JP2019039389A - Compression self-ignition engine with supercharger - Google Patents

Abstract

To provide a compression self-ignition engine with a supercharger for actualizing appropriate temperature control in a combustion chamber.SOLUTION: The compression self-ignition engine with a supercharger includes a supercharger 44, a selection unit (an electromagnetic clutch 45) for selecting the supercharger to be driven or not to be driven, an intercooler 46, a bypass passage 47 connecting the upstream of the supercharger and the downstream of the intercooler, a flow control valve (an air bypass valve 48) arranged in the bypass passage, a variable valve train (an intake air electrically-driven S-VT) for changing the opening/closing operation of an intake valve 21, a control valve (an ECU 10), and a temperature estimation unit for estimating a compression end temperature. When the supercharger is not driven, the control unit opens the flow control valve to cause air-fuel mixture in the combustion chamber of the engine to be combusted by compression self-ignition. If the compression end temperature exceeds a permissible temperature when the supercharger is not driven, the control unit changes a closing timing for the intake valve through the variable valve train to reduce the effective compression ratio of the engine.SELECTED DRAWING: Figure 1

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 compression ignition, the temperature in the combustion chamber must be adjusted to an appropriate range. For example, when the outside air temperature is high, the compression end temperature, which is the temperature in the combustion chamber when the compression top dead center is reached, becomes too high, the combustion due to compression ignition becomes steep, and the combustion noise exceeds the allowable value.

  The technology disclosed herein adjusts the combustion chamber to an appropriate temperature in a compression self-ignition engine with a supercharger.

  Specifically, a compression self-ignition engine with a supercharger disclosed herein includes an intake passage connected to a combustion chamber of the engine, a supercharger disposed in the intake passage, and driving of the supercharger A switching section that switches between non-drive, an intercooler disposed downstream of the supercharger in the intake passage, and a bypass passage that connects the upstream of the supercharger and the downstream of the intercooler in the intake passage A flow control valve disposed in the bypass passage, a variable valve mechanism configured to change an opening / closing operation of an intake valve interposed between a downstream end of the intake passage and the combustion chamber, The switching unit, the control unit connected to the flow control valve and the variable valve mechanism, and outputs a control signal to the switching unit, the flow control valve and the variable valve mechanism, and the piston reaches a compression top dead center. Said burning Comprising a temperature estimation unit that estimates a compression end temperature which is the temperature of the chamber, the.

  The control unit opens the flow rate control valve when the supercharger is not driven through the switching unit to operate the engine, and the engine burns the air-fuel mixture in the combustion chamber by compression self-ignition. To do.

  The control unit may also be configured such that the compression end temperature is a preset allowable temperature based on the compression end temperature estimated by the temperature estimation unit when the engine is operating with the supercharger being non-driven. Is exceeded, the closing timing of the intake valve is changed through the variable valve mechanism so that the effective compression ratio of the engine is lower than when the compression end temperature is equal to or lower than the allowable temperature.

  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.

  When the engine operates with the supercharger not driven, the flow control valve in the bypass passage is opened. The supercharger may be a mechanical supercharger driven by an engine. Further, it may be an electric supercharger that is driven by electric energy. When the supercharger is not driven, the intake air does not pass through the supercharger and the intercooler and enters the combustion chamber through the bypass passage. On the other hand, when the engine is operated with the supercharger being driven, the intake air enters the combustion chamber after being boosted by the supercharger and cooled by the intercooler. When the supercharger is driven, the supercharging pressure of the engine may be adjusted by appropriately adjusting the opening of the flow control valve.

  When the engine operates with the supercharger not driven, the air-fuel mixture in the combustion chamber burns by compression self-ignition. The combustion chamber must be adjusted to an appropriate temperature. When the compression end temperature exceeds a preset allowable temperature, the closing timing of the intake valve is changed through the variable valve mechanism so that the effective compression ratio of the engine is lower than when the compression end temperature is equal to or lower than the allowable temperature. For example, if the closing timing of the intake valve is delayed after bottom dead center, the effective compression ratio of the engine decreases. Note that changing the closing timing of the intake valve is not limited to changing the phase of the valve timing of the intake valve. For example, by changing the intake valve lift amount or changing the intake valve opening angle (that is, the length of the period during which the intake valve is open), the intake valve closing timing is changed. Also good.

