DK202070239A1 - Improvements relating to preloading wind turbine main shaft bearings - Google Patents

Abstract

A wind turbine powertrain comprising a main shaft extending along a main shaft axis, and defining a front end and a rear end, the main shaft being supported in a main bearing housing by a front bearing carried on the main shaft, and a rear bearing carried on the main shaft proximate the rear end thereof, wherein the rear end of the main shaft protrudes beyond an axial end face of the rear bearing. The powertrain also comprises a preload arrangement including a first arm, a second arm and a bridge section extending between the first and second arms, wherein the bridge section is attached to the rear end of the main shaft by way of a first circumferential fastening arrangement, and wherein the first arm extends along a portion of the radial outer-facing surface of the main shaft and engages a surface associated with the axial end face of the rear bearing, and wherein the second arm extends along a portion of a radial inner-facing surface of the main shaft. The powertrain further comprises a gearbox component attached to the rear end of the main shaft by way of a second circumferential fastening arrangement, wherein the second circumferential fastening arrangement has a pitch circle diameter that is less than a pitch circle diameter of the first circumferential fastening arrangement, and wherein the gearbox component is a separate component to the preload device. Beneficially, the preload device is configured to embrace the radial outer and inner facing surfaces of the rear end of the main shaft and so this causes the preload device to be constrained to the deformation of the main shaft as it rotates which reduces the dynamic load on the fastening arrangement fixing the preload device to the main shaft, thereby improving the reliability of the preload device.

Description

DK 2020 70239 A1 1

IMPROVEMENTS RELATING TO PRELOADING WIND TURBINE MAIN SHAFT BEARINGS

TECHNICAL FIELD The invention relates to preload arrangements for applying a preload force to bearings of a wind turbine main shaft.

BACKGROUND As is well-known, wind turbines convert kinetic energy from the wind into electrical energy, using a rotor carrying a number of rotor blades. A typical Horizontal Axis Wind Turbine (HAWT) comprises a tower, a nacelle on top of the tower, a rotating hub or ‘rotor’ mounted to the nacelle and a plurality of rotor blades coupled to the hub. The nacelle houses many functional components of the wind turbine, including for example a generator, gearbox and rotor brake assembly, as well as convertor equipment for converting the mechanical energy at the rotor into electrical energy for provision to the grid.

Central to the operation of the wind turbine is the main shaft arrangement to which the rotor is mounted and which transmits torque to the gearbox. In a typical arrangement a main shaft arrangement includes a main shaft that is supported on a bearing arrangement which supports the main shaft within a main shaft housing. A common configuration is for the bearing arrangement to include a forward bearing located towards the front end of the main shaft, near to a hub connection, and a rear bearing located towards the rear end of the main shaft, near to the gearbox. The bearings therefore are instrumental in transmitting operational loads from the main shaft to the main shaft housing and to the surrounding structure of the wind turbine, which typically includes a bed plate as an interface between the nacelle and the wind turbine tower.

It is common to apply a preload or ‘pretension’ to the main shaft bearings in order to eliminate manufacturing clearances in the bearing and to improve overall stiffness of the assembly and rotational accuracy.

It is against this background that the invention has been devised.

DK 2020 70239 A1 2

SUMMARY OF THE INVENTION According to a first aspect of the invention, there is provided a wind turbine powertrain comprising a main shaft extending along a main shaft axis, and defining a front end and a rear end, the main shaft being supported in a main bearing housing by a front bearing carried on the main shaft, and a rear bearing carried on the main shaft proximate the rear end thereof, wherein the rear end of the main shaft protrudes beyond an axial end face of the rear bearing. The powertrain also comprises a preload arrangement including a first arm, a second arm and a bridge section extending between the first and second arms, wherein the bridge section is attached to the rear end of the main shaft by way of a first circumferential fastening arrangement, and wherein the first arm extends along a portion of the radial outer-facing surface of the main shaft and abuts or engages a surface associated with the axial end face of the rear bearing, and wherein the second arm extends along a portion of a radial inner-facing surface of the main shaft. The powertrain further comprises a gearbox component attached to the rear end of the main shaft by way of a second circumferential fastening arrangement, wherein the second circumferential fastening arrangement has a pitch circle diameter that is less than a pitch circle diameter of the first circumferential fastening arrangement, and wherein the gearbox component is a separate component to the preload device.

