Abstract:
An assembly of rotor blades and hub for a turbine, such as a tidal current turbine. Each rotor blade includes a cavity and at least two ribs extending into the cavity at a radially inward (lower) region of the rotor blade. The hub includes a journal for each blade and the journal extends into the cavity and is supported by the at least two ribs.

Description:
RELATED APPLICATION 
     This is a U.S. National Phase of PCT/EP2013/000125 filed 17 Jan. 2013, which designated the U.S and claims priority to Austrian application no. A 62/2012 filed 20 Jan. 2012, the entirety of each of these applications are incorporated by reference. 
     BACKGROUND AND SUMMARY OF INVENTION 
     The present invention relates to a rotor blade for a turbine, where the rotor blade ( 1 ) has a cavity ( 10 ). Turbines of this type include wind turbines, ocean current turbines, and tidal current turbines. 
     At the base, i.e. at the connection to the turbine hub, the rotor blades are exposed to very high torques, which requires very large and expensive flanged connections, also in order to guarantee the necessary stiffness. Flange connections of this kind are known from WO 2010/084320 A2 or WO 2011/077454, for example. Thus, the contour of the blade must also be adapted to these geometrical dimensions and cannot be optimized for energy generation. In addition, there are blades or vanes that are cast or welded onto the hub, such as the ship&#39;s propeller in U.S. Pat. No. 3,310,116. In addition, WO 2002/42638 A1 shows a turbine blade with an internal cavity, where the blade is made up of two halves, and one half is provided with stays or ribs. There is no connection between the journal and these ribs. 
     The invention is thus characterized in that the rotor blade has a cavity and at least two ribs at its lower end, where a journal is provided for connecting to the hub of a turbine rotor that is inserted through an exactly fitting opening in the bottommost rib into the lower end of the rotor blade and reaches as far as the topmost rib, where it is inserted into a recess, and which is form-locked and/or force-locked with the ribs, where the journal has at least one cone or ledge and is connected to it with a rib in a force-locked connection. The blade thus has adequate stability, ever if the lower end has a smaller diameter, where the proportion of the total length of the rotor blade used for energy generation can be increased substantially. As a result of the firm connection between journal and rotor blade, torques can also be transferred effectively in addition to bending moments. 
     A favorable embodiment of the invention is characterized in that the blade is made of steel. The blade can be made much smaller as a result. It may be welded out of sheet steel, however the base can also he a casting should the situation arise. 
     A favorable development of the invention is characterized in that the journal is connected to at least one rib by means of at least one bolt disposed in axial direction, where it can also be connected to at least one rib by means of a bolt disposed in radial direction or a pin, respectively. 
     An alternative embodiment of the invention is characterized in that the journal has another cone or ledge inclined in the opposite direction to the first cone or ledge. As a result, the forces acting on the blade can be transferred favorably to the journal and, subsequently, to the hub. 
     If, preferably, a retaining ring is provided that can be joined in a form-locked connection to the other cone or ledge, the blade can be secured in place easily and the forces transferred. 
     A development according to the invention is characterized in that tie rods connected to at least one rib are provided. In this way, the fastening devices can be pre-assembled easily, resulting in shorter assembly times on site. It is especially favorable if the journal is joined to the at least two ribs in a force-locked connection by pre-stressing the tie rods. 
     As an alternative, the journal can end in a twin-fit with the at least two ribs, and be held in place in a form-locked and force-locked connection by means of a clamping ring. 
     The invention also relates to a turbine, especially a tidal current turbine with at least two, preferably three, rotor blades set up as described above. A stable rotor blade is needed especially for tidal current turbines, where the rotor blade according to the invention has the advantage of good conversion of energy within a very small space. Several blades may also be provided. The steel design, in particular, provides a compact and stable construction for tidal current turbines or run-of-river turbines. 
    
    
     
