Patent Publication Number: US-2017350411-A1

Title: Air blower

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on and incorporates herein by reference Japanese Patent Application No. 2015-7923 filed on Jan. 19, 2015. 
     TECHNICAL FIELD 
     The present disclosure relates to an air blower that drives a fan through an electric motor of an outer rotor type. 
     BACKGROUND ART 
     This type of air blower is disclosed in, for example, the patent literature 1. In order to introduce cooling air into an inside of the outer rotor to cool the electric motor, the air blower, which is disclosed in the patent literature 1, includes discharge outputs, which discharge the cooling air, and air-blowing projections, which generate the air flow in the inside of the outer rotor. The discharge outlets and the air-blowing projections are formed at a bottom portion of a yoke, which is shaped into a bottomed cylindrical tubular form. The air-blowing projections are respectively formed by cutting and generally perpendicularly bending a corresponding part of the bottom portion of the yoke, which forms the corresponding discharge outlet. 
     CITATION LIST 
     Patent Literature 
     [PATENT LITERATURE 1] JP2012-110130A 
     SUMMARY OF THE INVENTION 
     However, in the air blower of the patent literature 1, in a case where each of the air-blowing projections is formed at the inside of the yoke by cutting and bending the corresponding part of the bottom portion of the yoke, which forms the corresponding discharge outlet, a size of the electric motor is disadvantageously increased in an axial direction in order to avoid an interference of the air-blowing projections to, for example, stator coils received in the inside of the outer rotor. 
     On the other hand, in the air blower of the patent literature 1, in another case where each of the air-blowing projections is formed at the outside of the yoke by cutting and bending the corresponding part of the bottom portion of the yoke, which forms the corresponding discharge outlet, the size of the electric motor is also disadvantageously increased in the axial direction since the air-blowing projections project from the yoke in the axial direction. 
     As discussed above, although the air blower of the patent literature 1 improves the cooling performance of the electric motor with the air-blowing projections, the size of the electric motor is disadvantageously increased in the axial direction. As a result of the extensive study of the inventor, the above point is found. 
     The present disclosure is made in view of the above point, and it is an objective of the present disclosure to provide an air blower that can improve cooling performance of an electric motor of an outer rotor type while limiting an increase in a size of the electric motor in an axial direction. 
     In order to achieve the above objective, according to one aspect of the present disclosure, an air blower includes: a fan that includes: a fan boss, which is shaped into a bottomed tubular form; and a plurality of blades, which are formed at an outer side of the fan boss, wherein the fan is rotatable about a fan central axis; and an electric motor that includes: an outer rotor that is placed in an inside of the fan boss and includes a bottomed rotor member, wherein the bottomed rotor member is shaped into a bottomed tubular form and is rotatable integrally with the fan boss; and a stator that is a non-rotatable member placed in an inside of the bottomed rotor member, wherein: the bottomed rotor member includes a rotor member bottom portion that forms a bottom portion of the bottomed rotor member while an opening hole is formed in the rotor member bottom portion to extend through the rotor member bottom portion in an axial direction of the fan central axis; the fan boss includes: a fan boss bottom portion that is stacked on the rotor member bottom portion in the axial direction and forms a bottom portion of the fan boss; and a bottom portion rib that projects from the fan boss bottom portion toward the rotor member bottom portion side at a corresponding location of the fan boss bottom portion that is overlapped with the opening hole in the axial direction while the bottom portion rib promotes discharge of air from the inside of the bottomed rotor member through the opening hole in response to rotation of the fan. 
     With the above construction, the fan boss includes the bottom portion rib that promotes the discharge of the air from the inside of the bottomed rotor member through the opening hole in response to the rotation of the fan. Furthermore, the bottom portion rib projects from the fan boss bottom portion toward the rotor member bottom portion side at the corresponding location of the fan boss bottom portion that is overlapped with the opening hole in the axial direction. Therefore, a projecting height of the bottom portion rib can be increased by using a thickness of the rotor member bottom portion. Thereby, in comparison to the structure of the air blower of the patent literature 1, in which the air-blowing projection, which corresponds to the bottom portion rib, is formed in the yoke, which corresponds to the bottomed rotor member, it is possible to improve the cooling performance of the electric motor while limiting the increase in the size of the electric motor in the axial direction. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a front view of an air blower taken from an air intake side of the air blower according to a first embodiment. 
