JP6614216B2 - Control device for premixed compression ignition engine - Google Patents

Description

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

  Patent Document 1 describes an engine that burns an air-fuel mixture in a combustion chamber by compression ignition in a predetermined region of low load and low rotation. The engine burns the air-fuel mixture by spark ignition in a region where the load is higher than the predetermined region and a region where the rotational speed is higher than the predetermined region. The engine also promotes compression ignition of the air-fuel mixture by causing the spark plug to perform spark ignition near the compression top dead center even in the predetermined region.

  Patent Document 2 describes an engine that burns an air-fuel mixture in a combustion chamber by compression ignition in a high load region. This engine performs a small amount of fuel injection for assisting ignition between a front-stage injection and a rear-stage injection that form an air-fuel mixture for CI combustion in a high rotation range in a high load range. The fuel injected for the ignition assist forms a rich air-fuel mixture in the vicinity of the spark plug. When the spark plug ignites the rich air-fuel mixture and a flame is formed, the air-fuel mixture formed by the first-stage injection is compressed and ignited, and the air-fuel mixture formed by the second-stage injection performed simultaneously with the compression ignition is also Then, compression ignition is performed.

Japanese Patent No. 4082292 Japanese Patent No. 5447435

  By the way, combustion by compression ignition generates a relatively large combustion noise. For example, when the engine is operating in a high load region including a fully open load, if combustion is performed by compression ignition, combustion noise may exceed an allowable value.

  The technology disclosed herein has been made in view of the above points, and the purpose of the technology is to perform combustion with compression ignition while suppressing the combustion noise to a permissible value or less in a premixed compression ignition type engine. is there.

  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.

  When the engine is operating in a high load region, the amount of fuel injection increases and the temperature in the combustion chamber also increases. Therefore, even if SPCCI combustion is attempted, there is a risk that CI combustion will occur with the start of SI combustion. is there. In SPCCI combustion, if SI combustion is not performed sufficiently, combustion noise increases or the combustion temperature becomes too high, and NOx is generated.

  Accordingly, the inventors of the present application have made it possible to perform sufficient SI combustion in SPCCI combustion by stratifying the air-fuel mixture in the combustion chamber when the engine is operating in a high load region.

  Further, when the engine speed is low, the time required for the crank angle to change by 1 ° becomes long. In order to stratify the air-fuel mixture in the combustion chamber, for example, if fuel is supplied into the combustion chamber during the first half of the intake stroke or compression stroke, the reaction of the fuel may progress excessively during the compression stroke, leading to premature ignition. There is. When the engine is operating in the low speed region in the high load region, it becomes difficult to perform the aforementioned SPCCI combustion.

  Therefore, in the technology disclosed herein, the SCCCI combustion is performed by stratifying the air-fuel mixture in the combustion chamber in the high rotation region in the high load region, while the fuel injection timing is relatively delayed in the low rotation region. SI combustion is performed.

  Specifically, the technology disclosed herein relates to a control device for a premixed compression ignition engine, which includes an engine having a combustion chamber, an ignition unit disposed in a central portion of the combustion chamber, and the combustion A fuel injection unit disposed facing the room, and a control unit connected to the ignition unit and the fuel injection unit and outputting a control signal to each of the ignition unit and the fuel injection unit.

Then, the control unit, when operating in the first speed region in the high load region where the engine is set in advance, the fuel concentration of the mixture of the outer peripheral portion which is around the center portion of the front Symbol combustion chamber, A control signal is output to the fuel injection unit so that the fuel concentration of the air-fuel mixture in the central portion is higher than the fuel concentration in the central portion and the fuel amount in the air-fuel mixture in the outer peripheral portion is larger than the fuel amount in the air-fuel mixture in the central portion. The engine outputs a control signal to the ignition unit so as to ignite the air-fuel mixture in the central portion after all the fuel to be injected from the fuel injection unit has been injected during one combustion cycle of the engine. is the high when operating in the first speed region in the load region after the air-fuel mixture by the ignition of the igniter starts to SI combustion by flame propagation, CI retardant unburnt gas mixture by compression ignition The to.

When the engine is operated in a second rotation region having a lower rotational speed than the first rotation region in the high load region, the air-fuel mixture performs SI combustion by flame propagation by ignition of the ignition unit, and the control unit When the engine operates in the first rotation region in the high load region, a control signal is output to the fuel injection unit so as to inject fuel into the combustion chamber a plurality of times during a compression stroke period, and the control The control unit also controls the timing of the compression ignition by adjusting the heat generation amount of the SI combustion by adjusting the ignition timing of the ignition unit when the engine operates in the first rotation region in the high load region. To do.

  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. Further, the “high load region” may be a high load region including a fully open load, for example, in an operation region determined by the engine speed and load. Furthermore, the “second rotation region” may be a low rotation region when the entire operation region of the engine is divided into a low rotation region and a high rotation region, or the entire operation region of the engine may be a low rotation region and a medium rotation region. And it is good also as a low rotation area | region when dividing into a high rotation area | region. The “first rotation region” may be a high rotation region when the entire operation region of the engine is divided into a low rotation region and a high rotation region. The entire operation region of the engine may be a low rotation region, a medium rotation region, and A medium rotation region, a high rotation region, or a medium rotation and high rotation region when divided into high rotation regions may be used.

  According to this configuration, when the engine operates in the first rotation region in the preset high load region, fuel injection is performed a plurality of times during the compression stroke period. Accordingly, the fuel concentration of the air-fuel mixture in the outer peripheral portion of the combustion chamber is higher than the fuel concentration of the air-fuel mixture in the central portion, and the fuel amount of the air-fuel mixture in the outer peripheral portion is larger than the fuel amount of the air-fuel mixture in the central portion. To be. The temperature of the outer peripheral portion of the combustion chamber decreases due to the latent heat of vaporization of the fuel. Here, the fuel concentration and fuel amount of the air-fuel mixture are the fuel concentration and fuel amount at the time of ignition.

  Since the ignition unit is disposed at the center of the combustion chamber, the ignition unit ignites the air-fuel mixture at the center of the combustion chamber. The air-fuel mixture starts SI combustion by flame propagation by ignition of the ignition unit.

  Due to the heat generated by the SI combustion and the pressure increase, the unburned air-fuel mixture at the outer periphery of the combustion chamber is combusted by compression ignition. Since the temperature of the outer peripheral portion is lowered, it is possible to avoid that CI combustion starts immediately after ignition. SI combustion is 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.

  Since the temperature of the outer peripheral portion is low, CI combustion becomes moderate, and generation of combustion noise can be suppressed. Further, since the combustion period is shortened by CI combustion, it is possible to improve torque and heat efficiency in a high load region. This engine can improve fuel consumption performance while avoiding combustion noise in a high load region.

  When the engine operates in the second rotation region where the number of rotations is lower than that in the first rotation region, fuel injection is performed in the period from the latter stage of the compression stroke to the initial stage of the expansion stroke. Since the start of fuel injection is slow, premature ignition during the compression stroke is avoided. Further, when the engine operates in the second rotation region, ignition is performed after completion of fuel injection and after compression top dead center. Combustion begins in the expansion stroke. In this case, the air-fuel mixture is not subjected to compression ignition, and only SI combustion by flame propagation is performed.

When the engine operates in the first rotation region in the high load region , the control unit performs a first injection that forms an air-fuel mixture for SI combustion in the central portion in the first half of the compression stroke, and The control signal may be output to the fuel injection unit so that the second injection that forms the mixture for CI combustion is performed in the latter half of the compression stroke.

  Here, the “first half” and “second half” of the compression stroke may be the first half and the second half when the period of the compression stroke is divided into the first half and the second half.

