JP2021088956A - Engine control device - Google Patents

Abstract

To provide an engine control device capable of achieving favorable operation without degradation of emissions even when supplied with fuel having a different octane value.SOLUTION: An engine control device comprises: octane value determination means which executes specific partial compressive ignition combustion in a predetermined operation region and determines an octane value of fuel; and temperature change means which changes a temperature of cooling water. The engine control device executes water temperature reduction control to make the temperature of the cooling water when determining a low-octane value lower than that when determining a high-octane value and enrichment control to make an air-fuel ratio in the predetermined operation region with a lean air-fuel ratio set therein richer than the air-fuel ratio when determining the high-octane value. The engine control device also executes region reduction control to make the predetermined operation region smaller than that when determining the high-octane value.SELECTED DRAWING: Figure 11

Description

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

Patent Document 1 discloses an engine that uses three gasolines having different octane numbers.

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

The engine is also disclosed to advance the ignition timing of the engine to improve engine output when operating at high load with high octane gasoline.

Japanese Unexamined Patent Publication No. 2006-125288

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

Usually, the fuel to be refueled is specified in advance according to the engine. However, if fuels with different octane numbers can be refueled and the vehicle can be operated without problems, it will be possible to select good driving performance and good fuel economy according to taste. Therefore, it is preferable to be able to refuel fuels having different octane numbers.

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

Therefore, in order to refuel fuels with different octane numbers so that they can be operated without problems, it is necessary to determine the octane number of the fuel to be used and change the engine control amount 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, the fuel efficiency is deteriorated.

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 the cooling water is lowered, compression ignition becomes difficult due to the temperature decrease in the combustion chamber, and SPCCI combustion tends to become unstable.

In particular, in a lean operating region, since the amount of combustion heat generated is small, there is a possibility that SPCCI combustion cannot be performed. It is conceivable to change the air-fuel ratio to the rich side to raise the temperature of the combustion chamber, but in that case, the amount of NOx emissions increases, and the emissions deteriorate.

Therefore, the main purpose of the disclosed technology is to provide an engine control device capable of achieving good operation without causing deterioration of emissions even when fuels having different octane numbers are refueled.

The disclosed technology includes an injector that injects a predetermined fuel into the combustion chamber, an ignition plug that ignites an air-fuel mixture formed in the combustion chamber by the fuel, and an engine body that constitutes the combustion chamber. Is equipped with a cooling device for circulating cooling water, and in a predetermined operating region, a part of the air-fuel mixture is burned by combustion accompanied by flame propagation by ignition of the ignition plug, and then the remaining unburned air-fuel mixture is burned. It relates to an engine control device that performs a specific partial compression ignition combustion that is burned by self-ignition.

The predetermined operating region includes a first compartment region in which a lean air-fuel ratio is set. The engine control device includes an octane number determining means for determining the octane number of the fuel and a temperature changing means for changing the temperature of the cooling water, and the octane number of the fuel is less than a preset predetermined value. At the time of determining the low octane number to be determined, the water temperature lowering control for lowering the temperature of the cooling water than at the time of determining the high octane number at which the octane number of the fuel is determined to be equal to or higher than the predetermined value, and the air fuel ratio of the first compartment region are determined. The enrichment control for changing to the richer side than at the time of the high octane number determination is executed, and further, the area reduction control for reducing the first partition area from the time of the high octane number determination is executed.

That is, in this engine, SPCCI combustion having excellent fuel efficiency is performed in a predetermined operating region. The operating area includes a first section area in which a lean air-fuel ratio is set. Since the air-fuel ratio of the first section area is lean, fuel efficiency can be improved.

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

That is, when the low octane number is determined, the water temperature lowering control which lowers the temperature of the cooling water than when the high octane number is determined and the enrichment control which changes the air-fuel ratio of the first compartment region to the richer side than when the high octane number is determined are performed. Execute. Further, the area reduction control for reducing the first partition area as compared with the time of high octane value determination is also executed.

Abnormal combustion is likely to occur when the temperature of the combustion chamber is high. Therefore, abnormal combustion can be suppressed by executing the water temperature decrease control at the time of determining the low octane number. However, as described above, SPCCI combustion tends to become unstable due to difficulty in compression ignition when the temperature of the cooling water is lowered. In particular, in the lean first compartment region, since the amount of combustion heat generated is small, there is a possibility that SPCCI combustion cannot be performed.

Therefore, the enrichment control for changing the air-fuel ratio of the first compartment region to the rich side is executed. 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 NOx emissions increase and the emissions deteriorate, but by reducing the first compartment area, the increase in NOx emissions can be suppressed. ..

