JPH03141840A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To discriminate the misfire of an engine ignition system from that of a fuel system so as to facilitate the disposal of a failure by judging the misfire of the engine ignition system at the time of the auxiliary air-fuel ratio correction quantity reaching the lean side limit value, and displaying this. CONSTITUTION:When misfire is generated to an ignition system, unburnt gas and residual air are exhausted from a misfired cylinder even if the air-fuel ratios of all the cylinders are theoretical air-fuel ratios, so that an upstream side air-fuel ratio sensor performs lean output, and the main air-fuel ratio correction quantity is operated onto the rich side by a main air-fuel ratio correction quantity operating means and adjusted onto the rich side by an air-fuel ratio adjusting means. Influenced by this, a downstream side air-fuel ratio sensor performs rich output, so that an auxiliary air-fuel ratio correction quantity operating means operates the auxiliary air-fuel ratio correction quantity onto the lean side, and at the time of the auxiliary air-fuel ratio correction quantity reaching the lean side limit value MIN, an ignition system misfire display means judges the generation of misfire due to the abnormality of the ignition system and displays it accordingly. The misfire caused by the abnormality of the ignition system can be thus discriminated positively from that caused by the abnormality of a fuel system, thereby facilitating the disposal of a failure and preventing catalyst degradation.

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.
), the present invention relates to an air-fuel ratio control device for an internal combustion engine that performs air-fuel ratio feedback control using an upstream 02 sensor as well as air-fuel ratio feedback control using a downstream 02 sensor, and particularly relates to an ignition system misfire abnormality determination.

[Conventional technology]

In simple air-fuel ratio feedback control (single 02 sensor system), the 02 sensor that detects oxygen concentration is installed at a location in the exhaust system as close to the combustion chamber as possible, that is, at the gathering part of the exhaust manifold upstream of the catalytic converter. Improving the accuracy of air-fuel ratio control is hindered by variations in sensor output characteristics. It takes 02
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 02 sensor is performed. In addition, a double 02 sensor stem that performs air-fuel ratio feedback control using the downstream 02 sensor has already been proposed (
Reference: Japanese Patent Application Laid-Open No. 61-234241). In this double 02 sensor system, the 02 sensor provided 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 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 02 sensors, variations in the output characteristics of the upstream 02 sensor can be absorbed by the downstream 02 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 in the double 02 sensor system, even if the output characteristics of the upstream 02 sensor deteriorate, the exhaust emission characteristics do not deteriorate. In other words, in the double 02 sensor system, good exhaust emissions are guaranteed as long as the downstream 02 sensor maintains stable output characteristics.

[Problem to be solved by the invention]

However, the double 02 sensor system described above does not take any measures against abnormalities in the ignition system, so even if an abnormality occurs in the ignition system and a misfire occurs, the user can continue to operate the engine. However, as a result, there is a problem in that unburned gas and residual air react within the catalyst, overheating the catalyst and causing deterioration of the catalyst.

In addition, in the double 02 sensor system described above, even if a method of detecting by torque fluctuation using a combustion pressure sensor is introduced as a misfire determination method, it is still not possible to determine whether the cause of the misfire is the fuel system or the ignition system. It is not possible to determine if the misfire is due to the ignition system.

Therefore, an object of the present invention is to prevent catalyst deterioration by determining ignition system misfire in a double air-fuel ratio sensor system and ensuring failure diagnosis.

[Means to solve the problem]

A means for solving the above problem 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 CCRo installed in the exhaust passage of the internal combustion engine.
A downstream air-fuel ratio sensor is provided in the exhaust passage downstream of C2° to detect the air-fuel ratio of the engine. The main air-fuel ratio correction amount calculation means sets the main air-fuel ratio so that the air-fuel ratio of the engine is made lean when the output V1 of the upstream air-fuel ratio sensor is rich, and the air-fuel ratio of the engine is made rich when the output VI is lean. Calculating the correction amount, the auxiliary air-fuel ratio correction amount calculation means makes the air-fuel ratio of the engine lean when the output v2 of the downstream side air-fuel ratio sensor is rich, and makes the air-fuel ratio of the engine rich when the output V2 is lean. Calculate the fluid air-fuel ratio correction amount so that. The air-fuel ratio utilization means adjusts the air-fuel ratio of the engine according to the main air-fuel ratio correction amount and the auxiliary air-fuel ratio correction amount. The lean-side limit value reaching determination means determines whether the auxiliary air-fuel ratio correction amount has reached the lean-side limit value MIN, and as a result, when the auxiliary air-fuel ratio correction amount reaches the lean-side limit value, the ignition system The misfire abnormality display means determines and displays that the engine has an ignition system misfire abnormality.

