JPH01134022A - Exhaust manifold - Google Patents

Abstract

PURPOSE:To improve heat resistance and thermal impact resistance by constituting an exhaust manifold with an inside pipe body made of sintered fine ceramic, an elastic thermal insulating layer made of porous ceramic mold and an outside pipe body casted with the elastic layer. CONSTITUTION:In an exhaust manifold 1 where flow paths from a plurality of exhaust gas flow-in ports 2 are collected and coupled with an exhaust gas flow-out port 3, triple pipe structure comprising an inside pipe body 4 made of sintered fine ceramic, an elastic thermal insulating layer 5 made of porous ceramic mold and surrounding the outercircumference of the inside pipe body 4 and an outside pipe body 6 casted of metal together with the elastic layer 5 is employed. Sintered fine ceramic composing the inside pipe body 4 has three point bending strength higher than 1.0kg/mm<2> and thermal expansion coefficient of 1% at temperature of 20-1,000 deg.C, while porous ceramic mold composing the elastic thermal insulating layer 5 has thermal transmission coefficient lower than 0.5kcal/m.hr. deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an exhaust manifold used in an internal combustion engine. Specifically, the present invention relates to an exhaust manifold having a composite structure that has sufficient thermal shock resistance and strength, is lightweight, has a high heat resistance, and has high heat insulation properties.

(Prior Art) Generally, in a multi-cylinder internal combustion engine having a plurality of cylinders, exhaust gas discharged from each cylinder is connected directly to the exhaust port of each cylinder in order to collect the exhaust gas and send it to the muffler. An exhaust manifold is provided.

This exhaust manifold comes into contact with the high-temperature, high-pressure exhaust gas that flows out from the cylinder through the exhaust valve immediately after combustion, and is also subjected to a high temperature history immediately after startup, so it has excellent heat resistance, thermal shock resistance, and corrosion resistance. Conventionally, cast iron such as Fe12 or special alloy cast iron has been used.

However, in recent years, due to the demand for higher performance and higher output in the automobile field, etc., exhaust manifolds have been improved in terms of heat resistance, thermal shock resistance, corrosion resistance, etc., as well as insulation and weight reduction. Efforts are being made to provide such performance.

For example, a double tube structure has been proposed in which metal is cast inside a ceramic hollow sintered body made of S i A 1 ON or the like (Japanese Unexamined Patent Publication No. 55-53444). Using ceramic materials can be expected to significantly reduce weight compared to conventional cast iron materials, but when such inflexible ceramic sintered bodies are directly cast with metal, There is a high risk that the ceramic sintered body will be damaged due to thermal shock during casting, thermal stress due to engine stoppage, vibration, etc., and the heat insulation of such a dense ceramic sintered body is Because of this, it was necessary to use a highly heat-resistant metal such as cast iron as the metal constituting the outer tube, and it was impossible to reduce the weight by using aluminum alloy or the like.

In addition, for example, an exhaust manifold (Japanese Patent Laid-Open No. 1983-1999
-81420), an exhaust manifold with a protective layer such as wire mesh formed on the inner surface of the inner tube (Japanese Patent Application Laid-open No. 61-95923), or an exhaust manifold with a protective layer such as a wire mesh formed on the inner surface of the inner tube, or a ceramic fiber on the inner surface of the inner tube. Exhaust manifold made by combining particles (Japanese Patent Application Laid-open No. 6
No. 1-215415) has been proposed.

If a porous inner tube made of ceramic fiber is used in this way, the inner tube made of ceramic fiber is more flexible and has higher thermal shock resistance than a ceramic sintered body, so casting Although there is little risk of damage due to thermal shock during engine operation, thermal stress due to engine shutdown, etc., the inner tube made of ceramic fibers cannot be damaged even if a protective layer is provided on its inner surface or ceramic particles Even if they are combined and reinforced, the strength is not sufficient, and furthermore, the glass fibers such as alumina silica fibers or silica fibers that make up these inner tubes are exposed to high temperature and high pressure exhaust gas. As a result, the fibers crystallize, shrink in volume, and become brittle, resulting in a further decrease in strength, and the fibers tend to peel off and fall off due to the pulsations and vibrations of exhaust gas flowing at high speed. Furthermore, since the inner tube body is made of ceramic fibers, it certainly has a low thermal conductivity, but in such a double tube structure, the exhaust gas flows directly into the porous inner tube made of ceramic fibers. Because the exhaust gas hits the pipe, it passes through such a porous inner pipe, and the insulation effect of the inner pipe cannot be expected to be very good. The body naturally has a large fluid resistance, and there remained a problem in terms of exhaust efficiency.

