JPH02241944A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent deterioration of emission and drivability by adjusting the air-fuel ratio according to the air-fuel ratio correction amount when an engine is in the non- transient condition and according to the air-fuel ratio correction amount and a deposit learning value in the transient condition. CONSTITUTION:When an engine is in the non-transient condition, air-fuel ratio correction amount calculating means calculate air-fuel ratio correction amount from an air-fuel ration feedback constant calculated at a designated update speed by control constant calculating means according to the output V2 of a downstream O2 sensor and the output V1 of an upstream O2 sensor. On the other hand, when it is judged by judging means that the engine satisfies a deposit learning condition, deposit learning means obtain a deposit learning value according to a deviation of the output V1. When the learning value is more than a designated value, update speed calculating means increase the update speed to the rich side of a control constant at the time of acceleration and to the lean side at the time of deceleration. In the transient condition, the air-fuel ratio is adjusted according to the air-fuel ratio correction amount and a deposit learning value. Thus, the deterioration of exhaust or the like can be prevented.

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 the air-fuel ratio feedback control by the 02 sensor on the upstream side, the air-fuel ratio control for the internal combustion engine performs air-fuel ratio feedback control by the 0□ sensor on the downstream side and learning control of the fuel amount during transient times (during acceleration/deceleration). Regarding equipment.

[Conventional technology]

In simple air-fuel ratio feedback control (single 02 sensor system), oxygen concentration is detected. 2 sensors are installed in the exhaust system as close to the combustion chamber as possible, that is, in the exhaust manifold assembly section upstream of the catalytic converter, but due to variations in the output characteristics of the 0□ sensors, it is difficult to improve the accuracy of air-fuel ratio control. There is a problem. It takes 0□
In order to compensate for variations in sensor output characteristics, variations in parts such as fuel injection valves, and changes over time or aging, a second 02 sensor is provided downstream of the catalytic converter, and air-fuel ratio feedback control by the upstream O2 sensor is performed. In addition, a double 0□ sensor system that performs air-fuel ratio feedback control using a downstream 0□ sensor has already been proposed (
(Reference 2 Japanese Patent Application Laid-Open No. 61-234241). In this double 0□ sensor system, the 02 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 mentioned above, air-fuel ratio feedback control'! based on the outputs of the two 0□ sensors! 5 (double 0
2 sensor system), variations in the output characteristics of the upstream 02 sensor can be absorbed by the downstream 0□ sensor. In fact, as shown in Figure 2, in the single 02 sensor system, if the 02 sensor output characteristics deteriorate, it directly affects the exhaust emission characteristics, whereas the double 0□
In the sensor system, even if the output characteristics of the upstream 0□ sensor deteriorate, the exhaust emission characteristics do not deteriorate. In other words, in the double Ox sensor system, as long as the downstream 02 sensor maintains stable output characteristics, good exhaust emissions are guaranteed.

On the other hand, in order to deal with characteristic changes due to valve clearance, deposits on the injection valve nozzle, deposits on the back of the cylinder intake valve, etc., deposit learning control is performed as a correction during transient times (during acceleration/deceleration). (Reference: JP-A-59-203829, JP-A-59-1
28944, Japanese Patent Application Laid-Open No. 60-204937)
.

[Problem to be solved by the invention]

However, when the above-mentioned double 0□ sensor system and deposit learning control system are combined, air-fuel ratio feedback control by the downstream 0□ sensor is usually performed even when deposit learning control is executed, and as a result, the downstream 0□ There is a problem in that the air-fuel ratio feedback control by the sensor becomes unstable and the air-fuel ratio feedback control constant is disturbed, leading to deterioration of emissions, deterioration of drivability, deterioration of fuel efficiency, etc.

In other words, when the amount of deposit increases, it is no longer possible to maintain the control air-fuel ratio at the stoichiometric air-fuel ratio even if you increase or decrease the fuel injection amount during acceleration and deceleration.In other words, the air-fuel ratio upstream of the catalyst becomes lean during acceleration. Therefore, the air-fuel ratio downstream of the catalyst becomes lean and the air-fuel ratio feedback control constant becomes large (to the rich side).Conversely, during deceleration, the air-fuel ratio upstream of the catalyst becomes rich, and therefore the air-fuel ratio downstream of the catalyst becomes rich. As a result, the air-fuel ratio feed control constant becomes smaller (to the lean side). As a result, when there is a large amount of deposits, if deceleration is performed immediately after acceleration, the air-fuel ratio upstream of the catalyst becomes thicker (richer), resulting in worsening of emissions and
This will lead to deterioration in fuel efficiency, and conversely, if the vehicle is accelerated immediately after deceleration, the air-fuel ratio upstream of the catalyst will become significantly leaner, leading to deterioration in emissions and drivability.

