JP4454362B2 - Active silencer - Google Patents

Description

  The present invention is disposed in an exhaust gas path (an example of an acoustic propagation path) equipped with an engine as a noise source and a heat engine such as a gas turbine upstream for the purpose of silencing, and the acoustic propagation path is connected via a connection path. The present invention relates to an active silencer including a connected acoustic device.

As a conventional example of the active silencer, for example, there is a technique disclosed in Patent Document 1.
Prior to this technology, the acoustic equipment provided in the active silencer was directly connected to the acoustic propagation path via the connection path. Therefore, when the apparatus is installed in an exhaust gas passage such as an engine or a gas turbine, a gas having high temperature, high humidity, and corrosiveness flowing through the exhaust gas passage may reach the front surface of the acoustic device directly and be exposed to it.

  Therefore, in the technique disclosed in Patent Document 1, in order to reduce the effect of this kind of gas, a cooling fan is provided so that the high-temperature and corrosive gas flowing in the exhaust pipe does not directly reach the acoustic device. In addition, air is sucked from outside air and sent, and the heat from the exhaust gas pipe is cooled so that it is not directly transmitted to the acoustic equipment.

JP 2000-130146 (FIGS. 1 and 5)

  However, when the cooling gas is introduced into the front surface of the acoustic device, the back of the acoustic device is in a sealed state. Therefore, if a cooling gas having a pressure sufficient to overcome the gas pressure in the exhaust gas passage is flowed, the acoustic device is also affected. Pressure is applied to the front, deteriorating the acoustic performance of the equipment.

  In order to prevent this, if a partition plate capable of transmitting sound between the front and back surfaces is placed on the front surface of the audio equipment to avoid pressure from the front surface, sound loss due to the partition plate occurs. Performance decreases.

  Therefore, an object of the present invention is to obtain an active silencer capable of obtaining a desired silencer performance without providing a partition plate on the front side of an acoustic device.

To achieve the above object, the sound propagation path connected to the noise source, the characteristic structure of the active silencer comprising an acoustic device connected via a connecting channel, with the connection path, said sound- audio equipment back surface space comprising a first fan for blowing a first gas is ambient air for cooling the acoustic equipment front space, the rear surface side of the acoustic apparatus with respect to the connection path between the propagation route and the audio equipment A second gas that is dry compressed air is blown into the second fan different from the first fan, and
Between the acoustic device front space and the acoustic device back space, a communication path is provided to connect the gas in a communicable manner,
The gas pressure difference between the front and back surfaces of the acoustic device is to be adjusted.

In this active silencer, gas is blown into both the acoustic device front space and the acoustic device back space. Then, depending on the first gas is ambient air for cooling blown into audio equipment front space, for example, with the exhaust gas flowing through an acoustic propagation path from reaching the acoustic equipment fulfills the use of cooling.

On the other hand, regarding the second gas is a dry compressed air blown to the rear surface acoustic equipment, after which the gas is once blown into the rear surface acoustic device, via the communication path, to flow to the front audio equipment.

  By doing so, it is possible to prevent the gas pressure due to the blowing of the first gas from being directly applied to the acoustic device, and by adjusting the blowing amount of the second gas, the gas pressure between the front and back surfaces of the acoustic device can be reduced. Can be adjusted. As a result, a pressure state suitable for the operation of the audio equipment can be realized, and the operation of the audio equipment can be made accurate.

When the acoustic device is a speaker including a speaker vibrating body, it is preferable that the speaker vibrating body is adjusted to a vibration neutral position of the speaker vibrating body by adjusting the gas pressure difference.
Since the speaker is originally configured to exhibit the best characteristics in a state where the speaker vibrating body is in its vibration neutral position, in the case of the present application, by performing the above, it is possible to By setting the pressure difference between them, the vibrating body such as the speaker cone can be returned to the original position where the vibrating body is located without generating sound, and good characteristics can be exhibited while obtaining a large output.

