JP2019039391A - Compression self-ignition engine with supercharger - Google Patents

Abstract

To appropriately introduce an EGR gas into a combustion chamber in a compression self-ignition engine with supercharger.SOLUTION: A compression self-ignition engine with supercharger comprises: a supercharger 44; a bypass passage 47; a flow rate control valve (air bypass valve 48) which is disposed in the bypass passage; a variable valve mechanism (internal EGR system 552) which varies valve opening operations of a suction valve and an exhaust valve in such a manner that a combusted gas in a combustion chamber 17 is blown back into the combustion chamber; an external EGR system 551; and a control part (ECU 10). When operating the engine in a state where supercharge of sucked air by the supercharger is stopped by enlarging an aperture of the flow rate control valve, the control part introduces an internal EGR gas into the combustion chamber by the variable valve mechanism, and when operating the engine in a state where supercharge of sucked air is performed by the supercharger by reducing the aperture of the flow rate control valve, the control part introduces the external EGR gas into the combustion chamber by the external EGR system.SELECTED DRAWING: Figure 10

Description

  The technology disclosed herein relates to a compression self-ignition engine with a supercharger.

  Patent Document 1 describes an engine that burns an air-fuel mixture in a combustion chamber by compression ignition in a predetermined region of low load and low rotation. This engine has a negative overlap period in which the intake valve and the exhaust valve are both closed by setting the exhaust valve closing timing before top dead center and the intake valve opening timing after top dead center in the predetermined region. Is provided. Thereby, since high temperature EGR gas is introduced into the combustion chamber, the temperature in the combustion chamber becomes high, and the air-fuel mixture is compressed and ignited.

  Patent Document 2 describes an engine in which a mechanical supercharger and an intercooler are provided in an intake passage, and the supercharged intake air is cooled and supplied to the engine. In a predetermined operating state, the engine deactivates the mechanical supercharger by turning off the electromagnetic clutch, and closes the control valve in the air bypass passage that bypasses the mechanical supercharger and the inter. The mechanical supercharger is pre-rotated by the pressure difference. This prevents the occurrence of torque shock when the electromagnetic clutch is turned on.

JP 2009-197740 A Japanese Patent No. 3564989

  In combustion by self-ignition, the temperature in the combustion chamber must be adjusted to an appropriate range. The temperature in the combustion chamber may be adjusted, for example, by adjusting the amount of EGR gas introduced into the combustion chamber. The EGR gas is recirculated through the internal EGR gas introduced into the combustion chamber by blowing back the burned gas in the combustion chamber into the combustion chamber, the EGR passage connecting the intake passage and the exhaust passage of the engine, and the combustion chamber. And external EGR gas introduced into the.

  In an engine with a supercharger, the pressure state of the intake passage changes according to the operating state of the engine due to the level of the supercharging pressure. Therefore, the amount of internal EGR gas introduced into the combustion chamber and the amount of external EGR gas are affected by the operating state of the engine.

  According to the technology disclosed herein, EGR gas is appropriately introduced into a combustion chamber in a compression self-ignition engine with a supercharger.

  Specifically, the compression self-ignition engine with a supercharger disclosed here is an engine in which an air-fuel mixture in a combustion chamber burns by self-ignition, an intake passage connected to the combustion chamber, and an intake passage. A supercharger, a bypass passage connecting the upstream and downstream of the supercharger in the intake passage, a flow rate control valve disposed in the bypass passage, and burning the burned gas in the combustion chamber A variable valve mechanism that introduces internal EGR gas into the combustion chamber by varying the opening and closing operations of the intake valve and the exhaust valve so as to blow back into the chamber, and an EGR that connects the intake passage and the exhaust passage of the engine An external EGR system that introduces external EGR gas into the combustion chamber by returning a part of the exhaust gas to the intake passage through the passage, the flow control valve, the variable valve mechanism, and the And it is connected to a part EGR system includes the flow control valve, and a control unit for outputting a control signal to the variable valve mechanism and the external EGR system.

  The controller is configured to introduce at least internal EGR gas into the combustion chamber when the engine is operated in a state where supercharging of the intake air by the supercharger is stopped by increasing the opening of the flow control valve. When the engine is operated in a state where supercharging is performed by the supercharger by outputting a control signal to the variable valve mechanism and reducing an opening of the flow control valve, A control signal is output to the external EGR system so that at least the external EGR gas is introduced into the combustion chamber.

  Here, the “engine” may be a four-stroke engine that operates when the combustion chamber repeats an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. In the engine, the air-fuel mixture in the combustion chamber burns by self-ignition. In order to stabilize the combustion by self-ignition, it is preferable to appropriately adjust the temperature in the combustion chamber, and it is required to appropriately introduce EGR gas into the combustion chamber for temperature adjustment.

  When the opening degree of the flow control valve disposed in the bypass passage is large, the intake air passes through the bypass passage, so that the supercharging of the intake air by the supercharger stops. When the engine is operated in a state where supercharging of intake air by the supercharger is stopped, the pressure in the intake passage is low. Therefore, for example, if a positive overlap period in which both the intake valve and the exhaust valve are opened near the exhaust top dead center is provided, the burned gas can be discharged to the intake port through the intake valve that is opened during the exhaust stroke. During the intake stroke, the burned gas discharged to the intake port can be blown back into the combustion chamber as internal EGR gas. When the supercharging of the intake air by the supercharger is stopped, the internal EGR gas can be appropriately introduced by the variable valve mechanism. The internal EGR gas may be introduced into the combustion chamber (or confined in the combustion chamber) by providing a negative overlap period in which both the intake valve and the exhaust valve are closed. Further, when the supercharging of the intake air by the supercharger is stopped, not only the internal EGR gas but also the external EGR gas may be introduced.

  If the opening degree of the flow control valve disposed in the bypass passage is small, the intake air passes through the supercharger, so the intake air is supercharged by the supercharger. When the engine is operated in a state where the intake air is supercharged by the supercharger, the pressure in the intake passage increases. Therefore, for example, even if the intake valve is opened during the exhaust stroke, the burned gas is not easily discharged to the intake port. That is, the internal EGR gas cannot be properly introduced or is difficult to introduce appropriately.

  Therefore, when the engine is operated in a state where the intake air is supercharged by the supercharger, at least the external EGR gas is introduced into the combustion chamber by the external EGR system. That is, the external EGR gas is introduced into the combustion chamber by returning a part of the exhaust gas to the intake passage through the EGR passage connecting the intake passage and the exhaust passage of the engine. As a result, when the intake air is supercharged by the supercharger, the external EGR gas can be appropriately introduced into the combustion chamber.

  The control unit increases the opening of the flow rate control valve when the engine load is lower than a predetermined switching load and the engine speed is lower than a predetermined switching speed, The supercharging of the intake air by the supercharger is stopped, and the opening degree of the flow control valve is decreased when the engine load is equal to or higher than the switching load or the engine speed is equal to or higher than the switching speed. Accordingly, the supercharging of the intake air may be performed by the supercharger.

  When the engine load is lower than the switching load and the engine speed is lower than the switching speed, the supercharging of the intake air by the supercharger is stopped. At this time, the internal EGR gas is introduced into the combustion chamber by the variable valve mechanism. Since the internal EGR gas does not pass through the EGR passage, the temperature is higher than that of the external EGR gas.

  When the engine load is lower than the switching load and the engine speed is lower than the switching speed, a high temperature in the combustion chamber is required to stabilize the self-ignition of the air-fuel mixture. In the above configuration, since the high-temperature internal EGR gas can be appropriately introduced into the combustion chamber, the temperature in the combustion chamber can be appropriately increased. This is advantageous for stabilizing self-ignition of the air-fuel mixture.

  When the engine load is equal to or higher than the switching load or the engine speed is equal to or higher than the switching speed, intake air is supercharged by the supercharger. At this time, external EGR gas is introduced into the combustion chamber by the external EGR system. Since the external EGR gas passes through the EGR passage, the temperature is lower than that of the internal EGR gas.

  When the engine load is equal to or higher than the switching load or the engine speed is equal to or higher than the switching speed, a very high temperature is not required as the temperature in the combustion chamber. By appropriately introducing the external EGR gas by the external EGR system, the temperature in the combustion chamber can be appropriately adjusted. For example, it is advantageous in avoiding abnormal combustion such as premature ignition.

  The control unit may introduce both the internal EGR gas and the external EGR gas into the combustion chamber in an operation region including the switching load or the switching rotational speed.

  Since the external EGR system recirculates the exhaust gas through the EGR passage, the responsiveness when switching from non-introduction of external EGR gas to introduction is low. In an operation region including a switching load or switching speed for switching between supercharging stop and supercharging of the supercharger, both the internal EGR gas and the external EGR gas are supplied into the combustion chamber by both the variable valve mechanism and the external EGR system. If introduced, the introduction of external EGR gas will be delayed when the engine load increases or the engine speed increases and the turbocharger switches from supercharging stop to supercharging of intake air. Can be prevented.

  The compression self-ignition engine with a supercharger includes a switching unit that switches between driving and non-driving of the supercharger, and the control unit performs the switching when stopping supercharging of intake air by the supercharger. A control signal for non-driving the supercharger to the unit, and increasing the opening of the flow control valve to supercharge intake air by the supercharger. It is good also as outputting the control signal which drives A, and making the opening degree of the said flow control valve small.

  The supercharger may be a mechanical supercharger driven by an engine, for example. The supercharger may be an electric supercharger that is driven by electric energy.

  When the control unit outputs a control signal for non-driving the supercharger to the switching unit, the supercharger is not driven and stops supercharging of the intake air. At this time, the intake air is introduced into the combustion chamber bypassing the supercharger by increasing the opening of the flow control valve. Further, when the supercharger is not driven, the internal EGR gas can be appropriately introduced into the combustion chamber by the variable valve mechanism, and the temperature in the combustion chamber can be appropriately adjusted.

  When the control unit outputs a control signal for driving the supercharger to the switching unit, the supercharger is driven. At this time, by reducing the opening degree of the flow control valve, the intake air passes through the supercharger, and the supercharger supercharges the intake air. Further, when the supercharger is driven, the external EGR gas can be appropriately introduced into the combustion chamber by the external EGR system, and the temperature in the combustion chamber can be appropriately adjusted.

  The variable valve mechanism introduces internal EGR gas into the combustion chamber by providing an overlap period in which both the intake valve and the exhaust valve are open, and the variable valve mechanism Even when the engine is operated in a state in which intake air is supercharged by a charger, an overlap period in which both the intake valve and the exhaust valve are open is provided, so that the inside of the combustion chamber is The residual gas may be scavenged.

