Abstract:
Disclosed herein is a washing machine having an improved structure that maintains efficiency over a certain level both in washing and dehydration. The washing machine includes a body, a tub disposed within the body, a drum rotatably disposed within the tub, and a motor coupled to a rear surface of the tub to drive the drum. The motor includes a stator including a plurality of stator cores and a plurality of magnets arranged between the stator cores, and a rotor rotatably disposed at an inner side or outer side of the stator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2012-0023475, filed on Mar. 7, 2012 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Embodiments of the present disclosure relate to a motor to generate rotational force and a washing machine having the same. 
     2. Description of the Related Art 
     A washing machine, which washes clothes using electricity, is provided with a tub to reserve wash water, a drum rotatably installed within the tub, and a motor to rotate the drum. 
     Operation of a washing machine is divided into washing, during which dirt on the laundry is removed, and dehydration, during which the cleaned laundry is dehydrated. The drum rotates at low speed in washing operation with water contained therein, and rotates at high speed with water not contained therein when performing dehydration. 
     The motor mounted to the washing machine should meet these two speed conditions for operation of the washing machine. That is, the motor needs to rotate the drum with high torque for washing operation and to rotate drum at high speed in dehydration operation. 
     However, with a brushless direct current (BLDC) motor mounted to a conventional washing machine, it may be difficult to meet these two rotation conditions for operation of the washing machine. 
     SUMMARY 
     Therefore, it is an aspect of the present disclosure to provide a motor which has an improved structure ensuring that the motor operates with efficiency over a certain level in both washing and dehydration operations of a washing machine and a washing machine having the same. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned from practice of the invention. 
     In accordance with one aspect, a washing machine includes a body, a tub disposed within the body, a drum rotatably disposed within the tub, and a motor coupled to a rear surface of the tub to drive the drum, wherein the motor includes a stator including a plurality of stator cores and a plurality of magnets arranged between the stator cores, and a rotor rotatably disposed at an inner side or outer side of the stator. 
     Each of the stator cores may include a core body shaped in a circular arc, and a plurality of supports adapted to extend from the core body in a radial direction of the core body to support the magnets disposed on both sides of the core body. 
     The stator may include a first coil wound around the neighboring ones of the supports of a first one and a second one of the stator cores neighboring each other. 
     The stator may include a second coil wound around one of the magnets disposed between the neighboring ones of the supports. 
     The first coil may be positioned at an outer side of the second coil. 
     The magnets may have a shorter length than the stator cores in an axial direction of the stator. 
     The stator may include an insulator to cover the stator cores and the magnets to electrically insulate the stator cores and the magnets from the first coil and the second coil. 
     The rotor may include a rotor body formed in a circular shape, and a plurality of rotor cores adapted to extend from the rotor body in a radial direction of the rotor body, and arranged in a circumferential direction of the rotor body. 
     In accordance with one aspect, a motor includes a stator including a plurality of stator cores radially arranged separated from each other and a plurality of magnets inserted between the stator cores to form magnetic flux, and a rotor to electrically interact with the stator to rotate, the rotor including a rotor body and a plurality of rotor cores arranged in a circumferential direction of the rotor body. 
     Two neighboring ones of the stator cores may define a magnet accommodating portion therebetween to accommodate at least one of the magnets inserted thereinto. 
     Each of the stator cores may include a plurality of supports arranged parallel with the magnets to support the magnets, and a connector to connect the supports to each other. 
     The stator may include a first coil wound around neighboring ones of the supports of two different ones of the stator cores having at least one magnet of the magnets disposed therebetween to form magnetic flux in a first direction. 
     The stator may include a second coil wound around the at least one magnet to form magnetic flux in a direction different from the first direction. 
     The magnetic flux formed through the second coil according to electric current applied to the second coil may be superimposed on the magnetic flux formed by the magnet, or cancel out the magnetic flux formed by the magnet. 
     The first coil may be wound outside the second coil. 
     The at least one magnet may have a shorter length than the stator cores in an axial direction of the stator. 
