JPH01190939A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To permit the speedy restoration of the air-fuel ratio control constants RSR and RSL by substantially increasing the renewal speed of the annealed value of the air-fuel ratio control constant when the memory contents of a memory means is destroyed, in other words by increasing the learning speed. CONSTITUTION:A control constant calculating means calculates the air-fuel ratio feedback control constants RSR and RSL on the basis of the output of a downstream side O2 sensor for a three-component catalyst CCRO, and the air-fuel ratio correction quantity FAF is calculated from the output of an upstream side O2 sensor by a calculating means, and the air-fuel ratio is closed- loop-controlled, and the annealed value is memorized as learned value in a memory means. When a detecting means detects the anomaly of the memorized contents, the annealed value is set to the smaller value n2 from a normal value n1 by a setting means for a prescribed time, and the renewal speed for the annealed values of the air-fuel ratio control constants RSR and RSL is substantially increased, in other words the learning speed is increased. Therefore, when the memory contents are destroyed, the optimization (restoration) of the air-fuel ratio control constant is speedily carried out, and the deterioration of the exhaust emission and fuel consumption can be prevented.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides air-fuel ratio sensors (herein, oxygen concentration sensors (02 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 0□ sensor in addition to air-fuel ratio feedback control using an upstream 02 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. , variations in the output characteristics of the O2 sensor have caused problems in improving the accuracy of controlling the air-fuel ratio. It takes ot
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 AT sensor is provided downstream of the catalytic converter, and the upstream side 0! In addition to the air-fuel ratio feedback control by the sensor, the double 0. Sensor systems have already been proposed (
Reference: Japanese Patent Application Laid-Open No. 58-48756). This double 0
In a two-sensor system, the 0□ celesa installed downstream of the catalytic converter has a lower response speed than the upstream 02 sensor, but has the advantage of less variation in output characteristics for the following reason. ing.

(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 02 sensor is small.

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

Therefore, as described above, the air-fuel ratio feedback control (double 02 sensor system) based on the outputs of the two 0□ sensors allows the downstream 02 sensor to absorb variations in the output characteristics of the upstream 0□ sensor. In fact, as shown in Figure 2, single 0! In the 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 Ox
As long as the downstream 02 sensor in the sensor system maintains stable output characteristics, good exhaust emissions are guaranteed.

In the double 02 sensor system described above, the downstream o
During the air-fuel ratio feedback control of the two sensors, the air-fuel ratio control constants by the downstream side 02 sensor, such as the rounded values RSR and RSL of the skip amounts R3R and RSL, are learned and stored in the backup RAM, and during open loop control. Immediately after starting the air-fuel ratio feedback, the air-fuel ratio correction amount FAF is calculated using the learned values RAR and RSL stored in the backup RAM, and the air-fuel ratio is thereby adjusted. 60941).

[Problem to be solved by the invention]

However, in the above-mentioned learning control of the air-fuel ratio control constants R3R and RSL, when the memory contents of the backup RAM are destroyed, such as when the buffer is removed,
The learning value is initialized, for example, the learning value R5R (=RSL
) is 5%, and therefore, until the air-fuel ratio feedback control has sufficiently progressed, the air-fuel ratio control constants RSR, RS
L is not appropriate, and the control air-fuel ratio deviates from the optimum air-fuel ratio, resulting in problems such as deterioration of emissions, deterioration of fuel efficiency, and deterioration of drivability.

Therefore, an object of the present invention is to reduce the air-fuel ratio control amount RSR when the storage contents of the backup RAM are destroyed (abnormal).
The objective is to prevent deterioration of emissions, fuel consumption, drivability, etc. by quickly optimizing (restoring) the RSL.

[Means to solve the problem]

