JPH01106935A - Control device for air-fuel ratio of internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent erroneous judgment by providing O2 sensors before and behind a catalytic converter rhodium, making a minute current flow into the O2 sensor on the lower course side via a pull-up type input circuit, and judging activation when a defined time elapsed after the output of the sensor is lowered below an active level. CONSTITUTION:An upper-course side O2 sensor and a lower-course side O2 sensor are provided on the upper course side and lower course side of a catalytic converter rhodium, and a minute current is made flow into the lower-course side O2 sensor while a pull-up type input circuit into which the output thereof is inputted is connected to it. The output of the pull-up type input circuit is compared with an active level which is slightly higher than a rich output level after warming up by a comparing circuit and, when a defined time elapsed after the output is lowered below the active level, judgment is formed that the activation is completed. The controlling constant of an air-fuel ratio feedback control is operated based on the output of the lower-course side O2 sensor to perform the feedback control of the air-fuel ratio together with the output of the upper-course side O2 sensor.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides air-fuel ratio sensors (herein, oxygen concentration sensors (0□ sensors)) on the upstream and downstream sides of a catalytic converter.
), and in addition to air-fuel ratio feedback control by the upstream 02 sensor, a double air-fuel ratio sensor system that performs air-fuel ratio feedback control by the downstream 0□ sensor, or downstream of the catalytic converter or in the catalytic converter.
The present invention relates to a single air-fuel ratio sensor system that includes two sensors and performs air-fuel ratio feedback control using the 0□ sensor.

[Conventional technology]

In simple air-fuel ratio feedback control (single 0□ sensor system), the 0□ sensor that detects oxygen concentration is installed in the exhaust system as close to the combustion chamber as possible, that is, in the gathering part of the exhaust manifold upstream of the catalytic converter. , 0□ sensor output characteristics have caused problems in improving the control accuracy of the air-fuel ratio. It takes 02
In order to compensate for variations in sensor output characteristics, variations in components such as fuel injection valves, and changes over time or aging, a second 0□ sensor is provided downstream of the catalytic converter, and the air-fuel ratio feedback is provided by the upstream 0□ sensor. A double 0□ sensor system that performs air-fuel ratio feedback control using the downstream 02 sensor in addition to control has already been proposed (
Reference: Japanese Unexamined Patent Publication No. 58-4875f3). In this double 0□ sensor system, the 0□ sensor installed downstream of the catalytic converter has a
Although it has a low response speed, it has the advantage of small variations in output characteristics for the following reason.

(1) Downstream of the catalytic converter, the exhaust gas temperature is low, so there is little thermal influence.

(2) Since various poisons are trapped in the catalyst downstream of the catalytic converter, the amount of poisoning of the downstream 0□ sensor is small.

(3) The exhaust gas is sufficiently mixed downstream of the catalytic converter, and the oxygen concentration in the exhaust gas is close to an equilibrium state.

Therefore, as described above, by using air-fuel ratio feedback control (double 0□ sensor system) based on the outputs of the two 02 sensors, variations in the output characteristics of the upstream 0□ sensor can be absorbed by the downstream 0□ sensor. In fact, as shown in Figure 2, in a single 0□ sensor system, 0□
When the sensor output characteristics deteriorate, it directly affects the exhaust emission characteristics, whereas in the double 0□ sensor system, even if the output characteristics of the upstream 0□ sensor deteriorate, the exhaust emission characteristics do not deteriorate. In other words, double 0□
In the sensor system, good exhaust emissions are guaranteed as long as the lower m-side 0□ sensor maintains stable output characteristics.

On the other hand, as an input circuit for the output of the 0□ sensor, there is a pull-down type input circuit shown in FIG. 3A. In other words, the pull-down type input circuit (see Publication No. 187-5098) is
Pull-down resistor R+ and noise absorption capacitor CI
It is made up of. When the element temperature is low, the internal resistance R0 of the 02 sensor OX is large, and therefore, as shown in FIG. 4A, even if the base air-fuel ratio is rich and there is an electromotive force from the 02 sensor OX, the sensor output voltage is 0□. On the other hand, as the element temperature increases, the internal resistance R0 of the 0□ sensor OX becomes smaller, and when the base air-fuel ratio is rich, the electromotive force of the 0□ sensor OX causes the 0□ sensor output voltage ■. X becomes a high level equivalent to the electromotive force xR,/(RO+R1). When using such a pull-down type input circuit, the activation of the 0□ sensor OX is determined by the 0□ sensor output voltage ■. This is normally done based on whether or not X exceeds a predetermined value or is reversed, but if the base air-fuel ratio is lean, it will not be judged as active even if the 0□ sensor Ox is activated. .

