Patent Publication Number: US-2019181705-A1

Title: Rotor and method for designing rotor

Description:
BACKGROUND 
     The present disclosure relates to a rotor for an inner rotor type rotating electrical machine, including a rotor core and permanent magnets embedded in the rotor core, and to a method for designing the rotor. 
     A rotor described in Japanese Patent Application Publication No. 2006-254629 (JP 2006-254629A) is known as the rotor described above. JP 2006-254629A discloses a rotor in which a pair of permanent magnets that structure one magnetic pole are arranged in a V-shape so that the distance between the pair of permanent magnets increases toward an outer side in a radial direction. In this structure, a reluctance torque generated by magnetic saliency (Ld&lt;Lq) between a q-axis inductance (Lq) and a d-axis inductance (Ld) can be used in addition to a magnet torque generated by flux linkage (coil flux linkage) due to the permanent magnets. JP 2006-254629 A describes a technology for setting an open angle between the pair of permanent magnets so that the harmonic content in a magnetic flux waveform is a low value in order to reduce harmonic components of iron loss. 
     When the rotor embedded with the permanent magnets rotates, a counter-electromotive voltage (induced voltage) is generated on a coil of a stator due to the flux linkage from the permanent magnets. The counter-electromotive voltage increases as the rotation speed of the rotor increases. It is necessary that the peaks of the counter-electromotive voltage in a non-energized state do not exceed a withstand voltage of an element provided in a power supply-side device (such as an inverter device). The fundamental component of the counter-electromotive voltage has a relationship with the magnet torque, and it is therefore desirable that the peaks of the counter-electromotive voltage be reduced by reducing harmonic components of the counter-electromotive voltage. In this respect, the counter-electromotive voltage corresponds to a time derivative of the flux linkage, and therefore the harmonic components of the counter-electromotive voltage can be reduced by reducing the harmonic content in the magnetic flux waveform through the use of the technology described in JP 2006-254629 A. In the technology described in JP 2006-254629 A, however, the output torque of the rotating electrical machine is not appropriately taken into consideration when the open angle between the pair of permanent magnets is derived. Thus, the output torque of the rotating electrical machine may decrease. 
     SUMMARY 
     Therefore, there is a demand to attain a rotor in Which the peaks of a counter-electromotive voltage that may be generated on a stator coil can be reduced while increasing a torque of a rotating electrical machine and a method for designing the rotor. 
     In view of the above, a rotor for an inner rotor type rotating electrical machine, including a rotor core and permanent magnets embedded in the rotor core, has the following features in its structure. Magnetic poles are each formed by a pair of the permanent magnets arranged side by side in a circumferential direction. Of the pair of the permanent magnets that form one of the magnetic poles, the permanent magnet arranged on a first circumferential side that is one side in the circumferential direction is defined as a first permanent magnet, and the permanent magnet arranged on a second circumferential side that is the other side in the circumferential direction is defined as a second permanent magnet. A first magnetic pole surface that is a magnetic pole surface of the first permanent magnet that is oriented toward an outer side in a radial direction is arranged so that a portion of the first magnetic pole surface that is closer to the first circumferential side is located further outward in the radial direction. A second magnetic pole surface that is a magnetic pole surface of the second permanent magnet that is oriented toward the outer side in the radial direction is arranged so that a portion of the second magnetic pole surface that is closer to the second circumferential side is located further outward in the radial direction. The rotor core includes a first hole formed on the outer side in the radial direction with respect to the first magnetic pole surface at a position where the first hole overlaps, as viewed in the radial direction, a first end region including an end of the first magnetic pole surface on the first circumferential side, and a second hole formed on the outer side in the radial direction with respect to the second magnetic pole surface at a position where the second hole overlaps, as viewed in the radial direction, a second end region including an end of the second magnetic pole surface on the second circumferential side. 
     According to the features in the structure described above, the first hole and the second hole limit ranges in which coil flux linkage occurs on the first magnetic pole surface and the second magnetic pole surface while improving a reluctance torque (improving the usage of the reluctance torque) by appropriately setting ranges in the circumferential direction in which the first magnetic pole surface and the second magnetic pole surface are arranged. Therefore, a harmonic component of the counter-electromotive voltage generated on the stator coil can be reduced by adjusting a harmonic component of the coil flux linkage due to rotation of the rotor. Thus, the peaks of the counter-electromotive voltage that may be generated on the stator coil can be reduced while increasing the torque of the rotating electrical machine. 
     In view of the above, a method for designing a rotor for an inner rotor type rotating electrical machine, including a rotor core and permanent magnets embedded in the rotor core, has the following features in its structure. Magnetic poles are each formed by a pair of the permanent magnets arranged side by side in a circumferential direction. Of the pair of the permanent magnets that form one of the magnetic poles, the permanent magnet arranged on a first circumferential side that is one side in the circumferential direction is defined as a first permanent magnet, and the permanent magnet arranged on a second circumferential side that is the other side in the circumferential direction is defined as a second permanent magnet. The method includes arranging first magnetic pole surface that is a magnetic pole surface of the first permanent magnet that is oriented toward an outer side in a radial direction so that a portion of the first magnetic pole surface that is closer to the first circumferential side is located further outward in the radial direction, and arranging a second magnetic pole surface that is a magnetic pole surface of the second permanent magnet that is oriented toward the outer side in the radial direction so that a portion of the second magnetic pole surface that is closer to the second circumferential side is located further outward in the radial direction. The rotor core includes a first hole formed on the outer side in the radial direction with respect to the first magnetic pole surface at a position where the first hole overlaps, as viewed in the radial direction, a first end region including an end of the first magnetic pole surface on the first circumferential side, and a second hole formed on the outer side in the radial direction with respect to the second magnetic pole surface at a position where the second hole overlaps, as viewed in the radial direction, a second end region including an end of the second magnetic pole surface on the second circumferential side. The first hole and the second hole are formed so that harmonic components of a plurality of target orders on a fundamental component of a counter-electromotive voltage generated by rotation of the rotor on a coil of a stator arranged so as to face an outer peripheral surface of the rotor core are reduced as compared to a case where the first hole and the second hole are not provided. 
     According to the features in the structure described above, the first hole and the second hole limit the ranges in which the coil flux linkage occurs on the first magnetic pole surface and the second magnetic pole surface while improving the reluctance torque (improving the usage of the reluctance torque) by appropriately setting the ranges in the circumferential direction in which the first magnetic pole surface and the second magnetic pole surface are arranged. Therefore, the harmonic component of the counter-electromotive voltage generated on the stator coil can be reduced by adjusting the harmonic component of the coil flux linkage due to the rotation of the rotor. Thus, it is possible to attain a rotor in which the peaks of the counter-electromotive voltage that may be generated on the stator coil are reduced while increasing the torque of the rotating electrical machine. This structure can reduce the harmonic components of the plurality of target orders to be superposed on the fundamental component of the counter-electromotive voltage generated on the stator coil. Thus, it is possible to attain a rotor in which the peaks of the counter-electromotive voltage that may be generated on the stator coil are reduced effectively. 
