JP7287070B2 - CONTROL DEVICE AND CONTROL METHOD FOR INTERNAL COMBUSTION ENGINE - Google Patents

Description

The technology disclosed herein relates to a control device and control method for an internal combustion engine.

In Patent Document 1, after starting cranking of the engine and reaching the target rotation speed, in a period before starting the air-fuel ratio feedback control, if the combustion is unstable beyond the threshold value, the fuel injection amount is reduced. It is described that combustion stability is achieved by increasing the air-fuel ratio and making the air-fuel ratio on the rich side.

Japanese Unexamined Patent Application Publication No. 2008-2435

By the way, there is known an internal combustion engine that burns an air-fuel mixture leaner than the stoichiometric air-fuel ratio for the purpose of improving fuel efficiency and cleaning exhaust gas. In an internal combustion engine that operates lean-burn, making the mixture lean is advantageous for improving fuel efficiency and cleaner exhaust gas, but if it is made too lean, combustion fluctuations will increase and drivability will decrease. There is a problem that

In order to avoid this problem, in an internal combustion engine that performs lean burn operation, an allowable value for combustion fluctuation is determined based on the operating state of the internal combustion engine, and the lean limit of the air-fuel mixture is set so as to satisfy the allowable value for combustion fluctuation. It is conceivable to set

However, according to the study by the inventors of the present application, it has been found that the relationship between the combustion fluctuation and the fuel ratio varies from one internal combustion engine to another, and that the relationship between the combustion fluctuation and the fuel ratio changes over time. In other words, there is a risk that the lean limit determined from the relationship between the permissible value of combustion fluctuation and the fuel ratio deviates from the true lean limit, causing the combustion fluctuation to exceed the permissible value.

In addition, not only the so-called A/F lean operation in which the air-fuel mixture is leaner than the stoichiometric air-fuel ratio, but also the so-called G/F lean operation in which EGR gas is introduced into the cylinder while the air-fuel ratio is made the stoichiometric air-fuel ratio. problem arises.

The term "fuel ratio" is used here as a generic 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. Also, lean-burn operation includes both A/F lean-burn operation and G/F lean-burn operation.

The technology disclosed herein suppresses unstable combustion by appropriately setting a lean limit in an internal combustion engine that performs lean-burn operation.

The technology disclosed herein relates to a control method for an internal combustion engine capable of lean-burn operation. This control method is
a step in which a control unit sets an allowable value of combustion fluctuation , which is an allowable value predetermined for each operating state of the internal combustion engine, based on the operating state determined by the load and the rotational speed of the internal combustion engine;
The control unit determines a lean limit in the operating state of the internal combustion engine based on the set allowable value of combustion fluctuation and a model for setting the lean limit of the fuel ratio of the air-fuel mixture from the allowable value of combustion fluctuation. and setting
The control unit sets a target fuel ratio so that the fuel ratio does not exceed the lean limit and corresponds to the operating state of the internal combustion engine, and satisfies the set target fuel ratio. a step of adjusting the in-cylinder state quantity and the fuel quantity, which are gas quantities containing at least air, in the combustion chamber of the internal combustion engine through the state quantity adjusting unit and the fuel supply unit, and burning the air-fuel mixture;
a step in which the controller estimates the fuel ratio of the air-fuel mixture from the model and the combustion fluctuation estimated based on the signal output by the in-cylinder pressure sensor during combustion;
a step in which the control unit corrects the model so that the difference between the estimated fuel ratio and the actual fuel ratio is eliminated, based on a comparison between the estimated fuel ratio and the measured actual fuel ratio ;
It has

According to this configuration, the control unit estimates the fuel ratio of the air-fuel mixture from the model and the combustion fluctuation estimated based on the signal output by the in-cylinder pressure sensor, and estimates the estimated fuel ratio and the measured actual fuel ratio. Modify the model based on comparison with The model is a model used to set the lean limit from the permissible value of combustion fluctuation. By continuously modifying the model that defines the relationship between combustion variation and fuel ratio, the controller can accurately define the lean limit.

As a result, during lean-burn operation, combustion instability is suppressed by adjusting the fuel ratio based on the correct lean limit. A decrease in drivability of the automobile is suppressed. Also, based on the accurate lean limit, the fuel ratio can be made as lean as possible, which is advantageous for improving the fuel efficiency of automobiles.

The model is
a first model that defines the relationship between the combustion fluctuation and the average in-cylinder pressure;
a second model that defines the relationship between the thermal efficiency calculated based on the average in-cylinder pressure and the fuel injection amount and the specific crank angle at which the mass combustion ratio is a predetermined value;
a third model that defines the relationship between the specific crank angle and the combustion period;
a basic model block including a fourth model that defines the relationship between the combustion period and the lean limit;
a correction block that corrects the base value of the lean limit determined by the base model block;
The control unit may modify the correction block so that there is no difference between the estimated fuel ratio and the actual fuel ratio .

By doing so, the lean limit can be appropriately determined from the permissible value of combustion fluctuation.

