JPH0214962B2 - - Google Patents

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 the center tube 2 and a tail tube 4. It will be done.

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

However, in the case of such a silencer, since the pre- and main mufflers 3 and 5 described above have a silencing structure mainly aimed at reducing low and medium frequency components of exhaust noise, high-frequency airflow noise is In addition, if the inner diameter of the tail tube 4, etc. was enlarged in order to reduce the high frequency components of airflow noise, there was a problem in that the low frequency components deteriorated and indoor noise increased.

In addition, examples of using sound absorbing materials made of porous materials 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 has been made in view of these conventional problems, and an object of the present invention is to provide an exhaust silencing device that can effectively reduce exhaust noise in a wide frequency band including high frequencies.

Therefore, in this invention, the rear end of the tail tube forming the engine exhaust system is made of a sintered alloy such as aluminum powder, which has approximately the same inner diameter as the tail tube and has a porosity of 30 to 60%. An outer cylinder is provided which connects the open end of the sound absorbing cylinder, covers the outside of the sound absorbing cylinder, and extends rearward from the rear end of the sound absorbing cylinder, and between the outer cylinder and the sound absorbing cylinder, an outer cylinder is provided. A circumferential gap was formed that was open to the atmosphere and communicated from the upstream end to the downstream end.

According to this, while the acoustic sound absorbing effect as a porous sound absorbing material is obtained in the sound absorbing cylinder part,
Since the flow velocity of the exhaust gas is reduced by the diffusion effect of the gas flow in the pipe from the outer surface of the sound absorbing cylinder, the high-frequency jet noise generated behind the tail tube is reduced.

At the same time, the above-mentioned outer cylinder forms a back air layer with a predetermined circumferential gap outside the sound-absorbing cylinder, thereby reducing the sound of a predetermined frequency component of the exhaust sound transmitted through the sound-absorbing cylinder. .

Furthermore, since the sound absorbing tube is open at both ends, there is no increase in exhaust pressure.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

As shown in FIGS. 2A and 2B, the feature of this embodiment is that the rear end (discharge port) 4A of the tail tube 4
A sound absorbing tube 7 of a predetermined length (for example, about 170 mm) made of a porous material having air permeability and molded (fired) is connected to the sound absorbing tube 7 via a connector 6, which will be described later. The point is that an outer cylinder 8 made of a metal plate is disposed on the outside. The length of the outer cylinder 8 is slightly longer than that of the sound absorbing cylinder 7, and the outer cylinder 8 is arranged slightly shifted toward the rear (downstream side of the exhaust flow).

The sound absorbing tube 7 is formed into a true cylinder with an inner diameter that is approximately the same as that of the tail tube 4, while the outer tube 8 is formed with a rectangular cross section, and there is a circumferential gap between the sound absorbing tube 7 and the sound absorbing tube 7 in the vertical and horizontal directions in the figure. The rear air layer A with different values is now defined.

The upstream end of the circumferential gap may be open to the atmosphere or closed, but at least the downstream end thereof is open to the atmosphere.

Furthermore, the sound-absorbing cylinder 7 is provided with a front end and a rear end 7 in order to prevent damage due to easy thermal deformation, especially when the sound-absorbing cylinder 7 is formed into a cylinder shape by half-molding a plate-like cell material.
A and 7B are elastically supported with respect to the connector 6 and the outer cylinder 8.

That is, the tip portion 6A fits into the rear end portion 4A of the tail tube 4, and the rear end (support) portion 6B is slightly enlarged in diameter and has a large cutout on the side so that it becomes bifurcated in the vertical direction. On the inner peripheral surface of the connector 6,
An annular mounting bracket 9 whose cross section is approximately U-shaped and whose outer surface is bent into a chevron shape to provide a spring function is attached by welding. The tip portion 7A is inserted and supported. On the other hand, the inner circumferential surface of the outer cylinder 8 whose tip center portion 8A is welded to the outer periphery of the rear end portion 6B of the connector 6 and is supported in a cantilever manner has a spring function at two locations at its lower part. A hook-shaped mounting bracket 10 is attached by welding to the mounting bracket 10, and the rear end portion 7B of the sound absorbing cylinder 7 is inserted and supported by this mounting bracket 10.

The porous material of the sound absorbing tube 7 may be sintered metal such as aluminum powder, ceramics, single or multiple wire mesh, etc., with a porosity of 30% to 60% for a given volume.
% are selected.

The wall thickness of the sound absorbing tube 7 is approximately 2 to 4 mm, and the outer tube 8 is set as thin as possible in terms of weight reduction.

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 (or low-frequency) exhaust noise that has not been muffled by the pre-muffler 3 and main muffler 5 (see Figure 1) is caused by a jet stream behind the discharge port 4A of the tail tube 4, as described above. It tries to be released as noise.

