Patent Publication Number: US-8109743-B2

Title: Axial flow fan unit

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an axial flow fan unit including a plurality of axial flow fans connected in series. 
     2. Description of the Related Art 
     Conventionally, a cooling fan is installed inside a housing of various kinds of electronic devices to cool electronic parts thereof. As the electronic parts enjoy high performance and suffer from increased heat generation, there is a need to increase the static pressure and flow rate of the cooling fan. To meet this need, a serially arranged axial flow fan unit with a plurality of axial flow fans connected in series is used in recent years as a cooling fan that can secure a great enough static pressure and an increased flow rate. 
     The serially arranged axial flow fan unit includes a plurality of housings within which a plurality of motors are arranged. A plurality of lead lines is led from the motors to the outside of the housings through recess portions for lead line guidance provided on the side portions of the housings. 
     If the lead lines are not orderly led out of the housings, however, there is a fear that the lead lines are pushed out when mounting the serially arranged axial flow fan unit to the electronic devices or the like and are damaged or severed by physical interference with other parts. Inside the housings, the lead lines may be flexed to thereby impede airflow and increase noises attributable thereto. For the reasons noted above, the method of conducting the lead lines is of great importance in the serially arranged axial flow fan unit. 
     SUMMARY OF THE INVENTION 
     In order to overcome the problems described above, preferred embodiments of the present invention provide a serially arranged axial flow fan unit including a first axial flow fan and a second axial flow fan. The first and the second axial flow fans each preferably have a first motor and a second motor; a first impeller and a second impeller rotatable about a center axis by the first and the second motor; and a first housing and a second housing that are hollow to accommodate the first and the second motor and the first and the second impeller, respectively. In the first and the second housing, a first recess portion and a second recess portion are provided, respectively, wherein an inside and outside of the first and the second housings are joined at the first and the second recess portions, respectively. The first and the second recess portions are arranged in the circumferential direction about the center axis. The first lead lines and the second lead lines connected to the first and the second motors, respectively, extend to the outside of the first and the second housings via the first and the second recess portions. Thus, it is possible to guide the first and the second lead lines on the first and the second housings. 
     Further, at least one guide portion is provided on the first and the second housings to guide the first and the second lead lines therethrough. Thus, it is possible to guide the first and the second lead lines in a desired direction depending on the installed location of the axial flow fan unit. 
     Further, by provided an end portion hook and a guide portion hook in the guide portion, it is possible to guide the first and the second lead lines on the first and the second housings more reliably. 
     Furthermore, at least one of the first and the second recess portions has a first gap extending in the axial direction and a second gap extending from the first gap in the circumferential direction. By guiding the first and the second lead lines via the first and the second gaps, it is possible to prevent the lead lines from being bent. 
     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 perspective view showing a serially arranged axial flow fan unit in accordance with a first preferred embodiment of the present invention. 
         FIG. 2  is a vertical section view of the axial flow fan unit in accordance with the first preferred embodiment of the present invention. 
         FIG. 3  is a bottom view showing a first axial flow fan in the first preferred embodiment of the present invention. 
         FIG. 4  is an enlarged view showing a recess portion and its vicinity in the first preferred embodiment of the present invention. 
         FIG. 5  is an enlarged view showing a guide portion and its vicinity in the first preferred embodiment of the present invention. 
         FIG. 6  is a plan view showing a second axial flow fan in the first preferred embodiment of the present invention. 
         FIG. 7  is an enlarged view showing a guide portion and its vicinity in the first preferred embodiment of the present invention. 
         FIG. 8  is a sectional view showing a recess portion and its vicinity in the first preferred embodiment of the present invention. 
         FIG. 9  is an enlarged view showing a recess portion and its vicinity in a second preferred embodiment of the present invention. 
         FIG. 10  is an enlarged view showing a recess portion and its vicinity in another example of a third preferred embodiment of the present invention. 
         FIG. 11  is an enlarged view showing a recess portion and its vicinity in a fourth preferred embodiment of the present invention. 
         FIG. 12  is an enlarged view showing a recess portion and its vicinity in another example. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 1 through 12 , preferred embodiments of the present invention will be described in detail. It should be noted that in the explanation of the preferred embodiments of the present invention, when positional relationships among and orientations of the different components are described as being up/down or left/right, ultimately positional relationships and orientations that are in the drawings are indicated; positional relationships among and orientations of the components once having been assembled into an actual device are not indicated. In the following description, an axial direction indicates a direction parallel or substantially parallel to a rotation axis, and a radial direction indicates a direction perpendicular or substantially perpendicular to the rotation axis. 
       FIG. 1  is a perspective view showing a serially arranged axial flow fan unit  1  in accordance with a first preferred embodiment of the present invention. The axial flow fan unit  1  is a contra-rotating axial flow fan and includes a first axial flow fan  2  and a second axial flow fan  3  arranged along the center axis J 1  of the first axial flow fan  2 . In the present preferred embodiment, the center axis J 1  of the first axial flow fan  2  coincides with the center axis of the second axial flow fan  3 . 
