Pitch adjustment cylinder for adjustment of a pitch angle of a blade of a wind turbine

Pitch cylinders for adjusting a pitch angle of a blade, methods of assembling pitch cylinders, and the use of pitch cylinders in wind turbines are disclosed. The pitch cylinder includes a cylinder barrel having a first thread with a first pitch, a piston arranged in and extending out of the cylinder barrel for coupling to a blade or hub, and a trunnion to couple the cylinder barrel to the other of the blade or hub. The cylinder barrel extends through the trunnion. The trunnion has a first thread with a second pitch different from the first pitch, and a sleeve arranged between the trunnion and the cylinder barrel that extends through the sleeve. The sleeve has an inner sleeve thread with the first pitch engaged with the first cylinder barrel thread and an outer sleeve thread with the second pitch engaged with the first trunnion thread.

TECHNICAL FIELD

The present invention generally relates to wind turbines and, particularly, to devices and methods for adjusting a pitch angle of a blade of a wind turbine.

BACKGROUND

The blades of wind turbines may in general be adjusted in their pitch angle, i.e. rotated about their longitudinal axis, for instance in order to adapt to varying wind conditions. Pitch angle adjustment may be carried out via pitch drive arrangements, such as pitch adjustment cylinders, wherein a piston is coupled to one of the blade and a hub and movable relative to a cylinder barrel, which is coupled to the other one of the blade and the hub.

An object of the present invention is to provide improved solutions for adjusting a pitch angle of a blade of a wind turbine.

SUMMARY

The present invention provides pitch adjustment cylinders for adjusting a pitch angle, wind turbines comprising such pitch adjustment cylinders, methods of assembling such pitch adjustment cylinders and use of such pitch adjustment cylinders.

According to an aspect, a pitch adjustment cylinder for adjusting a pitch angle of a blade of a wind turbine is disclosed. The pitch adjustment cylinder comprises a cylinder barrel, a piston, a trunnion and a sleeve.

The pitch adjustment cylinder may be a hydraulically operated cylinder or a pneumatically operated cylinder.

The cylinder barrel (which can be also referred to as piston tube or cylinder tube) defines an inner space, in which the piston can be moved by, e.g. hydraulically and/or pneumatically.

The piston may comprise a piston head and a piston rod. The piston rod may be formed such that it provides the piston head as an integral part.

The piston is movably arranged in the inner space defined by the cylinder barrel. The piston and, if applicable, the piston rod extends out of the cylinder barrel to an extent that depends on the position/movement of the piston in the cylinder barrel.

The part of the piston extending out of the cylinder barrel and, particularly, the corresponding piston end is adapted to be coupled to one of the blade and a hub of the wind turbine. The trunnion is adapted to couple the cylinder barrel to the other one of the blade and the hub. For the purpose of illustrating the present teaching, reference will be made primarily to arrangements wherein the piston is for coupling to the blade and wherein the trunnion is adapted to couple to the hub. However, it shall be understood that arrangements wherein the piston is for coupling to the hub and wherein the trunnion is adapted to couple to the blade are equally disclosed.

Coupling to the blade may occur directly, for instance via a piston rod end, or indirectly via a blade adjustment mechanism, for instance comprising levers, arranged between the pitch cylinder and the blade.

The trunnion is adapted to couple the cylinder barrel to the other one of the blade and the hub (or any portion of the wind turbine, relative to which the pitch shall be adjusted). This coupling may be rigid or allow for certain degree of freedom. For instance, in some embodiments, the trunnion may be rotatable relative to the hub around an axis, which may be parallel to a longitudinal axis of the blade. The part of the wind turbine where the trunnion may be coupled may be adjacent to a support arrangement supporting the blade of the wind turbine.

The cylinder barrel extends through the trunnion and through the sleeve. The sleeve is arranged at least partially between the trunnion and the cylinder barrel.

