A root bushing, a bushing insert thereof, a wind turbine blade including the root bushing and a manufacturing method thereof

Abstract

The present invention relates to a root bushing, a root bushing insert, a wind turbine blade, and a method for manufacturing a wind turbine blade. The root bushing includes a bushing shell having an outer surface and a main bolt cavity. The outer surface is provided with an external threaded portion, which is arranged at a certain distance from a first end. The main bolt cavity has an internal threaded portion arranged at a certain distance from the first end. A cap element is positioned in the bushing shell at a certain distance from the second end and separates the main bolt cavity from the root insert cavity. The root insert cavity has a curved inner surface, which allows resin to fill the space between the inner surface and the end of the insert element.

Description

Technical Field

[0001] The present invention relates to a root bushing and a bushing insert for embedding in a root portion of a wind turbine blade, wherein the root bushing has a threaded outer surface and a main bolt cavity for accommodating a main bolt.

[0002] The present invention also relates to a wind turbine blade and a method for manufacturing the wind turbine blade. Background Art

[0003] It's no secret that wind energy production has grown rapidly over the past few decades and is widely recognized as a clean, cost-effective, and renewable energy source. To meet this growing demand for energy, wind turbines have become increasingly larger to reduce the cost of energy (COE). This increases the weight and cost of their components, particularly the size and weight of wind turbine blades. This has increased the demand for solutions that conserve material and reduce the overall weight of wind turbine blades.

[0004] As wind turbine blades increase in size, their root outer diameters also increase. This increases the amount of reinforcement material required and the total number of main bolts distributed along the circumference of the root end. This, in turn, requires the hub to have an increased blade root flange size to match the increased root end of the wind turbine blade.

[0005] EP2917568B1 discloses various cross-sectional elliptical profiles for root bushings, wherein the overall thickness of the root bushings is greater than the thickness of adjacent inserts, thereby increasing the surface area of ​​contact with the inner and outer fiber layers. EP3697603A1 discloses various cross-sectional profiles for bone-shaped inserts arranged between root bushings, wherein a space is formed between the side surfaces of the inserts and the outer surfaces of the adjacent bushings. In these embodiments, the bone-shaped inserts can be formed from a single piece or multiple sub-pieces.

[0006] EP3111083B1 discloses a root bushing for embedding in a wind turbine blade, wherein the bushing shell is provided with a corrugated outer surface. The corrugations are shaped into peaks and valleys, each extending around the perimeter of the bushing shell. The peaks and valleys are symmetrically arranged and function to provide a mechanically self-locking connection between the laminate and the bushing. The root bushing is provided with internal through-holes, which need to be sealed to prevent resin from entering the main bolt cavity. The time-consuming milling process required to form the symmetrical peaks and valleys can introduce thermal stresses in the bushing shell, potentially leading to bushing fracture or failure.

[0007] WO2019 / 110070A1 and WO2019 / 110071A1 disclose a method for producing two prefabricated bushing inserts by cutting a precured insert body diagonally into two identical workpieces. The bushing shell has an outer surface with grooves separated by ridges. The grooves and ridges are shaped into a wave shape, where the grooves are shallow and the pitch is large. This allows the transition fiber layer to be easily pulled into the grooves and anchored by one or more windings. The pultruded element is then arranged relative to the wound bushing shell to form a rectangular or trapezoidal cross-sectional profile. The entire dry structure is then placed in an insert mold and infused with resin, which is finally cured to form the insert body. Thereafter, the insert body is cut diagonally to form a pair of bushing inserts.

[0008] In this solution, the grooves can be formed as individual circumferential grooves or as spiral continuous grooves. However, this design also requires complex and time-consuming machining, which may introduce thermal stresses in the bushing housing.

[0009] WO2019 / 110070A1 and WO2019 / 110071A1 further disclose that the main bolt cavity is separated from the core cavity by a plug. It is stated that the plug can be integrated into the bushing housing. The plug can also be added as a separate component, but no further details are provided regarding this configuration or how the separate plug is secured.

[0010] CN209705035U discloses a root bushing for a wind turbine blade, wherein the outer surface includes a threaded intermediate portion disposed between two planar ends. A recess is formed at one end to allow contact with an end plug. A waterproof filler material is introduced into the inner hole through the recess, and then the end plug is pressed into place with a pressing tool to securely connect with the recess. When the main bolt is screwed into the bushing, the bolt end contacts the waterproof filler material.

[0011] Another prior art bushing design includes an outer surface with a threaded portion in which valleys have a semicircular cross-sectional profile and peaks between adjacent valleys. This design also requires complex and time-consuming machining. Therefore, there is a need for an improved bushing design that allows for faster and less expensive production.

