Patent Publication Number: US-2021167646-A1

Title: Motor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2019-0155669 filed on Nov. 28, 2019, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field 
     The disclosure relates to an outer rotor motor with a rotor arranged outside a stator. 
     2. Description of the Related Art 
     In general, motors are a device for converting electrical energy to mechanical energy. 
     The motors may be classified by position of the rotor against the stator into outer rotor motors with the rotor placed outside the stator and inner rotor motors with the rotor inside the stator. 
     The outer rotor motor has a merit of outputting high power as compared to the inner rotor motor having similar dimensions. That is why the outer rotor motor is used in various products required to have a smaller motor. 
     These days, there are attempts to further reduce the size of the products including motors. Hence, outer rotor motors that are smaller than the conventional outer rotor motor are required. 
     SUMMARY 
     The disclosure provides a motor in a reduced size. 
     The disclosure also provides a motor having reduced sizes in axial and radial directions. 
     The disclosure also provides a motor having a reduced size in an axial direction by enhancing a wire winding method and a wire supporting structure. 
     The disclosure also provides a motor having a reduced size in a radial direction by exposing a portion of a back yoke to the outside of the motor. 
     According to an aspect of the disclosure, a motor includes a stator, and a rotor arranged outside the stator and rotated by electromagnetically interacting with the stator, wherein the rotor includes a ring-shaped back yoke, a plurality of magnets separately arranged inside of the back yoke along a circumferential direction of the back yoke, and a frame arranged to combine the back yoke and the plurality of magnets, and having an open side through which an outer surface of the back yoke is exposed to an outside of the frame. 
     The back yoke may include a plurality of projections extending from an inner surface of the back yoke toward a center of the back yoke and arranged separately along the circumferential direction of the back yoke. 
     Each of the plurality of projections may be arranged between the magnets neighboring each other to prevent the magnets from being closer or farther in distance. 
     Given that length of the back yoke in a radial direction is thickness, thickness of each of the plurality of projections may be smaller than thickness of each of the plurality of magnets. 
     Given that the thickness of each of the plurality of thickness is t 1  and the thickness of each of the plurality of magnets is t 2 , the thicknesses may meet the following equation: 
         t 2/5&lt; t 1&lt; t 2/2. 
     The rotor may further include a shaft supporting member, to which a shaft corresponding to a rotation axis is inserted and coupled. 
     The frame may be provided to combine the back yoke, the plurality of magnets, and the shaft supporting member. 
     The rotor may be integrally formed by injection molding the frame between the back yoke, the plurality of magnets, and the shaft supporting member. 
     The rotor and the back yoke may have the same outside diameter. 
     The back yoke may further include a first sticking projection protruding from a top surface or bottom surface of the back yoke in an axial direction. 
     The frame may further include a second sticking projection protruding in an opposite direction to the first sticking projection from a top surface or bottom surface of the frame to match the first sticking projection. 
     The first sticking projection and the second sticking projection may be arranged to be interlocked with each other to prevent the back yoke from being rotated relatively to the frame. 
     The stator may include a stator core, an insulator arranged to cover the stator core, and a plurality of wires wound on the insulator and connected respectively to terminals of phases U, V, and W. 
     Some of the plurality of wires may be wound from one side of the insulator along an arc-shaped wall formed in a center of the insulator. 
     Some of the rest of the plurality of wires may be wound from the other side of the insulator along the arc-shaped wall formed in the center of the insulator. 
     The plurality of wires may include a first wire connecting a coil of U 1  phase terminal to a coil of U 2  phase terminal, a second wire connecting a coil of V 1  phase terminal to a coil of V 2  phase terminal, and a third wire connecting a coil of W 1  phase terminal to a coil of W 2  phase terminal. 
     The first wire may be wound from one side of the insulator along the arc-shaped wall in a first direction. 
     The second wire may be wound from the one side of the insulator along the arc-shaped wall in a second direction opposite the first direction. 
     The third wire may be wound from the other side of the insulator along the arc-shaped wall in the first direction or the second direction. 
     The first wire may be arranged separately from the second wire in the axial direction to avoid contacting the second wire when the first wire is wound from the one side of the insulator along the arc-shaped wall. 
     The insulator may include a first bottom wall arranged to support the first wire and a second bottom wall arranged to support the second wire. 
