Patent Publication Number: US-2019195230-A1

Title: Centrifugal fan

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2017-246706 filed on Dec. 22, 2017. The entire contents of this application are hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to a centrifugal fan. 
     2. Description of the Related Art 
     To date, a blowing device having a plurality of vanes is known. The existing blowing device relates to an electric blowing device including an impeller that has a plurality of vanes. A current of air sucked from a suction port by rotation of the vanes passes through the inside of the impeller, a diffuser, and a bracket, and, while cooling a stator, a rotor and the like, finally is exhausted to the outside of the electric blowing device. In addition, in this electric blowing device, by increasing the surface area of the stator core, the area of contact with the current of air is increased and cooling efficiency is improved. 
     However, in the existing electric blowing device, the surface area of the stator core is increased by stacking plural types of electromagnetic steel plates having different shapes. Therefore, there is a possibility that the manufacturing cost may become relatively high. 
     SUMMARY OF THE INVENTION 
     A centrifugal fan according to an exemplary embodiment of the present disclosure is a centrifugal fan that sends out in a radial direction a fluid sucked from an axial direction, and includes an impeller rotatable about a center axis extending in a top-bottom direction, and a motor that rotates the impeller. The motor includes a rotor rotatable about the center axis, and a stator that faces at least a portion of the rotor in the radial direction. The impeller includes an impeller hub fixed to the rotor, a plurality of centrifugal vanes disposed in a circumferential direction on a radial-direction outer side of the impeller hub, and a plurality of axial flow vanes disposed in the circumferential direction on a radial-direction inner side of the impeller hub. The axial flow vanes are disposed on an axial-direction upper side of the stator. 
     The above and other elements, features, steps, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a centrifugal fan as viewed from an axial-direction upper side. 
         FIG. 2  is a perspective view of the centrifugal fan as viewed from an axial-direction lower side. 
         FIG. 3  is a sectional view illustrating the centrifugal fan of a configuration example as viewed from a radial direction. 
         FIG. 4  is a sectional view illustrating the centrifugal fan of another configuration example as viewed from the radial direction. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments of the present disclosure will be described below with reference to the drawings. Further, in this specification, in a centrifugal fan  100 , a rotation axis of a motor  2  will be referred to as “center axis CA”, and a direction parallel to the center axis CA will be referred to as “axial direction”. As an axial side, the direction from a lower housing  32  (to be described later) toward an upper housing  31  (to be described later) along the axial direction will be referred to as “axial-direction upper side”. As another axial side, the direction from the upper housing  31  to the lower housing  32  along the axial direction will be referred to as “axial-direction lower side”. For each component, an end portion on the axial-direction upper side will be referred to as “upper end portion” and an end position on the axial-direction upper side will be referred to as “upper end”. For each component, an end portion on the axial-direction lower side will be referred to as “lower end portion” and an end position on the axial-direction lower side will be referred to as “lower end”. In addition, for the surfaces of each component element, a surface facing toward the axial-direction upper side will be referred to as “upper surface” and a surface facing toward the axial-direction lower side will be referred to as “lower surface”. 
     The direction perpendicular to the center axis CA will be referred to as “radial direction”, and the rotational direction of a rotor  21  about the center axis CA will be referred to as “circumferential direction”. The direction toward the center axis CA along the radial direction will be referred to as “radial-direction inner side” and the direction away from the center axis CA along the radial direction will be referred to as “radial-direction outer side”. For each component, an end portion on the radial-direction inner side will be referred to as a “radial-direction inner end portion” and an end position on the radial-direction inner side will be referred to as a “radial-direction inner end”. For each component, an end portion on the radial-direction outer side will be referred to as “radial-direction outer end portion” and an end position on the radial-direction outer side will be referred to as “radial-direction outer end”. In addition, for the side surfaces of each component, the side surface facing toward the radial-direction inner side will be referred to as “radial-direction inner side surface” and the side surface facing toward the radial-direction outer side will be referred to as “radial-direction outer side surface”. 
     Further, note that designations such as those of the directions, planes, and constituent parts described above do not indicate positional relationships, directions, and the like in the case of being incorporated in an actual device. 