  By reducing the effective compression ratio of the engine, the temperature rise associated with the compression of the gas in the combustion chamber during the compression stroke is reduced, so the compression end temperature is lowered accordingly. It is possible to keep the compression end temperature below the allowable temperature. Note that the temperature estimation unit may estimate the compression end temperature based on the detection values of various sensors.

  Here, when the compression end temperature becomes high, it is conceivable to reduce the temperature of the intake air supplied to the combustion chamber using, for example, an intercooler. However, if the turbocharger is driven so that the intake air passes through the intercooler, the fuel efficiency performance of the engine decreases.

  On the other hand, the above-described configuration for reducing the effective compression ratio of the engine by changing the closing timing of the intake valve can reduce the compression end temperature to the allowable temperature or less without reducing the fuel efficiency of the engine. As a result, when the engine is operating without the supercharger being driven, the air-fuel mixture in the combustion chamber can be appropriately combusted by compression self-ignition.

  The control unit deactivates the supercharger when the load on the engine is low, and the variable valve mechanism includes a mechanism for changing a phase of the valve timing of the intake valve, and the load on the engine Is low, by providing an overlap period in which both the intake valve and the exhaust valve are open, the EGR gas introduced into the combustion chamber is set to a predetermined ratio or more, and the control unit also When the engine is operating with the machine not driven, when the compression end temperature exceeds the allowable temperature, the overlap period is shorter than when the compression end temperature is equal to or lower than the allowable temperature, and The phase of the valve timing of the intake valve may be retarded through the variable valve mechanism so that the effective compression ratio of the engine is lowered.

  By providing an overlap period and introducing EGR gas in a predetermined ratio or more into the combustion chamber, the temperature in the combustion chamber can be increased. Combustion by compression self-ignition can be stabilized when the engine load is low. If the phase of the valve timing of the intake valve is retarded when the compression end temperature exceeds the allowable temperature, the overlap period becomes shorter than when the compression end temperature is equal to or lower than the allowable temperature. Thereby, since the amount of EGR gas introduced into the combustion chamber is reduced, the temperature in the combustion chamber before the compression is started is lowered. Further, if the closing timing of the intake valve is delayed after the bottom dead center by retarding the phase of the valve timing of the intake valve, the effective compression ratio of the engine is lowered.

  Therefore, the above-described configuration has the two effects of lowering the temperature in the combustion chamber before starting compression and lowering the effective compression ratio of the engine by retarding the phase of the valve timing of the intake valve. can get. As a result, the compression end temperature can be effectively reduced and the compression end temperature can be kept below the allowable temperature, so that the air-fuel mixture in the combustion chamber can be appropriately burned by compression self-ignition.

  When the compression end temperature exceeds the allowable temperature and the outside air temperature exceeds a predetermined temperature, the control unit disables the supercharger through the switching unit, and the compression end temperature is The flow rate control valve is closed more than when the temperature is lower than or equal to the allowable temperature, and the control unit is effective when the compression end temperature exceeds the allowable temperature and the outside air temperature is equal to or lower than the predetermined temperature. The closing timing of the intake valve may be changed through the variable valve mechanism so that the ratio is lower than when the compression end temperature is equal to or lower than the allowable temperature.

  When the outside air temperature exceeds the predetermined temperature and is too high, the compression end temperature may not be suppressed below the allowable temperature depending on the above-described configuration for reducing the effective compression ratio of the engine. Therefore, when the outside air temperature exceeds a predetermined temperature, the temperature of the intake air is lowered using an intercooler. Specifically, the supercharger is not driven and the flow control valve of the bypass passage is closed. As a result, a pressure difference is generated before and after the supercharger, the supercharger is rotated by the pressure difference (that is, pre-rotation), and intake air passes through the supercharger. The intake air that has passed through the supercharger enters the combustion chamber after being cooled by the intercooler. By adjusting the opening of the flow control valve of the bypass passage, the pressure difference before and after the supercharger changes, and the ratio between the intake air amount passing through the supercharger and the intercooler and the intake air amount passing through the bypass passage is change. Since the temperature of the intake air introduced into the combustion chamber can be adjusted, the compression end temperature can be suppressed to an allowable temperature or less even when the outside air temperature is too high. Although this configuration does not drive the supercharger, the pump loss slightly increases.

