JP7415887B2 - engine system - Google Patents

Description

The technology disclosed herein relates to an engine system.

Compression ignition combustion (hereinafter sometimes referred to as CI (Compression Ignition) combustion) improves the thermal efficiency of the engine. Patent Document 1 describes that when the engine load is low, the air-fuel mixture is subjected to CI combustion, more precisely HCCI (Homogeneous Charged Compression Ignition) combustion, and when the engine load is high, the mixture is burned using a spark plug. , an engine that performs SI (Spark Ignition) combustion of an air-fuel mixture is described. This engine switches the combustion mode when the engine load changes. In SI combustion, the air-fuel mixture is ignited and then burned by flame propagation, so hereinafter, SI combustion and flame propagation combustion are synonymous.

Japanese Patent Application Publication No. 2012-215098

By the way, the inventors of the present application have conducted intensive research on HCCI combustion and found that the controlling factors for CI combustion are mainly the mixture temperature in the cylinder and the mass ratio of the intake air in the cylinder containing burnt gas to the fuel ( G/F), and by setting the in-cylinder temperature (T _IVC ) and G/F at the timing when the intake valve closes to the target T _IVC and G/F, it is possible to control the ignition timing and combustion period of HCCI. Understood. Furthermore, according to research by the present inventors, under a predetermined T _IVC , there is a gap between a G/F capable of SI combustion and a G/F capable of CI combustion, and each combustion It was found that the G/F required for the engine changes depending on the engine speed.

Note that SI combustion is possible when the combustion stability of SI combustion satisfies standards and abnormal combustion such as knocking and pre-ignition can be suppressed. For example, if G/F is too high (that is, if G/F becomes too lean), the combustion stability of SI combustion will not meet the standard.

The fact that CI combustion is possible means that the combustion stability of CI combustion satisfies standards and that abnormal combustion such as too steep combustion and misfire can be suppressed. For example, if G/F is too low (that is, if G/F becomes too rich), HCCI combustion tends to lead to abnormal combustion.

Even if the engine described in Patent Document 1 switches from HCCI combustion to SI combustion or from SI combustion to HCCI combustion in response to changes in engine load, as described above, SI combustion The G/F that is possible and the G/F that allows CI combustion change depending on the engine speed. As long as this is the case, when an attempt is made to switch the combustion mode, the G/F conditions corresponding to the combustion mode to be switched to are not satisfied, and appropriate switching becomes difficult. Unless the combustion mode can be appropriately switched, fuel efficiency cannot be improved.

As a result of further intensive research to solve the above problems, the inventors of the present application have changed from the first combustion mode such as HCCI combustion in which all air-fuel mixtures are self-ignited to combustion, to at least one combustion mode such as SI combustion and SPCCI combustion. When attempting to switch to the second combustion mode in which the air-fuel mixture in the air is subjected to flame propagation combustion, or from the second combustion mode to the first combustion mode, the G/F conditions to be satisfied are determined by changing the engine speed. We have newly discovered that it can be changed depending on the number.

Specifically, the technology disclosed herein relates to an engine system. This engine system is
An engine having a cylinder and a piston reciprocatably housed in the cylinder;
an injector attached to the engine and injecting fuel into the cylinder;
a spark plug attached to the engine and igniting a mixture of fuel, air, and intake air containing burnt gas;
a variable valve device connected to each of the intake valve and the exhaust valve and controlling the opening and closing of the intake valve and the exhaust valve so as to adjust the intake air filling amount;
electrically connected to the injector, the spark plug, and the variable valve device, and controlling each of the injector, the spark plug, and the variable valve device according to a required engine load of the engine; and a controller to
The controller is
predicting the mass ratio of intake air in the cylinder containing burnt gas to fuel;
When the requested engine has the first engine load and the engine speed is the first engine speed, when the mass ratio is predicted to be lower than the first G/F, at least a portion of the air-fuel mixture in the cylinder The injector and the spark plug are controlled so that flame propagation combustion occurs, while when the mass ratio is predicted to be higher than the first G/F, all of the air-fuel mixture in the cylinder is controlled by compression ignition combustion. controlling the injector;
When the engine speed is a second engine speed that is lower than the first engine speed under the first engine load, the mass ratio is lower than a second G/F that is smaller than the first G/F. When predicting, the injector and the spark plug are controlled so that at least a part of the air-fuel mixture in the cylinder undergoes flame propagation combustion, while when predicting that the mass ratio is higher than the second G/F, The injector is controlled so that all of the air-fuel mixture in the cylinder undergoes compression ignition combustion.

According to this configuration, when the engine speed is the first engine speed under the first engine load and the controller predicts that the mass ratio (G/F) is lower than the first G/F, the controller The injector and the spark plug are controlled so that at least a portion of the air-fuel mixture is combusted by flame propagation.

As the controller controls the injector and the spark plug, at least a portion of the air-fuel mixture in the cylinder undergoes flame propagation combustion. Here, all of the air-fuel mixture in the cylinder may undergo flame propagation combustion, that is, SI combustion. Alternatively, the air-fuel mixture in the cylinder may be subjected to SPCCI (Spark Controlled Compression Ignition) combustion, or SI combustion and SPCCI combustion may be switched depending on the engine speed and the like. When the air-fuel mixture undergoes SPCCI combustion, at least a portion of the air-fuel mixture in the cylinder undergoes flame propagation combustion, and the remainder undergoes compression ignition combustion. Here, when G/F is relatively low (G/F<first G/F), the combustion stability of flame propagation combustion increases. Furthermore, by reducing the burnt gas and reducing the G/F, the in-cylinder temperature is lowered and abnormal combustion is suppressed.

Furthermore, when the engine speed is the first engine speed under the first engine load, when the controller predicts that the G/F is higher than the first G/F, the controller predicts that all of the air-fuel mixture in the cylinder is compressed. Control the injector to ignite and burn.

The controller controls the injector, so that all of the air-fuel mixture in the cylinder undergoes compression ignition combustion. Here, when G/F is relatively high (G/F>first G/F), it is advantageous for improving the fuel efficiency of the engine. Furthermore, if the amount of burnt gas is increased and the G/F is increased, the in-cylinder temperature will increase, which will improve the combustion stability of compression ignition combustion.

In this way, when the engine speed is the first engine speed under the first engine load, the controller controls the flame propagation combustion (at least part of the air-fuel mixture The engine is configured to use either compression ignition combustion (combustion mode in which all air-fuel mixtures are combusted by compression ignition).

On the other hand, when the engine speed is a second engine speed that is smaller than the first engine speed at the first engine load, the controller controls the G/F to be lower than the second G/F that is smaller than the first G/F. When the G/F is predicted to be lower than the second G/F, the injector and spark plug are controlled so that at least a portion of the air-fuel mixture in the cylinder undergoes flame propagation combustion, while when the G/F is predicted to be higher than the second G/F, the The injector is controlled so that all of the air-fuel mixture undergoes compression ignition combustion.

That is, when the engine speed is the second engine speed (<first engine speed) under the first engine load, the controller controls the flame speed at the second G/F (<first G/F). It is configured to use either propagation combustion or compression ignition combustion.

According to the inventors of the present application, since the piston speed is slower at the second engine speed than at the first engine speed, a longer reaction time within the cylinder is ensured. Therefore, at the second engine speed, even if G/F is lower than the first engine speed, compression ignition combustion can be appropriately achieved.

Therefore, at the second engine speed, the magnitude of the second G/F, which is the boundary between flame propagation combustion and compression ignition combustion, is set smaller than the first G/F at the first engine speed. As a result, it becomes possible to expand the range of G/F in which compression ignition combustion can be performed to the lower G/F side. By expanding the G/F range, it becomes possible to switch from flame propagation combustion to compression ignition combustion more quickly, which in turn makes it possible to improve fuel efficiency.

The controller is configured to: when the engine speed is the first engine speed at the first engine load;
When predicting that the mass ratio is higher than the third G/F, which is larger than the first G/F, the injector is adjusted so that the injection center of gravity based on the fuel injection timing and injection amount in one cycle is at the first timing. controlling the spark plug and not driving the spark plug so that all the air-fuel mixture in the cylinder undergoes compression ignition combustion;
When predicting that the mass ratio is higher than the first G/F and lower than the third G/F, the injector is controlled so that the injection center of gravity is at a second timing later than the first timing, and , the spark plug may not be driven so that all the air-fuel mixture in the cylinder undergoes compression ignition combustion.

When the engine speed is the first engine speed under the first engine load and the controller predicts that the G/F is higher than the relatively large third G/F, the controller controls the injector and the variable valve device. do. The injector injects fuel so that the center of gravity of the injection coincides with the first timing. The first timing is a relatively early timing. By injecting fuel into the cylinder at an early timing, the fuel is diffused by a relatively strong intake flow, so that a homogeneous or nearly homogeneous air-fuel mixture is formed in the cylinder. When G/F is higher than the third G/F, all the air-fuel mixture in the cylinder undergoes compression ignition combustion, that is, HCCI combustion. For example, if the amount of burnt gas introduced into the cylinder is increased to increase the G/F, the temperature inside the cylinder will increase, which will improve the combustion stability of HCCI combustion. Furthermore, a large G/F is advantageous in improving the fuel efficiency of the engine.

When the engine speed is the first engine speed at the first engine load and the controller predicts that the G/F is higher than the first G/F and lower than the third G/F, the controller determines that the combustion is called flame propagation combustion. The injector and the variable valve device are controlled so that the third combustion mode, which is different from HCCI combustion, is realized. The G/F of the air-fuel mixture in the cylinder can quickly change between the first G/F and the third G/F.

The injector injects fuel so that the injection center of gravity is at a relatively late second timing. Note that the injector may inject the fuel all at once or in parts. The injection center of gravity can be defined, for example, by the mass center of gravity of fuel injected once or in multiple times during one cycle, relative to the crank angle. If the injection center of gravity is relatively slow, the supply of fuel into the cylinder is slow, so the time from fuel injection to ignition of the air-fuel mixture is short. Unlike the G/F case described above, the air-fuel mixture within the cylinder is not homogeneous. Because the air-fuel mixture is not homogeneous, combustion that satisfies the combustion stability standards while suppressing abnormal combustion at an intermediate G/F between the first G/F and the third G/F, more specifically, , at least a portion of the air-fuel mixture is combusted by compression ignition.

Therefore, this engine can seamlessly switch the combustion mode to a combustion mode in which at least a portion of the air-fuel mixture undergoes flame propagation combustion, HCCI combustion, or a third combustion mode. This ensures combustion stability and suppresses abnormal combustion.

Furthermore, in each of the HCCI combustion and the third combustion mode, at least a portion of the air-fuel mixture is combusted by compression ignition, and the G/F of the air-fuel mixture is relatively high. This engine has high fuel efficiency.

