Centering sleeve, centering fastener, rotor blade of a wind turbine, and method of mounting a rotor blade to a hub of a wind turbine

Abstract

The present invention generally relates to a centering sleeve, a centering fastener with such a centering sleeve, a rotor blade of a wind turbine, and a method of mount- ing a rotor blade to a hub of a wind turbine using at least one such centering fastener In some illustrative embodiments herein, a centering sleeve 100 for a stud bolt of a rotor blade of a wind turbine is provided, wherein the centering sleeve comprises a cylindrically shaped sleeve body 101 formed of a material being softer than the stud bolt it is intended for use with.

Description

[0001] Centering Sleeve, Centering Fastener, Rotor Blade of a Wind Turbine, and Method of Mounting a Rotor Blade to a Hub of a Wind Turbine

[0002] BACKGROUND OF THE INVENTION

[0003] 1 . Field of the invention

[0004] The present invention relates to a centering sleeve, a centering fastener with such a centering sleeve, a rotor blade of a wind turbine, and a method of mounting a rotor blade to a hub of a wind turbine using at least one such centering fastener.

[0005] 2. Description of the related art

[0006] Wind turbines with wind turbine rotor blades are used to convert wind energy into electrical energy. A number of components of wind turbines are connected by means of a flange connection. For example, rotor blades have a have a rotor blade connection with a number of holes formed in a laminate of a rotor blade in the area of a rotor blade root. Typically, wind turbines are erected in areas with superior wind conditions such as rural areas comprising only a few obstacles. Wind turbines are erected with increasingly higher towers and rotor blades in order to most efficiently use the wind.

[0007] Fastening bolts (or studs) represent main connecting fasteners which play an important role in positioning and connecting the rotor blades of a wind turbine generator. When the wind turbine is in operation, and among others due to the complicated working conditions, the bolt or stud connections between parts are loaded complicat- edly and are subjected to variable loads, thereby requiring bolts or studs e.g. to have certain strength and size.

[0008] Typically, a large number of high-strength connecting bolts are evenly distributed around these connected components, for example, the high-strength connecting bolts are used for connection between tower segments, connection between a yaw bearing and a base, connection between a pitch bearing and a hub and connection of blades. However, and as an example, due to the conditions that installation of components such as wind turbine blades will sometimes take place under, and so as also to provide even further consistency and ease of installation, and subsequent also reliability of operation, the herein disclosed technology has been devised.

[0009] Currently, one method of blade installation, includes blade installation tools attached instead of some blade studs before installation of rotor blades on a rotor hub.

[0010] SUMMARY OF THE INVENTION

[0011] In a first aspect of the present disclosure, a centering sleeve for a stud bolt of a rotor blade of a wind turbine is provided. In accordance with illustrative embodiments of the first aspect, the centering sleeve comprises a cylindrically shaped sleeve body formed of a material being softer than the stud bolt it is intended for use with. Such a centering sleeve allows for streamlining assembly processes such that time and effort during flange connection assembly is saved.

[0012] In some illustrative embodiments of the first aspect, the material may be a thermoplastic material, such as a material comprising polyamide. Accordingly, the centering sleeve is adaptable to various designs and provides for reliable alignment even when exposed to varying loads. In some special example herein, the material may be nylon and the centering sleeve may be provided as a low-friction component. In some alternative embodiments herein, the material may be other than a plastic material, e.g. a soft metal able to be deformed.

[0013] In some other illustrative embodiments of the first aspect, the cylindrically shaped sleeve body may have a lengthwise slit completely extending along the cylindrically shaped sleeve body. Accordingly, the centering sleeve body may be adapted to varying stud bolt dimensions. In some illustrative examples herein, the slit may have an azimuthal extension range defined by an azimuthal angle out of a range from about 30° to about 180°, preferably from about 60° to about 120°, more preferably from about 90° to about 110°. Accordingly, reliable mounting of the centering sleeve on stud bolts may be achieved. According to an embodiment, the cylindrically shaped sleeve body is a one-piece body, such as a one-piece and monolithic construction. Accordingly, the cylindrically shaped sleeve body may be one-piece construction made from the same single material.

[0014] In some other illustrative embodiments of the first aspect, the cylindrically shaped sleeve body may have conically tapering end portions at opposite ends in a lengthwise direction of the cylindrically shaped sleeve body. In some illustrative examples herein each conically tapering end may have a tapering in a range from about 5° to about 20°, preferably from about 5° to about 15°, more preferably from about 8° to about 12°. One possible advantage of such conical shape can be seen to be easier insertion of the stud bolt it is intended for use with into a hole for the stud bolt with the sleeve.

[0015] In some other illustrative embodiments of the first aspect, the cylindrically shaped sleeve body may have a mesh structure. Accordingly, tangential mechanical stress acting an outer surface of the cylindrically shaped sleeve body may be absorbed.

[0016] In some other illustrative embodiments of the first aspect, the centering sleeve may have an inner diameter of the same or substantially the same as an outer diameter of a part of the stud bolt it is intended for use with when applied to the stud bolt. Accordingly, the centering sleeve may be reliably fixed to a stud bolt.

[0017] In some other illustrative embodiments of the first aspect, the centering sleeve may have an outer diameter of slightly less, such as 1 to 5% less, than an inner diameter of a through hole of a hub for receiving the stud bolt which the centering sleeve is intended for. Accordingly, reliable alignment of the stud bolt may be achieved in a flange connection.

