Abstract:
A rotating element with embedded permanent magnets is provided that includes: a rotor core adapted to be within the diameter direction of a stator; first permanent magnets embedded near the exterior circumference face of the core, and orthogonally extending with a d axis; and second permanent magnets embedded on both sides of each of the first magnets, and extending along a q axis. The rotating element further includes gaps formed in the core away from both circumference direction ends of the first magnets. The gaps further include exterior end parts at the furthermost exterior side with respect to the diameter direction of the core, and interior end parts at the furthermost interior side with respect to same. The magnetic pole faces of the first magnets are located between the exterior and interior end parts of the gaps.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a permanent-magnet-embedded rotor that includes a first permanent magnet embedded near an outer circumference surface of a rotor core and extending in a direction orthogonal to a d-axis, a second permanent magnet embedded in the rotor core and extending along a q-axis, and a gap formed in the rotor core to be distant from the first permanent magnet toward the second permanent magnet. The present invention also relates to a rotating electrical machine having the rotor. 
       BACKGROUND ART 
       [0002]    As illustrated in  FIG. 7 , a permanent-magnet reluctance rotating electrical machine  90  disclosed in Patent Document 1 includes a stator  92  having a plurality of armature coils  91 , and a rotor  93  arranged inwardly of the stator  92  in the radial direction. 
         [0003]    The rotor  93  includes a cylindrical rotor core  94 . The rotor core  94  is provided with a plurality of magnetic poles. A plurality of pairs of first hollows  95  in a rectangular shape are formed in the direction along each magnetic pole axis of the rotor core  94  with a clearance by what corresponds to a magnetic pole width. Each pair of the first hollows  95  are formed at locations holding each magnetic pole therebetween from both sides of the circumferential direction. A first permanent magnet  96  is embedded in each first hollow  95 . Moreover, second hollows  97  in a rectangular shape are formed between respective magnetic poles substantially along the outer circumference of the rotor core  94 . A second permanent magnet  98  is embedded in each second hollow  97 . 
         [0004]    The first permanent magnets  96  and the second permanent magnets  98  provided in the rotor core  94  increase reluctance torque. Hence, the permanent-magnet reluctance rotating electrical machine  90  has increased torque. 
       PRIOR ART DOCUMENT 
     Patent Document 
       [0005]    Patent Document 1: Japanese Patent No. 3597821 
       SUMMARY OF THE INVENTION 
       [0006]    Since the second permanent magnets  98  are located near the outer circumference surface of the rotor core  94 , the alternating field interlinking with the second permanent magnets  98  becomes large, and the second permanent magnets  98  produce a large eddy current loss. Such a large eddy current loss increases the temperatures of the second permanent magnets  98 , thereby reducing magnetic fluxes produced from the second permanent magnets  98 . Hence, the permanent-magnet reluctance rotating electrical machine  90  has the torque reduced. 
         [0007]    In order to reduce the eddy current loss, for example, adaptation of a magnet with a high coercive force as the second permanent magnet  98 , increase of the thickness of the second permanent magnet  98 , and division of the second permanent magnet  98  into a plurality of pieces are possible, but all result in the cost increase, which are undesirable. 
         [0008]    In order to reduce the alternating field interlinking with the second permanent magnets  98 , the second permanent magnet  98  may be located at a distant location from the outer circumference surface of the rotor core  94 , i.e., as illustrated in  FIG. 7  by dashed lines, the embedded location (the location where the second hollow  97  is formed) of the second permanent magnet  98  may be shifted toward the center of the rotor core  94 . When, however, the embedded location of the second permanent magnet  98  is shifted toward the center of the rotor core  94 , the second permanent magnet  98  becomes closer to the first permanent magnet  96 , and thus the short-circuit flux between the first and second permanent magnets  96  and  98  increases. This reduces the magnetic flux from the second permanent magnet  98  to the stator  92 . Accordingly, the permanent-magnet reluctance rotating electrical machine  90  has a reduce torque. 
         [0009]    It is an objective of the present invention to provide a permanent-magnet-embedded rotor and a rotating electrical machine having the same that are capable of reducing an eddy current loss without reducing torque. 
