Patent Publication Number: US-2019173339-A1

Title: Rotary electric machine

Description:
TECHNICAL FIELD 
     The present invention relates to a rotary electric machine. 
     BACKGROUND ART 
     In Patent Literature 1, there is disclosed a rotator in which permanent magnets are embedded in a rotator core, and the rotator core is step-skewed by a predetermined angle in an axial direction. In this structure, magnets of other poles in other stages are overlapped with each other as viewed in the axial direction. 
     Further, in Patent Literature 2, there is disclosed a stator core which is divided into a plurality of blocks in an axial direction so as to form a step skew between the blocks, and a rotator core in which a bridge portion is formed between magnet through holes and an outer peripheral surface of the rotator core. Further, a bridge angle is equal to or larger than a skew angle. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] JP 2004-248422 A 
     [PTL 2] JP 5774081 B2 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the configuration disclosed in Patent Literature 1, when the number of stacked sections of the rotator core is different, it is required to change a skew angle in a magnetizing yoke configured to magnetize the rotator in accordance with the number of stacked sections. Thus, there is a problem in that a magnetizing yoke that is not skewed and can be shared regardless of the number of stacked sections cannot be used. 
     Further, in the configuration disclosed in Patent Literature 2, the bridge angle is large, and the magnetizing yoke that is not skewed can be used. However, a bridge width is large, and hence there is a problem in that a leakage magnetic flux flowing from one magnetic pole of the rotator to a magnetic pole having a different polarity through the bridge is increased, thereby reducing torque. 
     The present invention has been made in view of the above, and has an object to provide a rotary electric machine, which does not necessarily require manufacture of a magnetizing yoke in accordance with the number of stacked sections, and is capable of reducing a leakage magnetic flux through a bridge. 
     Solution to Problem 
     In order to achieve the above-mentioned object, according to one embodiment of the present invention, there is provided a rotary electric machine, including: an armature; and a rotator, wherein the armature includes: a stator core including a plurality of magnetic teeth; and armature windings, which are formed of multi-layer multi-phase winding groups, are wound around the teeth, and are accommodated in slots between the teeth, wherein the rotator is arranged through a magnetic air gap defined between the rotator and the armature, and is provided so as to be rotatable about a rotation shaft, wherein the rotator includes a rotator core, and permanent magnets are embedded in the rotator core, wherein the rotator core has a step-skew structure with two or more stages in an axial direction, and wherein magnets having different polarities in different stages are arranged so as to be prevented from being overlapped with each other in a circumferential direction as viewed along the rotation shaft direction. 
     Advantageous Effects of Invention 
     According to the present invention, it is not necessarily required to manufacture a magnetizing yoke in accordance with the number of stacked sections, and it is possible to reduce a leakage magnetic flux through a bridge. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a front sectional view of a V-shaped IPM motor in a first embodiment of the present invention. 
         FIG. 2  is a transparent view of a rotor of the V-shaped IPM motor in the first embodiment as viewed in an axial direction. 
         FIG. 3  is a transparent view of a rotor that is step-skewed as an explanatory example as viewed in the axial direction. 
         FIG. 4  is a front sectional view of a rotor obtained by changing the first embodiment into an IPM motor of a flat-plate type in an example. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Now, an embodiment of the present invention is described with reference to the accompanying drawings. Note that, in the drawings, the same reference symbols represent the same or corresponding parts. 
     First Embodiment 
     In a first embodiment of the present invention, description is made of a multi-layer multi-phase winding AC rotary electric machine, which includes armature windings having multi-layer and multi-phase configurations, and in which the windings share a magnetic path at a gap at which a field pole and an armature are opposed to each other. More specifically, description is made of a multi-layer multi-phase winding permanent magnet motor as an example. Further, the multi-layer multi-phase winding permanent magnet motor can be applied to an electric power steering device as one example. 
       FIG. 1  is a front sectional view of a V-shaped interior permanent magnet (IPM) motor in the first embodiment of the present invention.  FIG. 2  is a transparent view of a rotor of the V-shaped IPM motor in the first embodiment as viewed in an axial direction. 
     A multi-layer multi-phase winding permanent magnet motor being a rotary electric machine includes an armature  3  and a rotator  5 . The armature  3  includes a stator core  9  and armature windings  13 . The stator core  9  includes a plurality of magnetic teeth  7 . The armature windings  13  are formed of multi-layer multi-phase winding groups, are wound around the teeth  7 , and are accommodated in slots  11  between the teeth  7 . 
     In  FIG. 1  corresponding to a plane in which a rotation center is defined as a perpendicular line, a hole having substantially a circular shape is formed at a center of the stator core  9 . Distal ends of the plurality of teeth  7  are located on one circumference. The rotator  5  is arranged in this hole. That is, the rotator  5  is arranged on an inner side of the armature  3  in a circumferential direction through a magnetic air gap  15  defined between the rotator  5  and the armature  3 , and is provided so as to be rotatable about a rotation shaft  17 . In the first embodiment, in other words, this magnetic air gap  15  is a portion of the hole, and is a hollow space. 
