Patent Publication Number: US-2022216752-A1

Title: Magnetization ring, magnetization method, magnetization apparatus, rotor, motor, compressor, and air conditioner

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a U.S. national stage application of International Application No. PCT/JP2019/022142, filed on Jun. 4, 2019, the contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a magnetization ring, a magnetization method, a magnetization apparatus, a rotor, a motor, a compressor, and an air conditioner. 
     BACKGROUND 
     In a permanent magnet embedded type motor, a permanent magnet is magnetized in such a manner that a rotor to which the permanent magnet is attached is incorporated in a stator or a magnetization yoke. In order to efficiently magnetize the permanent magnet, it is proposed to insert a strip having magnetism, between the stator and the rotor (see, for example, Patent Reference 1). 
     PATENT REFERENCE 
     
         
         [Patent Reference 1] Japanese Patent Application Publication No. 2015-180145 (paragraphs 0033-0034) 
       
    
     However, a gap between the stator and the rotor is as narrow as 0.25 to 1.5 mm, and thus it is not easy to insert the strip into the gap. For this reason, it is desired to enable efficient magnetization of a permanent magnet with a simple operation. 
     SUMMARY 
     The present invention is intended to solve the above-described problem, and an object of the present invention is to enable efficient magnetization of a permanent magnet with a simple operation. 
     A magnetization ring according to an aspect of the present invention is disposed between a rotor and a core portion surrounding the rotor. The rotor has a permanent magnet and an inter-pole portion which are arranged in a circumferential direction about an axis. The magnetization ring has a magnetic portion facing a center of the permanent magnet in the circumferential direction, a nonmagnetic portion facing the inter-pole portion, and a nonmagnetic annular portion on at least one side of the magnetic portion and the nonmagnetic portion in a direction of the axis. 
     A magnetization method according to another aspect of the present invention includes disposing a magnetization ring between a rotor and a core portion surrounding the rotor, the rotor having a permanent magnet and an inter-pole portion which are arranged in a circumferential direction about an axis, and magnetizing the permanent magnet by applying current to a coil wound on the core portion. The magnetization ring has a magnetic portion facing a center of the permanent magnet in the circumferential direction, a nonmagnetic portion facing the inter-pole portion, and a nonmagnetic annular portion on at least one side of the magnetic portion and the nonmagnetic portion in a direction of the axis. 
     A magnetization apparatus according to still another aspect of the present invention is to magnetize a permanent magnet of a rotor having the permanent magnet and an inter-pole portion which are arranged in a circumferential direction about an axis. The magnetization apparatus includes a magnetization yoke on which a coil is wound and which surrounds the rotor, a magnetization ring disposed between the magnetization yoke and the rotor, and a power source to apply current to the coil. The magnetization ring has a magnetic portion facing a center of the permanent magnet in the circumferential direction, a nonmagnetic portion facing the inter-pole portion, and a nonmagnetic annular portion on at least one side of the magnetic portion and the nonmagnetic portion in a direction of the axis. 
     A rotor according to yet another aspect of the present invention has a permanent magnet and an inter-pole portion which are arranged in a circumferential direction about an axis. The rotor is magnetized by the above described magnetization method. 
     In the present invention, the magnetic portion of the magnetization ring faces the center of the permanent magnet in the circumferential direction, and thus magnetization magnetic flux from the core portion can efficiently flow to the permanent magnet. Moreover, since the nonmagnetic portion of the magnetization ring faces the inter-pole portion, short-circuit of the magnetization magnetic flux can be suppressed. Further, the magnetic portion and the nonmagnetic portion constitute the magnetization ring, the magnetization ring can be easily handled. That is, the permanent magnet can be efficiently magnetized with a simple operation. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a sectional view illustrating a motor according to a first embodiment. 
         FIG. 2  is an enlarged diagram illustrating teeth and a slot of a stator according to the first embodiment. 
         FIG. 3  is a diagram illustrating a magnetization ring, the stator, and a rotor according to the first embodiment. 
         FIG. 4  is a perspective view illustrating the magnetization ring according to the first embodiment. 
         FIG. 5  is a flowchart illustrating a magnetization process according to the first embodiment. 
         FIGS. 6(A), 6(B) , and  6 (C) are perspective views illustrating steps of the magnetization process according to the first embodiment. 
         FIGS. 7(A) and 7(B)  are perspective views illustrating steps of the magnetization process according to the first embodiment. 
         FIG. 8  is a diagram illustrating a configuration for the magnetization according to the first embodiment. 
         FIG. 9(A)  is a diagram illustrating the magnetization process according to the first embodiment, and  FIG. 9(B)  is a diagram illustrating magnetization current flowing through coils. 
         FIGS. 10(A), 10(B) , and  10 (C) are perspective views illustrating steps of another example of the magnetization process according to the first embodiment. 
         FIG. 11  is a diagram illustrating the stator, and the rotor according to Comparative Example 1. 
         FIG. 12  is a flowchart illustrating a magnetization process according to Comparative Example 1. 
         FIGS. 13(A) and 13(B)  are perspective views illustrating steps of the magnetization process according to Comparative Example 1. 
         FIG. 14  is a graph illustrating a comparison between changes with time of the magnetization current in the first embodiment and Comparative Example 1. 
         FIG. 15  is a diagram illustrating a magnetization ring, the stator, and the rotor according to Comparative Example 2. 
         FIG. 16  is a diagram illustrating a magnetization ring, the stator, and the rotor according to a second embodiment. 
         FIG. 17  is a diagram illustrating a magnetization ring, the stator, and the rotor according to a third embodiment. 
         FIG. 18(A)  is a diagram illustrating a magnetization process according to the third embodiment, and  FIG. 18(B)  is a diagram illustrating magnetization current flowing through coils. 
         FIG. 19  is a diagram illustrating a magnetization ring, the stator, and the rotor according to the third embodiment. 
         FIG. 20  is a perspective view illustrating a magnetization ring according to a fourth embodiment. 
         FIG. 21  is a perspective view illustrating a magnetization ring according to a fifth embodiment. 
         FIG. 22  is a diagram illustrating the magnetization ring, the stator, and the rotor according to the fifth embodiment. 
         FIG. 23  is a diagram illustrating a magnetization apparatus according to a sixth embodiment. 
         FIG. 24  is a diagram illustrating a magnetization yoke of the magnetization apparatus according to the sixth embodiment. 
         FIG. 25  is a flowchart illustrating a magnetization process according to the sixth embodiment. 
         FIG. 26  is a diagram illustrating a compressor to which a motor according to each embodiment is applicable. 
         FIG. 27  is a diagram illustrating an air conditioner that includes the compressor illustrated in  FIG. 26 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will be described in detail below with reference to the figures. The present invention is not limited to these embodiments. 
