JP2003041934A - Exhaust system tail pipe - Google Patents

Abstract

(57) [Problem] To be manufactured easily and inexpensively with a simple structure, and to achieve both an increase in exhaust flow rate due to a reduction in pressure loss and a reduction in airflow noise due to exhaust gas at an excellent level. A tail pipe (10) is connected to a discharge pipe (9e) from a muffler (9), and has a connection part (10a) extending substantially linearly and substantially rearwardly with the same diameter as the discharge pipe (9e). And an enlarged-diameter portion 10b having a substantially elliptical cross-sectional shape. The elliptical shape, which is a cross section of the enlarged diameter portion 10b of the tail pipe 10,
The major axis is in the vehicle width direction and the minor axis is in the vertical direction. Both the major axis and the minor axis are formed larger than the diameter of the connecting portion. The elliptical aspect ratio is preferably between 1.2 and 1.4, and is about 1.3 in the present embodiment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust system tail pipe arranged at a rear end of an exhaust pipe from an engine.

[0002]

2. Description of the Related Art Conventionally, in the tail pipe of an engine exhaust system, in order to cope with high engine output, instead of a circular pipe tail pipe having a small diameter of exhaust gas,
A so-called diffuser-type tail pipe, which has a small pressure loss and spreads backward, is often used. But,
This conventional diffuser-type tail pipe has a problem in that fluctuations in the flow of exhaust gas increase, air flow noise is excited, and the air flow sound level becomes higher than that of a circular pipe tail pipe.

Therefore, for example, Japanese Patent Laid-Open No. 8-170518
Japanese Patent Laid-Open Publication No. 2004-242242 discloses a technique for avoiding a decrease in output due to an increase in exhaust resistance and the generation of air flow noise by providing a diffuser type tail pipe with a porous surface on the wall surface and providing a glass wool storage chamber on the outside thereof. . In addition, JP-A-6-2
Japanese Patent No. 80558 discloses a technique capable of reducing air flow noise by using a double pipe tail pipe.

[0004]

However, in the former case of the above-mentioned prior art, since glass wool is used, the structure is complicated and the cost is high, and the sound absorbing performance is deteriorated due to clogging of the glass wool and the glass wool is deteriorated due to high temperature gas. Durability problems will occur. Also in the latter case of the above-mentioned prior art, since the tail pipe is a double pipe, the structure is complicated, the manufacturing is difficult, and the cost becomes high.

The present invention has been made in view of the above circumstances.
It is an object of the present invention to provide an exhaust system tail pipe that can be manufactured easily and inexpensively with a simple structure and that can achieve an excellent level of both an increase in exhaust flow rate due to a reduction in pressure loss and a reduction in air flow noise due to exhaust gas. To do.

[0006]

In order to achieve the above object, a tail pipe for an exhaust system according to claim 1 of the present invention comprises:
In the tail pipe of the exhaust system disposed at the rear end of the exhaust pipe from the engine, a connecting portion that connects to the rear end of the exhaust pipe, and a rearwardly extending portion that extends rearward from the connecting portion, and has a substantially horizontal cross-sectional shape. It is characterized by having an enlarged diameter portion formed in an elliptical shape.

That is, in the exhaust system tail pipe according to the first aspect of the present invention, the exhaust flow rate can be increased by extending the enlarged diameter portion rearward from the connecting portion.
Further, by making the cross-sectional shape of the expanded diameter portion substantially elliptical, it is possible to reduce the fluctuation of the flow, which is the exciting force of the air flow noise, and therefore noise can be reduced. Furthermore, it can be realized without using glass wool or the like and without using a special structure such as a double tube structure, and can be manufactured easily and inexpensively with a simple structure.

