JPH08334017A - Double exhaust pipe of engine - Google Patents

Abstract

PURPOSE: To reliably absorb a thermal expansion difference between an outer tube and an inner tube by improving a temperature rising characteristic of exhaust gas when an engine is started. CONSTITUTION: In a double exhaust pipe of an engine which is provided with an outer tube 1 and an inner tube 2 constituted by respectively joining the circumferential directional side edges of divided circumferential walls 1A, 1B, 2A and 2B to each other and whose inner tube 2 is housed in the outer tube 1 by leaving a clearance and in which the inside of the inner tube 2 is formed as an exhaust gas passage, projecting edge parts 5A, 5B, 6A and 6B projecting while curving outward in the radial direction are arranged on the side edges of the respective divided circumferential walls 1A, 1B, 2A and 2B. The side edges are welded and joined together on the outside ends of the projecting edge parts 5A, 5B, 6A and 6B, and positions of a welding joining part 6 of the inner tube 2 and a welding joining part 5 of the outer tube 5 are dislocated in the circumferential direction.

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 arranged between an engine and a catalyst, and more particularly to a double exhaust pipe suitable for application to an exhaust manifold.

[0002]

2. Description of the Related Art In automobiles, a catalyst is arranged downstream of an exhaust pipe to purify exhaust gas. In this case, in terms of purification efficiency, there is a problem when the engine is started. When the engine is started, both the catalyst and the exhaust gas have a low temperature. Therefore, since the catalyst temperature does not reach the activation temperature, a chemical change does not occur, and a situation occurs in which the unburned components in the exhaust gas cannot fully react.

In order to deal with this, a double exhaust pipe has been proposed in which the temperature of the exhaust gas is kept warm. In the double exhaust pipe, the inner pipe is concentrically arranged with a gap inside the outer pipe, and a hollow heat insulating layer is secured between the outer pipe and the inner pipe.

In the double exhaust pipe, the structural strength is secured by the outer pipe, and the wall thickness of the inner pipe forming the exhaust gas passage is made as thin as possible to reduce the heat capacity of the portion in contact with the exhaust gas. You can Further, since the hollow heat insulating layer is provided between the inner pipe and the outer pipe, it is possible to reduce heat escape through the outer pipe. Therefore, when starting the engine,
The temperature of the inner wall of the exhaust pipe can be raised quickly,
The heat retention effect of exhaust gas can be enhanced. However, since a large temperature difference occurs between the inner pipe and the outer pipe, it is necessary to adopt a structure that absorbs the difference in thermal expansion between the two.

As a conventional example of this type of double exhaust pipe, FIG.
And the one shown in FIG. 10 is known.

FIG. 9 shows a double exhaust pipe described in JP-A-56-96114. In this double exhaust pipe, the outer pipe 1 is composed of the two half-cylindrical divided peripheral walls 1A and 1B, and similarly, the inner pipe 2 is composed of the two semi-cylindrical divided peripheral walls 2A and 2B. The inner pipe 2 is housed inside the outer pipe 1, and between the peripheral side edges 5A and 5B of the divided peripheral walls 1A and 1B of the outer pipe 1, the peripheral side edges 6A of the divided peripheral walls 2A and 2B of the inner pipe 2 are disposed. ,
6B is sandwiched, and the side edges 5A, 5B and the side edges 6A, 6B are welded and fixed at the same time to form a double exhaust pipe.

As described above, when the outer pipe and the inner pipe are constructed in a half-divided form, unlike the case where the pipe is bent, a material which is difficult to bend can be made. Therefore, even with a stainless material having high oxidation resistance and corrosion resistance, a complicatedly curved exhaust manifold can be relatively easily manufactured. In this case, it is particularly effective when the inner tube is made of a thin material.

FIG. 10 shows a double exhaust pipe described in Japanese Utility Model Laid-Open No. 56-67318.

In this double exhaust pipe, a spacer 8 is provided in the gap between the inner pipe 2 and the outer pipe 1, and the spacer 8 absorbs the difference in thermal expansion between the outer pipe 1 and the inner pipe 2.

