JPH1124671A - Muffler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a muffler in which S/N is improved more than in the past to precisely detect a sound to be detected while protecting a noise detector or silencing deviation detector from heat or exhaust gas. SOLUTION: A damper 38 as a resonant vibration preventing means is provided on the peripheral part of a heat insulating membrane 35 provided so as to partition a noise detector 2 (the same may be said of a silencing deviation detector 3) from the inner space of a sound absorbing duct 31. The noise detector 2 is mounted on the sound absorbing duct 31 through a cooling pipe 37 having sound absorbing materials 39a, 39b in the inner part, and the cooling pipe 37 is connected to the sound absorbing duct 31 through a vibration isolating member 61. The membrane 35 protects the noise detector 2 from heat or exhaust gas, and is prevented from being resonantly vibrated by the damper 38. Further, the radiating effect can be enhanced by the cooling pipe 37, and generation of a foreign sound by vibration can be also prevented by the internal sound absorbing materials 39a, 39b. Thus, N/S can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a muffler using active noise control (ANC) technology.

[0002]

2. Description of the Related Art As a prior art of this kind, there is a silencer having a configuration as shown in FIG. The muffler according to the present prior art includes a noise detector 2 for detecting noise P propagating in the direction of an arrow in a sound absorbing duct 31, a speaker 4 as a sound wave generator, and a muffling deviation detector 3 for detecting a muffling deviation level. And the output x of the noise detector 2 and the silencing deviation detector 3
Receiving the output e of the speaker 4, directs the sound-absorbing sound wave having the same magnitude and opposite phase as the noise P into the sound absorbing duct 31.
And a muffling signal generator 5 for forming a muffling signal y to be generated from.

[0003] The noise detector 2 and the noise reduction deviation detector 3 are each connected to a connecting portion 3 provided on the side wall of the sound absorbing duct 31.
The inside of casings 34 and 54 integrally attached to gaskets 33 and 53 to 2 and 52 are supported by elastic support members 36 and 56 made of, for example, rubber. The speaker 4 is fixed to a speaker attachment member 46 inside a casing 44 attached to the connection portion 42 via a gasket 43. On the front surfaces of the noise detector 2, the silencing deviation detector 3 and the speaker 4, a heat insulating film 3 is formed so as to be separated from the internal space of the sound absorbing duct 31.
5, 55 and 45 are provided.

Referring to FIG. 8, the details of the muffling signal generator 5 will be described. The output x of the noise detector 2 is
1. The signal is supplied to an adaptive filter (hereinafter abbreviated as ADF) 14 and a delay filter 13 via an A / D converter 12. Also, the output e of the silencing deviation detector 3
Is supplied to the coefficient calculator 15 via the amplifier 16 and the A / D converter 17. The ADF 14 has N taps, the coefficients of which are updated by the output of the coefficient calculator 15. The delay filter 13 has an acoustic transfer characteristic corresponding to a path from the speaker 4 to the muffling deviation detector 3. That is, the coefficient of the delay filter 13 is determined in consideration of the time delay, and is measured or identified in advance. Further, the coefficient calculator 15 calculates the ADF1
4 is an adaptive algorithm for sequentially calculating an optimum coefficient to be given to C.4. The muffling signal generator 5 has a configuration using the above-described well-known ANC control technology.

[0005] With the conventional silencer constructed as described above, the magnitude of the noise P is greatly reduced or eliminated, and the noise P is discharged from the discharge end of the sound absorbing duct 31. Further, the heat insulating films 35, 45 and 55 protect the noise detector 2, the silencing deviation detector 3 and the speaker 4 from high-temperature exhaust gas in the sound absorbing duct 31 when the noise source is an engine, and endurance thereof. I try to enhance the nature.

[0006]

However, in the conventional silencer constructed as described above, the noise detector 2 and the silence deviation detector 3 make the sound absorbing duct 31 inside the sound absorbing duct 31 by vibrating the films 35 and 55. Since the noise P and the silencing deviation level are detected, these films 35,
When the natural frequency of 55 approaches or coincides with the frequency of the sound wave in the sound absorbing duct 31, there is a problem that the films 35 and 55 cause resonance vibration. Film 35, 55
When the resonance vibration occurs, the amplitude becomes abnormally large, and a specific noise frequency is transmitted at a very high level at the peak of the vibration mode. Cannot be detected.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problem, and detects a sound to be detected with an improved S / N compared to the related art while protecting a noise detector and a noise reduction deviation detector from heat and exhaust gas. An object of the present invention is to provide a muffler capable of performing the above-described operations.