A means for solving the above-mentioned problems is shown in FIG. That is, an upstream air-fuel ratio sensor for detecting the air-fuel ratio of the engine is provided in the exhaust passage upstream of the three-way catalyst CC110 provided in the exhaust passage of the internal combustion engine, and an upstream air-fuel ratio sensor is provided on the downstream side of the three-way catalyst CC1°. A downstream air-fuel ratio sensor is provided in the exhaust passage for detecting the air-fuel ratio of the engine. The control constant calculation means calculates an air-fuel ratio feedback control constant, for example, skip 11R3R, according to the output 2 of the downstream air-fuel ratio sensor.
Calculate RSL. The smoothing value calculating means calculates smoothing values R5R, RSL of the air-fuel ratio feedback control constants, such as skip amounts R5R, RSL, using a predetermined smoothing ratio, and the storage means stores the smoothing values RSR, RSL. The memory abnormality detection means detects an abnormality in the memory contents of the storage means, and as a result,
The smoothing speed setting means sets the smoothing ratio to a first speed n when the stored contents of the storage means are normal, and sets the smoothing ratio to the first speed n for a predetermined period when the stored contents of the storage means are abnormal. The smaller second value n! Set to . The air-fuel ratio correction amount calculation means calculates the air-fuel ratio correction amount PAP according to the output V1 of the upstream air-fuel ratio sensor and the air-fuel ratio feedback control constants RSR, RSL of the control constant calculation means during closed-loop control of the engine; During open loop control of the engine, an air-fuel ratio correction amount FAF is calculated according to the output V of the upstream air-fuel ratio sensor and the rounded values R3R and RSL of the air-fuel ratio feedback control constants in the storage means, and the air-fuel ratio adjustment means is for adjusting the air-fuel ratio of the engine according to the air-fuel ratio correction amount FAF.

[For production]

According to the above-mentioned means, the storage means (backup RAM)
When the memory contents of R5 are destroyed, the air-fuel ratio control constant R5
The update speed of the rounded values of R and RSL becomes substantially faster,
In other words, the learning speed increases, and the contents stored in the storage means immediately reach the optimum value.

〔Example〕

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 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 the A/D converter 101 with a built-in multiplexer of the control circuit IO. The distributor 4 has a crank angle sensor 5 whose shaft generates a reference position detection pulse signal every 7206 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. 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 supplied to the CPU 1.
03 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 l. The water temperature sensor 9 indicates the temperature of the cooling water
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 IC, CO, and NO in the exhaust gas.

The exhaust manifold 11 includes a 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 hack-up RAM 106, a clock generation circuit 107, etc. are provided. Note that the backup RAM 106 retains its stored contents even when the power supply voltage is always supplied and the ignition key (not shown) is turned off.

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.
Preset to 08 and free knob 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 a clock signal (not shown) and finally when its carrier terminal reaches the "1" level, the flip-flop 109 is turned on and the drive circuit 110 stops energizing the fuel injector 7. . 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 taken in by an A/D conversion routine executed at predetermined time intervals and stored in a predetermined area of RA old 05. That is, data Q and TH- in the RAM 105 are 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. 4 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 yas.

In step 401, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the upstream O7 puller 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 warming, during power increase, during OTP increase to prevent catalyst overheating, the output signal of the upstream 02 sensor 13 is never reversed. When not, 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 427 and the air-fuel ratio correction coefficient FAF is set to 1.0. In addition, FAF is a closed-loop system '<
It may be done just before the end of 8. In this case, step 42
Proceed directly to step 8. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 402.

In step 402, the output of the upstream 02 sensor 13 is
is A/D converted and fetched, and in step 403, it is determined whether or not ■ is less than the comparison voltage Vll+, for example, 0.45V.In other words, it is determined whether the air-fuel ratio is rich or lean.In other words, if the air-fuel ratio is lean. If (V+≦V□), it is determined in step 404 whether the delay counter CDLY is positive or not, and if CDL\>O, in step 405 the CD
Set LY to 0 and proceed to step 506. Step 40
In step 6, the delay counter CDLY is subtracted by 1, and in steps 407 and 408, 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 409
The first air-fuel ratio flag F1 is set to "0" (lean). Note that the minimum value TDL is a lean delay state for maintaining the determination that the rich state is present even if there is a change from rich to lean in the output of the upstream Oz sensor 13, and is defined as a negative value. . On the other hand, rich (V+ 〉V
at), it is determined whether the delay counter CDLY is negative or not in step 410, and if CDLY<O, CDLY is set to 0 in step 411, and step 412
Proceed to.

In step 412, the delay counter CDLY is incremented by 1, and in steps 413 and 414, the delay counter CDLY is incremented by 1.
Guard LY with 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" (rich) in step 415. The maximum value TDR is a rich delay time for maintaining the determination that the engine is in a lean state even if there is a change from lean to rich in the output of the upstream 02 sensor 13, and is defined as a positive value. .

In step 416, 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 417, it is determined whether the reversal is from rich to lean or from lean to rich, based on the value of the first air-fuel ratio flag F1. If it is a reversal from rich to lean, in step 418 PAP←FAF + R5
If R is increased in a skip manner, and conversely, if it is a reversal from lean to rich, then in step 419 FAF←FAF
- Decrease RSL and skip. In other words, skip processing is performed.