The cylinder barrel, the trunnion and the sleeve are adapted to be coupled via threads connections: the cylinder barrel has an first cylinder barrel thread with a first thread pitch and the sleeve has an inner sleeve thread with the first thread pitch for engagement with the first cylinder barrel thread (and vice versa).

The trunnion has an first trunnion thread with a second thread pitch and the sleeve has an outer sleeve thread with the second thread pitch for engagenment with the first trunnion thread. The second thread pitch is different from the first thread pitch.

A value of thread pitch expresses the relationship between linear and rotational displacement in a substantially helical screw thread structure. For instance, the thread pitch translates rotational movement into a linear displacement. In such cases, the value of thread pitch may be the linear distance corresponding to a unit rotation or revolution of 360°.

A thread may be characterized by its threadform, i.e. cross-sectional shape of the thread. The various threads may be formed with one or more of the following threadforms: (essentially) triangular, (essentially) square, (essentially) trapezoidal, rounded, tilted, or a combination thereof.

Throughout the present disclosure, threads may typically be depicted as V-threads, i.e. with isosceles or equilateral triangles as cross-section. However, any other suitable threadform may be used to carry out the present teaching.

Each or any of the various threads may be formed as left- or right-handed thread.

The sleeve may be rotatable and/or adapted to remove or reduce play and/or clearance between the cylinder barrel and the trunnion.

Forces acting on the pitch adjustment cylinder may give rise to differential displacement of piston and trunnion. Such differential (or relative) displacement leads to play and/or clearance between trunnion and cylinder barrel and, thus piston and the location where the piston rod is coupled with the blade or the hub.

Such a differential (or relative) displacement is referred to a force-induced differential (or relative) displacement.

A result of force-induced differential displacement may be that force transmission between these elements may be hampered, which may would affect the adjustment operation of the pitch adjustment cylinder. Also risk for structural failure may increase. A further result may be relative movement between cylinder barrel and trunnion so that, e.g., the cylinder barrel may be moved out of its intended position in relation to the wind turbine hub and, particularly, the blade.

The sleeve may be used to compensate for such differential displacement. Rotation of the sleeve may—inter alia due to the difference in thread pitch between the inner sleeve thread and the outer sleeve thread—introduce a so-called sleeve-induced differential displacement of the sleeve relative to the cylinder barrel and/or the trunnion.

The sleeve-induced differential displacement may in particular be directed in axial direction (of the central axis of the pitch adjustment cylinder).

If sleeve-induced differential displacement is comparable in size to force-induced differential displacement and of opposite sign, the net differential displacement may be reduced or essentially removed, i.e. the play and/or clearance between cylinder barrel and trunnion may be reduced or essentially removed.

The difference between the first thread pitch and the second thread pitch may be chosen such that the sleeve is adapted to compensate a force-induced differential displacement typical for the operation of a pitch adjustment cylinder, e.g. to adjust the pitch angle of a wind turbine.

With removed or reduced play and/or clearance between the cylinder barrel and the trunnion, backlash during high load cycles may be avoided or reduced. Moreover, removing or reducing play and/or clearance allows to transfer force from the trunnion to the cylinder barrel efficiently.

In some embodiments, the cylinder barrel may have a second cylinder barrel thread. and the trunnion may have a second trunnion thread for engagement with the second cylinder barrel thread. The second cylinder barrel thread and the second trunnion thread may have identical thread pitches. In particular, the second cylinder barrel thread and the second trunnion thread may have the first thread pitch. The second cylinder barrel thread and the second trunnion thread may be adapted to provide, when coupled, a basic connection between the trunnion and the cylinder barrel. A sleeve with different inner and outer thread pitches as described above and throughout the present disclosure may then be used to remove or reduce any play and/or clearance arising from or despite the basic connection between the trunnion and the cylinder barrel. In other embodiments, the cylinder barrel and the trunnion may be connected via a welded connection.

For instance, the second cylinder barrel thread and the first cylinder barrel thread may be located at a same radial distance from a central axis of the pitch adjustment cylinder.

Alternatively, the second cylinder barrel thread may be located at a different radial distance than the first cylinder barrel, e.g. at the radial distance of the outer sleeve thread.

