JPH08144745A - Catalyst deterioration detecting device for internal combustion engine - Google Patents

Abstract

PURPOSE: To improve accuracy of catalyst deterioration detection by stopping detection of deterioration in a catalytic means when phase difference between output of an upstream side oxygen concentration detecting means and output of a downstream side oxygen concentration detecting means is a prescribed value or more. CONSTITUTION: A three way catalyst (C) for purifying exhaust gas is arranged in an exhaust pipe 12, an upstream side O2 sensor (FS) and a downstream side O2 sensor (RS) are arranged upstream and downstream of the catalyst (C), and each electric signal according to each detecting value is supplied to an ECU 5. When output of the upstream side O2 sensor (FS) is inverted and the output of the downstream side O2 sensor (RS) is not inverted within a prescribed time corresponding to a second prescribed value, namely, when a phase difference between output of the upstream side O2 sensor (FS) and output of the downstream side O2 sensor (RS) is in a prescribed value or more, it is judged that oxygen storage capacity of the catalyst (C) is large, and normal condition in a system is judged, and then a deterioration monitor is completed. It is thus possible to judge rapidly that condition of the catalyst (C) is in a normal condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst deterioration detecting device provided in an exhaust system of an internal combustion engine for detecting deterioration of a catalyst for purifying exhaust gas.

[0002]

2. Description of the Related Art As a method for detecting the deterioration of a catalyst for purifying exhaust gas of an internal combustion engine, the air-fuel mixture supplied to the engine in accordance with the output of an oxygen concentration sensor provided downstream of the catalyst in the exhaust passage of the engine is used. The one in which the fuel ratio is feedback-controlled and the deterioration of the catalyst is detected by using the inversion cycle of the oxygen concentration sensor output at that time has already been proposed by the present applicant (Japanese Patent Laid-Open No. 6-212955). Further, in this method, when the time from the reversal of the output of the downstream oxygen concentration sensor to the reversal is longer than a predetermined time, it is proposed that the catalyst is judged to be normal and the deterioration detection is ended (one-shot OK judgment method). (The same application).

[0003]

However, since the conventional one-shot OK determination method described above is based on the assumption that the engine operating state is in a steady state, there is a change in the air-fuel ratio due to a change in the operating state. In some cases, the catalyst may be erroneously determined to be normal despite the deterioration of the catalyst. For example, in an engine equipped with an evaporative fuel processing device that temporarily stores evaporative fuel and purges the fuel stored in a predetermined engine operating state into an intake system, purging is performed when the engine is decelerated and the downstream oxygen The value indicating the rich state of the concentration sensor output may be maintained for a relatively long period of time, that is, the output may not reverse for a long period of time.In such a case, it may be determined as normal even if the catalyst has deteriorated. there were.

The present invention has been made to solve this problem, and can detect the catalyst deterioration of the internal combustion engine which can improve the accuracy of the catalyst deterioration detection in the case where the air-fuel ratio changes due to the change of the engine operating condition. The purpose is to provide a device.

[0005]

To achieve the above object, the present invention is provided in an exhaust system of an internal combustion engine, and is provided with a catalyst means for purifying exhaust gas, and an upstream side of the catalyst means.
Upstream oxygen concentration detecting means for detecting the oxygen concentration in the exhaust gas, and downstream oxygen concentration detecting means provided downstream of the catalyst means for detecting the oxygen concentration in the exhaust gas, and the upstream and downstream sides. Air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine using at least one of the oxygen concentration detection means, and the output of the downstream side oxygen concentration detection means at the time of controlling the air-fuel ratio by the air-fuel ratio control means In the catalyst deterioration detecting device for an internal combustion engine, which comprises a catalyst deterioration detecting means for detecting deterioration of the catalyst means based on the above, the catalyst deterioration detecting means is one of the upstream oxygen concentration detecting means and the downstream oxygen concentration detecting means. When the output phase difference is equal to or greater than a predetermined value (TSTRG2), the detection of deterioration of the catalyst means is stopped.

The catalyst deterioration detecting means detects a change in the output of the downstream oxygen concentration detecting means over a predetermined period, and when the phase difference is equal to or more than the predetermined value, the catalyst means is normal. It is desirable to have a determining means for determining.

