Patent Publication Number: US-11664693-B2

Title: Rotating electrical machine

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a bypass continuation application of currently pending international application No. PCT/JP2018/048248 filed on Dec. 27, 2018 designating the United States of America, the entire disclosure of which is incorporated herein by reference. 
     This application is based on and claims the benefit of priority from Japanese Patent Applications No. 2017-255080 filed on Dec. 28, 2017, 2018-140738 filed on Jul. 26, 2018, and 2018-166446 filed on Sep. 5, 2018, the disclosure of each of which is incorporated in its entirety herein by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure generally relates to rotating electrical machines. 
     BACKGROUND 
     Interior permanent magnet (IPM) rotors for, for example, rotating electrical machines have become widespread. Such an IPM rotor includes a rotor core comprised of the stack of electromagnetic steel sheets. The rotor core has defined therein magnet installation holes, and magnets are installed in the respective magnet installation holes. 
     For example, patent literature 1 discloses a technology that devises the shape of each magnet installation hole to thereby reduce a magnetic field in a direction opposite to a direction of magnetic flux from a rotor to a stator, thus increasing magnetic flux interlinking to the stator. Such a rotating electrical machine is designed to optimize the shape of each permanent magnet, the rotor, and the stator to thereby aim to balance improvement of performance of the rotating electrical machine and improvement of resistance of the permanent magnet against demagnetization. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1 
     Japanese Patent Application Publication No. 2014-093859 
     SUMMARY 
     In addition to IPM rotors, surface permanent magnet (SPM) rotors for rotating electrical machines have been used. Like an IPM rotating electrical machine, an SPM rotating electrical machine is designed to optimize the shape of each permanent magnet, the rotor, and the stator to thereby aim to balance improvement of performance of the rotating electrical machine and improvement of resistance of the permanent magnet against a demagnetization field. 
     For example, a rotating electrical machine is known, which includes a Halbach array of permanent magnets with a higher magnetic flux density. The following describes such a Halbach array of permanent magnets in detail. 
     Specifically, permanent magnets arranged in such a Halbach array of a rotating electrical machine include first permanent magnets and second permanent magnets. Each of the first permanent magnets has a magnetic path directed in a corresponding radial direction of the rotating electrical machine. Each of the second permanent magnets has a magnetic path directed in a circumferential direction of the rotating electrical machine. 
     The first permanent magnets are arranged in the circumferential direction of the rotating electrical machine, and the second permanent magnets are each disposed between a corresponding pair of adjacent first permanent magnets. This arrangement of the first and second permanent magnets make it possible for the rotating electrical machine to have a higher magnetic density directed toward a stator of the rotating electrical machine, a smaller size, and higher output. 
     A rotating electrical machine, which includes a Halbach array of permanent magnets, may unfortunately have leakage flux from a side of each permanent magnet further from the stator, resulting in a reduction of the magnetic flux density from a closer side of the corresponding permanent magnet to the stator. 
     In view of the circumstances set forth above, the disclosure aims to mainly provide rotating electrical machines, each of which has a higher magnetic flux density thereof. 
     Various aspects disclosed in this specification respectively utilize technical measures, which are different from each other, for achieving respective objects. The objects, features, and effects disclosed in this specification are more clarified with reference to the following detailed-descriptions, and the accompanying figures. 
     The measure  1 A is a rotating electrical machine including a field generator that includes a magnet unit. The magnet unit has a plurality of magnetic poles whose polarities are alternately arranged in a circumferential direction. The rotating electrical machine includes an armature that includes a multi-phase armature winding member. One of the field generator and the armature serves as a rotor of the rotating electrical machine. 
     The magnet unit includes a plurality of first magnets and a plurality of second magnets. Each of the first magnets has a magnetic path that is aligned with a corresponding radial direction. Each of the second magnets has a magnetic path that is aligned with a circumferential direction. The first magnets are arrayed at given intervals away from each other in the circumferential direction. 
     Each of the second magnets is disposed between a corresponding adjacent pair of the first magnets in the circumferential direction. The armature includes an annular armature core member made of a soft magnetic material, and disposed to be farther from the armature than the magnet unit therefrom. The armature core member is radially stacked on the magnet unit. Each of the first magnets has a farther circumferential surface from the armature. The magnet unit and the armature core member are configured to satisfy the following relation:
 
 Br×Ma≤Bsc×Wsc  
 
     where: 
     Br represents a remanent flux density of the magnet unit; 
     Ma represents a distance of the farther circumferential surface of each of the first magnets in the circumferential direction; 
     Bsc represents a saturation magnetic flux density of the armature core member; and 
     Wsc represents a thickness of the armature core member in a radial direction thereof. 
     This layout of the first and second magnets enables the magnet unit to have a near-sinusoidal magnetic-flux density distribution, making it possible to achieve a higher level of torque, smaller eddy-current loss, and smaller torque ripples. 
     This layout of the first and second magnets may cause magnetic flux to be likely to leak from a farther side of the magnet unit from the armature. For addressing such leakage, the annular armature core member, which is made of a soft magnetic material, is preferably attached to the farther side of the magnet unit from the armature, so that the annular armature core member is radially stacked on the magnet unit. 
     The annular armature core member stacked on the magnet unit preferably has a radial thickness as thin as possible for a small size of the rotary electric machine and/or for a large volume of a radially inside region of the rotor. An excessively thin thickness of the annular armature core member may however result in magnetic flux leaking from the stacked structure of the magnet unit and the annular armature core member. 
     From this viewpoint, using the first and second magnets, which satisfy the relation of Br×Ma≤Bsc×Wsc, results in the rotating electrical machine having a thinner radial thickness thereof while reducing magnetic flux leakage. 
     In the measure  2 A, the first magnet or the second magnet has first shear stress in a radial direction thereof, and the armature core member has second shear stress in the radial direction thereof. The magnet unit and the armature core member are configured to satisfy the following relation:
 
 Tr×Ma&lt;Ts×Wsc  
 
     where: 
     Tr represents the first shear stress of the first magnet or the second magnet in the radial direction thereof; and 
     Ts represents the second shear stress of the armature core member in the radial direction thereof. 
     The first and second magnets, which are arranged in the circumferential direction, cause centrifugal forces to be individually generated from the respective first and second magnets while the rotor is rotating. If the rotating electrical machine is applied to a vehicle, vibrations of the first and second magnets due to vibrations of the vehicle running on a bumpy road may cause each of the first and second magnets to apply a corresponding force to the annular armature core member. 
     The annular armature core member thus needs suitable prestresses against the above external forces applied from the respective first and second magnets. That is, if the prestresses, i.e. shear stresses, of the annular armature core member were smaller than the external forces applied thereto, the annular armature core member might be likely to shear. 
     From this viewpoint, the first or second magnets and the annular armature core member are configured to satisfy the relation Tr×Ma&lt;Ts×Wsc. This enables the annular armature core member to have a thinner thickness while the first or second magnets and the annular armature core member having a suitable strength, that is, reliably retaining the first or second magnets. 
     In the measure  3 A, the magnet unit has an intrinsic coercive force of 400 kA/m or more, and has a remanent flux density of 1.0 T or more. 
     This enables each magnet of the magnet unit to have a higher level of magnetic flux density. In particular, the first or second magnets and the annular armature core member, which satisfy the relation of Br×Ma≤Bsc×Wsc, enable magnetic flux leakage to be efficiently reduced. 
     In the measure  4 A depending from any one of the measures  1 A to  3 A, the armature winding member includes a plurality of conductive members that face the armature and are arrayed at given intervals away from each other in the circumferential direction. The armature has any one of a first configuration and a second configuration. The first configuration having conductor-to-conductor members. Each of the conductor-to-conductor members is disposed between a corresponding adjacent pair of the conductive members of the armature winding member. The second configuration has no conductor-to-conductor member between each adjacent pair of the conductive members of the armature winding member. Each of the conductor-to-conductor members is made of any one of a magnetic material and a non-magnetic material. The magnetic material satisfies the following relation:
 
 Wt×Bs≤Wm×Br  
 
     where: 
     Wt represents a total circumferential width of one or more of the conductor-to-conductor members lying within a range of one of the magnetic poles of the magnet unit; 
     Bs represents a saturation magnetic flux density of the conductor-to-conductor members; 
     Wm represents a circumferential width of a portion of the magnet unit equivalent to one of the magnetic poles of the magnet unit; and 
     Br represents the remanent flux density of the magnet unit. 
     This prevents magnetic flux saturation in the armature while improving the magnetic flux density, thus eliminating restriction of torque due to the magnetic saturation. 
     In the measure  5 A depending from any one of the measures  1 A to  4 A, the armature winding member includes a plurality of conductive members that face the armature and are arrayed at given intervals away from each other in the circumferential direction. Each of the conductive members is made of a bundle of a plurality of wires. Each adjacent pair of the wires of the bundle has a first electrical resistivity. Each of the wires has a second electrical resistivity, and the first electrical resistivity is higher than the second electrical resistivity. 
     Using the magnet unit having a near-sinusoidal magnetic-flux density distribution and each of the conductive members, which is made of a bundle of a plurality of wires, makes it possible to achieve smaller eddy-current loss in the conductive members. 
     In the measure  6 A depending from any one of the measures  1 A to  5 A, the armature winding member includes a plurality of conductive members that face the armature and are arrayed at given intervals away from each other in the circumferential direction. Each of the conductive members has a thickness in the radial direction thereof, and the conductor members have a portion lying in a region of one of the magnetic pole for each phase in the circumferential direction. The portion of the conductor members has a width in the circumferential direction, and the thickness of each of the conductive members is set to be smaller than the width of the portion of the conductor members. 
     This measure  6 A achieves smaller eddy-current loss in the conductive members while achieving a higher level of torque. 
     Interior permanent magnet (IPM) rotors for, for example, rotating electrical machines have been widespread. Such an IPM rotor includes a rotor core comprised of the stack of electromagnetic steel sheets. The rotor core has defined therein magnet installation holes, and magnets are installed in the respective magnet installation holes. 
     Magnets used for such a rotor are for example disclosed in patent literature 2 corresponding to Japanese Patent Application Publication No. 2017-99071. Patent literature 2 discloses such magnets each having a surface magnetic-flux density distribution that is close to a sinusoidal waveform. Using the magnets disclosed in patent literature 2 results in a more gradual magnetic flux change than that of radial magnets, reducing eddy-current loss. Using the magnets disclosed in patent literature 2 also improves the magnetic flux density while reducing torque ripples. 
     Each magnet disclosed in patent literature 2 has curved magnetic paths. A method of magnetizing a magnet such that the magnetized magnet has curved magnetic paths needs to include a specific procedure of, for example, orienting easy axes of magnetization in the magnet to be respectively along their designed curved lines; this specific procedure is not necessarily required for a method of magnetizing a magnet such that the magnet has linear magnetic paths. 
     That is, manufacturing a magnet having curved magnetic paths may take more time than manufacturing a magnet having linear magnetic paths. 
     The following disclosure, which has been designed to address such an issue, aims to provide rotating electrical machines, each of which is capable of easily providing a magnet unit having a surface magnetic-flux density distribution that is close to a sinusoidal waveform. 
     The measure  1 B is a rotating electrical machine that includes a field generator that includes a magnet unit. The magnet unit has a plurality of magnetic poles that are alternately arranged in a circumferential direction. The rotating electrical machine includes an armature that includes a multi-phase armature winding member. One of the field generator and the armature serves as a rotor of the rotating electrical machine. 
     The magnet unit includes a plurality of first magnets and a plurality of second magnets. Each of the first magnets has a linear first magnetization vector, each of the second magnets having a linear second magnetization vector. The first magnets are arrayed at given intervals away from each other in the circumferential direction. Each of the second magnets is disposed between a corresponding adjacent pair of the first magnets in the circumferential direction. The first magnetization vector in each of the first magnets is aligned with a corresponding radial direction of the rotor, or aligned with a direction inclined toward a d-axis with respect to the corresponding radial direction, the d-axis representing a center of a corresponding one of the magnetic poles. The second magnetization vector in each of the second magnets is disposed to be closer to the circumferential direction than the first magnetization vector in each of the first magnets is. 
     The first magnets are arrayed at given intervals away from each other in the circumferential direction, and each of the second magnets is disposed between a corresponding adjacent pair of the first magnets in the circumferential direction. Orienting each first magnet such that the first magnet is configured as a parallel oriented magnet to have linear magnetic vectors, i.e. directions of magnetization, along a d-axis might result in the magnetic flux density being less likely to converge to the d-axis. In particular, the arrangement where the field generator is disposed to be radially inward of the armature may cause such an issue to become more pronounced. 
     From this viewpoint, the first magnetization vector in each of the first magnets is aligned with a corresponding radial direction of the rotor, or aligned with a direction inclined toward a d-axis with respect to the corresponding radial direction; the d-axis represents a center of a corresponding one of the magnetic poles. 
     This makes it easier for magnetic flux density to converge to the corresponding d-axis side although the first and second magnets, each of which has linear magnetization vectors, are used. This results in the surface magnetic-flux density distribution of each of the first magnets being closer to a sinusoidal waveform. 
     In the measure  2 B depending from the measure  1 B, the second magnetization vector in each of the second magnets is inclined toward the armature with respect to a predetermined direction, the predetermined direction being perpendicular to a q-axis, the q-axis representing a magnetic-pole boundary of the corresponding one of the magnetic poles. 
     Orienting each second magnet such that the second magnet is configured as a parallel oriented magnet to have linear magnetic vectors along a direction perpendicular to the q-axis might result in the magnetic flux density being less likely to converge to the d-axis. In particular, the arrangement where the field generator is disposed to be radially inward of the armature may cause such an issue to become more pronounced. 
     From this viewpoint, the second magnetization vector in each of the second magnets is inclined toward the armature with respect to a predetermined direction, the predetermined direction being perpendicular to the q-axis. 
     This makes it easier for magnetic flux density to converge to the corresponding d-axis side although the first and second magnets, each of which has linear magnetization vectors, are used. This results in the surface magnetic-flux density distribution of each of the second magnets being closer to a sinusoidal waveform. 
     The measure  3 B is a rotating electrical machine that includes a field generator that includes a magnet unit. The magnet unit has a plurality of magnetic poles that are alternately arranged in a circumferential direction. The rotating electrical machine includes an armature that includes a multi-phase armature winding member. One of the field generator and the armature serves as a rotor of the rotating electrical machine 
     The magnet unit includes a plurality of first magnets and a plurality of second magnets. Each of the first magnets has a linear first magnetization vector, each of the second magnets having a linear second magnetization vector. The first magnets are arrayed at given intervals away from each other in the circumferential direction. Each of the second magnets is disposed between a corresponding adjacent pair of the first magnets in the circumferential direction. The second magnetization vector in each of the second magnets is inclined toward the armature with respect to a predetermined direction. The predetermined direction is perpendicular to a q-axis. The q-axis represents a magnetic-pole boundary of a corresponding one of the magnetic poles. 
     The first magnetization vector in each of the first magnets is disposed to be closer to a corresponding radial direction than the second magnetization vector in each of the second magnets is. 
     Orienting each second magnet such that the second magnet is configured as a parallel oriented magnet to have linear magnetic vectors along a direction perpendicular to a q-axis might result in the magnetic flux density being less likely to converge to the d-axis. In particular, the arrangement where the field generator is disposed to be radially inward of the armature may cause such an issue to become more pronounced. 
     From this viewpoint, the second magnetization vector in each of the second magnets is inclined toward the armature with respect to a predetermined direction, the predetermined direction being perpendicular to the q-axis. 
     This makes it easier for magnetic flux density to converge to the corresponding d-axis side although the first and second magnets, each of which has linear magnetization vectors, are used. This results in the surface magnetic-flux density distribution of each of the second magnets being closer to a sinusoidal waveform. 
     In the measure  4 B depending from any one of the measures  1 B to  3 B, the first magnets include first A magnets and first B magnets. The first magnetization vector in each of the first A magnets is directed from an anti-armature side of the corresponding first A magnet to an armature side thereof, and the second magnetization vector in each of the first B magnets is directed from the stator side of the corresponding first B magnets to the anti-stator side thereof. The first A magnets and the first B magnets are alternately arranged in the circumferential direction. 
     The second magnetization vector in each of the second magnets is radially arranged about a center point, the center point being set to an anti-armature side of the corresponding second magnet. The center point of each second magnet is set to be closer to the corresponding adjacent first B magnet than to the corresponding adjacent first A magnet. 
     Orienting each second magnet such that the second magnet is configured as a parallel oriented magnet to have magnetic flux vectors parallel to each other may result in insufficient lengths of some magnetic paths depending on the size or shape (i.e., curvature) of the second magnet. From this viewpoint, the second magnetization vector in each of the second magnets is designed as a radial orientation that is radially arranged about a center point, the center point being set to an anti-armature side of the corresponding second magnet. The center point of each second magnet is set to be closer to the corresponding adjacent first B magnet than to the corresponding adjacent first A magnet. 
     This enables the length of each magnetic vector of each second magnet to be longer while each magnetic vector is more inclined toward the armature side than a direction perpendicular to a q-axis is 
     ; the q-axis represents a magnetic-pole boundary of a corresponding one of the magnetic poles. 
     In the measure  5 B depending from any one of the measures  1 B to  3 B, the first magnets include first A magnets and first B magnets. The first magnetization vector in each of the first A magnets is directed from an anti-armature side of the corresponding first A magnet to an armature side thereof, and the second magnetization vector in each of the first B magnets is directed from the stator side of the corresponding first B magnets to the anti-stator side thereof; 
     The first A magnets and the first B magnets are alternately arranged in the circumferential direction. Each of the second magnets disposed between the corresponding adjacent pair of the first magnets in the circumferential direction includes a first portion and a second portion. The first portion is disposed to be adjacent to the first A magnet, and the second portion is disposed to be adjacent to the first B magnet. 
     The second magnetization vector in the first portion disposed to be adjacent to the corresponding first A magnet is inclined toward the armature side with respect to the predetermined direction. The predetermined direction is perpendicular to the q-axis that represents the magnetic-pole boundary of the corresponding one of the magnetic poles. The second magnetization vector in the second portion disposed to be adjacent to the corresponding first B magnet is inclined toward the armature side with respect to the predetermined direction; the predetermined direction is perpendicular to the q-axis. 
     Each of the second magnets includes a first portion and a second portion in the circumferential direction. The second magnetization vector in the first portion disposed to be adjacent to the corresponding first A magnet is inclined toward the armature side with respect to the predetermined direction. The predetermined direction is perpendicular to the q-axis. The second magnetization vector in the second portion disposed to be adjacent to the corresponding first B magnet is inclined toward the anti-armature side with respect to the predetermined direction; the predetermined direction is perpendicular to the q-axis. 
     This enables the magnetization vectors to be closer to a curved line along the circumferential direction to thereby increase the length of each magnetic path, making it possible to improve magnetic flux density on the d-axis. This also enables the surface magnetic-flux density distribution of each of the second magnets to be closer to a sinusoidal waveform. 
     In the measure  6 B depending from any one of the measures  1 B to  5 B, the first magnetization vector includes a plurality of first magnetization vectors in each of the first A magnets, and each of the first magnetization vectors in each of the first A magnets is inclined by an angle with respect to the d-axis. The angle becomes larger as each of the first magnetization vectors becomes farther from the d-axis. 
     This improves the magnetic flux density on the d-axis while enabling the surface magnetic-flux density distribution to be closer to a sinusoidal waveform. 
     In the measure  7 B depending from any one of the measures  1 B to  6 B, the field generator is disposed to be radially inward of the armature. 
     This enables the surface magnetic-flux density distribution to be much closer to a sinusoidal waveform. 
     In the measure  8 B, the magnet unit has an intrinsic coercive force of 400 kA/m or more, and has a remanent flux density of 1.0 T or more. 
     This achieves a higher level of torque. 
     In the measure  9 B depending from any one of the measures  1 B to  8 B, the armature winding member includes a plurality of conductive members that face the armature and are arrayed at given intervals away from each other in the circumferential direction. Each of the conductive members has a radial thickness, and has a circumferential width for each phase within one of the magnetic poles of the magnet unit. The radial thickness of each of the conductive members is smaller than the circumferential width of the corresponding one of the conductive members for each phase within one of the magnetic poles of the magnet unit. 
     This achieves smaller eddy-current loss in the conductive members and a higher level of torque. 
     In the measure  10 B depending from any one of measures  1 B to  9 B, the armature winding member includes a plurality of conductive members that face the armature and are arrayed at given intervals away from each other in the circumferential direction. The armature has any one of a first configuration and a second configuration. The first configuration has conductor-to-conductor members, each of the conductor-to-conductor members being disposed between a corresponding adjacent pair of the conductive members of the armature winding member. The second configuration has no conductor-to-conductor member between each adjacent pair of the conductive members of the armature winding member. Each of the conductor-to-conductor members is made of any one of a magnetic material and a non-magnetic material, and the magnetic material satisfying the following relation:
 
