Main bearing arrangement for a wind turbine

A drivetrain for a horizontal axis wind turbine includes a main shaft, and a main bearing housing having a main body at least partly enclosing the main shaft and extending from a first end to a second end, a distance from the second end to the rotor attachment flange being larger than a distance from the first end to the rotor attachment flange. The main bearing housing: carries the main shaft via a first bearing and a second bearing, a distance between the second bearing and the rotor attachment flange being larger than a distance between the first bearing and the rotor attachment flange; has a first seat for the first bearing, and a second seat for the second bearing; and includes a seat flange extending from the main body at least partly radially inwards, the second seat being located on a distal end of the seat flange.

TECHNICAL FIELD

The invention relates to a drivetrain for a horizontal axis wind turbine, comprising a main shaft provided with a rotor attachment flange adapted to be connected to a rotor of the wind turbine, and a main bearing housing carrying the main shaft via a first bearing and a second bearing. The invention also relates to a main bearing housing for a horizontal axis wind turbine, adapted to at least partially enclose a main shaft connected to a rotor of the wind turbine, the main bearing housing presenting a substantially circular component attachment flange for a connection of the main bearing housing to a further drivetrain component, where the further drivetrain component and the rotor are located at opposite ends of the main bearing housing.

BACKGROUND

Horizontal axis wind turbines usually include a tower carrying on its top a nacelle, and a rotor mounted on a drivetrain which is housed in the nacelle, The drivetrain usually includes a main shaft, a gearbox and a generator. In many turbines, the main shaft is carried, via two axially offset bearings, by a main bearing housing. The connection between the main shaft and the gearbox input shaft can be of any suitable type, for example it could be a rigid connection, or it could include a low speed coupling as exemplified in WO2012052022A1 allowing some flexibility in the alignment of the shafts. In some cases, the main bearing housing, the gearbox and the generator each have their respective direct support to a carrying structure of the nacelle. In other cases the gearbox and the generator are cantilevered, as exemplified below, from the main bearing housing, and in such cases the joint between the main bearing housing and a fixed body of the gearbox will experience relatively large forces. In addition, certain types of low speed couplings have a relatively large diameter. This will require a large diameter of any fixed connection between the main bearing housing and the fixed body of the gearbox. For example, the main bearing housing and the gearbox might be connected via relatively large cover for a low speed coupling between the main shaft and the gearbox input shaft. However, it might be desired to provide a main shaft that has a relatively small diameter at its connection to the gearbox, and therefore a small bearing between the main shaft and the main bearing housing.

SUMMARY

It is an object of the invention to provide in a wind turbine an effective and reliable main shaft bearing support, and an effective connection, in particular regarding loads, between a main bearing housing and a further drivetrain component, such as a gearbox.

This object is reached with a drivetrain for a horizontal axis wind turbine, drivetrain for a horizontal axis wind turbine, comprisinga main shaft provided with a rotor attachment flange adapted to be connected to a rotor of the wind turbine, anda main bearing housing having a main body at least partly enclosing the main shaft and extending from a first end to a second end, a distance from the second end to the rotor attachment flange being larger than a distance from the first end to the rotor attachment flange, the main body presenting at the second end a component attachment flange for a connection of the housing to a further drivetrain component,the main bearing housing carrying the main shaft via a first bearing and a second bearing, a distance between the second bearing and the rotor attachment flange being larger than a distance between the first bearing and the rotor attachment flange,the main bearing housing having a first seat for the first bearing, and a second seat for the second bearing,the main bearing housing comprising a seat flange extending from the main body at least partly radially inwards, the second seat being located on a distal end of the seat flange.

Preferably, the main body of the main bearing housing extends along the rotational axis of the main shaft. In some embodiments, the further drivetrain component is a low speed coupling cover. In other embodiments, the component attachment flange of the main bearing housing is adapted for a connection of the housing directly to a fixed part of a gearbox or a generator.

The seat flange extending from the housing main body at least partly radially inwards, provides for the component attachment flange being located radially, in relation to a rotational axis of the main shaft, outside the second seat. I.e. the extension of the seat flange has a component in the radial direction; it could also have a component parallel to the rotational axis, but in any case the flange is oriented inwards from the main body, in a non-zero angle to the rotational axis.

The invention will allow for improving the force handling in drive trains where the further drivetrain component/components is/are cantilevered from the main bearing housing. The reason is that the connection between the further component(s) and the main bearing housing can be made relatively large to reduce the forces induced by the bending moment caused by the cantilevered arrangement, without compromising the design of the main shaft bearing arrangement, which can be kept relatively small as dictated by the size of the main shaft.

