JP2003097322A - Control device of air-fuel ratio of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To early return plural catalysts arranged in series within an appropriate purifying window after returning from a fuel cut. SOLUTION: When the present operation state is not in a state STA4 where both the first and second catalysts arranged in series are within the appropriate purifying window after returning from the fuel cut, the catalyst state is determined from an output value ro2sad1 of a sensor #1RO2 and an output value ro2sad2 of a sensor #2RO2 (S301, S302, S303), and a correction value kPARGi after the fuel cut is set according to the catalyst state (S304). A target air-fuel ratio is corrected by adding the correction value kPARGi after the fuel cut to the target air-fuel ratio, and an air-fuel ratio feedback control is performed using an air-fuel ratio feedback correction factor set on the basis of deviation between the corrected target air-fuel ratio and an actual air-fuel ratio basing on output of an LAF sensor, and thereby, the first and second catalysts are early returned within the appropriate purifying window and an exhaust emission after returning from the fuel cut is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an engine, which returns a plurality of catalysts arranged in series to each other within a proper purification window after returning from a fuel cut.

[0002]

2. Description of the Related Art In recent years, with the tightening of exhaust emission regulations for automobiles,
A system has been developed in which a plurality of catalysts are arranged in series to provide multiple stages in order to reduce exhaust emissions in the entire operating region immediately after the engine is started. For example, JP-A-200
No. 0-237541 discloses an underfloor three-way catalyst disposed immediately downstream of an exhaust manifold, an underfloor three-way catalyst disposed slightly downstream of the immediately below three-way catalyst, and an underfloor three-way catalyst. Located immediately downstream, HC (hydrocarbons)
An exhaust gas purification device including an adsorption catalyst that adsorbs is disclosed.

[0003]

However, in general, in air-fuel ratio control of an engine, fuel is cut for the purpose of improving fuel efficiency and purifying exhaust gas in an operating state such as during deceleration. Once implemented,
When fresh air enters the catalyst and goes out of the proper purification window (the range of the proper air-fuel ratio where the exhaust gas can be effectively purified by the catalyst), it becomes an excessive lean state, and after returning from the fuel cut, each catalyst is in the proper purification window. It takes time to return. For this reason, after returning from the fuel cut, a sufficient purifying action cannot be expected until each catalyst returns to within the proper purifying window, and the exhaust gas emission may deteriorate.

The present invention has been made in view of the above circumstances, and it is possible to improve the exhaust emission by returning a plurality of catalysts arranged in series within a proper purification window promptly after returning from a fuel cut. An object of the present invention is to provide an air-fuel ratio control device for an engine that can be used.

[0005]

In order to achieve the above object, the invention according to claim 1 is to arrange a plurality of catalysts in series in an exhaust system, and to arrange the most upstream catalyst upstream side and each catalyst downstream side. And an air-fuel ratio control device for an engine, each of which has an air-fuel ratio sensor, and determines the air-fuel ratio state of each catalyst after returning from fuel cut based on the output of the air-fuel ratio sensor on the downstream side of each catalyst. Catalyst state determination means, an air-fuel ratio correction amount setting means for setting an air-fuel ratio correction amount for returning each catalyst into an appropriate purification window according to the air-fuel ratio state of each catalyst, and a target air-fuel ratio correction amount based on the target air-fuel ratio correction amount. Air-fuel ratio feedback control means for correcting the fuel ratio and performing air-fuel ratio feedback control is provided.

According to a second aspect of the present invention, in the first aspect of the present invention, the air-fuel ratio feedback control means is based on the corrected target air-fuel ratio and the output of an air-fuel ratio sensor arranged upstream of the most upstream catalyst. The air-fuel ratio feedback control is performed based on the deviation from the actual air-fuel ratio.

That is, according to the first aspect of the invention, the air-fuel ratio state of each catalyst after returning from the fuel cut is judged based on the output of each air-fuel ratio sensor on the downstream side of the plurality of catalysts arranged in the exhaust system. Then, the air-fuel ratio correction amount for returning each catalyst into the proper purification window is set according to the determined air-fuel ratio state of each catalyst. Then, by correcting the target air-fuel ratio with this air-fuel ratio correction amount and performing air-fuel ratio feedback control,
After returning from the fuel cut, each catalyst is returned to the proper purification window early.

