JPH094433A - Muffler device - Google Patents

Abstract

PURPOSE: To enable reduction of size and eliminate influence of constant wave and howling by arranging a passive muffler between a microphone and a speaker in a sound propagation path in a muffler device having the muffler and an electronic sound absorbing device. CONSTITUTION: A muffler device which attenuates exhaust noises propagated to the outside through an exhaust duct 3 of an engine 10 has a muffler 1 arranged between a primary microphone composing an electronic muffler device 2 and a sound absorbing speaker 6. The muffler 1 is arranged inside a specified space L0 formed inside the exhaust duct 3 for managing treatment time required for controlling an output signal of the primary microphone 4 by means of the controller 5. A length L2 between a virtual sound source P generated in the muffler 1 and an exhaust port 3a of the exhaust duct 3 is reduced comparing with a conventional case, while suppressing generation of constant wave in a low sound area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a muffler for use in an exhaust duct of an engine or the like and for damping exhaust sound propagating in the exhaust duct and discharged to the outside.

[0002]

2. Description of the Related Art Generally, as a method of attenuating exhaust sound emitted from an exhaust duct, a method using a passive silencer, that is, a muffler, and a method using an active silencer, that is, an electronic silencer are known. There is. Among them, the muffler has a drawback that the muffler itself has a larger volume, that is, becomes larger as the frequency of the exhaust sound to be attenuated is lower. However, for example 500 Hz
When the exhaust sound in the above relatively high frequency range (high frequency component) is to be attenuated, even a relatively small one can be used, and therefore it is widely used for high frequency range attenuation.

On the other hand, the electronic silencer is
This exhaust noise is canceled or attenuated by interfering with a sound wave substantially equal in size and opposite in phase to the exhaust sound, which is advantageous in that it can be made much smaller than the muffler. However, in this electronic muffler, digital filtering using a CPU (central processing unit), a DSP (digital signal processing device), etc. is usually adopted for the processing, so that the exhaust noise to be attenuated is When the frequency becomes higher, the load on the CPU, DSP, etc. becomes greater, that is, it becomes difficult to muffle the exhaust sound in the high frequency range. Therefore, this electronic silencer is, for example, 500 Hz
It is suitable for so-called low-frequency attenuation, in which the exhaust sound in the relatively low-frequency range below is attenuated.

As described above, since the muffler is suitable for high range attenuation, and the electronic muffler is suitable for low range attenuation, by providing both of these muffler and electronic muffler at the same time, the low range is reduced. It is possible to realize a muffling device that can obtain a large silencing effect in a wide frequency range from a high frequency range. Conventionally, as such a silencer, for example, there is one as shown in FIG. In the figure, 10 is a noise source, for example, an engine. Exhaust sound generated from the engine 10 passes through a muffler 1 for silencing high frequencies above 500 Hz and an electronic silencing device 2 for silencing low frequencies below 500 Hz, for example. It is configured to be discharged from the exhaust port 3a of the exhaust duct 3.

The muffler 1 is, for example, of a sound absorbing type as shown in FIG. 7, and has a plurality of small holes 1 on its peripheral wall as shown in FIG.
, 11, ... Perforated tube 12, a hollow body 13 surrounding the outer circumference of this perforated tube 12, and this hollow body 13
And a sound absorbing material 14 filled between the perforated pipe 12 and the perforated pipe 12. The hollow portion of the perforated pipe 12 communicates with the inside of the exhaust duct 3, that is, forms a part of a sound propagation path through which exhaust sound propagates. With the above configuration,
The muffler 1 is capable of attenuating the exhaust sound propagating in the perforated pipe 12, and is particularly configured to obtain an attenuation effect of, for example, about 30 dB with respect to the above-described exhaust sound of 500 Hz or higher.

On the other hand, the electronic muffler 2 includes a primary microphone (reference microphone) 4 coupled to the exhaust duct 3 in the vicinity of the muffler 1 and the primary microphone 4.
Of the output electric signal of the controller 5, a speaker 6 for silencing which is driven by the output signal of the controller 5 and emits sound waves into the exhaust duct 3, and a secondary microphone (which is disposed at the exhaust port 3a of the exhaust duct 3). Error microphone) 7. Controller 5
A digital filter such as a DSP is formed therein. The primary microphone 4 picks up the exhaust sound of the engine 10. The output signal of the primary microphone 4 is filtered by the digital filter. Then, the output signal of the digital filter is supplied to the muffling speaker 6. The filter coefficient of the digital filter is configured to cancel the exhaust sound by causing the sound wave radiated from the silencer speaker 6 to interfere with the exhaust sound in the exhaust duct 3. That is, at the interference point, the exhaust sound and the sound wave radiated from the muffling speaker 6 are of equal magnitude and opposite phase.

