JP3006376B2 - Exhaust pipe of internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust pipe of an internal combustion engine having a double pipe structure.

[0002]

2. Description of the Related Art In recent years, exhaust gas regulations have become stricter, and it is necessary to activate a catalytic converter at an early stage when starting an engine. Japanese Utility Model Laid-Open No. 19522/1993 discloses, as an exhaust pipe for this purpose, an exhaust pipe having a double pipe structure comprising an outer pipe for maintaining strength and a thin inner pipe. In this exhaust pipe, in addition to the formation of an air layer as a heat insulating layer between the inner pipe and the outer pipe, the heat capacity of the thin inner pipe is small, so that the exhaust gas when starting the engine remains at a high temperature. The catalyst can be led to the catalytic converter, and the catalyst can be quickly brought to the activation temperature.

In the exhaust pipe having the double pipe structure, an inner pipe and an outer pipe which spread in a trumpet shape are firmly welded at one end, and the air layer is maintained at the other end while maintaining the air layer. In order to tolerate the difference in thermal expansion, a ring member which is welded only to one of the tubes and is slidable with the other tube is arranged between the two tubes.

[0004]

In the prior art described above, in addition to the mounting flanges being welded to both ends of the outer tube, the welding of both tubes at one end and the connection of one tube at the other end are performed. When the ring member is welded, there are many welded portions, the production time becomes longer, and the production cost may be increased.

Accordingly, it is an object of the present invention to provide an exhaust pipe of an internal combustion engine having a double pipe structure capable of reducing the manufacturing cost.

[0006]

An exhaust pipe of an internal combustion engine according to the present invention has an outer pipe to which a flange is welded at least at one end, and an inner pipe which is arranged substantially concentrically with the outer pipe with a predetermined gap. And a gap maintaining member disposed between the outer pipe and the inner pipe at least at one end to maintain the predetermined gap, in an exhaust pipe of an internal combustion engine, the gap maintaining member includes: It is arranged in contact with a welding portion between the flange and the outer tube, and is welded to the outer tube by a back bead generated at the time of welding between the flange and the outer tube.

[0007]

In the exhaust pipe of the internal combustion engine, a gap maintaining member for maintaining a predetermined gap between the outer pipe and the inner pipe is disposed in contact with a weld between the flange and the outer pipe. Since it is welded to the outer tube by the back bead generated at the time of welding with the tube, it is not necessary to weld the gap maintaining member to the outer tube or the inner tube again.

[0008]

1 is a partial sectional view showing a first embodiment of an exhaust pipe of an internal combustion engine according to the present invention. In the figure, reference numeral 1 denotes an outer tube, and 2 denotes an inner tube. At both ends of the outer tube 1,
A first flange 3 on the exhaust manifold side and a second flange 4 on the catalytic converter side are mounted. The second flange 4 has an elliptical shape as shown in FIG. 3 which is an enlarged view taken in the direction of the arrow P in FIG. 1, and a bolt hole 100 for connection with a catalytic converter case is provided on both sides in the longitudinal direction. ing. The outer pipe 1 is used to maintain the strength of the entire exhaust pipe.
It has a thickness of about 1.5 to 2 mm.

The inner tube 2 has a relatively thin thickness of about 0.6 to 1 mm.
Expanded portions 2a, 2 expanded substantially equal to the inner diameter of the outer tube 1
b is formed, and the end 2c on the first flange 3 side is expanded into a trumpet shape and inserted into the outer tube 1 in a straight state. Thereafter, the first flange side end 2c is welded to the outer tube 1 and the outer tube 1 is bent into a desired shape, thereby expanding the expanded tube portions 2a,
The inner tube 2 that is brought into contact with 2b is also bent into the same shape. The expanded portions 2a and 2b of the inner tube 2 are located at positions avoiding the curved portions, and as shown in FIG. 2, which is an enlarged sectional view taken along the line AA in FIG. It functions so as to maintain a predetermined gap 5 between the two tubes 1 and 2 in the vicinity.

