JP7347171B2 - 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, a diagonal swirl flow is generated in the combustion chamber and the flow is adjusted. By doing so, a desired air-fuel mixture distribution is formed in the combustion chamber at the ignition timing, and stable SPCCI combustion can be performed.

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 the octane number of the fuel, a swirl control valve that adjusts a swirl flow generated in the combustion chamber, and a detection value detected by the octane number detection means. and a control unit that inputs input and controls each of the spark plug, the injector, and the swirl control valve. The control unit controls the swirl control when the detected octane number is lower than the predetermined value, when the octane number is lower than when the detected octane number is higher than the predetermined value. Executes swirl enhancement control that changes the opening degree of the valve in the direction of closing.

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. The 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 unit, and a swirl control valve that adjusts the swirl flow generated in the combustion chamber. ing. The control unit compares the detected value input from the octane number detection means with a predetermined value, and determines whether the octane number of the fuel is high or low. Then, based on the determination result, the opening degree of the swirl control valve is changed to be closer than when the octane number is high so that the swirl flow is strengthened when the octane number is low.

When low octane fuel such as regular gasoline is used, abnormal combustion such as knocking and pre-ignition is more likely to occur than when using high octane fuel such as high octane gasoline. In SPCCI combustion, self-ignition occurs early, and CI combustion may not be performed at an appropriate timing.

In this engine, in order to suppress abnormal combustion and perform SPCCI combustion, control is performed to retard the ignition timing to delay combustion. When compared under the same combustion conditions, when the octane number is low, the need to retard and retard combustion increases to a greater extent than when the octane number is high. The more the engine is retarded, the more it deviates from the appropriate ignition position, resulting in lower combustion stability. Therefore, when the octane number is low, there is a possibility that stable SPCCI combustion cannot be performed as when the octane number is high.

In contrast, in this engine control device, when the control section determines that the octane number of the fuel is low, it changes the opening degree of the swirl control valve in the direction of closing to strengthen the swirl flow. By strengthening the swirl flow, fuel injected into the combustion chamber tends to collect in the center of the combustion chamber. By adjusting the injection timing, it is possible to create an air-fuel mixture distribution that is rich around the spark plug at the ignition timing.

As a result, even if the ignition timing is significantly retarded using low octane fuel, it becomes easier to ignite, so it is possible to suppress a decrease in combustion stability. Furthermore, since flame propagation is promoted, SI combustion is also stabilized. As a result, stable SPCCI combustion can be achieved. 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 control unit may also control the injector so that the fuel injected in the intake stroke is injected in the compression stroke while executing the swirl enhancement control.

By injecting the fuel that was previously injected during the intake stroke during the compression stroke, the mixing time for that fuel can be shortened. Thereby, even if the swirl flow is strengthened, the area around the spark plug can be made richer at the ignition timing.

The engine control device also includes a predetermined operating region in which the fuel is injected all at once during the intake stroke when the octane number is high, and the swirl enhancement control when the octane number is low in the predetermined operating region. At the same time, part of the fuel in the batch injection may be injected during the compression stroke, and split injection consisting of a front-stage injection in the intake stroke and a second-stage injection in the compression stroke may be performed.

If the fuel is injected all at once during the intake stroke, the swirl flow can be used to diffuse or collect the fuel by the ignition timing, and a mixture suitable for SPCCI combustion can be formed at the ignition timing. Therefore, high octane fuel can bring out the full performance of the engine. On the other hand, in the case of fuel with a low octane number, the ignition timing is retarded compared to fuel with a high octane number, so combustion stability decreases, and there is a risk that stable SPCCI combustion cannot be performed and a misfire occurs.

On the other hand, if the swirl flow is strengthened and a part of the bulk injection fuel is injected during the compression stroke, resulting in split injection consisting of a front-stage injection in the intake stroke and a second-stage injection in the compression stroke, ignition can be achieved by the front-stage injection. While forming a stratified air-fuel mixture at the same time, stratification can be promoted so that the central part of the combustion chamber becomes richer by the later injection. As a result, even if the ignition timing is greatly retarded, ignition becomes easier, so deterioration in combustion stability can be suppressed. Since flame propagation becomes easier and SI combustion is promoted, stable SPCCI combustion can be realized.

