JP6565985B2 - Control device for compression ignition engine - Google Patents

Description

  The technology disclosed herein relates to a control device for a compression ignition engine.

  In Patent Document 1, in a diesel engine that performs premixed compression ignition combustion, when the outside air temperature or the intake air temperature decreases, the amount of air sucked into the combustion chamber is increased, so that the air-fuel ratio of the mixture is made lean. It is described to do. As a result, the oxidation reaction between the fuel and air during premixing is promoted to obtain a desired heat release rate waveform.

JP 2013-44289 A

  The technique described in Patent Document 1 relates to a diesel engine using light oil as fuel. On the other hand, in an engine using a fuel containing at least gasoline, there is an attempt to burn the air-fuel mixture by compression ignition. However, in an engine that uses fuel containing gasoline, the timing of self-ignition greatly changes if the temperature in the combustion chamber before the start of compression varies.

  The technology disclosed herein stably performs combustion by compression ignition in a compression ignition type engine.

  The inventors of the present application have considered a combustion mode combining SI (Spark Ignition) combustion and CI (Compression Ignition) combustion. SI combustion is combustion with flame propagation that starts by forcibly igniting the air-fuel mixture in the combustion chamber. CI combustion is combustion that starts when the air-fuel mixture in the combustion chamber undergoes compression self-ignition. Combustion mode combining SI combustion and CI combustion means that when combustion is forcibly ignited in the air-fuel mixture in the combustion chamber and combustion by flame propagation is started, the heat generated by SI combustion and the pressure increase due to flame propagation The unburned air-fuel mixture in the combustion chamber is burned by compression ignition. Hereinafter, this combustion mode is referred to as SPCCI (SPark Controlled Compression Ignition) combustion.

  In the combustion by compression ignition, when the temperature in the combustion chamber before the start of compression varies, the timing of compression ignition changes greatly. In SPCCI combustion, by adjusting the calorific value of SI combustion, it is possible to absorb temperature variations in the combustion chamber before compression starts. If the start timing of SI combustion is adjusted by adjusting the ignition timing, for example, according to the temperature in the combustion chamber before the start of compression, the timing of compression ignition can be controlled. SPCCI combustion can control CI combustion by SI combustion.

  In SI combustion by flame propagation, since the pressure rise is more gradual than CI combustion, SPCCI combustion can suppress the generation of combustion noise. Further, since CI combustion has a shorter combustion period than SI combustion, SPCCI combustion is advantageous in improving fuel efficiency. Further, SPCCI combustion including CI combustion can ensure combustion stability even when the air-fuel ratio of the air-fuel mixture is lean, so that the fuel efficiency performance of the engine can be further improved while maintaining the exhaust emission performance.

  When SPCCI combustion is performed, combustion by compression ignition can be stably performed. According to the study by the inventors of the present application, SPCCI combustion is performed by compression ignition when the temperature of intake air introduced into the combustion chamber is low. Newly found that does not stabilize. As a result of CI combustion not being stabilized, exhaust emission performance may be degraded.

  Accordingly, the inventors of the present invention set the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio or the air-fuel ratio when the combustion by compression ignition is not stabilized due to the low temperature of the intake air introduced into the combustion chamber in an engine that performs SPCCI combustion. The exhaust gas was purified using a three-way catalyst by setting the air to the stoichiometric air-fuel ratio.

  Specifically, a compression ignition engine disclosed herein includes an engine in which an air-fuel mixture in a combustion chamber burns by compression ignition, a fuel injection unit attached to the engine, an engine attached to the engine, and a combustion chamber A state quantity adjusting unit for adjusting the introduction of at least fresh air into the combustion chamber, an ignition unit disposed facing the combustion chamber, a three-way catalyst provided in the exhaust passage of the engine, and the combustion chamber An intake air temperature acquisition unit that acquires parameters related to the temperature of the intake air, and the fuel injection unit, the state quantity adjustment unit, the ignition unit, and the intake air temperature acquisition unit, and from the intake air temperature acquisition unit And a control unit that outputs a control signal to the fuel injection unit, the state quantity adjustment unit, and the ignition unit.

  The control unit ignites the ignition unit at a predetermined timing so that the unburned air-fuel mixture is compressed and ignited at a predetermined timing after the ignited mixture starts combustion by flame propagation, and the control unit When the intake air temperature is lower than the predetermined intake air temperature, the air-fuel ratio of the air-fuel mixture is set to a substantially stoichiometric air-fuel ratio so that it falls within the purification window of the three-way catalyst.

  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. The “intake” introduced into the combustion chamber may include fresh air and burned gas. Further, the “substantially stoichiometric air / fuel ratio” includes the stoichiometric air / fuel ratio and an air / fuel ratio near the stoichiometric air / fuel ratio. The air-fuel ratio in the vicinity of the theoretical air-fuel ratio is limited to be within the purification window of the three-way catalyst. Further, the “state quantity adjusting unit” is not limited to the throttle valve disposed in the intake passage. For example, the amount of fresh air introduced may be adjusted by adjusting the valve timing and / or valve lift of the intake valve. Further, the state quantity adjusting unit may be configured to adjust the amount of fresh air introduced by adjusting the amount of EGR gas into the combustion chamber.

  The control unit ignites the ignition unit at a predetermined timing. After the ignited mixture starts combustion by flame propagation, the unburned mixture is compressed and ignited at a predetermined time. CI combustion can be performed while preventing combustion noise, for example, by adjusting the ignition timing in accordance with the temperature in the combustion chamber before the start of compression. The fuel efficiency of the engine can be improved.

