Abstract:
A cycloidal generator is provided to generate power from energy in a tidal flow. The generator includes a plurality of blades mounted on a hub for collective rotation about a hub axis, and a center shaft is positioned with its central axis oriented perpendicular to the tidal flow. Interconnecting the center shaft with each individual blade on the hub is a gear assembly that cyclically rotates the blade for autorotation of the hub in response to the tidal flow. A link assembly is also provided that interconnects the hub with the center shaft for rotation of the center shaft and the consequent generation of power in response to rotation of the hub.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention pertains generally to power generators. More particularly, the present invention pertains to systems and methods for using tidal movements for generating power. The present invention is particularly, but not exclusively, useful as a cycloidal tidal power generator that cyclically varies the respective angles of attack on a plurality of blades relative to a tide, to maintain a same direction rotational motion for the generation of power. 
       BACKGROUND OF THE INVENTION 
       [0002]    In order to generate power, it is necessary to have a source of energy. As is well known, there are many such sources, for example, fossil fuels. In recent years, however, there has been increased interest in so-called natural sources of energy, such as solar energy or the wind. Another source of natural energy which has great potential, but which has been somewhat overlooked, is the ocean. More particularly, tidal movements in large bodies of water (e.g. the ocean) are known to manifest vast amounts of energy. Heretofore, the problem has been to determine how best this energy can be harnessed. 
         [0003]    It is well known that power can be generated whenever something is moved (e.g. the armature of an electric power generator). When tidal movements are considered for this purpose, the task then becomes a matter of converting the movement of the tide (i.e. energy) into the movement of a structure that will generate power (e.g. an armature). In this context, and in accordance with well known aerodynamic and hydro-dynamic principles, it is known that the interaction of a fluid flow (gas or liquid) with an airfoil-like structure (e.g. a blade) will generate forces on the structure (blade) that can cause it to move. For example, a windmill generates power in response to air movements (i.e. the wind). Similarly, the rotor of an autogiro provides lift in response to airflow through the rotor (note: the rotor itself is un-powered). Further, helicopters, when they experience a power loss, can safely descend to a landing as the upward flow of air through the rotor slows its descent. In each of these examples, performance is accomplished by a phenomenon known as “autorotation.” These examples, however, all involve structures that react to air flow. In an underwater environment (e.g. when confronting a tidal flow), a more robust and compact structure will, most likely, be more appropriate. Nevertheless, autorotation is still a key concept. 
         [0004]    Autorotation, as the word indicates, is a phenomenon involving an un-powered rotation of a structure (i.e. a blade). Stated differently, with autorotation, the rotation is automatic and requires no external source of power. Essentially, this happens because the aerodynamic (hydro-dynamic) force that is generated on the blade is oriented with a component that will cause the blade to continue moving in a desired direction. For purposes of generating power, it is desirable that such forces be substantially constant, are effective regardless of the direction of fluid flow, and cause the blade to continuously move in a same direction. 
         [0005]    In light of the above, it is an object of the present invention to provide a tidal power generator that is effective in transforming the energy of tidal movements into useful power. Another object of the present invention is to provide a tidal power generator that is compact, robust and capable of continuous operation for extended periods of time. Still another object of the present invention is to provide a tidal power generator that is relatively easy to manufacture, is very simple to operate, and is comparatively cost effective. 
       SUMMARY OF THE INVENTION 
       [0006]    In accordance with the present invention, a cycloidal generator is provided for converting the energy of a tidal movement into useful power. To do this, the present invention includes a plurality of airfoil-shaped blades that are mounted, in parallel, on a substantially disk-shaped hub. As so mounted, the blades individually follow along a same circular blade path during their rotation about a common hub axis. This rotation of the blades about the hub axis is caused by the action of the tidal flow over the blades. In turn, this action on the blades rotates the hub. As intended for the present invention, a rotation of the hub is transferred directly to a center shaft for rotation of the center shaft about a central axis and, thus, for the generation of power. 
