JP3505280B2 - Electronic silencer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention attenuates the exhaust sound by superimposing a sound wave generated from a sound source, for example, an exhaust sound generated from an engine or the like, with a sound wave having substantially the same size and an opposite phase. The present invention relates to a so-called active type electronic silencer.

[0002]

2. Description of the Related Art Generally, as an electronic silencer as described above, for example, one shown in FIG. 7 is known. In the figure, reference numeral 1 denotes an engine, and exhaust sound generated together with exhaust gas from the engine 1 propagates through a sound propagation path, for example, a tubular exhaust duct 2 having an inner diameter φ of 300 mm to 700 mm and is discharged from an exhaust port 2a. It Also, the exhaust duct 2
In the middle of the process, for example, a tubular branch pipe 3 with an inner diameter d of 300 mm
Are connected to the exhaust duct 2 at a substantially right angle.
Then, on the side opposite to the side of the branch pipe 3 that is connected to the exhaust duct 2, the noise reduction speaker 4 exposes its sound wave emitting surface (vibration plate) 4 a into the branch pipe 3, that is, The branch pipe 3 is provided so as to radiate sound waves, and by extension, the branch pipe 3 is provided so as to radiate sound waves into the exhaust duct.

[0003] Further, the engine 1 side of the position where the exhaust duct 2 is connected to the branch pipe 3 side, for example, the engine 1
A primary microphone (reference microphone) 5 is coupled in the vicinity of. The output electric signal of the primary microphone 5 is input to a digital filter 6 configured by, for example, a DSP (digital signal processing device) or a CPU (central processing unit), and the digital filter 6 outputs the output electric signal. Is processed so that the processed signal is input to the muffling speaker 4 via the amplifier 7. Further, a secondary microphone (error microphone) 8 is attached to the outlet 2a of the exhaust duct 2.
Is placed, and the output of this secondary microphone 8 is
It is connected to the digital filter 6.

That is, in this electronic silencer, the exhaust sound propagating in the exhaust duct 2 is collected by the primary microphone 5. Then, a sound wave that is substantially equal in size and opposite in phase to the exhaust sound picked up by the primary microphone 5 is output from the muffling speaker 4.
So that the output electric signal of the primary microphone 5 is filtered by a digital filter 6 and the processed signal is amplified by an amplifier 7 and then input to the silence speaker 4. . And
A sound wave radiated by the sound-deadening speaker 4, that is, a sound wave substantially equal in magnitude and opposite in phase to the exhaust sound, is radiated into the exhaust duct 2 via the branch pipe 3 and propagates in the exhaust duct 2. By interfering with the above, the exhaust noise is cancelled, that is, attenuated. Further, the exhaust sound after being attenuated is detected by the secondary microphone 8,
The filter coefficient of the digital filter 6 is updated so that the exhaust sound level after the attenuation is minimized, that is, the exhaust sound discharged to the outside is as close to zero as possible.

In FIG. 7, a branch pipe 3 is provided between the exhaust duct 2 and the muffling speaker 4, which is
This is to prevent the sound wave emitting surface 4a of the noise reduction speaker 4 from coming into contact with the exhaust gas flowing through the exhaust duct 2 together with the exhaust sound as much as possible. That is, the exhaust gas has a high temperature and contains corrosive gas, and the branch pipe 3 is provided to protect the sound wave emitting surface 4a from the high temperature and corrosive gas.

As described above, this electronic silencer is a so-called mechanical device because it is composed of electronic components such as the primary microphone 5, the digital filter 6, the amplifier 7, the speaker 4 for silencing and the secondary microphone 8. It has an advantage that it can be made much smaller than a passive silencer, that is, a muffler. In particular, in the case of attenuating exhaust sound in a relatively low sound range (low frequency range) of 500 Hz or less, for example, if the muffler is attempted to attenuate the exhaust sound, the muffler itself has a very large capacity (large size). The advantages of the electronic silencer are more prominent. That is, this electronic silencer is very effective in attenuating the exhaust sound in the low sound range as described above.