     First Embodiment 
       FIG. 1  is a sectional view illustrating a motor  100  according to a first embodiment. The motor  100  of the first embodiment includes a rotatable rotor  5  and a stator  1  that surrounds the rotor  5 . An air gap of 0.25 to 1 mm is provided between the stator  1  and the rotor  5 . 
     Hereinafter, a direction of an axis C 1 , which is a rotating axis of the rotor  5 , is referred to as an “axial direction”. A circumferential direction about the axis C 1  is referred to as a “circumferential direction” and indicated by an arrow R 1  in  FIG. 1  and other figures. A radial direction about the axis C 1  is referred to as a “radial direction”.  FIG. 1  illustrates a cross-section in a plane perpendicular to the axial direction. 
     The rotor  5  includes a rotor core  50  and permanent magnets  55  attached to the rotor core  50 . The rotor core  50  has a cylindrical shape about the axis C 1 . The rotor core  50  is made of electromagnetic steel sheets which are stacked in the axial direction and fastened by crimping or the like. The sheet thickness of each electromagnetic steel sheet is, for example, 0.1 to 0.7 mm. 
     The rotor core  50  has a plurality of magnet insertion holes  51  along its outer circumference. In this example, six magnet insertion holes  51  are disposed at equal intervals in the circumferential direction. One permanent magnet  55  is disposed in each magnet insertion hole  51 . One permanent magnet  55  constitutes one magnetic pole. The number of permanent magnets  55  is six, which is the same as the number of magnet insertion holes  51 , and thus the number of poles of the rotor  5  is six. The number of poles of the rotor  5  is not limited to six, but only needs to be two or more. Two or more permanent magnets  55  may be disposed in one magnet insertion hole  51  so that the two or more permanent magnets  55  constitute one magnetic pole. 
     The permanent magnet  55  is a member in the form of a flat plate, and has a width in the circumferential direction and a thickness in the radial direction. The permanent magnet  55  is made of a rare earth magnet that contains neodymium (Nd), iron (Fe) and boron (B). The permanent magnet  55  is magnetized in its thickness direction, i.e., in the radial direction. The permanent magnets  55  adjacent to each other in the circumferential direction are magnetized in opposite directions. 
     As described above, the permanent magnet  55  constitutes the magnetic pole of the rotor  5 . A center of the permanent magnet  55  in the circumferential direction forms a pole center P ( FIG. 3 ) of the rotor  5 . An inter-pole portion M ( FIG. 3 ) of the rotor  5  is formed between the permanent magnets  55  adjacent to each other in the circumferential direction. 
     A circular shaft hole  57  is formed at a center of the rotor core  50  in the radial direction. A shaft  58  is fixed into the shaft hole  57  by press-fitting. A center axis of the shaft  58  coincides with the axis C 1  described above. 
     A flux barrier  52  is formed on each of both ends of the magnet insertion hole  51  in the circumferential direction. The flux barrier  52  is an opening extending in the radial direction from the end of the magnet insertion hole  51  in the circumferential direction toward the outer circumference of the rotor core  50 . The flux barrier  52  is provided to suppress leakage magnetic flux between the adjacent magnetic poles. 
     The stator  1  includes a stator core  10  and coils  2  wound on the stator core  10 . The stator core  10  is formed in an annular shape about the axis C 1 . The stator core  10  is made of a plurality of electromagnetic steel sheets which are stacked in the axial direction and fastened by crimping or the like. The thickness of each electromagnetic steel sheet is, for example, 0.1 to 0.7 mm. 
     The stator core  10  includes an annular core back  11  and a plurality of teeth  12  extending inward in the radial direction from the core back  11 . The core back  11  is formed in an annular shape about the axis C 1 , and is fitted inside a cylindrical frame  18 . 
     The teeth  12  are formed at equal intervals in the circumferential direction. A slot  15  is formed between each adjacent two of the teeth  12 . The coils  2  are wound around the teeth  12 . The number of teeth  12  is 18 in this example, but only needs to be two or more. 
     The coil  2  is made of a conductor such as aluminum and an insulating film covering the conductor. The coils  2  are wound around the teeth  12  in distributed winding as illustrated in  FIG. 1 , but the coils  2  may be wound in concentrated winding. 
       FIG. 2  is an enlarged diagram illustrating the teeth  12  and the slot  15 . A tip portion  13 , which is wide in the circumferential direction, is formed at a tip of each tooth  12  on the inner side in the radial direction. The tip portion  13  faces an outer circumferential surface of the rotor  5 . 
     The slot  15  is formed between adjacent two teeth  12 . The number of slots  15  is the same as the number of teeth  12  (18 in this example). The coil  2  wound around the tooth  12  is housed in the slot  15 . A slot opening  14  is formed at an end of the slot  15  on the inner side in the radial direction. The slot opening  14  is located between the tip portions  13  of the adjacent two teeth  12 . 
     (Magnetization of Permanent Magnet) 
     Next, a configuration for magnetization of the permanent magnets  55  and a magnetization method will be described. The permanent magnets  55  are magnetized in a state where the permanent magnets  55  are inserted into the magnet insertion holes  51  of the rotor core  50 . There are roughly two types of magnetization method for the permanent magnets  55 . 
     One method is to use the stator  1 . In this case, the rotor  5  is incorporated in the stator  1  as a core portion, and magnetization current is applied to the coils  2  to generate a magnetizing magnetic field, which magnetizes the permanent magnets  55  of the rotor  5 . This magnetization method is also referred to as a post-assembly magnetization. 
     Another method is to use a magnetization yoke  80  ( FIG. 24 ) of a magnetization apparatus  8 . In this case, the rotor  5  is incorporated in a magnetization yoke  80  as the core portion, and the magnetization current is applied to coils  9  ( FIG. 24 ) wound on the magnetization yoke  80  to thereby generate the magnetizing magnetic field. The magnetization method using the magnetization yoke  80  will be described in a sixth embodiment. 
     Hereinafter, a description will be made of the method of magnetizing the permanent magnets  55  in a state where the rotor  5  is incorporated in the stator  1 .  FIG. 3  is a schematic diagram illustrating a magnetization ring  3 , the stator  1 , and the rotor  5  according to the first embodiment. The magnetization of the permanent magnets  55  is performed in a state where the inter-pole portions M of the rotor  5  face the slot openings  14  of the stator  1 . The magnetization ring  3  is inserted between the stator  1  and the rotor  5 . 
       FIG. 4  is a perspective view illustrating the magnetization ring  3 . The magnetization ring  3  is a cylindrical member that has an outer circumferential surface  33  facing the stator  1  and an inner circumferential surface  34  facing the rotor  5 . 
