Patent Publication Number: US-2010129223-A1

Title: Bearing device and wind turbine having said bearing device

Description:
BACKGROUND 
     The present disclosure generally relates to wind turbines including a drive train having at least one rotor with at least one rotor blade attached to a hub, and especially relates to an apparatus for rotatably supporting a main shaft of a drive train of a wind turbine. Specifically, the present disclosure relates to the design and arrangement of bearings adapted for supporting the main shaft of the wind turbine. 
     Wind turbines are of increasing importance as an environmentally safe and relatively inexpensive energy source. Thus, an increased demand for an improved wind turbine performance has led to efforts concerning an energy-efficient bearing of a main shaft of a wind turbine. Bearing devices for such kind of main shafts may include complex lubrication systems. Typically, the main shaft of a wind turbine has a large diameter and rotates at a relatively low speed. Torque applied at the main shaft of a wind turbine can be relatively high in order to transfer wind energy from the rotor towards a speed adapter, e.g. a gearbox of the wind turbine. 
     SUMMARY 
     In view of the above, a bearing device for a main shaft of a wind turbine is provided, said bearing device including a fixed hollow-cylindrical portion adapted for being mounted at a machine nacelle of the wind turbine, wherein an inner diameter of the hollow-cylindrical portion is larger than the outer diameter of the main shaft such that a cavity is formed therebetween when the main shaft is inserted into the hollow-cylindrical portion, and a fitting adapted to provide a lubricating fluid to the cavity between the fixed hollow-cylindrical portion and the main shaft. 
     According to another aspect a bearing device for a hub of a wind turbine is provided, said bearing device including a protruding portion adapted for being mounted at a main frame of a machine nacelle of the wind turbine, a rotatable hollow-cylindrical portion adapted for being connected to the hub, wherein an inner diameter of the rotatable hollow-cylindrical portion is larger than an outer diameter of the protruding portion such that a cavity is formed therebetween when the protruding portion is inserted into the rotatable hollow-cylindrical portion and a fitting adapted to provide a lubricating fluid to the cavity between the protruding portion and the rotatable hollow-cylindrical portion. 
     Further exemplary embodiments are according to the dependent claims, the description and the accompanying drawings. 
    
    
     
       DRAWINGS 
       A full and enabling disclosure, including the best mode thereof, to one of ordinary skill in the art is set forth more particularly in the remainder of the specification including reference to the accompanying drawings wherein: 
         FIG. 1  shows a schematic side view of a wind turbine wherein the main axis of the wind turbine is oriented towards the incoming wind direction at the location of the wind turbine; 
         FIG. 2  is a schematic top view of typical components within a machine nacelle of the wind turbine wherein the main axis is supported by two bearings; 
         FIG. 3  illustrates a journal bearing wherein the main axis of the wind turbine rotates within a cavity filled with a high-viscosity oil, according to a typical embodiment; 
         FIG. 4  is a side view of typical components attached to a main shaft of a wind turbine, wherein the main shaft is supported by a journal bearing and a gearbox of the wind turbine, according to a typical embodiment; 
         FIG. 5  is a side view of typical components attached to a main shaft of the wind turbine, wherein the wind turbine is supported by two journal bearings, according to another typical embodiment; 
         FIG. 6  is a cross-sectional view of a journal bearing operated by an electrorheological fluid, according to yet another typical embodiment; and 
         FIG. 7  is a cross-sectional view of typical components of a drive train of a wind turbine, wherein the main shaft is fixed and the hub rotates about the main shaft, wherein the hub is supported by journal bearings, according to yet another typical embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the various exemplary embodiments, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the present disclosure includes such modifications and variations. 
     A number of embodiments will be explained below. In this case, identical structural features are identified by identical reference symbols in the drawings. The structures shown in the drawings are not depicted true to scale but rather serve only for the better understanding of the embodiments. 
