JP4239361B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine that feedback-controls an air-fuel ratio to a target air-fuel ratio based on a detected air-fuel ratio in an exhaust passage.
[0002]
[Prior art]
In general, an air-fuel ratio control apparatus for an internal combustion engine is provided with an exhaust sensor at a junction of exhaust pipes provided in accordance with a plurality of cylinders, and controls a fuel injection amount based on a detection result of the exhaust sensor. Is feedback-controlled so that becomes the target air-fuel ratio. However, the exhaust gas discharged for each cylinder may have different air-fuel ratios due to variations in intake air amount, fuel amount, etc., and the above-described air-fuel ratio control device makes it difficult to perform highly accurate air-fuel ratio control. . In this case, an exhaust sensor may be provided for each cylinder, and the fuel injection amount may be controlled for each cylinder based on the detection result of each exhaust sensor. However, the number of exhaust sensors increases, resulting in high costs.
[0003]
In view of this, what enables air-fuel ratio control for each cylinder without providing an exhaust sensor for each cylinder is disclosed in, for example, Japanese Patent Publication No. 4-77139 and Japanese Patent Application Laid-Open No. 10-9023. .
[0004]
In the "multi-cylinder engine air-fuel ratio control apparatus" disclosed in Japanese Patent Publication No. 4-77139, the exhaust gas concentration at the collecting portion of the exhaust manifold is detected by an exhaust sensor, and the exhaust by the exhaust sensor corresponding to the engine operating state is detected. The output of the exhaust sensor corresponding to each cylinder is obtained from the relationship between the delay time of the gas concentration detection and the reference working cylinder stroke of the engine, and the fuel injected into each cylinder is adjusted based on the output of the exhaust sensor.
[0005]
Further, in the “air-fuel ratio control device for an internal combustion engine” disclosed in Japanese Patent Laid-Open No. 10-9023, the time until the exhaust reaches the air-fuel ratio sensor from the combustion chamber of each cylinder is obtained based on the operating state of the engine. In this case, the air-fuel ratio is detected for each cylinder by determining the cylinder of the currently detected air-fuel ratio. In this case, the air-fuel ratio detection value of each cylinder is weighted in consideration of mixing with other cylinders. Thus, the weighted average value is obtained, and the air-fuel ratio for each cylinder is estimated.
[0006]
[Problems to be solved by the invention]
However, in the above-described “multi-cylinder engine air-fuel ratio control device”, the output of the exhaust sensor considering the delay time of exhaust gas concentration detection corresponding to the engine operating state is injected as the exhaust gas concentration of each cylinder. Although the amount of fuel to be adjusted is adjusted, the exhaust gas from one cylinder is mixed even when it is judged as the exhaust gas from one cylinder. The exhaust gas concentration cannot be said to be an exhaust gas concentration, and the exhaust gas concentration detected by the exhaust sensor includes a detection error, and the reliability is insufficient. As a result, control can diverge.
[0007]
In the above-mentioned “air-fuel ratio control apparatus for an internal combustion engine”, the air-fuel ratio for each cylinder is estimated in consideration of the mixture of exhaust gas with other cylinders. The air-fuel ratio step of the other cylinder with respect to this air-fuel ratio detection value is learned as a reference, and the air-fuel ratio step of the # 1 cylinder serving as the reference cannot be corrected. In addition, the air-fuel ratio for each cylinder is obtained by weighting and averaging the air-fuel ratio detection value of each cylinder. However, setting a mathematical formula for performing the weighted average requires a large amount of man-hours. The development cost of the control system will increase.