The controller is configured to: when the engine speed is the first engine speed at the first engine load;
When predicting that the mass ratio is higher than the third G/F, controlling the injector to inject fuel within an intake stroke period;
When predicting that the mass ratio is higher than the first G/F and lower than the third G/F, the injector is controlled to inject fuel in each of an intake stroke period and a compression stroke period. It may be said to do.

When the engine speed is the first engine speed under the first engine load and the G/F is predicted to be higher than the third G/F, the injector injects fuel into the cylinder within the intake stroke period. do. Since the fuel can be diffused using the intake flow, the air-fuel mixture in the cylinder is homogeneous or nearly homogeneous. A homogeneous mixture undergoes compression ignition combustion, or HCCI combustion.

When the engine speed is the first engine speed under the first engine load and the G/F is predicted to be higher than the first G/F and lower than the third G/F, the injector Fuel is injected into the cylinder during the compression stroke and during the compression stroke. Fuel injected during the intake stroke is diffused by the intake flow. The fuel injected during the intake stroke forms a homogeneous mixture. Fuel injected during the subsequent compression stroke renders the mixture inhomogeneous. A heterogeneous air-fuel mixture suppresses abnormal combustion and achieves combustion whose combustion stability satisfies standards.

When the controller controls the injector and the spark plug so that at least a part of the air-fuel mixture in the cylinder undergoes flame propagation combustion at the first engine load,
When predicting that the mass ratio is higher than a fourth G/F, driving the spark plug so that at least a portion of the air-fuel mixture in the cylinder undergoes flame propagation combustion and the remainder undergoes compression ignition combustion;
When it is predicted that the mass ratio is lower than the fourth G/F, the spark plug may be driven so that all of the air-fuel mixture in the cylinder undergoes flame propagation combustion.

When G/F is relatively high, the in-cylinder temperature becomes high. In this case, the controller drives the spark plug so that at least a portion of the air-fuel mixture undergoes flame propagation combustion and the remainder undergoes compression ignition combustion. The combustion form achieved in this case is none other than the above-mentioned SPCCI combustion. When G/F is relatively high, SPCCI combustion makes it possible to ensure combustion stability and suppress abnormal combustion.

When G/F is relatively low, as mentioned above, the combustion stability of flame propagation combustion increases, and by reducing burned gas and reducing G/F, the in-cylinder temperature decreases and abnormal combustion is prevented. suppressed. In this case, the controller controls the spark plugs so that all of the mixture undergoes flame propagation combustion. Flame propagation combustion is a combustion form suitable for low G/F.

The variable valve device opens and closes the intake valve and the exhaust valve so that the burned gas remains in the cylinder or is introduced into the cylinder through the intake valve or the exhaust valve. It may also be used to control.

By retaining or introducing so-called internal EGR gas into the cylinder, the temperature inside the cylinder can be increased. This is advantageous in improving the combustion stability of compression ignition combustion.

The engine may have a geometric compression ratio of 15 or more.

A high geometric compression ratio is advantageous for improving the combustion stability of compression ignition combustion. Also, a high geometric compression ratio improves the thermal efficiency of the engine.

As explained above, the engine system described above changes the mass ratio between flame propagation combustion and compression ignition combustion in response to changes in engine speed. It becomes possible to switch to combustion earlier, and as a result, it becomes possible to improve fuel efficiency.

FIG. 1 is a diagram illustrating an engine system. The upper diagram of FIG. 2 is a plan view illustrating the structure of the combustion chamber of the engine. The lower figure is a sectional view taken along line II-II of the upper figure, and is a diagram illustrating a state in which fuel is injected into the cylinder in the middle of the compression stroke. FIG. 3 is a block diagram of the engine system. FIG. 4 is a diagram illustrating a base map related to engine operation. FIG. 5 is a diagram illustrating the opening/closing operations of intake valves and exhaust valves, fuel injection timing, and ignition timing in each combustion mode. FIG. 6 is a diagram illustrating a state in which fuel is injected into the cylinder at the end of the compression stroke. FIG. 7 is a diagram illustrating the definition of the combustion center of gravity. FIG. 8 shows a modification of the opening and closing operations of the intake valve and exhaust valve in each combustion mode. FIG. 9 is a diagram illustrating the range defined by G/F and _TIVC in which each combustion form is established. FIG. 10 is a diagram illustrating a combustion form selection map within a low load region in which HCCI combustion is performed. FIG. 11 is a graph illustrating the relationship between the rotation speed and the switching G/F for switching between a combustion mode in which all of the air-fuel mixture is subjected to compression ignition combustion and a combustion mode in which at least a portion of the air-fuel mixture is burnt by flame propagation. It is. FIG. 12 is a flowchart illustrating a control procedure related to engine operation executed by the ECU. FIG. 13 is a flowchart illustrating a control procedure executed by the ECU regarding combustion mode selection.

Hereinafter, embodiments of an engine control method and an engine system will be described with reference to the drawings. The engine, engine system, and control method thereof described here are merely examples.

FIG. 1 is a diagram illustrating an engine system. FIG. 2 is a diagram illustrating the structure of a combustion chamber of an engine. The positions of the intake side and exhaust side in FIG. 1 and the positions of the intake side and exhaust side in FIG. 2 are reversed. FIG. 3 is a block diagram illustrating an engine control device.

The engine system includes an engine 1. The engine 1 has a cylinder 11. In the cylinder 11, an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke are repeated. Engine 1 is a four-stroke engine. Engine 1 is installed in a four-wheeled vehicle. The automobile travels as the engine 1 operates. The fuel for the engine 1 is gasoline in this configuration example.

(Engine configuration)
The engine 1 includes a cylinder block 12 and a cylinder head 13. Cylinder head 13 is mounted on cylinder block 12. A plurality of cylinders 11 are formed in the cylinder block 12. Engine 1 is a multi-cylinder engine. In FIG. 1 only one cylinder 11 is shown.

A piston 3 is inserted into each cylinder 11. The piston 3 is connected to a crankshaft 15 via a connecting rod 14. The piston 3 reciprocates inside the cylinder 11. The piston 3, cylinder 11 and cylinder head 13 form a combustion chamber 17.

The lower surface of the cylinder head 13, that is, the ceiling portion of the cylinder 11, is composed of an inclined surface 1311 and an inclined surface 1312, as shown in the lower diagram of FIG. The inclined surface 1311 is an inclined surface 1311 on the intake valve 21 side, which will be described later, and has an upward slope toward the center of the cylinder 11. The inclined surface 1312 is an inclined surface 1312 on the exhaust valve 22 side, and has an upward slope toward the center of the cylinder 11. The ceiling portion of the cylinder 11 is of a so-called pent roof type.

A cavity 31 is formed in the upper surface of the piston 3. The cavity 31 is recessed from the upper surface of the piston 3. In this configuration example, the cavity 31 has a shallow dish shape. The center portion of the cavity 31 is raised upward. The raised portion has a substantially conical shape.

The geometric compression ratio of the engine 1 is set to be 15 or more and, for example, 30 or less. As will be described later, in this engine 1, the air-fuel mixture undergoes compression ignition combustion in some operating regions. A relatively high geometric compression ratio stabilizes compression ignition combustion.

An intake port 18 is formed in the cylinder head 13 for each cylinder 11. The intake port 18 communicates with the inside of the cylinder 11. Although detailed illustration is omitted, the intake port 18 is a so-called tumble port. That is, the intake port 18 has a shape that causes a tumble flow to occur within the cylinder 11. The ceiling of the pent-roof type cylinder 11 and the tumble port generate a tumble flow inside the cylinder 11.

An intake valve 21 is provided in the intake port 18 . The intake valve 21 opens and closes the intake port 18. The valve train is connected to the intake valve 21. The valve train opens and closes the intake valve 21 at predetermined timing. A valve train is a variable valve system that makes valve timing and/or valve lift variable. As shown in FIG. 3, the valve train includes an intake S-VT (Sequential-Valve Timing) 231. The intake S-VT 231 is hydraulic or electric. The intake S-VT 231 continuously changes the rotational phase of the intake camshaft within a predetermined angular range.

The valve train also includes an intake CVVL (Continuously Variable Valve Lift) 232. The intake CVVL 232 can continuously change the lift amount of the intake valve 21 within a predetermined range, as illustrated in FIG. The intake CVVL 232 can adopt various known configurations. As an example, as described in Japanese Patent Laid-Open No. 2007-85241, the intake CVVL 232 can be configured to include a link mechanism, a control arm, and a stepping motor. The link mechanism causes a cam for driving the intake valve 21 to swing back and forth in conjunction with the rotation of the camshaft. The control arm variably sets the lever ratio of the link mechanism. When the lever ratio of the link mechanism changes, the amount of rocking of the cam that pushes down the intake valve 21 changes. The stepping motor changes the amount of rocking of the cam by electrically driving the control arm, thereby changing the amount of lift of the intake valve 21.

An exhaust port 19 is formed in the cylinder head 13 for each cylinder 11. The exhaust port 19 communicates with the inside of the cylinder 11.

The exhaust port 19 is provided with an exhaust valve 22 . The exhaust valve 22 opens and closes the exhaust port 19. The valve train is connected to an exhaust valve 22. The valve train opens and closes the exhaust valve 22 at predetermined timing. A valve train is a variable valve system that makes valve timing and/or valve lift variable. As shown in FIG. 3, the valve train includes an exhaust S-VT 241. The exhaust S-VT241 is hydraulic or electric. The exhaust S-VT 241 continuously changes the rotational phase of the exhaust camshaft within a predetermined angular range.

The valve train also has an exhaust VVL (Variable Valve Lift) 242. Although not shown, the exhaust VVL 242 is configured to be able to switch between cams that open and close the exhaust valve 22. The exhaust CVVL 242 can adopt various known configurations. As an example, as described in Japanese Unexamined Patent Publication No. 2018-168796, the exhaust VVL 242 includes a first cam, a second cam, a switching mechanism that switches between the first cam and the second cam, have. The first cam is configured to open and close the exhaust valve 22 during the exhaust stroke. As illustrated in FIG. 5, the second cam is configured to open and close the exhaust valve 22 during the exhaust stroke and to open and close the exhaust valve 22 again during the intake stroke. The exhaust VVL 242 can change the lift of the exhaust valve 22 by opening and closing the exhaust valve 22 using either the first cam or the second cam.

The intake S-VT 231, the intake CVVL 232, the exhaust S-VT 241, and the exhaust VVL 242 control the amount of air introduced into the cylinder 11 and the amount of burned gas by controlling the opening and closing of the intake valve 21 and the exhaust valve 22. Adjust the amount introduced. The intake S-VT 231, the intake CVVL 232, the exhaust S-VT 241, and the exhaust VVL 242 adjust the intake air filling amount.

