JP4385542B2 - 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]
For example, Japanese Patent Publication No. 4-8616 discloses an air-fuel ratio control for each cylinder without providing an exhaust sensor for each cylinder.
[0004]
Japanese Examined Patent Publication No. 4-8616 takes in air-fuel ratio detection values for each cylinder, and when the deviation between the maximum value of the air-fuel ratio detection values of all cylinders and the average value of all cylinders is equal to or greater than a predetermined value, the maximum value is set. A “cylinder-by-cylinder air-fuel ratio control device for an internal combustion engine” is disclosed in which the variation between the cylinders is reduced by correcting the air-fuel ratio correction value of the cylinder in order to reduce the fuel injection amount for the cylinder having the cylinder. .
[0005]
[Problems to be solved by the invention]
However, in the above-described conventional “cylinder-by-cylinder air-fuel ratio control device for internal combustion engine”, only the air-fuel ratio detection value at a specific crank angle corresponding to the engine speed is used to detect the air-fuel ratio of each cylinder. The detection for each cylinder is performed by relying on a single detection value of only a specific crank angle. Therefore, the air-fuel ratio detection value for each cylinder tends to be inaccurate, and as a result, there is a possibility that variations among the cylinders cannot be sufficiently eliminated, and there is room for improvement.
[0006]
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
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention has an air-fuel ratio detection means provided in an exhaust passage, and an internal combustion engine that feedback-controls the air-fuel ratio to a target air-fuel ratio based on the detection output of the air-fuel ratio detection means. In the air-fuel ratio control device, the average air-fuel ratio calculation 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 outputs the detection output of the air-fuel ratio detection means to the exhaust of each cylinder. The corresponding period is determined, and the cylinder-by-cylinder deviation average calculation means detects the output of the air-fuel ratio detection means a plurality of times during the period determined by the cylinder-by-cylinder timing determination means, and calculates the average deviation from the average air-fuel ratio for each cylinder, The correction control means corrects the air-fuel ratio control amount in such a direction that the deviation decreases with respect to the cylinder having the largest deviation.
[0008]
Therefore, the cylinder-by-cylinder air-fuel ratio detected by the cylinder-by-cylinder air-fuel ratio detection means is an air-fuel ratio in a state in which exhaust from other cylinders is mixed, but uses a deviation from the average air-fuel ratio that the exhaust of all cylinders affects, By correcting the air-fuel ratio for the cylinder with the largest average deviation, the air-fuel ratio control amount of each cylinder can be properly controlled in a state where the air-fuel ratio step due to the influence of the exhaust state is detected relatively accurately.
[0009]
The cylinder-by-cylinder deviation average calculating means calculates the cylinder-by-cylinder deviation average by adding up the deviation between the output of the air-fuel ratio detecting means and the average air-fuel ratio and dividing by the number of integrations every predetermined calculation period in the period. I have to.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0011]
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. A graph showing the air-fuel ratio corresponding to the period, and FIG. 4 shows a graph showing the relationship between the output voltage of the linear A / F sensor and the air-fuel ratio.
[0012]
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.
[0013]
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 mounting position of the linear A / F sensor 22 may be anywhere near the merging portion of the exhaust manifold 21 or downstream thereof. The engine 11 is provided with a crank angle sensor 24 that detects the crank position of each cylinder.
[0014]
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.
[0015]
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 used is simply determined, highly accurate air-fuel ratio control becomes difficult.
[0016]
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 cylinder-by-cylinder air-fuel ratio is detected (cylinder-by-cylinder air-fuel ratio detection means), and the detection output of the linear A / F sensor 22 is detected a plurality of times during the period determined by the cylinder-by-cylinder timing determination means. Is calculated (cylinder-specific deviation average calculation means), and the air-fuel ratio control amount is corrected (correction control means) in a direction in which the deviation decreases with respect to the cylinder having the largest average deviation.
[0017]
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.
[0018]
Here, the air-fuel ratio control (maximum deviation cylinder air-fuel ratio control) for the cylinder having the maximum deviation by the air-fuel ratio control apparatus for the internal combustion engine of the present embodiment will be described based on the flowchart of FIG.
