JP5447236B2 - Fuel injection control device for multi-cylinder internal combustion engine - Google Patents

Description

  The present invention relates to a fuel injection control device for a multi-cylinder internal combustion engine having a plurality of cylinders.

  In an internal combustion engine (hereinafter also referred to as an engine) mounted on a vehicle or the like, a deviation between an air-fuel ratio (actual air-fuel ratio) of a mixture burned in a combustion chamber (cylinder) and a target air-fuel ratio (for example, theoretical air-fuel ratio). Based on the above, the amount of fuel injected from the injector (fuel injection valve) (fuel injection amount) is feedback controlled (air-fuel ratio feedback control). By performing such air-fuel ratio feedback control, the air-fuel ratio can be accurately controlled, and exhaust emission can be improved.

  By the way, in a multi-cylinder internal combustion engine having a plurality of cylinders, the actual air-fuel ratio varies between cylinders due to variations in the injection performance of the injectors provided in each cylinder, variations in the intake air distribution amount among the cylinders, etc. (A / F imbalance), and in such a situation, emission may deteriorate due to deterioration of combustion in a specific cylinder (deterioration of lean combustion). As a countermeasure, there has been proposed a method of correcting the fuel injection amount for each cylinder based on the combustion parameter for each cylinder such as rotation fluctuation of the internal combustion engine.

  For example, in Patent Document 1 below, attention is paid to the fact that engine fluctuations are likely to occur because combustion deteriorates and the generated torque decreases in a cylinder with a lean air-fuel ratio. A technique has been proposed in which the engine rotational fluctuation is measured, and a fuel correction amount corresponding to a torque step is obtained from the rotational fluctuation for each cylinder to perform fuel injection control. Further, for example, control (fuel injection amount correction control) is performed in which a cylinder whose combustion has deteriorated (lean combustion deterioration) is specified based on engine rotation fluctuation, and the fuel injection amount of the specific cylinder is increased and corrected. Yes.

JP 2008-267239 A

  In the fuel injection amount correction control described above, if the fuel injection amount increase correction is performed for a plurality of cylinders in which rotational fluctuation has occurred, the fuel may be increased to the wrong cylinder. That is, among the plurality of cylinders in which the rotational fluctuation has occurred, the cylinders other than the cylinder having the largest rotational fluctuation may have a rotational fluctuation due to factors other than the deterioration of lean combustion. If the increase correction is performed, the emission may worsen due to the increase in fuel.

  The present invention has been made in view of such circumstances, and in a fuel injection control device capable of executing a control for increasing and correcting a fuel injection amount so as to suppress rotational fluctuations of a multi-cylinder internal combustion engine, The purpose is to realize a control capable of suppressing the deterioration of the emission due to the increase.

The present invention is applied to a multi-cylinder internal combustion engine having a plurality of cylinders, and includes fuel injection amount adjusting means capable of adjusting the fuel injection amount to each cylinder for each cylinder, and fuel to the cylinder based on engine rotational fluctuations. Assuming a fuel injection control device capable of executing control for increasing the injection amount, in such a fuel injection control device for a multi-cylinder internal combustion engine, when a variation in rotation occurs due to deterioration of lean combustion in a plurality of cylinders Of these cylinders, the technical feature is that only the cylinder with the largest rotational fluctuation is corrected to increase the fuel injection amount.

  In the present invention, for the cylinder having the largest rotational fluctuation, the rotational fluctuation is suppressed by assuming that the rotational fluctuation has occurred due to the deterioration of lean combustion, thereby increasing the fuel injection amount. For the other cylinders, the fuel injection amount increase correction is not performed even if there is a rotational fluctuation. That is, even if there is a rotational fluctuation in a cylinder other than the cylinder with the largest rotational fluctuation, the rotational fluctuation may occur in that cylinder due to factors other than the deterioration of lean combustion, so the fuel injection amount increase correction is performed. In this case, the risk of emission deterioration due to an erroneous fuel increase becomes high, so that the increase correction of the fuel injection amount is not performed in order to avoid the risk. By such control, it is possible to suppress the emission deterioration due to the fuel increase.

