JP4583281B2 - Axial fan - Google Patents

Description

The present invention relates to an axial fan used for cooling electronic devices and the like, and to an axial fan capable of improving efficiency .

In recent years, due to miniaturization of electronic equipment, the heat density has increased, and an example in which an axial fan is used for cooling the electronic equipment is increasing. As a result, there is a need for a low-noise and high-efficiency axial fan for noise control and energy saving of the entire electronic device.
In order to meet these demands, various efficiency improvement and noise reduction techniques have been proposed.

  16 and 17 are views showing the structure of the above-described general axial fan. The axial fan blows air by rotating a blade 100 having a plurality of blades 100a. The blades 100 are attached to a rotation shaft of a motor 102 disposed at the center position of a fan frame 101 formed in a rectangular frame shape. The motor 102 that supports the blade 100 is held at the center position of the fan frame 101 by a plurality of spokes 103.

  In such an axial fan, noise is generated by the interference between the spoke 103 and the blade 100 a as the blade 100 rotates. Therefore, conventionally, a structure for inclining the spoke 103 has been widely adopted as a countermeasure against the noise. In order to eliminate noise and reduce harsh sound by adopting this structure, an axial fan having a structure in which the spoke 103 is inclined is actively employed (Patent Documents 1 and 2).

  That is, in the spokes arranged radially around the motor, the pressure fluctuations generated by the blades fluctuate at the same time throughout the spokes and generate a loud sound, whereas if the spokes are inclined and arranged, Since the position where the pressure fluctuates on the spoke is shifted from time to time, the generation of sound is temporally dispersed, resulting in a small sound. At this time, the same effect can be obtained even if the spokes are inclined in the direction of rotation of the blades or in the direction opposite to the direction of rotation.

  On the other hand, there is also technical information that, if the spokes are arranged at an inclination, it can also contribute to efficiency improvement. In other words, the spokes are formed by tilting in the direction opposite to the blade rotation direction, but the technical ground is that the wings are generally advanced in the rotation direction, so the spokes are inclined in the rotation direction. Since the rear edge of the wing and the spoke overlap, the efficiency decreases due to an increase in pressure fluctuation, and the spoke is inclined in the direction opposite to the rotation direction (Patent Document 1).

  Presuming on the basis of the above technical basis, the spoke has a close relationship with the advancing angle of the blade, and the efficiency may not be improved simply by arranging the spoke in the reverse direction of the rotation direction. Moreover, since Patent Document 2 does not have a specific description about the attachment angle of the spoke, it is insufficient as technical information in designing the fan frame.

Incidentally, FIG. 18 illustrates a general air flow in the blades of the axial fan. In FIG. 18, since the blade 100a moves at a speed u, the air is a vector w1 with respect to the blade 100a. Flows in. The air that has passed between the blades flows out with the vector w2, but at this time, the flow is bent by the blade 100a. That is, when viewed from the blade 100a, the flow becomes a curve indicated as a relative streamline.
On the other hand, since the blade 100a is moving at a speed u, the flow seen from the fan frame is a curve obtained by subtracting the speed u from the relative streamline, and becomes a curve indicated as an absolute streamline. That is, the flow from the axial fan discharge port is a flow swirled in the blade rotation direction (Non-patent Document 1, Non-Patent Document 2).

Of the flow from the discharge port, the swirl component does not contribute to the blower output, so the swirl component is corrected to the axial flow by the stationary blade 104 fixed to the fan frame as shown in FIG. The efficiency can be improved by raising. The blower configured as described above is an axial flow blower called a rear stationary blade type.
Japanese Patent No. 1037013 JP 2002-188599 A Published by Yukio Harada “Fluid Machinery”, pages 34-35, Asakura Shoten, March 20, 1986 The 24th edition of the Turbomachinery Association “Turbomachine” published on December 28, 1989

  However, the axial fan attached to an electronic device or the like has no room for attaching the stationary blade 104 in order to make it thinner and smaller, and the efficiency improvement by the stationary blade 104 is impossible. Therefore, a structure that increases the air blowing efficiency without using the stationary blade 104 is required.