       SUMMARY OF THE DRAWINGS 
       The invention is now described on the basis of examples shown in the drawings, where: 
         FIG. 1  shows an arrangement for a turbine according to the invention, 
         FIG. 2  shows the connection of a blade to the shaft, 
         FIG. 3  shows a first variant for the connection between the journal and the blade, 
         FIG. 4  shows another variant for the connection between the journal and the blade, 
         FIG. 5  shows another variant according to the invention for the connection between the journal and the blade, 
         FIGS. 6   a, b, c  show assembly of the journal according to the variant in  FIG. 5 . 
         FIG. 6 d    shows a variant of the embodiment according to  FIGS. 6   a, b, c , and 
         FIG. 7  shows another variant according to the invention for the connection between journal and blade. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an arrangement for a turbine as is used to utilize energy from tidal currents. This turbine has, for example, three rotor blades  1 , which are connected to the shaft  5  via hub  4 . However, two, four, or more blades can also be used. 
       FIG. 2  shows how a rotor blade  1  is connected to the shaft  5 . Here, the journal  2  of the rotor blade  1  is secured via a bearing or other fastening  3  in the hub  4 , which is connected permanently to the shaft. Here, devices may be provided that can be used to rotate the rotor blade in the current for optimum energy generation. 
       FIG. 3  now shows a variant according to the invention of the connection between the journal  2  and the rotor blade  1 . The lower end  31  of the rotor blade  1  contains power transmission elements, which are shaped as ribs  32 ,  32 ′, in the cavity  10 . The journal  2  is inserted through an exactly fitting opening  33  in the bottommost rib  32  into the lower end  31  of the rotor blade  1  and reaches as far as the topmost rib  32 ′, where it is inserted into a recess  34 . Other ribs each with openings analogous to opening  33  can be disposed between the bottommost rib  32  and the topmost rib  32 ′. The journal  2  also has a limit stop  35 , which ends flush with the bottommost rib  32  on the outside as soon as the journal  2  has been fully inserted into the recess  34 . A bolt  37  is inserted through an opening  36  in the lower end  31  of the rotor blade and secured in the axle of the journal  2 . Several bolts disposed in axial direction can also be inserted, e.g. arranged in a kind of bolt circle. As a result, the bottommost rib  32  and the topmost rib  32 ′ are clamped together and, in this way, can effectively transfer the forces occurring, especially the torsional forces. 
       FIG. 4  shows an arrangement of a rotor blade  1  analogous to  FIG. 3 , where power transmission elements shaped as ribs  42 ,  42 ′ are located in the cavity  10  in the lower end  41  of the rotor blade  1 . The journal  2  is inserted through an exactly fitting opening  43  in the bottommost rib  42  into the lower end  41  of the rotor blade  1  and extends as far as the topmost rib  42 ′, where it is inserted through an opening  44 . Other ribs each with openings analogous to opening  43  can also be disposed here between the bottommost rib  42  and the topmost rib  42 ′. The journal  2  also has a limit stop  45  that ends flush with the bottommost rib  42  on the outside as soon as the journal  2  extends through the opening  44  in the topmost rib  42 ′. A stud bolt  47  is inserted through one or several holes  46  distributed round the circumference in the lower end of the rotor blade  1  and screwed tight in the journal  2 . Of course, it would also be possible to insert several stud bolts  47  distributed around the circumference. As a result, the bending moments and torques can be transferred effectively. 
       FIG. 5  shows another variant according to the invention of the connection between the journal  2  and the rotor blade  1 . Here, too, there are power transmission elements shaped as ribs  52 ,  52 ′ in the lower end  51  in the cavity  10  of the rotor blade  1 , where additional ribs can also be inserted. The journal  2  has two cone-shaped areas  56  and  58  here. The top area  56  of the journal  2  fits exactly into the likewise conical opening  54  in the topmost rib  52 ′ here. The lower cone-shaped area  58  of the journal  2  is also adapted to the likewise conical retaining ring  55 , which is fitted into the opening  53  of the bottom rib  52 , where a joint can be provided between retaining ring  55  and opening  53  to facilitate assembly work. The retaining ring  55  is now pressed against the top rib  52 ′ by means of tie rods  57 . It is an advantage if the top conical area  56  of the journal  2  has a flat angle so that it is self-locking and can absorb the torques and axial forces occurring. The lower conical area  58  of the journal  2  advantageously has a steep angle, which makes disassembly easier. With this fastening variant, the journal can be manufactured at low cost, and there are also no notches of any kind creating weak spots, e.g. feather keyways or transverse holes. The force can he transmitted to the rotor blade  1  through at least two ribs  52 ,  52 ′, and this makes a leaner blade structure possible. 
       FIGS. 6 a , 6 b , and 6 c    now show the assembly process for a connection according to the invention between journal  2  and rotor blade  1  as shown in  FIG. 5 . First of all, a one-piece retaining ring  65  is pushed onto a journal  2  with an upper conical area  66  and lower conical area  68 , and then the journal bearing  3  is mounted. ( FIG. 6 a   ) 
     On the other side, tie rods  67  are pre-assembled in the top rib  62 ′ of the rotor blade  1 . Subsequently, the journal  2  pre-assembled with the retaining ring  65  is inserted through the opening  63  in the bottommost rib  62  until its top conical area  66  latches into place towards the cavity  10  in the opening  64  in the topmost rib  62 ′. ( FIG. 6 b   ) 
     Subsequently, the tie rods  67  push the retaining ring  65  until it latches into the opening  63  in the bottommost rib  62  and is resting on the lower conical part  68  of the journal  2 . After this, the retaining ring  65  is bolted to the tie rods  67  via nuts  69  and, as a result, the two conical areas  66 ,  68  of the journal  2  are clamped to the bottommost rib  62  and the topmost rib  62 ′ such that power transmission is achieved free of clearance. ( FIG. 6 c   ) 
       FIG. 6 d    now shows a variant of the embodiment according to  FIGS. 6 a , 6 b , 6 c   . Instead of an upper and lower conical area, one ledge each  66 ′ and  68 ′, respectively, i.e. a step, is provided here, where the journal  2  between the two ledges  66 ′ and  68 ′ has a larger diameter than the remaining journal shaft and is joined to the ribs  62 ,  62 ′ of the blade  1  in a force-locked connection by means of the tie rods  67 . 
       FIG. 7  now shows another variant of a connection according to the invention between journal  2  and rotor blade  1 , where two ribs  72 ,  72 ′ are again shown at the lower end  71  of the rotor blade, whereby several ribs could also be provided here. The bottommost rib  72  here has a flange  76 , which forms an opening  73  for the journal  2 . The outermost rib  72 ′ has an opening  74  for the journal  2 . 
     In addition, the limit stop  75  of the journal  2  also has a flange-like edge. A clamping ring  77 , which is one-piece, but can also be two-piece, is now mounted round the two flanges. This likewise joins the journal  2  to the rotor blade  1  in such a way that it can effectively absorb the torques and axial forces arising.