In this case, preferably, the elliptical shape of the cross section of the expanded diameter portion is formed such that both the major axis and the minor axis are larger than the diameter of the connecting portion. Further, as described in claim 3, the cross section of the expanded diameter portion has an elliptical shape with an aspect ratio of 1.2 to 1.4.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 1 to 7 relate to an embodiment of the present invention, and FIG. 1 is a schematic configuration diagram of an intake and exhaust system of an engine,
2 is an explanatory view of the muffler and the tail pipe, FIG. 3 is an explanatory view of the shape of the tail pipe, FIG. 4 is an explanatory view comparing the flow velocity distribution of the air flow when discharged into the atmosphere with a conventional tail pipe, FIG. Is an explanatory diagram comparing the correlation between sound pressure measured by a microphone and flow velocity fluctuation with a conventional tail pipe, FIG. 6 is an explanatory diagram comparing the velocity fluctuation level with a conventional tail pipe, and FIG. 7 is a sound pressure level. It is explanatory drawing compared with the conventional tail pipe.

In FIG. 1, reference numeral 1 indicates an engine,
An intake pipe 3 communicates with an intake port 1a of the engine 1 via an intake manifold 2, and an air cleaner (not shown) is provided at the uppermost stream of the intake pipe 3. Further, a throttle valve 4 is provided in the middle of the intake pipe 3, and an air chamber 5 connected to the collecting portion of the intake manifold 2 is formed downstream of the throttle valve 4. Further, an injector 6 whose injection direction is directed to the intake port 1a side is fixed to the intake manifold 2.

On the other hand, an exhaust pipe 7 is connected to the exhaust port 1b of the engine 1, and a three-way catalyst 8 for purifying harmful components (CO, HC, NOx) in the exhaust gas is provided in the middle of the exhaust pipe 7. The muffler 9 is connected to the tail pipe 10 downstream of the muffler 9. Reference numeral 11 is an ignition plug.

The muffler 9 is, for example, as shown in FIG.
The exhaust pipe 7 has a first chamber 9a, a second chamber 9b, and a third chamber 9c, and has a known resonance, expansion, and sound absorption function to muffle sound.
The exhaust gas guided to the third chamber 9c reaches the first chamber 9a through the perforated pipe 9d provided in the second chamber 9b, and is discharged to the tail pipe 10 through the discharge pipe 9e.

The tail pipe 10 is, as shown in FIG.
A connecting portion 10a which is connected to the discharge pipe 9e from the muffler 9 and extends rearward in a straight line with a diameter substantially equal to that of the discharge pipe 9e, and a rearward-spreading extending from the connecting portion 10a, and has a cross-sectional shape. The enlarged diameter portion 10b is formed in a substantially elliptical shape.

The total length of the tail pipe 10, that is, the length L including the connecting portion 10a and the expanded diameter portion 10b is formed to be 162 mm, for example. The length of the enlarged diameter portion 10b is formed to be approximately 2 to 3 times the diameter of the connecting portion 10a.

The elliptical shape which is the cross section of the enlarged diameter portion 10b of the tail pipe 10 has a major axis in the vehicle width direction (Y axis direction) and a minor axis in the up and down direction (Z axis direction). The angle at which the diameter gradually increases in the vehicle width direction, that is, FIG. 3 (a)
The inside θy is about 10 °. Also, the ellipse is
The angle at which the diameter gradually increases in the vertical direction, that is, FIG.
Θz in (b) is about 4 °. The elliptical aspect ratio is preferably between 1.2 and 1.4, and is about 1.3 in this embodiment.

Further, the expansion rate Ae2 / Ae1 flow of the cross section of the expanded diameter portion 10b of the tail pipe 10 (Ae1: the cross-sectional area of the constant diameter circular pipe portion before expansion, Ae2: the cross-sectional area of the atmosphere discharge portion after expansion) is It is formed at 2.0.

By constructing the tail pipe 10 as described above, it is possible to reduce the pressure loss as compared with a straight pipe tail pipe having a constant diameter. Specifically, it has been confirmed by experiments that the flow rate increases by about 1.7 under a constant load condition by forming the expanded diameter portion 10b as described above.