Although the secondary microphone 8 is used to update the filter coefficient of the digital filter 6 as described above, the acoustic system is relatively stable and the filter coefficient of the digital filter 6 is updated. If there is no need to do so, the secondary microphone 8 is unnecessary.

Here, as described above, in this electronic silencer, sound waves having substantially the same size and opposite phase to the exhaust sound generated from the engine 1 are emitted from the silencer speaker 4 and interfere with each other ( The exhaust sound is attenuated by (superimposing). Therefore, when the amplitude of the exhaust sound, that is, the sound pressure level increases, the muffling speaker 4 correspondingly responds to the increase.
The sound pressure level of the sound wave radiated from also becomes large. if,
When the sound pressure level of the sound wave radiated from the muffling speaker 4 is smaller (insufficient) than the sound pressure level of the exhaust sound, the exhaust sound cannot be attenuated sufficiently. Conventionally, a speaker having a large output sound pressure level having a certain margin with respect to the sound pressure level of exhaust sound has been used as the muffling speaker 4 so as to prevent such a shortage of the sound pressure level. .

[0009]

That is, in the above-mentioned prior art, as the muffling speaker 4, a speaker having an output sound pressure level higher than necessary with respect to the sound pressure level of the exhaust sound to be attenuated, that is, Will use over-specified speakers. Therefore, there is a problem that the cost of the muffling speaker 4 and the cost of the electronic muffling device increase accordingly. In particular, when the exhaust sound in the low-pitched sound range (highly effective), which is a strong point of the electronic silencer, is to be attenuated, the silencer speaker 4 has a larger diameter and a higher output sound pressure level. The above problem becomes more prominent because it requires a speaker to be included.

According to the present invention, at the frequency f _P at which the exhaust sound shows a peak of the sound pressure level, the sound emission efficiency of the sound deadening speaker 4 and the discharge efficiency from the discharge port 2a are improved, so that the sound deadening speaker 4 is improved. It is an object of the present invention to provide an electronic silencer capable of sufficiently attenuating exhaust noise even when a speaker having a lower output sound pressure level than that of a conventional one is used.

[0011]

According to a first aspect of the present invention, there is provided an electronic silencer according to claim 1, wherein a sound propagation path for propagating a sound generated from a sound source and discharging the sound through a discharge port, and the sound propagation path coupled to the sound propagation path A microphone that picks up sound, a control unit that controls an output electric signal of the microphone, and a speaker that is driven by an output signal of the control unit and emits a sound wave to the sound propagation path, the control unit comprising: In the electronic silencer configured to control the output electrical signal in a state in which the amplitude and phase of the sound wave radiated from the speaker are in the amplitude and phase necessary to cancel the sound, the sound wave of the speaker The distance from the radiating sound wave emitting surface to the outlet through the sound propagation path is calculated from the sound source at steady state.
In the frequency characteristics of the sound produced above, the sound has a sound pressure level
The standing wave having the same frequency as the frequency f _P showing the peak is
It is characterized in that the standing wave generation distance is generated from the sound wave emitting surface of the speaker to the discharge port by the sound wave emitted from the speaker.

Here, a standing wave is generated in the sound propagation path by the sound wave emitted from the speaker at the frequency f _P at which the exhaust sound shows the peak of the sound pressure level. In such a state, since the antinode of the sound pressure of the standing wave is located on the sound wave emitting surface of the speaker, the position of the sound wave emitting surface of the speaker is the most of the sound pressure at the frequency f _P in the sound propagation path. This is a place with a large acoustic impedance, that is, a large acoustic impedance. Thus, in the frequency f _P, the radiation impedance of the speaker is maximized, the components of the frequency f _P of the sound waves radiated from the speaker is emitted at the highest efficiency. Further, in the above state, the antinode of the particle velocity of the standing wave is located at the outlet of the sound propagation path, and the particle velocity at the frequency f _P becomes maximum at the outlet of the sound propagation path. Therefore, of the sound waves emitted from the speaker, the component of the frequency f _P is discharged to the outside from the discharge port with the highest efficiency.