         [0010]    To achieve the foregoing objective and in accordance with one aspect of the present invention, a permanent-magnet-embedded rotor is provided that includes a rotor core, a first permanent magnet, second permanent magnets, and a gap. The rotor core is adapted to be arranged inwardly of a stator in a radial direction. The first permanent magnet is embedded in the rotor core near an outer circumferential surface thereof, and extends in a direction orthogonal to a d-axis. The second permanent magnets are embedded at both sides of the first permanent magnet in a circumferential direction, and extend along a q-axis. The gap is formed in the rotor core to be distant from both ends of the first permanent magnet in the circumferential direction toward the second permanent magnet. The gap includes, with respect to the radial direction of the rotor core, a radially outer end located at an outermost side and a radially inner end located at an innermost side. A pole face of the first permanent magnet is located between the radially outer end of the gap and the radially inner end thereof in the radial direction of the rotor core. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a plan view illustrating a permanent-magnet-embedded rotating electrical machine according to a first embodiment; 
           [0012]      FIG. 2  is a partial enlarged view illustrating magnetic poles in a permanent-magnet-embedded rotor of the permanent-magnet-embedded rotating electrical machine in  FIG. 1 ; 
           [0013]      FIG. 3  is a plan view illustrating a permanent-magnet-embedded rotating electrical machine according to a second embodiment; 
           [0014]      FIG. 4  is a partial enlarged view illustrating magnetic poles in a permanent-magnet-embedded rotor of the permanent-magnet-embedded rotating electrical machine in  FIG. 3 ; 
           [0015]      FIG. 5  is a partial enlarged view illustrating a modification of a second permanent magnet in the permanent-magnet-embedded rotating electrical machine in  FIG. 1 ; 
           [0016]      FIG. 6  is a partial enlarged view illustrating a modification of a second permanent magnet in the permanent-magnet-embedded rotating electrical machine in  FIG. 3 ; and 
           [0017]      FIG. 7  is a plan view illustrating a conventional permanent-magnet reluctance rotating electrical machine. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    A first embodiment according to the present invention will now be described with reference to  FIGS. 1 and 2 . 
         [0019]    As illustrated in  FIG. 1 , a permanent-magnet-embedded rotating electrical machine M includes an annular stator  10  and a permanent-magnet-embedded rotor  15  (hereinafter, simply referred to as a rotor  15 ) provided inwardly of the stator  10  in a rotational manner. The stator  10  includes an annular stator core  11 . The stator core  11  is formed by laminating a plurality of core plates formed of a magnetic material (steel sheet). 
         [0020]    A plurality of teeth  13  are arranged around the inner circumference of the stator core  11 . A slot  12  is formed between adjoining teeth  13  in the circumferential direction of the stator core  11 . A coil  30  is built in each slot  12 . As illustrated in  FIG. 2 , it is assumed that a length of a tooth  13  in a direction orthogonal to the radial direction of the stator core  11  is a width of the tooth  13 . It is also assumed that a straight line extending through the middle point of the width of the tooth  13  and extending in the radial direction of the stator core  11  is a center axis TL of the tooth  13 . Furthermore, it is assumed that a width between respective center axes TL of the pair of adjoining teeth  13  is a pitch P between the teeth  13 . The width between the center axes TL of the teeth  13  gradually increases from the tip of the tooth  13  (inner end in the radial direction) toward the basal end. Hence, according to this embodiment, the width between the center axes TL of the pair of teeth  13  at respective tips, i.e., the minimum value of the width between the center axes TL is defined as the pitch P. 
         [0021]    Next, a description will be given of the rotor  15 . As illustrated in  FIG. 1 , the rotor  15  includes an annular rotor core  16 . The rotor core  16  is formed by laminating a plurality of core plates  161  formed of a magnetic material (steel sheet). A shaft hole  16   a  extending all the way through the rotor core  16  is provided in the center of the rotor core. An output shaft (unillustrated) of the permanent-magnet-embedded rotating electrical machine M is fitted in and fixed to the shaft hole  16   a.    
         [0022]    Embedded in each of imaginary areas W obtained by equally dividing the rotor core  16  in the circumferential direction (in this embodiment, divided into eight areas) are a first permanent magnet  17  and two second permanent magnets  18 . The first and second permanent magnets  17  and  18  are each formed in a tabular shape, and formed to have a rectangular cross section orthogonal to a center axis C of the rotor core  16 . 
         [0023]    In each imaginary area W, a magnet group that is a set of one first permanent magnet  17  and two second permanent magnet  18  serves as a magnetic pole. According to this embodiment, the magnet groups are arranged at eight locations in the circumferential direction of the rotor core  16 , and thus the rotor  15  has eight magnetic poles. The plurality of magnetic poles is provided in such a manner as to have different polarities alternately in the circumferential direction of the rotor core  16 . A d-axis  26  illustrated in  FIG. 1  represents a direction of magnetic fluxes produced by one magnetic pole (a direction orthogonal to the lengthwise direction of the first permanent magnet  17  and extending through a space between the two second permanent magnets  18 ), a q-axis  27  represents an axis electrically and magnetically orthogonal to the d-axis  26 , and extends like an arcuate. 
         [0024]    As illustrated in  FIG. 2 , a first embedding hole  19  is formed in each imaginary area W near an outer circumferential surface  16   b  of the rotor core  16 . The first embedding hole  19  extends all the way through the rotor core  16  in a direction parallel to the center axis C of the rotor core  16 , and extends substantially in the circumferential direction of the rotor core  16  like a slit (rectangular). More specifically, the longer side of the first embedding hole  19  is orthogonal to the d-axis  26 . The first permanent magnet  17  is fitted in this first embedding hole  19 . 
         [0025]    The surface that forms the first embedding hole  19 , i.e., a forming face includes an outer forming face  19   a  that is a longer-side forming face near the outer circumferential surface  16   b  of the rotor core  16 , and an inner forming face  19   b  that is a longer-side forming face that faces the outer forming face  19   a  and is near the inner circumferential surface of the rotor core  16 . The first permanent magnet  17  fitted in the first embedding hole  19  includes an end face near the outer circumferential surface  16   b  of the rotor core  16 , i.e., a pole face  17   a  that is a surface facing the outer forming face  19   a,  and an end face near the inner circumferential surface of the rotor core  16 , i.e., an opposite pole face  17   b  that is a surface facing the inner forming face  19   b.  The first permanent magnet  17  also includes magnet end faces  17   c  that are end faces at both shorter sides. 
