Abstract:
A fluid driven energy conversion apparatus uses a harmonic drive, which employs a wave generator rotatably mounted within a nested pair of annular members. The wave generator is arranged to cyclically deflect a flexible inner one of the nested pair into an outline having a circumferentially varying radial dimension, and thereby engage the outer one of the pair at one or more orbiting contact zones. A turbine can rotate one of the nested pair of the harmonic drive about a given axis. An electrical generator is coupled to and rotatably driven by the wave generator at an angular speed exceeding that of the turbine.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to fluid turbine apparatus and methods, and in particular, to transmissions for coupling the turbine to an electrical generator 
         [0003]    2. Description of Related Art 
         [0004]    Traditionally used for powering grain milling machines, the windmill is an ancient device for harnessing wind energy. Modern wind turbines have been designed for generating electricity. Known wind turbines have mounted a number of blades on a hub that is rotatably mounted at a nacelle containing an electrical generator. This entire structure will be mounted atop a tower and can pivot there azimuthally to keep the turbine blades facing upwind. 
         [0005]    Other types of turbines include hydraulic turbines, which can be water turbines found in hydroelectric systems, or even simple paddle wheels. Other fluid turbines exist that are driven by various gasses or liquids. 
         [0006]    To run effectively, an electrical generator ought to rotate faster than the turbine. For this reason, a speed increasing transmission is often placed between the turbine and the electrical generator. In most cases, it is desirable to run the electrical generator fast enough to produce AC power at a frequency designed to enhance efficiency. Higher speeds will be desirable even for DC generators, because electromagnetic machines usually will have smaller magnetic cores at higher angular speeds. 
         [0007]    Frequently, an AC electrical generator will power an inverter (frequency converter) that rectifies the AC voltage and then produce a convenient output frequency. Normally this output frequency is consistent with power on the local electrical grid (e.g., 60 or 50 Hz in most regions). Even if wind-generated (or fluid-generated) electricity will not be transmitted to a larger electrical grid, many common electrical devices still require AC power in a specific frequency range in order to operate properly. 
         [0008]    A harmonic drive is a gearing system typically employing a rigid outer annulus having internal teeth. A flexible annular member (also known as a flexspline) located within the outer annulus will often be cup-shaped and have external teeth for engaging the internal teeth of the outer annulus. A known wave generator in the form of a rotor having, for example, a pair of lobes can be fitted inside this flexible annular member to deflect it into a non-circular, oval shape (or other multi-lobed or single lobed shape). The teeth along the major axis of this oval-shaped flexspline can engage teeth on the inside of the rigid outer annulus. Only a fraction of the teeth on the inner and outer members will engage. 
         [0009]    Taking the wave generator as a frame of reference, circulation of the flexible annular member (flexspline) on the wave generator will cause rotation of the rigid outer annulus. The flexible annular member will have fewer teeth than the rigid outer annulus, and so one cycle of the flexible annular member will rotate the rigid annulus less than 360°. If cycling of the flexible annular member is considered rotation at a positive speed (w 1 ), the rigid outer annulus will rotate in a positive direction but at a slower speed (w 2 ) proportional to the ratio (h) of the tooth counts (i.e., w 2 =h(w 1 )). Ratio h is the smaller tooth count divided by the larger. 
         [0010]    If the wave generator, the original frame of reference, is actually rotating at positive speed S relative to some inertial frame of reference, the angular speed of the flexible annular member in the new reference system will be s 1 =w 1 +S and the angular speed of the outer annulus will be s 2 =w 2 +S. The overall relation will be s 2 −h(s 1 )=(1−h) S. 
         [0011]    See also U.S. Pat. Nos. 3,668,946; 3,766,686; 4,945,293; 4,964,322; 6,439,081; and 6,953,086, as well as US Patent Application Publication Nos. 2005/0178892; 2008/0279686; 2008/0305934; 2009/0205451; and 2010/0303626. 
