JPS6318124A - Exhaust pipe structure - Google Patents

Abstract

PURPOSE:To improve the inner pressure proof strength of an inner pipe, and prevent breakage or the like due to the thermal expansion of the inner pipe, by forming a bead portion outwardly projecting from the inner pipe formed of a heat resistant metal, and contacting the bead portion with an inner surface of an outer pipe formed of a cast iron. CONSTITUTION:An exhaust pipe 1 is formed in a three-layer structure including an inner pipe 2 formed of a heat resistant metal such as stainless steel, a heat insulator 3 such as alumina fiber to be wound around the outer circumference of the inner pipe 2, and an outer pipe 4 formed of cast iron to be so formed as to surround these members 2 and 3. In this structure, the inner pipe 2 and the outer pipe 4 are expanded by the heat of exhaust gas flowing in the exhaust pipe 1, and there is created a difference in expansion between both the pipes 2 and 4. To absorb the difference in expansion, the inner pipe 2 which tends to expand more than the outer pipe 4 is formed with a bead portion 9 for adsorbing the expansion. A head 10 of the bead portion 9 contacts an inner surface 4a of the outer pipe 4. Accordingly, it is possible to prevent breakage due to the thermal expansion of the inner pipe 2 and improve the inner pressure proof strength of the inner pipe 2.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an exhaust pipe structure with high heat retention consisting of three layers: an inner pipe made of a heat-resistant metal, a heat insulating material, and an outer pipe made of cast iron. Regarding the exhaust pipe structure designed to improve durability.

[Prior Art] Generally, in the case of an internal combustion engine equipped with turbocharging, the turbocharger is supplied with high-temperature exhaust gas with high energy while minimizing heat loss in the exhaust gas discharged from the engine. When installing a variable capacity turbocharger with movable nozzle vanes, etc., it is better to It is necessary to provide a chamber in the side exhaust pipe (exhaust manifold).

For this reason, conventionally, as an exhaust manifold suitable for mounting a variable displacement turbocharger, an exhaust manifold as shown in FIG. 7 has been used. As shown in the figure, this exhaust manifold a collects the exhaust gas discharged from each separate cylinder in a chamber C formed in a rectangular parallelepiped box and buffers its pulsation, and then This is to flow out to the feeder side, and as shown in Figure 8, the stainless steel inner pipe d
is formed into a box shape, and a plurality of inlet pipes e forming branch pipes j for connecting to each cylinder of the internal combustion engine are provided along the longitudinal direction on one side, and a variable 8-tube turbo is provided on the other side. An outflow pipe f forming a discharge pipe k to the supercharging side is provided, and after wrapping a heat insulating material 9 such as alumina fiber (M2O3) around the outer circumference of this inner pipe d, this is cast and the outer circumferential side is A cast iron outer pipe is formed on the inside to provide high insulation properties.

[Problems to be Solved by the Invention] However, when looking at the operating conditions for the exhaust manifold a mentioned above, the exhaust gas temperature reaches a maximum of 850°C at the inflow port i at the inlet of the chamber C, and the exhaust pressure becomes R8 approximately 6 and 9/as2 in chamber C (when the exhaust brake is activated). Therefore, the temperature T1 of the stainless steel inner pipe d rises to about 800°C, and the temperature T2 of the cast iron outer pipe h0') via the heat insulation jtAg rises to about 500°C. Therefore, if we measure the elongation due to thermal expansion from point A to point P at the end of the box, then from point A to point P.
Assuming that the length to the point is 500 m, the elongation ΔJl' (d) of the stainless steel inner tube d is as follows: ΔJNd) = T + xα1xJ = 800X19X10 X 500 = 7.6 (am
) (α1: coefficient of thermal expansion), and the elongation ΔJll(b) of the cast iron outer pipe is ΔJ
l'(h) =T2 Xα2XJ = 500x llx 10 x 500= 2.7
5 (ash) (α2: coefficient of thermal expansion), and the difference between them is ΔJ (d) - ΔJ (h) = 7
．． 6-2.75 = 4.85 (m).

As a result, the inner tube d and the outer tube are stretched against each other, causing deformation of the thin stainless steel inner tube d, which has a wall thickness of about 1#1, and its various parts (especially the welded part of the inlet tube e).
There was a problem in that stress was concentrated on the parts and cracks were formed.

