JPH1037746A - Double exhaust pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve durability of a double exhaust pipe by enabling absorption of axial thermal expansion difference between an inner pipe and an outer pipe, and surely holding the inner pipe. SOLUTION: An exhaust manifold 1 has an inner pipe 6 and an outer pipe 7 arranged with a gap 8. The inner pipe 6 is composed of plural inner pipe parts 6a which are relatively movably connected to each other in the axial direction. Each inner pipe part 6a is composed of a pair of half pieces 6aa, 6ab connected to each other at a flange part 10. The outer pipe 7 is composed of a pair of half pieces 7a, 7b connected to each other at a flange part 11. The flange part 10 of the inner pipe part 6a of the inner pipe 6 is sandwiched by the flange part 11 of the outer pipe 7, and the inner pipe 6 is supported with the outer pipe 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double exhaust pipe.

[0002]

2. Description of the Related Art In an ordinary internal combustion engine, a catalyst is disposed in an exhaust passage to purify exhaust gas. However, if the catalyst temperature is lower than the activation temperature, it is not possible to secure a favorable exhaust gas purification action. Therefore, for example, it is necessary to quickly heat the catalyst to the activation temperature when starting the engine. Therefore, there has been conventionally known a double exhaust pipe including an inner pipe and an outer pipe which are arranged with a heat insulating layer interposed therebetween, and through which exhaust gas flows. By doing so, the amount of heat radiation from the exhaust gas to the exhaust pipe can be reduced, so that the catalyst temperature can be quickly raised.

[0003] In such a double exhaust pipe, the inner pipe is supported and connected to the outer pipe only at its inflow end and outflow end, for example, by welding. However, since the temperature of the inner tube is higher than the temperature of the outer tube, a large difference in thermal expansion in the axial direction occurs between the inner tube and the outer tube. Therefore, when the inner tube is supported as described above, a large internal stress is generated in the inner tube, and the inner tube may be deformed or the inner tube may be cracked. Therefore, a double exhaust pipe is known in which the inner pipe is formed from a plurality of pipe parts connected to be relatively movable in the axial direction (Japanese Patent Laid-Open No. 7-34).
865). In this way, the difference in the thermal expansion in the axial direction between the inner tube and the outer tube can be absorbed, so that the inner tube is prevented from being deformed or the inner tube from being cracked.

[0004]

However, even in the double exhaust pipe described in this publication, the inner pipe is still supported by the outer pipe only at the inflow end and the outflow end, so that the inner pipe is subject to exhaust pulsation and vibration of the engine body. The inner tube may vibrate, and if the inner tube vibrates and collides with the outer tube, there is a problem that the durability of the inner tube and the outer tube is reduced or a noise source is generated.

[0005]

According to the present invention, there is provided an inner pipe and an outer pipe which are arranged with a heat insulating layer therebetween, so that exhaust gas flows through the inner pipe. In a double exhaust pipe formed from a plurality of pipe sections connected so that the inner pipe is relatively movable in the axial direction, the outer pipe section and the inner pipe section are overlapped with each other and connected at the collar section. The inner pipe and the outer pipe are connected to each other by being formed from a pair of halves formed as described above, and the flange of each pipe portion of the inner pipe is sandwiched between the flanges of the outer pipe. That is,
Since the collar of each pipe portion of the inner pipe is connected to the collar of the outer pipe, the inner pipe is securely held, and since the pipe sections other than the collar can move relative to each other, the space between the inner pipe and the outer pipe is reduced. The axial thermal expansion difference is absorbed.

[0006]

FIG. 1 shows a case where the present invention is applied to an exhaust manifold of a four-cylinder internal combustion engine. Referring to FIG. 1, the exhaust manifold 1 includes a branch portion 2 and a collecting portion 3. Each branch 2 is fixed to an engine body (not shown) via a common flange 4. On the other hand, the collecting part 3 is fixed to a catalytic converter (not shown) via the flange 5.

