HEAT INSULATING COMBUSTION CHAMBER AND METHOD OF PRODUCING THE SAME

Abstract: The heat insulating combustion chamber (10) according to the present invention is provided with a surface layer (4), which faces a combustion chamber (5), of a head liner (1) consisting of an integrated structure of a lower surface portion (2) of a head and an upper portion (3) of a cylinder liner and made of a thin ceramic layer of the smallest possible thickness, and a heat insulating member (6, 8), i.e. a heat insulating layer consisting of a porous carbon structure and disposed between the head liner (1) and this thin layer (4) so as to improve the heat insulating functions of the combustion chamber (5), the thin layer (4) which faces the combustion chamber, and which is heated to a high temperature, being formed to have a small thermal capacity, whereby the suction efficiency in a suction stroke of the engine and the cycle efficiency are improved, the thin layer (4) the strength of which decreases due to the reduction of the thickness of the ceramic material constituting the same being reinforced by a latticed partition (7) inserted in the heat insulating layer (6, 8) so as to support the thin layer (4), the joint portions of the thin layer (4) and partition (7) being combined firmly with each other. The present invention further provides a method of producing a heat insulating combustion chamber of the above described construction very easily to have a high strength.

Description: This invention relates to a heat insulating combustion chamber for a ceramic engine and the like, and a method of producing the same. DESCRIPTION OF THE PRIOR ART: A conventional heat insulating structure for the wall of a combustion chamber in an engine is disclosed in, for example, Japanese Utility Model Laid-Open No. 58824/1985 filed by the applicant of the present invention. The heat insulating structure for the wall of the combustion chamber in an engine is such that a wall member composed of a porous ceramic material having a thickness of not more than 2.0 mm and a porosity of not less than 80%, and a layer of coating of a ceramic material having a thickness of not more than 0.1 mm and formed on the outer surface of the wall member, or a plate of a metal, such as stainless steel bonded to the outer surface of the wall member form an insulating wall, this heat insulating wall being provided on the inner surface of a cylinder head, the top end surface of a piston and the inner circumferential surface of a cylinder liner, which contact a combustion gas in the engine. In such a heat insulating structure for the wall of a combustion chamber for an engine, it is very difficult to combine an outer layer of coating of a ceramic material or a plate of a metal, such as stainless steel with the surface of the wall member of a ceramic material. If the porosity of the wall member is increased, the strength thereof decreases, though the heat insulating performance thereof is improved, so that it becomes more difficult to combine such an outer layer or metal plate with the surface of the wall member. If the wall member is made thicker so as to combine such a layer of coating with the wall member of a ceramic material more easily, the thermal capacity of the wall member increases. Consequently, the temperature in the combustion chamber becomes constantly high, and the suction efficiency in a suction stroke of the engine decreases. A further heat-insulating combustion chamber structure is disclosed in applicant's JP-A-60-184951 which teaches the covering of a combustion chamber by a carbon cloth, with a heat resisting metallic film being pasted onto the surface of this carbon cloth. Therefore, there has been a problem of how to construct a heat insulating combustion chamber which is capable of securing its heat insulating functions, and which has a combustion gas-exposed wall surface with the smallest possible thermal capacity and a sufficiently high strength. The techniques for forming a layer of coating of a ceramic material by chemical vapor deposition have already been disclosed in publications. The chemical vapor deposition is put into practice in various technical fields by utilizing the permeation characteristics thereof. It is utilized for sealing bores, bonding materials and parts, plating inner surfaces of minute bores and narrowly spaced materials and parts, and forming heat resisting, wear resisting and corrosion resisting protective films, decorative films and films of a functional substance having electrical and optical characteristics. A fluidized chemical vapor deposition apparatus uses as starting substances for chemical vapor deposition a coating reagent containing as a main component a substance to be applied to a substrate, and a gas source, such as a carrier gas and a reactive gas mixed with the vapor of the reagent and sending the plating vapor to the surface of the substrate in a reaction chamber. The coating reagent used consists mainly of a volatile metal or a halide, and the carrier gas and reactive gas a simple-substance gas composed of a hydrogen gas in most cases and nitrogen and argon in some cases and a hydrocarbon gas (refer to "Ceramic Coating Techniques" published on May 25, 1984 (date of issue) by the Sogo Gijutsu Center K.K. (publishing company)). In order to bond or chemically combine a ceramic material, such as Si₃N₄ and Si C to or with the wall of a combustion chamber, the chemical vapor deposition is conveniently used. The bonding of, for example, Si₃N₄ to the wall of a combustion chamber is effected by mixing gases, such as Si Cℓ₄, NH₃ and H₂ together, and subjecting the resultant mixed gas to a reaction in a chemical vapor deposition furnace, i.e. a high-temperature furnace. The present invention seeks to solve the above-mentioned problems and provide a heat insulating combustion chamber in which a surface layer, which faces a combustion chamber, of a head liner solve the above-mentioned problems and provide a heat insulating combustion chamber in which a surface layer, which faces a combustion chamber, of a head liner consisting of an integrated structure of a lower surface portion of a head and an upper portion of a cylinder liner, is made of a thin ceramic layer of the smallest possible thickness, a heat insulating member, i.e. a heat insulating layer which consists of a porous carbon structure is provided between the head liner and this thin layer so as to improve the heat insulating functions of the combustion chamber, the thin layer, which faces the combustion chamber and is heated to high temperature, is formed to have a small thermal capacity, whereby the suction efficiency in a suction stroke of the engine and the cycle efficiency are improyed, the thin layer the strength of which decreases due to the reduction of the thickness of the ceramic material constituting the same is reinforced by providing in the heat insulating layer a support member consisting of a latticed partition, and the joint portion between the thin layer and partition is combined firmly with each other. According to the present invention there is provided a heat insulating combustion chamber having a head liner comprising a head lower portion provided with a suction port and an exhaust port and consisting of a ceramic material, which head lower portion is unitarily formed with an annular cylinder liner upper portion consisting of a ceramic material identical with that of said head lower portion, a portion of a combustion chamber being defined by an inner side of said head liner, said heat insulating combustion chamber further comprising: a latticed partition consisting of a ceramic material fixed to the inner surface of said head liner, having carbon packed in a plurality of the hollow spaces formed in said partition, and a thin layer of a ceramic material formed so as to cover the whole of the inner surfaces of said partition and said carbon. Preferably, the ceramin material forming the head liner, the partition and the thin layer is silicon nitride. By providing a heat insulating combustion chamber wherein the thickness of the surface layer, i.e. the ceramic material constituting the thin layer, which is exposed to a high-temperature combustion gas, of the lower surface portion of the head and the upper portion of the cylinder liner which is opposed to the combustion chamber can be set to the lowest possible level by chemical vapor deposition, the thermal capacity of the thin layer being able to be reduced. The partition functions as a support member by receiving the force imparted to the thin layer. The thin layer of coating of a ceramic material may be formed on the inner surfaces of the suction and exhaust ports of a valve in the head liner, so that the heat insulating functions and thermal capacity of the suction and exhaust ports of the valve can be improved and reduced, respectively. The present invention further seeks to provide a heat insulating combustion chamber wherein the minimization, which is important for improving the suction efficiency of an engine, of the thermal capacity of an inner ceramic surface the temperature of which becomes high, is effected for the purpose of reducing to the lowest possible level the quantity of heat which the suction air receives from the inner surface of the combustion chamber of the heat insulated engine, i.e., forming the surface of the combustion engine to have a small thermal capacity enabling the same surface to be cooled immediately with the suction air at a suction stroke of the engine, so that a difference between the temperature of the suction air and that of the surface of the combustion chamber becomes small, whereby the suction air flows in easily at a suction stroke, the quantity of heat absorbed by the surface of the combustion chamber at the time of a maximum temperature in the combustion chamber being reduced to make small a difference between the temperature of the combustion gas and that of the surface of the combustion chamber, the quantity of thermal energy, which escapes to the outside via the cylinder head and cylinder block without being held by the head liner at the explosion and exhaust strokes, being able to be minimized, whereby it becomes possible to send the thermal energy in the combustion chamber to an energy recovery unit, which is provided at the