An injector 6 is attached to the cylinder head 13 for each cylinder 11. As shown in FIG. 2, the injector 6 is disposed at the center of the cylinder 11. More specifically, the injector 6 is disposed in the valley of the pent roof where the sloped surface 1311 and the sloped surface 1312 intersect.

The injector 6 injects fuel directly into the cylinder 11. Although detailed illustration is omitted, the injector 6 is a multi-nozzle type having a plurality of nozzles. The injector 6 injects fuel so as to spread radially from the center of the cylinder 11 toward the periphery, as shown by the two-dot chain line in FIG. As shown in the lower diagram of FIG. 2, the axis of the nozzle of the fuel spray injected by the injector 6 has a predetermined angle θ with respect to the central axis X of the cylinder 11. In the illustrated example, the injector 6 has ten nozzles arranged at equal angles in the circumferential direction, but the number and arrangement of the nozzles are not particularly limited.

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 stores the fuel pumped from the fuel pump 65 at high fuel pressure. When the injector 6 opens, the fuel stored in the common rail 64 is injected into the cylinder 11 from the nozzle of the injector 6. The pressure of fuel supplied to the injector 6 may be changed depending on the operating state of the engine 1. Note that the configuration of the fuel supply system 61 is not limited to the above configuration.

A first spark plug 251 and a second spark plug 252 are attached to the cylinder head 13 for each cylinder 11. The first spark plug 251 and the second spark plug 252 each forcibly ignite the air-fuel mixture in the cylinder 11 . As shown in FIG. 2, the first spark plug 251 is arranged between the two intake valves 21, and the second spark plug 252 is arranged between the two exhaust valves 22. The tip of the first spark plug 251 and the tip of the second spark plug 252 are located near the ceiling of the cylinder 11 on the intake side and the exhaust side, respectively, with the injector 6 in between. Note that the number of spark plugs may be one.

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. Air introduced into the cylinder 11 flows through the intake passage 40. An air cleaner 41 is provided at the upstream end of the intake passage 40 . Air cleaner 41 filters air. 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 provided between the air cleaner 41 and the surge tank 42 in the intake passage 40 . The throttle valve 43 can adjust the amount of air introduced into the cylinder 11 by adjusting the opening degree of the valve. The throttle valve 43 is basically fully open while the engine 1 is operating. The amount of air introduced is adjusted by the variable valve device described above.

The engine 1 has a swirl generating section that generates a swirl flow within the cylinder 11. The swirl generating section has a swirl control valve 56 attached to the intake passage 40. Although detailed illustration is omitted, the swirl control valve 56 is disposed downstream of the surge tank 42 in a secondary passage of the primary passage and the secondary passage connected to each cylinder 11. The swirl control valve 56 is an opening adjustment valve that can narrow the cross section of the secondary passage. If the opening degree of the swirl control valve 56 is small, the intake air flow rate flowing into the cylinder 11 from the primary passage is relatively large, and the intake air flow rate flowing into the cylinder 11 from the secondary passage is relatively small, so the swirl in the cylinder 11 is reduced. The current becomes stronger. When the degree of opening of the swirl control valve 56 is large, the flow rate of intake air flowing into the cylinder 11 from each of the primary passage and the secondary passage becomes approximately equal, so that the swirl flow within the cylinder 11 becomes weak. When the swirl control valve 56 is fully opened, no swirl flow occurs.

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 cylinder 11 flows. The upstream portion of the exhaust passage 50 constitutes an independent passage that branches for each cylinder 11, although detailed illustration is omitted. 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. The upstream catalytic converter includes, for example, a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512. The downstream catalytic converter has a three-way catalyst 513. Note that the exhaust gas purification system is not limited to the configuration shown in the figure. For example, GPF may be omitted. Further, the catalytic converter is not limited to one having a three-way catalyst. Furthermore, the arrangement order of the three-way catalyst and GPF may be changed as appropriate.

An EGR passage 52 is connected between the intake passage 40 and the exhaust passage 50. The EGR passage 52 is a passage for recirculating a portion of exhaust 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. A downstream end of the EGR passage 52 is connected between the throttle valve 43 and the surge tank 42 in the intake passage 40 .

A water-cooled EGR cooler 53 is disposed in the EGR passage 52. EGR cooler 53 cools exhaust gas. An EGR valve 54 is also provided in the EGR passage 52. The EGR valve 54 adjusts the flow rate of exhaust gas flowing through the EGR passage 52. By adjusting the opening degree of the EGR valve 54, the amount of recirculation of the cooled exhaust gas can be adjusted.

The control device for the engine 1 includes an ECU (Engine Control Unit) 10 for operating the engine 1, as shown in FIG. The ECU 10 is a controller based on a well-known microcomputer, and includes a central processing unit (CPU) 101, a memory 102, and an I/F circuit 103. CPU 101 executes a program. The memory 102 is configured with, for example, a RAM (Random Access Memory) or a ROM (Read Only Memory), and stores programs and data. The I/F circuit 103 inputs and outputs electrical signals. ECU10 is an example of a controller.

As shown in FIGS. 1 and 3, various sensors SW1 to SW10 are connected to the ECU 10. Sensors SW1 to SW10 output signals to ECU10. The sensors include the following sensors.
Air flow sensor SW1: disposed downstream of the air cleaner 41 in the intake passage 40 and measures the flow rate of air flowing through the intake passage 40.
Intake air temperature sensor SW2: Disposed downstream of the air cleaner 41 in the intake passage 40, and measures the temperature of the air flowing through the intake passage 40.
Intake pressure sensor SW3: attached to the surge tank 42 and measures the pressure of air introduced into the cylinder 11.
Cylinder pressure sensor SW4: attached to the cylinder head 13 corresponding to each cylinder 11, and measures the pressure inside each cylinder 11.
Water temperature sensor SW5: attached to the engine 1 and measures the temperature of the cooling water.
Crank angle sensor SW6: attached to the engine 1 and measures the rotation angle of the crankshaft 15.
Accelerator opening sensor SW7: attached to the accelerator pedal mechanism and measures the accelerator opening corresponding to the operation amount of the accelerator pedal.
Intake cam angle sensor SW8: attached to the engine 1 and measures the rotation angle of the intake camshaft.
Exhaust cam angle sensor SW9: attached to the engine 1 and measures the rotation angle of the exhaust camshaft.
Intake cam lift sensor SW10: attached to the engine 1 and measures the lift amount of the intake valve 21.

The ECU 10 determines the operating state of the engine 1 based on the signals from these sensors SW1 to SW10, and calculates the control amount of each device according to a predetermined control logic. Control logic is stored in memory 102. The control logic includes calculating a target amount and/or a control amount using a map stored in the memory 102.

The ECU 10 sends electrical signals related to the calculated control amounts to the injector 6, first spark plug 251, second spark plug 252, intake S-VT 231, intake CVVL 232, exhaust S-VT 241, exhaust VVL 242, fuel supply system 61, It is output to the throttle valve 43, EGR valve 54, and swirl control valve 56.

(Engine operation control map)
FIG. 4 illustrates a base map related to control of the engine 1. The base map is stored in the memory 102 of the ECU 10. The basemap includes a first basemap 401 and a second basemap 402. The ECU 10 uses a base map selected from two types of base maps to control the engine 1, depending on the level of the coolant temperature of the engine 1. The first base map 401 is a base map when the engine 1 is warm. The second base map 402 is a base map when the engine 1 is cold.

The first base map 401 and the second base map 402 are defined by the load and rotation speed of the engine 1. The first base map 401 is roughly divided into four regions, a first region, a second region, a third region, and a fourth region, based on the level of load and the number of rotations. More specifically, the first region includes a high rotation region 411 and a high load medium rotation region 412. The high rotation region 411 extends throughout the range from low load to high load. The second region corresponds to high load and low rotation regions 413 and 414. The third region corresponds to a low load region 415 that includes idling operation, and extends to low and medium rotation regions. The fourth region is a medium load region 416, 417 which has a higher load than the low load region 415 and a lower load than the high load medium rotation region 412 and the high load low rotation region 413, 414.

The high load low rotation areas 413 and 414 are a first high load low rotation area 413 where the load is relatively low and a second area where the load is higher than the first high load low rotation area 413 and includes the maximum load. It is divided into a high load low rotation region 414. The medium load areas 416 and 417 are divided into a first medium load area 416 and a second medium load area 417 having a lower load than the first medium load area 416.

The second base map 402 is divided into three regions: a first region, a second region, and a third region. More specifically, the first region includes a high rotation region 421 and a high load medium rotation region 422. The second region corresponds to high load and low rotation regions 423 and 424. The third region is a low-medium load region 425 that extends from a low load region including idling operation to a medium load region in the load direction, and extends to a low rotation and medium rotation region in the rotation speed direction.

The high load low rotation areas 423 and 424 are a first high load low rotation area 423 where the load is relatively low, and a second high load low rotation area 423 where the load is higher than the first high load low rotation area 423 and which includes the maximum load. It is divided into a high load low rotation region 424.

A first region of the second base map 402 corresponds to a first region of the first base map 401, a second region of the second base map 402 corresponds to a second region of the first base map 401, and a second region of the second base map 402 corresponds to a second region of the first base map 401. The third area of the base map 402 corresponds to the third area and the fourth area of the first base map 401.

Here, the low rotation region, medium rotation region, and high rotation region are respectively defined when the entire operating region of the engine 1 is divided into approximately three equal parts in the rotation speed direction: the low rotation region, the middle rotation region, and the high rotation region. It may also be a low rotation area, a medium rotation area, and a high rotation area.

In addition, the low load region, medium load region, and high load region are respectively defined when the entire operating region of the engine 1 is divided into approximately three equal parts in the load direction into the low load region, the medium load region, and the high load region. It may be a low load area, a medium load area, or a high load area.

(Engine combustion form)
Next, the operation of the engine 1 in each region will be explained in detail. The ECU 10 controls the opening and closing operations of the intake valve 21 and the exhaust valve 22, the fuel injection timing, and the ignition according to the required load for the engine 1 (required engine load) and the rotation speed of the engine 1 (engine rotation speed). Change presence or absence. The combustion form of the air-fuel mixture in the cylinder 11 changes by changing the intake air filling amount, the fuel injection timing, and the presence or absence of ignition. The combustion mode of this engine 1 changes to homogeneous SI combustion, retard SI combustion, HCCI combustion, SPCCI combustion, and MPCI combustion. FIG. 5 shows the opening/closing operations of the intake valve 21 and exhaust valve 22, fuel injection timing, ignition timing, and the waveform of the heat release rate generated in the cylinder 11 by combustion of the air-fuel mixture, corresponding to each combustion mode. , is exemplified. The crank angle progresses from left to right in FIG. Hereinafter, each combustion mode will be explained using the engine 1 when it is warm as an example.

