Patent Publication Number: US-2010107401-A1

Title: Method of manufacturing motor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a motor and a method of manufacturing a motor. More specifically, the present invention relates to a motor that can be used in a fuel pump and a method for manufacturing a motor that can be used in a fuel pump. 
     2. Description of the Related Art 
     Fuel pumps that use a brushless motor as a driving source have been known. These fuel pumps are mounted on vehicles, for example, and are used to deliver fuel, such as gasoline, from within a fuel tank to an engine. In such a fuel pump, a motor and a pump are contained inside a tubular casing, and the motor is rotated to drive the pump. The fuel pump is located inside the fuel tank so as to be immersed in the fuel. The fuel pump delivers the fuel drawn from the pump side to the engine through a fuel pipe, after allowing the fuel to pass through a motor portion. 
     In recent years, biofuel having ethanol or the like as its main component has been attracting attention as a vehicle fuel that can replace gasoline. However, biofuel has a hydrophilic nature, and accordingly has higher water content than the gasoline. Therefore, the motor in the fuel pump makes contact with much more moisture when the biofuel is used. In the case of a fuel pump that uses, as its driving source, the brushless motor in which windings are arranged on a stator, it is preferable that resin sealant be provided to prevent the windings and connection members, such as busbars, which are electrically connected to the windings, from gathering rust because of the moisture in the fuel. 
     However, in the case where the stator of the motor is sealed with resin in the fuel pump in which the motor and the pump are contained inside the tubular casing as in the above-described fuel pump, resin protruding beyond an outer circumference of the stator would prevent insertion of the stator into the casing. Therefore, when the stator is sealed with the resin, it is necessary to have a forming die pressed against the outer circumference of the stator, in order to prevent the resin from spreading out beyond the outer circumference of the stator. However, in the case where a core of the stator is formed by a so-called straight core, which is composed of a band of a plurality of core portions each including a tooth portion which are connected together via core bending portions, a plurality of segment cores each including the tooth portion, or the like, significant variations occur in circularity or diameter of the outer circumference between different stators. Therefore, it may sometimes be difficult to have the forming die pressed against the outer circumference of every stator without a gap in between. 
     SUMMARY OF THE INVENTION 
     According to a preferred embodiment of the present invention, a method of manufacturing a motor includes the steps of: a) winding a coil wire on a stator core, and forming a stator; b) press fitting the stator formed in step a) inside a casing; and c) sealing at least axial ends of the stator press fit inside the casing with resin. 
     In accordance with a method of manufacturing a motor according to a preferred embodiment of the present invention, since a stator is fit in a tubular casing, and thereafter at least axial ends of the stator are sealed with resin, it is possible to prevent the resin from spreading out beyond an outer circumference of the stator. 
     Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view illustrating the structure of a fuel pump according to a first preferred embodiment of the present invention. 
         FIG. 2  is a schematic cross-sectional view of the fuel pump taken along line II-II of  FIG. 1 . 
         FIG. 3  is a view of a stator as seen axially from above. 
         FIG. 4A  is a schematic view of a stator core in the form of a straight core in a process of manufacturing the stator. 
         FIG. 4B  is a schematic view of the straight core with windings thereon, in the process of manufacturing the stator. 
         FIG. 4C  is a schematic view of the straight core bent to substantially assume the shape of a tube, in the process of manufacturing the stator. 
         FIG. 5A  is a schematic diagram illustrating how the stator is press fit in a casing in a resin sealing step. 
         FIG. 5B  is a schematic diagram illustrating how a forming die is inserted within an inner circumference of the stator in the resin sealing step. 
         FIG. 5C  is a schematic diagram illustrating how the stator is placed between forming dies and sealed with resin in the resin sealing step. 
         FIG. 6A  is a schematic view of a segment core in a process of manufacturing a stator according to a second preferred embodiment of the present invention. 
         FIG. 6B  is a schematic view of the segment core with a winding thereon in the process of manufacturing the stator. 