     Air is drawn from the upper side of the first axial flow fan  2  and exhausted to the lower side of the second axial flow fan  3 . That is, an air stream moving along the center axis J 1  is generated in the axial flow fan unit  1 . Thus, a sufficient air volume is achieved and a static pressure is increased in the axial flow fan unit  1 . 
     The first axial flow fan  2  is provided with a plurality of first lead lines  91  and the second axial flow fan  3  is provided with a plurality of second lead lines  92 , the lead lines  91  and  92  being used to supply electric power. The first lead lines  91  are conducted to the outside from the lower end of a first housing  23  of the first axial flow fan  2  and are guided upwardly along a guide portion  235  on the first housing  23  in a substantially parallel relationship with the center axis J 1 . Similarly, the second lead lines  92  are conducted to the outside from the upper end of a second housing  33  of the second axial flow fan  3  and are guided upwardly on the first housing  23  together with the first lead lines  91  in a substantially parallel relationship with the center axis J 1 . A guide portion hook  2351  is provided on the outer surface of the first housing  23  and an end portion hook  2352  is provided at the end portion of the first housing  23 . The first lead lines  91  and the second lead lines  92  are held in place by the guide portion hook  2351  and the end portion hook  2352  against removal from the outer surface of the first housing  23 . Above the first housing  23 , the first lead lines  91  and the second lead lines  92  are preferably tied together by a tying member  93 . The first lead lines  91  and the second lead lines  92  are connected to an external power source (not shown). 
       FIG. 2  is a sectional view of the axial flow fan unit  1  in accordance with the first preferred embodiment of the present invention, which view is taken along a plane containing the center axis J 1 . The axial flow fan unit  1  includes a first motor  22 . The first motor  22  is supported by a plurality of (four in the present preferred embodiment, for example) first support ribs  24  and is designed to rotate a first impeller  21  about the center axis J 1 . The first housing  23  is a hollow member. The first impeller  21 , the first motor  22 , and the first support ribs  24  are arranged within the first housing  23 . The first support ribs  24  extend from the outer surface of a first base portion  2211  of the first motor  22  toward an inner surface  231  of the first housing  23  and are arranged along a circumferential direction so that they interconnect the first base portion  2211  and the first housing  23  (see  FIG. 3 ). The first impeller  21  is rotatably driven by the first motor  22  to thereby generate an air stream flowing in the direction parallel to the center axis J 1 . 
     The first impeller  21  has a cup  212 , i.e., a generally cylindrical closed-top member, arranged to cover the outer surface of the first motor  22 . The first impeller  21  has a plurality of (seven in the present preferred embodiment, for example) first blades  211  extending radially outward from the outer surface of the cup  212  with respect to the center axis J 1  and arranged at an equal pitch along the circumferential direction. The cup  212  and the first blades  211  are preferably a single member formed by injection-molding a resin material, for example. 
     The first motor  22  includes a first stator portion  221  and a first rotor portion  222  positioned axially above the first stator portion  221 . The first rotor portion  222  is provided with a yoke  2221 , a field magnet  2222 , and a shaft  2223 . The yoke  2221  is preferably made of a metal to define a magnetic body and has a generally cylindrical closed-top shape around the center axis J 1 . The field magnet  2222  has a substantially cylindrical shape and is fixedly secured to the inner surface of the yoke  2221 . The shaft  2223  is fixed at one end to the upper central portion of the yoke  2221 . Since the yoke  2221  is covered by the cup  212 , the first rotor portion  222  and the first impeller  21  define an integrally united member. 
     The first stator portion  221  is provided with the first base portion  2211 , a bearing holder portion  2212 , an armature  2213 , and a circuit board  2214 . The first base portion  2211  preferably is a substantially disk-shaped member and is arranged adjacent to the second axial flow fan  3 . The bearing holder portion  2212  is a substantially cylindrical member and is arranged in the central portion of the first base portion  2211  so that it can protrude upwardly. The armature  2213  is attached to the outer circumferential surface of the bearing holder portion  2212 . The circuit board  2214  having a substantially annular plate shape is arranged below the armature  2213  and is electrically connected to the armature  2213 . The circuit board  2214  is electrically connected to the first lead lines  91  so that an electric current from the external power source and a control signal can be supplied to the circuit board  2214  through the first lead lines  91 . The armature  2213  is radially opposite to the field magnet  2222  and is supplied with a driving current from the external power source through the circuit board  2214 . In response, the torque acting about the center axis J 1  is generated between the armature  2213  and the field magnet  2222 . Ball bearings  2215  and  2216  are arranged in the upper and lower portions within the bearing holder portion  2212  along the center axis J 1  to rotatably support the shaft  2223 . 