Since many wings are generally tilted forward in the rotational direction, when the spokes are tilted in the rotational direction, the trailing edges of the wings and the spokes overlap. Therefore, what is shown in the above-mentioned Patent Document 2 is to incline the spokes in the direction opposite to the rotation direction because the efficiency decreases due to an increase in pressure fluctuation.
However, if the fan has a fan-shaped fan, the efficiency can be improved by tilting the spoke in either direction. If the fan has a blade tilted in the direction opposite to the rotating direction, the spoke should be tilted in the rotating direction. The question remained.
As mentioned above, there is no method to determine the appropriate spoke arrangement in terms of both efficiency and noise, so far it has been designed by trial and error, or the product with efficiency and noise performance remaining incomplete. It is the actual situation.

  An object of the present invention is to provide an axial fan capable of solving the above-described problems and improving efficiency and reducing noise.

In order to solve the above problems, the present invention is a shaft in which a blade having a plurality of blades is mounted on a rotating shaft of a motor, and the motor is held at a central position of a frame surrounding the blade through a plurality of spokes. In the flow fan, the blade rotation with the angle between the spoke center line and the straight line passing the intersection of the spoke center line and the motor peripheral surface from the rotation axis center, the motor diameter as D and the spoke width as d It lies in the set to an angle defined by 90-Arccos ((D-d ) / D) of the opposite to the direction.

According to the axial flow fan of the present invention, the air blowing efficiency can be improved and the energy can be reduced.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments shown in the drawings will be described in detail below with reference to the drawings. FIG. 1 is a perspective view of an axial fan according to an embodiment of the present invention. FIG. 2 is a front view of the axial fan of FIG. FIG. 3 is a front view showing a frame of the axial fan of FIG.

  1 to 3, the axial fan includes a blade (propeller fan) 1 and a fan frame 2 to which the blade 1 is attached. The blade 1 includes a cylindrical hub 1a having a predetermined diameter and a plurality of blades 3 (five in the illustrated example) provided radially around the hub 1a at regular intervals. A plurality of these blades 3 are integrally formed with the hub 1a on the outer peripheral surface of the hub 1a at regular intervals along the circumferential direction.

  The fan frame 2 is formed by forming a cylindrical inner peripheral surface 2b in the axial direction inside a quadrangular frame 2a, and the blade 1 is placed at the center O of the rotating shaft 5 at a substantially central position of the cylindrical portion 2c. The motor 6 supported by the motor is supported via a plurality of spokes (three in the illustrated example) 4. The spoke 4 has one end connected to the peripheral surface of the motor 6 at a predetermined interval, and the other end is inclined to the direction opposite to the rotation direction of the blade 1 and is extended to the outside of the motor 6 so as to extend to the outside. The fan frame 2 is connected to the inner peripheral surface 2b.

A straight line passing through the intersection P between the spoke center line 8 of the spoke 4 and the outer periphery 7 of the motor 6 from the center O of the rotating shaft 5 of the motor 3, where D is the diameter of the motor 6 and d is the spoke width of the spoke 4. 9 and the angle β formed by the spoke center line 8 at the intersection P between the spoke center line 8 and the motor outer periphery 7 is 90-Arcos ((D−d) / D) in the direction opposite to the blade rotation direction. It is set in the range of 50% to 100% of the angle defined in degrees.
In the above embodiment, the arrangement of the spokes 4 of the fan frame 2 is inclined by 59 degrees in the direction opposite to the blade rotation direction, based on the present invention.

Here, the technical background from the above-described prior art to the present invention will be described.
Prior to the invention, the inventor returned to the basics and measured efficiency and noise by combining blades and spokes with a commercially available fan in the direction of rotation, or in the opposite direction of rotation, and radial. I tried.
In general, in the analysis of a blower (axial fan), the ratio between the blower output of the blower and the axial power of the electric motor is obtained as the efficiency. Further, the pressure-flow rate characteristics are compared in a dimensionless manner so as not to depend on the rotation speed and the blade diameter. That is, the evaluation is generally performed using the flow coefficient φ, the pressure coefficient ψ, and the efficiency η defined by the following formula (Non-patent Document 2).

