Blade attachment configuration for a wind turbine with flattened bolts

Abstract

Wind turbine (10) comprising: a plurality of wind turbine blades (16), each of the wind turbine blades having a blade root flange (50) secured to a rotor hub flange (52) of a rotor hub (18) by a plurality of circumferentially spaced blade bolts (55); wherein each leaf bolt (55) comprises: opposite cylindrical end portions (56) engaging the rotor hub flange (52) and the blade root flange (50), respectively; characterized by a non-cylindrical shaft (60) extending between the cylindrical end portions (56); and oppositely directed flattened sides (62) formed in the shaft (60) along a longitudinal axis (61) of the blade bolt (55), wherein the shaft (60) has rounded side edges (66) with a diameter (64) measured between the side edges (66) and a thickness (68) measured perpendicular to the flattened sides (62), the diameter (64) being substantially equal to or less than an outermost cylinder diameter of the blade bolt (55).

Description

The present invention relates generally to the field of wind turbines (wind turbines) and, more particularly, to a turbine blade attachment configuration.Power-supplyable wind turbines (i.e., wind turbines provided to supply electrical power to a utility grid) may have relatively large rotors (e.g., having a diameter of 30 meters or more) and a rotor hub height exceeding 100 meters. The extreme loads and fatigue loads imposed on the rotor blades of these turbines can be very significant. Forces such as horizontal and vertical wind shear, erratic yaw orientations, turbulence, and the like cause significant bending of the blades, contributing to the overall loads applied to the blades. An important design consideration in this regard is the connection between the blade root and the rotor hub.A conventional connecting structure uses circumferentially spaced apart leaf bolts to secure the bolts to the rotor hub. DE 10 2007 020 339 A1, for example, discloses a wind turbine having a rotor blade which is connected to a hub of the wind turbine by a bolt connection. WO 01 / 42 647 A2 also discloses such an article. A basic design consideration with respect to the bolts is to have a relatively flexible bolt and rigid flange so as to increase the fatigue strength of the bolt. It is estimated that about 40% to 80% of the total load applied to the bolts is fatigue bending load. These conventional bolts usually have threaded end portions which engage threaded bores in the blade root flange and the rotor hub flange, respectively. A more advanced blade bolt design for a wind turbine uses a reduced diameter shank portion between the threaded end portions to increase the axial and flexural flexibility of the bolt away from the threaded stress concentration. However, this construction also reduces the maximum load strength of the bolt due to the small shank diameter.Accordingly, the industry would benefit from a leaf bolt design that reduces bending or fatigue loads without sacrificing the overall maximum load strength of the bolt.Aspects and advantages of the invention are set forth in part in the description which follows, or may be obvious from the description, or may be learned by practice of the invention.In accordance with aspects of the invention, a wind turbine is provided that includes a plurality of turbine blades. Each of the blades has a round root flange that is secured to a round flange of a rotor hub by a plurality of circumferentially spaced blade bolts. The bolts have cylindrical end portions which engage the blade root flange and the rotor root flange, respectively. In a particular embodiment, these end portions are threaded. A non-cylindrical shank extends between the cylindrical end portions and includes oppositely facing flattened sides formed in the shank along a longitudinal axis of the leaf bolt. In a particularly unique embodiment, the flattened sides pointing in opposite directions lie in parallel planes along the longitudinal axis of the bolt. This unique shank profile provides the bolt with advantageous load and fatigue characteristics as compared to a round shank portion (full or reduced diameter), as discussed in greater detail herein.It should be understood that it is not a need of the present invention that all blade bolts securing the turbine blade to the rotor hub must be configured as described herein. The invention includes any configuration in which at least one of the leaf pins satisfies the aspects of the invention.In a particular embodiment, the blade pins, which may also be referred to herein simply as "pins", are positioned in the rotational direction such that the flattened sides are aligned with an axis that is tangential to the blade root flange or the rotor hub flange at the respective