  By doing so, the air-fuel mixture can be stratified in the central portion and the outer peripheral portion in the combustion chamber.

  A control device for a premixed compression ignition engine disclosed herein includes an engine having a combustion chamber, an ignition unit disposed in a central portion of the combustion chamber, a fuel injection unit disposed facing the combustion chamber, A control unit that is connected to the ignition unit and the fuel injection unit and outputs a control signal to each of the ignition unit and the fuel injection unit.

Then, the control unit, when operating in the first speed region in the high load region where the engine is set in advance, the fuel concentration of the mixture of the outer peripheral portion which is around the center portion of the front Symbol combustion chamber, A control signal is output to the fuel injection unit so that the fuel concentration of the air-fuel mixture in the central portion is higher than the fuel concentration in the central portion and the fuel amount in the air-fuel mixture in the outer peripheral portion is larger than the fuel amount in the air-fuel mixture in the central portion. The engine outputs a control signal to the ignition unit so as to ignite the air-fuel mixture in the central portion after all the fuel to be injected from the fuel injection unit has been injected during one combustion cycle of the engine. is the high when operating in the first speed region in the load region after the air-fuel mixture by the ignition of the igniter starts to SI combustion by flame propagation, CI retardant unburnt gas mixture by compression ignition The to.

When the engine is operated in a second rotation region having a lower rotational speed than the first rotation region in the high load region, the air-fuel mixture performs SI combustion by flame propagation by ignition of the ignition unit, and the control unit When the engine operates in the first rotation region in the high load region, a control signal is output to the fuel injection unit so as to start fuel injection into the combustion chamber during the intake stroke period, and the control unit Further, when the engine operates in the first rotation region in the high load region , the compression ignition timing is controlled by adjusting the heat generation amount of the SI combustion by adjusting the ignition timing of the ignition unit. .

  According to this configuration, when the engine operates in the first rotation region in the preset high load region, fuel injection is performed during the intake stroke period. Accordingly, the fuel concentration of the air-fuel mixture in the outer peripheral portion of the combustion chamber is higher than the fuel concentration of the air-fuel mixture in the central portion, and the fuel amount of the air-fuel mixture in the outer peripheral portion is larger than the fuel amount of the air-fuel mixture in the central portion. To be.

  When the ignition unit ignites, the air-fuel mixture at the center of the combustion chamber starts SI combustion by flame propagation. As described above, since the temperature of the outer peripheral portion of the combustion chamber is lowered by the latent heat of vaporization of the fuel, it is possible to avoid that CI combustion starts immediately after ignition. SI combustion is 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.

  In addition, CI combustion is also moderated, generation of combustion noise can be suppressed, and the combustion period is shortened by CI combustion, so that torque and thermal efficiency can be improved in a high load region.

  When the engine operates in the second rotation region where the number of rotations is lower than that in the first rotation region, fuel injection is performed in the period from the latter stage of the compression stroke to the initial stage of the expansion stroke. Premature ignition during the compression stroke is avoided. By performing ignition after the end of fuel injection and after compression top dead center, SI combustion by flame propagation is performed.

The control device for the premixed compression ignition type engine includes a swirl generating unit that generates a swirl flow in the combustion chamber, and the control unit operates when the engine operates in the first rotation region in the high load region. The control signal may be output to the swirl generator so that a stronger swirl flow is generated than when operating in the second rotation region in the high load region .

  When a swirl flow having a predetermined strength, that is, a relatively strong swirl flow, is generated in the combustion chamber, the outer peripheral portion of the combustion chamber becomes a strong swirl flow. On the other hand, the swirl flow at the center is relatively weak, but the turbulent energy at the center is increased by the vortex flow caused by the velocity gradient at the boundary between the center and the outer periphery.

  As a definition of the central portion and the outer peripheral portion of the combustion chamber, the outer peripheral portion may be a portion where the swirl flow is strong, and the central portion of the combustion chamber may be a portion where the swirl flow is weak.

  When a relatively strong swirl flow is generated in the first rotation region where the engine performs SPCCI combustion, SI combustion is stabilized by high turbulent energy and the combustion speed is increased.

  The flame of SI combustion propagates in the circumferential direction on a strong swirl flow in the combustion chamber. Thus, the temperature and pressure of the air-fuel mixture increase at a predetermined circumferential position on the outer peripheral portion of the combustion chamber, the unburned air-fuel mixture undergoes compression ignition, and CI combustion starts. By generating a strong swirl flow when performing SPCCI combustion, SI combustion is stabilized and CI combustion is optimized. Further, torque variation between cycles can be suppressed.

  In the second rotation region in which the engine performs SI combustion, since the time from the start of fuel injection to ignition is short, the injected fuel must be quickly transported to the vicinity of the ignition unit. The injected fuel can be quickly transported to the vicinity of the ignition unit by the swirl flow. On the other hand, if the swirl flow is too strong, the fuel is flowed in the circumferential direction and is separated from the vicinity of the ignition unit. In the second rotation region where the engine performs SI combustion, by relatively weakening the swirl flow, the fuel can be quickly transported to the vicinity of the ignition unit, and the ignitability is improved and the SI combustion is stabilized. .

When the engine operates in the first rotation region in the high load region , the control unit reduces the fuel concentration of the entire air-fuel mixture in the combustion chamber to 1 or less in the excess air ratio λ, and the engine When operating in the second rotation region in the high load region, the fuel concentration of the mixture in the entire combustion chamber is 1 or less in the excess air ratio λ, and the air in the first rotation region in the high load region The excess rate may be greater than or equal to λ.

  By setting the excess air ratio λ of the air-fuel mixture in the entire combustion chamber to 1 or less in the first rotation region where the rotational speed is relatively high, it is possible to obtain a feeling of torque with elongation. In the second rotation region, by setting the excess air ratio λ of the air-fuel mixture in the entire combustion chamber to 1 or less, sufficient torque can be secured in the high load region, and the excess air ratio in the first rotation region. By setting it to λ or more, it is advantageous for improving fuel efficiency.

  The engine may have a geometric compression ratio of 13 or more and 20 or less.

  Since SPCCI combustion controls CI combustion by SI combustion, it is not necessary to realize a high compression end temperature in order to compress and ignite the air-fuel mixture. Therefore, the geometric compression ratio of the engine can be lowered. Lowering the geometric compression ratio and lowering the compression end temperature is advantageous for reducing cooling loss and also for reducing mechanical loss. The fuel efficiency of the engine is improved.

  The high load region of the engine may be a region where the combustion pressure is 900 kPa or more.

  As described above, according to the control device for a premixed compression ignition engine, combustion noise of SPCCI combustion can be suppressed in a high load region.

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 II-II cross-sectional view. FIG. 3 is a plan view illustrating the configuration of the combustion chamber and the intake system. FIG. 4 is a block diagram illustrating the configuration of the engine control apparatus. FIG. 5 is a diagram illustrating an engine operating region map. FIG. 6 is a diagram illustrating fuel injection timing and ignition timing and combustion waveforms in each operation region. FIG. 7 is a diagram illustrating a rig test apparatus for swirl ratio measurement. FIG. 8 is a diagram illustrating the relationship between the opening ratio of the secondary passage and the swirl ratio. FIG. 9 is a diagram illustrating the state of the combustion chamber when performing the first injection and the state of the combustion chamber when performing the second injection in the high load mid-rotation region. FIG. 10 is a diagram illustrating an air-fuel mixture distribution in the combustion chamber in the high load mid-rotation region. FIG. 11 is a diagram illustrating a combustion concept in a high load mid-rotation region. FIG. 12 is a diagram for comparing combustion waveforms when the opening degree of the swirl control valve is changed in the high load mid-rotation region. FIG. 13 is a diagram illustrating the state of the combustion chamber when fuel injection is performed in the high-load low-rotation region. FIG. 14 is a flowchart illustrating an engine control process. FIG. 15 is a diagram illustrating fuel injection timing and ignition timing and combustion waveforms in each operation region, which are different from FIG. FIG. 16 is a diagram illustrating the state of the combustion chamber when fuel injection is performed in the high load mid-rotation region of FIG. 15.