At this time, the air-fuel ratio feedback control is based on the difference between the target air-fuel ratio and the actual air-fuel ratio based on the output of the air-fuel ratio sensor arranged upstream of the most upstream catalyst, as in the second aspect of the invention. It is desirable to carry out based on this.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 1 to 8 relate to an embodiment of the present invention, FIG. 1 is an overall view of an engine system, FIG. 2 is a circuit configuration diagram of an electronic control system, FIG. 3 is a flowchart of a fuel injection control routine, and FIG. 5 is a flowchart of a fuel ratio feedback correction coefficient setting routine, FIG. 5 is a flowchart of a fuel cut correction amount setting routine, FIG. 6 is an explanatory view of a catalyst state determination table, FIG. 7 is an explanatory view of a fuel cut correction amount table, and FIG. It is a time chart which shows a catalyst state after cutting.

First, the overall construction of the engine will be described with reference to FIG. In the figure, reference numeral 1 is an engine, and in the present embodiment, a horizontally opposed four-cylinder gasoline engine is shown. Cylinder heads 2 are provided on both left and right banks of a cylinder block 1a of the engine 1, and an intake port 2a and an exhaust port 2b are formed on each cylinder head 2.

An intake manifold 3 is communicated with each intake port 2a of the cylinder head 2, and a throttle valve 5a interlocked with an accelerator pedal is connected to the intake manifold 3 via an air chamber 4 in which the intake passages of each cylinder are gathered. Is connected to the throttle chamber 5. An air cleaner 7 is attached to the upstream side of the throttle chamber 5 via an intake pipe 6, and the air cleaner 7 is in communication with an air intake chamber 8. A bypass passage 9 that bypasses the throttle valve 5a is connected to the intake pipe 6, and the bypass passage 9
In addition, the bypass passage 9 may be opened depending on the valve opening degree during idling.
An idle speed control valve (ISC valve) 10 for controlling the idle speed by adjusting the amount of bypass air flowing through is installed.

An injector 11 is arranged immediately upstream of the intake port 2a of each cylinder of the intake manifold 3, and is connected to a fuel tank 13 via a fuel supply passage 12. An in-tank type fuel pump 14 is disposed in the fuel tank 13, and fuel from the fuel pump 14 is inserted into a fuel supply passage 12 to form a fuel filter 15.
Through injector 11 and pressure regulator 1
6, the pressure is returned to the fuel tank 13 from the pressure regulator 16, and the fuel pressure to the injector 11 is adjusted to a predetermined pressure. Furthermore, the cylinder head 2
An ignition plug 17 for exposing the discharge electrode at the tip to the combustion chamber is attached to each of the cylinders, and an ignition coil 18 having an igniter 19 built therein is connected to the ignition plug 17.

On the other hand, each exhaust port 2b of the Linda head 2
The exhaust manifold 20 is communicated with the exhaust manifold 21, and an exhaust pipe 21 is communicated with the collecting portion of the exhaust manifold 20, and a plurality of large-sized and multistage catalysts are arranged in series with the exhaust pipe 21. In the present embodiment, the first catalyst 22 is provided immediately downstream of the collecting portion of the exhaust manifold 20.
A is provided, and the second catalyst 22 is provided downstream of the first catalyst 22A.
B is provided and communicates with the muffler 23. In the present embodiment, the first and second catalysts 22A and 22B are three-way catalysts including an HC adsorption catalyst that adsorbs HC (hydrocarbon).

Next, sensors for detecting the engine operating state will be described. Air cleaner 7 for intake pipe 6
An intake air amount sensor 24 for measuring an intake air amount is provided immediately downstream of the throttle valve 5a provided in the throttle chamber 5 and a throttle opening degree for detecting the opening degree of the throttle valve 5a. The sensor 25 is arranged in series. Further, a knock sensor 26 is attached to the cylinder block 1a of the engine 1, and a cooling water temperature sensor 28 is exposed to a cooling water passage 27 that connects the left and right banks of the cylinder block 1a.