  On the other hand, when the outside air temperature is equal to or lower than the predetermined temperature, as described above, the compression end temperature is suppressed to the allowable temperature or lower by reducing the effective compression ratio of the engine. This configuration is advantageous in terms of the fuel efficiency of the engine because the turbocharger is not driven and the pump loss does not increase.

  The control unit drives the supercharger through the switching unit when the compression end temperature exceeds the allowable temperature and the outside air temperature exceeds a second predetermined temperature higher than the predetermined temperature. The flow control valve may be opened.

  This configuration is a configuration that enables the intake air to be effectively cooled using an intercooler when the outside air temperature is higher. That is, when the supercharger is driven and the flow rate control valve is opened, a part of the intake air whose temperature is lowered by passing through the supercharger and the intercooler enters the combustion chamber, and the rest passes through the bypass passage. Returned upstream of the turbocharger. The intake air that has returned upstream of the supercharger once again passes through the supercharger and the intercooler together with new intake air. A part of the intake air whose temperature is lowered by passing through the supercharger and the intercooler enters the combustion chamber, and the rest is returned again to the upstream of the supercharger through the bypass passage. In this way, a part of the intake air can be circulated in the circulation passage constituted by the intake passage provided with the intercooler and the bypass passage, so that even when the outside air temperature is high, the intercooler is sufficiently cooled. In addition, it can be introduced into the combustion chamber. As a result, it is possible to keep the compression end temperature below the allowable temperature.

  When the compression end temperature exceeds the allowable temperature and the driver is not performing an acceleration request operation, the control unit deactivates the supercharger through the switching unit, and the compression end temperature When the temperature is equal to or lower than the allowable temperature, the flow rate control valve is closed, and the control unit is when the compression end temperature exceeds the allowable temperature and the driver is performing an acceleration request operation. The closing timing of the intake valve may be changed through the variable valve mechanism so that the effective compression ratio of the engine is lower than when the compression end temperature is equal to or lower than the allowable temperature.

  Of the two configurations for reducing the compression end temperature, the configuration in which the supercharger is not driven and the flow control valve is closed can increase the intake resistance. Therefore, when the driver is performing an acceleration request operation, the acceleration response may be reduced. Therefore, when the compression end temperature exceeds the allowable temperature and the driver is performing an acceleration request operation, the closing timing of the intake valve is changed so as to lower the effective compression ratio of the engine. Since the intake resistance does not increase, it is possible to avoid a decrease in acceleration response when the driver is performing an acceleration request operation.

  On the other hand, when the compression end temperature exceeds the allowable temperature and the driver is not performing the acceleration requesting operation, the supercharger is not driven and the flow rate control valve is closed. This makes it possible to effectively reduce the temperature of the intake air introduced into the combustion chamber using the intercooler.

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

  A relatively high geometric compression ratio of the engine is advantageous for stabilizing combustion by compression self-ignition, but may also cause premature ignition. In an engine having a geometric compression ratio of 13 or more and 30 or less, as described above, by adjusting the compression end temperature, combustion by compression self-ignition can be stabilized while avoiding premature 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, the combustion chamber can be adjusted to an appropriate temperature.

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. 4 is a diagram illustrating the configuration of the main circuit of the engine cooling device, and the right diagram of FIG. 4 is a diagram illustrating the configuration of the sub circuit of the engine cooling device. FIG. 5 is a block diagram illustrating the configuration of the engine control device. FIG. 6 is a diagram illustrating an engine operating region map. FIG. 7 is a diagram illustrating fuel injection timing and ignition timing, and combustion waveforms in each operation region. FIG. 8 is a diagram illustrating a rig testing apparatus for swirl ratio measurement. FIG. 9 is a diagram illustrating the relationship between the opening ratio of the secondary passage and the swirl ratio. FIG. 10 is a diagram illustrating a gas flow in the intake passage when the supercharger is driven and when the circulation control of the supercharger is performed. FIG. 11 is a diagram corresponding to FIG. 10 illustrating the gas flow in the intake passage when the supercharger is not driven. FIG. 12 is a diagram corresponding to FIG. 10 illustrating the gas flow in the intake passage when the supercharger pre-rotation control is performed. FIG. 13 is a diagram illustrating the relationship between the flow rate of the intake air passing through the intercooler and the gas temperature in the surge tank when performing pre-rotation control of the supercharger. FIG. 14 is a diagram illustrating a change in the in-cylinder pressure and a change in the in-cylinder temperature when the closing timing of the intake valve is retarded. FIG. 15 is a flowchart illustrating an engine control process related to adjustment of the compression end temperature. FIG. 16 is a part of a flowchart illustrating a modified example of the engine control process.

