JP2020176592A - Control method and control device of engine - Google Patents

Abstract

To provide a control method and a control device of an engine capable of properly securing engine torque while improving fuel consumption performance.SOLUTION: In an operation in a first region A1, a stoichiometric/rich all-cylinder operation execution process is executed for determining an air-fuel ratio of each cylinder 2 to be a theoretical air-fuel ratio or less and burning an air-fuel mixture in all of the cylinders 2, when an operation in second regions B, C is determined, a lean cylinder-reduction operation execution process is executed for determining the air-fuel ratio of each of the cylinders 2 to be higher than the theoretical air-fuel ratio, and burning the air-fuel mixture only in a part of the cylinders, and a switching process is executed for increasing an amount of air to be introduced to each of the cylinders 2 so that the air-fuel ratio of each cylinder 2 becomes higher than the theoretical air-fuel ratio, and burning the air-fuel mixture in all of the cylinders 2 for a prescribed period from determination that the first region A1 is transited to the second regions B, C.SELECTED DRAWING: Figure 6

Description

The present invention relates to an engine control method and an engine control device.

As disclosed in Patent Document 1, in an engine including a plurality of cylinders, it has been studied to carry out a cylinder reduction operation in which the air-fuel mixture is burned only in a part of the cylinders in a part of the operation area. In the reduced cylinder operation, the operation of some cylinders is stopped, so that the fuel efficiency performance of the engine as a whole can be improved.

Further, as a configuration for improving fuel efficiency, a configuration is also known in which the air-fuel mixture is burned in a state where the air-fuel ratio is higher (lean) than the stoichiometric air-fuel ratio.

Japanese Unexamined Patent Publication No. 2006-183556

It is thought that fuel efficiency can be significantly improved if the cylinder reduction operation is carried out and the air-fuel ratio of the cylinders that are operated during the cylinder reduction operation (combustion of the air-fuel mixture is performed) is made higher than the stoichiometric air-fuel ratio. Be done. However, in the reduced cylinder operation with the air-fuel ratio of the cylinder higher than the stoichiometric air-fuel ratio, the engine torque obtained is relatively small, so in some operating regions the air-fuel ratio in the cylinder is close to the stoichiometric air-fuel ratio. It is necessary to do. From this, in the configuration in which the cylinder reduction operation is performed with the cylinder air-fuel ratio higher than the theoretical air-fuel ratio, the operation mode in which the cylinder reduction operation is performed with the cylinder air-fuel ratio higher than the theoretical air-fuel ratio is performed. And, it becomes necessary to switch between the operation mode in which the air-fuel ratio in the cylinder is controlled to be close to the stoichiometric air-fuel ratio. Here, even if the opening degree of the throttle valve is changed, the amount of air introduced into the cylinder does not change immediately. Therefore, immediately after switching from the operation mode in which the air-fuel ratio in the cylinder is controlled to be close to the stoichiometric air-fuel ratio to the operation mode in which the cylinder reduction operation is performed with the air-fuel ratio of the cylinder higher than the stoichiometric air-fuel ratio, each cylinder is used. There is a risk that a sufficient amount of air will not be introduced and proper combustion and thus proper engine torque will not be achieved.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an engine control method and a control device capable of appropriately securing engine torque while improving fuel efficiency.

In order to solve the above-mentioned problems, the present invention is a control method for an engine having a plurality of cylinders, the operation area determination step for determining an area in which the engine is operating, and a predetermined first operation area determination step. The stoichiometric / rich all-cylinder operation implementation process in which the air-fuel ratio of each cylinder is set to the stoichiometric air-fuel ratio or less and the air-fuel mixture is burned in all cylinders, which is carried out when it is determined that the vehicle is operated in one region, and the above-mentioned operation It is carried out when it is determined in the region determination step that the engine is operating in a predetermined second region, and the air-fuel ratio of each cylinder is made higher than the stoichiometric air-fuel ratio and the air-fuel mixture is burned only in some cylinders. When it is determined in the lean cylinder reduction operation execution process for executing the cylinder reduction operation and the operation point of the engine has shifted from the first region to the second region in the operation area determination process, and the lean cylinder reduction operation is started. A switch that is carried out for a predetermined period to increase the amount of air introduced into each cylinder and burn the air-fuel mixture in all cylinders so that the air-fuel ratio of each cylinder is higher than the stoichiometric air-fuel ratio. A method for controlling an engine, including a step, is provided (claim 1).

In this method, in the second region, a lean cylinder reduction operation is performed in which the air-fuel ratio of the cylinders is made higher than the stoichiometric air-fuel ratio and the air-fuel mixture is burned only in a part of the cylinders. Therefore, the fuel efficiency can be surely improved.

Moreover, in this method, the lean cylinder reduction operation is carried out from the first region where the stoichiometric / rich all-cylinder operation in which the air-fuel ratio of each cylinder is set to be equal to or less than the stoichiometric air-fuel ratio and the air-fuel mixture is burned in all cylinders is carried out. At the time of transition to the second region, the amount of air introduced into each cylinder so that the air-fuel ratio of each cylinder becomes higher than the stoichiometric air-fuel ratio during a predetermined period until the lean cylinder reduction operation is started. A switching step is carried out in which the air-fuel mixture is burned in all the cylinders while increasing the air-fuel ratio. That is, immediately after the transition, while the shortage amount of air in each cylinder (the shortage amount with respect to the amount suitable for combustion in the second region) is large, combustion is performed in all cylinders instead of cylinder reduction operation. Cylinder operation is being carried out. Therefore, it is possible to avoid a situation in which the number of operating cylinders is further reduced and an appropriate engine torque cannot be obtained in a state where an insufficient amount of air is large and it is difficult to realize appropriate combustion, and an appropriate engine torque can be secured. ..

The predetermined period can be a period from the transition of the operating point of the engine from the first region to the second region until the end of one combustion in at least all the cylinders (claim 2). ).

As a configuration different from the above, during the predetermined period, from the transition of the engine operating point from the first region to the second region until the amount of intake air introduced into each cylinder reaches a predetermined reference amount. It may be a period (claim 3).

According to these configurations, the cylinder reduction operation can be started when the amount of intake air introduced into each cylinder, that is, the amount of air in each cylinder becomes an air amount suitable for the cylinder reduction operation. It is possible to more reliably realize appropriate combustion.

Further, the present invention is an engine control device having a plurality of cylinders, that is, an air amount changing means capable of changing the amount of air introduced into each cylinder and a fuel supply means capable of supplying fuel to each cylinder individually. The air amount is changed so that the operating state of each cylinder can be switched between the all-cylinder operating state in which the air-fuel mixture burns in all cylinders and the reduced cylinder operating state in which the air-fuel mixture burns only in some cylinders. The control means includes means and a control means for controlling the fuel supply means, and the control means provides the air so that the air-fuel ratio of each cylinder becomes equal to or less than the stoichiometric air-fuel ratio when the engine is operated in a predetermined first region. While controlling the amount changing means, the fuel supply means is controlled so that the operating state of each cylinder becomes the operating state of all cylinders, and when the engine is operated in a predetermined second region, the air-fuel ratio of each cylinder is changed. The air amount changing means is controlled so as to be higher than the stoichiometric air-fuel ratio, and the fuel supply means is controlled so that the operating state of each cylinder is in the reduced cylinder operating state, and the operating point of the engine is the first region. When shifting to the second region, the operating state of each cylinder is in full-cylinder operation for a predetermined period after the transition to the second region and before the operating state of each cylinder is switched to the reduced cylinder operating state. The fuel supply means is controlled so as to be in a state, and the amount of air introduced into each cylinder by the air amount changing means is increased so that the air-fuel ratio of each cylinder becomes higher than the stoichiometric air-fuel ratio. Provided is an engine control device characterized in that the fuel supply means is controlled so that the operating state of each cylinder becomes the reduced cylinder operating state after the predetermined period elapses after shifting to the two regions (claimed). Item 4).