The second circumferential fastening arrangement may be provided on a flange that extends radially inwards. The preload device embraces the radial outer and inner facing surfaces of the rear end of the main shaft and so this causes the preload device to remain in alignment with the rear end of the main shaft as it rotates. The advantage of this is as the main shaft is deformed out of a true circular shape because of the bending moments exerted on the main shaft due to the mass of the rotor, the preload device deforms in the same way as the shaft. This effect means that the fasteners, usually being bolts, that secure the preload device to the main shaft are subject to reduced cyclical stress which reduces the risk of the bolts either being damaged or loosening. The reliability of the preload device is therefore improved as a result. In one example, the first arm extends from the bridge section in a direction along the main shaft axis for a greater distance than that of the second arm. In another example, the second arm extends from the bridge section in a direction along the main shaft axis for a

DK 2020 70239 A1 3 greater distance than that of the first arm.

This may improve the resilience of the second arm to induced stress during use.

In one example, the radial thickness of the first arm of the preload device is greater than the radial thickness of the second arm.

In another example, the radial thickness of the second arm of the preload device is greater than the radial thickness of the first arm.

The preload device may contact the rear bearing directly.

However, in one example, the surface associated with the axial end face of the rear bearing is provided by a shim or spacer component that is interposed between the rear bearing and the first arm of the preload arrangement.

The shim or spacer component can thus be configured to adjust the preload exerted on the rear bearing by the preload device and is a convenience means of doing so because different sized spacer components can be used for this purpose.

The shim or spacer component may be provided with a high-friction coating to increase friction between the bearing ring and the preload device.

In one example, the preload arrangement is ring-shaped.

However, advantages may be realised if the preload device is fabricated from a plurality of sections.

The invention may have particular utility in a wind turbine powertrain as defined above, including a hub connected to the main shaft, wherein the ratio of i) the distance between a centre of mass of the hub and the front bearing to ii) the distance between the front bearing and the rear bearing is greater than about 0.8. Furthermore, that powertrain may also be defined by a further key dimension such that the ratio of i) the radius of the main shaft at the rear end thereof and ii) the distance between the front bearing and the rear bearing, is greater than about 0.2. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination.

That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible.

The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

DK 2020 70239 A1 4

BRIEF DESCRIPTION OF THE DRAWINGS The above and other aspects of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a front view of a wind turbine in which the examples of the invention may be incorporated; Figure 2 is a perspective view of a wind turbine power train including a main bearing housing within which examples of the invention may be incorporated; Figure 3 is a schematic illustration of the main bearing housing in Figure 2, viewed as a longitudinal section, whereas Figure 4 is an enlarged view of a rear bearing arrangement of the main bearing housing of Figure 3 featuring a preload device in accordance with an example of the invention; Figure 5 is a perspective view of the preload device shown in Figure 4; Figures 6 and 7 are schematic views of alternative examples of the invention; and Figure 8 is a further schematic view of the powertrain in accordance with the invention which illustrates key dimension of the configuration. Note that features that are the same or similar in different drawings are denoted by like reference signs.

SPECIFIC DESCRIPTION A specific embodiment of the 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.

DK 2020 70239 A1

In order to place the embodiments of the invention in a suitable context, reference will firstly be made to Figure 1, which illustrates a typical Horizontal Axis Wind Turbine 1(HAWT) in which a bearing arrangement according to an example of the invention may be implemented.

