Field of the Invention

The present invention relates generally to the field of wind turbines, and more particularly to a lifting system for moment bearing of a wind turbine comprising a nacelle having a main structure, a rotor, which rotor comprises at least two rotor blades, each mounted to a rotor hub via a root end of the rotor blade, which rotor hub is connected with a moment bearing, which system comprises a bearing lifting tool.

Furthermore, the invention relates to a method of mounting and dismounting a moment bearing of a wind turbine bearing comprising a nacelle having a main structure, a rotor, which rotor comprises at least two rotor blades, each mounted to a rotor hub via a root end of the rotor blade, which rotor hub is connected with a main shaft via a moment bearing, and which wind turbine has a rotor shaft preferably having a tilt angle different from 0°.

Moreover, the invention relates to the use of such system and such method for mounting and dismounting a moment bearing.

Background of the Invention

There are more and stricter requirements for keeping a moment bearing as circular as possible. Even very small deviations from a plan circular bearing could destroy the moment bearing.

In general, the mounting and dismounting of a moment bearing is effected with a lift- ing eye provided in the outer surface of the outer ring of the moment bearing. However, when lifting the weight in the lifting eyelid there would be a risk that the circularity of the bearing is changed and that the bearing is destroyed.

There have been requirements for a more efficient and easy way to mount and dis- mount a moment bearing. These requirements are further problematic, seeing that the nacelle would normally be arranged with a rotor having a main shaft or axis of rota- tion which is arranged with a tilt angle. Normally, the tilt angle would be positive. The tilt angle is defined as the angle between a horizontal axis and a rotational axis for the rotor. A positive angle would increase the height of the hub and also the clearance to the tower.

When mounting the moment bearing with traditional tools, there are difficulties in aligning the moment bearing hanging in the eyelid to the angle of the tilted nacelle.

Moreover, the requirement for cutting down the cost in production and maintenance of wind turbines is increased. Therefore, it is also a desire to provide a system which is simple to manufacture and which could also decrease the time consumption when mounting and dismounting the moment bearing while simultaneously ensured that no deviation occurs in the circularity of the bearing. EP 2.226.496 A2 discloses a lifting system of the type mentioned by way of introduction. There exists a desire to provide a useful alternative to this prior art and to provide a lifting system which is suited for mounting and dismounting moment bearings of a wind turbine, preferably a wind turbine having a rotor shaft with a tilt angle different from 0°.

Object of the Invention

It is the object of the present invention to obtain a system which overcomes the drawbacks explained above and to provide a lifting system for mounting and dismounting moment bearings of a wind turbine, preferably a wind turbine having a rotor shaft with a tilt angle different from 0°.

Moreover, it is also the object that such lifting system should be simple to manufacture and easy to use.

Description of the Invention

This object is obtained with a system for load control of a wind turbine of the type mentioned in the introductory paragraph and being peculiar in that the bearing lifting tool comprises: a flange having a main body which has a first plane surface provided with holes arranged along a circle,

a lifting bracket which has a first end via an attachment area being attached to a second surface of the main body of the flange,

that said second end of the lifting bracket is provided with at least one main lifting eye intended to be hooked to a crane, which main lifting eye is arranged outside a gravitational plane containing the centre of gravity for the moment bearing, and

that said first plane surface, in use, will be the plane in which the lifting bracket is in contact with the bearing, preferably an inner ring of the bearing.

The object is also obtained with a method comprising the steps of:

providing a bearing lifting tool according to any one of the preceding claims, connecting the inner ring of the moment bearing with the holes arranged along a circle as bolts are inserted through the holes into threaded holes provided in the inner ring of the moment bearing,

providing a lifting or lowering of the moment bearing between ground level and the nacelle with the main lifting eye hooked to a crane.

The object is also obtained with the use of a system and a method according to the invention for mounting and dismounting a moment bearing of a wind turbine.

