JP5653282B2 - Axial fan - Google Patents

Description

  The present invention relates to an axial fan (impeller) used for cooling a ventilation fan, an air conditioner, or a device.

In general, an axial fan generates annoying noise called a blade passing frequency sound having a large peak at a certain discrete frequency. The frequency Fn can be obtained by the following equation from the number of blades Z and the number of rotations N of the blades per second.
Fn = n × Z × N (Hz) where n = 1, 2, 3,...

  Conventionally, the arrangement pitch of some of the blades of the axial fan is different from the arrangement pitch of other blades, or the rotation axis of some of the blades of the axial fan is It is disclosed that a plane shape along an orthogonal plane is different from the plane shape of other blades so that the phases of sound waves generated by the respective blades are not aligned, and the blade passing frequency sound is reduced (for example, patents). Reference 1).

JP 2001-214894 A

  However, according to the above conventional technique, in order to arrange wings of the same shape at unequal pitches, it is necessary to reduce the planar shape of each wing so that the wings do not overlap each other, and the air blowing characteristics deteriorate. There is a problem that. In addition, when the planar shape of some of the plurality of blades is reduced, the air blowing performance deteriorates, and stress concentrates on the base of the boss of the small blade, resulting in insufficient strength of the base of the blade. There is a problem.

  The present invention has been made in view of the above, and an object of the present invention is to obtain an axial fan that maintains air blowing performance and reduces blade passing frequency sound while ensuring blade strength.

  In order to solve the above-described problems and achieve the object, the present invention includes a boss attached to a rotating shaft of a motor, a plurality of blades arranged radially on the outer periphery of the boss, and blown in the direction of the rotating shaft. The position of the rotation axis on the projection of the axial flow fan projected on the plane orthogonal to the rotation axis is O, and the center point of the chord line on the outer peripheral portion of the boss of each blade is Pb, where the wing outer edge chord line center point of each wing is Pt, the boss outer chord line center points Pb of the respective wings are arranged at substantially equal intervals in the circumferential direction on the boss outer circumference, The angle δθt formed between the straight line O-Pb and the straight line O-Pt in at least some of the blades is different from the angle δθt formed between the straight line O-Pb and the straight line O-Pt in other blades.

  According to the present invention, it is possible to maintain blade performance and reduce blade passing frequency noise while ensuring blade strength.

FIG. 1 is a perspective view showing a general axial fan. FIG. 2 is a plan view showing one blade of a general axial fan. FIG. 3 is a cross-sectional development view in which one blade of a general axial fan is cut by a cylindrical surface having a radius R and the cross section is developed into a two-dimensional plane. FIG. 4 is a plan view showing an embodiment of an axial fan according to the present invention. FIG. 5 is a plan view showing a general axial fan in which blades having the same shape are arranged at equal intervals in the circumferential direction. FIG. 6 is a comparative view in which a general axial fan and the axial fan according to the embodiment are cut by a cylindrical surface having a blade outer edge radius Rt, and each cross-section is developed in a two-dimensional plane.

  Embodiments of an axial fan according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiments.
FIG. 1 is a perspective view showing a general axial fan, FIG. 2 is a plan view showing one blade of a general axial fan, and FIG. 3 shows a general axial fan. FIG. 4 is a cross-sectional development view in which one blade is cut by a cylindrical surface with a radius R and the cross section is developed on a two-dimensional plane.

  The axial fan 90 shown in FIG. 1 has four blades. However, in the present invention, the number of blades 1 is not limited and may be other plural numbers. As shown in FIG. 1, a general axial fan 90 has a plurality of blades 1 having a three-dimensional solid shape arranged radially on the outer periphery of a cylindrical boss 2. The boss 2 is attached to a rotating shaft 3 of a motor (not shown), and rotates around the rotating shaft 3 in the direction of arrow B in FIG.

  A blade 1 shown in FIG. 2 is obtained by projecting the blade 1 shown in FIG. 1 onto a plane orthogonal to the rotation axis 3. As shown in FIG. 2, the blade 1 is contoured by a blade leading edge 1a, a blade trailing edge 1b, a blade inner edge 1c, and a blade outer edge 1d. The blade inner edge portion 1c and the blade outer edge portion 1d are arcs centered on the rotation center O. In addition, you may form the wing | blade 1 radially on the outer peripheral part of the boss | hub 2 formed by bending a sheet metal into a disk shape. As the blade 1 rotates, an airflow in the direction of arrow A in FIG. 1 is generated.