  As described above, by providing an overlap period in which both the intake valve and the exhaust valve are open, the internal EGR gas is appropriately supplied into the combustion chamber when the supercharger is not supercharging the intake air. Can be introduced.

  In contrast, if an overlap period is provided while the turbocharger is supercharging the intake air, the burned gas in the combustion chamber is pushed out to the exhaust side due to the pressure difference between the intake side and the exhaust side of the engine. be able to. The temperature in the combustion chamber can be adjusted by scavenging the residual gas. Further, the amount of fresh air introduced into the combustion chamber can be increased when the supercharger performs supercharging of intake air. It is advantageous for improvement of engine torque and fuel efficiency.

  The engine may have a geometric compression ratio of 13 to 30.

  Increasing the geometric compression ratio of the engine is advantageous for stabilizing combustion by self-ignition, but may lead to premature ignition. As described above, this configuration can appropriately adjust the temperature in the combustion chamber by appropriately introducing EGR gas into the combustion chamber, so that it is excessive in an engine having a geometric compression ratio of 13 to 30. Combustion by self-ignition can be stabilized while avoiding early ignition.

  Further, not excessively increasing the geometric compression ratio is advantageous in reducing the cooling loss and also in reducing the mechanical loss. The fuel efficiency of the engine is improved.

  The fuel supplied to the combustion chamber may include at least gasoline.

  Fuel containing gasoline may cause premature ignition in a high-temperature combustion chamber. However, as described above, by adjusting the compression end temperature, an engine using fuel containing gasoline is premature. Combustion by compression self-ignition can be stabilized while avoiding ignition.

  As described above, according to the compression self-ignition engine with a supercharger, EGR gas can be appropriately introduced into the combustion chamber.

FIG. 1 is a diagram illustrating a configuration of an engine. FIG. 2 is a diagram illustrating the configuration of the combustion chamber, in which the upper diagram is a plan view equivalent view of the combustion chamber, and the lower portion is a cross-sectional view taken along line AA. FIG. 3 is a plan view illustrating the configuration of the combustion chamber and the intake system. FIG. 4 is a block diagram illustrating the configuration of the engine control apparatus. FIG. 5 is a diagram illustrating an engine operating region map. FIG. 6 is a diagram illustrating fuel injection timing and ignition timing and combustion waveforms in each operation region. FIG. 7 is a diagram illustrating a rig test apparatus for swirl ratio measurement. FIG. 8 is a diagram illustrating the relationship between the opening ratio of the secondary passage and the swirl ratio. FIG. 9 is a flowchart illustrating an engine control process related to supercharging of intake air and introduction of EGR. FIG. 10 is a diagram exemplifying changes in the EGR rate with respect to the engine load level, the driving state of the supercharger, the overlap amounts of the intake and exhaust valves, and the EGR valve opening.

  Hereinafter, an embodiment of a compression self-ignition engine with a supercharger will be described in detail based on the drawings. The following description is an example of an engine. FIG. 1 is a diagram illustrating a configuration of an engine. FIG. 2 is a diagram illustrating the configuration of the combustion chamber. FIG. 3 is a diagram illustrating the configuration of the combustion chamber and the intake system. In FIG. 1, the intake side is the left side of the drawing, and the exhaust side is the right side of the drawing. 2 and 3, the intake side is the right side of the drawing, and the exhaust side is the left side of the drawing. FIG. 4 is a block diagram illustrating the configuration of the engine control apparatus.

  The engine 1 is a four-stroke engine that operates when the combustion chamber 17 repeats an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. The engine 1 is mounted on a four-wheeled vehicle. The vehicle travels when the engine 1 is driven. The fuel of the engine 1 is gasoline in this configuration example. The fuel may be gasoline containing bioethanol or the like. The fuel of the engine 1 may be any fuel as long as it is a liquid fuel containing at least gasoline.

(Engine configuration)
The engine 1 includes a cylinder block 12 and a cylinder head 13 placed on the cylinder block 12. A plurality of cylinders 11 are formed inside the cylinder block 12. 1 and 2, only one cylinder 11 is shown. The engine 1 is a multi-cylinder engine.

  A piston 3 is slidably inserted in each cylinder 11. The piston 3 is connected to the crankshaft 15 via a connecting rod 14. The piston 3 defines a combustion chamber 17 together with the cylinder 11 and the cylinder head 13. The “combustion chamber” is not limited to the meaning of the space when the piston 3 reaches compression top dead center. The term “combustion chamber” may be used in a broad sense. That is, the “combustion chamber” may mean a space formed by the piston 3, the cylinder 11, and the cylinder head 13 regardless of the position of the piston 3.

  The lower surface of the cylinder head 13, that is, the ceiling surface of the combustion chamber 17, is composed of an inclined surface 1311 and an inclined surface 1312 as shown in the upper diagram of FIG. The inclined surface 1311 has an upward slope from the intake side toward an injection axis X2 of an injector 6 described later. The inclined surface 1312 has an upward slope from the exhaust side toward the injection axis X2. The ceiling surface of the combustion chamber 17 has a so-called pent roof shape.

  The upper surface of the piston 3 is raised toward the ceiling surface of the combustion chamber 17. A cavity 31 is formed on the upper surface of the piston 3. The cavity 31 is recessed from the upper surface of the piston 3. The cavity 31 faces an injector 6 described later.

  The center of the cavity 31 is shifted to the exhaust side from the center axis X1 of the cylinder 11. The center of the cavity 31 coincides with the injection axis X2 of the injector 6. The cavity 31 has a convex portion 311. The convex portion 311 is provided on the injection axis X <b> 2 of the injector 6. The convex part 311 is substantially conical. The convex portion 311 extends upward from the bottom of the cavity 31 toward the ceiling surface of the combustion chamber 17.

  The cavity 31 also has a concave portion 312 provided around the convex portion 311. The recessed portion 312 is provided so as to surround the entire circumference of the protruding portion 311. The cavity 31 has a symmetrical shape with respect to the injection axis X2.

  The peripheral side surface of the recessed portion 312 is inclined with respect to the injection axis X2 from the bottom surface of the cavity 31 toward the opening of the cavity 31. The inner diameter of the cavity 31 in the recessed portion 312 gradually increases from the bottom of the cavity 31 toward the opening of the cavity 31.

  The geometric compression ratio of the engine 1 is set to 13 or more and 30 or less. As will be described later, the engine 1 performs SPCCI combustion combining SI combustion and CI combustion in a part of the operation region. SPCCI combustion uses the heat generated by SI combustion and the pressure rise to control CI combustion. The engine 1 does not need to increase the temperature of the combustion chamber 17 (that is, the compression end temperature) when the piston 3 reaches the compression top dead center due to the self-ignition of the air-fuel mixture. That is, although the engine 1 performs CI combustion, the geometric compression ratio can be set relatively low. Lowering the geometric compression ratio is advantageous for reducing cooling loss and mechanical loss. The geometric compression ratio of the engine 1 may be 14 to 17 in the regular specification (the fuel octane number is about 91), and may be 15 to 18 in the high-octane specification (the fuel octane number is about 96).

  An intake port 18 is formed in the cylinder head 13 for each cylinder 11. As shown in FIG. 3, the intake port 18 has two intake ports, a first intake port 181 and a second intake port 182. The first intake port 181 and the second intake port 182 are aligned in the axial direction of the crankshaft 15, that is, the front-rear direction of the engine 1. The intake port 18 communicates with the combustion chamber 17. Although not shown in detail, the intake port 18 is a so-called tumble port. That is, the intake port 18 has such a shape that a tumble flow is formed in the combustion chamber 17.

  An intake valve 21 is disposed in the intake port 18. The intake valve 21 opens and closes between the combustion chamber 17 and the intake port 18. The intake valve 21 is opened and closed at a predetermined timing by a valve operating mechanism. The valve mechanism may be a variable valve mechanism that varies valve timing and / or valve lift. In this configuration example, as shown in FIG. 4, the variable valve mechanism has an intake electric S-VT (Sequential-Valve Timing) 23. The intake motor S-VT 23 is configured to continuously change the rotation phase of the intake camshaft within a predetermined angle range. Thereby, the opening timing and closing timing of the intake valve 21 change continuously. The intake valve mechanism may have a hydraulic S-VT instead of the electric S-VT.

  The cylinder head 13 is also provided with an exhaust port 19 for each cylinder 11. The exhaust port 19 also has two exhaust ports, a first exhaust port 191 and a second exhaust port 192, as shown in FIG. The first exhaust port 191 and the second exhaust port 192 are arranged in the front-rear direction of the engine 1. The exhaust port 19 communicates with the combustion chamber 17.

  An exhaust valve 22 is disposed in the exhaust port 19. The exhaust valve 22 opens and closes between the combustion chamber 17 and the exhaust port 19. The exhaust valve 22 is opened and closed at a predetermined timing by a valve mechanism. This valve mechanism may be a variable valve mechanism that makes the valve timing and / or valve lift variable. In this configuration example, as shown in FIG. 4, the variable valve mechanism has an exhaust electric S-VT 24. The exhaust electric S-VT 24 is configured to continuously change the rotation phase of the exhaust camshaft within a predetermined angle range. Thereby, the opening timing and closing timing of the exhaust valve 22 continuously change. The exhaust valve mechanism may have a hydraulic S-VT instead of the electric S-VT.

  The engine 1 adjusts the length of the overlap period related to the opening timing of the intake valve 21 and the closing timing of the exhaust valve 22 by the intake electric S-VT 23 and the exhaust electric S-VT 24. As a result, the residual gas in the combustion chamber 17 is scavenged. Further, by adjusting the length of the overlap period, an internal EGR (Exhaust Gas Recirculation) gas is introduced into the combustion chamber 17 or confined in the combustion chamber 17. In this configuration example, the intake electric S-VT 23 and the exhaust electric S-VT 24 constitute an internal EGR system 552. Note that the internal EGR system 552 is not necessarily configured by S-VT.

  An injector 6 is attached to the cylinder head 13 for each cylinder 11. The injector 6 is configured to inject fuel directly into the combustion chamber 17. The injector 6 is disposed in a valley portion of the pent roof where the intake-side inclined surface 1311 and the exhaust-side inclined surface 1312 intersect. As shown in FIG. 2, the injector 6 has an injection axis X <b> 2 disposed on the exhaust side of the center axis X <b> 1 of the cylinder 11. The injection axis X2 of the injector 6 is parallel to the central axis X1. The injection axis X2 of the injector 6 coincides with the position of the convex portion 311 of the cavity 31 as described above. The injector 6 faces the cavity 31. The injection axis X2 of the injector 6 may coincide with the center axis X1 of the cylinder 11. Also in that case, it is desirable that the injection axis X2 of the injector 6 and the position of the convex portion 311 of the cavity 31 coincide.