Furthermore, an inner core made of a corrosion-resistant material such as fused silica foam or spodumene clay foam and having an outer surface and an inner surface forming a fluid flow path, and an impermeable material provided on the inner surface of the inner core. A composite structure (U.S. Pat. No. 3,709,772 ) has also been proposed. In an exhaust manifold with such a composite structure, an inner core made of a porous ceramic foam and a layer made of an elastic cushioning material provide sufficient heat insulation and light weight. Because there is a layer of elastic buffer material between them, thermal shock during the casting of the metal shell, thermal stress caused by stopping the engine, vibrations, etc., are not directly transmitted to the ceramic inner core. There is also considered to be little risk of damage to the ceramic inner core. However, in this composite structure, a porous ceramic foam is used as the inner core to improve its insulation properties, but such a porous material is not strong enough, and fused silica foam, which is a preferable example, is Because the materials themselves, such as subdumen clay foam, do not have sufficient strength and heat resistance, there is a high risk of damage due to pulsation of high-temperature, high-pressure exhaust gas flowing at high speed, backfire within the manifold, etc. there were. Furthermore, in this composite structure, an impermeable layer is provided on the inner surface to prevent fluid from penetrating into such a porous inner core. It is formed by disposing powder of a material on the inner surface of the inner core and melting it, and because it is thin and does not have sufficient strength, there is a high risk that it will peel off or break during use.

In addition, if such an impermeable layer is damaged, the inner core is porous and exhaust gas easily permeates through it, causing problems such as corrosion or a reduction in heat insulation performance. In addition, the formation of such an impermeable layer has poor workability and is disadvantageous in terms of cost.

(Problems to be Solved by the Invention) As described above, conventional exhaust manifolds have a composite structure that improves performance such as heat resistance, thermal shock resistance, and corrosion resistance, and at the same time improves heat insulation and lightweight Although a lot of research has been carried out in an attempt to add performance such as oxidation, the current situation is that nothing that meets these demands has yet been developed.

Accordingly, it is an object of the present invention to provide a novel exhaust manifold. Another object of the present invention is to provide an exhaust manifold for an internal combustion engine that is lightweight and has high thermal insulation properties. A further object of the present invention is to provide an exhaust manifold that has sufficient thermal shock resistance and strength, is lightweight, has a high heat resistance, and has a composite structure with high heat insulation properties.

A further object of the present invention is to provide an exhaust manifold that can improve exhaust gas temperature. The present invention also provides
The purpose is to provide an exhaust manifold with high corrosion resistance.

(Means for solving the problem) The above conditions include a three-point bending strength of 1.0 kg/mm2 or more,
An inner tube made of a dense ceramic sintered body with a thermal expansion coefficient of less than 1% at 20 to 1000°C, and a thermal conductivity of 0.5 Kcal/m-hr formed by surrounding the outer peripheral surface of the inner tube.
An exhaust manifold for an internal combustion engine, characterized in that it is composed of an insulating elastic layer made of a porous ceramic molded body having a temperature of −°C or less, and an outer pipe body made of cast metal formed by enclosing this insulating elastic layer. achieved.

(Function) As described above, in the exhaust manifold of the present invention, a tube made of a dense ceramic sintered body having excellent strength and low thermal expansion is used as the inner tube, and this inner tube has extremely high thermal conductivity. Because it is covered with a heat-insulating elastic layer made of a low-porosity ceramic molded body, and this heat-insulating elastic layer is further cast with cast metal to form the outer tube,
The ceramic sintered body, which has a lower thermal conductivity than metals such as cast iron, and the ceramic molded body, which has an extremely low thermal conductivity, provide high heat insulation and at the same time reduce weight. Furthermore, since the surface in contact with the exhaust gas is a dense ceramic sintered body, high heat resistance, thermal shock resistance, and high strength are imparted.

Furthermore, because it is dense, it has low permeability to exhaust gas, and due to the characteristics of the ceramic material, it also has high corrosion resistance. In addition, since there is a heat insulating elastic layer made of an elastic porous ceramic molded body between the outer tube made of cast metal and the inner tube made of dense ceramic sintered body,
Thermal stress during casting of the outer tubular body and thermal stress due to engine shutdown are alleviated by the heat insulating elastic layer, eliminating the risk of damage to the inner tubular body. Similarly, shocks or vibrations from the outside of the exhaust manifold are relaxed and absorbed by the heat insulating elastic layer. There is no risk of damage due to stress.

