Abstract:
A multi-layer coil is wound around a bobbin having a center pillar and a small and a large flanges connected to longitudinal ends of the center pillar. A winding space having a trapezoidal cross-section in a plane cut through the center axis of the bobbin is formed outside the center pillar between both flanges. To wind the multi-layer coil in this winding space, a turning position where a layer of the coil moves up to a higher layer is set by a position setter, and the turning position is automatically shifted layer by layer to form a sloped outer surface of the coil. The coil is wound in a shape fitting the trapezoidal winding space without reducing the winding speed. The space factor of the coil in the winding space is improved, making the coil compact in size.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
         [0001]    This application is based upon and claims benefit of priority of Japanese Patent Application No. 2002-135460 filed on May 10, 2002, the content of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an apparatus for winding a multi-layer coil in a trapezoidal winding space, and a method of winding such a coil.  
           [0004]    2. Description of Related Art  
           [0005]    A conventional apparatus for winding a multi-layer coil in a winding space having a trapezoidal cross-section is shown in FIGS.  11 A- 11 D. A bobbin  100  is composed of a center pillar  102 , a small flange  104  connected to one end of the center pillar  102 , and a large flange  106  connected to the other end of the center pillar  102 . A wire  200  is wound in a winding space formed outside of the center pillar  102  between the small flange  104  and the large flange  106 . The winding space has a trapezoidal cross-section in a plane cut through a center axis of the center pillar  102 .  
           [0006]    The wire  200  is wound in the winding space in a winding process shown in FIG. 11A through FIG. 1D. The bobbin  100  is fixed to a rotating shaft such as a rotating spindle (not shown), and a wire  200  is fed from a feeder nozzle  36 . The feeder nozzle  36  is connected to a holder  34  that is supported on a shaft  32  and is movable back and forth in a direction along the center axis of the bobbin  100 . As shown in FIG. 11A, the wire  200  is wound in a space between the large flange  106  and the small flange  104  until layers of the wire reach a height of the small flange  104 . Thereafter, as shown in FIGS.  11 B- 11 D, the number of wire-turns in one layer is gradually decreased until a top layer reaches the height of the large flange  106 . In this particular example shown here, two turns, i.e., two-wire-pitches, are decreased layer by layer. According to the movement of the feeder nozzle  36  in the axial direction, the winding direction of each layer is switched at a turning position at the right side. In this manner, a coil  110  is wound in the trapezoidal winding space.  
           [0007]    Since the wire  200  is simply guided by the feeder nozzle  36  in the conventional winding process, the turning position of each layer may be deviated from an intended turning position. This means that the coil  110  may be wound in an irregular shape, resulting in decrease in a space factor of the coil  110  in the winding space. The space factor is defined as a ratio of a total cross-sectional area of the wire  200  relative to a cross-sectional area of the winding space. In addition, the wire  200  crosses over the wire of a lower layer at the turning position, and an outer diameter of the coil  110  is enlarged at the cross-over points. Therefore, if the turning positions deviate in the circular direction, the diameter of the coil  110  becomes large. This also results in a decrease in the space factor.  
           [0008]    It would be possible to suppress the deviation of the turning positions by decreasing a winding speed or by temporarily stopping the winding process at each turning position. However, this reduces the winding speed and sacrifices production efficiency.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an improved apparatus for winding a multi-layer coil in a trapezoidal winding space, which is able to keep the turning position at a required position and to improve the space factor without reducing the winding speed. Another object of the present invention is to provide an improved method of winding such a multi-layer coil.  
           [0010]    The multi-layer coil is wound around a bobbin composed of a center pillar, a small flange connected one longitudinal end of the center pillar and a large flange connected to the other end. A winding space around the bobbin is defined outside the center pillar and between both flanges. The winding space has a trapezoidal cross-section in a plane cut through the center axis of the center pillar.  
           [0011]    In a winding process, the center pillar is coupled to a rotating shaft to thereby rotate the bobbin. A wire to be wound is supplied from a wire feeder that moves in a direction parallel to the center axis. Inner layers of the coil are wound in an inner space having a rectangular cross-section between the small flange and the large flange until the height of the inner layers reaches the height of the small flange. Then, outer layers of the coil are wound around the inner layers in an outer space having a triangular cross-section. The number or turns in one layer is gradually reduced layer by layer by shifting a turning position where one layer moves up to a higher layer at the small flange side. The turning position is shifted toward the large flange by predetermined wire-pitches, e.g., two-wire-pitches.  
