JP4178368B2 - Low frequency attenuation type silencer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a low-frequency attenuation type anti OtoSo location to primarily attenuate low-frequency noise of the internal combustion engine.
[0002]
[Prior art]
The conventional method of attenuating noise from an internal combustion engine expands a part of the exhaust pipe to reduce the noise due to the expansion of the exhaust path, or branches the exhaust pipe path to provide a resonance chamber to resonate the noise. In general, sound absorbing materials such as glass fiber, carbon fiber, and metal fiber are used in combination or independently. In the method of aiming at attenuation by resonance, a cylindrical container is used as a resonance chamber as in Japanese Utility Model Laid-Open No. 1-174562, Japanese Patent Application Laid-Open No. 7-293377, and the volume in the container is changed by moving the piston-shaped lid forward and backward In some cases, the noise frequency to be silenced is adjusted to resonate. Further, as seen in Japanese Patent Application Laid-Open No. 8-137478 and the like, a sensor microphone that detects a noise wave propagating from a noise source and transmits a signal related to the noise wave to an active silencer speaker mechanism via a controller, There is also an example where it is arranged on the entrance side.
[0003]
The basic frequency of a multi-cylinder diesel engine is 20 to 100 Hz and the sound wavelength is as long as 5 to 30 m, and it is necessary to install a silencer with an excessive size for low frequency attenuation. Further, the noise from the marine internal combustion engine (diesel engine) is shown in the graph of FIG. 6 (when a solid line is a source sound and a two-dot chain line is provided with a silencer), from each cylinder of the internal combustion engine to the silencer. Since the exhaust gas piping distance is different, even if it can reduce 10 to 30 dB in the mid-high frequency range, it can hardly reduce the sound in the low frequency range. A possible reason is that, as shown in FIG. 8, in the generation source, as shown in FIG. 8, while a change in pressure (sound pressure) P accompanying periodic exhaust at regular intervals propagates to the silencer, as shown in FIG. In other words, low frequency noise is generated as a “beat” phenomenon.
[0004]
[Problems to be solved by the invention]
Therefore, the present inventors have found that even if the exhaust gas piping distance from each cylinder of the internal combustion engine to the silencer is different, there is no change in pressure (sound pressure) due to periodic exhaust for each cylinder while propagating to the silencer. We studied not to be evenly spaced, and studied to suppress the occurrence of low-frequency noise, which is a “beat” phenomenon. As a matter of course, it is possible to mute in the middle / high sound wave range by installing a muffler.
[0005]
[Means for Solving the Problems]
As a result of studying the above problems, by making the sound pressure propagation distance between each cylinder of the plurality of cylinders of the internal combustion engine and the muffler uniform in the exhaust gas flow path of the internal combustion engine, , in order to implement a low-frequency attenuation type silencer how you mute, so had the following low-frequency attenuation type muffler provided with a phase adjusting section on the upstream side of the silencer unit provided in an exhaust gas passage of an internal combustion engine is there.
[0006]
The silencer in the low frequency attenuation type silencer of this, may Ru provided a gap between the sound-absorbing material provided in an exhaust gas flow path and the silencer casing. The sound absorption rate of the sound absorbing material decreases rapidly in the low frequency range. Therefore, an air layer is provided between the sound absorbing material and the muffler casing to increase the heat insulation effect as well as the sound reduction effect. In addition, the thickness of the sound absorbing material can be increased.
[0007]
The phase adjustment unit in the low frequency attenuating silencer of the present invention, even if the pressure (sound pressure) change accompanying periodic exhaust at regular intervals propagates to the silencer, even if it becomes unequal intervals for each cylinder, again It is a means for performing adjustment to return to periodic exhaust at the original regular intervals. Various mechanisms for the phase adjustment unit are conceivable. For example, although there is a problem in practicality, an exhaust pipe system is installed so that each cylinder has the same length. Most preferred is a structure comprising adjustment pipe groups having different lengths for equalizing the sound pressure propagation distance of each cylinder of the internal combustion engine, and a shutter for selecting one of the adjustment pipe groups. The shutter preferably includes a rotation selection board having a vent hole in a part of the disk and a synchronous motor for driving the rotation selection board. The adjusting tube may be provided with a means for silencing such as a resonance chamber or an expansion chamber in the hollow tube.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a side view of an example in which a low frequency attenuation type silencer of the present invention is provided in a diesel engine. FIG. 2 is a cross-sectional view of the phase adjustment unit, and FIG. 3 is a cross-sectional view taken along line AA in FIG. The internal combustion engine 1 shown in this example is a 6-cylinder diesel engine having cylinders C1, C2, C3, C4, C5, and C6. A phase adjusting unit 3 and a silencer 4 are provided on the downstream side of the exhaust pipe 2 serving as an exhaust gas channel. The phase adjustment unit 3 is on the upstream side of the muffling unit 4. Sound pressure propagation distance to reach the phase adjusting unit 3 of the cylinder C1 is the longest, sequentially C2, C3, C4, C5, C6 and sound pressure propagation distance becomes longer.
[0009]
A structural example of the phase adjustment unit 3 is shown in FIG. There are an exhaust gas inlet 5 and an exhaust gas outlet 6 communicating with the cylindrical casing 3a through the exhaust gas passage of the exhaust pipe 2. Exhaust gas from the exhaust gas outlet 6 flows to the silencer 4. Inside the cylindrical casing 3a, a rotation selection board 7 is installed so as to be rotated by a synchronous motor 8. The rotation selection board 7 is provided with a vent hole 7a. The synchronous motor 8 rotates the rotation selection board 7 in synchronization with the driving of the cylinders C1, C2, C3, C4, C5 and C6.