     The second axial flow fan  3  has a structure obtained by vertically inverting the first axial flow fan  2 . The second axial flow fan  3  includes a second motor  32  arranged to rotate a second impeller  31  about the center axis J 1 . The second axial flow fan  3  further includes the second housing  33  which is a hollow member arranged to enclose the second motor  32  and the outer circumferential surface of the second impeller  31 . Inside the second housing  33 , there are arranged second support ribs  34  whose number is the same as that of the first support ribs  24  (i.e., four). The second support ribs  34  extend from the outer surface of a second base portion  3211  of the second motor  32  toward an inner surface  331  of the second housing  33  and are arranged along a circumferential direction so that they interconnect the second base portion  3211  and the second housing  33  (see  FIG. 6 ). In the axial flow fan unit  1 , the first impeller  21 , the first support ribs  24 , the second support ribs  34 , and the second impeller  31  are arranged in this order from the upper side to the lower side in an end-to-end relationship with one another. 
     The second impeller  31  includes a cup  312  arranged to cover the outer surface of a yoke  3221  and a plurality of (five in the present preferred embodiment, for example) second blades  311 . The second blades  311  extend radially outward from the outer surface of the cup  312  with respect to the center axis J 1  and are arranged at an equal pitch along the circumferential direction. The cup  312  and the first blades  311  are preferably a single member formed by injection-molding a resin material, for example. In the present preferred embodiment, the direction of rotation of the second impeller  31  is opposite to that of the first impeller  21 . An air stream flowing in the same direction as the air stream generated by the rotation of the first impeller  21  is generated by the rotation of the second impeller  31 . The air stream thus generated is discharged to the outside. As a result, the air stream generated by the axial flow fan unit  1  has an increased static pressure and an increased volume. 
     The second motor  3  has substantially the same structure as the first motor  22 , except that second motor  32  is a vertical inversion of the first motor  22 . In the second motor  32 , a second stator portion  321  is positioned above a second rotor portion  322 . The second rotor portion  322  is provided with the yoke  3221 , a field magnet  3222 , and a shaft  3223 . The yoke  3221  is preferably made of a metal to define a magnetic body and has a generally cylindrical closed-top shape around the center axis J 1 . The field magnet  3222  has a substantially cylindrical shape and is fixedly secured to the inner surface of the yoke  3221 . The shaft  3223  is arranged at the center of the yoke  3221  so as to protrude upwardly. 
     The second stator portion  321  is provided with the second base portion  3211  having a substantially disk-shaped shape, a bearing holder portion  3212 , and ball bearings  3215  and  3216 . The bearing holder portion  3212  has a substantially cylindrical shape and protrudes downwardly from the center of the second base portion  3211 . The ball bearings  3215  and  3216  are received within the bearing holder portion  3212  and held in the upper and lower portions of the bearing holder portion  3212 . An armature  3213  is attached to the outer circumferential surface of the bearing holder portion  3212 . A circuit board  3214  is arranged above the armature  3213  and is connected to the external power source through the second lead lines  92 . The second base portion  3211  is axially opposite to the first base portion  2211 . The armature  3213  is radially opposite to the field magnet  3222  and is supplied with a driving current and a control signal through the circuit board  3214 . In response, the torque acting about the center axis J 1  is generated between the armature  3213  and the field magnet  3222 . 
     In the present preferred embodiment, as shown in  FIGS. 1 and 2 , the first housing  23  has an outer side surface  232  extending substantially in a vertical direction between the substantially rectangular upper and lower surfaces. The first housing  23  defined by the outer side surface and the upper and lower surfaces has a substantially quadrangular prism-shaped contour. Similarly, the second housing  33  has an outer side surface  332  extending substantially in a vertical direction between the substantially rectangular upper and lower surfaces. The second housing  33  defined by the outer side surface and the upper and lower surfaces has a substantially quadrangular prism-shaped contour such that the four corner portions of the second housing  33  overlap with those of the first housing  23 . 
       FIG. 3  is a bottom view of the first axial flow fan  2  as seen from the exhaust side. In  FIG. 3 , the first impeller  21  is omitted to show a portion of the first lead lines  91 . As shown in  FIG. 3 , the end portion  2321  of the first housing  23  adjacent to the second housing  33  has a substantially square shape. Slanting surfaces  2311  extending gradually away from the center axis J 1  toward a lower surface  234  (the end surface of the end portion  2321 ) are provided in the four corner portions on the inner surface of the end portion  2321  (namely, the lower region of the inner surface  231  of the first housing  23  shown in  FIG. 2 ). 
     The cross-section of each of the first support ribs  24  taken along a plane perpendicular to the center axis J 1  has a substantially arc-shaped blade shape. The cross-section of each of the first support ribs  24  is not particularly limited but may be, e.g., a substantially flat shape. The first base portion  2211  has a cutout  2217  opposite to the guide portion  235  arranged to guide the first lead lines  91  and the second lead lines  92 . The first lead lines  91  are conducted from the lower surface of the circuit board  2214  toward the guide portion  235  through the cutout  2217 . 