[0007]

When the phase difference between the outputs of the upstream side oxygen concentration detecting means and the downstream side oxygen concentration detecting means is equal to or larger than the predetermined value (TSTRG2), the detection of the deterioration of the catalyst means is stopped.

When a change in the output of the downstream oxygen concentration detecting means is detected for a predetermined period and the phase difference is equal to or more than the predetermined value, the catalyst means is judged to be normal.

[0009]

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

FIG. 1 is an overall configuration diagram of an internal combustion engine (hereinafter referred to as "engine") in which a catalyst deterioration detecting device according to an embodiment of the present invention is incorporated, and a control device therefor. A throttle valve 3 is arranged in the middle of the intake pipe 2. A throttle valve opening degree (θTH) sensor 4 is connected to the throttle valve 3 and outputs an electric signal according to the opening degree of the throttle valve 3 to output an electronic control unit for engine control (hereinafter referred to as “ECU”) 5
Supply to.

The fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of the intake valve (not shown) in the intake pipe 2, and each injection valve is connected to a fuel pump (not shown). The valve opening time of fuel injection is controlled by a signal from the ECU 5 that is electrically connected to the ECU 5.

On the other hand, an intake pipe absolute pressure (PBA) sensor 7 is provided immediately downstream of the throttle valve 3, and the absolute pressure signal converted into an electric signal by the absolute pressure sensor 7 is supplied to the ECU 5. . Further, an intake air temperature (TA) sensor 8 is attached downstream thereof, detects the intake air temperature TA, outputs a corresponding electric signal, and supplies it to the ECU 5.

The engine water temperature (TW) sensor 9 mounted on the main body of the engine 1 is composed of a thermistor or the like, detects the engine water temperature (cooling water temperature) TW, outputs a corresponding temperature signal and supplies it to the ECU 5. The engine speed (NE) sensor 10 and the CRK sensor 11 are mounted around a cam shaft or a crank shaft (not shown) of the engine 1.
The engine speed sensor 10 outputs a pulse (hereinafter referred to as a "TDC signal pulse") at a predetermined crank angle position every 180 degrees rotation of the crankshaft of the engine 1, and the CRK sensor 11 outputs a predetermined crank angle, for example, 45 degrees. The signal pulse (hereinafter referred to as "CRK signal pulse") is output at the crank angle position of, and each of these signal pulses is E
Supplied to CU5.

A three-way catalyst (hereinafter referred to as a catalyst) C for purifying exhaust gas is provided in the exhaust pipe 12, and an upstream O 2 sensor FS as an oxygen concentration detecting means is provided at an upstream position of the catalyst C.
Is mounted, and a downstream side O2 sensor RS serving as an oxygen concentration detecting means is also mounted at a downstream position of the catalyst C. The oxygen concentration in the exhaust gas is detected and an electric signal (FVO2) corresponding to the detected value is detected. , RVO2) is the ECU 5
Is supplied to. Further, a catalyst temperature (TCAT) sensor 13 for detecting the temperature is attached to the catalyst C, and an electric signal corresponding to the detected catalyst temperature TCAT is supplied to the ECU.

The ECU 5 is further connected to a vehicle speed sensor (VH) 17 and an atmospheric pressure (PA) sensor 18 for detecting the speed of the vehicle on which the engine 1 is mounted, and the detection signals of these sensors are supplied to the ECU 5. To be done.

A canister (not shown) for adsorbing the evaporated fuel generated in the fuel tank is connected to the intake pipe 2 via a passage 19, and a purge control valve 20 is arranged in the middle of the passage 19. There is. The purge control valve 20 is the ECU 5
The ECU 5 controls the opening and closing of the valve. The purge control valve 20 is opened in a predetermined operating state of the engine 1, and supplies the evaporated fuel stored in the canister to the intake pipe 2.

The ECU 5 shapes the input signal waveforms from various sensors, corrects the voltage level to a predetermined level, converts an analog signal value into a digital signal value, and the like, a central processing circuit (a). Hereinafter, referred to as "CPU" 5b, a storage means 5c for storing various calculation programs executed by the CPU 5b and calculation results, an output circuit 5d for supplying a drive signal to the fuel injection valve 6, and the like.

