Abstract:
A wind turbine electrical generating device is described where the blades that comprise the airfoil are retractable during operation. This feature allows for a number of improvements over the current state of the art including damage protection and the ability to remain operational during high wind conditions. Further described is a computer feedback loop that controls the degree of retraction. In addition, lightweight airfoil turbine blades are described that are assembled from discrete segments.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority of U.S. provisional applications 61/204,747 filed on Jan. 8, 2009 and 61/216,907 filed on May 22, 2009. both of which are incorporated by reference herein in their entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    Both horizontal and vertical axis wind turbines have been developed that display high efficiencies in converting wind power into electrical power. However there are several issues that are still being addressed to further improve performance in these devices. This invention addresses many of these issues including the ability to self start and the ability to continue operation in a high wind state in addition to improving the overall efficiency of the device. In addition, low cost manufacturing improvements and light weight methods are utilized to improve efficiency by design. 
         [0004]    One limitation of wind turbines is often an effective way of protecting the device during periods of very high wind speed. Various braking devices and spoilers have been utilized to prevent harm to the turbine although they typically also take the turbine off-line resulting in a loss of production when the available power is the greatest. An embodiment of this invention utilizes an electronic feedback loop to partially collapse a vertical or horizontal wind turbine if the torque on the main shaft that turns the generator is above a critical level to keep a balance between wind speed and rated power output. 
         [0005]    Wind turbines cannot typically handle the stresses induced by very strong winds and so braking systems are used to stop blade rotation and avoid damage. Alternatively, methods to collapse blades such as that described by Yum in U.S. Pat. No. 4,624,624 in which a hinged structure folds in automatically during high winds or that described by Traudt in U.S. Pat. No. 4,632,637 in which spring biased control mechanism folds blades out of harms way have been developed. In U.S. Pat. No. 4,818,181 Kodric teaches a spring that allows the wind turbine to move to a neutral position during strong winds. International publication WO 2008/104060 A1 describes a wind turbine where blades are collapsible on hinged support arms, but the retracted mode is for transport and erection and is not regulated by wind speed. 
         [0006]    Methods have also been developed to actively control configurable wind turbine blades to account for different wind speeds. In U.S. Pat. No. 6,940,186 Weitkamp controls blades based on load feedback received from sensors mounted on the rotor blades and in U.S. Pat. No. 6,769,873 Beauchamp et al. configures wind turbine blades through actuators based on sensors measuring wind conditions. The present invention allows for the blades to collapse together based upon the rotating shaft torque feedback and continue to operate and generate power. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    It is an object of this invention to provide for a wind turbine electrical generating device where the blades that comprise the airfoil are collapsible during operation. This feature allows for a number of improvements over the current state of the art. Having a collapsible feature protects the turbine from damage during very heavy wind conditions, and even can keep the turbine operational to reap the power benefits of high winds. Collapsibility also enables portability by allowing for a compact device when completely retracted. Control over the retraction mechanism can be via a computer controlled feedback loop, or by mechanical means that automatically react to wind speed variations. 
         [0008]    To enable maximum portability and light yet strong construction, the airfoil blades of the collapsible wind turbines are constructed from attached segments. In an embodiment of this invention, hollow airfoil segments are connected and built up into a large airfoil. These segments could be made of moldable plastic or wrapped with thin metal or plastic airfoils over injection molded or cast metal airfoil spacers. In another embodiment, the segments are molded spars made of a polymer or metal and utilize an outer polymer, spray coated epoxy or urethane or PVC cloth cover to create an airfoil profile shape. In another embodiment, wing tips at the ends of the blades of vertical or horizontal wind turbines are used to prevent roll off for better efficiency and reduced noise. 
