Abstract:
A turbine has airfoils that are configured to extract work from a prevailing fluid flow. An actuator causes the airfoils to pivot or fold between a first position with their spans substantially normal to the flow direction and a second position with their spans substantially parallel to the flow direction, or any position in between. The variable geometry allows the airfoils to be sized for relatively light winds and to remain operational in relatively high winds without damage. Under extreme conditions the airfoils may be folded completely for safety.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Applications 61/189,950 entitled, “Fine Arts Innovations,” and filed Aug. 22, 2008, and 61/202,189 entitled “Folding Blade Turbine,” and filed Feb. 4, 2009, the disclosures of which are expressly incorporated herein by reference in their entireties. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    None. 
       NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
       [0003]    None. 
       BACKGROUND 
       [0004]    According to the U.S. Department of Energy, modern, wind-driven electricity generators were born in the late 1970&#39;s. See “20% Wind Energy by 2030,” U.S. Department of Energy, July 2008. Until the early 1970s, wind energy filled a small niche market supplying mechanical power for grinding grain and pumping water, as well as electricity for rural battery charging. With the exception of battery chargers and rare experiments with larger electricity-producing machines, the windmills of 1850 and even 1950 differed very little from the primitive devices from which they were derived. As of July 2008, wind energy provides approximately 1% of total U.S. electricity generation. 
         [0005]    As illustrated in  FIG. 1 , most modern wind turbines typically have 3-bladed rotors  10  with diameters of 10-80 meters mounted atop 60-80 meter towers  12 . The average turbine installed in the United States in 2006 can produce approximately 1.6 megawatts of electrical power. Turbine power output is controlled by rotating the blades  10  around their long axis to change the angle of attack (pitch) with respect to the relative wind as the blades spin around the rotor hub  11 . The turbine is pointed into the wind by rotating the nacelle  13  around the tower (yaw). Turbines are typically installed in arrays (farms) of 30-150 machines. A pitch controller (for blade pitch) regulates the power output and rotor speed to prevent overloading the structural components. Generally, a turbine will start producing power in winds of about 5.36 meters/second and reach maximum power output at about 12.52-13.41 meters/second (28-30 miles per hour). The turbine will pitch or feather the blades to stop power production and rotation at about 22.35 meters/second (50 miles per hour). 
         [0006]    In the 1980s, an approach of using low-cost parts from other industries produced machinery that usually worked, but was heavy, high-maintenance, and grid-unfriendly. Small-diameter machines were deployed in the California wind corridors, mostly in densely packed arrays that were not aesthetically pleasing in such a rural setting. These densely packed arrays also often blocked the wind from neighboring turbines, producing a great deal of turbulence for the downwind machines. Little was known about structural loads caused by turbulence, which led to the frequent and early failure of critical parts. Reliability and availability suffered as a result. 
       SUMMARY 
       [0007]    An objective of the invention is to provide an improved turbine capable of operating over a wide range of prevailing wind conditions and surviving storms. Further objects of the invention are: 
         [0008]    (i) to provide an improved turbine capable of controlled operation under mild as well as harsh (storm level) wind conditions up to hurricane strength; 
         [0009]    (ii) to provide an improved turbine with controllably-variable geometry; and 
         [0010]    (iii) to provide an improved turbine with blades that can be controllably folded to between a first position with their spans (lengths from root to tip) generally normal (at right angels) to the prevailing airflow under mild wind conditions and a second position with their spans generally parallel to the prevailing airflow under otherwise overpowering wind conditions. 
         [0011]    These and other objectives are achieved by providing an improved, axial-flow turbine with blades that are operable in a fully extended position with their spans oriented generally perpendicular to a prevailing airflow for relatively mild wind conditions. Blades may be folded to a closed position with their spans generally parallel to the prevailing airflow for relatively harsh wind conditions, such as open-ocean storms. An actuation mechanism controllably positions blades across the range from the extended position to partially- or fully-folded positions. The turbine preferably is operable with blades in the extended position and in partially and completely folded positions. 
         [0012]    The turbine utilizes a drive shaft for transferring torque from the blades to an electric generator or other energy-utilization device. A sliding shaft that is concentric with the drive shaft connects to a sliding hub and tie rods that control the degree of blade folding. The sliding shaft, sliding hub, and tie rods rotate with the blades so that the turbine remains operable with blades in folded positions. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0013]    Reference will be made to the following drawings, which illustrate preferred embodiments of the invention as contemplated by the inventor(s). 
           [0014]      FIG. 1  illustrates a prior art wind turbine. 
           [0015]      FIGS. 2   a  and  2   b  are rear and side views respectively of a folding-blade turbine generator with blades in the fully extended position. 
           [0016]      FIGS. 3   a  and  3   b  are rear and side views respectively of a folding-blade turbine with blades in the fully folded position. 
