JPH0828251A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the generation of the phase difference of a control value during feedback of an air-fuel ratio at each cylinder group by detecting the control position difference of each cylinder group and correcting a control constant the control period of which is regulatable according to a phase difference. CONSTITUTION:Through feedback control of the air-fuel ratio of each cylinder group, the phase difference of a control value at each cylinder group is produced. Thus, since a phase difference is produced between the detecting values of first and second air-fuel ratio sensors 14 and 15, based on the phase difference of a detecting value, the phase difference of a control value is detected by a control phase difference detecting means. By correcting a control constant the control period of which is regulatable, correction is effected in a direction in which a phase difference is removed through correction of a control period, and a control period is also corrected. In this case, if a control phase difference detecting means is constituted to detect the phase difference of the control value based on a time difference with which the output value of an air-fuel ratio detecting means at each cylinder group passes a reference value and the fluctuation direction of an output value, it is discriminated whether the phase of other cylinder group is an advance phase or a delay phase based on a reference cylinder group and from the phase difference, the magnitude of the phase difference can be determined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine for purifying pollutants in exhaust gas by an exhaust gas purification catalyst while maintaining an air fuel ratio at a target air fuel ratio by air fuel ratio feedback control.

[0002]

2. Description of the Related Art In an internal combustion engine for a vehicle, an air-fuel ratio sensor detects the concentration of a predetermined component such as oxygen in the exhaust gas to detect the air-fuel ratio, and based on the air-fuel ratio detection signal, the target air-fuel ratio ( Generally, while feedback control is performed to the stoichiometric air-fuel ratio), CO, HC (unburned fuel components) in exhaust gas are exhausted by an exhaust purification catalyst carrying a catalyst having the highest purification efficiency when the air-fuel ratio is controlled in the vicinity of the target air-fuel ratio. ), NO _{x, and} other pollutants have become commonplace.

By the way, since the exhaust purification catalyst deteriorates due to exhaust heat or the like after a long period of use and its catalytic action deteriorates, there is a system in which the deterioration is diagnosed. In the case where the deterioration diagnosis is performed, an air-fuel ratio sensor is also provided on the downstream side of the exhaust purification catalyst, and the fact that the oxygen storage amount of the exhaust purification catalyst decreases as the deterioration progresses compared to when the exhaust purification catalyst is new is used. That is, while performing the air-fuel ratio feedback control based on the detection value from the upstream side air-fuel ratio sensor, based on the detection value of the downstream side air-fuel ratio sensor, for example, to increase or decrease the proportional amount in the air-fuel ratio feedback control When the control (hereinafter referred to as DOS control) is performed, the reversal period of the downstream air-fuel ratio sensor mounted on the downstream side of the exhaust purification catalyst is approximately proportional to the oxygen storage amount of the exhaust purification catalyst. The ratio of the frequency of the downstream air-fuel ratio sensor with respect to the frequency of the air-fuel ratio sensor increases, and the deterioration is diagnosed by comparing this ratio with a reference value.

The DOS control is not only for deterioration diagnosis but also for highly accurate air-fuel ratio feedback control by compensating for variations in the output characteristics of the upstream air-fuel ratio sensor with the downstream air-fuel ratio sensor. It is also done for the purpose. On the other hand, in an engine in which an upstream exhaust passage is connected to each cylinder group, such as a V-type engine, a horizontally opposed engine, or an engine having a dual exhaust manifold, an air-fuel ratio sensor is provided for each exhaust passage and each air passage is provided. There is one in which air-fuel ratio feedback control is independently performed for each cylinder group based on a detection value from a fuel ratio sensor. That is, the deviation of the air-fuel ratio due to the variation inherent in each cylinder group (spray characteristic of the fuel injection valve, etc.) is independently feedback-corrected for each cylinder group so that good air-fuel ratio control can be performed.