         [0009]    It is another object of this invention that airfoil blade segments are connected via a swivel joint such that the through cables can allow the blade to flex in high winds without stressing the interface between segments. In another embodiment, the interface is shaped to provide an arc in the airfoil to allow the shape of the molded sail foils to create a C-shaped profile that can flex in the wind without the stresses of flat mating surfaces. In another embodiment of this invention, the stacking airfoil segments have mating interlocking male and female end caps to provide additional structural strength. In another embodiment of this invention the airfoil segments are hinged and cables run through the segments and allow the airfoils to bend in high winds. The hinged airfoils can also act as the frame to spin the generator. Another embodiment of this invention is a method of manufacturing airfoils by inserting tubing in the plastic mold of an airfoil before foam is added to stiffen the part and to allow a cable to pass through. This method effectively encapsulates the tubing, which may be comprised of metal, fiberglass, carbon, or other material, in the foam. 
         [0010]    It is a further object of this invention to provide for an collapsible wind generator that utilizes a plurality of airfoil units that are each comprised of concentric circles. The individual spin on each of these units enhances the revolution of their attachment arms to a central rotating shaft that powers a generator. 
         [0011]    It is a further object of this invention to provide for an improved wind generator with flexible blades that can be extended or retracted in the manner of an umbrella. When extended, the blades flex out such that the windmill has an overall spherical shape. The individual blades have an airfoil geometry. In one embodiment, the airfoil design is such that there is an integral flap which is open to catch the wind at low speeds and is pushed into a closed position during higher wind speeds. In another embodiment, a sail is included in the interior of the sphere to enhance low speed start up. 
         [0012]    It is a further object of this invention to provide for a carousel arrangement of wind turbines, either with individual generators or a gearbox system to power a central generator. The carousel configuration puts the wind turbines away from the main shaft such that this moment arm gives an effective multiplier effect of the wind speed. Thus, even in low wind conditions, this arrangement generates electricity as if operating at a higher wind speed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    To improve the understanding of this invention, figures are provided to better describe examples of design and operation. These drawings represent examples of preferred embodiments but additional designs and operational conditions may also be included. 
           [0014]      FIG. 1  shows a VAWT with an actuator mechanism to collapse the bracket that holds the airfoil blades. 
           [0015]      FIG. 2  is the VAWT of  FIG. 1  in the collapsed (high wind state) configuration. 
           [0016]      FIG. 3  shows the mechanism that measures load and controls the position of an airfoil bracket (for VAWT) or blades (HAWT). 
           [0017]      FIG. 4  is a HAWT with a spring mechanism to collapse the blades. 
           [0018]      FIG. 5  is a detail view of the HAWT of  FIG. 4 . 
           [0019]      FIG. 6  is a HAWT with an actuator mechanism to collapse the blades. 
           [0020]      FIG. 7  is a VAWT collapsible by pulleys and cables. 
           [0021]      FIG. 8  is a detail view of the mechanisms of  FIG. 7 . 
           [0022]      FIG. 9  shows the VAWT of  FIG. 7  in the retracted position. 
           [0023]      FIG. 10  is a wind turbine similar to  FIG. 7 , but with additional airfoil blades. 
           [0024]      FIG. 11  is a HAWT carousel. 
           [0025]      FIG. 12  is a HAWT carousel with a Savonius type start up mechanism. 
           [0026]      FIG. 13  is a VAWT carousel 
           [0027]      FIG. 14  is a collapsible wind turbine utilizing counter weights. 
           [0028]      FIG. 15  shows the turbine of  FIG. 14  in the retracted position. 
           [0029]      FIG. 16  is an airfoil with four blades, each comprised of a pair of wheel type airfoils. 
           [0030]      FIG. 17  shows the airfoil of  FIG. 16  in the retracted position. 
           [0031]      FIG. 18  is a collapsible wind turbine comprised of multiple airfoil blades and interior sails in the extended, spherical position. 
           [0032]      FIG. 19  is a collapsible wind turbine with two stacked assemblies, each comprised of multiple airfoil blades in the extended, circular configuration. 
           [0033]      FIG. 20  is an airfoil blade used for the HAWTs. 
           [0034]      FIG. 21  shows a ribbed hollow segmented airfoil blade with through rods and cables. 
           [0035]      FIG. 22  is an airfoil blade constructed from two halves. 
           [0036]      FIG. 23  shows a curved segmented airfoil. 