Although this particular image depicts an on-shore wind turbine, it will be 5 understood that equivalent features will also be found on off-shore wind turbines.

The wind turbine 1 comprises a tower 2, a nacelle 4 rotatably coupled to the top of the tower 2 by a yaw system (not shown), a rotating hub or ‘rotor’ 8 mounted to the nacelle 4 and a plurality of wind turbine rotor blades 10 coupled to the hub 8. The nacelle 4 and rotor blades 10 are turned and directed into the wind direction by the yaw system.

With reference to Figure 2, the nacelle 4 comprises a powertrain 20, which includes a gearbox 22 and a generator 24 which are driven by a main shaft 26. The main shaft 26 is supported by a main bearing housing 25 and is connected to, and driven by, the rotor 8 and provides input drive to the gearbox 22. The gearbox 22 steps up the rotational speed of the low speed main shaft 26 via internal gears (not shown) and drives a gearbox output shaft (not shown). The gearbox output shaft in turn drives the generator 24, which converts the rotation of the gearbox output shaft into electricity.

The electricity generated by the generator 24 may then be converted by other components (not shown) as required before being supplied to an appropriate consumer, for example an electrical grid distribution system.

As used here, the term ‘powertrain’ includes at least one component of the main shaft arrangement, gearbox and generator.

The main bearing housing 25 includes a set of supports or feet 30 by means of which the main bearing housing 25 is mounted to a base plate or bedplate (not shown). Although the base plate is not shown in this illustration, the skilled person would understand that it is the interface between the main bearing housing 25 and the base plate which is the main structural interface between the nacelle and the tower of the wind turbine.

The main bearing housing 25 supports high static and dynamic loads imposed on the main shaft 26 and transfers these loads to the main supporting structure of the wind turbine tower through the base plate.

The bearing support provided by the main bearing housing 25 to the main shaft 26 is therefore crucial to the correct operation of the power generating assembly.

It should be noted at this point that the general arrangement of the gearbox and generator are not central to the invention and should not be considered limiting the — scope of protection.

DK 2020 70239 A1 6 The configuration of the main bearing housing 25 is shown more clearly in Figure 3, which is a schematic representation of the main bearing housing and its internal components. As can be seen, the main shaft 26 extends horizontally through the main bearing housing 25 and is supported by a front bearing 32 and a rear bearing 34. The main shaft 26 is hollow, in the illustrated example, and includes a flared front end 36 which defines a hub connection flange 38. The main shaft 26 extends along a direction in line with a rotational axis R and defines an outer surface 39, and a rear end 40 distal from the flared front end

36. In the illustrated embodiment, the rear end 40 of the main shaft 26 is configured to interface with a gearbox component 42, more detail of which will be described later. The detail of the gearbox and other related components is not directly relevant to the invention so further discussion will not be provided. The front bearing 32 and the rear bearing 34 are shown here as single row arrangements of tapered roller bearings. It will be noticed that the front bearing 32 and the rear bearing 34 are spaced apart on the main shaft 26, such that the front bearing 32 is positioned towards the forward end of the main shaft 26 and the rear bearing 34 is positioned towards the rear end 40 of the main shaft 26. Since the main shaft 26 is configured to have a relatively thin wall, configuring the bearing in this way helps to maintain an acceptable stiffness in the main shaft 26. Stiffness of the main shaft is important in this configuration of powertrain since there is a direct connection between the main shaft housing 25 and the gearbox 22 The rear bearing 34 will now be described in more detail also with reference to Figure 4. As can been seen, the rear bearing 34 is proximate the rear end 40 of the main shaft but is set back from it slightly. As such, the rear end 40 of the main shaft 26 protrudes axially beyond the rear bearing 34. The rear bearing 34 comprises a first bearing ring 44 and a second bearing ring 46 which accommodate a plurality of rollers 48 between them, in a known manner. The first bearing ring 44 is in a radially inner position in the illustrated example, and so will be referred to as the inner bearing ring from now on. Similarly, the second bearing ring 46 is in a radially outer position compared to the inner bearing ring 44, and so will be referred to from now on as the outer bearing ring 46. The inner bearing ring 44 is fixed to the outer surface 39 of the main shaft. In a high load application such as this, the inner bearing ring 44 is typically attached to the main shaft by — an interference fit, through which the inner bearing ring 44 is heated to expand its internal diameter so that it is greater than the outside diameter of the main shaft, after which it is

