Abstract:
An axial gap rotating electrical device includes a stator and a rotor. The stator has a stator core and a stator coil. The rotor is disposed in an axial direction with respect to the stator. The rotor includes a plurality of separate rotor components circumferentially arranged. Each of the rotor components includes a permanent magnet facing the stator core and a high-strength member enveloping an outer surface of the permanent magnet. The high-strength member is configured to prevent a centrifugal force on the permanent magnet from being transmitted between adjacent ones of the high-strength member during a rotation of the rotor.

Description:
This application claims priority from Japanese Patent Application No. 2004-360973, filed Dec. 14, 2004, the entire contents of which is incorporated herein by reference. 
   TECHNICAL FIELD 
   The disclosure relates to electricity generation, and more specifically, devices which utilize stators and a rotor to generate electricity. 
   BACKGROUND 
   Electric motors that include a permanent magnet attached to a rotor surface have become versatile in expanding the application range of motors to electric vehicles and hybrid cars. These electric motors are beneficial due to the fact that they cause a little loss, are higher in efficiency, and higher in power. Essentially, reluctance torque is available from the motor instead of magnet torque. 
   An axial gap motor is a permanent magnet synchronous motor in which a stator and a rotor are placed opposite to an axial direction. The axial gap motor may be relatively small in size, and may be used for applications that have space limitations for appropriate motor implementation. 
   SUMMARY 
   In general, the invention is directed to a modified rotor of an axial gap motor. Permanent magnets placed within the rotor can produce great stress on members of the rotor that hold the permanent magnets in place radially. Rotor members are typically somewhat curved in shape at the outer contact area with the permanent magnets to distribute stresses during high rotation speed. A round member of the rotor may be constructed of a high-strength member to surround and secure the permanent magnets within the rotor. The round member is formed by combining several radial rotor components, where the rotor components include a high-strength member to circumferentially envelop a permanent magnet. 
   In one embodiment, an axial gap rotating electrical device comprises a rotor having a permanent magnet and including a round member formed by several radial rotor components and a stator having a stator core and a stator coil, wherein the rotor and the stator are oriented in an axial direction, and the rotor components include the permanent magnet facing the stator core with an outer surface of the permanent magnet radially enveloped by a high-strength member. 
   In another embodiment, a method comprises forming a round member of a rotor with a plurality of radial rotor components, wherein the rotor includes a permanent magnet and the radial rotor components include a high-strength member that radially envelops the permanent magnet, and rotating the rotor magnet produce electricity. 
   In an additional embodiment, an axial gap rotating electrical device comprises means for rotating a permanent magnet with respect to a stator and means for securing the permanent magnet radially during the permanent magnet rotation. 
   The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is an illustration that shows an axial gap rotating electrical device in which a first embodiment of a rotor structure is applied. 
       FIG. 2  is an illustration that shows a stator of the first embodiment of the rotor structure of the axial gap electrical device of  FIG. 1 . 
       FIG. 3  is a perspective view that shows a rotor axis and a rotor of the axial gap rotating electrical device of  FIG. 1 . 
       FIG. 4  is a front view of a rotor of the axial gap rotating electrical device of  FIG. 1 . 
       FIG. 5  is an illustration that shows a variant mechanism of a rotor base member at the rotor revolution of a conventional axial gap rotating electrical device. 
       FIG. 6  is an illustration that shows a variant mechanism of the rotor components at the rotor revolution of the axial gap rotating electrical device of  FIG. 1 . 
       FIG. 7  is a front view that shows an exemplary second embodiment of a rotor of the axial gap rotating electrical device. 
       FIG. 8  is a front view that shows an exemplary third embodiment of a rotor of the axial gap rotating electrical device similar to  FIG. 7 . 
       FIG. 9  is a front view that shows an exemplary third embodiment of a rotor of the axial gap rotating electrical device. 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates a first embodiment 1 rotor and 2 stator-type axial gap rotating electrical device.  FIG. 2  shows a front view of the stator of the axial gap rotating electrical device. The axial gap rotating electrical device has rotor axis  1 , rotor  2 , a pair of stators  3  and rotating electrical device case  4  that is placed opposite to rotor  2  and the pair of stators  3  in the axial direction. 