The CPU 5b, as will be described later, based on the various engine parameter signals described above, the air-fuel ratio feedback control region and a plurality of specific operation regions in which the air-fuel ratio feedback control is not performed (hereinafter referred to as "open loop control region").
Of various engine operating conditions), and calculates the fuel injection time TOUT of the fuel injection valve 6 synchronized with the TDC signal pulse based on the following equation (1) according to the determined engine operating condition. To do.

TOUT = Ti × KO2 × K1 + K2 (1) Here, Ti is the basic fuel injection time of the fuel injection valve 5, and is determined according to the engine speed NE and the intake pipe absolute pressure PBA.

KO2 is an air-fuel ratio correction coefficient (hereinafter, simply referred to as "correction coefficient"), which is obtained according to the oxygen concentration in the exhaust gas detected by the O2 sensors FS and RS during the air-fuel ratio feedback control. In the open loop control area, the value is set according to each operation area.

K1 and K2 are other correction coefficients and variables calculated according to various engine parameter signals, respectively, so that various characteristics such as fuel consumption characteristics and engine acceleration characteristics can be optimized according to the engine operating state. To a predetermined value.

The CPU 5b supplies a drive signal for opening the fuel injection valve 6 to the fuel injection valve 6 via the output circuit 5d on the basis of the fuel injection time TOUT obtained as described above, and also according to the engine operating state. Purge control valve 2
Open / close control of 0 is performed.

Next, the deterioration detection (deterioration monitor) of the catalyst C will be described.

Feedback control for monitoring deterioration of the catalyst C is performed by the output RVO2 of the downstream O2 sensor RS.
Only on the basis of. When the output RVO2 is inverted from the lean side to the rich side with respect to the predetermined reference voltage RVREF, the lean side special P term PLSP for skipping the correction coefficient KO2 from the rich side to the lean side with respect to the stoichiometric air-fuel ratio is provided. Occurred and output from this point RV
The time TL until the time when O2 is reversed in the opposite direction is detected. Further, when the output RVO2 is inverted from the rich side to the lean side with respect to the reference value RVREF, the correction coefficient KO2
The rich side special P term PRSP for skipping from the lean side to the rich side with respect to the stoichiometric air-fuel ratio is generated, and the time TR from this time to the time when the output RVO2 is reversed in the reverse direction is detected. Deterioration of the catalyst C is determined based on the time (reversal cycle) TL, TR.

The overall structure of the catalyst deterioration monitoring process will be described with reference to the flowchart of FIG. This program uses a timer to execute the CPU 5b every predetermined time (for example, 5 msec).
Run on.

First, in step S1, it is determined whether or not a precondition (hereinafter referred to as "precondition") for executing the deterioration monitor is satisfied. If the precondition is not satisfied, the deterioration monitor is performed. Instead, normal fuel control is performed (step S6), and this program ends. On the other hand, when the precondition is satisfied, the process proceeds to step S2, where the downstream O2 sensor output RV
The correction coefficient KO2 is calculated based on O2. Then,
The reversal times TL and TR are measured and the integrated value KO2SUM of the amount of change in the correction coefficient KO2 is calculated (step S3),
It is determined whether the integrated value KO2SUM is larger than the predetermined upper limit value KO2SUMMLMT (step S4).

In step S4, KO2SUM> KO2SU
When MLMT is established, the down count timer tCATM is set to the predetermined time TC without executing the deterioration monitor.
An ATM (for example, 5 sec) is set and started (step S5), and the process proceeds to step S6. This timer tCATM is used for precondition determination in the process of FIG.

On the other hand, in step S4, KO2SUM≤KO
When 2SUMMLMT is established, it is determined whether or not the measurement / calculation process (OSC measurement) in step S3 is completed (step S7), and when it is not completed, the deterioration determination process A in step S8 is executed. Deterioration determination process A
Indicates that the upstream O2 sensor output FVO2 is a predetermined reference value FVR.
After reversing with respect to EF, downstream O2 sensor output RV
When the predetermined time (for example, 0.3 seconds) elapses without O2 being inverted with respect to the predetermined reference value RVREF, the catalyst C is determined to be normal without executing the deterioration determination process B described later. Then, as a result of the deterioration determination process A,
It is determined whether or not the catalyst C is determined to be normal (step S10), and when determined to be normal, step S11.
Then, the deterioration monitoring is terminated, the flag FDONE67 is set to "1" to indicate this, and normal fuel control is performed. If it is not determined to be normal in step S10, this program is immediately terminated.