 Wt×Bs≤Wm×Br  
 
     where: 
     Wt represents a total circumferential width of one or more of the conductor-to-conductor members lying within a range of one of the magnetic poles of the magnet unit; 
     Bs represents a saturation magnetic flux density of the conductor-to-conductor members; 
     Wm represents a circumferential width of a portion of the magnet unit equivalent to one of the magnetic poles of the magnet unit; and Br represents the remanent flux density of the magnet unit. 
     This eliminates restriction of torque due to magnetic saturation. 
     In the measure  11 B depending from any one of the measures  1 B to  10 B, the armature winding member includes a plurality of conductive members that face the armature and are arrayed at given intervals away from each other in the circumferential direction. Each of the conductive members is made of a bundle of a plurality of wires. Each adjacent pair of the wires of the bundle has a first electrical resistivity. Each of the wires has a second electrical resistivity, the first electrical resistivity being higher than the second electrical resistivity. 
     This achieves smaller eddy-current loss in the conductive members. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective longitudinal sectional view of a rotating electrical machine. 
         FIG.  2    is a longitudinal sectional view of the rotating electrical machine. 
         FIG.  3    is a sectional view taken along the line III-III in  FIG.  2   . 
         FIG.  4    is a partially enlarged sectional view of part of  FIG.  3   . 
         FIG.  5    is an exploded view of the rotating electrical machine. 
         FIG.  6    is an exploded view of an inverter unit. 
         FIG.  7    is a graphic torque diagram which demonstrates a relationship between an ampere-turn and a torque density in a stator winding. 
         FIG.  8    is a transverse sectional view of a rotor and a stator. 
         FIG.  9    is an enlarged view of part of  FIG.  8   . 
         FIG.  10    is a transverse sectional view of a stator. 
         FIG.  11    is a longitudinal sectional view of a stator. 
         FIG.  12    is a perspective view of a stator winding. 
         FIG.  13    is a perspective view of a conductor. 
         FIG.  14    is a schematic view illustrating a structure of wire. 
         FIG.  15 ( a )  is a view showing the layout of conductors at the n th  layer position as the side of a stator coil is viewed. 
         FIG.  15 ( b )  is a view showing the layout of conductors at the n th  layer position as viewed in an axial direction of the stator coil. 
         FIG.  16    is a side view showing conductors at the n th  layer position and the (n+1) th  layer position. 
         FIG.  17    is a view representing a relation between an electrical angle and a magnetic flux density in a magnet unit of an embodiment. 
         FIG.  18    is a view which represents a relation between an electrical angle and a magnetic flux density in a magnet unit of a comparative example. 
         FIG.  19    is an electrical circuit diagram of a control system for a rotating electrical machine. 
         FIG.  20    is a functional block diagram which shows a current feedback control operation of a control device. 
         FIG.  21    is a functional block diagram which shows a torque feedback control operation of the control device. 
         FIG.  22    is a transverse sectional view of a rotor and a stator in the second embodiment. 
         FIG.  23    is a partially enlarged view of part of  FIG.  22   . 
         FIG.  24 ( a )  is a view illustrating flows of magnetic flux in a magnet unit according to a conventional structure in which the magnet unit is not equipped with magnetic members. 
         FIG.  24 ( b )  is a view illustrating flows of magnetic flux in a magnet unit according to the second embodiment in which the magnet unit is not equipped with the magnetic members. 
         FIG.  25    is a transverse sectional view of a rotor and a stator in the third embodiment. 
         FIG.  26    is a view demonstrating flows of magnetic flux in a magnet unit. 
         FIG.  27    is a transverse sectional view of a rotor and a stator in the fourth embodiment. 
         FIG.  28    is a transverse sectional view of a magnet unit in the fourth embodiment. 
         FIG.  29    is a transverse sectional view of a magnet unit in a comparison example. 
         FIG.  30 ( a )  is a development view of a first magnet that is linearly expanded. 
         FIG.  30 ( b )  is a development view of a first A magnet that is linearly expanded. 
         FIG.  31    is a graph schematically illustrating a relationship between a surface magnetic-flux distribution and an electrical angle. 
         FIG.  32    is a transverse sectional view of a magnet unit in the fifth embodiment. 
         FIG.  33    is a view schematically illustrating magnetic vectors in the magnet unit in the fifth embodiment. 
         FIG.  34    is a transverse sectional view of a magnet unit in the sixth embodiment. 
         FIG.  35    is a view schematically illustrating magnetic vectors in the magnet unit in the sixth embodiment. 
         FIG.  36    is a transverse sectional view of a magnet unit in another embodiment. 
         FIG.  37    is a transverse sectional view of a magnet unit in the seventh embodiment. 
         FIG.  38    is a sectional view of a stator in a modification 1. 
         FIG.  39    is a sectional view of a stator in the modification 1. 
         FIG.  40    is a sectional view of a stator in a modification 2. 
         FIG.  41    is a sectional view of a stator in a modification 3. 
         FIG.  42    is a sectional view of a stator in a modification 4. 
         FIG.  43    is a transverse sectional view of a rotor and a stator in a modification 7. 
         FIG.  44    is a functional block diagram which illustrates a portion of operations of an operation signal generator in a modification 8. 
         FIG.  45    is a flowchart representing a sequence of steps to execute a carrier frequency altering operation. 
         FIG.  46 ( a )  is a view which illustrates an electrical connection of first and second conductors that are the two pairs of conductors according to a modification 9. 
         FIG.  46 ( b )  is a view which illustrates a modification of the electrical connection of the first and second conductors. 
         FIG.  46 ( c )  is a view which illustrates another modification of the electrical connection of the first and second conductors. 
         FIG.  47    is a view which illustrates a stack of four pairs of conductors in the modification 9. 
         FIG.  48    is a transverse sectional view of an inner rotor type rotor and a stator in a modification 10. 
         FIG.  49    is a partially enlarged view of part of  FIG.  48   . 
         FIG.  50    is a longitudinal sectional view of an inner rotor type rotating electrical machine. 
         FIG.  51    is a longitudinal sectional view which schematically illustrates a structure of an inner rotor type rotating electrical machine. 
         FIG.  52    is a view which illustrates a structure of an inner rotor type rotating electrical machine in a modification 11. 
         FIG.  53    is a view which illustrates a structure of an inner rotor type rotating electrical machine in the modification 11. 
         FIG.  54    is a view which illustrates a structure of a revolving armature type of rotating electrical machine in a modification 12. 
         FIG.  55    is a sectional view which illustrates a structure of a conductor in a modification 14. 
         FIG.  56    is a view which illustrates a relation among reluctance torque, magnet torque, and distance DM. 
         FIG.  57    is a view which illustrates teeth. 
         FIG.  58    is a transverse sectional view of a magnet unit in another modification. 
         FIG.  59    is a transverse sectional view of a magnet unit in a further modification. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The embodiments will be described below with reference to the drawings. Parts of the embodiments functionally or structurally corresponding to each other or associated with each other will be denoted by the same reference numbers or by reference numbers which are different in the hundreds place from each other. The corresponding or associated parts may refer to the explanation in the other embodiments. 
     The rotating electrical machine in the embodiments is configured to be used, for example, as a power source for vehicles. The rotating electrical machine may, however, be used widely for industrial, automotive, domestic, office automation, or game applications. In the following embodiments, the same or equivalent parts will be denoted by the same reference numbers in the drawings, and explanation thereof in detail will be omitted. 
     First Embodiment 
     A rotating electrical machine  10  in this embodiment is a synchronous polyphase alternating-current motor having an outer rotor structure (i.e., an outer rotating structure). The outline of the rotating electrical machine  10  is illustrated in  FIGS.  1  to  5   . 
       FIG.  1    is a perspective longitudinal sectional view of the rotating electrical machine  10 .  FIG.  2    is a longitudinal sectional view along the rotating shaft  11  of the rotating electrical machine  10 .  FIG.  3    is a traverse sectional view (i.e., sectional view taken along the line III-III in  FIG.  2   ) of the rotating electrical machine  10  perpendicular to the rotating shaft  11 . 
       FIG.  4    is a partially enlarged sectional view of  FIG.  3   .  FIG.  5    is an exploded view of the rotating electrical machine  10 .  FIG.  3    omits hatching showing a section except the rotating shaft  11  for the sake of simplicity of the drawings. In the following discussion, a lengthwise direction of the rotating shaft  11  will also be referred to as an axial direction. A radial direction from the center of the rotating shaft  11  will be simply referred to as a radial direction. A direction along a circumference of the rotating shaft  11  about the center thereof will be simply referred to as a circumferential direction. 
     The rotating electrical machine  10  includes a bearing unit  20 , a housing  30 , a rotor  40 , a stator  50 , and an inverter unit  60 . These members are arranged coaxially with each other together with the rotating shaft  11  and assembled in a given sequence to complete the rotating electrical machine  10 . The rotating electrical machine  10  in this embodiment is equipped with the rotor  40  working as a magnetic field generator or a field system and the stator  50  working as an armature and engineered as a revolving-field type rotating electrical machine. 
     The bearing unit  20  includes two bearings  21  and  22  arranged away from each other in the axial direction and the retainer  23  which retains the bearings  21  and  22 . The bearings  21  and  22  are implemented by, for example, radial ball bearings each of which includes the outer race  25 , the inner race  26 , and a plurality of balls  27  disposed between the outer race  25  and the inner race  26 . The retainer  23  is of a cylindrical shape. The bearings  21  and  22  are disposed radially inside the retainer  23 . The rotating shaft  11  and the rotor  40  are retained radially inside the bearings  21  and  22  to be rotatable. The bearings  21  and  22  are used as a set of bearings to rotatably retain the rotating shaft  11 . 
     Each of the bearings  21  and  22  holds the balls  27  using a retainer, not shown, to keep a pitch between the balls  27  constant. Each of the bearings  21  and  22  is equipped with seals on axially upper and lower ends of the retainer and also has non-conductive grease (e.g., non-conductive urease grease) installed inside the seals. The position of the inner race  26  is mechanically secured by a spacer to exert constant inner precompression on the inner race  26  in the form of a vertical convexity. 
     The housing  30  includes a cylindrical peripheral wall  31 . The peripheral wall  31  has a first end and a second end opposed to each other in an axial direction thereof. The peripheral wall  31  has an end surface  32  on the first end and the opening  33  in the second end. The opening  33  occupies the entire area of the second end. The end surface  32  has formed in the center thereof a circular hole  34 . 
     The bearing unit  20  is inserted into the hole  34  and fixed using a fastener, such as a screw or a rivet. The rotor  40 , which has a hollow cylindrical shape, and the stator  50 , which has a hollow cylindrical shape, are disposed in an inner space defined by the peripheral wall  31  and the end surface  32  within the housing  30 . In this embodiment, the rotating electrical machine  10  is of an outer rotor type, so that the stator  50  is arranged radially inside the cylindrical rotor  40  within the housing  30 . The rotor  40  is retained in a cantilever form by a portion of the rotating shaft  11  close to the end surface  32  in the axial direction. 
     The rotor  40  includes a hollow cylindrical magnetic holder  41  and an annular magnet unit  42  disposed radially inside the magnet holder  41 . The magnet holder  41  is of substantially a cup-shape and works as a magnet holding member. The magnet holder  41  includes a cylinder  43 , an attaching portion  44  which is of a cylindrical shape and smaller in diameter than the cylinder  43 , and an intermediate portion  45  connecting the cylinder  43  and the attaching portion  44  together. The cylinder  43  has the magnet unit  42  secured to an inner peripheral surface thereof. 
     The magnet holder  41  is made of cold rolled steel (SPCC), forging steel, or carbon fiber reinforced plastic (CFRP) which have a required degree of mechanical strength. 
     The attaching portion  44  has a through-hole  44   a , and the rotating shaft  11  passes through the through-hole  44   a  of the attaching portion  44 . The attaching portion  44  is secured to a portion of the rotating shaft  11  disposed inside the through-hole  44   a . In other words, the magnet holder  41  is secured to the rotating shaft  11  through the attaching portion  44 . 
     The attaching portion  44  may preferably be joined to the rotating shaft  11  using concavities and convexities, such as a spline joint or a key joint, welding, or crimping, so that the rotor  40  rotates along with the rotating shaft  11 . 
     The bearings  21  and  22  of the bearing unit  20  are secured radially outside the attaching portion  44 . The bearing unit  20  is, as described above, fixed on the end surface  32  of the housing  30 , so that the rotating shaft  11  and the rotor  40  are retained by the housing  30  to be rotatable. The rotor  40  is, thus, rotatable within the housing  30 . 
     The rotor  40  is equipped with the attaching portion  44  arranged only one of ends thereof opposed to each other in the axial direction of the rotor  40 . This cantilevers the rotor  40  on the rotating shaft  11 . The attaching portion  44  of the rotor  40  is rotatably retained at two points of supports using the bearings  21  and  22  of the bearing unit  20  which are located away from each other in the axial direction. 
     In other words, the rotor  40  is held to be rotatable using the two bearings  21  and  22  which are separate at a distance away from each other in the axial direction on one of the axially opposed ends of the magnet holder  41 . This ensures the stability in rotation of the rotor  40  even though the rotor  40  is cantilevered on the rotating shaft  11 . The rotor  40  is retained by the bearings  21  and  22  at locations which are away from the center intermediate between the axially opposed ends of the rotor  40  in the axial direction thereof. 
     The bearing  22  of the bearing unit  20 , which is located closer to the center of the rotor  40  (a lower one of the bearings  21  and  22  in the drawings), has gaps between each of the outer and inner races  25  and  26  and the balls  27 , and the bearing  21  of the bearing unit  20 , which is located farther away from the center of the rotor  40  (i.e., an upper one of the bearings  21  and  22 ), has gaps between each of the outer and inner races  25  and  26  and the balls  27 . These gaps of the bearing  22  are different in dimension from these gaps of the bearing  21 . 
     For instance, the bearing  22  closer to the center of the rotor  40  is greater in the dimension of the gaps from the bearing  21 . This minimizes adverse effects on the bearing unit  20  which arise from deflection of the rotor  40  or mechanical vibration of the rotor  40  due to imbalance resulting from parts tolerance at a location of the bearing unit  20  close to the center of the rotor  40 . 
     Specifically, the bearing  22  closer to the center of the rotor  40  is engineered to have dimensions of the gaps or plays increased using precompression, thereby absorbing the vibration generating in the cantilever structure. 
     The precompression may be provided by either fixed position preload or constant pressure preload. In the case of the fixed position preload, the outer race  25  of each of the bearings  21  and  22  is joined to the retainer  23  using press-fitting or welding. The inner race  26  of each of the bearings  21  and  22  is joined to the rotating shaft  11  by press-fitting or welding. The precompression may be created by placing the outer race  25  of the bearing  21  away from the inner race  26  of the bearing  21  in the axial direction or alternatively placing the outer race  25  of the bearing  22  away from the inner race  26  of the bearing  22  in the axial direction. 
     In the case of the constant pressure preload, a preload spring, such as a wave washer  24 , is arranged between the bearing  22  and the bearing  21  to create the preload directed from a region between the bearing  22  and the bearing  21  toward the outer race  25  of the bearing  22  in the axial direction. In this case, the inner race  26  of each of the bearing  21  and the bearing  22  is joined to the rotating shaft  11  using press fitting or bonding. The outer race  25  of the bearing  21  or the bearing  22  is arranged away from the outer race  25  through a given clearance. This structure exerts pressure, as produced by the preload spring, on the outer race  25  of the bearing  22  to urge the outer race  25  away from the bearing  21 . The pressure is then transmitted through the rotating shaft  11  to urge the inner race  26  of the bearing  21  toward the bearing  22 , thereby bringing the outer race  25  of each of the bearings  21  and  22  away from the inner race  26  thereof in the axial direction to exert the preload on the bearings  21  and  22  in the same way as the fixed position preload. 
     The constant pressure preload does not necessarily need to exert the spring pressure, as illustrated in  FIG.  2   , on the outer race  25  of the bearing  22 , but may alternatively be created by exerting the spring pressure on the outer race  25  of the bearing  21 . The exertion of the preload on the bearings  21  and  22  may alternatively be achieved by placing the inner race  26  of one of the bearings  21  and  22  away from the rotating shaft  11  through a given clearance therebetween and joining the outer race  25  of each of the bearings  21  and  22  to the retainer  23  using press-fitting or bonding. 
     Further, in the case where the pressure is created to bring the inner race  26  of the bearing  21  away from the bearing  22 , such pressure is preferably additionally exerted on the inner race  26  of the bearing  22  away from the bearing  21 . Conversely, in the case where the pressure is created to bring the inner race  26  of the bearing  21  close to the bearing  22 , such pressure is preferably additionally exerted on the inner race  26  of the bearing  22  to bring it close to the bearing  21 . 
     In a case where the rotating electrical machine  10  is used as, for example, a power source for a vehicle, there is a possibility that mechanical vibration having a component oriented in a direction in which the preload is created may be exerted on the preload generating structure or that a direction in which the force of gravity acts on an object to which the preload is applied may be changed. In order to alleviate such a problem, the fixed position preload is preferably used in the case where the rotating electrical machine  10  is mounted in a vehicle. 
     The intermediate portion  45  includes an annular inner shoulder  49   a  and an annular outer shoulder  49   b.    
     The outer shoulder  49   b  is arranged outside the inner shoulder  49   a  in the radial direction of the intermediate portion  45 . The inner shoulder  49   a  and the outer shoulder  49   b  are separate from each other in the axial direction of the intermediate portion  45 . This layout results in a partial overlap between the cylinder  43  and the attaching portion  44  in the radial direction of the intermediate portion  45 . In other words, the cylinder  43  protrudes outside a base end portion (i.e., a lower portion, as viewed in the drawing) of the attaching portion  44  in the axial direction. The structure in this embodiment enables the rotor  40  to be retained by the rotating shaft  11  at a location closer to the center of gravity of the rotor  40  than a case where the intermediate portion  45  is shaped to be flat without any shoulder, thereby ensuring the stability in operation of the rotor  40 . 
     In the above described structure of the intermediate portion  45 , the rotor  40  has an annular bearing housing recess  46  which is formed in an inner portion of the intermediate portion  45  and radially surrounds the attaching portion  44 . The bearing housing recess  46  has a portion of the bearing unit  20  disposed therein. 
     The rotor  40  also has a coil housing recess  47  which is formed in an outer portion of the intermediate portion  45  and radially surrounds the bearing housing recess  46 . The coil housing recess  47  has disposed therein the coil end  54  of a stator coil  51  of the stator  50 , which will be described later in detail. The housing recesses  46  and  47  are arranged adjacent each other in the axial direction. In other words, a portion of the bearing unit  20  is laid to overlap the coil end  54  of the stator coil  51  in the axial direction. This enables the rotating electrical machine  10  to have a length decreased in the axial direction. 
     The intermediate portion  45  extends or overhangs outward from the rotating shaft  11  in the radial direction. The intermediate portion  45  is equipped with a contact avoider which extends in the axial direction and avoids a physical contact with the coil end  54  of the stator coil  51  of the stator  50 . The intermediate portion  45  will also be referred to as an overhang. 
     The coil end  54  may be bent radially inwardly or outwardly to have a decreased axial dimension, thereby enabling the axial length of the stator  50  to be decreased. A direction in which the coil end  54  is bent is preferably determined depending upon installation thereof in the rotor  40 . In the case where the stator  50  is installed radially inside the rotor  40 , a portion of the coil end  54 , which is inserted into the rotor  40 , is preferably bent radially inwardly. A coil end opposite the coil end  54  may be bent either inwardly or outwardly, but is preferably bent to an outward side where there is an enough space in terms of the production thereof. 
     The magnet unit  42  working as a magnetic portion is made up of a plurality of permanent magnets which are disposed radially inside the cylinder  43  to have different magnetic poles arranged alternately in a circumferential direction thereof. The magnet unit  42 , thus, has a plurality of magnetic poles arranged in the circumferential direction. The magnet unit  42  will also be described later in detail. 
     The stator  50  is arranged radially inside the rotor  40 . The stator  50  includes the stator coil  51  wound in a substantially cylindrical (annular) form and a stator core  52  used as a base member arranged radially inside the stator coil  51 . The stator coil  51  is arranged to face the annular magnet unit  42  through a given air gap therebetween. The stator coil  51  includes a plurality of phase windings each of which is made of a plurality of conductors which are arranged at given pitches away from one another in the circumferential direction and joined together. In this embodiment, first and second sets of three-phase windings: 
     The first set includes a U-phase winding, a V-phase winding, and a W-phase winging, and the second set includes an X-phase winding, a Y-phase winding, and a Z-phase winding. The stator coil  51  uses these first and second sets of three-phase windings so as to serve as a six-phase coil. 
     The stator core  52  is formed by an annular stack of magnetic steel plates made of soft magnetic material and mounted radially inside the stator coil  51 . The magnetic steel plates are, for example, silicone nitride steel plates made by adding a small percent (e.g., 3%) of silicon nitride to iron. The stator coil  51  corresponds to an armature winding. The stator core  52  corresponds to an armature core. 
     The stator coil  51  overlaps the stator core  52  in the radial direction and includes a coil side portion  53  disposed radially outside the stator core  52 , and the coil ends  54  and  55  overhanging respective ends of the stator core  52  in the axial direction. The coil side portion  53  faces the stator core  52  and the magnet unit  42  of the rotor  40  in the radial direction. The stator  50  is arranged inside the rotor  40 . The coil end  54 , which is one (i.e., an upper one, as viewed in the drawings) of the axially opposed coil ends  54  and  55  and arranged close to the bearing unit  20 , is disposed in the coil housing recess  47  defined by the magnet holder  41  of the rotor  40 . The stator  50  will also be described later in detail. 
     The inverter unit  60  includes a unit base  61  secured to the housing  30  using fasteners, such as bolts, and a plurality of electrical components  62  mounted on the unit base  61 . The unit base  61  is made from, for example, carbon fiber reinforced plastic (CFRP). The unit base  61  includes an end plate  63  secured to an edge of the opening  33  of the housing  30  and a casing  64  which is formed integrally with the end plate  63  and extends in the axial direction. The end plate  63  has a circular opening  65  formed in the center thereof. The casing  64  extends upward from a peripheral edge of the opening  65 . 
     The stator  50  is arranged on an outer peripheral surface of the casing  64 . Specifically, an outer diameter of the casing  64  is selected to be identical with or slightly smaller than an inner diameter of the stator core  52 . The stator core  52  is attached to the outer side of the casing  64  to complete a unit made up of the stator  50  and the unit base  61 . The unit base  61  is secured to the housing  30 , so that the stator  50  is unified with the housing  50  in a condition where the stator core  52  is installed on the casing  64 . 
     The stator core  52  may be bonded, shrink-fit, or press-fit on the unit base  61 , thereby eliminating positional shift of the stator core  52  relative to the unit base  61  both in the circumferential direction and in the axial direction. 
     The casing  64  has a radially inner storage space in which the electrical components  62  are disposed. The electrical components  62  are arranged to surround the rotating shaft  11  within the storage space. The casing  64  functions as a storage space forming portion. The electrical components  62  include semiconductor modules  66 , a control board  67 , and a capacitor module  68  which constitute an inverter circuit. 
     The unit base  61  serves as a stator holder (i.e., an armature holder) which is arranged radially inside the stator  50  and retains the stator  50 . The housing  30  and the unit base  61  define a motor housing for the rotating electrical machine  10 . In the motor housing, the retainer  23  is secured to a first end of the housing  30  which is opposed to a second end of the housing  30  through the rotor  40  in the axial direction. The second end of the housing  30  and the unit base  61  are joined together. For instance, in an electric-powered vehicle, such as an electric automobile, the motor housing is attached to a side of the vehicle to install the rotating electrical machine  10  in the vehicle. 
     The inverter unit  60  will be also described using  FIG.  6    that is an exploded view in addition to  FIGS.  1  to  5   . 
     The casing  64  of the unit base  61  includes a cylinder  71  and an end surface  72  that is one of ends of the cylinder  71  which are opposed to each other in the axial direction of the cylinder  71  (i.e., the end of the casing  64  closer to the bearing unit  20 ). The end of the cylinder  71  opposed to the end surface  72  in the axial direction is shaped to fully open to the opening  65  of the end plate  63 . 
     The end surface  72  has formed in the center thereof a circular hole  73  through which the rotating shaft  11  is insertable. The hole  73  has fitted therein a sealing member  171  which hermetically seals an air gap between the hole  73  and the outer periphery of the rotating shaft  11 . The sealing member  171  is preferably implemented by, for example, a resinous slidable seal. 
     The cylinder  71  of the casing  64  serves as a partition which isolates the rotor  40  and the stator  50  arranged radially outside the cylinder  71  from the electrical components  62  arranged radially inside the cylinder  71 . The rotor  40 , the stator  50 , and the electrical components  62  are arranged to be radially aligned from the inside of the cylinder  71  to the outside thereof. 
     The electrical components  62  are electrical devices making up the inverter circuit equipped with a motor function and a generator function. The motor function is to deliver electrical current to the phase windings of the stator coil  51  in a given sequence to turn the rotor  40 . The generator function is to receive a three-phase ac current flowing through the stator coil  51  in response to the rotation of the rotating shaft  11  and generate and output electrical power. The electrical components  62  may be engineered to perform either one of the motor function and the generator function. In a case where the rotating electrical machine  10  is used as a power source for a vehicle, the generator function serves as a regenerative function to output a regenerated electrical power. 
     Specifically, the electrical components  62 , as demonstrated in  FIG.  4   , include the capacitor module  68 , which has a hollow cylindrical shape, arranged around the rotating shaft  11 , and the semiconductor modules  66  mounted on the outer peripheral surface of the capacitor module  68 . The capacitor module  68  has a plurality of smoothing capacitors  68   a  connected in parallel to each other. 
     Specifically, each of the capacitors  68   a  is implemented by a stacked-film capacitor which is made of a plurality of film capacitors stacked in a trapezoidal shape in cross section. In this embodiment, twelve capacitors  68   a  are arranged annually to constitute the capacitor module  68 . 
     The capacitors  68   a  may be produced by preparing a long film which has a given width and is made of a stack of films and cutting the long film into isosceles trapezoids each of which has a height identical with the width of the long film and whose short bases and long bases are alternately arranged. Mounting electrodes to the thus produced capacitor devices enables the capacitors  68   a  to be completed. 
     Each semiconductor module  66  includes, for example, a semiconductor switch, such as a MOSFET or an IGBT and is of substantially a planar shape. In this embodiment, the rotating electrical machine  10  is, as described above, equipped with the first and second sets of three-phase windings and has the inverter circuits, one for each set of the three-phase windings. The electrical components  62 , therefore, include a total of twelve semiconductor modules  66  which are arranged in an annular form to make up a semiconductor module group  66 A. 
     The semiconductor modules  66  are interposed between the cylinder  71  of the casing  64  and the capacitor module  68 . The semiconductor module group  66 A has an outer peripheral surface placed in contact with an inner peripheral surface of the cylinder  71 . The semiconductor module group  66 A also has an inner peripheral surface placed in contact with an outer peripheral surface of the capacitor module  68 . This causes heat, as generated in the semiconductor modules  66 , to be transferred to the end plate  63  through the casing  64 , so that it is dissipated from the end plate  63 . 
     The semiconductor module group  66 A preferably has spacers  69  disposed radially outside the outer peripheral surface thereof, i.e., between the semiconductor modules  66  and the cylinder  71 . 
     A combination of the capacitor modules  68  is so arranged as to have a regular dodecagonal section extending perpendicular to the axial direction thereof, while the inner periphery of the cylinder  71  has a circular transverse section. The spacers  69  are, therefore, each shaped to have a flat inner peripheral surface and a curved outer peripheral surface. 
     The spacers  69  may alternatively be formed integrally with each other in an annular shape and disposed radially outside the semiconductor module group  66 A. The spacers  69  are highly thermally conductive and made of, for example, metal, such as aluminum or heat dissipating gel sheet. The inner periphery of the cylinder  71  may alternatively be shaped to have a dodecagonal transverse section like the capacitor modules  68 . In this case, the spacers  69  are each preferably shaped to have a flat inner peripheral surface and a flat outer peripheral surface. 
     In this embodiment, the cylinder  71  of the casing  64  has formed therein a coolant path  74  through which coolant flows. The heat generated in the semiconductor modules  66  is also released to the coolant flowing in the coolant path  74 . In other words, the casing  64  is equipped with a cooling mechanism. The coolant path  74  is, as clearly illustrated in  FIGS.  3  and  4   , formed in an annular shape and surrounds the electrical components  62  (i.e., the semiconductor modules  66  and the capacitor module  68 ). The semiconductor modules  66  are arranged along the inner peripheral surface of the cylinder  71 . The coolant path  74  is laid to overlap the semiconductor modules  66  in the radial direction. 
     The stator  50  is arranged outside the cylinder  71 . The electrical components  62  are arranged inside the cylinder  71 . This layout causes the heat to be transferred from the stator  50  to the outer side of the cylinder  71  and also transferred from the electrical components  62  (e.g., the semiconductor modules  66 ) to the inner side of the cylinder  71 . It is possible to simultaneously cool the stator  50  and the semiconductor modules  66 , thereby facilitating dissipation of thermal energy generated by heat-generating members of the rotating electrical machine  10 . 
     Further, at least one of the semiconductor modules  66 , which constitute part or all of the inverter circuits serving to energize the stator coil  51  to drive the rotating electrical machine, is arranged in a region surrounded by the stator core  52  disposed radially outside the cylinder  71  of the casing  64 . Preferably, one of the semiconductor modules  66  may be arranged fully inside the region surrounded by the stator core  52 . More preferably, all the semiconductor modules  66  may be arranged fully in the region surrounded by the stator core  52 . 
     At least a portion of the semiconductor modules  66  is arranged in a region surrounded by the coolant path  74 . Preferably, all the semiconductor modules  66  may be arranged in a region surrounded by the yoke  141 . 
     The electrical components  62  include an insulating sheet  75  disposed on one of axially opposed end surfaces of the capacitor module  68 , and a wiring module  76  disposed on the other end surface of the capacitor module  68 . The capacitor module  68  has two axially-opposed end surfaces: a first end surface and a second end surface. The first end surface of the capacitor module  68  closer to the bearing unit  20  faces the end surface  72  of the casing  64  and is laid on the end surface  72  through the insulating sheet  75 . The second end surface of the capacitor module  68  closer to the opening  65  has the wiring module  76  mounted thereon. 
     The wiring module  76  includes a resin-made circular plate-shaped body  76   a  and a plurality of bus bars  76   b  and  76   c  embedded in the body  76   a . The bus bars  76   b  and  76   c  electrically connect the semiconductor modules  66  and the capacitor module  68  together. Specifically, the semiconductor modules  66  are equipped with connecting pins  66   a  extending from axial ends thereof. The connecting pins  66   a  connect with the bus bars  76   b  radially outside the body  76   a . The bus bars  76   c  extend away from the capacitor module  68  radially outside the body  76   a  and have top ends connecting with the wiring members  79  (see  FIG.  2   ). 
     The capacitor module  68 , as described above, has the insulating sheet  75  mounted on the first end surface thereof. The capacitor module  68  also has the wiring module  76  mounted on the second end surface thereof. The capacitor module  68 , therefore, has first and second heat dissipating paths which respectively extend from the first and second end surfaces of the capacitor module  68  to the end surface  72  and the cylinder  71 . 
     Specifically, the first heat dissipating path is defined which extends from the first end surface to the end surface  72 . The second heat dissipating path is defined which extends from the second end surface to the cylinder  71 . This enables the heat to be released from the end surfaces of the capacitor module  68  other than the outer peripheral surface on which the semiconductor modules  66  are arranged. In other words, it is possible to dissipate the heat not only in the radial direction, but also in the axial direction. 
     The capacitor module  68  is of a hollow cylindrical shape, and the rotating shaft  11  is arranged within the capacitor module  68  at a given interval away from the inner periphery of the capacitor module  68 , so that heat generated by the capacitor module  68  will be dissipated from the hollow cylindrical space. The rotation of the rotating shaft  11  usually produces a flow of air, thereby enhancing cooling effects. 
     The control board  67 , which has a discotic shape, is mounted to the wiring module  76 . The control board  67  includes a printed circuit board (PCB) on which given wiring patterns are formed and also has ICs and the control device  77  mounted thereon. The control device  77  serves as a controller and is comprised of a microcomputer. The control board  67  is secured to the wiring module  76  using fasteners, such as screws. The control board  67  has formed in the center thereof a hole  67   a  through which the rotating shaft  11  passes. 
     The wiring module  76  has a first surface and a second surface opposed to each other in the axial direction, that is, a thickness-wise direction of the wiring module  76 . The first surface faces the capacitor module  68 . The wiring module  76  has the control board  67  mounted on the second surface thereof. The bus bars  76   c  of the wiring module  76  extend from one of surfaces of the control board  67  to the other. The control board  67  may have cut-outs for avoiding physical interference with the bus bars  76   c . For instance, the control board  67  may have the cut-outs formed in portions of the circular outer edge thereof. 
     The electrical components  62  are, as described already, arranged inside a space surrounded by the casing  64 . The housing  30 , the rotor  40 , and the stator  50  are disposed outside the space in the form of layers. This structure serves to shield against electromagnetic noise generated in the inverter circuits. 
     Specifically, each inverter circuit works to control switching operations of the corresponding semiconductor modules  66  in a PWM control mode using a given carrier frequency. The switching operations usually generate electromagnetic noise against which the housing  30 , the rotor  40 , and the stator  50  which are arranged outside the electrical components  62  shield. 
     Further, at least a portion of the semiconductor modules  66  is arranged inside the region surrounded by the stator core  52  located radially outside the cylinder  71  of the casing  64 , thereby minimizing adverse effects of magnetic flux generated by the semiconductor modules  66  on the stator coil  51  as compared with a case where the semiconductor modules  66  and the stator coil  51  are arranged without the stator core  52  interposed therebetween. 
     The magnetic flux created by the stator coil  51  also hardly affects the semiconductor modules  66 . It is more effective that the whole of the semiconductor modules  66  are located in the region surrounded by the stator core  52  disposed radially outside the cylinder  71  of the casing  64 . When at least a portion of the semiconductor modules  66  may be surrounded by the coolant path  74 , it offers a beneficial advantage that the heat produced by the stator coil  51  or the magnet unit  42  is prevented from reaching the semiconductor modules  66 . 
     The cylinder  71  has through-holes  78  which are formed near the end plate  63  and through which the wiring members  79  (see  FIG.  2   ) respectively pass to electrically connect the stator  50  disposed outside the cylinder  71  and the electrical components  62  arranged inside the cylinder  71 . The wiring members  79 , as illustrated in  FIG.  2   , connect with ends of the stator coil  51  and with the bus bars  76   c  of the wiring module  76  using crimping or welding techniques. 
     The wiring members  79  are implemented by, for example, bus bars whose joining surfaces are preferably flattened. A single through-hole  78  or a plurality of through-holes  78  are preferably provided. This embodiment has two through-holes  78 . The use of the two through-holes  78  facilitates the ease with which terminals extending from the two sets of the three-phase windings are connected by the wiring members  79 , and is suitable for achieving multi-phase wire connections. 
     The rotor  40  and the stator  50  are, as described already in  FIG.  4   , arranged within the housing  30  in this order in a radially inward direction. The inverter unit  60  is arranged radially inside the stator  50 . 
     If a radius of the inner periphery of the housing  30  is defined as d, the rotor  40  and the stator  50  are located radially outside a distance of d×0.705 away from the center of rotation of the rotor  40 . If a region located radially inside the inner periphery of the stator  50  (i.e., the inner circumferential surface of the stator core  52 ) is defined as a first region X 1 , and a region radially extending from the inner periphery of the stator  50  to the housing  30  is defined as a second region X 2 , an area of a transverse section of the first region X 1  is set greater than that of the second region X 2 . As viewed in a region where the magnet unit  42  of the rotor  40  overlaps the stator coil  51 , the volume of the first region X 1  is larger than that of the second region X 2 . 
     The rotor  40  and the stator  50  are fabricated as a magnetic circuit component assembly. In the housing  30 , the first region X 1 , which is located radially inside the inner peripheral surface of the magnetic circuit component assembly, is larger in volume than the region X 2 , which lies between the inner peripheral surface of the magnetic circuit component assembly and the housing  30  in the radial direction. 
     Next, the structures of the rotor  40  and the stator  50  will be described below in more detail. 
     Typical rotating electrical machines are known which are equipped with a stator with an annular stator core; the annular stator core is made of a stack of steel plates. The stator has stator windings wound in a plurality of slots arranged in a circumferential direction of the stator core. 
     Specifically, the stator core has teeth each extending in a corresponding radial direction thereof at a corresponding given interval away from a yoke. Each slot is formed between a corresponding pair of two radially adjacent teeth. In each slot, a plurality of conductors are arranged in the radial direction in the form of layers to form the stator windings. 
     However, the above described stator structure has a possibility that, when stator windings are energized, an increase in magnetomotive force based on the energized stator windings may result in magnetic saturation in the teeth of the stator core, thereby restricting torque density in the rotating electrical machine. In other words, rotational flux, as created by the energization of the stator windings of the stator core, may concentrate on the teeth, resulting in a possibility of causing magnetic saturation. 
     Generally, IPM (Interior Permanent Magnet) rotors are known which have a structure in which permanent magnets are arranged on a d-axis of a d-q axis coordinate system in a rotor core, and a portion of the rotor core is placed on a q-axis of the d-q axis coordinate system. Excitation of a stator winding near the d-axis causes an excited magnetic flux to flow from a stator to a rotor according to Fleming&#39;s rules. This causes magnetic saturation to occur widely in the rotor core on the q-axis. 
       FIG.  7    is a graphic torque diagram which demonstrates a relationship between an ampere-turn (AT) representing a magnetomotive force created by a stator winding and a torque density (Nm/L). A broken line indicates characteristics of a typical IPM rotor-rotating electrical machine.  FIG.  7    shows that, in the typical rotating electrical machine, an increase in magnetomotive force in a stator will cause magnetic saturation to occur at two places; one of the two places is each tooth between the corresponding adjacent pair of slots, and the other thereof is a q-axis core, which is a portion of the rotor core on the q-axis. This may result in a restriction of an increase in torque. In this way, a design value of the ampere-turn is restricted at A 1  in the typical rotating electrical machine. 
     In order to alleviate the above problem in this embodiment, the rotating electrical machine  10  is designed to have an additional structure, as will be described below, which aims to eliminate the restriction arising from the magnetic saturation. 
