The invention lies in the field of pitch bearing assemblies for rotationally supporting a turbine blade, especially the blades of a wind turbine, relative to a hub of the turbine.

Background of the invention

Wind turbines are designed to convert wind into electricity, by turning a shaft connected to a generator that is located in a nacelle. Rotation of the generator shaft is achieved by wind turbine blades, normally three, that rotate due to the wind. To enable optimization of the output power of the wind turbine, the blades are rotatable around their longitudinal axis, for adjusting a pitch angle of the blade.

Typically, wind turbine blades are connected to the hub using a slewing bearing with a diameter that is approximately equal to the diameter of the blade root. Wind turbines are becoming larger and larger, and the blade root can have a diameter of more than 3 metres. A slewing bearing with an equivalent diameter generates a substantial amount of friction. Also, the slewing bearings experience a high level of wear, due to the relatively small back and forth rotations that the bearing undergoes during operation, especially when individual pitch control is applied, and due to the associated difficulty of maintaining a good lubrication film. Consequently, the use of slewing bearings and other types of rolling element bearings as pitch bearings in wind turbines has disadvantages. An alternative design for a pitch bearing assembly is disclosed in DE2855992. The assembly comprises two axially spaced bearings which are connected to the blade and hub respectively via two mutually overlapping conical structures. The two bearings are rolling element bearings with a diameter that is considerably less than the blade root diameter, which is advantageous in terms of reducing friction. Each conical frame has three legs, whereby the legs of one frame pass between the legs of the other frame. To enable such an assembly to be constructed, at least one of the frames has detachable frame legs. In use, a wind turbine blade experiences high loads which are transmitted to the hub through the bearing construction. When the construction comprises conical frames of the type disclosed in DE2855992, it is important that the frames possess sufficient strength to transmit the loads. The use of high-strength materials is therefore advisable, but such materials are generally rather heavy, which could lead to an increase in weight of the hub and bearing system that is unacceptably high for commercially viable operation of the turbine.

There is thus room for improvement.

Summary of the invention

The present invention resides in an integrated hub and bearing system comprising a hub, configured for being connected to a main shaft of a turbine, and a bearing system comprising a plurality of bearing constructions, whereby each construction is adapted to support a turbine blade so as to be rotatable about a blade pitch axis, relative to the hub. Each bearing construction comprises a dynamic conical frame, configured for connection to a turbine blade, which has at least two circumferentially spaced dynamic frame legs, and further comprises a static conical frame, which has at least two circumferentially spaced static frame legs. The dynamic and static conical frames are mutually overlapping, such that the frame legs of one frame pass through openings between the frame legs of the other frame. Each bearing construction further comprises first and second axially spaced bearings, each having an inner ring and an outer ring, for rotationally supporting the dynamic conical frame relative to the static conical frame. Thus, each of the dynamic and static conical frames has a hub-side and a blade-side bearing seat for one ring of the first and second bearings respectively. According to the invention, the hub comprises a central portion that extends along an axis of the turbine main shaft and interconnects the hub-side bearing seat of each static conical frame in a central region of the hub. Furthermore, heavily loaded parts of the integrated hub and bearing system are made from one or more high-strength materials, while other parts of the system are made from one or more relatively lightweight materials. Specifically, the central portion comprises radially outer sections, which form part of a cone base of each static conical frame. At least these radially outer sections are made from a relatively lightweight material. The heavily loaded parts of the system, which are made from high-strength material, comprise at least one of: a static frame leg; a dynamic frame leg; and a bearing seat for the inner ring of one of the bearings. Preferably, each of these parts is made from a high-strength material.

The interconnection of the static frames in a central region of the hub, close to the main shaft axis, not only increases the strength and stiffness of the system, but also enables a compact construction, which facilitates weight reduction. Furthermore, the selective use of one or more high-strength materials in combination with one or more relatively lightweight materials facilitates an optimal strength-to-weight ratio of the system as a whole.

