JP7310574B2 - engine controller - Google Patents

Description

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

In recent years, in an engine that performs CI combustion of an air-fuel mixture in a combustion chamber by compression ignition, partial compression ignition combustion is performed in which a part of the air-fuel mixture is SI-burned by spark ignition, and then the remaining air-fuel mixture is CI-burned by compression ignition. there is something In an engine that performs partial compression ignition combustion, in addition to the timing of spark ignition, it is devised to adjust the timing of CI combustion by adjusting the state inside the combustion chamber.

For example, in the engine control device described in Patent Document 1, there is an EGR device that includes part of the burned gas generated in the combustion chamber as EGR gas in the mixture, and the ratio of the EGR gas introduced into the combustion chamber. an EGR operation unit capable of changing a certain EGR rate, and during execution of partial compression ignition combustion, the EGR operation unit is configured to increase the compression start temperature of the combustion chamber when the engine speed is high compared to when the engine speed is low. is used to adjust the EGR rate.

JP 2019-108813 A

Fuels supplied to the engine include high-octane fuel with a relatively high octane value such as high-octane gasoline and low-octane fuel with a relatively low octane value such as regular gasoline. A high-octane fuel is less prone to compression ignition than a low-octane fuel, and is advantageous from the viewpoint of suppressing abnormal combustion such as knocking. On the other hand, from the viewpoint of cost performance, low octane fuel is more advantageous than high octane fuel.

Therefore, in recent years, it has been considered to use both high-octane fuel and low-octane fuel. However, since low-octane fuel is more likely to self-ignite than high-octane fuel, if the same combustion control is performed for high-octane fuel and low-octane fuel, abnormal combustion such as knocking will occur when low-octane fuel is used. It may occur.

The technology disclosed herein suppresses abnormal combustion even if fuels with different octane numbers are supplied.

In order to solve the above problems, the technology disclosed herein has an injector that supplies fuel to a combustion chamber, and an ignition device that ignites the air-fuel mixture in the combustion chamber. An octane number detecting means for detecting the octane number of the fuel, and exhaust gas from the combustion chamber for a control device of an engine that performs SI combustion by ignition using the ignition device and then performs CI combustion of the remaining air-fuel mixture by compression ignition. An external EGR system for introducing external EGR gas into the combustion chamber by recirculating part of the burned gas delivered to the passage to the intake passage via the EGR passage, and controlling the external EGR system a control unit that outputs a signal ; and an internal EGR system that introduces internal EGR gas into the combustion chamber and receives a control signal from the control unit, and the control unit is detected by the octane number detection means. When the octane number of the fuel is less than the predetermined octane number, compared to when the octane number of the fuel is equal to or higher than the predetermined octane number, an external EGR rate, which is the ratio of the amount of external EGR gas to the total amount of gas introduced into the combustion chamber. Further, when the octane number of the fuel detected by the octane number detecting means is less than a predetermined octane number, the control unit outputs a control signal to the external EGR system so that the octane number of the fuel becomes higher than the predetermined octane number. A configuration of outputting a control signal to the internal EGR system so that the internal EGR rate, which is the ratio of the internal EGR gas amount to the total amount of gas introduced into the combustion chamber, is lower than in the above case. and

According to this configuration, when the octane number of the fuel is low, the external EGR rate of the gas introduced into the combustion chamber increases, so that the external EGR gas can lower the temperature in the combustion chamber. As a result, even if the octane number of the fuel is low, the mixture containing the fuel is less likely to undergo compression ignition, thereby suppressing pre-ignition and knocking. Therefore, even if fuel having a different octane number is supplied, abnormal combustion can be suppressed.

Further, according to this configuration, when the octane number of the fuel is low, the internal EGR rate of the gas introduced into the combustion chamber is lowered, so the temperature inside the combustion chamber can be lowered more efficiently. Thereby, abnormal combustion can be suppressed more effectively.

In the control device for the engine , the sum of the external EGR gas amount and the internal EGR gas amount is defined as the total EGR gas amount, and the control unit calculates the ratio of the total EGR gas amount to the total gas amount introduced into the combustion chamber. A control signal may be output to each of the external EGR system and the internal EGR system so that the total EGR rate remains the same regardless of the octane number of the fuel detected by the octane number detection means.

According to this configuration, the ratio of fresh air introduced into the combustion chamber does not depend on the octane number of the fuel, so the temperature in the combustion chamber tends to depend on the external EGR rate and the internal EGR rate. This makes it easier to control the temperature in the combustion chamber. As a result, abnormal combustion can be suppressed more effectively.

In an engine control device that changes the internal EGR rate according to the octane number of fuel, the control unit adjusts the internal EGR rate by adjusting a positive overlap period in which both the intake valve and the exhaust valve are open. A configuration may be employed in which a control signal is output to the internal EGR system so as to change the internal EGR system.

That is, the positive overlap period of the intake valve and the exhaust valve can be changed with relatively good responsiveness. Therefore, the temperature of the combustion chamber can be adjusted with good responsiveness by adjusting the internal EGR rate. As a result, abnormal combustion can be suppressed more effectively.

Another aspect of the technology disclosed herein includes an injector that supplies fuel to a combustion chamber and an igniter that ignites an air-fuel mixture in the combustion chamber, and ignites a portion of the air-fuel mixture using the igniter. A control device for an engine in which SI combustion is performed by first ignition and then CI combustion of the remaining air-fuel mixture is performed by compression ignition. an external EGR system for introducing external EGR gas into the combustion chamber by recirculating part of the burned gas into the intake passage through the EGR passage; and control for outputting a control signal to the external EGR system. wherein, when the octane number of the fuel detected by the octane number detecting means is less than a predetermined octane number, the control section compares the octane number of the fuel with the predetermined octane number or more to the combustion chamber. outputting a control signal to the external EGR system so that the external EGR rate, which is the ratio of the external EGR gas amount to the total amount of gas introduced into the A plurality of combustion control maps to be used are divided for each octane number of the fuel, and further, when the octane number of the fuel detected by the octane number detection means is less than a predetermined octane number, the control unit detects the octane number of the fuel. is equal to or higher than the predetermined octane rating, the combustion control map is switched to a different combustion control map.

According to this configuration, since the combustion control map is switched according to the octane number of the fuel, it is possible to easily switch the control of the external EGR system. That is, control according to the octane number of the fuel becomes easier, so that abnormal combustion can be suppressed more effectively.

As described above, according to the technology disclosed herein, abnormal combustion can be suppressed even if fuel having a different octane number is supplied.

