Abstract:
In this rotor ( 101 ), which has permanent magnets ( 105 ) inserted in a rotor core ( 102 ), main body sections ( 117 ) of magnetic shield sections ( 107 ) are formed in contact with the q-axis-side end faces ( 105   q ) of each permanent magnet ( 105 ). In addition, an extension section ( 127 ) for each magnetic shield section ( 107 ) is formed positioned more toward the outer periphery than the outer-periphery-side pole face ( 105   ou ) of the permanent magnet ( 105 ) and between the d-axis and the q-axis at an end face of the rotor core ( 102 ). Each extension section ( 127 ) is configured so as to gradually approach the outer periphery of the rotor core ( 102 ) while extending from the outer-periphery-side end of the main body section ( 117 ) from the q-axis to the d-axis side, and then gradually move away from the outer periphery of the rotor core ( 102 ) while extending from the q-axis side to the d-axis side.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a rotor of a permanent magnet motor which is devised to reduce cogging torque and torque ripples while securing mechanical strength. 
       BACKGROUND ART 
       [0002]    A rotor of a permanent magnetic motor of embedded magnet type (IPM motor: Interior Permanent Magnet motor) is configured in that permanent magnets are embedded into a rotor core. 
         [0003]    In such an interior permanent magnet motor, both of magnet torque generated by magnetic fluxes of the permanent magnets and reluctance torque generated through changes in magnetic resistances (reluctances) of the rotor core can be utilized as effective torque that contributes to rotating force. An interior permanent magnet motor is accordingly a motor of energy-saving type, of high efficiency and of high torque, and is used in various industrial fields. 
         [0004]    Cogging torque or torque ripples including such cogging torque are generated in an interior permanent magnet motor. For reducing such cogging torque and torque ripples, it is suggested to form magnetic shielding portions (details will be described later) at a rotor of a permanent magnet motor (see, for instance, Patent Literature 1). 
         [0005]    A prior art case in which cogging torque and torque ripples are reduced by forming magnetic shielding portions at a rotor of a permanent magnet motor will now be explained with reference to  FIG. 8 . 
         [0006]    In this respect, only a portion of one main magnetic pole is shown in  FIG. 8 , and since the other magnetic poles are of identical configuration as that of the main magnetic pole shown in  FIG. 8 , illustrations thereof are omitted. 
         [0007]    Further, in  FIG. 8 , lines of magnetic forces showing magnetic flux flows are indicated by dotted lines. 
         [0008]      FIG. 8  is a sectional view orthogonal to an axial direction in which a conventional rotor  1  used in an interior permanent magnet motor is shown upon extracting only a portion of one main magnetic pole. 
         [0009]    As shown in the drawing, a rotor core  2  of the rotor  1  is a substantially cylindrically shaped member formed by laminating silicon steel plates. A motor shaft  3  is fitted into an axial core portion of the rotor core  2 , and the motor shaft  3  is supported by a bearing (illustration omitted) in a freely rotatable manner. 
         [0010]    A permanent magnet inserting hole  4  is a hole which penetrates in the axial direction from one end surface up to the other end surface of the rotor core  2 . The permanent magnet inserting holes  4  are formed at the rotor core  2  at even intervals along a peripheral direction. 
         [0011]    A plate-like permanent magnet  5  is inserted into the permanent magnet inserting hole  4  to form a single main magnetic pole. Magnetic polarities of the permanent magnets  5  are set for each of the main magnetic poles such that an outer peripheral side magnetic pole surface  5   ou  of a permanent magnet  5  disposed to have an arbitrary main magnetic pole and an outer peripheral side magnetic pole surface  5   ou  of a permanent magnet  5  disposed at a main magnetic pole adjoining the main magnetic pole have mutually different magnetic polarities. With this arrangement, magnetic polarities of adjoining main magnetic poles (S poles, N poles) will be different from each other. 
         [0012]    In the rotor core  2  of the rotor  1 , an axis connecting the axial core of the rotor  1  (motor shaft  3 ) and a center of an arbitrary main magnetic pole generating magnetic torque (a central position in a peripheral direction of the permanent magnet  5 ) will be a d axis of a d-q axial coordinate. 
         [0013]    Further, from among the rotor core  2 , a core between an arbitrary main magnetic pole and a main magnetic pole adjoining the main magnetic pole in the peripheral direction will be an auxiliary magnetic pole portion  6  generating reluctance torque. An axis connecting the axial core of the rotor  1  (motor shaft  3 ) and a central axis of the auxiliary magnetic pole  6 , namely an axis orthogonal to the d axis at an electrical angle will be a q axis of the d-q axial coordinate. 
         [0014]    Further, the rotor core  2  is formed with a magnetic shielding portion  7  which is a hole penetrating in the axial direction from one end surface up to the other end surface. The magnetic shielding portion  7  is located between the d axis and the q axis of the d-q axial coordinate at an end surface of the rotor core  2 . In the example of  FIG. 8 , two magnetic shielding portions  7  are formed at an arbitrary magnetic pole. 
         [0015]    Explaining the shape and the configuration of the magnetic shielding portion  7  with reference to  FIG. 9 , the magnetic shielding portion  7  is constituted of a main body portion  17  and an extending portion  27  succeeding to (communicating with) the main body portion  17 . 