[0010]

By the way, in the double exhaust pipe shown in FIG. 9, since the inner pipe 2 is constrained to the outer pipe 1 by the welded joint, the elongation of the inner pipe 2 in the longitudinal direction is reduced. It cannot be absorbed and the inner tube is likely to be damaged. Also, the inner pipe 2
Is in contact with the outer pipe 1, there is a problem that heat is largely released and the temperature rise characteristic of the exhaust gas is deteriorated.

Further, when the double exhaust pipe shown in FIG. 10 is applied to an exhaust manifold in which several ports are gathered, such as an exhaust manifold, radial extension and stress are applied to the portion. Since the spacers 8 are concentrated, the spacer 8 cannot sufficiently absorb the deformation and the stress, and the inner pipe 2 may be damaged.

In consideration of the above circumstances, the present invention provides an engine which can improve the temperature rise characteristic of exhaust gas at the time of starting the engine and can surely absorb the difference in thermal expansion between the outer pipe and the inner pipe. An object is to provide a heavy pipe exhaust manifold.

[0013]

The invention according to claim 1 has an outer tube and an inner tube which are constructed by mutually joining the circumferential side edges of the divided peripheral walls, and there is a gap in the outer tube. In a double exhaust pipe of an engine in which an inner pipe is housed and the inside of which serves as a passage for exhaust gas, a projecting edge portion that projects while curving radially outward is provided at a side edge of each of the divided peripheral walls. The side edges are welded to each other at the outer end of the projecting edge portion, and the positions of the welded joint portion of the inner pipe and the welded joint portion of the outer pipe are displaced from each other in the circumferential direction.

According to a second aspect of the present invention, there is provided a dual exhaust pipe for an engine according to the first aspect, wherein the end portion of the inner pipe is projected outward from a flange provided at the end portion of the outer pipe. The projecting edge portion provided at the joint portion of the inner pipe is extended to the end portion of the inner tube, and the outer edge of the projecting edge portion is held by the inner peripheral edge of the gasket that is in close contact with the flange. Characterize.

According to a third aspect of the present invention, there is provided a dual exhaust pipe for an engine according to the first or second aspect, wherein a cylindrical portion protruding toward a downstream side is provided at an inner peripheral portion of a flange at an upstream end portion of the outer pipe. It is characterized in that the joint portion of the inner pipe is extended to the upstream end portion, an enlarged diameter portion is provided at the upstream end portion, and the tubular portion of the flange is inserted into the enlarged diameter portion.

A fourth aspect of the present invention is a double exhaust pipe for an engine according to any one of the first to third aspects, which is applied to an exhaust manifold, and the inner pipe is joined at an outlet portion of the exhaust manifold. The parts are arranged perpendicularly to the collecting direction of the ports of the exhaust manifold.

[0017]

According to the first aspect of the invention, the thermal expansion in the radial direction of the inner pipe at high temperature is absorbed by the deformation of the curved portion of the protruding edge portion. Further, the thermal expansion of the inner tube in the length direction is absorbed because the inner tube is not constrained by the outer tube. In addition, since the positions of the welded joint of the inner pipe and the welded joint of the outer pipe are displaced in the circumferential direction, when welding the outer pipe with the inner pipe housed inside during manufacturing, the inner pipe and the outer pipe are Can be prevented.

According to the second aspect of the present invention, since the inner tube is not bound by the outer tube, thermal expansion in the lengthwise direction of the inner tube is absorbed. Further, since the protruding edge portion provided at the joint portion of the inner pipe is held by the inner peripheral edge of the gasket, the inner pipe is not displaced.

According to the third aspect of the invention, since a part of the flange is inserted into the enlarged diameter portion formed at the upstream end portion of the inner pipe,
Exhaust gas can be prevented from flowing into the gap between the inner pipe and the outer pipe.

According to the fourth aspect of the present invention, due to the temperature distribution of the ports of the exhaust manifold, stress is generated due to the difference in thermal expansion in the direction in which the ports are assembled, but the stress is absorbed at the joint portion of the inner pipe.