The engine control device also operates in a predetermined operating region in which the engine performs split injection consisting of a front-stage injection in the intake stroke and a rear-stage injection in the compression stroke both at the high octane number and at the low octane number. When the octane number is low in the predetermined operating region, the swirl enhancement control may be executed and the proportion of the injection amount in the latter stage injection may be increased compared to when the octane number is high.

As the proportion of the injection amount in the post-injection increases, stratification can be promoted so that the central part of the combustion chamber becomes richer. Therefore, even if the ignition timing is greatly retarded, ignition becomes easier, so deterioration in combustion stability can be suppressed.

The engine control device is also configured to advance the injection timing of the post-injection during the low octane number when the engine rotation speed is equal to or higher than the predetermined rotation speed than when the engine rotation speed is less than the predetermined rotation speed. You can also make it corner.

As the engine speed increases, the period from fuel injection timing to ignition timing becomes shorter. Therefore, if a large amount of fuel is injected during the compression stroke close to the ignition timing, some of the fuel may not vaporize even at the ignition timing and may adhere to the piston or the like, resulting in worsening smoke.

On the other hand, if the injection timing of the post-injection is advanced when the engine speed is high, the time until the ignition timing can be lengthened even if the engine speed is high, so that deterioration of smoke can be suppressed.

In the engine control device, the engine may further include a cylinder pressure sensor that measures the internal pressure of the combustion chamber, and the octane number detection means may be configured using the cylinder pressure sensor.

If the in-cylinder pressure sensor is used, it can be used for both combustion control of partial compression ignition combustion and swirl enhancement control, so component costs can be reduced and it is efficient. Since the octane number of the fuel can be detected from the combustion state, highly accurate swirl enhancement control can be performed in a timely manner.

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 in a high load region. FIG. 3 is a diagram illustrating fuel injection timing, ignition timing, and combustion waveform when regular gasoline is used in a high load region. FIG. 3 is a diagram illustrating fuel injection timing, ignition timing, and combustion waveform when high-octane gasoline is used in a medium load region and a medium-high load boundary region. FIG. 3 is a diagram illustrating fuel injection timing, ignition timing, and combustion waveform when regular gasoline is used in a medium-high load boundary region. This is an example of controlling the opening degree of the swirl control valve. The solid line is an example of control when regular gasoline is used. The broken line is an example of control when using high-octane gasoline. FIG. 11 is a diagram corresponding to FIG. 10 illustrating an application example. 2 is a flowchart showing an example of combustion control using fuels with different octane numbers. It is a flow chart which shows an example of swirl reinforcement control.

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 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.

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.

In order to achieve stable SPCCI combustion, the ECU also controls at least a predetermined high load and low rotation area (high load low rotation area) among the areas A3, A4, and A5 where SPCCI combustion is performed. Now perform split injection.

Note that the high-load, low-rotation region referred to here is, as shown in FIG. 5, a region where the load is higher than the predetermined load L1 and the number of rotations is lower than the predetermined rotation speed N1. 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, a front-stage injection and a rear-end injection, are performed (see FIGS. 7 and 8).

Among the regions A3, A4, and A5 where SPCCI combustion is performed, in regions other than the high load low rotation region, for example, in a region where the load is lower than the high load low rotation region, the ECU 10 mainly Bulk injection is performed during the intake stroke (see Figure 9). The ECU 10 further changes the injection timing and the like according to the octane number of the fuel introduced into the combustion chamber 17, which will be described later.

(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 region 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 regular gasoline is used, abnormal combustion such as knocking and pre-ignition is more likely to occur than when high-octane gasoline is used. Therefore, in this engine 1, in order to suppress abnormal combustion and perform SPCCI combustion, control is performed to retard the ignition timing to delay combustion. When compared under the same operating conditions, when regular gasoline is used, the need to retard and retard combustion increases to a greater extent than when using high-octane gasoline.

The more the engine is retarded, the more it deviates from the appropriate ignition position, resulting in lower combustion stability. As a result, fuel efficiency deteriorates and there is a risk of misfire. Furthermore, this engine 1 performs SPCCI combustion which requires sophisticated control. When SI combustion becomes unstable, CI combustion also becomes unstable. Therefore, stable SPCCI combustion cannot be achieved.

