JPH01134046A - Air-fuel ratio controller - Google Patents

Abstract

PURPOSE:To solve a problem of slippage so quickly by increasing or decreasing an amount of supply fuel after an air-fuel ratio controlled variable made by an air-fuel ratio sensor at the downstream side of its catalyzer is reached to the guard value at one side of two banks with no air-fuel ratio sensor at the upstream side of the catalyzer, in the case where each air-fuel ratio in these two banks is slipped off. CONSTITUTION:A first means A adjusts an air-fuel ratio at a first bank on the basis of each output from respective air-fuel ratio sensors at both upstream and downstream sides of a first ternary catalyzer in the first bank. On the other hand, a means B operates an air-fuel ratio compensation value at a second bank on the basis of output out of the air-fuel ratio sensor at the downstream side of a second ternary catalyzer in the second bank. Likewise, a means C guards the air-fuel ratio compensation value to be within the range of specified tolerance, while a means D discriminates whether the air-fuel ratio compensation value is reached to the guard value or not. Then, a second means E adjusts the air-fuel ratio at the second bank on the basis of the air-fuel ratio compensation value and each output of respective air-fuel ratio sensors at the first bank, in accordance with a fact that whether the air-fuel ratio compensation value is reached to the guard value or not.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an air-fuel ratio control device for an internal combustion engine having two banks, such as a V-type or horizontally opposed type.

[Conventional technology]

Air-fuel ratio feedback control using an air-fuel ratio sensor (in this specification, oxygen concentration sensor (OX sensor)) is as follows:
There are a single 0□ sensor system based on a single 02 sensor and a double 02 sensor system based on two 0□ sensors installed upstream and downstream of the catalyst. −
There are two types: one type in which the 02 sensor is installed upstream of the medium, and another type in which the 02 sensor is installed downstream of the catalyst.

In the single 02 sensor system in which the 0□ sensor is installed upstream of the catalyst, the 0□ sensor is installed at a location in the exhaust system as close to the combustion chamber as possible, that is, at the collection point of the exhaust manifold upstream from the catalytic converter. For example, the reversal timing of the 02 sensor is shifted due to the presence of 0□ even though the air-fuel ratio is rich, and in a multi-cylinder engine, the influence of air-fuel ratio variations between cylinders. Therefore, the 0□ sensor cannot detect the average air-fuel ratio, and as a result, the accuracy of controlling the air-fuel ratio is low.

On the other hand, in a single 0□ sensor system in which the 0□ sensor is installed downstream of the catalyst, the unbalanced degree of exhaust gas and non-detection of the average air-fuel ratio are resolved, but the position of the OT sensor is far from the exhaust valve. In addition, the responsiveness of the 0□ sensor is low due to the capacity of the catalyst and the purification performance (02 storage effect, etc.), and therefore the responsiveness of the air-fuel ratio feedback control system deteriorates, resulting in the catalyst not being able to fully demonstrate its performance. This will lead to worsening of emissions.

In addition, double 0□ with 02 sensors installed upstream and downstream of the catalyst.
In the sensor system, in addition to air-fuel ratio feedback control by the upstream 0□ sensor, air-fuel ratio feedback control is performed by the downstream 0□ sensor. For example, the downstream 0□ sensor detects the average air-fuel ratio, and the result is reflected in the value of the skip amount, etc. of the air-fuel ratio feedback control by the upstream 02 sensor, thereby controlling the overall air-fuel ratio. Therefore, as long as the downstream Oz sensor maintains stable output characteristics, good exhaust emissions are guaranteed.

However, if the double 02 sensor system described above is applied to an internal combustion engine with two banks, such as a type or horizontally opposed type, four 0□ sensors are required, and a complicated control circuit is required for this purpose. do.

For this reason, the applicant has proposed an irregular double 0□ sensor system in which, for example, the right bank is provided with 02 sensors upstream and downstream of the catalyst, and the left bank is provided with a 0□ sensor only downstream of the catalyst ( Reference: Jitsugan Sho 62-1151
No. 4). In other words, the air-fuel ratio control of the first bank, which is the right bank, uses the double 0□ sensor system described above, but the air-fuel ratio control of the second bank, which is the left bank, uses the 02 sensor upstream of the catalyst of the first bank. An irregular double 02 sensor system is adopted based on the output and the output of the 02 sensor of the main stream of the catalyst in the second bank.

