JP7247873B2 - engine controller - Google Patents

Description

The disclosed technology relates to a control device for an engine that performs partial compression ignition combustion, specifically SPCCI (SPark Controlled Compression Ignition) combustion. Here, SPCCI combustion is a combustion technology proposed by the present applicant.

Patent Literature 1 discloses an engine that selectively uses three gasolines with different octane numbers.

Specifically, in that engine, three tanks each storing gasoline with different low, medium, and high octane numbers are connected to one injector that injects into the intake port. The gasoline to be supplied to the injector is switched according to the temperature of the cooling water of the engine. At that time, it is disclosed that the target cooling water temperature is also changed according to the octane number in order to reduce the sliding resistance of the piston.

It also discloses that the ignition timing of the engine is advanced to improve the engine output when the engine is operated under high load using high octane gasoline.

JP-A-2006-125288

Fuels on the market include fuels with different octane numbers (indicators of resistance to knocking), such as regular gasoline and high-octane gasoline. Since regular gasoline has a low octane number (for example, about 91 ron), knocking is likely to occur. Therefore, regular gasoline is less expensive than high-octane gasoline, but has the advantage of being inexpensive and excellent in fuel efficiency. On the other hand, high-octane gasoline is expensive, but has a high octane number (for example, about 100 ron), so knocking is less likely to occur. Therefore, there is an advantage that the performance of the engine can be fully exploited and good running can be realized.

Normally, the fuel to be refueled is specified in advance according to the engine. However, if you can refuel with different octane fuels and drive without problems, you can choose between good driving and good fuel economy according to your preference. Therefore, it is preferable to be able to refuel fuels with different octane numbers.

However, in an engine that specifies a fuel with a high octane number, engine control amounts (fuel injection timing, ignition timing, etc.) are set accordingly in order to bring out the performance of the engine sufficiently. Therefore, if a low octane fuel is used as it is in such an engine, abnormal combustion such as knocking and pre-ignition will occur.

Therefore, in order to refuel a fuel with a different octane number and drive without problems, it is necessary to determine the octane number of the fuel to be used and change the control amount of the engine accordingly. For example, when it is determined that the octane number of the fuel is low, abnormal combustion can be suppressed by retarding the ignition timing. However, in this case, deterioration of fuel consumption is caused.

Abnormal combustion is likely to occur when the temperature of the combustion chamber is high. Therefore, it is possible to suppress abnormal combustion by lowering the temperature of the cooling water as in the engine of Patent Document 1 described above.

However, in an engine that performs partial compression ignition combustion, specifically SPCCI combustion, when the temperature of cooling water is lowered, compression ignition becomes difficult due to the temperature drop in the combustion chamber, and SPCCI combustion tends to become unstable.

In particular, in the lean operating region, little combustion heat is generated, so there is a possibility that SPCCI combustion will not be possible. It is conceivable to increase the temperature of the combustion chamber by changing the air-fuel ratio to the rich side, but in such a case, the amount of NOx emissions increases, resulting in worse emissions.

Therefore, the main object of the disclosed technique is to provide an engine control device that can achieve good operation without causing deterioration in emissions even when fuels with different octane numbers are supplied.

The technology disclosed includes 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 an engine body that constitutes the combustion chamber. and a cooling device that circulates cooling water in a predetermined operating region, and after a part of the air-fuel mixture is burned by combustion accompanied by flame propagation due to the ignition of the spark plug, the remaining unburned air-fuel mixture is The present invention relates to a control device for an engine that performs specific partial compression ignition combustion by self-ignition.

The predetermined operating range includes a first segmented range in which a lean air-fuel ratio is set. The control device for the engine includes octane number determining means for determining the octane number of the fuel, and temperature changing means for changing the temperature of the cooling water. When determining a low octane number to be determined, water temperature reduction control for lowering the temperature of the cooling water than when determining a high octane number when the octane number of the fuel is determined to be equal to or higher than the predetermined value; Enrichment control is executed to change to a richer side than when the high octane number is determined, and region reduction control is executed to reduce the first partitioned area more than when the high octane number is determined.

That is, in this engine, SPCCI combustion with excellent fuel efficiency is performed in a predetermined operating range. The operating region includes a first segmented region in which a lean air-fuel ratio is set. Since the first partitioned region has a lean air-fuel ratio, it is possible to improve fuel efficiency.

This engine control device is provided with octane number determination means so that fuels with different octane numbers can be used, and the octane number of the fuel can be determined. Then, predetermined cooling control and combustion control are executed based on the determination result.

That is, when determining a low octane number, water temperature reduction control is performed to lower the temperature of the cooling water than when determining a high octane number, and enrichment control is performed to change the air-fuel ratio in the first partitioned region to a richer side than when determining a high octane number. Execute. Furthermore, area reduction control is also executed to reduce the first partitioned area more than when the high octane rating is determined.

Abnormal combustion is likely to occur when the temperature of the combustion chamber is high. Therefore, abnormal combustion can be suppressed by executing water temperature lowering control when a low octane rating is determined. However, as described above, when the cooling water temperature is lowered, the SPCCI combustion is likely to become unstable due to difficulty in compression ignition. In particular, the lean first partitioned region generates little heat of combustion, so there is a possibility that SPCCI combustion will not be possible.

Therefore, rich control is executed to change the air-fuel ratio of the first segmented region to the rich side. As a result, the temperature of the combustion chamber rises, so that appropriate SPCCI combustion can be stably performed even if the temperature of the cooling water is low. However, in such a case, if the lean air-fuel ratio is changed to the rich side, the amount of NOx emissions will increase and the emissions will deteriorate, but by reducing the first partitioned area, the increase in the amount of NOx emissions can be suppressed. .

Thus, according to this engine control device, it is possible to refuel fuels having different octane numbers, and to stably perform appropriate SPCCI combustion without causing deterioration of emissions. Therefore, good driving can be realized.

The control device for the engine may also reduce a boundary portion of at least one of the high load side and the high rotation side in the first partitioned area by the area reduction control.

In the first partitioned region, the amount of NOx emissions tends to increase particularly at the boundary portion on the high load side and the boundary portion on the high rotation side. Therefore, by reducing these boundary portions, it is possible to effectively suppress an increase in NOx emissions.