Also with this device, similarly to the above method, it is possible to appropriately secure the engine torque while improving the fuel efficiency performance.

The predetermined period can be a period from the transition of the operating point of the engine from the first region to the second region until the end of one combustion in at least all the cylinders (claim 5). ).

As a configuration different from the above, a predetermined period is set as a period from when the engine operating point shifts from the first region to the second region until the amount of intake air introduced into each cylinder reaches a predetermined reference amount. (Claim 6).

According to these configurations, the cylinder reduction operation is started when the amount of intake air introduced into each cylinder, that is, the amount of air in each cylinder becomes an air amount suitable for the cylinder reduction operation, as in the above method. This makes it possible to more reliably achieve appropriate combustion in each cylinder.

As described above, according to the engine control method and control device of the present invention, it is possible to secure an appropriate engine torque while improving fuel efficiency.

It is a system diagram which shows schematic the whole structure of the engine which concerns on one Embodiment of this invention. It is a block diagram which shows the control system of an engine. It is a map diagram which divided the operating area of an engine by the difference of an operating mode. It is a graph which shows the waveform of the heat generation rate at the time of SPCCI combustion. It is a figure which showed the waveform of the injection pattern and the heat generation rate at the time of SPCCI combustion. It is a flowchart which showed the flow of control when the operation area shifts. It is a figure which showed the time change of each parameter at the time of transition from a 2nd operation area to a lean SPCCI area.

(1) Overall Configuration of Engine FIG. 1 is a system diagram schematically showing the overall configuration of an engine to which the control method and control device of the engine of the present invention are applied. The engine system shown in this figure is mounted on a vehicle and includes an engine body 1 as a power source for traveling. In the present embodiment, a 4-cycle gasoline direct injection engine is used as the engine body 1. In the engine system, in addition to the engine body 1, an intake passage 30 through which intake air introduced into the engine body 1 flows, an exhaust passage 40 through which exhaust gas discharged from the engine body 1 flows, and an exhaust gas flowing through the exhaust passage 40 The EGR device 50 is provided so as to return a part of the EGR device to the intake passage 30.

The engine body 1 can slide back and forth between the cylinder block 3 in which the cylinder 2 is formed, the cylinder head 4 attached to the upper surface of the cylinder block 3 so as to block the cylinder 2 from above, and the cylinder 2. It has an inserted piston 5. The engine body 1 is a multi-cylinder type having a plurality of cylinders 2 (for example, four cylinders 2 arranged in a direction orthogonal to the paper surface of FIG. 1), but here, for simplification, only one cylinder 2 is used. The explanation will proceed focusing on.

A combustion chamber 6 is defined above the piston 5, and fuel containing gasoline as a main component is supplied to the combustion chamber 6 by injection from an injector 15, which will be described later. Then, the supplied fuel burns while being mixed with air in the combustion chamber 6, and the piston 5 pushed down by the expansion force due to the combustion reciprocates in the vertical direction. As the fuel injected into the combustion chamber 6, a fuel containing gasoline as a main component is used. This fuel may contain auxiliary components such as bioethanol in addition to gasoline. In the embodiment, the injector 15 corresponds to the "fuel supply means" of the claim.

Below the piston 5, a crankshaft 7, which is an output shaft of the engine body 1, is provided. The crankshaft 7 is connected to the piston 5 via a connecting rod 8 and is rotationally driven around the central axis in response to the reciprocating motion (vertical motion) of the piston 5.

The geometric compression ratio of the cylinder 2, that is, the ratio of the volume of the combustion chamber 6 when the piston 5 is at the top dead center and the volume of the combustion chamber 6 when the piston 5 is at the bottom dead center is determined by SPCCI combustion described later. A value suitable for (partially compressed ignition combustion) is set to 13 or more and 30 or less.

The cylinder block 3 is provided with a crank angle sensor SN1 that detects the rotation angle (crank angle) of the crankshaft 7 and the rotation speed (engine rotation speed) of the crankshaft 7. Further, the cylinder block 3 is provided with an engine water temperature sensor SN2 that detects the temperature of the engine cooling water for circulating the water jacket formed in the cylinder block 3 to cool the engine body 1.

The cylinder head 4 is provided with an intake port 9 and an exhaust port 10 that open into the combustion chamber 6, an intake valve 11 that opens and closes the intake port 9, and an exhaust valve 12 that opens and closes the exhaust port 10. The valve type of the engine of this embodiment is a 4-valve type of 2 intake valves x 2 exhaust valves, and the intake port 9, the exhaust port 10, the intake valve 11 and the exhaust valve 12 are 2 for each cylinder 2. It is provided one by one. In the present embodiment, a swirl valve 18 that can be opened and closed is provided in one of the two intake ports 9 connected to one cylinder 2, and the swirl flow in the cylinder 2 (turns around the cylinder axis). The strength of the swirling flow) is changed.

The intake valve 11 and the exhaust valve 12 are opened and closed and driven in conjunction with the rotation of the crankshaft 7 by the valve operating mechanisms 13 and 14 including a pair of camshafts and the like arranged on the cylinder head 4.

The valve operating mechanism 13 for the intake valve 11 has a built-in intake VVT 13a capable of changing at least the opening time of the intake valve 11. Similarly, the valve operating mechanism 14 for the exhaust valve 12 includes an exhaust VVT 14a capable of changing at least the closing time of the exhaust valve 12.

In the present embodiment, by controlling the intake VVT 13a and the exhaust VVT 14a, the closing time of the exhaust valve 12 is set to the time on the retard side of the opening time of the intake valve 11, and the intake valve 11 and the exhaust valve 12 are both set. Valve overlap that opens for a predetermined period of time has been realized. Further, by controlling the intake VVT 13a and the exhaust VVT 14a, the valve overlap period, which is the period during which both the intake valve 11 and the exhaust valve 12 are opened, is changed. When the intake valve 11 and the exhaust valve 12 are driven so as to overlap each other, the burned gas is discharged from the combustion chamber 6 to at least one of the intake passage 30 and the exhaust passage 40, and then the burned gas is discharged again. The internal EGR introduced into the combustion chamber 6 is performed. As a result, the burned gas (internal EGR gas) remains in the combustion chamber 6. The amount of the internal EGR gas, which is the burnt gas remaining in the combustion chamber 6, changes depending on the valve overlap period, and the amount of the internal EGR gas is adjusted by adjusting the valve overlap period. The intake VVT 13a (exhaust VVT 14a) may be a variable mechanism of a type that changes only the closing time (opening time) while fixing the opening time (closing time) of the intake valve 11 (exhaust valve 12). It may be a phase-type variable mechanism that simultaneously changes the opening time and closing time of the intake valve 11 (exhaust valve 12).