     The magnetization ring  3  has an outer diameter Do and an inner diameter Di, and also has a thickness T. The inner diameter Di of the magnetization ring  3  is larger than an outer diameter Dr ( FIG. 6(A) ) of the rotor  5  (Di&gt;Dr). The outer diameter Do of the magnetization ring  3  is smaller than an inner diameter Ds ( FIG. 6(C) ) of the stator  1  (Ds&gt;Do). The thickness T of the magnetization ring  3  is smaller than or equal to the gap G between the rotor  5  and the stator  1  (G≥T&gt;0). 
     The magnetization ring  3  includes a nonmagnetic portion  31  composed of a nonmagnetic body and a magnetic portion  32  composed of a magnetic body. The nonmagnetic portion  31  is desirably composed of a resin such as polyimide, but it may also be composed of a nonmagnetic metal such as stainless steel. The magnetic portion  32  is composed of a metal having magnetism such as an electromagnetic steel sheet or pure iron. 
     In the magnetization ring  3 , a plurality of nonmagnetic portions  31  and a plurality of magnetic portions  32  are alternately arranged in the circumferential direction. The number of nonmagnetic portions  31  and the number of magnetic portions  32  are both the same as the number of poles of the rotor  5 , which is six in this example. 
     The nonmagnetic portion  31  has a width W 1  in the circumferential direction. The width W 1  of the nonmagnetic portion  31  is constant along the axial direction. A width of the magnetic portion  32  in the circumferential direction is preferably wider than the width W 1  of the nonmagnetic portion  31  in the circumferential direction. 
     As illustrated in  FIG. 3 , the magnetization ring  3  is disposed in such a manner that the nonmagnetic portions  31  face the inter-pole portions M of the rotor  5  while the magnetic portions  32  face the pole centers P of the rotor  5 . The width W 1  of the nonmagnetic portion  31  in the circumferential direction is wider than a width W 2  of the slot opening  14  of the stator  1  in the circumferential direction. In other words, W 1 &gt;W 2  is satisfied. 
       FIG. 5  is a flowchart illustrating a magnetization process according to the first embodiment.  FIGS. 6(A) to 6(C)  and  FIGS. 7(A) and 7(B)  are perspective views illustrating steps of the magnetization process.  FIG. 8  is a diagram illustrating an apparatus used in the magnetization process. 
     In the magnetization process, as illustrated in  FIG. 6(A) , first, the magnetization ring  3  is attached to the rotor  5  by inserting the rotor  5  into the inside of the magnetization ring  3  (step S 11 ). Since the magnetization ring  3  is cylindrical and the inner diameter Di of the magnetization ring  3  is larger than the outer diameter Dr of the rotor  5  (Di&gt;Dr), this attachment can be carried out easily. 
     It is also possible to put the magnetization ring  3  on the outer side of the rotor  5  while expanding the magnetization ring  3  in the radial direction utilizing elastic deformation of the nonmagnetic portions  31 . In this case, the inner diameter Di of the magnetization ring  3  may be smaller than or equal to the outer diameter Dr of the rotor  5  (Di≤Dr). 
     Then, as illustrated in  FIG. 6(B) , the magnetization ring  3  is aligned with respect to the rotor  5  in the circumferential direction so that the nonmagnetic portions  31  of the magnetization ring  3  face the inter-pole portions M of the rotor  5  (step S 12 ). 
     Then, as illustrated in  FIG. 6(C) , the rotor  5  to which the magnetization ring  3  is attached is inserted into the inside of the stator  1  (step S 13 ). Since the outer diameter Do of the magnetization ring  3  is smaller than the inner diameter Ds of the stator  1 , this insertion can be carried out easily. Consequently, as illustrated in  FIG. 7(A) , the magnetization ring  3  is disposed between the rotor  5  and the stator  1 . 
     Then, the rotor  5  is aligned with respect to the stator  1  in the circumferential direction (step S 14 ). With this alignment, as illustrated in  FIG. 3 , the slot openings  14  face the inter-pole portions M of the rotor  5 , while three teeth  12  face each magnetic pole, i.e., each permanent magnet  55 . 
     In this state, the magnetization current is applied to the coils  2  (step S 15 ). As illustrated in  FIG. 8 , a power source  40  for magnetization has power source terminals  41 , which are connected to the coils  2  by lead wires  42 . In the power source  40 , an electric charge stored in a capacitor is discharged, and high current (i.e., magnetization current) instantaneously flows through the coils  2  (see  FIG. 14  described later). The magnetization current is higher than a drive current that flows through the coils  2  when the motor  100  is driven. 
       FIG. 9(A)  is a diagram illustrating the magnetization ring  3 , the stator  1 , and the rotor  5  during the magnetization process, and  FIG. 9(B)  is a diagram illustrating the magnetization current applied to the coils  2  during the magnetization process. The coils  2  include a U-phase coil portion  2 U, a V-phase coil portion  2 V, and a W-phase coil portion  2 W. As illustrated in  FIG. 9(A) , two slots  15  face one permanent magnet  55 , and the coil portions  2 V and  2 W are disposed in these two slots  15 . The coil portion  2 U is disposed in the slot  15  facing the inter-pole portion M. 
     As illustrated in  FIG. 9(B) , the coil portions  2 V and  2 W are short-circuited, and the magnetization current “i” is applied to the coil portion  2 U. The magnetization current of “i/2” is applied to each of the coil portions  2 V and  2 W. A flow direction of the magnetization current is a direction so as to generate the magnetic flux directed from outside to inside in the radial direction in the three teeth  12  facing the permanent magnet  55 . 
     The permanent magnet  55  adjacent to the permanent magnet  55  illustrated in  FIG. 3  is magnetized in the opposite direction, and thus the flow direction of the magnetization magnetic flux for the adjacent permanent magnet  55  is opposite to the above described flow direction. 
     The magnetization magnetic flux flows from the tip portions  13  of the teeth  12  to the rotor  5  through the magnetic portions  32  of the magnetization ring  3 . In the rotor  5 , the magnetization magnetic flux flows through the rotor core  50  and further flows in the radial direction through the permanent magnets  55  in the magnet insertion holes  51 . Consequently, the permanent magnets  55  are magnetized in the thickness direction. 
     Since the magnetic portion  32  of the magnetization ring  3  is disposed between the rotor  5  and the stator  1 , the magnetization magnetic flux from the stator  1  can be efficiently guided to the rotor  5  via the magnetic portion  32 , and guided to the permanent magnet  55 . 
     Further, the nonmagnetic portion  31  of the magnetization ring  3  faces the inter-pole portion M of the rotor  5 . With the nonmagnetic portion  31 , the magnetization magnetic flux from the tooth  12  can be inhibited from flowing to its adjacent tooth  12  across the inter-pole portion M. That is, short-circuit of the magnetization magnetic flux can be suppressed. 