     As shown in  FIGS. 1 and 3 , the guide portion  235  of the first housing  23  is provided near one side of the first housing  23 , which side is substantially parallel to the center axis J 1 . The guide portion  235  has a groove-shaped recess and extends from the lower end of the first housing  23  to the upper end thereof along the outer side surface. Four flange portions having fastener holes in the four corner portions are respectively provided in the upper and lower end portions of the first housing  23 . Two of the four flange portions overlap with the guide portion  235  (these two flange portions will be referred to as “guide flange portions  233 ” hereinbelow). As shown in  FIG. 3 , a first recess portion  2331  is provided in one corner portion of the end portion  2321  of the guide portion  235  adjacent to the second housing  33  (namely, in the vicinity of the lower guide flange portion  233 ). The first recess portion  2331  extends upwardly from the lower surface  234  and is continuous from the radial inner side of the first housing  23  to the radial outer side thereof. 
     Referring again to  FIG. 1 , the guide portion  235  has the guide portion hook  2351  and the end portion hook  2352 . As indicated by a broken line in  FIG. 3 , the guide portion hook  2351  is a substantially flat restraint portion and extends substantially in a horizontal direction along the substantially quadrangular prism-shaped contour of the first housing  23  from the outer side surface  232  toward the corner of the contour. In the vicinity of the first recess portion  2331  (namely, in the vicinity of the lower guide flange  233  shown in  FIG. 1 ), the guide portion hook  2351  serves to keep the first lead lines  91  and the second lead lines  92  from moving outward. Consequently, the first lead lines  91  and the second lead lines  92  are prevented from being pushed out beyond the contour of the first housing  23  in the vicinity of the first recess portion  2331 . As shown in  FIG. 1 , the end portion hook  2352  has a substantially flat restraint portion and extends substantially in a horizontal direction along the substantially quadrangular prism-shaped contour of the first housing  23  from the guide flange  233  toward the adjacent flange portion. 
       FIG. 4  is an enlarged view of the first recess portion  2331 , the below-mentioned second recess portion  3331  and their vicinity as seen from the outer side of the guide flange  233  of the axial flow fan unit  1  toward the center axis J 1  in  FIG. 1 . The first lead lines  91  and the second lead lines  92  are indicated by double-dotted chain lines. 
     In the position of the end portion  2321  where the first recess portion  2331  is provided, there are provided a first hook  2332  protruding from the right to the left in  FIG. 4  and a second hook  2333  protruding from the left to the right. The lower edges of the first hook  2332  and the second hook  2333  can be regarded as defining a portion of the lower surface  234 , i.e., the end surface, of the first housing  23 . A first gap  2334  is defined between the tip end of the first hook  2332  and the tip end of the second hook  2333  and extends substantially parallel to the center axis J 1  from the lower surface  234 . A second gap  2335  is defined between the upper edges of the first hook  2332  and the second hook  2333  and the portion of the first housing  23  opposite to the upper edges, and extends circumferentially about the center axis J 1  from the upper end of the first gap  2334 . 
     The first recess portion  2331  is opposite to the second housing  33  and has a generally T-shaped shape defined by the combination of the first gap  2334  and the second gap  2335 . The first hook  2332  has a circumferential length greater than that of the second hook  2333 . The position of the first gap  2334  is offset to the left from the center between the fixed ends of the first hook  2332  and the second hook  2333 . Each of the first gap  2334  and the second gap  2335  has a width greater than that of the first lead lines  91 . The first lead lines  91  are led from the first motor  22  (see  FIG. 2 ) and are conducted to the outside through the second gap  2335  of the first recess portion  2331 . 
       FIG. 5  is an enlarged view showing the guide portion  235  and its vicinity in the lower surface  234  of the first housing  23 . In  FIG. 5 , the contour of the first housing  23  is indicated by a double-dotted chain line  81  and the guide portion hook  2351  is indicated by a broken line. The guide portion  235  is in the shape of a groove extending substantially parallel to the center axis J 1 . As shown in  FIGS. 1 and 5 , the first lead lines  91  and the second lead lines  92  are guided substantially parallel to the center axis J 1  from the first recess portion  2331  toward the inner side of the substantially quadrangular prism-shaped contour  81 . As can be seen in  FIG. 5 , the guide portion  235  extends to the upper and lower end surfaces of the first housing  23  through the guide flange portions  233 . The first recess portion  2331  is positioned in the guide portion bottom surface  236  of the guide portion  235 . In other words, the surface of the first housing  23  (namely, the guide portion bottom surface  236 ) is positioned inward of the contour  81  of the first housing  23  in the vicinity of the first recess portion  2331 . 
     A protrusion portion  2353  protruding from the guide portion bottom surface  236  is provided in the end portion of the outer side surface  232  adjacent to the guide portion  235 . Therefore, in the vicinity of the lower end portion of the guide portion  235 , the movement of the first lead lines  91  and the second lead lines  92  in the substantially horizontal direction is restrained by the guide flange portion  233 , the protrusion portion  2353 , and the guide portion hook  2351 . 