         FIG. 2  is a back view of the air blower of  FIG. 1  taken from an opposite side that is opposite from the side shown in  FIG. 1 . 
         FIG. 3  is a view taken along line III-III in  FIG. 1 , showing an inside structure of the air blower according to the first embodiment. 
         FIG. 4  is a view taken in a direction of an arrow IV in  FIG. 3 , showing only a yoke and a fan boss, which are taken out from the air blower. 
         FIG. 5  is a perspective cross sectional view showing a cross section of only the yoke and the fan boss, which are taken out from the air blower, according to the first embodiment. 
         FIG. 6  is a view of the fan boss alone taken in the direction of the arrow IV in  FIG. 3  according to the first embodiment. 
         FIG. 7  is a view of the fan boss alone taken in the direction of the arrow IV in  FIG. 3  according to a second embodiment, corresponding to  FIG. 6  of the first embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In the following respective embodiments, portions, which are identical to each other or equivalent to each other, are indicated by the same reference signs in the drawings. 
     First Embodiment 
       FIG. 1  is a front view of an air blower  8  taken from an air intake side of the air blower according to the present embodiment.  FIG. 2  is a back view of the air blower  8  taken from an opposite side that is opposite from the side shown in  FIG. 1 . The air blower  8 , which is shown in  FIGS. 1 and 2 , is an axial blower that blows air drawn from one axial side of a fan central axis CLf (see  FIG. 3 ), which is a rotational center of a fan  20  of the air blower  8 , toward the other axial side. 
       FIG. 3  is a view taken along line III-III in  FIG. 1 , showing an inside structure of the air blower  8 . As shown in  FIGS. 1 and 3 , the air blower  8  blows the air along the fan central axis CLf, as indicated by an arrow FLf, when the fan  20  is rotated about the fan central axis CLf in a fan rotational direction DRf. 
     The air blower  8  includes an electric motor  10 , the fan  20 , a fan shroud  30  and a drive unit  40 . The electric motor  10  is an outer rotor type. The fan  20  is rotated by the electric motor  10  and generates a flow of the air. The fan shroud  30  surrounds the fan  20  and guides the air. The drive unit  40  controls energization of the electric motor  10 . 
     The electric motor  10  includes a housing  11 , a shaft  12 , an outer rotor  14 , and a stator  15 . 
     The housing  11  is a non-rotatable member fixed to the fan shroud  30 . The shaft  12 , which is shaped into a cylindrical column form and has the fan central axis CLf as a central axis thereof, is fixed to the housing  11 . 
     The outer rotor  14  includes a yoke  141 , which is made of metal, and permanent magnets  142 . The yoke  141  is a bottomed rotor member, which is shaped into a bottomed cylindrical tubular form and is made of metal. The yoke  141  is connected to the shaft  12  through a bearing and is rotatable about the fan central axis CLf relative to the shaft  12 . 
     The yoke  141  includes a yoke bottom portion  141   a  and a yoke tubular portion  141   b.  The yoke bottom portion  141   a  serves as a rotor member bottom portion that forms a bottom portion of the yoke  141 . The yoke tubular portion  141   b  is shaped into a cylindrical tubular form that has the fan central axis CLf as a central axis thereof. The yoke tubular portion  141   b  is joined to the yoke bottom portion  141   a  through one end  141   d  of the yoke tubular portion  141   b.  The permanent magnets  142  are fixed to an inner peripheral side of the yoke tubular portion  141   b.    
     Furthermore, as shown in  FIG. 4 , a plurality of opening holes  141   c  extends through the yoke bottom portion  141   a  in a fan axial direction that is an axial direction of the fan central axis CLf.  FIG. 4  is a view taken in a direction of an arrow IV in  FIG. 3 , showing only a yoke and a fan boss  21  of the fan  20 . The opening holes  141   c,  which are formed in the yoke bottom portion  141   a,  are arranged one after another at equal intervals in a fan circumferential direction, which is a circumferential direction about the fan central axis CLf. The opening holes  141   c  serve as cooling holes that conduct the air for cooling the electric motor  10 . 