The one or more relatively lightweight materials preferably comprise a cast metal such as cast steel or cast iron. The one or more high-strength materials preferably comprise forged steel with a yield strength of at least 800 MPa. Suitable examples include 34CrNiMo6 and 42CrMo4.

In one embodiment, at least one of the dynamic and static conical frames comprises a base part and a nose part, which are made from a relatively lightweight material. The base and nose parts are joined by the frame legs, whereby the frame legs are made from high-strength material. The frame legs are thus able to withstand and transmit the high application loads on the blade.

Advantageously, each nose part comprises a connection interface with a flat surface for the first end of each leg, and each base part comprises a connection interface with a flat surface for the second end of each leg. Correspondingly, the first and second ends of each leg have a connection portion with a flat surface, to enable a robust connection between the legs and the respective frames.

In a preferred example, the connection portion of each leg is bolted to the corresponding connection interface on the respective frame. Suitably, the connection surface area is sufficiently large to enable the use of a plurality of bolts. Thus, the leg connections are also able to withstand the high application loads on the blade. Suitably, each conical frame has three frame legs arranged at even angular intervals.

The flat connection surfaces on each static conical frame and/or on each dynamic conical frame may be provided on a circumferential surface of the frame nose part or base part. Alternatively, the nose part or base part of a dynamic or static conical frame may comprise at least two flange portions (one for each frame leg) that extend in a radially inward direction towards an axis of the frame. The flat connection surface for a leg end is suitably provided on at least one side of a flange portion. Preferably, both sides of the flange portion form connection surfaces for a leg end. The corresponding connection portion of the leg also extends in a direction towards the frame axis and has a greater thickness in this direction than in the circumferential direction. Advantageously, a frame leg - in a central region of the leg - has a greater thickness in radial direction towards the frame axis than in circumferential direction. The advantage of this is that the leg can have sufficient thickness to provide the necessary strength without adversely limiting the degree of relative rotation that is possible between the mutually overlapping frames.

In each bearing construction of a system according to the invention, the dynamic conical frame is rotationally supported on the static conical frame by means of the first bearing (hub-side bearing) and the second bearing (blade-side bearing), which is arranged at a distance along the pitch axis from the first bearing. Due to the axial spacing of the bearing units, the high bending moment of the blade is largely transformed into radial load. Each of the first and second bearings comprises a radial bearing, preferably a radial spherical plain bearing, that is mounted on a shaft component. The shaft component for the first bearing may form part of the static frame or may form part of the dynamic frame. Likewise, the shaft component for the second bearing may form part of the static frame or the dynamic frame. The first and second bearings have a diameter that is considerably less than a blade root diameter of the supported blade. The shaft components withstand high radial loads. Consequently, the shaft components are suitably made from a high-strength material.

In one embodiment, the shaft component which forms the bearing seat for an inner ring of at least one of the first and second bearings is a stub shaft. In an example, the hub-side bearing seat of each static frame is formed by a stub shaft. Preferably, each stub shaft is provided on single component - a bearing shaft section - that is made from high-strength material. The bearing shaft section thus forms part of the hub central portion, and is suitably arranged between a main shaft interface - which part is adapted to be coupled to the turbine main shaft - and a front section of the hub central portion. In accordance with the invention, the main shaft interface and the front section are suitably made from a relatively lightweight material such as cast iron. In a further embodiment, the shaft component which forms the bearing seat for an inner ring of at least one of the first and second bearings is a flanged shaft component that is detachably connected to the static conical frame or the dynamic conical frame. Suitably, the flanged shaft component is made of a high-strength material such as forged steel.

In one example, the hub-side bearing seat of the static frame is formed by a flanged shaft component that is e.g. bolted to the base part of the static conical frame, and the blade-side bearing seat of the static frame is formed by a flanged shaft component that is e.g. bolted to the nose part of the static frame. Alternatively, the hub-side and blade-side bearing seats of the dynamic frame may be formed by a flanged shaft component that is e.g. bolted to the nose part and the base part respectively of the dynamic frame. In a further alternative, the static conical frame comprises a first flanged shaft component and the dynamic conical frame comprises a second flanged shaft component. Several configurations are possible.