Therefore, an object of the present invention is to prevent deterioration of emissions, drivability, and fuel efficiency by preventing disturbances in the air-fuel ratio feedback control constant in a system in which a double air-fuel ratio sensor system and a deposit learning control system coexist. It's about doing.

[Means to solve the problem] A means for solving the above problem is shown in FIG.

That is, a three-way catalyst C installed in the exhaust passage of an internal combustion engine
An upstream air-fuel ratio sensor for detecting the air-fuel ratio of the engine is provided in the exhaust passage upstream of Cmo, and a three-way catalyst CC
A downstream air-fuel ratio sensor that detects the air-fuel ratio of the engine is provided in the exhaust passage downstream of the go. The control constant calculation means determines a predetermined update rate R1? according to the output ■2 of the downstream air-fuel ratio sensor. (RL) calculates air-fuel ratio feedback control constants, such as skip amounts R3R, RSL, and as a result, the air-fuel ratio correction amount calculation means determines whether the engine is air-fuel ratio feedback control constant R5I? , l? The air-fuel ratio correction IFAF is calculated according to sL and the output (1) of the upstream air-fuel ratio sensor.

On the other hand, the deposit learning condition determining means determines whether or not the engine satisfies the deposit learning condition, and as a result, when the engine satisfies the deposit learning condition, the deposit learning means detects the output of the upstream air-fuel ratio sensor. DC is calculated on the deposit learning value KAC, according to the deviation of 1. Further, when the deposit learning value KAC (and DC) is equal to or higher than a predetermined value, the update speed calculation means increases the update speed RR (RL) to the rich side of the air-fuel ratio feedback control constant R3R (RSL) during engine acceleration. However, during engine deceleration, the air-fuel ratio feedback control constant R5R (R
SL) update speed to lean side I'll? Increase (RL). The air-fuel ratio adjustment means adjusts the air-fuel ratio of the engine according to the air-fuel ratio correction IFAF when the engine is in a non-transient state, and adjusts the air-fuel ratio of the engine according to the air-fuel ratio correction amount FAF and deposit learning values KAC and KDC when the engine is in a transient state. This is to adjust the air-fuel ratio of the

C Effect] The effect of the above-mentioned means is shown in FIG. That is, when the intake air pressure PM changes as shown in the figure, if the deposit learning value is greater than a predetermined value (that is, if the deposit amount is large), the response delay of the air-fuel ratio sensor and the deposit,
As a result, the air-fuel ratio upstream of the catalyst becomes lean during acceleration, and therefore, the air-fuel ratio feedback control constant, for example, R2H becomes larger (becomes richer). As a result, when the speed is reduced thereafter, the air-fuel ratio upstream of the catalyst becomes much richer.

In the present invention, the hatched portion 1 (tz~t
3) Air-fuel ratio feedback control constant RSI? (RS
The update speed of L) to the rich side is increased. In the shaded portion n (ts to ta) of the deceleration state, the update speed of the air-fuel ratio feedback control constant RSR (RSL) toward the lean side is increased. As a result, the air-fuel ratio upstream of the catalyst immediately converges to the stoichiometric air-fuel ratio.

Although the applicant has not directly detected the deposit a, the applicant has already proposed increasing the update rate of the air-fuel ratio feedback control constant as the output of the downstream air-fuel ratio sensor deviates from the stoichiometric air-fuel ratio. (Reference: Japanese Patent Application 1986-
25589), if we focus on the acceleration, the air-fuel ratio feedback control constant is largely set to the lean side from 2' at the time shown in Fig. 3, and as a result, the air-fuel ratio upstream of the catalyst changes to the stoichiometric air-fuel ratio. Convergence will take time.

In addition, the applicant has already proposed that the update rate of the air-fuel ratio feedback control constant be increased as the rich or lean duration time of the downstream air-fuel ratio sensor increases (see: Japanese Patent Application No. 1983-1989). 25588), during acceleration, the update rate of the air-fuel ratio feedback control constant is increased to the rich side from time L2'' shown in FIG. 3, and therefore, the air-fuel ratio upstream of the catalyst converges to the stoichiometric air-fuel ratio. It will definitely take time.

〔Example〕

FIG. 4 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. 4, a pressure sensor 3 is provided in an intake passage 2 of an engine body l.

The pressure sensor 3 directly measures the absolute pressure PM of the intake air pressure, and is, for example, a semiconductor type sensor, which generates an analog voltage output signal proportional to the intake air pressure.

This output signal is the control circuit 10's multiplexer built-in A/
is provided to the D converter 101. The distributor 4 has a shaft with a crank angle of 720, for example.
A crank angle sensor 5 that generates a pulse signal for detecting a reference position every degree and a crank angle sensor 6 that generates a pulse signal for detecting a reference position every 30 degrees in terms of crank angle are 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
It is supplied to the interrupt terminal of U103.