     As shown in  FIG. 3 , the stator  15  includes coils  152  that are wound around an iron core, and the stator  15  is placed in an inside of the outer rotor  14 . The stator  15  is a non-rotatable member that is fixed to the housing  11 . The coils  152  of the stator  15  are energized by the drive unit  40 , and a voltage of the coils  152  is controlled by the drive unit  40 . 
     The fan  20  is an axial fan and includes the fan boss  21  and a plurality of blades  22  made of resin. The fan boss  21  is shaped into a bottomed cylindrical tubular form. The blades  22  are formed at an outer side of the fan boss  21 . Specifically, as shown in  FIG. 1 , the blades  22  are place at an outer peripheral side of the fan boss  21  and extend radially outer side from the fan boss  21 . The blades  22  are arranged one after another at equal intervals in the fan circumferential direction. The fan boss  21  and the blades  22  are integrally molded together as a one-piece body. 
     As shown in  FIG. 3 , the fan boss  21  includes a fan boss bottom portion  211  and a fan boss tubular portion  212 . The fan boss bottom portion  211  forms a bottom portion of the fan boss  21 . The fan boss tubular portion  212  is shaped into a cylindrical tubular form that has the fan central axis CLf as a central axis thereof. The fan boss tubular portion  212  is joined to the fan boss bottom portion  211  through one end  212   c  of the fan boss tubular portion  212 . 
     Specifically, the fan boss bottom portion  211  includes an insert member  211   a  and an outer peripheral resin portion  211   b.  The insert member  211   a  is a metal plate. The outer peripheral resin portion  211   b  is made of resin and is placed at an outer peripheral side of the insert member  211   a.  The insert member  211   a  and the outer peripheral resin portion  211   b  are integrally formed by insert molding. 
     Furthermore, the fan boss tubular portion  212  is placed on a radially outer side of the yoke  141 . In other words, the yoke  141  is placed at the inside of the fan boss  21 . The fan boss bottom portion  211  is stacked on the yoke bottom portion  141   a  in the fan axial direction and is fixed to the yoke bottom portion  141   a  with, for example, screws. In this way, the outer rotor  14 , which includes the yoke  141 , is rotated about the fan central axis CLf integrally with the fan  20 , which includes the fan boss  21 . 
     Furthermore, as shown in  FIGS. 4 and 5 , the fan boss  21  includes a plurality of bottom portion ribs  213 , which project from the fan boss bottom portion  211  toward the yoke bottom portion  141   a  side.  FIG. 5  is a perspective cross sectional view showing a cross section of only the yoke  141  and the fan boss  21 . The bottom portion ribs  213  of the fan boss  21  are respectively placed at corresponding locations of the fan boss bottom portion  211  that respectively overlap with the opening holes  141   c  of the yoke bottom portion  141   a.  The bottom portion ribs  213  promote discharge of the air from the inside of the yoke  141  through the opening holes  141   c  in response to the rotation of the fan  20 . This flow of the air is indicated by a dotted arrow FLa in  FIG. 3 . 
     Specifically, as indicated by the dotted arrow FLa in  FIG. 3 , a portion of the air, which is fed by the blades  22 , enters the inside of the yoke  141  from the side that is opposite from the yoke bottom portion  141   a  side. Then, this air in the inside of the yoke  141  flows through the opening holes  141   c  (see  FIG. 4 ) and enters an axial gap between the yoke bottom portion  141   a  and the fan boss bottom portion  211 . Furthermore, the air, which is supplied into this axial gap, is outputted to an outside of the fan boss  21  through a radial gap that is communicated with the axial gap and is formed between the yoke tubular portion  141   b  and the fan boss tubular portion  212 . 
     Specifically, as shown in  FIG. 5 , each of the bottom portion ribs  213  of the fan boss  21  is formed such that at least a portion of the bottom portion rib  213  (e.g., a distal end part  213   b  of the bottom portion rib  213 ) is inserted into the inside of the corresponding opening hole  141   c  of the yoke bottom portion  141   a.  Furthermore, each bottom portion rib  213  is formed such that the bottom portion rib  213  does not project from the opening hole  141   c  toward the stator  15  (see  FIG. 3 ) in the fan axial direction. 