[0010]
Similarly, phase adjusting tubes D1, D2, D3, D4, D5, and D6 having different sound pressure propagation distances are arranged concentrically within the cylindrical casing 3a. When the rotation selection board 7 is rotated, the vent hole 7a matches one of the phase adjustment pipes D, and the exhaust gas inlet 5, the phase adjustment pipe D, and the exhaust gas outlet 6 can be communicated with each other. In this example, the phase adjustment tube D is a hollow tube, but if necessary for sound silencing performance, means having a silencing action such as a resonance chamber or an expansion chamber may be provided in the hollow tube. The phase adjusting tubes are formed shorter in the order of D1-D2-D3-D4-D5-D6. The order of arrangement on the concentric circles is the firing order of D1-D5-D3-D6-D2-D4 in the rotational direction so as to correspond to the sound pressure propagation distances that are different in length. In the case of the maximum sound pressure propagation distance difference (maximum phase difference distance) L, the length of the longest phase adjusting tube D1 is suitably L / 2 to L.
[0011]
In the case of a diesel engine, the ignition sequence is ignited in the order of cylinders C1-C5-C3-C6-C2-C4 to provide a smooth drive source. As a result, the pressure (sound pressure) change associated with the conventional periodic exhaust for each cylinder in the above-described manner is propagated, resulting in unequal intervals (FIG. 8), resulting in a “beat” phenomenon. However, this problem is solved by providing the phase adjusting unit 3 upstream of the silencer 4 in the exhaust gas passage as in the present invention. That is, corresponding to the change in the sound pressure propagation distance of C1-C5-C3-C6-C2-C4 in the cylinder firing order, the arrangement order on the concentric circles is D1-D5-D3-D6-D2-D4 The ventilation hole 7a of the rotation selection board 7 which is the shutter of the base of the phase adjusting tube is rotated synchronously by the synchronous motor 8, and the silencer is selected while sequentially selecting the phase adjusting tubes D1-D5-D3-D6-D2-D4. The sound pressure propagation distance reaching 4 is adjusted (the sound pressure propagation distance is made uniform), and the phase is adjusted so that the sound pressure changes periodically (see FIG. 7) at regular intervals.
[0012]
FIG. 4 is a cross-sectional view of the silencer 4. The muffler 4 is disposed downstream of the phase adjuster 3, and silences the exhaust gas whose phase is adjusted by the phase adjuster 3 to periodically change sound pressure at regular intervals. The structure of the silencer 4 is a structure in which a gap 11 (50 to 300 mm) is provided between the silencer casing 9 and the sound absorbing material 10. The sound absorbing material 10 is provided so as to absorb sound from the outer periphery of the exhaust gas flow path, and the sound absorption rate of the sound absorbing material 10 rapidly decreases in the low frequency range. Therefore, the sound absorbing action in the low frequency region is increased by providing a gap 11 between the sound absorbing material 10 and the sound absorbing portion casing 9 and providing an air layer.
[0013]
This is shown in FIG. In addition to being able to reduce 10 to 30 dB in the mid-high sound range, it is also possible to reduce 20 dB in the low frequency range.
[0014]
【The invention's effect】
Low frequency attenuation type anti OtoSo location of the present invention, when the exhaust gas pipe distance from each cylinder to the muffler of a plurality of the internal combustion engine is different from the pressure (sound pressure) caused by periodic evacuation of each cylinder changes not Even in the case of equal intervals, the phase adjustment unit adjusts the phase to periodic sound pressure changes at regular intervals while propagating to the silencer, thus suppressing the occurrence of low-frequency noise, which is a “beat” phenomenon. can do.
[0015]
Moreover, in addition to the mid- and high-acoustic range silencing in the silencing section, the gap section is provided, so that the bass section can be muted. This eliminates the need for excessively sized silencers that were previously difficult, especially for low frequency attenuation in ships.
[Brief description of the drawings]
FIG. 1 is a side view of an example in which a diesel engine is provided with a low-frequency attenuation type silencer of the present invention.
FIG. 2 is a cross-sectional view of a phase adjustment unit.
FIG. 3 is a cross-sectional view taken along line AA in FIG.
FIG. 4 is a cross-sectional view of a silencer.
FIG. 5 is a graph of sound pressure measurement results for each frequency when the source sound and the silencer of the present invention are provided.
FIG. 6 is a graph of sound pressure at each frequency when a source sound and a conventional silencer are provided.
FIG. 7 is a graph showing changes in pressure (sound pressure) associated with periodic exhaust at regular intervals at a generation source;
FIG. 8 is a graph showing changes in pressure (sound pressure) that are unequal intervals during propagation to the silencer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Internal combustion (diesel) engine 2 Exhaust pipe line 3 Phase adjustment part 4 Silencer part 5 Exhaust gas inlet 6 Exhaust gas outlet 7 Rotation selection board 8 Synchronous motor 9 Silencer casing
10 Sound absorbing material
11 Gap
C1, C2, C3, C4, C5, C6 cylinder
D6, D5, D4, D3, D2, D1 Phase adjustment tube

Claims (2)

In a low- frequency attenuation type silencer having a phase adjuster upstream of the silencer provided in the exhaust gas flow path of the internal combustion engine , the phase adjuster equalizes the sound pressure propagation distance of each cylinder of the internal combustion engine A low-frequency attenuation type silencer comprising: an adjustment tube group having different lengths; and a shutter for selecting one of the adjustment tube groups. Shutter and rotating selection plate with vent holes on a part of the disc is the low-frequency attenuation type silencer synchronous motor and consists of claim 1, wherein the said rotary selection plate driving.

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