DK 2020 70239 A1 7 located in position on the main shaft and then allowed to cool, thereby fixing the inner bearing ring 44 in position. The outer bearing ring 46 is fixed to a radially inner surface 50 of the main bearing housing

25. The fit between the outer bearing ring 46 and the main bearing housing 25 may also be an interference fit, which may be achieved by cooling the outer bearing ring 46 so as to reduce its outside diameter to less than the internal diameter of the main bearing housing 25, following which the outer bearing ring 46 is positioned in the main bearing housing 25 and then allowed to warm up during which process the outer bearing ring 46 expands thereby defining a tight fit with the main bearing housing 25. In the illustrated example, the rollers 48 are tapered rollers which travel on an inclined race surface 49 provided by the inner bearing ring 44 and the outer bearing ring 46. Here, the inclination of the rollers 48 is such that their rolling axes Rb are inclined downwardly at — their forward end towards the rotational axis Rs of the main shaft. The gearbox component 42 is attached to an inwardly extending flange 54 defined by the rear end of the main shaft 26 by a suitable circumferential fastening arrangement 55. More specifically, the inwardly extending flange 54 comprises a plurality of circumferentially spaced holes 56 which are aligned with a corresponding set of circumferentially spaced holes 58 provided in the gearbox component 42. Respective connection rods 60 extend between an aligned pair of holes 56,58 in the inwardly extending flange 54 and gearbox component 42. The connection rods 60 may be expandable elements such as components known commercially as GripCon by Schaaf®, as would be known to the skilled person. In this way, the connection rods 60 provide torque transmission between the main shaft 26 and the gearbox component 42. A bolted connection (not shown) may also be provided between the gearbox component 42 and the main shaft 26 in order to provide an improved axial coupling between the two components. Although the connection rods 60 provide an excellent torque coupling, other fastening schemes could be used, such as a bolted connection. It should be noted at this point that the gearbox component 42 may be planet carrier for an epicyclic gearbox, or another type of gearbox connection shaft, or may be a coupling component for coupling a gearbox shaft to an input connection. In the technical context illustrated in Figures 1 and 2, it will be appreciated that the main shaft 26 carries the mass of the hub and rotor blades which applies a tremendous static bending load on the main shaft 26. The static and dynamic loads transmitted through the

DK 2020 70239 A1 8 main shaft 26 cause small deformations in the geometry of the main shaft 25 and also the geometry of the main bearing housing 25. Since the main shaft 26 rotates, in use, the loading on the main shaft 26 due to the mass of the rotor causes dynamic loading on the bearings, and particularly the rear bearing 34 which can cause the position of the bearing to shift. To guard against this, bearing arrangements in high load applications such as shown here typically include a mechanism to ensure that the bearings are kept in position. A known solution relies on a machined rib which forms a bearing abutment. Other solutions require a mechanism to apply a preload to the bearing, although such solutions can be challenging to implement due to the high loads experienced in use.

In the illustrated example, the rear bearing includes a preload or a ‘pretension’ arrangement 70 in order to apply and axial force to the rear bearing. The preload arrangement 70 will now be described in more detail with reference also to Figure 4 and Figure 5.