  As a specific configuration of the present invention, the engine rotational fluctuation amount is compared with a threshold value, and a cylinder exceeding the threshold value is recognized as a cylinder in which rotational fluctuation occurs. A configuration in which the fuel injection amount increase correction is performed only for the cylinder having the largest rotational fluctuation among the cylinders having the rotational fluctuation can be given. In this case, an increase correction amount (increase correction value) of the fuel injection amount may be set for the cylinder having the largest rotation fluctuation in accordance with the amount of the fluctuation fluctuation exceeding the threshold value. If it does in this way, the amount of rotation fluctuations of an engine can be controlled more effectively, and drivability can be improved.

As another solving means of the present invention, the invention is applied to a multi-cylinder internal combustion engine having a plurality of cylinders, and includes a fuel injection amount adjusting means capable of adjusting the fuel injection amount to each cylinder for each cylinder, and is based on the rotational fluctuation of the engine. The target fuel injection control device is capable of executing a control for increasing the fuel injection amount to the cylinder. In such a fuel injection control of a multi-cylinder internal combustion engine, the specific cylinder in which the rotational fluctuation occurs due to the deterioration of lean combustion is applied. On the other hand, when the fuel injection amount increase correction is performed, even if rotation fluctuation occurs in other cylinders, the fuel injection increase correction is limited (including the case where the increase correction is prohibited) for other cylinders. A configuration can be mentioned.

  Even in such a configuration, it is assumed that the rotation fluctuation is caused by the deterioration of the lean combustion for the cylinder having the largest rotation fluctuation, and the rotation fluctuation is suppressed by correcting the increase in the fuel injection amount. Further, by restricting the fuel increase for the cylinders other than the specific cylinder (other cylinders) in which the rotational fluctuation occurs, the deterioration of the emission due to the fuel increase is suppressed.

  Note that the control of the present invention (fuel injection amount increase correction control) is applicable not only when the engine is started but also when the engine is in another engine operating state such as during warm-up operation or idle operation.

  According to the present invention, in a multi-cylinder internal combustion engine capable of executing a control for increasing the fuel injection amount so as to suppress the rotation fluctuation of the cylinder, it is possible to suppress the deterioration of the emission due to the fuel increase.

It is a schematic structure figure showing typically an example of an engine (internal combustion engine) to which the present invention is applied. It is a schematic block diagram which shows only 1 cylinder of the engine of FIG. It is a block diagram which shows the structure of the control system of an engine. It is a timing chart which shows an example of fuel injection amount correction control. 6 is a timing chart showing another example of fuel injection amount correction control.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, an internal combustion engine (hereinafter also referred to as an engine) to which the present invention is applied will be described.

-Engine-
1 and 2 are diagrams showing a schematic configuration of an engine to which the present invention is applied. FIG. 2 shows only the configuration of one cylinder of the engine.

  The engine 1 of this example is a port injection type four-cylinder engine mounted on a vehicle, and reciprocates vertically in a cylinder block 1a constituting each cylinder # 1, # 2, # 3, # 4. A piston 1c is provided. The piston 1c is connected to the crankshaft 15 via the connecting rod 16, and the reciprocating motion of the piston 1c is converted into rotation of the crankshaft 15 by the connecting rod 16.

  A signal rotor 17 is attached to the crankshaft 15. A plurality of teeth (protrusions) 17a are provided on the outer peripheral surface of the signal rotor 17 at equal angles (in this example, 10 ° CA (crank excessive)). Further, the signal rotor 17 has a missing tooth portion 17b in which two teeth 17a are missing.

  A crank position sensor 31 that detects a crank angle is disposed near the side of the signal rotor 17. The crank position sensor 31 is an electromagnetic pickup, for example, and generates a pulsed signal (voltage pulse) corresponding to the teeth 17a of the signal rotor 17 when the crankshaft 15 rotates. The engine speed NE can be calculated from the output signal of the crank position sensor 31.

A three-way catalyst 8 is disposed in the exhaust passage 12 of the engine 1. In the three-way catalyst 8, oxidation of CO and HC and reduction of NOx in the exhaust gas exhausted from the combustion chamber 1d to the exhaust passage 12 is performed, and these are made harmless CO ₂ , H ₂ O, and N ₂ . In this way, the exhaust gas is purified.