(Example) Hereinafter, the present invention will be explained in more detail based on embodiments.

FIG. 1 shows an embodiment of the exhaust manifold of the present invention.
FIG. 2 is a partially sectional perspective view showing the structure of an exhaust manifold for a cylinder gasoline engine, and FIG. 2 is a joint sectional view of the same embodiment.

As shown in FIG. 1, the exhaust manifold 1 of the present invention has an exhaust gas outlet where flow paths from a plurality of exhaust gas inlets 2 connected to the exhaust ports of a plurality of cylinders are collected and connected to an exhaust pipe. 3, the manifold structure is integrally formed, and the pipe structure is similar to that shown in FIGS. 1 and 2.
As shown in the figure, an inner tube 4 made of a dense ceramic sintered body, an insulating elastic layer 5 made of a porous ceramic molded body formed surrounding the outer peripheral surface of the inner tube 4,
It is characterized by a triple-pipe structure composed of an outer tube body 6 made of cast metal and formed by enclosing this heat-insulating elastic layer 5. Note that the shape of the exhaust manifold 1 of the present invention is not limited to that in the embodiment shown in FIG. It can be set to any value with consideration. In addition, the term "exhaust manifold" used in this specification refers to the exhaust gas outlet of the plurality of exhaust manifolds and one It should be interpreted in a broad sense to include crossover pipes (connecting pipes) provided for connecting to exhaust pipes.

In the exhaust manifold 1 of the present invention, the ceramic sintered body constituting the inner pipe body 4 is dense, as described above.
For example, the porosity is about 0 to 35%, more preferably 0 to 20%.
It is said to be about %. This is because the dense material has high structural strength and stability, and is virtually impermeable to gases, making it less likely to suffer from corrosion or a decline in insulation performance due to exhaust gas penetration. . Furthermore, this ceramic sintered body has a three-point bending strength of 1.0 kg/mm2.
above, preferably 3 kg/mm2 or more, most preferably 5 to 25 kg/mm2, and 20 to 1000°C
is required to have a coefficient of thermal expansion of less than 1%, more preferably less than 0.5%, most preferably less than 0.3%.

In other words, if the three-point bending strength is less than 1.0 kg/mm2, there is a risk of damage due to repeated thermal history during long-term use, pulsation of exhaust gas, external shocks, vibrations, etc. It is. Moreover, if the coefficient of thermal expansion exceeds 1%, there is a risk of damage due to thermal shock caused by high-temperature, high-pressure exhaust gas and thermal shock during casting of the outer tube body 6.

In addition, the thermal conductivity of the ceramic sintered body constituting the inner tube body 4 is 1 to 10 Kcal/m-hr-℃,
More preferably, it is about 1 to 8 KCa1/m-hr·°C, most preferably about 2 to 5 KCa1/m·hr·°C, from the viewpoint of heat insulation.

Ceramic sintered bodies with high strength and low thermal expansion that satisfy these conditions include, for example, aluminum titanate (A12 Ti05), cordierite (2Mg0
・2A1203 ・5SiO2) and reactive sintered silicon nitride (reactive sintered Si3N4). Furthermore, when using such a ceramic sintered body,
The inside of the inner pipe body 4 has a temperature of 1000°C, which exceeds the exhaust gas temperature (750 to 800°C) in a conventional gasoline engine.
It can withstand even high-temperature gases flowing through it without causing damage, making it possible to improve the output of the internal combustion engine through high compression and high rotation.

Further, in the exhaust manifold 1 of the present invention, the wall thickness of the inner tube body 4 made of such a dense ceramic sintered body is preferably about 1 to 10 mm, more preferably about 3 to 5 mm. . That is, the inner tube body 4
If the wall thickness is less than 1 mm, thermal shock resistance or mechanical strength will not be sufficient, while if it exceeds 10 mm, the exhaust manifold will become heavier and larger. .

In order to construct the manifold inner pipe body 4 from the above-mentioned dense ceramic sintered body, the ceramic material is molded into a predetermined shape by, for example, atmospheric slurry casting, pressurized slurry casting, injection molding, etc. Depending on the type of fabric, firing may be carried out by normal pressure sintering, pressure sintering, or reaction sintering.

