Method for controlling engine

Abstract

To optimize the fuel consumption performance of an engine while taking into consideration various restrictions imposed on the engine.SOLUTION: A method for controlling an engine has: a step of selecting a control point consisting of a combination of injection timing of fuel and ignition timing of an air-fuel mixture so as to correspond to a selection on a parameter map Mlim having the injection timing as a first axis and the ignition timing as a second axis; defines a parameter region Rlim on the parameter map Mlim, which is surrounded by a first limit line Li1 indicating an advance limit at which preignition is restrained, a second limit line Li2 indicating an advance limit at which smoke is restrained, a third limit line Li3 indicating an advance limit at which knocking is restrained, and a fourth limit line Li4 indicating a retard limit at which combustion stability is ensured; and further has a step of selecting the control point so that the ignition timing is brought to maximum advance within the parameter region Rlim.SELECTED DRAWING: Figure 14

Description

Technical Field

[0001] The present disclosure relates to a method for controlling an engine.

Background Art

[0002] Patent Document 1 discloses a control device for a diesel engine. Specifically, the control device described in Patent Document 1 is configured to expand or contract a low-temperature premixed combustion region according to the setting of a premature ignition limit that is the limit of the fuel injection timing.

[0003] Further, Patent Document 2 discloses a control device for an internal combustion engine. Specifically, the control device described in Patent Document 2 is configured to keep the timing (final injection timing) at which the last fuel injection in one combustion cycle ends within a predetermined effective injection period.

[0004] Further, Patent Document 3 discloses another example of a control device for an internal combustion engine. Specifically, the control device described in Patent Document 3 is configured to perform ignition timing feedback control so as to keep the ignition timing at a knocking limit at which weak knocking occurs.

[0005] Further, Patent Document 4 discloses a control device for a vehicle. Specifically, the control device described in Patent Document 4 is configured to retard the ignition timing of an ignition plug within a range on the advanced angle side from a predetermined retard limit. Here, the retard limit described in Patent Document 4 means a limit value on the retard side at which the combustion stability of the engine is ensured.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0007] As described in Patent Documents 1 to 4 above, it has been known for a long time to consider the premature ignition limit, knocking limit, retard limit, etc. when setting the fuel injection timing and the ignition timing to the air-fuel mixture, respectively.

[0008] However, these constraints are defined from viewpoints different from the fuel consumption performance of the engine. Therefore, there is still room for optimization with respect to the fuel consumption performance of the engine.

[0009] The present disclosure has been made in view of such points, and an object thereof is to optimize the fuel consumption performance of an engine while considering various constraints imposed on the engine.

Means for Solving the Problems

[0010] A first aspect of the present disclosure relates to a method for controlling an engine using a cylinder, an injector that injects fuel into the cylinder, a spark plug that ignites an air-fuel mixture containing the fuel injected from the injector, and a controller that is electrically connected to the injector and the spark plug and controls each of the injector and the spark plug. This control method includes a step in which the controller selects a control point consisting of a combination of the injection timing and the ignition timing so as to correspond to a selection on a parameter map having the injection timing of fuel by the injector as a first axis and the ignition timing of the air-fuel mixture by the spark plug as a second axis. On the parameter map, a plurality of limit lines that change according to the operating state of the engine are provided. The plurality of limit lines include a first limit line indicating an advance angle limit for suppressing premature ignition, a second limit line indicating an advance angle limit for suppressing smoke, a third limit line indicating an advance angle limit for suppressing knocking, and a fourth limit line indicating a retard angle limit for ensuring combustion stability. The parameter map is partitioned into parameter regions surrounded by the plurality of limit lines, and the controller further has a step of selecting the control point so that the ignition timing is the most advanced within the range of the parameter region.

[0011] According to the first aspect, by determining the combination of the injection timing and the ignition timing within the parameter region, it becomes possible to set within the range of various constraints when selecting the injection timing and the ignition timing.

[0012] Furthermore, by setting the ignition timing to the most advanced within the parameter region, it is possible to optimize the fuel consumption performance of the engine while taking into account various constraints imposed on the engine.

[0013] Further, according to a second aspect of the present disclosure, when the control point goes outside the parameter region as the parameter region shrinks, the controller shifts the control point to any of the limit lines constituting the parameter region, and then, each time the combustion cycle is repeated, the controller stepwise shifts the control point so that the ignition timing is advanced to the maximum within the range of the shrunk parameter region.

[0014] According to the second aspect, even if the control point goes outside the parameter region, by shifting the control point to any of the limit lines, it is possible to preferentially respond to the constraints imposed on the engine. Thereafter, by gradually advancing the ignition timing, each process can be performed according to a desired priority order.

[0015] Further, according to a third aspect of the present disclosure, the controller may execute the step of shifting the control point to any of the limit lines by feedforward control based on the operating state of the engine within one combustion cycle.

[0016] According to the third aspect, within one combustion cycle, the control point will be shifted to the limit line. Thereby, it is possible to respond to the constraints imposed on the engine as quickly as possible.

[0017] Further, according to a fourth aspect of the present disclosure, when the ignition timing becomes non-advanced as the parameter region expands, the engine control method may further include a step of the controller stepwise shifting the control point each time the combustion cycle is repeated so that the ignition timing is advanced to the maximum within the range of the expanded parameter region.

[0018] According to the fourth aspect, with respect to the advancement of the ignition timing, it is to be carried out step by step for each combustion cycle. By changing the ignition timing step by step, the ignition timing can be more reliably shifted to the advanced angle point.

[0019] Further, according to the fifth aspect of the present disclosure, a piston is accommodated in the cylinder, a cavity is formed on the upper surface of the piston, and the plurality of limit lines may further include a fifth limit line indicating that the fuel injected from the injector reaches into the cavity.

[0020] According to the fifth aspect, an advanced angle stage for the fuel injected from the injector to reach into the cavity is incorporated into the plurality of limit lines. Thereby, constraints can be imposed on the engine from a more comprehensive perspective. This is advantageous for improving the performance of the engine.

[0021] Further, according to the sixth aspect of the present disclosure, the plurality of limit lines may further include a sixth limit line indicating an advanced angle limit for the fuel injected from the injector to reach the spark plug.

[0022] According to the sixth aspect, an advanced angle stage for the fuel injected from the injector to reach the spark plug is incorporated into the plurality of limit lines. Thereby, constraints can be imposed on the engine from a more comprehensive perspective. This is advantageous for improving the performance of the engine.

[0023] Further, according to the seventh aspect of the present disclosure, the fourth limit line may indicate the retard limit of the ignition timing.

[0024] According to the seventh aspect, a retard limit of the ignition timing is incorporated into the plurality of limit lines. Thereby, constraints can be imposed on the engine combustion control from a more important perspective. This is advantageous for improving the performance of the engine.

Advantages of the Invention

[0025] As described above, according to the present disclosure, it is possible to optimize the fuel consumption performance of the engine while considering various constraints imposed on the engine.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 14

Figure 15A

Figure 15B

Figure 15C

Figure 16

[0027] Hereinafter, a method for controlling an engine will be described with reference to the drawings. The engine and its control method described here are examples.

[0028] FIG. 1 is a diagram illustrating an engine system. FIG. 2 is a diagram illustrating the structure of a combustion chamber of the engine. The positions of the intake side and the exhaust side in FIG. 1 and the positions of the intake side and the exhaust side in FIG. 2 are interchanged. FIG. 3 is a block diagram illustrating a control device for the engine.

[0029] <1. Overall Configuration> The engine system has an engine 1. The engine 1 has a cylinder 11. In the cylinder 11, an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke are repeated. The engine 1 is a four-stroke engine. The engine 1 is mounted on a four-wheel automobile. When the engine 1 operates, the automobile runs.

[0030] Engine 1 is an engine compatible with multiple types of fuel. That is, this engine 1 is a so-called multi-fuel compatible engine. The fuel of engine 1 may be gasoline, an alternative fuel such as naphtha, various carbon-neutral fuels such as methanol, or a mixture of these fuels (a mixture of miscible fuels).

[0031] Also, as the fuel of engine 1, both high-octane fuel and low-octane fuel can be used. The octane number of the high-octane fuel is, for example, 100, and the octane number of the low-octane fuel is, for example, 91.

[0032] The user of the automobile can refuel the fuel tank 63 described later with the fuel included in the plurality of types of fuel. For example, after using up the fuel stored in the fuel tank 63, a different fuel can be added to the same fuel tank 63. The user can also add low-octane fuel to the fuel tank 63 storing high-octane fuel, and can add high-octane fuel to the fuel tank 63 storing low-octane fuel. When fuels with different octane numbers are added, the octane number of the fuel used by engine 1 becomes an intermediate octane number.

[0033] <2. Configuration of the Engine> Engine 1 includes a cylinder block 12 and a cylinder head 13. The cylinder head 13 is placed on the cylinder block 12. A plurality of cylinders 11 are formed in the cylinder block 12. Engine 1 is a multi-cylinder engine. In FIG. 1, only one cylinder 11 is shown.

[0034] A piston 3 is inserted (accommodated) into each cylinder 11. The piston 3 is connected to a crankshaft 15 via a connecting rod 14. The piston 3 reciprocates inside the cylinder 11. The piston 3, the cylinder 11, and the cylinder head 13 form a combustion chamber 17.

[0035] The lower surface of the cylinder head 13, that is, the ceiling portion of the cylinder 11, is composed of an inclined surface 1311 and an inclined surface 1312 as shown in the lower figure of FIG. 2. The inclined surface 1311 is the inclined surface 1311 on the intake valve 21 side described later, and has an upward gradient toward the central portion of the cylinder 11. The inclined surface 1312 is the inclined surface 1312 on the exhaust valve 22 side, and has an upward gradient toward the central portion of the cylinder 11. The ceiling portion of the cylinder 11 is of a so-called pentroof type.

[0036] 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. In this configuration example, the cavity 31 has a shallow dish shape. The central portion of the cavity 31 bulges upward. The bulging portion has a substantially conical shape.

[0037] Note that the shape of the combustion chamber 17 is not limited to the shape illustrated in FIG. 2. For example, the shape of the cavity 31, the shape of the upper surface of the piston 3, the shape of the ceiling surface of the combustion chamber 17, etc. can be changed as appropriate.

[0038] The geometric compression ratio of the engine 1 is set to be 10 or more and 30 or less. As will be described later, the engine 1 performs SPCCI combustion that combines SI (Spark Ignition) combustion and CI combustion (Compression Ignition) in some operating regions. The SPCCI combustion controls the CI combustion by heat generation and / or pressure increase by the SI combustion. The engine 1 is a compression ignition type engine. However, it is not necessary for the engine 1 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. Therefore, the engine 1 can be set to have a lower geometric compression ratio than an engine that does not perform SPCCI combustion. A lower geometric compression ratio is advantageous for reducing cooling loss and mechanical loss.

[0039] In the cylinder head 13, an intake port 18 is formed for each cylinder 11. The intake port 18 communicates with the inside of the cylinder 11. The intake port 18 is a so-called tumble port, although detailed illustration is omitted. That is, the intake port 18 has a shape such that a tumble flow is generated in the cylinder 11. The ceiling portion of the pentroof-type cylinder 11 and the tumble port generate a tumble flow in the cylinder 11.

[0040] An intake valve 21 is disposed in the intake port 18. The intake valve 21 opens and closes the intake port 18. The valve operating device is connected to the intake valve 21. The valve operating device opens and closes the intake valve 21 at a predetermined timing. The valve operating device is a variable valve operating device that makes the valve timing and / or the valve lift variable. As shown in FIG. 3, the valve operating device has an intake S-VT (Sequential-Valve Timing) 231. The intake S-VT 231 is hydraulic or electric. The intake S-VT 231 continuously changes the rotational phase of the intake camshaft within a predetermined angle range.

[0041] The valve operating device also has an intake CVVL (Continuously Variable Valve Lift) 232. As illustrated in FIG. 5, the intake CVVL 232 can continuously change the lift amount of the intake valve 21 within a predetermined range. The intake CVVL 232 can adopt various known configurations. As an example, as described in Japanese Patent Laid-Open No. 2006-85241, the intake CVVL 232 can be configured to include a link mechanism, a control arm, and a stepping motor. The link mechanism reciprocally oscillates a cam for driving the intake valve 21 in conjunction with the rotation of the camshaft. The control arm variably sets the lever ratio of the link mechanism. When the lever ratio of the link mechanism changes, the oscillation amount of the cam that pushes down the intake valve 21 changes. The stepping motor changes the oscillation amount of the cam by electrically driving the control arm, thereby changing the lift amount of the intake valve 21. Note that the intake CVVL 232 is not essential.

[0042] In the cylinder head 13, an exhaust port 19 is formed for each cylinder 11. The exhaust port 19 communicates with the inside of the cylinder 11.

[0043] An exhaust valve 22 is disposed in the exhaust port 19. The exhaust valve 22 opens and closes the exhaust port 19. The valve operating device is connected to the exhaust valve 22. The valve operating device opens and closes the exhaust valve 22 at a predetermined timing. The valve operating device is a variable valve operating device that makes the valve timing and / or valve lift variable. As shown in FIG. 3, the valve operating device has an exhaust S-VT 241. The exhaust S-VT 241 is hydraulic or electric. The exhaust S-VT 241 continuously changes the rotational phase of the exhaust camshaft within a predetermined angular range.

[0044] The valve operating device also has an exhaust VVL (Variable Valve Lift) 242. Although not shown, the exhaust VVL 242 is configured to be able to switch the cam that opens and closes the exhaust valve 22. The exhaust VVL 242 can adopt various known configurations. As an example, as described in Japanese Unexamined Patent Application Publication No. 2018-168796, the exhaust VVL 242 has a first cam, a second cam, and a switching mechanism that switches between the first cam and the second cam. The first cam is configured to open and close the exhaust valve 22 during the exhaust stroke. The second cam, as illustrated in FIG. 5, is configured to open and close the exhaust valve 22 during the exhaust stroke and also to open and close the exhaust valve 22 again during the intake stroke. The exhaust VVL 242 can change the lift of the exhaust valve 22 by opening and closing the exhaust valve 22 with either the first cam or the second cam. Note that the exhaust VVL 242 is not essential.