The technology disclosed herein relates to a control device for an internal combustion engine capable of lean burn operation. This control device
a fuel supply attached to the internal combustion engine;
a state quantity adjustment unit that adjusts an in-cylinder state quantity, which is an amount of gas containing at least air, in a combustion chamber of the internal combustion engine;
A control unit that outputs a control signal to the fuel supply unit and the state quantity adjustment unit so that the fuel ratio of the air-fuel mixture does not exceed a lean limit that is determined according to the operating state that is determined by the load and rotation speed of the internal combustion engine. and,
an in-cylinder pressure sensor connected to the control unit and outputting a signal corresponding to the pressure in the cylinder to the control unit;
a sensor connected to the control unit and outputting a signal related to the fuel ratio to the control unit;
The control unit
an allowable value setting unit for setting an allowable value of combustion fluctuation , which is an allowable value predetermined for each operating state of the internal combustion engine, based on the operating state of the internal combustion engine ;
A lean limit setting unit for setting a lean limit in the operating state of the internal combustion engine based on the set allowable value of combustion fluctuation and a model for setting the lean limit of the fuel ratio of the air-fuel mixture from the allowable value of combustion fluctuation. and,
A target fuel ratio is set so that the fuel ratio does not exceed the lean limit and corresponds to the operating state of the internal combustion engine, and the state quantity is set so that the set target fuel ratio is satisfied. a fuel ratio adjustment unit that adjusts the in - cylinder state quantity and the fuel amount of the internal combustion engine through the adjustment unit and the fuel supply unit and combusts the air-fuel mixture;
a fuel ratio estimating unit for estimating the fuel ratio of the air-fuel mixture from the combustion fluctuation estimated based on the signal output by the in-cylinder pressure sensor during combustion and the model;
a correction unit that corrects the model so that the difference between the estimated fuel ratio and the actual fuel ratio is eliminated based on a comparison between the estimated fuel ratio and the actual fuel ratio based on the sensor signal; have.

As described above, the control device and control method for an internal combustion engine adjusts the fuel ratio so that combustion does not become unstable by appropriately setting the lean limit in an internal combustion engine that performs lean burn operation. be able to.

FIG. 1 is a diagram illustrating the configuration of an engine. FIG. 2 is a diagram illustrating the configuration of the combustion chamber, the upper diagram being a plan view equivalent of the combustion chamber, and the lower diagram being a sectional view taken along line II-II. FIG. 3 is a block diagram illustrating the configuration of an engine control device. FIG. 4 is a diagram illustrating waveforms of SPCCI combustion. FIG. 5 is a diagram illustrating an engine operation map. FIG. 6 is a block diagram illustrating functional blocks of an ECU that executes engine fuel ratio adjustment control. FIG. 7 is a block diagram illustrating engine fuel ratio adjustment control. FIG. 8 is a block diagram illustrating the configuration of the basic model. FIG. 9 is a flowchart illustrating engine fuel ratio adjustment control.

An embodiment of a control device for an internal combustion engine will be described in detail below 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. Note that the intake side in FIG. 1 is on the left side of the paper, and the exhaust side is on the right side of the paper. The intake side in 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 an engine control device.

The engine 1 is a four-stroke engine that operates by repeating an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke in a combustion chamber 17 . The engine 1 is installed in a four-wheeled automobile. The automobile runs as the engine 1 operates. The fuel of the engine 1 is gasoline in this configuration example. The fuel may be liquid fuel containing at least gasoline. The fuel may be gasoline, including, for example, bioethanol.

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

A piston 3 is slidably inserted in each cylinder 11 . Piston 3 is connected to crankshaft 15 via connecting rod 14 . Piston 3 defines combustion chamber 17 together with cylinder 11 and cylinder head 13 . Incidentally, the term "combustion chamber" may be used in a broad sense. In other words, the "combustion chamber" may mean the 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 diagram of FIG. The inclined surface 1311 slopes upward from the intake side toward the injection axis X2 of the injector 6, which will be described later. The inclined surface 1312 slopes upward 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 protrudes toward the ceiling surface of the combustion chamber 17 . A cavity 31 is formed in the upper surface of the piston 3 . A cavity 31 is recessed from the upper surface of the piston 3 . The cavity 31 has a shallow plate shape in this configuration example. The center of the cavity 31 is shifted from the center axis X1 of the cylinder 11 toward the exhaust side.

The geometric compression ratio of the engine 1 is set to 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 some operating ranges. SPCCI combustion utilizes the heat generation and pressure increase due to SI combustion to control CI combustion. The engine 1 is of a compression ignition type. This engine 1 does not need to increase 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 have a relatively low geometric compression ratio. A lower geometric compression ratio favors lower cooling losses and lower mechanical losses. The geometric compression ratio of the engine 1 is 14 to 17 for regular specifications (low octane fuel with an octane number of about 91) and 15 for high octane specifications (high octane fuel with an octane number of about 96). ~18 may be used.

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 . Although detailed illustration is omitted, the intake port 18 is a so-called tumble port. That is, the intake port 18 has a shape that forms a tumble flow in the combustion chamber 17 .

An intake valve 21 is arranged in 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 a valve mechanism. The valve mechanism may be a variable valve mechanism that varies valve timing and/or valve lift. In this configuration example, the variable valve mechanism has an electric intake S-VT (Sequential-Valve Timing) 23, as shown in FIG. The electric intake S-VT 23 continuously changes the rotation phase of the intake camshaft within a predetermined angle range. The opening timing and closing timing of the intake valve 21 continuously change. The intake valve mechanism may have a hydraulic S-VT instead of the electric S-VT. The intake valve 21 and the electric intake S-VT 23 are an example of a state quantity control section.