     Specifically, as a first measure, the stator  50  is designed to have a slot-less structure for eliminating the magnetic saturation occurring in the teeth of the stator core of the stator and also to use an SPM (Surface Permanent Magnet) rotor for eliminating the magnetic saturation occurring in a q-axis core of the IPM rotor. The first measure serves to eliminate the above described two places where the magnetic saturation occurs, but however, may result in a decrease in torque in a low-current region (see an alternate long and short dash line in  FIG.  7   ). 
     For alleviating this problem, as a second measure, the rotating electrical machine  10  employs a polar anisotropic structure to increase a magnetic path of magnets in the magnet unit  42  of the rotor  40  to thereby enhance a magnetic force. This will result in an increase in a magnetic flux in the SPM rotor to minimize the torque decrease. 
     Additionally, as a third measure, the rotating electrical machine  10  employs a flattened conductor structure to decrease a thickness of conductors of the coil side portion  53  of the stator coil  51  in the radial direction of the stator  50  for compensating for the torque decrease. The above magnetic force-enhanced polar anisotropic structure would result in a flow of large eddy current in the stator coil  51  facing the magnet unit  42 . 
     From this viewpoint, the third measure is to employ the flattened conductor structure in which the conductors have a decreased thickness in the radial direction, thereby minimizing the generation of the eddy current in the stator coil  51  in the radial direction. The above first to third structures are, as indicated by a solid line in  FIG.  7   , expected to greatly improve the torque characteristics using high-magnetic force magnets and also alleviate a risk of generation of a large eddy current resulting from the use of the high-magnetic force magnets. 
     Additionally, as a fourth measure, the rotating electrical machine  10  employs a magnet unit, which has a polar anisotropic structure to create a magnetic density distribution approximating a sine wave. This increases a sine wave matching percentage using pulse control, as will be described later, to thereby enhance the torque and also results in a moderate change in magnetic flux, thereby minimizing an eddy-current loss (i.e., a copper loss caused by eddy current) as compared with radial magnets. 
     The sine wave matching percentage will be described below. 
     The sine wave matching percentage may be derived by comparing a waveform, a cycle, and a peak value of a surface magnetic flux density distribution measured by actually moving a magnetic flux probe on a surface of a magnet with those of a sine wave. The since wave matching percentage is given by a percentage of an amplitude of a primary waveform that is a waveform of a fundamental wave in a rotating electrical machine to that of the actually measured waveform, that is, an amplitude of the sum of the fundamental wave and harmonic components. 
     An increase in the sine wave matching percentage will cause the waveform in the surface magnetic flux density distribution to approach the waveform of the sine wave. When an electrical current of a primary sine wave is delivered by an inverter to a rotating electrical machine equipped with magnets having an improved sine wave matching percentage, it will cause a large degree of torque to be produced, combined with the fact that the waveform in the surface magnetic flux density distribution of the magnet is close to the waveform of a sine wave. The surface magnetic flux density distribution may alternatively be derived using electromagnetic analysis according to Maxwell&#39;s equations. 
     As a fifth measure, the stator coil  51  is designed to have a conductor strand structure made of a bundle of wires. In the conductor strand structure of the stator coil  51 , the wires are connected parallel to each other, thus enabling a high current or large amount of current to flow in the stator coil  51  and also minimizing an eddy current occurring in the conductors widened in the circumferential direction of the stator  50  more effectively than the third measure in which the conductors are flattened in the radial direction because each of the wires has a decreased transverse sectional area. 
     The use of the bundle of the wires will cancel an eddy current arising from magnetic flux occurring according to Ampere&#39;s circuital law in response to the magnetomotive force produced by the conductors. 
     The use of the fourth and fifth measures minimizes the eddy-current loss resulting from the high magnetic force produced by the high-magnetic force magnets provided by the second measure and also enhance the torque. 
     The slot-less structure of the stator  50 , the flattened conductor structure of the stator coil  51 , and the polar anisotropic structure of the magnet unit  42  will be described below. 
     The slot-less structure of the stator  50  and the flattened conductor structure of the stator coil  51  will first be discussed.  FIG.  8    is a transverse sectional view illustrating the rotor  40  and the stator  50 .  FIG.  9    is a partially enlarged view illustrating the rotor  40  and the stator  50  in  FIG.  8   .  FIG.  10    is a transverse sectional view of the stator  50  taken along the line X-X in  FIG.  11   .  FIG.  11    is a longitudinal sectional view of the stator  50 .  FIG.  12    is a perspective view of the stator coil  51 .  FIGS.  8  and  9    indicate directions of magnetization of magnets of the magnet unit  42  using arrows. 
     The stator core  52  has, as clearly illustrated in  FIGS.  8  to  11   , a cylindrical shape and is comprised of a plurality of magnetic steel plates stacked in the axial direction of the stator core  52  to have a given thickness in a radial direction of the stator core  52 . The stator coil  51  is mounted on the outer periphery of the stator core  52  which faces the rotor  40 . The outer peripheral surface of the stator core  52  facing the rotor  40  serves as a conductor mounting portion (i.e., a conductor area). The outer peripheral surface of the stator core  52  is shaped as a curved surface without any irregularities. 
     A plurality of conductor groups  81  are arranged on the outer peripheral surface of the stator core  52  at given intervals away from each other in the circumferential direction of the stator core  52 . The stator core  52  functions as a back yoke that is a portion of a magnetic circuit working to rotate the rotor  40 . The stator  50  is designed to have a structure in which no tooth (i.e., no portion of a core) made of a soft magnetic material is disposed between each pair of adjacent conductor groups  81  in the circumferential direction (i.e., the slot-less structure). 
     In this embodiment, a resin material of the sealing member  57  is disposed in the space or gap  56  between each pair of adjacent conductor groups  81 . In other words, the stator  50  has a conductor-to-conductor member which is disposed between the conductor groups  81  arranged adjacent each other in the circumferential direction of the stator  50  and made of a non-magnetic material. The conductor-to-conductor members serve as the sealing members  57 . 
     Before the sealing members  57  are placed to seal the gaps  56 , the conductor groups  81  are arranged in the circumferential direction radially outside the stator core  52  at a given interval away from each other through the gaps  56  that are conductor-to-conductor regions. This makes up the slot-less structure of the stator  50 . In other words, each of the conductor groups  81  is, as described later in detail, made of two conductors  82 . An interval between a respective two of the conductor groups  81  arranged adjacent each other in the circumferential direction of the stator  50  is occupied only by a non-magnetic material. The non-magnetic material, as referred to herein, includes a non-magnetic gas, such as air, or a non-magnetic liquid. In the following discussion, the sealing members  57  will also be referred to as conductor-to-conductor members. 
     The structure, as referred to herein, in which each of the teeth is disposed between the corresponding adjacent pair of the conductor groups  81  arrayed in the circumferential direction means that each of the teeth has a given thickness in the radial direction and a given width in the circumferential direction of the stator  50 , so that a portion of the magnetic circuit, that is, a magnet magnetic path, lies between each adjacent pair of the conductor groups  81 . 
     In contrast, the structure in which no tooth lies between the adjacent conductor groups  81  means that there is no magnetic circuit between each adjacent pair of the conductor groups  81 . 
     The stator coil (i.e., an armature coil)  51 , as illustrated in  FIG.  10   , has a given thickness T 2  (which will also be referred to below as a first dimension) and a width W 2  (which will also be referred to below as a second dimension). The thickness T 2  is given by a minimum distance between an outer side surface and an inner side surface of the stator coil  51  which are opposed to each other in the radial direction of the stator  50 . 
     The width W 2  is given by a dimension of a portion of the stator coil  51  which functions as one of multiple phases (i.e., the U-phase, the V-phase, the W-phase, the X-phase, the Y-phase, and the Z-phase in this embodiment) of the stator coil  51  in the circumferential direction. Specifically, in a case where one adjacent pair of the conductor groups  81  in the circumferential direction in  FIG.  10    serves as a corresponding one of the three phases, for example, the U-phase winding, a distance between circumferentially outermost ends of the conductor groups  81  of the circumferentially adjacent pair of the conductor groups  81  is the width W 2 . The thickness T 2  is smaller than the width W 2 . 
     The thickness T 2  is preferably set smaller than the sum of widths of the two conductor groups  81  within the width W 2 . If the stator coil  51  (more specifically, the conductor  82 ) is designed to have a true circular transverse section, an oval transverse section, or a polygonal transverse section, the cross section of the conductor  82  taken in the radial direction of the stator  50  may be shaped to have a maximum dimension W 12  in the radial direction of the stator  50  and a maximum dimension W 11  in the circumferential direction of the stator  50 . 
     The stator coil  51  is, as can be seen in  FIGS.  10  and  11   , sealed by the sealing members  57  which are formed by a synthetic resin mold. Specifically, the stator coil  51  and the stator core  52  are put in a mold together when the sealing members  57  are molded by the resin. The resin may be considered as a non-magnetic material or an equivalent thereof whose Bs (saturation magnetic flux density) is zero. 
     As a transverse section is viewed in  FIG.  10   , the sealing members  57  are provided by placing synthetic resin in the gaps  56  between the conductor groups  81 . The sealing members  57  serve as insulators arranged between the conductor groups  81 . In other words, each of the sealing members  57  functions as an insulator in one of the gaps  56 . The sealing members  57  occupy a region which is located radially outside the stator core  52 , and includes all the conductor groups  81 , in other words, which is defined to have a thickness dimension larger than that of each of the conductor groups  81  in the radial direction. 
     As a longitudinal section is viewed in  FIG.  11   , the sealing members  57  lie to occupy a region including the turns  84  of the stator coil  51 . Radially inside the stator coil  51 , the sealing members  57  lie in a region including at least a portion of the axially opposed ends of the stator core  52 . In this case, the stator coil  51  is fully sealed by the resin except for the ends of each phase winding, i.e., terminals joined to the inverter circuits. 
     The structure in which the sealing members  57  are disposed in the region including the ends of the stator core  52  enables the sealing members  57  to compress the stack of the steel plates of the stator core  52  inwardly in the axial direction. In other words, the sealing members  57  work to firmly retain the stack of the steel plates of the stator core  52 . In this embodiment, the inner peripheral surface of the stator core  52  is not sealed using resin, but however, the whole of the stator core  52  including the inner peripheral surface may be sealed using resin. 
     In a case where the rotating electrical machine  10  is used as a power source for a vehicle, the sealing members  57  are preferably made of a high heat-resistance fluororesin, epoxy resin, PPS resin, PEEK resin, LCP resin, silicon resin, PAI resin, or PI resin. In terms of a linear coefficient expansion to minimize breakage of the sealing members  57  due to an expansion difference, the sealing members  57  are preferably made of the same material as that of an outer film of the conductors of the stator coil  51 . The silicon resin whose linear coefficient expansion is twice or more those of other resins is preferably excluded from the material of the sealing members  57 . In a case of electrical products, such as electric vehicles equipped with no combustion engine, PPO resin, phenol resin, or FRP resin which resists 180° C. may be used, except in fields where an ambient temperature of the rotating electrical machine is expected to be lower than 100° C. 
     The degree of torque outputted by the rotating electrical machine  10  is usually proportional to the degree of magnetic flux. In a case where a stator core is equipped with teeth, a maximum amount of magnetic flux in the stator core is restricted depending upon the saturation magnetic flux density in the teeth, while in a case where the stator core is not equipped with teeth, the maximum amount of magnetic flux in the stator core is not restricted. Such a structure is, therefore, useful for increasing an amount of electrical current delivered to the stator coil  51  to increase the degree of torque produced by the rotating electrical machine  10 . 
     This embodiment employs the slot-less structure in which the stator  50  is not equipped with teeth, thereby resulting in a decrease in inductance of the stator  50 . Specifically, a stator of a typical rotating electrical machine in which conductors are disposed in slots isolated by teeth from each other has an inductance of approximately 1 mH, while the stator  50  in this embodiment has a decreased inductance of 5 to 60 pH. The rotating electrical machine  10  in this embodiment is of an outer rotor type, but has a decreased inductance of the stator  50  to decrease a mechanical time constant Tm. In other words, the rotating electrical machine  10  is capable of outputting a high degree of torque and designed to have a decreased value of the mechanical time constant Tm. If inertia is defined as J, inductance is defined as L, torque constant is defined as Kt, and back electromotive force constant is defined as Ke, the mechanical time constant Tm is calculated according to the equation of Tm=(J×L)/(Kt×Ke). This shows that a decrease in inductance L will result in a decrease in mechanical time constant Tm. 
     Each of the conductor groups  81  arranged radially outside the stator core  52  is made of a plurality of conductors  82  whose transverse section is of a flattened rectangular shape and which are disposed on one another in the radial direction of the stator core  52 . Each of the conductors  82  is oriented to have a transverse section meeting a relation of radial dimension&lt;circumferential dimension. This causes each of the conductor groups  81  to be thin in the radial direction. A conductive region of the conductor group  81  also extends inside a region occupied by teeth of a typical stator. This creates a flattened conductive region structure in which a sectional area of each of the conductors  82  is increased in the circumferential direction, thereby alleviating a possibility that the amount of thermal energy may be increased by a decrease in sectional area of a conductor arising from flattening of the conductor. A structure in which a plurality of conductors are arranged in the circumferential direction and connected in parallel to each other is usually subjected to a decrease in sectional area of the conductors by a thickness of a coated layer of the conductors, but however, has beneficial advantages obtained for the same reasons as described above. In the following discussion, each of the conductor groups  81  or each of the conductors  82  will also be referred to as a conductive member. 
     The stator  50  in this embodiment is, as described already, designed to have no slots, thereby enabling the stator coil  51  to be designed to have a conductive region of an entire circumferential portion of the stator  50  which is larger in size than a non-conductive region unoccupied by the stator coil  51  in the stator  50 . 
     In typical rotating electrical machines for vehicles, a ratio of the conductive region/the non-conductive region is usually one or less. In contrast, this embodiment has the conductor groups  81  arranged to have the conductive region substantially identical in size with or larger in size than the non-conductive region. If the conductor region, as illustrated in  FIG.  10   , occupied by the conductor  82  (i.e., the straight section  83  which will be described later in detail) in the circumferential direction is defined as WA, and a conductor-to-conductor region that is an interval between a respective adjacent two of the conductors  82  is defined as WB, the conductor region WA is larger in size than the conductor-to-conductor region WB in the circumferential direction. 
     The conductor group  81  of the stator coil  51  has a thickness in the radial direction thereof which is smaller than a circumferential width of a portion of the stator coil  51  which lies in a region of one magnetic pole and serves as one of the phases of the stator coil  51 . 
     In the structure in which each of the conductor groups  81  is made up of the two conductors  82  stacked in the form of two layers lying on each other in the radial direction, and the two conductor groups  81  are arranged in the circumferential direction within a region of one magnetic pole for each phase, a relation of Tc×2&lt;Wc×2 is met where Tc is the thickness of each of the conductors  82  in the radial direction, and Wc is the width of each of the conductors  82  in the circumferential direction. 
     In another structure in which each of the conductor groups  81  is made up of the two conductors  82 , and each of the conductor groups  81  lies within the region of one magnetic pole for each phase, a relation of Tc×2&lt;Wc is preferably met. 
     In other words, in the stator coil  51  which is designed to have conductor portions (i.e., the conductor groups  81 ) arranged at a given interval away from each other in the circumferential direction, the thickness of each conductor portion (i.e., the conductor group  81 ) in the radial direction is set smaller than the width of a portion of the stator coil  51  lying in the region of one magnetic pole for each phase in the circumferential direction. 
     In other words, each of the conductors  82  is preferably shaped to have the thickness Tc in the radial direction which is smaller than the width Wc in the circumferential direction. The thickness 2 Tc of each of the conductor groups  81  each made of a stack of the two conductors  82  in the radial direction is preferably smaller than the width Wc of each of the conductor groups  81  in the circumferential direction. 
     The degree of torque produced by the rotating electrical machine  10  is substantially inversely proportional to the thickness of the stator core  52  in the radial direction. The conductor groups  81  arranged radially outside the stator core  52  are, as described above, designed to have the thickness decreased in the radial direction. This design is useful in increasing the degree of torque outputted by the rotating electrical machine  10 . This is because a distance between the magnet unit  42  of the rotor  40  and the stator core  52  (i.e., a distance in which there is no iron) may be decreased to decrease the magnetic resistance. This enables interlinkage magnetic flux in the stator core  52  produced by the permanent magnets to be increased to enhance the torque. 
     The decrease in thickness of the conductor groups  81  facilitates the ease with which a magnetic flux leaking from the conductor groups  81  is collected in the stator core  52 , thereby preventing the magnetic flux from leaking outside the stator core  52  without being used for enhancing the torque. This avoids a drop in magnetic force arising from the leakage of the magnetic flux and increases the interlinkage magnetic flux in the stator core  52  produced by the permanent magnets, thereby enhancing the torque. 
     Each of the conductors  82  is made of a coated conductor formed by covering the surface of the conductor body  82   a  with the coating  82   b . The conductors  82  stacked on one another in the radial direction are, therefore, insulated from each other. Similarly, the conductors  82  are insulated from the stator core  52 . 
     The insulating coating  82   b  may be a coating of each wire  86 , as will be described later in detail, in a case where each wire  86  is made of wire with a self-bonded coating or may be made by an additional insulator disposed on a coating of each wire  86 . Each phase winding made of the conductors  82  is insulated by the coating  82   b  except an exposed portion thereof for joining purposes. The exposed portion includes, for example, an input or an output terminal or a neutral point in a case of a star connection. The conductor groups  81  arranged adjacent each other in the radial direction are firmly adhered to each other using resin or self-bonding coated wire, thereby minimizing a possibility of insulation breakdown, mechanical vibration, or noise caused by rubbing of the conductors  82 . 
     In this embodiment, the conductor body  82   a  is made of a collection of a plurality of wires  86 . Specifically, the conductor body  82   a  is, as can be seen in  FIG.  13   , made of a strand of the wires  86  each being twisted. Each of the wires  86  is, as can be seen in  FIG.  14   , made of a bundle of a plurality of thin conductive fibers  87 . 
     For instance, each of the wires  86  is made of a complex of CNT (carbon nanotube) fibers. The CNT fibers include boron-containing microfibers in which at least a portion of carbon is substituted with boron. Instead of the CNT fibers that are carbon-based microfibers, vapor grown carbon fiber (VGCF) may be used, but however, the CNT fiber is preferable. The surface of the wire  86  is covered with a layer of insulating polymer, such as enamel. The surface of the wire  86  is preferably covered with an enamel coating, such as polyimide coating or amide-imide coating. 
     The conductors  82  constitute n-phase windings of the stator coil  51 . The wires  86  of each of the conductors  82 , i.e., the conductor body  82   a  of each of the conductors  82 , are placed in contact with each other. Each of the conductors  82  has one or more portions which are formed by twisting the wires  86  and define one or more portions of a corresponding one of the phase-windings. A resistance value between the twisted wires  86  is larger than that of each of the wires  86 . In other words, the respective adjacent two wires  86  have a first electrical resistivity in a direction in which the wires  86  are arranged adjacent each other. Each of the wires  86  has a second electrical resistivity in a lengthwise direction of the wire  86 . 
     The first electrical resistivity is larger than the second electrical resistivity. Each of the conductors  82  may be made of an assembly of wires, i.e., the twisted wires  86  covered with insulating members whose first electrical resistivity is very high. The conductor body  82   a  of each of the conductors  82  is made of a strand of the twisted wires  86 . 
     The conductor body  82   a  is, as described above, made of the twisted wires  86 , thereby reducing an eddy current created in each of the wires  86 , which reduces an eddy current in the conductor body  82   a . Each of the wires  86  is twisted, thereby causing each of the wires  86  to have portions where directions of applied magnetic field are opposite each other, which cancels a back electromotive force. This results in a reduction in the eddy current. Particularly, each of the wires  86  is made of the conductive fibers  87 , thereby enabling the conductive fibers  87  to be thin and also enabling the number of times the conductive fibers  87  are twisted to be increased, which enhances the reduction in eddy current. 
     How to insulate the wires  86  from each other is not limited to the above described use of the polymer insulating layer, but the contact resistance may be used to resist a flow of current between the wires  86 . In other words, the above beneficial advantage is obtained by a difference in potential arising from a difference between the resistance between the twisted wires  86  and the resistance of each of the wires  86  as long as the resistance between the wires  86  is larger than that of each of the wires  86 . For instance, the contact resistance may be increased by using production equipment for the wires  86  and production equipment for the stator  50  (i.e., an armature) of the rotating electrical machine  10  as discrete devices to cause the wires  86  to be oxidized during a transport time or a work interval. 
     Each of the conductors  82  is, as described above, of a low-profile or flattened rectangular shape in cross section. The conductors  82  are arranged in the radial direction. Each of the conductors  82  is made of a strand of the wires  86  each of which is formed by a self-bonding coating wire equipped with, for example, a fusing or bonding layer or an insulating layer and which are twisted with the bonding layers fused together. Each of the conductors  82  may alternatively be made by forming twisted wires with no bonding layer or twisted self-bonding coating wires into a desired shape using synthetic resin. The insulating coating  82   b  of each of the conductors  82  may have a thickness of 80 μm to 100 μm which is larger than that of a coating of typical wire (i.e., 5 μm to 40 μm). In this case, a required degree of insulation between the conductors  82  is achieved even if no insulating sheet is interposed between the conductors  82 . 
     It is also advisable that the insulating coating  82   b  be higher in degree of insulation than the insulating layer of the wire  86  to achieve insulation between the phase windings. For instance, the polymer insulating layer of the wire  86  has a thickness of, for example, 5 μm. In this case, the thickness of the insulating coating  82   b  of the conductor  82  is preferably selected to be 80 μm to 100 μm to achieve the insulation between the phase windings. 
     Each of the conductors  82  may alternatively be made of a bundle of the untwisted wires  86 . In brief, each of the conductors  82  may be made of a bundle of the wires  86  whose entire lengths are twisted, whose portions are twisted, or whose entire lengths are untwisted. Each of the conductors  82  constituting the conductor portion is, as described above, made of a bundle of the wires  86 . The resistance between the wires  86  is larger than that of each of the wires  86 . 
     The conductors  82  are each bent and arranged in a given pattern in the circumferential direction of the stator coil  51 , thereby forming the phase-windings of the stator coil  51 . The stator coil  51 , as illustrated in  FIG.  12   , includes the coil side portion  53  and the coil ends  54  and  55 . The conductors  82  have the straight sections  83  which extend straight in the axial direction of the stator coil  51  and form the coil side portion  53 . 
     The conductors  82  have the turns  84  which are arranged outside the coil side portion  53  in the axial direction and form the coil ends  54  and  55 . Each of the conductor  82  is made of a wave-shaped string of conductor formed by alternately arranging the straight sections  83  and the turns  84 . The straight sections  83  are arranged to face the magnet unit  42  in the radial direction. The straight sections  83  are arranged at given intervals away from one another and joined together using the turns  84  located outside the magnet unit  42  in the axial direction. The straight sections  83  correspond to a magnet facing portion. 
     In this embodiment, the stator coil  51  is shaped in the form of an annular distributed coil. In the coil side portion  53 , the straight sections  83  are arranged at intervals away from one another for each phase; each of the intervals corresponds to a corresponding pole pair of the magnet unit  42 . 
     In each of the coil ends  54  and  55 , the straight sections  83  for each phase are joined together by the turns  84 , each of which is of a V-shape. The straight sections  83 , which are paired for each pole pair, are opposite to each other in a direction of flow of electrical current. 
     Combination of pairs of straight sections  83 , each joined together by a corresponding turn  84 , in the coil end  53  is different from combination of pairs of straight sections  83 , each joined together by a corresponding turn  84 , in the coil end  54 . The joints of the straight sections  83  by the turns  84  are arranged in the circumferential direction on each of the coil ends  54  and  55  to complete the stator winding in a hollow cylindrical shape. 
     More specifically, the stator coil  51  is made up of two pairs of the conductors  82  for each phase. The stator coil  51  is equipped with a first three-phase winding set including the U-phase winding, the V-phase winding, and the W-phase winding and a second three-phase phase winding set including the X-phase winding, the Y-phase winding, and the Z-phase winding. The first three-phase winding set and the second three-phase winding set are arranged adjacent each other in the radial direction in the form of two layers. If the number of phases of the stator coil  51  is defined as S (i.e.,  6  in this embodiment), the number of the conductors  82  for each phase is defined as m, 2×5×m=2Sm conductors  82  are used for each pole pair in the stator coil  51 . The rotating electrical machine in this embodiment is designed so that the number of phases S is 6, the number m is 4, and 8 pole pairs are used. 6×4×8=192 conductors  82  are arranged in the circumferential direction of the stator core  52 . 
     The stator coil  51  in  FIG.  12    is designed to have the coil side portion  53  which has the straight sections  82  arranged in the form of two overlapping layers disposed adjacent each other in the radial direction. Each of the coil ends  54  and  55  has a respective two of the turns  84  which extend from the radially overlapping straight sections  82  in opposite circumferential directions. In other words, the conductors  82  arranged adjacent each other in the radial direction are opposite to each other in direction in which the turns  84  extend except for ends of the stator coil  51 . 
     A winding structure of the conductors  82  of the stator coil  51  will be described below in detail. In this embodiment, the conductors  82  formed in the shape of a wave winding are arranged in the form of a plurality of layers (e.g., two layers) disposed adjacent or overlapping each other in the radial direction. 
       FIGS.  15 ( a ) and  15 ( b )  illustrate the layout of the conductors  82  which form the n th  layer.  FIG.  15 ( a )  shows the configuration of the conductors  82 , as the side of the stator coil  51  is viewed.  FIG.  15 ( b )  shows the configuration of the conductors  82  as viewed in the axial direction of the stator coil  51 . In  FIGS.  15 ( a ) and  15 ( b ) , locations of the conductor groups  81  are indicated by symbols D 1 , D 2 , D 3  . . . , and D 9 . For the sake of simplicity of disclosure,  FIGS.  15 ( a ) and  15 ( b )  show only three conductors  82  which will be referred to herein as the first conductor  82 _A, the second conductor  82 _B, and the third conductor  82 _C. 
     The conductors  82 _A to  82 _C have the straight sections  83  arranged at a location of the n th  layer, in other words, at the same position in the radial direction. Every two of the straight sections  82  which are arranged at  6  pitches (corresponding to 3×m pairs) away from each other in the circumferential direction are joined together by one of the turns  84 . In other words, in each of the conductors  82 _A to  82 _C, outermost two straight sections of the seven straight sections  83  arranged in the circumferential direction of the stator coil  51  on the same circle defined about the center of the rotor  40  are joined together using one of the turns  84 . For instance, in the first conductor  82 _A, the straight sections  83  placed at the respective locations D 1  and D 7  are joined together by the inverse V-shaped turn  84 . 
     The conductor  82 _B is arranged at the same location of the n th  layer to be circumferentially shifted by one pitch relative to the conductor  82 _A, and the conductor  82 _C is arranged at the same location of the n th  layer to be circumferentially shifted by one pitch relative to the conductor  82 _B. 
     In this layout, the conductors  82 _A to  82 _C are placed at a location of the same layer, thereby resulting in a possibility that the turns  84  thereof might physically interfere with each other. In order to alleviate such a possibility, each of the turns  84  of the conductors  82 _A to  82 _C in this embodiment is shaped to have an interference avoiding portion formed by offsetting a portion of the corresponding turn  84  in the radial direction. 
     Specifically, the turn  84  of each of the conductors  82 _A to  82 _C includes a slant portion  84   a , a head portion  84   b , a slant portion  84   c , and a return portion  84   d . The slant portion  84   a  extends in the circumferential direction of the same circle (which will also be referred to as a first circle). The head portion  84  extends from the slant portion  84   a  radially inside the first circle (i.e., upward in  FIG.  15 ( b ) ) to reach another circle (which will also be referred to as a second circle). 
     The slant portion  84   c  extends in the circumferential direction of the second circle. The return portion  84   d  returns from the second circle back to the first circle. The head portion  84   b , the slant portion  84   c , and the return portion  84   d  define the interference avoiding portion. The slant portion  84   c  may be arranged radially outside the slant portion  84   a.    
     In other words, each of the conductors  82 _A to  82 _C has the turn  84  shaped to have the slant portion  84   a  and the slant portion  84   c  which are arranged on opposite sides of the head portion  84   b  at the center in the circumferential direction. The locations of the slant portions  84   a  and  84   b  are different from each other in the radial direction (i.e., a direction perpendicular to the drawing of  FIG.  15 ( a )  or a vertical direction in  FIG.  15 ( b ) ). 
     For instance, the turn  84  of the first conductor  82 _A is shaped to extend from the location D 1  on the n th  layer in the circumferential direction, be bent at the head portion  84   b  that is the center of the circumferential length of the turn  84  in the radial direction (e.g., radially inwardly), be bent again in the circumferential direction, extend again in the circumferential direction, and then be bent at the return portion  84   d  in the radial direction (e.g., radially outwardly) to reach the location D 7  on the n th  layer. 
     With the above arrangements, the slant portions  84   a  of the conductors  82 _A to  82 _C are arranged vertically or downward in the order of the first conductor  82 _A, the second conductor  82 _B, and the third conductor  82 _C. The head portions  84   b  change the order of the locations of the conductors  82 _A to  82 _C in the vertical direction, so that the slant portions  84   c  are arranged vertically or downward in the order of the third conductor  82 _C, the second conductor  82 _B, and the first conductor  82 _A. This layout achieves an arrangement of the conductors  82 _A to  82 _C in the circumferential direction without any physical interference with each other. 
     In the structure wherein the conductors  82  are laid to overlap each other in the radial direction to form the conductor group  81 , the turns  84  leading to a radially innermost one and a radially outermost one of the straight sections  83  forming the two or more layers are preferably located radially outside the straight sections  83 . In a case where the conductors  83  forming the two or more layers are bent in the same radial direction near boundaries between ends of the turns  84  and the straight sections  83 , the conductors  83  are preferably shaped not to deteriorate the insulation therebetween due to physical interference of the conductors  83  with each other. 
     In the example of  FIGS.  15 ( a ) and  15 ( b ) , the conductors  82  laid on each other in the radial direction are bent radially at the return portions  84   d  of the turns  84  at the location D 7  to D 9 . It is advisable that the conductor  82  of the n th  layer and the conductor  82  of the n+1 th  layer be bent, as illustrated in  FIG.  16   , at radii of curvature different from each other. Specifically, the radius of curvature R 1  of the conductor  82  of the n th  layer is preferably selected to be smaller than the radius of curvature R 2  of the conductor  82  of the n+1 th  layer. 
     Additionally, radial displacements of the conductor  82  of the n th  layer and the conductor  82  of the n+1 th  layer are preferably selected to be different from each other. If the amount of radial displacement of the conductor  82  of the n th  layer is defined as S 1 , and the amount of radial displacement of the conductor  82  of the n+1 th  layer located radially outside the n th  layer defined as S 2 , the amount of radial displacement S 1  is preferably selected to be greater than the amount of radial displacement S 2 . 
     The above layout of the conductors  82  eliminates the risk of interference with each other, thereby ensuring a required degree of insulation between the conductors  82  even when the conductors  82  laid on each other in the radial direction are bent in the same direction. 
     The structure of the magnet unit  42  of the rotor  40  will be described below. In this embodiment, the magnet unit  42  is made of permanent magnets in which a remanent flux density Br=1.0 T, and an intrinsic coercive force Hcj=400 kA/m. The permanent magnets used in this embodiment are implemented by sintered magnets formed by sintering grains of magnetic material and compacting them into a given shape and have the following specifications. The intrinsic coercive force Hcj on a J-H curve is 400 kA/m or more. The remanent flux density Br on the J-H curve is 1.0 T or more. Magnets designed so that when 5,000 to 10,000 AT is applied thereto by phase-to-phase excitation, a magnetic distance between paired poles, i.e., between a N-pole and an S-pole, in other words, of a path in which a magnetic flux flows between the N-pole and the S-pole, a portion lying in the magnet has a length of 25 mm may be used to meet a relation of Hcj=10000 A without becoming demagnetized. 
     In other words, the magnet unit  42  is engineered so that a saturation magnetic flux density Js is 1.2 T or more, a grain size is 10 μm or less, and a relation of Js×a≥1.0 T is met where a is an orientation ratio. 
     The magnet unit  42  will be additionally described below. The magnet unit  42  (i.e., magnets) has a feature that Js meets a relation of 2.15 T≥Js≥1.2 T. In other words, magnets used in the magnet unit  42  may be FeNi magnets having NdFe11 TiN, Nd2Fe14B, Sm2Fe17N3, or L10 crystals. Note that samarium-cobalt magnets, such as SmCo5, FePt, Dy2Fe14B, or CoPt magnets cannot be used. When magnets in which high Js characteristics of neodymium are slightly lost, but a high degree of coercive force of Dy is ensured using the heavy rare earth dysprosium, like in homotopic compounds, such as Dy2Fe14B and Nd2Fe14B, sometimes meets a relation of 2.15 T≥Js≥1.2 T, they may be used in the magnet unit  42 . Such a type of magnet will also be referred to herein as [Nd1-xDyx]2Fe14B]. Further, a magnet contacting different types of compositions, in other words, a magnet made from two or more types of materials, such as FeNi and Sm2Fe17N3, may be used to meet a relation of 2.15 T≥Js≥1.2 T. A mixed magnet made by adding a small amount of, for example, Dy2Fe14B in which Js&lt;1 T to an Nd2Fe14B magnet in which Js=1.6 T, meaning that Js is sufficient to enhance the coercive force, may also be used to meet a relation of 2.15≥T≥Js 1.2 T. 
     In use of the rotating electrical machine at a temperature outside a temperature range of human activities which is higher than, for example, 60° C. exceeding temperatures of deserts, for example, within a passenger compartment of a vehicle where the temperature may rise to 80° C. in summer, the magnet preferably contains FeNi or Sm2Fe17N3 components which are less dependent on temperature. This is because motor characteristics are greatly changed by temperature-dependent factors thereof in motor operations within a range of approximately −40° which is within a range experienced by societies in Northern Europe to 60° C. or more experienced in desert region or at 180 to 240° C. that is a heat resistance temperature of the enamel coating, which leads to a difficulty in achieving a required control operation using the same motor driver. The use of FeNi containing the above described L10 crystals or Sm2Fe17N3 magnets will result in a decrease in load on the motor driver because characteristics thereof have temperature-dependent factors lower than half that of Nd2Fe14B magnets. 
     Additionally, the magnet unit  42  is engineered to use the above described magnet mixing so that a particle size of fine powder before being magnetically oriented is lower than or equal to 10 μm and higher than or equal to a size of single-domain particles. The coercive force of a magnet is usually increased by decreasing the size of powered particles thereof to a few hundred nm. In recent years, smallest possible particles have been used. If the particles of the magnet are too small, the BHmax (i.e., the maximum energy product) of the magnet will be decreased due to oxidization thereof. It is, thus, preferable that the particle size of the magnet is higher than or equal to the size of the single-domain particles. The particle size being only up to the size of the single-domain particles is known to increase the coercive force of the magnet. The particle size, as referred to herein, refers to the diameter or size of fine powdered particles in a magnetic orientation operation in production processes of magnets. 
     The magnet unit  42  includes a first magnet  91  and a second magnet  92 . Each of the first magnet  91  and the second magnet  92  of the magnet unit  42  is made of a sintered magnet formed by firing or heating magnetic powder at high temperatures and compacting it. The sintering is achieved so as to meet the conditions where the saturation magnetization Js of the magnet unit  42  is 1.2 T (Tesla) or more, the particle size of the first magnet  91  and the second magnet  92  is 10 μm or less, and Js×a is higher than or equal to 1.0 T (Tesla) where a is an orientation ratio. 
     Each of the first magnet  91  and the second magnet  92  is also sintered to meet the following conditions. By performing the magnetic orientation in the magnetic orientation operation in the production processes of the first magnet  91  and the second magnet  92 , the first and second magnets  91  and  92  have an orientation ratio different to the definition of orientation of magnetic force in a magnetization operation for isotropic magnets. The magnet unit  42  in this embodiment is designed to have 
     (1) The saturation magnetization Js more than or equal to 1.2 T 
     (2) The high orientation ratio a of each of the first magnet  91  and the second magnet  92  meeting a relation of Jr≥Js×a≥1.0 T 
     The orientation ratio a, as referred to herein, is defined in the following way. If each of the first magnet  91  and the second magnet  92  has six easy axes of magnetization, five of the easy axes of magnetization are oriented in the same direction A 10 , and the remaining one of the easy axes of magnetization is oriented in the direction B 10  angled at 90 degrees to the direction A 10 , then a relation of a=5/6 is met. 
     Alternatively, if each of the first magnet  91  and the second magnet  92  has six easy axes of magnetization, five of the easy axes of magnetization are oriented in the same direction A 10 , and the remaining one of the easy axes of magnetization is oriented in the direction B 10  angled at 45 degrees to the direction A 10 , then a relation of a=(5+0.707)/6 is met since a component oriented in the direction A 10  is expressed by cos 45°=0.707. The first magnet  91  and the second magnet  92  in this embodiment are, as described above, each made using sintering techniques, but however, they may be produced in another way as long as the above conditions are satisfied. For instance, a method of forming an MQ3 magnet may be used. 
     This embodiment uses permanent magnets, each of which is magnetically oriented to have a controlled easy axis of magnetization thereof, thereby enabling a magnetic circuit length within the corresponding one of the magnets to be longer than that within a typical linearly oriented magnet which produces a magnetic flux density of 1.0 T or more. 
     In other words, this embodiment enables the magnetic circuit length for one pole pair in the magnets in this embodiment to be achieved using magnets each with a smaller volume. Additionally, a range of reversible flux loss in the magnets is not lost when subjected to severe high temperatures, as compared with use of typical linearly oriented magnets. The disclosers or inventors of this application have found that characteristics similar to those of anisotropic magnets are obtained even using prior art magnets. 
     The easy axis of magnetization represents a crystal orientation in which a crystal is easy to magnetize in a magnet. The orientation of the easy axis of magnetization in the magnet, as referred to herein, is a direction in which an orientation ratio is 50% or more where the orientation ratio indicates the degree to which easy axes of magnetization of crystals are aligned with each other or a direction of an average of magnetic orientations in the magnet. 
     The magnet unit  42  is, as clearly illustrated in  FIGS.  8  and  9   , of an annular shape and arranged inside the magnet holder  41  (specifically, radially inside the cylinder  43 ). The magnet unit  42  is equipped with the first magnets  91  and the second magnets  92  which are each made of a polar anisotropic magnet. 