     Here, the fan boss bottom portion  211  includes a rib connecting part  211   c,  to which a base end  213   a  of each bottom portion rib  213  is joined, at a corresponding location of the fan boss bottom portion  211  that is overlapped with the opening holes  141   c  of the yoke bottom portion  141   a  in the fan axial direction. The rib connecting part  211   c  is spaced from the yoke bottom portion  141   a  in the fan axial direction by a corresponding distance. In other words, the rib connecting part  211   c  is placed such that the rib connecting part  211   c  forms an axial gap between the rib connecting part  211   c  and the yoke bottom portion  141   a.  Therefore, a height of the bottom portion rib  213  measured from the rib connecting part  211   c  is set to be equal to or smaller than a sum of a length of the axial gap discussed above and an axial thickness of the portion of the yoke bottom portion  141   a  located around the opening hole  141   c.    
     The bottom portion ribs  213  of the fan boss  21  are arranged one after another in the fan circumferential direction, as shown in  FIG. 4 . Each of primary air flow passages  211   d  is formed between corresponding adjacent two of the bottom portion ribs  213 . The primary air flow passage  211   d  extends from an inner side to an outer side in a radial direction of the fan central axis CLf. That is, the air, which is outputted from the opening hole  141   c  of the yoke bottom portion  141   a  to the outside of the yoke  141 , is guided by the primary air flow passage  211   d  toward the outer side in the radial direction of the fan central axis CLf (see  FIG. 3 ). 
     As shown in  FIG. 4 , the fan boss tubular portion  212  of the fan boss  21  is placed on the radially outer side of the yoke tubular portion  141   b  such that the radial gap discussed above is interposed between the yoke tubular portion  141   b  and the fan boss tubular portion  212 . The fan boss  21  includes a plurality of tubular portion ribs  214 , which project from the fan boss tubular portion  212  toward an inner side of the fan boss tubular portion  212  through the radial gap described above. The tubular portion ribs  214  are outer peripheral side ribs, which are located on the radially outer side of the bottom portion ribs  213  in the inside of the fan boss  21 . 
     Furthermore, as shown in  FIGS. 5 and 6 , in the inside of the fan boss  21 , each of the tubular portion ribs  214  extends along the fan boss bottom portion  211  from an inner peripheral surface  212   a  of the fan boss tubular portion  212  to a location of a radially outer side part of the bottom portion rib  213  in the radial direction of the fan central axis CLf.  FIG. 6  is a view after removal of the yoke  141  from  FIG. 4 , i.e., a view of the fan boss  21  alone taken in the direction of the arrow IV in  FIG. 3 . In the following discussion, the radial direction of the fan central axis CLf will be also referred to as a fan radial direction. 
     The tubular portion ribs  214  of the fan boss  21  are arranged one after another in the fan circumferential direction. Each of secondary air flow passages  212   b  is formed between corresponding adjacent two of the tubular portion ribs  214  such that the secondary air flow passage  212   b  extends in the fan axial direction along the inner peripheral surface  212   a  of the fan boss tubular portion  212 . That is, the secondary air flow passage  212   b  guides the air from the one end  212   c  side of the fan boss tubular portion  212 , which is the fan boss bottom portion  211  side in the fan axial direction, toward the other end  212   d  side of the fan boss tubular portion  212 , which is opposite from the one end  212   c  in the fan axial direction. Therefore, an upstream end of the secondary air flow passage  212   b  is located at the one end  212   c  side of the fan boss tubular portion  212 , and a downstream end of the secondary air flow passage  212   b  is located at the other end  212   d  side of the fan boss tubular portion  212 . 
     Furthermore, since the tubular portion ribs  214  extend to the fan boss bottom portion  211 , the upstream side of each secondary air flow passage  212   b  extends to the fan boss bottom portion  211 . Therefore, the primary air flow passages  211   d  are formed such that as indicated by dotted hatching in  FIG. 6 , each primary air flow passage  211   d  is continuous to corresponding one of the secondary air flow passages  212   b.  In other words, the bottom portion ribs  213  are respectively formed such that the flow of the air, which is outputted from the corresponding primary air flow passage  211   d,  extends continuously into the corresponding secondary air flow passage  212   b.    