The preload arrangement 70 includes a preload device 72 that is shown in cross section in Figures 3 and 4, but is shown in perspective in Figure 5, in which it can be seen as being an annular component. In the illustrated example, the preload device 72 is in the form of a complete ring that is machined as a single piece, although it is envisaged that this need not be the case and other examples may include the preload device 72 being fabricated in sections. Those section can either be attached to the main shaft individually to form the complete preload arrangement, or they may be coupled together as a first step, and then fixed to the rear end of the main shaft 26 as a subsequent step.

The preload device 72 is generally C-shaped in cross section and as such includes a first arm 74, second arm 76 and a bridge section 78. The first arm 74 extends away from one end of the bridge section 78 and the second arm extends away from the other end of the bridge section 78. Both of the first and second arms 74,76 extend away from the bridge section 78 in the same direction and are parallel to one another and also parallel to the rotation axis Rs of the main shaft 26, in this example.

The preload device 72 is attached to the rear end 40 of the main shaft. More specifically, in this example the preload device 72 is attached to a transverse end face 80 of the rear end 40 of the main shaft 26. As can be seen, the bridge section 78 is attached to the transverse end face 80 by a second circumferential fastening arrangement, which in this example is a bolt arrangement 82. The bolt arrangement 82 includes a plurality of

DK 2020 70239 A1 9 circumferentially arranged bolts 84 that extend through a respective set of circumferentially arranged bolt holes 86 provided in the preload device 72. The bolt arrangement 82 is viewed most clearly in Figure 5, and the relative positioning of an exemplary bolt 84 with respect to the bridge section 78 and the rear end 40 of the main shaft is most clearly seen in Figure 4. Although the bridge section 78 is fastened to the end face 80 by way of bolts 84 in this example, this is simply a common fastening scheme in this context but in principle other fastening schemes could be used.

Since the bridge section 78 is attached to the transverse end face 80 of the rear end 40 of the main shaft 26, the first and second arms 74,76 extend way from the bridge section 78 to bear against axial extending surfaces of the rear end 40. More specifically, the first arm 74 has an arm surface 88 that bears against a radially outer surface 90 of the rear end 40 of the main shaft 26. Similarly, the second arm 76 has an arm surface 92 that bears against a radially inner or inwardly-facing surface 91 of the rear end 40 of the main shaft.

In this example, the radially inner surface 90 is defined by a surface of an annular groove 93 in the transverse end face 40 of the main shaft 26. Expressed in another way, the first and second arms 74,76 embrace a protruding annular portion 94 of the rear end 40 of the main shaft, which is therefore received by the annular recess 96 defined by the space between the first and second arms 74, 76 of the preload device 72. In effect, therefore, the preload device 72 grips the protruding annular portion 94 of the rear end 40. As will be noted, in this example the two surfaces 90,91 are substantially parallel to one another.

In this context, it should be appreciate that the terms “radially inner” and “radially outer” are made with reference to the main shaft axis Rs, such that “inner” refers to a direction facing the shaft axis and “outer” refers to a direction facing away from the shaft axis.

The length of the first arm 74 of the preload device 72 is configured so as to apply an axial force to the rear bearing 34 when the preload device 72 is suitably secured to the main shaft 26. For this purpose, therefore, the first arm 74 contacts, abuts or engages a surface 100 associated with the rear bearing 34 and, more specifically, the inner bearing ring 44 thereof.

In this example the surface 100 associated with the rear bearing 34 is provided by a spacer or shim component 102 that is interposed between the first arm 74 of the preload device 72 and the inner bearing ring 44. The precise axial dimension, shown here as ‘L’, of the shim component 102 can be set to a predetermined depth in order to achieve the required axial force on the inner bearing ring 44. Therefore, it will be understood that the surface 100 of the shim component 102 in effects provides a further surface that is spaced