downstream side, at a maximal rate through an exhaust port, so that the thermal energy can be recovered at a maximal rate. The present invention further seeks to provide a method of producing very easily a heat insulating combustion chamber having a high strength. According to a further aspect of the present invention there is provided a method of producing a heat insulating combustion chamber comprising the steps of: forming a head liner consisting of a head lower portion provided with a suction port and an exhaust port and composed of a ceramic material, which is unitarily formed with an annular cylinder liner upper portion composed of a ceramic material identical with that of said head lower portion, such that said head liner defines a portion of a combustion chamber therein; forming a partition having a latticed structure of a ceramic material which is dimensioned to contact the whole of the inner surface of said head liner on the side thereof facing said combustion chamber; packing carbon powder in a plurality of the hollow spaces in said partition so as to form a compound body consisting of said partition and said carbon; polishing the inner surface of said compound body so that alternating regions of said partition and said carbon are exposed at the inner surface of the compound body, fitting said compound body in said head liner so that the outer surface of said compound body contacts the inner surface of said head liner, and forming a thin layer of a ceramic material on the inner surface of the compound body after said compound body has been fitted within said head liner, so as to cover the whole of the inner surface of said compound body. The step of forming the thin layer so as to cover the whole of the inner surface of the compound body may consist of depositing the ceramic material by chemical vapour deposition on the inner surface of said compound body so as to form a thin layer which is bonded to said partition of the compound body. The oxygen contained within the partition and the carbon may react with each other to generate carbon dioxide during said step of carrying out the chemical vapour deposition of ceramic material, whereby the carbon in the partition is imparted a porous structure owing to said carbon dioxide. An embodiment of the heat insulating combustion chamber according to the present invention will now be described by way of example only with reference to the following drawings in which: Fig. 1 is a sectional view, which is taken along the line I-I in Fig. 2, of an embodiment of the heat insulating combustion chamber according to the present invention; Fig. 2 is a sectional view taken along the line II-II in Fig. 1; and Fig. 3 is an enlarged sectional view taken along the line III-III in Fig. 2. In Figs. 1 and 2, a heat insulating combustion chamber according to the present invention is designated generally by a reference numeral 10. This heat insulating combustion chamber 10 is applied to a head liner 1, and discloses the technical concept connecting the heat insulating structure for a lower surface portion 2 of a head and an upper portion 3 of a cylinder liner 3 which constitute a head liner 1 in the heat insulated engine. The technical concept of the heat insulating combustion chamber 10 can, of course, be applied to a piston head. The heat insulating structures for a cylinder, a piston and suction and exhaust valves, which are other than the above-mentioned parts, are neither referred to nor illustrated. If heat insulating structures are formed out of a ceramic material, such as silicon nitride (Si₃N₄), and a heat insulating material for the cylinder, piston and suction and exhaust valves, the heat insulating purpose can, of course, be achieved more reliably. The head liner 1 consisting of an integrated structure of the lower surface portion 2 of the head and the upper portion 3 of the cylinder liner is fitted via a heat insulating material in a cylindrical portion of a cylinder head, which is provided with, for example, a suction port and an exhaust port, and, in addition to them, a fuel injection nozzle port in a diesel engine. A description of the head liner fitting method is omitted in this specification. As shown in Figs. 1 and 2, the heat insulating combustion chamber 10 according to the present invention is provided with a thin film member, i.e. a thin layer 4, which is formed on the parts, which are on the side of the interior of the combustion chamber 5, of the head liner 1, which consists of an integrated structure of the lower surface portion 2 of the head and the upper portion 3 of the cylinder liner, via a heat insulating layer consisting of carbon 6 and an air layer 8. The head liner 1 consists of a ceramic material, such as silicon nitride (Si₃N₄), and the lower surface portion 2 of the head liner 1 is provided with suction and exhaust valve seats 17 (only one of which is shown in Fig. 2). The thin layer 4 is formed to small thickness by the chemical vapor deposition of a ceramic material, such as silicon nitride (Si₃N₄) so that the thermal capacity of the layer becomes small. A latticed partition 7 consisting of a ceramic material, such as silicon