The standing wave generation distance is, for example, a quarter (1/4) of a wavelength λ _P (that is, a value obtained by dividing the sound velocity by the frequency f _P ) at which the exhaust sound shows a peak of the sound pressure level. )
Is set to an odd multiple of the value of, and is preferably a value obtained by performing tube end correction on this.

An electronic silencer according to a second aspect is the electronic silencer according to the first aspect, further comprising a sound wave transmission path for transmitting the sound wave between the sound wave emitting surface of the speaker and the sound propagation path. , At the interference point in the middle of the above sound transmission path
The sound waves emitted by the speaker and the sound transmission path.
The sound from the speaker is provided so that it interferes with the sound.
The standing wave generation distance is defined as the distance from the wave emitting surface to the outlet through the interference point .

Here, the sound wave emitted from the sound wave emitting surface of the speaker is discharged from the discharge port through the interference point . Therefore, the frequency of the standing wave generated in the sound propagation path by the sound wave emitted from the speaker, that is, the frequency component that the speaker wants to radiate with the highest efficiency and discharge to the outside, interferes with the sound wave emitting surface of the speaker. The length to the point and the
It depends on the sum of the length between the crossing point and the outlet .

[0016]

[0017]

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of an electronic silencer according to the present invention will be described with reference to FIGS. 1 to 6. FIG. 1 is a schematic configuration diagram of an electronic silencer showing the present embodiment. As shown in the figure, this electronic silencer has a structure substantially similar to that of the conventional device shown in FIG. However, in this electronic silencer, the distance L from the sound wave emitting surface 4a of the silencer speaker 4 to the exhaust port 2a through the branch pipe 3 and the exhaust duct 2 (in the same figure) in accordance with the frequency characteristic of the exhaust sound of the engine 1. L ₁ + L ₂ ) is set, which is the difference between the electronic silencer according to the present embodiment and the above-described conventional device. In the figure, L ₁ is the distance from the sound wave emitting surface 4a of the noise reduction speaker 4 to the interference point A between the exhaust sound in the exhaust duct 2 and the sound wave of the noise reduction speaker 4, and L ₂ is the interference point. It is the distance from A to the exhaust port 2a of the exhaust duct. Since the structure other than this is the same as the conventional device of FIG. 7,
Similar parts are designated by the same reference numerals, and detailed description thereof will be omitted.

That is, the distance L is set as follows. First, the engine 1 has, for example, the number of cylinders M and the number of revolutions N.
If steady operation is performed at [rps], the frequency characteristic of the exhaust noise is normally as shown in FIG. As shown in the figure, the frequency characteristic of this exhaust sound is the frequency f
_The sound pressure level peaks at _p [Hz], that is, it has the resonance frequency f _P. The resonance frequency f _P is expressed by the following equation 1 and is, for example, about 30 to 100 Hz.

[0020]

[Equation 1] f _P = M · N

Then, in accordance with this resonance frequency f _P ,
The distance L (L ₁ + L ₂ ) [m] is calculated from the following equation 2 and set. In the equation 2, c is the speed of sound [m /
s].

[0022]

## EQU2 ## L = [(2n + 1) c] / (4f _P ) (n
= 0, 1, 2, ...)

Therefore, assuming that the resonance frequency f _P of the exhaust sound is, for example, 30 Hz and the sound velocity c is, for example, 340 m / s, the distance L is from the equation 2 to about 2.8 m, 8.5 m, ...
··And it is sufficient. Of course, it goes without saying that the smaller the value of n in the above equation 2, the smaller the distance L and thus the electronic silencer itself.

When the resonance frequency f _P in the above equation 2 is represented by the wavelength λ _P [m], the distance L is f _P = c / λ
_From the relationship of _P, the following formula 3 is obtained.