In some embodiments, the first cylinder barrel thread and the second cylinder barrel thread may have a same direction of rotation or handedness.

In some embodiments, the first cylinder barrel thread and the second cylinder barrel thread may have different or opposite directions of rotation or handedness.

In some embodiments, the pitch adjustment cylinder may further comprise at least one tie rod.

In some embodiments, the trunnion may have at least one tie rod opening, which may be associated to a respective one or more of the tie rod(s). For example four tie rods and four tie rod openings may be provided, wherein each tie rod may be associated to a respective tie rod opening.

The at least one tie rod can be considered as support “skeleton” or frame for enhancing the overall constructural properties of the pitch adjustment cylinder, e.g. stiffness, resistance against bending and/or twisting.

Further the at least one tie rod may pretension and/or compress the cylinder barrel.

The at least one tie rod may be substantially parallel to the cylinder barrel and may extend through a respective one of the the at least one tie rod opening in the trunnion. The at least one tie rod is not in engagement with the trunnion and, for example, not rigidly connected to the trunnion.

However, the at least one tie rod may be rigidly connected to the cylinder barrel.

To this end, the pitch adjustment cylinder may comprise a first base member and a second base member. The first base member and the second base member may be coupled to the cylinder barrel, for example, at the end of the cylinder barrel in longitudinal direction.

The first base member and the second base member may be used to connect the at least one tie rod to the cylinder barrel and potentially pretension the at least one tie rod.

According to a further aspect, a wind turbine is disclosed, which comprises a pitch adjustment cylinder according to the first aspect.

According to a still further aspect, a method of assembling a pitch adjustment cylinder is disclosed. The method comprises arranging a sleeve between a cylinder barrel and a trunnion. The sleeve has an inner sleeve thread with a first thread pitch and an outer sleeve thread with a second thread pitch different from the first thread pitch. The inner sleeve thread engages with an first cylinder barrel thread of the cylinder barrel and the outer sleeve thread engages with an first trunnion thread of the trunnion.

In some embodiments, the sleeve is screwed, at least partially, into the trunnion. The trunnion with the sleeve may then be screwed onto a cylinder barrel.

According to a still further aspect, use of a pitch adjustment cylinder according to the first aspect is disclosed. The pitch adjustment cylinder is used in a wind turbine in particular for adjusting a pitch of a blade of the wind turbine and/or for removing play and/or clearance between the cylinder barrel and the trunnion of the pitch adjustment cylinder.

For adjusting a pitch angle of a blade of the wind turbine, the cylinder barrel of the pitch cylinder is coupled via the trunnion to one of the hub and the blade and the piston is coupled to the other one of the hub and the blade of the wind turbine. The piston of the pitch cylinder may be moved relative to the cylinder barrel and thereby relative to the hub (or the blade) by hydraulic and/or pneumatic means. The piston being coupled to the blade (or the hub) of the wind turbine such movement results in a movement of the blade relative to the hub. The trunnion (or the piston) being coupled to the hub in a rotatable manner this relative movement is of rotational nature, i.e. pitch-adjusting, as well. The rotation of the trunnion (or the piston) relative to the hub occurs around an axis, which is parallel to a longitudinal axis of the blade.

Use of the pitch adjustment cylinder may comprise rotating the sleeve to reduce or remove play and/or clearance between the cylinder barrel and the trunnion.

DETAILED DESCRIPTION

Any description given with respect to a specific drawing also applies to any other drawing unless explicitly indicated otherwise. Therefore, e.g., descriptions are not necessarily repeated if already presented, but may be nevertheless. Also, alternatives, options and the like indicated already are possible with any other embodiment.

FIG. 1shows a wind turbine10with three blades12mounted at a hub11. The hub is mounted at a nacelle13of the wind turbine10. A longitudinal axis of one of the blades12is indicated as L. Rotation of the blade12about axis L adjusts the pitch of the blade12.

