Generator-gearbox assembly for a wind turbine

A generator-gearbox assembly for a wind turbine includes a generator having a generator rotor, a gearbox including an output shaft, and a connection assembly. The connection assembly a hub abutment surface and a plurality of shaft bolt holes, a hub associated with the generator rotor with a first connecting portion (340) having a shaft abutment surface and at least one elongated slot extending through the first connecting portion. The number of elongated slots is less than or equal to the number of shaft bolt holes. A plurality of fasteners fixedly connect the hub to the hub abutment surface, each fastener extending through a respective elongated slot and a shaft bolt hole.

FIELD OF THE INVENTION

This invention relates to a connection assembly for fixedly connecting an output shaft of a gearbox of a wind turbine to a generator of the wind turbine, and a method of connecting an output shaft of a gearbox of a wind turbine to a generator of the wind turbine. The invention further relates to a generator-gearbox assembly and a wind turbine.

BACKGROUND ART

One very challenging aspect of assembling a wind turbine lies in connecting the gearbox output to the generator input of the wind turbine.

Conventionally, the generator rotor and the gearbox are connected at the output shaft of the gearbox by means of bolts. At the outer end of the output shaft, a plurality of bolt holes are usually provided in some arrangement. In such a configuration, a connection element of the rotor of the generator has a corresponding number and arrangement of bolt holes. So as to connect the generator and the output shaft of the gearbox, the output shaft is arranged to abut the connection element of the generator. The output shaft and/or the generator rotor then needs to be moved and/or rotated such that the bolt holes of the output shaft and the bolt holes of the generator rotor are perfectly aligned. Only then can bolts be fed through the bolt holes of the output shaft and the generator and securely fixed. To ensure fixed connection, a bolt must be passed through each bolt hole of the output shaft and each bolt hole of the generator.

During assembly of the wind turbine power train, the rotor of the generator and the gearbox output shaft are often locked into a random position and can only be moved or rotated to a limited degree. The weight of the parts and the tight spaces they are installed into make it even more difficult to manoeuvre accurately. Often, only the output shaft can be rotated over a maximum of 4 degrees either way, and special tools are needed for making this possible. As a result, it is very difficult to arrange the output shaft in the correct position with respect to the bolt holes of the generator for attachment. It is against this background that the invention has been devised.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided a generator-gearbox assembly for a wind turbine comprising a generator having a rotational element in the form of a generator rotor; a gearbox comprising an output shaft; and a connection assembly. The connection assembly comprises a hub abutment surface, provided at an end of the output shaft and a plurality of shaft bolt holes; a hub associated with the generator rotor and comprising a body and a first connecting portion having a shaft abutment surface facing towards the hub abutment surface and at least one elongated slot extending through the first connecting portion. The number of elongated slots is less than or equal to the number of shaft bolt holes. A plurality of fasteners fixedly connect the hub to the hub abutment surface, each fastener extending through a respective elongated slot and a shaft bolt hole.

Note that in this discussion, the connecting portions may be circular flanges.

The hub being arranged for fixed attachment to the rotational element and having a first flange with elongated slots reduces the likelihood of having to manoeuvre a cumbersome drive shaft into an exact position for attachment to a rotational element. Since the slots are elongated, when the drive shaft is arranged to abut the first flange during assembly it is more likely that the shaft bolt holes of the hub abutment surface align with the elongated slots of the first flange, and so it is more likely that a connection can be made between the drive shaft and the rotational element. If the number of elongated slots is less than the number of shaft bolt holes, the slots can be made larger and it is even more likely that the shaft bolt holes of the hub abutment surface align with the elongated slots of the first flange, and hence that a secure connection can be made.

Between every two adjacent slots, there is a bridge portion that depending on its width and rotational position with respect to the hub abutment surface may cover one or more shaft bolt holes. Where there are multiple slots, the number of bridge portions will be equal to the number of slots. When the width of the bridge portions is such that they can never cover more than one shaft bolt hole and the number of shaft bolt holes is a multiple of the number of slots, only two rotational configurations are possible. One configuration in which the bridge portions end up exactly in between two shaft bolt holes and all shaft bolt holes can receive a fastener. And one configuration in which each bridge portion, partly or fully, blocks one shaft bolt hole. In the latter configuration, the number of shaft bolt holes that can receive a fastener equals the number of shaft bolt hole minus the number of slots. If the number of slots is not a multiple of the number of slots, the number of blocked shaft bolt holes will be in between zero and the total number of slots.