[0008]
An object of the present invention is to solve such a problem, and to provide an air-fuel ratio control device for an internal combustion engine that can detect and control the air-fuel ratio of each cylinder with high accuracy without increasing the cost. And
[0009]
[Means for Solving the Problems]
In order to achieve the above-described object, the present invention has air-fuel ratio detection means provided at the junction of the exhaust passage, and feedback-controls the air-fuel ratio to the target air-fuel ratio based on the detection output of the air-fuel ratio detection means. In the air-fuel ratio control device for an internal combustion engine, the average air-fuel ratio calculating means calculates the average air-fuel ratio based on the detection output of the air-fuel ratio detection means, and the cylinder-by-cylinder timing determination means detects the detection output of the air-fuel ratio detection means for each cylinder. The period corresponding to the exhaust gas is determined, the cylinder-by-cylinder air-fuel ratio detection means detects the cylinder-by-cylinder air-fuel ratio during this period, and the air-fuel ratio control amount correction means is based on the deviation between the average air-fuel ratio and the cylinder-by-cylinder air-fuel ratio. The air-fuel ratio control amount of the corresponding cylinder is corrected.
[0010]
Therefore, the air-fuel ratio for each cylinder detected by the cylinder-by-cylinder air-fuel ratio detecting means is an air-fuel ratio in a state where exhaust from other cylinders is mixed, but use a deviation from the average air-fuel ratio affected by the exhaust of all cylinders. Thus, the air-fuel ratio step due to the influence of the exhaust state of the cylinder can be detected relatively accurately, and the air-fuel ratio control amount of each cylinder can be appropriately controlled.
[0011]
The period corresponding to the exhaust of each cylinder determined by the cylinder timing determination means is preferably set as a predetermined crank angle range in which the influence of the exhaust gas of this cylinder is most dominant for each cylinder. Generally, the exhaust gas is a mixture of exhaust gases from a plurality of cylinders, and the air-fuel ratio also corresponds to the exhaust gas, but the period in which the influence of the exhaust gas of each cylinder is the most dominant for each cylinder by the cylinder timing determination means. Since the deviation is obtained with respect to, control can be performed more accurately even in a state where exhaust gases of a plurality of cylinders are mixed. Further, the detection of the air-fuel ratio for each cylinder is executed a plurality of times during this period, and this deviation is preferably obtained based on the integrated value of the deviation between the average air-fuel ratio and each detected value of the air-fuel ratio for each cylinder.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0013]
FIG. 1 is a schematic diagram showing an air-fuel ratio control apparatus for an internal combustion engine according to an embodiment of the present invention, FIG. 2 is a flowchart of control by the air-fuel ratio control apparatus for the internal combustion engine of the present embodiment, and FIG. The graph showing the air fuel ratio corresponding to a period is shown.
[0014]
As shown in FIG. 1, the air-fuel ratio control apparatus for an internal combustion engine according to this embodiment is applied to a four-cylinder engine. The engine 11 includes an intake port and an exhaust port corresponding to each cylinder (combustion chamber). Is provided and can be opened and closed by an intake valve and an exhaust valve (not shown). The downstream side of the intake pipe 13 with the air cleaner 12 attached to the upstream part is connected to an intake manifold 15 via a surge tank 14, and four manifold parts formed in the intake manifold 15 are connected to each intake port of the engine 11. It is connected. An air flow sensor 16 is mounted upstream of the intake pipe 13 and a throttle valve 17 and a throttle opening sensor 18 are provided. Each manifold portion of the intake manifold 15 is provided with an injector 19 for injecting fuel.
[0015]
On the other hand, an exhaust manifold 21 is connected to the upstream side of the exhaust pipe 20 as an exhaust passage, and four manifold portions formed in the exhaust manifold 21 are connected to each exhaust port of the engine 11. A linear A / F sensor 22 as an air-fuel ratio detecting means is mounted on the upstream portion of the exhaust pipe 20, that is, on the downstream side where the manifold portion of the exhaust manifold 21 joins. A catalyst 23 is mounted. The engine 11 is provided with a crank angle sensor 24 that detects the crank position of each cylinder.
[0016]
Further, the vehicle is provided with an electronic control unit (ECU) 25 as a control device. The ECU 25 includes a storage device for storing an input / output device, a control program, a control map and the like, a central processing unit, a timer and a counter. The ECU 25 performs overall control of the engine 11. That is, the detection information of the various sensors 16, 18, 22, and 24 described above is input to the ECU 25. The ECU 25 determines the fuel injection amount, the ignition timing, and the like based on the detection information of the various sensors, and the injector 19 and the like. Is controlled.
