Abstract:
A wind turbine gear box having a compound planetary gear arrangement having bearings providing improved reliability and with greater accessibility for servicing. The gear box has planet pinions and planet gears being rotated by a planet carrier around a sun gear which drives a final reduction stage, the final reduction stage and the adjacent end of the planet carrier being removable from the gear box housing to allow easy removal of the planet pinions and their associated bearings.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application relies upon U.S. Provisional Patent Application Serial No. 60/447,976, filed on Feb. 18, 2003, and entitled “Gearbox for Wind Turbine.” 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0003]    1. Field of the Invention  
           [0004]    The present invention relates to a wind turbine and, in particular, to a gearbox interposed between a rotor of a wind turbine and an electrical generator.  
           [0005]    2. Background Art  
           [0006]    It is known to use a planetary gearbox to drive an electric generator in response to rotation of a rotor of a wind turbine. The rotor provides a low speed, high torque input to the gearbox. The gearbox provides a high speed, low torque output to the generator. This type of gearbox has been used in this application for approximately twenty years. It is also known that the planet gears of such a gear box, and the bearings associated therewith, are subjected to high lateral loads and thus suffer from high rates of wear under such demanding usage and do not provide ready accessibility for the maintenance, repair and replacement of these key wear components.  
           [0007]    U.S. Pat. No. 6,420,808 titled “Gearing for Wind Generator” shows a gearbox for driving a generator by wind force. The gearbox includes a multi-stage epicyclic gearing arrangement and a spur gear stage for the drive output to the generator. The input from the turbine rotor drives a ring gear to rotate about an axis. The ring gear meshes with planet gears at the interior of the ring gear, and the planet gears are fixed in position in a housing. The planet gears drive a sun gear rotatable about the centerline of the gear box and this in turn, through a set of spur gears, drives an output shaft connected to the generator. This gear box suffers from several limitations that reduce its reliability of operation, and make repair and replacement of key wear components more difficult. Planet gears  19  carried by planet gear shafts  17  overhang the adjacent outer bearings for these shafts (i.e., are mounted cantilevered relative to these bearings). This arrangement generates increased lateral forces on the outer and inner bearings. Moreover, the inner bearing is narrower and of smaller inner and outer diameter than the outer bearing, thereby reducing its load carrying capacity relative to the outer bearing. The reduced inner and outer diameters are necessitated by space constraints imposed by the inner end of the ring carrier  12 . In addition, access to both the inner and outer bearings for servicing requires disassembly of the entire gear box.  
           [0008]    As shown in U.S. Pat. No. 6,148,940, commonly assigned to General Electric Company, it is also known to use planetary gearboxes for motorized wheels of a large off-road vehicle, specifically, a vehicle used in open-pit mining. An electric motor, having a high speed, low torque output, is connected with the input of the gearbox. The gearbox in response provides a low speed, high torque output to the wheel, to rotate the wheel.  
           [0009]    U.S. Pat. No. 5,663,600 shows a large planetary gear set that is used in transferring torque from a wind rotor to a shaft/generator. The gear set includes a ring gear that rotates with the rotor.  
         BRIEF SUMMARY OF THE INVENTION  
         [0010]    The present invention includes, by way of example, a gearbox having a set of planet pinions carried by a planet carrier which is driven by a wind driven device such as a rotor blade. A set of gear teeth are formed on each planet pinion. Each planet pinion is caused to rotate faster than the rotor because of the meshing of its pinion gear teeth with a larger, substantially stationary, ring gear. A planet gear mounted to each planet pinion is rotated by its respective planet pinion. All of the planet gears mesh with and drive a smaller sun gear which rotates substantially about the central axis of the planet carrier. The sun gear rotates faster than the larger planet gears. The sun gear drives a larger final stage gear which is mounted on the sun gear by a splined connection. The final stage gear meshes with a smaller set of gear teeth on an output pinion and drives the output pinion faster than the sun gear.  
           [0011]    Planet bearings are located on each end of each planet pinion outboard of its pinion and planet gears, to support the planet pinions relative to the planet carrier. One end of the planet carrier is connected to and rotates along with the rotor, and the other end is open to receive the planet pinions. A carrier end plate is detachably secured to the planet carrier. A first bearing on a first end of each planet pinion supports the planet pinion from the planet carrier. A second bearing on the second end of each planet pinion supports the planet pinion from the carrier end plate. The output or final stage end of the gearbox housing is removable, along with the output pinion and the final stage gear, to allow removal of the carrier end plate. Removal of the carrier end plate allows for easy removal of the planet bearings on the second ends of the planet pinions. Then, the planet pinions can be removed from the planet carrier, followed by removal of the planet bearings on the first ends of the planet pinions.  