         [0016]    The main body portion  17  contacts a q-axis side end surface  5   q  which is an end surface of the permanent magnet  5  in the peripheral direction (succeeds to (communicates with) the permanent magnet inserting hole  4 ) and extends towards the outer peripheral surface of the rotor  1  from its axial core side portion  17 - 1  towards an outer peripheral side portion  17 - 2 . However, the outer peripheral side portion  17 - 2  of the main body portion  17  does not reach the outer peripheral surface of the rotor  1  and the rotor core  2  resides between the outer peripheral side portion  17 - 2  and the outer peripheral surface of the rotor  1 . 
         [0017]    The extending portion  27  is arranged in that its base end portion  27 - 1  succeeds to (communicates with) the outer peripheral side portion  17 - 2  of the main body portion  17  and extends from the outer peripheral side portion  17 - 2  of the main body portion  17  along the circumferential direction towards the d axis. However, a tip end portion  27 - 2  of the extending portion  27  does not reach the d axis. A distance between the extending portions  27  and the outer peripheral surface of the rotor  1  (direction in the radial direction) is substantially constant at any position in the extending direction of the extending portion  27 , and the rotor core  2  resides between the extending portion  27  and the outer peripheral surface of the rotor  1 . 
         [0018]    Since the magnetic shielding portion  7  is a hole (space), its magnetic permeability is remarkably smaller than that of the rotor core  2 , and since it is extremely hard for the magnetic flux to pass therethrough, it functions as a magnetic shielding portion. In this respect, also when the interior of the hole (space) forming the magnetic shielding portion  7  is filled with a non-magnetic metal of low magnetic permeability (such as aluminum or brass), adhesive, varnish or resin, it is still a magnetic shielding portion. 
         [0019]    Since such a magnetic shielding portion  7  is formed on end surfaces on both sides of the permanent magnet  5  in the peripheral direction, it has the following effects. 
         [0020]    (1) Since the magnetic shielding portions  7  for magnetically shielding a space between an arbitrary main magnetic pole and a main magnetic pole adjoining the main magnetic pole in the peripheral direction, it is possible to reduce magnetic flux (short-circuit flux) which is generated from the outer peripheral side magnetic pole surface  5   ou  of the permanent magnet  5  of the main magnetic pole, passes the auxiliary magnetic pole portion  6  of the rotor core  2  and reaches the outer peripheral side magnetic pole surface  5   ou  of the permanent magnet  5  of the main magnetic pole adjoining in the peripheral direction. Since the short-circuit flux is a torque which does not cross a stator and does not contribute to generation of magnetic torque, the effective torque is increased by decreasing such short-circuit flux. 
         [0021]    As for the reduction of the short-circuit flux, the shorter the distance between the extending portion  27  of the magnetic shielding portion  7  and the outer peripheral surface of the rotor  1  (distance in the radial direction) is and the longer the length of the extending portion  27  along the circumferential direction is, the more generation of short-circuit flux can be restrained. 
         [0022]    (2) Since the magnetic flux generated from the outer peripheral side magnetic pole surface  5   ou  of the permanent magnet  5  passes while bypassing towards a central side of the permanent magnet  5  so as to go round the magnetic shielding portion  7  of low magnetic permeability, changes in magnetic flux density distribution generated on the outer peripheral surface of the rotor  1  will become moderate by means of the permanent magnet  5 . More specifically, changes in magnetic flux density distribution will become moderate at both end portions of the main magnetic pole in the peripheral direction. 
         [0023]    In this manner, since especially changes at both end portions of the main magnetic pole in the peripheral direction from among the magnetic flux density distribution generated on the outer peripheral surface of the rotor  1  will become moderate, it is possible to reduce cogging torque and torque ripples. 
       CITATION LIST 
     Patent Literature 
       [0024]    PTL 1: Japanese Patent Application Laid-Open No. Hei. 11-98731 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0025]    The above prior art had the following problems. 
         [0026]    (1) The rotor  1  of the permanent magnet motor is arranged in that the distance between the extending portion  27  of the magnetic shielding portion  7  and the outer peripheral surface of the rotor  1  (distance in the radial direction) is made short and the length of the extending portion  27  along the circumferential direction is made large for restraining generation of short-circuit flux. With this arrangement, the rotor core  2  positioned between the extending portion  27  and the outer peripheral surface of the rotor  1  will have a small radial directional distance and a long peripheral directional length, and its mechanical strength will become small. Accordingly, it might be that the motor cannot stand centrifugal force when rotated at high speed. 
         [0027]    The rotor core  2  is configured by laminating silicon steel plates and forming the magnet inserting holes  4  and the magnetic shielding portions  7  or the like through punching. Accordingly. when the distance between the extending portion  27  of the magnetic shielding portion  7  and the outer peripheral surface of the rotor  1  (distance in the radial direction) is made short and the length of the extending portion  27  along the circumferential direction is made long, the rotor core  2  positioned between the extending portion  27  and the outer peripheral surface of the rotor  1  will have a small mechanical strength as mentioned above so that problems will be caused in performing punching. Namely, when performing punching of the silicon steel plates, the rotor core  2  positioned between the extending portion  27  and the outer peripheral surface of the rotor  1  is easily distorted and even cut in the worst case so that manufacture of the rotor core  2  might become difficult. 
