Method for operating a wind turbine with a bearing unit for an elongated rotor blade

Abstract

Method for operating a wind turbine with at least one bearing unit (1; 1') as a blade bearing for the rotatable connection of an elongated rotor blade (2) to a rotor hub (3) of a wind turbine, the storage unit (1; 1') comprising: - at least two axially offset raceways (22, 23, 37) with rotating rolling elements (24, 25) which have two annular connecting elements (13, 14; 13', 14') rotatable relative to each other, for indirect or direct connection to the rear end (5) of the respective rotor blade (2) on the one hand and to the rotor hub (3) on the other hand, wherein - the annular connecting elements (13, 14; 13', 14') have opposite end faces (15, 16) which serve as connection surfaces to the rotor hub (3) on the one hand and to the respective rotor blade (2) on the other hand, and - between the two connecting elements (13, 14; 13', 14') an annular gap is formed, sealed in the area of ​​the two connecting surfaces, wherein - the rolling elements (24, 25) of two axially offset raceways (22, 23, 37) have an approximately cylindrical shape, each with a cylindrical surface (26) that is rotationally symmetric to exactly one axis of rotation (31), wherein - these rolling elements (24, 25) are aligned such that their respective axes of rotation (31) are aligned approximately perpendicular to the longitudinal axis of the rotor blade (2) in question, and wherein a projecting, circumferential nose (21; 21') is provided on the outer side of a connecting element (14; 13') facing the other connecting element (13; 14'), wherein the two annular side surfaces (22, 23) of the nose (21; 21') serve as running surfaces for the approximately cylindrical rolling elements (24, 25) of each row of rolling elements, wherein the rolling elements (24, 25) roll without play between the side surfaces (22, 23) of the nose (21) on the one hand and the side surfaces (37) of a circumferential recess (36) of approximately rectangular cross-section provided on an outer or inner surface of the connecting element (13, 14), wherein - the rotor blade (2) is designed as a shell surface (4) surrounding an inner cavity, which transitions at the rear end (5) of the rotor blade (2) into a cylindrical shell shape up to a flat, rear connection surface (6), and wherein - by means of a hydraulic cylinder or a drive unit (47) the rotor blade (2) relative to the rotor hub (3) regardless of whether the wind turbine is in operation or not, or whether the wind turbine is stationary or not, or whether the rotor blades need to be adjusted or not, the rotor blade (2) is continuously and periodically rotated about its longitudinal axis relative to the rotor hub (3).

Description

[0001] The invention relates to a method for operating a wind turbine with at least one bearing unit for an elongated rotor blade. The rotor blade(s) in question are continuously rotated about its longitudinal axis(s) during operation of the wind turbine. The bearing unit has two annular elements rotatable relative to each other for direct or indirect connection to the rotor blade hub on the one hand and to the rotor blade on the other, and at least two axially offset raceways with rotating rolling elements of approximately cylindrical shape, i.e., each with a cylindrical surface that is rotationally symmetrical about exactly one axis of rotation (cylindrical, conical, needle-shaped, or barrel-shaped), wherein the bearing unit is designed to fully absorb the tilting moment resulting from the wind pressure on the rotor blade and on the bearing unit, and optionally to absorb other forces (blade weight, centrifugal force, etc.).) and other moments (for example, due to the temporary tilt of a blade relative to the vertical), two axially offset raceways with rotating rolling elements of approximately cylindrical shape are arranged between the two connecting elements, wherein these rolling elements are oriented such that their axes of rotation are directed approximately radially, i.e., approximately perpendicularly, with respect to the longitudinal axis of the rotor blade in question.

[0002] Wind turbines – and thus especially their rotor diameters – are becoming increasingly larger. Consequently, the stress on all supporting and bearing units is also increasing. This also applies to the blade bearings, which are used to adjust the blade pitch angle and allow adaptation to different wind speeds, both for optimal power control and for storm-force shutdown. The greatest stress here is the tilting moment, which is transferred to the blade bearings by the wind load concentrated at the center of pressure (Cp, approximately in the middle of the rotor blade length). With regard to this tilting moment, the blade bearings are considered the pivot point, and due to the considerable lever arm, the wind load results in very high bending stress on the blade root and the blade bearings.The bending moments at the blade bearings are therefore far more problematic than at the bearings for the rotor as a whole, because the bending moments generated by the rotor blades, which are mounted offset from each other by the same angle of rotation, largely cancel each other out there. Furthermore, the rotor of a wind turbine is always rotating during torque application, so the rolling elements there are in motion and no local continuous loads are to be expected, unlike at the rotor blade bearings, which are usually only rotated to adjust the rotor blade pitch angle when the average wind speed changes significantly, i.e., rather infrequently.