The cylinder head 4 ignites an injector 15 that injects fuel (mainly gasoline) into the combustion chamber 6 and a mixture of fuel injected from the injector 15 into the combustion chamber 6 and air introduced into the combustion chamber 6. An ignition plug 16 is provided. The cylinder head 4 is further provided with a cylinder pressure sensor SN3 that detects the pressure inside the cylinder, which is the pressure of the combustion chamber 6.

The injector 15 is a multi-injection type injector having a plurality of injection holes at its tip, and can inject fuel radially from the plurality of injection holes. The injector 15 is provided so that its tip portion faces the central portion of the crown surface of the piston 5. Although not shown, in the present embodiment, a cavity is formed in the crown surface of the piston 5 in which a region including the central portion thereof is recessed on the opposite side (lower side) of the cylinder head 4.

The spark plug 16 is arranged at a position slightly offset from the injector 15 on the intake side.

The intake passage 30 is connected to one side surface of the cylinder head 4 so as to communicate with the intake port 9. The air (intake, fresh air) taken in from the upstream end of the intake passage 30 is introduced into the combustion chamber 6 through the intake passage 30 and the intake port 9.

In the intake passage 30, in order from the upstream side, an air cleaner 31 that removes foreign matter in the intake air, a throttle valve 32 that can be opened and closed to adjust the flow rate of the intake air, and a supercharger 33 that sends out the intake air while compressing it are excessive. An intercooler 35 for cooling the intake air compressed by the turbocharger 33 and a surge tank 36 are provided.

Each part of the intake passage 30 is provided with an air flow sensor SN4 for detecting the flow rate (intake amount) of intake air and an intake air temperature sensor SN5 for detecting the temperature of intake air (intake air temperature). The air flow sensor SN4 is provided in a portion of the intake passage 30 between the air cleaner 31 and the throttle valve 32, and detects the flow rate of the intake air passing through the portion. The intake air temperature sensor SN5 is provided in the surge tank 36 and detects the temperature of the intake air in the surge tank 36.

The supercharger 33 is a mechanical supercharger (supercharger) that is mechanically linked to the engine body 1. The specific type of the turbocharger 33 is not particularly limited, but any known turbocharger such as a Rishorum type, a roots type, or a centrifugal type can be used as the supercharger 33. An electromagnetic clutch 34 capable of electrically switching between engagement and release is interposed between the supercharger 33 and the engine body 1. When the electromagnetic clutch 34 is engaged, the driving force is transmitted from the engine body 1 to the supercharger 33, and supercharging is performed by the supercharger 33. On the other hand, when the electromagnetic clutch 34 is released, the transmission of the driving force is cut off, and supercharging by the supercharger 33 is stopped.

The intake passage 30 is provided with a bypass passage 38 for bypassing the supercharger 33. The bypass passage 38 connects the surge tank 36 and the EGR passage 51, which will be described later, to each other. A bypass valve 39 that can be opened and closed is provided in the bypass passage 38. The bypass valve 39 is a valve for adjusting the intake pressure, that is, the boost pressure, which is introduced into the surge tank 36. For example, as the opening degree of the bypass valve 39 increases, the flow rate of the intake air flowing back to the upstream side of the supercharger 33 through the bypass passage 38 increases, and as a result, the boost pressure decreases.

The exhaust passage 40 is connected to the other side surface of the cylinder head 4 so as to communicate with the exhaust port 10. The burnt gas (exhaust) generated in the combustion chamber 6 is discharged to the outside through the exhaust port 10 and the exhaust passage 40.

A catalytic converter 41 is provided in the exhaust passage 40. The catalyst converter 41 includes a three-way catalyst 41a for purifying harmful components (HC, CO, NOx) contained in the exhaust gas, and a GPF (gasoline) for collecting particulate matter (PM) contained in the exhaust gas. -Particulate filter) 41b is built in from the upstream side in this order.

The exhaust passage 40 is provided with an exhaust temperature sensor SN6 that detects the exhaust temperature (exhaust temperature). The exhaust temperature sensor SN6 is provided in a portion of the exhaust passage 40 on the upstream side of the catalytic converter 41.

The EGR device 50 has an EGR passage 51 that connects the exhaust passage 40 and the intake passage 30, and an EGR cooler 52 and an EGR valve 53 provided in the EGR passage 51. The EGR passage 51 connects a portion of the exhaust passage 40 on the downstream side of the catalytic converter 41 and a portion of the intake passage 30 between the throttle valve 32 and the supercharger 33 to each other. The EGR cooler 52 cools the exhaust gas (external EGR gas) that is returned from the exhaust passage 40 to the intake passage 30 through the EGR passage 51 by heat exchange. The EGR valve 53 is provided so as to be openable and closable in the EGR passage 51 on the downstream side (the side closer to the intake passage 30) of the EGR cooler 52, and adjusts the flow rate of the exhaust gas flowing through the EGR passage 51.

The EGR passage 51 is provided with a differential pressure sensor SN7 for detecting the difference between the pressure on the upstream side and the pressure on the downstream side of the EGR valve 53.

(2) Control system FIG. 2 is a block diagram showing an engine control system. The ECU 100 shown in this figure is a microprocessor for comprehensively controlling an engine, and is composed of a well-known CPU, ROM, RAM, and the like.

Detection signals from various sensors are input to the ECU 100. For example, the ECU 100 is electrically connected to the crank angle sensor SN1, engine water temperature sensor SN2, cylinder pressure sensor SN3, airflow sensor SN4, intake air temperature sensor SN5, exhaust temperature sensor SN6, and differential pressure sensor SN7 described above. Information detected by the sensor (that is, crank angle, engine rotation speed, engine water temperature, cylinder pressure, intake amount, intake temperature, exhaust temperature, front-rear differential pressure of EGR valve 53) is sequentially input to the ECU 100. There is. Further, the vehicle is provided with an accelerator sensor SN8 that detects the opening degree of the accelerator pedal operated by the driver who drives the vehicle, and the detection signal by the accelerator sensor SN8 is also input to the ECU 100.

The ECU 100 controls each part of the engine while executing various determinations, calculations, and the like based on the input signals from the respective sensors. That is, the ECU 100 is electrically connected to the intake VVT 13a, the exhaust VVT 14a, the injector 15, the spark plug 16, the swirl valve 18, the throttle valve 32, the electromagnetic clutch 34, the bypass valve 39, the EGR valve 53, and the like. A control signal is output to each of these devices based on the results of the above. The ECU 100 corresponds to the "control means" of the claim. Further, in the present embodiment, the external EGR gas and the internal EGR gas can be introduced into the combustion chamber 6, and are introduced into the combustion chamber 6 depending on the amount of these gases in addition to the opening degree of the throttle valve 32. The amount of air is changing. As a result, the throttle valve 32, the EGR valve 53 that can change the amount of the external EGR gas introduced into the combustion chamber 6, and the intake VVT13a and the exhaust VVT14a that can change the amount of the internal EGR gas remaining in the combustion chamber 6 At least one of them corresponds to the "air amount changing means" of the claim.