The cylinder head 13 is also formed with an exhaust port 19 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 arranged in 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 a valve mechanism. This valve mechanism may be a variable valve mechanism that varies valve timing and/or valve lift. In this configuration example, the variable valve mechanism has an electric exhaust S-VT 24, as shown in FIG. The electric exhaust S-VT 24 continuously changes the rotation phase of the exhaust camshaft within a predetermined angle range. The opening timing and closing timing of the exhaust valve 22 continuously change. The exhaust valve mechanism may have a hydraulic S-VT instead of the electric S-VT. The exhaust valve 22 and the electric exhaust S-VT 24 are an example of a state quantity control section.

The electric intake S-VT 23 and the electric exhaust S-VT 24 adjust the length of the overlap period during which both the intake valve 21 and the exhaust valve 22 are open. By increasing the length of the overlap period, residual gases in the combustion chamber 17 can be scavenged. Also, internal EGR (Exhaust Gas Recirculation) gas can be introduced into the combustion chamber 17 by adjusting the length of the overlap period. The electric intake S-VT 23 and the electric exhaust S-VT 24 constitute an internal EGR system. Note that the internal EGR system is not limited to the S-VT.

An injector 6 is attached to the cylinder head 13 for each cylinder 11 . Injector 6 injects fuel directly into combustion chamber 17 . The injector 6 is an example of a fuel supply section. The injector 6 is arranged in the valley of the pent roof where the inclined surfaces 1311 and 1312 intersect. As shown in FIG. 2, the injection axis X2 of the injector 6 is positioned closer to the exhaust side than the center axis X1 of the cylinder 11. As shown in FIG. 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 are aligned. The injector 6 faces the cavity 31 . Note that the injection axis X2 of the injector 6 may coincide with the central axis X1 of the cylinder 11 . In that configuration, the injection axis X2 of the injector 6 and the center of the cavity 31 may coincide.

Although detailed illustration is omitted, the injector 6 is configured by a multi-orifice fuel injection valve having a plurality of orifices. The injector 6 injects the fuel so that the fuel spray spreads radially from the center of the combustion chamber 17, as indicated by the two-dot chain line in FIG. In this 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 connecting the fuel tank 63 and the injector 6 to each other. A fuel pump 65 and a common rail 64 are interposed in the fuel supply path 62 . Fuel pump 65 delivers fuel to common rail 64 . The fuel pump 65 is a plunger pump driven by the crankshaft 15 in this configuration example. Common rail 64 stores fuel sent from fuel pump 65 at 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 is capable of supplying high pressure fuel of 30 MPa or higher to the injector 6 . The pressure of fuel supplied to the injector 6 may be changed according to the operating state of the engine 1 . Note that the configuration of the fuel supply system 61 is not limited to the configuration described above.

A spark plug 25 is attached to the cylinder head 13 for each cylinder 11 . A spark plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17 . The spark plug 25 is disposed on the intake side of the central axis X1 of the cylinder 11 in this configuration example. A spark plug 25 is positioned between the two intake ports 18 . The spark plug 25 is attached to the cylinder head 13 so as to be tilted from top to bottom toward the center of the combustion chamber 17 . The electrode of the spark plug 25 faces the inside of the combustion chamber 17 and is positioned near the ceiling surface of the combustion chamber 17, as shown in FIG. Note that 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 center axis X1 of the cylinder 11. FIG.

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 . Gas introduced into the combustion chamber 17 flows through the intake passage 40 . An air cleaner 41 is arranged at the upstream end of the intake passage 40 . 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 . A downstream end of the independent passage is connected to the intake port 18 of each cylinder 11 .

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

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

An electromagnetic clutch 45 is interposed between the supercharger 44 and the engine 1 . Between the supercharger 44 and the engine 1 , the electromagnetic clutch 45 transmits driving force from the engine 1 to the supercharger 44 or cuts off transmission of the driving force. As will be described later, the ECU 10 switches between connection and disconnection of the electromagnetic clutch 45 to switch the supercharger 44 between on and off.

An intercooler 46 is arranged downstream of the supercharger 44 in the intake passage 40 . Intercooler 46 cools the gas compressed in supercharger 44 . The intercooler 46 may be configured to be water-cooled or oil-cooled, for example.

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 so as to bypass the supercharger 44 and the intercooler 46 . An air bypass valve 48 is arranged in the bypass passage 47 . The air bypass valve 48 adjusts the flow rate of gas flowing through the bypass passage 47 .

The ECU 10 fully opens the air bypass valve 48 when the turbocharger 44 is turned off (that is, when the electromagnetic clutch 45 is disconnected). 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 a 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). Part of the gas that has passed through the supercharger 44 flows back upstream of the supercharger 44 through the bypass passage 47 . When the ECU 10 adjusts the opening of the air bypass valve 48, the boost pressure of the gas introduced into the combustion chamber 17 changes. It should be noted that the term "supercharging" refers to the time when the pressure in the surge tank 42 exceeds the atmospheric pressure, and the term "non-supercharging" refers to the time when the pressure in the surge tank 42 falls below the atmospheric pressure. good too.

In this configuration example, a 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 quantity control section.

