Abstract:
A flywheel electric generator comprises a star-up motor, a flywheel rotary shaft rotated by the motor, a flywheel rotating by coupling with the rotary shaft, a plurality of permanent magnets disposed at substantially equal spaces of center angles on outer circumferential sections of the flywheel, a pair of electromagnets arranged fixedly at positions on a diameter line of the flywheel so as to face the permanent magnets and an electronic generator rotationally driven by the rotary shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2005-346002, filed on Nov. 30, 2005, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a flywheel electric generator utilizing rotational kinetic energy of a flywheel.  
         [0003]     The flywheel electric generator is an electric generator to discharge kinetic energy stored in the flywheel coupled to a rotor of the electric generator, as electric power. That is, the flywheel electric generator employs a system by which electric energy is converted into rotational energy of an object having large inertia moment to store it. In general, the flywheel electric generator is often utilized to supply electric power to a load in need of pulse-like large electric power.  
         [0004]     For instance, a nuclear fusion system confining plasma by means of a magnetic field supplies electric power of several hundreds of thousands kw in a short time such as several seconds sometimes, so that it is disagreeable to directly obtain such pulse-like electric power from a electric power system because the influence on the power system is too considerable. Therefore, such a field of the electric power system employs the flywheel electric generator. The flywheel electric generator operates in such a cycle that it increases the number of rotations of an electric generator over a time interval of several minutes to store the kinetic energy in the flywheel, and discharges the kinetic energy stored in the flywheel in supplying the electric power to a load to result in a decrease in the number of the rotations of the electric generator.  
         [0005]     Usually, a conventional flywheel electric generator directly couples an electric motor for driving to an electric generator. An output from the electric generator independents from the electric power system and the flywheel electric generator also varies the number of rotations of the electric generator with the power supply to the load, so that a frequency also varies in synchronization with the number of rotations thereof.  
         [0006]      FIG. 7  shows a configuration view of a control device of such conventional flywheel electric generator. A flywheel electric generator  51  is driven by an electric motor for driving  52  to store the kinetic energy in the flywheel electric generator  51 . The electric motor  52  is connected to a receiving-power-end bus-bar  53  of the electric power system through a breaker  54   a  and controlled by a Scherbius device  55  on the basis of the number of rotations from a means  56  for detecting the number of rotations. The Scherbius device  55  conducts secondary exciting control of the electric motor  52  to regenerate a part of secondary electric power generated on a secondary side to the bus-bar  53  through a breaker  54   b.    
         [0007]     To supply the electric power from the flywheel electric generator  51  to a load  57 , the electric generator  51  is excited by an exciting device  58  to generate the electric power and supplies it to the load  57  to decrease the number of its own rotations. The electric generator  51  supplies an excitation power source to the exciting device  58  from the bus-bar  53  through a breaker  54   c  (refer to, for instance, Japanese Patent Application KOKAI Publication No. 2001-258294).  
         [0008]     With respect to a structure of a fly wheel electric generator, in a conventional flywheel electric generator, other than one, in which a flywheel is attached to a usual salient pole type electric generator to operate it by using a usual bearing in the atmosphere, a technique using a magnetic shaft composed of a levitating magnet and a levitating bulk made of a high-temperature superconductor positioned facing the levitating magnet in a sealed container and operating the flywheel electric generator by setting surrounding atmospheric pressure of the rotor in the sealed container to a range within 0.1 atm to 0.4 atm is disclosed (refer to, for instance, Japan Patent Application KOKAI Publication No. 6-303738).  
         [0009]     In such a conventional flywheel electric generator, the heavier the weight of the flywheel becomes, the larger an energy storage quantity becomes and, on the other hand, the larger a mechanical loss at the bearing, etc., becomes. Therefore, in the case of use of a usual bearing for the flywheel electric generator, a requirement for a large output causes a large mechanical loss at the bearing and certainly causes a reduction in efficiency as the flywheel electric generator.  
         [0010]     As disclosed in the latter patent document given above, the technique, in which the magnetic shaft composed of the levitating magnet and the levitating bulk made of the high-temperature superconductor positioned facing the levitating magnet is used in the sealed container, needs a large-scaled device for operating the high-temperature superconductor sufficiently.  
         [0011]     As mentioned above, the system for housing the flywheel electric generator in the sealed container is not preferable because the whole of the system becomes complex and large and the system takes a great deal of time in working maintenance and inspection and in re-starting thereafter.  
       BRIEF SUMMARY OF THE INVENTION  
       [0012]     The present invention is invented on the basis of the foregoing situation, and an object of the invention is to provide a flywheel electric generator capable of obtaining an output with efficiency even in the atmosphere.  