         [0026]    A pair of second embedding holes  20  each in a rectangular shape is formed in each imaginary area W. Each second embedding hole  20  extends all the way through the rotor core  16  in the direction parallel to the center axis C, and has a longer side extending from the inner side of the rotor core  16  in the radial direction toward the outer side thereof in the radial direction. More specifically, each pair of the second embedding holes  20  is located in V-shape becoming distant from each other from the inner side of the rotor core  16  in the radial direction toward the outer side thereof in the radial direction. The longer sides of each pair of the second embedding holes  20  extend in parallel with (along) a part of the q-axis  27  near those second holes. The second permanent magnet  18  is fitted in each second embedding hole  20 . The surface forming each second embedding hole  20 , i.e., the forming face includes a first forming face  20   a  that is a longer-side forming face near the first embedding hole  19  and a second forming face  20   b  that is a longer-side forming face that faces the first forming face  20   a  and is near the second embedding hole  20  of the adjacent magnetic pole. 
         [0027]    Each pair of the second permanent magnets  18  is located such that the ends at the same side (e.g., a side of the rotor core  16  that corresponds to the outer-circumferential-surface- 16   b ) have the same polarity. Moreover, respective second permanent magnets  18  located at adjacent magnetic poles are located such that the ends at the same side have different polarities. When, for example, respective ends of the pair of the second permanent magnets  18  of any given magnetic pole at the side corresponding to the outer-circumferential-surface- 16   b  have southern polarity, then respective ends of the pair of the second permanent magnets  18  of the adjacent magnetic pole at the side corresponding to the outer-circumferential-surface- 16   b  have northern polarity. According to this embodiment, the pair of second permanent magnets  18  is located at locations line symmetric to the d-axis  26  so that the rotor  15  can rotate in both forward and reverse directions. 
         [0028]    The rotor core  16  has a pair of first gaps  21  formed to be continuous from both shorter sides of each first embedding hole  19 . Moreover, the rotor core  16  has a pair of second gaps  22  distant from the first permanent magnet  17  toward the second permanent magnet  18 , separate from the first gap  21 , and formed in a substantially sector shape. Respective first and second gaps  21  and  22  extend all the way through the rotor core  16  in the direction parallel to the center axis C. 
         [0029]    According to this embodiment, the first gap  21  and the second gap  22  located near each end of the first permanent magnet  17  form a gap portion  23 . 
         [0030]    The pair of first gaps  21  is formed in both shorter-side end faces of the first permanent magnet  17  to be gradually becoming thin as becoming distant from the corresponding first permanent magnet  17  toward the second permanent magnet  18 . The surface that forms the first gap  21 , i.e., the forming face of the first gap  21  includes a first forming face  21   a  continuous from the outer forming face  19   a  of the first embedding hole  19  and extending toward the inner side of the rotor core  16 , and a second forming face  21   b  extending from a magnet end face  17   c  toward the inner side of the rotor core  16 . 
         [0031]    The surface that forms the second gap  22 , i.e., the forming face of the second gap  22  includes an outer-circumferential-side forming face  22   a  extending in an arcuate shape along the outer circumferential surface  16   b  of the rotor core  16 , a d-axis-side forming face  22   b  extending from an end edge near the first permanent magnet  17  between both end edges of the outer-circumferential-side forming face  22   a , and a q-axis-side forming face  22   c  extending from the remaining end edge. The d-axis-side forming face  22   b  and the q-axis-side forming face  22   c  become close to each other toward the inner circumferential surface of the rotor core  16  from the proximity of the outer circumferential surface  16   b  thereof. The intersection between the d-axis-side forming face  22   b  and the q-axis-side forming face  22   c  is a radially inner end Y at the innermost location relative to the radial direction of the rotor core  16  in the second gap  22 . According to this embodiment, the outer-circumferential-side forming face  22   a  of the second gap  22  corresponds to a radially outer end at the outermost location relative to the radial direction of the rotor core  16  in the second gap  22 . 
         [0032]    An outer-circumferential-side bridge  24  that extends in the circumferential direction of the rotor core  16  at a constant width is formed between the outer circumferential surface  16   b  of the rotor core  16  and the outer-circumferential-side forming face  22   a  of the second gap  22 . That is, the side face of the outer-circumferential-side bridge  24  at the side corresponding to the second-gap- 22  is the outer-circumferential-side forming face  22   a  of the second gap  22 . 
         [0033]    In the rotor core  16 , a reinforcement bridge  25  is formed between the first and second gaps  21  and  22 . That is, the side face of the reinforcement bridge  25  at the side corresponding to the first gap  21  is the first forming face  21   a  of the first gap  21 , while the side face of the reinforcement bridge  25  at the side corresponding to the second gap  22  is the d-axis-side forming face  22   b  of the second gap  22 . The reinforcement bridge  25  runs at a constant width substantially same as the width of the outer-circumferential-side bridge  24 . Respective widths of the outer-circumferential-side bridge  24  and the reinforcement bridge  25  are preferably equal to or greater than twice the thickness of the core plate  161 . 