         [0028]    (2) In these days, it is desired to further reduce cogging torque and torque ripples for smoothly driving the motor and for reducing noise and oscillation. However, the above-mentioned prior art could not meet the demands of further reducing cogging torque and torque ripple. 
         [0029]    The present invention has been made in view of the above prior art, and it is an object thereof to provide a rotor of a permanent magnet motor capable of improving mechanical strength by reducing centrifugal force at the time of high speed rotation of the permanent magnetic motor and difficulties of manufacture and of additionally reducing cogging torque and torque ripples. 
       Solution to Problems 
       [0030]    The configuration of the present invention for solving the above problems is characterized in that it is
       a rotor of a permanent magnetic motor formed with a plurality of main magnetic poles along a peripheral direction of a rotor core by respectively comprising permanent magnets in permanent magnet inserting holes formed at a plurality of spots in a peripheral direction of the rotor core to penetrate in an axial direction from one end surface up to the other end surface of the rotor core, and   formed with magnetic shielding portions for each main magnetic pole which penetrate in the axial direction from the one end surface up to the other end surface of the rotor core and which are positioned between a d axis and a q axis of a d-q axial coordinate on the end surface of the rotor core,   wherein each magnetic shielding portion includes an extending portion,   wherein the extending portion is formed closer to an outer peripheral side than an outer peripheral side magnetic pole surface of the permanent magnet, and   wherein the extending portion also extends from the q axis side towards the d axis side and gradually separates from the outer peripheral surface of the rotor core while extending from the q axis side towards the d axis side.       
 
         [0036]    The configuration of the present invention is characterized in that it is
       a rotor of a permanent magnetic motor formed with a plurality of main magnetic poles along a peripheral direction of a rotor core by respectively comprising permanent magnets in permanent magnet inserting holes formed at a plurality of spots in a peripheral direction of the rotor core to penetrate in an axial direction from one end surface up to the other end surface of the rotor core, and   formed with magnetic shielding portions for each main magnetic pole which penetrate in the axial direction from the one end surface up to the other end surface of the rotor core and which are positioned between a d axis and a q axis of a d-q axial coordinate on the end surface of the rotor core,   wherein each magnetic shielding portion includes a main body portion and an extending portion succeeding to the main body portion,   wherein the main body portion is formed at a position opposing a q axis side end surface of the permanent magnet,   wherein the main body portion also extends towards an outer peripheral surface of the rotor core,   wherein the extending portion is formed closer to an outer peripheral side than an outer peripheral side magnetic pole surface of the permanent magnet, and   wherein the extending portion also extends from the q axis side towards the d axis side with the outer peripheral side portion of the main body being the starting point and gradually separates from the outer peripheral surface of the rotor core while extending from the q axis side towards the d axis side.       
 
         [0044]    The configuration of the present invention is characterized in that
       the extending portion has a bent shape being bent halfway while extending from the q axis side towards the d axis side or   the extending portion has a warped shape being warped while extending from the q axis side towards the d axis side.       
 
         [0047]    The configuration of the present invention is characterized in that
       the main body portion contacts the q axis side end surface or   the main body portion separates from the q axis side end surface.       
 
       Advantageous Effects of Invention 
       [0050]    According to the present invention, each extending portion of the magnetic shielding portion is arranged in that it is formed closer to the outer peripheral side than the outer peripheral side magnetic pole surface of the permanent magnet, and in that the extending portion also extends from the q axis side towards the d axis side and gradually separates from the outer peripheral surface of the rotor core while extending from the q axis side towards the d axis side. 
         [0051]    With this arrangement, it is possible to make changes in magnetic flux density distribution generated on the outer peripheral surface of the rotor by means of the permanent magnet, and especially the magnetic flux density distributions at both end portions of the main magnetic pole in the peripheral direction to be more moderate when compared to the prior art, to make the magnetic flux density distribution generated from the main magnetic pole to be closer to a sine wave, and to reduce cogging torque and torque ripples in a more effective manner. 
         [0052]    At a position of an extensional end point of the extending portion (portion close to the d axis), the distance between the extending portion and the rotor core (distance in the radial direction) will be long so that it is possible to secure mechanical strength of the rotor core which also makes processing easy. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0053]      FIG. 1  is a sectional view orthogonal to an axial direction showing a rotor of a permanent magnet motor according to Example 1 of the present invention. 
           [0054]      FIG. 2  is a block diagram showing a magnetic shielding portion of Example 1. 
           [0055]      FIG. 3  is a sectional view orthogonal to an axial direction showing a rotor of a permanent magnet motor according to Example 2 of the present invention. 
           [0056]      FIG. 4  is a sectional view orthogonal to an axial direction showing a rotor of a permanent magnet motor according to Example 3 of the present invention. 
           [0057]      FIG. 5  is a sectional view orthogonal to an axial direction showing a rotor of a permanent magnet motor according to Example 4 of the present invention. 
           [0058]      FIG. 6  is a sectional view orthogonal to an axial direction showing a rotor of a permanent magnet motor according to Example 5 of the present invention. 
           [0059]      FIG. 7  is a sectional view orthogonal to an axial direction showing a rotor of a permanent magnet motor according to Example 6 of the present invention. 
           [0060]      FIG. 8  is a sectional view orthogonal to an axial direction showing a rotor of a permanent magnet motor according to the prior art. 
