Abstract:
A double row tapered bearing assembly includes a first portion and a second portion. The first portion includes a first ring and a second ring. The first ring is connected with the second portion via at least one row of tapered rollers or balls. The second ring is also connected with the second portion via at least one row of tapered rollers or balls. The first ring and the second ring each includes at least one groove. The at least one groove in the first ring faces the at least one groove in the second ring to form a cavity. At least one member is placed in the cavity.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2011/062058, filed Jul. 14, 2011 and claims the benefit thereof. The International Application claims the benefits of European application No. 10192048.6 EP, filed Nov. 22, 2010. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to a double row tapered bearing assembly and to a wind turbine. 
       BACKGROUND OF INVENTION 
       [0003]    During extreme loading on the wind turbine rotor there is a risk that the internal bearing forces will cause the two inner rings of a double row tapered bearing to slide relative to each other. This is often referred to as cone shifting. When the load is reduced the two inner rings will then end up in a position of relative out of roundness. This geometric deviation will increase the hertzian stress level in the contact area between roller and raceway, which will increase the probability of bearing failure. 
       SUMMARY OF INVENTION 
       [0004]    This difficulty can be solved by shrink fitting a reinforcement tube inside the two inner rings. A difficulty with this solution is that it relies on high accuracy of the diameter of the shrink fitted tube. Moreover, it makes disassembly very difficult. Another possibility is to have a T- or I-shaped ring between the two inner rings. A basic difficulty with this solution is that it relies on high accuracy of the diameter of the rings to ensure that it fits properly. 
         [0005]    It is a first objective of the present invention to provide a double row tapered bearing assembly which reduces cone shifting in a cost effective and easy way. It is a second objective of the present invention to provide an advantageous wind turbine. 
         [0006]    The above objectives are achieved by the features of the independent claims. 
         [0007]    The inventive double row tapered bearing assembly comprises a first portion and a second portion. The first portion comprises a first ring and a second ring. The first ring is connected with the second portion by means of at least one row of tapered rollers or at least one row of balls. The second ring is connected with the second portion by means of at least one row of tapered rollers or at least one row of balls. 
         [0008]    The first ring and the second ring each comprise at least one groove. The at least one groove in the first ring faces the at least one groove in the second ring. The at least one groove of the first ring and the facing at least one groove in the second ring from a cavity. At least one member is placed in the cavity. By placing at least one member in the cavity formed by grooves of the first ring and the second ring a sliding of the rings in radial direction is avoided. This means that cone shifting is avoided as the member in the grooves of the bearing keeps the first ring and the second ring together in case of radial movement and/or radial forces acting on the bearing. Moreover, the invention is simpler than prior art solutions and easier to produce with larger tolerances. Moreover, the risk of fretting corrosion is low by having small areas of line contact under high surface pressure. 
         [0009]    The inventive bearing may comprise a rotation axis. The first portion may be located radially inside of the second portion or the second portion may be located radially inside of a first portion. 
         [0010]    Preferably the groove may have a rectangular or a tapered or an at least partly circular or an at least partly ellipsoid or an at least partly hypoellipsoid or an at least partly hyperellipsoid cross section. For example, the groove may have a half ellipsoid cross section. 
         [0011]    The at least one member placed in the groove may have a rectangular or a tapered or an at least partly circular or an at least partly ellipsoid or an at least partly hypoellipsoid or an at least partly hyperellipsoid cross section. In this way the at least one member fits into the space in the grooves of the first and the second ring and sliding of the rings in radial direction is avoided. 
         [0012]    Advantageously the at least one member placed in the groove comprises at least one segment, for instance a segment of a ring. This has the advantage, that the segments of the member can be easily placed in the groove. Moreover, a disassembly is very easy. 
         [0013]    Preferably, the at least one groove and/or the at least one member placed in the groove comprise at least one positive slip angle. Providing the member, which preferably comprises a number of segmented rings, and/or the grooves in the first ring and the second ring of the bearing with one or more positive slip angles an easy assembly of a segmented ring or member into the grooves can be ensured. 
         [0014]    Advantageously, the at least one member placed in the groove may have a cross sectional diameter of at least 5 mm, for example 8 mm. Furthermore, the at least one member placed in the groove may run all around the circumference of the groove except for a small gap to allow for tolerances. For example, the whole bearing may comprise a diameter size of e.g. 3000 mm or more and a width of e.g. 300 mm or more for a direct drive wind turbine. The wind turbine can be a 3 MW direct drive wind turbine. 