           [0012]    The turning position of each outer layer is set by a position setter that is movable to positions corresponding to respective layers. The position setter may include plural setting steps each corresponding to each layer. In this case, the position setter is fixed at one place, and turning positions of all the layers are set by respective setting steps. Alternatively, plural setting members each movable to the turning position of each layer may be used. Since the wire crosses over the wire of a lower layer at the turning position and diameter of the coil swells at the crossover point, it is preferable to place all the turning positions at a predetermined peripheral position or positions of the bobbin. By placing the turning positions at a predetermined periphery of the bobbin, the coils can be disposed in a close contact to each other in a small mounting space.  
           [0013]    The coils wound in the winding space having a trapezoidal cross-section can be used in various rotary electric machines. For example, plural coils can be circularly arranged in an armature of a fuel pump for pumping up fuel in a fuel tank. Because a sloped surface of a coil can closely contact with that of another coil, a space for mounting the coils in the armature is minimized.  
           [0014]    According to the present invention, since the turning positions are exactly set at predetermined positions, all the layers forming the coil are encompassed within the winding space having the trapezoidal cross-section. The space factor of the coil in the winding space is improved, and therefore the coil can be made compact in size. Further, the coil is wound at a high speed because the turning positions are set by means of the position setter without reducing the winding speed.  
           [0015]    Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiments described below with reference to the following drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1A is a front view showing an apparatus for winding a multi-layer coil in a trapezoidal winding space;  
         [0017]    [0017]FIG. 1B is a top view showing a part of the winding apparatus shown in FIG. 1A, viewed in direction B in FIG. 1A;  
         [0018]    [0018]FIG. 1C is a side view showing the winding apparatus shown in FIG. 1A, viewed in direction C in FIG. 1A;  
         [0019]    FIGS.  2 A- 2 D sequentially illustrate a winding process in a first embodiment of the present invention;  
         [0020]    [0020]FIGS. 3A and 3B are drawings for explaining turning positions of a wire wound in the process shown in FIGS.  2 A- 2 D;  
         [0021]    [0021]FIG. 4 is a flowchart showing the winding process illustrated in FIGS.  2 A- 2 D;  
         [0022]    FIGS.  5 A- 5 D sequentially illustrate a winding process in a modified form of the first embodiment;  
         [0023]    [0023]FIGS. 6A and 6B are drawings for explaining turning positions of a wire wound in the process illustrated in FIGS.  5 A- 5 D;  
         [0024]    [0024]FIG. 7 is a flowchart showing the winding process illustrated in FIGS.  5 A- 5 D;  
         [0025]    [0025]FIG. 8A is a cross-sectional view showing a fuel pump in which the coils wound according to the present invention are used;  
         [0026]    [0026]FIG. 8B is a cross-sectional view showing the fuel pump shown in FIG. 8A, taken along line VIIIB-VIIIB in FIG. 8A;  
         [0027]    FIGS.  9 A- 9 D sequentially illustrate a winding process in a second embodiment of the present invention;  
         [0028]    FIGS.  10 A- 10 D sequentially illustrate a winding process in a third embodiment of the present invention; and  
         [0029]    FIGS.  11 A- 11 D are drawings showing a conventional process for winding a multi-layer coil in a trapezoidal winding space. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    A first embodiment of the present invention will be described with reference to FIGS.  1 A- 4 . First, referring to FIGS.  1 A- 1 C, an apparatus for winding a multi-layer coil in a trapezoidal winding space will be described. A winding apparatus  10  includes a spindle  20  for rotating a bobbin  100 , a wire feeder  30 , a position setter  40  and a moving device  50 . A bobbin  100  is composed of a center pillar  102 , a small flange  104  connected to one end of the center pillar  102  and a large flange  106  connected to the other end of the center pillar  102 . A winding space of the bobbin  100  is formed outside of the center pillar  102  between the small flange  104  and the large flange  106 , and has a trapezoidal cross-section in a plane cut through a center axis of the center pillar  102 .  
