Patent Publication Number: US-2015061428-A1

Title: Axial gap-type power generator

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-177761, filed on Aug. 29, 2013; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an axial gap-type power generator. 
     BACKGROUND 
     In an axial gap-type power generator, a stator and a rotor are installed via a gap, along an axial direction of a rotation shaft. In the axial gap-type power generator, the stator is provided with a coil and the rotor is provided with a magnet (permanent magnet). The axial gap-type power generator is installed, for example, in a wind power generator 
     In the axial gap-type power generator, since heat generation occurs in a power generation operation, it is necessary to cool the stator and the rotor. Therefore, the axial gap-type power generator is configured such that a cooling wind flows through a gap between the stator and the rotor. For example, in the case of an “open type” in which the stator and the rotor are not housed in a housing, wind flowing in from the surroundings is used as a cooling wind. 
       FIG. 14  is a view illustrating an axial gap-type power generator according to a first related art.  FIG. 14  illustrates a cross section of the axial gap-type power generator. 
     As illustrated in  FIG. 14 , an axial gap-type power generator  100  is, for example, an open type and has a pair of rotors  21 ,  22  and a stator  31 . 
       FIG. 15A  and  FIG. 15B  are views illustrating the rotors in the axial gap-type power generator according to the first related art.  FIG. 15A  illustrates a first rotor  21  of the pair of rotors  21 ,  22 , and  FIG. 15B  illustrates a second rotor  22 .  FIG. 15A  illustrates a surface of the first rotor  21  facing the second rotor  22 .  FIG. 15B  illustrates a surface of the second rotor  22  facing the first rotor  21 . 
     In the axial gap-type power generator  100 , the first rotor  21  and the second rotor  22  are provided with openings  21 K,  22 K at their central portions respectively as illustrated in  FIG. 14 ,  FIG. 15A , and  FIG. 15B , and a rotation shaft  11  passes through the openings  21 K,  22 K. As illustrated in  FIG. 15A , and  FIG. 15B , the first rotor  21  and the second rotor  22  are connected to the rotation shaft  11  via ribs  11 R. 
     Further, as illustrated in  FIG. 14 ,  FIG. 15A , and  FIG. 15B , the first rotor  21  and the second rotor  22  have magnets  211 ,  221 , respectively. A plurality of each of magnets  211 ,  221  are provided on surfaces facing each other of the first rotor  21  and the second rotor  22 , respectively. In addition, guides  21 G,  22 G are provided at outer peripheral portions at the first rotor  21  and the second rotor  22 , respectively. 
     In the axial gap-type power generator  100 , the stator  31  is installed between the first rotor  21  and the second rotor  22  as illustrated in  FIG. 14 . The stator  31  has the gaps G 1 , G 2  intervening with respect to the first rotor  21  and the second rotor  22 , respectively. The stator  31  is formed with an opening  31 K at its central portion, and the rotation shaft  11  passes through the opening  31 K. 
     Further, the stator  31  has a coil  311  as illustrated in  FIG. 14 . The coil  311  is embedded inside the stator  31 . Though not illustrated, a plurality of the coils  311  are arranged in a rotation direction R (circumferential direction) of the rotation shaft  11  similarly to the plurality of magnets  211 ,  221 . The coil  311  is covered, for example, with an insulator (not illustrated) such as a resin and is thus insulated from the surroundings. 
       FIG. 16  is a view illustrating a flow of the cooling wind in the axial gap-type power generator according to the first related art.  FIG. 16  illustrates, similarly to  FIG. 14 , the cross section of the axial gap-type power generator, and schematically illustrates the outline of the cooling wind flowing in the cross section. 
     When the axial gap-type power generator  100  is the open type as illustrated in 
       FIG. 16 , the wind flowing in from the surroundings of the axial gap-type power generator  100  is used as cooling winds F 10 , F 11 , F 20 , F 21 . Here, for example, the wind flowing from the side of the first rotor  21  to the side of the second rotor  22  is used as the cooling winds F 10 , F 11 , F 20 , F 21  in the axial gap-type power generator  100 . 
     More specifically, the cooling wind F 10  is guided from the surroundings of the axial gap-type power generator  100  to the opening  21 K of the first rotor  21 . The cooling wind F 10  flows from the side of the first rotor  21  to the side of the second rotor  22  in the axial direction of the rotation shaft  11 , and passes through the opening  21 K of the first rotor  21 . Then, the cooling wind F 10  passed through the opening  21 K of the first rotor  21  flows into the gap G 1  between the first rotor  21  and the stator  31  and flows into the opening  31 K of the stator  31 . The cooling wind F 11  flowed into the gap G 1  between the first rotor  21  and the stator  31  flows from the inside to the outside in the radial direction of the rotation shaft  11 . Then, the cooling wind F 20  flowed into the opening  31 K of the stator  31  flows into the gap G 2  between the second rotor  22  and the stator  31  after passing through the opening  31 K. The cooling wind F 21  flowed into the gap G 2  between the second rotor  22  and the stator  31  flows from the inside to the outside in the radial direction of the rotation shaft  11 . 
     As in the above manner, cooling is performed for the first rotor  21 , the second rotor  22 , and the stator  31  in the axial gap-type power generator  100 . 
