JPH01170745A - Piston for internal combustion engine - Google Patents

Abstract

PURPOSE:To make the wall temperature of a combustion chamber higher so as to prevent an ignition lag by providing a surface layer which consists of ceramics sintered body and a heat insulating elastic layer which surrounds the outer peripheral surface side of the surface layer to form a recessed part, in a piston head in which the recessed part is provided. CONSTITUTION:A recessed part 2 is provided in the piston head of a piston 1 for an internal combustion engine. The recessed part 2 has a three layer structure which comprises a surface layer 3 that consists of ceramics sintered body, a heat insulating elastic layer 4 that consists of non-metallic inorganic porous body and surrounds the outer peripheral surface side of the surface layer 3, and a metal cast body 5 for forming the piston main body that is cast around the heat insulating elastic layer 4. The non-metallic inorganic porous body, which composes the heat insulating elastic layer 4, has low thermal conductivity and sufficient elasticity which can ease thermal stress that is generated by the difference of the coefficient of thermal expansion between the surface layer 3 and the metal cast body 5. Porous ceramics compact is preferably a non-metallic inorganic porous body. The surface layer 3 has divided structure which consists of two members 3a, 3b.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a piston for an internal combustion engine. Specifically, the present invention relates to a piston for an internal combustion engine that is suitable as a piston for a diesel engine and has a recessed portion in the piston head.

(Prior Art) In an internal combustion engine, the top of the piston, that is, the piston head (piston crown), forms a combustion chamber together with the inner surface of the cylinder head, and is directly exposed to the high temperature of combustion gas and at the same time is exposed to the explosion of the air-fuel mixture. Therefore, piston heads are required to have high heat resistance and high strength, especially when used in engines that generate high pressure and high heat load due to high compression, such as diesel engines. For example, in a piston that has a recess in the piston head and these four parts directly form the combustion chamber, such as those in direct injection diesel engines, the explosion pressure and heat load are concentrated in the recess. Therefore, a high level of consideration is required for this area.

Conventionally, pistons made of cast iron and heat-resistant aluminum alloys are known as pistons for internal combustion engines. Among these, pistons made of heat-resistant aluminum alloy are lightweight, have low inertia, and have good heat transfer.

Because of its conductivity, it can perform stable reciprocating motion even at high speed rotation, and there is little risk of problems caused by excessive temperature rise in the combustion chamber, so it is currently used as pistons for many internal combustion engines.

However, aluminum alloy pistons do not have sufficient heat resistance and have problems with high-temperature strength, so they are not suitable for use in diesel engines that are subject to high explosion pressure and heat loads as described above. It was something that didn't exist. Particularly, in pistons having a recessed portion in the piston head, such as those in direct injection diesel engines, the recessed portion has been found to be severely damaged, and improvements have been desired.

For this reason, for example, it is possible to construct the piston head from strong cast iron, but using cast iron increases the weight of the piston, which increases friction and increases the generation of noise and vibration. This makes it unsuitable for use in small, high-speed internal combustion engines. Further, even if the piston head is constructed of cast iron in this manner, the heat resistance and strength at high temperatures are not sufficient, and there remains a risk of damage occurring in the recesses to which the highest loads are applied.

Furthermore, for example, those that spray ceramics with low thermal conductivity such as zirconia and alumina on piston heads, etc.
JP 60-27820, JP 58-164775
Furthermore, a method of casting a ceramic sintered body (Japanese Patent Publication No. 56-616) has also been proposed. Providing a heat insulating material such as ceramics on the piston head in this way not only reduces the heat load on the piston base material through its heat insulating effect, but also increases the temperature of the combustion chamber wall. This is desirable because it improves ignition delay, which is the main cause of combustion noise in diesel engines, and further reduces heat loss through the piston body, improving combustion efficiency.

However, when a ceramic sprayed layer or a ceramic sintered layer is directly provided on the metal forming the piston base material as described above, the thermal history up to the high temperatures associated with the operation of an internal combustion engine is repeated, or the ceramic sintering process is repeated. When the body is cast into a piston base material, the heat generated during casting of the piston base material generates thermal stress due to the difference in thermal expansion coefficient between the metal and ceramics that make up the piston base material, resulting in ceramic spraying. This may cause layer separation or damage to the ceramic sintered body layer.

