JP2002256936A - Air fuel ratio control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air fuel ratio control device capable of detecting a trouble when an output characteristic change affecting the purging rate of a catalyst is caused in an oxygen concentration sensor. SOLUTION: An O2 sensor 18 is provided in the downstream of a three-way catalyst 19 and an LAF sensor 17 is provided in the upstream thereof in an exhaust system of an engine 1. In controlling the air fuel ratio according to the outputs of the sensors 18, 17, an ECU 5 can detect a trouble in the LAF sensor 17 in a stoichiometric region by determining the stoichiometric deterioration of the LAF sensor 17 when the average detection equivalance ratio KACTAV corresponding to the output average value of the LAF sensor 17 (upstream oxygen concentration sensor) when the target air fuel ratio is controlled according to the output of the O2 sensor 18 (downstream oxygen concentration sensor) exceeds a designated range.

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 device for detecting an abnormality of an oxygen concentration sensor which outputs a signal proportional to the oxygen concentration in exhaust gas.

[0002]

2. Description of the Related Art Conventionally, as a method of detecting a failure of an oxygen concentration sensor provided in an exhaust system of an engine, a method of detecting a failure by increasing an internal resistance of a sensor element is known. In this method, the voltage between the electrodes when oxygen ions move is measured, and when the measured voltage exceeds a predetermined value, it is determined that the internal resistance has increased and a failure is detected.

[0003]

However, the conventional failure detection method cannot detect a change in the output characteristics of the oxygen concentration sensor. When the air-fuel ratio changes, the air-fuel ratio in the exhaust gas, which is controlled based on the output of the oxygen concentration sensor, deviates from the stoichiometric air-fuel ratio, and there is a problem that the purification rate of the three-way catalyst cannot be sufficiently obtained.

Accordingly, an object of the present invention is to provide an air-fuel ratio control device capable of detecting a failure of an oxygen concentration sensor when a change in output characteristics affecting the purification rate of a catalyst occurs.

[0005]

In order to achieve the above object, an air-fuel ratio control apparatus according to the present invention comprises a catalyst provided in an exhaust system of an internal combustion engine, and an air-fuel ratio control device provided upstream of the catalyst and provided in an exhaust system. First air-fuel ratio detecting means for outputting a value proportional to the concentration, and second air-fuel ratio detecting means provided downstream of the catalyst and outputting a rich or lean value according to the air-fuel ratio in the exhaust gas. In the air-fuel ratio control device provided, target air-fuel ratio setting means for calculating a target air-fuel ratio by proportional integral control according to the output of the second air-fuel ratio detection means, and the output of the first air-fuel ratio detection means Air-fuel ratio control means for performing feedback control to the target air-fuel ratio calculated by the target air-fuel ratio setting means, and based on the output of the first air-fuel ratio detection means when the output of the second air-fuel ratio detection means is inverted. The first
And a failure detecting means for detecting a failure of the air-fuel ratio detecting means.

Further, the air-fuel ratio control device of the present invention comprises a catalyst provided in an exhaust system of an internal combustion engine, and a first air-fuel converter provided upstream of the catalyst and outputting a value proportional to the oxygen concentration in the exhaust gas. A fuel ratio detecting means provided downstream of the catalyst for outputting a rich or lean value in accordance with an air-fuel ratio in the exhaust gas;
An air-fuel ratio control device comprising:
Target air-fuel ratio setting means for calculating a target air-fuel ratio by proportional integration control in accordance with an output of the second air-fuel ratio detection means;
Air-fuel ratio control means for feedback-controlling the output of the first air-fuel ratio detection means to the target air-fuel ratio calculated by the target air-fuel ratio setting means; and the air-fuel ratio control means when the output of the second air-fuel ratio detection means is inverted. And a failure detecting means for detecting a failure of the first air-fuel ratio detecting means based on an average value of an output of the first air-fuel ratio detecting means.

In the air-fuel ratio control device according to the present invention, the target air-fuel ratio is set according to the output of the second air-fuel ratio detecting means which outputs a rich or lean value according to the air-fuel ratio in the exhaust gas by the target air-fuel ratio setting means. Is calculated according to the proportional integral control,
The output of the first air-fuel ratio detection means, which outputs a value proportional to the oxygen concentration in the exhaust gas, is feedback-controlled to the calculated target air-fuel ratio by the air-fuel ratio control means, and the second air-fuel ratio is output by the failure detection means. A failure of the first air-fuel ratio detecting means is detected based on the output of the first air-fuel ratio detecting means when the output of the detecting means is inverted.