         FIG. 6C  is a schematic view of segment cores which have been joined to one another so as to substantially assume the shape of a tube in the process of manufacturing the stator. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that preferred embodiments described below are merely preferred embodiments illustrative of the present invention, and should not be construed as limiting the present invention, its applications, or the range of its uses. 
     Motor Structure 
       FIG. 1  is a schematic diagram illustrating the structure of a fuel pump  1  including a motor  2  according to the first preferred embodiment of the present invention. The fuel pump  1  is preferably located inside a fuel tank arranged to store fuel, such as gasoline or diesel fuel, to be immersed in the fuel. The motor  2  is driven to rotate an impeller  3 , so that the fuel pump  1  draws the fuel into a casing  4  and then discharges the fuel. As a result, the fuel is delivered to an engine through a fuel pipe. 
     Specifically, in the fuel pump  1 , the motor  2  and the impeller  3  are contained inside the casing  4 , which is substantially tubular and preferably made of metal. The impeller  3  is connected to a rotating shaft  22  of the motor  2 , and the motor  2  and the impeller  3  are arranged one above the other along an axial direction. At an axial end of the motor  2 , the casing  4  is covered with an outlet side cover member  5  that is preferably made of resin. At an end on the impeller  3  side, the casing  4  is covered with a pump casing  11  and a pump cover  12 . The pump casing  11  and the pump cover  12  together define a pump chamber S. The pump chamber S accommodates the impeller  3 . 
     The outlet side cover member  5  is preferably defined by a substantially disc-shaped resin member. The outlet side cover member  5  has provided therein an outlet port  5   a  which defines a through aperture extending along the axial direction, and a recessed portion  5   b  arranged to accommodate a bearing  6 . The bearing  6  supports an end (hereinafter referred to as an “upper end”) of the rotating shaft  22  of the motor  2  to allow rotation of the rotating shaft  22 . In addition, the outlet side cover member  5  has provided therein a busbar aperture  5   c  arranged to allow an external busbar  36  that extends from a stator  31  of the motor  2  to pass there through to an outside of the fuel pump  1 . 
     Each of the pump casing  11  and the pump cover  12  is defined by a substantially disc-shaped resin member. The pump casing  11  and the pump cover  12  are arranged inside the casing  4  such that the pump casing  11  is located axially inward of the pump cover  12 . The pump cover  12  has provided therein an inlet port  12   a  which defines a through hole extending along the axial direction to communicate with the pump chamber S. The pump casing  11  has provided therein an inlet channel  11   a  which defines a through aperture extending along the axial direction to communicate with the pump chamber S. Thus, the interior of the casing  4  communicates with the outside of the fuel pump  1  through the inlet port  12   a , the pump chamber S, and the inlet channel  11   a.    
     On a surface of the pump casing  11  on the pump cover  12  side, a recessed portion  11   b  and a through hole  11   c  are provided. The recessed portion  11   b  defines the pump chamber S. The rotating shaft  22  of the motor  2  passes through the through hole  11   c.  On a surface of the pump casing  11  on the motor  2  side, an expanded hole portion  11   d  arranged to accommodate a bearing  7  is provided. The bearing  7  supports the other end (hereinafter referred to as a “lower end”) of the rotating shaft  22  to allow for rotation of the rotating shaft  22 . 
     The impeller  3  is preferably shaped in the form of a propeller, for example. The lower end of the rotating shaft  22  is connected to a substantially central portion, in plan view, of the impeller  3 . The impeller  3  is shaped so that the fuel will be drawn into the interior of the casing  4  through the inlet port  12   a  upon rotation of the impeller  3 . Thus, the rotation of the impeller  3  causes the fuel to be drawn into the pump chamber S through the inlet port  12   a , and then the fuel flows into the interior of the casing  4  of the fuel pump  1  through the inlet channel  11   a.  The fuel drawn into the interior of the casing  4  flows in a gap between a rotor  21  of the motor  2  and the stator  31 , and is discharged to the outside of the fuel pump  1  through the outlet port  5   a  provided in the outlet side cover member  5  (see hollow arrows in  FIG. 1 ). 