           [0017]      FIG. 4  is an exploded view of major assemblies of a folding-blade turbine. 
           [0018]      FIG. 5  is a partial sectional view of a turbine generator showing blades in the fully extended position. 
           [0019]      FIG. 6  is a partial sectional view of a turbine generator showing blades in the fully folded position. 
           [0020]      FIG. 7  is an exploded view of a drive assembly for a turbine generator. 
           [0021]      FIG. 8  is an exploded view of a sliding assembly for a turbine generator. 
           [0022]      FIG. 9  is a sectional view of a coupling between a sliding shaft and an actuator in a turbine generator. 
           [0023]      FIG. 10  is an exploded view of a turbine blade in a turbine generator. 
           [0024]      FIGS. 11A ,  11 B, and  11 C are side, front, and bottom views respectively of the turbine blade of  FIG. 10 . 
           [0025]      FIG. 12  is a cross sectional view of a rotor and stator of an electricity generator assembly for a turbine generator. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]      FIGS. 2   a  and  2   b  are rear and side views respectively of an exemplary, folding-blade turbine generator  20  with turbine blades  21  in the fully extended position. Blades  21  mount to a shaft (not shown) that is journeled within a nacelle  22 . The nacelle  22  mounts to a mast  23 , which in turn may be mounted to any of a variety of foundation structures. The mounting may allow the turbine generator to rotate in response to changing wind direction so that the turbine generator (e.g., axis of rotation of the blades) remains pointed along the direction of the prevailing wind. 
         [0027]    The turbine may be mounted in any location, but preferred foundations are marine structures, such as an oil drilling platform that has outlived its useful life, or a buoy that may also harvest wave power. Marine locations periodically experience extreme weather conditions such as gale force winds (39-54 mph or 63-87 km/h, sustained) and hurricanes (winds greater than 74 miles per hour, or 119 km/h, sustained). 
         [0028]    The turbine blades  21  include airfoils shaped to generate a torque about an axis of rotation  24  in the presence of a prevailing wind  25 . The turbine generator shown in  FIGS. 2   a  and  2   b  may be called an “axial-flow” turbine in that the blades are shaped to rotate when the direction of the prevailing wind  25  is aligned with the axis of rotation  24 . Preferably, the blades are shaped for nominal operation when positioned on the downwind side of the nacelle  22 . (The terms “forward” and “rearward” in this description refer to upwind and downwind directions respectively when the turbine generator is in this nominal operating position. For example, in normal operation, the blades  21  are “rearward” and “downwind” of the nacelle  22 . This designation is for convenience of description only and not intended to limit the scope of the invention.) In the fully extended position, the long axis of the blades along the airfoil span is in a normal direction (right angle) to the direction of the prevailing airflow. 
         [0029]      FIGS. 3A and 3B  are rear and side views respectively of an exemplary, folding-blade turbine generator  20  with turbine blades  21  in the fully folded position. Here, the long axis of the blades  21  are parallel to the axis of rotation, which also is the direction of the prevailing wind. Each blade  21  is pivotally mounted to a drive hub  30  that rotates with the blades  21 . Blades may pivot between extended and folded positions while rotating, as discussed more fully below. 
         [0030]      FIG. 4  is an exploded perspective view of major assemblies of the turbine generator  20  of  FIGS. 2A ,  2 B,  3 A, and  3 B. In addition to previously mentioned blades  21 , nacelle  22 , mast  23  and drive hub  30 , this figure illustrates drive shaft  40 , sliding shaft  41 , and sliding hub  42 . The blades  41  mount pivotally to drive hub  30 , which in turn is welded or otherwise affixed to drive shaft  40 . Drive shaft  40  in turn is journeled within nacelle  22 . 
         [0031]      FIG. 5  is a partial sectional view of an exemplary turbine generator  20  showing nacelle  22 , drive hub  30 , drive shaft  40 , sliding shaft  41 , and sliding hub  42  with blades  21  in the fully extended position. The sliding shaft  41  is longer than, and concentric with, drive shaft  40 . The sliding shaft extends beyond the drive shaft  40  in both the forward (upwind into nacelle  22 ) and rearward (downwind out of nacelle  22 ) directions. The sliding hub  42  attaches to the rearward end of sliding shaft  41  on the rearward (downwind) side of drive hub  30 . The forward end of sliding shaft  41  couples to an actuator (not shown), which is discussed further below. Tie rods  51  connect sliding hub  42  to blades  21 , as will be discussed in further detail below. A generator assembly  54  couples both to the nacelle  22  and to the drive shaft  41 , as also will be discussed in further detail below. A spring  53  mounts around the sliding shaft  41  between (i) a forward collar  55  fixed to the sliding shaft  53  near the sliding shaft forward end, and (ii) a seat  56  near the forward end of drive shaft  40 . An actuator  52  couples to the forward end of sliding shaft  53 , as will also be discussed further below. The actuator is of the linear type with a central shaft that extends and retracts along its long axis, which in the orientation of  FIG. 5  is coaxial with sliding shaft  53 . Shown with blades in the fully extended position, this figure shows the actuator  52  in a retracted position and sliding shaft  41  in a relatively forward position when compared with  FIG. 6 . The spring  53  is under relatively mild compression, which biases the sliding shaft forward against a thrust bearing  57  mounted to the rearward end of the actuator  52 . 
