Patent Publication Number: US-2021175763-A1

Title: Stator assembly of hairpin winding motor and manufacturing method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from and the benefit of Korean Patent Application No. 10-2019-0159500, filed on Dec. 4, 2019, which is incorporated by reference for all purposes as if fully set forth herein. 
     BACKGROUND 
     Field 
     Exemplary embodiments relates to a stator assembly of a hairpin winding motor and a manufacturing method thereof, and more specifically, to a stator assembly of a hairpin winding motor of which the weight and volume are reduced to reduce the weight and secure an inner space of an automobile and a manufacturing method thereof. 
     Discussion of the Background 
     Research and development, and commercialization of eco-friendly automobile-related parts have actively proceeded in the automobile industry according to international demands for greenhouse gas reduction regulations and improvement of fuel efficiency of automobiles. 
     A technology for exerting a driving force using an electric motor is in development as a kind of an eco-friendly automobile-related part, and especially for this, a motor productivity technology including motor operating efficiency is also required. 
     Carmakers and manufacturers of eco-friendly parts apply hairpin coils to driving motors as a part of technology development to reduce the weight and volume of the eco-friendly parts. 
     Due to development of a technology for reducing the weight and volume of the eco-friendly parts, the weight of a vehicle or an eco-friendly vehicle can be reduced and an inner space can be secured. 
     A stator core of a driving motor to which a hairpin coil is applied according to the related art is formed of a magnetic material, and includes a yoke forming a magnetic path and a plurality of teeth spaced apart from each other at intervals to protrude radially inward from the yoke, and a plurality of hairpin coils inserted into a plurality of slots formed by the plurality of teeth spaced apart from each other at intervals. 
     Meanwhile, a method of manufacturing the stator core according to the related art is generally classified into a method in which shoes are formed on end portions of the teeth of the stator core and the hairpin coils are inserted in an axial direction, and a method in which the shoes of the teeth are removed and the hairpin coils are inserted in a radial direction. 
     First, in the method in which shoes are formed on the end portions of the teeth of the stator core and the hairpin coils are inserted in the axial direction, the hairpin coil is molded or formed in a U-shaped shape so that a coil or ring having a generally angular cross-section can be inserted into the slot of the stator core in advance, thereby making the hairpin coil. 
     Further, the shoes formed on inner ends of the teeth in a radial direction fix the hairpin coils inserted into the slots. 
     A method of manufacturing the driving motor to which the hairpin coil is applied, in which the shoes are formed on the end portions of the teeth, and the hairpin coils are inserted in the axial direction includes winding by inserting roughly 100 to 150 hairpin coils into the stator core and then twisting and welding opposite end portions, and even when one welding defect occurs at the ends of the hairpin coils, there is a problem that the hairpin coils cannot be used as a whole welding failure. 
     Further, when coils each having an angular cross-sectional area are twisted and bent to wind the hairpin coils, a film is thinned or damaged and thus the insulation performance is degraded in a process of forming the coils at a high load. 
     In the method in which the shoes of the teeth are removed and the hairpin coils are inserted in the radial direction, because stator core shoe portions are removed when stator divided cores are inserted in a radial direction after a hairpin winding bundle is made, noise, vibration, and harshness (NVH) are generated due to an increase of cogging torque and torque ripples, and the performance is adversely affected. 
     Because a shape of the stator core is designed according to a shape of the hairpin coils after the hairpin coils are manufactured, magnetic flux cannot be uniformly designed, and thus the end portions of the teeth of the stator core are saturated, and the performance can be degraded. 
     Accordingly, a method of increasing productivity of the stator core by reducing a defective rate, reducing the cogging torque and the torque ripples, and improving a fixing force of the hairpin coils is being looked for, but no satisfactory results have yet been obtained. 
     The above information disclosed in this Background section is only for understanding of the background of the inventive concepts, and, therefore, it may contain information that does not constitute prior art. 
     SUMMARY 
     Exemplary embodiments of the present disclosure is directed to providing a stator assembly of a hairpin winding motor capable of increasing productivity of a stator core by reducing a defective rate, reducing cogging torque and torque ripples, and improving a fixing force of hairpin coils, and a manufacturing method thereof. 
