WO2013120495A1

WO2013120495A1 - Wind turbine blade bearing and seal arrangement

Info

Publication number: WO2013120495A1
Application number: PCT/DK2013/050023
Authority: WO
Inventors: Torben Friis Baun; Jesper Lykkegaard NEUBAUER
Original assignee: Vestas Wind Systems A/S
Priority date: 2012-02-19
Filing date: 2013-01-25
Publication date: 2013-08-22

Abstract

A blade bearing for mounting a blade of a wind turbine to a hub of the wind turbine comprises first and second bearing rings arranged next to each other and a seal arrangement covering a space between the first and second bearing rings. One of the first or second bearing rings is configured to mount to the blade, and the other is configured to mount to the hub. The first and second bearing rings each have an axially-facing surface and a radially-facing surface. The seal arrangement includes a first seal element statically coupled to the axially-facing surface of the first bearing ring, a second seal element statically coupled to the axially-facing surface of the second bearing ring, and a holding member secured to the axially-facing surface of the first bearing ring. The first seal element is statically coupled to the holding member. The second seal element is dynamically coupled to the holding member and/or the first seal element.

Description

WIND TURBINE BLADE BEARING AND SEAL ARRANGEMENT

Technical Field

[oooi] This application relates to blade bearings for mounting the blades of a wind turbine to a hub. More specifically, this application relates to a blade bearing with a seal arrangement that can be replaced while the blade bearing remains mounted to the blade and hub.

Background

[0002] Wind turbines convert the kinetic energy of the wind into rotational mechanical energy. In a horizontal-axis wind turbine, this is achieved by a rotor having large blades configured to be driven by the wind. The rotational mechanical energy is transferred directly or indirectly (e.g. , via drive train) to a generator, which then converts the energy into electrical power. The generator is housed within a nacelle supported on a tower. [0003] A modern wind turbine has many moving parts that facilitate converting the kinetic energy of the wind into electrical energy. As such, a wind turbine typically includes many bearings that provide relative movement between adjacent parts in a relatively efficient, low-friction manner. Most bearings include an inner ring, outer ring, and structural elements (e.g. , balls, rolling elements, or sliding pads) between the inner and outer rings. The structural elements facilitate relative movement between the inner and outer rings. Lubrication is provided between the inner and outer rings to reduce surface fatigue and wear. Although this may prolonging the lifetime of the bearing, there are challenges associated with confining the lubrication to the space between the inner and outer rings. [0004] For example, most bearings include a seal to prevent leakage of lubricant. The seal is typically a rubber element positioned between the inner and outer rings of the bearing. Although conventional seal designs may be satisfactory in many situations, the potential for unintended leakage remains. The seals may wear over time, especially if rust or corrosion develops on the surfaces of the bearing rings. This may compromise the ability of a seal to confine the lubricant between the rings. Additionally, replacement of a worn seal may be difficult or even impossible without removing the bearing given the confined space of a wind turbine. Therefore, replacement may be costly and increase the downtime of the wind turbine.

[0005] Even if a seal does perform effectively, there are indirect costs associated with providing the seal in the first place. To properly secure the seal to one of the bearing rings and have the seal effectively press against the other bearing ring to prevent leakage, the bearing rings must typically be extended in the axial direction. In other words, the bearing rings are first designed with dimensions sufficient to withstand certain loads. To then accommodate the seal, the height (i.e., axial length) of the bearing rings must typically be increased. This added material represents an increase in cost, particularly for larger bearings, such as blade bearings. This increased cost has become more

significant as wind turbines have grown in size because of the desire to capture more of the wind's available energy. Summary

A blade bearing for mounting a blade of a wind turbine to a hub of the wind turbine comprises first and second bearing rings arranged next to each other and a seal arrangement covering a space between the first and second bearing rings. One of the first or second bearing rings is configured to mount to the blade, and the other is configured to mount to the hub. The first and second bearing rings each have an axially- facing surface (e.g., upper or lower surface) and a radially-facing surface. The seal arrangement includes a first seal element statically coupled to the axially-facing surface of the first bearing ring, a second seal element statically coupled to the axially-facing surface of the second bearing ring, and a holding member secured to the axially-facing surface of the first bearing ring. The first seal element is statically coupled to the holding member. The second seal element is dynamically coupled to the holding member and/or the first seal element.

