Patent Publication Number: US-2023163669-A1

Title: Rotary electric machine and aircraft using rotary electric machine

Description:
TECHNICAL FIELD 
     The present disclosure relates to a rotary electric machine and an aircraft using the rotary electric machine. 
     BACKGROUND ART 
     Conventionally, regarding a stator core surrounded by two opposed movable parts in a rotary electric machine, it is disclosed that the stator core is formed by stacking thin sheets in a direction parallel to two surfaces facing the movable parts which are rotors and perpendicular to the movable direction of the movable parts, and retention members are fitted to holes provided so as to penetrate in the stacking direction, thereby retaining the stator core (for example, Patent Document 1). 
     Also, it is disclosed that a stator core, in a rotary electric machine, is formed by stacking thin sheets in a direction parallel to the two opposed movable parts and substantially parallel to the movable direction of the movable parts, bolt holes for retaining the stacked sheets are provided in a direction parallel to two surfaces of the stator core facing the movable parts which are rotors and perpendicular to the movable direction of the movable parts, and bolts are fastened, thereby retaining the stator core (for example, Patent Document 2). 
     CITATION LIST 
     Patent Document 
     Patent Document 1: Japanese Laid-Open Patent Publication No. 2019-37084 
     Patent Document 1: Japanese Laid-Open Patent Publication No. 2018-85886 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     In Patent Document 1, an electromagnetic force due to operation of the rotary electric machine acts in a direction to cause shear between the stacked sheets of the stator core, and therefore the retention members are fitted to the holes penetrating in the stacking direction, so as to retain the stator core. Thus, the retention members interfere with a magnetic path of the stator core, leading to size increase of the device and reduction in efficiency. 
     On the other hand, in Patent Document 2, since the stator core needs to be retained by applying a clamping force in the stacking direction, the magnetic property of the stator core is deteriorated. In addition, also in another example in Patent Document 2, the stator core is pressed by fitting portions and thus the magnetic property is deteriorated. 
     The present disclosure has been made to solve the above problem, and an object of the present disclosure is to provide a rotary electric machine in which a stator core is retained without increasing the size of the device and without deteriorating the magnetic property, and an aircraft using the rotary electric machine. 
     Solution to the Problems 
     A rotary electric machine according to the present disclosure includes: a stator core; and two movable parts which are placed with the stator core interposed therebetween and rotate about an identical rotary shaft. At least part of the stator core is formed by stacking thin sheets in a rotation direction of the two movable parts. The stator core has, at both ends, stator core retention portions extended in a direction parallel to surfaces thereof opposed to the two movable parts and perpendicular to the rotation direction of the movable parts. Retention surfaces of the stator core retention portions at both ends are respectively fixed in contact with retention members. The retention surfaces of the stator core retention portions at both ends are formed to face toward each other. 
     Effect Of The Invention 
     In the rotary electric machine according to the present disclosure, since the stator core is retained with tensile stress applied thereto, it becomes possible to retain the stator core without increasing the size of the device and without deteriorating the magnetic property of the stator core. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a sectional view along a rotary shaft of a rotary electric machine according to embodiment 1. 
         FIG.  2    is a sectional view along the rotary shaft of the rotary electric machine according to embodiment 1 and is a partial enlarged view of  FIG.  1   . 
         FIG.  3    is a sectional view along the rotary shaft of the rotary electric machine according to embodiment 1 and is a partial enlarged view of  FIG.  1   . 
         FIG.  4    is a partial sectional view along a direction perpendicular to the rotary shaft of the rotary electric machine according to embodiment 1. 
         FIG.  5    is a sectional view along a rotary shaft of a rotary electric machine according to embodiment 2. 
         FIG.  6    is a partial perspective view showing the structure of a stator of a rotary electric machine according to embodiment 3. 
         FIG.  7    is a partial perspective view showing the structure of the stator core of the rotary electric machine according to embodiment 3. 
         FIG.  8    is a partial perspective view showing the structure of the stator core of the rotary electric machine according to embodiment 3 and is a partial enlarged view of  FIG.  7   . 
         FIG.  9    is a perspective view showing a method for assembling the stator core of the rotary electric machine according to embodiment 3. 
         FIG.  10    is a partial perspective view showing the structure of another stator of the rotary electric machine according to embodiment 3. 
         FIG.  11    is a sectional view along a rotary shaft of a rotary electric machine according to embodiment 4. 
         FIG.  12    is a sectional view along a rotary shaft of a rotary electric machine according to embodiment 5. 
         FIG.  13    is a sectional view along the rotary shaft of the rotary electric machine according to embodiment 5 and is a partial enlarged view of  FIG.  12   . 
         FIG.  14    is a sectional view along the rotary shaft of the rotary electric machine according to embodiment 5 and is a partial enlarged view of  FIG.  12   . 
         FIG.  15    is a sectional view along a rotary shaft of a rotary electric machine according to embodiment 6. 
         FIG.  16    is a sectional view along a direction perpendicular to the rotary shaft of the rotary electric machine according to embodiment 6 and shows the structure of a stator. 
         FIG.  17    is a sectional view along a rotary shaft of a rotary electric machine according to embodiment 7. 
         FIG.  18    is a partial sectional view along a direction perpendicular to the rotary shaft of the rotary electric machine according to embodiment 7. 
         FIG.  19    is a sectional view along a rotary shaft of a rotary electric machine according to embodiment 8. 
         FIG.  20    is a partial sectional view along a direction perpendicular to the rotary shaft of the rotary electric machine according to embodiment 8. 
         FIG.  21    is a schematic view showing an aircraft using a rotary electric machine according to embodiment 9. 
         FIG.  22    is another schematic view showing another aircraft using a rotary electric machine according to embodiment 9. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments will be described with reference to the drawings. The drawings are schematically shown and some configurations are omitted or simplified for convenience of description. The relationship of sizes and positions of components and the like shown in different drawings are not necessarily precisely shown, and may be changed as appropriate. In the following description, the same constituent elements are denoted and shown by the same reference characters, and also they are the same in names and functions. Therefore, the detailed description thereof may be omitted for avoiding redundant description. 
     Embodiment 1 
     Hereinafter, a rotary electric machine according to embodiment 1 will be described with reference to the drawings. 