         [0034]    The pole face  17   a  of the first permanent magnet  17  is located inwardly of the outer-circumferential-side forming face  22   a  (radially outer end) of the second gap  22  in the radial direction of the rotor core  16 , and is located outwardly of the radially inner end Y of the second gap  22  in the radial direction of the rotor core  16 . That is, the pole face  17   a  of the first permanent magnet  17  is located between the outer-circumferential-side forming face  22   a  (the radially outer end) and the radially inner end Y in the radial direction of the rotor core  16 . It is assumed that a distance from the outer circumferential surface  16   b  of the rotor core  16  to the pole face  17   a  along the d-axis  26  is an embedded width F of the first permanent magnet  17 . It is preferable that the embedded depth F should satisfy 1/10 P&lt;F&lt;2/3 P, where P is the pitch between the teeth  13 . 
         [0035]    The two second permanent magnets  18  are arranged to make the gap therebetween narrowed toward the inner circumferential surface of the rotor core  16 . Hence, if the first permanent magnet  17  becomes close to the inner circumferential surface of the rotor core  16 , the magnet end face  17   c  of the first permanent magnet  17  becomes close to the second permanent magnets  18 . If the first permanent magnet  17  becomes close to the inner circumferential surface of the rotor core  16  with the embedded depth F that is larger than 2/3 P, it is undesirable since the short-circuit flux between the first and second permanent magnets  17  and  18  increases excessively. Conversely, if the first permanent magnet  17  becomes close to the outer circumferential surface  16   b  of the rotor core  16  with the embedded depth F that is smaller than 1/10 P, the alternating field interlinking with the first permanent magnet  17  increases, and thus it is undesirable since the eddy current loss at the surface of the first permanent magnet  17  increases. The embedded depth F is set within a range that allows the first permanent magnet  17  to be arranged between the pair of second gaps  22  in the radial direction of the rotor core  16 . 
         [0036]    A length N of the first permanent magnet  17  in the lengthwise direction is preferably within a range from one to three times the pitch P between the teeth  13 . When the length N is shorter than the pitch P, the first permanent magnet  17  is excessively downsized and the magnetism decreases, and thus it is undesirable since the magnetic flux produced from the first permanent magnet  17  decreases. Conversely, when the length N of the first permanent magnet  17  is larger than three times the pitch P, the first permanent magnet  17  becomes excessively long, and it is undesirable since appropriate disposition of the second gap  22  (the gap portion  23 ) and that of the second permanent magnet  18  become difficult from the standpoint of a magnetic pole. 
         [0037]    In each magnetic pole, a clearance H between each second gap  22  (gap portion  23 ) and the second permanent magnet  18  adjacent to that second gap  22  (an interval between the q-axis-side forming face  22   c  of the second gap  22  and the longer-side forming face  20   a  of the second embedding hole  20 ) is preferably within a range that is 0.3 times to twice the pitch P. When this clearance H becomes smaller than 0.3 times the pitch P, the magnetic flux passing through the space between the second permanent magnet  18  and the gap portion  23  (second gap  22 ) decreases, and thus it is undesirable since this results in a reduction of torque by the permanent-magnet-embedded rotating electrical machine M. Conversely, when the clearance H becomes larger than twice the pitch P, the magnetic flux that passes through the space between the second permanent magnet  18  and the gap portion  23  (second gap  22 ) can be increased, but torque ripples also increase, and thus it is undesirable. 
         [0038]    Next, a description will be given of operation of the permanent-magnet-embedded rotating electrical machine M having the rotor  15 . 
         [0039]    When a current is caused to flow through the coils  30 , a rotating magnetic field acting on the stator  10  is produced. 
         [0040]    This rotating magnetic field, magnetic suction force between the first permanent magnet  17  and the second permanent magnet  18 , and repulsion force cause the rotor  15  to rotate. At this time, since the rotor core  16  is provided with the first permanent magnets  17  and the second permanent magnets  18 , the reluctance torque increases in comparison with a case in which, for example, the rotor core  16  is provided with only either one of the first permanent magnet  17  or the second permanent magnet  18 , thereby increasing the torque of the permanent-magnet-embedded rotating electrical machine M. 
         [0041]    In the rotor core  16 , the first permanent magnets  17  are embedded in the rotor core  16  such that the embedded depth F of the first permanent magnet  17  satisfies 1/10 P&lt;F&lt;2/3 P. Hence, the first permanent magnet  17  is located at a location that is not too close to the outer circumferential surface  16   b  of the rotor core  16  and is also not too close to the inner circumferential surface thereof. Accordingly, it becomes possible to suppress a generation of an eddy current loss at the surface of the first permanent magnet  17 , and to reduce the short-circuit flux between the first and second permanent magnets  17  and  18 . 
         [0042]    According to the above-described embodiment, the following advantages are achieved. 