The engine control device may also set the air-fuel ratio of the first segmented region at the time of the high octane number determination to be approximately twice the stoichiometric air-fuel ratio.

If the air-fuel ratio is approximately twice the stoichiometric air-fuel ratio, almost no NOx is generated even if the fuel is burned. Therefore, almost no NOx is generated when the engine is running in the first partitioned region. Therefore, excellent driving can be performed in terms of both fuel consumption and emissions.

In the control device for the engine, the predetermined operating region further includes a second partitioned region in which a stoichiometric air-fuel ratio is set, and the second partitioned region is enlarged by reducing the first partitioned region. You can do it.

If the air-fuel ratio is the stoichiometric air-fuel ratio, NOx is generated during combustion. However, it can be effectively purified by installing a three-way catalyst. Therefore, by expanding the second partitioned region in which the stoichiometric air-fuel ratio is set instead of reducing the first region, it is possible to effectively suppress the deterioration of emissions.

In the control device for the engine, the first partitioned area may be partitioned into at least one of a low load side and a low rotation side of the second partitioned area.

When water temperature lowering control is executed, SPCCI combustion tends to become unstable especially in the low load side region and the low speed side region of the second partitioned region. Therefore, if the first partitioned area is partitioned into these areas, even better effects can be expected by executing the enrichment control and the area reduction control.

In the control device of the engine, the octane number determining means may determine the octane number of the fuel based on the amount of heat generated by combustion accompanied by flame propagation in the partial compression ignition combustion.

That is, since it is possible to determine the octane number of the fuel from the amount of heat generated by SI combustion in SPCCI combustion, it is utilized. In this case, there is an advantage that the octane number of the fuel used for combustion can be determined with high accuracy. Furthermore, since existing equipment can be used, there is no need to install new expensive sensors.

The control device for the engine further includes an exhaust shutter valve for adjusting the opening degree of an exhaust passage through which exhaust gas discharged from the combustion chamber flows, and when the enrichment control is executed, the exhaust shutter valve The opening degree of the valve may be adjusted in the closing direction.

By doing so, the degree of enrichment can be suppressed, and fuel efficiency can be improved. Adjusting the opening of the exhaust shutter valve in the closing direction increases the back pressure. The higher the back pressure, the more exhaust gas remains in the combustion chamber. If internal EGR gas is being introduced, the amount of introduction increases. As a result, the temperature in the combustion chamber rises and the amount of burnt gas in the air-fuel mixture increases. Even without increasing the fuel to enrich the air-fuel ratio, the SPCCI combustion becomes easier, so the fuel efficiency can be improved.

According to the engine control device to which the disclosed technique is applied, even if fuels with different octane numbers are supplied, good operation can be realized without causing deterioration of emissions.

It is a figure which illustrates a structure of an engine. 1 is a circuit diagram illustrating the main configuration of a cooling device; FIG. 1 is a block diagram illustrating an engine control device; FIG. FIG. 4 is a diagram for explaining determination of octane number based on SPCCI combustion; 1 is a block diagram illustrating a base set of engines; FIG. It is a figure for demonstrating water temperature fall control. FIG. 3 is a diagram illustrating an engine operating range map (high RON operating range map); FIG. 3 is a diagram illustrating an engine operating range map (low RON operating range map); It is a figure for demonstrating enrichment control. FIG. 4 is a diagram illustrating the relationship between the air-fuel ratio and the amount of NOx generated; 4 is a flowchart showing an example of cooling control by an engine control device; 4 is a flowchart showing an example of combustion control by an engine control device;

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

FIG. 1 is a diagram illustrating the configuration of an engine 1. As shown in FIG. FIG. 2 is a circuit diagram illustrating the main configuration of a cooling device that cools the engine 1. As shown in FIG. FIG. 3 is a block diagram illustrating the control device of the engine 1. As shown in FIG. 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 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. The engine 1 is installed in a four-wheeled automobile. The automobile runs as the engine 1 operates.

A control device for the engine 1 includes an ECU (Engine Control Unit) 10 . The ECU 10 controls the operation of various devices of the engine 1 based on signals input from various sensors SW1-SW11 installed in the engine 1. FIG.

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

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, it is not necessary to refuel only with a predesignated fuel, unlike the conventional art. The engine 1 can be stably operated while suppressing abnormal combustion such as knocking even if the gasolines have different octane numbers, such as regular gasoline and high-octane gasoline.

Therefore, fuel can be refueled according to preference. For example, if the engine 1 is supplied with fuel having a high octane number, knocking is less likely to occur, so the engine 1 can be operated in a state where its performance is fully exploited. As a result, the automobile can be adjusted to specifications that give priority to driving, such as sports driving.

Also, if the engine 1 is refueled with fuel having a low octane number, it is possible to run the vehicle at low cost and with excellent fuel efficiency. However, since low octane fuel tends to knock, if control is performed under the same conditions as for high octane fuel, abnormal combustion may occur and proper operation may not be possible.

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

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

<Engine>
The engine 1 includes an engine body 1a, injectors 6, spark plugs 25, an intake passage 40, an exhaust passage 50, a cooling device 70, and the like.

The engine body 1 a includes a cylinder block 12 and a cylinder head 13 . The cylinder head 13 is mounted on the cylinder block 12 . A plurality of cylinders 11 are formed in the cylinder block 12 . The engine 1 is a multi-cylinder engine. In FIG. 1 only one cylinder 11 is shown.

(combustion chamber)
A piston 3 is inserted in each cylinder 11 . Piston 3 is connected to crankshaft 15 via connecting rod 14 . The piston 3 reciprocates inside the cylinder 11 . The piston 3 , cylinder 11 and cylinder head 13 form a combustion chamber 17 . That is, the combustion chamber 17 is configured by the engine body 1a. The "combustion chamber" means a space formed by the piston 3, the cylinder 11 and the cylinder head 13 regardless of the position of the piston 3.

A lower surface of the cylinder head 13 constitutes an upper portion of the combustion chamber 17 . The upper part of the combustion chamber 17 is composed of two inclined planes. The ceiling surface of the combustion chamber 17 is of a so-called pent roof type. The upper surface of the piston 3 constitutes the lower portion of the combustion chamber 17 . A recess (cavity) is formed in the upper surface of the piston 3 .