(Homogeneous SI combustion)
When the operating state of the engine 1 is in the first region, that is, the high rotation region 411 or the high load medium rotation region 412, the ECU 10 causes the air-fuel mixture in the cylinder 11 to undergo flame propagation combustion. More specifically, the intake S-VT 231 sets the opening/closing timing of the intake valve 21 to a predetermined timing. The intake CVVL 232 sets the lift amount of the intake valve 21 to a predetermined lift amount. The lift amount of the intake valve 21 is substantially the same as the lift amount of the exhaust valve 22, which will be described later. The exhaust S-VT 241 sets the opening/closing timing of the exhaust valve 22 at a predetermined timing. The intake valve 21 and the exhaust valve 22 both open near the intake top dead center (see reference numeral 701). The exhaust VVL 242 causes the exhaust valve 22 to open and close only once. By opening and closing the intake valve 21 and the exhaust valve 22, a relatively large amount of air and a relatively small amount of burned gas are introduced into the cylinder 11. The burned gas is basically internal EGR gas remaining within the cylinder 11.

The injector 6 injects fuel into the cylinder 11 during the intake stroke (see 702). The injector 6 may perform batch injection as shown in the illustrated example. The fuel injected into the cylinder 11 is diffused by the strong intake flow. Inside the cylinder 11, an air-fuel mixture with a homogeneous fuel concentration is formed. The mass ratio of the air-fuel mixture, that is, the mass ratio G/F of the intake air in the cylinder 11 containing burnt gas to the fuel is approximately 20. Note that the mass ratio A/F of the air in the cylinder 11 to the fuel is the stoichiometric air-fuel ratio.

Both the first spark plug 251 and the second spark plug 252 ignite the air-fuel mixture near compression top dead center (see 703). The first spark plug 251 and the second spark plug 252 may be ignited at the same time, or may be ignited at different timings.

After the first spark plug 251 and the second spark plug 252 are ignited, the mixture undergoes flame propagation combustion (see 704). In a high rotation range 411 where the rotation speed is too high and compression ignition combustion is difficult, and in a high load medium rotation range 412 where the load is too high and compression ignition combustion is difficult, the engine 1 ensures combustion stability and prevents abnormalities. It can be operated while suppressing combustion.

Since this combustion type causes spark ignition combustion of a homogeneous air-fuel mixture, this combustion type is sometimes referred to as homogeneous SI combustion.

(Retard SI combustion)
When the operating state of the engine 1 is in the second region, that is, the first high load low speed region 413 or the second high load low speed region 414, the ECU 10 causes flame propagation combustion of the air-fuel mixture in the cylinder 11. . More specifically, when the operating state of the engine 1 is in the second high load/low rotation region 414, the intake S-VT 231 sets the opening/closing timing of the intake valve 21 to a predetermined timing. The intake CVVL 232 sets the lift amount of the intake valve 21 to a predetermined lift amount. The lift amount of the intake valve 21 is substantially the same as the lift amount of the exhaust valve 22, which will be described later. The exhaust S-VT 241 sets the opening/closing timing of the exhaust valve 22 at a predetermined timing. The intake valve 21 and the exhaust valve 22 both open near the intake top dead center (see reference numeral 705). The exhaust VVL 242 causes the exhaust valve 22 to open and close only once. By opening and closing the intake valve 21 and the exhaust valve 22, a relatively large amount of air and a relatively small amount of burned gas are introduced into the cylinder 11. The burned gas is basically internal EGR gas remaining within the cylinder 11. G/F is about 20.

When the operating state of the engine 1 is in the first high load low rotation range 413, the intake S-VT 231 sets the opening/closing timing of the intake valve 21 to a predetermined timing. The intake CVVL 232 makes the lift amount of the intake valve 21 smaller than that in the second high load low rotation region 414. The closing timing of the intake valve 21 is advanced in the first high load low rotation range 413 than in the second high load low rotation range 414 (see reference numeral 709). The exhaust S-VT 241 sets the opening/closing timing of the exhaust valve 22 at a predetermined timing. Both the intake valve 21 and the exhaust valve 22 open near the intake top dead center. The exhaust VVL 242 causes the exhaust valve 22 to open and close only once. Depending on the opening/closing configuration of the intake valve 21 and the exhaust valve 22, the amount of air introduced into the cylinder 11 is reduced and the amount of burned gas is increased compared to the case in the second high load low rotation region 414. The G/F of the first high load low rotation region 413 is leaner than the G/F of the second high load low rotation region 414, and the G/F is about 25.

The first high load low rotation region 413 or the second high load low rotation region 414 is a region where the load is high and the rotation speed is low, so abnormal combustion such as pre-ignition or knocking is likely to occur. The injector 6 injects fuel into the cylinder 11 during the compression stroke (see numerals 706 and 710). By delaying the timing of injecting fuel into the cylinder 11, occurrence of abnormal combustion is suppressed. The injector 6 may perform batch injection as shown in the illustrated example.

In the second high-load, low-speed region 414 where the load is relatively high, the injector 6 injects fuel into the cylinder 11 at a relatively late timing (see reference numeral 706). The injector 6 may inject fuel, for example, in the latter half of the compression stroke or at the end of the compression stroke. Note that the second half of the compression stroke corresponds to the second half when the compression stroke is divided into the first half and the second half. The final stage of the compression stroke corresponds to the final stage when the compression stroke is divided into three equal parts: initial stage, middle stage, and final stage. In the second high-load, low-speed region 414 where the load is high, slow fuel injection timing is advantageous for suppressing abnormal combustion.

In the first high-load, low-speed region 413 where the load is relatively low, the injector 6 injects fuel into the cylinder 11 at a relatively early timing (see reference numeral 710). The injector 6 may inject fuel, for example, in the middle of the compression stroke. Here, the middle stage of the compression stroke corresponds to the middle stage when the compression stroke is divided into three equal parts: the initial stage, the middle stage, and the final stage.

The fuel injected into the cylinder 11 during the compression stroke is diffused by the flow of the injection. In order to rapidly combust the air-fuel mixture, suppress the occurrence of abnormal combustion, and improve combustion stability, it is preferable that the fuel injection pressure be high. The high injection pressure creates a strong flow in the cylinder 11 where the pressure is high near compression top dead center. Strong flow promotes flame propagation.

Both the first spark plug 251 and the second spark plug 252 ignite the air-fuel mixture near compression top dead center (see numerals 707 and 711). The first spark plug 251 and the second spark plug 252 may be ignited at the same time, or may be ignited at different timings. In the second high-load, low-speed region 414 where the load is high, the first spark plug 251 and the second spark plug 252 perform ignition at a timing later than compression top dead center, corresponding to the retarded fuel injection timing. I do. After the first spark plug 251 and the second spark plug 252 are ignited, the mixture undergoes flame propagation combustion (see numerals 708 and 712).

In an operating state where the rotational speed is low and abnormal combustion is likely to occur, the engine 1 can be operated while ensuring combustion stability and suppressing abnormal combustion. Since this combustion form retards the injection timing, this injection form is sometimes called retarded SI combustion.

(HCCI combustion)
When the operating state of the engine 1 is in the third region, that is, the low load region 415, the ECU 10 causes the air-fuel mixture in the cylinder 11 to undergo compression ignition combustion. More specifically, when the operating state of the engine 1 is in the low load region 415, the exhaust VVL 242 causes the exhaust valve 22 to open and close twice. That is, between the first region, the second region, and the third region, the exhaust VVL 242 switches between the first cam and the second cam. The exhaust valve 22 opens and closes during the exhaust stroke and opens and closes during the intake stroke. The exhaust S-VT 241 sets the opening/closing timing of the exhaust valve 22 at a predetermined timing. The intake S-VT 231 retards the opening/closing timing of the intake valve 21. The intake CVVL 232 sets the lift amount of the intake valve 21 to a small value. The closing timing of the intake valve 21 is the most retarded (see reference numeral 713).

By opening and closing the intake valve 21 and the exhaust valve 22, a relatively small amount of air and a large amount of burned gas are introduced into the cylinder 11. The burned gas is basically internal EGR gas remaining within the cylinder 11. The G/F of the mixture is about 40. A large amount of internal EGR gas introduced into the cylinder 11 increases the temperature inside the cylinder.

The injector 6 injects fuel into the cylinder 11 during the intake stroke (see 714). As described above, the strong intake flow causes the fuel to diffuse and form a homogeneous air-fuel mixture within the cylinder 11. The injector 6 may perform batch injection as shown in the illustrated example. The injector 6 may perform split injection.

When the operating state of the engine 1 is in the low load region 415, both the first spark plug 251 and the second spark plug 252 do not ignite. The air-fuel mixture in the cylinder 11 undergoes compression ignition near the compression top dead center (see reference numeral 715). Since the load on the engine 1 is low and the amount of fuel is small, by making the G/F lean fuel, compression ignition combustion, more precisely, HCCI combustion, is realized while suppressing abnormal combustion. In addition, by introducing a large amount of internal EGR gas and increasing the in-cylinder temperature, the stability of HCCI combustion is enhanced and the thermal efficiency of the engine 1 is also improved.

(SPCCI combustion)
When the operating state of the engine 1 is in the second region, more specifically, in the first medium load region 416, the ECU 10 causes a part of the air-fuel mixture in the cylinder 11 to undergo flame propagation combustion, and causes the remainder to undergo compression ignition combustion. More specifically, the exhaust S-VT 241 sets the opening/closing timing of the exhaust valve 22 to a predetermined timing. The exhaust VVL 242 opens and closes the exhaust valve 22 twice (see 716). Internal EGR gas is introduced into the cylinder 11. The intake CVVL 232 sets the lift amount of the intake valve 21 to be larger than the lift amount in the low load region 415. The closing timing of the intake valve 21 is approximately the same as the closing timing of the low load region 415. The opening timing of the intake valve 21 is advanced relative to the opening timing of the low load region 415. Depending on the opening/closing configuration of the intake valve 21 and the exhaust valve 22, the amount of air introduced into the cylinder 11 increases and the amount of burned gas introduced decreases. The G/F of the mixture is, for example, 35.

The injector 6 injects fuel into the cylinder 11 during the compression stroke (see 717). The injector 6 may perform batch injection as shown in the illustrated example. Late fuel injection is advantageous in suppressing abnormal combustion, similar to retard SI combustion. Note that when the operating state of the engine 1 is low load, for example in the first medium load region 416, the injector 6 may inject fuel during each of the intake stroke period and the compression stroke period.

