JPH0988578A - Double pipe type exhaust manifold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve durability at a heat cycle by reducing thermal deformation of an inner pipe compared with a conventional type. SOLUTION: In a double pipe type exhaust manifold 17 wherein an inner pipe 13 comprising a collector 13a and a plurality of branches 13b extended from the collector 13a is covered with an outer pipe 15 with a prescribed gap therebetween, the inner pipe 13 is formed of ferrite stainless steel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double pipe type exhaust manifold mounted in a vehicle exhaust system, and more particularly to a double pipe type exhaust manifold for improving durability in a heat cycle.

[0002]

2. Description of the Related Art Generally, in a vehicle exhaust system, an exhaust manifold which collects exhaust gas emitted from an engine and sends the exhaust gas to a downstream side is mounted on a cylinder head of the engine. A manifold converter that is directly mounted on the exhaust gas exhaust port of the exhaust manifold is widely known as disclosed in Japanese Utility Model Laid-Open No. 5-12622, instead of the conventional catalytic converter.

In an exhaust manifold in which such a manifold converter is attached to the exhaust gas exhaust port, the purpose is to prevent the temperature of the exhaust gas from decreasing and to enhance the catalyst activity at the time of engine start. As shown in FIG. 2, the inner wall of the exhaust manifold is lined with ceramic, or as shown in FIG.
It is known that the inner tube 3 and the outer tube 5 that covers the inner tube 3 with a predetermined gap therebetween have a double tube structure.

In the exhaust manifold 1, the inner pipe 3 exposed to high-temperature exhaust gas is made of austenitic stainless steel (for example, SUS310S) having excellent high temperature strength, and the outer pipe 5 is cheaper than austenitic stainless steel. Ferritic stainless steel (eg SUS430)
The inner pipe 3 is constrained to the outer pipe 5 via a mounting flange 9 to the cylinder head 7 and a manifold converter mounting flange 11 mounted to the exhaust gas discharge port.

[0005]

However, the inner tube 3 described above is used.
The austenitic stainless steel, which is a molding material of No. 1, is superior in high temperature strength to the ferritic stainless steel, but has a linear expansion coefficient of 11.5 × 1 for SUS430.
The coefficient of linear expansion of SUS310S is 17.6 × 10 ⁻⁶ / ° C. while the coefficient of thermal expansion is 0 ⁻⁶ / ° C., and the coefficient of thermal expansion is larger than that of ferritic stainless steel.

Therefore, the collector 3a of the inner tube 3 is greatly extended in the longitudinal direction with the inflow of high-temperature exhaust gas, and
The collector 3a repeatedly contracts and extends by the heat cycle, but the branch 3b of the inner tube 3 is attached to the mounting flange 9
Since it is restrained by the outer tube 5 via the, the stress is concentrated on the connecting portion (A portion in the figure) of the collector 3a and the branch 3b due to the expansion and contraction of the collector 3a, and as a result, the connection is caused by long-term use. There was a risk that cracks would occur in the part.

The present invention has been devised in view of such circumstances, and an improvement has been made to a double-pipe type exhaust manifold consisting of an inner pipe and an outer pipe to reduce thermal deformation of the inner pipe as compared with the conventional one. It is an object of the present invention to provide a double pipe type exhaust manifold with improved durability in heat cycle.

[0008]

In order to achieve such an object, the invention according to claim 1 provides an inner pipe, which is composed of a collector and a plurality of branches extending from the collector, with a predetermined gap. In a double pipe type exhaust manifold covered with an outer pipe, the inner pipe is formed of ferritic stainless steel.