The engine 1 is a compression ignition engine. The engine 1 performs specific partial compression ignition combustion in some predetermined operating regions. Specifically, SPCCI combustion (SPark Controlled Compression Ignition), which is a combination of SI (Spark Ignition) combustion and CI (Compression Ignition) combustion, is performed.

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

By adjusting the amount of SI combustion, it is possible to absorb temperature variations in the combustion chamber 17 before the start of compression. The amount of SI combustion is adjusted by adjusting the ignition timing. By adjusting the ignition timing, the mixture self-ignites at the target timing. In SPCCI combustion, the amount of SI combustion controls the start timing of CI combustion.

In this way, SPCCI combustion controls CI combustion through heat generation and/or pressure increase due to SI combustion. 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.

(Valve mechanism, etc.)
Two intake ports 18 are formed in the cylinder head 13 for each cylinder 11 . These intake ports 18 communicate with the combustion chamber 17 . Although detailed illustration is omitted, the intake port 18 is a so-called tumble port. That is, the intake port 18 has a shape that generates a tumble flow in the combustion chamber 17 .

Each intake port 18 is provided with an intake valve 21 . The intake valve 21 opens and closes the intake port 18 at a predetermined timing by a valve mechanism. The valve mechanism may be a variable valve mechanism that varies valve timing and/or valve lift.

As shown in FIG. 3, the valve train has an electric intake S-VT (Sequential-Valve Timing) 23 . The electric intake S-VT 23 continuously changes the rotation phase of the intake camshaft within a predetermined angle range. The opening angle of the intake valve 21 does not change. The opening angle of the intake valve 21 is, for example, 240°CA. The valve mechanism may have a hydraulic S-VT instead of the electric S-VT.

Two exhaust ports 19 are formed in the cylinder head 13 for each cylinder 11 . These exhaust ports 19 also communicate with the combustion chamber 17 . Each exhaust port 19 is provided with an exhaust valve 22 . The exhaust valve 22 opens and closes the exhaust port 19 at a predetermined timing by a valve mechanism. The valve mechanism may be a variable valve mechanism that varies valve timing and/or valve lift.

As shown in FIG. 3, the valve mechanism has an electric exhaust S-VT 24 . The electric exhaust S-VT 24 continuously changes the rotation phase of the exhaust camshaft within a predetermined angle range. The opening angle of the exhaust valve 22 does not change. The opening angle of the exhaust valve 22 is, for example, 240° CA. The valve mechanism may have a hydraulic S-VT instead of the electric S-VT.

The electric intake S-VT 23 and the electric exhaust S-VT 24 adjust the length of the overlap period during which both the intake valve 21 and the exhaust valve 22 are open. 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 electric intake S-VT 23 and the electric exhaust S-VT 24 constitute an internal EGR system.

(injector)
An injector 6 is attached to the cylinder head 13 for each cylinder 11 . Injector 6 injects fuel directly into combustion chamber 17 . The injector 6 is arranged in the upper central portion of the combustion chamber 17 .

The injector 6 is of a multiple injection hole type having a plurality of injection holes. The injector 6 injects fuel radially and obliquely downward from the central portion of the ceiling surface of the combustion chamber 17 . The injector 6 has ten injection holes arranged at equal angular intervals in the circumferential direction.

A fuel supply system 61 is connected to the injector 6 . The fuel supply system 61 includes a fuel tank 63 that stores fuel and a fuel supply path 62 . A fuel supply path 62 connects the fuel tank 63 and the injector 6 to each other. A fuel pump 65 and a common rail 64 are interposed in the fuel supply path 62 .

Fuel pump 65 delivers fuel to common rail 64 . The fuel pump 65 is a plunger pump driven by the crankshaft 15 in this configuration example. Common rail 64 stores fuel sent from fuel pump 65 . The voltage inside the common rail 64 is high voltage. Injector 6 is connected to common rail 64 .

When the injector 6 opens, the high-pressure fuel in the common rail 64 is injected into the combustion chamber 17 through the nozzle hole of the injector 6 . The fuel supply system 61 of this configuration example can supply high pressure fuel of 30 MPa or more to the injector 6 . The maximum pressure of the fuel supply system 61 may be 200 MPa, for example. The fuel supply system 61 may change the fuel pressure according to the operating state of the engine 1 . Note that the configuration of the fuel supply system 61 is not limited to the configuration described above.

(spark plug)
A spark plug 25 is attached to the cylinder head 13 for each cylinder 11 . A spark plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17 . The spark plug 25 is arranged on the intake side of the cylinder 11 . A spark plug 25 is positioned between the two intake ports 18 . Electrodes of the ignition plug 25 face the inside of the combustion chamber 17 . The spark plug 25 may be arranged on the exhaust side of the cylinder 11 or may be arranged in the center of the cylinder 11 .

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

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

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

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

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

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

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

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

The intake passage 40 has two branch passages connected to each intake port 181 . A swirl control valve 56 is arranged in one of the branch passages. The swirl control valve 56 is an opening adjustment valve that can adjust the opening of the branch passage. If the opening is small, the swirl flow in the combustion chamber 17 will be strong, and if the opening is large, the swirl flow in the combustion chamber 17 will be weak.

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 (cylinder 11 flow) is generated in the combustion chamber 17. A swirl flow tilted with respect to the central axis) is generated.

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

An exhaust gas purification system having a plurality of catalytic converters is arranged in the exhaust passage 50 . Although not shown, these catalytic converters are arranged in the engine room. The upstream catalytic converter has a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512 . The downstream catalytic converter has a three-way catalyst 513 . It should be noted that the exhaust gas purification system is not limited to the configuration of the illustrated example. For example, GPF may be omitted. Also, the catalytic converter is not limited to having a three-way catalyst. Furthermore, the order in which the three-way catalyst and GPF are arranged may be changed as appropriate.

An EGR passage 52 is connected between the intake passage 40 and the exhaust passage 50 . The EGR passage 52 is a passage that recirculates part of the exhaust gas to the intake passage 40 . An upstream end of the EGR passage 52 is connected between the two catalytic converters in the exhaust passage 50 . A downstream end of the EGR passage 52 is connected to an upstream portion of the supercharger 44 in the intake passage 40 .