     However, in the axial gap-type power generator  100 , the cooling cannot be sufficiently performed to result in a decrease in power generation performance or the like in some cases. For example, when the rotation shaft  11  rotates through inertia in the case where there is weak or no wind in the surroundings, sufficient cooling wind does not flow into the gaps G 1 , G 2  between the stator  31  and the rotors  21 ,  22 , and therefore the cooling is insufficient. This may result in that the magnets increased in temperature are not sufficiently cooled in the axial gap-type power generator  100  to undergo demagnetization, thereby decreasing the power generation output. 
     For this reason, there are suggested various methods for effectively performing cooling in the axial gap-type power generator. 
     For example, it is suggested that a radial fan is installed on a surface of the rotor opposite to a surface thereof facing the stator and an air-exhaust port is provided outside in the radial direction. Further, a heat release fin is installed at an outer peripheral part of the stator and a cooling fan is installed at an outer peripheral part of the rotor to send a cooling wind to the heat release fin and the like are suggested. Further, it is suggested that a cooling passage is formed in the rotor and a fan is installed on the rotation shaft to send a cooling wind to the cooling passage 
       FIG. 17  is a view illustrating an axial gap-type power generator according to a second related art.  FIG. 17  illustrates, similarly to  FIG. 14 , a cross section of the axial gap-type power generator. 
     As illustrated in  FIG. 17 , in an axial gap-type power generator  100   b,  different from the above-described axial gap-type power generator  100  (see, for example,  FIG. 14  and so on), blades  212 J,  222 J are installed at the first rotor  21  and the second rotor  22  respectively to effectively performing the cooling. 
     Specifically, the blades  212 J are installed on a surface of the first rotor  21  opposite to a surface thereof facing the second rotor  22 . Further, the blades  222 J are installed on a surface of the second rotor  22  opposite to a surface thereof facing the first rotor  21 . 
       FIG. 18A  and  FIG. 18B  are views illustrating a flow of the cooling wind in the axial gap-type power generator according to the second related art.  FIG. 18A  and  FIG. 18B  illustrate the cross section of the axial gap-type power generator, similarly to  FIG. 17 , and schematically illustrates the outline of the cooling wind flowing in the cross section.  FIG. 18A  illustrates the case where there is no wind around the axial gap-type power generator  100   b,  and  FIG. 18B  illustrates the case where wind flows in as the cooling wind from the surroundings of the axial gap-type power generator  100   b.    
     As illustrated in  FIG. 18A , when the rotation shaft  11  rotates through inertia in the case where there is no wind in the surroundings, cooling winds M 10   j,  M 20   j  are generated by the blades  212 J,  222 J and flow. Here, the cooling wind M 10   j  flows from the inside to the outside in the radial direction of the rotation shaft  11 , on the side of the surface of the first rotor  21  opposite to the surface thereof facing the second rotor  22 . Further, the cooling wind M 20   j  flows from the inside to the outside in the radial direction of the rotation shaft  11 , on the side of the surface of the second rotor  22  opposite to the surface thereof facing the first rotor  21 . 
     As illustrated in  FIG. 18B , when the rotation shaft  11  rotates in the case where wind in the surroundings flows in as the cooling wind, the cooling winds M 10   j,  M 20   j  are generated by the blades  212 J,  222 J and flow, as in the case illustrated in  FIG. 18(   a ). In addition, the cooling winds F 10 , F 11 , F 20 , F 21  flow, as in the case illustrated in  FIG. 16 . 
     However, as is found from  FIG. 18A  and  FIG. 18B , when the axial gap-type power generator  100   b  is the open type, the cooling winds M 10   j,  M 20   j  generated by the blades  212 J,  222 J do not flow through the gap G 1  between the first rotor  21  and the stator  31  nor the gap G 2  between the second rotor  22  and the stator  31 . 
     Therefore, also in the axial gap-type power generator  100   b,  the cooling is not sufficient to cause a decrease in reliability and a decrease in power generation performance in some cases. For example, the magnets  211 ,  221  increased in temperature are not sufficiently cooled to undergo demagnetization, thereby decreasing the power generation output in some cases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view illustrating an axial gap-type power generator according to a first embodiment. 
         FIG. 2A  and  FIG. 2B  are views illustrating rotors in the axial gap-type power generator according to the first embodiment. 
         FIG. 3  is a view illustrating blades enlarged in the axial gap-type power generator according to the first embodiment. 
         FIG. 4A  and  FIG. 4B  are views illustrating a flow of a cooling wind in the axial gap-type power generator according to the first embodiment. 
         FIG. 5  is a view illustrating the flow of the cooling wind in the axial gap-type power generator according to the first embodiment. 
         FIG. 6  is a view illustrating an axial gap-type power generator according to a second embodiment. 
         FIG. 7A  and  FIG. 7B  are views illustrating rotors in the axial gap-type power generator according to the second embodiment. 
         FIG. 8A  and  FIG. 8B  are views illustrating a flow of a cooling wind in the axial gap-type power generator according to the second embodiment. 
         FIG. 9A  and  FIG. 9B  are views illustrating the flow of the cooling wind in the axial gap-type power generator according to the second embodiment. 
         FIG. 10  is a view illustrating an axial gap-type power generator according to a third embodiment. 