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 tic, CO, and NO in the exhaust gas.

In the exhaust manifold it, namely the catalytic converter 1
A first O2 sensor 13 is provided on the upstream side of the catalytic converter 12, and a second O2 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 of 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. The control circuit 10 is configured as a microcomputer, for example, and includes an A/D converter 1
01, input/output interface 102, CPU103
In addition to the above, 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 that generates a signal TA indicating a signal LL indicating whether or not the throttle valve 16 is fully closed. 10 input/output interfaces 102.

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, when the fuel injection amount TAU is calculated, the fuel injection amount TAU is preset in the down counter 108 and the 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 10 counts the clock signal (not shown) and finally its borrow out terminal becomes "L" level, the flip-flop 10
9 is set, and the drive circuit 110 stops energizing the fuel injection valve 7. 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.

f.
When 02 receives the pulse signal of the crank angle sensor 6,
When receiving an interrupt signal from the clock generation circuit 107,
etc.

The intake air pressure data PM and the cooling water temperature data THW of the pressure sensor 3 are taken in by an A/D conversion routine executed at a predetermined time or every predetermined crank angle and stored in the RAM.
105 in a predetermined area.

In other words, the data PM and T in the RAM 105
The HW is updated at predetermined intervals. Further, the rotational speed data Ne is calculated by an interrupt every 30'CA of the crank angle sensor 6 and stored in a predetermined area of the RAM 105.

FIG. 5 shows a first air-fuel ratio feedback control routine that calculates 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 501, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the upstream 0□ sensor 13 is satisfied. For example, when the cooling water temperature is below a predetermined value, the output signal of the upstream 0□ sensor 13 is The closed-loop condition is not satisfied in all cases such as fuel cut, etc., and the closed-loop condition is satisfied in all other cases. If the closed loop condition is not met, the process proceeds directly to step 527. Note that the air-fuel ratio correction coefficient FAF may be set to 1.0.

On the other hand, if the closed loop condition is satisfied, the process proceeds to step 502.

In step 502, the output v1 of the upstream 02 sensor 13 is
is A/D converted and taken in, and in step 503, it is determined whether ■ is less than the comparison voltage Vll+, for example, 0.45V, that is, it is determined whether the air-fuel ratio is rich or lean, that is, lean (V1≦ Vm+), skip 50
4, it is determined whether the delay counter CDLY is positive or not.
If CDLY>Q, set CDLY to 0 in step 505.
Then, the process proceeds to step 506. In step 506, the delay counter CDLY is decremented by 1, and in step 507.
At 508, the delay counter CDLY is guarded with the minimum value TDL. In this case, when the delay counter CDLY reaches the minimum value TDL, the first
The air-fuel ratio flag F1 is set to 0'' (lean).The minimum value TDL is set to maintain the judgment that the engine is in a rich state even if there is a change from rich to lean in the output of the upstream 0□ sensor 13. is a lean delay state defined by a negative value.On the other hand, lean (V + > V * I
), in step 510 the delay counter CD
It is determined whether LY is negative or not, and if CDLY<Q, CDLY is set to 0 in step 511 and the process proceeds to step 512. In step 512, the delay counter CDLY is set to 1.
Then, in steps 513 and 514, the delay counter CDLY is guarded at the maximum value TDR. In this case, when the delay counter CDIJ reaches the maximum value TDR, the first air-fuel ratio flag Fl is set to "l" in step 515.
11 (rich). Note that the maximum value TDR is 0 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 516, 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 517, 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, Sten 7'518 NiteFAF +FAF1R
If SR is increased in a skip manner and, conversely, lean is reversed to rich, FAF + F is increased in step 519.
AF-RSL and skipping decrease. In other words, skip processing is performed.

If the sign of the first air-fuel ratio flag F1 is not inverted in step 512, steps 520.521. , 522
Integration processing is performed at . That is, in step 520, F
1=“0゛”, and if F1=’“0゛° (lean), in step 621 FAP (-FAF+
On the other hand, if F1="1" (rich), then in step 522 FAF+FAF-KIL is set. Here, the integral constants KIR and NIL are the skip amount R5
It is set sufficiently small compared to R and RSL, that is,
KIR(KIL)<RSR(RSL). Therefore,
Step 521 gradually increases the fuel injection amount in a lean state (F1="0""), and step 522 gradually decreases the fuel injection amount in a rich state (F1="1").