           [0012]    In addition to this enhanced accessibility of the planet bearings in the event that servicing is required, the planet bearings of this invention have increased load carrying capacity and reliability. In that regard, the bearings at the first and second ends of the planet pinions are of approximately equal size and load carrying capability (i.e., of the same type and of generally the same width and inner and outer diameters). In addition, the outer diameter of each of these bearings is approximately twice that of its inner diameter, thereby providing adequate space for high capacity bearing members. The first and second bearings are positioned at the ends of the respective planet pinions, with the planet pinion gear teeth and planet gear being positioned between the planet bearings. Thus, the planet pinion is supported along its entire length by the bearings, with no overhanging or cantilevered portions that impose increased stress on the bearings.  
           [0013]    The novel features of this invention, as well as the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and in which:  
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a cut-away illustration of a wind turbine that includes a gearbox in accordance with one embodiment of the invention;  
         [0015]    [0015]FIG. 2 is a perspective view of the input end of the gearbox of FIG. 1;  
         [0016]    [0016]FIG. 3 is a perspective view of the output end of the gearbox of FIG. 1; and  
         [0017]    [0017]FIG. 4 is a longitudinal sectional view of the gearbox of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    The present invention relates to a wind turbine and, in particular, to a gearbox interposed between a rotor of a wind turbine and an electrical generator. The present invention is applicable to various gearbox constructions. FIG. 1 illustrates schematically a gearbox  10  in accordance with one embodiment of the invention.  
         [0019]    The gearbox  10  forms part of a wind turbine  12 . The wind turbine  12  includes a support post or pylon  14 . The pylon  14  supports a turbine housing  16 . The gearbox  10  is supported in the turbine housing  16 . The size of the gearbox  10  is indicated schematically by the silhouette  18  of the person standing inside the wind turbine housing  16 .  
         [0020]    A rotor  20  is supported on the turbine housing  16  for rotation relative to the turbine housing. The rotor  20  is connected by a rotor shaft  22  to the input end of the gearbox  10 . The output end of the gearbox  10  is connected by an output shaft  24  to a generator  26 .  
         [0021]    The rotor  20  rotates in response to air movement past the wind turbine  12 . The rotational force of the rotor  20  is transmitted through the rotor shaft  22 , the gearbox  10 , and the output shaft  24 , to the generator  26 . The generator  26  generates electricity.  
         [0022]    The gearbox  10  (FIGS. 2 through 4) includes a gear box housing  30  that as illustrated is made of several components or covers that are detachably secured together. The gear box housing  30 , as illustrated, includes an input end cover  82 , a planet gear cover  84 , and a final stage cover  92 . The gearbox housing  30  is supported on the turbine housing  16  by support pins  32 .  
         [0023]    The input end cover  82  of the gearbox housing  30  extends around and supports a planet carrier  40  (FIG. 4), for rotation of the planet carrier  40  relative to the housing  30  about a central axis  36  of the planet carrier  40 . An input hub  34  on a first end of the planet carrier  40  is coupled to the rotor shaft  22 , in a suitable manner, not shown, for rotation with the rotor  20 . The input hub  34  receives rotational force from the rotor  20  and rotates the planet carrier  40  relative to the gearbox housing  30  in response to that rotational force. The second end of the planet carrier  40 , as illustrated, is substantially open, with a detachably mounted end plate  88  attached to the second end of the planet carrier  40 . This removable carrier end plate  88  acts as a planet bearing support, as explained below.  
         [0024]    The planet carrier  40  supports a plurality of planet pinions  42  therein for orbital movement about the carrier axis  36 . In the illustrated embodiment, three planet pinions  42  are provided, spaced apart equally about the carrier axis  36 . Only one planet pinion  42  is visible in FIG. 4. Bearings support the planet pinions  42  for rotation relative to the planet carrier. Specifically, a first planet bearing  46 , mounted at the first end of the planet carrier  40 , engages and supports a first end of each planet pinion  42 , supporting that end of the planet pinion  42  directly from the planet carrier  40 . A second planet bearing  48 , which is mounted on the planet carrier end plate  88 , engages and supports a second end of each planet pinion  42 , thereby supporting the second end of the planet pinion  42  indirectly from the planet carrier  40 . Each one of the planet pinions  42  has a plurality of external gear teeth  44  which, in the illustrated embodiment, are spur gear teeth. The planet pinion gear teeth  44  can alternatively be helical gear teeth.  