     In particular, since the width W 1  of the nonmagnetic portion  31  is wider than the width W 2  of the slot opening  14  (W 1 &gt;W 2 ), the magnetization magnetic flux is less likely to flow between the tip portions  13  of the teeth  12  adjacent to each other across the inter-pole portion M. Thus, the effect of suppressing the short-circuit of the magnetization magnetic flux can be enhanced. 
     After the magnetization of the permanent magnets  55  is performed in this way, the magnetization ring  3  is detached from between the rotor  5  and the stator  1  as illustrated in  FIG. 7(B)  (step S 16 ). Since the magnetization ring  3  is cylindrical, this detachment can be carried out easily. 
     In steps S 11  to S 13  described above, the magnetization ring  3  is attached to the rotor  5 , and then the rotor  5  is inserted into the inside of the stator  1  ( FIGS. 6(A)  to (C)). However, the magnetization process is not limited to such a method. 
       FIGS. 10(A) to 10(C)  are perspective views illustrating steps of another example of the magnetization process according to the first embodiment. In this example, as illustrated in  FIG. 10(A) , the magnetization ring  3  is inserted into the inside of the stator  1 . 
     Then, the position of the magnetization ring  3  is adjusted with respect to the stator  1  in the circumferential direction as illustrated in  FIG. 10  (B). That is, the nonmagnetic portions  31  of the magnetization ring  3  are made to face the slot openings  14 . Then, as illustrated in  FIG. 10(C) , the rotor  5  is inserted into the inside of the stator  1  to which the magnetization ring  3  is attached. 
     Subsequently, the permanent magnets  55  are magnetized by applying the magnetization current to the coils  2  as described with reference to  FIG. 7  (A). Since the magnetization ring  3  is disposed between the rotor  5  and the stator  1 , the magnetization magnetic flux can be efficiently guided to the permanent magnets  55 . Thereafter, the magnetization ring  3  is detached from between the rotor  5  and the stator  1  as described with reference to  FIG. 7(B) . 
     (Functions) 
     Next, the functions of the first embodiment will be described in comparison with Comparative Examples 1 and 2.  FIG. 11  is a schematic diagram illustrating the stator  1  and the rotor  5  in a magnetization process according to Comparative Example 1.  FIG. 12  is a flowchart illustrating the magnetization process of Comparative Example 1.  FIGS. 13(A) and 13(B)  are perspective views illustrating steps of the magnetization process of Comparative Example 1. 
     In the magnetization process of Comparative Example 1, the magnetization ring  3  described in the first embodiment is not used. In this case, the rotor  5  is inserted into the inside of the stator  1  (step S 21 ), and then the rotor  5  is aligned with respect to the stator  1  in the circumferential direction (step S 22 ). Specifically, the inter-pole portions M of the rotor  5  are made to face the slot openings  14  of the stator  1 . Subsequently, the permanent magnets  55  are magnetized by applying the magnetization current to the coils  2  to generate the magnetization magnetic flux. 
     The magnetization magnetic flux generated by the magnetization current flows to the rotor  5  via the air gap between the rotor  5  and the stator  1 . The air in the air gap is nonmagnetic, and thus it is difficult to efficiently guide the magnetization magnetic flux to the permanent magnets  55 . 
     As described above, the magnetization current is higher than the drive current applied to the coils  2  when the motor  100  is driven. When the magnetization current is increased, it may cause wear of the coils  2  due to the Lorentz force. For this reason, it is necessary to limit the magnetization current, which makes it difficult to magnetize the permanent magnets  55  with high magnetic force. 
     In contrast, in the first embodiment, the magnetization ring  3  disposed between the rotor  5  and the stator  1  includes the magnetic portions  32  facing the pole centers P of the rotor  5  and the nonmagnetic portions  31  facing the inter-pole portions M. Thus, the magnetization magnetic flux from the stator  1  can be efficiently guided to the permanent magnets  55  via the magnetic portions  32 . Therefore, the magnetization current required to magnetize the permanent magnets  55  can be lowered, or the permanent magnets  55  with higher magnetic force can be magnetized with the same magnetization current. 
       FIG. 14  is a graph illustrating a comparison between changes with time of the magnetization current applied by the power source  40  to the coils  2  in the first embodiment and Comparative Example 1. The magnetization current in the first embodiment is indicated by a broken line, while the magnetization current in Comparative Example 1 is indicated by a solid line. 
     In the magnetization process, the permanent magnets  55  are magnetized by instantaneously applying the high magnetization current to the coils  2 . From  FIG. 14 , it is understood that the magnetization current required to magnetize the permanent magnets  55  in the first embodiment is lower than that in Comparative Example 1. 
       FIG. 15  is a diagram illustrating a magnetization ring  3 E, the stator  1 , and the rotor  5  according to Comparative Example 2. In  FIG. 15 , the magnetization ring  3 E, which is entirely made of a magnetic body, is disposed between the rotor  5  and the stator  1 . Since the magnetization ring  3 E is disposed between the rotor  5  and the stator  1 , the magnetization magnetic flux is likely to flow to the rotor  5 . 
     However, since the entire magnetization ring  3 E is made of the magnetic body, the magnetization magnetic flux from the tooth  12  flows to its adjacent tooth  12  across the inter-pole portion M through the magnetization ring  3 E (as indicated by an arrow L 1 ). That is, the short-circuit of the magnetization magnetic flux occurs. For this reason, it is difficult to efficiently guide the magnetization magnetic flux to the permanent magnets  55 . 
     In contrast, in the first embodiment, the magnetization ring  3  disposed between the rotor  5  and the stator  1  includes the magnetic portions  32  facing the pole centers P of the rotor  5  and the nonmagnetic portions  31  facing the inter-pole portions M. Thus, the magnetization magnetic flux from the stator  1  can be efficiently guided to the permanent magnets  55  by the magnetic portions  32 . In addition, since the nonmagnetic portions  31  face the inter-pole portions M of the rotor  5 , the short-circuit of the magnetization magnetic flux can be suppressed. As a result, the magnetization current required to magnetize the permanent magnets  55  can be lowered, or the permanent magnets  55  with higher magnetic force can be magnetized with the same magnetization current. 
     Effects of Embodiment 
     As described above, in the first embodiment, the magnetization ring  3  is disposed between the rotor  5  and the stator  1  as the core portion, and the magnetization ring  3  has the magnetic portions  32  facing the pole centers P of the rotor  5  and the nonmagnetic portions  31  facing the inter-pole portions M. Thus, the magnetization magnetic flux from the stator  1  can be efficiently guided to the permanent magnets  55 , and therefore the permanent magnets  55  can be efficiently magnetized. That is, the magnetization current required to magnetize the permanent magnets  55  can be lowered, or the permanent magnets  55  with higher magnetic force can be magnetized with the same magnetization current. Since the nonmagnetic portions  31  and the magnetic portions  32  constitute the magnetization ring  3 , the magnetization ring  3  can be easily handled. That is, it is possible to efficiently magnetize the permanent magnets  55  with a simple operation. 