location of the pin.The shaft has rounded side edges. The shaft has a diameter measured between the side edges and a thickness measured perpendicular to the flattened sides. The diameter is substantially equal to or smaller than an outermost cylinder diameter of the blade pin. In particular, the bolts may be shaped (as compared to machining) such that the diameter of the shank portion is substantially equal to the outermost cylinder diameter of the bolt. In other embodiments, the diameter of the shaft may be reduced.The diameter and thickness of the shank portion may be defined to achieve various fatigue and maximum load strength profiles. For example, for a given shank diameter (e.g., the outermost cylinder diameter), the shank thickness (measured between the flattened sides) may be defined to increase the fatigue strength of the bolt without decreasing the maximum load strength by more than a predetermined amount, which may be zero, less than 5%, less than 10%, or any other defined value. In an alternative embodiment, for a given shank gauge (e.g., the outermost cylinder diameter), the shank thickness may be defined to increase the maximum external load strength of the bolt without decreasing the fatigue strength by more than a defined amount that may be zero, less than 5%, less than 10%, or any other defined value.In one-way embodiments, the shank thickness at a given shank diameter is defined to maximize the fatigue strength of the bolt without decreasing the maximum external load strength, or to maximize the maximum load strength without decreasing the fatigue strength.These and other features, aspects and advantages of the present invention will be better understood by reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.A comprehensive and enabling disclosure of the present invention, including the best mode thereof, directed to one skilled in the art, is given in the specification, which makes reference to the appended figures, in which: FIG. 1 is a perspective view of a conventional wind turbine; FIG. 2 is an enlarged perspective view of an embodiment of a rotor hub illustrating, in particular, the rotor hub flanges; FIG. 3 is an enlarged perspective view of a root flange of a turbine blade illustrating conventional blade bolts; FIG. 4 is a schematic top view of a leaf bolt with flattened sides; FIG. 5 is a schematic side view of the bolt according to FIG. 4 ; FIGS. 6 to 8 show different cross-sectional profiles of a shank section of a leaf bolt; FIG. 9 is a schematic front view of a rotor hub or a rotor flange, specifically illustrating the rotational positions of the flattened blade bolts; FIG. 10 is a schematic view of various blade shaft profiles illustrating various diameter and thickness dimensions; and FIG. 11 is a table showing the results of the calculation based on the various profiles shown in FIG. 10.Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided to illustrate the invention, not to limit the invention. Indeed, it will be apparent to those skilled in the art that various modifications and changes may be made to the present invention without departing from the scope or spirit of the invention. For example, features illustrated or described as part of one embodiment may be used in another embodiment to yield yet another embodiment. Thus, it is intended that the present invention cover such modifications and variations as fall within the scope of the appended claims and their equivalents.FIG. 1 illustrates a wind turbine 10 or wind turbine of the conventional type. The wind turbine 10 includes a tower 12 having a nacelle 14 mounted thereon. A plurality of wind turbine blades 16, which may also be referred to herein as turbine blades, are mounted on a rotor hub 18, which in turn is connected to a main flange 20 that rotates a main rotor shaft 22. The main rotor shaft 22 is supported by a bearing 24 relative to a base plate 28. A main flange 20 is fixed to the main rotor shaft 22 at the front end thereof and is connected to the rotor hub 18. The opposite end of the main rotor shaft 22 is coupled to the transmission 30 via a shrink coupling 32. The transmission 30 is connected to a generator 15 via a high-speed shaft (not illustrated). The wind turbine blades 16 convert driving forces of the wind into rotational mechanical energy via the shaft 22 and the gearbox 30 to generate electricity with the generator 15.The view of FIG. 1 is provided for illustrative purposes only to place the present invention in a suitable area of application. It should be appreciated that the configuration of FIG. 1 is not limiting and that the invention may be used with any wind turbine configuration.FIG. 2 illustrates the rotor hub 18 having a plurality of rotor hub flanges 52 The wind turbine blades 16 (FIG. 1 ) include