[0018] In some other illustrative embodiments of the first aspect, the cylindrically shaped sleeve body may have a Rockwell Hardness of about R115 to about R120. Accordingly, the centering sleeve may reliable align a stud bolt in a flange connection and protect the stud bolt against unwanted mechanical stress during flange connection assembly, but still at least in part absorb any later transfer of forces should the bolt with the sleeve touch an inner diameter of a hole in which the stud is inserted.

[0019] In a second aspect of the present disclosure, a centering fastener for a rotor blade of a wind turbine is provided. In illustrative embodiments of the second aspect, the centering fastener comprises a stud bolt having two threaded ends oppositely arranged along a length direction of the stud bolt, and the centering sleeve according to the first aspect. The centering sleeve is arranged on an at least part of a bolt section extending between the two threaded ends. Accordingly, the centering fastener allows for streamlining assembly processes such that time and effort during flange connection assembly is saved, e.g. as no alignment tool is necessary which is to be replaced after alignment by a stud bolt.

[0020] In some illustrative embodiments, the centering sleeve may be removably fixed on the at least part of the bolt section extending between the two threaded ends, preferably snapped on the bolt section extending between the two threaded ends. Accordingly, stud bolts may be easily provided as alignment tools without having to replace the alignment tools after assembly. Alternatively, the centering sleeve may be permanently fixed on the at least part of the bolt section extending between the two threaded ends, preferably glued on the bolt section extending between the two threaded ends. Accordingly, centering sleeves may be reliably mounted to stud bolts.

[0021] In some other illustrative embodiments of the second aspect, the centering sleeve may be arranged along 5-70 percent of the length of the bolt section extending between the two threaded ends, such as 5-45 percent or such as 5-25 percent. Herein, the centering sleeve may be arranged on the stud bolt closer to one end of the stud bolt, preferably closer towards the blade root than the opposite end of the stud, such that the centering sleeve may be reliably arranged outside of a rotor blade to support alignment of the stud bolt during flange connection assembly.

[0022] In some other illustrative embodiments of the second aspect, the centering fastener may further comprise at least one second centering sleeve arranged on the bolt section extending between the two threaded ends. In some other illustrative embodiments of the second aspect, the bolt section extending between the two threaded ends may be at least in part a non-threaded bolt section, such as at least in part a bolt section having a diameter of one of the threaded ends minus a depth of a thread of one of the threaded ends or substantially having a diameter of one of the threaded ends minus a depth of a thread of one of the threaded ends. Accordingly, a reliable mechanical contact between the centering sleeve and the stud bolt is achieved.

[0023] In general, at least an extension of the bolt section, such as the extension intended to have the sleeve attached thereon, or an extension which is at least as long as the sleeve, may have a diameter which is smaller than the diameter of the threaded ends, i.e. a diameter of the threaded ends that includes the height of the thread.

[0024] In a third aspect of the present disclosure, a rotor blade of a wind turbine is provided. In illustrative embodiments of the third aspect, the rotor blade has a rotor root portion with plural mounting openings formed in the rotor blade at the rotor root portion, the mounting openings extending along a length direction of the rotor blade into the rotor root portion, and at least one centering fastener, each of which being provided by the centering fastener of the second aspect and inserted into a respective one of the mounting openings, wherein a first threaded end of the centering fastener is in mechanical engagement with a threaded portion of the mounting opening, the bolt section extending between the two threaded ends having an exposed section extending out of the mounting opening and the centering sleeve being only arranged on at least part of the exposed bolt section extending between the two threaded ends. Accordingly, a reliable rotor blade connection is provided.

[0025] In a fourth aspect of the present disclosure, a method of mounting a rotor blade to a hub of a wind turbine is provided. In illustrative embodiments of the fourth aspect, the method comprises providing the rotor blade, the rotor blade having a rotor root portion with plural mounting openings formed in the rotor blade at the rotor root portion, the mounting openings extending along a length direction into the rotor root portion, inserting stud bolts into the plural mounting openings for equipping each mounting opening with a respective stud bolt, each stud bolt having two threaded ends oppositely arranged along a length direction of the stud bolt and a bolt section extending between the two threaded ends, wherein a first threaded end of the stud bolt is in mechanical engagement with a threaded portion of the mounting opening, the bolt section extending between the two threaded ends and being exposed extending out of the mounting opening, on at least one of the stud bolts, arranging at least one centering sleeve over at least part of the exposed bolt section extending between the two threaded ends of the stud bolt, the at least one centering sleeve being provided in accordance with the centering sleeve of the first aspect, mounting the rotor blade to the hub, wherein the hub has a plurality of through holes for receiving the stud bolts, each stud bolt inserted into a respective one of the through holes, the at least one centering sleeve of each of the at least one stud bolt being inserted into respective ones of the through holes and second threaded ends of the stud bolts being at least partly passed through the through holes and being at least partly exposed at the hub, and screwing nuts on the exposed second threaded ends of the stud bolts. Accordingly, a streamlined assembly process is provided such that time and effort during flange connection assembly is saved.

[0026] In some other illustrative embodiments of the fourth aspect, arranging the at least one centering sleeve on at least part of one or more bolt sections extending between the two threaded ends may comprise providing the at least one centering sleeve as a shrinking tube on the at least part of a respective bolt section extending between the two threaded ends and shrinking the at least one centering sleeve to said bolt section. Accordingly, an easy and reliable provision of the centering sleeve on a stud bolt is achieved.