     The first bottom wall and the second bottom wall may be formed to have a step in the axial direction for the first wire and the second wire to be separated in the axial direction. 
     According to another aspect of the disclosure, a motor includes a stator including a stator core, an insulator arranged to cover the stator core, and a plurality of wires wound on the insulator and connected respectively to terminals of phases U, V, and W; and a rotor arranged outside the stator and rotated by electromagnetically interacting with the stator, 
     Some of the plurality of wires may be wound from one side of the insulator along an arc-shaped wall formed in a center of the insulator. 
     Some of the rest of the plurality of wires may be wound from the other side of the insulator along the arc-shaped wall formed in the center of the insulator. 
     The plurality of wires may include a first wire connecting a coil of U 1  phase terminal to a coil of U 2  phase terminal, a second wire connecting a coil of V 1  phase terminal to a coil of V 2  phase terminal, and a third wire connecting a coil of W 1  phase terminal to a coil of W 2  phase terminal. 
     The first wire may be wound from one side of the insulator along the arc-shaped wall in a first direction, 
     The second wire may be wound from the one side of the insulator along the arc-shaped wall in a second direction opposite the first direction. 
     The third wire may be wound from the other side of the insulator along the arc-shaped wall in the first direction or the second direction. 
     The first wire may be arranged separately from the second wire in the axial direction to avoid contacting the second wire when the first wire is wound from the one side of the insulator along the arc-shaped wall. 
     According to another aspect of the disclosure, a motor includes a stator including a stator core, an insulator arranged to cover the stator core, and a plurality of wires wound on the insulator and connected respectively to terminals of phases U, V, and W; and a rotor arranged outside the stator and rotated by electromagnetically interacting with the stator, and including a ring-shaped back yoke, an outer surface of the back yoke being exposed to an outside of the rotor, 
     Some of the plurality of wires may be wound from one side of the insulator along an arc-shaped wall formed in a center of the insulator. 
     Some of the rest of the plurality of wires may be wound from the other side of the insulator along the arc-shaped wall formed in the center of the insulator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a motor, according to an embodiment of the disclosure; 
         FIG. 2  shows a motor separated into a rotor and a stator, according to an embodiment of the disclosure; 
         FIG. 3  shows the rotor of  FIG. 2 ; 
         FIG. 4  is an exploded view of the rotor of  FIG. 3 ; 
         FIG. 5  is a cross-sectional view of the rotor of  FIG. 3 ; 
         FIG. 6  shows the stator of  FIG. 2 ; 
         FIG. 7  is an exploded view of the stator of  FIG. 6 ; 
         FIG. 8  shows a wire connecting between a first phase and a second phase in a motor viewed at a first angle, according to an embodiment of the disclosure; 
         FIG. 9  shows a wire connecting between a first phase and a second phase in a motor viewed at a second angle, according to an embodiment of the disclosure; 
         FIG. 10  shows a wire connecting between a first phase and a second phase in a motor viewed at a third angle, according to an embodiment of the disclosure; 
         FIG. 11  shows a wire connecting between a first phase and a second phase in a motor viewed at a fourth angle, according to an embodiment of the disclosure; and 
         FIG. 12  shows a wire connecting between a first phase and a second phase in a motor viewed at a fifth angle, according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments and features as described and illustrated in the disclosure are merely examples, and there may be various modifications replacing the embodiments and drawings at the time of filing this application. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the disclosure. It is to be understood that the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. It will be further understood that the terms “comprise” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     The terms including ordinal numbers like “first” and “second” may be used to explain various components, but the components are not limited by the terms. The terms are only for the purpose of distinguishing a component from another. Thus, a first element, component, region, layer or chamber discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the disclosure. 
     The terms “front”, “rear”, “upper”, “lower”, “top”, and “bottom” as herein used are defined with respect to the drawings, but the terms may not restrict the shape and position of the respective components. 
     Embodiments of the disclosure will now be described in detail with reference to accompanying drawings. 
       FIG. 1  is a perspective view of a motor, according to an embodiment of the disclosure. 
       FIG. 2  shows a motor separated into a rotor and a stator, according to an embodiment of the disclosure. 