Preferably, the connection assembly further comprises a washer and the washer comprises a plurality of washer bolt holes. The fasteners may successively extend through the washer bolt holes, the elongated slots and the shaft bolt holes. In contrast with the elongated shape of the slots, the washer bolt holes can be shaped to match the shape and dimension of the bolts, thereby allowing a bolt head to contact the washer around the whole circumference of the washer bolt hole. Such a washer can provide a more secure connection than when the bolt is directly inserted into the elongated slot.

For the purposes of this discussion, the term ‘washer’ should be interpreted as a shim-like element which functions as an intermediate element between two components to even out the compressive stress between those two components. As such, a washer may be a small ring of material that may be received over a single bolt. Alternatively, a washer may be a larger ring, or a ring section, that is penetrated by several apertures each of which apertures is suitable for receiving a bolt therethrough.

The number of washer bolt holes may be equal to the number of shaft bolt holes. With such a washer, and in configurations wherein none of the shaft bolt holes are blocked, all washer bolt holes can receive a bolt. In configurations where one or more of the shaft bolt holes are blocked, fewer bolt holes can receive a bolt. For a more standardized assembly process, it may be preferred to always use a number of bolts that equals the number of shaft bolt holes minus the number of slots. When that means that more than one fully accessible shaft bolt holes are not used, the not used shaft bolt holes are preferably symmetrically distributed around the circumference of the washer.

Alternatively, the number of washer bolt holes may be equal to the number of shaft bolt holes minus the number of elongated slots. Since using only this number of bolts is sufficient for ensuring a secure connection of the connection assembly, the missing holes won't be missed. By symmetrically distributing the missing holes around the circumference of the washer, it is ensured that the bolts used are symmetrically distributed too. This special washer makes thus makes it very easy to decide which shaft bolt holes to use for an optimally secure connection.

In a preferred embodiment, the number of shaft bolt holes equals a multiple of the number of elongated slots. This allows for the possibility of having the same number of bolts passing through each elongated slot, and hence can ensure symmetrical balance of the connection assembly.

The number of fasteners/bolts may be equal to the number of shaft bolt holes. This is only possible in the situation where the shaft bolt holes of the hub abutment surface align perfectly with the elongated slots of the first flange when the drive shaft is arranged to abut the hub during assembly. Alternatively, the number of bolts may be equal to the number of shaft bolt holes minus the number of elongated slots. This is the more likely scenario in which the shaft bolt holes of the hub abutment surface misalign with the first flange when the drive shaft is arranged to abut the hub during assembly. Whether the number of bolts equals the number of shaft bolt holes or the number of shaft bolt holes minus the number of elongated slots, the connection assembly provides a secure connection.

In a preferred embodiment, the shaft bolt holes are distributed around one or more concentric circles of the hub abutment surface. This allows for a simplified setting up of the connection assembly. The shaft bolt holes may be distributed substantially evenly around the one or more concentric circles of the hub abutment surface. This ensures a symmetrically balanced connection assembly.

The first flange may extend from a shaft end of the body, and the hub may comprise a second flange extending from a rotational element end of the body for fixedly attaching the hub to the rotational element. A second flange is preferable since it simplifies the process of fixedly attaching the hub to the rotational element. A circumference of the second flange may be larger than a circumference of the first flange. This is because it is advantageous for a secure connection to fix the hub as close as possible to an outer circumference rotational element and an outer circumference of the hub abutment surface and because the rotational element is usually much larger than the hub abutment surface. The body may have a portion that is substantially frustoconical in shape. This ensures that the loads are balanced symmetrically throughout the connection assembly. In the context of a frustoconical-shaped body portion, a wall angle of that frustoconical-shaped body portion that is about 45 degrees provides better access through the hub which is a benefit in terms of access to serviceable components such as sensors. It should be noted that other angles would be acceptable, for example about 40 degrees. Furthermore, a larger angle, for example 60 degrees or above, may provide further advantages in terms of access to components past the body. For the purposes of this discussion, the expressed angle is considered to be taken from the line of the body wall section to the rotational axis of the rotor, which is usually horizontal.