  When the intake air temperature is lower than the predetermined intake air temperature, the CI combustion is not stable, and the exhaust emission performance may be deteriorated. Therefore, when the intake air temperature is lower than the predetermined intake air temperature, the control unit sets the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio or the substantially stoichiometric air-fuel ratio so as to be within the purification window of the three-way catalyst. As a result, the exhaust gas discharged from the combustion chamber can be purified using the three-way catalyst provided in the exhaust passage, so that the exhaust emission performance is reduced when the intake air temperature is lower than the predetermined intake air temperature. Is prevented.

  The state quantity adjusting unit adjusts the introduction of fresh air and EGR gas into the combustion chamber, and the control unit substantially reduces the air-fuel ratio of the air-fuel mixture when the intake air temperature is lower than the predetermined intake air temperature. In addition to the theoretical air-fuel ratio, EGR gas may be introduced into the combustion chamber.

  The fuel efficiency performance of the engine can be improved by introducing EGR gas into the combustion chamber and diluting the air-fuel mixture. That is, by making the air-fuel ratio of the air-fuel mixture substantially the stoichiometric air-fuel ratio and introducing EGR gas into the combustion chamber, both improvement in fuel efficiency and maintenance of exhaust emission performance are achieved.

  The control unit may set G / F as an index related to a weight ratio of the total gas and fuel in the combustion chamber to 18 or more. According to the knowledge of the inventors of the present application, when the air-fuel ratio of the air-fuel mixture is set to a substantially stoichiometric air-fuel ratio and G / F is set to 18 or more, combustion noise is prevented from exceeding an allowable value in combustion by compression ignition. can do. Note that the G / F of the air-fuel mixture may be 50 or less, for example. According to the knowledge of the present inventors, if the G / F of the air-fuel mixture is 50 or less, SPCCI combustion can be performed stably.

  The control unit may make the air-fuel ratio of the air-fuel mixture leaner than the stoichiometric air-fuel ratio when the temperature of the intake air is equal to or higher than the predetermined intake air temperature.

  When the intake air temperature is equal to or higher than the predetermined intake air temperature, the stability of CI combustion in SPCCI combustion is ensured even if the air-fuel ratio of the mixture is made leaner than the stoichiometric air-fuel ratio. Further, the exhaust emission performance does not deteriorate. By making the air-fuel ratio of the air-fuel mixture leaner than the stoichiometric air-fuel ratio, it becomes more advantageous for improving the fuel efficiency performance of the engine.

  The control unit sets the air-fuel ratio of the air-fuel mixture to a substantially stoichiometric air-fuel ratio when the engine load is equal to or lower than the predetermined load and the intake air temperature is lower than the predetermined intake air temperature, and the engine load is equal to or lower than the predetermined load. In addition, when the temperature of the intake air is equal to or higher than the predetermined intake air temperature, the air-fuel ratio of the air-fuel mixture may be made leaner than the stoichiometric air-fuel ratio.

  By making the air-fuel mixture leaner than the stoichiometric air-fuel ratio when the engine load is low, it becomes more advantageous for improving the fuel efficiency of the engine. Further, when the engine load is low and the intake air temperature is lower than the predetermined intake air temperature, the air-fuel ratio of the air-fuel mixture is made to be substantially the stoichiometric air-fuel ratio, thereby preventing the exhaust emission performance from being deteriorated in SPCCI combustion. be able to.

  A control device for a compression ignition engine includes a swirl generating unit that generates a swirl flow in the combustion chamber, and a swirl flow that circulates along a wall is generated in the combustion chamber. The igniting unit may be ignited at a predetermined timing so that the unburned air-fuel mixture is compressed and ignited at a predetermined timing after the mixed gas mixture has started flame propagation along the wall of the combustion chamber by a swirl flow.

  The swirl flow is strong at the outer periphery of the combustion chamber near the wall surface and weak at the center of the combustion chamber away from the wall surface. The flame of SPCCI combustion rides on a swirl flow and propagates along the outer wall of the combustion chamber along the wall of the combustion chamber. Thereafter, at a predetermined timing, the unburned mixture is compressed and ignited, and CI combustion is performed at the outer peripheral portion and the central portion of the combustion chamber. By generating a swirl flow in the combustion chamber during SPCCI combustion, SI combustion can be sufficiently performed before the start of CI combustion. The generation of combustion noise can be suppressed, and the combustion temperature does not become too high, and the generation of NOx is also suppressed. Further, the compression ignition of the unburned mixture is performed at the target timing, and the stability of the SPCCI combustion is increased. As a result, it is possible to suppress the variation in torque between cycles.

  The control unit may set the state in the combustion chamber at the ignition timing to a swirl ratio of 4 or more through the swirl generation unit.

  When the swirl flow in the combustion chamber is strengthened, the above-described suppression of combustion noise, suppression of NOx, and suppression of torque variation can be more reliably realized.

  A wall temperature acquisition unit that acquires a parameter related to the wall temperature of the combustion chamber is provided, and the control unit is configured such that when the wall temperature of the combustion chamber is lower than a predetermined wall temperature or the temperature of the intake air is lower than the predetermined intake air temperature In this case, the air-fuel ratio of the air-fuel mixture may be substantially the stoichiometric air-fuel ratio so as to be within the purification window of the three-way catalyst.