[0017]
By the way, in the air-fuel ratio control in the engine 11 configured as described above, the ECU 25 performs feedback control of the air-fuel ratio to the target air-fuel ratio based on the detection output of the linear A / F sensor 22. However, the exhaust gas discharged from each cylinder of the engine 11 (each manifold portion of the exhaust manifold 21) is emptied due to variations in the amount of air flowing into each manifold portion of the intake manifold 15, the fuel injection amount from the injector 19, and the like. The fuel ratio may be different. Therefore, the concentration of exhaust gas flowing through the linear A / F sensor 22 provided in the exhaust pipe 20 on the downstream side of the exhaust manifold 21 is detected, and injection is performed on each manifold portion of the intake manifold 15 based on the detection result. Even if the amount of fuel to be determined is determined, highly accurate air-fuel ratio control becomes difficult.
[0018]
Therefore, in the air-fuel ratio control apparatus for the internal combustion engine of the present embodiment, the average air-fuel ratio is calculated (average air-fuel ratio calculating means) based on the detection output of the linear A / F sensor 22, and the linear A / F sensor is used. The detection output of 22 corresponds to the exhaust of each cylinder, and the period in which the influence of the exhaust of the cylinder seems to be dominant is determined (timing determination means for each cylinder), and the detection output of the linear A / F sensor 22 in this period The air-fuel ratio for each cylinder is detected based on the cylinder (air-fuel ratio detecting means for each cylinder), and the air-fuel ratio control amount for the corresponding cylinder is corrected based on the deviation between the average air-fuel ratio and the air-fuel ratio for each cylinder (air-fuel ratio control amount). Correction means).
[0019]
The determination of the period corresponding to the exhaust of each cylinder is made based on the detection signal SGT of the crank angle sensor 24 and the cam rotation position signal (not shown), as shown in FIG. That is, with reference to the # 1 cylinder compression TDC position, assuming that the deviation integration start crank angle of the # 1 cylinder is RA and the deviation integration crank angle width is RW, the exhaust period (integration range) R1 of the # 1 cylinder is set. The # 3, # 4, and # 2 cylinder integration ranges R3, R4, and R2 are set by adding 180 ° to the exhaust period R1 of the # 1 cylinder. For example, assuming that the # 1 cylinder compression TDC position at the right end in the figure is the reference, the # 1 cylinder deviation integration start crank angle RA is 890 ° BTDC and the deviation integration crank angle width RW is 150 °.
# 1 cylinder exhaust period R1 = 890-740 ° BTDC
# 3 cylinder exhaust period R3 = 710-560 ° BTDC
# 4 cylinder exhaust period R4 = 530-380 ° BTDC
# 2-cylinder exhaust period R2 = 350-200 ° BTDC
It becomes.
[0020]
Here, the air-fuel ratio control for each cylinder by the air-fuel ratio control apparatus of the internal combustion engine of the present embodiment will be described based on the flowchart of FIG.
[0021]
First, in step S1, the ECU 25 samples the LAFS output signal (voltage) of the linear A / F sensor 22 at predetermined time intervals. In this case, the sampling interval is an interval at which sampling is performed a plurality of times for each integration range R1 to R4 of each cylinder. In step S2, correction based on the exhaust gas pressure is performed. In step S3, it is determined whether or not the conditions for air-fuel ratio control for each cylinder are satisfied. The conditions of the air-fuel ratio control for each cylinder are that the stoichiometric feedback operation is being performed, that the coolant temperature of the engine 11 is equal to or higher than a predetermined temperature, and that the operation is not in the acceleration / deceleration operation but in the steady operation. The determination of the stoichiometric feedback operation is made to determine that it is in a predetermined operation region (a map of engine speed and volumetric efficiency).
[0022]
If the conditions for cylinder-by-cylinder air-fuel ratio control are satisfied in step S3, the average value LAFSAV is calculated by the following equation in step S4.
Average value LAFSAV = K1 × LAFSAV _(n−1) + (1−K1) × LAFS
In this case, the average value LAFSAV is actually a value that has passed through a filter, K1 is a filter constant, and LAFS is a value after exhaust pressure correction is performed on the detection output of the linear A / F sensor 22. If the condition for air-fuel ratio control for each cylinder is not satisfied in step S3, the previous value is held. When the ignition key switch is off, the battery is backed up.