     According to an aspect of the present disclosure, there is provided a stator assembly of a hairpin winding motor including hairpin coils continuously connected along a circumferential direction to form a coil winding; a stator core configured to fix the hairpin coils; and a support ring configured to surround an outer circumferential surface of the stator core, wherein the stator core is inserted into the hairpin coils forming the coil winding in a radial direction. 
     Each of the hairpin coils may include a head portion exposed to the outside of the stator core in an axial direction, and leg portions configured to extend from one end and the other end of the head portion to be inserted into a core slot of the stator core, and the leg portions may be formed in a shape which is repeated in the circumferential direction by one pole pitch to be continuously connected. 
     A cross section of the leg portion may be formed in a trapezoidal shape of which the outside is broad and the inside is narrow, and thus a width may decrease in a direction toward an inner diameter from an outer diameter of the stator core. 
     The hairpin coils may be formed of a first coil which is a pair of hairpin coils disposed adjacent to each other in the radial direction, and a second coil which is a pair of hairpin coils disposed adjacent to each other in a radially outward direction from the first coil. 
     A length of the first coil in the radial direction may be greater than a length of the second coil in the radial direction, and a width of the first coil in the circumferential direction may be smaller than a width of the second coil in the circumferential direction. 
     The stator core may include a yoke formed of a magnetic material to form a magnetic path, teeth protruding in the radial direction from an inner circumferential surface of the yoke, a plurality of coil slots formed between the plurality of teeth and into which the hairpin coils are inserted, and shoes configured to extend in the circumferential direction from both side surfaces of end portions of the teeth. 
     The yoke may include a yoke body part forming a body, a first protruding part protruding from one surface in the circumferential direction at a radially outer side of the yoke body part, a first recessed part recessed in the circumferential direction at a radially inner side of the first protruding part, a second protruding part protruding from the other surface in the circumferential direction at a radially inner side of the yoke body part, and a second recessed part recessed in the circumferential direction at a radially outer side of the second protruding part, and a side surface of each of the first protruding part and the first recessed part and a side surface of each of the second protruding part and the second recessed part may be inclined to form a center angle of the yoke body part. 
     Each of the teeth may be formed in a rectangular shape, and thus widths of one end and the other end thereof may be the same. 
     According to another aspect of the present disclosure, there is provided a stator assembly of a hairpin winding motor including hairpin coils continuously connected along a circumferential direction to form a coil winding; a plurality of stator cores disposed along the circumferential direction and configured to fix the hairpin coils; and a support ring configured to surround an outer circumferential surface of the stator core, wherein each of the stator cores includes a yoke formed of a magnetic material to form a magnetic path, and the yoke includes a yoke body part forming a body, a first protruding part protruding from one surface in the circumferential direction at a radially outer side of the yoke body part, a first recessed part recessed in the circumferential direction at a radially inner side of the first protruding part, a second protruding part protruding from the other surface in the circumferential direction at a radially inner side of the yoke body part, and a second recessed part recessed in the circumferential direction at a radially outer side of the second protruding part. 
     A side surface of the second protruding part and a side surface of the first recessed part may be inclined to form a center angle of the yoke body part, and a side surface of the first protruding part and a side surface of the second recessed part may be inclined in the circumferential direction from the side surface of the second protruding part and the side surface of the first recessed part. 
     According to still another aspect of the present disclosure, there is provided a stator assembly of a hairpin winding motor including hairpin coils continuously connected along a circumferential direction to form a coil winding; a plurality of stator cores disposed along the circumferential direction and configured to fix the hairpin coils; and a support ring configured to surround an outer circumferential surface of the stator core, wherein each of the stator cores includes a yoke formed of a magnetic material to form a magnetic path, and the yoke includes a protrusion part protruding in the circumferential direction from one surface thereof, and a protrusion groove formed in a shape corresponding to the protrusion part in the other surface thereof, and into which the protrusion part adjacent thereto is inserted. 