An air-fuel ratio (A / F) sensor 37 is disposed in the exhaust passage 12 upstream of the three-way catalyst 8 (upstream of the exhaust flow). The air-fuel ratio (A / F) sensor 37 is a sensor that exhibits linear characteristics with respect to the air-fuel ratio. An O ₂ sensor 38 is disposed in the exhaust passage 12 on the downstream side of the three-way catalyst 8. The O ₂ sensor 38 generates an electromotive force according to the oxygen concentration in the exhaust gas. When the output is higher than a voltage (comparison voltage) corresponding to the theoretical air-fuel ratio, the O ₂ sensor 38 determines that the output is rich and conversely compares it. When the output is lower than the voltage, it is judged as lean. The output signals of the air-fuel ratio (A / F) sensor 37 and the O ₂ sensor 38 are used for air-fuel ratio feedback control (for example, refer to the technology described in Japanese Patent Laid-Open No. 2010-007561).

  In the vicinity of the intake camshaft 21, a cam position sensor 39 that generates a pulse-like signal when the piston 1c of a specific cylinder (for example, the first cylinder # 1) reaches the compression top dead center (TDC) is provided. ing. The cam position sensor 39 is, for example, an electromagnetic pickup, and is disposed so as to face one tooth (not shown) on the outer peripheral surface of the rotor provided integrally with the intake camshaft 21. When the shaft 21 rotates, a pulse signal (voltage pulse) is output. Since the intake camshaft 21 (and the exhaust camshaft 22) rotates at a half speed of the crankshaft 15, the cam position sensor 39 becomes 1 each time the crankshaft 15 rotates twice (720 ° rotation). Two pulse signals are generated.

  An injector (fuel injection valve) 2 capable of injecting fuel is disposed in the intake port 11 a of the intake passage 11. The injector 2 is provided for each cylinder # 1 to # 4. These injectors 2... 2 are connected to a common delivery pipe 101. The delivery pipe 101 is supplied with fuel stored in a fuel tank 104 of a fuel supply system 100 (to be described later), whereby fuel is injected from the injector 2 into the intake port 11a. This injected fuel is mixed with intake air to form an air-fuel mixture and introduced into the combustion chamber 1 d of the engine 1. The air-fuel mixture (fuel + air) introduced into the combustion chamber 1d is ignited by the spark plug 3 and combusted / exploded. The piston 1c is reciprocated by the high-temperature and high-pressure combustion gas generated at this time, the crankshaft 15 is rotated, and the driving force (output torque) of the engine 1 is obtained. The combustion gas is discharged into the exhaust passage 12 when the exhaust valve 14 is opened. The engine 1 burns and explodes in the order of the first cylinder # 1, the third cylinder # 3, the fourth cylinder # 4, and the second cylinder # 2. The operating state of the engine 1 is controlled by an ECU (Electronic Control Unit) 200.

  On the other hand, the fuel supply system 100 includes a delivery pipe 101 commonly connected to the injectors 2... 2 of the cylinders # 1 to # 4, a fuel supply pipe 102 connected to the delivery pipe 101, a fuel pump (for example, an electric pump). ) 103, a fuel tank 104, and the like, and by driving the fuel pump 103, fuel stored in the fuel tank 104 can be supplied to the delivery pipe 101 via the fuel supply pipe 102. Then, fuel is supplied to the injectors 2 of the cylinders # 1 to # 4 by the fuel supply system 100 having such a configuration.

  In the fuel supply system 100 configured as described above, the driving of the fuel pump 103 is controlled by the ECU 200.

-ECU-
As shown in FIG. 3, the ECU 200 includes a CPU 201, a ROM 202, a RAM 203, a backup RAM 204, and the like. The CPU 201, ROM 202, RAM 203, and backup RAM 204 are connected to each other via a bus 207, and are connected to an input interface 205 and an output interface 206.

  The ECU 200 controls the drive of the injector 2 (fuel injection amount adjustment control), the ignition timing control of the spark plug 3, and the drive control of the throttle motor 6 of the throttle valve 5 based on the detection signals of the various sensors shown in FIG. Various controls of the engine 1 including (intake air amount control), air-fuel ratio feedback control, and the like are executed. Further, the ECU 200 executes the following “cylinder discrimination process”, “combustion deterioration cylinder identification process”, and “fuel injection amount correction control”.

  The fuel injection control device of the present invention is realized by the program executed by the ECU 200 described above.