       FIG.  1    is a sectional view along a rotary shaft, showing the structure of the rotary electric machine according to embodiment 1. In  FIG.  1   , a rotary electric machine  1  includes two rotors which are an inner rotor  10  and an outer rotor  20 , and a stator  30  provided between the two rotors in the radial direction, and is formed as a radial gap motor of a double-rotor type. 
     The inner rotor  10  includes a shaft  2 , a boss  12  press-fitted and fixed to the shaft  2 , and a permanent magnet  14  adhered and fixed to the radially outer side of the boss  12 . 
     The outer rotor  20  includes an outer shaft  21  fixed to the shaft  2 , and a permanent magnet  22  adhered and fixed to the radially inner side of the outer shaft  21 . 
     In the stator  30 , a stator core  31  is provided in the axial direction between a load-side base retention member  35  attached to a load-side stator base  34 , and a non-load-side stator base  33 , and a stator coil  32  is wound around the stator core  31 . The stator  30 , which is provided between the inner rotor  10  and the outer rotor  20 , rotatably retains the inner rotor  10  and the outer rotor  20  by a load-side inner bearing  3 , a load-side outer bearing  5 , a non-load-side inner bearing  4 , and a non-load-side outer bearing  6 . 
     At both ends in the axial direction, both side portions of the stator core  31  on the inner rotor  10  side and the outer rotor  20  side extend and protrude in the axial direction. Stator core load-side retention portions  36  which are distal end portions of the stator core  31  on the load side are bent inward in L shapes, and stator core non-load-side retention portions  37  which are distal end portions of the stator core  31  on the non-load side are bent outward in L shapes. The stator core  31  is formed of a steel sheet, and the stator core load-side retention portions  36  and the stator core non-load-side retention portions  37  are parts of the stator core  31  and are formed of the same steel sheet. That is, the stator core  31  is formed by stacking thin sheets in the rotation direction of the inner rotor  10  and the outer rotor  20 , and has, at both ends, stator core retention portions extended in a direction parallel to the surfaces opposed to the inner rotor  10  and the outer rotor  20  and perpendicular to the rotation direction. 
       FIG.  2    is an enlarged view in an area X 1  enclosed by a broken line in  FIG.  1   , and  FIG.  3    is an enlarged view in an area X 2  enclosed by a broken line in  FIG.  1   .  FIG.  2    and  FIG.  3    show structures at both ends in the axial direction of the stator core  31 . 
     In  FIG.  2   , the stator core load-side retention portions  36  which are the distal end portions extended toward the load side which is one side in the axial direction of the stator core  31 , are bent in L shapes so as to be within the axial-direction range of the stator core  31 , and are inserted in grooves in the load-side base retention member  35 . At this time, load-side retention surfaces  38  of the stator core load-side retention portions  36  are fixed in contact with the grooves in the load-side base retention member  35  provided to the load-side stator base  34 . 
     In  FIG.  3   , the stator core non-load-side retention portions  37  which are the distal end portions extended toward the non-load side which is the other side in the axial direction are respectively bent in L shapes such that the extended distal end portion on the inner rotor  10  side is bent toward the inner rotor  10  side from the axial direction of the stator core  31  and the extended distal end portion on the outer rotor  20  side is bent toward the outer rotor  20  side, and are inserted in the grooves in the non-load-side stator base  33 . At this time, non-load-side retention surfaces  39  of the stator core non-load-side retention portions  37  are fixed in contact with the grooves in the non-load-side stator base  33 . 
     In the stator core  31 , the direction in which the load-side retention surface  38  contacts with the load-side base retention member  35  and the direction in which the non-load-side retention surface  39  contacts with the non-load-side stator base  33  are opposed to each other in the axial direction as indicated by arrows in  FIG.  2    and  FIG.  3   . 
     Although not shown, the grooves in the load-side base retention member  35  attached to the load-side stator base  34  and the grooves in the non-load-side stator base  33  have, at some parts in the circumferential direction, openings having sizes enough to allow insertion of the stator core load-side retention portions  36  and the stator core non-load-side retention portions  37 . After the stator core load-side retention portions  36  and the stator core non-load-side retention portions  37  are inserted into the openings, rotation is performed in the circumferential direction to predetermined positions so that the stator core load-side retention portions  36  and the stator core non-load-side retention portions  37  are fixed so as not to come off in the axial direction. 
       FIG.  4    is a sectional view along a direction perpendicular to the rotary shaft of the rotary electric machine  1  and is a partial sectional view along an A-A line direction in  FIG.  1   . In the drawing, the rotary electric machine  1  has a concentrated-winding configuration with 48 poles and 72 slots. The stator core  31  is formed by stacking, substantially in the circumferential direction, thin steel sheets that are long in the axial direction. The steel sheets forming the stator core  31  are electromagnetic steel sheets manufactured by rolling, and are arranged such that the rolling direction coincides with the radial direction of the stator core. 
     The inner rotor  10  and the outer rotor  20  rotate at the same angular velocity counterclockwise in the drawing. That is, the inner rotor  10  and the outer rotor  20  are movable parts. 
     The load-side inner bearing  3  and the non-load-side inner bearing  4  shown in  FIG.  1    are angular bearings. Considering the axial-direction dimension of the stator core  31 , the load-side inner bearing  3  and the non-load-side inner bearing  4  are preloaded, and also, the load-side retention surfaces  38  of the stator core load-side retention portions  36  are pressed to the load-side stator base  34  (load-side base retention member  35 ) and the non-load-side retention surfaces  39  of the stator core non-load-side retention portions  37  are pressed to the non-load-side stator base  33 . 
     As described above, in the rotary electric machine of embodiment 1, since the stator core  31  is fixed with tensile stress applied thereto in the axial direction by the load-side retention surfaces  38  and the non-load-side retention surface  39 , magnetic property deterioration due to compressive stress does not occur and efficiency can be enhanced. In addition, end portions of the stator core  31  on the inner rotor  10  side and the outer rotor  20  side are flanges of a stator tooth and are parts where the stator coil  32  cannot be wound, and these parts are used as retention portions extended in the axial direction so as to be fixed. 
     Thus, it is possible to fix the stator  30  without reducing the winding space and without obstructing a magnetic path. 
     The stator core load-side retention portions  36  which are the distal end portions extended toward the load side which is one side in the axial direction are bent in L shapes so as to be within the axial-direction width of the stator core  31 . Thus, the stator core  31  can be retained in a limited storage space. 