     According to yet another aspect of the present disclosure, there is provided a method of manufacturing a stator assembly of a hairpin winding motor, in which hairpin coils are wound around a stator core having a plurality of coil slots, the method including providing the hairpin coils continuously connected to form a coil winding; inserting yokes forming the stator core into the hairpin coils; moving the hairpin coils outward from the inside of the hairpin coils to fix the hairpin coils to the plurality of yokes; and inserting a support ring configured to surround the stator core into an outer circumferential surface of the stator core, wherein a plurality of yokes are disposed along a circumferential direction. 
     The yokes may be inserted into the hairpin coils in a radially inward direction from the outside of the hairpin coils in inserting the yokes into the hairpin coils. 
     An outer diameter of the hairpin coil may be formed smaller than an outer diameter of the stator core in inserting the yokes into the hairpin coils. 
     In fixing the hairpin coils by the yokes, the outer diameter of the hairpin coil may be formed smaller than the outer diameter of the hairpin coil in inserting the yokes into the hairpin coils by pressurization of the yokes. 
     Teeth may protrude in a radial direction from inner circumferential surfaces of the plurality of yokes, and shoes may extend in the circumferential direction from both side surfaces of end portions of the teeth. 
     A distance between the shoes which are adjacent to each other may be greater than a thickness of the hairpin coil in inserting the yokes forming the stator core into the hairpin coils. 
     The distance between the shoes which are adjacent to each other may be smaller than the thickness of the hairpin coil in gathering the yokes in the radial direction to fix the hairpin coils. 
     The support ring may be inserted downward in an axial direction in inserting the support ring configured to surround the stator core into the outer circumferential surface of the stator core. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention, and together with the description serve to explain the principles of the invention. 
         FIG. 1  is a perspective view illustrating a stator assembly of a hairpin winding motor according to one embodiment of the present disclosure; 
         FIG. 2  is a plan view illustrating a coupling state between a hairpin coil, a stator core, and a support ring of the stator assembly of the hairpin winding motor according to one embodiment of the present disclosure; 
         FIG. 3  is an exploded perspective view illustrating the stator assembly of the hairpin winding motor according to one embodiment of the present disclosure; 
         FIG. 4  is a perspective view illustrating a yoke of the stator assembly of the hairpin winding motor according to one embodiment of the present disclosure; 
         FIG. 5  is a perspective view illustrating a yoke of a stator assembly of a hairpin winding motor according to another embodiment of the present disclosure; 
         FIG. 6  is a perspective view illustrating a yoke of a stator assembly of a hairpin winding motor according to still another embodiment of the present disclosure; 
         FIG. 7  is a flow chart illustrating a method of manufacturing the stator assembly of the hairpin winding motor according to one embodiment of the present disclosure; and 
         FIG. 8A ,  FIG. 8B ,  FIG. 8C  and  FIG. 8D  are assembly drawings illustrating the method of manufacturing the stator assembly of the hairpin winding motor according to one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     Advantages and characteristics of the present disclosure, and a method of achieving the above, will be apparent with reference to embodiments which will be described in detail in conjunction with the accompanying drawings. However, the inventive concepts are not limited to the embodiments which will be described below and may be implemented in different forms. The embodiments are provided to disclose the inventive concepts and convey the scope of the inventive concepts to those skilled in the art, and the inventive concepts are defined by the disclosed claims. Meanwhile, terms used in the description are provided not to limit the inventive concepts but to describe the embodiments. In the embodiment, the singular form is intended to also include the plural form unless the context clearly indicates otherwise. The terms “comprise” and/or “comprising” as used herein do not preclude the presence or addition of at least one other component, step, operation, and/or element other than the stated components, steps, operations and/or elements. It will be understood that for purposes of this disclosure, “at least one of X, Y, and Z” can be construed as X only, Y only, Z only, or any combination of two or more items X, Y, and Z (e.g., XYZ, XYY, YZ, ZZ). Unless particularly described to the contrary, the term “comprise”, “configure”, “have”, or the like, which are described herein, will be understood to imply the inclusion of the stated components, and therefore should be . . . . 
