Axial fan

Abstract

An axial fan includes a rotor portion including a shaft arranged to extend along a central axis extending in a vertical direction, a stator portion arranged radially opposite to the rotor portion, and an impeller hub fixed to the rotor portion, and arranged to be capable of rotating integrally with the rotor portion. The impeller hub includes a hub top plate portion arranged to extend perpendicularly to an axial direction; a hub tubular portion being tubular, and arranged to extend axially downward from an outer edge of the hub top plate portion; a plurality of blades arranged in a circumferential direction on an outer surface of the hub tubular portion; a plurality of wall portions arranged in the circumferential direction radially inside of the hub tubular portion, with a gap between every adjacent ones of the wall portions; and joining portions each of which is arranged to join a corresponding one of the wall portions to the hub tubular portion. The rotor portion includes a rotor tubular portion being tubular and arranged to extend in the axial direction. An outer surface of the rotor tubular portion is arranged to be in contact with an inner surface of at least one of the wall portions. Each of the at least one wall portion arranged to be in contact with the outer surface of the rotor tubular portion is joined to the hub tubular portion through two or more of the joining portions arranged in the circumferential direction.

What is claimed is: 
     
         1 . An axial fan comprising:
 a rotor portion including a shaft arranged to extend along a central axis extending in a vertical direction;   a stator portion arranged radially opposite to the rotor portion; and   an impeller hub fixed to the rotor portion, and arranged to be capable of rotating integrally with the rotor portion;   
       wherein
 the impeller hub includes:
 a hub top plate portion arranged to extend perpendicularly to an axial direction; 
 a hub tubular portion being tubular, and arranged to extend axially downward from an outer edge of the hub top plate portion; 
 a plurality of blades arranged in a circumferential direction on an outer surface of the hub tubular portion; 
 a plurality of wall portions arranged in the circumferential direction radially inside of the hub tubular portion, with a gap between every adjacent ones of the wall portions; and 
 a plurality of joining portions each of which is arranged to join a corresponding one of the wall portions to the hub tubular portion; 
 
 the rotor portion includes a rotor tubular portion being tubular and arranged to extend in the axial direction; 
 an outer surface of the rotor tubular portion is arranged to be in contact with an inner surface of at least one of the wall portions; and 
 each of the at least one wall portion arranged to be in contact with the outer surface of the rotor tubular portion is joined to the hub tubular portion through two or more of the joining portions arranged in the circumferential direction. 
 
     
     
         2 . The axial fan according to  claim 1 , wherein both circumferential end portions of each of the at least one wall portion arranged to be in contact with the outer surface of the rotor tubular portion are joined to the hub tubular portion through the corresponding joining portions. 
     
     
         3 . The axial fan according to  claim 1 , wherein each of the at least one wall portion arranged to be in contact with the outer surface of the rotor tubular portion is arranged to be in contact with the outer surface of the rotor tubular portion at a circumferential middle portion thereof. 
     
     
         4 . The axial fan according to  claim 3 , wherein a remaining portion of each of the at least one wall portion arranged to be in contact with the outer surface of the rotor tubular portion, excluding both circumferential end portions thereof, is arranged radially opposite to the hub tubular portion with a gap therebetween. 
     
     
         5 . The axial fan according to  claim 1 , wherein each of the at least one wall portion arranged to be in contact with the outer surface of the rotor tubular portion includes an increased thickness portion having a surface arranged at a shorter distance from the central axis than any other portion of the wall portion. 
     
     
         6 . The axial fan according to  claim 5 , wherein a distance of the increased thickness portion from the central axis is arranged to continuously increase from a circumferential middle of the increased thickness portion in circumferentially outward directions. 
     
     
         7 . The axial fan according to  claim 5 , wherein the increased thickness portion is defined by a rib arranged to project radially inward from an inner surface of the wall portion. 
     
     
         8 . The axial fan according to  claim 5 , wherein the increased thickness portion is arranged axially opposite to the hub top plate portion with a gap therebetween. 
     
     
         9 . The axial fan according to  claim 8 , wherein the hub top plate portion includes, in a region axially opposed to the increased thickness portion, a through hole arranged to pass therethrough in the axial direction. 
     
     
         10 . The axial fan according to  claim 1 , wherein
 the impeller hub further includes a recessed portion being recessed upward and defined radially between the hub tubular portion and the wall portions; and   the recessed portion is arranged to have an axial depth smaller than an axial dimension of the impeller hub.