       FIG. 1  is a perspective view of a centrifugal fan as viewed from the axial-direction upper side.  FIG. 2  is a perspective view of the centrifugal fan as viewed from the axial-direction lower side.  FIG. 3  is a sectional view illustrating the centrifugal fan of a configuration example as viewed from the radial direction. Further, in  FIG. 1 , in order to make the configuration easier to understand, a housing  3  is illustrated in a transparent manner. In addition,  FIG. 3  is a cross section of the centrifugal fan  100  taken along a plane including the center axis CA along a one-dot chain line A-A in  FIG. 1 . 
     The centrifugal fan  100  is a blowing device that sends out in a radial direction a fluid that is sucked from the axial direction. Further, in the present embodiment, the fluid that the centrifugal fan  100  sucks and sends out is air. The centrifugal fan  100  is used for, for example, a cooling fan of an electronic device that is required to be reduced in thickness. However, the application of the centrifugal fan  100  is not limited to this example. The centrifugal fan  100  includes an impeller  1  and the motor  2 . In the present embodiment, the centrifugal fan  100  further includes the housing  3  and a board  4 . 
     The impeller  1  is rotatable about the center axis CA that extends in the top-bottom direction. The impeller  1  is attached to the motor  2 . The impeller  1  has an impeller hub  11 , centrifugal vanes  13 , and axial flow vanes  15 . In the present embodiment, the impeller  1  further includes a flange portion  12 , a ring portion  14 , and a center connection portion  16 . The configuration of the impeller  1  will be described later. 
     The impeller  1  rotates integrally with the motor  2 . The motor  2  has the rotor  21  and a stator  22 . The motor  2  further includes a shaft  20 . The motor  2  rotates the impeller  1 . More specifically, the motor  2  rotates the impeller  1  together with the shaft  20  and the rotor  21  by rotating the shaft  20  about the center axis CA. 
     The shaft  20  is rotatable about the center axis CA and extends in the axial direction. The rotor  21  is fixed to the shaft  20 . 
     The rotor  21  is rotatable about the center axis CA. More specifically, the rotor  21 , together with the shaft  20 , is rotatable about the center axis CA. The impeller  1  is fixed to the rotor  21 . The rotor  21  has a rotor holder  211  and a magnet  212 . 
     The rotor holder  211  has a capped cylinder shape and is attached to the shaft  20 . In the present embodiment, the rotor holder  211  is composed of a plate portion  211   a  and a cylinder portion  211   b . The plate portion  211   a  is fixed to the shaft  20  and extends to the radial-direction outer side from the shaft  20 . The cylinder portion  211   b  extends to the axial-direction lower side from a radial-direction outer end portion of the plate portion  211   a . Through holes  211   c  penetrating the rotor holder  211  in the axial direction are provided on an upper surface of the rotor holder  211 . More specifically, the through holes  211   c  penetrating the plate portion  211   a  in the axial direction are provided in the plate portion  211   a . With this configuration, the airflow sent to the axial-direction lower side by the axial flow vanes  15  of the impeller  1  flows through the through holes  211   c  and into the motor  2 . Therefore, the interior of the motor  2  can be cooled by the airflow sent out by the axial flow vanes  15 . 
     The rotor holder  211  holds the magnet  212 . More specifically, the magnet  212  is provided on a radial-direction inner side surface of the cylinder portion  211   b  of the rotor holder  211 . The magnet  212  faces the stator  22  in the radial direction. The magnet  212  has a plurality of magnetic poles that are different from each other and that are disposed in the circumferential direction. 
     The stator  22  faces at least a portion of the rotor  21  in the radial direction. The rotor  21  rotates by interaction with the magnetic field generated by the stator  22 . An upper portion of the stator  22  is disposed on the radial-direction inner side of the cylinder portion  211   b  of the rotor holder  211  and the magnet  212 . 
     The centrifugal fan  100  includes the housing  3  as described above. The housing  3  houses the impeller  1  therein. In the present embodiment, the housing  3  further houses the motor  2  and the board  4  therein. The housing  3  is provided with an upper suction port  3   a  and a lower suction port  3   b . The upper suction port  3   a  is provided on an upper surface of the housing  3  and opens in the axial direction on the axial-direction upper side of the impeller  1 . The lower suction port  3   b  is provided on a lower surface of the housing  3  and opens in the axial direction on the axial-direction lower side of the impeller  1 . According to these configurations, because the upper suction port  3   a  and the lower suction port  3   b  are respectively provided above and below the impeller  1  in the axial direction, it is possible to increase the intake amount of air flowing into the impeller  1 . Accordingly, the blowing amount of airflow sent out by the centrifugal fan  100  increases. 