Further, the noise level at the exhaust port 3a of the exhaust duct 3 is detected by the secondary microphone 7, and the noise level is minimized, that is, the exhaust noise emitted to the outside is as close to zero as possible. The filter coefficient of the digital filter is updated. As a result, it is possible to follow changes in the acoustic characteristics of the sound propagation path and changes in the characteristics of the muffling speaker 6 with time.

The secondary microphone 7 is not always necessary. That is, when there is no change in the acoustic characteristics of the sound propagation path or the change in the characteristics of the muffling speaker 6 over time, and therefore there is no need to update the filter coefficient of the digital filter, it is not necessary to provide the secondary microphone 7.

The muffler speaker 6 is provided in the exhaust duct 3
From the coupling position with the primary microphone 4 toward the exhaust port 3a, that is, in the direction in which the exhaust sound propagates, a predetermined distance L
They are placed at positions separated by ₀ . This requires a certain amount of processing time for the controller 5 to control (process) the output electric signal of the primary microphone 4, so that the sound wave for canceling the exhaust sound picked up by the primary microphone 4 is silenced. This is because it takes some time before the sound is emitted from the speaker 6 for use. Therefore, in order to cover the processing time of the controller 5, the exhaust sound is collected 1
The predetermined distance L is provided between the next microphone 4 and the noise elimination speaker 6 that emits a sound wave for canceling the exhaust noise.
₀ is provided.

With the above structure, the silencer shown in FIG.
The exhaust sound of the engine 10 is sufficiently attenuated by the muffler 1 in the high frequency range, and is sufficiently attenuated by the electronic silencer 2 in the low frequency range, that is, a large silencing effect in a wide frequency range from the low frequency range to the high frequency range. Can be obtained.

In this silencer, the exhaust sound of the engine 10 propagates in a so-called sound propagation path between the muffler 1 (specifically, the perforated pipe 12 constituting the muffler 1) and the exhaust duct 3. Then, it is discharged from the exhaust port 3a, but a place P where the acoustic impedance suddenly changes occurs in this sound propagation path, especially in the muffler 1. Such sound propagation path is
It is considered that this corresponds to the closed tube 30 as shown in FIGS. 8A to 8C, and in this case, the closed end portion 30a of both ends of the closed tube 30 which is closed by the rigid material is the above-mentioned. It corresponds to the place P, and the opening 30b on the other end side corresponds to the exhaust port 3a side.

In the closed tube 30 as described above, the sound propagated from the closed end portion 30a side toward the opening portion 30b side is
The light is reflected at the opening 30b and travels in the opposite direction,
As a result, a standing wave is generated in the closed tube 30. This standing wave is c /, where L is the length of the closed tube 30 and c is the speed of sound.
It occurs at a frequency that is an odd multiple of (4L). That is, the frequency f of the standing wave generated in the closed tube 30 is given by
It is represented by

[0013]

## EQU1 ## f = (2n-1) {c / (4L)}
(N = 1, 2, ...)

8 (a) to 8 (c) show the sound pressure distributions of the standing wave generated in the closed tube 30 at the frequencies of 1 times, 3 times and 5 times that of c / (4L). Shows.
As shown in the figure, each standing wave has an antinode where the amplitude of the sound pressure is maximum and a node where the amplitude is minimum, but at the closed end portion 30a, they are common regardless of the respective frequencies. Position the belly, ie show the maximum amplitude.

Therefore, also in the silencer shown in FIG.
Similarly to the above, a standing wave due to the exhaust sound is generated in the sound propagation path between the virtual sound source point P and the exhaust port 3a (the portion indicated by L ₂₀ in the figure). This standing wave is c / (4L), where c is the speed of sound in the sound propagation path, as described above.
_It occurs at a frequency that is an odd multiple of ₂₀ ). Then, each standing wave shows a maximum amplitude in common at a place P which is considered to correspond to the closed end portion 30a in the sound propagation path regardless of each frequency. In other words, in this silencer, the phenomenon occurs that the place P corresponds to a noise source of exhaust noise, that is, the place P is a so-called virtual sound source point that can be called an apparent noise source.

At the frequency at which this standing wave is generated, its acoustic component is efficiently radiated from the exhaust port 3a,
The component of the above frequency in the exhaust sound tends to be large. Therefore, the output of the muffling speaker 6 for canceling the exhaust sound may be insufficient with respect to the level of the exhaust sound at the above frequency.