         [0007]    Structurally, the center shaft is individually connected to each blade via a gear assembly, and it is separately connected to the hub via a link assembly. Importantly, the gear assembly and link assembly act together to allow the hub, and its hub axis, to move relative to the center shaft. During any such movement, however, the hub axis remains parallel to the central axis. Further, the distance between the hub axis and the central axis is limited by the link assembly, and does not exceed a distance “d.” As intended for the present invention, this distance “d” will normally be less than the radius “r” of the gear. 
         [0008]    The gear assembly is provided to cyclically rotate each blade about its own individual blade axis. More specifically, the angle “α” each blade makes relative to the blade path will vary continuously as the blade travels on the blade path. Specifically, this variation in the angle “α” is dependent on the distance of the hub axis from the central axis of the center shaft. Further, during each revolution of the hub, the blade angle “α” will reciprocally vary between a positive angle β and a negative angle φ. In general, the maximum magnitude of these angles (i.e. β and φ) will be equal. Thus, β=+α and φ=−α. An important consequence of this variation is that the plurality of blades will, collectively, establish an autorotation effect. 
         [0009]    In detail, the gear assembly has three intermeshing gears for each respective blade. These include: a common center gear that is affixed to the center shaft; a blade gear that is affixed to each blade; and a middle gear that is engaged between the center gear and the blade gear. Together, the various gears act to allow for variations in the distance “d” between the hub axis and the central axis. 
         [0010]    As indicated above, the link assembly is provided to cause a rotation of the center shaft in response to a rotation of the hub. Functionally, the link assembly is also provided to maintain the gear meshing required for operation of the gear assembly. Structurally, the link assembly involves numerous links. These include a proximal hub link and a distal hub link. For these links, one end of the proximal hub link is pivotally attached to a peripheral point on the center gear and one end of the distal hub link is pivotally attached to the hub. The free ends of the proximal and distal hub links are then connected together to establish a free pivot. Also included in the link assembly is a gear link that interconnects the blade gear with the middle gear. Additionally, a reference link interconnects the middle gear with the free pivot. With this construction, the link assembly and the gear assembly, in concert, rotate the center shaft when the hub is rotated. 
         [0011]    For its operation, the cycloidal generator is positioned on the floor of a body of water; preferably in the coastal area of a sea or ocean where the water is known to have a substantially continuous flow (i.e. tidal movements). More specifically, the generator is positioned so that the central axis of the center shaft, the hub axis of the hub, and the respective blade axes of the plurality of blades will all be substantially perpendicular to the direction of the tidal flow. Importantly, the generator is anchored to the floor in a manner that will hold the center shaft stationary. With the generator positioned in this manner, the tidal flow will urge against the plurality of blades to collectively move the hub along with the blades, and thus the hub axis also, in a direction downstream from the central axis. Note: the actual direction of the tidal flow is immaterial and, indeed, is expected to vary. Nevertheless, the hub and its hub axis will always be moved downstream, relative to the direction of tidal flow. Furthermore, this movement will be stopped by the link assembly, only when the hub axis is at the distance “d” from the central axis. 