       SUMMARY OF THE INVENTION 
       [0012]    In accordance with the illustrative embodiments demonstrating features and advantages of the present invention, there is provided a fluid driven energy conversion apparatus. The apparatus includes a fluid driven turbine, an electrical generator, and a harmonic drive. The harmonic drive includes a wave generator and a nested pair of annular members. The nested pair includes an inner and an outer one. The inner one of the nested pair is flexible. The turbine is coupled to the harmonic drive to rotate one of the nested pair about a given axis. The wave generator is rotatably mounted within the nested pair of annular members and is sized to bring them into engagement at one or more discrete contact zones by deflecting the inner one into an outline having a circumferentially varying radial dimension. The electrical generator is coupled to and rotatably driven by the wave generator at an angular speed exceeding that of the turbine. 
         [0013]    In accordance with another aspect of the invention, a method of converting energy is provided. The method employs a harmonic drive coupled between a fluid driven turbine and an electrical generator. The harmonic drive has a wave generator and a nested pair of annular members. The method includes the step of facing the turbine in a direction to cause them to rotate. The method also includes the step of delivering torque from the turbine to rotate one of the nested pair of annular members about a given axis. Another step is transferring torque from the wave generator to the electrical generator at an angular speed exceeding that of the turbine by allowing the wave generator to cyclically deflect an inner one of the nested pair into engagement with an outer one at one or more orbiting contact zones. 
         [0014]    In accordance with yet another aspect of the invention, there is provided a fluid driven energy conversion apparatus. This apparatus includes a fluid driven turbine and a harmonic drive. The apparatus also includes an electrical generator adapted to deliver power to an electrical grid. The harmonic drive has a speed increasing ratio suitable for the electrical grid. The apparatus includes a frame for supporting the harmonic drive, the electrical generator, and the turbine. Also included is a tower for supporting the frame. The frame is azimuthally pivotable on the tower. The harmonic drive has a nested pair of annular members including an inner and an outer one. The turbine is coupled to the harmonic drive to rotate the outer one of the nested pair about a given axis. The outer one of the nested pair includes a rigid ring rotatably mounted about the frame. The inner one of the nested pair is flexible. The harmonic drive also includes a wave generator and a housing. The housing rotatably supports the outer one of the nested pair of annular members for rotation about the given axis. The inner one of the nested pair is affixed to the housing. The wave generator is rotatably mounted within the nested pair of annular members and is sized to bring them into engagement at one or more discrete contact zones by deflecting the inner one into an outline having a circumferentially varying radial dimension. The inner one of the nested pair is secured to the frame in order to prevent rotation relative to the given axis. The inner one of the nested pair has a plurality of external teeth. The outer one of the nested pair has a plurality of internal teeth that mesh with the external teeth at the one or more discrete contact zones. The wave generator has a rotor with at least two lobes. The rotor is journalled to the housing on one side and on the opposite side to the outer one of the nested pair. The rotor has an output shaft extending rearwardly. The outer one of the nested pair has a cup shaped portion and a forwardly extending input shaft. The electrical generator is coupled to and rotatably driven by the wave generator at an angular speed exceeding that of the turbine. 
         [0015]    By employing apparatus and methods of the foregoing type an improved energy conversion can be achieved. In a disclosed embodiment, turbine blades are rotatably mounted at a supporting frame atop a tower (or a water turbine is mounted to communicate with a fluid channel). The turbine blades are coupled through a harmonic drive to an electrical generator. The harmonic drive is arranged as a speed increaser. Specifically, the wave generator of the harmonic drive is used as the output for driving the electrical generator. In this embodiment the turbine blades rotate the rigid outer annulus, while the flexible annular member (flexspline) is held stationary. 
         [0016]    In this embodiment the rigid annulus is part of a cup-shaped member rotatably mounted inside a stationary cylindrical housing. This cup-shaped member has a forward coupling that is driven by the turbine blades. A flexible annular member is nested inside the rigid annulus and is affixed to the back of the cylindrical housing and thus remains stationary. A wave generator rotatably mounted inside the flexible annular member is journalled on one side to the cylindrical housing and on the opposite side to the cup-shaped member having the rigid annulus. 
         [0017]    The wave generator shaft will extend through an opening in the floor of the flexible annular member (flexspline). The shaft driving the rigid annulus will extend in a direction opposite to the wave generator shaft. 