     Radial-direction inner edge portions of the upper suction port  3   a  and the lower suction port  3   b  respectively surround the center axis CA. Here, the “radial-direction inner edge portions” of the upper suction port  3   a  and the lower suction port  3   b  are “radial-direction inner edge portions of opening regions” of the upper suction port  3   a  and the lower suction port  3   b , respectively. The opening regions of the upper suction port  3   a  and the lower suction port  3   b  are not particularly limited, and in the present embodiment, they are circular about the center axis CA. 
     In the present embodiment, a radial-direction inner edge of the upper suction port  3   a  and a radial-direction inner edge of the lower suction port  3   b  are located on the radial-direction inner side of a radial-direction outer end of the centrifugal vanes  13 . Further, note that the present invention is not limited to the example of the present embodiment and that at least one of the radial-direction inner edge of the upper suction port  3   a  and the radial-direction inner edge of the lower suction port  3   b  may have the same radial-direction position as the radial-direction outer end of the centrifugal vanes  13 . Alternatively, at least one of the radial-direction inner edge of the upper suction port  3   a  and the radial-direction inner edge of the lower suction port  3   b  may be located on the radial-direction outer side of the radial-direction outer end of the centrifugal vanes  13 . 
     In addition, the radial-direction inner edge of the upper suction port  3   a  is located on the radial-direction outer side of a radial-direction inner end of the centrifugal vanes  13 . In addition, the radial-direction inner edge of the lower suction port  3   b  is located on the radial-direction outer side of the radial-direction inner end of the centrifugal vanes  13 . According to these configurations, it is possible to increase the intake amount of air flowing into the spaces between the centrifugal vanes  13  from the upper suction port  3   a . In addition, it is possible to increase the intake amount of air flowing into the spaces between the centrifugal vanes  13  from the lower suction port  3   b . Therefore, the blowing amount of airflow sent out by the centrifugal fan  100  further increases. Further, note that the present invention is not limited to the example of the present embodiment and that at least one of the radial-direction inner edge of the upper suction port  3   a  and the radial-direction inner edge of the lower suction port  3   b  may have the same radial-direction position as the radial-direction inner end of the centrifugal vanes  13 . Alternatively, at least one of the radial-direction inner edge of the upper suction port  3   a  and the radial-direction inner edge of the lower suction port  3   b  may be located on the radial-direction inner side of the radial-direction inner end of the centrifugal vanes  13 . 
     In addition, the housing  3  is provided with an outlet port  3   c . The outlet port  3   c  is provided in a radial-direction outer side surface of the housing  3  and opens at least in the radial direction on the radial-direction outer side of the impeller  1 . 
     In addition, in the present embodiment, the housing  3  is composed of the upper housing  31  and the lower housing  32  that is attached to the axial-direction lower side of the upper housing  31 . The upper housing  31  has an upper plate portion  311  and a peripheral wall portion  312 . The lower housing  32  has a lower plate portion  321 . 
     The upper plate portion  311  has a plate shape that expands in the radial direction and is located on the axial-direction upper side of the impeller  1 . The upper plate portion  311  is provided with the upper suction port  3   a . The upper suction port  3   a  penetrates the upper plate portion  311  in the axial direction. 
     The peripheral wall portion  312  protrudes to the axial-direction lower side from a radial-direction outer end portion of the upper plate portion  311  and extends along a radial-direction outer end portion of the upper plate portion  311 . The peripheral wall portion  312  is provided with the outlet port  3   c . The outlet port  3   c  penetrates the peripheral wall portion  312  in the radial direction. 
     The lower plate portion  321  is attached to a lower end portion of the peripheral wall portion  312 . The lower plate portion  321  has a plate shape that expands in the radial direction and is located on the axial-direction lower side of the impeller  1 . The lower plate portion  321  is provided with the lower suction port  3   b . The lower suction port  3   b  penetrates the lower plate portion  321  in the axial direction. 