[0012] Purpose of the Invention

[0013] It is an object of the present invention to provide a liner, a liner insert, a wind turbine blade and a method that overcome the above-mentioned problems of the prior art, or at least provide an alternative solution.

[0014] It is an object of the present invention to provide a liner, a liner insert, a wind turbine blade and a method which allow for faster production and reduced production costs.

[0015] It is an object of the present invention to provide a root liner, a liner insert, a wind turbine blade and a method which allow easier lay-up of a blade root reinforcement. Summary of the Invention

[0016] One object of the present invention is achieved by a root bushing for a wind turbine blade according to claim 1, comprising a bushing shell having an outer surface, wherein a main bolt cavity is arranged within the bushing shell at a first end, and the outer surface comprises a root portion and an external threaded portion, wherein the external threaded portion is formed as a helical thread having an ISO metric cross-sectional profile.

[0017] This provides a root bushing that can be produced more quickly and at lower production costs. The external thread surface can thus be produced using standard milling cutters and a minimum of machining steps, without the need for custom tooling or multiple machining steps using different tools. The bushing design of the present invention also reduces the risk of thermal stresses in the bushing housing during production. This in turn ensures higher production quality and reduces the risk of structural failure during operation.

[0018] Here, the term "ISO metric" is defined in accordance with international standards, such as ISO 68-1. The thread of the present invention has a symmetrical cross-sectional profile, preferably a symmetrical V-shaped or substantially V-shaped profile. The thread forms a continuous or helical thread around the outer surface of the bushing housing.

[0019] The root bushing includes a bushing shell having an outer surface extending from a first end to a second end. When embedded in a wind turbine blade, the first end may be positioned at the root end of the wind turbine blade and the second end may face the tip end of the wind turbine blade. The bushing shell may be made of a metal or a metal alloy, such as steel or a steel alloy.

[0020] The bushing housing has an outer length L and an outer diameter D measured in the longitudinal direction and thickness direction respectively. o The outer length L can also be defined as the relative distance of 1, while the outer diameter D o It can also be defined as the relative thickness / diameter of 1. The size of the external ISO metric thread can be selected as a function of the outer diameter of the bushing housing. For example, but not limited to, the total length L can be between 350 mm and 380 mm. For example, but not limited to, the outer diameter D o It can be between 60 mm and 70 mm. For example, but not limited to, the size of the external ISO metric thread can be between M60–M70.

[0021] A first inner bore, or main bolt cavity, is disposed at the first end and extends toward the second end. The first inner bore is adapted to receive and retain the main bolt during installation of the wind turbine blade. The first inner bore has a first depth and a first inner diameter. Compared to conventional root bushings, the present invention allows for the use of shorter and / or thinner bolts.

[0022] According to one embodiment, the external threaded portion extends from a first starting position to the second end of the bushing housing, wherein the first starting position is determined to be a relative distance L from the first end. o And L o Select from 0 to 0.25.

[0023] The root bushing may have a root portion disposed at a first end and extending to a first starting position of the externally threaded portion. The externally threaded portion may extend from the first starting position to a second end. The root portion may have a flat outer surface, i.e., without any grooves or threads. The root portion may be configured to absorb compressive loads during operation when it is compressed by the bolted connection. The threaded portion may be configured to transfer loads between the bushing and the blade shell during pretensioning and during operation of the wind turbine.

[0024] Both the root and the externally threaded portion have a local outer diameter. Preferably, the local outer diameter of the externally threaded portion can be equal to the local outer diameter of the root portion. Thus, the root bushing can have a constant outer diameter along its length. This saves material and further reduces production costs.

[0025] Conventional root bushings, such as those disclosed in WO 2019 / 110070 A1 and WO 2019 / 110071 A1, typically have an enlarged root portion with an outer diameter greater than that of the adjacent externally threaded portion. This results in increased material waste and increased machining time.

[0026] The first starting position can be determined as a relative distance from the first end, preferably as a local length L of the root portion. o Ratio to the total length L of the bushing housing. For example, but not limited to, the first starting position may be selected from 0 to 0.25.

[0027] According to one embodiment, the cap element and the root insert cavity are further arranged within the bushing housing, wherein the root insert cavity is arranged at the second end of the bushing housing, and the cap element is configured to separate the main bolt cavity from the root insert cavity, and wherein the position of the cap element is determined by a relative distance L from the second end. w OK and select between 0 and 0.35.

[0028] A second inner bore or root insert cavity can be disposed at the second end of the bushing housing and can extend toward the first end. The second inner bore can be adapted to accommodate an end portion of an insert element formed from a core material. The core material can be made of metal, foam, or wood, such as, but not limited to, balsa wood, PVC (polyvinyl chloride), PET (polyethylene terephthalate), polyurethane (PU), or a polymer (e.g., fiber-reinforced polymer, FRP). The second inner bore can have a second inner diameter and a second depth.

