Abstract:
Disclosed is a split stator manufacturing method, which is enabled to enhance a production efficiency and to charge a thermoplastic resin between an insulator and a coil by molding the resin. The split stator manufacturing method comprises a setting step of setting an insulator and a split stator core element in a stationary mold and setting an edgewise coil in a movable mold, a resin injecting step of injecting a resin into a cavity with the stationary mold and the movable mold being half-opened, and a clamping step of clamping the stationary mold and the movable mold.

Description:
This is a 371 national phase application of PCT/JP2009/050413 filed 15 Jan. 2009, claiming priority to Japanese Patent Application No. 2008-007336 filed 16 Jan. 2008, the contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a method of manufacturing a split stator of a motor, suitable for manufacture with short takt time. 
     BACKGROUND OF THE INVENTION 
     There is known a method of manufacturing a stator by making a stator core of laminated steel plates each farmed by press punching, mounting a winding thereon, and coating a winding part and others with resin by injection molding. 
     On the other hand, there is also known another method of manufacturing a stator by using split stator members each including a split stator core element attached with a winding. Those split stator members are combined in one assembly with a shrink fit ring.
     Patent Literature 1 discloses a method of manufacturing a split stator member by coating a split core element by resin molding.   

     Specifically, it is disclosed that a winding is wound around a split core element having one teeth portion, the wound coil is pressed toward a central axis of the teeth portion and shaped by a press die and simultaneously resin molding is performed by injecting resin into an injection molding mold doubling as the press die. 
     This technique advantageously could increase a space factor of the coil. Furthermore, it is only necessary to coat only the coil with resin. The technique also advantageously could reduce an amount of resin used for the resin molding as compared with a conventional stator. 
     CITATION LIST 
     Patent Literature 
     
         
         JP 2007-143324 A 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, the invention disclosed in Patent Literature 1 would have the following disadvantages. 
     Concretely, Patent Literature 1 has no description relating to an insulator. If an insulator has been placed between the split core element and the winding, the winding is pressed by the press die and thus the resin could not enter between the insulator and the winding during injection molding. In a finished stator, the insulator and the winding are likely to directly contact with each other. 
     On the other hand, downsizing of a motor of a hybrid electric vehicle advances, showing a tendency of increasing a working current range. In this case, the amount of heat of the winding increases. Heat dissipation becomes more important because an enamel coating of the winding has an upper temperature limit. 
     Accordingly, it is necessary to bring the insulator and the stator core element in close contact with each other and particularly supply high heat-conductive resin between the insulator and the winding. This is because the heat has to be dissipated to a stator core side through a resin molded portion and the insulator. 
     In the case of using heat-hardening resin as a resin molding material, hardening takes several minute. Accordingly, it may be arranged to pressurize the resin to be injected to thereby cause the resin to enter between the insulator and the winding. 
     However, for example, if thermoplastic resin heated to a molten state at 300° C. is used to shorten a takt time to thereby enhance production efficiency, the resin is cooled and hardened in several tens of seconds by a mold heated at about 150° C. On the other hand, the thermoplastic resin has a viscosity of 100 Pa·sec, which is 20 to 100 times higher than the heat-hardening resin. The several tens of seconds are insufficient for the molten resin to sufficiently enter in a narrow gap. This causes a filling failure or shortage between the insulator and the winding. 
     The present invention has been made to solve the above problems and has a purpose to provide a method of manufacturing a split stator member including resin molding with thermoplastic resin to enhance production efficiency and surely fill the rein between an insulator and a winding. 
     Solution to Problem 
     (1) To achieve the above purpose, the invention provides a split stator manufacturing method comprising the steps of: setting an insulator and a split core element in a first mold and setting a formed coil in a second mold; injecting resin in a cavity while the first mold and the second mold are in a half-open state; and clamping the first and second molds together while keeping fluidity of the resin. 
     (2) In the split stator manufacturing method set forth in (1), preferably, the mold clamping step is started in process of the resin injecting step. 
     (3) The split stator manufacturing method set forth in (1), preferably, further comprises the step of compressing the injected resin by only the formed coil between the resin injecting step and the mold clamping step. 