     The motor  2  includes the rotor  21 , which is preferably substantially cylindrical, and the stator  31 , which is preferably substantially tubular. The stator  31  is arranged to surround the rotor  21 . The motor  2  is thus structured as a so-called brushless motor. Specifically, permanent magnets  25  are arranged inside the rotor  21 , while windings  33  are provided inside the stator  31 . In the motor  2 , the windings  33  in the stator  31  are energized with a specified timing to control the rotation of the rotor  21 . 
     The rotor  21  includes the rotating shaft  22  and a rotor core portion  23 . The rotating shaft  22  is supported by the bearings  6  and  7  at the both ends thereof such that the rotating shaft  22  is rotatable. The rotor core portion  23  is attached to the rotating shaft  22  to rotate integrally with the rotating shaft  22 . The rotor core portion  23  includes a substantially tubular rotor core  24  and the permanent magnets  25 . The rotor core  24  is preferably defined by laminated steel sheets, but any other desirable rotor core type could be provided. The permanent magnets  25  are provided within the rotor core  24 . As illustrated in  FIG. 2 , the rotor core portion  23  preferably has four, for example, slots  24   a  arranged to surround the rotating shaft  22  provided therein, and each of the slots  24   a  is preferably substantially in the shape of a rectangle in cross section. The permanent magnets  25  are inserted in each of the slots  24   a.    
     As illustrated in  FIG. 1 , preferably both axial ends of the rotor core portion  23  are covered with resin  26  so that the permanent magnets  25  may not be removed from the rotor core portion  23 . The resin  26  is preferably, fuel-tolerant. Since the both axial ends of the rotor core portion  23  are covered with the resin  26 , the permanent magnets  25  are prevented from gathering rust and from making contact with the fuel flowing through inside the motor  2 . In addition, the resin  26  is preferably arranged to substantially assume the shape of a hemisphere, with the thickness thereof gradually increasing toward a center of the rotation of the rotor core portion  23 . This contributes to reducing channel resistance at the axial ends of the rotor core portion  23  when the fuel flows through inside the motor  2 , resulting in an efficient flow of the fuel. Note that the resin  26  may be any resin material that is neither hydrolyzed nor dissolved in a solvent in the fuel. Examples of such resin materials include polyphenylene sulfide (PPS), polyacetal (POM), and polyphthalamide (PPA), for example. Although the resin  26  is arranged to substantially assume the shape of a hemisphere in the present preferred embodiment, this is not essential to the present invention. The resin  26  may be arranged to substantially assume the shape of a cone in other preferred embodiments of the present invention. 
     As illustrated in  FIG. 2 , the rotor core portion  23  preferably includes through holes  24   b  which are arranged to serve as so-called flux barriers. The through holes  24   b  are arranged between each pair of adjacent slots  24   a , and serve to prevent magnetic flux of any two adjacent permanent magnets  25  from interfering with each other to cause a short circuit. Each of the through holes  24   b  extends through the rotor core  24  in the axial direction. Accordingly, when the both axial ends of the rotor core portion  23  are sealed with the resin  26  as described above, the through holes  24   b  are filled in with the resin  26 . This results in union of the resins  26  on the both axial ends of the rotor core portion  23  through the resin  26  inside each of the through holes  24   b , resulting in increased strength of adhesion of the resins  26  to both axial ends of the rotor core  24 . 
     As illustrated in  FIGS. 1 and 2 , the stator  31  preferably includes a substantially tubular stator core  32  and the windings  33 . The stator core  32  is preferably defined by laminated steel sheets. Specifically, the stator core  32  includes a substantially annular core back portion  32   a  and a plurality of tooth portions  32   b . In the present preferred embodiment, the stator core  32  preferably has six, for example, tooth portions  32   b . Each of the tooth portions  32   b  protrudes radially inward from an inner circumference of the core back portion  32   a.  An expanded portion  32   c  spreading in a circumferential direction is provided as a tip portion of each of the tooth portions  32   b , so that each of the tooth portions  32   b  as a whole substantially assumes the shape of the letter “T” in cross section. In addition, a coil wire is wound around each of the tooth portions  32   b  to form the windings  33 . Note that the stator core  32  is defined by a so-called straight core composed of band of core portions  41  (shown in  FIG. 4A ), each including a single tooth portion  32   b , connected together, and that this straight core is bent to assume a tubular shape. In  FIG. 2 , reference symbol  32   d  designates a joint of the straight core, and reference symbol  32   e  designates seams between adjacent core portions  41  resulting from the bending of the straight core. 