     Referring to  FIGS. 1 and 2 , a motor  1  may include a rotor  100  and a stator  200 . The rotor  100  may be configured to be rotated relative to the stator  200 . The rotor  100  may be arranged to be rotated by electromagnetic interaction with the stator  200 . 
     In the disclosure, the motor  1  may be an outer rotor motor with the rotor  100  placed outside the stator  200 . As compared to an inner rotor motor with a rotor placed inside a stator, the outer rotor motor has a benefit of outputting high power for the motor size. Accordingly, the outer rotor motor is also able to be reduced in size because it is able to output high power with a relatively small size. 
     Although not shown, the motor  1  may be used in various products. For example, the motor  1  may be used in a compressor of an air conditioner, a compressor of a purifier for supplying cold water, etc., without being limited thereto. 
       FIG. 3  shows the rotor of  FIG. 2 .  FIG. 4  is an exploded view of the rotor of  FIG. 3 .  FIG. 5  is a cross-sectional view of the rotor of  FIG. 3 . 
     Referring to  FIGS. 3 and 4 , the rotor  100  may include a back yoke  110 , magnets  120  arranged inside the back yoke  10 , a shaft supporting member  130 , to which a shaft (not shown) is inserted, and a frame  140 . 
     The rotor  100  may include the back yoke  110  shaped like a ring that encloses a stator core  200 . In the disclosure, the back yoke  110  may be formed in one piece. In other words, the back yoke  110  may be manufactured into a single body without discontinuity along the circumference of the back yoke  110 . Accordingly, this may reduce a core loss that may occur from the back yoke  110 . 
     Furthermore, the number of manufacturing processes and material costs may be reduced when the back yoke  110  is manufactured. So far, a back yoke has been manufactured by bending an iron plate into a ring and welding the separated ends of the iron plate. Alternatively, the back yoke has been manufactured by bending an iron plate into a ring, forming grooves at an end of the iron plate and projections at the other end, and fitting them together. In the case of the back yoke resulting from these manufacturing methods, the back yoke is not formed in one piece, which causes a core loss and an increase in the number of manufacturing processes and material cost of the back yoke. 
     In the disclosure, the back yoke  110  may be manufactured by pressing a magnetic steel sheet to a predetermined thickness and then blanking the magnetic steel sheet in the predetermined thickness. Furthermore, the back yoke  110  and the stator core  210 , which will be described later, may be manufactured from a single basic substance. Specifically, the single basic substance may be pressed into an iron plate of a predetermined thickness, and both the back yoke  110  and the stator core  210  may be manufactured concurrently by blanking the iron plate. An iron plate that went through blanking may not usually be reused, so manufacturing the back yoke and the stator core from a single iron plate may have a reduced material cost and reduced number of manufacturing processes as compared to manufacturing them with different iron plates. According to the disclosure, the material cost may be reduced and productivity may be improved. 
     The back yoke  110  may include a projection  111  protruding from the inner surface of the back yoke  110  toward the center of the back yoke  110 . There may be a plurality of projections  111 . The plurality of projections  111  may be separately arranged along the circumference of the back yoke  110 . The projections  111  may temporarily fix positions of the magnets  120  before the frame  140  is injection molded. The projections  111  may also prevent the distance between the magnets  120  from increasing or decreasing during rotation of the rotor  100 . In other words, the projections  111  may fix the magnets  120  to prevent positions of the magnets  120  from being changed. 
     The back yoke  110  may include a first sticking projection  112  to prevent relative rotation of the back yoke  110  to the frame  140 . The first sticking projection  112  may be placed to be interlocked with a second sticking projection  145  arranged on the frame  140 , thereby preventing the relative rotation between the back yoke  110  and the frame  140 . 
     The magnets  120  may be arranged inside the back yoke  110 . The magnets  120  may be arranged such that the outer surface adjoins the inner surface of the back yoke  110 . There may be a plurality of magnets  120 . The plurality of magnets  120  may be arranged separately along the circumference of the back yoke  110 . Although there are eight magnets  120  shown, the number of magnets is not limited thereto. The number of magnets  120  may be more or fewer than eight. 
     The shaft supporting member  130  may include a shaft hole  131  provided for a shaft (not shown) to be inserted thereto. The shaft supporting member  130  may also include an anti-rotation groove  132  to prevent relative rotation against the frame  140 . There may be a plurality of anti-rotation grooves  132 . The plurality of anti-rotation grooves  132  may be arranged separately along the circumference of the shaft supporting member  130 . 
