JP2009299662A - Combustion control system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a combustion control system for a multi-cylinder internal combustion engine capable of sensing fluctuation in a combustion state among cylinders for effectively eliminating fluctuation in a combustion state. <P>SOLUTION: A/F lean control is carried out for temporarily shifting an air-fuel ratio to a lean side prior to fuel cut movement accompanied by accelerator-off operation. If a misfire accompanied by the execution of the A/F lean control may occur, the correction of increasing the fuel injection amount of the cylinder to an accidental fire is performed after the termination of the fuel cut movement. If the misfire does not occur, the air-fuel ratio is shifted further to the lean side when succeeding A/F lean control is executed, and the operation is repeated until the misfire occurs in part of the cylinders. If misfires may occur in a plurality of cylinders, the air-fuel ratio is shifted slightly to a rich side when the succeeding A/F lean control is executed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a combustion control device for an internal combustion engine such as an engine mounted on an automobile. In particular, the present invention relates to a measure for eliminating variations in the combustion state between cylinders in a multi-cylinder internal combustion engine.

  In an internal combustion engine, such as a multi-cylinder engine for automobiles, in which an air-fuel mixture (air-fuel mixture) is burned by providing an injector (fuel injection valve), a spark plug, or the like for each cylinder. Due to variations in the fuel injection amount, intake air amount, compression ratio, etc., there may be a difference in the combustion state (combustion force) between the cylinders. In such a situation, the torque generated in each cylinder is not uniform, and engine torque cannot be obtained stably, leading to deterioration of drivability. In addition, exhaust emission may be deteriorated.

  In particular, in the case of an independent throttle engine having a throttle valve for each cylinder or group of cylinders, compared to a single throttle engine having a throttle valve common to all cylinders, intake air caused by individual differences of the throttle valves. The variation in the amount tends to increase, and the difference in the combustion state between the cylinders tends to increase. Further, when the engine is under low load operation (when the amount of intake air is relatively small), the degree of influence due to the above-mentioned variation becomes large, so that the above problem becomes large during low load operation of the independent throttle engine.

  In view of the above, conventionally, there is a need for a technique for detecting the combustion state of each cylinder, and for eliminating the variation in the combustion state.

  In view of this point, Patent Document 1 and Patent Document 2 below have been proposed.

  In Patent Document 1, when the internal combustion engine is in a low load state, the amount of ions generated with combustion of the air-fuel mixture in each cylinder is detected as an ion current value, and the detected ions for each cylinder are detected. It is disclosed that the fuel injection amount for each cylinder is corrected based on the current value to reduce the variation in combustion between the cylinders.

Patent Document 2 below discloses that the fuel injection timing is corrected based on the ion current value in the homogeneous combustion execution region to reduce the variation in combustion between the cylinders.
JP 2000-45846 A JP 2000-80944 A

  By the way, the detection method of the combustion state for each cylinder disclosed in each patent document described above detects a slight difference in ionic current associated with combustion of the air-fuel mixture in each cylinder, and sets the combustion state of each cylinder. It has been found that there is variation, and requires a highly accurate determination logic for detecting this slight difference in ion current.

  In view of the fact that it is difficult for the inventor of the present invention to reliably determine the variation in the combustion state between the cylinders with the techniques disclosed in the above-mentioned patent documents, the fuel injection amount and the intake air between the cylinders are considered. A new method for detecting the occurrence of variations in air volume and compression ratio was studied. In addition, by performing a control operation that causes a phenomenon that does not appear in the other cylinders only in the cylinders that have lower combustion power than the other cylinders due to the variation, the combustion power is reduced. We studied a technology that can accurately extract the lower cylinders.

  The present invention has been made in view of the above points, and an object of the present invention is to detect a variation in the combustion state between the cylinders with high accuracy in a multi-cylinder internal combustion engine, and to detect the variation in the combustion state. It is an object of the present invention to provide a combustion control device for an internal combustion engine that can effectively eliminate the above.

-Solving principle-
The solution principle of the present invention taken in order to achieve the above object is to shift the air-fuel ratio of each cylinder of the internal combustion engine in the operating state to the lean side. By forcibly causing misfire to the low cylinder, it is possible to clearly determine that the combustion power is lower than that of the other cylinders. For example, when detecting the ionic current of each cylinder, there is a large difference in the detected value of the ionic current between the cylinder in which the air-fuel mixture is burned and the cylinder in which misfire has occurred. For this reason, the cylinder which was in the state with low combustion power can be extracted clearly by generating the forced misfire mentioned above. Then, by increasing the fuel injection amount (a parameter for changing the combustion force of the air-fuel mixture) to the cylinder in which this misfire has occurred (the cylinder in which the combustion force was low), the combustion force is reduced to another value. The cylinder is close to the cylinder so that uniform combustion power can be obtained for all cylinders.

-Solution-
Specifically, the present invention is premised on a combustion control device for an internal combustion engine for individually controlling the combustion state of the air-fuel mixture in each cylinder of the multi-cylinder internal combustion engine. The internal combustion engine combustion control device is provided with lean transition adjusting means, misfire occurrence cylinder recognizing means, and combustion force correcting means. The lean shift adjusting means shifts the air-fuel ratio of the air-fuel mixture supplied to each of the cylinders uniformly to the lean side. The misfire occurrence cylinder recognition means recognizes the misfire occurrence cylinder when a misfire occurs when the air-fuel ratio is shifted to the lean side by the lean transition adjustment means. When the misfire occurrence cylinder is recognized by the misfire occurrence cylinder recognition means, the combustion force correction means corrects a parameter for changing the combustion force of the air-fuel mixture so that the combustion force of the misfire occurrence cylinder is increased.

  By this specific matter, when individually controlling the combustion state of the air-fuel mixture in each cylinder, first, the air-fuel ratio of the air-fuel mixture supplied to each cylinder is uniformly shifted to the lean side. That is, the air-fuel mixture supplied to each cylinder is shifted to a state where it is easy to misfire. At this time, if misfire occurs in some cylinders, it can be determined that the combustion power of the cylinders is lower than that of other cylinders from the stage before the air-fuel ratio is shifted to the lean side. In other words, misfire is forcibly caused to a cylinder that has the lowest combustion power among a plurality of cylinders or a plurality of cylinders that have a low combustion power to other cylinders. By executing the air-fuel ratio control, it is possible to clearly discriminate between the cylinders in which the combustion power is low and other cylinders. After discriminating (extracting) the cylinder in which the combustion power is low in this way, the combustion power is increased with respect to this cylinder, such as correction for increasing the fuel injection amount (a parameter for changing the combustion power of the air-fuel mixture) Thus, a correction operation that increases the combustion power is performed. Thereby, the combustion power of the cylinder with low combustion power can be brought close to the combustion power of other cylinders. As a result, it is possible to reduce the difference in combustion power between cylinders due to variations in the fuel injection amount, intake air amount, compression ratio, etc. between the cylinders, and to improve drivability by stabilizing engine torque, and , Exhaust emissions can be improved. In addition, when the combustion power of some cylinders is increased in this manner, the combustion power of other cylinders (cylinders that have not been subjected to parameter correction) becomes relatively low. Similar to the operation, the cylinder having the low combustion power is determined, and the fuel injection amount is increased and corrected for the cylinder. By repeating this operation, the combustion power of all cylinders can be made substantially uniform.