     The airflow sucked from the upper suction port  3   a  and the lower suction port  3   b  by the centrifugal vanes  13  is sent out to the radial-direction outer side of the impeller  1 . The airflow, as viewed from the axial direction, flows along an inner surface of the peripheral wall portion  312  inside the housing  3  and is exhausted to the outside of the centrifugal fan  100  from the outlet port  3   c . Further, a portion of the airflow sucked from the upper suction port  3   a  is sent out to an upper portion of the motor  2  by the axial flow vanes  15  and flows through the through holes  211   c  of the rotor  21  to a lower portion of the motor  2  and then, together with the airflow sucked from the lower suction port  3   b , is sent out to the radial-direction outer side by the centrifugal vanes  13 . 
     In addition, the lower housing  32  is provided with a motor holding portion  321   a  and ribs  321   b . The motor holding portion  321   a  and the ribs  321   b  are, as viewed from the axial direction, disposed inside the lower suction port  3   b , more specifically, within the opening region of the lower suction port  3   b.    
     The motor holding portion  321   a  holds the motor  2  and the board  4 . More specifically, the motor  2  is held by the motor holding portion  321   a  with a holding member  2   a  therebetween. The board  4  faces an upper surface of the lower housing  32  with a gap therebetween and is held by the motor holding portion  321   a  with the holding member  2   a  therebetween. In the present embodiment, the motor holding portion  321   a  is circular about the center axis CA. 
     The ribs  321   b  support the motor holding portion  321   a . The ribs  321   b  extend toward the radial-direction inner side from a radial-direction inner edge portion of the opening region of the lower suction port  3   b . A radial-direction inner end portion of the ribs  321   b  is connected to a radial-direction outer end portion of the motor holding portion  321   a.    
     The centrifugal fan  100  has the board  4  as described above. The board  4  is, for example, electrically connected to the stator  22  and is electrically connected to an external circuit of the centrifugal fan  100  via a connection wire (not illustrated) drawn out to the outside of the centrifugal fan  100 . The board  4  is disposed on the axial-direction lower side of the motor  2  and is in the shape of a plate extending in the radial direction. In the present embodiment, a radial-direction outer edge of the board  4  is located on the radial-direction inner side of the radial-direction inner end of the centrifugal vanes  13 . According to this configuration, the outer edge of the board  4  is disposed on the radial-direction inner side of the radial-direction inner end of the centrifugal vanes  13  so that the board  4  does not interfere with the airflow. Therefore, it is possible to suppress a decrease in the blowing efficiency of the centrifugal vanes  13 . Further, note that the present invention is not limited to the example of the present embodiment and the radial-direction outer edge of the board  4  may have the same radial-direction position as the radial-direction inner end of the centrifugal vanes  13 . Alternatively, the radial-direction outer edge of the board  4  may be located on the radial-direction outer side of the radial-direction inner end of the centrifugal vanes  13 . 
     Next, the configuration of the impeller  1  will be described. As described above, the impeller  1  has the impeller hub  11 , the flange portion  12 , the centrifugal vanes  13 , the ring portion  14 , the axial flow vanes  15 , and the center connection portion  16 . 
     The impeller hub  11  houses an upper end portion of the motor  2  therein and is attached to the upper end portion of the motor  2 . More specifically, the impeller hub  11  is fixed to the rotor  21 . The impeller hub  11  has a cylindrical shape extending in the axial direction. According to this configuration, the air sent out by the axial flow vanes  15  easily flows to the axial-direction lower side. In addition, the rigidity of the impeller  1  is improved. 
     The impeller  1  has the flange portion  12  as described above. The flange portion  12  extends to the radial-direction outer side from a radial-direction outer side surface of the impeller hub  11 . Radial-direction inner end portions of the centrifugal vanes  13  are connected to the flange portion  12 . According to this configuration, the strength of the centrifugal vanes  13  can be improved. In addition, with the centrifugal vanes  13 , it is possible to send out the airflow sucked from the axial direction to the radial-direction outer side. 