DK 2020 70239 A1 10 from an axial end face 103 of the inner bearing ring 44, and via which surface 100 the preload device 72 applies a force to the bearing 34. It will be appreciated that different widths shim components 102 could be used to vary the biasing force that the preload device applied to the bearing in a more convenient way to changing the configuration of the preload device itself. Optionally, the spacer or shim component 102 may be enhanced by a high friction surface, which may be an electroless nickel coating carrying micrometre-sized diamond particles. Such a solution would reduce tangential movement between the preload device 72 and the bearing 34 due to the increased friction between the two components. It is also envisaged that one or both of the first arm 74 or the inner bearing ring may be treated with a high friction coating. It will be appreciated from the above discussion and the drawings that the preload device 72 embraces the radial outer and inner surfaces 90,91 of the rear end 40 of the main shaft

26. Advantageously, therefore, the preload device 72 tends to remain in alignment with the rear end 40 of the main shaft 26 as it rotates, and the main shaft 26 is deformed out of a true circular shape because of the bending moments exerted on the main shaft 26 due to the mass of the rotor. This effect means that the bolts 84 that secure the preload device 72 tothe main shaft 26 are subject to reduced cyclical stress which reduces the risk of the bolts either being damaged or loosening. As shown in the illustrated example, the axial length of the first arm 74 of the preload device 72 is unequal to the axial length of the second arm 76. More specifically, the axial length of the second arm 76 is greater than that of the first arm 74. The axial length of the first arm 74 is generally dictated by the need to engage with the rear bearing 34, but in principle the length of the first arm 74 is preferably as short as possible whilst still being able to engage the rear bearing and apply a preload force to it. In this respect, the thickness of the shim component 102 could be increased to reduce the length of the first arm 74. A shorter first arm 74 means that the preload device 72 is less ‘stiff which improves the ability of the preload device 72 to deflect together with the main shaft. The axial length of the second arm 76 is generally governed by the need for it to brace the preload device 72 against the radially facing inner surface 91 of the rear end 40 of the main shaft 26 and stresses induced in the material as the preload 72 deforms cyclically during use. Therefore, an increased axial length of the second arm 76 is typically preferred

DK 2020 70239 A1 11 in order to distribute the contact surface pressure over a larger area. Moreover, since the role of the second arm 76 is to withstand the induced stress without being damaged, typically the thickness of the second arm 76 in the radial direction is greater than the thickness of the first arm 74.

It should also be noted that conveniently the preload device 72 is a separate component to the gearbox component 42. In this sense, the preload device 72 is attached to the main shaft 26 by the first bolt arrangement 82, whilst the gearbox component 42 is attached to the main shaft 26 by virtue of the circumferentially arranged connection rods 60 provided inthe inwardly extending flange 54 of the rear end 40 of the main shaft 26. It will therefore be appreciated that the pitch circle diameter of the first bolt arrangement 82 is greater than the pitch circle diameter of the circumferentially arranged connection rods 60. That is to say, the bolt arrangement 82 is at a relatively radial outer position when compared to the radial position of the connection rods 60. The gearbox component 42 and the preload device 72 may therefore be assembled and disassembled onto the main shaft 26 separately from one another, which provides flexibility in the assembly process for the main shaft 26 into the main shaft housing 25. Various modifications may be made to the illustrated examples of the invention as discussed above. Some have already been explained, but others will now be mentioned for completeness. Two alternative examples are shown schematically in Figure 6 and 7. It should be noted at this point that as Figures 6 and 7 are schematic in nature and are focussed on the rear bearing 34, many components of the main shaft 26 and power train are omitted for clarity. Furthermore, it will be appreciated that many of the components and parts in the examples shown in Figures 6 and 7 are shared with the examples discussed previously. Therefore, those shared components and parts will be referred to with the same reference numerals and only significant differences will be discussed in detail. Referring firstly to Figure 6, as in the previous example, a preload device 72 is shown attached to a rear end 40 of the main shaft 26 by a circumferential bolt arrangement 82 that extends through the bridge section 78 of the preload device 72 into the body of the main shaft. In the example of Figure 4, the second arm 76 extended underneath the protruding annular section 84 of the rear end 40 and braced against the radially inward