Thus, an integrated hub and bearing system according to the invention comprises an assembly of separate parts which are capable of transmitting the application loads and are connected together in a robust manner. This is achieved without exceeding an unacceptable weight threshold, and the built-up structure also facilitates transport and on-site assembly of the system.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described below.

Brief description of the drawings

Fig.1 shows a cut perspective view through a first example of an integrated hub and bearing system according to the invention;

Fig. 2a shows a perspective view of an integrated hub comprising parts of the bearing system which are stationary relative to the hub;

Figs 2b, 2c show perspective views of components of the hub depicted in Fig.

2a;

Fig. 2d shows a front view of a dynamic frame for supporting a turbine blade, where the frame is suitable for use in a system according to the invention;

Fig. 3a shows a cross-section through a bearing construction for supporting a turbine blade in a second example of a hub and bearing system according to the invention;

Fig. 3b shows part of a built-up frame from the bearing construction of Fig.

3a;

Fig. 3c shows part of an alternative built-up frame;

Figs. 4, 5 show schematic, cross-sectional views of further examples of a bearing construction which form part of an integrated hub and bearing system according to the invention.

Fig. 6 is a front view of a wind turbine.

Detailed description of the invention

Figure 6 shows a front view of a wind turbine 5 comprising three blades 10 connected to a hub 20. The hub is connected via a main shaft (not shown) to a generator, arranged in a nacelle 30 mounted on a tower 40. To maximize the amount of energy captured by the blades while minimizing the load on the blades, the wind turbine is equipped with an individual pitch control system. Each blade 10 is rotatable relative to the hub 20 about a blade pitch axis, and is rotationally supported by a bearing construction.

In order to minimize friction, each bearing construction comprises axially spaced first and second bearings, which have a diameter that is significantly smaller than a blade root diameter of the turbine blade. The bearing construction further comprises mutually overlapping conical frames which connect the first and second bearings to each other. The frames must therefore be sufficiently robust to transmit the high application loads on the blade to the hub. It is also important, however, that the combined rotor mass of the hub and bearing constructions should be as low as possible, while retaining the necessary strength

This is achieved according to the invention in that one of the mutually overlapping frames of each bearing construction forms part of the hub, resulting in an integrated hub and bearing system. Furthermore, components of the system which carry high loads are made of a high-strength material, while other structural parts of the system are made of a lighter-weight material.

An example of an integrated hub and bearing system according to the invention is shown in Figure 1 . The system 100 is configured for rotationally supporting three turbine blades and comprises first, second and third bearing constructions 105A, 105B, 105C. The structure and operating principle of the first bearing construction 105A will be described, whereby it is to be understood that the description also applies to the second and third bearing constructions. Identical elements are indicated with the same reference numeral, although not all elements have been referenced, so as not to obscure the drawing.

The first bearing construction 105A comprises a dynamic frame 110, to which a turbine blade will be mounted. The dynamic frame has a conical geometry and preferably comprises three dynamic frame legs 115, with openings in between, arranged at even intervals around a circumference of the frame 100. In the depicted example, the dynamic frame comprises a first conical section 111 and a second conical section 112, which are oppositely oriented from each other and which have a common cone base. The dynamic frame legs 115 interconnect the first and second conical sections 111 , 112 and are arranged at the common cone base.

The first bearing construction 105A further comprises a static frame 120, which also has a conical geometry and has a cone base that forms part of the hub. A cone apex of the static frame 120 is joined to the cone base by three static frame legs 125 arranged at even circumferential intervals. The static frame legs 125 have openings in between and pass through the openings between the dynamic frame legs 11 5. Thus, a restricted amount of relative rotation is possible between the dynamic and static frames of the first bearing construction.