Exhaust gas flows in from the first flange 3 side and is exhausted from the second flange 4 side. At this time, since the end 2c of the inner pipe 2 on the first flange 3 side is welded to the outer pipe 1 over the entire circumference, the exhaust gas does not flow into the predetermined gap 5 between the pipes 1 and 2. , And surely passes through the inner tube 2.

In particular, when the engine is cold started, the catalyst temperature of the catalytic converter is so low that sufficient exhaust gas purification performance cannot be realized. The exhaust pipe having the double pipe structure as in the present embodiment includes an outer pipe 1.
The predetermined gap 5 formed between the inner tube 2 and the inner tube 2 forms an air layer as a heat insulating layer, and the inner tube 2 has a small heat capacity due to its thinness. Thus, the exhaust gas temperature can be led to the catalytic converter without much lowering, and the catalyst can be quickly warmed up.

In the exhaust pipe having the double pipe structure used in this manner, the temperature difference between the outer pipe 1 and the inner pipe 2 causes the two pipes 1, 2
In particular, a difference in thermal expansion in the axial direction occurs between the two. Inner tube 2
Since the length from the end of the first flange 3 to which the pipes 1 and 2 are fixed is relatively short, the thermal expansion difference between the pipes 1 and 2 generated in the pipe expansion sections 2a and 2b Is not so large, and the abrasion when the expanded portions 2a and 2b slide on the inner surface of the outer tube 1 is very small. Then
Since a large amount of abrasion occurs in the two pipes 1 and 2 due to the large sliding, and the mechanical strength of the entire exhaust pipe is reduced, generally, FIG. As shown, in order to maintain the predetermined gap 5 in this portion, a ring member 6 formed of a wire mesh having small sliding resistance is inserted between the two tubes 1 and 2.

The ring member 6 is fixed to only one of the tubes, thereby enabling relatively large sliding with little wear between the other tubes. As shown in FIG. 5 which is an enlarged sectional view of the conventional second flange 4 side, when this ring member 6 is fixed to the inner pipe 2 by spot welding, it is formed by a wire mesh which is very easy to melt. As a result, the sliding surface 6a of the ring member 6 has a recess formed in the spot welded portion, making the above-described sliding unstable, and the inner pipe 2 having a further reduced thickness at that portion, and having a durability. Decrease.

Further, when this spot welding is performed in addition to the welding at the first flange side end portion 2c of the inner pipe 2 as compared with a normal exhaust pipe having a single pipe structure, the number of welding locations increases. The manufacturing time is prolonged and the manufacturing cost is increased. In this embodiment, as shown in FIG. 4 which is an enlarged sectional view of the second flange 4 side in FIG. 1, a ring member 6 is arranged on the back side of the welded portion of the second flange 4 to the outer tube 1, and this welding is performed. The ring 6 is joined to the outer tube 1 by a back bead generated at this time.

Accordingly, the above-described spot welding is omitted, and accordingly, the manufacturing time can be shortened and the manufacturing cost can be reduced. Furthermore, the temperature of such a back bead is relatively low, so that the ring member 6 formed by the wire mesh is hardly melted, and of course, the inner tube 2 is prevented from being melted.

When such a double-pipe exhaust pipe is actually mounted on an internal combustion engine and used, relatively large vibrations may occur. In this embodiment, since the expanded portions 2a and 2b of the inner tube 2 are in close contact with the outer tube 1, both tubes vibrate in these portions in the same manner, and at the end of the second flange 4 side. The two tubes vibrate relatively freely, but the inner tube 2 and the outer tube 1 collide in any part to prevent the two tubes 1 and 2 from colliding with each other by the ring 6 formed by the wire mesh. No abnormal noise is generated.