DK 2020 70239 A1 12 facing surface 91. Comparing Figure 6 against Figure 4, it will be appreciated that the second arm 76 is configured in a very similar way to Figure 4, but is received into an annular recess, groove or socket 106 defined in the inwardly extending flange 54. Note that the second arm 76 still provides a radially outward facing surface 90 that engages with the radially inward facing surface 91 defined by the rear end 40 of the main shaft 26. In contrast to the example in Figure 4, the illustrated example of Figure 6 also includes an extension part 108 which extends in line with the bridge section 78. By virtue of the extension part 108, the bridge section 78 defines two axial contact faces that contact the rear end 40 of the main shaft 26. A first axial contact face 110 is defined by the bridge section 78 and contacts the protruding annular section 92, and a second axial contact face 112 is defined by the extension part and contacts a facing part of the inwardly extending flange 54. Such a configuration may provide the second arm 76 with improves stress resilience.

Turning now to the further example shown in Figure 7, the similarities with the example of Figure 6 will readily be appreciated in that the second arm 76 of the preload device 72 extends into an annular groove or socket 106 defined on the rear end 40 of the main shaft

26. The same general configuration of the interface between the second arm 76 and the groove 106 apply in the same way as discussed above in relation to Figure 6. However, what is to be noted is that the second arm 76 is in a position that is radially outside of the circumferential bolt arrangement 82. More specifically, here the second arm 76 is aligned with the wall of the main shaft 26.

Figure 8 is a schematic view of the powertrain 20 as discussed above, including the main bearing housing 25 and the main shaft 26 connected to its associated rotor or hub 8. Note that the hub 8 is shown here without blades attached. There are three key dimensions marked on Figure 8: the first is labelled ‘A’ and is the distance between the centre of mass 'M' of the hub 8 and the position of the front bearing 32 along the main axis R main shaft; the second is labelled 'B' and is the distance, along the axis R, between the front bearing 32 and the rear bearing 34; and the third dimension is labelled 'C' and is the radius of the main shaft 26 at its rear end, in the vicinity of the rear bearing 34. Note that the preload arrangement 70 is shown schematically in Figure 8 for simplicity. From this illustration, it will be appreciated that dimension A is about equal to dimension B. The relative distance between the hub mass centre M, the front bearing 32 and the rear bearing 34 influences the radial forces experienced particularly at the rear bearing 34 which in turn influences

DK 2020 70239 A1 13 the configuration of the rear end of the main shaft in the vicinity of the rear bearing 34 and particularly the radius C. Here it should be noted that the invention as described above has particular utility in a powertrain where the ratio of the dimension A to B is approximately 1:1, or at least greater than about 0.8. Such a configuration tends to lead to higher radial forces on the non-rotor end of the main shaft 26, which in turn means that a larger radius shaft is more suitable. As such, the dimension C as shown here is comparatively large, such that the ratio of C:B (i.e. the ratio of the shaft radius to the distance between the bearings) is greater than about 0.2, which represents a shaft having a relative compact length but a relatively wide diameter.

List of reference numerals 1 wind turbine 2 tower 4 nacelle 8 rotor/hub 10 blades powertrain 22 gearbox 20 24 generator main bearing housing 26 main shaft MBH supports 32 front bearing 25 34 rear bearing 36 front end of main shaft 38 hub connection flange 39 outer surface 40 rear end of main shaft 30 42 gearbox component 44 inner bearing ring 46 outer bearing ring 48 rollers 49 race surface 50 radially inner surface of MBH 54 inwardly extending flange