As described above, according to the control device of this engine, fuels having different octane numbers can be refueled, and appropriate SPCCI combustion can be stably performed without causing deterioration of emissions. Therefore, good operation can be realized.

The engine control device may also have the boundary portion of at least one of the high load side and the high rotation side of the first compartment region reduced by the region reduction control.

In the first section region, the amount of NOx discharged 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 have the air-fuel ratio of the first compartment region at the time of determining the high octane number set to be substantially twice the stoichiometric air-fuel ratio.

If the air-fuel ratio is approximately twice the theoretical air-fuel ratio, almost no NOx is generated even when burned. Therefore, when the engine is operating in the first compartment region, NOx is hardly generated. Therefore, it is possible to drive with excellent fuel efficiency and emissions.

The engine control device also includes a second compartment region in which the predetermined operating region is further set with a stoichiometric air-fuel ratio, and the second compartment region is expanded by reducing the first compartment region. You may do.

If the air-fuel ratio is the stoichiometric air-fuel ratio, NOx is generated when it burns. However, it can be effectively purified by installing a three-way catalyst. Therefore, if the second compartment region in which the stoichiometric air-fuel ratio is set is expanded instead of reducing the first region, deterioration of emissions can be effectively suppressed.

The engine control device may also have the first compartment region partitioned into at least one of the low load side and the low rotation side of the second compartment region.

When the water temperature decrease control is executed, SPCCI combustion tends to be unstable in the second compartment region, particularly in the region on the low load side and the region on the low rotation side. Therefore, when the first partition area is divided into these areas, even more excellent effects can be expected by executing the enrichment control and the area reduction control.

The engine control device may also have the octane number determining means determine the octane number of the fuel based on the amount of heat generated in the 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 a new expensive sensor.

The engine control device also further comprises an exhaust shutter valve for adjusting the opening degree of the exhaust passage through which the exhaust gas discharged from the combustion chamber flows, and the exhaust shutter is executed when the enrichment control is executed. 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. If the opening of the exhaust shutter valve is adjusted in the closing direction, the back pressure will increase. The higher the back pressure, the greater the amount of exhaust gas that remains in the combustion chamber. If the internal EGR gas is introduced, the amount of the internal EGR gas introduced will increase. As a result, the temperature inside the combustion chamber rises, and the amount of burned gas in the air-fuel mixture increases. Even if the amount of fuel is not increased to enrich the air-fuel ratio, SPCCI combustion becomes easier, so that fuel efficiency can be improved.

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

It is a figure which illustrates the structure of an engine. It is a circuit diagram which illustrates the main structure of a cooling device. It is a block diagram which illustrates the control device of an engine. It is a figure for demonstrating the determination of the octane number based on SPCCI combustion. It is a block diagram which illustrates the base set of an engine. It is a figure for demonstrating the water temperature decrease control. It is a figure which illustrates the operation area map (high RON operation area map) of an engine. It is a figure which illustrates the operation area map (low RON operation area map) of an engine. It is a figure for demonstrating the enrichment control. It is a figure which illustrates the relationship between the air-fuel ratio and the amount of NOx generated. It is a flowchart which shows an example of cooling control by an engine control device. It is a flowchart which shows an example of combustion control by an engine control device.

Hereinafter, the engine 1 to which the disclosed technology is applied and its control device will be described 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 the engine 1. FIG. 2 is a circuit diagram illustrating a main configuration of a cooling device for cooling the engine 1. FIG. 3 is a block diagram illustrating a control device of the engine 1. The intake side in FIG. 1 is on the left side of the paper surface, and the exhaust side is on the right side of the paper surface.

The engine 1 has a combustion chamber 17 in which an air-fuel mixture containing fuel and air is burned. The combustion chamber 17 repeats an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. The engine 1 is a 4-stroke engine. The engine 1 is mounted on a four-wheeled vehicle. The automobile runs when the engine 1 is driven.

The control device of 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 the signals input from the various sensors SW1-SW11 installed in the engine 1.

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

Further, there are various types of gasoline having different octane numbers (for example, research method octane number, so-called ron), and the fuel of the engine 1 may be gasoline having different octane numbers. The fuel of the engine 1 may also be in a state in which gasolines having different octane numbers are mixed.

That is, in this engine 1, it is not necessary to refuel only the fuel specified in advance as in the conventional case. Even gasolines having different octane numbers, such as regular gasoline and high-octane gasoline, can stably operate the engine 1 while suppressing abnormal combustion such as knocking.