If the frame legs 115, 125 were infinitely thin, then 120 degrees of relative rotation would be possible. The maximum possible relative angular displacement is thus governed by the thickness of the frame legs 115, 1 25 in circumferential direction. The frame legs need to be sufficiently thin to permit a relative angular displacement of approx. 90 degrees in pitch bearing applications, yet be sufficiently strong for transmitting the high loads on the blade, via the legs, to the hub. The frame legs 115, 125 are thus made from a high-strength material such as forged steel. 34CrNiMo6 is one example of a suitable high-strength steel, which enables the frame legs 1 15, 125 to have sufficient thinness and strength

To enable the relative angular adjustment, the dynamic frame 110 is rotationally supported relative to the static frame 1 20 by the first and second axially spaced bearings. These bearings will be referred to as a hub-side bearing 1 50 and a blade-side bearing 160. As mentioned, the hub-side and blade-side bearings have a diameter that is considerably smaller than the blade-root diameter. Preferably, each of the hub-side and blade-side bearings 150, 1 60 comprises a radial spherical plain bearing.

Accordingly, the dynamic frame has a blade-side bearing seat for a ring of the blade-side bearing 160 and has a hub-side bearing seat 1 50 for a ring of the hub- side bearing. In the depicted example, the hub-side and blade-side bearing seats are formed by a cylindrical housing with a bore for receiving an outer ring of the respective bearing. The cylindrical housings are arranged at the cone apex of each of the first and second conical sections 111 , 112. The static frame 120 also has a blade-side bearing seat for a ring of the blade-side bearing and a hub-side bearing seat for a ring of the hub-side bearing. In the depicted example, the blade-side bearing seat is formed by a stub shaft 127 for receiving an inner ring of the blade-side bearing 1 60, which is arranged at a cone apex of the static frame. The hub-side bearing seat is also formed by a stub shaft 126, which receives an inner ring of the hub-side bearing 150 and which is arranged in a central region of the hub. In an integrated hub and bearing system according the invention, the hub-side bearing seats 126 are interconnected at central region of the hub, close to an axis of the main shaft. The hub comprises a central portion, which is coupled to the turbine main shaft and which has an axis that coincides with the axis of the turbine main shaft. In the depicted example, the central portion comprises a bearing shaft section 130, which is a single component having three stub shafts 126 that extend radially at even circumferential intervals relative to the centre axis. The bearing shaft section 130 thus comprises the hub-side bearing seat 126 for the static frame 120 of the first bearing construction 105A and comprises the hub-side bearing seat for the static frame of the second and third bearing constructions 105A, 105B and interconnects the static frames 120 at the heart of the hub and bearing system 1 00. This not only increases the strength and stiffness of the overall assembly, but also enhances compactness and thus weight reduction. Furthermore, the loads on the hub-side bearing are transmitted to the hub at the bearing shaft section 130, enabling a more direct transfer of those loads to the turbine main shaft in comparison with conventional wind turbine hubs.

The most highly loaded parts of the hub and bearing system are the stub shafts that form the hub-side bearing seat 1 26 and blade-side bearing seat 127 of each static frame. Consequently, the bearing shaft section 130 and the stub shafts 127 that form the blade-side bearing seats are made of a high-strength material such as forged steel. To save weight, further parts of the hub and bearing system 100 are made of a lighter-weight material such as cast iron or cast steel.

Suitably, the central portion further comprises a main shaft interface (not visible), which couples the bearing shaft section to the turbine main shaft, and further comprises a front section (not visible) that extends from the bearing shaft section 130 to a front side of the hub. The main shaft interface and the front section of the hub central portion are made from cast steel in the example of Figure 1 .

A further example of an integrated hub according to the invention, comprising a hub central portion as described above, is depicted in more detail in Figure 2a. Like the example of Figure 1 , the hub comprises three static frames, each of which has a hub-side bearing seat formed by a stub shaft 226, which shafts are connected to each other at the heart of the hub by a bearing shaft section 230.