         FIG. 11A  and  FIG. 11B  are views illustrating rotors in the axial gap-type power generator according to the third embodiment. 
         FIG. 12A  and  FIG. 12B  are views illustrating a flow of a cooling wind in the axial gap-type power generator according to the third embodiment. 
         FIG. 13A  and  FIG. 13B  are views illustrating the flow of the cooling wind in the axial gap-type power generator according to the third embodiment. 
         FIG. 14  is a view illustrating an axial gap-type power generator according to a first related art. 
         FIG. 15A  and  FIG. 15B  are views illustrating rotors in the axial gap-type power generator according to the first related art. 
         FIG. 16  is a view illustrating a flow of a cooling wind in the axial gap-type power generator according to the first related art. 
         FIG. 17  is a view illustrating an axial gap-type power generator according to a second related art. 
         FIG. 18A  and  FIG. 18B  are views illustrating a flow of a cooling wind in the axial gap-type power generator according to the second related art. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments will be explained referring to the drawings. 
     An axial gap-type power generator in an embodiment includes a rotor provided with a magnet and a stator provided with a coil, the rotor and the stator being arranged via a gap in an axial direction of a rotation shaft. Further, a blade is installed at the rotor and the blade generates a cooling wind by rotation of the rotor. Here, the blade is installed at the rotor so that the cooling wind flows through the gap between the rotor and the stator from an inside to an outside in a radial direction of the rotation shaft. 
     First Embodiment 
     [A] Configuration of Axial Gap-Type Power Generator 
       FIG. 1  is a view illustrating an axial gap-type power generator according to a first embodiment.  FIG. 1  illustrates its cross section. 
     As illustrated in  FIG. 1 , an axial gap-type power generator  1  is, for example, an open type and has a pair of rotors  21 ,  22  and a stator  31 . 
     Though not illustrated, the axial gap-type power generator  1  is installed in an upwind-type wind power generator in which a plurality of windmill blades (not illustrated) extending along a radial direction of a rotation shaft  11  are fixed, for example, to the first rotor  21  and the second rotor  22 . In the axial gap-type power generator  1 , the plurality of windmill blades (not illustrated) receive wind flowing from the side of the first rotor  21  to the side of the second rotor  22  in the axial direction of the rotation shaft  11  and the rotation shaft  11  thereby rotates to perform power generation. 
     Components constituting the axial gap-type power generator  1  will be described in sequence. 
     [A-1] Regarding Pair of Rotors  21 ,  22   
       FIG. 2A  and  FIG. 2B  are views illustrating the rotors in the axial gap-type power generator according to the first embodiment. 
       FIG. 2A  illustrates the first rotor  21  of the pair of rotors  21 ,  22 , and  FIG. 2B  illustrates the second rotor  22 .  FIG. 2A  illustrates a surface of the first rotor  21  facing the second rotor  22 .  FIG. 2B  illustrates a surface of the second rotor  22  facing the first rotor  21 . 
     In the axial gap-type power generator  1 , the first rotor  21  and the second rotor  22  are plate-shaped bodies in a ring shape as illustrated in  FIG. 1 ,  FIG. 2A ,  FIG. 2B , and are formed with circular openings  21 K,  22 K at their central portions, respectively. The opening  21 K of the first rotor  21  and the opening  22 K of the second rotor  22  are formed to be equal in inner diameter to each other. 
     Both of the first rotor  21  and the second rotor  22 , in which the rotation shaft  11  passes through the circular openings  21 K,  22 K as illustrated in  FIG. 1 , are installed to be coaxial with the rotation shaft  11 . Both of the first rotor  21  and the second rotor  22  are connected to the rotation shaft  11  via ribs  11 R as illustrated in  FIG. 2A ,  FIG. 2B . More specifically, in each of the openings  21 K,  22 K of the first rotor  21  and the second rotor  22 , a plurality of ribs  11 R are provided to extend along the radial direction of the rotation shaft  11 , and each of the plurality of ribs  11 R has one end portion fixed to the rotation shaft  11  and the other end portion fixed to the first rotor  21  or the second rotor  22 . Note that though not illustrated, the rotation shaft  11  is rotatably supported by a bearing (not illustrated). Further, the illustration of the ribs  11 R is omitted in  FIG. 1 . 
     The first rotor  21  and the second rotor  22  have magnets  211 ,  221  (permanent magnets) respectively as illustrated in  FIG. 1 ,  FIG. 2A ,  FIG. 2B . As illustrated in  FIG. 1 , the magnets  211 ,  221  are provided on surfaces of the first rotor  21  and the second rotor  22  facing each other, respectively. The magnets  211 ,  221  are arranged such that their magnetization directions are along the axial direction of the rotation shaft  11 . As illustrated in  FIG. 2A  and  FIG. 2B , a plurality of each of the magnets  211 ,  221  are arranged around the rotation shaft  11  on the first rotor  21  and the second rotor  22  respectively so that their polarities are alternate in a rotation direction R of the rotation shaft  11 . 
