Abstract:
The invention relates to a lubrication system for a gearbox with stationary and rotating gearbox parts particularly in a wind turbine. The system includes lubrication distribution means in the stationary and rotating gearbox parts such as lubrication bores and openings. One or more rotary transmissions establish a transmission channel between lubrication distribution means in said stationary and rotating gearbox parts where said one or more rotary transmission include at least two connecting means. The invention also relates to a wind turbine with a drive train including a gearbox, and a lubrication system.

Description:
FIELD OF THE INVENTION 
     The invention relates to a lubrication system for a gearbox and a wind turbine. 
     BACKGROUND OF THE INVENTION 
     The invention concerns a system for supplying lubrication oil to the planet bearings in a gearbox, particularly a wind turbine gearbox. 
     There is a category of epicyclic gearboxes where the bearing is supported flexibly relative to the planet carrier, for in general improving load sharing between the planet gears, and load distribution across the width of the individual planet gear. 
     Examples are described in e.g. patent documents nos. WO 03/014566 (Hansen), U.S. Pat. No. 6,994,651 (Timken) and DE 10 2004 023151 (Jahnel-Kestermann). 
     Positive feed of oil to the planet bearings is in general a known technology for planetary gearboxes, and has for years been standard in e.g. automotive applications. Particularly for wind turbine gearboxes, a couple of specific solutions have been published e.g. in patent documents nos. WO 03/078870 (Hansen) or EP 1 431 575 (Winergy). 
     Particularly for such flexibly supported planet bearings, the known lubrication solutions have a shortcoming to bring the oil forward to the bearing. On the one hand, the oil system needs to be flexible enough to follow the motion of the planet shaft, and on the other hand the oil system must under no circumstances prevent the free translational motion of the planet shaft in the bearing. 
     It is an object of the present invention to provide a lubrication system without the abovementioned problem. 
     THE INVENTION 
     The invention relates to a lubrication system for a gearbox with stationary and rotating gearbox parts particularly in a wind turbine, the system comprising 
     lubrication distribution means in the stationary and rotating gearbox parts such as lubrication bores and openings, and 
     one or more rotary transmissions establishing a transmission channel between lubrication distribution means in the stationary and rotating gearbox parts 
     where the one or more rotary transmissions include at least two connecting means. 
     Hereby is established a lubrication system which allows more flexibility and displacement in a gearbox without interrupting the lubrication flow. Further, a flexible connection from rotary transmission to the individual lubrication points on the rotating gearbox parts is established, allowing translation of the lube point relative to the rotation structure in all directions. 
     In an aspect of the present invention, the at least two connecting means comprises two annulus and flexible U-profiles and the rotary transmission comprises two sets of lip means. Hereby is established a rotary transmission which tolerates axial offsets between the mounting surfaces, e.g. by the inner lip changing its position versus the outer lip. 
     In an aspect of the invention, the at least two connecting means comprise sets of lip means. This is advantageous in that lip means is a simple, efficient and inexpensive way of sealing a joint between rotating connecting means and a stationary connecting means. 
     In an aspect of the present invention, one of the at least two connecting means stretches into the other in order to establish a flexible transmission e.g. the initial sets of lip means in the lubricant flow direction being the inner lip means which are forced against the latter and outer set of lips. 
     Making the lip means overlap by stretching into each other is advantageous, in that pressure from the flowing lubricant will force the lip means together in the overlap zone, thereby further sealing the rotary transmission. 
     In an aspect of the present invention, one or both lip means comprises a tapering shape toward the contact area of the lip means. Hereby it is possible to establish a response of the rotary transmission in a given situation e.g. designing a self-protecting against excessive lubrication pressure in the rotary transmission by bending the outer lips outward at or above a defined value. 
     In an aspect of the present invention, at least one of the lip means are made from an elastic material such as plastic or rubber e.g. PTFE coated, a soft material such as brass or bronze, a compound such as rubber lips on a sheet metal carrier e.g. vulcanised. By the choice in materials, the lip means are advantageously less prone to wear. The carrier material may hold certain spring properties e.g. with the same effect as the tapered shape. 
     In an aspect of the present invention, the lubrication system includes a lubrication flow path comprising a bore in an annulus gear, a bore in the housing and/or a bore in a component attached to the housing as a stationary gearbox part and a bore in a planet carrier as a rotating gearbox part, a rotary transmission, a flexible external connection or an internal channel to distribution bores in or in proximity of a planet shaft. Hereby, the rotary transmission is located closest to the bearing which connects the rotating and the stationary system, meaning that the relative displacement between the parts is less than elsewhere, which makes the transmission easier, more reliable, and less prone to wear. 
     It should be noted that in this context, the term shaft is to be considered equivalent with any kind of axle, pin or other devices suited for serving as a more or less fixed mounting for a rotating part. 
     In an aspect of the present invention, the lubrication system includes at least two lubrication flow paths comprising at least one bore in an annulus gear, at least one bore in the housing and/or at least one bore in a component attached to the housing as a stationary gearbox part and at least one bore in a planet carrier as a rotating gearbox part, at least two rotary transmissions, at least one flexible external connection or at least one internal channel to distribution bores in or in proximity of a planet shaft. 
     Independent and redundant distribution systems for lubrication may hereby be established. Further, the lubrication system may have two channels for heavy load situations or emergency situations such as a blockage in one channel. 
     In an aspect of the present invention, a rotation connection comprising a pipe and a bushing between a flexible external connection and a planet shaft is established, hence allowing the planet shaft rotational freedom without influencing the lubrication path. 
     In an aspect of the present invention, the flexible external connection is a hose allowing for translational movements in the gearbox. 
     A hose is a simple and inexpensive way of establishing a flexible fluid connection between parts moving slightly in relation to each other in a wind turbine gearbox. 
     In an aspect of the present invention, the one or more rotary transmissions is positioned in an axial direction, in a radial direction or in both an axial direction and in a radial direction. 
     Placing the rotary transmissions in an axial direction, a radial direction or both is advantageous in that hereby the parts can be made less complex and in that this enables a more simple assembly procedure, thereby reducing the cost. 
     In an aspect of the present invention, the one or more rotary transmissions are positioned in an area between stationary and rotating gearbox parts in order to establish a transmission channel between lubrication distribution means in the stationary and rotating gearbox parts by the at least two connecting means extending out from the stationary and rotating gearbox parts. 
     Placing the rotary transmission in the area between a stationary and a rotating gearbox part is advantageous because it is thereby avoided to integrate the transmission in one or both of the parts and thereby costs are reduced. 
     The invention also relates to a wind turbine comprising a drive train including a gearbox, and a lubrication system as described above for the gearbox. 
     Wind turbine gearboxes are different from most other types of gearboxes by the fact that they have to be able to cope with much more flexure and deflection of both the nacelle structure in which the gearbox is mounted and in the gearbox strengthening structure itself. This is due to the massive size of modern wind turbines combined with the demand of low weight, low cost and high output. It is therefore particularly advantageous to use a lubrication system according to the present invention for transferring lubricant between mutually rotating parts of a wind turbine gearbox. 
     In an aspect of the present invention, the gearbox is an epicyclic gearbox such as a planetary, star or solar gearbox or any kind of compound gearbox and/or gearboxes with one or more bearing rows. 
     Epicyclic gearboxes are relatively low weight, low cost and small in relation to the load they are able to transfer but due to the generic design of the epicyclic gearboxes this gearbox type is more prone to flexure and deflections and it is therefore advantageous to use a lubrication system according to the present in a epicyclic gearbox. 
    