     The frame  140  may be provided to combine the back yoke  110 , the magnets  120 , and the shaft supporting member  130 . The frame  140  may be formed by injection molding. The rotor  100  may be provided by injection molding the frame  140  after the back yoke  110 , the magnets  120 , and the shaft supporting member  130  are placed in a mold. Specifically, the rotor  100  may be formed by injecting resin (not shown) to form the frame  140  after the back yoke  110 , the magnets  120 , resin may be injected thereto to form a frame  140  and the shaft supporting member  130  are inserted to an injection mold. With this manufacturing method, the rotor  100  may be integrally formed without an extra fastening member or adhesive member. In other words, the frame  140  may combine the back yoke  110 , the magnets  120 , and the shaft supporting member  130  even without an extra fastening member or adhesive member. 
     The frame  140  may be formed with a plastic substance that may be injection molded unlike the back yoke  110 , the magnets  120 , and the shaft supporting member  130  formed with metal substances. As the frame  140  is formed with the plastic substance, weight of the rotor  100  and thus the weight of the motor  1  including the rotor  100  may be reduced. Furthermore, with the frame  140  formed with the plastic substance, flux leakage due to the frame  140  may be reduced. Otherwise, when the frame is formed with metal, there is flux leakage occurring due to the metal frame. 
     The frame  140  may include an anti-rotation projection  141  arranged to match the anti-rotation groove  132  of the shaft supporting member  130 . The anti-rotation projection  141  may be arranged to be inserted to the anti-rotation groove  132 , thereby enabling the frame  140  and the shaft supporting member  130  to be rotated not relatively but together in unison. 
     The magnet  120  may include an inner surface  121  facing the center of the back yoke  110  and an outer surface  122  facing an inner surface  113  of the back yoke  110 . The magnet  120  may be provided such that the outer surface  122  is larger than the inner surface  121 . 
     The frame  140  may include a magnet hole  142  provided for the magnet  120  to be inserted thereto. The inner surface  121  of the magnet  120  may be inserted into the magnet hole  142 . The outer surface  122  of the magnet  120  may be provided to be larger than the magnet hole  142 . Accordingly, the inner surface  121  of the magnet  120  may be arranged to be exposed to the inside of the frame  140  through the magnet hole  142 . 
     The frame  140  may include a groove  143  provided for the projection  111  of the back yoke  110  to be inserted thereto, and a column  144  with the groove  143  formed thereon. There may be a plurality of columns  144 . The columns  144  may be arranged separately along the circumference of the frame  140 . The magnet hole  142  may be formed between the neighboring columns  144 . The grooves  143  may be formed on the respective columns  144 . The groove  143  may have the form to match the projection  111 . 
     The column  144  may be formed between the neighboring magnets  120 . In other words, the column  144  may be placed between magnets  120 . The column  144  may prevent a gap between the magnets  120  from being narrowed by centrifugal force while the rotor  100  is rotated at high speed. Similar to the column  144 , the projection  111  of the back yoke  110  may be arranged between the magnets  120  to prevent the distance between the magnets  120  from increasing or decreasing. 
     Referring to  FIG. 3 , the frame  140  may include the second sticking projection  145 . The second sticking projection  145  may be arranged to be interlocked with the first sticking projection  112 . The first sticking projection  112  and the second sticking projection  145  may protrude in opposite directions to be coupled together along the circumference of the back yoke  110 . The first sticking projection  112  and the second sticking projection  145  may be arranged to be interlocked together, thereby preventing relative rotation between the back yoke  110  and the frame  140 . 
     In the disclosure, the outer surface  114  of the back yoke  110  may be exposed to the outside of the frame  140 . Specifically, the outer surface  114  of the back yoke  110  may be exposed to the outside of the frame  140 , defining the side of the rotor  100 . Accordingly, the rotor  100  and the back yoke  110  may have the same outside diameter. In the disclosure, as the motor  1  is the outer rotor motor  1  with the rotor  100  placed outside the stator  200 , the size of the outside diameter of the motor  1  may be the same as the size of the back yoke  110 . In the disclosure, structures otherwise arranged on the outer surface of the back yoke  110  are removed to fix the back yoke  110 , leading to reduction in size of the motor  1  in the radial direction. 
