JP7435414B2 - engine system - Google Patents

Description

The technology disclosed herein belongs to the technical field related to engine systems.

It has been known that compression self-ignition combustion (hereinafter referred to as CI (Compression Ignition) combustion) improves the thermal efficiency of an engine.

For example, Patent Document 1 states that when the engine load is low, CI combustion, more precisely HCCI (Homogeneous Charged Compression Ignition) combustion is performed, and when the engine load is high, a spark plug is used. An engine that uses SI (Spark Ignition) combustion is described. The engine of Patent Document 1 is configured to switch 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 extensive research on CI combustion and found that the controlling factors for CI combustion are mainly the air-fuel mixture temperature in the cylinder and the mass ratio of intake air in the cylinder containing burnt gas to fuel ( G/F), and the ignition timing and combustion period of CI combustion can be controlled by setting the in-cylinder temperature ( _TIVC ) and G/F at the timing when the intake valve closes to the target T _IVC and G/F. I understand. According to the research conducted by the inventors of the present application, it has been found that the contribution of _TIVC is particularly large, and that there is a large gap between _TIVC capable of CI combustion and _TIVC capable of SI combustion.

The fact that SI combustion is possible means that the combustion stability of SI combustion satisfies standards and that abnormal combustion can be suppressed. The fact that CI combustion is possible means that the combustion stability of CI combustion satisfies standards and that abnormal combustion can be suppressed. In SI combustion, this abnormal combustion is knocking or pre-ignition when _TIVC is high, and in CI combustion, it is too steep combustion or misfire when _TIVC is low.

Even if switching from CI combustion to SI combustion, or from SI combustion to CI combustion, as in the engine described in Patent Document 1, the _TIVC in the cylinder is switched. It is difficult to instantaneously change to _TIVC corresponding to the previous combustion form.

Further, according to the research conducted by the inventors of the present application, it was found that the _TIVC that enables CI combustion differs depending on the engine speed. Therefore, even if the engine load is such that CI combustion is possible, CI combustion cannot be performed appropriately unless the _TIVC conditions are satisfied. If CI combustion cannot be performed appropriately, it is not possible to simultaneously improve fuel efficiency and combustion stability.

The technology disclosed herein was developed in view of these points, and its purpose is to improve fuel efficiency and improve combustion in an engine system that performs CI combustion depending on the engine load and engine speed. The goal is to achieve both improved stability and improved stability.

As a result of intensive research to solve the above problem, the inventors of the present application have found that even if the engine load is one that allows CI combustion, the _combustion We have discovered a third combustion form that meets standards for stability and suppresses abnormal combustion.

Specifically, the technology disclosed herein targets an engine system including an engine having a cylinder and a piston reciprocably housed in the cylinder, which is attached to the engine and supplies fuel into the cylinder. An injector that injects the fuel, a spark plug that is attached to the engine and that ignites a mixture of intake air containing fuel, air, and burnt gas, and that is connected to each of the intake valve and the exhaust valve and that adjusts the intake air filling amount. a variable valve device that controls opening and closing of the intake valve and the exhaust valve; and a variable valve device that is electrically connected to the injector, the spark plug, and the variable valve device, and that is adapted to the required engine load of the engine. Accordingly, the controller includes a controller that controls each of the injector, the spark plug, and the variable valve device, and the controller is configured to: , the controller is configured to control the injector and the spark plug to perform compression ignition combustion of the air-fuel mixture in the cylinder; If the engine rotation speed is the first engine rotation speed at the predetermined engine load, and the intake valve closing temperature is equal to or higher than the first temperature, the intake valve closing temperature is estimated to be the temperature within The injector is configured to perform compression ignition combustion of all the air-fuel mixture in the cylinder, while causing at least a portion of the air-fuel mixture in the cylinder to undergo flame propagation combustion when the intake valve closing temperature is lower than the first temperature. and controlling the spark plug, and when the engine speed is a second engine speed lower than the first engine speed at the predetermined engine load, the intake valve closing temperature is lower than the first temperature. When the temperature is at least a low second temperature, all of the air-fuel mixture in the cylinder is subjected to compression ignition combustion, while when the intake valve closing temperature is lower than the second temperature, at least part of the air-fuel mixture in the cylinder is performed. The injector and the spark plug are controlled to cause flame propagation combustion.

