking part is very insensitive to sudden accelerations that can be exerted on the actuating device in the event of choc. In particular, the unlocking device can be designed so that the unlocking part is movable in rotation about an axis of rotation passing through the center of gravity of the unlocking part.

It is thus possible to design a device incorporating a return member of reduced dimensions, as well as a drive member of reduced dimensions.

The device can also have the following characteristics:

the locking device comprises a tooth mounted integral in rotation with the first element, the locking piece being clean, in the locked position, to come into engagement with the tooth to prevent rotation of the first element,

the locking part comprises a clean pawl which comes into engagement with the tooth in the locked position,

the locking device comprises a roller carried by the unlocking part, capable of keeping the pawl in engagement with the tooth when the pawl is in the locked position,

the unlocking part comprises a pin which when the unlocking part is driven in rotation urges the pawl to pivot the pawl towards the unlocked position,

- The locking piece comprises a latch having a convex portion and a flat portion able to be selectively positioned facing the tooth, the convex portion being clean to interfere with the tooth when the convex portion is facing the tooth to prevent rotation of the first element, and the planar portion being suitable for allowing the rotation of the first element when the planar portion is opposite the tooth,

- the tooth is asymmetrical so that in the locked position, the locking piece prevents rotation of the first element in a first direction and allows rotation of the first element in a second direction, opposite to the first direction,

the locking part is able to mesh with the unlocking part so that the rotation of the unlocking part controls the rotation of the locking part,

- the drive member includes a rotating electromagnet,

the unlocking device comprises a return spring capable of urging the unlocking part towards the passive position,

the unlocking device comprises a stop and a retaining piece integral in rotation with the unlocking piece and movable in translation relative to the unlocking piece between a retaining position in which the rotation of the retaining piece is limited by the stop and a release position in which the retaining part is free to rotate,

- the actuation device comprises a return member adapted to urge the retaining part towards the retaining position,

- the actuation device comprises a rod movable in translation relative to the first element and being able to be urged by the second element to move the retaining part towards the release position,

- the movable rod extends at least partially inside the first element,

- the actuation device further comprises a manual unlocking device for rotating the retaining part in order to bring the unlocking part into the active position, without activating the drive member,

- the first element is the screw and the second element is the nut.

PRESENTATION OF THE DRAWINGS

Other characteristics and advantages will also emerge from the description which follows, which is purely illustrative and not limiting, and should be read with reference to the appended figures among which:

- Figure 1 schematically shows, in longitudinal section, a device according to a first embodiment of the invention,

FIG. 2 schematically represents, in perspective, part of the device of FIG. 1,

FIG. 3 schematically represents, from behind, the locking device of the device of FIG. 1,

FIG. 4 schematically represents, from behind, the device for unlocking the device of FIG. 1,

- Figure 5 is a detail view schematically showing the shape of a locking piece,

FIGS. 6A to 12C schematically represent steps in the operation of the device according to the first embodiment,

FIG. 13 schematically represents, in perspective, part of an actuation device according to a second embodiment of the invention,

FIGS. 14A and 14B schematically represent a rear view, the locking device of the device of FIG. 19, respectively in the unlocked position and in the locked position,

- Figures 15A and 15B schematically show in cross section, the unlocking device of the device of Figure 18, respectively in the passive position and in the active position.

DETAILED DESCRIPTION OF AN EMBODIMENT

In Figure 1, the device 1 shown comprises a housing 2, a screw 3 extending from the housing 2 and a nut 4.

The screw 3 has a body 10 of generally elongated cylindrical shape and is rotatably mounted relative to the casing 2 of the device around an axis of rotation X corresponding to the longitudinal axis of the screw 3 and also corresponding to an axis of deployment of the actuator.

The screw 3 comprises a first end 5 (or receiving end) intended to receive a driving torque and a second end 6 (or free end) extending at a distance from the first end 5. The actuator 1 comprises a bevel wheel inlet 7 mounted integral with the screw 3, at the first end 5 of the screw. The input bevel gear 7 meshes with a gear part 8 of a drive shaft 9, so as to transmit a rotational movement from the drive shaft 9 to the screw 3.

The nut 4 extends around the body 10 of the screw 3 and is intended to be fixed to an actuator tube 55 having an end 56 connected to a movable component of the thrust reverser (a movable cover for example) by means of a ball joint 57 with anti-rotation stops.

