JP2020169593A - Control device and control method for internal combustion engine - Google Patents

Abstract

To achieve both suppression of NOx emission and ensuring of combustion stability in an internal combustion engine capable of lean combustion operation.SOLUTION: A control method for an internal combustion engine (engine 1) includes: a step in which a control unit (ECU 10) sets a target value of a fuel ratio of an air-fuel mixture; a step in which the control unit estimates a fuel ratio in the case where the fuel ratio deviates maximally to a lean side with respect to the set target value, on the basis of an actual degree of variation in the fuel ratio; a step in which the control unit sets an initial value richer than the target value when the estimated fuel ratio exceeds a lean limit, which is determined based on combustion stability; a step in which the control unit adjusts an in-cylinder state quantity and a fuel amount of the internal combustion engine through a sate quantity adjustment part and a fuel supply part so as to have the initial value, and causes the air-fuel mixture to be combusted; and a step in which the control unit, after the combustion step, adjusts the in-cylinder state quantity and the fuel amount so as to have the target value or a fuel ratio close to the target value, and causes the air-fuel mixture to be combusted.SELECTED DRAWING: Figure 6

Description

The techniques disclosed herein relate to control devices and control methods for internal combustion engines.

U.S. Pat. ing. This engine delays the ignition timing to the extent that it does not misfire while increasing the boost pressure during the transition from the stoichiometric combustion mode to the lean combustion mode. As a result, the engine increases the boost pressure while maintaining the torque before switching. Then, when the boost pressure reaches the target boost pressure, the engine changes the air-fuel ratio to the lean air-fuel ratio.

JP-A-2018-48610

If the fuel ratio of the air-fuel mixture is made leaner than the stoichiometric air-fuel ratio, the three-way catalyst cannot purify NOx in the exhaust gas. Therefore, the engine must make the air-fuel mixture significantly lean so that the RawNOx generated in the combustion chamber during the lean combustion operation is reduced. The term "fuel ratio" is used here as a general term for the ratio of air to fuel in the combustion chamber (that is, A / F) and the ratio of gas to fuel in the combustion chamber (that is, G / F). ing.

On the other hand, even if the fuel ratio is adjusted to the target, due to the variation of the device that adjusts the amount of air and / or the amount of EGR gas introduced into the combustion chamber and the variation of the sensor that measures the fuel ratio, The actual fuel ratio varies with respect to the target fuel ratio.

If the target fuel ratio is significantly lean and the actual fuel ratio is leaner than the target fuel ratio, the air-fuel mixture becomes excessively lean and combustion may become unstable.

The technology disclosed herein achieves both suppression of NOx emissions and ensuring combustion stability in an internal combustion engine capable of lean combustion operation.

The technique disclosed herein relates to a control method for an internal combustion engine capable of lean combustion operation in which the fuel ratio of the air-fuel mixture introduced into the combustion chamber is made larger than the stoichiometric air-fuel ratio. This control method
A step in which the control unit sets a target value of the fuel ratio of the air-fuel mixture according to the operating state of the internal combustion engine.
A step in which the control unit estimates the fuel ratio when the fuel ratio deviates to the lean side as much as possible with respect to the set target value based on the actual degree of variation in the fuel ratio.
A step in which the control unit sets an initial value richer than the target value when the estimated fuel ratio exceeds the lean limit determined based on combustion stability.
A step of adjusting the in-cylinder state amount and the fuel amount of the internal combustion engine and burning the air-fuel mixture through the state amount adjusting unit and the fuel supply unit so that the control unit has the initial value.
After the combustion step, the in-cylinder state amount is reached through the state amount adjusting unit and the fuel supply unit so that the control unit reaches the target value or has a fuel ratio approaching the target value. And the step of adjusting the amount of fuel and burning the air-fuel mixture,
Is equipped with.

According to this configuration, the control unit sets a target value of the fuel ratio of the air-fuel mixture according to the operating state of the internal combustion engine. The target value may be set, for example, to be a fuel ratio that reduces RawNOx. In that case, the fuel ratio is significantly leaner than the stoichiometric air-fuel ratio.

When the target value is set, the control unit estimates the fuel ratio when the fuel ratio deviates to the lean side as much as possible with respect to the target value based on the actual degree of variation in the fuel ratio. The actual degree of variation in the fuel ratio may be determined based on various measured values measured during the operation of the internal combustion engine. If the estimated fuel ratio exceeds the lean limit, combustion may become unstable. When the estimated fuel ratio exceeds the lean limit, the control unit sets an initial value richer than the target value. The initial value may be set to a value that does not increase RawNOx. If the estimated fuel ratio does not exceed the lean limit, it is not necessary to set the initial value.

The control unit adjusts the in-cylinder state amount and the fuel amount so as to obtain the set initial value. The adjustment of the in-cylinder state amount is the adjustment of the amount of air and the amount of EGR gas introduced into the cylinder. Even if the actual fuel ratio deviates to the lean side as much as possible, the fuel ratio does not exceed the lean limit. The air-fuel mixture burns stably.

After the combustion step, the control unit adjusts the in-cylinder state amount and the fuel amount so as to reach the target value or to obtain a fuel ratio approaching the target value. That is, the fuel ratio is set to be leaner than the initial value. The fuel ratio of the air-fuel mixture can be changed to a fuel ratio corresponding to the operating state of the internal combustion engine while the air-fuel mixture is stably burned. As a result, in an internal combustion engine capable of lean combustion operation, both NOx emission suppression and combustion stability can be ensured. When the internal combustion engine operates in a lean combustion manner, the fuel efficiency of the automobile equipped with the internal combustion engine is improved.

The control unit may execute the step of bringing the fuel ratio closer to the target value a plurality of times.

That is, the control unit gradually brings the fuel ratio of the air-fuel mixture closer to the target value from the initial value. As a result, NOx emissions are suppressed and the combustion stability of the air-fuel mixture is ensured.

When the actual fuel ratio exceeds the lean limit, the control unit may stop bringing the fuel ratio closer to the target value.

By doing so, the fuel ratio does not become excessively lean, and the combustion of the air-fuel mixture is suppressed from becoming unstable.

The control unit may bring the fuel ratio closer to the target value by keeping the amount of fuel constant and increasing the opening degree of the throttle valve.

By doing so, it becomes possible to bring the fuel ratio closer to the target value while maintaining the combustion stability.

The control unit may set the initial value when switching the internal combustion engine from the stoichiometric combustion operation to the lean combustion operation.

When switching from the stoiki combustion operation to the lean combustion operation, the fuel ratio of the air-fuel mixture changes significantly. The variation in the fuel ratio at the time of switching becomes large, and the actual fuel ratio deviates from the target value, which may exceed the lean limit.