   Rotor axis  1  is rotatably held by first bearing  5  placed between rotating electrical device case  4  (front side case  4   a ) and second bearing  6  placed between rotating electrical device case  4  (rear side case  4   b ). Rotor axis  1  comprises an axle center oil line  7 , a first radial oil line  8  that cools stators  3  at the front side in communication with an axle center oil line  7 , a second radial oil line  9  that cools stators  3  at the rear side, a second bearing  6  in communication with said axle center oil line  7 , and a third radial oil line  10  that cools first bearing  5  in communication with axle center oil line  7 . 
   Rotor  2  is fixed to rotor axis  1  and is positioned between the pair of stators  3 . Rotor  2  consists of several radial rotor components, or radially combined rotor components, which radially envelop the outer circumference of permanent magnet  12  opposite stator core  14  and rotor axis retainer  11 . Rotor axis retainer  11  is located radially inward of permanent magnet  12 , using a high-strength member  24  (not shown in  FIGS. 1 and 2 ). Permanent magnet  12  is placed such that it produces a reactive force against the rotating flux derived from the pair of stators  3  while rotating around rotor axis  1 . Permanent magnets  12  are placed so that the adjacent magnetic poles (North Pole, South Pole) differ from each other. An axial direction gap, referred to as an air gap, exists between rotor  2  and stators  3 , preventing them from coming in contact with each other. 
   Stators  3  are respectively fixed to front side case  4   a  and rear side case  4   b  of rotating electrical device case  4 , and the fixed positions are positioned on both sides of rotor  2 . Stator  3  comprises a stator case  13  bolted to both side cases  4   a  and  4   b . Stator core  14  is made of laminate steel and stator coil  16  is wound around the stator core  14  via an insulator  15 . 
   As shown in  FIG. 2 , 12 pieces of stator core  14  with stator coil  16  are arranged equally spaced in a circumferential direction. Besides stator coil  16 , stator  3  has core base  17  equipped on the base of stator core  14 , a laminated busbar  18 , power transmission terminal  19  connected to the laminated busbar, a refrigerants gallery  20  built into stator case  13 , and resin mold part  21 . Resin mold part  21  fills the gap between stator core  14  with stator coil  16  and laminated busbar  18 . Laminated busbar  18  is a power dispatching structure to stator coil  16 . For power transmission terminal  19  in a motor mode, a direct current is converted from the battery to a three-phase alternating current via a strong electric unit with an inverter (not shown). The three-phase alternating current is supplied to stator coil  16  via laminated busbar  18 . In a generator mode, the three-phase alternating current generated by stator coil  16  is supplied to the strong electric unit with an inverter (not shown), and it is converted to a direct current by the strong electric unit to charge the battery. 
   Rotating electrical device case  4  comprises a front side case  4   a , a rear side case  4   b , and an outer circumference case  4   c  bolted to both side cases  4   a  and  4   b . As shown in  FIG. 1 , front side case  4   a  and rear side case  4   b  comprise a refrigerants supply port  22  to provide the refrigerants gallery with refrigerants (such as a cooling oil) and refrigerants emission port  23  to discharge refrigerants that draw heat from stators  3  in the refrigerants gallery. 
     FIG. 3  shows a perspective view of the rotor axis and the rotor of the axial gap rotating electrical device.  FIG. 4  shows a front view of rotor  2 , or the means for rotating permanent magnet  12 , of the axial gap rotating electrical device. As shown in  FIG. 4 , rotor  2  is includes rotor components formed by radially enveloping the outer circumference of permanent magnet  12  with high-strength member  24 , or means for securing permanent magnet  12 , wherein rotor  2  comprises 1 to 8 combined high strength members to each retain an individual permanent magnet. High strength member  24  is partially circular in shape, but may also be similar to a rounded triangle. Other shapes of member  24  may be appropriate for securing permanent magnet  12  as well. 
   High-strength member  24  is comprises continuous fiberglass reinforced plastic (such as Carbon-Fiberglass Reinforced Plastics, hereinafter called CFRP) in a shape roughly similar to a folding fan extended into a complete circle. 
