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Title:
WIND TURBINE BLADE
Document Type and Number:
WIPO Patent Application WO/2019/170656
Kind Code:
A1
Abstract:
The invention relates to a wind turbine blade (2) comprising a wind turbine flap (1). The wind turbine flap (1) comprises an outer flap shell (3), at least one interface (4) to interconnect the wind turbine flap (1) to the wind turbine blade (2) and at least one flap deployment unit (5) to adjust a position of the wind turbine flap (1). The flap deployment unit (5) is at least partially encompassed by the outer flap shell (3) and comprises further a motor (6) and a drive system (7), interconnecting the motor (6) arranged in the wind turbine flap (1) with the wind turbine blade (2) through the at least one interface (4).

Inventors:
NEUMANN, Stephan (Mozartstrasse 8, Übach-Palenberg, 52531, DE)
BERROTH, Jörg (Mathieustrasse 30, Aachen, 52074, DE)
PAMMER, Wolfgang (Pfongauerstrasse 8, 5202 Neumarkt am Wallersee, 5202, AT)
Application Number:
EP2019/055417
Publication Date:
September 12, 2019
Filing Date:
March 05, 2019
Export Citation:
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Assignee:
MUBEA CARBO TECH GMBH (Eugen-Müller-Strasse 16, 5020 Salzburg, 5020, AT)
International Classes:
F03D7/02; F03D1/06
Domestic Patent References:
WO2012083961A12012-06-28
WO2011064214A22011-06-03
WO2010106316A22010-09-23
Foreign References:
US20120070283A12012-03-22
DE102014102283A12015-08-27
US20100310372A12010-12-09
EP2233735A22010-09-29
Attorney, Agent or Firm:
RENTSCH PARTNER AG (Bellerivestrasse 203, Postfach, 8034 Zürich, 8034, CH)
Download PDF:
Claims:
PATENT CLAIMS

1. Wind turbine flap ( 1 ) for a wind turbine blade (2) comprising a. an outer flap shell (3) and b. at least one interface (4) to interconnect the wind turbine flap ( 1 ) to the wind turbine blade (2) and c. at least one flap deployment unit (5) to adjust a position of the wind turbine flap ( 1 ), said flap deployment unit (5) being at least partially encompassed by said outer flap shell (3), wherein said flap deploy ment unit (5) comprises i. a motor (6) and ii. a drive system (7), interconnecting the motor (6) in the wind turbine flap ( 1 ) with the wind turbine blade (2) through the at least one interface (4).

2. Wind turbine flap ( 1 ) according to claim 1 , characterized in that the flap deployment unit (5) comprises a torsion clutch (9) suitable to return the wind turbine flap ( 1 ) in an aerodynamically neutral position.

3. Wind turbine flap ( 1 ) according to claim 2, characterized in that the torsion clutch (9) comprises a first clutch element ( 1 0) and a second clutch element ( 1 1 ) and at least one actuator ( 1 9) to lock and/or unlock the first clutch ele ment ( 1 0) with respect to the second clutch element ( 1 1 ) in a rotational di- rection.

4. Wind turbine flap ( 1 ) according to claim 3, characterized in that the at least one actuator ( 1 9) comprises a magnetic actuator.

5. Wind turbine flap ( 1 ) according to one of the claims 3 to 4, characterized in that the first clutch element ( 1 0) and the second clutch element ( 1 1 ) are arranged rotatable to each other against the force of a first spring ( 1 6).

6. Wind turbine flap ( 1 ) according to one of the claims 3 to 5, characterized in that one of the first or the second clutch element ( 1 0, 1 1 ) is arranged rotat able and the other one non-rotatable.

7. Wind turbine flap ( 1 ) according to one of the claim 6, characterized in that the non-rotatable clutch element ( 1 0, 1 1 ) is displaceable in an axial direction of the axis of rotation of the torsion clutch (9).

8. Wind turbine flap ( 1 ) according to one of the claims 3 to 7, characterized in that the first clutch element ( 1 0) and the second clutch element ( 1 1 ) support one another via at least one ramp ( 1 5) of the first clutch element ( 1 0).

9. Wind turbine flap ( 1 ) according to claim 8, characterized in that the at least one ramp ( 1 5) interacts with at least one roller ( 1 3 ) of the second clutch el ement ( 1 1 ) .