[0023]
When the average value LAFSAV is calculated in step S4, the deviation LAFSD is calculated by the following formula in step S5.
Deviation LAFSD = LAFS−LAFSAV
Here, LAFS is an instantaneous value after exhaust pressure correction is performed on the detection output of the A / F sensor 22. If the obtained deviation LAFSD is positive, the air-fuel ratio is displaced to the lean side, and if it is negative, it is rich. It can be determined that it is displaced to the side.
[0024]
When the deviation LAFSD is calculated in step S5, the deviation integrated average value LAFSDA is calculated for each cylinder in step S6. In other words, the deviation integrated average value LAFSDA for each cylinder can be calculated by dividing the result obtained by integrating the deviation LAFSD for each cylinder integrated range R1, R3, R4, R2 by the number of integrations.
[0025]
In step S7, whether or not the absolute value of the deviation integrated average value LAFSDA is greater than or equal to a predetermined value B1 (map of engine speed and volumetric efficiency) for a cylinder, that is, the air-fuel ratio of this cylinder is the average air-fuel ratio of all cylinders. It is determined whether or not the difference should be corrected by a predetermined amount or more. Here, if the absolute value of the deviation integrated average value LAFSDA is greater than or equal to the predetermined value B1, the correction coefficient for correcting the air-fuel ratio is continuously set in the same direction (lean side or rich side) a predetermined number of times in step S8. It is determined whether B3 or more have been updated.
[0026]
In step S8, if the correction coefficient has not been continuously updated in the same direction for a predetermined number of times B3 or more, in step S9, whether or not the deviation integrated average value LAFSDA is positive, that is, the deviation integrated average value LAFSDA. Is positive and the air-fuel ratio is lean, so it is determined whether correction to the rich side is necessary. If the deviation integrated average value LAFSDA is positive, the cylinder-by-cylinder air-fuel ratio correction coefficient kcyl is updated to the rich side according to the following formula in step S10.
Air-fuel ratio correction coefficient for each cylinder kcyl _(n) = kcyl _(n-1) + B2
On the other hand, if the deviation integrated average value LAFSDA is negative and the air-fuel ratio is rich, it is necessary to correct to the lean side. In step S11, the cylinder-by-cylinder air-fuel ratio correction coefficient kcyl is updated to the lean side by the following formula. To do.
Air-fuel ratio correction coefficient for each cylinder kcyl _(n) = kcyl _(n-1) -B2
Note that the initial value of the cylinder-by-cylinder air-fuel ratio correction coefficient kcyl is 1.0, and an upper limit value and a lower limit value are set. B2 is a predetermined value set in advance.
[0027]
As described above, when the cylinder-by-cylinder air-fuel ratio correction coefficient kcyl _(n) is updated in steps S10 and S11, the fuel injection amount by the injector 19 of the corresponding cylinder is corrected in step S12. In other words, the cylinder-by-cylinder air-fuel ratio correction coefficient kcyl _(n) reflects the drive pulse width Tinj of the injector 19 of the corresponding cylinder by the following equation.
Drive pulse width Tinj = Tb x Kelse x kcyl + acceleration / deceleration correction + Td
Here, Tb is a basic pulse width determined by the engine operating state, Kelse is another correction factor, and Td is a dead time (a delay time from when the injector drive signal is transmitted until the fuel is actually injected from the injector). .
[0028]
In this way, in the determination processing of step S7, if the air-fuel ratio for a certain cylinder should be corrected different from the average air-fuel ratio of all the cylinders by a predetermined amount or more, the processing of steps S9, 10, 11, 12 is performed. By processing, the cylinder-by-cylinder air-fuel ratio correction coefficient kcyl _(n) is updated to correct the fuel injection amount. In this case, this process is performed for each of the four cylinders.