The engine 1 has a swirl generator in the combustion chamber 17 that generates a swirl flow. The swirl flow flows as indicated by 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 in the secondary passage of the primary passage leading to one of the two intake ports 18 and the secondary passage leading to the other intake port 18. are arranged. The swirl control valve 56 is an opening control valve capable of narrowing the cross section of the secondary passage. If the opening of the swirl control valve 56 is small, the amount of intake air entering the combustion chamber 17 from one intake port 18 is relatively large, and the amount of intake air entering the combustion chamber 17 from the other intake port 18 is relatively small. , the swirl flow in the combustion chamber 17 becomes stronger. When the opening of the swirl control valve 56 is large, the amount of intake air entering the combustion chamber 17 from each of the two intake ports 18 becomes substantially equal, so the swirl flow in the combustion chamber 17 becomes weak. When the swirl control valve 56 is fully opened, no swirl flow occurs.

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. An upstream portion of the exhaust passage 50 constitutes an independent passage that branches for each cylinder 11, though detailed illustration is omitted. 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 . Although not shown, the upstream catalytic converter is arranged in the engine room. The upstream catalytic converter has a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512 . A downstream catalytic converter is located outside the engine compartment. The downstream catalytic converter has a three-way catalyst 513 . It should be noted that the exhaust gas purification system is not limited to the configuration of the illustrated example. For example, GPF may be omitted. Also, the catalytic converter is not limited to having a three-way catalyst. Furthermore, the order in which the three-way catalyst and GPF are arranged may be changed as appropriate.

An EGR passage 52 that constitutes an external EGR system is connected between the intake passage 40 and the exhaust passage 50 . The EGR passage 52 is a passage for recirculating part of the exhaust gas to the intake passage 40 . The upstream end of the EGR passage 52 is connected between the upstream and downstream catalytic converters in the exhaust passage 50 . A downstream end of the EGR passage 52 is connected to an upstream portion of the supercharger 44 in the intake passage 40 . 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 arranged in the EGR passage 52 . The EGR cooler 53 cools the exhaust gas. An EGR valve 54 is also arranged in the EGR passage 52 . The EGR valve 54 adjusts the flow rate of exhaust gas flowing through the EGR passage 52 . By adjusting the opening 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 cooler exhaust gas to the combustion chamber 17 than the internal EGR system. The EGR system 55 is an example of a state quantity adjusting section.

1 and 3, reference numeral 57 denotes an alternator 57 connected to the crankshaft 15. As shown in FIG. Alternator 57 is driven by engine 1 .

The control device for the internal combustion engine includes an ECU (Engine Control Unit) 10 for operating the engine 1 . The ECU 10 is a well-known microcomputer-based controller, and as shown in FIG. (Read Only Memory) for storing programs and data, and an input/output bus 103 for inputting/outputting electrical signals. The ECU 10 is an example of a control section.

Various sensors SW1 to SW17 are connected to the ECU 10 as shown in FIGS. The sensors SW1 to SW17 output signals to the ECU 10. FIG. The sensors include the following sensors.

Airflow sensor SW1: arranged downstream of the air cleaner 41 in the intake passage 40, and measures the flow rate of fresh air flowing through the intake passage 40. First intake air temperature sensor SW2: arranged downstream of the air cleaner 41 in the intake passage 40, and , to measure the temperature of fresh air flowing through the intake passage 40. First pressure sensor SW3: arranged downstream of the connecting position of the EGR passage 52 in the intake passage 40 and upstream of the supercharger 44, and Second intake air temperature sensor SW4: arranged downstream of the turbocharger 44 in the intake passage 40 and upstream of the connecting position of the bypass passage 47, and flows out of the turbocharger 44 Second pressure sensor SW5 for measuring gas temperature Second pressure sensor SW5: Attached to surge tank 42 for measuring pressure of gas downstream of supercharger 44 In-cylinder pressure sensor SW6: Attached to cylinder head 13 corresponding to each cylinder 11 and measures the pressure in each combustion chamber 17 NOx sensor SW7: arranged downstream of the three-way catalyst 513 in the exhaust passage 50 and measures the NOx concentration in the exhaust gas that has passed through the three-way catalyst 513 Linear O _2- sensor SW8: arranged upstream of the upstream catalytic converter in the exhaust passage 50 and measures the oxygen concentration in the exhaust gas Lambda O _2- sensor SW9: arranged downstream of the three-way catalyst 511 in the upstream catalytic converter and , to measure the oxygen concentration in the exhaust gas Water temperature sensor SW10: Attached to the engine 1 to measure the temperature of cooling water Crank angle sensor SW11: Attached to the engine 1 to measure the rotation angle of the crankshaft 15 Accelerator 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 camshaft Exhaust Cam angle sensor SW14: Attached to the engine 1 to measure the rotation angle of the exhaust camshaft EGR differential pressure sensor SW15: Arranged in the EGR passage 52 to measure differential pressure upstream and downstream of the EGR valve 54 Fuel pressure sensor SW16: attached to the common rail 64 of the fuel supply system 61 and measures the pressure of the fuel supplied to the injector 6. Third intake air temperature sensor SW17: attached to the surge tank 42 and the temperature of the gas in the surge tank 42, in other words Then, the temperature of the intake air introduced into the combustion chamber 17 is measured.