(3) Basic Control FIG. 3 is a map diagram for explaining the difference in operation mode according to the engine speed and the engine load. As shown in this figure, the operating area of the engine is roughly divided into three operating areas, a first operating area A, a second operating area B, and a third operating area C.

The third operating region C is an region in which the engine speed is equal to or higher than the predetermined SI speed N4. The first operating region A is a region in which the engine speed is less than the SI implementation speed N4, excluding the region on the high load side, the region on the high speed side, and the region on the extremely low load side. The second operating area B is a residual area other than the first operating area A and the third operating area C.

The first operating region A is further divided into a reduced cylinder lean SPCCI region A1 on the low load side and a full cylinder lean SPCCI region A2 on the high load side. Specifically, in the cylinder reduction lean SPCCI region A1, the engine load is less than the switching load T3 and the cylinder reduction operation start load T1 or more, which is the lower limit load of the first operation region A, and the engine speed is the first rotation speed N1 or more. It is a region where the number of revolutions is less than N2. The whole cylinder lean SPCCI region A2 is a region of the first operating region A excluding the reduced cylinder lean SPCCI region A1. That is, in the all-cylinder lean SPCCI region A2, the engine load is lower than the switching load T3, the all-cylinder lean start load T2 or more and the stoichiometric start load T4 or less, and the engine speed is less than the third rotation speed N3. This is the area excluding a part of the side.

(3-1) SPCCI combustion In the first operating region A and the second operating region B, that is, in the reduced cylinder lean SPCCI region A1, the whole cylinder lean SPCCI region A2 and the second operating region B, SI combustion and CI combustion are performed. Mixed compression ignition combustion (hereinafter referred to as SPCCI combustion) is executed. In addition, "SPCCI" in SPCCI combustion is an abbreviation for "Spark Control Compression Ignition".

SI combustion is a form in which the air-fuel mixture is ignited by a spark plug 16 and the air-fuel mixture is forcibly burned by flame propagation that expands the combustion region from the ignition point to the surroundings. CI combustion is a form in which the air-fuel mixture is burned by self-ignition in an environment where the temperature and pressure are increased by the compression of the piston 5. Then, SPCCI combustion, which is a mixture of these SI combustion and CI combustion, involves SI combustion of a part of the air-fuel mixture in the combustion chamber 6 by spark ignition performed in an environment just before the air-fuel mixture self-ignites, and the SI is burned. It is a combustion mode in which the remaining air-fuel mixture in the combustion chamber 6 is CI-combusted by self-ignition after combustion (due to further increase in temperature and pressure accompanying SI combustion).

FIG. 4 is a graph showing a change in the heat generation rate (J / deg) with respect to the crank angle when SPCCI combustion occurs. In SPCCI combustion, the heat generation during SI combustion is gentler than the heat generation during CI combustion. For example, as shown in FIG. 4, the waveform of the heat generation rate when SPCCI combustion is performed has a relatively small rising slope. Further, the pressure fluctuation in the combustion chamber 6 (that is, dP / dθ: P is the in-cylinder pressure θ is the crank angle) is also gentler during SI combustion than during CI combustion. In other words, the waveform of the heat generation rate during SPCCI combustion is relative to the first heat generation rate portion (the part indicated by M1) formed by SI combustion and having a relatively small rising slope. The second heat generating portion (the portion indicated by M2) having a large rising slope is formed so as to be continuous in this order.

When the temperature and pressure in the combustion chamber 6 increase due to SI combustion, the unburned air-fuel mixture self-ignites and CI combustion is started. As illustrated in FIG. 4, the slope of the waveform of the heat generation rate changes from small to large at the timing of this self-ignition (that is, the timing when CI combustion starts). That is, the waveform of the heat generation rate in SPCCI combustion has an inflection point (X in FIG. 4) that appears at the timing when CI combustion starts.

After the start of CI combustion, SI combustion and CI combustion are performed in parallel. Since CI combustion generates more heat than SI combustion, the heat generation rate is relatively large. However, since CI combustion is performed after the compression top dead center, the slope of the heat generation rate waveform does not become excessive. That is, when the compression top dead center is passed, the motoring pressure decreases due to the lowering of the piston 5, and as a result of suppressing the increase in the heat generation rate, it is possible to avoid excessive dP / dθ during CI combustion. To. In this way, in SPCCI combustion, CI combustion is performed after SI combustion, so that dP / dθ, which is an index of combustion noise, is unlikely to become excessive, and simple CI combustion (when all fuels are CI-combusted). ), Combustion noise can be suppressed.

With the end of CI combustion, SPCCI combustion also ends. Since CI combustion has a faster combustion rate than SI combustion, the combustion end time can be earlier than that of simple SI combustion (when all fuels are SI-combusted). In other words, in SPCCI combustion, the combustion end time can be brought closer to the compression top dead center within the expansion stroke. As a result, in SPCCI combustion, fuel efficiency can be improved as compared with simple SI combustion.

(3-2) First operating region In the first operating region A, that is, in the reduced cylinder lean SPCCI region A1 and the all cylinder lean SPCCI region A2, the air-fuel ratio (A /) in the combustion chamber 6 is improved in order to improve fuel efficiency. SPCCI combustion is carried out while F) is higher (lean) than the stoichiometric air-fuel ratio. In the present embodiment, in the first operating region A, the air-fuel ratio in the combustion chamber 6 is increased to such an extent that the amount of rawNOx, which is NOx generated in the combustion chamber 6, is sufficiently small. For example, in the first operating region A, the air-fuel ratio in the combustion chamber 6 is set to about 30. In the following, SPCCI combustion of an air-fuel mixture having an air-fuel ratio higher than the stoichiometric air-fuel ratio is referred to as lean SPCCI combustion.

In the first operating region A, each part of the engine is driven as follows so that lean SPCCI combustion is realized.

In the first operating region A, the injector 15 injects into the combustion chamber 6 an amount of fuel such that the air-fuel ratio (A / F) in the combustion chamber 6 is higher than the theoretical air-fuel ratio as described above. In this embodiment, the injector 15 is driven so that almost all of the fuel to be supplied to the combustion chamber 6 during one cycle is injected into the combustion chamber 6 during the intake stroke. For example, as shown in FIG. 5, in the first operating region A, most of the fuel is injected during the intake stroke (Q1), and the remaining fuel is injected in two steps during the compression stroke (Q2, Q3). ).

In the first operating region A, as shown in FIG. 5, the spark plug 16 ignites the air-fuel mixture near the compression top dead center. SPCCI combustion is started with this ignition as a trigger, and a part of the air-fuel mixture in the combustion chamber 6 is burned by flame propagation (SI combustion), and then the remaining air-fuel mixture is burned by self-ignition (CI combustion). In addition, in order to activate the air-fuel mixture, additional ignition may be performed before the ignition performed near the compression top dead center.

In the first operating region A, the opening degree of the throttle valve 32 is set to be fully open or close to fully open.

In the first operating region A, the EGR valve 53 is fully closed so that the amount of external EGR gas introduced into the combustion chamber 6 is zero.

