WIND TURBINE MAIN SHAFT ASSEMBLY

Abstract

A wind turbine main shaft assembly is provided. The wind turbine main shaft assembly includes a wind turbine main shaft and a connecting piece attached to an end of the wind turbine main shaft. The wind turbine main shaft assembly further includes a first frictional connection between an axial end face at the end of the wind turbine main shaft and an axial face of the connecting piece and a second frictional connection provided by an interference fit between a circumferential portion at the end of the wind turbine main shaft and a corresponding circumferential portion of the connecting piece.

Claims

1. A wind turbine main shaft assembly comprising: a wind turbine main shaft; and a connecting piece attached to an end of the wind turbine main shaft; wherein the assembly comprises a first frictional connection between an axial end face at the end of the wind turbine main shaft and an axial face of the connecting piece; and a second frictional connection provided by an interference fit between a circumferential portion at the end of the wind turbine main shaft and a corresponding circumferential portion of the connecting piece.

2. The wind turbine main shaft assembly according to claim 1, wherein the main shaft comprises at its end an outer circumferential face providing the circumferential portion of the main shaft, and wherein the connecting piece comprises a protrusion having an inner circumferential face providing the circumferential portion of the connecting piece, the outer circumferential face of the main shaft and the inner circumferential face of the connecting piece forming the interference fit.

3. The wind turbine main shaft assembly according to claim 1, wherein at least part of the circumferential portion of the main shaft providing the interference fit is tapered, and/or wherein at least part of the circumferential portion of the connecting piece providing the interference fit is tapered.

4. The wind turbine main shaft assembly according to claim 2, wherein the outer circumferential face of the main shaft is at least partly tapered, the tapered portion of the outer circumferential face having an outer circumference that decreases towards the end face of the main shaft, and wherein the inner circumferential face of the connecting piece is at least partly tapered at a corresponding axial portion, the tapered portion of the inner circumferential face having an inner circumference that decreases towards the end face of the main shaft.

5. The wind turbine main shaft assembly according to claim 1, wherein the end of the main shaft is conical, and wherein the connecting piece has a cylindrical hollow protrusion having a conical inner circumferential face that provides the circumferential portion.

6. The wind turbine main shaft assembly according to claim 1, further comprising connecting members arranged so as to press together the axial end face of the wind turbine main shaft and the axial face of the connecting piece to provide the first frictional connection.

7. The wind turbine main shaft assembly according to claim 6, wherein the connecting members comprise bolts and/or screws.

8. The wind turbine main shaft assembly according to claim 6, wherein the connecting members extend into the end of the wind turbine main shaft through its axial end face, and further extend through the axial face of the connecting piece.

9. The wind turbine main shaft assembly according to claim 7, wherein the connecting members comprise threaded bolts that are screwed into the end face of the wind turbine main shaft, the bolts extending through an inner flange of the connecting piece on which the axial face is provided, wherein nuts are tightened to the bolts on a side of the inner flange opposite of the axial face.

10. The wind turbine main shaft assembly according to claim 9, wherein the nuts are locked to the bolts using a locking mechanism, wherein the locking mechanism comprises a keyway in the respective bolt and a break lip on the respective nut, the break lip being breakable so as to engage the keyway to thereby lock the nut in place on the bolt.

11. The wind turbine main shaft assembly according to claim 1, wherein the connecting piece is a flange piece, wherein the flange piece is configured for attachment to a wind turbine gear box.

12. A wind turbine, comprising the wind turbine main shaft assembly according to claim 1.

13. A method of assembling a wind turbine main shaft assembly, the method comprising: providing a wind turbine main shaft; providing a connecting piece; and attaching the connecting piece to an end of the wind turbine main shaft, wherein the attaching comprises: establishing a first frictional connection between an axial end face at the end of the wind turbine main shaft and an axial face of the connecting piece; and establishing a second frictional connection by an interference fit between a circumferential portion at the end of the wind turbine main shaft and a corresponding circumferential portion of the connecting piece.

14. The method according to claim 13, wherein the attaching further comprises: providing connecting members that are configured to press together the axial end face of the wind turbine main shaft and the axial face of the connecting piece; arranging the connecting piece at the end of the wind turbine main shaft; and tightening the connecting members to thereby press the connecting piece onto the end of the wind turbine main shaft to establish the second frictional connection by the interference fit and to establish the first frictional connection.

