Bearing for a wind turbine, wind turbine including the bearing, and method for producing a bearing ring

Abstract

The present invention relates to a bearing for a wind turbine, a wind turbine including the bearing, and a method for producing a bearing ring. A bearing for a wind turbine includes first and second rings (9, 10) arranged radially with respect to each other, wherein one ring (10) rotates about a rotational axis relative to the other ring (9), whereby the first ring (9) has a cylindrical ring section (21) and a collar (22) extending radially from the ring section (21), whereby the collar (22) has an axial support zone (23) for supporting an axial bearing element (15), characterized in that a plurality of pre-tensioning elements (25) generating compressive stress are fixed to the first ring (9) in a section of the collar (22) extending from the ring section (21).

Description

Technical Field

[0001] The present invention relates to a bearing for a wind turbine, which comprises a first and a second ring arranged radially to each other, one of the rings being rotatable relative to the other about a rotational axis, wherein the first ring has a cylindrical ring section and a collar extending radially from the ring section, and wherein the collar has an axial support zone for supporting an axial bearing element. Background Art

[0002] As is generally known, a wind turbine comprises a tower and a nacelle fixed to the top of the tower. A hub to which a plurality of rotor blades are attached is arranged at the nacelle. As is generally known, when the turbine blades interact with the oncoming wind, the hub rotates and drives a generator to generate electricity. Such a wind turbine comprises a plurality of rotating elements, which are arranged in respective bearings. An example is the main bearing of the generator in a direct drive wind turbine, while the turbine may also comprise one or more gears such as a planetary gear or a hydraulic gear train.

[0003] The bearing generally comprises two rings, namely, a first and a second ring which are generally arranged radially to each other. One ring is stationary, while the other ring rotates relative to the first ring. It is possible that the radially inner ring is stationary and coupled to the stationary main shaft of the wind turbine, while the outer ring rotates about the inner ring and is coupled to the rotor of the generator. Vice versa, it is also possible that the outer ring is stationary, while the inner ring rotates. However the bearing is arranged, the respective rotating ring is coupled to the hub and the respective component which needs to rotate, such that the rotation of the hub is transmitted to the component.

[0004] Although it is known that the bearing is a roller bearing comprising a plurality of rollers (which may be tapered rollers), it is also known to conceive the bearing as a sliding bearing or a plain bearing. The stationary ring is usually provided with a respective bearing element in the form of a sliding pad, on which the rotating ring slides and is supported by a very thin fluid film. A bearing pad (which may be tiltable and thus able to compensate for any geometric tolerances between the rings, especially those caused by the forces acting on the bearing) is arranged at the stationary ring having a specific ring design, and accordingly a geometry. This ring (which may also be referred to as a housing or bearing housing) comprises a cylindrical ring section, on which the other ring is radially supported by means of respective radial bearing elements. For axial bearing, the ring is provided with an axial bearing element, which is supported at a specific axial support zone realized at this ring. To realize this support zone, the ring comprises a collar, which extends radially from the cylindrical ring section. The axial ring surface of this collar is the axial support zone, on which the sliding bearing element is supported.

[0005] In operation, when the blowing wind interacts with the rotor blades, high loads remain on the bearings, and the loads are introduced via the rotor blades into the rotating ring of the bearings, and the bearings are axially supported as mentioned by axial bearing elements arranged at the stationary ring. These loads can also vary during operation. However, since the geometry of this stationary ring includes a cylindrical ring section and a radially extending collar, it has been found that in the region where the collar meets the cylindrical ring section, high stress concentrations occur, resulting in high tensile stresses in the bearing ring in the region where the collar and the ring section exhibit an almost rectangular design. To solve this problem and accordingly counteract these high tensile stresses or loads, materials with higher strength or stiffness can be used. This will result in higher costs because specific materials with less ductility and other mechanical properties need to be used. In an alternative, materials can be added, and accordingly rings with thicker ring sections and collars can be used. This will result in heavier bearings and accordingly structures, which again brings higher costs and is also unacceptable. Summary of the Invention

[0006] Accordingly, an object of the present invention is to provide an improved bearing.

