Abstract:
A rotor for a reluctance type rotating machine includes a rotor core formed by stacking a number of annular core materials each of which includes magnetic concave and convex portions alternately formed on an outer circumference thereof and a central through hole, the rotor core having a key axially extending on an outer circumference thereof, the rotor core being divided into a plurality of blocks, the core materials constituting at least one block having the magnetic concave and convex portions shifted by a predetermined angle relative to the core materials constituting the other or another block on the basis of a center line passing the key, and a rotational shaft inserted through the central hole of the rotor core, the shaft having a key groove engaging the key of the rotor core.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to a rotor for a reluctance type electric rotating machine which can achieve the similar effects to those achieved by skew.  
         [0003]     2. Description of the Related Art  
         [0004]     A reluctance type rotating machine or, for example, a reluctance type rotating machine provided with permanent magnets includes a rotor formed with a magnetic convex portion where a flux is easy to pass (d axis) and a magnetic concave portion where a flux is difficult to pass (q axis) and a permanent magnet which is disposed in a stator provided with a stator winding. The magnetic convex portion (d axis) has a high magnetic flux density in an air gap, whereas the magnetic concave portion (q axis) has a low magnetic flux density in an air gap. These variations in the magnetic flux density produce reluctance torque. Furthermore, torque is also developed by a magnetic attractive force and a magnetic repulsive force between poles of the permanent magnet and stator.  
         [0005]      FIGS. 16 and 17  illustrate an example of conventional rotor for a reluctance type rotating machine with permanent magnets. The illustrated machine is an 8-pole machine.  FIG. 16  is a side view of the rotor with an end plate and a rotational shaft being eliminated.  FIG. 17  is a sectional view taken along line  17 - 17 . Referring to  FIG. 16 , the rotor  100  includes a rotor core  101  made by stacking a number of annular silicon steel sheets. The rotor core  101  has pairs of generally rectangular magnet insertion holes  102  formed in an outer circumference thereof as shown in  FIG. 17 . Permanent magnets  103  are inserted and fixed in the insertion holes  102  respectively. The outer circumference of the rotor core  101  is further formed with cavities  104  located between the respective pairs of permanent magnets  103  as shown in  FIG. 17 . Each cavity  104  is formed into a generally triangular shape. In the rotor  100 , each pair of insertion holes  102 , permanent magnets  103  and each cavity  104  constitute the aforesaid magnetic concave portion  105  where a flux is difficult to pass (q axis). Each portion between the concave portions  105  constitutes the aforesaid magnetic convex portion  106  where a flux is easy to pass (d axis). The magnetic concave and convex portions  105  and  106  are formed alternately with a predetermined angle therebetween. See JP-A-2000-339922, for example.  
         [0006]     The rotor core  101  has keys  107  formed on an inner circumference thereof. The keys  107  are adapted to engage key grooves of a rotational shaft respectively. Furthermore, a center line Lo passing the keys  107  is adapted to pass the center of the magnetic convex portion  106 . A center line La passes the center of the magnetic convex portion  105  adjacent to the center line Lo. The center line Lo is adapted to meet the center line La at an angle θ. The angle θ is at 22.5 degrees when the rotor  100  has 8 poles. The rotor  100  is adapted to be disposed in a stator (not shown) provided with a stator winding.  
         [0007]     It is well known that squirrel-cage induction motors result in crawling due to torque developed by high harmonics. There is a possibility that permanent-magnet reluctance type rotating machines as the reluctance type rotating machine may cause the similar crawling to that caused by the squirrel-cage induction motors. As a result, the crawling results in torque ripple, oscillation, vibration and noise.  
       SUMMARY OF THE INVENTION  
       [0008]     Therefore, an object of the present invention is to provide a rotor for a reluctance type rotating machine which can achieve the similar effects to those achieved by skew and reduce torque ripple, oscillation, vibration and noise.  