     The stator  31  is arranged to define a gap G between an outer circumferential surface of the rotor  21  and the expanded portions  32   c  of the tooth portions  32   b . A surface of each expanded portion  32   c  opposite to the rotor  21  has a larger radius of curvature than that of the outer circumferential surface of the rotor  21 , so that the gap G is narrowest at a central portion of the expanded portion  32   c  and widest at both ends of the expanded portion  32   c.  Since the gap G is wider at the both ends of the expanded portion  32   c  of each tooth portion  32   b  than at the central portion of the expanded portion  32   c  of each tooth portion  32   b , a channel arranged to permit the fuel to flow in the gap G is widened at both ends in a width direction of each expanded portion  32   c , while at the same time the central portion of each expanded portion  32   c  is located closer to the rotor  21  where the magnetic flux is densest. This leads to a more efficient flow of the fuel in the motor  2 , and a decreased reduction in magnetic flux density due to the widened gap G, which in turn prevents a significant reduction in motor performance. 
     As illustrated in  FIG. 3 , each tooth portion  32   b  is preferably covered with an insulating member  34  from a radially outer circumference of the expanded portion  32   c  to an inner circumference of the core back portion  32   a.  The coil wire is wound around the tooth portion  32   b  with the intervening insulating member  34 . Each of the windings  33  is connected to a busbar  35 , preferably made of copper, to enter U, V, or W phase when energized. Each winding  33  is connected to a control circuit (not shown) through the external busbar  36 , made of copper, connected to the busbar  35 . 
     As with the rotor  21 , both axial ends of the stator  31  are also preferably covered with resin  37 . The resin  37  is preferably fuel-tolerant. At the both axial ends of the stator  31 , the insulating members  34 , the windings  33 , and the busbars  35  and  36  are sealed with the resin  37 . Moreover, an axially through space is defined between each pair of adjacent tooth portions  32   b , and these spaces are also filled in with the resin  37 . The sealing of the both axial ends of the stator  31  with the resin  37  prevents the metallic members, such as the copper busbars  35  and  36 , the coil wire, whose surface coating is partially removed to establish its connection with the busbars  35  and  36 , and the steel sheets of the stator core  32 , from making contact with the fuel when the fuel flows in the motor  2 . This prevents these metallic members from gathering rust because of the fuel. Moreover, since the space between each pair of adjacent tooth portions  32   b  is also sealed with the resin  37 , the coil wire and the stator core  32  are prevented from making contact with the fuel. Note that the resin  37  may be any resin material that is fuel-tolerant. Examples of such resin materials include PPS resin, POM resin, and PPA resin. 
     Method of Manufacturing Motor 
     A method of manufacturing the motor  2  will now be described below with reference to  FIGS. 4A to 5C . 
     The stator core  32  of the motor  2  is a so-called straight core composed of the band of the core portions  41 , each including a single tooth portion  32   b , connected together via core bending portions  42 . As illustrated in  FIG. 4C , the straight core is bent at the core bending portions  42  to form the substantially tubular stator core  32 . Specifically, an arc length of each core portion  41  is equal, and the band of the core portions  41  is bent at the core bending portions  42  to form the core back portion  32   a.    