[0045] The intake S-VT 231, intake CVVL 232, exhaust S-VT 241, and exhaust VVL 242 adjust the amount of air introduced into the cylinder 11 and the amount of introduced burned gas by controlling the opening and closing of the intake valve 21 and the exhaust valve 22. The intake S-VT 231, intake CVVL 232, exhaust S-VT 241, and exhaust VVL 242 adjust the intake charge amount.

[0046] An injector 6 for injecting fuel into the cylinder 11 is attached to the engine 1. Specifically, an injector 6 is attached to the cylinder head 13 for each cylinder 11. As shown in FIG. 2, the injector 6 is disposed at the center of the cylinder 11. More specifically, the injector 6 is disposed at the valley portion of the pentroof where the inclined surface 1311 and the inclined surface 1312 intersect.

[0047] The injector 6 directly injects fuel into the cylinder 11. The injector 6 is of a multi-nozzle type having a plurality of nozzles, although detailed illustration is omitted. As shown by the two-dot chain line in FIG. 2, the injector 6 injects fuel so as to radially spread from the central portion to the peripheral portion of the cylinder 11. As shown in the lower figure of FIG. 2, the axis of the nozzle of the injector 6 has a predetermined angle θ with respect to the central axis X of the cylinder 11. Incidentally, in the illustrated example, the injector 6 has ten nozzles arranged at equal angles in the circumferential direction, but the number and arrangement of the nozzles are not particularly limited.

[0048] An injector 6 is connected to a fuel supply system 61. The fuel supply system 61 includes a fuel tank 63 configured to store fuel, and a fuel supply line 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 line 62. The fuel pump 65 pumps 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 pumped from the fuel pump 65 at a high fuel pressure. When the injector 6 opens its valve, the fuel stored in the common rail 64 is injected into the cylinder 11 from the nozzle of 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. Note that the configuration of the fuel supply system 61 is not limited to the above configuration.

[0049] Spark plugs 251 and 252 for igniting the air-fuel mixture containing the fuel injected from the injector 6 are attached to the engine 1. Specifically, a first spark plug 251 and a second spark plug 252 are attached to the cylinder head 13 for each cylinder 11. The first spark plug 251 and the second spark plug 252 each forcibly ignite the air-fuel mixture in the cylinder 11. As shown in FIG. 2, the first spark plug 251 is disposed between two intake valves 21, and the second spark plug 252 is disposed between two exhaust valves 22. The tips of the first spark plug 251 and the second spark plug 252 are located near the ceiling portion of the cylinder 11 on the intake side and the exhaust side with the injector 6 interposed therebetween. Note that there may be one spark plug.

[0050] An intake passage 40 is connected to one side surface of the engine 1. The intake passage 40 communicates with the intake ports 18 of each cylinder 11. The air introduced into the cylinder 11 flows through the intake passage 40. An air cleaner 41 is disposed at the upstream end of the intake passage 40. The air cleaner 41 filters the air. A surge tank 42 is disposed near the downstream end of the intake passage 40. The intake passage 40 downstream of the surge tank 42 constitutes independent passages that branch for each cylinder 11. The downstream ends of the independent passages are connected to the intake ports 18 of the respective cylinders 11.

[0051] A throttle valve 43 is disposed between the air cleaner 41 and the surge tank 42 in the intake passage 40. The throttle valve 43 can adjust the amount of air introduced into the cylinder 11 by adjusting the opening degree of the valve. The throttle valve 43 is basically fully open during the operation of the engine 1. The amount of air introduced is adjusted by the variable valve device described above.

[0052] The engine 1 has a swirl generation part that generates a swirl flow in the cylinder 11. The swirl generation part has a swirl control valve 56 attached to the intake passage 40. Although detailed illustration is omitted, the swirl control valve 56 is disposed in the secondary passage among the primary passage and the secondary passage connected to each cylinder 11 downstream of the surge tank 42. The swirl control valve 56 is an opening degree adjustment valve that can narrow the cross-section of the secondary passage. When the opening degree of the swirl control valve 56 is small, the intake air flow rate flowing from the primary passage into the cylinder 11 is relatively large and the intake air flow rate flowing from the secondary passage into the cylinder 11 is relatively small, so the swirl flow in the cylinder 11 becomes stronger. When the opening degree of the swirl control valve 56 is large, the intake air flow rates flowing from the primary passage and the secondary passage into the cylinder 11 become substantially equal, so the swirl flow in the cylinder 11 becomes weaker. When the swirl control valve 56 is fully open, no swirl flow is generated. Note that the swirl generation part is not essential.

[0053] On the other side of the engine 1, an exhaust passage 50 is connected. The exhaust passage 50 communicates with the exhaust ports 19 of each cylinder 11. The exhaust passage 50 is a passage through which the exhaust gas discharged from the cylinder 11 flows. The upstream portion of the exhaust passage 50 constitutes an independent passage that branches for each cylinder 11, although detailed illustration is omitted. The upstream end of the independent passage is connected to the exhaust port 19 of each cylinder 11.

[0054] An exhaust gas purification system having a plurality of catalytic converters is disposed in the exhaust passage 50. The upstream catalytic converter has, for example, a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512. The downstream catalytic converter has a three-way catalyst 513. Note that the exhaust gas purification system is not limited to the configuration shown in the figure. For example, the GPF may be omitted. Also, the catalytic converter is not limited to having a three-way catalyst. Furthermore, the arrangement order of the three-way catalyst and the GPF may be changed as appropriate.

[0055] An EGR passage 52 is connected between the intake passage 40 and the exhaust passage 50. The EGR passage 52 is a passage for refluxing 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 between the throttle valve 43 and the surge tank 42 in the intake passage 40.

[0056] A water-cooled EGR cooler 53 is disposed in the EGR passage 52. The EGR cooler 53 cools the exhaust gas. An EGR valve 54 is also disposed in the EGR passage 52. The EGR valve 54 adjusts the flow rate of the exhaust gas flowing through the EGR passage 52. By adjusting the opening degree of the EGR valve 54, the reflux amount of the cooled exhaust gas can be adjusted.

[0057] <3. Basic Configuration of the Control Device> As shown in FIG. 3, the control device for the engine 1 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 includes a central processing unit (CPU) 100a, a memory 100b, and an I / F circuit 100c. The CPU 100a executes programs. The memory 100b is composed of, for example, a RAM (Random Access Memory) and a ROM (Read Only Memory) and stores programs and data. The I / F circuit 100c inputs and outputs electrical signals. The ECU 10 is an example of a controller. The ECU 10 as a controller constitutes an engine system together with the engine 1.

[0058] The ECU 10 is electrically connected to, for example, an injector 6, a first spark plug 251, and a second spark plug 252. The ECU 10 controls each of the injector 6, the first spark plug 251, and the second spark plug 252.

[0059] As shown in FIGS. 1 and 3, various sensors SW1 to SW10 are connected to the ECU 10. The sensors SW1 to SW14 output signals to the ECU 10. The sensors include the following sensors. The sensors SW11 to SW14 are shown only in FIG. 3. Airflow sensor SW1: It is arranged downstream of the air cleaner 41 in the intake passage 40 and measures the flow rate of the air flowing through the intake passage 40. Intake air temperature sensor SW2: It is arranged downstream of the air cleaner 41 in the intake passage 40 and measures the temperature of the air flowing through the intake passage 40. Intake air pressure sensor SW3: It is attached to the surge tank 42 and measures the pressure of the air introduced into the cylinder 11. In-cylinder pressure sensor SW4: It is attached to the cylinder head 13 corresponding to each cylinder 11 and measures the pressure in each cylinder 11. Engine water temperature sensor SW5: It is attached to the engine 1 and measures the temperature of the cooling water. Crank angle sensor SW6: Mounted on Engine 1 and measures the rotational angle of the crankshaft 15. Accelerator opening sensor SW7: Mounted on the accelerator pedal mechanism and measures the accelerator opening corresponding to the operation amount of the accelerator pedal. Intake cam angle sensor SW8: Mounted on Engine 1 and measures the rotational angle of the intake camshaft. Exhaust cam angle sensor SW9: Mounted on Engine 1 and measures the rotational angle of the exhaust camshaft. Intake cam lift sensor SW10: Mounted on Engine 1 and measures the lift amount of the intake valve 21. Fuel pressure sensor SW11: Mounted on the common rail 64 of the fuel supply system 61 and detects the pressure of the fuel supplied to the injector 6. EGR differential pressure sensor SW12: Detects the differential pressure between the upstream and downstream of the EGR valve 54 Linear O2 sensor SW13: Arranged upstream of the upstream catalytic converter in the exhaust passage 50 and detects the oxygen concentration in the exhaust gas Lambda O2 sensor SW14: Arranged downstream of the three-way catalyst 511 in the upstream catalytic converter and detects the oxygen concentration in the exhaust gas The ECU 10 determines the operating state of Engine 1 based on the signals of these sensors SW1 to SW10, and calculates the control amount of each device according to a predetermined control logic. The control logic is stored in the memory 100b. The control logic includes calculating the target amount and / or the control amount using a map stored in the memory 100b.

[0060] The ECU 10 outputs an electrical signal related to the calculated control amount to the injector 6, the first ignition plug 251, the second ignition plug 252, the intake S-VT 231, the intake CVVL 232, the exhaust S-VT 241, the exhaust VVL 242, the fuel supply system 61, the throttle valve 43, the EGR valve 54, and the swirl control valve 56.

[0061] <4. Engine operation control map> FIG. 4 illustrates a base map related to the control of the engine 1. The base map is stored in the memory 100b of the ECU 10. The base map includes at least a first base map 401 shown in FIG. 4. The ECU 10 may use another base map different from the first base map 401 according to the high or low coolant water temperature of the engine 1. The first base map 401 is a base map used for controlling the engine 1 during the warm state of the engine 1.

[0062] The ECU 10 may use another base map different from the first base map 401 according to the octane number of the fuel. The first base map 401 is a base map used, for example, when the octane number = 91.

[0063] The first base map 401 is defined by the load and the rotational speed of the engine 1. The first base map 401 is roughly divided into four regions: a first region, a second region, a third region, and a fourth region, according to the high or low load and the high or low rotational speed.

[0064] More specifically, the first region includes a high rotation region 411 and a low load region 412. The high rotation region 411 extends over the entire range from low load to high load. The low load region 412 extends over the regions of low rotation and medium rotation.

[0065] The second region corresponds to a first medium load region 413. The first medium load region 413 is adjacent to the high load side of the low load region 412, extends from low load to medium load, and extends over the regions of low rotation and medium rotation.

[0066] The third region includes a second medium load region 414 and a high load medium rotation region 415. The second medium load region 414 is adjacent to the high load side of the first medium load region 413, extends from medium load to high load, and extends over the regions of low rotation and medium rotation. The high load medium rotation region 415 is adjacent to the high load side of the second medium load region 414 and extends over the region of medium rotation.

[0067] The fourth region corresponds to the high-load low-speed region 416. The high-load low-speed region 416 is adjacent to the high-load side of the second medium-load region 414 and extends into the low-speed region. The fourth region is a region that includes the maximum load of the engine 1.

[0068] Here, the low-speed region, the medium-speed region, and the high-speed region may be respectively the low-speed region, the medium-speed region, and the high-speed region when the entire operating region of the engine 1 is roughly trisected in the rotational speed direction.

[0069] Also, the low-load region, the medium-load region, and the high-load region may be respectively the low-load region, the medium-load region, and the high-load region when the entire operating region of the engine 1 is roughly trisected in the load direction.

[0070] <5. Combustion Modes of the Engine> Next, the operation of the engine 1 in each region will be described in detail. The ECU 10 selects the combustion mode of the air-fuel mixture in the cylinder 11 by comparing the target load for the engine 1 and the rotational speed of the engine 1 with the first base map 401 illustrated in FIG. 4, respectively.

[0071] Then, the ECU 10 sets the opening and closing operations of the intake valve 21 and the exhaust valve 22, the number of fuel injections, the fuel split ratio in each injection, the fuel injection timing, and the ignition timing by the ignition plug 6 so as to realize the selected combustion mode.

[0072] The combustion modes realized in this engine 1 include homogeneous SI combustion, SPCCI combustion, and retarded SI combustion. For each combustion mode, at least one of the opening and closing operations of the intake valve 21 and the exhaust valve 22, the number of fuel injections, the fuel split ratio in each injection, the fuel injection timing, and the ignition timing by the ignition plug 6 is different.

[0073] Note that the "split ratio" mentioned here refers to the ratio of the injection amount at a specific injection timing to the total injection amount of fuel in one fuel cycle.

[0074] FIG. 5 illustrates the opening and closing operations of the intake valve 21 and the exhaust valve 22, the number of fuel injections, the fuel split ratio, the fuel injection timing, and the ignition timing corresponding to each combustion mode, and the waveform of the heat generation rate generated in the cylinder 11 when the air-fuel mixture burns. The crank angle progresses from left to right in FIG. 5. Hereinafter, taking the warm state of the engine 1 as an example, each combustion mode will be described.

[0075] (5-1. Homogeneous SI Combustion) When the operating state of the engine 1 is in the first region, that is, the high-speed region 411 or the low-load region 412, the ECU 10 causes the air-fuel mixture in the cylinder 11 to burn by flame propagation. More specifically, the intake S-VT 231 sets the opening and closing timing of the intake valve 21 to a predetermined timing. The intake CVVL 232 sets the lift amount of the intake valve 21 to a predetermined lift amount. The lift amount of the intake valve 21 is substantially the same as the lift amount of the exhaust valve 22 described later. The exhaust S-VT 241 sets the opening and closing timing of the exhaust valve 22 to a predetermined timing. The intake valve 21 and the exhaust valve 22 both open near the intake top dead center (see reference numeral 711). The exhaust VVL 242 opens and closes the exhaust valve 22 only once. With this opening and closing pattern of the intake valve 21 and the exhaust valve 22, a relatively large amount of air and a relatively small amount of burned gas are introduced into the cylinder 11. The burned gas is basically the internal EGR gas remaining in the cylinder 11.

