Direct-drive wind turbine The invention relates to a direct driven wind turbine and the main bearing used in such a wind turbine.

A wind turbine transfers the energy of moving air into elec ^¬ trical energy. The moving air accelerates the rotor of the wind turbine. The rotation of the rotor is transferred to an electrical generator. The electrical generator transforms the rotational energy into electrical energy.

In the last years the concept of a direct driven wind turbine was established. In a direct driven wind turbine the rota ^¬ tional energy of the rotor is transferred to the generator directly without the use of a gearbox.

In a direct driven wind turbine the rotor of the wind turbine is directly connected to the rotor of the electrical genera ^¬ tor. The chain of mechanically connected parts leading from the rotor of the wind turbine to the rotor of the generator is called the drive train of the wind turbine. To allow the rotational movement and to provide the necessary stability of the rotating parts, the drive train is mounted with at least one bearing. This bearing allows the drive train to rotate. At the same time it provides the necessary stability by supporting the radial and axial loads and the bending moments present in the drive train.

WO 2011/003482 A2 describes a wind turbine main bearing real ^¬ ized to bear a shaft of a wind turbine. The bearing comprises a fluid bearing with a plurality of bearing pads.

The document describes a bearing with a cylindrical bearing surface and a series of trust pads. The plain bearing has to provide a large surface to withstand the forces present in the drive train. As a consequence the pads used for the cylindrical bearing surface are very large, heavy and difficult to exchange.

It is the aim of the invention to provide a wind turbine with an improved plain bearing.

The aim is reached by the features of the independent claim. Preferred embodiments of the invention are described in the dependent claims.

A rotor of the wind turbine is directly connected with a ro ^¬ tating drive train of the wind turbine; the rotating drive train is directly connected with a rotor of an electrical generator of the wind turbine.

The rotating drive train is connected with a stationary part of the wind turbine via at least one bearing, which allows the rotation of the drive train in relation to the stationary part.

The at least one bearing is a plain bearing and the bearing is a tapered bearing, which comprises at least one conical shaped sliding surface. The drive train of the wind turbine comprises those parts that transfer the energy from the source to the generator. This includes the hub with at least one rotor blade and the rotor of the generator. In some constructive solutions of wind turbines the drive train includes a shaft in addition.

The stationary part of the wind turbine comprises the stator of the generator, the connection between the generator and the support structure, prepared to carry the aggregates of the nacelle of the wind turbine, and the connection to the tower of the wind turbine. A plain bearing is a bearing without rolling elements, like balls or rollers. A plain bearing is also known as a sliding bearing, a friction bearing or a floating bearing. The tapered bearing is capable to transfer axial and radial loads present in the drive train of the wind turbine, this can be done with one sliding surface. Thus only one sliding surface is needed to transfer axial and radial loads from the drive train to the stationary part of the wind turbine.

Thus the sliding surface and the amount of material used are minimized. Thus the bearing is cheaper to manufacture and less heavy. In a preferred configuration the bearing comprises a first conical shaped sliding surface and a second conical shaped sliding surface which are reversely sloped in the axial di ^¬ rection of the plain bearing. A bearing constructed according to this configuration presents a v-shaped structure of the sliding surfaces when the bearing is cut in the axial direction.

A bearing with this configuration is capable to withstand the radial and axial forces and the bending moments present in the drive train.

Thus one plain bearing build as a tapered bearing is suffi ^¬ cient to withstand the forces and there is no need for an ad- ditional bearing.

In a preferred configuration the bearing connects as a first bearing the rotor and the stator of the wind turbine genera ^¬ tor and the first bearing is located at a first end of the generator in respect to the axis of rotation of the genera ^¬ tor . The rotor and the stator of the generator are connected by a bearing to provide a mainly constant air gap between the ro ^¬ tor and the stator. The drive train is connected via a bear ^¬ ing to the stationary part of the wind turbine. For both pur- poses one bearing can be used that supports the drive train of the wind turbine and the rotor of the generator and con ^¬ nect them to the stationary part of the wind turbine.

Thus the wind turbine comprises only one main bearing. Thus this one bearing connects the whole drive train to the sta ^¬ tionary part of the wind turbine. Thus only one bearing is needed and maintenance only has to be performed at one bear ^¬ ing . Thus the maintenance is faster and cheaper. Also less mate ^¬ rial is used for one bearing as for separate bearings. Thus the wind turbine is cheaper and less heavy.

The first end of the generator preferably is the end of the generator pointing towards the hub of the wind turbine.

In another preferred construction a second bearing is arranged at a second end of the generator in respect to the axis of rotation of the generator.

A second bearing is arranged at the end opposite to the first end of the generator. This second bearing stabilizes the con ^¬ nection between the rotor and the stator of the generator. Thus the air gap between the rotor and the stator of the gen- erator is even more constant.

In addition the second bearing supports the loads in the drive train. Thus the loads on the first bearing are reduced due to the support of the second bearing. Especially the bending moments are supported by a combination of a first and a second bearing that are spaced in axial direction along the axis of rotation of a direct driven wind turbine. In a preferred embodiment the second bearing comprises a cy ^¬ lindrical bearing surface, which is prepared to support ra ^¬ dial loads and bending moments of the drive train. Thus the second bearing can support the drive train due to transferring the radial loads and the bending moments from the drive train to the stationary part of the wind turbine.

