Centrifugal fan

Abstract

There is provided a centrifugal fan including a casing having an upper casing with an opening and a lower casing with a recess, a motor disposed in the recess, and an impeller housed in the casing. The impeller includes an annular shroud formed with an inlet, plural blades which are arranged between the annular shroud and the lower casing, and a hub which is connected to respective inner sides of the blades. Each of the blades includes, at a pressure surface side, a first inclined surface which is inclined toward a negative pressure surface of the blade as approaching the lower casing from the annular shroud; and a second inclined surface which is provided closer to the lower casing than the first inclined surface, and is inclined toward the negative pressure surface at an angle steeper than that of the first inclined surface.

What is claimed is: 
     
         1 . A centrifugal fan comprising:
 a casing including an upper casing having an opening, a lower casing having a recess, and supports interposed between the upper casing and the lower casing;   a motor disposed in the recess of the lower casing; and   an impeller housed in the casing,   wherein the impeller includes:
 an annular shroud which has an upper inner portion formed with an inlet; 
 a plurality of blades which are arranged between the annular shroud and the lower casing while protruding downward from the annular shroud; and 
 a hub which is connected to respective inner sides of the plurality of blades, 
   wherein a fluid introduced from the inlet of the annular shroud is discharged to a side of the impeller according to rotation of the impeller,   wherein an upper surface of the lower casing faces the impeller and configures a portion of a wall surface which guides the fluid introduced from the inlet,   wherein each of the plurality of blades is inclined while being curved backward in a rotation direction of the impeller as approaching an outer side of the impeller, and   wherein each of the plurality of blades includes, at a pressure surface side:
 a first inclined surface which is inclined toward a negative pressure surface of the blade as approaching the lower casing from the annular shroud; and 
 a second inclined surface which is provided closer to the lower casing than the first inclined surface, and is inclined toward the negative pressure surface at an angle steeper than that of the first inclined surface. 
   
     
     
         2 . The centrifugal fan according to  claim 1 ,
 wherein an angle between the second inclined surface and a plane perpendicular to a rotation axis of the impeller is larger than 0° and smaller than 45°.   
     
     
         3 . The centrifugal fan according to  claim 1 ,
 wherein an angle between the second inclined surface and a plane perpendicular to a rotation axis of the impeller is within a range from 25° to 35°.   
     
     
         4 . The centrifugal fan according to  claim 1 ,
 wherein an angle between the first inclined surface and a rotation axis of the impeller is within a range from 4° to 8°.   
     
     
         5 . The centrifugal fan according to  claim 1 ,
 wherein the first inclined surface and the second inclined surface are connected through a curved surface having a chamfered round shape.   
     
     
         6 . The centrifugal fan according to  claim 1 ,
 wherein the motor is configured to rotate the impeller.