  Specific examples of the execution timing of the operation for uniformly shifting the air-fuel ratio of the air-fuel mixture to the lean side include the following. In other words, when the throttle valve provided in the intake system is substantially fully closed and the fuel cut condition is satisfied, the lean transition adjusting means uniformly sets the air-fuel ratio of the air-fuel mixture to the lean side prior to the fuel cut operation. It is set as the structure made to transfer to.

  If the air-fuel ratio of the air-fuel mixture is uniformly shifted to the lean side at such timing, the air-fuel ratio is once shifted to the lean side, and then the fuel cut operation is started, and this fuel cut operation is started. Drastic torque fluctuation at the time can be suppressed, the behavior of the vehicle can be suppressed, and drivability can be improved. That is, by shifting the air-fuel ratio of the air-fuel mixture to the lean side at this timing, it is possible to extract the cylinders in which the combustion power is low as described above while improving drivability. Further, when applied to an internal combustion engine for a vehicle, if the throttle valve is in a substantially fully closed state, it is assumed that the driver has not requested acceleration of the vehicle (the accelerator pedal is also in a fully closed state). Therefore, at this time, even if the air-fuel ratio is forcibly shifted to the lean side and the combustion power of each cylinder is reduced, the driver does not feel uncomfortable. In other words, the combustion force determination operation is performed at a timing that does not make the driver aware that the operation of determining the cylinders with low combustion power is being executed by performing control to forcibly misfire some cylinders. However, the operational effects according to the above-described solving means can be obtained.

  Further, the misfire occurrence cylinder recognition operation by the misfire occurrence cylinder recognition means is performed when the internal combustion engine is in the zero torque operation region or the negative torque operation region.

  In general, when a misfire occurs due to an abnormality such as a fuel injection valve or a spark plug, a misfire determination operation is performed when the internal combustion engine is generating a positive torque, and the misfire occurrence frequency is not less than a predetermined value. For example, the law requires that warnings be given to the driver. That is, when the internal combustion engine is in the zero torque operation region or the negative torque operation region, it is defined that it is not necessary to determine whether or not misfire has occurred. In the present solution, a cylinder with low combustion power is discriminated by forcibly generating misfire at a timing not required by this law. That is, it does not forcibly misfire during the period defined by the above-mentioned laws and regulations (during the period of occurrence of positive torque). For this reason, it is possible to avoid a situation in which misfire occurs during the positive torque generation period even though the abnormality does not occur, and the misfire due to the abnormality cannot be properly determined. For this reason, it is possible to obtain the operational effects (extracting the cylinders in which the combustion power is low) according to the above-described solving means while satisfying the legal requirements. In other words, this solution means that the above-mentioned effects can be achieved by effectively utilizing the system (misfire determination system) that has been required only during the period stipulated by the law, even outside the period stipulated by the law. It is something to get.

  Specifically, the parameter for changing the combustion power of the air-fuel mixture is the fuel injection amount. In this case, the combustion force correcting means is configured to increase and correct the fuel injection amount for the cylinder in which the misfire occurrence cylinder recognition means has recognized the occurrence of misfire.

  Further, as means for recognizing the misfire-occurring cylinder by the misfire-occurring cylinder recognizing means, specifically, misfire based on the ion current value detected according to the amount of ions generated in the cylinder during the expansion stroke of each cylinder. It is designed to recognize the cylinder that generated it.

  Specific examples of the operation of the lean shift adjusting means for uniformly shifting the air-fuel ratio of the air-fuel mixture to the lean side include the following. The lean shift adjusting means is configured to shift the air-fuel ratio of the air-fuel mixture supplied to each of the cylinders uniformly to the lean side when a predetermined combustion force determination operation execution condition is satisfied. If misfire does not occur even when the fuel ratio is uniformly shifted to the lean side, the air-fuel ratio is gradually shifted gradually to the lean side every time the above-described combustion force determination operation execution condition is satisfied, until misfire occurs. The operation is repeated. In this case, the combustion force determination operation execution condition includes, for example, a fuel cut execution condition of the internal combustion engine. That is, as described above, when the fuel cut execution condition is satisfied, the air-fuel ratio of the air-fuel mixture is uniformly shifted to the lean side prior to the fuel cut operation.

  When the combustion force determination operation execution condition is satisfied and the air-fuel ratio is uniformly shifted to the lean side, if no misfire occurs in any cylinder, the air-fuel ratio is further increased when the next combustion force determination operation execution condition is satisfied. To the lean side, making it more prone to misfire. By repeating such an operation, even if the combustion power of each cylinder before the start of the combustion force determination operation is relatively high, it is possible to extract a cylinder with a low combustion force, and accordingly, By performing the correction, the combustion force of each cylinder can be made substantially uniform.

  Further, when the misfire occurrence cylinder recognition means recognizes that a misfire has occurred in a plurality of cylinders, the air-fuel ratio change smaller than the air-fuel ratio change amount that has been gradually shifted to the lean side by the lean transition adjustment means. Rich transition adjusting means is provided for uniformly shifting the air-fuel ratio of the air-fuel mixture supplied to each of the cylinders in an amount to the rich side.

  When a plurality of cylinders misfire simultaneously, it is not possible to identify a cylinder having a low combustion power among these cylinders. That is, in this case, it is assumed that the amount of change in the air-fuel ratio that has been uniformly shifted to the lean side is the cause, and the amount of change in the air-fuel ratio that is smaller than the amount of change in the air-fuel ratio that has been shifted to the lean side. Thus, the air-fuel ratio is uniformly shifted to the rich side. That is, the air-fuel ratio before the air-fuel ratio is shifted to the lean side (the air-fuel ratio where no misfire has occurred in any cylinder) and the air-fuel ratio after the shift to the lean side (the air-fuel ratio where misfire has occurred in multiple cylinders) The air-fuel ratio is set to a value approximately in the middle of the air-fuel ratio) to detect the presence or absence of misfire. As a result, the possibility of misfiring only a single cylinder is increased, and the cylinder with the lowest combustion power can be extracted, and the combustion power of each cylinder is corrected by correcting the above parameters accordingly. Can be made substantially uniform.

  Further, as described above, when the misfire occurrence cylinder recognizing means does not recognize the misfire of the cylinder, the above-described combustion is further performed for the case where the air-fuel ratio of the air-fuel mixture supplied to each cylinder is uniformly shifted to the lean side. The force correction means corrects the parameter for changing the combustion force of the air-fuel mixture in the past so that the combustion force becomes lower for the cylinder that has been corrected so that the combustion force becomes higher.

  According to this, it is possible to avoid a situation in which the parameter for changing the combustion force of the air-fuel mixture becomes too high (combustion force becomes too high) in some cylinders, thereby improving the reliability of the combustion force correction operation. Can be planned.

  In this case, the correction amount for correcting the parameter to change the combustion force of the air-fuel mixture so that the combustion force becomes high is set smaller than the correction amount for correcting the parameter so that the combustion force becomes high.

