Abstract:
The invention relates to a wind turbine, comprising a hub, at least one blade, said blade being pivotably installed at said hub, at least one pitch bearing, said pitch bearing having an inner bearing ring and an outer bearing ring, said inner bearing ring having an inner wall in radial direction and a first end and a second end in axial direction and at least one reinforcing element to enhance the stiffness of said pitch bearing, wherein the reinforcing element is arranged adjoining the inner wall of the inner bearing ring.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a wind turbine comprising a reinforcing element to reduce deformations of a pitch bearing. 
       BACKGROUND ART 
       [0002]    A wind turbine known in the art comprises a hub to which at least one blade is mounted. In order to be able to control the load acting on the rotor blade of the wind turbine, the mounting of the blade to the hub is often done by means of a pitch bearing comprising an inner bearing ring and an outer bearing ring so that the blade can be pitched with respect to the incoming wind. In this case, the rotor blade is connected to the inner bearing ring of the pitch bearing, while the outer bearing ring is connected to the hub. 
         [0003]    Since the forces and moments resulting from the wind acting on the rotor blades have to be transmitted to the hub of the wind turbine generator, the pitch bearing is subjected to extreme strains and loads leading to damages and distortions of the pitch bearing. As the trend in wind turbine development is towards an increased size of wind turbines, the size of the blades as well as the loads to be transferred increase accordingly. Due to this development, the pitch bearing as the intermediate element of the load transfer between the blade and the hub is even more prone to damages and distortions. 
         [0004]    In order to ensure the durability and functionality of the pitch bearing it is known to use reinforcing elements for the bearing rings. In US 20080213095 A1, a reinforcing element is disclosed which is positioned at the axial end of the outer being ring. In addition, a further reinforcing element can be positioned at the axial lower end of the inner bearing ring. However, the arrangement at the axial ends of the bearing rings is disadvantageous as due to the loads acting on the bearing rings radial forces result whose strength depend on the axial location. The reinforcing element which is located axially to the bearing ring could experience other forces then the bearing ring itself leading to a disadvantageous load distribution for the reinforcing element and the bearing ring as well as their connection to each other. 
       SUMMARY OF INVENTION 
       [0005]    It is the object of the present invention to provide an improved wind turbine with an enhanced pitch bearing stiffening function. A further object of the invention is to improve the durability and functionality of the pitch bearing. 
         [0006]    According to the present invention, the wind turbine comprises a hub, at least one blade and at least one pitch bearing. The at least one blade of the wind turbine blade is pivotably installed at the hub by means of the pitch bearing which comprises an inner bearing ring and an outer bearing ring. While the blade is preferably mounted to the inner bearing ring of the pitch bearing, in particular by a bolt connection, the hub is preferably mounted to the outer bearing ring. Between the two bearing rings rolling elements are disposed which allow the rotation of the bearing rings with respect to each other so that the blade mounted to the inner bearing ring can be pivoted around its longitudinal axis. 
         [0007]    Furthermore, the wind turbine comprises a reinforcing element for enhancing the stiffness of the inner bearing ring of the pitch bearing. The inner bearing ring has an inner wall in radial direction and a first end and a second end in axial direction. The reinforcing element is arranged in such a way that it adjoins the inner wall of the inner bearing ring, i.e. the reinforcing element is arranged to be in contact with the inner wall of the inner bearing ring. By the use of the reinforcing element, axial and radial deformations of the bearing rings are reduced. 
         [0008]    In a preferred embodiment of the invention, the reinforcement element is mounted to the inner wall of the inner bearing ring. In an especially preferred embodiment the reinforcing element is not disposed between the blade and the pitch bearing, therefore reducing the number of intersection surfaces in the longitudinal direction of the blade compared to an arrangement between the blade and the pitch bearing. 
         [0009]    In another preferred embodiment, the inner wall of the inner bearing ring and the reinforcing element have a contact area between them. In addition, the inner wall of the inner bearing ring comprises an inner ring gear which is used for pitch rotation. The inner ring gear and the contact area between the inner wall of the inner bearing ring and the reinforcing element are disposed next to each other in axial direction of the inner bearing ring. In this context, the inner bearing ring and the reinforcing element can be arranged along the axial direction of the inner bearing ring one after another in such a way that they adjoin each other or alternatively that there is still a part of the inner wall of inner bearing ring which does not comprise an inner ring gear but is also not adjoined to the reinforcing element. 