The object is also obtained with the use of a system and a method according to the invention for mounting and dismounting a moment bearing of a wind turbine with a rotor shaft having a tilt angle different from 0°. With the term gravitational plane as used in the present invention is meant a plane which is perpendicular to the axis of rotation for the moment bearing and which contains the center of gravity of the moment bearing and which will be a vertically orientated plane, when the moment bearing is arranged in a vertical position with the axis of rotation orientated in a horizontal plane.

The moment bearing is constructed with two bearing rolls. Each of these bearing rolls will have an inner bearing ring and an outer bearing ring. In general, it is desired to have a certain distance between the two bearing rolls and a moment bearing may be asymmetric. Therefore, the gravitational plane might not be arranged at the middle of the moment bearing. Seeing that the bearing lifting tool of the system has a flange which is arranged with holes along the circle, it is possible to provide such holes with a positioning matching the existing holes in the inner ring of a moment bearing. This is preferred as the outer ring is used for mounting in the mating part on the main structure of the nacelle of the wind turbine.

Alternatively, it is also possible to have the holes aligned with the corresponding holes in the outer ring of a moment bearing.

It is possible to place the flange with the first plane surface in contact with the side surface of the moment bearing and use the holes for introduction of bolts which are screwed into the thread provided holes in a ring of the bearing.

Hereby, the flange will ensure that the bearing maintains its 100 % circular form when lifted in the lifting bracket.

The lifting bracket has a first end with an attachment area through which the bracket is attached to the second surface of the main body of the flange. The second surface would be the surface facing away from the moment bearing. The attachment area between the lifting bracket and the main body would extend across the center of the cir- cle along which the holes are arranged. The lifting bracket has a second end which is provided with at least one main lifting eye intended to be hooked to a crane.

The flange should preferably be arranged with a substantially C-formed curvature ensuring there is a free space between the first end attached to the main body and the second end arranged outside the circle. The C-form ensures that the bearing rings will not come into contact with the bearing lifting tool during use.

The second end of the lifting bracket is provided with one or more main lifting eyes. The eyes are intended to be hooked to a crane. Seeing that the lifting eyes are arranged outside of the gravitational plane, it is possible to have the moment bearing hanging with an angle compared to a vertical orientation. Depending on the distance which the main lifting eye is offset in relation to the gravitational plane, it is possible to adjust the angle.

Having a correct offset positioning of the main lifting eye compared to the gravitational plane, it is possible to obtain an angle of the moment bearing, when suspended in a crane, which corresponds to the tilt angle for an actual wind turbine. Therefore, when mounting or dismounting the moment bearing attached to the flange, the angle of the moment bearing would be easily aligned with the mating part on the main structure of the nacelle of the wind turbine.

A lifting bracket would have at least one main lifting eye. If more lifting eyes are provided, these would be offset with different distances to the gravitational plane. Here- by, it is possible with one lifting bracket to have an adaptation to different tilt angles.

Alternatively, one main lifting eye may also be provided which could be displaced in a direction perpendicular to the gravitational plane in order to obtain a connection point of the lifting eye which could have a variable distance to the gravitational plane. Hereby, it is also possible, very easily, to change the tilt angle to adept the lifting tool to any tilt angle.

Normally, the angle which the main lifting eye is offset would provide an angle of approximately 6°, seeing that a tilt angle for a nacelle would normally be around 6°. This is due to the desire for having a tower clearance for the rotor blades.

According to a further embodiment, the system according to the present invention is peculiar in that said first plane surface comprises an annular circular surface.

It is possible that the first plane surface of the flange could have different forms. It is preferred that it is an annular circular surface which would provide a stable surface for contact with the inner ring of the moment bearing. Alternatively, the first plane surface could have any other forms, e.g. being arranged with a number of struts which provide a plane surface for contact with the ring of the moment bearing. Such struts could extend from the main body to which the lifting bracket is attached.