     The stator core non-load-side retention portions  37  which are the distal end portions extended toward the non-load side which is the other side in the axial direction are bent in L shapes so as to bend toward the inner rotor  10  side and the outer rotor  20  side from the axial direction of the stator core  31 . Thus, the stator core non-load-side retention portions  37  can be largely provided and the retention strength can be enhanced. 
     In the present embodiment, the directions in which the stator core load-side retention portion  36  and the stator core non-load-side retention portion  37  are bent in L shapes are different from each other in the radial direction, so that they are less likely to come off in the radial direction. However, they may be bent in the same direction. 
     Embodiment 2 
     Hereinafter, a rotary electric machine according to embodiment 2 will be described with reference to the drawings. 
       FIG.  5    is a sectional view along the rotary shaft of the rotary electric machine  1  according to embodiment 2. In  FIG.  5   , at both ends in the axial direction, both side portions of the stator core  31  on the inner rotor  10  side and the outer rotor  20  side extend and protrude in the axial direction from a body portion. Difference from embodiment 1 is that the stator core load-side retention portions  36  which are the distal end portions on the load side are bent inward in L shapes at obtuse angles, and the stator core non-load-side retention portions  37  which are the distal end portions on the fixed side are bent outward in L shapes at obtuse angles. That is, the angles of the L shapes are different. The stator core  31  is formed of a steel sheet, and the stator core load-side retention portions  36  and the stator core non-load-side retention portions  37  are parts of the stator core  31  and are formed of the same steel sheet. 
     As in embodiment 1,the stator core load-side retention portions  36  which are the distal end portions extended toward the load side which is one side in the axial direction are inserted in grooves in the load-side base retention member  35  attached to the load-side stator base  34 . At this time, the load-side retention surfaces  38  of the stator core load-side retention portions  36  are fixed in contact with the grooves in the load-side base retention member  35 . 
     The stator core non-load-side retention portions  37  which are the distal end portions extended toward the non-load side which is the other side in the axial direction are respectively bent in L shapes such that the extended distal end portion on the inner rotor  10  side is bent toward the inner rotor  10  side from the axial direction of the stator core  31  and the extended distal end portion on the outer rotor  20  side is bent toward the outer rotor  20  side, and are inserted in the grooves in the non-load-side stator base  33 . 
     At this time, the non-load-side retention surfaces  39  of the stator core non-load-side retention portions  37  are fixed in contact with the non-load-side stator base  33 . 
     In the stator core  31 , the direction in which the load-side retention surface  38  contacts with the load-side base retention member  35  and the direction in which the non-load-side retention surface  39  contacts with the non-load-side stator base  33  are opposed to each other in the axial direction, though mutually having some components in the radial direction. 
     As described above, also with the configuration in embodiment 2, the same effects as in embodiment 1 are provided. In addition, since the stator core load-side retention portions  36  and the stator core non-load-side retention portions  37  have L shapes at obtuse angles, the radial-direction dimensions of the stator core load-side retention portions  36  and the stator core non-load-side retention portions  37  become small relative to the areas of the load-side retention surfaces  38  and the non-load-side retention surfaces  39 . Thus, the sizes of the openings of the load-side stator base  34  and the non-load-side stator base  33  can be reduced, whereby size reduction can be achieved. 
     Embodiment 3 
     Hereinafter, a rotary electric machine as an electromagnetic device according to embodiment 3 will be described with reference to the drawings. 
       FIG.  6    is a perspective view showing part of the structure of the stator  30  of the rotary electric machine according to embodiment 3,  FIG.  7    is a perspective view showing the structure of the stator core  31 , and  FIG.  8    is a partial enlarged view in a broken-line area X 3  in  FIG.  7   . In embodiments 1 and 2, the stator core  31  is formed by stacking, substantially in the circumferential direction, i.e., the rotation direction, thin steel sheets that are long in the axial direction. In the stator core  31  of embodiments 1 and 2, at both ends in the axial direction thereof, both side portions on the inner rotor  10  side and the outer rotor  20  side extend and protrude in the axial direction from the body portion, the distal end portions  31   c  thereof on the load side are bent inward in L shapes, and the distal end portions  31   d  thereof on the non-load side are bent outward in L shapes. On the other hand, the stator core  31  of embodiment 3 is different in that the stator core  31  includes side portions  311  respectively opposed to the inner rotor  10  and the outer rotor  20 , and a side-portion retention portion  312  retaining both side portions  311  and wound with the stator coil  32 . 
     As shown in  FIG.  7    and  FIG.  8   , both side portions  311  of the stator core  31  are formed by stacking, substantially in the circumferential direction, i.e., the rotation direction, thin electromagnetic steel sheets that are long in the axial direction. On the other hand, the side-portion retention portion  312  of the stator core  31  is formed by stacking, in the axial direction, electromagnetic steel sheets having a predetermined shape, to a height corresponding to the permanent magnets  14 ,  22  of the inner rotor  10  and the outer rotor  20 . The side-portion retention portion  312  has substantially a rectangular shape and has cutouts  312   a  at center parts on the inner circumferential side which is the inner rotor side and the outer circumferential side which is the outer rotor side. In the cutouts  312   a,  both side portions  311  are inserted and retained. In addition, flanges  312   b  may be provided in the circumferential direction from the cutout  312   a,  as shown in the drawings. Both side portions  311  of the stator core  31  are retained in close contact with the side-portion retention portion  312  so that a magnetic flux in a direction perpendicular to the rotary shaft flows seamlessly. Both side portions  311  extend toward both sides in the axial direction from the side-portion retention portion  312  so as to have distal end portions  31   c,    31   d  bent in L shapes. The distal end portions  31   c,    31   d  respectively correspond to the stator core load-side retention portions  36  and the stator core non-load-side retention portions  37  shown in embodiments 1 and 2. 
     The stator core  31  of embodiment 3 which includes both side portions  311  stacked in the circumferential direction and the side-portion retention portion  312  stacked in the axial direction is also retained with tensile stress applied thereto in the axial direction, as in embodiments 1 and 2. That is, in relation to  FIG.  1    in embodiment 1, the distal end portions  31   c,    31   d  of both side portions of the stator core  31  are fixed and the non-load-side retention surfaces  39  in the grooves in the non-load-side stator base  33  and the load-side retention surfaces  38  in the load-side base retention member  35  are arranged so as to be opposed to each other. That is, the L-shaped parts of the distal end portions  31   c  on one end side in the axial direction of the side portions  311  of the stator core  31  are retained by being fitted to the grooves in the load-side base retention member  35 , and the L-shaped parts of the distal end portions  31   d  on the other end side in the axial direction of the side portions  311  of the stator core  31  are retained by being fitted to the grooves in the non-load-side stator base  33 , so that tensile stress is applied. 