     In the guide portion  235 , the minimum value of the distance between the guide portion bottom surface  236  and the contour  81  of the first housing  23  (namely, the distance d 1  measured from the tip end of the protrusion portion  2353  to the guide portion bottom surface  236  in  FIG. 5 ) is equal to or greater than the diameter of the first lead lines  91  and the second lead lines  92 . Therefore, the first lead lines  91  and the second lead lines  92  are received within the guide portion  235  and are prevented from being pushed out beyond the contour of the first housing  23 . As a consequence, the first lead lines  91  and the second lead lines  92  are held against physical interference with other parts when the axial flow fan unit  1  is mounted in its installation position (e.g., within a housing of an electronic device). It is often the case that the first lead lines  91  are most severely flexed in the vicinity of the first recess portion  2331 . In view of this, the guide portion  235  may have a depth greater than the diameter of the first lead lines  91  only in the vicinity of the first recess portion  2331 . 
       FIG. 6  is a plan view of the second axial flow fan  3  as seen from the intake side. In  FIG. 6 , the second impeller  31  is omitted to show a portion of the second lead lines  92 . Referring to  FIGS. 1 and 6 , the second housing  33  has a shape substantially symmetrical with the first housing  23  in the up-and-down direction. The end portion  3321  of the second housing  33  adjacent to the first housing  23  has a substantially square shape. Slanting surfaces  3311  extending gradually away from the center axis J 1  toward the upper surface  334  of the end portion  3321  (the end surface of the end portion  3321 ) are provided in the four corner portions on the inner surface of the end portion  3321  (namely, the upper region of the inner surface  331  of the second housing  33  shown in  FIG. 2 ). 
     The cross-section of each of the second support ribs  34  taken along a plane perpendicular to the center axis J 1  has a substantially arc-shaped blade shape. The cross-section of each of the second support ribs  34  is not particularly limited but may be, e.g., a substantially flat shape. The substantially disk-shaped second base portion  3211  is held in place by the second support ribs  34  and has a cutout  3217  radially opposite a guide portion  335  of the second housing  33  positioned just below the guide portion  235  (see  FIG. 3 ). The second lead lines  92  are conducted from the lower surface of the circuit board  3214  toward the guide portion  335  through the cutout  3217 . 
     As shown in  FIGS. 1 and 6 , the guide portion  335  is provided near one side of the substantially quadrangular prism-shaped contour of the second housing  33 , which is substantially parallel to the center axis J 1 . The guide portion  335  includes a groove-shaped recess that defines an extension of the guide portion  235  and extends from the lower end of the second housing  33  to the upper end thereof along the outer side surface. Four flange portions having fastener holes provided in the four corner portions are respectively provided in the upper and lower end portions of the second housing  33 . Two of the four flange portions overlap with the guide portion  335  (the two flange portions will be referred to as “guide flange portions  333 ” hereinbelow). A second recess portion  3331  extending downwardly from the upper surface  334  and continuously extending from the inner side of the second housing  33  to the outer side thereof is provided in the corner portion near the guide flange portions  333  (namely, in the corner portion overlapped with the corner portion in which the first recess portion  2331  of the first housing  23  is provided). The second lead lines  92  pass through the second recess portion  3331 . 
     As illustrated in  FIG. 4 , in the position where the second recess portion  3331  is provided, there are provided a first hook  3332  protruding from the left to the right and a second hook  3333  protruding from the right to the left. As in case of the first recess portion  2331 , a first gap  3334  extending substantially parallel to the center axis J 1  from the upper surface  334 , i.e., the end surface, of the second housing  33  is defined between the first hook  3332  and the second hook  3333 . A second gap  3335  extending circumferentially about the center axis J 1  from the lower end of the first gap  3334  is provided along the lower edges of the first hook  3332  and the second hook  3333 . The second recess portion  3331  is opposite to the first housing  23  and has a generally T-shaped shape by the combination of the first gap  3334  and the second gap  3335 . 
     The circumferential position of the first gap  3334  is offset to the right from the center between the fixed ends of the first hook  3332  and the second hook  3333 . Therefore, the first gap  2334  of the first recess portion  2331  and the first gap  3334  of the second recess portion  3331  are arranged in the circumferential direction substantially in parallel to each other such that the first gap  2334  of the first recess portion  2331  is deviated relative to or partially overlapped with the first gap  3334  of the second recess portion  3331  along the circumferential direction. In other words, the first gap  2334  of the first recess portion  2331  is substantially in parallel with the first gap  3334  of the second recess portion  3331  such that the first gap  2334  does not face or partially faces the first gap  3334  in the axial direction. The first gap  3334  and the second gap  3335  have a width greater than that of the second lead lines  92 . The second lead lines  92  are conducted to the outside from the second motor  32  (see  FIG. 2 ) through the second gap  3335 . 
     In the present preferred embodiment, as shown in  FIG. 1 , the first lead lines  91  and the second lead lines  92  are conducted upwardly in  FIG. 1  by the guide portion  235 . Thus, the guide portion  335  is not in use. However, since the guide portion  335  provides a space arranged to guide the first lead lines  91  and the second lead lines  92  substantially parallel to the center axis J 1  from the first recess portion  2331  and the second recess portion  3331  within the quadrangular prism-shaped contour  82 , it is also possible to downwardly guide the first lead lines  91  and the second lead lines  92  in  FIG. 1 . In other words, since the first housing  23  and the second housing  33  are respectively provided with the guide portion  235  and the guide portion  335 , the first lead lines  91  and the second lead lines  92  can be guided toward either the first housing  23  or the second housing  33  depending on the location in which the axial flow fan unit  1  is installed. 