[0007] To solve this object, the bearing as described above is characterized in that several pre-tensioning elements that generate compressive stresses are fixed to the first ring in the section where the collar extends from the ring section.

[0008] According to the present invention, the first ring including a cylindrical ring section and a collar is provided with several pre-tensioning elements for generating internal compressive stresses in the first ring, and accordingly in the section where high tensile stresses occur due to the axial support of the axial bearing elements and accordingly the sliding pads. This introduced high compressive stress counteracts the induced tensile stress in a certain way and accordingly allows higher tensile stresses to be introduced until the tolerable tensile stress limit is reached. Therefore, with the help of these pre-tensioning elements, the first ring can be "strengthened", especially in the section where high tensile stresses are induced, that is, in the section where the collar extends from and accordingly merges with the ring section.

[0009] To generate compressive stresses in this area, the pre-tensioning elements are arranged at the first ring in this particular section or area where the collar extends from the ring section, such that the counteracting compressive stresses are accurately generated where they are needed (i.e., at the position in the first ring where tensile stresses generated by the operation of the turbine are induced).

[0010] The arrangement of the pre-tensioning elements is a cheap but very effective way to enhance the mechanical properties of the first ring so that the ring is more tolerant of the high tensile stresses generated by the corresponding loads. The first ring and accordingly the bearing housing material generally have a higher load-carrying capacity in view of fatigue and ultimate strength, in view of compressive loads rather than tensile loads. Therefore, with the help of the pre-tensioning elements, the strength of the first ring can be significantly increased.

[0011] In a preferred embodiment, each pre-tensioning element is at least a partially threaded bolt inserted into at least a partially threaded hole extending into the ring section, the bolt being directly or indirectly supported against the ring on a support surface. By means of these bolts, which are screwed with their respective threaded sections into the respective threaded holes and are supported against the ring on the support surface, corresponding compressive stresses can be generated and induced in the ring material. The bolts are firmly fixed by means of a section threaded at one end into the threaded hole and by means of their support against the ring at the other end, such that corresponding compressive stresses can be generated and adjusted according to the tension of the bolts by which they are tensioned. As will be explained later, various embodiments regarding these bolt elements and their fixation are possible. It can be a bolt-nut combination, where the nut is screwed onto the bolt and the nut is supported against a corresponding support surface, which can be provided directly at the ring or by means of a washer or the like. On the other hand, bolts with a hexagonal head can be used, which are directly supported on the ring support surface or at a corresponding intermediate washer or the like.

[0012] Although such bolt pre-tensioning elements are preferred because of their simple design and because the holes can be easily provided in the ring, other pre-tensioning elements can also be used, for example, clips such as a screw clip arrangement fixed to the ring can be used.

[0013] The holes into which the bolts are inserted and correspondingly screwed are preferably provided in the axial surface of the first ring and extend into the ring section. According to this embodiment, the holes are provided at the outer axial ring surface of the first ring and extend into the cylindrical ring section. The length of the holes depends on the thickness of the collar along the axial direction, as the holes need to extend quite deep into this ring section, preferably more than at least one-third of the axial thickness and correspondingly preferably about half of its axial thickness.

[0014] The holes and bolts are preferably arranged equidistantly around the rotational axis of the bearing. Around the axial ring surface, a corresponding number of bolts and holes are provided, for example, any number between 10 - 30 holes and correspondingly bolts, depending on the diameter of the ring. Preferably, the number is between 15 - 25, and most preferably between 18 - 22.

[0015] Regarding the orientation of the holes and thus the bolts, two alternatives are possible. In the first alternative, each hole and of course the corresponding bolt extends parallel to the rotational axis of the bearing. In an alternative, each hole and the corresponding bolt extend at an angle with respect to the rotational axis into the ring section. The orientation depends on the orientation of the collar. If the collar extends radially outwards from the cylindrical ring section, the holes and bolts are oriented towards the rotational axis. If the collar extends inwards, the longitudinal axes of the holes and bolts extend away from the rotational axis.

[0016] If the holes and the bolts are angled, the angle is preferably between 3° and 30°, most preferably between 5° and 20°. The angle chosen, of course, depends on the final geometry of the first ring in this area.