In order to avoid the above problem, it is effective to shorten the sound propagation path length L ₂₀ from the virtual sound source point P to the exhaust port 3a. That is, since the frequency f of the standing wave generated in the sound propagation path is an odd multiple of c / (4L ₂₀ ) as described above, by shortening the sound propagation path length L ₂₀ in this equation, The frequency f of the standing wave generated in the sound propagation path
Can be higher. When this frequency f becomes high,
In the low sound range where the electronic silencer 2 is targeted for attenuation, the standing wave does not occur. Therefore, in order to shorten the sound propagation path length L ₂₀ , the muffler 1 is preferably provided as close to the exhaust port 3a as possible.

[0018]

However, in the above-mentioned prior art, a predetermined interval L ₀ is provided between the primary microphone 4 and the sound-deadening speaker 6 which compose the electronic muffler 2. Since the muffler 1 is arranged in series with the electronic silencer 2, the distance L ₂₀ from the virtual sound source point P to the exhaust port 3a is at least larger than the predetermined interval L ₀ . That is, the frequency f of the standing wave generated in the sound propagation path from the virtual sound source point P to the exhaust port 3a depends on the predetermined interval L ₀ . That is, the calculation for the filtering of the digital filter in the controller needs to be performed at least within the time when the sound wave passes between the point of the primary microphone 4 and the point of the muffling speaker 6. Therefore, for example, in order to allow the processing time of the digital filter in the controller 5 which constitutes the electronic silencer 2 to have a margin, and in order to reduce the cost, the CPU or DSP which constitutes the digital filter has a low processing capacity (calculation). When using inexpensive parts (slow speed), it is necessary to increase the predetermined interval L ₀ . In such a case, the frequency f of the standing wave generated in the sound propagation path L ₂₀ becomes low. As a result, a standing wave is generated in the low sound range that the electronic silencer 2 is attenuating.

Further, as described above, since the muffler 1 and the electronic silencer 2 are arranged in series, the total length L ₁₀ of the sound propagation path becomes long, that is, the device itself becomes large. There is a problem that it ends up. Therefore, muffler 1
Although the individual electronic silencer 2 is downsized, the effect of downsizing is halved.

Further, in the above-mentioned prior art, the output electric signal of the primary microphone 4 is supplied to the controller 5, and the signal obtained by controlling the output electric signal by the controller 5 is supplied to the muffling speaker 6 for muffling. A so-called feedback loop is formed in which the sound wave radiated from the speaker 6 is input again to the primary microphone 4 via the inside of the exhaust duct 3. Therefore, there is a problem that howling is generated between the primary microphone 4 and the muffling speaker 6 due to the formation of this feedback loop, resulting in an uncontrollable state.

It is an object of the present invention to provide a muffler having both a muffler and an electronic muffler, which is downsized and which is less susceptible to standing waves and howling. And

[0022]

According to a first aspect of the present invention, there is provided a sound-deadening device, a sound propagation path for propagating the sound inputted from one end, for example, the exhaust sound so that the exhaust sound is discharged from the other end, and the sound propagation path. A microphone coupled to collect the exhaust sound, control means for controlling an electric signal output from the microphone, and driven by an output signal of the control means, for example, substantially equal in magnitude and opposite phase to the exhaust sound. Emits sound waves of
A speaker provided in a state of interfering with the exhaust sound at the other end side, that is, at a position at a predetermined distance in the propagation direction of the exhaust sound from the coupling position of the sound wave with the microphone in the sound propagation path; In the electronic silencer including the above, a passive silencer, that is, a muffler is provided between the microphone and the speaker in the sound propagation path.

A silencer according to a second aspect of the present invention is the silencer according to the first aspect of the present invention, between the sound wave emitting surface of the speaker that emits the sound wave and the position of interference between the sound and the sound wave in the sound propagation path. A sound wave transmission path for transmitting the sound wave is provided in the sound propagation path, and a position in which the standing wave that may occur in the sound propagation path has a maximum amplitude in common regardless of their frequencies, that is, the acoustic impedance suddenly changes. A value obtained by dividing the distance from the position of the so-called virtual sound source to the interference position by the speed of sound in the sound propagation path, and the distance from the sound wave emitting surface of the speaker to the interference position via the sound wave transmission path to the sound wave. It is characterized in that the value divided by the sound velocity in the transmission path is substantially equal.

[0024]

According to the first aspect of the invention, the muffler is interposed between the microphone and the speaker arranged at a predetermined interval in the sound propagation path. Here, the predetermined interval is provided in order to cover the time required for the control means to control the output electric signal of the microphone in the electronic silencer. That is, the muffler is arranged within the above-mentioned predetermined interval, which is provided as needed due to the structure of the electronic muffler, so that the muffler is in a state similar to that so-called built-in in the electronic muffler. Become.