The nut 4 is mounted movable in translation relative to the screw 3 along the longitudinal axis X of the screw 3 to move the actuator tube between two extreme positions corresponding respectively to a retracted configuration and to a deployed configuration of the actuator.

The body 10 of the screw has a cylindrical external surface 11 in which is formed a helical groove 12. The nut 4 has a cylindrical internal surface 13 in which is formed a helical groove 14. The screw 3 and nut 4 cooperate between them by means of the helical grooves 12 and 14 in which are housed balls 15 so that a rotation of the screw 3 relative to the housing 2 causes a translation of the nut 4 relative to the screw 3 in the direction X .

The device 1 also comprises a drive shaft 9 having a first end 15 and a second end 16. The first end 15 is shaped to be able to be connected to a first drive shaft of a thrust reverser or flexible shaft 58, the first motor shaft being connected to a drive motor arranged at a distance from the actuating device. The second end 16 comprises a bevel wheel 8 arranged to mesh with the input bevel wheel 7 of the screw 3 in order to drive the screw 3 in rotation.

When the engine is activated, the rotation of the screw 3 concomitantly causes the nut 4 to translate between a first extreme position (corresponding to a retracted configuration of the device) in which the mobile component of the thrust reverser is retracted and a second extreme position (corresponding to a deployed configuration of the device) in which the mobile component of the thrust reverser is deployed, thereby making it possible to divert the air flow towards the front of the nacelle.

The device 1 also includes a locking device 17 visible in FIG. 3 to block the screw 3 in rotation when the actuator is in the retracted configuration, and thus avoid inadvertent deployment of the actuator, in particular in flight phase.

The locking device 17 comprises a first locking piece 18 in the form of a pawl 46 rotatably mounted relative to the casing 2, and a second locking piece 19 having two teeth 20 and 21, the second locking piece 19 being mounted integral with screw 3. The pawl 46 is movable in rotation between a locked position (illustrated in FIG. 3) in which the pawl 46 comes into engagement with one of the teeth 21, thus preventing rotation of the screw 3, and an unlocked position (illustrated for example in FIG. 7) in which the pawl 46 is moved away from tooth 21, thus allowing rotation of the screw

3.

The locking device 17 further comprises a return spring 22 (such as a torsion spring) capable of urging the pawl 46 in rotation towards the locked position to maintain the pawl 46 in engagement with the tooth 21.

Furthermore, the device 1 comprises an unlocking device 23 comprising a drive member 24 and an unlocking part

25.

The unlocking part 25 is rotatably mounted relative to the casing 2 by means of a ball bearing 26 mounted between the casing 2 and the unlocking part 25. The unlocking part 25 is movable in rotation relative to the casing 2 around an axis of rotation coincident with the axis of rotation X of the screw 3, between an active position in which the unlocking part 25 urges the locking part 18 towards the unlocked position and a passive position in which the part unlocking 25 allows the locking piece 18 to return to the locked position.

The unlocking part 25 has a first cylindrical part 27 of small diameter and a second cylindrical part 28 of large diameter.

The unlocking part 25 further comprises a pin 29 visible in FIG. 3, arranged at the periphery of the cylindrical part 28 of large diameter. The pin 29 is able to come to urge the pawl 46 by pivoting it towards the unlocked position when the unlocking part 25 is rotated in a first direction (represented in FIG. 2 by the arrow A).

The unlocking part 25 also comprises a roller 30 carried by the unlocking part 25, also arranged at the periphery of the large diameter portion 28. The roller 30 is suitable for pressing on the pawl 46 to hold the pawl 46 in place. engagement with the tooth 21 when the pawl 46 is in the locked position and the unlocking part 25 is in the passive position.

The drive member 24 comprises an electromagnet 31 arranged around the part 27 of small diameter of the unlocking part 25. When activated, the electromagnet 31 rotates the unlocking part 25 in the first direction of rotation (arrow A) towards the active position in order to unlock the pawl 46.

The unlocking device 23 also includes a return spring 32 capable of urging the unlocking part 25 in a second direction of rotation (represented by arrow B), opposite the first direction of rotation towards the passive position, in order to bring the pawl back 46 in the locked position when the electromagnet 24 is not activated.