[0029]
On the other hand, if the correction coefficient has been continuously updated in the same direction for the predetermined number of times B3 or more in step S8, that is, even if the air-fuel ratio is updated to the rich side or the lean side for the predetermined number of times B3 or more, the deviation integrated average still remains. If the absolute value of the value LAFSDA is greater than or equal to the predetermined value B1, it is determined in step S13 whether or not the absolute value of the deviation integrated average value LAFSDA is greater than or equal to the predetermined value B4 greater than the predetermined value B1. In step S13, the absolute value of the deviation integrated average value LAFSDA is equal to or greater than the predetermined value B4. This means that even if the air-fuel ratio is updated to the rich side or lean side a predetermined number of times B3 or more, the air-fuel ratio of this cylinder and all This means that the difference from the average air-fuel ratio of the cylinder does not decrease. In step S14, the cylinder-by-cylinder air-fuel ratio correction coefficient kcyl _(n) is not updated, and the previous cylinder-specific air-fuel ratio correction coefficient kcyl _(n-1). Hold. That is, for this cylinder, even if the air-fuel ratio is updated and corrected, the difference from the average air-fuel ratio does not decrease.Therefore, the deviation LAFSD of this cylinder is greatly influenced by exhaust gases from other cylinders. Is assumed. Therefore, if the correction by updating the air-fuel ratio is continued as it is, the control may diverge, so once this cylinder is stopped, the update is stopped and the air-fuel ratio correction coefficient is held. It is intended to converge.
[0030]
In step S15, a predetermined period of time elapses when the number of strokes of the engine 11 after holding the cylinder-by-cylinder air-fuel ratio correction coefficient kcyl _(n-1) in step S14 is _equal to or greater than the predetermined stroke number B5, and If the absolute value of the deviation integrated average value LAFSDA is less than or equal to the predetermined value B6 for all other cylinders that are being updated other than the cylinder that has retained the cylinder-by _- cylinder air-fuel ratio correction coefficient kcyl _(n-1) in step S14, the other This means that the difference between the air-fuel ratios of all the cylinders and the average air-fuel ratio of all the cylinders has converged. In step S16, the cylinder holding the cylinder-by _- cylinder air-fuel ratio correction coefficient kcyl _(n-1) is held. To release. Thus, the cylinders that are easy to converge are first converged. As a result, the air-fuel ratio of this cylinder is controlled to an accurate target value. Therefore, even for exhaust gas mixed in the deviation integration range of other cylinders, the air-fuel ratio of the exhaust gas from this cylinder is accurately set to the target value. It will be. Therefore, it is easy to converge the cylinders that are initially determined to be difficult to converge.
[0031]
On the other hand, in step S15, even if the number of strokes of the engine 11 becomes equal to or greater than the predetermined stroke number B5, if the absolute value of the deviation integrated average value LAFSDA does not become the predetermined value B6 or less for all the other cylinders being updated, step S17 is performed. In step S18, it is determined whether or not the cylinder-by-cylinder air-fuel ratio correction coefficient kcyl is held in all the cylinders. In step S19, if the number of times the cylinder air-fuel ratio correction coefficient kcyl is released is greater than or equal to the predetermined number B7, the control may be diverged and the control may be considered to be in a fixed state. Even if it continues, it is thought that it does not converge, so each coefficient is initialized and control is performed again.
[0032]
As described above, in the air-fuel ratio control apparatus for an internal combustion engine of the present embodiment, the average value LAFSAV of the air-fuel ratio is calculated based on the LAFS output of the linear A / F sensor 22, and the instantaneous value and average value LAFSAV of the LAFS output are calculated. And calculating the deviation integrated average value LAFSDA in the integrated ranges R1, R3, R4, R2 set as the exhaust period for each cylinder, the average air-fuel ratio of all the cylinders and each cylinder The deviation from the air-fuel ratio is obtained, and when the deviation integrated average value LAFSDA is equal to or greater than the predetermined value B1, the cylinder-by-cylinder air-fuel ratio correction coefficient kcyl is updated to correct the fuel injection amount.