     Further, the first rotor  21  and the second rotor  22  are provided with guides  21 G,  22 G as illustrated in  FIG. 1 ,  FIG. 2A ,  FIG. 2B , respectively. The guides  21 G,  22 G are plate-shaped bodies in a ring shape and provided at outer peripheral portions of the first rotor  21  and the second rotor  22 , respectively. The guides  21 G,  22 G are smaller in thickness than the first rotor  21  and the second rotor  22 , and provided at portions on the sides of surfaces of the first rotor  21  and the second rotor  22  facing each other, respectively. 
     In this embodiment, a plurality of blades  212  are installed at the first rotor  21  as illustrated in  FIG. 1 ,  FIG. 2A . 
     The plurality of blades  212  are provided on an inner peripheral surface of the first rotor  21  as illustrated in  FIG. 1 ,  FIG. 2A . The plurality of blades  212  are arrayed to line up at regular intervals in the rotation direction R of the rotation shaft  11  inside the opening  21 K of the first rotor  21 . Though details will be described later, the plurality of blades  212  are configured such that when they are rotated with the rotation of the rotation shaft  11 , a cooling wind (not illustrated) flows from the side of the first rotor  21  to the side of the second rotor  22 . 
       FIG. 3  is a view illustrating the blades enlarged in the axial gap-type power generator according to the first embodiment. 
       FIG. 3  illustrates a part of the inner peripheral surface of the first rotor  21  in which the right side is the stator  31  side. 
     As illustrated in  FIG. 3 , each of the plurality of blades  212  is formed such that one end portion on the side of the stator  31  (right side) is located posterior in the rotation direction R to the other end portion. 
     [A-2] Regarding Stator  31   
     In the axial gap-type power generator  1 , the stator  31  is installed between the first rotor  21  and the second rotor  22  as illustrated in  FIG. 1 . A gap G 1  intervenes between the stator  31  and the first rotor  21 , and a gap G 2  intervenes between the stator  31  and the second rotor  22 . Though not illustrated, the stator  31  is supported by a support member (not illustrated). 
     As illustrated in  FIG. 1 , the stator  31  is formed with an opening  31 K at its central portion. The opening  31 K of the stator  31  is a circle through which the rotation shaft  11  passes. The stator  31  is installed to be coaxial with the rotation shaft  11  as with the first rotor  21  and the second rotor  22 . The opening  31 K of the stator  31  is formed to be smaller in inner diameter than the opening  21 K of the first rotor  21  and the opening  22 K of the second rotor  22 . 
     Further, as illustrated in  FIG. 1 , the stator  31  has a coil  311 . The coil  311  is embedded inside the stator  31 . Though not illustrated, a plurality of the coils  311  are arranged in the rotation direction R of the rotation shaft  11  as with the plurality of magnets  211 ,  221 . The coils  311  are covered with, for example, an insulator (not illustrated) such as a resin and thus electrically insulated from the surroundings. 
     [B] Regarding Flow of Cooling Wind 
       FIG. 4A ,  FIG. 4B , and  FIG. 5  are views illustrating the flow of the cooling wind in the axial gap-type power generator according to the first embodiment. 
       FIG. 4A  and  FIG. 4B  illustrate, similarly to  FIG. 1 , the cross section of the axial gap-type power generator, and schematically illustrate the outline of the cooling wind flowing in the cross section.  FIG. 4A  illustrates the case where there is no wind around the axial gap-type power generator  1 .  FIG. 4B  illustrates the case where wind flows in as the cooling wind from the surroundings of the axial gap-type power generator  1 . Further,  FIG. 5  illustrates, similarly to  FIG. 3 , the blades  212  enlarged, and schematically illustrates the outline of the cooling wind flowing in the enlarged part. 
     As illustrated in  FIG. 4A , when the rotation shaft  11  rotates through inertia in the case where there is no wind in the surroundings, a cooling wind M 10  is generated by the blades  212  and flows. The cooling wind M 10  flows from the first rotor  21  to the side of the second rotor  22 . More specifically, as illustrated in  FIG. 5 , the cooling wind M 10  flows between the plurality of blades  212 . 
     Thereafter, the cooling wind M 10  hits against the surface of the stator  31  on the side of the first rotor  21  and then flows into the gap G 1  between the first rotor  21  and the stator  31  as illustrated in  FIG. 4A . Then, a cooling wind M 11  flowed into the gap G 1  between the first rotor  21  and the stator  31  flows from the inside to the outside in the radial direction of the rotation shaft  11 . 
     As illustrated in  FIG. 4B , when the rotation shaft  11  rotates in the case where wind flows in as the cooling wind from the surroundings, a cooling wind M 10  is generated by the blades  212  and flows through the parts, as in the case illustrated in  FIG. 4A . 
     In addition, when the rotation shaft  11  rotates in the case where the wind flows in as the cooling wind from the surroundings, cooling winds F 10 , F 11 , F 20 , F 21  flow through the parts as illustrated in  FIG. 4B , as in the case illustrated in  FIG. 16 . Namely, the wind flowing from the side of the first rotor  21  to the side of the second rotor  22  is used as the cooling winds F 10 , F 11 , F 20 , F 21 . 