       FIG. 1  is a schematic view of a wind turbine  100  having a machine nacelle  103 , which is rotatably mounted on top of a tower  102 . The wind turbine  100  further includes a rotor having a hub  104  and at least one rotor blade  101 . The hub  104  is the central part of the rotor, and the at least one rotor blade  101  extends outwardly from the hub. 
     Although the wind turbine  100  illustrated in  FIG. 1  includes three rotor blades  101 , any number of rotor blades  101  may be provided. The nacelle  103  which is located on top of the tower  102  can be rotated about a central axis, e.g. a vertical axis  107  of the tower  102 . 
     The orientation of the machine nacelle  103  with respect to the central axis of the tower  102  is referred to as a yaw angle  106 . The yaw angle  106  is adjusted such that an axis of the main shaft  112  of the drive train of the wind turbine is typically directed towards an incoming wind direction  105 . 
     Moreover, the at least one rotor blade  101  may be adjusted with respect to its longitudinal axis such that a pitch angle  108  of the rotor blade may be adapted to the incoming wind velocity. A bending moment  109  may occur due to a vertical wind shear such that the main shaft  112  of the wind turbine experiences a bending force. The main shaft  112  of the wind turbine mechanically connects the hub  104  to a gearbox  111  such that a rotational momentum provided by the wind energy may be transferred to the gearbox  111  and further on to an electrical generator (not shown in  FIG. 1 ) for the generation of electric energy. 
     It is noted here, albeit not shown in  FIG. 1 , that instead of using a gearbox  111  in order to transform rotational energy at low rotational speeds into rotational energy at high rotational speeds, a magnetic speed adaptor may be used which does not require any mechanical gearboxes. 
     In  FIG. 1 , reference numeral  111  denotes a mechanical gearbox which is not detailed in the following description, because the gearbox itself does not contribute to the understanding of the present disclosure. A bearing device  200  is provided for rotatably supporting the main shaft  112  of the wind turbine  100 . 
       FIG. 2  is a schematic top view of the wind turbine  100  indicating typical components of the drive train of the wind turbine. The at least one rotor blade  101  is attached at the hub  104 , wherein the rotation of the hub  104  results in a rotation of the main shaft  112 . A rotation sensor  110  is provided in order to determine a rotational speed of the main shaft  112 . The main shaft  112  is supported by the bearing device  200  which will be described in detail hereinafter. The main shaft  112  furthermore is connected to the gearbox  111  which transforms a low rotational input speed into a high rotational output speed provided at a gearbox output shaft  115   a.    
     Typically, a drive train of a wind turbine  100  includes the rotor having at least one rotor blade  101  and the hub  104  and the main shaft  112 . The main shaft  112  is supported by at least one bearing device  200 . 
     A bearing device  200  according to a typical embodiment is illustrated in  FIG. 3 . 
       FIG. 3  is a cross-section of a main shaft  112  of a wind turbine  100  at the location of a bearing device  200 . The bearing device  200  according to the typical embodiment shown in  FIG. 3  includes a fixed hollow-cylindrical portion  202  used as a housing which has a fitting  203 . 
     The fitting  203  is adapted for inserting a high-viscosity fluid into the interior of the housing  202 . Within the housing, the main shaft  112  is supported rotatably. A reference numeral  113  denotes a rotation axis of the main shaft  112 . The housing  203  may be formed as a hollow-cylindrical portion having end covers in order to prevent the fluid leakage. 
     A high-viscosity fluid is distributed within a cavity  204  between the main shaft  112  and an inner wall of the housing  202 . According to the typical set-up of a journal bearing device  200  shown in  FIG. 3 , a frictionless environment is provided in order to support and guide the rotating main shaft  112 . Typical journal bearings  200  exhibit a long lifetime as compared to conventional roller bearings. 