[0003] DE 37 32 730 A1 discloses a pivot bearing for the rotor blades of wind turbines. In one embodiment, two bearing units spaced apart axially with respect to the axis of rotation are disclosed, each consisting of an angular contact ball bearing, a cylindrical roller bearing, and a needle roller bearing. The cylindrical roller bearing transmits radial forces and the needle roller bearing transmits axial forces from an outer ring unit to the outer ring of the angular contact ball bearing, whose inner ring transmits these forces together to the hub. Two bearing units are provided to control the considerable tilting moments resulting from the wind load. Since each such bearing unit has a thrust bearing and a radial bearing, each tilting moment or root bending moment resulting from the wind load generates a pair of opposing radial forces (one radial force at each radial bearing) and a pair of opposing axial forces (one at each thrust bearing).Since the tilting or root bending moment is distributed across all four bearing positions – due to the geometric distances between the bearings – into forces of a comparable magnitude, all radial and axial bearings must be designed for comparatively high loads. To reduce these loads to a tolerable level, a minimum distance between the two bearing units must be maintained, necessitating their separation. However, the use of two bearing units with a total of four bearing positions, all of which must be designed for high loads, entails increased design complexity, especially since each bearing requires a separate inner and outer ring as a raceway.

[0004] US 3,652,141 relates to a bearing unit comprising two axially offset raceways with rotating rolling elements, wherein two annular elements rotatable relative to each other are arranged for the indirect or direct connection of the parts to be supported, the rolling elements of the two axially offset raceways having an approximately cylindrical shape, i.e., each with a cylindrical surface that is rotationally symmetrical about exactly one axis of rotation, and wherein these rolling elements are oriented such that their axes of rotation are directed approximately radially, i.e., approximately perpendicularly, with respect to the longitudinal axis of the part to be supported. A similar arrangement is shown in DE 39 09 664 C1.

[0005] DE 123 805 A and DE 37 32 730 A1 do concern wind turbines, but do not show a rotor blade or details on rotor blade adjustment.

[0006] DE 956 390 B shows a rotor blade, but no details of its bearing or operation. It illustrates a rotary bearing on a shaft positioned in front of the actual rotor blade. Further technical background information can be found in DE 101 40 793 A1, DE 36 09 781 A1, DE 3 1 04 097 C2, DE 34 23 433 C2, US 4 573 811 A, US 4 463 995 A, US 4 422 697 A, CA 2 536 058 A1, DE 197 39 164 A1, EP 1 286 048 A1, US 3 652 141 A, EP 1 259 741 B1, DE 20 11 141 A1, DE 26 48 144 A1, EP 0 238 725 A2, DE 3 0 09 922 A1, EP 1 286 048 A1.

[0007] Erich Hau: “Wind Turbines”, Springer Verlag, pages 138-139, 228-234, 330, 457-459: In Fig. Section 8.15 on page 234 shows a rotor blade bearing arrangement with angular contact roller and crossed roller bearings. Section 7.5 shows rotor blades made of fiber-reinforced composite materials. Fig. Figure 7.14 on page 202 shows a typical rotor blade structure. The illustrated rotor blade has a hull surface surrounding an inner cavity, which transitions at one rear end of the rotor blade into a cylindrical hull shape leading to a flat, rear connection surface. Section 7.7 on page 207 shows a transverse bolt connection, as illustrated in the Fig. 7.20 explained. The rear connection surface is provided with bores that lead, on the one hand, to an anchoring body made of a hard material inserted into the rotor blade, where they continue as internal threaded bores. From the Fig. Section 7.22 indicates that the bores are arranged in a ring shape. According to section 15.2.2 on pages 457 to 459, the pitch angles of the rotor blades are adjusted accordingly during rotation to further increase the efficiency of the wind turbine.

[0008] Erich Hau: “Wind turbines: Fundamentals, technology, application, economic efficiency”, 2nd edition, Springer Verlag, pages 1, 2, 81-83, 198-209, 232-235, shows in Fig. 8.15, that the rolling elements of the two axially offset raceways are aligned such that their axes of rotation are directed radially and perpendicularly with respect to the longitudinal axis of the rotor blade concerned. Fig. Figure 8.15 also shows that the two connecting elements are arranged concentrically within each other, and that the bores are also arranged in a ring shape. Fig. Figure 8.15 shows that the annular gap between the connecting elements is sealed, and that the inner connecting element has a projecting nose facing the other connecting element. The nose serves as a running surface for the two rows of rolling bearings. Fig. 8.15 The raceways run along flat circular annular surfaces perpendicular to the longitudinal axis of the rotor blade, and a third bearing point is arranged between the two raceways and between the outer surfaces of the connecting elements. This third bearing point has rolling elements with a rotation axis parallel to the longitudinal axis of the rotor blade. These rolling elements are smaller than the rolling elements of the other bearings. This document describes theoretical possibilities for using certain bearing types and disregards the disadvantages of individual bearing types. It describes here that multi-row cylindrical roller bearings, while capable of handling high moment loads, are complex and expensive; a similar load capacity can be achieved with ball bearings at significantly lower costs.