Both the first spark plug 251 and the second spark plug 252 ignite the air-fuel mixture near the compression top dead center (see reference numeral 718). The air-fuel mixture starts flame propagation combustion near the compression top dead center after the first spark plug 251 and the second spark plug 252 are ignited. The heat generated by flame propagation combustion increases the temperature within the cylinder 11, and the flame propagation increases the pressure within the cylinder 11. As a result, the unburned air-fuel mixture self-ignites, for example, after compression top dead center, and compression ignition combustion begins. After the start of compression ignition combustion, flame propagation combustion and compression ignition combustion proceed in parallel. The waveform of the heat release rate may have two peaks as illustrated in FIG. 5 (see reference numeral 719).

By adjusting the calorific value of flame propagation combustion, variations in temperature within the cylinder 11 before the start of compression can be accommodated. By adjusting the ignition timing, the ECU 10 can adjust the amount of heat generated by flame propagation combustion. The air-fuel mixture will self-ignite at the desired timing. In SPCCI combustion, the ECU 10 adjusts the compression ignition timing by adjusting the ignition timing. In this combustion mode, ignition controls compression ignition, so this combustion mode is sometimes called SPCCI (Spark Controlled Compression Ignition) combustion.

(MPCI combustion)
When the operating state of the engine 1 is in the second medium load region 417, the ECU 10 causes the air-fuel mixture in the cylinder 11 to undergo compression ignition combustion. More specifically, the exhaust S-VT 241 sets the opening/closing timing of the exhaust valve 22 to a predetermined timing. The exhaust VVL 242 causes the exhaust valve 22 to open and close twice. Internal EGR gas is introduced into the cylinder 11. The intake CVVL 232 sets the lift amount of the intake valve 21 to be smaller than the lift amount of the first medium load region 416. The closing timing of the intake valve 21 is approximately the same as the closing timing of the first medium load region 416. The opening timing of the intake valve 21 is delayed from the opening timing of the first medium load region 416 (see 720 and 724). Depending on the opening/closing configuration of the intake valve 21 and the exhaust valve 22, the amount of air introduced into the cylinder 11 is reduced and the amount of burned gas introduced is increased. G/F is, for example, 35 to 38.

The injector 6 injects fuel into the cylinder 11 during the intake stroke and during the compression stroke. The injector 6 performs split injection. In the second medium load region 417, the ECU 10 selectively uses two injection forms: squish injection and trigger injection. Squish injection is an injection form in which the injector 6 injects fuel within the intake stroke period and in the middle of the compression stroke (see numerals 721 and 722). Trigger injection is an injection form in which the injector 6 injects fuel within the intake stroke period and at the end of the compression stroke (see numerals 725 and 726).

Squish injection is an injection form that slows compression ignition combustion. The fuel injected during the intake stroke is diffused into the cylinder 11 by the strong intake flow, as described above. A homogeneous air-fuel mixture is formed within the cylinder 11. The fuel injected in the middle of the compression stroke reaches the squish region 171 outside the cavity 31, as illustrated in the lower diagram of FIG. Since the squish region 171 is close to the cylinder liner, the temperature is originally low, and the temperature further decreases due to latent heat when the fuel spray vaporizes. As the temperature within the cylinder 11 locally decreases, the air-fuel mixture within the cylinder 11 becomes inhomogeneous. As a result, for example, when the in-cylinder temperature is high, the air-fuel mixture is compressed and ignited at a desired timing while suppressing the occurrence of abnormal combustion. Squish injection allows relatively slow compression ignition combustion.

The squares in FIG. 5 are the injection periods of the injector 6, and the area of the squares corresponds to the amount of fuel injected. In squish injection, the amount of fuel injected during the compression stroke is greater than the amount of fuel injected during the intake stroke. Since the fuel is injected into a wide area outside the cavity 31, smoke generation can be suppressed even if the amount of fuel is large. The greater the amount of fuel, the lower the temperature. The amount of fuel injected during the compression stroke may be set to an amount that can achieve the required temperature reduction.

Trigger injection is an injection form that promotes compression ignition combustion. The fuel injected during the intake stroke is diffused into the cylinder 11 by the strong intake flow, as described above. A homogeneous air-fuel mixture is formed within the cylinder 11. The fuel injected at the end of the compression stroke is difficult to diffuse due to the high pressure within the cylinder 11 and remains in the region within the cavity 31, as illustrated in FIG. Note that the region inside the cavity 31 means a region radially inward from the outer peripheral edge of the cavity 31 with respect to the radial direction of the cylinder 11. The inside of the cavity 31 recessed from the top surface of the piston 3 is also included in the area inside the cavity 31. The air-fuel mixture within cylinder 11 is heterogeneous. Furthermore, the center of the cylinder 11 is a region where the temperature is high because it is away from the cylinder liner. Since a fuel-rich mixture mass is formed in the high temperature region, compression ignition of the mixture is promoted. As a result, for example, when the G/F of the air-fuel mixture is large, the air-fuel mixture is quickly compressed and ignited after compression stroke injection, thereby promoting compression ignition combustion. Trigger injection increases combustion stability.

In trigger injection, the amount of fuel injected during the compression stroke is smaller than the amount of fuel injected during the intake stroke. Since the fuel injection during the compression stroke is performed at the end of the compression stroke as described above, the injected fuel remains in the cavity 31 and is difficult to diffuse. By reducing the amount of fuel, the generation of smoke can be suppressed. The amount of fuel injected during the compression stroke may be set to an amount that can achieve both the required effect of promoting compression ignition and suppressing the generation of smoke.

Both squish injection and trigger injection cause the mixture within cylinder 11 to be inhomogeneous. In this respect, it differs from HCCI combustion in which a homogeneous air-fuel mixture is formed. Both squish injection and trigger injection can control the timing of compression ignition by forming a heterogeneous mixture.

This combustion mode is sometimes called MPCI (Multiple Premixed Fuel Injection Compression Ignition) combustion because the injector performs fuel injection multiple times.

Note that when the engine 1 is cold, as shown in the second base map 402 in FIG. , homogeneous SI combustion, or SPCCI combustion. This is because compression ignition combustion becomes unstable because the temperature of the engine 1 is low. After the engine 1 is started, as the water temperature rises, the ECU 10 switches the base map from the second base map 402 when the engine is cold to the first base map 401 when the engine is warm. When the base map is switched, the ECU 10 may switch the combustion form from homogeneous SI combustion to HCCI combustion, for example, even if the rotation speed and load of the engine 1 do not change.

(Details of engine control for high and low engine loads)
Here, in the timing chart of each combustion mode shown in FIG. 5, the combustion mode at the bottom of the figure is the combustion mode when the load of the engine 1 is low, and the combustion mode at the top of the figure is the combustion mode when the engine load is high. It is a form of combustion. When the load on the engine 1 is high, the G/F of the air-fuel mixture is small. When the load on the engine 1 is low, the G/F of the air-fuel mixture is large. In other words, the amount of air introduced into the cylinder 11 is small and the amount of burned gas is large.

Next, the fuel injection timing will be compared as the engine load changes. Here, regarding the fuel injection timing, the injection gravity center is defined. FIG. 7 is a diagram for explaining the injection gravity center. The horizontal axis in FIG. 7 is the crank angle, and the crank angle progresses from left to right in the figure. The injection center of gravity is the center of mass of the fuel injected during one cycle relative to the crank angle. The injection center of gravity is determined from the injection timing and injection amount of fuel during one cycle. A chart 71 in FIG. 7 shows the injection timing soi_1 (start of injection) and the injection period pw_1 in the case of batch injection. The left end of the square in FIG. 7 is the injection start timing, the right end is the injection end timing, and the left and right lengths of the square correspond to the injection period. The fuel injection pressure in one combustion cycle is constant. Therefore, the injection amount is proportional to the injection period. When calculating the injection gravity center, the injection period can be substituted for the injection amount.

In the case of batch injection, the injection gravity center ic_g corresponds to the central crank angle ic_1 of one injection period. The crank angle ic_1, that is, the injection center of gravity ic_g can be expressed by the following equation (1) from the injection start timing soi_1, the injection period pw_1, and the rotation speed Ne of the engine 1.
ic_1=soi_1+(pw_1*Ne*360/60)/2=soi_1+3* pw_1*Ne (1)

Chart 72 in FIG. 7 shows an example in which the injection start timing is delayed compared to chart 71. Since the chart 72 is also a batch injection, the injection gravity center can be calculated using equation (1). In the case of batch injection, if the injection start timing is retarded, the injection center of gravity is also retarded.

Although not shown, if the injection start timing is the same and the injection period changes, the injection gravity center changes.

A chart 73 in FIG. 7 illustrates the case of split injection. The injection timing and injection period of the first injection in chart 73 are the same as the injection timing and injection period of the first injection in chart 71. The start timing of the second injection is later than the start timing of the first injection.

When two injections, the first injection and the second injection, are included, the injection center of gravity ic_g is the center of mass of the fuel injected during one cycle with respect to the crank angle, and is therefore defined by the following equation.
ic_g=(pw_1*ic_1+pw_2*ic_2)/(pw_1+pw_2) (2)

ic_1 can be calculated using equation (1). Similarly, ic_2 can be calculated using the following formula.
ic_2=soi_2+(pw_2*Ne*360/60)/2=soi_2+3*pw_2*Ne (3)

From equations (1), (2), and (3), the injection center of gravity ic_g can be calculated from the following equation.
ic_g=(pw_1*(soi_1+3*pw_1*Ne)+pw_2*(soi_2+3*pw_2*Ne))/(pw_1+pw_2) (4)

The injection center of gravity ic_g of the chart 73 in FIG. 7 is retarded than the injection center of gravity ic_g of the chart 71 due to the addition of the second injection to the first injection.

In addition, when formula (4) is generalized and the injector 6 injects fuel n times during one cycle, the injection gravity center ic_g can be calculated from the following formula.
ic_g＝
(pw_1*(soi_1+3*pw_1*Ne)+…+pw_n*(soi_n+3* pw_n*Ne))/(pw_1+…+pw_n) (5)

As shown in FIG. 5, when the load on the engine 1 is low, the G/F of the air-fuel mixture is large (for example, G/F=40). The injector 6 injects fuel during the intake stroke. The injection center of gravity is on the advance side. When the load on the engine 1 is high, the G/F of the air-fuel mixture is small (for example, G/F=35 or 38). The injector 6 injects fuel during the intake stroke and the compression stroke (numerals 721, 722, 725, 726). The injection center of gravity is relatively retarded.

When the load on the engine 1 is higher, the G/F of the air-fuel mixture is even smaller (for example, G/F=35). The injector 6 injects fuel during the compression stroke (717). The injection center of gravity is relatively further retarded.