[0033]
Therefore, the air-fuel ratio (LAFS output) for each cylinder detected by the linear A / F sensor 22 is an air-fuel ratio in a state where the exhaust of other cylinders is mixed, but the average air-fuel ratio average value affected by the exhaust of all cylinders. By using the deviation from LAFSAV, the air-fuel ratio step (deviation integrated average value LAFSDA) due to the influence of the exhaust state of the cylinder can be detected relatively accurately, and the air-fuel ratio control amount of each cylinder can be controlled appropriately. Further, for each cylinder, a deviation from the average value LAFSAV of the air-fuel ratio of all the cylinders in the crank angle ranges R1, R3, R4, and R2 that the exhaust of the cylinder seems to have the greatest influence on the air-fuel ratio (LAFS output). Since the control is performed by obtaining the integrated average value LAFSDA, it is possible to accurately control even in a state where exhausts of a plurality of cylinders are mixed.
[0034]
In the above-described embodiment, the linear A / F sensor 22 is used as the air-fuel ratio detection means, but a normal λ-O ₂ sensor may be used. In addition, the predetermined value B2 is added or subtracted in the process of updating the cylinder-by-cylinder air-fuel ratio correction coefficient kcyl _(n) in steps B11 and B12. The predetermined value B2 is added according to the magnitude of the deviation integrated average value LAFSDA. It may be changed, may be a value different between the rich side and the lean side, and may be further changed according to the operating conditions (engine speed, load) of the engine 11.
[0035]
In addition, although the update process of the cylinder-by-cylinder air-fuel ratio correction coefficient kcyl is integrated control, it may be PI control, PID control, differential control, or the like. For example, as an example of PID control:
Air-fuel ratio correction coefficient for each cylinder kcyl = 1.0 + kcylP + kcylI + kcylD
In this case,
Proportional coefficient kcylP = LASFDA x GP (GP: Proportional gain)
Integration coefficient kcyl I = Σ (LASFDA x GI) (GI: integral gain)
Derivative _{kcylD = (LASFDA (n) -LASFDA} (n-1) (G D proportional gain)
It becomes.
[0036]
Furthermore, if the conditions for cylinder-by-cylinder air-fuel ratio control are not satisfied in step S3, the cylinder-by-cylinder air-fuel ratio correction coefficient kcyl immediately before that may be used. In step S6, the deviation LAFSD is accumulated and divided by the number of accumulations to calculate the deviation accumulated average value LAFSDA for each cylinder. In order to increase the stability of the control, the deviation accumulated average value LAFSDA for several cycles is calculated. May be calculated. Similarly, when the deviation LAFSD exceeds the predetermined value B1 a predetermined number of times or more in several cycles (for example, about 10 to 200 cycles) in the determination processing in step S7, the cylinder-by-cylinder air-fuel ratio correction coefficient kcyl is updated. May be. The predetermined value B1 as the determination threshold may be changed according to the degree of deterioration of the catalyst, particularly the oxygen storage capacity. For example, the predetermined value B1 is decreased as the travel distance becomes longer. Furthermore, the predetermined values B1, B2, etc. may be changed and set for each cylinder according to the length of the exhaust pipe 20 for each cylinder.
[0037]
For the time being, the cylinder-by-cylinder air-fuel ratio correction coefficient kcyl of a specific cylinder may be changed and controlled based on the result. For example, before the process of step S7, the cylinder specific air-fuel ratio correction coefficient kcyl is intentionally enriched or leaned, and the process of step S7 is performed by observing the reaction of the change in the deviation LAFSD thereafter. do it. As a result, even if the deviation tendency of each cylinder is not clear yet, the deviation becomes large and the tendency can be clearly recognized and it becomes easy to control. Further, when the control is fixed and initialized in step S20, similarly, the control for intentionally changing the cylinder specific air-fuel ratio correction coefficient kcyl may be performed.