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

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

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

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

  The lower surface of the cylinder head 13, that is, the ceiling surface of the combustion chamber 17 is composed of an inclined surface 1311 and an inclined surface 1312 as shown in the lower diagram of FIG. 2. 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 with respect to the center axis X <b> 1 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 gradually increases from the bottom of the cavity 31 toward the opening of the cavity 31.

The shape of the combustion chamber 17 is not limited to the shape illustrated in FIG. For example, the shape of the cavity 31, the shape of the upper surface of the piston 3, the shape of the ceiling surface of the combustion chamber 17, and the like can be changed as appropriate. For example, the cavity 31 may be symmetric with respect to the central axis X1 of the cylinder 11. The inclined surface 1311 and the inclined surface 1312 may be symmetric with respect to the central axis X <b> 1 of the cylinder 11. Further, in the cavity 31, a shallow bottom portion that is shallower than the recessed portion 312 may be provided at a location facing a spark plug 25 described later.
The geometric compression ratio of the engine 1 is set to 13 or more and 20 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 performs CI combustion using heat generation and pressure increase due to SI 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, the engine 1 performs CI combustion, but its geometric compression ratio is set to be relatively low. Lowering the geometric compression ratio is advantageous in 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. This valve mechanism may be a variable valve mechanism that makes the valve timing and / or valve lift variable. In this configuration example, as shown in FIG. 4, the variable valve mechanism has an 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 valve opening timing and the valve closing timing of the intake valve 21 are continuously changed. The valve mechanism of the intake valve 21 may have a hydraulic S-VT instead of the electric S-VT.

  The cylinder head 13 is also provided with an exhaust port 19 for each cylinder 11. The exhaust port 19 also has two exhaust ports, a first exhaust port 191 and a second exhaust port 192, as shown in FIG. The first exhaust port 191 and the second exhaust port 192 are arranged in the front-rear direction of the engine 1. The exhaust port 19 communicates with the combustion chamber 17. An exhaust valve 22 is disposed in the exhaust port 19. The exhaust valve 22 opens and closes between the combustion chamber 17 and the exhaust port 19. The exhaust valve 22 is opened and closed at a predetermined timing by a valve mechanism. This valve mechanism may be a variable valve mechanism that makes the valve timing and / or valve lift variable. In this configuration example, as shown in FIG. 4, the variable valve mechanism has an exhaust electric S-VT 24. The exhaust electric S-VT 24 is configured to continuously change the rotation phase of the exhaust camshaft within a predetermined angle range. Thereby, the valve opening timing and the valve closing timing of the exhaust valve 22 continuously change. Note that the valve operating mechanism of the exhaust valve 22 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, hot burned gas is confined in the combustion chamber 17. That is, an internal EGR (Exhaust Gas Recirculation) gas is introduced into the combustion chamber 17. Further, the residual gas in the combustion chamber 17 is scavenged by adjusting the length of the overlap period.

  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 facing the combustion chamber 17 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 disposed in parallel to the central axis X <b> 1 of the cylinder 11. The injection axis X2 of the injector 6 is shifted from the central axis X1. The injection axis of the injector 6 coincides with the position of the convex portion 311 of the cavity 31. The injector 6 faces the cavity 31. The injection axis of the injector 6 may coincide with the central axis X1 of the cylinder 11. Even in this case, it is desirable that the injection axis of the injector 6 and the position of the convex portion 311 of the cavity 31 coincide with each other.

  Although not shown in detail, the injector 6 is constituted by a multi-injection type fuel injection valve having a plurality of injection holes. As shown by a two-dot chain line in FIG. 2, the injector 6 injects the fuel so that the fuel spray spreads radially from the center of the combustion chamber 17 and spreads obliquely downward from the ceiling of the combustion chamber 17. 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 on the intake side across the central axis X1 of the cylinder 11 as shown in FIG. The spark plug 25 is adjacent to the injector 6. 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. The electrode of the spark plug 25 faces the combustion chamber 17 and is located near the ceiling surface of the combustion chamber 17.

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

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

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

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

  The engine 1 has a swirl generator that generates a swirl flow in the combustion chamber 17. As shown in FIG. 3, the swirl generating unit is a swirl control valve 56 attached to the intake passage 40. The swirl control valve 56 is disposed in the secondary passage 402 among 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 counterclockwise in FIG. 3 as indicated by the arrows (see also the white arrows in FIG. 2).

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

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

  An exhaust gas purification system having a plurality of catalytic converters is disposed in the exhaust passage 50. Although not shown, the upstream catalytic converter is disposed in the engine room. The upstream catalytic converter includes a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512. The downstream catalytic converter is disposed outside the engine room. The downstream catalytic converter has a three-way catalyst 513. The exhaust gas purification system is not limited to the configuration shown in the figure.

  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.

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

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

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

  The ECU 10 determines the operating state of the engine 1 based on these detection signals and calculates the control amount of each device. The ECU 100 sends control signals relating to the calculated control amount to the injector 6, spark plug 25, intake electric S-VT 23, exhaust electric S-VT 24, fuel supply system 61, throttle valve 43, EGR valve 54, supercharger 44. Output to the electromagnetic clutch 45, the air bypass valve 48, and the swirl control valve 56. For example, the ECU 10 adjusts the boost pressure by adjusting the opening of the air bypass valve 48 based on the differential pressure across the turbocharger 44 obtained from the detection signals of the first pressure sensor SW3 and the second pressure sensor SW5. adjust. Further, the ECU 10 adjusts the opening degree of the EGR valve 54 based on the differential pressure across the EGR valve 54 obtained from the detection signal of the EGR differential pressure sensor SW15, whereby the amount of external EGR gas introduced into the combustion chamber 17 is adjusted. Adjust. Details of control of the engine 1 by the ECU 10 will be described later.

(Engine operating range)
FIG. 5 exemplifies operation region maps 501 and 502 of the engine 1. 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. 5, the rotation speed less than N1 is low rotation, the rotation speed N2 or more is high rotation, and the rotation speed N1 or more and less than N2 is medium rotation. For example, the rotational speed N1 may be about 1200 rpm, and the rotational speed N2 may be about 4000 rpm, for example. Further, the high load mid-rotation region (2) may be a region where the combustion pressure is 900 kPa or more. In FIG. 5, for easy understanding, the operation region maps 501 and 502 of the engine 1 are drawn in two parts. A map 501 shows the state of the air-fuel mixture and the combustion mode in each region, and the drive region and non-drive region of the supercharger 44. A map 502 shows the opening degree of the swirl control valve 56 in each region. Note that a two-dot chain line in FIG. 5 indicates a road-load line of the engine 1.

  The engine 1 compresses itself in a low load region (1) -1, a medium load region (1) -2, and a high load medium rotation region (2) mainly for improving fuel consumption and exhaust gas performance. Combustion by ignition. The engine 1 also performs combustion by spark ignition in other regions, specifically, in the high load low rotation region (3) and the high rotation region (4). Hereinafter, the operation of the engine 1 in each region will be described in detail with reference to the fuel injection timing and the ignition timing shown in FIG.