[0029] According to one embodiment, the bushing housing has a local wall thickness D measured at the second end. w , where the local wall thickness D w Choose from 0.5mm to 5mm.

[0030] The second inner bore may have an inner surface that projects inwardly from the second end. The second inner bore may have an overall tapered profile, wherein the maximum inner diameter may be located at the second end. The root bushing may have a local wall thickness D measured at the second end. w The local wall thickness D w It can be determined as the relative wall thickness or the difference between the inner diameter of the second inner bore and the outer diameter of the bushing housing. For example, but not limited to, the local wall thickness D w It can be selected from 0.5mm to 5mm.

[0031] A cap element can be positioned within the bushing housing between the first and second inner bores to separate the two cavities. The cap element can be positioned a distance from one end, forming an inner cap. The cap element can be made of a metal or metal alloy, such as steel or a steel alloy, a polymer material, or a closed-cell foam. This prevents the resin matrix material from entering the main bolt cavity during the infusion process.

[0032] The position of the cap element can be determined as a relative distance from the second end, preferably as a distance L w Ratio to the overall length L of the bushing housing. For example, but not limited to, the relative position of the cap element may be selected from 0 to 0.35.

[0033] According to one embodiment, the cap element is integrated into the bushing housing or is provided as a separate element which is shaped to be spaced at a relative distance L from the bushing housing. w The bushing housing can be embedded in the bushing housing.

[0034] The cap element can be simply integrated into the bushing housing, thereby forming a permanent seal between the two cavities. Thus, this seal can be produced when the main bolt cavity of the root bushing and the root insert cavity are machined.

[0035] Alternatively, the cap element may be formed as a separate element that can be fixed within the bushing housing. The first inner bore and the second inner bore may thus be formed to form a continuous inner bore extending from the first end to the second end. This allows for faster production and better tolerance control.

[0036] The cap element may be secured to the bushing housing by a press fit or form fit. Alternatively, the cap element may be secured by a threaded connection. The cap element may be provided with an external thread that engages with an internal thread on the bushing housing. The internal thread may be a separate internal thread or form part of the internal thread portion for the main bolt.

[0037] The cap element may optionally include a shoulder adapted to contact a matching shoulder on the bushing housing. The shoulder on the bushing housing may be arranged relative to the bottom of the root insert cavity. This defines a stop for the cap element.

[0038] According to one embodiment, the main bolt cavity comprises an internal threaded portion extending from a second starting position to a stop position, wherein the cap element is arranged adjacent to or within the internal threaded portion, wherein the second starting position is determined as a relative distance L from the first end c , and select between 0 and 0.5.

[0039] The bushing housing may further include an internally threaded portion disposed within the first inner bore. This internally threaded portion may extend from a second starting position to a stop position, thus having a partial length. The internally threaded portion may also be a helical thread, preferably having an ISO metric cross-sectional profile as defined above. The size of this internal ISO metric thread may be selected as a function of the inner diameter of the first inner bore or main bolt cavity. This allows the main bolt to be connected to the root bushing.

[0040] The second starting position can be determined as a relative distance from the first end, preferably as a local length L of a portion of the first inner hole. c The ratio of the second starting position to the total length L of the bushing housing. For example, but not limited to, the second starting position can be selected from 0 to 0.5.

[0041] The cap element can be positioned adjacent to the internally threaded portion, i.e., not positioned on the threaded portion. Alternatively, the cap element can be positioned within the internally threaded portion at a rest position. Alternatively, the cap element can be positioned at a distance from the internally threaded portion. This allows the cap element's positioning to be adapted to the configuration of the main bolt cavity.

[0042] According to one embodiment, the root insert cavity has an inner surface extending inwardly from the second end, wherein the inner surface is a curved surface having a radius R of at least 500 mm.

[0043] The inner surface of the second inner bore can be planar when viewed longitudinally. Alternatively, the inner surface can be curved to form a smooth transition toward the second end. This provides good structural strength to the second end and allows the resin matrix material to fill the space between the end of the insert element and the inner surface of the root insert cavity. The root insert cavity can thus be formed by arc machining, which facilitates faster production times.

[0044] The curvature of the inner surface may be determined, for example, as a function of the second depth, the maximum inner diameter and / or the minimum inner diameter. For example, but not limited to, the curvature of the inner surface may have a radius R of 500 mm or greater.