According to this configuration, when the required engine load is a predetermined engine load, it is possible to perform compression ignition combustion of the air-fuel mixture in the cylinder. This improves the fuel efficiency of the engine and improves fuel efficiency.

Further, when the operating state of the engine is such that the engine speed and engine load are such that compression ignition combustion is possible, and when the intake valve closing temperature ( _TIVC ) is equal to or higher than the first temperature, the controller controls the temperature of the mixture in the cylinder. All of the gas is subjected to compression ignition combustion (CI combustion). On the other hand, when the engine speed and engine load are such that compression ignition combustion is possible and the intake valve closing temperature ( _TIVC ) is lower than the first temperature, at least a portion of the air-fuel mixture in the cylinder is subjected to flame propagation combustion. (SI combustion).

That is, when T _IVC is lower than the first temperature, combustion stability deteriorates even if it is attempted to perform CI combustion of all the air-fuel mixture in the cylinder. Therefore, at least a part of the air-fuel mixture in the cylinder is subjected to SI combustion. With SI combustion, the air-fuel mixture can be stably combusted even if the _TIVC is somewhat low. Further, since the temperature inside the cylinder can be increased by SI combustion, the _TIVC can be raised to the first temperature or higher at an early stage, and all the air-fuel mixture in the cylinder can be subjected to CI combustion.

Further, when the engine speed is a second engine speed that is lower than the first engine speed, the combustion mode is switched at a second temperature that is lower than the first temperature. In other words, the _TIVC , which switches between a combustion mode in which all of the air-fuel mixture in the cylinder is subjected to CI combustion, and a combustion mode in which at least a portion thereof is SI combustion, is lowered. If the engine load is high, the amount of fuel injected is generally large, resulting in a relatively rich mixture, so even if the _TIVC is low, the combustion stability of CI combustion can be improved. Thereby, it is possible to switch to CI combustion at an early stage, and fuel efficiency can be improved.

Therefore, in an engine system that performs CI combustion, it is possible to improve both fuel efficiency and combustion stability.

In one embodiment of the engine system, when the engine speed is the first engine speed at the predetermined engine load and the intake valve closing temperature is lower than the first temperature, the controller: The spark plug is driven 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.

According to this configuration, when T _IVC is low, ignition assist is performed to perform compression ignition combustion, so-called SPCCI (Spark Controlled Compression Ignition) combustion. In other words, when the _TIVC is low, a part of the fuel is SI-combusted while the rest is CI-combusted, so that it is possible to further improve fuel efficiency while improving combustion stability.

In the engine system, when the engine speed is the first engine speed at the predetermined engine load, the combustion form when the intake valve closing temperature is equal to or higher than the first temperature is: The injector is controlled so that the injection center of gravity based on the fuel injection timing and injection amount during one cycle is at the first timing, and the spark plug is activated so that all the air-fuel mixture in the cylinder is subjected to compression ignition combustion. A first compression ignition combustion mode that is not driven, and controlling the injector so that the injection center of gravity is at a second timing later than the first timing, and controlling the ignition so that all the air-fuel mixture in the cylinder is compression ignited. a second compression ignition combustion mode in which the plug is not driven, and the controller is configured such that the intake valve closing temperature is higher than the first temperature when the predetermined engine load is the first engine rotation speed. When the temperature is at least the third temperature, the first compression ignition combustion mode is executed, while when the intake valve closing temperature is at least the first temperature and lower than the third temperature, the second compression ignition combustion mode is executed. It may be configured to execute.