In the exhaust manifold 1 of the present invention, the outer peripheral surface of the inner tube 4 is surrounded by the heat insulating elastic layer 5 made of a porous ceramic molded body, as described above. In this way, the heat insulating elastic layer 5 is composed of a porous ceramic molded body, and since it is made of ceramic, it has sufficient heat resistance and rigidity, and since it is porous, it has good heat insulating properties and good elasticity. It is located between the inner tubular body 2 and the outer tubular body 3 and can absorb the occurrence of thermal stress due to the difference in coefficient of thermal expansion, as well as vibrations or shocks from the outside. Furthermore, the porous ceramic molded body constituting this heat insulating elastic layer has a thermal conductivity of 20 to 1000 at an average temperature.
℃, it is necessary that it is 0.5 Kcal/m・hr・℃ or less, more preferably 0.3 Kcal/m・hr・'C or less, most preferably 0°IKcal/m・hr・℃ or less be done. That is, the thermal conductivity is 0.
This is because if it exceeds 5 Kcal/m-hr.degree. C., a sufficient heat insulating effect cannot be obtained, and for example, there is a risk that the outer tubular body cannot be constructed of an aluminum alloy with a low melting point.

Examples of porous ceramic molded bodies constituting such a heat insulating elastic layer include molded bodies made of ceramic fibers such as AlO2-8iO2 fibers, AI 02 fibers, SiO2 fibers, etc.
lO2-8i02-based powder, AlO2-based powder, S i 0
Molded bodies made of ceramic powders such as 2-based powders, and even porous ceramic powders, such as SiO2-T i 02-based porous powders sold under the trade name Microtherm by Nippon Aerosil Co., Ltd. Preferred examples include molded bodies. When AlO2SiO2 fiber is used, its bulk density is 0°2 to 1.0
It is preferable that the molded product has a particle size of about g/cm3, and the thermal conductivity in this case is 0.9 g/cm3 at an average temperature of 20 to 1000°C.
1 to 0.5 Kcal/m-br = 'C, and when 5i02 TiO2-based porous powder is used, it is preferable that the molded body has a bulk density of about 0.3 to 016 g/cm3, The thermal conductivity at this time is 20~
At 1000°C, 0.03 to 0.1 Kcal/m-
hr・℃.

Further, in the exhaust manifold 1 of the present invention, the heat insulating elastic layer 5 made of such a porous ceramic molded body is provided.
Although the wall thickness varies depending on the type of molded product, it is 1 to
It is desirable that the length be about 10 mm, more preferably about 2 to 8 mm.

That is, if the wall thickness of the heat insulating elastic layer 5 is less than 1 mm, the heat insulating effect will not be sufficient, and the thermal stress dispersion between the inner pipe body 4 and the outer pipe body 6 and impact or vibration from the outside will not be sufficient. This is because there is a risk that the buffering effect withstand may not be sufficient, and on the other hand, if it exceeds 10 mm, the weight and size of the exhaust manifold 1 will increase.

Note that in order to form the adiabatic elastic N5 made of the porous ceramic molded body as described above by surrounding the outer peripheral surface of the inner tube body 4, for example, when using ceramic fibers, paper-like ceramic fibers are used. For example, in the case of using ceramic powder, this can be suitably carried out by laminating them, or by holding the shape using waxes, organic binders, etc. Note that when waxes, organic binders, etc. are used to retain the shape in this manner, these are volatilized or burned off during casting of the outer tubular body 5 formed by casting the heat insulating elastic layer 5 as described later.

Further, in the exhaust manifold 1 of the present invention, the outer pipe body 6 is made of a cast metal formed by casting such a heat insulating elastic layer 5. Therefore, at the bonding interface between the heat insulating elastic layer 5 made of the porous ceramic molded body and the outer tube body 6 made of cast metal, the cast metal penetrates into the porous ceramic molded body and a strong mechanical bond is established. It will be done.

As the cast metal constituting the outer pipe body 6, cast iron such as ordinary cast iron and special alloy cast iron, cast steel, and aluminum alloy can be used. An aluminum alloy is particularly desirable from the viewpoint of reducing thermal stress. Note that even if the outer tube 6 is made of aluminum alloy in this way, the inner tube 4 and the heat insulating elastic layer 5 provide sufficient heat insulation, so even if exhaust gas at 1000° C. passes through the exhaust manifold 1. Aluminum alloy, which has a low melting point, will not melt.

Further, in the exhaust manifold 1 of the present invention, the wall thickness of the outer pipe body 6 made of such a cast metal is 1 to 10
It is desirable that the thickness be about 3 mm, more preferably about 3 to 6 mm. That is, if the wall thickness of the outer pipe body 6 is 1 mm without grooves, vibration resistance, impact resistance, or mechanical strength will not be sufficient, while if it exceeds 10 mm, the weight of the exhaust manifold 1 will increase. This is because it leads to larger size.

