JPS59190420A - Exhaust-noise suppressing apparatus for car - Google Patents

Abstract

PURPOSE:To effectively reduce the exhaust noise in a high frequency range by installing a noise suppressing cylinder which is made of porous material and has the equal inside diameter to that of a tail tube, at the rear edge of said tail tube. CONSTITUTION:A tail tube 4 is connected to a main muffler 5, and a noise suppressing cylinder 6 which is made by molding or firing the porous material having airing performance and has a prescribed length is connected to a discharge port 4A at the rear edge. Said noise suppressing cylinder 6 is fixed by a fixing metal fitting 7, after the front edge part is superposed by a prescribed length from outside onto the rear edge part 4A of the tail tube 4.

Description

[Detailed description of the invention] The present invention relates to an exhaust muffling device for an automobile.

In general, engine exhaust noise in automobiles is muffled (attenuated) by a muffler (silencer) interposed in the middle of the exhaust pipe, which is piping under the floor of the vehicle body.

For example, as shown in FIG. 1, a pre-muffler 3 is first interposed between a front tube 1 and a center tube 2, which are pipes under the floor of the vehicle body, and a main muffler 5 is interposed between jHj of the center tube 2 and tail tube 4. It will be done.

The pre-muffler 3 is formed in a relatively small size and has a resonant muffler structure, while the main muffler 5 has a large multi-chamber structure that reduces noise (silences) through the interaction of resonance and expansion. It is.

However, in such a muffling device, the above-mentioned brie and main muffler 3, 5 have a muffling structure mainly aimed at reducing low and medium frequency components in exhaust noise.
There is a problem in that the effect of reducing high-frequency airflow noise is not sufficient, and if the inner diameter of the tail tube 4 etc. is expanded to reduce the high-frequency components of airflow noise, the low-frequency components worsen and indoor noise increases. there were.

Incidentally, examples of using a sound absorbing material made of porous material have been proposed in Utility Model Application No. 56-22412 and No. 56-154514 to reduce exhaust noise in the high frequency range. Since both are configured to block the exhaust pipe etc. with a sound-absorbing material, they have the disadvantage that the exhaust pressure increases and the output performance of the engine decreases significantly.

The present invention was made in view of these conventional problems, and it is an object of the present invention to provide an exhaust silencing device that can effectively reduce exhaust noise in a high frequency range.

To this end, in the present invention, the rear end of the tail tube that forms the engine exhaust system has an inner diameter that is approximately the same as the inner diameter of the tail tube, and is constructed by connecting a sound absorbing tube made of a porous material. .

According to this, the above-mentioned sound-absorbing tube has an acoustic sound-absorbing effect as a porous sound-absorbing material and a diffusion effect (lower flow velocity) of the gas flow inside the tube from the outer surface of the sound-absorbing tube, which occurs behind the tail tube. High frequency jet noise is reduced.

Furthermore, since it is a sound absorbing tube with openings at both ends, there is no increase in exhaust pressure.

An embodiment of this invention will be described below based on the drawings.

As shown in FIGS. 2 (8) and (B), the feature of this embodiment is that the rear end (discharge port) 4A of the tail tube 4 is molded (fired) using a porous material having air permeability. Sound absorbing cylinders 6 having a predetermined length, for example, approximately 170 +n1n, are connected to each other.

The sound absorbing tube 6 has its front end connected to the rear end 4 of the tail tube 4.
After being superimposed on A from the outside for a predetermined length, it is fixed with a fixing fitting 7 such as a C clamp.

Therefore, the inner diameter of the sound absorbing cylinder 6 is larger than the inner diameter of the tail tube 4 by the thickness of the tail tube 4, but since the wall thickness of the tail cove 4 made of thin sheet metal is originally small, there is no big difference and the inner diameters are considered to be approximately the same. . Oh, sound absorbing tube 6
The wall thickness is approximately 2N*Tn~4. It is mm.

In addition, porous materials include sintered metals such as aluminum powder,
Ceramics, -it or multiple wire meshes, etc., with a b'f10 ratio of 30% to 60% for a given volume are selected.

The rest of the configuration is the same as that in FIG. 1, so a detailed explanation will be omitted here with reference to FIG.

Because of this configuration, the high-frequency exhaust noise that was currently being muffled by the pre-muffler 3 and main muffler 5 (see Figure 1) becomes jet noise behind the four discharge ports of the tail tube 4, as described above. is about to be released.

However, in this embodiment, since the sound absorbing tube 6 made of a porous material is connected to the rear end of the tail cove 4, the sound absorbing tube 6 has an acoustic sound absorbing effect (M friction, Attenuation effects such as small expansions and contractions occur), and the noise is absorbed and eliminated as it is reflected repeatedly at the sound absorbing cylinder 6.

At the same time, since the sound absorbing tube 6 has high air permeability, a part of the exhaust air diffuses through the sound absorbing tube 6, and a boundary layer that would otherwise be formed on the inner wall of the tube due to the viscosity of the fluid is not generated, so the flow rate of the gas flow inside the tube is reduced. The distribution is smoothed, and as a result, the maximum flow velocity of the exhaust gas, which is the energy source of the jet noise, is reduced without expanding the inner diameter of the tail tube 4, and high-frequency jet noise is significantly reduced. On the other hand, since the sound absorption @6 does not block the discharge port 4A of the tail tube "4", the exhaust pressure does not increase.

Experimental data by the applicant regarding these are shown in FIGS. 4 and 5.

In FIG. 4, it can be seen that the exhaust noise in the picture frequency range is significantly reduced by the sound-absorbing tube 6 as compared to that without the sound-absorbing tube 6 (see the shaded area in the figure), while in FIG. It can be seen that the amount of noise reduction can be further increased by making the length l as long as possible in terms of design.

Next, FIGS. 3(4) and 3(B) show another embodiment of the present invention.

This is an example in which a metal perforated thin plate 8 is attached to the outer surface of the sound absorbing tube 6 to improve the mounting strength, appearance, etc. while maintaining the above-described diffusion effect of the sound absorbing tube 6.

As explained above, according to the present invention, a sound absorbing tube made of a porous material having the same inner diameter as that of the tail tube is connected to the rear end of the tail tube. A good sound absorption effect and a diffusion effect of the gas flow in the tube can be obtained, and the effect that the jet noise generated at the rear of the tail tube can be effectively reduced by Vζ without increasing the exhaust pressure can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a conventional device, FIG.
Fig. 3 (5) and a3) are a sectional view and a perspective view of a main part of another embodiment of this invention, and Figs. 4 and 5 are characteristic diagrams showing the noise reduction effect of this invention. . 4...Tail tube, 4A...Rear end portion, 6...Sound absorbing tube, l...Effective length, Patent applicant Nissan Motor Co., Ltd.

Claims (1)

[Claims] 1. An exhaust silencer for an automobile, characterized in that a sound absorbing tube made of a porous material and having an inner diameter substantially the same as the inner diameter of the tail tube is connected to the rear end of a tail tube forming an engine exhaust system.