[0019]
First, in step S0, 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 S1, correction based on the exhaust gas pressure is performed, and in step S2, the LAFS output signal (voltage) of the linear A / F sensor 22 is converted to a value corresponding to the air-fuel ratio based on the map shown in FIG. F conversion). As shown in FIG. 4, the air-fuel ratio does not change constantly with respect to the LAFS output signal of the linear A / F sensor 22, and the slope changes around the stoichiometric vicinity. For this reason, the LAFS output signal of the linear A / F sensor 22 is converted into a value corresponding to the air-fuel ratio based on the map shown in FIG. Therefore, the values shown below are converted values corresponding to the air-fuel ratio, and what is described as the detection output of the linear A / F sensor 22 is converted based on the map shown in FIG. This value is equivalent to the air / fuel ratio. If the air-fuel ratio is not converted, the LAFS output signal (voltage) and the air-fuel ratio are not linear as shown in FIG.
[0020]
Then, in step S3, it is determined whether or not a condition for deviation maximum cylinder air-fuel ratio correction control is satisfied. The conditions of this deviation maximum cylinder air-fuel ratio correction control are that the stoichiometric feedback operation is being performed, that the cooling water temperature of the engine 11 is equal to or higher than a predetermined temperature, and that it is not in acceleration / deceleration operation but in 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).
[0021]
If the deviation maximum cylinder air-fuel ratio correction control condition is 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. Note that if the condition for deviation maximum cylinder air-fuel ratio correction control is not satisfied in step S3, the previous value is held. When the ignition key switch is off, the battery is backed up.
[0022]
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.
[0023]
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.
[0024]
In steps S7 to S9, the deviation integrated average value LAFSDA calculated for each cylinder is compared. That is, in step S7, the absolute value of deviation integrated average value LAFSDA of # 1 cylinder and # 2 cylinder is compared, and in step S8, the absolute value of deviation integrated average value LAFSDA of # 3 cylinder and # 4 cylinder is compared. In step S9, the cylinder having the largest absolute value of the deviation integrated average value LAFSDA from the # 1 cylinder to the # 4 cylinder is specified based on the results of steps S7 and S8. Depending on the performance of the ECU 25 and the like, it is also possible to identify the cylinder having the largest absolute value of the deviation integrated average value LAFSDA by comparing the absolute values of the deviation integrated average value LAFSDA of the # 1 cylinder to the # 4 cylinder at a time. .
[0025]
After the cylinder having the largest absolute value of the deviation integrated average value LAFSDA is specified in step S9, in step S10, whether or not the deviation integrated average value LAFSDA of the specified cylinder is positive, that is, the deviation integrated average value LAFSDA is positive. Then, since the air-fuel ratio is lean, it is determined whether it is necessary to correct to the rich side. If the deviation integrated average value LAFSDA is positive, in step S11, the deviation maximum cylinder air-fuel ratio correction coefficient kcyl is updated to the rich side by the following equation.
Deviation maximum cylinder air-fuel ratio correction coefficient 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 S12, the deviation maximum cylinder air-fuel ratio correction coefficient kcyl is set to the lean side according to the following equation. Update.
Deviation maximum cylinder air-fuel ratio correction coefficient kcyl _(n) = kcyl _(n-1) -B2
The initial value of the deviation maximum 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.
[0026]
As described above, when the deviation maximum cylinder air-fuel ratio correction coefficient kcyl _(n) is updated in steps S11 and S12, the fuel injection amount by the injector 19 of the cylinder with the largest deviation is corrected in step S13. That is, the deviation maximum cylinder air-fuel ratio correction coefficient kcyl _(n) is reflected in the drive pulse width Tinj of the injector 19 of the maximum deviation 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). .
[0027]
In this manner, the deviation maximum cylinder air-fuel ratio correction coefficient kcyl _(n) is updated in the processes of steps S10, 11, 12, and 13 to correct the fuel injection amount. Accordingly, during the period in which the output of the A / F sensor 22 corresponds to the exhaust of each cylinder, the air-fuel ratio for each cylinder is detected a plurality of times, and the average deviation from the average air-fuel ratio is calculated. Can be accurately determined. Since the air-fuel ratio control amount is corrected in the direction in which the deviation decreases with respect to the cylinder having the largest deviation average, the variation in the air-fuel ratio can be eliminated with high accuracy. Further, the deviation integrated average value LAFSDA is calculated for each cylinder by integrating the deviation LAFSD and dividing by the number of integrations, so that the output of the A / F sensor 22 corresponds to the exhaust of each cylinder for each cylinder. Since the deviation from the average air-fuel ratio is monitored, the deviation of the air-fuel ratio for each cylinder can be determined with higher accuracy, and variations in the air-fuel ratio can be eliminated with higher accuracy.
[0028]
It is possible to perform the above process only when the absolute value of the largest deviation integrated average value LAFSDA is equal to or greater than the predetermined value B1. Further, when correcting the fuel injection amount by the injector 19 of the cylinder with the largest deviation, it is also possible to carry out a control that positively prohibits the correction of the air-fuel ratio with respect to the other cylinders. Convergence is improved.