[Problems to be Solved by the Invention] However, in the left bank employing the irregular double 02 sensor system described above, the air-fuel ratio control of the left bank is also performed based on the air-fuel ratio of the right bank. Even if there is a deviation due to variations in fuel injection valves, etc., the deviation in the air-fuel ratio of the left bank must be corrected by the output of the 0□ sensor downstream of the catalyst. However, there is a certain guard on the control of the skip amount etc. by the catalyst downstream 02 sensor (reference: Japanese Patent Application Laid-Open No. 61-234241).
), therefore, the control air-fuel ratio cannot be changed significantly, that is, only fine adjustments can be made. As a result, if the air-fuel ratio difference between the left and right banks is large, the 02
There is a problem that the air-fuel ratio of the left bank, which is not equipped with a sensor, is deviated for a long period of time, leading to deterioration of emissions during this period.

Therefore, an object of the present invention is to provide a double air-fuel ratio sensor system for an internal combustion engine having two or more banks that prevents deterioration of emissions.

[Means for solving problems]

A means for solving the above-mentioned problems is shown in FIG. In FIG. 1, a case of an internal combustion engine having two or more banks, such as a ■-type, horizontally opposed type, etc., is shown. That is, first and second three-way catalysts CCR are installed in the exhaust passages of each bank of an internal combustion engine divided into at least first and second banks.
O is provided. In the exhaust passage upstream of the first three-way catalyst CCRO, there is a first
An upstream air-fuel ratio sensor for the bank is provided, and a downstream air-fuel ratio sensor for the first bank is provided in the exhaust passage downstream of the first three-way catalyst CCR8 to detect the air-fuel ratio of the first bank. Further, a downstream air-fuel ratio sensor for the second bank is provided in the exhaust passage downstream of the second three-way catalyst to detect the air-fuel ratio of the second bank. The first air-fuel ratio adjustment means adjusts the air-fuel ratio of the first bank according to an output V of the first bank upstream air-fuel ratio sensor and an output V2 of the first bank downstream air-fuel ratio sensor. do.

On the other hand, the air-fuel ratio control amount calculation means controls the second bank air-fuel ratio jBiik, for example, skip 1RsRL, according to the output V2' of the second bank downstream air-fuel ratio sensor.

RSLL is calculated, and the guard means guards the second bank air-fuel ratio control 1R3RL, RSLL within a predetermined allowable range. Furthermore, the guard value determining means determines whether the second bank air-fuel ratio control amount is 1? It is determined whether sRL and RSLL have reached a guard value within a predetermined tolerance range. As a result, the second
The air-fuel ratio adjusting means controls the second bank air-fuel ratio control amount R5.
When RL and RSLL have not reached the guard value in the predetermined tolerance range, the second bank air-fuel ratio control amount R5R
L, RSLL and the fuel amount according to the output ■1 of the upstream side air-fuel ratio sensor for the first bank is supplied to the second bank to adjust the air-fuel ratio of the second bank; When the air-fuel ratio control amounts R5RL, RSLL for the second bank reach the guard value within a predetermined range, the guarded air-fuel ratio control amounts R5RL, RSLL for the second bank and the output of the upstream air-fuel ratio sensor for the first bank ■1 The air-fuel ratio of the second bank is adjusted by increasing or decreasing the amount of fuel corresponding to the amount of fuel, for example, by increasing or decreasing the basic fuel amount.

[For production]

According to the above means, even if the air-fuel ratios of the first and second banks differ greatly, the air-fuel ratio downstream of the catalyst is Air-fuel ratio control amount R5RL, R by fuel ratio sensor
After the SLL reaches the guard value, the supplied fuel amount is directly increased or decreased, so that the deviation in the controlled air-fuel ratio is rapidly recovered.

〔Example〕

FIG. 2 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. In FIG. 2, the cylinders of the engine main body 1 are shown in a V-shape arranged in two rows, and an air flow meter 3 is provided in the intake passage 2 of the engine main body 1. The air flow meter 3 directly measures the intake air amount, has a built-in potentiometer, and generates an analog voltage output signal proportional to the intake air amount. This output signal is supplied to an A/D converter 101 with a built-in multiplexer of the control circuit 10. The distributor 4 has a crank angle sensor 5 whose shaft generates a reference position detection pulse signal every 720 degrees in terms of crank angle, and a crank angle sensor 5 which generates a reference position detection pulse signal every 30 degrees in terms of crank angle. A crank angle sensor 6 is provided. These pulse signals from the crank angle sensor 5.6 are supplied to the input/output interface 102 of the control circuit 10, and the output from the crank angle sensor 6 is supplied to an interrupt terminal of the CPU 103.

Further, the intake passage 2 is provided with a fuel injection valve 7 for supplying pressurized fuel from a fuel supply system to the intake port for each cylinder.