Therefore, the fuel can be refueled according to preference. For example, if the engine 1 is refueled with a fuel having a high octane number, knocking is unlikely to occur, so that the engine 1 can be operated in a state where the performance of the engine 1 is sufficiently brought out. As a result, the automobile can be adjusted to specifications that prioritize driving, such as sports driving.

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

Moreover, as will be described later, this engine 1 performs SPCCI combustion that combines SI combustion and CI combustion. SPCCI combustion requires a high degree of combustion control. Therefore, if fuels having 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 operated stably while suppressing abnormal combustion such as knocking even if the fuel has a different octane number (details). Will be described later). In the description, for convenience, regular gasoline may be used as an example of a fuel having a low octane number, and high-octane gasoline may be used as an example of a fuel having a high octane number.

<Engine>
The engine 1 is composed of an engine body 1a, an injector 6, a spark plug 25, an intake passage 40, an exhaust passage 50, a cooling device 70, and the like.

The engine body 1a includes a cylinder block 12 and a cylinder head 13. The cylinder head 13 is placed 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. FIG. 1 shows only one cylinder 11.

(Combustion chamber)
A piston 3 is inserted in each cylinder 11. The piston 3 is connected to the crankshaft 15 via a connecting rod 14. The piston 3 reciprocates inside the cylinder 11. The piston 3, the cylinder 11, and the cylinder head 13 form a combustion chamber 17. That is, the combustion chamber 17 is composed of 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.

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 composed of two inclined surfaces. The ceiling surface of the combustion chamber 17 is a so-called pent roof type. The upper surface of the piston 3 constitutes the lower part of the combustion chamber 17. A dent (cavity) is formed on the upper surface of the piston 3.

The engine 1 is a compression ignition type engine. The engine 1 performs a specific partial compression ignition combustion in a part of a predetermined operating region. 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 combustion form. That is, when the spark plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17, the air-fuel mixture starts SI combustion by flame propagation. After the start of SI combustion, (1) the temperature inside the combustion chamber 17 rises due to the heat generated by SI combustion, and (2) the pressure inside the combustion chamber 17 rises due to flame propagation, so that the unburned air-fuel mixture is generated. CI combustion by self-ignition.

By adjusting the combustion amount of SI combustion, it is possible to absorb the variation in temperature in the combustion chamber 17 before the start of compression. By adjusting the ignition timing, the amount of SI combustion is adjusted. If the ignition timing is adjusted, the air-fuel mixture will self-ignite at the target timing. In SPCCI combustion, the combustion amount of SI combustion controls the start timing of CI combustion.

As described above, the SPCCI combustion controls the CI combustion by the heat generation and / or the pressure increase due to the 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 correspond to main fuels having different octane numbers.

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

An intake valve 21 is provided at each intake port 18. The intake valve 21 opens and closes the intake port 18 at a predetermined timing by the valve operating mechanism. The valve operating mechanism may be a variable valve timing mechanism that makes the valve timing and / or the valve lift variable.

As shown in FIG. 3, the valve operating mechanism has an intake electric S-VT (Sequential-Valve Timing) 23. The intake electric S-VT23 continuously changes the rotation phase of the intake camshaft within a predetermined angle range. The valve opening angle of the intake valve 21 does not change. The valve opening angle of the intake valve 21 is, for example, 240 ° CA. The valve operating mechanism may have a hydraulic S-VT instead of the electric S-VT.

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

As shown in FIG. 3, the valve operating mechanism has an exhaust electric S-VT24. The exhaust electric S-VT24 continuously changes the rotation phase of the exhaust camshaft within a predetermined angle range. The valve 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 operating mechanism may have a hydraulic S-VT instead of the electric S-VT.

The intake electric S-VT23 and the exhaust electric S-VT24 adjust the length of the overlap period in which both the intake valve 21 and the exhaust valve 22 are opened. By adjusting the length of the overlap period, an internal EGR (Exhaust Gas Recirculation) gas, that is, a hot exhaust gas can be introduced into the combustion chamber 17. The intake electric S-VT23 and the exhaust electric S-VT24 constitute an internal EGR system.

(Injector)
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 central portion of the upper part of the combustion chamber 17.

The injector 6 is a multi-injector type having a plurality of injection holes. The injector 6 injects fuel radially and diagonally downward from the central portion of the ceiling surface of the combustion chamber 17. The injector 6 has 10 injection holes arranged at equal 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 for storing 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 a crankshaft 15. The common rail 64 stores the fuel sent from the fuel pump 65. The inside of the common rail 64 is high voltage. The injector 6 is connected to the common rail 64.