[0038]
Furthermore, first, each cylinder is intentionally enriched or leaned, the change pattern of the deviation LAFSD of each cylinder at that time is memorized, and after that, the change pattern of the deviation LAFSD is first verified. Control may be started. That is, for example, the cylinder-specific air-fuel ratio correction coefficient kcyl of the # 1 cylinder is intentionally made rich to a large extent, and it is stored whether the deviation LAFSD has changed to the rich side or the lean side for each cylinder at that time. Next, the cylinder-by-cylinder air-fuel ratio correction coefficient kcyl of the # 1 cylinder is intentionally made lean, and similarly, the change pattern of the deviation LAFSD is stored. This is performed for all cylinders, and the change patterns of the cylinder-by-cylinder air-fuel ratio correction coefficient kcyl and deviation LAFSD are stored. Then, the stored variation pattern of deviation LAFSD of each cylinder and the current variation pattern of deviation LAFSD are collated, and if they match, the cylinder-specific air-fuel ratio correction coefficient kcyl is intentionally changed when the variation pattern is stored. The cylinder specific air-fuel ratio correction coefficient kcyl is corrected in the reverse direction. By this method, the change tendency of the deviation can be determined first, and this method can be applied even when the control has to be initialized because it is in a divergent state or a fixed state. Note that the target air-fuel ratio when applying the above invention may be stoichiometric, rich or lean.
[0039]
【The invention's effect】
As described above in detail in the embodiment, according to the air-fuel ratio control apparatus for an internal combustion engine of the present invention, the air-fuel ratio for each cylinder in the period corresponding to the exhaust of each cylinder is detected, and the average air-fuel ratio and each cylinder Since the air-fuel ratio control amount of the corresponding cylinder is corrected based on the deviation from the air-fuel ratio, the air-fuel ratio for each cylinder detected by the cylinder-by-cylinder air-fuel ratio detection means is the air in the state where exhaust from other cylinders is mixed. By using the deviation from the average air-fuel ratio, which is the fuel ratio but affected by the exhaust of all cylinders, the difference in air-fuel ratio due to the influence of the exhaust state of this cylinder can be detected relatively accurately, increasing costs. Without this, it is possible to accurately detect the air-fuel ratio for each cylinder and control the control amount appropriately.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an air-fuel ratio control apparatus for an internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a flowchart of control by an air-fuel ratio control apparatus for an internal combustion engine according to the present embodiment.
FIG. 3 is a graph showing an air-fuel ratio corresponding to a detection period of each cylinder.
[Explanation of symbols]
11 Engine 13 Intake pipe 15 Intake manifold 19 Injector 20 Exhaust pipe 21 Exhaust manifold 22 Linear A / F sensor (air-fuel ratio detection means)
24 Crank angle sensor 25 Electronic control unit (ECU, average air-fuel ratio calculating means, cylinder-specific timing determining means, cylinder-specific air-fuel ratio detecting means, air-fuel ratio control amount correcting means)

Claims (1)

Having air-fuel ratio detection means provided at the confluence of the exhaust passage,
In an air-fuel ratio control apparatus for an internal combustion engine that performs feedback control of an air-fuel ratio to a target air-fuel ratio based on a detection output of the air-fuel ratio detection means,
Average air-fuel ratio calculating means for calculating an average air-fuel ratio based on the detection output of the air-fuel ratio detecting means;
A cylinder-by-cylinder timing determination unit that determines a period in which the detection output of the air-fuel ratio detection unit corresponds to the exhaust of each cylinder;
A cylinder-by-cylinder air-fuel ratio detection unit that detects a cylinder-by-cylinder air-fuel ratio based on a detection output of the air-fuel ratio detection unit in a period determined by the cylinder-by-cylinder timing determination unit;
When the deviation between the average air-fuel ratio calculated by the average air-fuel ratio calculating means and the cylinder-by-cylinder air-fuel ratio detecting means is greater than or equal to a predetermined value , the air-fuel ratio control corrects the air-fuel ratio control amount of the corresponding cylinder. A quantity correction means,
The period corresponding to the exhaust of each cylinder determined by the cylinder timing determination means is a predetermined crank angle range in which the influence of the exhaust gas of each cylinder is most dominant for each cylinder,
The air-fuel ratio control amount correction means holds the correction for the cylinder once when the deviation does not decrease even when the correction is continuously performed a predetermined number of times or more in the same direction for the same cylinder, and the correction in the other cylinders is performed. The air-fuel ratio control apparatus for an internal combustion engine, wherein the holding is released after the deviation has converged .

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