     Specifically, as shown in  FIG. 6 , each of the bottom portion ribs  213  is connected to a corresponding one of the tubular portion ribs  214  at a radially outer end of the bottom portion rib  213 . In this way, each of the primary air flow passages  211   d  is connected in series with the corresponding one of the secondary air flow passages  212   b.  The dotted hatching of  FIG. 6  indicates only one of the connections, each of which connects between the corresponding primary air flow passage  211   d  and the corresponding secondary air flow passage  212   b.    
     Furthermore, the bottom portion ribs  213  and the tubular portion ribs  214  are formed to function as fan blades of a centrifugal fan to generate the flow of the air from the radially inner side to the radially outer side in the fan radial direction in the primary and secondary air flow passages  211   d,    212   b.  Specifically, the bottom portion ribs  213  are curved in a common direction in the fan circumferential direction. 
     In the view taken in the fan axial direction, each of the bottom portion ribs  213  and the tubular portion ribs  214  is tilted relative a corresponding fan radial direction in a manner similar to that of fan blades of a turbo fan. That is, each of the tubular portion ribs  214  is tilted relative to the corresponding fan radial direction in a counter-rotational direction that is opposite from the fan rotational direction DRf such that the amount of displacement of the tubular portion rib  214 , which is measured from the corresponding fan radial direction of the fan central axis CLf in the counter-rotational direction, is progressively increased toward the radially outer side in the corresponding fan radial direction of the fan central axis CLf. Also, each of the bottom portion ribs  213  is tilted relative to the corresponding fan radial direction in the counter-rotational direction that is opposite from the fan rotational direction DRf such that the amount of displacement of the bottom portion rib  213 , which is measured from the corresponding fan radial direction of the fan central axis CLf in the counter-rotational direction, is progressively increased toward the radially outer side in the corresponding fan radial direction of the fan central axis CLf. 
     As discussed above, the bottom portion ribs  213  and the tubular portion ribs  214  are formed in the inside of the fan boss  21  and have the function of the centrifugal fan in response to the rotation of the fan  20 . Therefore, the bottom portion ribs  213  and the tubular portion ribs  214  promote the outflow of the air from the inside of the yoke  141  of the electric motor  10  (see  FIG. 3 ) to the outside of the yoke  141  through the opening holes  141   c  (see  FIG. 4 ). That is, the bottom portion ribs  213  and the tubular portion ribs  214  promote the cooling of the electric motor  10  by the air that flows in the inside of the yoke  141 . 
     As discussed above, according to the present embodiment, the fan boss  21  includes the bottom portion ribs  213 , which promote the discharge of the air from the inside of the yoke  141  through the opening holes  141   c  in response to the rotation of the fan  20 . Each of the bottom portion ribs  213  projects from the fan boss bottom portion  211  toward the yoke bottom portion  141   a  at the corresponding location of the fan boss bottom portion  211  where the bottom portion rib  213  is overlapped with the corresponding opening hole  141   c  of the yoke bottom portion  141   a  in the fan axial direction. Therefore, a projecting height of the bottom portion rib  213  can be increased by using the thickness of the yoke bottom portion  141   a.  As a result, in comparison to the structure of the air blower of the patent literature  1 , in which the air-blowing projections, which correspond to the bottom portion ribs  213 , are formed in the yoke, it is possible to improve the cooling performance for cooling the electric motor  10  by the air that flows in the inside of the yoke  141  while limiting an increase in a size of the electric motor  10  in the fan axial direction. 
     Here, it should be noted that the projecting height of each bottom portion rib  213 , which is formed in the inside of the fan boss  21 , may be increased within an extent that does not cause an interference of the bottom portion rib  213  with the non-rotatable member, such as the stator  15  formed in the inside of the outer rotor  14  of the electric motor  10 . Furthermore, it is confirmed that according to the present embodiment, when the bottom portion ribs  213  are formed, the amount of air flow, which flows between the corresponding tubular portion ribs  214 , is increased by about 9% in comparison to a comparative case, in which the bottom portion ribs  213  are absent. 