1 is a configuration diagram illustrating an engine controlled by a control device according to an exemplary embodiment; FIG. It is a figure which illustrates a combustion chamber, the upper figure is a top view of a combustion chamber, and the lower figure is a sectional view taken on the II-II line. FIG. 2 is a plan view illustrating combustion chambers and intake passages; 1 is a block diagram illustrating an engine control device; FIG. It is a figure which illustrates the control map of an engine, the upper figure is a control map at the time of warm, the middle figure is a control map at the time of semi-warming up, and the lower figure is a control map at the time of cold. FIG. 4 is a block diagram illustrating a low octane map and a high octane map; 4 is a graph illustrating changes in total EGR rate, external EGR rate, and internal EGR rate with respect to engine load; FIG. 4 is a schematic diagram showing an example of the history of heat release rates when a low octane fuel is burned and when a high octane fuel is burned. FIG. 4 is a diagram illustrating opening/closing patterns of intake valves and exhaust valves when changing an internal EGR rate; 4 is a flowchart of engine control executed by an ECU;

Exemplary embodiments are described in detail below with reference to the drawings.

FIG. 1 is a diagram illustrating an engine. FIG. 2 is a diagram illustrating the combustion chamber of the engine. FIG. 3 is a diagram illustrating combustion chambers and intake passages. Note that the intake side in FIG. 1 is on the left side of the paper, and the exhaust side is on the right side of the paper. The intake side in FIGS. 2 and 3 is on the right side of the paper, and the exhaust side is on the left side of the paper. FIG. 4 is a block diagram illustrating an engine control device.

The engine 1 has a combustion chamber 17 . The combustion chamber 17 repeats an intake stroke, a compression stroke, an expansion stroke and an exhaust stroke. Engine 1 is a four-stroke engine. The engine 1 is installed in a four-wheeled automobile. The automobile runs as the engine 1 operates. The fuel of the engine 1 is gasoline in this configuration example. The fuel may be liquid fuel containing at least gasoline. Gasoline as fuel may be regular fuel or high-octane fuel. The fuel may be gasoline, including, for example, bioethanol. The regular fuel is low octane fuel with an octane number of about 91. A high-octane fuel is a high-octane fuel with an octane number of about 100.

(Engine configuration)
The engine 1 has a cylinder block 12 and a cylinder head 13 . The cylinder head 13 is mounted on the cylinder block 12 .

A plurality of cylinders 11 are formed in the cylinder block 12 . The engine 1 is a multi-cylinder engine. 1 and 2 only one cylinder 11 is shown.

Each cylinder 11 has a piston 3 inserted therein. Piston 3 is connected to crankshaft 15 via 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 "combustion chamber" means a space formed by the piston 3, the cylinder 11 and the cylinder head 13 regardless of the position of the piston 3.

A lower surface of the cylinder head 13 constitutes a ceiling portion of the combustion chamber 17 . The ceiling is composed of two inclined planes, as shown in the lower diagram of FIG. The combustion chamber 17 is of the so-called pent roof type.

The piston 3 has a cavity 31 recessed downward from the upper surface. The cavity 31 has a shallow plate shape in this configuration example. The center of the cavity 31 is shifted from the center axis X1 of the cylinder 11 toward the exhaust side.

The geometric compression ratio of the engine 1 is set to 15-18. As will be described later, the engine 1 performs SPCCI combustion, which is a combination of SI (Spark Ignition) combustion and CI (Compression Ignition) combustion, in some operating ranges. SPCCI combustion controls CI combustion through heat generation and/or pressure increase due to SI combustion. The engine 1 is a compression ignition engine. This engine 1 does not need to raise the temperature of the combustion chamber 17 when the piston 3 reaches the compression top dead center.

An intake port 18 is formed in the cylinder head 13 for each cylinder 11 . The intake port 18 has a first intake port 181 and a second intake port 182, as shown in FIG. The intake port 18 communicates with the combustion chamber 17 . 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 generates a tumble flow in the combustion chamber 17 .

An intake valve 21 is arranged in the intake port 18 . The intake valve 21 opens and closes the intake port 18 . The valve mechanism opens and closes the intake valve 21 at predetermined timings. The valve mechanism may be a variable valve mechanism that varies valve timing and/or valve lift. As shown in FIG. 4, the valve train has an electric intake S-VT (Sequential-Valve Timing) 23 . The electric intake S-VT 23 continuously changes the rotation phase of the intake camshaft within a predetermined angle range. The opening angle of the intake valve 21 does not change. The opening angle of the intake valve 21 is, for example, 240° CA. The valve mechanism may have a hydraulic S-VT instead of the electric S-VT.

An exhaust port 19 is formed in the cylinder head 13 for each cylinder 11 . The exhaust port 19 also has a first exhaust port 191 and a second exhaust port 192, as shown in FIG. The exhaust port 19 communicates with the combustion chamber 17 .

An exhaust valve 22 is arranged in the exhaust port 19 . The exhaust valve 22 opens and closes the exhaust port 19 . The valve mechanism opens and closes the exhaust valve 22 at predetermined timings. The valve mechanism may be a variable valve mechanism that varies valve timing and/or valve lift. As shown in FIG. 4, the valve train has an electric exhaust S-VT 24 . The electric exhaust S-VT 24 continuously changes the rotation phase of the exhaust camshaft within a predetermined angle range. The opening angle of the exhaust valve 22 does not change. The opening angle of the exhaust valve 22 is, for example, 240°CA. The valve mechanism may have a hydraulic S-VT instead of the electric S-VT.

The electric intake S-VT 23 and the electric exhaust S-VT 24 adjust the length of the overlap period during which both the intake valve 21 and the exhaust valve 22 are open. Internal EGR (Exhaust Gas Recirculation) gas is introduced into the combustion chamber 17 by adjusting the length of the overlap period. That is, the electric intake S-VT 23 and the electric exhaust S-VT 24 constitute an internal EGR system that introduces internal EGR gas into the combustion chamber 17 .

An injector 6 is attached to the cylinder head 13 for each cylinder 11 . Injector 6 injects fuel directly into combustion chamber 17 . The injector 6 is arranged at the center of the ceiling of the combustion chamber 17 . More specifically, the injector 6 is arranged in the valley of the pent roof. As shown in FIG. 2, the injection axis X2 of the injector 6 is positioned closer to the exhaust side than the center axis X1 of the cylinder 11. As shown in FIG. The injection axis X2 of the injector 6 is parallel to the central axis X1. The injection axis X2 of the injector 6 and the center of the cavity 31 are aligned. The injector 6 faces the cavity 31 . The injection axis X2 of the injector 6 may coincide with the central axis X1 of the cylinder 11 . In that configuration, the injection axis X2 of the injector 6 and the center of the cavity 31 may coincide.

The injector 6 is of a multiple injection hole type having a plurality of injection holes. The injector 6 injects fuel radially and obliquely downward from the central portion of the ceiling of the combustion chamber 17, as indicated by a two-dot chain line in FIG. The injector 6 has ten injection holes in this configuration example. The ten injection holes are arranged at equal angular intervals in the circumferential direction.

