Thermally insulating engine

Abstract: The purposes of this invention are to integrate the combustors and the air intake/exhaust passages in the thermally insulating engine into an assembly so that the space required for respective parts can be increased as well as to avoid complex structure. The space between the subcombustion chamber 3 and the main combustion chamber above the piston 1 is reduced by the base 11a installed above the piston head 11. In addition, a plurality of connection hole 21c arranged in an oblique radial pattern is drilled in the reduced channel. As a result, vortex is obtained within the subcombustion chamber 3 in the compression process. In the combustion process, the flame from the subcombustion chamber 3 is carried on swirl and expands within the main combustion chamber and thus mixes with air for combustion. In the center of the cylinder, the subcombustion chamber 111 is installed and surrounded by the air intake passage 112 and the exhaust passage 113 separated with the side wall 114, which is made of thermal conductive ceramic, of the subcombustion chamber. The single-unit structure is made by using the said ceramics for the outer peripheral wall 115. In addition, a plurality of the air intake 141 and exhaust outlet of 151 is provided on the piston side so that resrespective channels have wide opening. In other configurations, the combustion chamber and the air intake and exhaust channels in the thermally insulating engine are made into a single-unit structure, and two turbochargers, which allow flexible serial/parallel connection of the supercharge system to be performed, are installed so that a compact and highly efficient system can be obtained.

Description: This invention relates to a thermally insulating engine consisting of an assembly of a combustion chamber to burn fuel in the internal combustion engine and its air intake and exhaust passages. In an engine using combustion energy of fuel as its power source, a considerable amount of energy is absorbed by the engine. As a result, thermal expansion causes deformation in the parts related to the combustion chamber. Also, inconvenience such as abnormal explosion of fuel or improper lubrication will occur. To prevent such inconvenience, a cooling device using air or water as a medium is used. Through this cooling, however, the thermal efficiency of the engine decreases. Recently, thermally insulating engines capable of withstanding high temperature and maintaining thermal insulation have been developed by using, for example, ceramics in the parts related to the combustion chamber of the engine. Thus, it is attempted to increase thermal efficiency and decrease the weight by omitting the cooling device, which was conventionally essential for engines. With this type of engine without a cooling device, the combustion chamber will require a thermally insulating structure if higher thermal insulation is to be achieved. In addition, the combustion chamber must be positioned in the centre. The drawback of such an engine is that the space for the combustion chamber and the air intake and exhaust passages will be reduced, and their structure will be complex. EP-A-0397521 discloses an engine in which a projection on the piston extends into a hole connecting the main combustion chamber with a subcombustion chamber. WO-A-85/02884 discloses a ceramic engine head. According to the present invention, there is provided a thermally insulating engine, for which the areas near the combustion chamber are made of insulating material, the engine comprising: a cylinder, in which a piston operates; a boss at the centre of the top surface of the piston; a cup-shape cylinder head which covers the top of the cylinder; a hole positioned on the central axis of the cylinder head and into which the boss on the top surface of the piston engages when the piston reaches top dead centre; a subcombustion chamber of ceramics which is installed over said hole and connected to the main combustion chamber formed by the said cylinder via said hole; and, a fuel injection nozzle for injecting fuel into the said subcombustion chamber; characterised by: an air connection passage radially outwards of said hole, either separate from said hole or formed as a groove in the wall of said hole, for coupling the subcombustion chamber and the main combustion chamber, and by: the boss having a truncated cone shape and the cylinder head being made of ceramics. In preferred aspects of the invention, the combustion chamber is positioned in the centre and surrounded with the air intake and exhaust passages separated with side walls of ceramics made of material of low thermal conduction, so that the engine is structured into an assembly by the outer peripheral walls of the intake and exhaust passages. Thus, the said combustion chamber can be installed in the centre and the parts contacting high-temperature gas generated through combustion will be insulated. Therefore, the air intake system and the exhaust system can coexist, each system is provided with a wide space, and structural complexity can be avoided. The said engine may be equipped with a plurality of connection holes arranged in an oblique radial pattern to generate a vortex in the subcombustion chamber to facilitate mixture with injected fuel. In the combustion process, the flame blown from the subcombustion chamber is carried by swirl generated by the oblique connection holes and mixed with air to perform good combustion. In the drawings: Fig. 1 is a cross-sectional profile of a first example of the combustor of the thermally insulating engine according to the invention; Fig. 2 is a top view of the first example of the combustor of the thermally insulating engine according to the invention; Fig. 3 is a cross section of a second example of the combustion chamber of the thermally insulating engine according to the invention; Fig. 4 is a drawing explaining the combustion condition of the second example; Fig. 5 is a top view of a third example; Fig. 6 is a cross-sectional profile of part of the third example; and, Fig. 7 is a drawing explaining the channels showing the relation between the air intake/exhaust channels and the valves in the third example. Fig. 1 shows the cross-sectional profile of the combustion chamber of the thermally insulating engine related to the invention. Fig. 2 shows a top view of the main combustion chamber showing the combustion process. In these drawings, the piston 1 has the piston head 11 and the piston body 12 made of ceramics with high strength and heat resistance. They are mutually linked with the coupling ring 13. In the centre on the upper surface of the piston head 11, a truncated cone boss lla having a bottom with gentle outline is installed. The upper surface of the piston head is formed in such a way that it slightly rises from the bottom to the peripheral portions and the main combustion chamber is formed between the upper inner wall of the cylinder and the upper surface of the piston head. The piston ring 14 is engaged in the upper portion of the piston body 12. The cylinder 2 has the cylinder head 21 and the cylinder liner 22 made of low thermal conductivity ceramics with resistance against high temperature. The subcombustion chamber 3 made of ceramics with high strength is installed on the upper portion of the hole 21a in the centre of the cylinder head 21. The corners of the hole edge 21b of the hole 21a, which is the channel between the subcombustion chamber 3 and the main combustion chamber, are cut according to the bottom of the boss lla of the said piston head 11. As shown in Fig. 2, a plurality of connection holes 21c is notched in the oblique radial direction at the specified angle. As Fig. 2 shows, the connection holes 21c are arranged in an oblique pattern to the virtual face, which extends in the radial direction from the centre line of the cylinder 2. The nozzle 4, which injects fuel, is installed in the centre of the upper wall of the subcombustion chamber 3. The nozzle 4 is designed to inject the fuel to the subcombustion chamber 3 at the end of the compression process, and the fuel is ignited in the subcombustion chamber by air of high temperature, the temperature having risen during adiabatic compression. Thus, the internal pressure in the subcombustion chamber 3 rises within a short time and the fuel is injected from the said connection hole 21c into the main combustion chamber between the piston 1 and the cylinder 2. The reduction of the gap between the hole 21a of the cylinder head 21 and the bottom of the boss lla of the piston head 11 at the top-dead centre of the piston 1 is designed so that the gap area is between 3 and 10 percent in comparison with the area of the piston. The connection holes 21c connecting the subcombustion chamber 3 and the main combustion chamber need not always be holes as shown in the example, and may be grooves instead. The following paragraphs explain the operations of the example 1 consisting of such a configuration. In the compression process, the piston 1 goes up according to the rotation of the crankshaft and compresses air, then compresses air in the subcombustion chamber 3. Towards the end of the process, the air current through the connection holes 21c generates a vortex in the subcombustion chamber when the peripheral edge of the boss lla approaches the lower edge of the hole 21a. This vortex expands from the lower portion towards the upper portion of the subcombustion chamber 3. When the peripheral edge of the boss 11a reaches the upper edge of the hole 21a, the space between the peripheral edge of the boss lla and the peripheral edge of the hole 21a is reduced. From this reduced space, air will be blown upwards through the hole 21a at high speed in the subcombustion chamber 3 because of the reduced area of the peripheral edge. When fuel is injected from the nozzle 4, the said air current generates mixed air in the subcombustion chamber 3, and the fuel is ignited. Thus, the pressure in the subcombustion chamber 3 will rapidly increase. However, the amount of oxygen within the subcombustion chamber 3 is insufficient to burn the entire amount of fuel. Therefore, unburned gas and combustion flame blow out in a swirl from the connections holes 21c into the main combustion chamber between the piston 1 and the cylinder 2 (see Fig. 2). The tip of the gas hits the face of the outer side wall of the main combustion chamber, and the unburned gas contacts and mixes with air in the extensive part within the main combustion chamber. As a result, combustion expands rapidly in the main combustion chamber, and combustion gas expands and pushes down the piston 1. The initial stage of combustion in the first example is performed with an abundance of fuel in the subcombustion chamber 3. Therefore, generation of NOx is controlled. The combustion condition of the middle to latter periods of combustion shows that unburned gas injected from the subcombustion chamber 3 into the main combustion chamber burns in an extensive area of the main combustion chamber and thus the fuel mixes well with air for combustion. Thus, generation of black smoke is controlled. The first example has the oblique connection holes to generate a vortex in the air, which passes between the main combustion chamber above the piston of the thermally insulating engine with a subcombustion chamber and the subcombustion chamber, or in the burning mixed air. Therefore, in the compression process, the air compressed by the piston generates a vortex in the subcombustion chamber and thus generation of mixed air is actively performed. As a result, mixed air, including flames from the subcombustion chamber, becomes a vortex in the combustion chamber above the piston during the initial stage of the combustion process. Thus, the vortex mixes well with air within the main combustion chamber for combustion. As a result, NOx and black smoke within exhaust gas will reduce. Fig. 3 shows the cross-sectional view of the second example of the thermally insulating engine according to the invention. Fig. 4 shows its longitudinal section. In these drawings, 102 is the cylinder, 103 is the piston. The combustor 101 in the second example is placed as the cylinder head on each cylinder. The combustor 101 has a flat cylindrical shape. Its structure will be explained in more detail below. Each of these combustors 101 is set into the cylinder head block (part of which is shown as 200 in Fig. 4), which is moulded by casting. The subcombustion chamber 111 is placed in the centre of the combustor 101. In the part near the outer peripheral wall 115, the air intake passage 112 and the exhaust passage 113, which are made into the shape of an arc, are provided. These passages as well as the side wall 114 of the subcombustion chamber 111 and the outer peripheral wall 115 have fine heat insulation. These parts use compound ceramics made of silicon nitride (Si 3 N 4 ), which has low thermal conductivity, and titanium oxide (TiO) or aluminum titanate (Al 2 TiO 5 ). To enhance moulding and casting performance, these parts are formed so that they have uniform wall thickness. The injection nozzle hole llla is drilled in the upper wall of the subcombustion chamber 111, and the hole 112a penetrating to the space 131, which is the combustion chamber on the top of the piston 103, is drilled in the lower wall. The outer wall 116 in the lower portion, which is coupled to the cylinder 102, uses ceramics made of silicon nitride (Si 3 N 4 ) with high strength. The boss 132 is installed on the top of the piston 103 and acts as the same as the boss lla in the first example. In the peripheral edge of the hole 112a, a plurality of connection grooves 112b is provided. Like the first example, the connection grooves 112b are cut to be oblique to the virtual face expanding in the radial direction from the centre line of the cylinder 102. The air intake 141 is equipped with the air intake valve 104 to guide fresh air by connecting the air intake passage 112 to the cylinder inside when the valve is open. To increase the area of the opening, two air intakes 141 are drilled, for example. The exhaust outlet 151 is equipped with the exhaust valve 105 to discharge exhaust gas after combustion via the exhaust passage 113 when the valve is open. Like the air intakes 141, two exhaust outlets are provided. The combustor 101 with the air intake/exhaust channels and the combustion chamber, as mentioned above, is moulded as a single unit by using ceramics only, without using metal. The following paragraphs explain the operations of the example consisting of such a configuration. As mentioned before, the subcombustion chamber 111, in which fuel is burned, and the exhaust passage 113 and the air intake passage 112, which are subject to high temperature, are separated by the side wall 114 and other parts made of ceramics of low thermal conductive material. Therefore, the high temperature caused by combustion heat will be blocked, even though these parts are adjacent to the subcombustion chamber by the single-unit structure. Thus, normal operation processes of the engine, including air intake, explosion and exhaust, will be performed without adverse influence. Also, the space required for the air intake passage 112 and the exhaust passage 113 can be reduced. In addition, a plurality of the air intakes 141 and the exhaust outlets 151 is installed, making air intake and exhaust to be efficiently performed. Thus, the piston 103 is powerfully driven to generate engine torque. According to the second example, the combustion chamber is positioned in the centre and the air intake and exhaust passages are arranged adjacent to the combustion chamber, the ceramics made of low thermal conductive material with heat resistance is used as side wall to form an assembly, and such an assembly is mounted on the top of the cylinder to form the thermally insulating engine. Thus, a wide space can be obtained for the combustion chamber and the air intake and exhaust passages. In addition, structural complexity of the combustion chamber can be avoided. In the second example, two air intakes and exhaust outlets are provided respectively. Thus, resistance in the air intake and exhaust channels is reduced, making it an efficient engine. Also, casting the ceramics by using a material with high casting performance will reduce the production costs. Fig. 5 shows the top view of the third example of the invention. Fig. 6 shows the cross-sectional profile of part of the third example. Fig. 7 shows the channel drawing explaining the relationship between the air intake and exhaust channels as well as the valves of the third example. In these drawings, a box 201 is positioned above the engine having four cylinders. Inside the box, the subcombustion chambers 203a to 203d corresponding the four cylinders, the air intake channels 204a to 204d, the exhaust channels 205a to 205d, and the connection channels are integrated into an assembly. These parts use material flexible for casting. They are moulded by casting and stored in the box. The following paragraphs explain the part of the assembly which is positioned to the left in Fig. 5. Separated by the peripheral wall 231a, which forms the subcombustion chamber 203a in its centre and which is made of ceramics using alumina (Al 2 O 3 ) or aluminum titanate (Al 2 TiO 5 ), the arc exhaust channel 205a to the left and the arc air intake channel 204a to the right are formed by the outer peripheral wall 202a and the air intake and exhaust partition 245a, which are made of ceramics of the same material. Thus, the combustion chamber and the air intake and exhaust channels are made into an assembly as the combustor 2A, below which the cylinder 12A with the piston 11A is installed as shown in Fig. 6. Thus, the engine having the air intake valve 13A and the exhaust valve 14A is formed. The boss 211 is installed on the top of the piston 11A and acts the same as the boss 11a in the first example. A plurality of connection grooves 232 is provided around the peripheral edge of the hole 231 coupling the subcombustion chamber 203a and the main combustion chamber. Like the first example, the connection grooves 232 are cut to be slanted to the virtual face extending from the centre line of the cylinder 12A in the radial direction. The combustor 2B is adjacent to the right side of the combustor 2A in the Fig. 5, and is made into almost the same structure as with the combustor 2A. The air intake coupling channel 204ab couples the mutual air intake channels 204a and 204b. The exhaust channels 205a and 205b are coupled by the exhaust coupling channel 205ab. The set of combustors 2C and 2D is made into almost the same structure as with the set of combustors 2A and 2B in such a manner that the left and right are reversed. The exhaust coupling channel 205ab and the exhaust coupling channel 205cd of respective sets are connected with the coupling channel 205ad, and the opening/closing valve V5 is installed in the middle of the channel. The channels at both ends of the coupling channel 205ad are guided to the side face of the box 201 and openings are made in the specified positions as the exhaust sending outlets 205Ea and 205Ed. The air intake channel 204b of the combustor 2B and the air intake channel 204c of the combustor 2C are also coupled in such a manner that they are mutually connected. Because these air intake channels are connected to the supercharged air channel from the two turbochargers, they are branched into two channels and openings are made in the specified positions in the side face of the box 201 as the air intakes 204Ib and 204Ic. The turbochargers 206 and 207 have the turbines 261 and 271, the compressors 262 and 272, and the rotary electric machines 263 and 273. Respective turbines driven by exhaust energy rotate the compressors respectively coupled to the turbines and compress air to supply it to the engine as supercharged air. Respective rotary electric machines mounted to the turbine shaft are supplied with power from the battery, etc. when the engine rotates at a low speed and under a high load in accordance with the operation condition of the engine to operate as an electric motor. The rotary electric machines are designed to increase the engine torque by increasing the supercharged air, or operate as an electric generator when there is sufficient exhaust energy to collect exhaust energy as electric power and increase engine torque by supplying the said power, for example, to the electric motor combined to the crankshaft. The turbine housings 206a and 207a with the turbine scroll of the turbochargers 206 and 207 are moulded by using ceramics material with heat resistance and high strength. Their exhaust intakes 206b and 207b are formed so that they are directly connected to the said exhaust outlets 205Ea and 205Ed. The supercharged air supply outlets 206c and 207c of these turbochargers are directly connected to the said air intakes 204Ib and 204Ic. The supercharged air supply channel 206c in the lower portion of the turbocharger 206 is coupled to the fresh-air intake 207d via the connection tube 267. The opening/closing valve V1 is installed in the middle of the connection tube 267, and the opening/closing valve V2 is installed in the direction of outside air of the fresh-air intake 207d. Therefore, if the opening/closing valve V2 is closed and V1 is opened when both turbochargers 206 and 207 are driven, the supercharger system of the both turbochargers is connected in series to perform 2-stage supercharging so that high-pressure supercharged air is supplied to the engine. The opening/closing valve V3 is provided in the supercharged air supply channel of the turbocharger 206. The opening/closing valve V4 is provided in the exhaust insertion channel to the turbocharger 207. Opening/closing of the valves V3 and V4 as well as the said valves V1, V2 and V5 is designed to be controlled by instruction from the controller consisting of an electronic control device. The following paragraphs explain the operations of the example 3 consisting of such a configuration. Inside the box 201, the combustors 2A to 2D for the four cylinders are installed. In other words, the subcombustion chambers 203a to 203d, the air intake channels 204a to 204d, the exhaust channels 205a to 205d, and their coupling channels are cast so that they are mutually coupled as mentioned before with respective incoming/outgoing channels from/to the turbochargers 206 and 207. Therefore, the four-cylinder engine is assembled by installing the box 201 on the upper portion of the four cylinders. The combustors 2A to 2D are respectively equipped with the subcombustion chamber in the centre and the respective air intake channels and exhaust channels adjacent to the subcombustion chamber separated with the peripheral wall and the air intake/exhaust partition made of low thermal conductive material. Because of the good thermal insulation, normal air intake, explosion and exhaust processes are performed without any problem and adverse influence to operate the engine. As shown in the diagram in Fig. 7, when the opening/closing valves V1 to V5 installed in the channels of the turbochargers 206 and 207 are controlled so that, for example, V5 of the exhaust system is closed and V4 is open, and V1 of the supercharged air system is closed and V2 and V3 are open, both the turbochargers 206 and 207 are driven by exhaust energy from the set of combustors 2A and 2B and the set of combustors 2C and 2D, which consists of two cylinders respectively, to perform parallel operation. Thus, supercharged air is supplied to the four combustors to perform normal operation. When controlling the opening/closing valve V5 of the exhaust system to close and V4 to open, V2 and V3 of the supercharged air system to close, and V1 to open, the compressed air produced by the operations of the turbocharger 206 is guided to the turbocharger 207 via the channel equipped with the opening/closing valve V1 to be recompressed. As a result, strong supercharged air produced by the 2-stage turbochargers 206 and 207, which are serially connected, is supplied to the respective combustors 2A to 2D to perform operation. In the example mentioned above, the combustion chamber for the four cylinders and its air intake and exhaust channels are separated with the wall made of material with low thermal conductivity to form the four compact combustors, which are placed adjacent, so that they are cast inside a single box. Therefore, the four-cylinder engine can be easily assembled by installing the box on the four cylinders. In addition, the supercharger system is designed to be flexibly switched between serial and parallel connection by installing the two turbochargers, which can be easily connected, and by controlling the opening/closing valves. Therefore, the supercharged air pressure can be properly controlled in accordance with the operation condition of the engine. As a result, a highly efficient engine can be obtained. Thus, the invention has been explained by using examples. Within the scope of the purpose of the invention as defined by the appended claims, variations and applications are possible to operate, for example, the rotary electric machine installed to the turbocharger as an electric motor or an electric generator in accordance with the operation condition of the engine. Therefore, these variations and applications should not be excluded from the scope of the invention as defined by the appended claims.

Claims: A thermally insulating engine, for which the areas near the combustion chamber are made of insulating material, the engine comprising: a cylinder (2,102,12A), in which a piston (1,103,11A) operates; a boss (11a,132,211) at the centre of the top surface of the piston (1,103,11A); a cup-shape cylinder head (21,200,201) which covers the top of the cylinder (2,102,12A); a hole (21a,112a,231) positioned on the central axis of the cylinder head (21,200,201) and into which the boss (11a,132,211) on the top surface of the piston (1,103,11A) engages when the piston (1,103,11A) reaches top dead centre; a subcombustion chamber (3,111,203a) of ceramics which is installed over said hole (21a,112a,231) and connected to the main combustion chamber formed by the said cylinder via said hole (21a,112a,231); and, a fuel injection nozzle (4,111a) for injecting fuel into the said subcombustion chamber (3,111,203a); characterised by: an air connection passage (21c,112b,232) radially outwards of said hole (21a,112a,23), either separate from said hole or formed as a groove in the wall of said hole, for coupling the subcombustion chamber (3,111,203a) and the main combustion chamber, and by: the boss (11a,132,211) having a truncated cone shape and the cylinder head being made of ceramics. A thermally insulating engine according to claim 1, wherein said air connection passage is a pluarlity of holes (21c). A thermally insulating engine according to claim 1, wherein said air connection passage is a plurality of grooves (112b,232). A thermally insulating engine according to any of claims 1 to 3, wherein said air connection passage penetrates in an oblique direction to the virtual face extending from the centre line of the cylinder in a radial direction. A thermally insulating engine according to any of claims 1 to 4, wherein said ceramics used in the said subcombustion chamber is of silicon nitride. A thermally insulating engine according to claim 1, wherein: the subcombustion chamber (111) is positioned in the centre of said cylinder head and surrounded with air intake and exhaust passages (112,113), said subcombustion chamber and said air intake and exhaust passages being separated with side walls (114) of ceramics made of material of low thermal conduction, so that the cylinder head is made into a single unit structure comprising the subcombustion chamber and the air intake and exhaust passages. A thermally insulating engine according to claim 6, wherein said cylinder head is set into the cylinder block. A thermally insulating engine according to claim 6, wherein the side wall of the subcombustion chamber and the outer peripheral wall (115) of the cylinder head are formed with uniform wall thickness. A thermally insulating engine according to claim 1, further comprising: a plurality of cylinders in each of which a piston reciprocates; a box (201) installed over said cylinders and which includes an assembly of the subcombustion chambers (203a-203d); each subcombustion chamber being separated from a surrounding air intake and exhaust channel (204,205) which channels are separated by partitions (245a) made of thermally insulating material with high strength, so that each subcombustion chamber is situated in the centre of its air intake and exhaust channels; two turbochargers (206,207) which are combined to the said air intake/exhaust channels and each of which has turbine scrolls made of the same material as the said partition; and, switching control means to switch the supercharger system of the turbocharger between serial and parallel operation in accordance with the combustion condition of fuel. A thermally insulating engine according to claim 9, wherein said insulating material is ceramics made of alumina (Al 2 O 3 ) or aluminum titanate (Al 2 TiO 5 ). A thermally insulating engine according to claim 9 or claim 10, wherein said switching control means are made by arranging opening/closing valves in the supercharger channel of the two turbochargers and by switching the supercharger system through selection control of operation of the said opening/closing valves.

Inventors: KAWAMURA HIDEO, KAWAMURA, HIDEO
Applicants: ISUZU CERAMICS RES INST, ISUZU CERAMICS RESEARCH INSTITUTE CO., LTD.
Application year: 1993
Main classification: F02B19
IPC codes: F02B19, F02F7, F02B37