           [0061]      FIG. 9  is a block diagram showing a conventional magnetic shielding portion in extracted and enlarged view. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0062]    The rotor of a permanent magnet motor according to the present invention will be explained in details based on examples thereof. 
       Example 1 
       [0063]    A rotor  101  of a permanent magnet motor according to Example 1 of the present invention will now be explained with reference to  FIG. 1 . 
         [0064]    In this respect, only one main magnetic pole is shown in  FIG. 1 , and since the other main magnetic poles are of identical configuration as that of the main magnetic pole shown in  FIG. 1 , illustration of the other main magnetic poles is omitted. 
         [0065]    Further, in  FIG. 1 , lines of magnetic forces showing magnetic flux flows are indicated by dotted lines. 
         [0066]      FIG. 1  is a sectional view orthogonal to the axial direction showing the rotor  101  of Example 1 used in an interior permanent magnet motor upon extracting only one main magnetic pole. 
         [0067]    As shown in the drawing, a rotor core  102  of the rotor  101  is a substantially cylindrical member formed by laminating silicon steel plates. A motor shaft  103  is fitted into an axial core portion of the rotor core  102 , and the motor shaft  103  is supported by a bearing (illustration omitted) in a freely rotatable manner. 
         [0068]    A permanent magnet inserting hole  104  is a hole which penetrates from one end surface up to the other end surface of the rotor core  102  in the same direction as the motor shaft  103 . The permanent magnet inserting holes  104  are formed at the rotor core  102  at even intervals in a peripheral direction of the rotor core  102 . 
         [0069]    In this example, a plate-like permanent magnet  105  is inserted into the permanent magnet inserting hole  104  to form a single main magnetic pole. Magnetic polarities of the permanent magnets  105  are set for each main magnetic poles such that an outer peripheral side magnetic pole surface  105   ou  of a permanent magnet  105  disposed at an arbitrary main magnetic pole and an outer peripheral side magnetic pole surface  105   ou  of a permanent magnet  105  disposed at a main magnetic pole adjoining the main magnetic pole have mutually different magnetic polarities. With this arrangement, magnetic polarities of adjoining main magnetic poles (S poles, N poles) will be different from each other. 
         [0070]    In this manner, a plurality of main magnetic poles with alternatively different magnetic polarities is formed at the rotor  101  along the peripheral direction of the rotor core  102 . 
         [0071]    In the rotor core  102  of the permanent magnet motor shown in  FIG. 1 , an axis connecting the axial core of the rotor  101  (motor shaft  103 ) and a center of an arbitrary main magnetic pole generating magnetic torque (a central position in a peripheral direction of the permanent magnet  105 ) will be a d axis of a d-q axial coordinate. 
         [0072]    Further, from among the rotor core  102 , the core between a permanent magnet  105  of one main magnetic pole corresponding to one magnetic pole and a permanent magnet  105  of a main magnetic pole adjoining the main magnetic pole in the peripheral direction will be an auxiliary magnetic pole portion  106  generating reluctance torque. An axis connecting the axial core of the rotor  101  (motor shaft  103 ) and a central axis of the auxiliary magnetic pole  106 , namely an axis orthogonal to the d axis at an electrical angle will be a q axis of the d-q axial coordinate. 
         [0073]    Further, the rotor core  102  is formed with a magnetic shielding portion  107  which is a hole penetrating from one end surface up to the other end surface in the same direction as the motor shaft  103 . The magnetic shielding portion  107  is positioned between the d axis and the q axis of the d-q axial coordinate at an end surface of the rotor core  102 . In the example of  FIG. 1 , two magnetic shielding portions  107  are formed at one main magnetic pole. 
         [0074]    Explaining the shape and the configuration of the magnetic shielding portion  107  with reference to  FIG. 2 , the magnetic shielding portion  107  is constituted of a main body portion  117  and an extending portion  127  succeeding to (communicating with) the main body portion  117 . Moreover, the extending portion  127  is constituted of a first extending portion  127   a  and a second extending portion  127   b.    
         [0075]    The main body  117  is formed at a position opposing a q axis side end surface  105   q  which is an end surface of the permanent magnet  105  in the peripheral direction. An axial core side portion  117 - 1  of the main body portion  117  contacts the q-axis end surface  105   q  of the permanent magnet  105 , succeeds to (communicates with) the permanent magnet inserting hole  104 , and extends towards the outer peripheral surface of the rotor  101  (rotor core  102 ) while being substantially parallel to the d axis. However, an outer peripheral side portion  117 - 2  of the main body portion  117  does not reach the outer peripheral surface of the rotor  101 , and the rotor core  102  resides between the outer peripheral side portion  117 - 2  and the outer peripheral surface of the rotor  101 . 
         [0076]    The extending portion  127  is formed closer to the outer peripheral side of the outer peripheral side magnetic pole surface  105   ou  of the permanent magnet  105  as well as at a position between the d axis and the q axis. The extending portion  127  is constituted of a linearly extending first extending portion  127   a  and a linearly extending second extending portion  127   b  succeeding to (communicating with) the first extending portion  127   a  in a bent state. The rotor core  102  resides between the extending portion  127  and the outer peripheral surface of the rotor  101 . 
         [0077]    The first extending portion  127   a  is arranged in that its base end portion  127   a - 1  succeeds to (communicates with) the outer peripheral side surface  117 - 2  of the main body portion  117  and extends from the q axis side towards the d axis side with the outer peripheral side portion  117 - 2  of the main body portion  117  being the starting point. 