According to this configuration, when the operating state of the engine is such that the engine speed and engine load are such that compression ignition combustion is possible, and the T _IVC is considerably high, the controller controls the injector so that the center of gravity of the injection is at the first timing. control. 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 almost homogeneous mixture of fuel is formed in the cylinder. All the air-fuel mixture in the cylinder undergoes compression ignition combustion, that is, HCCI combustion. Since T _IVC is sufficiently high, the combustion stability of HCCI combustion is increased. Note that 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.

On the other hand, when the T _IVC is higher than the first temperature but lower than the third temperature, the controller controls the injector and the like so that the combustion mode is different from HCCI combustion. Specifically, the controller controls the injector so that the injection center of gravity is at the relatively late second timing. Note that the injector may inject the fuel all at once or in parts. If the injection center of gravity is relatively late, the timing of supplying fuel into the cylinder is delayed, resulting in a short time from fuel injection to ignition. Therefore, unlike the case where the injection center of gravity is at the first timing, the air-fuel mixture in the cylinder does not become homogeneous. Due to the non-homogeneous mixture, relatively rich mixtures can be partially formed. As a result, even if _TIVC is slightly low, all of the air-fuel mixture in the cylinder can be subjected to compression ignition combustion.

Therefore, in an engine system that performs CI combustion, it is possible to more effectively improve both fuel efficiency and combustion stability.

As explained above, according to the technology disclosed herein, in an engine system that performs CI combustion according to the engine load and engine speed, the combustion form is switched according to the _TICV , and the combustion form is switched according to the engine speed. By changing the _TIVC , which switches the combustion mode, it is possible to improve both fuel efficiency and combustion stability.

FIG. 1 is a diagram illustrating an engine system. The upper diagram in FIG. 2 is a plan view illustrating the structure of the combustion chamber of the engine, and the lower diagram is a sectional view taken along line II-II in the upper diagram. 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 injection 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 regions defined by T _IVC and G/F in which each combustion form is established. FIG. 10 is a diagram illustrating a combustion mode selection map within the HCCI region. FIG. 11 is an example of a graph showing the relationship between engine load and _TIVC , which switches between a combustion mode in which all of the air-fuel mixture is subjected to compression ignition combustion, and a combustion mode in which flame propagation combustion is used for at least part of the air-fuel mixture. FIG. 12 is a part of a flowchart illustrating a control procedure related to engine operation executed by the ECU. FIG. 13 is the remainder of a flowchart illustrating a control procedure related to engine operation executed by the ECU.

Hereinafter, embodiments of the 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, and 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 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 is composed of a central processing unit (CPU) 101 that executes programs, and RAM (Random Access Memory) and ROM (Read Only Memory), for example. It is equipped with a memory 102 that stores programs and data, and an I/F circuit 103 that 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 100 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 of the engine 1 when it 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 divided into a first high load low rotation area 413 including the maximum load and a second high load low rotation area 414 having a higher load than the first high load low rotation area 413. 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 areas with a higher load than the first high load low rotation area 423 with a relatively low load and the first high load low rotation area 423, and are a second high load area including the maximum load. It is divided into a 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 changes the opening/closing operations of the intake valve 21 and the exhaust valve 22, the fuel injection timing, and the presence or absence of ignition according to the required engine load for the engine 1 and the rotation speed of the engine 1. The combustion form of the air-fuel mixture in the cylinder 11 changes by changing the intake air filling amount, fuel injection timing, and whether or not ignition occurs. This engine 1 changes the combustion form 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 generation rate generated in the cylinder 11 by combustion of the air-fuel mixture, corresponding to each combustion mode. and 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 to 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 to a predetermined timing. The intake valve 21 and the exhaust valve 22 both open near the intake top dead center. The exhaust VVL 242 opens and closes the exhaust valve 22 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.

The square in FIG. 5, where the load is relatively low, is the injection period of the injector 6, and the area of the square 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.

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 referred to as retard 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. The internal EGR gas introduced into the cylinder 11 in large quantities 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. 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. This HCCI combustion corresponds to the first compression ignition combustion mode.