In a preferred embodiment the bearing comprises a segmented sliding-surface . The segments of the sliding-surface are ar ^¬ ranged at a rotating part of the bearing, which is connected to the rotating drive train of the wind turbine, or the seg ^¬ ments are arranged at a stationary part of the bearing, which is connected to the stationary part of the wind turbine.

The sliding surface of the bearing is segmented into at least two parts. Preferably the segments are arranged along the di ^¬ rection of the rotation of the bearing. The sliding surface can be divided into pads arranged to build the sliding sur- face.

Thus the sliding surface is divided into smaller segments, which can be mounted and exchanged separately. Thus the mounting of the bearing is easier and also the exchange of the sliding surface is easier.

In a preferred embodiment the segments are arranged and con ^¬ nected within the plain bearing in a way that the exchange of an individual segment is permitted.

Thus a segment of the sliding surface can be exchanged with ^¬ out the need to exchange the complete sliding surface of the bearing. Thus just those segments that are worn are exchanged while those parts, that are still good enough, stay in the bearing. Thus material and maintenance time is saved.

Thus the parts that are exchanged are smaller then the com ^¬ plete sliding surface. Thus the exchange of parts of the sliding surface can be done during maintenance without the use of heavy machinery. Thus the maintenance is cheaper and faster . The segments of the sliding surface are small enough, so that they can be handled within the wind turbine. Thus the ex ^¬ change can be performed from within the wind turbine and the wind turbine doesn't have to be dismantled. Thus the exchange does not depend on the weather conditions at the side of the wind turbine.

This is especially advantageous when the wind turbine is an offshore wind turbine. In a preferred embodiment the segment comprises at least one tipping pad, while the surface of the tipping pad is capable to be aligned to the bearing surface of the counter side of the bearing. A tipping pad is a pad capable to tilt its surface in a way that the sliding surface aligns to the bearing surface of the counter side of the bearing. A tipping pad can be a tilting pad or a flexure pad for example. Thus the pad can tilt and the surface of the tipping pad ar ^¬ ranges itself to the counter side of the bearing. Thus the forces acting on the bearing act equally distributed on the sliding surface. Thus the wear and tear on the sliding surface is equally distributed. Thus the lifetime of the seg- ments is improved and the risks of damages in the bearing, which are caused by uneven wear and tear, are reduced.

In a preferred embodiment the bearing is a hydrodynamic bear ^¬ ing, where a lubrication film at the sliding surface is main- tained by the rotating bearing parts.

Thus the lubrication film is maintained during the rotation of the bearing. Thus the lubrication of the bearing surface is independent of additional aggregates, like pumps. Thus the risk of damage due to insufficient lubrication is minimized. Thus the performance of the wind turbine is increased. In a preferred embodiment the bearing is a hydrostatic bear ^¬ ing, where a lubrication film at the sliding surface is maintained by an applied pressure of an external pump.

Thus the lubrication is ensured independently of the rotation of the drive train. Thus the lubrications is also ensured when the wind turbine is stopping or starting rotation. Thus the lubrication is also sufficient in a low wind situation or in a situation when the wind is changing in speed and the wind turbine might stop and start repeatedly.

In a preferred embodiment the bearing is a hybrid bearing, where a lubrication film at the sliding surface is maintained by a combination of an applied pressure of an external pump and by rotating bearing parts.

The pump is only needed, when the wind turbine is starting or stopping rotation and the lubrication film can not be ensured just by the rotation of the rive train. Thus the lubrication is maintained independently of the rota ^¬ tion of the drive train. In addition the energy used to operate the pump can be saved when rotation of the drive train is maintaining the lubrication film and the pump are not needed. In a preferred embodiment the sliding surface of the plain bearing comprises a groove and/or a pocket, being used as inlet or outlet for lubrication purposes of the plain bearing . The lubrication can be distributed more equally by the help of grooves or pockets in the sliding surface. Thus the lubri ^¬ cation is more equally. Thus the risk of insufficient lubri ^¬ cation and thus the risk of damage in the bearing is reduced. Thus the lifetime of the bearing can be enhanced and the en ^¬ ergy production of the wind turbine can be increased.

The invention is shown in more detail by help of figures. The figures show a preferred configuration and do not limit the scope of the invention.

FIG 1 shows a wind turbine with a plain bearing. FIG 2 shows a second configuration of the plain bearing. FIG 3 shows a detail of a configuration. FIG 4 shows a detail of a bearing.

FIG 1 shows a wind turbine with a plain bearing.

FIG 1 shows a longitudinal cut through the hub 2, the plain bearing 1 and the electrical generator 7 of a direct driven wind turbine. The longitudinal cut is going along the axis of rotation of the electrical generator 7 of the wind turbine.

The hub 2 is connected to the rotor 3 of the generator and to the rotating side of the bearing 1. The stator 4 of the generator 7 is connected to the stationary side of the plains bearing 1.