     More specifically, as illustrated in  FIG. 4B , the cooling wind F 10  is guided from the surroundings of the axial gap-type power generator  1  to the opening  21 K of the first rotor  21 . The cooling wind F 10  flows from the side of the first rotor  21  to the side of the second rotor  22  in the axial direction of the rotation shaft  11 , and passes through the opening  21 K of the first rotor  21 . Then, the cooling wind F 10  passed through the opening  21 K of the first rotor  21  flows into the gap G 1  between the first rotor  21  and the stator  31 . The cooling wind F 11  flowed into the gap G 1  between the first rotor  21  and the stator  31  flows from the inside to the outside in the radial direction of the rotation shaft  11 . 
     Therefore, in this embodiment, as illustrated in  FIG. 4B , both of the cooling wind F 11  flowed in from the surroundings and the cooling wind M 11  generated by the blades  212  and flowed in flow through the gap G 1  between the first rotor  21  and the stator  31 . In short, a cooling wind (M11+F11) made by combining both of the winds flows from the inside to the outside in the radial direction. 
     As is understood from the above, the amount of the cooling wind flowing through the gap G 1  between the first rotor  21  and the stator  31  can be increased in this embodiment. 
     [C] Conclusion 
     As described above, in the axial gap-type power generator  1  in this embodiment, the blades  212  generating the cooling wind M 10  by the rotation of the first rotor  21  are installed at the first rotor  21 . Here, the blades  212  are installed at the first rotor  21  so that the cooling wind M 11  flows through the gap G 1  between the first rotor  21  and the stator  31  from the inside to the outside in the radial direction of the rotation shaft  11  by the cooling wind M 10  generated by the blades  212 . Therefore, the flow rate of the cooling wind flowing through the gap G 1  between the first rotor  21  and the stator  31  increases as described above in this embodiment (see  FIG. 4A ,  FIG. 4B  and so on). 
     Accordingly, in this embodiment, it is possible to effectively cool the first rotor  21  and the stator  31 , thereby realizing the improvement in reliability and the improvement in power generation performance. For example, it is possible to effectively cool the coils  311  increased in temperature due to the power generation operation. Further, it is possible to effectively cool the magnets  211  increased in temperature, thereby suppressing occurrence of demagnetization and preventing a decrease in power generation output. 
     [D] Modification Example 
     The case where the opening  31 K of the stator  31  is smaller in inner diameter than the opening  21 K of the first rotor  21  and the opening  22 K of the second rotor  22  has been described in the above embodiment, but it is not limited to this. For example, the opening  31 K of the stator  31  may be larger in inner diameter than the opening  21 K of the first rotor  21  and the opening  22 K of the second rotor  22 . In this case, when the cooling wind M 10  generated by the blades  212  flows through the opening  31 K of the stator  31  after passing through the opening  21 K of the first rotor  21 , the cooling wind M 10  hits against, for example, the ribs  11 R installed between the second rotor  22  and the rotation shaft  11 , and flows into the gap G 2  between the second rotor  22  and the stator  31 . Then, similarly to the above, the cooling wind flows through the gap G 2  between the second rotor  22  and the stator  31  from the inside to the outside in the radial direction of the rotation shaft  11  (see  FIG. 4A ,  FIG. 4B  and so on). 
     The case where the axial gap-type power generator  1  is the “open type” and the first rotor  21 , the second rotor  22 , and the stator  31  are not accommodated in a housing has been described in the above embodiment, but they are not limited to this. The first rotor  21 , the second rotor  22 , and the stator  31  may be accommodated in a housing. 
     The case where the axial gap-type power generator  1  is used for the wind power generator has been described in the above embodiment, but it is not limited to this. The axial gap-type power generator  1  may be used for another device. 
     The case where there are two rotors  21 ,  22  and one stator  31  has been described in the above embodiment, but they are not limited to this. The axial gap-type power generator may be configured such that, for example, there are two stators and one rotor located between the two stators. 
     Second Embodiment 
     [A] Configuration of Axial Gap-Type Power Generator 
       FIG. 6  is a view illustrating an axial gap-type power generator according to a second embodiment.  FIG. 6  illustrates, similarly to  FIG. 1 , its cross section. 
       FIG. 7A  and  FIG. 7B  are views illustrating rotors in the axial gap-type power generator according to the second embodiment.  FIG. 7A  illustrates, similarly to  FIG. 2A , the first rotor  21  of the pair of rotors  21 ,  22 , and  FIG. 7B  illustrates, similarly to  FIG. 2B , the second rotor  22 . 
     This embodiment is different from the first embodiment in installation positions of blades  212   b,    222   b  as illustrated in  FIG. 6 ,  FIG. 7A ,  FIG. 7B . Except this point and points related to this, this embodiment is the same as the first embodiment. Therefore, description of portions overlapped with those of the first embodiment will be accordingly omitted in this embodiment. 
     In this embodiment, as illustrated in  FIG. 6 ,  FIG. 7A ,  FIG. 7B , the blades  212   b ,  222   b  are provided on surfaces facing each other of the guide  21 G of the first rotor  21  and the guide  22 G of the second rotor  22  respectively, different from those in the first embodiment. Though details will be described later, the blades  212   b,    222   b  are configured such that when they rotate with the rotation of the rotation shaft  11 , a cooling wind (not illustrated) flows from the inside to the outside in the radial direction of the rotation shaft  11 . 
     More specifically, at the first rotor  21 , the plurality of blades  212   b  are arrayed at regular intervals in a rotation direction R of the rotation shaft  11  as illustrated in  FIG. 7A . Each of the plurality of blades  212   b  is formed such that one end portion located on the inside in the radial direction is located anterior in the rotation direction R to the other end portion located on the outside. 