     Hereinafter, embodiments of the inventive concepts will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a perspective view illustrating a stator assembly of a hairpin winding motor according to one embodiment of the inventive concepts,  FIG. 2  is a plan view illustrating a coupling state between a hairpin coil, a stator core, and a support ring of the stator assembly of the hairpin winding motor according to one embodiment of the inventive concepts,  FIG. 3  is an exploded perspective view illustrating the stator assembly of the hairpin winding motor according to one embodiment of the inventive concepts,  FIG. 4  is a perspective view illustrating a yoke of the stator assembly of the hairpin winding motor according to one embodiment of the inventive concepts,  FIG. 5  is a perspective view illustrating a yoke of a stator assembly of a hairpin winding motor according to another embodiment of the inventive concepts, and  FIG. 6  is a perspective view illustrating a yoke of a stator assembly of a hairpin winding motor according to still another embodiment of the inventive concepts. 
     Referring to  FIGS. 1 to 6 , the stator assembly of the hairpin winding motor according to one embodiment of the inventive concepts includes a hairpin coil  100 , a stator core  200 , and a support ring  300 . 
     The hairpin coil  100  is formed in plural, forms a coil winding in a circumferential direction, and is inserted into the stator core  200 . 
     Further, the hairpin coils  100  forms the coil winding as end portions exposed in an axial direction from the stator core  200  are connected to each other, and raw coils coated with a coating and formed to have a straight length of a predetermined diameter are processed through a coil processor, and have connecting portions connected to each other. 
     In addition, a predetermined number of hairpin coils  100  are fitted into one slot in a stacked state to form the winding. 
     The hairpin coil  100  includes a head portion  110 , leg portions  120 , and foot portion  130 . 
     The head and foot portions  110  and  130  are bent in a U shape and exposed to the outside of the stator core  200 , and serve as a connection portion configured to connect a pair of leg portions  120  due to extension of the leg portions  120  from the head portion  110  to the foot portion  130 . 
     The head portion  110  and foot portion  130  are items known to those skilled in the art, and thus are schematically illustrated not to obscure the principle of the inventive concepts. 
     The leg portions  120  extend from the head portion  110  to the foot portion  130  in parallel and are inserted into a core slot of the stator core  200 , and are repeated in a circumferential direction by one pole pitch and formed in a continuously connected shape. 
     Because the plurality of hairpin coils  100  are continuously connected, the coil winding is formed in a circumferential direction. 
     Further, in the hairpin coil  100 , two leg portions  120  disposed adjacent to each other in the circumferential direction are welded to each other. 
     Meanwhile, a cross-section of the leg portion  120  is formed in a trapezoidal shape. 
     More specifically, a cross-sectional shape of the leg portion  120  is formed in a shape of which the outside is broad and the inside is narrow, and thus a width decreases in an inner diameter direction from an outer diameter of the stator core  200 . 
     The hairpin coils  100  including the head portion  110  and the leg portions  120  are formed of a first coil  100 _ 1  and a second coil  100 _ 2  according to insertion positions in the stator core  200 . 
     As illustrated in  FIG. 2 , two hairpin coils  100  disposed adjacent to each other in a radial direction are a pair of first coils  100 _ 1 , and two hairpin coils  100  disposed adjacent to each other in a radially outward direction from the first coils  100 _ 1  are a pair of second coils  100 _ 2 . 
     That is, the pair of first coils  100 _ 1  and the pair of second coils  100 _ 2  each form the coil winding in the circumferential direction and are inserted into coil slots  240  of the stator core  200 . 
     A length of the pair of first coils  100 _ 1  in the radial direction is greater than a length of the pair of second coils  100 _ 2  in the radial direction, and a width of the pair of first coils  100 _ 1  in the circumferential direction is smaller than a width of the pair of second coils  100 _ 2  in the circumferential direction is formed. 
     Accordingly, because the hairpin coils  100  of the inventive concepts are formed of two types of coils such as the pair of first coils  100 _ 1  and the pair of second coils  100 _ 2 , a shape of the hairpin coil  100  may be optimized according to a shape of the coil slot  240  of the stator core  200  to reduce manufacturing costs of the hairpin coils  100  by roughly 20% to 40%. 