15. The method according to claim 14, wherein providing the connecting members comprises the screwing of bolts into the axial end face of the wind turbine main shaft, wherein the bolts protrude through holes in an inner flange of the connecting piece when the connecting piece is arranged on the end of the wind turbine main shaft, and wherein the tightening of the connecting members comprises the tightening of nuts on the bolts so as to press the inner flange of the connecting piece against the axial end face of the wind turbine main shaft.

Description

BRIEF DESCRIPTION

[0031] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0032] FIG. 1 is a schematic drawing showing a wind turbine including a wind turbine main shaft assembly according to an embodiment of the invention;

[0033] FIG. 2 is a schematic drawing showing a wind turbine main shaft assembly according to an embodiment of the invention;

[0034] FIG. 3 is a schematic drawing showing an enlarged region of the drawing of FIG. 2;

[0035] FIG. 4 is a schematic drawing illustrating the transfer of torque in the wind turbine main shaft assembly of FIG. 2;

[0036] FIG. 5 is a schematic drawing showing perspective view of the wind turbine main shaft assembly of FIG. 2; and

[0037] FIG. 6 is a schematic drawing showing a connecting member including a locking mechanism that may be used with embodiments of the wind turbine main shaft assembly.

DETAILED DESCRIPTION

[0038] In the following, embodiments of the invention will be described in detail with reference to the accompanying drawings. It is to be understood that the following description of the embodiments is given only for the purpose of illustration and is not to be taken in a limiting sense. It should be noted that the drawings are to be regarded as being schematic representations only, and elements in the drawings are not necessarily to scale with each other. Rather, the representation of the various elements is chosen such that their function and general purpose become apparent to a person skilled in the art. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted.

[0039] FIG. 1 schematically illustrates a wind turbine 100 that includes a rotor 101 with a rotor hub 102 and rotor blades 103. Wind turbine 100 further includes a nacelle 104 mounted on top of a wind turbine tower 105. The rotor 101 is coupled via a main shaft assembly 10 to a gearbox 110 arranged in nacelle 104. Main shaft assembly 10 includes the main shaft 20 having a flange 21 for attachment to the hub 102 and a connecting piece 30 for attachment to gearbox 110. Assembly 10 transmits torque from the rotor 101 to the gearbox 110. Generator 120 is coupled to gearbox 110 and receives the rotational mechanical energy at the desired rotational speed. In the example of FIG. 1, the main shaft 20 is supported by two main bearings 130. It should be clear that in other configurations, only one main bearing 130 or more main bearings may be provided, and that the main bearings may be arranged differently.

[0040] FIG. 2 shows a sectional view of the assembly 10 according to an exemplary embodiment. Main shaft 20 and flange 21 for attachment of the hub 102 are formed integrally, for example by casting, forging and respective machining. The main shaft 20 is rotationally symmetric about the rotational axis 25, which extends in the longitudinal direction of the main shaft. At the other end 22 of the main shaft 20, the connecting piece 30, which is provided in form a flange piece and may simply be termed “flange”, is attached. The connecting piece 30 includes, and in particular consists of, an outer flange 31 for attachment to the gearbox, an inner flange 35 for attachment to the end 22 of the main shaft 20 and a protrusion 32 that is provided for establishing an interference fit with the end 22 of the main shaft 20.

[0041] The area indicated by a square in FIG. 2 is shown enlarged in FIG. 3. Outer flange 31 includes radially distributed through-holes for attachment to the gearbox. The protrusion 32 has an outer cylindrical shape with a bulge 34 that extends circumferentially and that provides an increased strength and resistance against deformation for the interference fit. The protrusion 32 is hollow and has an inner circumferential surface 33 that provides a conical or tapered shape, wherein the inner circumference is decreasing when moving from the end of the protrusion towards the inner flange 35 in axial direction (axial direction being defined by the rotational axis 25). The end 22 of the main shaft 20 has likewise an outer circumferential surface 23 that is shaped conically or is tapered. The outer circumference of the outer surface 23 decreases when moving in axial direction towards the end face 26 of the main shaft 20. The tapering of the inner surface 33 corresponds to the tapering of the outer surface 23, so that the shapes of these surfaces match. However, the outer circumference of the outer surface 23 (or the radius in cross section of the shaft) is slightly larger than the circumference (or radius) of the inner surface 33, so that an interference fit is established when seating the connecting piece 30 on the end of the main shaft 20. It should be clear that different sizings of the conical “hole” provided by the protrusion 32 and by the main shaft with its conical end 22 are conceivable to establish interference fits of different strength, such as a driving fit or a forced fit or the like. The strength of the desired frictional connection and thus the amount of interference will generally be determined based on the torque that is to be transferred by the respective frictional connection.