   For rotor axis retainer  11 , or means for retaining the means for rotating the permanent magnet, hole  11   a  is bored for fixing rotor  2  to rotor axis  1 , or means for placing the means for rotating the permanent magnet. A pair of reinforced retainers  1   a , or means for attaching the means for retaining the means for rotating the permanent magnet, hold rotor axis retainer  11  fixed from both sides of the axial direction to rotor axis  1  ( FIG. 1 ), and rotor axis retainer  11  is bolted from both sides of the axial direction to a pair of reinforced retainers  1   a  using a bolt and nut  25 , or other means for securing the means for retaining the means for rotating the permanent magnet to the rotor axis, that inserts through holes  11   a  to fix the rotor axis to rotor  2 . A pair of reinforced retainers  1   a  is integrated with rotor axis  1 . As shown in  FIG. 3 , reinforced retainers  1   a  have a conical structure such that the axial direction thickness increases when it comes closer to rotor axis  1  and decreases when it comes closer to the permanent magnet  12 . The circumferential contact area of the rotor component is connected with an adhesive member “A” of lower rigidity (such as adhesives) than the rotor component and permanent magnet  12 . 
   For comparison purposes,  FIG. 5  illustrates an example of an earlier technology rotor of an axial gap rotating electrical device. In the example of  FIG. 5 , a rotor base member is used as a reinforced member. The reinforced rotor base member forms the framework and has holes for attaching magnets, where each hole holds a permanent magnet attached by an adhesive joint. 
   When the centripetal force generated on the permanent magnet with an independent mass acts on the outer circumference of the rotor base member, as shown by the dotted line in  FIG. 5 , stress concentrations occurs at the corner of the rotor base member corresponding to both of the outer circumferential corners of the permanent magnet. This causes distortion of the outer circumference towards the outside diameter. With the rotor base member following the same curvature throughout the rotor, it may be essential to optimize the curvature radius at the corner and check the component strength for reducing the stress concentration. 
   CFRP and other similar materials may be used for high stress applications, featuring high strength and low density. However, for a configuration having several holes for attaching magnets in the round rotor base member as shown in  FIG. 5 , it is difficult to evenly place the carbon-fiberglass, and the CFRP&#39;s original high-strength property in the direction of fiberglass is not fully effective to control stress concentrations. 
   In the rotor structure of the axial gap rotating electrical device as shown in  FIG. 4 , which is in contrast to that illustrated in  FIG. 5 , rotor  2  includes a round member formed by radially combining several rotor components that radially envelop the outer circumference of the permanent magnet  12 . Rotor axis retainer  11  is placed within permanent magnet  12  using high-strength member  24 . 
   Since the outer circumference of the individual permanent magnet  12  may be reinforced with high-strength member  24 , permanent magnet  12  suffers less damage at installation. In addition, the centripetal force, which acts on permanent magnet  12  by during rotation of rotor  2 , may be dispersed as tensile stress on the radial direction part of high-strength member  24  that radially envelops each permanent magnet  12 . As a result, a reduction in damage to permanent magnet  12  at installation is reached, as well as achieving higher rotational speed by providing sufficient rotational strength. 
   The centripetal force generated on permanent magnet  12  by the rotation of rotor  2  acts on high-strength member  24  that envelops the outer circumference of the rotor components. The force is also transmitted to rotor axis retainer  11  via high-strength member  24 , where it is supported by rotor axis  1  by passing using bolt and nut  25  through the holes  11   a  to hold the rotor axis created in the rotor axis retainer  11 . 
   In contrast to the earlier technology of  FIG. 5 ,  FIG. 6  shows high-strength member  24  distorted toward the outer diameter due to the action of centripetal force on permanent magnet  12 . The force is not transmitted between the adjacent rotor components. Therefore, the stress concentration is relieved in comparison with the stress generated by corner expansion that occurs in  FIG. 5 . However, since the hoop around the outer circumference does not inhibit the distortion as shown in the rotor structure of  FIG. 5 , the force to be shared by the radial direction parts  24   a  of high-strength member  24  increases, which causes further distortion. Furthermore, in this case, the radial direction parts  24   a  of high-strength member  24  do not become the weakest points due to tension distribution. 
   High-strength member  24  has an even wall thickness and a continuous cyclic shape that enables easy formation with carbon fiberglass. In addition, the load is directed close to the continuous fiber-glass, which allows full use of the material strength. 
   Furthermore, in the rotor structure of the axial gap rotating electrical device of  FIG. 4 , the circumferential contact area of the rotor component is connected with the rotor component and an adhesive member “A” of lower rigidity than permanent magnet  12  (such as adhesives). Therefore, considering each rotor component in comparison with the rotor structure shown in  FIG. 5 , in which the rotor base member is integrated, the possible radial acceleration is decreased because the mass is small. As a result, greater rotational speed may be obtained when utilizing a curved high-strength member  24 . 