     Since a plurality of nonmagnetic portions  31  and a plurality of magnetic portions  32  are arranged in the circumferential direction, a plurality of permanent magnets  55  of the rotor  5  can be efficiently magnetized. 
     Since the width W 1  of the nonmagnetic portion  31  is wider than the width W 2  of the slot opening  14  of the slot  15 , the effect of suppressing the short-circuit of the magnetization magnetic flux can be enhanced. 
     Since the gap G between the rotor  5  and the stator  1  and the thickness T of the magnetization ring  3  satisfy G≥T&gt;0, the magnetization ring  3  can be easily disposed in the air gap between the rotor  5  and the stator  1 . 
     The inner diameter Di of the magnetization ring  3  is larger than the outer diameter Dr of the rotor  5 , while the outer diameter Do of the magnetization ring  3  is smaller than the inner diameter Ds of the stator  1 . Thus, the attachment and detachment of the magnetization ring  3  can be facilitated. 
     Second Embodiment 
     Next, a second embodiment will be described.  FIG. 16  is a diagram illustrating a magnetization ring  3 A, the stator  1 , and the rotor  5  according to the second embodiment. As is the case with the magnetization ring  3  of the first embodiment, the magnetization ring  3 A includes nonmagnetic portions  31  facing the inter-pole portions M of the rotor  5  and magnetic portions  32  facing the pole centers P. 
     In the first embodiment described above, the width W 1  of the nonmagnetic portion  31  of the magnetization ring  3  is wider than the width W 2  of the slot opening  14  as illustrated in  FIG. 3 . In contrast, in the second embodiment, the width W 1  of the nonmagnetic portion  31  of the magnetization ring  3 A is wider than a distance WS between two slits  53  adjacent to each other across the inter-pole portion M. That is, W 1 &gt;WS is satisfied. 
     Since the width W 1  of the nonmagnetic portion  31  is wider than the distance WS between the slits  53 , the magnetization magnetic flux directed from the tooth  12  to the inter-pole portion M of the rotor  5  is blocked by the nonmagnetic portion  31  and is less likely to flow to its adjacent tooth  12 . As a result, the short-circuit of the magnetization magnetic flux indicated by the arrow L 1  in  FIG. 15  is suppressed. Thus, the magnetization magnetic flux can be guided to the permanent magnets  55  more efficiently than in the first embodiment. 
     As described above, in the second embodiment, the width W 1  of the nonmagnetic portion  31  of the magnetization ring  3 A is wider than the distance WS between two slits  53  adjacent to each other across the inter-pole portion M. Thus, the magnetization magnetic flux can be guided to the permanent magnets  55  more efficiently, in addition to the effects of the first embodiment. 
     Third Embodiment 
     Next, a third embodiment will be described.  FIG. 17  is a diagram illustrating a magnetization ring  3 B, the stator  1 , and the rotor  5  according to the third embodiment. 
     In the first and second embodiments described above, the permanent magnets  55  are magnetized in a state where the inter-pole portions M of the rotor  5  face the slot openings  14  of the stator  1 . In contrast, in the third embodiment, the permanent magnets  55  are magnetized in a state where the inter-pole portions M of the rotor  5  face the teeth  12  of the stator  1 . Each magnetic pole of the rotor  5 , i.e., each permanent magnet  55 , faces two teeth  12 . 
     The magnetization ring  3 B is disposed between the rotor  5  and the stator  1 . The magnetization ring  3 B includes nonmagnetic portions  31  facing the inter-pole portions M of the rotor  5  and magnetic portions  32  facing the pole centers P. The nonmagnetic portions  31  face the teeth  12 . The width W 1  of the nonmagnetic portion  31  in the circumferential direction is wider than a width WT of the tip portion  13  of the tooth  12 . 
       FIG. 18(A)  is a diagram illustrating the magnetization ring  3 B, the stator  1 , and the rotor  5  during the magnetization process.  FIG. 18(B)  is a diagram illustrating the magnetization current applied to the coils  2  during the magnetization process. The coils  2  wound around the teeth  12  include a U-phase coil portion  2 U, a V-phase coil portion  2 V, and a W-phase coil portion  2 W. 
     As illustrated in  FIG. 18(A) , one permanent magnet  55  faces three slots  15 , and the coil portions  2 V,  2 W, and  2 U are disposed in these three slots  15 . As illustrated in  FIG. 18(B) , no magnetization current is applied to the coil portion  2 W in the slot  15  located at the pole center P, while the magnetization current “i” is applied to each of the coil portions  2 U and  2 V in the slots  15  located on both sides of the pole center P. The flow direction of the magnetization current is a direction so as to generate the magnetic flux directed from outside to inside in the radial direction in the two teeth  12  facing the permanent magnet  55 . 
     The magnetization magnetic flux flows from the tip portions  13  of the teeth  12  to the rotor  5  through the magnetic portions  32  of the magnetization ring  3 B. In the rotor  5 , the magnetization magnetic flux flows through the rotor core  50  and further flows in the radial direction through the permanent magnets  55  in the magnet insertion hole  51 . Consequently, the permanent magnets  55  are magnetized in the thickness direction. 
     Since the magnetic portion  32  of the magnetization ring  3 B is disposed between the rotor  5  and the stator  1 , the magnetization magnetic flux from the stator  1  can be efficiently guided to the rotor  5  via the magnetic portion  32 , and guided to the permanent magnet  55 . 
     Further, the nonmagnetic portion  31  of the magnetization ring  3 B faces the inter-pole portion M of the rotor  5 , and the width W 1  of the nonmagnetic portion  31  is wider than the width WT of the tip portion  13  of the tooth  12  ( FIG. 17 ). With the nonmagnetic portion  31 , the magnetization magnetic flux from the tooth  12  facing the permanent magnet  55  can be inhibited from flowing to the tooth  12  facing the inter-pole portion M. That is, the short-circuit of the magnetization magnetic flux can be suppressed. 
     In order to enhance the effect of suppressing the short-circuit of the magnetization magnetic flux, it is desirable that the end of the nonmagnetic portion  31  in the circumferential direction reaches at least the center of the slot opening  14  in the circumferential direction as illustrated in  FIG. 17 . 
       FIG. 19  is a diagram illustrating a configuration example in which the width W 1  of the nonmagnetic portion  31  of the magnetization ring  3 B is narrower than the width WT of the tip portion  13  of the tooth  12 . If the width W 1  of the nonmagnetic portion  31  is narrower than the width WT of the tip portion  13  of the tooth  12 , the tooth  12  facing the permanent magnet  55  and the tooth  12  facing the inter-pole portion M both face a common magnetic portion  32 . Thus, the magnetization magnetic flux flowing through the tooth  12  facing the permanent magnet  55  may flow to the tip portion  13  of the tooth  12  facing the inter-pole portion M through the magnetic portion  32 . 