  That is, since this cylinder was determined to have been a cylinder with low combustion power in the past determination operation, the correction amount for correcting the above parameter so that the combustion power is low is set to the above parameter in the past. If the correction amount is corrected so as to increase the combustion force, the cylinder is likely to become a cylinder having a lower combustion force again. In this case, since sufficient convergence for making the combustion power of each cylinder substantially uniform cannot be ensured, the correction amount for correcting the above parameters so that the combustion power becomes low is set small. Thereby, the convergence of the control which makes the combustion power of each cylinder substantially uniform can be improved.

  The following configuration is exemplified as a configuration for improving the convergence for converging the above parameters to an appropriate value. That is, the correction amount of the parameter for changing the combustion force of the air-fuel mixture is changed according to a predetermined reflection rate, and the reflection rate is set smaller as the load factor of the internal combustion engine is higher.

  When the load factor of the internal combustion engine is high, the parameter (for example, the fuel injection amount) is also large. Even if the change rate of the parameter is the same, the change amount (fuel injection change amount) is equal to the load factor of the internal combustion engine. Increased compared to low case. That is, the above parameters may become larger than necessary. For this reason, as the load factor of the internal combustion engine is higher, the reflection rate is set to be smaller to suppress the parameter change amount from becoming larger than necessary, thereby improving control convergence. Conversely, when the load factor of the internal combustion engine is low, the parameter (for example, the fuel injection amount) is also small, and even if the change rate of the parameter is the same, the change amount (fuel injection change amount) is the same as that of the internal combustion engine. It is smaller than when the load factor is high. That is, it may take a long time to increase the parameter to an appropriate value. For this reason, the lower the load factor of the internal combustion engine, the larger the reflection rate is set to obtain a larger amount of parameter change, thereby improving the convergence.

  In the present invention, the air-fuel ratio of each cylinder of the internal combustion engine is shifted to the lean side, thereby forcibly causing misfire to the cylinder that has a low combustion power among the plurality of cylinders. This makes it possible to clearly determine that the combustion power was lower than that of the other cylinders. And the parameter which changes the combustion power of air-fuel | gaseous mixture is correct | amended with respect to the cylinder which this misfire occurred so that combustion power may become high. For this reason, the difference in the combustion force between the cylinders can be reduced, and the drivability can be improved by improving the torque and the exhaust emission can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a case where the present invention is applied to a multi-cylinder (for example, four-cylinder) gasoline engine mounted on an automobile will be described.

-Engine configuration description-
First, a schematic configuration of an engine (internal combustion engine) 1 according to the present embodiment will be described with reference to FIG. As shown in FIG. 1, the engine 1 according to the present embodiment includes a cylinder block 11 having cylinder bores 11 a for four cylinders (only one cylinder is shown in FIG. 1), and a cylinder head 12. Each cylinder bore 11a is provided with a piston 13 provided to be movable up and down, and this piston 13 is connected to a crankshaft 15 that is an output shaft of the engine 1 via a connecting rod (connecting rod) 14. A combustion chamber 16 is defined by a space surrounded by the piston 13 and the cylinder head 12 inside the cylinder bore 11a.

  A spark plug (a spark plug) 2 is attached to the cylinder head 12 corresponding to each combustion chamber 16. The cylinder head 12 is provided with an intake port 12a and an exhaust port 12b communicating with each combustion chamber 16, and an intake passage 3 and an exhaust passage 4 are connected to the intake port 12a and the exhaust port 12b, respectively. . An intake valve 31 and an exhaust valve 41 are provided at each open end leading to the combustion chamber 16 in the intake port 12a and the exhaust port 12b. The intake valve 31 and the exhaust valve 41 are opened and closed by an intake camshaft 32 and an exhaust camshaft 42 that are respectively rotated by the power of the crankshaft 15. The power of the crankshaft 15 is transmitted to the intake camshaft 32 and the exhaust camshaft 42 via the timing belt 15a and the timing pulleys 33 and 43.

  Further, in the vicinity of the intake port 12a, a fuel injection valve (injector) 5 is provided corresponding to each cylinder. Each injector 5 is supplied with fuel of a predetermined pressure via a fuel supply system.

  On the other hand, a surge tank 34 is provided in the intake passage 3, and a throttle valve 36 whose opening degree is adjusted by driving a throttle motor 36a is provided on the upstream side of the surge tank 34. The amount of intake air introduced into the intake passage 3 is adjusted according to the opening of the throttle valve 36. Furthermore, an air cleaner 37 for purifying the intake air is provided on the upstream side of the throttle valve 36.

  When the operation of the engine 1 is started, the intake air is introduced into the intake passage 3 and fuel is injected from the injector 5, whereby the intake air and the fuel are mixed to form an air-fuel mixture. In the intake stroke of the engine 1, the intake port 12a is opened by the intake valve 31, whereby the air-fuel mixture is taken into the combustion chamber 16 through the intake port 12a. The air-fuel mixture taken into the combustion chamber 16 is compressed in the compression stroke, and then ignited by the spark plug 2. The air-fuel mixture explodes and burns, and a driving force is applied to the crankshaft 15 (expansion stroke). . The exhaust gas after combustion is discharged to the exhaust passage 4 (exhaust stroke) by opening the exhaust port 12b by the exhaust valve 41, further purified through the catalyst 44, and then released to the outside. The spark plug 2 executes an ignition operation for the air-fuel mixture in accordance with the application timing of the high voltage output from the igniter 21.

-Description of control block-
The operating state of the engine 1 is controlled by an engine ECU (Electronic Control Unit) 6. As shown in FIG. 2, the engine ECU 6 includes a CPU (Central Processing Unit) 61, a ROM (Read Only Memory) 62, a RAM (Random Access Memory) 63, a backup RAM 64, and the like.

  The ROM 62 stores various control programs, maps that are referred to when the various control programs are executed, and the like. The CPU 61 executes arithmetic processing based on various control programs and maps stored in the ROM 62.

  The RAM 63 is a memory that temporarily stores calculation results in the CPU 61, data input from each sensor, and the like. The backup RAM 64 is a non-volatile memory that stores data to be saved when the engine 1 is stopped. is there. The ROM 62, CPU 61, RAM 63, and backup RAM 64 are connected to each other via a bus 67, and are also connected to an external input circuit 65 and an external output circuit 66.

The external input circuit 65 includes an accelerator opening sensor 70, a water temperature sensor 71, an air flow meter 72, an intake air temperature sensor 73, an O ₂ sensor 74, a throttle position sensor 75, a crank angle sensor 76, a cam angle sensor 77, a knock sensor 78, An intake pressure sensor 79 is connected to each other. On the other hand, the external output circuit 66 is connected to the injector 5, the igniter 21, the throttle motor 36a for driving the throttle valve 36, and the like.

  The accelerator opening sensor 70 detects the opening (operation amount) of the accelerator pedal 35 operated by the driver, and transmits the opening signal to the engine ECU 6.

  The water temperature sensor 71 detects the temperature of the cooling water flowing in the water jacket 11b formed in the cylinder block 11, and transmits the cooling water temperature signal to the engine ECU 6.

  The air flow meter 72 detects the intake air amount and transmits the intake air amount signal to the engine ECU 6.

  The intake air temperature sensor 73 is provided integrally with the air flow meter 72, detects the intake air temperature, and transmits the intake air temperature signal to the engine ECU 6.

