JPS63195352A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the overcorrection of the rich amount when the output performance is slow, by furnishing the first and the second O2 sensors at the front side and at the rear side of a catalyst, renewing the control constant depending on the output of the second O2 sensor, and making the renewed speed smaller until the output of the second O2 sensor is turned back. CONSTITUTION:A control circuit 10 computes a basic fuel injection quantity depending on the rotation frequencies from crank angle sensors 5 and 6 and the air intake amount from an air flow meter 3, and carrys out the feedback control of air-fuel ratio depending on the detected values of the first O2 sensor 13 and the second O2 sensor 15 which are furnished at the upper stream and the lower stream of a catalyst converter 12 respectively. That is, the rich skip amount is renewed larger when the second O2 sensor 15 indicates the lean output, while the lean skip amount is renewed larger when it indicates the rich output, and the feedback correction amount is computed from the renewed amount and the detected value of the first O2 sensor 13. The renewal value of the skip amount is set smaller until the control condition of the second O2 sensor 15 is accomplished and its output is reversed.

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 relates to an air-fuel ratio control device for an internal combustion engine that performs air-fuel ratio feedback control using a downstream Ot sensor in addition to air-fuel ratio feedback control using an upstream Ot sensor.

[Conventional technology]

Simple air-fuel ratio feedback control '4fJ (single 0□
In the sensor system), the 0□ sensor that detects oxygen concentration is installed in the exhaust system as close as possible to the combustion chamber, that is, in the gathering part of the exhaust manifold upstream of the catalytic converter. This poses a problem in improving the accuracy of air-fuel ratio control. In order to compensate for variations in the output characteristics of the 0□ sensor, variations in parts such as fuel injection valves, and changes over time or aging, a second Oz sensor is provided downstream of the catalytic converter, and the air-fuel ratio determined by the upstream 02 sensor is A double 02 sensor system that performs air-fuel ratio feedback control using a downstream 02 sensor in addition to feedback control has already been proposed (see Japanese Patent Laid-Open No. 58-48756). In this double 02 sensor system, the 0! Although the sensor has a lower response speed than the upstream OX sensor, it has the advantage of less variation 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 the rice poison is trapped in the catalyst downstream of the catalytic converter, the amount of poisoning of the downstream 02 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 air-fuel ratio feedback control (double 02 sensor system) based on the outputs of the two O2 sensors, variations in the output characteristics of the upstream 0□ sensor can be absorbed by the downstream 02 sensor. In fact, as shown in Figure 2, in a single 0□ sensor system, ot
If the output characteristics of the sensor deteriorate, it will directly affect the exhaust emission characteristics, whereas in the double 02 sensor system, the upstream 0. Even if the output characteristics of the sensor deteriorate,
Exhaust emission characteristics do not deteriorate, that is, double 0
In the photo sensor system, good exhaust emissions are guaranteed as long as the downstream 0□ sensor maintains stable output characteristics.

In the double 02 sensor system described above, the downstream 0
During execution of air-fuel ratio feedback control using 8 sensors, upstream side 0: Control constant of air-fuel ratio correction amount FAF based on sensor output, for example, rich skip amount R3R, lean skip amount RS-L, is output from downstream side 02 sensor. There is a system that performs variable control based on the downstream 0□ sensor, but due to the inactivity of the downstream 0□ sensor, etc. When stopping the variable control of the control constant based on the output of the sensor, the air-fuel ratio feedback control based only on the output of the upstream 02 sensor is performed using the value stored in the backup RAM etc. when the control constant was being variable controlled. (Reference: Japanese Unexamined Patent Publication No. 192828/1983).

[Problem that the invention seeks to solve]

However, the downstream side is 0! The conditions for stopping the variable control of the control constant by the sensor, that is, the conditions for prohibiting the air-fuel ratio feedback control by the downstream 03 sensor, are: the cooling water temperature is below a predetermined temperature, the engine is in a non-idling state, the fuel is being cut, and the engine is started. Because the downstream 02 sensor output never crosses the reference value, the downstream 0! Even if the variable control of the control constant based on the output of the sensor is resumed, the downstream 0□ sensor has not fully changed from the inactive state, and
Catalyst 0! There is also the influence of the storage effect, and therefore the output response from lean to rich may be extremely slow, or the response of the downstream 02 sensor may be slow due to product variations, changes over time, etc.