Here, Q, Pt, and ρ are the flow rate, total pressure, and air density, Dp is the blade diameter, and u is the speed of the blade outer periphery. T is the motor torque, and ω is the rotational angular velocity of the blade.
A commercially available axial fan used in the experiment is a general fan having a width of 92 mm and a thickness of 25.4 mm. There are three types of blades and eight types of fan frames 2 used in the experiment, some of which are shown in FIGS. 7 (a), (b), and (c) and FIGS. 8 (a), (b), and (c). FIG. 7A shows the blade 31 tilted by 20 degrees (degrees) in the direction opposite to the rotation direction of the blade 1. FIG. 7B shows the wings 32 arranged radially. FIG. 7C shows the blade 33 tilted by 20 degrees (degrees) in the same direction as the rotation direction of the blade 1. FIG. 8A shows the spoke 41 tilted in the direction opposite to the rotation direction of the blade 1. FIG. 8B shows the spokes 42 arranged radially. FIG. 8C shows the spoke 43 tilted in the same direction as the rotation direction of the blade 1.

Here, the value which a spoke attachment angle can take is demonstrated concretely based on FIG.
If the spoke 4 is tilted excessively, the line 11 outside the spoke protrudes from the motor outer periphery 7 of the motor 6, so that the function of the spoke 4 for holding the motor 6 cannot be performed. The condition that the line 11 outside the spoke does not protrude from the motor outer periphery 7 is the maximum value of the spoke attachment angle.

  In this state, as shown in FIG. 4, the spoke outer line 11 is in contact with the motor outer periphery 7. At this time, the straight line passing through the motor center from the intersection of the spoke outer line 11, the spoke center line 8 and the motor outer periphery 7. 13. A straight line 12 connecting the point P where the spoke outer line 11 contacts the motor outer periphery 7 and the motor center forms a right triangle. Since the spoke outer line 11 and the spoke center line 8 are parallel, the spoke center line 8, the straight line 12 connecting the motor center with the point where the spoke outer line 11 contacts the motor outer periphery 7, and the spoke center line 8 Similarly, a straight line 13 passing through the motor center 5 from the intersection P with the motor outer periphery 7 also forms a right triangle.

The angle α formed by the straight lines 13 and 12 in FIG. 4 is Arccos ((D−d) / D) where D is the motor diameter and d is the spoke width. Arcos is an inverse function of the cosine function cos. The attachment angle of the spokes, that is, the angle formed by the straight lines 13 and 14 is in the range of 0 to 90-Arcos ((D−d) / D) degrees. There are three types of Arccos values, deg, rad, and grad. Here, the value is determined in deg, that is, in degrees. Since the sample used in the experiment has D = 43 mm and d = 6 mm, the spoke attachment angle is 0 to 59 degrees.
As described above, among the prototypes of blades having various blade advancing angles and frames having various spoke attachment angles according to Table 1, no. 1 to No. FIG. 9 shows the fan characteristics measured with 15 samples.

  Since the number of data is large, FIG. 6, no. 7, no. 8, no. 9, no. Only 10 measurement results are shown. The efficiency of the fan changes according to the change of the flow rate, and the efficiency becomes the maximum around 2/3 of the maximum flow rate. FIG. 10 shows the change in the maximum efficiency for each blade advance angle and spoke attachment angle.

  From FIG. 10, when the wing is fan-shaped, that is, the advance angle is 0, the wing is advanced in the rotational direction, that is, the forward angle is positive, and the wing is retracted in the opposite direction of the rotational direction, that is, the forward angle is negative. It can be seen that the efficiency is greater when tilted forward in the direction opposite to the rotation direction, and if the absolute value of the spoke attachment angle is greater than or equal to a certain value, the efficiency remains saturated and maximum. That is, it can be seen that the positional relationship between the trailing edge of the wing and the spoke does not affect the efficiency, and the efficiency depends only on the attachment angle of the spoke with respect to the rotation direction.

On the other hand, a basic experiment was also conducted on noise, which will be described in detail.
Spoke inclination does not depend on the blade advancing angle, and it has been found that the inclination is high in the direction opposite to the blade rotation direction. Therefore, the inclination of the spoke is increased in the direction opposite to the blade rotation direction. For blades, noise was measured with a combination of 0 degree of advance angle.

  That is, No. 1 in Table 1. 6, no. 8, no. 16, no. 17, no. FIG. 11 shows the result of measuring the noise value in the open state with a microphone at a position 1 m from the fan inlet in the anechoic sound chamber.

