Abstract:
A horizontal-shaft wind machine having improved low wind speed performance and greater overall efficiency consists of multiple rotors, wherein each successive rotor is larger in diameter than the previous rotor moving from the most windward rotor to the most leeward rotor. Each rotor may be coupled to a separate concentric shaft, and all rotors may rotate in the same direction with the output shafts of each rotor coupled via an overrunning clutch to a single shaft, the output of which is used to drive the load. Winglets attached to the leading edge and tip of the rotor sails improve low wind startup torque.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to wind machines, and in particular to so-called horizontal-shaft wind machines. 
         [0002]    A wind machine is a device for extracting energy from the wind. A typical horizontal axis wind machine consists of a pivoting platform mounted to the top of a tower. Attached to the pivoting platform is a rotor assembly joined to a power transmission system by horizontal shaft. The power transmission system is coupled to a work-performing device, for example an electrical generator or pushrod for pumping water. Wind machines can generally be divided into two categories: Lift-type and drag-type. Lift-type wind machines use slender airfoils similar to airplane propellers, which create lift as the wind passes over the airfoils to rotate the wind machine rotor assembly. As with aircraft propellers, the pitch of the lift-type airfoils must be matched to the windspeed for maximum efficiency and the pitch typically varies from the root of the airfoil to the tip in order to compensate for the different path velocity of the airfoil along the leading edge. Drag-type wind machines use relatively wide sails with large surface areas, which act to slow the wind striking the sails and convert a portion of the kinetic energy of the wind into rotary motion of the wind machine rotor. Drag-type wind machines typically include a rudder that extends from the rear of the wind machine head for aligning the wind machine so that the rotor always faces the wind. 
         [0003]    Conventional wind machines, be they lift-type or drag-type typically comprise a single set of blades or a single rotor rotating about a horizontal shaft. Theoretically, the aerodynamic efficiency yielded by a single set of blades or by a single rotor cannot exceed 59.6% (See Betz, A. “Wind-Energie and Ihre Ausnutzun durch Windmuelen,” van den Hoeck &amp; Ruprech, Goettingen, 1926). In practice, the output of typical single-bladed wind machines is substantially below 59.6%. 
         [0004]    Multiple-rotor wind machines have been suggested as a solution to the limited aerodynamic efficiency of single bladed wind machines. U.S. Pat. No. 3,974,396 to Schonball discloses a lift-type windmill having two axially-displaced counter-rotating rotors in which one rotor drives the armature and the other rotor drives the stator of an electrical generator. This arrangement of counter-rotating blades enables the relative rotational speed between the armature and stator to be multiplied. 
         [0005]    U.S. Pat. No. 7,384,239 to Wacinski discloses a lift-type windmill having two axially-displaced coaxial counter-rotating rotors each having two or more airfoils. The output of the counter-rotating rotors is combined through a planetary transmission to drive the single input shaft of an electrical generator. 
         [0006]    U.S. Pat. No. 4,065,225 Allison discloses a multiple vane lift-type windmill having a plurality of axially-displaced rotors each having blades that are spring loaded to adjust the blade pitch as the rotor speed increases. The rotors of Allison are attached to a single shaft and do not counter-rotate. None of these patents suggest a drag-type wind machine in which the multiple rotors increase in diameter in a downwind direction, nor do they suggest a drag-type wind machine in which the rotors are angled rearward along a conical surface, nor a drag-type wind machine in which the sails have winglets formed on the leading and/or tip edges of the sails. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention comprises a horizontal wind machine having improved low-wind operability. According to one embodiment of the present invention, a wind machine comprises a horizontally extending shaft with sails coupled to the shaft, extending radially outward from the shaft for rotating the shaft. Each sail comprises a front surface facing the wind and a leading edge that moves through the air as the shaft rotates. A winglet extends outward from the leading edge of each sail and curls back over the front surface of the sail for improving the efficiency of the wind machine, by capturing wind that would otherwise slide off the leading edge of the sail. 
