Patent Publication Number: US-2023145591-A1

Title: Rotor of rotary electric machine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation Application of PCT Application No. PCT/JP2021/040763, filed Nov. 5, 2021, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to a rotor of a rotary electric machine including a permanent magnet. 
     BACKGROUND 
     Permanent magnet-type rotary electric machine comprise a cylindrical stator and a circular columnar rotor rotatably supported inside the stator. The rotor comprises a rotor core and a plurality of permanent magnets embedded in the rotor core. 
     As such a permanent magnet-type rotary electric machine, a rotary electric machine having a configuration in which two magnets are arranged in a V-shape per pole and a magnet slot which contain the magnets is open to the surface of the rotor core has been proposed. In a rotary electric machine having the above-described configuration, leakage of magnetic flux of the magnets in the bridge of the rotor core can be reduced and the magnet torque generated per magnet weight can be increased. Or, it is possible to reduce the magnet weight while maintaining the torque of the rotary electric machine. 
     However, with this configuration, under conditions where large torque is generated, electromagnetic force in the circumferential direction is applied to the core portion located on an inner side of magnets arranged into a V-shape, which causes strong bending stress to the bridge located near the center of the magnetic poles. This may result in insufficient strength of the bridge. Or, if the bridge is made thicker for stress resistance, the leakage of magnetic flux increases, making it difficult to reduce the magnet weight. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a lateral cross-sectional view of a permanent magnet-type rotary electric machine according to the first embodiment. 
         FIG.  2    is a partially enlarged lateral cross-sectional view of the rotor of the rotary electric machine. 
         FIG.  3    is a partially enlarged lateral cross-sectional view of a rotor of a rotor electric machine according to the second embodiment. 
         FIG.  4    is a partially enlarged lateral cross-sectional view of a rotor of a rotor electric machine according to the third embodiment. 
         FIG.  5    is a partially enlarged lateral cross-sectional view of a rotor of a rotor electric machine according to the fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments will be described hereinafter with reference to the accompanying drawings. 
     In general, according to one embodiment, a rotor of a rotary electric machine comprises a rotor core including a plurality of magnetic poles arranged in a circumferential direction around a central axis, each of the magnetic poles including a plurality of magnet holder slots which are arranged to be spaced apart from each other in the circumferential direction and each of which includes an opening end opened to an outer circumference of the rotor core, and a closed end, a first core portion located between adjacent magnet holder slots of the plurality of magnet holder slots in the circumferential direction, a second core portion located between the magnet holder slots and the central axis, and a bridge connecting the first core portion and the second core portion; a plurality of permanent magnets disposed within the respective magnet holder slots; and a non-magnetic filling material filled into a cavity between the permanent magnet and the opening end in the magnet holder slot and joined to the permanent magnet and an inner wall of the respective magnet holder slot. 
     Throughout the embodiments, common elements are denoted by like reference numerals, and a detailed description thereof may be omitted unless otherwise necessary. Further, in order to make the description clearer, the widths, thicknesses, shapes, etc., of the respective parts are schematically illustrated in the drawings, compared to the actual modes. These parts can be redesigned or remodeled as needed with reference to the following descriptions and the conventional techniques. 
     First Embodiment 
       FIG.  1    is a lateral cross-sectional view of a permanent magnet-type rotary electric machine according to the first embodiment, and  FIG.  2    is an enlarged lateral cross-sectional view of one polar part of the rotor. 
     As shown in  FIG.  1   , a rotary electric machine  10  is configured, for example, as an inner rotor-type rotary electric machine. The rotary electric machine  10  comprises an annular or cylindrical stator  12  supported by a fixed frame not shown in the figure, and a rotator  14  supported freely rotatable around a central axis C inside the stator, which is coaxial with the stator  12 . The rotary electric machine  10  can be suitably applied, for example, to a drive motor or a generator in, for example, hybrid electric vehicles (HEV) and electric vehicles (EV). 