[0025]

## EQU3 ## L = [(2n + 1) λ _P ] / 4

In the electronic silencer configured as described above, the sound wave emitted from the silencer speaker 4 as described above propagates through the branch pipe 3 and the exhaust duct 2 and is exhausted to the outside from the exhaust port 2a. To be done. At this time, the discharge port 2a
At, the acoustic impedance changes abruptly, so the sound wave is reflected by the outlet 2a and travels in the opposite direction. Then, the sound wave traveling in the opposite direction interferes with the sound wave propagating toward the discharge port 2 a through the branch pipe 3 and the exhaust duct 2, whereby a standing wave is generated in the branch pipe 3 and the exhaust duct 2. Occurs.

The branch pipe 3 and the exhaust duct 2 in such a state are considered to correspond to the closed pipe 20 whose one end is closed with a rigid material as shown in FIGS. 3 (a) and 3 (b). To be In this case, the closed end portion 20b on the closed side corresponds to the sound wave emitting surface 4a of the muffling speaker 4 in FIG. 1, and the opening portion 20a on the other end side is the discharge port 2a of the exhaust duct 2.
Equivalent to. 3A shows the sound pressure distribution of the standing wave, and FIG. 3B shows the particle velocity distribution. In this way, in the state where the standing wave is generated in the closed tube 20, the frequency f [Hz] of this standing wave and the tube length L [m] of the closed tube 20.
It is known that there is a relationship as shown in the following Equation 4.

[0028]

## EQU4 ## L = [(2n + 1) c] / (4f) (n =
0, 1, 2, ...)

Further, the frequency f of the standing wave in the equation 4 is
Is represented by a wavelength λ [m], the tube length L is given by the following equation 5 from the relation of f = c / λ.

[0030]

## EQU5 ## L = [(2n + 1) λ] / 4

As can be seen from the above equation (4) (or equation (5)), if the pipe length L is constant, the frequency f is
Standing waves of different (or wavelength λ), more specifically, frequencies that are odd multiples (or reciprocal multiples of odd numbers) of the lowest frequency f (or wavelength λ when n = 0 in Formula 4 or Formula 5). ) Will be generated in a plurality of standing waves. Further, as shown in FIGS. 3 (a) and 3 (b), these standing waves have an antinode whose sound pressure or particle velocity has the maximum amplitude and a node which has the minimum amplitude (almost zero). And these antinodes and nodes are inversely related to each other between sound pressure and particle velocity.

In this state, each standing wave is shown in FIG.
As shown in (a), an antinode having the maximum sound pressure is located at the closed end 20b of the closed tube 20. In this way, in the belly where the sound pressure is maximized in the closed tube 20, the acoustic impedance with respect to the frequency f of the standing wave is maximized. Further, as shown in FIG. 3 (b), each standing wave positions the antinode where the particle velocity is maximum at the opening 20 a of the closed tube 20. When the particle velocity is maximized in the opening 20a, the efficiency of emission (radiation) from the opening 20a to the outside with respect to the sound wave of the frequency f is maximized.

This also applies to the branch pipe 3 and the exhaust duct 2 in FIG. 1, that is, at the frequency f at which the standing wave is generated, the sound is emitted at the position of the sound wave emitting surface 4a of the muffling speaker 4. Maximum impedance. That is, in this state, since the radiation impedance of the muffling speaker 4 is maximized, the component of the frequency f among the sound waves emitted by the muffling speaker 4 is radiated with the highest efficiency. Then, the particle velocity at the discharge port 2a of the exhaust duct 2 is also maximized, and the discharge (radiation) efficiency of the sound wave of the frequency f at the discharge port 2a is maximized.

Therefore, of the sound waves emitted from the muffling speaker 4, the component of the frequency f is radiated into the exhaust duct 2 with the highest efficiency, and is discharged to the outside from the discharge port 2a with the highest efficiency. Then, the frequency f (or wavelength λ)
Is a distance (from the sound wave emitting surface 4a of the muffling speaker 4 to the branch pipe 3 and the exhaust duct 2) based on the relation of the above-mentioned Formula 4 (or Formula 5).
Via the distance to the discharge port 2a) L. The distance L corresponds to the standing wave generation distance described in the claims, and the distance L is hereinafter referred to as the standing wave generation distance L.
The branch pipe 3 corresponds to the sound wave transmission path described in the claims.