10. Wind turbine flap ( 1 ) according to one of the claim 9, characterized in that the second clutch element ( 1 0, 1 1 ) comprises a recess ( 1 4) to accommodate the at least one roller ( 1 3) in a locked state of the torsion clutch (9).

1 1. Wind turbine flap ( 1 ) according to one of the claim 1 0, characterized in that the at least one ramp ( 1 5) is inclined towards the recess ( 1 4) arranged next to the at least one ramp ( 1 5). 12. Wind turbine flap ( 1 ) according to claim 1 0 or 1 1 , characterized in that the at least one roller ( 1 3 ) is displaceable in an axial direction against the force of a second spring ( 1 7).

13. Wind turbine flap ( 1 ) according to one of preceding claims, characterized in that the flap deployment unit (5) comprises at least one gear box ( 21 ). 14. Wind turbine flap ( 1 ) according to one of the preceding claims, characterized in that at least two out of the group of the following elements are ar ranged coaxial with respect to each other: motor (6), torsion clutch (9), in terface (4).

15. Wind turbine blade (2) comprising at least one wind turbine flap ( 1 ) accord ing to one of the preceding claims.

16. Rotor for a wind turbine comprising several wind turbine blades (2) according to claim 1 5.

Description:
WIND TURBINE BLADE

FIELD OF THE INVENTION

The present invention relates to a wind turbine blade comprising a wind turbine flap for said wind turbine blade according to the patent claims.

BACKGROUND OF THE INVENTION

In the last decades wind turbine rotors increased in size in order to maximize the power output. However, longer rotor blades caused the fatigue loads on the blades to increase accordingly due to e.g. the larger difference in the incoming wind speed per revolution caused by the earth boundary layer or by local gusts. To reduce these fatigue loads on the rotor, control mechanism such as flaps may be used in order to regulate the loads locally on the blade. These mechanisms may be used addition ally for power regulations by taking influence on the aerodynamic behavior, such as e.g. the generation of more power in times of low overall wind speeds.

Flaps are well known from the aviation industry as a means for regulating the load on wings of airplanes especially during takeoff and landing. However, the means for deploying the flaps are not applicable to flaps on wind turbine blades due to the differences in structural properties, load cases, safety reguirements or factors such as the accessibility during maintenance and installation. From the prior art several approaches for the integration of flaps in wind turbines blades are known, which are introduced briefly in the following.

US2010310372 A, published on the 09.1 2.201 0 in the name of VESTAS Wind Systems, relates to a rotor blade for a wind turbine comprising a rotor blade body with a root for connecting the rotor blade to a hub of a wind turbine, a tip, a leading edge and a trailing edge. The blade has a movable part, and motion transmitting means for connecting to an actuator being placed preferably outside the blade body, and transmitting motion from the actuator to the movable part.

WO1 2083961 , published on the 28.06.201 2 also in the name of VESTAS Wind Systems, relates to flap for a rotor blade of a wind turbine which is movable be tween first and second configurations so as to change the aerodynamic surface shape of the rotor blade. The flap is attached to the distal end of a push-pull control cable. An actuator is remotely situated from the flap and is further connected to the proximal end of the push-pull control cable, such that the flap can be moved by energizing the actuator.

W01 1064214, published on the 03.06.201 1 in the name of VESTAS Wind Sys tems, discloses a wind turbine blade with flaps. An actuator mechanism for the flaps comprises a shaft extending along the blade length driven by a motor ar rangement toward the blade root. The flap is connected to the shaft through a link- age so that rotation of the shaft pivots the flap about a hinge line. An offset actua tion mechanism is provided for imparting movement to the linkage in addition to movement due to rotation of the shaft.

W010106316, published on the 23.09.201 0 also in the name of VESTAS Wind Systems, relates to a hinged connection apparatus for securing a wind turbine blade to a control surface. The blade or the control surface comprises at least one hinge housing in which a hinge pin is retained. The hinge pin may be extended from a retracted position into an extended position in which it engages with a hinge re cess on the other component to form a connection. A locking mechanism is pro- vided for securing the hinge pin in place. The hinge pin may be extended manually or automatically by an actuator.