     The stator may include a molding portion to connect the stator cores separated from each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a view illustrating a washing machine in accordance with an exemplary embodiment; 
         FIG. 2  is a view illustrating a stator and rotor of a motor in accordance with the exemplary embodiment; 
         FIG. 3  is an exploded perspective view illustrating the stator of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view taken along the line I-I of  FIG. 2 ; 
         FIG. 5  is a view illustrating magnetic flux flow between the stator and rotor of  FIG. 2 ; 
         FIG. 6  is a graph illustrating the characteristics of the motor in accordance with the exemplary embodiment; 
         FIG. 7  is a view illustrating a stator and rotor of a motor in accordance with one embodiment; 
         FIG. 8  is an exploded perspective view illustrating the stator of  FIG. 7 ; 
         FIG. 9  is a cross-sectional view taken along the line II-II of  FIG. 7 ; and 
         FIG. 10  is a view illustrating magnetic flux flow through the stator and rotor of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. Hereinafter, a description will be given of a washing machine with a motor, which is applicable to all kinds of apparatuses including an air conditioner, an electric vehicle, a light rail system, an electric bicycle and a small generator that employ a motor as a power source. 
       FIG. 1  is a view illustrating a washing machine in accordance with an exemplary embodiment. 
     As shown in  FIG. 1 , the washing machine  1  includes a cabinet  10  forming the outward appearance of the washing machine  1 , a tub  20  disposed within the cabinet  10 , a drum  30  rotatably disposed within the tub  20 , and a motor  40  to rotate the drum  30 . 
     The front portion of the cabinet  10  is provided with an inlet  11  through which laundry may be inserted into the drum  30 . The inlet  11  is opened and closed by a door  12  installed at the front of the cabinet  10 . 
     A water supply pipe  50  to supply wash water to the tub  20  is installed at the upper portion of the tub  20 . One end of the water supply pipe  50  is connected to an external water supply source (not shown), and the other end of the water supply pipe  50  is connected to a detergent supply unit  60 . The detergent supply unit  60  is connected to the tub  20  through a connection pipe  55 . Water flowing into the water supply pipe  50  is supplied to the tub  20  along with a detergent via the detergent supply unit  60 . 
     Installed at the bottom of the tub  20  are a drain pump  70  and drain pipe  75  to discharge the water in the tub  20  from the cabinet  10 . 
     A plurality of through holes  31  is formed around the drum  30  to allow flow of wash water therethrough, and a plurality of lifters  32  is installed on the inner circumferential surface of the drum  30  to allow the laundry to tumble during rotation of the drum  30 . 
     The drum  30  and motor  40  are connected to each other through a drive shaft  80 . The drive shaft  80  transmits the rotational force of the motor  40  to the drum  30 . One end of the drive shaft  80  is connected to the drum  30 , and the other end of the drive shaft  80  extends outside a rear wall of the tub  20 . 
     Installed at the rear wall  21  of the tub  20  is a bearing housing  82  by which the drive shaft  80  is rotatably supported. The bearing housing  82  may be formed of an aluminum alloy, and may be inserted the rear wall  21  of the tub  20  when the tub  20  is manufactured through injection molding. Bearings  84  are installed between a bearing housing  82  and the drive shaft  80  to ensure smooth rotation of the drive shaft  80 . 
     Hereinafter, a detailed description will be given of the structure and principles of the motor  40  mounted at the rear wall  21  of the tub  21  of the washing machine  1 . 
       FIG. 2  is a view illustrating a stator and rotor of a motor in accordance with an exemplary embodiment,  FIG. 3  is an exploded perspective view illustrating the stator of  FIG. 2 ,  FIG. 4  is a cross-sectional view taken along the line I-I of  FIG. 2 , illustrating the magnetic flux flow among the coil, stator core and magnets,  FIG. 5  is a view illustrating the magnetic flux flow between the stator and rotor of  FIG. 2 , and  FIG. 6  is a graph illustrating the characteristics of the motor in accordance with the exemplary embodiment of the present invention. The coil is not shown in  FIG. 3 . The motor according to embodiments may be an inner rotor-type motor which has a rotor disposed inside the stator, or an outer rotor-type motor which has a rotor disposed outside the stator. For convenience of description, the motor will hereinafter be assumed to be of the outer rotor type. 
     As shown in  FIGS. 1 to 5 , the motor  40  according to the illustrated embodiment is coupled to the outside of the tub  20  to drive the drum  30  to rotate in both directions. The motor  40  includes a stator  100  mounted at the rear wall  20  of the tub  20 , and a rotor  200  disposed around the stator  100  to electrically interact with the stator  100  to rotate. 
     The stator  100  includes a plurality of stator cores  110  radially arranged separated from each other and formed of a metal, a plurality of magnets  120  coupled between the stator cores  110 , a coil  130  wound around the stator cores  110  and magnets  120 , and an insulator  140  to cover the stator cores  110  and magnets  120 . 