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

(exhaust shutter valve)
An exhaust shutter valve 50a is provided between the branched portion of the EGR passage 52 in the exhaust passage 50 and the downstream catalytic converter. The exhaust shutter valve 50 a is an opening control valve that can adjust the opening of the exhaust passage 50 . Normally, the degree of opening is adjusted to be large (fully open), but if the degree of opening is made small, it becomes difficult for the exhaust gas to flow and the back pressure increases. The exhaust shutter valve 50a is used for enrichment control, which will be described later.

(Cooling system)
FIG. 2 shows a main configuration (circuit diagram) of the cooling device 70 related to cooling of the engine body 1a. As shown in the figure, the cooling device 70 includes a water pump (W/P) 71, a cooling water path 72, a radiator (RAD) 73, a thermostat valve 74, and the like. In addition, the cooling device 70 has a plurality of cooling water paths in addition to this, but illustration and description thereof are omitted.

The water pump 71 is installed on the side surface of the cylinder block 12 . The water pump 71 is connected to the crankshaft 15 via a belt and is rotationally driven by the crankshaft 15 . Therefore, the water pump 71 operates in synchronization with the operation of the engine 1 .

The cooling water path 72 is a path for circulating the cooling water discharged by the operation of the water pump 71 through the engine body 1a. Specifically, as indicated by arrows in FIG. 2, the cooling water path 72 passes cooling water discharged from the water pump 71 through a block-side water jacket 72a, a head-side water jacket 72b, and a radiator 73 in this order. and circulate back to the water pump 71.

The block-side water jacket 72 a is formed near the cylinders 11 in the cylinder block 12 . The head-side water jacket 72 b is formed near the combustion chamber 17 in the cylinder head 13 .

A radiator 73 is installed near the front grill in the engine room. The cooling water is cooled while passing through the radiator 73 by heat exchange with the wind or the like introduced into the engine room during running.

The thermostat valve 74 is installed in a portion between the radiator 73 and the water pump 71 in the cooling water path 72 . The thermostat valve 74 is composed of a valve body 74a, a heater 74b, and the like.

The valve body 74a opens and closes the cooling water flow path. The opening/closing of the valve body 74a is controlled based on a predetermined opening/closing determination temperature. That is, when the temperature of the cooling water passing through the thermostat valve 74 is equal to or higher than the opening/closing determination temperature, the valve body 74a is opened (fully opened). If the temperature of the cooling water passing through the thermostat valve 74 is lower than the opening/closing determination temperature, the valve body 74a is closed (fully closed).

The opening/closing determination temperature is changed by the heater 74b. That is, the heater 74b is energized under the control of the ECU. As a result, the heater 74b generates heat and its temperature rises. As the temperature of the heater 74b increases, the opening/closing determination temperature increases. As the temperature of the heater 74b becomes lower, the opening/closing determination temperature becomes lower.

When the valve body 74a is opened, the cooling water circulates through the cooling water path 72, so the cooling water cooled by the radiator 73 flows through the engine body 1a. On the other hand, when the valve main body 74a is closed, the cooling water does not circulate through the cooling water path 72, so that the cooling water cooled by the radiator 73 does not flow to the engine main body 1a.

A first water temperature sensor SW6a is installed in a portion between the water pump 71 and the cylinder block 12 in the cooling water path 72 . The first water temperature sensor SW6a detects the temperature of cooling water flowing into the engine body 1a (cooling water temperature). The temperature of the cooling water passing through the thermostat valve 74 is approximately the same as this cooling water temperature. Therefore, the thermostat valve 74 substantially opens and closes according to the cooling water temperature.

A second water temperature sensor SW6b is installed in a portion between the cylinder head 4 and the radiator 73 in the cooling water path 72 . The second water temperature sensor SW6b detects the temperature of cooling water (engine water temperature) flowing out from the engine body 1a. Since the cooling water flowing out from the engine main body 1a passes through the vicinity of the combustion chamber 17, the temperature of the combustion chamber 17 (the wall temperature of the combustion chamber 17) can be estimated based on the engine water temperature.

Based on signals input from each of the first water temperature sensor SW6a and the second water temperature sensor SW6b, the ECU 10 adjusts the amount of power supplied to the heater 74b. Thereby, the cooling water temperature is changed, and the cooling water temperature is controlled so that the engine water temperature is stabilized at the target temperature. That is, in the engine 1, the thermostat valve 74 and the ECU 10 constitute "temperature changing means".

<Engine control device>
FIG. 3 shows the ECU 10 and its main related devices.

The ECU 10 has a microcomputer 101 , a memory 102 and an I/F circuit 103 . The microcomputer 101 executes programs. Memory 102 stores programs and data. The memory 102 is, for example, RAM or ROM. The I/F circuit 103 inputs and outputs electrical signals.

Various sensors SW1-SW11 are connected to the ECU 10 as shown in FIGS. These sensors SW1-SW11 output signals to the ECU .

The airflow sensor SW1 is arranged 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 arranged 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 the 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 in-cylinder pressure sensor SW5 is attached to the cylinder head 13 for each cylinder 11 and measures the pressure inside each combustion chamber 17 .

As described above, the first water temperature sensor SW6a and the second water temperature sensor SW6b are attached to the engine 1 and measure the temperature of the cooling water. A crank angle sensor SW7 is attached to the engine 1 and measures the rotation angle of the crankshaft 15 .

The accelerator opening sensor SW8 is attached to the accelerator pedal mechanism and measures the accelerator opening corresponding to the amount of operation 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 level sensor SW11 is attached to the fuel tank 63 and measures the amount of stored fuel.

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

The ECU 10 transmits electric signals related to the control amount to the injector 6, the spark plug 25, the electric intake S-VT 23, the electric exhaust S-VT 24, the fuel supply system 61, the throttle valve 43, the EGR valve 54, the electromagnetic clutch of the supercharger 44. 45, air bypass valve 48, swirl control valve 56, exhaust shutter valve 50a, water pump 71, and heater 74b.

<Octane number determination means>
The control device for the engine 1 includes octane number determination means. The octane number determining means determines the octane number of the fuel. The octane number determining means may be capable of determining the octane number of the fuel, and its configuration can be selected according to the specifications.