     (4) In the split stator manufacturing method set forth in (3), preferably, the compressing step and the mold clamping step are started in process of the resin injecting step. 
     (5) In the split stator manufacturing method set forth in (3) or (4), preferably, the formed coil is vibrated in a direction of moving closer to or away from the insulator. 
     (6) In the split stator manufacturing method set forth in one of (1) to (5), preferably, the resin is thermoplastic resin. 
     Advantageous Effects of Invention  
     Next, operations and advantages of the split stator manufacturing method of the invention having the above configurations will be explained. 
     In the first step of the split stator manufacturing method of the invention, the split core element is set in the first mold (e.g., a fixed mold) and further the insulator is set on the split core element. On the other hand, the formed coil (e.g., a formed edgewise coil) is set in the second mold (e.g., a movable mold). 
     While the first mold and the second mold are in the half-open state, molten resin for resin molding is injected into the cavity defined between the first and second molds. This can temporarily form a space between the formed coil and the insulator, thereby allowing the molten resin to flow in the space between the formed coil and the insulator at that timing. 
     Then, the first mold in which the insulator is set on the split core element and the resin is injected over the insulator and the second mold in which the fanned coil is set are clamped. 
     As the first mold and the second mold move closer, the resin is pressed to flow upward in the space between the formed coil and the insulator by use of inclination. Accordingly, the formed coil moves into the molten resin supplied on the insulator, the mold clamping can be conducted while the molten resin exists between the insulator and the coil. 
     Consequently, the stator coated by resin molding can include the resin reliably filled between the insulator and the coil. 
     Since the molten resin is injected while the first mold and the second mold are in the half-open state, resin pressure can be reduced and thus deformation of the coil and others is reduced. 
     Herein, the mold clamping step is started in process of the resin injecting step. Thus, while the first mold and the second mold are clamped together, the resin is injected. This causes the resin to more efficiently flow between the insulator and the coil. Specifically, when the resin is first injected and then the mold clamping is performed, the resin is accumulated on the insulator and the coil moves therein. However, only small gaps finally exist between the insulator and the coil and therefore, in some cases, the resin could not flow into upper gaps. In this regard, since the resin is being injected during the mold clamping step, the resin can be reliably filled in small gaps between the insulator and the coil. In particular, it is preferable to continue resin injection to the end of the mold clamping step. 
     Furthermore, the compressing step is provided to compress the injected resin by only the formed coil between the resin injecting step and the mold clamping step. Accordingly, it is possible to move only the coil into the molten resin accumulated on the insulator, thereby reliably filling the resin in small gaps between the insulator and the coil. 
     Moreover, the compressing step and the mold clamping step are started in process of the resin injecting step. Accordingly, while the resin is being injected, the coil is moved in the injected resin, so that the resin can be filled more efficiently and more reliably in small gaps between the insulator and the coil. 
     Moreover, the formed coil is vibrated in the short-side direction of the coil while the formed coil is moved into the molten resin. This can increase the fluidity of the resin. In general, resin has a high viscosity and hence is hard to flow when sticks to the surface of the edgewise coil. 
     In the invention, however, firstly, the gaps between the insulator and the formed coil are changed and thus the resin is made easy to flow. Secondly, the resin is vibrated in a direction that separates the resin from the surface of the edgewise coil. Accordingly, the resin is unlikely to stick to the surface of the edgewise coil, increasing the fluidity of the resin. 
     This makes it possible to reliably fill even the resin having low fluidity such as thermoplastic resin in small gaps between the insulator and the edgewise coil. Herein, the vibration in the short-side direction of the coil is generated by for example an ultrasonic generating horn. 
     In the case where the resin is thermoplastic resin, particularly, the fluidity is low. It is therefore difficult to reliably fill the resin in small gaps between the insulator and the coil. On the other hand, according to the above invention, even when the thermoplastic resin is used, the resin can be reliably filled in small gaps between the insulator and the coil. 