Therefore, regardless of whether the base air-fuel ratio is rich or lean, 0□
The third B is used as an input circuit that can determine the activation of sensor OX.
The pull-up type input circuit shown in the figure (published technical report 87-509
(See No. 8) has been proposed.

In other words, the pull-up type input circuit has a pull-up resistor R
2 and a noise absorbing capacitor C2. When the element temperature is low, the internal resistance R6 of the 0□ sensor OX is larger than the pull-up resistor R2, and as shown in FIG. 4B, the 02 sensor output voltage V. X is a value almost close to the power supply voltage (VCCXRO/ (
On the other hand, as the element temperature increases, the internal resistance R0 of the Ot sensor oX becomes smaller than the pull-up resistance R2, and when the base air-fuel ratio is rich, the sensor output voltage becomes 0□. X is electromotive force operator vcc
It becomes a high level equivalent to X Ro / (Re + R2), and when the base air-fuel ratio is lean, the 0□ sensor output voltage VOX becomes
Rz) becomes a correspondingly low level. Therefore, when a pull-up type input circuit is used, the activation of the 0□ sensor OX is determined when the 02 sensor output voltage VOX is slightly higher than the rich output level after warm-up. It can be done depending on whether it is lower or not.

[Problem that the invention seeks to solve]

However, in the double 02 sensor system described above, when a pull-up type input circuit is used for the downstream 0□ sensor, the base air-fuel ratio is Immediately after the activation is determined when the engine is lean, there is erroneous control of the air-fuel ratio due to an erroneous rich judgment, and even after that, active/inactive hunting (range Y) occurs due to rich/lean reversal of the base air-fuel ratio. There is a problem that the air-fuel ratio shifts to rich. That is, if the activity discrimination value vA is set as shown in FIG. 5, when the base air-fuel ratio is rich, the element temperature T
3, it is determined to be active, but if the base air-fuel ratio is lean, it is determined to be active earlier at a lower element temperature T, and moreover,
In this case, the range X (T1 to T2) is erroneously determined to be rich, and as a result, the air-fuel ratio is erroneously controlled. Furthermore, when the element temperature is in the range T, ~T2, the activation,
There is a problem in that inactive hunting occurs, resulting in erroneous control of the air-fuel ratio.

Furthermore, to explain in detail using Figures 6A and 6B (enlarged view of part B in Figure 6A), if the downstream 02 sensor is determined to be active at time t0 while the base air-fuel ratio is lean, (vo, l<vA), air-fuel ratio feedback control by downstream 02 sensor For example, rich skip amount R3R
However, in this case, it is incorrectly determined to be rich (Vox>vR), so after the rich skip amount R3R is controlled to the lean side, at time t, the rich skip amount R3R becomes rich as originally. controlled by the side. Moreover,
At the initial stage of activation of the downstream 02 sensor, rich and lean variations in the base air-fuel ratio occur due to fuel cut, fuel increase, etc., and as shown in FIG. 6B, from time t2 to 1. ．． 14~j
From S, j6 to t, the downstream 02 sensor becomes inactive. During this time, the rich skip amount R3R is not updated, and the rich skip amount R3R is overcorrected to the rich side. Note that the dotted line R3R' indicates the case where there is no rich-side overcorrection.

In addition, in order to prevent the latter active/inactive hunting, the activity discrimination value ■ can be set to a high value.
In this case, the rich erroneous determination (to to 1+) takes a long time and the air-fuel ratio feedback is executed frequently in the life condition of 02 cm on the downstream side, so it cannot be adopted.

The above-mentioned problems also apply to a single 02 sensor system in which a 0□ sensor is provided only downstream of or inside the catalyst.

Therefore, it is an object of the present invention to prevent deterioration of emissions, deterioration of fuel efficiency, and
An object of the present invention is to provide a double air-fuel ratio sensor system and a single air-fuel ratio sensor system that prevent deterioration of drivability.

[Means for solving problems]

The means for solving the above problems are shown in Figures 1A and 1B.
As shown in the figure.

FIG. 1A shows a dual air/fuel ratio sensor system.