     Further features and advantages of the rotor and the method for designing the rotor will become more apparent from the following description of an embodiment with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view orthogonal to an axial direction of a rotating electrical machine according to an embodiment. 
         FIG. 2  is an enlarged view of a part of  FIG. 1 . 
         FIG. 3  is an enlarged view of a part of  FIG. 2 . 
         FIG. 4  is a diagram illustrating changes in a salient pole difference and a salient pole ratio relative to a first angle. 
         FIG. 5  is a diagram illustrating a change in a fundamental component of a flux linkage relative to a second angle. 
         FIG. 6  is a diagram illustrating a change in an 11th order component of the flux linkage relative to the second angle. 
         FIG. 7  is a diagram illustrating a change in a 13th order component of the flux linkage relative to the second angle. 
         FIG. 8  is a diagram illustrating a change in a counter-electromotive voltage relative to a rotor position. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     An embodiment of a rotor and a method for designing the rotor is described with reference to the drawings. In the following description, an “axial direction”, a “radial direction R”, and a “circumferential direction C” are defined with respect to a rotation axis X of a rotor core  11  (see  FIG. 1 ). The rotation axis X is an imaginary axis, and the rotor core  11  rotates about the rotation axis X. One side in the circumferential direction C is defined as a “first circumferential side C 1 ”, and the other side in the circumferential direction C (side opposite to the first circumferential side C 1 ) is defined as a “second circumferential side C 2 ”. Terms related to dimensions, arrangement directions, arrangement positions, and the like are herein used as concepts that encompass a condition with a difference caused by a deviation (deviation that is permissible in manufacturing). 
     As illustrated in  FIG. 1 , a rotor  10  is a rotor for an inner rotor type rotating electrical machine  1 . 
     That is, the rotor  10  is arranged on an inner side in the radial direction R with respect to a stator  90  while being rotatable relative to the stator  90 . The rotating electrical machine  1  is a revolving field type rotating electrical machine, and coils  94  (see  FIG. 2 ) are would around a stator core  91  that is a core of the stator  90 . In this embodiment, the rotating electrical machine  1  is a rotating electrical machine to be driven by three-phase alternating currents, and the coils  94  include three-phase coils that are a U-phase coil, a V-phase coil, and a W-phase coil. The rotor  10  rotates as a field system by a magnetic field generated from the stator  90 . The “rotating electrical machine” is herein used as a concept that encompasses any of a motor (electric motor), a generator (power generator), and a motor/generator that functions as both the motor and the generator as necessary. 
     As illustrated in  FIG. 2 , a plurality of slots  93  extending in the axial direction and in the radial direction R are arranged in the stator core  91  while being distributed in the circumferential direction C. Each slot  93  has openings on both sides in the axial direction and on the inner side in the radial direction R. In this embodiment, each slot  93  is formed so that the width in the circumferential direction C is uniform along the radial direction R. The plurality of slots  93  are arranged at regular intervals along the circumferential direction C. In this embodiment, U-phase slots  93 , V-phase slots  93 , and W-phase slots  93  are arranged so as to appear repetitively along the circumferential direction C. In this example, the number of slots for each pole and each phase is “2”, and the slots  93  for each phase are arranged in the stator core  91  so that every two slots  93  appear repetitively along the circumferential direction C. The number of magnetic poles for each phase is “16” (the number of magnetic pole pairs is “8”), and a total of 96 (=2×16×3) slots  93  are arranged in the stator core  91 . That is, in this example, as illustrated in  FIG. 2 , six slots  93  correspond to one magnetic pole P, and  12  slots  93  correspond to one magnetic pole pair. That is, in this embodiment, the number of slots M for one magnetic pole is “6”. A slot insertion portion  94   a  of the coil  94  is inserted into each slot  93 . Thus, the coil  94  of the stator  90  is arranged so as to thee an outer peripheral surface  11   a  of the rotor core  11 . 
     As illustrated in  FIG. 1  and  FIG. 2 , the rotor  10  includes the rotor core  11  and permanent magnets  30  embedded in the rotor core  11 . That is, the rotor  10  is a rotor to be used for a rotating electrical machine having an embedded magnet structure (in this embodiment, a synchronous electric motor). In the rotor core  11 , magnet insertion holes  20  (see  FIG. 3 ) in which the permanent magnets  30  are inserted are provided as many as the permanent magnets  30 . The magnet insertion hole  20  is formed in the rotor core  11  so as to extend in the axial direction. In this embodiment, the magnet insertion hole  20  is formed so as to extend in parallel to the axial direction. The sectional shape of the magnet insertion hole  20  that is orthogonal to the axial direction is uniform along the axial direction. In this embodiment, the magnet insertion hole  20  is formed so as to pass through the rotor core  11  in the axial direction. The axial length of the permanent magnet  30  is a length based on the axial length of the magnet insertion hole  20 . In this embodiment, the axial length of the permanent magnet  30  is equal to the axial length of the magnet insertion hole  20 . For example, the rotor core  11  is formed by stacking a plurality of annular sheet-shaped magnetic sheets (for example, electromagnetic steel sheets) in the axial direction, or is formed by including, as a main component, a green compact obtained through pressure molding of magnetic powder that is powder of a magnetic material. 
     As illustrated in  FIG. 1 , the rotor core  11  is formed into a cylindrical shape coaxial with the rotation axis X. The outer peripheral surface  11   a  of the rotor core  11  (see  FIG. 3 ) is formed into a cylindrical surface shape coaxial with the rotation axis X. In the rotor core  11 , a plurality of magnetic poles P formed by the permanent magnets  30  and extending in the axial direction L are formed while being distributed in the circumferential direction C. Two magnetic poles P adjacent to each other in the circumferential direction C have opposite polarities. In this embodiment,  16  magnetic poles P are formed at regular intervals along the circumferential direction C. As illustrated in  FIG. 2 , each magnetic pole P is formed by a pair of permanent magnets  30  arranged side by side in the circumferential direction C. Of the pair of permanent magnets  30  that form one magnetic pole P, the permanent magnet  30  arranged on the first circumferential side C 1  is defined as a first permanent magnet  31 , and the permanent magnet  30  arranged on the second circumferential side C 2  is defined as a second permanent magnet  32 . The magnet insertion hole  20  in which the first permanent magnet  31  is inserted is defined as a first magnet insertion hole  21 , and the magnet insertion hole  20  in which the second permanent magnet  32  is inserted is defined as a second magnet insertion hole  22  (see  FIG. 3 ). That is, the first permanent magnet  31  is inserted into the first magnet insertion hole  21  formed in the rotor core  11  so as to extend in the axial direction, and the second permanent magnet  32  is inserted into the second magnet insertion hole  22  formed in the rotor core  11  so as to extend in the axial direction. 