  Although not shown in detail, the injector 6 is constituted by a multi-injection type fuel injection valve having a plurality of injection holes. The injector 6 injects the fuel so that the fuel spray spreads radially from the center of the combustion chamber 17 as indicated by a two-dot chain line in FIG. In the present configuration example, the injector 6 has ten nozzle holes, and the nozzle holes are arranged at equal angles in the circumferential direction. As shown in the upper diagram of FIG. 2, the axis of the nozzle hole is displaced in the circumferential direction with respect to a spark plug 25 described later. That is, the spark plug 25 is sandwiched between the shafts of two adjacent nozzle holes. Thereby, it is avoided that the spray of the fuel injected from the injector 6 directly hits the spark plug 25 and wets the electrode.

  A fuel supply system 61 is connected to the injector 6. The fuel supply system 61 includes a fuel tank 63 configured to store fuel, and a fuel supply path 62 that connects the fuel tank 63 and the injector 6 to each other. A fuel pump 65 and a common rail 64 are interposed in the fuel supply path 62. The fuel pump 65 pumps fuel to the common rail 64. In this configuration example, the fuel pump 65 is a plunger-type pump driven by the crankshaft 15. The common rail 64 is configured to store the fuel pumped from the fuel pump 65 at a high fuel pressure. When the injector 6 is opened, the fuel stored in the common rail 64 is injected into the combustion chamber 17 from the injection port of the injector 6. The fuel supply system 61 is configured to be able to supply high pressure fuel of 30 MPa or more to the injector 6. The maximum fuel pressure of the fuel supply system 61 may be about 120 MPa, for example. The pressure of the fuel supplied to the injector 6 may be changed according to the operating state of the engine 1. The configuration of the fuel supply system 61 is not limited to the above configuration.

  A spark plug 25 is attached to the cylinder head 13 for each cylinder 11. The spark plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17. In this configuration example, the spark plug 25 is disposed closer to the intake side than the center axis X1 of the cylinder 11. The spark plug 25 is located between the two intake ports 18. The spark plug 25 is attached to the cylinder head 13 so as to be inclined from the top to the bottom toward the center of the combustion chamber 17. As shown in FIG. 2, the electrode of the spark plug 25 faces the combustion chamber 17 and is located near the ceiling surface of the combustion chamber 17. The spark plug 25 may be disposed on the exhaust side of the center axis X1 of the cylinder 11. In addition, the spark plug 25 may be disposed on the central axis X1 of the cylinder 11, while the injector 6 may be disposed on the intake side or the exhaust side with respect to the central axis X1 of the cylinder 11.

  An intake passage 40 is connected to one side of the engine 1. The intake passage 40 communicates with the intake port 18 of each cylinder 11. The intake passage 40 is a passage through which gas introduced into the combustion chamber 17 flows. An air cleaner 41 that filters fresh air is disposed at the upstream end of the intake passage 40. A surge tank 42 is disposed near the downstream end of the intake passage 40. The intake passage 40 downstream of the surge tank 42 constitutes an independent passage that branches for each cylinder 11. The downstream end of the independent passage is connected to the intake port 18 of each cylinder 11.

  A throttle valve 43 is disposed between the air cleaner 41 and the surge tank 42 in the intake passage 40. The throttle valve 43 is configured to adjust the amount of fresh air introduced into the combustion chamber 17 by adjusting the opening of the valve.

  A supercharger 44 is also arranged in the intake passage 40 downstream of the throttle valve 43. The supercharger 44 is configured to supercharge the gas introduced into the combustion chamber 17. In this configuration example, the supercharger 44 is a mechanical supercharger driven by the engine 1. The mechanical supercharger 44 may be, for example, a Rishorum type. The configuration of the mechanical supercharger 44 may be any configuration. The mechanical supercharger 44 may be a roots type, a vane type, or a centrifugal type.

  An electromagnetic clutch 45 is interposed between the supercharger 44 and the engine 1. The electromagnetic clutch 45 transmits a driving force from the engine 1 to the supercharger 44 between the supercharger 44 and the engine 1 or interrupts the transmission of the driving force. As will be described later, when the ECU 10 switches between disconnection and connection of the electromagnetic clutch 45, the supercharger 44 is switched on and off. The engine 1 can switch between the supercharger 44 supercharging the gas introduced into the combustion chamber 17 and the supercharger 44 not supercharging the gas introduced into the combustion chamber 17. It is configured.

  An intercooler 46 is disposed downstream of the supercharger 44 in the intake passage 40. The intercooler 46 is configured to cool the gas compressed in the supercharger 44. The intercooler 46 may be configured to be, for example, a water cooling type. The intercooler 46 may be oil-cooled.

  A bypass passage 47 is connected to the intake passage 40. The bypass passage 47 connects the upstream portion of the supercharger 44 and the downstream portion of the intercooler 46 in the intake passage 40 so as to bypass the supercharger 44 and the intercooler 46. More specifically, the bypass passage 47 is connected to the surge tank 42. An air bypass valve 48 is disposed in the bypass passage 47. The air bypass valve 48 adjusts the flow rate of the gas flowing through the bypass passage 47.

  When the supercharger 44 is turned off (that is, when the electromagnetic clutch 45 is disconnected), the air bypass valve 48 is fully opened. As a result, the gas flowing through the intake passage 40 bypasses the supercharger 44 and is introduced into the combustion chamber 17 of the engine 1. The engine 1 is operated in a non-supercharged state, that is, in a natural intake state.

  When the supercharger 44 is turned on (that is, when the electromagnetic clutch 45 is connected), part of the gas that has passed through the supercharger 44 flows back upstream of the supercharger 44 through the bypass passage 47. To do. Since the reverse flow rate can be adjusted by adjusting the opening degree of the air bypass valve 48, the supercharging pressure of the gas introduced into the combustion chamber 17 can be adjusted. The supercharging is defined as the time when the pressure in the surge tank 42 exceeds atmospheric pressure, and the non-supercharging is defined as the time when the pressure in the surge tank 42 is lower than atmospheric pressure. Also good.

  In this configuration example, the supercharger 44, the bypass passage 47, and the air bypass valve 48 constitute a supercharging system 49.

  The engine 1 has a swirl generator that generates a swirl flow in the combustion chamber 17. As shown in FIG. 3, the swirl generating unit is a swirl control valve 56 attached to the intake passage 40. The swirl control valve 56 is disposed in the secondary passage 402 of the primary passage 401 connected to the first intake port 181 and the secondary passage 402 connected to the second intake port 182. The swirl control valve 56 is an opening adjustment valve that can narrow the cross section of the secondary passage. When the opening of the swirl control valve 56 is small, the intake air flow rate flowing into the combustion chamber 17 from the first intake port 181 among the first intake port 181 and the second intake port 182 aligned in the front-rear direction of the engine 1 is relatively. And the intake flow rate flowing into the combustion chamber 17 from the second intake port 182 relatively decreases, so that the swirl flow in the combustion chamber 17 becomes stronger. When the opening of the swirl control valve 56 is large, the intake flow rate flowing into the combustion chamber 17 from each of the first intake port 181 and the second intake port 182 becomes substantially uniform, so the swirl flow in the combustion chamber 17 is weak. Become. When the swirl control valve 56 is fully opened, no swirl flow is generated. The swirl flow circulates in the counterclockwise direction in FIG. 3 as indicated by the white arrow (see also the white arrow in FIG. 2).

  The swirl generating unit shifts the valve opening periods of the two intake valves 21 instead of attaching the swirl control valve 56 to the intake passage 40 or in addition to attaching the swirl control valve 56, so that one of the intake valves 21 Alternatively, a configuration in which intake air can be introduced into the combustion chamber 17 from only the above may be employed. Since only one of the two intake valves 21 is opened, intake air is unevenly introduced into the combustion chamber 17, so that a swirl flow can be generated in the combustion chamber 17. . Further, the swirl generator may be configured to generate a swirl flow in the combustion chamber 17 by devising the shape of the intake port 18.

  An exhaust passage 50 is connected to the other side of the engine 1. The exhaust passage 50 communicates with the exhaust port 19 of each cylinder 11. The exhaust passage 50 is a passage through which exhaust gas discharged from the combustion chamber 17 flows. Although the detailed illustration is omitted, the upstream portion of the exhaust passage 50 constitutes an independent passage branched for each cylinder 11. The upstream end of the independent passage is connected to the exhaust port 19 of each cylinder 11.

  An exhaust gas purification system having a plurality of catalytic converters is disposed in the exhaust passage 50. Although not shown, the upstream catalytic converter is disposed in the engine room. The upstream catalytic converter includes a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512. The downstream catalytic converter is disposed outside the engine room. The downstream catalytic converter has a three-way catalyst 513. The exhaust gas purification system is not limited to the configuration shown in the figure. For example, GPF may be omitted. Further, the catalytic converter is not limited to one having a three-way catalyst. Furthermore, the arrangement order of the three-way catalyst and the GPF may be changed as appropriate.

  An EGR passage 52 constituting an external EGR system 551 is connected between the intake passage 40 and the exhaust passage 50. The EGR passage 52 is a passage for returning a part of burned gas to the intake passage 40. The upstream end of the EGR passage 52 is connected between the upstream catalytic converter and the downstream catalytic converter in the exhaust passage 50. The downstream end of the EGR passage 52 is connected to the upstream side of the supercharger 44 in the intake passage 40. More specifically, the downstream end of the EGR passage 52 is connected in the middle of the bypass passage 47. The EGR gas flowing through the EGR passage 52 does not pass through the air bypass valve 48 of the bypass passage 47 and enters the upstream of the supercharger 44 in the intake passage 40.

  A water-cooled EGR cooler 53 is disposed in the EGR passage 52. The EGR cooler 53 is configured to cool the burned gas. An EGR valve 54 is also disposed in the EGR passage 52. The EGR valve 54 is configured to adjust the flow rate of burnt gas flowing through the EGR passage 52. By adjusting the opening degree of the EGR valve 54, the recirculation amount of the cooled burned gas, that is, the external EGR gas can be adjusted.

  In this configuration example, the EGR system includes an external EGR system 551 configured to include an EGR passage 52, an EGR valve 54, and an EGR cooler 53, and the above-described intake electric S-VT 23 and exhaust electric S-VT 24. Internal EGR system 552. The EGR valve 54 also constitutes one of the state quantity setting devices. In the external EGR system 551, the EGR passage 52 is connected downstream of the GPF 512 and has an EGR cooler 53. , Can be supplied to the combustion chamber 17.