That is, a three-way catalyst C installed in the exhaust passage of an internal combustion engine
An upstream air-fuel ratio sensor that detects the air-fuel ratio of the engine is provided in the exhaust passage upstream of C+to, and a three-way catalyst C
A downstream air-fuel ratio sensor that detects the air-fuel ratio of the engine is provided in the exhaust passage downstream of the CRO. The pull-up type input circuit allows a minute current to flow into the downstream air-fuel ratio sensor, and also inputs the output of the downstream air-fuel ratio sensor. The comparison means compares the output ■2 of the pull-up type input circuit with the activation level V which is slightly higher than the rich output level after warm-up, and the delay means compares the output ■2 of the pull-up type input circuit with the activation level ■4. After a predetermined period of time after the air-fuel ratio becomes lower, the downstream air-fuel ratio sensor is determined to be in an active state. As a result, when the downstream side air-fuel ratio sensor is in the active state, the control constant calculation means calculates the air-fuel ratio feedback control constant, for example, the skip amounts R3R and R3L, according to the output (2) of the downstream side air-fuel ratio sensor. As a result, the air-fuel ratio correction amount calculation means calculates the air-fuel ratio correction amount FAF according to the air-fuel ratio feedback control constants RSR, R3L and the output vI of the upstream air-fuel ratio sensor. The air-fuel ratio adjustment means adjusts the air-fuel ratio of the engine according to the air-fuel ratio correction amount FAF.

FIG. 1B shows a single air/fuel ratio sensor system. That is, an air-fuel ratio sensor that detects the air-fuel ratio of the engine is provided in the exhaust passage downstream of the three-way catalyst CC*o or in the three-way catalyst. The pull-up type input circuit supplies a small current to the air-fuel ratio sensor and outputs v2 from the air-fuel ratio sensor.
Enter. The comparison means compares the output V2 of the pull-up type input circuit with an activation level VA slightly higher than the rich output level after warm-up, and the delay means compares the output V2 of the pull-up type input circuit with an activation level VA slightly higher than the rich output level after warm-up, and the delay means compares the output V2 of the pull-up type input circuit with an activation level VA slightly higher than the rich output level after warm-up. After a predetermined period of time, the air-fuel ratio sensor is determined to be in an active state. As a result,
When the air-fuel ratio sensor is in the active state, the control amount calculation means calculates the air-fuel ratio control amount FAF according to the output v2 of the air-fuel ratio sensor. The air-fuel ratio adjustment means is an air-fuel ratio control amount FAF.
The engine's air-fuel ratio is adjusted accordingly.

[For production]

According to the above means, the air-fuel ratio feedback control by the downstream air-fuel ratio sensor starts with a delay after the output of the downstream air-fuel ratio sensor, that is, the output V2 of the pull-up input circuit becomes lower than the activation level vA. Therefore, air-fuel ratio feedback control is performed in a time domain in which erroneous control is not performed.

〔Example〕

FIG. 7 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. 7, an air flow meter 3 is provided in the intake passage 2 of the engine body 1. As shown in FIG. 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. The pulse signals of these crank angle sensors 5 and 6 are supplied to the control circuit 100 input/output interface 102, and the output of the crank angle sensor 6 is sent to the CPU 10.
3 interrupt terminal.

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.

The exhaust system downstream of the exhaust manifold 11 is provided with a catalytic converter 12 that accommodates a three-way catalyst that simultaneously purifies three toxic components HC, Co, and NOx in the exhaust gas.

The exhaust manifold 11 includes a catalytic converter 1.
A first 02 sensor 13 is provided on the upstream side of the catalytic converter 12, and a second 0□ sensor 15 is provided on the exhaust pipe 14 on the downstream side of the catalytic converter 12.

The 0□ sensors 13 and 15 generate electrical signals corresponding to the concentration of oxygen components in the exhaust gas. That is, 0□ sensor 13
, 15 generate different output voltages to the A/D converter 101 via pull-up type input circuits 111 and 112 of the control circuit 10 depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio. . The control circuit 10 is configured as a microcomputer, for example, and includes an A/D converter 1011, an output interface 102, a CPU 103, and an R
OM104. RAM105, Bafuku Asop RAM10
6. A clock generation circuit 107 and the like 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 108,
Flip-flop 109 and drive circuit 110 are for controlling fuel injection valve 7.

That is, in the routine described later, the fuel injection amount TAU
is calculated, the fuel injection amount TAU is counted down by the down counter 1.
08 and flip-flop 109
is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts the clock signal (not shown) and the carrier voltage terminal finally reaches 1111 levels, the flip-flop 109 is reset and the drive circuit 110 activates the fuel injection valve 7. stop. That is, the fuel injection valve 7 is energized by the above-mentioned fuel injection amount TAU, so that an amount of fuel corresponding to the fuel injection amount TAU is sent into the combustion chamber of the engine body 1.

