JPH05209599A - Low noise air blower - Google Patents

Abstract

PURPOSE:To provide a low noise air blower relatively low-priced and wide in a frequency region of enabling the decrease of noise without the lowering of air blowing capacity. CONSTITUTION:There are provided plural air blowing units 3 of the same shape with air blowing fans 2 disposed at ventilation flues 1. The exhaust side opening ends of the ventilation flues 1 of each air blowing unit 3 are collected into one ventilation flue 11, and there is provided a control circuit 4 for keeping the rotational phase of the fans 2, provided at each air blowing unit 3, in the specified relation so as to enable the mutual denial of noise generated from each air blowing unit 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-noise blower which reduces noise mainly generated as a wind noise of a blower fan when blowing air.

[0002]

2. Description of the Related Art Conventionally, as a measure for reducing noise generated by a blower when blowing air, a method of using a sound absorbing material or generating a secondary sound wave for canceling the noise is known.

As a structure using a sound absorbing material, as shown in FIG. 4, a sound absorbing material 6 is generally lined on the entire inner surface of the ventilation passage 1. In this configuration, the noise generated by the blower fan 2 is absorbed by the sound absorbing material 6 arranged inside the ventilation passage 1 while passing through the ventilation passage 1.

On the other hand, as a configuration in which noise is canceled by a secondary sound wave, as shown in FIG. 5, a microphone for detecting noise is provided inside the ventilation passage 1 from the blower fan 2 to the opening on the exhaust side. There are speakers 7 and 8 and a speaker 9 for transmitting a secondary sound wave that cancels noise. That is, the noise detected by the microphones 7 and 8 is digitally processed by the signal processing device 10 to generate a secondary sound wave that cancels the noise, and the secondary sound wave is transmitted from the speaker 9.

[0005]

By the way, in the commonly used sound absorbing material 6, the frequency characteristic of the sound absorption coefficient depends on the thickness, and the sound absorption coefficient of the low frequency component decreases as the thickness decreases. .. Therefore, in the configuration of FIG. 4 using the sound absorbing material 6, if the thickness of the sound absorbing material 6 is reduced, there arises a problem that the low frequency noise generated by the blower fan 2 cannot be sufficiently absorbed. On the other hand, if the thickness of the sound absorbing material 6 is increased, the effective cross-sectional area of the ventilation passage 1 is reduced, so that the blowing capacity is reduced and the ventilation resistance is increased, which may rather increase noise.

In the configuration of FIG. 5 in which the noise is canceled by the secondary sound wave, these problems do not occur, but since complicated digital processing is performed on the noise, it is based on the noise detected by the microphones 7 and 8. A relatively large time delay occurs until the secondary sound wave is generated from the speaker 9, and it is effective only for noise in a specific frequency band determined by the positional relationship between the microphones 7 and 8 and the speaker 9. There is also a problem. In addition to the large number of constituent elements, the signal processing device 10 for performing complicated signal processing is required, which causes a problem that the cost is high, and the microphones 7 and 8 and the speaker 9 also require maintenance.

An object of the present invention is to solve the above problems, and to provide a low noise blower which can be provided at a relatively low cost without lowering the blowing ability and which can reduce noise and has a wide frequency range. It is what

[0008]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a plurality of blower units 3 of the same shape in which a blower fan 2 arranged in a ventilation passage is provided, and to exhaust the ventilation passage 1 of each ventilation unit 3. Blower fan 2 provided in each blower unit 3 so that the open ends on the side are integrated into one ventilation passage 11 so that the noises generated by each blower unit 3 cancel each other out.
The low noise blower is characterized in that it is provided with a control circuit 4 for keeping the rotation phase of the above in a predetermined relationship.

[0009]

[Operation] According to the above-mentioned configuration, the ventilation paths of the blower units having the same configuration have only one exhaust end on the exhaust side, and the rotation phase of the blower fan provided in each blower unit is maintained in a predetermined relationship. By controlling so that the noises generated by the blower fans cancel each other out, there is no influence on the blowing ability. In addition, since it only controls the rotation phase of the blower fan, it is relatively easy to control and can be provided at low cost. Furthermore, since sound is radiated from one opening end, the phase difference due to the difference in distance is There is no deviation, and the range of the sound deadening area is not limited.