         [0013]     A flywheel electric generator according to an embodiment of the present invention includes a start-up motor; a flywheel rotary shaft which is rotated by the start-up motor; a flywheel which rotates by coupling with the flywheel rotary shaft; a plurality of permanent magnets which are disposed at a substantially equal distance on outer circumferential sections of the flywheel; a pair of electromagnets arranged at fixed positions on both sides of the flywheel along its diameter direction so as to face the permanent magnets; and an electric generator which is rotationally driven by the flywheel rotary shaft.  
         [0014]     In the flywheel electric generator described above, the flywheel is composed of two pieces of circular plates which are arranged separately in parallel to each other and a plurality of support plates which are disposed so as to couple the two pieces of the circular plates with one another on circumferential sections thereof, and the plurality of permanent magnets are supported on the plurality of the support plates, respectively.  
         [0015]     Further, in the flywheel electric generator, the flywheel rotary shaft is coupled with the start-up motor and the electric generator, respectively, through a first and a second clutches.  
         [0016]     Further, in the flywheel electric generator, the facing surfaces of the permanent magnets and the electromagnets are arranged at prescribed inclination angle.  
         [0017]     Further, in the flywheel electric generator, the inclination angle is not more than 30° each.  
         [0018]     Further, in the flywheel electric generator, the inclination angle is approximately 22.5° each.  
         [0019]     Further, in the flywheel electric generator, the first and second clutches are electromagnetic clutches.  
         [0020]     Further, in the flywheel electric generator, the permanent magnets of an even number are arranged on the outer circumferential sections of the flywheel.  
         [0021]     And further, in the flywheel electric generator, a minimum gap between the facing surfaces of the electromagnets and the permanent magnets is 1 mm.  
         [0022]     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0023]     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
         [0024]      FIG. 1  is an exemplary schematic side elevation view showing an embodiment of a flywheel electric generator of the present invention;  
         [0025]      FIG. 2  is an exemplary schematic horizontal plan view of the flywheel electric generator shown in  FIG. 1 ;  
         [0026]      FIG. 3  is an exemplary horizontal cross sectional view of the flywheel shown in  FIG. 1 ;  
         [0027]      FIG. 4  is an exemplary graph indicating measured torque of a stepping motor shown in  FIG. 3 ;  
         [0028]      FIG. 5  is an exemplary partly enlarged view of the stepping motor shown in  FIG. 3 ;  
         [0029]      FIG. 6  is an exemplary explanatory view used for calculating torque in operating the flywheel electric generator; and  
         [0030]      FIG. 7  is an exemplary block diagram showing an example of use of a conventional flywheel electric generator. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]     Hereinafter, embodiments of the present invention will be described with reference to the drawings in detail.  FIG. 1  is an exemplary side elevation view showing a schematic configuration of a flywheel electric generator regarding an embodiment of the present invention, and  FIG. 2  is its exemplary plan view.  
         [0032]     A flywheel electric generator  1  of the embodiment includes three stages of angle structures  2 ,  3  and  4  which are arranged at each position of an upper stage, a middle stage and a lower stage in a vertical direction, respectively. The upper stage angle structure  2  is formed, as shown in  FIG. 2 , of three arms  2   a  which are coupled so that they form a planar shape of a triangle. An upper stage bearing  5  is supported with three arms  2   a  through three bearing support arms  5   a  at the central part of the upper stage angle structure  2 . The middle stage angle structure  3  is also has the approximately same structure as that of the upper angle structure  2 . That is, the middle stage angel structure  3  is formed, as partly shown in  FIG. 3 , of three arms  3   a  which are coupled with one another so that its planar shape becomes a triangle. A middle stage bearing  6  is supported by the three arms  3   a  through three bearing support arms  6   a  at the central part of the middle stage angel structure  3 . The lower stage angel structure  4  is also has the approximately same structure as that of the upper angle structure  2 . That is, the lower stage angel structure  4  is also formed, as a partly shown in  FIG. 3 , of three arms  4   a  which are coupled with one another so that its planner shape becomes a triangle. A lower stage bearing  7  is supported by the three arms  4   a  through three bearing support arms  7   a  at the central part of the lower stage angle structure  4 .  
         [0033]     The tops of the angle structures  2 ,  3  and  4  are fixed with three fixing poles  8  formed in a vertically elected state on leg bases  9 , respectively, and the angle structures  2 .  3  and  4  of the three stages are integrally coupled with one another.  
         [0034]     The flywheel  11  is fixed to a flywheel rotary shaft  11   a  pivoted by an upper stage bearing  5  disposed at the upper stage angle structure  2  and by a middle stage bearing  6  disposed at the middle stage angle structure  3  by use of a hub  12 . The rotary shaft  11   a  is extended downward from the middle stage bearing  6  and its lower end is coupled with a first electromagnetic clutch  13 . The first electromagnetic clutch  13  is also coupled with a first pulley rotary shaft  14   a . Thus, the flywheel rotary shaft  11   a  and the first pulley rotary shaft  14   a  are coupled or separated in accordance with opening/closing of the first electromagnetic clutch  13 , and as a result, electric power is transmitted or shut off.  