The ECU 10 determines the operating state of the engine 1 based on the signals from these sensors SW1 to SW17, and calculates control amounts for each device according to predetermined control logic. The control logic is stored in memory 102 . The control logic includes using maps stored in memory 102 to compute target and/or control variables.

The ECU 100 transmits electric signals related to the calculated control amount to the injector 6, the spark plug 25, the electric intake S-VT 23, the electric exhaust S-VT 24, the fuel supply system 61, the throttle valve 43, the EGR valve 54, the supercharger 44. , 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 supercharging pressure based on the signal from the accelerator opening sensor SW12 and the map. Then, the ECU 10 adjusts the opening degree of the air bypass valve 48 based on the target supercharging pressure and the differential pressure across 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 is brought to the target supercharging pressure.

Further, the ECU 10 sets the target EGR rate based on the operating state of the engine 1 and the map. EGR rate is the ratio of EGR gas to total gas in 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 based on the differential pressure across the EGR valve 54 obtained from the signal of the EGR differential pressure sensor SW15. The external EGR gas amount introduced into the combustion chamber 17 is made to match the target EGR gas amount by performing feedback control for adjusting the opening degree of the EGR valve 54 by means of the external EGR gas amount.

Furthermore, the ECU 10 executes air-fuel ratio feedback control when a predetermined control condition is satisfied. Specifically, the ECU 10 controls the fuel injection of the injector 6 so that the air-fuel ratio of the air-fuel mixture becomes a desired value based on the oxygen concentration in the exhaust gas measured by the linear _O2 sensor SW8 and the lambda _O2 sensor SW9. Adjust quantity.

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

(SPCCI combustion concept)
The main purpose of the engine 1 is to improve fuel efficiency and exhaust gas performance. In the self-ignition combustion, if the temperature in the combustion chamber 17 before the start of compression varies, the self-ignition timing changes greatly. Therefore, the engine 1 performs SPCCI combustion, which is a combination of SI combustion and CI combustion.

In the SPCCI combustion, the ignition plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17, and the air-fuel mixture undergoes SI combustion due to flame propagation, and the heat generated by the SI combustion causes the combustion in the combustion chamber 17. When the temperature rises and the pressure in the combustion chamber 17 rises due to flame propagation, the unburned air-fuel mixture undergoes self-ignition for CI combustion.

By adjusting the calorific value of SI combustion, it is possible to absorb temperature variations 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 the target timing.

In SPCCI combustion, the heat release during SI combustion is milder than that during CI combustion. FIG. 4 illustrates a heat release rate waveform 801 in SPCCI combustion. The heat release rate waveform 801 in SPCCI combustion has a rising slope smaller than that in the CI combustion waveform. 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 release rate waveform may change from small to large at the timing of self-ignition. The heat release rate waveform 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 release rate is relatively high. However, since the CI combustion is performed after the top dead center of the compression stroke, the slope of the heat release rate waveform is prevented from becoming too large. The pressure fluctuation (dp/dθ) during CI combustion also becomes relatively mild.

Pressure fluctuation (dp/dθ) can be used as an index representing combustion noise. As described above, SPCCI combustion can reduce the pressure fluctuation (dp/dθ), so it is possible to avoid excessive combustion noise. Combustion noise of the engine 1 is suppressed below the permissible level.

The SPCCI combustion ends when the CI combustion ends. CI combustion has a shorter combustion period than SI combustion. The SPCCI combustion has an earlier combustion end timing than the SI combustion.

The heat release rate waveform of SPCCI combustion is formed such that the first heat release rate portion _QSI formed by SI combustion and the second heat release portion _QCI formed by CI combustion are continuous in this order. It is

(engine operating range)
FIG. 5 exemplifies a driving map related to control of the engine 1. As shown in FIG. The driving map is stored in the memory 102 of the ECU 10. FIG. An operation map 501 illustrated in FIG. 5 is an operation map when the engine 1 is half warmed up, 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 level of the wall temperature of the combustion chamber 17 and the temperature of the intake air. The ECU 10 controls the engine 1 using the selected driving map.

Each operation map 501 , 502 is defined by the load and rotation speed of the engine 1 . The operation map 501 is divided into two areas depending on the rotation speed. Specifically, the operation map 501 is divided into a high rotation area A1 where the rotation speed is N3 or higher, and an area A2 extending to low rotation and medium rotation areas. Driving map 502 is divided into three areas. Specifically, the operation map 502 includes the above-described high rotation area A1, low rotation and medium rotation areas A2, and a predetermined rotation speed range from N1 to N2 and a predetermined load range from L1 to L2 within the area A2. and the area A3.

Here, the low speed region, the middle speed region, and the high speed region are obtained by dividing the entire operating region of the engine 1 in the rotational speed direction into approximately three equal parts: the low speed region, the middle speed region, and the high speed region. , a low rotation area, a middle rotation area, and a high rotation area.

Operation maps 501 and 502 in 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. The operation of the engine 1 in each area of the operation maps 501 and 502 in FIG. 5 will be described in detail below.

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

The EGR system 55 introduces EGR gas into the combustion chamber 17 in order to improve fuel efficiency of the engine 1 . Specifically, the electric intake S-VT 23 and the electric exhaust S-VT 24 provide a positive overlap period in which both the intake valve 21 and the exhaust valve 22 are opened near exhaust top dead center.