  Even when the wall temperature of the combustion chamber is low, combustion due to compression ignition in SPCCI combustion is difficult to stabilize. Further, as described above, in the configuration in which a swirl flow is generated in the combustion chamber and the flame of SPCCI combustion propagates along the wall of the combustion chamber, the SI combustion is cooled by the wall surface when the wall temperature of the combustion chamber is low. Therefore, the timing of compression ignition is delayed. When trying to compress and ignite the unburned mixture at the target timing, it is necessary to increase the amount of heat generated by SI combustion in SPCCI combustion, for example, by increasing the amount of fuel. However, if the amount of fuel is increased, exhaust emission performance decreases. There is a fear.

  Therefore, when the SPCCI combustion is performed, when the wall temperature is lower than the predetermined wall temperature or when the intake air temperature is lower than the predetermined intake air temperature, the air-fuel ratio of the air-fuel mixture is set to a substantially stoichiometric air-fuel ratio, so Since the exhaust gas can be purified by using this, it is possible to prevent the exhaust emission performance of the engine from being deteriorated.

  As described above, according to the compression ignition type engine, combustion by compression ignition can be performed stably.

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 a rig testing apparatus for swirl ratio measurement. FIG. 7 is a diagram illustrating the relationship between the opening ratio of the secondary passage and the swirl ratio. FIG. 8 is a diagram illustrating an engine operating region map. FIG. 9 is a diagram illustrating fuel injection timing and ignition timing and combustion waveforms in each operation region of the operation region map of FIG. FIG. 10 is a plan view equivalent view of the combustion chamber for explaining the concept of SPCCI combustion. FIG. 11 is a diagram illustrating the layer structure of the engine operation region map. FIG. 12 is a flowchart illustrating an engine control process related to layer selection of the operation region map.

  Hereinafter, an embodiment of a compression ignition type engine 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. In addition, the intake electric S-VT 23 and the exhaust electric S-VT 24 are each one of state quantity adjustment units that adjust the introduction of fresh air and EGR gas into the combustion chamber 17.

  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. The throttle valve 43 is one of the state quantity adjustment units.

  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 supercharging system 49 is one of the state quantity adjustment units.

  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).

  Here, the strength of the swirl flow will be described. The strength of the swirl flow can be expressed by the swirl ratio. The “swirl ratio” can be defined as a value obtained by dividing a 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. 6) generated in the cylinder 36 in response to intake air supply, and based on this, the intake air flow lateral angular velocity can be obtained. .

  FIG. 7 shows the relationship between the degree of opening of the swirl control valve 56 in the engine 1 and the swirl ratio. FIG. 7 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. 7, in the engine 1, the swirl ratio becomes about 6 when the swirl control valve 56 is fully closed. If the swirl ratio is 4 or more, the opening degree of the swirl control valve 56 may be adjusted in a range where the opening ratio is 0 to 15%.

  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 adjustment units. 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. The refrigerant (that is, the cooling water) 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 air, and a variable capacity that supplies the cooling water cooled by the main radiator 72 to the engine body 100 that includes the cylinder head 13 and the cylinder block 12. A water pump 74 of the type. The water pump 74 is driven by the engine 1. Although illustration of the cooling water supplied to the engine body 100 is omitted, the engine body 100 cools each part of the engine body 100 after flowing in a water jacket provided around the combustion chamber 17 in the engine body 100. It is discharged from 100 and returns to the main radiator 72. A water temperature sensor SW10 described later detects the temperature of the cooling water. The temperature of the cooling water detected by the water temperature sensor SW10 may be used for various controls of the engine 1 as the temperature of the engine body 100. Although details will be described later, the temperature of the cooling water detected by the water temperature sensor SW10 is used as the temperature of the wall temperature of the combustion chamber 17 and is used for selecting a layer in the operation region map of the engine 1.

  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 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> 17 are connected to the ECU 10. Sensors SW1-SW17 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 The second pressure sensor SW5 for detecting the pressure of the gas downstream of the feeder 44 and the temperature of the gas in the surge tank 42, in other words, introduced into the combustion chamber 17 A third intake air temperature sensor SW17 for detecting the temperature of the intake air, a finger pressure sensor SW6 for detecting the pressure in each combustion chamber 17, which is attached to the cylinder head 13 corresponding to each cylinder 11, and disposed in the exhaust passage 50; An exhaust temperature sensor SW7 that detects the temperature of the exhaust gas discharged from the combustion chamber 17, a linear O ₂ sensor SW8 that is arranged upstream of the upstream catalytic converter in the exhaust passage 50 and detects the oxygen concentration in the exhaust gas, A lambda O ₂ sensor SW9 that is disposed 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, the engine 1 and a crank angle sensor SW11 that detects the rotation angle of the crankshaft 15 An accelerator opening sensor SW12 that is attached to the accelerator pedal mechanism and detects the accelerator opening corresponding to the amount of operation of the accelerator pedal, and 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; an EGR differential pressure sensor SW15 that is disposed in the EGR passage 52 and detects a differential pressure upstream and downstream of the EGR valve 54; The fuel pressure sensor SW16 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.

  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. 8 illustrates an operation region map of the engine 1 during the warm time. 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, the middle rotation region, and the high rotation region may be used. In the example of FIG. 8, 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. 8 indicates a road-load line of the engine 1. In FIG. 8, for easy understanding, the operation region maps 501 and 502 of the engine 1 are drawn in two parts. A map 501 shows the state of the air-fuel mixture and the combustion mode in each region, and the drive region and non-drive region of the supercharger 44. A map 502 shows the opening degree of the swirl control valve 56 in each region.

