JP3148969B2 - Silencer - Google Patents

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, for example, which attenuates exhaust sound that propagates through the exhaust duct and is exhausted to the outside.

[0002]

2. Description of the Related Art In general, as a method of attenuating exhaust sound exhausted from an exhaust duct, a method using a passive silencer, that is, a muffler, and a method using an active silencer, that is, a method using an electronic silencer are known. I have. Among them, the muffler has a disadvantage that the volume of the muffler itself increases as the frequency of the exhaust sound to be attenuated becomes lower, that is, the muffler becomes larger. However, for example 500 Hz
When the exhaust sound in a relatively high frequency range (high-frequency component) is to be attenuated, even a relatively small one can cope with it, and is widely used for high frequency range attenuation.

[0003] On the other hand, the electronic silencer reduces exhaust noise.
The exhaust sound is canceled out, that is, attenuated by causing a sound wave having substantially the same phase as that of the exhaust sound and having an opposite phase to interfere therewith. This has an advantage that the size of the muffler can be significantly reduced as compared with the muffler. However, in this electronic silencer, digital filtering using a CPU (Central Processing Unit) or a DSP (Digital Signal Processing Unit) or the like is usually employed for the processing, so that the exhaust noise to be attenuated is reduced. As the frequency increases, the load on the CPU, DSP, and the like increases, that is, it becomes impossible to mute the exhaust sound in the high frequency range. Therefore, this electronic silencer is, for example, 500 Hz
It is suitable for so-called low-range attenuation, in which the following relatively low-range exhaust sound is attenuated.

As described above, the muffler is suitable for attenuating the high frequency range, and the electronic silencer is suitable for the attenuation in the low frequency range. Therefore, by providing both the muffler and the electronic silencer at the same time, the low frequency range is provided. Thus, it is possible to realize a muffling device capable of obtaining a large muffling effect in a wide frequency range ranging from a high frequency range to a high frequency range. Conventionally, as such a silencer, there is, for example, one shown in FIG. In FIG. 1, reference numeral 10 denotes a noise source, for example, an engine. An exhaust sound generated from the engine 10 passes through a muffler 1 for silencing a high frequency range of 500 Hz or higher and an electronic silencer 2 for low frequency range of 500 Hz or lower, for example. The exhaust duct 3 is configured to be exhausted from an exhaust port 3a.

The muffler 1 is of a sound absorbing type as shown in FIG. 7, for example, and as shown in FIG.
, A hollow body 13 surrounding the outer periphery of the perforated pipe 12, and a hollow body 13
And a sound-absorbing material 14 filled between 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 the exhaust sound propagates. With the above configuration,
The muffler 1 is configured to be capable of attenuating the exhaust noise propagating in the perforated pipe 12, and to provide an attenuation effect of, for example, about 30 dB with respect to the above-described exhaust noise of 500 Hz or more.

On the other hand, an electronic silencer 2 includes a primary microphone (reference microphone) 4 coupled to the exhaust duct 3 near the muffler 1 and a primary microphone 4
, A mute speaker 6 driven by the output signal of the controller 5 to emit a sound wave into the exhaust duct 3, and a secondary microphone disposed at the exhaust port 3 a of the exhaust duct 3 ( And an error microphone 7). Controller 5
Inside, for example, a digital filter by a DSP is formed. 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. 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 sound waves radiated from the silencing 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 equal in phase and opposite in 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 sound discharged to the outside is reduced to zero as much as possible. The filter coefficients of the digital filter are updated. Thereby, it is possible to follow the fluctuation of the acoustic characteristic of the sound propagation path and the temporal change of the characteristic of the muffling speaker 6.

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

Further, the muffling speaker 6 is provided with the exhaust duct 3.
A predetermined distance L 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.
They are arranged 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, and thus the sound waves for canceling the exhaust sound collected by the primary microphone 4 are muted. This is because it takes some time until the light is radiated from the speaker 6. Therefore, in order to cover the processing time of the controller 5, the exhaust sound is collected 1
The predetermined distance L between the next microphone 4 and the silencing speaker 6 that emits a sound wave for canceling the exhaust sound.
₀ is provided.