When switching from the stoiki combustion operation to the lean combustion operation, if the fuel ratio is adjusted based on the initial value, it is possible to suppress NOx emissions and secure combustion stability at the same time.

The technique disclosed herein relates to a control device for an internal combustion engine capable of lean combustion operation. In this control device, the fuel supply unit attached to the internal combustion engine, the state amount adjusting unit for adjusting the in-cylinder state amount of the internal combustion engine, and the fuel ratio of the air-fuel mixture set according to the operating state of the internal combustion engine. A control unit that outputs a control signal to the fuel supply unit and the state amount adjusting unit is provided according to the target value of.

The control unit
An estimation unit that estimates the fuel ratio when the fuel ratio deviates to the lean side to the maximum with respect to the set target value based on the actual degree of variation in the fuel ratio.
When the estimated fuel ratio exceeds the lean limit determined based on combustion stability, an initial value setting unit that sets an initial value richer than the target value, and an initial value setting unit.
It has a state amount adjusting unit and a fuel ratio adjusting unit that adjusts the in-cylinder state amount and the fuel amount through the fuel supply unit and burns the air-fuel mixture so as to have the initial values.
After the combustion, the fuel ratio adjusting unit is in the in-cylinder state through the state amount adjusting unit and the fuel supply unit so as to reach the target value or to have a fuel ratio approaching the target value. The amount and the amount of the fuel are adjusted, and the air-fuel mixture is burned.

The fuel ratio adjusting unit may execute the fuel ratio approaching the target value a plurality of times.

When the actual fuel ratio exceeds the lean limit, the fuel ratio adjusting unit may stop bringing the fuel ratio closer to the target value.

The fuel ratio adjusting unit may bring the fuel ratio closer to the target value by keeping the fuel amount constant and increasing the opening degree of the throttle valve.

The initial value setting unit may set the initial value when the internal combustion engine is switched from the stoichiometric combustion operation to the lean combustion operation.

As described above, the above-mentioned internal combustion engine control device and control method can both suppress NOx emissions and ensure combustion stability in an internal combustion engine capable of lean combustion operation.

FIG. 1 is a diagram illustrating an engine configuration. FIG. 2 is a diagram illustrating the configuration of the combustion chamber, the upper diagram is a plan view equivalent view of the combustion chamber, and the lower diagram is a sectional view taken along line II-II. FIG. 3 is a block diagram illustrating the configuration of the engine control device. FIG. 4 is a diagram illustrating a waveform of SPCCI combustion. FIG. 5 is a diagram illustrating an engine operation map. FIG. 6 is a diagram illustrating the relationship between the fuel ratio and RawNOx and the relationship between the fuel ratio and SDI. FIG. 7 is a block diagram illustrating a functional block of an ECU that executes control related to fuel ratio adjustment. FIG. 8 is a flowchart illustrating basic control of the engine. FIG. 9 is a flowchart relating to the setting of the target fuel ratio. FIG. 10 is a time chart illustrating changes in the operation mode, fuel ratio, throttle opening, fuel injection amount, and RawNOx when switching from the stoichiometric combustion operation to the lean combustion operation.

Hereinafter, embodiments relating to the control device of the internal combustion engine will be described in detail with reference to the drawings. The following description is an example of an engine as an internal combustion engine and an engine control device.

FIG. 1 is a diagram illustrating the configuration of an engine system. FIG. 2 is a diagram illustrating the configuration of the combustion chamber of the engine. The intake side in FIG. 1 is on the left side of the paper, and the exhaust side is on the right side of the paper. The intake side in FIG. 2 is on the right side of the paper, and the exhaust side is on the left side of the paper. FIG. 3 is a block diagram illustrating the configuration of the engine control device.

The engine 1 is a 4-stroke engine operated by the combustion chamber 17 by repeating an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. The engine 1 is mounted on a four-wheeled vehicle. When the engine 1 is driven, the automobile runs. The fuel of the engine 1 is gasoline in this configuration example. The fuel may be at least a liquid fuel containing gasoline. The fuel may be gasoline containing, for example, bioethanol.

(Engine configuration)
The engine 1 includes a cylinder block 12 and a cylinder head 13 mounted on the cylinder block 12. A plurality of cylinders 11 are formed inside the cylinder block 12. 1 and 2 show only one cylinder 11. The engine 1 is a multi-cylinder engine.

A piston 3 is slidably inserted in each cylinder 11. The piston 3 is connected to the crankshaft 15 via a connecting rod 14. The piston 3 partitions the combustion chamber 17 together with the cylinder 11 and the cylinder head 13. The "combustion chamber" may be used in a broad sense. That is, the "combustion chamber" may mean 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, that is, the ceiling surface of the combustion chamber 17, is composed of an inclined surface 1311 and an inclined surface 1312 as shown in the lower figure of FIG. The inclined surface 1311 has an upward slope from the intake side toward the injection axis X2 of the injector 6, which will be described later. The inclined surface 1312 has an upward slope from the exhaust side toward the injection axis X2. The ceiling surface of the combustion chamber 17 has a so-called pent roof shape.

The upper surface of the piston 3 is raised toward the ceiling surface of the combustion chamber 17. A cavity 31 is formed on the upper surface of the piston 3. The cavity 31 is recessed from the upper surface of the piston 3. The cavity 31 has a shallow dish shape in this configuration example. The center of the cavity 31 is displaced toward the exhaust side from the central axis X1 of the cylinder 11.

The geometric compression ratio of the engine 1 is set to 10 or more and 30 or less. As will be described later, the engine 1 performs SPCCI combustion, which is a combination of SI combustion and CI combustion, in a part of the operating region. SPCCI combustion controls CI combustion by utilizing heat generation and pressure increase due to SI combustion. The engine 1 is a compression ignition type. In this engine 1, it is not necessary to raise the temperature of the combustion chamber 17 (that is, the compression end temperature) when the piston 3 reaches the compression top dead center. The engine 1 can set the geometric compression ratio relatively low. Lowering the geometric compression ratio is advantageous in reducing cooling loss and mechanical loss. The geometric compression ratio of engine 1 is 14 to 17 for regular specifications (low octane fuel with a fuel octane number of about 91) and 15 for high octane specifications (high octane fuel with a fuel octane number of about 96). It may be ~ 18.

An intake port 18 is formed in the cylinder head 13 for each cylinder 11. Although not shown, the intake port 18 has a first intake port and a second intake port. The intake port 18 communicates 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 formed in the combustion chamber 17.