Further, a water temperature sensor 9 for detecting the temperature of cooling water is provided in the water jacket 8 of the cylinder block of the engine body 1. Water temperature sensor 9 indicates cooling water temperature TH
Generates an analog voltage electrical signal according to W. This output is also supplied to the A/D converter 101.

Right bank and left bank exhaust manifold 11R, I
In the exhaust system downstream from the IL, 3 in the exhaust gas is
A catalytic converter 12R912L is provided that houses a three-way catalyst that simultaneously purifies the three toxic components IC, Co, and NO.

A first O2 sensor 13 is provided in the right bank exhaust manifold IIR, that is, on the upstream side of the catalytic converter 12R, and an exhaust pipe 14 on the downstream side of the catalytic converter 12R.
R is provided with a second 02 sensor 15R. On the other hand, in the left bank, the 0□ sensor 15L is provided only in the exhaust pipe 14L downstream of the catalytic converter 12L. 0□Sensor 13, 15R.

15L generates an electric signal according to the oxygen component concentration in the exhaust gas. That is, 0□ sensor 13.15R.

15L outputs different output voltages depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.
occurs in converter 101. The control circuit 10 is configured as a microcomputer, for example, and includes an A/D converter 10.
1. In addition to the input/output interface 102 and the CP[1103, a ROM 104, a RAM 105, a backup RAM 106, a clock generation circuit 107, etc. are provided.

Further, the throttle valve 16 of the intake passage 2 is provided with an idle switch 17 for detecting whether the throttle valve 16 is fully closed, and this output signal is supplied to the input/output interface 102 of the control circuit 10. Ru.

Further, in the control circuit 10, a down counter 108R
, flip-flop 109R1 and drive circuit 110R
is for controlling the right bank fuel injection valve 7R, down counter 108L, flip-flop 109
L, and the drive circuit 110L are the fuel injection valves 7 of the left bank.
This is to control L.

That is, in the routine described later, the fuel injection amount TAU
When R(TAUL) is calculated, fuel injection l TAUR
(TAIL) is down counter 108R (108L
) and the flip-flop 109R
(109L) is also set. As a result, the drive circuit 11
0 R (110L) starts energizing the fuel injection valve 7R (7L). On the other hand, down counter 108 R (108
L) is a coefficient of a clock signal (not shown), and when its carrier terminal finally reaches the "1" level, the flip-flop 109R (109L") is turned on and the drive circuit 110R (IIOL) is turned on. Fuel injection valve 7R (
7L) is stopped. In other words, the above fuel injection amount T
The fuel injection valve 7R (7L) is energized by AUR (TAUL), and therefore, the amount of fuel corresponding to the fuel injection amount TAUR (TAIL) is sent into the fuel chamber of each bank of the engine body 1.

Note that the interrupt generation of the CPU 103 is caused by the A/D converter 10.
When the A/D conversion of step 1 is completed, the input/output interface 102
When the controller receives a pulse signal from the crank angle sensor 6, when it receives an interrupt signal from the clock generation circuit 107, etc.

The intake air amount data Q and cooling water temperature data THW of the air flow meter 3 are taken in by an A/D conversion routine executed at predetermined time intervals and stored in a predetermined area of the RAM 105. In other words, data Q and THW in RA old 05 are updated at predetermined intervals. Further, the rotational speed data Ne is calculated by interruption every 30'CA of the crank angle sensor 6 and stored in a predetermined area of the RAM 105.

FIG. 3 shows the air-fuel ratio correction coefficient PAPR for the right bank and the left bank based on the output of the upstream 0□ sensor 13.

This is a first air-fuel ratio feedback control routine that calculates FAFL, and is executed every predetermined period of time, for example, every 4 ms.

In step 301, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the upstream 02 sensor 13 is satisfied. For example, when the cooling water temperature is below a predetermined value, while the engine is starting, increasing the amount after starting, increasing the warm-up amount, increasing the power, increasing the OTP amount to prevent catalyst overheating and cooling, upstream side 02
When the output signal of the sensor 13 has never been inverted, the closed loop condition is not satisfied in any case such as a fuel cut, and the closed loop condition is not satisfied in any other case. If the closed loop condition is not met, the process proceeds to steps 328 and 329, where the two air-fuel ratio correction coefficients FAPR and FAFL are set to 1.0.

Note that FAFR and FAFL may be set to values immediately before the end of the closed loop control. In this case, proceed directly to step 330. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 302.