     A radial-direction outer end of the flange portion  12  is located on the radial-direction inner side of the radial-direction outer end of the centrifugal vanes  13 . According to this configuration, because the radial-direction dimension of the flange portion  12  is reduced, the weight of the impeller  1  can be reduced. 
     In addition, as viewed from the radial direction, the axial-direction position of the flange portion  12  with respect to the centrifugal vanes  13  is not particularly limited, but is preferably the axial-direction center position of the centrifugal vanes  13  as in the present embodiment. That is, the flange portion  12  is preferably connected to the centrifugal vanes  13  at an axial-direction middle position of the radial-direction inner end portions of the centrifugal vanes  13 . According to this configuration, at the time of rotation of the impeller  1 , the centrifugal vanes  13  are less likely to shake up and down in the axial direction. Therefore, the strength of the centrifugal vanes  13  in the axial direction can be improved. In addition, for example, in the case where air is sucked from both of the upper suction port  3   a  and the lower suction port  3   b  provided on both sides of the housing  3  in the axial direction, the flow of the air sucked from either the upper suction port  3   a  or the lower suction port  3   b  is also not hindered by the flange portion  12 . Therefore, the blowing efficiency is improved as compared with the case where the flange portion  12  is connected to the centrifugal vanes  13  at a position other than the axial-direction middle position of the radial-direction inner end portions of the centrifugal vanes  13 . 
     The centrifugal vanes  13  are disposed in the circumferential direction on the radial-direction outer side of the impeller hub  11 . The number of the centrifugal vanes  13  is not limited to a prime number, but is preferably a prime number. If the number of the centrifugal vanes  13  is a prime number, it is possible to suppress noise generated when the centrifugal vanes  13  send out air. 
     The centrifugal vanes  13  extend in the axial direction from the flange portion  12 . In the present embodiment, the radial-direction inner end portions of the centrifugal vanes  13  extend to the axial-direction upper side from an upper surface of the flange portion  12  and extend to the axial-direction lower side from a lower surface of the flange portion  12 . According to this configuration, the airflow sucked from the upper suction port  3   a  and the airflow sucked from the lower suction port  3   b  can be sent out in the radial direction by the centrifugal vanes  13 . However, the present invention is not limited to this example, and the radial-direction inner end portions of the centrifugal vanes  13  may extend to the axial-direction upper side from the upper surface of the flange portion  12  or may extend to the axial-direction lower side from the lower surface of the flange portion  12 . In other words, the radial-direction inner end portions of the centrifugal vanes  13  may extend in the axial direction from at least one of the upper surface and lower surface of the flange portion  12 . 
     In the present embodiment, the radial-direction inner end portions of the centrifugal vanes  13  are provided spaced apart from the radial-direction outer side surface of the impeller hub  11  in the radial direction. According to this configuration, it is possible to provide the centrifugal vanes  13  at a position away from the radial-direction outer side surface of the impeller hub in the radial direction. As a result, because the radial-direction length of the centrifugal vanes  13  can be shortened, the impeller  1  can be reduced in weight. Further, note that the present invention is not limited to the example of the present embodiment and the radial-direction inner end portions of the centrifugal vanes  13  may be connected to the radial-direction outer side surface of the impeller hub  11 . According to this configuration, the radial-direction inner end portions of the centrifugal vanes  13  extend to the radial-direction outer side from the radial-direction outer side surface of the impeller hub  11 . Therefore, the strength of the centrifugal vanes  13  can be improved. 
     The ring portion  14  has an annular shape about the center axis CA. The ring portion  14  is connected to a radial-direction outer end portion of each of the centrifugal vanes  13  in the circumferential direction. According to this configuration, the strength of the centrifugal vanes  13  can be further improved by the ring portion  14 . 
     As viewed from the radial direction, the axial-direction position of the ring portion  14  with respect to the centrifugal vanes  13  is not particularly limited, but is preferably the axial-direction center position of the centrifugal vanes  13  as in the present embodiment. That is, the ring portion  14  is preferably connected to the centrifugal vanes  13  at the axial-direction middle position of the radial-direction outer end portions of the centrifugal vanes  13 . According to this configuration, at the time of rotation of the impeller  1 , the centrifugal vanes  13  are less likely to shake up and down in the axial direction. Therefore, the strength of the centrifugal vanes  13  in the axial direction can be improved. In addition, for example, when air is sucked from both of the upper suction port  3   a  and the lower suction port  3   b  provided on both sides of the housing  3  in the axial direction, the flow of the air sucked from either the upper suction port  3   a  or the lower suction port  3   b  is also not hindered by the ring portion  14 . Therefore, as compared with the case where the ring portion  14  is connected to the centrifugal vanes  13  at a position other than the axial-direction middle position of the radial-direction outer end portions of the centrifugal vanes  13 , the blowing efficiency is improved. 