  The communication path is configured so that sound generated on the back surface of the speaker due to the vibration of the speaker vibrating body is transmitted in reverse phase to the front surface of the speaker via the communication path. It is preferable that the acoustic propagation path length is set.

  According to the operation of the speaker, the sound generated on the back side that is in reverse phase with respect to the sound generated on the front side of the speaker is propagated to the front side of the speaker via the communication path and overlaps with the sound generated on the front side. Thus, a stronger control sound can be obtained.

Now, it is preferable that the frequency of the sound propagated to the front side of the speaker through the communication path in this way is a band necessary for muffling and a band where the sound output is insufficient.
This type of band may be distributed up to about 10 to 1000 Hz depending on the speaker, but is particularly preferably 20 to 250 Hz which is a so-called low sound range.
In the case of the active silencer according to the present application, when the noise source is an engine, a frequency band in which a general silencer is difficult to mute is a low frequency region of 20 to 250 Hz. On the other hand, even with a speaker, a general-purpose speaker is often inferior in acoustic characteristics at 125 Hz or lower.
Therefore, if the above-described communication path configuration is not adopted, there are many cases where the silencing control in this frequency region cannot be performed well. However, by using a sound in opposite phases come to propagate to the scan peak mosquito front compensates for this drawback, it achieve good noise reduction control.

Furthermore, it is preferable to provide a gas drying means that uses the second gas introduced into the back surface space of the acoustic device as dry air .
Active silencer as the present application, when the temperature and humidity conditions are used in significantly changing environment is large, since the dew condensation is feared, because it is preferable to feed dry air as the second gas is there.

As described above, by the active silencer according to the invention, to place the first fan connection path between the acoustic propagation route in which for example the exhaust pipe and the speaker or the like, temperature, humidity, resistance The acoustic equipment does not need to have a special specification with respect to gas properties. Accordingly, it is possible to improve the reliability and durability by covering a wide range of specifications of the audio equipment.

  In addition, by devising the communication path that connects the duct that is the connection path and the back of the audio device, the characteristics of the audio device can be more effectively exhibited, and scavenging can be performed by introducing the second gas from the back side of the audio device. As a result, the environment on the back side of the audio equipment can be properly maintained, and the reliability and durability can be improved.

Hereinafter, an embodiment of an active silencer according to the present invention will be described with reference to the drawings.
FIG. 1 schematically shows the overall structure of the active silencer 1.
The exhaust gas from the engine 2 (corresponding to the noise source) passes through the exhaust pipe (corresponding to the acoustic propagation path) 4 in the direction indicated by the arrow 3, and at this time, the propagation sound wave from the engine 2 is also transmitted as noise.

A duct (an example of a connection path) 5 branches from the exhaust pipe 4, and an acoustic device according to the active silencer 1 is installed in the duct 5.
As a basic configuration, the apparatus 1 is provided on the upstream side of the speaker 6 in the exhaust pipe 4 serving as an acoustic propagation path from the engine 2 and provides information on the propagation sound wave, such as characteristics such as phase and sound pressure (amplitude). A first sensor microphone 7 for detection, a control device 8 that processes the detection information and creates information (electrical signal, etc.) representing an additional sound wave having an opposite phase and the same sound pressure as the propagation sound wave, and radiating the additional sound wave The speaker 6 that interferes and silences the transmitted sound wave, the second sensor microphone 9 that is provided on the downstream side of the speaker 6 and detects information for evaluating the effect of interference silence, and cooling that cools the speaker 6 with outside air It is comprised from the fan 10 grade | etc.,.

The duct 5 extends and is connected to the side of the exhaust pipe 4 that is an acoustic propagation path.
The duct 5a between the first sensor microphone 7 and the exhaust pipe 4 and the duct 5b between the second sensor microphone 9 and the exhaust pipe 4 are also arranged in the same manner with respect to the exhaust pipe 4. Yes.