[0076] The injector 6 injects fuel into the cylinder 11, for example, during the intake stroke (see reference numeral 712). The injector 6 may perform batch injection as shown in the illustrated example. The fuel injected into the cylinder 11 diffuses due to the strong intake flow. An air-fuel mixture with a uniform fuel concentration is formed in the cylinder 11. The mass ratio of the air-fuel mixture, that is, the mass ratio G / F of the intake air in the cylinder 11 including the burned gas to the fuel, becomes about 20, for example. Note that the mass ratio A / F of the air in the cylinder 11 to the fuel is the stoichiometric air-fuel ratio.

[0077] Both the first spark plug 251 and the second spark plug 252 ignite the air-fuel mixture near top dead center of compression (see reference numeral 713). The first spark plug 251 and the second spark plug 252 may ignite simultaneously or may ignite with a timing shift.

[0078] After the ignition of the first spark plug 251 and the second spark plug 252, the air-fuel mixture burns by flame propagation (see reference numeral 714). In the high-speed rotation region 411 where the rotational speed is too high for compression ignition combustion to occur and in the low-load region 412 where the load is too low for compression ignition combustion to occur, the engine 1 can operate while ensuring combustion stability and suppressing abnormal combustion.

[0079] Since this combustion mode ignites a homogeneous air-fuel mixture by spark ignition, this combustion mode may be called homogeneous SI combustion.

[0080] (5-2. SPCCI Combustion) When the operating state of the engine 1 is in the second region (the first medium load region 413) or the third region (the second medium load region 414 or the high load medium rotation region 415), the ECU 10 causes a part of the air-fuel mixture in the cylinder 11 to burn by flame propagation and the remainder to burn by compression ignition. More specifically, the exhaust S-VT 241 sets the opening and closing timing of the exhaust valve 22 to a predetermined timing. The exhaust VVL 242 opens and closes the exhaust valve 22 once or twice (see reference numerals 721, 731). The internal EGR gas is introduced into the cylinder 11. The intake CVVL 232 sets the lift amount of the intake valve 21 to be larger than the lift amount in the low load region 412. The closing timing of the intake valve 21 is substantially the same as the closing timing in the low load region 412. The opening timing of the intake valve 21 is advanced compared to the opening timing in the low load region 412. Due to this opening and closing pattern of the intake valve 21 and the exhaust valve 22, the amount of air introduced into the cylinder 11 increases and the amount of introduced burned gas decreases. The air-fuel ratio of the air-fuel mixture is, for example, 35.

[0081] The injector 6 injects fuel into the cylinder 11, for example, during the intake stroke (see reference numerals 722, 7321). The injector 6 may vary the number of fuel injections according to the target load of the engine 1 (or the required value of the filling efficiency).

[0082] As an example, when the operating state of the engine 1 according to this embodiment is in the second region (the first medium load region 413), the ECU 10 injects the fuel in a lump during the intake stroke (see reference numeral 722). On the other hand, when the operating state of the engine 1 is in the third region (the second medium load region 414 or the high load medium rotation region 415), for example, the ECU 10 performs the pre-stage injection 7321 during the intake stroke and performs the post-stage injection 7322 in the latter half or the end period of the compression stroke. The fact that the fuel injection timing is late in the third region with a high load is advantageous for suppressing abnormal combustion.

[0083] Note that the latter half of the compression stroke corresponds to the latter half when the compression stroke is bisected into a first half and a second half. The end period of the compression stroke corresponds to the end period when the compression stroke is trisected into an initial period, a middle period, and an end period.

[0084] Similarly, the first half of the compression stroke corresponds to the first half when the compression stroke is bisected into the first half and the second half. The initial stage of the compression stroke corresponds to the initial stage when the compression stroke is trisected into the initial stage, the middle stage, and the final stage. The middle stage of the compression stroke corresponds to the middle stage when the compression stroke is trisected into the initial stage, the middle stage, and the final stage.

[0085] Both the first ignition plug 251 and the second ignition plug 252 ignite the air-fuel mixture in the vicinity of the compression top dead center (see reference numerals 723 and 733). In the vicinity of the compression top dead center after the first ignition plug 251 and the second ignition plug 252 ignite, the air-fuel mixture starts flame propagation combustion. Due to the heat generation of the flame propagation combustion, the temperature in the cylinder 11 increases, and due to the flame propagation, the pressure in the cylinder 11 rises. As a result, the unburned air-fuel mixture self-ignites, for example, after the compression top dead center, and starts compression ignition combustion (see reference numerals 724 and 734). After the start of the compression ignition combustion, the flame propagation combustion and the compression ignition combustion proceed in parallel. The waveform of the heat generation rate may have two peaks, different from the illustrated example.

[0086] By adjusting the heat generation amount of the flame propagation combustion, it is possible to absorb the variation in the temperature in the cylinder 11 before the start of compression. The ECU 10 can adjust the heat generation amount of the flame propagation combustion by adjusting the ignition timing. The air-fuel mixture comes to self-ignite at the target timing. In SPCCI combustion, the ECU 10 adjusts the timing of compression ignition through the adjustment of the ignition timing. Since ignition controls compression ignition in this combustion mode, this combustion mode is sometimes called SPCCI (Spark Controlled Compression Ignition) combustion.

[0087] (5-3. Retarded SI Combustion) When the operating state of engine 1 is in the fourth region, that is, in the high-load and low-speed region 416, the ECU 10 causes the air-fuel mixture in cylinder 11 to undergo flame propagation combustion. More specifically, when the operating state of engine 1 is in the high-load and low-speed region 416, the intake S-VT 231 sets the opening and closing timing of the intake valve 21 to a predetermined timing. The intake CVVL 232 sets the lift amount of the intake valve 21 to a predetermined lift amount. The lift amount of the intake valve 21 is substantially the same as the lift amount of the exhaust valve 22 described later. The exhaust S-VT 241 sets the opening and closing timing of the exhaust valve 22 to a predetermined timing. The intake valve 21 and the exhaust valve 22 both open near the intake top dead center (see reference numeral 741). The exhaust VVL 242 opens and closes the exhaust valve 22, for example, once. Due to this opening and closing pattern of the intake valve 21 and the exhaust valve 22, a relatively large amount of air and a relatively small amount of burned gas are introduced into cylinder 11. The burned gas is basically the internal EGR gas remaining in cylinder 11. The G / F is about 20.

[0088] Since the high-load and low-speed region 416 is a region with high load and low rotational speed, abnormal combustion such as pre-ignition or knocking is likely to occur. The injector 6 injects fuel into cylinder 11 during the compression stroke (see reference numerals 7421, 7422). By delaying the timing of fuel injection into cylinder 11, the occurrence of abnormal combustion is suppressed. Instead of the injection times shown in the figure, the injector 6 may perform a batch injection.

[0089] The fuel injected into cylinder 11 during the compression stroke diffuses due to the flow of the injection. In order to rapidly burn the air-fuel mixture and suppress the occurrence of abnormal combustion and improve combustion stability, a higher injection pressure is preferable. The higher injection pressure generates a strong flow in cylinder 11 where the pressure is high near the compression top dead center. The strong flow promotes flame propagation.

[0090] Both the first ignition plug 251 and the second ignition plug 252 ignite the air-fuel mixture near top dead center of compression (see reference numeral 743). The first ignition plug 251 and the second ignition plug 252 may ignite simultaneously or may ignite with a timing shift. In the second high load and low rotation region 414 where the load is high, the first ignition plug 251 and the second ignition plug 252 may perform ignition at a timing after top dead center of compression corresponding to the retarded fuel injection timing. Alternatively, the first ignition plug 251 and the second ignition plug 252 may perform ignition at a timing before top dead center of compression, for example, during fuel injection from the injector 6. After ignition of the first ignition plug 251 and the second ignition plug 252, the air-fuel mixture undergoes flame propagation combustion (see reference numeral 744).

[0091] In an operating state where the rotational speed is low and abnormal combustion is likely to occur, the engine 1 can operate while ensuring combustion stability and suppressing abnormal combustion. Since this combustion mode retards the injection timing, this combustion mode may be referred to as retarded SI combustion. Similar to the above-described SPCCI combustion, the air-fuel mixture ignited in the fourth region may undergo compression ignition combustion after flame propagation combustion.

[0092]

[0093]

[0094] ​​ Moreover, as described above, a high injection pressure generates a strong flow. The strong flow can increase the turbulent combustion speed. Thereby, rapid combustion of the air-fuel mixture can be realized.

[0095] In addition, combined with injecting fuel in the latter half of the compression stroke and a high injection pressure, the period during which air and fuel are mixed (mixing period) becomes shorter compared with other combustion patterns such as homogeneous SI and SPCCI combustion. By forming the air-fuel mixture within a short period, the homogenization of the air-fuel mixture can be rapidly advanced to an equivalence ratio (local equivalence ratio in cylinder 11) that suppresses the generation of smoke.

[0096] As described above, the ECU 10 can vary the fuel injection pattern into cylinder 11 according to different combustion modes such as SPCCI combustion and retarded SI combustion. Alternatively, even when classified into the same combustion mode, different injection modes can be used within that combustion mode, such as SPCCI combustion at high ce and low ce.

[0097] The "injection mode" referred to here means the number of fuel injections in each stroke in one combustion cycle, such as "intake stroke 1 time + compression stroke 0 times", "intake stroke 1 time + compression stroke 1 time", "intake stroke 0 times + compression stroke 2 times", etc.

[0098] The ECU 10 according to this embodiment is configured to selectively use a plurality of types of combustion modes through this switching of the injection mode. That is, determining the injection mode is substantially equivalent to determining the fuel combustion mode. In this embodiment, the first base map 401 shown in FIG. 4 is defined as a map that defines the injection mode corresponding to each region instead of the combustion mode.

[0099] However, merely determining the injection mode does not uniquely determine the control parameters of engine 1. For example, after determining the injection mode, it is convenient to determine the control parameters of engine 1 in that injection mode. Here, the control parameters refer to a concept including at least the combination of the fuel injection timing and the ignition timing.

[0100] ECU 10 determines the combustion and control parameters of engine 1 for each combustion cycle. ECU 10 executes such determination at at least one of the first timing T1 and the second timing T2 in FIG. 5.

[0101] The first timing T1 is a calculation timing set within the range from the exhaust stroke, specifically from the middle to the end of the exhaust stroke. For example, the first timing T1 may be -480 degrees or more and -360 degrees or less after TDC, and specifically may be -440 degrees or more and -400 degrees or less after TDC. Here, TDC refers to "compression TDC" as shown in FIG. 5. In the following description, "compression TDC" may be simply referred to as "TDC" in some cases.

[0102] The first timing T1 is a calculation timing for executing processes related to fuel injection during the intake stroke (hereinafter also referred to as "first injection"), such as determination of the injection mode and pre-stage injection 7321 of high-load SPCCI combustion. The first injection can also be called "intake stroke injection".

[0103] The second timing T2 is a calculation timing set within the range from the compression stroke, specifically from the initial to the middle of the compression stroke. For example, the second timing T2 may be -240 degrees or more and -60 degrees or less after TDC, and specifically may be -150 degrees or more and -90 degrees or less after TDC.

[0104] The second timing T2 is an arithmetic timing for executing processes related to fuel injection during the compression stroke (hereinafter also referred to as "second injection"), such as the pre-stage injection 7421 and the post-stage injection 7422 of the retarded SI combustion, and the post-stage injection 7322 of the high-load SPCCI combustion. The second injection can also be called "compression stroke injection".

[0105] First, the ECU10 determines the injection mode at the first timing T1. In the case of homogeneous SI combustion and SPCCI combustion at low load (low ce), the ECU10 determines all control parameters at the first timing T1. In the case of SPCCI combustion at high load (high ce) and retarded SI combustion, the ECU10 determines some control parameters at the first timing T1 and then determines the remaining control parameters at the second timing T2. Note that a third timing (not shown) may be set at the end of the compression stroke, and partial control may be executed at the third timing T3.

[0106] In this way, the ECU10 constitutes a control device for the engine 1 that determines the injection mode and determines control parameters corresponding to the injection mode. Hereinafter, the configuration of the ECU10 as the control device and the determination procedure of the injection timing and the ignition timing as the control parameters will be described in detail.

[0107] <6. Details of the control device> FIG. 6 is a block diagram illustrating the details of the control device for the engine 1. As shown in FIG. 6, this control device includes a state quantity estimation unit 101, an injection mode determination unit 102, a first injection calculation unit 103, a first injection conversion unit 104, a second injection calculation unit 105, a second injection conversion unit 106, an ignition timing calculation unit 107, and an F / B term calculation unit 108. These elements are functional blocks of the ECU10. The control device sequentially sets control parameters during the operation of the engine 1.

[0108] (6-1. Operating state determination unit) The operating state determination unit 101 calculates the engine speed (ne) and the target load of Engine 1 based on the measurement signals of sensors SW1 - SW10. As is well known, the engine speed of Engine 1 (hereinafter simply referred to as "engine speed") can be calculated based on the detection signal of the crank angle sensor SW6.

[0109] In addition, the operating state determination unit 101 calculates the target filling efficiency (ce) of Engine 1 as a state quantity characterizing the target load of Engine 1. Not limited to the target filling efficiency, the air quantity supplied into cylinder 11 may be used. Hereinafter, the target filling efficiency may be referred to as "target air quantity" or simply as "target load" in some cases.

[0110] For example, the operating state determination unit 101 calculates the target engine torque based on the detection signal of the accelerator opening sensor SW7, and then calculates the target combustion pressure corresponding to the target engine torque. Next, the operating state determination unit 101 obtains the target filling efficiency based on the target combustion pressure. The operating state determination unit 101 sets various control targets characterizing the in - cylinder state of Engine 1, such as the target throttle opening and the target external EGR rate, so that the target filling efficiency is achieved.

[0111] In addition, the operating state determination unit 101 also sets the target value of the total fuel injection amount in one combustion cycle so that the air - fuel ratio of the air - fuel mixture becomes the target air - fuel ratio such as the stoichiometric air - fuel ratio based on the set target filling efficiency.