[0006] Unlike conventional blade bearing seals, this seal arrangement separates the dynamic seal interface from the second bearing ring. The dynamic seal interface is instead associated with the holding member, first seal element, or both. As a result, special finishing operations to make a surface on the second bearing ring suitable for a dynamic seal are not necessary. Moreover, the second ring itself can be designed with a shorter axial length (i.e., smaller height) because there is no need for such a dynamic sealing surface. This can represent a considerable savings in material cost given the size of modern wind turbine blade bearings.

[0007] The holding member may be designed in various ways. When the holding member extends over a space between the first and second bearing rings and contacts the first and second seal elements, another term appropriate for the holding member may be "connection member". The holding member in such embodiments effectively establishes a connection (hence the term "connection member") between the first and second seal elements, thereby allowing the seal arrangement to prevent leakage. One example of such a holding member is an annular plate secured to the first bearing ring at several locations and effectively pressed (i.e., pre-tensioned) against the first and second seal elements. The contact statically couples the plate to the first seal element and dynamically couples the plate to the second seal element. In other examples, different parts may be provided for the coupling and pre-tensioning functions— a first part contacting the first and second seal elements, and a second part secured to the first bearing ring and pressing against the first part.

[0008] These and other embodiments will be described in further detail below, making their advantages more readily apparent. Brief Description of the Drawings

[0009] Fig. 1 is a perspective view of a wind turbine.

[ooio] Fig. 2 is an exploded perspective view of a portion of the wind turbine shown in Fig. 1.

[ooii] Fig. 3 is an enlarged perspective view of a portion of a blade bearing according to one embodiment of the invention.

[0012] Fig. 4 is a cross-sectional view taken along line 4— 4 in Fig. 3.

[0013] Fig. 4A is an enlarged cross-sectional view of a portion of the blade bearing.

[0014] Fig. 4B is an enlarged cross-sectional view similar to Fig. 4A but showing one specific, non-limiting example of a spring element design used in a sealing arrangement of the blade bearing.

[0015] Fig. 5 is a cross-sectional view of a blade bearing according to an alternative embodiment of the invention. [0016] Fig. 6 is a cross-sectional view of a blade bearing according to another embodiment of the invention.

[0017] Fig. 6A is a cross-sectional view of a variation of the blade bearing shown in Fig. 6.

[0018] Fig. 7 is a cross-sectional view of a blade bearing according to yet another embodiment of the invention.

Detailed Description

[0019] Fig. 1 shows one example of a wind turbine 2. The wind turbine 2 includes a rotor 4 having blades 6 mounted to a hub 8, which is supported by a nacelle 10 on a tower 12. Although an onshore, three-bladed, horizontal-axis wind turbine is shown, it should be noted that the description below may be applicable to other types of wind turbines. Indeed, the description below focuses on particular component common to most wind turbines, namely blade bearings for mounting the blades to the hub.

[0020] Figs. 2-4A illustrate one example of a blade bearing 20. The blade bearing 20 includes first and second bearing rings 22, 24 arranged next each other. The first bearing ring 22 is configured to mount to the blade 6 via bolts (not shown) extending through bolt holes 26. The second bearing ring 24 is configured to mount to the hub via bolts 28 extending through bolt holes 30. Thus, the first bearing ring 22 is movable relative to the second bearing ring 24, which is considered stationary (in a relative sense). One or more rows of rolling elements 32 (e.g., balls or rollers; Fig. 4) are positioned between the first and second bearing rings 22, 24 to facilitate this relative movement. In other