[0009] EP 1 398 499 A1 relates to a wind turbine with one rotor and three rotor blades attached to the rotor. The rotor blades are each made of a fiber-reinforced composite material and have an airfoil shape, which is tubular in the area of ​​a rotor blade attachment for fastening to the rotor. In the area of ​​the rotor blade attachment, the rotor has a flange section with through holes. Blind holes aligned with the through holes are arranged in the outer surface of the rotor blade. The blind holes lead to an anchoring body inserted into the rotor blade. The blind holes and the through holes are each arranged in a ring shape.

[0010] WO 20 0 1 / 426 47 A2, DE 3 1 04 097 C2, DE 34 23 433 C2, US 4 573 811 A, US 4 463 995 A, US 4 422 697 A concern the use of anchoring elements, blind holes and through holes for fastening a rotor blade to a rotor unit.

[0011] US 3 81 488 A shows filler material in the annular gap between the two bearing parts.

[0012] Dubbel's "Pocketbook of Mechanical Engineering", 20th edition, Springer Verlag, pages G80 to G106, addresses, among other things, in the chapter "Rolling Bearings", pages G80 to G84, rolling elements with transition areas or crowns, and rolling elements with rounded end faces. The guide flanges should allow only the smallest possible axial play or be constructed as tightly as possible. From Fig. 2 on page G80 and Fig. 4 on page G81, spacers are known which are arranged between the rolling elements.

[0013] DE 42 02 098 A1 relates to a bearing with hollow rolling elements, wherein the rolling elements are connected to each other by end-face engaging connecting elements and are integrated into a cage.

[0014] The disadvantages of the described prior art result in the problem initiating the invention: to create a method for the operation of wind turbines that permanently meets the special requirements for components of the rotor blade bearing, in particular the much higher tilting moment under strong wind load than, for example, on the rotor bearings, and enables the relatively difficult load case during long operating periods.

[0015] This problem is solved by a method with the features of claim 1.

[0016] Due to the alignment of the longitudinal axes of these rolling elements, no radial forces are transmitted, only axial forces. The two pairs of raceways for the rolling elements are arranged on the two mutually rotatable connecting elements in such a way that one row of rolling elements can transmit axial compressive forces in one direction, while the other can transmit the same compressive forces diametrically opposite and acting in the opposite direction along the common axis of rotation. This arrangement is based on the fact that a rotor blade also has a considerable diameter of, for example, 2 to 3 meters, with the pivot points at the blade bearing for the tilting moment resulting from the wind load being located approximately on a line passing through the central longitudinal axis of the rotor blade and running perpendicular to the rotor axis. Therefore, it is not necessary to provide two additional radial bearings.Furthermore, the strong tilting moment triggered by the wind results in a bending moment at the root of the rotor blade around these pivot points or around the line connecting them. This bending moment manifests itself as axial tensile forces in the areas of the blade bearing that are offset by 90° from the line defining the pivot points, and as axial compressive forces on the opposite side. These axial forces are absorbed by the two bearing points according to the invention. The tilting moment generated by the wind pressure is supported exclusively by a pair of axial forces. This prevents the formation of radial forces, which would cause the bearing rings to expand radially and complicate the sealing process. This advantage is achieved precisely by eliminating the need for a pair of radial bearings. Furthermore, thanks to the invention, it becomes possible to dispense with angular contact bearings even at the blade bearings, which are rarely adjusted and therefore subject to very high load-bearing capacity. In addition, no axle journal is required.Since the tilting moment is fully supported by the axial force couple, a second bearing unit can be dispensed with, which significantly reduces the number of parts and thus also the susceptibility of the bearing unit; the design becomes extremely compact, and mutual adjustment of several bearing points is eliminated.

[0017] By arranging the two connecting elements concentrically within each other, both bearing points, which are offset from each other in the axial direction, can be accommodated between the connecting elements.

[0018] It has proven advantageous for both connecting elements to have mounting holes arranged in a ring. These can be threaded blind holes or, preferably, through holes for screws, bolts, or similar fasteners, which are screwed into or anchored to a rotor blade or rotor hub.

[0019] The opposing end faces of the ring-shaped connecting elements serve as connection surfaces to the rotor blade hub on one side and to the respective rotor blade on the other. This allows the bearing unit to be inserted between these two components.

[0020] Since the annular gap between the two connecting elements is sealed in the area of ​​the two contact surfaces, the rolling elements run in a space completely enclosed from the environment. This protects them from the influence of, for example, salty and therefore corrosive sea air, prevents the ingress of dust, and retains the lubricating grease or other lubricants in the area of ​​the rolling elements.

[0021] Further advantages arise from the fact that at least one projecting, circumferential lug is provided on the outer surface of at least one connecting element facing the other connecting element. An axial force can be introduced into the respective connecting element via its lateral surfaces.