     Each of the first magnets  91  and each of the second magnets  92  are different in polarity from each other. The first magnets  91  and the second magnets  92  are arranged alternately in the circumferential direction of the magnet unit  42 . Each of the first magnets  91  is engineered to have a portion creating an N-pole near the stator coil  51 . Each of the second magnets  92  is engineered to have a portion creating an S-pole near the stator coil  51 . The first magnets  91  and the second magnets  92  are each made of, for example, a permanent rare earth magnet, such as a neodymium magnet. 
     Each of the magnets  91  and  92  is engineered to have a direction of magnetization (which will also be referred to below as a magnetization direction) which extends in an annular shape in between a d-axis (i.e., a direct-axis) and a q-axis (i.e., a quadrature-axis) in a known d-q coordinate system where the d-axis represents the center of a magnetic pole, and the q-axis represents a magnetic boundary between the N-pole and the S-pole, in other words, where a density of magnetic flux is zero Tesla. In each of the magnets  91  and  92 , the magnetization direction is oriented in the radial direction of the annular magnet unit  42  close to the d-axis and also oriented in the circumferential direction of the annular magnet unit  42  closer to the q-axis. 
     This layout will also be described below in detail. 
     Each of the magnets  91  and  92 , as can be seen in  FIG.  9   , includes a first portion  250  and two second portions  260  arranged on opposite sides of the first portion  250  in the circumferential direction of the magnet unit  42 . In other words, the first portion  250  is located closer to the d-axis than the second portions  260  are. The second portions  260  are arranged closer to the q-axis than the first portion  250  is. The direction in which the easy axis of magnetization  300  extends in the first portion  250  is oriented more parallel to the d-axis than the direction in which the easy axis of magnetization  310  extends in the second portions  260 . In other words, the magnet unit  42  is engineered so that an angle θ 11  which the easy axis of magnetization  300  in the first portion  250  makes with the d-axis is selected to be smaller than an angle θ 12  which the easy axis of magnetization  310  in the second portion  260  makes with the q-axis. 
     More specifically, if a direction from the stator  50  (i.e., an armature) toward the magnet unit  42  on the d-axis is defined to be positive, the angle θ 11  represents an angle which the easy axis of magnetization  300  makes with the d-axis. Similarly, if a direction from the stator  50  (i.e., an armature) toward the magnet unit  42  on the q-axis is defined to be positive, the angle θ 12  represents an angle which the easy axis of magnetization  310  makes with the q-axis. In this embodiment, each of the angle θ 11  and the angle θ 12  is set to be 90° or less. 
     Each of the easy axes of magnetization  300  and  310 , as referred to herein, is defined in the following way. If in each of the magnets  91  and  92 , a first one of the easy axes of magnetization is oriented in a direction A 11 , and a second one of the easy axes of magnetization is oriented in a direction B 11 , an absolute value of cosine of an angle θ which the direction A 11  and the direction B 11  make with each other (i.e., |cos θ|) is defined as the easy axis of magnetization  300  or the easy axis of magnetization  310 . 
     The magnets  91  are different in easy axis of magnetization from the magnets  92  in regions close to the d-axis and the q-axis. Specifically, in the region close to the d-axis, the direction of the easy axis of magnetization is oriented approximately parallel to the d-axis, while in the region close to the q-axis, the direction of the easy axis of magnetization is oriented approximately perpendicular to the q-axis. Annular magnetic paths are created according to the directions of easy axes of magnetization. In each of the magnets  91  and  92 , the easy axis of magnetization in the region close to the d-axis may be oriented parallel to the d-axis, while the easy axis of magnetization in the region close to the q-axis may be oriented perpendicular to the q-axis. 
     Each of the magnets  91  and  92  is shaped to have a first peripheral surface facing the stator  50  (i.e., a lower surface viewed in  FIG.  9    which will also be referred to as a stator-side outer surface) and a second peripheral surface facing the q-axis in the circumferential direction. The first and second peripheral surfaces function as magnetic flux acting surfaces into and from which magnetic flux flows. The magnetic paths are each created to extend between the magnetic flux acting surfaces (i.e., between the stator-side outer surface and the second peripheral surface facing the q-axis). 
     In the magnet unit  42 , a magnetic flux flows in an annular shape between a respective adjacent two of the N-poles and the S-poles of the magnets  91  and  92 , so that each of the magnetic paths has an increased length, as compared with, for example, radial anisotropic magnets. A distribution of the magnetic flux density will, therefore, exhibit a shape similar to a sine wave illustrated in  FIG.  17   . This facilitates concentration of magnetic flux around the center of the magnetic pole unlike a distribution of magnetic flux density of a radial anisotropic magnet demonstrated in  FIG.  18    as a comparative example, thereby enabling the degree of torque produced by the rotating electrical machine  10  to be increased. It has also been found that the magnet unit  42  in this embodiment has the distribution of the magnetic flux density distinct from that of a typical Halbach array magnet. In  FIGS.  17  and  18   , a horizontal axis indicates the electrical angle, while a vertical axis indicates the magnetic flux density. 90° on the horizontal axis represents the d-axis (i.e., the center of the magnetic pole). 0° and 180° on the horizontal axis represent the q-axis. 
     Accordingly, the above described structure of each of the magnets  91  and  92  functions to enhance the magnet magnetic flux thereof on the d-axis and reduce a change in magnetic flux near the q-axis. This enables the magnets  91  and  92  to be produced which have a smooth change in surface magnetic flux from the q-axis to the d-axis on each magnetic pole 
     The sine wave matching percentage in the distribution of the magnetic flux density is preferably set to, for example, 40% or more. This improves the amount of magnetic flux around the center of a waveform of the distribution of the magnetic flux density as compared with a radially oriented magnet or a parallel oriented magnet in which the sine wave matching percentage is approximately 30%. By setting the sine wave matching percentage to be 60% or more, the amount of magnetic flux around the center of the waveform is improved, as compared with a concentrated magnetic flux array, such as the Halbach array. 
     In the radial anisotropic magnet demonstrated in  FIG.  18   , the magnetic flux density changes sharply near the q-axis. The more sharp the change in magnetic flux density, the more an eddy current generating in the stator coil  51  will increase. The magnetic flux close to the stator coil  51  also sharply changes. In contrast, the distribution of the magnetic flux density in this embodiment has a waveform approximating a sine wave. A change in magnetic flux density near the q-axis is, therefore, smaller than that in the radial anisotropic magnet near the q-axis. This minimizes the generation of the eddy current. 
     The magnet unit  42  creates a magnetic flux oriented perpendicular to the magnetic flux acting surface  280  close to the stator  50  near the d-axis (i.e., the center of the magnetic pole) in each of the magnets  91  and  92 . Such a magnetic flux extends in an arc-shape farther away from the d-axis as leaving the magnetic flux acting surface  280  close to the stator  50 . The more perpendicular to the magnetic flux acting surface the magnetic flux extends, the stronger the magnetic flux is. The rotating electrical machine  10  in this embodiment is, as described above, designed to shape each of the conductor groups  81  to have a decreased thickness in the radial direction, so that the radial center of each of the conductor groups  81  is located close to the magnetic flux-acting surface of the magnet unit  42 , thereby causing the strong magnetic flux to be applied to the stator  50  from the rotor  40 . 
     The stator  50  has the cylindrical stator core  52  arranged radially inside the stator coil  51 , that is, on the opposite side of the stator coil  51  to the rotor  40 . This causes the magnetic flux extending from the magnetic flux-acting surface of each of the magnets  91  and  92  to be attracted by the stator core  52 , so that it circulates through the magnetic path partially including the stator core  52 . This enables the orientation of the magnetic flux and the magnetic path to be optimized. 
     Steps to assemble the bearing unit  20 , the housing  30 , the rotor  40 , the stator  50 , and the inverter unit  60  illustrated in  FIG.  5    will be described below as a production method of the rotating electrical machine  10 . The inverter unit  60  is, as illustrated in  FIG.  6   , equipped with the unit base  61  and the electrical components  62 . Operation processes including installation processes for the unit base  61  and the electrical components  62  will be explained. In the following discussion, an assembly of the stator  50  and the inverter unit  60  will be referred to as a first unit. An assembly of the bearing unit  20 , the housing  30 , and the rotor  40  will be referred to as a second unit. 
     The production processes include: 
     a first step of installing the electrical components  62  radially inside the unit base  61 ; 
     a second step of installing the unit base  61  radially inside the stator  50  to make the first unit; 
     a third step of inserting the attaching portion  44  of the rotor  40  into the bearing unit  20  installed in the housing  30  to make the second unit; 
     a fourth step of installing the first unit radially inside the second unit; and 
     a fifth step of fastening the housing  30  and the unit base  61  together. The order in which the above steps are performed is the first step→the second step→the third step→the fourth step→the fifth step. 
     In the above production method, the bearing unit  20 , the housing  30 , the rotor  40 , the stator  50 , and the inverter unit  60  are assembled as a plurality of sub-assemblies, and the sub-assemblies are assembled, thereby facilitating handling thereof and achieving completion of inspection of each sub-assembly. This enables an efficient assembly line to be established and thus facilitates multi-product production planning. 
     In the first step, a high thermal conductivity material is applied or adhered to at least one of the radial inside of the unit base  61  and the radial outside of the electrical components  62 . Subsequently, the electrical components may be mounted on the unit base  61 . This achieves efficient transfer of heat, as generated by the semiconductor modules  66 , to the unit base  61 . 
     In the third step, an insertion operation for the rotor  40  may be achieved with the housing  30  and the rotor  40  arranged coaxially with each other. Specifically, the housing  30  and the rotor  40  are assembled while sliding one of the housing  30  and the rotor  40  along a jig which positions the outer peripheral surface of the rotor  40  (i.e., the outer peripheral surface of the magnetic holder  41 ) or the inner peripheral surface of the rotor  40  (i.e., the inner peripheral surface of the magnet unit  42 ) with respect to, for example, the inner peripheral surface of the housing  30 . This achieves the assembly of heavy-weight parts without exertion of unbalanced load to the bearing unit  20 . This results in improvement of reliability in operation of the bearing unit  20 . 
     In the fourth step, the first unit and the second unit may be installed while being placed coaxially with each other. Specifically, the first unit and the second unit are installed while sliding one of the first unit and the second unit along a jig which positions the inner peripheral surface of the unit base  61  with respect to, for example, the inner peripheral surfaces of the rotor  40  and the attaching portion  44 . This achieves the installation of the first and second units without any physical interference therebetween within a small clearance between the rotor  40  and the stator  50 , thereby eliminating risks of defects caused by the installation, such as physical damage to the stator coil  51  or damage to the permanent magnets. 
     The above steps may alternatively be scheduled as the second step→the third step→the fourth step→the fifth step→the first step. In this order, the delicate electrical components  62  is finally installed, thereby minimizing stress on the electrical components in the installation processes. 
     The structure of a control system for controlling an operation of the rotating electrical machine  10  will be described below.  FIG.  19    is an electrical circuit diagram of the control system for the rotating electrical machine  10 .  FIG.  20    is a functional block diagram which illustrates control steps performed by the controller  110 . 
       FIG.  19    illustrates two sets of three-phase windings  51   a  and  51   b . The three-phase windings  51   a  include a U-phase winding, a V-phase winding, and a W-phase winding. The three-phase windings  51   b  include an X-phase winding, a Y-phase winding, and a Z-phase winding. 
     The first inverter  101  and the second inverter  102  are provided as electrical power converters for the three-phase windings  51   a  and  51   b , respectively. The inverters  101  and  102  are made of bridge circuits with as many upper and lower arms as there are the phase-windings. The current delivered to the phase windings of the stator coil  51  is regulated by turning on or off switches (i.e., semiconductor switches) mounted on the upper and lower arms. 
     The dc power supply  103  and the smoothing capacitor  104  are connected parallel to the inverters  101  and  102 . The dc power supply  103  is made of, for example, a plurality of series-connected cells. The switches of the inverters  101  and  102  correspond to the semiconductor modules  66  in  FIG.  1   . The capacitor  104  corresponds to the capacitor module  68  in  FIG.  1   . 
     The controller  110  is equipped with a microcomputer made of a CPU and memories and works to perform control energization by turning on or off the switches of the inverters  101  and  102  using several types of measured information measured in the rotating electrical machine  10  or requests for a motor mode or a generator mode of the rotating electrical machine  10 . The controller  110  corresponds to the control device  77  shown in  FIG.  6   . 
     The measured information about the rotating electrical machine  10  includes, for example, an angular position (i.e., an electrical angle) of the rotor  40  measured by an angular position sensor, such as a resolver, a power supply voltage (i.e., voltage inputted into the inverters) measured by a voltage sensor, and electrical current delivered to each of the phase-windings, as measured by a current sensor. The controller  110  produces and outputs an operation signal to operate each of the switches of the inverters  101  and  102 . A request for electrical power generation is a request for driving the rotating electrical machine  10  in a regenerative mode, for example, in a case where the rotating electrical machine  10  is used as a power source for a vehicle. 
     The first inverter  101  is equipped with a series-connected part made up of an upper arm switch Sp and a lower arm switch Sn for each of the three-phase windings: the U-phase winding, the V-phase winding, and the W-phase winding. The upper arm switches Sp are connected at high-potential terminals thereof to a positive terminal of the dc power supply  103 . The lower arm switches Sn are connected at low-potential terminals thereof to a negative terminal (i.e., ground) of the dc power supply  103 . Intermediate joints of the upper arm switches Sp and the lower arm switches Sn are connected to ends of the U-phase winding, the V-phase winding, and the W-phase winding. The U-phase winding, the V-phase winding, and the W-phase winding are connected in the form of a star connection (i.e., Y-connection). The other ends of the U-phase winding, the V-phase winding, and the W-phase winding are connected with each other at a neutral point. 
     The second inverter  102  is, like the first inverter  101 , equipped with a series-connected part made up of an upper arm switch Sp and a lower arm switch Sn for each of the three-phase windings: the X-phase winding, the Y-phase winding, and the Z-phase winding. The upper arm switches Sp are connected at high-potential terminals thereof to the positive terminal of the dc power supply  103 . The lower arm switches Sn are connected at low-potential terminals thereof to the negative terminal (i.e., ground) of the dc power supply  103 . Intermediate joints of the upper arm switches Sp and the lower arm switches Sn are connected to ends of the X-phase winding, the Y-phase winding, and the Z-phase winding. The X-phase winding, the Y-phase winding, and the Z-phase winding are connected in the form of a star connection (i.e., Y-connection). The other ends of the X-phase winding, the Y-phase winding, and the Z-phase winding are connected with each other at a neutral point. 
       FIG.  20    illustrates a current feedback control operation to control electrical currents delivered to the U-phase winding, the V-phase winding, and the W-phase winding and a current feedback control operation to control electrical currents delivered to the X-phase winding, the Y-phase winding, and the Z-phase winding. The control operation for the U-phase winding, the V-phase winding, and the W-phase winding will first be discussed. 
     In  FIG.  20   , a current command determiner  111  uses a torque-dq map to determine current command values for the d-axis and the q-axis using a torque command value in the motor mode of the rotating electrical machine  10  (which will also be referred to as a motor-mode torque command value), a torque command value in the generator mode of the rotating electrical machine  10  (which will be referred to as a generator-mode torque command value), and an electrical angular velocity ω derived by differentiating an electrical angle θ with respect to time. The current command determiner  111  is shared between the U-, V-, and W-phase windings and the X-, Y-, and W-phase windings. The generator-mode torque command value is a regenerative torque command value in a case where the rotating electrical machine  10  is used as a power source of a vehicle. 
     A d-q converter  112  works to convert currents (i.e., three phase currents), as measured by current sensors mounted for the respective phase windings, into a d-axis current and a q-axis current that are components in a two-dimensional rotating Cartesian coordinate system in which a d-axis is defined as a direction of an axis of a magnetic field or field direction. 
     A d-axis current feedback control device  113  determines a command voltage for the d-axis as a manipulated variable for bringing the d-axis current into agreement with the current command value for the d-axis in a feedback mode. 
     A q-axis current feedback control device  114  determines a command voltage for the q-axis as a manipulated variable for bringing the q-axis current into agreement with the current command value for the q-axis in a feedback mode. The feedback control devices  113  and  114  calculates the command voltage as a function of a deviation of each of the d-axis current and the q-axis current from a corresponding one of the current command values using PI feedback techniques. 
     A three-phase converter  115  works to convert the command values for the d-axis and the q-axis into command values for the U-phase, V-phase, and W-phase windings. Each of the devices  111  to  115  is engineered as a feedback controller to perform a feedback control operation for a fundamental current in the d-q transformation theory. The command voltages for the U-phase, V-phase, and W-phase windings are feedback control values. 
     An operation signal generator  116  uses the known triangle wave carrier comparison to produce operation signals for the first inverter  101  as a function of the three-phase command voltages. Specifically, the operation signal generator  116  works to produce switch operation signals (i.e., duty signals) for the upper and lower arms for the three-phase windings (i.e., the U-, V-, and W-phase windings) under PWM control based on comparison of levels of signals derived by normalizing the three-phase command voltages using the power supply voltage with a level of a carrier signal, such as a triangle wave signal. 
     The same structure as described above is provided for the X-, Y-, and Z-phase windings. 
     A d-q converter  122  works to convert currents (i.e., three phase currents), as measured by current sensors mounted for the respective phase windings, into a d-axis current and a q-axis current that are components in the two-dimensional rotating Cartesian coordinate system in which the d-axis is defined as the direction of the axis of the magnetic field. 
     A d-axis current feedback control device  123  determines a command voltage for the d-axis. 
     A q-axis current feedback control device  124  determines a command voltage for the q-axis. 
     A three-phase converter  125  works to convert the command values for the d-axis and the q-axis into command values for the X-phase, Y-phase, and Z-phase windings. 
     An operation signal generator  126  produces operation signals for the second inverter  102  as a function of the three-phase command voltages. 
     Specifically, the operation signal generator  126  works to switch operation signals (i.e., duty signals) for the upper and lower arms for the three-phase windings (i.e., the X-, Y-, and Z-phase windings) based on comparison of levels of signals derived by normalizing the three-phase command voltages using the power supply voltage with a level of a carrier signal, such as a triangle wave signal. 
     A driver  117  works to turn on or off the switches Sp and Sn in the inverters  101  and  102  in response to the switch operation signals produced by the operation signal generators  116  and  126 . 
     Subsequently, a torque feedback control operation will be described below. This operation is to increase an output of the rotating electrical machine  10  and reduce torque loss in the rotating electrical machine  10 , for example, in a high-speed and high-output range wherein output voltages from the inverters  101  and  102  rise. The controller  110  selects one of the torque feedback control operation and the current feedback control operation and perform the selected one as a function of an operating condition of the rotating electrical machine  10 . 
       FIG.  21    shows the torque feedback control operation for the U-, V-, and W-phase windings and the torque feedback control operation for the X-, Y-, and Z-phase windings. In  FIG.  21   , the same reference numbers as employed in  FIG.  20    refer to the same parts, and explanation thereof in detail will be omitted here. The control operation for the U-, V-, and W-phase windings will be described first. 
     A voltage amplitude calculator  127  works to calculate a voltage amplitude command that is a command value of a degree of a voltage vector as a function of the motor-mode torque command value or the generator-mode torque command value for the rotating electrical machine  10  and the electrical angular velocity ω derived by differentiating the electrical angle θ with respect to time. 
     A torque calculator  128   a  works to estimate a torque value in the U-phase, V-phase, or the W-phase as a function of the d-axis current and the q-axis current converted by the d-q converter  112 . The torque calculator  128   a  may be designed to calculate the voltage amplitude command using a map listing relations among the d-axis current, the q-axis current, and the voltage amplitude command. 
     A torque feedback controller  129   a  calculates a voltage phase command that is a command value for a phase of the voltage vector as a manipulated variable for bringing the estimated torque value into agreement with the motor-mode torque command value or the generator-mode torque command value in the feedback mode. Specifically, the torque feedback controller  129   a  calculates the voltage phase command as a function of a deviation of the estimated torque value from the motor-mode torque command value or the generator-mode torque command value using PI feedback techniques. 
     An operation signal generator  130   a  works to produce the operation signal for the first inverter  101  using the voltage amplitude command, the voltage phase command, and the electrical angle θ. Specifically, the operation signal generator  130   a  calculates the command values for the three-phase windings based on the voltage amplitude command, the voltage phase command, and the electrical angle θ and then generates switching operation signals for the upper and lower arms for the three-phase windings by means of PWM control based on comparison of levels of signals derived by normalizing the three-phase command voltages using the power supply voltage with a level of a carrier signal, such as a triangle wave signal. 
     The operation signal generator  130   a  may alternatively be designed to produce the switching operation signals using pulse pattern information that is map information about relations among the voltage amplitude command, the voltage phase command, the electrical angle θ, and the switching operation signal, the voltage amplitude command, the voltage phase command, and the electrical angle θ. 
     The same structure as described above is provided for the X-, Y-, and Z-phase windings. A torque calculator  128   b  works to estimate a torque value in the X-phase, Y-phase, or the Z-phase as a function of the d-axis current and the q-axis current converted by the d-q converter  122 . 
     A torque feedback controller  129   b  calculates a voltage phase command as a manipulated variable for bringing the estimated torque value into agreement with the motor-mode torque command value or the generator-mode torque command value in the feedback mode. Specifically, the torque feedback controller  129   b  calculates the voltage phase command as a function of a deviation of the estimated torque value from the motor-mode torque command value or the generator-mode torque command value using PI feedback techniques. 
     An operation signal generator  130   b  works to produce the operation signal for the second inverter  102  using the voltage amplitude command, the voltage phase command, and the electrical angle θ. Specifically, the operation signal generator  130   b  calculates the command values for the three-phase windings based on the voltage amplitude command, the voltage phase command, and the electrical angle θ and then generates the switching operation signals for the upper and lower arms for the three-phase windings by means of PWM control based on comparison of levels of signals derived by normalizing the three-phase command voltages using the power supply voltage with a level of a carrier signal, such as a triangle wave signal. The driver  117  then works to turn on or off the switches Sp and Sn for the three-phase windings in the inverters  101  and  102  in response to the switching operation signals derived by the operation signal generators  130   a  and  130   b.    
     The operation signal generator  130   b  may alternatively be designed to produce the switching operation signals using pulse pattern information that is map information about relations among the voltage amplitude command, the voltage phase command, the electrical angle θ, and the switching operation signal, the voltage amplitude command, the voltage phase command, and the electrical angle θ. 
     The rotating electrical machine  10  has a possibility that generation of an axial current may result in electrical erosion in the bearing  21  or  22 . For example, when the stator coil  51  is excited or de-excited in response to the switching operation, a small switching time gap (i.e., switching unbalance) may occur, thereby resulting in distortion of magnetic flux, which may lead to the electrical erosion in the bearings  21  and  22  retaining the rotating shaft  11 . The distortion of magnetic flux depending upon the inductance of the stator  50  may create an electromotive force oriented in the axial direction, which may result in dielectric breakdown in the bearing  21  or  22  to develop the electrical erosion. 
     In order to avoid the electrical erosion, this embodiment is engineered to take three measures as discussed below. 
     The first erosion avoiding measure is to reduce the inductance by designing the stator  50  to have a core-less structure and also to shape the magnetic flux in the magnet unit  42  to be smooth to minimize the electrical erosion. 
     The second erosion avoiding measure is to retain the rotating shaft in a cantilever form to minimize the electrical erosion. 
     The third erosion avoiding measure is to unify the annular stator coil  51  and the stator core  52  using molding techniques using a molding material to minimize the electrical erosion. The first to third erosion avoiding measures will be described below in detail. 
     In the first erosion avoiding measure, the stator  50  is designed to have no teeth in gaps between the conductor groups  81  in the circumferential direction. The sealing members  57  made of non-magnetic material are arranged in the gaps between the conductor groups  81  instead of teeth (iron cores) (see  FIG.  10   ). This results in a decrease in inductance of the stator  50 , thereby minimizing the distortion of magnetic flux caused by the switching time gap occurring upon excitation of the stator coil  51  to reduce the electrical erosion in the bearings  21  and  22 . The inductance on the d-axis is preferably less than that on the q-axis. 
     Additionally, each of the magnets  91  and  92  is magnetically oriented to have the easy axis of magnetization which is directed near the d-axis to be more parallel to the d-axis than that near the q-axis (see  FIG.  9   ). This strengthens the magnetic flux on the d-axis, thereby resulting in a smooth change in surface magnetic flux (i.e., an increase or decrease in magnetic flux) from the q-axis to the d-axis on each magnetic pole of the magnets  91  and  92 . This minimizes a sudden voltage change arising from the switching imbalance to avoid the electrical erosion. 
     In the second erosion avoiding measure, the rotating electrical machine  10  is designed to have the bearings  21  and  22  located away from the axial center of the rotor  40  toward one of the ends of the rotor  40  opposed to each other in the axial direction thereof (see  FIG.  2   ). This minimizes the risk of the electrical erosion as compared with a case where a plurality of bearings are arranged outside axial ends of a rotor. In other words, in the structure wherein the rotor has ends retained by the bearings, generation of a high-frequency magnetic flux results in creation of a closed circuit extending through the rotor, the stator, and the bearings (which are arranged axially outside the rotor). This leads to a possibility that the axial current may result in the electrical erosion in the bearings. In contrast, the rotor  40  are retained by the plurality of bearings  21  and  22  in the cantilever form, so that the above closed circuit does not occur, thereby minimizing the electrical erosion in the bearings  21  and  22 . 
     In addition to the above one-side layout of the bearings  21  and  22 , the rotating electrical machine  10  also has the following structure. In the magnet holder  41 , the intermediate portion  45  extending in the radial direction of the rotor  40  is equipped with the contact avoider which axially extends to avoid physical contact with the stator  50  (see  FIG.  2   ). This enables a closed circuit through which the axial current flows through the magnet holder  41  to be lengthened to increase the resistance thereof. This minimizes the risk of the electrical erosion of the bearings  21  and  22 . 
     The retainer  23  for the bearing unit  20  is secured to the housing  30  and located on one axial end side of the rotor  40 , while the housing  30  and the unit base  61  (i.e., a stator holder) are joined together on the other axial end of the rotor  40  (see  FIG.  2   ). These arrangements properly achieve the structure in which the bearings  21  and  22  are located only on the one end of the length of the rotating shaft  11 . 
     Additionally, the unit base  61  is connected to the rotating shaft  11  through the housing  30 , so that the unit base  61  is located electrically away from the rotating shaft  11 . An insulating member such as resin may be disposed between the unit base  61  and the housing  30  to place the unit base  61  and the rotating shaft  11  electrically farther away from each other. This also minimizes the risk of the electrical erosion of the bearings  21  and  22 . 
     The one-side layout of the bearings  21  and  22  in the rotating electrical machine  10  in this embodiment decreases the axial voltage applied to the bearings  21  and  22  and also decreases the potential difference between the rotor  40  and the stator  50 . A decrease in the potential difference applied to the bearings  21  and  22  is, thus, achieved without use of conductive grease in the bearings  21  and  22 . The conductive grease usually contains fine particles such as carbon particles, thus leading to a risk of generation of acoustic noise. In order to alleviate the above problem, this embodiment uses a non-conductive grease in the bearings  21  and  22  to minimize the acoustic noise in the bearings  21  and  22 . For instance, in a case where the rotating electrical machine  10  is used with an electrical vehicle, it is usually required to take a measure to eliminate the acoustic noise. This embodiment is capable of properly taking such a measure. 
     In the third erosion avoiding measure, the stator coil  51  and the stator core  52  are unified together using a molding material to minimize a positional error of the stator coil  51  in the stator  50  (see  FIG.  11   ). The rotating electrical machine  10  in this embodiment is designed not to have conductor-to-conductor members (e.g., teeth) between the conductor groups  81  arranged in the circumferential direction of the stator coil  51 , thus leading to a concern about the positional error or misalignment of the stator coil  51 . The misalignment of the conductor of the stator coil  51  may be minimized by unifying the stator coil  51  and the stator core  52  in the mold. This eliminates risks of the distortion of magnetic flux arising from the misalignment of the stator coil  51  and the electrical erosion in the bearings  21  and  22  resulting from the distortion of the magnetic flux. 
     The unit base  61  serving as a housing to firmly fix the stator core  52  is made of carbon fiber reinforced plastic (CFRP), thereby minimizing electrical discharge to the unit base  61  as compared with when the unit base  61  is made of aluminum, thereby avoiding the electrical erosion. 
     An additional erosion avoiding measure may be taken to make at least one of the outer race  25  and the inner race  26  of each of the bearings  21  and  22  using a ceramic material or alternatively to install an insulating sleeve outside the outer race  25 . 
     Other embodiments will be described below in terms of differences between themselves and the first embodiment. 
     Second Embodiment 
     In this embodiment, the polar anisotropic structure of the magnet unit  42  of the rotor  40  is changed and will be described below in detail. 
     The magnet unit  42  is, as clearly illustrated in  FIGS.  22  and  23   , made using a magnet array referred to as a Halbach array. 
     Specifically, the magnet unit  42  is equipped with the first magnets  131  and the second magnets  132 . The first magnets  131  have a magnetization direction (i.e., an orientation of a magnetization vector thereof) oriented in the radial direction of the magnet unit  42 . The second magnets  132  have a magnetization direction (i.e., an orientation of the magnetization vector thereof) oriented in the circumferential direction of the magnet unit  42 . The first magnets  131  are arrayed at a given interval away from each other in the circumferential direction. Each of the second magnets  132  is disposed between the first magnets  131  arranged adjacent each other in the circumferential direction. The first magnets  131  and the second magnets  132  are each implemented by a rare-earth permanent magnet, such as a neodymium magnet. 
     The first magnets  131  are arranged away from each other in the circumferential direction so as to have N-poles and S-poles which are created in radially inner portions thereof and face the stator  50 . The N-poles and the S-poles are arranged alternately in the circumferential direction. The second magnets  132  are arranged to have N-poles and S-poles alternately located adjacent the first magnets  131  in the circumferential direction. The cylinder  43  which surrounds the magnets  131  and  132  may be formed as a soft magnetic core made of a soft magnetic material and which functions as a back core. The magnet unit  42  in this embodiment are designed to have the easy axis of magnetization oriented in the same way as in the first embodiment relative to the d-axis and the q-axis in the d-q axis coordinate system. 
     The magnetic members  133  each of which is made of a soft magnetic material are disposed radially outside the first magnets  131 , in other words, close to the cylinder  43  of the magnet holder  41 . Each of the magnetic members  133  may be made of magnetic steel sheet, soft iron, or a dust core material. Each of the magnetic members  133  has a length identical with that of the first magnet  131  (especially, a length of an outer periphery of the first magnet  131 ) in the circumferential direction. An assembly made up of each of the first magnets  131  and a corresponding one of the magnetic members  133  has a thickness identical with that of the second magnet  132  in the radial direction. In other words, each of the first magnets  131  has the thickness smaller than that of the second magnet  132  by that of the magnetic member  133  in the radial direction. The magnets  131  and  132  and the magnetic members  133  are firmly secured to each other using, for example, adhesive agent. In the magnet unit  42 , the radial outside of the first magnets  131  faces away from the stator  50 . The magnetic members  133  are located on the opposite side of the first magnets  131  to the stator  50  in the radial direction (i.e., farther away from the stator  50 ). 
     Each of the magnetic members  133  has the key  134  in a convex shape which is formed on the outer periphery thereof and protrudes radially outside the magnetic member  133 , in other words, protrudes into the cylinder  43  of the magnet holder  41 . The cylinder  43  has the key grooves  135  which are formed in an inner peripheral surface thereof in a concave shape and in which the keys  134  of the magnetic members  133  are fit. The protruding shape of the keys  134  is contoured to conform with the recessed shape of the key grooves  135 . As many of the key grooves  135  as the keys  134  of the magnetic members  133  are formed. The engagement between the keys  134  and the key grooves  135  serves to eliminate misalignment or a positional deviation of the first magnets  131 , the second magnets  132 , and the magnet holder  41  in the circumferential direction (i.e. a rotational direction). The keys  134  and the key grooves  135  (i.e., convexities and concavities) may be formed either on the cylinders  43  of the magnet holder  41  or in the magnetic members  133 , respectively. Specifically, the magnetic members  133  may have the key grooves  135  in the outer periphery thereof, while the cylinder  43  of the magnet holder  41  may have the keys  134  formed on the inner periphery thereof. 
     The magnet unit  42  has the first magnets  131  and the second magnets  132  alternately arranged to increase the magnetic flux density in the first magnets  131 . This results in concentration of magnetic flux on one surface of the magnet unit  42  to enhance the magnetic flux close to the stator  50 . 
     The layout of the magnetic members  133  radially arranged outside the first magnets  131 , in other words, farther away from the stator  50  reduces partial magnetic saturation occurring radially outside the first magnets  131 , thereby alleviating a risk of demagnetization in the first magnets  131  arising from the magnetic saturation. This results in an increase in magnetic force produced by the magnet unit  42 . In other words, the magnet unit  42  in this embodiment is viewed to have portions which are usually subjected to the demagnetization and replaced with the magnetic members  133 . 
       FIGS.  24 ( a ) and  24 ( b )  are illustrations which demonstrate flows of magnetic flux in the magnet unit  42 .  FIG.  24 ( a )  illustrates a conventional structure in which the magnet unit  42  is not equipped with the magnetic members  133 .  FIG.  24 ( b )  illustrates the structure in this embodiment in which the magnet unit  42  is equipped with the magnetic members  133 .  FIGS.  24 ( a ) and  24 ( b )  are linearly developed views of the cylinder  43  of the magnet holder  41  and the magnet unit  42 . Lower sides of  FIGS.  24 ( a ) and  24 ( b )  are close to the stator  50 , while upper sides thereof are farther away from the stator  50 . 
     In the structure shown in  FIG.  24 ( a ) , a magnetic flux-acting surface of each of the first magnets  131  and a side surface of each of the second magnets  132  are placed in contact with the inner peripheral surface of the cylinder  43 . A magnetic flux-acting surface of each of the second magnets  132  is placed in contact with the side surface of one of the first magnets  131 . Such layout causes a combined magnetic flux to be created in the cylinder  43 . The combined magnetic flux is made up of a magnetic flux F 1  which passes outside the second magnet  132  and then enters the surface of the first magnets  131  contacting the cylinder  43  and a magnetic flux which flows substantially parallel to the cylinder  43  and attracts a magnetic flux F 2  produced by the second magnet  132 . This leads to a possibility that the magnetic saturation may occur near the surface of contact between the first magnet  131  and the second magnet  132  in the cylinder  43   
     In the structure in  FIG.  24 ( b )  wherein each of the magnetic members  133  is disposed between the magnetic flux-acting surface of the first magnet  131  and the inner periphery of the cylinder  43  farther away from the stator  50 , the magnetic flux is permitted to pass through the magnetic member  133 . This minimizes the magnetic saturation in the cylinder  43  and increases resistance against the demagnetization. 
     The structure in  FIG.  24 ( b ) , unlike  FIG.  24 ( a ) , functions to eliminate the magnetic flux F 2  facilitating the magnetic saturation. This effectively enhances the permeance in the whole of the magnetic circuit, thereby ensuring the stability in properties of the magnetic circuit under elevated temperature. 
     As compared with radial magnets used in conventional SPM rotors, the structure in  FIG.  24 ( b )  has an increased length of the magnetic path passing through the magnet. This results in a rise in permeance of the magnet which enhances the magnetic force to increase the torque. Further, the magnetic flux concentrates on the center of the d-axis, thereby increasing the sine wave matching percentage. Particularly, the increase in torque may be achieved effectively by shaping the waveform of the current to a sine or trapezoidal wave under PWM control or using 120° excitation switching ICs 
     In a case where the stator core  52  is made of magnetic steel sheets, the thickness of the stator core  52  in the radial direction thereof is preferably half or greater than half the thickness of the magnet unit  42  in the radial direction. For instance, it is preferable that the thickness of the stator core  52  in the radial direction is greater than half the thickness of the first magnets  131  arranged at the pole-to-pole center in the magnet unit  42 . It is also preferable that the thickness of the stator core  52  in the radial direction is smaller than that of the magnet unit  42 . In this case, a magnet magnetic flux is approximately 1 T, while the saturation magnetic flux density in the stator core  52  is 2 T. The leakage of magnetic flux to inside the inner periphery of the stator core  52  is avoided by selecting the thickness of the stator core  52  in the radial direction to be greater than half that of the magnet unit  42 . 
     Magnets arranged to have the Halbach structure or the polar anisotropic structure usually have an arc-shaped magnetic path, so that the magnetic flux may be increased in proportion to a thickness of ones of the magnets which handle a magnetic flux in the circumferential direction. In such a structure, the magnetic flux flowing through the stator core  52  is thought of as not exceeding the magnetic flux flowing in the circumferential direction. In other words, when the magnetic flux produced by the magnets is 1 T, while ferrous metal whose saturation magnetic flux density is 2 T is used to make the stator core  52 , a light weight and compact electrical rotating machine may be produced by selecting the thickness of the stator core  52  to be greater than half that of the magnets. The demagnetizing field is usually exerted by the stator  50  on the magnetic field produced by the magnets, so that the magnetic flux produced by the magnets will be 0.9 T or less. The magnetic permeability of the stator core may, therefore, be properly kept by selecting the thickness of the stator core to be half that of the magnets. 
     Third Embodiment 
     The polar anisotropic structure of the magnet unit  42  of the rotor  40  according to the third embodiment is changed as compared with that according to the first embodiment, and the changed polar anisotropic structure of the magnet unit  42  will be described below in detail. 
     The magnet unit  42  is, as clearly illustrated in  FIGS.  25  and  26   , made using a magnet array referred to as a Halbach array. 