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

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

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

  By adjusting the calorific value of the SI combustion, the temperature variation in the combustion chamber 17 before the start of compression can be absorbed. Even if the temperature in the combustion chamber 17 before the start of compression varies, the self-ignition timing can be controlled by adjusting the SI combustion start timing by adjusting the ignition timing, for example.

  When performing SPCCI combustion, the spark plug 25 ignites the air-fuel mixture at a predetermined timing near the compression top dead center, thereby starting combustion by flame propagation. Heat generation during SI combustion is milder than heat generation during CI combustion. Therefore, the rising slope of the waveform of the heat generation rate is relatively small. Although not shown, the pressure fluctuation (dp / dθ) in the combustion chamber 17 is also gentler during SI combustion than during CI combustion.

  When the temperature and pressure in the combustion chamber 17 are increased by SI combustion, the unburned mixture is self-ignited. In the example of FIG. 6, the slope of the heat generation rate waveform 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 inclination of the waveform of the heat generation rate due to CI combustion becomes 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.

  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.

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

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

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

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

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

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

  When the engine 1 operates in the low load region (1) -1, the injector 6 basically injects fuel into the combustion chamber 17 during the intake stroke and during the compression stroke (reference number). 6011, 6012). The fuel injected during the intake stroke diffuses throughout the combustion chamber 17 until the ignition timing. The fuel injected during the intake stroke forms an air-fuel mixture at the center and the outer periphery. The fuel injected during the compression stroke is transported to the vicinity of the spark plug 25 at the center of the combustion chamber 17 by the swirl flow without much diffusion because the time until the ignition timing is short. The fuel injected during the compression stroke forms a central air-fuel mixture together with a part of the fuel injected during the intake stroke. The air-fuel mixture is stratified in the central portion and the outer peripheral portion of 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.

  When the engine 1 operates in the low load region (1) -1, the fuel injection timing and the number of injections are changed according to the load of the engine 1. Specifically, when the load on the engine 1 is low, the number of fuel injections during the compression stroke increases and the completion timing of fuel injection is retarded. That is, when the load on the engine 1 is low, the number of fuel injection divisions performed during the compression stroke is increased and the timing of the last fuel injection is retarded. When the load on the engine 1 is low, the amount of fuel supplied into the combustion chamber 17 is reduced. However, the number of fuel injections performed during the compression stroke is increased and the timing of the last fuel injection is retarded so that The diffusion of the fuel injected into the fuel is suppressed. As a result, the size of the air-fuel mixture layer formed at the center of the combustion chamber 17 and having a relatively high fuel concentration is reduced.

  When the load on the engine 1 is high, the number of fuel injections during the compression stroke is reduced and the injection timing is advanced. As a result of advancing the fuel injection timing, fuel may be dividedly injected during the intake stroke without performing fuel injection during the compression stroke. When the load on the engine 1 is high, batch injection may be performed during the intake stroke. When the load on the engine 1 increases, the amount of fuel supplied into the combustion chamber 17 increases, and the fuel is easily diffused by advancing the timing of fuel injection. As a result, the size of the air-fuel mixture layer formed at the center of the combustion chamber 17 and having a relatively high fuel concentration increases.

  In the low load region (1) -1, the engine 1 leans the air-fuel mixture from the stoichiometric air-fuel ratio and performs SPCCI combustion. Therefore, the low load region (1) -1 can be referred to as a "SPCCI lean region". .

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

  Reference numeral 602 in FIG. 6 indicates fuel injection timing (reference numerals 6021 and 6022) and ignition timing (reference numeral 6023) when the engine 1 is operating in the operating state 602 in the middle load region (1) -2, and An example of each combustion 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.

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

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

  When the engine 1 is operated in the medium load region (1) -2, the injector 6 performs the first injection (that is, the first injection, reference 6021) and the second injection (that is, the second injection, reference 6022) twice. The fuel is injected into the combustion chamber 17 separately. The front-stage injection injects fuel at a timing away from the ignition timing, and the rear-stage injection injects fuel at a timing close to the ignition timing. For example, the first-stage injection may be performed in the first half of the compression stroke, and the second-stage injection may be performed in the second half of the compression stroke, for example. The first half and the second half of the compression stroke may be respectively the first half and the second half when the compression stroke is divided into two equal parts with respect to the crank angle. For example, the front injection may be started at 100 ° CA before compression top dead center, and the rear injection may be started at 70 ° CA before compression top dead center, for example.

  The injector 6 has a plurality of nozzle holes whose nozzle shafts are inclined with respect to the central axis (that is, the cylinder axis) X1 of the cylinder 11, and radiates fuel radially outward from the center of the combustion chamber 17. Spray. When the injector 6 performs the pre-stage injection within the first half of the compression stroke, the piston 3 is away from the top dead center, so that the injected fuel spray rises toward the top dead center. Reaches the outside of the cavity 31. A region outside the cavity 31 forms a squish area 171 (see FIG. 2). The fuel injected by the pre-stage injection stays in the squish area 171 while the piston 3 ascends, and forms an air-fuel mixture in the squish area 171.

  When the injector 6 performs post-stage injection in the latter half of the compression stroke, the injected fuel spray enters the cavity 31 because the piston 3 is close to top dead center. The fuel injected by the latter-stage injection forms an air-fuel mixture in the region within the cavity 31. Here, the “region in the cavity 31” is a region obtained by combining the region from the projection surface obtained by projecting the opening of the cavity 31 onto the roof of the combustion chamber 17 to the opening of the cavity 31 and the region in the cavity 31. May mean. The region in the cavity 31 can also be referred to as a region other than the squish area 171 in the combustion chamber 17.

  As fuel is injected into the cavity 31 by the post-injection, gas flow occurs in the region within the cavity 31. If the time until the ignition timing is long, the turbulent energy in the combustion chamber 17 is attenuated as the compression stroke proceeds. However, since the injection timing of the second-stage injection is closer to the ignition timing than the first-stage injection, the spark plug 25 ignites the air-fuel mixture in the region within the cavity 31 while the turbulent energy in the cavity 31 is high. be able to. Thereby, the combustion speed of SI combustion increases. When the combustion speed of SI combustion is increased, SI combustion is stabilized, so that the controllability of CI combustion by SI combustion is enhanced.

  When the injector 6 performs the front-stage injection and the rear-stage injection, a substantially homogeneous mixture having an excess air ratio λ of 1.0 ± 0.2 is formed in the combustion chamber 17 as a whole. The 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. The fuel injected by the latter-stage injection mainly undergoes SI combustion. The fuel injected by the pre-stage injection mainly undergoes CI combustion. When the pre-injection is performed during the compression stroke, it is possible to prevent the fuel injected by the pre-injection from inducing abnormal combustion such as premature ignition. Moreover, the fuel injected by the latter stage injection can be stably burned by flame propagation.

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

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

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

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

  Reference numeral 603 in FIG. 6 denotes a fuel injection timing (reference numerals 6031 and 6032) and an ignition timing (reference numeral 6033) when the engine 1 is operating in the operating state 603 in the high load mid-rotation region (2), and An example of each combustion waveform (reference numeral 6034) is shown.

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

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

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

  When the engine 1 is operated in the high load mid-rotation region (2), the injector 6 performs the first stage injection (that is, the first injection, reference numeral 6031) and the second stage injection (that is, the second injection, reference numeral 6032) in the compression stroke. The fuel is injected into the combustion chamber 17 in two steps. For example, the first-stage injection may be performed in the first half of the compression stroke, and the second-stage injection may be performed in the second half of the compression stroke, for example. Specifically, the front stage injection may start fuel injection, for example, at 125 ° CA before compression top dead center, and the rear stage injection may start, for example, at 85 ° CA before compression top dead center.