The body may further comprise an auxiliary component portion which provides a connection region to an auxiliary component. The auxiliary component portion may be adjacent to the frustoconical-shaped body portion. Together, the auxiliary component portion and the frustoconical-shaped body portion may be located between the first flange and the second flange.

The invention extends to a generator-gearbox assembly of a wind turbine comprising: a generator having a generator rotor; a gearbox comprising an output shaft; and the connection assembly referred to above; wherein the hub abutment surface of the connection assembly is provided at an end of the output shaft and the body of the hub of the connection assembly is fixedly attached to the generator rotor of the generator.

The invention further extends to a wind turbine comprising the generator-gearbox assembly referred to above.

According to a further aspect of the invention, there is provided a method of connecting an output shaft of a gearbox of a wind turbine to a generator of the wind turbine; the method comprising the steps of: providing a hub abutment surface at an end of the output shaft, the hub abutment surface comprising a plurality of shaft bolt holes; providing a hub associated with the generator rotor and comprising a body and a first flange extending from the body, the first flange having a shaft abutment surface for abutment of the hub abutment surface and one or more elongated slots extending through the first flange, the number of elongated slots being less than or equal to the number of shaft bolt holes; arranging the hub abutment surface to abut the shaft abutment surface; providing a washer comprising a plurality of washer bolt holes; arranging the washer adjacent to the first flange; rotating the washer until at least a portion of the washer bolt holes align with the elongated slots and with the shaft bolt holes; providing a plurality of fasteners; inserting the fastenerssuccessively through the washer bolt holes, the elongated slots and the shaft bolt holes; and securely fastening the fasteners.

In this method, the step of inserting the plurality of fasteners may include identifying the shaft bolt holes which are fully visible through the one or more elongated slots for the insertion of respective fasteners, wherein the identification step is achieved without rotating the generator rotor with respect to the hub abutment surface. Therefore, all of the necessary bolted connections in the hub abutment surface may be identified through the elongated slots which means that the bolt holes become fully visible without having to physically rotate the heavy components of the rotor or the gearbox shaft.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Wind turbines convert kinetic energy from the wind into electrical energy, using a large rotor with a number of rotor blades. A typical Horizontal Axis Wind Turbine (HAVVT) comprises a tower, a nacelle on top of the tower, a rotating hub or ‘rotor’ mounted to the nacelle and a plurality of wind turbine rotor blades coupled to the hub. Depending on the direction of the wind, the nacelle and rotor blades are turned and directed into an optimal direction by a yaw system for rotating the nacelle and a pitch system for rotating the blades.

The nacelle houses many functional components of the wind turbine, including for example a generator, gearbox, drive train 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. The gearbox steps up the rotational speed of the low speed main shaft and drives a gearbox output shaft. The gearbox output shaft in turn drives the generator, which converts the rotation of the gearbox output shaft into electricity. The electricity generated by the generator may then be converted as required before being supplied to an appropriate consumer, for example an electrical grid distribution system. So-called “direct drive” wind turbines that do not use gearboxes are also known. In a direct drive wind turbine, the generator is directly driven by a shaft connected to the rotor.

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 in to 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 order to place the embodiments of the invention in a suitable context, reference will firstly be made toFIG.1, which illustrates a typical Horizontal Axis Wind Turbine (HAVVT)100in which embodiment of the invention may be implemented. It should be noted in this context that the wind turbine100may be on-shore or off-shore. Furthermore, although the wind turbine is question is referred to as having a ‘horizontal axis’, it will be appreciated by the skilled person that for practical purposes, the axis is usually slightly inclined to prevent contact between the rotor blades and the wind turbine tower in the event of strong winds.

FIG.1shows a wind turbine100comprising a tower120, a rotor140and a nacelle160. The nacelle160is rotatably mounted on the tower120by a yaw system (not shown) for allowing the rotor140to be yawed into the direction of the wind. The rotor140is rotatably mounted on the nacelle160. The rotor140comprises a rotor hub145and three rotor blades150coupled to the rotor hub145.