The O ₂ sensor 74 detects the oxygen concentration in the exhaust, determines whether or not the air-fuel ratio in the exhaust is at the stoichiometric air-fuel ratio, and transmits a determination signal to the engine ECU 6.

  The throttle position sensor 75 detects the opening of the throttle valve 36 and transmits a throttle opening detection signal to the engine ECU 6.

  The crank angle sensor 76 is disposed in the vicinity of the crankshaft 15 and detects the rotation angle (crank angle CA) and the rotation speed (engine speed Ne) of the crankshaft 15. Specifically, the crank angle sensor 76 outputs a pulse signal every predetermined crank angle (for example, 30 °). As an example of a crank angle detection method by the crank angle sensor 76, external teeth are formed every 30 ° on the outer peripheral surface of the rotor (NE rotor) integrally rotated with the crankshaft 15, and the external teeth face each other. The crank angle sensor 76 made of an electromagnetic pickup is disposed. The crank angle sensor 76 generates an output pulse when the external teeth pass in the vicinity of the crank angle sensor 76 as the crankshaft 15 rotates. In addition, as this NE rotor, the thing in which the external teeth formed in an outer peripheral surface are formed every 10 degrees may be applied. In this case, frequency division is performed in the engine ECU 6 to generate output pulses every 30 ° CA.

  The cam angle sensor 77 is disposed in the vicinity of the intake camshaft 32, and is used as a cylinder discrimination sensor by outputting a pulse signal corresponding to the compression top dead center (TDC) of the first cylinder, for example. . That is, the cam angle sensor 77 outputs a pulse signal for each rotation of the intake camshaft 32. As an example of the cam angle detection method by the cam angle sensor 77, external teeth are formed at one place on the outer peripheral surface of the rotor integrally formed with the intake camshaft 32, and the external teeth are opposed to each other by an electromagnetic pickup. The cam angle sensor 77 is arranged, and when the external teeth pass in the vicinity of the cam angle sensor 77 as the intake cam shaft 32 rotates, the cam angle sensor 77 generates an output pulse. . Since this rotor rotates at a half rotational speed of the crankshaft 15, an output pulse is generated every time the crankshaft 15 rotates 720 °. In other words, an output pulse is generated each time a specific cylinder reaches the same stroke (for example, when the first cylinder reaches compression top dead center).

  The knock sensor 78 is a vibration sensor that detects the vibration of the engine transmitted to the cylinder block 11 by a piezoelectric element type (piezo element type) or an electromagnetic type (magnet, coil).

  The intake pressure sensor 79 is provided in the surge tank 34, detects the pressure in the intake passage 3 (intake pipe pressure), and transmits the intake pressure signal to the engine ECU 6.

  The engine ECU 6 controls each part of the igniter 21, the injector 5, the throttle motor 36a and the like based on the output signals of the various sensors 70 to 79, thereby including the following fuel cut control and fuel injection continuation control. 1 is executed.

  As an example, the basic control of the ignition timing of the ignition plug 2 by the igniter 21 is that the ignition timing is advanced and corrected so that the ignition timing approaches MBT (Minimum Spark Advance for Best Torque). When knocking is detected by the knock sensor 78, control is performed such that knocking is canceled by correcting the retard of the ignition timing.

  As the fuel injection control of the injector 5, the target air-fuel ratio is calculated based on the engine load, the engine speed, etc., and the target air-fuel ratio is obtained based on the intake air amount detected by the air flow meter 72. In addition, control of the fuel injection amount (control of the valve opening time of the injector 5) is performed.

  Further, as drive control of the throttle motor 36a, the engine ECU 6 that has received the accelerator opening signal based on the opening of the accelerator pedal 35 operated by the driver sends a control signal to the throttle motor 36a, and the throttle position sensor 75 Based on the feedback signal of the opening of the throttle valve 36, the throttle valve 36 is controlled to an appropriate opening. Thereby, the amount of air introduced into the cylinder of the engine 1 is controlled.

-Ignition device-
FIG. 3 is a schematic configuration diagram showing an ignition device including an ignition circuit and an ion current detection circuit of an ignition device for igniting the ignition plug 2. This ion current detection circuit measures the amount of ions generated according to the combustion state in the cylinder as an ion current value, and contributes to recognition of the combustion state in the cylinder. That is, in the expansion stroke, when the discharge by the spark plug 2 occurs and the air-fuel mixture in the cylinder burns, the air-fuel mixture is ionized. When a voltage is applied between the electrodes of the spark plug 2 when the air-fuel mixture is in an ionized state as described above, an ionic current flows. The ion current detection circuit is provided to recognize the combustion state in the cylinder by detecting the ion current and performing an analysis process.

  The ignition device includes the ignition plug 2, an ignition coil 22, the igniter 21, a battery 8, a current detection circuit 9, and the like.

  The spark plug 2 includes a center electrode 23 and a ground electrode 24 that faces the center electrode 23 with a predetermined spark gap Ga therebetween.

  The current detection circuit 9 is a circuit that detects an ion current and a leakage current, and includes two Zener diodes 91 and 92, a capacitor 93, a current detection resistor 94, a resistor 95, an inverting amplifier circuit 96, and the like.

  The ignition coil 22 is composed of a primary coil 25 and a secondary coil 26. One end of the primary coil 25 is connected to the battery 8, and the other end is connected to the collector of the power transistor 27 built in the igniter 21. One end of the secondary coil 26 is connected to the spark plug 2, and the other end is grounded via two Zener diodes 91 and 92.

  The two Zener diodes 91 and 92 are connected in series in opposite directions, a capacitor 93 is connected in parallel to one Zener diode 91, and a current detection resistor 94 is connected in parallel to the other Zener diode 92. The potential Vin between the capacitor 93 and the current detection resistor 94 is input to the inverting input terminal (−) of the inverting amplifier circuit 96 via the resistor 95 and is inverted and amplified, and the output voltage V of the inverting amplifier circuit 96 is detected by current. The signal is input to the engine ECU 6 as a signal.

  In the above ignition device, during engine operation, the power transistor 27 is turned on / off at the rise / fall of the ignition command signal transmitted from the engine ECU 6 to the igniter 21. When the power transistor 27 is turned on, a primary current flows from the battery 8 to the primary coil 25 of the ignition coil 22. Thereafter, when the power transistor 27 is turned off, the primary current of the primary coil 25 is cut off, and a high voltage is electromagnetically induced in the secondary coil 26.

  Due to this high voltage, a discharge spark is generated between the center electrode 23 and the ground electrode 24 of the spark plug 2 to generate a flame, and combustion ions are present in the vicinity of the spark gap Ga. At this time, since the spark gap Ga of the spark plug 2 is in a conductive state, the discharge current flows from the ground electrode 24 of the spark plug 2 to the center electrode 23 and passes through the secondary coil 26 of the ignition coil 22 to the current detection circuit 9. The capacitor 93 is charged and flows to the ground side through the Zener diodes 91 and 92. After the capacitor 93 is charged, the current detection circuit 9 is driven using the charging voltage of the capacitor 93 regulated by the Zener voltage of the Zener diode 91 as a power source, and an ionic current (leakage current) is detected.