The amount of the external EGR gas is set to zero in order to appropriately carry out CI combustion of a part of the air-fuel mixture in the first operating region A. Specifically, in the first operating region A, the engine load is low and the heat energy generated in the combustion chamber 6 is small, so that the temperature in the combustion chamber 6 tends to be low. When the temperature in the combustion chamber 6 is low, the temperature of the air-fuel mixture is not sufficiently raised, so that the combustion rate of SI combustion becomes low and it becomes difficult to generate CI combustion at an appropriate timing. On the other hand, as described above, the external EGR gas is cooled by the EGR cooler 52, and the temperature of the external EGR gas is relatively low. Therefore, if an external EGR gas having a low temperature is introduced into the combustion chamber 6 in the first operating region A, the temperature of the air-fuel mixture may not rise sufficiently and appropriate CI combustion may not be realized. Therefore, in the first operating region A, the introduction of the external EGR gas into the combustion chamber 6 is stopped.

In the first operating region A, the intake VVT 13a and the exhaust VVT 14a drive the intake valve 11 and the exhaust valve 12 so that the intake valve 11 and the exhaust valve 12 overlap each other. In the present embodiment, the intake valve 11 and the exhaust valve 12 are driven so as to open the valve for a predetermined period across the exhaust top dead center. When the valve overlap between the intake valve 11 and the exhaust valve 12 is carried out, the internal EGR is executed as described above, and the high-temperature burnt gas remains in the combustion chamber 6. If the high-temperature burned gas remains in the combustion chamber 6, the temperature of the air-fuel mixture is raised, so that the air-fuel mixture can be appropriately CI-combusted. From this, in the first operation region A, the intake VVT 13a and the exhaust VVT 14a (intake valve 11 and exhaust valve 12) are controlled as described above. In the first operating region A, for example, the valve overlap period of the intake valve 11 and the exhaust valve 12 is set to about 50 to 70 ° CA (crank angle), and is substantially constant over the entire first operating region A.

In the first operating region A, the swirl valve 18 is fully closed or closed to a low opening close to fully closed.

In the first operating region A, the driving of the supercharger 33 is stopped. That is, the electromagnetic clutch 34 is released to release the connection between the supercharger 33 and the engine body 1, and the bypass valve 39 is fully opened to stop the supercharging by the supercharger 33.

The control performed in the first operating region A described above will be referred to as lean SPCCI control as appropriate below.

(All cylinder operation area and reduction cylinder operation area)
In both the reduced cylinder lean SPCCI region A1 and the whole cylinder lean SPCCI region A2, the lean SPCCI control is carried out, and the air-fuel mixture is burned by SPCCI while its air-fuel ratio is higher than the stoichiometric air-fuel ratio. However, the number of cylinders 2 to be operated is different between the reduced cylinder lean SPCCI region A1 and the all cylinder lean SPCCI region A2. In the all-cylinder lean SPCCI region A2, the all-cylinder operation is carried out in which combustion is performed in the combustion chambers 6 of all cylinders 2 and all cylinders 2 are operated. On the other hand, in the cylinder reduction lean SPCCI region A1, the cylinder reduction operation is performed in which combustion is performed only in the combustion chamber 6 of some cylinders 2 and only some cylinders 2 are operated. For example, in an engine having four cylinders 2, only two cylinders 2 are operated and the operation of the two cylinders 2 is stopped. In the following, the cylinder 2 that is operated during the cylinder reduction operation is referred to as an operating cylinder, and the cylinder 2 whose operation is stopped is referred to as a pause cylinder.

As described above, in the cylinder reduction lean SPCCI region A1, the lean SPCCI control is performed and the cylinder reduction operation is performed. On the other hand, in the all-cylinder lean SPCCI region A2, the lean SPCCI control is performed and the whole-cylinder operation is performed. In the cylinder reduction lean SPCCI region A1, as described above, the cylinder reduction operation is carried out while the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 is made higher than the stoichiometric air-fuel ratio. That is, in this cylinder reduction lean SPCCI region A1, a lean cylinder reduction operation is performed in which the air-fuel ratio of each cylinder 2 is set higher than the stoichiometric air-fuel ratio and the air-fuel mixture is burned only in a part of the cylinders 2. There is. From this, in the present embodiment, the reduced cylinder lean SPCCI region A1 corresponds to the "second region" of the claim.

In the present embodiment, the drive of the injector 15 of the pause cylinder 2 is stopped to stop the supply of fuel to the pause cylinder, and only the drive of the injector 15 of the active cylinder is maintained to supply fuel only to the operating cylinder. , Achieve cylinder reduction operation. However, the amount of fuel supplied to the combustion chamber 6 of each cylinder 2 during the cylinder reduction operation is larger than the amount of fuel supplied to the combustion chamber 6 of each cylinder 2 when the full cylinder operation is performed. .. Further, in the cylinder reduction lean SPCCI region A1, the lean SPCCI control is performed even during the cylinder reduction operation, so that the injector 15 of the operating cylinder 2 has a theoretical air-fuel ratio in the combustion chamber 6 as described above. Inject an amount of fuel that is leaner than the air-fuel ratio. In the present embodiment, in the cylinder reduction lean SPCCI region A1, the control of the intake valve 11 and the exhaust valve 12 of the rest cylinder 2 is also the control related to the lean SPCCI control even during the cylinder reduction operation. The intake valve 11 and the exhaust valve 12 of all the cylinders 2 are opened and closed.

(3-3) Second operating region In a region where the engine load or the engine speed is extremely low, the temperature of the air-fuel mixture can be kept low because the combustion energy generated in the combustion chamber 6 is low. In the region where the engine speed is high, the time of the valve overlap period of the intake valve 11 and the exhaust valve 12 is shortened, and the amount of burnt gas remaining in the combustion chamber 6 is reduced, so that the temperature of the air-fuel mixture can be kept low. From this, in these regions, SI combustion becomes slow and it becomes difficult to generate CI combustion at an appropriate timing. On the other hand, if the air-fuel ratio of the air-fuel mixture is set to be equal to or less than the stoichiometric air-fuel ratio, it becomes possible to increase the combustion rate of SI combustion and cause CI combustion at an appropriate timing, and NOx is used as a three-way catalyst 41a. It becomes possible to purify in. Further, in a region where the engine load is high, it becomes difficult to make the air-fuel ratio of the air-fuel mixture lean because the amount of fuel supplied into the combustion chamber 6 is large. From this, in the second operating region B including the extremely low load region, the region where the engine load is higher than the first operating region A, and the region where the engine speed is higher than the first operating region A, the combustion chamber 6 is contained. The air-fuel mixture is SPCCI-combusted while keeping the air-fuel ratio below the theoretical air-fuel ratio. In the present embodiment, in the second operating region B, the air-fuel ratio of the air-fuel mixture is substantially the stoichiometric air-fuel ratio.

In the second operating region B, the opening degree of the throttle valve 32 is set so that the amount of air corresponding to the engine load is introduced into the combustion chamber 6. In the present embodiment, the opening degree of the throttle valve 32 is set to be close to full opening in the second operating region B.