As a result, even if the air-fuel ratio downstream of the catalyst actually becomes rich, the downstream 02 sensor will show a lean output for a while,
Therefore, the control constant is over-corrected to the rich side, and the control constant sticks to the upper or lower limit value, and the effects remain for a long time, resulting in increases in HC and Co emissions, deterioration in fuel efficiency, etc. There was a problem in that it invited

Therefore, an object of the present invention is to prevent over-correction immediately after the variable control of the control constant by the output of the downstream air-fuel ratio sensor (0□ sensor) is resumed, thereby increasing IC and Co emissions and deteriorating fuel efficiency. The goal is to prevent

[Means for solving problems]

A means for solving the above-mentioned problems is shown in FIG.

In Figure 1, one
, each of which detects the concentration of a specific component in the exhaust gas.
, a second air-fuel ratio sensor is provided. The downstream air-fuel ratio feedback condition determination means determines whether the air-fuel ratio feedback condition by the downstream (second) air-fuel ratio sensor is satisfied, and as a result, when the air-fuel ratio feedback condition is satisfied. Then, the control constant updating means updates the air-fuel ratio feedback control constants, such as the rich skip amount R3R and the lean skip 11R3L, at a predetermined update rate ΔR5 in accordance with the output (2) of the downstream air-fuel ratio sensor. On the other hand, the reversal determining means uses the output V of the downstream air-fuel ratio sensor.
! Determine whether or not the has been reversed. The update speed calculation means sets the update speed ΔRS of the air-fuel ratio feedback control constants RSR and RSL to be small (ΔR3-RSI) from after the air-fuel ratio feedback condition is satisfied until the reversal of the output V2 of the downstream air-fuel ratio sensor; , after that it becomes large (ΔR3
=R32) (RSI <R52), and the air-fuel ratio correction amount calculation means uses the air-fuel ratio feedback control constant RS.
R.

RSL and the output V of the upstream (first) air-fuel ratio sensor,
The air-fuel ratio correction unit 1iFAF is calculated in accordance with the air-fuel ratio correction amount FAF, and the air-fuel ratio adjustment means adjusts the air-fuel ratio of the engine in accordance with the air-fuel ratio correction amount FAF.

[For production]

According to the above-described means, at the beginning of the variable control of the air-fuel ratio feedback control constant based on the output of the downstream air-fuel ratio sensor being resumed, the air-fuel ratio feedback control constant is updated at a small update rate.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 3 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. 3, an air flow meter 3 is provided in the intake passage 2 of the engine body l. The airflow meter 3 directly measures the amount of intake air, and includes a built-in potentiometer to generate an analog voltage output signal proportional to the amount of intake air. 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° in terms of crank angle, and a crank angle sensor 5 which generates a reference position detection pulse signal every 30' 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 input/output interface 102 of the control circuit 10, 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 boat 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 harmful components IC, Go, and NOx in the exhaust gas.

In the exhaust manifold 11, in other words, the catalyst converter 1
On the upstream side of 2 is the first O! A sensor 13 is provided, and a second 08 sensor 15 is provided in the exhaust pipe 14 on the downstream side of the catalytic converter 12.

The o2 sensors 13 and 15 generate electrical signals according to the concentration of oxygen components in the exhaust gas. That is, 0. Sensor 13
, 15, the control circuit 10 outputs different output voltages depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.
This occurs in the D converter 101.

Further, the throttle valve 16 of the intake passage 2 is provided with an idle switch 17 for determining whether the throttle valve 16 is fully closed or not, and this output signal is supplied to the input/output interface 102 of the control circuit 10. Ru.

The control circuit IO is configured as a microcomputer, for example, and includes an A/D converter 101, an input/output interface 102 . In addition to the CPU 103, there is a ROM 104.