[0021]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an external view of a double pipe exhaust manifold 20 to which the present invention is applied. FIG. 2 shows II- of FIG.
II is a cross-sectional view taken in the direction of the arrow, FIG. 3 is a cross-sectional view showing the structure in the middle of the double pipe exhaust manifold 20, and FIG.
FIG. 4 is a sectional view taken along the line IV. Further, FIG. 5 is a view on arrow V of FIG.
6 is a sectional view thereof, FIG. 7 is a diagram in which a gasket is attached to the flange of FIG. 5, and FIG. 8 is a sectional view thereof. The arrow F in each sectional view indicates the flow direction of the exhaust gas.

As shown in FIG. 2, the outer pipe 1 is formed to be thick so as to be a strength member of the exhaust manifold 20.
An inner pipe 2 formed to be thinner than the outer pipe 1 (for example, 0.5 mm) is concentrically arranged with a gap 3 in between, and the inside of the inner pipe 2 serves as an exhaust gas passage. Has become.
Flange 10, 3 with sufficient thickness on both ends of the outer tube 1.
0 is welded. The inner pipe 2 is exposed to high-temperature exhaust gas when traveling at high speed, and is therefore made of a stainless material to prevent deterioration due to oxidation and corrosion.

The inner pipe 2 is divided into right and left in FIG. 2, and two divided peripheral walls 2 formed by press working.
It consists of A and 2B. In this case, since it is made of a press-molded product, wrinkles and cracks generated by bending the pipe do not occur. On both side edges in the circumferential direction of each divided peripheral wall 2A, 2B,
Protruding edge portions 6A and 6B are provided so as to project (for example, 2 to 3 mm) while curving radially outward, and the divided peripheral walls 2A and 2B are welded to each other at the outer ends of the protruding edge portions 6A and 6B. ing. The joint is indicated by reference numeral 6.

The outer tube 1 is divided into upper and lower parts in FIG. 2 and is composed of two divided peripheral walls 1A and 1B formed by press working. Projecting edge portions 5A and 5B that project while curving radially outward are provided on both side edges in the circumferential direction of each of the divided peripheral walls 1A and 1B.
The divided peripheral walls 1A and 1B are welded to each other at the outer end of 5B. The joint is indicated by reference numeral 5.

With the inner pipe 2 and the outer pipe 1 assembled,
The joint portion 6 of the inner pipe 2 and the joint portion 5 of the outer pipe 1 have a phase difference of about 90 degrees, and the joint portion 6 and the joint portion 5 are deviated from each other by 90 degrees in the circumferential direction. For this reason, when the joint portion 5 of the outer pipe 1 is welded, the joint portion 6 of the inner pipe 2 is not welded and fixed together. Further, the outer end of the joint portion 6 of the inner pipe 2 is located inside the inner circumference of the outer pipe 1, and when the entire exhaust manifold 20 is at room temperature, the tips of the projecting edges 6A and 6B of the inner pipe 2 are the outer pipe. There is no contact with 1.

In the middle of the inner tube 2 in the longitudinal direction, as shown in FIG.
As shown in, an annular curved portion 22 is provided in which the tube wall is curved outwardly in a convex shape.

Next, the structure of the inlet portion of the exhaust manifold will be described with reference to FIG. Inner tube 2
The joint portion 6 is formed up to the tip of the inner tube 2, and there is no hole due to the joint portion 6 being terminated halfway. Further, the upstream end portion of the inner pipe 2 is provided with an enlarged diameter portion 12 whose diameter is expanded toward the inlet side. On the other hand, the inner circumference of the flange 10 is formed to have a diameter similar to that of the inner tube 2, and projects radially inward from the inner circumference position of the outer tube 1. The inner peripheral portion is provided with a tubular portion 14 that projects toward the downstream side, and the tubular portion 14 is fitted into the enlarged diameter portion 12 at the end portion of the inner pipe 2. In this case, the inner diameter of the tubular portion 14 is slightly smaller than the inner diameter of the normal diameter portion (the portion other than the enlarged diameter portion 12) of the inner pipe 2, or
It is set to the same level. The outer diameter is formed slightly smaller than the inner diameter of the expanded diameter portion 12 of the inner pipe 2. In addition,
A gap 15 for absorbing the extension of the inner pipe 2 is secured between the tip of the enlarged diameter portion 12 of the inner pipe 2 and the inner side surface of the flange 10.