An intake valve 21 is provided at the intake port 18. The intake valve 21 opens and closes between the combustion chamber 17 and the intake port 18. The intake valve 21 is opened and closed at a predetermined timing by the valve operating mechanism. The valve operating mechanism may be a variable valve operating mechanism that makes the valve timing and / or the valve lift variable. In this configuration example, as shown in FIG. 3, the variable valve timing 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 timing and valve closing timing of the intake valve 21 change continuously. The intake valve mechanism may have a hydraulic S-VT instead of the electric S-VT. The intake valve 21 and the intake electric S-VT23 are examples of the state quantity adjusting unit.

An exhaust port 19 is also formed in the cylinder head 13 for each cylinder 11. The exhaust port 19 also has a first exhaust port and a second exhaust port. The exhaust port 19 communicates with the combustion chamber 17.

An exhaust valve 22 is provided at the exhaust port 19. The exhaust valve 22 opens and closes between the combustion chamber 17 and the exhaust port 19. The exhaust valve 22 is opened and closed at a predetermined timing by the valve operating mechanism. This valve operating mechanism may be a variable valve operating mechanism that makes the valve timing and / or the valve lift variable. In this configuration example, as shown in FIG. 3, the variable valve 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 timing and valve closing timing of the exhaust valve 22 change continuously. The exhaust valve mechanism may have a hydraulic S-VT instead of the electric S-VT. The exhaust valve 22 and the exhaust electric S-VT24 are examples of the state quantity adjusting unit.

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 increasing the length of the overlap period, the residual gas in the combustion chamber 17 can be scavenged. Further, by adjusting the length of the overlap period, the internal EGR (Exhaust Gas Recirculation) 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. The internal EGR system is not limited to the one configured by S-VT.

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 an example of a fuel supply unit. The injector 6 is arranged at a valley portion of the pent roof where the inclined surface 1311 and the inclined surface 1312 intersect. As shown in FIG. 2, the injection axis X2 of the injector 6 is located on the exhaust side of the central axis X1 of the cylinder 11. The injection axis X2 of the injector 6 is parallel to the central axis X1. The injection axis X2 of the injector 6 and the center of the cavity 31 coincide with each other. The injector 6 faces the cavity 31. The injection axis X2 of the injector 6 may coincide with the central axis X1 of the cylinder 11. In the case of that configuration, the injection axis X2 of the injector 6 and the center of the cavity 31 may coincide with each other.

Although detailed illustration is omitted, the injector 6 is composed of a multi-injection type fuel injection valve having a plurality of injection ports. The injector 6 injects fuel so that the fuel spray spreads radially from the center of the combustion chamber 17, as shown by the alternate long and short dash line in FIG. In the present configuration example, the injector 6 has ten injection holes, and the injection holes are arranged at equal angles 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 configured to store fuel, and a fuel supply path 62 that 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 at a high fuel pressure. When the injector 6 opens, the fuel stored in the common rail 64 is injected into the combustion chamber 17 from the injection port of the injector 6. The fuel supply system 61 can supply fuel having a high pressure of 30 MPa or more to the injector 6. The pressure of the fuel supplied to the injector 6 may be changed according to the operating state of the engine 1. The configuration of the fuel supply system 61 is not limited to the above configuration.

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. In this configuration example, the spark plug 25 is arranged on the intake side of the central axis X1 of the cylinder 11. The spark plug 25 is located between the two intake ports 18. The spark plug 25 is attached to the cylinder head 13 so as to be inclined from the upper side to the lower side toward the center of the combustion chamber 17. As shown in FIG. 2, the electrode of the spark plug 25 faces the inside of the combustion chamber 17 and is located near the ceiling surface of the combustion chamber 17. The spark plug 25 may be arranged on the exhaust side of the central axis X1 of the cylinder 11. Further, the spark plug 25 may be arranged on the central axis X1 of the cylinder 11.

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 gas introduced into the combustion chamber 17 flows through the intake passage 40. An air cleaner 41 is provided at the upstream end of the intake passage 40. The air cleaner 41 filters fresh air. 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 constitutes an independent passage that branches for each cylinder 11. The downstream end of the independent passage is connected to the intake port 18 of each cylinder 11.

A throttle valve 43 is provided between the air cleaner 41 and the surge tank 42 in the intake passage 40. The throttle valve 43 adjusts the amount of fresh air introduced into the combustion chamber 17 by adjusting the opening degree of the valve. The throttle valve 43 is an example of a state amount adjusting unit.

In the intake passage 40, a supercharger 44 is also arranged downstream of the throttle valve 43. The supercharger 44 supercharges the gas to be introduced into the combustion chamber 17. In this configuration example, the supercharger 44 is a mechanical supercharger driven by the engine 1. The mechanical turbocharger 44 may be 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 transmits a driving force from the engine 1 to the supercharger 44 or cuts off the transmission of the driving force between the supercharger 44 and the engine 1. As will be described later, the turbocharger 44 is switched on and off by switching the connection and disconnection of the electromagnetic clutch 45 by the ECU 10.

An intercooler 46 is arranged downstream of the supercharger 44 in the intake passage 40. The intercooler 46 cools the gas compressed in the supercharger 44. The intercooler 46 may be configured as, for example, 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 so as to bypass the supercharger 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 turned off (that is, when the electromagnetic clutch 45 is disengaged). The gas flowing through the intake passage 40 bypasses the supercharger 44 and is introduced into 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 turned 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 turned on (that is, when the electromagnetic clutch 45 is connected). A part of the gas that has passed through the supercharger 44 flows back 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 boost pressure of the gas introduced into the combustion chamber 17 changes. The supercharging time is defined as the time when the pressure in the surge tank 42 exceeds the atmospheric pressure, and the non-supercharging time is defined as the time when the pressure in the surge tank 42 becomes the atmospheric pressure or less. May be good.

In this configuration example, the supercharging system 49 is configured by the supercharger 44, the bypass passage 47, and the air bypass valve 48. The supercharging system 49 is an example of a state amount adjusting unit.

The engine 1 has a swirl generating portion that generates a swirl flow in the combustion chamber 17. The swirl flow flows as shown by the white arrows in FIG. The swirl generator has a swirl control valve 56 attached to the intake passage 40. Although not shown in detail, the swirl control valve 56 is provided in a secondary passage among a primary passage connected to one intake port 18 of the two intake ports 18 and a secondary passage connected to the other intake port 18. It is arranged. The swirl control valve 56 is an opening degree adjusting valve capable of narrowing the cross section of the secondary passage. When the opening degree of the swirl control valve 56 is small, the intake flow from one intake port 18 to the combustion chamber 17 is relatively large, and the intake flow from the other intake port 18 to the combustion chamber 17 is relatively small. , The swirl flow in the combustion chamber 17 becomes stronger. When the opening degree of the swirl control valve 56 is large, the intake flow rates entering the combustion chamber 17 from each of the two intake ports 18 become substantially equal, so that the swirl flow in the combustion chamber 17 becomes weak. When the swirl control valve 56 is fully opened, no swirl flow is generated.