Here, in the electronic silencer according to the present embodiment, the standing wave generation distance L is set based on the above-mentioned equation 2 (or equation 3), but this equation 2 (or equation 3) ) Is equivalent to replacing the frequency f (or wavelength λ) in the equation 4 (or the equation 5) with the resonance frequency f _P of the exhaust sound. That is, by setting the standing wave generated distance L based on the number 2 (or Expression 3), the resonance frequency f _P of the exhaust sound, i.e. the frequency f _P of the exhaust sound indicating the maximum sound pressure level
In the above, a standing wave is generated in the branch pipe 3 and the exhaust duct 2 by the sound wave emitted from the muffling speaker 4. Then, at the frequency f _{P at} which this standing wave is generated, as described above, the emission efficiency of sound waves from the muffling speaker 4 is maximized, and the emission (radiation) efficiency of sound waves at the outlet 2a is maximized. Therefore, of the sound waves emitted from the muffling speaker 4, the component having the same frequency as the frequency f _P is radiated into the exhaust duct 2 with the highest efficiency and is discharged to the outside from the discharge port 2a with the highest efficiency.

That is, since the sound wave of the muffling speaker 4 can be efficiently radiated and discharged at the frequency f _P at which the exhaust sound to be attenuated shows the maximum sound pressure level, a large attenuation rate is obtained at the frequency f _P. That is, the exhaust sound can be efficiently attenuated in accordance with the frequency characteristic of the exhaust sound (the frequency f _P indicating the maximum sound pressure level). Therefore, the exhaust sound can be sufficiently attenuated even when a speaker having a smaller output sound pressure level than the conventional one is used as the sound deadening speaker 4.
There is an effect that the cost of the muffling speaker 4 and eventually the cost of the electronic muffler can be suppressed. In particular, the low-pitched sound range of electronic silencers, for example 500H
In the case where the exhaust sound of z or less is targeted for attenuation, the above effect is more prominent.

[0037] Then, the frequency f _P which can be efficiently attenuated frequency f _P for generating a standing wave, as described above, i.e., the exhaust sound is dependent on the standing wave generated distance L (L ₁ + L ₂₎ . For example, in FIG. 1, L ₁ is [(2n ₁ +
1) c] / 4f _P (where n ₁ = 0, 1, 2, ...)
Then, since the node of the sound pressure of the standing wave (antinode of the particle velocity) is located at the interference point A, in this case, L ₂ is (n ₂ · c) / 2f _P (however, n ₂ = 0, 1, 2, ...
·)And it is sufficient. In addition, L ₁ is (n ₁ · c) / 2f _P
(However, if n ₁ = 0, 1, 2, ...), the antinode of the sound pressure of the standing wave (the node of the particle velocity) is located at the interference point A. In this case, L ₂ to [(2n ₂ +1)
c] / 4f _P (where n ₂ = 0, 1, 2, ...).

The standing wave generation distance L (L ₁ +
L ₂ ) is determined by the length of the branch pipe 3 and at which position of the exhaust duct 2 the branch pipe 3 is connected. That is, the length of the branch pipe 3 and the connecting position of the branch pipe 3 with the exhaust duct 2 (that is, the length of the branch pipe 3 and the length from the connecting position of the branch pipe 3 with the branch pipe 3 to the exhaust port 2a). By changing one or both of the two, it is possible to set the frequency f _P , and thus the attenuation characteristic of the electronic silencer.

Further, the exhaust sound of the engine 1 may have peaks (resonance frequencies) at a plurality of frequencies f _p1 , f _p2 , f _p3, ... As shown in FIG. When a plurality of resonance frequencies f _p1 , f _p2 , f _p3 , ...
Usually, the lowest resonance frequency (f _p1 in FIG. 4) of the above resonance frequencies f _p1 , f _p2 , f _p3 , ... _{Is used} as the fundamental wave, and the remaining resonance frequencies f _p2 , f _p3 , ... In most cases, is a multiple of the frequency f _p1 of the fundamental wave, that is, a harmonic wave. In such a case, the sound pressure level of the exhaust sound is maximized at the fundamental wave frequency f _p1 in most cases.