As shown in FIGS. 2 and 4, the exhaust manifold 1 has an inner pipe 6 and an outer pipe 7. A gap 8 is formed between the inner pipe 6 and the outer pipe 7, and the gap 8 forms an air layer and acts as a heat insulating layer. The gap 8
Can be filled with a heat insulating material or the like. Further, the exhaust gas of the internal combustion engine flows through the inner pipe 6.

The inner tube 6 has a plurality of inner tube portions 6a divided in the axial direction. These inner pipe portions 6a are connected by fitting each other. That is, except for the inner pipe portion 6a located at the most upstream of exhaust, each inner pipe portion 6a
Is provided with protrusions 9 protruding from the upstream end thereof toward the exhaust upstream, and the downstream ends of the corresponding inner pipe portions 6a are slidable in receiving portions defined by the inner peripheral surfaces of these protrusions 9. Inserted.

Referring specifically to FIG. 5, each inner tube portion 6a has a pair of halves 6aa, 6a with a collar 10 at the periphery thereof.
The inner tube portion 6a is formed by connecting the flanges 10 of the halves 6aa and 6ab to each other.
When the plurality of inner tube portions 6a are connected to each other to form the inner tube 6, the flange portions 10 of the inner tube portions 6a are aligned with each other substantially along the axis of the inner tube 6. On the other hand, the outer tube 7 also has a pair of halves 7 each having a flange 11 around its periphery.
a, 7b, and the outer tube 7 is formed by connecting the flange portions 11 of the halves 7a, 7b to each other. In addition,
Each of the halves 6aa and 6ab of the inner tube portion 6a and the halves 7a and 7b of the outer tube 7 are formed by press-molding a metal plate such as aluminum or stainless steel. The thickness is smaller than the thickness of the tube 7.

As can be seen from FIG. 2, the inner tube 6 is fixed to and supported by the outer tube 7 at its upstream end 6u and downstream end 6d. Further, as shown in FIG. 5, the collar portion 10 of the inner tube 6 is sandwiched and fixed between the collar portions 11 of the outer tube 7, so that the inner tube 6 is
Supported by Therefore, to be precise, the flanges 11 of the halves 7a and 7b of the outer tube 7 are connected via the flange 10 of the inner tube. In this case, the flange portion 11 of the half body 7a of the outer tube 7,
Collar portion 10 of half 6aa of inner tube portion 6a, inner tube portion 6a
Of the half 6ab of the outer tube 7 and the flange 11 of the half 7b of the outer tube 7 in this order, and as a result, both the inner tube portion 6a and the outer tube 7 are simultaneously formed by one welding process. can do. In FIG. 5, reference numeral 12 denotes a bead.

Next, the operation of the exhaust manifold 1 shown in FIG. 1 will be described. The high-temperature exhaust gas discharged from the internal combustion engine is
When it comes to circulate inside the inner pipe 6 with the heat of the exhaust gas
Is heated. In this case, since the plate thickness of the inner tube 6 is made relatively small and the heat capacity is made small, the temperature of the inner tube 6 quickly rises. As a result, the temperature difference between the exhaust gas and the inner pipe 6 quickly decreases, and the inner pipe 6 is provided with a gap 8 which is a heat insulating layer.
, The amount of heat radiation from the exhaust gas to the inner tube 6 is kept small. In particular, in this embodiment, since the exhaust manifold 1 has a double pipe structure from the inflow end to the outflow end, the amount of heat radiation of the exhaust gas can be kept extremely small. Therefore, high-temperature exhaust gas can be passed through the catalyst disposed downstream of the exhaust manifold 1, and the catalyst temperature can be quickly raised.

As described above, the temperature of the inner tube 6 is relatively high, while the temperature of the outer tube 7 is relatively low.
A large temperature difference occurs between the inner tube 6 and the outer tube 7 and a large difference in thermal expansion in the axial direction occurs between the inner tube 6 and the outer tube 7. To be more precise, the collar 10 of each inner tube portion 6a is fitted to the collar 11 of the outer tube 7.
, There is no large temperature difference between the temperature of the inner tube 6 around the collar 10 and the temperature of the outer tube 7, and therefore a large difference in thermal expansion between the inner tube 6 and the outer tube 7 around the collar 10. Has not occurred. The fact that the thermal expansion is large is due to the pair of flanges 10.
It is an intermediate portion 13 between them (see FIGS. 4 and 5). However, as described above with reference to FIG. 4, the projecting portion 9 is formed on the intermediate portion 13, and the inner tube portions 6 are slidably connected to each other. As a result, when a large axial thermal expansion difference occurs between the inner pipe 6 and the outer pipe 7, the inner pipe portions 6a move relative to each other in the intermediate portion 13, and as a result, the large axial thermal expansion difference is well absorbed. can do. Therefore, it is possible to prevent the inner tube 6 from being deformed or the inner tube 6 from being cracked.