In step 302, the output of the upstream 0□ sensor 13 is
is A/D converted and taken in, and in step 303 it is determined whether ■1 is a comparison voltage ■□, for example, 0.45V or less,
That is, it is determined whether the air-fuel ratio is rich or lean. In other words, if the air-fuel ratio is lean (V+ ≦VRn), it is determined in skip 304 whether the delay counter CDLY is positive or not, and if CDLY>O. If so, select C in step 305.
Set DLY to O and proceed to step 306. In step 306, the delay counter CDLY is decremented by 1, and in steps 307 and 308, the delay counter CDLY is
is guarded by the minimum value TDL. In this case, when the delay counter CDLY reaches the minimum value TDL, the first air-fuel ratio flag F1 is set to "0" (lean) in step 309. Note that the minimum value TDL is the upstream value 02 sensor 1
This is a lean delay state for maintaining the determination that the state is in the rich state even if there is a change from rich to lean in the output of No. 3, and is defined as a negative value. On the other hand, Rich (V
+>V+++), it is determined in step 310 whether the delay counter CDLY is negative or not, and CDLY<O
If so, skip 311 to set CDLY to O, and proceed to step 312. In step 312, the delay counter CDLY is incremented by 1, and in steps 313 and 314, the delay counter CDLY is guarded at the maximum value TDR.

In this case, when the delay counter CDLY reaches the maximum value TDR, the first air-fuel ratio flag Fl is set to "1" (rich) in step 315. In addition, the maximum value TD
R is a rich delay time for maintaining the determination that the engine is in a lean state even if the output of the upstream 02 sensor 13 changes from lean to rich, and is defined as a positive value.

In step 316, it is determined whether the sign of the first air-fuel ratio flag Fl has been inverted, that is, it is determined whether the air-fuel ratio after the delay processing has been inverted. If the air-fuel ratio is reversed, in step 317, it is determined whether the reversal is from rich to lean or from lean to rich, based on the value of the first air-fuel ratio flag F1. If it is a reversal from rich to lean, in step 318, the air-fuel ratio correction coefficient F for the right bank is set.
APR is increased in a skip manner to FAFR4-FAFR+R3RR, and in step 3]9, the air-fuel ratio correction coefficient FAPL for the left bank is increased to FAFL-FAFL+
RSRL in a skip manner, and conversely, if it is a reversal from lean to rich, the right bank air-fuel ratio correction coefficient FAPR is changed to FAFR4-FAFR-R in step 820.
The SLR is decreased in a skip manner, and step 321
, set the air-fuel ratio correction coefficient FAPL for the left bank to FAFL
←FAFL -RSLL and decrease in a skip manner. In other words, skip processing is performed.

If the sign of the first air-fuel ratio flag F1 is not inverted in step 316, integration processing is performed in steps 322-326. That is, in step 322, F1="0"
If F1="0" (lean), then in step 323, set TRR to FAFR←FAFR+,
Also, in step 324, FAFL-FAFL +KI
RL, and if F1="1" (rich), set FAFL-FAPL- to ILL in step 325,
Also, in step 326, FAFL←FAFL-KIL
Let it be L. Here, the Ricci integral constant KIRR, IRL
and lean integral constants KILR, KILL are skip M
It is set sufficiently small compared to R5RR, RSLR, RSRL, and RSLL. Therefore, step 323,
Step 324 gradually increases the fuel injection amount in a lean state (F1="0"), and steps 325 and 326 gradually decrease the fuel injection amount in a rich state (F1="1").

The air-fuel ratio correction coefficients FAPR and FAFL calculated in steps 318 to 321 and 323 to 326 are calculated in step 327.
It is guarded at a minimum value of, for example, 0.8, and is guarded at a maximum value, for example, 1.2. As a result, when the air-fuel ratio correction coefficients FAFR and FAFL become too large or too small for some reason, the air-fuel ratio of the engine is controlled using those values to prevent over-rich and over-lean conditions.

FAPR and FAFL calculated as above are stored in RAM1.
05, and the routine ends at step 330.

The fourth is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. When the air-fuel ratio signal A/F for rich/lean discrimination is obtained from the output of the upstream 02 sensor 13 as shown in FIG. 4(A), the delay counter CDL
As shown in FIG. 4(B), Y is counted up in the rich state and counted down in the lean state. As a result, as shown in FIG. 4(C), a delayed air-fuel ratio signal A/F' (corresponding to flag F1) is formed.