Furthermore, as mentioned above, when the exhaust brake is activated, the exhaust pressure in chamber C is 6 to 9/al! Since it reaches 2,
If the inner tube d is box-shaped and has a rectangular cross section, there is a problem in that it cannot withstand the pressure and lacks strength, resulting in deformation and cracking.

Incidentally, deformation and cracking due to differences in elongation due to thermal expansion can be avoided by forming a bead in the inner pipe d to absorb thermal expansion, as disclosed in "Exhaust Manifold" in Japanese Utility Model Application Publication No. Ki 59-196514. This can be prevented by doing so.

[Means for Solving the Problems] In order to solve the above problems, the present invention configures the exhaust pipe structure as follows.

It consists of an inner tube made of heat-resistant metal such as stainless steel, a heat insulating material wrapped around the outer circumference of the inner tube, and an outer cast iron tube that encases these.The inner tube has beads to absorb the thermal expansion. The bead portion is formed by contacting the inner side of the outer tube.

[Function] The pressure of exhaust gas acts on the inner pipe of the exhaust pipe and tends to expand outward, but the bead formed on the inner pipe improves its strength against internal pressure.

Furthermore, since the end portion is in contact with the inside of the outer tube,
The load due to the internal pressure is supported by the outer tube from the bead portion, and deformation of the inner tube is suppressed as much as possible. This prevents the occurrence of cracks and the like due to deformation of the inner tube as much as possible, and greatly improves its durability.

[Embodiment] A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG.
It has a three-layer structure, consisting of a heat insulating material 3 such as alumina fiber (M2O3) wrapped around the outer circumference of the tube, and an outer tube 4 made of iron made by casting these materials to wrap around the outside. 2 is formed into a box with a rectangular cross section as a chamber 2a having a predetermined volume, as shown in FIG. ) A plurality of inflow pipes 6 are formed to form a branch pipe 5 for connecting to the variable traffic turbo supercharger side, and an outflow pipe 8 is formed on the other side to form a discharge pipe 7 for flowing exhaust gas to the variable foot turbo supercharger side. The main structure of the shade is the same as that of the conventional example described above.

By the way, in the present invention, in order to absorb the difference in elongation between the inner tube 2 and the outer tube 4, which expand due to the heat of the exhaust gas flowing inside the exhaust manifold 1, the inner tube 2, which has a larger elongation m, is made to elongate due to the thermal expansion. A bead portion 9 is provided for permissibly absorbing. This bead portion 9 is provided along the circumferential side between a plurality of inflow pipes 6 provided along the longitudinal direction at appropriate intervals, and has a U-shaped new surface as shown in FIG. It is formed so as to protrude outward.

The heat insulating material 3 is wrapped around almost the entire circumference of the inner tube 2 except for the head 10 of the bead 9, and the head 10 of the bead 9 connects the inner tube 2 and the heat insulating material 3. It comes into contact with the inner surface 4a of a cast iron outer tube 4 formed on the outside by casting.

In the exhaust manifold 1 formed in this way, the inner pipe 2
The difference in elongation due to thermal expansion between the inner tube 2 and the outer tube 4 is absorbed with low stress by the deformation of the bead portions 9 formed on the inner tube 2, which has a larger amount of elongation. Therefore, stress concentration due to thermal deformation does not occur in various parts such as the welded parts of each inflow pipe 6, and the durability of the inner pipe 2 is improved. The bead portion 9 can prevent this shift.

In addition, the box-shaped inner tube 2 is
tends to bulge outward and deform, but since the bead portion 9 functions as a reinforcing rib, its strength against internal pressure is improved, and the head portion 10 of the bead portion 9 contacts the inner surface 4a of the outer tube 4. Therefore, the load due to the internal pressure is supported by the outer tube 4. As a result, deformation of the inner tube 2 due to exhaust pressure can be suppressed as much as possible, durability is improved, and occurrence of cracks can be prevented as much as possible.

In addition, when casting the inner tube 2 and the heat insulating material 3 and molding the outer tube 4 on the outer circumferential side thereof, the head portion 1 of the bead portion 9 of the inner tube 2
It is necessary to prevent the 0 from being welded to the outer tube 4 to be molded. Therefore, as shown in FIG. 4, the bead portion 9 of the inner tube 2
A heat-resistant inorganic agent layer (for example, zircon coating, aron ceramic) 11 may be formed in advance on the contact portion of the head 10 to prevent welding.