         [0015]    The first ring and the second ring may comprise one or more grooves where a segmented ring shaped member can be placed in each groove. For example, the grooves may comprise preferably a cross section of somewhere between a half and one third or even less of an ellipsoid and/or hypoellipsoid and/or hyperellipsoid. This gives an open groove in which it is easy to fit a segmented ring shaped member. 
         [0016]    Preferably, the at least one member placed in the groove may comprise or consist of at least one thread with a fracture elongation of at least 5%. Moreover, a bend double thread may be used. Advantageously the at least one member placed in the groove comprises brass and/or bronze and/or non-hardened steel and/or heat-treated steel. 
         [0017]    For example, the segmented ring shaped member may comprise only one segment. The segment may be made by using a thread of brass or bronze or soft non-hardened steel or heat-treated steel or similar materials with a fracture elongation of 5% or more and with a cross sectional diameter of e.g. 8 mm. Alternatively a bend double thread maybe used giving a cross sectional diameter of e.g. 2×8 mm lying next to each other. The grooves in the first ring and the second ring, which may be radially inner rings, can than e.g. comprise a hypoellipsoid cross section e.g. with a=10, b=7.85 and n=1.7 using the Lamé-curve formula 
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         [0018]    The member with for example a circular cross section may then be pressed into the two grooves in the inner rings giving a tight connection which may even be oil tight. In this way a further seal connection between the first ring and the second ring can be avoided. 
         [0019]    The at least one member placed in the groove may comprise two sides with a different tapering angle. Moreover, the at least one member placed in the groove may comprise a side with a tapering angle which is less than the tapering angle of the side of the groove facing the side of the member. By using tapered grooves even larger tolerances can be used by the production of the grooves and the members. 
         [0020]    For example, the rectangular segments of the member may comprise tapered end parts. Also here larger tolerances can be used by the production of the grooves and the segments of a member. For example, only one of the grooves may be tapered. Moreover, the members that are placed in the grooves may be tapered in one or both sides of the sides that fit into the grooves of the rings. This ensures a better fit to the grooves and larger tolerances can be used by the production of the members. Furthermore, one side or end of the members may comprise a different tapering angle than the other side or end of the member. The members may comprise a tapered angle that is less than a tapered angle of the grooves of the first ring and the second ring. 
         [0021]    The at least one member may preferably comprise segments with an arc angle between 5° and 180°, advantageously between 10° and 20°. The segments of the segmented ring may preferably comprise an arc angle of 10 to 20 degrees giving respectively 18 to 36 segments. Also an arc angle of 5 to 10 degrees may be possible or even an arc angle of the segments of more than 20 degrees may be used though preferably not more than 180 degrees. What arc angle to choose depends on the actual size of the segmented ring due to transportation issues and due to the time it takes to install the chosen number of segments. 
         [0022]    Moreover, the at least one member can comprise at least one plastic deformable area, for example at least one local plastic deformable area, and/or at least one protrusion, for example a plastic deformable protrusion. The at least one plastic deformable area and/or protrusion ensures that the member fits tightly to the grooves when the first ring and the second ring are pressed together by a given force. In this way larger tolerances can be used by the production of the members and the grooves. 
         [0023]    The segments of the segmented ring-shaped member may comprise a material having a fracture elongation of more than 5%. This ensures that the segments are local deformable. This may even ensure an oil tight connection between the first ring and the second ring and the segments of the member when the first ring and the second ring and a segmented ring-shaped member in the grooves are pressed together with a certain force. By ensuring an oil tight connection directly at the grooves ensures a larger area with a large friction between the inner rings which counteracts the radial sliding movement of the inner rings in relation to each other. 
         [0024]    The segmented ring-shaped member located inside the grooves of the first ring and the second ring of a bearing for avoiding cone shifting may also be used in other types of bearings having two or more rows of rollers, preferably tapered rollers, and/or balls and having two or more inner rings and one or more outer rings where one or more segmented rings are located inside the grooves of each pair of inner rings. If more than one outer ring is present one or more segmented rings may also be located inside the grooves of each pair of outer rings of the bearing. 
         [0025]    The inventive wind turbine comprises a double tapered bearing assembly as previously described. The inventive wind turbine can comprise a generator with a rotor or a stator. The rotor or the stator may be supported by the inventive double tapered bearing assembly. Generally, the inventive wind turbine may be a gearless direct drive wind turbine. The inventive wind turbine has the same advantages as the previously described bearing assembly. 
         [0026]    Further features, properties and advantages of the present invention will become clear from the following description of an embodiment in conjunction with the accompanying drawings. All described features are advantageous separate or in any combination with each other. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    Elements corresponding to elements of previously described figures will be designated with the same reference numerals and will not be described again in detail. 