         [0078]    Further, the first extending portion  127   a  comes gradually closer to the outer peripheral surface of the rotor  101  (rotor core  102 ) in extending towards the d axis side. That is, a distance between the first extending portion  127   a  and the outer peripheral surface of the rotor  101  (rotor core  102 ) (distance in the radial direction) becomes gradually smaller with the first extending portion  127   a  extending towards the d axis. 
         [0079]    The second extending portion  127   b  is arranged in that its base end portion  127   b - 1  succeeds to (communicates with) a tip end portion  127   a - 2  of the first extending portion  127   a  and extends from the q axis side towards the d axis side with the tip end portion  127   a - 2  of the first extending portion  127   a  being the starting point. However, a tip end portion  127   b - 2  of the second extending portion  127   b  does not reach the d axis. 
         [0080]    Further, the second extending portion  127   b  gradually separates from the outer peripheral surface of the rotor  101  (rotor core  102 ) in extending towards the d axis. That is, a distance between the second extending portion  127   b  and the outer peripheral surface of the rotor  101  (rotor core  102 ) (distance in the radial direction) becomes gradually longer with the second extending portion  127   b  extending towards the d axis. 
         [0081]    Since the magnetic shielding portion  107  constituted of the main body portion  117  and the extending portion  127  (first and second extending portions  127   a,    127   b ) is a hole (space), its magnetic permeability is remarkably smaller than that of the rotor core  102 , and since it is extremely hard for the magnetic flux to pass therethrough, it functions as a magnetic shielding portion. In this respect, also when the interior of the hole (space) forming the magnetic shielding portion  107  is filled with a non-magnetic metal of low magnetic permeability (such as aluminum or brass), adhesive, varnish or resin, it is still a magnetic shielding portion. 
         [0082]    Since such a magnetic shielding portion  107  is formed on both sides of the permanent magnet  105  in the peripheral direction, the rotor  101  of the permanent magnet recited in Example 1 has the following effects. 
         [0083]    (1) In the rotor core  102 , the distance between the second extending portion  127   b  and the outer peripheral surface of the rotor  101  (distance in the radial direction) becomes gradually longer with the second extending portion  127   b  extending towards the d axis, and the distance between the second extending portion  127   b  and the outer peripheral surface of the rotor  101  (distance in the radial direction) is longest at the tip end portion  127   b - 2  of the second extending portion  127   b.    
         [0084]    Therefore, as indicated by the distribution of lines of magnetic force in  FIG. 1 , at a portion between the second extending portion  127   b  and the outer peripheral surface of the rotor  101  out of the rotor core  102  between the magnetic shielding portion  107  and the outer peripheral surface of the rotor  101 , magnetic saturation increases moderately from the central axial side towards the end portion side of the main magnetic pole in the peripheral direction. As a result, the distribution range of magnetic flux generated from the outer peripheral side magnetic pole surface  105   ou  of the permanent magnet  105  goes round the magnetic shielding portions  107  and reaches the surface of the rotor  101  towards the end portion side of the main magnetic pole in the peripheral direction becomes longer when compared to the prior art in which the second extending portion  127   b  is not provided. 
         [0085]    Therefore, changes in magnetic flux density distribution generated on the outer peripheral surface of the rotor  101 , and more specifically, changes in magnetic flux density distribution at both end portions of the main magnetic pole in the peripheral direction will become more moderate by means of the permanent magnet  105  when compared to the prior art in which the second extending portion  127   b  is not provided. 
         [0086]    As a result, changes in magnetic flux density distribution of magnetic flux generated from the main magnetic pole will be closer to a sine wave shape, and it is possible to reduce cogging torque and torque ripples in a more effective manner. 
         [0087]    (2) At the base end portion  127   a - 1  of the first extending portion  127   a  or the tip end portion  127   b - 2  of the second extending portion  127   b,  the distance between the extending portion  127  and the outer peripheral surface of the rotor  101  (distance in the radial direction) is longer. 
         [0088]    It is accordingly possible to improve the mechanical strength at the rotor core  102  between the extending portion  127  and the outer peripheral surface of the rotor  101  even when the length of the extending portion  127  in the peripheral direction is long such that it can stand centrifugal force and external shock or the like. 
         [0089]    Further, in performing punching of the silicon steel plates for forming the rotor core  102 , there will be no fear of deformation or cutting of the rotor core  102  positioned between the extending portion  127  and the outer peripheral surface of the rotor  101  so that punching can be easily performed at the time of manufacturing the rotor core  102 . 
         [0090]    (3) The rotor core  102  is arranged in that the distance between the extending portion  127  and the outer peripheral surface of the rotor  101  (distance in the radial direction) is smaller at the tip end portion  127   a - 2  of the first extending portion  127   a  or the base end portion  127   b - 1  of the second extending portion  127   b,  and the length of the extending portion  127  in the peripheral direction is longer. Since the magnetic resistance of the rotor core  102  becomes accordingly longer between the extending portion  127  and the outer peripheral surface of the rotor  101 , it is possible to reduce short-circuit flux and to effectively generate magnetic torque. 
         [0091]    (4) As indicated by the following equation (1), reluctance torque is generated by a difference in d axis inductance and q axis inductance. 