[For production]

According to the above-mentioned means, if there is an ignition system misfire abnormality, unburned gas and residual air (02) are discharged from the misfired cylinder even if the air-fuel ratio of all cylinders is near the stoichiometric air-fuel ratio. Therefore,
The upstream air-fuel ratio sensor sends out a lean output under the influence of the residual air (02), and as a result, the main air-fuel ratio correction amount calculation means changes the main air-fuel ratio correction amount (FAF) to the rich side (increase side). Based on the calculation, the air-fuel ratio utilizing means adjusts the air-fuel ratio of the engine to the rich side. On the other hand, the downstream side air-fuel ratio sensor sends out a rich output due to the influence of the rich side air-fuel ratio adjustment by the air-fuel ratio utilization means, and as a result, the auxiliary air-fuel ratio correction amount calculation means changes the auxiliary air-fuel ratio correction amount (R2H) to the lean side. calculate. Therefore, when the auxiliary air-fuel ratio correction amount reaches the lean limit value MIN, it is assumed that a misfire has occurred due to an abnormality in the ignition system.

In other words, the amount of deviation of the engine's air-fuel ratio toward the rich side is larger in the case of an abnormality in the ignition system than in the characteristic deviation of the upstream air-fuel ratio sensor, and as a result, in the case of an abnormality in the ignition system, The auxiliary air-fuel ratio correction amount (R3H) is smaller than the normally possible value.

Therefore, it is possible to detect an abnormality in the ignition system by determining whether or not the auxiliary air-fuel ratio correction amount has reached a predetermined limit value that is normally not possible for making the air-fuel ratio of the engine lean.

Note that if a misfire occurs due to an abnormality in the combustion system, the output of the upstream air-fuel ratio sensor will be greatly disturbed, and therefore the main air-fuel ratio correction amount FAF will also be greatly disturbed, and in response to this, the auxiliary air-fuel ratio correction 1R3R will be set to lean. Since the side limit value MIN is never reached, a misfire caused by an abnormality in the fuel system will not be mistaken as a misfire caused by an abnormality in the ignition system.

〔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, and includes, for example, a built-in potentiometer to generate an analog voltage output signal proportional to the intake air amount. This output signal is the control circuit 10's built-in multiplexer A.
/D converter 101. The distributor 4 has a shaft with a crank angle of 72, for example.
A crank angle sensor 5 that generates a reference position detection pulse signal every 0° and a crank angle sensor 6 that generates a reference position detection pulse signal every 30° in terms of crank angle are provided. The pulse signals of these crank angle sensors 5 and 6 are transmitted to the input/output interface 102 of the control circuit 10.
The output of the crank angle sensor 6 is supplied to CP.
It is supplied to the interrupt terminal of U103.

Furthermore, a fuel injection valve 7 is provided in the intake passageway 2 for each cylinder for supplying pressurized fuel from the fuel supply system to the intake port.

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
'Generate an analog voltage electrical signal according to vV. This output is also supplied to the A/D converter 101.

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

The exhaust manifold 11 includes a catalytic converter 1.
A first 02 sensor 13 is provided on the upstream side of the catalytic converter 12, and a second 02 sensor 15 is provided on the exhaust pipe 14 on the downstream side of the catalytic converter 12. 02 sensor 13.15 generates an electrical signal according to the concentration of oxygen components in the exhaust gas.

That is, the 02 sensor 13.15 generates different output voltages to the H/D converter 101 of the control circuit 10 depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio. The control circuit 10 is configured as a microcomputer, for example, and includes an A/D converter 101, a human output interface 102, a CPt 1103, and a RAM 104.
, RO5) 105, Backup RA! ,1106,
A clock generation circuit 107 and the like are provided.