A RAM 105, a backup RAM 106, a clock generation circuit 107, and the like are provided.

In addition, in the control circuit IO, 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 1tTAU is preset in the down counter 108 and the flip-flop 10
9 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, the down counter 108
counts the black signal (not shown) and finally when the carrier voltage terminal reaches the "1" level, the flip-flop 109 is set and the drive circuit 110 activates the fuel injector 7. Stop. In other words, the above fuel injection amount T
The fuel injection valve 7 is energized by AU, 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 103 is caused by the A/D converter 10.
1, 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 fetched 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° CA, and is stored in a predetermined area of the RAM 105.

First, the output V! of the downstream side 02 sensor 15 is determined using the timing diagrams shown in FIGS. 4 and 5. Problems with the lynch skip amount R3R and lean skip amount R3L as air-fuel ratio feedback control will be explained. In FIGS. 4 and 5, ■1 indicates 0 on the upstream side. The output of the sensor 13 is the output of the downstream side 08 sensor 15, and the rich skip amount R3R.

The lean skip amount R3L is calculated according to the comparison result between the output v3 of the downstream side 08 sensor 15 and the comparison voltage V□,
The air-fuel ratio correction coefficient FAF is 0 on the upstream side! Output v of sensor 13
Comparison result between I and comparison voltage v1 and skip amount R5R
, R5L.

FIG. 4 shows a case where the responsiveness of the downstream O2 sensor 15 from lean to rich is relatively fast. In this case, downstream O! 'The output V of the sensor 15 changes relatively quickly from lean level (low level) to color rich level (high level) as shown by arrow X after the start of air-fuel ratio feedback control by the downstream Ox sensor, so rich skip is detected. IR3R and lean skip amount R5L are maintained at appropriate levels, and therefore, the air-fuel ratio correction coefficient FAF is maintained at a stable level, that is, a level corresponding to the stoichiometric air-fuel ratio.

On the other hand, FIG. 5 shows a case where the response of the downstream Ot sensor 15 from lean to rich is relatively slow. In this case, the output v8 of the downstream Ot sensor 15 is
After starting the air-fuel ratio feedback control by the sensor, arrow Y
As shown in , since the lean level (low level) changes relatively slowly from the rich level (high level), the rich skip amount R3R and lean skip amount R3L are over-corrected to the rich side, and therefore the air-fuel ratio correction coefficient FAF is In other words, the level is on the richer side than the stoichiometric air-fuel ratio.

The present invention attempts to prevent rich-side overcorrection of the rich skip IIRS R and the lean skip amount R3L when the responsiveness from the lean output to the rich output of the downstream side 02 sensor 15 is slow. , downstream O
This is achieved by reducing the update speed changes of the rich skip 1iR3R and the lean skip amount RSL from the start of the air-fuel ratio feedback control by the be.

FIG. 6 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 02 sensor 13, and is executed every predetermined period of time, for example, every 4 m.

In step 601, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the upstream 08 sensor 13 is satisfied. For example, when the cooling water temperature is below a predetermined value (for example, 60 degrees Celsius), while the engine is starting, during engine startup, during warm-up increase, during acceleration increase (asynchronous injection), during power increase, upstream O! When the output signal of the sensor 13 has never been inverted, the closed loop condition is not met when the fuel is being cut (that is, LL = "1" and Ne is above a predetermined value), etc., and in other cases, the closed loop condition is not met. It is established.

If the closed loop condition is not satisfied, the process proceeds to step 627 and the air-fuel ratio correction coefficient FAF is set to 1.0. In addition, F.A.
F may be set to the value immediately before the end of the closed loop wi control. In this case, the process directly proceeds to step 628, or may be set to a learned value (value of the bank up RAM 106). On the other hand, if the closed loop condition is satisfied, step 602 Proceed to.

