Abstract:
This invention relates to a novel turbine design that increases turbine efficiency whereby turbine blades experience cyclic pitch variations while rotating about the blade axis which is accomplished by means of a concentric end cam double follower mechanism. This mechanism rotates the blades by 90 degrees about a horizontal axis which allows the blades rotating upstream and downstream to be oriented horizontally and vertically so minimum drag and maximum drag are obtained respectively. Since the aiding downstream drag is at a maximum, and the adverse upstream drag is at a minimum, this configuration allows for higher power output compared to conventional vertical axis wind turbines.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is entitled to the benefit of and incorporates by reference subject matter disclosed in Provisional Patent Application No. 62/183,980 tiled on Jun. 24,2015. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a vertical axis wind turbine. More particularly, the invention relates to a vertical axis wind turbine with a dual cam cyclic pitch control. 
       BACKGROUND OF THE INVENTION 
       [0003]    Wind turbines have been in use tor many centuries to perform various tasks. But there has been an increased interest in them for power generation in the last decade because of factors like global warming and the need to shift to greener power generation methods. Many different wind turbine designs exist today. The major classification of wind turbines is based on the position of the axis of rotation of the blades with respect to the wind flow direction. Wind turbines with their axes parallel to the flow are called horizontal axis wind turbines (HAWT) and they occupy a majority of the present share of commercial wind turbines. Their blades&#39; cross sections resemble an airfoil and produce lift and drag forces while wind blows over them. The lift forces generate torque and rotate the blades when wind velocity is sufficient. 
         [0004]    Unlike HAWTs, vertical axis wind turbines (VAWT) have blades with the axis of rotation perpendicular to the wind direction. Hence, they are also called cross flow turbines. Popular VAWTs include the Darrius Turbine and the Savonius Turbine. Different Damns Turbine configurations exist and in most cases they are not self-starting. They use the lift forces on their airfoil blades to generate the required torque. 
         [0005]    Savonius Turbines on the other hand are drag based turbines. Most of them have two buckets with an “S” shaped cross section and rotate about a symmetrical vertical axis. The shape of the turbine causes it to experience more drag in the down wind direction than that in the upwind direction and tits net drag forces the turbine to rotate. They are simple to construct, have cheaper maintenance and work independent of wind direction. The efficiency of these turbines drops very quickly with increase in rotational speed as it adversely alters the relative velocity between the wind and the buckets. Modifications to the Savonius turbine were made to minimize the upstream drag and increase efficiency which resulted in adverse inertial effects of moving parts at high speeds, in order to increase such a turbine&#39;s efficiency, it is necessary to maximize live aiding downstream drag and minimize the adverse upstream drag simultaneously. 
         [0006]    A similar mechanism is found in a helicopter which uses a device called swash plate. It has two circular discs which can be tilted about any planar axis passing through their center. The lower disc only tilts while the upper disc also rotates along with the blades of the helicopter. The upper disc has levers connected to the blades through a crank. When these discs are tilted, one half on their surface is elevated while the other half is lowered. The levers on the elevated side of the discs move up rotating the crank which results in having an increased pitch on those blades while the blades on the lower side experience decreased pitch by the same amount. So each blade experiences a reversal of the pitch about a mean position when it moves from the elevated side to the lowered side i.e. for every 180 degrees of rotation in a cyclic manner. The blades with increased pitch produce more thrust than the blades with reduced pitch and this difference in thrust is the reason a helicopter can pitch forward or backwards and roll to the left or right according to the input from the pilot. And the maximum pitch angle attained by each of the blades m each cycle is proportional to the angle by which the discs are tilted. The swash plate can also be moved up or down without tilting which would change the collective pitch resulting in increasing or decreasing the altitude of the helicopter. 
         [0007]    A swash plate converts linear input into rotary output which is the gradual continuous pitch variations spread uniformly over 360 degrees of rotation of a blade. But since, the turbine of the present invention benefits from quicker rotations which must happen when the blade is changing from upstream to downstream location and vice versa, an improved system is desired. 