[0022] Further pursuing this idea, it can also be provided that the axial extent of the nose corresponds to the axial distance between the rolling elements of the two bearings. This makes it possible to use or design the two annular side surfaces of the nose as the running surface for the approximately cylindrical rolling elements of each bearing position.

[0023] The invention can be further developed such that the raceways for the approximately cylindrical rolling elements run along approximately flat annular surfaces, which are intersected approximately perpendicularly by the longitudinal axis of the respective rotor blade. Flat surfaces are easier to manufacture than curved surfaces; furthermore, in the invention, only axial forces are transmitted by the respective bearings, so there is no reason to provide the raceways with a curvature or to design them at a (large) angle, e.g., on the order of approximately 45° to the longitudinal axis of the respective rotor blade, as is the case, for example, with double angular contact roller bearings.

[0024] Preferably, the bearing according to the invention has at least one third bearing point, which is inserted between two opposing outer surfaces of the two connecting elements. In contrast to the bearings described above, the latter is responsible for transmitting the wind pressure, which is also associated with the wind load, from the respective rotor blade to the rotor hub. Although the load on the bearing from the wind force itself is significantly lower than the load caused by the tilting moment resulting from the wind load, it cannot be neglected because the bearings according to the invention, with their approximately cylindrical rolling elements, cannot transmit radial forces. The additional bearing serves this purpose instead.

[0025] The invention prefers an arrangement in which the third bearing point is located between the two raceways for approximately cylindrical rolling elements, which are oriented such that their axes of rotation are approximately radial with respect to the longitudinal axis of the respective rotor blade. The result is a very space-saving design, as the third or additional bearing point is placed axially between the two first bearings, particularly in the area of ​​a lug between the two first bearings.

[0026] The third bearing can also be designed as a rolling bearing to ensure the smoothest possible rotor blade pitch adjustment, with the axes of rotation of its rolling elements being approximately parallel to the longitudinal axis of the rotor blade. Since, on the other hand, the forces to be transmitted by the third bearing are lower than those of the two bearings described first, a rolling element of the third bearing can have a smaller volume than a rolling element of one of the bearings with the rolling elements oriented approximately radially with respect to the longitudinal axis of the rotor blade.

[0027] On the other hand, it is also possible to design the third bearing point as a plain bearing. Since this bearing is only subjected to comparatively low forces, no significant frictional forces are generated within it.

[0028] Another consequence of the lower load on the third or additional bearing point is that the effective width of the raceway or sliding surface of a bearing point inserted between two facing cylindrical surfaces of the two connecting elements can be dimensioned smaller than the effective width of a raceway that comes into contact with a rolling element whose axis of rotation is directed approximately radially with respect to the longitudinal axis of the rotor blade in question.

[0029] To facilitate the assembly of the two ring-shaped connecting elements together with the rolling elements arranged between them and, if necessary, spacers or rolling element cages, the invention recommends designing a connecting element to be divided along a plane oriented approximately perpendicular to the longitudinal axis of the rotor blade, so that the two halves can be separated for the insertion of the rolling elements.

[0030] To ensure that the rolling elements are aligned parallel to the raceways with minimal tilting, especially under load, the cross-section of the raceways provided for inserting the rolling elements is designed, according to the invention, such that at least in certain areas it does not correspond to the longitudinal section of a rolling element to be inserted therein, but is preferably narrower in the axial direction and thus preloaded against the rolling elements. If the raceway then widens—partly under the influence of the rolling elements themselves, but also possibly under load—it nevertheless rests in a positive-locking position against the rolling elements, so that they cannot tilt. For this purpose, according to the invention, the axial extent of the cross-section of the raceways provided for inserting the rolling elements is chosen to be smaller, at least in certain areas, than the diameter of the corresponding section of a rolling element.

[0031] To increase the service life of the bearing according to the invention, the rolling elements, whose axes of rotation are directed approximately radially with respect to the longitudinal axis of the rotor blade in question, should have at least one crowned transition area between the outer surface and at least one adjacent end face, i.e., a flattening or rounding. This allows for tolerance of edge pressure against the raceway during elastic deformation of the bearing unit in operation, by ensuring sufficient contact area with the raceways in the region of the rounded transition, even in this case.

[0032] Another measure for reducing wear in the bearing according to the invention consists in the fact that the rolling elements, whose axes of rotation are directed approximately radially with respect to the longitudinal axis of the respective rotor blade, have at least one spherical end face. This increases the sliding surface area by allowing the radially outer end faces of a rolling element to slide along the inside of the connecting element there and therefore be subject to only minimal wear. In this respect, it is advantageous if the radius of curvature of the spherical end face corresponds approximately to or is smaller than the radius of the inside of the outer ring.