embodiments, the first bearing ring 22 may be positioned radially outward relative to the second bearing ring 24. Another alternative is that the first bearing ring 22 may be mounted to the hub 8 and the second bearing ring 24 may be mounted to the blade 6. [0021] Now referring to Figs. 4 and 4A, the blade bearing 20 further includes a seal arrangement 40 configured to cover a space between the first and second bearing rings 22, 24. The seal arrangement 40 includes a seal element for each bearing ring— i.e. , a first seal element 42 associated with the first bearing ring 22 and a second seal element 44 associated with the second bearing ring 24. Different shapes, types, and mountings of the seal elements are possible. In the embodiment shown in Figs. 3-4A, the first and second seal elements 42, 44 are positioned in recesses 46, 48 (e.g. , grooves) formed on axially-facing surfaces 50, 52 of the respective first and second bearing rings 22, 24. The first seal element 42 in this embodiment comprises a single o-ring made from rubber, and the second seal element 44 comprises a strip of plastic (e.g., PTFE). The second seal element 44 sits on one or more spring elements 54 in the groove 48, the purpose of which will be described in greater detail below.

[0022] The seal arrangement 40 further includes a holding member 60 secured to the first bearing ring 24. In the embodiment shown in Figs. 3 and 4, the holding member 60 comprises an annular plate secured to the first bearing ring 22 at several locations by bolts 62. The holding member 60 contacts the first seal element 42. Because there is no relative movement between the holding member 60 and first bearing ring 22, the first seal element 42 is statically coupled to these components. Therefore, such an arrangement results in a static seal during operation.

[0023] The holding member 60 also extends over the space between the first and second bearing rings 22, 24 and eventually contacts the second seal element 44. Here, however, the holding member 60 is dynamically coupled to the second seal element 44 (i.e., a dynamic seal is formed). In particular, the holding member 60 moves with the first bearing ring 22 relative to the second bearing ring 24; the second seal element 44 does not. Instead, the second seal element 44 remains stationary with respect to the second bearing ring 24 (i.e., statically coupled to the second bearing ring 24) so that there is sliding contact with a lower surface 66 of the holding member 60. There are many ways to ensure this occurs. For example, the material properties of the components may be selected to provide higher friction at the interface of the second sealing element 44 with the second bearing ring 24 and/or spring element 54 compared to the interface of the second sealing element 44 with the holding member 60. Thus, the axial ly-facing surface 52 of the second bearing ring 24 may have a first coefficient of friction and the lower surface 66 of the holding member 60 may have a second coefficient of friction that is less than the first coefficient of friction. The holding member 60 may be formed from metal with the lower surface 66 being polished, for example.

[0024] Alternatively or additionally, the second seal element 44 may be secured to the second bearing ring 24 by an interference fit, fasteners, or other conventional means. Other ways resulting in the second seal element 44 being statically coupled to the second bearing ring 24 and dynamically coupled to the holding member 60 will be appreciated by persons skilled in blade bearing seal designs. The various ways result in the interface between the second seal element 44 and holding member 60 forming a dynamic seal. [0025] Having a static seal formed with the first seal element 42 and a dynamic seal formed with the second seal element 44, the holding member 60 in this embodiment effectively "connects" the first and second seal elements 44, thereby allowing the seal arrangement 40 to prevent leakage from the space between the first and second bearing rings 22, 24. An alternative term for the holding member 60 may therefore be

"connection member". Several particular advantages are provided by separating the dynamic seal interface from the second bearing ring 24 and associating it with the holding member 60 instead. Unlike conventional designs, the second bearing ring 24 does not need a dedicated surface to form a dynamic seal with a seal element. Special finishing operations to make such a dedicated surface suitable for a dynamic seal are therefore not necessary.

[0026] Moreover, the dedicated surface in conventional designs typically results in a longer axial length such that there is a large offset between the upper surfaces of adjacent bearing rings. By eliminating the need for such a dedicated surface, dimensions of the first and second bearing rings 22, 24 can be kept to a minimum (i.e. , closer to the minimum dimensions required to withstand loads), as may the offset between their respective upper surfaces (axially-facing surfaces 50, 52). For example, in large blade bearings the first and second bearing rings 22, 24 may have axial lengths greater than 200 mm, but the upper surface of the second bearing ring may be arranged in a plane less than 5 mm offset from a plane including the upper surface of the first bearing ring 22. Even in smaller blade bearings the offset of the upper surfaces may be less than 3% of the axial length of the first bearing ring 22. The reduction in bearing ring material represents a considerable cost savings.