-Cylinder discrimination processing-
A cylinder discrimination process executed by the ECU 200 will be described.

  First, in the signal rotor 17 used for detecting the crank angle applied to this example, as shown in FIG. 2, each tooth 17a is formed at every 10 ° CA, and 34 teeth 17a lacking two are provided. have. When the toothless portion 17b of the signal rotor 17 passes in the vicinity of the crank position sensor (electromagnetic pickup) 31, the generation interval of the voltage pulse becomes long. The rotation phase (crank position) of the crankshaft 15 can be detected by the output of a signal (missing tooth signal) corresponding to the missing tooth portion 17b of the signal rotor 17, and the time when each cylinder is located at the top dead center. Can be recognized. The output signal (missing tooth signal) of the crank position sensor 31 corresponding to the missing tooth portion 17b of the signal rotor 17 is a signal for judging the top dead center position for cylinder discrimination, that is, the “top dead center position judging signal”. It has become.

  Here, in a four-cycle engine (four-cylinder engine), two rotations (720 ° CA) of the crankshaft that rotates according to the raising and lowering of the piston is one cycle of the engine cycle, and each cylinder is one cycle of the engine cycle. Located at top dead center twice each time. For this reason, it is impossible to determine which of the two dead centers is at the top dead center only by the output signal (missing tooth signal) of the crank position sensor 31 as described above. That is, cylinder discrimination cannot be performed. Therefore, in this example, the cylinder discrimination is enabled by combining the output signal (voltage pulse) of the cam position sensor 39 with the output signal (missing tooth signal) of the crank position sensor 31. The cylinder discrimination will be described below.

  First, as described above, the crank position sensor 31 outputs the missing tooth signal once (two times in one cycle of the engine cycle) while the crankshaft 15 makes one rotation (360 ° CA). In this example, the crank position sensor 31 outputs a missing tooth signal at a predetermined crank angle before the top dead center of the first cylinder # 1 and the fourth cylinder # 4.

  Further, as described above, the cam position sensor 39 outputs a voltage pulse once during the rotation of the crankshaft 15 (once in one cycle of the engine cycle). In this example, the cam position sensor 39 outputs a voltage pulse when the first cylinder # 1 is located at the compression top dead center and the fourth cylinder # 4 is located at the exhaust top dead center.

  With such a configuration, if the cam position sensor 39 generates a voltage pulse when the crank position sensor 31 outputs a missing tooth signal, the first cylinder # 1 is positioned at the compression top dead center, and the fourth cylinder # 4 is located at the exhaust top dead center. When the crank position sensor 31 outputs a missing tooth signal and the cam position sensor 39 does not generate a voltage pulse, the first cylinder # 1 is located at the exhaust top dead center and the fourth cylinder # 4 is compressed. It will be located at the dead center. The voltage pulse generated by the cam position sensor 39 in this way is a signal for performing cylinder discrimination, that is, a “cylinder discrimination signal”.

  Thus, based on the missing tooth signal of the crank position sensor 31 (first detection of the top dead center position determination signal) and the presence or absence of the generation of the cylinder determination signal (voltage pulse) of the cam position sensor 39 corresponding to the detection. Thus, cylinder discrimination (crank angle determination) can be performed during one revolution of the crankshaft 15 at the latest. By such cylinder discrimination, it is possible to recognize the piston positions (intake stroke, compression stroke, explosion stroke, exhaust stroke) of each cylinder # 1 to # 4 at the time of engine start / operation after start-up. Further, engine operation control such as precise fuel injection control and ignition timing control can be performed.

  In the above processing, cylinder discrimination (crank angle determination) and piston position recognition of each cylinder # 1 to # 4 are performed from the output signals of the crank position sensor 31 and the cam position sensor 39. The cylinder discrimination (crank angle determination) and the piston positions of the cylinders # 1 to # 4 may be recognized by the above means.

-Combustion deterioration cylinder identification process-
Next, the combustion deterioration cylinder specifying process executed by the ECU 200 will be described.

  First, for example, when combustion deterioration (lean combustion deterioration) occurs only in one cylinder (for example, the first cylinder # 1), the engine rotation speed in the explosion stroke of the cylinder gradually decreases. The time required for the crankshaft 15 to rotate at a constant crank angle during the explosion stroke of the cylinder (first cylinder # 1) in which the cylinder has occurred is the explosion of the other cylinders (second cylinder # 2 to fourth cylinder # 4). It will be longer than that time during the journey. Therefore, by measuring and comparing these times, it is possible to recognize the cylinder in which the combustion deterioration has occurred.