In addition, the first air-fuel ratio detecting means detects a fault based on an average value of the output of the first air-fuel ratio detecting means when the output of the second air-fuel ratio detecting means is inverted by the fault detecting means. Is detected.

Thus, when the target air-fuel ratio is controlled in accordance with the output of the downstream second air-fuel ratio detecting means, a change in the output characteristic of the upstream first air-fuel ratio detecting means is quantitatively measured. When a change in output characteristics affecting the purification rate of the catalyst occurs in the oxygen concentration sensor, the failure can be detected.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an internal combustion engine (hereinafter referred to as "engine") and a control device thereof according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a DOHC in-line four-cylinder engine in which each cylinder is provided with a pair of an intake valve and an exhaust valve (not shown).

An intake pipe 2 of the engine 1 communicates with a combustion chamber of each cylinder of the engine 1 via a branch (intake manifold) 11. A throttle valve 3 is provided in the intake pipe 2. Throttle valve opening (θTH) for throttle valve 3
The sensor 4 is connected, outputs an electric signal corresponding to the throttle valve opening θTH, and supplies it to an electronic control unit (hereinafter referred to as “ECU”) 5. An auxiliary air passage 6 that bypasses the throttle valve 3 is provided in the intake pipe 2, and an auxiliary air amount control valve 7
Is arranged. The auxiliary air amount control valve 7 is connected to the ECU 5, and the ECU 5 controls the valve opening amount.

An intake air temperature (TA) sensor 8 is mounted on the intake pipe 2 on the upstream side of the throttle valve 3, and a detection signal thereof is supplied to the ECU 5. A chamber 9 is provided between the throttle valve 3 of the intake pipe 2 and the intake manifold 11, and an absolute intake pressure (PBA) sensor 10 is attached to the chamber 9. The detection signal of the PBA sensor 10 is supplied to the ECU 5.

The main body of the engine 1 has an engine water temperature (T
W) The sensor 13 is mounted, and the detection signal is EC
It is supplied to U5. The ECU 5 is connected to a crank angle position sensor 14 that detects a rotation angle of a crankshaft (not shown) of the engine 1, and supplies a signal corresponding to the rotation angle of the crankshaft to the ECU 5. The crank angle position sensor 14 outputs a signal pulse (hereinafter referred to as a “CYL signal pulse”) at a predetermined crank angle position of a specific cylinder of the engine 1, and a top dead center (TDC) at the start of an intake stroke of each cylinder. ) At a crank angle position before a predetermined crank angle (for a four-cylinder engine, the crank angle is 18
A TDC sensor that outputs a TDC signal pulse and a pulse (hereinafter referred to as a “CRK signal pulse”) at a constant crank angle cycle (for example, a 30-degree cycle) shorter than the TDC signal pulse
), And a CYL signal pulse, a TDC signal pulse, and a CRK signal pulse
It is supplied to U5. These signal pulses are used for various timing controls such as fuel injection timing, ignition timing, and the like, and detection of the engine speed NE.

A fuel injection valve 12 is provided for each cylinder slightly upstream of the intake valve of the intake manifold 11, and each injection valve is connected to a fuel pump (not shown) and electrically connected to the ECU 5. The fuel injection timing and the fuel injection time (valve opening time) are controlled by a signal from the ECU 5. Engine 1 spark plug (not shown) is also EC
It is electrically connected to U5, and the ignition timing θIG is controlled by the ECU5.

The exhaust pipe 16 has a branch portion (exhaust manifold) 1
5 is connected to the combustion chamber of the engine 1. In the exhaust pipe 16, immediately downstream of the portion where the branch portions 15 gather,
Wide area air-fuel ratio sensor (hereinafter referred to as "LAF sensor") 17
Is provided. Further, a three-way catalyst 19 directly below and a three-way catalyst 20 below the floor are arranged downstream of the LAF sensor 17, and an oxygen concentration sensor (hereinafter referred to as an "O2 sensor") is provided between these three-way catalysts 19 and 20. 18 is mounted. The three-way catalysts 19 and 20 are used to remove HC, C in exhaust gas.
Purifies O, NOx, etc.

The LAF sensor 17 includes a low-pass filter 2
The ECU 2 is connected to the ECU 5 via the ECU 2 and outputs an electric signal substantially proportional to the oxygen concentration (air-fuel ratio) in the exhaust gas, and supplies the electric signal to the ECU 5. The output of the O2 sensor 18 has a characteristic that the output sharply changes before and after the stoichiometric air-fuel ratio, and the output becomes high level on the rich side and low level on the lean side from the stoichiometric air-fuel ratio. O2 sensor 18
Is connected to the ECU 5 via a low-pass filter 23, and the detection signal is supplied to the ECU 5.