     As illustrated in  FIG. 3 , the first permanent magnet  31  and the second permanent magnet  32  that structure one magnetic pole P are arranged plane-symmetrically across a reference plane Q. Along with this arrangement, the first magnet insertion hole  21  and the second magnet insertion hole  22  in which the pair of permanent magnets  30  that structure one magnetic pole P are inserted are formed into shapes that are plane-symmetrical across the reference plane Q. That is, the sectional shape of the first magnet insertion hole  21  that is orthogonal to the axial direction and the sectional shape of the second magnet insertion hole  22  that is orthogonal to the axial direction are shapes that are symmetrical across an axis of symmetry that is defined by a straight line along the reference plane Q. The reference plane Q is a plane passing through the rotation axis X (see  FIG. 1 ) and extending in the radial direction R at a center between the pair of permanent magnets  30  that form one magnetic pole P. In other words, the reference plane Q is a plane passing through the rotation axis X and extending in the radial direction R at a central portion of the magnetic pole P in the circumferential direction C. The pair of permanent magnets  30  that structure one magnetic pole P are arranged so that magnetic pole surfaces  40  having the same polarity (N pole or S pole) are oriented toward an outer side in the radial direction R. The magnetic pole surface  40  is an outer surface orthogonal to a magnetizing direction (polarizing direction), and is a surface where a magnetic flux of the permanent magnet  30  flows in and out. 
     As illustrated in  FIG. 3 , a first magnetic pole surface  41  that is the magnetic pole surface  40  of the first permanent magnet  31  that is oriented toward the outer side in the radial direction R is arranged so that a portion of the first magnetic pole surface  41  that is closer to the first circumferential side C 1  is located further outward in the radial direction R. A second magnetic pole surface  42  that is the magnetic pole surface  40  of the second permanent magnet  32  that is oriented toward the outer side in the radial direction R is arranged so that a portion of the second magnetic pole surface  42  that is closer to the second circumferential side C 2  is located further outward in the radial direction R. In this embodiment, as illustrated in  FIG. 3 , the pair of permanent magnets  30  that structure one magnetic pole P are arranged in a V-shape so that the distance between the pair of permanent magnets  30  increases toward the outer side in the radial direction R in a cross section orthogonal to the axial direction. In this embodiment, the sectional shape of each permanent magnet  30  that is orthogonal to the axial direction is a rectangular shape, and the magnetizing direction is parallel to the short side of the rectangle. Thus, a surface that forms the long side of the rectangle in the outer peripheral surface of the permanent magnet  30  (surface that forms the outer edge of the cross section orthogonal to the axial direction) structures the magnetic pole surface  40 . That is, in this embodiment, each of the first magnetic pole surface  41  and the second magnetic pole surface  42  is formed into a planar shape. 
     As illustrated in  FIG. 3 , in this embodiment, the magnet insertion hole  20  has magnetic resistance portions  23  that function as a magnetic resistance (flux barrier) to the magnetic flux flowing through the rotor core  11 . The magnetic resistance portion  23  reduces a leakage flux of the permanent magnet  30 . In this embodiment, assuming that a direction orthogonal to both the axial direction and the magnetizing direction (direction along the magnetic pole surface  40  in the cross section orthogonal to the axial direction) is a target direction, the magnetic resistance portions  23  are formed both at a part of the magnet insertion hole  20  on an outer side in the target direction and at a part of the magnet insertion hole  20  on an inner side in the target direction. The outer side in the target direction is a side in the target direction that is located away from the central portion of the magnetic pole P in the circumferential direction C. The inner side in the target direction is a side in the target direction that is located closer to the central portion of the magnetic pole P in the circumferential direction C. The magnetic resistance portion  23  formed at the part of the magnet insertion hole  20  on the outer side in the target direction is hereinafter referred to as an outer magnetic resistance portion  23   a.  The magnetic resistance portion  23  formed at the part of the magnet insertion hole  20  on the inner side in the target direction is hereinafter referred to as an inner magnetic resistance portion  23   b.  That is, in this embodiment, the outer magnetic resistance portion  23   a  is formed at a part of the first magnet insertion hole  21  on the first circumferential side C 1  with respect to a region where the first permanent magnet  31  is arranged, and the inner magnetic resistance portion  23   b  is formed at a part of the first magnet insertion hole  21  on the second circumferential side C 2  with respect to the region where the first permanent magnet  31  is arranged. Further, the outer magnetic resistance portion  23   a  is formed at a part of the second magnet insertion hole  22  on the second circumferential side C 2  with respect to a region where the second permanent magnet  32  is arranged, and the inner magnetic resistance portion  23   b  is formed at a part of the second magnet insertion hole  22  on the first circumferential side C 1  with respect to the region where the second permanent magnet  32  is arranged. 
     As illustrated in  FIG. 3 , the rotor core  11  includes a first hole portion  51  (first hole) and a second hole portion  52  (second hole). Each of the first hole portion  51  and the second hole portion  52  also functions as a magnetic resistance. Each of the first hole portion  51  and the second hole portion  52  is formed so as to extend in the axial direction. In this embodiment, each of the first hole portion  51  and the second hole portion  52  is formed so as to extend in parallel to the axial direction. The sectional shape of the first hole portion  51  that is orthogonal to the axial direction is uniform along the axial direction. The sectional shape of the second hole portion  52  that is orthogonal to the axial direction is uniform along the axial direction. In this embodiment, the first hole portion  51  and the second hole portion  52  are formed into shapes that are plane-symmetrical across the reference plane Q. That is, the sectional shape of the first hole portion  51  that is orthogonal to the axial direction and the sectional shape of the second hole portion  52  that is orthogonal to the axial direction are shapes that are symmetrical across the axis of symmetry that is defined by the straight line along the reference plane Q. In this embodiment, each of the first hole portion  51  and the second hole portion  52  is formed so as to pass through the rotor core  11  in the axial direction. 
     The first hole portion  51  is formed on the outer side in the radial direction R with respect to the first magnetic pole surface  41  at a position where the first hole portion  51  overlaps, as viewed in the radial direction R, a first end region A 1  including the end of the first magnetic pole surface  41  on the first circumferential side C 1 . As illustrated in  FIG. 3 , assuming that a position where the first magnetic pole surface  41  overlaps the end of the first hole portion  51  on the second circumferential side C 2  as viewed in the radial direction R is a first boundary portion  41   a,  the first end region A 1  is a part of the first magnetic pole surface  41  on the first circumferential side C 1  with respect to the first boundary portion  41   a.  The second hole portion  52  is formed on the outer side in the radial direction R with respect to the second magnetic pole surface  42  at a position where the second hole portion  52  overlaps, as viewed in the radial direction R, a second end region A 2  including the end of the second magnetic pole surface  42  on the second circumferential side C 2 . As illustrated in  FIG. 3 , assuming that a position where the second magnetic pole surface  42  overlaps the end of the second hole portion  52  on the first circumferential side C 1  as viewed in the radial direction R is a second boundary portion  42   a,  the second end region A 2  is a part of the second magnetic pole surface  42  on the second circumferential side C 2  with respect to the second boundary portion  42   a.  By providing the first hole portion  51  and the second hole portion  52  described above, the first hole portion  51  and the second hole portion  52  limit ranges in which coil flux linkage occurs on the first magnetic pole surface  41  and the second magnetic pole surface  42  while improving a reluctance torque (improving the usage of the reluctance torque) by appropriately setting ranges in the circumferential direction C in which the first magnetic pole surface  41  and the second magnetic pole surface  42  are arranged. Therefore, a harmonic component of a counter-electromotive voltage generated on the coil  94  can be reduced by adjusting a harmonic component of the coil flux linkage due to rotation of the rotor  10 . Thus, the peaks of the counter-electromotive voltage that may be generated on the coil  94  can be reduced while increasing the torque of the rotating electrical machine  1 . 
