JP2855377B2 - Active silencer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a speaker disposed at an end of a sound source pipe such as an engine exhaust pipe, and emits a sound having a phase opposite to the sound emitted from the sound source pipe from the speaker to perform a silencing operation. The present invention relates to an active silencer.

[0002]

2. Description of the Related Art Japanese Patent Laid-Open Publication No. Sho 62-74298 discloses an active silencer of this type.
In this publication, since the front surface of the speaker is exposed and lined up with the sound source pipe, when this device is used for silencing engine exhaust, the front surface of the speaker is filled with exhaust gas, and the heat and gas components affect the sound. It is inevitable that the speaker will deteriorate. Even if active silencing is obtained, the sound pressure on the back of the speaker is not processed, so the sound radiated to the back of the speaker is loud, and the sound waves on the front and back interfere with each other. The problem of not being expected is also expected.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of this point, and has been made to solve the problem of preventing deterioration of a loudspeaker and efficiently eliminating sound in a low frequency range.

[0004]

In order to achieve the above object, according to the present invention, a duct for collecting sound waves emitted from a speaker is provided at the front of a speaker, and a small-area opening formed inside the end of the duct is provided. The ejector that sucks out the air in the duct by the gas flow exhausted from the sound source pipe
A small tube located at the end of the sound source pipe so as to be
An air flow path for cooling the speaker is formed from the ventilation hole having a large area to the opening through a space having a large volume in the duct . The internal volume of the duct and the small area of the opening constitute a Helmholtz resonator.

[0005]

[Function] A kind of ejector is constituted by the opening of the duct,
The gas flow discharged from the sound source pipe becomes the driving fluid, and the air in the duct becomes the sending fluid, and the air in the duct is sucked out, so that the speaker is cooled. Ventilation holes are also used for exhaust gas flow.
Exhaust gas for cooling
By touching the exhaust gas without getting into the air
Speaker is prevented from deteriorating, and the cooling air flow path is
Has an inflatable silence structure that is squeezed by ventilation holes
So that the sound is sufficiently muted from low to high
No sound leaks. In addition, the frequency characteristics of the speaker are improved by the Helmholtz resonator, and the sound deadening effect is improved.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The illustrated embodiment will be described below. FIG.
FIG. 2 shows the main part of the first embodiment.
Is an exhaust pipe of the engine which is a sound source pipe, 2 is a plurality of speakers arranged around the end 1a of the exhaust pipe 1, 3
Is a duct, and its cylindrical portion 4a is externally fitted to the exhaust pipe 1,
For example, a flange-like support plate 5 attached to the exhaust pipe 1 by means described later is a rear cover.

Each speaker 2 is provided with a speaker box 2a, and is screwed to the support plate 4 with its front surface facing the end of the exhaust pipe 1 so that its axis is parallel to the exhaust pipe 1. A ventilation hole 6 is formed outside the portion of the support plate 4 where the speaker box 2a is attached. As is well known, this device outputs a drive signal from a control device (not shown) based on the exhaust sound detected at the upstream portion of the exhaust pipe 1, and drives each speaker 2 by the drive signal. It is configured.

The duct 3 is composed of a large-diameter portion 3a covering the entire exhaust pipe 1 and each speaker 2 and a small-diameter portion 3b slightly larger in diameter than the exhaust pipe 1 and covering the end 1b of the exhaust pipe 1. It is attached to the outer peripheral portion of the support plate 4 by an appropriate means and is integrated with the support plate 4. The small-diameter portion 3b is formed to have a length that protrudes to some extent from the edge 1b, and a small-area opening 3c is formed around the edge 1b of the exhaust pipe 1. The inside of the large-diameter portion 3a on the front surface of the speaker 2 is a ring-shaped space 3d having a considerable volume.
air flow path 7 for cooling the speaker reaching opening 3c
Is configured. The support plate 4 is fixed to the exhaust pipe 1 by a fixing bolt 4c that is inserted into an elongated hole or groove-shaped notch 4 formed in the cylindrical portion 4a in the axial direction and screwed to the exhaust pipe 1. by sliding the position using the groove-like cutout 4, is configured to adjust the length of the small areas between up space 3d and the opening 3c optionally as L ₁ or L ₂ I have.

