Axial flow fan

Abstract

An axial flow fan includes a housing defining an air inlet and an air outlet, a motor mounted to the housing and an impeller including blades. The housing includes an expanded portion adjacent the air outlet. In the expanded portion, the inner diameter of the housing increases towards the air outlet so that the expanded portion has an inner end where its diameter is smallest. The trailing edge of each blade is inclined, with respect to a plane perpendicular to the axis of rotation of the impeller, so as to extend toward the air inlet from a radially innermost end of the edge to a radially outermost end of the edge. The radially outermost end of the trailing edge is disposed closer to the air inlet than the inner end of the expanded portion, and the radially innermost end of the of the trailing edge is disposed closer to the air outlet than inner end of the expanded portion.

1 . An axial flow fan comprising:
 a housing defining an opening serving as an air inlet through which air is taken into the fan, an opening serving as an air outlet through which air is discharged from the fan, and a passage extending in an axial direction of the fan between the air inlet and the air outlet, wherein the air inlet and the air outlet are located at axial ends of the passage, respectively,   the housing having a base, and a side wall delimiting the passageway,   the base including a central portion, and a plurality of ribs connecting the central portion to the side wall, the ribs extending adjacent the air outlet,   the side wall of the housing having an expanded portion adjacent the air outlet, the cross-sectional area of that portion of the passageway delimited by the expanded portion of the side wall increasing as taken along the axial direction of the fan towards the air outlet from inside the housing;   a motor mounted to the base; and   an impeller having an impeller cup mounted to the motor so as to be rotatable about an axis of rotation extending in the axial direction, and a plurality of blades disposed about the axis of rotation and radiating outwardly from the impeller cup so as to rotate therewith, the side wall of the housing facing tips of and surrounding the blades,   each of the blades having a leading edge facing the air inlet and a trailing edge facing the air outlet, the trailing edge of each of the blades being inclined, with respect to a plane extending perpendicular to the axis of rotation, from a radially innermost end thereof proximate the impeller cup to a radially outermost end thereof at the tip of the blade, and   the expanded portion of the housing having an outer end at the air outlet and an inner end located inwardly from the outer end in the axial direction, the inner diameter of the expanded portion being smallest at its inner end such that an inner surface of the side wall of the housing has an inflection at the inner end of the expanded portion, the inflection extending along a boundary that surrounds the axis of rotation, and the inflection being located with respect to the axial direction between the radially outermost end and the radially innermost end of the trailing edge of each of the blades.   
   
   
       2 . The axial flow fan according to  claim 1 , wherein the housing is of a molded resin, and the housing includes a respective pedestal of resin at a location where each of the ribs joins the side wall of the housing. 
   
   
       3 . The axial flow fan according to  claim 2 , wherein the profile of the housing is approximately rectangular as viewed in the axial direction, whereby the housing has four corners. 
   
   
       4 . The axial flow fan according to  claim 3 , wherein the expanded portion of the housing comprises inclined surfaces adjacent the corners of the housing, respectively, the inclined surfaces being spaced from one another about the periphery of the housing, and each of the inclined surfaces being inclined relative to the axial direction in a radially outward direction from an inner end thereof to an outer end thereof at the air outlet. 
   
   
       5 . The axial flow fan according to  claim 4 , wherein each of the respective pedestals extends axially within and over the entire axial length of the expanded portion of the housing. 
   
   
       6 . The axial flow fan according to  claim 1 , wherein the leading edge of each of the blades is inclined, with respect to a plane extending perpendicular to the axis of rotation, towards the air inlet from a radially innermost end of the leading edge proximate the impeller cup to a radially outermost end of the leading edge at the tip of the blade. 
   
   
       7 . The axial flow fan according to  claim 6 , wherein the angle of inclination of the leading edge of each of the blades is different from the angle of inclination of the trailing edge thereof. 
   
   
       8 . The axial flow fan according to  claim 7 , wherein the angle of inclination of the leading edge of each of the blades is smaller than that of the trailing edge thereof. 
   
   
       9 . The axial flow fan according to  claim 7 , wherein the angle of inclination of the leading edge of each of the blades is approximately equal to that of the trailing edge thereof. 
   
   
       10 . The axial flow fan according to  claim 6 , wherein each of the leading and trailing edges of the blade extends linearly from the radially innermost end thereof to the radially outermost end thereof. 
   
   
       11 . The axial flow fan according to  claim 6 , wherein each of the leading and trailing edges of the blade is curved from the radially innermost end thereof to the radially outermost end thereof. 
   
   
       12 . The axial flow fan according to  claim 6 , wherein the leading edges of the blades are located entirely within the housing so as to not protrude from the air inlet. 
   
   
       13 . The axial flow fan according to  claim 1 , wherein each of the blades satisfies the following relationship:
   ( P   o )−5°≦( P   i )≦( P   o )+5°,   
     wherein P i  is a pitch of a radially inner section of the blade adjacent the impeller cup and P o  is a pitch of a radially outer section of the blade adjacent the tip of the blade, the pitch being a measure of the inclination of the section of the blade relative to a plane perpendicular to the axis of rotation, the section being that of the blade cut by a cylindrical surface which passes through the blade and which has a central longitudinal axis coincident with the axis of rotation. 
   
   
       14 . An electronic device comprising a heat generating element and an axial flow fan according to  claim 1 , wherein the axial flow fan is positioned to deliver air to the heat generating element. 
   
   
       15 . The electronic device according to  claim 14 , wherein the electronic device is a computer, and the heat generating element is a microprocessor.