     Each of the stator cores  110  includes a core body  112  shaped in a circular arc, and a plurality of supports  114  extending from the core body  112  in a direction in which the radius of the core body  112  increases. The core body  112  and the plurality of supports  114  of the stator cores  110  forms, for example, a V-shape configuration. The supports  114  are connected to both sides of the core body  112  to support the magnets  120  positioned on both sides of the stator core  110 , in the circumferential direction of the stator core  110 . The distance between the supports  114  widens along the direction in which the supports  114  extends. The core body  112  may be seen as a connector since it connects the supports  114  arranged on both sides thereof. 
     The stator cores  110  are arranged equally spaced apart in the circumferential direction of the stator  100  to define a magnet accommodating portion  116  therebetween to accommodate at least one magnet  120 . 
     Since the stator cores  110  are completely separated from each other, leakage of magnetic flux of the magnet  120  by flowing into the neighboring stator cores  110  may be prevented. 
     As the stator core  110  forms a path of magnetic flux through which a magnetic field is formed, it may be fabricated by processing and stacking metallic plates through press working. 
     The magnets  120 , which are disposed between the stator cores  110 , are arranged in the circumferential direction of the stator  100  to be radially positioned around the stator  100 . The magnet  120  may contain a rare-earth element such as ferrite, neodymium and samarium which may semi-permanently maintain the magnetic property of high energy density. 
     The magnetic fluxes created by the magnets  120  are arranged in the circumferential direction of the stator  100 , and the neighboring magnets  120  are disposed such that the portions thereof facing each other have the same polarity. If a magnetic circuit is formed in this way, the concentration of magnetic fluxes generated by the magnets  120  may be enhanced, and thus it may be possible to reduce the size of the motor  40  while improving the performance thereof. 
     The insulator  140  includes an upper insulator  142  and lower insulator  144  to vertically cover the stator cores  110  and magnets  120 . The upper insulator  142  and lower insulator  144  are vertically coupled to each other to support and combine the stator cores  110  and magnets  120  and to electrically insulate the stator cores  110  and magnets  120  from the coil  130 . Also, the upper insulator  142  and lower insulator  144  include a plurality of fixing holes  142   a  and a plurality of fixing holes  144   a  respectively to fix the stator  100  to the rear wall  21  of the tub  20 . The upper insulator  142  and lower insulator  144  may be fabricated through injection molding of plastics having the property of electrical insulation, and the fixing holes  142   a  and  144   a  may be integrally formed respectively in the upper insulator  142  and lower insulator  144  during injection molding process. Although not shown, instead of providing the upper insulator  142  and lower insulator  144  separately for the insulator  140 , the insulator  140  may be integrated with the stator cores  110  and magnets  120  by inserting the stator cores  110  and magnets  120  into a mold used to fabricate the insulator  140  in injection molding. 
     The coil  130  is wound around neighboring supports  114   a  and  114   b  of a first stator core  110   a  and second stator core  110   b  neighboring each other among other stator cores  110 . When electric current is supplied to the coil  130 , a magnetic field is formed in the radial direction of the stator  100  in accordance with the principle of electromagnetic induction. 
     The coil  130  may be wound to form 3-phase windings. If 3-phase alternating current (AC) power is applied to the coil  130 , a 3-phase rotating magnetic field is created at the stator  100 . By the 3-phase rotating magnetic field formed at the stator  100 , the rotor  200  is rotated around the stator  100 . 
     The rotor  200  includes a rotor body  210  formed in a circular shape, a plurality of rotor cores  220  extending inward from the rotor body  210  in a radial direction of the rotor body  210  and arranged spaced apart from each other in the circumferential direction of the rotor body  210 , a rotor frame  230  to combine the rotor  200  with the drive shaft  80 . As the rotor body  210  and rotor cores  220  define, along with the stator  100 , a path of magnetic flux allowing a magnetic field formed at the stator  100  to pass therethrough, they may be formed by processing and stacking metallic plates through press working. 
     Hereinafter, a description will be given of how the rotor  200  is rotated by electromagnetic interaction between the stator  100  and rotor  200  of the motor according to the illustrated embodiment of the present invention. 
     As shown in  FIGS. 4 and 5 , the magnets  120  disposed between the stator cores  110  have alternately arranged polarities such that the portions of the magnets  120  facing each other have the same polarity, thereby allowing concentrated magnetic flux to be created in the circumferential direction of the stator  100 . 