Further, the throttle valve 16 of the intake passage 2 is provided with an idle switch 17 that generates a signal LL indicating whether the throttle valve 16 is fully closed. This idle state output signal LL is transmitted to the human output interface 10 of the control circuit 10.
2.

Reference numeral 18 denotes a secondary air intake valve, which supplies secondary air to the exhaust pipe 11 during deceleration or idling to collect HC, CO, etc.
This is to reduce emissions.

Further, 19 is a misfire alarm due to an abnormality in the ignition system.

Furthermore, in the control circuit 10, a down counter 108
, flip-flop 109, and drive circuit 110 are for controlling the 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 108 counts the clock signal (not shown) and the borrow out terminal reaches the "1" level, the flip-flop 1
09 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.

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

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

In other words, the RAM, 1105 + data Q and THW are updated at predetermined intervals. Also, the rotational speed data Ne is calculated by the interrupt of the crank angle sensor 6 every 30° !, +105 are stored in a predetermined area.

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

In step 401, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the upstream 02 sensor 13 is satisfied. For example, when the cooling water temperature is below a predetermined value, the output signal of the upstream 0° sensor 13 is When there is no reversal, the closed-loop condition is not satisfied in any case such as a fuel cut, and the closed-loop condition is satisfied in other cases. If the closed loop condition is not met, the process proceeds directly to step 426. 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 402.

In step 402, the output V1 of the upstream 02 sensor 13 is
is A/D converted and taken in, and in step 403 it is determined whether or not Vl is less than the comparison voltage V□, for example, 0.45 V. That is, it is determined whether the air-fuel ratio is rich or lean. , ≦V, 1), step 404
Determine whether the delay counter CDLY is positive or not at C.
If DLY>0, CDLY is set to 0 in step 405 and the process proceeds to step 406. In step 406, the delay counter CDLY is decremented by 1, and in step 407.
At 408, 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 air-fuel ratio flag F1 is set to 0'' (lean) in step 409.The minimum value TDL is the change from rich to lean in the output of the upstream 02 sensor 13. This is a lean delay state to maintain the rich state even if there is a change, and is defined by a negative residue.On the other hand, if lean (V+ > Via), the delay counter is set at step 410. [: Determine whether DLY is negative or not, and if CDLY<Q, step 411
At step 412, CDLY is set to 0, and the process proceeds to step 412. In step 412, the delay counter CDLY is incremented by 1, and in steps 413 and 414, the delay counter CDLY is guarded at the maximum value TDR. In this case, when the delay counter CDLY reaches the maximum value TDR, the air-fuel ratio flag F1 is set to "1" (rich) in step 415. The maximum value TDR is a rich delay state 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 air-fuel ratio flag FL has been inverted, that is, it is determined whether the air-fuel ratio after the delay processing has been inverted. If the air-fuel ratio is reversed,
In step 417, it is determined based on the value of the air-fuel ratio flag F1 whether the reversal is from rich to lean or from lean to rich. If the reversal is from rich to lean, step 418 skip-increases FAF -PAF+R3R; conversely, if the reversal from lean to rich, step 419 skip-increases FAF 4-FAF-R3L. decrease to

In other words, skip processing is performed.

If the sign of the air-fuel ratio flag F1 is not inverted in step 412, integration processing is performed in steps 420, 421, and 422. That is, in step 420, F1=″0
If F1=“'0” (lean), FAF −FAF+KIR is set at step 421, and on the other hand, if Fl=“1” (rich>), step 4 is determined.
FAF 4-FAF-KIL at 22. Here, the integral constants KIR and KIL are the skip amounts R3R and R3
It is set sufficiently small compared to L, that is, KIR(
KIL) <R3R(R5L). Therefore, step 421 gradually increases the fuel injection amount in the lean state (F1="0"), and step 422 gradually increases the fuel injection amount in the rich state (F1="0").
"1") gradually reduces the fuel injection amount.

