JPH11133985A - Muffling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a muffling device which can generate a sound wave for muffling along a wide frequency band range. SOLUTION: The opening surface 37A of an acoustic pipe 37 is formed obliquely to the axial center of the acoustic pipe 37. As a result, the resonant effect of a resonance system which is determined by the stiffness of the air in an air chamber 10 and the air mass inside the acoustic pipe 37, is made gentle, so as to suppress the peak, and a high output sound pressure level can be generated along a wide frequency band range, so as to improve the muffling effect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silencer using active noise control (ANC) technology, and more particularly, to an air chamber defined between a front surface of a sound wave generator and an outer wall surface of an exhaust pipe. A casing, and an acoustic pipe having one end communicating with the air chamber and concentrically surrounding the opening of the exhaust pipe.The stiffness of air in the air chamber and the air mass inside the acoustic pipe constitute a resonance system. The present invention relates to a muffler that generates a sound wave for muffling using a resonance system.

[0002]

2. Description of the Related Art As a conventional technique of this kind, there is a silencer as shown in FIG. The exhaust pipe 1, one end of which is arranged near the noise source 9, has a speaker 4 as a sound wave generator.
A air chamber 10 between the front of A, 4C and the outer wall surface of exhaust pipe 1
Is provided, and an acoustic pipe 7 having one end communicating with the air chamber 10 is provided so as to concentrically surround the opening 1 a of the exhaust pipe 1. Speaker 4
The back space of A, 4C is defined by the back casings 8A, 8C. The speakers 4A and 4C drive a resonance system (Helmholtz resonator) determined by the stiffness of the air in the air chamber 10 and the air mass of the annular internal space 27 of the acoustic tube 7 to resonate at the main frequency of the noise P. The noise P is canceled by the interference between the noise-reducing sound wave radiated from the opening 7a and the noise P radiated from the opening 1a of the exhaust pipe 1.

[0003]

However, the conventional silencer has a problem that the efficiency of sound wave generation is high at a single resonance frequency, but the efficiency is reduced at other frequencies. In particular, when the noise source 9 of an engine having a sound pressure characteristic shown in FIG. 4, can generate a sound-absorbing sound waves with high efficiency with respect to the first peak values S ₁ of the noise P (frequency 90 Hz) However, a sound-absorbing sound wave having a sufficient sound pressure level cannot be generated in other frequency bands. Therefore, a sufficient noise reduction effect cannot be obtained for noise components exceeding 90 Hz. Further, the second and third peak values S ₂ of the noise P (frequency 180
Hz) and S ₃ (frequency 240 Hz) are also large, so that it is necessary to perform a silencing action on them as well.
_2, S ₃ peak areas of the sound-absorbing sound waves can not be matched against, it is impossible to obtain a sufficient silencing effect.
As described above, the conventional silencer has a problem that only a noise in a narrow frequency band can obtain a silencing effect.

[0004] The present invention has been made in view of the above-described problems, and has as its object to provide a muffler capable of efficiently generating sound waves in a wide frequency band.

[0005]

The object of the present invention is to provide an exhaust pipe having one end close to or in contact with a noise source, a noise detector for detecting noise of the noise source, and a noise reduction deviation detection for detecting a noise reduction deviation. And an output of the noise detector and an output of the silencing deviation detector, and forming a muffling signal for generating a sound wave having the same magnitude and opposite phase as the noise from at least one sound wave generator. A casing for defining an air chamber between a front surface of the sound wave generator and an outer wall surface of the exhaust pipe, one end of which communicates with the air chamber, and concentric with an opening of the exhaust pipe. A sound muffler provided with a sound tube that surrounds the sound tube, wherein the opening surface of the sound tube is formed obliquely with respect to the axis of the sound tube.

According to the present invention, by forming the opening surface of the sound tube obliquely with respect to the axis of the sound tube, the resonance effect is moderated, the peak is suppressed, and a high sound pressure level is generated over a wide frequency band. . Thereby, a high noise reduction effect can be obtained in a wide frequency band.