     Specifically, thermoplastic resin has a melt viscosity of about 100 Pa·sec and heat hardening resin has a melt viscosity of about 1 to 5 Pa·sec. Thus, the thermoplastic resin has poor fluidity twenty times lower than the thermoplastic resin. In addition, the thermoplastic resin needs heating to harden even when it is injected in a mold heated at about 150° C. Such hardening takes about 2 to 3 minutes. On the other hand, when the thermoplastic resin heated at about 300° C. is injected into the mold heated at about 150° C., it is cooled and hardens in several tens of seconds. 
     In the case of using the thermoplastic resin, accordingly, the conventional manufacturing method could not surely fill the resin in small gaps between the insulator and the coil. 
     To the contrary, according to the invention, even when the thermoplastic resin is used as a material, the resin can be reliably filled in small gaps between the insulator and the coil. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view showing a manufacturing procedure of a split stator; 
         FIG. 2  is a view showing a stator assembled of eighteen split stator members shrunk fit by an outer ring; 
         FIG. 3  is a sectional view of a split stator member; 
         FIG. 4  is a view showing a first step in a first embodiment of the split stator manufacturing method of the invention; 
         FIG. 5  is a view showing a second step in the first embodiment of the split stator manufacturing method of the invention; 
         FIG. 6  is a view showing a third step in the first embodiment of the split stator manufacturing method of the invention; 
         FIG. 7  is a view showing a fourth step in the first embodiment of the split stator manufacturing method of the invention; 
         FIG. 8  is a view showing a second embodiment of the split stator manufacturing method of the invention; 
         FIG. 9  is a perspective view showing a structure of a movable mold holding an edgewise coil; 
         FIG. 10A  is a perspective view showing a structure to hold the edgewise coil by a coil holding block; 
         FIG. 10B  is a perspective view showing a state where the coil holding block holds the edgewise coil; 
         FIG. 11  is a view showing a state where a split stator core element and an insulator are mounted in a fixed mold; 
         FIG. 12  is a view showing a relationship of the split stator core element and the insulator mounted in the fixed mold with respect to the edgewise coil; 
         FIG. 13  is a view showing a state where the edgewise coil is mounted in the fixed mold; 
         FIG. 14  is a view showing a state where the edgewise coil of  FIG. 13  is coated with resin; 
         FIG. 15  is a partial sectional view showing a state where the fixed mold and the movable mold are clamped; 
         FIG. 16  is a view showing a relationship between the coil holding block and a ultrasonic generating horn; 
         FIG. 17  is a time chart in the second embodiment; 
         FIG. 18  is a time chart in another example of the first embodiment; and 
         FIG. 19  is a time chart in the first embodiment. 
     
    
    
     REFERENCE SIGNS LIST 
     
         
           10  Split stator core element 
           11  Teeth portion 
           12  Insulator 
           13  Edgewise coil 
           13   a ,  13   b  Long end 
           18  Split stator member 
           20  Coil holding block 
           21  Fixed mold 
           21   a ,  21   b  Slide mold 
           21   c  Guide mold 
           21   d  Fixed-mold main body 
           22  Movable mold 
           22   a  Protruding portion 
       
    
     DETAILED DESCRIPTION 
     A detailed description of a preferred embodiment of a split stator and a split stator manufacturing method embodying the present invention will now be given referring to the accompanying drawings. 
       FIG. 1  shows a manufacturing procedure of a split stator member. A split stator core element (“core element”)  10  includes a teeth portion  11  on which a formed coil is mounted. The core element  10  is formed of steel plates made by press punching and laminated in layers. Herein, the core element  10  is designed so that eighteen core elements are assembled into an annular stator core. In  FIG. 1 , (a) shows the core element  10  and (b) shows a state where an insulator  12  is set on a teeth portion  11  of the core element  10 . The insulator  12  includes a sleeve part  12   b  covering the teeth portion  11 , a cover part  12   a  covering an inner surface portion of the teeth portion  11  of the core element  10  excepting a protruding portion and vertically extending, and two ribs  12   c  protruding upward and downward from the sleeve part  12   b  respectively. Herein, the insulator  12   b  has a side wall thickness of 0.2 to 0.3 mm. 