         [0035]     The first pulley  14  is coupled with a start-up motor  16  fixed on the lower surface of the middle stage angel structure  3  through a transmission belt  15 . The transmission belt  15 , accordingly, transmits the electric power from the start-up motor  16  to the first pulley  14 . The start-up motor  16  is, for example, a two-pole motor of 2.2 kw using an inverter and its number of rotations is 3,400 rpm.  
         [0036]     The flywheel  11  is a basket-shaped rotor in which two metallic circular plates  11   b  are supported in parallel to each other with a plurality of sheets of iron-made support plates  17 . Here, the support plates  17  are formed, for instance, by 18 sheets thereof and arranged at substantially an equal angular space of around 20° on the peripheral edges of each circular plate  11   b . Each plate-like permanent magnet  18  is fixed on a surface of the sheet at an approximately central section in a vertical direction of each support plate  17 .  
         [0037]      FIG. 3  is the horizontal cross sectional view of the flywheel  11  shown in  FIG. 1 . As shown in  FIG. 3 , each plate surface of the support plates  17  is not perpendicular to each radius direction of the flywheel  11  and arranged with an inclination thereto. Each plate surface of the plate-like permanent magnets  18  fixed on each plate surface of the support plates  17  is also arranged with an inclination to the radius direction. The inclination angle is around 67.5° at the cross angle between the radius direction of the flywheel  11  and the plate surface of the permanent magnet  18 , and around 22.5° at the cross angle between a tangent direction of a circle forming the outer circumference of the flywheel  11  and the plate surface of the permanent magnet  18 .  
         [0038]     A pair of electromagnets  19  is arranged at fixed positions on both sides of the flywheel  11  along its diameter direction so as to face the permanent magnet  18 .  
         [0039]      FIG. 5  is a partly enlarged view showing a positional relationship between the permanent magnet  18  fixed to the outer circumferential section of the flywheel  11  and the electromagnet  19  disposed to face the permanent magnet  18 . The permanent magnet  18  has a shape of which the horizontal cross sectional shape is a rectangular with a long side  18   a  and a short side  18   b , and each corner  18   c  at which the sides  18   a  and  18   b  are crossed is arranged on an outer circumferential edge C of the flywheel  11 . Here, the rotating direction of the flywheel  11  is indicated by an arrow A. The long side  18   a  is arranged with an inclination so as to be closer to a central side rather than the outer circumferential edge C toward the rotating direction. The inclination angle is experimentally confirmed that the above-described angle is preferable therefor.  
         [0040]     On the other hand, the pair of electromagnets  19  is disposed at positions facing the permanent magnets  18  which are fixed on the outer circumferential sections of the flywheel  11  with prescribed gaps. The electromagnets  19  are respectively disposed, as shown in  FIG. 3 , on the opposite sides on a diameter line (not shown) crossing the flywheel  11 . Not shown in the figure, the pair of electromagnets  19  is supported with fixing poles  18  fixing the angle structures  2 ,  3  and  4  at the circumferences of the flywheel  11 .  
         [0041]     With the arrangement given above, each of the permanent magnet  18  and the electromagnet  19  form a magnetic circuit for a motor. In other words, the magnet  18  forms a rotor, the pair of electromagnets  19  forms a stator, and the supplying a pulse signal to the pair of electromagnets  19  forms a stepping motor (pulse motor). The stepping motor drives the flywheel  11 , for instance, at a time when the number of rotations is 400 rpm.  
         [0042]     In the lower section of the first pulley  14 , a break disk  21  operating as a disk break is fixed to the first pulley rotary shaft  14   a , and a second electromagnetic clutch  22  is coupled to the lower end of the rotary shaft  14   a . The opposed end of the second electromagnetic clutch  22  is fixed to a pulley rotary shaft  23   a  of which the lower end is pivoted by a lower stage bearing  7 . A second pulley  23  is fixed to the second pulley rotary shaft  23   a . A transmission belt  25  couples the second pulley  23  with an electric generator pulley  27  fixed to a rotary shaft of an electric generator  26 . The electric generator  26  rotating in accordance with the rotation of the electric generator pulley  27  has, for instance, a rated power of 7.5 kw, an AC frequency of 30 Hz and the number of rotations of 600 rpm.  
         [0043]     Next to this, operations of the electric generator  26  having the flywheel  11  configured as mentioned above will be described by dividing them into three steps.  
         [0044]     (Step 1: Start-Up Step)  
         [0045]     The electric generator  26  closes the first clutch  13  to star-up the rotation of the start-up motor  16  in a state with the second clutch  22  opened therein, then, transmits its torque to the first pulley rotary shaft  14   a  through the transmission belt  15  and the first pulley  14  to rotate it. At this moment, the first clutch  13  having closed, the first pulley rotary shaft  14   a  and the flywheel rotary shaft  11   a  are coupled with each other. The rotation of the first pulley rotary shaft  14   a  is thereby transmitted to the flywheel rotary shaft  11   a  to rotate it and further rotate the flywheel  11  fixed to the flywheel rotary shaft  11   a.    