       FIGS. 4A-4C  illustrate a method of forming the stator  31  by using such a straight core. First, the stator core  32  is manufactured in the form of the straight core as illustrated in  FIG. 4A . Then, as illustrated in  FIG. 4B , the insulating member  34  is put on the tooth portion  32   b  of each core portion  41 , and the coil wire is wound on the insulating member  34  to form the winding  33 . Then, a substantially cylindrical mandrel  45  is placed at a position corresponding to an inside of the stator  31  in relation to the stator core  32  with the windings  33  thereon. Then, the stator core  32  is bent at the core bending portions  42  so that a top of the expanded portion  32   c  of each tooth portion  32   b  is brought into contact with an outer circumferential surface of the mandrel  45 . These steps result in the substantially tubular stator  31  as illustrated in  FIG. 4C . Notice here that, in the situation where the stator  31  is substantially in the shape of a tube as illustrated in  FIG. 4C , the core bending portions  42  become the seams  32   e  in  FIG. 4C , and that the both ends of the straight core become the joint  32   d  in  FIG. 4C . At the joint  32   d , the ends of the straight core are joined together by welding or other joining method or members, for example. 
     In the case where the above-described method of manufacturing stators is adopted, it is possible to wind the coil wire around the tooth portions  32   b  when the stator core  32  is in the form of the straight core, even when adjacent tooth portions  32   b  are very close to each other as in the case of the stator  31  according to the present preferred embodiment, and an improvement can be achieved in workability at the time of wire winding. However, in the case where the mandrel  45  is placed at the position corresponding to the inside of the stator  31 , and the straight core is bent as described above, an inner side of the stator  31  defines a reference surface. Accordingly, although an inner circumferential surface of the stator  31  can assume the shape of a circle with high precision, a same level of high precision cannot be achieved in circularity or diameter of the outer circumference of the stator  31 . 
     Meanwhile, in the case where the windings  33 , the busbars  35  and  36 , and so on are sealed with the resin as in the present preferred embodiment, low precision in the outer diameter of the stator  31  would result in a gap between the stator  31  and a forming die at the time of resin molding, and the resin would spread out beyond the outer circumference of the stator  31 . 
     As such, the method of manufacturing the motor in accordance with the present preferred embodiment uses the casing  4  to prevent the resin from spreading out beyond the outer circumference of the stator  31  as illustrated in  FIGS. 5A-5C . 
     Specifically, as illustrated in  FIG. 5A , the stator  31  is preferably first press fit in the substantially tubular, metallic casing  4 . Then, as illustrated in  FIG. 5B , a hollow forming die  46  substantially in the shape of a hexagon in cross section is inserted within the inner circumference of the stator  31 . In this situation, forming dies  47  and  48  are set from above and below, and molten resin is injected to an axial end of the stator  31 . As a result, the both axial ends and inside of the stator  31  are sealed with the resin  37 . 
     The above method prevents the resin from spreading out beyond the outer circumference of the stator  31  since the casing  4  is embedded in the outer circumference of the stator  31 , even when the precision is low in the circularity or diameter of the outer circumference of the stator  31 . Moreover, since the forming die  46  substantially in the shape of a hexagon in cross section is inserted within the inner circumference of the stator  31 , the resin is prevented from spreading beyond the inner circumference of the stator  31  as well. 
     Still further, since the sealing with the use of the resin  37  is performed after the stator  31  is press fit in the casing  4 , fine shavings and so on that result from the press fitting of the stator  31  in the casing  4  can be confined within the resin  37 . This prevents the shavings from being scattered in the motor  2 . 
     Here, regarding the above-described method of manufacturing the motor  2 , step a) corresponds to the step of winding the coil wire around the tooth portions  32   b  of the stator core  32  formed by the straight core to form the windings  33 , and thereafter bending the stator core  32  to shape it into a tubular form; step b) corresponds to the step of press fitting the tubular stator  31  in the casing  4 ; and step c) corresponds to the step of sealing the axial ends of the stator  31  with the resin in the situation where the casing  4  and the stator  31  are held by the forming dies  46  to  48 . 
     As described above, according to the present preferred embodiment, the stator  31  obtained by bending the straight core is press fit in the casing  4  of the fuel pump  1 , and thereafter the both axial ends of the stator  31  are sealed with the resin  37 . This prevents the occurrence of a gap between the stator  31  and the casing  4  even if the precision is low in the outer diameter of the stator  31 , and prevents the resin from spreading beyond the outer circumference of the stator  31 . 