  An example of the specific processing will be described. First, the ECU 200 takes in the output signals of the crank position sensor 31 and the cam position sensor 39 at every predetermined crank angle (for example, every 30 ° CA), and based on these signals, the first cylinder # 1 enters the explosion stroke. At one time, during this explosion stroke, the elapsed time T1 required for the crankshaft 15 to rotate at a constant crank angle (for example, 180 ° CA) and one time before the explosion stroke of the first cylinder # 1 (360) The difference from the elapsed time T2 required for the crankshaft 15 to rotate at a constant crank angle (for example, 180 ° CA) during the explosion stroke of the second cylinder # 2 that had reached the explosion stroke before ° CA) is calculated. Thus, the rotational fluctuation amount ΔNE1 (= T1-T2) of the first cylinder # 1 is obtained.

  Similarly, the elapsed time T3 (third cylinder # 3) required for the crankshaft 15 to rotate at a constant crank angle (for example, 180 ° CA) during the explosion stroke of the cylinders # 2 to # 4 of the engine 1 is the same. , T4 (fourth cylinder # 4), T2 (second cylinder # 2) are sequentially calculated, and the third cylinder # 3 rotational fluctuation amount ΔNE3 (= T3−T1), the fourth cylinder # 4 rotational fluctuation amount. ΔNE4 (= T4-T3) and the rotational fluctuation amount ΔNE2 (= T2-T4) of the second cylinder # 2 are obtained.

  The ECU 200 compares the rotation fluctuation amounts ΔNE1 to ΔNE4 of the cylinders # 1 to # 4 obtained by the above calculation with the determination threshold Th (see FIG. 4), and the rotation fluctuation amount ΔNE exceeds the determination threshold Th. When there is a cylinder, the cylinder is recognized as a “cylinder in which combustion has deteriorated”.

  The determination threshold Th set for the rotational fluctuation amount ΔNE is an experimental value of the rotational fluctuation amount of the engine 1 at which exhaust combustion deteriorates due to the deterioration of lean combustion (deterioration due to A / F imbalance) at the time of engine startup or the like. The value obtained by simulation or the like and empirically adapted based on the result. The determination threshold Th is stored in the ROM 202 of the ECU 200.

-Fuel injection amount correction control-
Next, fuel injection amount correction control for suppressing fluctuations in the rotation of the engine 1 will be described.

  First, FIG. 4 shows the engine speed NE and the rotational fluctuation amounts ΔNE1 to ΔNE4 of the cylinders # 1 to # 4.

  In FIG. 4, # 1ΔNE1, # 2ΔNE2, # 3ΔNE3, # 4ΔNE4 are the rotational fluctuation amount ΔNE1, the rotational fluctuation amount ΔNE3, which are repeatedly calculated every cycle (every 720 ° CA) in the above-described arithmetic processing. The rotational fluctuation amount ΔNE4 and the rotational fluctuation amount ΔNE2 are plotted for each cylinder (first cylinder # 1, second cylinder # 2, third cylinder # 3, fourth cylinder # 4) with time as a parameter. is there. In the example of FIG. 4, the cylinder in which the maximum rotational fluctuation occurs (the cylinder in which the rotational fluctuation amount ΔNE exceeds the determination threshold Th) is the first cylinder # 1, and the cylinder in which the rotational fluctuation amount ΔNE exceeds the determination threshold Th in addition to this. In this example, the second cylinder # 2 is present.

  Here, when a cylinder other than the cylinder having the largest rotational fluctuation has a rotational fluctuation, the cylinder (second cylinder # 2 in the example of FIG. 4) has a rotational fluctuation caused by factors other than the deterioration of lean combustion. There is also. In such a case, if the fuel injection amount increase correction is performed, the fuel increase to the wrong cylinder may occur and conversely the emission may deteriorate. When starting the engine, the emission deterioration due to combustion deterioration is greatest immediately after the engine starts, and the deterioration of emission decreases as the catalyst warms up. Even if this occurs, it may not be necessary to increase the fuel for the cylinder.