     The stator  12  comprises a cylindrical stator core  16  and an armature wound wire (coil)  18  wound around the stator core  16 . The stator core  16  is constituted by stacking a number of annular electromagnetic steel plates (core pieces) of a magnetic material, for example, silicon steel or the like, one on another in a concentric manner. In the inner circumferential portion of the stator core  16 , a plurality of slots  20  are formed. The slots  20  are arranged to be spaced apart from each other at equal intervals along the circumferential direction. Each of the slots  20  is open to an inner circumferential surface of the stator core  16  and extends from the inner circumferential surface in a radial direction. Each slot  20  extends over the entire axial length of the stator core  16 . With the plurality of slots  20  thus formed, an outer circumferential portion of the stator core  16  constitutes a circular yoke portion  16   a  and an inner circumferential portion of the stator core  16  constitutes a plurality (for example,  48  in this embodiment) of stator teeth  21  opposing the rotor  14 . The stator teeth  21  extend from the yoke portion  16   a  toward the central axis C in the radial direction. The armature wound wire  18  is inserted into the slots  20  and wound around each of the stator teeth  21 . When current is allowed to flow through the armature wound wire  18 , a predetermined chain flux is formed in the stator  12  (the stator teeth  21 ). 
     The rotor  14  includes a circular columnar shaft (rotation shaft)  22 , both ends of which are rotatably supported by bearings not shown in the figure, a cylindrical rotor core  24  fixed at an axial central portion of the shaft  22 , and a plurality of permanent magnets M embedded in the rotor core  24 . The rotor  14  is coaxially arranged inside the stator  12  with a small gap (air gap) therebetween. That is, the outer circumferential surface of the rotor  14  opposes the inner circumferential surface of the stator  12  with a slight gap therebetween. The rotor core  24  includes an inner hole  25  formed coaxially with the central axis C. The shaft  22  is inserted and fitted into the inner hole  25  and extends coaxially with the rotor core  24 . The rotor core  24  is constructed by stacking a number of magnetic plates, for example, circular electromagnetic steel plates (core pieces) such as silicon steel, into a multiplayer body stacked in a concentric manner. The rotor core  24  has the central axis C extending in the stacking direction of the core pieces and an outer circumferential surface coaxial with the central axis C. 
     In this embodiment, the rotor  14  includes a plurality of magnetic poles, for example, eight magnetic poles, arranged in a circumferential direction around the central axis C. In the rotor core  24 , the axis extending in the radial direction of the rotor core  24  and passing through the central axis line C and the boundary between a respective pair of magnetic poles adjacent to each other is referred to as a q-axis, and the axis electrically separated by 90 degrees in the circumferential direction from the q-axis, that is, the axis passing through the center of the magnetic pole and the central axis C, is referred to as a d-axis. The direction in which the chain flux formed by the stator  12  can easily flow is the q-axis. The d-axes and q-axes are alternately provided in the circumferential direction of the rotor core  24  and in predetermined phases. One magnetic polar portion of the rotor core  24  refers to an area between two adjacent q-axes in the circumferential direction (⅛ circumferential angular area). Thus, the rotor core  24  is constituted by eight poles (magnetic poles). The circumferential center of one pole is referred to as the d-axis. 
     As shown in  FIGS.  1  and  2   , in the rotor core  24 , a plurality of permanent magnets, for example, two permanent magnets M are embedded per one magnetic pole. In the circumferential direction of the rotor core  24 , magnet holder slots(, which may be, in some cases, referred to as magnet holding cavities or magnet embedding holes)  34  for loading the permanent magnets M are formed respectively on both sides of each d-axis. The two permanent magnets M are each loaded and disposed in each of the magnet holder slots  34  and secured to the rotor core  24  by, for example, adhesive. 
     As shown in  FIG.  2   , each magnet holder slot  34  is formed to penetrate the rotor core  24  in the axial direction. When viewed in a cross-sectional plane orthogonal to the central axis C of the rotor core  24 , the two magnet holder slots  34  are formed and arranged linearly symmetrical about the respective d-axis, and they are aligned in an approximately V-shaped arrangement, for example. Each magnet holder slot  34  includes an opening end which is opened or released to the outer circumference of the rotor core  24  and a closed end (the other end) that is located near the d-axis and closed. 
     Each magnet holder slot  34 , which functions as a flux barrier, includes a rectangular magnet loading area  34   a  corresponding to the cross-sectional shape of the permanent magnet M, an inner peripheral side cavity  34   b  extending from an inner peripheral end of the magnet loading area  34   a,  and an outer peripheral side cavity  34   c  extending from an outer peripheral end of the magnet loading area  34   a  and open to the outer circumference of the rotor core  24 . The outer peripheral side cavity  34   c  extends from the magnet loading area  34   a  to the opening end (opening  40 ) of the slot. The rotor core  24  includes a holder projection (step)  36   a  protruding in the outer peripheral side of the magnet loading area  34   a  from the inner edge  35   b  of the magnet holder slot  34  into the magnet holder slot  34 . 