If the sign of the first air-fuel ratio flag F1 is not inverted in step 416, integration processing is performed in steps 420, 421, and 422, that is, in step 420, F1
If F1=“O” (lean), FAF −FAF+Kfn is set in step 421, and if F1=“1” (rich), step 4
FAP-FAF-KIL at 22. Here, the integral constants KIR and KIL are set sufficiently small compared to the skip 1iRSR and RSL, that is, KIR([L
)<R5R(RSL). Therefore, step 42
1 gradually increases the fuel injection amount in a lean state (F1="0"), and step 422 gradually increases the fuel injection amount in a rich state [(F1="l").
) to gradually reduce the fuel injection amount.

The air-fuel ratio correction coefficient FAF calculated in steps 418, 419, 421, and 422 is guarded at a minimum value of, for example, 0.8 in steps 423 and 424, and is guarded at a maximum value of, for example, 1.2 in steps 425 and 426. will be guarded.

As a result, if the air-fuel ratio correction coefficient FAF becomes too large or too small for some reason, 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 428.

FIG. 5 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. 4. When the air-fuel ratio signal A/F for rich/lean discrimination is obtained from the output of the upstream O2 sensor 13 as shown in FIG. 5(A), the delay counter CD
As shown in FIG. 5(B), LY is counted up in a rich state and counted down in a lean state.

As a result, as shown in FIG. 5(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' remains lean for the rich delay time TDR, and then returns to time 1t. It becomes richer. Even if the air-fuel ratio signal A/F changes from rich to lean at time t,
The delayed air-fuel ratio signal A/F' is maintained rich for an amount equivalent to the spring delay time (-TDL), and then reaches time t4.
Changes to lean. However, the air-fuel ratio signal A/F' is at the time [,.

t6+t? When the rich delay time TDR is reversed as shown in the figure, the delay counter CDLY reaches the maximum value TDH.
As a result, the air-fuel ratio signal A/F' after the delay process is inverted at time t8. In other words,
The air-fuel ratio signal A/F' after the delay processing is more stable than the air-fuel ratio signal A/F before the delay processing. In this way, based on the stable air-fuel ratio signal A/F'' after the delay processing, the
) is obtained.

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 IR, KIL, delay time TDR, ↑DL, or comparison voltage V□ of the output v1 of the upstream 02 sensor 13 is made variable, and a system in which a second air-fuel ratio correction coefficient FAP2 is introduced.

For example, rich skip amount 1? sI? By increasing the lean skip amount R3L, 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.On the other hand, by increasing the lean skip amount R3L, the control air-fuel ratio can be shifted to the lean side. Furthermore, even if the rich skip amount R3R is reduced, 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 11R5R and the lean skip amount RSL in accordance with the output of the downstream 02 sensor 15. Furthermore, by increasing the rich integral constant KIR, the control air-fuel ratio can be shifted to the rich side, and even by decreasing the lean integral constant KIL, the control air-fuel ratio can be shifted to the rich side.On the other hand, by increasing the lean integral constant KIL, 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 integral constant KIR is made small, the controlled air-fuel ratio can be shifted to the lean side. Therefore, depending on the output of the downstream Of sensor 15, the Ricci integral constant KI
The air-fuel ratio can be controlled by correcting R and the lean integral constant KIL.

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) > Rich delay time (TDR
), the control 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 TOL according to the output of the downstream 02 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 Vll, the controlled air-fuel ratio can be shifted to the lean side. Therefore,
Comparison voltage Vll+ according to the output of downstream side 02 sensor 15
By correcting the air-fuel ratio, 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 described.

First, abnormality detection in the storage contents of the backup RIV will be explained with reference to the flowchart of FIG. Note that the routine in FIG. 6 is a part of the main routine. In step 601, it is determined whether or not the engine is starting by turning on a starter switch (not shown). Only when starting,
Steps 602-606 are performed. That is, in step 602, startup control (for example, increase in fuel amount) is performed, and step 602 is performed.

In PRO 03, RAM values and the like are initialized.

In step 604, it is determined whether the storage contents of the backup RAM 106 are abnormal. Note that the backup RAM 106 normally stores data and its inverted data.
One is written (Mira one type), backup RAM
These two data are read from 106, and an abnormality in the storage contents of backup RAM 106 can be detected based on whether they match or do not match. As a result, if the storage contents of the backup RAM 106 are abnormal, the abnormality flag FA is set in step 605, and the backup RA? Initialize '1106 and step 607
This routine ends. Note that in step 606, the smoothed value f1 of the rich skip amount R5R is set to 5%.