         [0012]    During operation of the cycloidal generator, the gear assembly will reciprocally vary the angle “α” of each blade as it travels on the blade path. Specifically, this variation will be between a maximum positive angle (i.e. α=β) at the most upstream position of the blade, and a maximum negative angle (i.e. α=φ) at its most downstream position. At both of these extreme positions, however, hydraulic forces on the blade will move the blade in a same direction on the blade path. Moreover, at intermediate positions, the cyclically varying angle “α” will maintain the autorotation effect, and will cause the hub to continuously rotate in a same direction. This will be so, regardless of the direction of tidal flow. The result is: autorotation of the hub creates forces that are transferred by the link assembly, and applied, as a torque on the center shaft. The rotation of the center shaft is then used to generate power. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
           [0014]      FIG. 1  is a perspective view of a cycloidal tidal generator in accordance with the present invention; 
           [0015]      FIG. 2  is a partial cross section view of a portion of the generator as seen along the line  2 - 2  in  FIG. 1 ; 
           [0016]      FIG. 3  is a top plan view of a gear assembly of the present invention as seen along the line  3 - 3  in  FIG. 1 ; 
           [0017]      FIG. 4  is a drawing of fluid dynamic forces acting on a blade, as the blade is moving through a fluid medium; 
           [0018]      FIG. 5  is a schematic drawing of the influence a tide has on the hub of the generator; 
           [0019]      FIG. 6  is a schematic drawing of the orientational relationship a blade has as it moves on its blade path in accordance with the present invention; 
           [0020]      FIG. 7A  is a schematic drawing of a gear assembly when its associated blade is in a downstream position relative to tidal flow; and 
           [0021]      FIG. 7B  is a schematic drawing of a gear assembly when its associated blade is in an upstream position relative to tidal flow. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    Referring initially to  FIG. 1 , a cycloidal tidal power generator in accordance with the present invention is shown and is generally designated  10 . As shown, the generator  10  includes a disk-shaped hub  12  and an end plate  14 . A plurality of blades  16   a ,  16   b , and  16   c  are mounted between the hub  12  and end plate  14 . The blades  16   a - c  are of equal length and are mounted substantially parallel to each other. Further, though pivotally connected to both the hub  12  and end plate  14 , the blades  16   a - c  will rotate with the hub  12  and end plate  14  about a common hub axis  18 . This rotation will be in a direction exemplified by the arrow  20 .  FIG. 1  also shows that the generator  10  is connected to a power cable  22  that will extend from the generator  10  to an on-shore power plant (not shown). 
         [0023]    Using the blade  16   a  as an example,  FIG. 2  shows that the blade  16   a  is fixedly attached to a blade shaft  24 . The blade shaft  24  is then mounted on the hub  12  by an upper bearing  26  and a lower bearing  28 . The blade shaft  24  is also shown in  FIG. 2  to be fixedly attached to a blade gear  30 . Importantly, although the bearings  26  and  28  allow the blade shaft  24 , blade gear  30  and blade  16   a  to rotate about a blade axis  32 , they also retain these components on hub  12 . With this construction, the blade  16 , blade gear  30 , and blade shaft  24  are able to reciprocally rotate about the blade axis  32  in either of the directions indicated by arrows  34 . As will be appreciated by the skilled artisan, a similar mechanism is provided for the blades  16   b  and  16   c.    
         [0024]    Turning now to  FIG. 3 , a combination gear/link assembly is shown and is generally designated  36 . Although both gears and links are incorporated into this same assembly  36 , and though they necessarily operate together, they have slightly different functions. Therefore, depending on the function involved, they are sometimes simply referred to as either the gear assembly  36  or the link assembly  36 . With this in mind,  FIG. 3  shows the gear assembly  36  includes the blade gear  30  along with a center gear  38 . With reference back to  FIG. 2 , it will be seen that the center gear  38  is affixed to a center shaft  40  for rotation about a central axis  42 . A middle gear  44  is provided to intermesh the blade gear  30  with the center gear  38 . 
         [0025]    Still referring to  FIG. 3  it will be seen that the link assembly  36  includes a proximal hub link  46  and a distal hub link  48 . Further, it will be seen that one end of the proximal hub link  46  is pivotally attached to a peripheral point  50  on the center gear  38 . The other end of the proximal hub link  46  is attached to an end of the distal hub link  48  at a free pivot  52 . The other end of the distal hub link  48  is pivotally attached to a connecting post  54  that is mounted on the hub  12  (see  FIG. 2 ).  FIG. 3  also shows that the link assembly  36  includes a gear link  56  that interconnects the blade shaft  24  with a center post  58  on the middle gear  44 . Also shown is a reference link  60  that interconnects the center post  58  with the free pivot  52 . 