EP2233735, published on the 29.09.201 0 in the name of VESTAS Wind Systems, relates to a wind turbine blade comprising a main blade body and trailing edge sec tion movably connected to the main blade body, as well as an actuator structure internally within the blade. The actuator interconnects the trailing edge section and the main blade body, and it comprises a stack of a plurality of piezoelectric elements, so that the stack of piezoelectric elements is capable of operating as a linear actu ator. The actuator structure is arranged such that it is capable of causing the trailing edge section to move or deform relative to the main blade body in response to aer- odynamic loads on the blade. The mechanism for flap deployment known from the prior art are often incompat ible to the blade structure a wind turbine blade. Furthermore, conseguences of sys tem failures can be fatal such that with the known concepts the wind turbines have to be shut down for safety reasons until the mechanisms is repaired.

SUMMARY OF THE INVENTION

It is an object of the invention to improve wind turbine flaps as known from the prior art and the flap deployment mechanism for such a wind turbine flap.

A wind turbine blade (blade) for a wind turbine has a certain similarity to a wing: The wing shaped wind turbine blade, during rotation about a center hub of the wind turbine, comprises a leading edge and a trailing edge and a there between extending first side surface (suction side) and a second side surface (pressure side).

A wind turbine blade according to one aspect of the invention comprises a wind turbine flap (flap) which is actuated by a flap deployment mechanism suitable to adjust the angle of attack of the wind turbine flap with respect to the wind turbine blade, to provide load and /or power regulation.

In case of system failure, such as motor fault, the deployment mechanism can be implemented such that it offers the possibility to return the flap automatically to a defined position, such that a continued and safe operation of the wind turbine in a conventional mode without support by the flap remains possible. Thereby un wanted system shut down can be avoided. In an active mode, the wind turbine flap allows the aerodynamic loads to be altered on the wind turbine blade by adopting the angle of attack of the wind turbine flap. The wind turbine flap normally extends along a trailing edge of the wind turbine blade at least over a certain distance. Al ternatively or in addition the wind turbine flap can be arranged on top of or inte grated into the suction side of the wing profile of the wind turbine blade. Alterna tively or in addition the wind turbine flap can comprise several segments which can be activated in a coordinated manner and/or independent from each other. Thereby the load acting on the blade can be changed such that e.g. negative fatigue loads on the structure can be reduced. In doing so the overall lifetime of the wind turbine can be increased and the cost of energy decreased. Furthermore, the flaps may be used e.g. in times of low incoming wind speed to increase the aerodynamic lift and thus enhance the overall power output. Especially on very large rotor diameters, wind turbine blades may even have multi ple flaps along the span of the rotor blade to react to localized wind speed changes or gradients. The wind turbine flap is advantageously a trailing edge flap, however the concepts as described hereinafter may also be applied to leading edge flaps or flexible flap structures. In a preferred variation, a wind turbine blade comprises a wind turbine flap with an outer flap shell as well as at least one flap deployment unit encompassed at least partially by the outer flap shell. The outer flap shell may be made e.g. from a fiber reinforced composite material. The outer flap shell may be manufactured in two parts such as an upper and a lower flap shell part subsequently assembled with or without the flap deployment unit already on the inside. For the integration of the subsequently described flap deployment unit in the outer shell of the wind turbine flap, the flap deployment unit may be arranged and supported as whole in a re spective frame which is in turn interconnected to the outer flap shell and forms part of an integral module.

The at least one flap deployment unit is a means to adjust a position (angle of attack) of the wind turbine flap in respect to the wind turbine blade. The wind turbine flap is arranged rotatable around a rotational axis which may e.g. extend along a lead ing edge of the wind turbine blade. Thus, the flap deployment unit may alter the flap deployment angle (angle of attack), which is measured between an aerody- namically neutral position where no additional (positive or negative) lift is gener ated and a deployed position of the flap. The deployed position can be a position, where the flap is angled towards the lower orthe upper surface (pressure or suction side) of the wind turbine blade, respectively to a position, where the flap generates additional lift or reduces the overall lift on that blade section. In most applications a maximal flap deployment angle (a) from around +/- 25° is sufficient to generate the desired lift difference. Depending on the design and field of application other configurations are possible.

The flap deployment unit normally comprises a motor and a thereto interconnected drive system to transmit the deployment forces and moments of the flap. Thus the drive system is actuated by said motor. The motor and the drive system are prefer ably integrated and fully encompassed by the outer flap shell. The drive system in terconnects the motor placed inside the outer shell of the wind turbine flap with the wind turbine blade through an interface for the engagement to the wind turbine blade. For an easy and fast assembly of the wind turbine flap in the wind turbine blade, respectively in a cut-out in the wind turbine blade foreseen to receive the flap, the interface can be arranged retractable inside the outer flap shell.