     The axial flow vanes  15  are provided on the radial-direction inner side of the impeller hub  11  and are disposed in the circumferential direction. The number of the axial flow vanes  15  is not limited to a prime number, but is preferably a prime number. If the number of the axial flow vanes  15  is a prime number, noise generated when the axial flow vanes  15  send out air can be suppressed. 
     The axial flow vanes  15  are disposed on the axial-direction upper side of the stator  22 . According to this configuration, a portion of the airflow sucked from the axial direction by the rotation of the impeller  1  having a simple configuration is sent toward the stator  22  inside the motor  2  by the axial flow vanes  15 . After cooling the motor  2 , for example, a portion of the airflow flows in the radial direction together with the airflow sent out by the centrifugal vanes  13  located on the radial-direction outer side of the impeller hub  11 . Therefore, the motor  2  can be cooled with a low-cost configuration. 
     In the present embodiment, the axial flow vanes  15  extend to the radial-direction inner side from an upper end portion of the impeller hub  11 , which has a cylindrical shape, and are connected to the center connection portion  16 . According to this configuration, the strength of the impeller  1  can be improved. In addition, because at least a portion of the rotor  21  can be disposed inside the impeller hub  11 , the axial-direction dimension of the centrifugal fan  100  can be reduced. 
     Radial-direction outer end portions of the axial flow vanes  15  are connected to the upper end portion of the impeller hub  11 . Radial-direction inner end portions of the axial flow vanes  15  are connected to the center connection portion  16  disposed at the center of the impeller hub  11 . According to this configuration, the strength of the axial flow vanes  15  can be improved. In addition, the strength of the impeller  1  can be improved. 
     In addition, in the present embodiment, a radial-direction outer end of the axial flow vanes  15  is disposed on the radial-direction inner side of the radial-direction inner edge of the upper suction port  3   a . According to this configuration, the intake amount of air flowing from the upper suction port  3   a  can be increased. In addition, it is easy to guide a portion of the air sucked from the upper suction port  3   a  to the radial-direction outer side of the radial-direction outer end of the axial flow vanes  15 . Therefore, the blowing amount of airflow sent out by the centrifugal fan  100  further increases. However, the present invention is not limited to the example of the present embodiment, and the radial-direction outer end of the axial flow vanes  15  may be disposed at the same radial-direction position as the radial-direction inner edge of the upper suction port  3   a . Alternatively, the radial-direction outer end of the axial flow vanes  15  may be disposed on the radial-direction outer side of the radial-direction inner edge of the upper suction port  3   a.    
     In the present embodiment, the axial-direction position of an axial-direction upper end of the axial flow vanes  15  is the same as the axial-direction position of an axial-direction upper end of the center connection portion  16 . However, the present invention is not limited to this example, and the axial-direction position of the axial-direction upper end of the axial flow vanes  15  may be on the axial-direction lower side of the axial-direction position of the axial-direction upper end of the center connection portion  16 . 
     Alternatively, the axial-direction position of an axial-direction upper end of the axial flow vanes  15  may be on the axial-direction upper side of the axial-direction position of the axial-direction upper end of the center connection portion  16 . In other words, at least a portion of the axial flow vanes  15  may face the radial-direction inner edge of the upper suction port  3   a  in the radial direction. According to this configuration, because the axial flow vanes  15  can be disposed on the axial-direction upper side as much as possible, more air can be sent from the upper suction port  3   a  to the axial flow vanes  15 . 