     In  FIG.  7   , the distal end portions  31   c,    31   d  in the axial direction of both side portions  311  are both bent inward toward the side-portion retention portion  312  side. However, as shown in  FIG.  1    and  FIG.  5   , the distal end portions on the fixed side may be bent outward. In addition, as shown in  FIG.  5   , they may be bent in L shapes at obtuse angles. 
     As in both side portions  311  of the stator core  31  in embodiment 3, parts of the stator core  31  are formed by stacking, substantially in the circumferential direction, i.e., the rotation direction, thin electromagnetic steel sheets that are long in the axial direction, and are retained with tensile stress applied thereto. Thus, magnetic property deterioration due to compressive stress is suppressed and efficiency can be enhanced. 
     Next, the side-portion retention portion  312  for retaining the side portions  311  of the stator core  31  will be described. In embodiments 1 and 2,the stator core  31  is formed by stacking, substantially in the circumferential direction, i.e., the rotation direction, thin steel sheets that are long in the axial direction. On the other hand, in embodiment 3, the side portions  311  are formed on both of the inner circumferential side and the outer circumferential side by stacking, substantially in the circumferential direction, i.e., the rotation direction, thin steel sheets that are long in the axial direction as in embodiments 1 and 2, and the side-portion retention portion  312  for retaining both side portions  311  is formed by stacking electromagnetic steel sheets in the axial direction. Therefore, as described above, in a direction perpendicular to the axis, a substantially rectangular piece corresponding to each of electromagnetic steel sheets composing the side-portion retention portion  312  is present and thus it becomes easy to perform working into a desired shape. As shown in  FIG.  7    and 
       FIG.  8   , the side-portion retention portion  312  has substantially a rectangular shape and has, at center parts on the inner circumferential side and the outer circumferential side, the cutouts  312   a  in which both side portions  311  are inserted and retained. The flanges  312   b  are provided in the circumferential direction from the cutout  312   a.  Working into such a shape also becomes easy. 
     Meanwhile, as shown in  FIG.  4   , in the axial-direction cross-section of the rotary electric machine  1 , the stator  30  is provided between the inner rotor  10  and the outer rotor  20 , and the stator cores  31  are arranged at constant intervals. Therefore, a magnetic flux due to the structure in which permeability is not constant as seen from the gaps between the stator  30 , and the inner rotor  10  and the outer rotor  20 , is generated. The generated magnetic flux is called a spatial harmonic, leading to loss. 
     In the present embodiment, the side-portion retention portions  312  have the flanges  312   b  serving to fill spaces between circumferential-direction adjacent parts of the stator  30 , whereby a spatial harmonic can be reduced. In addition, since the side-portion retention portion  312  is stacked in the rotary shaft direction, the area of the conductor interlinked by a circumferential-direction interlinkage magnetic flux is small. Thus, the resistance of the conductor increases and eddy current can be reduced. 
     Next, a method for attachment between the side portions  311  and the side-portion retention portion  312  will be described. 
     In  FIG.  9   ,  FIG.  9 A  shows the side-portion retention portion  312  stacked in the axial direction and  FIG.  9 B  shows both side portions  311  stacked in the circumferential direction. The cutout  312   a  of the side-portion retention portion  312  includes two types of cutouts, i.e., shallowly-cut cutouts  312   a   1  and deeply-cut cutouts  312   a   2 , and the side-portion retention portion  312  is stacked such that the cutouts  312   a   1  and  312   a   2  have predetermined thicknesses d 2 , d 1 , respectively. On both of the inner circumferential side and the outer circumferential side, the stacked parts at the shallowly-cut cutouts  312   a   1  project relative to the stacked parts at the deeply-cut cutouts  312   a   2 . 
     The side portions  311  are arranged such that the inner circumferential side and the outer circumferential side thereof are opposed to each other, and have, on the retention portion sides, protruding parts  311 A and recessed parts  311 B sequentially formed in lengths corresponding to the thicknesses d 1 , d 2 , respectively. A level difference d 3  between the protruding part  311 A and the recessed part  311 B corresponds to the difference between the cutting depths of the shallowly-cut cutout  312   a   1  and the deeply-cut cutout  312   a   2  of the side-portion retention portion  312 . The side-portion retention portion  312  in  FIG.  9 A  and both side portions  311  in  FIG.  9 B  are fitted such that the stacked part at the shallowly-cut cutout  312   a   1  and the recessed part  311 B are fitted to each other and the stacked part at the deeply-cut cutout  312   a   2  and the protruding part  311 A are fitted to each other. That is, the recess and protrusion shapes of both members are fitted to each other in the direction of arrows in the drawing, thus forming the stator core  31  as shown in  FIG.  6   . 
     As described above, since the recess and protrusion shapes formed on the cutouts  312   a  of the side-portion retention portion  312  and the recess and protrusion shapes formed on both side portions  311  are fitted to each other, the stator core  31  can be formed in a state in which the thin-sheet-shaped electromagnetic steel sheets stacked in directions different from each other are in close contact with each other without coming apart. 
     The recess and protrusion shapes formed on the cutouts  312   a  of the side-portion retention portion  312  and the recess and protrusion shapes formed on both side portions  311  are not limited to the above ones. For example, shapes not only for fitting in the radial direction but also for fitting or engaging in the axial direction may be adopted. 
       FIG.  10    shows a modification of  FIG.  6    and is a perspective view showing the configuration of another stator  30  according to embodiment  3 . Difference from  FIG.  6    is that, in both side portions  311  of the stator core  31 , parts on the rotation-direction advanced side in  FIG.  4    are formed by structural bodies  311   b  which are not stacked electromagnetic steel sheets and are made of a non-metal or non-magnetic material. Parts on the rotation-direction lagged side are formed by stacked bodies  311   a  of electromagnetic steel sheets. 