According to a further embodiment, the system according to the present invention is peculiar in that the attachment area extends over a center of said circle, preferable with an extension of more than 50% of the diameter of the circle, and more preferably more than 75% of the diameter of the circle. When the attachment area extends over the center of the circle with a substantial distance as explained, it is possible to obtain a secure connection between the lifting bracket and the main body of the flange. Moreover, such construction would make it easier to obtain any moment occurring in the flange when the lifting system is used and the weight of the moment bearing will induce a asymmetric load of the bearing lifting tool.

According to a further embodiment, the system according to the present invention is peculiar in that the main lifting eye is offset in relation to said gravitational plane in direction away from said second surface. It is possible to provide the main lifting eye being offset in both directions to the gravitational plane. However, when the lifting eye is offset in direction away from the second surface, it is ensured that the lifting wire of the crane would not make any problems due to the tilting of the moment bearing when aligning the moment with the mating part on the main structure of the nacelle. Accordingly, it is possible to effect a secure and quick aligning of the moment bearing with the nacelle.

According to a further embodiment, the system according to the present invention is peculiar in that the lifting bracket is provided with at least two main lifting eyes which are offset in different distances from the gravitational plane. As already mentioned, it is possible to adapt the bracket to different tilt angles by providing two or more lifting eyes which are offset in different distances from the gravitational plane.

According to a further embodiment, the system according to the present invention is peculiar in that the first end of the bracket is provided with at least one secondary lifting eye arranged in the bracket in a position over the center of said circle compared to the side where the main lifting eye is arranged, which secondary lifting eye is intended to be hooked to a crane. For a secure handling of the moment bearing, it is also important that not only the lifting and aligning when mounting and dismounting the moment bearing is effected, but also that a secure lifting of the moment bearing from the ground level is effected.

When the bracket is provided with at least one secondary lifting eye in a position over the center of the circle, then it is possible to use a crane hook for both the main lifting eye and the secondary lifting eye.

When the moment bearing is arranged with a horizontal orientation of the ground, a sling is connected to the two lifting eyes. First a crane would slowly hoist a bearing lifting tool with the use of two cranes. When lifting, one could gradually releases the rope from the second crane so that the lifting tools swing from the horizontal to a ver- tical position which is the hoisting position with the slight angle compared to vertical orientation.

Then the second crane will be disconnected, whereafter the moment bearing is only suspended in the main lifting eye. The moment bearing could now be lifted to the na- celle. Here, the moment bearing would be aligned with the mating part on the main structure of the nacelle.

When dismounting a moment bearing arranged in the nacelle, one would also start with the lifting tool in a horizontal position of the ground. Also in this position, it would have an initial lifting step where a crane is connected to each of the two lifting eyes.

When the lifting tool is lifted to the nacelle, it would be aligned with the moment bearing mounted in the nacelle. In this situation, the holes in the lifting tool will be aligned with the holes in the bearing ring. After this, the lifting tool will be bolted to the bearing. After this, the moment bearing could be detached from the nacelle. This could be done in a way which is also used when dismounting the moment bearing with a system according to prior art. After the moment bearing is lifted free from the nacelle, it would be lowered to a distance shortly above the ground. In this position, a crane hook is connected with the secondary lifting eye and the moment bearing would be arranged in a horizontal position before lowered slowly to the ground.

As it occurs from the above, the use of a secondary lifting eye would be especially advantageous when placing or lifting the moment bearing from the ground.

Here, it is important to note that the moment bearing, in order not to damage the circu- larity, should be arranged horizontally on the ground.

According to a further embodiment, the system according to the present invention is peculiar in that stiffening ribs are provided for connecting the lifting bracket with the main body of the flange. In order to have a flange which has sufficient stiffness, it is preferred to have stiffening ribs. Hereby, it is possible to obtain the forces which occur due to the tilted orientation when lifting and lowering the moment bearing. The stiffening ribs could be provided with an orientation substantially perpendicular to the orientation of the lifting bracket. Alternatively, there may be used more stiffening ribs having a star-like orientation extending from the center radially towards the outer cir- cle where the holes are provided.