     The first hole portion  51  and the second hole portion  52  are formed so that harmonic components of the plurality of target orders on a fundamental component of the counter-electromotive voltage generated by the rotation of the rotor  10  are reduced as compared to a case where the first hole portion  51  and the second hole portion  52  are not provided. That is, the shapes of the first hole portion  51  and the second hole portion  52  are designed for that purpose. Focusing on, for example, harmonic components of specific orders in the coil flux linkage that is linked to the coil  94  as illustrated in  FIG. 6  and  FIG. 7 , the magnetic flux amount of the harmonic component of each order periodically increases and decreases in accordance with a second angle θ 2  that is an angle in the circumferential direction C in a region of a combination of a part of the first magnetic pole surface  41  that does not overlap the first hole portion  51  and a part of the second magnetic pole surface  42  that does not overlap the second hole portion  52 . Therefore, in this embodiment, the first hole portion  51  and the second hole portion  52  are formed so as to deviate from the peaks of the periodic increase and decrease in accordance with the second angle θ 2  in the harmonic components of the plurality of target orders among the harmonic components of the coil flux linkage. Thus, the harmonic components of the plurality of target orders are reduced as compared to the case where the first hole portion  51  and the second hole portion  52  are not provided. This structure also reduces harmonic components to be superposed on the fundamental component of the counter-electromotive voltage generated on the coil  94 . Thus, for example, the peaks of the counter-electromotive voltage generated on the coil  94  can be reduced as indicated by a continuous line (example) in  FIG. 8  as compared to a case where a large amount of the harmonic component is superposed as indicated by a dashed line (comparative example) in  FIG. 8 . 
     In this embodiment, when M represents the number of slots for one magnetic pole in the stator  90 , the plurality of target orders that are reduction targets include at least a (2M−1)th order and a (2M+1)th order. This structure can reduce harmonic components of orders that particularly have significant influence among the harmonic components to be superposed on the fundamental component of the counter-electromotive voltage. That is, firstly, the change in the flux linkage (magnetic flux waveform) can approximate a rectangular wave, and therefore components of even number orders do not basically exist in the flux linkage. When the rotating electrical machine  1  is driven by three-phase alternating currents and when the phase coils of the respective phases are connected by Y-connection (star connection), 3n-th order (n is a natural number) components do not appear in a line-to-line voltage while being canceled. Further, higher-order harmonic components of a (2M+3)th order and higher do not significantly influence the counter-electromotive voltage. The magnetic resistance is higher at the openings of the slots  93  than teeth  92 . Therefore, when M represents the number of slots for each magnetic pole P, the magnetic resistance increases at 2M points in one period of an electrical angle. Based on the facts described above, the harmonic components of the (2M−1)th order and the (2M+1)th order particularly have significant influence among the harmonic components of the flux linkage on the coil  94  and furthermore the harmonic components to be superposed on the fundamental component of the counter-electromotive voltage. By setting the plurality of target orders that are reduction targets as described above, it is possible to effectively reduce the peaks of the counter-electromotive voltage that may be generated on the coil  94 . 
     In this embodiment, the first hole portion  51  is formed integrally with the first magnet insertion hole  21  so as to communicate with the first magnet insertion hole  21 . Further, the second hole portion  52  is formed integrally with the second magnet insertion hole  22  so as to communicate with the second magnet insertion hole  22 . Specifically, a part of the first hole portion  51  on the first circumferential side C 1  communicates with a part of the outer magnetic resistance portion  23   a  of the first magnet insertion hole  21  on the outer side in the radial direction R, and a part of the first hole portion  51  on the inner side in the radial direction R communicates with a part of the first magnet insertion hole  21  on the first circumferential side C 1  in the region where the first permanent magnet  31  is arranged. Further, a part of the second hole portion  52  on the second circumferential side C 2  communicates with a part of the outer magnetic resistance portion  23   a  of the second magnet insertion hole  22  on the outer side in the radial direction R, and a part of the second hole portion  52  on the inner side in the radial direction R communicates with a part of the second magnet insertion hole  22  on the second circumferential side C 2  in the region where the second permanent magnet  32  is arranged. In this embodiment, the end of the first hole portion  51  on the second circumferential side C 2  does not communicate with the first magnet insertion hole  21  in the radial direction R, and is formed away from the first magnet insertion hole  21  toward the outer side in the radial direction R. In this embodiment, the end of the second hole portion  52  on the first circumferential side C 1  does not communicate with the second magnet insertion hole  22  in the radial direction R, and is formed away from the second magnet insertion hole  22  toward the outer side in the radial direction R. In this embodiment, each of the first hole portion  51  and the second hole portion  52  is a hollow, but may have a structure filled with a non-magnetic substance. 
     As illustrated in  FIG. 3 , in this embodiment, each of the inner surface of the first hole portion  51  on the outer side in the radial direction R and the inner surface of the second hole portion  52  on the outer side in the radial direction R has a part parallel to the outer peripheral surface  11   a  of the rotor core  11 . Specifically, a part other than the end on the second circumferential side C 2  in the inner surface of the first hole portion  51  On the outer side in the radial direction R is formed in parallel to the outer peripheral surface  11   a  of the rotor core  11 , and a part other than the end on the first circumferential side C  1  in the inner surface of the second hole portion  52  on the outer side in the radial direction R is formed in parallel to the outer peripheral surface  11   a  of the rotor core  11 . Thus, the shape of a bridge portion (first bridge portion  61 ) formed between the first hole portion  51  and the outer peripheral surface  11   a  of the rotor core  11  in the radial direction R and the shape of a bridge portion (second bridge portion  62 ) formed between the second hole portion  52  and the outer peripheral surface  11   a  of the rotor core  11  in the radial direction R can be set to a shape that is narrow in the radial direction R and is long in the circumferential direction C (elongated shape extending in the circumferential direction C as viewed in the axial direction), thereby facilitating the occurrence of magnetic saturation in those bridge portions. As a result, the leakage flux of the permanent magnet  30  can further be reduced. 
