Technical Field

The invention relates to a wind turbine hub assembly including a hub adaptor which is located intermediate a blade bearing of the hub assembly and a wind turbine blade. The invention also relates to the hub adaptor itself.

Background to the Invention

Typically, a wind turbine blade is attached to a wind turbine hub directly by way of a hub bearing. A cylindrical blade root of the wind turbine blade usually comprises a circular array of bolt-receiving inserts which receive a corresponding set of blade bolts that extend from the hub bearing. In this connection scheme, it is necessary for the blade root to have a diameter that matches the diameter of the hub bearing

In some circumstances, however, it may be preferable to assemble a rotor hub with blades that it was not originally designed to use. For example, it may be required to use blades having a root diameter which is smaller than the hub bearing diameter of the rotor hub.

With this in mind, it is known to use a hub adaptor component that sits between the hub bearing and the blade root. Such a component decouples the pitch circle diameter of the ring of bolt inserts in the blade root and the pitch circle diameter of the bolts carried by the hub bearing which means that blade roots of a different diameter can be used with a single hub bearing. One example of such a scheme is disclosed in WO2011 050806. Whilst this has been a useful development, other design challenges remain to be solved by this approach.

One issue is the different stiffness of the blade root adaptor and the blade root. Typically a blade root adaptor is a very stiff component for example made of steel. In contrast, the blade root is a composite component and typically is less stiff than the hub adaptor. Over time, this can introduce wear issues at the blade root since the blade root is more flexible than the stiff than the hub and/or the hub bearing meaning that all the flex is borne by the blade root. It is against this background that the present invention is devised.

Summary of the Invention

According to a first aspect of the invention, there is provided a rotor hub adaptor for a wind turbine, comprising a body that defines a central axis and is configured with first connection means for connecting to a hub bearing of a wind turbine rotor hub and second connection means for connecting to a root section of a wind turbine blade. The first connection means defines a first pitch circle diameter and the second connection means defines a second pitch circle diameter, wherein the first pitch circle diameter is different to the second pitch circle diameter. The rotor hub adaptor defines, at the first pitch circle diameter, a first thickness along the axial direction, and further defines, at the second pitch circle diameter, a second thickness along the axial direction, wherein the second thickness is less than the first thickness, such that the rotor hub adaptor is more flexible at the second connection means than at the first connection means.

A benefit of the invention is that hub adaptor allows blades having a root diameter different to the corresponding hub bearing diameter to be mated together. However, the flexibility inherent in the reduced thickness at the second connection means has the advantage of improving the reliability of the connection between the blade and the hub.

In principle the second connection means may have a PCD that is greater than that of the first PCD, meaning that blades having root diameters greater than the respective hub bearing diameter can be fitted together. However, preferably the PCD at the second connection means is less than the PCD at the first connection means such that blades having a smaller root diameter can be fitted to relatively larger hubs. This provides more options for fitting different sized blades to the hubs that are already installed at wind turbine installations. In this context, the second pitch circle diameter PCD2 may be between 50% and 150% of PCD1 , and more preferably between 80% and 120%.

Preferred and/or optional features of the invention are apparent from the appended claims.

The invention also extends to a wind turbine including a tower that supports a nacelle to which a rotor hub is attached, the wind turbine further comprising a plurality of blades, each of which is connected to the rotor hub at a respective hub bearing by a respective rotor hub adaptor of any one of the preceding claims

Brief Description of the Drawings

The present invention will now be described, by way of example only, with reference to the attached drawings, in which:

Figure 1 is a front view of a horizontal axis wind turbine generator to which embodiments of the invention may be applied;

Figure 2 is a front view, in schematic format, of a rotor hub having a wind turbine blade attached thereto by a rotor hub adaptor in accordance with an example of the invention;

Figure 3 is a perspective view of the rotor hub adaptor shown in Figure 2;

Figure 4 is a cross-sectional view of the rotor hub adaptor of Figure 3; and

Figure 5 is a further cross-sectional view of the rotor hub adaptor of Figure 3.

Detailed Description

A specific embodiment of the present invention will now be described in which numerous features will be discussed in detail in order to provide a thorough understanding of the inventive concept as defined in the claims. However, it will be apparent to the skilled person that the invention may be put into effect without the specific details and that in some instances, well known methods, techniques and structures have not been described in detail in order not to obscure the invention unnecessarily.

In overview, the invention provides a design of rotor hub adaptor for a wind turbine that allows the use of blades with root diameters different to the diameter of the hub bearing of the wind turbine. In particular, the improvements in rotor hub adaptor illustrated here in the examples of the invention provide a rotor hub adaptor which mitigates against the effects of stress at the connection points between the blades, the rotor hub adaptor and the hub bearing.