[0033] Wear is also reduced by increasing the elasticity of the rolling elements, because under high loads and thus high elastic deformation of the bearing unit, they can then yield elastically, at least to a limited extent, and subsequently spring back without permanent deformation. Elasticity is increased, for example, by designing the rolling elements, whose axes of rotation are oriented approximately radially with respect to the longitudinal axis of the respective rotor blade, as hollow bodies. This can be achieved, for example, by coaxial drilling along their axis of rotation. Depending on the thickness of the bore or the remaining shell, the elasticity can be precisely adjusted.

[0034] Such cavities can be used to guide adjacent hollow rolling elements together using end-face connecting elements, thus maintaining a defined distance between them. These connecting elements engage, at least partially, in the cavities of the rolling elements. In the simplest case, they can, for example, have the shape of C-shaped clamps, the ends of which engage in a central or coaxial bore of two adjacent cylindrical or cylindrical rolling elements.

[0035] Such connecting elements, in turn, offer the possibility of being combined with one another to form one or more cages or cage segments. These cage segments extend, for example, only over a limited central angle and not over the entire circumference of a row of rolling elements, and / or they encompass the rolling elements at their inner or outer end faces, or on both sides.

[0036] Alternatively, a spacer can be inserted between adjacent rolling elements, the radial longitudinal section of which is smaller than or equal to the radial longitudinal section of a rolling element. In this case, the rolling elements themselves can be longer and thus have a maximum volume, enabling the transmission of greater forces, since no space is lost to a cage within a given installation space.

[0037] In a first embodiment of the invention, no toothing is provided on any connecting element; in such a case, the rotor blade adjustment is carried out, for example, by means of a hydraulic cylinder which is articulated eccentrically to the longitudinal axis of the rotor blade and is supported on the rotor hub, or vice versa.

[0038] On the other hand, for the purpose of rotor blade adjustment, a toothing is also provided on a connecting element, preferably on the inside of the inner ring, for the engagement of a toothed output element of a drive motor, e.g. a pinion.

[0039] A constant, i.e., continuous (small) twisting of the rotor blades supports the rotor blade bearing according to the invention by allowing the lubricating film between the rolling elements and running surfaces to regenerate continuously, thus preventing temporary dry running. This applies particularly to cases where, under constant wind conditions, the blade pitch angle hardly changes and the blade bearings therefore remain in one position.Even with such a quasi-constant blade pitch angle, adverse raceway wear can occur in the blade bearings, since, as the rotor blade passes the tower, a tilting moment load acts on the stationary (non-rotating) blade bearings due to aerodynamic suction and pressure. Without the inventive method, this load would disrupt the lubricating film between the rolling elements and the raceway, leading to raceway damage through so-called "false brinelling" (i.e., degeneration of the raceway due to high Hertzian pressure of the rolling elements on the raceways) as a result of recurring, alternating loads acting on the rolling bearing, which quickly lead to lubricating film displacement during the stationary period of the rolling bearing.

[0040] This so-called "false brinelling" occurs when the wind turbine is switched off for whatever reason, e.g., during maintenance / repair work or during a storm, and the rotor with its blades spins slowly freely ("freewheeling") without generating electrical energy. In this case, too, the application of the method according to the invention during the wind turbine's downtime can prevent or avoid runway damage caused by false brinelling.

[0041] A further advantage of the method according to the invention is the prevention of raceway wear caused by so-called "fretting corrosion." This occurs due to elastic deformation of the bearing unit / its connecting structure and the resulting sliding movement of the rolling elements along their longitudinal axis and thus along the raceway. The method according to the invention always ensures a rolling movement of the rolling elements and thus the formation of the necessary lubricating film between the rolling elements and the raceways, even when the rolling elements are subjected to detrimental sliding movements along their longitudinal axis. This applies regardless of whether the wind turbine is in operation or not, or whether the rotor blades need to be adjusted or not, as long as the continuous, i.e., uninterrupted (small), adjustment of the rotor blades is advantageously carried out.

[0042] The constant twisting is achieved by appropriately controlling the motor or cylinder for rotor blade pitch. It is advantageous to imprint a periodic motion as the constant twisting, because the resulting oscillating movement of a rotor blade leads to a particularly favorable lubricating film formation between the rolling elements and raceways.

[0043] The invention can be optimized by ensuring that the period of the rotor blade's oscillating rotation corresponds to the rotation period of the wind turbine. This achieves a mutual equalization of the loads exerted by the different rotor blades, thereby minimizing the resulting structural load. Conversely, the periodic movement should continue when the wind turbine is stationary (e.g., during calm conditions). In the lower speed range of the wind turbine, this may require decoupling the periodic adjustment from the turbine's rotational speed, for example, by ensuring that a minimum adjustment frequency is never undercut. This minimum adjustment frequency can be maintained during the wind turbine's start-up until an angular position synchronized with the turbine's angle is reached, allowing the pitch angle to then be adjusted accordingly.