The air-fuel ratio (A/F) of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio throughout the combustion chamber 17 (that is, 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 has finished injecting fuel, the spark plug 25 ignites the air-fuel mixture in the combustion chamber 17 . In the area A3, the engine 1 performs A/F lean combustion operation.

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

EGR system 55 introduces EGR gases into combustion chamber 17 . Specifically, the electric intake S-VT 23 and the electric exhaust S-VT 24 provide a positive overlap period in which both the intake valve 21 and the exhaust valve 22 are opened near exhaust top dead center. Internal EGR gases are introduced into the combustion chamber 17 . Also, 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 area A2. That is, the external EGR gas having a lower temperature than the internal EGR gas is introduced into the combustion chamber 17 . External EGR gas regulates the temperature in combustion chamber 17 to a suitable temperature. The EGR system 55 reduces the amount of EGR gas as the load on the engine 1 increases. The EGR system 55 may null EGR gases, including internal EGR gases and external EGR gases, at full load.

The air-fuel ratio (A/F) of the air-fuel mixture in the entire combustion chamber 17 is the stoichiometric air-fuel ratio (A/F≈14.7). By purifying the exhaust gas discharged from the combustion chamber 17 by the three-way catalysts 511 and 513, the exhaust gas performance of the engine 1 is improved. The A/F of the air-fuel mixture should be kept within the purification window of the three-way catalyst. The excess air ratio λ of the mixture may be 1.0±0.2. When the engine 1 is running at full load (that is, maximum load), even if the A/F of the air-fuel mixture is the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio in the entire combustion chamber 17, good (that is, the excess air ratio λ of the air-fuel mixture is λ≦1). The throttle valve 43 is adjusted to full open or intermediate opening.

Since the EGR gas is introduced into the combustion chamber 17, G/F, which is the weight ratio of the total gas and fuel in the combustion chamber 17, 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. Also, 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 the fuel. In the region A2, the engine 1 performs stoichiometric combustion operation. It can also be said that the engine 1 performs G/F lean combustion operation in the region A2.

(Engine operation in area A1)
When the rotation speed of the engine 1 is high, the time required for the crank angle to change by 1° is shortened. When the rotation speed of the engine 1 increases, 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.

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

The air-fuel ratio (A/F) of the air-fuel mixture is basically the stoichiometric 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 set to 1.0±0.2. The excess air ratio λ of the air-fuel mixture may be less than 1 when the engine 1 is operating near a fully open load. The throttle valve 43 is adjusted to full open or intermediate opening.

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.

(engine fuel ratio control)
When the lean combustion operation is performed in the region A3 described above, making the fuel ratio (that is, A/F) as lean as possible is advantageous for improving the fuel consumption performance and cleaning the exhaust gas. However, if the fuel ratio is made too lean, there is a problem that combustion variation (SDI (Standard Deviation of IMEP (Indicated Mean Effective Pressure))) increases and drivability deteriorates. Further, even when the stoichiometric combustion operation is performed in the region A2, making the fuel ratio (that is, G/F) as lean as possible is advantageous for improving the fuel efficiency and cleaning the exhaust gas. Similarly, if the engine is made too lean, the combustion fluctuation will increase and the drivability will deteriorate.

Therefore, a permissible value of combustion fluctuation is determined in advance for each operating point of the engine 1, and the ECU 10 sets a lean limit of the fuel ratio based on the permissible value of combustion fluctuation. By adjusting the fuel ratio so as not to exceed the set lean limit, the engine 1 achieves both improved drivability and improved fuel efficiency.

FIG. 6 exemplifies functional blocks of the ECU 10 that execute control related to fuel ratio adjustment. FIG. 7 exemplifies a control procedure regarding fuel ratio adjustment executed by the ECU 10 .

The ECU 10 has an allowable value setting section 104 , a lean limit setting section 105 , a fuel ratio adjustment section 106 , a fuel ratio estimation section 107 and a correction section 108 . A tolerance setting unit 104, a lean limit setting unit 105, and a fuel ratio adjustment unit 106 are related to adjustment of the fuel ratio. A fuel ratio estimator 107 and a modifier 108 are involved in modifying the model related to setting the lean limit.

Based on the operating state of the engine 1, the allowable value setting unit 104 sets the allowable combustion fluctuation value (that is, the allowable SDI) corresponding to the operating state. The permissible value of combustion fluctuation is set in advance for each operating point of the engine 1 and stored in the memory 102 .

Lean limit setting unit 105 sets the lean limit based on the allowable value of combustion fluctuation set by allowable value setting unit 104 and model 109 stored in memory 102 . The model 109 is composed of a basic model block 110 and a correction block 111, as shown in FIG. A basic model block 110 establishes a basic value for the lean limit from the allowable SDI. A correction block 111 corrects the base value of the lean limit defined by the base model block 110 .

The basic model block 110 includes a first model 81, a second model 82, a third model 83 and a fourth model 84, as shown in FIG.

The first model 81 defines the relationship between the combustion variation (SDI) and the average in-cylinder pressure Pmi in one cycle. Lean limit setting unit 105 sets average in-cylinder pressure Pmi based on allowable SDI and first model 81 .