         [0092]    In the present example, by providing the extending portion  127  extending in the peripheral direction to be closer to the outer peripheral side than the outer peripheral side magnetic pole surface  105   ou  of the permanent magnet  105 , the inductance of the d axis becomes small (since magnetic flux becomes harder to pass through) and the difference between the d axis inductance and the q axis inductance becomes large (L d &lt;L q ) so that the reluctance torque (torque of the second item of equation (1)) can be effectively used. 
         [0000]        T=P   n Φ m   i   q   +P   n ( L   d   −L   q ) i   d   i   q   (1)
       T: torque   P n : number of poles   Φ m : magnetic flux of permanent magnet   i q : q axis current   i d : d axis current   L q : q axis inductance   L d : d axis inductance       
 
       Example 2 
       [0100]    Next, a rotor  201  of a permanent magnet motor according to Example 2 of the present invention will be explained with reference to  FIG. 3 . In this respect, portions identical to those of Example 1 are marked with the same reference signs, and explanations of duplicated portions will be omitted. 
         [0101]    In the rotor  201  of Example 2, a magnetic shielding portion  207  is constituted of a main body portion  217  and an extending portion  227  succeeding to (communicating with) the main body portion  217 . 
         [0102]    The main body portion  217  is formed at a position opposing the q axis side end surface  105   q  of the permanent magnet  105 . The main body portion  217  contacts an end surface of the permanent magnet  105  in the peripheral direction, succeeds to (communicates with) the permanent magnet inserting hole  104 , and extends towards the outer peripheral surface of the rotor  201  (rotor core  102 ) while being substantially parallel to the d axis. 
         [0103]    An extending portion  227  is formed closer to the outer peripheral side than the outer peripheral side magnetic pole surface  105   ou  of the permanent magnet  105  and at a position between the d axis and the q axis. The extending portion  227  is constituted of a linearly extending first extending portion  227   a,  a second extending portion  227   b  extending linearly while succeeding to (communicating with) the first extending portion  227   a  in a bent manner, and a third extending portion  227   c  extending linearly while succeeding to (communicating with) the second extending portion  227   b  in a bent manner. Namely, the extending portion  227  bents in a two-staged manner. 
         [0104]    The first extending portion  227   a  gradually comes closer to the outer peripheral surface of the rotor  201  (rotor core  102 ) in extending from the q axis side towards the d axis side. 
         [0105]    The second extending portion  227   b  gradually separates from the outer peripheral surface of the rotor  201  (rotor core  102 ) in extending from the q axis side towards the d axis side, and the third extending portion  227   c  gradually separates from the outer peripheral surface of the rotor  201  (rotor core  102 ) in extending from the q axis side towards the d axis side. Moreover, the interval of the third extending portion  227   c  separating from the outer peripheral surface of the rotor  201  (rotor core  102 ) in extending from the q axis side to the d axis side of the third extending portion  227   c  (distance in the radial direction) is longer than that of the second extending portion  227   b.    
         [0106]    Since the extending portion  227  is bent in a two-staged manner in the rotor  201  of a permanent magnet motor of Example 2, the magnetic saturation increases in a more moderate manner from the central axis side towards the end portion side of the main magnetic pole in the peripheral direction at a portion of the rotor core  102  between the second extending portion  227   b  or the third extending portion  227   c  and the outer peripheral surface of the rotor  101  by adjusting respective lengths and bending angles of the extending portions  227   a,    227   b  and  227   c.  As a result, it is possible to adjust the distribution range of the magnetic flux which is generated from the outer peripheral side magnetic pole surface  105   ou  of the permanent magnet  105 , going round the magnetic shielding portion  207  and reaching the surface of the rotor  201  towards the end portion side of the main magnetic pole in the peripheral direction when compared to Example 1 in which no portion corresponding to the third extending portion  227   c  is provided. 
         [0107]    It is accordingly possible to make, by means of the permanent magnet  105 , changes in magnetic flux density distribution generated on the outer peripheral surface of the rotor  201 , and particularly changes in magnetic flux density distribution of both end portions of the main magnetic pole in the peripheral direction to be even more moderate when compared to Example 1 in which no portion corresponding to the third extending portion  227   c  is provided. 
         [0108]    As a result, by making the magnetic flux density distribution of magnetic flux generated from the main magnetic pole come close to a sine wave shape, it is possible to further reduce cogging torque or torque ripples. 
         [0109]    It is also possible to exhibit the same effects as those obtained in Example 1. 
         [0110]    In this respect, the bending in the extending portion  227  is not limited to the above-described two-staged one but might also be one of three or more stages. 
       Example 3 
       [0111]    Next, a rotor  301  of a permanent magnet motor according to Example 3 of the present invention will be explained with reference to  FIG. 4 . In this respect, portions identical to those of Example 1 are marked with the same reference signs, and explanations of duplicated portions will be omitted. 
         [0112]    In the rotor  301  of Example 3, a magnetic shielding portion  307  is constituted of a main body portion  317  and an extending portion  327  succeeding to (communicating with) the main body portion  317 . 
         [0113]    The main body portion  317  is formed at a position opposing the q axis side end surface  105   q  of the permanent magnet  105 . The main body portion  317  contacts the q axis side end surface  105   q  of the permanent magnet  105  (succeeds to (communicates with) the permanent magnet inserting hole  104 ) and extends towards the outer peripheral surface of the rotor  301  (rotor core  102 ) while being substantially parallel to the d axis. 