  The ionic current (leakage current) flows in the opposite direction to the discharge current. That is, after ignition is finished, a voltage is applied between the center electrode 23 and the ground electrode 24 of the spark plug 2 by the charging voltage of the capacitor 93, and this occurs when the air-fuel mixture burns in the cylinder of the engine 1. An ionic current flows between the center electrode 23 and the ground electrode 24 due to the combustion ions. This ionic current flows from the center electrode 23 to the ground electrode 24, and further passes from the ground side to the capacitor 93 through the current detection resistor 94. Flowing. At this time, the input potential Vin of the inverting amplifier circuit 96 changes according to the change of the ionic current flowing through the current detection resistor 94, and the voltage V corresponding to the ionic current is output from the output terminal of the inverting amplifier circuit 96 as a current detection signal. Is output. An ion current is detected from the output voltage V of the inverting amplifier circuit 96.

  By detecting the ionic current as described above, the presence or absence of misfire of the air-fuel mixture can be determined from the ionic current. That is, when the air-fuel mixture burns well in the cylinder, the amount of ions generated in the cylinder is sufficiently large, and the ion current becomes higher than a preset misfire determination current value (misfire determination line). . In this case, it can be determined that no misfire has occurred. On the other hand, when a misfire has occurred in the cylinder, the amount of ion generation in the cylinder is small, or the ion generation amount is “0”, and the ion current is higher than the misfire determination current value. Lower. In this case, it can be determined that a misfire has occurred in the cylinder that is executing the expansion stroke at a timing when the ion current is lower than the misfire determination current value.

-Fuel injection continuation control-
As one of the fuel injection control of the injector 5 in the present embodiment, the accelerator is turned off (accelerator) when a predetermined fuel cut (F / C) condition, for example, the engine speed is equal to or higher than a predetermined value (fuel cut permission speed). The fuel cut control is executed when the condition that the opening degree of the pedal 35 is “0”) is satisfied. And the engine 1 which concerns on this embodiment implements the fuel-injection continuation control which continues the fuel injection from the injector 5 only for the predetermined time, even if this condition is satisfied. This fuel injection continuation control will be briefly described below.

  When the throttle valve 36 is fully closed due to the driver's accelerator-off operation, if the engine speed is equal to or higher than the predetermined speed, fuel cut control for stopping fuel injection from all the injectors 5 is performed. When the throttle valve 36 is fully closed due to the driver's accelerator-off operation, the engine 1 is driven to rotate by the rotational force of the drive wheels. Then, as the accelerator operation of the driver at this time, when a sudden accelerator-off operation is performed from a state where the accelerator opening is relatively large, the engine 1 suddenly starts from a state where a relatively high torque is generated. Since the vehicle is in a driven state, a shock (vibration) is generated in the vehicle, and the passenger feels uncomfortable. In order to suppress such a situation, the fuel injection continuation control is performed. In other words, even if the throttle valve 36 is fully closed in accordance with the driver's accelerator-off operation, the fuel injection from the injector 5 is continued for a predetermined time (for example, 0.5 sec), so that a large torque fluctuation of the engine 1 occurs. The fuel cut control is started after the lapse of the predetermined time.

  When the speed of the vehicle decreases during the fuel cut and the engine speed becomes lower than the fuel cut permission speed, the fuel cut is stopped and fuel injection from the injector 5 is stopped in order to prevent engine stall. Resume. Also, when the accelerator pedal 35 is depressed during fuel cut (during acceleration), the fuel cut is stopped and fuel injection from the injector 5 is resumed.

-Combustion force correction operation-
Next, a combustion force correction operation that is a characteristic feature of this embodiment will be described. This combustion force correcting operation recognizes the variation when the combustion state (combustion force) varies between the cylinders, and eliminates the variation. In other words, if there are variations in the fuel injection amount, intake air amount, compression ratio, etc. between the cylinders, there may be a difference in the combustion state (combustion force) for each cylinder. It causes shortage and drivability deterioration. The combustion force correcting operation according to the present embodiment is executed to solve this problem, and the operation for recognizing the variation in the combustion state between the cylinders and the recognized variation are eliminated. Operations are performed in order.

  In the combustion force correcting operation described below, the variation in the combustion state is recognized, and the fuel injection amount from the injector 5 provided corresponding to each cylinder is changed by adjusting the fuel injection period. This variation is eliminated by correcting the fuel injection amount). This will be specifically described below.

  The combustion state variation recognition operation in this combustion force correction operation is performed during the period in which the fuel injection continuation control described above is being executed. That is, even if the throttle valve 36 is fully closed in accordance with the accelerator-off operation of the driver, the fuel injection from the injector 5 is continued by the fuel injection continuation control for a predetermined time (for example, 0.5 sec) thereafter. However, the target air-fuel ratio at that time is shifted to the lean side (for example, A / F = 18.0) from the target air-fuel ratio (for example, A / F = 14.5) before the start of the fuel injection continuation control. . That is, the air-fuel ratio of the air-fuel mixture supplied to each cylinder is uniformly shifted to the lean side, and operation is performed in this air-fuel ratio lean state for a predetermined period (for example, 0.5 sec) (by the lean transition adjusting means). Air-fuel ratio transition to lean side). Hereinafter, the operation during this period is referred to as A / F lean control. Then, after this A / F lean control, the fuel injection is stopped by the fuel cut control. The air-fuel ratio and the predetermined time described above are not limited to the above values, but the target air-fuel ratio in the A / F lean control is set to a value that does not cause all cylinders to misfire. There is a need.

  When misfire occurs in a certain cylinder during the execution period of the A / F lean control (recognition operation of a misfire occurrence cylinder by the misfire occurrence cylinder recognition means), the combustion power of the cylinder is After determining that the combustion power is lower than that of the other cylinder and releasing the fuel cut control, the fuel injection period is extended only for this cylinder and the fuel supplied to that cylinder is reduced. Increase the amount (correction operation by the combustion force correction means for the parameter that changes the combustion force of the mixture). Thereby, the combustion power of this cylinder is increased. Thereafter, when the combustion force correcting operation (operation for recognizing variation in combustion state and operation for resolving recognized variation) is started again, in the same manner as described above, for the misfired cylinder, The fuel injection period is extended to increase the combustion power of the cylinder. By repeating such an operation, the combustion power of all the cylinders is made uniform.

  Hereinafter, a specific operation procedure of the combustion force correcting operation will be described with reference to the flowchart of FIG. FIG. 5 shows the change in the throttle valve opening, the presence or absence of fuel cut, the change in the target air-fuel ratio (target A / F), and the state of the A / F lean control execution flag when this combustion force correction operation is performed. , Engine torque change and ion current detection value change are shown.

  First, when the driver opens the throttle pedal to “0” and the throttle valve opening becomes “0 (fully closed)” (timing T1 in FIG. 5), the execution condition of the combustion force correction operation (combustion) 4 is executed assuming that the force determination operation execution condition is satisfied.

  In step ST1, it is determined whether or not a fuel cut (F / C) is in progress. Immediately after the execution condition for the combustion force correction operation is established, the fuel injection continuation control is executed. Therefore, the fuel cut is not being performed, a NO determination is made in step ST1, and the process proceeds to step ST2.