   The first embodiment shown in  FIGS. 1-4  and  6  allows rotor  2  to achieve higher rotational speeds while retaining permanent magnet  12 . In addition, since high-strength member  24  may be composed of a filament winding method for carbon fiber-glass and Kevlar rather than a solid method (such as pure iron), these higher speeds may be possible. 
   High-strength member  24  comprises a continuous fiber reinforced plastic in a partially circular shape, which may look similar to a triangle. This shape may allow high-strength member  24  to bear the centripetal force on the permanent magnet  12  as a high-strength directional load for the continuous fiber reinforced plastic. As a result, high-speed rotation is made possible. In addition, the nonmetal structure allows suppression of the reduction in efficiency due to flux leakage and eddy-current loss. 
   Rotor  2  may be fixed to rotor axis  1  with high strength. Rotor  2  comprises a round member formed by radially combining several rotor components, and since the rotor axis retainer  11  was placed in the inner circumference of said permanent magnet  12 , a hole  11   a  is used to fix the rotor axis to rotor axis retainer  11 . A pair of reinforced retainers  1   a  which secure rotor axis retainer  11  from both sides of the axial direction are fixed to rotor axis  1 . Rotor axis retainer  11  is fixed to the pair of reinforced retainers  1   a  from both sides of the axial direction using bolt and nut  25  that is inserted through holes  11   a  to hold the rotor axis. 
   Since the circumferential contact area of the rotor component is attached to an adhesive member with lower rigidity than the rotor component and the permanent magnet, further improvement can be expected in the rotation speed able to be achieved. 
     FIG. 7  illustrates a second embodiment in which a toric member has been added to the outer circumference of rotor  2 . That is, for the rotor structure of the axial gap rotating electrical device as shown in  FIG. 7 , rotor  2  includes a round member formed by radially combining several rotor components and a toric member  26  placed on the outer circumference of the round member. It is possible to form toric member  26  by bonding or pressing a previously formed toric member with high-strength materials including carbon fiber-glass or Kevlar. Toric member  26  may also be formed by winding a high-strength fiber including carbon fiber-glass or Kevlar after creating a disk-like core. The circumferential contact area of the rotor components may slide without being attached to each other. In other aspects,  FIG. 7  is similar to  FIG. 4 . 
   The rotor structure of the embodiment shown in  FIG. 7  has toric member  26  on the outer circumference of the round member. The centripetal force on each permanent magnet  12  derived from the rotation of rotor  2  may be shared with high-strength member  24  and toric member  26 . Therefore, the force shared by radial parts  24   a  of the high-strength member  24  becomes lower than that of  FIG. 4 , which does not have the toric member  26 . The structure of  FIG. 7  may allow greater rotational speed relative to conventional rotor structures. The force on toric member  26  is in tension along the outer circumference of the round member. 
   In addition, the contact area of toric member  26  on the outer circumference of high-strength member  24  is slidable without being attached. This is because toric member  26  is created on the outer circumference for the round member that allows the toric member  26  to hold the rotor shape. Consequently, taking the individual rotor component into consideration, the specific frequency increases due to the small mass, in contrast to the earlier technology rotor structure shown in  FIG. 5  where the rotor base member is unified. Therefore, further increases in rotational speed and attenuation rate of the rotor structure may be possible, caused by radial sliding between adjacent high-strength members  24 . 
   Rotor  2  of  FIG. 7  comprises a round member formed by radially combining several rotor components and toric member  26  created on the outer circumference of the round member. This embodiment may be capable of higher rotational speeds as compared to the first embodiment shown in  FIG. 4 . 
   An additional embodiment of rotor  2  is shown in  FIG. 8 .  FIG. 8  illustrates a rotor structure in which a soft magnet is placed on both of the circumference surfaces of each permanent magnet  12 . The rotor structure of the axial gap rotating electrical device, in this embodiment, has means for passing flux but including no coercivity, and soft magnets  27 , which pass flux but have no coercivity. Both circumferential surfaces of each permanent magnet  12  include soft magnets  27  placed in rotor components. Soft magnets  27  are fixed to permanent magnet  12 . Other structures of  FIG. 8  are similar to  FIG. 7 . As for the mechanism, by placing soft magnets  27  in rotor  2 , reluctance torque is made possible along with magnet torque when implanting permanent magnets within rotor  2  for the radial gap rotating electrical device. 