    
     
       FIGURES 
       The invention will be described in the following with reference to the figures in which 
         FIG. 1  illustrates a large modern wind turbine, 
         FIG. 2  illustrates a first embodiment of a gearbox and lubrication system according to the invention, 
         FIG. 3  illustrates a further embodiment of a gearbox and lubrication system according to the invention, 
         FIGS. 4   a  to  4   d  illustrate embodiments of a rotary transmission in the lubrication system according to the invention, 
         FIG. 5  illustrates an embodiment of the lubrication system according to the invention with a lubrication bore in the planet carrier, 
         FIG. 6  illustrates an embodiment of the lubrication system according to the invention with two rotary transmissions, 
         FIG. 7  illustrates an embodiment of a vertical or radial rotary transmission in the lubrication system according to the invention, and 
         FIG. 8  illustrates an example of a rotation connection between a flexible external connection and a planet shaft. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a modern wind turbine  1  mounted on a foundation  8 . The wind turbine comprises a tower  2 , including a number of tower sections such as tower rings, and a wind turbine nacelle  3  positioned on top of the tower  2 . The wind turbine rotor  6 , comprising three wind turbine blades  5 , is connected to the hub  4  through pitch mechanisms  7 . Each pitch mechanism  7  includes a blade bearing which allows the blade  5  to pitch in relation to the wind. The hub  4  is connected to the nacelle  3  through a shaft which extends out of the nacelle front. The shaft is connected through a gearbox mechanism to an electric generator wherein the connection may comprise one or more shaft bearings such as rotor and generator bearings. 
       FIGS. 2 and 3  illustrate a first and further embodiment of gearbox  9  and a lubrication system according to the invention. The gearbox  9  is preferably a planetary gearbox in a wind turbine  1 . 
     The lubrication oil is supplied to the planet bearing  20  through the planet shaft  22 . 
     This requires (a) to transfer oil from a stationary frame  23  to the rotating system  11 , and (b) to conduct oil further on to the flexibly supported planet shafts  22 . 
     (a) For transferring oil from the stationary to the rotating system, a bore  14  is arranged in an axial direction through the annulus gear  10 . This bore is supplied with oil from the stationary housing  23 . A rotating transmission  15  feeds the oil from this bore  14  through the stationary annulus gear  10  towards the rotating planet carrier  11 . This position comes closest to the bearing  28  which connect the rotating and the stationary system, meaning that the relative displacement between the parts is less than elsewhere, which makes the transmission easier, more reliable, and less prone to wear. 
     It shall be emphasised that the transfer of lubrication oil may also be from a part of the housing  23  or any component mounted in a stationary manner to the housing  23  to the rotating system i.e. without using a path through the annulus gear  10 . 
     (b) Once transferred in the rotating system, the oil can either be conducted through channels (an embodiment illustrated in  FIG. 5 ) in the rotating planet carrier  11  to the planet shafts  22 , or by a flexible external connection  17  from the planet carrier  11  to the planet shaft  22 . This flexible connection  17  may for example be a simple hose  17 , which would be able to follow the planet shaft  22  without constraining displacements. 
     Wobbling is a local axial and/or radial uneven movement in the gearbox system and the flexibility of the lubrication system according to the invention is especially relevant in relation to: 
     1. Rotation of one gearbox part e.g. the planet carrier  11   
     2. Translation e.g. the flexible planet shaft  22   
     3. Rotation of the planet shaft  22  vs. the planet carrier  11   
     4. Axial movement 
     5. Radial movement 
       FIGS. 4   a  and  4   b  illustrate a preferred embodiment of a rotary transmission  15  in the lubrication system according to the invention. 
     The rotary transmission  15  may be arranged by two flexible U-profiles  24   a ,  24   b  engaging with each other and especially over an overlap distance L. The oil pressure injected through the bore  14  will cause the lips of the inner profile  24   a  to inflate, until they contact the outer profile  24   b . At the same time, the flexibility of the outer profile  24   b  will allow the two lips to follow each other in case of radial offsets between their mounting surfaces. The system can also tolerate axial offsets between the mounting surfaces, just by the inner lip  24   a  changing its position versus the outer lip  24   b  (i.e. a change in the distance L). 
     Wear in the contact between the lips  24   a  and  24   b  can be controlled by proper choice of materials (or surface treatment e.g. by coating with PTFE or alike), and is further reduced by the fact that this contact is always submerged in oil. 
     Depending on the surface area of the outer lip  24   b  which is exposed to the oil pressure, and the elasticity of this lip, the system may be designed to be self-protecting against excessive pressure. Too high pressure may cause the outer lip  24   b  to bend outwards, until some oil can escape, and the pressure is released until equilibrium is achieved. This functionality may be used to control the flow to the bearing  20  as a function of oil viscosity, which again is a function of oil temperature. 