  As shown in FIG. 1, a shut-off damper 11 for shutting off the speaker 6 from the exhaust gas flowing in the exhaust pipe 4 is installed on the connection side of the duct 5 as a connection path between the active silencer 1 and the exhaust pipe 4. Has been. The shut-off damper 11 is configured to be openable and closable both automatically and manually.

  The shut-off damper 11 rotates around the vertical axis 12, and the first state (solid line) in which the gas flowing through the acoustic propagation path circulates between the acoustic propagation path and the speaker 6 arrangement portion, and the first state that blocks the circulation. It can be switched between two states (broken line).

  A cooling fan 10 (an example of a first fan) for introducing outside air for cooling (an example of a first gas) is provided between the speaker 6 and the cutoff damper 11. The cooling fan 10 is connected to the duct 5 through the discharge port 13 and introduces outside air into the duct 5.

The above is the outline of the basic configuration of the active silencer 1 according to the present application. In the present application, a unique configuration is adopted around the speaker 6. FIG. 2 is a side view of the duct 5 shown in FIG.
As shown in FIGS. 1 and 2, (look from the exhaust pipe 4 back surface) back of the speaker 6 for introducing dry compressed air (an example of a second gas) to the speaker rear surface space 60 located, the A suction fan 15 (an example of a second fan) separate from the cooling fan 10 is provided. A dehumidifier 62 that uses the sucked outside air as dry air is provided in the introduction path 61 from the suction fan 15 to the speaker back surface space 60.

  FIG. 2 shows the details of the speaker back surface space 60. As shown in FIG. 2, the side of the speaker 6 is a space from the speaker back surface 60 and the front surface of the speaker to the blocking damper 11. A communication path 16 that communicates with the speaker front space 63 is provided. A sound-absorbing glass fiber 17 is disposed around the communication path 16 and on the inner wall surface.

FIG. 3 is a view of the speaker 6 as viewed from the side of the cutoff damper 11, and the openings 16 a of the communication path 16 are provided as four equally distributed rectangular openings at four outer peripheral portions of the speaker cone 64. Yes.
Therefore, the dry air introduced into the speaker back surface space 60 is sent into the speaker front space 63 through the communication path 16.

Thus, by the dry air by sucking outside air by the suction fan 15 to adjust the pressure of the space located to the speaker rear surface-front, with the cooling air introduced into the speaker front space 63 Ri by the cooling fan 10 Thus, the position of the speaker cone 64 can be kept at the vibration neutral position where the speaker performance is properly exhibited.

As the acoustic configuration of the communication path 16, a unique configuration is employed in the present application. That is, regarding the acoustic path from the speaker back surface 6b through the communication path 16 to the speaker front surface 6f, the acoustic phase reaches from the speaker back surface 6b to the speaker front surface 6f in an acoustic band of a frequency of 20 to 250 Hz, which is a problem in the present application. Thus, the acoustic path length of the communication path 16 is set so as to have an opposite phase (the same phase with respect to the sound generated from the speaker in front of the speaker).
By configuring the communication path in this manner, it is possible to appropriately set the speaker cone position to the vibration neutral position, and the sound sent from the speaker 6 to the exhaust pipe 4 side is sufficient even in a relatively low frequency region. Control sound can be generated.

[Verification results]
The relationship between the configuration around the speaker employed in the present application and the speaker characteristics will be described below.
4 (a), (b), (c), (d), and (e) are schematic diagrams around the speakers to be studied, and FIG. 5 is a graph showing acoustic characteristics (gains) of the speakers obtained corresponding to the configuration shown in FIG. )showed that. FIG. 6 shows the output characteristics of the speaker obtained corresponding to the configuration shown in FIG.
5 and 6, the characteristic indicated by the solid line a is the configuration shown in FIG. 4A, the characteristic indicated by the broken line b is the configuration shown in FIG. 4B, and the characteristic indicated by the alternate long and short dash line c is the characteristic shown in FIG. The characteristic indicated by the two-dot chain line d corresponds to the configuration shown in FIG. 4D, and the characteristic indicated by the dotted line e corresponds to the configuration shown in FIG.