Furthermore, a heat insulating layer formed by ceramic spraying or ceramic adhesive coating is provided in the concave portion of the piston head, and a heat-resistant metal fiber layer is provided on the circumferential annular portion of the top surface of the piston head surrounding the concave portion. A heat-insulating piston in which the surfaces of the heat-resistant metal fiber layer and the heat-resistant metal fiber layer are covered with a heat-resistant metal layer (Japanese Patent Application Laid-open No. 60-240855
) has also been proposed. When the heat insulating layer is covered with a metal surface layer in this way, the heat insulating layer undergoes repeated thermal history up to high temperatures associated with the operation of the internal combustion engine, and due to the difference in coefficient of thermal expansion between the metal surface layer and the metal piston base material. Even if cracks occur, there is no risk that the heat-insulating layer formed by thermal spraying or adhesive coating will fall off, but the surface layer made of heat-resistant metal such as stainless steel does not have sufficient strength at high temperatures. There remained a risk of damage occurring in the recesses to which the highest loads were applied.

Furthermore, the formation of such a metal surface layer is problematic because it increases the weight of the piston.

(Problems to be Solved by the Invention) Therefore, an object of the present invention is to provide a novel piston for an internal combustion engine. A further object of the present invention is to provide a piston for an internal combustion engine that is suitable as a piston for a diesel engine and has a recessed portion in the piston head. A further object of the present invention is to provide a piston for an internal combustion engine that has excellent heat resistance and high temperature strength. The present invention also provides
An object of the present invention is to provide a piston for an internal combustion engine that can improve combustion efficiency.

(Means for Solving the Problems) The above-mentioned features include a piston for an internal combustion engine having a recessed portion in the piston head, in which the recessed portion surrounds a surface layer made of a ceramic sintered body and an outer peripheral surface side of the surface layer. This is achieved by a piston for an internal combustion engine characterized by having a three-layer structure consisting of a heat insulating elastic layer made of a non-metallic inorganic porous material and a metal casting body forming a piston body surrounding the heat insulating elastic layer.

(Function) As described above, in the internal combustion engine piston of the present invention, the concave portion of the piston head, where the highest load is applied, is formed by a surface layer made of a ceramic sintered body and a non-metallic inorganic material surrounding the outer peripheral surface of the surface layer. It is characterized by having a three-layer structure consisting of a heat insulating elastic layer made of a porous body and a metal casting body forming a piston body surrounding the heat insulating elastic layer,
Since the surface layer is composed of a ceramic sintered body with excellent heat resistance and strength at high temperatures, the surface layer will not be damaged even if subjected to strong explosion pressure and heat load. The surface layer and the heat-insulating elastic layer made of a non-metallic inorganic porous material with extremely low thermal conductivity greatly reduce the thermal load during operation of the internal combustion engine, and the metal casting forming the piston body is sufficiently protected. In addition, there is a considerable difference in thermal expansion coefficient between the ceramic sintered body that forms the surface layer and the metal cast body that forms the piston body. Thermal stress is generated between the two due to repeated thermal history due to engine operation, but as mentioned above, in the piston of the present invention, the outer periphery of the surface layer formed of a ceramic sintered body is made of a non-metallic inorganic porous body. Since the heat insulating elastic layer can sufficiently absorb such thermal stress, there is no risk of damage to the surface layer due to generation of thermal stress.

(Example) The present invention will be described in detail below based on examples.

1 to 7 are schematic cross-sectional views showing the structure of an embodiment of a piston for an internal combustion engine according to the present invention.

As shown in FIGS. 1 to 7, a piston 1 for an internal combustion engine according to the present invention has a recess 2 in the piston head. Note that the shape of the recess 2 is not particularly limited, and may take any form such as a flat plate type, a hemispherical type, a toroidal type, an M type, an elliptical type, a square type, a reentrant type, and the like.

Accordingly, the recess 2 includes a surface layer 3 made of a ceramic sintered body, a heat insulating elastic layer 4 made of a non-metallic inorganic porous material surrounding the outer peripheral surface of the surface layer 3, and a heat insulating elastic layer 4 formed by casting. It has a three-layer structure with a metal casting body 5 forming the surrounding piston body.

Note that it is naturally possible for the recess 2 to have the above three-layer structure over its entire surface as shown in FIGS. 1 to 2 and 5 to 7; As shown, it is also possible that only a portion thereof has a three-layer structure as described above. In the embodiment shown in FIG. 3, only the main surface of the recess 2 has a three-layer structure in consideration of the possibility of the surface layer 3 falling off as described later when the recess 2 has a shallow flat plate shape or the like. In the embodiment shown in FIG. 4, the recess 2 has a shape that narrows at its opening, and the piston body or the piston head is made of a relatively heat-resistant material such as cast steel. In this case, only the overhanging opening of the recess 2, where the explosion stress is most concentrated, has such a three-layer structure.