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 passage 50 is a passage through which the exhaust gas discharged from the combustion chamber 17 flows. Although detailed illustration is omitted, the upstream portion of the exhaust passage 50 constitutes an independent passage that branches for each cylinder 11. The upstream end of the independent passage is connected to the exhaust port 19 of each cylinder 11.

An exhaust gas purification system having a plurality of catalytic converters is arranged in the exhaust passage 50. The upstream catalytic converter is arranged in the engine room, although not shown. The upstream catalytic converter has a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512. The downstream catalytic converter is located outside the engine compartment. 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 constituting an external EGR system 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 the upstream catalytic converter and the downstream catalytic converter 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. The EGR gas flowing through the EGR passage 52 enters the upstream portion of the supercharger 44 in the intake passage 40 without passing through the air bypass valve 48 of the bypass passage 47.

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. By adjusting the opening degree of the EGR valve 54, the recirculation amount of the cooled exhaust gas, that is, the external EGR gas can be adjusted.

In this configuration example, the EGR system 55 is composed of an external EGR system and an internal EGR system. The external EGR system can supply the combustion chamber 17 with exhaust gas having a lower temperature than the internal EGR system. The EGR system 55 is an example of a state quantity adjusting unit.

In FIGS. 1 and 3, reference numeral 57 is an alternator 57 connected to the crankshaft 15. The alternator 57 is driven by the engine 1.

The control device of the internal combustion engine includes an ECU (Engine Control Unit) 10 for operating the engine 1. The ECU 10 is a controller based on a well-known microcomputer, and as shown in FIG. 3, has a central processing unit (CPU) 101 for executing a program, and for example, a RAM (Random Access Memory) or a ROM. It includes a memory 102 composed of (Read Only Memory) for storing programs and data, and an input / output bus 103 for inputting / outputting electric signals. The ECU 10 is an example of a control unit.

As shown in FIGS. 1 and 3, various sensors SW1 to SW17 are connected to the ECU 10. The sensors SW1 to SW17 output a signal to the ECU 10. The sensors include the following sensors.

Air flow sensor SW1: Arranged downstream of the air cleaner 41 in the intake passage 40 and measuring the flow rate of fresh air flowing through the intake passage 40 First intake air temperature sensor SW2: Arranged downstream of the air cleaner 41 in the intake passage 40 First pressure sensor SW3 that measures the temperature of fresh air flowing through the intake passage 40: The supercharger 44 is located downstream of the connection position of the EGR passage 52 in the intake passage 40 and upstream of the supercharger 44. Second intake air temperature sensor SW4 that measures the pressure of the gas flowing into the intake passage 40: It is located downstream of the supercharger 44 in the intake passage 40 and upstream of the connection position of the bypass passage 47, and flows out from the supercharger 44. Second pressure sensor SW5 that measures the temperature of the gas: Attached to the surge tank 42 and measures the pressure of the gas downstream of the supercharger 44 In-cylinder pressure sensor SW6: Attached to the cylinder head 13 corresponding to each cylinder 11. NOx sensor SW7 that measures the pressure in each combustion chamber 17: Linear O that is arranged downstream of the ternary catalyst 513 in the exhaust passage 50 and measures the NOx concentration in the exhaust gas that has passed through the ternary catalyst 513. ₂ sensor SW8: arranged upstream of the upstream catalytic converter in the exhaust passage 50 and measuring the oxygen concentration in the exhaust gas Lambda O ₂ sensor SW9: arranged downstream of the ternary catalyst 511 in the upstream catalytic converter Water temperature sensor SW10 that measures the oxygen concentration in the exhaust gas: is attached to the engine 1 and measures the temperature of the cooling water Crank angle sensor SW11: is attached to the engine 1 and measures the rotation angle of the crank shaft 15. Opening sensor SW12: Attached to the accelerator pedal mechanism and measures the accelerator opening corresponding to the operation amount of the accelerator pedal Intake cam angle sensor SW13: Attached to the engine 1 and measures the rotation angle of the intake cam shaft Exhaust Cam angle sensor SW14: EGR differential pressure sensor SW15 attached to the engine 1 and measuring the rotation angle of the exhaust cam shaft: Fuel pressure sensor attached to the EGR passage 52 and measuring the differential pressure upstream and downstream of the EGR valve 54 SW16: Third intake air temperature sensor SW17 attached to the common rail 64 of the fuel supply system 61 and measuring the pressure of the fuel supplied to the injector 6 SW17: Attached to the surge tank 42 and the temperature of the gas in the surge tank 42, in other words. Then, it is introduced into the combustion chamber 17. Measure the temperature of the intake air.

The ECU 10 determines the operating state of the engine 1 based on the signals of the sensors SW1 to SW17, and calculates the control amount of each device according to a predetermined control logic. The control logic is stored in the memory 102. The control logic includes calculating a target amount and / or a control amount using the operation map stored in the memory 102.

The ECU 100 transmits an electric signal related to the calculated 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 supercharger 44. Outputs to the electromagnetic clutch 45, the air bypass valve 48, the swirl control valve 56, and the alternator 57.

For example, the ECU 10 sets the target torque of the engine 1 and determines the target boost pressure based on the signal of the accelerator opening sensor SW12 and the operation map. Then, the ECU 10 adjusts the opening degree of the air bypass valve 48 based on the target boost pressure and the front-rear differential pressure of the supercharger 44 obtained from the signals of the first pressure sensor SW3 and the second pressure sensor SW5. By performing feedback control, the supercharging pressure becomes the target supercharging pressure.

Further, the ECU 10 sets the target EGR rate based on the operating state of the engine 1 and the operation map. The EGR ratio is the ratio of the EGR gas to the total gas in the combustion chamber 17. The ECU 10 determines the target EGR gas amount based on the target EGR rate and the intake air amount based on the signal of the accelerator opening sensor SW12, and is based on the front-rear differential pressure of the EGR valve 54 obtained from the signal of the EGR differential pressure sensor SW15. By performing feedback control for adjusting the opening degree of the EGR valve 54, the amount of external EGR gas introduced into the combustion chamber 17 becomes the target EGR gas amount.