Next, the structure of each cylinder assembly outlet of the exhaust manifold 20 will be described with reference to FIGS. As shown in FIG. 6, the downstream end (front tube side end) of the inner pipe 2 projects outward (front tube side) from the flange 30 welded and fixed to the outer pipe 1. The joint portion 6 of is extended to the downstream side end portion thereof. In this case, the position of the joint portion 6 is arranged in a direction perpendicular to the direction in which the cylinders of the exhaust manifold 20 are assembled (the direction of arrow H in FIGS. 1 and 5). The inner diameter of the flange 30 is set larger than the dimension between the outer ends of the joint portion 6 of the inner pipe 2, and the inner pipe 2 is not in direct contact with the outer pipe 1 and the flange 30.

As shown in FIGS. 7 and 8, a gasket 32 is attached to the downstream end of the exhaust manifold 20 when the exhaust manifold 20 is connected to the front tube. The gasket 32 is sandwiched between the flange 30 of the exhaust manifold 20 and the flange of the front tube, and its inner diameter is set so that the inner peripheral edge 32 a thereof contacts the outer end of the joint portion 6 of the inner pipe 2. There is. Then, the gasket 32 holds the end portion of the inner pipe 2 so as not to be displaced.

Next, the operation will be described. First, the temperature rise of the exhaust gas temperature when the engine is started will be described. Except immediately after the engine is stopped, the temperature of the outer pipe 1 and the inner pipe 2 of the double-pipe exhaust manifold 20 at the time of engine start is the same as the outside temperature. The inner pipe 2 is first warmed by the exhaust gas flowing in the pipe 2. As a result,
Although the wall temperature of the inner pipe 2 rises, the temperature of the exhaust gas lowers by the amount of heat given to the inner pipe 2.

In this case, in this embodiment, since the wall thickness of the inner pipe 2 is thin, the heat capacity of the inner pipe 2 is small and the wall temperature of the inner pipe 2 rises early. Therefore, the amount of heat transferred from the exhaust gas to the inner pipe 2 is suppressed to a low level, and the temperature decrease of the exhaust gas is suppressed. As a result, the double pipe exhaust manifold 2
The inlet gas temperature of the catalyst installed behind 0 can be raised early.

The joint portions 5 and 6 of the inner pipe 2 and the outer pipe 1 are
Since there is a phase difference of about 90 degrees, the inner pipe 2 and the outer pipe 1 are not welded together during manufacturing of the exhaust manifold, and the inner pipe 2 and the outer pipe 1 are prevented from contacting with each other, and the inner pipe due to the contact is prevented. It is possible to prevent heat conduction from 2 to the outer tube 1.
Therefore, a decrease in exhaust gas temperature can be suppressed.

At the inlet of the exhaust manifold 20, the inner pipe 2 is fitted on the outer periphery of the tubular portion 14 of the flange 10, so that the exhaust gas flowing in the tubular portion 14 of the flange 10 is discharged to the inner pipe 2. The exhaust gas does not flow into the gap 3 of the outer pipe 1, and as a result, a decrease in the exhaust gas temperature due to the flow of exhaust gas into the gap 3 can be suppressed.

Further, since the enlarged diameter portion 12 is provided at the end portion of the inner pipe 2 and the cylindrical portion 14 of the flange 10 is inserted into the enlarged diameter portion 12, the cylindrical portion 14 of the flange 10 enters the inner pipe 2. Occasionally, a large diameter change or step does not occur. Therefore, the heat transfer coefficient of the exhaust gas is not significantly increased in this portion, and the amount of heat transfer from the exhaust gas to the inner pipe 2 is not increased. Therefore, the temperature rising characteristic of the exhaust gas can be improved, and the early activation of the catalyst can be achieved.

Next, when exhaust gas and exhaust manifold are sufficiently warmed when driving in urban areas, the inner pipe 2
A difference in thermal expansion between the inner pipe 2 and the outer pipe 1 occurs due to a difference in wall temperature between the outer pipe 1 and the outer pipe 1.