     As shown in  FIG. 1 , a guide portion hook  3351  and an end portion hook  3352  are provided in the guide portion  335 . The guide portion hook  3351  and the end portion hook  3352  are restraint portions that prevent the first lead lines  91  and the second lead lines  92  from moving outward in the vicinity of the second recess portion  3331 . Consequently, when downwardly guiding the first lead lines  91  and the second lead lines  92 , the first lead lines  91  and the second lead lines  92  are prevented from being pushed out beyond the contour of the second housing  33  in the vicinity of the second recess portion  3331 . 
       FIG. 7  is an enlarged view showing the guide portion  335  and its vicinity in the upper surface  334 . In  FIG. 7 , the contour of the second housing  33  is indicated by a double-dotted chain line  82  and the guide portion hook  3351  is indicated by broken lines. 
     Similar to the first housing  23 , the guide portion  335  extends to the upper and lower end surfaces of the second housing  33  through the guide flange portions  333 . The second recess portion  3331  is positioned in the guide portion bottom surface  336  of the guide portion  335 . In other words, the surface of the second housing  33  (namely, the guide portion bottom surface  336 ) is positioned radially inward of the contour  82  of the second housing  33  in the vicinity of the second recess portion  3331 . 
     A protrusion portion  3353  protruding from the guide portion bottom surface  336  is provided in the end portion of the outer side surface  332  of the second housing  33  adjacent to the guide portion  335 . In the guide portion  335 , the minimum value of the distance between the guide portion bottom surface  336  and the contour  82  (namely, the distance d 2  measured from the tip end of the protrusion portion  3353  to the guide portion bottom surface  336  in  FIG. 7 ) is equal to or greater than the diameter of the first lead lines  91  and the second lead lines  92 . Therefore, when conducting the first lead lines  91  and the second lead lines  92  within the guide portion  335 , it is possible to prevent the first lead lines  91  and the second lead lines  92  from being pushed out beyond the contour of the second housing  33 . The guide portion  335  may have a depth greater than the diameter of the second lead lines  92  only in the vicinity of the second recess portion  3331 . 
     When assembling the axial flow fan unit  1  according to an example of a preferred embodiment of the present invention, the first lead lines  91  and the second lead lines  92  are first led out from the first housing  23  and the second housing  33 . Then, the first lead lines  91  are conducted to the second gap  2335  through the first gap  2334  and are held on the right side of the second gap  2335  (see  FIG. 4 ). Similarly, the second lead lines  92  are conducted to the second gap  3335  through the first gap  3334  and are held on the left side of the second gap  3335 . Thereafter, the first housing  23  and the second housing  33  are coupled together so that the lower surface  234  and the upper surface  334  can overlap with each other. At this time, the fixed ends of the first hook  2332  and the second hook  2333  of the first housing  23  coincide in a circumferential position with the fixed ends of the first hook  3332  and the second hook  3333  of the second housing  33 . On the other hand, the first hook  2332  and the second hook  3333  are different from each other in their circumferential length. For that reason, the first gap  2334  and the first gap  3334  are circumferentially spaced apart from each other. The first lead lines  91  and the second lead lines  92  are arranged side-by-side in the circumferential direction and are guided upwardly from the guide portion  235 . 
     The gap size between the lower edges of the first hook  2332  and the second hook  2333  of the first recess portion  2331  and the upper edges of the first hook  3332  and the second hook  3333  of the second recess portion  3331  is smaller than the diameter of the first lead lines  91  and the second lead lines  92 . Thus, the second lead lines  92  held in the second recess portion  3331  are prevented from moving toward the first recess portion  2331  after the axial flow fan unit  1  has been assembled. 
       FIG. 8  is a sectional view taken along line A-A in  FIG. 4 . As shown in  FIG. 8 , the inner and outer corners of the portion of the first housing  23  facing toward the second gap  2335 , the inner and outer corners of the upper and lower edges of the first hook  2332 , the inner and outer corners of the upper and lower edges of the first hook  3332 , and the inner and outer corners of the portion of the second housing  33  facing toward the second gap  3335  are chamfered to have a substantially arc-shaped shape. Similarly, the inner and outer corners of the upper and lower edges of the second hooks  2333  and  3333  (see  FIG. 4 ) of the first recess portion  2331  and the second recess portion  3331  have a chamfered shape. Moreover, the inner and outer corners of the tip edges of the first hooks  2332  and  3332  and the second hooks  2333  and  3333  have a chamfered shape. 