     The magnet loading area  34   a  is formed between a flat inner edge (inner peripheral long edge)  35   b  and a flat outer edge (outer peripheral long edge)  35   a,  which oppose parallel to each other with an interval to the inner edge  35   b.  The inner edge  35   b  and the outer edge  35   a  extend and are inclined at an angle θ less than  90  degrees with respect to the d-axis. That is, the magnet loading area  34   a  is provided to gradually increase the distance from the d-axis from the inner circumferential edge to the outer circumferential edge, and gradually shorten the distance from the outer circumferential surface of the rotor core  24  from the inner circumferential edge to the outer circumferential edge, so as to be inclined. The angle θ is not limited to that of the example shown in the figure, but can be changed as desired. 
     The inner peripheral side cavity  34   b  extends from the inner circumferential end (d-axis end) of the magnet loading area  34   a  toward the d axis. The inner peripheral side cavity  34   d  is defined by an outer edge connected to be flush with the outer edge  35   b  of the magnet loading area  34   a,  an inner edge connected to be flush with the inner edge  35   b  of the magnet loading area  34   a,  and an end edge  35   c  extending approximately parallel to the d-axis and connected to the outer edge and the inner edge. End edge  35   c  constitutes the closed end of the slot. The end edge  35   c  constitutes a closed end of the slot. The end edge  35   c  opposes approximately parallel to the d-axis with an interval therebetween. 
     The outer peripheral side cavity  34   c  extends from the outer circumferential end of the magnet loading area  34   a  (the end of the rotor core on the outer circumferential surface) toward the outer circumferential surface of the rotor core  24  and is open or released to the outer circumference of the rotor core  24 . The outer peripheral side cavity  34   c  is defined between an outer edge  35   d  extending from one end of the outer edge  35   a  of the magnet loading area  34   a  to the outer circumference of the rotor core  24  so as to be flush with the outer edge  35   a,  and one end of the inner edge  35   b  of the magnet loading area  34   a,  that is, in this case, an inner edge  35   e  extending approximately parallel to the outer edge  35   a  from a projecting end of the holder projection  36   a  to the outer circumference of the rotor core  24 . The inner edge  35   e  is one step higher than the inner edge  35   b  by the height of the holder projection  36   a,  that is, in other words, closer to the side of the outer edge  35   d,  and extending from the projecting end of the holder projection  36   a  so as to be approximately parallel to the outer edge  35   d.  Further, the inner edge  35   e  bends toward the side of the outer edge  35   d  in the middle and then extends to the outer circumference of the rotor core  24 . With this configuration, in the outer peripheral side cavity  34   c,  the area on the side of the magnet loading area  34   a  has a width W 1  (the interval between the outer edge  35   d  and the inner edge  35   e ), whereas the opening  40  has a circumferential width W 2  which is less than the width W 1 . Note that the opening  40  is open over the entire axial length of the rotor core  24  to have the above-mentioned width. 
     Note that the outer edges  35   a  and  35   d  and the inner edges  35   b  and  35   e  of the magnet holder slot  34  are equivalent to the inner wall of the magnet holder slot  34 . 
     The inner peripheral side cavity  34   b  and the outer peripheral side cavity  34   c  of the magnet holder slot  34  function as magnetic cavities (flux barriers) which suppress leakage of magnetic flux from both longitudinal ends of the permanent magnet M to the rotor core  24 , and further contribute to weight reduction of the rotor core  24 . 
     The permanent magnets M are each formed, for example, into a slender flat plate with a rectangular cross-section, which has a length approximately equal to the axial length of the rotor core  24 . Each permanent magnet M is embedded over the entire axial length of the rotor core  24 . The permanent magnet M may be configured as a combination of magnets segmented along the axial (longitudinal) direction, in which case these magnets are formed to have a total length which is approximately equal to the axial length of the rotor core  24 . 
     As shown in  FIG.  2   , each permanent magnet M has a rectangular cross-sectional shape, which has a pair of long sides opposing parallel to each other and a pair of short sides opposing each other. The cross-sectional shape of the permanent magnet M is not limited to a rectangular shape (quadrangle), but may be a parallelogram. 
