Patent ID: 7445423

Claim:
A counter-rotating axial-flow fan comprising: a housing including an air channel therein, the air channel having a suction opening portion at one side in an axial direction thereof and a discharge opening portion at the other side in the axial direction; a first impeller including a plurality of front blades and rotating in the suction opening portion; a first motor that rotates the first impeller about an axial line of the fan in one of two rotating directions; a second impeller including a plurality of rear blades and rotating in the discharge opening portion; a second motor that rotates the second impeller about the axial line in the other rotating direction opposite to the one rotating direction; and a plurality of stationary blades radially extending and arranged stationary between the first impeller and the second impeller in the housing; wherein the number of the front blades is N, the number of the stationary blades is M, and the number of the rear blades is P; wherein each of N, M, and P is a positive integer and a relationship of N, M and P is N>P>M; and wherein a length, of each of the front blades, L 1 measured in the axial direction is longer than a length, of each of the rear blades, L 2 measured in the axial direction; wherein the first impeller includes an annular member having a peripheral wall onto which the N blades are mounted and disposed at a predetermined interval in a circumferential direction; wherein end portions of the N blades, located at a side to the discharge opening portion, extend toward a direction of the side to the discharge opening portion beyond an end portion of the peripheral wall of the annular member, located at the side to the discharge opening portion; wherein the second impeller includes annular member having a peripheral wall onto which the P blades are mounted and disposed at a predetermined interval in a circumferential direction; and wherein end portions of the P blades, located at a side to the suction opening portion, do not substantially extend beyond an end portion of the peripheral wall of the annular member located at the side to the suction opening portion, and end portions of the P blades, located at the side to the discharge opening portion, do not substantially extend beyond the end portion of the peripheral wall of the annular member located at the side to the discharge opening portion.