[0027] In the various aspects of the present disclosure, guiding of studs during flange connection assembly is achieved, ensuring precise alignment among the flange connection components. Accordingly, improved alignment of the flange connection components is possible where centering sleeves ensure that stud bolts align perfectly with mounting holes in a flange connection. Independently of a centering sleeve being removably fixed or e.g. glued to a bolt, the centering sleeve is intended to remain on the bolt after installation of the blades.

[0028] BRIEF DESCRIPTION OF THE DRAWINGS The invention will be hereinafter described with reference to the accompanying figures, in which:

[0029] Fig. 1 schematically illustrates a wind turbine;

[0030] Fig. 2 schematically illustrates, in a perspective view, a rotor blade of a wind turbine;

[0031] Fig. 3 schematically illustrates in a plane view a rotor blade flange of a rotor root portion;

[0032] Fig. 4 schematically illustrates, in a perspective view, a centering sleeve in accordance with some illustrative embodiments of the present disclosure;

[0033] Fig. 4a schematically illustrates a side view of a section along line a-a in Fig. 4;

[0034] Fig. 4b schematically illustrates a side view of a section along line b-b in Fig. 4a and oriented perpendicular to the paper plane of the illustration in Fig. 4a;

[0035] Fig. 4c schematically illustrates a plane view of the centering sleeve shown in Fig. 4;

[0036] Fig. 5 schematically shows a sectional view of a centering fastener in accordance with some illustrative embodiments of the present disclosure;

[0037] Fig. 5a schematically illustrates a sectional view along line b-b in Fig. 5;

[0038] Fig. 6 schematically illustrates, in a sectional view, a connection of a rotor blade to a rotor hub in accordance with some illustrative embodiments of the present disclosure.

[0039] The Figures accompanying the present disclosure are only provided for schematically showing some concepts and aspects of the present disclosure without showing all possible details of certain embodiments and without necessarily being actually to scale.

[0040] DETAILED DESCRIPTION

[0041] The present invention relates to a centering sleeve, a centering fastener with such a centering sleeve, a rotor blade of a wind turbine, and a method of mounting a rotor blade to a hub of a wind turbine using at least one such centering fastener. The preferred embodiments, as subsequently described, illustrate various embodiments of a centering sleeve and a centering fastener with such a centering sleeve as employed in flange connection of a wind turbine, e.g., in a connection of rotor blade of a wind turbine to a rotor hub of the wind turbine. Furthermore, illustrative embodiments of a method of mounting a rotor blade to a hub of a wind turbine using at least one such centering fastener will be described below with reference to the accompanying drawings.

[0042] Fig. 1 illustrates a wind turbine 1 with a tower 2 and a wind turbine nacelle 3 positioned on top of the tower 2. The wind turbine rotor comprises three rotor blades 5 mounted to a rotor hub 4 which is rotatably connected to the nacelle 3 through a main shaft which extends out of the nacelle front. As illustrated in Fig. 1 , wind beyond a certain level will activate the wind turbine rotor due to the lift induced on the rotor blades 5 and rotate the wind turbine rotor in a direction perpendicular to the wind. The rotational movement of the main shaft is converted via a generator in the wind turbine nacelle 3 to electric power, which may be supplied to the utility grid.

[0043] The rotor blades 5 and a mounting of the rotor blades 5 are now described in greater detail with respect to Fig. 2 and 3.

[0044] Figure 2 shows an exemplary rotor blade 51 which may represent each of the rotor blades 5 of the wind turbine 1 shown in Fig. 1 . The rotor blade 51 has the shape of a conventional rotor blade and extends along a lengthwise direction L as indicated in Fig. 2. The rotor blade 51 has a rotor root portion 5a which faces a rotor hub of a nacelle, such as the rotor hub 4 of the wind turbine 1 shown in Fig. 1 . The rotor root portion 5a has a substantially circular cross-section. The rotor root portion 5a is adjoined by a transition portion 5b and a profile portion 5c of the rotor blade 51 .

[0045] The rotor blade 51 has a suction side 54 and an opposite pressure side with a substantial linear edge at the pressure side. In the rotor root portion 5a, a rotor blade connection 56 with a flange connection 58 is provided, by means of which the rotor blade 51 is mechanically connected to a pitch bearing (not illustrated) provided at the rotor hub (not illustrated - such as rotor hub 4 of wind turbine 1 shown in Fig. 1 ). However, this is not limiting and the rotor blade may be mechanically connected to an extender (not illustrated).

[0046] The flange connection 58 of the rotor blade connection 56 comprises a plurality of holes or thread openings provided in the flange connection 58 of the rotor blade 54, the holes or thread openings extending in the lengthwise direction L into the rotor root portion 5a. The holes or thread openings may be formed circumferentially with equal distance at the flange connection 58.

[0047] Referring to Fig. 3, a flange connector 10 is schematically shown in a plan view along a half circle of the flange connector 10. The flange connector 10 may comprise the flange connection 58 of the rotor blade 51 shown in Fig. 2 in that an inner laminate layer 11 and an outer laminate layer 12 of the rotor blade 51 is shown. The inner and outer laminate layers 11 , 12 end at the flange connection 58 of the rotor blade 51 of Fig. 2 with holes or thread openings 14 with an internal thread. In some examples, the holes may have steel sleeves with internal thread inserted therein. However, it is also conceivable that no sleeve is flange inserted and internal threads may be directly drilled into holes of the flange connection 58 so as to provide threaded holes.