     As shown in  FIG. 4 , the upper and lower corners of the tip ends of the first hook  2332  and the second hook  2333  are chamfered to have a substantially arc-shaped shape when seen toward the center axis J 1 . In other words, the corner portion  2336  between the lower surface  234 , i.e., the end surface, of the first housing  23  (the lower edges of the first hook  2332  and the second hook  2333 ) and the first gap  2334  and the corner portion  2337  between the first gap  2334  and the second gap  2335  are chamfered to have a substantially arc-shaped shape. This holds true for the second housing  33 . The corner portion  3336  between the upper surface  334 , i.e., the end surface, of the second housing  33  (the upper edges of the first hook  3332  and the second hook  3333 ) and the first gap  3334 , and the corner portion  3337  between the first gap  3334  and the second gap  3335  are chamfered to have a substantially arc-shaped configuration. 
     By providing the corner portions  2336 ,  2337 ,  3336  and  3337  with a chamfered shape, the first lead lines  91  and the second lead lines  92  are prevented from being damaged when they pass through the first recess portion  2331  and the second recess portion  3331 . Furthermore, since the corners of the housings and the hooks have a chamfered shape in the vertical cross-section as shown in  FIG. 8 , the first lead lines  91  and the second lead lines  92  are prevented from being damaged when they are inserted into the first recess portion  2331  and the second recess portion  3331  or after they have been inserted into the recess portions  2331  and  3331 . The chamfered shape mentioned above is not particularly limited but may be, e.g., a so-called C-shaped bevel shape formed by cutting the corner portions at 45 degrees. 
     As described hereinabove, since the first gap  2334  of the first recess portion  2331  and the first gap  3334  of the second recess portion  3331  are staggered with each other as shown in  FIG. 4 , it is possible to prevent the second lead lines  92  from being moved into the first recess portion  2331  and becoming loose (more precisely, the second lead lines  92  are kept from becoming loose to a greater extent because they can move up to the first gap  2335 ). As shown in  FIGS. 3 and 5 , since the guide portion  235  is positioned radially inward of the contour of the first housing  23 , it is possible to prevent the first lead lines  91  and the second lead lines  92  from being pushed out beyond the contour of the first housing  23  or to reduce the amount the first lead lines  91  and the second lead lines  92  are pushed out. 
       FIG. 9  is an enlarged view showing a first recess portion  2331   a  of the first housing  23 , a second recess portion  3331   a  of the second housing  33  and their vicinity in a serially arranged axial flow fan unit  1   a  in accordance with a second preferred embodiment of the present invention. In  FIG. 9 , the first lead lines  91  and the second lead lines  92  are indicated by a double-dotted chain line. The axial flow fan unit  1   a  of the second preferred embodiment is the same as the axial flow fan unit  1  of the first preferred embodiment except for the difference in the shape of the first and second recess portions. 
     The first recess portion  2331   a  extends upwardly from the lower surface  234  of the first housing  23  and continuously extends from the inner side of the first housing  23  to the outer side thereof. The first recess portion  2331   a  has a depth greater than the diameter of the first lead lines  91  and a width greater than the total width of the first lead lines  91  arranged side-by-side. The second recess portion  3331   a  extends downwardly from the upper surface  334  of the second housing  33  and continuously extends from the inner side of the second housing  33  to the outer side thereof. The second recess portion  3331   a  has a depth slightly greater than the diameter of the second lead lines  92  and a width greater than the total width of the first lead lines  91  arranged side-by-side. The first lead lines  91  and the second lead lines  92  are led out from the first recess portion  2331   a  and the second recess portion  3331   a , respectively, and are conducted upwardly by the same guide portion as the guide portion  235  shown in  FIG. 1 . 
     When assembling the axial flow fan unit  1   a  of the second preferred embodiment, the first lead lines  91  and the second lead lines  92  are allowed to pass through the first recess portion  2331   a  and the second recess portion  3331   a . The first housing  23  and the second housing  33  are placed one upon another in the axial direction. At this time, the first recess portion  2331   a  and the second recess portion  3331   a  are partially overlapped and staggered in the circumferential direction. The clearance defined by the overlapping region of the first recess portion  2331   a  and the second recess portion  3331   a  (namely, the circumferential overlapping width of the first recess portion  2331   a  and the second recess portion  3331   a ) is smaller than the diameter of either the first lead lines  91  or the second lead lines  92 . Thus, the second lead lines  92  are prevented from coming out of alignment and moving into the first recess portion  2331   a , which would otherwise be caused by external shocks or the like. As a result, in the axial flow fan unit  1   a , it is possible to prevent the second lead lines  92  from being moved into the first recess portion  2331   a  and becoming loose. In the present preferred embodiment, the second recess portion  3331   a  has the same shape and size as the first recess portion  2331   a . However, the shape or size of the first recess portion  2331   a  and the second recess portion  3331   a  is not particularly limited but may be different from each other, insofar as the circumferential overlapping width of the first recess portion  2331   a  and the second recess portion  3331   a  is smaller than the diameter of either the first lead lines  91  or the second lead lines  92 . 