When the injector 6 opens, the high-pressure fuel in the common rail 64 is injected into the combustion chamber 17 from the injection hole of the injector 6. The fuel supply system 61 of this configuration example can supply fuel having 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 fuel pressure according to the operating state of the engine 1. The configuration of the fuel supply system 61 is not limited to the above configuration.

(Spark plug)
A spark plug 25 is attached to the cylinder head 13 for each cylinder 11. The spark plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17. The spark plug 25 is arranged on the intake side of the cylinder 11. The spark plug 25 is located between the two intake ports 18. The electrode of the spark plug 25 faces 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 at 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. The 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 is branched 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 degree of the valve.

The intake passage 40 is also provided with a supercharger 44 downstream of the throttle valve 43. The supercharger 44 increases the pressure of the intake gas introduced into the combustion chamber 17. In this configuration example, the turbocharger 44 is driven by the engine 1. The turbocharger 44 is a roots type, a Rishorum type, a vane type, or a 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 the driving force is transmitted from the engine 1 to the supercharger 44 and a state in which the transmission of the driving force is cut off. When the ECU 10 described later outputs a control signal to the electromagnetic clutch 45, the supercharger 44 is turned on or off.

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 a water-cooled type or an oil-cooled type.

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. The bypass passage 47 bypasses the turbocharger 44 and the intercooler 46. An air bypass valve 48 is provided in the bypass passage 47. The air bypass valve 48 regulates 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. The 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 the supercharged state. The ECU 10 adjusts the opening degree of the air bypass valve 48 when the supercharger 44 is on. A 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 degree of the air bypass valve 48, the pressure of the intake gas introduced into the combustion chamber 17 changes. In addition, "supercharging" means a state in which the pressure in the surge tank 42 dynamically exceeds the atmospheric pressure, and "non-supercharging" means a state in which the pressure in the surge tank 42 dynamically exceeds the atmospheric pressure. It may be defined as the state of becoming.

The intake passage 40 has two branch passages leading 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 degree adjusting valve capable of adjusting the opening degree of the branch passage. When the opening degree is small, the swirl flow in the combustion chamber 17 becomes strong, and when the opening degree is large, the swirl flow in the combustion chamber 17 becomes 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 (cylinder 11) containing a tumble component and a swirl component is contained in the combustion chamber 17. A swirl flow that is 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. The 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 is branched for each cylinder 11.

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. The exhaust gas purification system is not limited to the configuration shown in the figure. For example, GPF may be omitted. Further, the catalytic converter is not limited to the one having a three-way catalyst. Further, the order of the three-way catalyst and the 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 for returning a part of the 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. The downstream end of the EGR passage 52 is connected to the upstream portion of the turbocharger 44 in the intake passage 40.

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

(Exhaust shutter valve)
An exhaust shutter valve 50a is arranged between the branch portion of the EGR passage 52 in the exhaust passage 50 and the downstream catalytic converter. The exhaust shutter valve 50a is an opening degree adjusting valve capable of adjusting the opening degree of the exhaust passage 50. Normally, the opening degree is adjusted to be large (fully open), but if the opening degree is reduced, the exhaust gas becomes difficult to flow and the back pressure increases. The exhaust shutter valve 50a is used for enrichment control described later.

(Cooling system)
FIG. 2 shows a main configuration (circuit diagram) of the cooling device 70 related to the 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. The cooling device 70 has a plurality of cooling water paths other than the above, but illustration and description thereof will be 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 shown by an arrow in FIG. 2, the cooling water path 72 passes the cooling water discharged by the water pump 71 through the block side water jacket 72a, the head side water jacket 72b, and the radiator 73 in this order. Then, it is circulated so as to return to the water pump 71.

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

The radiator 73 is installed near the front grill in the engine room. The cooling water is cooled when it passes through the radiator 73 by heat exchange with the wind or the like introduced into the engine room during traveling.

The thermostat valve 74 is installed at a portion in the cooling water path 72 between the radiator 73 and the water pump 71. 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 flow path of the cooling water. The opening and closing of the valve body 74a is controlled based on a predetermined opening / closing determination temperature. That is, if 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 open / close determination temperature, the valve body 74a is closed (fully closed).

The open / close determination temperature is changed by the heater 74b. That is, the heater 74b is energized according to the control of the ECU. As a result, the heater 74b generates heat and the temperature rises. As the temperature of the heater 74b increases, the open / close determination temperature increases. When the temperature of the heater 74b becomes low, the open / close determination temperature becomes low.