[0048] Referring to Fig. 1 , the rotor blades 5 may be mounted to the rotor hub 4 as not described in connection with the rotor blade 51 of Fig 2 and the flange connector 10 of Fig. 3. When mounting a rotor blade to a rotor hub, e.g., mounting one of the rotor blades 5 to the rotor hub 4 of the wind turbine 1 , stud bolts are inserted into holes of a flange connection of the rotor blade, e.g., inserting stud bolts (not illustrated) into holes 14 of the flange connector 10 shown in Fig. 3. The rotor blade equipped with stud bolts is mounted to the rotor hub, e.g., a bearing ring of the rotor hub, the bearing ring having through holes corresponding to the holes of the flange connection of the rotor blade, wherein stud bolts are aligned with the through holes so as to at least insert the stud bolts into the through holes in a one to one correspondence. Upon fastening nuts to ends of the stud bolts inserted into the through holes, the rotor blade is mechanically mounted to rotor hub. Herein, aligning of the stud bolts with respect to the through holes is very important.

[0049] Referring to Fig. 4, a centering sleeve 100 is schematically shown in a perspective view. The centering sleeve 100 is configured for use with a stud bolt (not illustrated) of a rotor blade (not illustrated), such as the rotor blade 51 and flange connector 10 as described above with respect to Fig. 2 and 3.

[0050] As shown in Fig. 4, the centering sleeve 100 comprises a cylindrically shaped sleeve body 101. The cylindrically shaped body 101 may be monolithic and formed of a material softer than the stud bolt (not illustrated) it is intended for use with. For example, the material may be a thermoplastic material, such as a material comprising polyamide. However, this does not impose any limitation and the material may be other than a plastic material, e.g. a soft metal able to be deformed. In an example, the cylindrically shaped body 101 may be softer than steel such as softer than stainless steel.

[0051] With ongoing reference to Fig. 4, the cylindrically shaped sleeve body 101 has a lengthwise slit 104 completely extending along the cylindrically shaped sleeve body 101. A lengthwise direction is a direction along which the cylindrically shaped sleeve body 101 has a maximum dimension. The lengthwise slit 104 supports a mechanical deformability of the centering sleeve 100, allowing an easy mechanical arrangement of the centering sleeve 100 on a stud bolt (not illustrated) as described below in greater detail. The deformability, and ability to return to its initial shape, of the centering sleeve may be further improved by a groove 102 formed in an inner surface 100s of the centering sleeve. For example, the groove 102 may be of a rounded shape in sectional view and may extend in alignment with the lengthwise direction of the centering sleeve 100 or may extend substantially in alignment with the lengthwise direction of the centering sleeve 100. Referring to Fig. 4a, a side view of a section of the centering sleeve 100 along line a- a in Fig. 4 is illustrated. The slit 104 has an azimuthal extension range defined by an azimuthal angle a. The azimuthal angle a may be in a range from about 30° to about 180°, preferably from about 60° to about 120°, more preferably from about 90° to about 110°. The azimuthal angle a is measured in an azimuthal direction which indicates a direction in a plane perpendicular to the lengthwise direction.

[0052] An edge of the slit 104 may have a widening edge portion 105 and a radial edge portion 106 which radially or substantially radially extends towards and outer surface of the cylindrically shaped sleeve body 101. The widening edge portion 105 may be formed between the inner surface 100s and the radial edge portion 106 and may be inclined relative to a radial direction intersecting an edge between the inner surface 100s and the widening edge portion 105 at an angle out of a range from about 30° to about 60°, such as about 40° to about 50°, e.g., at about 45°.

[0053] A ratio between a width of the widening edge portion 105 to a width of the radial edge portion 106 (a width of each of the portions 105 and 106 being understood as indicating a dimension of each portion measured along an azimuthal direction in a plane perpendicular to the lengthwise direction of the cylindrical sleeve body 101 , e.g., an azimuthal direction in the sectional view of Fig. 4a) may be in a range from about 0.5 to 1 .5, such as about 0.8 to about 1 .2, e.g., about 0.9 to about 1.1 and in some special illustrative but non-limiting example at about 1.

[0054] With ongoing reference to Fig. 4a, the centering sleeve 100 has an inner diameter D1 of the same or substantially the same quantity as an outer diameter of a part of the stud bolt (not illustrated) it is intended for use with when applied to the stud bolt (not illustrated).

[0055] In some illustrative embodiments, the centering sleeve 100 may have an outer diameter D2 of slightly less than an inner diameter of a through hole (not illustrated) of a hub (not illustrated) for receiving the stud bolt (not illustrated) which the centering sleeve 100 is intended for. Herein, slightly less may be understood as 1 to 5% less. Referring to Fig. 4 and 4b, the centering sleeve 100 in accordance with some illustrative embodiments is illustrated, Fig. 4b illustrating the centering sleeve 100 in a side view along a cross-section perpendicular to line b-b in Fig. 4a and perpendicular to the paper plane of Fig. 4a. As shown in Fig. 4b, the cylindrically shaped sleeve body 101 has conically tapering end portions 100a and 100b at opposite ends in the lengthwise direction of the cylindrically shaped sleeve body 101. The conically tapering end portions 100a and 100b having surface portions tilted by an angle p with respect to a sleeve portion 100c extending between the conically tapering end portions 100a and 100b. The sleeve portion 100c may be substantially oriented such that a virtual line may be constructed which may extend within a surface of the sleeve portion 100c and collinear to a center line CL of the sleeve body 100, e.g., virtual line VL shown in Fig. 4b. The virtual line VL is oriented along the lengthwise direction of the centering sleeve 100. In some illustrative embodiments herein, each of the conically tapering ends 100a and 100b has a tapering angle p in a range from about 5° to about 20°. For example, the angle p may be in a range from about 5° to about 15°, e.g., from about 8° to about 12°.