a round blade root flange 50 (FIG. 3 ) attached to a respective rotor hub flange 52 by a plurality of blade bolts 54, as is well known in the art. FIG. 3 illustrates a conventional configuration of the leaf bolts 54 in which each of the bolts includes threaded cylindrical end portions 56 and a reduced diameter cylindrical shank portion 60. FIG. 3 is provided for purposes of illustrating the orientation and location of the leaf pins 54.FIGS. 4-6 illustrate embodiments of leaf bolts 55 in accordance with aspects of the invention. The blade bolts 55 have cylindrical end portions 56 configured for physical engagement with the rotor hub flange 52 and the blade root flange 50, respectively, by conventional means. For example, in a particular embodiment, each of the cylindrical end portions 56 includes a thread 58 for threaded engagement with a respective flange. In modified embodiments, the end portions may be configured for any other type of suitable engagement connection within the respective flanges.A non-cylindrical shank portion 60 is located between the cylindrical end portions 56. the shank portion 60 includes at least one "flattened" side defined along a longitudinal axis 61 of the leaf bolt 55. It should be understood that the term "flattened" is used herein to describe a profile that is not necessarily flat in a single plane (as illustrated in FIG. 6 ) but represents a defined side of the shank portion 60 that has a different profile compared to the uniform radius of a shank of cylindrical cross-section. In other words, this is a side of the shank on which it appears that a portion of the material has been removed from a shank cylinder of uniform radius, thus creating a reduced or "flattened" profile (side 62) which may be flat, curvilinear, serrated and the like.FIGS. 6, 7 and 8 illustrate various embodiments of a shank portion 60 having a profile with at least one flattened side 62. In Fig. 6, the oppositely facing sides 62 are flat and lie in parallel planes. In Fig. 7, the sides 62 have a slightly convex shape. In Fig. 8, the sides 62 have a slightly concave shape. It should thus be appreciated that the term "flattened" refers to the reduced aspect of the side 62 as compared to the uniform radius of the cylindrical cross section.Referring to FIGS. 5-8, the shank portions 60 have rounded side edges 66. These side edges 66 may have the same radius of curvature as the cylindrical end portions 56. More specifically, in an embodiment in which the leaf pins 55 are formed, the diameter 64 (FIG. 4 ) as measured between the rounded edges 66 is substantially equal to the nominal cylinder diameter of the pin. Referring to FIG. 5, the flattened sides 62 define a thickness parameter (thickness 68) of the shank portion 60 measured perpendicular to the flattened sides.It should be readily appreciated that the present invention includes machined leaf pins 55 in which the diameter 64 of the rounded edges is defined at any desired dimension.The wind turbine blades 16 are subjected to bending loads with respect to a neutral axis that is tangential to the round blade root flange 50. The present applicant has found that by ablating material from shank portion 60 at a location furthest from this bending axis, bending loads introduced into blade bolt 55 can be reduced even as compared to the reduced diameter shanks formed in conventional bolts. As explained in more detail below in connection with Figures 10 and 11, this reduction in bending loads can be achieved without suffering a loss of maximum load strength of the bolt. Further, as compared with the conventional reduced diameter shafts, the applicant has found that by adding material along the neutral axis, the load strength of the bolt can be increased without sacrificing the fatigue strength increase. In other words, the diameter of the shaft portion 60 along the neutral axis need not be reduced, but the sides of the shaft portion 60 perpendicular to the axis may be flattened or reduced.Figure 9 shows a plurality of the leaf bolts 55 having the shank portions 60 with oppositely facing flattened sides 62. The blade pins are oriented in the rotational direction such that the flattened sides 62 of each blade pin 55 lie in the neutral bending axis 63 of each pin location around the blade root flange 50 (or around the rotor hub flange 52), with the neutral bending axis 63 at the pin location being tangential to the flange.It should be appreciated that the relative dimensions of the diameter 64 and the thickness 68 of the shank portion may be selected to achieve certain desired load and fatigue strength properties. For example, for a given diameter of shank portion 60 (e.g., the nominal cylinder diameter), the thickness dimension (thickness 68) defined between flattened sides 62 may be