  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 diagram illustrating the configuration of the engine cooling device. FIG. 5 is a block diagram illustrating the configuration of the engine control device.

  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. 5, 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. 5, 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. Note that the internal EGR system 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 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 55 includes an external EGR system configured to include an EGR passage 52 and an EGR valve 54, and an internal configuration configured to include the above-described intake electric S-VT 23 and exhaust electric S-VT 24. And an EGR system. The EGR valve 54 also constitutes one of the state quantity setting devices. In the external EGR system, the EGR passage 52 is connected downstream of the GPF 512 and has the EGR cooler 53, so that burned gas having a temperature lower than that of the internal EGR system can be supplied to the combustion chamber 17. it can.

  As shown in FIG. 4, the cooling device 71 of the engine 1 includes a main circuit 71A and a sub circuit 71B. The main circuit 71A and the sub circuit 71B are independent of each other. That is, the refrigerant does not go back and forth between the main circuit 71A and the sub circuit 71B.

  The main circuit 71A has a main radiator 72 that cools the refrigerant using traveling wind, and a variable capacity type that supplies the refrigerant cooled by the main radiator 72 to the engine main body 100 that includes the cylinder head 13 and the cylinder block 12. The water pump 74 is provided. The water pump 74 is driven by the engine 1. The refrigerant supplied to the engine main body 100 cools each part of the engine main body 100, is then discharged from the engine main body 100, and returns to the main radiator 72.

  Similarly to the main radiator 72, the sub circuit 71B includes a sub radiator 75 that cools the refrigerant using traveling air, and an electric water pump 76 that supplies the refrigerant cooled by the sub radiator 75 to the intercooler 46. ing. The refrigerant supplied to the intercooler 46 cools the gas passing through the intercooler 46, is then discharged from the intercooler 46, and returns to the sub radiator 75.

  The refrigerant flowing through the main circuit 71A passes through the inside of the engine body 100. The refrigerant flowing through the sub circuit 71B does not pass through the engine body 100. Therefore, the refrigerant flowing through the main circuit 71A has a higher temperature than the refrigerant flowing through the sub circuit 71B. Although not shown, the EGR cooler 53 is connected to the main circuit 71A.

  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. 5, a central processing unit (CPU) 101 for executing a program, and a RAM (Random Access Memory) or ROM, for example. 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 5, 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 1 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 1 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. 6 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. 6, 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. 6 indicates a road-load line of the engine 1. In FIG. 6, for easy understanding, the operation region maps 501 and 502 of the engine 1 are divided into 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. 7 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. .

(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. 7 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. 7, 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-like rotor 37 is measured by an impulse meter 38 by a swirl (see an arrow in FIG. 8) generated in the cylinder 36 in response to the intake air supply, and based on this, the intake air flow lateral angular velocity can be obtained. .

  FIG. 9 shows the relationship between the opening degree of the swirl control valve 56 and the swirl ratio in the engine 1. FIG. 9 represents 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. 9, the swirl ratio of the engine 1 is 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. 7 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. 6, 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. 7 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 mid-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. 7 denotes 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. 7 denotes 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)
As shown in FIG. 6, the supercharger 44 is not driven in a predetermined operation region (that is, the S / C OFF region) of low load and low rotation, and the operation region other than the S / C OFF region (ie, 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. As indicated by solid arrows in FIG. 10, the intake air passes through the supercharger 44 and the intercooler 46 and then flows into the surge tank 42. The ECU 10 also outputs a control signal so that the opening degree of the air bypass valve 48 in the bypass passage 47 is adjusted when the engine 1 is operating in the S / CON region. When the air bypass valve 48 is opened, a part of the gas flows backward from the surge tank 42 through the bypass passage 47 and upstream of the supercharger 44 as indicated by the broken arrow in FIG. Thereby, the supercharging pressure of intake air is adjusted.

  The ECU 10 outputs a control signal so as to turn off the electromagnetic clutch 45 when the engine 1 is operating in the S / C OFF region. The ECU 10 also outputs a control signal so that the air bypass valve 48 is fully opened. As indicated by solid arrows in FIG. 11, the intake air flows into the surge tank 42 through the bypass passage 47 without passing through the supercharger 44 and the intercooler 46.