When the OSC measurement is completed in step S7, the deterioration determination process B is executed (step S9), and the process proceeds to step S11. The deterioration determination process B is performed in the inversion time T
The deterioration of the catalyst C is determined based on L, TR and the integrated value of change amount KO2SUM.

Next, the above-mentioned steps S1 to S3 and S8
The details of the processing of S9 and S9 will be sequentially described.

FIG. 3 is a flow chart of the precondition determination process of step S1 of FIG.

First, in step S21, the flag FGO is set.
It is determined whether 67 is "1". This flag FGO67
Is set to "0" when an O2 sensor deterioration monitor other than the catalyst deterioration monitor, evaporative emission control system failure monitor, fuel system abnormality monitor, etc. is running, and "1" when no other monitor is running. Is a flag set to. When the flag FGO67 is "0" and another monitor is being executed, the timer tCATM is set to the predetermined time TCATM and started as in step S5 of FIG. 2, and the precondition is not satisfied.

When the flag FGO67 is "1" and the catalyst deterioration monitor is permitted, the flag is set to "1" in the operating state where the purge of the evaporated fuel from the canister to the intake pipe 2 should be cut. It is determined whether or not FPGSCNT is "1" (step S22), and FPGSCNT = 1.
If the operating condition is such that the purge cut should be performed, the process proceeds to steps S30 and S32, and the precondition is not satisfied. F
When PGCNT = 0, it is determined whether the flag FKO2LMT is "1". The flag FKO2LMT is a flag that is set to "1" when the correction coefficient KO2 is stuck to the predetermined upper limit value or the lower limit value for a predetermined time or more (in the KO2 limit sticking state).

When FKO2LMT = 1 and the KO2 limit is stuck, the flag FDONE67 which indicates "1" to end the catalyst deterioration monitor is set to "1", and the process proceeds to step S30.

When FKO2LMT = 0 and the KO2 limit is not stuck, the intake air temperature TA is further reduced to a predetermined upper and lower limit value TACATCHKL (for example -0.2 ° C.), T
Whether or not the engine water temperature TW is within a range of ACATCHKH (for example, 100 ° C.) is a predetermined upper and lower limit value TWCATCH.
KL (eg 80 ° C.), TWCATCHKH (eg 1
Whether the engine speed NE is within a range of 00 ° C.), the engine speed NE is a predetermined upper and lower limit value NECATCHKL (for example, 2800 rp).
m), whether or not it is within the range of NECATCHKH (eg, 3200 rpm), the intake pipe absolute pressure PBA is a predetermined upper and lower limit value PBCATCHKL (eg, 410 mmHg), P
Whether or not the vehicle speed V is within a range of BCATCHKH (for example, 510 mmHg) is a predetermined upper and lower limit value VCATCHKL.
(Eg 32 km / h), VCATCHKH (eg 8
0 km / h) is determined (step S25), and when all of these operating parameters are within the predetermined upper and lower limit values, the temperature TCA of the catalyst C is further increased.
It is determined whether T is within a predetermined range (for example, 350 ° C. to 800 ° C.) (step S26). This catalyst temperature TC
The AT uses the detection value of the sensor, but may use the temperature value estimated according to the engine operating state.

When the catalyst temperature TCAT is within the predetermined range, it is further determined whether or not the vehicle is in a cruise state (step S27). This determination is performed, for example, by determining whether or not the fluctuation of the vehicle speed V is 0.8 km / sec or less for a predetermined time (for example, 2 seconds). When the vehicle is in the cruise state, the absolute pressure PB in the intake pipe is
A variation amount ΔPB4 (for example, variation amount during 5 msec)
Is below a predetermined value PBCAT (for example, 16 mmHg) or not (step S28). Here, the variation ΔPB4
Is less than or equal to the predetermined value PBCAT, it is further determined whether or not feedback control based on the upstream O2 sensor output FVO2 is being executed (step S29).