     The permanent magnet M is loaded into the respective magnet loading area  34   a  of the magnet holder slot  34 , in such a manner that one long side thereof is located to oppose and adjacent to or in contact with the outer edge  35   a  and the other long side is located to oppose and adjacent to or in contact with the outer edge  35   b.  One short side of the permanent magnet M, that is, one end portion of the short side on the outer circumferential side, is brought into contact with the holder projection  36   a.  With this arrangement, the permanent magnet M is held in the magnet loading area  34   a  in a state in which the longitudinal position is aligned. The permanent magnets M may be fixed to the rotor core  24  by adhesive or the like. The two permanent magnets M located on respective sides of the d-axis are arranged into an approximately V-shape. That is, the two permanent magnets M are arranged to incline so that the distance from the d-axis gradually increases from the inner circumferential end to the outer circumferential end and the distance from the outer circumferential surface of the rotor core  24  gradually shortens from the inner circumferential end to the outer circumferential end. 
     Each permanent magnet M is magnetized in the direction perpendicular to the long side. The two permanent magnets M located on respective circumferential sides of the d-axis, that is, two permanent magnets which constitute one magnetic pole, are arranged so that the magnetization directions thereof are identical to each other. On the other hand, two permanent magnets M located on respective circumferential sides of each q-axis are arranged so that the magnetization directions thereof are opposite to each other. In this embodiment, the rotating electric motor  10  constitutes a permanent magnets-embedded type rotary electric machine with eight polar (four pole pairs) in which permanent magnets M are arranged so that front and back sides of the N and S poles thereof alternate from each one pole to adjacent one. 
     As shown in  FIG.  2   , the rotor core  24  comprises, in each pole, a fan-shaped outer circumferential area (a first core portion)  24   a  located between the two magnet holder slots  34 , an inner circumferential area  24   b  of the rotor core  24  (an area between the magnet holder slots  34  and inner hole  25  (shaft  22 ), that is (a second core portion)), and a columnar bridge  50  which connects the first core portion  24   a  and the second core portion  24   b.  The bridge  50  is formed between the two inner peripheral side cavities  34   b  of the two magnet holder slots  34  of the two magnet holder slots  34  and extends along the d-axis. The number of bridge  50  is not limited to one, but a plurality of bridges may be provided. 
     The outer peripheral side cavity  34   c  of each magnet holder slot  34  is filled with a non-magnetic filling material SR. The filler material SR is joined or adhered to the short sides of the permanent magnet M, the outer edge  35   d  and the inner edge  35   e  of the outer peripheral side cavity  34   c,  and further blocks the opening  40 . In the opening  40 , the filler material SR is located to be substantially flush with the outer circumferential surface of the fixed core  24  and thus forms a part of the outer circumferential surface. 
     The filling material SR which fills the outer peripheral side cavity  34   c  is a low permeability material which has a magnetic permeability lower than that of the magnetic plate which forms the rotor core  24 , and a usable example thereof is resin. Apart from resin, the filler material SR may be a metal such as aluminum, stainless steel or the like, or carbon fiber-reinforced plastic. 
       FIG.  2    shows an example in which the entire outer peripheral side cavity  34   c  is filled with the filler material SR, but the configuration it is not limited to this. Note that it suffices if the filling material SR is applied by such an amount that at least the short sides of the permanent magnet M, part of the outer edge  35   d  of the outer peripheral side cavity  34   c,  and part of the inner edge  3  are joined. Further, the filling material SR may be applied to fill the inner peripheral side cavity  34   b  as well. 
     According to the rotor  14  of the rotary electric machine  10  according the first embodiment configured as described above, one end of the magnet holder slot is open to the outer circumference of the rotor core  24 , and with this configuration, the leakage flux of the permanent magnets can be reduced and the magnet torque generated per magnet weight can be increased. At the same time, with the configuration in which the outer peripheral side cavity  34   c  of the magnet holder slot is filled with the filler material SR such as resin, the filler material SR serves to suppresses the deformation of the magnetic plates which constitute the rotor core  24  and the deformation of the bridge  50 , thus making it possible to improve the strength of the rotor core  24  and the strength of the bridge  50 . Therefore, even when circumferential electromagnetic forces are applied to the outer circumferential area  24   a  of the rotor core  24  under conditions where large torque is generated, the deformation of the magnetic plates and bridge can be suppressed, and the outer circumferential area  24   a  of the rotor core  24  can be stably supported. In addition, it is possible to make the bridge  50  thinner. 