(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 performs compression ignition combustion of the air-fuel mixture in the cylinder 11. 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 in 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. The temperature within the cylinder 11 decreases locally, and the fuel becomes non-uniform throughout the cylinder 11. 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 fuel 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, the air-fuel mixture is quickly compressed and ignited after compression stroke injection, and compression ignition combustion can be promoted. Trigger injection increases combustion stability.

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. This MPCI combustion corresponds to the second compression ignition combustion mode.

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. As the load on the engine 1 increases, the G/F of the air-fuel mixture decreases. When the load on the engine 1 decreases, the amount of air introduced into the cylinder 11 decreases and the amount of burned gas increases.

Next, the fuel injection timing will be compared as the engine load changes. 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 fuel injection start timing and injection amount during one cycle, and is the median value of the crank angles from the time to the injection end timing. For example, the code chart 71 in FIG. 7 shows the injection timing soi_1 (start of injection) and the injection period pw_1 in the case of the batch injection shown in 4. 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 increases, the G/F of the air-fuel mixture decreases (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 retarded.

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

When the load on the engine 1 becomes higher, the G/F of the air-fuel mixture further decreases (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 injection center of gravity is 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. If this engine 1 only switches between HCCI combustion and homogeneous SI combustion or retard SI combustion, the load on engine 1 will change and the G/F of the mixture will need to be increased when switching the combustion form. Must be changed. 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 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.

Furthermore, even if the G/F is in a state where HCCI combustion can be performed, if the in-cylinder temperature T _IVC is low when the intake valve 21 is closed, the ignitability of the air-fuel mixture will decrease, so HCCI combustion can be performed normally. cannot be executed. In order to adjust this cylinder temperature T _IVC , it is necessary to adjust the intake air filling amount such as the amount of internal EGR gas. Therefore, as long as 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 very high, it is difficult to instantly change the in-cylinder temperature _TIVC . .

Although the details will be described later, MPCI combustion or SPCCI combustion aims to ensure combustion stability and suppress abnormal combustion when the air-fuel mixture is at an intermediate G/F and an intermediate in-cylinder temperature T _IVC . This is a combustion form that allows for This engine 1 quickly changes the G/F of the air-fuel mixture and the in-cylinder temperature _TIVC in response to changes in engine load, and changes the combustion mode to SI combustion, HCCI combustion, MPCI combustion, and SPCCI combustion. can be switched seamlessly. 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. Moreover, instead of split injection, the injector 6 may inject the fuel all at once so that the injection center of gravity is retarded than the injection center of gravity during HCCI combustion. 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.

(Modified example of opening/closing form of intake valve and exhaust valve)
FIG. 8 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. 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 the homogeneous SI, the lift curve 812 of the second retard SI, and the lift curve 813 of the first retard SI are the same as the lift curves 701, 705, and 709 in FIG. 5, respectively. The SPCCI lift curve 814, the MPCI lift curve 815, and the HCCI lift curve 816 are different from the 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 lift curve 814, the MPCI lift curve 815, and the HCCI 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 over period becomes longer as the load on the engine 1 becomes lower.

Although not shown, the variable valve system provides a positive overlap period in which both the intake valve 21 and the exhaust valve 22 are open, sandwiching 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 rotation 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 in-cylinder temperature _TIVC becomes high 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 cylinder temperature T _IVC reaches a certain level. If the cylinder temperature _TIVC becomes even 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 in-cylinder temperature _TIVC becomes too high, 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 and, for example, combustion noise exceeds an allowable range. 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 (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 and HCCI is performed in response to changes in the load of the engine 1, the G/F of the mixture and the in-cylinder temperature T will change according to the switching. _IVC has to 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, in homogeneous SI combustion, if the G/F of the mixture is made lean or if the in-cylinder temperature T _IVC is made high, 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 the operable range of homogeneous SI combustion.

(SPCCI combustion)
In the operational range of retard SI combustion, if the G/F of the air-fuel mixture is made leaner or the in-cylinder temperature T _IVC is made higher, flame propagation combustion occurs due to the ignition of the first spark plug 251 and the second spark plug 252. After this starts, mild compression ignition combustion begins, which is different from knocking. 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 the operable range of 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 fuel.