In this embodiment, as described above, the ring member 6 is formed by the back bead when the second flange 4 is welded to the outer tube 1.
, The back bead is not exposed to the predetermined gap 5. If such a back bead is exposed as in the related art shown in FIG. 5, the back bead may collide with the inner tube 2 due to deformation of the ring member 6 at the time of vibration, thereby generating abnormal noise. However, this embodiment can solve this problem at the same time.

FIG. 6 is a partial sectional view showing an exhaust pipe of an internal combustion engine according to a second embodiment of the present invention. The difference from the first embodiment is that the expanded portions 2a and 2b of the inner pipe 2 are omitted. Instead, a gap maintaining member 7 formed of a wire mesh is used. As shown in FIG. 7, which is an enlarged sectional view taken along the line BB of FIG.
Of the four radially located members 7a,
7b, 7c and 7d. The gap maintaining member 7 can maintain the predetermined gap 5 similarly to the ring member 6 described above, and can prevent collision between the two tubes 1 and 2 at the time of vibration.

When the predetermined gap 5 is maintained by such a wire mesh member, when the above-described outer pipe 1 and inner pipe 2 are bent, they are easily deformed.
It is necessary to fill the predetermined gap 5 with sand or the like. The gap maintaining member 7 has a shape in which a part thereof is omitted, not a ring shape, in order to enable sand removal after bending. Since the ring member 6 at the end of the second flange 4 is inserted after this sand removal and is welded in the same manner as in the first embodiment, the same effect as in the first embodiment can be obtained. it can.

Incidentally, when an oxygen sensor for detecting the oxygen concentration in the exhaust gas is attached to such a double-pipe exhaust pipe, this attachment position is advantageous for early warm-up of the oxygen sensor itself. The end on the first flange 3 side upstream of the exhaust is selected. Since a general mounting structure is unstable in strength when directly welded to the thin inner tube 2, the main body 10a of the oxygen sensor 10 is, as shown in FIG.
Is welded to the outer tube 1 having a sufficient strength, and the detecting portion 10b penetrates the inner tube 2 and projects into the inside. In such an installation, in order to make it difficult for exhaust gas to flow into the predetermined gap 5, the oxygen sensor 1
If the gap between the zero detection unit 10b and the through hole of the inner pipe 2 is reduced, or if a seal member or the like is disposed in this gap, the temperature difference between the outer pipe 1 and the inner pipe 2 due to the predetermined gap 5 There is a possibility that a bending stress is generated in the oxygen sensor 10 due to a difference in thermal expansion between the two and the oxygen sensor 10 is broken.

In the third embodiment of the exhaust pipe of the internal combustion engine according to the present invention, as shown in FIG.
The contact portion with the outer tube 1 in the trumpet-shaped expanded tube portion 2c is made relatively long, and the oxygen sensor 1 is inserted through the contact portion.
0 is welded to the outer tube 1. Thereby,
In this part, there is no gap between the outer pipe 1 and the inner pipe 2,
Since the temperatures of the two are substantially equal and no difference in thermal expansion occurs, the occurrence of bending stress in the oxygen sensor 10 is prevented.

Further, in the fourth embodiment of the exhaust pipe of the internal combustion engine according to the present invention, as shown in FIG. The welding position of the trumpet-shaped expanded portion 2c of the tube 2 to the outer tube 1 is deep, and the oxygen sensor 10 is attached to a portion where the outer tube 1 exists alone. This mounting structure is based on a difference in thermal expansion between the two tubes 1 and 2.
In addition to preventing the damage of the oxygen sensor 10, the heat capacity of the portion where the oxygen sensor 10 is mounted is smaller than that of the third embodiment due to the outer tube 1 alone. It is advantageous for its own early warm-up.