[0045] According to one embodiment, the bushing housing has an outer diameter and the main bolt cavity has an inner diameter measured at the internal threaded portion, wherein a ratio of the outer diameter to the inner diameter is selected between 1.7 and 1.9.

[0046] The inner diameter D of the main bolt cavity can be measured at the internal thread part t This measurement also defines the size of the internal ISO metric thread.

[0047] The size of the root bushing can be determined as the outer diameter D of the bushing shell o The inner diameter D of the internal thread part t For example, but not limited to, the ratio may be selected between 1.7 and 1.9. This allows for better alignment during the layup process and more fiber material to be added to the root end of the wind turbine blade, which in turn may reduce the root outer diameter of larger wind turbine blades.

[0048] According to one embodiment, at least one set of windings is arranged at a threaded portion on the outer surface.

[0049] The yarn may be wound around at least a portion of the outer surface of the root bushing. Preferably, the yarn is wound around the threaded portion of the root bushing. One or more layers of windings may be arranged along the outer surface. In one embodiment, at least one first layer of windings may be arranged directly on the threaded portion. This improves the priming process and enhances the quality of the joint.

[0050] Optionally, at least one fiber layer and / or at least one second winding layer can be arranged on one or more first winding layers. This can further improve the infusion process and the joining quality.

[0051] The object of the present invention is also achieved by a root bushing insert for a wind turbine blade according to claim 10, comprising a root bushing having a root insert cavity and an insert element adapted to be inserted into the root insert cavity, wherein the root bushing is configured as described above.

[0052] The root bushing of the present invention may be fitted with an insert element at its second end to form a root bushing insert. The insert element may be simply held in place by friction or a form fit. Alternatively, the insert element may be bonded to the root bushing by applying an adhesive between the contacting surfaces. The adhesive may be a pressure-sensitive adhesive.

[0053] The insert element may have an end adapted to be inserted into the root insert cavity of the bushing housing. The end may have a tapered profile with a flat or curved surface, preferably following the contour of the root insert cavity. The insert element may taper toward an opposite end to form a smooth transition between the inner and outer fiber layers of the wind turbine blade.

[0054] Optionally, at least one set of windings and / or at least one fiber layer is arranged on at least a portion of an outer surface of the bushing and / or the insert element.

[0055] The yarn wound around the threaded portion of the outer surface of the sleeve may further extend along at least a portion of the outer surface of the insert. Furthermore, the one or more layers of windings may further extend along the outer surface of the insert. Alternatively, individual yarns may be wound around the sleeve and the insert to form individual winding layers.

[0056] Optionally, at least one fiber layer and / or at least one second winding layer can be arranged on top of the winding layer on the insert element. This can further improve the potting process and the joining quality.

[0057] Alternatively, the yarn may be wrapped around only the insert element or the sleeve.

[0058] According to one embodiment, one or more additional insert elements are positioned relative to the root bushing and the insert element, wherein the one or more additional insert elements extend along outer surfaces of the root bushing and the insert element.

[0059] Two or more additional insert elements may extend along the outer surface of the root bushing and / or insert element. The additional insert elements may be distributed along the perimeter of the root bushing and / or insert element to form a desired cross-sectional profile of the root bushing insert. The additional insert elements may be made of any structural material capable of transferring shear loads to the bushing, such as pultruded elements, fiber rods, dry fibers, or any combination thereof.

[0060] During the layup process in the aerogenerator blade mould, the additional insert element may be arranged relative to the root bushing and / or the insert element. This enables the root bushing insert to be assembled directly in the aerogenerator blade mould.

[0061] Alternatively, the additional insert element can be secured to the root bushing and / or the insert element separately from the wind turbine blade mold to form a dry structure. The additional insert element can be secured by gluing or by wrapping a tape, yarn, or at least one fiber layer around the additional insert element, the root bushing, and the insert element. Optionally, the additional insert element can be arranged between the layers of the first winding and the aforementioned fiber layers and / or the layers of the second winding. The dry structure can then be lifted into position on the wind turbine blade mold during the layup process.

[0062] The object of the present invention is also achieved by a wind turbine blade for a wind turbine according to claim 12, comprising a blade shell having a root end and a tip end, wherein a plurality of root bushings or root bushing inserts are embedded in the root portion of the blade shell, wherein the root bushings or root bushing inserts are configured as described above.

[0063] The root bushing of the present invention allows for better bonding between the root bushing and the fiber layer of the root section. This allows for the use of shorter and / or thinner bolts, and for the addition of additional fiber layers to the root section. This increases the structural strength of the root section and allows for a reduction in the main bolt circle diameter, particularly for large wind turbine blades.

[0064] According to one embodiment, a wedge-shaped element is arranged between a pair of adjacent root bushings or root bushing inserts, wherein the wedge-shaped element has an asymmetric or symmetric cross-sectional profile perpendicular to the longitudinal direction.