With the above configuration, the silencer shown in FIG.
The exhaust sound of the engine 10 is sufficiently attenuated by the muffler 1 for the high range and sufficiently attenuated by the electronic silencer 2 for the low range, that is, a large noise reduction effect over a wide frequency range from the low range to the high 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, the air is discharged from the exhaust port 3a, but a place P where the acoustic impedance changes suddenly occurs in the sound propagation path, especially in the muffler 1. Such a sound propagation path is
It is considered to correspond to the closed tube 30 as shown in FIGS. 8A to 8C. In this case, the closed end 30a of the both ends of the closed tube 30 which is closed by a rigid material is The opening 30b on the other end side corresponds to the exhaust port 3a side.

In the closed pipe 30 as described above, the sound transmitted from the closed end 30a toward the opening 30b 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. When the length of the closed tube 30 is L and the speed of sound is c, the standing wave is c /
Occurs at an odd multiple of (4L). That is, the frequency f of the standing wave generated in the closed tube 30 is expressed by the following equation (1).
It is represented by

[0013]

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

FIGS. 8 (a) to 8 (c) show the sound pressure distributions of the standing wave generated in the closed tube 30 at the frequency of 1, 3, 5 and 5 times of c / (4L), respectively. Is shown.
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 is common at the closed end 30a regardless of the respective frequencies. Position the belly, ie show the maximum amplitude.

Therefore, in the silencer shown in FIG.
As described above, the acoustic impedance changes suddenly as described above.
Week P to the sound propagation path between the to the exhaust port 3a (a portion indicated by L ₂₀ in the figure), the standing wave is generated by the exhaust sound.
As described above , this standing wave is generated at an odd multiple of c / (4L ₂₀ ), where c is the sound speed in the sound propagation path. Each of the standing waves has a maximum amplitude in common at the place P, which is considered to correspond to the closed end portion 30a in the sound propagation path, regardless of each frequency. That is, in this silencer, a phenomenon occurs as if the place P corresponds to a noise source of exhaust noise, that is, the place P is a so-called virtual sound source point which can be said to be an apparent noise source.

At the frequency where the standing wave is generated, the 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 at the above frequency with respect to the level of the exhaust sound.

[0017] To avoid the above problem, it is effective to shorten the sound propagation path length L ₂₀ from the virtual source point P to the exhaust port 3a. That is, since the frequency f of the standing wave generated in the sound propagation path becomes an odd multiple of c / (4L ₂₀ ) as described above, by shortening the sound propagation path length L ₂₀ in this equation, Frequency f of the standing wave generated in the sound propagation path
Can be higher. When this frequency f increases,
In the low sound range that the electronic silencer 2 is to attenuate, no standing wave is generated. Therefore, in order to shorten the sound propagation path length L _20, muffler 1, that as much as possible provided in the vicinity of the exhaust port 3a desirable.

[0018]

[SUMMARY OF THE INVENTION However, in the above conventional art, the predetermined distance L ₀ is provided between the primary microphone 4 constituting the electronic silencer 2 and silencing speaker 6, the since the state of the muffler 1 is so to speak disposed in series with the electronic silencer 2, the distance L ₂₀ from the virtual source point P to the exhaust port 3a is larger than at least the predetermined distance L _0. That is, the frequency f of the standing wave generated in the sound propagation path between from the virtual source point P to the exhaust port 3a will depend on the predetermined distance L _0. That is, the calculation for filtering the digital filter in the controller needs to be performed at least within the time when the sound wave passes from the point of the primary microphone 4 to the point of the muffling speaker 6. Therefore, for example, in order to allow a margin for the processing time of the digital filter in the controller 5 constituting the electronic silencer 2 or to reduce the cost, the CPU or DSP constituting the digital filter has a low processing capability (calculation). or when using a slow) inexpensive parts, it is necessary to increase the predetermined distance L _0. In such a case, the frequency f of the standing wave generated in the sound propagation path L ₂₀ is lowered. As a result, a standing wave is generated in a low sound range that the electronic silencer 2 targets for attenuation.