The nacelle160houses many functional components of the wind turbine100, including a drive train, power generation equipment and a rotor brake assembly, as well as convertor equipment for converting the mechanical energy of the wind into electrical energy for provision to an electrical grid distribution system. As shown inFIGS.2and3, the nacelle160houses a rotor shaft170that is fixedly connected to the rotor hub145at a rotor end175of the rotor shaft170. The nacelle160further comprises a generator-gearbox assembly200which is fixedly connected to the low speed rotor shaft170at a gearbox end180(opposite the rotor end175) of the rotor shaft170.

The generator-gearbox assembly200comprises a gearbox220and a generator240. The gearbox220is fixedly connected to the gearbox end180of the rotor shaft170and comprises an output shaft230which extends along a longitudinal axis L. The gearbox220also comprises gear stage(s)225which steps up the relatively slow rotation of the rotor shaft so that the output shaft230rotates at a higher speed that is more appropriate for the generator240. The high-speed output shaft230is fixedly connected to the generator240at a leading end235of the output shaft230(opposite the gears225of the gearbox220).

The generator240is configured to produce electricity using the rotational energy of the output shaft230. To this end, the generator240comprises a generator rotor245to which the output shaft230is fixedly connected and which rotates as the output shaft230rotates, and a generator stator250comprising associated windings (not shown).

So as to fixedly connect the output shaft230of the gearbox220to the generator240in accordance with the invention, the generator-gearbox assembly200comprises a connection assembly300. The connection assembly300comprises a hub abutment surface310, a hub320, and a plurality of bolts (not shown), each of which will now be described in detail. In one embodiment, the connection assembly300comprises an intermediate member or ‘coupling element’ in the form of a washer which ensures a more secure connection for the connection assembly300.

As shown inFIG.4, the hub abutment surface310is provided at the leading end235of the output shaft230. The hub abutment surface310may be integral with the output shaft230, fixedly attached to the output shaft230or removably attached to the output shaft230as required. Expressed another way, the hub abutment surface310may be provided on a different component from the output shaft230. For optimal torque transfer between the output shaft230and the generator rotor245, a rotationally tight connection between the hub abutment surface310and the output shaft230is needed.

The hub abutment surface310comprises a plurality of shaft bolt holes315. The shaft bolt holes315are distributed around a circle of the hub abutment surface310and are preferably located near the outer circumference of the hub abutment surface310so as to allow for the greatest number of bolts (not shown) and the securest possible connection assembly300. The shaft bolt holes315are distributed substantially evenly around the circle of the hub abutment surface310. A circular and symmetric arrangement is optimal for bearing high loads.

It should be noted at this point that the hub320may abut the hub abutment surface310of the output shaft230directly, or indirectly, in that one or more intermediate elements may be included such as the aforementioned washer. Another example is that one or more friction shims could be included. Also, such intermediate elements may be common to the bolts that fix the shaft230to the hub, but each bolt may include its own respective intermediate element (e.g. small washers provided on each bolt).

The hub320will now be described with reference toFIGS.5,6,7and8.FIGS.5and8each show a hub320in perspective, whileFIGS.6and7each show a cross-section of a hub320. It will be appreciated that the view of the hub310inFIGS.6,7and8is from the opposite viewing direction to that ofFIG.5.

The hub320comprises a body325that extends along the longitudinal axis L. The hub320is arranged for fixed attachment to the hub abutment surface310of the output shaft230. To this end, the hub320comprises a substantially circular first connecting portion or ‘flange’340that extends from a shaft end326of the body325. The first flange340extends substantially in the plane perpendicular to the longitudinal axis L. InFIGS.4to8, the first flange340adjoins the body325at an outer edge of the first flange340. The first flange340may also adjoin the body325at an inner edge of the first flange340, though this may complicate the process of fixedly attaching the first flange340to the hub abutment surface310during an assembly of the connection assembly300, because the acute angle with the hub body325may make it more difficult to reach and fasten the bolts.