[0005]

However, in the case where the air-fuel ratio feedback control is independently performed by using the signal of the upstream side air-fuel ratio sensor corresponding to each cylinder group such as the V-type engine, the DOS control is performed. Meanwhile, if an attempt is made to perform a deterioration diagnosis of the exhaust purification catalyst, a phase shift of the air-fuel ratio feedback control may occur between the air-fuel ratio sensors for each of the cylinder groups due to the degree of progress of deterioration or product variation. In that case, in the exhaust gas that has merged on the downstream side, the rich / lean component of the exhaust gas from one cylinder group is canceled by the lean / rich component of the exhaust gas from the other cylinder group, and the exhaust gas introduced into the exhaust purification catalyst is theoretical. When it stabilizes near the air-fuel ratio, the air-fuel ratio sensor on the downstream side of the exhaust purification catalyst does not reverse for a long time, and even if the phase difference is small, the inversion cycle is prolonged due to that, so it can be distinguished from the cycle increase due to deterioration. Therefore, there is a drawback that an accurate deterioration diagnosis cannot be performed.

The present invention has been made in view of such conventional problems, and is provided with an air-fuel ratio detecting means for each cylinder group on the upstream side of the exhaust purification catalyst and also an air-fuel ratio detecting means on the downstream side of the exhaust purification catalyst. In an air-fuel ratio control device for an internal combustion engine including the above, it is an object to eliminate the phase difference of the control values in the air-fuel ratio feedback control for each cylinder group, and eventually to match the control cycle.

It is another object of the present invention to improve the accuracy of the deterioration diagnosis by performing the deterioration diagnosis of the exhaust purification catalyst in the state where there is no phase difference. Also, DO without phase difference
By performing the S control, it is an object to perform the air-fuel ratio feedback control with the highest possible accuracy for each cylinder group.
Furthermore, as a result, the ultimate aim is to enhance exhaust purification performance as much as possible.

[0008]

Therefore, according to the present invention, as shown by a solid line in FIG. 1, at least one of exhaust gas passages on the upstream side connected to each of a plurality of divided cylinder groups and each of these exhaust passages are connected. The exhaust passage connected to the downstream side is provided with air-fuel ratio detection means for detecting the air-fuel ratio of the engine intake air-fuel mixture by detecting a predetermined component in the exhaust gas, and the upstream-side air-fuel ratio detection means and the downstream side. An exhaust gas purification catalyst is provided between the air-fuel ratio detecting means and the air-fuel ratio is made to approach the target air-fuel ratio based on the detection values of the upstream side air-fuel ratio detecting means and the downstream side air-fuel ratio detecting means under at least a predetermined operating condition. In an air-fuel ratio control device for an internal combustion engine having an air-fuel ratio feedback control means for feedback control, the air-fuel ratio of each cylinder group based on the detection value of the air-fuel ratio detection means of the reference cylinder group under the predetermined operating conditions. Control phase difference detection means for detecting the phase difference between the control values of the reference cylinder group and the non-reference cylinder group while performing feedback control, and a direction for eliminating the phase difference based on the phase difference between the detected control values And a control constant correcting means for correcting a control constant capable of adjusting the control cycle in the air-fuel ratio feedback control of the non-reference cylinder group.

The control phase difference detecting means may determine the control value based on, for example, the time difference when the output value of the air-fuel ratio detecting means for each cylinder group passes the reference value and the increasing / decreasing direction of the output value. It can be configured to detect the phase difference. Further, the control constant corrected by the control constant correcting means may include, for example, an integration constant.

Further, the control constant corrected by the control constant correcting means may include a proportional constant, for example. Further, the reference cylinder group may be selected so as to be a cylinder group having a control phase difference on the advance side with respect to the non-reference cylinder group. Further, as shown by the chain line in FIG. 1, while performing the air-fuel ratio feedback control, the number of times the output value of the upstream side air-fuel ratio detecting means is reversed and the number of times the output value of the downstream side air-fuel ratio detecting means is reversed within a unit time. The exhaust gas purification catalyst may be configured to include catalyst deterioration diagnosis means for performing deterioration diagnosis of the exhaust purification catalyst based on the ratio.

[0011]

When the air-fuel ratio feedback control of each cylinder group is performed based on the detection value of the air-fuel ratio detecting means of the upstream reference cylinder group, deterioration of parts such as the fuel injection valve for each cylinder group and manufacturing variation can be caused. Causes a phase difference in control value for each cylinder group. When a phase difference in the control value is generated, a phase difference occurs in the detection value of the upstream side air-fuel ratio detection means between the reference cylinder group and the non-reference cylinder group, so the control phase difference detection means determines the phase difference between these detection values. Based on this, the phase difference between the control values is detected.