Further, an air-fuel ratio sensor 29A is arranged upstream of the first catalyst 22A, and the air-fuel ratio sensor 29A is arranged downstream of the first catalyst 22A.
A first rear air-fuel ratio sensor 29B and a second rear air-fuel ratio sensor 29C are arranged downstream of the catalyst 22B, respectively. In the present embodiment, the air-fuel ratio sensor 29A on the upstream side of the first catalyst 22A is a wide-range air-fuel ratio sensor that can continuously detect the air-fuel ratio from rich to lean including the theoretical air-fuel ratio, and is linear according to the air-fuel ratio. The linear air-fuel ratio sensor (LAF sensor) having output characteristics, and the first rear air-fuel ratio sensor 29B and the second rear air-fuel ratio sensor 29C are O2 sensors that detect the air-fuel ratio from the oxygen concentration in the exhaust gas. Hereinafter, the air-fuel ratio sensor 29A will be referred to as the LAF sensor 29A,
Replace the first rear air-fuel ratio sensor 29B with the # 1RO2 sensor 29.
B, the second rear air-fuel ratio sensor 29C is the # 2RO2 sensor 2
It is described as 9C.

Further, the crankshaft 30 of the engine 1
A crank angle sensor 32 for detecting a crank angle is provided on the outer periphery of a crank rotor 31 axially attached to the cam rotor 34. A cylinder discrimination sensor 35 for discriminating the present combustion stroke cylinder, fuel injection target cylinder, or ignition target cylinder is provided oppositely.

The engine 1 described above is controlled by an electronic control unit (ECU) 40 shown in FIG. ECU 40
Is mainly composed of a microcomputer in which a CPU 41, a ROM 42, a RAM 43, a backup RAM 44, a counter / timer group 45, and an I / O interface 46 are connected to each other via a bus line. Constant voltage circuit 47 for supplying
Drive circuit 48 connected to I / O interface 46
Also, peripheral circuits such as the A / D converter 49 are built in.
The counter / timer group 45 is a free-run counter,
Various counters such as a counter for counting the number of cylinder discrimination sensor signals (cylinder discrimination pulses), a fuel injection timer, an ignition timer, a periodic interrupt timer for generating periodic interrupts, a crank angle sensor signal input interval timing timer , And various timers such as a watchdog timer for system abnormality monitoring are collectively referred to for convenience, and other various software counter timers are used.

The constant voltage circuit 47 is connected to the battery 51 via the first relay contact of the power supply relay 50 having two relay contacts, and is also directly connected to the battery 51, and the ignition switch 52 is connected to the constant voltage circuit 47. When the contact of the power relay 50 is closed by being turned on, power is supplied to each part in the ECU 40, while the ignition switch 52 is turned on.
Regardless of ON or OFF, backup RAM4 is always
Supply power to 4 for backup. Further, the fuel pump 14 is connected to the battery 51 via a relay contact of the fuel pump relay 53. The power relay 50
A power supply line for supplying power from the battery 51 to each actuator is connected to the second relay contact of the.

The input port of the I / O interface 46 is connected to the ignition switch 52 and the knock sensor 2.
6, a crank angle sensor 32, a cylinder discrimination sensor 35, a vehicle speed sensor 36 for detecting a vehicle speed, etc. are connected, and further, an intake air amount sensor 24 and a throttle opening sensor are connected via an A / D converter 49. Degree sensor 25, cooling water temperature sensor 28, LAF sensor 29A, # 1RO2 sensor 29
B, # 2RO2 sensor 29C and the like are connected, and the battery voltage VB is input and monitored. On the other hand, I /
At the output port of the O interface 46, each relay coil of the power relay 50, the fuel pump relay 53, the ISC
The valve 10, the injector 11 and the like are connected via the drive circuit 48, and the igniter 19 is also connected.