The air-fuel ratio correction coefficient FAF calculated in steps 518, 519, 521, and 522 is guarded at a minimum value of, for example, 0.8 in steps 523 and 524, and is guarded at a maximum value of, for example, 1.2 in steps 525 and 526. will be guarded. As a result, for some reason, the air-fuel ratio correction coefficient F
When A and F become too large or too small, the engine's air-fuel ratio is controlled using those values to prevent over-richness.
Prevent over lean.

The FAF calculated as described above is stored in the RAM 105, and the routine ends in step 527.

FIG. 6 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. 6(A), the delay counter CD
As shown in FIG. 6(B), LY is counted up in a rich state and counted down in a lean state.

As a result, as shown in FIG. 6(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) After being held rich by a considerable amount, it changes to lean at time 4. However, the air-fuel ratio signal A/F' is at time j
When the rich delay time TDR is inverted in a short period like s+tb, L7, the delay counter CDLY reaches the maximum value T.
It takes time to reach DR, and as a result, the air-fuel ratio signal A/F' after the delay process is inverted at a certain time. 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. 6(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 0□ sensor 15 will be explained. The second air-fuel ratio feedback control includes skip amounts R3R and R5L as first air-fuel ratio feedback control constants, and an integral constant KI.
R, to IL, delay time TDI? , T.D.L.

Or the comparison voltage V of the output of the upstream side 02 sensor 13 ■1
A system that makes RI variable and a second air-fuel ratio correction coefficient F
There is a system that introduces AF2.

For example, by increasing the rich skip IR3R, the control air-fuel ratio can be shifted to the rich side, and even if the lean skip amount R3L is small, the control 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 1iR3R is reduced, 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 IR3R and the lean skip amount R3L according to the output of the downstream Ot sensor 15. Furthermore, by increasing the rich integral constant KIR, the control air-fuel ratio can be shifted to the rich side; If KIR is increased, the controlled air-fuel ratio can be shifted to the lean side, and even if the rich integral constant KIR is decreased, the controlled air-fuel ratio can be shifted to the lean side. Therefore, downstream side 0□
By correcting the rich integral constant KIR and the lean integral constant KIL according to the output of the sensor 15, the air-fuel ratio can be controlled. Increase the rich delay time TDR.
By setting the lean delay time (-TDL) small, the control air-fuel ratio can shift to the rich side; conversely, by setting the lean delay time (-TDL)
If the rich delay time (TDR) is set large or the rich delay time (TDR) is set small, the controlled 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 0□ sensor 15. Furthermore, by increasing the comparison voltage ■□, the controlled air-fuel ratio can be shifted to the rich side, and by decreasing the comparison voltage ■□, 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 02 sensor 15, the air-fuel ratio can be controlled.

Making the skip amount, integral constant, delay time, and comparison voltage variable by the downstream 0□ 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 described.

FIG. 7 shows a second air-fuel ratio feedback control routine based on the output of the downstream 02 sensor 15, which is executed every predetermined period of time, for example, every 512 m5.

In steps 701 to 705, it is determined whether the downstream side 02 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 701), when the cooling water temperature THW is below a predetermined value (for example, 70'C) (step 702), the throttle valve 16 is fully closed (LL= '“1”) (step 70
3), when the load is light (Q/Ne<X+) (step 70
4) When the downstream 02 sensor 15 is not activated (
In step 705), etc., the closed-loop condition is not satisfied, and in other cases, the closed-loop condition is satisfied. If the condition is not a closed loop condition, the process proceeds to step 716, and if the condition is a closed loop condition, the process proceeds to step 706.

In step 706, the output ■2 of the downstream sensor 15
is A/D converted and fetched, and in step 707 it is determined whether or not (2) is less than the comparison voltage (2), for example, 0.55V, that is, it is determined whether the air-fuel ratio is rich or lean. In addition, the comparison voltage VR2 is set higher than the comparison voltage ■□ of the output of the upstream side 02 sensor 13, taking into account that the output characteristics differ due to the influence of raw gas and the rate of deterioration differs between the upstream and downstream of the catalytic converter 12. However, this setting may be optional. As a result, if ■2≦V, 2 (lean), proceed to steps 708, 709, 710, and ■2>
■, if I2 (rich), steps 711.712.
Proceed to 713. That is, in step 708, R2H
+-RSR+RR, that is, rich skip 1R3
R is increased to shift the air-fuel ratio to the rich side, and steps 709 and 710 Teja and R2H are set to the maximum value MAX (=7.5
%), and on the other hand, at step 711, RSR←
R5R-RL, that is, Tsuchiskip IR3R
is reduced to shift the air-fuel ratio to the lean side, and step 7
At 12.713, set R2H to the minimum value MIN (=2.5%)
Guard at. 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.

Next, in step 714, the lean skip amount R3L is calculated as follows: R5L←10%-R2H. In other words, RSR+l? SL = 10
Control by %.

In step 715, a learned value FGR5R of the center value of rich skip fiR3R is calculated.