Furthermore, the air-fuel ratio correction coefficient FAF is learned in steps 423 and 424 for each skip process. That is, in step 423, it is determined whether the learning conditions are satisfied. For example, the intake air amount data Q is read from RAJO5, and it is determined whether Q is a constant value or not.

If Q≧constant value, the process directly advances to step 425 and learning control is not performed. This is because if learning control is performed when the intake air amount Q is large, the learning value FGHAC will change due to the influence of the evaporator.
This is because there is a possibility that this learning (over-correction) will be performed. On the other hand, if the learning conditions are satisfied, the air-fuel ratio correction coefficient FAF is learned in step 424. The learning step 424 will be described later.

Next, the air-fuel ratio correction coefficient FAF calculated in steps 418, 419, 421, and 422 is guarded at a minimum value, for example, 0.8, at step 425, and is also guarded at a maximum value, for example, 1.2. . 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 RA! , + 1 (
15, and the routine ends at step 426.

FIG. 5 is a detailed flowchart of the learning step 424 in FIG.
Under the air-fuel ratio feedback control, when the learning condition is satisfied, the air-fuel ratio correction coefficient FAF is executed every time the air-fuel ratio correction coefficient FAF is skipped.

That is, in step 501, the air-fuel ratio correction coefficient FAF
The average value FAFAV of FAFAV is calculated as follows: FAFAV←(FAF + FAFO) / In addition, FAFO is calculated using the FAF value immediately after the previous skip, and in step 502, FAF is prepared for the next calculation and is set as FAFO←FAF. Next, in step 503, ΔFAF - FAFAV-1,0 is calculated.

Next, in step 504, it is determined whether ΔFAF>Q, and as a result, if ΔFAF>0, the learning correction amount FGHAC is increased to FGH8C←FGHAC+ΔFGHAC in step 505, and the process proceeds to steps 506 and 507. For example, the maximum value is 1.
Guard with 05. On the other hand, if ΔFAF≦0, in step 508 the learning correction amount FGIIAC is changed to FGIIA
C4-FG [(AC-ΔF G )I AC is reduced to a minimum value, e.g.
．． Guard at 90. Note that FGI (AC may be updated only when △FAF1>K (positive value). In this way, according to the learning control, the air-fuel ratio correction coefficient FAF
is 1. The learning correction amount PGHAC is increased or decreased so that it converges to O.

FIG. 6 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. 4. When the air-fuel ratio signal H/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 C
As shown in FIG. 6(B), DLY is grounded in a rich state and counted down in a lean state. As a result, a delayed air-fuel ratio signal A/F' (corresponding to flag Fl) is formed as shown in FIG. 6(C).

For example, time 1. Even if the air-fuel ratio signal A changes from lean to rich, the delayed air-fuel ratio signal A
/F' changes to rich at time t2 after being held strong for the rich delay time TDR. Even if the air-fuel ratio signal A/F changes from rich to lean at time t3, the air-fuel ratio signal A/F' subjected to the delay processing is delayed by the lean delay time (-TD
L) After being kept rich for a considerable amount, it changes to lean at time t4. However, the air-fuel ratio signal A/F' at time tS+
When the rich delay time TDR is reversed in a short period like t6+t7, the delay counter CDLY becomes lower than the maximum value DR.
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 sixth
The air-fuel ratio correction coefficient FAF shown in Figure (D) 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 a skip amount RS RR5L as a first air-fuel ratio feedback control constant, and an integral constant K.
There is a system in which IR, KIL, delay time TDR, TDL, or comparison voltage VRl of the output V+ of the upstream 0□ sensor 13 is made variable, and a system in which a second air-fuel ratio correction coefficient FAF2 is introduced.

For example, if rich skip 1RsR is increased, the controlled air-fuel ratio can be shifted to the rich side, and even if lean skip fiR3L is decreased, the controlled air-fuel ratio can be shifted to the rich side.On the other hand, if lean skip 1R3L is increased,
The controlled air-fuel ratio can be shifted to the lean side, and even if the rich skip 1R3R 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 amount R8R and the lean skip amount R3L according to the output of the downstream 02 sensor 15.