A fuel supply system 61 is connected to the injector 6 . The fuel supply system 61 includes a fuel tank 63 that stores fuel and a fuel supply path 62 . A fuel supply path 62 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 . Fuel pump 65 delivers fuel to common rail 64 . The fuel pump 65 is a plunger pump driven by the crankshaft 15 in this configuration example. Common rail 64 stores fuel sent from fuel pump 65 . The voltage inside the common rail 64 is high voltage. Injector 6 is connected to common rail 64 . When the injector 6 opens, the high-pressure fuel in the common rail 64 is injected into the combustion chamber 17 through the nozzle hole of the injector 6 . The fuel supply system 61 of this configuration example can supply high pressure fuel of 30 MPa or more to the injector 6 . The maximum pressure of the fuel supply system 61 may be 200 MPa, for example. The fuel supply system 61 may change the fuel pressure according to the operating state of the engine 1 . Note that the configuration of the fuel supply system 61 is not limited to the configuration described above.

A spark plug 25 is attached to the cylinder head 13 for each cylinder 11 . A spark plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17 . The spark plug 25 is an example of an ignition device. The spark plug 25 is arranged on the intake side of the central axis X1 of the cylinder 11, as shown in FIG. A spark plug 25 is positioned between the two intake ports 18 . Electrodes of the ignition plug 25 face the inside of the combustion chamber 17 . Note that the spark plug 25 may be arranged on the exhaust side of the central axis X1 of the cylinder 11 . Also, the spark plug 25 may be arranged on the central axis X1 of the cylinder 11 .

An intake passage 40 is connected to one side surface of the engine 1 . The intake passage 40 communicates with the intake port 18 of each cylinder 11 . Intake gas introduced into the combustion chamber 17 flows through the intake passage 40 . An air cleaner 41 is arranged at the upstream end of the intake passage 40 . A surge tank 42 is arranged near the downstream end of the intake passage 40 . The intake passage 40 downstream of the surge tank 42 branches for each cylinder 11 .

A throttle valve 43 is arranged between the air cleaner 41 and the surge tank 42 in the intake passage 40 . The throttle valve 43 adjusts the amount of fresh air introduced into the combustion chamber 17 by changing the opening of the valve.

A supercharger 44 is also arranged in the intake passage 40 downstream of the throttle valve 43 . The supercharger 44 increases the pressure of intake gas introduced into the combustion chamber 17 . In this configuration example, the supercharger 44 is driven by the engine 1 . The supercharger 44 may be of the Roots, Lysholm, vane, or centrifugal type.

An electromagnetic clutch 45 is interposed between the supercharger 44 and the engine 1 . The electromagnetic clutch 45 switches between a state in which driving force is transmitted from the engine 1 to the supercharger 44 and a state in which transmission of the driving force is interrupted. The turbocharger 44 is turned on or off by outputting a control signal to the electromagnetic clutch 45 from the ECU 10, which will be described later.

An intercooler 46 is arranged downstream of the supercharger 44 in the intake passage 40 . The intercooler 46 cools the intake gas compressed by the supercharger 44 . The intercooler 46 is water cooled or oil cooled.

A bypass passage 47 is connected to the intake passage 40 . The bypass passage 47 connects the upstream portion of the supercharger 44 and the downstream portion of the intercooler 46 in the intake passage 40 to each other. A bypass passage 47 bypasses the supercharger 44 and the intercooler 46 . An air bypass valve 48 is arranged in the bypass passage 47 . The air bypass valve 48 adjusts the flow rate of gas flowing through the bypass passage 47 .

The ECU 10 fully opens the air bypass valve 48 when the supercharger 44 is off. Intake gas flowing through the intake passage 40 bypasses the supercharger 44 and the intercooler 46 and reaches the combustion chamber 17 of the engine 1 . The engine 1 operates in a non-supercharged state, that is, in a naturally aspirated state.

When the supercharger 44 is on, the engine 1 operates in a supercharged state. The ECU 10 adjusts the opening of the air bypass valve 48 when the supercharger 44 is on. Part of the intake gas that has passed through the supercharger 44 and the intercooler 46 returns to the upstream of the supercharger 44 through the bypass passage 47 . When the ECU 10 adjusts the opening of the air bypass valve 48, the pressure of the intake gas introduced into the combustion chamber 17 changes. "Supercharging" is defined as a state in which the pressure in the surge tank 42 exceeds the atmospheric pressure, and "non-supercharging" is defined as a state in which the pressure in the surge tank 42 is below the atmospheric pressure. You may

The engine 1 has a swirl generator that generates a swirl flow within the combustion chamber 17 . The swirl generator has a swirl control valve 56 attached to the intake passage 40, as shown in FIG. The intake passage 40 has a primary passage 401 connected to the first intake port 181 and a secondary passage 402 connected to the second intake port 182 . Swirl control valve 56 is arranged in secondary passage 402 . The swirl control valve 56 is an opening control valve capable of narrowing the cross section of the secondary passage 402 . When the opening of the swirl control valve 56 is small, the flow rate of intake air flowing into the combustion chamber 17 from the first intake port 181 is large and the flow rate of intake air flowing into the combustion chamber 17 from the second intake port 182 is small. The swirl flow in chamber 17 becomes stronger. When the opening degree of the swirl control valve 56 is large, the flow rates of the intake air flowing into the combustion chamber 17 from the first intake port 181 and the second intake port 182 become substantially equal, so that the swirl flow in the combustion chamber 17 is increased. become weak. When the swirl control valve 56 is fully opened, no swirl flow occurs. The swirl flow circulates in the counterclockwise direction in FIG. 3, as indicated by the white arrow.

As described above, since the intake port 18 of the engine 1 is a tumble port, when the swirl control valve 56 is closed, an oblique swirl flow containing a tumble component and a swirl component is generated in the combustion chamber 17 . The oblique swirl flow is a swirl flow that is tilted with respect to the central axis X1 of the cylinder 11 . The inclination angle of the oblique swirl flow is generally about 45° with respect to the plane perpendicular to the central axis X1. The tilt angle may be set in the range of 30° to 60°.

An exhaust passage 50 is connected to the other side surface of the engine 1 . The exhaust passage 50 communicates with the exhaust port 19 of each cylinder 11 . Exhaust gas discharged from the combustion chamber 17 flows through the exhaust passage 50 . The upstream portion of the exhaust passage 50 branches for each cylinder 11, although detailed illustration is omitted.

An exhaust gas purification system having a plurality of catalytic converters is arranged in the exhaust passage 50 . Although not shown, these catalytic converters are arranged in the engine room. The upstream catalytic converter has a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512 . The downstream catalytic converter has a three-way catalyst 513 . It should be noted that the exhaust gas purification system is not limited to the configuration of the illustrated example. For example, GPF may be omitted. Also, the catalytic converter is not limited to having a three-way catalyst. Furthermore, the order in which the three-way catalyst and GPF are arranged 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 that recirculates part of the exhaust gas to the intake passage 40 . An upstream end of the EGR passage 52 is connected between the two catalytic converters in the exhaust passage 50 . A downstream end of the EGR passage 52 is connected to an upstream portion of the supercharger 44 in the intake passage 40 .

A water-cooled EGR cooler 53 is arranged in the EGR passage 52 . The EGR cooler 53 cools the exhaust gas. An EGR valve 54 is also arranged in the EGR passage 52 . The EGR valve 54 adjusts the flow rate of exhaust gas flowing through the EGR passage 52 . The EGR valve 54 adjusts the amount of recirculated external EGR gas. EGR passage 52, EGR cooler 53, and EGR valve 54 constitute an external EGR system.