         [0043]    (1) In the rotor core  16  of the rotor  15 , the first permanent magnets  17  elongated long and thin are located near the outer circumferential surface  16   b  of the rotor core  16 . Moreover, in the rotor core  16 , the two second permanent magnets  18  are arranged to hold the one first permanent magnet  17  therebetween. The first permanent magnet  17  is embedded in the rotor core  16  such that the pole face  17   a  at the side corresponding to the outer-circumferential-surface- 16   b  is located inwardly of the outer-circumferential-side forming face  22   a  of the second gap  22  at the side corresponding to the outer-circumferential-surface- 16   b  in the radial direction of the rotor core  16 , and is also located outwardly of the radially inner end Y of the second gap  22  in the radial direction of the rotor core  16 . By setting the embedded location of the first permanent magnet  17  in this manner, it becomes possible to prevent the first permanent magnet  17  from becoming too close to the outer circumferential surface  16   b  of the rotor core  16  even if the first permanent magnet  17  is located near the outer circumferential surface  16   b  of the rotor core  16 , and to suppress a generation of an eddy current loss at the surface of the first permanent magnet  17 . Moreover, it becomes possible to prevent the first permanent magnet  17  from becoming too close to the inner circumferential surface of the rotor core  16 , thereby reducing the short-circuit flux between the first and second permanent magnets  17  and  18 . 
         [0044]    Hence, the temperature rise of the first permanent magnet  17  inherent to the eddy current loss is reduced, thereby suppressing a reduction of the magnetic flux produced by the first permanent magnet  17  and an increase of the short-circuit flux. This results in a suppression of a reduction of the torque by the permanent-magnet-embedded rotating electrical machine M. Since the eddy current loss of the first permanent magnet  17  is suppressed, it becomes unnecessary to employ a magnet having a large coercive force as the first permanent magnet  17 , to make the first permanent magnet  17  thickened, and to divide the first permanent magnet  17  into a plurality of pieces. Accordingly, it becomes possible to avoid a cost increase of the first permanent magnet  17  in order to suppress a torque reduction. 
         [0045]    (2) Since the embedded depth F of the first permanent magnet  17  is set to satisfy 1/10 P&lt;F&lt;2/3 P, the eddy current loss is reduced without reducing the torque by the permanent-magnet-embedded rotating electrical machine M. 
         [0046]    (3) The length N of the first permanent magnet  17  in the lengthwise direction is preferably within a range from one to three times the pitch P between the teeth  13 . Setting of the range of the length N of the first permanent magnet  17  in this manner allows the second gap  22  (the gap portion  23 ) and the second permanent magnet  18  to be located appropriately in the magnetic pole while suppressing a reduction of the magnetic flux generated from the first permanent magnet  17  that occurs when the first permanent magnet  17  is too short. 
         [0047]    (4) The clearance H between the second gap  22  and the adjacent second permanent magnet  18  is preferably within a range from 0.3 times to twice the pitch P. By setting the clearance H in this manner, it becomes possible to suppress an increase of the torque ripple while suppressing a reduction of the torque by the permanent-magnet-embedded electrical rotating machine M. 
         [0048]    (5) The two second permanent magnets  18  are arranged in each magnetic pole in such a manner as to hold the one first permanent magnet  17  therebetween and to be in a V shape that spreads from the inner side of the rotor core  16  in the radial direction toward the outer side thereof in the radial direction. Hence, the magnetic flux passing through the q-axis  27  of each magnetic pole is increased, thereby increasing the reluctance torque. 
         [0049]    (6) The first gaps  21  are provide at both magnetic end faces  17   c  of the first permanent magnet  17 , and the second gap  22  is located between the first permanent magnet  17  and the second permanent magnet  18 . Hence, the gap portion  23  (the first gap  21  and the second gap  22 ) reduces the short-circuit flux between the first and second permanent magnets  17  and  18 . 
         [0050]    (7) Setting is made such that the width of the outer-circumferential-side bridge  24  and that of the reinforcement bridge  25  are equal to or greater than twice the thickness of the core plate  161 , the core plate  161  ensures the strength when the core plate is punched. Accordingly, a deformation of the portions where the outer-circumferential-side bridge  24  and the reinforcement bridge  25  are to be formed is suppressed at the time of punching. 
         [0051]    Next, a second embodiment according to the present invention will be described below with reference to  FIGS. 3 and 4 . The same or similar parts as those of the first embodiment will be denoted by the same reference numerals, and the detailed description thereof will be omitted. 