     As described above, according to the first embodiment, it is possible to improve the torque and output of a rotary electric machine of the same size, or to reduce the size and weight of the rotary electric machine while maintaining the same output. Furthermore, the cost of the rotor can be lowered by reducing the weight of the magnets used. 
     Next, rotors of rotary electric machines according to other embodiments of this invention will be described. In the other embodiments described below, parts identical to the above-described first embodiment will be designated by the same reference symbols, and their detailed descriptions will be omitted or simplified. The parts that differ from those of the first embodiment will be mainly described in detail. 
     Second Embodiment 
       FIG.  3    is a lateral cross-sectional view of a part of the rotor of the rotary electric machine according to the second embodiment. 
     As shown in the figure, according to the second embodiment, in the rotor core  24 , the magnet loading area  3  of the magnet holder slot  34  is formed to have a width  34   a  (the distance between the outer edge  35   a  and the inner edge  35   b ), which is greater than the width (thickness) of the permanent magnets M. With this configuration, a gap (first gap) G 1  of about several millimeters is formed between the outer edge  35   a  and the outer long side of the respective permanent magnet M. The gap G 1  includes one end connected to the outer peripheral side cavity  34   c  and the other end adjacent to the inner peripheral side cavity  34   b.    
     The rotor core  24  has a holder projection (the first projection) protruding into the inner peripheral side cavity  34   b  from the inner circumferential end of the outer edge  35   a.  The holder projection  36   b  abuts on an end portion of the short side of the permanent magnet M to align the permanent magnet M, and also functions as a leakage stopper which seals the other end of the inner circumference side of the gap G 1 . 
     The non-magnetic filling material SR is filled into the outer peripheral side cavity  34   c  and further into the gap G 1 . The filler material SR which fills the gap G 1  is joined to the long side portion of the permanent magnet M and the outer edge  35   a  of the magnet loading area  34   a.  The filling material SR is restricted from leaking to the side of the inner peripheral side cavity  34   b  by the holder projection  36   b.    
     In the second embodiment, the other configuration of the rotor is similar to that of the rotor in the first embodiment described above. 
     According to the second embodiment having the above-described configuration, the width (thickness) of the permanent magnets M is set less than the width of the magnet holder slot  34 , and therefore each permanent magnet M can be easily inserted into and set in the magnet holder slot  34  when the rotor is assembled. Then, the gap G 1  between the permanent magnet M and the magnet holder slot  34  is filled with the filling material SR, and thus the permanent magnet M can be held without rattling. Variations in the machining accuracy of the electromagnetic steel plates which constitute the rotor core  24  can be absorbed by the filler material SR, and adverse effects on the permanent magnets M can be suppressed. Further, with the projecting portion  36   b  provided for stopping leakage, the leakage of the filler material SR can be prevented and the filler material SR can be filled and held at the desired location. The other advantageous effects similar to those of the first embodiment described above can be obtained as well in the second embodiment. 
     Third Embodiment 
       FIG.  4    is a lateral cross-sectional view of a part of the rotor of the rotary electric machine according to the third embodiment. 
     As shown in the figure, according to the third embodiment, in the rotor core  24 , the width (thickness) of the permanent magnets M is set further less than the width of the magnet loading area  34   a (, that is, the distance between the outer edge  35   a  and the inner edge  35   b ). Thus, a gap G 1  of several millimeters (mm) is created between the outer edge  35   a  and the outer long side of the permanent magnet M, and a gap (second gap) G 2  of several millimeters (mm) is created between the outer edge  35   a  on the opposite side and the inner long side of the permanent magnet M. The gap G 2  includes one end connected to the outer peripheral side cavity  34   c  and the other end adjacent to the inner peripheral side cavity  34   b.    
     The rotor core  24  includes, in addition to the holder projection (first projecting portion)  36   b  protruding from the inner circumferential end of the outer edge  35   a  into the inner circumferential gap  34   b,  a holder projection (second projecting portion)  36   c  protruding from the inner circumferential end of the inner edge  35   b  into the inner peripheral side cavity  34   b.  The holder projections  36   b  and  36   c  each abut to the short side of the permanent magnet M to align the permanent magnet M and further function as a leak stopper which seals the other inner circumferential ends of the gaps G 1  and G 2 . Respective ends of the gaps G 1  and G 2 , that is, the outer circumferential ends thereof, are each connected to the outer peripheral side cavity  34   c.    