[0017] To firmly fix each bolt in the hole, the bolt as mentioned is at least partially threaded at least at one end, this end being inserted into a threaded hole which can be threaded over its entire length or only in its inner end region. Of course, it is possible that the bolt is also threaded over its entire length.

[0018] According to the first embodiment, each bolt can project from the hole with a threaded end, whereby a nut is screwed onto the thread, the nut being supported on a support surface. In this embodiment, the bolt is a simple threaded stud which can be threaded over its entire length or only in the corresponding end region, one end region being screwed into the hole thread. The other end projects from the hole. A nut is screwed onto this end and the nut is firmly screwed against the corresponding support surface, thus tensioning the bolt, respectively the stud, and together with this first ring. The tension can be appropriately adjusted by the torque applied to the nut.

[0019] In a second alternative, each bolt has a bolt head which includes an attachment section for a tool, the bolt head being supported on a support surface. Here, the bolt can be provided, for example, with a hexagonal head. The bolt is threaded at its opposite end section or over its entire length and is screwed into the hole thread until the bolt head is supported on the support surface. Again, here, the tension of the bolt, and thus the applied compressive stress, can be appropriately adjusted according to the torque applied to the bolt head.

[0020] As mentioned, it is possible that the holes and the bolts, respectively their longitudinal axes, are angled towards the axis of rotation. To achieve a uniform local load distribution of the nut, respectively the bolt head, on the support surface, another embodiment of the invention provides that the nut or the bolt head of each bolt arranged at an angle towards the axis of rotation is supported on a support surface oriented perpendicular to the longitudinal hole axis. This embodiment allows a perfect uniform or symmetric load distribution of the load applied by the nut, respectively the bolt head, to the support surface. Both the nut and the bolt head have flat contact surfaces. To ensure that this flat contact surface is fully supported on the corresponding support surface and since the longitudinal axis of the bolt is angled towards the axis of rotation, this angle is compensated for by also arranging the support surface in the corresponding angled position. According to this embodiment of the invention, the support surface is oriented perpendicular to the longitudinal hole axis and thus parallel to the corresponding contact surface of the nut, respectively the bolt head. This ensures that the nut or bolt head contact surface is fully supported on the corresponding support surface such that any load is evenly distributed over this contact area.

[0021] The corresponding support surface may be integral with the first ring. The ring is machined at its front axial surface where it is supposed to support the nut or bolt head, so as to machine a corresponding annular area with an angled support surface. Since the hole is also provided exactly in this area, the support surface can be provided with an excellent orientation.

[0022] In an alternative, a corresponding washer including a support surface may also be provided. Here, the axial ring surface is flat. The washer is attached to this ring surface, and the bolt is inserted through the washer into the hole. The washer itself includes a corresponding angled support surface. Here, it is necessary to adjust the orientation of the washer around the hole axis so that the contact surface of the nut or bolt head has a flat overall contact on the corresponding washer support surface. However, this embodiment also allows an excellent load distribution.

[0023] The bearing element supported at the first ring and correspondingly fixed to it at the collar is preferably antiltilting fluid film bearing pads, and a second ring having, for example, a rectangular cross section is axially supported thereon. Thus, the bearing itself is a fluid film bearing and correspondingly a sliding bearing.

[0024] The invention further relates to a wind turbine including at least one bearing as previously mentioned. This bearing is preferably the main bearing of the turbine.

[0025] The first ring is preferably an inner ring and is coupled to the stationary shaft, while the second ring is an outer ring and is coupled to the rotor of the generator.

[0026] Finally, the invention also relates to a method for producing the first ring of the bearing as previously mentioned. The method is characterized in that a pre-tensioning element is first fixed to the ring and tensioned to generate a compressive stress, and then the support area of the collar is machined. This method of the invention solves the fact that in a fluid film bearing using corresponding tilting sliding pads, it is important to have a highly precise machined surface at the corresponding first ring and correspondingly the bearing housing, on which the individual sliding pads rest. This means that the support surface of the collar needs to be machined perfectly to ensure the most uniform load distribution between the sliding pads. When the pre-tensioning element, correspondingly the bolt, is tensioned, the first ring and correspondingly the bearing housing will be slightly deformed, resulting in a slightly uneven support surface provided at the collar. This leads to a poor load sharing distribution between the individual adjacent tilting pads. To solve this problem, the method of the invention proposes first fixing and tensioning all the pre-tensioning elements and generating the requested and clearly defined compressive stress, the fixing resulting in the mentioned slight deformation of the support surface. After tensioning all the pre-tensioning elements, the corresponding collar support surface is machined so as to ensure that this support surface is completely flat to perfectly support all the sliding pads. Description of the Drawings