The exhaust gas recirculation mechanism 30 connects the chamber 9 of the intake pipe 2 to the exhaust pipe 16 and an exhaust gas recirculation valve (EGR) provided in the exhaust gas recirculation path 31 for controlling the amount of exhaust gas recirculated. Valve 32) and a lift sensor 33 that detects the valve opening of the EGR valve 32 and supplies a detection signal to the ECU 5. The EGR valve 32 is an electromagnetic valve having a solenoid, and the solenoid is connected to the ECU 5 so that the valve opening can be linearly changed by a control signal from the ECU 5.

In the fuel vapor processing apparatus 40, the fuel tank 4
1 communicates with the canister 45 via the passage 42, and the canister 45 communicates with the chamber 9 of the intake pipe 2 via the purge passage 43. The canister 45 includes the fuel tank 41
It has a built-in adsorbent for adsorbing fuel vapor generated inside and has an outside air intake. A two-way valve 46 including a positive pressure valve and a negative pressure valve is provided in the middle of the passage 42, and a purge control valve 44, which is a duty control type electromagnetic valve, is provided in the middle of the purge passage 43. Purge control valve 4
4 is connected to the ECU 5 and the purge control valve is connected to the EC
It is controlled according to the signal from U5.

The ECU 5 has an input circuit having a function of shaping input signal waveforms from the above-described various sensors to correct a voltage level to a predetermined level, changing an analog signal value to a digital signal value, and the like, and a central processing circuit. (CPU), a storage circuit including a ROM and a RAM for storing various arithmetic programs executed by the CPU, various maps and arithmetic results described later, and drive signals to various solenoid valves such as the fuel injection valve 12 and the ignition plug. And an output circuit for outputting the same.

The ECU 5 determines various engine operation states such as a feedback control operation area and an open control operation area corresponding to the outputs of the LAF sensor 17 and the O2 sensor 18 based on the various engine operation parameter signals described above. Fuel injection valve 1 according to the engine operating state
The second fuel injection time TOUT is calculated, and a signal for driving the fuel injection valve 12 is output based on the calculation result.

The calculation of the fuel injection time TOUT includes LAF
The PID correction coefficient KLAF calculated by the normal PID control according to the output of the sensor 17 is applied.

TOUT = K1 × KLAF × KCMD × Ti + K2 Here, Ti is a basic fuel amount basically set according to the engine speed NE and the intake pipe absolute pressure PBA. K1 is a correction coefficient obtained according to the operation state, and K2 is a correction amount obtained according to the operation state.

First, the PI corresponding to the output of the LAF sensor
The D correction coefficient KLAF calculation processing will be described with reference to FIG. FIG. 2 is a flowchart showing the PID correction coefficient KLAF calculation processing.

First, in step S301, it is determined whether or not the hold flag FKLAFHOLD is "1". During open loop control, FKLAFHOLD = 1, and this process is immediately terminated. When FKLAFHOLD = 0, the KLAF reset flag FKLAFRESET is set. Is determined as "1" (step S302). As a result, when FKLAFRESET = 1, step S3
03, the PID correction coefficient KLAF is set to 1.0, and the integral control gain KI and the target equivalent ratio KCM are set.
The deviation DKAF between D and the detected equivalent ratio KACT is set to “0”, the coefficients are initialized, and the process ends. The detected equivalent ratio KACT is obtained by converting the output of the LAF sensor 17 into an equivalent ratio.

In step S302, FKLAFRESET is set.
If = 0, the process proceeds to step S304, in which a proportional control gain KP, an integral control gain KI, and a differential control gain KD are searched from a map set according to the engine speed NE and the intake pipe absolute pressure PBA. However, in the idle state, an idle gain is adopted. Next, the deviation DKAF between the target equivalent ratio KCMD and the detected equivalent ratio KACT
(K) (= KCMD (k) -KACT (k)) is calculated (step S305), and the deviation DKAF (k) and the respective control gains KP, KI, and KD are applied to the following equation to obtain the proportional term K
LAFP (k), integral term KLAFI (k) and derivative term K
LAFD (k) is calculated (step S306).

KLAFP (k) = DKAF (k) × KP KLAFI (k) = DKAF (k) × KI + KLAF (k−1) KLAFD (k) = (DKAF (k) −DKAF (k−1)) × KD In the following steps S307 to S310, the integral term KLAF
The limit processing of I (k) is performed. That is, KLAFI
(K) Values are predetermined upper and lower limit values KLAFILMTH, KLAF
It is determined whether or not it is within the range of ILMTL (step S
307, S308), KLAFI (k)> KLAFIL
If MTH, KLAFI (k) = KLAFLM
TH (step S310), and KLAFI (k) <K
If LAFILMTL, KLAFI (k) = K
LAFILMTL is set (step S309).