When the load on the engine 1 is higher, the G/F of the air-fuel mixture is even smaller (for example, G/F=20 or 25). The injector 6 injects fuel during the intake stroke (702) or during the compression stroke (706, 710). The center of gravity of the injection is relatively advanced or retarded.

Comparing HCCI combustion and homogeneous SI combustion, or comparing HCCI combustion and retard SI combustion, HCCI combustion has a large air-fuel mixture G/F, while homogeneous SI combustion or retard SI combustion has a large mixed The G/F of Qi is small. Assume that this engine 1 is an engine that simply switches between HCCI combustion and homogeneous SI combustion or retard SI combustion. In this case, when the load on the engine 1 changes and the combustion mode is switched, the G/F of the air-fuel mixture must be changed significantly. However, the responsiveness of the variable valve system including the intake S-VT 231, intake CVVL 232, exhaust S-VT 241, and exhaust VVL 242 is not so high. It is difficult to instantly change the G/F of the air-fuel mixture.

In MPCI combustion or SPCCI combustion, the G/F of the air-fuel mixture is intermediate between the G/F of HCCI combustion and the G/F of SI combustion. Changing the G/F between the G/F of HCCI combustion and the G/F of MPCI combustion or SPCCI combustion, or between the G/F of SI combustion and the G/F of MPCI combustion or SPCCI combustion. Changing the G/F can be performed quickly.

Although the details will be described later, in MPCI combustion or SPCCI combustion, the injection center of gravity is retarded than in HCCI combustion, so that combustion stability can be ensured when the air-fuel mixture is at an intermediate G/F. This is a combustion form that makes it possible to suppress abnormal combustion. This engine 1 quickly changes the G/F of the air-fuel mixture in response to changes in engine load, and seamlessly switches the combustion form between SI combustion, HCCI combustion, MPCI combustion, and SPCCI combustion. be able to. As a result, combustion stability is ensured and abnormal combustion is suppressed over the entire load range of the engine 1.

In MPCI combustion, the injector 6 performs injection during the intake stroke period and injection during the compression stroke period. When the G/F of the air-fuel mixture is between the G/F of HCCI combustion and the G/F of SI combustion, the injector 6 has an injection center of gravity that is different from that of HCCI combustion, instead of split injection. The fuel may be injected all at once so that the injection angle is delayed relative to the center of gravity of the injection. If the injection center of gravity is retarded, the time from fuel injection to ignition becomes shorter, so the air-fuel mixture in the cylinder 11 becomes less homogeneous. A heterogeneous air-fuel mixture ensures combustion stability and suppresses abnormal combustion in the case of an intermediate G/F.

(Modified example of opening/closing form of intake valve and exhaust valve)
FIG. 5 shows an example in which the exhaust VVL 242 is configured to open the exhaust valve 22 in each of the exhaust stroke and the intake stroke. The configuration example of the variable valve device is not limited to this. Next, a modification of the variable valve device will be described with reference to FIG. 8.

Reference numeral 81 in FIG. 8 indicates a lift curve of the exhaust valve 22 that is different from the above. The lift curve 811 of homogeneous SI combustion, the lift curve 812 of second retard SI combustion, and the lift curve 813 of first retard SI combustion are the same as lift curves 701, 705, and 709 in FIG. 5, respectively. The lift curve 814 for SPCCI combustion, the lift curve 815 for MPCI combustion, and the lift curve 816 for HCCI combustion are different from lift curves 716, 720, 724, and 713 in FIG. At reference numeral 81 in FIG. 8, the exhaust valve 22 opens during the exhaust stroke, and after exceeding the maximum lift and gradually decreasing the lift amount, the exhaust valve 22 maintains a predetermined lift without closing. The exhaust valve 22 does not close, but closes at a predetermined timing in the intake stroke beyond the intake top dead center. By maintaining the exhaust valve 22 in an open state without closing it, it is advantageous to reduce loss in the engine 1. Note that in each of the SPCCI combustion lift curve 814, the MPCI combustion lift curve 815, and the HCCI combustion lift curve 816, the lift curves of the intake valve 21 are the same as the lift curves 716, 720, 724, and 713 in FIG. .

Reference numeral 82 in FIG. 8 shows a lift curve of yet another exhaust valve 22. In this modification, the variable valve device does not include an intake CVVL 232 and an exhaust VVL 242. The variable valve device includes an intake S-VT 231 and an exhaust S-VT 241. The variable valve device can change the opening/closing timing of the intake valve 21 and the exhaust valve 22.

Reference numeral 82 holds the internal EGR gas within the cylinder 11 by providing a negative overlap period in which both the intake valve 21 and the exhaust valve 22 are closed across the intake top dead center. In other words, the exhaust valve 22 is closed before reaching the intake top dead center.

When the load on the engine 1 decreases and the amount of burned gas introduced into the cylinder 11 is increased, the closing timing of the exhaust valve 22 is advanced. Furthermore, when reducing the amount of air introduced into the cylinder 11, the closing timing of the intake valve 21 is retarded so as to move away from intake bottom dead center. The negative overlap period becomes longer as the load on the engine 1 becomes lower.

Although not shown in the drawings, the variable valve system prevents internal EGR gas by providing a positive overlap period in which both the intake valve 21 and the exhaust valve 22 are open across the intake top dead center. may be reintroduced into the cylinder 11.

(Determination of combustion form)
The ECU 10 determines the operating state of the engine 1 based on measurement signals from the various sensors SW1 to SW10 described above. The ECU 10 controls the intake S-VT 231, intake CVVL 232, exhaust S-VT 241, and exhaust VVL 242 according to the determined operating state. The intake S-VT 231, the intake CVVL 232, the exhaust S-VT 241, and the exhaust VVL 242 control opening and closing of the intake valve 21 and the exhaust valve 22 in response to control signals from the ECU 10. Thereby, the amount of intake air charged into the cylinder 11 is adjusted. More specifically, the amount of air introduced into the cylinder 11 and the amount of burned gas are adjusted.

The ECU 10 also adjusts the fuel injection amount and injection timing depending on the operating state of the engine 1. The injector 6 receives a control signal from the ECU 10 and injects a specified amount of fuel into the cylinder 11 at a specified timing.

The ECU 10 further controls the first spark plug 251 and the second spark plug 252 according to the operating state of the engine 1. The first spark plug 251 and the second spark plug 252 receive a control signal from the ECU 10 and ignite the air-fuel mixture at specified timing. The ECU 10 may not output a control signal to the first spark plug 251 and the second spark plug 252. In this case, the first ignition plug 251 and the second ignition plug 252 do not ignite the air-fuel mixture.

As described above, the engine 1 operates by switching between a plurality of combustion modes depending on its operating state. This ensures combustion stability and suppresses abnormal combustion over a wide operating range.

FIG. 9 illustrates the relationship between the G/F of the air-fuel mixture and the in-cylinder temperature T _IVC , which makes it possible to ensure combustion stability and suppress abnormal combustion in each combustion mode. More precisely, the cylinder temperature T _IVC is the cylinder temperature when the intake valve 21 is closed. Further, FIG. 9 shows an example in which the rotational speed of the engine 1 is 2000 rpm and the IMEP (Indicated Mean Effective Pressure) is approximately 400 kPa.

(Homogeneous SI combustion)
Homogeneous SI combustion can ensure combustion stability and suppress abnormal combustion when G/F is relatively small. As G/F increases, that is, as G/F becomes leaner, the combustion period of the air-fuel mixture becomes longer. Even if an attempt is made to shorten the combustion period by advancing the ignition timing, if the G/F becomes too large, combustion stability cannot be ensured. In other words, there is a maximum G/F that allows homogeneous SI combustion (see the solid line in FIG. 9).

Furthermore, when the _TIVC becomes high in temperature due to an increase in the amount of internal EGR gas, the combustion period becomes longer due to slower combustion. The combustion period can be shortened by advancing the ignition timing until the _TIVC reaches a certain temperature. If the temperature of the _TIVC becomes higher, abnormal combustion is more likely to occur. Even if an attempt is made to suppress abnormal combustion by retarding the ignition timing, if the _TIVC becomes too high temperature, the ignition timing becomes too late and combustion stability cannot be ensured. In other words, there is also a maximum in-cylinder temperature T _IVC that allows homogeneous SI combustion.

(HCCI combustion)
HCCI combustion can ensure combustion stability and suppress abnormal combustion when G/F is relatively large and in-cylinder temperature T _IVC is relatively high. When G/F becomes small, that is, when G/F becomes rich, compression ignition combustion becomes too intense, leading to abnormal combustion. Even if an attempt is made to slow combustion by delaying the ignition timing by lowering the in-cylinder temperature T _IVC , if the in-cylinder temperature T _IVC becomes too low, combustion stability will deteriorate. In other words, there is a minimum G/F that allows HCCI combustion, and a minimum in-cylinder temperature T _IVC that allows HCCI combustion (see the solid line in FIG. 9).

As is clear from FIG. 9, the "G/F-T _IVC range" where homogeneous SI combustion is possible and the "G/F-T _IVC range" where HCCI combustion is possible are far apart. As mentioned above, if only the switching between homogeneous SI combustion and HCCI combustion is performed in response to changes in the load of the engine 1, the G/F of the mixture and the in-cylinder Temperature _TIVC must be changed significantly. The G/F of the mixture and the cylinder temperature T _IVC are mainly adjusted by adjusting the intake air charging amount, but due to the response delay of the intake S-VT231, intake CVVL232, exhaust S-VT241, and exhaust VVL242, It is difficult to instantaneously change the G/F of the air-fuel mixture and the in-cylinder temperature T _IVC in response to switching the combustion mode.

(Retard SI combustion)
As mentioned above, if the G/F of the air-fuel mixture is made lean or the in-cylinder temperature _TIVC is made high within the operable range of homogeneous SI combustion, combustion stability cannot be ensured. In retard SI combustion, as described above, the injector 6 injects fuel into the cylinder 11 near compression top dead center, that is, before the first spark plug 251 and the second spark plug 252 are ignited. Since fuel is not injected into the cylinder 11 until just before ignition, pre-ignition can be avoided.

Fuel injection near compression top dead center creates a flow within the cylinder 11, and after the first spark plug 251 and second spark plug 252 are ignited, the flame quickly propagates using the flow. In this way, rapid combustion is achieved, and combustion stability can be ensured while suppressing knocking. The "G/F-T _IVC range" where retard SI combustion is possible has a larger G/F of the mixture than the "G/F-T _IVC range" where homogeneous SI combustion is possible (see the broken line in Figure 9). . Retard SI combustion expands the operable range to the lean side of G/F compared to homogeneous SI combustion.