       SUMMARY OF THE INVENTION 
       [0008]    In at least one embodiment, the present disclosure describes a dual cam pitch turbine assembly in which the turbine blades are rotated or pitched cyclically by means of a dual cam to obtain maximum differential drag between the drive stroke and the recovery stroke of the turbine cycle to maximize the efficiency and/or power output from a VAWT. This is analogous to the motion of an oar blade in the sport of shell rowing. The water is pushed backwards by an oar blade held perpendicular to the water surface during the drive stroke, and then the blade is rotated parallel to the water surface and pulled back to the initial position during the recovery. The drive stroke force and hence the work done is much larger during the recovery stroke, and net positive work is done on the system. 
         [0009]    The system regains its initial state after completing one cycle. During this cycle, a small portion of work generated during the drive stroke is used to complete the recovery. Thus, the system can work independently and generate net positive work while capturing energy from the fluid flow. 
         [0010]    In at least one embodiment, the present disclosure provides turbine blades that each rotate by 90 degrees twice in one cycle i.e. once each at the end of the drive stroke and then recovery stroke by means of a dual mechanical cam. The rotation can either be in the same direction or m the opposite as it would not have any effect on the resulting state. This is because rotating a blade by 90 degrees twice and rotating by 90 degrees in a certain direction and then rotating it back by 90 degrees results in a similar configuration. 
         [0011]    In at least one embodiment, the present disclosure provides a dual cam combining two concentric end cams with a sharp rise and a sharp fall of the outer end cam aligned with a sharp fall and sharp rise respectively of the inner end cam. Followers which move over the end cams slide on the cams and rotate by 90 degrees whenever they move over the rise/fall of the end cams. The 90 degree rotation of the followers result in pitching motions of blades attached thereto. Where most mechanical cams convert input rotary motion of a shaft into a controlled linear or radial motion which can either be sudden or gradual based on requirements, linear cams convert linear motion into a modified still linear motion but in a direction perpendicular to the direction of initial motion. The dual cam of the present disclosure modifies the cam mechanism to output rotary motion from an input rotary motion. 
         [0012]    In at least one embodiment, the present disclosure provides a dual cam cyclic pitch system with three turbine blades. Three blades are found to keep at least one blade in the drive stroke at all times, provides a compromise between simplicity and uniformity in power output However, it is understood that more or fewer blades may be utilized based on other design preferences. 
         [0013]    In at least one embodiment the present disclosure provides for blade shapes as thin, rectangular plates. Though a rectangle may not be the optimal shape for the blades, rectangular plates are being used for simplicity and ease of analysis and comparison with other drag based VAWTs. However, the present disclosure recommends the use of a variety of known blade shapes including airfoils, variable pitch blades, oar shaped blades and the like. 
         [0014]    The dual cam pitch turbine assembly disclosed herein is not limited to VAWT applications, or to tidal energy systems, but may be utilized in turbines of various applications such as wind turbines, propellers, and industrial turbines. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate the presently preferred embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain the features of the invention. In the drawings: 
           [0016]      FIG. 1  is a perspective view of a dual cam cyclical pitch turbine assembly in accordance with an embodiment of the present disclosure. 
           [0017]      FIG. 2  is a perspective simplified partial view illustrating the dual cam and two of the follower mechanisms of  FIG. 1 . 
           [0018]      FIG. 3  is a perspective view of a dual cam in accordance with an embodiment of the present disclosure. 
           [0019]      FIG. 4  is a top plan view of a dual cam in accordance with an embodiment of the present disclosure. 
           [0020]      FIG. 5  is a right side elevational view of a dual cam in accordance with an embodiment of the present disclosure, a left side elevational view being a mirror image thereof. 
           [0021]      FIG. 6  is a from elevational view of a dual cam in accordance with an embodiment of the present disclosure. 
           [0022]      FIG. 7  is a bottom plan, view of a dual cam in accordance with an embodiment of the present disclosure. 
           [0023]      FIG. 8  is a perspective view of a dual cam cyclic pitch turbine assembly in accordance with a second embodiment of the present disclosure. 
           [0024]      FIG. 9  is a cross sectional view of the dual cam cyclical pitch turbine assembly of  FIG. 8  taken through line B-B. 
           [0025]      FIG. 10  is an enlarged exploded view of turbine blade follower bearing assembly of  FIG. 7 . 
           [0026]      FIG. 11  is an enlarged assembled view of the turbine blade follower bearing assembly of  FIG. 7 . 
           [0027]      FIG. 12  is an enlarged exploded perfective view of a hub of  FIG. 7 . 
           [0028]      FIG. 13  is an enlarged perspective view of a double connector of  FIG. 7 . 