[0007]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 and FIG. 2 show a silencer according to an embodiment of the present invention, which is indicated generally by 21. One end of the exhaust pipe 1 is arranged close to a noise source (the engine in the engine generator system in the present embodiment) 9. A noise detector 2 for detecting noise P from a noise source 9 is provided inside the exhaust pipe 1.
A silencing deviation detector 3 is provided outside a. The muffling signal generating device 5 receiving the output x of the noise detector 2 and the output e of the muffling deviation detector 3 outputs a muffling sound wave having the same magnitude and opposite phase as the noise P to the speakers 4A as sound wave generators, Form a silencing signal y to be generated from 4B, 4C and 4D.

FIG. 5 shows the details of the muffling signal generator 5. The output x of the noise detector 2 is supplied through an amplifier 11 and an A / D converter 12 to an adaptive filter (hereinafter referred to as A
Abbreviated as DF. ) 14 and the delay filter 13. The ADF 14 has N taps, the output of which is updated by the output of the coefficient calculator 15. The delay filter 13 has an acoustic transfer characteristic corresponding to a path from the speakers 4A to 4D → the air chamber 10 → the acoustic tube 7 → the silencing deviation detector 3. That is, the coefficient of the delay filter 13 is determined in consideration of the time delay, and is measured or identified in advance. The output e of the silencing deviation detector 3 is supplied to the amplifier 16 and the A / D converter 1.
7 is supplied to the coefficient calculator 15. Coefficient calculator 1
Reference numeral 5 denotes an adaptive algorithm for sequentially calculating an optimum coefficient to be given to the ADF 14. The muffling signal y formed by the ADF 14 is supplied to the speakers 4A to 4D via the D / A converter 18 and the amplifier 19, and generates muffled sound waves having the same magnitude as the noise P and having the opposite phase. .
The muffling signal generator 5 has a configuration using the above-described well-known ANC control technology.

[0010] Four speakers 4A to 4D are arranged on the side wall surface of the casing 26 defining the air chamber 10, and
The acoustic pipe 37 having one end communicating with the air chamber 10 is an exhaust pipe 1
Are concentrically surrounded. And air chamber 1
A resonance system (Helmholtz resonator) determined by the stiffness of the air inside 0 and the mass of the air in the annular inner space 27 of the acoustic tube 37 is driven by these speakers 4A to 4D, and the main frequency of the noise P (in the present embodiment). (90 Hz), and a sound-absorbing sound wave is radiated from the opening 37 a of the acoustic tube 37. The rear spaces of the speakers 4A to 4D are respectively provided with rear casings 8A, 8B, 8C and 8C.
D, and has a sufficient volume that does not affect the vibration of the diaphragm of each of the speakers 4A to 4D.

In this embodiment, the circular opening surface 37A of the acoustic tube 37 is formed obliquely at an inclination angle θ. As a result, as shown by the solid line in FIG. 3, the resonance effect is moderated, the peak of the silencing sound wave is suppressed, the foot is widened, and the sound pressure level is increased over a wide frequency band. As a result, compared with the output sound pressure characteristic of the conventional silencer shown by the broken line in the drawing, the sound wave generation efficiency can be increased particularly in a frequency band of 90 Hz to 180 Hz. It is to be noted that the angle θ is suitably from about 20 ° to about 60 °, and the resonance effect becomes milder as the magnitude of θ increases.

Further, in the present embodiment, the axial length L ₁ of the air chamber 10 is set to the second peak value S ₂ of the noise P (FIG. 4).
And sets to resonate at the frequency indicating the reference) (180 Hz), the length L ₂ from the casing 26 side end portion of the acoustic tube 37 to the center of the aperture plane 37A, the third noise P
It is set to resonate at the frequency showing the peak value S ₃ of (240 Hz) (see FIG. 3). As a result, the noise P
Can generate sound-absorbing sound waves in a frequency region corresponding to the second and third peak values S ₂ and S ₃ at a sufficient sound pressure level, and can improve the sound-absorbing effect as compared with the related art.
Further, since the resonance effect is mild (the output sound pressure near the peak is high), even if the peak of the output sound pressure shifts due to a temperature change, the influence can be reduced.

