JP7380150B2 - engine control device - Google Patents

Description

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

In recent years, in engines that perform CI combustion of the mixture in the combustion chamber by compression ignition, partial compression ignition combustion is performed in which a part of the mixture is SI-combusted by spark ignition, and then the remaining mixture is CI-combusted by compression ignition. There is something. In engines that perform partial compression ignition combustion, in addition to the timing of spark ignition, the timing of CI combustion is adjusted by adjusting the conditions inside the combustion chamber.

For example, the engine control device described in Patent Document 1 uses an EGR system that is installed in the engine and configured to change the EGR rate, which is the ratio of the amount of EGR gas contained in the air-fuel mixture in the combustion chamber. In addition, a control signal is output to the EGR system so that the EGR rate is higher when the engine speed is higher than when it is low in an operating range where supercharging by the supercharger is not performed.

Japanese Patent Application Publication No. 2018-193987

Incidentally, the fuels supplied to the engine include high-octane fuels with a relatively high octane number, such as high-octane gasoline, and low-octane fuels, with a relatively low octane number, such as regular gasoline. High octane fuel is less prone to compression ignition than low octane fuel, and is advantageous from the viewpoint of suppressing abnormal combustion such as knocking. On the other hand, from the perspective 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, low-octane fuel is more likely to self-ignite than high-octane fuel, so if the same combustion control is performed for high-octane fuel and low-octane fuel, abnormal combustion such as knocking may occur when low-octane fuel is used. There is a possibility that this may occur.

In particular, when the intake air temperature is high, the temperature of the air-fuel mixture is high and self-ignition is likely to occur, so abnormal combustion is particularly likely to occur.

The technology disclosed herein suppresses abnormal combustion even when fuels with different octane numbers are supplied when the intake air temperature is high.

In order to solve the above problem, the technology disclosed herein includes an injector that supplies fuel to a combustion chamber, and an ignition device that ignites the air-fuel mixture in the combustion chamber, and ignites a part of the air-fuel mixture into the air-fuel mixture. An octane number detection means for detecting the octane number of the fuel, and an intake air temperature detecting means for detecting the octane number of the fuel, which is intended for a control device for an engine that performs SI combustion by ignition using an ignition device, and then performs CI combustion of the remaining air-fuel mixture by compression ignition. a temperature detection device, an internal EGR system for introducing internal EGR gas into the combustion chamber, a control unit capable of outputting a control signal to the internal EGR system, and a gas installed in the engine and introduced into the combustion chamber. a supercharging system configured to supercharge the intake valve, and the control unit adjusts the opening timing of the intake valve while keeping the opening period of the intake valve constant. The internal EGR rate , which is the ratio of the internal EGR gas amount to the total gas amount introduced into the combustion chamber, is changed by adjusting the positive overlap period during which both the valve and the exhaust valve are open. A control signal is output to the internal EGR system, and a first condition is that the octane number of the fuel detected by the octane number detection means is less than a predetermined octane number, and the intake air temperature detected by the intake air temperature detection device is equal to or higher than a predetermined temperature. When both of the second conditions are satisfied, a control signal is output to the internal EGR system so that the internal EGR rate is lower than when the first condition is not satisfied, and the engine The supercharging system performs supercharging when the load is in a first region where the load is greater than or equal to a predetermined load, and the supercharging system does not perform supercharging when the engine load is in a second region where the engine load is less than the predetermined load. A control signal is output to the supercharging system, and when the first condition is satisfied, in the second region, the larger the engine load is, the more the opening timing of the intake valve is retarded to prevent overflow. While the internal EGR rate is lowered by shortening the wrap period, in the first region, the opening timing of the intake valve is advanced compared to the second region to achieve positive overlap. The configuration is such that the internal EGR rate is lowered by lengthening the period.

According to this configuration, when the octane number of the fuel is low and the intake air temperature is high, a control signal is output to the internal EGR system to reduce the internal EGR rate. Thereby, it is possible to suppress the temperature of the combustion chamber from increasing due to the internal EGR gas. As a result, early ignition of the air-fuel mixture in the combustion chamber is suppressed, and abnormal combustion can be suppressed.

Further, 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. In addition, when internal EGR gas is introduced into the combustion chamber by providing a positive overlap period, compared to introducing internal EGR gas into the combustion chamber through negative overlap, which traps high-temperature burnt gas in the combustion chamber as it is. The temperature of the combustion chamber can be lowered. Therefore, abnormal combustion can be suppressed more effectively.

Furthermore, since the supercharging gas has a high temperature, the internal EGR rate is required to be lower in the first region where supercharging is performed than in the second region where supercharging is not performed, preferably to approximately zero. When the supercharged gas is introduced into the combustion chamber, the burned gas is scavenged by the supercharged gas. Therefore, by lengthening the positive overlap period in the first region as in the above configuration, the scavenging effect of the supercharged gas allows burnt gas to be efficiently delivered to the exhaust port, thereby increasing the internal EGR rate. can be lowered. Thereby, abnormal combustion can be suppressed more effectively.

In the engine control device, the control unit is configured to increase the internal EGR rate when the first condition is satisfied and when the second condition is satisfied, compared to when the second condition is not satisfied. A configuration may also be adopted in which a control signal is output to the internal EGR system so that the internal EGR system becomes low.

That is, when the intake air temperature is high, the air-fuel mixture in the combustion chamber is more likely to self-ignite than when the intake air temperature is low. Therefore, when the second condition is satisfied, the internal EGR rate is further reduced to suppress the temperature of the combustion chamber from increasing. Thereby, abnormal combustion can be suppressed more effectively.

The engine control device further includes a first water temperature detection device that detects the temperature of engine cooling water for cooling the inside of the combustion chamber, and the control section is configured to satisfy the first condition and the second condition. , when the third condition that the temperature of the engine cooling water detected by the first water temperature detection device is equal to or higher than the first predetermined water temperature is satisfied, the internal EGR is lower than when the first condition is not satisfied. A configuration may also be adopted in which a control signal is output to the internal EGR system so that the rate is lowered.