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

The first water temperature sensor SW6a is installed at 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 the cooling water (cooling water temperature) flowing into the engine body 1a. The temperature of the cooling water passing through the thermostat valve 74 is substantially the same as the 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 at 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 the cooling water (engine water temperature) flowing out from the engine body 1a. Since the cooling water flowing out of the engine body 1a passes near the combustion chamber 17, the temperature of the combustion chamber 17 (wall temperature of the combustion chamber 17) can be estimated based on the engine water temperature.

The ECU 10 adjusts the amount of electricity supplied to the heater 74b based on the signals input from each of the first water temperature sensor SW6a and the second water temperature sensor SW6b. As a result, the cooling water temperature is changed, and the temperature of the cooling water is controlled so that the engine water temperature stabilizes at the target temperature. That is, in this engine 1, a "temperature changing means" is configured by the thermostat valve 74 and the ECU 10.

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

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

As shown in FIGS. 1 and 3, various sensors SW1-SW11 are connected to the ECU 10. These sensors SW1-SW11 output a signal to the ECU 10.

The air flow 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 air gas introduced into the combustion chamber 17. The intake pressure sensor SW4 is attached to the surge tank 42 and measures the pressure of the 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 in 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. The 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 of the sensors SW1-SW11. The ECU 10 also calculates the control amount of each device according to a predetermined control logic. The control logic is stored in the memory 102.

The ECU 10 transmits an electric signal related to the control amount to the injector 6, the spark plug 25, the intake electric S-VT23, the exhaust electric S-VT24, the fuel supply system 61, the throttle valve 43, the EGR valve 54, and the electromagnetic clutch of the supercharger 44. Outputs to 45, an air bypass valve 48, a swirl control valve 56, an exhaust shutter valve 50a, a water pump 71, and a heater 74b.

<Octane number determination means>
The control device of the engine 1 includes octane number determination means. The octane number determination means determines the octane number of the fuel. The octane number determination means only needs to be able to determine 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 the fuel may be installed in the fuel supply system 61 and determined by the detected octane number. Further, the octane number may be determined by using a knock sensor or the like.

In the case of the engine 1, in order to perform 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 use this to determine the octane number.

Specifically, the octane number is determined based on the amount of heat generated by SI combustion in SPCCI combustion. With the in-cylinder pressure sensor SW5, such a heat quantity can be detected with high accuracy, so that the octane number can be determined with high accuracy. Moreover, since the existing device is used, there is no need to install a new expensive sensor.

(Judgment of octane number based on SPCCI combustion)
FIG. 4 illustrates a combustion form of SPCCI combustion. In SPCCI combustion, when the spark plug 25 ignites the air-fuel mixture in the combustion chamber 17, SI combustion starts, and the remaining unburned air-fuel mixture is continuously CI-combusted.

The amount of heat (assisted heat amount: Qsa) generated in SI combustion from the ignition timing to the start time of self-ignition 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 that the amount of assist heat is reduced. On the contrary, when the octane number of the fuel is high, the fuel is hard to self-ignite, so that the amount of assist heat increases.

However, the correlation is affected by the operating conditions of the engine, such as the engine load, the engine speed, and the outside air temperature. Therefore, in the memory 102 of the ECU 10, data and a program (heat / RON correlation information) that enable the determination of the octane number of the fuel from the actually measured assist calorific value in consideration of such external factors based on experiments or the like in advance. Is stored.

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

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

(Engine base set)
The ECU 10 changes the basic conditions (base set) for controlling 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 when the octane number of the fuel is equal to or more than a predetermined value. Has a base set of (high octane number map 602).

The predetermined value (octane number that serves as a reference for determining the high or low octane number of the fuel, RON determination value: R0) is an octane number (ron) that can be refueled to the engine 1 and that each of the fuels having different octane numbers can be distinguished. The RON determination value is stored in the memory 102. The RON determination value is preferably a value that can distinguish between regular gasoline and high-octane gasoline. The RON determination value can be set to, for example, "96".

The 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 appropriately burned. 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, in this engine 1, SPCCI combustion is performed as described above. Since SPCCI combustion requires a high degree of combustion control, combustion tends to become unstable when fuels having different octane numbers are used. 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 the SPCCI combustion can be appropriately performed.

The low octane number map 601 mainly sets conditions suitable for fuels having a low octane number (mainly regular gasoline in this case). The high octane number map 602 mainly sets conditions suitable for fuels having a high octane number (here, mainly high-octane gasoline).