Further, as described above, since the state of the muffler 1 and the electronic silencer 2 is so to speak disposed in series, becomes long overall length L ₁₀ of the sound propagation path, i.e. apparatus itself in size Problem. Therefore, muffler 1
Although each of the electronic silencers 2 is downsized, the effect of the downsizing is reduced by half.

Further, in the above-mentioned prior art, an output electric signal of the primary microphone 4 is supplied to a controller 5, and a signal obtained by controlling the output electric signal by the controller 5 is supplied to a mute speaker 6, and the mute speaker 6 is provided. A so-called feedback loop is formed in which sound waves emitted from the speaker 6 are again input to the primary microphone 4 via the inside of the exhaust duct 3. Therefore, there is a problem that howling occurs between the primary microphone 4 and the muffling speaker 6 due to the formation of the feedback loop, and the control becomes impossible.

It is an object of the present invention to provide a silencer having both a muffler and an electronic silencer, which can be reduced in size and is less affected by standing waves, howling and the like. And

[0022]

A sound muffler according to the present invention has a sound propagation path for transmitting the exhaust sound so as to discharge a sound input from one end, for example, an exhaust sound from the other end, and is coupled to the sound propagation path. A microphone that picks up the exhaust sound
Control means for controlling an output electric signal of the microphone; and, for example, a sound wave which is driven by the output signal of the control means and which is substantially equal in phase to the exhaust sound and has a phase opposite to that of the exhaust sound, emits the sound wave through the sound propagation path. An electronic silencer comprising: a speaker provided to interfere with the exhaust sound at a position separated by a predetermined distance from the coupling position with the microphone at the other end side, that is, at a position spaced in a direction in which the exhaust sound propagates. Further, a passive silencer having a place where the acoustic impedance changes suddenly, a so-called virtual sound source, that is, a muffler, is provided between the microphone and the speaker in the sound propagation path.

Further, the sound deadening device according to the present invention is characterized in that the sound wave transmission path for transmitting the sound wave from the sound wave emitting surface of the speaker emitting the sound wave to the interference position between the sound and the sound wave in the sound propagation path. the provided Rutotomoni, the sound propagation path
Under certain conditions where the temperature differs between the inside and inside the sound wave propagation path.
The time required for the exhaust sound to propagate from the position of the virtual sound source in the muffler to the interference position, and the sound wave emitted by the speaker from the sound wave emission surface via the sound wave transmission path to the interference position And the time required for the light to propagate therethrough is substantially equal.

[0024]

According to the present 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 the electronic silencer in order to cover the time required for the control means to control the output electric signal of the microphone. That is, since the muffler is arranged within the above-described predetermined interval provided as necessary due to the configuration of the electronic muffler, the muffler is in a state similar to what is built in the electronic muffler. Become.

Further, in the muffler in the sound propagation path, the acoustic impedance changes suddenly, and a so-called virtual sound source is generated as if the location corresponds to a noise source of exhaust noise. In addition, since the sound source is interposed between the microphone and the speaker constituting the electronic silencer, the distance between the virtual sound source and the other end of the sound propagation path, that is, the outlet of the exhaust sound is reduced. That is, apparently, the length of the sound propagation path through which the exhaust sound generated from the virtual sound source propagates is reduced. Therefore, the frequency f of the standing wave generated in the sound propagation path due to the exhaust sound increases.

Further, according to the present invention, the sound wave radiated from the sound wave radiating surface of the speaker passes through the sound wave transmission path and interferes with the exhaust sound at the interference position in the sound propagation path. Where the example
For example, the sound propagation path, which is the path of exhaust sound, and the speaker
The sound wave propagation path, which is the propagation path of the radiated sound wave,
Are different from each other, which leads to
It is assumed that the sound speeds are different. Under certain conditions like this
The time required for the exhaust sound to propagate from the virtual sound source to the interference position, in other words, the 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, and the sound wave emitted by the speaker Is the time required for the sound to propagate from the sound wave emitting surface of the speaker to the interference position via the sound wave transmission path, in other words, the distance from the sound wave emitting surface of the speaker to the interference position via the sound wave transmission line is the sound velocity in this sound wave transmission line. Is substantially equal to the value obtained by dividing by .