         [0052]    As illustrated in  FIG. 3 , the forming face of the first gap  21  includes an outer-circumferential-side forming face  21   g  extending in an arcuate shape along the outer circumferential surface  16   b  of the rotor core  16 , and a d-axis-side forming face  21   h  that extends from end edge near the inner side of the first permanent magnet  17  in the circumferential direction between both end edges of the outer-circumferential-side forming face  21   g  in parallel with the d-axis  26 . Moreover, the forming face of the first gap  21  includes a forming face  21   c  that runs from the inner end edge of the d-axis-side forming face  21   h  in the radial direction toward the second permanent magnet  18  in parallel with the pole face  17   a,  and an extended face  21   d  that extends from the end edge of the forming face  21   c  in parallel with the d-axis  26 . Furthermore, the forming face of the first gap  21  includes a q-axis-side forming face  21   e  that extends from the end edge of the outer-circumferential-side forming face  21   g  near the second permanent magnet  18  toward the inner side of the rotor core  16  in the radial direction, and an inner-circumferential-side forming face  21   f  that extends from the end edge of the q-axis-side forming face  21   e  toward the magnet end face  17   c  of the first permanent magnet  17 . The forming face of the first gap  21  includes the outer-circumferential-side forming face  21   g,  the d-axis-side forming face  21   h,  the forming face  21   c,  the extended face  21   d , the q-axis-side forming face  21   e,  and the inner-circumferential-side forming face  21   f.    
         [0053]    The forming face of the second gap  22  includes the outer-circumferential-side forming face  22   a  that extends in an arcuate shape along the outer circumferential surface  16   b  of the rotor core  16 , the d-axis-side forming face  22   b  that extends from the end edge of the outer-circumferential-side forming face  22   a  between both end edges near the first permanent magnet  17  in parallel with the q-axis-side forming face  21   e,  and the q-axis-side forming face  22   c  that extends from the end edge of the outer-circumferential-side forming face  22   a  near the second permanent magnet  18  along the q-axis  27 . 
         [0054]    The side face of the reinforcement bridge  25  at the side corresponding to the first-gap- 21  is the q-axis-side forming face  21   e  of the first gap  21 , while the side face of the reinforcement bridge  25  at the side corresponding to the second-gap- 22  is the d-axis-side forming face  22   b  of the second gap  22 . The width of the reinforcement bridge  25 , i.e., the clearance between the q-axis-side forming face  21   e  and the d-axis-side forming face  22   b  is constant across the whole length of the reinforcement bridge  25 . The reinforcement bridge  25  has a width that is preferably equal to or greater than twice the thickness of the core plate  161 . Formed in each imaginary area W (magnetic pole) is the pair of reinforcement bridges  25  at both magnet end faces  17   c  of the first permanent magnet  17 . The pair of reinforcement bridges  25  is disposed in a reversed V shape that has a pitch therebetween spreading from the side corresponding to the outer-circumferential-surface- 16   b  of the rotor core  16  toward the inner side thereof in the radial direction. 
         [0055]    Formed between the outer circumferential surface  16   b  of the rotor core  16  and the outer-circumferential-side forming faces  21   g  and  22   a  of the first and second gaps  21  and  22  is the outer-circumferential-side bridge  24  that extends at a constant width in the circumferential direction of the rotor core  16 . The outer-circumferential-side bridge  24  has a width that is preferably equal to or greater than twice the thickness of the core plate  161 . 
         [0056]    The first gap  21  extends outwardly of the pole face  17   a  of the first permanent magnet  17  in the radial direction, and toward the second permanent magnet  18  over the magnet end face  17   c.  When the thickness of the first permanent magnet  17  along the d-axis  26  is T, and the shortest distance from the magnet end face  17   c  to the q-axis-side forming face  21   e  along a direction orthogonal to the d-axis  26  is V, the first gap  21  is formed to satisfy 1/3 T&lt;V≦T. 
         [0057]    When the shortest distance V becomes smaller than 1/3 T, the pole face  17   a  of the first permanent magnet  17  and the reinforcement bridge  25  becomes close to each other, the magnetic flux path from the pole face  17   a  and passing through the reinforcement bridge  25  becomes short, and thus it is undesirable since the magnetic resistance at the magnetic flux path becomes small. Moreover, it is undesirable since the open width of the first gap  21  becomes narrow, and the short-circuit magnetic flux from the magnet end face  17   c  to the reinforcement bridge  25  increases. Conversely, when the shortest distance V becomes larger than the thickness T of the first permanent magnet  17 , the first gap  21  becomes too large, and thus it becomes difficult to appropriately dispose the first and second gaps  21  and  22  in the magnetic pole, which is undesirable. 
         [0058]    In the first gap  21 , when a straight line extending through the extended face  21   d  and the magnet end face  17   c  and extending in parallel with the d-axis  26  is an imaginary line E, the first gap  21  includes a base  211  at the side corresponding to the second-permanent-magnet- 18  over the imaginary line E and an extended part  212  extended inwardly of the first permanent magnet  17  in the circumferential direction over the imaginary line E. The base  211  is located at a location closer to the second permanent magnet  18  from the first permanent magnet  17 , and the extended part  212  extends inwardly of the first permanent magnet  17  in the circumferential direction from the base  211 . 
         [0059]    The extended part  212  is formed of a part of the outer-circumferential-side forming face  21   g  inwardly of the first permanent magnet  17  in the circumferential direction over the imaginary line E, the d-axis-side forming face  21   h,  and the forming face  21   c.  The open width of the extended part  212  in the radial direction of the rotor core  16  is narrower than that of the base  211 . Hence, the magnetic flux is not likely to pass through the base  211 , but is likely to pass through the extended part  212  having the narrower open width. Accordingly, in the first gap  21 , the extended part  212  has a smaller magnetic resistance than that of the base  211 . 