         [0031]    The center pillar  102  is a hollow pillar having a rectangular cross-section. Both of the small flange  104  and the large flange  106  are rectangular plates connected to the center pillar  102 . The center pillar  102  is coupled to rotating spindle shaft  22 . The wire feeder  30  includes a shaft  32 , holder  34  supported by the shaft  32  and a feeder nozzle  36  connected to the holder  34 . The holder  34  slidably moves on the shaft  32  in a direction parallel to the center axis of the bobbin  100 . The holder  34  is reciprocated back and forth on the shaft  32  by a mechanism such as a driving screw. A wire  200  to be wound in the winding space of the bobbin  100  is fed from the feeder nozzle  36 . One end of the wire  200  is connected to the spindle  20 , and the wire  200  fed from the feeder nozzle  36  is wound around the center pillar  102  of the bobbin  100 .  
         [0032]    The position setter  40  is held by a holder  46  that is connected to a shaft  48 . The holder  46  connected to the shaft  48  is driven in both directions X and Z (shown in FIG. 1B) by a supporter  52 . The supporter  52  is slidably coupled to a shaft  54  extending in direction X and another shaft  56  extending in direction Z. In this manner, the position setter  40  having a guide surface  42  for guiding the wire  200  is movable in both the axial direction (direction Z) and the direction (direction X) perpendicular to the axial direction.  
         [0033]    Referring to FIGS.  2 A- 2 D, operation of the winding apparatus  10  will be described. As shown in FIG. 2A, inner layers of the coil  110  are wound in a space between the small flange  104  and the large flange  106  until the inner layers reach a height of the small flange  104 . The wire  200  is guided back and forth in direction Z by the feeder nozzle  36 . As shown in FIGS.  2 B- 2 C, outer layers of the coil  110  are wound in a space having a triangular cross-section. As shown in FIG. 2B, a first layer of the outer layers is wound from the large flange  106  toward the small flange  104 , and turned at a first turning position that is set by the position setter  40 . Then, a second layer of the outer layer is wound toward the large flange  106  starting at a second turning position set by the position setter  40 . As shown in FIGS. 2C and 2D, this process is repeated until the outer layers of the coil  110  completely fills the upper layer space. In this manner, the wire  200  is wound to fill the entire trapezoidal winding space, thereby forming the coil  110 .  
         [0034]    As shown in FIG. 3A, the rectangular bobbin  100  has a pair of short sides “a” and “c”, and a pair of long sides “b” and “d”. The position setter  40  having the guide surface  42  slanted as shown in FIG. 3B smoothly guides the wire  200  during the winding process. The position setter  40  sets the respective turning positions of each outer layer, so that the number of turns in each outer layer is gradually reduced by a predetermined number of turns. In this particular embodiment, two turns are reduced layer by layer. In other words, the right side end of each outer layer is shifted toward the large flange  106  by two-wire-pitches. FIG. 3B shows an exploded view of the four sides a-d of the bobbin  100 . As shown in FIG. 3B, the turning positions of all outer layers are set on the short side “a”. At each turning position, the wire  200  crosses over the wire  200  of a lower layer.  
         [0035]    Now, the winding process described above will be further explained with reference to a flowchart shown in FIG. 4. At step S 300 , the inner layers of the coil  110  are wound up to the height of the small flange  104  by reciprocating the feeder nozzle  36  in the axial direction of the bobbin  100 . At step S 302 , the position setter  40  is placed at the first turning position before the first outer layer wound from the large flange side toward the small flange side reaches the first turning position. At step S 304 , the first outer layer is wound, starting from the large flange  106 , toward the small flange  104 . The first outer layer is stopped at the first turning position set by the position setter  40 , and the second outer layer is wound from the small flange side toward the large flange side while the starting position of the second outer layer is shifted toward the large flange side by two-wire-pitches. At step S 308 , the next turning position is set by the position setter  40 . At step S 310 , the steps S 304 -S 308  are repeated until the all layers are wound, forming the coil  110 . If it is determined that an entire winding process is completed, the process comes to the end.  
         [0036]    Referring to FIGS.  5 A- 5 D and FIGS.  6 A- 6 B, a modified form of the first embodiment will be described. In the first embodiment, all the turning positions are set on the short side “a” of the bobbin  100 , and two-wire-pitches are shifted at each turning position. In this modified form, however, only one-wire-pitch is shifted at the turning position set on the short side “a”, and another one-wire-pitch is shifted on the next short side “c”, as shown in FIG. 6B. A position setter  60  guides the wire  200  to shift the wire on both short sides “a” and “b” by one-wire-pitch each, as illustrated in FIGS.  5 A- 5 D. The number of turns in each outer layer is reduced by two turns layer by layer in the same manner as in the first embodiment.  