     At the second rotor  22 , the plurality of blades  222   b  are arrayed at regular intervals in the rotation direction R of the rotation shaft  11  as illustrated in  FIG. 7B . Each of the plurality of blades  222   b  is formed such that one end portion located on the inside in the radial direction is located anterior in the rotation direction R to the other end portion located on the outside. 
     [B] Regarding Flow of Cooling Wind 
       FIG. 8A ,  FIG. 8   b,    FIG. 9A , and  FIG. 9B  are views illustrating the flow of the cooling wind in the axial gap-type power generator according to the second embodiment. 
       FIG. 8A  and  FIG. 8B  illustrate, similarly to  FIG. 6 , the cross section of the axial gap-type power generator, and schematically illustrate the outline of the cooling wind flowing in the cross section. Here,  FIG. 8A  illustrates the case where there is no wind around the axial gap-type power generator, and  FIG. 8B  illustrates the case where wind flows in as the cooling wind from the surroundings of the axial gap-type power generator. Further,  FIG. 9A  illustrates, similarly to  FIG. 7A , the first rotor  21  of the pair of rotors  21 ,  22 , and  FIG. 9B  illustrates, similarly to  FIG. 7B , the second rotor  22 .  FIG. 9A  and  FIG. 9B  schematically illustrate the outline of the cooling winds flowing through the first rotor  21  and the second rotor  22 , respectively. 
     As illustrated in  FIG. 8A , when the rotation shaft  11  rotates through inertia in the case where there is no wind in the surroundings, cooling winds M 12   b,  M 22   b  are generated by the blades  212   b,    222   b  and flow. The cooling winds M 12   b,  M 22   b  flow from the inside to the outside in the radial direction of the rotation shaft  11 . More specifically, as illustrated in  FIG. 9A  and  FIG. 9B , the cooling winds M 12   b,  M 22   b  flow between the plurality of blades  212   b,    222   b.  Therefore, as illustrated in  FIG. 8A , air in the gap G 1  between the first rotor  21  and the stator  31  and in the gap G 2  between the second rotor  22  and the stator  31  flows from the inside to the outside by the cooling winds M 12   b , M 22   b  generated by the blades  212   b,    222   b.  In other words, a cooling wind M 11   b  flows through the gap G 1  between the first rotor  21  and the stator  31  and a cooling wind M 21   b  flows through the gap G 2  between the second rotor  22  and the stator  31 . 
     As illustrated in  FIG. 8B , when the rotation shaft  11  rotates in the case where the cooling wind flows in from the surroundings, the cooling winds M 12   b,  M 22   b  are generated by the blades  212   b,    222   b  and flow as in the case illustrated in  FIG. 8A . Therefore, similarly to the case illustrated in  FIG. 8A , the cooling wind Ml lb flows through the gap G 1  between the first rotor  21  and the stator  31  and the cooling wind M 21   b  flows through the gap G 2  between the second rotor  22  and the stator  31 . 
     In addition, when the rotation shaft  11  rotates in the case where the wind flows in as the cooling wind from the surroundings, the cooling winds F 10 , F 11 , F 20 , F 21  flow as illustrated in  FIG. 8B , as in the case illustrated in  FIG. 16 . Namely, the cooling wind F 11  flows through the gap G 1  between the first rotor  21  and the stator  31  from the inside to the outside in the radial direction of the rotation shaft  11 . Further, the cooling wind F 21  flows through the gap G 2  between the second rotor  22  and the stator  31  from the inside to the outside in the radial direction of the rotation shaft  11 . 
     Therefore, in this embodiment, as illustrated in  FIG. 8B , both of the cooling wind F 11  flowed in from the surroundings and the cooling wind M 11   b  generated by the blades  212   b  flow through the gap G 1  between the first rotor  21  and the stator  31 . In short, a cooling wind (M11b+F11) made by combining both of the winds flows from the inside to the outside in the radial direction. Further, both of the cooling wind F 11  flowed in from the surroundings and the cooling wind M 12   b  generated by the blades  212   b  flow also outside the gap G 1 . 
     Similarly to the above, in this embodiment, as illustrated in  FIG. 8B , both of the cooling wind F 21  flowed in from the surroundings and the cooling wind M 21   b  generated by the blades  222   b  flow also through the gap G 2  between the second rotor  22  and the stator  31 . In short, a cooling wind (M21b+F21) made by combining both of the winds flows from the inside to the outside in the radial direction. Further, both of the cooling wind F 21  flowed in from the surroundings and the cooling wind M 22   b  generated by the blades  222   b  flow also outside the gap G 2 . 
     As is understood from the above, in this embodiment, the amounts of the cooling winds flowing respectively through the gap G 1  between the first rotor  21  and the stator  31  and through the gap G 2  between the second rotor  22  and the stator  31  can be increased. 