In the second operating region B, the injector 15 injects into the combustion chamber 6 an amount of fuel such that the air-fuel ratio becomes the stoichiometric air-fuel ratio as described above. In this embodiment, the injector 15 is driven so that most of the fuel to be injected during one cycle is injected during the intake stroke and the remaining fuel is injected during the compression stroke.

Also in the second operating region B, the spark plug 16 ignites the air-fuel mixture near the compression top dead center. In the second operating region B as well, SPCCI combustion is started by this ignition, a part of the air-fuel mixture in the combustion chamber 6 is burned by flame propagation (SI combustion), and then the remaining air-fuel mixture is self-ignited. Combustion (CI combustion).

In the second operating region B, the EGR valve 53 is opened and the external EGR gas is introduced into the combustion chamber 6 in order to reduce the NOx generated in the combustion chamber 6. However, when the engine load is high, a large amount of air must be introduced into the combustion chamber 6, so it is necessary to reduce the amount of external EGR gas introduced into the combustion chamber 6. From this, in the second operation region B, the opening degree of the EGR valve 53 is controlled so that the amount of the external EGR gas introduced into the combustion chamber 6 decreases as the load side increases, and the EGR in the region where the engine load becomes maximum. The valve 53 is fully closed.

Also in the second operating region B, the intake VVT 13a and the exhaust VVT 14a drive the intake valve 11 and the exhaust valve 12 so that the intake valve 11 and the exhaust valve 12 overlap each other.

In the second operating region B, the swirl valve 18 is opened to an appropriate intermediate opening degree excluding fully closed / fully opened, and the opening degree is increased as the engine load is higher.

The supercharger 33 is stopped on the side of the second operating region B where both the engine speed and the engine load are low. On the other hand, in the other area of the second operating area B, the supercharger 33 is operated. That is, the electromagnetic clutch 34 is engaged, and the supercharger 33 and the engine body 1 are connected. At this time, the opening degree of the bypass valve 39 is controlled so that the pressure (supercharging pressure) in the surge tank 36 matches the target pressure predetermined for each operating condition (rotation speed / load).

The control performed in the second operating region B described above will be appropriately referred to as stoichiometric SPCCI control below. In the second operating region B, as described above, the whole cylinder operation is performed while the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 is set to be equal to or less than the stoichiometric air-fuel ratio. That is, in the second operating region B, the stoichiometric / rich all-cylinder operation in which the air-fuel ratio of each cylinder 2 is set to the stoichiometric air-fuel ratio or less and the air-fuel mixture is burned in all the cylinders 2 is carried out. In the embodiment, the second operating area B corresponds to the "first area" of the claim.

(3-4) Third Operating Region In the third operating region C, relatively orthodox SI combustion is executed. In order to realize this SI combustion, in the third operating region C, the injector 15 injects fuel for a predetermined period at least overlapping with the intake stroke. The spark plug 16 ignites the air-fuel mixture near the compression top dead center. In the third operating region C, SI combustion is started triggered by this ignition, and all of the air-fuel mixture in the combustion chamber 6 is burned by flame propagation.

In the third operating area C, the supercharger 33 is operated. The throttle valve 32 is fully opened. The opening degree of the EGR valve 53 is controlled so that the air-fuel ratio in the combustion chamber 6 is equal to or less than the stoichiometric air-fuel ratio. For example, in the third operating region C, the opening degree of the EGR valve 53 is controlled so that the air-fuel ratio in the combustion chamber 6 becomes the stoichiometric air-fuel ratio or slightly smaller than this. In the third operating region C, the swirl valve 18 is fully opened. In the third operation area C, the whole cylinder operation is carried out.

The control performed in the third operating region C will be referred to as SI control as appropriate below.

Here, in the present embodiment, even in the third operating region C, the whole cylinder operation is carried out while the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 is set to be equal to or less than the stoichiometric air-fuel ratio. The "first region" also includes the third operating region C.

(4) Operation Mode Switching Control The flow of control executed by the ECU 100 will be described with reference to the flowchart of FIG.

First, in step S1, the ECU 100 acquires the values detected by the sensors SN1 to SN8.

Next, in step S2, the ECU 100 has an operating region in which the engine is currently operating, that is, an operating region including the current operating point (hereinafter, appropriately referred to as a current operating region). It is determined whether it is A2, B, or C. Specifically, the ECU 100 has a current engine load, that is, a required engine torque (required) based on the opening degree of the accelerator pedal detected by the accelerator sensor SN8, the engine speed detected by the crank angle sensor SN1, and the like. (Engine torque) is calculated, and the current operating range is determined from the calculated engine load and the current engine speed.

Next, in step S3, the ECU 100 determines whether or not the current operating region determined in step S2 is the reduced cylinder lean SPCCI region A1.

If the determination in step S3 is NO and the current operating area is not the reduced cylinder lean SPCCI area A1, the process proceeds to step S8. In step S8, it is determined whether or not the current operating area is the all-cylinder lean SPCCI area A2. If this determination is YES and the current operating area is the all-cylinder lean SPCCI area A2, the process proceeds to step S9. In step S9, the ECU 100 executes lean SPCCI control and performs all-cylinder operation to end the process (returns to step S1).

On the other hand, if the determination in step S8 is NO and the current operating area is not the all-cylinder lean SPCCI area A2, the process proceeds to step S10. In step S10, the ECU 100 determines whether or not the current operation area is the second operation area B (stoiki SPCCI area) in which the stoichiometric SPCCI control is performed. If the determination in step S10 is YES and the current operating area is the second operating area B, the process proceeds to step S11. In step S11, the ECU 100 executes stoichiometric SPCCI control and all-cylinder operation to end the process (return to step S1). If the determination in step S10 is NO and the current operating area is not the second operating area B, the process proceeds to step S12. In step S12, the ECU 100 executes SI control, performs all-cylinder operation, and ends the process (returns to step S1).

Returning to step S3, if the determination in step S3 is YES and the current operating area is the reduced cylinder lean SPCCI area A1, the process proceeds to step S4.

In step S4, the ECU 100 determines whether or not it is time to shift from the stoichiometric / rich region to the reduced cylinder lean SPCCI region A1. The stoichiometric / rich region is an operating region in which the air-fuel mixture in the combustion chamber 6 is set to be equal to or lower than the stoichiometric air-fuel ratio, and is a second operating region B and a third operating region C. That is, in step S4, it is determined whether or not the operation point of the engine has shifted from the second operation area B or the third operation area C to the reduced cylinder lean SPCCI area A1. Specifically, in step S4, in step S4, the engine was operated in the second operating region B or the third operating region C before one calculation cycle, and the engine is currently operated in the reduced cylinder lean SPCCI region A1. It is determined whether or not the condition that the condition is satisfied is satisfied.

When the determination in step S4 is NO and not at the time of transition from the stoichiometric region to the reduced cylinder lean SPCCI region A1, for example, at the time of transition from the whole cylinder lean SPCCI region A2 or at the time of transition to the reduced cylinder lean SPCCI region A1. If it is after the switching time described later has elapsed, the process proceeds to step S7.

In step S7, the ECU 100 executes lean SPCCI control and also performs cylinder reduction operation (if these have already been implemented, it is continuously executed).

On the other hand, if the determination in step S4 is YES and the transition from the stoichiometric / rich region to the reduced cylinder lean SPCCI region A1 is in progress, the process proceeds to step S5.