In the example of Figure 2a, each static frame 220 comprises a nose part 123 which is joined to the base part of a conical frame by three evenly spaced static frame legs 225. Each static frame further comprises a blade-side bearing seat 227 in the form of a stub shaft for receiving an inner ring of the blade side bearing. The blade-side stub shaft 227 is made of a high-strength material such as forged steel and is joined to the nose part 223, which is made of a lighter material such as cast iron, to reduce the weight of the hub. The hub central portion comprises a main shaft interface 232, which, in use, is coupled to the main shaft of the turbine, and further comprises a front section 235 which extends axially towards the front side of the hub. Between the main shaft interface 232 and the front section 235 of the central portion, the bearing shaft section 230 is arranged. The bearing shaft section, comprising the three hub-side stub shafts 226, is made of forged steel. The main shaft interface 232 and the front section 235 of the hub central portion are less heavily loaded than the bearing shaft section 230 and are made of cast iron, to save weight.

The legs of each static frame are also highly loaded components, and in the depicted example each static frame leg 225 is made of a high-strength material such as forged steel. A first end 225a of each leg is attached to the nose part 223 of a static frame 220 and a second end 225b of each leg is attached to the hub central portion, whereby two of the legs in one frame are attached at their second end 225b to the main shaft interface 232 and the third static frame leg is attached at its second end to the front section 235 of the hub central portion.

The connection interfaces between the legs and the parts they are connected to must also be able to withstand high loads. Consequently, flat connection interfaces are preferred. Suitably, the first end 225a of each static frame leg has a flat geometry and is connected to a flat connection surface on the nose part 223. In the depicted example, each nose part 223 has three flange sections 224 that extend from an outer conical surface of the nose part towards a centre axis of the nose part. In the depicted example, the first end 225a of a static frame leg 225 is connected to a flange section 224 of the nose part by means of two connection plates 241 . The connection plates are joined using e.g. fitted bolts to opposite flat sides of a flange section 224 and to opposite flat sides of the first end 225a of a static frame leg. Preferably, the connection plates 241 are made of forged steel. As mentioned, the static frame legs 225 are highly loaded and therefore need to have a certain thickness to withstand these high loads. In a penetration region of the static frame 220, being a region where a dynamic frame leg will pass between the circumferential space between two static frame legs, the static frame legs have a greater thickness in radial direction (towards the centre axis of the conical frame) than in the circumferential direction. This is beneficial in terms of maximising the range of relative angular rotation that is possible between the mutually overlapping frames.

The first end 225a of each static frame leg is also relatively thinner in circumferential direction than in radial direction. The second end 225b of each static frame leg, by contrast, is relatively thicker in the circumferential direction. Again, the second end of each leg has a flat geometry and is suitably connected to a flat connection surface on either the main shaft interface 232 or on the front section 235 of the hub central portion. A perspective view of the main shaft interface and the front section are shown in Figures 2b and 2c respectively.

At a radially outer section of the main shaft interface 232, three flat connection areas 233 are provided. Each connection area is adapted to receive the second end 225b of a static frame leg 225 of one static frame 220 and the second end of a static frame leg of an adjacent static frame. The two second ends are connected to the flat connection area 233 via a flat plate 242 using e.g. fitted bolts. The legs of adjacent frames are thus interconnected via the flat plate 242, which provides extra strength and stiffness. Preferably, the flat plates 242 are made of forged steel.

A radially outer section of the front section 237 is likewise provided with three flat connection areas 238, each of which is adapted to receive the second end 225b of one static frame leg 225 from each of the three static frames 220. The second end of these legs are connected to the flat connection areas 238 via a three-armed plate 243 using e.g. fitted bolts. The three-armed plate 243 thus interconnects one frame leg of each of the static frames, again providing additional strength and stiffness to the construction as a whole. Preferably, the three-armed plate 243 is made of forged steel.

Thus, the hub is built from different materials to optimise strength while retaining a relatively low weight. Suitably, each dynamic frame that cooperates with a static frame is constructed in a similar fashion from parts made of at least two different materials. An example of a built-up dynamic frame for use in a hub and bearing system according to the invention is shown in Figure 2d.