(Adjusting the temperature in the combustion chamber)
In the operation region map 501 shown in FIG. 6, in each region where SPCCI combustion is performed, it is necessary to adjust the inside of the combustion chamber 17 to an appropriate temperature range in order to stably perform SPCCI combustion. For example, when the outside air temperature is high, the temperature of the intake air introduced into the combustion chamber 17 becomes high, so the temperature in the combustion chamber 17 becomes too high, and the timing of self-ignition may be accelerated. Also, when the temperature of the engine 1 becomes too high, the temperature in the combustion chamber 17 becomes too high, and the self-ignition timing may be accelerated.

  When the engine 1 is operated with the supercharger 44 turned on in the region where the SPCCI combustion is performed, the intake air that has passed through the intercooler 46 downstream of the supercharger 44 is introduced into the combustion chamber 17 as shown in FIG. Therefore, even when the outside air temperature is high or the temperature of the engine 1 is high, the temperature in the combustion chamber 17 can be avoided from becoming too high.

  On the other hand, when the engine 1 is operated with the supercharger 44 turned off, the intake air cannot be cooled using the intercooler 46 because the intake air does not pass through the intercooler 46 as shown in FIG.

  Therefore, when operating the engine 1 with the supercharger 44 turned off, the engine 1 changes the effective compression ratio of the engine 1 by changing the closing timing of the intake valve 21, thereby changing the inside of the combustion chamber 17. Adjust the temperature. Since this control is performed in the S / C OFF region, it is performed in a part of the low load region (1) -1 and a part of the medium load region (1) -2.

  Here, the change of the valve timing of the intake valve 21 will be described with reference to FIG. As indicated by a valve lift curve indicated by reference numeral 1401, in the low load region (1) -1 and the medium load region (1) -2, a positive overlap period of the intake valve 21 and the exhaust valve 22 is provided (exhaust valve 22 (see the solid line showing the valve lift of 22 and the broken line showing the valve lift of the intake valve 21). The closing timing of the intake valve 21 is later than the intake bottom dead center and is in the compression stroke.

  In this state, if the valve timing of the intake valve 21 is retarded as shown by the white arrow in FIG. 14, the valve lift of the intake valve 21 changes as shown by the thick solid line. The overlap period 22 is shortened (see the hatched portion in the figure), and the closing timing of the intake valve 21 is further delayed during the compression stroke. The intake valve 21 is so-called delayed closing.

  Since the intake valve 21 is closed late, the timing at which the compression of the combustion chamber 17 starts is delayed, so the effective compression ratio of the engine 1 decreases. As shown in the graph of reference numeral 1402 in FIG. 14, the pressure in the combustion chamber 17 when the piston 3 reaches the compression top dead center decreases when the intake valve 21 is closed late (see the white arrow). .

  Further, since the positive overlap period of the intake valve 21 and the exhaust valve 22 is shortened, the amount of EGR gas reintroduced into the combustion chamber 17 is reduced. Thereby, as shown in the graph of the code | symbol 1403, the temperature at the time of the compression start of the combustion chamber 17 falls.

  When the temperature at the start of compression of the combustion chamber 17 decreases and the effective compression ratio of the engine 1 decreases, as shown in a graph 1403, when the piston 3 reaches compression top dead center. The temperature in the combustion chamber 17 (so-called compression end temperature) decreases and can be within an allowable range.

  Further, when the engine 1 is operated with the supercharger 44 turned off, the outside air temperature is too high, and the temperature in the combustion chamber 17 is changed to an appropriate temperature by changing the effective compression ratio of the engine 1. When the range cannot be adjusted, although the supercharger 44 is not driven, cooling using the intercooler 46 is performed by allowing some of the intake air to pass through the supercharger 44 and the intercooler 46. This control is called pre-rotation control of the supercharger 44 because the supercharger 44 is rotated in the non-drive region of the supercharger 44.

  The pre-rotation control of the supercharger 44 will be described with reference to FIGS. 12 and 13. FIG. 12 shows the flow of intake air during pre-rotation control of the supercharger 44. When performing the pre-rotation control, the ECU 10 outputs a control signal to turn off the electromagnetic clutch 45 and adjusts the opening of the air bypass valve 48 to the closed side. As a result, a pressure difference is generated between the upstream side and the downstream side of the supercharger 44, and the rotor of the supercharger 44 is rotated by the pressure difference. A part of the intake air passes through the supercharger 44 and the intercooler 46 and is introduced into the combustion chamber 17 as indicated by broken lines. A part of the intake air is also introduced into the combustion chamber 17 through the bypass passage 47 as shown by the solid line.