[0027] Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. However, the drawings are only schematic sketches designed for illustrative purposes only and do not limit the present invention. The drawings show:

[0028] Figure 1 is a schematic perspective view of a wind turbine,

[0029] Figure 2 is a partial cross-sectional view of the hub, main shaft and generator including the corresponding bearings of the present invention,

[0030] Figure 3 is a cross-section of the bearing of the present invention in a region without a pre-tensioning element, which is used to illustrate the induced tensile stress,

[0031] Figure 4 is a three-dimensional cross-section of the bearing of the present invention in a region with a pre-tensioning element arranged at an angle to the axis of rotation,

[0032] Figure 5 is a three-dimensional view of the bearing of the present invention from the side where the pre-tensioning element is arranged, and

[0033] Figure 6 is a schematic cross-sectional view with a pre-tensioning element arranged parallel to the axis of rotation. Detailed description

[0034] Figure 1 shows a schematic illustration of a wind turbine 1, which includes a rotor 2, a nacelle 3 and a tower 4, and the nacelle 3 is arranged on top of the tower 4. The rotor 2 includes three rotor blades 5 attached to a hub 6. This principle arrangement of a wind turbine is known.

[0035] In a more detailed cross-section according to Figure 2 the wind turbine 1 includes a stationary main shaft 7, and the stationary main shaft 7 is connected to a main bearing 8. This main bearing 8 includes an inner ring or first ring 9, which is stationary and connected to the stationary main shaft 7. The bearing 8 further includes a radially outer ring or second ring 10, which rotates relative to the stationary first ring 9 about the bearing axis of rotation. The hub 6 is connected to this second ring 10 such that the rotation of the hub 6 causes the rotation of the second ring 10. In addition, the rotor 11 of the generator 12 is connected to this second ring 10 such that this rotor 11 rotates when the hub 6 rotates. The generator 12 further includes a stator 13, and the stator 13 is stationary and connected to the stationary shaft 7. Similarly, this arrangement of a direct-drive wind turbine 1 is generally known.

[0036] The focus of the present invention lies in the arrangement of the bearing 8. Figure 3Shows a cross-section of bearing 8. It shows an inner first ring 9 and an outer second ring 10. The bearing 8 itself is a fluid film sliding bearing, in which the rotatable outer second ring 10 is radially and axially guided on the stationary inner second ring 9 by means of corresponding radial and axial bearing elements in the form of sliding pads and a fluid film provided between the second ring 10, respectively its sliding surface and the corresponding sliding pads. In the cross-section according to Figure 3 , only the axial sliding pad 14 at the inner bearing side oriented towards the main shaft 7 and the sliding pad 15 at the outer side of the bearing 8 are shown. The bearing element in the form of the sliding pad 15 is a tilting element as shown at the sliding pad 15. A mounting base 16 is provided, by means of which each sliding pad is mounted, respectively supported, at the first ring 9. The sliding pad 15 guiding the corresponding ring is attached to the mounting base 16 by means of a ball-and-socket joint 17, thus allowing the sliding pad 15 to tilt slightly relative to the mounting base 16. As shown, the sliding pad 15 has a flat sliding surface 18, while the second ring 10 has a flat axial sliding surface 19, and the flat axial sliding surface 19 slides on the sliding surface 18 by means of an intermediate fluid film 20. The same applies to the sliding pad 14.