The CPU 41 processes the detection signals from the sensors and switches input via the I / O interface 46, the battery voltage and the like according to the control program stored in the ROM 42, and stores various data in the RAM 43. Based on the data, various learning value data stored in the backup RAM 44, fixed data stored in the ROM 42, etc., the fuel injection amount, the ignition timing, I
The duty ratio of the drive signal for the SC valve 10 is calculated, and engine control such as fuel injection control, ignition timing control, idle speed control, etc. is performed.

Here, in the air-fuel ratio control (fuel injection control) by the ECU 40, fuel cut is performed at the time of deceleration or the like to stop the fuel supply to the engine, thereby improving fuel efficiency and purifying exhaust gas. But first due to fuel cut
The air-fuel ratio state of the catalyst 22A and the second catalyst 22B becomes lean, and after returning from the fuel cut, it takes time for the state of the first catalyst 22A and the second catalyst 22B to return to the proper purification window, and the exhaust gas emission It may get worse.

Therefore, in the ECU 40, after returning from the fuel cut, the first catalyst 22A and the second catalyst 22B are detected from the outputs of the # 1RO2 sensor 29B and the # 2RO2 sensor 29C.
To determine the air-fuel ratio state (catalyst state) in Then, the target air-fuel ratio is corrected according to the determined catalyst state, and the air-fuel ratio feedback control is performed based on the deviation between the corrected target air-fuel ratio and the output of the LAF sensor 29A, whereby the first catalyst 2
The states of 2A and the second catalyst 22B are returned to the proper purification window early.

That is, the ECU 40 has the functions of the catalyst state determination means, the air-fuel ratio correction amount setting means, and the air-fuel ratio feedback control means according to the present invention, and specifically, by the routines shown in FIGS. Realize the function of each means.
Hereinafter, the processing relating to the fuel injection control executed by the ECU 40 will be described with reference to the flowcharts of FIGS.

FIG. 3 is a fuel injection control routine executed every predetermined period after the ECU 40 is powered on and the system is initialized.
At 01, the basic fuel injection pulse width Tp that determines the basic fuel injection amount is calculated from the intake air amount Q based on the signal from the intake air amount sensor 24 and the engine speed NE based on the signal from the crank angle sensor 32 ( Tp ← K × Q / N
E; K is an injector characteristic correction constant).

Next, in step S102, the basic fuel injection pulse width Tp based on the intake air amount Q and the engine speed NE is set to converge the air-fuel ratio to the target air-fuel ratio based on the output of the LAF sensor 29A. The air-fuel ratio feedback correction coefficient LAMBDA and the air-fuel ratio learning correction coefficient KB for rapidly correcting the deviation of the air-fuel ratio due to variations in production of the intake air amount measurement system and fuel supply system or changes over time.
Air-fuel ratio correction term by LRC (LAMBDA + KBLRC
-1), and further, various correction coefficients COEF relating to cooling water temperature correction, acceleration / deceleration correction, full throttle increase correction, post-idle increase correction, etc., fuel cut coefficient K for performing fuel cut
The effective injection pulse width Te is calculated by multiplying FC (Te
← Tp × (LAMBDA + KBLRC-1) × COEF
X KFC).

After that, the routine proceeds to step S103, where the effective injection pulse width Te is added with the invalid pulse width Ts for compensating for the invalid injection time of the injector 11 which changes according to the battery voltage VB, and the final fuel injection amount is obtained. The fuel injection pulse width Ti is set (Ti ← Te + Ts).
Then, in step S104, this fuel injection pulse width T
Set i to the injection timer and exit the routine.

As a result, during normal operation, the fuel cut coefficient KFC is KFC = 1.0, and the drive pulse signal having the normal fuel injection pulse width Ti is supplied to the injector 1 of the corresponding cylinder.
1, the injector 11 is driven, and the amount of fuel corresponding to the fuel injection pulse width Ti is injected. On the other hand, when the fuel cut condition is satisfied during deceleration operation and the fuel cut coefficient KFC is set to KFC = 0, the fuel injection pulse width Ti becomes Ti = Ts and the driving of the injector 11 is substantially stopped. Due to the fuel cut, the fuel supply to the engine 1 is stopped.