In the internal combustion engine piston 1 of the present invention, the ceramic sintered body constituting the surface layer 3 in the recess 2 has sufficient heat resistance, thermal shock resistance, mechanical strength at high temperatures,
Any ceramic sintered body can be used as long as it has toughness, etc., but SiAlON, Al2O3
, SiC, Mg-ZrO2, 3A1203 ・2Si0
2 and Si3N4 can be preferably used.

Furthermore, such a ceramic sintered body has a three-point bending strength of 30 kg/mm2 or more, more preferably 60 k
g/mm2 or more is a desirable characteristic since it can sufficiently withstand explosion pressure at high compression. Further, in the internal combustion engine piston 1 of the present invention, the ceramic sintered body constituting the surface layer 3 is not particularly required to have heat insulation properties as long as it has sufficient heat resistance and strength as described above. , preferably 0 to 1000
It is preferable that the thermal conductivity at °C is about 50 Kcal/m·hr·°C or less.

In order to construct the surface layer 3 from such a ceramic sintered body, depending on the shape of the concave portion 2 of the piston head to be obtained, a predetermined shape is formed by, for example, atmospheric slurry casting, pressurized slurry casting, injection molding, etc. This can be carried out by molding the ceramic into a shape and firing it by normal pressure sintering, pressure sintering, or reaction sintering depending on the material of the ceramic. Note that when the recess 3 is designed to have a shape that narrows at its opening, as in the embodiments shown in FIGS. 1, 2, and 6, the surface layer 3 is, for example, As shown in FIG. 2, a first member 3a forming the bottom side of the recess 3 and a second member 3b forming an overhanging surface with respect to the first member 3a are formed, and then mechanically joined such as by fitting, or It is also possible to construct the structure by joining by appropriate means such as an adhesive method or a welding method. Further, when the surface layer 3 is constituted by the first member 3a and the second member 3b in this manner, each member may be constituted by a different type of ceramic sintered body.

In the piston 1 for an internal combustion engine of the present invention, the nonmetallic inorganic porous body constituting the heat insulating elastic layer 4 surrounding the outer peripheral surface side of the surface layer 3 as described above has a low thermal conductivity and constitutes the surface layer 3. It has elasticity sufficient to relieve thermal stress caused by the difference in coefficient of thermal expansion between the ceramic sintered body and the cast metal body 5 constituting the piston body, and rigidity sufficient to support the surface layer 3. More specifically, porous molded bodies of ceramics or vitreous honey may be mentioned, but preferably porous ceramic molded bodies. Furthermore, as a porous ceramic molded body, for example, AlO
Preferred examples include fibers or fine particles made of ceramics such as 25i02 series, A l 02 series, 5i02 series, etc., or molded bodies made of aggregation of porous fibers or porous fine particles. Note that such fiber-like materials usually have a diameter of 1 to 5.
The molded product has a bulk density of about 0.1 to 0.3 g/cm3. In addition, as fine particles, the particle size is usually 0.1 μm.
A molded product having a bulk density of about 0.2 to Ig/cm3 is used. In addition, when the heat insulating elastic layer 4 is constituted by a molded body made by gathering such fibers or fine particles, the fibers or fine particles may be laminated to form a molded body at the time of construction. It is also possible to use fibers and the like.

Furthermore, in the heat insulating elastic layer composed of such a nonmetallic inorganic porous material, the thermal conductivity at 0 to 1000°C is 0.5 Kcal/m-hr ·°C or less, more preferably Q, IKcal/m·hr · ℃ is desirable in order to sufficiently reduce the thermal load on the cast metal body constituting the piston body.

In order to construct the heat insulating elastic layer 4 using such a non-metallic porous body, a non-metallic porous body must be formed on the outer peripheral surface side of the surface layer 3 formed as described above, that is, the surface that will be cast into the cast metal body 5 constituting the piston body. This can be done by arranging a porous body, but such a heat insulating elastic layer 4 is formed by forming a surface layer 3 and a cast metal body 5.
It is necessary to form the cast metal body 5 so that it completely covers the surface to be cast so that it does not come into direct contact with the cast metal body 5.