     [C] Conclusion 
     As described above, an axial gap-type power generator  1   b  in this embodiment has the blades  212   b,    222   b.  Here, the blades  212   b  are installed at the first rotor  21  so that the cooling wind M 11   b  flows through the gap G 1  between the first rotor  21  and the stator  31  from the inside to the outside in the radial direction of the rotation shaft  11  with the rotation of the rotation shaft  11 . Further, the blades  222   b  are installed at the second rotor  22  so that the cooling wind M 21   b  flows through the gap G 2  between the second rotor  22  and the stator  31  from the inside to the outside in the radial direction of the rotation shaft  11  with the rotation of the rotation shaft  11 . As a result, in this embodiment, the flow rates of the cooling winds flowing respectively through the gap G 1  between the first rotor  21  and the stator  31  and through the gap G 2  between the second rotor  22  and the stator  31  increase as described above (see  FIG. 8A ,  FIG. 8B  and so on). 
     Accordingly, in this embodiment, it is possible to effectively cool the first rotor  21 , the second rotor  22 , and the stator  31 , thereby realizing the improvement in reliability and the improvement in power generation performance. For example, it is possible to effectively cool the coils  311  increased in temperature due to the power generation operation. Further, it is possible to effectively cool the magnets  211 ,  221  increased in temperature, thereby suppressing occurrence of demagnetization and preventing a decrease in power generation output. 
     Note that in this embodiment, the blades  212   b,    222   b  are provided on the surfaces facing each other of the guide  21 G of the first rotor  21  and the guide  22 G of the second rotor  22 , respectively. In other words, since the blades  212   b,    222   b  are provided at portions outside in the radial direction of the gap G 1  between the first rotor  21  and the stator  31  and the gap G 2  between the second rotor  22  and the stator  31  in this embodiment. Therefore, in this embodiment, the blades  212   b,    222   b  are not provided between the first rotor  21  and the stator  31  and between the second rotor  22  and the stator  31 , thereby suppressing the breakage and so on of the blades  212   b,    222   b.  Further, the gaps G 1 , G 2  can be narrowed. 
     [D] Modification Example 
     The case where the blades  212   b  are installed at the guide  21 G of the first rotor  21  and the blades  222   b  are installed at the guide  22 G of the second rotor  22  has been described in the above embodiment, but they are not limited to this. The blades are preferably installed at both of the guides but may be installed at one of them. 
     Third Embodiment 
     [A] Configuration of Axial Gap-Type Power Generator 
       FIG. 10  is view illustrating an axial gap-type power generator according to a third embodiment.  FIG. 10  illustrates, similarly to  FIG. 1 , its cross section. 
       FIG. 11A  and  FIG. 11B  are views illustrating rotors in the axial gap-type power generator according to the third embodiment.  FIG. 11A  illustrates, similarly to  FIG. 2A , the first rotor  21  of the pair of rotors  21 ,  22 , and  FIG. 11B  illustrates, similarly to  FIG. 2B , the second rotor  22 . 
     This embodiment is different from the first embodiment in installation positions of blades  212   c,    222   c  as illustrated in  FIG. 10 ,  FIG. 11A ,  FIG. 11B . Except this point and points related to this, this embodiment is the same as the first embodiment. Therefore, description of portions overlapped with those of the first embodiment will be accordingly omitted in this embodiment. 
     In this embodiment, as illustrated in  FIG. 10 ,  FIG. 11A ,  FIG. 11B , the blades  212   c,    222   c  are provided on a surface of the first rotor  21  facing the stator  31  and a surface of the second rotor  22  facing the stator  31 , different from those in the first embodiment. 
     Though details will be described later, the blades  212   c,    222   c  are configured such that when they rotate with the rotation of the rotation shaft  11 , a cooling wind (not illustrated) flows from the inside to the outside in the radial direction of the rotation shaft  11 . 
     More specifically, at the first rotor  21 , the blades  212   c  are installed on the magnets  211  as illustrated in  FIG. 10 . At the first rotor  21 , a plurality of blades  212   c  are arrayed at regular intervals in the rotation direction R of the rotation shaft  11  as illustrated in  FIG. 11A . Each of the plurality of blades  212   c  is formed such that one end portion located on the inside in the radial direction is located anterior in the rotation direction R to the other end portion located on the outside. 
     Similarly, at the second rotor  22 , the blades  222   c  are also installed on the magnets  221  as illustrated in  FIG. 10 . Further, at the second rotor  22 , a plurality of blades  222   c  are arrayed at regular intervals in the rotation direction R of the rotation shaft  11  as illustrated in  FIG. 11B . Each of the plurality of blades  222   c  is formed such that one end portion located on the inside in the radial direction is located anterior in the rotation direction R to the other end portion located on the outside. 
     [B] Regarding Flow of Cooling Wind 
       FIG. 12A ,  FIG. 12B ,  FIG. 13  and  FIG. 13B  are views illustrating the flow of the cooling wind in the axial gap-type power generator according to the third embodiment. 
       FIG. 12A  and  FIG. 12B  illustrate, similarly to  FIG. 10 , the cross section of the axial gap-type power generator, and schematically illustrate the outline of the cooling wind flowing in the cross section. Here,  FIG. 10A  illustrates the case where there is no wind around the axial gap-type power generator, and  FIG. 10B  illustrates the case where wind flows in as the cooling wind from the surroundings of the axial gap-type power generator. Further,  FIG. 13A  illustrates, similarly to  FIG. 11A , the first rotor  21  of the pair of rotors  21 ,  22 , and  FIG. 13B  illustrates, similarly to  FIG. 11B , the second rotor  22 .  FIG. 13A  and  FIG. 13B  schematically illustrate the outline of the cooling winds flowing through the first rotor  21  and the second rotor  22 , respectively. 