After that, when the fuel cut condition is not established and the fuel cut coefficient KFC becomes KFC = 1.0, and the fuel cut is resumed, the first catalyst 22A and the second catalyst 22B are returned.
The target air-fuel ratio is corrected by the air-fuel ratio correction amount (after-fuel-cut correction amount kPARGi) described below.
By the air-fuel ratio feedback control via the air-fuel ratio feedback correction coefficient LAMBDA based on the deviation between the corrected target air-fuel ratio and the actual air-fuel ratio, the first catalyst 22A and the second catalyst 22B are returned to the proper purification window early.

Hereinafter, the air-fuel ratio feedback correction coefficient LA
The air-fuel ratio feedback correction coefficient setting routine of FIG. 4 for setting MBDA and the post-fuel cut correction amount setting routine of FIG. 5 for setting the post-fuel cut correction amount kPARGi will be described.

The air-fuel ratio feedback correction coefficient setting routine shown in FIG. 4 is executed every predetermined period.
At 201, it is determined whether or not the F / B condition (air-fuel ratio feedback condition) is satisfied. F / B condition is NE =
In the zero engine non-rotation state, during engine cranking, and in the initial state in which any condition within the set time is satisfied after the engine is started, the LAF sensor 29A, # 1RO2
When the output voltage of the sensor 29B or # 2RO2 sensor 29C does not reach the set value and the state of the predetermined range does not continue for the set time or more in the inactive state, or during the acceleration / deceleration, during the fuel cut, the engine transient operation state When, it is judged that the F / B condition is not satisfied, and if neither condition is satisfied, F
/ B condition is determined to be satisfied.

When the F / B condition is not satisfied, the routine proceeds from step S201 to step S202, where the air-fuel ratio feedback correction coefficient LAMBDA is set to LAMBDA.
= 1.0 (LAMBDA ← 1.0) and exits the routine. That is, when the air-fuel ratio feedback condition is not satisfied, the air-fuel ratio feedback correction coefficient LAMBDA
Is fixed or clamped at 1.0, and the LAF sensor 2
The air-fuel ratio feedback correction based on the output of 9A is stopped.

On the other hand, if the F / B condition is satisfied in step S201, steps S201 to S20 are performed.
3 and subsequent steps, the current target air-fuel ratio AF according to the operating state
RTGT is corrected by the correction amount kPARGi after fuel cut,
Calculate new target air-fuel ratio AFRTGTN (AFRT
GTN ← AFRTGT + kPARGi). The post-fuel cut correction amount kPARGi is an air-fuel ratio correction amount for returning the first catalyst 22A and the second catalyst 22B after returning from the fuel cut into the proper purification window early, and the fuel of FIG. 5 described below. It is set by the post-cut correction amount setting routine.

Thereafter, the routine proceeds to step S204, where the deviation between the target air-fuel ratio AFRTGTN and the actual air-fuel ratio AFRREAL based on the output of the AF sensor 29A is multiplied by the control gain G to calculate the air-fuel ratio feedback correction coefficient LAMBDA (LAMBDA ← ( AFRTGTN-AFRREA
L) × G), exit the routine.

Next, the post-fuel cut correction amount setting routine of FIG. 5 for setting the post-fuel cut correction amount kPARGi will be described. In this post-fuel cut correction amount setting routine, first, in step S301, it is checked whether or not the current operating state is after the return from the fuel cut. Then, if it is not after the return from the fuel cut, the routine exits as it is, and if it is after the return from the fuel cut, step S3
At 02, it is checked whether the previous catalyst state is the state SAT4.

As explained below, the state STA4 is
Both the first catalyst 22A and the second catalyst 22B have returned to the proper purification window, and the correction amount after fuel cutoff kP
A state where air-fuel ratio correction by ARGi is not required (kPARG
i = kPARG4 = 0). Therefore, when the catalyst state is the state SAT4, the step S302 is directly performed.
If the catalyst state is not the state STA4, the routine is exited from step S302 to step S303.
Proceed to and the output value ro2sad of the # 1 RO2 sensor 29B
The catalyst state is judged from 1 and the output value ro2sad2 of the # 2 RO2 sensor 29C.