To adjust the pitch of the blade, the blade12is rotated relative to the hub11. Rotation of the blade about axis L may be carried out using a pitch adjustment cylinder according to the present disclosure. The pitch adjustment cylinder (not shown) may be mounted at hub11, such that the pitch adjustment cylinder is rotatable relative to the hub around an axis, which is parallel to axis L, and coupled to the blade12.

FIG. 2shows a pitch adjustment cylinder20for adjusting a pitch angle. The pitch adjustment cylinder20comprises a cylinder barrel22, a piston23, a trunnion24and a sleeve25, tie rods26as well as a first base member29aand a second base member29b.

The piston23is movably arranged in an inner space22adefined by the cylinder barrel22.

The piston23extends out of the cylinder barrel22to an extent that depends on the position/movement of the piston23in the cylinder barrel22.

A part of the piston23extending out of the cylinder barrel22, such as the piston end23c, is adapted to be coupled to the blade of the wind turbine.

The trunnion24is arranged around the cylinder barrel22and for coupling the pitch adjustment cylinder20to a hub of the wind turbine. The coupling to the hub (or another structural component near the blade(s)) may be such that (essentially) no relative movement between the pitch adjustment cylinder20and the hub is possible.

However, as disclosed in the following, the coupling to the hub may be adapted to allow for movement and, particularly, rotation of the pitch adjustment cylinder relative to the hub.

One or more studs24aof the trunnion24may be mounted in a bearing, located at the hub (not shown), such that the studs24aare free to rotate around an axis A. The rotation of the pitch adjustment cylinder20around axis A may essentially be the only degree of freedom of the trunnion24relative to the hub.

The mounting of trunnion24at the hub, i.e. the orientation of the bearing at the hub and the orientation of the axis A, may typically be chosen such that the axis A is essentially parallel to a longitudinal axis of the blade to be adjusted.

The tie rods26are connected to the piston barrel22by means of the first base member29aand the second base member29b, which are arranged at the outer end of the cylinder barrel22. The first base member29aand the second base member29brespectively comprise tie rod openings or throughholes through which the tie rods26extend. According to the drawings, the outer ends of the tie rods26are provided with threads at their ends so that the tie rods26extending through the openings tie rod openings can be fastened to the the first base member29aand the second base member29b, with respective tie rod bolts28. In further embodiments, the tie rod openings can include respective inner threads for engagement with the threads at the end of the tie rods26for connecting the same to the cylinder barrel22.

The tie rods26are intended to to increase structural strength of the pitch adjustment cylinder20. To this end, the tie rods26may be pre-tensioned.

The sleeve25is adapted to be rotated with respect to the cylinder barrel22and the trunnion24. The sleeve25is used to remove or reduce play and/or clearance between the trunnion24and the cylinder barrel22. Structural and functional features of sleeve25will be described in further detail with respect to further embodiments below.

FIG. 3shows a pitch adjustment cylinder20for adjusting a pitch angle. The pitch adjustment cylinder20comprises a cylinder barrel22, a piston23, a trunnion24and a sleeve25.

The piston23comprises a piston head23aand a piston rod23bwith a piston end23c.

The piston23is movably arranged in an inner space22adefined by the cylinder barrel22. The piston23, in particular the piston rod23b, extends out of the cylinder barrel22to an extent that depends on the position/movement of the piston23in the cylinder barrel22.

A part of the piston23extending out of the cylinder barrel22, such as the piston rod23band/or its piston end23c, is adapted to be coupled to the blade of the wind turbine.

The trunnion24is adapted to couple the cylinder barrel22to a hub of the wind turbine. If coupled to the hub, the trunnion24may be rotatable relative to the hub around an axis, which is parallel to a longitudinal axis of the blade and which may for instance be in the figure plane ofFIG. 3(see alsoFIG. 2, rotation axis A).

The cylinder barrel22extends through the trunnion24and through the sleeve25. The sleeve25is arranged at least partially between the trunnion24and the cylinder barrel22.

The cylinder barrel22, the trunnion24and the sleeve25are coupled via various threads, as will be described further below.