In each of the low octane value map 601 and the high octane number map 602, the main control conditions related to combustion correspond to the high and low rotation speeds in the entire operating region of the engine 1 and the high and low loads in the entire operating region of the engine 1. The value is set. Both the low octane number map 601 and the high octane number map 602 are stored in the memory 102.

Specifically, the low octane value 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 intake air. 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, the high octane value 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, when the octane number of the fuel changes from less than the predetermined octane number to more than the predetermined octane number, the ECU 10 switches the low octane number map 601 to the high octane number map 602. Since a plurality of conditions that need to be switched are switched at once, control can be simplified and efficient.

(Cooling water temperature)
Low octane fuels are more prone to abnormal combustion than high octane fuels. Abnormal combustion can be suppressed by performing control that retards the ignition timing (ignition retard control), but in this case, fuel consumption deteriorates. On the other hand, abnormal combustion can also be suppressed by lowering the engine water temperature by adjusting the cooling water and lowering the temperature of the combustion chamber 17. In this case, there is an advantage that the fuel consumption is not deteriorated unlike the ignition retard control.

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

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

On the other hand, at the time of determining the low octane number, the ECU 10 sets, for example, the target engine water temperature to 80 ° C. in order to suppress abnormal combustion. Then, the ECU 10 adjusts the amount of electricity supplied to the heater 74b so that the temperature is maintained at the temperature t1'(for example, ± 5 ° C.) before and after that, and sets the cooling water temperature t1. As a result, the temperature of the combustion chamber 17 (the wall temperature of the combustion chamber 17) is lower than that at the time of determining the high octane number, so that the fuel is less likely to self-ignite and abnormal combustion can be suppressed.

(Operating area of engine 1)
7A and 7B show an example of an operating area map of the engine 1. FIG. 7A is an operation area map at the time of high octane value determination (high RON operation area map 7a), and FIG. 7B is an operation area map at the time of low octane value determination (low RON operation area map 7b). These operating area maps are stored in the memory 102.

These operating area maps are maps of normal operating conditions, so-called warm hours. Other maps are used under certain conditions, such as when cold. The engine 1 operates based on these operating area maps. That is, these operating area maps correspond to the operating areas of the engine 1.

As shown in FIG. 7A, the high RON operating area map 7a is defined by the load of the engine 1 and the rotation speed of the engine 1. The high RON operation region map 7a is divided into four regions, region A1, region A2, region A3, and region A4. The region A1 is a region having a higher rotation speed than Na. The region A2 is a region where the load is lower than La in the region where the rotation speed is Na or less. The region A3 is a region where the load is La or more among the regions where the rotation speed is Na or less. La may be 1/2 of the maximum load of the engine 1.

The area A4 is a specific area partitioned within the area A2. The area A4 is divided into the area A2 and the area A3 on the low load side and the low rotation side. The region A4 corresponds to a specific region on the low load side and the low rotation side even in the entire operating region of the engine 1. The "low speed side" referred to here corresponds to the low speed side when the entire operating region of the engine 1 is bisected into the low speed side and the high speed side. The "low load side" corresponds to the low load side when the entire operating region of the engine 1 is bisected into 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 operated by combustion accompanied by flame propagation due to ignition of the spark plug 25. Intentionally, CI combustion due to self-ignition does not occur.

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

When the engine 1 operates in the area A2, the area A3, and further the area A4, the ECU 10 controls the engine 1 to perform SPCCI combustion. That is, the region A2, the region A3, and the region A4 correspond to a "predetermined operating region" in which a 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 appropriately purified.

In region A3, the turbocharger 44 is on. That is, SPCCI combustion is performed in a supercharged state (supercharged SPCCI). On the other hand, in the area A2, the turbocharger 44 is off. That is, SPCCI combustion is performed by naturally aspirated engine (non-supercharged SPCCI). The turbocharger 44 is also off in the area A4 partitioned in the area A2.

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

Therefore, the operation in the area A4 is superior in fuel efficiency to the operation in the area A2. The regions A2 and A3 in which the stoichiometric air-fuel ratio is set correspond to the "second compartment region", and the region A4 in which the lean air-fuel ratio is set corresponds to the "first compartment region".

When the engine 1 operates in the region A4, the ECU 10 controls to provide an overlap period in which both the intake valve 21 and the exhaust valve 22 are opened. As a result, at the time of combustion, the internal EGR gas is introduced into the combustion chamber 17, and the temperature inside the combustion chamber 17 rises. The ECU 10 stabilizes the SPCCI combustion by adjusting the amount of the internal EGR gas introduced in the region A4.