     There is no preference whether the inner lip  24   a  is mounted on the stationary or the rotary part, the system can work both ways. 
       FIG. 4   b  illustrates inner and outer lip means  24   a ,  24   b  of the rotary transmission  15  in an enlarged view. The outer lips are shown with a tapering shape toward the contact area of the lips and the inner lips with a uniform shape, but any type of relevant shape may be used for the lips. 
       FIG. 4   c  illustrates an embodiment of the inner and outer lips  24   a ,  24   b  of the rotary transmission  15  in a further enlarged view and with a different profiling of the lips by introducing a number of outward elevations in the inner lips  24   a  and/or a number of inward elevations in the outer lips  24   b.    
       FIG. 4   d  illustrates a further embodiment of inner lips  24   a  with a compound solution. As illustrated, a sheet metal carrier in the lips is applied with a rubber coating e.g. in a vulcanising process in order to establish a flexible lip means. It shall be emphasised that the solution may be used in the inner as well as the outer lips  24   a ,  24   b.    
       FIG. 5  illustrates an embodiment of the lubrication system according to the invention wherein the bore  16  in the planet carrier is continued to a position in proximity of the planet bearing  20 . A hose  17  connects the bore  16  with a bore  18  in a bearing support or raceway  29 . The hose  17  may be replaced by different bores in the planets  21  or moved to the other side of the planets  21  by bores through the planets  21 . 
       FIG. 6  illustrates an embodiment of the lubrication system according to the invention with two rotary transmissions  15   a ,  15   b . Each of the two rotary transmissions  15   a ,  15   b  is connected to separate bores  14   a ,  16   a ;  14   b ,  16   b  in the stationary annulus gear  10  and/or planet carrier  11 , respectively. The two bores  16   a ,  16   b  in the planet carrier  11  are connected to a common hose  17 . 
     A lubrication system including two rotary transmissions  15   a ,  15   b  (or more) may be used as independent and redundant distribution systems for lubrication e.g. if a lubrication component fails in one system the other system may continue the lubrication. 
     Further, the lubrication system may have two channels including two rotary transmissions  15   a ,  15   b  (or more) but no further redundancy e.g. one channel for normal lubrication situations and one more for heavy load situations or emergency situations such as a blockage in the normal situation channel. 
     The figure illustrates the lubrication system as positioned inside a main bearing  28  in relation to the centre line CL of the gearbox  9 . However, it shall be emphasised that the lubrication system may also be positioned on the outside of the main bearing  28 . 
       FIG. 7  illustrates an embodiment of a vertically or radially aligned rotary transmission  15  in the lubrication system with the lip means  24   a ,  24   b  facing up and down, respectively in order to establish an overlap distance L. 
       FIG. 8  illustrates an example of a rotation connection  27  between a flexible external connection  17  and a planet shaft  22 . 
     For a gearbox design where the planet shaft  22  has the freedom to constantly or occasionally rotate relative to the planet carrier  11 , for example in compound epicyclic arrangements, a rotation connection  27  from the flexible hose  17  to the planet shaft  22  may be required. 
     One simple execution of this transmission could be a bushing  26  from a soft material with low friction (such as PTFE or bronze) fitted into the planet shaft  22 . The hose  17  could then be connected to one end of a pipe  25  which is non-rotatably but else free linked to the planet carrier  11 , whilst the other end of the pipe  25  protrudes into the planet shaft  22  through the bushing  26 . It is not required that the seat between bushing  26  and pipe  25  is oil tight. The gap must only be tight enough to create a flow resistance that is larger than the passage through the planet bearing  20 . 
     The illustrated outer bearing  20  should be understood as a symbolic indication of the planets  21  further rotation inside the gearbox. 
     The solution is particularly relevant for bearings  20  with more bearing rows, where the oil is distributed through channels in the inner ring, or between the bearings. 
     The invention described has been exemplified above with reference to specific examples of epicyclic gearboxes  9  e.g. planetary gearboxes with a stationary annulus gear  10 . However, it should be understood that the invention is not limited to the particular examples but may be designed and altered in a multitude of varieties within the scope of the invention as specified in the claims e.g. epicyclic gearboxes  9  with stationary sun  12  or planet gear  21  (solar or star gearboxes). 
     Further, the epicyclic gear  9  may comprise more than one stage wherein different connection parts between the stages may comprise bores  14 , 16 , 18  or flexible connections  17  such as hoses in order to establish the necessary distribution channels in the lubrication system. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Reference list 
               