         [0009]     The present invention provides a rotor for a reluctance type rotating machine comprising a rotor core formed by stacking a number of annular core materials each of which includes magnetic concave and convex portions alternately formed on an outer circumference thereof and a central through hole, the rotor core having a key axially extending on an outer circumference thereof, the rotor core being divided into a plurality of blocks, the core materials constituting at least one block having the magnetic concave and convex portions shifted by a predetermined angle relative the iron core materials constituting the other or another block on the basis of a center line passing the key, and a rotational shaft inserted through the central hole of the rotor core, the shaft having a key groove engaging the key of the rotor core.  
         [0010]     In the above-described construction, the core materials constituting at least one block are formed so that the magnetic concave and convex portions are shifted by a predetermined angle from the core materials constituting the other or another block relative to a center line passing the key. Accordingly, for example, a center line passing the center of the magnetic concave portion of at least one block has a locus shifted from one of another or the other block. Consequently, since the similar effects to those achieved by skew can be achieved, the torque ripple, oscillation, vibration and noise can be reduced.  
         [0011]     Each block may include the magnetic concave portions each of which is provided with a pair of magnet insertion holes which are opposed to each other so that a distance therebetween is gradually increased as the insertion holes proceed nearer to the outer circumference of the rotor, and permanent magnets may be inserted and fixed in the insertion holes respectively.  
         [0012]     A magnetic torque by the permanent magnets can also be achieved in addition to reluctance torque. Furthermore, harmonic values of counter electromotive force can be reduced by the similar effects to those achieved by skew. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     Other objects, features and advantages of the present invention will become clear upon reviewing the following description of the embodiments made with reference to the accompanying drawings, in which:  
         [0014]      FIGS. 1A and 1B  are sectional views taken along lines  1 A- 1 A and  1 B- 1 B in  FIG. 2 , showing the rotor in accordance with a first embodiment of the present invention;  
         [0015]      FIG. 2  is a side view of the rotor core of the rotor;  
         [0016]      FIG. 3  is a partial plan view of the rotor;  
         [0017]      FIG. 4  is a longitudinal section of the rotor;  
         [0018]      FIG. 5  is a longitudinal section of the reluctance type rotating machine with permanent magnets;  
         [0019]      FIG. 6  is a view similar to  FIG. 2 , showing the rotor in accordance with a second embodiment of the invention;  
         [0020]      FIG. 7  is a view similar to  FIG. 3 ;  
         [0021]      FIG. 8  is a sectional view taken along line  8 - 8  in  FIG. 6 ;  
         [0022]      FIG. 9  is a view similar to  FIG. 2 , showing the rotor in accordance with a third embodiment of the invention;  
         [0023]      FIG. 10  is a view similar to  FIG. 3 ;  
         [0024]      FIG. 11  is a sectional view taken along line  11 - 11  in  FIG. 9 ;  
         [0025]      FIG. 12  is a view similar to  FIG. 2 , showing the rotor in accordance with a fourth embodiment of the invention;  
         [0026]      FIG. 13  is a view similar to  FIG. 3 ;  
         [0027]      FIG. 14  is a view similar to  FIG. 2 , showing the rotor in accordance with a fifth embodiment of the invention;  
         [0028]      FIG. 15  is a sectional view taken along line  15 - 15  in  FIG. 14 ;  
         [0029]      FIG. 16  is a side view of a rotor of a conventional reluctance type rotating machine with permanent magnets; and  
         [0030]      FIG. 17  is a sectional view taken along line  17 - 17  in  FIG. 16 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]     Several embodiments of the present invention will be described.  FIGS. 1A  to  5  illustrate a first embodiment in which the invention is applied to a reluctance type rotating machine with permanent magnets. The reluctance type rotating machine possesses eight poles. A rotor  1  of the reluctance type rotating machine includes a rotor core  2  made by stacking a number of annular silicon steel sheets serving as a core material. The rotor core  2  is divided into four blocks  3  and  4  having the same thickness as shown in  FIG. 2 . The blocks  3  and  4  are stacked alternately.  
