JPS6255944B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat insulating structure for exhaust gas discharged from a combustion chamber of an internal combustion engine, and more particularly to a structure of a heat insulating layer forming body for heat insulating.

It is known that insulating the combustion chamber of an internal combustion engine increases combustion temperature and improves thermal efficiency, and is also effective in reducing the HC concentration in exhaust gas. Additionally, as a measure against exhaust pollution, thermal reactors and catalytic converters have been installed in the exhaust system, but these types of devices do not provide sufficient exhaust purification until the exhaust reaches a predetermined temperature. I can't get it. Therefore, in order to operate these devices effectively, it is desirable to keep the temperature of the exhaust gas discharged from the combustion chamber as low as possible.

In order to insulate the exhaust gas, ceramics itself, which serves as a heat insulating material, has been directly fixed or thermally sprayed on the inside of the combustion chamber, the top of the piston, and the inside of the exhaust port. However, even if a ceramic heat insulating layer is formed using this method, there may be a difference in thermal expansion coefficient between the ceramic and the engine structural metal,
The effects of vibration and impact can cause ceramics to crack and peel off, causing problems in terms of durability.Furthermore, in the case of combustion chambers, there are unavoidable shortcomings that significantly shorten the engine life, which is a problem. Ta. That is,
The biggest challenge has been how to form a heat insulating layer that can withstand extremely harsh usage conditions, or in other words, how to combine ceramics with metal materials to withstand even the harshest conditions.

The present invention has been made in view of this point,
It is an object of the present invention to provide a structure of a heat insulating layer forming body for heat insulating the exhaust gas of an internal combustion engine, which eliminates the conventional drawbacks and can withstand even severe conditions.

This structure is characterized by a heat insulating material made by impregnating ceramics with pores or a metal material with a large number of voids to absorb differences in thermal expansion, and then casting the fired heat insulating material into predetermined positions of engine structural members. It is something to do.

That is, due to this feature, the heat insulating layer forming body according to the present invention can obtain excellent heat insulating properties by combining ceramics, which itself has a small thermal conductivity, and a metal material with many pores or voids that absorb the difference in thermal expansion.
Moreover, since this heat insulating material is cast into the engine structural members, it is securely fixed, and the negative effects caused by differences in thermal expansion coefficients are absorbed by the metal material with many pores or voids, preventing cracks from occurring in the ceramic layer. The risk of them falling off is significantly reduced.

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

In the embodiment shown in FIG. 1, a range A indicated by a series of circles for convenience is a metal material 1 with many holes or voids that absorbs the difference in thermal expansion and becomes the core material of the heat insulating material. It is. A ceramic layer B is formed by impregnating the metal material 1 over a certain area on one side with a ceramic 2 indicated by a dot. The other side of the metal material 1 is cast so as to be embedded within a certain range of the engine structural member 3 shown by diagonal lines on the right. That is, in this configuration, the metal material 1 acts as a core material for the ceramics, and therefore serves as a support for the ceramics 2 as well as a connecting body with the structural member 3, and the ceramic layer B serves as the main heat insulating layer forming body. It is composed of

For example, such a configuration first includes a porous metal material 1.
A heat insulating material is formed by impregnating and applying ceramics 2 to the material and firing the material, and then these heat insulating materials are placed together in a predetermined position when casting an engine component to which it is desired to be installed for exhaust heat insulation. This can be achieved by immersing yourself in the

In this embodiment, the ceramic layer B impregnated with the metal material 1 and fired can also have some porosity, and unburned HC can be trapped in this ceramic layer B and burned during engine operation. Therefore, the effect of further reducing HC emissions can be obtained. Furthermore, when the structural member 3 is cast, the cast metal penetrates into the pores or voids of the metal material 1, so that strong fixation, that is, the connection and fixation of the cast metal and the heat insulating material can be achieved. Furthermore, the deformation of the ceramic layer B due to thermal stress etc. that occurs during engine operation is sufficiently absorbed because the metal material 1, which is the core material, absorbs the difference in thermal expansion, and the ceramic layer 2 is peeled off, causing damage to the combustion chamber. The risk of the material falling off due to other factors can be sufficiently reduced by strong bonding.

The embodiment shown in FIG. 2 shows a structure in which, in addition to the above-mentioned embodiment, the stress absorbability of the metal material 1 is further improved. That is, a layer C of only the metal material 1 is formed between the ceramic layer B and the interface 4 of the component 3. With this configuration, most of the stress between the component 3 and the ceramic layer B is absorbed by the layer C, so there is an advantage that the occurrence of cracks in the ceramic layer B is further reduced.

The embodiment shown in FIG. 3 has a structure in which, when forming the heat insulating material, the surface of the ceramic layer B is further subjected to surface treatment by metal spraying, metal dip, etc. to form a coating layer D, and this is cast into the structural member 3. It shows.
By forming the coating layer D in this manner, even if a crack occurs in the ceramic layer B, there is an advantage that the risk of small pieces of the broken ceramic 2 falling off is greatly reduced.

In each of the embodiments shown in FIGS. 4 to 6, the thickness of the ceramic layer B in the embodiments shown in FIGS. 1 to 3 is increased to form a portion E consisting only of ceramics 2. It is something. By forming the portion E of only the ceramics 2 in this way,
Since ceramics itself has a low thermal conductivity, it is possible to further improve the heat insulation effect, which is extremely advantageous for achieving the desired heat retention.

To give a numerical example here, for example, the thickness of the metal material 1 which is a core material and has many pores or voids that absorb the difference in thermal expansion, that is, A is approximately 6 mm to 8 mm,
The thickness of the ceramic layer B is approximately 3 mm to 4 mm, the depth at which the cast metal 3 penetrates into the metal material 1 is approximately 2 mm to 3 mm, and the thickness of the layer C of the metal material 1 itself is approximately 2 mm to 3 mm. It has been found that satisfactory results can be obtained with a thickness of approximately 3 mm to 4 mm.