Figure 7 shows downstream O! This is a second air-fuel ratio feedback control routine that calculates the skip amounts RSR and R5L based on the output of the sensor 15, and is performed for a predetermined period of time, e.g.
Executed every m5. In steps 701 to 706, 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 by the downstream 0□ sensor 13 (step 701), the cooling water temperature TH
When W is below a predetermined value (for example, 70°C) (step 7
02), when the throttle valve 16 is fully closed (LL="1") (step 703), when the downstream 0□ sensor 15 is not activated (step 704), when the load is not within the predetermined load range (Q/Ne < Xl, Q/N* > Xl) (step 705), when not in the predetermined rotational speed region (Ne <
Y.

N th > Y z), etc., the closed loop condition is not satisfied, and in other cases, the closed loop condition is satisfied. If it is not a closed loop condition, proceed to steps 720 and 721.

If the closed loop condition is satisfied, steps 707-71
Proceed to step 9. That is, in step 707, the output (2) of the downstream side 02 sensor 15 is A/D converted and taken in, and in step 708, it is determined whether or not (2) is less than the comparison voltage Vlt, for example, 0.55V. Note that the comparison voltage v0 is higher than the comparison voltage ■□ of the output of the upstream 0□ sensor 13, taking into account that the output characteristics are different due to the influence of raw gas and the deterioration rate is different between the upstream and downstream of the catalytic converter 12. This setting may be optional. In other words, it determines whether the air-fuel ratio is rich or lean. As a result, if ■2≦VR2 (lean) in step 708, step 7
On the other hand, if Vz>VRZ (rich), the process proceeds to step 710.

In step 709, rich skip is performed from the RAM 105.

The amount R5R is read and set to RSR-R5R+ΔRS (constant value), that is, the rich skip 1R3R is increased to shift the air-fuel ratio to the rich side.On the other hand, when v2>VR□ (rich), the amount is read from the RAM 105 in step 710. Read the rich skip amount RSR, R5R←RSR-
ΔRS, that is, the rich skip amount RSR is decreased to shift the air-fuel ratio to the lean side. In step 711, the RSR calculated as described above is guarded, for example, with the maximum value MAX = 7.5% and the minimum value MIN = 2.5%. Note that the minimum value MIN
is a value at a level at which the transient followability is not impaired, and the maximum value MAX is at a level at which drivability does not deteriorate due to air-fuel ratio fluctuations.

In step 712, the lean skip IRsL is set to RA
Calculate with M105-RSR. That is, R3R+RSL=10%.

In step 713, it is determined whether the abnormality flag FA is set because the storage contents of the backup RAM 106 have been destroyed. If the result is normal (FA
="0"), the process proceeds to step 714, and the smoothed value of the rich skip amount RSR is calculated using n+1. For example, n is 15, 31, etc.

On the other hand, if it is abnormal (F, = “l”), step 715
, 716, time is measured by the counter C, and the rich skip amount RSR is directly used as the smoothed value only within a predetermined time (Co x 512a+s). That is, in this case, the raw ratio n corresponds to 0. After a predetermined period of time has elapsed, the abnormality flag Fa is reset in step 718. In step 719, step 714 or 717
Back up the rounded value RSR calculated in RAM1
06 and proceeds to step 722. Note that when the abnormality flag FA="1", the smoothing calculation is substantially stopped, but the smoothing calculation may be performed using a smaller smoothing ratio than in the normal case.

For example, the smoothing ratio in the normal case is rlI (step 7
14, n = n, ), and the annealing ratio nz (<
Set it as no.

On the other hand, in step 720, the backup RAM 106
Read out the smoothed value m, set it as the RAM value RSR, and
In step 721, the lean skip amount RSL is set to R5.
After calculating L-10%-RSR, the process proceeds to step 722.

As described above, according to the routine shown in FIG.
The update speed of M106 rounding is substantially increased.

FIG. 8 is a modification example of FIG. 7, in which steps 801 to 807 are added to the routine of FIG.
Steps 5 to 718 correspond to steps 802 to 807 and are therefore deleted. However, the routine in Figure 8, for example,
It is executed every s, and Alas in step 801 is 4.
rms −X N t , B+ms in step 806
is 4m5XN, and Nl <Nl, therefore,
A<B. As a result, if it is abnormal (FA="1
”), the flow goes through steps 801 to 80 for every All5.
5 to the air-fuel ratio control routine after step 701, and if normal (FA""0"), the flow proceeds to the air-fuel ratio control routine after step 701 via steps 801, 806, and 807 for each Bms. Proceed to routine.