  The control device for the compression self-ignition engine includes an ECU (Engine Control Unit) 10 for operating the engine 1. The ECU 10 is a controller based on a well-known microcomputer, and as shown in FIG. 4, a central processing unit (CPU) 101 for executing a program and, for example, a RAM (Random Access Memory) or ROM A memory 102 configured by (Read Only Memory) and storing programs and data, and an input / output bus 103 for inputting and outputting electrical signals are provided. The ECU 10 is an example of a control unit.

  As shown in FIGS. 1 and 4, various sensors SW <b> 1 to SW <b> 16 are connected to the ECU 10. Sensors SW1-SW16 output a detection signal to ECU10. The sensors include the following sensors.

That is, the air flow sensor SW1 that is disposed downstream of the air cleaner 41 in the intake passage 40 and detects the flow rate of fresh air flowing through the intake passage 40, the first intake temperature sensor SW2 that detects the temperature of fresh air, and the intake passage 40, the first pressure sensor SW3 that is disposed downstream of the connection position of the EGR passage 52 and upstream of the supercharger 44 and detects the pressure of the gas flowing into the supercharger 44, and supercharging in the intake passage 40 The second intake air temperature sensor SW4, which is disposed downstream of the machine 44 and upstream of the connection position of the bypass passage 47 and detects the temperature of the gas flowing out from the supercharger 44, is attached to the surge tank 42, and A second pressure sensor SW5 for detecting the pressure of the gas downstream of the feeder 44, attached to the cylinder head 13 corresponding to each cylinder 11, and each A finger pressure sensor SW6 that detects the pressure in the firing chamber 17, an exhaust temperature sensor SW7 that is disposed in the exhaust passage 50 and detects the temperature of the exhaust gas discharged from the combustion chamber 17, and is upstream of the upstream catalytic converter in the exhaust passage 50. And a linear O ₂ sensor SW8 that detects the oxygen concentration in the exhaust gas, and a lambda O ₂ sensor SW9 that is arranged downstream of the three-way catalyst 511 in the upstream catalytic converter and detects the oxygen concentration in the exhaust gas. A water temperature sensor SW10 that is attached to the engine 1 and detects the temperature of the cooling water, a crank angle sensor SW11 that is attached to the engine 1 and detects the rotation angle of the crankshaft 15, an accelerator pedal mechanism, and an accelerator pedal Accelerator opening sensor SW1 for detecting the accelerator opening corresponding to the operation amount 2. An intake cam angle sensor SW13 that is attached to the engine 1 and detects the rotation angle of the intake camshaft, an exhaust cam angle sensor SW14 that is attached to the engine 1 and detects the rotation angle of the exhaust camshaft, and the EGR passage 52 An EGR differential pressure sensor SW15 that is disposed and detects the differential pressure upstream and downstream of the EGR valve 54, and a fuel pressure sensor that is attached to the common rail 64 of the fuel supply system 61 and detects the pressure of the fuel supplied to the injector 6 SW16.

  The ECU 10 determines the operating state of the engine 1 based on these detection signals and calculates the control amount of each device. The ECU 100 sends control signals relating to the calculated control amount to the injector 6, spark plug 25, intake electric S-VT 23, exhaust electric S-VT 24, fuel supply system 61, throttle valve 43, EGR valve 54, supercharger 44. Output to the electromagnetic clutch 45, the air bypass valve 48, and the swirl control valve 56.

  For example, the ECU 10 sets the target torque of the engine 10 and determines the target boost pressure based on the detection signal of the accelerator opening sensor SW12 and a preset map. Then, the ECU 10 adjusts the opening degree of the air bypass valve 48 based on the target supercharging pressure and the differential pressure across the supercharger 44 obtained from the detection signals of the first pressure sensor SW3 and the second pressure sensor SW5. Thus, feedback control is performed so that the supercharging pressure becomes the target supercharging pressure.

  Further, the ECU 10 sets a target EGR rate (that is, a ratio of EGR gas to all gases in the combustion chamber 17) based on the operating state of the engine 10 and a preset map. The ECU 10 determines the target EGR gas amount based on the target EGR rate and the intake air amount based on the detection signal of the accelerator opening sensor SW12, and before and after the EGR valve 54 obtained from the detection signal of the EGR differential pressure sensor SW15. By adjusting the opening degree of the EGR valve 54 based on the differential pressure, feedback control is performed so that the external EGR gas amount introduced into the combustion chamber 17 becomes the target EGR gas amount.

Further, the ECU 10 executes air-fuel ratio feedback control when a predetermined control condition is satisfied. Specifically, the ECU 10 controls the fuel of the injector 6 so that the air-fuel ratio of the air-fuel mixture becomes a desired value based on the oxygen concentration in the exhaust gas detected by the linear O ₂ sensor SW8 and the lambda O ₂ sensor SW9. Adjust the injection amount.

  Details of other controls of the engine 1 by the ECU 10 will be described later.

(Engine operating range)
FIG. 5 illustrates an operation region map of the engine 1 in the warm state. The operation region maps 501 and 502 of the engine 1 are determined by the load and the rotational speed, and are divided into five regions with respect to the load level and the rotational speed level. Specifically, the five regions include a low load region (1) -1 including idle operation and extending to a low rotation region and a medium rotation region, a region having a higher load than the low load region, and a low rotation region and a medium rotation region. Medium load region (1) -2 spreading in the middle, region having higher load than medium load region (1) -2 and high rotation region including fully open load (2), medium rotation region in high load region Low rotation region (3) with a lower rotational speed than (2), low load region (1) -1, medium load region (1) -2, high load medium rotation region (2), and high load low It is a high rotation area (4) having a higher rotation speed than the rotation area (3). Here, the low rotation region, the medium rotation region, and the high rotation region are each when the entire operation region of the engine 1 is divided into approximately three equal parts of the low rotation region, the medium rotation region, and the high rotation region in the rotation speed direction. The low rotation region, medium rotation region, and high rotation region may be used. In the example of FIG. 5, the rotation speed less than N1 is low rotation, the rotation speed N2 or more is high rotation, and the rotation speed N1 or more and less than N2 is medium rotation. For example, the rotational speed N1 may be about 1200 rpm, and the rotational speed N2 may be about 4000 rpm, for example. Note that a two-dot chain line in FIG. 5 indicates a road-load line of the engine 1. In FIG. 5, for easy understanding, the operation region maps 501 and 502 of the engine 1 are drawn in two parts. A map 501 shows the state of the air-fuel mixture and the combustion mode in each region, and the drive region and non-drive region of the supercharger 44. A map 502 shows the opening degree of the swirl control valve 56 in each region.

  The engine 1 compresses itself in a low load region (1) -1, a medium load region (1) -2, and a high load medium rotation region (2) mainly for improving fuel consumption and exhaust gas performance. Combustion by ignition. The engine 1 also performs combustion by spark ignition in other regions, specifically, in the high load low rotation region (3) and the high rotation region (4). Hereinafter, the operation of the engine 1 in each region will be described in detail with reference to the fuel injection timing and the ignition timing shown in FIG. Note that reference numerals 601, 602, 603, 604, 605, and 606 in FIG. 6 correspond to the operating state of the engine 1 indicated by reference numerals 601, 602, 603, 604, 605, and 606 in the operation region map 501 in FIG. 5, respectively. .

(Low load area (1) -1)
When the engine 1 is operating in the low load region (1) -1, the engine 1 performs CI combustion. In the combustion by self-ignition, when the temperature in the combustion chamber 17 before the start of compression varies, the timing of self-ignition greatly changes. Therefore, the engine 1 performs SPCCI combustion combining SI combustion and CI combustion in the low load region (1) -1.

  Reference numeral 601 in FIG. 6 indicates fuel injection timing (reference numerals 6011 and 6012) and ignition timing (reference numeral 6013) and combustion when the engine 1 is operating in the operating state 601 in the low load region (1) -1. A waveform (that is, a waveform indicating a change in the heat generation rate with respect to the crank angle, reference numeral 6014) is shown.

  In the SPCCI combustion, the spark plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17 so that the air-fuel mixture undergoes SI combustion by flame propagation, and the heat in the combustion chamber 17 generates heat from the SI combustion. As the temperature rises and the pressure in the combustion chamber 17 rises due to flame propagation, the unburned mixture undergoes CI combustion by self-ignition.

  By adjusting the calorific value of the SI combustion, the temperature variation in the combustion chamber 17 before the start of compression can be absorbed. Even if the temperature in the combustion chamber 17 before the compression starts varies, the air-fuel mixture can be self-ignited at the target timing by adjusting the SI combustion start timing by adjusting the ignition timing, for example.

  When performing SPCCI combustion, the spark plug 25 ignites the air-fuel mixture in the vicinity of the compression top dead center, thereby starting combustion by flame propagation. Heat generation during SI combustion is milder than heat generation during CI combustion. Accordingly, the heat generation rate waveform 6014 has a relatively small rising slope. The pressure fluctuation (dp / dθ) in the combustion chamber 17 is also gentler during SI combustion than during CI combustion.

  When the temperature and pressure in the combustion chamber 17 are increased by SI combustion, the unburned mixture is self-ignited. In the example of FIG. 6, the slope of the heat generation rate waveform 6014 changes from small to large at the timing of self-ignition. That is, the heat generation rate waveform has an inflection point at the timing when CI combustion starts.

  After the start of CI combustion, SI combustion and CI combustion are performed in parallel. Since CI combustion generates more heat than SI combustion, the heat generation rate is relatively large. However, since CI combustion is performed after compression top dead center, the piston 3 is lowered by motoring. It is avoided that the slope of the heat generation rate waveform 6014 becomes too large due to CI combustion. Dp / dθ during CI combustion also becomes relatively gentle.

  dp / dθ can be used as an index representing combustion noise. However, since SPCCI combustion can reduce dp / dθ as described above, it is possible to avoid excessive combustion noise. . Combustion noise can be suppressed below an acceptable level.

  When CI combustion ends, SPCCI combustion ends. CI combustion has a shorter combustion period than SI combustion. In SPCCI combustion, the combustion end timing is earlier than SI combustion. In other words, SPCCI combustion can bring the combustion end time during the expansion stroke closer to the compression top dead center. The SPCCI combustion is more advantageous for improving the fuel efficiency of the engine 1 than the SI combustion.