[0027] Note that blade bearings experience significant loads and, due to their unique loading, are susceptible to greater deflections than other large bearings in a wind turbine. The one or more spring elements 54 help the seal arrangement 40 accommodate these deflections so that the sealing function of the seal arrangement 40 is maintained. A generic spring element 54 is shown in Figs. 4 and 4A because many different

designs/arrangements are possible for this purpose. One specific example is shown in Fig. 4B, where two o-rings 54a, 54b are stacked on top of each other in the groove 48. The o-rings 54a, 54b are compressed by the holding member 60 pressing the second seal element 44 against the uppermost o-ring 54a. If there are deflections of the first or second bearing ring 22, 24 in the axial direction, the resiliency of the o-rings 54a, 54b helps maintain contact between the second seal element 44 and holding member 60. The stacked arrangement of the o-rings 54a, 54b helps accommodate greater deflections in the axial direction without increasing the width of the groove 48 (e.g. , to accommodate a single, larger o-ring).

[0028] Thus, the resiliency of the seal arrangement 40 is primarily provided by the o- rings 54 rather than the second seal element 44. The o-rings 54 are made of a flexible material, such as rubber. Separating the flexibility and resiliency of the seal arrangement 40 from its sealing function makes it easier to use a harder material for the second seal element 44. For example, as mentioned above, the second seal element 44 may be formed from PTFE or a similar plastic material. Such materials are generally more resistant to wear than rubber, which typically forms the dynamic seals in existing designs. As a result, wind turbines with the seal arrangement 40 may be operated for longer periods of time before replacement of the seal arrangement 40 is required.

[0029] Even if replacement is eventually required, the seal arrangement 40 has the advantage of allowing the procedure to be performed without removing the blade bearing 20 from the blade 6 or hub 8. The holding member 60 is releasable from the second bearing ring 24 when the blade bearing 20 is mounted. For example, in the embodiment shown in Figs. 4 and 4A the bolts 62 may be accessed and removed while the first bearing ring 22 remains mounted to the blade 6. This allows the holding member 60 to be moved away from the second seal element 44, which may then be accessed and removed itself.

[0030] After removing the second seal element 44 from the axially-facing surface 52 of the second bearing ring 24, a new seal element may be positioned on the axially-facing surface 52 (and into the groove 48) to replace the second seal element 44. The holding member 60 is then re-secured to the first bearing ring 22 if it was previously fully released from the first bearing ring 22. If it was never fully released to access and replace the second seal element 44, the holding member 60 is simply restored to its fully secured position by re-tightening the bolts 62. Either way, the holding member 60 is moved into contact with the new seal element so that a dynamic seal may once again be formed. [0031] Again, this procedure may take place while the first and second bearing rings 22, 24 remain mounted to the blade 6 and hub 8. Performing the procedure "up tower" saves the time, cost, and complexity associated with removing a blade bearing.

[0032] Several alternative embodiments will now be described with reference to Figs. 5- 7, where similar reference numbers are used to refer to structures corresponding to those discussed above. In the embodiment shown in Fig. 5, the axially-facing surfaces 50, 52 of the first and second bearing rings 22, 24 terminate in recesses 70, 72 so as to form shoulders or ledges at the respective radially-facing surfaces. The first seal element 42 is positioned on the shoulder of the first bearing ring 22. The second seal element 44 rests against an o-ring 54 (or other spring element) positioned on the shoulder of the second bearing ring 24. As with the embodiment of Figs. 4 and 4A, the second seal element 44 may comprise a strip of plastic material. Here, however, the shape of the second seal element 44 is different due to the different overall design of the seal arrangement 40.