         [0032]      FIG. 6  is a partial sectional view of an exemplary turbine generator  20  showing blades  21  in the fully folded position. Here, actuator  52  is extended in the rearward direction, as are sliding shaft  41  and sliding hub  42  when compared to their positions in  FIG. 5 . Tie rods  51  are displaced rearward and inward. Blades  21  are pivoted about their drive-hub connections  60  to the folded position. Spring  53  is relatively highly compressed. Drive shaft  40  and drive hub  30  maintain the same axial position relative to those shown in  FIG. 5 . 
         [0033]      FIG. 7  is an exploded view of an exemplary drive assembly including drive shaft  40  and drive hub  30  as mentioned previously. Drive hub  30  includes a station for each blade (not shown). An exemplary station has mounting holes  70  for pivot pins  71 . Each pivot pin  71  passes through a mounting structure on a blade (not shown) and holds a blade pivotally in its station, while rings  72  hold pivot pins in the drive hub  30 . Bush rings  73  hold forward and rearward bearings  74  for concentric sliding shaft (not shown). Retaining rings  75   a ,  75   b  engage with the generator assembly ( FIG. 5 , item  54 ) or other fixed structure to limit axial movement of the drive shaft  40 . Slots  76  in the drive shaft  40  are provided to receive keys ( FIG. 12 , items  125 ) that lock the drive shaft  40  to the rotor of an electric generator (not shown), as discussed further below. Screws  77  rotationally couple the drive shaft  40  to siding shaft (not shown) while allowing the sliding shaft to move axially relative to the drive shaft  40 . 
         [0034]      FIG. 8  is an exploded view of an exemplary sliding assembly including sliding shaft  41 , sliding hub  42 , spring  53  and forward collar  55 ′ as mentioned previously. Sliding shaft  41  bears an axial groove  84  into which extend screws ( FIG. 7 , items  77 ) of the drive shaft assembly, as will be discussed further below. Sliding hub  42  includes stations for each tie rod (not shown) with mounting holes  80  for tie-rod pins  81 . Each tie-rod pin  81  passes through a corresponding hole in a tie rod and holds a tie rod pivotally in its station, while rings  82  hold tie-rod pins in the sliding hub  42 . 
         [0035]      FIG. 9  is a sectional view of an exemplary coupling between sliding shaft  41  and actuator  52 . A bolt  91  and cap  92  hold thrust bearing  94  to the actuator  52 . Retaining ring  95  holds push plate  93  in place on actuator  52 . The forward end of sliding shaft  41  seats in a beveled recess in the rear of the push plate  93 . 
         [0036]      FIG. 10  is an exploded view of an exemplary turbine blade  21 , while  FIGS. 11A ,  11 B, and  11 C are side, front, and bottom views of the turbine blade of  FIG. 10 . Complementary clamp plates  100  attach to one another through front and back surfaces of the root of an airfoil  101 . One of the clamp plates bears a hollow cylindrical sleeve  102 , which has its axis aligned along the airfoil span. Set screws  103   a  passing through weld nuts  103   b  attached on the exterior of cylindrical sleeve  102  hold a grooved cylindrical post  104  within the cylindrical sleeve  102 . Short lengths of the post  104  are partially drilled out (or were cast to have a central void) along the central axis near the ends. A portion of the post  104  extends beyond the root of the airfoil  101 , and radially through that portion runs a first set of mounting holes used to couple the blade to the drive hub. A blade pin ( FIG. 7 , item  71 ) passing through the first set of mounting holes and seated in the drive hub ( FIG. 5 , item  30 ) couples blades to the drive hub. The opposite end of the post  104  has a second set of radial holes used to couple the blade to a tie rod (not shown). A tie-rod pin  105  passing through a tie rod ( FIG. 5 , item  51 ) and seated in the second set of mounting holes couples blades to tie rods. This arrangement is by way of example only, and other arrangements for mounting blades may be used. 