FIG. 11 is an enlarged sectional view showing the fifth embodiment of the exhaust pipe of the internal combustion engine according to the present invention at the end on the first flange 3 side. The difference from the first embodiment is that a trumpet-shaped expanded portion 2c is not provided at the end of the inner tube 2 'on the first flange 3 side, and only this portion 2'c has the same thickness as the outer tube 1. The first flange 3 is welded to the end. Further, a trumpet-shaped expanded portion 1'a is formed at the end of the outer tube 1 'on the first flange 3 side, and the expanded portion 1'a is attached to the aforementioned portion 2'c of the inner tube 2 by the first flange 3'. From the outer tube 1 'and the inner tube 2' so that a predetermined gap 5 is formed. The oxygen sensor 10 is adapted to be welded to the aforementioned portion 2'c of the inner tube 2 '.

The mounting structure of the oxygen sensor 10 has the same effect as that of the fourth embodiment, and furthermore, since the welding portion of the two tubes 1 and 2 is exposed, the welding can be performed very easily. It is possible.

In all the embodiments, the ring member 6 formed of a wire mesh used as a gap maintaining member at the end on the second flange side is not limited to the present invention. Other materials can be used, and even if the shape is divided and located radially as used in the middle of the exhaust pipe, the reduction in manufacturing cost, which is the object of the present invention, is sufficiently achieved.

[0026]

As described above, according to the exhaust pipe of the internal combustion engine according to the present invention, the outer pipe having the flange welded to at least one end thereof and the inner pipe arranged substantially concentrically with a predetermined gap from the outer pipe. A pipe, a gap maintaining member disposed between the outer pipe and the inner pipe at least at one end to maintain a predetermined gap,
In the exhaust pipe of the internal combustion engine, the gap maintaining member is disposed in contact with a weld between the flange and the outer pipe, and is welded to the outer pipe by a back bead generated at the time of welding between the flange and the outer pipe. Therefore, as compared with the case where the gap maintaining member is newly welded to the outer pipe or the inner pipe, the manufacturing time of the exhaust pipe is reduced, and the cost can be reduced accordingly.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing a first embodiment of an exhaust pipe of an internal combustion engine according to the present invention.

FIG. 2 is an enlarged sectional view taken on line AA of FIG. 1;

FIG. 3 is an enlarged view as seen from an arrow P in FIG. 1;

FIG. 4 is an enlarged sectional view of a second flange side end portion of FIG. 1;

FIG. 5 is an enlarged sectional view of a conventional second flange side end.

FIG. 6 is a partial sectional view showing a second embodiment of the exhaust pipe of the internal combustion engine according to the present invention.

FIG. 7 is an enlarged sectional view taken along the line BB of FIG. 6;

FIG. 8 is a cross-sectional view showing a conventional oxygen sensor mounting structure at a first flange side end.

FIG. 9 is a cross-sectional view of a third embodiment of an exhaust pipe of an internal combustion engine according to the present invention at an end on a first flange side.

FIG. 10 is a sectional view of a fourth embodiment of an exhaust pipe of an internal combustion engine according to the present invention at an end on a first flange side.

FIG. 11 is a sectional view of a fifth embodiment of an exhaust pipe of an internal combustion engine according to the present invention at an end on a first flange side.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Outer tube 2 ... Inner tube 3 ... 1st flange 4 ... 2nd flange 5 ... Predetermined clearance 6 ... Ring member 7 ... Gap maintenance member 10 ... Oxygen sensor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-115718 (JP, A) JP-A-58-162394 (JP, U) JP-A-59-135323 (JP, U) JP-A-5-162323 19522 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 7/08 F01N 7/18

Claims (1)

(57) [Claims] 1. An outer pipe to which a flange is welded at least at one end, an inner pipe arranged substantially concentrically with a predetermined gap with the outer pipe, and at least the one end to maintain the predetermined gap. A gap maintaining member disposed between the outer tube and the inner tube, wherein the gap maintaining member is disposed in contact with a weld between the flange and the outer tube. An exhaust pipe for an internal combustion engine, wherein the exhaust pipe is welded to the outer pipe by a back bead generated when welding the flange and the outer pipe.