         [0026]    It is to be appreciated that the respective ends of all links in the link assembly  36  are free to pivot. Specifically, the proximal hub link  46  rotates/pivots about both the peripheral point  50  and the free pivot  52 . The distal hub link  48  rotates/pivots about the free pivot  52  and the connecting post  54 . Similarly, the gear link  56  rotates/pivots about the blade axis  32  and the center post  58 , while the reference link  60  rotates/pivots about the center post  58  and the free pivot  52 . Functionally, this structural cooperation (i.e. link assembly  36 ), together with the gear disclosed above (i.e. gear assembly  36 ) accomplishes two significant purposes. For one, with the center gear  38  considered as being held stationary, the gears  30 ,  38  and  44  cooperate to cause a rotation of the blade shaft  24  as the distance between the center shaft  40  (i.e. central axis  42 ) and the blade shaft  24  (i.e. blade axis  32 ) is varied. This is the primary function of gear assembly  36 . For another, as hub  12  rotates about the hub axis  18 , forces are transferred from the connecting post  54  on the hub  12 , through the link assembly  36 , to the peripheral point  50  on the center gear  38 . This will cause the center gear  38  and its center shaft  40  to rotate about the central axis  42 . With the gear link  56  and the reference link  60 , the link assembly  36  also maintains a mesh engagement for the gears  30 ,  38  and  44 . 
         [0027]    With reference back to  FIG. 1 , it will be appreciated that as the hub  12  rotates about its hub axis  18 , the blades  16   a - c  will follow along a common blade path  62  (represented in  FIG. 1  by a dashed line). As mentioned earlier, the movement of the blades  16   a - c  is the result of a phenomenon known as “autorotation.” Theoretically, autorotation can be briefly explained with reference to  FIG. 4 . In  FIG. 4 , the blade  16  is considered to be moving to the right along the blade path  62 . This movement, with respect to the tidal flow  64 , causes the blade  16  to experience a relative flow  66 . A known consequence here is that the blade  16  will establish an incident angle “ρ” with the relative flow  66  (i.e. the angle between the relative flow  66  and the chord line  68  of blade  16 ). In accordance with well known fluid dynamics this creates a resultant force “R” on the blade  16 . Importantly, as shown, the orientation of the force “R” establishes a component “T” of the force “R” that is parallel (or tangent) to the blade path  62 . It is this force component “T” that causes the blade  16  to move along the blade path  62  in autorotation. For reference purposes, and to not confuse the incident angle “ρ” disclosed here with the angle “α” referred to elsewhere, it is to be noted that the angle “α” is used to identify the angle between the chord line  68  of respective blades  16   a - c  and the blade path  62 . 
       OPERATION 
       [0028]    For the operation of the generator  10 , the generator  10  is submerged into a body of water which is known to have a substantial and predictable tidal flow  64 . Most likely, such a body of water will be in the coastal areas of an ocean or sea, or in a large river. In any event, as mentioned above, the generator  10  is positioned in the body of water so that the central axis  42 , the hub axis  18  and the respective blade axes  32  are all substantially perpendicular to the tidal flow  64 . Importantly, the generator  10  is anchored to the floor of the body of water so that the central axis  42  remains stationary. When this is done,  FIG. 5  indicates that the tidal flow  64  will cause the hub  12  to move with the tidal flow  64  through a distance “d” in a downstream direction from the central axis  42 . Preferably, this distance “d” will be less than the radius “r” of the gear (blade path  62 ). The consequence of this movement is shown in  FIG. 5 , where representations of the blade path  62  are given under different conditions. For one, with the hub axis  18  co-axially aligned with the central axis  42 , the blade path  62 ′ results. On the other hand, when the hub  12  (i.e. hub axis  18 ) is moved through the distance “d” under the influence of the tidal flow  64 , the blade path  62  results. What this movement of the hub  12  (hub axis  18 ) does to the individual blades  16   a - c  will be best appreciated with reference to  FIG. 6 . 