[0008]

SUMMARY OF THE INVENTION The above objects are attained by a noise detector (2) for detecting noise of a noise source (for example, corresponding to a reference symbol P in the embodiment, the same applies hereinafter), and detecting a noise reduction deviation level. And the output (x) of the noise detector (2) and the output (e) of the noise reduction deviation detector (3), the magnitude of which is equal to the noise (P);
And a muffling signal generator (5) for forming a muffling signal (y) for generating a sound wave of opposite phase from the sound wave generator (4) toward the sound absorbing duct (31), and the noise detector ( 2) and / or a sound deadening device provided with a heat insulating film (35, 55) so as to partition the sound deadening deviation detector (3) and the internal space of the sound absorbing duct (31). , 55) provided with resonance vibration preventing means (38, 58) for preventing resonance vibration of the coating (35, 55).

According to the present invention, the sound wave in the sound absorbing duct (31) is faithfully detected by providing the film (35, 55) with the resonance vibration preventing means (38, 58). (3), so that the noise and the silencing deviation level can be accurately detected.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION As a structural example of a resonance vibration preventing means according to the present invention, a damper is attached to a peripheral portion of a film to prevent a vibration peak by lowering a vibration peak of the film, or a reinforcement is provided on a vibration surface of the film. Ribs are provided to increase the rigidity of the film itself to prevent resonance vibration. In addition, a predetermined weight is provided at the center of the film to set the resonance frequency of the film in a frequency region different from the frequency region of the noise.

The film is formed of a heat insulating material. When the noise source is an engine, it is desirable that the film has resistance to corrosive components such as acid and alkali in the exhaust gas. For example, fluorocarbon resins such as carbon, carbon cloth, ceramic, asbestos, mica, and polytetrafluoroethylene (trade name: Teflon) may be used.

If the noise source is an engine, the exhaust gas has a high temperature, and the heat transfer from the sound absorbing duct may cause insufficient protection of the noise detector and the noise reduction deviation detector from the heat of the exhaust gas. There is. In such a case, a configuration is known in which the noise detector and the noise reduction deviation detector are attached to a sound absorbing duct via a cooling pipe to enhance a heat radiation effect. This is made of a metal tubular member, which enhances the heat radiation effect and protects the noise detector and the silencing deviation detector from heat. However, since the cooling pipe itself has the property of emitting sound under the influence of the outside,
There is a new problem that abnormal noise is generated inside the cooling pipe due to the propagation of the vibration of the sound absorbing duct to the cooling pipe, which has led to a reduction in S / N.

Although the present invention has been made so that sound waves can be accurately detected even in a configuration provided with such a cooling pipe, it will be described in detail in the following embodiments.

[0014]

FIG. 1 shows a silencer according to an embodiment of the present invention. Parts corresponding to those in FIG. 7 are denoted by the same reference numerals, and a detailed description thereof will be omitted.

In this embodiment, the noise detector 2 and the silencing deviation detector 3 are respectively connected to a connecting portion 32 of the sound absorbing duct 31,
52 is attached via cooling pipes 37 and 57. Since the cooling pipes 37 and 57 have the same configuration, the details of the cooling pipe 37 on the noise detector 2 side will be typically described with reference to FIG.

The cooling pipe 37 is made of a metal, and 37a and 37b
And are integrally fixed by bolts via a dust seal 64, not shown. Film 35
The peripheral edge of the is fixed between the cooling pipe 37 and the connection portion 32 of the sound absorbing duct 31 via a heat insulating packing 60 and a vibration isolating member 61 made of rubber. These are integrally fixed by tightening a bolt 62 and a nut 63 via a rubber member 65. On the inner wall surface and the bottom wall surface of the cooling pipe 37, sound absorbing materials 39a and 39b made of, for example, glass fiber are provided.
Is attached. The noise detector 2 is supported inside the cooling pipe 37 via the elastic support member 30.

The film 35 according to the present embodiment is not only formed of a heat insulating material but also a material having resistance to corrosive gas such as acid or alkali, for example, carbon cloth, ceramic, asbestos, mica, silica or Teflon ( (Trade name). That is, it is formed of a material having resistance to exhaust gas.

At the lower peripheral portion of the film 35, the film 35
A damper 38 as a resonance vibration preventing means for preventing the resonance vibration is provided. The damper 38 is made of an annular elastic material (for example, urethane rubber, urethane foam, or the like), and is fixed in a state where the upper end thereof is in contact with the lower surface of the film 35.

In the present embodiment, the length L from the opening to the bottom of the cooling pipe 37 must be reduced in order to prevent resonance of sound waves (so-called air column resonance) generated inside the cooling pipe 37. It is shorter than the half wavelength of the highest frequency. That is, assuming that the wavelength L of the primary resonance is λ, the frequency is f, and the speed of sound is V, the length L required to cause resonance inside the cooling pipe 37 is L = λ / 2 = V / (2f). Therefore, if L is made shorter than this, the occurrence of resonance can be prevented. Therefore, if the sound speed V is 340 m / s, the length L decreases as the noise frequency increases, such as 57 cm at 300 Hz, 34 cm at 500 Hz, and 21 cm at 800 Hz. Therefore, according to the above equation, if the length L of the cooling pipe 37 is shorter than １ ／ wavelength of the highest frequency of the noise to be silenced, the resonance of the sound wave inside the cooling pipe 37 can be prevented.