Furthermore, the actuating device 1 comprises a retaining device 33 making it possible to keep the pawl 46 in the unlocked position as long as the actuator is not in the retracted configuration, even when the electromagnet 24 is not activated.

The retaining device 33 comprises a retaining part 34 and a stop 35 capable of cooperating with the retaining part 34 to selectively prevent or allow rotation of the unlocking part 25.

The retaining part 34 comprises a pusher 36 extending inside the unlocking part 25 in the direction X, and a retaining finger 37 fixed to one end of the pusher 36 and extending in a radial direction relative to to the pusher 36. More specifically, the pusher 36 extends inside the part 27 of small diameter of the unlocking part 25. The pusher 36 is rotationally integral with the unlocking part 25, but is movable in translation relative to the unlocking part 25, in the direction X. For this purpose, the external surface 38 of the pusher 36 and the internal surface 39 of the unlocking part 25 are provided with longitudinal grooves, the grooves of the rod 38 being able to cooperate with the grooves of the unlocking part 25 to allow a translation of the rod 38 relative to the unlocking part 25 while preventing rotation of the pusher 36 by relative to the unlocking part 25.

The retaining part 34 is movable in translation relative to the unlocking part 25 between a retaining position (illustrated for example in FIG. 12A) in which the rotation of the retaining part 34 is limited by the stop 35 and a position release (illustrated for example in Figure 1) in which the retaining piece 34 is out of reach of the stop 35 and is therefore free to rotate.

The actuating device 1 also comprises a rod 40 movable in translation relative to the screw 3, the movable rod 40 extending at least partially inside the screw 3. The movable rod 40 is able to be stressed in translation by the nut 4 when the nut 4 reaches the first extreme position corresponding to the retracted configuration of the device 1.

The retaining part 34 is able to be urged by the movable rod 40 to move the retaining part 34 in a first direction (represented in FIG. 1 by the arrow C) towards the release position.

Furthermore, the retaining device 33 comprises a return spring 41 capable of urging the retaining part 34 in a second direction (represented by the arrow D), opposite to the first direction, to bring the retaining part 34 back to the position of retained when the movable rod 40 no longer biases the retaining part 34.

The stop 35 is fixed to the casing 2 and comprises a pin 42 projecting from the casing 2 in a direction substantially parallel to the direction X. The pin 42 is able to cooperate with the finger 37 to prevent rotation of the retaining piece 34 (and consequently of the unlocking part 25) relative to the casing 2. More precisely, when the retaining part 34 is in the retaining position, the finger 37 comes into radial abutment against the pin 42 under the action of the spring 32, the pin 42 preventing the rotation of the retaining part 34.

As can be seen in FIG. 4, the actuation device 1 further comprises a manual unlocking device 54 for rotating the retaining part 34 in order to bring the unlocking part into the active position, in the case of assembly or maintenance of the actuating device. More specifically, the manual unlocking device 54 comprises a push button that can be moved manually to urge the finger 37 to rotate the retaining part 34, and consequently, the unlocking part 25 towards the active position.

FIG. 5 is a detail view schematically showing the shape of the pawl 46.

As illustrated in FIG. 5, the pawl 46 has a second recessed portion 45 capable of coming into contact with the unlocking pin 29 when the unlocking part 25 biases the pawl 46 towards the unlocked position. The shape of the second recessed portion 45 makes it possible to reduce the friction force due to the support of the pawl 46 on the pin 29 at the end of unlocking and when the pawl 46 is held in the unlocked position.

FIGS. 7A to 12C schematically represent stages of operation of the actuation device 1.

The actuating device is initially in the retracted configuration (FIG. 6A), the nut 4 being in the first extreme position.

As illustrated in Figure 6B, the pawl 46 is in the locked position. The free end 43 of the pawl abuts the tooth 21, which prevents any rotation of the screw 3. In addition, the roller 30 maintains the pawl 46 in the locked position. In this configuration, deployment of the actuation device 1 is not possible.

Furthermore, as illustrated in FIGS. 6A and 6C, the retaining part 34 is in the release position, the finger 37 of the retaining part being out of the range of the stop 35.

When the pilot orders the deployment of the thrust reverser, a control system triggers the supply of the electromagnet 31 (FIG. 7A). The electromagnet 31 then applies a torque to the unlocking part 25, which has the effect of rotating the unlocking part 25 about the axis X, in the first direction indicated by the arrow A (FIGS. 7B and 7C) .