If appropriate, the drive system comprises more than one shaft interconnected through a gear wheel transmission to transmit the deployment moment from the motor to the interface. To obtain a self-locking effect and to reduce the size of the motor, the motor is dimensioned to have high rotation per minutes and the drive system features a corresponding high transmission ratio. A cascade of multiple shafts and interconnecting gear wheel transmissions is advantageous in terms of a flat and space saving design and as well as an optimal force transmission. Addition- ally or alternatively, the flap deployment unit may comprises at least one gear box e.g. placed between the motor and the drive system. The gear box may be e.g. de signed as a planetary gear transmission.

In a variation of the invention, the flap deployment unit additionally comprises a special torsion clutch placed on a shaft in the drive system between the interface and the motor and suitable to return the wind turbine flap in an aerodynamically neutral position, as described above. Preferably, the torsion clutch is designed such that in case of emergency the flap returns into the neutral position without electrical means, such as e.g. in case of power loss. The first clutch element and the second clutch element are arranged rotatable to each other against the force of a first spring to return automatically to said neutral position of the flap.

If appropriate, the torsion clutch can be foreseen to lock and/or unlock the flap in said neutral position. Thereby the wind turbine blade may be used safely in a con ventional mode, where the flap is secured in the neutral position. The torsion clutch may comprise a first clutch element and a second clutch element, wherein one clutch element is arranged rotatable and the other clutch element is arranged non- rotatable. The rotatable clutch element may be designed as a separate element or as an integral part of the respective shaft. For a compact and space saving design, the non-rotatable clutch element may further comprise a clearance hole for the shaft on which the rotatable clutch element is placed.

The torsion clutch can further comprise at least one actuator to actively lock and /or unlock the first and the second clutch element with respect to each other. When the first and second clutch element are locked with respect to each other, un wanted shaft rotation is prevented and the wind turbine flap is locked in its foreseen position. When the flap is locked in the aerodynamically neutral position the wind turbine blade can be used in a conventional manner. Good results can be achieved by a magnetic actuator which relies on the presence of an electrical voltage. In a variation of the invention the first clutch element and the second clutch element support one another via at least one contact surface on the first clutch element. Preferably the at least one contact surface is hereby (with respect to the direction of movement) an inclined surface such as a ramp. The contact surface, respectively the ramp, can interact with a roller arranged at the opposite second clutch element. The least one roller is rotatable around a rotational axis of the roller. During flap deployment or retraction, respectively during a rotational displacement of the first and the second clutch element with respect to each other, the roller interacts with the contact surface on which the roller may roll off. In the case that the contact surface is designed as a ramp, the rotational displacement thus results in the roller moving up or down said ramp causing an additional axial displacement of the first and the second clutch element in respect to each other.

For good rolling motion of the at least one roller, the roller may e.g. have the shape of a ball, a cylinder or a conical frustum interacting with the contact surface. For a smooth rolling motion the rotational axis of the individual roller further intersects with the rotational axis of the rotational axis of the rotatable clutch element. If mul- tiple rollers are present, the rollers are preferably orientated over the circumference and around a rotational axis of the rotatable clutch element. Advantageously, all rotational axes of the rollers further intersect with the rotational axis of the rotata ble clutch element on the same point. Additionally, an orientation of the at least one roller with the rotational axis (of the roller) being perpendicular to the rota- tional axis of the rotatable clutch element is beneficial.

For the locking of the clutch, a recess may be arranged next to the ramp on the first clutch element (opposite clutch element on which the roller is placed). The recess is foreseen to accommodate the at least one roller in the locked state. If the roller is in the locked state, respectively accommodated in the recess, the first and the sec ond clutch elements are both blocked from rotating. As described above, it is ad vantageous, if the rotational position of the rotatable clutch element in the locked state corresponds to the aerodynamically neutral position of the flap. Hence pref erably, no additional lift enhancement or reduction is performed in said neutral po sition of the respective wind turbine blade section.

In order to unlock the clutch, the roller is lifted out of the recess in an unlocked state of the clutch enabling a relative rotation of the first and second clutch element to each other. Therefore, the roller may be displaced in the axial direction of the shaft on which the torsion clutch (rotatable clutch element) is placed. Preferably the axial displacement of the roller out of the recess and in an unlocked state is against the force of a second spring of the second clutch element. Thus, in the unlocked state the at least one roller is disengaged from the recess and held against said force of the second spring. This may be achieved by the above described actuator which lifts the roller out of the corresponding recess.