           [0037]      FIG. 24  shows a portion of a fingerjoint segmented airfoil. 
           [0038]      FIG. 25  is an airfoil blade made of bulkheads, cables and an outer fabric. 
           [0039]      FIG. 26  shows the construction mechanism of  FIG. 25   
           [0040]      FIG. 27  is a flexible blade wind turbine 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]      FIG. 1  shows one embodiment of this invention. In this embodiment a VAWT is built from blades comprised of segments  1  and with wing tips  2 . The blades are attached by a bracket  3  that envelopes an actuator  4  that slides on the central shaft  5 . The actuator moves to extend or retract the bracket depending upon wind conditions and is controlled by a torque sensor on the main shaft in a feedback loop described in  FIG. 3 . This type of system can also be used for VAWTs with single piece blades or without wingtips or with a different number of total blades.  FIG. 2  shows the turbine during a high wind state as the actuator  4  has moved down the central shaft  5  causing the hinges on the bracket  3  to retract the blades. This retracted position protects the turbine from damage at high wind speeds yet enables it to continue spinning and supplying the generator with energy. Most wind turbines cannot operate at high wind speeds due to centrifugal forces that are damaging to the mechanical system and thus are turned off and are not able to take advantage of the high power output that high winds could generate 
         [0042]      FIG. 3  is another embodiment of this invention that is a schematic of the mechanism used to control the shape of the turbine. Either an actuator or ball screw motor  6  moves up or down as controlled by the motor driver  7  which in turn receives a signal from the central processing unit (CPU)  8 . The CPU receives input from the speed sensor  9  that monitors the torque of the central shaft  10  that powers the generator  11 . In this way the extension of the turbine blades is able to constantly be at the optimum position through this monitor-feedback-control loop. With the control system described here, the turbines can still operate efficiently in a partially collapsed configuration during moderately high winds and can still spin and power the generator when fully collapsed if necessary. Actuators or springs mounted on the main shaft are used as torque measuring and control devices for either vertical or horizontal wind turbines and are utilized in a computer controlled closed loop feedback. 
         [0043]      FIG. 4  is another embodiment of this invention showing a three bladed HAWT that uses a mechanical control mechanism. Each blade  12  is attached to an angled blade mount  13  and the three spoked hub  14  is attached to the blade holder by a hinged blade base  15 . A rod  16  connects each blade holder to a hub  17  that can slide on the central shaft  18 . Atop the hub is a spring  19  contained by a nut  20  that is used to monitor and control the position of the blades based upon the wind speed. During periods of high wind, the spring will compress and collapse the blades to a smaller spin diameter protecting them from damage yet allowing the wind turbine to generate electricity during high winds. The shaft drives the generator  21  that is covered by a housing  22 .  FIG. 5  shows more detail of this HAWT with a clearer view of the spring  19  that is used to monitor and control the extension or retraction of the blades as it moves the hub  17  up or down the central shaft  18 . Another embodiment is shown in the HAWT of  FIG. 6  where instead of a spring mechanism, an actuator  23  is used to monitor the torque of the central shaft  18  and control the disposition of the blades  12 . The actuator is controlled by the feedback loop described earlier in  FIG. 3 . 
         [0044]      FIG. 7  shows a VAWT with five airfoil blades  24  that are mounted by brackets  25  and connecting rods  26  to brackets on the central shaft  27 . The generator  28  is powered by the rotation of the central shaft  29 . This view is in the fully operational position. Finer detail is shown in  FIG. 8  where the connection between the airfoil blades  24  by connecting rods  26  to the brackets on the central shaft  27  are by a cables  31  connected by cable hinges  32  between the rods. The cables go over cable guides  33  down the central shaft and to a swivel joint  30  (shown in  FIG. 7 ) that prevents entanglement of the cables from the spinning wind turbine and connects to a crank or motor driven actuator (not shown) that receives wind speed information from a shaft torque sensor and controls the length of the cable to open and close the turbine as per the control feedback loop described earlier. Even in the fully collapsed position of  FIG. 9 , the airfoil blades  24  remain vertical and operational. The connecting rods  26  are now almost vertical as the cables have been tensioned.  FIG. 10  is a collapsible VAWT but with some horizontal airfoil blades for better efficiency. The vertical airfoild blades  24  have brackets  25  that are used to connect rods  26  to brackets on the central shaft  27 . A collar  28  controls the position or amount of collapse by moving up or down the central shaft  29 . In this configuration, additional horizontal airfoil blades have been added between the vertical blades and central shaft such that the connecting rods run through them  31 , and another set has been added atop the vertical blades  32 . These horizontal blades provide for both drag for easier start up, and additional lift during normal operation. 