On the other hand, in this engine 1, as described above, SPCCI combustion is stabilized by varying the strength of the diagonal swirl flow (specifically, the strength of the swirl component, the swirl strength). The present inventors have discovered that by increasing the swirl strength, the central portion of the combustion chamber 17 can be stratified to become richer by utilizing the oblique swirl flow.

Therefore, in a predetermined operating region (medium-high load boundary region to be described later), when using a low-octane fuel such as regular gasoline, the ECU 10 controls the swirl control valve 56 more than when using a high-octane fuel such as high-octane gasoline. Control is performed to increase the swirl strength of the diagonal swirl flow (swirl enhancement control) by changing the opening degree in the closing direction.

In this engine 1, when performing SPCCI combustion, fuel injection control is performed using an oblique swirl flow so that a predetermined air-fuel mixture distribution is formed in the combustion chamber 17 at the ignition timing. By increasing the swirl strength, the fuel injected into the combustion chamber 17 tends to collect in the central portion of the combustion chamber 17 where the spark plug 25 is located.

Thereby, by increasing the swirl strength, it is possible to form a richer air-fuel mixture distribution around the spark plug 25 at the ignition timing. If the air-fuel mixture around the ignition plug 25 becomes rich at the ignition timing, it becomes easier to ignite, so that deterioration in combustion stability can be suppressed. If the swirl strength increases, the fluidity within the combustion chamber 17 increases and flame propagation is promoted, thereby stabilizing SI combustion. As a result, CI combustion is also stabilized, making it possible to realize stable SPCCI combustion.

(Swirl enhancement control)
FIG. 11 shows an example of control of the opening degree of the swirl control valve 56 performed at the predetermined rotation speed N0 shown in FIG. This control example shows the opening degree of the swirl control valve (SCV) 56, which changes in size depending on the level of the load on the engine 1.

This control is performed based on the first SCV map 601b and the second SCV map 602b. The solid line is an example of control when regular gasoline is used. The broken line is an example of control when using high-octane gasoline. Note that the rotation speed N0 is located on the low rotation side of the operating range of the engine 1 rather than the high rotation side.

In a low load region including no load, there is little combustion heat, so abnormal combustion is unlikely to occur. Therefore, the difference in octane number of fuels has little effect on combustion. The ECU 10 sets the opening degree of the swirl control valve 56 to be substantially fully closed regardless of whether regular gasoline or high-octane gasoline is used.

When the load increases from the low load region, the amount of gas and fuel introduced into the combustion chamber 17 increases, but the combustion heat is not so large that abnormal combustion becomes a problem. Therefore, in a medium load region (a region where the load is greater than a low load region and smaller than a high load region), the ECU 10 changes the opening degree of the swirl control valve 56, regardless of whether regular gasoline or high-octane gasoline is used. Change direction.

The degree of opening is, for example, about 30% to 60% (half-open). The ECU 10 maintains the opening degree of the swirl control valve 56 in a half-open state until the load reaches a predetermined value or more. Note that the opening degree may be varied to some extent depending on the combustion state.

As a result, an oblique swirl flow having an appropriate swirl strength is formed in the combustion chamber 17. At this time, the ECU 10 controls the injector 6 to inject the fuel all at once during the intake stroke, regardless of whether regular gasoline or high-octane gasoline is used. FIG. 9 illustrates the fuel injection timing 901, ignition timing 902, and combustion waveform 903.

The total amount of fuel required for one combustion cycle is injected at a predetermined timing during the intake stroke. Thereby, the injected fuel moves in a diagonal swirl flow, and is controlled so that an air-fuel mixture suitable for SPCCI combustion is distributed in the combustion chamber 17 at the ignition timing.

Ignition timing 902 is approximately near compression top dead center TDC. Ignition timing 902 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.

On the other hand, in a high load region including a fully open load, the amount of gas and fuel introduced into the combustion chamber 17 is large, so the combustion heat is large and abnormal combustion is likely to occur. In particular, regular gasoline is more likely to cause abnormal combustion than high-octane gasoline.

Therefore, in this engine 1, when using high-octane gasoline in a high load region, particularly in the above-mentioned high load and low rotation region, the ECU 10 performs front stage injection in the intake stroke and performs rear stage injection in 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 in the high load region shown in FIG.