In step 602, the output v1 of the upstream 0□ sensor 13 is
In step 603, it is determined whether or not (1) is less than the comparison voltage Vll, for example, 0.45V. In other words, it determines whether the air-fuel ratio is rich or lean. If lean (v1≦Vm+), it is determined in step 604 whether the delay counter CDLY is positive or not, and CDLY>
If Q, CDLY is set to O in step 605 and the process proceeds to step 606. In steps 607 and 608, the delay counter CDLY is guarded at the minimum value TDL, and in this case, when the delay counter CDLY reaches the minimum value TDL, the step is stopped. At 609, set the air-fuel ratio flag F1 to 0.
'' (lean).The minimum value TDL is 0 on the upstream side.
This is a one-step delay time for maintaining the determination that the rich state is in the rich state even if the output of the wealth sensor 13 changes from rich to lean, and is defined as a negative value. On the other hand,
If it is rich (vg>v□), it is determined in step 610 whether the delay counter CDLY is negative or not, and CDLY is
If <0, step 611 sets cDIJ to 0 and proceeds to step 612. In steps 613 and 614, the delay counter CDLY is guarded at the maximum value TDR; in this case, the delay counter CDLY is set to the maximum value TDR.
When the air-fuel ratio flag F reaches step 615, the air-fuel ratio flag F
1 is "l" (rich), and the maximum value TDR is 0.1 on the upstream side. This is a 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 616, it is determined whether the sign of the 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 has been reversed, in step 617, it is determined based on the value of the air-fuel ratio flag Fl whether the reversal from rich to lean is the reversal from lean to rich. If it is a reversal from rich to lean, then in step 618 FAF←FAF +R5R is increased in a skip manner, and conversely, if it is a reversal from lean to rich, FAF←FAF-R5L is increased in a skip manner in step 619. decrease to That is, if the sign of the air-fuel ratio flag Fl is not inverted in step 616, in which skip processing is performed, integration processing is performed in steps 620, 621, and 622. That is, in step 620, Fl−“θ′″
If it is Fl-“0” (lean), go to step 621 and set FAF 4-FAF +KIR.
On the other hand, if it is Fl-41'' (rich), step 622
FAF 4-PAP-KIL. Here, the integral constant KIR (KIL) is set sufficiently smaller than the skip constants RSR and R9L, that is, KIl? (K
fL) < R2H(R5L). Therefore, step 621 gradually increases the fuel injection amount in the lean state (F1="O"), and step 622 gradually increases the fuel injection amount in the rich state (Fl-
"1") gradually reduces the fuel injection amount. Step 6
The air-fuel ratio correction coefficient FAF calculated at 18,619°621.622 is guarded at the maximum value, for example, 1.2 at step 623.624, and is guarded at the maximum value, for example, 1.2 at step 625.6.
26 is guarded at a minimum value, for example, 0.8. As a result, if the air-fuel ratio correction coefficient FAF becomes too small or too large for some reason, the air-fuel ratio of the engine is controlled using that value to prevent over-lean or over-rich conditions.

The FAF calculated as described above is stored in the RAM 105, and the routine ends in step 628.

FIG. 7 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. 6. When the air-fuel ratio signal A/F for rich/lean discrimination is obtained from the output of the upstream Oz sensor 13 as shown in FIG. 7(A), the delay counter CD
As shown in FIG. 7 (CB), LY is counted up in the rich state and counted down in the lean state.

As a result, a delayed air-fuel ratio signal A/F' (corresponding to flag F1) is formed as shown in FIG. 7(C). For example, at time t1, the air-fuel ratio signal A/F is lean Even if the air-fuel ratio changes from rich to rich, the delayed air-fuel ratio signal A/
F1' is kept lean for the rich delay time TDR and then changes to rich at time 1z. 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%
+1 & , 1. If the delay counter CDLY is reversed in a period shorter than the rich delay time TDR, it will take time for the delay counter CDLY to reach the maximum value TDR, and as a result, the time t.
At , the air-fuel ratio signal A/F' after the delay process is inverted. In other words, the air-fuel ratio signals A/, F' after the delay processing are more stable than the air-fuel ratio signals A/F before the delay processing. In this manner, the air-fuel ratio correction coefficient FAF shown in FIG. 7(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 Oz sensor 15 will be explained. As the second air-fuel ratio feedback control, the skip amount RSR, R5L as the first air-fuel ratio feedback control constant, the integral constant K
IR, KIL, delay time TDR, TDL.