Hereinafter, the configuration around the speaker and the speaker characteristics will be described.
5 and 6, the horizontal axis represents frequency, and the vertical axis represents gain and output.
Regarding the exhaust noise generated from the engine by the horizontal solid lines with the double-ended arrows shown in FIG. 5 (the upper end frequency and the lower end frequency are indicated by the vertical dotted lines), the frequency range in which active silencing control according to the present application is mainly required is shown. It was. Further, a frequency range higher than the upper end frequency is a frequency range that can be handled by a conventional silencer or the like.
Furthermore, the acoustic range on the higher frequency side than the frequency whose lower limit frequency is indicated by a one-dot chain line in the vertical direction indicates the acoustic range controlled by the active silencer according to the present application.

The verification conditions are as follows.
Volume of speaker back space 40 liters Temperature 40 ° C
Humidity 60% RH

Demonstration result 1 Example 1 (corresponding to Fig. 4 (a))
In this example, the pressure exerted on the speaker from the front and the back is examined, and the characteristics exhibited by the speaker in a normal use state are examined.
From the result of the solid line “a” in FIG. 5, when a decrease in gain is observed at a frequency of 60 Hz or less, an engine is generated, and the speaker performance cannot be sufficiently exhibited on the low frequency side (35 to 60 Hz) of the frequency to be controlled. I know that there is.

2 Example 2 (corresponding to FIG. 4 (b))
In this example, the characteristics exhibited by the speaker when the pressure from the front is applied to the speaker and the vibration center of the speaker cone is shifted are examined.
From the result of the broken line b in FIG. 5, it can be seen that the frequency band causing the gain reduction is lowered. However, as shown by a broken line b in FIG. 6, a sufficient speaker output cannot be obtained in this state.

3 Example 3 (corresponding to FIG. 4 (c))
In this example, as described above, air is sent to the speaker back space, the vibration center is returned to the original center position in the speaker cone, a communication path is provided, and the phase is reversed in the acoustic path from the speaker back to the front. It is set as the structure made.
As shown by the one-dot chain line c in FIG. 5, the gain has a flat characteristic from a high frequency range to a low frequency range of about 25 Hz, and it can be seen that a good characteristic is obtained as a speaker used for active silencing control. .

4 Example 4 (corresponding to Fig. 4 (d))
In this example, the characteristics of the example in which the communication path according to the present application is provided when the pressure from the front of the speaker is high are examined.
The result of the two-dot chain line d in FIG. 5 indicates that the gain increases in the low frequency range of 25 Hz to 70 Hz, but the increase in the low frequency range is significant, and is not good as a speaker used for active silencing control. ing. Further, as indicated by a two-dot chain line d in FIG. 6, a sufficient output cannot be obtained in a specific frequency range.

5 Example 5 (corresponding to FIG. 4 (e))
In this example, the characteristics exhibited by the speaker when the simple communication structure is adopted without adjusting the acoustic length of the communication path are examined.
From the result of the dotted line e in FIG. 5, it can be seen that the result is not preferable .

[Another embodiment]
7 (a) to 7 (f) show various other embodiments of the cooling fan 15 suitable for use in the active silencer according to the present invention.
Various configurations can be adopted for the structure of the cooling fan 15, the connection location and connection method to the duct 5, and the positional relationship with respect to the speaker 13 as shown in the drawings.

7 (b), the discharge port 16 of the cooling fan 15 is disposed to face the speaker 13. By disposing the cooling fan 15 facing the speaker 13, it is easy to prevent condensation at the front portion of the speaker 13.