It should be noted at this point that although the flange340is a relative thin component in the axial direction, as is illustrated in the drawings, this should not be considered limiting. Instead the function of the flange340should be considered as of prime importance. The flange340functions to enable the hub to connect to the output shaft230so this functionality could be provided by a flange or ‘connecting portion’ of much thicker dimensions. Therefore, the term ‘flange’ used herein should not be interpreted exclusively as requiring a relatively thin radially extending surface or collar and should cover other configurations of connecting portion that enable the hub body325to be connected to a shaft abutment surface310by a series of bolts, as will be described.

The first flange340comprises a shaft abutment surface345for abutment of the hub abutment surface310of the output shaft230. In one embodiment, the first flange340comprises a washer abutment surface350(opposite the shaft abutment surface345) for abutment of a washer380. The first flange340further comprises a plurality of elongated slots360extending or penetrating through the first flange340. As can be seen inFIGS.5to8, the elongated slots360are arced around a circle at the first flange340. Importantly, the arrangement of the elongated slots360of the first flange340corresponds to the arrangement of the shaft bolt holes315of the hub abutment surface310. That is to say, they can be considered to share the same ‘pitch circle diameter’.

An arc length between any two elongated slots360of the first flange340is preferably not larger than an arc length between any two shaft bolt holes315of the hub abutment surface310, because otherwise the material of the first flange340may simultaneously cover more than one of the shaft bolt holes315. For optimal structural strength of the flange340, it may be beneficial to use elongated slots360with rounded edges365. While the number of elongated slots360in the first flange340may vary from hub320to hub320, to ensure a balanced connection assembly300all slots360in a particular hub320preferably have the same length. Alternatively, slots360of two or more different lengths may be arranged symmetrically around the circumference of the flange340.

InFIGS.7and8, the hub abutment surface310of the output shaft230is shown abutting the shaft abutment surface345of the first flange340. The first flange340and the hub abutment surface310are arranged concentrically. In this embodiment, the number of elongated slots360in the first flange340is less than the number of shaft bolt holes315in the shaft and the slot length is large enough to always allow full access to at least two of the shaft bolt holes315, irrespective of the relative orientation of the first flange340with respect to the hub abutment surface310. Moreover, the number of shaft bolt holes315is a multiple of the number of elongate slots360, ensuring that the same number of bolts can be inserted through each elongated slot360for a balanced connection.

In the ‘perfectly aligned’ optimal relative orientation shown inFIG.8, exactly three shaft bolt holes315are fully accessible in each one of the elongated slots360. In this configuration the number of bolts (not shown) that can be inserted into each elongated slot360equals the number of shaft bolt holes315divided by the number of elongated slots360.

If the hub320ofFIG.8is rotated over a small angle, the elongated slots360and shaft bolt holes315will be “misaligned”: that is, some of the shaft bolt holes315are partly, or fully blocked by the first flange340such that a bolt (not shown) is not feedable through an elongated slot360and each of these shaft bolt holes315. When misaligned in this way, the number of bolts (not shown) that can be installed equals the number of shaft bolt holes315minus the number of elongated slots360. Expressed another way, the number of bolts that can be inserted into each elongated slot360is equal to the total amount of available bolts divided by the number of elongated slots360.

In decreasing the number of elongated slots360of the first flange340, and thus also the total amount of flange material between elongated slots360, fewer shaft bolt holes315are blocked by the first flange340when the first flange is arranged to abut the hub abutment surface310. However, a first flange340with fewer, but longer, elongated slots360may also be more fragile.

The hub320is also arranged for fixed attachment to the generator rotor245of the generator240. To this end, the hub320comprises a substantially circular second connecting portion or ‘flange’370(best seen inFIGS.7and8) that extends from a generator end327(opposite the shaft end326) of the body325. Like the first flange340, the second flange370extends substantially in the plane perpendicular to the longitudinal axis L. That is, the first340and second345flanges extend in parallel. InFIGS.4to8, the second flange370adjoins the body325at an inner edge of the second flange370.

The second flange370may also adjoin the body325at an outer edge of the second flange370, though this may complicate the process of fixedly attaching the second flange370to generator240during assembly of the connection assembly300, because the acute angle with the hub body325may make it more difficult to reach and fasten the bolts.

