Abstract:
A method of resin-sealing a laminated core, including inserting permanent magnets  24  into magnet insertion holes  18  of a core body  15 , pressing the body  15  with upper and lower dies  11, 12 , and injecting resin  29  to the holes  18  from a resin reservoir  17  of the die  11  or  12  via a runner  19  in a removable cull plate  14 , one end of the runner  19  having plural resin injection holes  33, 34  per hole  18 . The resin  29  presses the magnets  24  in the holes  18  to one sides in a radial direction of the holes  18 . Thereby, resin-sealing is performed using the plate  14  and the magnets  24  are arranged in radially outward or inward sides even with narrow gaps between the magnets  24  and the holes  18  or without resin injection holes in centers in a width direction of the holes  18.

Description:
TECHNICAL FIELD 
     The present invention relates to a method of resin-sealing a laminated core formed by laminating a plurality of core pieces, in which magnet insertion holes each having a permanent magnet (including unmagnetized one) inserted therein are sealed with resin. 
     BACKGROUND ART 
     In a conventional method of resin-sealing a laminated core, a resin reservoir is provided in an upper die or a lower die, resin inside the resin reservoir is heated, and the resin is pushed out with a plunger and poured into magnet insertion holes formed in the laminated core. Also, to facilitate a removal of resin culls remained on a surface of the laminated core after a resin-sealing process, Patent Literature 1 discloses a technique in which a cull plate including a runner (a resin passage) and a gate hole is placed on the surface of the laminated core and the resin is poured into the magnet insertion holes through the cull plate. 
     Furthermore, in some cases, the laminated core is manufactured such that the permanent magnets inserted in the magnet insertion holes are gathered in a radially outward side or a radially inward side of the laminated core. When the permanent magnets are placed in outward sides of the magnet insertion holes, a motor effective in reducing noises, losses, and oscillations can be manufactured. When the permanent magnets are placed in inward sides of the magnet insertion holes, breakages or damages of the permanent magnets can be avoided (see Patent Literature 2). 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2008-054376 
         Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2006-238584 (FIG. 15, FIG. 19) 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     As shown in  FIG. 5 , if resin is poured from a center in an inward side of a magnet insertion hole  61  into which a permanent magnet  60  is inserted with or without a cull plate, the resin can be stably poured. Particularly, in a case where a laminated core  62  includes resin injection holes  63  each located at the center in the inward side or an outward side of the magnet insertion hole  61 , the permanent magnets  60  are easily pressed to the outward sides or the inward sides of the magnet insertion holes  61 . 
     As shown in  FIG. 6(A) , due to a structural problem of a laminated core  65 , if a resin injection hole  66  is located off a center in a width direction of a magnet insertion hole  67 , a permanent magnet  68  cannot be evenly covered with resin and thereby the permanent magnet  68  is fixed in a way that the permanent magnet  68  is inclined with respect to the magnet insertion hole  67 . 
     In addition,  FIG. 6(B)  shows a case where a resin injection hole is not provided in a center in a width direction of a magnet insertion hole  71  of a laminated core  70 . In this case, even if resin is poured from one part located in a center of a permanent magnet  72 , a narrow gap between a wall surface of the permanent magnet  72  and the magnet insertion hole  71  prevents the resin from evenly flowing, thereby the magnet insertion hole remains unfilled. In light of this, a way of pouring the resin from corners  73 ,  74  each having a large gap between the magnet insertion hole  71  and the permanent magnet  72  is disclosed (see Patent Literature 2). However, this case also causes a problem like the one in the laminated core  65 . The resin does not flow around a center of the wall surface of the permanent magnet  72 , thus the wall surface of the permanent magnet  72  inclines toward a wall surface of the magnet insertion hole  71 . These problems frequently occur in a particular case where plural permanent magnets are inserted in one magnet insertion hole. For example, if one permanent magnet among the plural permanent magnets is fixed in a tilted position, all of the permanent magnets can not be pressed uniformly in the outward side or the inward side of the magnet insertion hole. 
     The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method of resin-sealing a laminated core, in which resin-sealing is performed using a cull plate and permanent magnets can be gathered in a radially outward side or a radially inward side when a gap between the permanent magnets and the magnet insertion hole is narrow or when a center in a width direction of the magnet insertion hole does not include a resin injection hole. 