     In electromagnetic steel sheets stacked in the circumferential direction, in-plane eddy current is generated and the generated eddy current tends to be greater on the rotation-direction advanced side. Therefore, if the parts on the rotation-direction advanced side are formed by members that are not electromagnetic steel sheets as shown in  FIG.  10   , loss due to eddy current on the rotation-direction advanced side can be reduced. In the present embodiment, high-strength resin is used as the structural bodies  311   b  made of a non-metal or non-magnetic material. The shapes of the structural bodies  311   b  and the stacked bodies  311   a  of electromagnetic steel sheets are not limited to the shown ones, and they may be different in size in the circumferential direction, or the like. 
     As described above, according to embodiment 3, both side portions  311  composing the stator core  31  are formed by stacking, substantially in the circumferential direction, i.e., the rotation direction, thin electromagnetic steel sheets that are long in the axial direction, and tensile stress is applied thereto. Thus, as in embodiments 1 and 2, magnetic property deterioration due to compressive stress is suppressed and efficiency can be enhanced. 
     In addition, the side-portion retention portion  312  of the stator core for retaining both side portions  311  is formed by stacking substantially-rectangular electromagnetic steel sheets in the axial direction, and has flange shapes on the inner circumferential side and the outer circumferential side. Such a structure contributes to suppression of a spatial harmonic and eddy current, thus achieving efficiency enhancement. 
     Further, in both side portions  311  composing the stator core  31 , parts on the rotation-direction advanced side are formed by the structural bodies  311   b  which are not stacked bodies of electromagnetic steel sheets and are made of a non-metal or non-magnetic material. Thus, it becomes possible to reduce loss due to eddy current. 
     Embodiment 4 
     Hereinafter, a rotary electric machine according to embodiment 4 will be described with reference to the drawings. 
       FIG.  11    is a sectional view along the rotary shaft of the rotary electric machine  1  according to embodiment 4. 
     In  FIG.  11   , difference from embodiment 1 is that, at both ends in the axial direction, radial-direction center parts of the stator core  31  extend and protrude in the axial direction while having smaller widths than the width of the stator core  31  opposed to the inner rotor  10  and the outer rotor  20 . The stator core load-side retention portion  36  which is the protruding distal end portion on the load side and the stator core non-load-side retention portion  37  which is the protruding distal end portion on the fixed side are formed in T shapes. In the T shape, a connection portion between a part extending in the axial direction and a part extending in the radial direction has a tapered shape. The stator core  31  is formed of an electromagnetic steel sheet, and the stator core load-side retention portion  36  and the stator core non-load-side retention portion  37  are parts of the stator core  31  and are formed of the same steel sheet. 
     As in embodiments 1 and 2, the stator core load-side retention portion  36  which is the distal end portion extended toward the load side which is one side in the axial direction is inserted in the groove in the load-side base retention member  35  attached to the load-side stator base  34 . At this time, the load-side retention surface  38  of the radial-direction part of the stator core load-side retention portion  36  formed in the T shape is fixed in contact with the groove in the load-side base retention member  35 . 
     The stator core non-load-side retention portion  37  which is the distal end portion extended toward the non-load-side which is the other side in the axial direction is inserted in the groove in the non-load-side stator base  33 . At this time, the non-load-side retention surface  39  of the radial-direction part of the stator core non-load-side retention portion  37  formed in the T shape is fixed in contact with the non-load-side stator base  33 . 
     Also in the present embodiment, in the stator core  31 , the direction in which the load-side retention surface  38  contacts with the load-side base retention member  35  and the direction in which the non-load-side retention surface  39  contacts with the non-load-side stator base  33  are opposed to each other in the axial direction, though mutually having some components in the radial direction. 
     As described above, also with the configuration in embodiment 4, the same effects as in embodiment 1 are provided. In addition, the stator core load-side retention portion  36  and the stator core non-load-side retention portion  37  have T shapes, and the radial-direction dimensions of the stator core load-side retention portion  36  and the stator core non-load-side retention portion  37  are small relative to the areas of the load-side retention surface  38  and the non-load-side retention surface  39 . Therefore, the sizes of the opening of the load-side base retention member  35  attached to the load-side stator base  34  and the opening of the non-load-side stator base  33  can be reduced. In addition, since the stator core load-side retention portion  36  and the stator core non-load-side retention portion  37  are each provided at one part in the axial direction, the number of the retention portions can be decreased and thus size reduction can be achieved. Further, in the T shapes of the stator core load-side retention portion  36  and the stator core non-load-side retention portion  37 , the connection portion between the part extending in the axial direction and the part extending in the radial direction has a tapered shape. Therefore, the connection portion can be ensured to have a certain strength. 
     Embodiment 5 
     Hereinafter, a rotary electric machine according to embodiment 5 will be described with reference to the drawings. 
       FIG.  12    is a sectional view along the rotary shaft of the rotary electric machine  1  according to embodiment 5. In  FIG.  12   , difference from embodiment 1 is that, at both ends in the axial direction, radial-direction center parts of the stator core  31  extend and protrude in the axial direction while having smaller widths than the width of the stator core  31  opposed to the inner rotor  10  and the outer rotor  20 . In addition, difference from embodiment 3 is that the distal end portions extending and protruding in the axial direction have engagement holes. The stator core  31  is formed of an electromagnetic steel sheet, and the stator core load-side retention portion  36  and the stator core non-load-side retention portion  37  are parts of the stator core  31  and are formed of the same steel sheets. 
       FIG.  13    is an enlarged view in an area X 4  enclosed by a broken line in  FIG.  12   , and  FIG.  14    is an enlarged view in an area X 5  enclosed by a broken line in  FIG.  12   .  FIG.  13    and  FIG.  14    show structures at both ends in the axial direction of the stator core  31 . 
     In the drawings, a hole  36   a  provided in the stator core load-side retention portion  36  which is the distal end portion extended toward the load side which is one side in the axial direction is fitted to a fixation pin  40  attached to the load-side base retention member  35 , and thus the load-side retention surface  38  is fixed to the load-side stator base  34  while contacting with the fixation pin  40  of the load-side base retention member  35 . 
     A hole  37   a  provided in the stator core non-load-side retention portion  37  which is the distal end portion extended toward the non-load side which is the other side in the axial direction is fitted to a fixation pin  40  attached to the non-load-side stator base  33 , and thus the non-load-side retention surface  39  is fixed to the non-load-side stator base  33  while contacting with the fixation pin  40  of the non-load-side stator base  33 . 
