CLIAMS:1. A method for flushing grease from a main bearing and main bearing housing of a wind turbine comprising the steps of:
a) providing access to the main bearing;
b) installing a flushing means on the housing, in which the flushing means comprises a plurality of sealable holes allowing access to the main bearing;
c) spraying a cleaning fluid via one of the sealable holes onto the main bearing to remove grease, the remaining holes being sealed stopping the cleaning fluid and removed grease escaping;
d) pumping cleaning fluid and removed grease out of the housing; and
e) repeating steps c) and d) as required, spraying the fluid via one or more of the remaining sealable holes.

2. A method according to claim 1, in which the flushing means comprises a plurality of holes arranged around an outer region allowing access to the main bearing.

3. A method according to any preceding claim, in which the step of spraying a cleaning fluid comprises:
providing a reservoir containing cleaning fluid;
providing a spraying means; and
providing a first pumping means for pumping cleaning fluid from the reservoir to the spraying means via a supply hose.

4. A method according to claim 3, the spraying means comprising one or more spray nozzles.

5. A method according to claim 3 or claim 4, the supply hose comprising one or more supply filters.

6. A method according to claim 5, providing connection means for connecting the one or more supply filters to the supply hose.

7. A method according to any of claims 3 to 6, providing connection means for connecting the first pumping means to the supply hose.

8. A method according to any of claims 3 to 7, providing connection means for connecting the spraying means to the supply hose.

9. A method according to any preceding claim, in which the step of pumping cleaning fluid out of the bearing housing additionally comprises providing a second pumping means for pumping cleaning fluid to the reservoir via a return hose;
wherein, in use, the cleaning fluid is recycled during the replacing of the grease.

10. A method according to claim 9, the return hose comprising one or more return filters.

11. A method according to claim 9, providing connection means for connecting the one or more return filters to the return hose.

12. A method according to any of claims 9 to 11, the port comprises an exit port in the flushing cover, whereby the return hose is connected to the exit port.

13. A method according to any of claims 9 to 12, providing connection means for connecting the second pumping means to the return hose.

14. A method according to any of claims 9 to 13, providing connection means for connecting the exit port to the return hose.

15. A method according to any of claims 6 to 8 and 12 to 14, in which the connection means is a dry break coupling.

16. A method according to any of claims 5 to 17, in which the first pumping means is a pressure pump

17. A method according to any of claims 9 to 16, in which the second pumping means is a suction pump

18. A method according to any of claims 9 to 17, providing a module comprising the reservoir, the first pumping means and the second pump means.

19. A method according to claim 18, providing a module comprising the supply filter,

20. A method according to claim 18 or claim 19, providing a module comprising the return filter;

21. A method according to any of claims 3 to 20, in which the reservoir has a capacity in the range of 10 to 50L.

22. A method according to any of claims 3 to 20, in which the reservoir has a capacity of 25 to 35L.

23. A method according to any preceding claim, in which the cleaning fluid comprises a solvent.

24. A method according to claim 23, in which the solvent is a high flash point solvent.

25. A method according to any of claims 1 to 23, in which the cleaning fluid comprises oil.

26. A method according to claim 25, in which the oil is hot oil.

27. A method according claim 25 or claim 26, in which the method further comprises providing heating means for heating the oil.

28. A method according to claim 27, in which the heating means comprises indirect heating means.

29. An apparatus for flushing grease from a main bearing of a wind turbine, the apparatus comprising:
a flushing cover comprising attachment means for mounting on the housing of the main bearing, the flushing cover further comprising a plurality of holes, the flushing cover further comprising an exit port;
a corresponding plurality of removable plugs for sealing the holes;
a reservoir containing the cleaning fluid;
a spraying means;
a first pumping means for pumping cleaning fluid from the reservoir to the spraying means via a supply hose;
a second pumping means for pumping cleaning fluid from the exit port to the reservoir via a return hose;
in which the flushing cover comprises at least two parts, the parts fitting around the main shaft, each part comprising sealing means on a radially inner surface wherein, when attached to the bearing housing, the flushing cover forms a seal with the main shaft; and wherein, pumping cleaning fluid to the spraying means and spraying the cleaning fluid onto the main bearing via one of the holes for

admission of a cleaning fluid, the remaining holes being sealed by a corresponding removable plug, flushes grease from the main bearing.
,TagSPECI:FORM 2

THE PATENTS ACT, 1970
(39 of 1970)

&

THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
[See section 10, Rule 13]

BEARING GREASE;

ROMAX TECHNOLOGY LIMITED, A CORPORATION ORGANISED AND EXISTING UNDER THE LAWS OF UNITED KINGDOM, WHOSE ADDRESS IS ROMAX TECHNOLOGY CENTRE, UNIVERSITY OF NOTTINGHAM INNOVATION PARK, TRIUMPH ROAD, NOTTINGHAM NG7 2TU, UNITED KINGDOM