Also, in the sound propagation path, especially in the muffler, the acoustic impedance changes suddenly, and a so-called virtual sound source is generated such that the place corresponds to a noise source of exhaust noise.
Since the muffler is interposed between the microphone and the speaker that form the electronic silencer as described above, the distance between the virtual sound source and the other end of the sound propagation path, that is, the exhaust sound outlet is shortened. That is, apparently, the sound propagation path length through which the exhaust sound generated from the virtual sound source propagates becomes short. Therefore, the frequency f of the standing wave generated in the sound propagation path by the exhaust sound is
Will be higher.

According to the second invention, the sound wave emitted from the sound wave emitting surface of the speaker interferes with the exhaust sound at the interference position in the sound propagation path through the sound wave transmission path. A value obtained by dividing the distance from the position of the virtual sound source to the interference position by the speed of sound in the sound propagation path, that is, the time required for the exhaust sound to propagate from the virtual sound source to the interference position, and the sound wave from the sound wave emitting surface of the speaker. The value obtained by dividing the distance to the interference position via the transmission path by the sound velocity in the sound wave transmission path, that is, the time required for the sound wave emitted by the speaker to propagate from the sound wave emitting surface of the speaker to the interference position is substantially equal. .

Here, the frequency of the standing wave generated by the exhaust sound is determined by dividing the speed of sound in the sound propagation path by the distance from the virtual sound source to the outlet of the sound propagation path, as can be seen from the above-mentioned formula 1. That is, it is determined by the time required for the exhaust sound to propagate from the virtual sound source to the outlet of the sound propagation path. In addition, a standing wave is also generated by the sound wave emitted from the speaker between the sound wave transmission path and the outlet of the sound propagation path. The frequency of this standing wave is also the same as above.
It is determined by the time required for the sound wave to propagate from the sound wave emitting surface of the speaker through the sound wave transmission path to the outlet of the sound propagation path.

Therefore, the time required for the exhaust sound to propagate from the virtual sound source to the outlet of the sound propagation path, and the sound wave emitted by the speaker from the sound wave emitting surface of the speaker to the outlet of the sound propagation path via the sound wave transmission path. When the time required for propagation is equal to each other, the frequencies of the standing waves generated by the exhaust sound and the sound waves of the speaker match each other.

Of the paths through which the exhaust sound and the sound waves of the speaker propagate, the section from the interference position in the sound propagation path to the outlet is a common propagation path, so the exhaust sound and the speaker The time required for the sound waves to propagate through this common section is equal. According to the second aspect of the invention, of the paths through which the exhaust sound and the sound waves of the speaker propagate, the time required for each to propagate through each path except the common section, that is, the exhaust sound, is a virtual sound source. To the interference position, and regarding the sound waves of the speaker, the time required to propagate from the sound wave emitting surface of the speaker to the interference position via the sound wave transmission path is said to be substantially equal. Therefore, the frequency of the standing wave generated by the exhaust sound and the frequency of the standing wave generated by the sound wave emitted from the speaker are substantially the same.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a silencer according to the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of the silencer of the first embodiment. As shown in FIG. 6, this muffler is equipped with both the muffler 1 and the electronic muffler 2 as in the conventional muffler shown in FIG. 6 described above. The difference from the conventional device is that the muffler 1 is arranged in the exhaust duct 3 between the primary microphone 4 and the muffling speaker 6 that constitute the electronic muffler 2. Since the structure other than this is the same as that of the conventional device of FIG. 6, the same parts are denoted by the same reference numerals and detailed description thereof will be omitted.

That is, the muffler 1 is provided in the exhaust duct 3 in order to cover the processing time required for the controller 5 constituting the electronic silencer 2 to control the output electric signal of the primary microphone 4. It is arranged within the interval L ₀ (that is, the interval L ₀ provided as needed in constructing the electronic silencer 2). Therefore, in this muffler, unlike the conventional technique in which the muffler 1 and the electronic muffler 2 are arranged in series as shown in FIG. 6, the muffler 1 is the same as the so-called built-in muffler 1 in the electronic muffler 2. It becomes a state. Also in the silencer shown in FIG. 1, a virtual sound source point P is generated in the sound propagation path, particularly in the muffler 1, similarly to the conventional silencer shown in FIG. 6 described above.