         [0032]     Each block  3  or the silicon steel sheets composing each block  3  will be described with reference to  FIG. 1A . Each block  3  has a number of pairs of generally rectangular magnet insertion holes  5  formed in an outer circumferential portion thereof. The paired magnet insertion holes  5  are opposed to each other so that a distance therebetween is gradually increased as the magnet insertion holes  5  near an outer circumferential edge. Permanent magnets  6  are inserted into the paired magnet insertion holes  5  respectively and fixed by an adhesive agent, filler or the like. The outer circumferential portion of each block  3  also has cavities  7  formed between the permanent magnets  6  of each pair. Each cavity  7  is formed into a generally triangular shape having two sides parallel to the paired permanent magnets  6  and the other side extending along the outer circumference. The two sides of each cavity  7  may or may not be parallel to the paired permanent magnets  6 .  
         [0033]     Each block  3  includes each portion thereof corresponding to the paired magnet insertion holes  5 , permanent magnets  6  and cavity  7  and serving as a magnetic concave portion  8  (q axis) where a flux is difficult to pass. Each block  3  further includes each portion thereof located between the magnetic concave portion  8  and serving as a magnetic convex portion  9  (d axis) where a flux is easy to pass. The magnetic concave and convex portions  8  and  9  are formed alternately so that each of the magnetic concave and convex portions  8  and  9  meets the other at a predetermined angle. Each block  3  further has two keys  10  and  11  which are formed on the inner circumference thereof so as to be 180-degree apart from each other and so as to extend axially.  
         [0034]     A center line Lo passing the centers of the keys  10  and  11  also passes the magnetic convex portions  9  in each block  3 . Now, assume a center line Loa shifted from the center line Lo by a predetermined angle Δθ in the direction opposite the direction of rotation of the rotor (clockwise). The center line Loa forms a predetermined angle θ with a center line Lb passing the center of the magnetic concave portion  8  adjacent to the center line Loa. Accordingly, the center line Loa passes the center of the magnetic convex portion  9 . The angle θ is represented as 180/n when n is the number of poles of the rotor  1 . Furthermore, when a stator  50  (see  FIG. 5 ) has slots the number of which is represented as 6×n, the magnetic concave and convex portions  8  and  9  representative of a pole position of each block  3  are shifted by the slot pitch a relative to the center line Lo. Accordingly, the angle Δθ is obtained from: 
 
Δθ=(360× a )/(6× n )=(60× a )/ n  
 
 Thus, the angle Δθ is represented as −(60×a)/n in degree. The minus sign indicates shift in the direction opposite the direction of rotation of the rotor (clockwise). 
 
         [0036]     Each block  4  or the silicon steel sheets composing each block  4  will be described with reference to  FIG. 1B . Each block  4  has magnet insertion holes  12  which are similar to the magnet insertion holes  5  and formed in an outer circumferential portion thereof. Permanent magnets  13  are inserted into the paired magnet insertion holes  12  respectively and fixed by an adhesive agent, filler or the like. The outer circumferential portion of each block  4  also has cavities  14  which are similar to the cavities  7  and are formed between the permanent magnets  13  of each pair.  
         [0037]     Each block  4  includes each portion thereof corresponding to the paired magnet insertion holes  12 , permanent magnets  13  and cavity  14  and serving as a magnetic concave portion  15  (q axis) where a flux is difficult to pass. Each block  4  further includes each portion thereof located between the magnetic concave portion  15  and serving as a magnetic convex portion  16  (d axis) where a flux is easy to pass. The magnetic concave and convex portions  8  and  9  are formed alternately so that each of the magnetic concave and convex portions  8  and  9  meets the other at a predetermined angle. Each block  4  further has two keys  10  and  11  which are formed on the inner circumference thereof so as to be 180-degree apart from each other and so as to extend axially.  