         [0010]    In a further preferred embodiment, the inner ring gear and the contact area between the inner wall of the inner bearing ring and the reinforcing element are arranged adjoining each other and extend along the entire axial length of the inner radial wall so that they cover the inner radial wall of the inner bearing ring entirely from its first axial end to the second axial end. 
         [0011]    In another preferred embodiment of the invention, the reinforcing element does axially not extend beyond the first end and the second end of the inner bearing ring respectively. The reinforcing element is hence restricted to the distance between the first end and the second end of the inner bearing ring in axial direction. Preferably, the reinforcing element ends at flush level with at least one of the axial ends of the inner bearing ring. 
         [0012]    In a preferred embodiment of the invention, the reinforcing element has an outer face in radial direction of the inner bearing ring which partly adjoins the radial inner wall of the blade and partly adjoins the inner wall of the inner bearing ring. Preferably, part of the reinforcing element can be mounted to the inner wall of the blade, while another part of the reinforcing element can be mounted to the inner wall of the inner bearing ring. Further, it is advantageous when the outer face is formed continuous. 
         [0013]    According to another preferred embodiment of the invention, part of the reinforcing element is disposed between the blade and the inner bearing ring, preferably with its outer surface ending at flush level with the outer radial wall of the blade. Due to the partial arrangement of the reinforcement element between the blade and the inner bearing ring, the reinforcing element is fixated in addition to a possible installation to the inner wall of the inner bearing ring. 
         [0014]    In another embodiment of the invention, the reinforcing element has the shape of a ring or circular plate and preferably has at least one opening in axial direction. Alternatively, the reinforcing element can be at least one reinforcing web or bar. 
         [0015]    In another embodiment of the invention, the radial outer wall of the reinforcing element comprises a step. Preferably, the step defines a first part and a second part of the reinforcing element in axial direction comprising different diameters. In other words, the reinforcing element is formed as a two-step annular portion. The first part has a smaller outer diameter than the second part and is arranged adjoining the inner wall of the inner bearing ring, while the second part with the bigger outer diameter is partly arranged between the blade and the inner bearing ring. Preferably, the first part and the second part comprise the same inner diameter. 
         [0016]    In another preferred embodiment of the invention, the inner ring gear is disposed at the inner wall of the inner bearing ring in such a way that it provides a supporting surface for the reinforcing element wherein the supporting surface extends in radial direction of the inner bearing ring. In this way, the geometry of the inner bearing ring can be used for positioning and supporting the reinforcing element. Preferably, the reinforcing element ends at flush level with said supporting surface with one end and, in particular, it also ends at flush level with at least one axial end of the inner bearing ring with the other end. 
         [0017]    In another preferred embodiment, the reinforcing element is mounted to the inner bearing ring, preferably to its radial inner wall, by heating, such as for example induction heating. The reinforcing element can also be mounted by means of cooling. The connection between reinforcing element and inner bearing ring can also be formed by welding, gluing or press fitting. In particular, the reinforcing element can have a transition fit with the inner bearing ring which allows a secure hold of the reinforcing element but at the same time its disassembly if necessary. 
         [0018]    In an alternative preferred embodiment, the reinforcing element is formed integrally with the inner bearing ring. This can be achieved by providing an inner bearing ring with an increased wall thickness wherein the increased wall thickness extends radially to the inside of the inner bearing ring. In other words, the usually cylindrical inner bearing ring comprises a constant outer radial diameter while the inner diameter is decreased in the section with the increased thickness. Preferably, the increased wall thickness has its maximum at one of the axial ends of the inner bearing ring and decreases towards the inner wall of the normally cylindrical inner bearing ring in axial direction. 
         [0019]    Preferably, the material of the reinforcing element comprises casted metal, plate metal of fiber reinforced material, such as fiber reinforced plastic. In particular, the reinforcing element is made entirely of one of the above materials. 