Further, the ECU 10 executes the air-fuel ratio feedback control when a predetermined control condition is satisfied. Specifically ECU10 includes a linear O ₂ sensor SW8, and, based on the oxygen concentration in the exhaust gas lambda O ₂ sensor SW9 is measured, so that the air-fuel ratio of the mixture has a desired value, the fuel injection of the injector 6 Adjust the amount.

The details of the control of the engine 1 by the other ECU 10 will be described later.

(SPCCI combustion concept)
The engine 1 performs combustion by compression self-ignition when it is in a predetermined operating state for the main purpose of improving fuel efficiency and exhaust gas performance. In the combustion by self-ignition, when the temperature in the combustion chamber 17 before the start of compression fluctuates, the timing of self-ignition changes significantly. Therefore, the engine 1 performs SPCCI combustion that combines SI combustion and CI combustion.

In SPCCI combustion, the ignition plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17, so that the air-fuel mixture undergoes SI combustion by flame propagation, and the heat generated by SI combustion causes SI combustion in the combustion chamber 17. This is a form in which the unburned air-fuel mixture undergoes CI combustion by self-ignition as the temperature rises and the pressure in the combustion chamber 17 rises due to flame propagation.

By adjusting the calorific value 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 by the ECU 10, the air-fuel mixture can be self-ignited at a target timing.

In SPCCI combustion, the heat generation during SI combustion is milder than the heat generation during CI combustion. FIG. 4 illustrates the waveform 801 of the heat generation rate in SPCCI combustion. In the waveform 801 of the heat generation rate in SPCCI combustion, the slope of the rising edge is smaller than the slope of the rising edge in the waveform of CI combustion. Further, the pressure fluctuation (dp / dθ) in the combustion chamber 17 is also gentler during SI combustion than during CI combustion.

When the unburned air-fuel mixture self-ignites after the start of SI combustion, the slope of the heat generation rate waveform may change from small to large at the timing of self-ignition. The waveform of the heat generation rate may have an inflection point X at the timing θci at which 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 the CI combustion is performed after the compression top dead center, it is avoided that the slope of the heat generation rate waveform becomes too large. The pressure fluctuation (dp / dθ) during CI combustion is also relatively gentle.

The pressure fluctuation (dp / dθ) can be used as an index representing the combustion noise. As described above, in SPCCI combustion, the pressure fluctuation (dp / dθ) can be reduced, so that it is possible to avoid the combustion noise becoming too large. The combustion noise of the engine 1 is suppressed to an allowable level or less.

When the CI combustion ends, the SPCCI combustion ends. CI combustion has a shorter combustion period than SI combustion. SPCCI combustion has a combustion end time earlier than SI combustion.

The heat generation rate waveform of SPCCI combustion is formed so that the first heat generation rate part Q _SI formed by SI combustion and the second heat generation part Q _CI formed by CI combustion are continuous in this order. Has been done.

(Engine operating area)
FIG. 5 illustrates an operation map related to the control of the engine 1. The operation map is stored in the memory 102 of the ECU 10. The operation map 501 illustrated in FIG. 5 is an operation map when the engine 1 is semi-warm, and 502 is an operation map when the engine 1 is warm. The ECU 10 selects the operation map 501 or the operation map 502 according to the height of each of the wall temperature of the combustion chamber 17 and the intake air temperature. The ECU 10 controls the engine 1 using the selected operation map.

The operation maps 501 and 502 are defined by the load and the rotation speed of the engine 1. The operation map 501 is divided into two regions according to the high and low rotation speeds. Specifically, the operation map 501 is divided into a high rotation region A1 having a rotation speed of N3 or more and a region A2 extending over a low rotation and medium rotation region. The operation map 502 is divided into three areas. Specifically, the operation map 502 is a predetermined load range of N1 to N2 and a predetermined load range of L1 to L2 in the above-mentioned high rotation region A1, low rotation and medium rotation region A2, and region A2. It is divided into the area A3 of.

Here, in the low rotation region, the medium rotation region, and the high rotation region, when the entire operation region of the engine 1 is divided into substantially three equal parts of the low rotation region, the medium rotation region, and the high rotation region in the rotation speed direction, respectively. It may be a low rotation region, a medium rotation region, and a high rotation region.

The operation maps 501 and 502 of FIG. 5 show the state of the air-fuel mixture and the combustion mode in each region. The engine 1 performs SI combustion in the region A1. Engine 1 also performs SPCCI combustion in regions A2 and A3. Hereinafter, the operation of the engine 1 in each region of the operation maps 501 and 502 of FIG. 5 will be described in detail.

(Engine operation in area A3)
When the engine 1 is operating in the region A3, the engine 1 performs SPCCI combustion.

In order to improve the fuel efficiency of the engine 1, the EGR system 55 introduces EGR gas into the combustion chamber 17. Specifically, the intake electric S-VT23 and the exhaust electric S-VT24 provide a positive overlap period in which both the intake valve 21 and the exhaust valve 22 are opened near the exhaust top dead center.

The air-fuel ratio (A / F) of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio in the entire combustion chamber 17 (that is, the excess air ratio λ> 1). More specifically, the A / F of the air-fuel mixture in the entire combustion chamber 17 is 25 or more and 31 or less. By doing so, the generation of RawNOx can be suppressed, and the exhaust gas performance can be improved. The throttle valve 43 is fully open.

After the injector 6 finishes fuel injection, the spark plug 25 ignites the air-fuel mixture in the combustion chamber 17. In the region A3, the engine 1 performs a lean combustion operation.

(Engine operation in area A2)
When the engine 1 is operating in the region A2, the engine 1 performs SPCCI combustion.

The EGR system 55 introduces EGR gas into the combustion chamber 17. Specifically, the intake electric S-VT23 and the exhaust electric S-VT24 provide a positive overlap period in which both the intake valve 21 and the exhaust valve 22 are opened near the exhaust top dead center. The internal EGR gas is introduced into the combustion chamber 17. Further, the EGR system 55 introduces the exhaust gas cooled by the EGR cooler 53 into the combustion chamber 17 through the EGR passage 52 in at least a part of the region A2. That is, the external EGR gas, which has a lower temperature than the internal EGR gas, is introduced into the combustion chamber 17. The external EGR gas adjusts the temperature inside the combustion chamber 17 to an appropriate temperature. The EGR system 55 reduces the amount of EGR gas as the load on the engine 1 increases. The EGR system 55 may zero the EGR gas, including the internal EGR gas and the external EGR gas, at full open load.