It is envisaged that a practical configuration will be for the hub320to be a component that is separate to the generator rotor245, which is why the illustrated embodiment is shown as including a second flange370. However, it should be noted that this need not be the case and that the hub320may be an integral component to the supporting structure of the generator rotor245. In either case, the hub320can be considered to be ‘associated’ with the generator rotor245.

The second flange370is fixedly attached to the generator240by means of generator bolts (not shown). To this end, the second flange370comprises flange bolt holes375, as shown inFIG.7, and the generator rotor245comprises stator bolt holes (not shown)

The stator bolt holes are located near the outer circumference of the generator rotor245to make use of the greatest number of generator bolts (not shown) and to ensure the strongest possible connection.

The hub320is arranged such that a circumference of the second flange370is larger than a circumference of the first flange340as the shaft and the hub abutment surface310are smaller than the generator240and the generator rotor245. The first340and second345flanges are arranged substantially concentrically for balance and for translating rotational forces more efficiently. The body325of the hub320extends between the first flange340and the second flange370, and, as such, the body of the hub320is a substantially frustoconical body325. The body325may be solid, as inFIGS.8and7, or it may be provided with suitable apertures that allow access through the body, such as circular openings330, as inFIG.5or a grid-like structure335, as inFIG.6.

It should be noted that that in the illustrated embodiment, the wall section of the frustoconical body defines an angle of about 45 degrees with the major axis of the generator (i.e. the rotational axis L), which is usually horizontal. This is beneficial since it helps maintenance works gain access through the body325, for example to access component or sensors that may need adjustment or removal. An angle of 45 degrees is just an example, and so it should be appreciated that other angles are acceptable, either less than or greater than 45 degrees. For example, an angle of 40 degrees may still provide useful access, and an angle of 60 degrees may provide improved access.

Alternatively, the hub320does not comprise a second flange370and the hub320is fixedly attached to the generator240directly through the body325of the hub325. In another embodiment, the hub320may be integral with the generator240.

The washer380will now be described with reference toFIG.9. Note that the washer may also be referred to as an intermediate element, element, or washer element. However, the term ‘washer’ will be used here for simplicity.

Since each elongated slot360of the first flange340is larger than each shaft bolt hole315of the shaft, it can be beneficial to use a washer380so as to provide a more secure connection for the connection assembly300. The washer380may be a substantially circular disc385and may have a substantially circular opening390: that is, the washer380may be substantially annular in order to reduce weight and the amount of material used.

In this embodiment, the washer380comprises washer bolt holes395distributed around a circle of the washer380. The washer bolt holes395preferably have the same size as the shaft bolt holes315and match the diameter of the bolts that are used. Importantly, the arrangement of many of the washer bolt holes395correspond to the arrangement of respective shaft bolt holes315of the hub abutment surface310and to elongated slots360of the first flange340. As such, a bolt can be put through a washer hole, an elongated slot and a shaft bolt hole, thereby providing the clamping and friction required for a tight fit in the connection assembly300.

The number of washer bolt holes395in the washer380is preferably equal to the number of shaft bolt holes315or to the number of shaft bolt holes315minus the number of elongated slots360. When the number of washer bolt holes395is equal to the number of shaft bolt holes315, the arrangement of the washer bolt holes395of the washer380corresponds to the arrangement of a shaft bolt holes315of the hub abutment surface310.

When the number of washer bolt holes395is equal to the number of shaft bolt holes315minus the number of elongated slots360, the arrangement of the washer bolt holes395of the washer380corresponds to the arrangement of the shaft bolt holes315of the hub abutment surface310, except that every nthwasher bolt hole395is missing, where n is the number of shaft bolt holes315divided by the number of elongated slots360. As such, connection forces are always evenly distributed around the washer380.

Because the washer380is a loose part, it can be rotated freely until the washer bolt holes395are aligned with the shaft bolt holes315that are visible through the elongated slots360. The washer380allows for an easy connection of the output shaft230and the generator240, since only the washer380needs rotating to form an attachment and not the output shaft230or the generator rotor245and since the washer380is much easier to manoeuvre than the output shaft230or the generator rotor245.