         [0025]    The gearbox  10  includes a ring gear  50 . The ring gear  50  is substantially fixed relative to the interior of the gearbox housing  30 . That is, the ring gear  50  has external splines which mate with splines on the interior of the housing  30 , preventing the ring gear  50  from rotating relative to the housing  30 . The ring gear  50  basically floats relative to the housing  30 , in that it can move radially a slight amount, within the clearance between the external splines on the ring gear  50  and the internal splines on the housing  30 . As illustrated, the ring gear  50  has a diameter of about fifty inches. The planet pinions  42  are substantially smaller in diameter than the ring gear  50 .  
         [0026]    The ring gear  50  has an array of internal spur or helical gear teeth  52 . The internal gear teeth  52  on the ring gear  50  are in meshing engagement with the external gear teeth  44  on the planet pinions  42 . As a result, orbital movement of the planet pinions  42  about the central axis  36 , in response to rotation of the input hub  34  and the planet carrier  40  about the central axis, causes the planet pinions  42  to rotate about their own axes relative to the planet carrier  40 . The rotational force transmitted from the rotor  20  to the input hub  34  is thus transmitted entirely to the planet pinions  42  to drive the planet pinions  42  to rotate about their own axes.  
         [0027]    The gearbox  10  includes a plurality of planet gears  54 . The number of planet gears  54  is equal to the number of planet pinions  42 . In the illustrated embodiment, therefore, three planet gears  54  are provided; one is visible in the sectional view of FIG. 4.  
         [0028]    Each of the planet gears  54  is fixed to one of the planet pinions  42  for rotation with its associated planet pinion  42 . Thus, the gearbox  10  is a “compound” planetary gearbox. When the input hub  34  and the planet carrier  40  rotate, therefore, the rotational force of the input hub  34  is entirely transmitted through the planet pinions  42  to the planet gears  54  to drive the planet gears to rotate about the planet pinion axes.  
         [0029]    The planet gears  54  are substantially larger in diameter than the planet pinions  42 . Each one of the planet gears  54  has a plurality of external gear teeth  56  which, in the illustrated embodiment, are spur gear teeth. The planet gear teeth  56  may alternatively be helical gear teeth. If the planet gear teeth  56  and the planet pinion gear teeth  44  are helical, they are designed to be of generally equal but opposite inclination, so that their respective axial thrust forces cancel.  
         [0030]    The gearbox  10  also includes a sun gear  60  mounted within the planet carrier  40 , surrounded by the planet pinions  42 . The sun gear  60  is radially supported by contact with the surrounding planet gears  54 , for rotation of the sun gear  60  relative to the gear box housing  30  about the central axis  36 . The sun gear  60  has a hollow bore along its axis, and along the axis of its shaft extension. A hollow tube  96 , fixed to the final stage cover  92  on the gearbox housing  30 , passes through the bore of the sun gear  60  and its shaft extension, substantially along the axis  36 , to conduct control wiring (not shown) through the gear box  10  to the rotor  20 . The sun gear  60  rotates relative to, but does not contact, the hollow tube  96 . The sun gear  60  is substantially smaller in diameter than the planet gears  54 .  
         [0031]    The sun gear  60  has a plurality of external spur or helical gear teeth  61  that are in meshing engagement with the external gear teeth  56  on the planet gears  54 . As a result, rotation of the planet gears  54  about their axes, in response to rotation of the input hub  34  and the planet pinions  42 , causes the sun gear  60  to rotate about the central axis  36 . The rotational force of the input hub  34  and the planet carrier  40  is thus entirely transmitted through the planet gears  54  to the sun gear  60 , driving the sun gear for rotation about the central axis  36 .  
         [0032]    The gearbox  10  also includes a final stage  90 , including a final stage end plate  94 , the final stage cover  92 , an output pinion  70 , and a final stage gear  62 . The final stage gear  62  is a spur or helical gear which rotates within bearings mounted to the final stage cover  92  and the final stage end plate  94 . The final stage gear  62  is rotated with the sun gear  60 , about the central axis  36 , by a splined connection  64  at the end of the shaft extension of the sun gear  60 . The splined end of the shaft extension of the sun gear  60  floats within the clearance in this splined connection to the final stage gear  62 . The final stage gear  62  is substantially larger in diameter than the sun gear  60 . The final stage gear  62  has a plurality of external spur or helical gear teeth  66 .  