(Configuration of engine control device)
A control device for the engine 1 includes an ECU (Engine Control Unit) 10 . The ECU 10 is an example of a control section. The ECU 10 includes a microcomputer 101, a memory 102, and an I/F circuit 103, as shown in FIG. The microcomputer 101 executes programs. Memory 102 stores programs and data. The memory 102 is, for example, a RAM (Random Access Memory) or a ROM (Read Only Memory). The I/F circuit 103 inputs and outputs electrical signals.

Various sensors SW1 to SW11 are connected to the ECU 10 as shown in FIGS. The sensors SW1 to SW11 output signals to the ECU 10. FIG. The sensors include the following sensors.

The airflow sensor SW1 measures the flow rate of fresh air flowing through the intake passage 40 . The airflow sensor SW1 is arranged downstream of the air cleaner 41 in the intake passage 40. The first intake air temperature sensor SW2 measures the temperature of fresh air flowing through the intake passage 40. FIG. The first intake air temperature sensor SW2 is arranged downstream of the air cleaner 41 in the intake passage 40. The second intake air temperature sensor SW3 measures the temperature of the intake gas introduced into the combustion chamber 17. FIG. The second intake air temperature sensor SW3 is attached to the surge tank 42. The intake air pressure sensor SW4 measures the pressure of the intake gas introduced into the combustion chamber 17. FIG. The intake pressure sensor SW4 is attached to the surge tank 42. The in-cylinder pressure sensor SW5 measures the pressure inside each combustion chamber 17. FIG. The in-cylinder pressure sensor SW5 is attached to the cylinder head 13 for each cylinder 11, and the water temperature sensor SW6 measures the temperature of the cooling water. A water temperature sensor SW6 is attached to the engine 1. A crank angle sensor SW7 measures the rotation angle of the crankshaft 15. FIG. The crank angle sensor SW7 is attached to the engine 1. The accelerator opening sensor SW8 measures the accelerator opening corresponding to the operation amount of the accelerator pedal. The accelerator opening sensor SW8 is attached to the accelerator pedal mechanism. The intake cam angle sensor SW9 measures the rotation angle of the intake camshaft. The intake cam angle sensor SW9 is attached to the engine 1. The exhaust cam angle sensor SW10 measures the rotation angle of the exhaust camshaft. The exhaust cam angle sensor SW10 is attached to the engine 1. The fuel pressure sensor SW11 measures the pressure of the fuel supplied to the injector 6. Fuel pressure sensor SW11 is attached to common rail 64 of fuel supply system 61 .

The ECU 10 determines the operating state of the engine 1 based on the signals from these sensors SW1 to SW11. The ECU 10 also calculates the control amount of each device according to predetermined control logic. The control logic is stored in memory 102 .

The ECU 100 transmits electric signals related to the control amount to the injector 6, the spark plug 25, the electric intake S-VT 23, the electric exhaust S-VT 24, the fuel supply system 61, the throttle valve 43, the EGR valve 54, the electromagnetic clutch of the supercharger 44. 45 , air bypass valve 48 and swirl control valve 56 .

(SPCCI combustion concept)
The main purpose of the engine 1 is to improve fuel efficiency and exhaust emission performance. If the temperature in the combustion chamber 17 before the start of compression varies, the timing of self-ignition changes greatly. Therefore, the engine 1 performs SPCCI combustion, which is a combination of SI combustion and CI combustion.

SPCCI combustion is the following form of combustion. That is, the ignition plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17, whereby the air-fuel mixture starts SI combustion due to flame propagation. After the start of SI combustion, (1) the temperature in the combustion chamber 17 increases due to the heat generated by the SI combustion, and (2) the pressure in the combustion chamber 17 increases due to flame propagation. CI combustion is performed by self-ignition.

The ECU 10 adjusts the ignition timing so that the air-fuel mixture self-ignites at the target timing. In SPCCI combustion, the amount of SI combustion controls the start timing of CI combustion.

(engine operating range)
FIG. 5 illustrates control maps 501 , 502 , 503 of the engine 1 . Control maps 501 , 502 and 503 are stored in the memory 102 of the ECU 10 . The ECU 10 operates the engine 1 based on control maps 501 , 502 and 503 . The control map includes three types of control maps: first control map 501 , second control map 502 and third control map 503 . The ECU 10 selects control from among the first control map 501, the second control map 502, and the third control map 503 according to the level of the wall temperature (or engine water temperature) of the combustion chamber 17 and the temperature of the intake air. A map is used to control the engine 1 .

The ECU 10 selects the first control map 501 when the wall temperature of the combustion chamber 17 is equal to or higher than a first wall temperature (eg, 80° C.) and the intake air temperature is equal to or higher than a first intake air temperature (eg, 50° C.). The first control map 501 is a map when the engine 1 is warm.

When the wall temperature of the combustion chamber 17 is lower than the first wall temperature and equal to or higher than the second wall temperature (eg 30°C) and the intake air temperature is lower than the first intake air temperature and equal to or higher than the second intake air temperature (eg 25°C), the ECU 10 , selects the second control map 502 . The second control map 502 is a map when the engine 1 is half warmed up. When the wall temperature of the combustion chamber 17 is less than the second wall temperature or the intake air temperature is less than the second intake air temperature, the ECU 10 selects the third control map 503 . The third control map 503 is a map when the engine 1 is cold.

Instead of the wall temperature of the combustion chamber 17, the ECU 10 may select the control maps 501, 502, 503 based on the temperature of the cooling water of the engine 1 measured by the water temperature sensor SW6, for example. Further, the ECU 10 can estimate the wall temperature of the combustion chamber 17 based on various measurement signals. The intake air temperature is measured by a second intake air temperature sensor SW3. Further, the ECU 10 may estimate the intake air temperature based on various measurement signals.

Each map 501 , 502 , 503 is defined by the load of the engine 1 and the rotation speed of the engine 1 . The first control map 501 is divided into five areas: area A1, area A2, area A3, area A4, and area A5. Region A1 is a region where the number of revolutions is lower than that of Na. The idling operation of the engine 1 is included in the region A1. Region A2 is a region where the rotational speed is higher than Nb. A region A3 is a region in which the load is lower than La in the region where the rotational speed is from Na to Nb. A region A4 is a region in which the load is La or higher in the region in which the rotational speed ranges from Na to Nb. Note that La may be half the maximum load of the engine 1 . Area A5 is a specific area on the low load side within area A3. Region A5 corresponds to a specific region of low rotation and low load in the entire operating region of engine 1 . It should be noted that the term "low rotation" as used herein corresponds to the low rotation side when the entire operating range of the engine 1 is divided into the low rotation side and the high rotation side. "Low load" corresponds to the low load side when the entire operating range of the engine 1 is divided into two equal parts, the low load side and the high load side.