DK 2020 70239 A1 14 55 circumferential fastening arrangement 56 holes 58 gearbox component holes 60 connection rods 70 preload arrangement 72 preload device 74 first arm 76 second arm 78 bridge section 80 transverse end face 82 circumferential (fastening) bolt arrangement 84 circumferentially arranged bolts 86 circumferentially arranged bolt holes 88 arm surface of first arm 90 radially outer surface of rear end 91 radially inner surface of rear end 92 arm surface of second arm 93 annular groove 94 protruding annular section of the rear end 96 annular recess of preload device 100 surface associated with rear bearing 102 shim component 103 axial end face of inner bearing ring

Claims (13)

DK 2020 70239 A1 15 CLAIMS

1. A wind turbine powertrain comprising: a main shaft (26) extending along a main shaft axis (Rs) and defining a front end and a rear end (40), a front bearing (32) carried on the main shaft (26), and a rear bearing (34) carried on the main shaft (26) proximate the rear end (40) thereof, wherein the rear end (40) of the main shaft (26) protrudes beyond an axial end face of the rear bearing (34), a preload arrangement (70,72) including a first arm (74), a second arm (76) and a bridge section (78) extending between the first and second arms (74,76), wherein the bridge section (78) is attached to the rear end (40) of the main shaft (26) by way of a first circumferential fastening arrangement (82), and wherein the first arm (74) extends along a portion (90) of the radial outer-facing surface (90,39) of the main shaft (26) and engages a surface (100) associated with the axial end face (103) of the rear bearing (34), and wherein the second arm (76) extends along a portion of a radial inner-facing surface (91) of the main shaft, the wind turbine powertrain further comprising a gearbox component (42) attached to the rear end (40) of the main shaft (26) by way of a second circumferential fastening arrangement (55), wherein the second circumferential fastening arrangement (55) has a pitch circle diameter that is less than a pitch circle diameter of the first circumferential fastening arrangement (82), and wherein the gearbox component (42) is a separate component to the preload device (72) .

2. The wind turbine powertrain of Claim 1, wherein the first arm (74) extends from the bridge section (78) in a direction along the main shaft axis (Rs) for a greater distance than that of the second arm (76).

3. The wind turbine powertrain of Claim 1, wherein the second arm (76) extends from the bridge section (78) in a direction along the main shaft axis (Rs) for a greater distance than that of the first arm (74).

DK 2020 70239 A1 16 4, The wind turbine powertrain of any of the preceding claims, wherein the radial thickness of the first arm of the preload device is greater than the radial thickness of the second arm.

5. The wind turbine powertrain of any of Claims 1 to 3, wherein the radial thickness of the second arm of the preload device is greater than the radial thickness of the first arm.

6. The wind turbine powertrain of any of the preceding claims, wherein the surface (100) associated with the axial end face (103) of the rear bearing (34) is provided by a shim component (102) that is interposed between the rear bearing (34) and the first arm (74) of the preload arrangement (70).

7. The wind turbine powertrain of Claim 6, wherein the shim component (102) includes a high-friction coating.

8. The wind turbine powertrain of any of the preceding claims, wherein the preload arrangement (70) is ring-shaped.

9. The wind turbine powertrain of any of the preceding claims, wherein the rear bearing (34) is a tapered roller bearing.

10. The wind turbine powertrain of any of the preceding claims, wherein the second circumferential fastening arrangement (55) is provided on a flange (54) that extends radially inwards.

11. The wind turbine powertrain of any of the preceding claims, wherein the gearbox component (42) is a planet gear carrier component for a gearbox of the wind turbine powertrain.

12. The wind turbine powertrain of any of the preceding claims, including a hub (8) connected to the main shaft (26), wherein the ratio of i) the distance (A) between a centre of mass (M) of the hub (8) and the front bearing (32) to ii) the distance (B) between the front bearing (32) and the rear bearing (34) is greater than about 0.8.

DK 2020 70239 A1 17

13. The wind turbine powertrain of any preceding claims, wherein the ratio of i) the radius (C) of the main shaft (26) at the rear end (40) thereof and ii) the distance (B) between the front bearing (32) and the rear bearing (34), is greater than about 0.2.