         [0045]      FIG. 11  is carousel of horizontal axis wind turbines. Each turbine  34  has a separate generator  35  and in addition to spinning, the entire carousel rotates and the connecting rods  36  spin the main shaft and power the central generator  37 . Perhaps the best advantage of a carousel system like this is to take advantage of the additional rotational speed possible for the main shaft coming from the long moment arms of the individual turbines thus providing a multiplying effect of the actual wind speed.  FIG. 12  is another example of a carousel arrangement. In this configuration the individual turbines  38  each have a gearbox and are connected to the main shaft by connecting rods  39  with an internal drive  40  that powers a single central generator. This design also shows an optional Savonius type central drag mechanism  41  to improve efficiency at start up.  FIG. 13  is an example of a carousel arrangement with vertical axis wind turbines  42 . This example also shows the optional Savonius central mechanism  43 . While this configuration could be used on land, the example in the figure shows a further Savonius mechanism underwater  44  to provide additional power to the generator. 
         [0046]      FIG. 14  is an example of a collapsible wind turbine that is controlled by purely mechanical means. Vertical segmented airfoil blades  45  are connected via rods  46  by an attachment means at both the top and bottom of the blades  47  and the rods are attached to a spoked hub  48  on the central shaft  49 . Weights  50  are also connected to the spoked hub and control the level of retraction of the mechanism. In a very high wind state, shown in  FIG. 15 , the weights  50  are forced outward as the turbine spins, increasing their effective force and pulling the lower spoked hub  48  down the central shaft  49 , effectively collapsing the wind turbine. As the wind dissipates, the weights will again travel inwards, lessening the retraction and thus providing a mechanical means of self regulation. 
         [0047]    Another wind generator comprised of multiple circular airfoil units is shown in  FIG. 16 . Each circular airfoil is comprised of a wheel shaped airfoil comprised of an outer  52 , a middle  53  and an inner  54  concentric airfoil circle and arced airfoil spokes  55 . Each unit is then mounted on an arm  56  that connects with a central hub  57  that transmits power to the central rotating shaft  58 . The number of units could be varied but in this example, four sets of two are used. In this embodiment, the arms can hold the units at right angles to the central shaft, but as shown in  FIG. 17  this wind generator could be collapsed to a portable position. In this figure the circular airfoils are shown retracted on their connecting arms. 
         [0048]      FIG. 18  shows another embodiment of this invention where the wind turbine is comprised of an assembly of multiple flexible airfoil blades  59 . The blades are flexed such that the assembly is spherical, although the blades could also be collapsed down around the central shaft  60  for portability. Each blade is attached to a floating hub at the bottom  61  and a fixed hub at the top  62 , and can be fixed in place by a pin  63  in the central shaft. The large surface area and long blade length of the airfoils should allow this assembly to start in low wind speeds, however optional interior sails are also useful to catch the wind for start up. Once the assembly starts to spin centrifugal forces will stretch it into a larger shape supplying an increased mechanical torque to power the generator  64 . 
         [0049]      FIG. 19  is a wind generator similar to that of  FIG. 18  except that there are two sets of blades. Each blade  65  is attached to the central rotating shaft  66  by a lower floating hub  67  that has been slid up to contact the fixed hub  68  for each set of blades, thus forcing each flexible blade into a circular configuration. 
