Centrifugal fan

Abstract

A centrifugal fan includes an impeller, a motor rotating the impeller about a center axis, and a housing accommodating the impeller. The housing includes an intake port arranged above the impeller, an exhaust port arranged radially outward of the impeller, an annular upper flow path, and a lower flow path arranged below the upper flow path and connected to the upper flow path. The annular upper flow path can be partially arranged between a housing inner circumferential surface and the impeller in a radial direction. The upper flow path and the lower flow path are arranged to define a flow path having a scroll shape. The lower flow path extends along the housing inner circumferential surface. The lower flow path has a lower flow path terminal end opened toward the exhaust port. The lower flow path has a lower flow path start end closed with respect to the exhaust port.

What is claimed is: 
     
         1 . A centrifugal fan comprising:
 an impeller arranged to rotate about a center axis extending in an up-down direction;   a motor arranged below the impeller and arranged to rotate the impeller about the center axis; and   a housing arranged to accommodate the impeller,   wherein the housing includes an intake port arranged above the impeller, an exhaust port arranged radially outward of the impeller, an annular upper flow path at least partially arranged between a housing inner circumferential surface as an inner circumferential surface of the housing and the impeller in a radial direction, and a lower flow path arranged below the upper flow path and connected to the upper flow path,   the upper flow path and the lower flow path are arranged to define a flow path having a scroll shape,   the lower flow path extends along the housing inner circumferential surface,   the lower flow path has a lower flow path terminal end as one circumferential end thereof opened toward the exhaust port, and   the lower flow path has a lower flow path start end as the other circumferential end thereof closed with respect to the exhaust port.   
     
     
         2 . The fan according to  claim 1 , wherein a radial dimension of the lower flow path grows larger from the lower flow path start end toward the lower flow path terminal end. 
     
     
         3 . The fan according to  claim 1 , wherein the housing includes an upper housing having the intake port and a lower housing attached to a lower side of the upper housing. 
     
     
         4 . The fan according to  claim 3 , wherein the lower housing includes a portion of the upper flow path and the lower flow path, and
 an axial dimension of the lower flow path in the vicinity of the exhaust port is one half or more of an internal axial dimension of the lower housing.   
     
     
         5 . The fan according to  claim 3 , wherein the upper housing includes an upper housing cover portion having the intake port and overlapping with the impeller in an axial direction and a upper housing wall portion connected to a lower end of the upper housing cover portion and arranged to surround the impeller in a circumferential direction, and
 the upper housing wall portion has an inner circumferential surface extending downward and radially outward.   
     
     
         6 . The fan according to  claim 1 , wherein a radial dimension of the upper flow path grows larger as the upper flow path extends from a reference position existing between the exhaust port and the lower flow path start end toward the exhaust port in a rotation direction of the impeller. 
     
     
         7 . The fan according to  claim 1 , wherein the exhaust port is connected to the upper flow path and the lower flow path. 
     
     
         8 . The fan according to  claim 7 , wherein an axial dimension of a portion of the exhaust port connected to the lower flow path is larger than an axial dimension of a portion of the exhaust port connected to the upper flow path. 
     
     
         9 . The fan according to  claim 1 , wherein the exhaust port is connected to only the lower flow path. 
     
     
         10 . The fan of  claim 1 , wherein a position of a lower end portion of the lower flow path goes away from the upper flow path as the lower flow path extends from the lower flow path start end toward the lower flow path terminal end. 
     
     
         11 . The fan according to  claim 1 , wherein an axial dimension of the lower flow path is larger than an axial dimension of the upper flow path. 
     
     
         12 . The fan according to  claim 1 , wherein the entirety of the lower flow path is opened toward the upper flow path. 
     
     
         13 . The fan according to  claim 1 , wherein the housing includes a tongue portion arranged between the exhaust port and the lower flow path start end in a circumferential direction, and
 when seen in a plan view, the lower flow path start end is located in a position where a circumferential angle from a straight line passing through the center axis and meeting with the tongue portion becomes 75 degrees or less.   
     
     
         14 . The fan according to  claim 1 , wherein the motor is arranged radially inward of the lower flow path,
 the housing includes a motor cover portion arranged to cover the motor, and   the lower flow path is arranged between an outer circumferential surface of the motor cover portion and the housing inner circumferential surface.