     Meanwhile, for convenience of description, in the inventive concepts, it is described that four hairpin coils  100  are formed, and the hairpin coils  100  are formed of the pair of first coils  100 _ 1  and the pair of second coils  100 _ 2 , but four or more, for example, four to ten or more hairpin coils  100  may be repeatedly formed in the radial direction. 
     The stator core  200  is disposed in plural along the circumferential direction, and fixes the hairpin coils  100 , and is inserted into the hairpin coils  100  forming the coil winding, in the radial direction. 
     The stator core  200  includes a yoke  210 , tooth  220 , a shoe  230 , and a coil slot  240 . 
     The yoke  210  forms a body of the stator core  200 , and is formed of a magnetic material to form a magnetic path. 
     Further, as illustrated in  FIG. 3 , a single yoke  210  is part of a plurality of yokes  210  that are disposed along a circumferential direction. 
     The plurality of yokes  210  are coupled inward from an outer side in a radial direction. 
     Typically, when one of the plurality of yokes  210  is separated from coupling, the coupling of the plurality of yokes  210  is released. 
     To prevent this, the yoke  210  of the inventive concepts includes a yoke body part  211 , a first protruding part  212 , a first recessed part  213 , a second protruding part  214 , and a second recessed part  215 . 
     The yoke body part  211  forms a body of the yoke  210 . 
     The first protruding part  212  protrudes from a radially outer side of the yoke body part  211  in a circumferential direction. 
     Further, the first recessed part  213  is recessed in a circumferential direction from a radially inner side of the yoke body part  211  as the first protruding part  212  projects outwards in the circumferential direction from a radially outward portion of the yoke body part  211 . 
     Accordingly, a first step  218  is formed between the first protruding part  212  and the first recessed part  213 . 
     The second protruding part  214  protrudes from another surface in the circumferential direction at a radially inner side of the body part  211 , that is, a surface opposite the first recessed part  213 . 
     Further, the second recessed part  215  is recessed in the circumferential direction at a radially outer side of the second protruding part  214 , that is, a surface opposite the first protruding part  212  that is formed from the yoke body part  211 . 
     Accordingly, a second step  219  is formed between the second protruding part  214  and the second recessed part  215 . 
     Further, the first protruding part  212  protrudes in a shape corresponding to the second recessed part  215 , and the first recessed part  213  protrudes in a shape corresponding to the second protruding part  214 . 
     In addition, as illustrated in  FIG. 4 , a side surface of each of the first protruding part  212  and the first recessed part  213  and a side surface of each of the second protruding part  214  and the second recessed part  215  are inclined to form a center angle θ 1  of the yoke body part  211 . The center angle θ 1  corresponds to a distance between the first step  218  and the second step  219 . 
     That is, the first protruding part  212  of the yoke  210  comes into contact with the second recessed part  215  of the yoke  210  adjacent to the yoke in one direction, and the second protruding part  214  of the yoke  210  comes into contact with the first recessed part  213  of the yoke  210  adjacent to the yoke in the other direction. 
     Accordingly, the yoke  210  may solidly prevent separation from the inner side to the outer side or the outer side to the inner side due to the first step  218  formed between the first protruding part  212  and the first recessed part  213  and the second step  219  formed between the second protruding part  214  and the second recessed part  215 . 
     In another embodiment of the yoke  210  of the inventive concepts, a shape of each of the first protruding part  212  and the second recessed part  215  may be different. 
     For example, as illustrated in  FIG. 5 , the side surfaces of the second protruding part  214  and the first recessed part  213  are inclined to form reference lines for the center angle θ 1  of the yoke body part  211 . The side surface of the first protruding part  212  and the side surface of the second recessed part  215  may be formed in at inclined angle θ 2  in a circumferential direction from the side surface of the second protruding part  214  and the side surface of the first recessed part  213 . 
     Accordingly, because adjacent yokes  210  come in contact with each other at the various step portions  218  and  219 , the yokes  210  according to another embodiment of the inventive concepts may be solidly coupled to each other. 
     In still another embodiment of yokes  210  of the inventive concepts, a protrusion part  216  and a protrusion groove  217  may be formed at two side surfaces of the yoke  210  to prevent separation of the plurality of yokes  210  coupled to each other in a radial direction. 
