Background Art In electrical power generator in wind turbines it is known to lubricate the bearings with grease, such grease lubrication involving relatively short service intervals for replenish- ing the grease and from time to time exchange of the grease. In connection with off- shore wind turbines such relatively short service intervals are not acceptable. Further- more, the large sizes of wind turbines developed require correspondingly large power generators with correspondingly large size bearings. Such large size bearings result in increased peripheral speeds, which have a tendency to separate the lubricating grease into soap and oil. Furthermore, the large size bearings do not provide an optimal heat dispersion from the bearing to the machine construction.

Disclosure of the Invention It is the object of the present invention to provide an apparatus for lubricating the bear- ings of an electrical power generator in a wind turbine, with which it is possible to extend the service intervals and at the same time improve the heat dispersion features and in- crease bearing lifetime, and this object is achieved with an apparatus for lubricating the bearings of an electrical power generator in a wind turbine which, according to the in- vention comprises features set forth in the characterizing clause of claim 1. With this ar- rangement the bearings are lubricated with oil supplied to the bearings by a pumping function, thereby ensuring a circulation of oil, improving the heat dispersion from the bearings and giving a possibility of performing a measurement on, and possibly condi- tioning of, the circulated oil, thus attaining relatively long service intervals for the bear- ings of the electrical power generator.

Brief Description of the Drawings In the following detailed part of the description the invention will be explained in more

detail with reference to the exemplary embodiment of an apparatus for lubricating the bearings of an electrical power generator in a wind turbine according to the invention shown in the drawings, in which Fig. 1 schematically shows an end view of a bearing construction incorporation the pre- sent invention, Fig. 2 schematically shows a cross-section in the bearing of fig. 1 along the lines 11-11, and Fig. 3 shows a corresponding cross-section along the lines 111-111.

Description of the Preferred Embodiment The bearing construction shown in figs. 1-3 is constructed to provide a lubrication of the bearings in accordance with the present invention and for use in an electrical power generator in a wind turbine. In the shown construction the bearing 1 is surrounded by a closed space 2 through which lubricating oil is circulated by means of a pumping device schematically shown at 3. The circulated oil enters the closed space 2 surrounding the bearing 1 through an inlet 7, in fig. 3 shown as two separate inlets, one for each side of the bearing 1, said inlet 7 being positioned close to the top of the bearing 1. By gravity the oil entering the closed space 2 at the top of the bearing 1 will flow down to the bot- tom of the closed space 2, some of the oil entering the bearing construction 1 and lubri- cating the bearing, i. e. the races and the balls of the ball bearing shown. At the bottom of the closed space 2 the oil will reach a level 6 due to the offset position of the outlet 8 from the closed space 2. The oil level 6 will ensure a certain minimum lubrication of the bearing 1 if the oil circulation should fail. From the outlet 8 the circulated oil is led to an oil reservoir 4, from which the pumping device 3 pumps the oil to the inlet 7.

As an alternative, shown in broken line, a raised level oil reservoir 9 can be used for supplying the oil to the inlet 7.

In a preferred embodiment the pumping device 3 and the reservoir 4 are built into the closed space 2 and possibly a raised level oil reservoir 9 is also provided inside the closed space 2, whereby no external connections are needed.

The pumping device 3 may be an electrically driven oil pump or a mechanically driven oil pump e. g. driven by the rotation of the generator axle 11. In the closed version with all

components inside the closed space 2, the pumping device 3 may be provided in the form of a gravitation ring on the generator axle 11 delivering the oil to a raised level res- ervoir 9 and taking up the oil from the combined oil reservoir 4 and 5.

As another alternative, the oil can be supplied to the inlet 7 from the gearbox (not shown) connecting the wings of the wind turbine to the generator. This gearbox will normally comprise an oil reservoir 4, a pumping device 3 and means for performing measurements on and conditioning of the circulated oil. By connecting the pumping de- vice 3 of the gearbox to the inlet 7 to the closed space 2 surrounding the bearing 1 and connecting the outlet 8 from the closed space 2 to the gearbox oil reservoir the lubrica- tion of the bearing 1 is provided in a simple manner.

Although the invention has been described above in connection with a number of pre- ferred embodiments thereof it will be evident for a person skilled in the art that several modifications are possible within the scope of the following claims.