  When the blade 1 is cut by a cylindrical surface having an arbitrary radius R, the arc 1aR-PR-1bR in the plan view of FIG. Here, PR is the midpoint of the arc 1aR-1bR, and the chord line center point in the plan view.

  Here, PR is referred to as a chord line center point as shown in FIG. 3 in an exploded view obtained by cutting the blade 1 with a cylindrical surface having an arbitrary radius R and developing the cross section on a two-dimensional plane. This is because it represents the center point of the straight line 1aR-1bR that is a chord line connecting the blade leading edge 1aR and the blade trailing edge 1bR at the radius R. As shown in FIG. 3, with respect to the airflow direction A, the upstream surface of the blade 1 is a negative pressure surface 1e with a low pressure, and the downstream surface is a positive pressure surface 1f with a high pressure.

  In order to quantify the position of the chord line center point PR in the plan view of FIG. 2, the boss outer chord line center point in the plan view when the wing 1 is cut by the cylindrical surface of the boss outer radius Rb. A coordinate system with the position O as the origin is set as a plane projection with the straight line O-Pb connecting Pb and the rotation center O as the X axis.

  The blade outer edge chord line center point Pt is the chord line center point at the radius Rt of the blade outer edge portion 1d. In the above coordinate system, if the angle between the straight line O-PR and the X axis is δθ and the distance is R, the circumferential position of the chord line center point PR is displayed in polar coordinates (R, δθ). Can do. Here, an angle formed by the straight line O-Pt and the X axis is δθt.

  FIG. 4 is a plan view showing an embodiment of an axial fan according to the present invention, and FIG. 5 is a plan view showing a general axial fan in which blades having the same shape are arranged at equal intervals in the circumferential direction. FIG. 6 is a comparative view in which a general axial fan and the axial fan according to the embodiment are cut by a cylindrical surface having a blade outer edge radius Rt, and each cross-section is developed in a two-dimensional plane.

As shown in FIG. 4, the boss outer peripheral chord line center points Pb of the respective blades 10 of the axial flow fan 80 of the embodiment are arranged at substantially equal intervals in the circumferential direction of the boss outer peripheral portion. The position (R, δθ) in the circumferential direction of the chord line center point PR at an arbitrary radius R of each wing 10 can be obtained by the following equation from the angle δθt formed by the straight line O-Pt and the X axis. .
δθ = δθt × (R−Rb) / (Rt−Rb)

  Since the axial fans 80 have different values of δθt for each blade 10, the circumferential position of the chord line center point Pt at the blade outer edge radius Rt of each blade 10 is different for each blade 10. Are arranged at unequal intervals in the circumferential direction. In addition, the planar projection shape of the wing 10 is also different for each wing 10. In the axial flow fan 80 of the embodiment, the values of δθt of the respective blades 10 are all different, but the values of δθt of at least some of the blades 10 are different from the values of δθt of the other blades 10. You can do it.

  As shown in FIG. 5, a general axial fan 90 has blades 1 of the same shape arranged at equal intervals in the circumferential direction, and an angle δθt formed by a straight line O-Pt and the X axis is equal to all the blades 1. Are equal. Hereinafter, this general axial fan 90 will be referred to as an equidistant axial fan 90.

FIG. 6 is a diagram in which the equally-spaced axial flow fan 90 and the axial flow fan 80 of the embodiment are cut by a cylindrical surface having a blade outer edge radius Rt and the respective cross sections are developed in a two-dimensional plane. 6 indicates the attachment interval Tt at the blade outer edge radius Rt when the attachment interval T of the blades 1 and 10 at the arbitrary radius R of the equally spaced axial flow fan 90 is represented by the following equation.
T = 2πR / Z (Z is the number of blades)

  Whereas the blades 1 of the axial flow fan 90 are arranged at equal intervals in the circumferential direction, the blade 10 of the axial flow fan 80 of the embodiment has an angle δθt formed by the straight line O-Pt and the X axis. The values of the wings 10 are different, and the chord line center points Pt of the wings 10 are arranged at unequal intervals in the circumferential direction.