In the following step S311, a PID correction coefficient KLAF (k) is calculated by the following equation.

KLAF (k) = KLAFP (k) + KL
AFI (k) + KLAFD (k) +1.0 Next, the KLAF (k) value is increased to a predetermined upper limit value KLAFLMT.
It is determined whether it is greater than H (step S312), and K
When LAF (k)> KLAFLMTH, KLA
F (k) = KLAFLMTH (step S31
6), end this processing.

In step S312, KLAF (k) ≦ K
If the value is LAFLMTH, it is determined whether the KLAF (k) value is smaller than a predetermined lower limit value KLAFLMTL (step S314), and KLAF (k) ≧ KLAFLMTL.
If this is the case, the process immediately ends, while KLAF (k)
<KLAFLMTL, KLAF (k) = K
The process ends as LALMTL (step S315).

In this process, the PID correction coefficient KLAF is calculated by performing PID control so that the detected equivalent ratio KACT matches the target equivalent ratio KCMD.

Next, the process of determining the deterioration of the LAF sensor 17 will be described. FIG. 6 is a diagram for explaining the stoichiometric deterioration determination processing. When the deterioration determination processing is performed, the output of the O2 sensor 18 is at a high level (indicating that the air-fuel ratio is richer than the stoichiometric air-fuel ratio). , The target equivalence ratio KCMD is gradually decreased, while, when the level is low (indicating that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio), the target equivalent ratio KCMD is gradually increased. Value K of detected equivalent ratio KACT in, C, D, E
ACTAV (= (KACT (B) + KACT (C) + K
ACT (C) + KACT (D)) / 4) is calculated. When the KACTAV value deviates from 1.0 by a predetermined amount or more, it is determined that stoichiometric deterioration has occurred. The average value KACTA
The number of KACT values used for calculating V is not limited to four, but the number of detection values on the lean side and the rich side needs to be the same.

FIG. 7 is an explanatory diagram showing a deviation amount VLFST of the output RVIP of the LAF sensor 17. LAF sensor 1
7, the output RVIP shifts to the lean side or the rich side by the shift amount VLFST.

FIG. 3 is a flowchart showing the overall configuration of the process for determining the deterioration of the LAF sensor. This process is executed every predetermined time (for example, 10 msec).

First, in step S501, it is determined whether or not the engine is in the starting mode, that is, whether or not cranking is being performed. If the engine is in the starting mode, the process is immediately terminated. If it is not the start mode, the stoichiometric deterioration determination processing (step S502), the response deterioration determination processing (step S503), and the lean deterioration determination processing (step S504) are sequentially performed. Then, it is determined whether or not a stoichiometric deterioration flag FLFSTNG indicating that stoichiometric deterioration is detected is "1" is "1" (step S505). When FLFSTNG = 0, it is determined that response deterioration is detected as "1". Response degradation flag FLFR
It is determined whether or not PNG is "1" (step S506),
When FLFRPNG = 0, it is determined whether or not a lean deterioration flag FLFLNNG indicating "1" indicating that lean deterioration has been detected is "1" (step S507).

As a result, if any one of the steps S505 to S507 is affirmative (YES) and any deterioration is detected, the OK indicating that the LAF sensor 17 has not deteriorated is indicated by "1". Flag FOK61 is set to "0"
(Step S511), and the process ends.

On the other hand, if all of the answers in steps S505 to S507 are negative (NO), the stoichiometric deterioration determination end flag FLF which indicates the end of the stoichiometric deterioration determination processing by "1".
It is determined whether STEND is "1" (step S50).
8), when FLFSTEND = 1, the response deterioration determination end flag FLF indicating the end of the response deterioration determination process by “1”
It is determined whether RPEND is “1” (step S50)
9). As a result, when the answer to step S508 or S509 is negative (NO), this process is immediately terminated, while the answer to both steps S508 and S509 is affirmative (YE
In the case of S), the OK flag FOK61 is set to “1”.

FIGS. 4 and 5 show steps S502 in FIG.
6 is a flowchart showing a stoichiometric deterioration determination process in FIG.

First, in step S521, the end of the stoichiometric deterioration determination is indicated by "1". It is determined whether or not the stoichiometric deterioration determination end flag FLFSTEND is “1”, and
When TEND = 0, that is, when the deterioration determination is not completed, it is determined whether or not a monitor condition flag FLFMCHK indicating "1" that the monitor condition is satisfied is "1" (step S522). Here, the monitor condition is:
This is a condition for permitting the execution of the deterioration determination, and the flag FLFMCHK
Is set in the processing of FIG. 10 described later.