FIG. 4shows a longitudinal cross section of a pitch adjustment cylinder20. The pitch adjustment cylinder20ofFIG. 4is similar to the pitch adjustment cylinder ofFIG. 3in that it comprises a cylinder barrel22and piston23arranged in therein. The piston23may be moved relative to the barrel22by hydraulic and/or pneumatic means. The cylinder barrel22extends through a trunnion24and a sleeve25which is arranged partially between cylinder barrel22and trunnion24.

In addition, a first base member29aand a second base member29bare arranged at opposite ends of the pitch adjustment cylinder20. The first base member29aand the second base member29bare connected to and via two tie rods26. Other embodiments of pitch adjustment cylinders may feature other numbers of tie rods, such as one, three, four, five, six or more tie rods. In general, the tie rods may be arranged in rotational symmetry about a central axis of the pitch adjustment cylinder.

The tie rods26may be connected to the first base member29aand the second base member29be.g. as described above with respect toFIG. 2and/or pre-tensioned.

The first base member29aand the second base member29bare coupled to the cylinder barrel22and, in case the tie rods26are pre-tensioned, transfer pre-tension of the tie rods26as a compressive force onto the cylinder barrel22along the length of the pitch adjustment cylinder20. Compressive stress in the cylinder barrel22allows to decrease the risk of fatigue cracks, in particular at any threaded interfaces between cylinder barrel22and trunnion24.

The piston23(particularly the piston rod23band the piston end23c) extends through an opening of the second base member29b. The piston23may be moved into and/or out of the cylinder barrel22, through the opening of the second base member29bessentially without experiencing the pre-tension of the tie rods26or the compression of the cylinder barrel22.

Each of the two tie rods26extends through the trunnion24through a respective one of two tie rod openings27. The outer diameter of the tie rods26and the inner diameter of the tie rod openings27of the trunnion24are dimensioned or designed such that essentially no or substantially reduced forces are transmitted from the tie rods26to the trunnion24and vice versa.

For example, as in the depicted case, the tie rod openings27may have an inner diameter, which is larger than the outer diameter of the tie rods26so that the tie rods26are not in direct contact with the trunnion24. In particular, the tie rods26are not in rigid connection to the trunnion24.

As a result, forces acting on the trunnion24are not transferred to the tie rods26and vice versa. Forces acting on the trunnion24are transferred essentially exclusively to the cylinder barrel24via the sleeve25. Conversely, forces output by the pitch adjustment cylinder20, e.g. during operation as pitch drive, are transferred essentially exclusively through the cylinder barrel22, i.e. without substantial forces acting directly on the tie rods. As a result, the risk of fatigue failure of the tie rods is at least reduced.

FIG. 5shows two views of a sleeve25. The sleeve25may be of a type to be used in any embodiment of a pitch adjustment cylinder described herein although other sleeves may be used alternatively. The sleeve25has a generally cylindrical shape along a central axis25a.

FIG. 5Ashows a top view of sleeve25.FIG. 5Bshows a cross section of the sleeve25ofFIG. 5A.FIGS. 5A and 5Bwill be described jointly in the following.

Sleeve25comprises an outer sleeve thread35balong its full length around its central longitudinal axis25awhich is also an axis of symmetry for the generally cylindrical sleeve. Moreover, sleeve25comprises an inner sleeve thread35aaround the same axis however, at a smaller radius (i.e. a smaller radial distance from the central longitudinal axis25a). Inner sleeve thread35aand outer sleeve thread35bhave different thread pitches, namely a first thread pitch and a second thread pitch, respectively.

The sleeve25, in particular with its two threads35aand35bat different radii and with different thread pitches, may be used for the teaching according to the present disclosure. In particular, the sleeve25may be mounted at least partially between a trunnion and a piston of a pitch adjustment cylinder and used to reduce or remove, by rotation, play and/or clearance between the trunnion and the cylinder barrel.