         [0008]    In another embodiment of the present invention, the sails extend from the shaft in a direction that is not in a plane perpendicular to the shaft, but instead the sails are angled backward along a conical surface. This configuration will cause wind that strikes the sail and slides along the surface to be caught by the winglets at the ends of the rotor blades to impart more force in the direction of rotation, thus improving the efficiency of the wind machine. 
         [0009]    In another embodiment, the wind machine comprises a first rotor coupled to a first shaft and a second rotor coupled to a second shaft, wherein the second shaft is coaxial with the first shaft. The second shaft is coupled to the first shaft via an overrunning clutch mechanism, such as a ratchet and pawl, which allows the second shaft to transmit torque to the first shaft if the second shaft would otherwise rotate faster than the first shaft. The coupled rotors produce more torque than a conventional wind machine having only one rotor sail assembly of equal outer diameter. Each rotor sail assembly may have non-planar sail orientations as described above and/or winglets extending from either or both of the leading edges of the sails or the tips of the sails. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0010]    The present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawing Figs. in which like references designate like elements and, in which: 
           [0011]      FIG. 1  is a front-perspective view of a wind machine incorporating features of the present invention; 
           [0012]      FIG. 2  is a side-view of one of the wind machine rotors shown in the embodiment of  FIG. 1 ; 
           [0013]      FIG. 3  is a perspective view of one of the wind machine sails shown in the embodiment of  FIG. 2 ; 
           [0014]      FIG. 4  is a front plan view of the embodiment of  FIG. 1 ; 
           [0015]      FIG. 5  is a side view of a the embodiment of  FIG. 1 ; 
           [0016]      FIG. 6  is a rear perspective view of the embodiment of  FIG. 1  showing details of the power transmission system; and 
           [0017]      FIG. 7  is a side view of an alternative embodiment of a wind machine incorporating lift-type rotors in lieu of drag-type rotors. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The drawing figures are intended to illustrate the general manner of construction and are not necessarily to scale. In the detailed description and in the drawing figures specific illustrative examples are shown and herein described in detail. It should be understood, however, that the drawing figures and detailed description are not intended to limit the invention to the particular form disclosed, but are merely illustrative and intended to teach one of ordinary skill how to make and/or use the invention claimed herein and for setting forth the best mode for carrying out the invention. 
         [0019]    With reference to  FIGS. 1-6  and in particular  FIG. 1 , a horizontal wind machine  10  incorporating features of the present invention comprises a wind machine head  12  which supports a horizontal shaft  14 . Horizontal shaft  14 , in turn, supports wind machine rotors  16 ,  18  and  20 . Wind machine head  14  is attached to the vertical support column  22  by a thrust bearing (not shown), which enables wind machine head  14  to be aligned so that the rotational axis  24  of shaft  14  can be aligned with the wind direction. Wind machine  10  further comprises a tail section or rudder  26 , which aligns the wind machine head  12  so that rotors  16 ,  18  and  20  face the wind. 
         [0020]    Each of rotors  16 ,  18  and  20  have a plurality of sails  28  attached substantially equidistant from shaft  14  to create a substantially rotationally balanced circular rotor. Each of the plurality of sails  28  has a root  30 , a tip  32 , a leading edge  34 , and a trailing edge  36 . Sails  28  may be of any conventional construction, for example fabric, sheet metal, or ultraviolet-resistant plastic, but in the illustrative embodiment are formed of galvanized steel sheet. The support structure of rotors  16 ,  18  and  20  is of conventional design as may be found on prior art drag-type wind machines. 
         [0021]    As shown most clearly in  FIG. 2 , each of sails  28  has a concave front surface  38  that faces the wind and a convex back surface  40  that faces away from the wind. Each of sails  28  further comprises one or more winglets  42  formed at the tip  32  and/or leading edge  34  of sail  28 . With further reference to  FIG. 3 , each of winglets  42  comprises a substantially circular or arcuate section  44  that extends in the windward direction over the front surface of sail  28  and curls back over the front surface  38  of sail  28 . Although not wishing to be held to any particular theory of operation, it is believed that without winglets, especially in low-wind conditions, a significant portion of the wind actually spills over the leading-edge and tip of a conventional wind machine sail. Winglets  44  capture the energy of this wind, which would otherwise be lost. 