[0056] In some illustrative embodiments, a thickness of the centering sleeve 100 may be constant along the sleeve portion 100c and may be decreasing at least at one of the conically tapering end portions 100a and 100b towards an edge of the conically tapering end portions 100a and 100b.

[0057] Referring to Fig. 4c, a plan view of the centering sleeve 100 of Fig. 4 is shown. In some illustrative embodiments, the sleeve portion 100c of the cylindrically shaped sleeve body 101 may have a length dimension L1 in a range from about 20 mm to about 70 mm, e.g., in a range from about 30 mm to about 60 mm such as in a range from about 45 mm to about 55 mm. For example, the length L1 may be 50 mm. A length L2 of the cylindrically shaped sleeve body 101 may be in a range from about 60 mm to about 100 mm, preferably from about 80 mm to about 95 mm, more preferably from about 85 mm to about 90 mm. A ration L1 / L2 may be in a range from about 0.2 to 0.8 such as in a range from about 0.4 to about 0.6, e.g., from about 0.50 to about 0.60. For example, at about 0.55. In some illustrative embodiments, the cylindrically shaped sleeve body 101 may have a mesh structure. For example, the whole centering sleeve 100 may be formed as a mesh, or a material with an immense amount of holes and configuring the material such that transfer of orthogonal loads and forces in the centering sleeve 100 is suppressed. Herein, orthogonal loads and forces is understood as mechanical loads and forces acting substantially tangential to an outer surface of the centering sleeve 100.

[0058] In some illustrate but non-limiting examples, the cylindrically shaped sleeve body 101 may have a Rockwell Hardness of about R115 to about R120. The Rockwell Hardness may be chosen for 'harder' plastics such as nylon, polycarbonate, polystyrene, and acetal where the resiliency or creep of the polymer is less likely to affect the results. Measuring the Rockwell Hardness may use the Ball Indentation Hardness test according to ISO 2039-1 I DIN 53456 which is used in Europe much more often than in North America. In a specific illustrative but non-limiting test, a specimen of at least 1 / 4 inches (6.4 mm) thickness may be indented by a steel ball, where a small load is applied, the apparatus is zeroed, and then a larger load is applied and removed, the remaining indentation being read from the scale after a short time with the preload still applied. The referenced disclosure is incorporated in entirety by reference.

[0059] With reference to Fig. 5, a centering fastener 200 in accordance with some illustrative embodiments is schematically illustrated in a cross-sectional view. The centering fastener 200 is adapted to or may be configured for use as a fastening means of a rotor blade of a wind turbine, such as one of the rotor blades 5 of the wind turbine 1 shown in Fig. 1 as described with respect to the rotor blade 51 disclosed in Fig. 2 in conjunction with the description above. For example, the centering fastener 200 may be employed in the flange connector 10 described above and the disclosure of which is incorporated by reference in its entirety as will become apparent from the following description.

[0060] The centering fastener 200 comprises a stud bolt 201 having two threaded ends 202a and 202b oppositely arranged along a length direction of the stud bolt 201. A length direction may be identified with a direction along which the stud bolt 201 has a maximum dimension. The stud bolt 201 may be a stud bolt of a wind turbine blade as described above. The centering fastener 200 further comprises a centering sleeve 100 which may correspond to the centering sleeve 100 as described above with respect to Fig. 4 and 4a to 4c. As shown in Fig. 5, the centering sleeve 100 is arranged on an at least part of a bolt section 203 extending between the two threaded ends 202a and 202b.

[0061] Referring to Fig. 5a, some illustrative embodiments are described. Fig. 5a shows a schematic cross section along line a-a in Fig. 5. The centering sleeve 100 partially surrounds the stud bolt 201 on the bolt section 203 such that a surface portion of the bolt section 203 is exposed by a slit 204 with slit edge portions 204 and 205. For example, the centering sleeve 100 may surround the bolt section 203 by at least 180°, e.g., at least 240° or at least 230°. In some illustrative embodiments, the slit 204 may correspond to the slit 104 with the edge portions 104 and 105.

[0062] With ongoing reference to Fig. 5 and 5a, the centering sleeve 100 may be removably fixed on the at least part of the bolt section 203 extending between the two threaded ends 202a and 202b. For example, the centering sleeve 100 may be snapped on the bolt section 203 extending between the two threaded ends 202a and 202b and clamped to the at least part of the bolt section 203 such that any sliding movement of the centering sleeve 100 is suppressed or inhibited. In this case, there is no gap between the bolt section 203 and the centering sleeve 100 and the centering sleeve 100 is in direct mechanical contact with the bolt section 203.

[0063] Independently of the centering sleeve(s) being removably fixed or e.g. glued to the centering sleeve, the centering sleeve(s) are intended to remain on the bolt(s) after installation of the blades.

[0064] In some other illustrative embodiments, the centering sleeve 100 may be permanently fixed on the at least part of the bolt section 203 extending between the two threaded ends 202a and 202b. For example, the centering sleeve 100 may be glued on the bolt section 203 extending between the two threaded ends 202a and 202b and a gap shown schematically in Fig. 5a may be at least partially filled with a gluing agent.