     FIG. 8 , therefore, includes soft magnets  27 , which pass flux but have no coercivity, equipped on both of the circumference surfaces of each permanent magnet  12  placed in the said rotor components. Reluctance torque is made possible, and soft magnets  27  may be kept together with permanent magnet  12  by the high-strength member  24  and toric component  26 . As a result, improvement in torque and an increase in rotation speed may be possible. 
     FIG. 9  shows a fourth embodiment of a rotor structure in which a soft magnet is placed in the middle point where the adjacent rotor components meet. This may be an alternative to the rotor structure shown in  FIG. 7 . In other words, the rotor structure of the axial gap rotating electrical device embodiment shown in  FIG. 9  includes a soft magnet  27 , which passes flux but has no coercivity, is placed at the middle point where adjacent rotor components meet. Soft magnets  27  may also contact toric member  26  in the radial direction. Soft magnet  27  may be retained with toric member  26  and fixed together with permanent magnet  12 . Placing soft magnet  27 , as shown in  FIG. 9 , may help to improve the torque so that reluctance torque can be used in addition to magnet torque. Furthermore, cogging torque is reduced due to the smooth flux variation. 
   Soft magnet  27 , which passes flux but has no coercivity, is placed at the middle point where adjacent rotor components meet in the opposite circumferential direction. Soft magnets  27  also contact toric member  26  in a radial direction. Torque improvement may be enabled by the use of reluctance torque, and it is also possible to reduce flux leakage from the soft magnet  27  part because permanent magnet  12  and soft magnet  27  do not directly contact each other. Furthermore, as flux varies with stators  3  (shown in  FIG. 1 ) smoothly performed by soft magnet  27 , the soft magnet reduces cogging torque. 
   As described above, the rotor structure of the axial gap rotating electrical device is described in several different embodiments. However, the claimed structures are not limited to these embodiments. Variations of these embodiments are possible, as these embodiments provided in the FIGS. are exemplary embodiments. 
   For example, in addition to the structures described  FIGS. 1-9 , it is possible to place a thin plate or a sheet-like continuous fiber fabric on one or both sides of the round member (including the toric member and others). In this case, in addition to higher rotational speeds, the following features may be improved. Dimensional accuracy in the axial direction of the permanent magnet, shatter resistance of the permanent magnet, and rigidity of the rotor structure may be improved. 
   In summary, as discussed above,  FIG. 4  illustrates an example of a round member of rotor  2  in which the circumferential contact area of the rotor component is connected using an adhesive member of lower rigidity (such as adhesive agents) than the rotor component and the permanent magnet.  FIGS. 6-9  illustrate examples of alternative embodiments of round members of rotor  2  in which the circumferential contact area of the rotor components are made slidable without attaching the components. It is also possible to secure the circumferential contact area. 
   Moreover,  FIG. 4  illustrates an example of integrating a pair of reinforced retainers with the rotor axis. It is also possible to create one or both of the pair of the reinforced retainers separately from the rotor axis and fix the distinct reinforced retainer to the rotor axis with other structures. 
   Thus, the embodiments shown in  FIGS. 4 , and  6 - 9  are examples of alternative embodiments of round members of rotor  2  having an axial air gap between the rotor and the stator as an axial gap rotating electrical device. It is also applicable to an axial gap rotating electrical device, for example, in which there is only an axial gap made up of an oil film in place of an air gap between the rotor and the stator. 
   The axial gap rotating electrical device described in embodiments of FIGS.  4  and  6 - 9  may be applied as an axial gap motor as well as an axial gap generator. In addition, these embodiments represent examples of a 1 rotor and 2 stators axial gap rotating electrical device. The disclosure is also applicable to the axial gap rotating electrical device, which has a different number of stators and rotors from the description in the embodiments, such as an axial rotating electrical device with 1 rotor and 1 stator, 2 rotors and 1 stator, 2 rotors/2 stators, and so on. 
   Some embodiments described herein may provide certain advantages. Securing a permanent magnet with a round member capable of high stress resistance may allow the rotor to rotate at higher speeds than other rotors without the round member described herein. In addition, other embodiments may provide a further toric member that encompasses the rotor to aid in the distribution of stresses on round members of the rotor that occur during high rotational speeds. The embodiments described herein may be manufactured at a facility to conform the description of each figure. 
   Various embodiments of the invention have been described. However, the present disclosure is not limited to the embodiments described herein. These and other embodiments are within the scope of the following claims. Embodiments including modifications or changes are applicable to the extent of operation and description of the disclosure.