  When the engine 1 is warm, the engine 1 mainly has a low load region (1) -1, a medium load region (1) -2, a high load medium rotation region ( In 2), combustion is performed by compression self-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).

(SPCCI combustion concept)
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 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. This is a form in which the unburned air-fuel mixture undergoes CI combustion by self-ignition as the temperature rises and the pressure in the combustion chamber 17 rises due to flame propagation.

  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.

  In SPCCI combustion, heat generation during SI combustion is milder than heat generation during CI combustion. The waveform of the heat generation rate in the SPCCI combustion has a relatively small rising slope as illustrated by reference numerals 6014, 6024, 6034, and 6043 in FIG. 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 examples of the heat generation rate waveforms 6014, 6024, 6034, and 6043 shown in FIG. 9, the slope of the waveform 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 slopes of the heat generation rate waveforms 6014, 6024, 6034, and 6043 due to CI combustion become too large. 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.

  Thus, the heat generation rate waveform of SPCCI combustion has a relatively large rising slope formed by CI combustion and a first heat generation rate portion formed by SI combustion and having a relatively small rising slope. The second heat generation rate portion is formed to be continuous in this order. Moreover, the start timing of CI combustion (that is, the second heat generation rate portion) is changed by changing the heat generation amount of SI combustion (that is, the first heat generation rate portion) according to the operating state of the engine. Combustion control means (for example, EGR system, variable valve mechanism, intake air amount control means) is controlled so as to reach a target CI combustion start timing set according to the state.

  The engine 1 generates a strong swirl flow in the combustion chamber 17 when performing SPCCI combustion. The swirl ratio may be 4 or more, for example.

  FIG. 10 shows the concept of SPCCI combustion. When a strong swirl flow is generated in the combustion chamber 17, the outer periphery of the combustion chamber 17 has a strong swirl flow, as indicated by the white arrow in FIG. 10. On the other hand, the swirl flow in the central part is relatively weak, but the turbulent energy is increased in the central part due to the eddy current caused by the velocity gradient at the boundary between the central part and the outer peripheral part.

  When the spark plug 25 ignites the air-fuel mixture at the center, the SI combustion is stabilized by increasing the combustion speed due to the high turbulent energy, and the SI combustion flame is indicated by a black arrow in FIG. It rides on the strong swirl flow in the combustion chamber 17 and propagates in the circumferential direction. When the combustion chamber 17 is divided into four parts, that is, an intake-rear side part, an exhaust-rear side part, an exhaust-front side part, and an intake-front side part, the spark plug 25 has an intake-exhaust direction. Since the swirl flow is in the counterclockwise direction in FIG. 10 and is disposed on the intake side from the central axis X1 of the cylinder 11, the SI combustion flame is discharged from the intake-rear side portion to the exhaust- The intake-front side portion is reached through the rear side portion and the exhaust-front side portion. Due to the heat generated by the SI combustion and the pressure increase due to the flame propagation, the unburned air-fuel mixture undergoes compression ignition in the intake-front side portion as shown by the broken arrow in FIG. Combustion takes place.

  In this SPCCI combustion concept, by 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.

  Further, the concept of SPCCI combustion is that the flame of SI combustion propagates in the circumferential direction along the wall surface of the combustion chamber 17, so that the spark plug 25 is disposed in the center of the cylinder 11, and from the center of the combustion chamber 17 in the radial direction. Compared with general SI combustion in which a flame is propagated outward, there is an advantage that knocking accompanied with high-frequency vibration is difficult to occur. In addition, as described above, the pressure fluctuation during the CI combustion in the SPCCI combustion is relatively gentle, so that the occurrence of diesel knock can also be suppressed.

(Engine operation in each area)
Hereinafter, the operation of the engine 1 in each region of the operation region maps 501 and 502 of FIG. 8 will be described in detail with reference to the fuel injection timing and the ignition timing shown in FIG. The horizontal axis in FIG. 9 is the crank angle. Note that reference numerals 601, 602, 603, 604, 605, and 606 in FIG. 9 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. 8, respectively. .

(Low load area (1) -1)
When the engine 1 is operating in the low load region (1) -1, the engine 1 performs SPCCI combustion.

  Reference numeral 601 in FIG. 9 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 heat generation rate with respect to a crank angle, reference numeral 6014) is shown.

  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 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. When the engine 1 operates in the low load region (1) -1, the swirl ratio may be 4 or more and 6 or less. The opening degree of the swirl control valve 56 may be adjusted in a range where the opening ratio is 0 to 15% as shown in FIG. By strengthening the swirl flow in the combustion chamber 17, SPCCI combustion can be performed appropriately.

  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. By setting the A / F of the air-fuel mixture close to the spark plug 25 to 20 or more and 30 or less, the generation of RawNOx during SI combustion can be suppressed while enabling SI combustion flame propagation. Moreover, CI combustion can be stably performed by setting the A / F of the air-fuel mixture in the outer peripheral portion to 35 or more.

  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). The air-fuel mixture is stratified in the central portion and the outer peripheral portion of the combustion chamber 17 by a plurality of 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, the engine 1 performs SPCCI combustion with the air-fuel mixture leaner than the stoichiometric air-fuel ratio (that is, SPCCI lean). The fuel consumption performance of the engine 1 can be greatly improved.