[0042] In FIG. 3, arrows 51 indicate the compressive force that is applied between the surfaces 23 and 33 due to the interference fit, i.e., the force/pressure that the protrusion 32 applies to face 23 by the interference fit, and the corresponding reactive force/pressure applied by the end of the main shaft to face 33. Arrow 52 indicates the friction that results from these forces.

[0043] It should be clear that the interference fit does not need to be established over the whole length of the protrusion 32, but may be established only in one or more portions thereof, and in one or more corresponding portions of the end of the main shaft 20. Further, it should be clear that different shapes of the inner surface 33 and the outer surface 23 are conceivable, such as a cylindrical shape of both surfaces, or an only partially tapered or conical shape.

[0044] Besides the frictional connection 62 established by the interference fit, a further frictional connection 61 is established between an end face 26 of the main shaft 20 and an axial face 36 provided on the inner flange 35 of connecting piece 30. By using connecting members 40, the inner flange 35 is pressed onto the end face 26 of end 22 of main shaft 20. The resulting forces in normal direction of faces 26, 36 cause friction (in particular stiction) between the end of the main shaft and the connecting piece 30 parallel to the faces 26, 36 and thus establish a further frictional connection 61. The strength of the frictional connection 61 depends on the amount of force exerted perpendicular to the faces 26, 36 by connecting members 40.

[0045] In the illustrated example of FIG. 3, connecting member 40 includes a bolt 41 that is screwed and tightened into a hole provided in the end 22 of main shaft 20. The bolt 41 extends through holes in the inner flange 35, and a nut 42 is tightened to the end of bolt 41. To establish the interference fit, the connecting piece 30 needs to be forced onto the end 22 of main shaft 20 in the direction indicated by arrow 53. Assembly can thus occur by placing the connecting piece 30 onto the end of main shaft 22 and tightening the connecting members 40 (e.g., nuts 42) to thereby force the connecting piece 30 onto the end 22. Thereby, the first frictional connection 61 is established due to the compressive force applied by the connecting members 40 and indicated by arrows 54. At the same time, the second frictional connection is established since the displacement of connecting piece 30 along arrow 53 causes the establishing of the interference fit. The compressive forces 51 are thereby put into action, thus resulting in the second frictional connection.

[0046] Besides such method of establishing the interference fit, it should be clear that other methods are conceivable, such as using a press to force the connecting piece 30 onto the end of the shaft 20.

[0047] FIG. 4 illustrates in more detail the compressive forces 51 applied by the interference fit to the outer surface 23 of main shaft 20. The respective frictional connection 62 is capable of transmitting a torque MT.sub.1, that is proportional to the compressive force 51 (FA) normal to the respective surface and a friction coefficient. The compressive force 54 established by the tightening of the connecting members 40 and exerted on the end face 26 of the main shaft results in the frictional connection 61, that is capable of transmitting a torque MT.sub.2. The torque MT.sub.2 is again proportional to the compressive force 54 (FB) normal to the end face 26 and to a respective frictional coefficient.

[0048] The total torque that the coupling between the main shaft and connecting piece 30 is capable to transmit is accordingly composed of a portion through the conical end 22 and another portion through the end face of the shaft, the overall torque being

MT=MT.sub.1+MT.sub.2.

[0049] The desired torque to be transmitted can be assigned to each of the respective frictional connections 62, 61 as desired, for example by using a partition coefficient Kr:

MT.sub.1=Kr×MT;

MT.sub.2=(1−Kr)×MT.

