JPS61261645A - Heat insulating wall structure of thermal engine - Google Patents

Abstract

PURPOSE:To prevent the blowing-off of combustion gas or intrusion into basic material, developing heat insulating effect, by joining the back surface of a heat insulating member made of formed ceramics onto the wall surface of a combustion chamber and forming a ceramics-coated layer onto the back surface of the heat insulating member made of foamed ceramics. CONSTITUTION:The heat insulating structure of a combustion chamber of the piston 2 of a Diesel engine is constituted so that a recess 4 is formed at the center of the upper surface 3 of the piston 2, and the fuel jetted inside said recess 4 is ignited. In this case, a heat insulating member 12 made of foamed ceramics is connected onto the upper surface 3 and the surface of the recess 4 which are exposed to combustion gas, and heat transmission to the piston 2 is suppressed. Said heat insulating member 12 is formed from the ceramics having continuous gas holes 17, and a ceramics-coated layer 15 is formed onto the surface 13 which is formed flat and closes the gas holes 17. The back surface of the heat insulating member 12 thus formed is jointed onto the upper surface 3 and the recess 4 of the piston 2 by adhesive 16.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to heat insulating wall structures for heat engines and the like.

[Prior Art] The use of ceramics as a heat insulating material has already been widely proposed for combustion chambers of internal combustion engines. However, in the conventional technology, ceramics having a dense structure as a whole is thermally sprayed on the wall of the combustion chamber, or a pre-sintered ceramic insulation material is bonded to the wall of the combustion chamber by appropriate means. is common. When using such a ceramic insulation material that is dense throughout, the heat conduction is approximately 1/3 to 1/10 of that of metal, and if we look only at the degree of insulation, it is not much better than stainless steel. No significant effects can be expected. However, even if the surface temperature rises, ceramic heat insulators can suppress the rise in temperature of the base material and the resulting decrease in strength, so ceramic heat insulators are put into practical use in some areas.

In order to improve the insulation of walls exposed to combustion gases,
It is effective to increase the porosity. The method for manufacturing this high-porosity ceramic insulation material is to suck a mixture of ceramics and water into urethane foam, dry it, and then fire it. At this stage, the urethane foam is burned out to create a ceramic material with a predetermined shape that has pores. There are known methods of forming . According to this method, it is possible to make one sponge-like foamed ceramic insulation material with a porosity of about 95%, and it is also possible to obtain one with considerably high strength. This foamed ceramic insulation material has a degree of insulation corresponding to 10 to 25 mm (depending on the shape) of a solid (dense) ceramic insulation material for a thickness of 1 mm. However, this foamed ceramic insulation material is not closed pore and has air permeability, so even if it is bonded to the surface of an internal combustion engine piston or the like, combustion gas will blow through into the base material, and no insulation effect can be expected.

It should be noted that providing dense ceramics on the outermost layer of the wall surface to be insulated by thermal spraying is disclosed in Japanese Patent Application Laid-Open No. 58-15742J.
This is proposed in Publication No. 14, etc., but this requires 1 bond with the base material, 1 thermal spray layer, and 3! The organization structure of the king is quite complicated, and the process is also complicated.

[Problems to be Solved by the Invention] The purpose of the present invention is to make full use of the thermal insulation properties of foamed ceramics, to prevent combustion gases from blowing through or permeating into the base material, and to create a process that is simple. Heat 8 is easy to mass produce!
The purpose of the present invention is to provide a heat insulating U structure such as a leapfrog.

[Means for solving the problem] In order to achieve the above object, the structure of the present invention combines the surface of the foamed ceramic heat insulating material with the wall surface of the combustion chamber, and
A ceramic coating layer is provided on the surface of the foamed ceramic heat insulating material.

[Function] For example, foamed ceramic insulation materials used on the walls of combustion chambers of internal combustion engines are coated with a heat-resistant coating material that prevents gas permeation in a so-called blinding manner in order to prevent combustion gases from permeating into the base material. The treatment forms a coating layer. If the coating is simply applied directly to the cross-sectional area of the foamed ceramic, the coating layer will become quite thick, and this thickness will become uneven, causing problems such as reliability problems. Furthermore, as the coating layer becomes thicker, its heat capacity also increases, which ultimately suppresses the temperature drop in the combustion chamber during the intake process and reduces the intake air amount (weight).

In the present invention, the surface on which the coating layer is to be provided is determined in advance from the stage of manufacturing the foamed ceramic insulation material, and the surface to be coated is made to be a flat surface with almost no pores, and the dimensional accuracy is determined based on this surface. is ensured. In this way, by providing a partially dense and flat surface, the penetration of the coating material is prevented, so the bed pressure is uniform and the penetration of combustion gas can be prevented.
A coating layer is formed, and an insulating wall structure such as a heat engine with a small heat capacity and excellent insulation degree can be obtained.

[Examples of the Invention] The present invention will be described based on Examples. FIG. 1 shows an embodiment of a heat insulating wall structure of a combustion chamber of a piston 2 of a diesel engine. A recess 4 is provided in the center of the upper surface 3 of the piston 2, and the fuel injected inside this recess 4 is ignited. A foamed ceramic insulation material 12 according to the present invention is provided on the surfaces of the upper surface 3 and the recess 4 exposed to the combustion gas.
are coupled to each other and configured to suppress heat transfer to the piston 2.