         [0018]    Accordingly, the turbine will rotate the rigid annulus, which will tend to distort the stationary flexspine, causing the wave generator to rotate and drive the electrical generator. In this manner, the harmonic drive will increase the speed from the turbine based on the ratio of (a) the tooth count in the rigid annulus, to (b) the difference in the tooth count (rigid annulus versus flexspline). Accordingly, the electrical generator will be drive at a higher angular speed and will operate at efficient frequencies. This higher angular speed will be beneficial even for DC generators. Most commonly, the generator will deliver AC power, either directly or through an inverter, at a frequency consistent with the local electrical grid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The above brief description as well as other objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of illustrative embodiments in accordance with the present invention when taken in conjunction with the accompanying drawings, wherein: 
           [0020]      FIG. 1  is an elevational view of a fluid driven energy conversion apparatus that implements a method, all according to principles of the present invention; 
           [0021]      FIG. 2  is an elevational, sectional view taken along the axis of the harmonic drive of  FIG. 1 ; and 
           [0022]      FIG. 3  is a cross-sectional view taken along line  3 - 3  of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Referring to  FIG. 1 , a fluid driven energy conversion apparatus is shown with a hub  10  supporting turbine blades  12 , which are all rotatably mounted on supporting frame  14 . Blades  12  are designed to be driven by wind and are herein referred to as a fluid driven turbine (wind being considered a fluid). Frame  14  can be azimuthally pivoted on tower  16  so that blades  10  can face upwind. Hub  10  is connected to input coupling  18  of harmonic drive  20 . 
         [0024]    Harmonic drive  20  has an output shaft  22  that connects to and drives electrical generator  24 . As explained further hereinafter, harmonic drive increases the angular speed applied to generator  24 , allowing it to work at a higher frequency. In most cases, electrical energy at higher frequency is more easily handled, especially in electromagnetic devices where the size of a magnetic core will be affected by frequency. 
         [0025]    Electrical generator  24  will have an AC generator that powers an inverter, which rectifies the AC voltage and then produces electrical energy at a convenient frequency. While such an inverter may be located on tower  16 , in some cases, the inverter may be located at the foot of the tower, or elsewhere. In still other embodiments no inverter will be used and power from an AC or DC generator will be used directly without an intervening inverter. 
         [0026]    In most instances, the electrical output  26  of generator  24  will be incorporated into an electrical grid or will be dedicated to powering one or more specific electrical devices. In this embodiment output  26  will be AC at a frequency consistent with the local grid, e.g. 50 or 60 Hz. However, in some embodiments output  26  may be DC power. 
         [0027]    Referring to  FIGS. 2 and 3 , drive  20  is shown employing housing  28 , composed of housing shell  30  and circular backplate  32 . Shell  30  is primarily a hollow cylinder, open at both ends and formed with mounting feet  30 A that are used to bolt shell  32  to the previously mentioned frame  14 . Shell  30  is shown attached by bolts  34  into an annular ledge in backplate  32 . 
         [0028]    An inwardly facing, cylindrical hub  32 A on backplate  32  is fitted with annular grease seal  36  (or oil seals) and ball bearings  38 , although other embodiments may use angular contact bearings or roller bearings. Bearings  38  rotatably support the outer end of cylindrical sleeve  40 . Rigid ring  42  is sandwiched between sleeve  40  and input coupling  18 , and all three are held together by bolts  46 . Coupling  18  is primarily a solid of revolution whose forward end is formed into shaft  18 A having a keyway  18 B. The inside end of coupling  18  has a bowl shape with an annular recess that is fitted with ball bearings  44  to engage and support rotation within previously mentioned housing shell  30 . 
         [0029]    Rigid ring  42  has a number of internal teeth designed to engage external teeth on cup-shaped flexspline  48 . The base of flexspline  48  has an opening bordered by a flange  50  (open collar) that is attached to hub  32 A by bolts  52  inserted through the flange. 
         [0030]    Previously mentioned output shaft  22  is machined with a variety of diameters with the largest diameter at a midsection that passes through a complementary hole in the base of flexspline  48 . 
         [0031]    A forward portion of shaft  22  is rotatably supported in a throughbore in backplate  32  by ball bearings  54 , which are encompassed by snap ring  56  and grease seal  58 , although other devices may be used such angular contact bearings or roller bearings fitted with oil seals and held in place by implements other than snap rings. The rearwardmost end of shaft  22  has a reduced diameter and a keyway  22 A. The forwardmost end  226  of shaft  22  has a reduced diameter and is supported in a cavity in coupling  18  by needle bearings  60 . 