     Specifically, the magnet unit  42  is equipped with first magnets  1131  and second magnets  1132 . The first magnets  1131  have a magnetization direction (i.e., an orientation of a magnetization vector thereof) oriented in the radial direction of the magnet unit  42 . The second magnets  1132  have a magnetization direction (i.e., an orientation of the magnetization vector thereof) oriented in the circumferential direction of the magnet unit  42 . Each of the first magnets  1131  has the easy axis of magnetization oriented in a corresponding radial direction, so that each of the first magnets  1131  has a radial magnetic path directed in the easy axis of magnetization thereof. Similarly, each of the second magnets  132  has the easy axis of magnetization oriented in the circumferential direction, so that each of the second magnets  1132  has a circumferential magnetic path directed in the easy axis of magnetization thereof. 
     The first magnets  1131  of the magnet unit  42  are arrayed at a given interval away from each other in the circumferential direction. Each of the second magnets  1132  of the magnet  42  is disposed between the first magnets  1131  arranged adjacent each other in the circumferential direction. The first magnets  1131  and the second magnets  1132  are each implemented by a rare-earth permanent magnet, such as a neodymium magnet. 
     The first magnets  1131  are arranged away from each other in the circumferential direction so as to have N-poles and S-poles which are created in radially inner portions thereof and face the stator  50 . The N-poles and the S-poles are arranged alternately in the circumferential direction. The second magnets  1132  are arranged to have N-poles and S-poles alternately located adjacent the first magnets  1131  in the circumferential direction. The cylinder  43  which surrounds the magnets  1131  and  1132  may be formed as a soft magnetic core made of a soft magnetic material and which functions as a back core. 
     The first magnets  1131  and  1132 , which are alternately arranged in the circumferential direction to constitute the magnet unit  42 , increase the magnetic flux density in the first magnets  1131 . This results in concentration of magnetic flux on one surface of the magnet unit  42  to enhance the magnetic flux close to the stator  50 . 
     The layout of the circumferentially alternating first and second magnets  1131  and  1132  enables the magnet unit  42  to have a near-sinusoidal magnetic-flux density distribution, making it possible to achieve a higher level of torque, smaller eddy-current loss, and smaller torque ripples; this eddy-current loss may result from a gradual magnetic-flux change of the magnet unit  42 . 
     The layout of the circumferentially alternating first and second magnets  1131  and  1132  may cause magnetic flux to be likely to leak from a farther side of the magnet unit  42  from the stator, i.e. the armature. For addressing such leakage, an annular cylinder  43 , which is made of a soft magnetic material, can be preferably attached to the farther side of the magnet unit  42  from the stator, so that the annular cylinder  43  is radially stacked on the magnet unit  42 . 
     The cylinder  43  to be stacked on the magnet unit  42  preferably has a radial thickness as thin as possible for a small size of the rotary electric machine  10  and/or for a large volume of a radially inside region of the rotor  40 . An excessively thin thickness of the cylinder  43  may however result in magnetic flux leaking from the stacked structure of the magnet unit  42  and the cylinder  43 . 
     The magnets  1131  and  1132 , which are alternately secured to the inner peripheral surface of the cylinder  43  in the circumferential direction, cause centrifugal forces to be individually generated from the respective magnets  1131  and  1132  while the rotor  40  is rotating. In other words, the centrifugal forces individually generated from the respective magnets  1131  and  1132  are applied to the cylinder  43  while the rotor  40  is rotating. 
     If the rotating electrical machine  10  is applied to a vehicle, vibration of the magnets  1131  and  1132  due to vibration of the vehicle running on a bumpy road may cause each of the magnets  1131  and  1132  to apply a corresponding force to the cylinder  43 . 
     The cylinder  43  thus needs suitable prestresses against the above external forces applied from the respective magnets  1131  and  1132 . That is, an excessively thin thickness of the cylinder  43  might decrease the strength, so that the cylinder  43  might be likely to shear. 
     From this viewpoint, the first magnets  1131  and the cylinder  43  are configured to satisfy the following first and second conditions. 
     In the third embodiment, the remanent flux density of the magnet unit  42 , i.e. each of the first magnets  1131 , will be referred to as Br, and the saturation magnetic flux density will be referred to as Bsc. In the third embodiment, each first magnet  1131  has a closer peripheral surface (i.e., a closer circumferential surface) to the stator, and a farther peripheral surface (i.e., a farther circumferential surface)  1131   a  from the stator, and the farther circumferential surface  1131   a  from the stator, which will be referred to as an anti-stator circumferential surface  1131   a , has a distance in the circumferential direction; the distance will be referred to as Ma. 
     The cylinder  43  has a thickness in the radial direction; the thickness will be referred to as Wsc. Each first magnet  1131  has shear stress (i.e., breaking strength) in the radial direction, which will be referred to as Tr, and the cylinder  43  has shear stress (i.e., breaking strength) in the radial direction, which will be referred to as Ts. 
     The first condition is that each first magnet  1131  and the cylinder  43  satisfy the relation of Br×Ma≤Bsc×Wsc for reducing magnetic flux leakage. 
     For example, if the effective magnetic flux density of the magnet unit  42  (more specifically, each first magnet  1311 ) is 1.0 T and the saturation magnetic flux density of the cylinder  43  is 2.0 T, a value of the thickness Wsc is determined to satisfy the relation of Ma/2≤Wsc. That is, a value of the thickness Wsc is set to be equal to or longer than half of the distance Ma of the anti-stator circumferential surface  1131   a  in the circumferential direction of the first magnet  1131 . 
     Neodymium magnets or SS-FeNi magnets are currently considered to have a highest value 1.6 T of the saturation magnetic flux density Js, and available magnets have a value of the saturation magnetic flux density within not more than the range from 1.0 to 1.5 T inclusive. Even if rotating electrical machines or linear motors are designed not to use expensive magnets or designed to use a large number of magnets, they are predicted to be within the range from 0.3 to 1.0 T, because they have manufacturing tolerances and/or a non-contact air gap that enables their movement. In addition, non-oriented magnetic steel sheets have a value of the saturation magnetic flux density within the range from 1.8 to 1.9 T, and steel sheets, such as SUY, have a value 2.2 T of the saturation magnetic flux density. 
     For the above reasons, each first magnet  1311  and the cylinder  43 , which are designed to satisfy the relation of Ma/2 Wsc, normally prevent magnetic flux leakage. 
     The second condition is that each first magnet  1131  and the cylinder  43  satisfy the relation of Tr×Ma&lt;Ts×Wsc for causing the cylinder  43  to have suitable strength. 
     For example, if the shear stress of each first magnet  1131  in the radial direction is 60 MPa and the shear stress of the cylinder  43  in the redial direction is 240 Mpa, a value of the thickness Wsc is determined to satisfy the relation of Ma/4 Wsc. That is, a value of the thickness Wsc is set to be longer than quarter of the distance Ma of the anti-stator circumferential surface  1131   a  in the circumferential direction of the first magnet  1131 . 
     For example, the thickness Wsc of the cylinder  43  is set to be equal to or longer than half of the distance Ma of the anti-stator circumferential surface  1131   a  in the circumferential direction of the first magnet  1131 , making it possible to satisfy the first and second conditions. 
     This setting of the thickness Wsc of the cylinder  43  enables the thickness of the rotor  40  to be thinner while suitably reducing magnetic flux leakage. This setting of the thickness Wsc of the cylinder  43  also enables the first magnets  1131  and the cylinder  43  to have proper strength while the thickness of the rotor  40  becomes thinner, making it possible to reliably retain the magnets  1131  and  1132 . 
     The magnets  1131  and  1132  and the cylinder  43  according to the second embodiment may be designed to satisfy the first and second conditions. 
     Fourth Embodiment 
     The polar anisotropic structure of a magnet unit  1042  according to the fourth embodiment is changed as compared with the magnet unit  42  according to each of the above embodiments, and the changed polar anisotropic structure of the magnet unit  1042  will be described below in detail. 
     The magnet unit  1042  of the fourth embodiment is, as illustrated in  FIG.  27   , arranged radially outside of the stator  50  to face the stator  50 , which is similar to the magnet unit  42  according to each of the above embodiments. Like the above embodiments, the magnet unit  1042  is secured to the inner peripheral surface of the cylinder  43 . 
     The magnet unit  1042  is, as illustrated in  FIGS.  27  and  28   , made using a magnet array referred to as a Halbach array. 
     Specifically, the magnet unit  1042  is comprised of first magnets  1010  and second magnets  1020 . Each of the first magnets  1010  has linear first magnetization vectors, and each of the second magnets  1020  has second magnetization vectors. Each of the first magnetization vectors has a given orientation, and each of the second magnetization vectors has a given orientation that is different from the orientation of each of the first magnetization vectors. 
     That is, each first magnetization vector of the first magnets  1010  is oriented to be closer to the corresponding radial direction than each second magnetization vector of the second magnets  1020 . Each second magnetization vector of the second magnets  1020  is oriented to be closer to the circumferential direction than each first magnetization vector. 
     The first magnets  1010  are arrayed at given intervals away from one another in the circumferential direction. Each of the second magnets  1020  is disposed between a corresponding adjacent pair of the first magnets  1010  in the circumferential direction. 
     The first magnets  1010  and the second magnets  1020  of the fourth embodiment are arranged in the form of an arc in the circumferential direction of the rotor  400  such that one of circumferential ends of each first magnet  1010  abuts on an adjacent one of circumferential ends of a corresponding adjacent second magnet  1020 . That is, the first magnets  1010  and the second magnets  1020  are alternately arranged with no gaps therebetween, so that the magnet unit  1042  is arranged annularly, i.e., concentrically with respect to the rotor  40 . 
     Each of the arc-shaped first magnets  1010  has the corresponding d-axis, which represents the center of the corresponding magnetic pole, at the center thereof in the circumferential direction. Each of the arc-shaped second magnets  1020  has the corresponding q-axis, which represents a corresponding magnetic-pole boundary, at the center thereof in the circumferential direction. 
     The following describes the first and second magnetization vectors of the first and second magnets  1010  and  1020 . 
     First, the following describes an overall orientation of the first magnetization vectors, and an overall orientation of the second magnetization vectors. 
     The first magnets  1010  of each circumferentially adjacent pair have different overall orientations, that is, opposite overall orientations, of the first magnetization vectors. Specifically, the first magnets  1010  of the fourth embodiment may be categorized into two groups: 
     The first magnets  1010  categorized in the first group, each of which has the first magnetization vectors oriented from an anti-stator circumferential-surface side to the stator side, i.e. the radially inward direction, will also be referred to as first A magnets  1011 . In contrast, the first magnets  1010  categorized in the second group, each of which has the first magnetization vectors oriented from the stator side to the anti-stator circumferential-surface side will also be referred to as first B magnets  1012 . 
     Similarly, the second magnets  1020  of each circumferentially adjacent pair have different orientations, that is, opposite orientations, of the second magnetization vectors. Each of the second magnetization vectors of the second magnets  1020  is oriented to flow from a corresponding adjacent first B magnet  1012  to a corresponding adjacent first A magnet  1011 . The second magnets  1020  of the fourth embodiment may be categorized into two groups: 
     The second magnets  1020  categorized in the first group, each of which has the second magnetization vectors oriented in a counter clockwise direction in  FIG.  28   , will also be referred to as second A magnets  1021 . In contrast, the second magnets  1020  categorized in the second group, each of which has the second magnetization vectors oriented in a clockwise direction in  FIG.  28   , will also be referred to as second B magnets  1022 . 
     Next, the following describes the individual directions of the first magnetization vectors of the first magnets  1010 , and the individual directions of the second magnetization vectors of the second magnets  1020  in detail. 
     The first magnetization vectors of each first A magnet  1011 , passing through corresponding circumferential positions of the first A magnet  1011 , are directed in the corresponding respective radial directions. 
     That is, the first magnetization vectors of each first A magnet  1011  radially extend in the corresponding respective radial directions through the center axis of the rotor  40 . In other words, each of the first A magnets  1011  is configured as a radially oriented magnet having magnetic orientations with respect to the center axis of the rotor  40 . This results in the first magnetization vector of the first A magnet  1011  passing through the d-axis as the center of the corresponding magnetic pole being parallel to the d-axis. In contrast, this results in the first magnetization vectors of the first A magnet  1011  being more inclined toward the d-axis as the first magnetization vectors are farther from the d-axis. 
     Similarly, the second magnetization vectors of each first B magnet  1012 , passing through corresponding circumferential positions of the second A magnet  1012 , are directed in the corresponding respective radial directions. That is, the first magnetization vectors of each first B magnet  1012  radially extend in the corresponding respective radial directions through the center axis of the rotor  40 . In other words, each of the first B magnets  1012  is configured as a radially oriented magnet having magnetic orientations with respect to the center axis of the rotor  40 . This results in the first magnetization vector of the first B magnet  1012  passing through the d-axis as the center of the corresponding magnetic pole being parallel to the d-axis. 
     In contrast, this results in the first magnetization vectors of the first B magnet  1012  being more inclined away from the d-axis as the first magnetization vectors are located farther from the d-axis. 
     The second magnetization vectors of each second magnet  1020  are directed to be perpendicular to the q-axis. That is, each of the second magnets  1020  is configured as a parallel oriented magnet having magnetic orientations that are each parallel to the direction perpendicular to the corresponding q-axis. This results in the second magnetization vectors of each second magnet  1020  being non-orthogonal to and being inclined to an abutment surface  1023  that abuts on the corresponding adjacent first magnet  1010 . For example, the second magnetization vectors of each second magnet  1020  are each inclined to the abutment surface  1023  by an angle θ 101 . 
     That is, the second magnetization vectors of each second magnet  1020  are inclined to a normal line to the abutment surface  1023  by the angle θ 101  so as to be farther from the stator radially outwardly. In addition, the second magnetization vectors of each second magnet  1020  are inclined to an abutment surface  1024  that abuts on the corresponding adjacent first B magnet  1012  so as to be closer to the stator radially inwardly. 
     The following describes how to configure the first and second magnetization vectors in detail. 
     Each of the first magnets  1010  has easy axes of magnetization, which are oriented in the corresponding respective radial directions, and therefore has magnetic paths aligned with the respective easy axes of magnetization. 
     The magnetic paths aligned with the respective easy axes of magnetization in each first A magnet  1011  enables magnetization vectors to be aligned toward the radially inward direction, i.e. the stator side; each of the magnetization vectors represents the direction of magnetization. The magnetic paths aligned with the respective easy axes of magnetization in each first B magnet  1012  enables magnetization vectors to be aligned toward the radially outward direction, i.e. the anti-stator side; each of the magnetization vectors represents the direction of magnetization. 
     Each of the second magnets  1020  has easy axes of magnetization, which are oriented to be perpendicular to the corresponding q-axis, and therefore has magnetic paths aligned with the respective easy axes of magnetization. 
     The magnetic paths aligned with the respective easy axes of magnetization in each second A magnet  1021  enables magnetization vectors to be aligned toward the counter-clockwise, i.e. toward the corresponding adjacent first A magnet  1011 . The magnetic paths formed along the respective easy axes of magnetization in each second B magnet  1022  enables magnetization vectors to be aligned toward the clockwise, i.e. the corresponding adjacent first A magnet  1011 . 
       FIG.  29    illustrates, as a comparison example, a magnet unit  2042  that is comprised of 
     1. First magnets  2010 , each of which has magnetization vectors that are parallel to the corresponding d-axis 
     2. Second magnets  2020 , each of which has magnetization vectors that are perpendicular to the corresponding q-axis 
     The other pieces of information about the magnet unit  2042 , such as the shape and arrangement of the magnet unit  2042 , are identical to those about the magnet unit  1042 . 
     The magnetization vectors at each circumferential end of the first magnet  2010  according to the comparison example are inclined toward the corresponding adjacent second magnet side i.e. the circumferential outward, with respect to the corresponding respective radial directions at respective angles θ 102 .  FIG.  30 ( a )  is a development view of the first magnet  2010  that is linearly expanded. The magnetization vectors at each circumferential end of the first magnet  2010 , as illustrated in  FIG.  30 ( a ) , are more inclined toward the corresponding adjacent second magnet side, i.e. the radially outward direction as they are closer to the corresponding circumferential end. This may make it difficult for magnetic flux of the first magnet  2010  to converge to the corresponding d-axis, resulting in a reduction in the since wave matching percentage of the magnetic flux density distribution of the first magnet  2010  (see a dashed curve in  FIG.  31   ). 
     In contrast, the magnetization vectors at each circumferential end of the first magnet  1010  of the magnet unit  1042  according to the fourth embodiment are parallel to the corresponding respective radial directions.  FIG.  30 ( b )  is a development view of the first A magnet  1011  that is linearly expanded. The magnetization vector at any circumferential position of the first A magnet  1011 , as illustrated in  FIG.  30 ( b ) , is parallel to the corresponding radial direction. This therefore makes it easier for magnetic flux of the first A magnet  1011  to converge to the corresponding d-axis, resulting in the since wave matching percentage of the magnetic flux density distribution of the first magnet  2010  being higher (see a solid curve in  FIG.  31   ). 
     The above fourth embodiment has the following beneficial advantages: 
     The first magnets  1010  are arranged at given intervals away from one another in the circumferential direction, and each of the second magnets  1020  is disposed between a corresponding adjacent pair of the first magnets  1010  in the circumferential direction. In this arrangement, if linear magnetization vectors (i.e. their magnetization directions) were aligned with the corresponding d-axis to provide a parallel magnetized orientation as illustrated in  FIG.  29    as the comparative example, this alignment would make it difficult for magnetic flux to converge to the corresponding d-axis. This difficulty in convergence of magnetic flux to the corresponding d-axis becomes more pronounced as the rotor  40  is arranged to be more radially inward of the stator  50 . This difficulty in convergence of magnetic flux to the corresponding d-axis also becomes more pronounced as the number of magnetic poles of the rotor  40  is lower, so that the diameter of the rotor  40  is lower. 
     From this viewpoint, the magnetization vectors of the first magnet  1010  are respectively aligned along the corresponding radial directions to provide a radial magnetized orientation. This makes it easier for magnetic flux density to converge to the corresponding d-axis side although the first and second magnets  1010  and  1020 , each of which has linear magnetization vectors, are used, resulting in the magnetic flux density distribution of each of the first and second magnets  1010  and  1020  being closer to a sinusoidal waveform. This therefore reduces torque ripple and cogging torque, the generation of eddy current, and an eddy-current loss. 
     Fifth Embodiment 
     The fifth embodiment is configured such that magnetization vectors of each first magnet  3010  are changed as compared with those according to the fourth embodiment, and the changed portion will be described below in detail. 
     Each first magnetization vector of the first magnet  3010  according to the fifth embodiment becomes closer to the parallel direction of the corresponding radial axis as the first magnet vector becomes closer to the corresponding d-axis, i.e., the circumferential center of the first magnet  3010 . In addition, each first magnetization vector of the first magnet  3010  according to the fifth embodiment is more inclined toward the corresponding radial axis as the first magnet vector becomes closer to one of the corresponding q-axes. That is, an angle θ 103  made between each magnetization vector and the corresponding radial direction becomes larger as the magnetization vector becomes closer to one of the corresponding q-axes. In particular, the magnetization vector on the corresponding d-axis is designed to be parallel to the corresponding radial direction. 
     The first magnets  3010  include first A magnets  3011  and first B magnets  3012  that are circumferentially adjacent to one another. The direction of each magnetization vector in the first A magnet  3011  is identical to the direction of each magnetization vector in the first B magnet  3012 , and an inclination angle of each magnetization vector in the first A magnet  3011  with respect to the corresponding radial direction is identical to an inclination angle of each magnetization vector in the first B magnet  3012 , except that the orientation of each magnetization vector in the first A magnet  3011  is opposite to that of each magnetization vector in the first B magnet  3012 . 
     The following describes how to configure the first and second magnetization vectors in detail. The easy axes of magnetization in each first magnet  3010  are oriented such that 
     1. Each of the easy axes of magnetization becomes closer to the parallel direction of the corresponding radial axis as the corresponding one of the easy axes of magnetization becomes closer to the corresponding d-axis side 
     2. Each of the easy axes of magnetization is more inclined toward the corresponding d-axis side as the corresponding one of the easy axes of magnetization becomes closer to one of the corresponding q-axes 
     In the first A magnet  3011 , the magnetic paths are aligned with the respective easy axes of magnetization such that the magnetization vectors are oriented toward the radially inward side, i.e. the stator side, of the rotor. 
     In contrast, in the second A magnet  3012 , the magnetic paths are aligned with the respective easy axes of magnetization such that the magnetization vectors are oriented toward the radially outward side, i.e. the anti-stator side, of the rotor. 
     Each of the magnetization vectors of the magnet unit  3042  of the fifth embodiment is more inclined toward the corresponding d-axis with respect to the corresponding radial direction as the corresponding one of the magnetization vectors becomes closer to the corresponding to each circumferential end of the first magnet  3010 . 
       FIG.  33    is a development view of the first A magnet  3011  that is linearly expanded according to the fifth embodiment. As illustrated in  FIG.  33   , this makes it easier for magnetic flux of the first A magnet  3011  to converge to the corresponding d-axis as compared with the magnet unit  1042  or the comparative example illustrated in  FIG.  29   , resulting in the since wave matching percentage of the magnetic flux density distribution of the first magnet  2010  being higher. This therefore reduces torque ripple and cogging torque, the generation of eddy current, and an eddy-current loss. 
     Sixth Embodiment 
     The polar anisotropic structure of a magnet unit  4042  according to the sixth embodiment is changed as compared with the magnet unit  42  of the rotor  40 , and the changed polar anisotropic structure of the magnet unit  4042  will be described below in detail. 
     The magnet unit  4042  of the sixth embodiment is arranged radially outside of the stator  50  to face the stator  50 , which is similar to the magnet unit  42  according to each of the above embodiments. Like the above embodiments, the magnet unit  4042  is secured to the inner peripheral surface of the cylinder  43 . 
     The magnet unit  4042  is, as illustrated in  FIG.  34   , made using a magnet array referred to as a Halbach array. 
     Specifically, the magnet unit  4042  is comprised of first magnets  4010  and second magnets  4020 . Each of the first magnets  4010  has linear first magnetization vectors, and each of the second magnets  4020  has linear second magnetization vectors. Each of the first magnetization vectors has a given orientation, and each of the second magnetization vectors has a given orientation that is different from the orientation of each of the first magnetization vectors. 
     That is, each first magnetization vector of the first magnets  4010  is oriented to be closer to the corresponding radial direction than each second magnetization vector of the second magnets  4020 . Each second magnetization vector of the second magnets  4020  is oriented to be closer to the circumferential direction than each first magnetization vector. 
     The first magnets  4010  are arrayed at given intervals away from one another in the circumferential direction. Each of the second magnets  4020  is disposed between a corresponding adjacent pair of the first magnets  4010  in the circumferential direction. 
     The first magnets  4010  and the second magnets  4020  of the sixth embodiment are arranged in the form of an arc in the circumferential direction of the rotor  400  such that one of circumferential ends of each first magnet  4010  abuts on an adjacent one of circumferential ends of a corresponding adjacent second magnet  4020 . That is, the first magnets  4010  and the second magnets  4020  are alternately arranged with no gaps therebetween, so that the magnet unit  1042  is arranged annularly, i.e., concentrically with respect to the rotor  40 . 
     Each of the arc-shaped first magnets  4010  has the corresponding d-axis, which represents the center of the corresponding magnetic pole, at the center thereof in the circumferential direction. Each of the arc-shaped second magnets  4020  has the corresponding q-axis, which represents a corresponding magnetic-pole boundary, at the center thereof in the circumferential direction. 
     The following describes the first and second magnetization vectors of the first and second magnets  4010  and  4020 . 
     First, the following describes an overall orientation of the first magnetization vectors, and an overall orientation of the second magnetization vectors. 
     The first magnets  4010  of each circumferentially adjacent pair have different overall orientations, that is, opposite overall orientations, of the first magnetization vectors. Specifically, the first magnets  4010  of the sixth embodiment may be categorized into two groups: 
     The first magnets  4010  categorized in the first group, each of which has the first magnetization vectors oriented from the anti-stator circumferential-surface side to the stator side, i.e. the radially inward direction, will also be referred to as first A magnets  4011 . In contrast, the first magnets  4010  categorized in the second group, each of which has the first magnetization vectors oriented from the stator side to the anti-stator circumferential-surface side will also be referred to as first B magnets  4012 . 
     Similarly, the second magnets  4020  of each circumferentially adjacent pair have different orientations, that is, opposite orientations, of the second magnetization vectors. Each of the second magnetization vectors of the second magnets  4020  is oriented to flow from a corresponding adjacent first B magnet  4012  to a corresponding adjacent first A magnet  4011 . The second magnets  4020  of the sixth embodiment may be categorized into two groups: 
     The second magnets  4020  categorized in the first group, each of which has the second magnetization vectors oriented in a counter clockwise direction in  FIG.  34   , will also be referred to as second A magnets  4021 . In contrast, the second magnets  4020  categorized in the second group, each of which has the second magnetization vectors oriented in a clockwise direction in  FIG.  34   , will also be referred to as second B magnets  4022 . 
     Next, the following describes the individual directions of the first magnetization vectors of the first magnets  4010 , and the individual directions of the second magnetization vectors of the second magnets  4020  in detail. 
     The first magnetization vectors of each first A magnet  4011  are directed to be parallel to the corresponding respective radial directions, and the second magnetization vectors of each first B magnet  4012  are similarly directed to be parallel to the corresponding respective radial directions. 
     The second magnetization vectors of each second magnet  1020  are inclined toward the stator side with respect to the direction perpendicular to the q-axis. That is, each of the second magnets  1020  is configured as a parallel oriented magnet having magnetic orientations that are parallel to a predetermined direction; the predetermined direction is inclined by a predetermined angle θ 103  with respect to the direction perpendicular to the corresponding q-axis. 
     The predetermined angle θ 103  of each second magnetization vector by which the corresponding second magnetization vector is inclined with respect to the direction perpendicular to the corresponding q-axis is preferably set to be equal to or more than a predetermined angle θ 101 ; the predetermined angle θ 101  is formed between the q-axis and an abutment surface  4023 ; the abutment surface  4023  is an abutment surface of the second magnet  4020 , which abuts on a corresponding adjacent circumferential end of the adjacent first A magnet  4011 . That is, the abutment of the  4023  of the second magnet  4020  is a circumferential end surface thereof, which abuts on a corresponding adjacent circumferential end of the adjacent first A magnet  4011 . 
     Setting the predetermined angle θ 103  to a value equal to or more than the predetermined angle θ 101  formed between the q-axis and the abutment surface  4023  enables the second magnetization vectors of the second magnet  4020  to be perpendicular to the abutment surface  4023  or inclined toward the stator with respect to the abutment surface  4023 .  FIG.  34    illustrates a case where the predetermined angle θ 103  is identical to the predetermined angle θ 101 , so that the second magnetization vectors of the second magnet  4020  are orthogonal to the abutment surface  4023 . 
     The following describes how to configure the first and second magnetization vectors in detail. 
     Each of the second magnets  4020  has easy axes of magnetization, which are oriented to be inclined by the predetermined angle θ 103  with respect to the direction perpendicular to the corresponding q-axis toward the stator, and therefore has magnetic paths formed along the respective easy axes of magnetization. 
     The magnetic paths formed along the respective easy axes of magnetization in each second A magnet  4021  enables magnetization vectors to be aligned toward the counter-clockwise, and the magnetic paths formed along the respective easy axes of magnetization in each second B magnet  4022  enables magnetization vectors to be aligned toward the clockwise. 
     The following demonstrates a result of comparison between the magnet unit  4042  and the magnet  2042  illustrated as the comparison example illustrated in  FIG.  29   . 
     The magnetization vectors at each circumferential end of the second magnet  2020  according to the comparison example, as illustrated in  FIG.  30 ( a ) , are non-orthogonal to the abutment surface  4023  and are each inclined, by the predetermined angle θ 101 , with respect to a normal line perpendicular to the abutment surface  4023 . This may make it difficult for magnetic flux of the second magnet  2023  to converge to the corresponding d-axis, resulting in a reduction in the since wave matching percentage of the magnetic flux density distribution of the second magnet  2020 . This difficulty in convergence of magnetic flux to the corresponding d-axis becomes more pronounced as the number of magnetic poles of the rotor  40  becomes lower, and/or the diameter of the magnet unit  2042  becomes lower (i.e., the curvature of the magnet unit  2042  becomes greater). 
     In contrast, the magnetization vectors at each circumferential end of the second magnet  4020  of the magnet unit  4042  according to the sixth embodiment are perpendicular to the abutment surface  4023  or are inclined toward the stator with respect to the normal line perpendicular to the abutment surface  4023 .  FIG.  35    is a development view of the second magnet  4020  that is linearly expanded. This makes it easier for magnetic flux of the second magnet  4020  to converge to the corresponding d-axis, resulting in the since wave matching percentage of the magnetic flux density distribution of the second magnet  4020  being higher. This therefore reduces torque ripple and cogging torque, the generation of eddy current, and an eddy-current loss. 
     The sixth embodiment can be combined to the fourth embodiment or the fifth embodiment. For example, as illustrated in  FIG.  36   , the second magnet  4020  of the sixth embodiment and the first magnet  1010  of the fourth embodiment can be combined to each other to constitute a magnet unit  42 . 
     Seventh Embodiment 
     The seventh embodiment is configured such that magnetization vectors of each second magnet  5020  are changed as compared with those according to the sixth embodiment, and the changed portion will be described below in detail. Description of one or more parts of the seventh embodiment, which are identical to those of the sixth embodiment, in detail will be omitted here. 
     As illustrated in  FIG.  37   , the second magnet  5020  of the seventh embodiment is configured as a radially oriented magnet. Specifically, the second magnet  520  has magnetization vectors that are radially oriented about a center point O defined at the anti-stator side portion (i.e., the anti-armature side portion or the radially outward portion) of the rotor  40 . The center point O is disposed to be closer to the first B magnet  4012  than to the first A magnet  4011 . The second magnet  5020  has anti-stator side corners, and a selected one of the anti-stator side corners, which is closer to the first B magnet  4012  than the other of the anti-stator side corners, is defined as the center point O according to the seventh embodiment. The magnetization vectors of the second magnet  5020  are radially oriented about the center point O. 
     The following describes how to configure the second magnetization vectors in detail. 
     Each of the second magnets  5020  has easy axes of magnetization, which are radially oriented about the center point O, and therefore has magnetic paths formed along the respective easy axes of magnetization. 
     One of the magnetization vectors in the magnet unit  5042  of the seventh embodiment, which is oriented from the center point O toward a corner P 100  of the second magnet  5020 , is inclined toward the stator side, i.e., the radially inward side, with respect to the direction perpendicular to the q-axis. The corner P 100  of the second magnet  5020  is a corner of the second magnet  5020 , which is closer to the first A magnet  4011  and closer to the stator. This enables the length of the magnetic path of the second magnet  5020  from the center point O to the corner P 100  to be longer. 
     This configuration of the second magnet  5020  therefore enables the second magnet  5020  to be less likely to demagnetize, and makes it easier for magnetic flux of the second magnet  5020  to converge to the corresponding d-axis, resulting in the since wave matching percentage of the magnetic flux density distribution of the second magnet  5020  being higher. This therefore reduces torque ripple and cogging torque, the generation of eddy current, and an eddy-current loss. 
     The seventh embodiment can be combined to the fourth embodiment or the fifth embodiment. That is, the second magnet  5020  of the seventh embodiment and the first magnet  1010  of the fourth embodiment or the first magnet  2010  of the fifth embodiment can be combined to each other to constitute a magnet unit. 
     Modifications of the above structure will be described below. 
     Modification 1 
     In the above embodiment, the outer peripheral surface of the stator core  52  has a curved surface without any irregularities. The plurality of conductor groups  81  are arranged at given intervals away from one another on the outer peripheral surface of the stator core  52 . This layout may be changed. For instance, the stator core  52  illustrated in  FIG.  38    is equipped with the circular ring-shaped yoke  141  and the protrusions  142 . The yoke  141  is located on the opposite side (i.e., a lower side, as viewed in the drawing) of the stator coil  51  to the rotor  40  in the radial direction. Each of the protrusions  142  protrudes into a gap between a respective two of the straight sections  83  arranged adjacent each other in the circumferential direction. The protrusions  142  are arranged at given intervals away from one another in the circumferential direction radially outside the yoke  141 , i.e., close to the rotor  40 . Each of the conductor groups  81  of the stator coil  51  engages the protrusions  142  in the circumferential direction, in other words, the protrusions  142  are used as positioners to position and array the conductor groups  81  in the circumferential direction. The protrusions  142  correspond to conductor-to-conductor members. 
     A radial thickness of each of the protrusions  142  from the yoke  141 , in other words, a distance W, as illustrated in  FIG.  38   , between the inner surface  320  of the straight sections  82  which is placed in contact with the yoke  141  and the top of the protrusion  412  in the radial direction of the yoke  141  is selected to be smaller than half a radial thickness (as indicated by H 1  in the drawing) of the straight sections  83  arranged adjacent the yoke  141  in the radial direction. In other words, non-conductive members (i.e., the sealing members  57 ) preferably each occupy three-fourths of a dimension (i.e., thickness) T 1  (i.e., twice the thickness of the conductors  82 , in other words, a minimum distance between the surface  320  of the conductor group  81  placed in contact with the stator core  52  and the surface  330  of the conductor group  81  facing the rotor  40 ) of the conductor groups (i.e., conductors)  81  in the radial direction of the stator coil  51  (i.e., the stator core  52 ). Such selection of the thickness of the protrusions  142  causes each of the protrusions  142  not to function as a tooth between the conductor groups  81  (i.e., the straight sections  83 ) arranged adjacent each other in the circumferential direction, so that there are no magnetic paths which would usually be formed by the teeth. The protrusions  142  need not necessarily to be arranged between a respective circumferentially adjacent two of all the conductor groups  81 , but however, a single protrusion  142  may be disposed at least only between two of the conductor groups  81  which are arranged adjacent each other in the circumferential direction. For instance, the protrusions  142  may be disposed away from each other in the circumferential direction at equal intervals each of which corresponds to a given number of the conductor groups  81 . Each of the protrusions  142  may be designed to have any shape, such as a rectangular or arc-shape. 
     The straight sections  83  may alternatively be arranged in a single layer on the outer peripheral surface of the stator core  52 . In a broad sense, the thickness of the protrusions  142  from the yoke  141  in the radial direction may be smaller than half that of the straight sections  83  in the radial direction. 
     If an imaginary circle whose center is located at the axial center of the rotating shaft  11  and which passes through the radial centers of the straight sections  83  placed adjacent the yoke  141  in the radial direction is defined, each of the protrusions  142  may be shaped to protrude only within the imaginary circle, in other words, not to protrude radially outside the imaginary circle toward the rotor  40 . 
     The above structure in which the protrusions  142  have the limited thickness in the radial direction and do not function as teeth in the gaps between the straight sections  83  arranged adjacent each other in the circumferential direction enables the adjacent straight sections  83  to be disposed closer to each other as compared with a case where teeth are provided in the gaps between the straight sections  83 . This enables a sectional area of the conductor body  82   a  to be increased, thereby reducing heat generated upon excitation of the stator coil  51 . The absence of the teeth enables magnetic saturation to be eliminated to increase the amount of electrical current delivered to the stator coil  51 . It is, however, possible to alleviate the adverse effects arising from an increase in amount of heat generated by the increase in electrical current delivered to the stator coil  51 . The stator coil  51 , as described above, has the turns  84  which are shifted in the radial direction and equipped with the interference avoiding portions with the adjacent turns  84 , thereby enabling the turns  84  to be disposed away from each other in the radial direction. This enhances the heat dissipation from the turns  84 . The above structure is enabled to optimize the heat dissipating ability of the stator  50 . 
     The radial thickness of the protrusions  142  may not be restricted by the dimension H 1  in  FIG.  38    as long as the yoke  141  of the stator core  52  and the magnet unit  42  (i.e., each of the magnets  91  and  92 ) of the rotor  40  are arranged at given distances away from one another. Specifically, the radial thickness of the protrusions  142  may be larger than or equal to the dimension H 1  in  FIG.  38    as long as the yoke  141  and the magnet unit  42  arranged 2 mm or more away from each other. For instance, in a case where the radial thickness of the straight section  83  is larger than 2 mm, and each of the conductor groups  81  is made up of the two conductors  82  stacked in the radial direction, each of the protrusions  142  may be shaped to occupy a region ranging to half the thickness of the straight section  83  not contacting the yoke  141 , i.e., the thickness of the conductor  82  located farther away from the yoke  141 . In this case, the above beneficial advantages will be obtained by increasing the conductive sectional area of the conductor groups  81  as long as the radial thickness of the protrusions  142  is at least H 1 ×3/2. 
     The stator core  52  may be designed to have the structure illustrated in  FIG.  39   .  FIG.  39    omits the sealing members  57 , but the sealing members  57  may be used.  FIG.  39    illustrates the magnet unit  42  and the stator core  52  as being arranged linearly for the sake of simplicity. 
     In the structure of  FIG.  39   , the stator  50  has the protrusions  142  as conductor-to-conductor members each of which is arranged between a respective two of the conductors  82  (i.e., the straight sections  83 ) located adjacent each other in the circumferential direction. The stator  50  is equipped with the portions  350  each of which magnetically operates along with one of the magnetic poles (i.e., an N-pole or an S-pole) of the magnet unit  42  when the stator coil  51  is excited. The portions  350  extend in the circumferential direction of the stator  50 . If each of the portions  350  has a length Wn in the circumferential direction of the stator  50 , the sum of widths of the protrusions  142  lying in a range of this length Wn (i.e., the total dimension of the protrusions  412  in the circumferential direction of the stator  50  in the range of length Wn) is defined as Wt, the saturation magnetic flux density of the protrusions  412  is defined as Bs, a width of a portion of the magnet unit  42  equivalent to one of the magnetic poles of the magnet unit  42  in the circumferential direction of the magnet unit  42  is defined as Wm, and the remanent flux density in the magnet unit  42  is defined as Br, the protrusions  142  are made of a magnetic material meeting a relation of
 