On the other hand, during the oven loop, in step 716, the learned value FGR5R of the center value of the rich skip amount R3R is read from the backup RAM 106, and R2H4-FG
R5R, and in step 717, similarly to step 714,
Calculate lean skip amount R3L.

The routine then ends at step 718.

FIG. 8 shows a routine for calculating the update speeds RR and RL used in steps 708 and 711 in FIG. 7, and is executed at every predetermined crank angle.

In step 801, the difference ΔPM←PM from the previous value PMO
-PMO is calculated and it is determined whether the engine is in an acceleration state by determining whether ΔPM>A (positive predetermined value). As a result, the process proceeds to steps 802 to 811 only in the accelerated state, and proceeds to step 812 in other cases.

In step 802, the acceleration continuation counter CA is counted up by +1, and in steps 803 and 804, it is guarded at the maximum value B. Further, in step 805, the deceleration continuation counter CD is counted down by 1, and in step 806.8
Guard with 0 at 07. In step 808, the acceleration increase coefficient K calculated in the deposit learning routine described later is
By comparing AC with a predetermined value C, it is determined whether the deposit amount is large. Only if the deposit amount is large (K
AC>C), proceed to step 809; otherwise proceed to step 829. As a result, in step 809, C
It is determined whether D<D (predetermined value) or not, and during the period of CD≧D, in step 810, the update speeds RR and RL are changed to RR←0.
015% RL←0.005%, and during the period when CD<D, update speed R is set in step 811.
11.I? Let L be RR← o, oto% RL← 0.005%. Please note that the deposit amount is low (KAC≦
In C), as shown in step 829, RR←0.0
05% RL←0.005%. Therefore, in step 810, the update rate RR of the rich skip amount R3R to the rich side is increased, but when CD≧D, that is, when the deceleration duration is long, when the deceleration frequency is high, or when the acceleration is performed immediately after deceleration, Since the rich skip amount R3R deviates greatly, the update speed RR of the rich skip 11R3R to the rich side is further increased a little.

On the other hand, in step 812, it is determined whether the engine is in a deceleration state by determining whether ΔPM>E (predetermined negative value). As a result, step 81 occurs only in the deceleration state.
Proceed to steps 3-822, otherwise proceed to steps 823-82
Proceed to step 9.

In step 813, the deceleration continuation counter CD is counted up by +1, and in steps 814 and 815, it is guarded at the maximum value F. Further, in step 816, the acceleration continuation counter CA is counted down by 1, and in step 817.8
Guard with 0 at 18. In step 819, the deceleration reduction coefficient KD calculated in the deposit learning routine described later is
By comparing C with a predetermined value G, it is determined whether the deposit amount is large.

Only when the deposit amount is large (KDC>G), the process proceeds to step 820; otherwise, the process proceeds to step 829.

As a result, in step 820, it is determined whether CA<H (predetermined value), and during the period of CA≧H, in step 821,
The update rates RR and RL are set as RR4-0,005% RL←0.015%, and the CASH period is updated at step 822.
1? , RL is set as RR←0.005% RL←0.010%. In addition, the state where the deposit is small (KDC≦G)
Then, in step 829, RR←0.005% RL←0.005%. Therefore, in step 821, the update speed RL of the rich skip amount R3R to the lean side is increased, but when CA≧H, that is, when the acceleration duration is long, when the acceleration frequency is high, or when decelerating immediately after acceleration, the rich skip amount R3R is increased. Since the skip amount R3R is largely deviated, the update speed RL of the rich skip amount R3R to the lean side is
Make it slightly larger.

The routine then ends at step 830.

If it is not in the acceleration/deceleration state (E≦ΔPM≦A), the acceleration continuation counter CA is counted down by 1 in step 823, is guarded at 0 in steps 824 and 825, and the deceleration carrying counter is counted down in step 826. Count down the CD by 1, and guard with O at steps 827 and 828. Then, in step 829, RR←0.005
% RL 4-0.005%.

In this way, when there is a large amount of deposit I, the rich skip IR3R is greatly updated to the rich side during acceleration,
During deceleration, control of the rich skip amount F25R is stabilized by largely updating the rich skip amount R8R toward the lean side.

FIG. 9 is a detailed flowchart of the R3R learning step 717 of FIG. In addition, R5RM8X, RSRM
IN is set to RSRMAX in an initial routine (not shown).
It is assumed that it has been initialized as =RSRoldN=FGRSR.