     Also in the present embodiment, the direction in which the load-side retention surface  38  contacts with the load-side base retention member  35  and the direction in which the non-load-side retention surface  39  contacts with the non-load-side stator base  33  are opposed to each other in the axial direction, though mutually having some components in the radial direction. 
     As described above, also with the configuration in embodiment 5, the same effects as in embodiment 1 are provided. In addition, since the stator core load-side retention portion  36  and the stator core non-load-side retention portion  37  are engaged with the fixation pins  40 , openings for inserting the stator core load-side retention portion  36  and the stator core non-load-side retention portion  37  in the non-load-side stator base  33  and the load-side stator base  34  are not needed, and thus size reduction can be achieved. In addition, as in embodiment 4, since the stator core load-side retention portion  36  and the stator core non-load-side retention portion  37  are each provided at one part in the axial direction, the number of the retention portions can be decreased and this also contributes to size reduction. 
     Embodiment 6 
     Hereinafter, a rotary electric machine according to embodiment 6 will be described with reference to the drawings. 
       FIG.  15    is a sectional view along the rotary shaft, showing the structure of a rotary electric machine  1 A according to embodiment 6, and  FIG.  16    is a sectional view showing the structure of a stator  30 A and is a partial sectional view along a B-B line direction in  FIG.  15   . In the drawings, the rotary electric machine  1 A includes two rotors which are a non-load-side rotor  10 A and a load-side rotor  20 A, and a stator  30 A provided between the two rotors in the radial direction, and is formed as an axial gap motor of a double-rotor type. 
     The non-load-side rotor  10 A includes a shaft  2 A, a non-load-side boss  12 A press-fitted and fixed to the shaft  2 A, and a permanent magnet  14 A adhered and fixed to the load side of the non-load-side boss  12 A. 
     The load-side rotor  20 A includes a load-side boss  21 A fixed to the shaft  2 A, and a permanent magnet  22 A adhered and fixed to the non-load side of the load-side boss  21 A. 
     The stator  30 A is provided between the non-load-side rotor  10 A and the load-side rotor  20 A, and rotatably retains the non-load-side rotor  10 A and the load-side rotor  20 A by a load-side inner bearing  3 A and a non-load-side inner bearing  4 A. 
     In the stator  30 A, a stator core  31 A is provided between a radially-outer-side retention member  35 A and a radially-inner-side retention member  33 A, and a stator coil  32 A is wound around the stator core  31 A. The radially-outer-side retention member  35 A is attached to a non-load-side base  41 A and a load-side base  41 B provided separately from the shaft  2 A, thus surrounding the two rotors, i.e., the non-load-side rotor  10 A and the load-side rotor  20 A. The shaft  2 A rotatably protrudes from a center part of the load-side base  41 B and is separate from the load-side base  41 B. 
     The stator core  31 A is formed by stacking, substantially in the circumferential direction, i.e., the rotation direction, thin steel sheets that are long in the radial direction. At both ends in the radial direction, both radial-direction side portions of the stator core  31 A on the non-load-side rotor  10 A side and the load-side rotor  20 A side extend and protrude. 
     Of both protruding side portions of the stator core  31 A, stator core radially-outer-side retention portions  36 A on the radially outer side have L-shaped distal end portions bent outward in the axial direction, i.e., bent such that both side portions are separated from each other. Each L-shaped part is engaged with a groove  35 Aa in the radially-outer-side retention member  35 A, and a radially-outer-side retention surface  38 A of the stator core radially-outer-side retention portion  36 A on the radially outer side is fixed in contact with the groove  35 Aa. 
     Of both protruding side portions of the stator core  31 A, stator core radially-inner-side retention portions  37 A on the radially inner side have L-shaped distal end portions bent inward in the axial direction, i.e., bent such that both side portions are opposed to each other. Each of them is engaged with an L-shaped groove  33 Ab provided in the radially-inner-side retention member  33 A, and a radially-inner-side retention surface  39 A of the stator core radially-inner-side retention portion  37 A is fixed in contact with the groove  33 Ab. 
     In the stator core  31 A, the direction in which the radially-outer-side retention surface  38 A contacts with the groove  35 Aa in the radially-outer-side retention member  35 A and the direction in which the radially-inner-side retention surface  39 A contacts with the groove  33 Ab provided in the radially-inner-side retention member  33 A are opposed to each other in the radial direction. That is, the stator core  31 A is fixed with tensile stress applied thereto. 
     Also in the configuration of the axial gap motor according to embodiment 6, the stator core  31 A is fixed with tensile stress applied thereto, whereby the same effects as in embodiment 1 are provided. That is, magnetic property deterioration due to compressive stress does not occur and torque is improved. Thus, a high-efficiency rotary electric machine can be provided. 
     The rotary electric machine  1 A according to embodiment 6 has a concentrated-winding configuration with 10 poles and 12 slots. The stator core 31A is formed by stacking, substantially in the circumferential direction, thin steel sheets that are long in the radial direction, as described above. The non-load-side rotor  10 A and the load-side rotor  20 A rotate at the same angular velocity. The thin steel sheets of the stator core  31 A are electromagnetic steel sheets manufactured by rolling, and are arranged such that the rolling direction coincides with the axial direction of the stator core  31 A, i.e., the direction in which the non-load-side rotor  10 A and the load-side rotor  20 A are opposed to each other. 
     Embodiment 7 
     Hereinafter, a magnetic gear as a rotary electric machine according to embodiment 7 will be described with reference to the drawings.  FIG.  17    is a sectional view along the rotary shaft, showing the structure of a magnetic gear  1 B according to embodiment 7, and  FIG.  18    is a partial sectional view along a C-C line direction. The magnetic gear  1 B does not include the stator coil  32 . As shown in  FIG.  18   , the stator core  31  is flat and does not have bent portions (flanges) at both side portions in the radial direction. For the inner rotor  10  and the outer rotor  20 , the stator cores  31  serve as pole pieces for modulating magnetic fluxes of the inner rotor  10  and the outer rotor  20  in accordance with greatness/smallness of magnetic resistance based on presence/absence of the stator cores  31  in the circumferential direction. 