(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 in-cylinder temperature _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 in-cylinder temperature T _IVC is lowered from 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 to the lower temperature side of the cylinder temperature _TIVC 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 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 T _IVC 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 load and rotation speed of the engine 1. The inside of the low load area 415 is further subdivided as illustrated in FIG. In the selection map of FIG. 10, as an example, the low load region 415 is divided into three parts according to the rotation speed, but the number of divisions is not particularly limited. Although not shown, a selection map is set for each region 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 rotation speed of the engine 1. In particular, as illustrated in FIG. 11, when the required load of the engine 1 is constant, the T _IVC changes greatly depending on the rotation speed of the engine 1.

FIG. 11 shows the relationship between the switching temperature for HCCI combustion and the rotation speed of the engine 1 under the same load. The required load is a load that allows HCCI combustion, and is an example where IMEP is approximately 300 kPa. The rotation speed range shown in FIG. 11 is a value below the required load that allows HCCI combustion shown in FIGS. 4 and 10. The vertical axis of FIG. 11 is the switching temperature between MPCI combustion and SPCCI combustion, and the ECU 10 executes MPCI combustion or HCCI combustion if it is above this switching temperature, while performing SPCCI combustion or retard if it is lower than this switching temperature. Execute SI combustion or SI combustion.

The black circles (●) in FIG. 11 are when G/F is relatively high, and the black triangles (▲) are when G/F is relatively low.

As shown in FIG. 11, it can be seen that regardless of the value of G/F, the switching temperature is lower when the rotational speed is lower than when the rotational speed is high. In particular, it can be seen that the lower the rotation speed, the lower the switching temperature. If the rotation speed is low, the time it takes for the piston 3 to reach compression top dead center becomes longer. This increases the time for the air-fuel mixture in the cylinder 11 to be warmed. Therefore, even if the in-cylinder temperature T _IVC is low, the air-fuel mixture can be brought to a temperature at which compression self-ignition occurs stably, that is, a temperature at which HCCI combustion is stabilized. On the other hand, if the rotational speed is high, the time it takes for the piston 3 to reach the compression top dead center becomes shorter, so the time for warming the air-fuel mixture in the cylinder 11 becomes shorter. Therefore, unless the in-cylinder temperature T _IVC is made as high as possible, the air-fuel mixture cannot be brought to a temperature at which HCCI combustion is stabilized. Therefore, the lower the rotation speed, the higher the switching temperature can be set.

As shown in Fig. 11, the switching temperature also depends on the G/F, but it is small compared to the rotation speed, so basically, the switching temperature should be set according to the rotation speed. Can be done.

For these reasons, in the present embodiment, the ECU 10 sets the in-cylinder temperature T _IVC to a relatively high first temperature when the rotation speed is a relatively low first engine rotation speed at a predetermined required engine load. When the above is the case, HCCI combustion or MPCI combustion is performed without using SI combustion, while when the in-cylinder temperature T _IVC is lower than the first temperature, SPCCI combustion, retard SI combustion, or retard SI combustion is performed using SI combustion. When SI combustion is executed and the rotation speed is a relatively low second engine rotation speed at a predetermined required engine load, when the in-cylinder temperature _TIVC is equal to or higher than the relatively low second temperature, HCCI combustion is performed. Alternatively, MPCI combustion is performed, while when the in-cylinder temperature T _IVC is lower than the second temperature, SPCCI combustion, retard SI combustion, or SI combustion is performed. Note that the predetermined required engine load is a required load arbitrarily set within a range in which HCCI combustion is possible. As a result, when the in-cylinder temperature _TIVC is low, the combustion mode uses SI combustion for at least part of the combustion mode, increasing combustion stability and raising the temperature in the cylinder, making it possible to perform HCCI combustion and MPCI combustion. The in-cylinder temperature T _IVC can be set to a certain value. Therefore, it is possible to both improve fuel efficiency and improve combustion stability.