The frame 21 0 comprises a base part 212 and a nose part 213 which are joined by three legs 315 arranged at equidistant circumferential intervals. The base part and the nose part are made of a relatively lightweight metal such as cast iron, while the dynamic frame legs 21 5 are made of a high-strength material such as forged steel. In this example, the first and second ends of each leg 215 are provided with first and second connection portions 215a, 215b which are spaced in a circumferential direction. The legs have a narrow section in the middle, which curves smoothly outwards towards the first and second connection portions at each end. Circumferentially spaced connection interfaces are suitably provided on the base part 212 and on the nose part 213 of the frame 210, and the connection portions 215a, 215b at each leg end are e.g. bolted to the corresponding connection interface. Again, connection interfaces with a flat surface area are preferred, to prevent stress concentrations. The advantage of two connection portions at each leg end is a larger connection surface area, enabling several bolts to be used. Also, the forces which are transmitted through each leg 215 are directed in an essentially diagonal direction from the first connection portion 215a at the base part 212 to the second connection portion 21 5b at the nose part 213, and from second connection portion 215b at the base part 212 to the first connection portion 215a at the nose part 213. As a result, compressive and tensile forces are the dominant forces through the leg 215, which optimizes leg strength.

Part of a further example of an integrated hub and bearing system 300 according to the invention is shown Figure 3. A bearing construction 305, comprising one pair of mutually overlapping frames, and part of the hub are depicted in cross-section. The bearing construction 305 is configured to rotationally support a wind turbine blade 10 relative to the wind turbine hub 20 about a pitch axis A. The construction comprises a dynamic conical frame 310, to which the blade 10 is attached, and a static conical frame 320 that forms part of the hub 20. The dynamic conical frame is rotationally supported on the static conical frame by means of a hub-side bearing 1 50 and a blade-side bearing 160, which is axially spaced from the first bearing unit along the pitch axis A. The static conical frame has a base part 322 and a nose 323 part, which are connected by three evenly spaced static frame legs 325. Similarly, the dynamic conical frame 31 0 has a base part 31 2 and a nose part 315 which are connected by three evenly spaced dynamic frame legs 31 5, each of which passes through an opening between adjacent legs 325 of the static frame 320.

In accordance with the invention, the legs 315 of the dynamic conical frame 310 and the legs 325 of the static conical frame 320 are made of a high-strength material such as high-strength steel, while the base parts 312, 322 and nose parts 313, 323 of each conical frame are made from a lighter-weight material such as cast steel. 34CrNiMo6 is one example of a suitable high-strength steel; EN-GJS- 400-18U-LT is one example of suitable cast steel. As mentioned before, the connection between the first end of each leg 315, 325 and the respective nose part 313, 323 and the connection between the second end of each leg and the respective base part 312, 322 also needs to be sufficiently strong to transmit the high loads acting on the turbine blade 10.

This is achieved in that the base part 312, 322 and the nose part 313, 323 of each conical frame are provided with connection interfaces having a flat connection surface and in that the first and second ends of each leg have a connection portion that is correspondingly provided with a flat connection surface. In the depicted example, the connection interfaces are provided on a radially oriented surface of the base part 312, 322 and nose part 313, 323 of each conical frame 310, 320.

Part of the static frame 320 is shown in Fig. 3b, in which the connections between the legs and the frame are more clearly depicted. The connection interfaces 330 on the base part 322 and on the nose part 323 of the frame 320 are formed by raised sections with a flat surface. The raised sections protrude from the radially outer surface of the base and nose parts. The legs 325 have a flat connection portion 335 at each end. In a preferred example, the leg connection portion 335 at each leg end is bolted to the appropriate connection interface 330 on the base and nose part of the frame 320. Each leg may have a flat cross-section, or a profiled cross-section, such as a T-profile or a U-profile. Further, the connection portion 335 at the end of each leg, and the corresponding interface 330, are suitably wider than a central section of the leg between the two ends. The relatively large connection surface area enables the use of several bolts, to provide the connection with sufficient strength. Suitably, each leg 325 is designed with a smooth, curved transition between the narrow section in the middle and the connection portion 335 at each end, to prevent stress risers.