[0065] Referring to Fig. 5, the centering sleeve 100 may be arranged along 5-70 percent of a length of the bolt section 203 extending between the two threaded ends 202a and 202b along the lengthwise direction of the stud bolt 201. It is also possible that the centering sleeve 100 may have a length so that it extends over the entire length or extends substantially over the entire length of the bolt section 203, e.g. so that the centering sleeve 100 extends over 90-100% of the length of the bolt section. For example, the length of the bolt section 203 may extending along 5-45 percent between the two threaded ends 202a and 202b; 364a, 364b), such as 5-25 percent.

[0066] Although Fig. 5 only shows one centering sleeve 100, this does not impose any limitation and at least one additional centering sleeve 100 may be arranged on the bolt section 203 extending between the two threaded ends 202a and 202b, such as in total two centering sleeves or three centering sleeves or four centering sleeves or more than four centering sleeves are arranged on the bolt section 203 extending between the two threaded ends 202a and 202b.

[0067] With ongoing reference to Fig. 5, the bolt section 203 extending between the two threaded ends 202a and 202b may be at least in part a non-threaded bolt section. For example, the bolt section 203 may be at least in part a bolt section having a diameter of one of the threaded ends 202a, 202b minus a depth of a thread of one of the threaded ends 202a, 202b or substantially having a diameter of one of the threaded ends 202a, 202b minus a depth of a thread of one of the threaded ends 202a, 202b.

[0068] Referring to Fig. 6, a flange connection 300 of rotor blade 310 of a wind turbine with a hub 340 of the wind turbine is shown, where the rotor blade 310 may correspond to one of the rotor blades 5 of the wind turbine 1 disclosed above in combination with Fig. 1 and the rotor blade 51 disclosed above in combination with Fig. 2. That is, the flange connection 300 may correspond to the flange connection 58 as disclosed above with respect to Fig. 2 and apply to the flange connector 10 as disclosed above with respect to Fig. 3.

[0069] As schematically shown in Fig. 6, the rotor blade 310 has a rotor root portion 320 with plural mounting openings, one of which is schematically shown by mounting opening 320a for ease of illustration. The mounting openings, and in particular the mounting opening 320a, are formed in the rotor blade 310 at the rotor root portion 320 similar to the plurality of holes or thread openings provided in the flange connection 58 of the rotor blade 54 shown in Fig. 2 and the holes or thread openings 14 of the flange connector 10 of Fig. 3.

[0070] With ongoing reference to Fig. 6, the mounting opening 320a extends along a length direction of the rotor blade 310 into the rotor root portion 320, wherein the length direction of the rotor blade 310 may correspond to a direction along which the rotor blade 310 has a maximum dimension. A centering fastener 360 is inserted into the mounting opening 320a and, in general, at least some of the remaining mounting openings may be equipped with centering fasteners and / or at least some others the mounting openings may be equipped with pure stud bolts instead of centering fasteners. Alternatively, all remaining mounting openings may be equipped with either one of centering fasteners and pure stud bolts. Although in the following, the centering fastener 360 is only described with respect to the mounting opening 320a, this does not impose any limitation and the disclosure accordingly applies to each mounting opening equipped with a centering fastener. At least one stud should be equipped with at least one centering sleeve, but preferably at least two, three, four, five, 10 or more stud bolts are each provided with at least one centering sleeve.

[0071] The centering fastener 360 may correspond to the centering fastener 200 as described above in combination with Fig. 5 and 5a.

[0072] As shown in Fig. 6, the centering fastener 360 has a stud bolt 362 with threaded ends 364a and 364b and a bolt section 366 extending between the threaded ends 364a, 364b. The threaded end 364b of the centering fastener 360 is in mechanical engagement with a threaded portion 322 of the mounting opening 320a. For example, the mounting opening 320a may have a threaded sleeve (not illustrated) inserted therein for providing the threaded portion 322 or the threaded portion 322 may be formed in an inner sidewall surface of the mounting opening 320a by cutting the threaded portion 322 into the inner sidewall surface of the mounting opening. The threaded portion 322 may be formed on at least a portion of the inner sidewall surface of the mounting opening 320a. The bolt section 366 extending between the two threaded ends 364a and 364b has an exposed section extending out of the mounting opening 320a. The centering fastener 360 further comprises a centering sleeve 368 which is arranged on at least part of the exposed bolt section 366 extending between the two threaded ends 364a and 364b. The centering sleeve 368 may correspond to at least one of the centering sleeves 100 and 200 as described above.

[0073] Although Fig. 6 shows the shank in a very schematic way, this does not imply any limitation and the bolt section 366 may have same diameter or different diameter when compared to diameter(s) of the threaded ends 364a, 364b, leaving differences in diameters out for simplicity in illustration. For example, the bolt section 366 may be gradually decreasing in diameter in shank diameter beyond the depth of threads of the threaded ends 364a, 364b. In some illustrative but non-limiting examples, the stud bolt 362 may be formed similar or equal to the stud bolt 201 disclosed above with respect to Fig. 5 and the bolt section 366 may be formed similar or equal to the bolt section 203 disclosed above with respect to Fig. 5.