         [0046]     (Step 2: Flywheel Rotation Step)  
         [0047]     After starting up the rotation of the flywheel  11 , the electric generator  26  opens the first clutch  13  to disconnect the flywheel rotary shaft  11   a  from the rotary shaft  14   a  of the first pulley  14 . In this state, the pair of electromagnets  19  is supplied with pulse currents by a pulse signal generator, which is not shown in the drawings. The pulse currents are applied at timing right after each permanent magnet  18  has passed through the position facing each electromagnet  19  by the rotations of the flywheel  11 . As the result of the excitation caused by the pulse signals from the electromagnets  19 , repulsive force generated between the electromagnets  19  and the permanent magnets  18  further applies torque to the flywheel  11  in the rotating direction thereof.  
         [0048]      FIG. 4  is a graph showing a result of measurement of relationships between relative positions of the permanent magnets  18  against the electromagnets  19  disposed on the flywheel  11  and the torque (knockout force). During the measurement, each plate face of the permanent magnet  18  is disposed in a state in which it is not inclined to the radius direction of the flywheel  11  but orthogonal thereto and each opposing gap between the permanent magnet  18  and the electromagnet  19  in the radius direction is kept at 1 mm. The lateral axis of  FIG. 4  indicates the distance (mm) between the permanent magnet  18  and electromagnet  19  in the rotating direction of the flywheel  11  in a range of 0 to 20 mm, and the longitudinal axis indicates the torque (kg) at the stepping motor.  
         [0049]     As cleared from  FIG. 4 , the torque of the stepping motor reaches a maximum value of around 8 kg when the distance between the permanent magnet  18  and the electromagnet  19  in the rotating direction is around 8 mm. The maximum torque is generated as pulling force when the distance between the permanent magnet  18  and the electromagnet  19  becomes 8 mm before the permanent magnet  18  passes through the position facing the electromagnet  19  (entrance side), and as reaction force when the distance between the permanent magnet  18  and the electromagnet  19  becomes 8 mm after the permanent magnet  18  passes through the position facing the electromagnet  19  (exit side). In the embodiment of the invention, however, as shown in  FIG. 5 , each plate surface of the permanent magnet  18  is inclined to the radius direction of the flywheel  11 , and the pulse currents are applied at the timing right after the permanent magnet  18  has passes through the position opposite to the electromagnet  19  by the rotation of the flywheel  11 . In other words, if the pulse currents for the electromagnet  19  are applied at the exit side, the electric generator  26  can continuously operate the torque also to the side  18   b  of the permanent magnet  18  after operating the torque to the side  18   a  of the outer circumferential side of the permanent magnet  18 . The operation results in enabling the electric generator  26  to apply a strong knockout force to the permanent magnet  18 . This fact is also confirmed experimentally.  
         [0050]     After the rotating speed of the flywheel  11  has reached a sufficient speed, even when the electric generator  26  stops applying the pulse currents to the electromagnet  19 , the flywheel  11  keeps the rotations by itself over a prescribed time interval by inertia.  
         [0051]     (Step 3: Power Generation Step)  
         [0052]     When the flywheel  11  reaches the prescribed number of rotations, the electric generator  26  brings both first and second clutches  13  and  22  into closed states. The operations of two clutches  13  and  22  produce coupling among the flywheel rotary shaft  11   a , the first pulley rotary shaft  14   a  and the second pulley rotary shaft  23   a  with one another. The coupling results in the transmission of the rotations of the flywheel  11  to the second pulley rotary shaft  23   a  through the flywheel rotary shaft  11   a  and the first pulley rotary shaft  14   a  to make the second pulley rotary shaft  23   a  rotate. The rotations of the second pulley rotary shaft  23   a  makes the second pulley  23  rotate and further makes the electric generator pulley  27  rotate through the transmission belt  25 . The electric generator pulley  27  being fixed to the rotary shaft of the electric generator  26 , the electric generator  26  generates the electric power. The electric generator  26  can be stopped by operating the break disk  21 .  
         [0053]     Successively, the torque acting on the flywheel rotary shaft  11   a  in operating the flywheel electric generator  1  will be described by referring to the explanatory view of the flywheel electric generator of the present invention shown in  FIG. 6 . In  FIG. 6 , two clutches  13  and  22  are in a state of closing in generating the electric power. Thus, each of the rotary shafts  11   a ,  14   a  and  23   a  being possible to be regarded as a single shaft, the clutches  13  and  22  are omitted from  FIG. 6 .  
         [0054]     The torque (TF) of the flywheel rotary shaft  11   a  becomes the sum of the torque (TA) from the start-up motor  16  and the torque (TB) from the stepping motor formed on the outer circumferential section of the flywheel  11 . Hereinafter, the torque (TF), (TA) and (TB) will be explained in turn.  
         [0055]     (a) Torque (TA) from the Start-up Motor  16  of the Flywheel Rotary Shaft  11   a    
         [0056]     The following Formula 1 is satisfied for the relationship among the torque (TF), (TA) and (TB) where the number of rotations of the start-up motor  16  is N (rpm), a torque is T (Nm) and rated electric power is H (kw).
 