For example, a predetermined sensor capable of detecting the octane number of fuel may be installed in the fuel supply system 61 and the detected octane number may be used for determination. Alternatively, the octane rating may be determined using a knock sensor or the like.

Since the engine 1 performs SPCCI combustion, an in-cylinder pressure sensor SW5 capable of measuring the internal pressure of each combustion chamber 17 with high accuracy is installed. Therefore, the engine 1 is configured to determine the octane number using this.

Specifically, the octane number is determined based on the amount of heat generated by SI combustion in SPCCI combustion. Since the in-cylinder pressure sensor SW5 can detect such heat quantity with high accuracy, the octane rating can be determined with high accuracy. Moreover, since an existing device is used, there is no need to newly install an expensive sensor.

(Determination of octane number based on SPCCI combustion)
FIG. 4 illustrates the combustion morphology of SPCCI combustion. In SPCCI combustion, the ignition plug 25 ignites the air-fuel mixture in the combustion chamber 17 to initiate SI combustion, followed by CI combustion of the remaining unburned air-fuel mixture.

The heat quantity (assist heat quantity: Qsa) generated in SI combustion from the ignition timing to the self-ignition start timing θci is correlated with the octane number of the fuel used for the combustion. That is, when the octane number of the fuel is low, the fuel tends to self-ignite, so the amount of assist heat is small. Conversely, if the octane number of the fuel is high, the fuel is difficult to self-ignite, so the amount of assist heat increases.

However, the correlation is affected by the operating conditions of the engine, such as the load and speed of the engine, and the outside air temperature. Therefore, in the memory 102 of the ECU 10, data and programs (heat/RON correlation information) are stored in the memory 102 of the ECU 10, which enable determination of the octane number of the fuel from the actually measured amount of assist heat in consideration of such external factors based on experiments. is stored.

The ECU 10 calculates the amount of assist heat based on the signal input from the in-cylinder pressure sensor SW5, and determines the octane number of the fuel based on the calculated amount of assist heat and the heat/RON correlation information. In other words, in the engine 1, the in-cylinder pressure sensor SW5 and the ECU 10 constitute "octane number determination means".

<Response to fuels with different octane ratings>
As described above, the engine 1 performs SPCCI combustion, which requires advanced combustion control, mainly in order to obtain excellent fuel efficiency. Therefore, when the octane number of the fuel changes, the combustion tends to become unstable. Therefore, in the control device for the engine 1, cooling control and combustion control are devised so that the engine 1 can be stably operated while suppressing abnormal combustion even with fuels having different octane numbers.

(engine base set)
The ECU 10 changes the basic conditions (base set) for control of the engine 1 according to the determined octane number of the fuel.

Specifically, as shown in FIG. 5, the control device of the engine 1 has a base set (low octane number map 601) when the octane number of the fuel is less than a predetermined value, and a base set (high octane map 602).

A predetermined value (an octane number that serves as a reference for judging whether the octane number of fuel is high or low, RON judgment value: R0) is an octane number (ron) capable of distinguishing between fuels with different octane numbers that can be supplied to the engine 1 . The RON determination value is stored in memory 102 . The RON determination value is preferably a value that allows discrimination between regular gasoline and high-octane gasoline. The RON determination value can be set to "96", for example.

Conditions suitable for combustion do not match between regular gasoline and high-octane gasoline. That is, even under the same combustion conditions, both regular gasoline and high-octane gasoline may be properly combusted. On the other hand, there are cases where high-octane gasoline cannot be properly burned under combustion conditions suitable for regular gasoline, and regular gasoline cannot be properly burned under combustion conditions suitable for high-octane gasoline.

In particular, the engine 1 performs SPCCI combustion as described above. SPCCI combustion requires a high level of combustion control, so if fuels with different octane numbers are used, combustion tends to be unstable. Therefore, in this engine 1, the base set is switched to either the low octane number map 601 or the high octane number map 602 based on the determination result of the octane number of the fuel so that SPCCI combustion can be performed appropriately.

The low octane number map 601 mainly sets conditions suitable for low octane number fuel (mainly regular gasoline here). 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 corresponds to main control conditions related to combustion, such as high and low rotation speeds in all operating regions of the engine 1 and high and low load in all operating regions of the engine 1. A value is set. Both the low octane map 601 and the high octane map 602 are stored in the memory 102 .

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

Similarly, high octane maps 602 include 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.

The ECU 10 switches the low octane number map 601 to the high octane number map 602, for example, when the octane number of the fuel changes from less than a predetermined octane number to a predetermined octane number or more. Since a plurality of conditions requiring switching are switched collectively, the control can be simplified and efficient.

(Cooling water temperature)
A fuel with a low octane number is more prone to abnormal combustion than a fuel with a high octane number. Abnormal combustion can be suppressed by controlling the ignition timing to be retarded (ignition retard control), but in this case, the fuel consumption will be worsened. On the other hand, abnormal combustion can also be suppressed by lowering the temperature of the combustion chamber 17 by lowering the engine water temperature by adjusting the cooling water. In this case, unlike ignition retard control, there is an advantage that deterioration of fuel consumption is not caused.

Therefore, the control device for the engine 1 executes control (water temperature lowering control) for switching the temperature of the cooling water based on the determination result of the octane number of the fuel. Specifically, when the octane number of the fuel is determined to be less than the RON determination value (R0) (during determination of the low octane number), the ECU 10 determines that the octane number of the fuel is equal to or greater than the RON determination value (R0) ( Control is performed to lower the temperature of the cooling water than when the high octane number is determined).

FIG. 6 shows an example of water temperature reduction control. When determining a high octane number, the ECU 10 sets the target engine water temperature to, for example, 100° C. so that appropriate combustion can be performed. Then, the ECU 10 adjusts the amount of power supplied to the heater 74b and sets the cooling water temperature t2 so that the temperature t2' (for example, ±5° C.) before and after that temperature is maintained.

On the other hand, when the low octane rating is determined, the ECU 10 sets the target engine water temperature to 80° C., for example, in order to suppress abnormal combustion. Then, the ECU 10 adjusts the amount of power supplied to the heater 74b to set the cooling water temperature t1 so that the temperature t1' (for example, ±5° C.) around that temperature is maintained. As a result, the temperature of the combustion chamber 17 (the wall temperature of the combustion chamber 17) is lowered compared to when the high octane rating is determined, so that the self-ignition of the fuel becomes difficult and abnormal combustion can be suppressed.