When the answer to step S522 is affirmative (YES), it is determined whether or not the variation | DPBA4 | of the intake pipe negative pressure is equal to or less than a predetermined variation DPBLFM (step S5).
22B). If affirmative (YES), it is determined whether or not a stoichiometric degradation determination execution flag FLFSTM indicating that stoichiometric degradation determination is being performed is "1" is "1" (step S522C), and if affirmative (YES), The difference between the maximum negative pressure PBCTMAX and the minimum negative pressure PBCTMIN in the intake pipe,
That is, the maximum fluctuation amount of the negative pressure in the intake pipe is equal to the predetermined fluctuation amount DPBL.
It is determined whether it is equal to or less than AFG (step S522D).

If affirmative (YES) in step S522D or if stoichiometric deterioration determination execution flag FLFSTM is "0" in step S522C, step S522 is executed.
Proceed to 523.

In step S523, the O2 sensor output (S
VO2) It is determined whether or not the monitoring flag FSVO2LAF is “1”. Then, the answer of step S523 is negative (N
In the case of O), the process proceeds to step S527, while when the answer in step S521 or S523 is affirmative (YES), or when any of the answers in steps S522, S522B and S522D is negative (NO), the stoichiometric deterioration determination is performed. SVO2 monitoring flag FSVO2LA
F is set to "0" (step S524), the stoichiometric deterioration determination execution flag FLFSTM is set to "0" (step S525), and the down-count timer tm is set.
The predetermined time TFSTM is set in the LFSTM (step S526), and the process ends.

In step S527, the target equivalence ratio KCMD which is the target of feedback by the processing of FIG.
In the following step S528, the stoichiometric deterioration determination execution flag FLFSTM is set to “1”, and the flow proceeds to step S529.

In step S529, the inversion flag FKACTT, which is set in the processing of FIG. 9 described later and indicates "1" indicating that a predetermined time has elapsed after the O2 sensor output has been inverted from rich to lean or from lean to rich, is set to "1". If FKACTT = 0, that is, if the output of the O2 sensor is not inverted, step S526 is performed.
It is determined whether the value of the timer tmLFSTM set in (or step S532 described later) is “0” (step S530). As a result, if tmLFSTM> 0 and the predetermined time TLFSTM has not elapsed, the present process is immediately terminated.
The VO2 monitoring flag FSVO2LAF is set to "1" (step S531), and the process ends.

If FKACTT = 1 in step S529 and the O2 sensor output is inverted from rich to lean or from lean to rich, the down count timer tmLFSTM is set to a predetermined time TLFSTM and started (step S532). , Counter NKA
It is determined whether or not the value of CT is “0” (Step S53)
3). Since NKACT = 0 at first, step S5
In S35, the counter NKACT is incremented by "1" (step S535), and it is determined whether or not the value is smaller than a predetermined value NKACTC (for example, 5) (step S536). At first NKACT <NKACT
Since this is C, this processing is immediately terminated.

Next, when the O2 sensor output is inverted, the answer to step S533 is negative (NO), and the integrated value KACTT of the detected equivalent ratio KACT is calculated by the following equation (step S534), and the process proceeds to step S535.

KACTT = KACTT + KACT When the number of inversions reaches a predetermined value, step S536 is performed.
Becomes NKACT = NKACTC in step S537.
The average detection equivalent ratio KACTAV is calculated by the following equation.

KACTAV = KACTT / (NKACT-1) Thus, KACT at points B, C, D, and E in FIG.
The KACTAV value is calculated as the average value.

After the detection is started in this way, the KA at the four points B, C, D and E excluding the first inversion (A in FIG. 6).
Since the average of CT is calculated, the accuracy of detection can be improved (control may not be stable at point A, and using this point for calculating the average value may increase the error).

In the following steps S538 and S539, it is determined whether or not the average value KACTAV is larger than a predetermined lower limit value KACTAVL and whether it is smaller than a predetermined upper limit value KACTAVH. As a result, KACTAVL <KACTAV <
If KACTAVH, it is determined that there is no deterioration, and the flag FLFSTNG is kept at "0".

Then, in step S539A, VLFS
The shift amount VLFST with respect to the average value KACTAV is calculated with reference to the T table. FIG. 8 is an explanatory diagram showing a VLFST table.

Thereafter, the process proceeds to step S541, in which the stoichiometric deterioration determination end flag FLFSTEND is set to "1", and in step S541A, the stoichiometric deterioration determination execution flag FLFSTM is set to "0", and this processing ends.