         [0114]    An extending portion  327  is formed closer to the outer peripheral side than the outer peripheral side magnetic pole surface  105   ou  of the permanent magnet  105  and at a position between the d axis and the q axis. The extending portion  327  is constituted of a first extending portion  327   a  having an arc shape which is convex with respect to the outer peripheral surface of the rotor  301  (rotor core  102 ) and extending in a warped manner, and a second extending portion  327   b  extending while succeeding to (communicating with) the first extending portion  327   a  in a warped manner. 
         [0115]    The first extending portion  327   a  gradually comes closer to the outer peripheral surface of the rotor  301  (rotor core  102 ) in extending from the q axis side towards the d axis side. 
         [0116]    On the other hand, the second extending portion  327   b  gradually separates from the outer peripheral surface of the rotor  301  (rotor core  102 ) in extending from the q axis side towards the d axis side. 
         [0117]    Since the extending portion  327  is warped in arc shape in the rotor  301  of a permanent magnet motor of Example 3, it is possible to avoid that mechanical stress focuses at corner portions formed at boundaries of each of the extending portions so as to further increase mechanical strength. 
         [0118]    It is also possible to exhibit the same effects as those obtained in Example 1. 
       Example 4 
       [0119]    Next, a rotor  401  of a permanent magnet motor according to Example 4 of the present invention will be explained with reference to  FIG. 5 . In this respect, portions identical to those of Example 1 are marked with the same reference signs, and explanations of duplicated portions will be omitted. 
         [0120]    In the rotor  401  of Example 4, the magnetic shielding portion  107  is constituted of the main body portion  117  and the extending portion  127  succeeding to (communicating with) the main body portion  117 . Moreover, the extending portion  127  is constituted of the first extending portion  127   a  and the second extending portion  127   b.  Namely, the shape of the magnetic shielding portion  107  itself is identical to that of Example 1. 
         [0121]    However, while the main body  117  of the magnetic shielding portion  107  is formed at a position opposing a q axis side end surface  105   q  of a permanent magnet  105 , it is disposed while being apart from the q axis side end surface  105   q  of the permanent magnet  105  in the peripheral direction. 
         [0122]    It is possible to exhibit the same effects as those obtained in Example 1 also with the rotor  401  of a permanent magnet motor of Example 4. 
       Example 5 
       [0123]    Next, a rotor  501  of a permanent magnet motor according to Example 5 of the present invention will be explained with reference to  FIG. 6 . In this respect, portions identical to those of Example 1 are marked with the same reference signs, and explanations of duplicated portions will be omitted. 
         [0124]    In the rotor  501  of Example 5, one main magnetic pole is formed with two permanent magnet inserting holes  104   a,    104   b.  The permanent magnet inserting holes  104   a,    104   b  are line symmetric with the center being the d axis when seen from an end surface of the rotor  501  and become wider in extending from an axial core side of the rotor  501  towards an outer peripheral surface side of the rotor  501  so that the permanent magnet inserting holes  104   a,    104   b  have a so-called “V-shaped” form. 
         [0125]    Permanent magnets  105   a,    105   b  are inserted into each of the permanent magnet inserting holes  104   a,    104   b,  and the state of disposing the permanent magnets  105   a,    105   b  is also of “V-shaped” form. 
         [0126]    At this time, outer peripheral side magnetic pole surfaces  105   ou  of both permanent magnets  105   a,    105   b  are of identical magnetic polarity (S pole or N pole). With this arrangement, the permanent magnets  105   a,    105   b  form one main magnetic pole. 
         [0127]    The permanent magnet  105   a  is positioned on one side of the main magnetic pole in the peripheral direction (clockwise direction). A magnetic shielding portion  107 - 1  is formed on an end surface side of the one permanent magnet  105   a  in the clockwise direction. 
         [0128]    The magnetic shielding portion  107 - 1  includes a main body portion  117 - 1  and an extending portion  127 - 1 . 
         [0129]    The main body  117 - 1  contacts an end surface of the permanent magnet  105   a  in the clockwise direction and succeeds to (communicates with) the magnet inserting hole  104   a.  The main body portion  117 - 1  extends towards the outer peripheral surface of the rotor core  102  in a state in which it inclines towards the d axis. However, an outer peripheral side portion of the main body portion  117 - 1  does not reach the outer peripheral surface of the rotor  501  (rotor core  102 ). The rotor core  102  resides between the main body portion  117 - 1  and the outer peripheral surface of the rotor  501 . 
         [0130]    The extending portion  127 - 1  is arranged in that its base portion (portion of the q axis side) succeeds to (communicates with) the outer peripheral side portion of the main body portion  117 - 1  and extends along the outer peripheral surface of the rotor core  102  from the q axis side towards the d axis side with the outer peripheral side portion of the main body portion  117 - 1  being the starting point and gradually separates from the outer peripheral surface of the rotor core  102  while further extending from the q axis side towards the d axis side. The rotor core  102  resides between the extending portion  127 - 1  and the rotor  501 . 
         [0131]    The permanent magnet  105   b  is positioned on the other side of the main magnetic pole in the peripheral direction (counterclockwise direction). A magnetic shielding portion  107 - 2  is formed on an end surface side of the other permanent magnet  105   b  in the counterclockwise direction. 
