BLADE MOUNTING ARRANGEMENT

Abstract

Provided is a blade mounting arrangement at the interface between a hub and a rotor blade of a wind turbine, which blade mounting arrangement includes at least an annular bearing including a stationary part mounted to the hub and a rotating part mounted to the root end of the blade; and a reinforcing ring arranged between the bearing rotating part and the root end of the blade, which reinforcing ring includes a cylindrical body portion shaped as an extension of the root end of the blade. A wind turbine including a hub and a number of blades mounted to the hub, and with such a blade mounting arrangement at the interface between the hub and each rotor blade is also provided. A method of realizing an interface between a hub and a rotor blade of a wind turbine is also provided.

Claims

1. A blade mounting arrangement at the interface between a hub and a rotor blade of a wind turbine, which blade mounting arrangement comprises at least an annular bearing comprising a stationary part mounted to the hub and a rotating part mounted to the root end of the blade; and a reinforcing ring arranged between the bearing rotating part and the root end of the blade, which reinforcing ring includes a cylindrical body portion shaped as an extension of the root end of the blade.

2. The blade mounting arrangement according to claim 1, wherein the dimensions and material properties of the reinforcing ring are chosen to achieve an increase in stiffness over a comparable blade mounting arrangement in which a blade root end is mounted directly to an annular bearing.

3. The blade mounting arrangement according to claim 1, wherein a main diameter of the reinforcing ring corresponds to a main diameter of the root end of the blade.

4. The blade mounting arrangement according to claim 1, wherein the reinforcing ring has an H-shaped cross-section comprising a flange at either end of a straight cylindrical web.

5. The blade mounting arrangement according to claim 4, wherein the width of a flange corresponds to the wall thickness of the root end of the blade.

6. The blade mounting arrangement according to claim 4, wherein the width of the web is at most 50% of the wall thickness of the root end of the blade.

7. The blade mounting arrangement according to claim 1, wherein the height of the reinforcing ring exceeds the height of the annular bearing.

8. The blade mounting arrangement according to claim 1, wherein the reinforcing ring is made of metal.

9. The blade mounting arrangement according to claim 1, comprising a number of reinforcing plates, wherein a reinforcing plate is attached to the bearing.

10. A wind turbine comprising a hub and a number of blades mounted to the hub, and further comprising a blade mounting arrangement according to claim 1 at the interface between the hub and each rotor blade.

11. The wind turbine according to claim 10, wherein the main diameter of the root end of a rotor blade comprises at least 3.0 m.

12. A method of realizing an interface between a hub and a rotor blade of a wind turbine, which method comprises the steps of providing an annular bearing at the interface between the hub and a rotor blade and mounting a stationary part of the annular bearing to the hub; arranging a reinforcing ring between the rotating part of the annular bearing and the root end of the blade, which reinforcing ring comprises a body portion shaped as an extension of the root end of the blade; and forming a mechanical connection between the rotating part of the annular bearing, the reinforcing ring, and the root end of the blade.

Description

BRIEF DESCRIPTION

[0019] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0020] FIG. 1 shows a known blade mounting arrangement;

[0021] FIG. 2 indicates an in-plane bearing deformation of the known blade mounting arrangement of FIG. 1;

[0022] FIG. 3 shows a further known blade mounting arrangement;

[0023] FIG. 4 indicates an out-of-plane bearing deformation of the known blade mounting arrangement of FIG. 3;

[0024] FIG. 5 shows a cross-section through an embodiment of the inventive blade mounting arrangement;

[0025] FIG. 6 shows that a more detailed cross-section through the embodiment of FIG. 5;

[0026] FIG. 7 shows an embodiment of the reinforcing ring in which the flanges are equal in size;

[0027] FIG. 8 shows an alternative embodiment of the reinforcing ring; and

[0028] FIG. 9 shows further embodiments of the inventive blade mounting arrangement.

[0029] In the diagrams, like numbers refer to like objects throughout. Objects in the diagrams are not necessarily drawn to scale.

DETAILED DESCRIPTION

[0030] FIG. 1 shows a blade mounting realisation known from the known art. Here, three rotor blades 2 are mounted to the hub 4 of a wind turbine 8 (the diagram only partially shows one blade 2 for the sake of clarity). The hub 4 is at the front end of a nacelle 80, which in turn is mounted on top of a tower 81. The root end 20 of each blade 2 is bolted to a circular pitch bearing 3 arranged at a suitably shaped opening in the hub 4. The blades 2 can be subject to very strong forces, mainly due to wind loading. Significant forces can be transferred to the hub 4 and can act in any direction at any point along the root/hub interface 24 of a blade 2. For example, deflection of the blade airfoil can result in a bending moment at the root/hub interface. The forces transferred from one blade 2 to the hub 4 can result in slight deformation of the hub 4, and such deformations can result in deformation of the circular bearings 3 of the blades 2. FIG. 2 indicates in exaggerated manner an in-plane deformation generally referred to as “ovalization”, in which the otherwise circular shape of the bearing 3 becomes slightly oval, resulting in an “ovalized” bearing 3X. Even a very slight ovalization can greatly detract from the performance of the bearing.