nitride (Si₃N₄) is provided in a vertically fixed state between the thin layer 4 and head liner 1, and a heat insulating layer is formed between the wall members 7 of this partition 7. The heat insulating layer consists of a porous structure composed of carbon 6 as heat insulating material, and pores 8 in the same material. The heat insulating combustion chamber 10 constructed as described above can be formed by the following manufacturing method. First, a ceramic material, such as silicon nitride (Si₃N₄) is injected from a nozzle, for example, a T-shaped nozzle or a cross-shaped nozzle of an injection molding machine into a mold, and a latticed partition 7 is thereby injection molded, the partition 7 being used to integrally mold a portion 12 positioned on the lower surface of the head and a portion 13 positioned on the upper section of the cylinder liner. For example, as shown in Fig. 3, carbon powder is then packed in a plurality of cross-sectionally rectangular spaces 14 formed among the wall members of the partition 7, to obtain a molded product consisting of a compound material, i.e. a compound product. The inner surface of this compound product is polished so that the surfaces of the carbon 6 and wall members of the partition 7 are exposed alternately on the same inner surface. In other words, the polishing is done so that rectangular surface portions defined by the wall members of the partition 7 are exposed on the inner surface of the compound product. The compound product the inner surface of which has been polished is fitted in a contacting state in the inner surface of the head liner 1 which consists of an integrated structure of the lower surface portion 2 of the head and the upper portion 3 of the cylinder liner, and which are composed of a ceramic material, such as silicon nitride (Si₃N₄). The resultant product is placed in a chemical vapor deposition furnace and subjected to the chemical vapor deposition of a ceramic material, such as silicon nitride (Si₃N₄) to form a thin layer 4, which consists of a film of this ceramic material, on the whole of the exposed inner surfaces of the partition 7 and carbon 6. Since the partition 7 and thin layer 4 consist of the same ceramic material, they are combined very firmly at the joint portions 9, the thin layer 4 being formed as a layer of coating 11 on the partition 7 and carbon 6. This thin layer 4 is positioned on the side facing the combustion chamber 5 of the engine. When the exposed surface of the compound product is subjected to chemical vapor deposition to increase the temperature thereof, the oxygen contained among the particles of the carbon powder performs an oxidation reaction with a part of the carbon 6 to be turned into carbon dioxide. These portions of the generated carbon dioxide turn into pores 8 among the particles of the carbon 6, so that the carbon 6 among the latticed body of the partition 7 is formed into porous structures. Namely, the cross-sectionally rectangular portions 14 defined by the partition 7 are formed into heat insulating layers each of which consists of carbon and air layers. The spaces, which are formed to a cross-sectionally rectangular shape, among the walls of the partition 7 shown in the drawings may, of course, be formed to any other shape, for example, a cross-sectionally square shape, a cross-sectionally triangular shape and a cross-sectionally hexagonal shape. Moreover, since the latticed body of the partition 7 functions as a support, the thin layer 4 is supported very firmly by the partition 7. Therefore, the thin layer 4, which consists of a thin film, can serve as a member of a high strength facing the combustion chamber 5 of the engine. Moreover, since the carbon 6 is packed in the latticed partition so that the density and thermal conductivity of the carbon become low, very good heat insulating performance can be obtained owing to the heat insulating layer consisting of the porous structures of the carbon 6, though a part of the carbon 6 is oxidized at a high temperature. A layer of coating 11 of a ceramic material, such as silicon nitride (Si₃N₄) is formed on the inner surface of a passage 18 for the suction and exhaust valves, which is formed in the lower surface portion 2 of the head, and this layer of coating 11 is covered with a thin layer 4. Since the heat insulating combustion chamber 10 according to the present invention is constructed as described above, the thin layer 4, a ceramic member, provided on the inner surface of the cylinder head liner 1 and exposed to the high-temperature gas in the combustion chamber 5 of the engine can be formed to the smallest possible thickness by chemical vapor deposition, whereby the thermal capacity of the thin layer 4 can be reduced. In order to prevent the reduced thickness of the thin layer 4 from causing the strength of the same layer to decrease, this layer 4 is strengthened by applying the latticed ceramic partition 7 to the outer side thereof. Owing to the heat insulating layer consisting of the carbon 6 packed among the walls of the partition 7 and pores 8, the heat insulating performance of the heat insulating combustion chamber can be improved.