         [0050]      FIG. 20  shows the detail of an airfoil blade for a collapsible HAWT or VAWT of this invention. These blades are are true airfoils with a leading edge  69  and a trailing edge  70 . In a preferred embodiment the blades also have wingtips  71  to further enhance performance. These blades are attached to the turbine via a mounting plate  72 . These blades can be made from lightweight material in segments and contain internal stiffening rods  73 . These type of wind turbine blades are very portable, yet strong and stiff. Most large airfoils are manufactured from expensive composites, fiberglass or heavier metals that can overburden the frame design. The airfoils described in this invention may be manufactured from low cost lightweight polymers and would thus be more easily transported and assembled. The airfoils can be foam filled and inserted with metal tubes for additional strength. 
         [0051]    In another embodiment of this invention the configuration and structure of lightweight airfoil wind turbine blades and their construction method is provided.  FIG. 21  shows an airfoil constructed from individual segments. Each segment is the shape of an airfoil with a leading edge  74  and a trailing edge  75 . The segment is constructed from a lightweight material and is essentially hollow with interior stiffening ribs  76  for structural integrity. One side of each segment has a narrower connector tab  77  that fits into the next segment to mechanically lock the segments together to form a longer airfoil blade. In this example, the blade is further stiffened by through rods  78  and strengthened by through cables  79 . This approach to wind turbine blade construction allows for easier transportability than that of large individual piece blades and the flexibility to allow for blades of different lengths as required. The lightweight nature of the blades also reduces stresses on the wind turbine assembly and can thus improve the service life. The through stiffeners can utilize oversized extruded plastic or metal cable bearings to reduce stress on the lightweight polymer from the metal cable. The plastic airfoil floats freely on the metal cables and the cables act as the framework that transfers kinetic energy into rotational power with very little stress on the plastic. 
         [0052]    In another embodiment,  FIG. 22  shows an airfoil constructed of segments that are configured as an upper half  80  and a lower half  81  with holes  82  and through rods  83  and through cables  84  for stiffening and strengthening. The holes are included to accommodate rivets or fasteners that join the two segments together. By having a hemisphere in each half airfoil, the blade is stiffened and the hole dimension can be held to a tighter tolerance than by later cutting a hole through a thin skin in a whole airfoil. In other embodiments, the segmented blades described may be strengthened by cables alone, without through rods thus allowing the blades to flex during operation. In addition, the mechanical fastening of the segments may be improved by the use of adhesives or additional locking mechanisms. 
         [0053]    In  FIG. 23 , a curved blade is fabricated from curved blade segments  85  with connecting segments  86  that would be made from a more compliant material. The blade can then be stiffened or strengthened by inserting rods or cables through the holes  87  in the blade. In another preferred embodiment,  FIG. 24  is an example of another flexible wind turbine blade constructed from individual segments. Each blade segment  88  has finger joints  89  on each end that interlock with the adjacent segment. Holes  90  through the finger joints allow for a fastening rod to lock the segments together and cables  91  through the blade increases the overall strength while preserving flexibility. 
         [0054]      FIG. 25  is another blade design with a leading edge  92  and a trailing edge  93 . The construction is by multiple cross-member bulkheads  94  and stiffening through rods  95  and a fabric cover  96 . This airfoil blade can be easily collapsed by removing the rods to provide for portability. In this manner, large airfoil blades can be set up on site and can be lightweight and strong.  FIG. 26  shows the mechanism that holds this type of collapsible blade together. The through rod diameter steps down  97  and stops against a similar diameter step in the endcap  98  as a mechanical stop so that when the bolt  99  is tightened, the outer fabric  97  is pulled tight and the blade assembly is strong and secure. Other methods of securing the through rod to the end cap may also be used to ensure a tight, stiff structure when the bolt is tightened. 
         [0055]      FIG. 27  is an example of a flexible blade wind turbine with airfoil that mounts on a pole  100 . The airfoil blades  101  are made of a flexible material so that they will flex in the wind and yet still be operational at even high wind speeds. The blades have pegs  102  at the bottom which sit in a holder  103  that is connected to a central rotating shaft  104  that powers the generator. Alternatively, the rigid holder may be replaced by a spring mechanism that could allow the blades to collapse all the way down to the pole.