Axial flow fan

An axial flow fan comprising:

• an impeller including a hub having an annular peripheral wall portion, and a plurality of blades each having a base portion which is integrally fixed to an outer wall of the peripheral wall portion of the hub, extending from the outer wall of the peripheral wall portion outwardly in a radial direction of the peripheral wall portion, and disposed at an interval in a circumferential direction of the peripheral wall portion;
• a housing having a cylindrical air channel in which the impeller rotates;
• and
• a motor fixed to the housing and including a rotary shaft having a front end portion to which the impeller is fixed and a rear end portion, wherein
• assuming that an imaginary line passing one end of the base portion of the blade positioned on the rear end portion side of the rotary shaft and extending in parallel to an axial line of the rotary shaft and along an outer peripheral surface of the peripheral wall portion, the base portion of the blade is inclined in a direction from the one end of the base portion to the other end thereof so as to be gradually away from the imaginary line in a rotation direction of the impeller, and is curved so as to be convex in a direction opposite to the rotation direction;
• each blade has a curved portion formed in the vicinity of a radially outer end portion positioned opposite to the base portion in the radial direction, the curved portion being convex in the rotation direction, being concave in the direction opposite to the rotation direction;
• the curved portion extends along the radially outer end portion from a rear end edge of the blade to the vicinity of a front end edge of the blade, the rear end edge being positioned on a side where the one end of the base portion is positioned and extending in the radial direction, the front end edge of the blade being positioned on a side where the other end of the base portion is positioned and extending in the radial direction;
• the width of the curved portion as measured in the radial direction and the depth of a concave portion formed in the curved portion are determined to gradually decrease in a direction from the rear end edge toward the front end edge of the blade;
• and
• wherein each blade has a first and a second outer surface portion that are positioned on opposite sides of the curved portion in the radial direction such that said first outer surface portion is radially outside said curved portion and said second outer surface portion is radially inside said curved portion, and
• wherein said first and second outer surface portions are on a same curved surface that is convex in the direction opposite to the rotation direction such that said first outer surface portion exists on an extension of said second outer surface portion.