     In this embodiment, the inner surface of the outer magnetic resistance portion  23   a  on the outer side in the radial direction R also has a part parallel to the outer peripheral surface  11   a  of the rotor core  11 . Specifically, in the first magnet insertion hole  21 , a part other than the end on the first circumferential side C 1  in the inner surface of the outer magnetic resistance portion  23   a  on the outer side in the radial direction t is formed in parallel to the outer peripheral surface  11   a  of the rotor core  11 . In the second magnet insertion hole  22 , a part other than the end on the second circumferential side C 2  in the inner surface of the outer magnetic resistance portion  23   a  on the outer side in the radial direction R is formed in parallel to the outer peripheral surface  11   a  of the rotor core  11 . 
     As illustrated in  FIG. 3 , an angle formed in the circumferential direction C about the rotation axis X (see  FIG. 1 ) between the end of the first magnetic pole surface  41  on the first circumferential side C 1  and the end of the second magnetic pole surface  42  on the second circumferential side C 2  is defined as a first angle  91 . Further, an angle formed in the circumferential direction C about the rotation axis X between the end of the first magnetic pole surface  41  on the first circumferential side C 1  at the part that does not overlap the first hole portion  51  as viewed in the radial direction R (first boundary portion  41   a ) and the end of the second magnetic pole surface  42  on the second circumferential side C 2  at the part that does not overlap the second hole portion  52  as viewed in the radial direction R (second boundary portion  42   a ) is defined as the second angle  82 . Designing is performed for the formation of the first hole portion  51  and the second hole portion  52  so that the second angle θ 2  corresponds to an electrical angle at which the harmonic components of the plurality of target orders on the fundamental component of the counter-electromotive voltage generated by the rotation of the rotor  10  are reduced together. Regarding the structure according to this embodiment, the inventors have found that the peaks of the counter-electromotive voltage that may be generated on the coil  94  can be reduced while increasing the torque of the rotating electrical machine  1  by setting the first angle θ 1  to an angle within a range of 128°±10° in terms of the electrical angle and setting the second angle θ 2  to an angle within a range of 104°±10° in terms of the electrical angle. 
     Specifically, by setting the first angle θ 1  to the angle within the range of 128°±10° in terms of the electrical angle, a large difference is secured between a q-axis inductance and a d-axis inductance. Thus, the reluctance torque can be improved (the usage of the reluctance torque can be improved).  FIG. 4  illustrates results of simulation of changes in a salient pole difference and a salient pole ratio relative to the first angle θ 1  for the rotor  10  according to this embodiment described with reference to  FIG. 1  to  FIG. 3 . The salient pole difference is the difference (Lq−Ld) between the q-axis inductance (Lq) and the d-axis inductance (Ld). The salient pole ratio is the ratio (Lq/Ld) between the q-axis inductance (Lq) and the d-axis inductance (Ld).  FIG. 4  demonstrates that the salient pole difference is maximum when the first angle θ 1  is 128° in terms of the electrical angle. The reluctance torque is proportional to the salient pole difference. Thus, the reluctance torque is maximum when the first angle θ 1  is 128° in terms of the electrical angle. Accordingly, the first angle θ 1  is set with respect to the angle at which the salient pole difference is maximum. It is further appropriate that the first angle θ 1  be set to an angle within a range of 128°±5° in terms of the electrical angle. 
     By setting the second angle θ 2  to the angle within the range of 104°±10° in terms of the electrical angle, an 11th order component and a 13th order component of the flux linkage (coil flux linkage) are both reduced, and therefore the peaks of the counter-electromotive voltage can be reduced. Further, the leakage fluxes of the first permanent magnet  31  and the second permanent magnet  32  are reduced by the first hole portion  51  and the second hole portion  52 , respectively, and therefore a magnet torque can be improved (the usage of the magnet torque can be improved).  FIG. 5  to  FIG. 7  illustrate results of simulation for the rotor  10  according to this embodiment described with reference to  FIG. 1  to  FIG. 3 .  FIG. 5  illustrates a change in a fundamental component of the flux linkage relative to the second angle θ 2 .  FIG. 6  illustrates a change in the 11th order component of the flux linkage relative to the second angle θ 2 .  FIG. 7  illustrates a change in the 13th order component of the flux linkage relative to the second angle θ 2 . The first angle θ 1  is set to 128° in terms of the electrical angle.  FIG. 5  to  FIG. 7  demonstrate that the amplitude of the fundamental component of the flux linkage is maximum or close to the maximum and the amplitudes of both the 11th order component and the 13th order component of the flux linkage are minimum or close to the minimum when the second angle θ 2  is 104° in terms of the electrical angle (angle indicated by dashed lines in the figures). That is, when the second angle θ 2  is 104° in terms of the electrical angle, the amplitude of the fundamental component of the flux linkage that contributes to the magnet torque is increased and the amplitudes of the 11th order component and the 13th order component of the flux linkage that cause an increase in the peaks of the counter-electromotive voltage are reduced to lower levels. Accordingly, the second angle θ 2  is set with respect to the angle at which the amplitudes of the 11th order component and the 13th order component of the flux linkage are minimum. The range of the second angle θ 2  from 94° to 114° in terms of the electrical angle is a range that does not include an angle at which the amplitude of the 11th order component of the flux linkage is maximum and an angle at which the amplitude of the 13th order component of the flux linkage is maximum. From the viewpoint of reducing the peaks of the counter-electromotive voltage, it is further appropriate that the second angle θ 2  be set to an angle within a range of 104°±5° in terms of the electrical angle. 
       FIG. 8  illustrates results of simulation of a change in the counter-electromotive voltage relative to a rotor position in the case where the first angle θ 1  is set to 128° in terms of the electrical angle and the second angle θ 2  is set to 104° in terms of the electrical angle. The counter-electromotive voltage indicated by the dashed line as the comparative example is a result of simulation in the case where the first hole portion  51  and the second hole portion  52  are not provided. The counter-electromotive voltage corresponds to a time derivative of the flux linkage, and therefore the harmonic component of the flux linkage is included in the counter-electromotive voltage as a harmonic component of the same order.  FIG. 8  demonstrates that the harmonic components to be superposed on the fundamental component of the counter-electromotive voltage are reduced and the waveform of the counter-electromotive voltage approximates a sinusoidal wave when the first hole portion  51  and the second hole portion  52  are provided and when the first angle θ 1  is set to 128° in terms of the electrical angle and the second angle θ 2  is set to 104° in terms of the electrical angle. 
     The reason why the peaks of the counter-electromotive voltage are reduced by reducing the 11th order component and the 13th order component of the flux linkage is as follows. Firstly the change in the flux linkage (magnetic flux waveform) can approximate a rectangular wave, and therefore components of even number orders do not basically exist in the flux linkage. Further, the rotating electrical machine  1  according to this embodiment is a rotating electrical machine to be driven by three-phase alternating currents. Therefore, when the phase coils of the respective phases are connected by Y-connection (star connection), 3n-th order (n is a natural number) components do not appear in a line-to-line voltage while being canceled. Further, higher-order components of a 17th order and higher are generated, but do not significantly influence the counter-electromotive voltage. Therefore, 5th, 7th, 11th, and 13th order components may be included in the flux linkage as major components. As described above, in this embodiment, the number of slots M for one magnetic pole is “6”, and 12 slots  93  correspond to one magnetic pole pair. The magnetic resistance is higher at the openings of the slots  93  than the teeth  92 . Therefore, the magnetic resistance increases at 12 points in one period of the electrical angle. As a result, the components of the 11th and 13th orders that are (12±1)th orders prevail in the rotor  10  according to this embodiment. 