     Moreover, the placing of the forming die  46  inside the inner circumference of the stator  31  when the both axial ends of the stator  31  are sealed with the resin  37  prevents the resin from spreading beyond the inner circumference of the stator  31 . 
     Next, a second preferred embodiment of the present invention will now be described below with reference to  FIGS. 6A-6B . As illustrated in  FIG. 6A , the present preferred embodiment is preferably substantially the same as the first preferred embodiment except that a stator core  52  is formed by a plurality of segment cores  53 . Accordingly, like portions are designated by like reference numerals and the following description focuses on the difference. 
     Specifically, the plurality of segment cores  53  are joined to one another at core back portions  53   a  to form the stator core  52 . Each of the segment cores  53  includes a tooth portion  53   b . As illustrated in  FIG. 6B , in connection with the stator core  52 , the insulating member  34  is put on the tooth portion  53   b  of each segment core  53 , and thereafter the coil wire is wound on the insulating member  34  to form the winding  33 . Then, as illustrated in  FIG. 6C , the plurality of segment cores  53 , each with the winding  33  thereon, are arranged to form a ring shape, and each pair of adjacent core back portions  53   a  are joined together by welding to obtain the stator. 
     The above arrangement allows the winding  33  to be put on each segment core  53  as illustrated in  FIG. 6B  before the segment cores  53  are joined together, even when adjacent tooth portions  53   b  of the stator core  52  are very close to each other as illustrated in  FIG. 6C . This prevents a reduction in workability when the windings  33  are put on the segment cores  53 . 
     As illustrated in  FIG. 6C , when the segment cores  53  are joined together by welding at the core back portions  53   a , the substantially cylindrical mandrel  45  is arranged so that an inner circumference of the tooth portions  53   b  of the segment cores  53  is in contact therewith. That is, in the present preferred embodiment the inner circumference of the stator core  52  defines a reference surface and significant variations are likely to occur in the diameter of the outer circumference between separate stator cores  52 . As such, the use of the manufacturing method as described above with reference to the first preferred embodiment prevents the resin from spreading beyond the outer circumference of the stator core  52 . 
     While preferred embodiments of the present invention have been described above, note that the present invention is not limited to the above-described preferred embodiments, but that various modifications are possible. 
     The hollow forming die  46  substantially in the shape of a hexagon in cross section is preferably used when the both axial ends of the stator  31  are sealed with the resin, but this is not essential to the present invention. For example, the mandrel may be used in place of the forming die  46 . In this case, it is preferable that the mandrel be not in the shape of a cylinder but substantially in the shape of a hexagon in cross section as with the forming die  46 . This eliminates the need to prepare the additional forming die to be inserted within the inner circumference of the stator  31 , when the both axial ends of the stator  31  are sealed with the resin. This contributes to reduced cost and also eliminates the need for the operation of inserting the forming die, leading to improved workability. 
     In the above-described preferred embodiments, the casing  4  of the fuel pump  1  preferably is substantially tubular and preferably made of metal. Note, however, that the casing may be made of any material that allows its outer diameter to be formed more precisely than that of the stator core. Also note that the casing may be in any shape that allows the stator to be press fit therein. 
     Further, in the above-described preferred embodiments, the outlet side cover member  5 , the pump casing  11 , and the pump cover  12  are preferably defined by resin members. However, this is not essential to the present invention. The outlet side cover member  5 , the pump casing  11 , and the pump cover  12  may be formed by other types of members than the resin members. Examples of such other types of members include metallic members such as aluminum die-cast members. 
     Still further, the above-described preferred embodiments are directed to the method of manufacturing the motor  2  preferably for use in the fuel pump  1 . Note, however, that this is not essential to the present invention. Other embodiments of the present invention may be applied to motors designed for other applications, as long as both axial ends of the motor are sealed with resin. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.