If KACTAV ≦ KACTAVL or KACTAV ≧ KACTAVH, it is determined that stoichiometric deterioration has occurred, and the flag FLFSTNG is set to “1” (step S540), and the routine proceeds to step S539A. The deterioration of the output deviation of the LAF sensor is determined as described above.

FIG. 9 is a flowchart showing a process for calculating the target equivalent ratio KCMD during execution of the stoichiometric deterioration determination.

First, in step S801, it is determined whether or not the O2 sensor output SVO2 is larger than a predetermined reference value SVREF. If SVO2> SVREF and the ratio is richer than the stoichiometric air-fuel ratio, the first rich flag FAFR1 is set to "1". 1 ”(step S803), and SVO2 <SV
If it is REF and leaner than the stoichiometric air-fuel ratio, the flag FAFR1 is set to "0" (step S80).
2), proceed to step S804.

In step S804, it is determined whether or not the first rich flag FAFR1 has been inverted, that is, whether or not the output of the O2 sensor has been inverted from rich to lean or from lean to rich. If not, step S808 is immediately performed. To the first rich flag F
It is determined whether AFR1 is "1", that is, whether or not AFR1 is rich (step S805). When FAFR1 = 1 (rich), a rich-side predetermined time TRD is set in a down-count timer tmDLYR that measures the time after inversion and started (step S80).
7) On the other hand, when FAFR1 = 0 (when lean), the timer tmDLYR is set to the predetermined lean side time TL.
D is set (step S806), and step S808 is performed.
Proceed to.

In step S808, it is determined whether or not the stoichiometric deterioration determination execution flag FLFSTM is "1".
When FLFSTM = 0 and the determination is started from this time, the integrated value KACTT of the detected equivalent ratio KACT and the counter NK incremented in step S535 of FIG.
ACT is both set to “0” (step S809),
The second rich flag FAFR2 is changed to the first rich flag FAF.
R1 and the target equivalent ratio KCMD is set to a predetermined value KCM.
CHK (for example, 1.0) (step S81
0), and proceed to step S813.

In step S813, the inversion flag FKA
CTT is set to “0” and then the second rich flag FA
It is determined whether FR2 is “0” (step S81)
4). As a result, when FAFR2 = 0, the rich-side integral term IRSP is added to the target equivalent ratio KCMD (step S815), and when FAFR2 = 1, KCM
The lean integration term ILSP is subtracted from the D value (step S816), and the process proceeds to step S822.

In step S808, FLFSTM =
If it is 1 and the stoichiometric deterioration determination is being executed, the process proceeds to step S811 to determine whether the first rich flag FAFR1 and the second rich flag FAFR2 are equal, and
If FR1 = FAFR2, the process proceeds to step S81.
Proceed to 3. If FAFR1 ≠ FAFR2, it is determined whether the value of the timer tmDLYR started in step S806 or S807 is “0” (step S812). Immediately after the inversion of the first rich flag FAFR1, since tmDYLR> 0, step S81 is performed.
3, the delay time TR or TL elapses, and tm
When DYLR = 0, the second rich flag FAFR2 is made equal to the first rich flag FAFR1 in step S817, and then the inversion flag FKACTT is set to "1" (step S818).

In the following step S819, it is determined whether or not the first rich flag FAFR1 is "1".
If it is 0, the rich side proportional term PRSP is added to the target equivalent ratio KCMD (step S820), and FAFR1 =
When it is 1, the lean proportional term PLS is calculated from the KCMD value.
P is subtracted (step S821), and step S822 is performed.
Proceed to.

In step S822, a limit check process is executed, and the process ends.

In this way, the target equivalent ratio KCMD is calculated by PI control based on the output of the O2 sensor.

FIG. 10 is a flowchart showing a process for determining the above-mentioned monitor condition. This process is executed in a background where no high-priority process is executed.

First, in step S572, the O2 sensor 1
8 is in an active state, an activation flag nO indicating "1"
It is determined whether or not 2R is “1”, and when nO2R = 1, it is determined whether or not the driving state of the engine 1 and the vehicle on which the engine 1 is mounted are in a predetermined area (step S5).
73).

That is, when the engine coolant temperature TW is equal to the predetermined upper / lower limit value T,
Whether it is within the range of WLAFMH, TWLAFML,
When the intake air temperature TA is a predetermined upper / lower limit value TALAFMH, TALAF
ML, whether the engine speed NE is within the range of predetermined upper and lower limit values NELAFMH, NELAFML, and whether the intake pipe absolute pressure PBA is higher than the predetermined upper and lower limit value PBL.
It is determined whether or not the vehicle speed V is within the range of AFMH and PBLAFML and whether or not the vehicle speed V is within the range of the predetermined upper and lower limit values VLAFMH and VLAFML, and all answers are affirmative (YES).
At this time, it is determined that the operating state is in a predetermined area.