  Since the spoke attachment angle in FIG. 11 has already been known from the experiment of efficiency that it is better to incline the spoke in the direction opposite to the blade rotation direction, only the size is shown here. That is, the spoke attachment angle indicates an angle opposite to the rotation direction of the blade, and the spoke attachment angle in FIG. 10 corresponds to a negative range.

  From FIG. 11, it can be seen that the spoke attachment angle is 30 degrees or more, and the noise is stabilized to a low level. In other words, the noise value is the smallest when the maximum spoke attachment angle can be obtained, but the noise value does not change much when the spoke attachment angle is 50% or more of the maximum value, and the spoke attachment angle is the maximum value. It can be seen that a sufficiently low noise level can be obtained by designing with any of 50% to 100%.

  As a known technique, if Patent Document 1 is used, the spoke may be oriented in the rotational direction or in the reverse direction of the rotational direction. Also, in Patent Document 2, from the description, it is sufficient that the trailing edge of the wing and the spoke intersect. Therefore, in the case of a fan-shaped wing, the spoke may be reverse in the rotational direction or in the rotational direction. become. Therefore, in the conventional example, the spoke is inclined 59 degrees in the direction of the rotation direction (see FIGS. 16 and 17).

FIG. 5 shows the measurement results of the fan characteristics in the example of the present invention and the conventional example.
The fan characteristics are dimensionless and are represented by a flow coefficient and a pressure coefficient. FIG. 6 shows noise frequency characteristics in the embodiment of the present invention and the conventional example. Table 2 shows a comparison of measurement results of maximum efficiency and noise between the example of the present invention and the conventional example. FIG. 5 shows that in the embodiment of the present invention, when the flow coefficient is 0.1 or more, the pressure coefficient is larger than that of the conventional example and the efficiency is higher than that of the conventional example.

The efficiency and noise comparison with the conventional example are summarized in a table as shown in Table 2. As shown in Table 2, the maximum efficiency in the conventional example is 0.27, whereas the maximum efficiency in the embodiment of the present invention is about 0.32. It turns out that it is 1.2 times .

Now, the technical reason why the efficiency can be improved by the present invention will be described in detail.
The inventor has found that a specific spoke arrangement works in the same way as the vane described in the prior art. The technical principle of the present invention takes advantage of this.
Hereinafter, the result obtained by the numerical fluid analysis of the axial flow fan of the present invention and the flow from the discharge port in the conventional example will be described in detail with reference to FIG. 12, FIG. 13, FIG.
The software used for the numerical fluid analysis is a commercially available numerical analysis code, and has a proven record in the analysis of axial flow fans.

  FIG. 14 shows the flow at the discharge port of a conventional axial fan as viewed from the suction port side. It can be seen that the flow swirls in the direction of blade rotation. In FIG. 14, the portion where the vector is small is the flow immediately after the spoke. In FIG. 14, since the spokes are inclined in the direction of swirling of the flow, it can be seen that when the flow hits the spoke, the flow is swirled further outward as a whole.

  On the other hand, FIG. 12 shows the flow at the discharge port in the axial flow fan of the present invention as seen from the suction port side, but the spoke is inclined in the direction opposite to the swirling direction of the flow, so the flow hits the spoke. And try to change the direction toward the center. However, since the central portion is high in pressure, it cannot go to the center, and it goes to the axial direction, that is, the back side of the paper in FIG. 12, and this, like the conventional stationary blade, causes the swirl component of the flow. It becomes a mechanism to correct the axial component, improving the efficiency.

In order to see the above results numerically, FIGS. 13 and 15 show the magnitude of the swirl component of the flow at the discharge port in shades. In FIGS. 13 and 15, it is shown that the swirl component is larger as the portion is closer to black, and the swirl component is smaller as the portion is closer to white.
FIG. 15 shows the magnitude of the turning component in the conventional example, and FIG. 13 shows the magnitude of the turning component in the embodiment of the present invention.