The cooling pipe 57 on the side of the silencing deviation detector 3 is also constructed in the same manner, and a detailed description thereof will be omitted.
As shown in the figure, the connecting portion 5 between the cooling pipe 57 and the sound absorbing duct 31
A damper 58 as a resonance vibration preventing means is provided below a peripheral portion of the coating 55 provided between the cooling pipe 57 and the cooling pipe 57, and sound absorbing materials 59a and 59b are provided inside the cooling pipe 57. The silencing deviation detector 3 is supported inside the cooling pipe 57 via an elastic support member 50 made of rubber.

The silencer according to the present embodiment is constructed as described above. Next, this operation will be described.

The noise P generated from the engine, which is a noise source (not shown), propagates through the sound absorbing duct 31 and is detected by the noise detector 2 via the film 35. The film 35 vibrates according to the magnitude (amplitude) and frequency of the noise P, and the noise P
Is transmitted to the noise detector 2. In addition, the noise detector 2 detects the exhaust gas flowing through the sound absorbing duct 31 together with the noise P.
To protect and increase its durability. The coating 55 provided on one of the noise reduction deviation detectors 3 also performs a similar operation, and protects the noise reduction deviation detector 3 from exhaust gas flowing through the sound absorption duct 31.

Further, the film 35 has a magnitude (amplitude) of the noise P.
When oscillating in accordance with the frequency or the frequency, a specific noise frequency region approaches or coincides with the natural frequency of the film 35 and induces resonance vibration of the film 35. Since the vibration peak of the film 35 can be suppressed by the damper 38 provided on the periphery of the film 35, the resonance vibration of the film 35 that vibrates with a large amplitude can be suppressed. Thereby, S / N is improved, and the noise detector 2 can accurately detect the noise P in the sound absorbing duct 31. Similarly, the silencing deviation detector 3 can accurately detect the silencing deviation level.

Further, the cooling pipes 37 and 57 are connected to the sound absorbing duct 3
Since the function of radiating the heat inside 1 to the outside is performed, the noise detector 2 and the silencing deviation detector 3 can be effectively protected from the heat. Therefore, according to this embodiment, since the cooling pipes 37 and 57 are attached to the sound absorbing duct 31 via the vibration isolating member 61, the cooling pipes 37 and 57
In addition to suppressing the propagation of vibrations to the cooling pipe 7, sound absorbing members 39 a, 39 b, 59 a, 59 b provided inside the cooling pipes 37, 57 absorb sound waves generated by vibrations of the cooling pipes 37, 57. Therefore, generation of abnormal noise inside the cooling pipes 37 and 57 can be reliably prevented, and
The noise detector 2 and the silencing deviation detector 3 can detect the noise P and the silencing deviation level, respectively, with a high S / N.

Since the muffling signal generator 5 is the same as the conventional muffling signal generator described with reference to FIG. 8, its detailed description is omitted, but the output x of the noise detector 2 and the muffling deviation are omitted. Upon receiving the output e of the detector 3, a mute signal y is formed. The silencing signal y is supplied to the drive unit of the speaker 4, and generates a silencing sound wave having the same magnitude as the noise P and having an opposite phase toward the sound absorbing duct 31. Therefore, according to the present embodiment, as described above, the output x of the noise detector 2 and the output e of the silencing deviation detector 3 are signals detected with high accuracy, respectively. Thereby, the silencing effect can be performed most efficiently. At this time, the film 45 vibrates according to the sound-absorbing sound waves and protects the speaker 4 from exhaust gas.

Therefore, according to the present embodiment, not only can the noise detector 2, the silencing deviation detector 3, and the speaker 4 be effectively protected from exhaust gas, but also the noise detector 2, the silencing deviation detector 3, and the like. Since it is possible to reliably prevent the generation of abnormal noise inside the cooling pipes 37 and 57 while reliably protecting against the heat of exhaust gas, it is possible to detect sound waves with a higher S / N than before. it can. Thereby, the silencing effect can be enhanced.

Although the embodiments of the present invention have been described above, the present invention is, of course, not limited thereto, and various modifications can be made based on the technical concept of the present invention.

For example, in the above embodiment, the coatings 35, 55
Although the dampers 38 and 58 as the resonance vibration preventing means for preventing the resonance vibration of the above are constituted by separate members respectively, a sound absorbing material attached to the inner wall surface of the cooling pipe 37 (57) as shown in FIG. Extend the upper end of the damper 21
It may be configured as 1a. In this case, the damping effect of the film can be enhanced by forming the sound absorbing material 21 from an elastic material such as a rubber material mixed with metal powder.