     In contrast, as illustrated in  FIG. 17 , when the width W 1  of the nonmagnetic portion  31  is wider than the width WT of the tip portion  13  of the tooth  12 , the nonmagnetic portion  31  inhibits the magnetization magnetic flux from the tooth  12  facing the permanent magnet  55  from flowing to the tip portion  13  of the tooth  12  facing the inter-pole portion M. 
     As described above, in the third embodiment, when the permanent magnets  55  are magnetized in a state where the inter-pole portions M of the rotor  5  face the teeth  12  of the stator  1 , the nonmagnetic portions  31  of the magnetization ring  3 B face the inter-pole portions M of the rotor  5 , and the width W 1  of each nonmagnetic portion  31  is wider than the width WT of the tip portion  13  of the tooth  12 . Therefore, the short-circuit of the magnetization magnetic flux can be suppressed by the nonmagnetic portions  31 . 
     Fourth Embodiment 
     Next, a fourth embodiment will be described.  FIG. 20  is a perspective view illustrating a magnetization ring  3 C according to the fourth embodiment. The magnetization ring  3 C has annular portions  35  and  36  provided on both ends thereof in the axial direction, in addition to the nonmagnetic portions  31  and the magnetic portions  32  described in the first embodiment. 
     Each of the annular portions  35  and  36  has an annular shape and is composed of a nonmagnetic body. The annular portions  35  and  36  are desirably formed continuously with the nonmagnetic portions  31 . The configurations of the nonmagnetic portion  31  and the magnetic portion  32  are as described in the first embodiment. 
     The magnetization ring  3 C has the annular portions  35  and  36 , and thus a user can handle the magnetization ring  3 C by gripping one or both of the annular portions  35  and  36 . Therefore, the magnetizing operation can be carried out easily. 
     In the magnetization process, the nonmagnetic portions  31  and the magnetic portions  32  of the magnetization ring  3 C are disposed between the rotor  5  and the stator  1 . In this state, the annular portions  35  and  36  protrude from the rotor  5  and the stator  1  in the axial direction. Thus, the magnetization ring  3 C can be easily detached. 
     In the example illustrated in  FIG. 20 , the annular portions  35  and  36  are provided on both ends of the magnetization ring  3 C in the axial direction, but the annular portion may be provided on only one end of the magnetization ring  3 C in the axial direction. The magnetization ring  3 C and the magnetization method in the fourth embodiment are the same as those in the first embodiment, except for the points described above. 
     As described above, in the fourth embodiment, the magnetization ring  3 C has the annular portion on at least one end thereof in the axial direction, and thus the handling of the magnetization ring  3 C can be further facilitated. 
     Fifth Embodiment 
     Next, a fifth embodiment will be described.  FIG. 21  is a perspective view illustrating a magnetization ring  3 D according to the fifth embodiment. The magnetization ring  3 D has the magnetic portions  32  disposed similarly to those in the first embodiment, and films  71  and  72  on outer and inner sides of the magnetic portions  32  in the radial direction. The films  71  and  72  are composed of a nonmagnetic resin, for example, polyimide. 
       FIG. 22  is a sectional view illustrating the stator  1 , the rotor  5 , and the magnetization ring  3 D according to the fifth embodiment. Each magnetic portion  32  is formed at a position facing the pole center P of the rotor  5 . The magnetic portion  32  is not provided at a position facing the inter-pole portion M of the rotor  5 , and a hollow portion  38  is formed between adjacent two magnetic portions  32  in the circumferential direction. 
     The hollow portion  38  and the films  71  and  72  on the outer side and inner side of the hollow portion  38  in the radial direction constitute a nonmagnetic portion  70 . That is, the nonmagnetic portion  70  is formed at the position facing the inter-pole portion M of the rotor  5 . 
     The magnetization ring  3 D has annular portions  75  and  76  ( FIG. 21 ) on both ends thereof in the axial direction. Each of the annular portions  75  and  76  is a nonmagnetic body in an annular shape. Each of the annular portions  75  and  76  is obtained by bonding the films  71  and  72  to each other. The films  71  and  72  are bonded to each other at the nonmagnetic portions  70  and at the annular portions  75  and  76  in such a manner that the magnetic portions  32  are sandwiched between the films  71  and  72 . 
     As shown in  FIG. 22 , when the permanent magnets  55  are magnetized in a state where the inter-pole portions M of the rotor  5  face the slot openings  14  of the stator  1 , the nonmagnetic portions  70  of the magnetization ring  3 D face the slot openings  14 . 
     As described in the first embodiment, in order to enhance the effect of suppressing the short-circuit of the magnetization magnetic flux, the width W 1  ( FIG. 3 ) of the nonmagnetic portion  70  in the circumferential direction is desirably wider than the width W 2  ( FIG. 3 ) of the slot opening  14  in the circumferential direction. As described in the second embodiment, it is further desirable that the width W 1  of the nonmagnetic portion  70  in the circumferential direction is wider than the distance WS ( FIG. 16 ) between two slits  53  adjacent to each other across the inter-pole portion M. 
     As described in the third embodiment, when the permanent magnets  55  are magnetized in a state where the inter-pole portions M of the rotor  5  face the teeth  12  of the stator  1 , the nonmagnetic portions  70  face the tip portions  13  of the teeth  12 . In this case, in order to enhance the effect of suppressing the short-circuit of the magnetization magnetic flux, the width W 1  ( FIG. 17 ) of the nonmagnetic portion  70  in the circumferential direction is desirably wider than the width WT of the tip portion  13  of the tooth  12 . It is further desirable that the end of the nonmagnetic portion  70  in the circumferential direction reaches the center of the slot opening  14  in the circumferential direction. 
     In this example, the magnetization ring  3 D includes the films  71  and  72  on the stator  1  side and the rotor  5  side, respectively. However, the magnetization ring  3 D may have only one of the films  71  and  72 . The magnetization ring  3 D and the magnetization method in the fifth embodiment are the same as those in the first embodiment, except for the points described above. 
     As described above, in the fifth embodiment, the magnetization ring  3 D includes the film on at least one side thereof in the radial direction. Thus, wear due to contact between the magnetization ring  3 D and the stator  1  or the rotor  5  can be suppressed, and the life of the magnetization ring  3 D can be extended, in addition to the effects described in the first embodiment. Furthermore, adhesion of foreign matters such as magnetic powder generated by the wear to the rotor  5  can be suppressed, and thus the reliability of the motor  100  can be improved. 