     Some conventional motors use an extra adhesive to combine the back yoke and the magnet. These motors may have assembly tolerances due to the use of the adhesive. Furthermore, when the motor is used in a compressor for cold air conditioning, refrigerant or oil in the compressor may react with the adhesive and thus cause a fault. Hence, the use of such motors that use an adhesive is restricted in various environments. In the disclosure, the motor  1  may be used even in the compressor that uses refrigerant or oil because the motor  1  combines the back yoke  110  and the magnet  120  without an extra adhesive. Accordingly, the motor  1  in accordance with the disclosure may be used in various environments. 
     Referring to  FIG. 5 , thickness t 1  of the projection  111  of the back yoke  110  may be smaller than thickness t 2  of the magnet  120 . The length of the projection  111  in the radial direction of the back yoke  110  is the thickness t 1  of the projection  111 , and the length of the magnet  120  in the radial direction of the back yoke  110  is the thickness t 2  of the magnet  120 . In this case, the thickness t 1  of the projection  111  may be smaller than the thickness t 2  of the magnet  120 . 
     When the thickness t 1  of the projection  111  becomes larger than necessary, the projection  111  that is formed with a metal substance may disturb flows of magnetic flux between the neighboring magnets  120 . On the contrary, when the thickness t 1  of the projection  111  is too small, the projection  111  has difficulty in fixing the position of the magnet  120  when inserted to a mold for injection molding the frame  140 . Hence, the thickness t 1  of the projection  111  needs to be set suitably. 
     In an embodiment of the disclosure, the thickness t 1  of the projection  111  and the thickness t 2  of the magnet  120  may satisfy the following equation: 
         t 2/5&lt; t 1&lt; t 2/2. 
     When the equation is met, the projection  111  may fix the position of the magnet  120  without excessively disturbing the flows of magnetic flux between the magnets  120 . 
       FIG. 6  shows the stator of  FIG. 2 .  FIG. 7  is an exploded view of the stator of  FIG. 6 . 
     Referring to  FIGS. 6 and 7 , a structure of the stator according to an embodiment of the disclosure will now be described in detail. 
     In an embodiment of the disclosure, the stator  200  may include the stator core  210 , a first insulator  220  coupled to an upper portion of the stator core  210 , a second insulator  230  coupled to a lower portion of the stator core  210 , a first housing  240  coupled to the top of the first insulator  220  and a second housing  250  coupled to the bottom of the second insulator  230 . 
     The stator core  210  may include a ring-shaped core  211  and a plurality of teeth  212  extending radially from the core  211 . As described above, the stator core  210  may be manufactured from the same basic substance as the back yoke  110  by simultaneously blanking the basic substance with a press. Accordingly, the material cost may be reduced and productivity may be improved by reducing the number of manufacturing processes. 
     In an embodiment of the disclosure, the stator core  210  may include six teeth  212 . The first to third teeth  212  may be respectively assigned terminals of phases U 1 , V 1 , W 1 , and the fourth to sixth teeth  212  may be respectively assigned terminals of phases U 2 , V 2 , W 2 . This will be described later. 
     The first insulator  220  and the second insulator  230  may be coupled to the upper portion and the lower portion of the stator core  210  with the stator core  210  placed in between. The first insulator  220  and the second insulator  230  may be coupled to each other to cover the top and the bottom of the stator core  210 . 
     Once the first insulator  220  and the second insulator  230  are coupled to each other, a coil (see  FIG. 8 ) may be wound around the teeth  212  of the stator core  210 . This will be described in more detail later. 
     The first insulator  220  and the second insulator  230  may be formed with an insulation material. For example, the first insulator  220  and the second insulator  230  may be an injection molded product. The coil may be wound on the first insulator  220  and the second insulator  230 , which cover the teeth  212 . The first insulator  220  and the second insulator  230  may cover the teeth  212  to prevent the coil from directly contacting the stator core  210 . 
     The first housing  240  and the second housing  250  may be provided to respectively cover the first insulator  220  and the second insulator  230  from the top and from the bottom. The first housing  240  and the second housing  250  may cover the first insulator  220  and the second insulator  230  to prevent foreign materials from being brought to the coil arranged inside the housings  240  and  250 . 