However, in this embodiment, since the sound absorbing tube 7 made of a porous material and the outer tube 8 made of a metal plate are connected to the rear end of the tail tube 4 in a double tube structure, first the sound absorbing tube 7 is connected to the rear end of the tail tube 4. As a porous sound absorbing material, an acoustic sound absorbing effect (damping effect such as friction, small expansion, contraction, etc.) is produced in the part, and the noise is absorbed and eliminated as it is repeatedly reflected in the part of the sound absorbing tube 7.

At the same time, since the sound absorbing tube 7 has high air permeability, a part of the exhaust air diffuses through the sound absorbing tube 6, and the 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 pressure of the gas flow in the tube is reduced. As the flow rate gradually decreases, the flow velocity distribution becomes smoother, and as a result, the maximum flow velocity of the exhaust gas, which is the energy source of the jet noise, can be reduced without expanding the inner diameter of the tail tube 4, and the difference between the diffused gas and the air flow in the circumferential gap can be reduced. Since the mixing is carried out over a wide area around the outer periphery of the sound absorbing cylinder 7, no jet vortex is generated, and therefore high frequency jet noise is significantly reduced.

On the other hand, in the outer cylinder 8 section, a rear air layer A with a predetermined circumferential gap is formed, so that the frequency band corresponding to each circumferential gap of the exhaust sound transmitted through the sound absorbing tube 7 also exists in this part. noise is reduced.

This is mainly because the exhaust gas flowing out from the outer surface of the sound-absorbing cylinder gradually mixes with the atmosphere introduced between the sound-absorbing cylinder and the outer cylinder and diffuses therein.

As a result, a sound absorption effect over a wide frequency band can be obtained as shown in FIG. In the figure, the solid line indicates the conventional example, the chain line indicates only the sound absorbing tube 7, and the broken line indicates the noise level characteristic due to the double pipe structure of the present embodiment.

As can be seen from FIG. 5, the length (effective length l) of the sound absorbing tube 7 is preferably made as long as possible in terms of design. That is, FIG. 5 shows the length of the sound absorbing tube 7 on the horizontal axis and the amount of overall noise reduction relative to this on the vertical axis.

In addition, in this embodiment, the double pipe structure described above also provides a function as a differential user, and the exhaust gas temperature is effectively lowered, so that the adverse effects of high temperature exhaust gas being discharged can be prevented.
In particular, since the sound absorbing tube 7 does not block the discharge port 4A of the tail tube 4 in any way, the exhaust pressure does not increase.

Next, FIGS. 3A and 3B show another embodiment of the present invention. By changing the cross-sectional shape of the outer cylinder 8, the rear air layer I is made wider, and sound absorption in a wider frequency band is achieved. This is an example of aiming for effectiveness. In other words, in FIG. 3A, the outer cylinder 8 is formed in concentric circles to reduce the noise of one type, and in FIG. 3B, it is formed in an ellipse to reduce the noise of at least two types of frequency components.

As explained above, according to the present invention, the rear end of the tail tube is made of a sintered alloy such as aluminum powder, which has approximately the same inner diameter as the tube and has a porosity of 30 to 60%, and is a straight tube with an open rear end. At the same time, an outer cylinder is provided that covers the outside of the sound-absorbing cylinder and extends rearward from the rear end of the sound-absorbing cylinder, and between this outer cylinder and the sound-absorbing cylinder, the upstream side of the outer cylinder is provided. By forming a circumferential gap that is open to the atmosphere and communicating from the end to the downstream end, in addition to acoustically silencing the exhaust gas flow in the sound absorbing tube, hydrodynamic silencing effects such as boundary layer control and diffusion are implemented. By doing so, jet noise, which is the main exhaust noise, is reduced, so exhaust noise in a wide frequency band including high frequencies can be effectively reduced without increasing exhaust pressure.

In addition, in the present invention, the sound absorbing tube is made of a sintered alloy made of aluminum powder, etc., so it can be expected to have an excellent acoustic sound absorbing effect unique to the material. Another advantage is that the burden can be reduced.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of a conventional device, Fig. 2A is a longitudinal sectional front view of a main part of an embodiment of the present invention, Fig. 2B is a sectional view taken along line A-A of Fig. side view,
FIGS. 3A and 3B are longitudinal sectional side views of other embodiments of the present invention, and FIGS. 4 and 5 are characteristic diagrams showing the noise reduction effect of the present invention. 4...Tail tube, 4A...Rear end, 6...
...Connector, 7...Sound absorbing tube, 8...Outer tube, I...
rear air layer.

Claims (1)

[Claims] 1 At the rear end of the tail tube that forms the engine exhaust system, a tube with approximately the same inner diameter as the tail tube and a porosity of 30~
It is made of a sintered alloy such as 60% aluminum powder, and is a straight pipe that connects the tip of a sound-absorbing tube with an open rear end, covers the outside of the sound-absorbing tube, and extends rearward from the rear end of the sound-absorbing tube. An automobile exhaust silencer characterized in that a cylinder is disposed, and a circumferential gap is formed between the outer cylinder and the sound-absorbing cylinder, which is open to the atmosphere and communicates from the upstream end to the downstream end of the outer cylinder. Device.