FIG. 6shows a cross section of a portion of a pitch adjustment cylinder20, namely at a region of connection of cylinder barrel22, trunnion24and sleeve25. Cylinder barrel22has a first cylinder barrel thread32aand a second cylinder barrel thread32b, both with a first thread pitch P1.

Sleeve25has an inner sleeve thread35awith the first thread pitch P1and an outer sleeve thread35bwith a second thread pitch P2. In the depicted case, the second thread pitch P2is larger than the first thread pitch P1. In other embodiments, the first thread pitch P1may be larger than the second thread pitch P2. In general, the first thread pitch and the second thread pitch differ from each other and, i.e. are not identical.

The inner sleeve thread35aengages with the first cylinder barrel thread32a. The outer sleeve thread35bengages with a first trunnion thread34a(which also has the second thread pitch). A second trunnion thread34bengages directly with the second cylinder barrel thread32b.

The cylinder barrel22is thus connected to the trunnion24via three threaded interfaces, namely (i) a first interface I1between inner sleeve thread35aand first cylinder barrel thread32a, (ii) a second interface12between outer sleeve thread35band first trunnion thread34a, and (iii) a third interface13between second trunnion thread34band second cylinder barrel thread32b. The first interface I1and the second interface12are essentially at identical locations along the central axis of the cylinder barrel22, however at different radial locations. The second interface12is located at a larger radius from the central axis of the pitch adjustment cylinder20.

In the depicted embodiment, the third interface13is located at a different position along the central axis of the pitch adjustment cylinder20and at the same radial position as the first interface I1. Alternatively, in some embodiments, it may located at a different radial position than the first interface I1, e.g. at the same radial position as the second interface12.

The sleeve25is rotatable. Upon rotation, sleeve25is moved relative to cylinder barrel22with the transmission given by the first thread pitch P1. Sleeve25is, upon rotation, also moved relative to trunnion24, with the transmission given by second thread pitch P2. The first thread pitch P1and second thread pitch P2being different, stress in axial direction is built up through sleeve25. If stress or play was previously present, in axial direction, rotation of sleeve25serves to release play or stress. Reducing play or stress enables forces to be transferred from the trunnion24to the cylinder barrel22efficiently. Structural failure due to fatigue may be reduced.

FIG. 7shows a cross section of a pitch adjustment cylinder20. As a backbone to the structural strength of the pitch adjustment cylinder, a first base member29aand a second base member29bare arranged at opposite ends of the pitch adjustment cylinder20. The first base member29aand the second base member29bare connected to and via tie rods26, which extend parallel to the central axis of the pitch adjustment cylinder and which are pre-tensioned, namely each tie rod by means of a respective tie rod bolt28.

The first base member29aand second base member29bare coupled to a cylinder barrel22and may transfer, if applicable, pre-tension of the tie rods26as a compressive force onto the cylinder barrel22along the central axis of the pitch adjustment cylinder20.

The cylinder barrel22partially encloses a piston23, which is hydraulically and/or pneumatically movable relative to the cylinder barrel22, e.g. by means of pressurized liquids, such as oil and/or gas. The piston23extends through an opening of the second base member29b. The piston23may be moved into and/or out of the cylinder barrel22, through the opening of the second base member29bessentially without experiencing the pre-tension of the tie rods26or the compression of the cylinder barrel22.

The cylinder barrel22extends through a trunnion24and a sleeve25which is arranged partially between cylinder barrel22and trunnion24. The sleeve25is rotatable and adapted to remove or reduce play and/or clearance between trunnion24and cylinder barrel22as will be described with reference toFIG. 8below.

FIG. 8illustrates a magnified view of a portion of the pitch adjustment cylinder ofFIG. 7, namely a portion in vicinity of the sleeve25with various threads. The sleeve25is arranged partially between the cylinder barrel22and the trunnion24.

Three threaded regions are indicated by the reference signs of the respective complementary threads, which engage to form the respective threaded region or interface. In this context, complementary threads are understood to have matching thread pitches.