As described above, in the muffler shown in FIG. 1, since the muffler 1 is arranged between the primary microphone 4 and the muffling speaker 6 which constitute the electronic muffler 2, the muffler 1 is arranged. The distance L ₂ between the virtual sound source point P generated inside and the exhaust port 3a of the exhaust duct 3 is shorter than the distance L ₂₀ in the conventional silencer shown in FIG. 6 described above. Therefore, the frequency f of the standing wave generated in the sound propagation path between the primary microphone 4 and the muffling speaker 6 can be made higher than in the conventional case, and the electronic muffling device 2 is thus attenuated. It is possible to suppress the occurrence of standing waves in the target low sound range, that is, it is possible to prevent the influence of standing waves as in the above-described conventional technique.

Here, by arranging the muffler 1 in the sound propagation path as described above, it is possible to suppress a relatively low frequency standing wave generated in the sound propagation path. Will be described with reference to. The graph of the figure shows that the exhaust sound generated from the engine 10 has a relatively low frequency,
For example, for a sound of 100 Hz, the pipe length L ₁ is 6 m, for example.
3 shows a sound pressure distribution in the length direction of the sound propagation path. A graph A shown by a solid line in the figure is a sound pressure distribution when the muffler 1 is not provided (when the sound propagation path is formed only by the exhaust duct 3). It can be seen that a standing wave is generated at. On the other hand, a graph B of a dotted line shows a sound pressure distribution when the muffler 1 is arranged over the sound propagation path, that is, between the 1.8 m point and the 3.5 m point from the exhaust port 3a of the exhaust duct 3. As can be seen from the graph B, by providing the muffler 1, the standing wave with the frequency of 100 Hz is eliminated,
That is, it is possible to suppress the generation of a standing wave due to a sound having a frequency of 100 Hz.

In order to shift the frequency f of the standing wave generated in the sound propagation path to a higher frequency side, the muffler 1 is arranged as close as possible to the exhaust port 3a side of the exhaust duct 3 and the virtual sound source is arranged. It goes without saying that the distance L ₂ from the point P to the exhaust port 3a of the exhaust duct 3 should be as short as possible.

Further, since the muffler shown in FIG. 1 is configured so that the muffler 1 is so-called built-in in the electronic muffler 2 as described above, the total length L ₁ of the sound propagation path is the same as in the conventional case. It becomes shorter than the total length L ₁₀ of the sound propagation path in the technology by at least the length of the muffler 1, that is, the silencer itself can be made smaller than before. By the way, in the case of a silencer having a diameter of the exhaust duct 3 of, for example, about 200 mm, the sound propagation path length L ₁₀ is about 10 m in the conventional technique shown in FIG. 6, whereas in the silencer shown in FIG. The sound propagation path length L ₁ is about 8 m, which is shorter than the above.

By the way, the muffler 1 provided in this muffler is mainly for attenuating exhaust sound having a relatively high frequency range (high frequency range), for example, a frequency of 500 Hz or higher. It also has some attenuation characteristics in the following relatively low tone range. FIG. 3 shows the sound pressure distribution for the sound of 300 Hz of the exhaust sound generated from the engine 10 under the same conditions as in FIG. 2 described above, and the solid line graph X shows the case where the muffler 1 is not provided. The sound pressure distribution is shown, and the dotted line graph Y shows the sound pressure distribution when the muffler 1 is provided. From the graph in the figure, muffler 1
It is understood that the exhaust sound of 300 Hz, that is, the sound of a frequency lower than the frequency range (500 Hz or higher) targeted for attenuation by the muffler 1 itself is slightly attenuated.

That is, in the silencer shown in FIG. 1, the muffler 1 having a slight attenuation characteristic in the relatively low tone range (low frequency region) as described above is provided with the primary microphone 4.
The sound wave emitted from the sound-deadening speaker 6 is attenuated to some extent by the muffler 1 even if the sound wave radiated from the sound-deadening speaker 6 travels toward the primary microphone 4 side. That is, unlike the conventional technique shown in FIG. 6, the sound wave radiated from the muffling speaker 6 is not directly input to the primary microphone 4, so that the muffling speaker 6 as in the related art is not used. 1
The howling phenomenon that occurs between the microphone 4 and the next microphone 4 can be suppressed.

Incidentally, between the other microphone, that is, between the secondary microphone 7 and the muffling speaker 6,
Although no sound pressure resistance like the muffler 1 is interposed, the output signal of the secondary microphone 7 is used only as a parameter for changing the filter coefficient of the digital filter in the controller 5. Therefore, the howling phenomenon does not occur between the secondary microphone 7 and the muffling speaker 6.

As described above, in the muffler of the first embodiment, the muffler 1 is arranged in the exhaust duct 3 between the primary microphone 4 and the muffler speaker 6 which constitute the electronic muffler 2. Since it is possible to reduce the size of the device itself, it is possible to prevent the influence of standing waves and howling.