     In  FIG. 1 , (c) illustrates a state where a formed edgewise coil  13  is mounted on the teeth portion  11  through the sleeve part  12   b  of the insulator  12 . The edgewise coil  13  is made of a coil wire having a flat rectangular cross section and is formed to have inner sides according to the shape of the teeth portion  11 . 
     The edgewise coil  13  is held in close contact with the core element  10  through the cover part  12   a . The edgewise coil  13  is positioned in a lateral direction by the teeth portion  11  through the sleeve part  12   b  and in a vertical direction by the protrusions  12   c  of the insulator  12 . Thus, the edgewise coil  13  is located in place with respect to the core element  10 . The edgewise coil  13  includes a long end  13   a  protruding upward near the cover part  12   a  and another long end  13   b  protruding upward near an end face of the teeth portion  11 . 
     This embodiment exemplifies the edgewise coil  13  as a formed coil. As alternatives, any other coils each having a finished form may be adopted irrespective of circular or rectangular in cross section. 
     In  FIG. 1 , (d) shows a resin-molded split stator member  18  in which a resin molded portion  14  is formed around the edgewise coil  13  shown in (c). A method of forming the resin molded portion  14  will be explained later in detail. The pair of long ends  13   a  and  13   b  protrudes from the resin molded portion  14  of the split stator member  18 .  FIG. 3  shows a sectional view of the resin-molded split stator member  18 . This sectional view shows a positional relationship between the edgewise coil  13  and the resin molded portion  14 . 
     The edgewise coil  13  is mounted on the core element  10  through the insulator  12  and the resin molded portion  14  is formed only around a coiled portion of the edgewise coil  13 .  FIG. 3  shows a state where bus bar holders  16  ( 16 A,  16 B,  16 C) made of resin for holding bus bars  17  ( 17 A,  17 B,  17 C) are attached on the core element  10 . The long ends  13   a  and  13   b  are connected to the bus bars  17 . 
       FIG. 2  shows a stator  19  assembled of eighteen split stator members  18 . Specifically, eighteen split stator members  18  are combined in annular form and attached from outside with an outer ring  15  that has been heated and expanded to have an enlarged inner diameter. When this assembly is cooled in room temperature and the inner diameter of the outer ring  15  contracts, the eighteen split stator members  18  are shrink fitted, integrally forming the stator  19 . This is so-called shrink fitting of the outer ring. 
     In the next step, not illustrated, the long end  13   a  of one split stator member  18  is connected to the long end  13   b  of a third split stator member  18  by skipping two split stator members leftward, through the bus bar  17  in the bus bar holder  16 . In this way, the long ends of eighteen split stator members  18  are sequentially connected through the bus bars  17  in the bus bar holders  16  to form three motor coils of U phase, V phase, and W phase. 
     Next, the split stator manufacturing method of the invention to manufacture the split stator member  18  will be explained.  FIGS. 4 to 7  show steps in the first embodiment of the split stator manufacturing method of the invention.  FIG. 12  shows a relationship between the core element  10  and the insulator  12  set in a fixed mold  21  and the edgewise coil  13 . 
     A molding mold structure for forming the resin molded portion is first explained. As shown in  FIGS. 4 and 12 , the fixed mold  21  serving as a first mold includes a main body  21   d , a pair of slide molds  21   a  which will hold the core element  10  from either side thereof, a pair of guide parts  21   c  protruding from the main body  21   d , and a slide mold  21   b  slidable along the pair of guide parts  21   c.    
     The core element  10  is sandwiched between the pair of slide molds  21   a  from either side and fixed by the slide mold  21   b  in a direction perpendicular to the holding direction of the slide molds  21   a . On the teeth portion  11  of the core element  10 , the insulator  12  is mounted. 
     On the other hand,  FIGS. 10A and 10B  show the shape of the formed edgewise coil  13 .  FIGS. 10A and 10B  are perspective views showing a structure of a coil holding block  20  for holding the edgewise coil  13 . 
     As shown in  FIG. 10A , the edgewise coil  13  includes two long ends  13   a  and  13   b . The almost cube-shaped coil holding block  20  is formed with holes  20   a  and  20   b  in which the long ends  13   a  and  13   b  of the edgewise coil  13  are inserted and fitted. This block  20  is further formed with a slant portion  20   c  on one side. 