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

The present invention relates to improvements to the lubrication of wind turbine main bearings. In particular it relates to the flushing of grease from a wind turbine main bearing during replacement of the grease during maintenance.
Wind or water turbine main bearing are typically formed of roller bearings. Effective lubrication difficult to achieve because of the slow rotation speeds of the rotor and the wide ranges of operating temperature. Grease lubrication is widely used for such bearings, and its consistency prevents it from leaking out of the bearing, makes it easy to use, and gives it good sealing properties. However packed grease does not move around within the bearing arrangement under typical turbine operating conditions. This means that debris from bearing wear does not escape from the bearing, and will contribute to further wear and damage.
The present invention provides apparatus and methods for removing old grease from a wind turbine main bearing by a flushing process. The invention provides efficient ways of utilising small volumes (less than 50L) of cleaning fluid to flush out and clean rolling elements of a main bearing during grease replacement in maintenance. Typically, the cleaning fluid is a solvent, preferably a high flash point solvent, or oil.
According to a first aspect of the invention, there is provided a method for replacing grease in a main bearing of a wind turbine, the main bearing located in a housing and the housing has at least one cover plate. The method comprising the steps of: removing the bearing cover plate from the housing; manually removing grease from the main bearing;installing a flushing cover on the housing in place of the bearing cover plate, in which the flushing cover comprises a plurality of holes allowing access to the main bearing; inserting removable plugs into one or more of the holes in order to stop cleaning fluid used for flushing, or grease escaping; spraying a cleaning fluidvia one of the holes onto the main bearing to remove grease, the remaining holes being sealed by a corresponding removable plug; pumping cleaning fluid out of the housing via a port at the bottom of the housing; repeating steps d and e) for each hole;removing the flushing cover; packing the main bearing with grease; and reinstalling the bearing cover. The flushing cover comprises at least two parts, the parts fitting around the main shaft, each part comprising sealing means on a radially inner surface. When attached to the bearing housing, the flushing cover forms a seal with the main shaft. The step of spraying a cleaning fluid comprises: providing a reservoir containing cleaning fluid; providing a spraying means; and providing a first pumping means for pumping cleaning fluid from the reservoir to the spraying means via a supply hose; and in which the step of pumping cleaning fluid out of the bearing housing additionally comprises providing a second pumping means for pumping cleaning fluid to the reservoir via a return hose; wherein, in use, the cleaning fluid is recycled during the replacing of the grease.
The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Figure 1 shows an external view of an offshore wind turbine;
Figure 2 shows an embodiment of a method of the present invention; and
Figure 3 shows an embodiment of an apparatus of the present invention.
Figure1 is a perspective view of an example of a wind turbine. Although an offshore wind turbine is shown, it should be noted that the description below may be applicable to other types of wind turbines. The wind turbine 102 includes rotor blades 104 mounted to a hub 100, which is supported by a nacelle 108 on a tower 114. Wind causes the rotor blades 104 and hub 106 to rotate about a main axis. This rotational energy is delivered to a main shaft, which is part of a power transmission system housed within the nacelle 108. The main shaft is supported by a bearing arrangement within a bearing housing. The bearing housing is attached to a mainframe (not shown) via bolts. An upwind and a downwind bearing cover are attached to the bearing housing via fastener means.
Figure 2 shows a method for performing a main bearing flush, in which the grease in a main bearing of a wind turbine is replaced, for example, when maintenance or inspection is required. In a first step, the bearing cover plate is removed from the housing. This opens the bearing and it permits grease sampling or inspection. In a second step, much of the grease in the bearing is removed manually, but this leaves residual grease within the housing. In a third step, a flushing cover is installed on the housing in place of the bearing cover plate. The flushing cover comprises a plurality of holes arranged radially around the main bearing – these allow access to the main bearing and correspond to the roller pockets.
At this point (step 4), a spray cycle is done, typically of 3 minutes duration per flushing cover hole or roller pocket. This involves spraying a cleaning fluid via one of the holes onto the main bearing to remove grease, the remaining holes being sealed by a corresponding removable plug.
In step 5 the dirty cleaning fluid from this cycle is pumped out of the housing via a port at the bottom of the housing; this is a continuous process occurring at the same time as step 4.
Step 6 is similar to steps 4 and 5 together, except that in these steps, the cleaning fluid is filtered to remove particulate material, typically less than 10 microns. These steps are also of shorter duration, typically 30s per roller pocket.