 Wt×Bs≤Wm×Br   (1)
 
     The range Wn is defined to contain ones of the conductor groups  81  which are arranged adjacent each other in the circumferential direction and which overlap in time of excitation thereof with each other. It is advisable that a reference (i.e., a border) used in defining the range Wn be set to the center of the gap  56  between the conductor groups  81 . For instance, in the structure illustrated in  FIG.  39   , the plurality of conductor groups  81  lying in the range Wn include the first, the second, the third, and the fourth conductor groups  81  where the first conductor group  81  is closest to the magnetic center of the N-pole. The range Wn is defined to include the total of those four conductor groups  81 . Ends (i.e., outer limits) of the range Wn are defined to lie at the centers of the gaps  56 . 
     In  FIG.  39   , the range Wn contains half of the protrusion  142  inside each of the ends thereof. The total of the four protrusions  142  lie in the range Wn. If the width of each of the protrusions  142  (i.e., a dimension of the protrusion  142  in the circumferential direction of the stator  50 , in other words, an interval between the adjacent conductor groups  81 ) is defined as A, the sum of widths Wt of the protrusions  142  lying in the range Wn meets a relation of Wt=1/2A+A+A+A+1/2A= 4 A. 
     Specifically, the three-phase windings of the stator coil  51  in this embodiment are made in the form of distributed windings. In the stator coil  51 , the number of the protrusions  142  for each pole of the magnet unit  42 , that is, the number of the gaps  56  each between the adjacent conductor groups  81  is selected to be “the number of phases×Q” where Q is the number of the conductors  82  for each phase which are placed in contact with the stator core  52 . In other words, in the case where the conductors  82  are stacked in the radial direction of the rotor  40  to constitute each of the conductor groups  81 , Q is the number of inner ones of the conductors  82  of the conductor groups  81  for each phase. In this case, when the three-phase windings of the stator coil  51  are excited in a given sequence, the protrusions  142  for two of the three-phases within each pole are magnetically excited. The total circumferential width Wt of the protrusions  142  excited upon excitation of the stator coil  51  within a range of each pole of the magnet unit  42 , therefore, meets a relation of “the number of the phases excited×Q×A=2×2×A where A is the width of each of the protrusions  142  (i.e., the gap  56 ) in the circumferential direction. 
     The total width Wt is determined in the above way. Additionally, the protrusions  142  of the stator core  52  are made of magnetic material meeting the above equation (1). The total width Wt is also viewed as being equivalent to a circumferential dimension of where the relative magnetic permeability is expected to become greater than one within each pole. The total width Wt may alternatively be determined as a circumferential width of the protrusions  142  in each pole with some margin. Specifically, since the number of the protrusions  142  for each pole of the magnet unit  42  is given by the number of phases×Q, the width of the protrusions  412  in each pole (i.e., the total width Wt) may be given by the number of phases×Q×A=3×2×A= 6 A. 
     The distributed winding, as referred to herein, means that there is a pair of poles (i.e., the N-pole and the S-pole) of the stator coil  51  for each pair of magnetic poles. The pair of poles of the stator coil  51 , as referred to herein, is made of the two straight sections  83  in which electrical current flows in opposite directions and the turn  84  electrically connecting them together. Note that a short pitch winding or a full pitch winding may be viewed as an equivalent of the distributed winding as long as it meets the above conditions. 
     Next, the case of a concentrated winding will be described below. The concentrated winding, as referred to herein, means that the width of each pair of magnetic poles is different from that of each pair of poles of the stator coil  51 . An example of the concentrated winding includes a structure in which there are three conductor groups  81  for each pair of magnetic poles, in which there are three conductor groups  81  for two pairs of magnetic poles, in which there are nine conductor groups  81  for four pairs of magnetic poles, or in which there are nine conductor groups  81  for five pairs of magnetic poles. 
     In the case where the stator coil  51  is made in the form of the concentrated winding, when the three-phase windings of the stator coil  51  are excited in a given sequence, a portion of the stator coil  51  for two phases is excited. This causes the protrusions  142  for two phases to be magnetically excited. The circumferential width Wt of the protrusions  142  which is magnetically excited upon excitation of the stator winding in a range of each pole of the magnet unit  42  is given by Wt=A×2. The width Wt is determined in this way. The protrusions  142  are made of magnetic material meeting the above equation (1). In the above described case of the concentrated winding, the sum of widths of the protrusions  142  arranged in the circumferential direction of the stator  50  within a region surrounded by the conductor groups  81  for the same phase is defined as A. The dimension Wm in the concentrated winding is given by [an entire circumference of a surface of the magnet unit  42  facing the air gap]×[the number of phases]÷[the number of the distributed conductor groups  81 ]. 
     Usually, a neodymium magnet, a samarium-cobalt magnet, or a ferrite magnet whose value of BH is higher than or equal to 20[MGOe (kJ/m{circumflex over ( )}3)] has Bd=1.0 T or more. Iron has Br=2.0 T or more. The protrusions  142  of the stator core  52  may, therefore, be made of magnetic material meeting a relation of Wt&lt;1/2×Wm for realizing a high-power motor. 
     In a case where each of the conductors  82  is, as described later, equipped with the outer coated layer  182 , the conductors  82  may be arranged in the circumferential direction of the stator core with the outer coated layers  182  placed in contact with each other. In this case, the width Wt may be viewed to be zero or equivalent to thicknesses of the outer coated layers  182  of the conductors  82  contacting with each other. 
     The structure illustrated in  FIG.  38  or  39    is designed to have conductor-to-conductor members (i.e., the protrusions  142 ) which are too small in size for the magnet-produced magnetic flux in the rotor  40 . The rotor  40  is implemented by a surface permanent magnet rotor which has a flat surface and a low inductance, and does not have a salient pole in terms of a magnetic resistance. Such a structure enables the inductance of the stator  50  to be decreased, thereby reducing a risk of distortion of the magnetic flux caused by the switching time gap in the stator coil  51 , which minimizes the electrical erosion of the bearings  21  and  22 . 
     Modification 2 
     The stator  50  equipped with the conductor-to-conductor members made to meet the above equation may be designed to have the following structure. In  FIG.  40   , the stator core  52  is equipped with the teeth  143  as conductor-to-conductor members which are formed in an outer peripheral portion (an upper portion, as viewed in the drawing) of the stator core  52 . The teeth  143  protrude from the yoke  141  and are arranged at given intervals away from one another in the circumferential direction of the stator core  52 . Each of the teeth  143  has a thickness identical with that of the conductor group  81  in the radial direction. The teeth  143  have side surfaces placed in contact with the conductors  82  of the conductor groups  81 . The teeth  143  may alternatively be located away from the conductors  82  through gaps. 
     The teeth  143  are shaped to have a restricted width in the circumferential direction. Specifically, each of the teeth  143  has a stator tooth which is very thin for the volume of magnets. Such a structure of the teeth  143  serves to achieve saturation by the magnet-produced magnetic flux at 1.8 T or more to reduce the permeance, thereby decreasing the inductance. 
     If a surface area of a magnetic flux-acting surface of the magnet unit  42  facing the stator  50  for each pole is defined as Sm, and the remanent flux density of the magnet unit  42  is defined as Br, the magnetic flux in the magnet unit  42  will be Sm×Br. A surface area of each of the teeth  143  facing the rotor  40  is defined as St. The number of the conductors  83  for each phase is defined as m. When the teeth  143  for two phases within a range of one pole are magnetically excited upon excitation of the stator coil  51 , the magnetic flux in the stator  50  is expressed by St×m×2×Bs. The decrease in inductance may be achieved by selecting the dimensions of the teeth  143  to meet a relation of
 