     Specifically, as illustrated in  FIG. 6 , the protrusion part  216  protrudes from a center of one surface of the yoke body part  211  in a circumferential direction, and the protrusion groove  217  is formed in a shape corresponding to the protrusion part  216  in the other surface of the yoke body part  211 , and thus the protrusion part  216  of the yoke  210  adjacent to the other surface of the yoke body part  211  is inserted. 
     That is, in the yokes  210  according to embodiments of the inventive concepts, an area in which the protrusion part  216  and the protrusion groove  217  provides an alternative for solid coupling between adjacent yokes  210  to prevent the separation of the plurality of yokes  210  coupled in a radial direction. 
     Teeth  220  protrude from inner circumferential surfaces of the yokes  210  in a radial direction, and may be continuously disposed in the radial direction from the yoke body parts  211  of the yokes  210  disposed in a circumferential direction to form an overall circular ring shape. 
     Further, because each of the teeth  220  is formed to have a width smaller than that of the yoke body part  211 , coil slots  240  into which hairpin coils  100  are inserted may each be formed between the plurality of teeth  220 . 
     In addition, because the leg portion  120  of the hairpin coil  100  inserted into the coil slot  240  is formed in a trapezoidal shape of which the outside is broad and the inside is narrow, a cross-sectional shape of each of the teeth  220  is formed in a rectangular shape. 
     Accordingly, as illustrated in  FIG. 4 , because each of the teeth  220  is formed in a rectangular shape, a width W 1  of one end which is an insertion direction into the coil slot  240  and a width W 2  of the other end which is a direction opposite the insertion direction into the coil slot  240  are formed to be substantially the same. 
     Accordingly, because a space factor between the leg portions  120  and a stator core  200  increases and a saturation degree of the stator core  200  decreases, magnetic flux density is uniform and thus the output performance of a driving motor may be improved by roughly 3% to 5%. 
     Shoes  230  extend in a circumferential direction from both side surfaces of end portions which extend from the yoke body part  211  of the tooth  220 , and prevent separation of the hairpin coil  100  inserted into the coil slot  240  in a center direction of the yoke body part  211 . 
     The coil slots  240  are formed between the plurality of teeth  220  and allow the hairpin coils  100  to be inserted thereinto, and the coil slots  240  are formed by the teeth  220  and thus the center direction of the yoke body part  211  is opened, and a direction toward the yoke body part  211  and an outer side surface thereof are closed. 
     Further, the coil slot  240  is formed in a trapezoidal shape of which the outside is broad and the inside is narrow to correspond to a cross-sectional shape of the hairpin coil  100 . 
     That is, because the coil slot  240  is formed in the trapezoidal shape along the circumferential direction of the yoke  210  which is formed in a circular shape as a whole, the cross-sectional shape of the teeth  220  is formed in a rectangular shape and thus cross-sectional thicknesses of the teeth  220  are formed to be the same. 
     A support ring  300  surrounds an outer circumferential surface of the stator core  200 , that is, outer circumferential surfaces of the plurality of yokes  210  divided into a plurality in the circumferential direction, and presses and fixes the divided yokes  210  in an axial direction. 
     Accordingly, the support ring  300  may solidly fix the yokes  210  divided into a plurality. 
     Hereinafter, a method of manufacturing the hairpin coils  100  according to one embodiment of the inventive concepts will be described in detail with reference to the accompanying drawings. 
       FIG. 7  is a flow chart illustrating a method of manufacturing the stator assembly of the hairpin winding motor according to one embodiment of the inventive concepts, and  FIGS. 8A to 8D  are assembly drawings illustrating the method of manufacturing the stator assembly of the hairpin winding motor according to one embodiment of the inventive concepts. 
     Referring to  FIGS. 7 and 8A , first, a plurality of hairpin coils  100  continuously connected to each other in the circumferential direction to form a coil winding are provided (S 110 ). 
     In the hairpin coils  100  of the inventive concepts which form the coil winding, raw coils coated with a coating and formed to have a straight length of a predetermined diameter are processed through a coil processor, and have connecting portions connected to each other. 