Here, the frequency of the standing wave generated by the exhaust sound is determined by the value obtained 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 Equation (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. Also, the standing wave is generated by the sound wave radiated from the speaker through the sound wave transmission path to the outlet of the sound propagation path, and the frequency of the standing wave is also the same as described above.
It is determined by the time required for the sound wave to propagate from the sound wave emitting surface of the speaker via 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 times required for propagation are equal, the frequencies of the standing waves generated by the exhaust sound and the sound waves of the loudspeakers match each other.

Since the section from the interference position in the sound propagation path to the outlet is a common propagation path among the paths through which the exhaust sound and the sound wave of the speaker propagate, respectively, the exhaust sound and the speaker sound are transmitted. The time required for a sound wave to propagate through this common section is equal. According to the second aspect, the time required for each of the paths through which the exhaust sound and the sound waves of the speaker propagate, excluding the common section, that is, the exhaust sound, It is assumed that the time required to propagate from the speaker to the interference position, and the time required for the sound wave of the speaker to propagate from the sound wave emitting surface of the speaker to the interference position via the sound wave transmission path are substantially equal. Therefore, as described above,
And the temperature inside the sound wave propagation path is different
Under the conditions, the frequency of the standing wave generated by the exhaust sound substantially matches the frequency of the standing wave generated by the sound wave radiated from the speaker.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a muffler 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 the drawing, this silencer includes both a muffler 1 and an electronic silencer 2 as in the conventional silencer shown in FIG. 6 described above. The difference from the prior art device is that the muffler 1 is arranged in the exhaust duct 3 between the primary microphone 4 and the sound deadening speaker 6 constituting the electronic sound deadening device 2. Since the other structure is the same as that of the conventional device of FIG. 6, the same reference numerals are given to the same parts, and the detailed description is 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 necessary in configuring the electronic silencer 2). Therefore, in this silencer, unlike the prior art in which the muffler 1 and the electronic silencer 2 are arranged in series, as shown in FIG. 6, the muffler 1 is similar to the so-called built-in muffler 1 in the electronic silencer 2. State. In the muffler shown in FIG. 1 as well, the virtual sound source point P is generated in the sound propagation path, particularly in the muffler 1, as in the conventional muffler shown in FIG.

As described above, in the muffler shown in FIG. 1, since the muffler 1 is arranged between the primary microphone 4 and the muffler speaker 6 constituting the electronic muffler 2, the muffler 1 distance L ₂ between the exhaust port 3a of the virtual source point P and the exhaust duct 3 for generating within is shorter than the distance L ₂₀ in the conventional muffler 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, whereby the electronic muffling device 2 can reduce the attenuation. It is possible to suppress the generation of a standing wave in the target bass range, that is, it is possible to prevent the effect of the standing wave as in the related art.

Here, the arrangement of the muffler 1 in the sound propagation path as described above makes it possible to suppress a relatively low-frequency standing wave generated in the sound propagation path, as shown in FIG. This will be described with reference to FIG. The graph of FIG. 3 shows a relatively low frequency of exhaust noise generated from the engine 10.
For example, for 100Hz of sound, the pipe length L ₁ is, for example, 6m
3 shows the 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. On the other hand, a dotted line graph B shows the sound pressure distribution when the muffler 1 is arranged over the sound propagation path, that is, between the point 1.8 m and the point 3.5 m from the exhaust port 3 a of the exhaust duct 3. As can be seen from the graph B, the provision of the muffler 1 eliminates the standing wave having the frequency of 100 Hz.
That is, generation of a standing wave due to a sound having a frequency of 100 Hz can be suppressed.

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 Needless to say about it is sufficient as short as possible the distance L ₂ from the point P to the exhaust port 3a of the exhaust duct 3.

The muffler shown in FIG. 1 has the muffler 1 incorporated in the electronic muffler 2 as described above, so that the total length L ₁ of the sound propagation path is smaller than that of the conventional muffler. at least equivalent to the length only muffler 1 becomes shorter than the total length L ₁₀ of the sound propagation path in the art, that is, it can be made smaller than before the muffler itself. Incidentally, if the diameter of the exhaust duct 3 is for example 200mm approximately silencer, while the sound propagation path length L ₁₀ is about 10m in the prior art shown in FIG. 6, the muffler shown in FIG. 1 sound propagation path length L ₁ is shorter than about 8m next above.