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

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

On the other hand, in 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) can be performed. It may disappear. Similarly, even on the low rotation side, the combustion period becomes long, so that the amount of heat dissipated increases. As a result, self-ignition becomes difficult due to the temperature drop during combustion, and stable SPCCI combustion (CI combustion) may not be possible.

Further, since lean SPCCI is performed in the region A2 and the region A4 partitioned on the low load side and the low rotation side of the region A3, the amount of heat generated is further smaller. Self-ignition becomes even more difficult. Since the air-fuel mixture around the spark plug 25 tends to be diluted, the ignitability due to ignition also deteriorates. Therefore, there is a risk of misfire or incomplete combustion.

Therefore, when the low octane number is determined, the ECU 10 executes a control (riching control) in which the air-fuel ratio of the region A4 is changed to a richer side than when the high octane number is determined. By changing the air-fuel ratio to the rich side, the amount of fuel increases relatively. As a result, it becomes easy to form an air-fuel mixture that serves as a fire source around the spark plug 25. 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 be stabilized. Therefore, even if the temperature of the combustion chamber 17 is low, appropriate SPCCI combustion can be stably performed.

FIG. 8 shows a portion of the region A4 of the low RON operation region map 7b. In FIG. 8, the degree of enrichment of the air-fuel ratio is schematically shown by dividing it into regions. In the area A4 of the low RON operation area map 7b, the air-fuel ratio is set to be richer than that of the area A4 of the high RON operation area map 7a in the entire area.

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

That is, the higher the load, the richer the air-fuel ratio, that is, the smaller the air-fuel ratio is set (the air-fuel ratio of r5 <r4, the air-fuel ratio of r3, the air-fuel ratio of r2, and the air-fuel ratio of r1). Fuel ratio <air-fuel ratio of region A4 of high RON operating region map 7a). Then, on the high load side, the enrichment is further advanced (the amount of fuel is increased) in response to the change in the load, as compared with the low load side.

Further, the control device of 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, in the region A4 on the low load side (for example, r1), the ECU 10 adjusts the opening degree of the exhaust shutter valve 50a in the closing direction. As a result, the back pressure increases. As described above, since the overlap period is provided in the region A4, the amount of the internal EGR gas introduced into the combustion chamber 17 increases as the back pressure increases. As a result, the temperature inside the combustion chamber 17 rises, and the amount of burned gas in the air-fuel mixture increases. Even if the amount of fuel is not increased to enrich the air-fuel ratio, SPCCI combustion becomes easier, so that fuel efficiency can be improved.

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

(Reduction of area)
When the lean air-fuel ratio of the region 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 is about 15), the combustion temperature is high, so a large amount of NOx is generated. On the other hand, in a lean air-fuel ratio where there is an excess of air with respect to the fuel as in region A4, NOx is hardly generated. When such a lean air-fuel ratio is changed to the rich side as shown by an arrow in FIG. 9, the amount of NOx generated increases. Since the air-fuel ratio at that time deviates greatly from the theoretical air-fuel ratio, it is difficult to properly purify with a three-way catalyst. As a result, NOx emissions increase, leading to deterioration of emissions.

Therefore, the control device of the engine 1 executes control (area reduction control) to reduce the area A4 of the low RON operation area map 7b to be smaller than the area A4 of the high RON operation area map 7a. Specifically, as shown in FIG. 7B, the ECU 10 controls so that the boundary portion of both the high load side and the high rotation side of the area A4 of the low RON operation area map 7b is reduced. Depending on the specifications, the boundary portion of either the high load side or the high rotation side may be controlled to be reduced.

The boundary portion on the high load side of the region A4 has a particularly large amount of fuel in the region A4. Therefore, the amount of NOx emissions that increase due to the enrichment control also increases. Therefore, by reducing such a region, the amount of NOx emissions can be suppressed.

The boundary portion on the high rotation side of the region A4 has a particularly short combustion period and a high combustion temperature in the region A4. Therefore, the amount of NOx emissions that increase due to 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 expanded accordingly. In region A2, since the air-fuel ratio is set to the stoichiometric air-fuel ratio, even if the amount of NOx emissions is large, it can be effectively purified by the three-way catalyst. 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.