[0037] As Figure 3 shown, the first ring 9 has a specific L-shaped cross-section design. It includes a cylindrical ring section 21 to which several not-shown radial sliding bearing pads are attached, on which the second ring 10 is radially guided. Also, here, corresponding fluid film sliding bearing contact is achieved. From this cylindrical ring section 21, a collar 22 extends radially to the outer side of the ring 9, as Figure 3 shown. This collar provided at the axial end of the ring 9 is provided with an axial support area 23, which is a flat ring support surface, on which the corresponding flat contact surface 24 of the mounting base 16 is supported, and accordingly, the corresponding flat contact surface 24 of the mounting base 16 is fixed thereto. Thus, obviously, the cylindrical ring section 21 and the collar 22 form an L-shaped cross-section.

[0038] As shown by the arrow P1, the axial sliding pad 15 exerts an axial force on the support area 23 and thus on the collar 22. This induces high tensile stresses in the area where the collar 22 extends from the ring section 21 (i.e., in the area where they merge). The double arrow P2 is a vector showing the tensile stress in the material, respectively the area of the first ring 9, that gives this high tensile stress. Given fatigue and extreme loads, this high tensile stress is a problem for the structural integrity of the first ring 9, respectively the entire fluid film bearing 8.

[0039] To counteract these high tensile stresses, respectively their negative effects, several pre-tensioning elements 25 are fixed to the first ring 9. The first ring 9 is provided with several holes 26, which extend from the outer axial front surface 27 of the ring 9, respectively the ring section 21, into the ring section 21, as Figure 4is shown. The hole 26 is provided with threads 28 at least at its inner end or over its entire length. A bolt 29 is screwed into this threaded hole 26. The bolt 29 includes threads 30 at least at its inner end, which inner end is screwed into the threads 28 of the hole 26. The opposite end of the bolt 29 extends out of the hole 26 and is also provided with threads 31. A nut 32 is screwed onto these threads 31, and the nut 32 is supported on a corresponding support surface 34 with its flat contact surface 33. This flat support surface 34 is provided integrally at the ring 9, respectively at the corresponding axial front surface 27, as Figure 5 is shown.

[0040] as Figure 4 is shown, the longitudinal axis of the hole 26, and thus also the longitudinal axis of the bolt 29, is angled with respect to the rotational axis of the bearing. The angle α is shown in Figure 4 is. To ensure that any load applied to the nut 32 for tensioning the bolt 29 is evenly distributed over its contact surface 33 with the support surface 34, the support surface 34 is also angled accordingly. It corresponds to the corresponding angled arrangement of the hole 26, respectively the bolt 29, and is perpendicular to the longitudinal axis of the hole 26, respectively the bolt 29. This allows for a very even load distribution.

[0041] When the corresponding threaded bolt 29 is screwed into the threaded hole 26 and has reached its final position, the nut 32 is screwed onto the bolt 29 and tightened with a well - defined torque. When the bolt 29 is fixed in the hole 26, the first ring 9 is compressed, resulting in a compressive force mainly oriented along the bolt axis as shown by the double arrow P3. The double arrow P3 shows the corresponding vector of the compressive stress induced by the pre - tensioning element 25. This induced compressive stress cancels or compensates the induced tensile stress, respectively allowing for a higher tensile stress to be tolerated, such that during operation, any tensile stress induced via the bearing element 15 does not negatively affect the bearing, respectively the ring material.

[0042] Finally, Figure 6 shows another embodiment of the first ring 9, which includes a cylindrical ring section 21 and a collar 22. Again, an axial bearing element 15, respectively a sliding pad, not shown, is axially supported on the collar 22 in the same manner as described with respect to Figure 3 is described.

[0043] Moreover, in this embodiment, a pre-tensioning element 26 is provided at the first ring 9. The first ring 9 is provided with a corresponding number of threaded holes 26. Bolts 29 are screwed into each hole 26. The bolts 29 include integral bolt heads 35 in the form of hexagon heads here, allowing a tool to engage at the bolt heads 35. Washers 36 are arranged between the bolt heads 35 and the axial front surface 27, which provide corresponding support surfaces 37 on which the corresponding contact surfaces 38 of the bolt heads 35 are supported. In this embodiment, the holes 26 and thus the longitudinal axes of the bolts 29 are parallel to the rotational axis.

[0044] As mentioned, a plurality of pre-tensioning elements 25 are provided evenly, correspondingly equidistantly distributed around the circumference of the first ring 9, as Figure 5 shown. The number of pre-tensioning elements 25 is selected according to the expected tensile stress to be compensated, correspondingly the load.