           [0028]      FIG. 1  schematically shows part of a double tapered roller bearing in a sectional view. 
           [0029]      FIG. 2  schematically shows a wind turbine. 
           [0030]      FIG. 3  schematically shows a cross section of two grooves facing each other and a member placed in the groove. 
           [0031]      FIG. 4  schematically shows part of an inventive double tapered roller bearing in a sectional view. 
           [0032]      FIG. 5  schematically shows a variant of part of an inventive double tapered roller bearing in a sectional view. 
           [0033]      FIG. 6  schematically shows a member for placing into a cavity in a sectional and perspective view. 
           [0034]      FIG. 7  schematically shows a member for placing into a cavity in a sectional view. 
           [0035]      FIG. 8  schematically shows a further variant of a member in a sectional view. 
           [0036]      FIG. 9  schematically shows a further variant of a member in a sectional view. 
           [0037]      FIG. 10  schematically shows another variant of a member in a sectional view. 
           [0038]      FIG. 11  shows a ring segment is shown in a perspective and sectional view. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0039]      FIG. 1  schematically shows part of a known double tapered roller bearing  1  in a sectional view. The bearing  1  comprises a first portion  2  and a second portion  3 . The first portion  2  comprises a first ring  4  and a second ring  5 . Between the first ring  4  and the second portion  3  a first row of rollers  6  is located. Between the second ring  5  and the second portion  3  a second row of rollers  7  is located. The rotation axis of the bearing  1  is indicated by reference numeral  9 . 
         [0040]    Moreover, a spacer ring  8  is placed between the first ring  4  and the second ring  5 . The spacer ring  8  has an I-shape with a number of protrusions to avoid a radial movement of the first ring  4  and the second ring  5  relatively to each other. To effectively avoid a radial movement the rings  4 ,  5  and  8  have a diameter of high accuracy. 
         [0041]      FIG. 2  schematically shows a wind turbine  51 . The wind turbine  51  comprises a tower  52 , a nacelle  53  and a hub  54 . The nacelle  53  is located on top of the tower  52 . The hub  54  comprises a number of wind turbine blades  55 . The hub  54  is mounted to the nacelle  53 . Moreover, the hub  54  is pivot-mounted such that it is able to rotate about a rotation axis  59 . A generator  56  is located inside the nacelle  53  or the generator may be attached to a structure part of the nacelle in such a way that it is located on one end part of the nacelle and further attached to a rotor hub. The wind turbine  51  is a direct drive wind turbine. The generator  56  comprises a rotor and a stator and an inventive double tapered bearing, as previously described, supporting the rotor or the stator. 
         [0042]    An embodiment of the present invention will now be described with reference to  FIGS. 3 to 11 .  FIG. 3  schematically shows a cross section of two grooves facing each other and a member placed in the groove. Using the Lamé-curve formula 
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         [0043]    The curve  11  is obtained by choosing the parameters a=10, b=7.85 and n=1.7. The obtained hypoellipsoid cross section  11  represents the cross section of the cavity which is formed by a groove in the first ring and a groove in the second ring facing each other. The curve  12 , which has a circular shape, represents the cross section of a member placed in the groove. In  FIG. 3  the member placed in the groove has a cross sectional diameter of 16 mm. Of course, other cross section diameters can be used. 
         [0044]      FIG. 4  schematically shows part of an inventive double tapered roller bearing in a sectional view. In  FIG. 4  the first ring  4  comprises a first groove  15  and the second ring  5  comprises a second groove  25 . Each groove  15  and  25  has a rectangular cross section. The grooves  15  and  25  are facing each other forming the cavity with a rectangular cross section. A member  17  with a corresponding rectangular cross section is placed in the cavity. 
         [0045]    The first portion  2  comprises a hole  16  with a centre line  13  for fixation of the first ring  4  and the second ring  5  with each other. Moreover, a sealing means  14  is placed between the first ring  4  and the second ring  5  for providing a tight connection which may even be oil tight. In an alternative variant the sealing means  14  can be omitted. 
         [0046]      FIG. 5  schematically shows a variant of part of an inventive double tapered roller bearing in a sectional view. In  FIG. 5  the first ring  4  comprises a groove  35  with a first side  31  and a second side  32 . The second ring  5  comprises a groove  45  with a first side  41  and a second side  42 . The grooves  45  and  35  are facing each other. The first sides  31  and  41  are tapered in relating to the rotation axis  9 . The second sides  32  and  42  are also tapered in relation to the rotation axis  9 . The first sides  41  and  31  are tapered with a tapering angle which is less than the tapering angle of the second sides  32  and  42 . The tapering angle is defined as the angle between the particular side  31 ,  32 ,  41 ,  42  with respect to the rotation axis  9 . 