Alternatively, as shown by a dashed line in FIG. 3, the cooling pipe 37 (57) and the connecting pipe 32 of the sound absorbing duct 31 are connected.
(52), the inner peripheral edge of the vibration isolating member 61 may be further extended inward to constitute a damper.

FIG. 4 shows another resonance vibration preventing means.
As shown in the figure, a weight 23 having a predetermined weight may be provided at the center of the film 35 (55). This is the film 35 (5
The resonance frequency of the film is prevented by making the natural frequency of 5) significantly different from the frequency of the noise.

Further, a resonance vibration preventing means as shown in FIGS. 5 and 6 may be constituted. That is, the reinforcing ribs 25, 2 are provided on the lower surface of the vibration surface of the film 35 (55).
By providing 5, ..., the rigidity of the film is increased,
Thereby, resonance vibration of the film is prevented. Further, for the same purpose, the same effect can be achieved by increasing the thickness of the film or by making the upper and lower vibrating surfaces curved.

In the above embodiment, the cooling pipes 37, 57
The length L of the cooling pipes 37, 57 is set to one of the highest frequencies of the noise to be silenced in order to prevent the resonance of the sound wave from occurring inside the inside.
/ 2 wavelength, but the length L and inner diameter D of the cooling pipe are changed so that the resonance frequency determined by the air mass inside the cooling pipe and the spring constant of the film is shifted from the noise frequency band. Even if it is changed, the same effect as described above can be obtained.

In the above embodiment, the noise detector 2 and the noise elimination deviation detector 3 are mounted on the sound absorbing duct 31 via the cooling pipes 37 and 57, respectively, but they may be omitted depending on the noise source. Good. This is because a cooling pipe is not necessarily required if no high heat is present in the sound absorbing duct 31. Similarly, in the above embodiment, the cooling pipes 37 and 57 are provided in both the noise detector 2 and the silencing deviation detector 3, but may be provided in only one of them.

[0034]

As described above, according to the sound deadening device of the present invention, the resonance vibration of the film is prevented in the film partitioning the noise detector and / or the noise reduction deviation detector and the internal space of the sound absorbing duct. Since the resonance vibration preventing means is provided, the S / N can be improved as compared with the related art while protecting the noise detector and / or the silencing deviation detector from exhaust gas and heat. It can be detected accurately. Thereby, the silencing effect can be enhanced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a silencer according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a portion related to the noise detector.

FIG. 3 is a partial sectional view showing a modification of FIG. 2;

FIG. 4 is a partial sectional view showing another modification of FIG. 2;

FIG. 5 is a partial sectional view showing still another modification of FIG. 2;

6 is a sectional view taken along line [6]-[6] in FIG.

FIG. 7 is a sectional view showing a conventional silencer.

FIG. 8 is a block diagram illustrating a configuration example of a muffling signal generation device.

[Explanation of symbols]

 Reference Signs List 2 noise detector 3 muffling deviation detector 4 speaker 5 muffling signal generator 23 weight 25 rib 31 sound absorbing duct 35 film 37 cooling pipe 38 damper 39a sound absorbing material 39b sound absorbing material 55 film 57 cooling tube 58 damper 59a sound absorbing material 59b sound absorbing material 61b Anti-vibration member

Claims (7)

[Claims] A noise detector for detecting noise of a noise source;
A silencing deviation detector for detecting a silencing deviation level, receiving the output of the noise detector and the output of the silencing deviation detector, and directing a sound wave having the same magnitude and opposite phase as the noise into the sound absorbing duct. A muffling signal generating device for forming a muffling signal to be generated from the generator, wherein a heat insulating film is provided so as to partition the noise detector and / or the muffling deviation detector and the internal space of the sound absorbing duct. Wherein the film is provided with a resonance vibration preventing means for preventing resonance vibration of the film. 2. The muffler according to claim 1, wherein said resonance vibration preventing means is a damper attached to a peripheral portion of said film. 3. The noise detector and / or the noise reduction deviation detector are attached to the sound absorbing duct via a cooling pipe having a predetermined length in which a sound absorbing material is attached, and
3. The muffler according to claim 1, wherein the cooling pipe is connected to the sound absorbing duct via a vibration isolator. 4. The muffler according to claim 3, wherein a part of said sound absorbing material or said vibration damping material is formed as said damper. 5. The muffler according to claim 3, wherein a predetermined length of the cooling pipe is shorter than a half wavelength of a maximum frequency of the noise to be muffled. 6. The silencer according to claim 1, wherein said resonance vibration preventing means is provided with a predetermined weight at the center of said film. 7. The silencer according to claim 1, wherein said resonance vibration preventing means comprises a reinforcing rib provided on a vibration surface of said film.