  When a strong swirl flow is generated in the combustion chamber 17, the fuel injected into the combustion chamber 17 when the first stage injection is performed in the first half of the compression stroke is performed as shown in the left diagram of FIG. 9. It is bent by the flow and the penetration decreases. The fuel of the pre-stage injection stays in the central portion of the combustion chamber 17 and mainly forms an air-fuel mixture in the central portion of the combustion chamber 17. As will be described later, the air-fuel mixture in the center portion is mainly burned by SI combustion.

  On the other hand, as shown in the right diagram of FIG. 9, when post-stage injection is performed in the second half of the compression stroke, the piston is raised in the second half of the compression stroke, and the swirl flow is also attenuated. The fuel injected into the combustion chamber 17 reaches the outer periphery of the combustion chamber 17. The fuel of the post-injection mainly forms an air-fuel mixture at the outer peripheral portion of the combustion chamber 17. The air-fuel mixture at the outer peripheral portion is mainly burned by CI combustion, as will be described later.

  Then, by the fuel injection that performs the front stage injection and the rear stage injection, the fuel concentration of the air-fuel mixture in the outer peripheral portion of the combustion chamber 17 is higher than the fuel concentration of the air-fuel mixture in the central portion, and the fuel amount of the air-fuel mixture in the outer peripheral portion The fuel amount of the air-fuel mixture in the center is set to be larger. What is necessary is just to make the injection quantity of front | former stage injection larger than the injection quantity of back | latter stage injection. As an example, the ratio between the injection amount of the upstream injection and the injection amount of the subsequent injection may be 7: 3.

  When the engine 1 is operated in the high load mid-rotation region (2), for example, as shown in FIG. 10, the air-fuel ratio in the center portion where the spark plug 25 is disposed preferably has an excess air ratio λ of 1 or less. The air-fuel mixture at the outer peripheral portion has an excess air ratio λ of 1 or less, preferably 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 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 and the stoichiometric air-fuel ratio or less, preferably 11 or more and 12 or less. When the excess air ratio λ at the outer peripheral portion of the combustion chamber 17 is less than 1, the amount of fuel in the air-fuel mixture increases at the outer peripheral portion, so that the temperature can be lowered by 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 and the stoichiometric air-fuel ratio or less, preferably 12.5 or more and 13 or less.

  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). 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.

  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.

  FIG. 11 shows the concept of combustion in the high load mid-rotation region (2). 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. 11. 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.

  As described above, 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 shown by the black arrow in FIG. As shown in Fig. 2, 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. Is arranged on the intake side and the swirl flow is in the counterclockwise direction in FIG. 11, the SI combustion flame flows from the intake-rear side portion to the exhaust-rear side portion and the exhaust-front side. It leads to the intake-front side part through the part. Due to the heat generated by the SI combustion and the pressure increase due to flame propagation, the unburned mixture undergoes compression ignition at the outer peripheral portion of the intake-front side portion and CI combustion starts as shown by the broken arrow in FIG.

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

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

  Here, FIG. 12 compares the combustion waveforms of SPCCI combustion when the opening degree of the swirl control valve (SCV) is changed in the high load mid-rotation region (2). The combustion waveform shows the change in the heat generation rate with respect to the crank angle. The opening degree of the swirl control valve 56 is represented by the opening ratio with respect to the fully open section of the secondary passage 402, as in FIG.

  First, as shown by a broken line in FIG. 12, when the opening of the swirl control valve 56 is fully opened (that is, the opening ratio is 100%), no swirl flow is generated in the combustion chamber 17. After the spark plug 25 ignites the air-fuel mixture, combustion by flame propagation starts, but the rise of SI combustion becomes gradual. If swirl flow does not occur, CI combustion does not occur and only SI combustion occurs. As a result, the combustion center of gravity is separated from the compression top dead center, and the combustion period is lengthened.

  When the opening of the swirl control valve 56 is fully closed (that is, the opening ratio is 0%), 5%, and 10%, the rise of SI combustion is steeper in the combustion waveform than when the swirl control valve 56 is fully opened. become. The combustion rate of SI combustion increases. When the swirl flow is generated, CI combustion occurs after the start of SI combustion. By performing SPCCI combustion, the combustion center of gravity approaches from the compression top dead center, and the combustion period is shortened.

  When the opening of the swirl control valve 56 is set to 15%, the rise of SI combustion becomes gentle in the combustion waveform. Thereafter, although CI combustion occurs, the combustion period becomes relatively long.

  From FIG. 12, it is effective to make the opening degree of the swirl control valve 56 less than 15% in order to bring the combustion center of gravity closer to the compression top dead center and shorten the combustion period. Moreover, as shown in FIG. 8, if the opening degree of the swirl control valve 56 is less than 15%, the swirl ratio becomes 4 or more. Therefore, when the engine 1 is operating in the high load mid-rotation region (2), the opening degree of the swirl control valve 56 is less than 15% (that is, 0 to 15%), and the swirl ratio is 4 or more (that is, SPCCI combustion can be performed appropriately by setting the pressure to about 4-6.

  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, so the high load mid-rotation region (2) is “SPCCIλ ≦ 1 region”. Can be called.

(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. In the high load low rotation region (3), as in the high load medium rotation region (2), for example, if fuel is injected into the combustion chamber 17 in the first half of the intake stroke or compression stroke, the reaction of the fuel proceeds excessively. May cause premature ignition. When the engine 1 is operating in the high-load low-rotation region (3), it is difficult to perform the aforementioned SPCCI combustion.

  Therefore, when the engine 1 is operating in the high load low rotation region (3), the engine 1 performs SI combustion instead of SPCCI combustion.

  Reference numeral 604 in FIG. 6 denotes a fuel injection timing (reference numeral 6041) and an ignition timing (reference numeral 6042) and a combustion waveform when the engine 1 is operating in the operating state 604 in the high load low rotation region (3). (Reference numeral 6043) Each example 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 low rotation region (3). The engine 1 reduces the amount of EGR gas as the load increases. At full open load, the 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). The excess air ratio λ may be greater than or equal to the excess air ratio λ, preferably greater than the excess air ratio λ in the high load mid-rotation region (2).

  When the engine 1 operates in the high-load low-rotation region (3), the injector 6 has a combustion chamber 17 at a timing within a period from the end of the compression stroke to the beginning of the expansion stroke (hereinafter, this period is referred to as a retard period). The fuel is injected into the inside (reference numeral 6041). 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. Further, the initial stage of the expansion stroke may be an initial stage when the expansion stroke is divided into three equal parts in the initial stage, the middle period, and the final stage.

  By making the fuel injection timing late, it is possible to avoid pre-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. 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 6042). The spark plug 25 may ignite after compression top dead center, for example. 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 retards the fuel injection timing as the rotational speed of the engine 1 decreases. The fuel injection may end during 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 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.

  As illustrated in FIG. 13, when the injector 6 injects fuel in the period from the end of the compression stroke to the early stage of the expansion stroke, the piston 3 is located near the compression top dead center. While mixing, it 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. The fuel injected during the retard period can be quickly transported to the vicinity of the spark plug 25.

  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 region (3), the opening of the swirl control valve (SCV) 56 is larger than when operating in the high load medium rotation region (2). The opening degree of the swirl control valve 56 may be about 50% (that is, half open), for example.