[0045] For the production of the corresponding first ring 9, correspondingly for the setting of the bearing 8, a specific time sequence of the corresponding steps is appropriate. After providing the corresponding holes 26 with their threads 28, the pre-tensioning elements 25, correspondingly the bolts 29, are inserted and the nuts 32 are firmly tightened with a corresponding torque, or the bolts 29 are firmly tightened via the bolt heads 35 of the bolts 29 in order to provide the necessary and requested compressive stress within the material. Since this induced compressive stress causes a certain but very small deformation in the regions of the collar 22 and the support zone 23, the support zone 23 is finally machined when all the bolts 29 are fixed. Any deformation caused by the fixing of the bolts 29 is removed, and finally the support zone 23 is as flat as possible to provide an ideal surface to support the corresponding bearing elements 15, correspondingly their mounting bases 17. This determines the proper load sharing between the bearing elements 15 around the entire circumference of the ring 9.

[0046] Although the invention has been described in detail with reference to the preferred embodiments, the invention is not limited to the disclosed examples, and those skilled in the art can derive other variations without departing from the scope of the invention according to the disclosed examples.

Claims

1. A bearing for a wind turbine, comprising a first and a second ring (9, 10) arranged radially to each other, wherein the second ring (10) rotates relative to the first ring (9) about a rotational axis, whereby the first ring (9) has a cylindrical ring section (21) and a collar (22) extending radially from the ring section (21), whereby the collar (22) has an axial support zone (23) for supporting an axial bearing element (15), characterized in that A plurality of pre-tensioning elements (25) generating compressive stress are fixed to the first ring (9) in a section where the collar (22) extends from the ring section (21).

2. The bearing according to claim 1, wherein Each pre-tensioning element (25) is at least partially threaded bolt (29) inserted into at least partially threaded hole (26) extending into the ring section (21), and the bolt (29) abuts against the first ring (9) and is supported on a support surface (34) directly or indirectly.

3. The bearing according to claim 2, characterized in that The holes (26) are provided in the axial surface (27) of the first ring (9) and extend into the ring section (21).

4. The bearing according to claim 3, characterized in that The holes (26) and the bolts (29) are equidistantly arranged around the rotation axis.

5. The bearing according to one of claims 2 to 4, characterized in that Each hole (26) extends parallel to the rotation axis, or is characterized in that each hole (26) extends into the ring section (21) at an angle (α) relative to the rotation axis.

6. The bearing according to claim 5, characterized in that The angle (α) is between 3° and 30°.

7. The bearing according to one of claims 2 to 4, characterized in that Each bolt (29) extends out of the hole (26) with a threaded end, whereby a nut (32) is screwed onto the thread (31), and the nut (32) is supported on the support surface (34).

8. The bearing according to claim 7, characterized in that Each bolt (29) has a bolt head (35) including an attachment section for a tool, and the bolt head (35) is supported on the support surface (34).

9. The bearing according to claim 8, characterized in that The nut (32) arranged at an angle towards the rotation axis or the bolt head (35) of each bolt (29) is supported on a support surface (34) oriented perpendicular to the longitudinal hole axis.

10. The bearing according to claim 9, characterized in that The support surface (34) is integral with the first ring (9), or is characterized in that a washer (36) including the support surface (34) is provided.

11. The bearing according to one of claims 2 to 4 as described above, characterized in that The bearing element (15) is a tiltable fluid film bearing pad.

12. A wind turbine comprising at least one bearing (1) according to one of claims 1 to 11.

13. The wind turbine according to claim 12, characterized in that The bearing (1) is the main bearing (1) of the wind turbine.

14. The wind turbine according to claim 12 or 13, characterized in that The first ring (9) is an inner ring and is connected to the stationary main shaft (7), while the second ring (10) is an outer ring and is connected to the rotor (11) of the generator (12).

15. A method for producing a first ring of a bearing according to one of claims 1 to 10, characterized in that First, the pre-tensioning elements (25) are fixed to the first ring (9) and tensioned to generate compressive stress, and then the axial support area (23) of the collar (22) is machined.

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