The control constant correcting means corrects the control constant capable of adjusting the control period in the air-fuel ratio feedback control of the non-reference cylinder group based on the detected phase difference of the control value to correct the control period. The correction is performed in the direction of eliminating the phase difference, whereby the phase difference is eliminated and the control period is also corrected at the same time. here,
The control phase difference detecting means is configured to detect the phase difference of the control value based on the time difference when the output value of the air-fuel ratio detecting means for each cylinder group passes the reference value and the increasing / decreasing direction of the output value. For example, it is possible to determine whether the phase of the other cylinder group with respect to the reference cylinder group is the lead phase or the lag phase depending on the increasing / decreasing direction of each output value, and the magnitude of the phase difference can be obtained from the time difference.

In the case where the control constant for correcting the control phase difference is configured to include the integration constant, the integration constant is increased or decreased to reduce or increase the control cycle while eliminating the control phase difference. You can make corrections. Similarly, when a proportional constant is included as the control constant for correcting the control phase difference, the proportional constant is increased or decreased to reduce or increase the control cycle while eliminating the control phase difference. You can do it.

Further, if the reference cylinder group is selected so that the control phase difference is on the advance side with respect to the non-reference cylinder group, the correction is performed only in the phase advance direction. Therefore, it is possible to perform correction in the direction of improving the response delay of the air-fuel ratio feedback control. Further, according to the catalyst deterioration diagnosing means, the output of the downstream side air-fuel ratio detecting means relative to the number of reversals of the output value of the upstream side air-fuel ratio detecting means within a unit time due to the oxygen storage amount of the exhaust purification catalyst which decreases with the progress of deterioration. Since the ratio of the number of times of inversion of the value increases, it can be performed based on the ratio of the times of inversion. By correcting the deterioration diagnosis performance in the direction of eliminating the control phase difference, the rich / lean of the air-fuel ratio is not canceled between the cylinder groups, so that the deterioration diagnosis performance can be favorably maintained.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 2 showing the configuration of one embodiment, an air flow meter 3 for detecting an intake air flow rate Q and a throttle valve 4 for controlling the intake air flow rate Q in conjunction with an accelerator pedal are provided in an intake passage 2 of a V-type internal combustion engine 1. An electromagnetic fuel injection valve 5 is provided for each cylinder in the downstream manifold portion.

The fuel injection valve 15 is opened and driven by an injection pulse signal from a control unit 6 having a built-in microcomputer, and is fuel-fed from a fuel pump (not shown) to be supplied under pressure controlled by a pressure regulator. . Further, a water temperature sensor 7 for detecting the cooling water temperature Tw in the cooling jacket of the engine 1 is provided.

On the other hand, in the exhaust passage, the cylinder group of one of the V-shaped banks is the first cylinder group, and the cylinder group of the other bank is the second cylinder group, and the exhaust passages on the upstream side, respectively. 8 and 9 are connected, and the downstream side of these upstream side exhaust passages 8 and 9 merge to form one exhaust passage 10. Preliminary exhaust purification catalysts 11 and 12 are mounted in the exhaust passages 8 and 9 on the upstream side, respectively, and a main exhaust purification catalyst 13 is mounted to the exhaust passage 20 on the downstream side. Further, the first air-fuel ratio sensor 14 as an air-fuel ratio detecting means for detecting the air-fuel ratio by detecting the oxygen concentration in the exhaust gas upstream of the preliminary exhaust gas purification catalysts 11, 12 in the upstream side exhaust passages 8, 9 respectively. Second
The air-fuel ratio sensor 15 is attached, and a third air-fuel ratio sensor 16 as an air-fuel ratio detecting means is also attached downstream of the main exhaust purification catalyst 13 in the downstream side exhaust passage 10. The exhaust purification catalysts 11 to 13 are used to oxidize CO and HC in the exhaust gas and NO.
A three-way catalyst that reduces and purifies _X is used.

Further, the distributor (not shown) has a built-in crank angle sensor 17, which counts a crank unit angle signal output from the crank angle sensor 17 in synchronization with the engine rotation for a certain period of time, or The engine speed N is detected by measuring the cycle of the reference angle signal. Then, the control unit 6 controls the fuel injection amount according to the operating state based on the detection signals from the various sensors to perform the air-fuel ratio control, while the exhaust purification catalysts 11 to 13 are controlled as described later. When the deterioration diagnosis is performed and it is determined that the exhaust purification catalyst is deteriorated, the warning lamp 18 is turned on.