     Since the magnetization ring  3 D includes the annular portions  75  and  76 , the user can handle the magnetization ring  3 D by griping one or both of the annular portions  75  and  76 . Therefore, the magnetizing operation can be carried out easily. 
     In  FIG. 21 , the magnetization ring  3 D has the annular portions  75  and  76  on both ends thereof in the axial direction, but the magnetization ring  3 D may have only one of the annular portions  75  and  76 . Alternatively, the magnetization ring  3 D may be formed to have none of the annular portions  75  and  76 . 
     Sixth Embodiment 
     Next, a sixth embodiment will be described. In the first to fifth embodiments, the permanent magnets  55  are magnetized in a state where the rotor  5  is incorporated in the stator  1  of the motor  100 . In the sixth embodiment, the permanent magnets  55  are magnetized in a state where the rotor  5  is incorporated in a magnetization yoke  80  of a magnetization apparatus  8 . 
       FIG. 23  is a schematic diagram illustrating the magnetization apparatus  8  according to the sixth embodiment. The magnetization apparatus  8  includes the magnetization yoke  80 , a power source  86 , lead wires  87  that connect the magnetization yoke  80  and the power source  86 , a base  88 , and supporting portions  89  that support the magnetization yoke  80  on the base  88 . 
       FIG. 24  is a sectional view illustrating the magnetization yoke  80 . The magnetization yoke  80  is an annular member formed of a magnetic body. The magnetization yoke  80  includes a core back  81  of an annular shape about the axis C 1  and a plurality of teeth  82  protruding from the core back  81  toward the axis C 1 . 
     The number of teeth  82  is the same as the number of poles of the rotor  5 , which is six in this example. A slot  85  is formed between each two of the teeth  82  adjacent to each other in the circumferential direction. A slot opening  84  is formed at an end of the slot  85  on the inner side in the radial direction. 
     The coils  9  are wound around the teeth  82  in the concentrated winding or the distributed winding. The coils  9  are connected to the power source  86  illustrated in  FIG. 23 . 
     The magnetization ring  3  is fixed to the inner circumference of the magnetization yoke  80 . The magnetization ring  3  includes the nonmagnetic portions  31  facing the slot openings  84  and the magnetic portions  32  facing the tip portions  83  of the teeth  82  on the inner side in the radial direction. As described in the first embodiment, the nonmagnetic portions  31  and the magnetic portions  32  are alternately disposed in the circumferential direction. The number of nonmagnetic portions  31  and the number of magnetic portions  32  are both the same as the number of poles of the rotor  5 , which is six in this example. 
     The rotor  5  is disposed on the inner side of the magnetization yoke  80 . In  FIG. 24 , positions of the pole centers P and the inter-pole portions M of the rotor  5  are indicated by dash-dotted lines. When the rotor  5  is disposed on the inner side of the magnetization yoke  80 , the nonmagnetic portions  31  of the magnetization ring  3  face the inter-pole portions M of the rotor  5 , while the magnetic portions  32  face the pole centers P. 
     The width of the nonmagnetic portion  31  in the circumferential direction is the same as the width of the slot opening  84  of the slot  85  in  FIG. 24 , but may be wider than the width of the slot opening  84  as described in the first embodiment. This enhances the effect of suppressing the short-circuit of the magnetization magnetic flux. As described in the second embodiment, the width of the nonmagnetic portion  31  in the circumferential direction may be wider than the distance WS ( FIG. 16 ) between the slits  53  of the rotor  5 . 
     The gap G ( FIG. 2 ) between the rotor  5  and the magnetization yoke  80  and the thickness T ( FIG. 4 ) of the magnetization ring  3  in the radial direction desirably satisfy G≥T&gt;0. Thus, the magnetization ring  3  can be easily disposed in the gap between the rotor  5  and the magnetization yoke  80 . 
     The inner diameter Di of the magnetization ring  3  is desirably larger than the outer diameter Dr ( FIG. 6  (A)) of the rotor  5  (Di&gt;Dr). Thus, the rotor  5  can be easily disposed inside the magnetization ring  3  and can be easily detached from the magnetization ring  3 . 
     In the magnetization apparatus  8 , the magnetization ring  3  is fixed to the inner circumference of the magnetization yoke  80 , and thus it is not necessary to detach the magnetization ring  3  from the magnetization yoke  80 . Thus, the outer diameter Do of the magnetization ring  3  may desirably be larger than or equal to the inner diameter Ds of the magnetization yoke  80  (Do≥Ds). 
     In place of the magnetization ring  3 , the magnetization ring  3 D that has at least one of the films  71  and  72  as described in the fifth embodiment may be used. 
       FIG. 25  is a flowchart illustrating the magnetization process. In the magnetization process, the rotor  5  is mounted in the magnetization apparatus  8  (step S 31 ). Thus, the rotor  5  is inserted into the inside of the magnetization ring  3  fixed to the magnetization yoke  80 . 
     Then, the rotor  5  is aligned with respect to the magnetization yoke  80  in the circumferential direction (step S 32 ). With this alignment, the slot openings  84  face the inter-pole portions M of the rotor  5 , while each tooth  82  faces one magnetic pole, i.e., one permanent magnet  55 . 
     In this state, the magnetization current is applied to the coils  9  by the power source  86 , thereby generating the magnetization magnetic flux (step S 33 ). The current is applied to the coils  9  so as to generate the magnetization magnetic flux flowing through the teeth  82  in the radial direction. The flow directions of the magnetization magnetic fluxes flowing through the adjacent teeth  82  are opposite to each other. 
     The magnetization magnetic flux flows from the tip portions  83  of the teeth  82  to the rotor  5  through the magnetic portions  32  of the magnetization ring  3 . In the rotor  5 , the magnetization magnetic flux flows through the rotor core  50  and further flows in the radial direction through the permanent magnets  55  in the magnet insertion holes  51 . Consequently, the permanent magnets  55  are magnetized in the thickness direction. 
     Since the magnetic portions  32  of the magnetization ring  3  are disposed between the teeth  82  and the rotor  5 , the magnetization magnetic flux from the teeth  82  can be efficiently guided to the permanent magnets  55 . 
     Further, since the nonmagnetic portions  31  of the magnetization ring  3  face the inter-pole portions M of the rotor  5 , the magnetization magnetic flux from the tooth  82  is inhibited from flowing into its adjacent tooth  82  across the inter-pole portion M. That is, the short-circuit of the magnetization magnetic flux can be suppressed. 
     After the magnetization of the permanent magnets  55  is completed, the rotor  5  is detached from the magnetization apparatus  8  (step S 34 ). This completes the magnetization process of the permanent magnets  55 . Thereafter, the rotor  5  is incorporated into the stator  1 , and the motor  100  is completed. 