     In addition, in the present embodiment, the axial-direction position of the axial-direction lower end of the axial flow vanes  15  is on the axial-direction upper side of the axial-direction position of the axial-direction lower end of the center connection portion  16 . However, the present invention is not limited to this example, and the axial-direction position of the axial-direction lower end of the axial flow vanes  15  may be the same as the axial-direction position of the axial-direction lower end of the center connection portion  16 . With this configuration, it is possible to make the centrifugal fan  100  thinner and increase the axial-direction width of the axial flow vanes  15 . Therefore, for example, the rotational-direction front side of the axial flow vanes  15  can be inclined to the axial-direction lower side going toward the rotational-direction front side of the axial flow vanes  15 . Therefore, the blowing amount of the centrifugal fan  100  can be improved. 
     In addition, in the present embodiment, the axial flow vanes  15  are disposed on the axial-direction upper side of an axial-direction upper end of the centrifugal vanes  13 . With this configuration, on the upstream side of the airflow drawn by the centrifugal vanes  13 , air can also be sent to the axial flow vanes  15 . Therefore, the amount of air that can be sent out by the axial flow vanes  15  can be increased. However, the present invention is not limited to the example of the present embodiment, and the axial flow vanes  15  may be disposed at the same axial-direction position as the centrifugal vanes  13  or may be disposed on the axial-direction lower side of the centrifugal vanes  13 . 
     The center connection portion  16  is disposed on the radial-direction inner side of the impeller hub  11  and is fixed to an upper end portion of the shaft  20 . In the present embodiment, the center connection portion  16  has a plate shape extending in the radial direction from the center axis CA, but it is not limited to this example. The center connection portion  16  may have an annular shape about the center axis CA through which the shaft  20  is inserted. 
     Next, a modification example of the present embodiment will be described. Hereinafter, a configuration different from the above embodiment will be described. In addition, the same reference numerals are given to the same constituent elements as those in the above-described embodiment and description thereof may be omitted. 
       FIG. 4  is a sectional view illustrating the centrifugal fan  100  of another configuration example as viewed from the radial direction. Further,  FIG. 4  is a cross section of the centrifugal fan  100  taken along a plane including the center axis CA along a one-dot chain line A-A in  FIG. 1 . 
     In the centrifugal fan  100  according to the modification example, the impeller  1  includes the impeller hub  11  and the centrifugal vanes  13 . In addition, in this modification example, the impeller  1  further includes the flange portion  12  and the ring portion  14 . That is, the impeller  1  according to the modification example does not have the axial flow vanes  15  and the center connection portion  16  of the above-described embodiment. On the other hand, the rotor  21  further includes axial flow vanes  213  in addition to the rotor holder  211  and the magnet  212 . The magnet  212  faces the stator  22  in the radial direction. The rotor holder  211  holds the magnet  212 . The axial flow vanes  213  are disposed in the circumferential direction on the radial-direction inner side of the impeller hub  11 . Furthermore, the rotor  21  further has a center connection portion  214 . The impeller hub  11  is fixed to the rotor  21 . The centrifugal vanes  13  are disposed in the circumferential direction on the radial-direction outer side of the impeller hub  11 . 
     In the modification example, the axial flow vanes  213  are disposed in the circumferential direction on the radial-direction inner side of the impeller hub  11  and the rotor holder  211  of the rotor  21 . The axial flow vanes  213  are provided in the rotor holder  211  and are located on the axial-direction upper side of the stator  22 . According to this configuration, a portion of the airflow sucked from the axial direction by the rotation of the rotor  21  and the impeller  1  is sent toward the inside of the motor  2  by the axial flow vanes  213 . After cooling the motor  2 , for example, a portion of the airflow flows in the radial direction together with the airflow sent out by the centrifugal vanes  13  located on the radial-direction outer side of the impeller hub  11 . Therefore, the motor  2  can be cooled with a low-cost configuration. In addition, for example, when the rotor holder  211  is formed of metal, the rigidity of the axial flow vanes  213  can be improved. 
     In addition, the axial flow vanes  213  extend to the radial-direction inner side from an upper end portion of the rotor holder  211  of the rotor  21  and are connected to the center connection portion  214 . According to this configuration, the strength of the impeller  1  can be improved. In addition, the rotor  21  can be disposed on the radial-direction inner side of the impeller hub  11 . In other words, the rotor  21  can be disposed inside the impeller hub  11 . Therefore, the axial-direction dimension of the centrifugal fan  100  can be reduced. 