               
                 In the drawings the following reference numbers refer to: 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  1. 
                 Wind turbine 
               
               
                   
                  2. 
                 Wind turbine tower 
               
               
                   
                  3. 
                 Wind turbine nacelle 
               
               
                   
                  4. 
                 Wind turbine hub 
               
               
                   
                  5. 
                 Wind turbine blade 
               
               
                   
                  6. 
                 Wind turbine rotor with at least one blade 
               
               
                   
                  7. 
                 Blade pitch mechanism 
               
               
                   
                  8. 
                 Wind turbine foundation 
               
               
                   
                  9. 
                 Gearbox such as planetary gearbox 
               
               
                   
                 10. 
                 Annulus gear or ring gear 
               
               
                   
                 11. 
                 Planet carrier 
               
               
                   
                 12. 
                 Sun gear 
               
               
                   
                 13. 
                 Output shaft or high speed shaft 
               
               
                   
                 14. 
                 Bore in the annulus gear 
               
               
                   
                 15. 
                 Rotary transmission 
               
               
                   
                 16. 
                 Bore in the planet carrier 
               
               
                   
                 17. 
                 Flexible external connection e.g. a hose 
               
               
                   
                 18. 
                 Bore in the planet shaft 
               
               
                   
                 19. 
                 Opening in the planet carrier for e.g. a hose 
               
               
                   
                 20. 
                 Planet bearings 
               
               
                   
                 21. 
                 Planet gear 
               
               
                   
                 22. 
                 Planet shaft 
               
               
                   
                 23. 
                 Stationary housing of the gearbox 
               
               
                   
                 24a, 24b. 
                 Sets of lips in the rotary transmission 
               
               
                   
                 25. 
                 Pipe 
               
               
                   
                 26. 
                 Bushing 
               
               
                   
                 27.  
                 Rotation connection between flexible  
               
               
                   
                   
                 external connection and planet shaft 
               
               
                   
                 28.  
                 Bearing e.g. a main bearing 
               
               
                   
                 29.  
                 Bearing support or raceway 
               
               
                   
                 L. 
                 Overlap distance 
               
               
                   
                 CL.  
                 Centre line of gearbox