Next, various control routines by the control unit 6 will be described with reference to the flowcharts shown in the drawings. FIG. 3 shows a fuel injection amount setting routine, which is performed at predetermined intervals (for example, every 10 ms). In step (denoted as S in the figure) 1, the intake air amount per unit rotation is calculated based on the intake air flow rate Q detected by the air flow meter 3 and the engine speed N calculated based on the signal from the crank angle sensor 17. Fuel injection amount T equivalent to
Calculate _P by the following formula.

T _P = K × Q / N (K is a constant) In step 2, in order to enrich various correction factors COEF and the air-fuel ratio during acceleration on the basis of the cooling water temperature Tw detected by the water temperature sensor 17, etc. Acceleration increase correction coefficient KACC,
A fuel cut coefficient KFC set to 0 to stop fuel supply at a predetermined deceleration, a fuel adhesion correction coefficient KX for correcting the influence of adhered fuel on the intake manifold wall, and an injection of the fuel injection valve 15 due to battery voltage fluctuations. The voltage correction amount T _S for correcting the flow rate change is set.

In step 3, the cylinder group to which the latest fuel-injected cylinder belongs is determined. If it is determined to be the first cylinder group, the process proceeds to step 4, and if it is determined to be the second cylinder group, the process proceeds to step 5, and the air-fuel ratio feedback correction set by the air-fuel ratio feedback correction coefficient setting routine described later is performed. The coefficient ALPHA1 (for the first cylinder group) or ALPHA2 (for the second cylinder group) and the learning correction coefficient KBLRC learned so that the center value of the air-fuel ratio feedback correction coefficient that varies for each cylinder group approaches the reference value.
1 (for the first cylinder group) or KBLRC2 (for the second cylinder group;
The learning correction coefficient KBLRC1 of the first cylinder group is calculated by adding a learned value of a feedback correction coefficient for phase difference correction described later).

Further, when it is determined that the cylinder group is the first cylinder group, the routine proceeds to step 6, where the final fuel injection amount (fuel supply amount) T _i
1 is calculated according to the following equation. That is, the fuel injection amount T _i 1 of the first cylinder group is T _i 1 = T _P × ALPHA1 × KBLRC1 × (COE
F + KACC) × KFC × KX Further, when it is determined that the cylinder group is the second cylinder group, the process proceeds to step 7, and the final fuel injection amount T _I 2 is similarly calculated according to the following equation.

T _i 2 = T _P × ALPHA 2 × KBLRC
2 × (COEF + KACC) × KFC × KX In step 8, the calculated fuel injection amount T _i 1 or T _i
2 is set in the output register. As a result, when the predetermined fuel injection timing of engine rotation synchronization is reached,
A drive pulse signal having a pulse width of the calculated fuel injection amount T _i 1 or T _i 2 is given to the corresponding fuel injection valve 5 to perform fuel injection.

Next, the air-fuel ratio feedback correction coefficient setting routine will be described with reference to FIGS. This routine is executed in synchronization with the engine rotation. This function corresponds to the air-fuel ratio feedback control means. Step 101
Then, it is determined whether or not the air-fuel ratio feedback control condition is satisfied. In the case of NO, the routine proceeds to step 102, where the feedback correction coefficients ALPHA1,2 are fixed to 1 and the feedback control is stopped.

In step 103, the output value OSR1 of the air-fuel ratio sensor 14 on the first cylinder group side and the output value OSR3 of the air-fuel ratio sensor 16 on the downstream side of the exhaust purification catalyst are input. Step 10
At 4, OSR1 is compared with the reference value SLF, and OSR1 ≦
In the case of SLF, the air-fuel ratio is judged to be lean and step 105
Then, the rich / lean discrimination flag F1 is reset to 0, and if OSR1> SLF, the air-fuel ratio is judged to be rich, and the routine proceeds to step 106, where the flag F1 is set to 1, and then the routine proceeds to step 107.