By the way, the muffler 1 provided in this silencer is mainly for attenuating exhaust noise having a relatively high frequency range (high frequency range), for example, a frequency of 500 Hz or more. It has some attenuation characteristics even in the following relatively low frequency range. FIG. 3 shows the sound pressure distribution of the 300 Hz sound among the exhaust sounds generated from the engine 10 under the same conditions as in FIG. 2 described above. The solid line graph X indicates 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 of FIG.
It can be seen that is that the muffler 1 itself slightly attenuates the exhaust sound of 300 Hz, that is, the sound of a frequency lower than the frequency range (500 Hz or more) which is the attenuation target of the muffler 1 itself.

That is, in the muffler shown in FIG. 1, the muffler 1 having a slight attenuation characteristic even in a relatively low frequency range (low frequency range) as described above is connected to the primary microphone 4
Since the sound wave radiated from the sound deadening speaker 6 is directed to the primary microphone 4 side, the sound wave is attenuated to some extent by the muffler 1. That is, unlike the prior art 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 1
The howling phenomenon occurring between the next microphone 4 can be suppressed.

Incidentally, between the other microphone, that is, the secondary microphone 7 and the muffling speaker 6,
No sound pressure resistance such as the muffler 1 is interposed, but 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, a 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 disposed in the exhaust duct 3 between the primary microphone 4 and the muffler speaker 6 constituting the electronic muffler 2. Therefore, the size of the device itself can be reduced, and the effects of standing waves, howling, and the like can be prevented.

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

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

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

The branch pipe 8 is connected to the exhaust duct 3 at a substantially right angle. Then, the sound wave radiated from the sound deadening speaker 6 into the exhaust duct 3 through 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
Through this branch pipe 8 from the sound wave emitting surface 6a of the mute speaker 6 above point (i.e., the interference point between the sound waves radiated from the muffler speaker 6 and the exhaust sound) the distance L ₅ to Q in the branch pipe in 8 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, inside 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 speed c ₁ (in the exhaust duct 3) is equal.

Here, from the virtual sound source point P to the interference point Q
The value (L ₃ / c ₁ ) obtained by dividing the distance L ₃ to the sound velocity c ₁ in the exhaust duct 3 (L ₃ / c ₁ ) 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 and t ₁₎ indicate a. Further, the sound wave emitting surface 6a of the sound deadening speaker 6
The value (L ₅ / c ₂ ) obtained by dividing the distance L ₅ from the distance through the branch pipe 8 to the interference point Q by the sound velocity c ₂ in the branch pipe 8 is defined as (L ₅ / c ₂ ). From the interference point Q
The time required to propagate to (this time is t ₂ )
Is shown. Therefore, according to the above configuration, the propagation times t ₁ and t ₂ of the exhaust sound and the sound wave of the sound deadening 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
The reason why the sound speeds are separately taken into consideration is that the temperature inside the exhaust duct 3 and the temperature inside the branch pipe 8 greatly differ, and therefore the sound speed may greatly differ. Sound velocity 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]

## EQU2 ## c = 331.5 + 0.6 × T

For example, if the temperature T ₁ in the exhaust duct 3 is T ₁
= 400 ° C., and the temperature T ₂ in the branch pipe 8 may be T ₂ = 70 ° C. In this case, from the above equation (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 constructed as described above, the frequency f _{1 of the} standing wave generated by the exhaust sound is such that the sound velocity in the exhaust duct 3 is c ₁ , and the virtual sound source point P the distance to the third discharge port 3a When L _2, an odd multiple of c ₁ / (4L _2). Here, when the time that the exhaust sound takes to propagate from the virtual source point P to the discharge port 3a to t _10, the t ₁₀ is, t ₁₀ = L
₂ / c ₁ , the frequency f _{1 of the} standing wave is
It is an odd multiple of 1 / (4t ₁₀ ). That is, the frequency f _{1 of the} standing wave generated by the exhaust sound is such that the exhaust sound is
Determined by the time t ₁₀ required for propagation to the discharge port 3a from.