In the first embodiment, the muffler 1
Although the sound absorbing type is used as the above, the present invention is not limited to this, and a muffler of another type such as a reactive type may be used.

As a means for controlling the output electric signal of the primary microphone 4, digital filtering processing is performed in the controller 5, but the invention is not limited to this.
Other control means may be used, such as a phase shift circuit that changes the phase of the output electric signal and a variable gain amplifier that adjusts the amplitude by using an analog circuit.

FIG. 4 is a schematic configuration diagram showing a second embodiment of the silencer according to the present invention. The muffler shown in FIG. 4 is different from the muffler of the first embodiment shown in FIG.
A sound wave transmission path for transmitting the sound waves, for example, a branch pipe 8 is added between the sound wave emission surface 6a of the sound deadening speaker 6 and the exhaust duct 3, and the sound deadening speaker 6 enters the exhaust duct 3 through the branch pipe 8. It is configured to emit sound waves. The structure other than this is the same as that of the first embodiment shown in FIG. 1, and the same parts are designated by the same reference numerals,
Detailed description thereof will be omitted.

The branch pipe 8 is connected to the exhaust duct 3 at a right angle. The sound wave radiated from the muffling speaker 6 into the exhaust duct 3 via the branch pipe 8 is configured to interfere with the exhaust sound propagating in the exhaust duct 3 at a point Q shown in FIG. . Furthermore, this branch pipe 8
The distance L ₅ from the sound wave emitting surface 6a of the muffling speaker 6 to the above point Q (that is, the point of interference between the exhaust sound and the sound wave emitted from the muffling speaker 6) through the branch pipe 8 is set in the branch pipe 8 by a distance L _5. The value (L ₅ / c ₂ ) divided by the sound velocity c ₂ and the distance L ₃ from the virtual sound source point P (here, in the muffler 1) in the sound propagation path to the interference point Q in the sound propagation path. The length is set so that the value (L ₃ / c ₁ ) divided by the sound velocity c ₁ (in the exhaust duct 3) becomes equal.

Here, from the virtual sound source point P to the interference point Q
The distance (L ₃ / c ₁ ) obtained by dividing the distance L ₃ to the sound velocity c ₁ in the exhaust duct 3 is the time required for the exhaust sound to propagate from the virtual sound source point P to the interference point Q (this time is t ₁ ). Also, the sound wave emitting surface 6a of the muffling speaker 6
The value obtained by dividing the distance L ₅ to interference point Q through the branch pipe 8 at the speed of sound c ₂ of the branch pipe in 8 (L ₅ / c ₂₎ and the radiation sonic sound wave emitting surface 6a of the mute speaker 6 To the above interference point Q
Time required to propagate to (this time is t ₂ )
Is shown. Therefore, with the above configuration, the propagation times t ₁ and t ₂ of the sound waves of the exhaust sound and silencing speaker 6 to the interference point Q are equal to each other.

As described above, the inside of the exhaust duct 3 and the branch pipe 8 are
The reason for separately considering the sound velocities inside and inside is that the temperatures inside the exhaust duct 3 and inside the branch pipe 8 are significantly different, and thus the sound velocities may be greatly different. Speed of sound c (m /
It is known that there is a relationship between s) and the temperature T (° C.) as shown in the following Expression 2.

[0046]

(2) c = 331.5 + 0.6 × T

For example, if the temperature T ₁ in the exhaust duct 3 is T ₁
= 400 ° C., the temperature T ₂ in the branch pipe 8 may become T ₂ = 70 ° C. In this case, from the above formula 2, the sound speed c ₁ in the exhaust duct 3 is c ₁ = 571.5 m / s, and the sound speed c ₂ in the branch pipe 8 is c ₂ = 373.5 m / s.

In the silencer configured as described above, the frequency f _{1 of the} standing wave generated by the exhaust noise is, as described above, the speed of sound in the exhaust duct 3 is c ₁ , and the virtual sound source point P to the exhaust duct. If the distance to the discharge port 3a of 3 is L ₂ , then it becomes an odd multiple of c ₁ / (4L ₂ ). Here, when the time required for the exhaust sound to propagate from the virtual sound source point P to the discharge port 3a is t ₁₀ , this t ₁₀ is t ₁₀ = L
Since it is expressed by ₂ / c ₁ , the frequency f _{1 of the} standing wave is
It is an odd multiple of 1 / (4t ₁₀ ). That is, at the frequency f _{1 of the} standing wave generated by the exhaust sound, the exhaust sound is the virtual sound source point P.
Is determined by the time t ₁₀ required to propagate from the discharge port 3a to the discharge port 3a.