That is, since the outer tube 1 is not directly exposed to the exhaust gas and is cooled by the running wind, the surface temperature is low and the thermal expansion is less than that of the inner tube 2. On the other hand, the inner pipe 2 that is directly exposed to the high-temperature exhaust gas and is thermally insulated by the air layer in the gap 7 between the inner pipe 2 and the outer pipe 1 has a high temperature and a large thermal expansion occurs.

At the inlet of the exhaust manifold 20, the thermal expansion in the lengthwise direction of the inner pipe 2 is absorbed by the gap 15 between the enlarged diameter portion 12 at the tip of the inner pipe 2 and the flange 10, and the thermal expansion in the radial direction occurs. Are absorbed in the gap between the inner pipe 2 and the outer pipe 1.

At this time, the inner tube 2 and the tubular portion 1 of the flange 10
Due to the temperature difference of 4 and the difference in the radial structure, a difference in expansion due to thermal expansion occurs in the radial direction between the inner tube 2 and the tubular portion 14 of the flange 10, and a gap is generated between the inner tube 2 and the tubular portion 14. . Therefore, the exhaust gas may leak from the gap to the gap 3 between the inner pipe 2 and the outer pipe 1 and the temperature of the exhaust gas may decrease. The inflow does not deteriorate the performance of the catalyst because the exhaust gas is sufficiently warmed and the catalyst in the latter stage of the exhaust manifold 20 is sufficiently activated. Rather, when the exhaust gas temperature is high, the exhaust gas flows into the gap 3 between the outer pipe 1 and the inner pipe 2 and the exhaust gas is cooled, so that the catalyst is prevented from deterioration due to high temperature.

In the middle of the exhaust manifold 20, the thermal expansion of the inner pipe 2 in the lengthwise direction is absorbed by the annular curved portion 22 formed in the inner pipe 2. in this case,
Since the inner pipe 2 and the outer pipe 1 are not fixed to each other, the inner pipe 2
The movement of the inner pipe 2 is not hindered by the extension in the length direction of the inner pipe 2, and the inner pipe 2 is prevented from being damaged. Further, the thermal expansion in the radial direction is absorbed by the curved shapes of the projecting edge portions 6A and 6B included in the joint portion 6 of the inner pipe 2.

Furthermore, the thermal expansion absorption of the inner pipe 2 is the same at each cylinder collecting outlet of the exhaust manifold 20. However, at the cylinder collecting outlets of the exhaust manifold 20, since the cylinders having different lengths are gathered, the exhaust gas temperature gathered in the gathering portion is different for each cylinder. Since the exhaust gas temperature of the short cylinder becomes high, each inner pipe 2
A temperature distribution occurs every time, and as a result, the thermal expansion of the inner tube 2 is not uniform. Therefore, the outlets of the respective cylinders of the exhaust manifold 20 shown in FIG. 1 are subjected to a stress in the left-right direction in the figure due to thermal expansion of the inner pipe 2 of the cylinder having a short length.

In this respect, when the joint portion of the inner pipe and the joint portion of the outer pipe are integrally fixed as in the conventional example described above (see FIG. 9).
Or when the inner tube is held by a spacer (see Fig. 10)
May not be able to absorb the stress applied to the inner pipe and may cause damage to the inner pipe 2. However, in the case of the present embodiment, as shown in FIG. Since there is no joint 6 in the direction in which the inner tube 2 receives stress (the direction of arrow H), a sufficient gap is secured,
The stress due to the difference in thermal expansion of the inner pipe 2 can be absorbed, and the inner pipe 2 can be prevented from being damaged.

In the double pipe exhaust manifold 20, the most problematic problem is thermal fatigue due to repeated thermal expansion of the inner pipe 2 at high temperature and contraction of the inner pipe 2 at low temperature. An annular curved portion 22 formed on the way
And curved protruding edges 6A, 6B at the joint 6 of the inner tube 2.
Since the thermal deformation is absorbed by and, the inner tube 2 is not damaged by thermal fatigue.

[0043]

As described above, according to the invention of claim 1, since the position of the joint portion between the inner pipe and the outer pipe is displaced in the circumferential direction, it is possible to prevent the inner pipe and the outer pipe from being fixed to each other. Therefore, it is possible to prevent the exhaust gas temperature from decreasing due to heat conduction from the inner pipe to the outer pipe, and as a result, it is possible to promote the early activation of the catalyst in the subsequent stage. Also, in addition to preventing the inner and outer tubes from sticking together,
Since a curved protruding edge is provided at the joint of the inner pipe,
The thermal expansion of the inner pipe can be reliably absorbed, and the inner pipe can be prevented from being damaged.