Here, the above equation 2 (or equation 3) and the figure
As can be seen from 3, the standing wave generation distance L is fixed.
In the branch pipe 3 and the exhaust duct 2, the frequency f_P
(Or wavelength λ_P) Different standing waves are generated. Immediately
The frequency f at which exhaust noise can be efficiently attenuated
_PThere are multiple
f _PThe lowest of all (when n = 0 in Equation 2)
Efficiently attenuates exhaust noise at frequencies that are an odd multiple of the wavenumber.
Can be made. In the electronic silencer showing the present embodiment
The fundamental wave that maximizes the sound pressure level of exhaust noise
Frequency f_p1To effectively attenuate the exhaust sound
Since the standing wave generation distance L is set,
Automatically the fundamental frequency f_p13f which is an odd multiple of
_p1(That is, f in FIG._p3) 5f_p1(Not shown),
.. Even in the case of ...
It is very effective.

In the electronic silencer shown in FIG. 1, the case where the branch pipe 3 is joined to the exhaust duct 2 at a right angle has been described. However, as shown in FIG. 5, the branch pipe 3 is connected to the exhaust duct. It can also be applied to the case of coupling the two diagonally. That is, the engine 1 along with the exhaust sound
In order to make it more difficult for high-temperature and corrosive exhaust gas discharged from the exhaust gas to flow into the muffling speaker 4 side through the branch pipe 3,
As shown in the figure, the branch pipe 3 may be joined to the portion of the exhaust duct 2 closer to the engine 1 than the joint position of the exhaust duct 2 with the branch pipe 3 at an acute angle. In this case, the standing wave generation distance L (L ₁ +
L ₂ ) will change. Therefore, in this case, the intersection point of the center lines of the branch pipe 3 and the exhaust duct 2 (the one-dot chain line in the figure) is set as the interference point A, that is, the branch pipe 3 and the exhaust duct 2 are separated from the sound wave emitting surface 4a of the silencer speaker 4. The standing wave generation distance L is the average of the distances to the discharge port 2a.

Although the branch pipe 3 is provided in the electronic silencer of FIG. 1, the sound wave emitting surface 4a of the sound deadening speaker 4 is made of a heat-resistant and corrosion-resistant material, or the sound wave emission is performed. When it is not necessary to provide the branch pipe 3 in order to protect the sound wave emitting surface 4a from exhaust gas, such as when the surface 4a is protected by a heat-resistant and corrosion-resistant material, FIG.
The muffler speaker 4 may be directly coupled to the exhaust duct 2 as shown in FIG. In this case, as shown in the figure, the distance from the coupling position (specifically, the center of the coupling position) of the muffling speaker 4 to the outlet 2a of the exhaust duct 2 corresponds to the standing wave generation distance L.

In general, when sound is radiated from one end of a tube having an inner diameter a, the length of the air column on which the tube resonates due to the influence of the radiative reactance due to the sound being radiated from the tube opening.
It is known to be about 0.6a longer than the actual tube length. Therefore, also in the electronic silencer according to the present embodiment, it is preferable to perform the pipe end correction in consideration of this influence. If this tube end correction is applied, L ₁ shown in FIG.
L _2, phi, and represented by the number 2 [(2n + 1) c] /
The relationship of (4f _P ) is as in the following Expression 6.

[0044]

[Equation 6] L ₁ + L ₂ + 0.6φ = [(2n + 1) c] /
(4f _P ) (n = 0, 1, 2, ...)

Further, in the electronic muffler according to the present embodiment, the secondary microphone 8 is provided to update the filter coefficient of the digital filter 6, but the acoustic system is stable and the filter of the digital filter 6 is stable. If it is not necessary to update the coefficient, it is not necessary to provide the secondary microphone 8.