In this case, it is further determined whether or not a flag FCRS indicating "1" indicating that the vehicle is in a cruise state in which the rate of change of the vehicle speed is small is "1" (step S574), and FCRS = 1. , The reset flag F
It is determined whether or not KLAFRESET is “0” (step S575).

As a result of the above determination, steps S572 to S572
If any of the answers to 575 is negative (NO), it is determined that the monitoring condition is not satisfied, and the process proceeds to step S580, and then the down count timer tmLFMCHK is set to the predetermined time TL.
FMCHK is set and started (step S58)
1) The monitor condition flag FLFMCHK is set to “0” (step S583), and the down count timer tmL
A predetermined time TLFRPMS is set in FRPMS and started (step S586), and a response deterioration determination start flag FLFRPMS is set to “0” (step S58).
8), end this processing.

Also, at step S575, FKLAFRE
When SET = 0 and in the air-fuel ratio feedback control region, it is determined whether or not the monitor flag FLFMCHK is “1” (step S576).
When it is 1, the process immediately proceeds to step S578,
When FLFMCHK = 0, the target equivalent ratio KCMD
Is greater than or equal to a predetermined value KCMDZML (for example, a value corresponding to the stoichiometric air-fuel ratio, that is, set to 1.0) (step S577). And KCMD <KCMD
When ZML is satisfied, it is determined that the monitoring condition is not satisfied, and the process proceeds to step S580. When KCMD ≧ KCMDZML, the process proceeds to step S578.

In step S578, it is determined whether or not the LAF sensor deterioration determination end flag FLFRPEND is "1". If FLFRPEND = 1 and the determination is completed, the flow advances to step S580. Also, FLFRPE
When ND = 0, the purge cut flag FLAFP
G is set to "1" and purge cut is performed (step S57).
9) Eliminate the influence of purge gas during diagnosis. It is determined whether the value of the timer tmLFMCHK started in step S581 is "0" (step S582). At first, since tmLFMCHK> 0, step S5
When tmFMCHHK = 0, it is determined that the monitoring condition is satisfied, the flag FLFMCHK is set to “1” (step S584), and it is determined whether the stoichiometric deterioration determination end flag FLFSTEND is “1” (step S584). S585).

As a result, if FLFSTEND = 0 and the stoichiometric deterioration determination has not been completed, the process proceeds to step S586, where the stoichiometric deterioration determination has been completed and the FLF STEND
When STEND = 1, the process proceeds to step S587, and the timer tmLFRPMS started in step S586
It is determined whether or not the value is “0” (step S587).
At first, since tmLFRPMS> 0, the process proceeds to step S588. When tmLFRPMS = 0, the response deterioration determination start flag FLFRPMS is set to “1” (step S589), and the start of the response deterioration determination is permitted.

Next, the correction of the detected equivalent ratio KACT based on the output of the LAF sensor will be described. FIG. 11 is a flowchart showing a process of correcting the detected equivalent ratio KACT. It is determined whether or not the O2 sensor 18 (SVO2) has deteriorated (step S601). If the O2 sensor 18 (SVO2) has deteriorated, the process proceeds to step S606.
Monitor flag FLFMCH indicating that it is in the monitor area
It is determined whether or not K is "1" (step S602), and if the answer is affirmative (YES) and it is in the LAF monitor area, it is determined whether or not the stoichiometric deterioration determination end flag FLFSTEND is "1" (step S603). When the answer is negative (NO), the process proceeds to step S606.

If negative (NO) in step S602,
Alternatively, if affirmative (YES) in step S603, it is determined whether or not the fuel cut flag FFC indicating "1" is "1" while the fuel is being cut. When the answer is affirmative (YES) and the fuel is being cut, the process proceeds to step S606, and when the answer is negative (NO), the process proceeds to step S605.

In step S605, the LAF sensor 17
The output RVIP value is corrected by adding the deviation amount VLFST calculated in step S539A of FIG. In step S606, the corrected RVIP value is corrected according to the atmospheric pressure PA and the exhaust pressure PBOUT to calculate the detected equivalent ratio KACT, and the process ends.

As described above, according to the air-fuel ratio control apparatus of the present embodiment, the LA when the target air-fuel ratio is controlled based on the output of the O2 sensor 18 (downstream oxygen concentration sensor).
When the average detection equivalent ratio KACTAV corresponding to the output average value of the F sensor 17 (upstream oxygen concentration sensor) exceeds a predetermined range, it is determined that the stoichiometric deterioration of the LAF sensor 17 has occurred, and the failure of the LAF sensor 17 in the stoichiometric region is determined. Can be detected.