Further, in this embodiment, the inner pipe 6 is divided into four parts for one exhaust gas path, so that the axial length of each inner pipe part 6a is made as short as possible. As described above, when the length of each inner tube portion 6a in the axial direction is shortened, the amount of thermal expansion in the axial direction of each inner tube portion 6a can be reduced, so that the inner tube 6 is deformed or the inner tube 6 is cracked. Can be more reliably prevented.

Further, the inner tube 6 is supported by the outer tube 11 not only at its upstream end 6u and its downstream end 6d but also at a collar portion 10 extending substantially the entire length of its axis, so that the inner tube 6 is securely supported. can do. Therefore, the vibration of the inner pipe 6 due to the exhaust pulsation and the vibration of the engine body can be reduced, so that the inner pipe 6 can be prevented from colliding with the outer pipe 7, and the generation of wear and fatigue cracks due to the vibration can be reduced. And thus the inner tube 6 and the outer tube 7
Can be further improved in durability. Also, noise can be reduced.

In this embodiment, a protrusion 9 is formed at the upstream end of the inner tube portion 6a and extends toward the exhaust gas upstream, and the inner tube positioned upstream of the exhaust gas is formed in the receiving portion defined by the inner wall surface of the protrusion 9. The downstream end of the portion 6a is inserted (see FIG. 4). However, at the downstream end of the inner pipe portion 6a, a protrusion extending toward the exhaust downstream is formed, and the upstream end of the inner pipe portion 6a located downstream of the exhaust is provided in a receiving portion defined by the inner wall surface of the protrusion. It can also be inserted.
However, when the downstream end of the inner pipe portion 6a located upstream of the exhaust is inserted into the upstream end of the inner pipe portion 6a located downstream of the exhaust while maintaining the inner diameter as in the present embodiment, the exhaust gas Therefore, it is possible to prevent the formation of an extremely high-temperature portion locally in the inner tube 6. In this case, it is also possible to ensure a good sealing effect of the exhaust gas.

[0016]

As described above, the durability of the double exhaust pipe can be improved since the inner pipe can be securely held while absorbing the difference in thermal expansion in the axial direction between the inner pipe and the outer pipe.

[Brief description of the drawings]

FIG. 1 is an overall view of an exhaust manifold to which the present invention is applied.

FIG. 2 is a cross-sectional view of the exhaust manifold taken along line II-II of FIG.

FIG. 3 is a partially enlarged sectional view of a portion III in FIG. 2;

FIG. 4 is a side view of part III of FIG. 2 with the outer tube removed.

FIG. 5 is a cross-sectional view of the exhaust manifold taken along line VV of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Exhaust manifold 6 ... Inner tube 6a ... Inner tube part 6aa, 6ab ... Half of inner tube part 7 ... Outer tube 7a, 7b ... Half of outer tube 8 ... Gap 9 ... Protrusion 10 ... Collar of inner tube 11 ... collar part of outer tube 13 ... middle part

Claims (1)

[Claims] 1. An inner pipe and an outer pipe arranged with a heat insulating layer interposed therebetween, and an exhaust gas flows through the inner pipe. The inner pipe is connected so as to be relatively movable in an axial direction. In a double exhaust pipe formed from a plurality of pipe parts, each of the outer pipe and the inner pipe is formed from a pair of halves that are superimposed on each other and connected at the brim portion, and each pipe part of the inner pipe is formed. A double exhaust pipe in which the inner pipe and the outer pipe are connected to each other by sandwiching the outer pipe by the outer pipe.