The inventions according to claim 2 and claim 3 are the double-tube exhaust manifold according to claim 1, wherein the outer tube is formed of ferritic stainless steel or austenitic stainless steel. is there. The invention according to claim 4 is the double-pipe type exhaust manifold according to any one of claims 1 to 3, wherein the ferritic stainless steel forming the inner pipe has a linear expansion coefficient of about 11.5. × 10 ^-6
/ ° C., high temperature strength at 900 ° C. is 2 kgf / mm ² or more. The invention according to claim 5 is the double pipe type exhaust manifold according to claim 4, wherein the ferritic stainless steel is Molybdenum 2%, Niobium 0.4%, Chromium 1
It is characterized by containing 8.5%.

[0010]

According to the inventions according to each of the claims, the exhaust gas discharged from the engine is guided from each branch to the manifold converter through the collector, and the outer pipe prevents the temperature of the exhaust gas from being lowered to prevent the engine from starting. It will increase the catalytic activity. Also, with the inflow of high-temperature exhaust gas, the collector expands in the longitudinal direction of the inner pipe due to thermal expansion, and
The collector repeatedly shrinks and expands due to heat cycles, but the inner tube is made of ferritic stainless steel, so the thermal deformation of the inner tube will be greatly reduced compared to the conventional double-tube exhaust manifold. .

According to the invention of claim 3, the temperature difference between the inner tube and the outer tube is absorbed by the difference in thermal expansion of the molding material.
Further, according to the invention of claim 5, since the inner pipe has excellent high-temperature strength, it is not damaged by high-temperature exhaust gas.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows an embodiment of a double pipe type exhaust manifold according to claim 1, claim 2, claim 4 and claim 5, wherein 13 is a collector 13a and the collector 13 concerned.
An inner pipe composed of a plurality of branches 13b extending from a, and 15 is an outer pipe that covers the inner pipe 13 with a predetermined gap therebetween, like the exhaust manifold 1 shown in FIG.
Is restrained by the outer pipe 15 via a mounting flange 9 to the cylinder head 7 and a manifold converter mounting flange 11 mounted to the exhaust gas discharge port.

The outer tube 15 is made of SUS4 as in the conventional case.
Although the exhaust manifold 17 according to the present embodiment is formed of ferritic stainless steel of No. 30, the conventional SUS3 is used.
Inner tube 1 instead of austenitic stainless steel such as 10S
3 is molybdenum 2%, niobium 0.4%, chromium 18.
It is characterized by being formed from ferritic stainless steel containing 5%.

Thus, according to the ferritic stainless steel containing a plurality of kinds of materials as described above, the ordinary SUS430 is used.
While maintaining a linear expansion coefficient substantially similar to, the high temperature strength (tensile strength) at 900 ° C. where the temperature of the inner tube 13 rises is SUS43
It increased from 1.3 kgf / mm ² 0 to 2.2 kgf / mm ^2, comes to have excellent high-temperature strength. Since the exhaust manifold 17 according to the present embodiment is configured in this manner, the exhaust gas emitted from the engine is guided from each branch 13b to the manifold converter (not shown) via the collector 13a as in the conventional case, and , Outer tube 15
Prevents the temperature of the exhaust gas from decreasing and enhances the catalytic activity at the engine start.

In addition, with the inflow of high-temperature exhaust gas, the inner pipe 13
Due to thermal expansion, the collector 13a extends in the longitudinal direction,
Then, the collector 13a repeatedly contracts and expands by the heat cycle, but as described above, the ferritic stainless steel which is the molding material of the inner tube 13 has substantially the same linear expansion coefficient as SUS430. The thermal deformation is reduced by about 35% as compared with the inner pipe 3, and since it has excellent high temperature strength, the inner pipe 13 is not damaged by high temperature exhaust gas.

Therefore, according to the exhaust manifold 17 of the present embodiment, the thermal deformation of the inner pipe 13 is significantly alleviated as compared with the conventional one, so that the stress generated at the connecting portion between the collector 13a and the branch 13b is reduced, Of course, the inner tube 13 has excellent high-temperature strength, and the durability in the heat cycle is improved. In addition, the austenitic stainless steel, which is the molding material for the inner pipe 3 shown in FIG. 2, is expensive because it uses nickel as the base material. However, the double-tube exhaust manifold 17 according to this embodiment is such an austenitic stainless steel. Since stainless steel is not used as the molding material, it is possible to reduce the material cost compared to the conventional method.