  In the pre-rotation control of the supercharger 44, the amount of intake air that passes through the supercharger 44 and the intercooler 46 and enters the combustion chamber 17 and the bypass passage 47 are adjusted by adjusting the opening degree of the air bypass valve 48. Thus, the ratio of the amount of intake air entering the combustion chamber 17 is changed. Since the amount of intake air cooled by the intercooler 46 changes, the temperature in the combustion chamber 17 changes. FIG. 13 shows the relationship between the flow rate of the intake air passing through the intercooler 46 (horizontal axis) and the temperature in the surge tank 42 (horizontal axis). The flow rate of the intake air passing through the intercooler 46 is related to the opening degree of the air bypass valve (ABV) 48 as described above. When the opening degree of the air bypass valve 48 is large, the flow rate ratio of the intake air passing through the intercooler 46 decreases. When the opening degree of the air bypass valve 48 is small, the flow rate ratio of the intake air passing through the intercooler 46 increases. The temperature in the surge tank 42 corresponds to the temperature of the intake air introduced into the combustion chamber 17. As shown in FIG. 13, the temperature in the surge tank 42 can be lowered by reducing the opening degree of the air bypass valve 48 and increasing the flow rate of the intake air passing through the intercooler 46. Since the temperature of the intake air introduced into the combustion chamber 17 can be within the appropriate range S1, the compression end temperature can be within the allowable range.

  Further, when the engine 1 is operated with the supercharger 44 turned off, the outside air temperature is higher, so that the temperature in the combustion chamber 17 is appropriately adjusted even by the pre-rotation of the supercharger 44 described above. When the temperature cannot be adjusted, the supercharger 44 is turned on, and a part of the intake air is circulated through the supercharger 44, the intercooler 46, and the bypass passage 47, thereby cooling the intercooler 46. Do. This control is called circulation control of the supercharger 44.

  The flow of intake air during the circulation control of the supercharger 44 is substantially the same as the flow of intake air during the supercharging shown in FIG. That is, when performing the circulation control, the ECU 10 outputs a control signal to turn on the electromagnetic clutch 45 and adjusts the opening of the air bypass valve 48 to the open side. Thus, the intake air is cooled by passing through the intercooler 46 after passing through the supercharger 44. A part of the cooled intake air is introduced from the surge tank 42 into the combustion chamber 17, and the remaining intake air that is not introduced into the combustion chamber 17 flows back through the bypass passage 47, together with new intake air. And reintroduced into the supercharger 44. Thus, part of the intake air passes through the intercooler 46 a plurality of times, and when the outside air temperature is extremely high, the temperature of the intake air introduced into the combustion chamber 17 can be efficiently reduced.

(Engine control process)
Next, the operation control of the engine 1 executed by the ECU 10 will be described with reference to the flowchart of FIG. This flowchart relates to temperature adjustment in the combustion chamber 17.

  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 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 S9, and when the determination is NO, the process proceeds to step S4.

  In step S9, the ECU 10 turns on the electromagnetic clutch 45 of the supercharger 44. As a result, the intake air passes through the supercharger 44 and the intercooler 46 and is introduced into the combustion chamber 17. Since the intake air is cooled by passing through the intercooler 46, the temperature in the combustion chamber 17 can be kept within an appropriate temperature range even when the outside air temperature is high or the temperature of the engine 1 is high. .

  In step S4, the ECU 10 turns off the electromagnetic clutch 45 of the supercharger 44. Further, the ECU 10 opens the air bypass valve 48. As a result, 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.

  In step S5, the ECU 10 determines whether or not the compression end temperature of the combustion chamber 17 exceeds a preset allowable range. The ECU 10 predicts the compression end temperature based on various sensor values. The ECU 10 is an example of a temperature estimation unit. If the determination in step S5 is no, the process proceeds to step S10. If the determination in step S5 is yes, the process proceeds to step S6.

  In step S6, the ECU 10 determines whether or not the outside air temperature exceeds a preset second predetermined temperature. The second predetermined temperature is a temperature at which the outside air temperature is extremely high. When the determination in step S6 is YES, the process proceeds to step S12. When the determination is NO, the process proceeds to step S7.