Note that the interrupt generation of the CPU 1103 is caused by the A/D converter 1.
When the A/D conversion of 01 is completed, the input/output interface 10
2 receives a pulse signal from the crank angle sensor 6, 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. That is, data Q and THW in RAM 105 are updated at predetermined time intervals. Further, the rotational speed data Ne is calculated by the interruption of the crank angle sensor 6 every 30 degrees Celsius, and is stored in a predetermined area of the RAM 105.

FIG. 8 shows a first air-fuel ratio feedback control routine for calculating an air-fuel ratio correction coefficient FAF based on the output of the upstream 0□ sensor 13, and is executed every predetermined period of time, for example, every 4 ms.

In step 801, 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, during engine startup, during engine warm-up, during power increase, during OTP increase to prevent catalyst overheating, 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 satisfied, the process proceeds to step 827 and the air-fuel ratio correction coefficient FAF is set to 1.0. Note that FAF may be set to a value immediately before the end of closed loop control. In this case, step 8
Proceed directly to 28. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 802.

In step 802, the output vI of the upstream 0□ sensor 13 is
is A/D converted and fetched, and in step 803 it is determined whether or not the comparison voltage VRI, for example, 0.45V or less, that is, it is determined whether the air-fuel ratio is rich or lean. If (V, ≦V R1), it is determined whether the delay counter CDLY is positive or not in skip 804, and if CDLY>0, the CD is detected in step 805.
Set LY to 0 and proceed to step 806. Step 806
Then, the delay counter CDLY is subtracted by 1, and in steps 807 and 808, the delay counter CDLY is guarded at the minimum value TDL. In this case, the delay counter CD
When LY reaches the minimum value TDL, step 809
The first air-fuel ratio flag F1 is set to 0'' (lean).The minimum value TDL is used to determine that the state is rich even if there is a change from rich to lean in the output of the upstream value 02 sensor 13. Lean delay state for holding, defined as a negative value; on the other hand, rich (Vl > VR
I), the delay counter C is set in step 810.
It is determined whether DLY is negative or not, and if CDLY<Q, CDLY is set to O in skip 811 and the process proceeds to step 812. In step 812, the delay counter CDLY is incremented by 1, and in steps 813 and 814, 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 F1 is set to "1" in step 815.
” (rich).The maximum value TDR is 0 on the upstream side.
□Rich delay time for maintaining the determination that the lean state is present even if the output of the sensor 13 changes from lean to rich, and is defined as a positive value.

In step 816, it is determined whether the sign of the first air-fuel ratio flag F1 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 817, depending on the value of the first air-fuel ratio flag F1, it is either reversed from rich to lean or lean.
Determine whether it is reversed to the inch. If it is a reversal from rich to lean, in step 818 FAF 4-FAF+R
3R and increase in a skip manner, and conversely, if it is a reversal from lean to rich, FAF - FA is increased in step 819.
Decrease in skips with F-R3L. In other words, skip processing is performed.

If the sign of the first air-fuel ratio flag Fl is not inverted in step 812, integration processing is performed in steps 820 and 821822. That is, in step 820, F1=
Determine whether it is “0” or not, and if F1=“0” (lean), set FAF 4-FAF+KIR in step 821, and if F1-“1” (rich), step 8
22 as FAF 4-FAR-KIL. Here, the integral constants KTR and KIL are the skip amounts RSR and R5L.
is set sufficiently small compared to KIR(K
IL) <R3R(R3L). Therefore, step 821 gradually increases the fuel injection amount in a lean state (F1="0"), and step 822 gradually increases the fuel injection amount in a rich state (F1="0").
1”) to gradually reduce the fuel injection amount.

The air-fuel ratio correction coefficient FAF calculated in steps 818, 819, 821, and 822 is guarded at a minimum value of, for example, 0.8 in steps 823 and 824, and is guarded at a maximum value of, for example, 1.2 in steps 825 and 826. will be guarded. As a result, for some reason, the air-fuel ratio correction coefficient FA
When F becomes too large or too small, the air-fuel ratio of the engine is controlled using that value to prevent over-rich or over-lean conditions.

The FAF calculated as described above is stored in the RAM 105, and the routine ends at step 828.

FIG. 9 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. 8. 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. 9(A), the delay counter CD
As shown in FIG. 9(B), LY is counted up in a rich state and counted down in a lean state.