When the operating state determined by the load and rotation speed of the engine 1 is within the region A1, the ECU 10 controls the engine 1 to perform SI combustion. The air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio or substantially the stoichiometric air-fuel ratio. The air-fuel ratio of the air-fuel mixture should be included in the purification window of the three-way catalysts 511 and 513 . Note that the air-fuel ratio is the average air-fuel ratio in the entire combustion chamber 17 . The ECU 10 controls the engine 1 to perform SI combustion even when the operating state of the engine 1 is within the region A2. The air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio or substantially the stoichiometric air-fuel ratio.

When the operating state of the engine 1 is within region A3, the ECU 10 controls the engine 1 to perform SPCCI combustion. The air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio or substantially the stoichiometric air-fuel ratio. Further, when the operating state of the engine 1 is within the region A3, the supercharger 44 is off. When the operating state of the engine 1 is within the region A4, the ECU 10 controls the engine 1 to perform SPCCI combustion. The air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio or substantially the stoichiometric air-fuel ratio. Further, when the operating state of the engine 1 is within the region A4, the supercharger 44 is on.

When the operating state of the engine 1 is within the region A5, the ECU 10 controls the engine 1 to perform SPCCI combustion. The air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio. Specifically, the average air-fuel ratio in the entire combustion chamber 17 is 30 or more and 40 or less. When the operating state of the engine 1 is within the area A5, the supercharger 44 is off. Further, when the operating state of the engine 1 is within the region A5, the ECU 10 also provides an overlap period during which both the intake valve 21 and the exhaust valve 22 are opened. Internal EGR gases are introduced into the combustion chamber 17 . This causes the temperature in the combustion chamber 17 to rise. In the region A5 where the load of the engine 1 is low, the CI combustion of the SPCCI combustion is stabilized due to the high temperature in the combustion chamber 17 . Note that the area A5 is hereinafter referred to as the SPCCI lean area A5.

The second control map 502 is divided into four areas: area B1, area B2, area B3, and area B4. Region B1 is a region where the number of revolutions is lower than Na, and corresponds to region A1 of first control map 501 . Region B2 is a region where the rotation speed is higher than Nb, and corresponds to region A2 of first control map 501 . A region A3 is a region in which the load is lower than La in the region in which the rotational speed ranges from Na to Nb, and corresponds to the region A3 of the first control map 501 . A region B4 is a region in which the load is La or higher among the regions in which the rotational speed ranges from Na to Nb, and corresponds to the region A4 of the first control map 501 . Second control map 502 does not have an area corresponding to area A5 of first control map 501 . This is because SPCCI combustion of a lean air-fuel mixture becomes unstable when the temperature is low.

When the operating state of the engine 1 is within the region B1, the ECU 10 controls the engine 1 to perform SI combustion. The air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio or substantially the stoichiometric air-fuel ratio. Even when the operating state of the engine 1 is within the region B2, the ECU 10 controls the engine 1 to perform SI combustion. The air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio or substantially the stoichiometric air-fuel ratio. When the operating state of the engine 1 is within the region B3, the ECU 10 controls the engine 1 to perform SPCCI combustion. The air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio or substantially the stoichiometric air-fuel ratio. Further, when the operating state of the engine 1 is within the region B3, the supercharger 44 is off. When the operating state of the engine 1 is within the region B4, the ECU 10 controls the engine 1 to perform SPCCI combustion. The air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio or substantially the stoichiometric air-fuel ratio. Further, when the operating state of the engine 1 is within the region B4, the supercharger 44 is on.

The third control map 503 has only area C1. Region C1 extends over the entire operating region of engine 1 . When the operating state of the engine 1 is within the region C1, the ECU 10 controls the engine 1 to perform SI combustion. The air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio or substantially the stoichiometric air-fuel ratio.

(Differences in control content due to fuel octane rating)
The control device of the engine 1 changes the contents of control of the engine 1 according to the octane rating of the fuel introduced into the combustion chamber 17 . Specifically, as shown in FIG. 6, the control device of the engine 1 provides a combustion control map (hereinafter referred to as a low octane number map 601) when the octane number of the fuel is less than a predetermined octane number, and a and a combustion control map (hereinafter referred to as a high octane number map 602). Both low octane map 601 and high octane map 602 are stored in memory 102 . The predetermined octane number is a value that allows discrimination between regular fuel and high-octane fuel, and is set to 96, for example. In the following description, regular fuel may be referred to as low-octane fuel, and high-octane fuel may be referred to as high-octane fuel.

As shown in FIG. 6, the low octane number map 601 includes a first injection timing map 601a indicating the fuel injection timing by the injector 6, a first SCV (Swirl Control Valve) map 601b indicating the opening of the swirl control valve 56, and an external A first external EGR map 601c used to control the EGR system (particularly the EGR valve 54) and a first internal EGR map used to control the internal EGR system (particularly the electric intake S-VT 23 and the electric exhaust S-VT 24) 601d. High octane map 602 includes a second injection timing map 602a, a second SCV map 602b, a second external EGR map 602c, and a second internal EGR map 602d. For example, when the octane number of the fuel changes from less than a predetermined octane number to a predetermined octane number or more, the ECU 10 switches all the maps included in the low octane number map 601 to the corresponding maps included in the high octane number map 602.

The ECU 10 controls the injection timing of fuel from the injector 6 according to the first and second injection timing maps 601a and 602a, while controlling the injection amount of fuel according to the amount of air introduced into the combustion chamber 17. to control.

The octane number of the fuel can be determined, for example, from the change in heat quantity before self-ignition. That is, since the fuel with a higher octane number is more difficult to self-ignite, when the octane number of the fuel is less than the predetermined octane number, the amount of heat before self-ignition is smaller than when the octane number of the fuel is equal to or higher than the predetermined octane number. By using this difference, the octane number of the fuel can be determined. Since the in-cylinder pressure sensor SW5 can detect such heat quantity with high accuracy, the octane number in a dynamic state can be determined with high accuracy. Moreover, since an existing device is used, there is no need to newly install an expensive sensor. That is, in this engine 1, the in-cylinder pressure sensor SW5 constitutes octane number detection means. Incidentally, since the amount of heat before self-ignition also changes depending on the engine load, it is preferable to determine the octane number in consideration of the engine load.

In addition to the above-described method, for example, the octane number of the fuel introduced into the combustion chamber 17 may be detected by detecting the octane number of the fuel stored in the fuel tank 63 with a sensor such as an ultrasonic sensor. good too.

(EGR control)
In the present embodiment, the control device of the engine 1 controls at least an operating region in which SPCCI combustion is performed, that is, when the engine 1 is in a semi-warmed state and the operating region of the engine 1 is in regions B2 and B4, the EGR gas is introduced into the combustion chamber 17 . This suppresses abnormal combustion such as knocking and pre-ignition, thereby improving combustion stability.

FIG. 7 shows the relationship between engine load and EGR rate. The upper diagram in FIG. 7 shows changes in the total EGR rate, which is the ratio of the EGR gas amount, which is the sum of the external EGR gas amount and the internal EGR gas amount, to the total gas amount introduced into the combustion chamber 17 . The middle diagram in FIG. 7 shows changes in the external EGR rate, which is the ratio of the external EGR gas amount to the total gas amount. The lower diagram in FIG. 7 shows changes in the internal EGR rate, which is the ratio of the internal EGR gas amount to the total amount of gas introduced into the combustion chamber 17 . The external EGR rate and internal EGR rate are represented by the following equations. The EGR rate may be regarded as the sum of the external EGR rate and the internal EGR rate.