For example, time 1. Even if the air-fuel ratio signal A/F' changes from lean to rich, the delayed air-fuel ratio signal A/F' changes from lean to rich.
F' is maintained lean for the rich delay time TDR and then changes to rich at time t2. Even if the air-fuel ratio signal A/F changes from rich to lean at time t, the air-fuel ratio signal A/F' subjected to the delay processing is delayed by the lean delay time (-T
DL) After being held rich by a considerable amount, it changes to lean at time t4. However, the air-fuel ratio signal A/F' at time t
,.

t6+t? When the rich delay time TDR is reversed as shown in the figure, the delay counter CDLY reaches the maximum value TDR.
As a result, the air-fuel ratio signal A/F' after the delay process is inverted at time t. In other words,
The air-fuel ratio signal A/F' after the delay processing is more stable than the air-fuel ratio signal A/F before the delay processing. In this way, based on the stable air-fuel ratio signal A/F' after the delay processing, the air-fuel ratio signal shown in Fig. 4 (
D), air-fuel ratio correction coefficients FAPR and FAFL shown in (E)
is obtained.

Next, the downstream side 0. The second air-fuel ratio feedback control using the sensor 15 will be explained. The second air-fuel ratio feedback control includes skip amounts R5RR, RSLR, and RSRL as the first air-fuel ratio feedback control constants.
, RSLL integral constants KIRR, KILR.

KIRL, KILL, delay time TDR, TDL variable system, and second air-fuel ratio correction coefficient FAF2
There is a system that introduces

For example, if the rich skip amount RSRR (RSRL) is increased, the right bank control air-fuel ratio (left bank control air-fuel ratio) can be shifted to the rich side, and even if the lean skip amount R5LR (RSLL) is decreased, the right bank control air-fuel ratio (left bank control air-fuel ratio) can be shifted to the rich side. The control air-fuel ratio (control air-fuel ratio of the left bank) can be shifted to the rich side,
On the other hand, if the lean skip amount RSLR (RSLL) is increased, the control air-fuel ratio of the right bank (control air-fuel ratio of the left bank) can be shifted to the lean side, and the rich skip amount RS
Even if RR (RSRL) is made smaller, the control air-fuel ratio of the right bank (the control air-fuel ratio of the left bank) can be shifted to the lean side. Therefore, the downstream side is 0! The rich skip amount RSRR (RSRL) and the lean skip amount R are determined according to the output of the sensor 15.
By correcting 5LR (RSLL), the air-fuel ratio of the right bank (the air-fuel ratio of the left bank) can be controlled. Furthermore, by increasing the rich integral constant KIRR (KrRL), the control air-fuel ratio of the right bank (control air-fuel ratio of the left bank) can be shifted to the rich side, and the lean integral constant KILR (KIL
Even if L) is decreased, the right bank control air-fuel ratio (left bank control air-fuel ratio) can be shifted to the rich side.On the other hand, if the lean integral constant KILR (KILL) is increased, the right bank control air-fuel ratio (left bank control air-fuel ratio) can be shifted to the rich side. The bank control air-fuel ratio) can be shifted to the lean side, and the rich integral constant KIRR (KIRL) can be shifted to the lean side.
Even if it is made smaller, the control air-fuel ratio of the right bank (the control air-fuel ratio of the left bank) can be shifted to the lean side. Therefore, downstream side 0□
The air-fuel ratio can be controlled by correcting the rich integral constant KIRR (to IRL) and the lean integral constant KILR (KILL) according to the output vz (vz') of the sensor 15R (15L). If you set the rich delay time TDR > lean delay time (-TDL), the control air-fuel ratio can shift to the rich side, and conversely, if you set the lean delay time (-TDL) > rich delay time (TDR). , the controlled air-fuel ratio can be shifted to the lean side. In other words, the downstream Oz sensor 15R (15
Delay time TDR, T according to output ■2 (vz') of L)
By correcting DL (in this case, TDRR and TDLR for the right bank and TDRL and TOLL for the left puncture are provided), the air-fuel ratio of each bank can be controlled.

Making these skip amount, integral constant, and delay time variable by the downstream O2 sensor 15R (15L) has its own advantages. For example, the delay time allows for very delicate air-fuel ratio adjustment, and the skip amount can be controlled with good response without lengthening the air-fuel ratio feedback period unlike the delay time. Therefore, naturally, two or more of these variable amounts can be used in combination.

Figure 5 shows the output of downstream 02 sensor 15R (15L) ■2
Skip based on (■2') IRsRR, R3LR
The second air-fuel ratio feedback control routine calculates (R3RL, RSLL), and is executed every predetermined period of time, for example, every 512 m5. In steps 501 to 504, it is determined whether the downstream 0□ sensors 15R and 15L have a common closed loop condition. For example, the closed loop condition is not met by the upstream 0° sensor 13 (step 501).
In addition, the cooling water temperature T HW is set to a predetermined value (for example, 70℃
) (step 502), when the throttle valve 16 is fully open (LL="1") (step 503), when the load is light (Q/N e < X + ) (step 504), etc. are common to each bank. The closed-loop condition is not satisfied, and the closed-loop condition is not satisfied in other cases. If the condition is not a closed loop condition, the process directly proceeds to step 524.