FIG. 4 is a flow velocity distribution when the air flow is discharged into the atmosphere from the tail pipe, and FIG. 4 (a) shows a result with a conventional tail pipe having a circular cross section and a diffuser shape, and FIG. ) Is the tail pipe 10 according to the present embodiment.
The results are shown below. P1 in FIG. 4A and FIG.
The position of each point of P2 in (b) is the position where the flow velocity fluctuation in each tail pipe is the maximum.
As can be seen from FIG. 4B, since the tail pipe 10 according to the present embodiment is an enlarged tail pipe having an elliptical cross section, the flow can be biased with respect to the main flow direction, and a strong flow fluctuation (vortex) is generated. (Variation) can be prevented, so that the flow fluctuation level becomes smaller than that of the conventional tail pipe, and the reduction of air flow noise is realized.

Further, FIG. 5 shows that the flow direction is 45 °,
6 is a contour diagram showing the correlation between sound pressure measured by a microphone installed at a position 500 mm away from the center of the tail pipe rear end cross section and flow velocity fluctuation. Figure 5
FIG. 5A shows a result with a conventional tail pipe having a circular cross section and a diffuser shape, and FIG. 5B shows a result with the tail pipe 10 according to the present embodiment. The position where the correlation between the sound and the velocity fluctuation of the flow (vortex fluctuation) is large (the position where the sound easily becomes sound) is P3 in FIG. 5A and P in FIG. 5B.
The positions of the respective points of No. 4 and the respective speed fluctuation levels are shown in FIG. Here, both the conventional tail pipe and the tail pipe 10 according to the present embodiment have substantially the same pipe length, and therefore have the same resonant frequency for excitation. Further, in the tail pipe 10 according to the present embodiment, the speed fluctuation (vortex fluctuation) that is an exciting force can be reduced, so that it is possible to reduce the excited air flow sound level.

Further, FIG. 7 shows the sound pressure level measured using a microphone. The peak frequency corresponds to the resonance frequency of the pipe length of the tail pipe. The pipe length is
Since both the conventional tail pipe and the tail pipe 10 according to the present embodiment are substantially the same, the resonance frequencies to be excited are also the same. As can be seen from FIG. 7, since the sound generated from the tail pipe 10 according to the present embodiment has a large high frequency component, the overall level becomes higher than that of the conventional tail pipe. However, the peak level of sound pressure, which is the most important in terms of feeling, can be reduced compared to the conventional tail pipe (especially 350).
It becomes remarkable in the vicinity of Hz and 650 Hz).

Further, the tail pipe 1 according to the present embodiment.
At 0, both pressure loss and air flow noise can be achieved without using a sound absorbing material such as glass wool, so that problems such as durability and performance deterioration do not occur.

[0022]

As described above, according to the present invention,
It can be manufactured easily and inexpensively with a simple structure, and it is possible to achieve both an increase in the exhaust flow rate due to a reduction in pressure loss and a reduction in air flow noise due to exhaust gas at an excellent level.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an intake and exhaust system of an engine.

FIG. 2 is an explanatory view of a muffler and a tail pipe.

FIG. 3 is an explanatory diagram of the shape of the tail pipe.

FIG. 4 is an explanatory diagram comparing the flow velocity distribution of the air flow when discharged into the atmosphere with a conventional tail pipe.

FIG. 5 is an explanatory diagram comparing the correlation between sound pressure measured by a microphone and flow velocity fluctuation with a conventional tail pipe.

FIG. 6 is an explanatory diagram comparing the speed fluctuation level with a conventional tail pipe.

FIG. 7 is an explanatory diagram comparing the sound pressure level with a conventional tail pipe.

[Explanation of symbols]

1 engine 7 exhaust pipe 8 three-way catalyst 9 muffler 10 tail pipe 10a connecting part 10b Expanding part

Claims (3)

[Claims] 1. A tail pipe of an exhaust system disposed at a rear end of an exhaust pipe from an engine, a connecting portion connecting to a rear end of the exhaust pipe, and a rearwardly extending portion extending from the connecting portion, and A tail pipe for an exhaust pipe, comprising: an enlarged diameter portion having a substantially elliptical cross section. 2. The tail pipe for an exhaust system according to claim 1, wherein the elliptical cross section of the expanded diameter portion has a major axis and a minor axis both larger than the diameter of the connecting portion. 3. The exhaust system according to claim 1, wherein the enlarged diameter portion has an elliptical cross-section with an aspect ratio of 1.2 to 1.4. Tail pipe.