(External EGR rate) = (external EGR gas amount/total gas amount)
(Internal EGR rate) = (internal EGR gas amount/total gas amount)
In the graphs showing the external EGR rate and the internal EGR rate, the solid line indicates the case of low octane fuel, and the dashed line indicates the case of high octane fuel. As for the total EGR rate, only the solid line is shown because the combustion is the same for low octane fuel and high octane fuel. The difference in external and internal EGR between regular fuel and high-octane fuel will be described later. FIG. 7 is a diagram when the rotational speed of the engine 1 is in the range from Na to Nb.

As shown in FIG. 7, EGR gas is introduced into the combustion chamber 17 when the engine load exceeds a certain load. The purpose of this EGR is to introduce EGR gas into the combustion chamber 17 to quickly raise the temperature in the combustion chamber 17 when the engine load is low. Therefore, when the engine load is low, the high-temperature internal EGR gas is introduced into the combustion chamber 17 by increasing the ratio of the internal EGR gas to the external EGR gas. By this. Since the temperature in the combustion chamber 17 rises early, misfire can be suppressed.

As shown in FIG. 7, the total EGR rate maintains a substantially constant value after increasing. At this time, the external EGR rate gently increases as the engine load increases. On the other hand, the internal EGR rate increases once and then gradually decreases as the engine load increases. This is to prevent pre-ignition from occurring due to an excessive increase in the temperature of the combustion chamber 17 when the engine load is high. That is, by increasing the external EGR rate and introducing the external EGR gas cooled by the EGR cooler 53 into the combustion chamber 17, the inside of the combustion chamber 17 is cooled by the external EGR rate. At the same time, by decreasing the internal EGR rate, introduction of high-temperature internal EGR gas into the combustion chamber 17 is suppressed, and an increase in temperature inside the combustion chamber 17 is suppressed. Thereby, pre-ignition can be suppressed.

Then, when the operating state of the engine 1 enters the supercharging region (region B4), the internal EGR rate is further reduced, and finally made substantially zero, as shown in FIG. This is to prevent the internal EGR gas from excessively increasing the temperature in the combustion chamber 17 . Also, in the supercharging region, the total EGR rate decreases as the engine load increases. This is because supercharging increases the ratio of fresh air to the total amount of gas introduced into the combustion chamber 17 . Thereby, combustion can be stabilized. Note that "making the internal EGR rate substantially zero" means that the internal EGR rate is lowered to such an extent that the internal EGR gas does not affect the temperature of the combustion chamber 17. It includes cases where it is set to 0.

By adjusting the external EGR rate and the internal EGR rate in this way, knocking and pre-ignition can be suppressed, and combustion stability can be improved.

Here, the low octane fuel has a higher ignitability than the high octane fuel. Therefore, if the EGR gas control is the same for the low octane fuel and the high octane fuel, as shown in FIG. Abnormal combustion such as knocking may occur earlier than the high octane fuel (solid line).

Therefore, as shown in FIG. 7, the ECU 10 in the present embodiment controls the external EGR system so that the external EGR rate is higher when low octane fuel is used than when high octane fuel is used. Output a signal. That is, when the fuel is low octane fuel, the amount of external EGR gas introduced into the combustion chamber 17 is increased compared to when high octane fuel is used. Thereby, the temperature in the combustion chamber 17 can be positively lowered. In particular, since the EGR cooler 53 is provided in the EGR passage 52 in the present embodiment, sufficiently cooled external EGR gas is introduced into the combustion chamber 17 . As a result, as shown in FIG. 8, the self-ignition timing for low octane fuel can be brought closer to the self-ignition timing for high octane fuel. Therefore, abnormal combustion can be suppressed.

The ECU 10 adjusts the external EGR rate by adjusting the opening degree of the EGR valve 54 in the EGR passage 52 . That is, the ECU 10 increases the opening of the EGR valve 54 when low octane fuel is used as compared to when high octane fuel is used. As a result, when low octane fuel is used as the fuel, the external EGR rate can be made higher than when high octane fuel is used. The ECU 10 estimates the external EGR rate from the differential pressure between the upstream side (exhaust passage 50 side) and the downstream side (intake passage 40 side) of the EGR valve 54 and the opening degree of the EGR valve 54 . Therefore, the ECU 10 appropriately adjusts the opening degree of the EGR valve 54 according to the differential pressure between the upstream side and the downstream side of the EGR valve 54 .

Further, in the present embodiment, as shown in FIG. 7, the ECU 10 controls the internal EGR system so that the internal EGR rate is lower when low octane fuel is used than when high octane fuel is used. Output a signal. That is, since the internal EGR gas introduces high-temperature burned gas into the combustion chamber 17 , it basically raises the temperature in the combustion chamber 17 . Therefore, if the internal EGR rate is lowered, the temperature rise of the combustion chamber 17 due to the internal EGR gas is suppressed. As a result, the self-ignition timing for low octane fuel can be brought closer to the self-ignition timing for high octane fuel. Therefore, abnormal combustion can be suppressed more effectively.

The ECU 10 changes the internal EGR rate by adjusting the positive overlap period during which both the intake valve 21 and the exhaust valve 22 are opened by the electric intake S-VT 23 and the electric exhaust S-VT 24 . That is, as shown in FIG. 9, the ECU 10 shortens the positive overlap period when low octane fuel is used as compared to when high octane fuel is used. In particular, in this embodiment, the ECU 10 retards the opening timing of the intake valve 21 by the electric intake S-VT 23 to shorten the overlap period.

When the opening timing of the intake valve 21 is before exhaust top dead center, burned gas enters the intake port 18 as the piston 3 rises. As a result, when the piston 3 descends, the burned gas is introduced (injected back) from the intake port 18 into the combustion chamber 17 together with fresh air. When the opening timing of the intake valve 21 is retarded, the amount of burned gas (internal EGR gas) injected back from the intake port 18 is reduced, so the internal EGR rate is reduced.

Further, even when the opening timing of the intake valve 21 is retarded beyond the exhaust top dead center, the intake air is drawn into the combustion chamber 17 from the exhaust port 20 by changing the timing of introducing the intake air into the combustion chamber 17. The amount of burnt gas changes. Therefore, by retarding the opening timing of the intake valve 21, the internal EGR rate can be reduced.

Basically, it is preferable that the retardation range of the intake valve 21 is the range before the exhaust top dead center. This is because adjusting the opening timing of the intake valve 21 before the exhaust top dead center makes it easier to adjust the internal EGR rate.