The rear cover 5 is composed of a flange-shaped rear plate 5a and an inner cylindrical portion 5b. The rear cover 5 is attached to the rear end of the large-diameter portion 3a of the duct 3 so as to cover the periphery of each speaker box 2a. A ring-shaped space 5c that covers the rear surface is formed, and a ventilation inlet 8 is formed at a gap between the edge of the inner cylindrical portion 5b and the support plate 4, and the ventilation hole 6 extends from the ventilation inlet 8 through the space 5c. , An air flow path 9 for cooling the speaker box is formed. The air flow path 9 is bent from between the exhaust pipe 1 and the inner cylindrical portion 5b of the rear cover 5 to enter the ventilation inlet 8 and reach the ventilation hole 6, or bypasses the speaker box 2a, and has a narrow ventilation. Because of the inflow port 8 and the ventilation hole 6, the air flow path has a sufficient noise reduction function.

The embodiment is configured as described above and operates as follows. That is, in a state where the engine is operated and exhaust gas is exhausted from the exhaust pipe 1 and each speaker 2 is operating, a sound having a phase opposite to the exhaust sound emitted from the exhaust pipe 1 is emitted from each speaker 2. However, since each speaker 2 is provided with the speaker box 2a, sound waves on the front and back sides do not interfere with each other, and the sound is effectively eliminated.

Further, the duct 3 has the above-described configuration.
A type of ejector is formed at the opening 3c, and the exhaust gas flow (solid arrow) discharged from the exhaust pipe 1 serves as a driving fluid , and the air in the duct 3 serves as a delivery fluid.
With stationary engines that cannot use the traveling wind like
Even if there is, the air in the duct 3 is surely sucked out from the opening 3c. Then, a new air is sucked into the rear cover 5 from the ventilation inlet 8, passes through the ventilation hole 6, passes through the front surface of the speaker 2, and is exhausted from the opening 3 c together with the exhaust gas flow, thereby generating an air flow as indicated by a broken arrow. Then, the speaker box 2a and the speaker 2 are cooled. In addition, since the ventilation inlet 8 is located at a position opposite to the direction in which the exhaust gas is discharged, the exhaust gas is not sucked into the air passages 9 and 7, and the speaker 2 touches the exhaust gas. Deterioration is prevented.

The air passages 7 and 9 are provided with ventilation holes 6 having a small area.
Since squeezed in by has an expansion-type configuration with a sufficient silencing function, air flow back from the exhaust noise ventilation hole 6 which came through the sound and the air flow passage 7 coming from the front of the speaker 2 Even if it leaks into the passage 9, these sounds do not leak from the ventilation inlet 8 to the outside, and the muffling function of the device is not impaired due to the cooling air flow path. In this embodiment, an air flow path 9 for cooling the outer surface of the speaker box 2a is provided.
Although the muffler also has a silencing function, a single silencer may be directly attached to the ventilation hole 6 without providing such an air passage 9.

Next, a second embodiment shown in FIGS. 3 to 5 will be described. The same parts as those in the above-described embodiment are denoted by the same reference numerals, and different points will be mainly described.
In FIG. 3, the air passage 9 in the above-described embodiment is not provided, but it is optional to attach a muffler to the ventilation hole 6 of the support plate 4 or provide the air passage 9 having a muffling function. An air passage 7 for cooling is formed inside the duct 3, passes through the front surface of the speaker 2 through the ventilation hole 6, and passes through the opening 3.
c, the speaker 2 is cooled by the generation of an air flow as shown by a broken line arrow that is discharged together with the exhaust gas flow,
Exhaust gas is not sucked into the air flow path 7 and deterioration of the speaker 2 due to the exhaust gas is prevented as in the above-described embodiment.

This embodiment is characterized in that the internal volume of the large-diameter portion 3a of the duct 3 and the opening 3c having a small area constitute a Helmholtz resonator. That is, in the Helmholtz resonator having such a configuration, if the resonance frequency fr is V, the internal volume of the large diameter portion 3a is V, the area of the small area up to the opening 3c is S, and the length is L, FIG. The shape and size of the large-diameter portion 3a and the opening 3c are selected so that the resonance frequency fr becomes a desired frequency in a low-frequency range where the frequency characteristic is reduced as shown by the solid line in the drawing. The radiation characteristics in the low frequency range are improved as shown by the broken line in FIG. Therefore, when the silencing operation is performed as the active silencer, the silencing effect on the exhaust sound in the low frequency range is efficiently performed, and a more sufficient silencing effect than the conventional silencing device is obtained.