That is, the engine cooling water is warmed by heat absorption from the combustion chamber. Therefore, the temperature of the engine cooling water qualitatively represents the temperature of the combustion chamber. According to the above configuration, the third condition regarding the temperature of the engine cooling water is taken into consideration, so that the current temperature of the combustion chamber is taken into consideration. Thereby, it is possible to more accurately estimate whether or not the environment is likely to cause abnormal combustion. Therefore, abnormal combustion can be suppressed more effectively.

The engine control device further includes a supercharging system attached to the engine and configured to supercharge gas introduced into the combustion chamber, the supercharging system configured to cool the supercharged gas. an intercooler through which intercooler cooling water flows, and a second water temperature detection device that detects the water temperature of the intercooler cooling water; outputting a control signal to the supercharging system so that the supercharging system does not perform supercharging when the charging system performs supercharging and the engine load is in a second region where the engine load is less than the predetermined load; In addition to the first condition and the second condition, when a fourth condition that the intercooler cooling water temperature detected by the second water temperature detection device is equal to or higher than a second predetermined water temperature is satisfied, the control section The configuration may be such that a control signal is output to the internal EGR system so that the internal EGR rate is lower than when the first condition is not satisfied.

That is, if the intake air is cooled by the intercooler, the temperature of the air-fuel mixture decreases, making abnormal combustion less likely to occur. Therefore, as in the above configuration, by considering the fourth condition regarding the intercooler, abnormal combustion can be suppressed even more effectively .

As described above, according to the technology disclosed herein, abnormal combustion can be suppressed even when fuels with different octane numbers are supplied when the intake air temperature is high.

1 is a configuration diagram illustrating an engine controlled by a control device according to an exemplary embodiment. FIG. 1 is a diagram illustrating a combustion chamber, the upper diagram is a plan view of the combustion chamber, and the lower diagram is a sectional view taken along the line II-II. FIG. 3 is a plan view illustrating a combustion chamber and an intake passage. FIG. 2 is a block diagram illustrating an engine control device. It is a figure which illustrates the control map of an engine, The upper figure is a control map when it is warm, the middle figure is a control map when it is semi-warmed up, and the lower figure is a control map when it is cold. FIG. 2 is a block diagram illustrating a low octane map and a high octane map. FIG. 2 is a schematic diagram showing an example of the history of heat release rate when low octane fuel is combusted under extreme heat conditions, when low octane fuel is combusted under normal conditions, and when high octane fuel is combusted. FIG. 3 is a diagram illustrating an opening/closing pattern of an intake valve and an exhaust valve when changing an internal EGR rate. FIG. 3 is a diagram illustrating a part of a flowchart of engine control executed by an ECU. FIG. 3 is a diagram illustrating the remainder of a flowchart of engine control executed by an ECU. It is a time chart showing changes in intake air temperature, engine water temperature, intercooler water temperature, engine load, positive overlap period, and internal EGR rate.

Hereinafter, exemplary embodiments will be described in detail with reference to the drawings.

FIG. 1 is a diagram illustrating an engine. FIG. 2 is a diagram illustrating a combustion chamber of an engine. FIG. 3 is a diagram illustrating a combustion chamber and an intake passage. 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 page, and the exhaust side is on the left side of the page. 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. 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. The fuel may be any liquid fuel containing at least gasoline. Gasoline as a fuel may be regular fuel or high octane fuel. The fuel may be, for example, gasoline containing bioethanol or the like. Note that the regular fuel is a low octane fuel with an octane number of about 91. High-octane fuel is a high-octane fuel with an octane number of about 100.

(Engine configuration)
The engine 1 includes a cylinder block 12 and a cylinder head 13. Cylinder head 13 is placed on cylinder block 12 .

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

Each cylinder 11 has a piston 3 inserted therein. 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. Note that the term "combustion chamber" refers to a space formed by the piston 3, the cylinder 11, and the cylinder head 13, regardless of the position of the piston 3.

The lower surface of the cylinder head 13 constitutes the ceiling of the combustion chamber 17. As shown in the lower diagram of FIG. 2, the ceiling section is composed of two inclined surfaces. The combustion chamber 17 is of a so-called pent roof type.

The piston 3 has a cavity 31 that is recessed downward from the top surface. In this configuration example, the cavity 31 has a shallow dish shape. 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 regions. SPCCI combustion controls CI combustion by heat generation and/or pressure increase due to SI combustion. Engine 1 is a compression ignition engine. This engine 1 does not require increasing the temperature of the combustion chamber 17 when the piston 3 reaches 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. Intake port 18 communicates with 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 causes a tumble flow to occur within the combustion chamber 17.

An intake valve 21 is provided 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 timing. The valve mechanism may be a variable valve mechanism that varies valve timing and/or valve lift. As shown in FIG. 4, the valve mechanism includes an intake electric S-VT (Sequential-Valve Timing) 23. The electric intake S-VT 23 continuously changes the rotational phase of the intake camshaft within a predetermined angular 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. Note that the valve train may include 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. Exhaust port 19 communicates with combustion chamber 17 .

The exhaust port 19 is provided with an exhaust valve 22 . The exhaust valve 22 opens and closes the exhaust port 19. The valve mechanism opens and closes the exhaust valve 22 at predetermined timing. 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 includes an exhaust electric S-VT24. The electric exhaust S-VT 24 continuously changes the rotational phase of the exhaust camshaft within a predetermined angular 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. Note that the valve train may include a hydraulic S-VT instead of the electric S-VT.

The intake electric S-VT 23 and the exhaust electric S-VT 24 adjust the length of the overlap period in which both the intake valve 21 and the exhaust valve 22 are open. By adjusting the length of the overlap period, internal EGR (Exhaust Gas Recirculation) gas is introduced into the combustion chamber 17. That is, the intake valve 21, the exhaust valve 22, the intake electric S-VT 23, and the exhaust electric 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. The injector 6 injects fuel directly into the 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 located closer to the exhaust side than the central axis X1 of the cylinder 11. The injection axis X2 of the injector 6 is parallel to the central axis X1. The injection axis X2 of the injector 6 and the center of the cavity 31 coincide with each other. The injector 6 faces the cavity 31. Note that the injection axis X2 of the injector 6 may coincide with the central axis X1 of the cylinder 11. In the case of this configuration, the injection axis X2 of the injector 6 and the center of the cavity 31 may coincide.

