Blower fan and working machine provided with the same
A blower fan includes: an impeller having a predetermined number of blades; a fan casing having an air-intake port disposed to face a central portion of base of the impeller and eccentrically housing the blower fan and defining a spiral scroll passageway between an inner wall thereof and an external circumference of the impeller, the spiral scroll passageway having an inlet portion constituting a narrow nose portion and an outlet portion constituting a wide discharge port; and a driving source for rotating the impeller. In order to minimize the noise to be released from the nose portion, the blower fan further includes a sound-reflecting means which is disposed to cover a portion of the air inlet port at a location spaced away from the nose portion by a distance corresponding to ½ of wavelength of noise in an emanating direction of noise.
1. A blower fan comprising:
a circular impeller having a base and a predetermined number of curved blades radially arranged at equiangular intervals on the base;
a fan casing having an air-intake port disposed to face a central portion of a substrate of the impeller and eccentrically housing the blower fan and defining a spiral scroll passageway between an inner wall thereof and an external circumference of the impeller, the spiral scroll passageway having an inlet portion comprising a narrow nose portion and an outlet portion which comprises a wide discharge port;
a driving source for rotating the impeller;
a narrow nose portion that is a noise source of said fan, wherein a force of air within the fan is most greatly compressed in the inside of the spiral scroll passageway; and
a sound-reflecting member formed as a blind patch portion that covers part of the air intake port in order to minimize the noise to be released to the external environments from the narrow nose portion as a source of noise, where the blind patch portion is disposed at a position whose center is spaced away in an emanating direction of noise from the narrow nose portion by a distance corresponding to a half (½) of wavelength of noise.
2. The blower fan according to claim 1 , wherein the sound reflecting member comprises a tray-shaped fan cover having a lattice-shaped framework provided with at least three air-intake openings and disposed to cover the air inlet port, wherein at least two of the air-intake openings are closed to form a blind patch.
3. The blower fan according to claim 2 , wherein the sound-reflecting member is capable of varying in position correlating to the revolving speed of the impeller.
4. An air blast working machine comprising the blower fan of claim 3 .
5. An air blast working machine comprising the blower fan of claim 2 .
6. The blower fan according to claim 1 , wherein the sound-reflecting member is capable of varying in position correlating to the revolving speed of the impeller.
7. An air blast working machine comprising the blower fan of claim 6 .
8. An air blast working machine comprising the blower fan of claim 1 .
9. A blower fan comprising:
a circular impeller having a base and a predetermined number of curved blades radially arranged at equiangular intervals on the base;
a fan casing having an air-intake port disposed to face a central portion of a substrate of the impeller and eccentrically housing the blower fan and defining a spiral scroll passageway between an inner wall thereof and an external circumference of the impeller, the spiral scroll passageway having an inlet portion comprising a narrow nose portion and an outlet portion which comprises a wide discharge port;
a driving source for rotating the impeller;
a narrow nose portion that is a noise source of said fan, wherein a force of air within the fan is most greatly compressed in the inside of the spiral scroll passageway; and
a sound-reflecting member made of a thin membrane, the sound-reflecting member being formed as a blind patch portion that covers part of the air intake port in order to minimize the noise to be released to the external environments from the narrow nose portion as a source of noise, where the blind patch portion is disposed at a position whose center is spaced away in an emanating direction of noise from the narrow nose portion by a distance corresponding to a half (½) of wavelength of noise.
10. The blower fan according to claim 9 , wherein the sound reflecting member comprises a tray-shaped fan cover having a lattice-shaped framework provided with at least three air-intake openings and disposed to cover the air inlet port, wherein at least two of the air-intake openings are closed to form a blind patch.
11. The blower fan according to claim 10 , wherein the sound-reflecting member is capable of varying in position correlating to the revolving speed of the impeller.
12. An air blast working machine comprising the blower fan of claim 11 .
13. An air blast working machine comprising the blower fan of claim 10 .
14. The blower fan according to claim 9 , wherein the sound-reflecting member is capable of varying in position correlating to the revolving speed of the impeller.
15. An air blast working machine comprising the blower fan of claim 14 .
16. An air blast working machine comprising the blower fan of claim 9 .