         [0033]    The output pinion  70  has a set of external helical gear teeth  72 . The output pinion  70  is supported by the final stage end plate  94  and the final stage cover  92 , for rotation relative to the housing  30 , about an axis  74  that extends parallel to the central axis  36 . The output pinion  70  has a portion  76  that projects beyond the gearbox housing  30 , for connection with the generator  26  via the output shaft  24 .  
         [0034]    The gear teeth  72  on the output pinion  70  are in meshing engagement with the external gear teeth  66  on the final stage gear  62 . As a result, rotational force from the rotor  20 , transmitted through the input hub  34 , the planet carrier  40 , the planet pinions  42 , the planet gears  54 , and the sun gear  60 , is transmitted through the final stage gear  62  to the output pinion  70 . Rotation of the output pinion  70  drives the generator  26  thereby producing electrical energy.  
         [0035]    The gearbox  10  provides a gear reduction which, in the illustrated embodiment, can be, for example, a 72:1 (seventy-two to one) ratio. The rotor  20  rotates in response to wind movement past the wind turbine  12  at a low speed with a high torque. The low speed, high torque input of the rotor  20  is converted by the gearbox  10  to a high speed, low torque output suitable for driving the generator  26 .  
         [0036]    Input torque from the rotor  20  and the input hub  34  is split among the three planet pinions  42  and thus among the three planet gears  54 , for transmission to the sun gear  60 . This configuration spreads the high torque provided by the rotating input hub  34  among multiple transmission paths. At the only point in the gear train in which all the torque is concentrated in one gear and one path, that is, at the location of the sun gear  60 , the amount of torque is substantially lower than the input torque, because the sun gear is rotating faster. In this manner, no portion of the gear train of the gearbox  10  is subjected to all the input torque. This helps to increase durability and reliability of the gear train in the gearbox  10 .  
         [0037]    The planet pinions  42 , which engage the ring gear  50 , do not directly engage the sun gear  60 . Instead, the planet pinions  42  rotate the planet gears  54 , which engage and drive the sun gear  60 . Therefore, there is no reverse bending of the gear teeth  44  on the planet pinions  42 , which might result if the planet pinions were interposed directly between the ring gear  50  and the sun gear  60 . This elimination of reverse bending helps to increase the life of the planet pinions  42  and thus the reliability of the gearbox  10 .  
         [0038]    It can also be seen from FIG. 4 that the final stage section  90  of the gear box  10 , including the final stage end plate  94 , the final stage cover  92 , the output pinion  70 , and the final stage gear  62 , are removable (indeed, removable as a single unit) from the gear box  10 , leaving the carrier end plate  88  exposed. Then, the carrier end plate  88  is removable from the second (or open) end of the planet carrier  40 , exposing the planet bearings  48  on the second ends of the planet pinions  42  for removal. Thereafter, the planet pinions  42  and the planet bearings  46  on the first ends of the planet pinions  42  can be removed.  
         [0039]    As compared to the prior art, the compound planetary gearbox  10  of the present invention can provide a higher power output (more torque at the same speed) from a gearbox that occupies the same volume of space. Alternatively, the same power output can be provided from a smaller volume of space. Further, the gear box  10  of the present invention enables much easier access to the planet pinions and planet bearings, for maintenance purposes.  
         [0040]    The planet bearings  46 ,  48  also provide enhanced reliability, in that both the inner bearings and the outer bearings are subjected to similar loading patterns and have generally similar load carrying capability for providing generally the same reliability and the same servicing requirements. In that regard, the bearings  46 ,  48  at the first and second ends of the planet pinions  42  are of approximately equal size and load carrying capability (i.e, they are of the same type and of generally the same width and inner and outer diameters). In addition, the outer diameter of each of these bearings is approximately twice that of the inner diameter, thereby providing adequate space for high-capacity bearing members. The first bearings  46  and the second bearings  48  are positioned at the ends of the respective planet pinions  42 , with the plant pinion gear teeth  52  and planet gear  54  being positioned between the planet bearings  46 ,  48 . Thus, the planet pinion  42  is supported along its entire length by the bearings  46 ,  48 , with no overhanging or cantilevered portions that impose increased stress on the bearings.  
         [0041]    While the particular invention as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages hereinbefore stated, it is to be understood that this disclosure is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended other than as described in the appended claims.