  As shown 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 caused to flow in the circumferential direction, away from the vicinity of the spark plug 25, and the fuel cannot be quickly transported to the vicinity of the spark plug 25. Therefore, when the engine 1 is operated in the high load low rotation region (3), the swirl flow is weaker than that in the high load medium rotation region (2). As a result, the fuel can be quickly transported to the vicinity of the spark plug 25, so that the ignitability of the air-fuel mixture can be improved and the SI combustion can be stabilized.

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

(High rotation area (4))
When the rotational speed of the engine 1 is high, the time required for the crank angle to change by 1 ° is shortened. Therefore, for example, in the high rotation region in the high load region, as described above, it is difficult to stratify the air-fuel mixture in the combustion chamber 17 by performing the divided injection during the compression stroke. 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 605 in FIG. 6 denotes a fuel injection timing (reference numeral 6051) and an ignition timing (reference numeral 6052) when the engine 1 is operating in the operating state 605 in the high speed region (4), and a combustion waveform (reference numeral 6053) An example of each 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 rotation region (4). The engine 1 reduces the amount of EGR gas as the load increases. At full open load, the EGR gas may be zero.

  When the engine 1 is operated in the high speed region (4), the swirl control valve (SCV) 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 high load region including 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. In the operation state 6051, the load of the engine 1 is high, so the fuel injection amount is large. The fuel injection period changes according to the fuel injection amount. 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 rotation speed, the fuel vaporization time can be ensured as long as possible, so that unburned loss can be reduced and soot generation can be suppressed.

  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 6052).

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

(Comparison of engine control in each operation area)
First, when comparing the low load region (1) -1 with the high load mid-rotation region (2), as shown in the map 501 in FIG. While the excess ratio λ is set to a value exceeding 1, the excess air ratio λ of the air-fuel mixture is set to 1 or less in the high load mid-rotation region (2). In the low load region (1) -1, fuel efficiency can be improved. On the other hand, in the high load mid-rotation region (2), a sense of torque with elongation can be obtained.

  Further, in the low load region (1) -1, the fuel concentration of the air-fuel mixture at the center portion of the combustion chamber 17 is made higher than the fuel concentration of the air-fuel mixture at the outer peripheral portion. In contrast, 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 made higher than the fuel concentration of the air-fuel mixture at the central portion. In the low load region (1) -1, since the fuel concentration of the air-fuel mixture to be ignited is high, it is possible to improve the ignitability of SI combustion and stabilize SI combustion. In the high load mid-rotation region (2), it is avoided that the CI combustion is started early because the temperature of the outer peripheral portion is lowered, so that the CI combustion can be started after the SI combustion is sufficiently performed. it can. This is advantageous for suppressing combustion noise and can suppress variation in torque between cycles.

  In addition, the point which closes the swirl control valve 56 in each of the low load area | region (1) -1 and the high load middle rotation area | region (2) is the same.

  Next, when comparing the high load low rotation region (3) and the high load medium rotation region (2), as shown in FIG. In contrast, in the high-load low-rotation region (3), the combustion is performed in the period from the late stage of the compression stroke to the initial stage of the expansion stroke, which is retarded from the injection start timing of the high-load medium rotation region (2). Inject fuel into the room. In the high load mid-rotation region (2), the air-fuel mixture can be stratified in the central portion and the outer peripheral portion of the combustion chamber 17. In the high load low rotation region (3), pre-ignition can be avoided.

  Further, as shown in a map 501 in FIG. 5, in the high load low rotation region (3), the excess air ratio λ of the air-fuel mixture is set to approximately 1, whereas in the high load medium rotation region (2). The air excess ratio λ of the air-fuel mixture is set to 1 or less. In the high-load low-rotation region (3), while improving the torque and improving the fuel efficiency, in the high-load mid-rotation region (2) where the rotational speed is relatively high, it is possible to obtain an extended torque feeling. it can.

  Further, in the high load low rotation region (3), the opening degree of the swirl control valve 56 is made half open. On the other hand, the swirl control valve 56 is closed in the high load mid-rotation region (2). In the high-load low-rotation region (3), by reducing the swirl flow, the fuel spray can be quickly transported to the vicinity of the spark plug 25, while avoiding premature ignition and ignitability of SI combustion. The stability of SI combustion can be improved. On the other hand, in the high load mid-rotation region (2), by strengthening the swirl flow, SI combustion can be sufficiently performed in SPCCI combustion, and it is advantageous for suppressing combustion noise and improving fuel consumption.

  Next, comparing the high rotation region (4) with the high load medium rotation region (2), as shown in FIG. 6, in the high load medium rotation region (2), a plurality of times during the compression stroke period. In contrast to fuel injection, in the high rotation region (4), fuel injection is started at a timing advanced from the injection start timing of the high load medium rotation region (2). In the high load mid-rotation region (2), the air-fuel mixture can be stratified in the central portion and the outer peripheral portion of the combustion chamber 17. In the high rotation region (4), a homogeneous or substantially homogeneous mixture can be formed, and unburned loss can be reduced and soot generation can be suppressed.

  Further, as shown in the map 502 of FIG. 5, the swirl control valve 56 is fully opened in the high rotation region (4), whereas the swirl control valve 56 is closed in the high load medium rotation region (2). . In the high speed region (4), pump loss can be reduced by not closing the swirl control valve 56. On the other hand, in the high load mid-rotation region (2), by increasing the swirl flow, SI combustion can be sufficiently performed in SPCCI combustion, which is advantageous for suppressing combustion noise and improving fuel consumption.

  Next, comparing the medium load region (1) -2 and the high load low rotation region (3), as shown in the map 502 of FIG. 5, in the medium load region (1) -2, the swirl control valve In contrast, the swirl control valve 56 is half-opened in the high-load low-rotation region (3). In the middle load region (1) -2, by closing the swirl control valve 56, SI combustion can be sufficiently performed in SPCCI combustion, which is advantageous for suppressing combustion noise and improving fuel consumption. On the other hand, in the high-load low-rotation region (3), the ignitability of SI combustion and the stability of SI combustion can be improved as described above by weakening the swirl flow.

  Further, as shown in FIG. 6, in the middle load region (1) -2, the first stage injection is performed in the first half of the compression stroke and the second stage injection is performed in the second half of the compression stroke, whereas the high load low rotation region ( In 3), fuel is injected into the combustion chamber in the period from the late stage of the compression stroke to the early stage of the expansion stroke. In the medium load region (1) -2, a homogeneous or substantially homogeneous mixture can be formed in the entire combustion chamber 17. In the high load low rotation region (3), pre-ignition can be avoided.

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

  In step S3, the ECU 10 determines whether or not the engine 1 is operated in the “SPCCI lean region” (that is, the low load region (1) -1). When the determination in step S3 is YES, the process proceeds to step S8, and when the determination is NO, the process proceeds to step S4.

  In step S4, the ECU 10 determines whether or not the engine 1 operates in the “SPCCIλ = 1 region” (that is, the medium load region (1) -2). When the determination in step S4 is YES, the process proceeds to step S9, and when the determination is NO, the process proceeds to step S5.

  In step S5, the ECU 10 determines whether or not the engine 1 operates in the “SPCCIλ ≦ 1 region” (that is, the high load mid-rotation region (2). If the determination in step S5 is YES, the process proceeds to step S10. If NO, the process proceeds to step S6.

  In step S6, the ECU 10 determines whether or not the engine 1 operates in the “retarded SI region” (that is, the high load low rotation region (3). If the determination in step S6 is YES, the process proceeds to step S11. Proceed, if no, the process proceeds to step S7.

  In step S7, the ECU 10 determines whether or not the operation region of the engine 1 is the “intake SI region” (that is, the high rotation region (4). If the determination in step S7 is YES, the process proceeds to step S12. Proceed, if NO, the process returns to step S1.