In order to form such an outer tube body 6 by casting the heat insulating elastic layer 5, it is possible to use a ceramic casting method, for example, by casting the outside of the inner tube body 4 as described above. This can be done by forming the insulating elastic layer 5 surrounding the surface, positioning it in a mold, and pouring molten metal into the mold.

(Effects of the Invention) As described above, the exhaust manifold of the present invention has an inner side made of a dense ceramic sintered body with a three-point bending strength of 1.0 kg/mm2 or more and a coefficient of thermal expansion of less than 1% at 20 to 1000°C. A tube body, a heat insulating elastic layer made of a porous ceramic molded body having a thermal conductivity of 0.5 Kcal/m・hr・℃ or less and formed around the outer peripheral surface of the inner tube body, and this heat insulating elastic layer formed by casting. Since it is characterized by being composed of an outer tube body made of cast metal, it has high heat insulation properties, for example, even when exhaust gas of 1000 degrees Celsius is passed through, its outer surface temperature remains at 300 degrees Celsius. It has high heat insulation properties ranging from ℃ to 200℃, and when used in automobiles, for example, it can keep the temperature of the engine room low, making electrical wiring in the engine room easier and lower costs. This makes it possible to design the engine room more compactly. In addition, the exhaust manifold of the present invention is lightweight and can contribute to improving the fuel efficiency of internal combustion engines since it is approximately 50% lighter than conventional cast iron exhaust manifolds. Exhaust manifolds have high heat resistance and thermal shock resistance, and are capable of passing extremely high temperature exhaust gas of, for example, 1000°C, making them fully compatible with high-output, high-speed engines. If it is possible to improve the temperature of the exhaust gas, it will improve the heat insulation property, in other words, the heat retention property, and reduce the amount of unburned HC, reduce the amount of catalyst installed in the exhaust path, and improve the performance when installing a turbocharger. This can be expected to improve efficiency. In addition, since the exhaust manifold of the present invention has excellent corrosion resistance and sufficient strength, it is susceptible to damage, especially on the exhaust gas flow path surface, due to external shocks or vibrations, or repeated thermal history over a long period of time. It does not cause damage, and even when a turbocharger or the like is installed, there is no risk of damage to the rotor due to breakage or detached pieces.

[Brief explanation of the drawing]

FIG. 1 is a partially sectional perspective view showing the structure of an embodiment of the exhaust manifold of the present invention, and FIG. 2 is a longitudinal sectional view of the same embodiment. 1...Exhaust manifold, 2...Exhaust gas inlet,
3...Exhaust gas outlet, 4...Inner pipe body, 5...
Heat insulating elastic layer, 6...outer pipe body.

Claims (7)

[Claims] (1) 3-point bending strength 1.0kg/mm^2 or more, 20~
An inner tube made of a dense ceramic sintered body with a coefficient of thermal expansion of less than 1% at 1000°C, and a tube formed around the outer peripheral surface of the inner tube with a thermal conductivity of 0.5 Kcal/m・hr・℃ or less a heat insulating elastic layer made of a porous ceramic molded body;
An exhaust manifold for an internal combustion engine, comprising an outer pipe body made of cast metal and formed by enclosing this heat insulating elastic layer. (2) The exhaust manifold according to claim 1, wherein the dense ceramic sintered body constituting the inner pipe body has a thermal conductivity of 1 to 10 Kcal/m·hr·°C. (3) The exhaust manifold according to claim 1 or 2, wherein the cast metal constituting the outer pipe body is an aluminum alloy. (4) The exhaust manifold according to claim 1 or 2, wherein the cast metal constituting the outer pipe body is cast iron or cast steel. (5) Claim 1, wherein the dense ceramic sintered body constituting the inner tube is made of aluminum titanate, cordierite, or reaction-sintered silicon nitride.
The exhaust manifold according to any one of items 1 to 4. (6) The exhaust manifold according to any one of claims 1 to 5, wherein the porous ceramic molded body constituting the heat insulating elastic layer is a ceramic fiber molded body or a ceramic powder molded body. (7) The porous ceramic molded body constituting the heat insulating elastic layer may be an alumina-silica fiber molded body, an alumina-silica fiber molded body, or an alumina-silica fiber molded body.
The exhaust manifold according to claim 6, which is a silica powder compact or a porous silica-titania powder compact.