(SPCCI combustion)
When the G/F of the air-fuel mixture is made leaner or the in-cylinder temperature T _IVC is made higher than in the operable range of retard SI combustion, the flame is increased by the ignition of the first spark plug 251 and the second spark plug 252. After propagation combustion begins, mild compression ignition combustion, which is different from knocking, begins. SPCCI combustion, which includes controlled compression ignition combustion, has a larger G/F than the "G/F-T _IVC range" in which retard SI combustion is possible (see the dashed line in FIG. 9). SPCCI combustion expands the operable range to the lean side of G/F compared to homogeneous SI combustion and retard SI combustion. However, a large gap still exists between the "G/F-T _IVC range" of SPCCI combustion and the "G/F-T _IVC range" of HCCI combustion.

(MPCI combustion)
Compared to the operable range of HCCI combustion, MPCI combustion expands the operable range to the rich side of G/F and the low temperature side of _TIVC .

First, when the G/F of the air-fuel mixture is made richer than the range in which HCCI combustion can be operated, compression ignition combustion becomes intense, leading to abnormal combustion. In order to slow compression ignition combustion, squish injection in MPCI combustion injects fuel into the cylinder 11 in the middle of the compression stroke. As described above, the injected fuel reaches the squish region 171 outside the cavity 31, locally increases the fuel concentration in the squish region 171, and lowers the temperature. As a result, the timing of compression ignition is retarded and combustion becomes slower. Squish injection mainly expands the operable range to the rich side of G/F compared to the operable range of HCCI combustion.

Next, when the T _IVC is lowered to a lower temperature than the operable range of HCCI combustion, the timing of compression ignition is retarded, combustion becomes too slow, and combustion stability deteriorates. Trigger injection for MPCI combustion injects fuel into the cylinder 11 at the end of the compression stroke so that the timing of compression ignition is advanced. As described above, the injected fuel does not diffuse within the cavity 31 and forms an air-fuel mixture having a high fuel concentration. As a result, compression ignition starts immediately after the fuel is injected, and the surrounding homogeneous air-fuel mixture also quickly undergoes self-ignition combustion. Trigger injection mainly expands the operable range of _TIVC to the low temperature side compared to the operable range of HCCI combustion.

A portion of the "G/F-T _IVC range" of MPCI combustion overlaps with the "G/F-T _IVC range" of the SPCCI region. The gap between the "G/F-T _IVC range" of homogeneous SI combustion and retard SI combustion and the "G/F-T _IVC range" of HCCI combustion is filled.

Here, the "G/F-T _IVC range" of MPCI combustion is divided into a region where squish injection is performed and a region where trigger injection is performed (see the dividing line shown by the broken line in FIG. 9). The region where squish injection is performed is the region where G/F is relatively small and the in-cylinder temperature TIVC is relatively high in the "G/F-T _IVC range" of MPCI combustion. The region where trigger injection is performed is the region where G/F is relatively large and the in-cylinder temperature T _IVC is relatively low in the "G/F-T _IVC range" of MPCI combustion.

(engine operation control)
The ECU 10 adjusts the G/F of the air-fuel mixture and the in-cylinder temperature T _IVC in accordance with the base map shown in FIG. 4 so as to realize a combustion form corresponding to the required load and rotation speed of the engine 1.

However, due to a delay in response of the variable valve system, etc., the G/F of the air-fuel mixture and/or the in-cylinder temperature _TIVC may deviate without corresponding to the operating state of the engine 1. If the air-fuel mixture G/F and/or in-cylinder temperature T _IVC deviates from the target G/F and/or target in-cylinder temperature T _IVC , the air-fuel mixture will not be combusted in the targeted combustion form. This may result in decreased combustion stability or abnormal combustion. Therefore, the ECU 10 temporarily sets a combustion form according to the operating state of the engine 1, determines a target G/F and/or a target in-cylinder temperature T _IVC , and controls the variable valve system. The ECU 10 also switches the combustion mode according to the actual G/F and/or the actual in-cylinder temperature T _IVC , or more precisely, the predicted G/F and/or the predicted in-cylinder temperature T _IVC . , adjusts fuel injection timing and whether or not ignition is necessary.

FIG. 10 illustrates a selection map related to operation control of the engine 1. FIG. 10 shows an enlarged view of the third region in which HCCI combustion is performed in the first base map 401 of FIG. 4, that is, the low-load region 415. The low load region 415 is defined by the rotation speed and load of the engine 1. The low load region 415 is further subdivided with respect to the load and rotation speed of the engine 1, as illustrated in FIG. In the selection map of FIG. 10, as an example, the low load area 415 is divided into nine parts, but the number of divisions is not particularly limited. Although not shown, a selection map is also set for each area in the base map of FIG. 4.

A “G/F-T _IVC range” corresponding to FIG. 9 is set for each divided area within the low load area 415. As described above, the "G/F-T _IVC range" defines the combustion form according to the G/F of the air-fuel mixture and the in-cylinder temperature T _IVC . The ECU 10 sets the combustion form (that is, provisionally sets) according to the required load and rotation speed of the engine 1 according to the base map shown in FIG. , the combustion form is finally determined according to the required load and rotational speed, the predicted G/F, and the predicted in-cylinder temperature T _IVC .

Here, as illustrated in FIG. 10, the "G/F-T _IVC range" changes depending on the load and rotation speed of the engine 1. When the rotation speed is high, HCCI combustion, MPCI combustion, and SPCCI combustion are possible even if the cylinder temperature is high. When the rotational speed of the engine 1 is low, HCCI combustion and MPCI combustion are not possible unless the temperature decreases.

In addition, when comparing under the same load, the higher the rotation speed of engine 1, the larger the "G/F-T _IVC range" of SPCCI combustion, and the larger the "G/F-T _IVC range" of retard SI combustion. to shrink. Conversely, as the rotational speed of the engine 1 decreases, the "G/F-T _IVC range" of SPCCI combustion becomes smaller, and the "G/F-T _IVC range" of retard SI combustion expands.

In addition, when comparing at the same rotation speed, the "G/F-T _IVC range" of both HCCI combustion and MPCI combustion is such that the lower the load of engine 1, the lower the minimum temperature of the cylinder temperature T _IVC is on the high temperature side. Move to.

In this way, the "G/F-T _IVC range" changes depending on the load and rotation speed of the engine 1. In particular, as illustrated in FIG. 11, among the control factors, the magnitude of G/F (hereinafter also referred to as switching G/F), which is the boundary between the combustion modes to be selected, is determined by the in-cylinder temperature T _IVC . If the required load is constant and fixed, it will vary greatly depending on the engine speed.

_FIG . 11 shows a combustion mode in which all of the air-fuel mixture is subjected to compression ignition combustion (MPCI combustion or HCCI combustion) and a combustion mode in which at least a portion of the air-fuel mixture is subjected to flame propagation combustion (SPCCI combustion, 3 is a graph illustrating a relationship between a switching G/F that is a boundary between retard SI combustion (retard SI combustion or homogeneous SI combustion) and engine rotation speed.

Here, the in-cylinder temperature T _IVC in FIG. 11 is a temperature at which at least HCCI combustion can be realized, and is set to, for example, around 400K. Further, the range of the required load in FIG. 11 is a value below the required load that allows HCCI combustion shown in FIGS. 4 and 10.

The vertical axis in FIG. 11 is the switching G/F that is the boundary between MPCI combustion and SPCCI combustion, and is defined by the "G/F-T _IVC range" of MPCI combustion. The ECU 10 executes MPCI combustion or HCCI combustion if the switching G/F is greater than or equal to this switching G/F, while executing SPCCI combustion, retard SI combustion, or homogeneous SI combustion if it is lower than this switching G/F.

In addition, in FIG. 11, the plots indicated by black squares indicate the switching G/F when the required load is relatively high, and the plots indicated by black circles indicate that the required load is relatively higher than the plots indicated by black squares. The plot shown by a black triangle shows the switching G/F when the required load is relatively lower than the plot shown by a black circle.

For example, plots A1 to A3 in FIG. 11 correspond to plots A1 to A3 shown in FIG. 10, respectively. Of course, the selection map shown in FIG. 10 and the graph shown in FIG. 11 are merely examples for explanation. The aspect of the selection map changes seamlessly depending on the required load and rotation speed. According to the change, the graph shown in FIG. 11 also changes continuously. In other words, although each plot shown in FIG. 11 corresponds to each map in FIG. 10, these plots are merely examples, and similar trends will be shown if the in-cylinder temperature T _IVC is kept constant. There is.

As shown in Fig. 11, when the required load is fixed, the magnitude of the switching G/F when the rotational speed (engine rotational speed) is low is smaller than the switching G/F when the rotational speed is high. Recognize. When the rotation speed is relatively low, the piston speed is slower than when it is relatively high. Therefore, when the rotation speed is low, the switching G/F is smaller than the switching G/F when the rotation speed is high. Even if /F is used, MPCI combustion and HCCI combustion can be appropriately realized.

As shown in FIG. 11, although the switching G/F also depends on the required load, at least when the required load is fixed, the relationship between the switching G/F and the rotation speed is the same for each required load. Become common.

Based on these facts, in the present embodiment, the ECU 10 predicts the mass ratio (G/F) of intake air in the cylinder containing burnt gas to fuel, and determines that the required load is the first engine load and the rotational speed is is the first engine rotation speed, and when G/F is predicted to be higher than the first G/F, the injector 6, the first spark plug 251, and the second spark plug 252 are controlled to perform HCCI combustion or MPCI combustion. While combustion is executed, when the G/F is predicted to be lower than the first G/F, the injector 6 is controlled to execute SPCCI combustion, retard SI combustion, or homogeneous SI combustion.

In the present embodiment, when the rotation speed is a second engine rotation speed smaller than the first engine rotation speed under the first engine load, the ECU 10 controls a second G/F smaller than the first G/F when the rotation speed is a second engine rotation speed smaller than the first engine rotation speed. /F is predicted to be lower than the second G/F, the injector 6, the first spark plug 251, and the second spark plug 252 are controlled to perform HCCI combustion or MPCI combustion, while the G/F is higher than the second G/F. When predicting this, the injector 6 is controlled to execute SPCCI combustion, retard SI combustion, or homogeneous SI combustion.

Here, the first engine load is a required load arbitrarily set within a range in which at least HCCI combustion or MPCI combustion can be performed.

Therefore, at the second engine speed, the ECU 10 according to the present embodiment is configured to switch G, which is a boundary between a combustion mode in which at least a part of the air-fuel mixture is flame propagation combustion and a combustion mode in which all the air-fuel mixtures are subjected to compression ignition combustion. /F (second G/F) is set smaller than the switching G/F (first G/F) at the first engine speed. As a result, it becomes possible to expand the range of G/F in which MPCI combustion or HCCI can be performed to the low G/F side. By expanding the range of G/F, it becomes possible to switch from flame propagation combustion to compression ignition combustion more quickly, which in turn makes it possible to improve fuel efficiency.