     Solution to Problem 
     To accomplish the above object, the present invention provides a method of resin-sealing a laminated core, comprising: laminating a plurality of core pieces to form a core body including a plurality of magnet insertion holes circumferentially; inserting permanent magnets into each of the magnet insertion holes of the core body; pressing the core body with an upper die and a lower die in a direction where the core pieces are laminated; and injecting resin to the magnet insertion holes from a resin reservoir provided in the upper die or the lower die via a runner formed in a removable cull plate and thereby fixing the permanent magnets; wherein one end of the runner comprises a plurality of resin injection holes with respect to the one magnet insertion hole, and the injected resin presses the permanent magnets inserted in the magnet insertion holes to one side in a radial direction of each of the magnet insertion holes. 
     In the method of resin-sealing a laminated core according to the present invention, it is possible that a terminal end of the runner includes a penetrated passage vertically penetrating the cull plate, and a part shared by the penetrated passage and the magnet insertion hole forms the resin injection hole. 
     In the method of resin-sealing a laminated core according to the present invention, it is preferable that the plurality of the magnet insertion holes are formed along longitudinal sidewalls of the permanent magnets each having a rectangular cross section. Here, the rectangular includes a rectangular shape with rounded corners or chamfered corners (the same can be applied in the description hereinbelow). 
     In the method of resin-sealing a laminated core according to the present invention, it is preferable that the plurality of the resin injection holes are located in radially inward sides or radially outward sides of the magnet insertion holes. 
     In the method of resin-sealing a laminated core according to the present invention, it is preferable that each of the resin injection holes has an identical cross sectional area. 
     In the method of resin-sealing a laminated core according to the present invention, it is acceptable that each of the resin injection holes has a different cross sectional area. 
     Advantageous Effects of Invention 
     In the method of resin-sealing a laminated core according to the present invention, the end of the runner includes the plural resin injection holes per magnet insertion hole. Thus, even when the gaps between the permanent magnets and the magnet insertion holes are small or when the resin injection holes are not provided in centers in the width direction of the magnet insertion holes, the resin can be freely injected to balanced positions in view of the tilt of the permanent magnets, i.e., positions where the permanent magnets are not tilted. Thereby, the permanent magnets inserted in the magnet insertion holes can be placed one side (i.e., outward side or inward side) in the radial direction of the magnet insertion hole without any influence from shapes of the magnet insertion holes. 
     Particularly, in the method of resin-sealing a laminated core according to the present invention, when a terminal end of the runner includes the penetrated passage vertically penetrating the cull plate and a part shared by the penetrated passage and the magnet insertion hole forms the resin injection hole, the resin flows more smoothly and the tilt of the permanent magnet is surely prevented. In addition, when culls are removed from the cull plate, the resin exposes from a part of the penetrated passage, which makes it advantageously easy to remove the culls. At the same time, the core body is used for a part of the resin injection hole and thus wears of the cull plate can be reduced. 
     Furthermore, the position of the penetrated passage can be freely chosen, and thus the cull plate can be designed in accordance with the shape of the core body. 
     In the method of resin-sealing a laminated core according to the present invention, when the plural resin injection holes are formed along the longitudinal sidewalls of the permanent magnets each having the rectangular cross section, inflow passages of the resin can be surely secured. Even if the permanent magnets are placed in the magnet insertion hole in a tilted manner, the permanent magnets can be certainly pressed to a wall of the magnet insertion hole. 
     Particularly, in the method of resin-sealing a laminated core according to the present invention, when each of the resin injection holes has the identical cross sectional area, the permanent magnets are given a more even force. Thereby, the permanent magnets are more evenly pressed to the wall of the magnet insertion hole. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view of a device used in a method of resin-sealing a laminated core according to a first embodiment of the present invention. 
         FIG. 2  is an explanatory diagram of a method of resin-sealing a laminated core according to a first embodiment of the present invention. 
         FIG. 3  is an explanatory diagram of a method of resin-sealing a laminated core according to a second embodiment of the present invention. 
         FIG. 4  is an explanatory diagram of a method of resin-sealing a laminated core according to a third embodiment of the present invention. 
         FIG. 5  is a plain view explaining a method of manufacturing a laminated core according to a conventional example. 
         FIGS. 6(A) and 6(B)  are explanatory diagrams showing a method of manufacturing a laminated core according to a conventional example, respectively. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Referring to the accompanying drawings, embodiments of the present invention will be described. 
       FIGS. 1(A) and 1(B)  show a resin-sealing device  10  used in a method of resin-sealing a laminated core according to a first embodiment of the present invention. The resin-sealing device  10  includes a pair of an upper die  11  and a lower die  12 . The upper die  11  (or the lower die  12 , or both of the upper and lower dies) includes an unillustrated elevating means to press a core body  15  placed on the lower die  12  via a cull plate (dummy plate)  14  in a lamination direction (a direction in which core pieces are laminated). In this embodiment, a laminated rotor core is described as an example of a laminated core including the core body  15  as an element, but the present invention can be used for a laminated stator core. 