         [0029]    In  FIG. 6 , the blade  16   a  (exemplary) is shown traveling along the circular blade path  62  between an upstream position  70  and a downstream position  72 .  FIG. 6  also shows that as the blade  16   a  makes a complete revolution by traveling from its upstream position  70 , sequentially through a mid-position  74   a , the downstream position  72 , another mid-position  74   b , and back to the upstream position  70 , the angle “α” between the chord line  68  of blade  16   a  and the blade path  62  varies. More specifically, at the upstream position  70 , the blade  16   a  is shown to have a positive angle “β” (β=+α). At the mid-position  74   a , however, the angle “α” is shown to be zero. Then, when blade  16   a  reaches the downstream position  72 , the angle “α” becomes a negative angle “φ” (φ=−α). At the mid-position  74   b , the angle “α” returns to zero. And, again, at the upstream position  70 , the blade  16   a  is shown to have returned to a positive angle “β” (β=+α). This sequence continues through each revolution of the hub  12  and, importantly, continues regardless of the actual direction of tidal flow  64 . The result is a continuous autorotation of the hub  12  in a direction indicated by the arrow  76 . The mechanics of rotation for the blade  16   a  for the above described sequence will be best appreciated with reference to  FIGS. 7A and 7B . 
         [0030]    The configuration of gear assembly  36  that is shown in  FIG. 7A  corresponds to conditions at the downstream position  72  (see  FIG. 6 ). Similarly, the configuration of gear assembly  36  in  FIG. 7B  corresponds to conditions at the upstream position  70  (also see  FIG. 6 ). Consider the downstream position  72  first. As noted above, when blade  16   a  is at the downstream position  72 , the angle “α” becomes a negative angle “φ” (φ=−α). This happens because the tidal flow  64  has moved the hub axis  18  through the distance “d” in the downstream direction (see  FIG. 5 ). Recall, the central axis  42  remains stationary. With this movement, the blade gear  30  moves in the direction of arrow  78  and the distance between the central axis  42  and the hub axis  18  increases to a distance “r+d” (see  FIG. 7A ). In turn, this causes the middle gear  44  to move in the direction of arrow  80  and to rotate in a clockwise direction. By considering the center gear  38  to remain stationary, the clockwise rotation of middle gear  44  is compensated for by a counterclockwise rotation of the blade gear  30 . The result here is that the angle blade  16   a  makes with the blade path  62  is at its maximum, and is negative (i.e. (φ=−α). 
         [0031]    Now consider the upstream position  70  with the gear assembly  36  configured as shown in  FIG. 7B . As noted above, when blade  16   a  is at the upstream position  70 , the angle “α” becomes a positive angle “β” (β=+α). In this case, the blade gear  30  has moved in the direction of arrow  82  and the distance between the central axis  42  and the hub axis  18  has decreased to a distance “r−d” (see  FIG. 7B ). This causes the middle gear  44  to move in the direction of arrow  84  and to rotate in a counterclockwise direction. Again, when considering the center gear  38  remains stationary, the counterclockwise rotation of middle gear  44  is compensated for by a clockwise rotation of the blade gear  30 . The result here is that the angle blade  16   a  makes with the blade path  62  is at its maximum, but is positive (i.e. β=+α). It will be noted that at the mid-positions  74   a - b , there will be no effect from tidal flow  64  (i.e. d=0). Consequently, “α” will also be zero. 
         [0032]    For purposes of the present invention, the angles β and φ will most likely be equal to each other. Changes to the gear assembly  36 , however, can be made to alter this relationship, if desired. For most applications, it is envisioned that the angles β and φ will be in a range between approximately plus thirty degrees and minus thirty degrees. 
         [0033]    While the particular Cycloidal Power Generator as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.