In addition, as shown in FIG. 10, in addition to switching G/Fs (1st G/F, 2nd G/F) for selectively using MPCI combustion or HCCI combustion, SPCCI combustion, retard SI combustion, or homogeneous SI combustion, Furthermore, a switching G/F (third G/F) for selectively using MPCI combustion and HCCI combustion is also set. Specifically, when controlling the injector 6 so that all the air-fuel mixtures in the cylinder 11 undergo compression ignition combustion, the ECU 10 according to the present embodiment selects a third G/F whose G/F is larger than the first G/F. When the G/F is predicted to be higher than the first G/F and lower than the third G/F, the MPCI combustion is executed.

As described above, when performing HCCI combustion, the ECU 10 controls the injector 6 to inject fuel within the intake stroke period, and when performing MPCI combustion, the ECU 10 controls the injector 6 to inject fuel during the intake stroke period and during the compression stroke period when performing MPCI combustion. The injector 6 is configured to be controlled to inject fuel during each stroke period.

Furthermore, as shown in FIG. 10, a switching G/F (fourth G/F) for selectively using SPCCI combustion, retard SI combustion, or homogeneous SI combustion is also set. Specifically, the ECU 10 according to the present embodiment controls the G When /F is predicted to be higher than the fourth G/F, SPCCI combustion is performed, and when G/F is predicted to be lower than the fourth G/F, retard SI combustion or homogeneous SI combustion is performed.

In this way, by setting the switching G/F corresponding to each combustion mode, at least a part of the air-fuel mixture can be set to a combustion mode in which flame propagation combustion occurs (homogeneous SI combustion, retard SI combustion, SPCCI combustion), or all The combustion mode can be seamlessly switched to a combustion mode in which the mixture is subjected to compression ignition combustion (MPCI combustion, HCCI combustion). This ensures combustion stability and suppresses abnormal combustion.

Next, a procedure for controlling the operation of the engine 1 executed by the ECU 10 will be described with reference to FIGS. 12 and 13. First, in step S1, the ECU 10 acquires measurement signals from various sensors, and in the subsequent step S2, the ECU 10 calculates the target torque Tq (or required load) from the engine rotation speed Ne and the accelerator opening degree APO. .

In step S3, the ECU 10 selects the first base map 401 or the second base map 402 in FIG. , tentatively determine the combustion form from the selected base map.

In step S4, the ECU 10 calculates a target valve timing TV and a target valve lift VL for each of the intake valve 21 and the exhaust valve 22 from the operating state of the engine 1. The target valve lift VL includes the valve lift of the intake valve 21 that is continuously changed by the intake CVVL 232 and the cam of the exhaust valve 22 that is changed by the exhaust VVL 242. Furthermore, in step S4, the ECU 10 calculates a target fuel injection amount Qf.

In step S5, the ECU 10 outputs control signals to the intake S-VT 231, intake CVVL 232, exhaust S-VT 241, and exhaust VVL 242 so that the target valve timing VT and valve lift VL are achieved.

In step S6, the ECU 10 determines the actual valve timing VT and valve lift VL of the intake valve 21, and the actual valve lift VL of the intake valve 21, based on the measurement signals of the intake cam angle sensor SW8, the exhaust cam angle sensor SW9, and the intake cam lift sensor SW10. 22 actual valve timing VT and valve lift VL are detected.

In step S7, the ECU 10 controls the _{amount of} burned gas (EGR amount) and the amount of air.

Then, in step S8, the ECU 10 predicts the G/F of the air-fuel mixture and the in-cylinder temperature T _IVC from the fuel injection amount Qf and the amount of burned gas and air amount estimated in step S7.

Next, in step S9, a G/F for switching the combustion form, that is, a switching G/F is set based on the target torque Tq calculated in step S2 and the rotational speed Ne acquired in step S1. This switching G/F is set for each of HCCI combustion, MPCI combustion, SPCCI combustion, and SI combustion, like the first and second G/F, third G/F, and fourth G/F described above. Note that the term "SI combustion" herein includes retard SI combustion and homogeneous SI combustion.

In step S10, the ECU 10 determines a combustion form according to the G/F predicted in step S8. Specifically, in this step S10, the ECU 10 executes the flow shown in FIG. 13.

Specifically, in step S101, the ECU 10 determines whether the predicted G/F is greater than or equal to the switching G/F to HCCI combustion. If the predicted G/F is equal to or higher than the switching G/F to HCCI combustion (step S101: YES), the ECU 10 proceeds to step S102, while the predicted G/F is the switching G/F to HCCI combustion. If it is lower than /F (step S101: NO), the process advances to step S103.

When proceeding to step S102, the ECU 10 sets the combustion form to HCCI combustion.

On the other hand, if the process proceeds to step S103, the ECU 10 determines whether the predicted G/F is greater than or equal to the switching G/F to MPCI combustion. If the predicted G/F is equal to or higher than the switching G/F to MPCI combustion (step S103: YES), the ECU 10 proceeds to step S104, while switching the predicted G/F to MPCI combustion. If it is lower than G/F (step S103: NO), the process advances to step S105.

When proceeding to step S104, the ECU 10 sets the combustion form to MPCI combustion.

On the other hand, if the process proceeds to step S105, the ECU 10 determines whether the predicted G/F is greater than or equal to the switching G/F to SPCCI combustion. If the predicted G/F is greater than or equal to the predicted G/F for switching to SPCCI combustion (step S105: YES), the ECU 10 proceeds to step S106, while changing the predicted G/F for switching to SPCCI combustion. If it is lower than F (step S105: NO), the process advances to step S107.

When proceeding to step S106, the ECU 10 sets the combustion form to SPCCI combustion.

On the other hand, if the process proceeds to step S107, the ECU 10 sets the combustion mode to SI combustion.

Returning to FIG. 12, after the selection of the combustion form is completed in step S10, the process proceeds to step S11, where the ECU 10 selects the ignition timing IGT and the injection pattern, that is, the injection timing, corresponding to the determined combustion form. decide.

In step S12, the ECU 10 outputs a control signal to the injector 6. The injector 6 injects fuel according to the determined injection pattern. The ECU 10 also outputs a control signal to the first spark plug 251 and the second spark plug 252 when igniting. The first spark plug 251 and the second spark plug 252 ignite the air-fuel mixture.

By following the flow shown in FIG. 11, the ECU 10 sets the timing at which the injector 6 injects fuel, taking into account the response delay of the variable valve system when changing the G/F of the air-fuel mixture according to the requested engine load. can. Since the air-fuel mixture is combusted in a combustion form that is compatible with the conditions inside the cylinder 11, the engine 1 has combustion stability that satisfies standards and can suppress abnormal combustion.

Note that the engine to which the technology disclosed herein is applicable is not limited to the engine with the above-described configuration. The technology disclosed herein is applicable to engines of various configurations.

1 Engine 10 ECU (controller)
11 Cylinder 21 Intake valve 22 Exhaust valve 231 Intake S-VT (variable valve mechanism)
232 Intake CVVL (variable valve mechanism)
241 Exhaust S-VT (variable valve mechanism)
242 Exhaust VVL (variable valve mechanism)
251 First spark plug 252 Second spark plug 3 Piston 31 Cavity 6 Injector

Claims (6)

An engine having a cylinder and a piston reciprocatably housed in the cylinder;
an injector attached to the engine and injecting fuel into the cylinder;
a spark plug attached to the engine and igniting a mixture of fuel, air, and intake air containing burnt gas;
a variable valve device connected to each of the intake valve and the exhaust valve and controlling the opening and closing of the intake valve and the exhaust valve so as to adjust the intake air filling amount;
electrically connected to the injector, the spark plug, and the variable valve device, and controlling each of the injector, the spark plug, and the variable valve device according to a required engine load of the engine; and a controller to
The controller is
predicting the mass ratio of intake air in the cylinder containing burnt gas to fuel;
When the requested engine has the first engine load and the engine speed is the first engine speed, when the mass ratio is predicted to be lower than the first G/F, at least a portion of the air-fuel mixture in the cylinder The injector and the spark plug are controlled so that flame propagation combustion occurs, while when the mass ratio is predicted to be higher than the first G/F, all of the air-fuel mixture in the cylinder is controlled by compression ignition combustion. controlling the injector;
When the engine speed is a second engine speed that is lower than the first engine speed under the first engine load, the mass ratio is lower than a second G/F that is smaller than the first G/F. When predicting, the injector and the spark plug are controlled so that at least a part of the air-fuel mixture in the cylinder undergoes flame propagation combustion, while when predicting that the mass ratio is higher than the second G/F, controlling the injector so that all of the air-fuel mixture in the cylinder undergoes compression ignition combustion;
An engine system characterized by: The engine system according to claim 1,
The controller is configured to: when the engine speed is the first engine speed at the first engine load;
When predicting that the mass ratio is higher than the third G/F, which is larger than the first G/F, the injector is adjusted so that the injection center of gravity based on the fuel injection timing and injection amount in one cycle is at the first timing. controlling the spark plug and not driving the spark plug so that all the air-fuel mixture in the cylinder undergoes compression ignition combustion;
When predicting that the mass ratio is higher than the first G/F and lower than the third G/F, the injector is controlled so that the injection center of gravity is at a second timing later than the first timing, and , the spark plug is not driven so that all the air-fuel mixture in the cylinder undergoes compression ignition combustion;
An engine system characterized by: The engine system according to claim 2,
When the engine rotation speed is the first engine rotation speed at the first engine load, the controller:
When predicting that the mass ratio is higher than the third G/F, controlling the injector to inject fuel within an intake stroke period;
When predicting that the mass ratio is higher than the first G/F and lower than the third G/F, the injector is controlled to inject fuel in each of an intake stroke period and a compression stroke period. do,
An engine system characterized by: The engine system according to claim 2 or 3,
When the controller controls the injector and the spark plug so that at least a part of the air-fuel mixture in the cylinder undergoes flame propagation combustion at the first engine load,
When predicting that the mass ratio is higher than a fourth G/F, driving the spark plug so that at least a portion of the air-fuel mixture in the cylinder undergoes flame propagation combustion and the remainder undergoes compression ignition combustion;
When predicting that the mass ratio is lower than the fourth G/F, driving the spark plug so that all of the air-fuel mixture in the cylinder undergoes flame propagation combustion.
An engine system characterized by: The engine system according to any one of claims 1 to 4,
The variable valve device opens and closes the intake valve and the exhaust valve so that the burned gas remains in the cylinder or is introduced into the cylinder through the intake valve or the exhaust valve. control,
An engine system characterized by: The engine system according to any one of claims 1 to 5,
the engine has a geometric compression ratio of 15 or more;
An engine system characterized by:

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