     The terms “upper portion” or “top” and “lower portion” or “bottom” are mentioned based on  FIGS. 6 and 7 , and the forms and positions of the elements are not limited by the terms. 
       FIG. 8  shows a wire connecting between a first phase and a second phase in a motor viewed at a first angle, according to an embodiment of the disclosure.  FIG. 9  shows a wire connecting between a first phase and a second phase in a motor viewed at a second angle, according to an embodiment of the disclosure.  FIG. 10  shows a wire connecting between a first phase and a second phase in a motor viewed at a third angle, according to an embodiment of the disclosure. 
     Referring to  FIGS. 8 and 10 , a wire winding method and arrangement according to an embodiment of the disclosure will now be described in detail. 
       FIGS. 8 and 9  show the stator  200  with the second insulator  230  located on the top and the first and second housings  240  and  250  left out.  FIG. 10  shows the stator  200  with the first insulator  220  located on the top and the first and second housings  240  and  250  left out. 
     Referring to  FIGS. 8 to 10 , the stator  200  may include a wire  260  defining the coil. 
     In an embodiment of the disclosure, phase U may have phase U 1  and phase U 2  connected in series, phase V may have phase V 1  and phase V 2  connected in series, and phase W may have phase W 1  and phase W 2  connected in series. The wire  260  may include a first wire connecting between the phase U 1  and the phase U 2 , a second wire connecting between the phase V 1  and the phase V 2 , and a second wire connecting between the phase W 1  and the phase W 2 . 
     The first wire  261  to the third wire  263  are required not to contact each other. This is because contact between two or more of the first wire  261  to the third wire  263  blocks formation of a three phase circuit. Hence, the first wire  261  to the third wire  263  are required not to come into contact at all to secure electrical reliability. 
     In a conventional method, a structure extending in the axial direction of a shaft (not shown) is arranged at the insulator or the housing to prevent contact between wires. Contact between the wires may be prevented by winding the respective wires on the structure at different heights. In the conventional method, however, length of the stator in the axial direction becomes thick due to the structure. When the stator has large thickness in the axial direction, the size of the motor in the axial direction increases as well, and thus there is a limit to reduction in size of the motor. 
     In the disclosure, thickness of the motor in the axial direction may be reduced by enhancing the wire winding method and wire supporting structure. 
     In the disclosure, the first wire  261  and the second wire  262  may connect the first phase to the second phase through a second core part  231  of the second insulator  230 , and the third wire  263  may connect the first phase to the second phase through a first core part  221  of the first insulator  220 . The first insulator  220  may include the first core part  221  provided to cover the core  211  of the stator core  210  from one side of the stator core  210 , and the second insulator  230  may include the second core part  231  provided to cover the core  211  of the stator core  210  from the other side of the stator core  210 . 
     A first direction in which the first wire  261  is wound on the second core part  231  when the first wire  261  is wound from the phase U 1  to the phase U 2 , and a second direction in which the second wire  262  is wound on the second core part  231  when the second wire  261  is wound from the phase V 1  to the phase V 2  may be opposite to each other. For example, the first direction may be a counterclockwise direction while the second direction may be a clockwise direction. Alternatively, the first direction may be a clockwise direction while the second direction may be a counterclockwise direction. 
     The first core part  221  may include a first inner wall  222  and a first outer wall  223 . This will be described later. 
     The second core part  231  may include a second inner wall  232  and a second outer wall  233 . The second inner wall  232  may be provided to have no protruding or concave portion in the axial direction. The second outer wall  233  may include a groove formed by being sunken in the axial direction. Specifically, the second outer wall  233  may include a first groove  233   a,  a second groove  233   b,  a third groove  233   c,  and a fourth groove  233   d.    
     The first wire  261  or the second wire  261  may be inserted to the first to fourth grooves  233   a,    233   b,    233   c,  and  233   d.  The first wire  261  drawn from the phase U 1  may be inserted to the first groove  233   a.  The first wire  261  drawn from the phase U 1  and entering to the phase U 2  may be inserted to the second groove  233   b.  The second wire  262  drawn from the phase V 1  may be inserted to the third groove  233   c.  The second wire  262  drawn from the phase V 1  and entering to the phase V 2  may be inserted to the fourth groove  233   d.    