           [0029]      FIG. 13A  is an enlarged cross sectional view of the double connector along the line A-A of  FIG. 13 . 
           [0030]      FIG. 14  is an enlarged perspective view of a first follower part of  FIG. 7 . 
           [0031]      FIG. 15  is an enlarged perspective view of a second follower part of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    In the drawings, like numerals indicate like elements throughout. Certain terminology is used herein for convenience only and is not to be taken as a limitation on the present invention. The following describes preferred embodiments of the present invention. However, it should be understood, based on this disclosure, that the invention is not limited by the preferred embodiments described herein, or to the particular systems, devices and methods described, as these can vary. 
         [0033]    Referring to  FIGS. 1-7 , the present disclosure relates to a dual cam turbine blade assembly  100  in which a disk shaped dual cam  20  is configured with an inner cylindrical end cam  21  concentric to a cylindrical outer end cam  23  on an upper surface, and a bottom surface  18  that has an annular neck  19  for affixation to a drive shaft  98 , The dual cam  20  is designed to interact with a moving follower shaft  103  so that under a fluid force the rotational interaction between the dual cam  20  and follower shaft  103  cause a turbine blade  10  affixed at one end of the follower shaft  103  to undergo a cyclical pitch motion by means of an inner lobe  101  and an outer lobe  102  which are located on the follower shaft  103  at locations that will interact with the inner cam  21  and outer cam  23  of the dual cam  20 . 
         [0034]    The inner cam  21  and the outer  23  cam of the dual cam  20  are uniformly molded, each having a lower surface area  26 ,  27  respectively, a raised surface area  28 ,  29  respectively, and a pair of sloping rises  22 ,  24  each respectively, rite inner and outer cams  21 ,  23  used in conjunction with the inner and outer lobes  101 ,  102  of a follower shaft  103  act as mechanical switches which are activated when a fluid flow moves the turbine blades  10 , causing the inner and outer lobes  101 ,  102  to rotatingly interact with sloping rises  22 ,  24  of the inner and outer cams  21 ,  23 , thereby changing the pitch of the turbine blades  10  with respect to the fluid by 90 degrees with each interaction. With continued movement of the follower shaft  103 , the inner and outer lobes  101 ,  102  continue to interact with the sloping rises  22 ,  24 , so that the turbine blades  10  undergo another rotation of 90 degrees back to their initial pitched profile positions. These changes in pitch occur in continuous cycles. 
         [0035]    Referring to  FIGS. 3-7 . the position of the sloping rises  24  of the outer cam  23  with respect to the sloping rises  22  of the inner cam  21  of the dual cam  20  determines whether the inner and outer lobes  101 ,  102  of the follower shaft  103  rotate continuously in one direction or rotate back and forth in each successive pitching motion. The inner cam  21  is typically out of phase with respect to the outer cam  23  by 90 degrees, The sloping rises  22  of the inner cam  21  typically also coincide with the opposite sloping rises  24  of the outer cam  23 , and vice versa which allows the inner and outer lobes  101 ,  102  to rotating roll without interference. 
         [0036]    The dual cam  20  design allows for the inner and outer lobes  101 ,  102  of a follower shaft  103  to rotate twice in the same direction whenever the lobes move over one of the sloping rises  22 ,  24  of one of the inner or outer lobes  101 ,  102 , which coincides the sloping rises  22 ,  24  of the opposing toner or outer cam  21 ,  23 . The sloping rises  22 ,  24  are positioned such that they are typically 180 degrees apart but can be as little as 60 degrees apart. A turbine blade  10  connected to a follower shaft  103  rotates when the inner or outer lobe  101 ,  102  interacts with the sloping rise  22 ,  24  of the inner or outer cam  21 ,  23  respectively. The turbine blade  10  remains in the rotated position for the next 60 to 180 degrees of follower shaft  103  rotation and then again rotates by 90 degrees when the inner or outer lobe  101 ,  102  interacts with the opposite sloping rise  22 ,  24  of the inner or outer cam  21 ,  23  respectively, and then remains in that position for the next 60 to 180 degrees. The rotation of the turbine blades  10  is not abrupt, and is not preferred, as rotating the turbine blade  10  sharply might result in vibrations and might require more energy because the fluid around the turbine blade  10  would be displaced at a rate proportional to the speed of rotation of the follower shaft  103 . 
