JPS6158647B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust system for an internal combustion engine that improves the noise prevention effect.

Conventionally, the exhaust system of an internal combustion engine is composed of relatively thin-walled pipes, so the strong pressure waves of the exhaust flow cause the pipe walls to vibrate. In the expansion chamber, the amplitude of the pressure wave is large, so the vibration is large, and this is propagated to the surrounding atmosphere and causes noise.

As a countermeasure to this problem, increasing the thickness of the tube wall to increase its rigidity has been considered, but this not only causes problems such as processing difficulties and increased costs, but also has an insufficient effect in preventing vibration noise.

This invention was made based on the above-mentioned circumstances, and an object thereof is to obtain an exhaust system for an internal combustion engine that is effective in preventing noise due to the high vibration absorption capacity of the pipe wall, is easy to manufacture, and can be provided at a low cost. shall be.

That is, in order to achieve the above object, the present invention provides a first expansion chamber with a double pipe structure over its entire length, in which the cross-sectional area of the passage increases as it progresses toward the downstream side of the exhaust gas. The inner and outer diameters of the material constituting the inner tube are the same, and a concave portion is provided around the inner tube that continues in the axial direction, and when the inner tube is inserted into the outer tube, the diameter of the inner tube is reduced using the concave portion as an escape. In addition, the tubes are brought into close contact with each other by the elastic restoring force of the concave portion, and a tension force is applied to the outer tube.

The present invention will be explained below based on an embodiment shown in the drawings.

Figures 1 to 3 show the structure of the exhaust system,
Reference numeral 2 in the figure is an exhaust pipe led out from an exhaust port of an internal combustion engine, and an exhaust pipe 1 having a muffling mechanism 3 installed therein is connected to the downstream side of the exhaust pipe 2.
The muffling mechanism 3 has a tapered first expansion chamber 4 in the upstream part of the exhaust gas connected to the exhaust pipe 2, the passage cross-sectional area of which increases toward the downstream side of the exhaust pipe compared to the exhaust pipe 2. On the downstream side of the exhaust gas, there is a partition plate 5...
..., a plurality of expansion chambers 8 and contraction chambers 9 formed by the inner cylinder 6 and the spacer 7...
are formed by sequentially communicating with each other. By the way, the first expansion chamber 4 has a diameter of 2 over its entire length and circumference.
It has a double-pipe structure, and its inner pipe 10 is composed of an inner tapered pipe 11 connected to the exhaust pipe 2 and an inner straight pipe 12 connected to the rear thereof, and its outer pipe 13 is , an outer tapered tube 14 that covers the inner tapered tube 11 and an outer straight tube 15 that covers the inner straight tube 12 are integrated. and,
The inner tube 10 and the outer tube 13 are tightly fitted, and the inner tube 10 is biased to expand its diameter, and the outer tube 13 has its outer circumferential surface so as to suppress the expansion force of the inner tube 10. is closely related to For this reason, the outer tube 13
A tension force is applied to the inner tube 10 by the inner tube 10, and a tightening force is applied to the inner tube 10 by the outer tube 13. In this embodiment, the means for applying expansion force to the inner tube 10 includes recesses 16 that extend inwardly in the tube walls of the inner tapered tube 11 and the inner straight tube 12, respectively, along the tube axis direction. , 17, and connect the inner tapered pipe 11 and the inner straight pipe 12 to the outer tapered pipe 14 and the outer straight pipe 1.
5, the diameters of the inner tapered tube 11 and the inner straight tube 12 are reduced by using the recesses 16 and 17 as clearance parts, and when the fitting is completed, the diameters of the inner tapered tube 11 and the inner straight tube 12 are reduced. is designed to have an elastic return force.

In order to further understand this situation, the manufacturing method is shown step by step in FIGS. 4a to 4h, and will be explained based thereon.

That is, FIG. 4a shows a material A to be processed into the inner straight tube 12, and this material A is processed into the outer straight tube 15.
It is formed to have the same inner and outer diameters as the inner and outer diameters of.
FIG. 4b shows the mold B, which has an outer diameter that is approximately the same as the inner diameter of the material A, and has a concave portion C along the axial direction on its outer surface. Fit the above material A to the outside of the mold B,
When the wall of the material A is inserted into the recess C using a punch as shown in Fig. 4c, the recess 17 is formed in the pipe wall along the entire length in the axial direction, as shown in cross section in Fig. 4D. A shaped tube 12 is created.

Along with this, as shown in FIG. 4e, the outer tube 13
A tapered pipe material E having the same inner and outer diameters as the inner and outer diameters of the outer tapered pipe 14 is formed into a mold shown in FIG. An inner tapered pipe 11 in which a recess 16 is formed in the pipe wall along the entire length in the axial direction.
Manufacture. Next, the outer tube 13 is formed by integrally forming the outer tapered tube 14 and the outer straight tube 15 in advance.
Then, the inner tapered tube 11 and the inner straight tube 12 are fitted, but in this case, as shown in FIG. The inner straight tube 12 is then driven into the predetermined position by being reduced, and the inner straight tube 12 is then driven in the direction of the arrow.
The diameter is reduced by the relief of the hole, and it enters into a predetermined position. In this way, the inner tapered tube 11 and the inner straight tube 12 are elastically restored and expanded within the outer tube 13 in an attempt to restore the relief of the recesses 16 and 17, respectively, and are brought into close contact with the inner surface of the outer tube 13.

Therefore, the outer tube 13 is connected to these inner tapered tubes 1.
1 and the inner straight tube 12, tension is applied uniformly over the entire length.