This catalyst state is determined by each output value ro2sad.
1, ro2sad2 to the first and second catalysts 22A and 22B
6 to determine whether the first and second catalysts 22A and 22B are in the rich state or the lean state by comparing with the determination threshold value set in the appropriate purification window of FIG.
With reference to the determination table of No. 1, the states STA1 to STA4 shown in the following (1) to (4) are determined. However, state STA
After it is determined to be 2 and the correction is made in this state STA2, the state STA5 shown in (5) below is set in order to shift to the state STA4.

(1) State STA1 Both the first catalyst 22A and the second catalyst 22B are lean (le).
an) state, which promotes enrichment of the air-fuel ratio.

(2) State STA2 Only the second catalyst 22B is in the lean state, and the first catalyst 22A
The air-fuel ratio is enriched to about the upper limit of the window to enrich the second catalyst 22B.

(3) State STA3 Only the first catalyst 22A is in the lean state, and the second catalyst 22B.
The air-fuel ratio is gradually made rich while purifying the exhaust gas depending on

(4) State STA4 Both the first catalyst 22A and the second catalyst 22B are within the proper purification window, and the correction amount kPAR after fuel cut is substantially the same.
No correction by Gi is performed.

(5) State STA5 This is a state in which the state STA2 is shifted to the state STA4, and the first catalyst 22 is used to enrich the second catalyst 22B.
Since it is considered that A is excessively rich, the first catalyst 22A is made lean and returned to the proper purification window.

After that, the routine proceeds to step S304, where the post-fuel-cut correction amount kPA is adjusted to the catalyst state by referring to the post-fuel-cut correction amount table based on the above state SATi.
Set RGi (i = 1 to 5) and exit the routine. As shown in FIG. 7, the post-fuel-cut correction amount table shows the post-fuel-cut correction amount kPARG corresponding to the states STA1 to STA5.
1 to 5 are stored, and an air-fuel ratio correction amount that can be returned to an appropriate purification window early is obtained by a simulation or an experiment in consideration of the engine type and the exhaust system configuration, and the correction after fuel cut is performed. It is stored as a quantity. For example, kPARG1 = correction amount equivalent to 4%, kPARG2 = correction amount equivalent to 2%, kPARG3 =
A correction amount corresponding to 2%, a correction amount corresponding to kPARG4 = 0% (no correction), and a correction amount corresponding to kPARG5 = 1%.

Then, as described above, the post-fuel-cut correction amount kPARGi is added to the target air-fuel ratio AFRTGT set according to the operating state, the target air-fuel ratio is offset-corrected, and a new target air-fuel ratio AFRTGTN after correction is made. And the actual air-fuel ratio AFRRE based on the output of the LAF sensor 29A
Using the air-fuel ratio feedback correction coefficient LAMBDA set based on the deviation from AL, air-fuel ratio feedback control is performed so that the first catalyst 22A and the second catalyst 22B return to the proper purification window early.

That is, as shown in the time chart of FIG. 8, immediately after returning from the fuel cut, the output value ro2sad1 of the # 1RO2 sensor 29B downstream of the first catalyst 22A and the second value
Output value ro of the # 2RO2 sensor 29C downstream of the catalyst 22B
When both 2sad2 and lean indicate a lean state, it is determined that the catalyst state is the state STA1, and correction in the rich direction by the post-fuel cut correction amount kPARG1 (for example, 4
% Equivalent) is made. When the first catalyst 22A is returned to the proper purification window by the correction of the air-fuel ratio in the rich direction and only the second catalyst 22B is in the lean state, the state STA2 is determined and the post-fuel cut correction amount kPARG is determined.
By 2, the correction in the rich direction (for example, a correction equivalent to 2%) is performed within a range not exceeding the upper limit of the proper purification window of the first catalyst 22A.