         [0038]     A center line Lo passing the centers of the keys  10  and  11  also passes the magnetic convex portions  16  in each block  4 . Now, assume a center line Lob shifted from the center line Lo by a predetermined angle Δθ in the rotation direction X of the rotor (counterclockwise). The center line Lob forms a predetermined angle θ with a center line Lc passing the center of the magnetic concave portion  15  adjacent to the center line Lob. Accordingly, the center line Lob passes the center of the magnetic convex portion  16 . The angle θ is represented as 180/n when n is the number of poles of the rotor  1 . The angle Δθ is represented as +(60×a)/n in degree. The plus sign indicates deviation in the rotation direction X of the rotor (counterclockwise).  
         [0039]     As obvious from  FIGS. 1A and 1B , the block  4  is made by stacking the silicon steel sheets which are the same as those of the block  3  and reversed inside out. Accordingly, the blocks  3  and  4  of the rotor core  2  can be composed of a single type of silicon steel sheets. Two annular end plates  17  and  18  are attached to both ends of the rotor core  2  respectively as shown in  FIG. 4 .  
         [0040]     The rotating shaft  19 , rotor core  2  and end plates  17  and  18  are integrated together by shrinkage fitting thereby to be assembled. In this case, as shown in  FIG. 4 , the keys  10  and  11  of the rotor core  2  are adapted to correspond with key grooves  20  of the rotating shaft  19  respectively. Only one of the key grooves  20  is shown in  FIG. 4 . The rotating shaft  19  is formed with a flange  21  for positioning the rotor core  2  and end plates  17  and  18 .  
         [0041]     Upon completion of assembly of the rotor  1 , the magnetic concave and convex portions  8  and  9  of the block  3  are shifted by the predetermined angle Δθ in the direction opposite the rotation direction X (clockwise) on the basis of the center line Lo. Further, the magnetic concave and convex portions  15  and  16  of the block  4  are also shifted by the predetermined angle Δθ in the rotation direction X (counterclockwise) on the basis of the center line Lo. As a result, the center lines Lb and Lc of the blocks  3  and  4  have linear loci which are zigzagged but not straightforward as in the conventional reluctance type rotating machines, as shown in  FIG. 3 . Accordingly, the rotor  1  can achieve the effects similar to those of skew in the rotors for squirrel-cage induction motors. In this case, an amount of shift is required to be ±0 between the center lines Lb and the center lines Lc. More specifically, the sum total of a shift angle Δθ (−) of the center lines Lb and a shift angle Δθ (+) of the center lines Lc is required to be ±0 and the sum total of loci lengths of the center lines Lb (total thickness of the block  3 ) is required to be equal to the sum total of loci lengths of the center lines Lc (total thickness of the block  4 ) or the difference between both sums is required to be ±0.  
         [0042]     The permanent-magnet reluctance type rotating machine  60  comprises the rotor  1  disposed in the stator provided with stator winding (not shown) as shown in  FIG. 5 . The rotor  1  includes the magnetic concave portions  8  and  15  (q axis) where a flux is difficult to pass and the magnetic convex portions  9  and  16  (d axis) where a flux is easy to pass. By causing electric current to flow into the stator winding, magnetic energy is stored in air gaps over the magnetic concave and convex portions  8  and  15 , and  9  and  16  respectively. The magnetic energy differs from one air gap to another. The changes in the magnetic energy develop reluctance torque. Furthermore, since the rotor  1  is provided with the permanent magnets  6  and  13 , torque is also developed by a magnetic attractive force and magnetic repulsive force between the permanent magnets  6  and  13  and magnetic poles of the stator. Consequently, the rotor  1  is rotated.  
         [0043]     In the foregoing embodiment, the magnetic concave and convex portions  8  and  9  of the block  3  are shifted by the predetermined angle Δθ in the direction opposite the rotation direction X (clockwise) on the basis of the center line Lo. Further, the magnetic concave and convex portions  15  and  16  of the block  4  are also shifted by the predetermined angle Δθ in the rotation direction X (counterclockwise) on the basis of the center line Lo. As a result, the linear loci of the center lines Lb and Lc of the blocks  3  and  4  are zigzagged and accordingly, the rotor  1  can achieve the effects similar to those of skew in the rotors for squirrel-cage induction motors. Consequently, torque ripple, oscillation, vibration and noise can be reduced in the permanent-magnet reluctance type rotating machine, and a peak value of back electromotive force can be reduced in the stator winding.  