Further, the deviation VLFST from the stoichiometric air-fuel ratio in accordance with the average detected equivalent ratio KACTAV is determined by the LAF sensor 1.
By correcting the output RVIP to 7, the air-fuel ratio is appropriately controlled to the stoichiometric air-fuel ratio, and the purification rate of the catalyst can be secured.

[0076]

According to the present invention, when the target air-fuel ratio is controlled in accordance with the output of the downstream second air-fuel ratio detecting means, the output characteristic of the upstream first air-fuel ratio detecting means is changed. The measurement can be performed quantitatively, and when a change in output characteristics affecting the purification rate of the catalyst occurs in the oxygen concentration sensor, the failure can be detected.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an engine and a control device thereof according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a PID correction coefficient KLAF calculation process.

FIG. 3 is a flowchart illustrating an overall configuration of a deterioration determination process of the LAF sensor.

FIG. 4 is a flowchart showing a stoichiometric deterioration determination process in step S502 of FIG. 3;

FIG. 5 is a flowchart showing a stoichiometric deterioration determination process following FIG. 4;

FIG. 6 is an explanatory diagram showing a stoichiometric deterioration determination process.

FIG. 7 shows a deviation amount VLFST of the LAF sensor output RVIP.
FIG.

FIG. 8 is an explanatory diagram showing a VLFST table.

FIG. 9 is a target equivalent ratio KCMD during execution of a stoichiometric deterioration determination.
5 is a flowchart showing a calculation process of the above.

FIG. 10 is a flowchart illustrating a process of determining a monitoring condition.

FIG. 11 is a flowchart illustrating a correction process of a detected equivalent ratio KACT.

[Explanation of symbols]

 1 engine 5 ECU 17 LAF sensor 18 O2 sensor

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/22 305 F02D 41/22 305K 45/00 368 45/00 368F (72) Inventor Katsushi Watanabe Saitama 1-4-1 Chuo, Wako-shi, Honda R & D Co., Ltd. (72) Inventor Yukio Noda 1-4-1, Chuo, Wako-shi, Saitama F-term in Honda R & D Co., Ltd. 3G084 AA03 BA24 DA30 EA02 EA11 EB09 EB14 EB15 FA30 3G091 AA02 AA10 AA11 AA17 AB03 BA27 CB02 DB04 DB05 DB06 DC03 EA34 FB11 FC04 HA36 HA37 3G301 HA01 HA06 HA13 HA14 JB01 KA21 MA01 NA03 NA04 NA05 NC04 ND05 PD03 PD04 PD03 PD04

Claims (2)

[Claims] 1. A catalyst provided in an exhaust system of an internal combustion engine, first air-fuel ratio detection means provided upstream of the catalyst and outputting a value proportional to the oxygen concentration in exhaust gas, and downstream of the catalyst. And a second air-fuel ratio detecting means for outputting a rich or lean value in accordance with the air-fuel ratio in the exhaust gas, wherein the second air-fuel ratio detecting means is provided in accordance with an output of the second air-fuel ratio detecting means. Target air-fuel ratio setting means for calculating a target air-fuel ratio by proportional integral control, and air-fuel ratio control means for feedback-controlling the output of the first air-fuel ratio detecting means to the target air-fuel ratio calculated by the target air-fuel ratio setting means. And a failure detecting means for detecting a failure of the first air-fuel ratio detecting means based on an output of the first air-fuel ratio detecting means when an output of the second air-fuel ratio detecting means is inverted. Air-fuel ratio control device characterized by the following: . 2. A catalyst provided in an exhaust system of an internal combustion engine, first air-fuel ratio detecting means provided upstream of the catalyst and outputting a value proportional to the oxygen concentration in exhaust gas, and downstream of the catalyst. And a second air-fuel ratio detecting means for outputting a rich or lean value in accordance with the air-fuel ratio in the exhaust gas, wherein the second air-fuel ratio detecting means is provided in accordance with an output of the second air-fuel ratio detecting means. Target air-fuel ratio setting means for calculating a target air-fuel ratio by proportional integral control, and air-fuel ratio control means for feedback-controlling the output of the first air-fuel ratio detecting means to the target air-fuel ratio calculated by the target air-fuel ratio setting means. Failure detecting means for detecting a failure of the first air-fuel ratio detecting means based on an average value of the output of the first air-fuel ratio detecting means when the output of the second air-fuel ratio detecting means is inverted; Air fuel characterized by having The control device.