 St×m× 2× Bs&lt;Sm×Br   (2).
 
     In a case where the dimension of the magnet unit  42  is identical with that of the teeth  143  in the axial direction, the above equation (2) may be rewritten as an equation (3) of Wst×m×2×Bs&lt;Wm×Br where Wm is the circumferential width of the magnet unit  42  for each pole, and Wst is the circumferential width of the teeth  143 . For example, when Bs=2 T, Br=1 T, and m=2, the equation (3) will be Wst&lt;Wm/8. In this case, the decrease in inductance may be achieved by selecting the width Wst of the teeth  143  to be smaller than one-eighth (⅛) of the width Wm of the magnet unit  42  for one pole. When m is one, the width Wst of the teeth  143  is preferably selected to be smaller than one-fourth (1/4) of the width Wm of the magnet unit  42  for one pole. 
     “Wst×m×2” in the equation (3) corresponds to a circumferential width of the teeth  143  magnetically excited upon excitation of the stator coil  51  in a range of one pole of the magnet unit  42 . 
     The structure in  FIG.  40    is, like in  FIGS.  38  and  39   , equipped with the conductor-to-conductor members (i.e., the teeth  143 ) which are very small in size for the magnet-produced magnetic flux in the rotor  40 . Such a structure is capable of reducing the inductance of the stator  50  to alleviate a risk of distortion of the magnetic flux arising from the switching time gap in the stator coil  51 , which minimizes the probability of the electrical erosion of the bearings  21  and  22 . Note that the definitions of parameters, such as Wt, Wn, A, and Bs, associated with the stator  50  or parameters, such as Wm and Br, associated with the magnet unit  42  may refer to those in the above described modification 1. 
     Modification 3 
     The above embodiment has the sealing members  57  which cover the stator coil  51  and occupy a region including all of the conductor groups  81  radially outside the stator core  52 , in other words, lie in a region where the thickness of the sealing members  57  is larger than that of the conductor groups  81  in the radial direction. This layout of the sealing members  57  may be changed. For instance, the sealing members  57  may be, as illustrated in  FIG.  41   , designed so that the conductors  82  protrude partially outside the sealing members  57 . Specifically, the sealing members  57  are arranged so that portions of the conductors  82  that are radially outermost portions of the conductor groups  81  are exposed outside the sealing members  57  toward the stator  50 . In this case, the thickness of the sealing members  57  in the radial direction may be identical with or smaller than that of the conductor groups  81 . 
     Modification 4 
     The stator  50  may be, as illustrated in  FIG.  42   , designed not to have the sealing members  57  covering the conductor groups  81 , i.e., the stator coil  51 . In this case, a gap is created between the adjacent conductor groups  81  arranged in the circumferential direction without a conductor-to-conductor member therebetween. In other words, no conductor-to-conductor member is disposed between the conductor groups  81  arranged in the circumferential direction. Air may be arranged in the gaps between the conductor groups  81 . The air may be viewed as a non-magnetic member or an equivalent thereof whose Bs is zero (0). 
     Modification 5 
     The conductor-to-conductor members of the stator  50  may be made of a non-magnetic material other than resin. For instance, a non-metallic material, such as SUS304 that is austenitic stainless steel. 
     Modification 6 
     The stator  50  may be designed not to have the stator core  52 . Specifically, the stator  50  is made of the stator coil  51  shown in  FIG.  12   . The stator coil  51  of the stator  50  may be covered with a sealing member. The stator  50  may alternatively be designed to have an annular winding retainer made from non-magnetic material such as synthetic resin instead of the stator core  52  made from soft magnetic material. 
     Modification 7 
     The structure in the first embodiment uses the magnets  91  and  92  arranged in the circumferential direction to constitute the magnet unit  42  of the rotor  40 . The magnet unit  42  may be made using an annular permanent magnet. For instance, the annular magnet  95  is, as illustrated in  FIG.  43   , secured to a radially inner periphery of the cylinder  43  of the magnet holder  41 . The annular magnet  95  is equipped with a plurality of different magnetic poles whose polarities are arranged alternately in the circumferential direction of the annular magnet  95 . The magnet  95  lies integrally both on the d-axis and the q-axis. The annular magnet  95  has a magnetic orientation directed in the radial direction on the d-axis of each magnetic pole and a magnetic orientation directed in the circumferential direction on the q-axis between the magnetic poles, thereby creating arc-shaped magnetic paths. 
     The annular magnet  95  may be designed to have an easy axis of magnetization directed parallel or near parallel to the d-axis near the d-axis and also to have an easy axis of magnetization directed perpendicular or near perpendicular to the q-axis near the q-axis, thereby creating the arc-shaped magnetic paths. 
     Modification 8 
     This modification is different in operation of the controller  110  from the above embodiment or modifications. Only differences from those in the first embodiment will be described below. 
     The operations of the operation signal generators  116  and  126  illustrated in  FIG.  20    and the operation signal generators  130   a  and  130   b  illustrated in  FIG.  21    will first be discussed below using  FIG.  44   . The operations executed by the operation signal generators  116 ,  126 ,  130   a , and  130   b  are basically identical with each other. Only the operation of the operation signal generator  116  will, therefore, be described below for the sake of simplicity. 
     The operation signal generator  116  includes the carrier generator  116   a , the U-phase comparator  116   b U, the V-phase comparator  116   b V, and the W-phase comparator  116   b W. The carrier generator  116   a  produces and outputs the carrier signal SigC in the form of a triangle wave signal. 
     The U-, V-, and W-phase comparators  116   b U,  116   b V, and  116   b W receive the carrier signal SigC outputted by the carrier generator  116   a  and the U-, V-, and W-phase command voltages produced by the three-phase converter  115 . The U-, V-, and W-phase command voltages are produced, for example, in the form of a sine wave and outputted 120° out of electrical phase with each other. 
     The U-, V-, and W-phase comparators  116   b U,  116   b V, and  116   b W compare the U-, V-, and W-phase command voltages with the carrier signal 
     SigC to produce operation signals for the switches Sp and Sn of the upper and lower arms in the first inverter  101  for the U-, V-, and W-phase windings under PWM (Pulse Width Modulation) control. Specifically, the operation signal generator  116  works to produce operation signals for the switches Sp and Sn of the upper and lower arms for the U-, V-, and W-phase windings under the PWM control based on comparison of levels of signals derived by normalizing the U-, V-, and W-phase command voltages using the power supply voltage with a level of the carrier signal SigC. The driver  117  is responsive to the operation signals outputted by the operation signal generator  116  to turn on or off the switches Sp and Sn in the first inverter  101  for the U-, V-, and W-phase windings. 
     The controller  110  alters the carrier frequency fc of the carrier signal SigC, i.e., a switching frequency for each of the switches Sp and Sn. The carrier frequency fc is altered to be higher in a low torque range or a high-speed range in the rotating electrical machine  10  and alternatively lower in a high torque range in the rotating electrical machine  10 . This altering is achieved in order to minimize a deterioration in ease of control of electrical current flowing through each of the U-, V-, and W-phase windings. 
     In brief, the core-less structure of the stator  50  serves to reduce the inductance in the stator  50 . The reduction in inductance usually results in a decrease in electrical time constant in the rotating electrical machine  10 . This leads to a possibility that a ripple of current flowing through each of the phase windings may be increased, thereby resulting in the deterioration in ease of control of the current flowing through the phase winding, which causes control divergence. The adverse effects of the above deterioration on the ease of control usually become higher when the current (e.g., an effective value of the current) flowing through the winding lies in a low current region than when the current lies in a high current range. In order to alleviate such a problem, the controller  110  in this embodiment is designed to alter the carrier frequency fc. 
     How to alter the carrier frequency fc will be described below with reference to  FIG.  45   . This operation of the operation signal generator  116  is executed by the controller  110  cyclically at a given interval. 
     First, in step S 10 , it is determined whether electrical current flowing through each of the three-phase windings  51   a  lies in the low current range. This determination is made to determine whether torque now produced by the rotating electrical machine  10  lies in the low torque range. Such a determination may be achieved according to the first method or the second method, as discussed below. 
     First Method 
     The estimated torque value of the rotating electrical machine  10  is calculated using the d-axis current and the q-axis current converted by the d-q converter  112 . If the estimated torque value is determined to be lower than a torque threshold value, it is concluded that the current flowing through the winding  51   a  lies in the low current range. Alternatively, if the estimated torque value is determined to be higher than or equal to the torque threshold value, it is concluded that the current lies in the high current range. The torque threshold value is selected to be half, for example, the degree of starting torque (also called locked rotor torque) in the rotating electrical machine  10 . 
     Second Method 
     If an angle of rotation of the rotor  40  measured by an angle sensor is determined to be higher than or equal to a speed threshold value, it is determined that the current flowing through the winding  51   a  lies in the low current range, that is, in the high speed range. The speed threshold value may be selected to be a rotational speed of the rotating electrical machine  10  when a maximum torque produced by the rotating electrical machine  10  is equal to the torque threshold value. 
     If a NO answer is obtained in step S 10 , meaning that the current lies in the high current range, then the routine proceeds to step S 11  wherein the carrier frequency fc is set to the first frequency fL. 
     Alternatively, if a YES answer is obtained in step S 10 , then the routine proceeds to step S 12  wherein the carrier frequency fc is set to the second frequency fH that is higher than the first frequency fL. 
     As apparent from the above discussion, the carrier frequency fc when the current flowing through each of the three-phase windings lies in the low current range is selected to be higher than that when the current lies in the high current range. The switching frequency for the switches Sp and Sn is, therefore, increased in the low current range, thereby minimizing a rise in current ripple to ensure the stability in controlling the current. 
     When the current flowing through each of the three-phase windings lies in the high current range, the carrier frequency fc is selected to be lower than that when the current lies in the low current range. The current flowing through the winding in the high current range usually has an amplitude larger than that when the current lies in the low current range, so that the rise in current ripple arising from the reduction in inductance has a low impact on the ease of control of the current. It is, therefore, possible to set the carrier frequency fc in the high current range to be lower than that in the low current range, thereby reducing a switching loss in the inverters  101  and  102 . 
     This modification is capable of realizing the following modes. 
     If a YES answer is obtained in step S 10  in  FIG.  45    when the carrier frequency fc is set to the first frequency fL, the carrier frequency fc may be changed gradually from the first frequency fL to the second frequency fH. 
     Alternatively, if a NO answer is obtained in step S 10  when the carrier frequency fc is set to the second frequency fH, the carrier frequency fc may be changed gradually from the second frequency fH to the first frequency fL. 
     The operation signals for the switches may alternatively be produced using SVM (Space Vector Modulation) instead of the PWM. The above altering of the switching frequency may also be made. 
     Modification 9 
     In each of the embodiments, two pairs of conductors making up the conductor groups  81  for each phase are, as illustrated in  FIG.  46 ( a ) , arranged parallel to each other.  FIG.  46 ( a )  is a view which illustrates an electrical connection of the first and second conductors  88   a  and  88   b  that are the two pairs of conductors. The first and second conductors  88   a  and  88   b  may alternatively be, as illustrated in  FIG.  46 ( b ) , connected in series with each other instead of the connection in  FIG.  46 ( a ) . 
     Three or more pairs of conductors may be stacked in the form of multiple layers.  FIG.  47    illustrates four pairs of conductors: the first to fourth conductors  88   a  to  88   d  which are stacked. The first conductor  88   a , the second conductor  88   b , the third conductor  88   c , and the fourth conductor  88   d  are arranged in this order from the stator core  52  in the radial direction. 
     The third and fourth conductors  88   c  and  88   d  are, as illustrated in  FIG.  46 ( c ) , connected in parallel to each other. The first conductor  88   a  is connected to one of joints of the third and fourth conductors  88   c  and  88   d . The second conductor  88   b  is connected to the other joint of the third and fourth conductors  88   c  and  88   d . The parallel connection of conductors usually results in a decrease in current density of those conductors, thereby minimizing thermal energy produced upon energization of the conductors. Accordingly, in the structure in which a cylindrical stator winding is installed in a housing (i.e., the unit base  61 ) with the coolant path  74  formed therein, the first and second conductors  88   a  and  88   b  which are connected in non-parallel to each other are arranged close to the stator core  52  placed in contact with the unit base  61 , while the third and fourth conductors  88   c  and  88   d  which are connected in parallel to each other are disposed farther away from the stator core  52 . This layout equalizes the cooling ability of the conductors  88   a  to  88   d  stacked in the form of multiple layers. 
     The conductor group  81  including the first to fourth conductors  88   a  to  88   d  may have a thickness in the radial direction which is smaller than a circumferential width of the conductor groups  81  for one phase within a region of one pole. 
     Modification 10 
     The rotating electrical machine  10  may alternatively be designed to have an inner rotor structure (i.e., an inward rotating structure). In this case, the stator  50  may be mounted, for example, on a radial outside within the housing  30 , while the rotor  40  may be disposed on a radial inside within the housing  30 . The inverter unit  60  may be mounted one or both axial sides of the stator  50  or the rotor  40 .  FIG.  48    is a transverse sectional view of the rotor  40  and the stator  50 .  FIG.  49    is an enlarged view which partially illustrates the rotor  40  and the stator  50  in  FIG.  48   . 
     The inner rotor structure in  FIGS.  48  and  49    is substantially identical with the outer rotor structure in  FIGS.  8  and  9    except for the layout of the rotor  40  and the stator  50  in the radial direction. In brief, the stator  50  is equipped with the stator coil  51  having the flattened conductor structure and the stator core  52  with no teeth. The stator coil  51  is installed radially inside the stator core  52 . The stator core  52 , like the outer rotor structure, has any of the following structures. 
     (A) The stator  50  has the conductor-to-conductor members each of which is disposed between the conductor portions in the circumferential direction. As the conductor-to-conductor members, magnetic material is used which meets a relation of Wt×Bs≤Wm×Br where Wt is a width of the conductor-to-conductor members in the circumferential direction within one magnetic pole, Bs is the saturation magnetic flux density of the conductor-to-conductor members, Wm is a width of the magnet unit equivalent to one magnetic pole in the circumferential direction, and Br is the remanent flux density in the magnetic unit.
 
(B) The stator  50  has the conductor-to-conductor members each of which is disposed between the conductor portions in the circumferential direction. The conductor-to-conductor members are each made of a non-magnetic material.
 
(C) The stator  50  has no conductor-to-conductor member disposed between the conductor portions in the circumferential direction.
 
     The same is true of the magnets  91  and  92  of the magnet unit  42 . Specifically, the magnet unit  42  is made up of the magnets  91  and  92  each of which is magnetically oriented to have the easy axis of magnetization which is directed near the d-axis to be more parallel to the d-axis than that near the q-axis which is defined on the boundary of the magnetic poles. The details of the magnetization direction in each of the magnets  91  and  92  are the same as described above. The magnet unit  42  may be the annular magnet  95  (see  FIG.  43   ). 
       FIG.  50    is a longitudinal sectional view of the rotating electrical machine  10  designed to have the inner rotor structure.  FIG.  50    corresponds to  FIG.  2   . Differences from the structure in  FIG.  2    will be described below in brief. In  FIG.  50   , the annular stator  50  is retained inside the housing  30 . The rotor  40  is disposed inside the stator  50  with an air gap therebetween to be rotatable. The bearings  21  and  22  are, like in  FIG.  2   , offset from the axial center of the rotor  40  in the axial direction of the rotor  40 , so that the rotor  40  is retained in the cantilever form. The inverter  60  is mounted inside the magnet holder  41  of the rotor  40 . 
       FIG.  51    illustrates the inner rotor structure of the rotating electrical machine  10  which is different from that described above. The housing  30  has the rotating shaft  11  retained by the bearings  21  and  22  to be rotatable. The rotor  40  is secured to the rotating shaft  11 . Like the structure in  FIG.  2   , each of the bearings  21  and  22  is offset from the axial center of the rotor  40  in the axial direction of the rotor  40 . The rotor  40  is equipped with the magnet holder  41  and the magnet unit  42 . 
     The rotating electrical machine  10  in  FIG.  51    is different from that in  FIG.  50    in that the inverter unit  60  is not located radially inside the rotor  40 . The magnet holder  41  is joined to the rotating shaft  11  radially inside the magnet unit  42 . The stator  50  is equipped with the stator coil  51  and the stator core  52  and secured to the housing  30 . Note that the definitions of parameters, such as Wt, Wn, Wm, and Bs, associated with the stator  50  or parameters, such as θ 11 , θ 12 , X 1 , X 2 , Wm, and Br, associated with the magnet unit  42  may refer to those in the above described first embodiment or the modification 1. 
     Modification 11 
     The inner rotor structure of a rotating electrical machine which is different from that described above will be discussed below.  FIG.  52    is an exploded view of the rotating electrical machine  200 .  FIG.  53    is a sectional side view of the rotating electrical machine  200 . In the following discussion, a vertical direction is based on the orientation of the rotating electrical machine  200 . 
     The rotating electrical machine  200 , as illustrated in  FIGS.  52  and  53   , includes the stator  203  and the rotor  204 . The stator  203  is equipped with the annular stator core  201  and the multi-phase stator winding  202 . The rotor  204  is disposed inside the stator core  201  to be rotatable. The stator  203  works as an armature. The rotor  204  works as a field magnet. The stator core  201  is made of a stack of silicon steel plates. The stator winding  202  is installed in the stator core  201 . 
     Although not illustrated, the rotor  204  is equipped with a rotor core and a plurality of permanent magnet arranged in the form of a magnet unit. The rotor core has formed therein a plurality of holes which are arranged at equal intervals away from each other in the circumferential direction of the rotor core. The permanent magnets which are magnetized to have magnetization directions changed alternately in adjacent magnetic poles are disposed in the holes of the rotor core. The permanent magnets of the magnet unit may be designed, like in  FIG.  23   , to have a Halbach array structure or a similar structure. The permanent magnets of the magnet unit may alternatively be made of anisotropic magnets, as described with reference to  FIG.  9  or  43   , in which the magnetic orientation (i.e., the magnetization direction) extends in an arc-shape between the d-axis which is defined on the magnetic center and the q-axis which is defined on the boundary of the magnetic poles. 
     The stator  203  may be made to have one of the following structures. 
     (A) The stator  203  has the conductor-to-conductor members each of which is disposed between the conductor portions in the circumferential direction. As the conductor-to-conductor members, magnetic material is used which meets a relation of Wt×Bs≤Wm×Br where Wt is a width of the conductor-to-conductor members in the circumferential direction within one magnetic pole, Bs is the saturation magnetic flux density of the conductor-to-conductor members, Wm is a width of the magnet unit equivalent to one magnetic pole in the circumferential direction, and Br is the remanent flux density in the magnetic unit.
 
