Patent Publication Number: US-2005127774-A1

Title: Electric motor

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to the insulation of a coil inserted into a stator core slot of an electric motor.  
      2. Description of the Patented Art  
       FIGS. 3 and 4  are views showing a method of insulating a coil, inserted into a slot of a stator core, which is commonly used.  FIGS. 3 and 4  show examples of the stator core of a linear motor. In the example shown in  FIG. 3 , the coil  3  inserted into the slot  2  of the stator core  1  is previously wrapped in a sheet of insulating paper  4 . The coil  3  previously wrapped in the sheet of insulating paper  4  is inserted into the slot  2  of the stator core  1  and then molded by a resin  5  having an insulating property. In this case, there is a possibility that a step portion is generated at the end portion  4   a  of the sheet of insulating paper  4 , so that a void  6 , in which the resin  5  is not filled, is formed.  
      In the example shown in  FIG. 4 , the coil  3  is wrapped by the sheet of insulating paper  4  except for a portion of the coil  3  located on the opening portion side of the slot  2  of the stator core  1  and inserted into the slot  2 . After that, the sheet of insulating paper  4   b  functioning as a lid is inserted into the slot  2 . After insulating operation has been conducted, before molding, in this way, the coil  3  is molded by the resin  5  having an insulating property. In this case, the sheet of insulating paper  4   b  forming the lid in the opening portion side of the slot  2  can prevent the resin  5  from entering a bottom portion of the slot  2 . Accordingly, there is a possibility that a void  6 , which is not filled with the resin, is generated in the bottom portion of the slot  2  below the sheet of insulating paper  4   b  forming the lid.  
      Concerning the method of insulating the coil inserted into the slot of the stator core, the aforementioned method is commonly used, and a method of insulation, and an electric motor related to the present invention described later, have not been discovered.  
      As described before, in the conventional case of insulation of the coil inserted into the slot, there is a high possibility that a void is generated in the slot. According to the method of previously wrapping the coil  3  in the sheet of insulating paper  4  and inserting the coil  3  into the slot  2  of shown in  FIG. 3 , there is a possibility that a void is generated in the end portion  4   a  of the sheet of insulating paper  4 . According to the method shown in  FIG. 4 , there is a high possibility that a void  6  is generated in the lower region (on the bottom side of the slot) of the sheet of insulating paper  4   b  forming the lid. In the case of using an electric motor in which insulation is placed between the coil  3  and the stator core  1  by the method described above, if a void is generated between the coil  3  arranged in the slot  2  and the stator core  1 , an electric charge is concentrated upon this portion and the dielectric breakdown may result.  
      It is an object of the present invention to provide an electric motor, the dielectric strength of which is enhanced by removing the void or reducing the generation of the void.  
     SUMMARY OF THE INVENTION  
      According to the present invention, a coil is wrapped in a sheet of insulating paper arranged along an inner face profile of a slot and open to a slot opening portion, and is arranged in a stator core. Insulating resin is filled into the slot of the stator core. Further, when it is composed in such a manner that the thickness of the insulating resin in the direction from an end portion of the coil to the opening portion of the slot is formed to be not less than the thickness of the insulating resin necessary to insulate the coil, the coil can be positively insulated from the stator core.  
      The sheet of insulating paper is not provided with folded and bent portions in the direction in which a bubble of air is generated at the time of filling the insulating resin into the slot.  
      As the sheet of insulating paper is open onto the opening portion side of the stator core, when the insulating resin is filled into the stator core, air in the stator core can be smoothly discharged from the opening portion of the stator core without staying in the stator core. Therefore, no voids are generated or the generation of void is reduced.  
      Since no voids are generated or the generation of voids is reduced, it is possible to provide an electric motor, the dielectric strength of which is high. As it is unnecessary to wrap the coil in the sheet of insulating paper and to attach a lid of the insulating paper on the slot, it is possible to reduce the number of manufacturing process, and further a quantity of insulating paper can be decreased. Accordingly, the cost of manufacturing an electric motor can be reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1   a  is a schematic illustration showing a primary portion of the first embodiment of the present invention applied to a linear motor.  
       FIG. 1   b  is a schematic illustration showing a primary portion of the first embodiment of the present invention applied to a linear motor.  
       FIG. 2  is a schematic illustration showing a primary portion of the second embodiment of the present invention applied to a rotary type electric motor.  
       FIG. 3  is a schematic illustration for explaining a conventional method of insulation between a stator core and a coil.  
       FIG. 4  is a schematic illustration for explaining another conventional method of insulation between a stator core and a coil. 
    
    
     DETAILED DESCRIPTION  
       FIGS. 1   a  and  1   b  are schematic illustrations showing a primary portion of an embodiment of the present invention applied to a linear motor.  FIG. 1   a  is a view showing a state before molding of insulating resin, and  FIG. 1   b  is a view showing a state after molding of insulating resin. Reference numeral  1  designates a stator core, and reference numeral  2  designates a slot provided in the stator core  1 . Reference numeral  3  designates a coil, and reference numeral  4  designates a sheet of insulating paper. In this connection, the same parts in  FIGS. 1   a  and  1   b  are indicated by same reference numerals as in  FIGS. 3 and 4  in which the conventional examples are shown.  
      The coil  3  is inserted into each slot  2  of the stator core  1  in such a manner that the coil  3  is wrapped in the sheet of insulating paper  4  which is arranged along an inner face profile of the slot except for the opening portion side of the slot  2 . This state of insertion of the coil  3  is illustrated in  FIG. 1   a.  As shown in  FIG. 1   b,  on the opening portion side of the slot  2 , under the condition that the coil  3  is not wrapped in the sheet of insulating paper  4 , molding is conducted on the stator so that the opening portion of the slot  2  can be closed by the insulating resin  5  having an insulating property. In this case, it is composed in such a manner that the thickness of the insulating resin  5  from the end portion  3   a  of the coil  3  in the opening portion of the slot  2 , that is, the thickness of the insulating resin  5  from the end portion  3   a  of the coil  3  in the direction of the depth of the slot is large sufficient to insulate the coil  3 .  
      At the time of molding, the resin  5  enters into the slot  2 , and air is discharged from the slot. At this time, as one end portion of the slot  2  is open as shown in  FIG. 1   a,  air can be smoothly discharged from the slot  2 . Accordingly, there is little possibility of the generation of a void. In the case of the conventional example shown in  FIG. 3 , there is a possibility that a void is generated, as follows. There is a step portion at the end portion  4   a  of the sheet of insulating paper  4 . Therefore, when air flows, to be discharged, toward the opening portion side by entering the resin  5  into the slot  2 , the flow of air is blocked by this step portion. Accordingly, a void, which is a bubble of air, may be generated in this portion. In the case of the conventional example shown in  FIG. 4 , there is a possibility that a void is generated as follows. In the case where the opening portion of the slot  2  is closed by the sheet of insulating paper  4   b  forming a lid, resin  5  can not enter into the slot  2 . Accordingly, there is a possibility that a gap is formed between the sheet of insulating paper  4   b  forming the lid and the bottom portion of the slot  2 . Even when the resin  5  enters this gap, the sheet of insulating paper  4   b  prevents the air from flowing out to the opening portion, so that a void, which is a bubble of air, is generated. However, according to the present embodiment, when the resin  5  enters into the slot  2 , nothing blocks the flow of air. On the sheet of insulating paper  4 , no bent portions and no folded portions are formed so that no bubble of air can be generated. Further, the sheet of insulating paper  4  is not formed into a profile preventing an air from flowing to the opening portion of the slot  2 . Therefore, nothing blocks a flow of air at the time of entering of the resin  5 . Accordingly, air can be smoothly discharged and no bubble of air is generated.  
       FIG. 2  is a schematic illustration for explaining an example in which the present invention is applied to a rotary type electric motor. The coil  13  is inserted into the slot  12  of the stator core  11  in such a manner that the coil  13  is wrapped in the sheet of insulating paper  14  which is arranged along an inner face profile of the slot  12  open to the opening portion of the slot  12 . After that, molding is conducted by the insulating resin  15  so that the coil  13  can be insulated. The thickness of the insulating resin  15  in the direction from the end portion  13   a  of the coil  13  to the opening of the slot is arranged so that the thickness can be large sufficient to insulate the coil  3 . Even in this case, the sheet of insulting paper  14  on the opening portion side of the slot  12  is open. Therefore, at the time of molding of the insulating resin  15 , an air flow in the slot is not blocked by the resin which enters into the slot  12 . Accordingly, air can be smoothly discharged, and the generation of a void can be prevented.  
      As described above, in each embodiment of the present invention, the generation of voids such as cavities and empty holes is prevented, and it becomes possible to form a coil and stator core having less voids. Therefore, it is possible to provide an electric motor, the dielectric strength of which is high.  
      It is unnecessary to conduct the wrapping operation of the coil  3 ,  13  in a sheet of insulating paper. Further, it is unnecessary to conduct the attaching operation to attach a lid of the insulating paper to the slot after inserting the coil into the slot. Therefore, the number of manufacturing process can be reduced. Further, it is possible to decrease a quantity of the insulating paper to be used. Accordingly, the cost of manufacturing an electric motor can be reduced.  
      Although the invention has been shown and described with exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto without departing from the spirit and the scope of the invention.