Or the comparison voltage V of the output vI of the upstream 02 sensor 13
A system for making ll variable and a second air-fuel ratio correction coefficient F
There is a system that introduces AF2.

For example, if you increase rich skip 1lR3R,
The control air-fuel ratio can be shifted to the rich side, and even if the lean skip amount R3L is reduced, the control air-fuel ratio can be shifted to the rich side. On the other hand, if the lean skip amount R3L is increased,
The control air-fuel ratio can be shifted to the lean side, and even if the rich skip amount R5R is decreased, the control air-fuel ratio can be shifted to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the rich skip 11R3R and the lean skip amount RSL according to the output of the downstream Ot sensor 15. Furthermore, if the rich integral constant KIR is increased, the controlled air-fuel ratio can be shifted to the rich side, and even if the lean integral constant KIL is decreased, the controlled air-fuel ratio can be shifted to the rich side;
By increasing L, the control air-fuel ratio can be shifted to the lean side,
Further, even if the rich integral constant KIR is made smaller, the controlled air-fuel ratio can be shifted to the lean side. Therefore, downstream Of sensor 1
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 5. Rich delay time TDR > Lean delay time (-TDL)
If set as
R), the control '8 air-fuel ratio can be shifted to the lean side. That is, the air-fuel ratio can be controlled by correcting the delay times TDR and TDL according to the output of the downstream Oz sensor 15. Furthermore, by increasing the comparison voltage V□, the controlled air-fuel ratio can be shifted to the rich side, and by decreasing the comparison voltage V□, the controlled air-fuel ratio can be shifted to the lean side.

Therefore, by correcting the comparison voltage ■□ according to the output of the downstream side Ot sensor 15, the air-fuel ratio can be controlled.

Set these skip amount, integral constant, delay time, and comparison voltage to 0 on the downstream side! Each sensor has its own advantages. For example, the delay time allows 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.

Referring to FIG. 8, the double 0.0. The sensor system will be explained.

FIG. 8 shows a second air-fuel ratio feedback control routine that calculates the skip amounts RSR and RSL based on the output of the downstream 02 sensor 15, and is executed at predetermined intervals, for example, every IS. In steps 801 to 803, downstream 0
8 sensor 15 determines whether the condition is a closed loop condition or not. For example, upstream side 0. In addition to the failure of the closed loop condition determined by the sensor 13 (step 801), when the cooling water temperature THW is below a predetermined value (for example, 70°C) (step 802)
, when the throttle valve 16 is fully closed (LL="l") (step 803), etc., the closed loop condition is not satisfied, and in other cases, the closed loop condition is satisfied. If the closed loop condition is not met, the process advances to step 822 and the air-fuel ratio reversal flag FB is set.
t-″01. In this case, RSR.

RSL is held at the value immediately before the end of the closed loop.

Downstream side 0. If the closed loop condition is satisfied by the sensor 15, the process proceeds to steps 804 to 806, and the rich skip IR
SR, the update rate ΔR5 of the lean skip amount RSL is calculated. That is, it is determined in step 804 whether the air-fuel ratio reversal flag FB is "0" or not, and when FB=@0'', ΔR5-RSI is set in step 805, and when FB-"1", in step 806 ΔR
5←R32, however, RSI<R52.

Next, in step 807, the downstream side 0. The output ■2 of the sensor 15 is A/D converted and taken in, and in step 809 v
It is determined whether t is less than the comparison voltage V1g, for example 0.55V, that is, it is determined whether the air-fuel ratio is rich or lean.

In step 808, if V, ≦Vat (lean), proceed to steps 809 to 814; on the other hand, v, >vat
(rich), the process advances to steps 815 to 821.

In step 809, RSR4-RSR+ΔR5,
That is, the rich skip amount R3R is increased to shift the air-fuel ratio to the rich side. In step 810.811 R
The SR is guarded at the maximum value MAX, for example 7.5%.