     As illustrated in  FIG. 12A , when the rotation shaft  11  rotates through inertia in the case where there is no wind in the surroundings, cooling winds M 11   c , M 21   c  are generated by the blades  212   c,    222   c  and flow. The cooling winds M 11   c , M 21   c  flow from the inside to the outside in the radial direction of the rotation shaft  11  through the gap G 1  between the first rotor  21  and the stator  31  and through the gap G 2  between the second rotor  22  and the stator  31 . More specifically, as illustrated in  FIG. 13A  and  FIG. 13B , the cooling winds M 11   c , M 21   c  flow between the plurality of blades  212   b,    222   c.    
     As illustrated in  FIG. 12B , when the rotation shaft  11  rotates in the case where the cooling wind flows in from the surroundings, the cooling winds M 11   c , M 21   c  are generated by the blades  212   c,    222   c  and flow. Therefore, similarly to the case illustrated in  FIG. 12A , the cooling wind M 11   c  flows through the gap G 1  between the first rotor  21  and the stator  31 , and the cooling wind M 21   c  flows through the gap G 2  between the second rotor  22  and the stator  31 . 
     In addition, when the rotation shaft  11  rotates in the case where the wind flows in as the cooling wind from the surroundings, the cooling winds F 10 , F 11 , F 20 , F 21  flow as illustrated in  FIG. 12B , as in the case illustrated in  FIG. 16 . Namely, the cooling wind F 11  flows through the gap G 1  between the first rotor  21  and the stator  31  from the inside to the outside in the radial direction of the rotation shaft  11 . Further, the cooling wind F 21  flows through the gap G 2  between the second rotor  22  and the stator  31  from the inside to the outside in the radial direction of the rotation shaft  11 . 
     Therefore, in this embodiment, as illustrated in  FIG. 12B , both of the cooling wind F 11  flowed in from the surroundings and the cooling wind M 11   c  generated by the blades  212   c  flow through the gap G 1  between the first rotor  21  and the stator  31 . In short, a cooling wind (M11 c +F11) made by combining both of the winds flows from the inside to the outside in the radial direction. 
     Similarly to the above, in this embodiment, as illustrated in  FIG. 12B , both of the cooling wind F 21  flowed in from the surroundings and the cooling wind M 21   c  generated by the blades  222   c  flow also through the gap G 2  between the second rotor  22  and the stator  31 . In short, a cooling wind (M21 c +F21) made by combining both of the winds flows from the inside to the outside in the radial direction. 
     As is understood from the above, in this embodiment, the amounts of the cooling winds flowing respectively through the gap G 1  between the first rotor  21  and the stator  31  and through the gap G 2  between the second rotor  22  and the stator  31  can be increased. 
     [C] Conclusion 
     As described above, an axial gap-type power generator  1   c  in this embodiment has the blades  212   c,    222   c.  Here, the blades  212   c  are installed at the first rotor  21  so that the cooling wind M 11   c  generated by the rotation of the blades  212   c  flows through the gap G 1  between the first rotor  21  and the stator  31  from the inside to the outside in the radial direction. In addition, the blades  222   c  are installed at the second rotor  22  so that the cooling wind M 21   c  generated by the rotation of the blades  222   c  flows through the gap G 2  between the second rotor  22  and the stator  31  from the inside to the outside in the radial direction. As a result, in this embodiment, the flow rates of the cooling winds flowing respectively through the gap G 1  between the first rotor  21  and the stator  31  and through the gap G 2  between the second rotor  22  and the stator  31  increase as described above (see  FIG. 12A ,  FIG. 12B  and so on). 
     Accordingly, in this embodiment, it is possible to effectively cool the first rotor  21 , the second rotor  22 , and the stator  31 , thereby realizing the improvement in reliability and the improvement in power generation performance. For example, it is possible to effectively cool the coils  311  increased in temperature due to the power generation operation. Further, it is possible to effectively cool the magnets  211 ,  221  increased in temperature, thereby suppressing occurrence of demagnetization and preventing a decrease in power generation output. 
     Note that in this embodiment, the blades  212   c,    222   c  are provided on the surface of the first rotor  21  facing the stator  31  and the surface of the second rotor  22  facing the stator  31 . In other words, the blades  212   c  are installed at the first rotor  21  to be sandwiched between the first rotor  21  and the stator  31 , and the blades  222   c  are installed at the second rotor  22  to be sandwiched between the second rotor  22  and the stator  31 . Therefore, in this embodiment, the cooling winds M 11   c , M 21   c  are generated and flow from the inside to the outside in the radial direction through the gap G 1  between the first rotor  21  and the stator  31  and through the gap G 2  between the second rotor  22  and the stator  31 , and therefore can perform more effective cooling. 
     [D] Modification Example 
     The case where the blades  212   c  are installed at the first rotor  21  and the blades  222   c  are installed at the second rotor  22  has been described in the above embodiment, but they are not limited to this. The blades are preferably installed at both of the rotors but may be installed at one of them. 
     &lt;Others&gt; 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.