         [0020]    In a further preferred embodiment of the invention, the stiffness of the connection between the inner bearing ring and the blade corresponds to the stiffness of the connection between the hub and the outer bearing ring. In particular, this is achieved by the use of the reinforcing element which influences the stiffness of the inner bearing ring and therefore the stiffness of the connection between the inner bearing ring and the blade. The corresponding stiffness of the two connections of the pitch bearing has a positive impact on the loads acting on the pitch bearing and consequently its durability. In contrast, a difference in stiffness will result in an uneven distribution of the load within the pitch bearing. This uneven load distribution can result in damages and critical deformations of the bearing rings, such as an ovalization of the bearing rings. 
         [0021]    Another embodiment of the invention comprises a hub transition tube and a torque transfer means for transferring the torque of the hub to a generator of the wind turbine. The hub transition tube has a first end and a second end having an outer diameter respectively. The hub transition tube is arranged between the hub and the torque transfer means in such a way that with its first end it is installed at the hub and to its second end the torque transfer means is mounted. The hub transition tube has at least one outer diameter between its first end and its second end which is smaller than the outer diameter of the hub transition tube at its second end. 
         [0022]    The torque transfer means, preferably the main shaft of the wind turbine, is preferably housed in the nacelle and rotates with the blades. Preferably, the hub transition tube connects the flange of the torque transfer means and the flange of the hub which usually connects the hub and the torque transfer means. 
         [0023]    The above embodiment results in the advantage that the hub can be designed smaller than in some configurations necessary. Normally, the dimensions of the hub are determined by the outer diameter of the flanges of the pitch bearings and the outer diameter of the flange of the torque transfer means in such a way that the hub comprises matching flanges for the connection to the pitch bearings and the torque transfer means respectively. If the hub is dimensioned according to the diameter of the flange of the torque transfer means, the hub would usually have to be enlarged so that its flange matches to the flange of the torque transfer means in order to enable a connection between the two. Due to this dimensioning restriction, the hub can become unnecessary large and heavy leading especially to handling problems and immensely increased component costs and costs of transportation. The above embodiment of the invention provides a hub transition tube which can function as an adapter between differently sized flanges of the hub and the torque transfer means, especially in the above described case that the diameter of the flange of the hub should be dimensioned smaller than the preset diameter of the torque transfer means. Therefore, the hub transition tube allows keeping the hub smaller than usually possible. 
         [0024]    In another preferred embodiment, the hub transition tube has one diameter which is both smaller than the diameter of its second end and the diameter of its first end. Preferably, the diameter of the hub transition tube changes continuously from the first end to the second end of the hub transition tube and has a minimum in between the two ends. 
         [0025]    In another preferred embodiment of the invention, the outer surface of the hub transition tube follows a curve in a longitudinal section view of the hub transition tube. Preferably, the two curves defined by the outer surface of the hub transition tube as seen in a longitudinal section are continuous functions. In particular, the curves both have a stationary point at which the gradient changes its sign. 
         [0026]    According to another preferred embodiment of the invention, the torque transfer means and the hub transition tube are connected by means of connection means. Preferably, the torque transfer means and the hub transition tube are connected by a bolt connection wherein the bolt connection either comprises through holes or blind holes for the insertion of bolts. 
         [0027]    In another preferred embodiment, the hub transition tube is manufactured as a monolithic part of the hub and projects away from it so that a connection of the hub to the torque transfer means, which is preferably positioned in the nacelle, is possible. 
         [0028]    According to another preferred embodiment, part of the hub transition tube adjoins the outer bearing ring of the at least one pitch bearing, preferably the axial end of the outer bearing ring. This arrangement of the hub transition tube enhances the stiffness of the outer bearing ring of the pitch bearing in its axial direction, in particular by the curve of the hub transition tube as seen in a longitudinal section view. Preferably, the wind turbine comprises multiple blades which are mounted to the hub using multiple pitch bearings. In this case, the hub transition tube comprises one part for the adjoining arrangement to the outer bearing ring of each pitch bearing. Preferably, the part of the hub transition tube is connected to the outer bearing ring. In particular, the part of the hub transition tube adjoining the outer bearing ring has a curved form as seen in a longitudinal section which is continuous with the curve defined by the outer surface of the outer bearing ring. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0029]    The invention will be described below with reference to the following figures which show in schematic representation. 