[0112] In addition, the operating state determination unit 101 estimates the state quantity in cylinder 11 at the time when the intake valve 21 closes (that is, the IVC time). Hereinafter, this state quantity is also referred to as "IVC state quantity". To estimate the IVC state quantity, the operating state determination unit 101, in addition to the detection signal of the crank angle sensor SW6 described above, acquires the measurement signals of the intake cam angle sensor SW8, the exhaust cam angle sensor SW9, and the intake cam lift sensor SW10, and, when fuel injection is being performed during the intake stroke, the signal related to the fuel injection amount.

[0113] Based on these measurement signals, the driving state determination unit 101 estimates the IVC state quantity. Specifically, the driving state determination unit 101 estimates, for example, the in-cylinder temperature T at the IVC time IVC , the oxygen concentration [O2] in the cylinder IVC , and the fuel concentration [F] IVC . As one of the IVC state quantities, the driving state determination unit 101 also acquires the in-cylinder pressure P at the IVC time IVC .

[0114] Note that for various calculations based on the target engine torque, target combustion pressure, etc., the methods described in, for example, Japanese Patent Application Laid-Open No. 2018-84181, Japanese Patent Application Laid-Open No. 2018-84182, Japanese Patent Application Laid-Open No. 2020-101163, etc. can be adopted, so the details are omitted.

[0115] Similarly, for the estimation of the IVC state quantity, since it is described in, for example, Japanese Patent Application Laid-Open No. 2023-53507, etc., the details are omitted.

[0116] In addition, the driving state determination unit 101 can also estimate the octane number of the fuel poured into the fuel tank 63. Since the calculation procedure of this estimated value (hereinafter also referred to as "RON estimated value") can adopt the methods described in, for example, Japanese Patent Application Laid-Open No. 2021-92198, Japanese Patent Application Laid-Open No. 2021-92200, etc., the details are omitted.

[0117] The driving state determination unit 101 executes these calculations at the aforementioned first timing T1, and inputs various calculation results including the engine speed and the target load to the injection mode determination unit 102, the first injection calculation unit 103, the second injection calculation unit 105, and the ignition timing calculation unit 107.

[0118] (6-2. Injection Mode Determination Unit) Based on at least the engine speed and the target load (target air quantity), the injection mode determination unit 102 determines the injection mode to be performed during the operation of the engine 1.

[0119] First, the injection mode determination unit 102 reads a base map corresponding to the RON estimated value, and determines a combustion mode (specifically, an injection mode) corresponding to the operating state of the engine 1 by collating the engine speed and the target load with the base map (for example, the first base map 401).

[0120] The injection mode determination unit 102 continues to execute these operations following the operations by the operating state determination unit 101 starting at the first timing T1, and inputs a signal (mode signal) indicating the determined injection mode to the first injection calculation unit 103 and the second injection calculation unit 105.

[0121] (6-3. First injection calculation unit) FIG. 7 is a block diagram illustrating the configuration of the first injection calculation unit 103. The first injection calculation unit 103 is a functional block that determines target values of control parameters characterizing intake stroke injection. The control parameters determined by the first injection calculation unit 103 include the injection timing during the intake stroke and the fuel injection amount during the intake stroke.

[0122] To determine those control parameters, the first injection calculation unit 103 shown in FIG. 7 includes a first SOI determination unit 103a, a first split ratio determination unit 103b, and a first injection amount determination unit 103c.

[0123] [6-3-1. First SOI determination unit] The first SOI determination unit 103a determines the start of injection timing (SOI) of the intake stroke injection based on the mode signal, the engine speed, and the target load. This determination can be made, for example, by comparing the values of the engine speed and the target load with an intake SOI map M31 corresponding to the injection mode.

[0124] Here, the intake SOI map M31 is a map associating the values of the engine speed and the target load with the SOI of the intake stroke injection. A plurality of intake SOI maps M31 are prepared for each injection mode, for example, and are stored in advance in the memory 100b.

[0125] [6-3-2. First injection ratio determination unit] The first injection ratio determination unit 103b determines the injection ratio of the intake stroke injection based on the mode signal, the engine speed and the target load, and the target external EGR rate. This determination can be made, for example, by comparing the values of the engine speed, the target load and the external EGR rate with the intake split ratio map M32 corresponding to the injection mode.

[0126] Here, the intake split ratio map M32 is a map associating the values of the engine speed and the target load with the injection ratio of the intake stroke injection. The intake split ratio map M32 is prepared in a plurality for each injection mode, for example, and is set so that the split ratio changes continuously according to the external EGR rate, and is stored in advance in the memory 100b respectively. If the compression stroke injection is not performed, this split ratio becomes 1.

[0127] [6-3-3. First injection amount determination unit] The first injection amount determination unit 103c multiplies the injection ratio determined by the first injection ratio determination unit 103b by the target injection amount set by the operation state determination unit 101 to determine the fuel injection amount in the intake stroke injection. The target injection amount here is the target value of the total injection amount of fuel in one fuel cycle as described above.

[0128] [6-3-4. Calculation timing] The first injection calculation unit 103 continues to execute these calculations following the calculations by the operation state determination unit 101 and the injection mode determination unit 102 starting at the first timing T1. The first injection calculation unit 103 inputs signals indicating the SOI of the intake stroke injection and the fuel injection amount in the intake stroke injection to the first injection conversion unit 104, the second injection calculation unit 105, etc. respectively.

[0129] Hereinafter, the SOI of the intake stroke injection may be referred to as the "first SOI", the injection ratio of the intake stroke injection may be referred to as the "first injection ratio", and the fuel injection amount in the intake stroke injection may be referred to as the "first injection amount".

[0130] Also, when intake stroke injection is not performed as in retarded SI combustion, the calculation of the first SOI is skipped and the first split ratio becomes zero.

[0131] (6-4. First injection conversion unit) The first injection conversion unit 104 generates a drive current for the injector 6 based on the first SOI and the first injection amount determined by the first injection calculation unit 103. The ECU 10 inputs the drive current generated by the first injection conversion unit 104 to the injector 6.

[0132] (6-5. Second injection calculation unit) FIG. 8 is a block diagram illustrating the configuration of the second injection calculation unit 105. The second injection calculation unit 105 is a functional block that determines target values of control parameters characterizing compression stroke injection. The control parameters determined by the second injection calculation unit 105 include the injection timing during the compression stroke and the fuel injection amount during the compression stroke.

[0133] To determine those control parameters, the second injection calculation unit 105 shown in FIG. 7 includes a second SOI determination unit 105a, a second split ratio determination unit 105b, a second injection amount determination unit 105c, an F / B correction unit 105d, a cavity limit calculation unit 105e, a premature ignition limit calculation unit 105f, and an advance angle limit determination unit 105g.

[0134] [6-5-1. Second SOI determination unit] The second SOI determination unit 105a determines the start of injection timing (SOI) of the compression stroke injection based on the mode signal, the engine speed, and the target load. Hereinafter, the SOI corresponding to each compression stroke injection is referred to as the "second SOI". The determination of the second SOI can be performed, for example, by comparing the values of the engine speed and the target load with the compression SOI map M51 corresponding to the injection mode.

[0135] Here, the compression SOI map M51 is a map that associates the values of the engine speed and the target load with the SOI of the compression stroke injection. A plurality of compression SOI maps M51 are prepared for each injection mode, for example, and are each pre-stored in the memory 100b.

[0136] Also, when multiple compression stroke injections are performed, the second SOI determination unit 105a determines the SOI for each of the multiple compression stroke injections. In that case, by using the compression SOI map M51 set for each fuel injection, the SOI for each compression stroke injection can be determined.

[0137] The second SOI determination unit 105a inputs the second SOI in the final-stage compression stroke injection close to the compression TDC among one or more second SOIs to the F / B correction unit 105d, while inputting all the second SOIs including the final-stage compression stroke injection to the second injection conversion unit 106. Hereinafter, the second SOI in the final stage is also referred to as the "final-stage SOI". Also, the output value of the second SOI determination unit 105a corresponds to the provisional value of the final-stage SOI. Hereinafter, this provisional value is also referred to as the "provisional final-stage SOI".

[0138] [6-5-2. Second division ratio determination unit] When multiple compression stroke injections are performed, the second division ratio determination unit 105b determines the division ratio for each of the multiple compression stroke injections. Hereinafter, the division ratio corresponding to each compression stroke injection is referred to as the "second division ratio". The second division ratio may be the ratio of the fuel injection amount of each compression stroke injection to the total fuel injection amount of the entire compression stroke.

[0139] For example, when only one compression stroke injection is performed, the second division ratio is 1. On the other hand, in the injection mode where two compression stroke injections are performed, such as retarded SI combustion, the second division ratio is the ratio of the fuel injection amount of the latter-stage injection 7422 to the total fuel injection amount of the former-stage injection 7421 and the latter-stage injection 7422.

[0140] Specifically, the second split ratio determination unit 105b determines the second split ratio based on the mode signal, the engine speed and the target load, and the target external EGR rate. This determination can be made, for example, by comparing the values of the engine speed, the target load, and the external EGR rate with a compression split ratio map M52 corresponding to the injection mode. When making this determination, the value of the first split ratio may be combined and calculated.

[0141] Here, the compression split ratio map M52 is a map associating the values of the engine speed and the target load with the second split ratio. A plurality of compression split ratio maps M52 are prepared, for example, according to the presence or absence of the external EGR rate, and are each stored in advance in the memory 100b.

[0142] [6-5-3. Second injection quantity determination unit] The second injection quantity determination unit 105c determines the fuel injection quantity in each compression stroke injection based on the split ratio determined by the second split ratio determination unit 105b and the first injection quantity determined by the first injection quantity determination unit 103c. Hereinafter, the fuel injection quantity corresponding to each compression stroke injection is referred to as the "second injection quantity".

[0143] Specifically, the second injection quantity determination unit 105c first calculates the total amount of the fuel injection quantity in the compression stroke injection by subtracting the first injection quantity from the target injection quantity. The second injection quantity determination unit 105c determines each second injection quantity by multiplying the calculated value by each second split ratio.

[0144] Among one or more second injection quantities, the second injection quantity determination unit 105c differentiates the second injection quantity in the final-stage compression stroke injection close to the compression TDC from the other injection quantities, and inputs all the second injection quantities to the premature ignition limit calculation unit 105f. The second injection quantity determination unit 105c also inputs all the second injection quantities to the second injection conversion unit 106. Hereinafter, the second injection quantity in the final stage is also referred to as the "final-stage injection quantity".

[0145] [6-5-4. F / B correction unit] The F / B correction unit 105d adds the F / B term to the provisional final stage SOI determined by the second SOI determination unit 105a. The F / B term, when added to the provisional final stage SOI, advances or retards the provisional final stage SOI. Details of the F / B term will be described later.

[0146] The provisional final stage SOI to which the F / B term is added by the F / B correction unit 105d is input to the advance angle limit determination unit 105g. Hereinafter, the output value of the F / B correction unit 105d is also referred to as the "provisional final stage SOI".

[0147] [6-5-5. Transport limit calculation unit] The cavity limit calculation unit 105e calculates a fifth limit line Li5 based on the operating state of the engine 1. The fifth limit line Li5, together with the first limit line Li1 described later, defines the lower limit value (advance angle limit) of the final stage SOI. The fifth limit line Li5 indicates the limit value for the fuel injected from the injector 6 to reach inside the cavity 31.

[0148] That is, if the final stage SOI is advanced excessively, fuel injection will occur with the piston 3 in an excessively lowered state relative to the injector 6. In this case, the spray injected from the injector 6 is disposed outside the cavity 31, and there is a possibility that a sufficient air-fuel mixture does not reach near the first and second spark plugs 251, 252. As a result, ignition by the first and second spark plugs 251, 252 may not be stable. The destabilization of ignition is disadvantageous because it may cause deterioration of fuel consumption performance.

[0149] In contrast, the cavity limit calculation unit 105e according to the present embodiment determines the fifth limit line Li5 as the advance angle limit of the final stage SOI based on the fuel pressure and the engine speed.

[0150] For example, as the fuel pressure increases, the cavity limit calculation unit 105e shifts the fifth limit line Li5 toward the advance side with respect to the compression TDC. This is because when the fuel pressure is high, fuel can reach the first and second spark plugs 251 and 252 more easily than when it is low, so it is permissible to set the advance limit of the final-stage SOI more toward the advance side.

[0151] Similarly, as the engine speed increases, the cavity limit calculation unit 105e shifts the fifth limit line Li5 toward the advance side with respect to the compression TDC. Generally, when the engine speed is high, the time required for the crank angle to change by 1° is shorter compared to when it is low. Therefore, when spraying from the injector 6, the piston 3 can approach the injector 6 in a short time. Thus, when the engine speed is high, fuel can reach the first and second spark plugs 251 and 252 more easily than when it is low, so it is permissible to set the advance limit of the final-stage SOI more toward the advance side.

[0152] In this way, the cavity limit calculation unit 105e determines the fifth limit line Li5 based on the fuel pressure and the engine speed. This determination can be made, for example, by comparing the measured values of the fuel pressure and the engine speed with the fifth limit map M53 that defines the fifth limit line Li5.

[0153] Here, the fifth limit map M53 is a map that associates the values of the fuel pressure, the engine speed, and the target load with the value of the fifth limit line Li5. The specific value of the fifth limit line Li5 is tuned according to the geometric shape of the cavity 31 and the layouts of the injector 6, the first spark plug 251, and the second spark plug 252. The fifth limit map M53 is pre-stored in the memory 100b.

[0154] The fifth limit line Li5 determined by the cavity limit calculation unit 105e is input to the advance limit determination unit 105g.

[0155] [6-5-6. Premature Ignition Limit Calculation Unit] The premature ignition limit calculation unit 105f calculates a first limit line Li1 based on the operating state of the engine 1. The first limit line Li1, together with the aforementioned fifth limit line Li5, defines the lower limit value (advance angle limit) of the final-stage SOI. The first limit line Li1 indicates the limit value at which premature ignition is suppressed.