     The magnetic flux created by a first magnet  120   a  disposed between the first stator core  110   a  and the second stator core  110   b  forms a closed loop path (I) along a support  114   b  of the second stator core  110   b  adjoining the first magnet  120   a , a second rotor core  220   b , a rotor body  210 , a first rotor core  220   a , and a support  114   a  of the first stator core  110   a  adjoining the first magnet  120   a , while the magnetic flux created by a second magnet  120   b  disposed between the second stator core  110   b  and the third stator core  110   c  forms a closed loop path (II) along a support  114   b  of the second stator core  110   b  adjoining the second magnet  120   b , a third rotor core  220   c , a rotor body  210 , a fourth rotor core  220   d , and a support  114   c  of the third stator core  110   c  adjoining the second magnet  120   b . Other magnets  120  arranged alternately with the first magnet  120   a  or the second magnet  120   b  also form the same closed loop path of magnetic flux as those of the first magnet  120   a  and second magnet  120   b.    
     When AC power is applied to the coil  130  wound around the stator  100 , magnetic fluxes A 1  and A 2  are formed around the coil  130  in a radial direction. The magnetic fluxes formed around the coil  130  are superimposed on the magnetic fluxes formed by the magnets  120  to increase the magnetic flux density or to cancel the magnetic fluxes formed by the magnets  120  to decrease the magnetic flux density. As shown in  FIG. 5 , the magnetic flux A 1  formed around the coil  130  decreases the density of magnetic flux formed in and around the support  114   a  of the first stator core  110   a , and increases the density of magnetic flux formed in and around the support  114   b  of the second stator core  110   b . Likewise, the magnetic flux A 2  formed around the coil  130  decreases the density of magnetic flux formed in and around the support  114   c  of the third stator core  110   c , and increases the density of magnetic flux formed in and around the support  114   b  of the second stator core  110   b.    
     The directions and densities of magnetic fluxes formed, around the stator cores  110  including the first stator core  110   a , second stator core  110   b  and third stator core  110   c , by the magnets  120  may be controlled by adjusting the AC power applied to the coil  130 , and the speed and direction of rotation of the rotor  200  controlled by adjusting the densities of the magnetic fluxes around the stator cores  110 . 
     As such, by using both the magnetic flux created by the magnet  120  inserted between the stator cores  110  and the magnetic flux created by the coil  130  wound around the magnet  120 , the density of magnetic flux formed around the stator  100  may be adjusted in a wide range. That is, as shown in  FIG. 6 , toque may be increased in a region of operation of the washing machine  1  such as washing which requires high torque by adjusting the AC power applied to the coil  130  to allow the magnetic flux created by the magnet  120  to be superimposed on the magnetic flux created by the coil  130 , and the rotational speed of the rotor  200  may be increased in a region of operation of the washing machine  1  such as dehydration which requires high rotational speed by adjusting the AC power applied to the coil  130  to allow the magnetic flux created by the magnet  120  and the magnetic flux created by the coil  130  to cancel each other out. 
     Hereinafter, a motor  40   a  according to one embodiment will be described in detail. For convenience of description, description of the parts of the motor  40   a  identical to those of the motor  40  is omitted. 
       FIG. 7  is a view illustrating a stator and rotor of a motor in accordance with one embodiment,  FIG. 8  is an exploded perspective view illustrating the stator of  FIG. 7 ,  FIG. 9  is a cross-sectional view taken along the line II-II of  FIG. 7 , illustrating magnetic flux flow through a coil, stator core, and magnet, and  FIG. 10  is a view illustrating magnetic flux flow through the stator and rotor of  FIG. 7 . The coil is omitted from  FIG. 8 . 
     As shown in  FIGS. 7 to 10 , the motor  40   a  according to the illustrated embodiment of the preset invention includes a stator  300  mounted at the rear wall  21  of the tub  20 , and a rotor  400  disposed around the stator  300  to electrically interact with the stator  300  to rotate. 
     The stator  300  includes a plurality of stator cores  310  radially arranged spaced apart from each other and formed of a metal, a plurality of magnets  320  coupled between the stator cores  310 , a first coil  330  and a second coil  340  wound around the stator cores  310  and magnets  320 , and an insulator  350  to cover the stator cores  310  and magnets  320 . 