The second model 82 defines the relationship between the thermal efficiency calculated based on the average in-cylinder pressure Pmi and the fuel injection amount Qin and mfb50. mfb50 means the crank angle at which 50% of the total injection amount of fuel is burned. In other words, mfb50 corresponds to a specific crank angle at which the mass combustion ratio becomes a predetermined value. Lean limit setting unit 105 sets mfb50 based on average in-cylinder pressure Pmi, fuel injection amount Qin, and second model 82 .

A third model 83 defines the relationship between mfb 50 and combustion duration. The combustion period here means the crank angle period from mfb10 to mfb50. A lean limit setting unit 105 sets the combustion period based on the mfb 50 and the third model 83 .

A fourth model 84 defines the relationship between combustion duration and fuel ratio. Based on the combustion period and the fourth model 84, the lean limit setting unit 105 sets the fuel ratio, that is, the lean limit corresponding to the permissible value of combustion fluctuation.

In this way, when the basic value of the lean limit is set by the first model 81 to the fourth model 84, the lean limit setting unit 105 corrects the basic value. The correction block 111 will be described later.

Based on the operating state of the engine 1 and the set lean limit, the fuel ratio adjusting unit 106 adjusts the target fuel ratio so as not to exceed the set lean limit and to correspond to the operating state of the engine 1. set. The fuel ratio adjusting unit 106 also adjusts the in-cylinder state quantity and the fuel injection amount so as to satisfy the set target fuel ratio, thereby combusting the air-fuel mixture. Specifically, the fuel ratio adjustment unit 106 outputs a signal related to fuel injection to the injector 6, and the electric intake S-VT 23, the electric exhaust S-VT 24, the throttle valve 43, the EGR valve 54, and the air bypass valve 48, It outputs a signal related to the adjustment of the in-cylinder state quantity.

The fuel ratio estimating unit 107 estimates the fuel ratio of the air-fuel mixture from the model 109 and the combustion fluctuation estimated based on the signal output from the in-cylinder pressure sensor SW6 during combustion. The model 109 is stored in the memory 102 and is the same as the model 109 used when the lean limit setting unit 105 sets the lean limit as shown in FIG.

Here, the fuel ratio estimator 107 may use Bayesian estimation when estimating the combustion fluctuation. The operating state of the engine 1 changes moment by moment, and the same operating state rarely continues. However, if Bayesian estimation is used, it is possible to accurately estimate combustion fluctuations from a small number of samples.

The correction unit 108 measures the actual 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 airflow sensor SW1. Corrector 108 also compares the measured actual fuel ratio with the fuel ratio estimated by fuel ratio estimator 107, and corrects correction block 111 of model 109 based on the comparison. The modified correction block 111 is stored in memory 102 .

Instead of correcting the correction block 111, the basic model block 110 may be corrected. In that case, the correction block 111 may be omitted.

The relationship between the combustion fluctuation and the fuel ratio has individual differences for each engine 1 and changes with age. By comparing the measured fuel ratio and the fuel ratio estimated using the model 109 by the correction unit 108, the model 109 can be corrected as needed.

As a result, the lean limit setting unit 105 can accurately set the lean limit based on the accurate model 109 . The ECU 10 adjusts the fuel ratio based on the exact lean limit when the engine 1 is performing A/F lean-burn operation or when performing G/F lean-burn operation (that is, stoichiometric burn operation). Therefore, unstable combustion is suppressed. A decrease in the drivability of the automobile is suppressed. Also, the A/F or G/F can be made as lean as possible based on the accurate lean limit, which is advantageous for improving the fuel efficiency of automobiles.

Next, the control of the engine 1 executed by the ECU 10 will be described with reference to the flowchart of FIG. The flow chart of FIG. 9 relates to adjustment control of the fuel ratio of the engine 1 . Note that the order of each step in the flowchart of FIG. 9 can be changed.

In step S1, the ECU 10 reads signals from the sensors SW1 to SW17. In subsequent step S2, the fuel ratio estimator 107 of the ECU 10 estimates the fuel ratio based on the signal from the in-cylinder pressure sensor SW6 and the model 109 stored in the memory 102, as described above. In the next step S3, the correction section 108 of the ECU 10 measures the actual fuel ratio based on the fuel injection amount and the signal of the airflow sensor SW1.

In step S4, correction unit 108 determines whether or not there is a discrepancy between the fuel ratio estimated in step S2 and the fuel ratio measured in step S3. If there is no deviation, the process proceeds to step S6, otherwise the process proceeds to step S7. In step S<b>6 , the correction unit 108 does not correct the model 109 . In step S<b>7 , the correction unit 108 corrects the correction block 111 of the model 109 according to the deviation and stores it in the memory 102 .

In step S8, the lean limit setting unit 105, based on the allowable combustion fluctuation value (that is, allowable SDI) set by the allowable value setting unit 104 based on the operating point of the engine 1 and the model 109 stored in the memory 102, Set lean limits.

In step S9, the fuel ratio adjustment unit 106 sets the target fuel ratio so as not to exceed the lean limit set in step S8. , to output control signals to each device.

Note that the technology disclosed herein is not limited to application to the engine 1 having the configuration described above. Various configurations can be adopted for the configuration of the engine 1 .