When the first catalyst 22A becomes excessively rich due to the air-fuel ratio correction in the state STA2, next,
The air-fuel ratio correction (correction equivalent to 1%) is performed by the post-fuel cut correction amount kPARG5 in the state STA5. as a result,
The first catalyst 22A is returned to within the proper purification window, and the state becomes STA4, and the correction of the target air-fuel ratio ends (kPA.
RG4 = 0).

Immediately after returning from the fuel cut, if only the first catalyst 22A is in the lean state, it is judged that the catalyst state is the state STA3, and the exhaust purification is performed by the second catalyst 22B within the proper purification window. While performing the correction, the air-fuel ratio is gradually corrected in the rich direction by the post-fuel cut correction amount kPARG3 (for example, correction corresponding to 2%), and the state 4 is entered.

As a result, the first catalyst 2 arranged in series
2A and the second catalyst 22B can be quickly returned to the proper purification window after returning from the fuel cut, and the exhaust emission after returning from the fuel cut can be improved.

[0048]

As described above, according to the present invention, it is possible to improve the exhaust emission by returning a plurality of catalysts arranged in series into the proper purification window early after returning from the fuel cut. it can.

[Brief description of drawings]

[Figure 1] Overall view of the engine system

FIG. 2 is a circuit configuration diagram of an electronic control system.

FIG. 3 is a flowchart of a fuel injection control routine.

FIG. 4 is a flowchart of an air-fuel ratio feedback correction coefficient setting routine.

FIG. 5 is a flowchart of a correction amount setting routine after fuel cut.

FIG. 6 is an explanatory diagram of catalyst state determination.

FIG. 7 is an explanatory diagram of a correction amount table after fuel cut.

FIG. 8 is a time chart showing a catalyst state after fuel cut.

[Explanation of symbols]

1 engine 22A, 22B catalyst 29A, 29B, 29C air-fuel ratio sensor 40 electronic control unit (catalyst state determination means, air-fuel ratio correction amount setting means, air-fuel ratio feedback control means) SATi catalyst state kPARGi correction amount after fuel cut (air-fuel ratio correction Amount) AFRTGT Target air-fuel ratio AFRREAL Actual air-fuel ratio

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02D 45/00 368 F02D 45/00 368F F term (reference) 3G084 BA09 CA09 DA10 EA07 EA11 EB08 EB16 FA03 FA05 FA07 FA10 FA20 FA30 FA38 FA39 3G091 AA02 AA17 AA23 AA28 AA29 AB03 BA14 BA15 BA19 CB02 DA01 DA02 DA03 DB10 DC02 EA00 EA01 EA05 EA07 EA12 EA16 EA26 EA28 EA30 EA34 EA39 FA05 FA17 FA18 FA19 FB10 FB11 FB12 GA06 HA12 HA42 HA47 HB02 3G301 JA21 KA11 KA26 LB02 MA01 MA25 NC02 ND12 ND15 PA01Z PA11Z PC08Z PD04A PD04Z PD09Z PE03Z PE05Z PE08Z PF01Z PG01Z

Claims (2)

[Claims] 1. An air-fuel ratio control device for an engine, wherein a plurality of catalysts are arranged in series in an exhaust system, and air-fuel ratio sensors are respectively arranged on the upstream side of the upstreammost catalyst and on the downstream side of each catalyst. The catalyst state determination means for determining the air-fuel ratio state of each catalyst after returning from the fuel cut based on the output of the air-fuel ratio sensor on the downstream side of each catalyst, and each catalyst according to the air-fuel ratio state of each catalyst. An air-fuel ratio correction amount setting means for setting an air-fuel ratio correction amount for returning to the proper purification window, and an air-fuel ratio feedback control means for correcting the target air-fuel ratio by the air-fuel ratio correction amount and performing air-fuel ratio feedback control An air-fuel ratio control device for an engine. 2. The air-fuel ratio feedback control means performs air-fuel ratio feedback control based on a deviation between the corrected target air-fuel ratio and the actual air-fuel ratio based on the output of an air-fuel ratio sensor arranged upstream of the most upstream catalyst. The air-fuel ratio control device for an engine according to claim 1, wherein the air-fuel ratio control device is performed.