  In consideration of such points, in this example, when there are a plurality of cylinders (cylinders in which the rotational fluctuation occurs) in which the rotational fluctuation amount ΔNE is larger than the determination threshold Th, fuel injection is performed for all of these cylinders. Rather than performing an increase correction of the amount, an increase correction of the fuel injection amount is performed only for the cylinder (first cylinder # 1 in the example of FIG. 4) in which the rotational fluctuation is maximum, and the rotational fluctuation ( In the example of FIG. 4, even if the rotation fluctuation of the second cylinder # 2 occurs, the fuel injection amount increase correction is not performed for that cylinder.

  Thus, the risk of fuel increase to the wrong cylinder can be avoided by performing the fuel injection amount increase correction only for the cylinder with the largest rotational fluctuation.

  Specifically, in the example of FIG. 4, in the example of FIG. 4, the increase in the fuel injection amount is corrected for the cylinder having the largest rotational fluctuation, that is, the first cylinder # 1 on the assumption that the rotational fluctuation has occurred due to the deterioration of lean combustion. Do. On the other hand, the rotation fluctuation of the second cylinder may occur due to factors other than the deterioration of lean combustion (Note that the emission deterioration is less due to the progress of catalyst warm-up and the fuel injection amount needs to be increased. May not be.) Therefore, if the fuel injection amount increase correction is performed for the second cylinder # 2, the risk of emission deterioration due to an incorrect fuel increase increases. Therefore, in order to avoid the risk (wrong cylinder increase), the second cylinder # 2 is avoided. Regarding 2, the emission deterioration is suppressed by not performing the increase correction of the fuel injection amount. Here, the rotational fluctuation of the second cylinder # 2 (the cylinder other than the cylinder with the largest rotational fluctuation) may be a rotational fluctuation due to the deterioration of lean combustion, but the fuel increase to the second cylinder # 2 is not performed. The effect of this is small compared to the risk due to the increase in erroneous cylinders (emission deterioration due to unnecessary increase in fuel). Therefore, priority is given to avoiding the risk due to the increase in erroneous cylinders. This is advantageous.

  In this example, the increase correction of the first cylinder # 1 may be terminated when, for example, the rotational fluctuation of the first cylinder # 1 has subsided.

  In the example of FIG. 4 described above, the case where the cylinder having the largest rotational fluctuation is the first cylinder # 1, but the cylinders in which the largest rotational fluctuation occurs are the second cylinder # 2, the third cylinder # 3, Alternatively, it may be the case of the fourth cylinder # 4, and the fuel injection amount increase correction is performed only for the cylinders (second cylinder # 2, third cylinder # 3, fourth cylinder # 4) whose rotation fluctuation is maximum. Should be done.

  Further, in this example, even when there are two or more cylinders in which the rotational fluctuation occurs in addition to the cylinder in which the largest rotational fluctuation occurs (for example, the first cylinder # 1), the fuel injection amount for these cylinders. Do not perform an increase correction of.

  In this example, the increase correction value of the cylinder (for example, the first cylinder # 1) in which the rotational fluctuation is maximum may be a fixed value (a constant value), or the rotational fluctuation amount (for example, the first cylinder # 1). In accordance with the amount of rotation fluctuation amount ΔNE1) exceeding the determination threshold Th (for example, [maximum value of ΔNE1] −Th), the larger the amount exceeding the determination threshold Th (rotation fluctuation amount), the larger the increase correction value. You may set so that. Thus, when the increase correction value is set to be variable, the rotational fluctuation of the engine 1 can be more effectively suppressed, and emission can be suppressed and drivability can be improved. Note that the increase correction value may be set variably according to the magnitude of the rotational fluctuation amount itself.

  In this example, the rotational fluctuation amount ΔNE1, the rotational fluctuation amount ΔNE3, the rotational fluctuation amount ΔNE4, and the rotational fluctuation amount ΔNE2 are repeatedly calculated for each engine cycle (every 720 ° CA). Instead, the rotational fluctuation amount ΔNE1, the rotational fluctuation amount ΔNE3, the rotational fluctuation amount ΔNE4, and the rotational fluctuation amount ΔNE2 may be repeatedly calculated for each of a plurality of cycles.