If any of the answers in steps S25 to S29 is negative (NO), the process proceeds to step S30, while if all the answers are affirmative (YES), that is, the operating state becomes a predetermined state. If so, it is determined whether or not the count value of the timer tCATM started in step S30 is "0". At first, since tCATM> 0, the precondition is not satisfied (step S32), and it is determined that the precondition is satisfied when a predetermined time TCATM (for example, 5 seconds) elapses after the operating state becomes the predetermined state.

4 and 5 are flowcharts of the KO2 calculation process executed in step S2 of FIG.

First, in step S41, counters and flags used in this processing and processing described later are initialized. This initialization processing is performed as shown in FIG.

In step S71 of the same figure, the previous downstream side O
It is determined whether or not the feedback control based on the two-sensor output RVO2 is performed, and if the answer is affirmative (YES), the initialization has already been completed, so this processing is immediately terminated. When starting feedback control from this time,
In step S72, the inversion times TL and TR are reset (set to “0”), and the number of times nTL and nTR of the inversion times TL and TR are measured and the inversion time integrated value TLSU.
M, TRSUM, the previous value KO2BF of the value immediately after the lean side special P term PLSP of the correction coefficient KO2 (hereinafter referred to as "the value immediately after PLSP") and the current value KO2AF, the integrated value KO2SUM of the change amount of the correction coefficient KO2, and the deterioration determination process TL which indicates that the measurement of the reversal time TL is started by the one-shot OK determination counter CSTRG and “1” used in A.
The measurement flag FTLST is set to "0".

Next, it is determined whether or not the downstream O2 sensor output RVO2 is smaller than the downstream reference value RVREF (for example, 0.45V) (step S73), and RVO2 <RV
When REF is established, the first and second downstream rich flags FAFR1, FAFR2 are both set to "0" (step S74), while when RVO2 ≧ RVREF is established, the first and second downstream sides are set. Both the rich flags are set to "1" (step S75). Here, the first downstream rich flag FAFR1 is shown in FIGS. 7 (a) and 7 (b).
Is a flag that is set to "1" when the downstream O2 sensor output RVO2 is in a rich state higher than the downstream reference value RVREF, and the second downstream rich flag FAF
R2 is the first flag FAFR as shown in FIG.
The first flag F is delayed for a certain time from the time when 1 is inverted.
This is a flag that is set to the same value as AFR1.

In the following step S76, the upstream O2 sensor output FVO2 is set to the upstream reference value FVREF (for example, 0.
45V) and whether or not it is smaller than FVO2 <FVR
When EF is established, the upstream upstream rich flag FAF is set last time.
While 1B is set to "0" (step S77), RVO2
When ≧ RVREF is established, the previous upstream rich flag FAF1B is set to “1” (step S78).
Here, the previous upstream rich flag FAF1B is a flag that is set to "1" when FVO2> FVREF at the previous execution of this program.

Returning to FIG. 4, at step S42, it is judged if the downstream O2 sensor output RVO2 is smaller than the downstream reference value RVREF. When the answer is affirmative (YES), that is, when the air-fuel ratio state is the lean state (FIG. 7 (b), T1, T4, T5, T7, T10), the first downstream rich flag is set. FAFR1 is set to 0, and 1 is subtracted from the count value CDLYR of the special P term occurrence delay counter (step S
43). Next, the count value CDLYR delays the delay time TRD (<0, for example, -40 mse for delaying the generation of the lean side special P term PLSP (lean skip amount).
If the answer is negative (NO), the process proceeds immediately to step S49, while if the answer is affirmative (YES), , Count value CDLYR to delay time TRD
Set to (<0) (step S45), step S
Proceed to 49.

If the answer to step S42 is negative (NO), that is, if the air-fuel ratio is rich (FIG. 7 (b), T2, T3, T6, T8, T9), the first
The downstream rich flag FAFR1 is set to 1 and 1 is added to the count value CDLYR. Next, the count value CDLYR is the rich side special P term PRS.
It is determined whether or not it is longer than the delay time TLD (> 0, for example, set to 40 msec) for delaying the occurrence of P (rich skip amount) (step S47), and when the answer is negative (NO), Immediately proceeds to step S49, and when the answer is affirmative (YES), sets the count value CDLYR to TLD (> 0) (step S48) and proceeds to step S49.