[0046]

The electronic silencer according to the first aspect of the present invention makes the radiation impedance of the sound wave of the speaker maximum at the frequency f _P at which the exhaust sound shows the peak of the sound pressure level, and the sound wave to the outside. It is configured to maximize the discharge efficiency. With this configuration, the sound waves of the speaker can be efficiently radiated and emitted in accordance with the frequency characteristics of the exhaust sound to be attenuated (the frequency indicating the maximum sound pressure level). Can be efficiently attenuated. Therefore, even a speaker having a smaller output sound pressure level than the conventional one can be sufficiently dealt with, and thus, there is an effect that the cost of the speaker and the cost of the electronic silencer can be suppressed. In particular, when the exhaust sound in the low-pitched sound range (which is highly effective), which is an advantage of the electronic silencer, is targeted for attenuation, the above-mentioned effect is more prominent.

[0047] In the electronic noise suppressor according to claim 2, while the radiation at the highest efficiency among the sound waves radiated from the speaker, the frequency components to be discharged with the highest efficiency,
The distance from the sound wave emitting surface of the speaker to the interference point and the interference point
Depends on the sum from the length to the outlet . Therefore, the frequency characteristics of the sound waves, and thus the attenuation characteristics of the electronic silencer , the length from the sound wave emitting surface of the speaker to the interference point,
Since it can be changed by either one or both of the length from the interference point to the discharge port, there is an effect that the degree of freedom in designing the attenuation characteristic of the electronic silencer is improved.

[0048]

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an embodiment of an electronic silencer according to the present invention.

FIG. 2 is a graph showing frequency characteristics of exhaust sound in the electronic silencer.

FIG. 3 shows a standing wave generated in a closed pipe that models an exhaust duct in the electronic silencer, and is represented by equation 2 (or equation 3).
In the figure showing the case where n in each is 0, 1, 2,
(A) shows a sound pressure distribution, and (b) shows a particle velocity distribution.

FIG. 4 is a graph showing a frequency characteristic of exhaust sound in the electronic silencer, showing a case where a plurality of resonance frequencies exist.

FIG. 5 is a schematic configuration diagram showing a modified example of the electronic silencer.

FIG. 6 is a schematic configuration diagram showing a modified example of the electronic silencer.

FIG. 7 is a diagram showing a schematic configuration of a conventional electronic silencer.

[Explanation of symbols]

1 engine 2 exhaust duct 2a outlet 3 branches 4 silencer speaker 4a Sound wave emitting surface 5 Primary microphone 6 Digital filter 7 amplifier 8 secondary microphone

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G10K 11/178 F01N 1/00 G10K 11/16

Claims (2)

(57) [Claims] 1. A sound propagation path for propagating a sound generated from a sound source and discharging the sound from an outlet, a microphone coupled to the sound propagation path for collecting the sound, and an output electric signal of the microphone. The control means includes a speaker driven by an output signal of the control means to emit a sound wave to the sound propagation path, and the control means controls the sound wave whose amplitude and phase are emitted from the speaker. In an electronic silencer configured to control the output electric signal to a state in which the amplitude and phase are required to cancel the above, the discharge port from the sound wave emitting surface of the speaker that emits the sound wave passes through the sound propagation path and the discharge port. Distance from the above sound source
In the frequency characteristics of the above sound generated during steady state, the sound
Standing at the same frequency as the frequency f _P that shows the peak of the pressure level
An electronic silencer, wherein a wave has a standing wave generation distance generated from a sound wave emitting surface of the speaker to the discharge port by a sound wave emitted from the speaker . 2. A sound wave transmission path for transmitting the sound wave is provided between the sound wave emitting surface of the speaker and the sound propagation path.
At the interference point in the middle of the sound propagation path, the speaker emits
The emitted sound wave and the sound propagating through the sound propagation path interfere with each other.
And the interference from the sound wave emitting surface of the speaker.
The electronic silencer according to claim 1, wherein a distance to the discharge port via a point is set as the standing wave generation distance.