The rotation of the unlocking part 25 has the effect, firstly, of releasing the roller 30 from the pawl 46 (FIG. 9B) and simultaneously of pivoting the finger 37.

While the unlocking part 25 is rotated by the electromagnet 31 (Figure 8A), the pin 29 comes, in a second step, to urge the pawl 46 (Figure 8B) to move the pawl 46 away from tooth 21. More specifically, the pin 29 comes to urge the pawl 46 once the roller 30 is no longer in contact with the pawl 46. Furthermore, the finger 37 pivots (FIG. 8C) and passes beyond the stop 35.

Once the pawl 46 is in the unlocked position (Figures 9A and 9B), the actuating device 1 can be deployed. Indeed, the pawl 46 allows rotation of the screw 3. The screw 3 is rotated so that the nut 4 translates along the screw 3 in the direction X away from the first extreme position. By moving away from the first extreme position, the nut 4 ceases to urge the movable rod 40 and consequently the retaining part 34. The retaining part 34 is moved in translation along the axis X in the second direction D under the action of the return spring 41. This has the effect that the finger 37 comes to be positioned behind the stop 35 (FIGS. 9A and 9C), the stop 35 preventing the rotation of the retaining part 34 (and consequently of the part 25) in the second direction (arrow B).

From this instant, the electromagnet 31 can be deactivated, without the pawl 46 returning to the locked position. In fact, the retaining part 34 maintains the unlocking part 25 in the active position, that is to say a position in which the unlocking part 25 maintains the pawl 46 in the unlocked position.

This has the consequence that the actuating device 1 cannot be locked until the nut 4 has returned to the first extreme position, that is to say as long as the actuating device is not not returned in retracted configuration.

When the thrust reverser is retracted, the screw 3 is rotated so that the nut 4 translates along the screw 3 in the direction X to the first extreme position. Approaching the first extreme position, the nut 4 comes to urge the movable rod 40 and consequently the retaining part 34. The retaining part 34 is moved in translation along the axis X in the first direction C (FIG. 10A) under the effect of the pushing of the rod 40. This has the effect of moving the finger 37 out of the range of the stop 35.

Once the finger 37 is outside the range of the stop 35 (FIGS. 11A and 9C), the stop 35 no longer prevents the rotation of the retaining part 34 (and consequently of the unlocking part 25). The retaining part 34 (and consequently the unlocking part 25) is rotated in the second direction (arrow B) under the effect of the return spring 32 (FIG. 11 B). The unlocking part 25 releases the pawl 46 which pivots towards the locked position under the action of the return spring 22.

The rotation of the unlocking part 25 also has the effect of bringing the roller 30 in contact with the pawl 46 (FIG. 12B) and simultaneously of pivoting the finger 37. The free end of the pawl 46 abuts against the tooth 21 and the roller 30 comes to bear on the pawl to maintain the pawl 46 in engagement with the tooth 21.

Thus, the complete retraction of the actuating device results in an automatic return of the locking device to the locked position. Once the locking device in the locked position, the locking device can no longer be unlocked, unless the pilot orders the deployment of the thrust reverser again, which triggers activation of the electromagnet.

FIG. 13 schematically represents an actuation device 1 according to a second embodiment of the invention.

The actuating device 1 according to the second embodiment is identical to the device of the first embodiment, with the exception that the locking piece 18 is a round latch 47 rotatably mounted relative to the casing 2 around a X 'axis parallel to the X axis.

The round lock 47 comprises on the one hand a locking portion 48 and on the other hand a drive portion 49.

As illustrated in FIGS. 16A and 16B, the locking portion 48 has a half-moon shape. More specifically, the locking portion 48 comprises a convex engagement portion 50 and a flat disengagement portion 51 (or substantially concave) capable of being selectively positioned facing the tooth 21 when the latch is driven in rotation.

When the latch 47 is in the unlocked position (FIG. 14A), the flat portion 51 is positioned opposite the tooth 21 so as to allow the rotation of the second locking piece 19 (and consequently of the screw). When the lock 47 is in the locked position (FIG. 14B), the convex portion 50 is positioned opposite the tooth 21 so as to interfere with the tooth 21 and thus prevent the rotation of the screw 3.