  In order to improve the fuel efficiency performance of the engine 1, the EGR system 55 introduces EGR gas into the combustion chamber 17 when the engine 1 is operating in the low load region (1) -1. Specifically, the exhaust gas is discharged from the combustion chamber 17 to the intake port 18 and the exhaust port 19 by providing a positive overlap period in which both the intake valve 21 and the exhaust valve 22 are opened in the vicinity of the exhaust top dead center. Part of the exhaust gas is reintroduced into the combustion chamber 17. Since the hot burned gas is introduced into the combustion chamber 17, the temperature in the combustion chamber 17 can be increased, which is advantageous for stabilizing the SPCCI combustion. A negative overlap period in which both the intake valve 21 and the exhaust valve 22 are closed may be provided.

  When the engine 1 is operating in the low load region (1) -1, a strong swirl flow is formed in the combustion chamber 17. The swirl flow is strong at the outer periphery of the combustion chamber 17 and weak at the center. The swirl control valve 56 has a predetermined opening on the fully closed or closed side. As described above, since the intake port 18 is a tumble port, an oblique swirl flow having a tumble component and a swirl component is formed in the combustion chamber 17.

  When the engine 1 operates in the low load region (1) -1, the swirl ratio becomes 4 or more. Here, the swirl ratio is defined. The “swirl ratio” is a value obtained by dividing the value obtained by measuring and integrating the intake flow lateral angular velocity for each valve lift by the engine angular velocity. The intake flow lateral angular velocity can be obtained based on the measurement using the rig testing apparatus shown in FIG. That is, in the apparatus shown in the figure, the cylinder head 13 is installed upside down on the base, and the intake port 18 is connected to an intake air supply device (not shown), while the cylinder 36 is installed on the cylinder head 13. At the same time, an impulse meter 38 having a honeycomb rotor 37 is connected to the upper end thereof. The lower surface of the impulse meter 38 is positioned at a position of 1.75 D (D is a cylinder bore diameter) from the mating surface of the cylinder head 13 and the cylinder block. Torque acting on the honeycomb-shaped rotor 37 is measured by an impulse meter 38 by a swirl (see an arrow in FIG. 7) generated in the cylinder 36 in response to intake air supply, and the intake flow lateral angular velocity can be obtained based on the measured torque. .

  FIG. 8 shows the relationship between the degree of opening of the swirl control valve 56 and the swirl ratio in the engine 1. FIG. 8 shows the opening degree of the swirl control valve 56 by the opening ratio with respect to the fully open section of the secondary passage 402. When the swirl control valve 56 is fully closed, the opening ratio of the secondary passage 402 becomes 0%, and when the opening of the swirl control valve 56 increases, the opening ratio of the secondary passage 402 becomes larger than 0%. When the swirl control valve 56 is fully open, the opening ratio of the secondary passage 402 is 100%. As illustrated in FIG. 8, in the engine 1, the swirl ratio becomes about 6 when the swirl control valve 56 is fully closed. When the engine 1 operates in the low load region (1) -1, the swirl ratio may be 4 or more and 6 or less. What is necessary is just to adjust the opening degree of the swirl control valve 56 in the range from which an opening ratio will be 0 to 15%.

  When the engine 1 operates in the low load region (1) -1, the air-fuel ratio (A / F) of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio in the entire combustion chamber 17. In other words, the excess air ratio λ of the air-fuel mixture exceeds 1 in the entire combustion chamber 17. More specifically, the A / F of the air-fuel mixture is 30 or more in the entire combustion chamber 17. By carrying out like this, generation | occurrence | production of RawNOx can be suppressed and exhaust gas performance can be improved.

  When the engine 1 operates in the low load region (1) -1, the air-fuel mixture is stratified between the central portion and the outer peripheral portion in the combustion chamber 17. A central portion in the combustion chamber 17 is a portion where the spark plug 25 is disposed, and an outer peripheral portion is a portion around the central portion and in contact with the liner of the cylinder 11. You may define the center part in the combustion chamber 17 as a part with a weak swirl flow, and an outer peripheral part as a part with a strong swirl flow.

  The fuel concentration of the air-fuel mixture at the center is higher than the fuel concentration at the outer periphery. Specifically, the A / F of the air-fuel mixture in the central part is 20 or more and 30 or less, and the A / F of the air-fuel mixture in the outer peripheral part is 35 or more. Note that the value of the air-fuel ratio is the value of the air-fuel ratio at the time of ignition and is the same in the following description.

  When the engine 1 operates in the low load region (1) -1, the injector 6 injects fuel into the combustion chamber 17 a plurality of times during the compression stroke (reference numerals 6011 and 6012). As described above, the air-fuel mixture is stratified in the central portion and the outer peripheral portion of the combustion chamber 17 by the multiple fuel injections and the swirl flow in the combustion chamber 17.

  After completion of fuel injection, the spark plug 25 ignites the air-fuel mixture at the center of the combustion chamber 17 at a predetermined timing before compression top dead center (reference numeral 6013). Since the air-fuel mixture in the central portion has a relatively high fuel concentration, the ignitability is improved and SI combustion by flame propagation is stabilized. By stabilizing the SI combustion, the CI combustion starts at an appropriate timing. In SPCCI combustion, controllability of CI combustion is improved. As a result, when the engine 1 is operated in the low load region (1) -1, both the suppression of the generation of combustion noise and the improvement of the fuel consumption performance due to the shortening of the combustion period are compatible.

  As described above, in the low load region (1) -1, since the engine 1 performs the SPCCI combustion by leaning the air-fuel mixture from the stoichiometric air-fuel ratio, the low load region (1) -1 is “SPCCI lean region”. Can be called.

(Medium load area (1) -2)
Even when the engine 1 is operating in the medium load region (1) -2, the engine 1 performs SPCCI combustion as in the low load region (1) -1.

  Reference numeral 602 in FIG. 6 indicates fuel injection timing (reference numerals 6021 and 6022) and ignition timing (reference numeral 6023) and combustion when the engine 1 is operating in the operation state 602 in the medium load region (1) -2. A waveform (reference numeral 6024) is shown.

  The EGR system 55 introduces EGR gas into the combustion chamber 17 when the operating state of the engine 1 is in the medium load region (1) -2. Specifically, as in the low load region (1) -1, by providing a positive overlap period in which both the intake valve 21 and the exhaust valve 22 are opened in the vicinity of the exhaust top dead center, Part of the exhaust gas discharged from the inside to the intake port 18 and the exhaust port 19 is reintroduced into the combustion chamber 17. That is, the internal EGR gas is introduced into the combustion chamber 17. Further, in the medium load region (1) -2, the exhaust gas cooled by the EGR cooler 53 is introduced into the combustion chamber 17 through the EGR passage 52. That is, an external EGR gas having a temperature lower than that of the internal EGR gas is introduced into the combustion chamber 17. In the middle load region (1) -2, the internal EGR gas and / or the external EGR gas is introduced into the combustion chamber 17 to adjust the temperature in the combustion chamber 17 to be appropriate.

  Further, when the engine 1 is operated in the medium load region (1) -2, a strong swirl flow having a swirl ratio of 4 or more is entered in the combustion chamber 17 as in the low load region (1) -1. Is formed. The swirl control valve 56 has a predetermined opening on the fully closed or closed side. By strengthening the swirl flow, the turbulent energy in the combustion chamber 17 increases, so that when the engine 1 is operated in the medium load region (1) -2, the flame of SI combustion propagates quickly and SI combustion occurs. Is stabilized. The controllability of CI combustion is enhanced by the stabilization of SI combustion. By optimizing the timing of CI combustion in SPCCI combustion, it is possible to suppress the generation of combustion noise and improve fuel efficiency. Further, torque variation between cycles can be suppressed.

  When the engine 1 is operated in the medium load region (1) -2, the air-fuel ratio (A / F) of the air-fuel mixture is the stoichiometric air-fuel ratio (A / F≈14.7) in the entire combustion chamber 17. As the three-way catalyst purifies the exhaust gas discharged from the combustion chamber 17, the exhaust gas performance of the engine 1 is improved. The A / F of the air-fuel mixture may be set within the purification window of the three-way catalyst. Therefore, the excess air ratio λ of the air-fuel mixture may be set to 1.0 ± 0.2.

  When the engine 1 operates in the medium load region (1) -2, the injector 6 performs fuel injection during the intake stroke (reference numeral 6021) and fuel injection during the compression stroke (reference numeral 6022). By performing the first injection 6021 during the intake stroke, the fuel can be distributed substantially uniformly in the combustion chamber 17. By performing the second injection 6022 during the compression stroke, the temperature in the combustion chamber 17 can be lowered by the latent heat of vaporization of the fuel. It is possible to prevent the air-fuel mixture including the fuel injected by the first injection 6021 from being prematurely ignited. In the middle load region (1) -2, the second injection 6022 can be omitted particularly when the engine is in an operating state with a low load.

  When the injector 6 performs the first injection 6021 and the second injection 6022, the combustion chamber 17 has a substantially uniform mixing with an excess air ratio λ of 1.0 ± 0.2 as a whole. Qi is formed. Since the air-fuel mixture is substantially homogeneous, it is possible to improve fuel efficiency by reducing unburned loss and to improve exhaust gas performance by avoiding the generation of smoke. The excess air ratio λ is preferably 1.0 to 1.2.

  When the spark plug 25 ignites the air-fuel mixture at a predetermined timing before the compression top dead center (reference numeral 6023), the air-fuel mixture burns by flame propagation. After the start of combustion by flame propagation, the unburned mixture self-ignites and CI burns.

  Accordingly, in the medium load region (1) -2, the engine 1 performs the SPCCI combustion with the air-fuel mixture as the stoichiometric air-fuel ratio, and therefore, the medium load region (1) -2 can be referred to as “SPCCIλ = 1 region”. .

  Here, as shown in FIG. 5, the turbocharger 44 is turned off in a part of the low load region (1) -1 and a part of the medium load region (1) -2 (S / (See C OFF). Specifically, the supercharger 44 is turned off in the low rotation side region in the low load region (1) -1. In the region on the high rotation side in the low load region (1) -1, the supercharger 44 is turned on in order to ensure a necessary intake charge amount corresponding to the increase in the rotational speed of the engine 1. Increase the boost pressure. Further, the supercharger 44 is turned off in the low load / low rotation side region in the medium load region (1) -2, and the fuel injection amount in the high load side region in the medium load region (1) -2. The turbocharger 44 is turned on in order to ensure the necessary intake charge amount corresponding to the increase in the engine speed, and is necessary in response to the increase in the rotational speed of the engine 1 in the high speed region. In order to ensure the intake charge amount, the supercharger 44 is turned on.