Note that when the rotation speed is a relatively high first engine rotation speed under a predetermined load, from the viewpoint of improving the thermal efficiency of the engine 1 as much as possible, when the in-cylinder temperature _TIVC is lower than the first temperature, SPCCI combustion I am trying to run it. Furthermore, as shown in FIGS. 9 and 10, there is some overlap between the operable range of MPCI combustion and the operable range of SPCCI combustion, but in this embodiment, MPCI combustion is given priority over SPCCI combustion. .

In addition, in this embodiment, from the viewpoint of further improving the combustion stability of CI combustion, the first combustion mode is capable of HCCI combustion or MPCI combustion, that is, a combustion mode in which all the air-fuel mixture in the cylinder 11 can be subjected to CI combustion. In the operable range above the temperature, MPCI combustion is performed when the in-cylinder temperature T _IVC is relatively low, and HCCI combustion is performed when the in-cylinder temperature T _IVC is relatively high.

In this embodiment, the switching temperature between HCCI combustion and MPCI combustion is also set to be lower as the rotation speed is lower. Thereby, the combustion mode can be switched to HCCI combustion as early as possible, and the fuel efficiency of the engine 1 can be further improved.

(flowchart)
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. Note that the engine load belongs to the engine load that executes HCCI combustion in the map of FIG.

First, in step S1, the ECU 10 acquires measurement signals from various sensors, and in the subsequent step S2, the ECU 10 calculates a target torque Tq from the engine rotation speed Ne and the accelerator opening degree APO. As described above, this target torque Tq (or required load) belongs to the engine load that executes HCCI combustion in the map of FIG. 4.

In step S3, the ECU 10 selects the first base map 401 or the second base map 402 of FIG. 4 based on the coolant temperature of the engine 1, and also selects the calculated target torque Tq and the rotation speed of the engine 1. The combustion form is tentatively determined based on the selected base map.

In step S4, the ECU 10 calculates target valve timing VT and 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, the ECU 10 sets the in-cylinder temperature T _IVC for switching the combustion mode, that is, the switching temperature, from the rotational speed Ne obtained in step S1 and the G/F predicted in step S8. This switching temperature is the switching temperature between HCCI combustion, MPCI combustion, SPCCI combustion, and SI combustion, the switching temperature between HCCI combustion and MPCI combustion, the switching temperature between MPCI combustion and SPCCI combustion, and the switching temperature between SPCCI combustion and SI combustion. Contains switching temperature. SI combustion includes retard SI combustion and homogeneous SI combustion.

In step S10, as shown in FIG. 13, the ECU 10 determines a combustion form according to the in-cylinder temperature T _IVC predicted in step S8.

Specifically, in step S101, the ECU 10 determines whether the predicted in-cylinder temperature T _IVC is equal to or higher than the switching temperature to HCCI combustion. When the predicted in-cylinder temperature T _IVC is higher than or equal to the switching temperature to HCCI combustion (YES), the _{ECU 10} proceeds to step S102; If so, the process advances to step S103.

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

On the other hand, in step S103, the ECU 10 determines whether the predicted in-cylinder temperature T _IVC is equal to or higher than the switching temperature to MPCI combustion. When the predicted in-cylinder temperature T _IVC is higher than or equal to the switching temperature to MPCI combustion (YES), the _{ECU 10} proceeds to step S104; If so, the process advances to step S105.

In step S104, the ECU 10 sets the combustion mode to MPCI combustion.

On the other hand, in step S105, the ECU 10 determines whether the predicted in-cylinder temperature T _IVC is a temperature that allows SPCCI combustion. When the predicted in-cylinder temperature _TIVC is a temperature that allows SPCCI combustion (YES), the ECU 10 proceeds to step S106, while when the predicted in-cylinder temperature _TIVC is a temperature that does not allow SPCCI combustion (NO), the ECU 10 proceeds to step S106. In some cases, the process advances to step S107.