[0074] In some illustrative embodiments, the stud bolt 362 may be inserted into the mounting opening 320a and the centering sleeve 368 may be arranged on the stud bolt 362. Alternatively, the centering fastener 360 as such may be inserted into the mounting opening 320a. Accordingly, one or more mounting openings, including the mounting opening 320a, may be equipped with a stud bolt or a centering fastener. Additionally or alternatively, one or more stud bolts inserted into respective mounting openings may be equipped with a centering sleeve.

[0075] In the flange connection 300 shown in Fig. 6, the rotor blade 310 is mounted to the hub 340. The hub 340 has a plurality of through holes for receiving the stud bolts, for ease of illustration only one through hole 342b with sidewalls 342a is shown. The hub 340 may, for example, comprise a pitching bearing comprising an inner bearing ring 342 and an outer bearing ring 344. As shown in Fig. 6 and without limitation, the through hole 342b may be formed in the inner bearing ring 342. However, this does not imply any limitation and the through hole 342b may be formed in the outer bearing ring 344 instead or the pitch bearing may be omitted in the hub 340.

[0076] The stud bolt 362 of the centering fastener 360 is inserted into the through hole 342b such that the centering sleeve 368 is inserted into the through hole 342b. In illustrative examples herein, the centering sleeve 368 may be completely arranged within the through hole 342b. However, the centering sleeve 368 may alternatively extend out of the through hole 342b and may be partially exposed at the side of the threaded end 364a. As shown in Fig. 6, the centering sleeve 368 provides for a centering alignment of the stud bolt 362 in the through hole 342b and mechanical contact between the stud bolt 362 only occurs via the centering sleeve 368. The threaded end 364a of the stud bolt 362 is at least partly passed through the through hole 342b and is at least partly exposed at the hub 340 as shown in Fig. 6. The flange connection 300 may be completed by a nut element (not illustrated) screwed on the threaded end 364a of the stud bolt 362 and tightened for establishing a tight and secure connection in the flange connection 300.

[0077] In some illustrative embodiments, the centering sleeve 368 may be arranged on the stud bolt 362 via snapping on the centering sleeve 368 onto the at least part of the bolt section 366 extending between the two threaded ends 364a and 364b in the through hole 342b or permanently fixing the centering sleeve 368 on the at least part of the bolt section 366 extending between the two threaded ends 364a and 364b within the through hole 342b.

[0078] In some other illustrative embodiments, the centering sleeve 368 may be arranged on the bolt section 366 extending between the two threaded ends 364a and 364b by providing the centering sleeve 368 as a shrinking tube on the bolt section 366 and shrinking the centering sleeve 368 to said bolt section 366.

[0079] Although Fig. 6 only shows one centering sleeve 368, this does not impose any limitation and at least one additional centering sleeve (not illustrated) may be arranged on the bolt section 366 extending between the two threaded ends 364a, 364b, the at least one additional being either completely arranged within the through hole 342b or being partially exposed at the side of the threaded end 364a of the stud bolt 362.

[0080] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and / or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

[0081] Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about”, “approximately” and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and / or interchanged, such ranges are identified and include all the subranges contained therein unless context or language indicates otherwise. “Approximately” or “substantially” as applied to a particular value of a range applies to both values, and unless other-wise dependent on the precision of the instrument measuring the value, may indicate + / - 10% of the stated value(s).

[0082] The descriptions of the various embodiments of the present invention have been presented for purposes of illustration but are not intended to be exhaustive or limited to the embodiments dis-closed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

Claims1. A centering sleeve (100; 368) for a stud bolt (201 ; 362) of a rotor blade (310) of a wind turbine, wherein the centering sleeve (100; 368) comprises a cylindrically shaped sleeve body (101 ) formed of a material being softer than the stud bolt (201 ; 362) it is intended for use with, wherein the cylindrically shaped sleeve body (101) has a lengthwise slit (104) completely extending along the cylindrically shaped sleeve body (101 ) and wherein the cylindrically shaped sleeve body (101 ) is a one-piece body.2.. The centering sleeve (100; 368) of claim 1 , wherein the material is a thermoplastic material, such as a material comprising polyamide.

3. The centering sleeve (100; 368) of claim 2, wherein the slit (104) has an azimuthal extension range defined by an azimuthal angle out of a range from about 30° to about 180°, preferably from about 60° to about 120°, more preferably from about 90° to about 110°.

4. The centering sleeve (100; 368) of one of claims 1 to 3, wherein the cylindrically shaped sleeve body (101 ) has conically tapering end portions (100a, 100b) at opposite ends in a lengthwise direction of the cylindrically shaped sleeve body (101 ).

5. The centering sleeve (100; 368) of claim 4, wherein each conically tapering end (100a, 100b) has a tapering in a range from about 5° to about 20°, preferably from about 5° to about 15°, more preferably from about 8° to about 12°.

6. The centering sleeve (100; 368) of one of claims 1 to 5, wherein the cylindrically shaped sleeve body (101) has a mesh structure.

7. The centering sleeve (100; 368) of one of claims 1 to 6, wherein the centering sleeve (100; 368) has an inner diameter (D1 ) of the same or substantially the same as an outer diameter of a part of the stud bolt (201 ; 362) it is intended for use with when applied to the stud bolt (201 ; 362).

8. The centering sleeve (100; 362) of one of claims 1 to 6, wherein the centering sleeve (100; 368) has an outer diameter (D2) of slightly less, such as 1 to 5% less, than an inner diameter of a through hole (342b) of a hub (340) for receiving the stud bolt (201 ; 362) which the centering sleeve (100; 362) is intended for.