  In step ST2, it is determined whether or not the A / F lean control (A / F lean control immediately before F / C executed prior to the fuel cut operation) is being executed. Since the A / F lean control is being executed at the beginning of the start of the fuel injection continuation control, Yes is determined in step ST2, and the process proceeds to step ST3. If the A / F lean control is not being executed, a NO determination is made in step ST2, and this routine is terminated as it is.

  If YES is determined in step ST2 and the process proceeds to step ST3, the A / F lean control execution flag (xlnbfc) is set to “1” (timing T2 in FIG. 5). Thereafter, the process proceeds to step ST4.

  In step ST4, during the A / F lean control, the current detection circuit 9 is used to detect the ion current, and it is determined whether or not the detected ion current value is below a predetermined misfire determination line. To do. When the ion current value falls below the misfire determination line for each expansion stroke of each cylinder, the misfire counter of the corresponding cylinder is counted (incremented) each time. In FIG. 5, one misfire has occurred in the cylinder that has reached the expansion stroke at timing T4, and the ion current value is below the misfire determination line. In the case of this waveform, only one cylinder is misfired.

  Further, since the target air-fuel ratio is shifted to the lean side (for example, A / F = 18.0) by the A / F lean control, the engine torque rapidly decreases with the start of the A / F lean control. At timing T3 in FIG. 5, the zero torque operation region (the zero torque line in the figure) is reached, and then the negative torque operation region is reached. In the waveform showing the change in the engine torque, the solid line represents the change in the engine torque accompanying the execution of the A / F lean control. On the other hand, the broken line represents a change in engine torque in the conventional control in which the A / F lean control is not executed. That is, it represents a change in engine torque when the opening degree of the throttle valve becomes “0 (fully closed)” without changing the target air-fuel ratio to the lean side. As is apparent from these waveforms, the A / F lean control is executed, so that the operating state of the engine 1 is shifted to the zero torque operating region in a short time.

  The zero torque operation region is a state in which the engine 1 generates a low torque that does not give driving force to the drive wheels, and is a state in which the road surface resistance and the engine torque are substantially balanced. Further, the negative torque operation region is a so-called driven state of the engine 1 and is a state in which the engine 1 is rotationally driven by the rotational force of the driving wheel. The zero torque operation region and the negative torque operation region are operation regions where it is not required by law to detect the misfire occurrence frequency of the engine 1, and it is assumed that misfire is forcibly generated during this period. However, it will not have any adverse effect on the misfire detection required by law.

  The above operation is repeated until Yes is determined in step ST1 (until the A / F lean control is finished and the fuel cut is started). That is, during the period from the start of A / F lean control to the start of fuel cut (for example, during a 0.5 sec period), the number of misfires in each cylinder is individually added to the misfire counter.

  Further, during this A / F lean control and not in the misfire determination period required by the law and in the zero torque operation region and the negative torque operation region (period A in FIG. 5), each cylinder is individually controlled. On the other hand, the presence or absence of misfire may be determined, and when a misfire occurs, the number of misfires may be individually added to the misfire counter for each cylinder.

  When the above-described A / F lean control is completed and fuel cut is started (timing T5 in FIG. 5), a Yes determination is made in step ST1, and in step ST5, the A / F lean control execution flag (xlnbfc) is determined. ) Is “1”, that is, whether or not the fuel cut operation is performed after the A / F lean control is executed. If the determination is No here, this routine is terminated as it is. On the other hand, if Yes is determined in step ST5, the process proceeds to step ST6, where the A / F lean control execution flag (xlnbfc) is reset to “0” (timing T6 in FIG. 5).

  Then, the process proceeds to step ST7, and it is determined whether or not a misfire has occurred during the A / F lean control executed in steps ST2 to ST4. Here, the count value of the misfire counter is read, and if the misfire counter is at least “1” in at least one of the cylinders, a Yes determination is made.

  If a misfire has occurred in at least one of the cylinders, and if any of the misfire counters has a value of “1” or more, the process proceeds to step ST8. In this step ST8, it is determined whether or not only one cylinder has misfired. That is, it is determined whether or not only a single cylinder has a misfire counter value of “1” or more.

  If only one cylinder has misfired and it is determined Yes in step ST8, the process proceeds to step ST9, and the fuel injection period TAU (fuel for defining the fuel injection amount) for the misfired cylinder. This is an injection period, hereinafter simply referred to as “fuel injection amount TAU”), and the amount of fuel supplied to the cylinder is increased. Specifically, the fuel injection amount TAU is increased by 1% (operation for correcting a parameter that changes the combustion force of the air-fuel mixture so that the combustion force becomes higher). As a result, when the fuel cut control currently performed is canceled and fuel injection is resumed, the combustion power of the cylinder in which this misfire has occurred is increased, and the combustion power of the other cylinders is increased. Will approach. In this case, the upper limit of the correction amount of the fuel injection amount TAU is set to “+ 5%” with respect to the basic fuel injection amount before this increase correction is performed, and the fuel injection amount for a specific cylinder becomes too large. To prevent that.

  After the fuel injection amount increase correction is performed as described above, in step ST10, the count value of the misfire counter for each cylinder is cleared for all the cylinders (returned to "0"). This is because when the next A / F lean control is executed, there is no influence of the count value of the misfire occurring in the previous A / F lean control. This is to accurately detect the number of cylinder misfire occurrences.

  On the other hand, in step ST7, when no misfire has occurred during the A / F lean control, that is, when the air-fuel mixture is burned in all the cylinders during the A / F lean control, Moving to step ST11, the air-fuel ratio (A / F) to be set in the next A / F lean control is set to the lean side. Specifically, the target air-fuel ratio set in the A / F lean control (A / F lean control determined in step ST2) is shifted to the lean side by “0.5”. For example, when the target air-fuel ratio in the A / F lean control performed this time is “18.0”, the target air-fuel ratio in the next A / F lean control is set to “18.5”. As a result, in the next A / F lean control, a misfire is more likely to occur, and the possibility of extracting a cylinder having a low combustion power increases. In this case, the upper limit of the air-fuel ratio to be changed is set to “20” to prevent the air-fuel ratio (A / F) from becoming too high.

  Thereafter, the process proceeds to step ST12, and there is a cylinder in which the fuel injection amount is corrected to be increased with respect to the basic fuel injection amount (1% increase correction in step ST9) in the combustion power correction operation performed in the past. It is determined whether or not there is a cylinder with increased misfire, and if there is, a decrease correction of the fuel injection amount for that cylinder is performed. Specifically, the fuel injection amount is reduced by 0.25%. For example, in a cylinder that has been subjected to one increase correction in the past, the fuel injection amount is set to be increased by 0.75% with respect to the basic fuel injection amount by this decrease correction. In this case, the lower limit of the correction amount of the fuel injection amount is set to 0% (basic fuel injection amount that is not corrected) to prevent the fuel injection amount for a specific cylinder from becoming too small.

  In this case, the correction amount (0. 25%: correction amount in step ST12) is set small. The reason is as follows. That is, since this cylinder was determined to have been a cylinder with low combustion power in the past combustion force correction operation, the fuel injection amount decrease correction amount is the same as the past fuel injection amount increase correction amount. If the amount (1%) is used, there is a high possibility that this cylinder will become a cylinder with low combustion power again. In this case, since the convergence for making the combustion power of each cylinder substantially uniform cannot be ensured, the fuel injection amount reduction correction amount is set small. Thereby, the convergence of the control which makes the combustion power of each cylinder substantially uniform can be improved.