In step S106, the ECU 10 sets the combustion mode to SPCCI combustion.

On the other hand, in 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.

Then, 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. After step S12, the process returns.

When changing the combustion mode according to the required load, it is possible to select an appropriate combustion mode and set the timing at which the injector 6 injects fuel, taking into account the response delay of the variable valve system. Since the air-fuel mixture is combusted in a combustion form suitable for the conditions inside the cylinder 11, combustion stability satisfies standards and abnormal combustion can be suppressed.

(summary)
Therefore, in this embodiment, the engine system includes an injector 6 that is attached to the engine 1 and injects fuel into the cylinder 11, and an injector 6 that is attached to the engine 1 and mixes the fuel with intake air containing air and burnt gas. It is connected to the first and second spark plugs 251 and 252 that ignite the air, and to the intake valve 21 and the exhaust valve 22, respectively, and controls the opening and closing of the intake valve 21 and the exhaust valve 22 so as to adjust the intake air filling amount. The variable valve device (intake S-VT231, intake CVVL232, exhaust S-VT241, exhaust VVL242), the injector 6, the first and second spark plugs 251, 252, and the variable valve device 231, 232, 241, 242, and each of the injector 6, the first and second spark plugs 251, 252, and the variable valve device 231, 232, 241, 242 is electrically connected to the engine load required by the engine 1. It includes an ECU 10 for controlling. When the required engine load is a predetermined engine load at a predetermined engine speed, the ECU 10 controls the injector 6 and the first and second spark plugs 251 and 252 to cause compression ignition combustion of the air-fuel mixture in the cylinder 11. It is configured to be able to execute the combustion mode that causes Furthermore, the ECU 10 estimates the in-cylinder temperature T _IVC , which is the temperature inside the cylinder 11 when the intake valve 21 is closed, and if the engine speed is the first engine speed at a predetermined engine load, the in-cylinder temperature When T _IVC is higher than the first temperature, all of the air-fuel mixture in the cylinder 11 is CI-combusted, while when the in-cylinder temperature T _IVC is lower than the first temperature, at least part of the air-fuel mixture in the cylinder 11 is burned. The injector 6 and the first and second spark plugs 251, 252 are controlled to perform SI combustion, and the engine rotation speed is a second engine rotation speed lower than the first engine rotation speed at the predetermined engine load. In this case, when the in-cylinder temperature T _IVC is equal to or higher than a second temperature lower than the first temperature, all of the air-fuel mixture in the cylinder 11 is subjected to CI combustion, while the in-cylinder temperature T _IVC is lower than the second temperature. When the temperature is low, the injector 6 and the first and second spark plugs 251 and 252 are controlled so that at least a portion of the air-fuel mixture in the cylinder 11 is SI-combusted. Thereby, the timing at which the injector 6 injects fuel can be set in consideration of the response delay of the variable valve device. Since the air-fuel mixture is combusted in a combustion form suitable for the conditions inside the cylinder 11, combustion stability satisfies standards and abnormal combustion can be suppressed. In particular, when the engine speed is low and it takes a long time to warm up the air-fuel mixture, by lowering the in-cylinder temperature _TIVC at which the combustion mode is switched, it is possible to quickly switch to the combustion mode in which all of the air-fuel mixture is combusted by CI. As a result, the thermal efficiency of the engine 1 can be improved at an early stage, and fuel efficiency can be improved. Therefore, it is possible to both improve fuel efficiency and improve combustion stability.

Further, in the present embodiment, when the engine speed is a relatively high first engine speed under a predetermined engine load, when the in-cylinder temperature T _IVC is lower than the first temperature, the air-fuel mixture in the cylinder 11 is The first and second spark plugs 251 and 252 are driven so that SPCCI combustion occurs. Thereby, when the in-cylinder temperature T _IVC is quite low, compression ignition can be performed even if the in-cylinder temperature T _IVC is quite low by performing SPCCI combustion. Further, if the in-cylinder temperature T _IVC increases due to SPCCI combustion, the combustion can be shifted to MPCI combustion or HCCI combustion, and all of the air-fuel mixture in the cylinder 11 can be compression ignited. Thereby, fuel efficiency can be further improved while improving combustion stability.