If the common closed loop condition is met, step 505
Then, it is determined whether or not the downstream side 02 sensor 15R of the right bank is activated. For example, in an activation determination routine (not shown), it is determined whether the output v2 of the downstream 0□ sensor 15R has never crossed the reference voltage, and an activation flag is set only when it crosses the reference voltage even at - degrees. , activation is determined by setting and resetting this activation flag. When the downstream 0□ sensor 15R of the right bank is activated, the skip amounts RSRR and R5LR for the right bank are updated in steps 506 to 511, and when the downstream 0□ sensor 15R of the right bank is not activated. , proceed to step 512.

Steps 506 to 511 will be explained. Step 5
In 06, the output ■2 of downstream side 0□ sensor 15R is A/D
Convert and import, in step 508 ■2 is the comparison voltage V
II! For example, it is determined whether the voltage is 0.55V or less, that is, it is determined whether the air-fuel ratio is rich or lean. The comparison voltage ■8□ is the comparison voltage ■□ of the output of the upstream 0□ sensor 13, taking into account that the output characteristics are different due to the influence of raw gas and the deterioration rate is different between upstream and downstream of the catalytic converter 12. Although it is set higher, this setting may be arbitrary.

If v2≦V (lean) in step 507, the process advances to step 508, and RSRR4-R5RR+ΔRS (
In other words, the rich skip amount RSRR is increased to shift the air-fuel ratio of the right bank to the rich side, and on the other hand,
If VZ>VH2 (rich), the process proceeds to step 509, where RSRR-RSRR-ΔR5 is set, that is, the rich skip amount RSRR is decreased to shift the air-fuel ratio to the lean side. Next, in step 510, the rich skip amount R5RR is set to a maximum value MAX=8% and a minimum value M
Guard at IN=2%. Note that the minimum value MIN is a value at a level that does not impair transient followability, and the maximum value MAX is a value at a level at which drivability does not deteriorate due to air-fuel ratio fluctuations. And step 511
Then, calculate the lean skip amount RSLR as follows: RSLR←10%-RSRR. In other words, Su Nochi Skip 1lR5R
The sum of R and lean skip 1R5LR is constant, for example 1
It is 0%.

In step 512, the left bank downstream 0□ sensor 15
Determine whether L is activated. As a result, when the left bank downstream O2 sensor 15L is activated, the skip amounts RSRL and RSLL for the left bank are updated and guard processing is performed in steps 513 to 523, and the left bank downstream Ot sensor 15L is activated. If it is not activated, the process advances to step 524.

Steps 513 to 523 will be explained. Step 5
13, the output ■2' of the downstream side 02 sensor 15L is A/
The data is converted into D and taken in, and in step 514, it is determined whether (2) is less than the comparison voltage v, l□, for example, 0.55V, that is, it is determined whether the air-fuel ratio is rich or lean.

If y, L≦V*z (lean) in step 514, the process proceeds to step 515, and R3RL −R3RL+Δ
RS, that is, the rich skip amount R3RL is increased to shift the bank air-fuel ratio to the rich side, and on the other hand, ■2
'〉V*z (rich), proceed to step 516,
RSRL←RSRL-ΔR5, that is, the rich skip 11R3RL is decreased to shift the air-fuel ratio to the lean side.

In step 517, it is determined whether the rich skip amount RSRL has reached the maximum value MAX, and RSRL > MA
Only when X, RSRL is set to MAX in step 518, and then, in step 519, basic injection amount TAUP
The coefficient KTPL for calculating L is KTPL= a
-KTP, where a is greatly increased to a constant larger than l (for example, 1.1). As a result, the control air-fuel ratio of the left bank is greatly moved to the rich side.

In step 520, it is determined whether the rich skip amount RSRL has reached the minimum value MIN, and RSRL < MI
Only when N, RSRL is set to MIN in step 521, and then the basic injection amount TAUP is set in step 522.
The coefficient KTPL for calculating L is KTPL 4-b
-KTP, where b is greatly reduced to a constant smaller than 1 (for example, 0.9). This causes the left bank control air-fuel ratio to be significantly leaner.

Then, in step 523, the lean skip amount R5L
Calculate L as R5LL←l 0%-RSRL.