  Note that, in each of the high-load medium rotation region (2), the high-load low-rotation region (3), and the high-rotation region (4), the supercharger 44 is turned on over the entire region (S / (See CON).

(High load medium rotation range (2))
Even when the engine 1 is operating in the high load mid-rotation region (2), the engine 1 performs SPCCI combustion in the same manner as the low load region (1) -1 and the medium load region (1) -2.

  Reference numeral 603 in FIG. 6 indicates fuel injection timings (reference numerals 6031 and 6032) and ignition timings (reference numeral 6033) when the engine 1 is operating in the low-rotation-side operation state 603 in the high-load middle rotation region (2). In addition, a combustion waveform (reference numeral 6034) is shown. Further, reference numeral 604 denotes a fuel injection timing (reference numeral 6041) and an ignition timing (reference numeral 6042) when the engine 1 is operating in the high-rotation-side operation state 604 in the high load mid-rotation region (2), and A combustion waveform (reference numeral 6043) is shown.

  The EGR system 55 introduces EGR gas into the combustion chamber 17 when the operating state of the engine 1 is in the high load mid-rotation region (2). The engine 1 reduces the amount of EGR gas as the load increases. At full load, EGR gas may be zero.

  Further, when the engine 1 is operated in the high load mid-rotation region (2), a strong swirl flow having a swirl ratio of 4 or more is entered in the combustion chamber 17 as in the low load region (1) -1. Is formed. The swirl control valve 56 has a predetermined opening on the fully closed or closed side.

  When the engine 1 operates in the high load mid-rotation region (2), the air-fuel ratio (A / F) of the air-fuel mixture is richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio in the entire combustion chamber 17 (that is, The excess air ratio λ of the mixture is λ ≦ 1).

  When the engine 1 operates in the operation state 603 in the high load mid-rotation region (2), the injector 6 performs the front injection 6031 in the intake stroke and performs the rear injection 6032 in the compression stroke. The pre-stage injection may be started, for example, in the first half of the intake stroke, and the post-stage injection may be performed, for example, at the end of the compression stroke. The first half of the intake stroke may be the first half when the intake stroke is divided into two equal parts. Specifically, in the front stage injection, for example, fuel injection may be started at 280 ° CA before compression top dead center.

  If the injection start of the front injection 6031 is in the first half of the intake stroke, although not shown in the drawing, a part of the fuel is squished in the squish area 171 of the combustion chamber 17 (that is, the cavity The region outside 31 (see FIG. 2)) and the remaining fuel enters the region inside cavity 31. The swirl flow is strong at the outer periphery of the combustion chamber 17 and weak at the center. Therefore, a part of the fuel that has entered the squish area 171 enters the swirl flow, and the remaining fuel that has entered the region within the cavity 31 enters the inside of the swirl flow. The fuel that has entered the swirl flow remains in the swirl flow during the intake stroke to the compression stroke, and forms an air-fuel mixture for CI combustion at the outer peripheral portion of the combustion chamber 17. The fuel that has entered the swirl flow also remains inside the swirl flow during the intake stroke to the compression stroke, and forms an air-fuel mixture for SI combustion in the central portion of the combustion chamber 17.

  When the engine 1 operates in the high load mid-rotation region (2), the fuel concentration of the air-fuel mixture at the outer peripheral portion of the combustion chamber 17 is higher than the fuel concentration of the air-fuel mixture at the central portion and the fuel of the air-fuel mixture at the outer peripheral portion. The amount is made larger than the fuel amount of the air-fuel mixture in the central part. Specifically, the air-fuel ratio in the central portion where the spark plug 25 is disposed has an excess air ratio λ of 1 or less, and the air-fuel mixture in the outer peripheral portion has an air excess ratio λ of less than 1. The air-fuel ratio (A / F) of the air-fuel mixture in the center may be, for example, 13 or more and the theoretical air-fuel ratio (14.7) or less. The air-fuel ratio of the air-fuel mixture at the outer peripheral portion may be, for example, 11 or more, the stoichiometric air-fuel ratio or less, or 11 or more and 12 or less. Since the amount of fuel in the air-fuel mixture increases, the temperature of the outer peripheral portion of the combustion chamber 17 decreases due to the latent heat of vaporization of the fuel. The air-fuel ratio of the entire air-fuel mixture in the combustion chamber 17 may be 12.5 or more, the stoichiometric air-fuel ratio or less, or 12.5 or more and 13 or less.

  The end of the compression stroke may be the end when the compression stroke is divided into three equal parts, the initial period, the middle period, and the final period. For example, the post-injection 6032 performed at the end of the compression stroke may start fuel injection at 10 ° CA before top dead center. By performing the post-stage injection immediately before the top dead center, the temperature in the combustion chamber can be lowered by the latent heat of vaporization of the fuel. The fuel injected by the pre-injection 6031 undergoes a low-temperature oxidation reaction during the compression stroke and shifts to a high-temperature oxidation reaction before the top dead center. However, the post-injection 6032 is performed immediately before the top dead center to burn the fuel. By lowering the indoor temperature, it is possible to suppress the transition from the low temperature oxidation reaction to the high temperature oxidation reaction, and it is possible to suppress the occurrence of premature ignition. In addition, the ratio of the injection amount of the front stage injection and the injection amount of the rear stage injection may be 95: 5 as an example.

  The spark plug 25 ignites the air-fuel mixture in the center of the combustion chamber 17 in the vicinity of the compression top dead center (reference numeral 6033). The spark plug 25 performs ignition after the compression top dead center, for example. Since the spark plug 25 is disposed at the center of the combustion chamber 17, the air-fuel mixture at the center starts SI combustion by flame propagation by the ignition of the spark plug 25.

  When the engine 1 is operated in the operation state 604 in the high load mid-rotation region (2), the injector 6 starts fuel injection in the intake stroke (reference numeral 6041).

  The injection 6041 that starts in the intake stroke may start fuel injection in the first half of the intake stroke, as described above. Specifically, the injection 6041 may start fuel injection at 280 ° CA before top dead center. The end of the injection 6041 may be during the compression stroke beyond the intake stroke. By starting the injection 6041 in the first half of the intake stroke, as described above, an air-fuel mixture for CI combustion is formed in the outer peripheral portion of the combustion chamber 17, and a mixture for SI combustion is formed in the central portion of the combustion chamber 17. Qi can be formed. As described above, the air-fuel mixture in the center portion where the spark plug 25 is disposed preferably has an excess air ratio λ of 1 or less, and the air-fuel mixture in the outer peripheral portion has an air excess ratio λ of 1 or less, preferably 1 Is less than. The air-fuel ratio (A / F) of the air-fuel mixture in the center may be, for example, 13 or more and the theoretical air-fuel ratio (14.7) or less. The air-fuel ratio of the air-fuel mixture at the center may be leaner than the stoichiometric air-fuel ratio. The air-fuel ratio of the air-fuel mixture at the outer peripheral portion may be, for example, 11 or more, the stoichiometric air-fuel ratio or less, or 11 or more and 12 or less. The air-fuel ratio of the entire air-fuel mixture in the combustion chamber 17 may be 12.5 or more, the stoichiometric air-fuel ratio or less, or 12.5 or more and 13 or less.

  When the rotation speed of the engine 1 increases, the time for the fuel injected by the injection 6041 to react becomes shorter. Therefore, the latter stage injection for suppressing the reaction of the air-fuel mixture can be omitted.

  The spark plug 25 ignites the air-fuel mixture at the center of the combustion chamber 17 in the vicinity of the compression top dead center (reference numeral 6042). The spark plug 25 performs ignition after the compression top dead center, for example.

  In the high load region, the fuel injection amount increases and the temperature of the combustion chamber 17 also increases, so that the CI combustion is likely to start early. In other words, pre-ignition of the air-fuel mixture tends to occur in the high load region. However, as described above, since the temperature of the outer peripheral portion of the combustion chamber 17 is lowered by the latent heat of vaporization of the fuel, it is avoided that the CI combustion starts immediately after the mixture is sparked. Can do.

  By stratifying the air-fuel mixture in the combustion chamber 17 and generating a strong swirl flow in the combustion chamber 17, SI combustion can be sufficiently performed before the start of CI combustion. As a result, the generation of combustion noise can be suppressed, and the generation of NOx is also suppressed without the combustion temperature becoming too high. Further, torque variation between cycles can be suppressed.

  Moreover, since the temperature of the outer peripheral portion is low, CI combustion becomes moderate, and the generation of combustion noise can be suppressed. Furthermore, since the combustion period is shortened by CI combustion, torque can be improved and thermal efficiency can be improved in a high load region. Therefore, the engine 1 can improve fuel efficiency while avoiding combustion noise by performing SPCCI combustion in a high load region.

  As described above, since the engine 1 performs SPCCI combustion with the air-fuel mixture richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio in the high-load mid-rotation region (2), the high-load mid-rotation region (2) It can be referred to as “SPCCIλ ≦ 1 region”.

(High load, low rotation range (3))
When the rotational speed of the engine 1 is low, the time required for the crank angle to change by 1 ° becomes long. The reaction of the fuel injected into the combustion chamber 17 has progressed too much, and there is a risk of premature ignition even if SPCCI combustion is attempted. Therefore, when the engine 1 is operating in the high load mid-rotation region (3), the engine 1 performs SI combustion instead of SPCCI combustion.

  Reference numeral 605 in FIG. 6 indicates fuel injection timing (reference numerals 6051 and 6052) and ignition timing (reference numeral 6053) and combustion when the engine 1 is operating in the operating state 605 in the high load mid-rotation region (3). A waveform (reference numeral 6054) is shown.

  The EGR system 55 introduces EGR gas into the combustion chamber 17 when the operating state of the engine 1 is in the high load mid-rotation region (3). The engine 1 reduces the amount of EGR gas as the load increases. At full load, EGR gas may be zero.

  When the engine 1 is operating in the high-load low-rotation region (3), the air-fuel ratio (A / F) of the air-fuel mixture is the stoichiometric air-fuel ratio (A / F≈14.7) in the entire combustion chamber 17. is there. The A / F of the air-fuel mixture may be set within the purification window of the three-way catalyst. Therefore, the excess air ratio λ of the air-fuel mixture may be set to 1.0 ± 0.2. By setting the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio, the fuel consumption performance is improved in the high load low rotation region (3). When the engine 1 is operated in the high load low rotation region (3), the fuel concentration of the entire air-fuel mixture in the combustion chamber 17 is 1 or less in the excess air ratio λ and the high load medium rotation region (2). It may be larger than the excess air ratio λ.