[0156] That is, if the final-stage SOI is advanced excessively, as a result of the fuel injection from the injector 6 being too early, there is a possibility of causing premature ignition before ignition. The occurrence of premature ignition is disadvantageous in improving the fuel consumption performance of the engine 1 and is also disadvantageous in that it can damage the engine 1.

[0157] In contrast, as shown in FIG. 8, the premature ignition limit calculation unit 105f according to the present embodiment determines the first limit line Li1 as the advance angle limit of the final-stage SOI based on the RON estimated value, the IVC state quantity, and the second injection quantity. The IVC state quantity referred to here includes, for example, the in-cylinder temperature T at the time of IVC IVC , the oxygen concentration [O2] in the cylinder IVC , the fuel concentration [F] IVC and the in-cylinder pressure P IVC .

[0158] The premature ignition limit calculation unit 105f according to the present embodiment searches for the lower limit value (advance angle limit) of the final-stage SOI such that the value of the Livengood-Wu integral (LW value) that defines the reaction rate at which the substance reaches self-ignition falls below the reference value. In this search, the premature ignition limit calculation unit 105f uses a model M54 that defines the relationship between the first limit line Li1 and the LW limit value LW limit (details are shown in FIG. 10 described later). The premature ignition limit calculation unit 105f sets the lower limit value to the first limit line Li1 indicating the advance angle limit of the final-stage SOI.

[0159] Note that since the definition of the Livengood-Wu integral is described in, for example, Japanese Patent Application Laid-Open No. 2019-39384 and Japanese Patent Application Laid-Open No. 2022-12228, etc., the details thereof are omitted.

[0160] As is well known, the Livengood-Wu integral is the time integral of the reaction rate defined by the reciprocal of the ignition delay τ. The ignition delay τ varies depending on the concentration (e.g., mole fraction) of each substance in the cylinder, pressure, temperature, etc.

[0161] Here, the substance concentration, pressure, and temperature in the cylinder change significantly with the first injection timing (the first second SOI) and the second injection timing (the second second SOI, which corresponds to the final stage SOI) as boundaries when two fuel injections are performed during the compression stroke, for example, in retarded SI combustion.

[0162] Therefore, the inventors of the present application divided the integration section of the reaction rate into a section from the first injection timing to the final stage SOI, which is the second injection timing, and a section from the second injection timing to a predetermined timing after the compression TDC. Hereinafter, the former section is referred to as the first section In1, the latter section is referred to as the second section In2, and the predetermined timing is also referred to as the "LW value determination timing".

[0163] Let the ignition delay in the first section In1 be τ1, the ignition delay in the second section In2 be τ2, the first injection timing be Ti1, the LW value determination timing be Ti2, and for simplicity of description, the final stage SOI is simply denoted as "SOI". Then, the time integral indicating the LW value can be modeled as shown in the following formula (1) and Figure 9.

[0164]

Equation

[0165] In Equation (1), Ti1 is a crank angle set within the range from the middle of the compression stroke to the end of the compression stroke, and is a predetermined value set, for example, within the range of -70 [°CA] or more and -50 [°CA] or less after compression TDC. On the other hand, Ti2 is a crank angle set within the range at the beginning of the expansion stroke in the case of retarded SI combustion, and is a predetermined value set, for example, within the range of 20 [°CA] or more and 60 [°CA] or less after compression TDC.

[0166] In the present embodiment, the final stage SOI (SOI) is searched within the range where the LW value defined by Equation (1) does not exceed a predetermined value near 1 (for example, 0.9). Hereinafter, this predetermined value is referred to as the LW limit value LW limit and is called as such.

[0167] Also, both τ1 and τ2 can be modeled as in the following Equation (2).

[0168]

Equation

[0169] In Equation (2), a, b, c, d, e, and f are numerical parameters obtained as a result of intensive studies by the inventors of the present application. All of these parameters are positive in the present embodiment.

[0170] Also, YF X is the molar fraction of substance X, and F(RON) is a function with the RON estimated value as an argument. This F is a function with a positive value and has a positive correlation with the RON estimated value. Also, β is a constant that can have different values in the first section In1 and the second section In2, and is a parameter stored in advance in the memory 100b.

[0171] The pre-ignition limit calculation unit 105f reads the RON estimated value and reads different β values in the first section In1 and the second section In2, and substitutes them into Equation (2), respectively.

[0172] Further, the pre-ignition limit calculation unit 105f calculates the in-cylinder pressure P and the in-cylinder temperature T at the time of Ti1 and the in-cylinder pressure P and the in-cylinder temperature T at a predetermined time near the final-stage SOI based on the IVC state quantity, the second injection quantity, etc., and substitutes them into Equation (2), respectively.

[0173] Here, the "predetermined time near the final-stage SOI" is, for example, a crank angle set within the range of the end period of the compression stroke, and is a predetermined value set within a range of, for example, -35 [°CA] or more and -15 [°CA] or less after the compression TDC. The value of the final-stage SOI may be used for the "predetermined time near the final-stage SOI".

[0174] Further, the pre-ignition limit calculation unit 105f calculates the nuclear YF X for each substance, calculates the molar fraction YF, and substitutes them into Equation (2), respectively. Each molar fraction YF is calculated based on a part of the second injection quantity (compression stroke injection) excluding the final-stage injection quantity in the first section In1, and is calculated based on the sum of the second injection quantities including the final-stage injection quantity in the second section In2.

[0175] By completing the substitution of these parameters, the above Equation (1) becomes a model equation that associates the final-stage SOI (SOI) with the LW value. FIG. 9 shows a graph of the time integration according to the present embodiment. This graph shows the behavior of the time integration of the reciprocals of the ignition delays τ1 and τ2 when the models of Equations (1) and (2) are adopted. The value on the vertical axis at the LW value determination timing Ti2 indicates the magnitude of the LW value represented by Equation (1).

[0176] Of the first section In1 and the second section In2 set within the compression stroke, the second section In2 is a section closer to the compression TDC than the first section In1. Therefore, the in-cylinder pressure P and the in-cylinder temperature T in the second section In2 are relatively higher than those in the first section In1. This acts in a direction to make the slope (= 1 / τ2) of the LW value in the second section In2 steeper than the slope (= 1 / τ1) of the LW value in the first section In1.

[0177] Also, the molar fraction YF of fuel in the second interval In2 Fuel is larger than the molar fraction YF of fuel in the first interval In1, including the fuel injected at the final-stage SOI. Fuel This also acts in the direction of making the slope (= 1 / τ2) of the LW value in the second interval In2 steeper than the slope (= 1 / τ1) of the LW value in the first interval In1.

[0178] Therefore, the slope of the LW value in the second interval In2 is larger than the slope of the LW value in the first interval In1. Thus, as shown in the upper diagram of Fig. 9 (SOI: advanced angle), the more the final-stage SOI (SOI) is advanced toward the first injection timing Ti1, the shorter the first interval In1 becomes, and the second interval In2 becomes longer by that amount. As a result of the different slopes in each interval, the value of the time integral (LW value) at the LW value determination timing Ti2 becomes larger.

[0179] On the other hand, as shown in the lower diagram of Fig. 9 (SOI: retarded angle), the closer the final-stage SOI (SOI) is to the LW value determination timing Ti2, the longer the first interval In1 becomes, and the second interval In2 becomes shorter by that amount. As a result, the value of the time integral (LW value) at the LW value determination timing Ti2 becomes smaller.

[0180] The relationship between the final-stage SOI (SOI) and the LW value is consistent with the finding that the more the final-stage SOI is advanced, the easier it is to cause pre-ignition. Depending on the setting of the final-stage SOI (SOI), the LW value may exceed the LW limit value LW limit

[0181] Here, the LW value represented by Equation (1) can be regarded as a function with the final-stage SOI (SOI) as an argument. The graph of this function is the graph shown in Fig. 10. This graph is a graph of the model M54 representing the change in the LW value with respect to the final-stage SOI (SOI).

[0182] The pre-ignition limit calculation unit 105f uses the graph shown in Fig. 10 and the LW limit value LW limit ​And, search for the intersection point therewith. This search may be performed, for example, by solving Equation (1) for SOI after substituting the LW limit value LW into the left side of Equation (1). limit This may be done by solving Equation (1) for SOI after substituting the LW limit value LW into the left side of Equation (1).

[0183] Finally, the premature ignition limit calculation unit 105f sets the advanced angle limit at which the final stage SOI (SOI) at the intersection point, that is, the boundary at which the LW value exceeds the LW limit value LW, to the first limit line Li1. limit The first limit line Li1 determined by the premature ignition limit calculation unit 105f is input to the advanced angle limit determination unit 105g.

[0184]

[0185] [6-5-7. Advanced Angle Limit Determination Unit] The advanced angle limit determination unit 105g reads the provisional final stage SOI, the first limit line Li1, and the fifth limit line Li5, selects the maximum value among them, and outputs it. This output value becomes the final value of the final stage SOI. Here, the "maximum value" refers to the crank angle that is the most retarded with respect to the compression TDC in one combustion cycle.

[0186] For example, when the SOI base value is retarded with respect to both the fifth limit line Li5 and the first limit line Li1, the advanced angle limit determination unit 105g outputs the provisional final stage SOI as the final stage SOI. On the other hand, when the provisional final stage SOI is retarded with respect to the fifth limit line Li5 but advanced with respect to the first limit line Li1, the advanced angle limit determination unit 105g outputs the value on the first limit line Li1 as the final stage SOI.

[0187] [6-5-8. Calculation Timing] The second injection calculation unit 105 starts these calculations from the second timing T2. The second injection calculation unit 105 inputs signals indicating the SOI (second SOI) of the compression stroke injection including the final stage SOI and the fuel injection amount (second injection amount) in the compression stroke injection to the second injection conversion unit 106 respectively.

[0188] (6-6. Second Injection Conversion Unit) The second injection conversion unit 106 generates a drive current for the injector 6 based on the second SOI (including the final stage SOI) and the second injection amount determined by the second injection calculation unit 105. The ECU 10 inputs the drive current generated by the second injection conversion unit 106 to the injector 6.

[0189] (6-7. Ignition timing calculation unit) FIG. 11 is a block diagram illustrating the configuration of the ignition timing calculation unit 107. The ignition timing calculation unit 107 is a functional block that determines target values of ignition timing by the first and second spark plugs 251 and 252 as an example of control parameters.

[0190] To determine the target value of the ignition timing, the ignition timing calculation unit 107 shown in FIG. 11 includes a target combustion timing setting unit 107a, a target combustion period determination unit 107b, an ignition timing conversion unit 107c, a transport limit calculation unit 107d, a smoke limit calculation unit 107e, and an advance limit determination unit 107f.

[0191] Note that in the following description, the "combustion center of gravity position" refers to the timing (crank angle) at which 50% of the total heat generation amount generated during one combustion cycle occurs. This combustion center of gravity position can also be referred to as the timing (crank angle) at which 50% of the total injection amount during one combustion cycle burns, that is, the mass fraction burned 50% (mfb50).

[0192] And, as is well known, when mfb50 is the so-called MBT (Minimum Advance for Best Torgue), the torque is maximized, and as mfb50 retards, the torque gradually decreases.

[0193] The ECU 10 is configured to adjust the ignition timing using this mfb50 as an index. Specifically, the ECU 10 determines the mfb50 according to the operating state of the engine 1, and sets the target ignition timing based on the target mfb50 position. That is, the ECU 10 determines the target ignition timing so that the first and second spark plugs 251 and 252 perform forced ignition at a timing when the target mfb50 position is achieved.

[0194] [6-7-1. Target Combustion Center of Gravity Setting Unit] The target combustion center of gravity setting unit 107a includes a torque reduction calculation unit 1071, a knock limit calculation unit 1072, a retard limit calculation unit 1073, and a combustion center of gravity selection unit 1074.

[0195] - Torque Reduction Calculation Unit - When there is a torque reduction request, the torque reduction calculation unit 1071 determines the target position of mfb50 based on a predetermined retard limit so that mfb50 does not exceed the retard limit. More specifically, when there is a torque reduction request, the torque reduction calculation unit 1071 determines the target position of mfb50 based on the retard limit.

[0196] The torque reduction request is, for example, in an automobile equipped with an automatic transmission, a request to reduce the torque on the engine 1 during an upshift of the automatic transmission. Also, the torque reduction request is a request to reduce the torque of the engine 1 when the driver sets the accelerator opening to zero. Furthermore, the torque reduction request is a request to reduce the torque of the engine 1 in response to the driver's steering operation or the like to change the acceleration acting on the automobile for the sake of the driving stability of the automobile.

[0197] As described above, the position of mfb50 is related to the ignition timing. Determining the target position of mfb50 is equivalent to determining the target value of the ignition timing as a result.

[0198] Retarding the ignition timing so that mfb50 is retarded can reduce torque more quickly than reducing the air amount by adjusting the opening degree of the throttle valve 43 to reduce torque.

[0199] Specifically, the torque reduction calculation unit 1071 determines the target position of mfb50 based on the retard limit by comparing the mode signal, the load and the rotational speed of the engine 1 with a pre - determined torque reduction map M71. The target value of mfb50 is determined based on the standard deviation σ of mfb50 and the retard limit such that the retard limit becomes 3σ of mfb50.

[0200] Note that since various calculations related to the torque reduction calculation unit 1071 can adopt the methods described in, for example, Japanese Patent Application Laid - Open No. 2020 - 169594, etc., the details are omitted.

[0201] -Knock limit calculation unit- The knock limit calculation unit 1072 calculates a third limit line Li3 based on the operating state of the engine 1. The third limit line Li3 defines the lower limit value (advance angle limit) of the ignition timing. The third limit line Li3 indicates the limit value at which knocking is suppressed.

[0202] That is, if the ignition timing is advanced too much, there is a possibility of causing combustion noise due to knocking. There is an advance angle limit for suppressing combustion noise in the ignition timing. The magnitude of this combustion noise is characterized by cplf (cylinder pressure level filtered), which is a combustion noise index. The applicant of the present application has disclosed in the following publications, etc. that the correlation between this cplf and mfb50 is high. This cplf is the frequency spectrum of the pressure change in the combustion chamber.