       FIG. 10B  shows a state where the end portions of the long ends  13   a  and  13   b  of the edgewise coil  13  are inserted and fitted in the holes  20   a  and  20   b  of the coil holding block  20 . In a manufacturing step, many coil holding blocks  20  are prepared in such a way that the edgewise coils  13  are individually set in advance as in the state of  FIG. 10B . After completion of a later molding step, the coil holding block  20  is collected and will be reused as a jig any number of times. 
     The fixed mold  21  and the movable mold  22  in this embodiment are configured as a laterally clamping mold in which the movable mold is horizontally moved. 
     While the core element  10  is fixed in the fixed mold  21  as shown in  FIG. 4  and the movable mold  22  serving as an upper mold is fully opened, the coil holding block  20  is attached to the movable mold  22 . Thus, the coil holding block  20  constitutes part of the movable mold  22  and the edgewise coil  13  is held in a position shown in  FIG. 4 , that is, at a distance of 1.5 mm apart from the movable mold  22  toward the fixed mold  21 . 
     As shown in  FIG. 16 , furthermore, the movable mold  22  is attached with an ultrasonic generating horn  30  in a position facing a side surface of the coil holding block  20 . 
     The movable mold  22  is formed with a pair of protruding portions  22   a  each having an acute-angled triangular shape in section. The inner surfaces of the protruding portions  22   a  are located near the outer periphery of the edgewise coil  13  with a slight clearance therebetween. 
     Subsequently, the movable mold  22  is moved toward the fixed mold  21  into a half-open state shown in  FIG. 5 . In this half-open state, the fixed mold  21  and the movable mold  22  are apart by 3 mm from a fully closed position. In this state, the edgewise coil  13  is located in an intermediate position between the movable mold  22  and the fixed mold  21 . 
     While the movable mold  22  is in the half-open state shown in  FIG. 5 , a resin injection device not shown starts injection of PPS resin  25  that is a thermoplastic resin molten at 320° C. into a cavity. The PPS resin  25  is injected and supplied into the cavity through two injection ports  21   e  formed in the fixed-mold main body  21   d . The injection ports  21   e  are located outside of the insulator  12 . The injected resin will flow over the insulator  12  to the center of each end of the edgewise coil  13  (in its longitudinal direction).  FIG. 15  is a partial sectional view showing a state where the fixed mold  21  and the movable mold  22  are clamped. 
     The molds in this embodiment are a laterally clamping type and thus the injected resin flows in a longitudinal direction of the edgewise coil  13 . In  FIG. 5 , the PPS resin  25  is illustrated for convenience but a flow pathway of the flowing PPS resin  25  is complicated. 
       FIG. 13  is an imaginary view showing that the edgewise coil  13  is set in the fixed mold  21 .  FIG. 14  shows a state where the coil  13  of  FIG. 13  is formed with the resin molded portion  14 . 
       FIG. 19  is a time chart of an injection step in the first embodiment. A total time period of the injection step is as very short as 0.2 second. Even though the fixed mold  21  and the movable mold  22  are heated at 150° C., the PPS resin  25  which is thermoplastic resin is hardened in short time. The total injection period is therefore set to a very short time. 
     In a period from 0.05 to 0.12 seconds from the start of injection of the PPS resin  25 , as shown in  FIG. 6 , the coil holding block  20  is moved by 1.5 mm toward the fixed mold  21 . In this state, the edgewise coil  13  is vibrated laterally as indicated by arrows A in  FIG. 6  by the ultrasonic generating horn  30  through the coil holding block  20 . Herein, a vibration time period is as very short as 0.07 seconds and thus the ultrasonic vibration can only apply small oscillations. 
     Accordingly, the edgewise coil  13  is brought into contact with the insulator  12  set in the fixed mold  21  as shown in  FIG. 6 . 