     Other Embodiments 
     Other embodiments of the rotor are described. The structures disclosed in the following embodiments are also applicable in combination with the structures disclosed in the other embodiments without causing any contradiction. 
     (1) In the embodiment described above, description is given of the exemplary structure in which the first hole portion  51  and the second hole portion  52  are formed so that the harmonic components of the plurality of target orders in the counter-electromotive voltage are reduced. However, the present disclosure is not limited to this structure. It is also appropriate to employ a structure in which the first hole portion  51  and the second hole portion  52  are formed so that a harmonic component of one target order is reduced. This structure can also reduce the peaks of the counter-electromotive voltage that may be generated on the coil  94 . 
     (2) in the embodiment described above, description is given of the exemplary structure in which the plurality of target orders include at least the (2M−1)th order and the (2M+1)th order. However, the present disclosure is not limited to this structure. It is also appropriate that harmonic components of orders other than the (2M−1)th order and the (2M+1)th order be set as target orders and the first hole portion  51  and the second hole portion  52  be formed so that the harmonic components of the target orders are reduced. This structure can also reduce the peaks of the counter-electromotive voltage that may be generated on the coil  94 . 
     (3) in the embodiment described above, description is given of the exemplary structure in which the first hole portion  51  is formed integrally with the first magnet insertion hole  21  so as to communicate with the first magnet insertion hole  21  and the second hole portion  52  is formed integrally with the second magnet insertion hole  22  so as to communicate with the second magnet insertion hole  22 . However, the present disclosure is not limited to this structure. There may be employed a structure in which one or both of the first hole portion  51  and the second hole portion  52  are formed as holes independent of the magnet insertion holes  20  (the first magnet insertion hole  21  for the first hole portion  51  and the second magnet insertion hole  22  for the second hole portion  52 ). 
     (4) In the embodiment described above, description is given of the exemplary structure in which each of the inner surface of the first hole portion  51  on the outer side in the radial direction R and the inner surface of the second hole portion  52  on the outer side in the radial direction R has the part parallel to the outer peripheral surface  11   a  of the rotor core  11  However, the present disclosure is not limited to this structure. There may be employed a structure in which one or both of the inner surface of the first hole portion  51  on the outer side in the radial direction R and the inner surface of the second hole portion  52  on the outer side in the radial direction R do not have the part parallel to the outer peripheral surface  11   a  of the rotor core  11 . 
     (5) In the embodiment described above, description is given of the exemplary structure in which the number of slots for each pole and each phase is “2” and the number of slots for one magnetic pole is “6”. However, the present disclosure is not limited to this structure. The number of slots for each pole and each phase may be “1” or an integer equal to or larger than “3”, and accordingly the number of slots M for one magnetic pole may be any number that is an integral multiple of the number of phases of alternating currents. 
     (6) In the embodiment described above, description is given of the exemplary structure in which the number of magnetic poles for each phase is “16”. However, the present disclosure is not limited to this structure. There may be employed a structure in which the number of magnetic poles for each phase is a number other than “16”. For example, there may be employed a structure in which the number of magnetic poles for each phase is “8” or “12”. 
     (7) Regarding other structures as well, it should be understood that the embodiment disclosed herein is only illustrative in all respects. Thus, various modifications may be made as appropriate by persons having ordinary skill in the art without departing from the spirit of the disclosure. 
     Summary of Embodiment 
     A summary of the rotor described above is described below. 
     The rotor ( 10 ) is the rotor ( 10 ) for the inner rotor type rotating electrical machine ( 1 ), including the rotor core ( 11 ) and the permanent magnets ( 30 ) embedded in the rotor core ( 11 ). The magnetic poles (P) are each formed by a pair of the permanent magnets ( 30 ) arranged side by side in the circumferential direction (C). Of the pair of the permanent magnets ( 30 ) that form one of the magnetic poles (P), the permanent magnet ( 30 ) arranged on the first circumferential side (C 1 ) that is one side in the circumferential direction (C) is defined as the first permanent magnet ( 31 ), and the permanent magnet ( 30 ) arranged on the second circumferential side (C 2 ) that is the other side in the circumferential direction (C) is defined as the second permanent magnet ( 32 ). The first magnetic pole surface ( 41 ) that is the magnetic pole surface ( 40 ) of the first permanent magnet ( 31 ) that is oriented toward the outer side in the radial direction (R) is arranged so that the portion of the first magnetic pole surface ( 41 ) that is closer to the first circumferential side (C 1 ) is located further outward in the radial direction (R). The second magnetic pole surface ( 42 ) that is the magnetic pole surface ( 40 ) of the second permanent magnet ( 32 ) that is oriented toward the outer side in the radial direction (R) is arranged so that the portion of the second magnetic pole surface ( 42 ) that is closer to the second circumferential side (C 2 ) is located further outward in the radial direction (R). The rotor core ( 11 ) includes the first hole portion ( 51 ) formed on the outer side in the radial direction (R) with respect to the first magnetic pole surface ( 41 ) at the position where the first hole portion ( 51 ) overlaps, as viewed in the radial direction (R), the first end region (A 1 ) including the end of the first magnetic pole surface ( 41 ) on the first circumferential side (C 1 ), and the second hole portion ( 52 ) formed on the outer side in the radial direction (R) with respect to the second magnetic pole surface ( 42 ) at the position where the second hole portion ( 52 ) overlaps, as viewed in the radial direction (R), the second end region (A 2 ) including the end of the second magnetic pole surface ( 42 ) on the second circumferential side (C 2 ). 
     According to the structure described above, the first hole portion ( 51 ) and the second hole portion ( 52 ) limit the ranges in which the coil flux linkage occurs on the first magnetic pole surface ( 41 ) and the second magnetic pole surface ( 42 ) while improving the reluctance torque (improving the usage of the reluctance torque) by appropriately setting the ranges in the circumferential direction (C) in which the first magnetic pole surface ( 41 ) and the second magnetic pole surface ( 42 ) are arranged. Therefore, the harmonic component of the counter-electromotive voltage generated on the stator coil ( 94 ) can be reduced by adjusting the harmonic component of the coil flux linkage due to the rotation of the rotor ( 10 ). Thus, the peaks of the counter-electromotive voltage that may be generated on the stator coil ( 94 ) can be reduced while increasing the torque of the rotating electrical machine ( 1 ), 
     It is appropriate that the first hole portion ( 51 ) and the second hole portion ( 52 ) be formed so that the harmonic components of the plurality of target orders on the fundamental component of the counter-electromotive voltage generated by the rotation of the rotor ( 10 ) on the coil ( 94 ) of the stator ( 90 ) arranged so as to face the outer peripheral surface ( 11   a ) of the rotor core ( 11 ) are reduced as compared to the case where the first hole portion ( 51 ) and the second hole portion ( 52 ) are not provided. 