As a result, as shown in FIG. 9(C), a delayed air-fuel ratio signal A/F' (corresponding to flag F1) is formed. For example, even if the air-fuel ratio signal A/F' changes from lean to rich at time t, the delayed air-fuel ratio signal A/F' is maintained lean for the rich delay time TDR and then returns to time t2. It becomes richer. 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 (
-TDL), and then changes to lean at time t4. However, when the air-fuel ratio signal A/F' is reversed in a short period of the rich delay time TDR as at times 19 and 16.17, it takes time for the delay counter CDLY to reach the maximum value TDR, and as a result, at time t
At step 6, the air-fuel ratio signal A/F' after the delay processing is inverted. In other words, the air-fuel ratio signal A/F' after the delay process is more stable than the air-fuel ratio signal A/F before the delay process. In this manner, the air-fuel ratio correction coefficient FAF shown in FIG. 9(D) is obtained based on the stable air-fuel ratio signal A/F' after the delay processing.

Next, the second air-fuel ratio feedback control by the downstream 02 sensor 15 will be explained. The second air-fuel ratio feedback control includes skip amounts RSR, R3L as the first air-fuel ratio feedback control constants, and an integral constant K.
There is a system in which the comparison voltage (■□) of IR, KIL, delay time TDR, TDL, or output (■) of the upstream 02 sensor 13 is made variable, and a system in which a second air-fuel ratio correction coefficient FAF2 is introduced.

For example, if the rich skip amount R3R is increased, the controlled air-fuel ratio can be shifted to the rich side, and even if the lean skip amount R3L is decreased, the controlled air-fuel ratio can be shifted to the rich side.On the other hand, if the lean skip amount R3L is increased, the controlled air-fuel ratio can be shifted to the rich side. , the controlled air-fuel ratio can be shifted to the lean side, and even if the rich skip amount R3R is made small, the controlled air-fuel ratio can be shifted to the lean side.

Therefore, the air-fuel ratio can be controlled by correcting the rich skip amount R3R and the lean skip amount R5L according to the output of the downstream 02 sensor 15.

In addition, by increasing the rich integral constant KIR, the control air-fuel ratio can be shifted to the rich side, and the lean integral constant KIL
On the other hand, increasing the lean integral constant KIL allows the controlled air-fuel ratio to be shifted to the lean side, and even if the rich integral constant KIR is decreased, the controlled air-fuel ratio cannot be shifted to the rich side. You can move to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the rich integral constant KIR and the lean integral constant KIL according to the output of the downstream 0□ sensor 15. If rich delay time TDR>lean delay time (-TDL) is set, the control air-fuel ratio can be shifted to the rich side, and conversely, lean delay time (-TDL)>>
By setting the rich delay time (TDR), the controlled air-fuel ratio can be shifted to the lean side. In other words, the downstream side 02 sensor 15
The air-fuel ratio can be controlled by correcting the delay times TDR and TDL in accordance with the output of . Furthermore, the comparison voltage■□
When the comparison voltage VRI is increased, the controlled air-fuel ratio can be shifted to the rich side, and when the comparison voltage VRI is decreased, the controlled air-fuel ratio can be shifted to the lean side. Therefore, by correcting the comparison voltage VH1 according to the output of the downstream 0□ sensor 15, the air-fuel ratio can be controlled.

Making these skip amount, integral constant, delay time, and comparison voltage variable by the downstream 02 sensor 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.

Next, a double 02 sensor system in which the skip amount as an air-fuel ratio feedback control constant is made variable will be explained, but before that, the activation determination of the downstream 0□ sensor 15 will be explained in FIGS. 10A, 10B, and 10C. , will be explained with reference to FIG. 10D. Note that these routines are executed every predetermined time, for example, 512n+s.

In FIG. 10A, a delay time is introduced when the downstream 0□ sensor 15 changes from an inactive state to an active state, and a delay time is introduced when it changes from an active state to an inactive state. do not have. Referring to the timing diagram of FIG. 11, at time t. Previously, the downstream 0□ sensor 15 was in an inactive state, that is, the activation flag F'ac was "0". In this state, in step 1001, the downstream
The output V t of the 2 sensor 15 (in this case, the output of the pull-up type input circuit 112) is A/D converted and taken in, and in step 1002 it is determined whether or not V2 is lower than the activation level vA. As a result, since V,>V, the process advances to step 1009 via step 1008, and the flow ends.

Next, when time t0 is reached, the flow in step 1002 proceeds to step 1003, where the activation flag F'Ac=
Since it is "0", the activation determination counter CA is incremented by +1 in step 1004, and the process proceeds to step 1009 via step 1005, and the flow ends. This state continues until time t.