To provide context for the invention, Figure 1 shows a typical horizontal axis wind turbine generator, also referred to below as a wind turbine 2, that includes a nacelle 4, mounted atop a tower 6, which supports a front facing rotor 8 comprising a plurality of coplanar blades 10. As is conventional, the blades 10 each define an elongated structure having an aerofoil-shaped profile suitable for providing an aerodynamic lift when acted on by a flow of wind. The rotor 8 is connected to a powertrain housed within the nacelle 4. The powertrain (not shown) comprises components required to convert rotation of the rotor 8 into electricity, including but not limited to a gearbox, a generator and a power converter.

The rotor 8 comprises a rotor hub 12. The rotor hub 12 is a structure provided with means for connecting the blades 10 to the rotor 8 and is connected to a shaft (not shown) for transferring the rotational energy of the blades utilising the components of the drivetrain.

Figure 2 illustrates the rotor hub 12 in accordance with the invention in a schematic format. Note that in Figure 2 only a single blade 10 is shown attached to the rotor hub 12 for brevity, but it should be appreciated that a similar attachment arrangement may be provided for each blade 10 of the wind turbine 2.

The rotor hub 12 comprises hub bearings 20 which serve as the interface between the rotor hub 12 and the respective blades 10. Conventionally, the hub bearings 20 are rotational bearings and, as such, enable the blades 10 to pitch around their longitudinal axes so as to be able to capture the flow of wind more effectively.

Although rotational bearings are common, particularly in large utility-scale wind turbines, it should be noted that a static bearing point may be suitable in some other applications.

Hub bearings for wind turbines are conventional technology so no further discussion will be provided here. Further, the hub bearing 20 denoted in Figure 2 having a blade 10 attached thereto is shown as a single component, this simplification being a convenience for the current discussion. However, the skilled person would understand that hub bearings are complex assemblies usually include inner and outer bearing rings, rotationally separated by appropriate rollers or equivalent bearing elements. The blade 10 is connected to its respective hub bearing 20 by its blade root 22. Blade roots are generally cylindrical in shape rather than having an aerofoil profile, but this is not excluded. Rather than being connected directly to the hub bearing 20, a hub adaptor 24 is provided intermediate the hub bearing 20 and the blade root 22.

The hub adaptor 24 has a first side S1 that faces the hub bearing and a second side S2 that faces the blade root 22. Further, the hub adaptor 24 defines a first connection means 26 for connecting the hub adaptor 24 to the hub bearing 20 and second connection means 28 for connecting the hub adaptor 24 to the blade root 22.

The first connection means 26 is constituted by a first set of holes 27 defined in the first side S1 of the hub adaptor. As will be appreciated more fully later, the first set of holes 27 is arranged in a circular formation on the first side S1 of the hub adaptor 24.

The second connection 28 means is constituted by a second set of holes 29 defined in the second side S2 of the hub adaptor 24. The second set of holes 29 is also arranged in a circular formation on the second side S2 of the hub adaptor 24.

The first connection means 26 accommodates a respective first set of mechanical fasteners 30, such as bolts, which serve to couple the hub adaptor 24 to the hub bearing 20. Accordingly, the hub bearing 20 includes its own set of holes 31 into which the first set of mechanical fasteners 30 are received thereby to join the hub adaptor 24 to the hub bearing 20. It will therefore be appreciated that the first connection means 26 of the hub adaptor 24 defines a first pitch circle diameter, labelled as PCD 1 in Figure 2, and this pitch circle diameter PCD1 will be substantially the same as the pitch circle diameter of the holes of the hub bearing 20.

The second connection means 28 accommodates a respective second set of mechanical fasteners 32, such as bolts, which serve to couple the hub adaptor 24 to the blade root 22. Accordingly, the blade root 22 includes a ring of holes 33 provided by appropriate inserts in its structure by which means it can accommodate the second set of mechanical fasteners and, thus, be joined to the hub adaptor 24. Since the second connection means 26 is defined by the second set of holes 29 that are arranged in a circle, as is conventional, it will be appreciated that the second connection means 28 defines a second pitch circle diameter or PCD, labelled as PCD 2 on Figure 2, and this pitch circle diameter PCD2 will be substantially the same as the pitch circle diameter of the holes 33 of the blade root 22.

It will be noted in Figure 2 that the hub bearing 20 functions to adapt the dimensions of the blade root 22 to the dimensions of the hub bearing 20. As such, it will be appreciated that the dimension of PCD2 is less than PCD1. This means that different sized blades can in principle be used on the same hub bearing 20 by using such a hub adaptor.