FIG. 9 shows an enlarged view of the joint part of the conventional branch pipe j with the cylinder head 1. In the conventional exhaust manifold a, the outer pipe of the branch pipe J and the inner pipe d are damaged due to thermal expansion. Since there was a risk of axis misalignment between the branch pipe and
The ends of the inner +jdd and outer pipes were brought into surface contact so that they could move relative to each other to prevent stress concentration there.

For this reason, there is a problem in that a minute gap is created between these surface contact parts and exhaust gas leaks, and the leaked gas enters between the inner pipe d and the outer pipe and moves the heat insulating material q. Ta.

However, in the exhaust manifold 1 of the present invention, the thermal expansion of the inner tube 2 can be absorbed by the bead portion, so that the axes of the inner tube 2 and the outer tube 4 will not be misaligned.

For this reason, as shown in FIG. 5 or 6, the branch pipe 5
The end portion is a flange portion 4 that forms the tube end of the inner tube 2 into the outer tube 4.
b, so that it can be rigidly connected to prevent leakage of exhaust gas from here and movement of the heat insulating material 3 due to this leakage gas.

[Effects of the Invention] As described above, the present invention exhibits the following excellent effects.

(1) The amount of thermal expansion in an exhaust pipe with a three-layer structure, in which a heat-resistant metal inner pipe is wrapped with heat insulating material and then cast iron is cast to form a cast iron outer pipe on the outer periphery of the heat-resistant metal inner pipe. The inner tube, which has a large diameter, has a bead section to absorb the elongation, and the head of the bead section is brought into contact with the inner circumferential surface of the outer tube, which prevents damage due to thermal expansion of the inner tube. In addition, the bead part can improve the internal pressure resistance of the inner pipe, and the internal pressure can support the outer pipe from the bead part and prevent deformation of the inner pipe. It is possible to suppress damage as much as possible and prevent damage, thereby improving durability.

(2) Since the internal pressure resistance of the inner pipe can be improved, even if a box-shaped chamber with a rectangular cross section is formed in the exhaust pipe, damage such as cracks to the box-shaped inner pipe can be prevented as much as possible. As a result, the durability of a displacement type exhaust pipe with high insulation properties suitable for mounting a variable displacement rotor turbocharger can be greatly improved.

[Brief explanation of drawings]

1 is a partially cutaway side view showing a preferred embodiment of an exhaust manifold employing the exhaust pipe structure according to the present invention; FIG. 2 is a partially cutaway side view of the inner pipe shown in FIG. 1; Figure 3 is an enlarged view of the main part in Figure 1, Figure 4 is an enlarged view of the main part showing a modification of the main part shown in Figure 3, and Figures 5 and 6 respectively show the end structure of the branch pipe. The figures shown in FIGS. 7 to 9 are views showing conventional exhaust pipe structures. In the figure, 1 is the exhaust manifold, 2 is the inner pipe, and 3 is the exhaust manifold.
is a heat insulating material, 4 is an outer pipe, 6 is an inflow pipe, 9 is a bead part, 10
1 is a head which is a contact part, and 11 is a heat-resistant inorganic agent layer.

Claims (3)

[Claims] (1) Consists of an inner tube made of heat-resistant metal such as stainless steel, a heat insulating material wrapped around the outer circumference of the inner tube, and an outer cast iron tube that encases these.The inner tube absorbs the thermal expansion. 1. An exhaust pipe structure characterized in that a bead portion is formed for the purpose of the exhaust pipe, and the bead portion is formed in contact with the inside of the outer pipe. (2) The exhaust pipe structure according to claim 1, wherein the bead portion has a heat-resistant inorganic agent layer for preventing welding at the contact portion with the outer pipe. (3) The inner pipe is a box with a rectangular cross section, and has a plurality of inflow pipes on one side thereof to be connected to each cylinder along the longitudinal direction, and the bead is provided between each of the inflow pipes. The exhaust pipe structure according to claim 1 or 2, wherein the exhaust pipe structure is formed with a portion.