The injector 6 is a multi-nozzle type having a plurality of nozzle holes. The injector 6 injects fuel radially and diagonally downward from the center of the ceiling of the combustion chamber 17, as shown by the two-dot chain line in FIG. In this configuration example, the injector 6 has ten nozzle holes. The ten nozzle 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. The 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 . The fuel pump 65 sends 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 fuel sent from the fuel pump 65. The inside of the common rail 64 is under high pressure. The injector 6 is connected to a common rail 64. When the injector 6 opens, high-pressure fuel in the common rail 64 is injected into the combustion chamber 17 from the nozzle hole of the injector 6. The fuel supply system 61 of this configuration example can supply fuel at a high pressure of 30 MPa or more to the injector 6. The maximum pressure of the fuel supply system 61 may be, for example, 200 MPa. The fuel supply system 61 may change the pressure of fuel 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 spark plug 25 is attached to the cylinder head 13 for each cylinder 11. The spark plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17. The spark plug 25 is an example of an ignition device. As shown in FIG. 2, the spark plug 25 is disposed on the intake side of the central axis X1 of the cylinder 11. The spark plug 25 is located between the two intake ports 18. The electrode of the spark plug 25 faces into the combustion chamber 17. Incidentally, the spark plug 25 may be arranged on the exhaust side with respect to the central axis X1 of the cylinder 11. Further, 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 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 provided at the upstream end of the intake passage 40 . A surge tank 42 is disposed near the downstream end of the intake passage 40. The intake passage 40 downstream of the surge tank 42 branches for 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 adjusts the amount of fresh air introduced into the combustion chamber 17 by changing the opening degree of the valve.

A supercharger 44 is also disposed 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 is of the Roots type, Lysholm type, vane type, or centrifugal type. Supercharger 44 constitutes part of a supercharging system.

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 ECU 10, which will be described later, outputs a control signal to the electromagnetic clutch 45, thereby turning the supercharger 44 on or off. Electromagnetic clutch 45 constitutes a part of the supercharging system.

An intercooler 46 is disposed 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. Intercooler 46 constitutes a part of the supercharging system.

A bypass passage 47 is connected to the intake passage 40 . The bypass passage 47 connects the upstream part of the supercharger 44 and the downstream part of the intercooler 46 in the intake passage 40 to each other. Bypass passage 47 bypasses supercharger 44 and intercooler 46. An air bypass valve 48 is provided in the bypass passage 47 . Air bypass valve 48 adjusts the flow rate of gas flowing through 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 degree of the air bypass valve 48 when the supercharger 44 is on. A portion of the intake gas that has passed through the supercharger 44 and intercooler 46 returns to the upstream side of the supercharger 44 through a bypass passage 47 . When the ECU 10 adjusts the opening degree of the air bypass valve 48, the pressure of intake gas introduced into the combustion chamber 17 changes. In addition, "supercharging" is defined as a state in which the pressure within the surge tank 42 exceeds atmospheric pressure, and "non-supercharging" is defined as a state in which the pressure within the surge tank 42 is below atmospheric pressure. You may.

The engine 1 includes a swirl generating section that generates a swirl flow within the combustion chamber 17. The swirl generator includes 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 disposed in secondary passage 402. The swirl control valve 56 is an opening adjustment valve that can narrow the cross section of the secondary passage 402. When the opening degree 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, so that combustion The swirl flow inside chamber 17 becomes stronger. When the degree of opening of the swirl control valve 56 is large, the flow rate of intake air flowing into the combustion chamber 17 from each of the first intake port 181 and the second intake port 182 becomes approximately equal, so that the swirl flow inside the combustion chamber 17 is increased. become weak. When the swirl control valve 56 is fully opened, no swirl flow occurs. Note that the swirl flow circulates in the counterclockwise direction in FIG. 3, as shown 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 inclined with respect to the central axis X1 of the cylinder 11 (see FIG. 6). The inclination angle of the oblique swirl flow is generally about 45° with respect to a plane perpendicular to the central axis X1. The inclination angle may be set in the range of 30° to 60°.

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. Exhaust gas discharged from the combustion chamber 17 flows through the exhaust passage 50. Although detailed illustration is omitted, the upstream portion of the exhaust passage 50 branches for each cylinder 11.

An exhaust gas purification system having a plurality of catalytic converters is disposed in the exhaust passage 50. Although not shown, these catalytic converters are arranged in the engine room. The upstream catalytic converter includes a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512. The downstream catalytic converter has a three-way catalyst 513. Note that the exhaust gas purification system is not limited to the configuration shown in the diagram. 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 that recirculates a portion of exhaust gas to the intake passage 40. The upstream end of the EGR passage 52 is connected between 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 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. The EGR valve 54 adjusts the amount of external EGR gas recirculated. EGR passage 52, EGR cooler 53, and EGR valve 54 constitute an external EGR system.

(Configuration of engine control device)
The control device for the engine 1 includes an ECU (Engine Control Unit) 10. The ECU 10 is an example of a control unit. As shown in FIG. 4, the ECU 10 includes a microcomputer 101, a memory 102, and an I/F circuit 103. Microcomputer 101 executes a program. 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.

As shown in FIGS. 1 and 4, various sensors SW1 to SW12 are connected to the ECU 10. Sensors SW1 to SW12 output signals to the ECU 10. The sensors include the following sensors.

The air flow sensor SW1 measures the flow rate of fresh air flowing through the intake passage 40. The air flow 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. 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 intake gas introduced into the combustion chamber 17. The second intake air temperature sensor SW3 is attached to the surge tank 42. The intake pressure sensor SW4 measures the pressure of intake gas introduced into the combustion chamber 17. The intake pressure sensor SW4 is attached to the surge tank 42. The cylinder pressure sensor SW5 measures the pressure inside each combustion chamber 17. The cylinder pressure sensor SW5 is attached to the cylinder head 13 for each cylinder 11. The engine water temperature sensor SW6 measures the temperature of the cooling water that cools the combustion chamber 17. Engine water temperature sensor SW6 is installed so as to face the water jacket of engine 1. Crank angle sensor SW7 measures the rotation angle of crankshaft 15. 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 fuel supplied to the injector 6. The fuel pressure sensor SW11 is attached to the common rail 64 of the fuel supply system 61. The intercooler water temperature sensor SW12 measures the temperature of the cooling water flowing to the intercooler 46. Intercooler water temperature sensor SW12 is attached to engine 1.

ECU 10 determines the operating state of engine 1 based on signals from these sensors SW1 to SW12. The ECU 10 also calculates the control amount of each device according to predetermined control logic. Control logic is stored in memory 102.

The ECU 10 sends electrical signals related to control amounts to the injector 6, the spark plug 25, the intake electric S-VT 23, the exhaust electric S-VT 24, the fuel supply system 61, the throttle valve 43, the EGR valve 54, and the electromagnetic clutch of the supercharger 44. 45, air bypass valve 48, and swirl control valve 56.

(SPCCI combustion concept)
The engine 1 performs combustion by compression self-ignition when in a predetermined operating state, with the main purpose of improving fuel efficiency and improving exhaust emission performance. If the temperature in the combustion chamber 17 before the start of compression varies, the timing of self-ignition will change significantly. Therefore, the engine 1 performs SPCCI combustion, which is a combination of SI combustion and CI combustion.

SPCCI combustion has the following combustion form. That is, the spark plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17, so that 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, which causes the unburnt mixture to become CI combustion occurs by self-ignition.

By adjusting the ignition timing by the ECU 10, the air-fuel mixture self-ignites at the target timing. In SPCCI combustion, the combustion amount of SI combustion controls the start timing of CI combustion.

(engine operating range)
FIG. 5 illustrates control maps 501, 502, and 503 for the engine 1. Control maps 501, 502, and 503 are stored in the memory 102 of the ECU 10. ECU 10 operates engine 1 based on control maps 501, 502, and 503. The control map includes three types of control maps: a first control map 501, a second control map 502, and a third control map 503. The ECU 10 performs control selected from among a first control map 501, a second control map 502, and a third control map 503 depending on the wall temperature (or engine water temperature) of the combustion chamber 17 and the intake air temperature. The 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 the first wall temperature (eg, 80° C.) and the temperature of the intake air is equal to or higher than the 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 less than the first wall temperature and more than the second wall temperature (for example, 30°C), and the intake air temperature is less than the first intake temperature and more than the second intake temperature (for example, 25°C), the ECU 10 , selects the second control map 502. The second control map 502 is a map when the engine 1 is partially warmed up. When the wall temperature of the combustion chamber 17 is less than the second wall temperature or when 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.

Note that the ECU 10 may select the control maps 501, 502, and 503 based on the temperature of the cooling water of the engine 1 measured by the water temperature sensor SW6, for example, instead of the wall temperature of the combustion chamber 17. Furthermore, 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. Area A1 is an area where the rotational speed is lower than Na. Idle operation of the engine 1 is included in area A1. Region A2 is a region where the rotation speed is higher than Nb. Region A3 is a region where the load is lower than La among the regions where the rotational speed is from Na to Nb. Region A4 is a region where the load is equal to or higher than La among the regions where the rotational speed is from Na to Nb. Note that La may be a half load of 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 all operating regions of the engine 1. Note that "low rotation" here corresponds to the low rotation side when the entire operating range of the engine 1 is divided into two, a low rotation side and a high rotation side. "Low load" corresponds to the low load side when the entire operating range of the engine 1 is divided into two, a low load side and a high load side.

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

When the operating state of the engine 1 is within the region A3, the ECU 10 controls the engine 1 to perform SPCCI combustion. Note that the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio or approximately 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. Note that the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio or approximately 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 range A5, the ECU 10 controls the engine 1 to perform SPCCI combustion. Note that 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 range 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 in which the intake valve 21 and the exhaust valve 22 are both opened. Internal EGR gas is introduced into the combustion chamber 17. This increases the temperature inside the combustion chamber 17. In region A5 where the load on the engine 1 is low, the temperature in the combustion chamber 17 is high, so that CI combustion of SPCCI combustion is stabilized. In addition, below, area|region A5 is called SPCCI lean area|region 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 rotation speed is lower than Na, and corresponds to region A1 of the first control map 501. Region B2 is a region where the rotation speed is higher than Nb, and corresponds to region A2 of the first control map 501. Region B3 is a region where the load is lower than La among the regions where the rotational speed is from Na to Nb, and corresponds to region A3 of the first control map 501. Region B4 is a region where the load is greater than or equal to La among the regions where the rotational speed is from Na to Nb, and corresponds to region A4 of the first control map 501. The second control map 502 does not have an area corresponding to area A5 of the first control map 501. This is because if the temperature is low, SPCCI combustion of a lean mixture becomes unstable.

When the operating state of the engine 1 is within the region B1, the ECU 10 controls the engine 1 to perform SI combustion. Note that the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio or approximately 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. Note that the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio or approximately the stoichiometric air-fuel ratio. When the operating state of the engine 1 is within region B3, the ECU 10 controls the engine 1 to perform SPCCI combustion. Note that the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio or approximately 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 region B4, the ECU 10 controls the engine 1 to perform SPCCI combustion. Note that the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio or approximately 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 the area C1. Region C1 extends over the entire operating region of engine 1. When the operating state of the engine 1 is within the range C1, the ECU 10 controls the engine 1 to perform SI combustion. Note that the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio or approximately the stoichiometric air-fuel ratio.

(Differences in control content depending on fuel octane number)
The control device for the engine 1 changes the control content of the engine 1 according to the octane number of the fuel introduced into the combustion chamber 17. Specifically, as shown in FIG. 6, the control device of the engine 1 uses a combustion control map (hereinafter referred to as a low octane map 601) when the octane number of the fuel is less than a predetermined octane number, and a combustion control map when the octane number of the fuel is less than the predetermined octane number. (hereinafter referred to as 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 regular fuel and high-octane fuel to be distinguished, and is set to, for example, 96. 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 showing the fuel injection timing by the injector 6, a first SCV (Swirl Control Valve) map 601b showing the opening degree 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 601d used to control the internal EGR system (particularly the intake electric S-VT 23 and the exhaust electric S-VT 24). and a severe heat EGR map 601e used for controlling the internal EGR system when the temperature of the gas in the combustion chamber 17 becomes high. The 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 above a predetermined octane number, 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 the fuel from the injector 6 according to the first and second injection timing maps 601a and 602a, and controls the injection amount of the fuel according to the amount of air introduced into the combustion chamber 17. control.

