JP4159032B2 - Device for damping resonance in a conduit - Google Patents

Description

[0001]
【Technical field】
The present invention relates to an apparatus for attenuating resonance in a conduit for conveying exhaust gas from an internal combustion engine.
[0002]
[Background]
In most cases, the exhaust silencer consists of one or more chambers with intermediate conduits. The sound pressure inside the conduit will vary at locations along the conduit. Within the exhaust system, in-pipe resonances can sometimes occur. What happens at that time is that ignition pulses from the engine are reflected between the outlet of the exhaust pipe and the part preceding the exhaust system, often the chamber in the silencer closest to the end pipe. In most cases, this only occurs at a specific engine speed where the wavelength of the ignition frequency matches the length between two adjacent reflector ends.
[0003]
When resonance occurs in the tube, the difference in sound pressure at different locations will be particularly large. In that case, a high sound pressure is generated in the end pipe, and the sound that escapes from the mouth to the surrounding environment becomes louder than in other cases. Conventional solutions to this problem are generally to insert additional silencers, but this can increase costs and increase pressure drop.
[0004]
DISCLOSURE OF THE INVENTION
Accordingly, one object of the present invention is to produce a device that solves this problem without significant price increases and cost increases.
[0005]
To this end, the device according to the invention is characterized in that at least one perforation is provided at a distance from the outer end of the conduit. By configuring the device in this way, an effective reduction of the resonance level is simply brought about.
[0006]
Advantageous explanatory embodiments of the invention emerge from the dependent claims.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
The invention will now be described in more detail with reference to the illustrative embodiments shown in the accompanying drawings.
[0008]
The present invention relates to a device which can be applied to various types of internal combustion engines, for example the exhaust and silencers of engines which function according to the Otto, Diesel or Wankel principle. The engine can be mounted on a vehicle such as a passenger car, a truck, a work vehicle, or a ship. The present invention can also be applied to fixed engine facilities such as engine driven power plants. In that case, the device can be placed at various locations along the tube portion that forms part of the engine exhaust and silencer. Such a tube portion may, for example, form an end tube that carries exhaust gas from the muffler pot to the surrounding environment.
[0009]
FIG. 1 shows a substantially right-angled tube section 10 having an outlet end 11 and an inlet end 12, the wall 13 of which is provided with perforations 14 inside the curvature. Perforations connect the interior of the tube with the surrounding environment. Resonance will occur when a tube portion is attached to an exhaust system, for example, as an end tube, and a pulsating exhaust gas flow is passed through the tube portion. A portion of this resonant sound pressure can escape through the perforations 14 to the surrounding environment. That is, it means that the magnitude of resonance decreases. Thus, the sound escaping from both the mouth and the perforations will originate from a considerably lower sound pressure level. Overall, a small amount of sound is emitted from the exhaust system to the surrounding environment.
[0010]
Since the perforations 14 are located in a portion of the flow passage where the static pressure is relatively lower than the rest of the passage, exhaust can be avoided from being released through the perforations 14.
[0011]
FIG. 2 shows a modified embodiment of the invention on an enlarged scale, in which a number of perforations 14 are provided in the tube wall 13 of the tube 10 in a portion 10a with a slightly reduced flow area. For this reason, the flow rate increases in this part, and as a result, the static pressure in the pipe decreases, that is, the ambient air can be sucked into the pipe through the perforations, and the exhaust gas does not escape.
[0012]
FIG. 3 shows a further modification of the invention, in which a tube wall 13 is provided with a recess 15 in which the flow area is reduced. On the downstream side of the recess 15, a step portion 16 is formed on the tube wall that is substantially perpendicular to the normal cross section. A perforation 14 is disposed on the downstream side of the stepped portion. The exhaust gas flow through the tube portion of FIG. The reduced pressure will draw air from the ambient environment of the tube through the perforations 14.
[0013]
As an alternative to avoiding exhaust gas leaks through the perforations, a partially acoustically permeable material that functions as a flow resistance can be introduced. This material can be deposited on the outside of the tube, inside the tube, or inside the perforation itself. This material can be steel, other metals, glass fibers, fabrics, ceramics, and the like. The material can have structures in the form of, for example, nets, unstructured or structured fabrics, and porous media.
[0014]
FIG. 4 shows a modification of the invention in which a conduit constructed according to FIG. 2 is provided with an outer sleeve 17 covering the perforations and having a number of small perforations 18. The purpose of the outer sleeve 17 is essentially to “hide” the perforations 14. The outer sleeve 17 can also suppress sound leakage through the perforations 14 to some extent. This leakage can be further suppressed by filling the space 19 between the conduit 10 and the outer sleeve with a suitable damping material, such as mineral cotton.
[0015]
FIG. 5 shows another variation of the present invention in which the conduit constructed according to FIG. 2 is provided with an internal cuff formed of an acoustically permeable nonwoven fabric.
[0016]
As can be seen from FIGS. 6 and 7, the perforations 14 can be formed in many different ways. The present invention has holes generally formed in a geometric shape such as, for example, a round shape, a square shape, a V shape, a slot shape or other shapes.
[0017]
The present invention is not limited to the above-described illustrative embodiments, but should be construed as being capable of making various other changes and modifications within the scope of the claims. For example, a device according to the invention can have a combination of multiple tube sections 10 arranged in series or in parallel.
[Brief description of the drawings]
FIG. 1 is a schematic plan view of a portion of a conduit constructed in accordance with a first example of the present invention.
FIG. 2 is a longitudinal cross-sectional view of a portion of a conduit constructed in accordance with a second example of the present invention.
FIG. 3 is a longitudinal cross-sectional view of a portion of a conduit constructed in accordance with a third example of the present invention.
FIG. 4 is a variation of the example of the invention shown in FIG.
FIG. 5 is a variation of the example of the invention shown in FIG.
FIG. 6 shows a portion of the plate wall of the conduit in cross-section and various plan views, each in plan view.
FIG. 7 shows in cross section a portion of the plate wall of the conduit, and shows various examples of perforations, each in plan view.

Claims (3)

In an apparatus for damping resonance in a conduit (10) for conveying exhaust gas from an internal combustion engine, the conduit (10) is spaced from its outer end (11) and slightly downstream. A device provided with at least one perforation (14) only at a point where the static pressure is relatively lower than the pressure of the position , wherein a depression (15) is provided in the tube wall (13) of the conduit (10), A stepped portion (16) that is substantially perpendicular to the outer diameter direction from the tube wall is formed on the downstream side of the recessed portion (15), and the perforation (14) is disposed on the downstream side of the stepped portion (16). The perforation (14) allows a part of the sound pressure of the resonance to escape to the ambient atmosphere through the perforation (14) by communicating between the inside of the conduit (10) and the ambient atmosphere. And the ambient air is guided through the perforations (14). (10) drawn into the apparatus, characterized in the said conduit (10) in that as the exhaust gas does not escape. The low static pressure near the perforations (14) is caused by a change in the direction of gas flow in the conduit, and the change in direction of the gas flow is caused by a curvature of the conduit. The apparatus according to 1 . Said perforations (14), according to claim 1 or 2, characterized in that they are covered by acoustically transparent fabric (20) which can be released inside or outside of the sound pressure of the conduit (10) apparatus.

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