In steps 901 and 902, it is determined whether RSR is greater than RSRMAX, and only when RSR>RSRMAX, RSRMAX is replaced with RSR. Similarly, in steps 903 and 904, it is determined whether RSR is smaller than RSRMIN, and only when RSR<RSRMIN, RSRMIN is replaced with RSR. In other words, R.S.R.
The maximum value RSRMAX and minimum value R5RMI of the change amplitude of
N is calculated. In step 905, the learning value FGR5
R is calculated using the center value of RSR (RSRMAX + RSRMIN of the average (I), and in step 906, FGR5R is guarded with a maximum value of 6.0% and a minimum value of 4%, and stored in the backup RAM 106.

This routine then ends in step 907.

FIG. 1O shows a deposit learning routine, which is executed at every predetermined crank angle, for example, 360° CA.

In step 1001, similarly to step 501 in FIG. 5, it is determined whether the closed loop condition of the air-fuel ratio by the upstream 02 sensor 3 is satisfied. In other words, upstream side 0
This is because air-fuel ratio control by the upstream 0□ sensor 3 is essential in order to perform deposit learning control based on the output deviation of the 2 sensor 3. Therefore, when the closed loop condition is not satisfied, counters CAC, CLRN1, and CLRN2 are initialized in step 1032,
No deposit learning is performed and the process proceeds to step 1002 and subsequent steps only when the closed loop condition is satisfied.

In the routine shown in FIG.
The air-fuel ratio deviation CA C (CA
C = O is equivalent to the stoichiometric air-fuel ratio), and the acceleration increase coefficient K is determined so that this deviation converges within a predetermined range (B<CAC<K).
Learn AC. In addition, the air-fuel ratio deviation CAC according to the output ■1 of the upstream 0□ sensor 13 during a predetermined period (0≦CLRN 2≦P) after the deceleration state (ΔPM≦T) is determined, and this deviation is within a predetermined range (R<CAC< The deceleration reduction coefficient KDC is learned so as to converge to Q).

First, updating of the acceleration increase coefficient KAC will be explained.

When the engine is in an accelerating state and the intake air pressure deviation ΔPM exceeds S, the flow moves from step 1028 to step 1.
Proceeding to step 029, the counter CLRN 1 is set to 1 and the counter CLRN 1 is triggered. As a result, the next time this routine is executed, the flow advances from step 1002 to steps 1003-1014.

Step 1003 decelerates (Δ
This is to stop updating the learning value KAC when PM≦I) occurs. This prevents erroneous learning. In step 1004, the counter CLRN1 is incremented by one. Further, in step 1005, even after the acceleration state, the air-fuel ratio deviation CAC is not calculated for a predetermined period (CLRN 1 < J) in consideration of the delay in exhaust gas transportation to the upstream 0□ sensor 13. It is something.

After the predetermined period has elapsed (CLRN 1≧J), the air-fuel ratio deviation CAC is calculated in steps 1006 to 1009.

That is, in step 1006, the upstream 0□ sensor 13
A/D convert the output ■1 and import it, step 1007
It is determined whether ■, ≦■□ (lean). As a result, ■1≦■8. (Lean), Stellaf “100”
8, the counter CAC is counted up by +1, and on the other hand,
If V+>V+++ (rich), step 1009
The counter CAC is counted down by one. In other words, in this case, if the counter CAC is large (positive side),
This indicates that the air-fuel ratio is biased toward the lean side compared to the stoichiometric air-fuel ratio, and conversely, if the counter CAC is small (negative side), it indicates that the air-fuel ratio is biased toward the lean side from the stoichiometric air-fuel ratio.

This air-fuel ratio deviation CAC is calculated in step 1010.

1033, the period during which the deposit affects the air-fuel ratio (C
Only LRN1<K) are executed.

Next, when the above-mentioned state continues until CLRN 1 = K, the air-fuel ratio deviation CAC is determined in steps 1011 to 1014.
The acceleration increase coefficient KAC is updated accordingly. That is, C
If AC≧L (the air-fuel ratio deviates to the lean side), the acceleration increase coefficient KAC is increased in step 1014, and the CAC
If ≦M (air-fuel ratio deviates to the rich side), step 10
13, the acceleration increase coefficient KAC is decreased, and M<CAC.
<L, the acceleration increase coefficient KAC is not changed.

In this way, the acceleration increase coefficient KAC is updated,
KAC will be stored in backup RAM 106.

Next, updating of the deceleration reduction coefficient KDC will be explained.

When the engine is decelerated and the intake air pressure deviation ΔPM becomes less than or equal to T, the flow moves from step 1030 to step 1.
Proceeding to 031, counter CLRN2 is set to 1 and counter CLRN2 is triggered. As a result, the next time this routine is executed, the flow proceeds from step 1015 to steps 1016-1027.

In step 1016, even after the deceleration state, the acceleration (Δ
This is to stop updating the learning value KDC when PM≧N) occurs. This prevents erroneous learning. In step 1017, the counter CLRN2 is incremented by one. Further, step 1018 is for not calculating the air-fuel ratio deviation CAC for a predetermined period (CLRN 2 < O) even after the deceleration state, taking into account the delay in transporting exhaust gas to the upstream 02 sensor 13. It is.