     Furthermore, each of the bottom portion ribs  213  of the fan boss  21  is formed such that at least a portion of the bottom portion rib  213  is inserted into the inside of the corresponding opening hole  141   c  of the yoke bottom portion  141   a.  Therefore, in comparison to a structure, in which the bottom portion rib  213  is not inserted into the opening hole  141   c,  the projecting height of the bottom portion rib  213  can be increased. Thereby, the cooling performance of the electric motor  10  can be improved. Furthermore, when the fan  20  is installed to the yoke  141 , the bottom portion ribs  213  can be used for the positioning of the fan  20  relative to the yoke  141 . Thereby, the assemblability of the fan  20  relative to the yoke  141  can be improved. 
     Furthermore, according to the present embodiment, the bottom portion ribs  213  are respectively formed such that the bottom portion rib  213  does not project from the corresponding opening hole  141   c  of the yoke bottom portion  141   a  toward the stator  15  side. Therefore, when the fan  20  is rotated, it is possible to limit interference between each bottom portion rib  213  and the non-rotatable member installed in the inside of the yoke  141 . Furthermore, it is possible to limit an increase in the size of the electric motor  10  in the fan axial direction, which would be otherwise caused by the provision of the bottom portion ribs  213 . 
     According to the present embodiment, the rib connecting part  211   c,  which is the part of the fan boss bottom portion  211  and to which the base end  213   a  of each bottom portion rib  213  is joined, is spaced from the yoke bottom portion  141   a  in the fan axial direction by the corresponding distance. Therefore, the projecting height of the bottom portion rib  213  can be increased by the amount, which corresponds to this distance between the rib connecting part  211   c  and the yoke bottom portion  141   a  in the fan axial direction. 
     Furthermore, according to the present embodiment, each primary air flow passage  211   d,  which guides the air discharged from the corresponding opening hole  141   c  of the yoke bottom portion  141   a  toward the outer side in the radial direction of the fan central axis CLf, is formed between the corresponding adjacent two of the bottom portion ribs  213 . Therefore, the air, which is outputted from the opening hole  141   c,  is smoothly guided to the outer side in the radial direction of the fan central axis CLf. Thereby, the outflow of the air from the inside of the yoke  141  through the opening holes  141   c  can be promoted. 
     Furthermore, according to the present embodiment, the bottom portion ribs  213  are respectively formed such that the flow of the air, which is outputted from the corresponding primary air flow passage  211   d,  extends continuously into the corresponding secondary air flow passage  212   b  that guides the air from the one end  212   c  side to the other end  212   d  side of the fan boss tubular portion  212 . Therefore, the air, which flows in the primary air flow passage  211   d,  is guided to the outside of the fan boss  21  through the corresponding secondary air flow passage  212   b.  Thereby, it is possible to promote the outflow of the air from the inside of the yoke  141  through the opening holes  141   c.    
     Furthermore, according to the present embodiment, each of the tubular portion ribs  214  is tilted relative to the corresponding fan radial direction in the counter-rotational direction that is opposite from the fan rotational direction DRf such that the amount of displacement of the tubular portion rib  214 , which is measured from the corresponding fan radial direction of the fan central axis CLf in the counter-rotational direction, is progressively increased toward the radially outer side in the corresponding fan radial direction of the fan central axis CLf. Also, each of the bottom portion ribs  213  is tilted relative to the corresponding fan radial direction in the counter-rotational direction that is opposite from the fan rotational direction DRf such that the amount of displacement of the bottom portion rib  213 , which is measured from the corresponding fan radial direction of the fan central axis CLf in the counter-rotational direction, is progressively increased toward the radially outer side in the corresponding fan radial direction of the fan central axis CLf. Therefore, the bottom portion ribs  213  and the tubular portion ribs  214  function as the fan blades of the turbo fan. Thereby, it is possible to promote the outflow of the air from the inside of the yoke  141  through the opening holes  141   c.    
     Furthermore, according to the present embodiment, the bottom portion ribs  213 , which promote the cooling of the electric motor  10 , are parts of the fan boss  21 . Therefore, it is not required to separately provide a member that promotes the cooling of the electric motor  10 . Thereby, it is possible to simplify the structure of the air blower  8 . 
     Second Embodiment 
     Next, a second embodiment will be described. In the present embodiment, differences, which are different from the first embodiment, will be mainly described, and the discussion of the identical portions or the equivalent portions will be omitted or simplified. 
