JPH06117399A - Muffler device for air jetting blower - Google Patents

Abstract

PURPOSE:To provide a silencer device with a high noise reduction effect by the combination with a conventional silencer case using a damper material effective for noise reduction in high frequency range since low frequency range is reduced by active noise control(ANC). CONSTITUTION:A jet fan with an improved noise reduction effect is constituted such that a speaker is arranged to output sound with the reverse phase to noise and the same frequency and sound level with the noise by the adoption of ANC principle to a jet fan composed of a motor 2, a main body case 3 having a built-in impeller 1 connected to the electric motor 2, a silencer case 4 equipped with a sound absorbing material 7 for reducing noise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silencer for a jet fan suitable as a silencer for a jet blower (hereinafter referred to as a jet fan) used in a ventilation facility of an automobile tunnel, and more particularly to an active noise control (hereinafter referred to as ANC). Say) used.

[0002]

2. Description of the Related Art A conventional jet fan is as described in Road Tunnel Technical Standards (Ventilation) / Commentary (December 1985), Japan Road Association, pages 141-145.
It is composed of an electric motor, a main body case containing an impeller directly connected to the electric motor, and a silencer case provided in front of and behind the main body case. This silencer case has a structure in which a perforated steel plate is provided on the ventilation surface side, and a sound absorbing material having good sound absorbing characteristics is sandwiched between the perforated steel plate and the outer steel plate.

[0003]

Since the conventional silencer has a structure of a sound absorbing material, it is necessary to lengthen the silencer portion in order to increase the volume of noise and to reduce the noise of the jet fan. However, it is not desirable to install the jet fan on the ceiling of the tunnel and to make it long in terms of efficiency.

On the other hand, the frequency characteristic of the noise of the jet fan shows that the fundamental frequency (the number of blades x the number of revolutions) is 100 Hz to 40 Hz.
Since it is as low as 0 Hz and the sound absorption coefficient in the low frequency region is small due to the characteristics of the sound absorbing material, even if the silencer portion is lengthened, the low frequency region remains and the overall noise level reduction effect is small.

An object of the present invention is to provide a silencer which is smaller than conventional ones and which can obtain a silencing effect by using the ANC method for silencing the low frequency region and using the conventional sound absorbing method for the high frequency region.

[0006]

In order to achieve the above object, the present invention uses a sound source different from noise generated by an electric motor and an impeller to generate a sound wave having a phase opposite to that of the noise, the same frequency and the same sound pressure level from a speaker. An active noise control is provided to generate and actively attenuate noise.

[0007]

According to the above means, sound waves having an opposite phase, the same frequency, and the same sound pressure level as the noise are generated from the speaker and are combined with the noise in the case, whereby the noise is actively reduced and the sound absorbing material is also provided. The noise level of the overall can be reduced by attaching it to the jet fan together with the silencer case using.

[0008]

EXAMPLE A jet fan installed in a tunnel uses an induction motor 2 as shown in FIG. 3 and operates at a constant rotation, so that the generated noise hardly changes and is considered to be a steady noise. Therefore, as shown in FIG. 4, a constant sound wave having an opposite phase, the same frequency, and the same sound pressure level as the noise generated from the electric motor 2 and the impeller 1 is output from the speaker 3 provided in the silencer case 9 to reduce the noise. It can be offset to reduce the sound.

However, theoretically as described above,
Only by generating a constant sound wave from the speaker due to a change in ambient temperature, etc., a sound wave having a phase opposite to that of noise cannot be obtained, and the sound reduction effect cannot be enhanced. Therefore, as shown in FIG. 5, the error microphone 5 is installed in the silencer case 9, the synthesized sound is taken in from the error microphone, and is fed back through the controller 4 provided on the outer plate portion of the silencer case 9.
The muffling effect can be improved by changing the sound generated from the speaker.

In addition to the above, it is considered that the sound is actually different between the suction side and the discharge side. Therefore, as shown in FIG. 6, error microphones 5 are installed on the discharge side and the suction side, respectively, and a plurality of speakers 3 for generating optimum sound waves are installed on the suction side and the discharge side via the controller 4, respectively. By outputting, the noise can be reduced.

As described above, although the ANC is excellent in silencing in the low frequency region, the noise reduction effect becomes smaller as the cross section of the silencer case becomes larger. Therefore, the cross sectional dimension where the ANC is installed is less than half the wavelength of the fundamental frequency. As shown in FIG. 1, a partition is installed as shown in FIG. 1, the jet fan is divided into a plurality of cross sections, and a speaker is installed in each of them, so that noise in a low frequency region can be efficiently reduced. Further, by using it in combination with a silencer case that is conventionally used and uses a sound absorbing material that is excellent in sound deadening effect in a high frequency range, overall noise can be reduced.

[0012]

According to the present invention, since the low frequency region can be reduced by ANC, it can be compared with the conventional method by combining with a conventional silencer case using a sound absorbing material effective for silencing the high frequency region. It is possible to provide a silencer having a great silencing effect.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a jet fan provided with a speaker, an error microphone, a controller, and a partition wall in the jet direction.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a sectional view of a conventional jet fan in a jet flow direction.

FIG. 4 is a cross-sectional view in the jet direction in which only a speaker is installed in a conventional jet fan.

FIG. 5 is a cross-sectional view in which an error microphone and a controller are installed in FIG.

6 is a cross-sectional view in which the error microphone and the controller of FIG. 5 are installed on the suction side, the discharge side, and both sides.

[Explanation of symbols]

1 ... Impeller, 2 ... Electric motor, 3 ... Speaker, 4 ... Controller, 5 ... Error microphone, 6 ... Sound absorbing material, 7 ... Partition.

Claims (1)

[Claims] 1. A jet flow comprising an electric motor, a main body case having a built-in impeller directly connected to the electric motor, and a silencer case equipped with cylindrical sound absorbing materials provided in front of and behind the main body case to reduce noise. In the blower, active noise control for actively attenuating noise by adding sound waves having a phase opposite to that of the noise, the same frequency, and the same sound pressure level from a sound source different from the noise generated from the electric motor and the impeller is provided. A silencer for a jet blower characterized by being provided.