At step 107, it is judged whether or not the flag F1 is inverted. If YES, the value of the flag F1 is determined in step 108, and in the rich determination that F1 is 1, in step 109, the feedback correction coefficient ALPHA1 of the first cylinder group is subtracted from the proportional correction amount P _L in the lean correction direction. It is updated with a value obtained by adding a proportional correction amount PHOS (which takes positive and negative values) obtained based on the detection result of the downstream side air-fuel ratio sensor 16 described later. Next, the routine proceeds to step 110, where the air-fuel ratio correction amount ALPHA2 'for correcting the phase difference between the second cylinder group and the later-described first cylinder group is adjusted based on the phase difference as described later from the previous value. It is updated with a value obtained by subtracting the proportional amount P ₂ of.

When the lean judgment that F1 is 0 is made in step 107, the feedback correction coefficient AL is made in step 111.
After updating PHA1 with a value obtained by adding the proportional P _R in the rich correction direction and the proportional correction amount PHOS,
At 112, the air-fuel ratio adjustment amount ALP for phase difference correction of the second cylinder group
HA2 ′ is updated with the value obtained by adding the proportional amount P ₂ to the previous value.

On the other hand, if it is determined in step 107 that the flag F1 is not inverted, the process proceeds to step 113, where F
At the time of rich judgment of 1 being 1, in step 114, the feedback correction coefficient ALPHA1 is set to the integral amount I _{L in the} lean correction direction.
Is updated with a value obtained by subtracting, and then the routine proceeds to step 115, where the air-fuel ratio correction amount ALPHA2 ′ for phase difference correction of the second cylinder group
Is updated with a value obtained by subtracting the integral I ₂ for adjustment set based on the phase difference as described later from the previous value.

If F1 is 0 in step 113, the feedback correction coefficient ALP is determined in step 116.
After updating HA1 with a value obtained by adding the integral I _R in the rich correction direction, the routine proceeds to step 117, where the air-fuel ratio correction amount ALPHA2 'for phase difference correction of the second cylinder group is integrated from the previous value for phase difference adjustment. Update with the value obtained by adding I ₂ . After the air-fuel ratio correction amount ALPHA2 'for phase difference correction of the second cylinder group is set in each of steps 110, 112, 115 and 117 in this way, the process proceeds to step 118 to set the final feedback correction amount ALPHA2 of the second cylinder group to the first value. It is set to a value obtained by adding the feedback correction amount ALPHA2 ′ for phase difference correction to the feedback correction amount ALPHA1 of the cylinder group.

As described above, the air-fuel ratio A for phase difference correction is set.
Setting LPHA2 ′ separately and adding it to the feedback correction amount ALPHA1 of the first cylinder group is used to set the feedback correction amount ALPHA1 of the first cylinder group in setting the feedback correction amount ALPHA2 of the second cylinder group. This is equivalent to setting the proportional component P and the integral component I by using the proportional component P ₂ and the integral component which are respectively corrected by the proportional component P ₂ and the integral component I ₂ for phase difference correction.

That is, in this way, by correcting the proportional component and the integral component for setting the feedback correction amount of the second cylinder group by the proportional component P ₂ and the integral component I ₂ for the control phase difference correction, the control speed is changed. It is accelerated and the response delay is corrected. However, as will be described later, when the second cylinder group is ahead of or in phase with the first cylinder group, the proportional component P ₂ and the integral component I ₂ are set to 0 and are substantially corrected. Is not done.

Next, in step 119, the flag F1 is set.
It is judged whether or not the value of is reversed, and if it is reversed, the routine proceeds to step 120, where the third air-fuel ratio sensor 16 on the downstream side is
The AD conversion value OSR3 of is compared with the reference value SLR. When it is determined that OSR3 ≦ SLR, the exhaust purification catalyst
13 It is determined that the air-fuel ratio detected from the exhaust components on the downstream side is lean, and the routine proceeds to step 121, where PHOS is set to a predetermined amount Δ.
Update with the value obtained by adding PHOS (> 0), and step 122
When it is determined that OSR2> SLR in step 122, the process proceeds to step 122, and PHOS is updated with a value obtained by subtracting a predetermined amount ΔPHOS.