Therefore, according to the sound deadening device 21 of the present embodiment, since the sound deadening sound wave can be efficiently generated over a wide frequency band, a large sound deadening effect can be obtained for the noise P over a wide frequency band. be able to. In addition, a sufficient silencing effect can be obtained for the _second and _third peaks S ₂ and S ₃ of the noise P.

Although the embodiment of the present invention has been described above, the present invention is, of course, not limited to this, and various modifications can be made based on the technical concept of the present invention.

For example, in the above-described embodiment, an example has been described in which the present invention is applied to an engine generator system for a private, emergency or cogeneration system. However, the present invention is also applicable to, for example, an automobile engine. . In this case, one end of the exhaust pipe 1 is arranged in contact with the cylinder block of the engine.

In each of the above embodiments, four speakers 4A to 4D are used as sound wave generators. However, the number of speakers is increased or decreased according to the type of target noise or the noise source. It is possible. In this case, the length L ₂ is also a suitable length L ₁ and acoustic pipe 37 of the air chamber 10 can be varied.

Further, in the above embodiment, the exhaust pipe 1
The opening 1a is formed obliquely similarly to the acoustic tube 37, but is not limited to this, and may be formed perpendicular to the axis of the exhaust pipe 1 as in the related art. Also, the opening surface 3 of the acoustic tube 37
The direction of 7A can be appropriately changed depending on the direction in which the exhaust pipe 1 is provided, and in this case, the same effect as in the above-described embodiment can be obtained.

[0018]

As described above, according to the sound deadening device of the present invention, since the opening surface of the sound tube is formed obliquely with respect to the axis of the sound tube, the output sound pressure characteristic is made gentler than before. As a result, a high sound pressure level can be generated over a wide frequency band, so that sound waves in a wide frequency band can be efficiently generated, and the sound deadening effect can be enhanced.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a muffler according to an embodiment of the present invention.

FIG. 2 is a front view of the same.

FIG. 3 is a graph comparing an output sound pressure characteristic according to an embodiment of the present invention with an output sound pressure characteristic according to a conventional technique.

FIG. 4 is a graph showing a relationship between a frequency of a noise source and a sound pressure level.

FIG. 5 is a block diagram illustrating a configuration of a muffling signal generation device.

FIG. 6 is a side sectional view showing a conventional silencer.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 exhaust pipe 2 noise detector 3 silencing deviation detector 4A speaker 4B speaker 4C speaker 4D speaker 5 silencing signal generator 9 noise source 10 air chamber 21 silencer 26 casing 37 acoustic pipe 37A opening surface

Claims (3)

[Claims] An exhaust pipe having one end close to or in contact with a noise source, a noise detector for detecting noise of the noise source, a noise reduction deviation detector for detecting a noise reduction deviation, and an output of the noise detector. And a muffling signal generator that receives an output of the muffling deviation detector and forms a muffling signal for generating sound waves having the same magnitude as the noise and having an opposite phase from at least one sound wave generator, A casing defining an air chamber between the front surface of the sound wave generator and an outer wall surface of the exhaust pipe; and an acoustic pipe having one end communicating with the air chamber and concentrically surrounding the opening of the exhaust pipe. The sound deadening device according to claim 1, wherein an opening surface of the sound tube is formed obliquely with respect to an axis of the sound tube. 2. The muffler according to claim 1, wherein an axial length of the air chamber is set so as to resonate at a frequency indicating a second peak value of the noise. 3. The apparatus according to claim 1, wherein a length from the one end of the acoustic tube to a center of the opening surface is set to resonate at a frequency indicating a third peak value of the noise. Alternatively, the muffler according to claim 2.