         [0044]     Additionally, an amount of shift is set so as to be ±0 between the center lines Lb and the center lines Lc in the rotor core  2 . Consequently, magnetic obstacle can be prevented although the rotor  1  can achieve the effects similar to those of skew in the rotors for squirrel-cage induction motors.  
         [0045]     FIGS.  6  to  8  illustrate a second embodiment of the invention. Describing the difference of the second embodiment from the first embodiment, the rotor core  26  employed instead of the rotor core  2  includes blocks  3  and  27  stacked alternately. Each block  27  comprises the silicon steel sheets which are the same as those of each block  4  but are reversed by 180 degrees or more specifically, each block  4  is reversed by 180 degrees. The other construction of the rotor of the second embodiment is the same as that of the first embodiment.  
         [0046]     In the construction of the second embodiment, too, the linear loci of the center lines Lb and Lc of the blocks  3  and  27  are zigzagged in the same manner as in the first embodiment. Consequently, the rotor of the second embodiment can achieve the same effects as those of the first embodiment.  
         [0047]     The annular silicon steel sheets constituting the rotor core  26  are formed by punching a rolled elongated silicon steel sheet. It is well known that the rolling results in shift in the thickness in the rolling direction and in the direction perpendicular to the rolling direction. In the second embodiment, however, the blocks  27  obtained by reversing the blocks  4  by 180 degrees. Consequently, since the deviation in the thickness is absorbed, the thickness of the rotor core  26  can be rendered uniform.  
         [0048]     The thicknesses of the four blocks  3  and  27  are equal to one another in the second embodiment. However, the total thickness of the blocks having the respective center lines Lb may be equal to the total thickness of the blocks having the respective center lines Lc.  
         [0049]     FIGS.  9  to  11  illustrate a third embodiment of the invention. Describing the difference of the third embodiment from the first embodiment, the rotor core  28  employed instead of the rotor core  2  is divided into four blocks  29 ,  30  and  31 . Each block  29  has a thickness set to be equal to or less than one half of that of each of blocks  30  and  31 . The thickness of each block  29  is set at one half of that of each of the blocks  30  and  31  in the embodiment. The block  30  is formed by stacking the same silicon steel sheets as those of each block  4  (see  FIG. 1B ). The block  31  is formed by stacking the same silicon steel sheets as those of each block  3  (see  FIG. 1A ). The block  30  has a thickness equal to one of the block  31  and larger than the blocks  3  and  4 . The rotor core  28  has a thickness equal to that of the rotor core  2 .  
         [0050]     Each block  29  or the silicon steel sheets composing each block  29  will be described with reference to  FIG. 11 . Each block  29  has a number of pairs of generally rectangular magnet insertion holes  32  which are formed in an outer circumferential portion thereof and are similar to the insertion holes  5 . The permanent magnets  33  are inserted into the paired magnet insertion holes  32  respectively and fixed by an adhesive agent, filler or the like. The outer circumferential portion of each block  29  also has cavities  34  which are formed between the permanent magnets  33  of each pair and are similar to the cavities  7 .  
         [0051]     Each block  29  includes each portion thereof corresponding to the paired magnet insertion holes  32 , permanent magnets  33  and cavity  34  and serving as the magnetic concave portion  35  (q axis) where a flux is difficult to pass. Each block  29  further includes each portion thereof located between the magnetic concave portion  35  and serving as a magnetic convex portion  36  (d axis) where a flux is easy to pass. The magnetic concave and convex portions  35  and  36  are formed alternately with a predetermined angle therebetween. Each block  29  further has two keys  10  and  11  which are formed on the inner circumference thereof so as to be 180-degree apart from each other and so as to extend axially.  
