Serial axial flow fan

Abstract

A serial axial flow fan in which an end portion of a first axial flow fan on an exhaust side, and an end portion of a second axial flow fan on an intake side are connected to each other. At least either of a plurality of first blades of a first impeller of the first axial flow fan, and a plurality of second blades of a second impeller of the second axial flow fan are provided with auxiliary blade portions. Furthermore, Nin<Nout<Nrib is satisfied, where a number of first blades is Nin, a number of second blades is Nout, and a number of first support ribs and a number of second support ribs are each Nrib.

What is claimed is: 
     
         1 . A serial axial flow fan comprising:
 a first axial flow fan that blows out air drawn in from an intake side to an exhaust side;   a second axial flow fan connected to the first axial flow fan along a central axis of the first axial flow fan, the second axial flow fan blowing out the air drawn in from an intake side to an exhaust side, wherein an end portion of the first axial flow fan on the exhaust side and an end portion of the second axial flow fan on the intake side are connected to each other;   the first axial flow fan including
 a first impeller that rotates about the central axis, 
 a first motor portion that rotates the first impeller, 
 a first housing that includes a first cylindrical portion that surrounds an outside of the first impeller in a radial direction, and 
 a first support rib that extends inwards from an inner surface of the first cylindrical portion and that supports the first motor portion; 
   the first impeller including a plurality of first blades that extend outwards in the radial direction and that are arranged in a circumferential direction;   the second axial flow fan including
 a second impeller that rotates about the central axis, 
 a second motor portion that rotates the second impeller, 
 a second housing that includes a second cylindrical portion that surrounds an outside of the second impeller in the radial direction, and 
 a second support rib that extends inwards from an inner surface of the second cylindrical portion and that supports the second motor portion, a number of the second support ribs being equal to a number of the first support ribs; and 
   the second impeller including a plurality of second blades that extend outwards in the radial direction and that are arranged in the circumferential direction;   auxiliary blade portions being included in at least either of the first blades and the second blades; and   Nin<Nout<Nrib being satisfied, where a number of first blades is Nin, a number of second blades is Nout, and a number of first support ribs and a number of second support ribs are each Nrib.   
     
     
         2 . The serial axial flow fan according to  claim 1 ,
 wherein the auxiliary blade portions are provided at outer edge portions of the first blades in the radial direction.   
     
     
         3 . The serial axial flow fan according to  claim 2 ,
 wherein outsides of the auxiliary blade portions in the radial direction are warped towards the intake side.   
     
     
         4 . The serial axial flow fan according to  claim 1 ,
 wherein Nin, Nout, and Nrib are a set of positive integers that do not have a common divisor other than 1.   
     
     
         5 . The serial axial flow fan according to  claim 1 ,
 wherein Nin is 5.   
     
     
         6 . The serial axial flow fan according to  claim 1 ,
 wherein Nout is 7.   
     
     
         7 . The serial axial flow fan according to  claim 1 ,
 wherein the first support rib is disposed on the exhaust side of the first housing,   wherein the second support rib is disposed on the intake side of the second housing, and   wherein a surface of the first support rib that faces the exhaust side and a surface of the second support rib that faces the intake side overlap each other in an axial direction.   
     
     
         8 . The serial axial flow fan according to  claim 1 ,
 wherein Nrib is 11.