(Operating range of engine 1)
7A and 7B illustrate operating range maps of the engine 1. FIG. FIG. 7A is an operating range map (high RON operating range map 7a) when determining a high octane number, and FIG. 7B is an operating range map (low RON operating range map 7b) when determining a low octane number. These operating area maps are stored in memory 102 .

These operating range maps are maps for a normal operating state, that is, a so-called warm state map. Other maps are used under certain conditions, such as when cold. The engine 1 operates based on these operating range maps. That is, these operating range maps correspond to the operating range of the engine 1. FIG.

As shown in FIG. 7A, the high RON operating range map 7a is defined by the load of the engine 1 and the rotation speed of the engine 1 . The high RON operating region map 7a is partitioned into four regions: region A1, region A2, region A3, and region A4. Region A1 is a region where the number of revolutions is higher than that of Na. Area A2 is an area where the load is lower than La among the areas where the rotational speed is equal to or lower than Na. A region A3 is a region in which the load is La or higher among the regions in which the rotational speed is Na or lower. Note that La may be half the maximum load of the engine 1 .

Area A4 is a specific area partitioned within area A2. The area A4 is defined on the low load side and the low rotation side of the area A2 and the area A3. The region A4 corresponds to a specific region on the low load side and the low speed side in the entire operating range of the engine 1 as well. The "low rotation side" referred to here corresponds to the low rotation side when the entire operating range of the engine 1 is divided into the low rotation side and the high rotation side. "Low load side" corresponds to the low load side when the entire operating range of the engine 1 is divided into two equal parts, the low load side and the high load side.

When the engine 1 operates in the region A1, the ECU 10 controls the engine 1 to perform SI combustion instead of SPCCI combustion. The engine 1 is driven by combustion accompanied by flame propagation due to ignition of the spark plug 25 . Intentionally, no CI combustion occurs due to autoignition.

The air-fuel ratio (A/F) of the air-fuel mixture set in the region A1 is the stoichiometric air-fuel ratio (excess air ratio: λ=1). The set value is the stoichiometric air-fuel ratio, but the stoichiometric air-fuel ratio may vary to some extent in practice. In short, the air-fuel ratio should be included in the purification window of the three-way catalysts 511 and 513 . The air-fuel ratio is the average air-fuel ratio in the entire combustion chamber 17 (the same applies hereinafter).

When the engine 1 operates in the regions A2 and A3, and also in the region A4, the ECU 10 controls the engine 1 to perform SPCCI combustion. That is, the areas A2, A3, and A4 correspond to "predetermined operating areas" in which specific partial compression ignition combustion (SPCCI combustion) is performed.

The air-fuel ratio of the air-fuel mixture set in the regions A2 and A3 is the stoichiometric air-fuel ratio. Therefore, the engine 1 can stably perform SPCCI combustion with an appropriate amount of fuel. NOx and the like can also be purified appropriately.

In region A3, the supercharger 44 is on. That is, SPCCI combustion is performed in a supercharged state (supercharging SPCCI). On the other hand, in area A2, the supercharger 44 is off. That is, SPCCI combustion is performed with naturally aspirated air (non-supercharged SPCCI). Region A4, which is defined within region A2, also has the supercharger 44 off.

The air-fuel ratio of the air-fuel mixture set in region A4 is leaner than the stoichiometric air-fuel ratio. Specifically, the air-fuel ratio in the region A4 is set to approximately twice the stoichiometric air-fuel ratio, that is, approximately 30. Approximately 30 can be, for example, 25-35 or 28-32. The engine 1 performs SPCCI combustion in region A4 with less fuel than in region A2 (lean SPCCI).

Therefore, driving in the region A4 is more fuel efficient than driving in the region A2. The areas A2 and A3 where the stoichiometric air-fuel ratio is set correspond to the "second divided area", and the area A4 where the lean air-fuel ratio is set corresponds to the "first divided area".

When the engine 1 operates in the region A4, the ECU 10 performs control to provide an overlap period during which both the intake valve 21 and the exhaust valve 22 are opened. Thereby, during combustion, internal EGR gas is introduced into the combustion chamber 17 and the temperature in the combustion chamber 17 increases. In region A4, the ECU 10 stabilizes SPCCI combustion by adjusting the amount of internal EGR gas introduced.

(Correction of air-fuel ratio)
As described above, when judging a high octane number, the engine water temperature (100° C.) is set so that a fuel with a high octane number such as high-octane gasoline can perform appropriate SPCCI combustion. On the other hand, when the low octane rating is determined, water temperature reduction control is performed and the engine water temperature is set to a low temperature (80° C.) in order to suppress abnormal combustion.

As a result, abnormal combustion can be effectively suppressed by lowering the temperature of the combustion chamber 17 in a region where the combustion heat generated in the combustion chamber increases, such as the region A3, particularly on the high load side thereof. As a result, appropriate SPCCI combustion can be stably performed without excessive ignition retard control. Therefore, deterioration of fuel consumption can be suppressed.

On the other hand, in the region A2, especially in the region where the combustion heat generated in the combustion chamber 17 is small, such as the low load side thereof, self-ignition becomes difficult due to the temperature drop during combustion, and stable SPCCI combustion (CI combustion) cannot be achieved. may disappear. Similarly, even on the low rotation side, the combustion period becomes longer, so the amount of heat released increases. As a result, self-ignition becomes difficult due to a temperature drop during combustion, and there is a risk that stable SPCCI combustion (CI combustion) will not be possible.

Furthermore, since lean SPCCI is performed in region A4, which is defined on the low-load side and low-speed side of regions A2 and A3, the amount of heat generated is even smaller. Self-ignition becomes even more difficult. Since the air-fuel mixture around the spark plug 25 also tends to become lean, the ignitability of the ignition also deteriorates. Therefore, misfire or incomplete combustion may occur.