[0065] A wedge-shaped element may be disposed between each pair of root bushings. The wedge-shaped element may extend longitudinally along the root bushings and the insert element. The wedge-shaped element may have an overall dog-bone shaped cross-sectional profile. The wedge-shaped element may be a pultruded element and / or formed from a single workpiece or from multiple sub-workpieces. The wedge-shaped element may be formed from a fiber layer or a laminated material.

[0066] The wedge-shaped element can have a symmetrical or asymmetrical cross-sectional profile about a line of symmetry perpendicular to the longitudinal direction. The line of symmetry can be arranged parallel to the circumferential direction or the thickness direction. The wedge-shaped element can have a local height along the thickness direction that is substantially equal to or less than the local height of the root bushing. This increases the total surface contact area with the fiber layer, which improves adhesion between the fiber layer and the root bushing. It also reduces the risk of wrinkles forming in the fiber layer, particularly at the ends of the insert element and the wedge-shaped element.

[0067] According to one embodiment, the root portion comprises a first root bushing and at least a second root bushing, wherein a starting position of the internally threaded portion of the first root bushing is different from a starting position of the internally threaded portion of the at least second root bushing.

[0068] The present invention may also include a set of root bushings or bushing inserts for a wind turbine blade. The set may include a plurality of root bushings or bushing inserts intended for placement in the root portion of a wind turbine blade. The number of individual root bushings may correspond to the number of root bushings required to form the root portion of the wind turbine blade.

[0069] Preferably, the starting position L of the internal thread portion c It is possible to vary between the individual root bushings and bushing inserts of the set. Alternatively, the root bushings or bushing inserts may be arranged in groups, each group having the same starting position L of the internal threaded portion. c For example, the starting position of the internal thread portion of the first root bushing (e.g., L c / L ratio) may be different from the starting position of the internal threaded portion of at least the second root bushing (e.g., L c ' / L ratio). Optionally, the root portion may further include a third root bushing, a fourth root bushing, etc., each having a unique starting position of the internal threaded portion that is different from the starting position of the internal threaded portion of the first root bushing and / or the second root bushing. The first root bushing or the set of first root bushings and the second root bushing or the set of second root bushings may be arranged in an alternative order or another predetermined order along the circumferential direction of the root portion. For example, a root bushing with a shorter starting position L c The root bushing can be positioned at a longer starting position L c between an adjacent pair of root bushings and vice versa.

[0070] Therefore, the starting positions of the internal threaded sections do not coincide between all root bushings of the root section, but are staggered. This results in an optimized shear stress distribution and allows for less material between two adjacent bushings, thereby further resulting in the blade root being able to accommodate more root bushings / bushing inserts at the same main BCD (bolt circle diameter).

[0071] The object of the present invention is also achieved by a method for manufacturing a wind turbine blade according to claim 15, which comprises the following steps:

[0072] - laying one or more first fiber layers in a blade mould;

[0073] - arranging a plurality of root bushings or root bushing inserts on the first fiber layer, wherein the root bushings or root bushing inserts are configured as described above;

[0074] - Optionally, a plurality of wedge-shaped elements are arranged between the root bushings or the root bushing inserts;

[0075] - laying one or more second fiber layers on top of the root bushing or root bushing insert and optionally the wedge elements,

[0076] - infusing at least the first and second fiber layers with a resin matrix material;

[0077] - Curing the infused structure to form the blade shell component.

[0078] This allows the root bushing or root bushing insert of the present invention to be positioned in the aerogenerator blade mold during layup and cast along with the rest of the aerogenerator blade. The root bushing of the present invention also allows for better root bushing alignment during layup and the addition of more fiber layers. This allows for the manufacture of larger aerogenerator blades with reduced main bolt diameters.

[0079] The wind turbine blade mold is initially prepared for the molding process. One or more first fiber layers, forming the outer skin of the blade, are then laid onto the molding surface. Blade reinforcements are then positioned over the first fiber layers along the length of the wind turbine blade. This involves placing multiple root bushings and insert elements over the root section. Optionally, a wedge-shaped element can be placed between each pair of root bushings. Subsequently, one or more second fiber layers, forming the inner skin, are laid over the root bushings and, optionally, over the wedge-shaped elements.

[0080] After layup is complete, the inlet and outlet channels of the vacuum pump and resin mixing system are installed on the structure, and the structure is enclosed in a vacuum bag. The structure, such as the fiber layer, can then be infused with a resin matrix material. The resin matrix material can be, for example, but not limited to, epoxy resin, vinyl ester, polyurethane, or thermoplastic. After the infusion process is complete, the infused structure is then set to cure. Once cured, the structure is removed from the wind turbine blade mold.