In step S5, the ECU 100 performs lean SPCCI control and full-cylinder operation. In addition, the whole cylinder operation is always carried out in the region other than the reduced cylinder lean SPCCI region A1, and in step S5, the whole cylinder operation is maintained.

Here, as described above, in the lean SPCCI control, each part of the engine is controlled so that the air-fuel ratio in the combustion chamber 6 is higher than the stoichiometric air-fuel ratio. On the other hand, in the stoichiometric / rich region (second operating region B and third operating region C), the air-fuel ratio in the combustion chamber 6 is set to be close to the stoichiometric air-fuel ratio. From this, in step S5, each part of the engine is controlled so that the amount of air introduced into the combustion chamber 6 increases. For example, the throttle valve 32 is opened and the EGR valve 53 is closed.

After step S5, the process proceeds to step S6. In step S6, the ECU 100 determines whether or not a predetermined switching time has elapsed since the operating region shifts from the stoichiometric region to the reduced cylinder lean SPCCI region A1. In the present embodiment, the switching time is set to the time during which combustion is performed once in all cylinders. For example, in a 4-cylinder 4-cycle engine, the switching time is 4 cycles (720 ° CA: CA is the crank angle). The ECU 100 calculates the switching time from the current engine speed and uses it for the determination in step S6.

If the determination in step S6 is NO and the switching time has not yet elapsed since the operation region has shifted from the stoichiometric / rich region to the reduced cylinder lean SPCCI region A1, the ECU 100 returns to step S5. To carry out. That is, the ECU 100 continuously executes the lean SPCCI control and continues the whole cylinder operation.

On the other hand, if the determination in step S6 is YES and the switching time elapses after the operating region shifts from the stoichiometric / rich region to the reduced cylinder lean SPCCI region A1, the process proceeds to step S7. In step S7, the ECU 100 executes lean SPCCI control, performs cylinder reduction operation, and ends the process (returns to step S1). That is, the ECU 100 starts the cylinder reduction operation while continuously performing the lean SPCCI control.

As described above, in the present embodiment, when the operating region shifts from the stoichiometric region to the reduced cylinder lean SPCCI region A1, the lean SPCCI control is performed while the whole cylinder operation is maintained, and the operating region shifts from the stoichiometric region to the reduced cylinder lean SPCCI. The cylinder reduction operation is started only after the switching time elapses after the transition to the area A1.

Here, in the present embodiment, the region in which the engine is being operated is determined in step S2, and step S2 corresponds to the "operating region determination step" of the claim. Further, in step S11, the stoichiometric SPCCI control is carried out so that the air-fuel ratio in the combustion chamber 6 is set to be equal to or less than the stoichiometric air-fuel ratio and the whole cylinder operation is carried out, and this step S11 is the "stoichiki" of the claim. / It corresponds to "rich whole cylinder operation implementation process". Further, in step S7, lean SPCCI control is carried out so that the air-fuel ratio in the combustion chamber 6 is made higher than the stoichiometric air-fuel ratio and the cylinder reduction operation is carried out, and this step S7 is the claim " Corresponds to the "lean reduction cylinder operation implementation process". Further, in step S5, lean SPCCI control is carried out so that the whole cylinder operation is carried out while the air-fuel ratio in the combustion chamber 6 is made higher than the stoichiometric air-fuel ratio, and this step S5 is the claim. Corresponds to the "switching process".

(5) Action, etc. FIG. 7 shows the time change of each parameter when the operating region shifts from the stoichiometric / rich region to the reduced cylinder lean SPCCI region A1. FIG. 7 shows an example in which the operating point of the engine shifts from the point P1 to P2 and the operating region of the engine shifts from the second operating region B to the reduced cylinder lean SPCCI region A1 as shown by the arrow Y1 in FIG. Shown. Further, in an engine having four cylinders 2, the case where the operation of the two cylinders 2 is stopped during the cylinder reduction operation is illustrated.

Until time t1, all cylinders are operated and the number of operating cylinders is four. Further, the stoichiometric SPCCI control is carried out until the time t1. As described above, in the stoichiometric SPCCI control, the external EGR is performed, and the EGR valve 53 is opened until the time t1. In the example of FIG. 7, since the engine load at the operation point P1 is relatively low, the opening degree of the throttle valve 32 is set to the opening side on the closed side rather than the fully opened side until the time t1.

When the amount of depression of the accelerator pedal (accelerator opening) decreases at time t1 and the operating region shifts to the reduced cylinder lean SPCCI region A1, lean SPCCI control is started and the opening of the throttle valve 32 is fully opened. As it is increased, the EGR valve 53 is closed so as to be fully closed. Along with this, the amount of intake air, which is the amount of air introduced into the combustion chamber 6, increases from time t1. However, the throttle valve 32 and the EGR valve 53 have a drive delay. Further, these valves 32 and 53 are separated from the combustion chamber 6, and even if the opening degree of these valves 32 and 53 is changed, the intake air amount is not changed immediately. Therefore, even if the lean SPCCI control is started, the intake amount does not increase immediately, and during the predetermined period after the time t1, the target value of the intake amount at the operation point after the transition shown by the broken line in FIG. 7, that is, , The intake amount is insufficient with respect to the intake amount required to realize appropriate SPCCI combustion at the operation point after the transition.

In such a state where the intake amount is insufficient, appropriate SPCCI combustion cannot be realized. Therefore, if the cylinder reduction operation is started in this state and the number of operating cylinders is reduced, the engine output may be significantly reduced.

On the other hand, in the present embodiment, the number of operating cylinders is maintained at four even after the time t1, and the operation of all cylinders is continued. Therefore, combustion energy can be obtained from all the cylinders 2, and a decrease in engine output is avoided.

Then, when the switching time elapses (at time t2) after the lean SPCCI control is started, the number of operating cylinders is reduced to two and the cylinder reduction operation is started.

At time t2 when the switching time elapses after the lean SPCCI control is started, the intake amount is close to the target value, and the engine output is secured even when the cylinder reduction operation is started. In other words, the switching time is set to the time from the start of the lean SPCCI control to the time when the engine output can be secured even if the intake amount becomes close to the target value and the cylinder reduction operation is started. Since it is known that this switching time is about the same as the time during which combustion is performed once in all cylinders, in the present embodiment, as described above, this switching time is once in all cylinders. It is set to the time when combustion is performed one by one.

As described above, in the present embodiment, in the reduced cylinder lean SPCCI region A1, a combustion mode in which the air-fuel mixture is burned in a state where the air-fuel ratio in the combustion chamber 6 is higher than the stoichiometric air-fuel ratio is adopted, and the operating cylinder is operated. The cylinder reduction operation is carried out. Therefore, the fuel efficiency can be surely improved. In particular, in the present embodiment, SPCCI combustion having high fuel efficiency is carried out in the reduced cylinder lean SPCCI region A1, and the fuel efficiency can be significantly improved. Then, in the second operating region B and the third operating region C where the engine load is high, the engine load is dealt with by introducing a large amount of air into the combustion chamber 6 with the air-fuel ratio in the combustion chamber 6 being close to the stoichiometric air-fuel ratio. It is also possible to achieve a high engine torque. Further, by setting the air-fuel ratio in the combustion chamber 6 to be close to the stoichiometric air-fuel ratio even in a region where the engine load is extremely low, it is possible to prevent deterioration of combustion stability in such a region.