Although not described, the construction of the Helmholtz resonator is the same in the embodiment of FIG. Further, the resonance frequency of the Helmholtz resonator does not necessarily need to be selected in the low frequency range. When the level of the exhaust sound of a specific frequency other than the low frequency range is high, for example, the support plate 4 illustrated in FIG. By sliding the duct 3 along the exhaust pipe 1 using the mounting structure, it is possible to make the resonance frequency coincide with a high-level frequency, and to take appropriate measures such as enhancing the sound-muffling effect on the exhaust sound of the specific frequency. is there. This makes it possible to effectively mute the sound and to reduce the size and capacity of the speaker and the driving amplifier.

By the way, in each of the above-described embodiments, a common duct 3 and a rear cover 5 are provided for a plurality of (four in this embodiment) speakers 2, so that a dedicated The duct 3 and the rear cover 5 are required, which is disadvantageous in terms of management and cost. FIG. 6 et seq. Show an embodiment in which individual speakers are made independent to solve such a problem. That is, in this embodiment, a duct 3 and a rear cover 5 are provided for each speaker box 2a to which the speakers 2 are attached as shown in the figure, and are fixed independently to the outer periphery of the exhaust pipe 1. What is necessary is just to employ | adopt well-known appropriate means as a fixing means,
The contents of the above-described embodiment can be implemented, such as forming a Helmholtz resonator for each speaker 2 or providing an air flow path 9 having a silencing function.

With such a configuration, it is possible to freely cope with various exhaust pipes 1 having different sizes, and since the volume and the resonance frequency can be set for each speaker, the silencing process becomes easy and the number of parts is reduced. Therefore, the management is easy and the cost is advantageous. FIG. 6 shows a structure in which the end 1b of the exhaust pipe 1 is extended to the same position as the end 3e of the duct 3, and the opening 3c is formed by providing a cutout 1c in a portion covered by the duct 3. I have. This portion covers the end 3e of the duct 3 as shown in FIG.
Other structures can be adopted, such as forming an opening 3c by providing a hole 1d at the end 1a of the hole.

[0018]

As is apparent from the above description, according to the present invention, a duct for collecting sound waves emitted from a speaker is provided at the front of the speaker, and a small area opening at the tip of the duct is located at the end of the sound source pipe. While forming an ejector, and providing a ventilation hole at a position away from the exhaust gas flow of the sound source pipe,
The air in the duct is sucked out by the exhaust gas flow to cool the speaker , and this cooling air flow path is
The expansion type silencing structure is squeezed on the way . Therefore, since the speaker is cooled and does not touch the gas flow exhausted from the sound source pipe, even when this active silencer is used to muffle engine exhaust, the speaker may be affected by the heat of exhaust gas and specific components. Deterioration can be prevented. In addition, stationary type that cannot use traveling wind
The engine can always provide a sufficient cooling effect during operation
The ventilation holes are located away from the exhaust gas stream
The expansion-type features are also exhibited, and it is sufficient from the low range to the high range
Noise from the cooling air flow path
Not even.

Further, by forming a Helmholtz resonator by the internal volume of the duct and the small area of the opening,
In addition to simply preventing interference between sound waves on the front and rear sides of the speaker, it can positively improve the frequency characteristics of the speaker. For example, the radiation characteristics in the low range can be enhanced to efficiently muffle the low range. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a sectional view of a main part of another embodiment.

FIG. 4 is a sectional view taken along line BB of FIG. 3;

FIG. 5 is an explanatory diagram of frequency characteristic improvement.

FIG. 6 is a sectional view of a main part of another embodiment.

FIG. 7 is a sectional view taken along lines CC and DD in FIG. 6;

FIG. 8 is a modification of the embodiment of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Exhaust pipe (sound source pipe) 1a End part 2 Speaker 2a Speaker box 3 Duct 3a Large diameter part 3b Small diameter part 3c Opening 6 Ventilation hole 7 Air flow path 8 Ventilation flow inlet 9 Air flow path

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F01N 1/00 F01N 1/06

Claims (2)

(57) [Claims] 1. A speaker is arranged at an end of a sound source pipe,
An active silencer configured to have a sound-muffling effect by emitting a sound having a phase opposite to a sound emitted from a sound source pipe from the speaker, and a duct for collecting sound waves emitted by the speaker is provided on a front surface of the speaker. A small-area opening formed inside the distal end of the duct is positioned at the end of the sound source pipe so that an ejector configured to suck air in the duct by a gas flow discharged from the sound source pipe is formed. Duct through a small area ventilation hole located away from the exhaust gas flow of the pipe
An active silencer wherein an air flow path for cooling the speaker is formed to reach the opening through a space having a large volume inside . 2. The active silencer according to claim 1, wherein a Helmholtz resonator is formed by the internal volume of the duct and a small area of the opening.