         [0037]    Referring to the flowchart shown in FIG. 7, the modified form of the winding process shown in FIGS.  5 A- 5 D will be further explained. At step S 320 , the inner layers of the coil  110  are wound until the inner layers reach the height of the small flange  104 . At step S 322 , the position setter  60  is placed at the first turning position before the first outer layer is wound. The first turning position is set on the short side “a” with one-slot-pitch shifted toward the large flange  106 . At step S 324 , the first outer layer is wound from the large flange side toward the small flange side and is stopped at the first turning position. At step S 326 , the wire is turned at the first turning position to wind the second outer layer from the short flange side toward the large flange side.  
         [0038]    Then, at step S 328 , the position setter  60  is shifted one-wire-pitch toward the large flange side on the short side “c”. At step S 330 , the wire is shifted one-wire-pitch toward the large flange  106  on the short side “c”, guided by the position setter  60 . At step S 332 , the position setter  60  is placed at the next turning position on the short side “a”. Then, at step S 334 , the steps S 324 -S 332  are repeated until all the outer layers are wound to fill the outer layer space having a triangular cross-section. When the entire winding process completed, the process comes to the end.  
         [0039]    A second embodiment of the present invention will be described with reference to FIGS.  9 A- 9 D. In this embodiment, the position setter  40  used in the first embodiment is replaced with a position setter  90 , and other structures are the same as those of the first embodiment. The position setter  90  has plural setting steps  92 , each of which corresponds to the turning position of each outer layer. In this embodiment, the position setter  90  is not moved during the winding process. The turning positions of each outer layer are set by the respective setting steps  92  without changing the position of the position setter  90 .  
         [0040]    A third embodiment of the present invention will be described with reference to FIGS.  10 A- 10 D. In this embodiment, plural setting members  96  each corresponding to each outer layer are employed. Each position setter  96  is individually controlled, so that each position setter  96  is placed at a turning position required for each outer layer.  
         [0041]    Advantages attained in the foregoing embodiments and their modified forms will be summarized below. Since the turning positions of the outer layers to be wound in the outer space having a triangular cross-section are set by the position setter, the turning positions are exactly determined without deviation. Accordingly, the coil  110  can be correctly shaped to be encompassed within the winding space having a trapezoidal cross-section. Therefore, the space factor of the coil  110  in the winding space is greatly improved, and the coil  110  can be made small in size. This can be achieved without slowing down the winding speed. Therefore, the production efficiency is improved. In addition, the crossover points of the wire  200  are set on a predetermined bobbin side “a”, or predetermined bobbin sides “a” and “c”. This also contributes to reducing the coil size.  
         [0042]    The coil  110  wound in the winding space having a trapezoidal cross-section can be used in various electric machines. A fuel pump in which the coils  110  are used is shown in FIGS. 8A and 8B as an example. The fuel pump  70  is submerged in a fuel tank of an automotive vehicle to pump up fuel and to supply the pumped up fuel to an automotive engine. The fuel pump  70  is mainly composed of a cylindrical housing  72 , four permanent magnets  74  connected to an inner bore of the cylindrical housing  72 , an armature  80  rotatably supported inside the permanent magnets  74 , and an impeller  86  rotated by the armature  80 . The armature  80  includes an inner core  82 , an outer core  84  and six coils  110  disposed between the inner core  82  and the outer core  84 .  
         [0043]    The inner core  82  has six legs extending in the radial direction, and each leg is inserted into the bobbin  100  of the coil  110  so that the large flange  106  is positioned outside and the short flange  104  inside. The coils  110  are circularly arranged so that the sloped outer surfaces of the neighboring coils  110  closely contact each other, as shown in FIG. 8B. In this manner, a space required for disposing six coils inside the outer core  84  is minimized. The crossover points of the wire  200  are positioned on the short side “a” or on short sides “a” and “c” as described above, and no crossover point is positioned on the long sides “b” and “d”. Since the coils  110  are disposed so that the sloped surfaces formed on the long sides contact each other, the sloped surfaces contacting each other do not include the crossover points that irregularly increase the outer diameter of the coil  110 . Therefore, six coils  110  can be disposed inside the outer core  84  in a space-saving manner.  
         [0044]    While the present invention has been shown and described with reference to the foregoing preferred embodiments, it will be apparent to those skilled in the art that changes in form and detail may be made therein without departing from the scope of the invention as defined in the appended claims.