       FIG. 7  is a view of the fan boss  21  alone taken in the direction of the arrow IV in  FIG. 3  according to the present embodiment, corresponding to  FIG. 6  of the first embodiment. In the view taken in the fan axial direction, each of the bottom portion ribs  213  and the tubular portion ribs  214  of the first embodiment is tilted relative the corresponding fan radial direction in the manner similar to that of the fan blades of the turbo fan. In contrast, each of the bottom portion ribs  213  and the tubular portion ribs  214  of the present embodiment is tilted relative the corresponding fan radial direction in a manner similar to that of fan blades of a sirocco fan. Specifically, each of the tubular portion ribs  214  is tilted relative to the corresponding fan radial direction in the fan rotational direction DRf such that the amount of displacement of the tubular portion rib  214 , which is measured from the corresponding fan radial direction of the fan central axis CLf in the fan rotational direction DRf, is progressively increased toward the radially outer side in the corresponding fan radial direction of the fan central axis CLf. Also, each of the bottom portion ribs  213  is tilted relative to the corresponding fan radial direction in the fan rotational direction DRf such that the amount of displacement of the bottom portion rib  213 , which is measured from the corresponding fan radial direction of the fan central axis CLf in the fan rotational direction DRf, is progressively increased toward the radially outer side in the corresponding fan radial direction of the fan central axis CLf. 
     The bottom portion ribs  213  and the tubular portion ribs  214  are formed in the above described manner, so that the bottom portion ribs  213  and the tubular portion ribs  214  function as the fan blades of the sirocco fan. Therefore, it is possible to promote the outflow of the air from the inside of the yoke  141  through the opening holes  141   c.    
     In the present embodiment, the advantages, which are achieved by the structure that is common to the first embodiment described above, can be achieved like in the first embodiment. 
     Other Embodiments 
     (1) In each of the above embodiments, the fan  20  includes the insert member  211   a  made of the metal, and thereby the fan  20  is made from the resin material and the metal material through the insert molding. However, this is merely one example, and the fan  20  may be formed only from the resin through injection molding, which is other than the insert molding. 
     (2) In each of the above embodiments, the bottom portion ribs  213  of the fan boss  21  are respectively formed such that the bottom portion rib  213  does not project from the corresponding opening hole  141   c  of the yoke bottom portion  141   a  toward the stator  15  side in the fan axial direction. However, this is merely one example, and each of the bottom portion ribs  213  may project from the opening hole  141   c  toward the stator  15  side within an extent that does not cause an interference of the bottom portion rib  213  with the non-rotatable member, such as the stator  15 . 
     (3) In each of the above embodiments, each of the bottom portion ribs  213  of the fan boss  21  is connected to the corresponding one of the tubular portion ribs  214 . However, this is merely one example, and the bottom portion rib  213  may not be connected to the tubular portion rib  214  as long as the air, which is outputted from the primary air flow passage  211   d,  can smoothly flow into the secondary air flow passage  212   b.    
     (4) In each of the above embodiments, the bottom portion ribs  213  project from the fan boss bottom portion  211 . Specifically, as shown in  FIG. 5 , the bottom portion ribs  213  are formed in the outer peripheral resin portion  211   b  of the fan boss bottom portion  211 . However, this is merely one example, and the bottom portion ribs  213  may not be formed in the insert member  211   a  of the fan boss bottom portion  211 . 
     (5) In each of the above embodiments, the fan  20  is the axial fan. However, this is mere one example, and the fan  20  may be another type that is other than the axial type as long as the outer rotor  14  of the electric motor  10  is placed in the inside of the fan boss  21 . For example, the fan  20  may be a centrifugal fan or a mixed-flow fan. 
     The present disclosure should not be limited to the above embodiments. The present disclosure encompasses various modifications and variations within the equivalent scope. In each of the above embodiments, it is clear that the components of the embodiment are not necessarily indispensable unless the components are explicitly stated as indispensable and thought to be theoretically indispensable. When numerals such as the number, values, amounts, and ranges of components of each embodiment are referred to in each above embodiment, the numerals are not limited to the specific ones unless the numerals are explicitly indispensable and clearly thought to be theoretically limited to the specific ones. In each of the above embodiments, when materials, shapes and positional relationships of the components are referred to, the materials, shapes and positional relationships are not limited to the specific ones unless the materials, shapes and positional relationship are explicitly shown and theoretically limited to the specific ones.