(B) The stator  203  has the conductor-to-conductor members each of which is disposed between the conductor portions in the circumferential direction. The conductor-to-conductor members are each made of a non-magnetic material.
 
(C) The stator  203  has no conductor-to-conductor member disposed between the conductor portions in the circumferential direction.
 
     The rotor  204  has the magnet unit which is made up of a plurality of magnets each of which is magnetically oriented to have the easy axis of magnetization which is directed near the d-axis to be more parallel to the d-axis than that near the q-axis which is defined on the boundary of the magnetic poles. 
     The annular inverter case  211  is disposed on one end side of an axis of the rotating electrical machine  200 . The inverter case  211  has a lower surface placed in contact with an upper surface of the stator core  201 . The inverter case  211  has disposed therein a plurality of power modules  212  constituting an inverter circuit, the smoothing capacitors  213  working to reduce a variation in voltage or current (i.e., a ripple) resulting from switching operations of semiconductor switches, the control board  214  equipped with a controller, the current sensor  215  working to measure a phase current, and the resolver stator  216  serving as a rotational speed sensor for the rotor  204 . The power modules  212  are equipped with IGBTs serving as semiconductor switches and diodes. 
     The inverter case  211  has the power connector  217  which is disposed on a circumferential edge thereof for connection with a dc circuit for a battery mounted in a vehicle. The inverter case  211  also has the signal connector  218  which is disposed on the circumferential edge thereof for achieving transmission of signals between the rotating electrical machine  200  and a controller installed in the vehicle. The inverter case  211  is covered with the top cover  219 . The dc power produced by the battery installed in the vehicle is inputted into the power connector  217 , converted by the switches of the power modules  212  to an alternating current, and then delivered to phase windings of the stator winding  202 . 
     The bearing unit  221  and the annular rear case  222  are disposed on the opposite end side of the axis of the stator core to the inverter case  211 . The bearing unit  221  retains a rotation axis of the rotor  204  to be rotatable. The rear case  222  has the bearing unit  221  disposed therein. The bearing unit  221  is equipped with, for example, two bearings and offset from the center of the length of the rotor  204  toward one of the ends of the length of the rotor  204 . The bearing unit  221  may alternatively be engineered to have a plurality of bearings disposed on both end sides of the stator core  201  opposed to each other in the axial direction, so that the bearings retain both the ends of the rotation shaft. The rear case  222  is fastened to a gear case or a transmission of the vehicle using bolts, thereby securing the rotating electrical machine  200  to the vehicle. 
     The inverter case  211  has formed therein the cooling flow path  211   a  through which cooling medium flows. The cooling flow path  211   a  is defined by closing an annular recess formed in a lower surface of the inverter case  211  by an upper surface of the stator core  201 . The cooling flow path  211   a  surrounds a coil end of the stator winding  202 . The cooling flow path  211   a  has the module cases  212   a  of the power modules  212  disposed therein. Similarly, the rear case  222  has formed therein the cooling flow path  222   a  which surrounds a coil end of the stator winding  202 . The cooling flow path  222   a  is defined by closing an annular recess formed in an upper surface of the rear case  222  by a lower surface of the stator core  201 . Note that the definitions of parameters, such as Wt, Wn, Wm, and Bs, associated with the stator  50  or parameters, such as θ 11 , θ 12 , X 1 , X 2 , Wm, and Br, associated with the magnet unit  42  may refer to those in the above described first embodiment or the modification 1. 
     Modification 12 
     The above discussion has referred to the revolving-field type of rotating electrical machines, but a revolving armature type of rotating electrical machine may be embodied.  FIG.  54    illustrates the revolving armature type of rotating electrical machine  230 . 
     The rotating electrical machine  230  in  FIG.  54    has the bearing  232  retained by the housings  231   a  and  231   b . The bearing  232  retains the rotating shaft  233  to be rotatable. The bearing  232  is made of, for example, an oil-impregnated bearing in which a porous metal is impregnated with oil. The rotating shaft  233  has secured thereto the rotor  234  which works as an armature. The rotor  234  includes the rotor core  235  and the multi-phase rotor winding  236  secured to an outer periphery of the rotor core  235 . The rotor core  235  of the rotor  234  is designed to have the slot-less structure. 
     The multi-phase rotor winding  236  has the flattened conductor structure as described above. In other words, the multi-phase rotor winding  236  is shaped to have an area for each phase which has a dimension in the circumferential direction which is larger than that in the radial direction. 
     The stator  237  is disposed radially outside the rotor  234 . The stator  237  works as a field magnet. The stator  237  includes the stator core  238  and the magnet unit  239 . The stator core  238  is secured to the housing  231   a . The magnet unit  239  is attached to an inner periphery of the stator core  238 . The magnet unit  239  is made up of a plurality of magnets arranged to have magnetic poles alternately arrayed in the circumferential direction. Like the magnet unit  42  described above, the magnet unit  239  is magnetically oriented to have the easy axis of magnetization which is directed near the d-axis to be more parallel to the d-axis than that near the q-axis that is defined on a boundary between the magnetic poles. The magnet unit  239  is equipped with magnetically oriented sintered neodymium magnets whose intrinsic coercive force is 400 [kA/m] or more and whose remanent flux density is 1.0 [T] or more. 
     The rotating electrical machine  230  in this embodiment is engineered as a two-pole three-coil brush coreless motor. The multi-phase rotor winding  236  is made of three coils. The magnet unit  239  is designed to have two poles. A ratio of the number of poles and the number of coils in typical brush motors is 2:3, 4:10, or 4:21 depending upon intended use. 
     The rotating shaft  233  has the commutator  241  secured thereto. A plurality of brushes  242  are arranged radially outside the commutator  241 . The commutator  241  is electrically connected to the multi-phase rotor winding  236  through the conductors  234  embedded in the rotating shaft  233 . The commutator  241 , the brushes  242 , and the conductors  243  are used to deliver dc current to the multi-phase rotor winding  236 . The commutator  241  is made up of a plurality of sections arrayed in a circumferential direction thereof depending upon the number of phases of the multi-phase rotor winding  236 . The brushes  242  may be connected to a dc power supply, such as a storage battery, using electrical wires or using a terminal block. 
     The rotating shaft  233  has the resinous washer  244  disposed between the bearing  232  and the commutator  241 . The resinous washer  244  serves as a sealing member to minimize leakage of oil seeping out of the bearing  232 , implemented by an oil-impregnated bearing, to the commutator  241 . 
     Modification 13 
     Each of the conductors  82  of the stator coil  51  of the rotating electrical machine  10  may be designed to have a stack of a plurality of insulating coatings or layers laid on each other. For instance, each of the conductors  82  may be made by covering a bundle of a plurality of insulating layer-coated conductors (i.e., wires) with an insulating layer, so that the insulating layer (i.e., an inner insulating layer) of each of the conductors  82  is covered with the insulating layer (i.e., an outer insulating layer) of the bundle. The outer insulating layer is preferably designed to have an insulating ability greater than that of the inner insulating layer. Specifically, the thickness of the outer insulating layer is selected to be larger than that of the inner insulating layer. For instance, the outer insulating layer has a thickness of 100 μm, while the inner insulating layer has a thickness of 40 μm. Alternatively, the outer insulating layer may have a permittivity lower than that of the inner insulating layer. Each of the conductors  82  may have any of the above structure. Each wire is preferably made of a collection of conductive members or fibers. 
     As apparent from the above discussion, the rotating electrical machine  10  becomes useful in a high-voltage system of a vehicle by increasing the insulation ability of the outermost layer of the conductor  82 . The above structure enables the rotating electrical machine  10  to be driven in low pressure conditions such as highlands. 
     Modification 14 
     Each of the conductors  82  equipped with a stack of a plurality of insulating layers may be designed to have at least one of a linear expansion coefficient and the degree of adhesion strength different between an outer one and an inner one of the insulating layers. The conductors  82  in this modification are illustrated in  FIG.  55   . 
     In  FIG.  55   , the conductor  82  includes a plurality of (four in the drawing) wires  181 , the outer coated layer  182  (i.e., an outer insulating layer) with which the wires  181  are covered and which is made of, for example, resin, and the intermediate layer  183  (i.e., an intermediate insulating layer) which is disposed around each of the wires  181  within the outer coated layer  182 . Each of the wires  181  includes the conductive portion  181   a  made of copper material and the conductor-coating layer (i.e., an inner insulating layer) made of electrical insulating material. The outer coated layer  182  serves to electrically insulate between phase-windings of the stator winding. Each of the wires  181  is preferably made of a collection of conductive members or fibers. 
     The intermediate layer  183  has a linear expansion coefficient higher than that of the coated layer  181   b , but lower than that of the outer coated layer  182 . In other words, the linear expansion coefficient of the conductor  82  is increased from an inner side to an outer side thereof. Typically, the outer coated layer  182  is designed to have a linear expansion coefficient higher than that of the coated layer  181   b . The intermediate layer  183 , as described above, has a linear expansion coefficient intermediate between those of the coated layer  181   b  and the outer coated layer  182  and thus serves as a cushion to eliminate a possibility that the inner and outer layers may be simultaneously broken. 
     Each of the wires  181  of the conductor  82  has the conductive portion  181   a  and the coated layer  181   b  adhered to the conductive portion  181   a . The coated layer  181   b  and the intermediate layer  183  are also adhered together. The intermediate layer  183  and the outer coated layer  182  are adhered together. Such joints have a strength of adhesion decreasing toward an outer side of the conductor  82 . In other words, the strength of adhesion between the conductive portion  181   a  and the coated layer  181   b  is lower than that between the coated layer  181   b  and the intermediate layer  183  and between the inter mediate layer  183  and the outer coated layers  182 . The strength of adhesion between the coated layer  181   b  and the intermediate layer  183  may be higher than or identical with that between the intermediate layer  183  and the outer coated layers  182 . Usually, the strength of adhesion between, for example, two coated layers may be measured as a function of a tensile strength required to peel the coated layers away from each other. The strength of adhesion of the conductor  82  is selected in the above way to minimize the possibility that the inner and outer layers may be broken together arising from a temperature difference between inside and outside the conductor  82  when heated or cooled. 
     Usually, the heat generation or temperature change in the rotating electrical machine results in copper losses arising from heat from the conductive portion  181   a  of the wire  181  and from an iron core. These two types of loss result from the heat transmitted from the conductive portion  181   a  in the conductor  82  or from outside the conductor  82 . The intermediate layer  183  does not have a heat source. The intermediate layer  183  has the strength of adhesion serving as a cushion for the coated layer  181   b  and the outer coated layer  182 , thereby eliminating the possibility that the coated layer  181   b  and the outer coated layer  182  may be simultaneously broken. This enables the rotating electrical machine to be used in conditions, such as in vehicles, wherein a resistance to high pressure is required, or the temperature greatly changes. 
     In addition, the wire  181  may be made of enamel wire with a layer (i.e., the coated layer  181   b ) coated with resin, such as PA, PI or PAI. Similarly, the outer coated layer  182  outside the wire  181  is preferably made of PA, PI, and PAI and has a large thickness. This minimizes a risk of breakage of the outer coated layer  182  caused by a difference in linear expansion coefficient. Instead of use of PA, PI, PAI to make the outer coated layer  182  having a large thickness, material, such as PPS, PEEK, fluorine, polycarbonate, silicon, epoxy, polyethylene naphthalate, or LCP which has a dielectric permittivity lower than that of PI or PAI is preferably used to increase the conductor density of the rotating electrical machine. The use of such resin enhances the insulating ability of the outer coated layer  182  even when it has a thickness smaller than or equal to that of the coated layer  181   b  and increases the occupancy of the conductive portion. Usually, the above resin has the degree of electric permittivity higher than that of an insulating layer of enamel wire. Of course, there is an example where the state of formation or additive results in a decrease in electric permittivity thereof. Usually, PPS and PEEK is higher in linear expansion coefficient than an enamel-coated layer, but lower than another type of resin and thus is useful only for the outer of the two layers. 
     The strength of adhesion of the two types of coated layers arranged outside the wire  181  (i.e., the intermediate insulating layer and the outer insulating layer) to the enamel coated layer of the wire  181  is preferably lower than that between the copper wire and the enamel coated layer of the wire  181 , thereby minimizing a possibility that the enamel coated layer and the above two types of coated layers are simultaneously broken. 
     In a case where the stator is equipped with a water cooling mechanism, a liquid cooling mechanism, or an air cooling mechanism, thermal stress or impact stress is thought of as being exerted first on the outer coated layers  182 . The thermal stress or the impact stress is decreased by partially bonding the insulating layer of the wire  181  and the above two types of coated layers together even if the insulation layer is made of resin different from those of the above two types of coated layers. In other words, the above described insulating structure may be created by placing a wire (i.e., an enamel wire) and an air gap and also arranging fluorine, polycarbonate, silicon, epoxy, polyethylene naphthalate, or LCP. In this case, adhesive which is made from epoxy, low in electric permittivity, and also low in linear expansion coefficient is preferably used to bond the outer coated layer and the inner coated layer together. This eliminates breakage of the coated layers caused by friction arising from vibration of the conductive portion or breakage of the outer coated layer due to the difference in linear expansion coefficient as well as the mechanical strength. 
     The outermost layer which serves to ensure the mechanical strength or securement of the conductor  82  having the above structure is preferably made from resin material, such as epoxy, PPS, PEEK, or LCP which is easy to shape and similar in dielectric constant or linear expansion coefficient to the enamel coated layer, typically in a final process for a stator winding. 
     Typically, the resin potting is made using urethane or silicon. Such resin, however, has a linear expansion coefficient approximately twice that of other types of resin, thus leading to a possibility that thermal stress is generated when the resin is subjected to the resin potting, so that it is sheared. The above resin is, therefore, unsuitable for use where requirements for insulation are severe and 60V or more. The final insulation process to make the outermost layer using injection molding techniques with epoxy, PPS, PEEK, or LCP satisfies the above requirements. 
     Other modifications will be listed below. 
     The distance DM between a surface of the magnet unit  42  which faces the armature and the axial center of the rotor in the radial direction may be selected to be 50 mm or more. For instance, the distance DM, as illustrated in  FIG.  4   , between the radial inner surface of the magnet unit  42  (i.e., the first and second magnets  91  and  92 ) and the center of the axis of the rotor  40  may be selected to be 50 mm or more. 
     The small-sized slot-less structure of the rotating electrical machine whose output is several tens or hundreds watt is known which is used for models. The disclosers or inventors of this application have not seen examples where the slot-less structure is used with large-sized industrial rotating electrical machines whose output is more than 10 kW. The disclosers or inventors have studied the reason for this. 
     Modern major rotating electrical machines are categorized into four main types: a brush motor, a squirrel-cage induction motor, a permanent magnet synchronous motor, a reluctance motor. 
     Brush motors are supplied with exciting current using brushes. Large-sized brush motors, therefore, have an increased size of brushes, thereby resulting in complex maintenance thereof. With the remarkable development of semiconductor technology, brushless motors, such as induction motors, have been used instead. In the field of small-sized motors, a large number of coreless motors have also come on the market in terms of low inertia or economic efficiency. 
     Squirrel-cage induction motors operate on the principle that a magnetic field produced by a primary stator winding is received by a secondary stator core to deliver induced current to bracket-type conductors, thereby creating magnetic reaction field to generate torque. In terms of small-size and high-efficiency of the motors, it is inadvisable that the stator and the rotor be designed not to have iron cores. 
     Reluctance motors are motors designed to use a change in reluctance in an iron core. It is, thus, inadvisable that the iron core be omitted in principle. 
     In recent years, permanent magnet synchronous motors have used an IPM (Interior Permanent Magnet) rotor. Especially, most large-sized motors use an IPM rotor unless there are special circumstances. 
     IPM motors has properties of producing both magnet torque and reluctance torque. The ratio between the magnet torque and the reluctance torque is timely controlled using an inverter. For these reasons, the IMP motors are thought of as being compact and excellent in ability to be controlled. 
     According to analysis by the disclosers or inventors, torque on the surface of a rotor producing the magnet torque and the reluctance torque is expressed in  FIG.  43    as a function of the distance DM between the surface of the magnet unit which faces the armature and the center of the axis of the rotor, that is, the radius of a stator core of a typical inner rotor indicated on the horizontal axis. 
     The potential of the magnet torque, as can be seen in the following equation (eq1), depends upon the strength of magnetic field created by a permanent magnet, while the potential of the reluctance torque, as can be seen in the following equation (eq2), depends upon the degree of inductance, especially, on the q-axis.
 
The magnet torque= k·Ψ·Iq   (eq1)
 
The reluctance torque= k ·( Lq−Ld )· Iq·Id   (eq2)
 
     Comparison between the strength of magnetic field produced by the permanent magnet and the degree of inductance of a winding using the distance DM shows that the strength of magnetic field created by the permanent magnet, that is, the amount of magnetic flux Ψ is proportional to a total area of a surface of the permanent magnet which faces the stator. In case of a cylindrical stator, such a total area is a cylindrical surface area of the permanent magnet. Technically speaking, the permanent magnet has an N-pole and an S-pole, the amount of magnetic flux W is proportional to half the cylindrical surface area. The cylindrical surface area is proportional to the radius of the cylindrical surface and the length of the cylindrical surface. When the length of the cylindrical surface is constant, the cylindrical surface area is proportional to the radius of the cylindrical surface. 
     The inductance Lq of the winding depends upon the shape of the iron core, but its sensitivity is low and rather proportional to the square of the number of turns of the stator winding, so that it is strongly dependent upon the number of the turns. The inductance L is expressed by a relation of L=μ·N{circumflex over ( )}2×S/δ where μ is permeability of a magnetic circuit, N is the number of turns, S is a sectional area of the magnetic circuit, and δ is an effective length of the magnetic circuit. The number of turns of the winding depends upon the size of space occupied by the winding. In the case of a cylindrical motor, the number of turns, therefore, depends upon the size of space occupied by the winding of the stator, in other words, areas of slots in the stator. The slot is, as demonstrated in  FIG.  57   , rectangular, so that the area of the slot is proportional to the product of a and b where a is the width of the slot in the circumferential direction, and b is the length of the slot in the radial direction. 
     The width of the slot in the circumferential direction becomes large with an increase in diameter of the cylinder, so that the width is proportional to the diameter of the cylinder. The length of the slot in the radial direction is proportional to the diameter of the cylinder. The area of the slot is, therefore, proportional to the square of the diameter of the cylinder. It is apparent from the above equation (eq2) that the reluctance torque is proportional to the square of current in the stator. The performance of the rotating electrical machine, therefore, depends upon how much current is enabled to flow in the rotating electrical machine, that is, depends upon the areas of the slots in the stator. The reluctance is, therefore, proportional to the square of the diameter of the cylinder for a cylinder of constant length. Based on this fact, a relation of the magnetic torque and the reluctance torque with the distance DM is shown by plots in  FIG.  56   . 
     The magnet torque is, as shown in  FIG.  56   , increased linearly as a function of the distance DM, while the reluctance torque is increased in the form of a quadratic function as a function of the distance DM.  FIG.  56    shows that when the distance DM is small, the magnetic torque is dominant, while the reluctance torque becomes dominant with an increase in diameter of the stator core. The disclosers or inventors of this application have arrived at the conclusion that an intersection of lines expressing the magnetic torque and the reluctance torque in  FIG.  56    lies near 50 mm that is the radius of the stator core. It seems that it is difficult for a motor whose output is 10 kW and whose stator core has a radius much larger than 50 mm to omit the stator core because the use of the reluctance torque is now mainstream. This is one of reasons why the slot-less structure is not used in large-sized motors. 
     The rotating electrical machine using an iron core in the stator always faces a problem associated with the magnetic saturation of the iron core. Particularly, radial gap type rotating electrical machines has a longitudinal section of the rotating shaft which is of a fan shape for each magnetic pole, so that the further inside the rotating electrical machine, the smaller the width of a magnetic circuit, so that inner dimensions of teeth forming slots in the core become a factor of the limit of performance of the rotating electrical machine. Even if a high performance permanent magnet is used, generation of magnetic saturation in the permanent magnet will lead to a difficulty in producing a required degree of performance of the permanent magnet. It is necessary to design the permanent magnet to have an increased inner diameter in order to eliminate a risk of generation of the magnetic saturation, which results in an increase size of the rotating electrical machine. 
     For instance, a typical rotating electrical machine with a distributed three-phase winding is designed so that three to six teeth serve to produce a flow of magnetic flux for each magnetic pole, but encounters a possibility that the magnetic flux may concentrate on a leading one of the teeth in the circumferential direction, thereby causing the magnetic flux not to flow uniformly in the three to six teeth. For instance, the flow of magnetic flux concentrates on one or two of the teeth, so that the one or two of the teeth in which the magnetic saturation is occurring will move in the circumferential direction with rotation of the rotor, which may lead to a factor causing the slot ripple. 
     For the above reasons, it is required to omit the teeth in the slot-less structure of the rotating electrical machine whose distance DM is 50 mm or more to eliminate the risk of generation of the magnetic saturation. The omission of the teeth, however, results in an increase in magnetic resistance in magnetic circuits of the rotor and the stator, thereby decreasing torque produced by the rotating electrical machine. The reason for such an increase in magnetic resistance is that there is, for example, a large air gap between the rotor and the stator. The slot-less structure of the rotating electrical machine whose distance DM is 50 mm or more, therefore, has room for improvement for increasing the output torque. There are numerous beneficial advantages to use the above torque-increasing structure in the slot-less structure of rotating electrical machines whose distance DM is 50 mm or more. 
     Not only the outer rotor type rotating electrical machines, but also the inner rotor type rotating electrical machines are preferably designed to have the distance DM of 50 mm or more between the surface of the magnet unit which faces the armature and the center of the axis of the rotor in the radial direction. 
     The stator coil  51  of the rotating electrical machine  10  may be designed to have only the single straight section  83  of the conductor  82  arranged in the radial direction. Alternatively, a plurality of straight sections  83 , for example, three, four, five, or six straight sections  83  may be stacked on each other in the radial direction. 
     For example, the structure illustrated in  FIG.  2    has the rotating shaft  11  extending outside the ends of length of the rotating electrical machine  10 , but however, may alternatively be designed to have the rotating shaft  11  protruding outside only one of the ends of the rotating electrical machine  10 . In this case, it is advisable that a portion of the rotating shaft  11  which is retained by the bearing unit  20  in the cantilever form be located on one of the ends of the rotating electrical machine, and that the rotating shaft  11  protrude outside such an end of the rotating electrical machine. This structure has the rotating shaft  11  not protruding inside the inverter unit  60 , thus enabling a wide inner space of the inverter unit  60 , i.e., the cylinder  71  to be used. 
     The above structure of the rotating electrical machine  10  uses non-conductive grease in the bearings  21  and  22 , but however, may alternatively be designed to have conductive grease in the bearings  21  and  22 . For instance, conductive grease containing metallic particles or carbon particles may be used. 
     A bearing or bearings may be mounted on only one or both axial ends of the rotor  40  for retaining the rotating shaft  11  to be rotatable. For example, the structure of  FIG.  1    may have a bearing or bearings mounted on only one side or opposite sides of the inverter unit  60  in the axial direction. 
     The magnet holder  41  of the rotor  40  of the rotating electrical machine  10  has the intermediate portion  45  equipped with the inner shoulder  49   a  and the annular outer shoulder  49   b , however, the magnet holder  41  may alternatively be designed to have the flat intermediate portion  45  without the shoulders  49   a  and  49   b.    
     The conductor body  82   a  of each of the conductors  82  of the stator coil  51  of the rotating electrical machine  10  is made of a collection of the wires  86 , however, may alternatively be formed using a square conductor having a rectangular cross section. The conductor  82  may alternatively be made using a circular conductor having a circular cross section or an oval cross section. 
     The rotating electrical machine  10  has the inverter unit  60  arranged radially inside the stator  50 , but however, may alternatively be designed not to have the inverter  60  disposed inside the stator  50 . This enables the stator  50  to have a radial inner void space in which parts other than the inverter unit  60  may be mounted. 
     The rotating electrical machine  10  may be designed not to have the housing  30 . In this case, the rotor  40  or the stator  50  may be retained by a wheel or another part of a vehicle. 
     Each of the second magnets disposed between a corresponding adjacent pair of the first A and B magnets  4011  and  4012  can be comprised of a plurality of magnets having the second magnetization vectors that have respectively different directions. 
     For example, as illustrated in  FIG.  58   , each of the second magnets  4021  includes a second A magnet  4025  and a second B magnet  4025 . The second A magnet  4025  is disposed to be closer to the first A magnet  4011  than the second B magnet  4026 . The second magnetization vectors in the second A magnet  4025  are inclined toward the stator side with respect to a predetermined direction; the predetermined direction is perpendicular to the q-axis representing the boundary of the corresponding magnetic pole. 
     A predetermined angle θ 105  of each of the second magnetization vectors in the second A magnet  4025  inclined toward the stator side with respect to the predetermined direction is preferably set to be larger than the predetermined angle θ 101  formed between the q-axis and the abutment surface  4023 . The abutment surface  4023  is an abutment surface of the second magnet  4020 , which abuts on a corresponding adjacent circumferential end of the adjacent first A magnet  4011 . 
     In addition, the second B magnet  4026  is disposed to be closer to the first B magnet  4012  than the first B magnet  4025 . The second magnetization vectors in the second B magnet  4026  are inclined toward the anti-stator side with respect to the predetermined direction; the predetermined direction is perpendicular to the q-axis representing the boundary of the corresponding magnetic pole. 
     A predetermined angle θ 106  of each of the second magnetization vectors in the second B magnet  4026  inclined toward the anti-stator side with respect to the predetermined direction is preferably set to be larger than a predetermined angle θ 107  formed between the q-axis and an abutment surface  4024 . The abutment surface  4024  is an abutment surface of the second magnet  4020 , which abuts on a corresponding adjacent circumferential end of the adjacent first B magnet  4012 . Each of the second B magnets  4022  can have the same configuration as the second A magnet  4021 . 
     This configuration of the second magnets  4020  enable each of the magnetic paths of the second magnets  4020  to be closer to a circular arc, thus enabling the magnetic paths to be longer. This therefore results in the second magnets  420  being less likely to demagnetize. 
     Like the third embodiment, each of the fourth to sixth embodiments can use an additional magnetic member attached to the farther side of a selected one of the first magnet and the second magnet from the stator; the selected one of the first and second magnets is designed to have a thinner thickness in the radial direction. 
     For example, as illustrated in  FIG.  59   , the magnetic member  133  can be attached the farther side, i.e. the radially outward side, of each first magnet  1010  of the fourth embodiment. This reduces magnetic saturation of each first magnet  1010  and results in each first magnet  1010  being less likely to demagnetize, making it possible to increase torque. The additional magnetic members can be formed integrally with the cylinder  43 , making it possible to stop rotation of the first and second magnets. 
     The disclosure of the specification is not limited to the disclosed embodiments. The disclosure of the specification can include not only the disclosed embodiments but also skilled-person&#39;s modifications based on the disclosed embodiments. For example, the disclosure of the specification is not limited to combinations of the components and/or elements disclosed in the disclosed embodiments, and therefore can be implemented by various combinations within the disclosed embodiments. 
     The disclosure of the specification can include additional elements to the disclosed embodiments. The disclosure of the specification can include the disclosed embodiments from which one or more components and/or elements have been removed. The disclosure of the specification can include replacement of one or more elements or components in one of the disclosed embodiments with one or more elements or components in another one of the disclosed embodiments. The disclosure of the specification can include combinations of one or more elements or components in one of the disclosed embodiments with one or more elements or components in another one of the disclosed embodiments. 
     The disclosed technical scopes of the disclosure of the specification are not limited to the descriptions of the disclosed embodiments. Some of the disclosed technical scopes of the disclosure of the specification are shown by the descriptions of claims, and various changes of the disclosed technical scopes within the equivalent meanings and/or equivalent scopes of the descriptions of the claims should be therefore accepted. 
     While illustrative embodiments of the present disclosure have been described herein, the present disclosure is not limited to the embodiments described herein, but includes any and all embodiments having modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and/or alternations as would be appreciated by those in the art based on the present disclosure. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive.