JP7354805B2 - engine control device - Google Patents

Description

The technology disclosed herein relates to a control device for an engine mounted on a vehicle.

Patent Document 1 discloses an engine that performs partial compression ignition combustion, specifically SPCCI combustion (details will be described later). In this engine, the total amount of gasoline required in one combustion cycle is divided into multiple injections during the compression stroke, making it possible to perform SPCCI combustion in a relatively high load region (Patent Document 1). (See chart (d) in FIG. 6).

Patent Document 2 discloses a high-octane engine that can use regular gasoline. This engine utilizes the fact that high-octane gasoline and regular gasoline have different appropriate ignition timings, and uses a knock sensor to determine whether the fuel used is high-octane gasoline or regular gasoline.

If the fuel used is regular gasoline and the load is increased, the batch injection in the intake stroke is switched to two split injections in each of the intake stroke and the compression stroke. By doing so, the air-fuel ratio becomes rich around the ignition plug, the latent heat of vaporization of the fuel increases, and a temperature rise is suppressed. This makes it possible to suppress the occurrence of pre-ignition even when using regular gasoline.

JP 2019-108813 Publication Japanese Patent Application Publication No. 2004-52624

Commercially available fuels include fuels with different octane numbers (an indicator of the difficulty of knocking), such as regular gasoline and high-octane gasoline. Regular gasoline has a low octane number (for example, about 91 ron), so knocking is likely to occur. Therefore, regular gasoline has the advantage of being cheaper and more fuel efficient than high-octane gasoline, although it is harder to achieve performance than high-octane gasoline. On the other hand, high-octane gasoline is expensive, but since it has a high octane number (for example, about 100 ron), knocking is less likely to occur. Therefore, there is an advantage that the performance of the engine can be fully brought out and good running can be achieved.

Usually, the gasoline to be refueled is specified in advance according to the engine. However, if you can refuel with gasoline of different octane numbers without any problems, you will be able to choose between good driving performance and fuel efficiency according to your preferences.

Therefore, the main purpose of the disclosed technology is to provide an engine control device that can supply fuel with different octane numbers and achieve good operation.

The disclosed technology includes an injector that injects a predetermined fuel into a combustion chamber, and a spark plug that ignites an air-fuel mixture formed in the combustion chamber by the fuel, and by ignition of the spark plug, The present invention relates to an engine control device that combusts a portion of an air-fuel mixture through combustion accompanied by flame propagation, and then combusts the remaining unburned air-fuel mixture through self-ignition.

The engine control device includes an octane number detection means capable of detecting an octane number of the fuel, and a control section that inputs a detection value detected by the octane number detection means and controls each of the spark plug and the injector. , is provided. Then, when the detected octane number is a high octane number determined to be equal to or higher than a predetermined value, intake stroke injection is performed to inject the fuel within the intake stroke, and when the detected octane number is lower than the predetermined value, When the octane number is determined to be low, the control unit controls the injector so that the injection timing of the intake stroke injection is retarded and compression stroke injection is performed in which the fuel is injected within the compression stroke.

That is, the disclosed technology is based on a control device for an engine that performs the above-mentioned partial compression ignition combustion, particularly SPCCI combustion. This engine control device is equipped with an octane number detection means that detects the octane number of the fuel and outputs the detected value to the control section. The control unit compares the detected value with a predetermined value and determines whether the octane number of the fuel is high or low. Based on the determination result, the control unit controls the injector so that when the octane number is low, the injection timing of the intake stroke injection performed when the octane number is high is retarded and compression stroke injection is executed.

With high-octane fuel such as high-octane gasoline, by injecting the fuel during the intake stroke, the fuel can be sufficiently mixed using the period up to the ignition timing. Therefore, a stratified air-fuel mixture suitable for SPCCI combustion can be formed at the ignition timing, and stable SPCCI combustion can be achieved.

However, under such combustion control, if the fuel is changed to a fuel with a low octane number such as regular gasoline, self-ignition tends to occur early, making it impossible to achieve stable SPCCI combustion. On the other hand, the control unit determines whether the octane number is high or low, and when the octane number of the fuel is low, switches the fuel injection in the intake stroke to the fuel injection in the compression stroke.

If it is a compression stroke, the period until ignition timing is short. This shortens the fuel mixing time, making it easier for the injected fuel to remain in the periphery of the combustion chamber. As a result, a so-called reverse stratified air-fuel mixture is formed in which the peripheral portion of the combustion chamber is richer than the central portion, so that self-ignition can be suppressed. Stable SPCCI combustion can be achieved even with fuels with different octane numbers. Therefore, according to this engine control device, fuels with different octane numbers can be supplied, and good operation can be realized.

In the engine control device, the injector may be controlled by the control unit in a low rotational speed region of a predetermined rotational speed or less in an operating region of the engine.

The lower the engine speed, the longer the period until the ignition timing, even if fuel is injected at the same time. Therefore, the above-mentioned control of the injector is more effective in the low-speed operating range than in the high-speed operating range, and by specifying the effective range in advance and performing the control, the efficiency of the control can be improved.

The control device for the engine is also configured such that fuel injection is performed multiple times during the intake stroke and the compression stroke, and when the octane number is high, the intake stroke injection is performed at least once, and when the octane number is low, the fuel injection is performed only during the compression stroke. It may be said that it is carried out.

Mixing of fuel can be promoted by performing split injection including intake stroke injection. By adjusting the individual injection timings, the mixture can be stratified to form a mixture suitable for SPCCI combustion with high octane fuel at the ignition timing. Mixing of fuel can be suppressed by making split injection only compression stroke injection. By adjusting the individual injection timings, it is possible to reverse stratify the mixture and form a mixture suitable for SPCCI combustion with low octane fuel at the ignition timing.

The engine control device is also configured such that the fuel injection consists of two injections, a pre-stage injection and a post-stage injection, and when the octane number is high, the pre-stage injection is the intake stroke injection, and the post-stage injection is the compression stroke injection. When the octane number is low, both the first-stage injection and the second-stage injection may be the compression stroke injection.

If the first-stage injection is intake stroke injection and the second-stage injection is compression stroke injection, by performing the second-stage injection just before the ignition timing, it is possible to form a rich air-fuel mixture that becomes a spark around the spark plug. Thereby, stratification of the air-fuel mixture can be further promoted at the ignition timing. If both the front-stage injection and the rear-stage injection are compression stroke injections, mixing of fuel can be suppressed and the air-fuel mixture can be reversely stratified.

The engine control device may also be configured to retard the timing of the last fuel injection when the octane number is low than when the octane number is high.

In this way, the time required for the fuel injected in the last fuel injection to be ignited is further shortened. Therefore, the occurrence of early abnormal combustion during the compression stroke can be further suppressed.

The engine control device may also increase the injection pressure of the fuel when the octane number is low compared to when the octane number is high.

In compression stroke injection, there is hardly any mixing time, so if there is a large amount of fuel, vaporization of the fuel will be insufficient and smoke will likely occur. By increasing the fuel injection pressure, the vaporization of the fuel can be promoted, so the generation of smoke can be suppressed. The cooling effect also increases. Reverse stratification can also be promoted. Therefore, even more appropriate SPCCI combustion can be achieved.

According to the engine control device to which the disclosed technology is applied, fuels with different octane numbers can be supplied, and good operation can be achieved.

FIG. 1 is a configuration diagram illustrating an engine including a control device. FIG. 2 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. 4 is a block diagram illustrating an engine control device. FIG. 5 is a diagram illustrating a control map for the engine. The upper diagram is a control map when the engine is warm, the middle diagram is a control map when the engine is semi-warmed up, and the lower diagram is a control map when the engine is cold. FIG. 2 is a block diagram illustrating a low octane map and a high octane map. FIG. 3 is a diagram illustrating fuel injection timing, ignition timing, and combustion waveform when high-octane gasoline is used. FIG. 3 is a diagram illustrating fuel injection timing, ignition timing, and combustion waveform when regular gasoline is used. 2 is a flowchart showing an example of combustion control using fuels with different octane numbers.

Hereinafter, an engine 1 to which the disclosed technology is applied and a control device thereof will be described with reference to the drawings. The engine 1 and control device described here are merely examples.

FIG. 1 is a diagram illustrating an engine 1. As shown in FIG. FIG. 2 is a diagram illustrating a combustion chamber of the engine 1. FIG. 3 is a diagram illustrating the combustion chamber 17 and the intake passage 40. 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 a control device for the engine 1. As shown in FIG. FIG. 5 is a diagram illustrating a control map for the engine 1.

The engine 1 has a combustion chamber 17 in which a mixture containing fuel and air is combusted. 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.

<Fuel>
The main fuel for the engine 1 is gasoline. The fuel for the engine 1 may be only gasoline, or may contain additional fuel such as bioethanol and/or additives.

Further, there are various types of gasoline with different octane numbers (for example, research octane numbers, so-called RON), and the fuel for the engine 1 may be gasoline with different octane numbers. The fuel for the engine 1 may also be a mixture of gasolines with different octane numbers.

That is, in this engine 1, there is no need to refuel only a pre-specified fuel as in the conventional case. Even if the gasoline has a different octane number, such as regular gasoline or high-octane gasoline, the engine 1 can be stably operated while suppressing abnormal combustion such as knocking.

Therefore, you can refuel according to your preference. For example, if the engine 1 is refueled with a high octane fuel, knocking is less likely to occur, so the engine 1 can be operated to its full potential. This allows the car to be adjusted to specifications that prioritize driving, such as sports driving.

Furthermore, by refueling the engine 1 with a low octane fuel, it is possible to run the vehicle at low cost and with excellent fuel efficiency. However, since fuel with a low octane number is prone to knocking, if it is controlled under the same conditions as fuel with a high octane number, abnormal combustion may occur and proper operation may not be possible.

Moreover, this engine 1 performs SPCCI combustion, which is a combination of SI combustion and CI combustion, as described later. SPCCI combustion requires sophisticated combustion control. Therefore, when fuels with different octane numbers are used, combustion tends to become unstable.

In contrast, in this engine 1, combustion control is devised so that even if fuels with different octane numbers are used, the engine 1 can be operated stably while suppressing abnormal combustion such as knocking (details will be described later). . In the description, for convenience, regular gasoline may be used as an example of fuel with a low octane number, and high-octane gasoline may be used as an example of fuel with a high octane number.

<Engine 1>
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.

(Combustion chamber 17)
A piston 3 is inserted into each cylinder 11. The piston 3 is connected to a crankshaft 15 via a connecting rod 14. The piston 3 reciprocates inside the cylinder 11. The piston 3, cylinder 11 and cylinder head 13 form a combustion chamber 17. 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 upper part of the combustion chamber 17. The upper part of the combustion chamber 17 is constituted by two inclined surfaces, as shown in the lower diagram of FIG. The combustion chamber 17 is of a so-called pent roof type.

The upper surface of the piston 3 constitutes the lower part of the combustion chamber 17. A cavity 31 is formed in the upper surface of the piston 3. The cavity 31 is recessed from the top surface of the piston 3. 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 14 or more and 18 or less (preferably 15±1) so as to be compatible with main fuels having different octane numbers. 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.

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 at predetermined timing using a valve operating mechanism. The valve mechanism may be a variable valve mechanism that makes valve timing and/or valve lift variable.

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 at predetermined timing using a valve mechanism. The valve mechanism may be a variable valve mechanism that makes valve timing and/or valve lift variable.

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, that is, high temperature exhaust gas, can be introduced into the combustion chamber 17. The intake electric S-VT 23 and the exhaust electric S-VT 24 constitute an internal EGR system.

(Injector 6)
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 in the upper center 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.

(Spark plug 25)
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. 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.

(Intake passage 40)
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.

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.

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.

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. Note that "supercharging" refers to a state in which the pressure in the surge tank 42 dynamically exceeds atmospheric pressure, and "non-supercharging" refers to a state in which the pressure in the surge tank 42 dynamically exceeds atmospheric pressure. It may also be defined as the state in which

(Swirl control valve 56)
As shown in FIG. 3, the engine 1 includes a swirl control valve 56 that generates a swirl flow within the combustion chamber 17. 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. 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 of the oblique swirl flow may be set in the range of 30° to 60°.

(Exhaust passage 50)
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 recirculation of external EGR gas, that is, low temperature exhaust gas. EGR cooler 53 and EGR valve 54 constitute an external EGR system.

(Octane number detection means)
The engine 1 includes octane number detection means. The octane number detection means detects the octane number of the fuel and outputs the detected value to the ECU 10. The octane number detection means only needs to be able to detect the octane number of the fuel, and its configuration can be selected depending on the specifications.

For example, a predetermined sensor capable of detecting the octane number of fuel may be installed in the fuel supply system 61 to constitute the octane number detection means. In this case, the octane number of the fuel can be directly detected in a static state (the state of the fuel before combustion).

Further, as in Patent Document 2 mentioned above, the octane number detection means may be configured using a knock sensor or the like. In this case, the octane number of the fuel can be detected indirectly in a dynamic state (in a state where the fuel is being combusted). The latter has better control responsiveness than the former because the octane number of the fuel can be determined at the appropriate time and for each combustion.

In the case of the engine 1, since SPCCI combustion is performed, a cylinder pressure sensor SW5 that can measure the internal pressure of each combustion chamber 17 with high accuracy is installed, as will be described later. Therefore, in the engine 1, it is preferable to use this to detect the octane number.

That is, the octane number can be determined from the difference in combustion heat. Since fuel with a higher octane number is more difficult to ignite, a difference in combustion heat occurs depending on the difference in octane number. Therefore, for example, by comparing the amount of heat generated during a predetermined period from the start of SI combustion to the start of CI combustion, the octane number of the fuel used for combustion can be estimated.

The in-cylinder pressure sensor SW5 can detect such amount of heat with high accuracy, so the octane number in a dynamic state can be determined with high accuracy. Moreover, since existing equipment is used, there is no need to install new expensive sensors. Therefore, in this engine 1, the cylinder pressure sensor SW5 constitutes an octane number detection means.

<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.

Various sensors SW1 to SW11 are connected to the ECU 10, as shown in FIGS. 1 and 4. These sensors SW1 to SW11 output signals to the ECU 10.

The air flow sensor SW1 is disposed downstream of the air cleaner 41 in the intake passage 40, and measures the flow rate of fresh air flowing through the intake passage 40. The first intake air temperature sensor SW2 is disposed downstream of the air cleaner 41 in the intake passage 40 and measures the temperature of fresh air flowing through the intake passage 40. The second intake air temperature sensor SW3 is attached to the surge tank 42 and measures the temperature of intake gas introduced into the combustion chamber 17.

The intake pressure sensor SW4 is attached to the surge tank 42 and measures the pressure of intake gas introduced into the combustion chamber 17. The cylinder pressure sensor SW5 is attached to the cylinder head 13 for each cylinder 11 and measures the pressure inside each combustion chamber 17. The water temperature sensor SW6 is attached to the engine 1 and measures the temperature of the cooling water. Crank angle sensor SW7 is attached to engine 1 and measures the rotation angle of crankshaft 15.

The accelerator opening sensor SW8 is attached to the accelerator pedal mechanism and measures the accelerator opening corresponding to the operation amount of the accelerator pedal. The intake cam angle sensor SW9 is attached to the engine 1 and measures the rotation angle of the intake camshaft. The exhaust cam angle sensor SW10 is attached to the engine 1 and measures the rotation angle of the exhaust camshaft. The fuel pressure sensor SW11 is attached to the common rail 64 of the fuel supply system 61 and measures the pressure of fuel supplied to the injector 6.

ECU 10 determines the operating state of engine 1 based on signals from these sensors SW1-SW11. 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 combustion amount of SI combustion, variations in temperature within the combustion chamber 17 before the start of compression can be absorbed. The combustion amount of SI combustion is adjusted by the ECU 10 adjusting the ignition timing. When the ECU 10 adjusts the ignition timing, 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.

<Operating range of engine 1>
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.

(First control map 501)
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 region 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.

When the operating state of the engine 1 is within the region A1, the ECU 10 controls the swirl control valve 56 to a substantially fully closed state (substantially closed state, substantially fully closed state). In terms of the "opening degree" of the swirl control valve 56, where 0% indicates fully closed and 100% indicates fully open, substantially fully closed is, for example, greater than 0% and less than 20%. When the operating state of the engine 1 is within the range A2, the ECU 10 controls the swirl control valve 56 to a substantially fully open state (substantially fully open state, substantially fully open state). In terms of "opening degree", approximately fully open is, for example, smaller than 100% and larger than 80%.

When the operating state of the engine 1 is within the range A3, A4, or A5, the ECU 10 opens the swirl control valve 56 in a range from substantially fully closed to substantially fully open, depending on the operating state of the engine 1. Adjust the degree. As a result, the strength of the oblique swirl flow formed in the combustion chamber 17 changes in size. Accordingly, the distribution of the air-fuel mixture formed in the combustion chamber 17 changes. The ECU 10 stabilizes SPCCI combustion by controlling the change.

(Second control map 502)
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 A3 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.

(Third control map 503)
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.

<Support for fuels with different octane numbers>
The ECU 10 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 (low octane number map 601) when the octane number of the fuel is less than a predetermined octane number, and a combustion control map (low octane number map 601) when the octane number of the fuel is equal to or higher than the predetermined octane number. It has a combustion control map (high octane number map 602).

The predetermined octane number is an octane number (ron) at which fuels with different octane numbers that can be supplied to the engine 1 can be distinguished. Here, the value is such that regular gasoline and high-octane gasoline can be distinguished, and is set to "96", for example.

Regular gasoline and high-octane gasoline do not have the same conditions for combustion. That is, even under the same combustion conditions, both regular gasoline and high-octane gasoline may be able to be burned appropriately. On the other hand, high-octane gasoline may not be combusted properly under combustion conditions suitable for regular gasoline, and regular gasoline may not be appropriately combusted under combustion conditions suitable for high-octane gasoline.

In particular, this engine 1 performs SPCCI combustion as described above. Since SPCCI combustion requires sophisticated combustion control, combustion tends to become unstable if fuels with different octane numbers are used. Therefore, in this engine 1, the map is switched to either the low octane number map 601 or the high octane number map 602 so that SPCCI combustion can be performed appropriately regardless of whether regular gasoline or high octane gasoline is used.

The low octane number map 601 mainly sets conditions suitable for fuel with a low octane number (here, mainly regular gasoline). The high octane number map 602 mainly sets conditions suitable for fuel with a high octane number (here, mainly high-octane gasoline).

Each of the low octane number map 601 and the high octane number map 602 has information on main control conditions related to combustion, corresponding to high and low rotational speeds in all operating ranges of the engine 1 and high and low loads in all operating ranges of the engine 1. Value is set. Both low octane map 601 and high octane map 602 are stored in memory 102.

Specifically, the low octane number map 601 includes a first injection timing map 601a used for setting the fuel injection timing, a first SCV (Swirl Control Valve) map 601b used for setting the opening degree of the swirl control valve 56, and an intake map 601b. It includes a first intake S-VT map 601c used for volume control, a first external EGR map 601d used for controlling the external EGR system, and a first internal EGR map 601e used for controlling the internal EGR system.

Similarly, the high octane map 602 includes a second injection timing map 602a, a second SCV map 602b, a second intake S-VT map 602c, a second external EGR map 602d, and a second internal EGR map 602e.

For example, the ECU 10 switches the low octane number map 601 to the high octane number map 602 when the octane number of the fuel changes from less than a predetermined octane number to a predetermined octane number or more. Since multiple conditions that require switching are switched at once, control can be simplified and efficient.

<Efforts to achieve stable SPCCI combustion with fuels with different octane numbers>
As described above, the engine 1 switches to either the low octane number map 601 or the high octane number map 602 to ensure proper combustion regardless of whether regular gasoline or high octane gasoline is used.

However, when combustion is performed using regular gasoline, abnormal combustion such as knocking and pre-ignition is likely to occur, especially in high-load operating ranges where the amount of heat generated is high. Furthermore, in a low-speed operating range where the combustion period is relatively long, low-temperature oxidation reactions are promoted, making pre-ignition more likely to occur.

When regular gasoline is used, it is necessary to avoid these problems, making it difficult to achieve stable combustion as with high-octane gasoline. Furthermore, this engine 1 performs SPCCI combustion which requires sophisticated control.

That is, this engine 1 performs SPCCI combustion in each of the regions A3, A4, and A5 of the first control map 501, and in each of the regions B3 and B4 of the second control map 502. In order to realize stable SPCCI combustion, the ECU performs split injection in at least a predetermined high load and low rotation area (high load low rotation area) among these areas.

Note that the high-load, low-rotation region referred to here is a region where the load is higher than the predetermined load L1 and the number of revolutions is lower than the predetermined rotation speed N1 (for example, the region where point P1 shown in FIG. 5 is located). The predetermined load L1 may be 1/3 of the maximum load of the engine 1, or may be 1/2 of the maximum load of the engine 1. The predetermined rotation speed N1 may be 1/3 of the maximum rotation speed of the engine 1, or may be 1/2 of the maximum rotation speed of the engine 1.

In this high-load, low-speed region, the ECU 10 injects the total amount of gasoline required for one combustion cycle in multiple injections within the intake stroke and compression stroke. More specifically, two fuel injections are performed: front-stage injection and rear-end injection. Note that such split injection may be performed in areas other than the high load and low rotation range.

When using fuel with a high octane number, for example, high-octane gasoline, the ECU 10 performs front-stage injection during the intake stroke and performs rear-stage injection during the compression stroke. FIG. 7 illustrates fuel injection timings 701 and 702, ignition timing 703, and combustion waveform 704 when performing SPCCI combustion with high-octane gasoline at point P1.

The pre-injection 701 is performed approximately in the middle of the intake stroke. Both the injection start time and the injection end time are located within the intake stroke. Post-injection 702 is performed in the latter half of the compression stroke. Both the injection start time and the injection end time are located within the compression stroke. The ratio of the amount of fuel to be injected is larger in the first stage injection 701 than in the second stage injection 702. The ratio is, for example, approximately 9:1.

At this time, the ECU 10 uses the fact that the injected fuel diffuses and gathers due to the diagonal swirl flow to distribute the air-fuel mixture in a predetermined state in the combustion chamber 17 at the ignition timing 703. , controls the injection timing and/or injection amount of the pre-injection 701. The ECU 10 also controls the injection timing and/or injection amount of the post-injection 702 so that a rich air-fuel mixture that becomes a spark is formed around the spark plug 25 at the ignition timing 703 . The injection amount of the post-injection 702 is set to a small amount because the purpose is to generate sparks. Most of the fuel is injected in the pre-injection 701.

That is, the ECU 10 forms a so-called stratified air-fuel mixture, in which a relatively lean and homogeneous air-fuel mixture is distributed in the peripheral portion of the combustion chamber 17 and a relatively rich air-fuel mixture is distributed in the central portion of the combustion chamber 17. Pre-injection 701 in the intake stroke and post-injection 702 in the compression stroke are performed so as to

Ignition timing 703 is approximately near compression top dead center TDC. Ignition timing 703 is adjusted for each combustion depending on the operating state of engine 1. If abnormal combustion such as knocking is likely to occur, the ignition timing 703 is retarded. As a result, SPCCI combustion, in which SI combustion and CI combustion occur consecutively, is performed at optimal timing.

However, when a fuel with a low octane number, such as regular gasoline, is used instead of high-octane gasoline, SPCCI combustion cannot be performed appropriately if fuel injection is performed under the same conditions as for high-octane gasoline.

That is, there is a relatively sufficient time from the pre-injection 701 to the ignition timing 703 in the intake stroke. This is especially true in high-load, low-speed ranges. Therefore, the fuel injected in the pre-injection 701 is sufficiently mixed in the combustion chamber 17 and homogenization is promoted, making it easier to self-ignite. As a result, even if the ignition timing 703 is retarded to its limit, the air-fuel mixture self-ignites early, and SPCCI combustion cannot be performed at the optimal timing.

Therefore, when using regular gasoline under such a situation, the ECU 10 changes the fuel injection timing from when using high-octane gasoline. Specifically, as shown in FIG. 8, the injection timing of fuel injection performed in the intake stroke is retarded with respect to the compression stroke.

More specifically, the ECU 10 controls the injector 6 so that the injection timing of the pre-injection 701 (intake stroke injection) is retarded and fuel is injected within the compression stroke. Therefore, when regular gasoline is used, both the front injection 801 and the rear injection 802 are injected in the compression stroke, resulting in only compression stroke injection.

Pre-stage injection 801 is performed during a period from the first half to the middle of the compression stroke. Both the injection start time and the injection end time are located within the compression stroke. Post-injection 802 is performed in the latter half of the compression stroke. Both the injection start time and the injection end time are located within the compression stroke.

As a result, the time from fuel injection to ignition timing 703 is shortened, making it difficult for fuel to mix. That is, the fuel that is injected and reaches the periphery of the combustion chamber 17 has almost no time to move, so it is unevenly distributed in the periphery of the combustion chamber 17. As a result, unlike in the case of high-octane gasoline, a so-called reverse stratified air-fuel mixture is formed in which the air-fuel mixture is richer in the peripheral portion of the combustion chamber 17 than in the central portion of the combustion chamber 17.

When an oblique swirl flow is formed in the combustion chamber 17, the central portion of the combustion chamber 17 tends to have a higher temperature than the peripheral portion due to its influence. Therefore, self-ignition tends to occur more easily in the central part of the combustion chamber 17 than in the peripheral part of the combustion chamber 17.

On the other hand, in the case of regular gasoline, a reverse stratified mixture is formed, so self-ignition can be suppressed. By shortening the time until ignition, it becomes difficult for the low-temperature oxidation reaction to proceed, so the occurrence of abnormal combustion such as pre-ignition can be suppressed. Therefore, even in the case of regular gasoline, appropriate SPCCI combustion can be achieved.

In addition to retarding the injection timing of the first-stage injection 701, the injection timing of the second-stage injection 702 (last fuel injection) is also retarded. As a result, the time until the fuel injected in the post-injection 802 is ignited is further shortened, so that the occurrence of early abnormal combustion during the compression stroke can be further suppressed.

Along with these changes in the fuel injection timing, the ECU 10 also changes the fuel injection ratios for each of the pre-stage injection and the post-stage injection. Although the ratio of the amount of fuel to be injected is higher in front injection than in rear injection, the amount of fuel injected in front injection 801 is smaller than in front injection 701 and rear injection 702 in the case of high-octane gasoline. , the injection amount in the post-injection 802 is changed a lot. The ratio is, for example, approximately 6:4.

By increasing the amount of post-injection, a cooling effect due to latent heat of vaporization can also be obtained, so abnormal combustion can be further suppressed. In the case of regular gasoline, the total amount of fuel to be injected is the same as in the case of high-octane gasoline (total amount of front injection 701 and rear injection 702 = total amount of front injection 801 and rear injection 802).

Furthermore, when using regular gasoline, it is preferable to increase the fuel injection pressure compared to when using high-octane gasoline. In this engine 1, in addition to changing the fuel injection timing, control is also performed to increase the fuel injection pressure. For example, it is preferable to increase by about 1.5 to 2.5 times.

In compression stroke injection, there is hardly any mixing time, so if there is a large amount of fuel, vaporization of the fuel will be insufficient and smoke will likely occur. By increasing the fuel injection pressure, the vaporization of the fuel can be promoted, so the generation of smoke can be suppressed. The cooling effect also increases. Reverse stratification can also be promoted. Therefore, even more appropriate SPCCI combustion can be achieved, and good operation can be achieved.

<Example of combustion control using fuels with different octane numbers>
FIG. 9 shows an example of combustion control performed by the ECU 10 when fuels with different octane numbers are supplied to the engine 1. The fuel supplied to the engine 1 may be regular gasoline or high-octane gasoline. These fuels may be mixed, such as by adding high-octane gasoline to regular gasoline.

The ECU 10 reads signals from various sensors SW1 to SW11 in order to determine the operating state of the engine 1 and perform combustion control accordingly (step S1). The ECU 10 also detects the octane number of the fuel and makes a determination thereof (step S2). For example, since the engine 1 is equipped with an in-cylinder pressure sensor SW5, the octane value (detected value) of the fuel currently being combusted can be estimated based on its measurement signal. The octane number of the mixed fuel can also be detected.

The memory 102 of the ECU 10 stores in advance a predetermined value (predetermined octane number, 96ron) that serves as a criterion for determining the octane number. The ECU 10 compares the predetermined value with the detected value (the detected octane number value). By doing so, it is determined whether the detected value is lower than a predetermined value (step S3).

As a result, when it is determined that the detected value is lower than the predetermined value (low octane) (Yes in step S3), the low octane map 601 is selected (step S4). That is, since the octane number of the fuel used for combustion is low, combustion control is performed under conditions corresponding to the low octane number, and the engine 1 is operated (step S5).

Specifically, the first injection timing map 601a is used to set the fuel injection timing, and the first SCV map 601b is used to set the opening degree of the swirl control valve 56. The first intake S-VT map 601c is used to control the intake air amount, the first external EGR map 601d is used to control the external EGR system, and the first internal EGR map 601d is used to control the internal EGR system. 601e is used.

In the first injection timing map 601a, the injection timing and injection amount of the fuel consisting of the pre-stage injection 801 and the post-stage injection 802 corresponding to regular gasoline as described above are set. Therefore, the ECU 10 controls the injector 6 based on the first injection timing map 601a so that both the pre-stage injection and the post-stage injection are performed in the compression stroke.

As a result, proper SPCCI combustion can be stably achieved using regular gasoline even in areas where abnormal combustion is likely to occur and SPCCI combustion cannot normally be performed properly, such as the above-mentioned high load and low rotation area. realizable.

At this time, the ECU 10 in this embodiment also increases the fuel injection pressure. Therefore, appropriate SPCCI combustion can be achieved even more stably.

On the other hand, when it is determined that the detected value is greater than or equal to the predetermined value (high octane) (No in step S3), the high octane map 602 is selected (step S6). That is, since the octane number of the fuel used for combustion is high, combustion control is performed under conditions corresponding to the octane number, and the engine 1 is operated (step S7).

Specifically, the second injection timing map 602a is used to set the fuel injection timing, and the second SCV map 602b is used to set the opening degree of the swirl control valve 56. A second intake S-VT map 602c is used to control the intake air amount, a second external EGR map 602d is used to control the external EGR system, and a second internal EGR map 602d is used to control the internal EGR system. 602e is used.

In the second injection timing map 602a, the injection timing and injection amount of the fuel consisting of the pre-stage injection 701 and the post-stage injection 702 corresponding to high-octane gasoline as described above are set. Therefore, the ECU 10 controls the injector 6 based on the second injection timing map 602a so that the first stage injection is performed in the intake stroke and the second stage injection is performed in the compression stroke.

Appropriate SPCCI combustion can be stably realized even in a region where abnormal combustion is likely to occur, such as the above-mentioned high-load, low-speed region, without distinguishing it from other regions. Since there is no need to significantly change the control conditions, smooth operation of the engine 1 can be maintained.

Note that the disclosed technology is not limited to the embodiments described above, and includes various other configurations. For example, the predetermined fuel is not limited to regular gasoline and high-octane gasoline. It can be applied to fuels with different octane numbers. Split injection is not limited to two injections either. It may be three or more times.

The compression stroke injection only needs to be one in which most of the injection occurs during the compression stroke, and the injection start timing may fall into the intake stroke to some extent. In this respect, the same applies to intake stroke injection. The end timing of injection may fall somewhat into the compression stroke.

The detection of octane number is not limited to the methods described above. 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.

1 Engine 10 ECU (control unit)
11 Cylinder 17 Combustion chamber 25 Spark plug 56 Swirl control valve 6 Injector SW5 Cylinder pressure sensor (octane number detection means)

Claims (6)

It includes an injector that injects a predetermined fuel into a combustion chamber, and a spark plug that ignites a mixture formed in the combustion chamber by the fuel, and a part of the mixture is ignited by the ignition of the spark plug. An engine control device that burns the remaining unburned air-fuel mixture by self-ignition after burning it by combustion accompanied by flame propagation,
Octane number detection means capable of detecting the octane number of the fuel;
a control unit that inputs a detection value detected by the octane number detection means and controls each of the spark plug and the injector;
Equipped with
The fuel injection includes:
a pre-stage injection consisting of an intake stroke injection that injects the fuel within the intake stroke or a compression stroke injection that injects the fuel within the compression stroke;
Consisting of two times: a post-stage injection consisting of the compression stroke injection,
As the pre-injection, the intake stroke injection is performed when the detected octane number is determined to be higher than or equal to the predetermined value, and the intake stroke injection is performed when the detected octane number is determined to be lower than the predetermined value. Sometimes, the control unit controls the injector so that the injection timing of the intake stroke injection is retarded so that the compression stroke injection is performed without injecting the fuel during the intake stroke. . The engine control device according to claim 1,
An engine control device in which the injector is controlled by the control unit in a low rotation range of a predetermined rotation speed or less in an operating range of the engine. The engine control device according to claim 1 or 2,
An engine control device in which the intake stroke injection is performed at least once when the octane number is high. The engine control device according to claim 1 ,
An engine control device in which the control unit controls the injector so that the ratio of the amount of fuel to be injected is larger in the first stage injection than in the second stage injection both at the high octane number and at the low octane number. The engine control device according to claim 1 ,
An engine control device in which the timing of the last fuel injection is retarded when the octane number is low than when the octane number is high. The engine control device according to any one of claims 1 to 5,
An engine control device that increases the injection pressure of the fuel when the octane number is low compared to when the octane number is high.

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