     Each of the stator cores  310  includes a core body  312  shaped in a circular arc, and a plurality of supports  314  extending from the core body  312  in a direction in which the radius of the core body  312  increases. The supports  314  are connected to both sides of the core body  312  to support, in the circumferential direction of the stator core  310 , the magnets  320  positioned at both sides of the stator core  310 . The distance between the supports  314  widens along the direction in which the supports  314  extends. The core body  312  and the plurality of supports  314  of the stator cores  310  forms, for example, a V-shape configuration. The core body  312  may be seen as a connector since it connects the supports  314  arranged on both sides thereof. 
     The stator cores  310  are arranged equally spaced apart in the circumferential direction of the stator  300  to define a magnet accommodating portion  116  therebetween to accommodate at least one magnet  320 . 
     Since the stator cores  310  are completely separated from each other, leakage of magnetic flux of the magnet  320  through flow into the neighboring stator cores  310  may be prevented. 
     As the stator core  310  forms a path of magnetic flux through which a magnetic field is formed, it may be fabricated by processing metallic plates in press working and stacking the same. 
     The magnets  320 , which are disposed between the stator cores  310 , are arranged in the circumferential direction of the stator  300  to be radially positioned around the stator  300 . To form windings of the second coil  340 , the magnets  320  may be adapted to have a shorter length than the stator cores  310  in the axial direction of the stator  300 . As shown in  FIG. 8 , the magnet  320  may be formed in a rectangular shape. Although not shown in  FIG. 8 , each corner of the magnet  320  may be rounded, or the magnet  320  may be formed in various shapes such as circular and polygonal shapes. The magnet  320  may contain a rare-earth element such as ferrite, neodymium and samarium which may semi-permanently maintain the magnetic property of high energy density. 
     The magnetic fluxes created by the magnets  320  are arranged in the circumferential direction of the stator  300 , and the neighboring magnets  320  are disposed such that the portions thereof facing each other have the same polarity. If a magnetic circuit is formed in this way, the concentration of magnetic flux generated by the magnets  320  may be enhanced, and thus it may be possible to reduce the size of the motor  40   a  while improving the performance thereof. 
     The insulator  350  includes an upper insulator  352  and lower insulator  354  to vertically cover the stator cores  310  and magnets  320 . The upper insulator  352  and lower insulator  354  are vertically coupled to each other to support and combine the stator cores  310  and magnets  320  and to electrically insulate the stator cores  310  and magnets  320  from the first coil  330  and second coil  340 . Also, the upper insulator  352  and lower insulator  354  include a plurality of fixing holes  352   a  and a plurality of fixing holes  354   a  to fix the stator  300  to the rear wall  21  of the tub  20 . The upper insulator  352  and lower insulator  354  may be fabricated through injection molding of plastics having the property of electrical insulation, and the fixing holes  352   a  and  354   a  may be integrally formed respectively in the upper insulator  352  and lower insulator  354  during injection molding of the upper insulator  352  and lower insulator  354 . Although not shown, instead of providing the upper insulator  352  and lower insulator  354  separately for the insulator  350 , the insulator  350  may be integrated with the stator cores  310  and magnets  320  by inserting the stator cores  310  and magnets  320  into a mold used to injection mold the insulator  350 . 
     The insulator  350  includes a first coil wound portion  350   a  wound by the first coil  330 , and a second coil wound portion  350   b  wound by the second coil  340 . The first coil wound portion  350   a  and second coil wound portion  350   b  are connected to each other, and are arranged in a stepped manner such that when the first coil  330  and the second coil  340  do not interfere with each other when windings thereof are formed around the first coil wound portion  350   a  and second coil wound portion  350   b.    
     The first coil  330  is wound around neighboring supports  314   a  and  314   b  of a first stator core  310   a  and second stator core  310   b  neighboring each other among other stator cores  310 . When electric current is supplied to the first coil  330 , a magnetic field is formed in the radial direction of the stator  300  in accordance with the principle of electromagnetic induction. 
     The first coil  330  may be wound to form 3-phase windings. If 3-phase AC power is applied to the first coil  330 , a 3-phase rotating magnetic field is created at the stator  300 . By the 3-phase rotating magnetic field formed at the stator  300 , the rotor  400  is rotated about the stator  300 . 
     The second coil  340  is wound, in a different direction than the first coil  330 , around the magnet  320  disposed between the first stator core  310   a  and the second stator core  310   b  neighboring each other among other stator cores  310 . When electric current is supplied to the coil  340 , a magnetic field is formed in the circumferential direction of the stator  300  in accordance with the principle of electromagnetic induction. 