The difference in thermal expansion varies depending on the materials of the cast metal and ceramics, but in the case of a combination of Al and Sic, it is about 10 to 50μ, and is absorbed by a metal material with many pores or voids.

In addition, in the above explanation, the general term "porous metal material" was used, but metal materials with a certain degree of porosity such as powder sintered porous bodies, fiber sintered porous bodies, and spongy metals can be used. For example, a foamed metal with a porosity of about 30 to 70% is preferable as the spongy metal, and a metal scrubber-like material made of a heat-resistant metal sold under the trade name "Gutsudoropatsukin" is also preferably used. I can do it.

For example, a Ni-based heat-resistant alloy such as a nickel-chromium alloy can be used as a metal material with many pores or voids, and a nickel-chromium alloy with a Ni-based composition that absorbs thermal expansion differences can be used. It can also be used as In addition, to briefly explain the manufacturing method and manufacturing conditions for metal materials with many pores or voids, for example, urethane foam resin is filled with metal powder that has been made into a slurry by adding a liquid, and then dried. After heating, the urethane is baked. After that, the temperature is further increased to 1300°C to 1400°C for sintering. As a result, a metal material that can be used as a metal material with many pores or voids that absorb the above-mentioned difference in thermal expansion can be obtained.

On the other hand, examples of the composition of ceramics that can be used include silicon nitride (Si ₃ N ₄ ). As a method for impregnating ceramic into a metal material with many pores or voids, for example, silicon nitride powder can be mixed with Si powder, and the clay-like mixture can be pressed onto the metal material to impregnate it. The impregnation thickness of the ceramic is, for example, 3 to 4 mm. Firing of ceramics is carried out, for example, by impregnating the above-mentioned ceramic into the above-mentioned metal material, heating it in, for example, a nitrogen atmosphere, and sintering it at around 1300°C.

For example, a method of casting a heat insulating material made by firing ceramics into a metal material with many pores or voids into predetermined locations of the structural members of an internal combustion engine is known as
This is carried out by the method described in Publication No. 52-48602, etc. Such methods are well known to those skilled in the art, and the method for placing the insulation material in a predetermined position within the mold can be any suitable method used in conventional cast casting methods. good. Furthermore, when casting into an internal combustion engine component made of aluminum alloy, for example, the casting temperature is about 670°C to 720°C, and it goes without saying that no damage will occur to the heat insulating material.

The heat insulating material according to the present invention as described above, that is, the porous metal material 1 serving as the core material is impregnated with ceramics 2 and fired, and further, optionally, a covering layer D is formed, and the heat insulating material is actually placed at a suitable location in the engine. This state is shown in FIGS. 7 to 9. FIG. 7 shows a case where a heat insulating material S is provided along the entire circumference of the inner surface of the combustion chamber of the cylinder head 6 and the upper side wall of the cylinder bore.
FIG. 8 shows a case in which a heat insulating material S is provided on the upper surface of the piston 7, and FIG. 9 shows a case in which a heat insulating material S is provided along the wall surface of the cylinder head 6, especially the exhaust port 10. . By arranging and combining the heat insulating materials S in this way, it is possible to sufficiently retain heat in the combustion chamber and the exhaust port 10, improving thermal efficiency in the combustion chamber and as described above.
HC emissions are reduced, the exhaust gas continues to be oxidized at the exhaust port 10, and effective operation of the thermal reactor and catalytic converter can be ensured by heat retention.

As explained above, the structure of the heat insulating layer forming body according to the present invention has excellent heat insulating properties, extremely high fixing strength of ceramics, and can absorb stress to ceramics, so durability is greatly improved. Since the material is formed in advance and then cast in a predetermined position, it has the advantage that it can be easily disposed within, for example, an exhaust port, which is extremely advantageous in practice.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of a heat insulating layer forming body according to a first embodiment of the present invention. FIG. 2 is a sectional view showing the structure of an embodiment in which a layer of the core material itself is formed in the embodiment of FIG. 1. FIG. 3 is a sectional view showing the structure of an embodiment in which a covering layer is formed on the embodiment of FIG. 2. 4 to 6 are cross-sectional views showing the structure of each embodiment in which the ceramic layer of the embodiment shown in FIGS. 1 to 3 is thickened and a layer of ceramic itself is formed. 7 to 9 are cross-sectional views showing the state in which the heat insulating layer forming body according to the present invention is formed on the inner surface of the combustion chamber, the inner surface of the cylinder bore, the upper surface of the piston, and the wall surface of the exhaust port, respectively. 1... Porous metal material, 2... Ceramics,
3... Engine structural member, 4... Interface, 6... Cylinder head, 7... Piston, 10... Exhaust port.

Claims (1)

[Claims] 1. A heat insulating material is formed by impregnating ceramics into a metal material with many pores or voids that absorb differences in thermal expansion, and this heat insulating material is cast into a predetermined position during casting of engine component parts. A heat insulating layer forming body for an internal combustion engine, characterized in that: 2. The internal combustion engine according to claim 1, wherein a layer made of only the metal material is formed between the impregnated and fired ceramic layer of the ceramic and the interface of the impregnated cast part of the structural member. Engine insulation layer forming body. 3. The heat insulating layer forming body for an internal combustion engine according to claim 1, wherein the ceramic layer is comprised of a portion impregnated with the metal material and fired and a portion of the ceramic itself. 4. The heat insulating layer forming body for an internal combustion engine according to any one of claims 1 to 3, wherein a coating layer made of metal is formed on the surface of the ceramic layer.