The pre-injection 701 is performed approximately in the middle of the intake stroke. Post-injection 702 is performed in the latter half of 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 sets the opening degree of the swirl control valve 56 to approximately fully closed, as shown in FIG. Since the amount of gas introduced into the combustion chamber 17 is large, an oblique swirl flow with high swirl strength is formed in the combustion chamber 17. The ECU 10 utilizes this oblique swirl flow to control the injection timing and/or injection amount of the pre-injection 701 so that the air-fuel mixture in a predetermined state is distributed in the combustion chamber 17 at the ignition timing 703.

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 Since the swirl strength is high, a rich air-fuel mixture distribution in the central portion of the combustion chamber 17 can be formed at the ignition timing.

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.

On the other hand, when regular gasoline is used in a high load region, the ECU 10 retards the fuel injection timing and performs pre-injection and post-injection in the compression stroke. FIG. 8 illustrates these fuel injection timings 801 and 802 when performing SPCCI combustion with regular gasoline at point P1 in the high load region.

Pre-stage injection 801 is performed during a period from the first half to the middle of the compression stroke. Post-injection 802 is performed in the latter half of the compression stroke. The ratio of the amount of fuel to be injected is larger in the first stage injection 801 than in the second stage injection 802. The ratio is, for example, approximately 6:4. 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).

As a result of retarding the fuel injection timing, the time from fuel injection to ignition timing 703 is shortened. As a result, even if an oblique swirl flow with high swirl strength is formed in the combustion chamber 17, it becomes difficult to mix the fuel. 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, heat tends to collect in the central portion of the combustion chamber 17, so that the central portion of the combustion chamber 17 tends to have a higher temperature than the peripheral portion. 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.

As shown in FIG. 11, the ECU 10 also controls the opening degree of the swirl control valve 56 to be slightly more open than when using high-octane gasoline. For example, it is set from approximately fully closed to a state in which it is opened by several percent to 10% (semi-fully closed state). As a result, the swirl strength is weakened, so that reverse stratification is further promoted.

Furthermore, when using regular gasoline, it is preferable to increase the fuel injection pressure compared to when using high-octane gasoline. Therefore, the ECU 10 executes control to increase the fuel injection pressure. By increasing the fuel injection pressure, the vaporization of the fuel can be promoted, so the generation of smoke can be suppressed.

As shown in FIG. 11, when the load increases from the medium load region, the ECU 10 changes the opening degree of the swirl control valve 56 from a half-open state to a substantially fully closed state or a semi-fully closed state in the closing direction.

In this engine 1, the swirl enhancement control described above is executed in the boundary area between the medium load area and the high load area (medium/high load boundary area). That is, when the ECU 10 uses regular gasoline, it changes the opening degree of the swirl control valve 56 in the closing direction so that the swirl strength is higher than when using high-octane gasoline.

When using high-octane gasoline, stable SPCCI combustion can be performed without excessive retardation even in a high load region. Therefore, even if the combustion conditions change somewhat, stable SPCCI combustion can be maintained. The ECU 10 maintains the batch injection shown in FIG. 9 even when entering the medium-high load boundary area from the medium load area. The ECU 10 controls the injector 6 to switch to the split injection shown in FIG. 7 at the timing of switching from the medium-high load boundary region to the high load region.

On the other hand, when regular gasoline is used in a high load region, the retard is greater than when high-octane gasoline is used, resulting in a decrease in combustion stability. Therefore, if it is controlled in the same way as high-octane gasoline, there is a risk of misfire. Therefore, the ECU 10 controls the injector 6 so that the fuel injected in the intake stroke is injected in the compression stroke in the medium-high load boundary region.

Specifically, the ECU 10 controls the injector 6 so that part of the fuel for the batch injection is injected during the compression stroke, and split injection consisting of a front-stage injection during the intake stroke and a second-stage injection during the compression stroke is performed. Control. FIG. 10 illustrates these fuel injection timings 1001 and 1002, ignition timing 1003, and combustion waveform 1004 at point P0 in the medium-high load boundary region shown in FIG.