Furthermore, in step 812, RSL←RSL −ΔR5
In other words, the rich skip amount R3L is decreased to shift the air-fuel ratio to the rich side. Step 813.814
Then, the RSL is guarded at a minimum value MIN, for example, 2.5%.

On the other hand, V! >V. (Rich), step 8
In step 15, RSR←R5R-ΔR5 is established, that is, the rich skip amount R3R is decreased to shift the air-fuel ratio to the lean side. Step 819.820 sets the RSL to maximum M
Guard with AX. Furthermore, in step 821, the air-fuel ratio is inverted and the flag FB is set to "l".

That is, in this example, while the second air-fuel ratio feedback control is stopped, the downstream side is 0! Assuming that the output v2 of the sensor 15 is lean, if there is a rich output after the second air-fuel ratio feedback control condition is satisfied, the downstream side 0□sensor 1
It is assumed that the output v2 of 5 is inverted.

Note that after the second air-fuel ratio feedback control, the downstream side 0: sensor 1 is sent immediately before step 823 instead of step 821.
Of course, the flag FB may be operated depending on whether or not the output ■ wealth of No. 5 crosses a reference value (for example, V*z).

RSR and RSL calculated as described above are stored in the RAM 105.
The routine ends at step 823.

Note that FAF calculated during air-fuel ratio feedback,
RSR, RSL are temporarily changed to other values PAP', RSR'
, RSL' and stored in the backup RAM 106. By using these values during air-fuel ratio oven loop control, for example, at the time of restart, immediately after startup, etc., or 0! It is also useful for improving drivability when the sensor is inactive. The minimum value MIN in FIG. 8 is a value at a level that does not impair transient followability, and
The maximum value MAX is a value at which drivability does not deteriorate due to air-fuel ratio fluctuations.

The flowchart of FIG. 8 will be further explained with reference to FIG. 9.

In FIG. 9, when the air-fuel ratio feedback control by the downstream side 08 sensor 15 starts at time t, the air-fuel ratio reversal flag FB is 0'' at this point, so the flow in step 804 is changed to step 805. Then, the update rate ΔR3 is set to a small value R5I.

If the above state (FB-“O”) continues, as shown in FIG. 9, rich skip I! R8R increases slowly;
The lean skip amount R3L decreases slowly. Rich-side overcorrection of the skip amounts R5R and R5L is suppressed.

Next, at time t8, the downstream side 0. Output v of sensor 15
8 changes from lean to rich, the flow at step 804 proceeds to step 806, where the update rate ΔR3 is set to a large value R32. As a result, the skip amount R9R
, RSL are significantly updated to the lean side, and the air-fuel ratio inversion flag FB is inverted from "O" to @1.

Thereafter, if air-fuel ratio feedback control is being performed by the downstream O2 sensor 15, the air-fuel ratio reversal flag FB is 11'', so the update speed is set high.

As described above, according to the routine shown in FIG. 8, from time t1 to t8 in FIG. 9, the skips 11RsR and RSL are updated at the update rate R3I, and after time t8, they are updated at the large update rate R52.

In addition, in FIG. 9, when the times t and -t are also updated with the skip amounts R5R and RSL at a large update speed R52,
Skip NR5R and RsL are overcorrected to the rich side as shown by the dotted line, and the effect remains for a while, which is disadvantageous in terms of IC, CO emissions, and fuel efficiency.

In particular, frequent air-fuel ratio feedback control is prohibited when downstream air-fuel ratio feedback control is held while downstream air-fuel ratio feedback control is stopped, and when downstream air-fuel ratio feedback control is restarted, control is started from that value. , Each time permission is repeated, the phenomenon shown by the dotted line at t and Nt occurs, and the control constant may diverge, which is undesirable, but in this example, the erroneous correction is reduced and the emission is not worsened. .

FIG. 10 shows an injection amount calculation routine, which is executed every predetermined crank angle, for example, 360° CA. In step 1001, the intake air amount data Q and the rotational speed data Ne are read out from the RAM 105 to calculate the basic injection amount TAUP. For example, TAUP←α·Q/Ne (α is a constant). At step 1002, 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.