Thus, when the internal EGR gas is introduced into the combustion chamber 17 by providing the positive overlap period, the high-temperature burned gas temporarily moves to the intake port 19 and the exhaust port 20 . Therefore, when the internal EGR gas is introduced into the combustion chamber 17 by positive overlap, compared to the case where the internal EGR gas is introduced into the combustion chamber 17 by negative overlap, which confines the high-temperature burned gas in the combustion chamber 17 as it is. Therefore, the temperature of the combustion chamber 17 can be lowered. Therefore, the temperature of the combustion chamber 17 can be effectively lowered, and abnormal combustion can be effectively suppressed.

The internal EGR rate may be reduced by advancing the closing timing of the exhaust valve 22 by the electric exhaust S-VT 24 . Alternatively, the opening timing of the intake valve 21 may be retarded and the closing timing of the exhaust valve 22 may be advanced to reduce the internal EGR rate.

As described above, in this embodiment, the total EGR rate is the same when the fuel is low octane fuel and when the fuel is high octane fuel. That is, in the present embodiment, the ECU 10 adjusts the external EGR rate and the internal EGR rate in accordance with the octane number of the fuel so that the total EGR rate remains the same regardless of the octane number of the fuel. They respectively output control signals to the internal EGR system. The proportion of fresh air introduced into the combustion chamber 17 is thereby independent of the octane number of the fuel. Therefore, combustion stability can be improved.

The control of the external EGR rate and the internal EGR rate according to the octane number of these fuels includes the first external EGR map 601c and the first internal EGR map 601d of the low octane number map 601 and the second external EGR map 602c of the high octane number map 602. and the second internal EGR map 602d. That is, the ECU 10 adjusts the opening degree of the EGR valve 54 based on the first and second external EGR maps 601c, 602c. The ECU 10 controls the electric intake S-VT 23 and the electric exhaust S-VT 24 based on the first and second internal EGR maps 601d, 602d to adjust the valve timings of the intake valve 21 and the exhaust valve 22, respectively.

Here, as described above, adjustment of the external EGR gas rate is performed by selection of the external EGR map. Also, adjustment of the internal EGR gas rate is performed by selection of the internal EGR map. Therefore, even if the low octane number map 601 is selected, the timing of self-ignition may differ between when the octane number of the fuel is close to the predetermined octane number and when it is sufficiently lower than the predetermined octane number. In particular, when high octane fuel remains in the fuel tank 63 and low octane fuel is supplied, the octane value approaches the predetermined octane value. Therefore, even if the timing of self-ignition is adjusted by adjusting the external EGR gas rate, the timing of self-ignition is slightly shifted from the self-ignition timing of the high octane fuel, as indicated by the dashed line in FIG.

Therefore, in this embodiment, when the octane number of the fuel is less than the predetermined octane number and the low octane number map 601 is selected, the ignition timing of the ignition plug 25 is adjusted according to the octane number. That is, when the low octane number map 601 is selected and the self-ignition timing deviates from the target timing, the control device of the engine 1 changes the ignition timing by the spark plug 25 . As a result, the self-ignition timing when low octane fuel is used can be matched to the self-ignition timing of high octane fuel. As a result, abnormal combustion can be suppressed more effectively.

This adjustment of the ignition timing of the spark plug 25 is executed even when the ECU 10 selects the high octane number map 602 as the combustion control map for the engine 1 . That is, even if the octane number is equal to or higher than the predetermined octane number, when the octane number is substantially the same as the predetermined octane number, the self-ignition timing may be earlier than the target timing. Therefore, even when the high octane number map 602 is selected, the ignition timing is adjusted according to the octane number to bring the self-ignition timing closer to the target timing.

Next, a processing operation for controlling the engine 1 executed by the ECU 10 will be described with reference to the flowchart of FIG.

First, in step S101, the ECU 10 reads detection signals from the sensors SW1 to SW11.

In the next step S102, the ECU 10 calculates the octane number. In this step S102, for example, the octane number is calculated from the change in the amount of heat before self-ignition.

In subsequent step S103, the ECU 10 determines whether or not the octane number calculated in step S102 is less than a predetermined octane number. When the octane rating is less than the predetermined octane rating (YES), the process proceeds to step S104, while when the octane rating is equal to or higher than the predetermined octane rating (NO), the process proceeds to step S106.

In step S<b>104 , the ECU 10 selects the low octane number map 601 as the combustion control map for the engine 1 .

In the next step S105, the ECU 10 sets the external EGR rate higher than the high octane rate and the internal EGR rate to the high octane rate, based on the first external EGR map 601c and the first internal EGR map 601d of the low octane rate map 601. Make it lower than when After step S105, the process proceeds to step S108.

In step S<b>106 to which the ECU 10 proceeds when the determination in step S<b>103 is NO, the ECU 10 selects the high octane number map 602 as the combustion control map for the engine 1 .

In the next step S107, the ECU 10 sets the external EGR rate lower than the low octane rate and the internal EGR rate to the low octane rate based on the second external EGR map 602c and the second internal EGR map 602d of the high octane rate map 602. Make it lower than when

In step S108, the ignition timing of the ignition plug 25 is adjusted according to the octane rating calculated in step S102. After step S108, the process returns.

Therefore, in the present embodiment, octane number detecting means for detecting the octane number of fuel and part of the burned gas delivered from the combustion chamber 17 to the exhaust passage 50 are recirculated to the intake passage 40 via the EGR passage 52. Thus, it comprises an external EGR system (EGR passage 52, EGR cooler 53, and EGR valve 54) for introducing external EGR gas into the combustion chamber 17, and an ECU 10 for outputting a control signal to the external EGR system. When the octane number of the fuel detected by the octane number detecting means is less than the predetermined octane number, the external EGR gas with respect to the total amount of gas introduced into the combustion chamber 17 is lower than when the octane number of the fuel is equal to or higher than the predetermined octane number. A control signal is output to the external EGR system so that the external EGR rate, which is a proportion of the amount, increases. As a result, when the octane number of the fuel is low, the external EGR rate of the gas introduced into the combustion chamber 17 increases, so that the temperature in the combustion chamber 17 can be lowered by the external EGR gas. As a result, even if the octane number of the fuel is low, the mixture containing the fuel is less likely to undergo compression ignition, thereby suppressing pre-ignition and knocking. Therefore, even if fuel having a different octane number is supplied, abnormal combustion can be suppressed.

Further, in this embodiment, an internal EGR system (in particular, an electric intake S-VT 23 and an electric exhaust S-VT 24) that introduces internal EGR gas into the combustion chamber 17 and receives a control signal from the ECU 10 is further provided. When the octane number of the fuel detected by the octane number detecting means is less than the predetermined octane number, the internal EGR gas with respect to the total amount of gas introduced into the combustion chamber 17 is lower than when the octane number of the fuel is equal to or higher than the predetermined octane number. A control signal is output to the internal EGR system so that the internal EGR rate, which is a proportion of the amount, becomes low. As a result, when the octane number of the fuel is low, the internal EGR rate of the gas introduced into the combustion chamber 17 is lowered, so that it is possible to suppress the temperature rise in the combustion chamber 17 due to the internal EGR gas. Therefore, the temperature in the combustion chamber 17 can be lowered more efficiently. As a result, abnormal combustion can be suppressed more effectively.