selected to increase the fatigue strength of the bolt without decreasing the maximum load strength of the bolt. In this regard, the thickness may be defined to maximize the fatigue strength of the bolt without decreasing the maximum load strength. In an alternative embodiment, the thickness dimension (thickness 68) may be defined at the same given diameter to increase the maximum load strength of the bolt without decreasing the fatigue strength. For example, the thickness may be defined to maximize the maximum load strength of the bolt without decreasing the fatigue strength.In still further modified embodiments, the thickness dimension (thickness 68) may be defined for a given dimension of diameter 64 to increase the fatigue strength of the bolt without decreasing the maximum load strength by more than a certain amount, e.g., by more than about 5%. In this regard, the thickness dimension may be defined to increase the fatigue strength of the bolt by a minimum amount, e.g., 10%, without decreasing the maximum load strength of the bolt by more than a certain amount, e.g., about 1%.In yet another embodiment, the thickness dimension (thickness 68) at the given diameter 64 of the shank portion 60 may be defined to increase the maximum load strength of the bolt without decreasing the fatigue strength by more than a certain amount, e.g., by more than about 10%.FIGS. 10 and 11 illustrate certain characteristics of the leaf pins 55 described herein. FIG. 10 illustrates three schematic representations of a leaf pin. The first illustration illustrates a conventional reduced diameter leaf bolt having a shank diameter A of about 23.1 mm. The second illustration illustrates a bolt having a full nominal cylinder diameter of about 27.7 mm. The third illustration in FIG. 10 illustrates a leaf bolt provided in accordance with aspects of the present invention having a shank portion diameter A equal to the full nominal diameter of 27.7 mm and a flattened shank thickness value B having the values indicated in the table of FIG. 11. FIG. 10 further illustrates the neutral bending axis 63.FIG. 11 shows a table illustrating certain calculations reflecting the advantages of the flattened side shank configuration. The first column in Figure 11 refers to the conventional reduced diameter shank bolt, the full nominal diameter of the bolt having been reduced from 27.7 mm to 23.1 mm. This reduced diameter profile gives a shank area of 419 mm 2 and a total fatigue index of 1.40. As such, the increase in fatigue strength and the increase in ultimate strength for this profile are fixed at 0%. The second column 11 illustrates the full diameter shank profile which produces a cross-sectional area of 602.6 mm 2 with a total fatigue index of 2.17. Compared to the control profile, this profile gives an increase in ultimate strength of about 43.8%, but reduces fatigue strength by 35.4% compared to the control profile.The next three columns in Figure 11 illustrate the various results of providing the full nominal diameter shank portion with flattened sides. In the third column, the thickness dimension B of the flattened sides is 16.0 mm. This profile gives a total fatigue index of 1.24, with an increase in fatigue strength of 13.1% compared to the control and with a decrease in ultimate strength of only 0.5% compared to the reduced diameter control profile.The fourth column in FIG. 11 shows a thickness dimension B of 18 mm, which forms a cross-sectional area of 640 mm 2. This profile gives a total fatigue index of 1.41 with an increase in ultimate strength of 9.8% compared to the control profile and with a decrease in fatigue strength of only 0.9%.The next column in FIG. 11 illustrates the results of increasing the thickness dimension B of the shank portion to about 19.4 mm, resulting in a cross-sectional area of the shank portion of 489 mm 2 with a total fatigue index of 1.54. This profile results in an increase in ultimate strength of about 16.7%, but with a loss in fatigue strength of about 9.0% as compared to the reduced diameter control profile.The sixth column in FIG. 11 illustrates an embodiment in which the thickness dimension B is selected to maximize the fatigue strength increase without reducing the maximum strength of the bolt compared to the reduced diameter control profile. In this embodiment, the thickness dimension is set at 16.1 mm, resulting in an increase in fatigue strength of about 12.5% without any reduction in ultimate strength as compared to the reduced diameter control profile.The final column in FIG. 11 illustrates an embodiment in which the thickness dimension B is selected to maximize an increase in maximum strength without a loss of fatigue strength. In this embodiment, the thickness dimension B is defined at 17.9 mm, resulting in an