[0044] During the periodic rotation of a rotor blade, its angle of attack oscillates between two extreme values. Mutual compensation of differing deflections of the various rotor blades can be achieved if the maxima of the periodic angle of attack deflection for each rotor blade are reached at a predetermined rotation angle of the respective rotor blade around the rotor axis. Such a deflection, for example a sinusoidal one, results, with three rotor blades, in the periodic deviations of adjacent rotor blades from the mean value differing by 120° at any given time; generally, i.e., with n rotor blades, by 360° / n.

[0045] Excellent results can be achieved when the extremes of the periodic angle of attack deflection occur approximately at the highest and lowest points of the rotor blade. The blade angle at the highest point should correspond to a higher wind speed, and at the lowest point to a lower wind speed. This is because, naturally, wind speed is greater at higher altitudes than near the ground.

[0046] Optimization of the individual blade pitch angle is achieved when the amplitude of the periodic deflection of the rotor blade pitch angle depends on the wind speed, which increases with height, for example, being approximately proportional to it. With such a control system, care should be taken to ensure that the deflection amplitude does not fall below a lower limit, even when the wind speed or the difference between the wind speed at the top and bottom of the turbine approaches zero (e.g., in absolutely calm conditions).

[0047] Finally, it is in accordance with the teaching of the invention that the mean value between the extreme values ​​of the twist depends on the wind speed. As before, the mean value of the rotor blade pitch angle is used to achieve optimal adaptation of the rotor blade position to the specific wind conditions. By preferably choosing the previously statically set rotor blade pitch angle as the mean value, optimal conditions are achieved for each individual rotor blade.

[0048] Further features, properties, advantages, and effects based on the invention will become apparent from the following description of some preferred embodiments of the invention and from the drawings. These show: Fig. 1 a section through a rotor blade bearing unit according to the invention in the installed state, partially broken off; Fig. 2 the blade storage unit Fig. 1 in its fully assembled state, also broken off; Fig. 3 A view of the lateral surface of a rolling element of the blade bearing unit from the Fig. 1 and Fig. 2; as well as Fig. 4 one of the Fig. 1 corresponding view of a modified embodiment of the invention.

[0049] A blade bearing 1 according to the invention is used in wind turbines and serves there for the rotatable connection of a rotor blade 2 to the rotor hub 3.

[0050] The rotor blade 2 is typically made of fiber-reinforced composite material and is designed in the manner of a wing. To save weight, the rotor blade 2 is designed as a shell surface 4 surrounding an inner cavity, which transitions at the rear end 5 of the rotor blade 2 into a cylindrical shell-shaped section with a diameter of, for example, approximately 2 m to 3 m. Accordingly, the flat rear connection surface 6 has an annular outline. This connection surface 6 contains blind holes 7 arranged in a ring, each leading to an anchoring body 8 made of a hard material, e.g., iron, inserted into the rotor blade 2. The blind holes 7 continue as internal threaded bores in the anchoring bodies 8.

[0051] The rotor hub 3 has a rigid bulge 9 with a flat, annular contact surface 10 for each rotor blade 2, which surrounds a circular opening 11. These contact surfaces 10 also have blind bores 12 arranged in a ring and provided with an internal thread.

[0052] In the illustrated embodiment, the inner diameter of such a circular opening 11 is larger than the outer diameter of the rotor blade 2 at its rear end 5. The bearing unit 1, which has two annular connecting elements 13, 14 that are concentric to each other and rotatable relative to each other, is located between the two connecting surfaces 6, 10. Each of two opposite end faces 15, 16 of these connecting elements 13, 14 bears fully against one of the connecting surfaces 6, 10.

[0053] For the secure connection of the connecting elements 13, 14 to the rotor blade 2 on the one hand and the rotor hub 3 on the other, through-holes 17, 18 arranged in a ring shape are provided in each of the connecting elements 13, 14. The number, diameter, and orientation of the through-holes 17 of the inner connecting element 13 correspond to the blind holes 7 in the mounting surface 6 of the rotor blade 2 such that each through-hole 17 aligns with each blind hole 7, allowing the insertion of a stud bolt 19. Once all nuts on the stud bolts 19 are tightened, the inner ring 13 is securely connected to the rear end 5 of the rotor blade 2, preferably such that the central axis of the inner ring 13 is aligned with the longitudinal axis of the rotor blade 2.

[0054] The through holes 18 of the outer connecting element 14 correspond in number, diameter, and orientation to the blind holes 12 in the connecting surface 10 of the rotor hub 3 such that each through hole 18 is aligned with each blind hole 12, allowing the insertion of a stud bolt 20. Once all nuts on the stud bolts 20 are tightened, the outer ring 14 is firmly connected to the recess 9 of the rotor hub 3.