FIG. 6 shows a routine for detecting a control phase difference between the first cylinder group and the second cylinder group and setting a proportional component and an integral component for correcting the phase difference. This routine is executed while the routines shown in FIGS. 4 and 5 are being executed. Step 20
At 1, it is determined whether the output value OSR1 of the first air-fuel ratio sensor 14 has passed a predetermined reference value, that is, whether the output value OSR1 has changed from the reference value to the rich side to the lean side or from the lean side to the rich side. In this case, the reference value may be the same as the reference value SLF for rich / lean determination in the normal air-fuel ratio feedback control. In that case, the output value OSR1 and the reference value SLF are the same as in the air-fuel ratio feedback control. The value of the flag F1 may be distributed and set according to the size while comparing, and determination may be made depending on whether or not the value of the flag F1 is inverted.

When the value of the flag F1 is inverted, it is determined that the reference value SLF has been passed, and in step 202 a timer TIM for measuring the elapsed time after passing the reference value is started. Next, at step 203, it is similarly determined whether or not the output value OSR2 of the second air-fuel ratio sensor 15 has passed the same reference value SLF as described above. Further, in step 204, the first
Direction of the air-fuel ratio sensor 14 of the second air-fuel ratio sensor (from rich to lean or lean to rich) and the second air-fuel ratio sensor
It is determined whether or not 15 passes through the reference value in the same direction. This is the value of the flag F1 before the inversion of the first air-fuel ratio sensor 14 or after the determination, and the second air-fuel ratio sensor 15 set in the same manner.
It can be determined by whether or not the value of the flag F2 before or after the inversion is the same.

When it is determined that the reference value passing directions of the air-fuel ratio sensors are the same, the value of the timer TIM, that is, the second value after the first air-fuel ratio sensor 14 has passed the reference value. The elapsed time until the air-fuel ratio sensor 15 passes the reference value in the same direction is read. This elapsed time corresponds to the control phase difference between the first cylinder group and the second cylinder group. It is considered that this control phase difference occurs due to the difference in response speed of each air-fuel ratio sensor.However, in order to eliminate the control phase difference, adjusting the control cycle to the air-fuel ratio sensor on the slower response speed side is Is not preferable. So step 205
Then, the control phase difference is compared with a predetermined value, and when it is larger than the predetermined value, it is determined that the second air-fuel ratio sensor 15 has a faster response speed than the first air-fuel ratio sensor 14 and the phase advances. In step 206, the values of the proportional component P ₂ and the integral component I ₂ for the control phase difference correction of the second cylinder group are set to 0 to prohibit the control phase difference correction. The predetermined value for this determination may be set in advance by the control cycle according to the operating condition for executing the air-fuel ratio feedback control, but the average value of the control cycle of the air-fuel ratio sensor 14 during the air-fuel ratio feedback control is set. If it is calculated and set to, for example, about 3/4 of the periodic average value and the elapsed time is longer than that, it is determined that the phase of the second air-fuel ratio sensor 15 is advanced. You may.

If the elapsed time is less than the predetermined value, the step
207 to respond to the elapsed time, that is, the control delay of the second cylinder group.
P for proportional phase difference correction₂, Integral I₂Figure 7
Search from the characteristic map as shown in. I will show in the characteristics
As shown in FIG.₂And product
Minute I₂By increasing the
Steps 110, 112, 115, 117 during fuel ratio feedback control
Proportional P given by ₂And integral I₂By Figure 8
As shown by the dotted line, the control speed increases and the control cycle shortens.
As a result, the control phase difference disappears. This will be described later.
In the exhaust catalyst deterioration diagnosis,
Of the air-fuel ratio of the exhaust gas from each cylinder group
Due to the offsetting of Litchi lean, the air-fuel ratio is constantly close to the theoretical air-fuel ratio.
It is possible to prevent inability to diagnose due to
Can be kept.

In this embodiment, only the second cylinder group side is corrected. Therefore, the correction phase is corrected only when the control phase on the second cylinder group side is delayed. However, the control phase on the second cylinder group side is corrected. Is more advanced, the proportional component P ₁ and the integral component I ₁ for phase difference correction during the air-fuel ratio feedback control on the first cylinder group side.
May be corrected so that the phase delay side is aligned with the lead side so that the phase correction can always be performed.