         [0060]    In the first gap  21 , the inner-circumferential-side forming face  21   f  corresponds to an inner end located at the innermost location with respect to the radial direction of the rotor core  16  in the radial direction, and the outer-circumferential-side forming face  21   g  corresponds to an outer end located at the outermost location with respect to the radial direction of the rotor core  16  in the radial direction. 
         [0061]    The pole face  17   a  of the first permanent magnet  17  is located inwardly of the outer-circumferential-side forming face  21   g  (radial outward end) of the first gap  21  in the radial direction of the rotor core  16 , and is located at the closer location to the outer circumferential surface of the rotor core  16  than the inner-circumferential-side forming face  21   f  of the first gap  21 . That is, the pole face  17   a  of the first permanent magnet  17  is located between the outer-circumferential-side forming face  21   g  (the radial outward end) of the first gap  21  and the inner-circumferential-side forming face  21   f  thereof in the radial direction of the rotor core  16 . It is assumed that a distance from the outer circumferential surface  16   b  of the rotor core  16  to the pole face  17   a  along the d-axis  26  is the embedded depth F of the first permanent magnet  17 . It is preferable that the embedded width should be 1/10 P&lt;F&lt;2/3 P, where P is the pitch between the teeth  13 . The embedded width F is set within a range that permits the first permanent magnet  17  to be located between the pair of second gaps  22  (the gap portions  23 ). 
         [0062]    Because of the centrifugal force produced by the rotation of the rotor  15 , force toward the outer circumferential surface  16   b  of the rotor core  16  acts on the first permanent magnet  17 , but the reinforcement bridge  25  having the mechanical strength prevents the first permanent magnet  17  from being displaced. 
         [0063]    The magnetic flux produced by the rotating magnetic field produced at the stator  10  and the magnetic flux from the pole face  17   a  of the first permanent magnet  17  are concentrated at a space between the magnet end face  17   c  and the outer circumferential surface  16   b  of the rotor core  16 . Assumed that the amount of current fed to the coil  30  increases, and a magnetic saturation is caused between the first gap  21  and the outer circumferential surface  16   b  of the rotor core  16 . In this case, since the shortest distance V from the first gap  21  is set to be within a predetermined range and the reinforcement bridge  25  is moved apart from the magnet end face  17   c  by a predetermined distance, the magnetic flux path from the pole face  17   a  to the reinforcement bridge  25  is long, and the magnetic resistance increases. Hence, the short-circuit flux flowing from the pole face  17   a  to the reinforcement bridge  25  is reduced. 
         [0064]    According to the above-described second embodiment, in addition to the advantages (2) to (5) and (7) of the first embodiment, the following advantages are achieved. 
         [0065]    (1) The shortest distance V from the magnet end face  17   c  of the first permanent magnet  17  to the q-axis-side forming face  21   e  of the first gap  21  in the direction orthogonal to the d-axis  26  satisfies 1/3 T&lt;V≦T, where T is the thickness of the first permanent magnet  17 . Hence, the gap portion  23  is formed such that the reinforcement bridge  25  is apart from the magnet end face  17   c  by a predetermined distance. Accordingly, the magnetic resistance at the magnetic flux path from the pole face  17   a  to the outer circumferential surface  16   b  of the rotor core  16  or the opposite pole face  17   b  through the reinforcement bridge  25  is increased, and thus the short-circuit magnetic flux passing through the reinforcement bridge  25  is reduced. As a result, the short-circuit magnetic flux passing through the reinforcement bridge  25  is reduced, thereby suppressing a reduction of the torque by the permanent-magnet-embedded rotating electrical machine M without changing the width of the reinforcement bridge  25 , i.e., with the mechanical strength thereof being maintained. 
         [0066]    (2) In each magnetic pole, the pair of reinforcement bridges  25  located at both ends corresponding to the magnet-end-face- 17   c  of the first permanent magnet  17  is arranged in a reversed V shape having the pitch therebetween becoming wider from the side corresponding to the outer-circumferential-surface- 16   b  of the rotor core  16  toward the inner side thereof in the radial direction. Hence, the distance from the magnet end face  17   c  to the q-axis-side forming face  21   e  that is a side face of the reinforcement bridge  25  gradually becomes large from the side corresponding to the outer-circumferential-surface- 16   b  toward the inner side in the radial direction. Accordingly, the magnetic resistance by the first gap  21  becomes larger from the side corresponding to the outer-circumferential-surface- 16   b  toward the inner side in the radial direction, and thus the short-circuit magnetic flux to the reinforcement bridge  25  through the first gap  21  is reduced. 
         [0067]    (3) The first gap  21  is formed to extend from the pole face  17   a  of the first permanent magnet  17  toward the outer circumferential surface  16   b  of the rotor core  16 , and the reinforcement bridge  25  is apart from the magnet end face  17   c  by the predetermined distance. Accordingly, the magnetic flux from the pole face  17   a  flows through the first gap  21  toward the outer-circumferential-surface- 16   b  of the rotor core  16  before flowing through the reinforcement bridge  25 . Accordingly, the magnetic resistance at the magnetic flux path reaching the reinforcement bridge  25  is increased in addition to ensuring the shortest distance V, and the short-circuit magnetic flux through the reinforcement bridge  25  is further reduced. 