         [0037]      FIG. 12  illustrates an exemplary generator assembly  54 , which was mentioned above in connection with  FIG. 5 . The generator assembly  54  includes a rotor  121  and a stator  122 . The rotor  121  preferably includes permanent magnets or electromagnets, while the stator  122  preferably includes electrically conductive coils. The stator  122  is fixed relative to the nacelle  22  while the rotor  121  rotates about a central axis  123 . When assembled, retaining rings  75   a  hold bearings  124  in the alternator housing support and allow rotation of the drive shaft (not shown) about the central axis  123 . Keys  125  in the rotor  121  mate with slots in the drive shaft ( FIG. 7 , item  76 ) in order to transfer rotational power for generating electricity. Air gap plugs  125  expose a view port for inspecting alignment of the rotor  121  and stator  122 . 
         [0038]    An exemplary turbine may have 7 blades approximately 51 inches in length, tie rods approximately 9 inches in length, a sliding shaft approximately 28 inches in length, a drive shaft approximately 12 inches in length, a stepper-motor actuator model number D-B.125-HT23-8-2N0-TSS/4 with an eight-inch stroke made by Ultra Motion of Cutchogue, N.Y., and an alternator assemble model number 300STK4M made by Alxion Automatique of Colombes, France. This example is not meant to be limiting of the invention, which may be scaled and adapted for a wide variety of wind resources and applications. For larger-scale machines, the actuator  52  may be hydraulic or pneumatic. The Ultra Motion actuator mentioned above has adjustable sensors indicating stop positions at the full open and full closed positions. Additional sensors, or alternate actuators, may be used to provide an electronic measure of shaft position, which in turn is a measure of blade fold angle. 
         [0039]    It is believed that operation of the exemplary, folding-blade turbine generator  20  is self-evident from the structure and description above; nevertheless, several observations will be made here to facilitate understanding. 
         [0040]      FIG. 5  illustrates a turbine generator with blades  21  in the fully-extended position. Nominally, the nacelle  22  and blades  21  would be oriented so that the direction of a prevailing airflow  25  is generally parallel to the blade rotational axis, which is the rotational axis of the sliding shaft  41  and drive shaft  40 . The blades  21  preferably will be on the downwind of the nacelle  22 . The aerodynamic shape of the blades  21  causes them to generate a torque about the rotational axis, which in turn rotates the drive hub  30 , drive shaft  40 , and rotor  121 . The rotating fields of the rotor magnets induce electric currents in the coils of the stator  122 . 
         [0041]    The blades preferably are shaped to be efficient at extracting energy from winds typically blowing at the installation site. The spring  53  preferably is sized to hold the blades  21  in the open position for winds up to a maximum nominal speed corresponding to the turbine generator rated operating speed. In more detail, the spring  53  biases the sliding shaft  41  forward, which in turn biases the sliding hub  42  forward and biases the tie rods  51  outwards. As wind speeds exceed the maximum nominal speed, the axial aerodynamic load on the blades  21  overcomes the force of the spring  53 , and the blades will fold. The folding of blades  21  alters the overall geometry of the turbine. As can be seen by comparing  FIGS. 2   a  and  3   a , the folding of blades  21  reduces the turbine&#39;s exposed cross-section. This folding reduces the area of blades  21  exposed to the wind, which in turn reduces the aerodynamic loading to a point that balances the force of the spring  53 . Hydraulic damping may be provided to minimize oscillation. In partially- or fully-folded positions, the blades  21  may continue to absorb energy from the prevailing wind and hence maintain operation. The sliding shaft  41  continues to rotate because screws ( FIG. 7 , item  77 ) riding in the slot ( FIG. 8 , item  84 ) of the sliding shaft  41  continue to lock the sliding shaft  41  rotationally to the drive shaft  40 . The turbine airfoils may be shaped with relatively high exposed areas for operation at relatively low winds, and they can be folded to maintain a rated level of power extraction at high winds without being overpowered or damaged. 
         [0042]    The actuator  52  may also be used to fold the blades from the fully-extended position toward the fully-folded position as shown in  FIG. 6 , or any position in between. In more detail, extension of actuator  52  displaces sliding shaft  41  rearward. Rearward displacement of the sliding shaft  41  moves sliding hub  42  rearward. Tie rods  51  in turn pull the posts ( FIG. 10 , item  104 ) of the blades  21  rearward and downward, which pivots the blades  21  about their mounting points  60  in the drive hub  30  toward the folded position. Rearward displacement of the sliding rod  41  also compresses the spring  53 . 
         [0043]    The actuator  52  may be controlled in a variety of modes. In a first mode, the actuator  52  may be operated manually to set the blades at a desired fold angle. This mode is desirable for maintenance, transport, and diagnostic operation. In a second mode, the turbine generator may monitor rotational speed of the rotating shaft and fold the blades to prevent unsafe operation, such as overspeed. Other safety parameters may be monitored, such as alternator temperature or electrical output level. 
         [0044]    The embodiments described above are intended to be illustrative but not limiting. Various modifications may be made without departing from the scope of the invention. The breadth and scope of the invention should not be limited by the description above, but should be defined only in accordance with the following claims and their equivalents.