           [0030]      FIG. 1  is a perspective view of a cross section of a blade, a pitch bearing, a hub and a reinforcing element; 
           [0031]      FIG. 2  is a perspective view of a cross section of a blade, a pitch bearing, a hub and a reinforcing element; 
           [0032]      FIG. 3  is a perspective view of a cross section of a blade, a pitch bearing, a hub and a reinforcing element; 
           [0033]      FIG. 4  is a perspective view of a longitudinal cross section of a hub transition tube; and 
           [0034]      FIG. 5  is a side view of a hub. 
           [0035]      FIG. 6  is a side view of a hub. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0036]      FIG. 1  shows a cross section of the connection area between a blade  11 , a pitch bearing  14  and a hub  13  of a wind turbine in perspective view. The blade  11  comprises an inner wall  12 . The blade  11  is connected to the hub  13  via a pitch bearing  14  which comprises an outer bearing ring  15 , an inner bearing ring  16  and rolling elements  17  situated between both rings  15 ,  16 . The inner bearing ring  16  comprises an inner wall  18  in radial direction and a first end  19  and a second end  20  in axial direction. 
         [0037]    The blade  11  is mounted to the inner bearing ring  16  by means of a bolt connection utilizing longitudinal bolts  28  which are disposed within the inner bearing ring  16  and the blade  11 . The outer bearing ring  15  is also mounted to the hub  13  by means of a bolt connection with longitudinal bolts  28 . Due to the rolling elements  17  the inner bearing ring  16  and the outer bearing ring  15  can be rotated with respect to each other so that the blade  11  mounted to the inner bearing ring  16  can be pivoted around its longitudinal axis. 
         [0038]    A reinforcing element  23  in form of a ring plate is arranged adjoining the radial inner wall  18  of the inner bearing ring  16  forming a contact area  27  between the reinforcing element  23  and the radial inner wall  18  of the inner bearing ring  16 . In this embodiment, the reinforcing element  23  is fixedly mounted to the radial inner wall  18  of the inner bearing ring  16  by induction heating and is not disposed with any of its parts between the blade  11  and the pitch bearing  14 . The reinforcing element  23  does not extend beyond the first axial end  19  of the inner bearing ring  16 . 
         [0039]    The radial inner wall  18  of the inner bearing ring  16  further comprises an inner ring gear  21  which is disposed next to (i.e. below) the contact area  27  in axial direction of the inner bearing ring  16 . The contact area  27  and the inner ring gear  21  cover the entire axial length of the radial inner wall  18  of the inner bearing ring  16  from its first axial end  19  to its second axial end  20 . Due to the arrangement of the inner ring gear  21 , the radial inner wall  18  of the inner bearing ring  16  is formed stepped. The inner ring gear  21  therefore provides a supporting surface  22  extending in radial direction of the inner bearing ring  16  for supporting the reinforcing element  23 . The reinforcing element  23  can also be fixedly mounted to the supporting surface  22 , either in addition or alternatively to the mounting to the radial inner wall  18  of the inner bearing ring  16 . 
         [0040]      FIG. 2  shows a perspective view of a cross section of the connection area between a blade  11 , a pitch bearing  14  and a hub  13  and relates to another embodiment of the present invention. A ring-shaped reinforcing element  23  is with its outer face  24  arranged adjoining the radial inner wall  18  of the inner bearing ring  16 . The reinforcing element  23  comprises a first part  25  and a second part  26  which are disposed consecutively in axial direction and arranged adjoining each other. The first part  25  and the second part  26  are integrally formed. The first part  25  of the reinforcing element  23  comprises a smaller outer diameter than the second part  26  of the reinforcing element  23  so that the outer face  24  of the reinforcing element  23  is formed stepped. The first part  25  of the reinforcing element  23  is arranged adjoining the inner wall  18  of the inner bearing ring  16 , wherein the outer section  26   a  of the second part  26  of the reinforcing element  23  is disposed between the blade  11  and the inner bearing ring  16 . The reinforcing element  23  is mounted fixedly to the inner bearing ring  16  by gluing the first part  25  to the inner radial wall  18  of the inner bearing ring. In addition, the outer section  26   a  of the second part  26  of the reinforcing element  23  is fixedly mounted by means of bolts  28  which at the same time mount the blade  11  to the inner bearing ring  16 . 