On the other hand, also by the sound waves emitted from the sound-deadening speaker 6, as in the case of FIGS. 8A to 8C described above, the distance from the branch pipe 8 to the exhaust port 3a of the exhaust duct 3 (L ₅ +
A standing wave is generated in L ₄ ). Also, regarding the frequency f ₂ of this standing wave, similarly to the standing wave due to the exhaust noise,
It is determined by the time required for the sound wave of the muffling speaker 6 to propagate from the sound wave emitting surface 6a through the branch pipe 8 to the discharge port 3a (this time is t ₂₀ ).

That is, when the times t ₁₀ and t ₂₀ are equal to each other (t ₁₀ = t ₂₀ ), the frequencies f ₁ and f ₂ of the respective standing waves generated by the sound waves emitted from the exhaust sound and silencing speaker 6 are Will match each other.

Here, the exhaust sound and silencing speaker 6 is used.
Among the paths of the sound waves of, the section L ₄ from the interference point Q in the exhaust duct 3 to the discharge port 3a is a common propagation path, so the sound waves of the exhaust sound and silencing speaker 6 are The time required to propagate the common section L ₄ (this time is t ₀ ) is equal. Then, as described above, in FIG. 4, among the paths in which the sound waves of the exhaust sound and the muffling speaker 6 propagate, the time required for each to propagate in each path except the common section L ₄ , that is, the exhaust gas For sound, the time t ₁ required to propagate from the virtual sound source point P to the interference point Q (L ₃ ), and for the sound wave of the muffling speaker 6 from the sound wave emitting surface 6 a of the muffling speaker 6 to the branch pipe 8. The time t ₂ required for propagating (L ₅ ) through the path to the interference point Q is set to be equal to each other.

With this configuration, the time t ₁₀ (t ₁₀ = t ₁ + t ₀ ) required for the exhaust sound to propagate from the virtual sound source point P to the exhaust port 3a of the exhaust duct 3 and the muffling speaker Time t ₂₀ (t ₂₀ = t ₂₀ = t 2 =
t ₂ + t ₀ ) becomes equal. Therefore, the frequency f _{1 of the} standing wave generated by the exhaust sound and the frequency f _{2 of the} standing wave generated by the sound wave radiated from the noise elimination speaker 6 match.

As described above, in the second embodiment,
Since the frequencies f ₁ and f _{2 of the} standing waves generated by the sound waves of the exhaust sound and the muffling speaker 6 are matched, when the standing wave is generated by the exhaust sound, at the same time, A standing wave is also generated by the sound waves emitted from the muffling speaker 6. Therefore, at the frequency f ₁ (or f ₂ ) at which the standing wave is generated, the emission efficiency of the exhaust sound from the sound source (virtual sound source point P) is increased, but at the same time, the sound emission efficiency of the sound deadening speaker 6 is increased. Also, the exhaust sound can be sufficiently canceled by the sound wave emitted from the sound deadening speaker 6. That is, it is possible to effectively cancel the frequency f ₁ (or f ₂ ) component of the standing wave generated in the noise due to the exhaust sound, and thus the standing wave is suppressed even in the frequency range where the electronic silencer 2 is to be attenuated. Even if occurs, the influence of this standing wave can be reliably prevented.

Although FIG. 4 shows the case where the virtual sound source point P is located on the exhaust sound output side (exhaust port 3a side) in the muffler 1, the virtual sound source point P is the exhaust sound of the muffler 1. When located at the output end, as shown in FIG. 5, the sound wave emitting surface 6a of the muffling speaker 6 is directly connected to the exhaust sound output end of the muffler 1 in the exhaust duct 3 without providing the branch pipe 8. May be. In this case, the short path from the sound wave emitting surface 6a of the sound deadening speaker 6 to the interference point Q in FIG. 5 is the sound wave transmission path.

Further, in the second embodiment, the branch pipe 8 is connected to the exhaust duct 3 at a right angle, but the connecting angle is not limited to this. For example, the branch pipe 8 may be connected to the exhaust duct 3, particularly in a state of forming an acute angle with the engine 10 side of the exhaust duct 3 (that is, the upstream side of exhaust sound).

Further, in order to shorten the length L ₅ of the branch pipe 8 as much as possible and miniaturize the muffler, the interference point Q may be arranged as close as possible to the muffler 1.