Here, it should also be noted that the main body of the lifting bracket preferably is provided in a substantially circular form. According to a further embodiment, the system according to the present invention is peculiar in that the main body and the lifting bracket are made of plate elements being welded together. When the main body and the lifting bracket and stiffening ribs are made of plate elements which are welded together, it is possible to provide a low cost structure which is able to obtain the forces occurring when lifting and lowering the moment bearing. Such structure would be simpler and more cost effective compared to a lifting tool which is provided in a cast form. According to a further embodiment, the system according to the present invention is peculiar in that said second end extends to a position outside said circle along which the holes are arranged.

The second end is preferably arranged outside the circle. Hereby, the lifting eye is also arranged outside the moment bearing and may not touch the moment bearing during lifting and lowering the moment bearing hooked to a crane. However, it might also be possible to have the second end, and accordingly also the main lifting eye, arranged inside the circle.

According to a further embodiment, the method according to the present invention is peculiar in that said wind turbine has a rotor shaft having a tilt angle different from 0° and providing the main lifting eye with a displacement from the gravitational plane which ensures that the moment bearing is orientated with such tilt angle during lifting.

According to a further embodiment, the method according to the present invention is peculiar in that said method for mounting the moment bearing further comprises the steps of:

initially lifting the bearing free of the ground with the main lifting eye and the secondary lifting eye hooked to a crane,

- lowering the secondary lifting eye until the moment bearing hangs in the main lifting eye, and

- unhooking the secondary lifting eye before lifting the bearing to the nacelle.

As already mentioned, the initially lifting of the bearing free of the ground would be effected with a crane connected to the main lifting eye and the secondary lifting eye.

When the initial lifting is effected, the moment bearing would be free of the ground and then the lowering of the second lifting eye could be effected until the moment bearing hangs freely in the main lifting eye. After this, it is possible to unhook the secondary lifting eye. After this, the lifting of the bearing to the nacelle would be effected with the crane lifting in the main lifting eye. According to a further embodiment, the method according to the present invention is peculiar in that said method for dismounting the moment bearing further comprises the steps of:

initially connecting the crane with the main lifting eye,

hooking the secondary lifting eye to a crane after the moment bearing in the main lifting eye has been lowered to a position just before the bearing touches the ground,

- lifting the secondary lifting eye until the bearing is in a horizontal position, and lowering the bearing to the ground in both lifting eyes.

Already a short mentioning of the dismounting has been explained. Initially a crane hook would be connected with the main lifting eye. After having dismounted the mo- ment bearing from the nacelle and lifted the moment bearing to a position just before it touches the ground, the secondary lifting eye would be connected to a crane.

Then a lifting would be effected in the secondary lifting eye until the moment bearing is arranged in a substantial horizontal position. Following this, it is possible slowly to lowering the moment bearing to the ground with a lowering in the two lifting eyes. Hereby, a secure placing of the moment bearing on the plane horizontal surface is obtained.

It is noted that the above embodiments are examples and that it is possible to have other embodiments that the ones described. Within the scope of the claims, several embodiments are possible. What is important is that it is possible to lift and lower the moment bearing with a lifting tool which provides the tilted orientation of the moment bearing. Such structure will ensure that the moment bearing could be mounted and dismounted in an efficient way, and since the time for aligning the moment bearing with the mating on the main structure of the nacelle is reduced, also the total time for mounting and dismounting is reduced.

Description of the Drawing

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings, in which: Fig. 1 shows a perspective view of a wind turbine,

Fig. 2 shows a moment bearing,

Fig. 3 shows a bearing lifting tool, in which a moment bearing is mounted,

Fig. 4 shows a view in a first direction of a bearing lifting tool,

Fig. 5 shows a lifting tool seen perpendicular to the view of Fig. 4,

Fig. 6 shows an enlarged view of a part of the bearing lifting tool,

Fig. 7 shows a schematic view of a wind turbine illustrating tilt angle, and

Fig. 8 shows a cross-section through a moment bearing. Detailed Description of the Invention

In the following text the figures will be described one by one, and the different parts and positions seen in the figures will be numbered with the same numbers in the different figures. Not all parts and positions indicated in a specific figure will necessarily be discussed together with that figure.