In the present embodiment, the ECU 10 controls the total EGR rate, which is the ratio of the total EGR gas amount to the total gas amount introduced into the combustion chamber 17, regardless of the fuel octane number detected by the octane number detection means. Control signals are respectively output to the external EGR system and the internal EGR system so that As a result, the ratio of fresh air introduced into the combustion chamber 17 does not depend on the octane number of the fuel, so the temperature inside the combustion chamber 17 tends to depend on the external EGR rate and the internal EGR rate. Therefore, temperature control in the combustion chamber 17 becomes easier. As a result, abnormal combustion can be suppressed more effectively.

Further, in the present embodiment, the ECU 10 outputs a control signal to the internal EGR system so as to change the internal EGR rate by adjusting the overlap period during which both the intake valve 21 and the exhaust valve 22 are open. do. That is, the overlap period of the intake valve 21 and the exhaust valve 22 can be changed with relatively good responsiveness. Therefore, the temperature of the combustion chamber 17 can be adjusted with good responsiveness by adjusting the internal EGR rate. As a result, abnormal combustion can be suppressed more effectively.

Further, in the present embodiment, the ECU 10 has two combustion control maps, which are used for controlling at least the external EGR system, for each octane number of the fuel. When the octane number of the fuel is less than the predetermined octane number, the combustion control map (low octane number map) is switched to a different combustion control map (low octane number map) than when the octane number of the fuel is equal to or higher than the predetermined octane number. Since the combustion control map is switched according to the octane number of the fuel, the control of the external EGR system can be easily switched. That is, control according to the octane number of the fuel becomes easier, so that abnormal combustion can be suppressed more effectively.

<Other embodiments>
The technology disclosed herein is not limited to the above-described embodiments, and substitutions are possible without departing from the scope of the claims.

For example, in the above-described embodiment, in addition to the external EGR rate, the internal EGR rate is also adjusted according to the fuel octane number. Not limited to this, the internal EGR rate may be the same value regardless of the octane number of the fuel. In this case, for example, it is preferable to increase the difference in the external EGR rate for each octane number of the fuel.

Further, in the above-described embodiment, the internal EGR rate is changed by adjusting the overlap period during which both the intake valve 21 and the exhaust valve 22 are open. Not limited to this, for example, when internal EGR is introduced into the combustion chamber 17 by opening the exhaust valve 22 twice, the internal EGR rate is changed by adjusting the second opening period of the exhaust valve 22. good too.

In the above embodiment, the memory 102 of the ECU 10 stores two types of maps, a low octane map 601 and a high octane map 602, as combustion control maps corresponding to the octane number of fuel. The memory 102 may store three or more types of maps as combustion control maps corresponding to the octane number of the fuel.

Also, detection of the octane number is not limited to the method described above. For example, when the octane number is detected by a sensor installed in the fuel supply system, the reciprocal of the detected value may be used for determination. In this case, when the detected value is low, it is determined that the octane number is high, and when the detected value is high, it is determined that the octane number is low.

The above-described embodiments are merely examples, 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 within the equivalent range of the claims are within the scope of the present disclosure.

The technology disclosed herein is useful as a control device for an engine that performs SI combustion of part of the air-fuel mixture by ignition and CI combustion of the remaining air-fuel mixture by compression ignition.

1 engine 6 injector 10 ECU (control unit)
17 combustion chamber 21 intake valve 22 exhaust valve 23 electric intake S-VT (internal EGR system)
24 exhaust electric S-VT (internal EGR system)
25 spark plug (igniter)
40 intake passage 50 exhaust passage 52 EGR passage (external EGR system)
53 EGR cooler (external EGR system)
54 EGR valve (external EGR system)
601 low octane map (combustion control map)
602 high octane map (combustion control map)
SW5 cylinder internal pressure sensor (octane number detection means)

Claims (4)

Equipped with an injector that supplies fuel to the combustion chamber and an ignition device that ignites the air-fuel mixture in the combustion chamber, and after a part of the air-fuel mixture is SI-burned by ignition using the ignition device, A control device for an engine that CI burns air by compression ignition,
Octane number detection means for detecting the octane number of the fuel;
an external EGR system for introducing external EGR gas into the combustion chamber by recirculating part of the burned gas delivered to the exhaust passage from the combustion chamber to the intake passage via the EGR passage;
a control unit that outputs a control signal to the external EGR system;
an internal EGR system that introduces internal EGR gas into the combustion chamber and receives a control signal from the control unit ;
When the octane number of the fuel detected by the octane number detecting means is less than a predetermined octane number, the control unit controls the amount of gas introduced into the combustion chamber to be lower than when the octane number of the fuel is equal to or higher than the predetermined octane number. outputting a control signal to the external EGR system so that the external EGR rate, which is the ratio of the external EGR gas amount to the amount, increases ;
Further, when the octane number of the fuel detected by the octane number detecting means is less than a predetermined octane number, the control unit reduces the total amount of fuel introduced into the combustion chamber compared to when the octane number of the fuel is equal to or higher than the predetermined octane number. A control device for an engine, wherein a control signal is output to the internal EGR system so that an internal EGR rate, which is a ratio of internal EGR gas amount to gas amount, is lowered. In the engine control device according to claim 1 ,
Assuming the sum of the external EGR gas amount and the internal EGR gas amount as the total EGR gas amount,
The control unit controls the total EGR rate, which is the ratio of the total EGR gas amount to the total gas amount introduced into the combustion chamber, to be the same regardless of the octane number of the fuel detected by the octane number detection means. An engine control device that outputs control signals to the external EGR system and the internal EGR system, respectively. In the engine control device according to claim 1 or 2 ,
The control unit outputs a control signal to the internal EGR system so as to change the internal EGR rate by adjusting a positive overlap period in which both the intake valve and the exhaust valve are open. engine controller. Equipped with an injector that supplies fuel to the combustion chamber and an ignition device that ignites the air-fuel mixture in the combustion chamber, and after a part of the air-fuel mixture is SI-burned by ignition using the ignition device, A control device for an engine that CI burns air by compression ignition,
Octane number detection means for detecting the octane number of the fuel;
an external EGR system for introducing external EGR gas into the combustion chamber by recirculating part of the burned gas delivered to the exhaust passage from the combustion chamber to the intake passage via the EGR passage;
a control unit that outputs a control signal to the external EGR system,
When the octane number of the fuel detected by the octane number detecting means is less than a predetermined octane number, the control unit controls the amount of gas introduced into the combustion chamber to be lower than when the octane number of the fuel is equal to or higher than the predetermined octane number. outputting a control signal to the external EGR system so that the external EGR rate, which is the ratio of the external EGR gas amount to the amount, increases;
Further , the control unit has a plurality of combustion control maps used for controlling at least the external EGR system, divided for each octane number of fuel,
Further, when the octane value of the fuel detected by the octane value detecting means is less than a predetermined octane value, the control unit switches to a different combustion control map than when the octane value of the fuel is equal to or higher than the predetermined octane value. engine controller.

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