In addition, the skip amounts RSRR, RSLR, RSRL,
RSLL and the coefficient KTPL of the basic injection amount TAUPL for the left bank are stored in the backup RAM 106.

The routine of FIG. 5 then ends at step 524.

In the routine of FIG. 5, the rich skip 1lRsRL for the left bank is updated only by integral control using the speed ΔRS, but when the determination result in step 514 is reversed, skip control is introduced to update the rich skip amount RsRL. The update rate may be increased.

FIG. 6 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360° CA. Step 60
1, the cooling water temperature data THW is read from the RAM 105 and a warm-up increase value FWL is calculated by interpolation using a one-dimensional map stored in the ROM 104. Step 7 602-60
4 is for the right bank. That is, in step 602, the intake air amount data Q and rotational speed data Ne are read out from the RAM 105, and the basic injection amount TAUPR for the right bank is calculated. For example, TA[1PR-KTPR-Q /
Let N e (KTPR is a constant). In step 603, the final injection amount TAUR for the right bank is set to TAtlR-T.
Calculate by AUPR-FAFR (FWLfl+α)+β.

Next, in step 604, the injection amount TAUR is set in the right bank down counter 108R and the flip-flop 109R is set to start fuel injection.

Steps 605-607 are for the left bank. That is, in step 605, the basic injection amount TAUP for the left bank is
L is calculated by TPL-Q/Ne as TAUPL←, and in step 606, the final injection ITAUL for the left bank is calculated as
TAUL -TAUPL-FAFL・(FWLf1 +
Calculate by α) + β. Next, in step 607, the injection ITAUL is transferred to the left bank down counter 108L.
At the same time, the flip-flop 109L is set to start fuel injection. And step 608
This routine ends.

In addition, as mentioned above, the injection amount TAUR or TAIL
When the time corresponding to 10 days has passed, the down counter 10 days R
Alternatively, the flip-flop 109R or 109L is reset by the carrier signal of 108L, and the fuel injection ends.

FIG. 7 is a timing diagram for supplementary explanation of the flowcharts in FIGS. 5 and 7.
This explains the air-fuel ratio of the left bank, which does not have The output V2' of the left bank downstream 0□ sensor 15L is
As shown in FIG. 7(A), when the left bank rich skip amount R5RL and lean skip il? s
LL changes as shown in FIGS. 7(B) and (C).

In the illustrated example, skip control is introduced when the output (2) is inverted. At this time, the left bank air-fuel ratio correction coefficient F
APL is the output VI of the upstream 0□ sensor 13 of the right bank.
Therefore, when the difference between the air-fuel ratios of the left and right banks becomes large at time t1, the air-fuel ratio of the left bank becomes the output of the downstream side 0□ sensor 15L of the left bank, as shown in FIG. 7(E). Skip amount RSRL due to V2',
Fine tuning of the RSLL cannot quickly compensate. Therefore, in the present invention, the ski/knob amounts R5RL, RSLL
At time t2 when TATlPL reaches the guard values MAX and MIN, the coefficient KTPL of the basic injection amount TAtlPL is suddenly changed to bring the control air-fuel ratio of the left bank to the stoichiometric air-fuel ratio (λ-1), as shown in Fig. 7 (D). approach quickly. Therefore, after that, skip 1RsRL, RSLL are set to guard values MAX, M
The withdrawal comes from IN. Note that the average air-fuel ratio of the right bank is as shown in Figure 7 (F).
Since it exhibits a true double 0□ sensor system using the z sensor, it is always at almost the stoichiometric air-fuel ratio.

Note that the first air-fuel ratio feedback control is performed every 4 ms.
Moreover, the second air-fuel ratio feedback control is performed every 512 m5 because the air-fuel ratio feedback control is mainly performed by the upstream 02 sensor with good response.
This is because control by the downstream 0□ sensor, which has poor responsiveness, is performed in a secondary manner.

In addition, other control constants in air-fuel ratio feedback control by the upstream 0□ sensor, such as delay time, integral constant, etc., are corrected by the output of the downstream 02 sensor.
The invention can be applied to two-sensor systems as well as double-02 sensor systems that introduce a second air-fuel ratio correction factor. Furthermore, controllability can be improved by simultaneously controlling two of the skip amount, delay time, and integral constant.

Furthermore, it is also possible to fix one of the skip IRsR, R3L and make only the other variable.
It is also possible to fix one of them and make only the other variable, or to fix one of the rich integral constant KTR and lean integral constant KIL and make the other variable.

Furthermore, instead of the air flow meter, a Karman vortex sensor, a heat wire sensor, or the like may be used as the intake air amount sensor.