         [0068]    (4) The first gap  21  includes the base  211  and the extended part  212 , and the extended part  212  has the open width that is in the radial direction of the rotor core  16  and is smaller than that of the base  211 . Accordingly, the magnetic flux is likely to pass through the extended part  212  in comparison with the base  211 , and the extended part  212  has a smaller magnetic resistance. Hence, in the rotor core  16 , the base  211  and the extended part  212  cause the magnetic resistance to become gradually smaller toward the center of the first permanent magnet  17  in the circumferential direction. In comparison with a case in which no extended part  212  is formed, a change in the magnetic resistance at the rotor core  16  becomes gentle when the rotor  15  rotates, and the torque ripple of the permanent-magnet-embedded rotating electrical machine M is suppressed. 
         [0069]    (5) The pole face  17   a  of the first permanent magnet  17  at the side corresponding to the outer-circumferential-surface- 16   b  is located inwardly of the outer-circumferential-side forming face  21   g  of the first gap  21  at the side corresponding to the outer-circumferential-surface- 16   b  in the radial direction of the rotor core  16 , and is located closer to the outer circumferential surface of the rotor core  16  than the inner-circumferential-side forming face  21   f  of the first gap  21 . By arranging the first permanent magnet  17  in this manner, even if the first permanent magnet  17  is locate near the outer circumferential surface  16   b  of the rotor core  16 , the first permanent magnet  17  is prevented from becoming too close to the outer circumferential surface  16   b,  thereby suppressing an occurrence of the eddy current loss at the surface of the first permanent magnet  17 . Moreover, the first permanent magnet  17  is prevented from becoming too close to the inner circumferential surface of the rotor core  16 , thereby reducing the short-circuit magnetic flux between the first and second permanent magnets  17  and  18 . 
         [0070]    The above-described embodiments may be modified as follows. 
         [0071]    As illustrated in  FIGS. 5 and 6 , respectively, the second embedding hole  20  formed in the rotor core  16  may be formed in an arcuate shape that extends along the q-axis  27  and is recessed from the outer side of the rotor core  16  in the radial direction toward the inner side thereof in the radial direction, and the second permanent magnet  18  fitted in the second embedding hole  20  may be a piece of permanent magnet having an arcuate cross-sectional shape. 
         [0072]    According to the first and second embodiments, the pair of second embedding holes  20  is formed in each imaginary area 
         [0073]    W of the rotor core  16 , and the second permanent magnet  18  is fitted in each second embedding hole  20 . Instead of such a structure, a successive second embedding hole  20  in a V shape may be formed in the rotor core  16 , and a second permanent magnet  18  in a V shape may be fitted in that second embedding hole  20 . The V-shaped second permanent magnet  18  may be a piece of second permanent magnet  18  formed integrally, or may be a set of second permanent magnets  18  divided into a plurality of pieces. 
         [0074]    Although the second gap  22  is formed in a substantially sector shape in the first embodiment, the shape of the second gap  22  may be changed and modified as needed. 
         [0075]    According to the first and second embodiments, the first permanent magnet  17  and the pair of second permanent magnets  18  are arranged in a manner line-symmetric with the d-axis  26  so that the permanent-magnet-embedded rotor  15  can rotate in both forward and reverse directions. When, however, the permanent-magnet-embedded rotor  15  is configured to rotate only in one direction, it is fine if the first permanent magnet  17  and the two second permanent magnets  18  are arranged in a manner not line-symmetric with the d-axis  26 . 
         [0076]    Although the number of magnetic poles in the first and second embodiments is eight, the number of magnetic poles may be changed. 
         [0077]    According to the second embodiment, the pair of reinforcement bridges  25  is arranged in a reversed V shape to spread the pitch therebetween from the side corresponding to the outer-circumferential-surface- 16   b  of the rotor core  16  toward the inner side thereof in the radial direction. Instead of such a structure, the pair of reinforcement bridges  25  may be arranged in a V shape to reduce the pitch therebetween from the side corresponding to the outer-circumferential-surface- 16   b  of the rotor core  16  toward the inner side thereof in the radial direction. Moreover, the pair of reinforcement bridges  25  may be arranged to have a constant clearance therebetween. 
         [0078]    In the second embodiment, the outer-circumferential-side bridge  24  and the reinforcement bridge  25  may have respective widths equal to or smaller than twice the thickness of the core plate  161 . 
         [0079]    According to the second embodiment, the extended part  212  of the first gap  21  may be formed to gradually become thin toward the d-axis  26  from the base  211 . In this case, the open width of the extended part  212  in the radial direction of the rotor core  16  gradually becomes small toward the d-axis  26  from the base  211 . Hence, the magnetic resistance of the rotor core  16  gradually becomes small toward the d-axis  26  from the base  211 , and thus a change in the magnetic resistance of the rotor core  16  becomes gentle, thereby suppressing a torque ripple.