  In step S7, the ECU 10 determines whether or not the outside air temperature exceeds a preset first predetermined temperature. The first predetermined temperature is a temperature lower than the second predetermined temperature. When the determination in step S7 is YES, the process proceeds to step S13, and when the determination is NO, the process proceeds to step S8. That is, in this control process, the outside air temperature is determined in three steps of “very high”, “high”, and “slightly high” in step S6 and step S7. When the outside air temperature is extremely high, the process proceeds to step S12 as described above. When the outside air temperature is high, the process proceeds to step S13. When the outside air temperature is slightly high, the process proceeds to step S8.

  In step S12, the ECU 10 performs the circulation control of the supercharger 44 described above. That is, in the non-supercharging region, the electromagnetic clutch 45 of the supercharger 44 is turned on to drive the supercharger 44 and adjust the opening of the air bypass valve (ABV) 48 to the open side. As a result, as shown in FIG. 10, a part of the intake air is circulated in the supercharger 44, the intercooler 46, and the bypass passage 47, and the temperature of the intake air introduced into the combustion chamber 17 is lowered.

  In step S13, the ECU 10 performs the pre-rotation control of the supercharger 44 described above. That is, the opening degree of the air bypass valve 48 is adjusted to the closed side with the electromagnetic clutch 45 of the supercharger 44 turned off. As a result, as shown in FIG. 12, the supercharger 44 pre-rotates, so that intake air that has passed through the supercharger 44 and the intercooler 46 can be introduced into the combustion chamber 17. The intake air cooled by the intercooler 46 can be introduced into the combustion chamber 17.

  In step S8, the ECU 10 outputs a control signal to the intake electric S-VT 23 so that the valve timing of the intake valve 21 is retarded. By slowly closing the intake valve 21, the compression end temperature of the combustion chamber 17 is lowered by reducing the effective compression ratio of the engine 1 and shortening the overlap period of the intake valve 21 and the exhaust valve 22 (see FIG. 14). .

  In step S10, the ECU 10 determines whether or not the compression end temperature is below the allowable range. If no, the process returns. If yes, the process proceeds to step S11. In step S11, the ECU 10 outputs a control signal to the intake electric S-VT 23 so that the valve timing of the intake valve 21 is advanced. By bringing the closing timing of the intake valve 21 close to top dead center, the effective compression ratio of the engine 1 is increased and the overlap period of the intake valve 21 and the exhaust valve 22 is increased. Contrary to the case where the intake valve 21 is closed late, the compression end temperature of the combustion chamber 17 can be raised, and the compression end temperature can be kept within an allowable range.

(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.

  FIG. 16 shows a part of a flowchart showing a modification of the control process of the engine 1. Steps S14, S15, and S16 in this flowchart relate to switching between pre-rotation control of the supercharger 44 and delayed closing of the intake valve 21, and replace steps S7, S8, and S13 in the flowchart shown in FIG. Can do.

  In the flowchart shown in FIG. 15, when the outside air temperature exceeds the first predetermined temperature, the pre-rotation control of the supercharger 44 is performed in step S13, and when the outside air temperature is equal to or lower than the first predetermined temperature, the intake air is taken in step S8. The valve 21 is closed late. On the other hand, in the flowchart of FIG. 16, the pre-rotation control of the supercharger 44 and the slow closing of the intake valve 21 are switched depending on whether or not the driver has requested acceleration.

  Specifically, the ECU 10 determines in step S14 whether or not there is a driver acceleration request operation. When there is an acceleration request operation, that is, when the driver depresses the accelerator pedal, the process proceeds to step S15, and when there is no acceleration request operation, the process proceeds to step S16.

  When there is an acceleration request operation, the intake air introduced into the combustion chamber 17 must be increased. In the pre-rotation control of the supercharger 44, since the supercharger 44 is rotated by a pressure difference, the intake resistance becomes high. Therefore, if the pre-rotation control of the supercharger 44 is performed at the time of acceleration at which an increase in intake air is required, the increase in intake air will be delayed. The acceleration response may be reduced.

  Therefore, when there is an acceleration request operation, in step S15, control is performed to retard the phase of the intake valve 21, and the temperature in the combustion chamber 17 is lowered. Thereby, the temperature in the combustion chamber 17 can be kept within an allowable range while preventing a decrease in acceleration response.