The pre-injection 1001 is performed approximately in the middle of the intake stroke. Post-injection 1002 is performed in the latter half of the compression stroke. The ratio of the amount of fuel to be injected is larger in the first stage injection 1001 than in the second stage injection 1002. The ratio is, for example, approximately 8:2. Compared to split injection when using high-octane gasoline, the proportion of the injection amount in the latter stage injection is increased. The more fuel that is injected in the latter stage injection, the richer the air-fuel mixture around the spark plug 25 can be, which improves the combustion stability.

Then, as shown in FIG. 11, when the ECU 10 enters from the medium load region to the medium-high load boundary region, the ECU 10 changes the opening degree of the swirl control valve 56 in the closing direction (swirl enhancement control). Specifically, the opening degree of the swirl control valve 56 is switched from a half-open state to a semi-fully closed state. That is, when regular gasoline is used, the range in which the swirl strength is increased is expanded to the low load side compared to when high-octane gasoline is used.

As a result, when regular gasoline is used in the medium-high load boundary region, the swirl strength becomes higher than when high-octane gasoline is used. When the swirl strength increases, the fuel injected into the combustion chamber 17 becomes easier to move along the diagonal swirl flow. As shown in FIG. 10, since a portion of the fuel is injected during the intake stroke, the fuel is diffused or collected by the diagonal swirl flow, and a stratified air-fuel mixture is formed at the ignition timing. Since the swirl strength is high and fuel is injected even during the compression stroke, a richer air-fuel mixture can be formed in the central portion of the combustion chamber 17.

As a result, even if the ignition timing is greatly retarded, ignition becomes easier, so deterioration in combustion stability can be suppressed. Since flame propagation becomes easier and SI combustion is promoted, stable SPCCI combustion can be achieved even when the ignition timing is greatly retarded.

Then, the ECU 10 controls the injector 6 to switch to the split injection shown in FIG. 8 at the timing of switching from the medium-high load boundary region to the high load region. Thereby, even when regular gasoline is used, it is possible to smoothly transition from a medium load range to a high load range while maintaining stable SPCCI combustion.

(Application example)
As the rotational speed of the engine 1 increases, the period from the fuel injection timing to the ignition timing becomes shorter. Therefore, if a large amount of fuel is injected during the compression stroke close to the ignition timing, some of the fuel may not vaporize even at the ignition timing and may adhere to the piston or the like, resulting in worsening smoke.

Therefore, when the engine speed increases, as shown in Fig. 12, when regular gasoline is used in the middle-to-high load boundary region, the injection timing of the late injection, which injects fuel during the compression stroke, is advanced. is preferred. Specifically, a predetermined number of revolutions is set in advance in the memory of the ECU 10, and when the number of revolutions of the engine is equal to or higher than the predetermined number of revolutions, the injection timing of the later stage injection is advanced than when the number of revolutions is less than the predetermined number of revolutions. Note that the predetermined rotation speed here may be selected according to the specifications of the engine 1.

In this way, even if the rotational speed becomes high, the time until the ignition timing can be extended, so that deterioration of smoke can be suppressed.

<Example of combustion control using fuels with different octane numbers>
FIG. 13 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 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 S-VT map 601c is used to control the intake air amount and the exhaust amount, the first external EGR map 601d is used to control the external EGR system, and the first internal EGR map 601c is used to control the internal EGR system. Map 601e is used.

In the first injection timing map 601a, the injection timing and injection amount of fuel consisting of pre-stage injection and post-stage injection 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. The second S-VT map 602c is used to control the intake air amount and the exhaust amount, the second external EGR map 602d is used to control the external EGR system, and the second internal EGR map 602c is used to control the internal EGR system. Map 602e is used.

In the second injection timing map 602a, the injection timing and injection amount of fuel consisting of front-stage injection and rear-stage injection, which correspond 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.

(Swirl enhancement control)
FIG. 14 shows an example of swirl reinforcement control. The ECU 10 determines whether the load on the engine 1 has increased and the operating region of the engine 1 has entered the medium-high load boundary region from the medium load region (step S20). Note that the first SCV map 601b and the second SCV map 602b are used for the swirl enhancement control.