(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. 9 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, when the engine 1 operates in the medium load region (1) -2, the SPCCI combustion can be appropriately performed.

  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 catalysts 511 and 513 purify 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. As described above, since EGR gas is introduced into the combustion chamber 17, G / F, which is the weight ratio of the total gas in the combustion chamber 17 to the fuel, is lean. When the engine 1 is operated in the medium load region (1) -2, G / F may be 18 or more. By doing so, the occurrence of so-called knocking can be avoided. G / F may be set in the range of 18 to 30. Further, G / F may be set at 18 or more and 50 or less.

  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. The operation state 602 is an operation state with a relatively high load in the medium load region (1) -2. In the middle load region (1) -2, the second injection 6022 can be omitted. In particular, the second injection 6022 may be omitted when the engine is in a low load operating state in the medium load region (1) -2.

  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.

  Therefore, in the medium load region (1) -2, the engine 1 performs SPCCI combustion with the air-fuel mixture as the stoichiometric air-fuel ratio (that is, SPCCIλ = 1). The exhaust gas discharged from the combustion chamber 17 can be purified using the three-way catalysts 511 and 513. Moreover, the fuel efficiency performance of the engine 1 is improved by introducing EGR gas into the combustion chamber 17 and diluting the air-fuel mixture.

  Here, as shown in FIG. 8, 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. 9 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.

  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. Since the swirl flow is strong, SPCCI combustion can be performed appropriately.

  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 is operated in the high load mid-rotation region (2), G / F may be 18 or more. G / F may be set in the range of 18 to 30. Further, G / F may be set at 18 or more and 50 or less.

  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 (that is, the cavity) of the combustion chamber 17 by the fuel spray hitting the opening edge of the cavity 31. 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, the fuel that has entered the squish area 171 enters the swirl flow, and the 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 quantity of front | former stage injection and the injection quantity of back | latter stage injection is good also as 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. The generation of combustion noise can be suppressed, and the combustion temperature does not become too high, and the generation of NOx is also suppressed. 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, in the high load mid-rotation region (2), the engine 1 performs SPCCI combustion with the air-fuel mixture richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio (that is, SPCCIλ ≦ 1). Even in this region, the exhaust gas discharged from the combustion chamber 17 can be purified using the three-way catalysts 511 and 513. Moreover, the fuel efficiency performance of the engine 1 is improved by introducing EGR gas into the combustion chamber 17 and diluting the air-fuel mixture.

(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. 9 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 fuel spray is mixed with fresh air because the piston 3 is located near the compression top dead center, although illustration is omitted. However, the gas flows downward along the convex portion 311 of the cavity 31 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 beginning of the expansion stroke (that is, retard-SI). In this region, the exhaust gas discharged from the combustion chamber 17 can be purified using the three-way catalysts 511 and 513 by setting the air-fuel ratio of the air-fuel mixture to a substantially stoichiometric air-fuel ratio. By performing SI combustion, abnormal combustion can be avoided.

(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. 9 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 speed 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 (that is, intake-SI). Also in this region, the exhaust gas discharged from the combustion chamber 17 can be purified using the three-way catalysts 511 and 513 by setting the air-fuel ratio of the air-fuel mixture to a substantially stoichiometric air-fuel ratio. Moreover, abnormal combustion can be avoided by performing SI combustion.

(Layer structure of driving area map)
As shown in FIG. 11, the operation region maps 501 and 502 of the engine 1 shown in FIG. 8 are configured by superimposing three layers of layer 1, layer 2, and layer 3.

  Layer 1 is a base layer. Layer 1 extends over the entire driving area map. Layer 1 consists of a low load area (1) -1, a medium load area (1) -2, a high load medium rotation area (2), a high load low rotation area (3), and a high rotation area (4). Of the area.

  Layer 2 is a layer overlying layer 1. Layer 2 includes a low load region (1) -1, a medium load region (1) -2, and a high load medium rotation region (excluding the high rotation region (4) and the high load low rotation region (3). 2).

  Layer 3 is a layer overlying layer 2. Layer 3 includes the low load region (1) -1.

  Layer 1, layer 2, and layer 3 are selected according to the level of the wall temperature of the combustion chamber 17 and the temperature of the intake air. Although details will be described later, there are three types of layer selection: selecting only layer 1, selecting layer 1 and layer 2, and selecting layer 1, layer 2, and layer 3. . The engine 1 operation region map 501 shown in FIG. 8 corresponds to the case where layer 1, layer 2, and layer 3 are selected.

  In the driving region map configured by selecting layer 1, layer 2, and layer 3 and superimposing these layer 1, layer 2, and layer 3, low load region (1) -1 is the highest in the region Layer 3 is enabled, and the medium load region (1) -2 and the high load medium rotation region (2) have the highest layer 2 enabled in those regions, and the remaining high load low rotation region (3) ) And the high rotation region (4), layer 1 is effective.

  Unlike the above, in the operation region map configured by selecting layer 1 and layer 2 and overlapping these layer 1 and layer 2, low load region (1) -1 and medium load region (1) -2 and the high-load medium rotation region (2), the uppermost layer 2 is effective in those regions, and the remaining high-load low-rotation region (3) and high-rotation region (4) are layer 1 validate.

  Unlike the above, in the operation region map configured by selecting only layer 1 and including only this layer 1, low load region (1) -1, medium load region (1) -2, high load medium rotation region (2) The layer 1 is effective in each of the high load low rotation region (3) and the high rotation region (4).