increase of about 9.1% in the ultimate strength without any loss of fatigue strength as compared to the reduced diameter control profile.While the present subject matter has been described in detail with reference to specific exemplary embodiments and methods thereof, it will be appreciated that those skilled in the art, having obtained an understanding of the foregoing, may readily produce alterations, modifications, and equivalent forms of such embodiments. Accordingly, the scope of the present disclosure is for purposes of example only and not limitation, and the subject disclosure does not exclude such modifications, changes, and / or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art.A wind turbine 10 includes a plurality of wind turbine blades 16, each of the blades having a blade root flange 50 attached to a rotor hub flange 52 of a rotor hub 18 by a plurality of circumferentially spaced apart blade bolts 55. The blade bolts have opposite cylindrical end portions 56 that engage the rotor hub flange and the blade root flange, respectively, and a non-cylindrical shank 60 that extends between the cylindrical end portions. At least one flattened side 62 is formed in the shank along a longitudinal axis of the bolt.Parts List10 Wind turbine (wind turbine) 12 tower 14 nacelle 15 generator 16 wind turbine blades (turbine blades) 18 rotor hub 20 main flange 22 rotor shaft 24 bearing 28 base plate 30 gearbox 32 shrink coupling 34 pitch control 50 blade root flange 52 rotor hub flange 54 blade bolts (conventional) 55 blade bolts 56 cylindrical end portion 58 threads 60 shank portion 61 axle 62 flattened side 64 diameter 66 sides 68 thickness

Claims

A wind turbine (10) comprising: a plurality of wind turbine blades (16), each of the wind turbine blades comprising a blade root flange (50) attached to a rotor hub flange (52) of a rotor hub (18) by a plurality of circumferentially spaced apart blade bolts (55); each blade bolt (55) comprising: opposing cylindrical end portions (56) engaging the rotor hub flange (52) and the blade root flange (50), respectively; characterised bya non-cylindrical shank (60) extending between the cylindrical end portions (56); and oppositely facing flattened sides (62) formed in the shank (60) along a longitudinal axis (61) of the leaf bolt (55), the shank (60) having rounded side edges (66) with a diameter (64) measured between the side edges (66) and a thickness (68) measured perpendicular to the flattened sides (62), the diameter (64) being substantially equal to or less than an outermost cylinder diameter of the leaf bolt (55).The wind turbine (10) of claim 1, wherein the flattened sides (62) lie in parallel planes along the longitudinal axis of the blade bolt (55).The wind turbine (10) of claim 1 or 2, wherein the blade pins (55) are positioned rotationally such that the flattened sides (62) are aligned with an axis (63) that is tangential to the rotor hub flange (52) at each location of a respective blade pin.The wind turbine (10) of claim 1, 2, or 3, wherein at the given diameter (64), the thickness (68) is defined to increase the fatigue strength of the blade bolt (55) without decreasing the maximum load strength.The wind turbine (10) of claim 4, wherein at the given diameter (64), the thickness (68) is defined to maximize the fatigue strength of the blade bolt (55) without decreasing the maximum load strength.The wind turbine (10) of claim 4, wherein the blade pins (55) are shaped and the given diameter (64) is substantially equal to a nominal cylinder diameter of the blade pin (55).The wind turbine (10) of claim 4, wherein the blade bolts (55) are shaped and the given diameter (64) is substantially equal to a nominal cylinder diameter of the blade bolt (55), and wherein the given diameter defines the thickness (68) to increase the fatigue strength of the blade bolt (55) without decreasing the maximum load strength by greater than about 5.0%.The wind turbine (10) of claim 7, wherein the thickness (68) is defined to increase the fatigue strength of the blade bolt (55) by at least 10% without decreasing the maximum load strength by greater than about 1.0%.The wind turbine (10) of claim 4, wherein the blade bolts (55) are shaped and the given diameter (64) is substantially equal to a nominal cylinder diameter of the blade bolt (55), and wherein at the given diameter the thickness (68) is defined to increase the maximum load strength of the blade bolt (55) without decreasing the fatigue strength by greater than about 10.0%.The wind turbine (10) of claim 9, wherein the thickness (68) is defined to increase the maximum load strength of the blade bolt (55) by at least 10% without decreasing the fatigue strength by greater than about 1.0%.

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