 H={T (2π N )/60}/1,000  (Formula 1)
 
         [0057]     With modification of Formula 1, the following Formula 2 is satisfied where unit conversions are 1 kg=9.80 Nm, and NM=0.101972 kg·m.
 
 T =(60,000/2π) H/N   (Formula 2)
 
         [0058]     The Formula 2 is modified as follows: where the output from the start-up motor  16  is 2.2 kw and the number of rotations of flywheel rotary shaft  11   a  is 400 rpm 
 
 TA ( Nm )=(60,000/2π)2.2/400 
 
         [0059]     With performing a unit conversion from Nm into kg, the following formula is satisfied.  
               TA   ⁢           ⁢     (   kg   )       =       (     974   ×   2.2     )     /   400                 =     5.36   ⁢           ⁢     kg   ·   m                 
 
         [0060]     Therefore, the torque TA from the start-up motor  16  of the flywheel rotary shaft  11   a  becomes 5.36 kg·m.  
         [0061]     (b) Torque (TB) from the Stepping Motor formed on the Outer Circumferential Section of the Flywheel  11   
         [0062]     Since the diameter of the flywheel  11  is 1.5 m, the torque (knockout force) by the repulsive force from the permanent magnet  18  and the electromagnet  19  to the flywheel  11  is 8 kg, and the electromagnets  19  are disposed at two spots, respectively, the torque TB from the stepping motor is expressed as follows:
 
 TB =(8×1.5/2)×2=12 kg·m
 
         [0063]     Accordingly, the torque (TF) from the flywheel rotary shaft  11   a  is expressed as follows:
 
 TF=TA+TB= 5.36 kg·m+12 kg·m=17.36 kg·m
 
         [0064]     Next, in a calculation of the torque (TG) of the electric generator  26  by the torque (TF) of the flywheel rotary shaft  11   a , because the number of the rotations of the electric generator  26  is 600 rpm, the torque (TG) is obtained as follow:
 
 TG= 17.36/(600/400)=11.57 kg·m
 
         [0065]     On the other hand, performing a single calculation of the torque (TH) of the rotary shaft of the electric generator  26  by use of Formula 2, because the output from the electric generator  26  is 67 kw and the number of rotations thereof is 600 rpm, the torque (TH) is obtained as follows:
 
 TH =(6.7×974)/600=10.87 kg·m
 
         [0066]     Here, comparing the torque (TG) of the rotary shaft of the electric generator  26  obtained from the torque (TF) of the flywheel rotary shaft  11   a  to the torque (TH) singly calculated by use of Formula 2, the relationship between the torques (TG) and (TH) is expressed as follows:
 
 TG= 11.57 kg·m&gt;TH=10.87 kg·m
 
         [0067]     That is to say, the flywheel  11  applies, to the electric generator  26 , torque not smaller than the rated power of the electric generator  26 . Consequently, it has become obvious that the flywheel electric generator  1  can increase the generated electric power which is output from the electric generator  26 .  
         [0068]     The present invention is not limited to the specific details and representative embodiments shown and described herein, this invention may be modified in various forms without departing from the sprit or scope of the general inventive concept thereof.