The octane number of the fuel can be determined, for example, by a change in the amount of heat before self-ignition. That is, since 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 greater than or equal to the predetermined octane number. By utilizing this difference, the octane number of the fuel can be determined. The in-cylinder pressure sensor SW5 can detect the amount of heat with high precision, and therefore can determine the octane number in a dynamic state with high precision. Moreover, since existing equipment is used, there is no need to install new expensive sensors. That is, in this engine 1, the cylinder pressure sensor SW5 constitutes an octane number detection means. Note that since the amount of heat before self-ignition changes depending on the engine load, it is actually preferable to take the engine load into consideration when determining the octane number.

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

(Control of internal EGR rate)
In the present embodiment, the control device for the engine 1 introduces internal EGR gas into the combustion chamber 17 at least when the operating region in which SPCCI combustion is performed, particularly when the operating region of the engine 1 is in region B2. Thereby, the temperature of the combustion chamber 17 is maintained at a temperature necessary for self-ignition of the fuel, thereby improving combustion stability.

As previously mentioned herein, low octane fuels tend to self-ignite relative to high octane fuels. For this reason, if the internal EGR rate is made the same when the fuel is low octane fuel and when the fuel is high octane fuel, when the fuel is low octane fuel, the , the air-fuel mixture self-ignites early, resulting in abnormal combustion such as knocking. In particular, in an environment where the intake air temperature is high and the temperature of the gas in the combustion chamber 17 is high (hereinafter referred to as an extremely hot environment), the timing of self-ignition of the air-fuel mixture tends to be even earlier, as shown in FIG. Combustion is very likely to occur. Note that the internal EGR rate is the ratio of the amount of internal EGR gas to the total amount of gas introduced into the combustion chamber 17, and is a value expressed by the following formula.

(Internal EGR rate) = (Internal EGR gas amount/Total gas amount)
Therefore, in this embodiment, the ECU 10 adjusts the internal EGR rate using parameters related to the octane number of the fuel and the temperature of the gas in the combustion chamber 17. Specifically, first, when the first condition that the octane number of the fuel is less than the predetermined octane number is satisfied, the ECU 10 compares the first condition with the case where the first condition is not satisfied (that is, the octane number of the fuel is equal to or higher than the predetermined octane number). Then, a control signal is output to the internal EGR system to reduce the internal EGR rate. Then, in a state where the first condition is satisfied, the ECU 10 sets a second condition that the intake air temperature is equal to or higher than a predetermined temperature Ta, and a water temperature of the engine cooling water (hereinafter referred to as engine water temperature) is equal to or higher than a first predetermined water temperature Tw1. When the third condition that the temperature of the cooling water of the intercooler (hereinafter referred to as intercooler water temperature) is the second predetermined temperature Tw2 are all satisfied, at least one of the second to fourth conditions is not satisfied. A control signal is output to the internal EGR system in order to further reduce the internal EGR rate compared to when the internal EGR rate is lowered. Note that the predetermined temperature Ta is, for example, 35°C, the first predetermined water temperature Tw1 is, for example, 100°C, and the second predetermined water temperature Tw2 is, for example, 40°C.

Furthermore, when the first condition is satisfied and the engine load becomes equal to or higher than the predetermined load La (that is, the operating region becomes region B4), the ECU 10 reduces the internal EGR rate to substantially 0. . This is because supercharged gas has a high temperature, so if internal EGR gas is introduced into the combustion chamber 17, the temperature of the combustion chamber 17 will become excessively high, and there is a high possibility that abnormal combustion will occur. Note that "making the internal EGR rate substantially 0" means reducing the internal EGR rate to such an extent that the internal EGR gas does not affect the temperature of the combustion chamber 17; This includes cases where it is set to 0.

By lowering the internal EGR rate, the temperature of the combustion chamber 17 can be lowered. Thereby, even if the fuel is a low octane fuel, the timing of self-ignition can be adjusted to an appropriate timing. In particular, in extremely hot environments, the internal EGR rate is further reduced. This makes it possible to adjust the timing of self-ignition and suppress abnormal combustion even in extremely hot environments.

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 open using the intake electric S-VT 23 and the exhaust electric S-VT 24. In particular, in this embodiment, the ECU 10 adjusts the positive overlap period depending on the engine load. That is, when the engine load is less than the predetermined load La, the ECU 10 shortens the positive overlap period to lower the internal EGR rate, while when the engine load is greater than or equal to the predetermined load La, the ECU 10 shortens the positive overlap period to reduce the internal EGR rate. The internal EGR rate is reduced to substantially zero by making the positive overlap period longer than when it is less than. In this embodiment, the ECU 10 adjusts the opening timing of the intake valve 21 using the intake electric S-VT 23 to adjust the positive overlap period.

When the engine load is less than the predetermined load La, supercharging by the supercharger 44 is not performed, so the intake pressure is atmospheric pressure. Therefore, when the opening timing of the intake valve 21 is before the exhaust top dead center, burned gas enters the intake port 18 as the piston 3 rises. As a result, when the piston 3 descends, burnt gas is introduced (blown back) into the combustion chamber 17 along with fresh air from the intake port 18. When the opening timing of the intake valve 21 is retarded, the amount of burnt gas (internal EGR gas) that is blown back from the intake port 18 decreases, resulting in a decrease in the internal EGR rate.

Furthermore, when the engine load is less than the predetermined load La, even if the opening timing of the intake valve 21 is retarded to after exhaust top dead center, the timing at which intake air is introduced into the combustion chamber 17 changes. , the amount of burned gas drawn into the combustion chamber 17 from the exhaust port 20 changes. Therefore, by retarding the opening timing of the intake valve 21 and shortening the positive overlap period, the internal EGR rate can be reduced.

The ECU 10 adjusts the positive overlap period between the intake valve 21 and the exhaust valve 22 so that the internal EGR rate decreases as the engine load increases in a range where the engine load is less than the predetermined load La. Specifically, the positive overlap period is shortened as the engine load increases.