     This structure can reduce the harmonic components of the plurality of target orders to be superposed on the fundamental component of the counter-electromotive voltage generated on the stator coil ( 94 ). Thus, it is possible to effectively reduce the peaks of the counter-electromotive voltage that may be generated on the stator coil ( 94 ). 
     It is appropriate that, when M represents the number of slots for one of the magnetic poles in the stator ( 90 ), the plurality of target orders include at least the (2M−1)th order and the (2M+1)th order. 
     This structure can reduce the harmonic components of the orders that particularly have significant influence among the harmonic components to be superposed on the fundamental component of the counter-electromotive voltage. Thus, it is possible to further effectively reduce the peaks of the counter-electromotive voltage that may be generated on the stator coil ( 94 ). 
     It is appropriate that the angle (θ 1 ) formed in the circumferential direction (C) about the rotation axis (X) of the rotor core ( 11 ) between the end of the first magnetic pole surface ( 41 ) on the first circumferential side (C 1 ) and the end of the second magnetic pole surface ( 42 ) on the second circumferential side (C 2 ) be the angle within the range of 128°±10° in terms of the electrical angle, and the angle (θ 2 ) formed in the circumferential direction (C) about the rotation axis (X) between the end of the first magnetic pole surface ( 41 ) on the first circumferential side (C 1 ) at the part that does not overlap the first hole portion ( 51 ) as viewed in the radial direction (R) and the end of the second magnetic pole surface ( 42 ) on the second circumferential side (C 2 ) at the part that does not overlap the second hole portion ( 52 ) as viewed in the radial direction (R) be the angle within the range of 104°±10° in terms of the electrical angle. 
     By providing the first hole portion ( 51 ) and the second hole portion ( 52 ) described above, magnetic characteristics of the rotor ( 10 ) can be designed not only by the angle (hereinafter referred to as “first angle”) formed in the circumferential direction (C) about the rotation axis (X) of the rotor core ( 11 ) between the end of the first magnetic pole surface ( 41 ) on the first circumferential side (C 1 ) and the end of the second magnetic pole surface ( 42 ) on the second circumferential side (C 2 ) but also by the angle (hereinafter referred to as “second angle”) formed in the circumferential direction (C) about the rotation axis (X) of the rotor core ( 11 ) between the end of the first magnetic pole surface ( 41 ) on the first circumferential side (C 1 ) at the part that does not overlap the first hole portion ( 51 ) as viewed in the radial direction (R) and the end of the second magnetic pole surface ( 42 ) on the second circumferential side (C 2 ) at the part that does not overlap the second hole portion ( 52 ) as viewed in the radial direction (R). As a result of extensive studies, the inventors have found that the peaks of the counter-electromotive voltage that may be generated on the coil ( 94 ) can be reduced while increasing the torque of the rotating electrical machine ( 1 ) by setting the first angle (θ 1 ) to the angle within the range of 128°±10° in terms of the electrical angle and setting the second angle (θ 2 ) to the angle within the range of 104°±10° in terms of the electrical angle as in the structure described above. That is, by setting the first angle (θ 1 ) to the angle within the range of 128°±10° in tarns of the electrical angle, a large difference is secured between the q-axis inductance and the d-axis inductance. Thus, the reluctance torque can be improved (the usage of the reluctance torque can be improved). By setting the second angle (θ 2 ) to the angle within the range of 104°±10° in terms of the electrical angle, the 11th order component and the 13th order component of the flux linkage are both reduced, and therefore the peaks of the counter-electromotive voltage can be reduced. Further, the leakage fluxes of the first permanent magnet ( 31 ) and the second permanent magnet ( 32 ) are reduced by the first hole portion ( 51 ) and the second hole portion ( 52 ), respectively, and therefore the magnet torque can be improved (the usage of the magnet torque can be improved). 
     It is appropriate that the first permanent magnet ( 31 ) be inserted into the first magnet insertion hole ( 21 ) formed in the rotor core ( 11 ) so as to extend in the axial direction, the second permanent magnet ( 32 ) be inserted into the second magnet insertion hole ( 22 ) formed in the rotor core ( 11 ) so as to extend in the axial direction, the first hole portion ( 51 ) be formed integrally with the first magnet insertion hole ( 21 ) so as to communicate with the first magnet insertion hole ( 21 ), and the second hole portion ( 52 ) be formed integrally with the second magnet insertion hole ( 22 ) so as to communicate with the second magnet insertion hole. ( 22 ). 
     This structure can further reduce the leakage flux of the first permanent magnet ( 31 ) by using the communicating part between the first hole portion ( 51 ) and the first magnet insertion hole ( 21 ), and can further reduce the leakage flux of the second permanent magnet ( 32 ) by using the communicating part between the second hole portion ( 52 ) and the second magnet insertion hole ( 22 ). The structure described above facilitates manufacturing of the rotor core ( 11 ) as compared to the case where the first hole portion ( 51 ) is formed as a hole independent of the first magnet insertion hole ( 21 ) and the case where the second hole portion ( 52 ) is formed as a hole independent of the second magnet insertion hole ( 22 ). 
     It is appropriate that each of the inner surface of the first hole portion ( 51 ) on the outer side in the radial direction (R) and the inner surface of the second hole portion ( 52 ) on the outer side in the radial direction (R) have the part parallel to the outer peripheral surface ( 11   a ) of the rotor core ( 11 ). 