The plain bearing 1 is located between the hub 2 of the wind turbine and the electrical generator 7 of the wind turbine. So it is connected with the stationary side to the hub-sided end of the stator 4 of the generator 7 and with the rotating side to the hub 2 of the wind turbine.

The plain bearing 1 is a tapered bearing. The cut through the bearing shows a V-shaped arrangement of two sliding surfaces 5a and 5b, which are tilted and arranged in a way that they are reversely sloped in axial direction in respect to the axis of rotation of the electrical generator 7. The bearing surface 5a, 5b is equipped with segments 6 that are connected in the bearing to build the sliding surface 5a, 5b. The segments can be tilting pads. The surface of the tilting pads is capable to be aligned to the bearing surface 5a, 5b of the counter side of the bearing 1, which is sliding along the pads when the bearing 1 is rotating. The plain bearing 1 connects the rotating drive train of the wind turbine with the stationary part of the wind turbine in a rotatable manner.

The rotating drive train comprises the hub 2 of the wind tur- bine that is connected to the rotor 3 of the electrical gen ^¬ erator 7. The stationary part of the wind turbine comprises the stator 4 of the electrical generator 7. The bearing connects the rotating drive train of the wind turbine and the rotor 3 of the electrical generator 7 with the stator 4 of the electrical generator 7.

The plain bearing 1 is constructed to bear the radial and ax ^¬ ial forces and the bending moments present in the drive train. In this example there is only one bearing 1, with two sliding surfaces 5a and 5b, that connects the rotating drive train of the wind turbine with the stationary part of the wind turbine.

FIG 2 shows a second configuration of the plain bearing.

Fig 2 shows a cut along the axis of rotation of the electri ^¬ cal generator 7. The cut shows the hub 2 of the wind turbine, the rotor 3 and the stator 4 of the electrical generator 7, the plain bearing 1 and a load bearing structure 8 that con ^¬ nects the stationary part of the wind turbine to the tower.

The plain bearing 1 is a tapered bearing and shows a tilted sliding surface 5a. The first plain bearing 1 is combined with a second bearing 11. The second bearing 11 is a plain bearing that is located at the second end of the electrical generator 7.

The second end of the electrical generator 7 is the end oppo- site the end where the first bearing 1 is located. Opposite ends of the electrical generator 7 are seen in respect to the axis of rotation of the generator.

The second bearing 11 is a tapered bearing with a tilted bearing surface 5b. In this case the bearing surfaces 5a of the first bearing 1 and the sliding surface 5b of the second bearing 11 are reversely sloped in axial direction in respect to the axis of rotation of the generator. The second bearing 11 can also be a plain bearing with a cylindrical bearing surface.

The first plain bearing 1 and the second plain bearing 11 are constructed to bear the radial and axial forces and the bend- ing moments present in the drive train of the wind turbine.

FIG 3 shows a detail of a configuration.

FIG 3 shows an axial cut through the plain bearing 1 in the wind turbine. The plain bearing 1 is a tapered bearing and comprises two sliding surfaces 5a and 5b.

The sliding surfaces 5a, 5b are equipped with segments 6 that are connected within the bearing to provide the sliding sur ^¬ faces 5a, 5b. The segments can be attached to the stationary side of the bearing or to the rotating side of the bearing.

The segments 6 can be tilting pads, which have a surface that is capable to be aligned to the bearing surface 5a, 5b of the counter side of the bearing 1, which is sliding along the pads when the bearing 1 is rotating.

The segments of the sliding surface 5a, 5b of the plain bear ^¬ ing 1 are connected in a way that they can be exchanged indi- vidually without the need to exchange the whole bearing or the whole sliding surface.

FIG 4 shows a detail of a plain bearing.

FIG 4 shows a cut along the axis of rotation through the sec ^¬ ond bearing 9. The second bearing 9 is arranged at the end of the electrical generator 7 that is opposite of the end where the first plain bearing is located. The second bearing 9 is located between the rotor 3 and the stator 4 of the electrical generator 7. The stator 4 is connected to the stationary part of the wind turbine. The stator 4 of the electrical generator 7 and the stationary part of the wind turbine are connected to the load bearing structure 8 that connects the stationary part of the wind turbine to the tower.

In this configuration the second bearing 9 is a plain bearing with a sliding surface 10. The sliding surface can be

equipped with segments that are arranged and connected to build the sliding surface 10 of the second bearing 9. The segments can be connected to the rotating part of the second bearing 9 or to the stationary part of the second bearing 9. The segment can also be tilting pads that comprise a sliding surface 10 that is capable to be aligned to the bearing sur ^¬ face of the counter side of the bearing 9, which is sliding along the pads when the bearing 1 is rotating. In this configuration the second bearing 9 shows a cylindrical bearing surface. A cylindrical bearing surface 10 is preferably combined with a tapered bearing as a first bearing at the opposite side of the electrical generator 7. The first bearing and the second bearing 9 are constructed in a way to bear the radial and axial forces and the bending mo ^¬ ments present in the drive train of the wind turbine.