Thus, the reduced forces will allow for reducing the material. Also, since the connection between the main bearing housing and the further drivetrain component can be designed independently of the main shaft bearing arrangement, a relatively straight load path can be provided in the main bearing housing for stresses incurred by the cantilevered arrangement, with a large diameter at the connection to the further drivetrain component.

Also, the invention will be advantageous where a low speed coupling has a relatively large diameter requiring a large cover for the coupling. The component attachment flange can be made large for a connection to the cover, while the main shaft bearing can be kept considerably smaller to accommodate the main shaft.

Preferably, the seat flange is shaped as a truncated cone, where the distal end is the narrower end of the truncated cone, and where the distance from the distal end to the rotor attachment flange is larger than the distance from the wider end of the truncated cone to the rotor attachment flange. The truncated cone shape of the seat flange will provide an alignment of the seat flange with the force path associated with the second bearing, in particular where the second bearing is a tapered roller bearing, angled in the following manner (as exemplified in the drawings described below): The bearing rollers each have a first roller end and a second roller end, the distance between the rotor attachment flange and the first roller end being smaller than the distance between the rotor attachment flange and the second roller end, and the distance between the rotational axis of the main shaft and the first roller end being smaller than the distance between the rotational axis and the second roller end.

The invention also provides a main bearing housing for a horizontal axis wind turbine, adapted to at least partially enclose a main shaft connected to a rotor of the wind turbine, the main bearing housing presenting a substantially circular component attachment flange for a connection of the main bearing housing to a further drivetrain component, where the further drivetrain component and the rotor are located at opposite ends of the main bearing housing, the main bearing housing having a first seat for a first bearing between the main bearing housing and the main shaft, and a second seat for a second bearing between the main bearing housing and the main shaft, the distance from the component attachment flange to the first bearing seat being larger than the distance from the component attachment flange to the second bearing seat, the diameter of component attachment flange being larger than the diameter of the first bearing seat, and the diameter of the second bearing seat being equal to, or smaller than, the diameter of the first bearing seat.

Thereby, as has been mentioned above, the large component attachment flange provides for a good force handling capacity in view of the further drivetrain component being cantilevered from the main bearing housing, while a relatively small second bearing can be provided so as to be adapted for an optimized main shaft design.

Here the diameter of the component attachment flange is understood as the diameter of a region for transfer of loads between the component attachment flange and the further drivetrain component. For example. where there is a bolt connection between the component attachment flange and the further drivetrain component, with a single row of bolts and with the bolts oriented substantially in parallel to a rotational axis of the main shaft, the diameter of the component attachment flange is the diameter of an imaginary circle formed by the center lines of the series of bolts distributed along the component attachment flange. The diameters of the bearing seats are understood as the diameters of respective surfaces of the seats facing radially inwards and supporting the respective bearings.

Preferably, the difference between the component attachment flange diameter and the second bearing seat diameter is at least twice, preferably three times, as large as the difference between the diameters of the first and second bearing seats. Preferably, the diameter of the component attachment flange is at least 30%, preferably at least 40%, more preferably at least 50%, larger than the second bearing seat diameter.

DETAILED DESCRIPTION

The horizontal axis wind turbine1inFIG. 1includes a tower2carrying on its top a nacelle3adapted to swing around a vertical axis in relation to the tower2. The wind turbine also includes a rotor4with a hub41carrying three blades42; alternatively there could be fewer or more than three blades on the hub41. The hub is mounted on a drivetrain which is housed in the nacelle3, The drivetrain includes a main shaft5, gearbox6and a generator7.

FIG. 2shows parts of the drivetrain including the main shaft5. The rotational axis of t e rotor4and the main shaft5is indicated inFIG. 2with a broken line A. The main shaft5is at a first end (to the left inFIG. 2) provided with a rotor attachment flange5C which is fixedly connected to the hub41(FIG. 1). At a second end (to the right inFIG. 2), the main shaft5is connected to a low speed coupling61, in turn connected to an input shaft62of the gearbox6. The main shaft5is carried via a main bearing arrangement52,53by a main bearing housing51. As can be seen inFIG. 3, the main bearing housing51is fixedly mounted on a bed frame31of the nacelle structure. As can be seen inFIG. 2, the main bearing arrangement includes a first and a second bearing52,53distributed along the rotational axis A of the main shaft5. The first and second bearings are in this embodiment roller bearings, but any of them could alternatively be of any type of bearing, e.g. a ball bearing.

The first bearing52is located closer to the hub than the second bearing53. The first bearing52, or more specifically, an outer ring of the first bearing52, is fitted in a first seat511presented by the main bearing housing51. The second bearing53is located close to the low speed coupling61. An outer ring of the second bearing53, is fitted in a second seat512also presented by the main bearing housing. Inner rings of the first and second bearings52,53are fitted in respective seats5A,5B presented by the main shaft5.