     According to this structure, the shape of the bridge portion ( 61 ) formed between the first hole portion ( 51 ) and the outer peripheral surface ( 11   a  ) of the rotor core ( 11 ) in the radial direction (R) and the shape of the bridge portion ( 62 ) formed between the second hole portion ( 52 ) and the outer peripheral surface ( 11   a ) of the rotor core ( 11 ) in the radial direction (R) can be set to a shape that is narrow in the radial direction (R) and is long in the circumferential direction (C) (elongated shape extending in the circumferential direction (C) as viewed in the axial direction). Thus, the occurrence of magnetic saturation is facilitated in those bridge portions ( 61 ,  62 ). As a result, the leakage flux of the permanent magnet ( 30 ) can be reduced to a lower level, 
     The method for designing the rotor ( 10 ) is the method for designing the rotor ( 10 ) for the inner rotor type rotating electrical machine ( 1 ), including the rotor core ( 11 ) and the permanent magnets ( 30 ) embedded in the rotor core ( 11 ). The magnetic poles (P) are each formed by a pair of the permanent magnets ( 30 ) arranged side by side in the circumferential direction (C). Of the pair of the permanent magnets ( 30 ) that form one of the magnetic poles (P), the permanent magnet ( 30 ) arranged on the first circumferential side (C 1 ) that is one side in the circumferential direction (C) is defined as the first permanent magnet ( 31 ), and the permanent magnet ( 30 ) arranged on the second circumferential side (C 2 ) that is the other side in the circumferential direction (C) is defined as the second permanent magnet ( 32 ). The first magnetic pole surface ( 41 ) that is the magnetic pole surface ( 40 ) of the first permanent magnet ( 31 ) that is oriented toward the outer side in the radial direction (R) is arranged so that the portion of the first magnetic pole surface ( 41 ) that is closer to the first circumferential side (C 1 ) is located further outward in the radial direction (R). The second magnetic pole surface ( 42 ) that is the magnetic pole surface ( 40 ) of the second permanent magnet ( 32 ) that is oriented toward the outer side in the radial direction (R) is arranged so that the portion of the second magnetic pole surface ( 42 ) that is closer to the second circumferential side (C 2 ) is located further outward in the radial direction (R). The rotor core ( 11 ) includes the first hole portion ( 51 ) formed on the outer side in the radial direction (R) with respect to the first magnetic pole surface ( 41 ) at the position where the first hole portion ( 51 ) overlaps, as viewed in the radial direction (R), the first end region (A 1 ) including the end of the first magnetic pole surface ( 41 ) on the first circumferential side (C 1 ), and the second hole portion ( 52 ) formed on the outer side in the radial direction (R) with respect to the second magnetic pole surface ( 42 ) at the position where the second hole portion ( 52 ) overlaps, as viewed in the radial direction (R), the second end region (A 2 ) including the end of the second magnetic pole surface ( 42 ) on the second circumferential side (C 2 ). The first hole portion ( 51 ) and the second hole portion ( 52 ) are formed so that the harmonic components of the plurality of target orders on the fundamental component of the counter-electromotive voltage generated by the rotation of the rotor ( 10 ) on the coil ( 94 ) of the stator ( 90 ) arranged so as to face the outer peripheral surface ( 11   a ) of the rotor core ( 11 ) are reduced as compared to the case where the first hole portion ( 51 ) and the second hole portion ( 52 ) are not provided. 
     According to the structure described above, the first hole portion ( 51 ) and the second hole portion ( 52 ) limit the ranges in which the coil flux linkage occurs on the first magnetic pole surface ( 41 ) and the second magnetic pole surface ( 42 ) while improving the reluctance torque (improving the usage of the reluctance torque) by appropriately setting the ranges in the circumferential direction (C) in which the first magnetic pole surface ( 41 ) and the second magnetic pole surface ( 42 ) are arranged. Therefore, the harmonic component of the counter-electromotive voltage generated on the stator coil ( 94 ) can be reduced by adjusting the harmonic component of the coil flux linkage due to the rotation of the rotor ( 10 ). Thus, it is possible to attain a rotor in which the peaks of the counter-electromotive voltage that may be generated on the stator coil ( 94 ) are reduced while increasing the torque of the rotating electrical machine ( 1 ). This structure can reduce the harmonic components of the plurality of target orders to be superposed on the fundamental component of the counter-electromotive voltage generated on the stator coil ( 94 ). Thus, it is possible to attain a rotor in which the peaks of the counter-electromotive voltage that may be generated on the stator coil ( 94 ) are reduced effectively. 
     In the designing method, it is appropriate that the first hole portion and the second hole portion be formed so that the angle formed in the circumferential direction about the rotation axis between the end of the first magnetic pole surface on the first circumferential side at the part that does not overlap the first hole portion as viewed in the radial direction and the end of the second magnetic pole surface on the second circumferential side at the part that does not overlap the second hole portion as viewed in the radial direction corresponds to the electrical angle at which the harmonic components of the plurality of target orders on the fundamental component of the counter-electromotive voltage are reduced together. 
     This structure can reduce together the harmonic components of the plurality of target orders to be superposed on the fundamental component of the counter-electromotive voltage generated on the stator coil ( 94 ). Thus, it is possible to attain a rotor in which the peaks of the counter-electromotive voltage that may be generated on the stator coil ( 94 ) are reduced effectively. 
     In the designing method, it is appropriate that the angle (θ 1 ) formed in the circumferential direction (C) about the rotation axis (X) of the rotor core ( 11 ) between the end of the first magnetic pole surface ( 41 ) on the first circumferential side (C 1 ) and the end of the second magnetic pole surface ( 42 ) on the second circumferential side (C 2 ) be set to the angle within the range of 128°±10° in terms of the electrical angle, and the angle (θ 2 ) formed in the circumferential direction (C) about the rotation axis (X) between the end of the first magnetic pole surface ( 41 ) on the first circumferential side (C 1 ) at the part that does not overlap the first hole portion ( 51 ) as viewed in the radial direction (R) and the end of the second magnetic pole surface ( 42 ) on the second circumferential side (C 2 ) at the part that does not overlap the second hole portion ( 52 ) as viewed in the radial direction (R) be set to the angle within the range of 104°±10° in terms of the electrical angle. 
     Thus, the magnetic characteristics of the rotor ( 10 ) can be designed not only by the angle (hereinafter referred to as “first angle”) formed in the circumferential direction (C) about the rotation axis (X) of the rotor core ( 11 ) between the end of the first magnetic pole surface ( 41 ) on the first circumferential side (C 1 ) and the end of the second magnetic pole surface ( 42 ) on the second circumferential side (C 2 ) but also by the angle (hereinafter referred to as “second angle”) formed in the circumferential direction (C) about the rotation axis (X) of the rotor core ( 11 ) between the end of the first magnetic pole surface ( 41 ) on the first circumferential side (C 1 ) at the part that does not overlap the first hole portion ( 51 ) as viewed in the radial direction (R) and the end of the second magnetic pole surface ( 42 ) on the second circumferential side (C 2 ) at the part that does not overlap the second hole portion ( 52 ) as viewed in the radial direction (R). As a result of extensive studies, the inventors have found that the peaks of the counter-electromotive voltage that may be generated on the coil ( 94 ) can be reduced while increasing the torque of the rotating electrical machine ( 1 ) by setting the first angle (θ 1 ) to the angle within the range of 128°±10° in terms of the electrical angle and setting the second angle (θ 2 ) to the angle within the range of 104°±10° in terms of the electrical angle as in the structure described above. That is, by setting the first angle (θ 1 ) to the angle within the range of 128°±10° in terms of the electrical angle, a large difference is secured between the q-axis inductance and the d-axis inductance. Thus, the reluctance torque can be improved (the usage of the reluctance torque can be improved). By setting the second angle (θ 2 ) to the angle within the range of 104°±10° in terms of the electrical angle, the 11th order component and the 13th order component of the flux linkage are both reduced, and therefore the peaks of the counter-electromotive voltage can be reduced. Further, the leakage fluxes of the first permanent magnet ( 31 ) and the second permanent magnet ( 32 ) are reduced by the first hole portion ( 51 ) and the second hole portion ( 52 ), respectively, and therefore the magnet torque can be improved (the usage of the magnet torque can be improved).