     As described above, in the sixth embodiment, the magnetization ring  3  is disposed between the magnetization yoke  80  as the core portion and the rotor  5 , and the magnetization ring  3  includes the magnetic portions  32  facing the centers of the permanent magnets  55  of the rotor  5  in the circumferential direction and the nonmagnetic portions  31  facing the inter-pole portions M. Thus, the magnetization magnetic flux from the magnetization yoke  80  can be efficiently guided to the permanent magnets  55 , and thus the permanent magnets  55  can be efficiently magnetized. That is, the current required to magnetize the permanent magnets  55  can be lowered, or the permanent magnets  55  with higher magnetic force can be magnetized with the same current. 
     In particular, since the magnetization ring  3  is fixed to the magnetization yoke  80 , the magnetization ring  3  can be disposed between the rotor  5  and the magnetization yoke  80  by inserting the rotor  5  into the inside of the magnetization ring  3 . 
     The first to sixth embodiments described above can be combined as appropriate. 
     (Compressor) 
     Next, a compressor  300  to which the motor of each embodiment described above is applicable will be described.  FIG. 26  is a sectional view illustrating the compressor  300 . The compressor  300  is a rotary compressor and includes a frame (closed container)  301 , a compression mechanism  310  disposed in the frame  301 , and the motor  100  that drives the compression mechanism  310 . 
     The compression mechanism  310  includes a cylinder  311  having a cylinder chamber  312 , a rolling piston  314  fixed to the shaft  58  of the motor  100 , a vane (not shown) separating the inside of the cylinder chamber  312  into a suction side and a compression side, and an upper frame  316  and a lower frame  317  which close the end surfaces of the cylinder chamber  312  in the axial direction and through which the shaft  58  is inserted. An upper discharge muffler  318  and a lower discharge muffler  319  are mounted onto the upper frame  316  and the lower frame  317 , respectively. 
     The frame  301  is a cylindrical container. At the bottom of the frame  301 , refrigerant oil (not shown) for lubricating sliding portions of the compression mechanism  310  is stored. The shaft  58  is rotatably held by the upper frame  316  and the lower frame  317 . 
     The cylinder  311  has the cylinder chamber  312  therein. The rolling piston  314  eccentrically rotates in the cylinder chamber  312 . The shaft  58  has an eccentric shaft portion  58   a  onto which the rolling piston  314  is fitted. 
     The stator core  10  of the motor  100  is attached to the inside of the frame  301  by shrink-fitting. The coils  2  wound on the stator core  10  are supplied with power from a glass terminal  305  fixed to the frame  301 . The shaft  58  is fixed to the shaft hole  57  ( FIG. 1 ) of the rotor  5 . 
     An accumulator  302  that stores a refrigerant gas is attached to the outer side of the frame  301 . A suction pipe  303  is fixed to the frame  301 , and the refrigerant gas is supplied from the accumulator  302  to the cylinder  311  via the suction pipe  303 . A discharge pipe  307  through which the refrigerant is discharged to the outside is provided in an upper portion of the frame  301 . 
     The operation of the compressor  300  is as follows. The refrigerant gas supplied from the accumulator  302  is supplied through the suction pipe  303  into the cylinder chamber  312  of the cylinder  311 . When the motor  100  is driven and the rotor  5  rotates, the shaft  58  rotates with the rotor  5 . Then, the rolling piston  314  fitted to the shaft  58  eccentrically rotates inside the cylinder chamber  312 , thereby compressing the refrigerant in the cylinder chamber  312 . The compressed refrigerant passes through the discharge mufflers  318  and  319 , flows upward inside the frame  301  through holes (not shown) provided in the motor  100 , and is discharged through the discharge pipe  307 . 
     The compressor  300  is supplied with a mixture of a low-pressure refrigerant gas and a liquid refrigerant from a refrigerant circuit of the air conditioner  400  ( FIG. 27 ). If the liquid refrigerant flows into and is compressed in the compression mechanism  310 , it may cause the failure of the compression mechanism  310 . Thus, the accumulator  302  separates the refrigerant into the liquid refrigerant and the refrigerant gas and supplies only the refrigerant gas to the compression mechanism  310 . 
     The motor  100  described in each of the above-described embodiments is applicable to a drive source of the compressor  300 . Thus, the manufacturing cost of the compressor  300  can be reduced, or the output of the compressor  300  can be improved. 
     (Air Conditioner) 
     Next, the air conditioner  400  including the compressor  300  illustrated in  FIG. 26  will be described.  FIG. 27  is a diagram illustrating the air conditioner  400 . The air conditioner  400  illustrated in  FIG. 27  includes the compressor  300 , a four-way valve  401  as a switching valve, a condenser  402  to condense a refrigerant, a decompression device  403  to decompress the refrigerant, an evaporator  404  to evaporate the refrigerant, and a refrigerant pipe  410  connecting these components. 
     The compressor  300 , the four-way valve  401 , the condenser  402 , the decompression device  403 , and the evaporator  404  are connected together by the refrigerant pipe  410  to constitute a refrigerant circuit. The compressor  300  includes an outdoor fan  405  facing the condenser  402  and an indoor fan  406  facing the evaporator  404 . 
     The operation of the air conditioner  400  is as follows. The compressor  300  compresses the sucked refrigerant and sends out the compressed refrigerant as a high-temperature and high-pressure refrigerant gas. The four-way valve  401  switches the flow direction of the refrigerant. During a cooling operation, the four-way valve  401  delivers the refrigerant sent out from the compressor  300 , to the condenser  402  as illustrated in  FIG. 27 . 
     The condenser  402  exchanges heat between the refrigerant sent out from the compressor  300  and the outdoor air fed by the outdoor fan  405  to condense the refrigerant and then sends out the refrigerant as a liquid refrigerant. The decompression device  403  expands the liquid refrigerant sent out from the condenser  402  and then sends out the expanded refrigerant as a low-temperature and low-pressure liquid refrigerant. 
     The evaporator  404  exchanges heat between the indoor air and the low-temperature and low-pressure liquid refrigerant sent out from the decompression device  403  to evaporate (vaporize) the refrigerant and then sends out the refrigerant as the refrigerant gas. Thus, air from which the heat is removed in the evaporator  404  is supplied by the indoor fan  406  to the interior of a room, which is a space to be air-conditioned. 
     During a heating operation, the four-way valve  401  delivers the refrigerant sent out from the compressor  300 , to the evaporator  404 . In this case, the evaporator  404  functions as a condenser, while the condenser  402  functions as an evaporator. 
     The motor  100  described in each embodiment is applicable to the compressor  300  in the air conditioner  400 . Thus, the manufacturing cost of the air conditioner  400  can be reduced, or the output of the air conditioner  400  can be improved. 
     Although the desirable embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications and changes can be made to those embodiments without departing from the scope of the present invention.