Centrifugal fan

Abstract

A centrifugal fan includes a motor having a rotor, an impeller that is fixed to the rotor, a circuit board electrically connected to the motor, and a casing that accommodates the motor, the impeller, and the circuit board. The impeller includes a cylindrical boss portion fixed to the rotor, a plurality of blade portions that are arranged in a circumferential direction and extend radially outward, an upper shroud having an annular shape and connecting axially upper portions of the blade portions, and a lower shroud having an annular shape and connecting axially lower portions of the blade portions. The casing has a lower casing disposed axially below the impeller. The lower casing has a board accommodating portion for accommodating the circuit board, and a cover member facing a lower end face of the blade portions and an upper face of the circuit board in the axial direction.

What is claimed is: 
     
         1 . A centrifugal fan comprising:
 a motor having a rotor configured to rotate about a center axis;   an impeller fixed to the rotor, wherein the impeller is configured to rotate together with the rotor, and the impeller comprises:
 a boss portion fixed to the rotor; 
 a plurality of blade portions, wherein adjacent blades of the plurality of blades are arranged at intervals in a circumferential direction on a radially outer side of the boss portion, and each of the plurality of the blade portions extends radially outward; 
 an upper shroud connected to a first portion of each of the plurality of blade portions; and 
 a lower shroud connected to a second portion of each of the plurality of blade portions, wherein the first portion is opposite the second portion; 
   a circuit board electrically connected to the motor; and   a casing accommodates the motor, the impeller, and the circuit board, wherein the casing includes a lower casing, and the lower casing comprises:
 a board accommodating portion recessed away from the impeller in a direction parallel to the center axis, the board accommodating portion accommodating the circuit board; and 
 a cover member, wherein a first surface of the cover member and a surface of each of the plurality of blade portions defines a first gap, a second surface of the cover member and a surface of the circuit board defines a second gap, and the first surface is opposite the second surface. 
   
     
     
         2 . The centrifugal fan according to  claim 1 , wherein the lower casing has a flange portion extending radially outward from an outer peripheral edge of the board accommodating portion. 
     
     
         3 . The centrifugal fan according to  claim 2 , wherein the cover member is fixed to the flange portion. 
     
     
         4 . The centrifugal fan according to  claim 1 , wherein
 a radially inner edge of the cover member is positioned radially inside a radially outer edge of the lower shroud.   
     
     
         5 . The centrifugal fan according to  claim 4 , wherein an first surface of the cover member is between a portion of the lower shroud and the circuit board. 
     
     
         6 . The centrifugal fan according to  claim 1 , wherein a radially inner end surface of the cover member overlaps with a radially outer end surface of the lower shroud in a radial direction. 
     
     
         7 . The centrifugal fan according to  claim 1 , wherein the lower shroud has an inclined portion inclined toward the circuit board from an inside toward an outside in a radial direction. 
     
     
         8 . The centrifugal fan according to  claim 7 , wherein the lower shroud has a flat portion extending radially outside of the inclined portion, and the flat portion extends perpendicular to the center axis. 
     
     
         9 . The centrifugal fan according to  claim 1 , wherein a radially outer edge of the lower shroud is coplanar with a position of a radially inner edge of the upper shroud in a radial direction. 
     
     
         10 . The centrifugal fan according to  claim 1 , wherein a radially outer edge of the lower shroud is radially inward from the radially inner edge of the upper shroud. 
     
     
         11 . The centrifugal fan according to  claim 1 , wherein
 an inner peripheral surface of the board accommodating portion and a radially outer edge of the circuit board define a third gap.   
     
     
         12 . The centrifugal fan according to  claim 11 , wherein the first gap is in communication with the third gap. 
     
     
         13 . The centrifugal fan according to  claim 1 , wherein the casing has an upper casing, and the impeller is between the circuit board and the upper casing. 
     
     
         14 . The centrifugal fan according to  claim 13 , wherein the upper casing has an air intake port facing a radially center portion of the impeller. 
     
     
         15 . The centrifugal fan according to  claim 1 , wherein the boss portion has a cylindrical shape. 
     
     
         16 . The centrifugal fan according to  claim 1 , wherein the upper shroud has an annular shape. 
     
     
         17 . The centrifugal fan according to  claim 1 , wherein the lower shroud has an annular shape. 
     
     
         18 . A centrifugal fan comprising:
 a motor having a rotor configured to rotate about a center axis;   an impeller fixed to the rotor, wherein the impeller is configured to rotate together with the rotor, and the impeller comprises:
 a boss portion fixed to the rotor; 
 a plurality of blade portions, wherein adjacent blades of the plurality of blades are arranged at intervals in a circumferential direction on a radially outer side of the boss portion, and each of the plurality of the blade portions extends radially outward; 
 an upper shroud connected to a first portion of each of the plurality of blade portions; and 
 a lower shroud connected to a second portion of each of the plurality of blade portions, wherein the first portion is opposite the second portion; 
   a circuit board electrically connected to the motor; and   a casing accommodates the motor, the impeller, and the circuit board, wherein the casing includes a lower casing, and the lower casing comprises:
 a board accommodating portion recessed axially away from the impeller, the board accommodating portion accommodating the circuit board; and 
 a cover member extending radially inward from an outer surface of the board accommodating portion, wherein the cover member is between at least a portion of the circuit board and the impeller. 
   
     
     
         19 . The centrifugal fan according to  claim 18 , wherein a radially outer edge of the lower shroud is coplanar with a position of a radially inner edge of the upper shroud in a radial direction. 
     
     
         20 . The centrifugal fan according to  claim 18 , wherein a radially outer edge of the lower shroud is radially outward from the radially inner edge of the cover member.