     Permanent magnets  21  are embedded in the rotator  5 . Although detailed description is made later, a rotator core  5   a  has a step-skew structure with two or more stages, and those stages are arrayed in a rotation shaft direction (direction in which the rotation shaft extends, that is, direction in which the rotation center extends). Further, magnets having different polarities in different stages are arranged so as to be prevented from being overlapped with each other in the circumferential direction as viewed along the rotation shaft direction. 
     Now, the above-mentioned configuration is described in more detail. The stator includes a first armature winding, a second armature winding, and the stator core  9 . The stator core  9  includes an annular core back  9   a  and the teeth  7 . The annular core back  9   a  is formed of a magnetic material such as a magnetic steel sheet. The teeth  7  extend from the core back  9   a  to the inner side in the circumferential direction. Although not illustrated, for example, insulating paper is inserted between the armature windings and the stator core to secure electrical insulation. 
     As one example, in the first embodiment, forty-eight teeth  7  are formed in total. Therefore, the number of the slots  11  is also forty-eight. Four coils of the armature winding are accommodated in one slot. 
     The first armature winding is formed of three phases of a U1 phase, a V1 phase, and a W1 phase, and the second armature winding is formed of three phases of a U2 phase, a V2 phase, and a W2 phase. The armature windings are arranged in the order of the U1, U2, W1, W2, V1, and V2 phases from the first slot. The armature windings are arranged in the seventh and subsequent slots also in the order of the U1, U2, W1, W2, V1, and V2 phases, and are arranged in the same order to the forty-eighth slot. 
     However, for example, the armature windings are arranged so that directions of currents of the U1 phase in the first slot and the U1 phase in the seventh slot are reverse to each other. That is, the armature winding has a configuration of a distributed winding, which is wound from the first slot to the seventh slot, and the armature winding covers six teeth in total. This corresponds to an electrical angle of 180°, and a short pitch winding factor is 1. Further, the armature windings are driven at a phase difference in which electrical angles are different from each other by 30°. Thus, a distributed winding factor is 1. As a result, a winding factor is 1. Therefore, there is obtained such an effect that a motor that is reduced in size and high in torque is obtained, and that a usage amount of the permanent magnets is small as compared to a motor that is small in winding factor to achieve reduction in cost. 
     Two permanent magnets  21  are allocated for one pole, and the two permanent magnets  21  are arranged in a V shape in each magnetic pole. In the illustrated example, a total of sixteen permanent magnets  21  are embedded, and the rotator  5  having eight poles is described. The permanent magnets  21  are, for example, anisotropic magnets. 
     Eight magnet accommodating holes  23  are formed in the rotator core  5   a . That is, one magnet accommodating hole  23  is allocated for one pole. In  FIG. 1 , the magnet accommodating holes  23  each include a pair of rectangular portions  23   a , a pair of flux barrier portions  23   b , and one center portion  23   c . In the same pole, the pair of rectangular portions  23   a  extend so that an interval of portions thereof in the circumferential direction is reduced toward a radially inner side. Corresponding permanent magnets  21  are arranged in the pair of rectangular portions  23   a , respectively. The one center portion  23   c  is located between end portions of the pair of rectangular portions  23   a  on the radially inner side. The pair of flux barrier portions  23   b  are located more on a radially outer side with respect to end portions of corresponding rectangular portions  23   a  on the radially outer side. That is, the flux barrier portions  23   b  are located between the end portions of the corresponding rectangular portions  23   a  on the radially outer side and an outer peripheral surface  5   b  of the rotator core  5   a.    
     In  FIG. 1 , an outer shape of the rotator core  5   a  is a flower shape partially having a radius smaller than a radius of the true circle from the rotation center. Through formation of the rotator core into the flower shape, a torque ripple can be reduced, thereby obtaining a motor that is small in torque ripple. 
     The rotator core  5   a  is also formed by stacking thin sheet-like members formed of a plurality of magnetic materials such as a plurality of magnetic steel sheets in the rotation shaft direction. 
     The rotator core  5   a  has a two-step skew structure. In the two-step skew structure, stage portions of the rotator core, which have the same shape, are stacked in two stages in the rotation shaft direction. For example, when a two-step skew of a mechanical angle of around 3.75° is formed in the rotator core, an electrical angle 12th-order component of a cogging torque ripple can be reduced, thereby obtaining an advantage in that a motor that is small in clogging torque ripple is obtained to improve a steering feeling of a driver. 