     During this period, the PPS resin  25  is being injected through the injection ports  21   e . The PPS resin  25  flows in gaps between the insulator  12  and the edgewise coil  13  while its fluidity is increased by the laterally vibrating edgewise coil  13 . Specifically, if the PPS resin  25  having a high viscosity sticks to the surface of the edgewise coil  13 , the resin  25  becomes hard to flow. In this embodiment, however, vibration is applied to the PPS  25  in a direction that separates the PPS resin  25  from the surface of the edgewise coil  13 . The PPS resin  25  is therefore unlikely to stick to the surface of the edgewise coil  13  and hence the fluidity of the PPS resin  25  is increased. 
     This makes it possible to reliably fill even the resin having low fluidity such as thermoplastic resin in small gaps between the insulator  12  and the edgewise coil  13 . 
     After a lapse of 0.12 seconds from the injection start of the PPS resin  25 , movement of the edgewise coil  13  toward the fixed mold  21  is stopped and simultaneously movement of the movable mold  22  toward the fixed mold  21  is started to perform mold compression. This mold compression is terminated after a lapse of 0.27 seconds from the injection start. In this period, the injection of the PPS resin  25  is stopped after a lapse of 0.20 seconds from the injection start. A clamping pressure of 800 kN is kept for 5 seconds after the end of the mold compression. 
     After a lapse of 0.12 to 0.27 seconds from the injection start, the PPS  25  is injected until a lapse of 0.20 seconds from the injection start. After a lapse of 0.12 to 0.20 seconds from the injection start, while the PPS resin  25  is being injected, mold compression is performed to fully fill the PPS resin  25  in small gaps between the edgewise coil  13  and the inner surfaces of the protruding portions  22   a  of the movable mold  22 . 
     It is then waited until the PPS resin  25  is hardened, and thereafter the movable mold  22  is moved upward. 
     In the embodiment mentioned above, the edgewise coil  13  is laterally vibrated in moving into the PPS resin  25 . Alternatively, as shown in a time chart in  FIG. 18 , the edgewise coil  13  may be moved in the PPS resin  25  without being laterally vibrated. 
     According to the split stator manufacturing method in the present embodiment, as explained above in detail, in the first step, the core element  10  is set in the fixed mold  21  and the insulator  12  is set on the core element  10 . On the other hand, the edgewise coil  13  is set in the movable mold  22 . 
     Successively, while the fixed mold  21  and the movable mold  22  are in the half-open state, injection of molten resin for resin molding into the cavity is started. 
     Furthermore, a compressing step is conducted to compress the injected resin by only the edgewise coil  13 . 
     In this compressing step, only the edgewise coil  13  can be moved into the molten resin staying in the cavity. This can more reliably fill the PPS resin  25  in small gaps between the insulator  12  and the edgewise coil  13 . 
     In particular, while the molten PPS resin  25  is moved into the edgewise coil  13 , the edgewise coil  13  is vibrated in a short-side direction of the coil (i.e., in a direction of moving closer to or away from the insulator  12 ), thereby changing the gaps between the insulator  12  and the edgewise coil  13 . Thus, the PPS resin  25  is allowed to smoothly flow. Since the fluidity of the PPS resin  25  is enhanced, the PPS resin  25  can be more reliably filled in the small gaps between the insulator  12  and the edgewise coil  13 . Herein, the edgewise coil  13  is vibrated in the direction that separates the PPS resin  25  from the surface of the edgewise coil  13 . Accordingly, the PPS resin  25  is unlikely to stick to the surface of the edgewise coil  13  and hence the fluidity of the PPS resin  25  is increased. 
     Since the compressing step and the mold clamping step are started in process of the resin injecting step, the edgewise coil  13  is moved into the PPS resin  25  while the PPS resin  25  is being injected. It is consequently possible to more efficiently and more reliably fill resin in small gaps between the insulator  12  and the edgewise coil  13 . 
     A second embodiment will be explained below. The second embodiment is substantially identical to the first embodiment and describes only differences therefrom. The same contents are not explained below. 
     The second embodiment is directed to a manufacturing method that does not include the step of compressing the PPS resin  25  by only the edgewise coil  13 . To be concrete, while the edgewise coil  13  is held in a final position by the coil holding block  20  with respect to the movable mold  22  from the beginning, the movable mold  22  is moved close to the fixed mold  21  to directly perform mold compression. 