The air-fuel ratio (A / F) of the air-fuel mixture is the theoretical air-fuel ratio (A / F≈14.7) in the entire combustion chamber 17. The three-way catalysts 511 and 513 purify the exhaust gas discharged from the combustion chamber 17, so that the exhaust gas performance of the engine 1 is improved. The A / F of the air-fuel mixture may be contained in the purification window of the three-way catalyst. The excess air ratio λ of the air-fuel mixture may be 1.0 ± 0.2. When the engine 1 is operating at a fully open load (that is, the maximum load), the A / F of the air-fuel mixture may be richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio in the entire combustion chamber 17. Good (that is, the air-fuel ratio λ of the air-fuel mixture is λ ≦ 1). The throttle valve 43 is adjusted to a fully open or intermediate opening degree.

Since the EGR gas is introduced into the combustion chamber 17, the G / F, which is the weight ratio of the total gas in the combustion chamber 17 to the fuel, becomes leaner than the stoichiometric air-fuel ratio. The G / F of the air-fuel mixture may be 18 or more. By doing so, it is possible to suppress the occurrence of so-called knocking. G / F may be set at 18 or more and 30 or less. Further, the G / F may be set at 18 or more and 50 or less.

The spark plug 25 ignites the air-fuel mixture at a predetermined timing near the compression top dead center after the injector 6 injects fuel. In the region A2, the engine 1 performs a stoichiometric combustion operation.

(Engine operation in region A1)
When the rotation speed of the engine 1 is high, the time required for the crank angle to change by 1 ° becomes short. When the number of revolutions of the engine 1 becomes high, it becomes difficult to perform SPCCI combustion.

Therefore, when the engine 1 is operating in the region A1, the engine 1 performs SI combustion instead of SPCCI combustion.

The EGR system 55 introduces EGR gas into the combustion chamber 17. The EGR system 55 reduces the amount of EGR gas as the load increases. The EGR system 55 may have zero EGR gas at full open load.

The air-fuel ratio (A / F) of the air-fuel mixture is basically the theoretical air-fuel ratio (A / F≈14.7) in the entire combustion chamber 17. The excess air ratio λ of the air-fuel mixture may be 1.0 ± 0.2. When the engine 1 is operating in the vicinity of the fully open load, the excess air ratio λ of the air-fuel mixture may be less than 1. The throttle valve 43 is adjusted to a fully open or intermediate opening degree.

The spark plug 25 ignites the air-fuel mixture at an appropriate timing near the compression top dead center after the injector 6 finishes injecting fuel.

(Switching engine operation mode)
As shown in FIG. 5, when the operating state of the engine 1 shifts from the region A2 to the region A3 as the load and / or the number of revolutions of the engine 1 changes, the engine 1 shifts from the stoichiometric combustion operation to the lean combustion. Switch to driving. Further, when the wall temperature and the intake air temperature of the combustion chamber 17 increase and the operation map 501 is switched to the operation map 502, the engine 1 is operated from the stoichiometric combustion operation to the lean combustion operation even if the load and the rotation speed of the engine 1 do not change. Switch to.

Here, FIG. 6 shows the relationship between the fuel ratio of the air-fuel mixture and RawNOx (solid line), and the fuel ratio and SDI (Standard Deviation of IMEP (Indicated Mean Effective Pressure)) as an index of combustion stability. The relationship (single point chain line) is illustrated. The horizontal axis of FIG. 6 is the fuel ratio (that is, A / F or G / F), and the fuel becomes leaner in the air-fuel mixture as it goes to the right of the figure. Further, the vertical axis on the left side of FIG. 6 is RawNOx, and the amount of RawNOx increases as it goes up in the figure.

From the solid line in FIG. 6, when the air-fuel mixture becomes lean, RawNOx decreases. When the air-fuel mixture has a stoichiometric air-fuel ratio (that is, when λ = 1), there is a large amount of RawNOx, but RawNOx can be reduced by a three-way catalyst. In order to keep RawNOx below the NOx limit, the fuel ratio must be significantly lean.

On the other hand, when the fuel ratio is lean, combustion becomes unstable as shown by the alternate long and short dash line in FIG. The fuel ratio that satisfies the NOx limit is close to the lean limit as the fuel ratio that can ensure combustion stability. Leaning the fuel ratio to satisfy the NOx limit can lead to instability in combustion.

Here, consider a case of switching from the stoichiometric combustion operation shown by reference numeral 601 in FIG. 6 to the lean combustion operation shown by reference numeral 602. The ECU 10 sets the fuel ratio of the air-fuel mixture to the target value 602, adjusts the amount of air and EGR gas introduced into the combustion chamber 17 by each device, and the injector 6 adjusts the amount corresponding to the operating state of the engine 1. When the fuel is supplied into the combustion chamber 17, the actual fuel ratio of the air-fuel mixture varies as shown by the double-ended arrows in FIG. If the target value 602 is close to the lean limit in order to reduce RawNOx, the actual fuel ratio may exceed the lean limit and combustion may become unstable, as illustrated in FIG. When the opening degree of the throttle valve 43 is increased and the amount of air into the combustion chamber 17 is increased as in the case of switching from the stoiki combustion operation to the lean combustion operation, the variation in the fuel ratio becomes even larger. Is prone to instability.

Therefore, this engine 1 is characterized by adjusting the fuel ratio in order to achieve both suppression of RawNOx emissions and ensuring combustion stability. Specifically, when the ECU 10 sets the target fuel ratio according to the operating state of the engine 1, the fuel ratio deviates to the lean side as much as possible with respect to the set target fuel ratio based on the actual degree of variation in the fuel ratio. Estimate the fuel ratio of the case. The data of the actual degree of variation in the fuel ratio is stored in the memory 102.

FIG. 7 illustrates a functional block of the ECU 10 that executes control related to fuel ratio adjustment. The ECU 10 has a target value setting unit 104, an estimation unit 105, an initial value setting unit 106, a fuel ratio adjusting unit 107, and a fuel ratio measuring unit 108.

The target value setting unit 104 sets a target value of the fuel ratio. As described above, the target value setting unit 104 sets the target fuel ratio according to the operating state of the engine 1.

The estimation unit 105 is the fuel when the fuel ratio deviates to the lean side as much as possible with respect to the target fuel ratio set by the target value setting unit 104 based on the actual degree of variation of the fuel ratio stored in the memory 102. Estimate the ratio.

When the fuel ratio estimated by the estimation unit 105 exceeds the lean limit, the initial value setting unit 106 sets an initial value richer than the target value. The initial value is set so that the lean limit is not exceeded even if the actual fuel ratio deviates to the lean side as much as possible. Reference numeral 603 in FIG. 6 is an example of an initial value set by the initial value setting unit 106.

The fuel ratio adjusting unit 107 adjusts the in-cylinder state amount and adjusts the fuel injection amount so that when the initial value setting unit 106 sets the initial value of the fuel ratio, the initial value is the initial value. To burn. Specifically, the fuel ratio adjusting unit 107 outputs a signal regarding fuel injection to the injector 6, and also outputs an intake electric S-VT23, an exhaust electric S-VT24, a throttle valve 43, an EGR valve 54, and an air bypass valve 48. Outputs a signal related to the adjustment of the in-cylinder state amount.

The fuel ratio measuring unit 108 measures the actual air-fuel ratio of the air-fuel mixture based on the fuel injection amount set by the ECU 10 according to the operating state of the engine 1 and the signal of the air flow sensor SW1.

The fuel ratio adjusting unit 107 will be described in detail later, but based on the measurement result of the fuel ratio measuring unit 108, until the fuel ratio reaches the target value or until the fuel ratio does not exceed the lean limit. Bring the fuel ratio closer to the target value (see reference numeral 604 in FIG. 6). By adjusting the fuel ratio in this way, the engine 1 can achieve both suppression of NOx emissions and ensuring combustion stability in the lean combustion operation.

The ECU 10 updates the data of the degree of variation in the fuel ratio stored in the memory 102 based on the actual air-fuel ratio measured by the fuel ratio measuring unit 108.

Next, the control of the engine 1 executed by the ECU 10 will be described with reference to the flowcharts of FIGS. 8 and 9. The order of each step in the flowcharts of FIGS. 8 and 9 can be changed.

The flowchart of FIG. 8 is a flowchart relating to the basic control of the engine 1. The ECU 10 operates the engine 1 according to the control logic stored in the memory 102. The ECU 10 determines the operating state of the engine 1 based on the signals of the sensors SW1 to SW17, sets the target torque, and determines the state amount in the combustion chamber 17 so that the engine 1 outputs the target torque. Calculations for adjusting, adjusting the injection amount, adjusting the injection timing, and adjusting the ignition timing are performed.

Specifically, in step S1 of the flowchart of FIG. 8, the ECU 10 reads the signals of the sensors SW1 to SW17, and in the following step S2, the ECU 10 sets a lean limit of the fuel ratio corresponding to the operating state of the engine 1. To do. As described above, the lean limit means the lean limit of the fuel ratio of the air-fuel mixture, which can ensure the combustion stability of the air-fuel mixture.

Next, in step S3, the ECU 10 determines whether or not to operate the engine 1 in lean combustion based on the operation maps 501 and 502 and the operating state of the engine 1. When the engine 1 is operated in lean combustion, the process proceeds to step S7, and when the engine 1 is not operated in lean combustion, in other words, when the engine 1 is operated in stoichiometric combustion, the process proceeds to step S4.

Steps S4 to S6 are steps related to stoichiometric combustion operation. In step S4, the ECU 10 sets the target torque, and in the following step S5, the ECU 10 sets the target air amount. Then, in step S6, the ECU 10 sets the target fuel injection amount so that the air-fuel ratio of the air-fuel mixture becomes the stoichiometric air-fuel ratio based on the set target air amount.

After that, the ECU 10 outputs a signal to each device so as to reach the set target air amount and target fuel injection amount in step S11. The engine 1 performs a stoichiometric combustion operation.

On the other hand, steps S7 to S10 are steps related to the lean combustion operation. In step S7, the ECU 10 sets the target torque in the same manner as in step S4, and in the subsequent step S8, the ECU 10 sets the target fuel injection amount corresponding to the target torque.

The ECU 10 sets the target fuel ratio in the next step S9. FIG. 9 is a flowchart relating to the setting of the target fuel ratio in step S9. In step S21 of the flow of FIG. 9, the ECU 10 determines whether or not the engine 1 is in the transitional period of switching from the stoichiometric combustion operation to the lean combustion operation. If the determination in step S21 is YES, the process proceeds to step S23, and if NO, the process proceeds to step S22. As will be described later, after the switch to the lean combustion operation is completed, the process proceeds to step S22.

In step S22, the ECU 10 sets the target fuel ratio according to the operating state of the engine 1. Since it is a lean combustion operation, the fuel ratio is set so as to be leaner than the theoretical air-fuel ratio and below the NOx limit.

In step S23, the ECU 10 determines whether or not the initial value has already been set. The initial value is the target air-fuel ratio initially set when switching from the stoichiometric combustion operation to the lean combustion operation. As mentioned above, the initial value may be set richer than the target fuel ratio. If the determination in step S23 is YES, the process proceeds to step S27, and if NO, the process proceeds to step S24.

In step S24, the ECU 10 sets the target fuel ratio according to the operating state of the engine 1. The ECU 10 sets the target fuel ratio so that RawNOx falls below the NOx limit. The target fuel ratio is also richer than the lean limit.

In the following step S25, the ECU 10 determines whether or not the lean limit is exceeded when the fuel ratio deviates to the lean side as much as possible with respect to the target fuel ratio based on the actual degree of variation in the fuel ratio. If the lean limit is exceeded, the process proceeds to step S26. In step S26, the ECU 10 sets an initial value richer than the target fuel ratio. On the other hand, if the lean limit is not exceeded in step S25, the process returns. The target fuel ratio set in step S24 becomes the initial value.

After setting the initial value, the process returns to the flowchart of FIG. In step S10, the ECU 10 sets the target air amount based on the set initial value, and then in step S11, the ECU 10 outputs a control signal to each device.

In the next combustion cycle, the determination in step S23 of FIG. 9 is YES, and the process proceeds to step S27. The ECU 10 measures the actual air-fuel ratio of the air-fuel mixture based on the set fuel injection amount and the signal of the air flow sensor SW1, and determines whether or not the actual air-fuel ratio exceeds the lean limit. If the actual air-fuel ratio exceeds the lean limit, the process proceeds to step S28. If the fuel ratio is made leaner than this, combustion stability cannot be ensured. Therefore, the ECU 10 keeps the fuel ratio as it is without approaching the target air-fuel ratio. This means that the switch from the stoiki combustion operation to the lean combustion operation has been completed.

If the actual air-fuel ratio does not exceed the lean limit, the process proceeds from step S27 to step S29. In step S29, the ECU 10 determines whether or not the actual fuel ratio is the target air-fuel ratio initially determined in step S24. If the actual fuel ratio is the target air-fuel ratio, the process returns, assuming that the switch from stoichiometric combustion operation to lean combustion operation is complete. At the next combustion cycle, the determination in step S21 becomes NO, and the process proceeds to step S22.