FIG. 9 shows a routine for judging the deterioration diagnosis condition of the exhaust purification catalyst. In the figure, in step 11, the engine cooling water temperature T _W is equal to or higher than a predetermined value, or in steps 12 to 15
Then, it is determined whether the vehicle speed VSP, the basic fuel injection amount T _P , the engine rotation speed N, and the vehicle speed change amount ΔVSP are within their respective set ranges. Further, at step 16, the air-fuel ratio shown in FIG. Whether the control for correcting the proportional P based on the detection value of the sensor 16 (hereinafter referred to as DOS control) is being executed, the throttle opening is at a predetermined value or more in step 17, and the deterioration diagnosis of the exhaust purification catalyst is currently in operation in step 18. It is determined whether or not each of them has been performed, and when all the conditions are satisfied, it is determined that the diagnostic condition is satisfied, and the diagnostic execution flag FLGCAT is set to 1 in step 19, and any condition is not satisfied. At this time, the diagnosis execution flag FLGCAT1 is reset to 0 in step 20 because the diagnosis condition is not satisfied. That is, the engine operation and the vehicle running state are both in a steady state, the exhaust gas flow rate and the temperature are sufficiently stable, that is, the high diagnostic accuracy is obtained, and the diagnosis is started during the DOS control in which the diagnosis can be performed. . In addition, the phase correction is performed only on the second cylinder group side as in the above-described embodiment,
If the phase correction is prohibited when the phase of the cylinder group is advanced, if the advance of the phase is larger than a predetermined amount, the diagnosis accuracy is deteriorated due to the phase shift, so the diagnosis is prohibited. You may do it.

The diagnostic execution flag FLGCAT is
After the ignition switch is turned on and the starter switch is turned on during the next operation, it is reset to 0.
Next, a deterioration diagnosis routine of the exhaust purification catalyst will be described according to the flowchart shown in FIG. In step 21, it is judged whether or not the diagnosis execution flag FLGCAT1 is set to 1. If not, this routine is ended, and if it is set to 1, the process proceeds to step 22.

In step 22, the previous diagnosis execution flag F
It is determined whether the value of LGCAT1 is 0. When the previous value is 0 and the current value is 1, the deterioration diagnosis is started. First, in step 23, the inversion counter CNTF for counting the number of times the output value OCR1 of the air-fuel ratio sensor 14 on one cylinder group side, for example, the first cylinder group side, is started to be counted, and at the same time, the third empty space on the downstream side is started. The inversion counter CNTR for counting the number of inversions of the output value OCR3 of the fuel ratio sensor 16 is started.

In step 24, the timer CNTTIM for measuring the monitoring time of the number of inversions is started. When the count of the number of times of inversion is started in this way, the process proceeds from step 22 to step 25 after the second time, and it is determined whether or not the count value of the timer CNTTIM has reached a predetermined value corresponding to the inversion number monitoring time. Then
When it reaches, the routine proceeds to step 26, where after the count value of the timer CNTTIM is cleared, the routine proceeds to step 27 where the ratio of the number of reversals of the upstream side first cylinder group air-fuel ratio sensor 14 to the number of reversals of the downstream side air-fuel ratio sensor 16 RBK = (CNTF / CNT
R) is calculated.

At step 28, it is judged whether or not the reversal number ratio RBK is equal to or more than a predetermined value which is a reference for deterioration diagnosis, and when it is judged that it is more than the predetermined value, the routine proceeds to step 29,
It is diagnosed that the exhaust purification catalyst 13 is deteriorated, and the failure diagnosis flag CATNGFLG is set to 1. Meanwhile, step
If it is determined at 28 that the reversal ratio RBK is less than the predetermined value, the routine proceeds to step 30, where it is diagnosed that the exhaust purification catalyst 13 has not deteriorated, and CATNGFLG is set to 0.

Finally, in step 31, the values of the respective inversion counters CNTF and CNTR are cleared in preparation for the next diagnosis. In this way, since the deterioration diagnosis is performed after eliminating the control phase difference between the two cylinder groups, the diagnosis cannot be performed or the diagnosis accuracy is deteriorated due to the rich / lean phase shift of the combined exhaust on the downstream side. It can be prevented.

Even when the deterioration diagnosis is not performed as described above, the air-fuel ratio feedback control is independently performed for each cylinder group by using the air-fuel ratio sensor provided for each cylinder group and the downstream air-fuel ratio sensor. Also in the DOS control, since the control phase difference between the cylinder groups is eliminated, the control accuracy is improved and the exhaust gas purification performance can be improved as much as possible.
Further, as the control constant capable of adjusting the control period for correcting the control phase difference, only one of the proportional component and the integral component may be corrected.