As illustrated in FIGS. 15A and 15B, the drive portion 49 comprises a toothed sector 52. The unlocking part 25 also includes a toothed sector 53 arranged to mesh with the toothed sector 52 of the latch 47. Thus, the rotation of the latch 47 is controlled by the rotation of the unlocking part 25.

The rotation of the unlocking part 25 in the first direction of rotation (arrow A) has the effect of pivoting the latch 47 towards the unlocked position (illustrated in FIG. 15B).

Conversely, the rotation of the unlocking part 25 in the second direction (arrow B), opposite to the first direction, has the effect of pivoting the lock 47 towards the locked position (illustrated in FIG. 15A).

The operation of the actuation device 1 according to the second embodiment is identical to the operation of the actuation device 1 according to the first embodiment.

Claims (13)

1. Actuation device (1) for moving a movable cover of a thrust reverser, comprising: - An actuator comprising a first element (3) and a second element (4) mounted movable in translation relative to the first element, one of the first element and of the second element being a screw, and the other being a nut specific to cooperate with the screw, so that a rotation of the first element (3) relative to the second element (4) causes the second element (4) to translate relative to the first element (3), and - a locking device (17) comprising a locking piece (18) movable in rotation between a locked position in which the locking piece (18) prevents rotation of the first element (3), and an unlocked position in which the piece locking device (18) allows the first element (3) to rotate, in which the locking device (17) comprises a tooth (20, 21) mounted in rotation with the first element (3), and the locking piece (18 ) comprises a latch (47) having a convex portion (50) and a flat or substantially concave portion (51) able to be selectively positioned facing the tooth (20, 21), the convex portion (50) being able to interfere with the tooth (20, 21) when the convex portion (50) is opposite the tooth (20, 21) to prevent rotation of the first element (3), and the planar or substantially concave portion (51) being suitable for allowing the rotation of the first element (3) when ue the flat or substantially concave portion (51) is opposite the tooth (20, 21). 2. Device according to claim 1, wherein the locking piece (18) is clean, in the locked position, to come into engagement with the tooth (20, 21) to prevent rotation of the first element (3). 3. Device according to one of claims 1 and 2, wherein the tooth (20, 21) is asymmetrical so that in the locked position, the locking piece (18) prohibits rotation of the first element (3) in a first direction (A) and allows rotation of the first element (3) in a second direction (B), opposite to the first direction. 4. Device according to one of claims 1 to 3, further comprising an unlocking device (23) comprising an unlocking part (25) movable in rotation between an active position in which the unlocking part (25) biases the part locking (18) to the unlocked position and a passive position in which the unlocking part (25) allows a return of the locking part (18) in the locked position, and a drive member (24) suitable for driving in rotate the unlocking piece (25) so that the unlocking piece (25) moves the locking piece (18) to the unlocked position. 5. Device according to claim 4, wherein the locking piece (18) is able to mesh with the unlocking piece (25) so that the rotation of the unlocking piece (25) controls the rotation of the locking piece (18). 6. Device according to one of claims 4 and 5, wherein the drive member (24) comprises a rotary electromagnet (31). 7. Device according to one of claims 4 to 6, in which the unlocking device (23) comprises a return spring (32) capable of urging the unlocking part (25) towards the passive position. 8. Device according to one of claims 4 to 7, wherein the unlocking device (23) comprises a stop (35) and a retaining part (34) integral in rotation with the unlocking part (25) and movable in translation relative to the unlocking part (25) between a retaining position in which the rotation of the retaining part (34) is limited by the stop (35) and a release position in which the retaining part (34) is free to rotate. 9. Device according to claim 8, comprising a return member (41) adapted to urge the retaining part (34) towards the retaining position. 10. Device according to one of claims 8 or 9, comprising a rod 5 (40) movable in translation relative to the first element (3) and being able to be urged by the second element (4) to move the retaining part (34) towards the release position. 11. Device according to claim 10, wherein the movable rod (40) 10 extends at least partially inside the first element (3). 12. Device according to one of claims 8 to 11, further comprising a manual unlocking device (54) for biassing the retaining piece (34) in order to bring the unlocking piece (25) to the active position 15 without activating the drive member (24). 13. Device according to one of the preceding claims, in which the first element (3) is the screw and the second element (4) is the nut.