When the engine 1 operates in the high-load low-rotation region (3), the injector 6 injects fuel in the intake stroke (reference numeral 6051), and a period from the end of the compression stroke to the initial stage of the expansion stroke (hereinafter, this period is referred to as “period”). The fuel is injected into the combustion chamber 17 at a timing within the retard period (reference numeral 6052). The initial stage of the expansion stroke may be the initial stage when the expansion stroke is divided into three equal parts in the initial stage, the middle period, and the final stage.
By injecting fuel during the intake stroke (reference numeral 6051), it is possible to secure a sufficient time for forming the air-fuel mixture. Further, by injecting fuel within the retard period (reference numeral 6052), the gas flow in the combustion chamber 17 can be strengthened immediately before ignition. The fuel pressure is set to a high fuel pressure of 30 MPa or more. By increasing the fuel pressure, the fuel injection period and the mixture formation period can be shortened, and the gas flow in the combustion chamber 17 can be made stronger. As an example, the upper limit value of the fuel pressure may be 120 MPa.

  The spark plug 25 ignites the air-fuel mixture at a timing near the compression top dead center after fuel injection (reference numeral 6053). The spark plug 25 may perform ignition after compression top dead center. The air-fuel mixture undergoes SI combustion in the expansion stroke. Since SI combustion starts in the expansion stroke, CI combustion does not start.

  In order to avoid premature ignition, the injector 6 may retard the fuel injection timing as the rotational speed of the engine 1 decreases. The fuel injection within the retard period may end in the expansion stroke.

  When the engine 1 operates in the high-load low-rotation region (3), the time from the start of fuel injection to ignition within the retard period is short. In order to improve the ignitability of the air-fuel mixture and stabilize the SI combustion, it is necessary to quickly transport the fuel to the vicinity of the spark plug 25.

  When the injector 6 injects fuel during the period from the end of the compression stroke to the initial stage of the expansion stroke, the piston 3 is located near the compression top dead center, so that the fuel spray is mixed with fresh air and the convexity of the cavity 31 is increased. The gas flows downward along the part 311 and flows radially outward from the center of the combustion chamber 17 along the bottom surface and the peripheral side surface of the cavity 31. Thereafter, the air-fuel mixture reaches the opening of the cavity 31 and flows from the radially outer side toward the center of the combustion chamber 17 along the inclined surface 1311 on the intake side and the inclined surface 1312 on the exhaust side.

  Further, when the engine 1 is operated in the high load low rotation region (3), the swirl flow is weaker than that in the high load medium rotation region (2). When operating in the high load low rotation range (3), the opening of the swirl control valve 56 is larger than when operating in the high load mid rotation range (2). The opening degree of the swirl control valve 56 may be about 50% (that is, half open), for example.

  As illustrated by the two-dot chain line in the upper diagram of FIG. 2, the axis of the injection hole of the injector 6 is displaced in the circumferential direction with respect to the spark plug 25. The fuel injected from the nozzle hole flows in the circumferential direction by the swirl flow in the combustion chamber 17. By the swirl flow, the fuel can be quickly transported to the vicinity of the spark plug 25. The fuel can be vaporized while being transported in the vicinity of the spark plug 25.

  On the other hand, if the swirl flow is too strong, the fuel is flowed in the circumferential direction and is away from the vicinity of the spark plug 25. Therefore, when the engine 1 is operated in the high load low rotation region (3), the swirl flow is weaker than that in the high load medium rotation region (2). As a result, the fuel can be quickly transported to the vicinity of the spark plug 25, so that the ignitability of the air-fuel mixture can be improved and the SI combustion can be stabilized.

  In the high-load low-rotation region (3), the engine 1 performs SI combustion by injecting fuel during the retard period from the end of the compression stroke to the early stage of the expansion stroke. It can be called a “retard-SI region”.

(High rotation area (4))
When the rotational speed of the engine 1 is high, the time required for the crank angle to change by 1 ° is shortened. Therefore, for example, in the high rotation region in the high load region, it becomes difficult to stratify the air-fuel mixture in the combustion chamber 17 as described above. When the rotational speed of the engine 1 becomes high, it becomes difficult to perform the aforementioned SPCCI combustion.

  Therefore, when the engine 1 is operating in the high speed region (4), the engine 1 performs SI combustion instead of SPCCI combustion. The high rotation region (4) extends over the entire load direction from a low load to a high load.

  Reference numeral 606 in FIG. 6 indicates a fuel injection timing (reference numeral 6061) and an ignition timing (reference numeral 6062) and a combustion waveform when the engine 1 is operating in a high-load operating state 606 in the high-rotation region (4). (Reference numeral 6063).

  The EGR system 55 introduces EGR gas into the combustion chamber 17 when the operating state of the engine 1 is in the high rotation region (4). The engine 1 reduces the amount of EGR gas as the load increases. At full load, EGR gas may be zero.

  When the engine 1 is operated in the high speed region (4), the swirl control valve 56 is fully opened. A swirl flow is not generated in the combustion chamber 17 and only a tumble flow is generated. By fully opening the swirl control valve 56, the charging efficiency can be increased in the high rotation region (4), and the pump loss can be reduced.

  When the engine 1 operates in the high speed region (4), the air-fuel ratio (A / F) of the air-fuel mixture is basically the stoichiometric air-fuel ratio (A / F≈14.7) in the entire combustion chamber 17. It is. The excess air ratio λ of the air-fuel mixture may be 1.0 ± 0.2. Note that the excess air ratio λ of the air-fuel mixture may be less than 1 in the vicinity of the fully open load in the high rotation region (4).

  When the engine 1 operates in the high speed region (4), the injector 6 starts fuel injection during the intake stroke. The injector 6 injects fuel in a lump (reference numeral 6061). By starting fuel injection during the intake stroke, a homogeneous or substantially homogeneous mixture can be formed in the combustion chamber 17. Further, when the engine 1 has a high rotational speed, the fuel vaporization time can be ensured as long as possible, so that unburned loss can be reduced.

  The spark plug 25 ignites the air-fuel mixture at an appropriate timing before the compression top dead center after the fuel injection is completed (reference numeral 6062).

  Therefore, in the high speed region (4), the engine 1 starts fuel injection in the intake stroke and performs SI combustion, so the high speed region (4) can be referred to as an “intake-SI region”.

(Supercharger control and EGR system control)
As shown in FIG. 5, the supercharger 44 is not driven in a predetermined operation region (that is, S / C OFF region) of low load and low rotation, and is in an operation region other than the S / C OFF region (that is, S / CON area). The ECU 10 outputs a control signal to turn on the electromagnetic clutch 45 when the engine 1 is operating in the S / C ON region. Thereby, the pressure on the intake side of the engine 1 becomes higher than the pressure on the exhaust side. When the supercharger 44 performs supercharging, if the intake electric S-VT 23 and the exhaust electric S-VT 24 provide a positive overlap period in which both the intake valve 21 and the exhaust valve 22 are opened, the intake air Since the air is blown from the intake side to the exhaust side, the residual gas in the combustion chamber 17 is scavenged. In this case, the internal EGR gas cannot be introduced into the combustion chamber 17. If EGR gas is to be introduced into the combustion chamber 17, the external EGR system 551 is used.

  When the engine 1 is operating in the S / C OFF region, the ECU 10 outputs a control signal so that the electromagnetic clutch 45 is turned off. As a result, the pressure on the intake side of the engine 1 is lower than that during supercharging. If the intake electric S-VT 23 and the exhaust electric S-VT 24 provide a positive overlap period in which both the intake valve 21 and the exhaust valve 22 are opened when the supercharger 44 is not supercharging, the exhaust stroke The burned gas discharged into the intake port 18 or the exhaust port 19 can be blown back into the combustion chamber 17 in the intake stroke. That is, the internal EGR gas can be introduced into the combustion chamber 17.

  The engine 1 appropriately introduces EGR gas into the combustion chamber 17 by combining on / off of the supercharger 44 and switching between the external EGR system 551 and the internal EGR system 552.

  FIG. 9 is a flowchart showing control related to on / off of the supercharger 44 and switching between the external EGR system 551 and the internal EGR system 552. In accordance with the flowchart of FIG. 9, the ECU 10 turns on / off the supercharger 44 and switches between the external EGR system 551 and the internal EGR system 552. FIG. 10 shows a change in the EGR rate with respect to a change in the load of the engine 1 when the turbocharger 44 is turned on / off and the external EGR system 551 and the internal EGR system 552 are switched according to the flow of FIG. (Reference numeral 1001), ON / OFF change of the supercharger 44 (reference numeral 1002), positive overlap period (ie, overlap amount) of the intake valve 21 and the exhaust valve 22 (reference numeral 1003), and EGR valve The change of the opening degree of 54 (code | symbol 1004) is illustrated. FIG. 10 corresponds to the case where the load of the engine 1 changes between the operating states 601, 602, and 603 in FIG.

  First, in step S1 after the start, the ECU 10 reads signals from the sensors SW1 to SW16. The ECU 10 determines the operating region of the engine 1 in the subsequent step S2.

  In step S3, the ECU 10 adjusts the overlap amount between the intake valve 21 and the exhaust valve 22 through the intake electric S-VT 23 and the exhaust electric S-VT 24. In the vicinity of the exhaust top dead center, a positive overlap period is provided in which both the intake valve 21 and the exhaust valve 22 are opened. As shown in a graph 1003 in FIG. 10, the overlap amount is constant or substantially constant regardless of the load level of the engine 1.

  In step S4, the ECU 10 determines whether or not the operating state of the engine 1 is in a region where the supercharger 44 is turned on. When the determination in step S3 is YES, the process proceeds to step S7, and when the determination is NO, the process proceeds to step S5.

  In step S8, the ECU 10 turns on the electromagnetic clutch 45 of the supercharger 44. In FIG. 10, the area on the right side of the load L1 is a region for supercharging. The ECU 10 also adjusts the opening degree of the air bypass valve (ABV) 48 so as to obtain a desired supercharging pressure. The supercharger 44 supercharges intake air. The process then proceeds to step S9.

  In step S9, the ECU 10 adjusts the opening degree of the EGR valve 54. As a result, the external EGR gas is introduced into the combustion chamber 17 by the external EGR system 551. That is, external EGR gas is introduced into the combustion chamber 17 when the supercharger 44 is supercharging intake air.