         [0047]      FIG. 6  schematically shows a member for placing into a cavity formed by the grooves between the first ring  4  and the second ring  5  in a sectional and perspective view. The member  27  shown in  FIG. 6  has a shape of a section of a ring. Its cross section comprises a first end  71 , a second end  72  and a first side  73  and a second side  74 . The centre line perpendicular to the rotation axis  9  is indicated by reference numeral  75 . The centre line  75  divides the first side  73  and the second side  74  into equal portions. The portions of the first side  73  and the second side  74  which adjoin to the first end  71  are tapered towards the first end  71 . The portions of the first side  73  and the second side  74  which adjoin to the second end  72  are tapered towards the second end  72 . Consequently the cross section of the member  27  has a double trapezoid shape. 
         [0048]    In  FIG. 6  the tapered portions  80  of the first side  73  are adjoining to each other. Also the tapered portions  80  of the second side  74  are adjoining each other. 
         [0049]      FIG. 7  schematically shows a member for placing into a cavity formed by the grooves of the first ring and the second ring in a sectional view. The cross section of the member  37  shown in  FIG. 7  has a rectangular shape. 
         [0050]      FIG. 8  schematically shows a further variant of a member in a sectional view. The member  47  shown in  FIG. 8  comprises a partly tapered first side  73  and a partly tapered second side  74 . The first side  73  and the second side  74  are tapered towards the second end  72 . 
         [0051]    In  FIG. 8  the first side  73  comprises a tapered portion  80  adjoining the second end  72  and adjoining a non-tapered portion  81  of the first side  73 . Also the second side  74  comprises a tapered portion  80  which adjoins to the second end  72 . The tapered portion  80  of the second side  74  adjoins a non-tapered portion  81  of the second side  74 . The non-tapered portions  81  of the first side  73  and of the second side  74  are adjoining the first end  71 . 
         [0052]      FIG. 9  schematically shows a further variant of a member in a sectional view. The member  57  shown in  FIG. 9  comprises a first side  73  and a second side  74 . Both sides  73  and  74  are partly tapered towards the first end  71  and partly tapered towards the second end  72 . In  FIG. 9  the first side  73  comprises a non-tapered area  81  in between a first tapered area  80  towards the first end  71  and a second tapered area  80  towards a second end  72 . Accordingly the second side  74  comprises a non-tapered area  81  in between a first tapered area  80  towards the first end  71  and a second tapered  80  area towards the second end  72 . 
         [0053]      FIG. 10  schematically shows another variant of a member in a sectional view. The member  67  which is shown in  FIG. 10  has a rectangular cross section. The first side  73  and the second side  74  each comprise a number of protrusions  66 . The protrusions  66  may be plastic deformable giving a better fit between the grooves in the first ring  4  and the second ring  5  and the member  67 . 
         [0054]    In  FIG. 11  a ring segment is shown in a perspective and sectional view. The member  77  in form of a bend ring segment has a circular cross section. It may have a cross sectional diameter of for example 8 mm. Instead of bending one ring segment as shown in  FIG. 11  two ring segments or members with circular cross section may be joined together, for example by means like glue, welding or similar means. 
         [0055]    Generally, the described members may comprise brass, bronze, soft non-hardened steel, heat-treated steel or a similar material with a fracture elongation of 5% or more. 
       REFERENCE LISTING 
       [0000]    
       
         
           
               1  double tapered roller bearing 
               2  first portion 
               3  second portion 
               4  first ring 
               5  second ring 
               6  first row of rollers 
               7  second row of rollers 
               8  spacer ring 
               9  rotation axis 
               10  double tapered roller bearing 
               11  cross section of the grooves 
               12  cross section of the member 
               13  centre line 
               14  sealing means 
               15  groove 
               16  hole for fixation 
               17  member 
               20  double tapered roller bearing 
               25  groove 
               27  member 
               31  first side 
               32  second side 
               35  groove 
               37  member 
               41  first side 
               42  second side 
               45  groove 
               47  member 
               51  wind turbine 
               52  tower 
               53  nacelle 
               54  hub 
               55  blade 
               56  generator 
               57  member 
               59  rotation axis 
               66  protrusions 
               67  member 
               71  first end 
               72  second end 
               73  first side 
               74  second side 
               75  centre line 
               77  member 
               80  tapered portion 
               81  non-tapered portion