[0081] According to one embodiment, the method further comprises the step of winding a yarn around at least a portion of the outer surface of the bushing or bushing insert, wherein the yarn forms at least one layer of windings.

[0082] Prior to laying the bushing or bushing insert, the yarn can be wrapped around at least the threaded portion of the bushing's outer surface and / or along a portion of the insert's outer surface. This can be accomplished manually or automatically. The yarn can be wrapped with a predetermined force to ensure close contact with the bushing's or insert's outer surface. This improves the infusion process and enhances bond quality.

[0083] If necessary, further winding layers and / or fiber layers can be wrapped around the lining or insert element prior to laying. BRIEF DESCRIPTION OF THE DRAWINGS

[0084] The present invention is described by way of example only and with reference to the accompanying drawings, in which:

[0085] Figure 1 An exemplary embodiment of a wind turbine is shown;

[0086] Figure 2 An embodiment of a wind turbine blade according to the present invention is shown;

[0087] Figure 3 A first embodiment of a root portion is shown;

[0088] Figure 4 A second embodiment of the root portion is shown;

[0089] Figure 5a - b shows two exemplary embodiments of bushing inserts according to the invention;

[0090] Figure 6 An exemplary embodiment of a wedge-shaped element is shown;

[0091] Figure 7 A first embodiment of a root bushing with a cap element according to the invention is shown;

[0092] Figure 8 Shown Figure 7 the outer surface of the root bushing;

[0093] Figure 9 An enhanced view of the second end of the root bushing is shown;

[0094] Figure 10 Shown Figure 7 Root bushing without cap element;

[0095] Figure 11 An enlarged view of the threaded portion of the outer surface is shown;

[0096] Figure 12a -b shows two exemplary embodiments of cap elements;

[0097] Figure 13 A second embodiment of the root bushing and cap member is shown; and

[0098] Figure 14 A third embodiment of a root bushing and cap element is shown. DETAILED DESCRIPTION

[0099] In the following, the drawings will be described one by one, and different parts and positions seen in the drawings will be numbered with the same numbers in different drawings. Not all parts and positions indicated in a particular figure are necessarily the same as those in that figure. Figure 1 Start a discussion.

[0100] Figure 1 An exemplary embodiment of a wind turbine 1 is shown, comprising a wind turbine tower 2, a nacelle 3 being arranged on top of the wind turbine tower 2, and a rotor being rotatably arranged relative to the nacelle 3. The rotor comprises a hub 4, which is connected to at least two wind turbine blades 5. Here, three wind turbine blades 5 are shown.

[0101] Figure 2 An embodiment of an aerogenerator blade 5 is shown, of which only one blade shell component is shown. The blade shell component is arranged in an aerogenerator blade mould 6. The aerogenerator blade 5 extends from a root end 7 to a tip end 8 and further from a leading edge 9 to a trailing edge 10.

[0102] The root portion 11 of the wind turbine blade 5 includes an array of root reinforcements, such as Figure 3-6 shown.

[0103] Figure 3 A first embodiment of a root portion 11 is shown, viewed from the root end 7. The root portion 11 comprises one or more first fiber layers 12, which define the outer skin of the aerogenerator blade 5. A plurality of root bushings 13 are arranged on top of the first fiber layers 12. A wedge-shaped element 14 is arranged between each pair of root bushings 13. One or more second fiber layers 15, which define the inner skin of the aerogenerator blade 5, are arranged on top of the root bushings 13 and the wedge-shaped elements 14.

[0104] Here, the wedge-shaped element 14 has a symmetrical cross-sectional profile about a symmetry line 16 parallel to the thickness direction. Optionally, the wedge-shaped element 14 may also have a symmetrical cross-sectional profile about another symmetry line 17 parallel to the circumference direction.

[0105] Figure 4 A second embodiment of the root portion 11 is shown, seen from the root end 7. Here, the wedge-shaped element 14' has an asymmetrical cross-sectional profile about a line of symmetry 16. Alternatively or additionally, the wedge-shaped element 14' may also have an asymmetrical cross-sectional profile about another line of symmetry 17.

[0106] Figure 5a -b shows two exemplary embodiments of a bushing insert 18 according to the present invention. The bushing insert 18 comprises a root bushing 13 and an insert element 19. The insert element 19 has a main bolt cavity (see FIG. Figure 9 ) in the end 20.

[0107] The end portion 20 may be secured to the root bushing 13 by friction or adhesive.

[0108] The additional insert element 21 is arranged relative to the outer surface of the root bushing 13 and the insert element 19. The additional insert element 21 extends along the length of the root bushing 13 and the insert element 19.