     The non-magnetic filler material SR is filled into the outer peripheral side cavity  34   c  and further into the gaps G 1  and G 2 . The filler material SR which fills the gap G 1  is joined to the long side portion of the permanent magnet M and the outer edge  35   a  of the magnet loading area  34   a.  The filler material SR which fills the gap G 2  is joined to the long side portion of the permanent magnet M and the inner edge  35   b  of the magnet loading area  34   a.  The filler material SR is restricted from leaking to the side of the inner peripheral side cavity  34   b  by the holder projections  36   b  and  36   c.    
     In the third embodiment, the other configurations of the rotor is similar to those of the rotor in the first embodiment described above. 
     In the third embodiment of the above-described configuration as well, advantageous effects similar to those of the second embodiment and the first embodiment, described above, can be obtained. 
     Fourth Embodiment 
       FIG.  5    is a lateral cross-sectional view of a part of the rotor of the rotary electric machine according to the fourth embodiment. 
     As shown in the figure, according to the fourth embodiment, the rotor core  24  includes at least one projecting portion protruding into the opening  40  of the magnet holder slot  34 . In this embodiment, the stator core  24  includes a pair of projecting portions  40   a  and  40   b  protruding into the opening  40  from respective circumferential sides of the opening  40 . Thus, the opening  40  is partially blocked by the pair of projecting portions  40   a  and  40   b,  the opening  40  formed between the projecting portions  40   a  and  40   b  has a width sufficiently less as compared the width of the outer peripheral side cavity  34   c  and the width of the magnet loading area  34   c,  that is, for example, about ⅓ of the width. 
     The outer edge  35   d  of the outer peripheral side cavity  34   a  extends from the outer edge  35   a  of the magnet loading area  34   a  to be flush with the outer edge  35   a,  and then bends toward the opening  40  near the outer circumference of the rotor core  24 . It further extends in the circumferential direction along the projecting portion  40   a,  and bends at a right angle toward the outer circumferential surface to extend thereto. The inner edge  35   e  of the outer peripheral side cavity  34   c  extends from the protruding end of the holder projection  36  substantially parallel to the outer edge  35   d,  and bends, in the middle, toward the side of the outer edge  35   d.  Then, it bends toward the opening  40  near the outer circumference of the rotor core  24 , and extends in the circumferential direction along the projecting portion  40   b.  Further, it bends at right angles to the side of the outer circumferential surface to extend thereto. 
     As described, the pair of projecting portions  40   a  and  40   b  reduce the width of the opening  40  and further form a pair of shoulder portions or stopper portions extending in the circumferential direction in the vicinity of the opening  40 . The non-magnetic filler material RS is filled into the outer peripheral side cavity  34   c  and the gaps G 1  and G 2 . In the outer peripheral side cavity  34   c,  the filler material RS is joined to the short side of the permanent magnet M, the outer edge  35   d  including the shoulder portion (projecting portion  40   a ), and the inner edge  35   e  including the shoulder portion (projecting portion  40   b ). 
     In the fourth embodiment, the other configurations of the rotor are similar to those of the rotor of the third embodiment described above. 
     According to the fourth embodiment with the above-described configuration, with the projecting portions (shoulder portions)  40   a  and  40   b  provided near the opening  40 , the filling material RS can be prevented from being extracted or popped out therefrom, and thus the filling material RS can be held securely in the outer peripheral side cavity  34   c.    
     Usually, as the filler material (resin) and the rotor core  24 , which have linear expansion coefficients different from each other undergo repeated temperature changes, delamination occurs at the interface between the filler material and the rotor core, and repeated centrifugal force can cause the resin to crack and pop out to the outer circumferential side, which may interfere with the rotation. 
     In contrast, according to this embodiment, the projecting portions  40   a  and  40   b  or shoulder portions can reliably prevent popping out of the filler material and improve reliability. In addition, in the fourth embodiment as well, advantageous effects similar to those of the second embodiment and the first embodiment, described above, can be obtained. 
     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. 
     For example, the number of poles, dimensions, shape, etc., of the rotor are not limited to those of the embodiments described above, but can be changed in various ways depending on the design. The number of permanent magnets installed in each pole of the rotor is not limited to two, but can be increased as needed. The filler material is not limited to those listed in the embodiments, but can be selected from a variety of other filler materials.