Abstract:
A self-acting variable pitch vertical axis wind turbine is provided with asymmetrically mounted blade paddles rotatably mounted for limited movement such that at one limit of the rotation, a paddle is operational to rotate the impeller and at the other limit of the rotation the paddle feathers.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is related to the field of self-acting variable pitch vertical axis wind turbines, and is more particularly directed to such turbines employed for generating power. 
       BACKGROUND OF THE INVENTION 
       [0002]    Self-acting variable pitch vertical axis wind turbines (SAVPVAWTs) are known and have been developed to compensate for wind direction variations to the extent that approximately constant and predicable performance may be achieved with improved efficiency. 
         [0003]    For example US Patent Application Publication No. 20070014658 to Mollinger describes a windmill provided with a vertical shaft from which radially extend four arms at right angles to each other, each of the four arms having attached thereto a variable pitch, flat three section blade mounted on a vertical axis and a booster curtain within a structural frame located next to the blade. The pitch of the blade is changed by a variable-speed electric motor and the booster curtain is opened or closed by a bi-directional electric motor, the speed and the direction of the electric motors being controlled by a weather vane so as to maintain maximum torque on the vertical shaft from wind blowing from any horizontal direction. As will readily be appreciated, the cost and complexity of such equipment with concomitant maintenance requirements render it of doubtful commercial viability. 
         [0004]    Accordingly, there is a need for a simpler improved SAPVAWT. 
       SUMMARY OF THE INVENTION 
       [0005]    It is therefore a general object of the present invention to provide an improved self-acting variable pitch vertical axis wind turbine. 
         [0006]    A further object of the present invention is to provide a simple mechanical means of effecting a variation in turbine blade pitch without the need for external and power consumptive actuation. 
         [0007]    A still further object of the present invention is to provide a SAVPVAWT coupled to a generator for generating electrical power. 
         [0008]    According to the present invention there is provided a self-acting variable pitch vertical axis wind turbine which comprises:
       a fixed mounting base defining a centrally positioned bore;   a fixed shaft extending through and secured within the bore;   an electric power generator associated with the fixed shaft and including a rotor rotating about a turbine axis and a stator mounting on the fixed shaft; and   a plurality of blades each having a paddle asymmetrically carried by a spindle, the spindle rotatably mounting on the rotor about a spindle axis.       
 
         [0013]    In one embodiment, the rotor is formed of a split casing including two complementary top and bottom halves, the stator is enclosed within the split casing of the rotor, and the wind turbine further includes:
       blade mounting for each said blade and formed on the split casing of the rotor, each mounting defining a generally hemi-cylindrical cavity; and   each said spindle carrying thereon a generally quadrant-shaped cam for reception within said cavity and for rotational movement therewithin, the range of relative rotational movement of the blade spindle being limited by the cam and the cavity of the mounting.       
 
         [0016]    In one embodiment, each paddle defines a paddle plane and each blade is rotatable about the respective spindle axis between first and second blade position, with the paddle plane being substantially parallel to the turbine axis when in the first blade position and with the paddle plane being substantially perpendicular to the turbine axis when in the second blade position. The first and second blade positions being typically limited by the rotational displacement of the cam within the cavity of the mounting. 
         [0017]    The fixed shaft may conveniently be hollow and one or more power take-off cables may be accommodated therein for conveying electrical power to a load, for example a light bulb, radio receiver or any other appropriate appliance. 
         [0018]    The stator may be of any convenient and conventional construction and of a size to be fitted within the casing of the rotor. 
         [0019]    The split casing of the rotor is in two halves and each half in combination constitutes the commutator of the generator, whereby rotation of the rotor in use generates power within the windings of the stator and that power is fed to a load by the cable(s) as aforesaid. The rotor casing is mounted on the shaft for rotation thereabout and a ball bearing race is provided for that purpose on either side of the stator. 
         [0020]    Each half of the split casing is provided with for example four mating halves of blade mountings, each mounting advantageously being of aerodynamic shape and orientation. In one embodiment of the present invention, four such mountings are provided equidistantly spaced about the circumference of the casing and each mates with its corresponding half such that the spindle of a blade is held therewithin in rotatable manner, the angular range of such rotation being limited as indicated supra. In this latter respect, the quadrant-shaped cam in use moves within the hemi-cylindrical cavity, thus giving a 90° range of movement. The two halves of the rotor casing are secured one to the other by suitable fixtures, such as screws or nuts and bolts. 
         [0021]    The blade paddles are asymmetrically mounted on a respective spindle such that the centre of gravity of each blade is offset from the mid-point of the paddle for a purpose to be hereinafter described. Each spindle may advantageously be mounted in at least one ball bearing race. 
         [0022]    The blade paddles may be of generally rectangular form or may in the alternative be curved or may be provided with surface embellishments such as in relief or intaglio. Further the paddles may be of shapes representative of different interests such as sport, nature, politics and/or may be adorned with slogans or advertising material in general. 