[0057]

The muffler of the first invention is a muffler having both a muffler and an electronic muffler, and is provided in the sound propagation path between the microphone and the speaker constituting the electronic muffler. A muffler is arranged. With this configuration, the distance from the virtual sound source generated in the muffler to the other end of the sound propagation path, that is, the exhaust sound exhaust port is shorter than in the conventional case. Therefore, the frequency f of the standing wave generated in the sound propagation path can be made higher than that of the conventional one, thereby suppressing the generation of the standing wave in the low sound range that the electronic silencer is subject to attenuation, That is, there is an effect that the influence of standing waves can be prevented.

Further, as described above, the muffler 1 and the electronic muffler 2 shown in FIG. 6 are so-called because the muffler is arranged within the predetermined interval provided as necessary due to the structure of the electronic muffler. Unlike the prior art in which the muffler is arranged in series, the muffler is in the same state as in the electronic muffler. Therefore, compared with the above-mentioned conventional technique, there is an effect that the total length of the sound propagation path can be shortened by the amount of the muffler, that is, the device itself can be downsized.

As described above, since the muffler which is the acoustic resistance is interposed between the microphone and the speaker,
Sound waves emitted from the speaker are not directly input to the microphone. Therefore, there is an effect that the howling phenomenon occurring between the microphone and the speaker can be suppressed.

In the muffler of the second invention, the time required for the exhaust sound and the sound wave of the speaker to propagate through the respective paths from the sound wave emitting surface of the virtual sound source and the speaker to the discharge port of the sound propagation path are approximately respectively. The frequency of the standing wave generated by the exhaust sound is equal to the frequency of the standing wave generated by the sound wave emitted from the speaker. With such a configuration, at the frequency at which the standing wave is generated by the exhaust sound, the standing wave is also generated by the sound wave emitted from the speaker. Therefore, even if the radiation efficiency from the noise source increases at the frequency at which the standing wave is generated, the radiation efficiency of the sound wave from the speaker also increases at the same time, so the sound wave emitted from the speaker effectively cancels the above-mentioned frequency component. be able to. Therefore, even if a standing wave is generated in the frequency range targeted for attenuation by the electronic muffler, the effect of the standing wave can be prevented more reliably than in the first aspect of the invention.

[Brief description of drawings]

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

FIG. 2 is a diagram showing sound pressure distributions for sounds at 100 Hz in an exhaust duct with and without a muffler in the embodiment.

FIG. 3 is a diagram showing sound pressure distributions for a sound of 300 Hz in an exhaust duct with and without a muffler in the embodiment.

FIG. 4 is a schematic configuration diagram showing a second embodiment of the silencer according to the present invention.

FIG. 5 is a modification of the same embodiment (FIG. 4).

FIG. 6 is a schematic configuration diagram of a conventional silencer.

FIG. 7 is a side sectional view of a passive silencer (muffler).

FIG. 8 is a diagram showing a sound pressure distribution of a standing wave generated in a closed tube. (A) shows a case where the wavelength λ of the standing wave is four times the tube length L, and (b) shows a wavelength of the standing wave. When λ is 4/3 times the tube length L, (c) shows the case where the wavelength λ of the standing wave is 4/5 times the tube length L.

[Explanation of symbols]

 1 muffler 2 electronic silencer 3 exhaust duct 3a exhaust port 4 primary microphone (reference microphone) 5 controller 6 silencer speaker 7 secondary microphone (error microphone) 8 branch pipe 10 engine

Claims (2)

[Claims] 1. A sound propagation path for propagating the sound so that a sound input from one end is discharged from the other end, a passive silencer provided in the sound propagation path, and a sound propagation path coupled to the sound propagation path. A microphone for picking up the sound, a control means for controlling an output electric signal of the microphone, a sound wave radiated by being driven by the output signal of the control means, and the sound wave with the microphone in the sound propagation path. A speaker provided in a state of interfering with the sound at a position spaced from the coupling position to the other end side by a predetermined distance, wherein the control means controls the amplitude and phase of the sound wave emitted from the speaker. In a silencer configured to control the output electrical signal in a state in which the amplitude and phase are necessary to cancel the sound, the passive silencer is used in the sound propagation path. Muffler, characterized in that arranged between the Rohon and the speaker. 2. A sound transmission path for transmitting the sound wave is provided between a sound wave emitting surface of the speaker for emitting the sound wave and an interference position between the sound and the sound wave in the sound propagation path, and the sound propagation path is provided. A value obtained by dividing the distance from the position where the standing wave that may occur in the sound propagation path shows a maximum amplitude in common regardless of their frequency to the interference position by the speed of sound in the sound propagation path; The value obtained by dividing the distance from the sound wave emitting surface of the speaker through the sound wave transmission path to the interference position by the speed of sound in the sound wave transmission path is substantially equal. The silencer described.