         [0032]    Keyed onto shaft  22  is a collar  61  encircled by sleeve  62 . Oval rotor  64  is attached on sleeve  62  and has on its perimeter, ball bearings  66 , shown riding between inner race  66 A and outer race  66 B. Inner race  66 A directly engages and conforms to the periphery of rotor  64  and outer race  66 B directly engages the inside surface of flexspline  48 , opposite its external teeth. 
         [0033]    Coupling  18 , rigid ring  42 , sleeve  40 , shaft  22  and rotor  64  all rotate about common axis  68  (also referred to as a given axis). 
         [0034]    Flexspline  48  is nested inside rigid ring  42 , and these elements  48  and  42  are herein referred to as an inner one and an outer one, respectively, of a nested pair of annular members. Rotor  64  is seen journalled on one side in housing  28  (specifically backplate  32 ), and on the opposite side in coupling  18 , which is part of the outer one of the nested pair of annular members that includes rigid ring  42 . 
         [0035]    Rotor  64  is oval, and is mounted to drive shaft  22 . Therefore, rotor  64  and bearing  66  (with races  66 A and  66 B) will function as a wave generator to deflect flexspline  48 , which is made of relatively flexible material. Being oval, this wave generator rotor  64  effectively has two lobes, although in some embodiments a different number of lobes may be employed. 
         [0036]    The wave generator shaft  22  will extend through an opening in the floor of flexspline  48  in one direction. The coupling  18  driving the rigid annulus  42  will extend in a direction opposite to the wave generator shaft  22 . These opposing directions place the input and output on opposite sides and facilitates placement of the harmonic drive between turbine blades  12  ( FIG. 1 ) and the electrical generator  24 . 
         [0037]    To facilitate an understanding of the principles associated with the foregoing apparatus, its operation will be briefly described.  FIG. 3  may be considered the initial condition where the orientation of major axis  70  of oval rotor  64  dictates where the teeth of flexspline  48  are extended radially the most and therefore engage the teeth of rigid ring  42 . 
         [0038]    Rigid ring  42  has more teeth than flexspline  48 . In this embodiment ring  42  has 160 teeth, while flexspline  48  has 158 teeth. As explained further below, this achieves a speed increasing ratio of 80:1, although it will be understood that in other embodiments different tooth counts and speed increasing ratios may be employed depending upon the generator type, desired AC frequency, etc. 
         [0039]    Effectively, teeth on annular members  42  and  48  will mesh over two limited contacts zones at opposite ends of major axis  70 . Teeth close to axis  70  will tend to be aligned while meshing teeth removed slightly from the axis will tend to be somewhat misaligned. Thus if the 160th tooth on ring  42  and the 158th tooth on flexspline  48  are aligned to mesh at one end of axis  70 , at the other end of the axis, the 80th tooth on ring  42  will be aligned to mesh with the 79th tooth on flexspline  48 . 
         [0040]    Frame  14  will be azimuthally turned upwind to power turbine blades  12 . Consequently, blades  12  will rotate hub  10  and input coupling  18  of harmonic drive  20 . Blades  12  typically are relatively long (e.g. 10 m long) and will not rotate at a speed appropriate for generator  24 . For this reason, harmonic drive  20  is arranged to act as a speed increaser offering a predetermined speed increasing ratio. 
         [0041]    Torque generated by blades  12  will rotate input coupling  18  and rigid ring  42  as well. This rotation about axis  68  is supported by bearings  44  and  38  on housing  28  (i.e., elements  30  and  32 ). Housing  28  is bolted onto frame  14  through mounting feet  30 A and thus will not rotate about axis  68 . 
         [0042]    The torque applied to rigid ring  42  will be transmitted to flexspline  48 . However, flexspline  48  is affixed to housing  28  by bolts  52  and cannot rotate about axis  68 . Instead, the applied torque will be transferred through ball bearings  66  (and races  66 A and  66 B) to rotor  64  which will rotate in the same direction as rigid ring  42 . 
         [0043]    Basically the teeth of ring  42  in the trailing regions of the zones of contact near axis  70  will tend to cam the trailing teeth of flexspline  48  downwardly, which tends to produces a camming action that turns rotor  64  in the same direction as ring  42 . 