     The rotor  400  includes a rotor body  410  formed in a circular shape, a plurality of rotor cores  420  extending inward from the rotor body  210  in a radial direction of the rotor body  410  and arranged spaced apart from each other in the circumferential direction of the rotor body  410 , and a rotor frame  430  to combine the rotor  400  with the drive shaft  80 . As the rotor body  410  and rotor cores  420  define, along with the stator  300 , a path of magnetic flux allowing a magnetic field formed at the stator  300  to pass therethrough, they may be formed by processing stacking metal plates through press working. 
     Hereinafter, a description will be given of how the rotor  400  is rotated by electromagnetic interaction between the stator  300  and rotor  400  of the motor according to the illustrated embodiment of the present invention. 
     As shown in  FIGS. 9 and 10 , the magnets  320  arranged between the stator cores  310  have alternately arranged polarities such that the portions of the magnets  320  facing each other have the same polarity, thereby allowing concentrated magnetic flux to be created in the circumferential direction of the stator  300 . 
     The magnetic flux created by a first magnet  320   a  disposed between the first stator core  310   a  and the second stator core  310   b  forms a closed loop path (III) along a support  314   b  of the second stator core  310   b  adjoining the first magnet  320   a , a second rotor core  420   b , a rotor body  410 , a first rotor core  420   a , and a support  314   a  of the first stator core  310   a  adjoining the first magnet  320   a , while the magnetic flux created by a second magnet  320   b  disposed between the second stator core  310   b  and the third stator core  310   c  forms a closed loop path (IV) along a support  314   b  of the second stator core  310   b  adjoining the second magnet  320   b , a third rotor core  420   c , a rotor body  410 , a fourth rotor core  420   d , and a support  314   c  of the third stator core  310   c  adjoining the second magnet  320   b . Other magnets  320  arranged alternately with the first magnet  320   a  or the second magnet  320   b  also form the same closed loop path of magnetic flux as those of the first magnet  320   a  and second magnet  320   b.    
     When AC power is applied to the first coil  330 , magnetic fluxes B 1  and B 2  are formed around the first coil  330  in a radial direction. The magnetic fluxes B 1  and B 2  formed around the first coil  330  are superimposed on magnetic fluxes formed by the magnets  320  to increase the magnetic flux density or to cancel the magnetic fluxes formed by the magnets  320  to decrease the magnetic flux density. As shown in  FIG. 10 , the magnetic flux B 1  formed around the first coil  330  decreases the density of magnetic flux formed in and around the support  314   a  of the first stator core  310   a , and increases the density of magnetic flux formed in and around the support  314   b  of the second stator core  310   b . Likewise, the magnetic flux B 2  formed around the first coil  330  decreases the density of magnetic flux formed in and around the support  314   c  of the third stator core  310   c , and increases the density of magnetic flux formed in and around the support  314   b  of the second stator core  310   b.    
     When AC power is applied to the second coil  340 , magnetic fluxes B 3  and B 4  are formed around the second coil  340  in a circumferential direction. The magnetic fluxes B 3  and B 4  formed by the second coil  340  in a circumferential direction are substantially in the same direction as or the opposite direction to that of the magnetic fluxes formed by the first magnet  320   a  or second magnet  320   b . As shown in  FIG. 10 , the magnetic flux B 3  formed by the second coil  340  is superimposed on the magnetic flux formed by the first magnet  320   a , and the magnetic flux B 4  formed by the second coil  340  cancels out the magnetic flux formed by the second magnet  320   b . As such, the second coil  340  substantially increases or decreases the densities of the magnetic fluxes formed by the magnets  320 . 
     The directions and densities of magnetic fluxes formed by the magnets  320  around the stator cores  310  including the first stator core  310   a , second stator core  310   b  and third stator core  310   c  may be controlled by adjusting AC power applied to the first coil  330  and second coil  340 , and the speed and direction of rotation of the rotor  400  may be controlled by adjusting the densities of the magnetic fluxes around the stator cores  310 . Wherein the AC power is applied independently to the first coil  330  and the second coil  340  allowing for greater control of the direction and densities of the magnetic fluxes. 
     By using both the magnetic flux created by the magnet  320  inserted between the stator cores  110  and the magnetic fluxes created by the first coil  330  and second coil  340  wound around the stator cores  310  and the magnet  320 , the density of magnetic flux formed around the stator  300  may be adjusted in a wide range as in the motor  40  according to the previous embodiment. 
     As is apparent from the above description, magnets are included in a stator and the intensity of magnetic flux formed by the magnets included in the stator is varied, and thereby requirements for washing and dehydration operations of a washing machine may be efficiently met. 
     Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.