  If misfire has occurred in a plurality of cylinders in the A / F lean control, the determination in step ST8 is No, and the process proceeds to step ST13. In step ST13, the target air-fuel ratio (A / F) to be set in the next A / F lean control is set to a richer side. Specifically, the air / fuel ratio set in the A / F lean control is shifted to the rich side by “0.5” (the operation of shifting the air / fuel ratio to the rich side by the rich transition adjusting means). For example, when the target air-fuel ratio in the A / F lean control performed this time is “18.0”, the target air-fuel ratio in the next A / F lean control is set to “17.5”. As a result, in the next A / F lean control, a situation where a plurality of cylinders misfire is avoided, and a situation where only a single cylinder with the lowest combustion power is misfired is easily obtained. In this case, the lower limit of the air-fuel ratio to be changed is set to “16” to prevent the air-fuel ratio (A / F) from becoming too low. After the target air-fuel ratio (A / F) to be set in the next A / F lean control is set to the rich side in this way, the operation proceeds to step ST9 described above. That is, an increase correction of the fuel injection amount TAU is performed for a plurality of cylinders in which misfire has occurred.

  As described above, in the present embodiment, the air-fuel ratio of each cylinder of the engine 1 in the operating state is shifted to the lean side, and forcibly applied to the cylinders in which the combustion power is low among the plurality of cylinders. Thus, it is possible to clearly determine that the combustion power is low with respect to other cylinders by causing misfire. Then, by correcting the fuel injection amount to be increased for the cylinders in which the combustion power is low, the combustion power is brought close to other cylinders so that uniform combustion power is obtained for all the cylinders. Yes. For this reason, engine torque can be obtained stably and good drivability can be ensured. In addition, exhaust emission can be improved.

  In the above-described combustion force correction operation, if misfire occurs in a plurality of cylinders (when No is determined in step ST8 in FIG. 4), the target air-fuel ratio (A / F) to be set in the next A / F lean control After setting F) to a richer side (step ST13), the fuel injection amount TAU is increased for the misfire cylinder (step ST9). Instead, when misfire occurs in a plurality of cylinders (when No is determined in step ST8 in FIG. 4), the target air-fuel ratio (A / F) to be set in the next A / F lean control is set. After setting to a richer side (step ST13), without performing the operation of changing the fuel injection amount TAU, until a misfire occurs in a single cylinder in the next A / F lean control (Yes in step ST8). Up to) The fuel injection amount TAU may not be increased. That is, in the flowchart of FIG. 4, as indicated by a broken line arrow, after performing the process of step ST <b> 13, the count value of the misfire counter is cleared and returned in step ST <b> 10.

(Modification)
Next, a modified example of the present invention will be described. This modification is different from that of the above-described embodiment in the method for performing the increase correction of the fuel injection amount for the cylinder in which misfire has occurred. Since other configurations and operations are the same as those of the above-described embodiment, only the operation when the fuel injection amount increase correction is performed on the cylinder where misfire has occurred will be described here.

  FIG. 6 is a flowchart showing the procedure of the combustion force correction operation in this modification. In FIG. 6, steps showing the same operations as those in the flowchart (FIG. 4) showing the procedure of the combustion force correcting operation according to the embodiment described above are denoted by the same step numbers as those in FIG. Omitted.

  Each operation of step ST1 to step ST8, step ST10, step ST11, and step ST13 is the same as that of the flowchart shown in FIG. 4 in the above-described embodiment.

  If it is determined in step ST8 that the misfire has occurred in only one cylinder during the A / F lean control and the determination is Yes, the process proceeds to step ST9 '. In this step ST9 ', an increase correction of the cylinder specific increase value (kcyl) assigned in advance to the misfire cylinder is performed. Specifically, 1% is added to the current cylinder-by-cylinder increase value (kcyl), and this is registered as a new cylinder-by-cylinder increase value (kcyl). In this case, the upper limit of the value to be added is set to “+ 5%” to prevent the fuel injection amount for a specific cylinder from being excessively increased.

  On the other hand, in step ST11, after misfire does not occur during A / F lean control and the air-fuel ratio (A / F) to be set in the next A / F lean control is set to the lean side, step ST12 ' In the combustion force correction operation performed in the past, it is determined whether or not there is a cylinder whose cylinder-specific increase value (kcyl) is corrected to increase. The cylinder increment value (kcyl) is subtracted by 0.25%, and this is registered as a new cylinder increment value (kcyl). In this case, the lower limit of the value to be subtracted is set to 0% to prevent the fuel injection amount for a specific cylinder from becoming too small.

  In step ST14, as described above, the fuel injection amount for each cylinder is calculated using the cylinder-by-cylinder increase value (kcyl) registered in step ST9 'or step ST12'. Specifically, a fuel injection amount (TAUINJ) is calculated by the following formula (1), and fuel injection is performed with the obtained fuel injection amount.

TAUINJ ← basic injection amount TAU × (1 + kcyl × kcylref) (1)
Here, kcylref is a reflection rate to the TAU with respect to the engine load factor (KL), and is obtained from the graph shown in FIG. The relationship between the engine load factor and the reflection rate to the TAU is obtained in advance by experiments or the like and stored in the ROM 62. The engine load factor is a value indicating the current load ratio with respect to the maximum engine load of the engine 1, and is, for example, a load factor map based on the intake air amount detected by the air flow meter 72 and the engine speed. Is calculated with reference to FIG.

  Here, the relationship between the engine load factor and the TAU reflection rate will be described. As shown in FIG. 7, the lower the engine load factor, the higher the reflection rate to the fuel injection amount TAU, and conversely, the higher the engine load factor, the lower the reflection rate to the fuel injection amount TAU. This is because when the engine load factor is high, the fuel injection amount increases, and even if the rate of change of the fuel injection amount (1% in the above case) is the same, the fuel injection change amount is the engine load amount. Compared to a low rate. That is, there is a possibility that the corrected fuel injection amount becomes larger than necessary. For this reason, the higher the engine load factor, the smaller the reflection rate is set, so that the corrected fuel injection amount is prevented from becoming unnecessarily large, and the convergence of control is enhanced.

  Conversely, when the engine load factor is low, the fuel injection amount is also small, and even if the rate of change of the fuel injection amount (1% in the above case) is the same, the fuel injection change amount is the engine load. It is smaller than when the rate is high. That is, it may take a long time to increase the corrected fuel injection amount to an appropriate value. For this reason, the lower the engine load factor, the larger the reflection rate is set, and the corrected fuel injection amount is obtained to increase the convergence.

  Note that the relationship between the engine load factor and the TAU reflection rate shown in FIG. 7 is an example, and the present invention is not limited to this.

  As described above, in this modified example, when the increase correction of the fuel injection amount for the cylinder having a low combustion power is performed, the correction amount is also changed depending on the engine load factor. Thereby, the convergence of the control which makes the combustion power of each cylinder substantially uniform can be improved.

