Counter-rotating fan

Abstract

A counter-rotating fan includes a first fan including a first impeller including first blades radially arranged around a predetermined center axis, a first motor that rotates the first impeller around the center axis, and a first case surrounding an outer circumference of the first impeller, and a second fan including a second impeller including second blades radially arranged around the center axis, a second motor that rotates the second impeller around the center axis, and a second case surrounding an outer circumference of the second impeller. The first blades include a front edge located foremost in a rotation direction and a rear edge located rearmost in the rotation direction. A radially outermost end of the rear edge is located closer to the second fan than a radially innermost end.

What is claimed is: 
     
         1 . A counter-rotating fan comprising:
 a first fan including a first impeller including a plurality of first blades radially arranged around a predetermined center axis, a first motor that rotates the first impeller around the center axis, and a first case surrounding an outer circumference of the first impeller; and   a second fan including a second impeller including a plurality of second blades radially arranged around the center axis, a second motor that rotates the second impeller around the center axis, and a second case surrounding an outer circumference of the second impeller; wherein   the plurality of first blades include a front edge located foremost in a rotation direction and a rear edge located rearmost in the rotation direction; and   a radially outermost end of the rear edge is located closer to the second fan than a radially innermost end.   
     
     
         2 . The counter-rotating fan according to  claim 1 , wherein when the first motor and the second motor are rotationally driven, air is taken in from a side of the first fan, and delivered to a side of the second fan to generate a flow of air in a direction of the center axis. 
     
     
         3 . The counter-rotating fan according to  claim 1 , wherein the rear edge is moved closer to the second fan from the radially innermost end toward the radially outermost end. 
     
     
         4 . The counter-rotating fan according to  claim 3 , wherein the first fan includes a first case surrounding a radial outside of the first impeller and a plurality of first support ribs that extend radially around the center axis, are connected to the first case, and support the first motor, and an axial gap between the rear edge and an end on a side of the first impeller of each of the first support ribs decreases toward a radially outer region. 
     
     
         5 . The counter-rotating fan according to  claim 1 , wherein
 the first impeller includes a first blade support with a covered cylindrical shape and supporting the plurality of first blades; and   the radially outermost end of the rear edge is located closer to the second fan than a lower end of the first blade support.   
     
     
         6 . The counter-rotating fan according to  claim 1 , wherein the first motor includes a stator, a rotor, a bearing, and a first circuit board, the first circuit board is disposed on a side of the second fan of the stator, and the radially outermost end of the rear edge is located closer to the second fan than an upper end of the first circuit board. 
     
     
         7 . The counter-rotating fan according to  claim 1 , wherein
 the plurality of second blades include a front edge located foremost in the rotation direction and a rear edge located rearmost in the rotation direction;   an axial distance between the radially outermost end of the front edge of the plurality of first blades and the radially outermost end of the rear edge is larger than an axial distance between the radially outermost end of the front edge of the plurality of second blades and the radially outermost end of the rear edge.