Further, in the present embodiment, when the engine speed is the first engine speed under a predetermined engine load, the ECU 10 executes MPCI combustion at a relatively low in-cylinder temperature T _IVC , and executes MPCI combustion at a relatively high in-cylinder temperature T _IVC. Perform HCCI combustion. Since MPCI combustion is stable even if the in-cylinder temperature T _IVC is somewhat low, such a configuration can further improve the combustion stability of CI combustion.

(Other embodiments)
The technology disclosed herein is not limited to the embodiments described above, and may be substituted without departing from the spirit of the claims.

In the embodiment described above, the combustion mode was selected after setting the switching temperature for switching the combustion mode based on the G/F and the rotation speed. The present invention is not limited to this, and the combustion mode may be determined by applying the G/F, rotation speed, and in-cylinder temperature T _IVC to a map as shown in FIG. 10.

The above-described embodiments are merely illustrative and should not be construed as limiting the scope of the present disclosure. The scope of the present disclosure is defined by the claims, and all modifications and changes that come within the range of equivalents of the claims are intended to be within the scope of the present disclosure.

The technology disclosed herein is useful in achieving both improved fuel efficiency and stability of combustion mode in an engine system including an engine having a cylinder and a piston reciprocatably housed in the cylinder.

1 Engine 3 Piston 6 Injector 10 ECU (controller)
11 Cylinder 21 Intake valve 22 Exhaust valve 31 Cavity 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

Claims (3)

An engine system including 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
When the required engine load is a predetermined engine load at a predetermined engine speed, the controller can control the injector and the spark plug to execute a combustion mode in which the air-fuel mixture in the cylinder is subjected to compression ignition combustion. It is composed of
Furthermore, the controller includes:
Estimating an intake valve closing temperature, which is the temperature inside the cylinder when the intake valve is closed;
When the engine speed is a first engine speed under the predetermined engine load, when the intake valve closing temperature is equal to or higher than the first temperature, all the air-fuel mixture in the cylinder is subjected to compression ignition combustion; When the intake valve closing temperature is lower than the first temperature, controlling the injector and the spark plug to cause flame propagation combustion of at least a portion of the air-fuel mixture in the cylinder;
When the engine rotation speed is a second engine rotation speed lower than the first engine rotation speed at the predetermined engine load, and when the intake valve closing temperature is equal to or higher than a second temperature lower than the first temperature, , all of the air-fuel mixture in the cylinder is subjected to compression ignition combustion, while at least a portion of the air-fuel mixture in the cylinder is subjected to flame propagation combustion when the intake valve closing temperature is lower than the second temperature; An engine system that controls the injector and the spark plug. The engine system according to claim 1,
The controller controls at least one of the air-fuel mixtures in the cylinder when the intake valve closing temperature is lower than the first temperature when the engine speed is the first engine speed at the predetermined engine load. An engine system characterized in that the spark plug is driven so that a part of the spark plug undergoes flame propagation combustion and the remainder causes compression ignition combustion. The engine system according to claim 1 or 2,
The controller controls the combustion mode when the intake valve closing temperature is equal to or higher than the first temperature when the engine speed is the first engine speed at the predetermined engine load.
The injector is controlled so that the injection center of gravity based on the fuel injection timing and injection amount during one cycle is at the first timing, and the spark plug is activated so that all the air-fuel mixture in the cylinder is subjected to compression ignition combustion. a first compression ignition combustion mode that is not driven;
A second compression ignition combustion mode in which 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 is compression ignited. and,
including;
The controller controls the first compression ignition combustion mode when the intake valve closing temperature is a third temperature higher than the first temperature when the predetermined engine load is the first engine rotation speed. The engine system is characterized in that, when the intake valve closing temperature is equal to or higher than the first temperature and lower than a third temperature, the second compression ignition combustion mode is executed.

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