At step 7, a borescope can be used to assess the progress of the flushing / cleaning process. If it is adjudged to be complete (step 8), for example by an apparent absence of grease, then in step 9 the bearings are given an oil rinse of about 30s per roller pocket to remove traces of cleaning fluid. If not then steps 6 and 7 are repeated.When the required cleanliness level is reached, the flushing covers are removed at this point and in step 9, the bearing is hand packed with grease.
In step 10, the bearing cover plate is re-installed. A grease sample for analysis can be taken after a short period of operation (step 11).
A feature of this approach is that the flushing cover comprises at least two parts whichfit around the main shaft, each part comprising sealing means on a radially inner surface so that when attached to the bearing housing, the flushing cover forms a seal with the main shaft. Another advantage of this approach is the use of a reservoir containing cleaning fluid, and pumping cleaning fluid from this reservoir, via filters if required, to the spraying device used in steps 4 and 6. Used cleaning fluid is pumped out of the bottom of the housing / flushing cover and back to the reservoir. This means that the cleaning fluid is recycled during the replacing of the grease, and as little as 30L of cleaning fluid may be used to provide efficient removal in situ of old grease.
Figure 3 shows a schematic of an apparatus for flushing grease from a main bearing of a wind turbine. The apparatus comprises flushing cover 7 which has fastenings for mounting it on the housing of the Main Bearing. As shown, flushing cover 7 goes around the main shaft. Flushing cover 7 is on the downwind (generator) side of the main bearing, an equivalent flushing cover 8 can be attached on the upwind (rotor side) of the bearing. Depending on the Main Bearing arrangement one or both flushing covers are used. The flushing has a plurality of holes as described above, and it includes an exit port, although in some situation a drain from the bearing housing might be use. There is a corresponding plurality of removable plugs for sealing the holes (not shown). A reservoir 1 contains the cleaning fluid and is connected to a spraying means 6, typically a spray nozzle held by an operator. Cleaning fluid is pumped from the reservoir to the spraying means 6 via a supply hose in the direction shown by the arrowsby pressure pump 4. Pressure pump 4 can be electric. A second pump, this time a suction pump, movescleaning fluid from the exit port to the reservoir via a return hose 3.
Where the cleaning fluid used is oil, it may be heated or where it is a solvent, it is typically at ambient temperature. Wherethe cleaning fluid used is heated oil, heating may be provided directly by, for example, immersion heaters in the reservoir, or more beneficially heating may be provided indirectly, either via a heat exchanger or by heaters on the outside of the reservoir. This avoids problems of over-heating the oil.
The flushing cover comprises at least two parts as described above, and in use these fit around the main shaft, each part comprising sealing means on a radially inner surface. When attached to the bearing housing, the flushing cover thus forms a seal with the main shaft. Pumping cleaning fluid to the spraying means and spraying the cleaning fluid onto the main bearing via one of the holes for admission of a cleaning fluid, the remaining holes being sealed by a corresponding removable plug, flushes grease from the main bearing.
In the above, the flushing cover is described as being, in effect, a replacement for the bearing cover. The flushing cover may also be fitted between the bearing cover and the bearing housing, and the axially arranged bolt holes engage with the housingthrough the flushing cover. The flushing cover thus acts as an intermediate spacer with flushing holes. Alternatively, the flushing cover is attached to the housing and the bearing cover is attached to the flushing cover. The flushing cover has radially arranged sealable holes around its perimeter for providing access to the spraying means. In these arrangements, the flushing cover can be a permanent part of the bearing arrangement, simplifying subsequent maintenance activities.
The spraying means 6 typically comprises a spray nozzle, which means that cleaning fluid is introduced under pressure to push grease off bearing surfaces.
The supply hose comprises one or more supply filters 5, typically 10 micron, which means when recirculated, the cleaning fluid is cleaned and particulate material which could damage the bearing surfaces is removed.
Connection means, shown generally as 2, connect the one or more supply filters to the supply hose, which means the filter can be easily removed and replaced.
Similarly the return hose may comprise one or more return filters to return filtered cleaning fluid returned to reservoir, removing particulate material. Again, connection means 2, connect the one or more return filters to the return hose, which means the filter can be easily removed and replaced.
Other connection means 2 connect the first pumping means to the supply hose, the second pumping means to the return hose, the spraying means to the supply hose, and the exit port to the return hose. The connection means is a dry break coupling, which means that connections can be easily made and unmade, even in use.
As mentioned above, the first pumping means is a pressure pump and the second pumping means is a suction pump.
The apparatus is advantageously provided as a module comprising the reservoir, the first pumping means and the second pump means, held in a chassis to facilitate hoisting from the ground into the nacelle.
In addition, the module can comprise the supply filter and/or the return filter.
This provides a kit-like approach to the flushing problem
The reservoir has a capacity in the range of 10 to 50L, and more typically is 25 to 35 L.