[0055] Further details of storage unit 1 are more easily seen in the illustration according to Fig. 2. A circumferential, collar-shaped nose 21 with an approximately rectangular cross-section is clearly visible on the inside of the outer connecting element 14. The annular side surfaces 22, 23 of this nose 21 serve as running surfaces for a row of rolling elements 24, 25.

[0056] Such a rolling element 24, 25 is in Fig. Figure 3 is shown in isolation. The approximately cylindrical shape is recognizable, with a cylindrical outer surface 26 in the central region and the convex, i.e., rounded, transitions 27, 28 into the end faces 29, 30. All rolling elements 24, 25 are oriented such that their longitudinal axes 31 run radially to the longitudinal axis of the rotor blade 2. Thus, each rolling element 24, 25 has a radially outer end face 29 and a radially inner end face 30. The outer end face 29 is convexly curved outwards, in a spherical shape. The radius of curvature of this spherical projection corresponds approximately to the inner diameter of the outer ring 14 laterally adjacent to the nose 21 or axially offset from it, or is slightly smaller than the latter. Therefore, there is no contact with the inner surface of the outer ring 14 in the region of the circumference 27 of this end face, and thus no friction.For this purpose, 14 additional circumferential depressions 32 can be provided at the relevant points of the outer ring.

[0057] The radial extent of the nose 21 with respect to the bearing axis of rotation corresponds approximately to the length of a rolling element 24, 25. A running surface 34 in the form of a groove-shaped recess for a further bearing point 35 is provided in the inner end face 33 of the nose 21, which is preferably also constructed in the manner of a cylindrical roller bearing. The width of this running surface 34 is smaller than the width of the running surfaces 22, 23 of the other two bearing points 24, 25.

[0058] The radially inner connecting element 13 has a circumferential recess 36 of approximately rectangular cross-section on its outer surface. While the depth of this recess 36 corresponds approximately to the length of a rolling element 24, 25, its width is the sum of the diameters of a rolling element 24 of the upper bearing point facing the rotor blade 2 and of a rolling element 25 of the lower bearing point facing the rotor hub 3, plus the axial extent of the intermediate lug 21. If this condition is maintained as precisely as possible, the rolling elements 24, 25 roll without play between the side surfaces 22, 23 of the lug 21 on the one hand and the side surfaces 37 of the recess 36 on the other.

[0059] The recess 36 is bounded laterally and axially by a collar-shaped, radially outwardly projecting nose 38, 39. Between these and the corresponding areas of the inside of the outer ring there is an annular sealing element 40, 41.

[0060] The inner ring 13 is divided into two halves, an upper 43 and a lower 44, along a central plane 42 perpendicular to the bearing axis of rotation. These halves 43, 44 are separated during assembly of the blade bearing 1 and are only reassembled after the rolling elements 24, 25, 35 have been inserted and fixed together by means of axially oriented screws 45. One of the two halves 43, 44 also contains the radially inner running surface for the third bearing point 35.

[0061] The rolling elements 24, 25, 35 of each rolling bearing are kept at a distance by inserted spacers or by cages.

[0062] The rolling elements 24, 25, whose longitudinal or rotational axes 31 are oriented radially with respect to the bearing axis of rotation, primarily serve to transmit relatively high tilting or blade root bending moments caused on the rotor blade 2 by the wind pressure. The smaller rolling elements 35 transmit the wind pressure from the rotor blade 2 to the blade hub 3.

[0063] In this embodiment, a change in the rotor blade pitch angle is effected, for example, by a hydraulic cylinder that is articulated to the rotor blade 2 on one side and the rotor hub 3 on the other. Preferably, this cylinder is continuously adjusted so that the rolling elements 24, 25, 35 are constantly moving and the lubricating film covering them is maintained.

[0064] In Fig.Figure 4 shows another bearing unit 1' with an alternative mechanism for changing the rotor blade pitch angle. For this purpose, an internal toothing 46 is provided on the inside of the inner ring 13'. A drive unit 47 is fixed on the housing side in the recess 11 of the bulge 9 of the rotor hub 3, while an output pinion 48 meshes with the internal toothing 46. This rotates the inner ring 13' and, with it, the rotor blade 2 relative to the rotor hub 3. The drive unit 47 can consist of a motor 49, a downstream gearbox 50, and a brake 51. Preferably, the motor 49 is also continuously adjusted to maintain the lubricating film on the rolling elements 24, 25, 35.In order to avoid having to assemble the ring carrying the internal toothing 46 from several parts, which entails additional adjustment problems, in this embodiment 1' the subdivision 42' is provided on the outer ring 14' and not on the inner ring 13'; accordingly, the central nose 21' is located on the outside of the inner ring 13' instead of on the inside of the outer ring 14'.