     Referring to  FIGS. 8 and 9 , the first wire  261  inserted to the first groove  233   a  may extend counterclockwise along the second core part  231 . After the first wire  261  drawn from the phase U 1  is inserted to the first groove  233   a,  the first wire  261  may extend counterclockwise through a space between the second inner wall  232  and the second outer wall  233 . The first wire  261  extending counterclockwise along the second core part  231  may be inserted to the second groove  233   b,  and then wound on the insulators  220  and  230  to form a coil of the phase U 2 . 
     Referring to  FIGS. 8 and 9 , the second wire  262  inserted to the third groove  233   c  may extend clockwise along the second core part  231 . After the second wire  262  drawn from the phase V 1  is inserted to the third groove  233   c,  the second wire  262  may extend clockwise through the space between the second inner wall  232  and the second outer wall  233 . The second wire  262  extending clockwise along the second core part  231  may be inserted to the fourth groove  233   d,  and then wound on the insulators  220  and  230  to form a coil of the phase V 2 . 
     As described above, a direction in which the first wire  261  extending from the phase U 1  to the phase U 2  is wound on the second core part  231 , and a direction in which the second wire  262  extending from the phase V 1  to the phase V 2  is wound on the second core part  231  may be opposite to each other. This may reduce area in the second core part  231  where the first wire  261  and the second wire  261  vertically overlap each other. 
     Referring to  FIGS. 8 and 9 , the first wire  261  and the second wire  262  wound on the second core part  231  clockwise or counterclockwise may be arranged separately in the vertical direction. In other words, even when there is an area where the first wire  261  and the second wire  262  vertically overlap each other, the first wire  261  and the second wire  262  may not contact each other because they are arranged separately in the vertical direction. 
     The second core part  231  may include a bottom wall  234 . The second core part  231  including the second inner wall  232 , the second outer wall  233 , and the bottom wall  234  may have the form of a circular rib with the top open. 
     The bottom wall  234  of the second core part  231  may include a first bottom wall  234   a  and a second bottom wall  234   b  for the first wire  261  and the second wire  262  wound on the second core part  231  to be separately arranged in the vertical direction without contacting each other. 
     The first bottom wall  234   a  and the second bottom wall  234   b  may be arranged at different locations in the axial direction. In other words, the first bottom wall  234   a  and the second bottom wall  234   b  may be located at different heights. Accordingly, connection walls  234   c  and  234   d  may be provided between the first bottom wall  234   a  and the second bottom wall  234   b  to connect the first bottom wall  234   a  and the second bottom wall  234   b.    
     In an embodiment of the disclosure, the first bottom wall  234   a  may be located higher than the second bottom wall  234   b.  The first bottom wall  234   a  may be provided to support the first wire  261 . The second bottom wall  234   b  may be provided to support the second wire  262 . With this structure, the first wire  261  may be wound on the second core part  231  at a higher location than the second wire  262  without contacting the second wire  262 . As described above, the first wire  261  may be wound on the second core part  231  counterclockwise. Likewise, the second wire  262  may be wound on the second core part  231  at a lower location than the first wire  261  without contacting the first wire  261 . The second wire  262  may be wound on the second core part  231  clockwise. 
     Referring to  FIG. 10 , the first core part  221  may include the first inner wall  222  and the first outer wall  223 . In  FIG. 10 , 
     The first outer wall  223  may have the form of an arc according to an embodiment of the disclosure. The first inner wall  222  may be provided to have the form of a ring-shaped rib. The first outer wall  223  may include a first groove  223   a  and a second groove  223   b.    
     The third wire  263  may be inserted to the first groove  223   a  and the second groove  223   b  of the first outer wall  223 . The third wire  263  drawn from the phase W 1  may be inserted to the first groove  223   a.  The third wire  263  drawn from the phase W 1  and entering to the phase W 2  may be inserted to the second groove  223   b.    
     Referring to  FIG. 10 , the third wire  263  inserted to the first groove  223   a  may extend clockwise along the first core part  221 . The term ‘clockwise’ is used based on  FIG. 10 , which may appear to be counterclockwise based on  FIGS. 8 and 9 . After the third wire  263  drawn from the phase W 1  is inserted to the first groove  223   a,  the third wire  263  may extend clockwise through a space between the first inner wall  222  and the first outer wall  223 . The third wire  263  extending clockwise along the first core part  221  may be inserted to the second groove  223   b,  and then wound on the insulators  220  and  230  to form a coil of the phase W 2 . 