[0203] The knock limit calculation unit 1072 advances mfb50 as much as possible within the range that does not exceed the limit value of cplf. The advance angle limit at that time becomes the limit value corresponding to the aforementioned third limit line Li3.

[0204] Specifically, the knock limit calculation unit 1072 first sets the limit value of cplf based on the load and rotational speed of the engine 1 and the like. The knock limit calculation unit 1072 also sets the target cplf so as not to exceed the limit value in consideration of the variation of cplf caused by the combustion of the air-fuel mixture.

[0205] After that, the knock limit calculation unit 1072 calculates the target position of mfb50 at the ignition advance limit by comparing the load, rotational speed, and target cplf of the engine 1 with a previously determined knock limit map M72.

[0206] As described above, the position of mfb50 is related to the ignition timing. Determining the target position of mfb50 at the ignition advance limit is equivalent to determining the third limit line Li3 indicating the ignition advance limit of the ignition timing.

[0207] Note that various operations related to the target cplf in the knock limit calculation unit 1072 can adopt the methods described in, for example, Japanese Patent Application Laid-Open No. 2020-112095, etc., so the details are omitted. The knock limit calculation unit 1072 can also refer to the RON estimated value when setting the third limit line Li3. For example, as the RON estimated value increases, the third limit line Li3 shifts toward the advance side (shifts in the direction allowing the ignition advance of the ignition timing).

[0208] -Retard limit calculation unit- The retard limit calculation unit 1073 calculates the fourth limit line Li4 based on the operating state of the engine 1. The fourth limit line Li4 defines the upper limit value (retard limit) of the ignition timing. The fourth limit line Li4 indicates the limit value at which combustion stability is ensured. The fourth limit line Li4 can also be regarded as the limit value at which misfire is suppressed.

[0209] That is, if the ignition timing is retarded too much, CI combustion in SPCCI combustion does not occur, or the stability of the SI combustion part in retarded SI combustion and SPCCI combustion decreases. There is a retard limit for the ignition timing to ensure combustion stability.

[0210] Therefore, the retard limit calculation unit 1073 calculates the target position of mfb50 at the retard limit by comparing the load and rotational speed of the engine 1 with a pre-determined retard limit map M73.

[0211] As described above, the position of mfb50 is related to the ignition timing. Determining the position of mfb50 at the retard limit is equivalent to determining the fourth limit line Li4 indicating the retard limit of the ignition timing.

[0212] The retard limit map M73 defines the relationship between the load and rotational speed of the engine 1 and the position of mfb50 at the retard limit. The lower the rotational speed and the higher the load of the engine 1 (i.e., the higher the filling efficiency), the more fuel there is and the higher the combustion stability. Also, since the time from ignition to combustion is long even if the ignition timing is retarded, misfires and the like can be suppressed. The lower the rotational speed and the higher the load of the engine 1, the greater the ignition timing can be retarded. The position of mfb50 at the retard limit is retarded as the rotational speed of the engine 1 is low and the load is high, and advanced as the rotational speed is high and the load is low (i.e., the filling efficiency is low).

[0213] Note that various calculations related to the retard limit calculation unit 1073 can adopt the methods described in, for example, Japanese Patent Application Laid-Open No. 2018-84181, Japanese Patent Application Laid-Open No. 2020-16197, Japanese Patent Application Laid-Open No. 2020-16197, etc., so the details are omitted.

[0214] -Combustion center selection unit- The combustion center selection unit 1074 selects one of the positions of mfb50 calculated by the torque reduction calculation unit 1071, the knock limit calculation unit 1072, and the retard limit calculation unit 1073, respectively.

[0215] For example, when there is a torque reduction requirement, the combustion center selection unit 1074 selects the position of mfb50 calculated by the torque reduction calculation unit 1071 and sets this as the target mfb50.

[0216] On the one hand, when there is no torque reduction requirement, the combustion center of gravity selection unit 1074 selects the mfb50 position calculated by the knock limit calculation unit 1072 as long as it is on the advanced angle side of the mfb50 position calculated by the retard limit calculation unit 1073. The combustion center of gravity selection unit 1074 sets the mfb50 position calculated by the knock limit calculation unit 1072 as the target mfb50.

[0217] Also, when the mfb50 position calculated by the knock limit calculation unit 1072 shifts to the retard angle side of the mfb50 position calculated by the retard limit calculation unit 1073, the combustion center of gravity selection unit 1074 selects the mfb50 position calculated by the retard limit calculation unit 1073. The combustion center of gravity selection unit 1074 sets the mfb50 position calculated by the retard limit calculation unit 1073 as the target mfb50.

[0218] [6-7-2. Target Combustion Period Determination Unit] The target combustion period determination unit 107b includes a base period calculation unit 1075 and a base period correction unit 1076.

[0219] Note that the "combustion period" in the following description refers to the period from the time (crank angle) when 10% of the total heat generation occurs to the time (crank angle) when 50% of the total heat generation occurs among the total heat generation amount generated during one combustion cycle. This combustion period is equal to the period from mfb50 minus the mass combustion ratio of 10% (mfb10) in one combustion cycle. Hereinafter, this period is denoted as "mfb1050".

[0220] As is well known, mfb1050 changes according to the fuel ignition timing. In other words, according to the target mfb1050, the ignition timing to achieve that target will change.

[0221] Therefore, the ECU 10 is configured to adjust the ignition timing using this mfb1050 as an index. Specifically, the ECU 10 determines the mfb1050 according to the operating state of Engine 1, and sets the target ignition timing based on the target mfb1050. That is, the ECU 10 determines the target ignition timing at a timing such that not only the position of the target mfb50 but also the target mfb1050 is achieved.

[0222] -Base Period Calculation Unit- The base period calculation unit 1075 calculates the basic value (base period) of mfb1050 by comparing the mode signal, as well as the load and rotational speed of Engine 1, with the base period estimation map M74 or substituting them into a base period estimation model (not shown).

[0223] For example, when all parameters other than the injection mode are the same, the combustion period of CI combustion is shorter than that of SI combustion. Therefore, the combustion period of SPCCI combustion is shorter than that of retarded SI combustion. The base period increases or decreases depending on the injection mode.

[0224] In addition, the base period calculation unit 1075 estimates a shorter base period as the rotational speed of Engine 1 increases. Basically, this is because the flame propagation speed increases as the rotational speed of Engine 1 increases, and the combustion of the air-fuel mixture progresses steeply.

[0225] In addition, the base period calculation unit 1075 estimates a longer base period as the load of Engine 1 increases. Basically, this is because the time required for the combustion of the fuel increases as the fuel injection amount increases.

[0226] -Base Period Correction Unit- The base period correction unit 1076 determines the target value of mfb1050 by performing various corrections on the base period calculated by the base period calculation unit 1075, such as corrections according to the split ratio of retarded SI.

[0227] The corrections performed by the base period correction unit 1076 include corrections based on the external EGR rate, the target equivalence ratio, and the above-mentioned split costs, etc. For example, as the external EGR rate increases, more gas will dilute the fuel, so the combustion period will become longer. On the other hand, as the target equivalence ratio decreases, more air will dilute the fuel, so the combustion period will become longer.

[0228] The base period correction unit 1076 outputs the base period after performing the above-mentioned corrections as the target mfb1050.

[0229] [6-7-3. Ignition timing conversion unit] The ignition timing conversion unit 107c converts the target mfb50 and the target mfb1050 into the base values (base periods) of the ignition timing by substituting the target mfb50 and the target mfb1050 into the ignition timing conversion model M75.

[0230] When the value of the target mfb1050 is fixed, the more the target mfb50 is retarded, the more necessary it is to retard the ignition timing. Similarly, when the value of the target mfb50 is fixed, the longer the target mfb1050 is, the more necessary it is to advance the ignition timing.

[0231] The ignition timing conversion model M75 is a model that formulates these tendencies, and by substituting the target mfb50 and the target mfb1050, the base period corresponding to those target values can be calculated.

[0232] The base period obtained by the ignition timing conversion unit 107c is input to the advance limit determination unit 107f.

[0233] [6-7-4. Transport limit calculation unit] The transport limit calculation unit 107d calculates a sixth limit line Li6 based on the operating state of the engine 1. The sixth limit line Li6, together with the second limit line Li2 described later, defines the lower limit value (advance angle limit) of the ignition timing. The sixth limit line Li6 indicates the limit value for the fuel injected from the injector 6 to reach the first and second spark plugs 251 and 252 through the cavity 31.

[0234] That is, if the ignition timing is advanced excessively, the piston 3 will ignite in a state where it has descended excessively with respect to the injector 6. In this case, there is a possibility that ignition will occur before the air-fuel mixture generated by the spray injected from the injector 6 reaches the first and second spark plugs 251 and 252 sufficiently. As a result, the ignition by the first and second spark plugs 251 and 252 may become unstable. The destabilization of ignition is disadvantageous because it may lead to a deterioration in fuel consumption performance.

[0235] Also, the transport limit is considered to be related to the retard limit of the final stage SOI. That is, if the final stage SOI is retarded excessively, the time interval between the end time of fuel injection and the ignition timing becomes short, and it is considered that the air-fuel mixture may not reach the first and second spark plugs 251 and 252 sufficiently. This is considered to cause destabilization of ignition for the same reason as described above.

[0236] On the other hand, the transport limit calculation unit 107d according to the present embodiment determines the sixth limit line Li6 as the advance angle limit of the ignition timing based on the engine speed, the final stage SOI, the final stage injection amount, and the fuel pressure.

[0237] For example, the transport limit calculation unit 107d shifts the sixth limit line Li6 toward the advance side with respect to the compression TDC as the fuel pressure increases. This is because when the fuel pressure is high, fuel is more likely to reach the first and second spark plugs 251 and 252 compared to when it is low, so it is permissible to set the advance angle limit of the ignition timing more on the advance side.

[0238] Further, as the engine speed increases, the transport limit calculation unit 107d shifts the sixth limit line Li6 toward the advanced angle side with respect to the compression TDC. Generally, when the engine speed is high, the time required for the crank angle to change by 1° is shorter compared to when it is low. Therefore, when spraying from the injector 6, the piston 3 can be brought closer to the injector 6 in a short time. Accordingly, when the engine speed is high, fuel can reach the first and second spark plugs 251 and 252 more easily compared to when it is low, so it is allowed to set the ignition timing advance limit more on the advanced angle side.

[0239] Also, as the final-stage SOI advances, the transport limit calculation unit 107d shifts the sixth limit line Li6 toward the advanced angle side with respect to the compression TDC. When the final-stage SOI is advanced, it is possible to ensure a longer time for guiding the fuel injected from the injector 6 to the first and second spark plugs 251 and 252. Therefore, the mixture gas can easily reach the vicinity of the first and second spark plugs 251 and 252, and it is allowed to set the ignition timing advance limit more on the advanced angle side.

[0240] Also, as the final-stage injection amount increases, the transport limit calculation unit 107d shifts the sixth limit line Li6 toward the retarded angle side with respect to the compression TDC. When the final-stage injection amount is increased, the injection amount up to that point decreases according to the split ratio, and the in-cylinder A / F excluding the contribution of the final-stage injection amount becomes lean. Therefore, as a result, the sixth limit line Li6 is shifted toward the retarded angle side.

[0241] In this way, the transport limit calculation unit 107d determines the sixth limit line Li6 based on the engine speed, the final-stage SOI, the final-stage injection amount, and the fuel pressure. This determination can be made, for example, by comparing the values of the engine speed, the final-stage SOI, the final-stage injection amount, and the fuel pressure with the transport limit map M76 that defines the sixth limit line Li6.

[0242] Here, the transport limit map M76 is a map that associates the values of the engine speed, the final stage SOI, the final stage injection amount, and the combustion pressure with the values of the sixth limit line Li6. The specific values of the sixth limit line Li6 are tuned according to the geometric shape of the cavity 31 and the layouts of the injector 6, the first ignition plug 251, and the second ignition plug 252. The transport limit map M76 is pre-stored in the memory 100b.

[0243] The sixth limit line Li6 determined by the transport limit calculation unit 107d is input to the advance angle limit determination unit 107f.

[0244] [6-7-5. Smoke limit calculation unit] The smoke limit calculation unit 107e calculates the second limit line Li2 based on the operating state of the engine 1. The second limit line Li2, together with the aforementioned sixth limit line Li6, defines the lower limit value (advance angle limit) of the ignition timing. The second limit line Li2 indicates the limit value at which the generation of smoke is suppressed.

[0245] That is, if the ignition timing is advanced too much, ignition will start before the fuel has sufficiently evaporated, which is considered to cause the generation of smoke. The generation of smoke is disadvantageous in improving the fuel consumption performance and emission performance of the engine 1.

[0246] Also, the generation of smoke is considered to be related to the retard limit of the final stage SOI. That is, if the final stage SOI is retarded too much, the time interval between the end time of fuel injection and the ignition timing becomes short, and it is considered that the evaporation of the fuel may also become insufficient. This is considered to cause the generation of smoke for the same reason as described above.

[0247] In contrast, as shown in FIGS. 11 and 12, the smoke limit calculation unit 107e according to the present embodiment determines the second limit line Li2 as the advance angle limit of the ignition timing based on the final stage injection amount, the combustion pressure, the final stage SOI, the engine coolant temperature, and various IVC state quantities.

[0248] Specifically, as illustrated in FIGS. 11 and 12, the smoke limit calculation unit 107e includes an evaporation end time estimation unit 1077 and a smoke limit inverse calculation unit 1078.

[0249] -Evaporation End Time Estimation Unit- The evaporation end time estimation unit 1077 includes an injection period map M77, a crank angle conversion unit 1077a, a first addition unit 1077b, an evaporation period estimation unit 1077c, and a second addition unit 1077d.

[0250] The injection period map M77 calculates the injection period of fuel (especially the injection period related to the final stage injection amount) in units of time based on the final stage injection amount and the combustion pressure. The crank angle conversion unit 1077a converts the calculated injection period into units of crank angle.

[0251] Let this injection period be T inj and the end time of the final stage compression stroke injection (End Of Injection timing: EOI) be "final stage EOI", then the injection period T inj can be described as in the following formula (3).