Position number list

1 Wind turbine

2 Wind turbine tower

3 Foundation

4 Nacelle

5 Rotor hub

6 Wind turbine rotor blade

7 First end of blade (root end)

8 Second end of blade (tip end)

9 Moment bearing

10 Inner ring

11 Outer ring

12 Inner ring holes

13 Outer ring holes

14 Eye fixture

15 Bearing lifting tool

16 Flange

17 Bracket

18 First plane surface 19 Circle

20 Hole

21 First end

22 Second end

23 Second surface

24 Attachment area

25 Main lifting eye

26 Gravitational plane

27 Center of gravity

28 Center of circle (19)

29 Distance (between main lifting eye and gravitational plane)

30 Secondary lifting eye

31 Stiffening rib

32 Main body (of flange)

33 Tilt angle

34 Bearing roll

35 Axis of rotation

Detailed Description of the Invention

In fig. 1 a typical wind turbine 1 is seen comprising a tower 2 installed at a foundation 3. At the top of the tower 2, a nacelle 4 comprising e.g. a gearbox, a generator and other components is seen. At the nacelle 4, a shaft for carrying a rotor comprising a hub 5 and three wind turbine rotor blades 6 is also installed. The rotor blades 6 are arranged at the hub 5 at a first end 7 called the root end of the rotor blade 6. The second end 8 of the rotor blades 6 constitutes a tip end.

Fig. 2 shows a moment bearing 9 which comprises an inner ring 10 and an outer ring 11. The inner ring is provided with holes 12 arranged along a circle (see Fig. 4). Also the outer ring comprises a number of holes 13.

The holes 13 in the outer ring 11 are used for attaching the moment bearing to the mating part on the main structure of the nacelle 4 of the wind turbine. The holesl2 in the inner ring is arranged along a circle 19 (see Fig. 4). The holes 12 are provided with threads.

Three eye fixtures 14 are arranged equally spaced in the inner ring holes 12. These eye fixtures are used for lifting the moment bearing and placing it on a plane surface when the moment bearing is arranged in a horizontal position before starting a lifting procedure to the nacelle 4.

When the moment bearing 9 is arranged in a horizontal position on a flat and dry plat- form, it is connected with a bearing lifting tool 15 which is explained below.

Fig. 3 illustrates the bearing lifting tool 15. This tool comprises a flange 16 and a bracket 17. The flange has a first plane surface 18 (see Fig. 5). At the first plane surface 18, holes 20 are arranged along a circle 19 (see Fig. 4). The holes 20 are arranged in positions corresponding to the holes 12 in the inner ring 10.

The lifting bracket 17 has a first end 21 and a second end 22. The first end 21 is attached to a second surface 23 of the main body 32 of the flange 16. The attachment is effected through an attachment area 24. This area extends across a substantial part of the diameter of the flange 16. Hereby, a large area is used for attachment which gives a secure and strong connection. Moreover, stiffening ribs 31 are used for effecting a stiffening of the bracket 17, seeing that this is made of plate elements.

At the first end 21, the attachment is effected through welding to the main body 32 of the flange 16.

At the second end 22 of the bracket 17, a main lifting eye 25 is provided. The main lifting eye 25 is intended for being hooked to a crane. Figs. 4 and 5 show the bearing lifting tool 15 seen from two directions perpendicular to each other. Here, it is seen that the main lifting eye 25 is provided in a distance 29 from a plane which is denoted as gravitational plane 26 which comprises the center of gravity 27 for the moment bearing (see Fig. 8). Fig. 4 illustrates the circle 19 along which the holes 20 are arranged. This circle 19 has a center 28. It is seen that the bracket 17 extends across the center 28. The bracket 17 is at the first end 21 provided with a secondary lifting eye 30. As it occurs from Figs. 4 and 5, the secondary lifting eye 30 is arranged on the opposite side of the center 28 compared to the positioning of the main lifting eye 25.