After the predetermined period has elapsed (CLRN 2≧0), the air-fuel ratio deviation CAC is calculated in steps 1019 to 1022.

That is, in step 1019, the upstream 02 sensor 13
A/D convert and import the output ■, step 1020
It is determined whether V, ≦Vat (lean). As a result, if ■1≦VRI (lean), step 1
At step 021, the counter CAC is counted down by one, and on the other hand, if Vl>VRI (rich), step 102
2, the counter CAC is incremented by +1. In other words, in this case, if the counter CAC is large (positive side)
, indicates that the air-fuel ratio is biased towards the richer side than the stoichiometric air-fuel ratio; conversely, if the counter CAC is small (negative side),
This shows that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio.

This air-fuel ratio deviation CAC is calculated in step 1023.

1033, the period during which the deposit affects the air-fuel ratio (C
Only LRN2<P) are executed.

Next, when the above-mentioned state continues until CLRN 2 = P, the air-fuel ratio deviation CAC is determined in steps 1024 to 1025.
The deceleration reduction coefficient KDC is updated accordingly. That is, C
If AC≧Q (the air-fuel ratio deviates to the rich side), the deceleration reduction coefficient KDC is increased in step 1127, and the CAC
If ≦R (air-fuel ratio leans toward the lean side), step 10
26, the deceleration reduction coefficient KDC is decreased, R<CAC
<Q, the deceleration reduction coefficient KDC is not changed.

In this way, the deceleration reduction coefficient KDC is updated,
The KDC will be stored in backup RAM 106.

Note that if the engine is in a steady state (T<ΔPM<S), neither the counters CLRN 1 nor CLRN 2 are triggered, and therefore the learned values KAC and KDC are not updated.

FIG. 11 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, 360° CA. Step 11
In step 01, the intake air pressure data PM and the rotational speed data N e @ PI are output from the RAM 105, and the basic injection 11TP is calculated by interpolation using the two-dimensional map stored in the ROM 104. In step 1102, the transient basic injection amount TP
AE police, TPAEW = ΔPM − f (Ne, TIIW)
Calculate by Note that during acceleration, ΔPM>O, which makes the transient basic fuel injection time TPAEH positive, and during deceleration, ΔPM<O, so the transient basic fuel injection time T
PAE- becomes negative.

Next, in steps 1103 to 1107, a transient correction amount K is calculated. That is, in step 1103, it is determined whether or not the vehicle is being accelerated (ΔPM>2 mmHg), and in step 1104, it is determined whether or not the vehicle is being decelerated (ΔPM<-2 mmHg). As a result, if accelerating, step 1
At step 107, -KAC is set. If the vehicle is decelerating, at step 1106, it is set at -KDC. If it is steady, at step 1105, K←0 is set.

In step 1108, the final injection amount TAU is set to TALI
+(TP + K -TPAEW)・FAF・α+
Calculate by β.

Note that α and β are correction amounts determined by other operating state parameters. Next, in step 1109, injection I
The TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. This routine then ends at step 111o.

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

In addition, in the above-mentioned FIG. 7 and FIG. 8, the integral amounts RR and RL as the update speed of the rich skip amount R3R are deposited)! However, skip control may be introduced to the rich skip amount RSR to make the skip amount variable depending on the deposit amount and the acceleration/deceleration state. That is, in this case, the routine in Figure 7 is changed to the routine in Figure 12, and the routine in Figure 8 is changed to the routine in Figure 1.
Change to the routine shown in Figure 3.

In FIG. 12, steps 1201 to 1210 are provided in place of steps 708 to 713 in FIG. In step 1201, the second air-fuel ratio flag F2 is set to 0 par (lean), and in step 1202, the second air-fuel ratio flag F2 is set to 1° (rich).
In 203, it is determined whether the sign of the second air-fuel ratio flag F2 has been inverted, that is, it is determined whether the air-fuel ratio downstream of the catalyst has been inverted. If the air-fuel ratio is inverted, in step 1204, the value of the second air-fuel ratio flag F2 is determined as follows.
Determine whether the reversal is from rich to lean or from lean to rich.If it is a reversal from rich to lean,
In step 1205, RSR-R3R+RSRR is increased in a skip manner, and conversely, if it is a reversal from lean to rich, RSR-RSR-RSR is increased in step 1206.
Decrease in skipping with L. In other words, skip processing is performed.