  Layer 3 performs SPCCI combustion. Layer 3 also makes the air-fuel ratio of the air-fuel mixture in the entire combustion chamber 17 leaner than the stoichiometric air-fuel ratio in the low load region (1) -1 (that is, λ> 1). The layer 3 is selected when the wall temperature of the combustion chamber 17 is equal to or higher than a first predetermined wall temperature (for example, 80 ° C.) and the intake air temperature is equal to or higher than the first predetermined intake temperature (for example, 50 ° C.). Note that the wall temperature of the combustion chamber 17 may be substituted by the temperature of the cooling water of the engine 1 detected by the water temperature sensor SW10, for example. Further, the wall temperature of the combustion chamber 17 may be estimated based on the temperature of the cooling water and other detection results. The intake air temperature is detected by, for example, a third intake air temperature sensor SW17 that detects the temperature in the surge tank 42. Further, the intake air temperature introduced into the combustion chamber 17 may be estimated based on various detection results.

  As described with reference to FIG. 10, the SPCCI combustion is performed by generating a strong swirl flow in the combustion chamber 17. In SI combustion, a flame propagates along the wall of the combustion chamber 17, so that the flame propagation of SI combustion is affected by the wall temperature. When the wall temperature is low, the flame of SI combustion is cooled, and the timing of compression ignition is delayed.

  As shown in the operation region map 501 of FIG. 8, when the engine 1 is operating in the low load region (1) -1, the air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio. In this operating state, when the compression ignition timing is advanced to the target timing when the wall temperature of the combustion chamber 17 is low, the injection amount of fuel burned by SI combustion is increased to increase the amount of heat generated by SI combustion, for example. It is possible to increase. However, if the air-fuel ratio of the air-fuel mixture in the central portion of the combustion chamber 17 for SI combustion is brought closer to the stoichiometric air-fuel ratio from the lean air-fuel ratio of A / F = 20 to 30 as described above, the combustion temperature of SI combustion is increased. It becomes high and much RawNOx is generated. On the other hand, when the engine 1 is operating in the low load region (1) -1, as described above, the air-fuel ratio of the mixture in the entire combustion chamber 17 is leaner than the stoichiometric air-fuel ratio. The catalysts 511 and 513 cannot purify RawNOx discharged from the combustion chamber 17.

  Further, since SPCCI combustion is a combustion mode that combines SI combustion and CI combustion, it is not only influenced by the wall temperature of the combustion chamber 17. The CI combustion in the SPCCI combustion is performed from the outer peripheral portion of the combustion chamber 17 to the central portion after the flame propagates along the wall, so that it is affected by the temperature of the central portion of the combustion chamber 17. If the temperature at the center is low, CI combustion becomes unstable. The temperature at the center of the combustion chamber 17 depends on the temperature of the intake air introduced into the combustion chamber 17. That is, when the intake air temperature is high, the temperature at the center of the combustion chamber 17 is high, and when the intake air temperature is low, the temperature at the center is low.

  Therefore, when the wall temperature of the combustion chamber 17 is equal to or higher than the first predetermined wall temperature and the intake air temperature is equal to or higher than the first predetermined intake air temperature, the SPCCI combustion can be performed stably, so the layer 3 is selected. Thus, the low load region (1) -1 is a region where the SPCCI combustion is performed with the air-fuel ratio of the air-fuel mixture leaner than the stoichiometric air-fuel ratio. By making the air-fuel ratio of the air-fuel mixture leaner than the stoichiometric air-fuel ratio when the load on the engine 1 is low, the fuel efficiency performance of the engine 1 can be greatly improved.

  Layer 2 performs SPCCI combustion. Layer 2 also makes the air-fuel ratio of the mixture in the entire combustion chamber 17 the stoichiometric or substantially stoichiometric air-fuel ratio in the low load region (1) -1 and the medium load region (1) -2 (that is, λ = 1). Further, the layer 2 makes the air-fuel ratio of the air-fuel mixture in the entire combustion chamber 17 richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio in the high-load mid-rotation region (2) (that is, λ ≦ 1). The layer 2 introduces EGR gas into the combustion chamber 17 in each of the low load region (1) -1, the medium load region (1) -2, and the high load medium rotation region (2). The G / F of the air-fuel mixture is set to 18 or more. Layer 2 is selected when the wall temperature of the combustion chamber 17 is equal to or higher than a second predetermined wall temperature (eg, 30 ° C.) and the intake air temperature is equal to or higher than a second predetermined intake temperature (eg, 25 ° C.). The layer 2 is also selected when the wall temperature of the combustion chamber 17 is equal to or higher than the first predetermined wall temperature or when the intake air temperature is equal to or higher than the first predetermined intake air temperature.

  As described above, when the wall temperature of the combustion chamber 17 is low and / or the air temperature is low, the air-fuel ratio of the air-fuel mixture can be made leaner than the stoichiometric air-fuel ratio, and SPCCI combustion can be performed stably. It becomes difficult.

  Further, if the wall temperature of the combustion chamber 17 is too low and / or the air temperature is too low, it is difficult to perform CI combustion stably even in SPCCI combustion using the heat generated by SI combustion.