Whilst Figure 2 shows the hub adaptor 24 in a schematic form, reference will now be made to Figures 3, 4 and 5 which show the hub adaptor in more detail. Note that Figure 3 depicts the hub adaptor 24 in isolation from other components, whilst Figure 4 depicts the hub adaptor coupled to the blade 10 mounted to it on one side S2 and the hub bearing 20 on its other side S1.

From viewing Figures 3-5 it will be apparent that the hub adaptor 24 comprises a body 25 that is generally disc- or ring-shaped in form and which defines a central or rotational axis A. As the hub adaptor 24 is generally annular in this example, it has a squat/relatively short cylindrical profile having a radially outward periphery which defines an outer diameter D1 , and a radially inner periphery defining an inner diameter D2. It should be noted that although only the first side S1 of the hub adaptor 24 can be viewed in Figure 3, the second side S2 is identical to the first side S1 , in the illustrated example, as can be appreciated from Figures 4 and 5. Note that although the body 25 has an open central area in the illustrated example, in other examples, the body may be defined by a solid disc.

As a result, the hub adaptor 24 has rotational symmetry about the central axis A. Furthermore, the hub adaptor is symmetric about a transverse plane P, as shown in Figure 4. It should be noted that this symmetry around the transverse plane P arises due to the first 26 and second 28 connection means extending through the body of the hub adaptor 24. In some embodiments, either the first 26 and/or second 28 connection means will not extend through the body of the hub adaptor 24. In such embodiments, the noted symmetry may not be present.

Figure 4 illustrates a cross section through the hub adaptor 24 through a plane passing though the central axis A. In Figure 4, the hub bearing 20 is shown connected to the first side S1 of the hub adaptor 24 at the first connection means 26 and the blade root 22 is seen connected to the second side S2 of the hub adaptor S2 at the second connection means 28.

The first connection means 26, that is the first set of bolt holes 27 (defining a first bolt hole array), in this example, are defined at a substantially flat surface of the hub adaptor 24 at the radial location PCD1. At this point, the hub adaptor 24 is at its maximum thickness, as is illustrated by T1. In the illustrated example, the bolt holes 27 extend through the entire thickness T1 of the body 25. A threaded section may be provided in some examples, as illustrated here by the reduced diameter section of the bolt holes 27.

In contrast, the second connection means 28, that is the second set of bolt holes 29 (defining a second bolt hole array), in this example are defined at another flat surface of the hub adaptor 24 at the radial position PCD2. Similar to the first set of bolt holes 27, the bolt holes 29 of the second set extend through the entire thickness T2 of the body 25.

As has been discussed, PCD2 is less than PCD1 in the illustrated embodiment such that the first connection means 26 is at a relative radially outwards position compared to the second connection means 28, and similarly the second connection means 28 is radially inwards of the first connection means 26. It will be appreciated that the relative size of PCD1 and PCD2 may vary depending on the application. For example, in some examples, it is envisaged that the length of PCD2 may be between 50% and 150% of the length of PCD1 , and more preferably between 80% and 120%. As such, the second connection means 28 may be radially outwards of the first connection means 26. Considered another way, the second pitch circle diameter PCD2 may be less than the first pitch circle diameter PCD1 in the range of approx. 50% to 99%, and preferably between 80% to 99%. Conversely, the second pitch circle diameter PCD2 may be larger than first pitch circle diameter PCD1 , for example in the range of approx. 101% and 150%, or preferably between 101 % and 120%.

Significantly, it will be noted that the thickness of the hub adaptor 24 along its radial cross section is not uniform. More specifically, the hub adaptor 24 reduces in thickness between the first connection means 26 and the second connection means 28, such that the hub adaptor 24 is thinner at the second connection means 28, as defined by thickness T2, compared to the thickness T1 at the first connection means 26. In this specific example, the hub adaptor 24 includes a maximum thickness portion P1 , which includes the first connection means 26, and a reduced thickness portion P2. The maximum thickness portion P1 is an area of maximum thickness of the hub adaptor 24 in the axial direction. It is to be appreciated that in some examples, the first connection means 26 may be positioned away from the maximum thickness portion P1.

In turn, the reduced thickness portion P2 includes a tapering portion P3 and a minimum thickness portion P4. The thickness of the hub adaptor 24 tapers through tapering portion P3 from the radial position of the maximum thickness portion P1 towards the radial position of the minimum thickness portion P4. The minimum thickness portion P4 is an area of minimum thickness of the hub adaptor 24 in the axial direction.