  In this example, the calculation of the rotational fluctuation amount ΔNE1, the rotational fluctuation amount ΔNE3, the rotational fluctuation amount ΔNE4, and the rotational fluctuation amount ΔNE2 is continued even after the cylinder with the maximum rotational fluctuation is specified. Without any change, the fuel injection amount increase correction is performed only for the cylinder in which the maximum rotation fluctuation occurs (the cylinder in which the rotation fluctuation amount ΔNE exceeds the determination threshold Th), and after the increase correction is completed, the rotation of each cylinder is corrected. The calculation of the fluctuation amount ΔNE may be stopped. In this way, a reduction in calculation load during control can be expected.

-Other examples of fuel injection amount correction control-
Next, another example of the fuel injection amount correction control will be described with reference to FIG.

  In the example of FIG. 5, the cylinder in which the rotational fluctuation first occurs at the time of starting the engine or the like (the cylinder in which the rotational fluctuation ΔNE first exceeds the determination threshold Th) is the first cylinder # 1, and thereafter the rotational fluctuation occurs. An example in which the generated cylinder (cylinder whose rotation fluctuation exceeds the determination threshold Th) is the second cylinder # 2 is shown.

  In the example of FIG. 5 as well, the rotational fluctuation of the first cylinder # 1 is the largest as in the above-described example. Therefore, it is assumed that the rotational fluctuation occurs in the first cylinder # 1 due to the deterioration of lean combustion. Increase correction of the injection amount.

  However, for the second cylinder, the fluctuation in rotation is suppressed by restricting the fuel increase to a small value and correcting the increase in the fuel injection amount. That is, in consideration of the case where the second cylinder # 2 undergoes rotational fluctuation due to deterioration of lean combustion, the drivability is improved by performing the minimum amount of fuel increase to suppress the rotational fluctuation. . In this case, when the increase correction of the fuel injection amount of the second cylinder # 2 is not necessary, the fuel increase is excessive, but by suppressing the fuel increase to the minimum, the deterioration of the emission due to the fuel increase is suppressed as much as possible. However, drivability can be improved.

  In this example, the increase correction for the first cylinder # 1 is terminated when, for example, the rotational fluctuation of the first cylinder # 1 is stopped, and the increase correction for the second cylinder # 2 is performed for the second cylinder # 2, for example. The process ends when the rotational fluctuation is settled.

  Here, in the example of FIG. 5 described above, the case where the first cylinder # 1 has the largest rotational fluctuation at the time of engine start or the like has been described. However, the rotational fluctuation first occurs at the time of engine start or the like. Even when the cylinder is the second cylinder # 2, the third cylinder # 3, or the fourth cylinder # 4, the fuel injection amount correction similar to the above may be performed. Further, even when the cylinder in which the rotational fluctuation occurs after the maximum rotational fluctuation first is a cylinder other than the second cylinder # 2, the fuel injection in which the increase correction amount is limited to be small as described above. What is necessary is just to perform quantity increase correction.

  In this example, the amount of increase correction of the cylinder (for example, the first cylinder # 1) in which the rotational fluctuation is maximum may be a fixed value (a constant value), or the rotational fluctuation amount (for example, the first cylinder # 1). In accordance with the amount of rotation fluctuation amount ΔNE1) exceeding the determination threshold Th (for example, [maximum value of ΔNE1] −Th), the larger the amount exceeding the determination threshold Th (rotation fluctuation amount), the larger the increase correction value. You may set so that. Thus, when the increase correction value is set to be variable, the rotational fluctuation of the engine 1 can be more effectively suppressed, and emission can be suppressed and drivability can be improved. Note that the increase correction value may be set variably according to the magnitude of the rotational fluctuation amount itself.

  Further, regarding the increase correction amount (limit increase correction amount) of the cylinder (for example, the second cylinder # 2) in which the rotation fluctuation occurs after the maximum rotation fluctuation occurs, the deterioration of the emission can be suppressed as much as possible even if the cylinder increase is excessive. Such values may be adapted by experiments, simulations, or the like. This limit increase correction amount may also be a fixed value (a constant value), or may be set variably according to rotational fluctuations.