         [0132]    The magnetic shielding portion  107 - 2  includes a main body portion  117 - 2  and an extending portion  127 - 2 . 
         [0133]    The main body portion  117 - 2  contacts an end surface of the permanent magnet  105   b  in the counterclockwise direction and succeeds to (communicates with) the magnet inserting hole  104   b.  The main body portion  117 - 2  extends towards the outer peripheral surface of the rotor core  102  in a state in which it inclines towards the d axis. However, an outer peripheral side portion of the main body portion  117 - 2  does not reach the outer peripheral surface of the rotor  501  (rotor core  102 ). The rotor core  102  resides between the main body portion  117 - 2  and the outer peripheral surface of the rotor  501 . 
         [0134]    The extending portion  127 - 2  is arranged in that its base portion (portion of the q axis side) succeeds to (communicates with) the outer peripheral side portion of the main body portion  117 - 2  and extends along the outer peripheral surface of the rotor core  102  from the q axis side towards the d axis side with the outer peripheral side portion of the main body portion  117 - 1  being the starting point and gradually separates from the outer peripheral surface of the rotor core  102  while further extending from the q axis side towards the d axis side. The rotor core  102  resides between the extending portion  127 - 2  and the rotor  501 . 
         [0135]    It is possible to exhibit the same effects as those obtained in Example 1 also with the rotor  501  of a permanent magnet motor of Example 5. 
         [0136]    In this respect, the state of disposing the permanent magnets is not limited to the above-described “V-shaped” form, and the same effects as those of Example 1 can be obtained also with “reversed V-shaped”, “U-shaped”, “arch-like” or “trapezoid” forms. 
       Example 6 
       [0137]    Next, a rotor  601  of a permanent magnet motor according to Example 6 of the present invention will be explained with reference to  FIG. 7 . In this respect, portions identical to those of Example 1 are marked with the same reference signs, and explanations of duplicated portions will be omitted. 
         [0138]    In the rotor  601  of Example 6, a magnetic shielding portion  607  is constituted of an extending portion  627  and does not comprise a main body portion unlike the above-described examples. The extending portion  627  is constituted of a first extending portion  627   a  and a second extending portion  627   b  succeeding to (communicating with) the first extending portion  627   a  in a bent condition. 
         [0139]    The first extending portion  627   a  extends linearly from the q axis side towards the d axis side with a portion close to a q axis side end surface  105   q  of the permanent magnet  105  from among the outer peripheral side magnetic pole surface  105   ou  of the permanent magnet  105   a  being a starting point and comes gradually closer to the outer peripheral surface of the rotor  601  (rotor core  102 ) in extending. 
         [0140]    The second extending portion  627   b  extends linearly from the q axis side towards the d axis side with a tip end portion of the first extending portion  627   a  being a starting point and gradually separates from the outer peripheral surface of the rotor  601  (rotor core  102 ) in extending. 
         [0141]    It is possible to exhibit the same effects as those obtained in Example 1 also with the rotor  601  of Example 6. 
         [0142]    In this respect, while the extending portion  627  of Example 6 has an overall bent shape, it could also have an overall warped shape. 
         [0143]    Further, in Example 6, while the first extending portion  627   a  of the extending portion  607  contacts the outer peripheral side magnetic pole surface  105   ou,  it is also possible to form the extending portion  607  such that the first extending portion  627   a  separates from the outer peripheral side magnetic pole surface  105   ou,  is closer to the outer peripheral side than the outer peripheral surface magnetic pole surface  105   ou  and is positioned between the d axis and the q axis. 
         [0144]    In this respect, while a single permanent magnet is inserted into one permanent magnet inserting hole in the above-described examples, the permanent magnets which are inserted into the permanent magnet inserting holes are not limited to single magnets but might be divided in any one of the axial direction, radial direction or peripheral direction. 
         [0145]    In the above examples, while magnetic shielding portions are formed on both sides of a single main magnetic pole in the peripheral direction, it is possible to reduce cogging torque and torque ripples by forming the magnetic shielding portion only on one side of a single main magnetic pole in the peripheral direction. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1 ,  101 ,  201 ,  301 ,  401 ,  501 ,  601  . . . rotor 
           2 ,  102  . . . rotor core 
           3 ,  103  . . . motor shaft 
           4 ,  104 ,  104   a,    104   b  . . . permanent magnet inserting hole 
           5 ,  105 ,  105   a,    105   b  . . . permanent magnet 
           105   ou  . . . outer peripheral side magnetic pole surface 
           105   q  . . . q axis side end surface 
           6 ,  106  . . . auxiliary magnetic pole 
           7 ,  107 ,  107 - 1 ,  107 - 2 ,  207 ,  307 ,  607  . . . magnetic shielding portion 
           117 ,  217 ,  317  . . . main body portion 
           117 - 1  . . . axial core side portion 
           117 - 2  . . . outer peripheral side portion 
           127 ,  227 ,  627  . . . extending portion 
           127   a,    227   a,    327   a,    627   a  . . . first extending portion 
           127   a - 1  . . . base end portion 
           127   a - 2  . . . tip end portion 
           127   b,    227   b,    327   b,    627   b  . . . second extending portion 
           127   b - 1  . . . base end portion 
           127   b - 2  . . . tip end portion 
           227   c  . . . third extending portion