         [0041]      FIG. 3  shows a perspective view of a cross section of the connection area between a blade  11 , a pitch bearing  14  and a hub  13  of yet another embodiment of the present invention. A reinforcing element  23  is arranged adjoining the radial inner wall  18  of an inner bearing ring  16  wherein the reinforcing element  23  extends beyond the first axial end  19  of the inner bearing ring  16 . The outer face  24  of the reinforcing element  23  therefore comprises a first part  24   a  which is arranged adjoining the radial inner wall  12  of a blade  11  and a second part  24   b  which is arranged adjoining the radial inner wall  18  of the inner bearing ring  16 . The reinforcing element  23  does not extent between the blade  11  and the pitch bearing  14 . The reinforcing element  23  is mounted fixedly by means of gluing the second part  24   b  of the outer face  24  of the reinforcing element  23  to the radial wall  18  of the inner bearing ring  16 . In addition, the first part  24   a  of the outer face  24  of the reinforcing element  23  can be glued to the inner wall  12  of the blade  11 . 
         [0042]      FIG. 4  is a perspective view of a longitudinal cross section of a hub transition tube  29 . The hub transition tube  29  in this embodiment is integrally formed with a hub  13  from which it projects away to the outside of the hub  13 . Furthermore, the hub transition tube  29  comprises a second end  31  with an outer diameter  32 . To the second end  31  of the hub transition tube  29  a torque transfer means  34 , i.e. a rotor shaft, is mounted. 
         [0043]    At the hub side the hub transition tube  29  is arranged adjoining the axial end of the outer bearing ring  15 . Starting from this end towards its second end  31 , the hub transition tube  29  extends substantially in the axial direction of the outer bearing ring  15  projecting slightly away from the hub  13 . The diameter of the hub transition tube  29  decreases until a stationary point  41  is reached from which the diameter of the hub transition tube  29  increases again towards its second end  31 , at which a flange  42  is formed for the connection to the torque transfer means  34 . Due to this arrangement of the hub transition tube  29 , its outer face  37  is formed curved as seen in the longitudinal cross section. Starting from the hub side towards the second end  31  of the hub transition tube  29 , its outer face  37  has a high gradient until a stationary point  41  is reached. From this stationary point  41 , the outer face  37  of the hub transition tube  29  has a smaller gradient with an opposite sign. 
         [0044]    Due to the curved form of the hub transition tube, it comprises a part in which the outer diameter of the hub transition tube is smaller than the outer diameter  32  of its second end  31 . As an example, the outer diameter  33  at the stationary point  41  is shown in  FIG. 4 , which is smaller than the outer diameter  32  of the second end  31 . 
         [0045]      FIG. 5  shows a schematic side view of a hub  13 . The hub comprises three flanges  38  for the connection to the outer bearings rings of three pitch bearings. The circle indicates the required outer diameter  39  for the connection of the hub  13  to a torque transfer means  34 . As it can be seen in the figure, the required outer diameter  39  for the connection to a torque transfer means  34  and the flanges  38  for the connection to the outer bearing rings interfere. In order to be able to connect a hub  13  with the shown dimensions, in particular the height  40   a , to a torque transfer means  34  with the required outer diameter  39 , a hub transition tube  29  is used. The hub transition tube  29  projects away from the hub  13  in such a way that the connection area to the torque transfer means  34  and the hub  13  are locally separated. In this way, an interference between the dimensions of the hub, especially its height  40   a , and the connection requirements to the torque transfer means can be prevented. Therefore, the height  40   a  of the hub  13  can be smaller than usually possible. 
         [0046]    In contrast,  FIG. 6  shows a schematic side view of a hub  13  from the prior art with a height  40   b . The hub  13  again comprises three flanges  38  for the connection to the outer bearings rings of three pitch bearings. The circle indicates the required outer diameter  39  for the connection to a torque transfer means  34  which is the same size as the required diameter  39  of  FIG. 5 . For connecting the hub  13  to the torque transfer means  34 , the hub  13  will have to be enlarged in contrast to the hub of  FIG. 5  so that the required outer diameter  39  for the connection to the torque transfer means  34  does not interfere with the flanges  38  for the connection to the outer bearing rings. Therefore, the height  40   b  of the hub from prior art of  FIG. 6  is significantly larger than the height  40   a  of the hub of  FIG. 5 .