On the other hand, when the engine load is equal to or higher than the predetermined load La, supercharging is performed by the supercharger 44, so the intake pressure becomes higher than atmospheric pressure. Therefore, when the intake valve 21 is opened, the burned gas in the combustion chamber 17 is scavenged into the exhaust port 19 by the supercharged gas. Therefore, if the opening timing of the intake valve 21 is advanced to make the positive overlap period longer than when the engine load is less than the predetermined load La, the scavenging of the burnt gas by the supercharged gas can be actively performed. be able to. Therefore, when the engine load is greater than or equal to the predetermined load La, the internal EGR rate can be made substantially zero by making the positive overlap period longer than when the engine load is less than the predetermined load La.

When internal EGR gas is introduced into the combustion chamber 17 by providing a positive overlap period, the high-temperature burnt gas temporarily moves to the intake port 18 and exhaust port 19. Therefore, when internal EGR gas is introduced into the combustion chamber 17 using positive overlap, it is compared to when internal EGR gas is introduced into the combustion chamber 17 using negative overlap, which traps high-temperature burnt gas in the combustion chamber 17 as it is. Therefore, the temperature of the combustion chamber 17 can be easily lowered. Therefore, the temperature of the combustion chamber 17 can be effectively lowered, and abnormal combustion can be effectively suppressed.

Note that the internal EGR rate may be reduced by adjusting the closing timing of the exhaust valve 22 using the exhaust electric S-VT 24. Furthermore, the internal EGR rate may be reduced by adjusting both the opening timing of the intake valve 21 and the closing timing of the exhaust valve 22.

Control of the internal EGR rate according to the octane number of these fuels is stored in the first internal EGR map 601d and the internal EGR map 601e for extreme heat of the low octane number map 601, and the second internal EGR map 602d of the high octane number map 602, respectively. ing. That is, the ECU 10 controls the intake electric S-VT 23 and the exhaust electric S-VT 24 based on the first internal EGR map 601d, the extreme heat internal EGR map 601e, and the second internal EGR map 602d, and controls the intake valve 21 and Adjust the valve timing of each exhaust valve 22.

For example, when the low octane number map 601 is selected as the combustion control map and the octane number of the fuel is close to the predetermined octane number, the timing of self-ignition of the air-fuel mixture containing the fuel may deviate slightly from the target timing. There is sex. Therefore, the timing of self-ignition may be finely adjusted by adjusting the ignition timing of the spark plug 25 according to the octane number of the fuel.

Next, processing operations for controlling the engine 1 executed by the ECU 10 will be described with reference to flowcharts in FIGS. 9 and 10.

First, in step S101, the ECU 10 reads detection signals from each sensor SW1 to SW12.

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

In subsequent step S103, the ECU 10 determines whether the octane number calculated in step S102 is less than a predetermined octane number. If the octane number is less than the predetermined octane number (YES), the process proceeds to step S104, while if the octane number is greater than or equal to the predetermined octane number (NO), the process proceeds to step S116.

In step S104, 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 determines whether the intake air temperature is equal to or higher than a predetermined temperature Ta. When the ECU 10 determines YES that the intake air temperature is equal to or higher than the predetermined temperature Ta, the process proceeds to step S106. On the other hand, if the intake air temperature is lower than the predetermined temperature Ta (NO), the ECU 10 proceeds to step S111.

In step S106, it is determined whether the engine water temperature is equal to or higher than the first predetermined water temperature Tw1. If the engine water temperature is equal to or higher than the first predetermined water temperature Tw1 (YES), the ECU 10 proceeds to step S107. On the other hand, when the engine water temperature is less than the first predetermined water temperature Tw1 (NO), the ECU 10 proceeds to step S111.

In step S107, it is determined whether the intercooler water temperature is equal to or higher than the second predetermined water temperature Tw2. When the intercooler water temperature is equal to or higher than the second predetermined water temperature Tw2 (YES), the ECU 10 proceeds to step S108. On the other hand, when the intercooler water temperature is lower than the second predetermined water temperature Tw2 (NO), the ECU 10 proceeds to step S111.

In step S108, the ECU 10 selects the extreme heat internal EGR map 601e as a map for controlling the internal EGR system.

In the next step S109, the ECU 10 determines whether the engine load is less than a predetermined load La. When the engine load is less than the predetermined load La (YES), the ECU 10 proceeds to step S110. On the other hand, when the engine load is equal to or higher than the predetermined load La (NO), the ECU 10 proceeds to step S111.

In step S110, the ECU 10 shortens the positive overlap period between the intake valve 21 and the exhaust valve 22 to reduce the internal EGR rate. On the other hand, in step S111, the ECU 10 lengthens the positive overlap period between the intake valve 21 and the exhaust valve 22 to lower the internal EGR rate. After step S110 and step S111, the process returns.

In step S112, which is proceeded to when any one of steps S105 to S107 is NO, the ECU 10 selects the first internal EGR map 601d as a map for controlling the internal EGR system.

In the next step S113, the ECU 10 determines whether the engine load is less than a predetermined load La. When the ECU 10 determines YES that the engine load is less than the predetermined load La, the process proceeds to step S114. On the other hand, when the engine load is equal to or higher than the predetermined load La (NO), the ECU 10 proceeds to step S115.

In step S114, the ECU 10 shortens the positive overlap period between the intake valve 21 and the exhaust valve 22 to reduce the internal EGR rate. On the other hand, in step S115, the ECU 10 lengthens the positive overlap period between the intake valve 21 and the exhaust valve 22 to lower the internal EGR rate. After step S114 and step S115, the process returns.

On the other hand, in step S116, which is proceeded when the determination in step S103 is NO, the ECU 10 selects the high octane number map 602. At this time, the ECU 10 selects the second internal EGR map 602d as the map for controlling the internal EGR system. After step S116, the process returns.

Although not shown in FIG. 10, when the ECU 10 selects the high octane number map 602 in step S116, the positive overlap period of the intake valve and exhaust valve is also adjusted according to the engine load. Specifically, as with the low octane map, when the engine load is less than the predetermined load La, the ECU 10 shortens the positive overlap period to lower the internal EGR rate, while when the engine load is equal to or higher than the predetermined load La, the ECU 10 shortens the positive overlap period to lower the internal EGR rate. Sometimes the positive overlap period is lengthened to reduce the internal EGR rate.