According to the second aspect of the present invention, since the protruding edge portion of the inner pipe is held by the gasket, the inner pipe can be held without displacement and the thermal expansion of the inner pipe can be reliably absorbed.

According to the third aspect of the invention, the joint portion of the inner pipe is extended to the upstream end portion, and the tubular portion of the flange is inserted into the inner pipe to hold the inner pipe. The portion that may lead to the gap between the tubes can be closed as much as possible with the tubular portion of the flange. Therefore, it is possible to prevent the exhaust gas from flowing into the gap between the inner pipe and the outer pipe, suppress the decrease in the exhaust gas temperature, and promote the activation of the catalyst.

According to the invention of claim 4, since the joint portion of the inner pipe is arranged perpendicularly to the collecting direction of the ports, the thermal stress due to the temperature distribution of the inner pipe can be surely absorbed, and the inner pipe can be surely absorbed. Can be prevented from being damaged.

[Brief description of drawings]

FIG. 1 is an external view of a double pipe exhaust manifold according to an embodiment of the present invention.

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

FIG. 3 is a cross-sectional view showing the structure in the middle of the exhaust manifold of the same embodiment in the longitudinal direction.

4 is a sectional view taken along the line IV-IV in FIG.

5 is a view on arrow V in FIG. 1. FIG.

6 is a cross-sectional view taken along the line VI-VI of FIG.

7 is a diagram showing a state in which a gasket is attached to the state of FIG.

8 is a sectional view taken along the line VIII-VIII in FIG.

FIG. 9 is a partial cross-sectional view of a conventional double exhaust pipe.

FIG. 10 is a partial cross-sectional view of another conventional double exhaust pipe.

[Explanation of symbols]

 1 Outer pipe 1A, 1B Divided peripheral wall 2 Inner pipe 2A, 2B Divided peripheral wall 3 Gap 5 Joined portion 5A, 5B Projected edge portion 6 Joined portion 6A, 6B Projected edge portion 10, 30 Flange 12 Expanded portion 14 Cylindrical portion 20 Double Pipe Exhaust Manifold 32 Gasket 32a Inner peripheral edge

Claims (4)

[Claims] 1. An outer pipe and an inner pipe, each of which is configured by mutually joining circumferential side edges of divided peripheral walls, wherein the inner pipe is accommodated with a gap in the outer pipe, and the inner pipe has exhaust gas inside. In the double exhaust pipe of the engine, which is defined as the passage of the above, a protruding edge portion that protrudes while curving radially outward is provided at a side edge of each of the divided peripheral walls, and the outer edge of the protruding edge portion serves as the side portion. A double exhaust pipe for an engine, characterized in that the edges are welded and the positions of the welded joint of the inner pipe and the welded joint of the outer pipe are displaced in the circumferential direction. 2. The double exhaust pipe for an engine according to claim 1, wherein the end portion of the inner pipe is projected outward from a flange provided at the end portion of the outer pipe, and the inner pipe is joined. The protruding edge portion provided on the portion is extended to the end portion of the inner pipe, and the outer edge of the protruding edge portion is held by the inner peripheral edge of the gasket that is in close contact with the flange. Double exhaust pipe. 3. The double exhaust pipe for an engine according to claim 1, wherein a cylindrical portion protruding toward the downstream side is provided on an inner peripheral portion of a flange at an upstream end portion of the outer pipe, A double exhaust pipe for an engine, characterized in that the joint portion of the above is extended to an upstream end portion, an enlarged diameter portion is provided at the upstream end portion, and the cylindrical portion of the flange is inserted into the enlarged diameter portion. 4. The double exhaust pipe of the engine according to claim 1, which is applied to an exhaust manifold, and a joint portion of the inner pipe is provided at an outlet portion of the exhaust manifold.
A double exhaust pipe for an engine, which is arranged perpendicularly to the direction in which each port of the exhaust manifold is assembled.