     Further, referring to  FIGS. 7 and 8B , yokes  210  forming a stator core  200  are inserted into the hairpin coils  100  (S 120 ). 
     Meanwhile, the yokes  210  are continuously connected to each other in the circumferential direction to be inserted radially inward from the outside of the plurality of hairpin coils  100  forming the coil winding. 
     In this case, the plurality of yokes  210  are disposed to be spaced a distance apart from each other 
     An outer diameter D 2  of the plurality of yokes  210  disposed to be the distance spaced apart from each other is formed to be greater than an outer diameter D 1  of the hairpin coils  100 . 
     Further, teeth  220  protrude from the inner circumferential surfaces of the plurality of yokes  210  in the radial direction, and shoes  230  extend in a circumferential direction from both side surfaces of end portions of the teeth  220 , a distance between the shoe  230  and the shoe  230  of the yoke  210  which is disposed adjacent to the shoe  230  is formed to be greater than a thickness of the hairpin coil  100 . 
     Accordingly, the hairpin coil  100  may easily pass through a space between the shoe  230  and the shoe  230  of the yoke  210  which is disposed adjacent to the shoe  230  to be inserted into the coil slot  240 . 
     Further, referring to  FIGS. 7 and 8C , the hairpin coils  100  are moved outward from the inside to be fixed to the coil slots  240  of the yokes  210  (S 130 ). 
     In addition, distances between the shoe  230  of the plurality of yokes  210  and the shoe  230  of the yoke  210  which is disposed adjacent to the shoe  230  are formed to be smaller than the thickness of the hairpin coil  100 . 
     Accordingly, the hairpin coils  100  may solidly prevent the separation from the coil slot  240  in a center direction of the yoke body part  211  of the yoke  210 . 
     Further, a support ring  300  which surrounds the stator core  200  is inserted onto the outer circumferential surface of the stator core  200  (S 140 ). 
     In this case, the support ring  300  which surrounds the stator core  200  is inserted downward in an axial direction when inserted onto the outer circumferential surface of the stator core  200 . 
     Accordingly, the support ring  300  may solidly fix the yokes  210  which are divided into a plurality. 
     Further, an outer diameter D 3  of the hairpin coils  100  is formed to be smaller than the outer diameter D 1  of the hairpin coils  100  in the operation S 120  due to a pressure from the plurality of yokes  210 . 
     As described above, in the stator assembly of the hairpin winding motor according to the inventive concepts, because the stator core  200  is formed of a plurality of divided yokes  210 , the yokes  210  which are adjacent to each other may be easily inserted into the hairpin coils  110  in the radial direction, the hairpin coils  100  may be solidly fixed to the stator core  200 , and assembly productivity of the stator assembly may be improved. 
     Further, because the shoes  230  are formed on the end portions of teeth  220 , cogging torque and torque ripples decrease and thus noise, vibration, and harshness (NVH) decrease, and accordingly, the performance of the driving motor may be improved. 
     In addition, because the leg portion  120  is formed in the trapezoidal shape of which the outside is broad and the inside is narrow, the magnetic flux density of the stator core  200  is uniform by increasing a space factor between the leg portion  120  and the slot, and accordingly, the output performance of the driving motor may be improved. 
     In a stator assembly of a hairpin winding motor according to the inventive concepts, because a stator core is formed of a plurality of divided yokes, the yokes which are adjacent to each other can be easily inserted into hairpin coils in a radial direction, the hairpin coils can be solidly fixed to the stator core, and the assembly productivity of the stator assembly can be improved. 
     Further, because shoes are formed on end portions of teeth, cogging torque and torque ripples decrease and thus noise, vibration, and harshness (NVH) decrease, and accordingly, the performance of a driving motor can be improved. 
     In addition, because a leg portion is formed in a trapezoidal shape of which the outside is broad and the inside is narrow, the magnetic flux density of a stator core is uniform by increasing a space factor between the leg portion and a slot, and accordingly, the output performance of a driving motor can be improved. 
     The inventive concepts are not limited to the above-described embodiments and may be variously modified within the scope of the technical spirit of the inventive concepts.