     In  FIG.  17    and  FIG.  18   , the inner rotor  10  and the outer rotor  20  of the magnetic gear  1 B are not connected to each other. The inner rotor  10  rotates counterclockwise in the drawing, and the outer rotor  20  rotates clockwise in the drawing at the same electric angular velocity as the inner rotor  10 . Here, for example, it is assumed that the number of poles of the outer rotor  20  is 60 and the number of poles of the inner rotor  10  is 12, so that the number of poles of the outer rotor  20  is 5 times the number of poles of the inner rotor  10 . In this case, the magnetic gear having a speed reduction ratio of 5 can be obtained. While the number of poles of the outer rotor  20  which is a low-speed rotor is  60  and the number of poles of the inner rotor  10  which is a high-speed rotor is 12, the number of the stator cores  31  which are pole pieces in the circumferential direction is set to satisfy (number of pole pieces)=(number of poles of low-speed rotor)±(number of poles of high-speed rotor). Therefore, the number of the stator cores  31  is 60±12=72 or 48, and in this example, is set to 48. 
     At both ends in the axial direction, radial-direction center parts of the stator core  31  extend and protrude in the axial direction. The stator core load-side retention portion  36  which is the distal end portion extended toward the load side which is one side in the axial direction has an engagement hole as in embodiment 4, and the hole is fitted to the fixation pin  40  of the load-side base retention member  35  provided to the load-side stator base  34 , so that the load-side retention surface  38  is fixed in contact with the fixation pin  40  of the load-side base retention member  35 . 
     The stator core non-load-side retention portion  37  which is the distal end portion extended toward the non-load side which is the other side in the axial direction is formed in a T shape as in embodiment 3 and is inserted in the groove in the non-load-side stator base  33 . At this time, the non-load-side retention surface  39  of the radial-direction part of the stator core non-load-side retention portion  37  formed in the T shape is fixed in contact with the non-load-side stator base  33 . 
     The stator core  31  is formed of an electromagnetic steel sheet, and the stator core load-side retention portion  36  and the stator core non-load-side retention portion  37  are parts of the stator core  31  and are formed of the same steel sheet. The other configurations are the same as in embodiment 1. 
     Also in the present embodiment, in the stator core  31 , the direction in which the load-side retention surface  38  contacts with the load-side base retention member  35  and the direction in which the non-load-side retention surface  39  contacts with the non-load-side stator base  33  are opposed to each other in the axial direction, though mutually having some components in the radial direction. That is, the stator core  31  is fixed with tensile stress applied thereto. 
     As described above, also with the structure of the magnetic gear according to embodiment 7, the same effects as in embodiment 1 are provided. That is, in the magnetic gear  1 B, the stator core  31  is extended in the axial direction and fixed with tensile stress applied thereto, whereby the stator core  31  can be retained without deteriorating the magnetic property thereof. Thus, efficiency and torque of the magnetic gear can be enhanced. In addition, since the stator core load-side retention portion  36  and the stator core non-load-side retention portion  37  are each provided at one part in the axial direction, the number of the retention portions can be decreased and thus size reduction can be achieved. 
     Also in the other embodiments, the retention structures of the stator core load-side retention portion  36  and the stator core non-load-side retention portion  37  may be different from each other as in the present embodiment. 
     In the above description, it is described that the rotation directions of the inner rotor  10  and the outer rotor  20  are the same, but their rotation directions may be opposite to each other. In this case, the number of the stator cores  31  which are pole pieces may be  72  instead of  48 . In addition, the numbers of poles of the inner rotor  10  and the outer rotor  20  may be set in accordance with the change gear ratio of the magnetic gear for targets to be driven by the inner rotor  10  and the outer rotor  20 . 
     Embodiment 8 
     Hereinafter, a rotary electric machine according to embodiment 8 will be described with reference to the drawings. 
       FIG.  19    is a sectional view along the rotary shaft, showing the structure of the rotary electric machine  1  according to embodiment 8. In  FIG.  19   , difference from embodiment 1 is that the outer shaft  21  is not fixed to the shaft  2 . This rotary electric machine  1  corresponds to a magnetic geared motor obtained by winding the stator coil  32  around the magnetic gear of embodiment 7. Therefore, the inner rotor  10  and the outer rotor  20  of the rotary electric machine  1  are not connected to each other, and for example, the inner rotor  10  and the outer rotor  20  rotate in directions opposite to each other, and the outer rotor  20  rotates at an angular velocity that is ½ of the angular velocity of the inner rotor  10 . 
       FIG.  20    is a sectional view along a direction perpendicular to the rotary shaft of the rotary electric machine  1  and is a partial sectional view along a D-D line direction in  FIG.  19   . In  FIG.  20   , the inner rotor  10  rotates counterclockwise and the outer rotor  20  rotates clockwise. The stator core  31  is formed by stacking, substantially in the circumferential direction, thin electromagnetic steel sheets that are long in the axial direction. The side portions which are both side portions along the axial direction of the stator core  31  and are opposed to the inner rotor  10  and the outer rotor  20 , do not have bent portions (flanges). 
     The other configurations are the same as in embodiment 1, and as described in embodiment 7, the stator core  31  in embodiment 8 is also attached with tensile stress applied thereto. 
     In the above description, the example in which the inner rotor  10  and the outer rotor  20  rotate in directions opposite to each other and the angular velocity of the outer rotor  20  is ½ of that of the inner rotor  10 , has been shown. However, the rotation directions of the inner rotor  10  and the outer rotor  20  may be the same and their rotation speeds may be set independently of each other. 
     As described above, according to embodiment 8, the same effects as in embodiment 1 are provided. That is, the stator  30  is provided between the inner rotor  10  and the outer rotor  20  which are movable with the shaft  2  as an axis, and the stator  30  includes the stator core  31  formed by stacking thin sheets in the rotation direction and is retained with tensile stress applied thereto in the axial direction, whereby the stator core  31  can be retained without deteriorating the magnetic property thereof. Thus, efficiency and torque of the rotary electric machine can be enhanced. 
     In addition, since the inner rotor  10  and the outer rotor  20  of the rotary electric machine  1  are not connected to each other, the rotation directions and the rotation speeds of the respective rotors can be set independently of each other. Therefore, even in a case where the respective rotors drive different targets, control can be performed with their rotation directions and rotation speeds set respectively. 
     Embodiment 9 
     Hereinafter, an aircraft according to embodiment 9 will be described. 