In step S49, the count value CDLY
It is determined whether R is inverted from positive to negative or from negative to positive, and the answer is affirmative (YES) (FIG. 7 (c),
At t2, t4, t8, t10), it is determined whether or not the first downstream rich flag FAFR1 is 0 in step S50.

If the answer to step S50 is affirmative (YES), that is, the output R after the count value CDLYR is inverted
When the air-fuel ratio state corresponding to VO2 is the lean state (FIG. 7 (c), t4, t10), the second downstream rich flag FAFR2 is set to 0 (step S51), and the count value CDLYR is delayed. The time TRD is set (step S52), and proportional control is performed to add the rich side special P term PRSP (for example, 0.068) to the immediately preceding value of the correction coefficient KO2 (step S53).

When the answer to step S50 is negative (NO), that is, the output RV after the count value CDLYR is inverted.
When the air-fuel ratio state corresponding to O2 is the rich state (Fig. 7
In (c), t2, and t8, the second downstream rich flag FAFR2 is set to 1 (step S54), the count value CDLYR is set to the delay time TLD (step S55), and immediately before the correction coefficient KO2. Proportional control is performed to subtract the lean side special P term PLSP (for example, 0.068) from the value (step S56).

When the answer to step S49 is negative (NO), that is, when the count value CDLYR is not inverted, the second downstream rich flag FA is determined in step S57.
It is determined whether FR2 is 0, and the answer is affirmative (YE
S), the flag FAFR is set in step S58.
It is determined whether 1 is 0. The answer is negative (NO)
, That is, when the flag FAFR1 is 1 and the flag FAFR2 is 0 (FIG. 7B, T).
2, T6, T8), immediately proceed to step S60,
Integral control is performed to add the special I term IRSP (for example, 0.000091) to the value immediately before the correction coefficient KO2. On the other hand, if the answer to step S58 is affirmative (YES),
That is, when both the flags FAFR1 and FAFR2 are 0 (FIG. 7 (b), T1, T5, T7), the count value CDLYR is set to the delay time TRD (step S59), and the process proceeds to step S60.

When the answer to step S57 is negative (NO), it is determined in step S61 whether the first downstream rich flag FAFR1 is 1. When the answer is negative (NO), that is, when the flag FAFR1 is 0 and the flag FAFR2 is 1 (FIG. 7).
In (b), T4, T10), the process immediately proceeds to step S63, where the special I term IL is calculated from the value immediately before the correction coefficient KO2.
Integral control for subtracting SP (for example, 0.000091) is performed. On the other hand, when the answer to step S61 is affirmative (YES), that is, when both the flags FAFR1 and FAFR2 are 1 (FIG. 7 (b), T3 and T9), the count value CDLYR is set to the delay time TLD. Then (step S62), the process proceeds to step S63.

In step S53, step S56, step S60 or step S63, the correction coefficient KO2
After calculating, the limit check of the correction coefficient KO2 is performed in step S64, and this program ends.

According to the programs shown in FIGS. 4 and 5, as shown in FIG. 7, a predetermined time (T2, T) has passed since the downstream O2 sensor output RVO2 was inverted (t1, t3, t7, t9).
4, T8, T10) and proportional control is executed with a delay (t
2, t4, t8, t10), and integration control in the increasing direction of the KO2 value is executed during the period of the second downstream rich flag FAFR2 = 0 (T1, T2, T5 to T8), and FAFR2.
During the period of = 1, integral control in the decreasing direction of the KO2 value is executed (T3, T4, T9, T10). In addition, from time t5
The sensor output RVO2 fluctuates in a short cycle between t7, but since the fluctuation cycle is shorter than the delay time of the proportional control corresponding to the delay time TRD, the second downstream rich flag FAF
R2 does not reverse and proportional control is not executed.

FIG. 8 is executed in step S3 of FIG.
7 is a flowchart of a process of measuring inversion times TL and TR and calculating an integrated value KO2SUM.