Note that the end of the inner tapered tube 11 and the outer tube 13
The end of the outer tapered pipe 14 is integrally fixed to a connecting member 18 connected to the exhaust stack 2 of the internal combustion engine,
In addition, the inner straight pipe 12 is fixed to the outer pipe 13 at its exhaust rear end by means such as spot welding, and the inner pipe 10 and the outer pipe 13 are not fixed at any point other than the above-mentioned points. It is something.

Note that the means for forming the recesses 17 and 16 in the materials A and E may be the methods shown in FIGS. 4i and 4j. In other words, in this method, a recess is formed at the end of the mold shown in FIG. Then, the thus formed material A or E is pushed into the outer tube 15 or 14 from the recessed side of the outer tube 15 or 14 via a pressing jig N, as shown in FIG. 4J. On this occasion,
The outer diameter of the material A or E is sequentially reduced by the outer tube 15 or 14, and the recess RI grows in the axial direction, forming a recess 17 or 16 over the entire length of the material A or E. This simplifies the punching operation and increases the degree of adhesion between the outer tube and the inner tube.

For an exhaust system with such a configuration,
The high temperature flowing through the exhaust stack 2 of the internal combustion engine
Moreover, the exhaust gas with a large amplitude of pulsating waves is expanded in the first expansion chamber 4, and then expands and contracts repeatedly at the expansion chamber 8 and the contraction rate 9, thereby cooling and reducing the pulsation. and released into the outside air.

In this case, the exhaust gas flowing into the first expansion chamber 4 has a large pressure wave, so vibrations due to pulsation are transmitted to the pipe wall, but this vibration generally has a component that is displaced in the axial direction due to the nature of pulsation. , and a radially displaced component. As for the radial component, the tube diameter is not displaced uniformly over the entire circumference, but as shown by the imaginary line in Figure 2, a portion of the tube contracts toward the center and the other portion contracts in the centrifugal direction. It is thought that it is displaced so that it stretches to .

By the way, according to the above configuration, not only the inner tube 10 and the outer tube 13 are in close contact with each other, but also the outer tube 13
Since tension is applied by the inner tube 10, local expansion and contraction occurs in the inner tube 10 due to the components of the vibration partly in the contraction direction and partly in the expansion direction. For this reason, the inner circumferential surface of the outer tube 13 is
A local frictional force is generated between the outer circumferential surface of the
When the outer tube 13 is displaced by overcoming this frictional force,
This will be propagated to the outside air, but the amount of this propagation to the outside air will be reduced by the amount absorbed by the friction, and the vibration noise propagated to the outside air will be reduced.

In addition, since the outer tube 13 and the inner tube 10 are in close contact with each other, the same rigidity as that achieved by increasing the wall thickness can be obtained, and this also makes it possible to suppress the occurrence of vibration.

Furthermore, according to the above configuration, the recesses 16 and 17 are provided on the circumferential surfaces of the inner tapered tube 11 and the inner straight tube 12 that constitute the inner tube 10, which provide relief when fitting, so that a double tube structure is achieved. Despite the fact that the outer tube 13
Both the inner tube 10 and the inner tube 10 can be molded from materials of the same size. Therefore, the number of types of materials can be reduced, and the dimensions of this material can be easily controlled, making it easy to manufacture and provide at low cost.

According to the present invention described in detail above, when exhaust gas flows into the first expansion chamber having a large passage cross-sectional area through the exhaust stack, the inner tube is displaced due to vibrations accompanying the pulsation of the exhaust gas; Since this is attenuated by the frictional force generated between the outer tube and the outer tube, the displacement of the outer tube, that is, vibration, which is a source of noise, is suppressed accordingly.
Therefore, the vibration noise transmitted from the peripheral wall of the exhaust pipe to the outside air, that is, the so-called squealing sound, is reduced, and the noise can be reduced.

Moreover, this product has a double pipe structure in the first expansion chamber where relatively large pressure waves exist, and the outer pipe and inner pipe are brought into close contact, so it has high rigidity, and in this respect, the exhaust pipe is Vibration is suppressed to a minimum,
Contributes to improving the noise prevention effect.

In addition, we have provided a recess around the inner tube to provide relief when mating, so even though it has a double tube structure,
Both the outer tube and the inner tube can be constructed from materials with the same inner and outer diameters. Therefore, the number of types of materials can be reduced, and the dimensions of this material can be easily controlled, making it easy to manufacture and provide at low cost.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, in which FIG. 1 is a partially sectional side view of the exhaust system, FIG. 2 is a cross-sectional view taken along the line - in FIG. 1, and FIG. 4A to 4H are sequential views for explaining the manufacturing method, and FIGS. 4I to J are views showing another manufacturing method. DESCRIPTION OF SYMBOLS 1... Exhaust pipe, 4... First expansion chamber, 10... Inner pipe, 13... Outer pipe, 16, 17... Recessed portion.

Claims (1)

[Scope of Claims] 1. In an exhaust system for an internal combustion engine, in which a first expansion chamber is formed in an exhaust pipe connected to an exhaust stack, the cross-sectional area of the passage increases as the exhaust progresses toward the downstream side, wherein the first expansion chamber has a full length. In order to create a double-tube structure, the outer and inner tubes are made of the same material with the same inner and outer diameters, and a recess that continues in the axial direction is provided on the circumferential surface of the inner tube to separate the inner tube from the outside. When inserted into the tube, the diameter of the inner tube is reduced using the recessed portion as a relief, and the elastic restoring force of the recessed portion causes the tubes to come into close contact with each other, thereby applying tension to the outer tube. An exhaust system for an internal combustion engine characterized by: