JP2005201075A - Internal combustion engine capable of self-ignition operation allowing compression self-ignition of air-fuel mixture - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a lowering of exhaust temperature in a premix compression self-ignition combustion system. <P>SOLUTION: This internal combustion engine is designed such that a cylinder head 130 is dividable along a plane for vertically dividing an exhaust port 135 into two, and a heat insulating member 172 is arranged on the inner wall of the exhaust port 135, which is a part in the vicinity of an exhaust valve seat 133. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a technique for suppressing a decrease in exhaust temperature in an internal combustion engine capable of a self-ignition operation in which an air-fuel mixture is compressed and ignited.

  In recent years, as a combustion method for internal combustion engines, a new combustion method has been sought that replaces the "premixed spark ignition combustion method" like a normal gasoline engine or the "diffuse combustion method" like a normal diesel engine. . As one of such new combustion methods, there is a “premixed compression self-ignition combustion method” in which an air-fuel mixture is formed in advance in a combustion chamber, and this is compressed and self-ignited and combusted. The premixed compression auto-ignition combustion method is a combustion method that compresses an ultra-lean mixture at a high compression ratio, completes combustion in a short time by self-ignition combustion at once, and in principle it is included in the exhaust gas It is considered that the amount of NOx and the fuel consumption can be reduced at the same time.

  However, HC and CO, which are air pollutants other than NOx, still need to be purified by promoting chemical reactions with catalysts. Here, the catalyst does not work sufficiently if the exhaust temperature is not high to some extent, but the premixed compression auto-ignition combustion method is a combustion method that burns a super lean mixture, so the exhaust temperature is different from other combustion methods. Tends to be low. Therefore, in an internal combustion engine using a premixed compression auto-ignition combustion method, a heating type catalyst such as a heater or a temperature raising means such as addition of fuel to the exhaust is required in order to make the catalyst sufficiently act at the time of warm-up or light load. It was. As a result, the cost was significantly increased and the fuel consumption was deteriorated.

  As a technology to suppress the exhaust temperature drop, a technology for assembling a port liner (heat insulating material) to the exhaust port, or a number of recesses on the surface of the port liner, and a heat insulating space between the port liner and the inner wall surface of the exhaust port Techniques for forming are known.

JP-A-5-133225 JP-A-5-042660

  However, in the premixed compression auto-ignition combustion system, the exhaust temperature is lower than in other combustion systems, and thus the above technique has not sufficiently suppressed the decrease in the exhaust temperature.

  The present invention has been made to solve the above-described conventional problems, and an object of the present invention is to provide a technique that can further suppress a decrease in exhaust temperature in a premixed compression auto-ignition combustion system. And

In order to solve the above problems, an internal combustion engine of the present invention is an internal combustion engine capable of premixed compression self-ignition operation,
A combustion chamber composed of a cylinder and a piston;
An exhaust valve for opening and closing an exhaust port through which combustion gas is discharged from the combustion chamber;
An exhaust valve seat closely contacting the exhaust valve when the exhaust valve is closed;
An exhaust port that is provided in a cylinder head of the cylinder and discharges combustion gas discharged from the exhaust port;
With
The cylinder head portion has a structure that can be divided along a plane that divides the exhaust port into two in the vertical direction,
A heat insulating material is provided on an inner wall of at least a portion near the exhaust valve seat of the exhaust port.

  In this internal combustion engine, since the cylinder head portion can be divided along a plane that divides the exhaust port into two in the vertical direction, heat insulating material can be easily provided on the inner wall of the exhaust port in the vicinity of the exhaust valve seat. Can do. Therefore, it is possible to insulate the exhaust port inner wall in the vicinity of the exhaust valve seat where the heat transfer coefficient is maximized, and to further suppress the decrease in the exhaust temperature.

In the internal combustion engine, the inner wall of the exhaust port is provided with a plurality of convex portions that support the heat insulating material,
A heat insulating space may be provided between the inner wall of the exhaust port and the heat insulating material.

  According to this configuration, the presence of the heat insulating space can further improve the heat insulating effect, and can further suppress the decrease in the exhaust temperature. Furthermore, since the shape of the heat insulating material can be a simple shape, the cost can be reduced and the surface area of the flow path through which the exhaust gas passes can be reduced, further increasing the heat insulating effect and exhausting. A decrease in temperature can be further suppressed.

In the internal combustion engine, the inner wall of the exhaust port is provided with a plurality of recesses,
A plurality of closed heat insulation spaces may be constituted by the plurality of recesses and the heat insulating material.

  Also with this configuration, the heat insulation effect can be further improved by the presence of the heat insulation space, and a decrease in the exhaust temperature can be further suppressed. Furthermore, since the heat insulation space is partitioned into a plurality of closed heat insulation spaces by the plurality of recesses and the heat insulating material, air convection can be suppressed, and the heat insulation effect can be further enhanced and the exhaust temperature can be lowered. Further suppression can be achieved.

The internal combustion engine may include a plurality of the exhaust ports and the exhaust valves,
The exhaust valve moves up and down;
The exhaust port has an exhaust chamber (chamber) in which combustion gases rising from a plurality of the exhaust ports are combined, and an exhaust passage for leading the combustion gas from the exhaust chamber to the outside,
The exhaust chamber and the discharge passage may be provided horizontally, and may be divided into two at the center by a plane that divides the cylinder head portion.

  According to this configuration, the flow rate of the high-temperature exhaust gas can be lowered due to the presence of the exhaust chamber, so that the heat transfer coefficient to the wall surface can be reduced and the decrease in the exhaust gas temperature can be suppressed. Thereby, the catalyst warm-up property can be improved and the turbo efficiency can be improved. Further, since the exhaust chamber and the discharge passage are divided into two in the middle by a plane that divides the cylinder head portion, a heat insulating material can be easily provided on the inner wall of the exhaust chamber and the portion of the exhaust passage near the exhaust valve seat. Can do. Therefore, it is possible to insulate the portion in the vicinity of the exhaust valve seat where the heat transfer coefficient is maximized, and to further suppress the decrease in the exhaust temperature. In addition, since the back pressure is reduced, exhaust gas escape is improved and the influence of exhaust pulsation of other cylinders is suppressed. Can be enlarged.

  In the internal combustion engine, the internal combustion engine includes three or more exhaust ports and exhaust valves, and is connected to a peripheral wall of the cylinder, and an opening facing the cylinder is opened and closed by the vertical movement of the piston. The engine may be a two-cycle internal combustion engine having at least one scavenging port.

  According to this configuration, a large curtain area can be secured without increasing the valve area, combustion gas can be discharged efficiently even during high-rotation and high-load operation, and stable compression itself. Ignition operation can be performed. Moreover, the blow-through of fresh air and injected fuel can be suppressed.

  In the internal combustion engine, the cylinder may have a monoblock structure in which the cylinder head portion and the cylinder block portion are integrally formed.

  According to this configuration, it is possible to improve the gas sealing performance at the time of high pressure in the cylinder. Moreover, bore distortion is suppressed and the amount of blow-by gas can be reduced. In addition, dead volume can be reduced and HC emissions can be reduced. Furthermore, the cost can be reduced, the weight can be reduced, the reliability can be improved, and the degree of freedom in arranging the spark plug and the fuel injection valve can be improved by reducing the number of parts.

  The present invention can be realized in various modes, and can be realized in modes such as an internal combustion engine, an exhaust device of the internal combustion engine, an exhaust method of the internal combustion engine, and the like.

Next, embodiments of the present invention will be described in the following order based on examples.
A. First embodiment:
B. Second embodiment:
C. Third embodiment:
D. Variation:

A. First embodiment:
FIG. 1 is an explanatory view conceptually showing the structure of a gasoline engine in the first embodiment of the present invention. FIG. 1 shows the structure of a cylinder when a cross section is taken at the center of the cylinder of a gasoline engine.

  The combustion chamber of the gasoline engine 100 includes a hollow cylindrical cylinder 142 provided in the cylinder block 140, a piston 152 that slides up and down in the cylinder 142, and a cylinder head 130 provided on the cylinder block 140. And is formed by. In this embodiment, an example of a monoblock structure in which the cylinder block 140 and the cylinder head 130 are integrated is shown. A cylindrical body constituted by the cylinder block 140 and the cylinder head 130 is called a “cylinder” in a broad sense. In the present specification, the direction in which the piston 152 approaches the cylinder head 130 along the central axis of the cylinder 142 is described as an upward direction, and the direction in which the piston 152 moves away from the cylinder head 130 is described as a downward direction. In this specification, “horizontal” means a state in which there is almost no vertical displacement.

  The cylinder head 130 is provided with an exhaust valve 132 that opens and closes an exhaust port through which the combustion gas in the combustion chamber flows out, an exhaust port 135 through which exhaust gas that is the combustion gas that flows out from the exhaust port, and an ignition plug 136. ing. The exhaust valve 132 is driven by an electromagnetic actuator 164 via a drive arm 162. The electromagnetic actuator 164 can open and close the exhaust valve 132 at an arbitrary timing. Note that the exhaust valve 132 may be driven by another type of variable valve mechanism such as a hydraulic actuator or a cam mechanism instead of the electromagnetic actuator.

  The cylinder block 140 is provided with two types of scavenging ports 146 and 148 (detailed shapes will be described later) through which fresh air flows into the cylinder 142. The openings (scavenging ports) facing the cylinder 142 of the scavenging ports 146 and 148 are configured to be opened and closed by the vertical movement of the piston 152 and to be fully opened in the vicinity of the bottom dead center of the piston 152. The scavenging ports 146 and 148 are connected to an air supply surge tank 144 provided in the cylinder block 140 at the end opposite to the cylinder 142.

  As described above, the gasoline engine 100 is a so-called uniflow type two-cycle engine in which the scavenging ports 146 and 148 are connected to the lower portion of the cylinder 142 and the exhaust valve 132 is provided in the cylinder head 130. Since the two-stroke engine has a scavenging stroke in which both the scavenging port and the exhaust port are in an open state, the so-called “blow-through” in which fresh air or injected fuel supplied from the scavenging port to the cylinder flows out from the exhaust port as it is. Is likely to be a problem. When fresh air or injected fuel blows out, the pressure in the scavenging port must be increased more than necessary, leading to deterioration of fuel consumption due to supercharging loss. In addition, the air-fuel mixture in the cylinder does not become sufficiently lean, and premature ignition tends to occur. Uniflow type two-cycle engines have a greater distance between the scavenging port and the exhaust port, so fresh air and injected fuel can be blown out compared to other types of two-cycle engines such as overhead valve type and schneille type. Suppressed and preferred.

  The scavenging ports 146 and 148 are connected to an intake passage 12 for introducing fresh air via a supply surge tank 144, and the exhaust port 135 is connected to an exhaust passage 16 through which exhaust gas passes. Downstream of the exhaust passage 16, a catalyst 26 for purifying air pollutants and a turbine 52 of the supercharger 50 are provided. Exhaust gas passing through the exhaust passage 16 is released into the atmosphere after rotating the turbine 52. The intake passage 12 is provided with a compressor 54 for the supercharger 50. The compressor 54 is connected to the turbine 52 via a shaft 56, and the compressor 54 also rotates when the turbine 52 rotates by the exhaust gas. As a result, the compressor 54 pressurizes the air sucked from the air cleaner 20 and then pumps it toward the scavenging ports 146 and 148.

  Since air temperature rises when pressurized by the compressor 54, an intercooler 62 is provided downstream of the compressor 54 in order to cool the intake air. A surge tank 60 and a throttle valve 22 are also provided in the intake passage 12. The surge tank 60 has a function of relaxing pressure waves generated when the combustion chamber sucks air, and the throttle valve 22 is set to an appropriate opening degree by the electric actuator 24 to adjust the intake air amount. It has a function to do.

  The piston 152 is connected to a crankshaft 156 via a connecting rod 154, and a crank angle sensor 32 that detects a crank angle is attached to the crankshaft 156.

  The operation of the gasoline engine 100 is controlled by an engine control unit (hereinafter referred to as ECU) 30. The ECU 30 detects the engine rotational speed Ne and the accelerator opening degree θac, and executes control of the opening degree of the throttle valve 22, ignition timing control of the spark plug 136, and control of the electromagnetic actuator 164 based on these. The engine rotation speed Ne is detected by a crank angle sensor 32, and the accelerator opening degree θac is detected by an accelerator opening degree sensor 34 built in the accelerator pedal.

  FIG. 2 is an explanatory diagram showing an enlarged cross section of a cylinder of the gasoline engine in the first embodiment. FIG. 3 is an explanatory view showing the AA cross section of FIG. As shown in FIG. 2, the gasoline engine 100 according to the first embodiment has a structure in which the cylinder head 130 can be vertically divided along the dividing surface DF. FIG. 3 shows a state in which a portion below the dividing surface DF of the cylinder head 130 is viewed from above.

  In the gasoline engine 100, a spark plug 136 is provided in the approximate center of the cylinder head 130, and three exhaust valves 132 are provided around the spark plug 136. All of the valve head portions 132a of the exhaust valve 132 have the same diameter, and are arranged around the central axis of the cylinder 142 so that the intervals are equal. The three exhaust valves 132 are installed in the cylinder head 130 so that the central axes of the shaft portions 132b are parallel to each other and are substantially parallel to the central axis of the cylinder 142.

  An exhaust port 135 provided in the cylinder head 130 includes an exhaust chamber (chamber) 135b in which exhaust gases discharged from exhaust ports opened and closed by the three exhaust valves 132 are combined, and from the exhaust chamber 135b to the exhaust passage 16. And a discharge passage 135a for guiding the exhaust gas. The discharge passage 135a and the exhaust chamber 135b are provided horizontally, and are provided at positions such that the discharge passage 135a and the exhaust chamber 135b are divided into two vertically at the center by the dividing surface DF.

  By providing the exhaust chamber 135b in the cylinder head 130, the flow rate of the high-temperature exhaust gas immediately after being discharged from the combustion chamber can be reduced, and the heat transfer rate to the wall surface of the exhaust port 135 is reduced to reduce the exhaust gas temperature. Can be suppressed. Thereby, catalyst warm-up property can be improved. In addition to improving turbo efficiency, the back pressure is reduced, so that exhaust gas escape is improved and the influence of exhaust pulsation of other cylinders is suppressed, and operation by premixed compression auto-ignition combustion is performed. The possible area can be expanded to the high rotation and high load area.

  Further, a stainless heat insulating material 172 is assembled to the inner wall of the exhaust port 135 (the exhaust passage 135a and the exhaust chamber 135b). As shown in FIG. 2, the stainless steel heat insulating material 172 is provided on the entire inner wall of the exhaust port 135 including the portion in the vicinity of the valve seat 133.

  The portion of the exhaust port 135 near the valve seat 133 is a place where the heat transfer coefficient is the highest because the flow velocity is the highest immediately after the exhaust gas is discharged from the exhaust port. By providing the stainless steel heat insulating material 172 also in the vicinity of the valve seat 133, it is possible to insulate the place where the heat transfer coefficient is maximized, and thus it is possible to suppress a decrease in the exhaust temperature to a minimum. Therefore, the activation of the catalyst can be accelerated, and there is no need for a temperature raising means such as a heating type catalyst or fuel addition to the exhaust, or the use range can be greatly reduced, resulting in an improvement in fuel consumption and cost reduction. I can plan. Moreover, turbo efficiency can also be improved.

  The installation of the stainless steel heat insulating material 172 is easily made possible by the structure in which the cylinder head 130 is vertically divided into two along a plane passing through the center of the discharge passage 135a and the exhaust chamber 135b. Is. In this way, by making the cylinder head 130 into a vertically divided structure, it is possible to improve productivity and reduce costs in installing the heat insulating material.

  In the present specification, the portion of the exhaust port 135 near the valve seat 133 refers to a portion of the exhaust port 135 that is within a distance of 10 mm from the exhaust valve seat 133.

  In the first embodiment, a monoblock structure in which the cylinder block 140 and the cylinder head 130 are integrated is adopted. The adoption of the monoblock structure is such that the central axis of the exhaust valve 132 is parallel to the central axis of the cylinder 142, and drilling for the exhaust valve 132 in the cylinder head 130 can be performed from the lower side of the cylinder block 140. It has become possible. By adopting a monoblock structure, it is possible to improve the gas sealing performance at high pressure in the cylinder. Moreover, bore distortion is suppressed and the amount of blow-by gas can be reduced. In addition, dead volume can be reduced and HC emissions can be reduced. Furthermore, the cost can be reduced, the weight can be reduced, the reliability can be improved, and the degree of freedom in arranging the spark plug and the fuel injection valve can be improved by reducing the number of parts.

  FIG. 4 is an explanatory diagram schematically showing an enlarged cross section of the exhaust passage 135a of the exhaust port 135 (cross section BB in FIG. 2). FIG. 4 shows a state in which the stainless steel heat insulating material 172 is provided on the inner wall of the discharge passage 135 a of the exhaust port 135 provided in the cylinder head 130. As shown in FIG. 4, in this embodiment, the stainless steel heat insulating material 172 is molded so as to have a plurality of convex portions. Therefore, when the stainless steel heat insulating material 172 is installed on the inner wall of the discharge passage 135a, an air layer 174 is formed between the stainless steel heat insulating material 172 and the inner wall of the discharge passage 135a.

  Similarly, the stainless steel heat insulating material 172 provided on the inner wall of the exhaust chamber 135b of the exhaust port 135 (not shown) is also molded in the same shape, and the air is interposed between the stainless steel heat insulating material 172 and the inner wall of the exhaust chamber 135b. Layer 174 is formed.

  As described above, when the air layer 174 is formed between the stainless steel heat insulating material 172 and the inner wall of the exhaust port 135, the air layer 174 functions as a heat insulating space. The decrease can be further suppressed.

  FIG. 5 is an explanatory diagram showing a configuration of a mechanism for driving the exhaust valve. FIG. 5A shows a shape of the drive arm 162 for pushing the valve shaft of the exhaust valve 132 as viewed from above, and FIG. 5B shows an enlarged cross section of the cylinder with the cylinder head 130 as the center. It shows. A drive arm 162 is provided above the cylinder head 130. The drive arm 162 is substantially triangular when viewed from above, and the upper end of the exhaust valve 132 is connected to each of the three apex portions. An electromagnetic actuator 164 is installed above the drive arm 162, and is arranged so that the electromagnetic actuator 164 acts on the center of gravity of the drive arm 162 in a substantially triangular position (the intersection of the dashed line in FIG. 5A). Yes.

  When the electromagnetic actuator 164 receives a valve opening command from the ECU 30, the electromagnetic actuator 164 applies a force to the position of the center of gravity of the drive arm 162 and translates the drive arm 162 downward. The drive arm 162 is connected to the upper ends of the three exhaust valves 132, and since the central axes of the three exhaust valves are parallel to each other, when the drive arm 162 moves downward, the three exhaust valves At the same time, the valve 132 moves downward along the axial direction of the exhaust valve 132. When the exhaust valve 132 moves downward, the exhaust port opens and the combustion gas in the cylinder 142 is discharged toward the exhaust port 135. The amount of movement of the exhaust valve 132 in the axial direction from the original position when the exhaust valve 132 moves downward is referred to as a lift amount. The product of the lift amount and the circumferential length of the valve head portion 132a of the exhaust valve 132 is called a curtain area. The larger the curtain area, the more efficiently the exhaust gas in the cylinder 142 is discharged.

  In a premixed compression self-ignition combustion type two-cycle engine, in order to perform compression self-ignition operation without causing premature ignition even at high rotation and high load, it is necessary to efficiently discharge the combustion gas. . In order to efficiently discharge the combustion gas, the curtain area may be set large as described above. However, if the area of the valve head of the exhaust valve (valve area) is increased in an attempt to increase the curtain area, the power for driving the exhaust valve increases, and in particular, the in-cylinder pressure becomes very high. In a two-cycle engine of a premixed compression auto-ignition combustion system, it is not preferable. Therefore, it is desirable to increase the curtain area of the exhaust valve without increasing the valve area of the exhaust valve.

  FIG. 6 is an explanatory diagram showing the relationship between the number of exhaust valves, the valve area, and the curtain area. The figure shows how the total valve area and total curtain area of the arranged exhaust valves are relative to the standard when the number of valves is increased with the number of exhaust valves as one reference. It shows whether the rate of increase is reached. In general, when the exhaust valve is disposed in the cylinder head, it is necessary to ensure a predetermined clearance between the exhaust valve and the cylinder and between adjacent exhaust valves. In this embodiment, as a condition for disposing the exhaust valve 132 corresponding to the number of valves in the cylinder head 130, the diameter Db of the cylinder 142 is 81 millimeters, the required clearance Ls between the cylinder 142 and the exhaust valve 132 is 5 millimeters, The required clearance Lv between adjacent exhaust valves 132 is 5 millimeters. The diameter Dv of the valve head portion 132a of the exhaust valve 132 is set to the maximum value that can be taken on the premise of this condition. If the exhaust valves 132 are arranged according to such conditions, the exhaust valves 132 are arranged at equal intervals around the center axis of the cylinder 142. If the diameter Dv of the valve head portion of the exhaust valve 132 is set, the valve area and the curtain area can be calculated.

  Referring to FIG. 6, the total valve area is minimized when the number of exhaust valves 132 is 2, but when the number of valves is 3 or more, the valve area gradually decreases as the number of valves increases. On the other hand, the total curtain area is minimized when the number of exhaust valves 132 is 2, and when the number of valves is 3 or more, the curtain area increases greatly as the number of valves increases. Therefore, if the number of exhaust valves 132 is three or more, a large curtain area can be secured without increasing the valve area, and combustion gas can be efficiently discharged even during high-rotation and high-load operation. It is possible to perform a stable compression self-ignition operation.

  Even if the number of exhaust valves is three or more, as in this embodiment, it is possible to drive three or more exhaust valves 132 with one drive arm 162 and one electromagnetic actuator 164, which reduces cost and mountability. And weight reduction of the moving parts can be achieved. In particular, a 2-cycle engine has twice the operating frequency of the valve system compared to a 4-cycle engine, and the maximum number of revolutions tends to be reduced due to the surging limit of the valve. The limit rotational speed can be increased.

  FIG. 7 is an explanatory view showing a CC cross section of FIG. The scavenging port 146 is formed so as to be substantially parallel to a plane perpendicular to the central axis of the cylinder 142 (see FIG. 2), and fresh air flows in a direction shifted from the central axis of the cylinder 142. Thus, it is connected to the cylinder 142 (see FIG. 7). Therefore, fresh air that has flowed into the cylinder 142 from the scavenging port 146 moves along the inner periphery of the cylinder 142, and generates a vortex (swirl) in a plane perpendicular to the central axis of the cylinder 142 in the cylinder 142. . In this specification, such a scavenging port 146 is referred to as a “tangential port”. In this embodiment, two scavenging ports (tangential ports) 146 are provided in the cylinder 142 so as to generate swirls in the same direction.

  Further, a rib (projection) 145 is provided in the vicinity of the opening (scavenging port) facing the cylinder 142 of the scavenging port (tangential port) 146 (FIG. 7), and the scavenging port of the scavenging port 146 is formed by the rib 145. It is divided into left and right. Since the scavenging port is divided into left and right parts, the piston ring 153 (FIG. 2) is prevented from being caught due to the vertical movement of the piston 152. Further, a fuel injection valve 15 for injecting fuel spray into the port is provided in the vicinity of one of the two scavenging ports 146 (FIG. 7). By providing the fuel injection valve 15 in the scavenging port 146, it is possible to promote mixing of the air-fuel mixture by placing the fuel spray on the scavenging airflow, and to employ a low-pressure injection valve. Cost reduction is possible. The fuel injection control of the fuel injection valve 15 is performed by the ECU 30 (FIG. 1). The vicinity of the opening (scavenging port) of the scavenging port 146 is preferably within the scavenging port 146 and closer to the cylinder 142 than the intermediate point in the length direction of the scavenging port 146.

  On the other hand, the scavenging port 148 is formed with a gradient so that fresh air flows into the cylinder 142 obliquely downward with respect to a plane perpendicular to the central axis of the cylinder 142 (see FIG. 2). The scavenging port 148 is connected to the cylinder 142 so that fresh air flows toward the central axis of the cylinder 142 (see FIG. 7). In this specification, such a scavenging port 148 is referred to as a “straight port”. In this embodiment, two scavenging ports (straight ports) 148 are provided to face each other with the cylinder 142 interposed therebetween. Therefore, fresh air that has flowed into the cylinder 142 from the scavenging port 148 collides with the top surface of the piston 152, turns its direction diagonally upward (see FIG. 2), and fresh air from the two opposing scavenging ports 148 Collide in the vicinity of the center axis of the cylinder 142 (see FIG. 7), and therefore, an upward air flow that rises in the vicinity of the center axis of the cylinder 142 is generated in the cylinder 142.

  Further, a rib (projection) 147 is provided in the vicinity of the opening (scavenging port) facing the cylinder 142 of the scavenging port (straight port) 148 (FIG. 7), and the scavenging port of the scavenging port 148 is formed by the rib 147. It is divided into left and right. Since the scavenging port is divided into left and right parts, the piston ring 153 is prevented from being caught due to the vertical movement of the piston 152. Further, a fuel injection valve 14 for injecting fuel spray into the port is provided in the vicinity of one of the two scavenging ports 148 (FIG. 7). By providing the fuel injection valve 14 in the scavenging port 148, a low-pressure injection valve can be adopted, so that the cost of the fuel injection valve and the fuel pump can be reduced. The fuel injection control of the fuel injection valve 14 is performed by the ECU 30 (FIG. 1). The vicinity of the opening (scavenging port) of the scavenging port 148 is preferably in the scavenging port 148 and closer to the cylinder 142 than the intermediate point in the length direction of the scavenging port 148.

  In addition, it is preferable that the scavenging port 148 is formed with an obliquely downward gradient from the viewpoint of preventing blow-through of the fuel spray injected by the fuel injection valve 14. Further, the scavenging port 148 is provided so as to oppose the cylinder 142 so that the fuel spray injected by the fuel injection valve 14 adheres to the inner wall surface of the cylinder 142, and HC (unburned fuel) or smoke It is preferable also from the point which prevents that discharge | emission amount increases.

  Each of the two scavenging ports (straight ports) 148 is provided with an air supply control valve 149 (FIGS. 2 and 7) as an opening / closing mechanism, and by rotation about the axis of the air supply control valve 149 The scavenging port 148 can be opened and closed. The opening / closing control of the air supply control valve 149 is performed by the ECU 30 (FIG. 1).

  During the low rotation and low load operation, the ECU 30 performs control such that the air supply control valve 149 provided in the scavenging port (straight port) 148 is closed. In other words, fresh air is supplied into the cylinder 142 only by the scavenging port (tangential port) 146 during the low rotation and low load operation. At this time, the flow rate of fresh air increases, and the mixing of the residual gas in the cylinder 142 and the air-fuel mixture is promoted, so that a stable compression auto-ignition combustion operation can be performed even at the time of low rotation and low load operation. .

  Further, as described above, the scavenging port (tangential port) 146 is formed so as to generate a swirl in the cylinder 142, so that the relatively low temperature fresh air that has flowed into the cylinder 142 flows into the inner wall surface of the cylinder 142. The hot residual gas is distributed near the center of the cylinder 142. Therefore, when the fresh air takes heat from the inner wall surface of the cylinder 142, the temperature drop of the residual gas is suppressed, and a stable compression auto-ignition combustion operation can be performed even during the low rotation and low load operation.

  Further, since there is no air flow directly from the scavenging port 146 to the exhaust port, it is possible to suppress blow-through of fresh air and injected fuel, and to prevent deterioration of fuel consumption due to supercharging loss.

  Note that, during low rotation and low load operation, fuel injection is performed by the fuel injection valve 15 provided in the scavenging port (tangential port) 146. As the fuel injection valve, there are known a hollow cone type, a multi-hole collision spray type, a fan spray type, a solid cone type, a slit type, etc., but the fuel injection valve 15 has a relatively low injection rate and a spray penetration force. It is preferable to adopt a small hollow cone type or a multi-hole collision spray type. In this way, the fuel spray can be easily placed on the swirl generated by the scavenging port 146, and mixing of the air-fuel mixture can be promoted.

  On the other hand, at the time of high rotation and high load operation, the ECU 30 performs control to open the air supply control valve 149 provided in the scavenging port (straight port) 148. That is, during high-speed and high-load operation, fresh air is supplied into the cylinder 142 from both the scavenging port (tangential port) 146 and the scavenging port (straight port) 148. During high-speed and high-load operation, the amount of air and fuel supplied into the cylinder is large and the mixing time is short, but by using both scavenging ports, scavenging is performed quickly by increasing the area of the scavenging port. And a stable compression auto-ignition combustion operation can be performed.

  Further, since the scavenging port (straight port) 148 is formed in the cylinder 142 so as to generate an updraft along the center axis of the cylinder 142, the residual gas that tends to remain in the vicinity of the center axis of the cylinder 142 is surely secured. It is possible to increase the scavenging rate and to prevent the temperature of the air-fuel mixture from rising more than necessary. Therefore, even during the high rotation and high load operation, the compression self-ignition combustion operation can be performed without causing premature ignition.

  Note that, during high-speed and high-load operation, the fuel injection valve 14 provided in the scavenging port (straight port) 148 or the fuel injection valve 15 provided in the fuel injection valve 14 and the scavenging port (tangential port) 146. Then, fuel injection is performed. The fuel injection valve 14 is preferably a fan spray type, a solid cone type, or a slit type that has a relatively high injection rate and a large spray penetration force. In this way, it is possible to inject the required amount of fuel in a short time even during high-rotation and high-load operation, and to prevent the fuel spray from being blown through the updraft generated by the fresh air from the scavenging port 148. it can.

  It should be noted that the swirl generated by the scavenging port (tangential port) 146 and the rising air flow generated by the scavenging port (straight port) 148 are both symmetric with respect to the central axis of the cylinder 142. That is, the airflow is less biased in the cross section perpendicular to the central axis of the cylinder 142. Therefore, exhaust gas can be exhausted evenly from the exhaust valves 132 arranged at equal intervals in the cylinder head 130, and the efficiency of exhaust (scavenging) can be improved.

  The scavenging ports 146 and 148 are connected to an air supply surge tank 144 provided in the cylinder block 140 at an end opposite to the cylinder 142 (see FIGS. 2 and 7), and fresh air is supplied to the intake passage. 12 is supplied to scavenging ports 146 and 148 via an air supply surge tank 144 (see FIG. 1). In this embodiment, the supply surge tank 144 is formed integrally with the cylinder block 140 (see FIG. 2). The supply surge tank 144 is also connected to a scavenging port of another cylinder (not shown), and supplies fresh air to the other cylinder.

  In the scavenging stroke, when the scavenging port opens and fresh air begins to flow into the cylinder 142 from the scavenging ports 146 and 148, a negative pressure wave is generated in the scavenging ports 146 and 148 due to inertia. This negative pressure wave goes back through the scavenging ports 146 and 148, and when it reaches the opening (open end) facing the supply air surge tank 144, it returns to the scavenging port as an antiphase positive pressure wave. Come. When this positive pressure wave returns when the scavenging port is still open, the air supply efficiency is improved by pushing new air into the cylinder. In the present embodiment, the tube length of the scavenging ports 146 and 148 can be shortened by forming the supply surge tank 144 integrally with the cylinder block 140. In this way, the reciprocation time of the pressure wave can be shortened, and the supply efficiency can be improved by using the pressure wave. In addition, it is possible to reduce the size of the multi-cylinder engine.

  As described above, the gasoline engine 100 can be stably operated by premixed compression self-ignition combustion from the time of low rotation and low load operation to the time of high rotation and high load operation. Therefore, during start-up and warm-up when the load is extremely small and compression auto-ignition combustion is difficult, operation by spark ignition combustion is performed, and operation by premixed compression auto-ignition combustion is performed in other operation regions. You can also. FIG. 8 is a map showing the operation mode of the gasoline engine 100 in the first embodiment. In FIG. 8, the horizontal axis represents the engine speed, and the vertical axis represents the load (torque).

  The operation mode of the gasoline engine 100 is divided into two operation regions R1 and R2 according to the rotation speed and the load. The first operation region R1 is an operation region in which starting and warming up of an extremely low rotation and extremely low load are performed. In this operation region R1, operation by spark ignition combustion is performed. On the other hand, the second operation region R2 is an operation region other than the operation region R1, and is an operation region that covers a wide range of rotation speed and load. In this operation region R2, operation by compression self-ignition combustion is performed.

  As described above, if the operation is performed by spark ignition combustion at the time of start-up and warm-up, and if the operation is performed by premixed compression auto-ignition combustion in other operation regions, the spark plug 136 (FIG. 2) is It can be dedicated for start-up and warm-up, and can be downsized. If the spark plug 136 can be reduced in size, the degree of freedom regarding the size and arrangement of the exhaust valve 132 (FIG. 2) installed in the cylinder head 130 can be increased, and the degree of freedom in arrangement of the spark plug 136 itself can be increased. Furthermore, the cooling device for the spark plug 136 can be eliminated, and the igniter can be reduced in cost. Further, since it is not necessary to switch the combustion method after warming up, drivability is improved, and torque adjustment control for torque shock countermeasures at the time of switching the combustion method, which causes a deterioration in fuel consumption, is unnecessary.

  The gasoline engine 100 is set to a long stroke having a stroke / bore ratio value of 1.2 or more. FIG. 9 is an explanatory diagram showing the relationship between the stroke / bore ratio, the piston top area, and the combustion chamber clearance height. In this embodiment, the displacement per cylinder is set to 500 cc, and the compression ratio is set to 15. As shown in FIG. 9, when the piston top area is based on an engine having a stroke / bore ratio value of 1 (square engine), the piston top area decreases as the stroke / bore ratio value increases. The gasoline engine 100 is set to a high compression ratio in order to perform compression self-ignition combustion, and since the combustion of the air-fuel mixture is performed almost simultaneously by compression self-ignition combustion, the pressure in the cylinder 142 is very high. Become. In such a gasoline engine 100, if the stroke / bore ratio is set to 1.2 or more to make a long stroke, the piston top area is reduced by 10% or more compared to the square engine. Therefore, the pressure acting on the top surface of the piston 152 is also reduced by 10% or more, and it is possible to reduce the weight of the parts and improve the reliability. Further, the ratio between the surface area and the volume of the combustion chamber (S / V ratio) is reduced, and the fuel consumption can be improved by suppressing the cooling loss. Furthermore, as shown in FIG. 9, when the value of the stroke / bore ratio is increased, the combustion chamber clearance height can be increased. The gasoline engine 100 has a small combustion chamber volume in order to perform a high compression ratio operation, but by setting the stroke / bore ratio to 1.2 or more, a sufficient clearance between the piston 152 and the cylinder head 130 can be secured, and the airflow It is possible to eliminate the need to install a valve recess that leads to a hindrance to the S / V ratio.

B. Second embodiment:
FIG. 10 is an explanatory diagram schematically showing an enlarged cross section (cross section BB in FIG. 2) of the discharge passage 135a of the exhaust port 135 in the second embodiment. The difference from the first embodiment shown in FIG. 4 is that a plurality of convex portions 131 are provided on the inner wall of the discharge passage 135 a of the exhaust port 135. And the stainless steel heat insulating material 172 is installed so that it may be supported in each vertex part of the some convex part 131. FIG.

  Similarly, a plurality of convex portions 131 are also provided on the inner wall of the exhaust chamber 135b of the exhaust port 135 (not shown) so that the stainless steel heat insulating material 172 is supported at each vertex of the plurality of convex portions 131. Is installed.

  Even if it does in this way, the air layer 174 is formed between the stainless steel heat insulating material 172 and the exhaust port 135 inner wall, and a heat insulation effect can be improved further, and the fall of exhaust temperature can further be suppressed. Furthermore, in the second embodiment, since the shape of the stainless steel heat insulating material 172 can be a simple shape without unevenness, the cost can be reduced and the surface area of the flow path through which the exhaust gas passes can be reduced. It is possible to further increase the heat insulation effect and further suppress the decrease in the exhaust temperature.

C. Third embodiment:
FIG. 11 is an explanatory view schematically showing a perspective view of the cross section of the discharge passage 135a of the exhaust port 135 in the third embodiment. In FIG. 11, only the lower half of the exhaust port 135 is shown for easy understanding of the structure. Further, the left side of the figure is the exhaust chamber 135b side, and the right side of the figure is the exhaust passage 16 side. In the third embodiment, a plurality of recesses 176 defined by grid-like ribs 137 are provided on the inner wall of the exhaust passage 135 a of the exhaust port 135. And the stainless steel heat insulating material 172 which is not shown in figure is installed so that it may be supported in the front-end | tip part of the grid | lattice-like rib 137.

  Similarly, the inner wall of the exhaust chamber 135b of the exhaust port 135 (not shown) is also provided with a plurality of recesses 176 that are partitioned by the grid-like ribs 137, and the stainless steel insulation 172 (not shown) is connected to the grid-like ribs. It is installed so as to be supported at the tip of 137.

  Even if it does in this way, an air layer is formed between the stainless steel heat insulating material 172 and the recessed part 176 provided in the inner wall of the exhaust port 135, and a heat insulation effect can be improved further, and the fall of exhaust temperature is further suppressed. Can do. Further, in the present embodiment, the air layer is partitioned by the ribs 137, so that air convection can be suppressed, the heat insulation effect can be further enhanced, and the exhaust temperature decrease can be further suppressed.

D. Variation:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

D1. Modification 1:
In the above embodiment, a two-cycle engine has been described as an example. However, the present invention is not limited to a two-cycle engine, and may be applied to other types of engines such as a four-cycle engine. Can do. That is, in other types of engines, exhaust gas is provided by providing a heat insulating material on the inner wall of the exhaust port near the exhaust valve seat or by providing an air layer between the heat insulating material and the inner wall of the exhaust port. A decrease in temperature can be suppressed.

D2. Modification 2:
In the above embodiment, the example in which the exhaust port 135 has the exhaust chamber 135b has been described. However, in the present invention, the exhaust port 135 does not have the exhaust chamber 135b, that is, only the exhaust passage 135a. This can also be applied to the case where At this time, the exhaust gas from each exhaust port is exhausted through the exhaust port 135 (that is, the exhaust passage 135a) connected thereto. Even in such a case, it is possible to reduce the exhaust temperature by providing a heat insulating material on the inner wall of the exhaust port near the exhaust valve seat or by providing an air layer between the heat insulating material and the inner wall of the exhaust port. Can be suppressed.

D3. Modification 3:
In the said Example, although demonstrated using the stainless steel heat insulating material 172 as an example of the heat insulating material provided in the inner wall of the exhaust port 135, a heat insulating material may be another heat insulating material. For example, the heat insulating material can be formed by thermal spraying of ceramic such as zirconia.

D4. Modification 4:
In the above embodiment, the heat insulating material is provided on both the inner wall of the discharge passage 135a and the inner wall of the exhaust chamber 135b, but the heat insulating material may be provided on only one of them.

D5. Modification 5:
In the above embodiment, the cylinder head 130 is provided with three or more exhaust valves 132. However, the present invention is also applicable when the cylinder head 130 is provided with one or two exhaust valves 132. is there.

D6. Modification 6:
In the above embodiment, the gasoline engine 100 is a monoblock engine in which the cylinder head 130 and the cylinder block 140 are integrated. However, the gasoline engine 100 is an engine in which the cylinder head 130 and the cylinder block 140 are divided. It may be.