When lifting the moment bearing in both lifting eyes 25, 30, it is thus possible to have it arranged in a horizontal position as explained later.

Fig. 6 shows an enlarged view of the second end 22 of the bracket 17. This view shows that two main lifting eyes 25 are provided. These two lifting eyes are arranged in different distance from the gravitational plane 26 (see Fig. 5).

Fig. 7 shows a wind turbine in which the nacelle 4 is arranged with a tilt angle 33. This tilt angle 33 is a positive angle which will increase the height of the hub 5 and also obtain a better tower clearance as the blades would be orientated away from the tower.

Fig. 8 illustrates a cross-section through a moment bearing 9. It is seen that two bearing rolls 34 are used for the moment bearing 9. In this situation a gravitational plane 26 is arranged in the central plane. However, this gravitational plane can be offset if the bearing rolls are of a different size and therefore also have a different weight.

Fig. 8 illustrates the situation where the moment bearing is arranged in a vertical orientation of the gravitational plane and where the moment bearing has an axis of rota- tion 35 orientated in a horizontal plane. In this position, the center is gravity 27 will be arranged in the middle of the moment bearing. However, if the moment bearing is arranged under an angle different from vertical then the center of gravity 27 will be displaced either to the right hand side or left hand side as seen in Fig. 8. This shifting of the center of gravity 27 is used for adapting the position of the moment bearing to an angle - in relation to a vertical plane - corresponding to the tilt angle 33.

When the lifting system according to the invention is used for lifting a moment bear- ing, the arrangement of the main lifting eye outside the gravitational plane 26 will cause an orientation different from a vertical position of the moment bearing. This difference from the horizontal position can be adjusted to the actual tilt angle 33 whereby it is easier to mount the moment bearing in the mating part on the main structure of the wind turbine.

When mounting and dismounting the moment bearing 9, the bearing lifting tool 15 is attached to the inner ring 10 of the moment bearing. This is effected with bolts entering into the holes 12 which are provided with threads. A crane is hooked on the main lifting eye 25 and the secondary lifting eye 30. When the moment bearing is lifted free of the ground, the crane connected to the secondary lifting eye is lowered and when the moment bearing is hanging freely in the main lifting eye 25 the crane is detached from the secondary lifting eye 30. In this position, the moment bearing will be arranged under an angle different from vertical due to the offset position of the main lifting eye 25 compared to the gravitational plane 26.

The moment bearing is in this way lifted from ground level to the nacelle. Here, it will be aligned with the mating part of the nacelle and be mounted in a traditional way as the outer ring is attached to the main structure of the nacelle.

When removing a moment bearing 9 from the nacelle 4, the moment bearing will be lowered until a position slightly above the ground level in the main lifting eye 25. A second crane is attached to the secondary lifting eye 30 and a lifting is effected until the moment bearing 9 is arranged in the substantially horizontal position. This is pos- sible, seeing that the main lifting eye 25 and secondary lifting eye 30 are provided on each side of the center 28 of the circle 19 at which the bearing lifting tool 15 is attached to the moment bearing.

In this way, the moment bearing is lowered until it is arranged on a flat horizontal surface. In this position the bearing lifting tool 15 is detached from the crane and detached from the moment bearing.

As it occurs from the above during lifting and lowering of a moment bearing, it is possible to have a strong connection between the flange and the inner ring of the moment bearing. Hereby, it is ensured that the moment bearing will maintain its circularity.

It is noted that the embodiments illustrated above are examples, and that modifications are possible. It is also possible to combine the features from different embodiments.