Impeller for axial flow fan and axial flow fan using the same

1. An impeller for an axial flow fan that is operable in a normal rotation and in a reverse rotation, the impeller comprising:

a plurality of blades arranged in a circumferential direction,

wherein each of the blades has:

a first face that has a first three-dimensional shape and serves as a pressure surface during the normal rotation;

a second face that has a second three-dimensional shape that is different from the first three-dimensional shape and serves as a suction surface during the normal rotation;

a leading edge portion that connects the first face and the second face and is located at a front side during the normal rotation; and

a trailing edge portion that connects the first face and the second face and is located at a rear side during the normal rotation,

wherein the first face and the second face are configured to have a different cross-sectional shape with each other,

wherein the leading edge portion and the trailing edge portion are configured to have a line-symmetric shape with respect to a center point of a chord length L,

wherein each of the first face and the second face is defined to have a center portion and end portions that are arranged at each of two sides of the center portion and smoothly connected with the center portion,

wherein each of the end portions of the first face is formed in an arc shape having a curvature radius R 1 and a center of curvature being located adjacent the second face,

wherein the center portion of the first face is formed in an arc shape having a curvature radius R 2 and a center of curvature being located adjacent the first face,

wherein each of the end portions of the second face is formed in an arc shape having a curvature radius R 3 and a center of curvature being located adjacent the first face, and

wherein the center portion of the second face is formed in an arc shape having a curvature radius R 4 and a center of curvature being located adjacent the first face,

wherein the curvature radius R 1 is set to be in a range from 0.6 to 0.8 times of the chord length L,

wherein the curvature radius R 2 is set to be in a range from 70 to 90 times of the chord length L,

wherein the curvature radius R 3 is set to be in a range from 3 to 4 times of the chord length L, and

wherein the curvature radius R 4 is set to be in a range from 4 to 5 times of the chord length L.

2. The impeller according to claim 1 ,

wherein a length X from a blade chord line to a surface of the first face is larger than a length Y from the blade chord line to a surface of the second face except at a center of the blade where the length X is equal to the length Y.

3. The impeller according to claim 1 ,

wherein the first face serves as a suction surface during the reverse rotation, and

wherein the second face serves as a pressure surface during the reverse rotation.

4. An axial flow fan comprising:

an impeller including a plurality of blades arranged in a circumferential direction;

a motor, attached to the impeller, which rotates the impeller in a normal rotation and in a reverse rotation; and

a casing that accommodates the impeller and has a base portion that supports the motor,

wherein each of the blades has:

a first face that has a first three-dimensional shape and serves as a pressure surface during the normal rotation;

a second face that has a second three-dimensional shape that is different from the first three-dimensional shape and serves as a suction surface during the normal rotation;

a leading edge portion that connects the first face and the second face and is located at a front side during the normal rotation; and

a trailing edge portion that connects the first face and the second face and is located at a rear side during the normal rotation,

wherein the first face and the second face are configured to have a different cross-sectional shape with each other,

wherein the leading edge portion and the trailing edge portion are configured to have a line-symmetric shape with respect to a center point of a chord length L,

wherein each of the first face and the second face is defined to have a center portion and end portions that are arranged at each of two sides of the center portion and smoothly connected with the center portion,

wherein each of the end portions of the first face is formed in an arc shape having a curvature radius R 1 and a center of curvature being located adjacent the second face,

wherein the center portion of the first face is formed in an arc shape having a curvature radius R 2 and a center of curvature being located adjacent the first face,

wherein each of the end portions of the second face is formed in an arc shape having a curvature radius R 3 and a center of curvature being located adjacent the first face, and

wherein the center portion of the second face is formed in an arc shape having a curvature radius R 4 and a center of curvature being located adjacent the first face,

wherein the curvature radius R 1 is set to be in a range from 0.6 to 0.8 times of the chord length L,

wherein the curvature radius R 2 is set to be in a range from 70 to 90 times of the chord length L,

wherein the curvature radius R 3 is set to be in a range from 3 to 4 times of the chord length L, and

wherein the curvature radius R 4 is set to be in a range from 4 to 5 times of the chord length L.

5. The axial flow fan according to claim 4 ,

wherein a length X from a blade chord line to a surface of the first face is larger than a length Y from the blade chord line to a surface of the second face except at a center of the blade where the length X is equal to the length Y.

6. The axial flow fan according to claim 4 ,

wherein the first face serves as a suction surface during the reverse rotation, and

wherein the second face serves as a pressure surface during the reverse rotation.