  In step S8, the ECU 10 outputs a control signal to the swirl control valve (SCV) 56 so as to close the valve. Further, as indicated by reference numeral 601 in FIG. 6, the ECU 10 outputs a control signal to the injector 6 so that the pre-stage injection is performed during the intake stroke and the post-stage injection is performed during the compression stroke. A stratified mixture can be formed in the combustion chamber 17 where a strong swirl flow is generated. In subsequent step S13, the ECU 10 outputs a control signal to the spark plug 25 so as to perform ignition at a predetermined timing before the compression top dead center. Thereby, the engine 1 performs SPCCI combustion.

  In step S9, the ECU 10 outputs a control signal to the swirl control valve 56 so as to close the valve. Further, as indicated by reference numeral 602 in FIG. 6, the ECU 10 outputs a control signal to the injector 6 so as to perform the front injection and the rear injection in the compression stroke. A mixture of λ = 1 can be formed in the combustion chamber 17 where a strong swirl flow is generated. In the subsequent step S13, the ECU 10 outputs a control signal to the spark plug 25 so as to perform ignition at a predetermined timing before the compression top dead center. Thereby, the engine 1 performs SPCCI combustion.

  In step S10, the ECU 10 outputs a control signal to the swirl control valve 56 so as to close the valve. Further, the ECU 10 outputs a control signal to the injector 6 so that fuel is dividedly injected in the compression stroke (see reference numerals 6031 and 6032 in FIG. 6). A stratified mixture can be formed in the combustion chamber 17 where a strong swirl flow is generated. In the subsequent step S13, the ECU 10 outputs a control signal to the spark plug 25 so as to perform ignition at a predetermined timing before the compression top dead center. Thereby, the engine 1 performs SPCCI combustion.

  In step S11, the ECU 10 outputs a control signal to the swirl control valve 56 so that the valve is half open. In step S13, the ECU 10 outputs a control signal to the injector 6 so that fuel injection is performed from the end of the compression stroke to the beginning of the expansion stroke, as indicated by reference numeral 604 in FIG. The ECU 10 outputs a control signal to the spark plug 25 so that ignition is performed at a predetermined timing after completion of fuel injection and after compression top dead center. Thereby, the engine 1 performs SI combustion.

  In step S12, the ECU 10 outputs a control signal to the swirl control valve 56 to open the valve. Further, the ECU 10 outputs a control signal to the injector 6 so as to perform fuel injection in the intake stroke. A homogeneous or substantially homogeneous mixture can be formed in the combustion chamber 17. In subsequent step S13, the ECU 10 outputs a control signal to the spark plug 25 so as to perform ignition at a predetermined timing before the compression top dead center. Thereby, the engine 1 performs SI combustion.

(Modification of combustion injection timing and ignition timing in each region)
FIG. 15 shows a modification of the combustion injection timing and the ignition timing in each region of the operation region maps 501 and 502 of FIG. Reference numerals 601, 602, 603, 604, 605, and 606 in FIG. 15 correspond to the operating states 601, 602, 602, 603, 604, 605, and 606 in FIG. 5, respectively. The operating state 606 corresponds to an operating state with a high rotational speed in the high load mid-rotation region (2).

  When the engine 1 is operated in the operation state 601 in the low load region (1) -1, the injector 6 injects fuel into the combustion chamber 17 in a plurality of times during the compression stroke (reference numeral 6015, 6016). Due to the split injection of fuel and the strong swirl flow in the combustion chamber 17, the air-fuel mixture is stratified in the central portion and the outer peripheral portion of the combustion chamber 17 as described above.

  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 (see 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. When the SI combustion is stabilized, the CI combustion starts at an appropriate timing (see the combustion waveform 6014). 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.

  When the engine 1 is operated in the operation state 602 in the medium load region (1) -2, the injector 6 performs fuel injection during the intake stroke (reference numeral 6025) and fuel injection during the compression stroke (reference numeral 6026). I do. By performing the first injection 6025 during the intake stroke, the fuel can be distributed substantially uniformly in the combustion chamber 17. By performing the second injection 6026 during the compression stroke, when the load is high in the middle load region (1) -2, the temperature in the combustion chamber 17 is lowered by the latent heat of vaporization of the fuel to cause abnormal combustion such as knocking. To prevent. For example, the ratio of the injection amount of the first injection 6025 and the injection amount of the second injection 6026 may be 95: 5. The second injection 6026 may be omitted in the low load operating state in the middle load region (1) -2.

  As a result of the injector 6 performing the first injection 6025 during the intake stroke and the second injection 6026 during the compression stroke, the excess air ratio λ as a whole in the combustion chamber 17 is 1. An air-fuel mixture that is 0 ± 0.2 is formed. Since the fuel concentration of the air-fuel mixture is substantially uniform, it is possible to improve fuel efficiency by reducing unburned loss and 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 at the target timing and performs CI combustion (see combustion waveform 6024).

  When the engine 1 is operated in the low-rotation-side operation state 603 in the high load mid-rotation region (2), the injector 6 injects fuel in the intake stroke (reference numeral 6035), and injects fuel at the end of the compression stroke. Injection is performed (reference numeral 6036).

  The pre-injection 6035 that starts in the intake stroke may start fuel injection in the first half of the intake stroke. The first half of the intake stroke may be the first half when the intake stroke is divided into two equal parts. Specifically, the pre-injection may start fuel injection at 280 ° CA before top dead center.

  When the injection start of the front injection 6035 is in the first half of the intake stroke, as shown in FIG. 16, a part of the fuel enters the squish area 171 of the combustion chamber 17 by the fuel spray hitting the opening edge of the cavity 31. The remaining fuel enters the area within the cavity 31. The swirl flow is strong at the outer periphery of the combustion chamber 17 and weak at the center. Therefore, a part of the fuel that has entered the squish area 171 enters the swirl flow, and the remaining fuel that has entered the region within the cavity 31 enters the inside of the swirl flow. The fuel that has entered the swirl flow remains in the swirl flow during the intake stroke to the compression stroke, and forms an air-fuel mixture for CI combustion at the outer peripheral portion of the combustion chamber 17. The fuel that has entered the swirl flow also remains inside the swirl flow during the intake stroke to the compression stroke, and forms an air-fuel mixture for SI combustion in the central portion of the combustion chamber 17.

  Similarly to the above, the air-fuel ratio in the central part 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 part 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 and the stoichiometric air-fuel ratio or less, preferably 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 and the stoichiometric air-fuel ratio or less, preferably 12.5 or more and 13 or less.

  The post-injection 6036 performed at the end of the compression stroke may start the fuel injection at 10 ° CA before top dead center, for example. 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 6035 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 6036 is performed immediately before the top dead center and burned. 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 the front | former stage injection 6035 and the injection quantity of the back | latter stage injection 6036 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 6037). 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. As shown in FIG. 11, the SI combustion flame rides on the strong swirl flow in the combustion chamber 17 and propagates in the circumferential direction. At a predetermined circumferential position in the outer peripheral portion of the combustion chamber 17, the unburned mixture undergoes compression ignition, and CI combustion starts (see combustion waveform 6034).

  When the engine 1 operates in the high-rotation-side operation state 606 in the high load mid-rotation region (2), the injector 6 starts fuel injection in the intake stroke (reference numeral 6061).