         [0044]    To accommodate rotation of rigid ring  42 , rotor  64  must rotate much faster. If rigid ring  42  advances the width of one tooth on flexspline  48  ( 1/158 of a turn), rotor  64  must advance the zone of contact (i.e., axis  70 ) to a position where the teeth of annular members  42  and  48  are again centered so that the intertooth camming force subsides. 
         [0045]    Specifically, rotor  64  will advance 180° plus 1/158 of a turn, that is 80/158 of a turn. This translates into a speed increasing ratio of 80:1. This speed increasing ratio is based on the relative tooth counts: Specifically, the tooth count of ring  42  (160 teeth) divided by the difference in tooth counts (2 tooth difference). In operation, the major axis  70  will rotate to produce orbiting, discrete contacts zones at either end of the axis. While the foregoing describes two discrete contacts zones, other embodiments can employ a greater number of zones, or only one contact zone. 
         [0046]    For many installations the angular speed of turbine blades  12  will be in the range of 5-20 rpm. This speed range can be narrowed by adjusting the angle of attack of the blades  12  in a conventional manner. In addition, blades  12  can be braked or even feathered in the presence of extremely strong winds. Using such techniques, and assuming adequate wind, the angular speed can be kept in a smaller range, e.g. 17 rpm (plus or minus 2 rpm). With the angular speed of blades  12  in the foregoing range, the angular speed produced by harmonic drive  20  will be in the range of 1200-1520 rpm. 
         [0047]    Generator  24  will be designed to accommodate the angular speed from harmonic drive  20 . For example, a six pole generator driven at 1200 rpm will produce AC power at 60 Hz. A four pole generator driven at 1500 rpm will produce AC power at 50 Hz. It will be understood that different angular speeds and different frequencies can be employed in other embodiments. This AC power can be used directly, but in this embodiment frequency conversion will be achieved by rectifying the AC power and driving an inverter. In a known manner the inverter can produce an AC power at a frequency that can be regulated by the inverter. In some embodiments, the inverter will produce an AC voltage synchronous with a local power grid. 
         [0048]    Output  26  of generator  24  can be dedicated to supply power to certain electrical equipment; for example, the domestic electricity needs of a group of residences. Alternatively, the power from output  26  can be supplied to a larger grid that receives power from other turbines or from more traditional electrical power stations. When supplied to a larger grid, care will be taken to synchronize output  26  to the established phase of the grid. 
         [0049]    Referring to  FIG. 4 , components corresponding to those previously described in  FIGS. 1-3  bear the same reference numeral but increased by 100. In this embodiment fluid driven turbine  112  is driven by water flow  72  arriving through channel  74 A and discharging through channel  74 B. While water is described, it will be appreciated that fluids of various types may be employed instead, such as a variety of other liquids or gases. For example, the fluid flow can be exhaust gas from an engine, or sewage flowing through a sewer pipe. 
         [0050]    Turbine  112  may be of the type used in a hydroelectric plant. In other embodiments of turbine  112  may be a hydraulic motor having impeller blades of various types. Channels  74 A and  74 B may be pipes connected to turbine  112 , but in some embodiments the channels may be a free-flowing stream of water and turbine  112  a paddlewheel. In still other embodiments the fluid flow may be water flows driven by ocean waves or by tides. 
         [0051]    The output of turbine  112  is connected to harmonic drive  120 , which may be identical to the previously illustrated drive (drive  20  of  FIG. 1 ). As before, harmonic drive  120  operates through shaft  122  to power electrical generator  124 , which may be identical to the previously illustrated generator (generator  24  of  FIG. 1 ). Generator  124  provides electrical power on line  126 . 
         [0052]    Harmonic drive  120  operates in a similar manner to that described previously in order to increase the speed from turbine  112  to shaft  122  of generator  124 . 
         [0053]    It is appreciated that various modifications may be implemented with respect to the above described embodiments. Instead of using the rigid annulus an the input drive, some embodiments may use the flexspline instead as the input drive. The component sizes and the material used will depend on the expected power, speed and torque as well as the desired strength, reliablity, etc. The foregoing bearing are exemplary and may be replaced with any one of a variety of different bearings, such as roller bearings, needle bearings, ball bearings, etc. In some cases the harmonic drive may have a cooling system to prevent overheating. 
         [0054]    Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.