  When there is no acceleration request operation, it is possible to allow the intake resistance to increase, so in step S16, the pre-rotation control of the supercharger 44 is performed, and the temperature in the combustion chamber 17 is lowered. Thereby, since intake air can be cooled efficiently, the temperature in the combustion chamber 17 can be kept within an allowable range.

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

  In addition to using the intake electric S-VT 23 that changes the phase of the valve timing of the intake valve 21, the technique described above uses a variable valve mechanism that changes the lift amount of the intake valve 21, It can also be realized by using a variable valve mechanism that changes the valve opening angle.

  Further, 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, temperature estimation unit)
17 Combustion chamber 23 Intake motorized 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)

Claims (7)

An intake passage connected to the combustion chamber of the engine;
A supercharger disposed in the intake passage;
A switching unit that switches between driving and non-driving of the supercharger;
An intercooler disposed downstream of the supercharger in the intake passage;
A bypass passage connecting the upstream of the supercharger and the downstream of the intercooler in the intake passage;
A flow control valve disposed in the bypass passage;
A variable valve mechanism configured to change an opening / closing operation of an intake valve interposed between a downstream end of the intake passage and the combustion chamber;
A controller that is connected to the switching unit, the flow control valve, and the variable valve mechanism, and that outputs a control signal to the switching unit, the flow control valve, and the variable valve mechanism;
A temperature estimation unit that estimates a compression end temperature that is a temperature in the combustion chamber when the piston reaches compression top dead center;
The control unit opens the flow rate control valve when the supercharger is not driven through the switching unit to operate the engine, and the engine burns the air-fuel mixture in the combustion chamber by compression self-ignition. And
The control unit may also be configured such that the compression end temperature is a preset allowable temperature based on the compression end temperature estimated by the temperature estimation unit when the engine is operating with the supercharger being non-driven. When the pressure exceeds the compression compression ignition with a supercharger that changes the closing timing of the intake valve through the variable valve mechanism so that the effective compression ratio of the engine is lower than when the compression end temperature is lower than or equal to the allowable temperature. Expression engine. The compression self-ignition engine with a supercharger according to claim 1,
The control unit deactivates the supercharger when the engine load is low,
The variable valve mechanism includes a mechanism for changing the phase of the valve timing of the intake valve, and when the load on the engine is low, an overlap period during which both the intake valve and the exhaust valve are open is provided. By providing, the EGR gas introduced into the combustion chamber is set to a predetermined ratio or more,
The control unit may also be configured such that when the compression end temperature exceeds the allowable temperature when the engine is operating with the supercharger being non-driven, the compression end temperature is lower than or equal to the allowable temperature. A supercharged compression self-ignition engine that retards the phase of the valve timing of the intake valve through the variable valve mechanism so that the overlap period is shortened and the effective compression ratio of the engine is lowered. The compression self-ignition engine with a supercharger according to claim 1 or 2,
When the compression end temperature exceeds the allowable temperature and the outside air temperature exceeds a predetermined temperature, the control unit disables the supercharger through the switching unit, and the compression end temperature is Close the flow rate control valve than when it is below the allowable temperature,
When the compression end temperature exceeds the allowable temperature and the outside air temperature is equal to or lower than the predetermined temperature, the control unit determines the effective compression ratio of the engine from that when the compression end temperature is equal to or lower than the allowable temperature. A compression self-ignition engine with a supercharger that changes the closing timing of the intake valve through the variable valve mechanism so as to lower the intake valve. The compression self-ignition engine with a supercharger according to claim 3,
The control unit drives the supercharger through the switching unit when the compression end temperature exceeds the allowable temperature and the outside air temperature exceeds a second predetermined temperature higher than the predetermined temperature. A compression self-ignition engine with a supercharger that opens the flow control valve. The compression self-ignition engine with a supercharger according to claim 1 or 2,
When the compression end temperature exceeds the allowable temperature and the driver is not performing an acceleration request operation, the control unit deactivates the supercharger through the switching unit, and the compression end temperature Close the flow rate control valve than when the temperature is below the allowable temperature,
When the compression end temperature exceeds the allowable temperature and the driver is performing an acceleration request operation, the control unit determines the effective compression ratio of the engine, and the compression end temperature is equal to or lower than the allowable temperature. A compression self-ignition engine with a supercharger that changes the closing timing of the intake valve through the variable valve mechanism so as to be lower than the time. 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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