     Also in this embodiment, plural resin reservoirs  17  are provided in the lower die  12  and resin  29  is injected to magnet insertion holes  18  corresponding to the resin reservoirs  17  via the cull plate  14 . Here, the resin  29  (thermosetting resin) can be injected from one resin reservoir  17  to plural magnet insertion holes  18  via a runner  19  formed in the cull plate  17  and plural resin injection holes  33 ,  34 . 
     The core body  15  to be the laminated core is manufactured by punching a magnetic steel plate to produce plural core pieces  21  each having a predetermined shape and laminating and interlocking the core pieces  21 . The core body  15  includes a shaft hole  22  in a center thereof and the plural magnet insertion holes  18  around the shaft hole  22 . Each of the magnet insertion holes  18  includes one or more permanent magnets (unmagnetized)  24  inserted therein in advance. A small gap  26  (0.5-2 mm) is provided between each top end of the inserted permanent magnets  24  and a top end surface  25  of the core body  15 . 
     The resin reservoir  17  provided in the lower die  12  includes a plunger  28 , which is inserted from a bottom of the resin reservoir  17  and moves up and down. Also, the lower die  12  includes a heater for heating the lower die  12 , which can keep the resin  29  inside the resin reservoir  17  dissolved in a predetermined temperature. 
     The detachable cull plate  14  is made of, for example, a hard steel plate or stainless steel plate with a thickness of 3-10 mm. As shown in  FIG. 2 , the cull plate  14  includes a counterbore  30  and the runner  19 , in which the counterbore  30  is dovetailed with the resin reservoir  17  and a base of the runner  19  is continuing to the counterbore  30 . The runner  19  has a channel section opening downward and extends to a center in a longitudinal direction of the magnet insertion hole  18  located in a downstream side. A terminal end in a radially outward side of the runner  19  includes a penetrated passage  32  broadened in a circumferential direction (i.e., a direction perpendicular to the radial direction). A width of the penetrated passage  32  is preferably in a range of 0.2-0.8 times a longitudinal width of the permanent magnet  24 . 
     The penetrated passage  32  penetrates the cull plate  14  vertically and connects with a radially outward area of the runner  19 . The penetrated passage  32  is symmetry with respect to a center line m of the runner  19  in the circumferential direction. Both ends in the circumferential direction of the penetrated passage  32  extending to a radially outward side include areas overlapping with the magnet insertion hole  18  of the core body  15  located above, and the resin injection holes  33 ,  34  having the same size with these areas are provided therein. The resin injection holes  33 ,  34  are arranged bilaterally symmetric with respect to a shaft center of the magnet insertion hole  18 . Furthermore, the resin injection holes  33 ,  34  are located radially inward from the magnet insertion hole  18 . 
     Now, the core body  15  is placed between the upper die  11  and the lower die  12  by the cull plate  14 , the upper die  11  is moved down to sandwich (press) the core body  15  between the upper die  11  and the lower die  12 . Then, the resin  29  stored in the resin reservoir  17  beforehand is ejected by pushing up the plunger  28 . The resin  29  flows from the counterbore  30  to the penetrated passage  32  via the runner  19  and thereafter flows from the resin injection holes  33 ,  34  into the magnet insertion hole  18 . 
     Since the resin injection holes  33 ,  34  are symmetric with respect to the magnet insertion hole  18  in the circumferential direction and located in the radially inward side of the magnet insertion hole  18  such that the resin injection holes  33 ,  34  have the same cross-sectional area, the permanent magnets  24  inside the magnet insertion hole  18  are evenly pressed to the radially outward side and then the resin  29  is cured. In this case, pressure exerted by the resin to the permanent magnets  24  works evenly from side to side, which prevents the permanent magnets  24  from leaning to the magnet insertion hole  18 . 
     When the permanent magnets  24  are arranged in the radially inward side of the magnet insertion hole  18 , as shown in  FIG. 2  with two-dot chain lines, a penetrated passage  36  formed in the radially outward side of the magnet insertion hole  18  is used. An inverted-groove-shaped runner  37  is formed from the counterbore  30  to the penetrated passage  36 . The penetrated passage  36  is symmetric with respect to the magnet insertion hole  18  in the circumferential direction, and parts of the penetrated passage  36  overlapping with the magnet insertion hole  18  are resin injection holes  39 ,  40 . 