The blade passing frequency sound is generated by a pressure discontinuity between the pressure surface 1f and the suction surface 1e of the blades 1 and 10 due to the rotation of the blades 1 and 10 and passing through the space. . In the equidistant axial flow fan 90, since the blades 1 are arranged at equal intervals in the circumferential direction, pressure fluctuations periodically occur, and as described above, noise having a large peak in the frequency of the following equation is generated. Occur.
Fn = n × Z × N (Hz) where n = 1, 2, 3,...

  In the axial fan 80 according to the embodiment, the circumferential position of the blade outer edge chord line center point Pt at the blade outer edge radius Rt of each blade 10 is different in each blade 10 and is unequally spaced in the circumferential direction. Further, the plane projection shape of the blades 10 is also different for each blade 10, so that the periodicity of pressure fluctuation is weakened and the peak of blade passing frequency sound is reduced. In addition, since the outer edge side of the blade 10 having a high peripheral speed is dominant in the portion serving as the sound source of the blade passing frequency sound, the outer edge side of the blade 10 is unequally spaced as in the axial fan 80 of the embodiment. The effect of reducing the wing-passing frequency sound can be greatly reduced by simply disposing it in the position.

  According to the two-dimensional blade cascade theory, an axial fan has an unambiguous air flow and static pressure when the blade attack angle, warp angle, and chord length at the chord line center point PR, which is the center of the blade element, are determined. Therefore, the spatial position of the chord line center point PR does not affect the air volume and the static pressure. Therefore, the axial fan 80 according to the embodiment differs from the equally spaced axial fan 90 in that the δθt of each blade 10 is different and only the spatial position of the chord line center point PR is different. Has no effect. Further, the shape of the blade inner edge portion where the stress of the blade 10 of the axial fan 80 is concentrated is substantially the same as that of the equally spaced axial fan 90, and the strength of the blade 10 can be ensured.

1, 10 blades 1a blade leading edge 1b blade trailing edge 1c blade inner edge 1d blade outer edge 1e negative pressure surface 1f positive pressure surface 2 boss 3 rotating shaft 80 axial fan 90 axial fan (equally spaced axial fan)
A Airflow direction B Blade rotation direction Fn Blade passing frequency Sound frequency Z Number of blades N Rotation number O Rotation center R Arbitrary radius Rb Boss outer radius Rt Blade outer edge radius PR Chord line center point at arbitrary radius R Pb Boss Center point of outer peripheral chord line Pt Blade center point of outer blade edge part δθ Angle formed by straight line O-PR and X axis δθt Angle formed by straight line O-Pt and X axis T Blade of equidistant axial flow fan at arbitrary radius R Mounting interval Tt Blade mounting interval of equidistant axial fan at blade outer edge radius Rt

Claims (3)

An axial fan comprising: a boss attached to a rotating shaft of a motor; and a plurality of blades arranged radially on the outer peripheral portion of the boss and blowing air in the rotating shaft direction,
The position of the rotation axis on the projection of the axial fan projected onto the plane orthogonal to the rotation axis is O, the boss outer peripheral chord line center point of each blade is Pb, and the blade outer edge of each blade when the chord line center point and Pt, boss outer peripheral portion chord line center point Pb of the respective blades are arranged at equal intervals in the boss outer peripheral portion in a circumferential direction, a straight line O-Pb in at least a portion of the blade And an angle δθt formed by the straight line O-Pt is different from an angle δθt formed by the straight line O-Pb and the straight line O-Pt in other blades.   2. The axial fan according to claim 1, wherein angles δθt formed by the straight lines O-Pb and O-Pt in the respective blades are all different. The radius of the outer peripheral portion of the boss on the projection view of the axial fan projected onto the plane orthogonal to the rotation axis is Rb, the radius of the blade outer edge is Rt, and the chord line center point at an arbitrary radius R is PR, 3. The axial flow according to claim 1, wherein δθ = δθt × (R−Rb) / (Rt−Rb), where δθ is an angle formed between the straight lines O-Pb and O-PR. fan.

Images