     Next, description will be made with respect to a third preferred embodiment of the present invention.  FIG. 10  is an enlarged view showing the first recess portion  2331   a  of the first housing  23 , the second recess portion  3331  of the second housing  33  and their vicinity in a serially arranged axial flow fan unit  1   b  in accordance with the third preferred embodiment of the present invention. 
     It is not necessary to provide the first hooks  2332  and  3332  and the second hooks  2333  and  3333  in both the first housing  23  and the second housing  33 . The first hooks  2332  and  3332  and the second hooks  2333  and  3333  may be provided in at least one of the first recess portion  2331  and the second recess portion  3331 . In the first housing  23  and the second housing  33 , there may be provided only the hooks for holding the first lead lines  91  and the second lead lines  92  along the guiding direction of the first lead lines  91  and the second lead lines  92 . 
     Referring to  FIG. 10 , a first recess portion  2331   a  is provided in the first housing  23  and a second recess portion  3331  is provided in the second housing  33 . In order to guide the first and the second lead lines  91  and  92  in the upward direction (namely, toward the first housing  23 ), a first hook  3332  and a second hook  3333  are provided only in the second housing  33  on the opposite side from the first housing  23 . This makes it easy to hold the second lead lines  92  when assembling the axial flow fan unit  1   b . Thus, the second lead lines  92  are prevented from being moved into the first recess portion  2331  and becoming loose. In case where the first lead lines  91  and the second lead lines  92  are conducted in the downward direction (namely, toward the second housing  33 ), the first hook  2332  and the second hook  2333  may be provided only in the second housing  33 . 
     Next, description will be made with respect to a fourth preferred embodiment of the present invention.  FIG. 11  is an enlarged view showing the first recess portion  2331   b , the second recess portion  3331   b  and their vicinity in a serially arranged axial flow fan unit  1   c  in accordance with the fourth preferred embodiment of the present invention. 
     As shown in  FIG. 11  and unlike the first recess portion  2331  shown in  FIG. 4 , the first hook  2332  alone is provided in the first recess portion  2331   b  with the second hook  2333  omitted. In other words, the first recess portion  2331   b  has a generally L-shaped shape between the tip and upper edges of the first hook  2332  and the portion of the first housing  23  opposite to the edges. Similarly, the first hook  3332  alone is provided in the second recess portion  3331   b  of the second housing  33  with the second hook  3333  omitted. Just like the first recess portion  2331   b , the second recess portion  3331   b  has a generally L-shaped shape. In this case, each of the first recess portion  2331   b  and the second recess portion  3331   b  has a shape obtained by combining the first gap  2334  or  3334  extending substantially parallel to the center axis J 1  from the end surfaces of the first housing  23  and the second housing  33  and the second gap  2335  or  3335  circumferentially extending from the end of the first gap  2334  or  3334 . The first lead lines  91  and the second lead lines  92  are conducted outward through the second gaps  2335  and the  3335  thereby preventing removal of the lead lines which would otherwise occur in the process of assembling the fan. 
     It is not necessary to provide the guide portions  235  and  335  in both the first housing  23  and the second housing  33 . The guide portions  235  and  335  may be provided only in one of the first housing  23  and the second housing  33 . The shape of the first recess portions  2331   a  and  3331   a  is not limited to the rectangular or substantially rectangular shape but may be other shapes (e.g., a semicircular or substantially semicircular shape or a polygonal or substantially polygonal shape). As shown in  FIG. 12 , the first recess portion  2331   a  and the second recess portion  3331   a  may be arranged in completely spaced-apart positions without circumferentially overlapping each other. That is, the first recess portion  2331   a  may be opposite to the end surface of the second housing  33 , with the second recess portion  3331   a  opposite to the end surface of the first housing  23 . 
     The contour of the first housing  23  and the second housing  33  is not particularly limited to the substantially quadrangular prism shape. In this regard, the contour of the first housing  23  and the second housing  33  may have a cylindrical columnar shape or other columnar shapes such as a polygonal prism shape. Further, the first recess portion  2331  may be slightly deviated relative to (namely, close to) the second recess portion  3331  in the circumferential direction about the center axis J 1 , or partially overlapped with the second recess portion  3331  in the circumferential direction wherein an overlapping width is equal to or smaller than the width of the lead lines. It is also preferred that the guide portions  235  and  335  are provided outward of the first recess portion  2331  and the second recess portion  3331  but inward of the contour in the first housing  23  or the second housing  33 . 
     Since the distance between the surface of the first housing  23  and the second housing  33  and the contour thereof is greater than the diameter of the first lead lines  91  and the second lead lines  92  in the vicinity of the first recess portion  2331  and the second recess portion  3331 , the first lead lines  91  and the second lead lines  92  are prevented from being pushed out beyond the contour of the first housing  23  and the second housing  33 . In this case, it is preferred that the guide portions  235  and  335  have restraint portions (guide portion hooks) arranged to prevent outward movement of the first lead lines  91  and the second lead lines  92  in the vicinity of the first recess portion  2331  and the second recess portion  3331 . In addition, it is preferred that both the first housing  23  and the second housing  33  have the guide portions  235  and  335 . 
     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.