     As shown in  FIG. 10 , only the third wire  263  may be wound on the first core part  221  of the first insulator  220 . Accordingly, as the third wire  263  is safe from contact with other wires, the first core part  221  may not include bottom walls of different heights. In an embodiment of the disclosure, however, the first core part  221  may include a first bottom wall  224   a  supporting the third wire  263  and a second bottom wall  224   b  located at a higher position than the first bottom wall  224   a.  In this case, the second bottom wall  224   b  is provided not to place the third wire  263  separately from other wires in the vertical direction but to reinforce strength of the first core part  221 . Accordingly, unlike what is shown in the drawings, it is also possible for the first core part  221  to include the first bottom wall  224   a  only. 
       FIG. 11  shows a wire connecting between a first phase and a second phase in a motor viewed at a fourth angle, according to an embodiment of the disclosure.  FIG. 12  shows a wire connecting between a first phase and a second phase in a motor viewed at a fifth angle, according to an embodiment of the disclosure. 
       FIG. 11  is a top view of the second insulator  230 , and  FIG. 12  is a top view of the first insulator  220 . 
     What are described above will be further described with reference to  FIGS. 11 and 12 . 
     Referring to  FIG. 11 , the first wire  261  may be wound counterclockwise along the space between the second outer wall  233  and second inner wall  232  of the second core part  231  when extending from the phase U 1  to the phase U 2 . The second wire  262  may be wound clockwise along the space between the second outer wall  233  and second inner wall  232  of the second core part  231  when extending from the phase V 1  to the phase V 2 . Accordingly, an area where the first wire  261  and the second wire  262  overlap in the vertical direction may be minimized, as shown in  FIG. 11 . 
     Referring to  FIG. 12 , the third wire  263  may be wound clockwise along the space between the first outer wall  223  and the first inner wall  222  of the first core part  221  when extending from the phase W 1  to the phase W 2 . Unlike the first and second wires  261  and  262 , the third wire  263  may extend along the first core part  221  of the first insulator  220  to connect between the phase W 1  and the phase W 2 . Accordingly, the third wire  263  may be prevented from coming into contact with the first wire  261  and/or the second wire  262 . 
     According to the disclosure, the size of the stator  200  in the axial direction may be reduced. The stator  200  may have U, V, and W phase wires  261 ,  262 , and  263  distributed and arranged on the first insulator  220  and the second insulator  230 . For example, the first wire  261  connecting between the phase U 1  and the phase U 2  and the second wire  262  connecting between the phase V 1  and the phase V 2  may be wound on the second insulator  230 . The third wire  263  connecting between the phase W 1  and the phase W 2  may be wound on the first insulator  220 . The stator  200  may have the first wire  261  and the second wire  262  separately arranged in the vertical direction not to contact each other. For this, the core part  231  of the second insulator  230  may include the first bottom wall  234   a  and the second bottom wall  234   b  at different heights. 
     According to the disclosure, wires may be divided and placed in upper and lower portions of the stator  200  without the need for an extra structure extending in the axial direction of the stator  200 . Furthermore, the wires may be placed separately in the vertical direction in an overlapping area, thereby avoiding contacting each other. According to the disclosure, the size of the stator  200  in the axial direction may be reduced. Furthermore, with the reduced size of the stator  200  in the axial direction, the size of the motor  1  in the axial direction may be reduced as well. Accordingly, the motor  1  may become smaller in size. 
     According to the disclosure, a motor in a reduced size may be provided. 
     According to the disclosure, a motor having reduced sizes in axial and radial directions may be provided. 
     According to the disclosure, a motor having a reduced size in an axial direction may be provided by enhancing a wire winding method and a wire supporting structure. 
     According to the disclosure, a motor having a reduced size in a radial direction may be provided by exposing a portion of a back yoke to the outside of the motor. 
     Several embodiments of the disclosure have been described above, but a person of ordinary skill in the art will understand and appreciate that various modifications can be made without departing the scope of the disclosure. Thus, it will be apparent to those ordinary skilled in the art that the true scope of technical protection is only defined by the following claims.