In a preferred variation of the invention, two ramps are arranged next to the recess, each inclined towards the recess, to interact with the at least one roller during de ployment of the wind turbine flap (in the unlocked state of the clutch). Thus if the wind turbine flap is deployed, respectively the first and the second clutch element rotated in respect to each other from the neutral position, the roller rolls along the inclined ramp and thereby relatively displaces the first and the second clutch ele ment in the axial direction away from each other.

Preferably, the non-rotatable clutch element is therefore arranged displaceable in the axial direction (direction of the axis of rotation of rotatable clutch element) against the force of the at least one first spring (as mentioned above). The first spring may e.g. be a disk spring arranged on the non-rotatable clutch element working against the displacement of the same. Thus, the first spring urges the non- rotatable clutch element back in its initial axial position which thereby interacts though the at least one roller and the ramp with the rotatable clutch element urging it back in the neutral position with the at least one roller being at the same rotational position as the respective recess. If the rollers are in a position above the recess the second spring further presses the roller in the recess and thus locking the clutch and the flap in the neutral position if the actuator is not activated. This is especially ad vantageous in case of a systems failure, where a flap in the neutral position ensures that the wind turbine may be continued to be used in a conventional mode with no flap deployed.

It is pointed out, that a wind turbine blade may feature at least one wind turbine flap as described above, however also multiple flaps at various different sections along the blade are possible. Preferably, the wind turbine flap is a trailing edge flap, however, the flap deployment unit may also be used for e.g. leading edge flaps. If appropriate, the wind turbine flap may be operated with multiple flap deployment units such as e.g. one flap deployment unit at each end of the flap in longitudinal direction (radial direction of the respective wind turbine blade). The wind turbine flap may further be used in combination with sensors for e.g. the incoming wind speed or the blade stress level which may provide an input value for the calculation of the appropriate deployment angle of the flap, respectively the rotational dis- placement of the drive system by the motor. For maintenance of the flap deploy ment unit, the wind turbine flap may feature at least one maintenance access in the outer flap shell to access the inner mechanics of the wind turbine flap, without hav ing to disengage the entire flap from the blade.

It is to be understood that both the foregoing general description and the following detailed description present embodiments, and are intended to provide an over view or framework for understanding the nature and character of the disclosure. The accompanying drawings are included to provide a further understanding, and are incorporated into and constitute a part of this specification. The drawings illus trate various embodiments, and together with the description serve to explain the principles and operation of the concepts disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The herein described invention will be more fully understood from the detailed de scription given herein below and the accompanying drawings which should not be considered limiting to the invention described in the appended claims. The draw- ings are showing: Fig. 1 A wind turbine blade 2 having a wind turbine flap 1 according to the invention;

Fig. 2 a variation of the wind turbine flap 1 according to the invention in a per spective and partly sectionized view ; Fig. 3 flap deployment unit 5 according to Figure 1 in a view from above;

Fig. 4 clutch 9 according to Figure 2 in a view from the side in a locked state ;

Fig. 5 clutch 9 according to Figure 2 in a view from the side in an unlocked state;

Fig. 6 clutch 9 according to Figure 2 in a view from the side in a deployed po- sition of the wind turbine flap 1 ;

Fig. 7 clutch 9 in a deployed position of the wind turbine flap 1 according to

Figure 6 in a perspective and party sectionized view.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to certain embodiments, examples of which are illustrated in the accompanying drawings, in which some, but not all features are shown. Indeed, embodiments disclosed herein may be embodied in many dif ferent forms and should not be understood as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Whenever possible, like reference numbers will be used to refer to like components or parts.