     The housing  202  is provided as a cylinder surrounding the main shaft  112  wherein the cavity  204  between the outer surface of the main shaft  112  and the inner surface of the housing  202  is filled with a fluid lubricant, e.g. a high-viscosity oil. In the bearing arrangement shown in  FIG. 3 , the main shaft  112  is supported by the fluid lubricant when the main shaft  112  is rotating. Hydrodynamic principles which are active as the main shaft  112  rotates support the main shaft  112  and relocate it within the cavity  204 . 
     Typically, high-viscosity lubricants are filled into the cavity  204  for providing a bearing for slowly rotating main shafts  112  of wind turbines  100 . Reference numeral  201  in  FIG. 3  indicates a rotation direction. 
       FIG. 4  is a side view of a drive train of a wind turbine  100 , wherein the drive train typically includes the hub  104  and the main shaft  112  which is connected to the hub  104 . In the typical embodiment illustrated in  FIG. 4 , the main shaft  112  furthermore is connected to the gearbox  111  which can be provided as a speed adapter. The gear box  111  is supported by a second mounting unit  210  such that one end of the main shaft  112  is supported. 
     The other end of the main shaft  112  is supported by a bearing device  200  which is provided as a journal bearing according to a typical embodiment. The bearing device  200  is supported by a first mounting unit  209 . Both the first mounting unit  209  and the second mounting unit  210  are fixed at a main frame (not shown in  FIG. 4 ) of the machine nacelle  103  of the wind turbine  100 . 
     According to a typical embodiment, the first mounting unit  209  and the second mounting unit  210  may be provided as elastic supports for the journal bearings in order to absorb extreme loads and/or bending moments explained above. 
     Furthermore, a thrust bearing  205  is provided in order to define an axial position of the main shaft  112 . The thrust bearing  205  may be provided as a conventional roller bearing and/or as a journal bearing. 
     It is noted here that, albeit a single journal bearing device  200  is shown in  FIG. 4 , two or more journal bearing devices  200  may be provided in order to rotatably support the main shaft  112  of the drive train of the wind turbine  100 . In the typical embodiment shown in  FIG. 4 , the main shaft  112  is supported, on the left side in  FIG. 4 , by the bearing device  200  and on the right side of  FIG. 4 , by the gearbox  111 . 
       FIG. 5  is a side view of a drive train arrangement according to another typical embodiment. The drive train includes a hub  104  in the main shaft  112 , wherein the main shaft  112  is a connection means between the hub  104  and the gearbox  111 . In the typical embodiment illustrated in  FIG. 5 , two journal bearing devices  200  are provided in order to rotatably support the main shaft  112  of the wind turbine  100 . 
     The two bearing devices  200  are supported by a first mounting unit  209  and a second mounting unit  210 . It is noted here that the first and second mounting units  209 ,  210  may be provided as elastic supports in order to absorb extreme loads and/or bending moments from the main shaft  112 . In the typical embodiment shown in  FIG. 5 , the gearbox  111  is attached to one side of the main shaft  112 . Furthermore, thrust bearings  205  which can be provided as journal bearings are used in order to axially define the position of the main shaft  112 . 
     Materials used for the at least one journal bearing device  200 , in particular for the housing  202  of the at least one journal bearing device  200  include, but are not restricted to, white metal, babbit metal, composite material, high performance plastic material and phosphor bronze. According to a further typical embodiment, metal with tailor-made coatings can be applied such as hard-coated nickel-chrome-boron. 
     Furthermore, high-performance plastic material can be used between a metallic part and a plastic portion. Typically, the high-viscosity oil which is used in the journal bearings  200  according to the typical embodiments has viscosities over 1,000 cSt (centi-Stokes; 1 cSt=10 −6  m 2  s −1 ) at 40° C. Moreover, according to a typical embodiment, polyalphaolefin having a viscosity of approximately 43,000 cSt that will allow to have the required oil film may be used. 
     The outer surface of the main shaft  112  at the location of the journal bearing  200  can be polished. Furthermore, the inner surface of the housing  202  of the journal bearing can have a polished structure. The fluid lubricant such as the high-viscosity oil is fed into the cavity  204  of the bearing  200  via the fitting  203  (see  FIG. 3 ). The filling of the journal bearing  200  with the fluid lubricant may be performed under high pressure. 