From time t1 to t2, V 2 > Va, and as a result, the flow at step 1002 changes to step 1008.
Go to step 10 and set the activation flag FAc to "θ".
Proceed to 09.

In this way, time t. ~t1, t2~t3, t4~
At t5 and from t6 to t7, the activity determination counter CA is incremented and the time 1. From -121.13 to t4 and from t5 to t6, the activity determination counter CA is held.

At time t, the activation determination counter CA is at the predetermined value CA. As a result, the flow at step 1005 proceeds to step 1006, where the activation flag FAc is set, and at step 1007, the activation discrimination counter CA is reset. Then, the process advances to step 1009.

After time t7, active v2〈VA and flag pttc
is set, step 1002.

The flow at 1003 proceeds to step 1007, and as a result, the activation determination counter CA is held at O.

In this way, the activation flag FAC is set after the time DLI has elapsed from the time t0 when 2<vA was reached for the first time.

FIG. 10B shows a modification of FIG. 10A, in which step 1010 is added to FIG. 10A. That is, V
2>V, the activation determination counter CA is reset in step 1010, and therefore, as shown by the dotted line in FIG. By appropriately setting the value CL, the delay time DLI can be made comparable to that in FIG. 10A.

FIG. 12A also shows a modification of FIG. 10A;
Steps 1201-12 instead of step 1008 in the diagram
05 is provided. That is, downstream side 02 sensor 1
A delay time is introduced when 5 changes from an inactive state to an active state, and a delay time is also introduced when it changes from an active state to an inactive state.

To explain the change from the active state to the inactive state with reference to the timing diagram of FIG. 13, before time t0, the downstream O2 sensor 15 is in the active state, that is, the activation flag FAc is "1". . In this state, step 10
At step 01, the output 2 of the downstream side 02 sensor 15 is A/D converted and taken in. At step 1002, it is determined whether or not V2 is lower than the activation level VA. As a result, ■2〈vA
Therefore, the process proceeds through steps 1003 and 1007, and the flow ends.

Next, time t. ', the flow in step 1002 proceeds to step 1201, where the active flag FAC-
Since it is "1", the deactivation discrimination counter CD is incremented by +1 in step 12o2, and the process proceeds to step 1009 via step 1203, and the flow ends.

This state continues until time t, L.

Time 1. /~t2', V2<VA, and as a result, the flow at step 1002 changes to step 1003.
, 1007 to step 1009.

In this way, the times t0'~t, J, t2'~t
3', t4' to t,', the inactivity discrimination counter C
Step D, time t, l~t2', t31~t4'
Then, the deactivation determination counter CD is held.

At times t and l, the inactivation determination counter CD is at the predetermined value CD.
, and as a result, the flow at step 1203 proceeds to step 1204, where the activation flag FAc is reset, and at step 1205, the deactivation determination counter CD is reset. Then, the process advances to step 1009.

After time t51, active ■2>V and flag FAC
has been reset, so step 1002゜120
The flow at step 1 proceeds to step 1205, and as a result, the deactivation determination counter CD is held at O.

In this way, the time t is when VZ>V for the first time. ′
The activation flag FAc will be reset after time DL2 has elapsed.

FIG. 12B shows a modification of FIG. 12A, in which steps 1206 and 1207 are added to FIG. 12A. That is, each time VZ>V, the activation determination counter CA is reset in step 1206, and
<Every time vA is reached, the inactivity discrimination counter CD also steps 1.
207. Therefore, as shown by the dotted line in FIG. 13, the deactivation determination counter CD also rises that much later. In this case, the predetermined value CDo is set small. Note that, compared to the case of FIG. 12A, the operation in FIG. 12B is stable because the inactive state (VZ > VA) is not accumulated.

The activation flag FAc obtained as described above is used in the routine shown in FIG.

FIG. 14 shows a second air-fuel ratio feedback control routine that calculates the skip amounts R5R and R3L based on the output of the downstream side 02 sensor 15.
Executed every 2m5. In steps 1401 to 1405, it is determined whether the downstream 0□ sensor 15 is in a closed loop condition. For example, in addition to the failure of the closed loop condition determined by the upstream 0□ sensor 13 (step 1401), when the cooling water temperature THW is below a predetermined value (for example, 70° C.) (step 1402), the throttle valve 16 is fully closed (LL=
"l") (step 1'403), when the load is light (Q/Ne<X,) (step 1404), and when the downstream 0□ sensor 15 is not activated (step 14).
05) etc., the closed loop condition is not satisfied, and in other cases, the closed loop condition is not satisfied. If the condition is not a closed loop condition, the process directly advances to step 1413.