In step 1003, the final injection amount TAU is determined as TAU ←TAUP-PAP ・(FWL+β+1)
Calculate by +T. Note that β and γ are correction amounts determined by other operating state parameters. Next, in step 1004, 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 1005. In addition, as mentioned above, the injection amount T
When the time corresponding to AU has passed, the down counter 10
The flip-flop 109 is activated by the carrier signal of 8.
is reset and fuel injection ends.

The first air-fuel ratio feedback control is performed every 4ais, and the second air-fuel ratio feedback control is performed every IS because the air-fuel ratio feedback control is mainly controlled by the upstream O2 sensor with good response. This is because the control by the downstream O2 sensor, which has poor responsiveness, is performed as a subsidiary.

Also, upstream side 0. A double Ox sensor system that corrects other control constants in air-fuel ratio feedback control by the sensor, such as an integral constant, delay time, comparison voltage v□ of the upstream 02 sensor, etc. The present invention can also be applied to a double 0□ sensor system that introduces an air-fuel ratio correction factor of 2. Moreover, controllability can be improved by simultaneously controlling two of the skip amount, integral constant, and delay time. In addition, skip 1l
It is possible to fix one of R5R and R5L and make only the other variable, or to fix one of the integral constants KIR and KIL and make only the other variable, or to change one of the delay times TDR and TDL. It is also possible to have one fixed and 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 1001 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 rotational speed of the engine, and in step 1003 The supplied air amount corresponding to the final fuel injection amount TAU is calculated.

Further, in the above embodiment, an Ot sensor is 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, even if the output characteristic of the downstream side air-fuel ratio sensor from lean to lean is slow, excessive rich correction of control constants etc. can be prevented, reducing exhaust emissions and improving fuel efficiency. This will help you improve your skills.

[Brief explanation of the drawing]

Figure 1 is an overall block diagram for explaining the present invention in detail, Figure 2 is a single 02 sensor system and double Ox
FIG. 3 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. 4 and 5 are diagrams showing problems to be solved by the present invention. Figures 6, 8, and 10 are flowcharts to explain the operation of the control circuit in Figure 3, and Figure 7 is a supplementary explanation of the flowchart in Figure 6. FIG. 9 is a timing diagram supplementary to the flowchart in FIG. 8. l... Engine body, 3... Air flow meter,
4... Distributor 5.6... Crank angle sensor, 10... Control circuit, 12... Catalytic converter, 13... Upstream side (first) O2 sensor, 15...
Downstream side (second) 0! Sensor, 17...Idle switch.

Claims (1)

[Scope of Claims] 1. A first catalytic converter installed on the upstream side and downstream side of a catalytic converter for purifying exhaust gas provided in the exhaust system of an internal combustion engine, and configured to detect the concentration of a specific component in the exhaust gas. a second air-fuel ratio sensor; a downstream air-fuel ratio feedback condition determining means for determining whether an air-fuel ratio feedback condition by the second air-fuel ratio sensor is satisfied; control constant updating means for updating an air-fuel ratio feedback control constant at a predetermined update rate in accordance with the output of the second air-fuel ratio sensor; and determining whether or not the output of the second air-fuel ratio sensor has been inverted. and a reversal determination means that changes the update rate of the air-fuel ratio feedback control constant to the second one after the air-fuel ratio feedback condition is satisfied.
The period up to the reversal of the output of the air-fuel ratio sensor is small; on the other hand,
an update speed calculation means for increasing the update speed thereafter; an 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 first air-fuel ratio sensor; An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine accordingly. 2. The air-fuel ratio of the internal combustion engine according to claim 1, wherein the air-fuel ratio feedback control constant is held at a value immediately before the air-fuel ratio feedback control condition was not satisfied when the air-fuel ratio feedback control condition is not satisfied. Control device. 3. The internal combustion engine according to claim 1, wherein the update rate calculation means reduces the update rate of the air-fuel ratio feedback control constant only when the output of the second air-fuel ratio sensor indicates lean. Air-fuel ratio control device.