In the following embodiments, an example of two air blowing units is shown, but the number of air blowing units is not limited to this.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a blower unit 2 is constructed by arranging a blower fan 2 at the end of a tubular ventilation passage 1. The opening end on the exhaust side of the blower unit 3 is unified. A blower fan 2 having the same size and shape is installed at the other end.

The two ventilation passages until the ventilation unit 3 is integrated have the same size and the same shape.

The blower fan 2 is so constructed that it can output an angle signal corresponding to the rotation angle and that the rotation angle can be controlled by an external signal. Blower fan 2 of this kind
For this, for example, a servo motor may be used as the drive source. As shown in FIG. 2, the angle signals output from both the blower fans 2 are input to the control circuit 4, and a drive signal is sent from the control circuit 4 via the drive circuit 5 to the blower fan 2.
Entered in. In the control circuit 4, based on the circuit signal,
The drive signal is output so that the rotation angles of both blower fans 2 are maintained in a predetermined relationship.

That is, most of the noise generated at the time of blowing air is the wind noise generated by the rotation of the blower fan 2, and is sent out from the opening surface on the exhaust side through the ventilation passage 1, so that both blowing air are blown. When the phase of the rotation angle of the fan 2 is shifted by about 180 degrees, both noises interfere with each other and are canceled. In order to satisfy such a condition, when the number of blades of the blower fan 2 is m, (360 / m) · (2n + 1) / 2
The rotation phase of both blower fans 2 is feedback-controlled so that the rotation angle is deviated by just that. Here, n is an integer.

In FIG. 1, the blower fan 2 has a diameter of 100 m.
m, the number of wings is 5, and the rotation speed is 1920 r.p.m. p. m. FIG. 3A shows the sound pressure level at a wind noise frequency of 160 Hz at a point 1000 mm away from the opening end on the exhaust side when the length of the blower unit is 1400 mm. In FIG. 3, point a is the front surface of the opening end, and points b to d are points deviated from the front surface of the opening end by 30 °, 60 °, and 90 °, respectively. As a comparative example, the sound pressure level when only one of the blower fans is driven is shown in FIG. 3B. It can be seen from FIG. 3 that the sound pressure level of 4 to 6 dB is reduced in this embodiment as compared with the case where only one of the blower fans is driven, and this embodiment is effective.

[0016]

As described above, according to the present invention, a plurality of blower units of the same shape in which a blower fan is arranged are provided in the ventilation passage, and each ventilation unit has one opening end on the exhaust side of the ventilation passage. A control circuit is provided to keep the rotation phase of the blower fans provided in each blower unit in a predetermined relationship so that the noises generated by each blower unit cancel each other out, and the noises generated by the blower fans cancel each other out. Since this is done, there is an advantage that there is no effect on the blowing capacity and the blowing capacity is not reduced. In addition, since it only controls the rotation phase of the blower fan, it has the effect of being relatively easy to control and can be provided at a low cost. Furthermore, since sound is emitted from one opening end, there is a difference in distance. There is an advantage that the phase shift does not occur and the range of the muffling area is not limited.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a circuit diagram of the same.

FIG. 3 is a graph showing sound pressure levels of Examples and Comparative Examples.

FIG. 4 is a sectional view showing a conventional example.

FIG. 5 is a schematic configuration diagram showing another conventional example.

[Explanation of symbols]

 1 Ventilation path 2 Blower fan 3 Blower unit 4 Control circuit 5 Drive circuit

Claims (1)

[Claims] 1. A plurality of blower units 3 having the same shape, in which a blower fan 2 is arranged in the ventilation passage 1, are provided, and the open ends of the ventilation passages 1 of each ventilation unit 3 on the exhaust side are combined into one ventilation passage 11. A low-noise blower characterized by comprising a control circuit 4 for keeping a rotation phase of a blower fan 2 provided in each blower unit 3 in a predetermined relationship so that noises generated by each blower unit 3 cancel each other out.