The activation of the downstream side 02 sensor 15 in step 1405 is determined based on the activation flag FAc obtained in the routine of FIG. 10A, FIG. 10B, FIG. 12A, or FIG. 12B.

If the closed loop condition is satisfied, the process proceeds to step 1406, where the output v2 of the downstream side 02 sensor 15 is A/D converted and taken in. In step 1407, it is determined whether ■2 is lower than the comparison voltage ■8□, for example, 0.55V. In other words, it is determined whether the air-fuel ratio is rich or not.

In addition, the comparison voltage ■7□ is set at the upstream side 02 sensor 13, taking into account that the output characteristics are different due to the influence of raw gas and the deterioration rate is different upstream and downstream of the catalytic converter 12.
This is set higher than the comparison voltage of the output of ■□, but this setting may be arbitrary.

If v2≦VR2 (lean) in step 1407, proceed to steps 1408 and 1409; on the other hand, if VZ>V,
If it is 2 (rich), the process advances to steps 1410 and 1411.

In step 1408, 115R4-R3R+ΔR3 is set, that is, the rich skip amount R3R is increased to shift the air-fuel ratio to the rich side, and in step 1409, R5L←R5L-ΔR3 is set, that is, the lean skip amount R3L is decreased. The air-fuel ratio is further shifted to the rich side. On the other hand, in step 1410 R3R←R3R−
ΔR3, that is, the rich skip amount R3R is decreased to shift the air-fuel ratio to the lean side, and step 1
At 411, R3L −RSL+ΔI? S, that is,
The lean skip amount R3L is increased to further shift the air-fuel ratio to the lean side.

Step 1412 is R5R calculated as described above.

This is to perform guard processing of R3L, for example, guarding at maximum value MAX=7.5% and minimum value MIN=2.5%. Note that the minimum value MEN 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.

The routine of FIG. 14 then ends at step 1413.

When the output of the downstream 02 sensor 15, that is, the output v2 of the pull-up input circuit 112 changes in this way, the downstream 02 sensor 15 becomes active (FAc="1") after a delay time has elapsed since VZ<VA. Therefore, the rich skip amount R3R and the lean skip amount R3L are not over-corrected to the rich side. In addition, when activation is determined when the base air-fuel ratio is lean, there will be no erroneous erroneous determination immediately after activation determination.

FIG. 15 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360° CA.

In step 1501, the intake air amount data Q and the rotational speed data Ne are read from the RAM 105, and the basic injection amount T is read out.
Calculate AUP. For example, TAUP←α・Q/Ne(
α is a constant). At step 1502, the RAM 105
The cooling water temperature data THW is read out, and a warm-up increase value FWL is calculated by interpolation using the one-dimensional map stored in the ROM 104. In step 1503, the final injection amount TAU is
TAU 4-TAUP-PAF ・(FWL+β)
Calculate by +γ. Note that β and T are correction amounts determined by other operating state parameters. Next, in step 1504, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. This routine then ends in step 1505.

As described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the carrier signal of the down counter 108, and the fuel injection ends.

In addition, in a single 0□ sensor system in which a 0□ sensor is provided only downstream of the catalyst or in the catalyst and performs air-fuel ratio feedback control, the RSR of the second air-fuel ratio feedback routine is used instead of the first air-fuel ratio feedback routine described above. , R3L as PAF. In addition, although the output value of the pull-up input circuit was used as the output of the sub-02 sensor to be reflected in the air-fuel ratio feedback, the downstream sub-02
The output of the sensor can also be used directly.

In addition, the first air-fuel ratio feedback control is performed every 4 ms.
In addition, the second air-fuel ratio feedback control is performed every 512 m5, because the air-fuel ratio feedback control mainly controls the upstream 0□ sensor, which has good response, and controls the downstream 02 sensor, which has poor response. This is for the purpose of doing so.

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 present invention can be applied to a □ sensor system as well as a double 0□ sensor system that introduces 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 amounts R5R, 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 KIR 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, devices that adjust the amount of secondary air sent to the exhaust system of an engine, and the like. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 1501 is determined by the carburetor itself, that is, it is determined according to the intake pipe negative pressure depending on the intake air amount and the engine rotation speed, and in step 1503 The supplied air amount corresponding to the final fuel injection amount TAU is calculated.