A first interface I1(35a/32a) between inner sleeve thread35aand first cylinder barrel thread32acouples the sleeve25with the cylinder barrel22. The inner sleeve thread35aand first cylinder barrel thread32ashare a first thread pitch P1, such that the first interface I1(35a/32a) has the first thread pitch P1.

A second interface12(35b/34a) between outer sleeve thread35band first trunnion thread34acouples sleeve25with trunnion24. The outer sleeve thread35band first trunnion thread34ashare a second thread pitch P2, such that the second interface12(35b/34a) has the second thread pitch P2. In the depicted case, the second thread pitch P2is larger than the first thread pitch P1. In other embodiments, the first thread pitch P1may be larger than the second thread pitch P2.

The second interface12(35b/34a) is essentially at the same location along the central axis of the pitch adjustment cylinder as the first interface I1(35a/32a). The second interface12is located at a different radial location, namely at a larger radius from the central axis of the pitch adjustment cylinder20.

A third interface13(32b/34b) between second trunnion thread34band second cylinder barrel thread32bcouples trunnion24with cylinder barrel22.

The second trunnion thread34band second cylinder barrel thread32bshare the first thread pitch P1, such that the third interface13(32b/34b) has the first thread pitch P1. In this embodiment, the first cylinder barrel thread32aand the second cylinder barrel thread32bshare the first thread pitch P1, such that they may be manufactured in a single run, e.g. of cutting or milling.

In the depicted embodiment, the third interface13is located at a different position along the central axis of the pitch adjustment cylinder20and at the same radial position as the first interface I1.

The sleeve25is rotatable. Upon rotation, sleeve25is moved relative to cylinder barrel22with the transmission given by the first thread pitch P1. Sleeve25is, upon rotation, also moved relative to trunnion24, with the transmission given by second thread pitch P2. The first thread pitch P1and the second thread pitch P2being different, this means that differential displacement is built up through sleeve25. If play and/or clearance was previously present, rotation of sleeve25may serve to release this previously present play and/or clearance. Minimizing play and/or clearance enables forces to be transferred from the trunnion24to the cylinder barrel22efficiently.

FIG. 9shows a cross section of a pitch adjustment cylinder20with a cylinder barrel22which extends through a trunnion24. Four tie rods26extend through four tie rod openings27of the trunnion24. Tie rods26are not in rigid connection to the trunnion. In particular, the tie rods26are not in contact with the trunnion24. The cylinder barrel22has a cylinder barrel thread32b. The trunnion24has a trunnion thread34b. The cylinder barrel22and the trunnion24are coupled via cylinder barrel thread32band trunnion thread34b, which are engaged.

The tie rods26may be pretensioned to thereby compress the cylinder barrel22. The compressively loaded cylinder barrel22is less prone to fatigue cracks. The tie rods26not being in rigid connection with the trunnion24, in the present case for instance by means of the tie rod openings27, affects the strength of the pitch adjustment cylinder20under load. In particular, forces on the cylinder barrel22are not directly transferred to the tie rods and therefore do not affect the structural integrity of the tie rods.

FIG. 10shows a cross section of a pitch adjustment cylinder20with a piston23, cylinder barrel22, sleeve25, trunnion24and four tie rods26. The tie rods extend in parallel to the cylinder barrel (i.e. perpendicular to the paper plane ofFIG. 10) through respective tie rod openings27through the trunnion24.

The sleeve25is arranged at least partially between the trunnion24and the cylinder barrel22. The sleeve25has two threads, an inner sleeve thread and an outer sleeve thread, with different thread pitches, namely a first thread pitch P1and a second thread pitch P2.

The inner sleeve thread engages the cylinder barrel22, whereas the outer sleeve thread engages the trunnion24. By rotation of the sleeve25, play and/or clearance between the trunnion24and the cylinder barrel22may be removed or at least reduced.

At the same time, the tie rods26not being in rigid connection with the trunnion24, they experience essentially no or at least substantially reduced forces (e.g. lead cycling output) from the pitch adjustment cylinder20.