FIG. 11 is a time chart showing changes in each parameter when the internal EGR system is controlled by the control device for the engine 1 according to the present embodiment.

In the initial conditions, the intake air temperature is less than the predetermined temperature Ta, the engine water temperature is less than the first predetermined water temperature Tw1, the intercooler water temperature is more than the second predetermined water temperature Tw2, and the engine load is less than the predetermined load La. At this time, the ECU 10 has selected the low octane number map 601 as the combustion control map for the engine 1, and has selected the first internal EGR map 601d as the map for controlling the internal EGR system in the low octane number map 601.

Assume that at time t1, the intake air temperature becomes equal to or higher than a predetermined temperature Ta. At this time, since the engine water temperature is still below the first predetermined water temperature Tw1, the ECU 10 continues to select the first internal EGR map 601d as the map for controlling the internal EGR system.

Assume that at time t2, the engine water temperature becomes equal to or higher than the first predetermined water temperature Tw1. At this time, the ECU 10 determines that the condition is extreme heat and switches the map for controlling the internal EGR system from the first internal EGR map 601d to the extreme heat internal EGR map 601e. As a result, the positive overlap period between the intake valve 21 and the exhaust valve 22 is shortened, and the internal EGR rate is reduced.

From time t2 to time t3, the engine load is constant and the internal EGR rate is also maintained constant. It is assumed that the engine load increases due to acceleration or the like from time t3. At this time, the ECU 10 shortens the positive overlap period as the engine load increases so that the internal EGR rate decreases as the engine load increases.

Then, at time t4, the engine load becomes equal to or higher than the predetermined load La, and the operating range of the engine 1 enters the supercharging range. At this time, the ECU 10 makes the positive overlap period longer than when the engine load is less than the predetermined load La. Due to the scavenging effect of the supercharged gas, the internal EGR rate becomes substantially zero.

As described above, the internal EGR rate is adjusted according to the temperature of the gas introduced into the combustion chamber 17 from the intake port 18. This prevents the temperature of the combustion chamber 17 from becoming excessively high, so even if fuel with a different octane number, especially fuel with a lower octane number, is supplied when the intake air temperature is high, abnormal combustion can be suppressed. I can do it.

Therefore, in this embodiment, the octane number detection means for detecting the octane number of fuel, the intake air temperature sensor SW2 for detecting the intake air temperature, and the internal EGR system for introducing internal EGR gas into the combustion chamber 17 (in particular, the intake electric -VT 23 and exhaust electric S-VT 24), and an ECU 10 capable of outputting a control signal to the internal EGR system, and the ECU 10 meets the first condition that the octane number of the fuel detected by the octane number detection means is less than a predetermined octane number. , and the second condition that the intake air temperature detected by the intake air temperature sensor SW2 is equal to or higher than the predetermined temperature Ta, the intake air is introduced into the combustion chamber 17 compared to when the first condition is not satisfied. A control signal is output to the internal EGR system so that the internal EGR rate, which is the ratio of the internal EGR gas amount to the total gas amount, is reduced. As a result, when the octane number of the fuel is low and the intake air temperature is high, a control signal is output to the internal EGR system to reduce the internal EGR rate. Thereby, it is possible to suppress the temperature of the combustion chamber 17 from increasing due to the internal EGR gas. As a result, early ignition of the air-fuel mixture in the combustion chamber 17 is suppressed, and abnormal combustion can be suppressed.

Furthermore, in the present embodiment, the ECU 10 is configured such that when the first condition is satisfied and the second condition is satisfied, the internal EGR rate is lower than when the second condition is not satisfied. , outputs a control signal to the internal EGR system. That is, when the intake air temperature is high, the air-fuel mixture in the combustion chamber 17 is more likely to self-ignite than when the intake air temperature is low. Therefore, when the second condition is satisfied, the internal EGR rate is further reduced to suppress the temperature of the combustion chamber 17 from increasing. Thereby, abnormal combustion can be suppressed more effectively.

Further, in this embodiment, the engine water temperature sensor SW6 is further provided to detect the temperature of engine cooling water for cooling the inside of the combustion chamber 17, and in addition to the first condition and the second condition, the ECU 10 When the third condition that the temperature of the engine cooling water detected by SW6 is equal to or higher than the first predetermined water temperature Tw1 is satisfied, the internal EGR rate is lower than when the first condition is not satisfied. Outputs a control signal to the internal EGR system. That is, the engine cooling water is warmed by heat absorption from the combustion chamber 17. Therefore, the temperature of the engine cooling water qualitatively represents the temperature of the combustion chamber 17. According to this embodiment, the current temperature of the combustion chamber 17 is taken into consideration by taking into consideration the third condition regarding the temperature of the engine cooling water. Thereby, it is possible to more accurately estimate whether or not the environment is likely to cause abnormal combustion. Therefore, abnormal combustion can be suppressed more effectively.

Further, in this embodiment, a supercharging system (particularly a supercharger 44, an electromagnetic clutch 45, and an intercooler 46) that is attached to the engine 1 and configured to supercharge gas introduced into the combustion chamber 17 is further provided. The supercharging system includes an intercooler 46 through which intercooler cooling water flows to cool the supercharged gas, and an intercooler water temperature sensor SW12 that detects the temperature of the intercooler cooling water. The supercharging system performs supercharging when the engine load is in the first region where the engine load is equal to or higher than La, and the supercharging system does not perform supercharging when the engine load is in the second region where the engine load is less than the predetermined load La. The ECU 10 outputs a control signal to the system, and furthermore, in addition to the first condition and the second condition, a fourth condition that the intercooler cooling water temperature detected by the intercooler water temperature sensor SW12 is equal to or higher than the second predetermined water temperature Tw1 is set. When the first condition is satisfied, a control signal is output to the internal EGR system so that the internal EGR rate is lower than when the first condition is not satisfied. That is, if the intake air is cooled by the intercooler 46, the temperature of the air-fuel mixture decreases, making abnormal combustion less likely to occur. Therefore, by considering the fourth condition regarding the intercooler 46 as in this embodiment, abnormal combustion can be suppressed even more effectively.