7 (b), the discharge port 16 of the cooling fan 15 is provided at a plurality, intervals to each other in the circumferential direction along the inner peripheral surface of the duct 5. In the case of this structure, there is an effect that the cooling air can be dispersed and the cooling effect can be made uniform.

In FIG. 7 (c), the discharge port 16 of the cooling fan 15 is disposed toward the exhaust pipe 4. In the case of this structure, there is an effect that introduction of high-temperature and high-humidity exhaust gas from the exhaust pipe 4 into the duct 5 is suppressed by the cooling air from the discharge port 16.

7 (d), as in the example of FIG. 7 (c), the discharge port 16 of the cooling fan 15 is disposed toward the exhaust pipe 4. Furthermore, in this example, a plurality of discharge ports 16 are provided in the vertical direction. In the case of this structure, in addition to the effects achieved from the structure shown in FIG. 7 (c), further effects so that possible homogeneous cooling effect.

7 (e), as compared to the embodiment described above, the cooling fan 15 is installed at a position close to the exhaust pipe 4. By disposing the cooling fan 15 close to the exhaust pipe 4, there is an effect that introduction of high-temperature and high-humidity exhaust gas from the exhaust pipe 4 into the duct 5 is suppressed.

In FIG. 7 (f), the outside air duct 17 detours around the duct 5 and then is introduced into the duct 5. In the case of this structure, by providing means (not shown) for cooling the outside air in the middle of detouring, cooling air having a temperature lower than that of the outside air is introduced into the duct 5 to further enhance the cooling effect. Is possible.

  Furthermore, in the present invention, the cross-sectional shape of the exhaust pipe 4 can be an arbitrary shape such as a circular shape or an elliptical shape in addition to a rectangular shape.

  It was possible to obtain an active silencer capable of ensuring good operation of the audio equipment.

The figure which shows schematic structure of the active silencer installed in the exhaust gas pipe The figure which shows the side cross-section structure of the principal part The figure which shows the structure which looked at the speaker from the front side Explanatory drawing for function explanation Diagram showing the state of gain in the frequency domain corresponding to different configurations Diagram showing the state of output in the frequency domain corresponding to different configurations Diagram showing another configuration example of the present application

Explanation of symbols

1 Active silencer 2 Engine (noise source)
4 Exhaust pipe 5 Duct (connection pipe)
6 Speaker 6f Speaker front surface 6b Speaker back surface 10 Cooling fan (first fan)
15 Suction fan (second fan)
16 communication path 60 speaker back space 61 introduction path 62 dehumidifier 63 speaker front space 64 speaker cone (speaker vibrating body)

Claims (5)

In an active silencer having an acoustic device connected to a sound propagation path connected to a noise source via a connection path,
In the connecting passage, a first fan for blowing a first gas is ambient air for cooling the acoustic equipment front space between the sound-propagation route and the acoustic device, the acoustic equipment to the connection path A second gas that is dry compressed air is blown into the back surface space of the acoustic device that is the back side of the second fan, different from the first fan, and
Between the acoustic device front space and the acoustic device back space, a communication path is provided to connect the gas in a communicable manner,
An active silencer in which a gas pressure difference between the front and back surfaces of the acoustic device is adjusted. The acoustic device is a speaker including a speaker vibrating body,
The active silencer according to claim 1, wherein the speaker vibrating body is adjusted to a vibration neutral position of the speaker vibrating body by adjusting the gas pressure difference.   The communication path is configured such that sound generated on the back surface of the speaker due to vibration of the speaker vibrating body is transmitted in reverse phase to the front surface of the speaker via the communication path. 3. The active silencer according to claim 2, wherein a general propagation path length is set.   The active silencer according to claim 3, wherein a frequency range of sound transmitted in reverse phase to the front surface of the speaker through the communication path is 20 to 250 Hz. The active silencer according to any one of claims 1 to 4, further comprising a gas drying unit that uses the second gas introduced into the back surface space of the acoustic device as dry air .

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