[0109] Figure 6 An exemplary embodiment of a wedge-shaped element 14, 14' is shown. The wedge-shaped elements 14, 14' extend along the length of the root bushing 13 and the insert element 19. The wedge-shaped elements 14, 14' have tapered ends shaped to form a smooth transition between the inner and outer skins of the root portion 11.

[0110] Figure 7 A first embodiment of a root bushing 13 having a cap element 22 according to the present invention is shown. The root bushing 13 has a bushing housing 23 extending from a first end to a second end. A main bolt cavity 24 is provided at the first end and extends toward the second end. The main bolt cavity 24 has an internally threaded portion 25 adapted to engage a main bolt when inserted into the main bolt cavity 24.

[0111] A root insert cavity 26 is arranged at the second end and extends towards the first end. The root insert cavity 26 is adapted to receive the end 20 of the insert element 19.

[0112] The outer surface 27 has a root portion (28) and a threaded portion (29), the threaded portion (29) extending from a first starting point (see Figure 10 ) extends to the second end.

[0113] Figure 8 There is shown the outer surface 27 of the root bushing 13. Here it is clearly shown that the external threaded portion (29) is a helical thread.

[0114] Figure 9 An enhanced view of the second end of the root bushing 13 is shown, clearly showing the root insert cavity 26. The root insert cavity 26 has an inner surface 30 extending from the second end towards the first end. The inner surface 30 is curved and has a radius of curvature of 500mm or more.

[0115] At least one layer of windings 35 is optionally arranged on the threaded portion 29 by wrapping the yarn around the outer surface 27 of the sleeve 13. The windings 35 are located in the threads of the threaded portion 29.

[0116] Figure 10 The root bushing 13 is shown without the cap element 22. The bushing housing 23 has an overall length L and an outer diameter D o The first starting position 31 of the external threaded portion 29 can be determined as the local length L of the root 28 o The ratio to the total length L of the bushing housing 23. The external threaded portion 29 extends from a first starting position 31 to a second end.

[0117] The second starting position 32 of the internal threaded portion 25 is located at a distance L from the first end. c The internal thread portion 25 extends from the second starting position 32 to the stop position 33. The second starting position 32 is determined as the local length L of the outer portion of the first inner hole. c The ratio of the length L of the bushing housing 23 to the total length L of the bushing housing 23.

[0118] The cap member 22 is positioned at a distance L from the second end. w The bushing housing 23 optionally includes a shoulder 34 adapted to contact a matching shoulder on the cap member 22 (see Figure 12a ). The position of the cap member 22 can be determined as a distance L w The ratio to the total length L of the bushing housing 23.

[0119] The root bushing 13 is sized to be the outer diameter D of the bushing housing 23 o The inner diameter D of the internal thread portion 25 tThe root bushing 13 has a local wall thickness D measured at the second end. w .

[0120] Optionally, the present invention also includes a set of root bushings 13, 13' for a wind turbine blade 5, comprising a first root bushing 13 and at least one second root bushing 13'. The second starting position 32 of the internal threaded portion 25 of the first root bushing 13 is different from the second starting position 32' of the internal threaded portion 25' of at least the second root bushing 13'.

[0121] Figure 11 There is shown an enlarged view of the threaded portion 29 of the outer surface 27. The threaded portion 29 is formed as a helical thread having an ISO metric cross-sectional profile.

[0122] The thread has a pitch p and a height h as well as a bottom width d and an inclination angle α. These values ​​are determined according to international standards.

[0123] Figure 12a -b shows two exemplary embodiments of cap elements 22 , 22 ′ adapted to be fixed in a bushing housing 23 .

[0124] The cap element 22 has a partial shoulder which is shaped to contact a shoulder 34 on the bushing housing 23. The cap element 22 is fixed by a force fit or a form fit.

[0125] The cap element 22 ′ has an external thread arranged on the side and is adapted to be fixed to an internal thread of the bushing housing 23 .

[0126] Figure 13 A second embodiment of the root bushing 13' and the cap element 22' is shown. Here, the internal threaded portion 25' extends into the root insert cavity 26. The cap element 22' is thus fixed to the internal threaded portion 25' in a stop position 33.

[0127] Figure 14 A third embodiment of a root bushing 13 ″ and a cap element 22 ″ is shown. Here, the main bolt cavity 24 and the root insert cavity 26 are separated by the cap element 22 ″. The cap element 22 ″ is integrated into the bushing housing 23 .