In an alternative example, as depicted in Figure 3b, the static frame 320' may comprise frame legs which have an outer leg 325a and an inner leg 325b. Suitably, a connection interface 330 is provided on opposite radial surfaces of the base part 322 and nose part 323 of the frame for attachment of the legs 325a, 325b. The leg connections of the dynamic conical frame may also be executed as described with reference Figures 3b and 3c. Alternatively, the dynamic frame may be executed as shown in the example of Figure 2d. Referring again to Figure 3, the bearing construction 305 in this example comprises a seat for the hub-side bearing 150 and a seat for the blade side bearing 160, which are formed by first and second flanged shaft components 326, 327. According to the invention, each flanged shaft component is made of a high strength material such as forged steel. 34CrNiMo6 and 42CrMo4 are examples of suitable steels.

The second flanged shaft 327 is connected by means of e.g. bolts to the nose part 323 of the static frame 320. The first flanged shaft 326 is connected to part of a central portion 330 of the base part 322 of the static frame. The central portion of the base part also forms part of the hub central portion. As explained previously with reference to the examples of Figures 1 and 2a, the hub central portion extends along the main axis of the turbine and interconnects the hub-side bearing seat 327 of each static frame in a central region of the hub, close to the main shaft axis. The hub central portion and the base part 322 of each static conical frame are preferably cast as one piece.

In the depicted example, the first and second flanged shafts 326, 327 form part of the static frame and each is adapted to receive an inner ring of the hub-side and blade-side bearings respectively. Alternative configurations are shown in Figures 4 and 5.

In the bearing construction 405 according to the configuration of Figure 4, the first flanged shaft component 426, forming the hub-side bearing seat of the static frame, is coupled to the base part 422 of the static frame. The blade-side bearing seat 427 of the static frame is formed by a housing component provided in the nose part of the static frame. The nose part and the base part 422 of the static frame are joined by three static frame legs 425. A second flanged shaft component 41 7 forms the blade-side bearing seat of the dynamic frame, and is coupled to the base part 412 of the dynamic frame. The hub-side bearing seat 416 is formed by a housing component provided at the nose part of the dynamic frame. The nose part and the base part 412 of the dynamic frame are joined by three dynamic frame legs 41 5. In accordance with the invention, the frame legs 415, 425 and the first and second flanged shaft components 426, 41 7 are made of a high strength material such as forged steel, while the base parts and nose parts of the frames are made of a lighter-weight material.

In the bearing construction 505 according to the configuration of Figure 5, a first flanged shaft component 51 6 is coupled to the nose part of the dynamic frame, and forms the hub-side bearing seat of the dynamic frame. The blade-side bearing seat 51 7 of the dynamic frame is formed by a second flanged shaft component that is coupled to the base part 512 of the dynamic frame. The nose part and the base part 512 of the dynamic frame are joined by three dynamic frame legs 51 5. The hub-side bearing seat 526 of the static frame is formed by a housing component provided in the base part 522 of the static frame. The blade-side bearing seat 527 of the static frame is formed by a housing component provided in the nose part of the static frame. The nose part and the base part 522 of the static frame are joined by three static frame legs 525. In accordance with the invention, the frame legs 515, 525, the first and second flanged shaft components 516, 517 are made of a high strength material such as forged steel, while the base parts and nose parts of the frames are made of a lighter-weight material.

As will be clear to the skilled person, other configurations are possible. A number of aspects/embodiments of the invention have been described. It is to be understood that each aspect/embodiment may be combined with any other aspect/embodiment. Moreover the invention is not restricted to the described embodiments, but may be varied within the scope of the accompanying patent claims.