On the other hand, if the sign of the second air-fuel ratio flag F2 is not inverted in step 1203, steps 1207 and 120
8, integral processing is performed at 1209. That is, in step 1207, it is determined whether F2-"0'° or not, and F2-
If “0” (lean), RS in step 1208
R−RSR+RR, and on the other hand, if F2=°“1 par (rich), RSR4−RSR− is set in step 1209.
Let it be RL. Here, the integral constants RR and RL are skip f
iR5RR.

It is set sufficiently small compared to RSRL, and is, for example, 0.005% as described above. Therefore, step 1208 gradually increases the rich skip amount R3R in the lean state (F2-"O'"), and step 1209 gradually increases the rich skip amount R3R in the rich state (F2='"1").
Gradually decrease R.

Steps 1205, 1206, 1208, 120
The rich skip amount R3R calculated in step 9 is
210 with a minimum value of 2.5% and a maximum value of 7.
Guarded at 5%.

The skip amounts RSRR and RSRL in FIG. 12 are the first
This is changed by the routine shown in Figure 3. In FIG. 13, steps 1301 to 1305 are provided in place of steps 810, 811, 821, 822, 829 in FIG.

That is, if the deposit amount is large (KAC>C), skip 1lRsRR at step 1301 during acceleration.
Alternatively, control of the rich skip amount R5R is stabilized by greatly updating it to the rich side in step 1302, and greatly updating the skip 1iR3RR to the lean side in step 1303 or 1304 during deceleration.

Note that in FIG. 13, the values SKP and Δ are constant values.

Note that 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, which is because the air-fuel ratio feedback control is mainly performed by the upstream 02 sensor, which has good responsiveness, and is secondary to the control by the downstream 0□ sensor, which has poor responsiveness. This is for the purpose of doing so.

In addition, other control constants in the air-fuel ratio feedback control by the upstream 02 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 amounts R3R and RSL and make only the other variable, so that the delay time TD[? , T
It is also possible to fix one of DL and make only the other variable, or to set the rich integral constant KIR or the lean integral constant KI.
It is also possible to have one of L 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 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 1101 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 1108 The supplied air amount corresponding to the final fuel injection amount TAU is calculated.

Furthermore, in the above embodiment, the 02 sensor was used as the air-fuel ratio sensor, but a Co sensor, a lean mixture sensor, etc. may also be used. In particular, when a Ti0z sensor is used as the upstream air-fuel ratio sensor, control responsiveness improves,
Overcorrection due to the output of the downstream air-fuel ratio sensor can be prevented.

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, when the deposit amount is large, the downstream air-fuel ratio feedback control is set to the rich side during acceleration, and the downstream air-fuel ratio feedback control is set to the lean side during deceleration, thereby reducing the downstream air-fuel ratio. Fuel ratio feedback control can be stabilized, and therefore deterioration of emissions, drivability, fuel efficiency, etc. can be prevented.

[Brief explanation of drawings]

Figure 1 is an overall block diagram for explaining the present invention in detail, Figure 2 is a single 02 sensor system and double 0□
3 is a diagram illustrating the present invention in detail; FIG. 4 is an overall schematic diagram illustrating an embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention; Fig. 7, Fig. 8, Fig. 9, Fig. 10A, Fig. 10
Figures B, 11, 12, and 13 are flowcharts for explaining the operation of the control circuit in Figure 5, Figure 6 is a timing diagram for supplementary explanation of the flowchart in Figure 5, and Figure 1O. The figure is a block diagram showing a combined state of FIGS. 10A and 10B. 1... Engine body, 2... Air flow meter,... Distributor 1. 6... Crank angle sensor, 0... Control circuit, 12... Catalytic converter, 3... Upstream 0□ sensor, 4... Downstream 0□ sensor, 7... 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 air-fuel ratio; a control constant calculation means that calculates an air-fuel ratio feedback control constant at a predetermined update rate according to the output of the downstream air-fuel ratio sensor; an air-fuel ratio correction amount calculating means for calculating an air-fuel ratio correction amount according to a control constant and an output of the upstream air-fuel ratio sensor; and a deposit learning condition determining means for determining whether or not the engine satisfies a deposit learning condition. , a deposit learning means for calculating a deposit learning value according to the output deviation of the upstream air-fuel ratio sensor when the engine satisfies a deposit learning condition; and when the deposit learning value is equal to or higher than a predetermined value, update rate calculation means for increasing the update rate toward the rich side of the air-fuel ratio feedback control constant during acceleration, and increasing the update rate toward the lean side of the air-fuel ratio feedback control constant during deceleration of the engine; , when the engine is in a non-transient state, the air-fuel ratio of the engine is adjusted according to the air-fuel ratio correction amount, and when the engine is in a transient state, the air-fuel ratio of the engine is adjusted according to the air-fuel ratio correction amount and the deposit learning value. An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio adjusting means for adjusting the air-fuel ratio;