Furthermore, in the piston 1 for an internal combustion engine of the present invention, the heat insulating elastic layer 4 made of a non-metallic porous body as described above and formed to surround the outer circumferential side of the surface layer 3 is a cast metal body 5 constituting the piston body. It is instilled by. Therefore, at the bonding interface between the adiabatic elastic N4 made of a nonmetallic porous body and the cast metal body 5, the cast metal penetrates into the nonmetallic inorganic porous body and a strong mechanical bond is formed. Note that, as described above, since the heat insulating elastic layer N4 has sufficient rigidity, even if one surface layer 3 is held through such a heat insulating elastic layer 4, there is extremely little risk that the surface layer N3 will fall off during operation. However, preferably, as in the embodiments shown in FIGS. 2, 3, 4, and 6, the cast metal body 5 constituting the piston body is provided with a heat insulating elastic layer from the top side of the piston 1. 4 and the surface layer 3 is preferably structured.

Alternatively, as shown in FIG. 7, the ceramic sintered body constituting the surface layer 3 may be shaped so that the bottom side of the recess 2 is widened to prevent it from falling off.

As the cast metal body 5 constituting the piston body, cast iron such as ordinary cast iron and special alloy cast iron, cast steel, and aluminum alloy can be used. From this point of view, it is particularly desirable to use an aluminum alloy. Even if the piston body is not made of aluminum alloy in this way, the surface layer 3 and the heat insulating elastic layer 4 provide sufficient heat insulation in the recess 2, so the aluminum alloy will not be damaged by heat load. do not have.

(Effects of the Invention) As described above, the piston for an internal combustion engine of the present invention is a piston for an internal combustion engine having a recessed portion in the piston head, and the recessed portion includes a surface layer made of a ceramic sintered body, and a surface layer formed of a ceramic sintered body. It is characterized by a three-layer structure consisting of a heat insulating elastic layer made of a non-metallic inorganic porous material surrounding the outer peripheral surface of the piston, and a metal casting body forming a piston body surrounding the heat insulating elastic layer. Therefore, for example, in a direct injection diesel engine, the recess that forms the combustion chamber will not be damaged even if high explosion pressure and high heat load are applied due to high compression, and the recessed part that forms the combustion chamber will not be damaged due to its excellent heat insulation effect. In addition to being able to raise the temperature, the ignition delay, which is the main cause of combustion noise in diesel engines, is improved, and heat loss through the piston body is reduced, which improves combustion efficiency. It is.

Furthermore, since the piston for internal combustion engines of the present invention can exhibit the above-mentioned excellent characteristics with an extremely lightweight structure, it can be used even in small, high-speed internal combustion engines without causing problems such as noise and vibration. It is preferably used.

[Brief explanation of the drawing]

1 to 7 are schematic cross-sectional views showing the structure of an embodiment of a piston for an internal combustion engine according to the present invention. 1... Piston for internal combustion engine, 2... Recessed part, 3...
Surface layer, 3a... Surface layer first member, 3b... Surface layer second member, 4... Heat insulating elastic layer, 5... Cast metal body. Patent applicant Nippon Steel Corporation representative
Patent Attorney 8 1) Mikio (Ig) Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

Claims (6)

[Claims] (1) In a piston for an internal combustion engine having a recessed portion in the piston head, the recessed portion includes a surface layer made of a ceramic sintered body, and a heat insulating elastic layer made of a nonmetallic inorganic porous material surrounding the outer peripheral surface side of the surface layer. A piston for an internal combustion engine characterized by having a three-layer structure including a metal casting body forming a piston body surrounding the heat insulating elastic layer. (2) The piston for an internal combustion engine according to claim 1, wherein the ceramic sintered body constituting the surface layer is a ceramic sintered body having a three-point bending strength of 30 kg/mm^2 or more. (3) The ceramic sintered body constituting the surface layer is SiAl
ON, Al_2O_3, SiC, Mg-ZrO_2,3
Al_2O_3・2SiO_2 and Si_3N_4
The piston for an internal combustion engine according to claim 1 or 2, which is any one obtained from the group consisting of. (4) The piston for an internal combustion engine according to claim 1, wherein the nonmetallic inorganic porous body forming the heat insulating elastic layer is a porous ceramic molded body. (5) The piston for an internal combustion engine according to claim 1, wherein the nonmetallic inorganic porous body forming the heat insulating elastic layer is a ceramic fiber molded body or a ceramic fine particle molded body. (6) The piston for an internal combustion engine according to claim 1 or 2, wherein the heat insulating elastic layer has a thermal conductivity of 0.5 Kcal/m·hr·°C or less at 0 to 1000°C.