・Pa Foamed ceramic insulation material 12
As shown in FIG. 2, it is molded from ceramics having continuous pores 17, this surface 13 is constructed flat, and this surface 13 is coated with ceramics! 1115
is formed, thereby closing the pores 17. The surface of the foamed ceramic heat insulating material 12 thus constructed is bonded to the upper surface 3 and recess 4 of the piston 2 made of cast iron or aluminum alloy as a base material by an adhesive 16. Zirconia or the like is suitable as the ceramic to be used, and the ceramic coating layer 15 on the surface 13 is made of ceramic paint (with a heat resistance of 1000°C or more).
silica, zirconia, etc.), and its thickness is 15
It is about ~50 μm. The entire thickness of the foamed ceramic heat insulating material 12 is about 2 mm, and its porosity is 70% or more.

Next, a method for manufacturing the foamed ceramic heat insulating material 12 according to the present invention will be explained. First, an organic foam material 26 such as urethane foam is loaded into a mold 22.21 as shown in FIG. 3, and a mixture of water and a predetermined ceramic powder is poured into the pores of the organic foam material 26. infiltrate. In this case, as shown in FIG.
Inside the mold 21 , a synthetic resin material containing a foaming material is applied to the surface of the mold 21 and foamed to form an organic foaming material 26 .

Second, the ceramics infiltrated into the organic foam material 26 is dried and pre-fired to burn out the organic foam material 26,
A foamed ceramic heat insulating material having pores 17 ] 2 is formed.

Thirdly, an upper mold (not shown) is pressed against the mold 21 to form the fired foamed ceramic ITi heat material 12 in close contact with the surface of the mold 21, and then the final firing is performed.

Fourth, the foamed ceramic heat insulating material 12 is arranged in order from the mold 21, and as shown in FIG. bind with an agent.

Fifth, as shown in FIG. 2, the surface 13 of the foamed ceramic heat insulating material 12, which has been flattened by the surface 21a of the mold 21, is coated with a ceramic coating material to form a dense ceramic coating that suppresses the pores 17. This is completed by forming layer 15.

In the piston 2 configured in this manner, the upper surface 3 and the recess 4 exposed to combustion gas are covered with the foamed ceramic insulation material 12 with high porosity, and the pores 17 are closed on the surface 13 of the foamed ceramic insulation material 12. Since the dense ceramic coating WJ15 is formed, this ceramic coating layer 15 prevents the combustion gas from blowing into the pores 17 of the foamed ceramic heat insulating material 12, and the presence of the pores 17 prevents the piston 2 from flowing from the coating layer 15. Heat transfer to the base metal is suppressed.

Since the foamed ceramic insulation material 12 according to the present invention has pores 17, its heat capacity is extremely small compared to dense ceramic materials, and the surface of the wall surface, that is, the ceramic coating layer 15, which is exposed to the combustion gas of the piston 2 at the end of the exhaust stroke. The temperature decreases, and the temperature rise of the intake air sucked into the syricinda during the subsequent suction stroke is suppressed, and the suction efficiency is improved accordingly.

[Effects of the Invention] As described above, the present invention combines a foamed ceramic insulation material having a large number of pores on the wall surface exposed to combustion gas, and provides a ceramic coating layer on the surface of the foamed ceramic insulation material. Since the pores of the insulation material are closed, the layer thickness of the foamed ceramic insulation material is thinner than conventional examples, and the internal pores are closed by the ceramic coating layer, improving the degree of insulation of the combustion chamber. be done. Furthermore, the heat capacity of foamed ceramic insulation is small due to the presence of pores.
The amount of heat transferred to the intake air is small, and a decrease in intake efficiency due to an increase in intake air temperature can be suppressed.

The insulation effect of foamed ceramic insulation material effectively suppresses heat dissipation from the combustion chamber, significantly increasing the temperature of the exhaust gas sent to the turbocharger, and effectively recovering heat in the turbocharger. can. At the same time, the heat insulating effect of the foamed ceramic insulation material lowers the temperature of the base material of the walls that partition the combustion chamber.
Its durability can be maintained. Furthermore, the processing steps of the present invention are much simpler than those using thermal spraying, and costs can be easily reduced through mass production.

[Brief explanation of the drawing]

Fig. 1 is a front cross-sectional view of a piston equipped with a heat insulating wall structure according to the present invention, Fig. 2 is an enlarged view of the main part, and Figs. 3 and 4 show the manufacturing process of the foamed ceramic heat insulating material according to the present invention. FIG. 2: Piston 3: Top surface 12: Foamed ceramic insulation material 13: Surface 15: Ceramic coating WI
26: Organic foam material patent applicant: Isuzu Motors Co., Ltd. Representative Patent attorney: Toshio Yamamizu Figure 1 Figure 4 Figure 2 Figure 3

Claims (1)

[Claims] A heat insulating wall structure for a heat engine or the like, characterized in that a surface of a foamed ceramic heat insulating material is bonded to a wall surface of a combustion chamber, and a ceramic coating layer is provided on the surface of the foamed ceramic heat insulating material.