     Radial-direction outer end portions of the axial flow vanes  213  are connected to the upper end portion of the rotor holder  211 . Radial-direction inner end portions of the axial flow vanes  213  are connected to a radial-direction outer end portion of the center connection portion  214  disposed at the center of the rotor holder  211 . According to this configuration, the strength of the axial flow vanes  213  can be improved. 
     In addition, in the present embodiment, a radial-direction outer end of the axial flow vanes  213  is disposed on the radial-direction inner side of the radial-direction inner edge of the upper suction port  3   a . According to this configuration, it is possible to increase the intake amount of air flowing into the spaces between the axial flow vanes  213  and the spaces between the centrifugal vanes  13  at the upper suction port  3   a . Therefore, the blowing amount of airflow sent out by the centrifugal fan  100  further increases. However, the present invention is not limited to the example of the present embodiment, and the radial-direction outer end of the axial flow vanes  213  may be disposed at the same radial-direction position as the radial-direction inner edge of the upper suction port  3   a . Alternatively, the radial-direction outer end of the axial flow vanes  213  may be disposed on the radial-direction outer side of the radial-direction inner edge of the upper suction port  3   a.    
     In the present embodiment, the axial-direction position of an axial-direction upper end of the axial flow vanes  213  is the same as the axial-direction position of an axial-direction upper end of the center connection portion  214 . However, the present invention is not limited to this example, and the axial-direction position of the axial-direction upper end of the axial flow vanes  213  may be on the axial-direction lower side of the axial-direction position of the axial-direction upper end of the center connection portion  214 . Alternatively, the axial-direction position of the axial-direction upper end of the axial flow vanes  213  may be on the axial-direction upper side of the axial-direction position of the axial-direction upper end of the center connection portion  214 . In other words, at least a portion of the axial flow vanes  213  may be disposed inside the upper suction port  3   a . According to this configuration, on the upstream side of the airflow drawn by the centrifugal vanes  13 , more air can be sent to the axial flow vanes  213 . 
     In addition, in the present embodiment, the axial-direction position of an axial-direction lower end of the axial flow vanes  213  is on the axial-direction upper side of the axial-direction position of an axial-direction lower end of the center connection portion  214 . However, the present invention is not limited to this example, and the axial-direction position of the axial-direction lower end of the axial flow vanes  213  may be the same as the axial-direction position of the axial-direction lower end of the center connection portion  214 . According to this configuration, it is possible to make the centrifugal fan  100  thinner and increase the axial-direction width of the axial flow vanes  213 . Therefore, the blowing amount of the centrifugal fan  100  can be improved. 
     In addition, in the present embodiment, the axial flow vanes  213  are disposed on the axial-direction upper side of the axial-direction upper end of the centrifugal vanes  13 . According to this configuration, on the upstream side of the airflow drawn by the centrifugal vanes  13 , air can also be sent to the axial flow vanes  213 . However, the present invention is not limited to the example of the present embodiment, and the axial flow vanes  213  may be disposed at the same axial-direction position as the centrifugal vanes  13  or may be disposed on the axial-direction lower side of the centrifugal vanes  13 . 
     The center connection portion  214  is disposed on the radial-direction inner side of the rotor holder  211  of the rotor  21  and is fixed to the upper end portion of the shaft  20 . In the present embodiment, the center connection portion  214  has a plate shape extending in the radial direction from the center axis CA, but is not limited to this example. The center connection portion  214  may have an annular shape about the center axis CA through which the shaft  20  is inserted. 
     For example, in the above-described embodiment and the modification example thereof, air is exemplified as the fluid to be sucked and sent out by the centrifugal fan  100 ; however, the present disclosure is not limited to this example. For example, the fluid to be sucked and sent out by the centrifugal fan  100  may be a gas other than air or may be a liquid such as water. 
     The present disclosure is useful as, for example, a thin blowing fan. However, in the application of the present disclosure, it is not limited to this example. 
     Features of the above-described preferred embodiments and the modifications thereof may be combined appropriately as long as no conflict arises. 
     While preferred embodiments of the present disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present disclosure. The scope of the present disclosure, therefore, is to be determined solely by the following claims.