Therefore, the ECU 10 executes control (enrichment control) to change the air-fuel ratio in the area A4 to the richer side than when determining the high octane number when determining the low octane number. By changing the air-fuel ratio to the rich side, the fuel amount relatively increases. As a result, it becomes easier to form an air-fuel mixture around the spark plug 25 as an ignition source. As a result, ignitability is improved and SI combustion can be stabilized. Since the amount of heat generated increases, self-ignition becomes easier, and CI combustion can also be stabilized. Therefore, even if the temperature of the combustion chamber 17 is low, appropriate SPCCI combustion can be stably performed.

FIG. 8 shows the region A4 portion of the low RON operating region map 7b. FIG. 8 schematically shows the degree of enrichment of the air-fuel ratio divided into regions. In the region A4 of the low RON operating region map 7b, the air-fuel ratio is set to be richer than in the region A4 of the high RON operating region map 7a.

The air-fuel ratio in the region A4 of the high RON operating region map 7a is set to the same value over the entire region. On the other hand, the degree of enrichment of the air-fuel ratio in the region A4 of the low RON operating region map 7b is set according to the load.

That is, the higher the load, the richer the air-fuel ratio becomes, that is, the air-fuel ratio is set to decrease (air-fuel ratio of r5 < air-fuel ratio of r4 < air-fuel ratio of r3 < air-fuel ratio of r2 < air-fuel ratio of r1). fuel ratio<air-fuel ratio in region A4 of high RON operating region map 7a). Then, on the high load side, the engine is set to be richer (the amount of fuel increases more) with respect to changes in the load than on the low load side.

Furthermore, the control device for the engine 1 adjusts the opening degree of the exhaust shutter valve 50a when the enrichment control is executed. By doing so, it is devised so that enrichment can be suppressed.

Specifically, the ECU 10 adjusts the opening degree of the exhaust shutter valve 50a in the direction of closing in a low-load-side region (for example, r1) of the region A4. This increases the back pressure. As described above, since the overlap period is provided in the region A4, the amount of internal EGR gas introduced into the combustion chamber 17 increases due to the increased back pressure. As a result, the temperature in the combustion chamber 17 rises and the amount of burnt gas in the air-fuel mixture increases. Even without increasing the fuel to enrich the air-fuel ratio, the SPCCI combustion becomes easier, so the fuel efficiency can be improved.

On the other hand, in the area A4, the amount of exhaust gas is larger in the area on the high load side (eg, r5) than in the area on the low load side. Therefore, if the opening degree of the exhaust shutter valve 50a is adjusted in the closing direction, the exhaust cannot be properly performed, and there is a risk that the SPCCI combustion will become unstable. Therefore, the ECU 10 adjusts the opening of the exhaust shutter valve 50a in the direction of opening in the high load side of the region A4. The opening degree of the exhaust shutter valve 50a may be adjusted stepwise according to the load, or the opening degree may be switched between large and small depending on a predetermined load.

(reduction of area)
If the lean air-fuel ratio in the area A4 is enriched by the enrichment control, the amount of NOx emissions increases, which may lead to deterioration of emissions.

FIG. 9 illustrates the relationship between the air-fuel ratio and the amount of NOx generated. Near the stoichiometric air-fuel ratio (A/F of about 15), the combustion temperature is high, so NOx is generated in large amounts. On the other hand, at a lean air-fuel ratio in which air is excessive relative to fuel, as in region A4, almost no NOx is generated. When such a lean air-fuel ratio is changed to the rich side as indicated by the arrow in FIG. 9, the amount of NOx generated increases. Since the air-fuel ratio at that time deviates greatly from the stoichiometric air-fuel ratio, it is difficult to properly purify the air with the three-way catalyst. As a result, the amount of NOx emitted increases, leading to deterioration of emissions.

Therefore, the control device for the engine 1 executes control (region reduction control) to reduce the region A4 of the low RON operating region map 7b relative to the region A4 of the high RON operating region map 7a. Specifically, as shown in FIG. 7B, the ECU 10 performs control so that the boundary portions of both the high load side and the high rotation side of the region A4 of the low RON operating region map 7b are reduced. Depending on the specifications, control may be performed so that either one of the high load side and the high rotation side boundary portion is reduced.

The boundary portion on the high load side of the region A4 has a particularly large amount of fuel even within the region A4. Therefore, the amount of NOx emissions, which increases as a result of the enrichment control, also increases. Therefore, by reducing such a region, the amount of NOx emissions can be suppressed.

The boundary portion of the region A4 on the high rotation side has a particularly short combustion period and a high combustion temperature in the region A4. Therefore, the amount of NOx emissions, which increases as a result of the enrichment control, also increases. Therefore, by reducing such a region, the amount of NOx emissions can be suppressed.

By reducing the area A4, the area A2 is enlarged accordingly. In the region A2, the air-fuel ratio is set to the stoichiometric air-fuel ratio, so even if the amount of NOx emissions is large, the three-way catalyst can effectively purify the NOx. Therefore, there is no risk of worsening emissions.

<Control example>
10 and 11 show an example of cooling control and combustion control by the control device of the engine 1. FIG.

(cooling control)
As shown in FIG. 10, when the operation of the engine 1 is started, the ECU 10 receives signals from various sensors SW1 to SW11 and reads these signals (step S1). Then, the ECU 10 calculates the assist heat quantity (Qsa) based on the signal input from the in-cylinder pressure sensor SW5 when the SPCCI combustion is executed, that is, when the engine 1 is operating in the regions A2, A3, and A4. . Then, the ECU 10 determines the octane number of the fuel based on the calculated amount of assist heat and the heat/RON correlation information (step S2).

The ECU 10 compares the determined octane number with the RON determination value (R0), and determines whether or not the fuel octane number is less than the RON determination value (step S3). As a result, when it is determined that the octane number of the fuel is less than the RON determination value (during low octane number determination), the ECU 10 determines that low octane fuel such as regular gasoline is being used. Then, the ECU 10 sets a low octane number flag (step S4), and executes water temperature lowering control to set the set water temperature of the cooling water to 80° C. (step S5).

Specifically, the ECU 10 adjusts the amount of power supplied to the heater 74b so that the cooling water temperature becomes 80° C. based on signals input from the first water temperature sensor SW6a and the second water temperature sensor SW6b.