[0033] The holding member 60 in Fig. 5 comprises a strip (e.g. , bar or sheet) of material 78 positioned over the space between the first and second bearing rings 22, 24 and contacting the first and second seal elements 42, 44. The strip 78 may be metal or plastic, as long as friction at the interface between the strip 78 and second seal element 44 is lower than friction at the interface between the second seal element 44 and second bearing ring 24. The latter interface is largely defined by the o-ring 54. The strip 78 is retained against the first and second seals 42, 44 by one or more clamps or brackets 80. In particular, the bolts 62 secure the clamps 80, which in turn extend over the strip 78 and press it against the first and second seal elements 42, 44. There may be one clamp 80 associated with each bolt 62, multiple clamps each associated with several bolts and covering an increased circumferential length of the strip 78, or even a single clamp covering all or substantially all of the strip 78. The strip 78 and clamps 80 are therefore different parts of the holding member 60 providing different functions (one forming seals with the seal elements and the other providing pre-tensioning).

[0034] As can be appreciated, the embodiment of Fig. 5 still offers the advantages mentioned above with respect to the embodiment of Figs. 4 and 4A. The holding member 60 (or "connection member") is dynamically coupled to the second seal element 44, which is statically coupled to the second bearing ring 24 thereby separating the dynamic sealing interface from the second bearing ring 24. The o-ring 54 helps

accommodate deflections and facilitates the use of plastic for the second seal element 44. If desired, in alternative embodiments the first seal element 42 may have a similar construction despite being statically coupled to the holding member 60 and forming a static seal. Thus, the first seal element 42 may alternatively be a strip of plastic like the second seal element 44 and may rest against an o-ring in direct contact with the first bearing ring 22.

[0035] Fig. 6 illustrates a further variant where the first and second seal elements 42, 44 slidably engage each other. Thus, in addition to contacting the holding member 60, the second seal element 44 contacts the first seal element 42. Friction at the interface between the second seal element 44 and second bearing ring 24 (indirectly via the o-ring 54 and/or directly) is still greater than the combined friction of the interfaces the second seal element 44 has with the holding member 60 and first seal element 42. Thus, the second seal element 44 remains statically coupled to the second bearing ring 24 such that the contact with the holding member 60 and first seal element 42 is a dynamic coupling. Both the holding member 60 and first seal element 42 slide relative to the second seal element 44 while contacting it to form dynamic seals.

[0036] The dynamic seal formed between the first and second seal elements 42, 44 in Fig. 6 is sufficient to prevent leakage from the space between the first and second bearing rings 22, 24. Thus, although contact with the holding member 60 may serve as a back-up (i.e., provide redundant sealing), it is not necessary. Fig. 6A, for example, shows a variant where the holding member 60 only extends over and contacts the first seal element 42. An additional holding member 84 secured to the second bearing ring 24 extends over and contacts the second seal element 44. Separate holding members may therefore be provided for the first and second seal elements 42. 44 when the second seal element 44 is dynamically coupled to the first seal element 42.

[0037] Fig. 7 illustrates an alternative embodiment where the second seal element 44 surrounds a portion of the holding member 60. In particular, the second seal element 44 includes a base portion 90 and head portion 92. The base portion 90 is positioned in the recess or groove 48 on the second bearing ring 24. An interference fit may be provided to help maintain a static coupling. The head portion 92 includes upper and lower extensions or "jaws" 94, 96 that extend under and over the holding member 60. Thus, the holding member 60 is effectively received between the upper and lower jaws 94, 96 of the head portion 92. A dynamic coupling characterizes the interfaces with the upper and lower jaws 94, 96, as the holding member 60 is able to slide relative to the second seal element 44. This results in dynamic seals being formed by each of the upper and lower jaws 94, 96, thereby providing the sealing arrangement 40 with some redundancy.

[0038] The embodiments described above are merely examples of the invention defined by the claims that appear below. Additional embodiments, modifications, and advantages will be appreciated by skilled persons based on the description. For example, although seal arrangements are described above in connection with the upper surfaces of the first and second bearing rings, similar seal arrangements may be used on the other side of the bearing. Thus, seal arrangements may be provided for either or both axially-facing surfaces of the first and second bearing rings.