Further, in the above embodiment, a 0□ sensor was used as the air-fuel ratio sensor, but a CO sensor, a 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, a delay time is introduced in determining the activation of the downstream air-fuel ratio sensor, so hunting in determining activation or inactivity is eliminated, and activation is determined when the base air-fuel ratio is lean. This eliminates rich misjudgments immediately after activation discrimination, which eliminates erroneous control of the air-fuel ratio.As a result, over-correction of control constants, air-fuel ratio control amounts, etc. can be prevented, reducing exhaust emissions, improving fuel efficiency, This is useful for preventing deterioration of drivability.

[Brief explanation of the drawing]

Figures 1A and 1B are overall block diagrams for explaining the present invention in detail. Figure 2 is a single 0□ sensor system and a double 0□ sensor system.
Figures 3A and 3B are circuit diagrams showing an example of the input circuit for the output of the 02 sensor. Figures 4A and 4B are the diagrams of the circuits in Figures 3A and 3B. Output characteristic diagram, Figure 5 is a diagram explaining the activation determination of the 02 sensor, Figures 6A and 6B are timing diagrams explaining the problems to be solved by the present invention, and Figure 7 is the internal combustion diagram according to the present invention. Overall schematic diagram showing one embodiment of an air-fuel ratio control device for an engine, Fig. 8, Fig. 10A, Fig. 10B, Fig. 12A, Fig. 12.
Figures B, 14, and 15 are flowcharts for explaining the operation of the control circuit in Figure 7, Figure 9 is a timing diagram for supplementary explanation of the flowchart in Figure 8, and Figure 11 is a flowchart for explaining the operation of the control circuit in Figure 10A. FIG. 13 is a timing diagram supplementary to the flowcharts in FIGS. 12A and 12B. l... Engine body, 3... Air flow meter, 4... Distributor, 5.6... Crank angle sensor, 10... Control circuit, 12... Catalytic converter, 13... Upstream side 02 sensor, 15... Downstream 02 sensor, 17... Idle switch.

Claims (1)

[Claims] 1. Three-way catalyst (12) provided in the exhaust passage of an internal combustion engine
an upstream air-fuel ratio sensor (13) provided in the exhaust passage upstream of the three-way catalyst to detect the air-fuel ratio of the engine; and an upstream air-fuel ratio sensor (13) provided in the exhaust passage downstream of the three-way catalyst to detect the air-fuel ratio of the engine. a downstream air-fuel ratio sensor (15) that detects the air-fuel ratio of the downstream air-fuel ratio; a pull-up input circuit (112) that supplies a minute current to the downstream air-fuel ratio sensor and inputs the output of the downstream air-fuel ratio sensor; a comparison means for comparing the output of the pull-up type input circuit with an activation level (V_A) slightly higher than the rich output level after warm-up; and a predetermined time period after the output of the pull-up type input circuit becomes lower than the activation level. a delay means that later determines that the downstream air-fuel ratio sensor is in an active state; and a control constant that calculates an air-fuel ratio feedback control constant according to the output of the downstream air-fuel ratio sensor when the downstream air-fuel ratio sensor is in the active state. calculation means; air-fuel ratio correction amount calculation means for calculating an air-fuel ratio correction amount according to the air-fuel ratio feedback control constant and the output of the upstream air-fuel ratio sensor; An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio adjusting means for adjusting; and an air-fuel ratio control device for an internal combustion engine. 2. The internal combustion engine according to claim 1, wherein the downstream air-fuel ratio sensor is determined to be in an inactive state after a predetermined period of time after the output of the pull-up input circuit becomes higher than the activation level. air-fuel ratio control device. 3. Three-way catalyst (12) installed in the exhaust passage of an internal combustion engine
and an air-fuel ratio sensor (provided in the exhaust passage downstream of the three-way catalyst or in the three-way catalyst) that detects the air-fuel ratio of the engine.
15), and a pull-up type input circuit (112) that flows a minute current into the air-fuel ratio sensor and inputs the output of the air-fuel ratio sensor.
and comparing means for comparing the output of the pull-up type input circuit with an activation level (V_A) slightly higher than the rich output level after warm-up, and when the output of the pull-up type input circuit becomes lower than the activation level. delay means for determining that the downstream side air-fuel ratio sensor is in an active state after a predetermined period of time; and a control amount calculation means for calculating an air-fuel ratio control amount according to the output of the air-fuel ratio sensor when the air-fuel ratio sensor is in the active state. An air-fuel ratio control device for an internal combustion engine, comprising:; and an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the calculated air-fuel ratio control amount. 4. The internal combustion engine according to claim 3, wherein the downstream air-fuel ratio sensor is determined to be in an inactive state after a predetermined period of time after the output of the pull-up input circuit becomes higher than the activation level. air-fuel ratio control device.