[0031] FIG. 3 shows a further blade mounting realisation known from the known art. Here, to avoid an in-plane deformation of the bearing 3, circular reinforcing plates 11A, 11B are secured on either side of the bearing 3, i.e. one plate 11A on the inner side or hub side of the bearing 3 and one plate 11B on the outer side or blade side of the bearing 3. While these reinforcing plates 11A, 11B can prevent ovalization of the bearing 3, they cannot prevent an out-of-plane deformation of the bearing 3. FIG. 4 indicates in exaggerated manner an out-of-plane deformation, in which the otherwise flat plane of the bearing 3 becomes distorted, resulting in a “warped” bearing 3Y. In this case also, even a very slight out-of-plane distortion can greatly detract from the performance of the bearing. Even a bearing with a relatively large thickness or height H.sub.3 may be subject to deformation.

[0032] FIG. 5 shows a cross-section through an embodiment of the inventive blade mounting arrangement 1. As in the previous diagrams, three rotor blades 2 are mounted to the hub 4 of a wind turbine. The root end 20 of each blade 2 is bolted to an annular pitch bearing 3. In this embodiment, a pair of circular reinforcing plates 11A, 11B as described in FIG. 3 above is secured on either side of the annular bearing 3 so that in-plane deformation of the bearing 3 is effectively prevented. In addition to this measure, a reinforcing ring 10 is arranged between the bearing 3 and the blade root end 20. The reinforcing ring 10 has the same diameter as the blade root end 20. In this embodiment, the outer reinforcing plate 11B is effectively “sandwiched” between the reinforcing ring 10 and the bearing 3.

[0033] FIG. 6 shows that the cross-section of the reinforcing ring 10 has the shape of a capital “H” lying on its side (or an upright capital “I”), with flanges 101, 102 at the inner and outer ends of the reinforcing ring 10. The main cylindrical body may be regarded as the web. The skilled person will be familiar with this shape, which is used in the construction industry (generally at a much larger scale) in straight I-beams or H-beams that are used to provide structural strength in buildings.

[0034] This diagram also shows the bearing 3 to be composed of an inner bearing part 3A and an outer bearing part 3B. The inner bearing part 3A rotates as one with the blade root end 20, while the outer bearing part 3B is stationary and is secured to the hub 4. In this exemplary embodiment, the bearing 3 is realized as a ball bearing, but can of course be realized using any appropriate bearing design. The diameter D.sub.20 measured between midpoints of the reinforcing ring 10 is essentially the same as the root end diameter D.sub.20, measured between midpoints of the root end wall.

[0035] FIG. 7 shows an embodiment of the reinforcing ring 10 in which the flanges 101, 102 are equal in size and have a width w.sub.20 that is essentially the same as the wall thickness at the blade root end 20. The web or main body of the reinforcing ring 10 need not be as wide as the flanges 101, 102, and the diagram shows that the web has a significantly smaller thickness w.sub.10. This allows a relatively light reinforcing ring 10 which still delivers the desired structural stiffness to the overall mounting arrangement 1. The web thickness w.sub.10 may be at most 50% of the flange width w.sub.20 or even less. The ring height H.sub.10 may be at least as thick as the bearing height H.sub.3.

[0036] FIG. 8 shows an alternative embodiment of the reinforcing ring 10. Here, to avoid an in-plane deformation of the bearing 3, the reinforcing ring 10 is mounted directly onto the rotating part of the bearing 3. This embodiment is similar to that of FIG. 6, but does not use the reinforcing plates. The combined stiffness of the bearing 3 and reinforcing ring 10 may be sufficient to avoid deformation if the bearing diameter is relatively small and/or if the bearing 3 itself is relatively stiff and/or if the reinforcing ring 10 is relatively thick.

[0037] The reinforcing ring 10 can be secured to the bearing 3 and to the blade root end 20 by means of bolts or other fasteners inserted through an appropriate number of through-holes. For example, a bolt can be inserted from the hub end through a series of matching through-holes formed in the inner reinforcing plate 11A, the rotating part 3A of the bearing 3, the outer reinforcing plate 11B, the reinforcing ring 10, and the blade root end 20. Such a bolt may be threaded to engage with an inner thread of a bushing embedded in the blade root end 20, for example. Alternatively, as shown in FIG. 9, bolts 5 can be embedded in the blade root end 20 to extend through a series of matching through-holes formed in the reinforcing ring 10, the outer reinforcing plate 11B, the rotating part 3A of the bearing 3, and the inner reinforcing plate 11A. A nut 50 can be tightened around the threaded outer end of each bolt 5.

[0038] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0039] For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.