[0252] T inj = final stage EOI - final stage SOI …(3) The first addition unit 1077b adds the final stage SOI to the injection period T inj and outputs the addition result. As is clear from the above formula (3), the output value by the first addition unit 1077b is nothing but the value of the final stage EOI.

[0253] The evaporation period estimation unit 1077c estimates the period (evaporation period) until the fuel injected until the final stage EOI evaporates based on the combustion pressure, the engine water temperature, the IVC state quantity, and a map or a model.

[0254] The evaporation period estimation unit 1077c estimates the evaporation period using, for example, a model based on the evaporation rate of fuel. In such an estimation, for example, as described in Japanese Patent Application Laid-Open No. 2013-11176, International Publication No. 2012 / 046312, etc., a fuel droplet model can be used.

[0255] Let this evaporation period be T eva and if the estimated value of the end of evaporation timing (EOE), which indicates the time when the evaporation of fuel is completed, is denoted as "EOE", the evaporation period T eva can be described as in the following formula (4).

[0256] T eva = EOE - final stage EOI …(4) The second addition unit 1077d adds the final stage EOI to the evaporation period T eva and outputs the addition result. As is clear from the above formula (4), the output value by the second addition unit 1077d is nothing but the value of EOE.

[0257] - Smoke limit inverse calculation unit - The smoke limit inverse calculation unit 1078 has a standby period map M78 and a third addition unit 1078a.

[0258] The injection period map M77 calculates a standby period, which will be described later, based on the load and rotational speed of the engine 1. This standby period is the standby period from when the evaporation of fuel ends until ignition is started. By setting this standby period to a value greater than 0, it becomes possible to start ignition after reliably waiting for the end of fuel evaporation.

[0259] The injection period map M77 increases the standby period as the load of the engine 1 increases and also increases the standby period as the rotational speed of the engine 1 increases.

[0260] Let this standby period be T stb and if the ignition advance limit is IG, the standby period T stb can be described as in the following formula (5).

[0261] T stb =IG - EOE …(5) The third adder 1078a adds EOE to the standby period T and outputs the addition result. As is clear from the above formula (5), the output value by the third adder 1078a is nothing but the value of IG. stb As is clear from the above formula (5), the output value by the third adder 1078a is nothing but the value of IG.

[0262] The value of IG in formula (5) is the ignition advance limit at which smoke suppression is guaranteed, and corresponds to the aforementioned second limit line Li2.

[0263] Thus, the smoke limit inverse calculation unit 1078 outputs the second limit line Li2.

[0264] Note that when factors other than the final stage SOI, such as the fuel pressure, the load and rotational speed of engine 1, the final stage injection amount, and the engine coolant temperature, are fixed, the output value by the third adder 1078a can be described as in formula (6).

[0265] IG = Con + final stage SOI …(6) In the above formula (6), Con is a parameter that depends on factors such as the fuel pressure, the load and rotational speed of engine 1. When factors other than the final stage SOI are fixed as described above, Con becomes a constant term.

[0266] Considering that IG on the left side in the above formula (6) corresponds to the second limit line Li2, it can be seen that the advance limit for suppressing smoke (= the second limit line Li2) is a linear function with a slope of 1 with the final stage SOI as a variable. The second limit line Li2 is strongly correlated with the final stage SOI.

[0267] [6 - 7 - 6. Advance Limit Determination Unit] The ignition angle limit determination unit 107f reads the base timing of the ignition timing, the sixth limit line Li6, and the second limit line Li2, selects the maximum value among them, and outputs it. This output value becomes the final value of the ignition timing. Here, the "maximum value" refers to the crank angle that is retarded the most with respect to the compression TDC in one combustion cycle.

[0268] For example, when the base timing is retarded with respect to both the sixth limit line Li6 and the second limit line Li2, the ignition angle limit determination unit 107f outputs the base timing as the ignition timing. On the other hand, when the base timing is retarded with respect to the sixth limit line Li6 but advanced with respect to the second limit line Li2, the ignition angle limit determination unit 105g outputs the value on the second limit line Li2 as the ignition timing.

[0269] [6-7-7. Calculation Timing] The ignition timing calculation unit 107 continues to execute these calculations following the calculations by the second injection calculation unit 105 starting at the second timing T2. The ignition timing calculation unit 107 inputs a signal indicating the ignition timing to the first ignition plug 251 and the second ignition plug 252.

[0270] (6-8. F / B Term Calculation Unit) The F / B term calculation unit 108 calculates the F / B term based on the current value of the final stage SOI, the second limit line Li2, and the third limit line Li3 in order to execute feedback control regarding the final stage SOI.

[0271] Specifically, the F / B term calculation unit 108 searches for the intersection point of the current value of the final stage SOI and the second limit line Li2, and determines the ignition timing on the second limit line Li2 corresponding to the current value of the final stage SOI. Hereinafter, the ignition timing on the second limit line Li2 is also referred to as the "smoke limit timing".

[0272] Similarly, the F / B term calculation unit 108 searches for the intersection of the current value of the final-stage SOI and the third limit line Li3, and converts the intersection point (mfb50) into the ignition timing. The F / B term calculation unit 108 determines the ignition timing on the third limit line Li3 corresponding to the current value of the final-stage SOI. Hereinafter, the ignition timing on the third limit line Li3 is also referred to as the "knock limit timing".

[0273] Next, the F / B term calculation unit 108 compares the smoke limit timing and the knock limit timing. The F / B term calculation unit 108 determines the F / B term based on the comparison result. The sign of the F / B term is illustrated in FIG. 13.

[0274] Specifically, when the smoke limit timing is greater than the knock limit timing, the F / B term calculation unit 108 sets the F / B term to a negative predetermined value. This setting corresponds to shifting the final-stage SOI in the advance direction.

[0275] Also, when the smoke limit timing is less than the knock limit timing, the F / B term calculation unit 108 sets the F / B term to a positive predetermined value. This setting corresponds to shifting the final-stage SOI in the retard direction.

[0276] Also, when the smoke limit timing is equal to the knock limit timing, the F / B term calculation unit 108 sets the F / B term to zero. This setting corresponds to not shifting the final-stage SOI any further.

[0277] <7. Basic Concepts Related to Parameter Map> As described with reference to FIGS. 6 to 12, the ECU 10 according to the present embodiment determines a combination of the final-stage SOI (hereinafter, also simply referred to as the "injection timing") and the ignition timing corresponding to the final-stage SOI.

[0278] Such a determination by the ECU 10 is a parameter map M with the injection timing as the first axis and the ignition timing as the second axis. limThis corresponds to the step of selecting a combination of injection timing and ignition timing so as to correspond to the selection above. Hereinafter, the combination of injection timing and ignition timing may be referred to as a "control parameter" or a "control point" as described above.

[0279] FIG. 14 shows a schematic diagram of a parameter map M lim FIG. 13 is an illustration with the compression TDC as the origin, the first axis as the x-axis, and the second axis as the y-axis.

[0280] The parameter map M lim will be provided with a plurality of limit lines that change according to the operating state of the engine 1. The plurality of limit lines are the first limit line Li1 to the sixth limit line Li6 described above.

[0281] That is, as described above, in the injection timing, there are a first limit line Li1 indicating an advance angle limit corresponding to suppression of premature ignition and a fifth limit line Li5 indicating an advance angle limit corresponding to a cavity limit.

[0282] In the case of the example of FIG. 14, the first limit line Li1 is a straight line substantially parallel to the y-axis (ignition timing). Specifically, the first limit line Li1 is a straight line that advances the injection timing very slightly as the ignition timing advances (that is, a straight line having a slight dependence on the ignition timing). This reflects the influence of the interval between the injection timing and the ignition timing. When the ignition timing becomes earlier, although it is slight, it becomes advantageous and further advance angle is allowed. Each point on the first limit line Li1 basically has a negative value.

[0283] The fifth limit line Li5 is a straight line parallel to the y-axis (ignition timing). Specifically, the fifth limit line Li5 is a straight line that keeps the injection timing constant with respect to the increase and decrease of the ignition timing (that is, a straight line having no dependence on the ignition timing). Each point on the fifth limit line Li5 has a negative value.

[0284] Similarly, at the ignition timing, there are a second limit line Li2 indicating an ignition advance limit corresponding to suppression of smoke generation, a third limit line Li3 indicating an ignition advance limit corresponding to suppression of knocking occurrence, a fourth limit line Li4 indicating a retard limit corresponding to ensuring combustion stability, and a sixth limit line Li6 indicating an ignition advance limit corresponding to a transport limit.

[0285] Here, the third limit line Li3 and the fourth limit line Li4 are the ignition advance limit and retard limit that are indirectly incorporated into the determination of the ignition timing through the setting of the target mfb50.

[0286] Also, as described above, at least the second limit line Li2 and the sixth limit line Li6 depend not only on the ignition timing but also on the injection timing (final stage SOI).

[0287] In the case of the example in FIG. 14, the fourth limit line Li4 is a straight line substantially parallel to the x-axis (injection timing). Specifically, the fourth limit line Li4 is a straight line that slightly retards the ignition timing according to the retard of the injection timing (that is, a straight line with a slight dependence on the injection timing). This reflects the influence of the interval between the injection timing and the ignition timing. When the injection timing becomes later, although slightly, it becomes advantageous and a further retard is allowed. Each point on the fourth limit line Li4 basically has a positive value.

[0288] The second limit line Li2, the third limit line Li3, and the sixth limit line Li6 are straight lines that depend on the injection timing. In particular, the second limit line Li2 is a linear function with a slope of 1 as exemplified in Equation (6).

[0289] Among the first limit line Li1 to the sixth limit line Li6, at least the first limit line Li1 to the fourth limit line Li4 are on the parameter map M lim and demarcate a parameter region R lim surrounded by the first limit line Li1 to the fourth limit line Li4.

[0290] When determining control parameters, the ECU 10 takes into account the first to fourth limit lines Li1 to Li4. This is equivalent to selecting a combination of injection timing and ignition timing within the parameter range R lim And, the ECU 10 according to the present embodiment selects control parameters so that the ignition timing is the most advanced within the range of the parameter region R

[0291] Then, the ECU 10 according to the present embodiment selects control parameters so that the ignition timing is the most advanced within the range of the parameter region R lim Hereinafter, this selection will be described using a conceptual example

[0292] <8. Specific Example of Processing Related to Parameter Map> The following description starts from a state where the ignition timing is the most advanced within the range of the parameter region R ad as shown by the control point P in FIG. 14 lim When the parameter region R

[0293] When the parameter region R lim shrinks or expands, the ECU 10 executes at least one of feedback control and feedforward control for the injection timing, while executing feedforward control for the ignition timing. Feedforward control is a process that is performed before actually igniting the air-fuel mixture in each combustion cycle. Feedback control is a process that is repeatedly and stepwise performed each time the combustion cycle is repeated

[0294] As shown in FIG. 15A, for example, consider a situation where as a result of a decrease in the fuel pressure, the third limit line Li3 corresponding to the knock limit has shifted to the retarded side (it has become difficult to suppress combustion noise). In this case, since the F / B term is not calculated without passing through the ignition timing calculation unit 107, feedback control for the injection timing is not executed until the first combustion cycle after the shift is performed. Also, since the magnitude relationship with the first limit line Li1 and the fifth limit line Li5 has not changed, feedforward control for the injection timing is not executed either

[0295] On the other hand, as a result of the shift of the third limit line Li3, the parameter region Rlim will be reduced. Along with this reduction, the ignition timing at the initial position of the control point P ad will be outside the range of the parameter region R lim .

[0296] In this case, the knock limit calculation unit 1072 of the ignition timing calculation unit 107 shifts the ignition timing onto the shifted third limit line Li3A. Since this third limit line Li3A is on the retard side of the second limit line Li2 and the sixth limit line Li6, the guard by both limit lines becomes unnecessary. The process of shifting the ignition timing is feedforward control based on the operating state of the engine 1.

[0297] Parameter region R lim In the first combustion cycle after reduction, only the ignition timing is shifted prior to ignition of the air-fuel mixture (see control point P a1 ). The ECU 1 burns the air-fuel mixture with only the ignition timing shifted.

[0298] By shifting the ignition timing, information related to the third limit line Li3A and the second limit line Li2 used for the shift is fed back to the F / B term calculation unit 108.

[0299] The F / B term calculation unit 108 calculates the F / B term through the process described based on FIG. 13, based on the fed-back information. In the example of FIG. 15A, the knock limit timing is greater than the smoke limit timing. Therefore, the F / B term calculation unit 108 determines the F / B term in the direction of retarding the injection timing.

[0300] In the second combustion cycle after the shift, along with the addition of the F / B term, the injection timing shifts to the retard side (see control point P a2 ). The process of shifting the injection timing is feedback control based on the operating state of the engine 1.

[0301] However, this control point P a2There is still a margin for advancing the ignition timing related to the knock limit. Therefore, the knock limit calculation unit 1072 shifts the ignition timing onto the third limit line Li3A after the shift. This shift is a feedforward control as before.

[0302] Each time the combustion cycle is repeated, the ECU 10 gradually shifts the injection timing. This shift is a feedback control based on the operating state of the engine 1. At this time, even if the injection timing passes the desired control point (the most advanced ignition timing point), the magnitude relationship between the knock limit timing and the smoke limit timing will be reversed. The F / B term calculation unit 108 can surely reach the desired control point by combining the application of the F / B term in the direction of retarding the injection timing and the application of the F / B term in the direction of advancing the injection timing.

[0303] In this way, by repeating the feedback control and the feedforward control, the control point P a3 reaches the intersection of the third limit line Li3A and the second limit line Li2. This intersection is the control point where the knock limit timing and the smoke limit timing coincide. Therefore, the F / B term calculation unit 108 sets the F / B term to zero.

[0304] By setting the F / B term to zero, the feedback control of the injection timing ends. Since the ignition timing is also located at the intersection of the third limit line Li3A and the second limit line Li2, there is no further margin for advancing the ignition timing, and the feedforward control of the ignition timing also ends.

[0305] The control point P thus reached a3 corresponds to the most advanced ignition timing point in the reduced parameter region R lim A.