         [0022]    The rotor design described herein will improve low wind speed start up torque. The winglet along the leading edge of the sail will capture some of the wind energy that would otherwise slide off the sail. The winglet at the tip of the sail also captures some wind that would otherwise slide off the tip. A rotor equipped with winglets will start to rotate and impart meaningful energy to a driveshaft in a lower wind speed than a rotor without winglets. The leading edge winglets and the sail tip winglets may be used separately or in conjunction, depending on the design requirements. If used alone, the tip winglets should wrap around to encompass a part of the leading edge near the top end of the sail. 
         [0023]    With additional reference to  FIG. 4 , the tips  32  of sails  28  forming rotor  16  form a circle having an outer diameter d 1 . Similarly the tips  32  of sails  28  forming rotor  18  form a circle having an outer diameter d 2  and the tips  32  of sails  28  forming rotor  20  form a circle having an outer diameter d 3 . The outer diameter d 1  of rotor  16  is smaller than the outer diameter d 2  of rotor  18  and the outer diameter d 2  of rotor  18  is smaller than diameter d 3  of rotor  20 . The roots  30  of sails  28  forming rotor  16  also form a circle having an inner diameter d 4 . Similarly the roots  30  of sails  28  forming rotor  18  form a circle having an inner diameter d 5  and the roots  30  of sails  28  forming rotor  20  form a circle having an inner diameter d 6 . The inner diameter d 4  of rotor  16  is smaller than the inner diameter d 5  of rotor  18  and the inner diameter d 5  of rotor  18  is smaller than diameter d 6  of rotor  20 . Preferably, the inner diameter d 5  of rotor  18  is equal to the outer diameter d 1  of rotor  16  within ±50% of the length of blade  28  (from root  30  to tip  32 ) and the inner diameter d 6  of rotor  20  is equal to the outer diameter d 2  of rotor  18  within ±50% of the length of blade  28 . 
         [0024]    With reference to  FIG. 5 , the sails  28  forming rotor  16  do not lie in a plane that is perpendicular to shaft  14 . Instead sails  28  forming rotor  16  lie along a conical surface tapering downwind at an angle θ 1  measured perpendicular to shaft  14 . Similarly, sails  28  forming rotor  18  lie along a conical surface having an angle θ 2  measured perpendicular to shaft  14  and sails  28  forming rotor  2  lie along a conical surface having an angle θ 3  measured perpendicular to shaft  14 . The angles θ 1 , θ 2 , and θ 3  may be equal or may be unequal. Preferably the angles θ 1 , θ 2 , and θ 3  are at least 8 degrees and are preferably from 11-25 degrees and most preferably are about 15±2 degrees. The conical orientation of the rotors causes wind that would otherwise slide off the root of the sail instead to slide toward the tip of the sail, imparting force to the sail surface during the process. 
         [0025]    Referring now to  FIGS. 5-6 , horizontal shaft  14  is made up of three concentric shaft members  50 ,  52  and  54 . Shaft members  52  and  54  are hollow tubes. The forward end of shaft member  50  is supported by a bearing  56  received within the hollow end of shaft member  52 . Shaft member  52 , in turn is supported by a bearing  58  received within the hollow end of shaft member  54 . Shaft member  54  is attached to wind machine head by bearings mounted within housings  60  and  62 , which are attached to wind machine head  12 . The rearward ends of shaft members  50  and  52  are supported within shaft members  52  and  54  in a like-manner and therefore will not be discussed in detail. 
         [0026]    As shown most clearly in  FIG. 6 , shaft members  50 ,  52  and  54  are coupled together by means of overrunning clutches  66  and  68 . Overrunning clutch  66  allows shaft member  50  to rotate faster than shaft member  52 . Overrunning clutch  68  allows shaft member  52  to rotate faster than shaft member  54 . In the illustrative embodiment of  FIG. 6 , overrunning clutches  66  and  68  comprise ratchets consisting of ratchet wheels  70  and  72  together with corresponding ratchet pawls  74  and  76 . 