FIG.10shows a washer380abutting the washer abutment surface350of the first flange340and the shaft abutment surface345of the first flange340abutting hub abutment surface310of the output shaft230. The first flange340, the hub abutment surface310, and the washer380are all arranged substantially concentrically. This washer380is lacking every third washer bolt hole395. Though not visible because it is sandwiched between the hub320and the hub abutment surface310of the gearbox output shaft230, the first flange340has a number of elongated slots360that equals the number of “missing” washer bolt holes395in the washer380, and the hub abutment surface310has a number of shaft bolt holes315that equals the number of washer bolt holes395plus the number of elongated slots360.

Since the arc length between any two adjacent elongated slots360of the first flange340is less than the arc length between any two adjacent shaft bolt holes315of the hub abutment surface310, a number of shaft bolt holes315equalling the number of elongated slots360may be blocked by the first flange340whenever the output shaft230and the first flange340are arranged to abut.

By arranging the washer380so that the washer bolt holes395align with the unblocked shaft bolt holes315, and inserting bolts successively through the washer bolt holes395of the washer380, through the first flange340and through the unblocked shaft bolt holes315in the hub abutment surface310, a fixed connection between the hub320and the hub abutment surface310is achieved. In this configuration, the point in the circle of the washer380where no washer bolt hole395is present aligns with the point between the elongated slots360in the first flange340.

Despite not using all of the shaft bolt holes315for connection, such an arrangement is very secure. This secure connection is achieved without requiring a perfect alignment of the hub320and the output shaft230. Such a perfect alignment is almost always very unlikely since manoeuvring the output shaft230or the generator rotor245is very difficult.

While it may be possible that the elongated slots360and the shaft bolt holes align perfectly, a number of bolts equalling the number of shaft bolt holes does not need to be used to ensure a secure connection. Indeed, this is why a washer having a number of washer bolt holes equal to the number of shaft bolt holes minus the number of elongated can always be used in accordance with the invention.

Alternatively, a washer380may be used having a number and spatial arrangement of washer bolt holes395that corresponds to that of the shaft bolt holes315of the hub abutment surface310. However, the washer bolt holes395that are blocked by flange material between two elongated slots360cannot be used for inserting bolts (not shown).

An exemplary embodiment of the connection assembly300includes a hub abutment surface310with twenty one shaft bolt holes315, a first flange340with three elongated slots360and a washer380with either twenty one or eighteen washer bolt holes395. Even when the elongated slots360and the shaft bolt holes315misalign, eighteen bolts can be used, ensuring a very secure connection between the output shaft230and the generator240.

Now, a method for assembling the connection assembly300above, and for connecting the output shaft230to the generator240, will be described.

The method comprises a step of providing the hub abutment surface310at the end of the output shaft230. This may include integrally forming the hub abutment surface310out of the output shaft230, fixedly attaching a component defining the hub abutment surface310to the output shaft230or removably attaching the hub abutment surface310to the output shaft230.

The method then comprises the steps of providing the hub320and fixedly attaching the hub320to the generator240. This may include fixedly attaching the second flange370of the hub320to the generator240or directly connecting the body325of the hub320to the generator240. Alternatively, the hub320may be connected to the generator240before the hub abutment surface310is provided, or the hub320is integrally formed out of the generator240and does not need to be attached.

Then, the hub abutment surface310of the output shaft230is arranged to abut the shaft abutment surface345of the hub320. In this position, the hub abutment surface310and the first flange340are arranged as concentrically as possible. At this point, it most likely that the elongated slots360and the shaft bolt holes315misalign such that a number of shaft bolt holes315equal to the number of elongated slots360are blocked by the first flange340. Next, the method includes a step of providing the washer380and a step of arranging it adjacent to the first flange340. The washer380is arranged to abut the washer abutment surface350of hub320where it can easily be rotated.

The method then includes a step of rotating the washer380until at least a portion of the washer bolt holes395align with the elongated slots360and with the shaft bolt hole, i.e. until at least a number of washer bolt holes315equalling the total number of shaft bolt holes315minus the number of elongated slots360align with the unblocked shaft bolt holes315. The method then includes a step of providing the bolts (not shown), a step of inserting the bolts successively through the washer bolt holes395, the elongated slots360and the shaft bolt holes315; and a step of securely fastening the bolts.