  The front injection 6061 that starts in the intake stroke may start fuel injection in the first half of the intake stroke in the same manner as the front injection 6035 in the operating state 603. Specifically, the front injection 6061 may start fuel injection at 280 ° CA before top dead center. The end of the front injection may exceed the intake stroke and be in the compression stroke. By starting the injection of the front injection 6061 in the first half of the intake stroke, an air-fuel mixture for CI combustion is formed in the outer peripheral portion of the combustion chamber 17 and an air-fuel mixture for SI combustion is formed in the central portion of the combustion chamber 17. can do. Since the rotational speed is high and abnormal combustion is unlikely to occur, the latter-stage injection 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 6062). The spark plug 25 performs ignition after the compression top dead center, for example. Thereby, SPCCI combustion is performed (see combustion waveform 6063).

  When the engine 1 is operated in the operation state 604 in the high-load low-rotation region (3), the injector 6 burns at each timing during the intake stroke and the retard period from the end of the compression stroke to the beginning of the expansion stroke. Fuel is injected into the chamber 17 (reference numerals 6044 and 6045). By injecting fuel in two steps, the amount of fuel injected within the retard period can be reduced. By injecting fuel during the intake stroke (reference numeral 6044), it is possible to secure a sufficient time for forming the air-fuel mixture. Further, by injecting fuel during the retard period (reference numeral 6045), the flow in the combustion chamber 17 can be increased immediately before ignition, which is advantageous for stabilizing SI combustion. This form of fuel injection is particularly effective when the geometric compression ratio of the engine 1 is low.

  The spark plug 25 ignites the air-fuel mixture at a timing near the compression top dead center after fuel injection (reference numeral 6042). The spark plug 25 may ignite after compression top dead center, for example. The air-fuel mixture undergoes SI combustion in the expansion stroke. Since SI combustion starts in the expansion stroke, CI combustion does not start (see combustion waveform 6043).

  The fuel injection timing (reference numeral 6051) and the ignition timing (reference numeral 6052) when the engine 1 is operated in the operating state 605 in the high speed region (4) are the same as those in FIG. When the engine 1 operates in the high speed region (4), SI combustion is performed (see reference numeral 6053).

  Note that the fuel injection timing and ignition timing shown in FIG. 6 and the fuel injection timing and ignition timing shown in FIG. 17 can be interchanged in the same region. For example, the fuel injection timing and ignition timing shown in FIG. 17 are adopted in the high load mid-rotation region (2), while the fuel injection timing and ignition timing shown in FIG. 6 are adopted in the high load low rotation region (3). It may be adopted.

  In addition, when the fuel injection timing shown in FIG. 17 is adopted, steps S8 to S12 in the flow of FIG. 14 may be appropriately changed.

(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.

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

1 Engine 10 ECU (control unit)
17 Combustion chamber 171 Squish area 25 Spark plug (ignition part)
3 Piston 31 Cavity 401 Primary passage (first intake passage)
402 Secondary passage (second intake passage)
56 Swirl control valve (swirl generator)
6 Injector (fuel injection part)

Claims (7)

An engine having a combustion chamber;
An igniter disposed in the center of the combustion chamber;
A fuel injection section disposed facing the combustion chamber;
A controller that connects the ignition unit and the fuel injection unit and outputs a control signal to each of the ignition unit and the fuel injection unit; and
Wherein, when operating in the first speed region in the high load region where the engine is set in advance, the fuel concentration of the mixture of the outer peripheral portion which is around the center portion of the front Symbol combustion chamber, the central and darker than the fuel concentration of the mixture parts, together with the fuel amount of the mixture of the outer peripheral portion, and outputs a control signal to the fuel injection unit so as to be larger than the amount of fuel-air mixture of the central portion, the By outputting a control signal to the ignition unit so as to ignite the air-fuel mixture in the central part after completing the injection of all the fuel to be injected from the fuel injection unit during one combustion cycle of the engine, When operating in the first rotation region in the high load region , after the air-fuel mixture starts SI combustion by flame propagation by ignition of the ignition unit, the unburned air-fuel mixture performs CI combustion by compression ignition,
When the engine operates in a second rotation region having a lower rotational speed than the first rotation region in the high load region, the air-fuel mixture performs SI combustion by flame propagation by ignition of the ignition unit,
The control unit outputs a control signal to the fuel injection unit so as to inject fuel into the combustion chamber a plurality of times during a compression stroke when the engine operates in the first rotation region in the high load region. And
The control unit also adjusts the compression ignition timing by adjusting the heat generation amount of the SI combustion by adjusting the ignition timing of the ignition unit when the engine operates in the first rotation region in the high load region. A control device for a premixed compression ignition engine that controls the engine. The control device for a premixed compression ignition engine according to claim 1,
When the engine operates in the first rotation region in the high load region , the control unit performs a first injection that forms an air-fuel mixture for SI combustion in the central portion in the first half of the compression stroke, and A control device for a premixed compression ignition type engine that outputs a control signal to the fuel injection unit so that a second injection that forms a mixture for CI combustion is performed in the latter half of the compression stroke. An engine having a combustion chamber;
An igniter disposed in the center of the combustion chamber;
A fuel injection section disposed facing the combustion chamber;
A controller that connects the ignition unit and the fuel injection unit and outputs a control signal to each of the ignition unit and the fuel injection unit; and
Wherein, when operating in the first speed region in the high load region where the engine is set in advance, the fuel concentration of the mixture of the outer peripheral portion which is around the center portion of the front Symbol combustion chamber, the central and darker than the fuel concentration of the mixture parts, together with the fuel amount of the mixture of the outer peripheral portion, and outputs a control signal to the fuel injection unit so as to be larger than the amount of fuel-air mixture of the central portion, the By outputting a control signal to the ignition unit so as to ignite the air-fuel mixture in the central part after completing the injection of all the fuel to be injected from the fuel injection unit during one combustion cycle of the engine, When operating in the first rotation region in the high load region , after the air-fuel mixture starts SI combustion by flame propagation by ignition of the ignition unit, the unburned air-fuel mixture performs CI combustion by compression ignition,
When the engine operates in a second rotation region having a lower rotational speed than the first rotation region in the high load region, the air-fuel mixture performs SI combustion by flame propagation by ignition of the ignition unit,
When the engine operates in the first rotation region in the high load region, the control unit outputs a control signal to the fuel injection unit so as to start fuel injection into the combustion chamber during an intake stroke period. ,
The control unit also adjusts the compression ignition timing by adjusting the heat generation amount of the SI combustion by adjusting the ignition timing of the ignition unit when the engine operates in the first rotation region in the high load region. A control device for a premixed compression ignition engine that controls the engine. In the control device of the premixed compression ignition engine according to any one of claims 1 to 3,
A swirl generator for generating a swirl flow in the combustion chamber;
When the engine operates in the first rotation region in the high load region , the control unit is configured to generate a stronger swirl flow than when operating in the second rotation region in the high load region. A control device for a premixed compression ignition engine that outputs a control signal to a generator. In the control device of the premixed compression ignition engine according to any one of claims 1 to 4,
When the engine operates in the first rotation region in the high load region , the control unit reduces the fuel concentration of the entire air-fuel mixture in the combustion chamber to 1 or less in the excess air ratio λ, and the engine When operating in the second rotation region in the high load region, the fuel concentration of the mixture in the entire combustion chamber is 1 or less in the excess air ratio λ, and the air in the first rotation region in the high load region A control device for a premixed compression ignition engine with an excess ratio λ or more. In the control device of the premixed compression ignition type engine according to any one of claims 1 to 5,
The engine is a control device for a premixed compression ignition type engine having a geometric compression ratio of 13 or more and 20 or less. In the control device for the premixed compression ignition engine according to any one of claims 1 to 6,
The control device for a premixed compression ignition type engine, wherein the high load region of the engine is a region where the combustion pressure is 900 kPa or more.

Images