Patent ID: 7618239

Claim:
A multi-blade fan having an impeller equipped with a plurality of blades attached to an air-cooled internal combustion engine to be rotated to blow air toward the engine to cool, comprising: an inlet angle β 1 defined to be an angle between a relative velocity direction and a peripheral direction on an inlet side of the blades, an outlet angle β 2 defined to be an angle between the relative velocity direction and the peripheral direction on an outlet side of the blades; and an angle β′ 2 defined to be a difference obtained by subtracting the outlet angle β 2 from 180°, wherein a sum of the inlet angle β 1 and the angle β′ 2 is made less than 80°, and wherein an angle θ 1 is given a value that is between 40% and 50% of an angle θ 0 , where the angle θ 0 is an angle between L 1 and L 2 ; the angle θ 1 is angle between L 1 and L 3 ; L 1 is a straight line obtained by connecting the inlet side of the blades with a center of rotation of the impeller; L 2 is a straight line obtained by connecting an intersection of a circumference of the outlet side of the blades and the direction of the inlet side relative velocity with the center of rotation of the impeller; and L 3 is a straight line obtained by connecting the outlet side of the blades with the center of rotation of the impeller.