[0029]
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. The deviation LAFSD is calculated and the deviation accumulated average value LAFSDA in the accumulated ranges R1, R3, R4, R2 set as the exhaust period for each cylinder is obtained, and the average air-fuel ratio of all the cylinders and the air-fuel ratio for each cylinder are calculated. The deviation maximum cylinder air-fuel ratio correction coefficient kcyl is updated for the cylinder having the maximum deviation integrated average value LAFSDA to correct the fuel injection amount.
[0030]
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 deviation of the air-fuel ratio (deviation integrated average value LAFSDA) due to the influence of the exhaust state of the cylinder can be accurately detected, and the deviation of each cylinder can be obtained appropriately. For each cylinder, the 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 integrated average value LAFSDA is obtained and the air-fuel ratio correction control of the cylinder having the maximum deviation integrated average value LAFSDA is performed, it is possible to accurately control with good convergence even in a state where exhaust of multiple cylinders is mixed.
[0031]
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 update process of the deviation maximum cylinder air-fuel ratio correction coefficient kcyl _(n) in steps S11 and S12. The predetermined value B2 is determined according to the magnitude of the deviation integrated average value LAFSDA. Or may be different between the rich side and the lean side, and may be changed according to the operating conditions (engine speed, load) of the engine 11.
[0032]
In addition, although the update process of the deviation maximum cylinder air-fuel ratio correction coefficient kcyl is the integral control, it may be PI control, PID control, differential control, or the like. For example, as an example of PID control:
Deviation maximum cylinder air-fuel ratio correction coefficient 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.
[0033]
Furthermore, if the maximum deviation cylinder air-fuel ratio control condition is not satisfied in step S3, the maximum deviation cylinder air-fuel ratio correction coefficient kcyl may be used for the maximum deviation cylinder immediately before that. 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. When the absolute value of the deviation integrated average value LAFSDA of a certain cylinder exceeds a predetermined value B1 for a predetermined number of times or more in several cycles (for example, about 10 to 200 cycles), the deviation maximum cylinder air-fuel ratio correction coefficient kcyl May be updated. Further, the predetermined value (threshold value) B1 may be changed according to the degree of deterioration of the catalyst, particularly the O ₂ storage capacity. For example, the predetermined value B1 may be decreased as the travel distance increases.
[0034]
【The invention's effect】
According to the air-fuel ratio control apparatus for an internal combustion engine of the present invention, the output of the air-fuel ratio detection means is detected a plurality of times in a period corresponding to the exhaust of each cylinder, and the average of the deviation from the average air-fuel ratio is calculated for each cylinder. Since the air-fuel ratio control amount is corrected in a direction in which the deviation decreases with respect to the cylinder having the largest average, the air-fuel ratio for each cylinder detected by the cylinder-by-cylinder air-fuel ratio detection means includes exhaust from other cylinders. The air / fuel ratio in the state is the air / fuel ratio due to the influence of the exhaust state by using the deviation from the average air / fuel ratio affected by the exhaust of all cylinders and correcting the air / fuel ratio for the cylinder with the largest deviation. The air-fuel ratio control amount of each cylinder can be properly controlled in a state in which the deviation is accurately detected. As a result, it is possible to accurately determine the deviation of the air-fuel ratio for each cylinder and eliminate the variation in the air-fuel ratio.
[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.
FIG. 4 is a graph showing the relationship between the output voltage of the linear A / F sensor and the air-fuel ratio.
[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)

Claims (2)

In an air-fuel ratio control apparatus for an internal combustion engine, having an air-fuel ratio detection means provided in an exhaust passage, and performing feedback control of the 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 deviation average calculating means for each cylinder for detecting an output of the air-fuel ratio detecting means a plurality of times in the period determined by the timing determining means for each cylinder and calculating an average of deviation from the average air-fuel ratio for each cylinder;
An air-fuel ratio control apparatus for an internal combustion engine, comprising: correction control means for correcting an air-fuel ratio control amount in a direction in which the deviation decreases with respect to a cylinder having the maximum deviation. In claim 1,
The cylinder-by-cylinder deviation average calculation means calculates the cylinder-by-cylinder deviation average by integrating the deviation between the output of the air-fuel ratio detection means and the average air-fuel ratio every predetermined calculation period in the period and dividing by the number of integrations. An air-fuel ratio control apparatus for an internal combustion engine, characterized in that:

Images