  Therefore, when the wall temperature of the combustion chamber 17 is lower than the first predetermined wall temperature or when the intake air temperature is lower than the first predetermined intake air temperature, the wall temperature of the combustion chamber 17 is equal to or higher than the second predetermined wall temperature and the intake air temperature is the first. 2 When the intake air temperature is equal to or higher than the predetermined intake air temperature, layer 2 is selected and layer 3 is not selected. By selecting layer 2, when the wall temperature of the combustion chamber 17 is lower than the first predetermined wall temperature or when the intake air temperature is lower than the first predetermined intake air temperature, the air-fuel mixture is emptied in the low load region (1) -1. SPCCI combustion is performed with the fuel ratio set to the stoichiometric air fuel ratio or substantially the stoichiometric air fuel ratio. SPCCI combustion can be stabilized. When the wall temperature of the combustion chamber 17 is equal to or higher than the second predetermined wall temperature and the intake air temperature is equal to or higher than the second predetermined intake air temperature, the low load region (1) -1, the medium load region (1) -2, and the high The fuel consumption performance of the engine 1 can be improved by performing SPCCI combustion in each of the on-load rotation regions (2).

  Layer 1 starts fuel injection during the intake stroke in the low load region (1) -1, the medium load region (1) -2, the high load medium rotation region (2), and the high rotation region (4). SI combustion is performed by spark ignition (that is, intake air-SI). Further, in the high load low rotation region (3), the layer 1 performs SI combustion by injecting fuel during the intake stroke and within the retard period from the end of the compression stroke to the beginning of the expansion stroke (that is, retard − SI). Therefore, in the layer 1, SI combustion by spark ignition is performed instead of SPCCI combustion in the entire operation region of the engine 1. The air-fuel ratio of the air-fuel mixture is basically a stoichiometric air-fuel ratio or a substantially stoichiometric air-fuel ratio. Layer 1 is a layer that is always selected regardless of the wall temperature of the combustion chamber 17 and the intake air temperature.

  When the wall temperature of the combustion chamber 17 is lower than the second predetermined wall temperature or when the intake air temperature is lower than the second predetermined intake air temperature, combustion stability can be ensured by performing SI combustion in all operating regions. Variations in torque between cycles can be suppressed. Moreover, since the exhaust gas can be purified using the three-way catalysts 511 and 513 by making the air-fuel ratio of the air-fuel mixture substantially the stoichiometric air-fuel ratio, it is possible to prevent the exhaust emission performance from being deteriorated. it can.

  Thus, the layer structure of the operation region map is based on the characteristics of SPCCI combustion. By selecting the layer 1, layer 2 and layer 3 according to the wall temperature and intake air temperature of the combustion chamber 17, it is possible to maximize the fuel efficiency performance of the engine 1 while avoiding deterioration of the exhaust emission performance of the engine 1. It can be improved to the limit.

(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 the layer selection of the driving region map.

  First, in step S1 after the start, the ECU 10 reads signals from the sensors SW1 to SW17. In the subsequent step S2, the ECU 10 determines whether the wall temperature of the combustion chamber 17 is 3 ° C. or higher and the intake air temperature is 25 ° C. or higher. When the determination in step S2 is YES, the process proceeds to step S3, and when the determination is NO, the process proceeds to step S7. In step S7, the ECU 10 selects only the layer 1 because the wall temperature of the combustion chamber 17 is too low or the intake air temperature is too low. Therefore, when the engine 1 is operated in each of the low load region (1) -1, the medium load region (1) -2, the high load medium rotation region (2), and the high rotation region (4), While operating with “intake-SI”, when operating in the high load low rotation range (3), operate with “retard-SI”. The process then proceeds to step S5.

  In step S3, the ECU 10 determines whether the wall temperature of the combustion chamber 17 is 80 ° C. or higher and the intake air temperature is 50 ° C. or higher. When the determination in step S3 is YES, the process proceeds to step S4. When the determination is NO, the process proceeds to step S8.

  In step S8, the ECU 10 selects layer 1 and layer 2. Therefore, when the engine 1 is operated in each of the low load region (1) -1 and the medium load region (1) -2, the engine 1 is operated according to the “SPCCCIλ = 1” and the high load medium rotation region ( When driving in 2), the driving is performed according to “SPCCIλ ≦ 1”. Further, the engine 1 is operated by the “intake-SI” when operated in the high rotation region (4), and is operated by the “retard-SI” when operated in the high load low rotation region (3). . The process then proceeds to step S5.

  In step S4, the ECU 10 selects layer 1, layer 2, and layer 3. Accordingly, when the engine 1 is operated in the low load region (1) -1, the engine 1 operates according to the “SPCCIλ> 1”, and when the engine 1 is operated in the medium load region (1) -2, the engine is operated according to the “SPCCIλ = 1”. In addition to driving, when driving in the high load mid-rotation region (2), driving is performed according to the above-mentioned "SPCCCIλ≤1". Further, the engine 1 is operated by the “intake-SI” when operated in the high rotation region (4), and is operated by the “retard-SI” when operated in the high load low rotation region (3). . The process then proceeds to step S5.

  In step S5, the ECU 10 determines the operation state of the engine 1 based on the various detection signals acquired in step S1, and in the subsequent step S6, the operation region map based on the layer selected in step S4, S7, or S8. In accordance with the operating state of the engine 1 determined in step S5, state quantity adjustment (that is, adjustment of A / F and / or G / F of the air-fuel mixture), adjustment of fuel injection timing, and The ignition timing is adjusted and the engine 1 is operated.