[0065] The invention allows for a number of further modifications; for example, the inner ring 13 can also be fixed to the rotor hub 3 and the outer ring 14 to the rotor blade 2. The rings 13, 14 can be axially offset from one another or have different axial extensions. Some or all of the through holes 17, 18 can be replaced by blind holes.

[0066] The outer ring 14 attached to the hub 3 can have a recess 36, if conversely the inner ring 13 has a nose 21.

[0067] The outer ring 14 could have external teeth similar to those of the inner ring 13', 46 and be connected to the rotor blade 2, if conversely the inner ring 13 were connected to the rotor hub 3.

[0068] Ring 44 could be connected to rotor blade 2 if, conversely, ring 43 served as the bearing surface for the nut of stud bolt 19.

[0069] Instead of the studs 19, 20, screws, especially machine screws, could be used.

Claims

[1] Method for operating a wind turbine with at least one bearing unit (1; 1') as a blade bearing for the rotatable connection of an elongated rotor blade (2) to a rotor hub (3) of a wind turbine, the storage unit (1; 1') comprising: - at least two axially offset raceways (22, 23, 37) with rotating rolling elements (24, 25) which have two mutually rotatable, annular connecting elements (13, 14; 13', 14') for indirect or direct connection to the rear end (5) of the respective rotor blade (2) on the one hand and to the rotor hub (3) on the other hand, wherein - the annular connecting elements (13, 14; 13', 14') have mutually opposite end faces (15, 16) which serve as connecting surfaces to the rotor hub (3) on the one hand and to the relevant rotor blade (2) on the other hand, and - an annular gap sealed in the area of ​​the two connection surfaces is formed between the two connection elements (13, 14; 13', 14'), wherein - the rolling elements (24, 25) of two axially offset raceways (22, 23, 37) have an approximately cylindrical shape, each with a lateral surface (26) which is rotationally symmetrical to exactly one axis of rotation (31), wherein - these rolling elements (24, 25) are aligned such that their respective axes of rotation (31) are aligned approximately perpendicular to the longitudinal axis of the respective rotor blade (2), and wherein a projecting, all-round nose (21; 21') is provided on the shell side of a connecting element (14; 13') facing the other connecting element (13; 14'), wherein the two circular side surfaces (22, 23) of the nose (21; 21') serve as a running surface for the approximately cylindrical rolling elements (24, 25) of each row of rolling elements, whereby the rolling elements (24, 25) roll without play between the side surfaces (22, 23) of the nose (21) on the one hand and the side surfaces (37) of a circumferential depression (36) of approximately rectangular cross-section provided on an outer surface or inner surface of the connecting element (13, 14), wherein - the rotor blade (2) is designed as a shell surface (4) surrounding an inner cavity, which at the rear end (5) of the rotor blade (2) merges into a cylindrical shell-shaped course up to a flat, rear connection surface (6), and wherein - by means of a hydraulic cylinder or a drive unit (47), the rotor blade (2) is constantly and periodically rotated about its longitudinal axis relative to the rotor hub (3), regardless of whether the wind turbine is in operation or not, or whether the wind turbine is stationary or not, or whether the rotor blades need to be adjusted or not. [2] Method according to claim 1, characterized by that the constant rotation of a rotor blade (2) is an oscillating movement. [3] Method according to claim 2, characterized by that the period of rotation of a rotor blade (2) corresponds to the rotation period of the wind turbine. [4] Method according to claim 2 or 3, characterized by that the period of rotation of a rotor blade (2) is kept approximately constant when the rotation period of the wind turbine falls below a predetermined lower limit value. [5] Method according to one of claims 2 to 4, characterized by that the adjustment movement oscillates between two extreme values. [6] Method according to claim 2, characterized bythat the amplitude of the twisting of a rotor blade (2) is specified as a function of the different wind speeds above ground, which act on the rotor blades approximately at their uppermost and lowermost positions, either on the basis of a measurement of this different wind speed or on the basis of a control-technical specification. [7] Method according to claim 6, characterized by that during operation the amplitude of the twisting of a rotor blade (2) does not fall below a predetermined, non-zero limit value. [8] Method according to one of the preceding claims, characterized bythat the rotor blade(s) in question (2) is / are constantly rotated about its / their longitudinal axis(es) at least during operation of the wind turbine, so that the rolling elements (24, 25, 35) move constantly and thereby a lubricating film covering them is maintained, and a rolling movement of the rolling elements (24, 25, 35) is effected to build up the lubricating film between the rolling elements (24, 25, 35) and the raceways (22, 23, 37). [9] Method according to claim 1, wherein blind holes (7) are provided in the rear connection surface (6), which on the one hand lead to an anchoring body (8) made of a hard material inserted into the rotor blade (2), in which they continue as internally threaded holes, and which on the other hand correspond with through holes (17) distributed in a ring shape in the respective connection element (13, 13') in terms of number, diameter and orientation in such a way that they are aligned and thereby allow the insertion of a stud bolt (19) in each case.

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