In the above embodiment, the outer tube 15 is made of SUS4.
The ferritic stainless steel of No. 30 was used for molding.
Like the double pipe type exhaust manifold according to the present invention, an inner pipe having a high temperature is formed from the same ferritic stainless steel as the inner pipe 13, and SUS310S and SU excellent in high temperature strength are formed.
The outer tube may be formed using austenitic stainless steel such as S304.

Thus, according to this embodiment as well, the thermal deformation of the inner pipe can be alleviated as compared with the conventional case, and according to this embodiment, the temperature difference between the inner pipe and the outer pipe is formed. It has the advantage that it can be absorbed by the difference in thermal expansion of the materials. Further, in the above-described embodiment, the ferritic stainless steel for forming the inner tube 13 is
2% molybdenum, 0.4% niobium, and 18.5% chromium were added to increase the high-temperature strength. However, for improving the high-temperature strength, others such as 2% molybdenum, 0.6% niobium, and 19% chromium. , 0.2% of silicon or 0.8% of niobium, and 19% of chromium, and the like, and the inner tube 13 may be formed of ferritic stainless steel containing these to enhance high temperature strength.

Furthermore, the linear expansion coefficient and high temperature strength of the ferritic stainless steel forming the inner tube 13 are not limited to the above values, and the linear expansion coefficient is about 11.5 × 10 ^-6 /
As long as the ferritic stainless steel has a high temperature strength at 900 ° C. of 2 kgf / mm ² or more at 900 ° C., it is possible to achieve the intended purpose as in the embodiment shown in FIG.

[0021]

As described above, according to the double pipe type exhaust manifold according to each of the claims, the thermal deformation of the inner pipe can be remarkably alleviated as compared with the conventional one. The stress generated at the connection part was reduced, and the durability in the heat cycle was improved.

According to the invention of claim 2, since austenitic stainless steel is not used as the molding material, the material cost can be reduced as compared with the conventional one, and according to the invention of claim 3, the inner pipe is And the temperature difference between the outer tube and the outer tube can be absorbed by the difference in thermal expansion of the molding material. Further, according to the double-pipe type exhaust manifold according to claim 4 and claim 5, the inner pipe has excellent high temperature strength, and therefore, in the heat cycle as compared with the invention according to claim 1. The durability will be further improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an embodiment of a double pipe type exhaust manifold according to claim 1, claim 2, claim 4 and claim 5.

FIG. 2 is a cross-sectional view of a conventional double pipe type exhaust manifold.

[Explanation of symbols]

 13 inner pipe 13a collector 13b branch 15 outer pipe 17 exhaust manifold

Claims (5)

[Claims] 1. A collector (13a) and the collector (1)
3a) and an inner pipe (13) composed of a plurality of branches (13b) extending from the outer pipe (1).
A double-tube type exhaust manifold (17) covered with 5), characterized in that the inner tube (13) is formed of ferritic stainless steel. 2. The double pipe type exhaust manifold according to claim 1, wherein the outer pipe (15) is made of ferritic stainless steel. 3. The double pipe type exhaust manifold according to claim 1, wherein the outer pipe (15) is formed of austenitic stainless steel. 4. The ferritic stainless steel forming the inner pipe (13) has a linear expansion coefficient of about 11.5 × 10 ⁻⁶ / ° C.,
The double pipe type exhaust manifold according to any one of claims 1 to 3, wherein the high temperature strength at 900 ° C is 2 kgf / mm ² or more. 5. The double pipe type exhaust manifold according to claim 4, wherein the ferritic stainless steel contains 2% of molybdenum, 0.4% of niobium and 18.5% of chromium.