On the other hand, in the same way as in FIGS. 8A to 8C, the sound wave radiated from the sound deadening speaker 6 also passes through the branch pipe 8 to the outlet 3a of the exhaust duct 3 (L ₅ +
A standing wave is generated at L ₄ ). Then, the frequency f ₂ of the standing wave, like the standing wave by the exhaust sound,
Determined by the acoustic muffling speaker 6 through the branch pipe 8 from the sound wave emitting surface 6a time required to propagate 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 standing waves generated by the sound waves radiated from the exhaust sound and the silencing speaker 6 are: They will match each other.

Here, the exhaust sound and silencing speaker 6
Of the path waves are propagated respectively, because for the section L ₄ from the interference point Q in the exhaust duct 3 to the discharge port 3a is a common propagation path in each sonic exhaust sound and the silencing speaker 6 is the common section L ₄ time required to propagate (the time is t ₀₎ are each equal. Then, as described above, in FIG. 4, among the paths acoustic exhaust sound and the silencing speaker 6 is propagated each time, each required to propagate the paths excluding the common section L _4, i.e. exhaust For the 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 silencing speaker 6, the sound is emitted from the sound emitting surface 6 a of the silencing speaker 6 to the branch pipe 8. , The time t ₂ required to propagate (L ₅ ) to the interference point Q is 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 outlet 3 a of the exhaust duct 3, and the muffling speaker Time t ₂₀ (t ₂₀ = t _{20) in which} the sound wave of No. 6 propagates from the sound wave emitting surface 6 a to the outlet 3 a of the exhaust duct 3 via the branch pipe 8.
t ₂ + t ₀ ). Therefore, the frequency f _{1 of the} standing wave generated by the exhaust sound matches the frequency f _{2 of the} standing wave generated by the sound wave radiated from the sound deadening speaker 6.

As described above, in the second embodiment,
Since the frequencies f ₁ and f _{2 of the} standing waves generated by the exhaust sound and the sound wave of the muffling speaker 6 are configured to be the same, when the standing wave is generated by the exhaust sound, A standing wave is also generated by the sound wave emitted from the muffling speaker 6. Therefore, at the frequency f ₁ (or f ₂ ) at which the standing wave is generated, the radiation efficiency of the exhaust sound from the sound source (virtual sound source point P) increases, but at the same time, the sound radiation efficiency of the sound deadening speaker 6 increases. Therefore, the exhaust sound can be sufficiently canceled out by the sound waves emitted by the sound deadening speaker 6. That is, it is possible to effectively cancel the frequency f ₁ (or f ₂ ) component of the noise caused by the exhaust sound, in which the standing wave is generated. Even if the noise occurs, the effect of the standing wave can be reliably prevented.

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, and 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, without providing the branch pipe 8, the sound emitting surface 6a of the muffling speaker 6 is directly coupled to the vicinity of the exhaust sound output end of the muffler 1 in the exhaust duct 3. You may. In this case, a short path from the sound wave emitting surface 6a of the sound deadening speaker 6 to the interference point Q in FIG. 5 is a sound wave transmission path.

In the second embodiment, the branch pipe 8 is connected to the exhaust duct 3 at a right angle, but the connection angle is not limited to this. For example, the branch pipe 8 may be coupled to the exhaust duct 3 at an acute angle with respect to the engine 10 side of the exhaust duct 3 (that is, the upstream side of the exhaust sound).

In order to reduce the length L ₅ of the branch pipe 8 as much as possible and to reduce the size of the muffler, the interference point Q may be arranged as close as possible to the muffler 1.

[0057]

The muffler according to the present invention is a muffler provided with both a muffler and an electronic muffler. The muffler is provided in a sound propagation path between a microphone and a speaker constituting the electronic muffler. It is arranged. With such a configuration, the distance from the virtual sound source generated in the muffler to the other end of the sound propagation path, that is, the outlet of the exhaust sound is shorter than before. Therefore, the frequency f of the standing wave generated in this sound propagation path can be made higher than before, thereby suppressing the generation of the standing wave in the low frequency range that the electronic silencer is attenuating, That is, there is an effect that the influence of the standing wave can be prevented.