  Therefore, when the engine is operated in the low load region (1) -1 where the load of the engine 1 is equal to or lower than the predetermined load, the wall temperature of the combustion chamber 17 is lower than the predetermined wall temperature or the intake air temperature is lower than the predetermined intake air temperature. When the air-fuel ratio of the air-fuel mixture is made approximately the stoichiometric air-fuel ratio by layer 2 and the wall temperature of the combustion chamber 17 is equal to or higher than the predetermined wall temperature and the intake air temperature is higher than the predetermined intake air temperature, the air-fuel ratio of the air-fuel mixture is theoretically determined by layer 3 It will be leaner than the air-fuel ratio.

  Here, although the layer is selected in consideration of both the wall temperature and the intake air temperature, the layer may be selected based on the intake air temperature.

(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.

  For example, the engine 1 may include a turbocharger instead of the mechanical supercharger 44.

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

1 Engine 10 ECU (control unit)
17 Combustion chamber 23 Intake electric S-VT (state quantity adjustment unit)
24 Exhaust electric S-VT (state quantity adjustment unit)
25 Spark plug (ignition part)
43 Throttle valve (state quantity adjustment unit)
44 Supercharger 49 Supercharging system (state quantity adjustment unit)
511, 513 Three-way catalyst 55 EGR system (state quantity adjustment unit)
56 Swirl control valve (swirl generator)
6 Injector (fuel injection part)
SW10 Water temperature sensor (wall temperature acquisition unit)
SW17 Third intake air temperature sensor (intake air temperature acquisition unit)

Claims (8)

An engine in which the air-fuel mixture in the combustion chamber burns by compression ignition;
A fuel injection part attached to the engine;
A state quantity adjusting unit which is attached to the engine and adjusts introduction of at least fresh air into the combustion chamber;
An ignition unit disposed facing the combustion chamber;
A three-way catalyst provided in the exhaust passage of the engine;
An intake air temperature acquisition unit for acquiring a parameter related to the temperature of intake air introduced into the combustion chamber;
The fuel injection unit, the state quantity adjustment unit, the ignition unit, and the intake air temperature acquisition unit, and receives a detection signal from the intake air temperature acquisition unit, and the fuel injection unit, the state quantity adjustment unit And a control unit that outputs a control signal to the ignition unit,
When the temperature of the intake air is lower than a predetermined intake air temperature , the control unit starts flame propagation combustion while controlling the air-fuel ratio of the air-fuel mixture to a substantially stoichiometric air-fuel ratio so that it falls within the purification window of the three-way catalyst . The ignition timing is controlled by the igniter so that the unburned mixture is self-ignited and combusted later. When the intake air temperature is equal to or higher than the predetermined intake air temperature, the state quantity adjusting unit determines the air-fuel ratio of the mixture. A control device for a compression ignition engine that controls ignition timing by the igniter so that an unburned mixture self-ignites after starting flame propagation combustion while controlling leaner than the air-fuel ratio . The control apparatus for a compression ignition engine according to claim 1,
The state quantity adjusting unit adjusts the introduction of fresh air and EGR gas into the combustion chamber,
When the intake air temperature is lower than the predetermined intake air temperature, the control unit sets the air-fuel ratio of the air-fuel mixture to a substantially stoichiometric air-fuel ratio and introduces EGR gas into the combustion chamber. The control apparatus for a compression ignition engine according to claim 2,
The control unit is a control device for a compression ignition engine in which G / F as an index relating to a weight ratio of all the gases in the combustion chamber to fuel is 18 or more. The control apparatus for a compression ignition engine according to claim 1,
The control unit controls the ignition timing of the self-ignition combustion by changing a heat generation amount of the flame propagation combustion according to an operating state of the engine by controlling an ignition timing by ignition of the ignition unit. Control device for ignition engine. In the control device for the compression ignition engine according to any one of claims 1 to 4,
The control unit sets the air-fuel ratio of the air-fuel mixture to a substantially stoichiometric air-fuel ratio when the engine load is equal to or lower than the predetermined load and the intake air temperature is lower than the predetermined intake air temperature, and the engine load is equal to or lower than the predetermined load. In addition, when the intake air temperature is equal to or higher than the predetermined intake air temperature, the control device for the compression ignition engine that makes the air-fuel ratio of the air-fuel mixture leaner than the stoichiometric air-fuel ratio. In the control device for the compression ignition engine according to any one of claims 1 to 5,
A swirl generator for generating a swirl flow in the combustion chamber;
A swirl flow that circulates along the wall is generated in the combustion chamber,
The control unit ignites the ignition unit at a predetermined timing so that the unburned mixture is compressed and ignited at a predetermined timing after the ignited mixture starts to propagate through the wall of the combustion chamber by a swirl flow. Control device for compression ignition engine. The compression ignition type engine control device according to claim 6,
The control unit is a control device for a compression ignition type engine in which the state in the combustion chamber at the timing of ignition is set to a swirl ratio of 4 or more through the swirl generation unit. In the control device for a compression ignition engine according to any one of claims 1 to 7,
A wall temperature acquisition unit for acquiring a parameter related to the wall temperature of the combustion chamber;
When the wall temperature of the combustion chamber is lower than a predetermined wall temperature or when the temperature of the intake air is lower than the predetermined intake air temperature, the control unit fits the air-fuel ratio of the air-fuel mixture in the purification window of the three-way catalyst. A control device for a compression ignition engine having a substantially stoichiometric air-fuel ratio.

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