On the other hand, when the octane value of the fuel is determined to be equal to or higher than the RON determination value (during high octane value determination), the ECU 10 determines that high octane fuel such as high-octane gasoline is being used. Then, the ECU 10 sets a high octane number flag (step S6), and sets the coolant temperature to 100° C. (step S7).

It is preferable to set the set water temperature of one of the cooling waters when the operation of the engine 1 is started. In the case of this engine 1, the geometric compression ratio and the like are set so that stable SPCCI combustion can be performed even with a high-octane fuel. Temporarily, the temperature may be set to an intermediate temperature, such as 90°C.

(combustion control)
As shown in FIG. 11, when the operation of the engine 1 is started, the ECU 10 receives signals from various sensors SW1 to SW11 and reads these signals (step S10). Then, the ECU 10 determines whether or not the engine 1 is operating in the regions where SPCCI combustion is performed, that is, regions A2, A3, and A4 (step S11).

As a result, when it is determined that the engine 1 is not operating in the regions A2, A3 and A4, that is, it is operating in the region A1, the ECU 10 sets the air-fuel ratio to the stoichiometric air-fuel ratio (λ=1), SI combustion is controlled (steps S12 and S13).

On the other hand, when it is determined that the engine 1 is operating in the regions A2, A3, and A4, the ECU 10 determines whether or not the octane rating flag indicates a low octane rating (step S14). As a result, when it is determined that the octane rating flag is not the low octane rating flag, that is, the high octane rating flag is set, the ECU 10 determines whether or not the operating region is region A4 (step S15).

As a result, when it is determined that the operating region is region A4, the ECU 10 sets the air-fuel ratio to a predetermined lean value (step S16) and executes SPCCI combustion (step S17). On the other hand, when it is determined that the operating region is not region A4, that is, region A2 or region A3, the ECU 10 sets the air-fuel ratio to the stoichiometric air-fuel ratio (step S18), and executes SPCCI combustion (step S17).

On the other hand, when it is determined in step S14 that the octane rating flag is low, that is, the low octane rating flag is set, the ECU 10 performs region reduction control to reduce the region A4 of the high RON operating region map 7a. Execute (step S19). Thereby, as shown in FIG. 7B, a low RON operating range map 7b is obtained. Note that the low RON operating region map 7b may be set in advance by performing region reduction control in advance.

Then, the ECU 10 determines whether or not the operating range is the range A4 (step S20). As a result, when it is determined that the operating region is not region A4, that is, region A2 or region A3, the ECU 10 sets the air-fuel ratio to the stoichiometric air-fuel ratio (step S18), and executes SPCCI combustion (step S17).

On the other hand, when it is determined that the operating region is region A4, the ECU 10 executes rich control as shown in FIG. 8 to change the air-fuel ratio in region A4 to the rich side (step S21). At this time, SPCCI combustion is executed (step S17) while adjusting the opening degree of the exhaust shutter valve 50a according to the load of the engine 1 (step S22).

When fuel with a low octane number is used, the temperature of the combustion chamber 17 is made relatively low, so appropriate SPCCI combustion can be stably performed without excessive ignition retard control. Therefore, deterioration of fuel consumption can be suppressed. In the region A4 where lean SPCCI combustion is performed, the air-fuel ratio is corrected to the rich side, so stable lean SPCCI combustion can be maintained even if the temperature of the combustion chamber 17 is low. In that case, the amount of NOx emissions may increase, but the region where the amount of NOx emissions particularly increases is reduced, so the amount of NOx emissions can also be suppressed.

As described above, according to the control device of the engine 1, it is possible to supply fuels having different octane numbers, and to stably carry out appropriate SPCCI combustion without deteriorating emissions. Therefore, good driving can be realized.

1 engine 1a engine body 10 ECU (control device)
17 Combustion chamber 25 Spark plug 6 Injector 50a Exhaust shutter valve 70 Cooling device 74 Thermostat valve (temperature changing means)
SW5 cylinder internal pressure sensor (octane number determination means)

Claims (7)

An injector for injecting a predetermined fuel into a combustion chamber, a spark plug for igniting an air-fuel mixture formed in the combustion chamber by the fuel, and a cooling water circulating through the engine body that constitutes the combustion chamber. In a predetermined operating range, the ignition of the spark plug burns a part of the air-fuel mixture by combustion accompanied by flame propagation, and then the remaining unburned air-fuel mixture is burned by self-ignition. , a control device for an engine that performs a specific partial compression ignition combustion,
The predetermined operating region includes a first partitioned region in which a lean air-fuel ratio is set,
octane number determination means for determining the octane number of the fuel;
temperature changing means for changing the temperature of the cooling water;
with
Water temperature reduction for lowering the temperature of the cooling water when determining a low octane value in which the octane value of the fuel is determined to be less than a predetermined value, compared to when determining a high octane value in which the octane value of the fuel is determined to be equal to or greater than the predetermined value. and enrichment control for changing the air-fuel ratio of the first partitioned region to a richer side than when the high octane number was determined, and further reducing the first partitioned region compared to when the high octane number was determined. A controller for the engine that performs region reduction control. In the engine control device according to claim 1,
A control device for an engine, wherein a boundary portion of at least one of a high load side and a high rotation side of the first divided region is reduced by the region reduction control. The engine control device according to claim 1 or 2,
An engine control device, wherein the air-fuel ratio of the first segmented region when the high octane rating is determined is set to approximately twice the stoichiometric air-fuel ratio. In the engine control device according to any one of claims 1 to 3,
The predetermined operating region further includes a second partitioned region in which the stoichiometric air-fuel ratio is set,
A control device for an engine, wherein the second partitioned area is enlarged by reducing the first partitioned area. In the engine control device according to claim 4,
The engine control device, wherein the first partitioned area is partitioned into at least one of a low load side and a low rotation side area of the second partitioned area. In the engine control device according to any one of claims 1 to 5,
The engine control device, wherein the octane number determining means determines the octane number of the fuel based on the amount of heat generated by combustion accompanied by flame propagation in the partial compression ignition combustion. In the engine control device according to any one of claims 1 to 6,
The engine further comprises an exhaust shutter valve that adjusts the opening of an exhaust passage through which exhaust gas discharged from the combustion chamber flows,
An engine control device that adjusts the opening degree of the exhaust shutter valve in a closing direction when executing the enrichment control.

Images