  In this example, the rotational fluctuation amount ΔNE1, the rotational fluctuation amount ΔNE3, the rotational fluctuation amount ΔNE4, and the rotational fluctuation amount ΔNE2 are repeatedly calculated for each cycle of the engine (every 720 ° CA). Without being limited thereto, the rotation fluctuation amount ΔNE1, the rotation fluctuation amount ΔNE3, the rotation fluctuation amount ΔNE4, and the rotation fluctuation amount ΔNE2 may be repeatedly calculated for each of a plurality of cycles.

  Note that the control of the present invention (fuel injection amount increase correction control) is applicable not only when the engine is started but also when the engine is in another engine operating state such as during warm-up operation or idle operation.

-Other embodiments-
In the present invention, the rotational fluctuation amount of each cylinder may be detected for a predetermined period, and the cylinder having the largest rotational fluctuation amount may be determined, and the increase correction only for the same cylinder may be made.

  In the above example, during the explosion stroke of each cylinder, engine rotation fluctuation is recognized from the time required for the crankshaft to rotate at a constant crank angle, but engine rotation fluctuation is recognized based on other parameters. You may make it do.

  In the above example, the example in which the present invention is applied to the fuel injection control of a four-cylinder gasoline engine has been shown. However, the present invention is not limited to this, and for example, any other number of cylinders such as six cylinders and eight cylinders. The present invention is also applicable to a fuel injection control device for a multi-cylinder internal combustion engine.

  In the above example, the present invention is applied to the fuel injection control of the port injection type gasoline engine. However, the present invention is not limited to this and is also applied to the fuel injection control of the in-cylinder direct injection type gasoline engine. Is possible. In addition to the in-line multi-cylinder gasoline engine, the present invention can be applied to fuel injection control of a V-type multi-cylinder gasoline engine.

  Further, the present invention is not limited to a gasoline engine, and the present invention can also be applied to fuel injection control of a flex fuel internal combustion engine that can use, for example, an alcohol-containing fuel in which gasoline and alcohol are mixed at an arbitrary ratio.

  The present invention can be used for fuel injection control of a multi-cylinder internal combustion engine having a plurality of cylinders, and more specifically, fuel for a multi-cylinder internal combustion engine that performs control for increasing and correcting the fuel injection amount so as to suppress rotational fluctuations. It can be used for an injection control device.

1 engine # 1 to # 4 cylinder 1d combustion chamber 2 injector (fuel injection valve)
3 Spark plug 31 Crank position sensor 39 Cam position sensor 200 ECU

Claims (4)

Applied to a multi-cylinder internal combustion engine having a plurality of cylinders, equipped with a fuel injection amount adjusting means capable of adjusting the fuel injection amount to each cylinder for each cylinder, and increasing the fuel injection amount to the cylinder based on the engine rotational fluctuation In the fuel injection control device capable of executing the correction control,
A fuel for a multi-cylinder internal combustion engine, wherein when a rotational fluctuation occurs due to deterioration of lean combustion in a plurality of cylinders, the fuel injection amount increase correction is performed only for the cylinder having the largest rotational fluctuation among these cylinders. Injection control device. The fuel injection control device for a multi-cylinder internal combustion engine according to claim 1,
The engine rotation fluctuation amount is compared with a threshold value, a cylinder exceeding the threshold value is recognized as a cylinder in which the rotation fluctuation occurs, and the cylinder having the largest rotation fluctuation among the cylinders in which the rotation fluctuation occurs The fuel injection control device for a multi-cylinder internal combustion engine is characterized by performing an increase correction of the fuel injection amount only for. The fuel injection control device for a multi-cylinder internal combustion engine according to claim 2,
A fuel injection control device for a multi-cylinder internal combustion engine, wherein an increase correction amount of a fuel injection amount is set for a cylinder having the largest rotational fluctuation in accordance with the amount of rotational fluctuation exceeding the threshold value. Applied to a multi-cylinder internal combustion engine having a plurality of cylinders, equipped with a fuel injection amount adjusting means capable of adjusting the fuel injection amount to each cylinder for each cylinder, and increasing the fuel injection amount to the cylinder based on the engine rotational fluctuation In the fuel injection control device capable of executing the correction control,
When the fuel injection amount increase correction is performed for a specific cylinder whose rotation fluctuation has occurred due to the deterioration of lean combustion, even if the rotation fluctuation occurs in other cylinders, the fuel injection amount increase correction for other cylinders A fuel injection control device for a multi-cylinder internal combustion engine characterized by limiting

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