  Since the supercharger 44 supercharges intake air, the pressure in the intake passage 40 increases. It becomes difficult to introduce the internal EGR gas into the combustion chamber 17. By introducing the external EGR gas into the combustion chamber 17 by the external EGR system 551, the EGR gas can be appropriately introduced into the combustion chamber 17. As shown on the right side of the graph 1004 in FIG. 10, the opening degree of the EGR valve 54 is adjusted according to the load of the engine 1. Specifically, in the control example of FIG. 10, when the load on the engine 1 increases, the opening degree of the EGR valve 54 decreases, and when the load on the engine 1 decreases, the opening degree of the EGR valve 54 increases. Thereby, as shown in a graph 1001, the EGR rate due to the external EGR gas decreases as the load on the engine 1 increases, and increases as the load on the engine 1 decreases. Note that the relationship between the load of the engine 1 and the opening of the EGR valve 54 is not always continuous as shown in FIG.

  The external EGR gas passes through the EGR passage 52 and the EGR cooler 53 is disposed in the EGR passage 52, so that the temperature is lower than that of the internal EGR gas. As shown in FIG. 5, the region where the supercharger 44 is turned on is a region where the load or the rotation is higher than the region where the supercharger 44 is turned off, and the temperature in the combustion chamber 17 is high. Therefore, by introducing the low-temperature external EGR gas into the combustion chamber 17, the temperature in the combustion chamber 17 can be adjusted appropriately. As a result, it is possible to stabilize SPCCI combustion.

  Further, as described above, it is difficult to introduce the internal EGR gas when the supercharger 44 is on, but the overlap period of the intake valve 21 and the exhaust valve 22 is provided. Thereby, scavenging of the residual gas in the combustion chamber 17 is performed. This also contributes to appropriately adjusting the temperature in the combustion chamber 17.

  Further, when the load on the engine 1 is high or the rotational speed is high, the amount of new air introduced into the combustion chamber 17 can be increased by scavenging the residual gas. This is advantageous for improving fuel efficiency.

  Further, since the intake electric S-VT 23 and the exhaust electric S-VT 24 do not move even when the load of the engine 1 changes, the control robustness against the change of the load of the engine 1 is enhanced (see graph 1003 in FIG. 10).

  Returning to the flowchart of FIG. 9, the ECU 10 turns off the electromagnetic clutch 45 of the supercharger 44 in step S5 (see graph 1002 of FIG. 10). Further, the ECU 10 opens the air bypass valve 48. Thus, the intake air is introduced into the combustion chamber 17 through the bypass passage 47 without passing through the supercharger 44 and the intercooler 46. When the supercharger 44 is not supercharging the intake air, the pressure in the intake passage 40 is lower than that during supercharging, and therefore, when the intake valve 21 is opened during the exhaust stroke, A part of the burned gas is discharged to the intake port 18. In the intake stroke, the burned gas discharged to the intake port 18 is blown back into the combustion chamber 17 as internal EGR gas. When the supercharger 44 is not supercharging intake air, the internal EGR system 552 can appropriately introduce the internal EGR gas into the combustion chamber 17. Since the overlap amount of the intake valve 21 and the exhaust valve 22 is constant (see graph 1003), the EGR rate by the internal EGR gas is constant or substantially constant regardless of the load level of the engine 1 (see graph 1001). ).

  The internal EGR gas has a higher temperature than the external EGR gas. As shown in FIG. 5, the region where the supercharger 44 does not supercharge intake air is a region where the load of the engine 1 is low and the rotational speed is low, and the temperature in the combustion chamber 17 becomes low. By introducing the high-temperature internal EGR gas into the combustion chamber 17, the temperature in the combustion chamber 17 can be adjusted to a temperature suitable for SPCCI combustion.

  In step S6 after step S5, the ECU 10 determines whether or not the operating state of the engine 1 is in front of the supercharging region. That is, when the operating state of the engine 1 is near the boundary between the S / C OFF region and the S / C ON region in the S / C OFF region, the determination in step S5 is YES, and otherwise The determination in step S5 is NO. If the determination in step S6 is no, the process proceeds to step S7. If the determination in step S6 is yes, the process proceeds to step S9.

  In step S7, the ECU 10 closes the EGR valve 58. In this case, only the internal EGR gas is introduced into the combustion chamber 17 (see graphs 1001 and 1004 in FIG. 10).

  On the other hand, the ECU 10 adjusts the opening degree of the EGR valve 58 in step S9. That is, the external EGR gas is also introduced into the combustion chamber 17 by opening the EGR valve 58 in the S / C OFF region where the internal EGR system 552 introduces the internal EGR gas into the combustion chamber 17. This is to cope with the response delay of the external EGR system 551. When the operating state of the engine 1 enters the S / CON region and the external EGR gas is introduced into the combustion chamber 17, the EGR valve 58 is opened in advance so that the external EGR is introduced into the combustion chamber 17. Gas can be introduced quickly.

  In FIG. 10, the load L <b> 1 corresponds to a load that switches the supercharger 44 on and off. As indicated by a solid line in the graph 1004, the EGR valve 54 changes from a valve closing state to a valve opening state at a load L2 lower than the load L1. The EGR valve 54 remains open when the load of the engine 1 is higher than the load L2. In the region of the load L2 or more in the S / C OFF region, both the internal EGR gas and the external EGR gas are introduced into the combustion chamber 17.

  Note that, as indicated by the alternate long and short dash line in the graph 1004, the opening degree of the EGR valve 54 may gradually increase as the load of the engine 1 increases from the load L2 to the load L1.

  As described above, in the engine 1, the internal EGR gas is changed into the combustion chamber 17 by switching between driving and non-driving of the supercharger 44 without changing the positive overlap amount of the intake valve 21 and the exhaust valve 22. And scavenging the residual gas in the combustion chamber 17 can be switched.

10 shows a change in EGR rate (reference numeral 1001), a change in ON / OFF of the supercharger 44 (reference numeral 1002), and a positive overlap period of the intake valve 21 and the exhaust valve 22 with respect to a change in the load of the engine 1. (In other words, a change in the overlap amount (reference numeral 1003) and a change in the opening degree of the EGR valve 54 (reference numeral 1004) are illustrated. However, the change in the EGR rate with respect to the change in the engine 1 speed, The change of ON / OFF of the feeder 44, the change of the positive overlap period of the intake valve 21 and the exhaust valve 22, and the change of the opening degree of the EGR valve 54 are also the same as in FIG.
(Other embodiments)
The technique disclosed here is not limited to being applied to the engine 1 having the above-described configuration. As the configuration of the engine 1, various configurations can be adopted.

  The engine 1 may include a turbocharger instead of the mechanical supercharger 44.

  Further, the internal EGR system 552 provides a negative overlap period for closing both the intake valve 21 and the exhaust valve 22 instead of providing a positive overlap period for opening both the intake valve 21 and the exhaust valve 22. Thus, the internal EGR gas may be introduced into the combustion chamber 17 (or the internal EGR gas is confined in the combustion chamber 17).

  Furthermore, the technology disclosed herein can be widely applied not only to engines that perform SPCCI combustion but also to engines that perform self-ignition combustion.

1 Engine 10 ECU (control unit)
17 Combustion chamber 23 Intake motorized S-VT (variable valve mechanism)
24 Exhaust Electric S-VT (Variable Valve Mechanism)
40 Intake passage 44 Supercharger 45 Electromagnetic clutch (switching part)
46 Intercooler 47 Bypass passage 48 Air bypass valve (flow adjustment valve)
551 External EGR system 552 Internal EGR system

Claims (7)

An engine in which the air-fuel mixture in the combustion chamber burns by self-ignition,
An intake passage connected to the combustion chamber;
A supercharger disposed in the intake passage;
A bypass passage connecting the upstream and downstream of the supercharger in the intake passage;
A flow control valve disposed in the bypass passage;
A variable valve mechanism that introduces internal EGR gas into the combustion chamber by varying the opening and closing operations of the intake valve and the exhaust valve so that the burned gas in the combustion chamber is blown back into the combustion chamber;
An external EGR system that introduces external EGR gas into the combustion chamber by returning a part of the exhaust gas to the intake passage through an EGR passage connecting the intake passage and the exhaust passage of the engine;
A controller that is connected to the flow control valve, the variable valve mechanism, and the external EGR system, and that outputs a control signal to the flow control valve, the variable valve mechanism, and the external EGR system;
The controller is configured to introduce at least internal EGR gas into the combustion chamber when the engine is operated in a state where supercharging of the intake air by the supercharger is stopped by increasing the opening of the flow control valve. When the engine is operated in a state where supercharging is performed by the supercharger by outputting a control signal to the variable valve mechanism and reducing an opening of the flow control valve, A compression self-ignition engine with a supercharger that outputs a control signal to the external EGR system so as to introduce at least an external EGR gas into the combustion chamber. The compression self-ignition engine with a supercharger according to claim 1,
The control unit increases the opening of the flow rate control valve when the engine load is lower than a predetermined switching load and the engine speed is lower than a predetermined switching speed, The supercharging of the intake air by the supercharger is stopped, and the opening degree of the flow control valve is decreased when the engine load is equal to or higher than the switching load or the engine speed is equal to or higher than the switching speed. Thus, a compression self-ignition engine with a supercharger that supercharges intake air by the supercharger. The compression self-ignition engine with a supercharger according to claim 2,
The control unit is a compression self-ignition engine with a supercharger that introduces both the internal EGR gas and the external EGR gas into the combustion chamber in an operation region including the switching load or the switching rotational speed. In the compression self-ignition engine with a supercharger according to any one of claims 1 to 3,
A switching unit that switches between driving and non-driving of the supercharger,
When the control unit stops supercharging of intake air by the supercharger, the control unit outputs a control signal for non-driving the supercharger to the switching unit, and increases the opening of the flow control valve, When supercharging the intake air by the supercharger, a compression self-ignition engine with a supercharger that outputs a control signal for driving the supercharger to the switching unit and reduces the opening of the flow control valve . The compression self-ignition engine with a supercharger according to claim 4,
The variable valve mechanism introduces an internal EGR gas into the combustion chamber by providing an overlap period in which both the intake valve and the exhaust valve are open,
The variable valve mechanism is an overlap period in which both the intake valve and the exhaust valve are open even when the engine is operated in a state in which intake air is supercharged by the supercharger. A compression self-ignition engine with a supercharger for scavenging residual gas in the combustion chamber. The compression self-ignition engine with a supercharger according to any one of claims 1 to 5,
The engine is a compression self-ignition engine with a supercharger having a geometric compression ratio of 13 to 30. In the compression self-ignition type engine with a supercharger according to any one of claims 1 to 6,
The fuel supplied to the combustion chamber is a compression self-ignition engine with a supercharger including at least gasoline.

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