In addition, by increasing the rich integral constant KIR, the control air-fuel ratio can be shifted to the rich side, and the lean integral constant KIL
On the other hand, increasing the lean integral constant KIL allows the controlled air-fuel ratio to be shifted to the lean side, and even if the rich integral constant KIR is decreased, the controlled air-fuel ratio cannot be shifted to the rich side. You can move to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the rich integral constant KIR and the lean integral constant KIL according to the output of the downstream 02 sensor 15. If the rich delay time TDR is set large or the lean delay time (-TDL) is set small, the control air-fuel ratio can be shifted to the rich side; conversely, if the lean delay time (-TDL) is set large or the lean delay time (-TDL) is set small
By setting a small TDR), the control air-fuel ratio can be shifted to the lean side. In other words, downstream/it, IJ○2 sensor 1
The air-fuel ratio can be controlled by correcting the delay times TDR and TDL according to the output of No. 5. Furthermore, the comparison voltage V
By increasing RI, the control air-fuel ratio can be shifted to the rich side,
Further, by reducing the comparison voltage Vtt+, the control air-fuel ratio can be shifted to the lean side. Therefore, by correcting the comparison voltage V according to the output of the downstream side 02 sensor 15, the air-fuel ratio can be controlled.

Making these skip amount, integral constant, delay time, and comparison voltage variable by the downstream 02 sensor has its own advantages. For example, the delay time and the air-fuel ratio can be adjusted very delicately, and the skip amount can be controlled with good response without lengthening the feedback period of the air-fuel ratio 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, 512 ms. Step 701
In steps 706 to 706, it is determined whether the downstream 0□ sensor 15 is in a closed loop condition. For example, upstream side 02 sensor 13
In addition to the failure of the closed loop condition (step 701), the cooling water temperature THW is lower than a predetermined value (for example, 70°C) (step 702), and the throttle valve 16 is fully closed (L
When L=“1” (step 703), the rotational speed Ne
, when the secondary air is not introduced based on the vehicle speed, the signal LL of the idle switch 17, the cooling water temperature THW, etc. (Step 704), when the load is light (Q/Ne <XI
) (step 705), the downstream 0□ sensor 15 is not activated (step 706), 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 717, and if the condition is a closed loop condition, the process proceeds to step 707.

In step 707, the output v2 of the downstream sensor 15
In step 709, it is determined whether V2 is lower than the comparison voltage VII, for example, 0.55 V, that is, it is determined whether the air-fuel ratio is rich or lean. Note that the comparison voltage VR2 is upstream of the catalytic converter 12,
The upstream side 0□sensor 1
3 output comparison voltage V.

Although it is set higher, this setting may be arbitrary.

As a result, if V2≦Vl12('J-n), step 709.710.7111. : Advance, V2 > VR2
(!For J Petucci, step 712.713.714
．． Proceed to 715. That is, in step 709, R2
H-! l5R-! −ΔR3 (constant value), that is, the rich skip amount R3R is increased to shift the air-fuel ratio to the rich side, and in steps 710 and 711, R2H is guarded at the maximum value MAX (=7.5%), On the other hand, in step 712, R2H-R2H-ΔR3 is set, that is, the rich skip amount R3R is decreased to shift the air-fuel ratio to the lean side, and in steps 713 and 714, R2H is set to the minimum value M.
Guard at IN (=2.5%). Note that the minimum value MI
N is a value at a level that does not impair transient followability, and maximum value MAX is a value at a level at which drivability does not deteriorate due to air-fuel ratio fluctuations.

Further, when the rich skip amount R3R sticks to the minimum value (lean side limit 1st shift) MIN in steps 713 and 714, the ignition system misfire alarm 19 is detected in step 715.
energize.

In step 715, the lean skip fiR3L is
3L←10%-R2H. That is, R5R+R5L=10%.

The routine then ends at step 717.

FIG. 8 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, 360° CA. Step 801
Then, the intake air amount data Q and rotational speed data Ne are read from RA1, 1105, and the basic injection amount TALIP is calculated. For example, TA[IP←α・Q/Ne (α is a constant)
shall be. In step 802, the final injection ff1TAU is converted to TA[I4-TAUP・(FAF+FAHAC
)・β+γ. Note that β·T is a correction amount determined by other operating state parameters. Next, in step 803, the injection amount TAU is counted down by the down counter 10.
8 and also sets the flip-flop 109 to start fuel injection. The routine then ends at step 804.