Furthermore, in this embodiment, the ECU 10 sends a control signal to the internal EGR system to change the internal EGR rate by adjusting the positive overlap period in which both the intake valve 21 and the exhaust valve 22 are open. Output. That is, the positive 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. In addition, introducing internal EGR gas into the combustion chamber 17 by providing a positive overlap period is compared with introducing internal EGR gas into the combustion chamber 17 through negative overlap, which traps high-temperature burnt gas in the combustion chamber 17 as it is. As a result, the temperature of the combustion chamber 17 can be lowered. Therefore, abnormal combustion can be suppressed more effectively.

Furthermore, in this embodiment, the ECU 10 sends a control signal to the internal EGR system to change the internal EGR rate by adjusting the positive overlap period in which both the intake valve 21 and the exhaust valve 22 are open. Further, when the first condition is satisfied, the ECU 10 makes the positive overlap period longer in the first region than in the second region. That is, since the supercharging gas has a high temperature, the internal EGR rate is required to be lower in the first region where supercharging is performed than in the second region where supercharging is not performed, preferably to approximately zero. When the supercharged gas is introduced into the combustion chamber 17, the burned gas is scavenged by the supercharged gas. Therefore, as in the present embodiment, by lengthening the positive overlap period in the first region, the scavenging effect of the supercharged gas allows burnt gas to be efficiently delivered to the exhaust port, increasing the internal EGR rate. can be lowered. Thereby, abnormal combustion can be suppressed more effectively.

<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.

For example, in the embodiment described above, the ECU 10 determines that when the first condition regarding the octane number is satisfied, the second condition regarding the intake air temperature, the third condition regarding the engine water temperature, and the fourth condition regarding the intercooler water temperature are all satisfied. , the internal EGR map 601e for severe heat of the low octane number map 601 was configured to be used. The present invention is not limited to this, and the third condition and the fourth condition do not necessarily need to be set. That is, the ECU 10 may be configured to use the extreme heat internal EGR map 601e when both the first condition and the second condition are satisfied, even if the third condition and the fourth condition are not satisfied.

Furthermore, in the embodiment described above, the internal EGR rate was changed by adjusting the overlap period in 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 can be changed by adjusting the second opening period of the exhaust valve 22. Good too.

Moreover, the detection of octane number is not limited to the above-mentioned method. For example, when detecting the octane number with a sensor installed in the fuel supply system, the determination may be made using the reciprocal of the detected value. 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 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 as an engine control device that performs SI combustion of a portion of the air-fuel mixture by ignition, and then performs CI combustion of the remaining mixture by compression ignition.

1 Engine 6 Injector 10 ECU (control unit)
17 Combustion chamber 21 Intake valve 22 Exhaust valve 23 Intake electric S-VT (internal EGR system)
24 Exhaust electric S-VT (internal EGR system)
25 Spark plug (ignition device)
44 Supercharger (supercharging system)
45 Electromagnetic clutch (supercharging system)
46 Intercooler 601 Low octane map (combustion control map)
602 High octane map (combustion control map)
SW2 Intake air temperature sensor (intake air temperature detection device)
SW5 Cylinder pressure sensor (octane number detection means)
SW6 Engine water temperature sensor (first water temperature detection device)
SW12 Intercooler water temperature sensor (second water temperature detection device)

Claims (4)

It includes an injector that supplies fuel to a 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 ignited using the ignition device to cause SI combustion, the remainder is mixed. A control device for an engine that performs CI combustion of air by compression ignition,
Octane number detection means for detecting the octane number of the fuel;
an intake air temperature detection device that detects intake air temperature;
an internal EGR system for introducing internal EGR gas into the combustion chamber;
a control unit capable of outputting a control signal to the internal EGR system;
a supercharging system attached to the engine and configured to supercharge gas introduced into the combustion chamber,
The control unit includes:
By adjusting the opening timing of the intake valve while keeping the opening period of the intake valve constant, the positive overlap period during which both the intake valve and the exhaust valve are open is adjusted . outputting a control signal to the internal EGR system to change an internal EGR rate that is a ratio of the internal EGR gas amount to the total gas amount introduced into the combustion chamber ;
Both a first condition that the octane number of the fuel detected by the octane number detection means is less than a predetermined octane number and a second condition that the intake air temperature detected by the intake air temperature detection device is equal to or higher than the predetermined temperature are satisfied. when the first condition is not satisfied, outputting a control signal to the internal EGR system so that the internal EGR rate is lower than when the first condition is not satisfied;
The supercharging system performs supercharging when the engine load is in a first region where the engine load is above a predetermined load, and the supercharging system performs supercharging when the engine load is in a second region where the engine load is less than the predetermined load. outputting a control signal to the supercharging system to prevent
When the first condition is satisfied, in the second region, as the engine load increases, the opening timing of the intake valve is retarded and the overlap period is shortened, thereby lowering the internal EGR rate. On the other hand, in the first region, compared to the second region, the internal EGR rate is lowered by advancing the opening timing of the intake valve and lengthening the positive overlap period. An engine control device featuring: The engine control device according to claim 1,
The control unit is configured to control the internal EGR rate so that when the first condition is satisfied and the second condition is satisfied, the internal EGR rate is lower than when the second condition is not satisfied. An engine control device characterized by outputting a control signal to an internal EGR system. The engine control device according to claim 1 or 2,
further comprising a first water temperature detection device that detects the temperature of engine cooling water for cooling the inside of the combustion chamber,
In addition to the first and second conditions, when a third condition that the temperature of the engine cooling water detected by the first water temperature detection device is equal to or higher than a first predetermined water temperature is satisfied, An engine control device that outputs a control signal to the internal EGR system so that the internal EGR rate is lower than when the first condition is not satisfied. The engine control device according to any one of claims 1 to 3,
The supercharging system includes:
An intercooler through which intercooler cooling water flows to cool the supercharged gas;
a second water temperature detection device that detects the temperature of the intercooler cooling water;
In addition to the first and second conditions, when a fourth condition that the temperature of the intercooler cooling water detected by the second water temperature detection device is equal to or higher than a second predetermined water temperature is satisfied, the control unit: An engine control device characterized in that a control signal is output to the internal EGR system so that the internal EGR rate is lower than when the first condition is not satisfied.

Images