         [0052]     The center line Lo passing the centers of the keys  10  and  11  also passes the magnetic convex portions  36  in each block  29 . The center line Lo forms a predetermined angle θ with a center line Ld passing the center of the magnetic concave portion  35  adjacent to the center line Lo. The angle θ is represented as 180/n when n is the number of poles of the rotor  1 . Thus, the silicon steel sheets constituting each block  29  are similar to those employed in the conventional rotor core as shown in  FIG. 17 .  
         [0053]     In the above-described construction, the center lines Lb and Lc of the blocks  31  and  30  have linear loci which are zigzagged. Accordingly, the rotor can achieve the effects similar to those of skew in the rotors for squirrel-cage induction motors as in the first embodiment. In particular, the center lines Ld of the blocks  29  located at both ends of the rotor core  28  have loci are located between the loci of the center lines Lc and Lb. Accordingly, since the mechanical balance can be improved between the rotor core  28  and the stator winding, the waveform characteristic of the back electromotive force can be improved in the stator winding.  
         [0054]      FIGS. 12 and 13  illustrate a fourth embodiment of the invention. The difference of the fourth embodiment from the first embodiment will be described. The rotor core  39  employed instead of the rotor core  2  includes a block  40  formed by integrating the blocks  3  and a block  41  formed by integrating the blocks  4 .  
         [0055]     In the foregoing construction, the loci of the center lines Lb and Lc of the respective blocks  40  and  41  are as shown in  FIG. 13 . Accordingly, the fourth embodiment can achieve the same effects as those of the first embodiment.  
         [0056]      FIGS. 14 and 15  illustrate a fifth embodiment of the invention. The difference of the fifth embodiment from the fourth embodiment will be described. The rotor core  42  employed in the fifth embodiment includes blocks  43  and  44 . One half  44   a  of the block  44  is formed by stacking the silicon steel sheets (see  FIG. 1B ) which are the same as those of the block  41 . The other half  44   b  of the block  44  is formed by stacking the silicon steel sheets (see  FIG. 8 ) which are the same as those of the block  27 . Furthermore, one half  43   a  of the block  43  is formed by stacking the silicon steel sheets ( FIG. 1A ) which are the same as those of the block  40 . The other half  43   b  is formed by reversing by 180 degrees and stacking the silicon steel sheets which are the same as those of the block  40  or more specifically, by reversing the portion  43   a  by 180 degrees. The other construction of the rotor of the fifth embodiment is the same as that of the first embodiment. Consequently, the fifth embodiment can achieve the same effects as those of the fourth and second embodiments.  
         [0057]     The portions  43   a  and  43   b  and the portions  44   a  and  44   b  constituting the respective blocks  43  and  44  are set at one halves of the thicknesses of the blocks  43  and  44  respectively in the fifth embodiment. However, these portions may be set substantially at one halves respectively.  
         [0058]     The permanent magnets are provided on the rotor core in each of the foregoing embodiments. However, the permanent magnets may or may not be provided on the rotor core. Further, the generally triangular cavities are formed in the rotor core so as to compose the concave and convex portions in each of the foregoing embodiments. However, the cavities may be circular, elliptic, rectangular or rhombic. Additionally, the rotor core may have mechanical concave and convex portions formed therein so that the magnetic concave and convex portions are formed.  
         [0059]     The number of poles of the rotor should not be limited to eight. The same effect can be achieved even when the number of poles is any other number. Furthermore, the number of slots of the stator may be set at any suitable number. Additionally, the number of blocks of the rotor should not be limited to two and four. Five or more blocks may be provided by stacking the silicon steel sheets having the magnetic concave and convex portions shifted. In this case, an amount of shift of the center line is required to be ±0.  
         [0060]     The foregoing description and drawings are merely illustrative of the principles of the present invention and are not to be construed in a limiting sense. Various changes and modifications will become apparent to those of ordinary skill in the art. All such changes and modifications are seen to fall within the scope of the invention as defined by the appended claims.