It should be noted that geometrical taper at the reduced thickness portion P2 may be a continuous linear taper, as illustrated, but this is not essential. As such the thickness reduction, and therefore the improved flexibility, may be achieved by other forms, such as a non-linear taper i.e. a curved cross sectional form, or a series of stepped reductions in material thickness.

Beneficially, the fact that the blade root 22 is attached to the rotor hub adaptor 24 at the second connection means 28 at which point the thickness of the hub adaptor 24 is less than at the first connection means 26, means that there is inherent flexibility in the hub adaptor 24 to enable it to flex out of the plane P by a small amount as the blade is loaded due to the aerodynamic forces applied to the blade in use. In effect, therefore, the hub adaptor 24 acts as an interface to the relatively more rigid component of the hub bearing and the more flexible component of the blade root.

The second connection means 28 is defined at the base of a circular channel 60 defined within the minimum thickness portion P4. The circular channel has a radially outer wall 62 and a radially inner wall 64. The tapering portion P3 terminates at the radially outer wall 62. The radially outer wall 62 and the radially inner wall 64 extend generally in the axial direction of the hub adaptor 24. In some embodiments, the radially outer wall 62 and the radially inner wall 64 are parallel to one another. It is to be appreciated that the circular channel 60 extends throughout the hub adaptor 24 at the same radial position. It is further noted that the circular channel 60 and the minimum thickness portion P4 coincide in the example of Figure 4. As seen in Figure 4, the circular channel 60 is provided in the second side S2 of the hub adaptor 24. An identical circular channel 60’ is also provided in the first side S1 of the hub adaptor 24 due to its symmetry about plane P.

In this specific example, a tapering extension portion P5 is also provided. The extension portion P5 extends in the radial direction beyond the second connection means 28. The thickness of the extension portion P5 tapers with reducing thickness from a position at the radially inner wall 64 and terminates at the inner diameter D2 of the hub adaptor 24. However, it is to be noted that the radial extension portion P5 has a greater material thickness compared to the thickness of the rotor hub adaptor 24 at the second connection means 28. The relatively increased thickness of the extension portion P5 helps the stiffness properties of the reduced thickness portion P2 to be adjusted during design and manufacture to what is required by a particular combination of hub and blade. The cross- sectional geometry of the extension portion P5 is provided with rounded corners which acts as a stress management feature. It should be noted that other geometries for the extension portion P5 may be acceptable. For example, rather than being generally trapezoidal in form, as shown here, the geometry may instead be more triangular in form.

Although in the illustrated example the second connection means 28, i.e. the bolt boles 29, is defined at the bottom of the circular channel 60, it should be noted that this precise structure is not essential. In other examples, it is envisaged that the tapering portion P3 may taper continuously to a thickness equal to the minimum thickness T2.

Figure 5 illustrates the radial cross section through the hub adaptor 24 of Figure 5, zoomed in on one side of the adaptor 24. The same features as described with reference to Figure 4 can be seen in greater detail in the illustration of Figure 5.

In the illustrated example, it will be noted that the second connection means 28 includes a single circular array of bolt holes 29 to enable one size of blade to be attached to the hub adaptor. However, in a variant of this design, it is envisaged that the second connection means 28 may include one or more further sets of bolt holes (not shown) with a different pitch circle diameter. As the skilled person would appreciate, such a design would enable a differently-sized blades to be coupled selectively to the hub adaptor 24.

It is to be appreciated that whilst the illustrated example shows the first connection 26 and second 28 connection means as being a set of bolt holes, any suitable connection means may be used which enables the adaptor 24 to be affixed to the rotor hub 12 and the blade root 22 respectively. For example, any one of the first 26 and second 28 connection means may be embodied by rods, e.g. threaded rods, positioned on the first side S1 and the second side S2 respectively, connectable with matching receiving fastening features, e.g. holes, provided in a blade root 22 or a hub bearing 20.

In the illustrated, the first connection means 26 and the second connection means 28 are shown as including an equal number of bolt holes. As such a bolt hole in the first connection means 26 is aligned radially with a corresponding bolt hole in the second connection means 28.

Some variants on the illustrated examples have already been described above. The skilled person would understand that other adaptions could be made without falling outside of the scope of the invention as defined by the claims.

In the illustrated embodiment, the second connection means 28 is at a radially inner position with respect to the first connection means 26, which corresponds to the blade root 22 having a smaller diameter than the hub bearing 20, as is typically the case. However, the invention also anticipates an arrangement where the hub bearing 20 may have a smaller diameter than the blade root 22.