The main bearing housing51comprises a main body514that encloses the main shaft5and extends substantially in parallel with the rotational axis A from a first end5141to a second end5142. The first end is closer to the rotor that the second end. At the second end5142the main body514presents a component attachment flange513for a fixed connection of the main bearing housing51to a low speed coupling cover611, (see alsoFIG. 3), arranged to cover the low speed coupling61. The component attachment flange has a substantially circular cross-section. The component attachment flange513is located radially, in relation to the rotational axis A, outside the second seat512. In other words, the component attachment flange513is located further away from the rotational axis A than the second seat512.

As illustrated inFIG. 4, the gearbox6and the generator7are not support directly on the nacelle structure. Instead they are cantilevered from the main bearing housing51via the low speed coupling cover611. This means that the main bearing housing51and the low speed coupling cover611will be subjected to relatively large forces from the weights of the cantilevered components6,7. As can be seen inFIG. 3, the main bearing housing main body514is at a portion516extending from the component attachment flange513towards the rotor attachment flange5C shaped as a truncated cone. This will provide for a relatively straight load path for stresses in the main body caused by the cantilevered components.

To provide for the shorter radial distance of the second seat512, the main bearing housing is provided with a seat flange515. The seat. flange515extends radially inwards from an inner surface of the main body514. The seat flange515is provided with the second seat at its inner distal end. The seat flange515presents a non-zero angle to an imaginary plane oriented perpendicular to the rotational axis A, and has therefore the shape of a truncated cone with the end with the second seat512being the narrower end5151of the truncated cone and located further away from the rotor4compared to the wider end5152of the truncated cone where the seat flange515joins the main body514. The junction between the seat flange515and the main body514is located at a distance from the second end5142and the component attachment flange513.

The low speed coupling61can be of any type, e.g. one of the solutions described in WO2012052022A1 incorporated herein by reference. In this example, the low speed coupling has two flexible discs612, which are at respective inner edges fixedly connected to the main shaft5and the gearbox input shaft62, respectively. At respective outer edges the flexible discs612are fixedly joined via a cylinder613. Such a low speed coupling will provide some flexibility to allow for misalignment and other un-desired phenomena that can occur in the drivetrain.

Due to the design of the low speed coupling61, it will have a relatively large diameter, and therefore so will also the low speed coupling cover611. As stated, the main bearing housing main body514is at a portion516extending from the component attachment flange513towards the rotor shaped as a truncated cone, (FIG. 3), and this provides a relatively straight load path for stresses incurred by the cantilevered arrangement. In addition, the seat flange515will allow for the main bearing housing main body514to present the large diameter component attachment flange513, while at the same time providing a rigid support for the second bearing53. Actually, the diameter of the main body514is larger at the second end5142than at the first end5141. The large diameter of the component attachment flange513is beneficial in view of the loads, since the bending moment caused by the cantilevered arrangement will be counteracted by forces in the component attachment flange513that are lesser than they would have been with a smaller component attachment flange.

Furthermore, the truncated cone shape of the seat flange515provides an alignment of the flange with the force path associated with the second bearing53, in particular where the latter is a tapered roller bearing, angled as indicated in the drawings. As can be seen inFIG. 2, the bearing rollers each have a first roller end531and a second roller end532, the distance between the rotor attachment flange5C and the first roller end531being smaller than the distance between the rotor attachment flange5C and the second roller end532, and the distance between the rotational axis A of the main shaft5and the first roller end531being smaller than the distance between the rotational axis A and the second roller end532.

The diameter of component attachment flange513is larger than the diameter of the first bearing seat511, and the diameter of the second bearing seat512is smaller than the diameter of the first bearing seat511. There is a bolt connection between the component attachment flange513and the low speed coupling cover611, with a single row of bolts5131oriented substantially in parallel to the rotational axis A. Here, the diameter of the component attachment flange513is understood as the diameter of an imaginary circle formed by the center lines of the series of bolts5131distributed along the component attachment flange513. The diameters of the bearing seats511,512are understood as the diameters of respective surfaces of the seats facing radially inwards and supporting the respective bearings52,53.

FIG. 5shows an embodiment where the component attachment flange513is located adjacent to the outer periphery of the seat flange515. I.e. the component attachment flange513is located adjacent to the connection between the seat flange515and the main bearing housing main body514.

The invention is applicable also to turbines without any gearbox in the drivetrain, i.e. so called direct drive turbines. Thereby, the invention could be particularly useful where, as illustrated inFIG. 6, the generator7is cantilevered from the main bearing housing51, and the main shaft5is connected to a rotor71of the generator7, e.g. directly (as inFIG. 6) or via a low speed coupling, e.g. as described in said WO2012052022A1.