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

In this way, in the case of a misfire abnormality caused by the ignition system, the upstream 02 sensor 13 sends out a lean output in response to the residual air (02) in the misfiring cylinder, and therefore the air-fuel ratio correction coefficient FAF
is made to the rich side (increase side), but in this case FAF
The increase in the amount of
Since it is absorbed into the learned value FG)IAC by the learning routine shown in the figure, the air-fuel ratio correction coefficient FAF is still substantially 1.0.

Even in such a state, the air-fuel ratio is rich, so the downstream 02 sensor 15 decreases the rich skip amount R3R as an air-fuel ratio feedback control constant, and the lower limit value M
It will stick to IN. Utilizing this, the present invention determines whether a misfire occurs due to the ignition system.

The first air-fuel ratio feedback control is 4ms@, and
The second air-fuel ratio feedback control is performed every 512 m5.The air-fuel ratio feedback control is performed primarily by the upstream 02 sensor, which has a good response, and is secondary to the control by the downstream 02 sensor, which has a poor response. It's for a reason.

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, R3L and make only the other variable.
It is also possible to fix one of them and make only the other variable, or to change the Ricci integral constant KIR, IJ-
It is also possible to have one of them 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 TA[lP in step 801 is determined by the carburetor itself, that is, it is determined according to the intake pipe negative pressure according to the intake air amount and the rotational speed of the engine, At step 802, the amount of supplied air corresponding to the final fuel injection amount TAU is calculated.

Further, in the above-described embodiment, the 02 sensor was used as the air-fuel ratio sensor, but a C○ sensor, a lean mixture sensor, etc. may also be used. In particular, when a TlO2 sensor is used as the upstream air-fuel ratio sensor, control responsiveness is improved.

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

〔Effect of the invention〕

As described above, according to the present invention, it is possible to reliably distinguish a misfire caused by an abnormality in the ignition system from a misfire caused by an abnormality in the fuel system, and as a result, troubleshooting can be facilitated and deterioration of the catalyst 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 a double 02 sensor system.
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; Figs. 4, 5, and 7 are , FIG. 8 is a flowchart for explaining the operation of the control circuit of FIG. 3, and FIG. 6 is a timing diagram for supplementary explanation of the flowchart of FIG. 4. DESCRIPTION OF SYMBOLS 1... Engine body, 2... Air flow meter, 4... Distributor, 5.6... Crank angle sensor, 10... Control circuit, 12... Catalytic converter, 13... Upstream side 02 sensor, 15...downstream side 0
2 sensors, 17...idle switch.

Claims (1)

[Claims] 1. Three-way catalyst (12) provided in the exhaust passage of an internal combustion engine
an upstream air-fuel ratio sensor (13) provided in the exhaust passage upstream of the three-way catalyst to detect the air-fuel ratio of the engine; and an upstream air-fuel ratio sensor (13) provided in the exhaust passage downstream of the three-way catalyst to detect the air-fuel ratio of the engine. a downstream air-fuel ratio sensor (15) that detects the air-fuel ratio of the engine; when the output of the upstream air-fuel ratio sensor is rich, the air-fuel ratio of the engine is lean; when the output is lean, the air-fuel ratio of the engine is set lean; main air-fuel ratio correction amount calculation means for calculating a main air-fuel ratio correction amount so that the output of the downstream side air-fuel ratio sensor is rich; auxiliary air-fuel ratio correction amount calculation means for calculating an auxiliary air-fuel ratio correction amount so as to make the air-fuel ratio of the engine rich at times; an air-fuel ratio utilizing means for adjusting the auxiliary air-fuel ratio correction amount; a lean-side limit value reaching determination means for determining whether the auxiliary air-fuel ratio correction amount has reached the lean-side limit value; 1. An air-fuel ratio control device for an internal combustion engine, comprising: an ignition system misfire abnormality display means that determines and displays that the engine has an ignition system misfire abnormality when the engine reaches the ignition system misfire abnormality.