9. The centering sleeve (100; 362) of one of claims 1 to 8, wherein the cylindrically shaped sleeve body (101 ) has a Rockwell Hardness of about R115 to about R120.

10. A centering fastener (200; 360) for a rotor blade (310) of a wind turbine, wherein the centering fastener (200; 360) comprises a stud bolt (201 ; 362) having two threaded ends (202a, 202b; 364a, 364b) oppositely arranged along a length direction of the stud bolt (201 ; 362), and a centering sleeve (100; 362) of one of claims 1 to 10, the centering sleeve (100; 362) being arranged on an at least part of a bolt section (203; 366) extending between the two threaded ends (202a, 202b; 364a, 364b).

11. The centering fastener (200; 360) of claim 10, wherein the centering sleeve (100; 362) is one of removably fixed on the at least part of the bolt section (203; 366) extending between the two threaded ends (202a, 202b; 364a, 364b), preferably snapped on the bolt section (203; 366) extending between the two threaded ends (202a, 202b; 364a, 364b), and permanently fixed on the at least part of the bolt section (203; 366) extending between the two threaded ends (202a, 202b; 364a, 364b), preferably glued on the bolt section (203; 366) extending between the two threaded ends (202a, 202b; 364a, 364b).

12. The centering fastener (200; 360) of claim 10 or 11 , wherein the centering sleeve (100; 362) is arranged along 5-70 percent of the length of the bolt section (203; 366) extending between the two threaded ends (202a, 202b; 364a, 364b), such as 5-45 percent or such as 5-25 percent.

13. The centering fastener (200; 360) of one of claims 10 to 12, further comprising at least one second centering sleeve arranged on the bolt section extending between the two threaded ends (202a, 202b; 364a, 364b).

14. The centering fastener (200; 360) of one of claims 10 to 13, wherein the bolt section (203; 366) extending between the two threaded ends (202a, 202b; 364a, 364b) is at least in part a non-threaded bolt section, such as at least in part a bolt section having a diameter of one of the threaded ends minus a depth of a thread of one of the threaded ends or substantially having a diameter of one of the threaded ends minus a depth of a thread of one of the threaded ends.

15. A rotor blade (310) of a wind turbine, wherein the rotor blade (310) has a rotor root portion (320) with plural mounting openings (320a) formed in the rotor blade (310) at the rotor root portion (320), the mounting openings (320a) extending along a length direction of the rotor blade (310) into the rotor root portion (320), and at least one centering fastener (360), each of which being provided by the centering fastener of one of claims 10 to 14 and inserted into a respective one of the mounting openings (320a), wherein a first threaded end (364b) of the centering fastener (360) is in mechanical engagement with a threaded portion (322) of the mounting opening (320a), the bolt section (366) extending between the two threaded ends (364a, 364b) having an exposed section extending out of the mounting opening (320a) and the centering sleeve (360) being only arranged on at least part of the exposed bolt section extending between the two threaded ends (364a, 364b).

16. A method of mounting a rotor blade (310) to a hub (340) of a wind turbine, the method comprising: providing the rotor blade (310), the rotor blade having a rotor root portion (320) with plural mounting openings (320a) formed in the rotor blade (310) at the rotor root portion (320), the mounting openings (320a) extending along a length direction into the rotor root portion (320);inserting stud bolts(362) into the plural mounting openings (320a) for equipping each mounting opening (320a) with a respective stud bolt (362), each stud bolt (362) having two threaded ends (364a, 364b) oppositely arranged along a length direction of the stud bolt (36a) and a bolt section (366) extending between the two threaded ends (364a, 364b), wherein a first threaded end (364b) of the stud bolt (362) is in mechanical engagement with a threaded portion (322) of the mounting opening (320a), the bolt section (366) extending between the two threaded ends (364a, 364b) and being exposed extending out of the mounting opening (320a); on at least one of the stud bolts (362), arranging at least one centering sleeve (368) over at least part of the exposed bolt section extending between the two threaded ends (364a, 364b) of the stud bolt (362), the at least one centering sleeve (368) being provided in accordance with the centering sleeve (368) of one of claims 1 to 10; mounting the rotor blade (310) to the hub (340), wherein the hub (340) has a plurality of through holes for receiving the stud bolts, each stud bolt (362) inserted into a respective one of the through holes (342b), the at least one centering sleeve (368) of each of the at least one stud bolt (362) being inserted into respective ones of the through holes (342b) and second threaded ends (364a) of the stud bolts (362) being at least partly passed through the through holes and being at least partly exposed at the hub (340); and screwing nuts on the exposed second threaded ends (364a) of the stud bolts (362).

17. The method of claim 16, wherein arranging the at least one centering sleeve (368) on at least part of one or more bolt sections (366) extending between the two threaded ends (364a, 364b) comprises snapping on the at least one centering sleeve (368) onto the at least part of the bolt section (366) extending between the two threaded ends (364a, 364b) of the at least one stud bolt (362) or permanently fixing the at least one centering sleeve (368) on the at leastpart of the bolt section (366) extending between the two threaded ends (364a, 364b).

18. The method of claim 16, wherein arranging the at least one centering sleeve (368) on at least part of one or more bolt sections (366) extending between the two threaded ends (364a, 364b) comprises providing the at least one centering sleeve (368) as a shrinking tube on the at least part of a respective bolt section (366) extending between the two threaded ends (364a, 364b) and shrinking the at least one centering sleeve (368) to said bolt section (366).

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