       FIG. 17  is a time chart of an injecting step. A total time period of the injecting step is as very short as 0.2 second. The fixed mold  21  and the movable mold  22  have been heated at 150° C. However, the PPS resin  25  which is thermoplastic resin is hardened in short time and thus the total injection time is set to be very short. 
     After a lapse of 0.05 to 0.20 seconds from the start of injection of the PPS resin  25 , as shown in  FIG. 8 , the movable mold  22  is moved close to the fixed mold  21  to perform mold compression. After a lapse of 0.20 seconds from the injection start, the mold compression and the injection of the PPS resin  25  are stopped at the same time. A clamping pressure of 800 kN is kept for  5  seconds after the end of the mold compression. 
     After a lapse of 0.05 to 0.20 seconds from the injection start, while the PPS resin  25  is being injected, the mold compression is performed by moving the edgewise coil  13  into the PPS resin  25  injected and accumulated in the cavity. This can cause the PPS resin  25  to move or flow in small gaps between the insulator  12  and the edgewise coil  13 . 
     Simultaneously, the PPS resin  25  is also sufficiently filled in small gaps between the edgewise coil  13  and the inner surfaces of the protruding portions  22   a  of the movable mold  22 . 
     It is then waited until the PPS resin  25  is hardened, and thereafter the movable mold  22  is moved upward. 
     According to the second embodiment, as explained above in detail, without adopting a complicated step of first moving the edgewise coil  13  into the PPS resin  25  in the cavity, it is possible to fill the PPS resin  25  in small gaps between the insulator  12  and the edgewise coil  13  to a certain degree. 
     The molten PPS resin  25  is injected while the fixed mold  21  and the movable mold  22  are in a half-open state. Accordingly, resin injection does not need large pressure and hence no pressurizing device is required. 
     Since the mold clamping step is started in process of the resin injecting step, the PPS resin  25  is injected while the fixed mold  21  and the movable mold  22  are being clamped. Thus, the PPS resin  25  is caused to more efficiently flow into gaps between the insulator  12  and the edgewise coil  13 . 
     In the case where the PPS resin  25  is injected first and then the mold clamping is performed, the PPS resin  25  is accumulated in the cavity and the coil is moved therein. However, only small gaps finally exist between the insulator and the coil and therefore, in some case, the resin could not flow into upper gaps. In this regard, since the PPS resin  25  is being injected during the mold clamping step, the resin can be reliably filled in small gaps between the insulator  12  and the edgewise coil  13 . In particular, the resin injection is preferably continued partway in the mold clamping step. 
     Since the split stator members  18  are individually shaped, a molding cavity in one injection molding is small in size. Thus, low fluidity resin such as thermoplastic resin can be used directly. A motor for driving a hybrid electric vehicle needs high torque, flows a relatively high voltage, and generates a large amount of heat. Thus, heat conductivity of the resin molded portion has to be enhanced. For this end, additives are added to the resin, resulting in decreased fluidity. It is therefore technically difficult to fill such resin in every corner of the molding cavity, in particular, in the internal space of the wound portion of the coil without gaps. 
     According to the split stator member of the invention, the volume of the molding cavity is small, so that the resin can be reliably filled in every corner of the internal space of the wound portion of the coil. Thus, the efficient of dissipating the heat from the coil outward through the resin molded portion can be enhanced. 
     The present invention is not limited to the above embodiments and may be embodied in other specific forms without departing from the essential characteristics thereof. 
     For instance, the above embodiment describes the core element  10  including one edgewise coil  13 . In an alternative, a split stator core element may be configured to have two teeth portions  11  so that two edgewise coils  13  are mounted on the teeth portions  11  respectively, and the entire assembly is coated by resin molding. In another alternative, a split stator core element may be configured to have three teeth portions  11  so that three edgewise coils  13  are mounted on the teeth portions  11  respectively, and the entire assembly is coated by resin molding. 
     As explained in the above embodiments, the invention may be applied to any formed coils whose winding cross section is of a circular, square, or another shape as well as the edgewise coil mentioned in the embodiments. 
     The above embodiments explain the case of using thermoplastic resin. As an alternative, the invention may be applied to the case of using heat hardening resin.