1 engine (internal combustion engine)
10 ECU (control unit)
104 allowable value setting unit 105 lean limit setting unit 106 fuel ratio adjustment unit 107 fuel ratio estimation unit 108 correction unit 109 model 21 intake valve (state quantity adjustment unit)
22 Exhaust valve (state quantity control unit)
23 Electric intake S-VT (state quantity adjustment unit)
24 exhaust electric S-VT (state quantity control unit)
43 Throttle valve (state quantity control unit)
44 turbocharger (state quantity control unit)
49 supercharging system (state quantity control part)
54 EGR valve (state quantity control unit)
55 EGR system (state quantity control unit)
6 injector (fuel supply unit)
81 First model 82 Second model 83 Third model 84 Fourth model SW1 Airflow sensor SW6 In-cylinder pressure sensor

Claims (4)

A control method for an internal combustion engine capable of lean-burn operation, comprising:
a step in which a control unit sets an allowable value of combustion fluctuation , which is an allowable value predetermined for each operating state of the internal combustion engine, based on the operating state determined by the load and the rotational speed of the internal combustion engine;
The control unit determines a lean limit in the operating state of the internal combustion engine based on the set allowable value of combustion fluctuation and a model for setting the lean limit of the fuel ratio of the air-fuel mixture from the allowable value of combustion fluctuation. and setting
The control unit sets a target fuel ratio so that the fuel ratio does not exceed the lean limit and corresponds to the operating state of the internal combustion engine, and satisfies the set target fuel ratio. a step of adjusting the in-cylinder state quantity and the fuel quantity, which are gas quantities containing at least air, in the combustion chamber of the internal combustion engine through the state quantity adjusting unit and the fuel supply unit, and burning the air-fuel mixture;
a step in which the controller estimates the fuel ratio of the air-fuel mixture from the model and the combustion fluctuation estimated based on the signal output by the in-cylinder pressure sensor during combustion;
a step in which the control unit corrects the model so that the difference between the estimated fuel ratio and the actual fuel ratio is eliminated, based on a comparison between the estimated fuel ratio and the measured actual fuel ratio ;
A control method for an internal combustion engine comprising In the method for controlling an internal combustion engine according to claim 1,
The model is
a first model that defines the relationship between the combustion fluctuation and the average in-cylinder pressure;
a second model that defines the relationship between the thermal efficiency calculated based on the average in-cylinder pressure and the fuel injection amount and the specific crank angle at which the mass combustion ratio is a predetermined value;
a third model that defines the relationship between the specific crank angle and the combustion period;
a basic model block including a fourth model that defines the relationship between the combustion period and the lean limit;
a correction block that corrects the base value of the lean limit determined by the base model block;
The method of controlling an internal combustion engine, wherein the control unit corrects the correction block so that there is no difference between the estimated fuel ratio and the actual fuel ratio . A control device for an internal combustion engine capable of lean-burn operation,
a fuel supply attached to the internal combustion engine;
a state quantity adjustment unit that adjusts an in-cylinder state quantity, which is an amount of gas containing at least air, in a combustion chamber of the internal combustion engine;
A control unit that outputs a control signal to the fuel supply unit and the state quantity adjustment unit so that the fuel ratio of the air-fuel mixture does not exceed a lean limit that is determined according to the operating state that is determined by the load and rotation speed of the internal combustion engine. and,
an in-cylinder pressure sensor connected to the control unit and outputting a signal corresponding to the pressure in the cylinder to the control unit;
a sensor connected to the control unit and outputting a signal related to the fuel ratio to the control unit;
The control unit
an allowable value setting unit for setting an allowable value of combustion fluctuation , which is an allowable value predetermined for each operating state of the internal combustion engine, based on the operating state of the internal combustion engine ;
A lean limit setting unit for setting a lean limit in the operating state of the internal combustion engine based on the set allowable value of combustion fluctuation and a model for setting the lean limit of the fuel ratio of the air-fuel mixture from the allowable value of combustion fluctuation. and,
A target fuel ratio is set so that the fuel ratio does not exceed the lean limit and corresponds to the operating state of the internal combustion engine, and the state quantity is set so that the set target fuel ratio is satisfied. a fuel ratio adjustment unit that adjusts the in - cylinder state quantity and the fuel amount of the internal combustion engine through the adjustment unit and the fuel supply unit and combusts the air-fuel mixture;
a fuel ratio estimating unit for estimating the fuel ratio of the air-fuel mixture from the combustion fluctuation estimated based on the signal output by the in-cylinder pressure sensor during combustion and the model;
a correction unit that corrects the model so that the difference between the estimated fuel ratio and the actual fuel ratio is eliminated based on a comparison between the estimated fuel ratio and the actual fuel ratio based on the sensor signal; A control device for an internal combustion engine having In the control device for an internal combustion engine according to claim 3,
The model is
a first model that defines the relationship between the combustion fluctuation and the average in-cylinder pressure;
a second model that defines the relationship between the thermal efficiency calculated based on the average in-cylinder pressure and the fuel injection amount and the specific crank angle at which the mass combustion ratio is a predetermined value;
a third model that defines the relationship between the specific crank angle and the combustion period;
a basic model block including a fourth model that defines the relationship between the combustion period and the lean limit;
a correction block that corrects the base value of the lean limit determined by the base model block;
A control device for an internal combustion engine, wherein the correction unit corrects the correction block so as to eliminate a difference between the estimated fuel ratio and the actual fuel ratio.

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