     Magnetic pole portions of the rotator core  5   a  are connected to each other through a bridge  25 . More specifically, the bridge  25  being a part of the rotator core  5   a  is present between the flux barrier portions  23   b  of adjacent magnetic poles. A leakage magnetic flux flows through the bridge  25  in the rotator core. Thus, a magnetic flux originally supposed to flow from the magnetic pole of the rotator to the stator through an air gap to generate torque is reduced. When a bridge width (distance between the pair of adjacent flux barrier portions  23   b  in the circumferential direction) is large, the leakage magnetic flux is increased, and the torque of the motor is reduced, which is not favorable for a high output motor. In contrast, when the bridge width is reduced, the leakage magnetic flux can be reduced, but the level of difficulty of press working is increased, thereby degrading productivity. In general, in the press working, a thickness in the vicinity of a punched portion is reduced due to shear droop caused during the press working unless a punching width as large as a thickness of the rotator core is secured. In this case, the bridge cannot be sufficiently held to cause distortion, and hence a shape of the bridge portion is not stabilized. Therefore, there is a negative influence in that the steering feeling of a driver is degraded due to increase in torque ripple. In the first embodiment, the bridge width is set as large as the thickness of the rotator core to achieve a configuration in which increase in output of the motor and reduction in torque ripple can be both achieved. 
       FIG. 2  is a transparent view of the rotator  5  skewed in two stages as viewed in the rotation shaft direction. In the illustrated configuration, the permanent magnets  21  having different polarities in different stages are prevented from being overlapped with each other. That is, in  FIG. 2 , it is found that the permanent magnets  21  of a first pole each indicated by the solid line in a relatively upper stage are arranged so as to be prevented from being overlapped with the permanent magnets  21  of a second pole each indicated by the dotted line in a relatively lower stage in the circumferential direction as viewed along the rotation shaft direction. Meanwhile, in  FIG. 3 , a rotator as an explanatory example is illustrated. In a configuration of this rotator, in order to set an angle that can cancel torque ripples in stages so as to reduce the torque ripples, magnets having different polarities are overlapped with each other as illustrated in  FIG. 3 . That is, in  FIG. 3 , as viewed along the rotation shaft direction, it is found that there is formed a region  31  in which the permanent magnets having different polarities in different stages are overlapped with each other in the circumferential direction. In the first embodiment, in the permanent magnet motor of a two-layer three-phase winding, energization phases of the first armature winding and the second armature winding are shifted by 30° to cancel six peaks of the torque ripples during one electrical angle cycle. It is not required to set a large step skew angle of a mechanical angle of around 7.5°(value obtained by dividing the electrical angle of 30° by the number of pole pairs of 4) so as to cancel the torque ripples, and it is only required to set a small step skew angle of around 3.75° so as to reduce twelve peaks of the torque ripples, which are the second most important. Therefore, it is relatively easy to achieve a configuration in which magnets having different polarities in different stages are prevented from being overlapped with each other. In the motor in the explanatory example, in order to set a step skew angle of around 7.5°, it is required to reduce the width of the magnetic pole. Thus, the magnet amount is reduced, and the torque is reduced, which is not favorable for the high output motor. 
     As described above, according to the first embodiment, in the permanent magnet motor in which the rotator core is step-skewed in the axial direction, and the magnetic poles of the rotator are formed of the rotator core, when the torque or the output of the motor is to be changed by changing the number of stacked sections of the rotator core, it is not required to manufacture a magnetizing yoke in accordance with the number of stacked sections, and a magnetizing yoke having the same specification can be shared regardless of the number of stacked sections. Thus, reduction in cost of a manufacturing device and reduction in loss of production efficiency due to a setup operation of the magnetizing yoke are achieved, thereby being capable of achieving mass production at low cost. 
     In addition, the leakage magnetic flux through the bridge can be reduced while avoiding distortion or deformation during the press working at the width of the bridge of the rotator core, which is configured to connect the magnetic poles having different polarities at the rotator outer peripheral portion. That is, an object is to enable easy production of a high output motor different in motor output due to a difference in motor length. 
     Further, when the rotary electric machine of the present invention is implemented as a permanent magnet motor for electric power steering, in the permanent magnet motor for electric power steering, assist torque with respect to steering of a driver differs for each of vehicle types having different vehicle weights. Therefore, in motors having the same sectional shape, it is required to adjust torque or output by changing the motor length. Further, in an in-vehicle motor, the motor weight affects a fuel economy. Thus, a motor that is reduced in weight and high in output is demanded. Therefore, in the permanent magnet motor in which the rotator core is step-skewed in the axial direction, and the magnetic poles of the rotator are formed of the rotator core, when the torque or the output of the motor is to be changed by changing the number of stacked sections of the rotator core, it is not required to manufacture a magnetizing yoke in accordance with the number of stacked sections, and the magnetizing yoke having the same specification can be shared regardless of the number of stacked sections. With this, reduction in cost of a manufacturing device and reduction in loss of production efficiency due to a setup operation of the magnetizing yoke are achieved, thereby being capable of achieving mass production at low cost. 
     Although the details of the present invention are specifically described above with reference to the preferred embodiment, it is apparent that persons skilled in the art may adopt various modifications based on the basic technical concepts and teachings of the present invention. 
     For example, even in a rotary electric machine using permanent magnets  121  of a flat plate shape as illustrated in  FIG. 4 , effects similar to those of the above-mentioned first embodiment are obtained. 
     REFERENCE SIGNS LIST 
       3  armature,  5  rotator,  5   a  rotator core,  7  tooth,  11  slot,  13  armature winding,  15  magnetic air gap,  17  rotation shaft,  21 ,  121  permanent magnet,  25  bridge