[0050] Based on the torque MT.sub.1 to be transmitted and the geometry of the conical end, the required pressure “p” on the tapered surface 23 can be deduced, and thus the necessary force that needs to be exerted by the connecting members for establishing the interference fit (preload). This preload defines the type and quantity n.sub.1 of the connecting members necessary for establishing the respective second frictional connection, and they may be either screws or bolts. The pressure should of course be adequate so as to prevent a permanent deformation of the connecting piece, in particular its protrusion 32, or of the end of the shaft. The geometry of the conical section may for example be dimensioned based on DIN 7190-2 taking into account the friction coefficients. Furthermore, the possibility may be taken into account that at some time, it may be desirable to dismount the connecting piece 30 from the end of the main shaft 20, for example by using screw-type extractors.

[0051] Based on the torque MT.sub.2 to be transmitted by the first frictional connection 61 established at the end face 26 of the main shaft and the respective coefficient of friction in the front area, the number n.sub.2 and type of connecting elements, in particular screws or bolts, required to establish the desired compressive force can be deduced. The numbers n.sub.1 and n.sub.2 and the type of the connecting elements may be the same or may be different, as appropriate. The higher number of n.sub.1 and n.sub.2 is used so that the requirements for both connections to be established can be met.

[0052] FIG. 5 shows a perspective view of the assembly 10 of FIG. 2, showing the main shaft 20 with its flange 21 for connection to the rotor hub and its opposite end 22. The axial end face 26 and the holes 27 extending therethrough into the end 22 are visible. On the connecting piece 30, the outer circumferential flange 31 with respective through-holes for attachment to the gearbox and the inner flange 35 with through-holes 37 are visible.

[0053] Connecting members 40 extend through the holes 37 into holes 27 when assembled. On the inner flange, three threaded holes 39 are provided for receiving extractor bolts that can be used to dismount the connecting piece 30 from end 22 of main shaft 20. Main shaft 20 is generally hollow.

[0054] Prior to mounting the connecting piece 30, one or more main bearings may be mounted to the main shaft 20, as shown in FIG. 1. For disassembly, the connecting piece 30, in particular its protrusion 32, may be heated in order to facilitate the disengagement of the interference fit.

[0055] FIG. 6 illustrates a possible implementation of the connecting members 40. Connecting member 40 includes a bolt 41 and a nut 42. The bolt is at least partially threaded (indicated in FIG. 6), so that it can be screwed into threaded holes 27 provided in end 22 of main shaft 20, and so that it can receive nut 42. The threaded portions are shown as recessed areas in FIG. 3. After the bolt has been tightened into hole 27, for example using a square or hex head 45 provided on top of the bolt, nut 42 is tightened to apply the compressive force 54. The connecting member 40 includes a locking mechanism that keeps connecting member 40 in place once it is tightened. In the example of FIG. 6, the locking mechanism includes a keyway 46 in bolt 41 and a breaking lip 47 on nut 42. Once tightened, the breaking lip 47 at the position of keyway 46 is broken such that a part of the lip engages keyway 46 to thereby lock the nut 42 in place. This may be done by a chisel or other tool.

[0056] The connecting piece 30 may in particular consist of the outer flange, the inner flange and the protrusion, which may extend in axial direction from a position between the outer and inner flanges. Protrusion 42 may have a cylindrical shape with a circumferential bulge and an inner conical circumferential surface.

[0057] By means of the embodiments described herein, large torques can be transmitted via the connecting piece coupled to a drive shaft, which has particular advantages in coupling the main shaft to the gearbox of the wind turbine. The torque is essentially transmitted completely by the friction generated at the first and second connections between the connecting piece and the main shaft. The friction is in particular generated at the end face of the main shaft and in the outer conical area at the end of the main shaft, which is cylindrical in classical main shafts. The coupling mechanism is thus relatively simple and simple mechanical theory can be used to calculate the transmitted torques. Once the total torque to be transmitted has been determined, the configuration can be adjusted as desired. Further, it provides an ease of assembly and does not need maintenance. The costs of the coupling are also reduced. In particular, removability of the connecting piece allows the replacing of the bearings, which is a significant advantage over conventional solutions that provide a fixed and not removable attachment.

[0058] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0059] For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.