When it is determined that the operating range of the engine 1 has entered the medium-high load boundary region from the medium load region, the ECU 10 determines whether the combustion is performed using low octane fuel such as regular gasoline or high octane gasoline. It is determined when high octane fuel is used for combustion (step S21).

As a result, when the octane number is low, the opening degree of the swirl control valve 56 is changed in the closing direction, that is, from a half-open state to a semi-fully closed state (step S22). When the octane value is high, the degree of opening of the swirl control valve 56 is not changed and the half-open state is maintained (No in step S21).

The ECU 10 also determines whether the load on the engine 1 has decreased and the operating range of the engine 1 has entered the medium-high load boundary range from the high load range (step S23).

When determining that the operating range of the engine 1 has entered the medium-high load boundary range from the high load range, the ECU 10 determines whether the operating range is low octane or high octane (step S24).

As a result, if the octane value is high (No in step S24), the opening degree of the swirl control valve 56 is changed from the opening direction, that is, from the substantially fully closed state to the half open state (step S25). When the octane value is low, the opening degree of the swirl control valve 56 is not changed and the semi-fully closed state is maintained (Yes in step S24).

In parallel with such control of the swirl control valve 56, the ECU 10 executes the above-described fuel injection control using the first injection timing map 601a and the second injection timing map 602a.

Thereby, according to the control device for the engine 1, fuels having different octane numbers can be supplied, and good operation can be achieved.

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.

When high octane fuel is used in the medium-high load boundary region, split injection may be performed in the same way as in the high-load, low-speed region. In this case, when fuel with a low octane number is used, the proportion of the injection amount in the later stage injection is increased than when using fuel with a high octane number. Therefore, the air-fuel mixture around the spark plug can be enriched, so combustion stability can be improved.

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)

An injector that injects a predetermined fuel into a combustion chamber, a spark plug that ignites an air-fuel mixture formed in the combustion chamber by the fuel , and a cylinder attached to each cylinder forming the combustion chamber. an internal pressure sensor, each of the cylinder pressure sensors measures the internal pressure of the combustion chamber, and after igniting the spark plug, a part of the air-fuel mixture is combusted by combustion accompanied by flame propagation, and then the remaining A control device for an engine that burns unburned air-fuel mixture by self-ignition,
Octane number detection means capable of detecting the octane number of the fuel;
a swirl control valve that adjusts the swirl flow generated in the combustion chamber;
a control unit that inputs a detection value detected by the octane number detection means and controls each of the spark plug, the injector, and the swirl control valve;
Equipped with
When the control unit determines that the detected octane value is lower than a predetermined value in a medium-high load boundary area that exists at the low-load boundary of a high load area that includes a full-open load, the detected octane value is lower than a predetermined value. Swirl enhancement control is executed to change the opening degree of the swirl control valve in a direction closer than when the octane value is determined to be greater than or equal to the predetermined value.
The degree of opening of the swirl control valve in the medium-high load boundary region is set to a closer side when the octane number is low than when the octane number is high, and
An engine control device , wherein the degree of opening of the swirl control valve in the high load region is set to be more open when the octane number is low than 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 fuel injected in the intake stroke is injected in the compression stroke while executing the swirl enhancement control. The engine control device according to claim 2,
The engine has a predetermined operating region in which fuel is injected all at once during the intake stroke when the octane number is high;
At the time of the low octane number in the predetermined operating region, in addition to executing the swirl enhancement control, a part of the fuel in the batch injection is injected in the compression stroke, and a part of the fuel is injected in the intake stroke as a pre-injection and as a post-injection in the compression stroke. A control device for an engine that performs split injection. The engine control device according to claim 2,
The engine has a predetermined operating region in which split injection consisting of a front stage injection in an intake stroke and a rear stage injection in a compression stroke is performed both at the high octane number and at the low octane number,
An engine control device that executes the swirl enhancement control when the octane number is low in the predetermined operating range, and increases a proportion of the injection amount in the latter stage injection compared to when the octane number is high. The engine control device according to claim 3 or 4,
An engine control device that advances the injection timing of the post-injection during the low octane number when the engine rotation speed is a predetermined rotation speed or higher than when the engine rotation speed is less than the predetermined rotation speed. The engine control device according to any one of claims 1 to 5,
An engine control device, wherein the octane number detection means is configured using the cylinder pressure sensor.

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