However, the reduced cylinder lean SPCCI region A1 region in which the cylinder reducing operation is performed while burning the air-fuel mixture in a state where the air-fuel ratio in the combustion chamber 6 is higher than the theoretical air-fuel ratio in this way, and the air-fuel ratio in the combustion chamber 6 When the region where the air-fuel ratio is equal to or less than the theoretical air-fuel ratio, that is, the stoichiometric / rich region is mixed, and the transition from the stoichiometric / rich region to the reduced cylinder lean SPCCI region A1 region, as described above, the air in the combustion chamber 6 There is a risk that the cylinder reduction operation will be carried out in a state where the amount is insufficient, and the engine output may decrease accordingly. On the other hand, in the present embodiment, lean SPCCI control is performed from the above transition to the elapse of the switching period, and the EGR valve 53 is fully closed or the throttle valve 32 is opened. While increasing the amount of air introduced into each combustion chamber 6 so that the air-fuel ratio in the combustion chamber 6 is higher than the theoretical air-fuel ratio, the whole cylinder operation is continued to generate combustion energy in more cylinders 2. I am doing it. Therefore, it is possible to prevent the engine output from dropping sharply with the transition.

(6) Modified Example In the above embodiment, the case where the air-fuel mixture is SPCCI-combusted in the operation region in which the cylinder reduction operation is performed while making the air-fuel ratio of the combustion chamber 6 higher than the theoretical air-fuel ratio has been described. The combustion form of the air-fuel mixture in the region is not limited to SPCCI combustion. However, as described above, if SPCCI combustion is carried out, the fuel efficiency performance can be remarkably improved. Further, the combustion mode in other operating regions is not limited to the mode described in the above embodiment.

Further, in the above-described embodiment, both when the operating region shifts from the second operating region B to the reduced cylinder lean SPCCI region A1 and when the operating region shifts from the third operating region C to the reduced cylinder lean SPCCI region A1. In the above section, the case where the whole cylinder operation is performed while the lean SPCCI control is performed has been described, but only when the cylinder is reduced from one of the operation areas B and the third operation area C to the reduced cylinder lean SPCCI area A1. It may be configured to carry out whole cylinder operation while carrying out SPCCI control.

Further, in the above-described embodiment, the case where the switching time is set to the time during which combustion is performed once in all the cylinders 2 has been described, but the switching time is not limited to this and is set to a preset time. May be good. Further, the switching time is determined by the amount of intake air introduced into the combustion chamber 6, that is, the amount of air introduced into the combustion chamber 6 after the operating region shifts from the stoichiometric / rich region to the reduced cylinder lean SPCCI region A1. It may be set to the time until it becomes a fixed amount. In this way, it is possible to start the cylinder reduction operation when the intake amount is more reliably secured, so that the air-fuel mixture can be reliably burned in an appropriate state in each cylinder 2. , It is possible to surely avoid a decrease in engine output. In particular, if the predetermined amount is set to the target value in the transition destination, that is, the cylinder reduction lean SPCCI region A1, the cylinder reduction operation can be started more reliably in a state where the intake air amount is appropriately secured, which is even more reliable. Appropriate combustion can be achieved. Further, the number of cylinders of the engine is not limited to four, and in the present embodiment, it can be applied to an engine having a plurality of cylinders 2.

1 Engine body 2 Cylinder 6 Combustion chamber 15 Injector (fuel supply means)
32 Throttle valve (means for changing air volume)
53 EGR valve (air amount changing means)
100 ECU (control means)
A1 reduced cylinder lean SPCCI area (first area)
B Second operating area (second area)
C Third operating area (second area)

Claims (6)

A control method for an engine with multiple cylinders.
An operating area determination process that determines the area in which the engine is operating, and
It is carried out when it is determined in the operation area determination step that the vehicle is operating in a predetermined first region, and the air-fuel ratio of each cylinder is set to be equal to or less than the stoichiometric air-fuel ratio, and the air-fuel mixture is burned in all cylinders. All cylinder operation implementation process and
It is carried out when it is determined in the operation area determination step that the vehicle is operating in a predetermined second region, the air-fuel ratio of each cylinder is made higher than the stoichiometric air-fuel ratio, and the air-fuel mixture is burned only in some cylinders. Lean cylinder reduction operation implementation process and lean cylinder reduction operation
Each cylinder is carried out for a predetermined period when it is determined in the operation area determination step that the operation point of the engine has shifted from the first area to the second area and before the lean cylinder reduction operation is started. An engine control method comprising a switching step of increasing the amount of air introduced into each cylinder and burning the air-fuel mixture in all cylinders so that the air-fuel ratio of the engine becomes higher than the stoichiometric air-fuel ratio. .. In the engine control method according to claim 1,
The predetermined period is a period from the transition of the operating point of the engine from the first region to the second region until the end of one combustion in at least all the cylinders. Control method. In the engine control method according to claim 1,
The predetermined period is a period from when the operating point of the engine shifts from the first region to the second region until the amount of intake air introduced into each cylinder reaches a predetermined reference amount. How to control the engine. An engine control device with multiple cylinders
An air amount changing means that can change the amount of air introduced into each cylinder,
A fuel supply means that can supply fuel to each cylinder individually,
The air amount changing means and the above-mentioned air amount changing means so that the operating state of each cylinder can be switched between the all-cylinder operating state in which the air-fuel mixture burns in all cylinders and the reduced cylinder operating state in which the air-fuel mixture burns only in some cylinders. A control means for controlling the fuel supply means is provided.
The control means
When the engine is operating in the predetermined first region, the air amount changing means is controlled so that the air-fuel ratio of each cylinder becomes equal to or less than the stoichiometric air-fuel ratio, and the operating state of each cylinder becomes the operating state of all cylinders. By controlling the fuel supply means so as to
When the engine is operating in a predetermined second region, the air amount changing means is controlled so that the air-fuel ratio of each cylinder becomes higher than the stoichiometric air-fuel ratio, and the operating state of each cylinder is set to the reduced cylinder operating state. By controlling the fuel supply means so as to
When the operating point of the engine shifts from the first region to the second region, during a predetermined period after the shift to the second region and before the operating state of each cylinder is switched to the reduced cylinder operating state. The fuel supply means is controlled so that the operating state of each cylinder becomes the operating state of all cylinders, and the fuel supply means is introduced into each cylinder by the air amount changing means so that the air-fuel ratio of each cylinder becomes higher than the stoichiometric air-fuel ratio. The fuel supply means is controlled so that the amount of air is increased and the operating state of each cylinder becomes the reduced cylinder operating state after the predetermined period elapses after shifting to the second region. Engine control device. In the engine control device according to claim 4,
The predetermined period is a period from the transition of the operating point of the engine from the first region to the second region until the end of one combustion in at least all the cylinders. Control device. In the engine control device according to claim 4,
The predetermined period is a period from when the operating point of the engine shifts from the first region to the second region until the amount of intake air introduced into each cylinder reaches a predetermined reference amount. Engine control device.

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