[0306] Also, as shown in FIG. 15B, consider a situation where, for example, as a result of newly injecting low-octane fuel, the first limit line Li1 corresponding to pre-ignition has shifted to the retarded side (making it difficult to suppress pre-ignition). In this case, since the F / B term is not calculated without going through the ignition timing calculation unit 107, in the first combustion cycle after the shift, feedback control for the injection timing is not executed. Although omitted in FIG. 15B, in this case, the third limit line Li3 will also shift to the retarded side.

[0307] However, as a result of the shift of the first limit line Li1, the parameter region R lim will shrink. Along with this shrinkage, since the injection timing at the initial position of the control point P ad is located on the advanced side of the first limit line Li1, it will be outside the range of the parameter region R lim .

[0308] In this case, the pre-ignition limit calculation unit 105f and the advance limit determination unit 105g of the second injection calculation unit 105 shift the injection timing onto the shifted first limit line Li1B (refer to the control point P b1 ). Since this first limit line Li1B is on the retarded side of the fifth limit line Li5 (not shown), the guard by the fifth limit line Li5 becomes unnecessary. This process is a feedforward control based on the operating state of the engine 1.

[0309] In addition, the smoke limit calculation unit 107e and the advance limit determination unit 107f of the ignition timing calculation unit 107 shift the ignition timing onto the second limit line Li2. Since this second limit line Li2 is on the retarded side of the third limit line Li3 and the sixth limit line Li6, the guards by both limit lines become unnecessary. The process of shifting the ignition timing is a feedforward control based on the operating state of the engine 1.

[0310] In the first combustion cycle after the shrinkage of the parameter region R lim , prior to ignition of the air-fuel mixture, the injection timing and the ignition timing are shifted (control point P b2(see). The ECU 10 burns the air-fuel mixture with only the injection timing and the ignition timing shifted.

[0311] By shifting the ignition timing, information related to the third limit line Li3 and the second limit line Li2 used for the shift is fed back to the F / B term calculation unit 108.

[0312] Based on the fed-back information, the F / B term calculation unit 108 calculates the F / B term through the process described with reference to FIG. 13. In the example of FIG. 15B, the knock limit timing is smaller than the smoke limit timing. Therefore, the F / B term calculation unit 108 determines the F / B term in the direction of advancing the injection timing.

[0313] In the second combustion cycle after the shift, although the F / B term is added to the injection timing, since the first limit line Li1B after the shift serves as a guard, the injection timing is shifted onto the first limit line Li1B by feedforward control. Along with the shift of the injection timing, the ignition timing is shifted onto the second limit line Li2. By repeating such processing, the finally selected control point P b3 is nothing but the most advanced ignition timing point in the reduced parameter region R lim B.

[0314] In this way, the ECU 10 guides the control point P a3 to the most advanced ignition timing point in the parameter region R lim B by at least executing feedforward control.

[0315] Also, as shown in FIG. 15C, consider a situation where, for example, as a result of newly injecting fuel with a low octane number when the engine is cold, the first limit line Li1 and the third limit line Li3 have shifted toward the advanced angle side. In this case, since the F / B term is not calculated without going through the ignition timing calculation unit 107, in the first combustion cycle after the shift, feedback control for the injection timing is not executed. Also, since the magnitude relationship between the first limit line Li1 and the fifth limit line Li5 has not changed, feedforward control for the injection timing is not executed either.

[0316] On the other hand, as a result of the first limit line Li1 and the third limit line Li3 shifting toward the advanced angle side, the parameter region R lim will expand. Along with this expansion, the ignition timing at the initial position of the control point P ad is within the range of the parameter region R lim but is not the most advanced angle.

[0317] In this case, since the ignition timing is also on the second limit line Li2, feedforward control for the ignition timing is not executed either.

[0318] However, information related to the third limit line Li3A and the second limit line Li2 used for determining the necessity of feedforward control is fed back to the F / B term calculation unit 108.

[0319] The F / B term calculation unit 108 calculates the F / B term through the process described with reference to FIG. 13 based on the fed-back information. In the case of the example in FIG. 15C, the knock limit timing is smaller than the smoke limit timing. Therefore, the F / B term calculation unit 108 determines the F / B term in the direction of advancing the injection timing.

[0320] In the second combustion cycle after the shift, with the addition of the F / B term, the injection timing shifts toward the advanced angle side (see control point P c1 ). The process of shifting the injection timing is feedback control based on the operating state of the engine 1.

[0321] However, for this control point P a2 there is still a margin of ignition advance related to the knock limit. Therefore, the knock limit calculation unit 1072 shifts the ignition timing onto the third limit line Li3C after the shift. This shift is feedforward control with respect to the ignition timing.

[0322] Each time the combustion cycle is repeated, the ECU 10 gradually shifts the injection timing step by step. This shift is feedback control based on the operating state of the engine 1. At this time, even if the injection timing passes the desired control point (the most advanced ignition timing point), the magnitude relationship between the knock limit timing and the smoke limit timing will be reversed. The F / B term calculation unit 108 can surely reach the desired control point by combining the application of the F / B term in the direction of retarding the injection timing and the application of the F / B term in the direction of advancing the injection timing.

[0323] In this way, by repeating the feedback control and the feedforward control, the control point P c2 reaches the intersection of the third limit line Li3C and the second limit line Li2. This intersection is the control point where the knock limit timing and the smoke limit timing coincide. Therefore, the F / B term calculation unit 108 sets the F / B term to zero.

[0324] By setting the F / B term to zero, the feedback control of the injection timing ends. Since the ignition timing is also located at the intersection of the third limit line Li3C and the second limit line Li2, there is no further margin for ignition advance, and the feedforward control of the ignition timing also ends.

[0325] The control point P thus reached c2 corresponds to the most advanced ignition timing point in the enlarged parameter region R lim A.

[0326] Figure 16 is a flowchart illustrating processing related to the movement of control points. First, in step S1, the ECU 10 sets the base value of the control point of engine 1. This control point is a combination of the final-stage SOI and the ignition timing as described above, and is set based on the operating state of engine 1.

[0327] In parallel with or before and after step S101, the ECU 10 determines the parameter area R based on the operating environment such as changes in engine coolant temperature, changes in octane number, transitions between cold and warm operations, etc., and the operating state such as the engine speed and load of engine 1. lim (Step S102).

[0328] In the subsequent step S103, the ECU 10 determines whether the control point is within the parameter area R. lim As described with reference to FIGS. 6 to 12, the determination of whether the final-stage SOI is within the parameter area R and the determination of whether the ignition timing is within the parameter area R may be performed individually and continuously. lim lim

[0329] If the determination in step S103 is YES, the ECU 10 advances the control process to step S105. If the determination in step S103 is NO, the ECU 10 advances the control process to step S104.

[0330] In step S104, the ECU 10 shifts the control point onto the limit line by using the advance limit determination unit 105g for the final-stage SOI, the advance limit determination unit 107f for the ignition timing, etc. For example, if the ignition timing is advanced beyond the second limit line Li2, the ECU 10 shifts the ignition timing onto the second limit line Li2. The process of step S104 is feedforward control performed prior to ignition of the air-fuel mixture in one combustion cycle.

[0331] ​​As described with reference to FIG. 15B, the feedforward control in step S104 is also performed on the final-stage SOI. When the process of step S104 is completed, the ECU 10 advances the control process to step S105.

[0332] In step S105, the ECU 10 determines whether or not the ignition timing is the most advanced (the most advanced ignition timing) within the parameter region R lim If this determination is YES, the ECU 10 ends the control process shown in FIG. 16. If the determination in step S105 is NO, the ECU 10 advances the control process to step S106.

[0333] In step S106, the ECU 10 shifts the final-stage SOI and the ignition timing toward the most advanced ignition timing. For the final-stage SOI, feedback control is performed to shift it step by step toward the intersection of the two lines, which is set based on the magnitude relationship between the second limit line Li2 and the third limit line Li3. This feedback control is performed in each combustion cycle every time the combustion cycle is repeated.

[0334] On the other hand, in step S106, feedforward control is performed to shift the ignition timing onto the second limit line Li2 or the third limit line Li3. That is, every time the final-stage SOI is shifted step by step, the ignition timing will move away from the second limit line Li2 or the third limit line Li3. By performing the feedforward control each time, it becomes possible to maintain the ignition timing on the second limit line Li2 or the third limit line Li3.

[0335] <9. Summary> As described above, according to the embodiment, the control points composed of the combination of the injection timing and the ignition timing are determined within the parameter region R lim partitioned by a plurality of limit lines. Thereby, when selecting the injection timing and the ignition timing, it becomes possible to set them within the range of various constraints.

[0336] Furthermore, by setting the ignition timing to the most advanced angle within the parameter region R lim while taking into account various constraints imposed on the engine 1, the fuel consumption performance of the engine 1 can be optimized.

[0337] Also, as illustrated in FIGS. 15A and 15B, even if the control point P ad goes outside the parameter region, the control point is shifted to any one of the limit lines such as the third limit line Li3A and the first limit line Li1B. Thereby, it is possible to preferentially respond to the constraints imposed on the engine 1. Thereafter, by gradually performing the advancement of the ignition timing, each process can be performed according to a desired priority order.

[0338] Also, as illustrated in FIGS. 15A and 15B, within one combustion cycle, the control point P ad is shifted to the limit lines such as the third limit line Li3A and the first limit line Li1B. Thereby, it is possible to respond to the constraints imposed on the engine 1 as quickly as possible. At that time, the shift may be made by shifting the ignition timing as shown in FIG. 15A, or by shifting the injection timing as shown in FIG. 15B.

[0339] Also, as shown by each arrow in FIGS. 15A to 15C, the advancement of the ignition timing is to be performed step by step for each combustion cycle. By changing the ignition timing step by step, the ignition timing can be more surely shifted to the most advanced angle point.

[0340] Also, as shown in FIG. 8, as one of a plurality of limit lines, a fifth limit line Li5 indicating an advancement stage for allowing the fuel injected from the injector 6 to reach within the cavity 31 is incorporated. Thereby, constraints can be imposed on the engine 1 from a more comprehensive perspective. This is advantageous for improving the performance of the engine 1.

[0341] Also, as shown in FIG. 11, among a plurality of limit lines, as one of them, a sixth limit line Li6 indicating an advance angle stage for allowing the fuel injected from the injector to reach the first and second spark plugs 251 and 252 is incorporated. Thereby, constraints can be imposed on the engine 1 from a more multifaceted viewpoint. This is advantageous for improving the performance of the engine 1.

[0342] Also, as shown in FIG. 11, a fourth limit line Li4 indicating a retard limit of the ignition timing is incorporated into the plurality of limit lines. Thereby, constraints can be imposed on the combustion control of the engine 1 from a more important viewpoint. This is advantageous for improving the performance of the engine 1.

[0343] <10. Other Embodiments> In the above embodiment, although the ECU 10 does not actually store the parameter map M lim it was configured to perform processing equivalent to the selection of control points on the parameter map M lim However, the present disclosure is not limited to such a configuration. The ECU 10 may be configured to store and read the parameter map M lim and actually search for control points on the parameter map M lim

Description of Reference Numerals

[0344] 1 Engine 10 ECU 108 F / B Term Calculation Unit 11 Cylinder 6 Injector 251 First Spark Plug (Spark Plug) 252 Second Spark Plug (Spark Plug) L1 First Limit Line L2 Second Limit Line L3 Third Limit Line L4 Fourth Limit Line L5 Fifth Limit Line L6 Sixth Limit Line M lim Parameter Map​ R lim Parameter area

Claims

1. A method for controlling an engine using a cylinder, an injector for injecting fuel into the cylinder, a spark plug for igniting an air-fuel mixture containing the fuel injected from the injector, and a controller electrically connected to the injector and the spark plug and controlling each of the injector and the spark plug, comprising: a step of selecting a control point consisting of a combination of the injection timing and the ignition timing so as to correspond to a selection on a parameter map having the injection timing of fuel by the injector as a first axis and the ignition timing of the air-fuel mixture by the spark plug as a second axis; a plurality of limit lines that change according to the operating state of the engine are provided on the parameter map; the plurality of limit lines are: a first limit line indicating an advance angle limit for suppressing pre-ignition; a second limit line indicating an advance angle limit for suppressing smoke; a third limit line indicating an advance angle limit for suppressing knocking; a fourth limit line indicating a retard angle limit for ensuring combustion stability, and a parameter region surrounded by the plurality of limit lines is partitioned on the parameter map; the controller further has a step of selecting the control point so that the ignition timing is the most advanced within the range of the parameter region; A method for controlling an engine, characterized by the above.

2. In the method for controlling an engine according to Claim 1, when the control point goes outside the parameter region as the parameter region shrinks, a step of shifting the control point to any one of the limit lines constituting the parameter region by the controller; subsequently, a step of gradually shifting the control point each time the combustion cycle is repeated so that the ignition timing is the most advanced within the range of the shrunk parameter region by the controller; A method for controlling an engine, characterized by the above.

3. In the method for controlling an engine according to Claim 2, the controller executes the step of shifting the control point to any one of the limit lines by feedforward control based on the operating state of the engine within one combustion cycle; A method for controlling an engine, characterized by the above.

4. In the method for controlling an engine according to Claim 1, When the ignition timing becomes non-optimal with the expansion of the parameter area, the controller further has a step of gradually shifting the control point each time the combustion cycle is repeated so that the ignition timing becomes optimal within the range of the expanded parameter area. A method for controlling an engine, characterized by the above.

5. In the method for controlling an engine according to claim 1, A piston is accommodated in the cylinder, A cavity is formed on the upper surface of the piston, The plurality of limit lines further includes a fifth limit line indicating an advance angle limit for allowing the fuel injected from the injector to reach the cavity. A method for controlling an engine, characterized by the above.

6. In the method for controlling an engine according to claim 1, The plurality of limit lines further includes a sixth limit line indicating an advance angle limit for allowing the fuel injected from the injector to reach the spark plug. A method for controlling an engine, characterized by the above.

7. In the method for controlling an engine according to claim 1, The fourth limit line indicates a retard angle limit of the ignition timing. A method for controlling an engine, characterized by the above.

Images