If, as will usually be the case, the elongated slots360and shaft bolt holes315are not perfectly aligned a number of bolts (not shown) is used that equals the total number of shalt bolt holes315minus the number of elongated slots360. If, coincidentally, the elongated slots360and shaft bolt holes315are perfectly aligned, either the same number of bolts as the number of shalt bolt holes315is used or a number of bolts equalling the total number of shaft bolt holes315minus the number of elongated slots360. Both options ensure a secure connection between the output shaft230and the hub abutment surface310.

It will be appreciated by those skilled in the art that the invention has been described by way of example only, and that a variety of alternative approaches may be adopted. For example, in one embodiment, the first flange has only one elongated slot360that extends entirely around the first flange340in a circle. This embodiment may be less preferable, although technically possible, since a first flange340with only one slot360is more difficult to handle.

In another embodiment, the shaft bolt holes315, the elongated slots360and the washer380are distributed around two or more concentric circles, thus allowing for a more secure connection.

In the above embodiments, the term ‘bolt’ has been used to refer to the mechanical threaded fasteners that are used to connect the hub to the shaft. However, it should be noted that within the present invention other suitable mechanical fasteners could be used, for example, screws, threaded rods or studs. Moreover, a mix of different fasteners could be used. Threaded fasteners are preferred due to the requirement to apply a compressive force between the hub body325and the components to which it attaches. However, non-threaded fasteners such as dowels may be used in combination with threaded fasteners.

In another embodiment, the number of elongated slots360in the first flange340is equal to the number of shaft bolt holes315in the output shaft. Since the elongated slots360are elongated, this arrangement allows for a slight misalignment of the output shaft230and the hub during assembly. The shaft bolt holes315don't have to line up exactly at the centre of the elongated slots360. However, if the flange material partly or fully blocks the shaft bolt holes315, the gearbox output shaft230(and/or the generator rotor345) will have to be rotated over a small angle in order to unblock the shaft bolt holes315. Though this may not be an ideal embodiment in terms of automatically aligning elongated slots360and shaft bolt holes315, it does ensure that all shaft bolt holes315can actually be used and an even more secure connection is obtained.

It is noted that, although the invention is described with reference to an output shaft of a wind turbine that is connected to the rotor part of a wind turbine generator, the invention is not limited to this specific application. The connection assembly300may also be suitable for fixedly connecting other drive shafts to rotational elements. In any situation where it is difficult to rotationally align a drive shaft with a second rotating element, the advantages of this connection assembly300will be apparent.

In the illustrated embodiments, the hub320includes a frustoconical body325that extends between a first connecting flange340and a second connecting flange370. However, other configurations are envisaged. One of these alternative configurations is shown inFIG.11, in which parts in common with the previous drawings are labelled with the same reference numerals.

In this embodiment, the hub320includes a first connecting flange340, a second connecting flange370and a body325that extends between the first and second connecting flanges. In the same way, the first flange340is penetrated by elongated slots360for attachment to a hub abutment surface310(not shown inFIG.11) which is associated with the gearbox output shaft.

The body325has a portion325awhich is frustoconical and which flares radially outwards from the first flange340when extending towards the second flange370. However, in this embodiment, it will be noted that the frustoconical portion325adoes not merge into the second flange370as was the case with previous embodiments. Instead, the body includes a further portion325bwhich has a constant diameter, in this embodiment, and extends in the axial direction between the radially outer edge of the frustoconical section325aand the second flange370. Note that the constant diameter portion325bhas a diameter that is larger than the frustoconical portion325aand so defines a pair of opposed axially facing circular connecting surfaces/flanges398. The constant diameter portion325bmay provide for an auxiliary function. For example, the radially outer surface of the constant diameter portion325bmay provide a friction surface or clamping surface for a generator brake arrangement. In the illustrated embodiment, one of the flanges398is provided with a series of holes400(only two of which are shown, for clarity) that may mate with suitable mechanical fasteners to secure a brake disc to the body325, for example. Other configurations are possible. The constant diameter portion325bcan therefore be considered to be an auxiliary-component portion of the body325since it allows for the engagement, coupling or securement of an auxiliary component to the body325.

These and other variations are possible without departing from the scope of the invention as defined by the appended claims