     Referring to  FIG. 3 , a description will be given on a method of resin-sealing a laminated core according to a second embodiment of the present invention. In the method according to the second embodiment of the present invention, a penetrated passage  42  continuing to the runner  19  (a center line of which is m) formed in a cull plate  41  is asymmetric with respect to the magnet insertion hole  18  in the circumferential direction (the direction perpendicular to a radius). Also, resin injection holes  43 - 45  are formed in intersections of the penetrated passage  42  and the magnet insertion hole  18 . The resin injection holes  43 - 45  are arranged in both sides in the circumferential direction with the center line m of the runner  19  in a way that an area of the resin injection hole  43  is identical with a total area of the resin injection holes  44 ,  45 . 
     Alternatively, the following option can be taken: provided that the area of the resin injection hole  43  is S1, the areas of the resin injection holes  44 ,  45  are S2, S3, and distances from the center line m to the resin injection holes  43 ,  44 ,  45  are d1, d2, d3, then S1×d1≈S2×d2+S3×d3. By this, the permanent magnets  24  are more evenly pressed to the radially outward side of the magnet insertion hole  18 . 
     Furthermore, when the permanent magnets  24  are arranged in the radially inward side of the magnet insertion hole  18 , the penetrated passage is located in the radially outward area of the magnet insertion hole  18  and the resin injection holes are formed by the intersections of the magnet insertion hole  18  and the penetrated passage. 
       FIG. 4  shows a method of resin-sealing a laminated core according to a third embodiment of the present invention. As shown in the figure, a runner  47  having a groove shape opening downward extends from the counterbore  30  to the radially outward side. The runner  47  extends to near an inward end of a magnet insertion hole  48 , and an end of the runner  47  includes a penetrated passage  49  broadened in a circumferential direction. The penetrated passage  49  is asymmetric with respect to the center line m, and one end of the penetrated passage  49  includes a resin injection hole  50  overlapping with the magnet insertion hole  48 . The magnet insertion hole  49  located in the other end of the penetrated passage  49  includes a groove  52  having an arc-shaped cross section in a vertical direction. The other end of the penetrated passage  49  is overlapped with grove  52 , forming a resin injection hole  53 . 
     In this embodiment, the resin injection hole  50  formed in one side of the penetrated passage  49  and the groove  52  of the resin injection hole  53  formed in the other side of the penetrated passage  49  are approximately the same in a range of ±80%, and the distances thereto from the centerline m are also approximately the same in a range of ±80%. Therefore, the permanent magnets  24  are evenly pressed by the resin injected from the resin injection holes  50 ,  53  to sidewalls of the magnet insertion hole  48 . 
     When the resin injection hole is formed in the radially outward side of the magnet insertion hole, the runner is extended to the radially outward side of the magnet insertion hole, the wide penetrated passage is formed in the circumferential direction, and an end of the penetrated passage is connected to the magnet insertion hole. In this case, (a) the magnet insertion hole is rectangular in cross-section and the penetrated passage overlaps with the magnet insertion hole or (b) a recess (vertical groove) is formed inside the magnet insertion hole and the penetrated passage communicates with the recess. 
     In other words, in the above-described embodiments, the plural resin injection holes are formed along longitudinal sidewalls of the permanent magnets having rectangular cross sections. 
     The present invention is not limited to the above-described embodiments, but can include modifications within a scope of the present invention. For example, the position of the counterbore can be changed. The runner does not need to continue to the base of the counterbore, the runner can continue to the inside of the counterbore. 
     In the above-described embodiments, the resin reservoir is provided in the lower die. However, the present invention can be used in a case where the resin reservoir is provided in the upper die. 
     In addition, the present invention can be used in a case where the resin is injected from one resin reservoir to the plural magnet insertion holes. 
     Furthermore, it is obvious to form the cull plate with one material plate, but the cull plate can be formed with the two material plates or three or more of the material plates. 
     REFERENCE SIGNS LIST 
       10 : resin-sealing device,  11 : upper die,  12 : lower die,  14 : cull plate,  15 : core body,  17 : resin reservoir,  18 : magnet insertion hole,  19 : runner,  21 : core piece,  22 : shaft hole,  24 : permanent magnet,  25 : top end surface,  26 : gap,  28 : plunger,  29 : resin,  30 : counterbore,  32 : penetrated passage,  33 ,  34 : resin injection hole,  36 : penetrated passage,  37 : runner,  39 ,  40 : resin injection hole,  41 : cull plate,  42 : penetrated passage,  43 - 45 : resin injection hole,  47 : runner,  48 : magnet insertion hole,  49 : penetrated passage,  50 : resin injection hole,  52 : groove,  53 : resin injection hole