If the determination in step S29 is NO, the process proceeds to step S210. In step S210, the ECU 10 brings the fuel ratio of the next combustion cycle closer to the target fuel ratio initially determined in step S24. Then, at the next combustion cycle, the determination of step S27 and step S29 is performed again. In this way, the process repeats step 210 a plurality of times, so that the fuel ratio gradually approaches the target fuel ratio. The fuel ratio eventually reaches the target air-fuel ratio or reaches the lean limit. As a result, NOx emissions are suppressed and the combustion stability of the air-fuel mixture is ensured.

10 shows, when the fuel ratio is adjusted according to the flowcharts of FIGS. 8 and 9, the operation mode change 901, the fuel ratio change 902, the throttle opening change 903, the fuel injection amount change 904, and It is a time chart which illustrates the change 905 of RawNOx.

First, until time t1, as shown in 901, the engine 1 is in a stoichiometric combustion operation. The target fuel ratio is the theoretical air-fuel ratio, as shown in 902. The fuel ratio is adjusted to the stoichiometric air-fuel ratio. The opening degree of the throttle valve 43 is relatively small as shown in 903. As shown in 905, the three-way catalyst 511 and 513 reduce RawNOx, although the amount of RawNOx increases.

At time t1, the engine 1 switches from the stoichiometric combustion operation to the lean combustion operation (see 901). As shown in 902, an initial value richer than the target fuel ratio is set. Also, the initial value is richer than the lean limit. As shown in 903, the opening degree of the throttle valve 43 increases to correspond to the fuel ratio set to lean. RawNOx is below the NOx limit, as shown in 905.

The fuel ratio then gradually approaches the target fuel ratio, as shown in 902. The fuel injection amount is constant as shown in 904, while the opening degree of the throttle valve 32 gradually increases as the fuel ratio becomes lean, as shown in 903. By doing so, it becomes possible to bring the fuel ratio closer to the target value while maintaining the combustion stability. Then, in the example of FIG. 10, the fuel ratio reaches the target fuel ratio at time t2, and the switching from the stoichiometric combustion operation to the lean combustion operation is completed.

The technique disclosed herein is not limited to being applied to the engine 1 having the above-described configuration. As the configuration of the engine 1, various configurations can be adopted.

1 engine (internal combustion engine)
10 ECU (control unit)
105 Estimating unit 106 Initial value setting unit 107 Fuel ratio adjustment unit 21 Intake valve (state amount adjustment unit)
22 Exhaust valve (state amount adjustment unit)
23 Intake electric S-VT (state amount adjustment unit)
24 Exhaust electric S-VT (state amount adjustment unit)
43 Throttle valve (state amount adjustment unit)
44 Supercharger (state amount adjustment unit)
49 Supercharging system (state amount adjustment unit)
54 EGR valve (state amount adjuster)
55 EGR system (state amount adjustment unit)
6 Injector (fuel supply unit)

Claims (10)

It is a control method for an internal combustion engine capable of lean combustion operation in which the fuel ratio of the air-fuel mixture introduced into the combustion chamber is made larger than the stoichiometric air-fuel ratio.
A step in which the control unit sets a target value of the fuel ratio of the air-fuel mixture according to the operating state of the internal combustion engine.
A step in which the control unit estimates the fuel ratio when the fuel ratio deviates to the lean side as much as possible with respect to the set target value based on the actual degree of variation in the fuel ratio.
A step in which the control unit sets an initial value richer than the target value when the estimated fuel ratio exceeds the lean limit determined based on combustion stability.
A step of adjusting the in-cylinder state amount and the fuel amount of the internal combustion engine and burning the air-fuel mixture through the state amount adjusting unit and the fuel supply unit so that the control unit has the initial value.
After the combustion step, the in-cylinder state amount is reached through the state amount adjusting unit and the fuel supply unit so that the control unit reaches the target value or has a fuel ratio approaching the target value. And the step of adjusting the amount of fuel and burning the air-fuel mixture,
A method of controlling an internal combustion engine. In the method for controlling an internal combustion engine according to claim 1,
The control unit is a control method for an internal combustion engine that executes a plurality of steps to bring the fuel ratio closer to the target value. In the method for controlling an internal combustion engine according to claim 2.
The control unit is a control method for an internal combustion engine that stops bringing the fuel ratio closer to the target value when the actual fuel ratio exceeds the lean limit. In the method for controlling an internal combustion engine according to any one of claims 1 to 3.
The control unit is a control method for an internal combustion engine that brings the fuel ratio closer to the target value by keeping the amount of fuel constant and increasing the opening degree of the throttle valve. In the method for controlling an internal combustion engine according to any one of claims 1 to 4.
The control unit is a control method for an internal combustion engine that sets the initial value when the internal combustion engine is switched from a stoichiometric combustion operation to a lean combustion operation. A control device for an internal combustion engine capable of lean combustion operation.
The fuel supply unit attached to the internal combustion engine and
A state amount adjusting unit that adjusts the state amount in the cylinder of the internal combustion engine,
A control unit that outputs a control signal to the fuel supply unit and the state amount adjusting unit is provided according to a target value of the fuel ratio of the air-fuel mixture set according to the operating state of the internal combustion engine.
The control unit
An estimation unit that estimates the fuel ratio when the fuel ratio deviates to the lean side to the maximum with respect to the set target value based on the actual degree of variation in the fuel ratio.
When the estimated fuel ratio exceeds the lean limit determined based on combustion stability, an initial value setting unit that sets an initial value richer than the target value, and an initial value setting unit.
It has a state amount adjusting unit and a fuel ratio adjusting unit that adjusts the in-cylinder state amount and the fuel amount through the fuel supply unit and burns the air-fuel mixture so as to have the initial values.
After the combustion, the fuel ratio adjusting unit is in the in-cylinder state through the state amount adjusting unit and the fuel supply unit so as to reach the target value or to have a fuel ratio approaching the target value. A control device for an internal combustion engine that adjusts the amount and the amount of fuel and burns the air-fuel mixture. In the control device for an internal combustion engine according to claim 6.
The fuel ratio adjusting unit is a control device for an internal combustion engine that executes the fuel ratio to approach the target value a plurality of times. In the control device for an internal combustion engine according to claim 7.
The fuel ratio adjusting unit is a control device for an internal combustion engine that stops bringing the fuel ratio closer to the target value when the actual fuel ratio exceeds the lean limit. In the control device for an internal combustion engine according to any one of claims 6 to 8.
The fuel ratio adjusting unit is a control device for an internal combustion engine that brings the fuel ratio closer to the target value by keeping the fuel amount constant and increasing the opening degree of the throttle valve. In the control device for an internal combustion engine according to any one of claims 6 to 9.
The initial value setting unit is a control device for an internal combustion engine that sets the initial value when the internal combustion engine is switched from a stoichiometric combustion operation to a lean combustion operation.

Images