Claims: 1. A heat insulating combustion chamber having a head liner (1) comprising a head lower portion (2) provided with a suction port (17) and an exhaust port (17) and consisting of a ceramic material, which head lower portion (2) is unitarily formed with an annular cylinder liner upper portion (3) consisting of a ceramic material identical with that of said head lower portion (2), a portion of a combustion chamber (5) being defined by an inner side of said head liner (1), said heat insulating combustion chamber further comprising: a latticed partition (7) consisting of a ceramic material fixed to the inner surface of said head liner (1), having carbon (6) packed in a plurality of the hollow spaces formed in said partition (7), and a thin layer (4) of a ceramic material formed so as to cover the whole of the inner surfaces of said partition (7) and said carbon (6). 2. A heat insulating combustion chamber according to claim 1, wherein said ceramic material forming said head liner (1), said partition (7) and said thin layer (4) is silicon nitride. 3. A heat insulating combustion chamber according to claim 1 or 2, wherein said carbon (6) is packed in the hollow spaces among the walls of said partition (7) so that the density and thermal conductivity thereof becomes low. 4. A heat insulating combustion chamber according to claim 1, 2 or 3, wherein said partition (7) is arranged to function as a support member by receiving force imparted to said thin layer (4). 5. A heat insulating combustion chamber according to any preceding claim, wherein said head liner (1) is fitted within a cylindrical recessed portion formed on a cylinder head provided with suction and exhaust ports (17). 6. A method of producing a heat insulating combustion chamber comprising the steps of: forming a head liner (1) consisting of a head lower portion (2) provided with a suction port (17) and an exhaust port (17) and composed of a ceramic material, which is unitarily formed with an annular cylinder liner upper portion (3) composed of a ceramic material identical with that of said head lower portion (2), such that said head liner (1) defines a portion of a combustion chamber (5) therein; forming a partition (7) having a latticed structure of a ceramic material which is dimensioned to contact the whole of the inner surface of said head liner (1) on the side thereof facing said combustion chamber (5); packing carbon powder in a plurality of the hollow spaces (8) in said partition (7) so as to form a compound body consisting of said partition (7) and said carbon (6); polishing the inner surface of said compound body so that alternating regions of said partition (7) and said carbon (6) are exposed at the inner surface of the compound body, fitting said compound body in said head liner (1) so that the outer surface of said compound body contacts the inner surface of said head liner (1), and forming a thin layer (4) of a ceramic material on the inner surface of the compound body after said compound body has been fitted within said head liner (1), so as to cover the whole of the inner surface of said compound body. 7. A method of producing a heat insulating combustion chamber according to claim 6, wherein said step of forming said thin layer (4) so as to cover the whole of the inner surface of said compound body consists of depositing the ceramic material by chemical vapour deposition on the inner surface of said compound body so as to form a thin layer (4) which is bonded to said partition (7) of the compound body. 8. A method of producing a heat insulating combustion chamber according to claim 6 or 7, wherein oxygen contained within said partition (7) and the carbon (6) react with each other to generate carbon dioxide during said step of carrying out the chemical vapour deposition of ceramic material, whereby the carbon (6) in the partition (7) is imparted a porous structure owing to said carbon dioxide.

Inventors: KAWAMURA, HIDEO
Applicants: ISUZU MOTORS LIMITED
Application year: 1988
Main classification: F02B77
IPC codes: C04B41, F02B23, F02F7, F02F1, F02B77