[0039] Skilled persons will also understand how features of the various embodiments may be combined in different ways. With this in mind, the details of any particular embodiment described above should not be seen to necessarily limit the scope of the claims below.

Claims

1. A blade bearing for mounting a blade of a wind turbine to a hub of the wind turbine, comprising:

first and second bearing rings arranged next to each other, one of the first or second bearing rings being configured to mount to the blade and the other being configured to mount to the hub, wherein the first and second bearing rings each have an axially-facing surface and a radially-facing surface; and

a seal arrangement covering a space between the first and second bearing rings, the seal arrangement including:

a first seal element statically coupled to the axially-facing surface of the first bearing ring;

a second seal element statically coupled to the axially-facing surface of the second bearing ring; and

a holding member secured to the axially-facing surface of the first bearing ring and statically coupled to the first seal element, wherein the second seal element is dynamically coupled to the holding member and/or the first seal element.

2. A blade bearing according to claim 1 , wherein the first holding member is a plate extending over the space between the first and second bearing rings, the plate being secured to the first bearing ring at several locations.

3. A blade bearing according to claim 1 or 2, wherein the second seal element is dynamically coupled to the holding member and spaced from the first seal element.

4. A blade bearing according to any of the preceding claims, wherein the second bearing ring includes a surface with a first coefficient of friction and the holding member includes a surface with a second coefficient of friction that is less than the first coefficient of friction.

5. A blade bearing according to any of the preceding claims, wherein the second seal element is positioned in a recess in the axially-facing surface of the second bearing ring.

6. A blade bearing according to claim 5, wherein the recess in the axially-facing surface of the second bearing ring is a groove spaced from the radially-facing surface.

7. A blade bearing according to any of the preceding claims, wherein the second seal element is coupled to the second bearing ring by an interference fit in a portion of the second bearing ring.

8. A blade bearing according to any of the preceding claims, wherein the first and second bearing rings have axial lengths of at least 200 mm, and further wherein the axially-facing surface of the second bearing ring is arranged in a plane less than 4 mm offset from a plane including the axially-facing surface of the first bearing ring.

9. A blade bearing according to any of the preceding claims, wherein the axially-facing surface of the second bearing ring is arranged in a plane offset from a plane including the axially-facing surface of the first bearing ring, the offset being less than 2% of an axial length of the first bearing ring.

10. A blade bearing according to any of the preceding claims, wherein the seal arrangement further comprises:

at least one spring element positioned between the second seal element and the second bearing ring, the holding member extending over the second seal element and the at least one spring element.

1 1 . A blade bearing according to claim 10, wherein the at least one spring element comprises rubber and the second seal element comprises plastic.

12. A blade bearing according to any of claim 1 -9, wherein the second seal element surrounds a portion of the holding member.

13. A blade bearing according to claim 1 , wherein the seal arrangement further comprises:

an additional holding member secured to the axially-facing surface of the second bearing ring and statically coupled to the second seal element, wherein the first and second seal elements slidably engage each other.

14. A wind turbine, comprising:

a hub;

a blade; and a blade bearing according to any of the preceding claims rotatably mounting the blade to the hub, wherein the holding member is releasable from the second bearing ri when the blade bearing is mounted.

15. A wind turbine according to claim 14, wherein the first bearing ring is mounted to the blade and the second bearing ring is mounted to the hub.

16. A method of servicing a blade bearing according to any of claims 1 -13 when one of the first or second bearing rings is mounted to the blade and the other is mounted to the hub, the method comprising:

(a) moving the holding member or additional holding member away from the second seal element to provide access thereto;

(b) removing the second seal element from the axially-facing surface of the second bearing ring;

(c) positioning a new seal element on the axially-facing surface of the second bearing ring to replace the second seal element; and

(d) moving the holding member or additional holding into contact with the new seal element to form a dynamic seal with the new seal element,

wherein the first and second bearing rings remain mounted to the blade and hub during steps (a)-(d).