D7. Modification 7:
In the above-described embodiment, the engine in which four scavenging ports including two tangential ports 146 and two straight ports 148 are connected to the cylinder 142 has been described. However, the scavenging port connected to the cylinder 142 has one scavenging port. It may be a port (tangential port) 146. Alternatively, the scavenging ports connected to the cylinder 142 may be a total of two scavenging ports, one scavenging port (tangential port) 146 and one straight port 148. Alternatively, the scavenging port connected to the cylinder 142 may be one or more arbitrarily shaped scavenging ports.

D8. Modification 8:
In the above embodiment, two fuel injection valves, the fuel injection valve 15 in the scavenging port (tangential port) 146 and the fuel injection valve 14 in the scavenging port (straight port) 148, are provided. Only the fuel injection valve 15 may be provided.

D9. Modification 9:
In the above embodiment, each of the two scavenging ports (straight ports) 148 is provided with an air supply control valve 149 as an opening / closing mechanism, but only one air scavenging port 148 is provided with an air supply control valve 149. It is good. Alternatively, the air supply control valve 149 may be provided not only in the scavenging port 148 but also in at least one arbitrary scavenging port.

D10. Modification 10:
In the above embodiment, in the opening / closing control of the air supply control valve 149, all the air supply control valves 149 are controlled to be opened or closed at the same time. Or it is good also as control which opens or closes for every some air supply control valve 149. FIG.

Explanatory drawing which showed notionally the structure of the gasoline engine in 1st Example of this invention. Explanatory drawing which expands and shows the cross section of the cylinder of the gasoline engine in 1st Example. Explanatory drawing which shows the AA cross section of FIG. Explanatory drawing which expands and shows schematically the cross section (BB cross section of FIG. 2) of the discharge passage of an exhaust port. Explanatory drawing which shows the structure of the mechanism which drives an exhaust valve. Explanatory drawing which shows the relationship between the number of valves of an exhaust valve, valve area, and curtain area. Explanatory drawing which shows the CC cross section of FIG. The map which shows the operation mode of the gasoline engine in 1st Example. Explanatory drawing which shows the relationship between stroke-bore ratio, piston top area, and combustion chamber clearance height. Explanatory drawing which expands and shows schematically the cross section (BB cross section of FIG. 2) of the exhaust passage of the exhaust port in 2nd Example. Explanatory drawing which shows schematically the state which looked at the cross section of the exhaust passage of the exhaust port in 3rd Example.

Explanation of symbols

12 ... Intake passage 14 ... Fuel injection valve 15 ... Fuel injection valve 16 ... Exhaust passage 20 ... Air cleaner 22 ... Throttle valve 24 ... Electric actuator 26 ... Catalyst 32. ..Crank angle sensor 34 ... Accelerator opening sensor 50 ... Supercharger 52 ... Turbine 54 ... Compressor 56 ... Shaft 60 ... Surge tank 62 ... Intercooler 100 .. Gasoline engine 130 ... Cylinder head 131 ... Convex part 132 ... Exhaust valve 132a ... Valve head part 132b ... Shaft part 133 ... Exhaust valve seat 135 ... Exhaust port 135a .. Discharge passage 135b ... exhaust chamber 136 ... ignition plug 137 ... rib 140 ... cylinder block 142 ... cylinder 144 ... supply surge tank 145 ... rib 146 ... scavenging port 147 ... Rib 148 ... Scavenging port 149 ... Air supply control valve 152 ... Piston 153 ... Piston ring 154 ... Connecting rod 156 ... Crankshaft 162 ... Drive arm 164 ... Electromagnetic actuator 172 ... Stainless steel insulation 174 ... Air layer 176 ... Recess

Claims (6)

An internal combustion engine capable of premixed compression self-ignition operation,
A combustion chamber composed of a cylinder and a piston;
An exhaust valve for opening and closing an exhaust port through which combustion gas is discharged from the combustion chamber;
An exhaust valve seat closely contacting the exhaust valve when the exhaust valve is closed;
An exhaust port that is provided in a cylinder head of the cylinder and discharges combustion gas discharged from the exhaust port;
With
The cylinder head portion has a structure that can be divided along a plane that divides the exhaust port into two in the vertical direction,
An internal combustion engine, wherein a heat insulating material is provided on an inner wall of at least a portion near the exhaust valve seat of the exhaust port. The internal combustion engine according to claim 1,
The inner wall of the exhaust port is provided with a plurality of convex portions that support the heat insulating material,
An internal combustion engine having a heat insulating space between an inner wall of the exhaust port and the heat insulating material. The internal combustion engine according to claim 1,
The inner wall of the exhaust port is provided with a plurality of recesses,
An internal combustion engine in which a plurality of closed heat insulation spaces are constituted by the plurality of recesses and the heat insulating material. An internal combustion engine according to any one of claims 1 to 3,
A plurality of the exhaust port and the exhaust valve;
The exhaust valve moves up and down;
The exhaust port has an exhaust chamber (chamber) in which combustion gases rising from a plurality of the exhaust ports are combined, and an exhaust passage for leading the combustion gas from the exhaust chamber to the outside,
The internal combustion engine, wherein the exhaust chamber and the discharge passage are horizontally provided and are divided into two at the center by a plane that divides the cylinder head portion. An internal combustion engine according to claim 4,
The internal combustion engine includes three or more exhaust ports and exhaust valves, and is connected to a peripheral wall of the cylinder, and has at least one scavenging port that opens and closes an opening facing the cylinder by the vertical movement of the piston. An internal combustion engine that is a two-cycle internal combustion engine. An internal combustion engine according to any one of claims 1 to 5,
The internal combustion engine, wherein the cylinder has a monoblock structure in which the cylinder head portion and the cylinder block portion are integrally formed.

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