       FIG.  21    shows an example of an aircraft  100  according to embodiment 9, and the rotary electric machine described in each embodiment 1 to 8 is provided thereto. In  FIG.  21   , in an engine case  210  of the aircraft  100 , a fan  230 , the rotary electric machine  1 ,  1 A, the magnetic gear  1 B, and an engine  220  are arranged and connected via a shaft. The rotary electric machine  1 ,  1 A is a motor and is used for driving the fan  230 . The magnetic gear  1 B is used as a transmission for increasing/reducing the speed. 
     In the case where the rotary electric machine  1 ,  1 A is provided, although not shown, a gear for changing the number of revolutions may be provided between the fan  230  and the rotary electric machine  1 ,  1 A and/or between the rotary electric machine  1 ,  1 A and the engine  220 . In this case, the gear may be a mechanical gear such as a spur gear or a planetary gear, or may be the magnetic gear  1 B. 
     In the case where the rotary electric machine  1 ,  1 A is provided, in  FIG.  16   , the rotary electric machine  1 ,  1 A and the engine  220  are arranged coaxially with the fan  230 . However, they may be arranged with different axes via a gear or the like, whereby the same effects are provided. 
     In the rotary electric machine shown in each embodiment 1 to 6, 8, since tensile stress is applied to the stator core, the stator core can be assuredly retained without deteriorating the magnetic property and high torque output can be obtained. Therefore, the rotary electric machine is suitably applied to a rotation target provided to the aircraft. 
     In the magnetic gear shown in embodiment 7, the stator core can be assuredly retained without deteriorating the magnetic property and a part subjected to wear is not present as compared to a mechanical gear. Therefore, the magnetic gear is suitably applied to a mechanism component provided to the aircraft. 
       FIG.  22    shows another example of the aircraft  100  according to embodiment 9.  FIG.  22 A  shows the aircraft  100  having a fan case  240  at a tail, and  FIG.  22 B  is a schematic enlarged view of the fan case  240 . In the drawings, similarly, the rotary electric machine described in each embodiment 1 to 8 is provided. In  FIG.  21   , the rotary electric machine is stored in the same engine case  210  as the engine  220 , whereas, as shown in  FIG.  22   , the rotary electric machine may be stored in a case different from the case for the engine  220 , to drive a driving target.  FIG.  22    shows the example in which the rotary electric machine  1 ,  1 A or the magnetic gear  1 B is connected via a shaft to the fan  230  in the fan case  240  at the tail. In the case where the magnetic gear  1 B is connected, the rotary electric machine  1 ,  1 A or the engine  220  is further connected to perform driving. 
     Alternatively, without having the engine  220 , the aircraft  100  may have the rotary electric machine  1 ,  1 A, as a drive motive-power source. Although not shown, the rotary electric machine  1 ,  1 A may be attached to a blade of a helicopter, a multicopter having a plurality of rotor blades, or the like, instead of the aircraft  100  having fixed wings, so as to be used as a drive source. 
     As described above, according to embodiment 9, the rotary electric machine shown in each embodiment 1 to 8 is applied to an aircraft. Thus, the stator core can be assuredly retained without deteriorating the magnetic property and high torque output can be obtained, whereby the flight range per fuel can be improved. 
     Modification and supplementary note of embodiments In the above embodiments, it is desirable that the stator core is retained with tensile stress applied thereto at a level not exceeding 100 MPa, but the tensile stress level may be such a level as not to cause breakdown or breakage by the stress. 
     In the above embodiments, the load-side stator base  34  and the non-load-side stator base  33  may be made of a magnetic material such as iron, but it is desirable that they are made of a material having small permeability or a non-magnetic material. Thus, such a magnetic flux as to pass between the stator cores  31  in the circumferential direction via the load-side stator base  34  and the non-load-side stator base  33  can be reduced or eliminated, whereby torque can be enhanced and the size and the weight can be reduced. 
     In the above embodiments, the rotary electric machines  1 ,  1 A are described as a motor. However, the same effects are provided even when the rotary electric machines  1 ,  1 A operate as an electric generator. 
     Although the disclosure is described above in terms of various exemplary embodiments and implementations, it should be understood that the various features, aspects, and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment with which they are described, but instead can be applied, alone or in various combinations to one or more of the embodiments of the disclosure. 
     It is therefore understood that numerous modifications which have not been exemplified can be devised without departing from the scope of the present disclosure. For example, at least one of the constituent components may be modified, added, or eliminated. At least one of the constituent components mentioned in at least one of the preferred embodiments may be selected and combined with the constituent components mentioned in another preferred embodiment. 
     DESCRIPTION OF THE REFERENCE CHARACTERS 
     
         
           1 ,  1 A rotary electric machine 
           1 B magnetic gear 
           2 ,  2 A shaft 
           3 ,  3 A load-side inner bearing 
           4 ,  4 A non-load-side inner bearing 
           5  load-side outer bearing 
           6  non-load-side outer bearing 
           10  inner rotor 
           10 A non-load-side rotor 
           12  boss 
           12 A non-load-side boss 
           14 ,  14 A permanent magnet 
           20  outer rotor 
           20 A load-side rotor 
           21  outer shaft 
           21 A load-side boss 
           22 ,  22 A permanent magnet 
           30 ,  30 A stator 
           31 ,  31 A stator core 
           32 ,  32 A stator coil 
           33  non-load-side stator base 
           33 A radially-inner-side retention member 
           33 Ab groove 
           34  load-side stator base 
           35  load-side base retention member 
           35 A radially-outer-side retention member 
           35 Aa groove 
           36  stator core load-side retention portion 
           36   a,    37   a  hole 
           36 A stator core radially-outer-side retention portion 
           37  stator core non-load-side retention portion 
           37 A stator core radially-inner-side retention portion 
           38  load-side retention surface 
           38 A radially-outer-side retention surface 
           39  non-load-side retention surface 
           39 A radially-inner-side retention surface 
           40  fixation pin 
           41 A non-load-side base 
           41 B load-side base 
           100  aircraft 
           210  engine case 
           220  engine 
           230  fan 
           240  fan case 
           311  side portion 
           311 A protruding part 
           311 B recessed part 
           311   a  stacked body 
           311   b  structural body 
           312  side-portion retention portion 
           312   a,    312   a   1 ,  312   a   2  cutout 
           312   b  flange