[0045]

As described above, according to the present invention, the control phase difference for each cylinder group is detected, and the control constants such as the integral and proportional parts for which the control cycle can be adjusted are corrected according to the phase difference. As a result, the control phase difference between the cylinder groups and the control cycle can be eliminated. As a result, the DOS while performing the air-fuel ratio feedback control without the difference between the cylinder groups with respect to the inherent variation among the cylinder groups. The accuracy of control can be improved, and good diagnostic performance can be ensured in the case where the deterioration diagnosis of the exhaust purification catalyst is performed in the inversion cycle of the air-fuel ratio on the upstream side and the downstream side.

Further, while the control constant correcting means feedback-controls the air-fuel ratio of the cylinder group based on the detection value of the upstream side air-fuel ratio detecting means of one cylinder group serving as a reference,
With the configuration in which the control constant of the cylinder group whose phase is on the delay side is corrected, correction in the direction of improving the response delay of the air-fuel ratio feedback control can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration and functions of the present invention.

FIG. 2 is a system configuration diagram of an embodiment of the present invention.

FIG. 3 is a flowchart showing a fuel injection amount control routine of the above embodiment.

FIG. 4 is a flowchart showing a front part of an air-fuel ratio feedback correction coefficient setting routine.

FIG. 5 is a flowchart showing the latter part of the air-fuel ratio feedback correction coefficient setting routine.

FIG. 6 is a flowchart showing a control phase difference detection routine.

FIG. 7 is a characteristic map of an integral part for similarly correcting the control phase difference.

FIG. 8 is a time chart showing a state of control phase difference correction control according to the embodiment.

FIG. 9 is a flowchart showing the same and a deterioration diagnosis condition determination routine.

FIG. 10 is a flowchart showing an embodiment of a deterioration diagnosis routine.

[Explanation of symbols]

 1 V type internal combustion engine 5 Fuel injection valve 6 Control unit 8, 9 Upstream exhaust passage 10 Downstream exhaust passage 11, 12 Preliminary exhaust purification catalyst 13 Main exhaust purification catalyst 14 First air-fuel ratio sensor 15 Second air-fuel ratio sensor 16 Third air-fuel ratio sensor

Claims (6)

[Claims] 1. Detection of a predetermined component in exhaust gas in an upstream exhaust passage connected to each of a plurality of divided cylinder groups and an exhaust passage connected to a downstream side of each exhaust passage. And an air-fuel ratio detecting means for detecting the air-fuel ratio of the engine intake air-fuel mixture by means of the exhaust gas purifying catalyst between the upstream side air-fuel ratio detecting means and the downstream side air-fuel ratio detecting means. An air-fuel ratio control device for an internal combustion engine, comprising an air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio to approach the target air-fuel ratio based on the detection values of the side air-fuel ratio detection means and the downstream side air-fuel ratio detection means, While performing air-fuel ratio feedback control of each cylinder group based on the detection value of the air-fuel ratio detection means of the reference cylinder group under a predetermined operating condition, the phase difference between the control values of the reference cylinder group and the non-reference cylinder group. Inspection Control phase difference detecting means for controlling the control constant in the air-fuel ratio feedback control of the non-reference cylinder group in the direction of eliminating the phase difference based on the detected phase difference of the control value. An air-fuel ratio control device for an internal combustion engine, comprising: 2. The control phase difference detection means determines the phase difference between the control values based on the time difference when the output value of the air-fuel ratio detection means for each cylinder group passes a reference value and the increasing / decreasing direction of the output value. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio control device detects the air-fuel ratio. 3. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the control constant corrected by the control constant correction means includes an integration constant. 4. The air-fuel ratio control of an internal combustion engine according to claim 1, wherein the control constant corrected by the control constant correction means includes a proportional constant. apparatus. 5. The reference cylinder group is selected to be a cylinder group having a control phase difference on the advance side with respect to a non-reference cylinder group. An air-fuel ratio control device for an internal combustion engine according to one. 6. The air-fuel ratio feedback control is performed, and based on the ratio between the number of times the output value of the upstream side air-fuel ratio detecting means is inverted and the number of times the output value of the downstream side air-fuel ratio detecting means is inverted within a unit time. The air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 5, wherein the air-fuel ratio control device includes a catalyst deterioration diagnosing means for diagnosing deterioration of the exhaust purification catalyst.