         [0023]    Other objects and advantages of the present invention will become apparent from a careful reading of the detailed description provided herein, with appropriate reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    Other objects and advantages of the present invention will become apparent from a careful reading of the detailed description provided herein, with appropriate reference to the accompanying drawings, in which similar references used in different Figures denote similar components, and wherein: 
           [0025]      FIG. 1  is an external perspective view of a self-acting variable pitch vertical axis wind turbine (SAVPVAWT) in accordance with an embodiment of the present invention; 
           [0026]      FIG. 2  is a perspective exploded view of the embodiment of  FIG. 1 ; 
           [0027]      FIG. 3  is a perspective scrap view of a blade spindle; 
           [0028]      FIG. 3   a  is a similar view to that of  FIG. 3  with ball bearing races indicated in ghosted outline; 
           [0029]      FIG. 4  is a schematic cross sectional view of a blade mounting (not to scale relative to the blade paddle) taken along line  4 - 4  of  FIG. 1 ; and 
           [0030]      FIGS. 4   a  and  4   b  are schematic cross sectional views of a blade mounting (not to scale relative to the blade paddle) taken along line  4 - 4  of  FIG. 1  showing different operational orientations of the blade paddles. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    With reference to the annexed drawings the preferred embodiment of the present invention will be herein described for indicative purpose and by no means as of limitation. 
         [0032]    Now referring to  FIGS. 1 and 2 , a self-acting variable pitch vertical axis wind turbine in accordance with an embodiment 1 of the present invention (hereinafter referred to as a ‘SAVPVAWT’) comprises a fixed mounting base  2  shown bolted to a stand, for example a pylon  4 . The SAVPVAWT has a rotatable impeller generally indicated by the reference number  6  mounted on the base  2 , the impeller  6  having five substantially planar blade paddles  8 , defining respective paddle planes, generally equi-spaced circumferentially thereof and extending from a hub  10  housing an electric generator  12  with power delivery cables  13  extending therefrom. 
         [0033]    The generator  12  comprises a stator  14  and a rotor  16 , which latter consists of a split casing  18  having an upper half and a complementary lower half  20 ,  22  respectively. The stator  14  and the rotor  16 , rotating about a generally vertical turbine axis  17 , are provided with appropriate windings (not shown) in conventional manner. 
         [0034]    A hollow fixed mounting shaft  24  accommodates the cables  13  and is secured within a central bore  26  formed in the base  2 , the shaft and the base being fixed such for example by a set screw (not shown). The stator  14  is rigid with the shaft  24 , the stator being enclosed within the two halves  20 ,  22  of the casing  18  of the rotor  16 . The casing halves  20 ,  22  are secured together by suitable fixtures (not shown). 
         [0035]    Each half  20 ,  22  of the rotor casing  18  is provided externally thereof with five blade mountings  30  spaced apart equally about the periphery thereof and are aerodynamically contoured from the periphery towards the centre of the hub  10 . At the end of each mounting  30 , remote from the centre of the hub  10  at the periphery thereof, there is defined a clamping region  32  (see  FIG. 4 ) for a spindle  34  of each blade paddle  8 , the clamping region  32  being located between the casing halves  20 ,  22 . Each clamping region  32  has a hemi-cylindrical cavity  36  within which locates a quadrant-shaped cam  38  (see  FIG. 3 ) mounted on the spindle  34 , the range of free rotational movement as between the cam  38  and thus the spindle  34 , and the cavity  36  being substantially 90° about a spindle axis  35  being substantially perpendicular to the turbine axis  17 . It will be understood that the clamping region  32  serves to locate and hold the respective spindle  34  in relation to the casing halves  20 ,  22 , but allowing the rotational movement described. In order to ensure a free displacement of the spindle  34  and cam  38  within the respective cavity  36 , ball bearing races  40  or the like, indicated in ghosted outline in  FIG. 3   a , could be provided between the spindle  34  and the casing halves  20 ,  22 . 
         [0036]    Each blade paddle  8  is of generally rectangular shape and is asymmetrically fixed to its respective spindle  34  as can clearly be seen from  FIGS. 1 and 2 , such that its centre of gravity X, represented as the center of gravity of its cross-section (because of the generally rectangular shape), generally falls on the longer part of the side of attachment to the spindle  34  as shown in  FIG. 4 . 
         [0037]    In use, the SAVPVAWT is located on the pylon  4  in an appropriate site to take advantage of the wind element. The wind turns the impeller  6  and electrical power is generated by the generator  12  with electricity being delivered by the cables  13  to a load (not shown). The mode of operation of the present invention is as follows. 
         [0038]    With the wind direction as indicated by arrows A in  FIG. 4   a , the blade paddle  8  with its centre of gravity X as shown assumes a first blade position in a generally vertical alignment, with the paddle plane generally parallel to the turbine axis  17 , and takes the full force of the wind, the impeller  6  thus turning in the direction of arrow B. The blade paddle  8  therefore is self-acting and its pitch is automatically selected by dint of its asymmetry. As the impeller  6  rotates this blade paddle  8  moves around and takes less, of the wind force and accordingly can automatically feather in a second blade position, with the paddle plane generally perpendicular to the turbine axis  17 , with its orientation shown in  FIG. 4   b : again the pitch is variable in a self-acting manner in that the hemi-cylindrical cavity  36  and the cam  38  define its range of rotational movement about the centre line of the spindle  34 , limiting it to 90°. In  FIG. 4   b  the blade paddle  8  is shown horizontal and accordingly the paddle feathers with little or no adverse effect upon the rotation of the impeller  6 . 
         [0039]    It will be understood that the surface area of each paddle and the location of its centre of gravity are important parameters in terms of how and when the paddle moves in response to the torque and/or the desired rotational speed. 
         [0040]    Although the blade paddles  8  have been described in the specific embodiment as being planar, their shape and surface embellishment may be different and may be customized, provided that the required asymmetry and rotational capability are maintained. 
         [0041]    Although the present invention has been described with a certain degree of particularity, it is to be understood that the disclosure has been made by way of example only and that the present invention is not limited to the features of the embodiments described and illustrated herein, but includes all variations and modifications within the scope and spirit of the invention as hereinafter claimed.