         [0037]    Still referring again to  FIGS. 1-7 , the inner and outer lobes  101 ,  102  are typically positioned out of phase with respect to each other by 180 degrees. The inner lobe  101  interacts with the inner cam  21 . and the outer lobe  102  interacts with the outer cam  23  of the dual cam  20 . While the inner lobe is active and is undergoing rotation over either of the sloping rises  22  or  24  of the inner cam  21 , the outer lobe is passive and vice versa. And this happens alternatively for the pitching motion to be occur continuously. The inner and outer cams  21 ,  23  can be modified to obtain any number rotations of the follower shaft  103  by having the corresponding number of rises  22 ,  24  on the inner and outer cams  21 ,  23 . 
         [0038]    The turbine blade  10  is connected to the follower shaft  103  and rotates along with the follower shaft  103 . The follower shaft  103  is connected to the dual cam turbine blade assembly  100  through a roller bearing to the hub  90  of the assembly  100  to which all the power is transferred. A drive shaft  98  is connected to the hub  90  and is concentric to the dual cam  20  and rotates through a roller bearing about a vertical axis whenever the turbine blades  10  rotate about the same axis. 
         [0039]    Referring now to  FIGS. 8-16 , a second embodiment of a dual cam turbine blade assembly  150  is disclosed. Each of a plurality of turbine blades  10  and followers  50  work in conjunction with the dual cam  20  to provide cyclical pitch to the turbine blades  10  upon interaction with fluid forces with reduced friction by incorporation of rotatable bearings,  60  of suitable material. 
         [0040]    As shown in  FIGS. 8-16 , each follower  50  is comprised of a plurality of interlocking parts to form cam lobes which are fastened together by means of a bolt  30  whose bolt shaft  34  passes through the open centers of the plurality of parts starting at erne distal end and threadingly attaches with a threaded section  36  to a securing nut  38 . The bolt head  32  is secured within a central hub  90  along with a washer  40  and a hub bearing  42 , through which the bolt shaft  34  passes when the hub cover  94  cut outs  97  are snapped over and affixed to the hub apertures  92 . The hub  90  is affixed at a lower distal end to a drive shaft  98 . Extending outwardly from the hub  90 , the bolt shaft  34  passes through the central openings of a first bearing lobe  50 , a crisscross uniformly molded lobe connector  70 , a second bearing lobe  80  and the nut  38 . The adjacent affixation of the first bearing lobe  50 , the crisscross lobe connector  70 , and the second bearing lobe  80  form orthogonal parts that interact with the dual cam  20  to create the cyclic pitch motion of the turbine blade  10 . 
         [0041]    Lobe bearings  60  for the reduction of friction are secured within the follower  50  in compression by the bolt  30  and securing out  38  in between the first bearing lobe  50  find an upper surface  72  of the crisscross lobe connector  70 , as well as in between the lower surface  74  of the crisscross lobe connector  70  and the second bearing lobe  80 . 
         [0042]    Still referring to  FIGS. 8-16 , the first bearing lobe  50  includes a flange  56 , a neck extending outwardly front the flange  56  in a first direction, and a pair of first lobe pins  54 , extending outwardly from the flange  56  in an opposite direction. The first lobe pins  54  are cylindrical and formed to pass through the cam bearing  60  then to rotatingly engage with annular holes  78  in an upper flange  72  of the crisscross lobe connector  70 . 
         [0043]    The second bearing lobe  80  has second lobe pins  82  at one end and turbine blade prongs  84  at an opposite end. The second lobe pins  82  are cylindrical and pass through bearing cams  60  then rotatingly engage with annular holes  78  in a lower flange  74  of the crisscross lobe connector  70  which is uniformly molded with a cylindrically shaped middle  76  connecting the upper flange  72  to the lower flange  74 . The turbine blade prongs  84  each include a hole  86  for attaching a turbine blade  10  using a pair of standard nuts and bolts  11 . 
         [0044]    When comparing the invention herein with other drag based VAWTs, it is apparent that since the adverse drag force, which reduces the power output by a large amount, is considerably reduced it results in better efficiency. 
         [0045]    These and other advantages of the present invention will be apparent to those skilled in the art from the foregoing specification. Accordingly, it will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It should therefore be understood that this invention is not limited to the particular embodiments described herein, but is intended to include ail changes and modifications that are within the scope and spirit of the invention as defined in the claims.