Furthermore, in the above embodiment, the fuel injection amount is calculated according to the intake air amount and the engine rotation speed, but the fuel injection amount is calculated according to the intake air pressure and the engine rotation speed, or the throttle valve opening and the engine rotation speed. The fuel injection amount may also be calculated.

Further, in the above embodiment, an internal combustion engine is shown in which the amount of fuel injected into the intake system is controlled by a fuel injection valve, but the present invention can also be applied to a carburetor type internal combustion engine. For example, an electric air control valve (EACV) adjusts the intake air amount of the engine to control the air-fuel ratio, and an electric bleed air control valve adjusts the amount of air bleed from the carburetor to control the main system passage and The present invention can be applied to devices that control the air-fuel ratio by introducing atmospheric air into the slow system passage, and devices that adjust the amount of secondary air sent to the exhaust system of an engine.

In this case, the basic fuel injection amount corresponding to the basic injection amount in steps 602 and 605 is determined by the carburetor itself, that is, it is determined according to the intake pipe negative pressure according to the intake air amount and the rotational speed of the engine, and 603,
At 606, the amount of supplied air corresponding to the final fuel injection amount is calculated.

Furthermore, in the above embodiment, the 02 sensor was used as the air-fuel ratio sensor, but a CO sensor, lean mixture sensor, etc. may also be used.

Furthermore, although the embodiments described above are constructed using a microcomputer, that is, a digital circuit, they may also be constructed using an analog circuit.

〔Effect of the invention〕

As explained above, according to the present invention, even if the air-fuel ratio of a bank that employs the irregular double chamber fuel ratio sensor system deviates due to a deviation in the air-fuel ratio between the two banks, the air-fuel ratio can be returned to the stoichiometric air-fuel ratio. , Therefore, it is useful for preventing deterioration of emissions.

[Brief explanation of the drawing]

FIG. 1 is an overall block diagram for explaining the present invention in detail; FIG. 2 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention; FIGS. 3 and 5; Figure 6 is a flowchart for explaining the operation of the control circuit in Figure 2, Figure 4 is a timing diagram to supplement the flowchart in Figure 3, and Figure 7 is a flowchart for Figures 5 and 6. FIG. 2 is a diagram for supplementary explanation. DESCRIPTION OF SYMBOLS 1... Engine body, 3... Air flow meter, 4... Distributor, 5.6... Crank angle sensor, lO... Control circuit, 12R, 12L... Catalytic converter, 13... Upstream side 02 sensor, 15R, 15L...Downstream side 0. Sensor, 17...Idle switch.

Claims (1)

[Scope of Claims] 1. First and second three-way catalysts provided in the exhaust passages of each bank of an internal combustion engine divided into at least first and second banks; and the first three-way catalyst. a first bank upstream air-fuel ratio sensor that is provided in an upstream exhaust passage of the first bank and detects the air-fuel ratio of the first bank; and a first bank upstream air-fuel ratio sensor that is provided in an exhaust passage downstream of the first three-way catalyst; a first bank downstream air-fuel ratio sensor that detects the air-fuel ratio of the first bank; and a first bank downstream air-fuel ratio sensor that is provided in the exhaust passage downstream of the second three-way catalyst and detects the air-fuel ratio of the second bank. a second downstream air-fuel ratio sensor for the bank; and an air-fuel ratio sensor for the first bank in accordance with the output of the upstream air-fuel ratio sensor for the first bank and the output of the downstream air-fuel ratio sensor for the first bank. a first air-fuel ratio adjustment means for adjusting the fuel ratio; an air-fuel ratio control amount calculation means for calculating a second bank air-fuel ratio control amount according to the output of the second bank downstream air-fuel ratio sensor; a guard means for guarding a second bank air-fuel ratio control amount within a predetermined allowable range; and a guard value for determining whether the second bank air-fuel ratio control amount has reached a guard value within the predetermined allowable range. a determining means; when the second bank air-fuel ratio control amount has not reached the guard value of the predetermined tolerance range, the second bank air-fuel ratio control amount and the first bank upstream air-fuel ratio; The air-fuel ratio of the second bank is adjusted by supplying an amount of fuel according to the output of the sensor to the second bank, and the air-fuel ratio control amount for the second bank reaches a guard value in the predetermined range. Sometimes, the air-fuel ratio of the second bank is adjusted by supplying an increased or decreased amount of fuel according to the guarded air-fuel ratio control amount for the second bank and the output of the upstream air-fuel ratio sensor for the first bank. An air-fuel ratio control device for an internal combustion engine, comprising a second air-fuel ratio adjusting means.