  Comparing FIG. 13 and FIG. 15, it can be seen that there are many lighter portions in FIG. 13, and the magnitude of the swirl component is smaller than that in FIG. That is, the swirl component in the axial fan of the present invention is smaller than the swirl component in the conventional example of FIG. 15 in FIG. 13, and the swirl component is corrected to the axial component in the axial fan of the present invention, thereby improving efficiency. It can be seen that this contributes to

  As described above, the present invention utilizes the fact that the specific spoke arrangement works in the same manner as the above-described stationary blade, and technically corrects the swirling component of the flow from the discharge port. It is clear from the comparison with Patent Document 2 that the efficiency is improved but cannot be easily achieved.

  As described above, the blowing efficiency of the axial fan in the embodiment of the present invention is 32%, which can improve the efficiency by 5% compared to the blowing efficiency of 27% in the conventional example. This indicates that 27/32 = 84.4% of energy is sufficient to obtain an output equivalent to the conventional example, and it can be seen that the energy can be reduced by about 15%.

In addition to the spoke arrangement of the present invention, there are various methods for improving efficiency and reducing noise, such as a blade shape and a frame discharge port shape, which are independent of the present invention. The embodiment and the effect of the present invention are not changed by the combination with this method. Furthermore, it is possible to further improve the efficiency or reduce the noise by making the spoke cross-sectional shape into a blade shape or a cross-sectional shape with less fluid resistance, but it goes without saying that the embodiments and effects of the present invention do not change by them. .

  Furthermore, in the axial fan according to the embodiment of the present invention, the spoke shape seen from the front is a straight line, but it is also possible to make this a curved line, and the effect of improving the product design or improving the efficiency and reducing the noise. However, it is needless to say that this does not change the embodiments and effects of the present invention.

1 is a perspective view of an axial fan according to an embodiment of the present invention. It is the front view seen from the suction inlet of the axial-flow fan by embodiment of this invention. It is a front view of the fan frame of the axial-flow fan by embodiment of this invention. It is a figure which shows the relationship between the motor diameter of the axial flow fan by embodiment of this invention, spoke width, and a spoke attachment angle. It is the figure which compared the fan characteristic in the axial flow fan by embodiment of this invention, and a prior art example. It is the figure which compared the noise frequency characteristic in the axial fan by embodiment of this invention, and a prior art example. (A) (b) (c) is a conceptual diagram which shows the blade | wing used for spoke arrangement | positioning and the basic experiment of efficiency. (A) (b) (c) is a conceptual diagram which shows a part of fan frame used for the basic experiment of spoke arrangement and efficiency. It is the figure which compared the fan characteristic among the basic experiment results of spoke arrangement and efficiency. It is a figure which shows the relationship between the spoke attachment angle and efficiency which were obtained from the basic experiment of spoke arrangement | positioning. It is a figure which shows the relationship between the spoke attachment angle and the noise to the blade rotation reverse direction obtained from the basic experiment of spoke arrangement | positioning. It is the figure which carried out the vector display of the discharge outlet flow in embodiment of this invention. It is the figure which displayed the magnitude | size of the turning component of the discharge outlet flow in embodiment of this invention with the shading. It is the figure which carried out the vector display of the discharge port flow in the conventional axial flow fan. It is the figure which displayed the magnitude | size of the turning component of the discharge port flow in the conventional axial flow fan with the shading. It is a perspective view of the conventional axial fan. It is the front view seen from the suction inlet of the conventional axial fan. It is the figure which showed typically the flow between axial flow fan blades. It is the figure which showed typically the flow between axial flow fan blades.

Explanation of symbols

1 blade 2 fan frame 3 blade 4 spoke 5 shaft center 6 motor 7 motor outer periphery 8 spoke center line 9 straight line passing the intersection of the spoke center line and the motor outer periphery from the center of the rotating shaft 11 line outside the spoke 12 line outside the spoke A straight line that connects the motor center and the point that contacts the motor outer periphery 13 A straight line that passes through the motor center from the intersection of the spoke center line and the motor outer periphery 14 Spoke center line extension part O Rotational axis center P Q The point where the outer line of the spoke touches the outer circumference of the motor β Spoke inclination angle

Claims (1)

In an axial fan in which blades having a plurality of blades are mounted on a rotation shaft of a motor and the motor is held at a center position of a frame surrounding the blades via a plurality of spokes, The angle formed by the straight line passing through the intersection of the center line and the peripheral surface of the motor and the spoke center line is 90-Arccos ((D -An axial fan characterized by being set to an angle defined by d) / D) degrees.

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