       FIG. 6  is a cross-sectional view of a journal bearing  200  according to yet another typical embodiment. The journal bearing  200  shown in  FIG. 6  has a housing  202  and a high-performance plastic material  208  which is attached at the inner wall of the hollow-cylindrical housing  202 . Within the high-performance plastic material  208 , a cylindrical electrode  207  is embedded. Reference numeral  201  in  FIG. 3  indicates a rotation direction of the main shaft  112  about the rotation axis  113 . 
     The cavity  204  between the main shaft  112  and the housing  202  (denoted by a reference numeral  204  in  FIG. 3 ) is filled by an electrorheological fluid  206 . The electrorheological fluid  206  is a fluid the viscosity of which can be controlled by means of an electric field applied across the fluid layer. 
     The electrorheological fluid  206  is introduced into the cavity  204  by means of a fitting  203 . In a typical embodiment, the electrorheological fluid  206  is introduced under high pressure. 
     According to a typical embodiment, a power supply (not shown) is used in order to apply a potential difference between the electrode  207  and the electrically conducting main shaft  112 . The larger the electric field applied between the electrode  207  and the main shaft  112 , the larger is the viscosity of the fluid lubricant, i.e. the electrorheological fluid  206 . The viscosity of the electrorheological fluid  206  may be adjusted in accordance with an environmental temperature such that a constant viscosity can be provided for the journal bearing  200  even if environmental temperatures change due to, e.g. summer/winter season. 
     Furthermore, it is possible to introduce a magnetorheological fluid into the cavity  204  between the main shaft  112  and the housing  202 . 
     The magnetorheological fluid is controllable by means of a magnetic field. Thus, a magnetically transmitting material has to be provided for the housing  202  of the bearing device  200  in addition to a magnetic field generation means (not shown in the drawings), instead of the electrode configuration  207 ,  112 . The magnetic field created in a direct drive can be used for that purpose and the control of the magnetic and/or electric field can be embedded in the control of the generator/converter. 
       FIG. 7  is a side sectional view of a drive train of the wind turbine according to yet another typical embodiment. In the arrangement shown in  FIG. 7 , a main frame  114  is fixed, whereas the hub  104  together with the at least one rotor blade  101  (not shown in  FIG. 7 ) is rotating about a fixed protruding portion  115  of the fixed main frame  114 . 
     The rotation axis  113  coincides with the central axis of the main shaft  112 . The protruding portion  115  may be hollow such that the main shaft  112  can be inserted into the protruding portion. Thus the main shaft  112  is adapted for rotating within the fixed protruding portion  115  of the fixed main frame  114 . The support of the hub  104  is provided by journal bearing devices  200  at two axial positions along the fixed protruding portion  115  of the fixed main frame  114 . The bearing devices may include a fitting  203  adapted to provide a lubricating fluid. Furthermore, thrust bearings  205  are provided in order to define an axial position of the rotating hub  104 . A mechanical connection of the hub  104  to the main shaft  112  is provided by an axis support unit  116 . 
     It is noted here, albeit not shown in  FIG. 7  that the main axis  112  can be supported by at least one journal bearing device  200  according to a typical embodiment (see e.g.  FIG. 3 . 
     The invention has been described on the basis of embodiments which are shown in the appended drawings and from which further advantages and modifications emerge. However, the disclosure is not restricted to the embodiments described in concrete terms, but rather can be modified and varied in a suitable manner. It lies within the scope to combine individual features and combinations of features of one embodiment with features and combinations of features of another embodiment in a suitable manner in order to arrive at further embodiments. 
     It will be apparent to those skilled in the art, based upon the teachings herein, that changes and modifications may be made without departing from the disclosure and its broader aspects. That is, all examples set forth herein above are intended to be exemplary and non-limiting.