Claims

1. A wind turbine blade for a wind turbine (1), characterized in that: A blade shell having a root end (7) and a tip end (8), wherein a plurality of root bushings (13) or root bushing inserts (18) are embedded in a root portion (11) of the blade shell, wherein the root bushing (13) comprises a bushing shell (23) having an outer surface (27), wherein a main bolt cavity (24) is arranged in the bushing shell (23) at a first end, the outer surface (27) comprising a root portion (28) and an externally threaded portion (29), wherein the externally threaded portion (29) is formed as a helical thread having an ISO metric cross-sectional profile, wherein the helical thread is manufactured using a standard milling cutter and a minimum of machining steps to reduce thermal stresses introduced into the bushing shell; the root bushing insert (18) comprises a root bushing (13) having a root insert cavity (26) and an insert element (19) adapted to be inserted into the root insert cavity (26); The starting position (32) of the internal threaded portion (25) is staggered between all the root bushings (13) of the root portion (11).

2. The wind turbine blade according to claim 1, characterized in that: The external thread portion (29) extends from a first starting position (31) to the second end of the bushing housing (23), wherein the first starting position (31) is determined as a relative distance L0 from the first end and is selected from 0 to 0.

25.

3. The wind turbine blade according to claim 1, characterized in that: A cap element (22) and a root insert cavity (26) are further provided in the bushing housing (23), wherein the root insert cavity (26) is provided at the second end of the bushing housing (23), the cap element (22) is configured to separate the main bolt cavity (24) from the root insert cavity (26), and wherein the position of the cap element (22) is determined to be a relative distance L from the second end w , and select between 0 and 0.

35.

4. The wind turbine blade according to any one of claims 2 or 3, characterized in that: The bushing housing (23) has a local wall thickness D measured at the second end. w , wherein the local wall thickness D w Choose from 0.5mm to 5mm.

5. The wind turbine blade according to claim 3, characterized in that: The cap element (22) is integrated into the bushing housing (23) or is provided as a separate element which is shaped to be spaced at a relative distance L. w The bushing is fixed to the bushing housing (23).

6. The wind turbine blade according to claim 3, characterized in that: The main bolt cavity (24) includes an internal threaded portion (25) extending from a second starting position (32) to a stop position (33), wherein the cap element (22) is arranged adjacent to or within the internal threaded portion (25), wherein the second starting position (32) is determined as a relative distance L from the first end c And choose from 0 to 0.

5.

7. The wind turbine blade according to claim 2 or 3, characterized in that: The root insert cavity (26) has an inner surface (30) extending inwardly from the second end, the inner surface (30) being a curved surface with a radius R of at least 500 mm.

8. The wind turbine blade according to claim 3, characterized in that: The bushing housing (23) has an outer diameter (D o ), and the main bolt cavity (24) has an inner diameter (D t ); the outer diameter (D o ) and inner diameter (D t ) ratio is selected between 1.7 and 1.

9.

9. The wind turbine blade according to claim 1, characterized in that: At least one set of windings is provided at the external threaded portion (29) of the outer surface (27).

10. The wind turbine blade according to claim 9, characterized in that: One or more additional insert elements (21) are positioned relative to the root bushing (13) and the insert element (19), wherein the one or more additional insert elements (21) extend along outer surfaces of the root bushing (13) and the insert element (19).

11. The wind turbine blade according to claim 1, characterized in that: A wedge-shaped element (14, 14') is provided between a pair of adjacent root bushings (13) or root bushing inserts (18), wherein the wedge-shaped element (14, 14') has an asymmetric or symmetric cross-sectional profile perpendicular to the longitudinal direction.

12. The wind turbine blade according to claim 1 or 11, characterized in that: The root portion (11) comprises a first root bushing (13) and at least a second root bushing (13'), wherein a starting position (32) of the internal threaded portion (25) of the first root bushing (13) is different from a starting position (32') of the internal threaded portion (25') of at least the second root bushing (13').

13. A method for manufacturing a wind turbine blade, characterized in that: The following steps are involved: - laying one or more first fiber layers (12) in a blade mold (6); - arranging a plurality of root bushings (13) or root bushing inserts (18) on the first fiber layer, wherein the root bushings (13) or root bushing inserts (18) are configured according to any one of claims 1 to 12; - a plurality of wedge-shaped elements (14, 14') are arranged between the root bushings (13) or the root bushing inserts (18); - laying one or more second fiber layers (15) on top of the root liner (13) or root liner insert (18) and the wedge-shaped elements (14, 14'); - infusing at least the first and second fiber layers (12, 15) with a resin matrix material; - Curing the infused structure to form the blade shell.

14. The method according to claim 13, characterized in that The method further comprises the step of wrapping a yarn around at least a portion of the outer surface of the liner or liner insert, wherein the yarn forms at least one layer of windings.

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