That is, for a predetermined period after the storage contents of the backup RAM 106 are destroyed, the air-fuel ratio closed loop system is used. 11 (steps 701 to 719) is executed more frequently than when the backup RAM 106 is normal.
The update speed of the 'J-/chip skip amount R5R of 5 and the update speed of the smoothed value of the backup RAM 106 further increase.

FIG. 9 is also a modification of the routine in FIG.
Steps 901 to 903 are added to the routine shown in the figure. That is, in the event of an abnormality (FA="1"), steps 902 and 903 are executed instead of steps 705 and 706 of the closed loop establishment condition. Here, each value
+ , Xz , '/+ , Yz 1 XI' lX,
' , Y, ' , Y, ' are executed as shown in FIG. Steps 707 to 719) are executed more often. As a result, the update speed of the rich skip amount RSR of the RAM 105 and the backup RAM 1
The update speed of the smoothed value 100 of 06 is further increased.

FIG. 11 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360' CA.

In step 1101, intake air amount data Q and rotational speed data Ne are successively outputted from the RAM 105, and the basic injection amount R is
Calculate AUP. For example, TAUI'-α・Q/Ne
(α is a constant). At step 1102, RAM10
5, 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 1103, the final injection amount TAU
Wow, TAU-TAUP-FAF・(FWL+β)+7
Calculate by

Note that β and T are correction amounts determined by other operating state parameters. Next, in step 1104, 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 1105.

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.

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

In addition, other control constants in the air-fuel ratio feedbank control by the upstream Ot sensor, such as delay time, integral constant, etc., are corrected by the output of the downstream Ot sensor.
The present invention can be applied to a two-sensor system as well as a double O2 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 RSR, RSL 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 the lean integral constant 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.

Furthermore, in the above-described embodiment, an internal combustion engine was shown in which the amount of fuel injected into the intake system was controlled by a fuel injection valve, but 1. The present invention can also be applied to carbureted internal combustion engines. For example, electric air control valve (EACV)
The electric link bleed air control pulp adjusts the air bleed amount of the carburetor and introduces atmospheric air into the main system passage and slow system passage to control the air-fuel ratio. The present invention can be applied to things that control the fuel ratio, things that adjust the amount of secondary air sent to the exhaust system of an engine, etc. In this case, the basic injection 1TAUP in step 1101
A corresponding basic fuel injection amount is determined by the carburetor itself, that is, depending on the intake pipe negative pressure depending on the intake air amount and the engine rotational speed, and in step 1103, the supply air corresponding to the final fuel injection amount TAU is determined. The quantity 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, the backup RA
When the memory contents of M are destroyed (abnormal), the air-fuel ratio control constant J? 5RJSL optimization (restoration) can be performed quickly, and as a result, deterioration of emissions, deterioration of fuel efficiency,
Deterioration of drivability, etc. can be prevented.

[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 0□
Fig. 3 is an overall schematic diagram showing an embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention; Fig. 4, Fig. 6, Fig. 7, Fig. 8; , Figures 9 and 11 are flow charts for explaining the operation of the control circuit in Figure 3, Figure 5 is a timing diagram for supplementary explanation of the flow chart in Figure 4, and Figure 1O is a flow chart for explaining the operation of the control circuit in Figure 3. Steps 705, 706, 902,
903 is a graph that provides supplementary explanation. DESCRIPTION OF SYMBOLS 1... Engine body, 3... Air flow meter, 4... Distributor, 5.6... Crank angle sensor, 10... Control circuit, 12... Catalytic converter, 13... Upstream side 0□sensor, 15...downstream 02 sensor, 17...idle switch. NOx A/F

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 control constant calculation means that calculates an air-fuel ratio feedback control constant according to the output of the downstream air-fuel ratio sensor; and smoothing of the air-fuel ratio feedback control constant. A smoothing value calculation means for calculating a value using a predetermined smoothing ratio, a storage means for storing the rounded value, a memory abnormality detection means for detecting an abnormality in the storage contents of the storage means, and a storage contents of the storage means. When the content stored in the storage means is normal, the smoothing ratio is set to a first value, and when the content stored in the storage means is abnormal, the smoothing ratio is set to a second value smaller than the first value for a predetermined period. and an air-fuel ratio correction amount according to the output of the upstream air-fuel ratio sensor and the air-fuel ratio feedback control constant of the control constant calculation means during closed-loop control of the engine, and performs open-loop control of the engine. an air-fuel ratio correction amount calculation means for calculating an air-fuel ratio correction amount sometimes in accordance with the output of the upstream air-fuel ratio sensor and a rounded value of the air-fuel ratio feedback control constant of the storage means; 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.