Figure 1 illustrates a wind turbine blade 2 with a wind turbine flap 1 according to the invention having an outer flap shell 3. Figure 2 shows a first variation of the wind turbine flap 1 according to the invention in a perspective and partly section- ized view, such that at least one flap deployment unit 5 is visible. During assembly, the wind turbine flap 1 is received in a respective cut-out 22 in the wind turbine blade 2. An interface 4 foreseen to engage to the wind turbine blade 2 - in order to support and thus move the wind turbine flap 1 in respect to said blade 2 - extends at least partially over the outer shell 3 of the flap 2. For the assembly into the cut out 22 the interface may be arranged retractable inside the outer flap shell 3. Figure 3 shows one variation of the flap deployment unit 5 in a view from above. The flap deployment unit 5, as illustrated, comprises a motor 6 interconnected to a gear box 21 . A drive system 7 comprising multiple shafts 1 2 interconnected through gear wheels 8 is shown. Through the gear wheel transmission the rotational mo ment implied by the motor 6 on the drive system 7 is transferred to the interface 4, in the shown case represented by a final interconnection gear 4. In between the gear box 21 and the interface 4, a torsion clutch 9 is placed on one shaft 1 2 of the drive system 7. Each shaft 1 2 of the drive system 7 has at least one bearing 1 8 and is interconnected through gear wheel transmissions to subsequent shafts 1 2. The torsion clutch 9 comprises a first and a second clutch element 1 0, 1 1 . In the case shown the first clutch element 1 0 is rotatable and attached to the respective shaft 1 2 on which the torsion clutch 9 is placed and a non-rotating second clutch ele ment 1 1 . (It is however understood, that in other embodiments the first clutch el ement may be fixed in the rotational position and meanwhile the second clutch el- ement 1 1 is arranged rotatable). Meanwhile the first clutch element 1 0 rotates to gether with said shaft 1 2 the second clutch element 1 1 is not rotatable. Preferably, the second clutch element 1 1 is built up such that the second clutch element 1 1 comprises clearance hole 20. The at least one shaft 1 2 is guided through the clear ance hole 20 on which the first clutch element 1 0 is placed. In a preferred variation at least one roller 1 3 attached to the second clutch element 1 1 is orientated be tween the first clutch element 1 0 and she second clutch element 1 1 in such a way that if the first clutch element 1 0 is rotated around its rotational axis, the at least one roller 1 3 of the second clutch element 1 1 rolls over a respective contact surface 1 5 of the first clutch element 1 0. Preferably, the torsion clutch 9 features two positions: a locked state, where the second clutch element 1 1 blocks the first clutch element 1 0 from being rotated and an unlocked state, where the first clutch element 1 0 may be rotated and thus the wind turbine flap 1 may be deployed respectively. Advantageously, the wind tur bine flap 1 is hereby in a neutral, non-deployed position, if the torsion clutch 9 is in the locked state. Figure 4 illustrates the clutch 9 according to Figure 3 in a view from the side in a locked state, meanwhile Figure 5 illustrates the clutch 9 in an unlocked state with the flap (not shown) still in a neutral position. In the locked state of the clutch 9, the at least one roller 1 3 of the second clutch element 1 1 is locked in a recess 1 4 of the first clutch element 1 0, preventing the rotation of the first clutch element 1 0 in respect to the second clutch element 1 1 . In order to rotate the drive system 7, and thus the wind turbine flap 1 , the roller 1 3 needs to be lifted out of the recess 1 4 in an unlocked state, where a rotation of the first clutch ele- ment 1 0 is not prohibited. This may be archived by an actuator 1 9 not shown in detail. Preferably, the actuator 1 9 lifts the roller 1 3 out of the recess 1 4 against a force of a second spring 1 7 (not shown in detail).

Figure 6 and Figure 7 showthe torsion clutch 9 in the unlocked state with the wind turbine flap 1 (not shown) being further in a deployed state. Thus the first clutch element 1 0 is rotated in respect to the second clutch element 1 1 . If the first clutch element 1 0 is rotated, the roller 1 3 of the second clutch element 1 1 is rolled along a contact surface 1 5 of the first clutch element 1 0. Since the contact surfaces are designed as inclined ramps 1 5 on both sides of the recess 1 4, the rotation of the first clutch element 1 0, displaces the second clutch element 1 1 in the axial direction (direction of the shaft 1 2) against the force of a first spring 1 6, as indicated by the arrows in Figure 6. Hence the second clutch element 1 1 may not be rotated but can be displaced together with the at least one roller 1 3 in the axial direction.

The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. LIST OF DESIGNATIONS

1 Wind turbine flap 1 3 Roller

2 Wind turbine blade 1 4 Recess

3 Outer flap shell 1 5 Contact surface / Ramp

4 Interface 1 6 First spring

5 Flap deployment unit 1 7 Second spring

6 Motor 1 8 Bearing

7 Drive system 1 9 Actuator

8 Gear wheel 20 Clearance hole

9 Torsion clutch 21 Gear box

1 0 First clutch element 22 Cut-out

1 1 Second clutch element

1 2 Shaft