-Other embodiments-
In the embodiment and the modification described above, the case where the present invention is applied to the four-cylinder gasoline engine 1 mounted on an automobile has been described. The present invention is applicable not only to automobiles but also to engines used for other purposes. Also, the number of cylinders and the engine type (separate types such as in-line type, V type, and horizontally opposed type) are not particularly limited.

  Further, in the above embodiment and the modification, the A / F lean control is executed prior to the fuel cut operation, so that the cylinder having a low combustion power is extracted. The present invention is not limited to this, and the scope of the technical idea is that the A / F lean control is performed at an arbitrary timing.

  In the above embodiment and the modification, the parameter for changing the combustion force of the air-fuel mixture is the fuel injection amount (fuel injection period). However, by correcting other parameters, the combustion force of the air-fuel mixture is changed. It may be. For example, the combustion force of the air-fuel mixture may be increased by changing the timing of fuel injection from the injector 5, or the combustion force of the air-fuel mixture may be increased by extending the valve opening period of the intake valve 31 or increasing the lift amount. You may make it raise.

  In the embodiment and the modification described above, the case where the present invention is applied to a one throttle engine provided with a throttle valve 36 common to all cylinders has been described. The present invention is not limited to this, and can also be applied to an independent throttle engine having a throttle valve for each cylinder or each cylinder group. In this independent throttle engine, the variation in intake air amount due to individual differences in each throttle valve tends to be large, and the difference in combustion state between each cylinder tends to be large. The effect of doing so is greatly obtained.

  Further, in the above embodiment and the modification, the ion current value is detected as a method for recognizing the misfire-occurring cylinder. The present invention is not limited to this, and a misfire-occurring cylinder may be recognized based on the difference in the rotational speed of the crankshaft in each expansion stroke between cylinders whose expansion strokes are adjacent to each other.

  In addition, in the above-described embodiment and modification, the target air-fuel ratio when performing one A / F lean control is fixed to a constant value, and the target air-fuel ratio is set when performing the next A / F lean control. Was supposed to change. The present invention is not limited to this. For example, in a situation where the execution period of the A / F lean control is relatively long, the target air-fuel ratio is gradually shifted to the lean side during the one A / F lean control. Alternatively, misfire may be forcibly generated in some cylinders.

1 is a system configuration diagram illustrating a schematic configuration of an engine according to an embodiment. It is a figure which shows the outline of the control block of an engine. It is a figure which shows the circuit structure of an ignition device. It is a flowchart figure which shows the procedure of combustion force correction | amendment operation | movement. Indicates the change in throttle valve opening, fuel cut execution, target air-fuel ratio change, A / F lean control execution flag state, engine torque change, and ion current detection value change when the combustion force correction operation is executed. It is a timing chart figure. It is a flowchart figure which shows the procedure of the combustion force correction | amendment operation | movement in a modification. It is a figure which shows an example of the relationship between an engine load factor and the reflection rate to fuel injection quantity.

Explanation of symbols

1 engine (internal combustion engine)
36 Throttle valve 6 Engine ECU
9 Current detection circuit

Claims (10)

In a combustion control device for an internal combustion engine for individually controlling the combustion state of an air-fuel mixture in each cylinder of a multi-cylinder internal combustion engine,
Lean shift adjusting means for uniformly shifting the air-fuel ratio of the air-fuel mixture supplied to each of the cylinders to the lean side;
A misfire occurrence cylinder recognition means for recognizing the misfire occurrence cylinder when a misfire occurs when the air-fuel ratio is shifted to the lean side by the lean transition adjustment means;
Combustion force correction means for correcting a parameter for changing the combustion force of the air-fuel mixture so that the combustion force of the misfire occurrence cylinder is increased when the misfire occurrence cylinder is recognized by the misfire occurrence cylinder recognition means. A combustion control apparatus for an internal combustion engine. In the internal combustion engine combustion control device according to claim 1,
The lean shift adjusting means uniformly sets the air-fuel ratio of the air-fuel mixture to the lean side prior to the fuel cut operation when the throttle valve provided in the intake system is substantially fully closed and the fuel cut condition is satisfied. A combustion control device for an internal combustion engine, characterized by being configured to shift. In the internal combustion engine combustion control apparatus according to claim 1 or 2,
A combustion control device for an internal combustion engine, wherein the operation for recognizing a misfire occurrence cylinder by the misfire occurrence cylinder recognition means is executed when the internal combustion engine is in a zero torque operation region or a negative torque operation region. In the combustion control device for an internal combustion engine according to claim 1, 2, or 3,
The parameter that changes the combustion power of the air-fuel mixture is the fuel injection amount,
The combustion control apparatus for an internal combustion engine, wherein the combustion force correction means is configured to increase and correct a fuel injection amount for a cylinder whose occurrence of misfire has been recognized by the misfire occurrence cylinder recognition means. In the combustion control device for an internal combustion engine according to any one of claims 1 to 4,
The misfire occurrence cylinder recognition means is configured to recognize a misfire occurrence cylinder based on an ion current value detected according to the amount of ions generated in the cylinder during the expansion stroke of each cylinder. A combustion control device for an internal combustion engine. In the combustion control device for an internal combustion engine according to any one of claims 1 to 5,
The lean shift adjusting means is configured to shift the air-fuel ratio of the air-fuel mixture supplied to each of the cylinders uniformly to the lean side when a predetermined combustion force determination operation execution condition is satisfied. If misfire does not occur even when the fuel ratio is uniformly shifted to the lean side, the air-fuel ratio is gradually shifted gradually to the lean side every time the above-described combustion force determination operation execution condition is satisfied, until misfire occurs. A combustion control apparatus for an internal combustion engine, characterized in that the operation is repeated. In the internal combustion engine combustion control apparatus according to claim 6,
When the misfire occurrence cylinder recognizing means recognizes that a misfire has occurred in a plurality of cylinders, the air / fuel ratio change amount is smaller than the air / fuel ratio change amount gradually shifted to the lean side by the lean transition adjusting means. A combustion control device for an internal combustion engine, comprising rich transition adjusting means for uniformly shifting the air-fuel ratio of the air-fuel mixture supplied to each of the cylinders to the rich side. In the internal combustion engine combustion control apparatus according to claim 6,
When the misfire occurrence cylinder recognition means does not recognize the misfire of the cylinder, the lean transition adjustment means uniformly shifts the air-fuel ratio of the air-fuel mixture supplied to each cylinder to the lean side, and the combustion force correction means For a cylinder that has been corrected so that the combustion power of the parameter that changes the combustion power of the air-fuel mixture in the past is corrected, the parameter is corrected so that the combustion power is reduced. Combustion control device for an internal combustion engine. In the internal combustion engine combustion control apparatus according to claim 8,
The correction amount for correcting the parameter for changing the combustion force of the air-fuel mixture so that the combustion force becomes higher is set smaller than the correction amount for correcting the parameter so that the combustion force becomes higher. A combustion control device for an internal combustion engine. In the combustion control device for an internal combustion engine according to any one of claims 1 to 9,
The correction amount of the parameter for changing the combustion force of the air-fuel mixture is changed according to a predetermined reflection rate, and the reflection rate is set smaller as the load factor of the internal combustion engine is higher. A combustion control apparatus for an internal combustion engine.

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