As described above, the muffler 1 and the electronic muffler 2 shown in FIG. 6 are so-called, since the muffler is arranged within a predetermined interval provided as necessary due to the structure of the electronic muffler. Unlike the prior art in which the mufflers are arranged in series, the muffler is built in the electronic silencer. Therefore, as compared with the above-described prior art, the overall 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 an acoustic resistor, is interposed between the microphone and the speaker,
Sound waves radiated from the speaker are not directly input to the microphone. Therefore, there is an effect that a howling phenomenon occurring between the microphone and the speaker can be suppressed.

Further, in the sound propagation path which is the propagation path of the exhaust sound.
And the sound propagation, which is the propagation path of the sound wave radiated by the speaker
Under certain conditions where the temperature differs between the inside and the road
Exhaust sound propagates from the virtual sound source to the outlet of the sound propagation path
And the sound waves emitted by the speaker
Propagation from the sound emission surface of the speaker to the outlet of the sound propagation path
And the time required for each
Have been. With this configuration, the exhaust noise
And the frequency of the standing wave
Frequency of the standing wave generated by the
You. For this reason, at the frequency at which the standing wave is generated by the exhaust sound, the standing wave is also generated by the sound wave radiated 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 of the speaker also increases at the same time, and the above-mentioned frequency component is effectively canceled by the sound wave emitted by the speaker. be able to. Therefore, even if a standing wave is generated in the frequency region to which the electronic silencer is to be attenuated, the effect of the standing wave can be more reliably prevented than in the first aspect.

[Brief description of the 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 a sound pressure distribution with respect to 100 Hz sound in an exhaust duct when a muffler is provided and when no muffler is provided in the embodiment.

FIG. 3 is a diagram showing a sound pressure distribution of a 300 Hz sound in an exhaust duct when a muffler is provided and when no muffler is provided in the embodiment.

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

FIG. 5 is a modification of the 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).

8A and 8B are diagrams showing a sound pressure distribution of a standing wave generated in a closed tube, wherein FIG. 8A shows a case where the wavelength λ of the standing wave is four times the tube length L, and FIG. 8B shows a wavelength of the standing wave. In the case where 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]

 DESCRIPTION OF SYMBOLS 1 Muffler 2 Electronic silencer 3 Exhaust duct 3a Exhaust port 4 Primary microphone (reference microphone) 5 Controller 6 Silencer 7 Secondary microphone (error microphone) 8 Branch pipe 10 Engine

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F01N 1/00 G10K 11/178 H04R 1/00

Claims (1)

(57) [Claims] 1. A sound propagation path for propagating the sound so that a sound input from one end is emitted from the other end, and a passive silencer provided in the sound propagation path and forming a part of the sound propagation path. A microphone coupled to the sound propagation path for collecting the sound, control means for controlling an output electric signal of the microphone, and a sound wave driven by the output signal of the control means to emit a sound wave; A speaker provided at a position at a predetermined distance from the coupling position of the sound propagation path with the microphone to the other end side so as to interfere with the sound, wherein the control means radiates from the speaker A muffler configured to control the output electric signal to a state where the amplitude and phase of the sound wave are equal to the amplitude and phase necessary to cancel the sound, wherein the passive silencer includes: To, be one having a place to sudden change in the acoustic impedance, acoustic radiation the passive silencer, disposed between the microphone and the speaker in the sound propagation path, emits the sound wave of the speaker From above
To the interference position between the sound and the sound wave in the sound propagation path
While providing a sound wave transmission path for transmitting the sound wave between,
The temperature is different between the sound propagation path and the sound wave propagation path.
Under the following conditions, the sound propagating in the sound propagation path
The acoustic impedance in the passive silencer
Required to propagate from a sudden change in
And the sound waves emitted by the speaker
From the wave radiation surface to the interference position via the sound wave transmission path.
And the time required to carry
A silencer characterized by the following .