(Cooling control)
As shown in FIG. 10, when the operation of the engine 1 is started, the ECU 10 inputs signals from various sensors SW1-SW11 and reads these signals (step S1). Then, the ECU 10 calculates the assist heat amount (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 assist calorific value 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 octane number of the fuel 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 (at the time of low octane number determination), the ECU 10 determines that a fuel having a low octane number such as regular gasoline is used. Then, the ECU 10 sets a low octane number flag (step S4), and executes a water temperature lowering control for setting the set water temperature of the cooling water to 80 ° C. (step S5).

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

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

When the operation of the engine 1 is started, it is preferable to set the set water temperature of one of the cooling waters. In the case of this engine 1, since the geometric compression ratio and the like are set so that stable SPCCI combustion can be performed even with a fuel having a high octane number, it is usually preferable to set the temperature to 100 ° C. Temporarily, the temperature may be set to an intermediate temperature between these, for example, 90 ° C.

(Combustion control)
As shown in FIG. 11, when the operation of the engine 1 is started, the ECU 10 inputs signals from various sensors SW1-SW11 and reads these signals (step S10). Then, the ECU 10 determines whether or not the engine 1 is operating in the region where SPCCI combustion is performed, that is, in the 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 theoretical air-fuel ratio (λ = 1). Control is performed so that SI combustion is performed (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 number determination flag has a low octane number (step S14). As a result, when it is determined that the octane number determination flag is not a low octane number, that is, a high octane number flag is set, the ECU 10 determines whether or not the operating region is the region A4 (step S15).

As a result, when it is determined that the operating region is the 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 the region A4, that is, the region A2 or the 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 number determination flag is set to have a low octane number, that is, a low octane number flag is set, the ECU 10 performs region reduction control for reducing the region A4 of the high RON operation region map 7a. Execute (step S19). As a result, as shown in FIG. 7B, the low RON operation area map 7b is acquired. The low RON operation area map 7b may be set in advance by executing the area reduction control in advance.

Then, the ECU 10 determines whether or not the operating region is the region A4 (step S20). As a result, when it is determined that the operating region is not the region A4, that is, the region A2 or the 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 the region A4, the ECU 10 executes the enrichment control and changes the air-fuel ratio of the region A4 to the rich side (step S21). At this time, SPCCI combustion is executed while adjusting the opening degree of the exhaust shutter valve 50a according to the load of the engine 1 (step S22) (step S17).

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

As described above, according to the control device of the engine 1, fuels having different octane numbers can be refueled, and appropriate SPCCI combustion can be stably performed without causing deterioration of emissions. Therefore, good operation 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 In-cylinder pressure sensor (octane number determination means)

Claims (7)

Cooling water is circulated through an injector that injects a predetermined fuel into the 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. A cooling device is provided, and in a predetermined operating region, a part of the air-fuel mixture is burned by combustion accompanied by flame propagation by ignition of the spark plug, and then the remaining unburned air-fuel mixture is burned by self-ignition. An engine controller that performs specific partial spark plug combustion,
The predetermined operating region includes a first compartment region in which a lean air-fuel ratio is set.
An octane number determining means for determining the octane number of the fuel and
A temperature changing means for changing the temperature of the cooling water and
With
At the time of low octane number determination in which the octane number of the fuel is determined to be less than a preset predetermined value, the water temperature is lowered to lower the temperature of the cooling water as compared with the case of high octane number determination in which the octane number of the fuel is determined to be equal to or higher than the predetermined value. Control and enrichment control for changing the air-fuel ratio of the first compartment region to a richer side than at the time of the high octane number determination are executed, and further, the first compartment region is reduced compared to the time of the high octane number determination. An engine controller that performs area reduction control. In the engine control device according to claim 1,
An engine control device in which at least one boundary portion on the high load side and the high rotation side of the first compartment area is reduced by the area reduction control. In the engine control device according to claim 1 or 2.
An engine control device in which the air-fuel ratio of the first compartment region at the time of determining the high octane number is set to be 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 compartment region in which the stoichiometric air-fuel ratio is set.
An engine control device in which the second compartment area is expanded by reducing the first compartment area. In the engine control device according to claim 4,
An engine control device in which the first compartment region is partitioned into at least one of a low load side and a low rotation side region of the second compartment region. In the engine control device according to any one of claims 1 to 5.
An engine control device in which the octane number determining means determines the octane number of the fuel based on the amount of heat generated in 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 includes an exhaust shutter valve that adjusts the opening degree of the exhaust passage through which the exhaust gas discharged from the combustion chamber flows.
An engine control device that adjusts the opening degree of the exhaust shutter valve in the closing direction when the enrichment control is executed.

Images