         [0027]    As can be determined from an inspection of  FIG. 6 , if shaft member  52  tries to rotate in a counterclockwise direction at a speed that is equal to or faster than the counterclockwise rotation of shaft member  50 , then torque is transmitted from shaft member  52  to shaft member  50  via overrunning clutch  66 . However, if shaft member  52  rotates at a slower speed than shaft member  50 , no torque is transmitted between the two shafts. Overrunning clutch  68  similarly transmits torque from shaft member  54  to shaft member  52  only if shaft member  54  is trying to turn faster than shaft member  52 . 
         [0028]    Wind machine  10  generates more torque than a conventional wind machine of the same size because there are three different sets of sails each generating torque and transmitting that torque to one of the coupled shaft members  50 ,  52 ,  54 . The coupled shafts then combine the torque and transmit it to the load via vertical shaft  80  and right-angle drive  78 . 
         [0029]    With further reference to  FIG. 6 , because the longitudinal axis  15  of horizontal shaft  14  is offset by a distance Δ from the vertical pivot axis  82  of wind machine head  12 , the force of the wind acting on rotors  16 ,  18  and  20  produces a torque about vertical pivot axis  82 . In extreme high wind conditions, this torque will cause longitudinal axis  15  to swing away from the wind direction thereby preventing an overspeed condition. As wind machine head  12  swings away from the wind direction, rudder  26  pivots relative to wind machine head  12 . Rudder  26  is mounted on a pivot  84  that is canted at an angle φ relative to vertical. Thus, as rudder  26  pivots relative to wind machine head  12  rudder  26  swings upward. The upward motion of rudder  26  generates a restoring torque that moves longitudinal axis  15  back into the wind when the extreme high wind conditions subside. 
         [0030]    Although certain illustrative embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the invention. For example, although the illustrative embodiment of  FIGS. 1-6  contemplates three rotors and three shafts all rotating in the same direction, two rotors and two shafts rotating in the same directions, or greater than three rotors and three shafts rotating in the same or different directions are contemplated as being within the scope of the invention. Further, it should be understand that it is within the scope of the invention for the multi-rotor wind machine design described herein to be utilized either separate from or in conjunction with sails having winglets. Similarly, although wind machine  10  is shown with overrunning clutches  66  and  68  comprising ratchet and pawls, other equivalent overrunning clutches such as ramp-and-ball, sprag-clutches or any other similar coupling means are considered to be equivalents and therefore within the scope of the invention. 
         [0031]    Additionally, as shown in  FIG. 7 , wind machine  100  incorporating features of the present invention may incorporate airfoil lift-type rotors  86 ,  88  and  90  in lieu of the drag-type rotors of the embodiment of  FIGS. 1-6 . As with the embodiment of  FIGS. 1-6 , rotors  86 ,  88  and  90  may be of equal outside diameter, but preferably rotors  86 ,  88  and  90  increase in diameter in the downwind direction. This arrangement prevents the upwind rotor(s) from blocking the wind from the downwind rotor(s). Also, as with the embodiment of  FIGS. 1-6 , rotors  86 ,  88  and  90  are preferably coupled to concentric shafts  50 ,  52 ,  54  respectively, which are coupled together by means of overrunning clutches  66  and  68 . 
         [0032]    Wind machine  10  may be used for AC or DC electric power generation, pumping water, or any other task performed by wind machines and therefore the invention is not intended to be limited to the manner in which the power is transmitted to the ultimate load. Accordingly, it is intended that the invention should be limited only to the extent required by the appended claims and the rules and principles of applicable law. Additionally, as used herein, unless otherwise specifically defined, the terms “substantially” or “generally” when used with mathematical concepts or measurements mean within ±10 degrees of angle or within 10 percent of the measurement, whichever is greater.