In step S81, it is determined whether or not the second downstream rich flag FAFR2 is inverted, and when it is inverted, it is determined whether or not this flag FAFR2 is "1" (step S93). Then, when FAFR2 = O (t4 in FIG. 7), the measurement of the inversion time TR is started (step S101), and this processing is ended. Also FAFR2
When = 1 (t2, t8 in FIG. 7), the measurement of the inversion time TL is started, and the TL measurement flag FTLST is set to "1" (step S94). Then, by the following equation (2), P
The current value KO2AF immediately after the LSP is calculated (step S95).

KO2AF = KO2-PLSP (2) In the subsequent step S96, the TL measurement number nTL is "0".
Whether or not it is the first TL measurement is determined, and the first
At the time of the second time, the process immediately proceeds to step S98, and at the time of the second time and thereafter, the integrated value KO2SUM is calculated by the following equation (3), and the process proceeds to step S98.

KO2SUM = KO2SUM + | KO2AF-KO2BF | (3) Here, KO2SUM on the right side is a previously calculated value, and K
O2BF is the previous value immediately after PLSP.

From the above equation (3), the integrated value KO2SUM
Is KO2 immediately after the lean side special P term PLSP occurs
It is calculated as an integrated value of the amount of change in value.

In step S98, the current value KO2AF immediately after PLSP is set to the previous value KO2BF, and then it is determined whether or not the number of times nTR of measuring the inversion time TR is equal to or more than a predetermined value (step S99). Then, if the number of times of measurement nTR has not reached the predetermined value, this processing is immediately terminated, while if it has reached, the measurement end flag FO indicating the end of measurement of the inversion time.
Set SCEND to "1" (step S100),
This process ends.

When the second downstream rich flag FAFR2 is not inverted in step S81, it is determined in step S82 whether the first downstream rich flag FAFR1 is inverted. As a result, when none of the flags is inverted, this processing is immediately terminated.

The second flag FAFR2 is not inverted and the first flag FAFR2 is not inverted.
When only the flag FAFR1 of No is reversed, step S
Proceed to 83, one shot OK used in the deterioration determination process A of FIG.
Judgment counter CSTRG and inversion flag FHANTE
N is set to "0", and then it is determined whether or not the inversion time TL or TR is being measured (step S84). As a result, if the measurement is not in progress, the present process is immediately terminated, while if the measurement is in progress, it is determined whether or not the first downstream rich flag FAFR1 is "1" (step S85).

When FAFR1 = 0 (FIG. 7, t3, t3
9) and the measurement of the inversion time TL is completed (step S8).
6), the integrated value TLSU of the inversion time TL by the following equation (4)
While calculating M, the TL measurement number nTL is incremented by "1" (step S87), and this processing is ended.

TLSUM = TLSUM + TL (4) When FAFR1 = 1 in step S85 (FIG. 7, t5), the measurement of the reversal time TR is completed (step S5).
88), the integrated value TRS of the inversion time TR by the following equation (5)
The UM is calculated and the TR measurement number nTR is incremented by "1" (step S89).

TRSUM = TRSUM + TR (5) Next, it is determined whether or not the number of times nTR of measurement of the inversion time TR is “1” (step S90), and when nTR = 1, the number of times of measurement nTL of the inversion time TL is further increased. It is determined whether it is "0" (step S91). When nTR ≠ 1 or nTL ≠ 0, this processing is immediately terminated and nTR ≠ 1.
= 1 and nTL = 0, the integrated value T of the TR measurement times
The RSUM and TR measurement number nTR is set to "0" (step S92), and this processing ends.

Here, in steps S90 to S92, since it is necessary to start the measurement of the inversion time from TL, T
When starting from R, it is provided to reset the integrated value TRSUM and the number of times of measurement nTR.

By the processing of FIG. 8, the integrated values TLSUM, TRSUM and P of the inversion times TL and TR shown in FIG. 7D are obtained.
Change in value immediately after LSP (time t2, t8) | KO2AF
An integrated value KO2SUM of −KO2BF | is calculated.

FIG. 9 is a flowchart of the deterioration determination process A executed in step S8 of FIG.

First, in step S111, the count value of the one-shot OK determination counter CSTRG is the first predetermined value TS.
It is determined whether it is larger than TRG (for example, set to a value corresponding to 4 seconds), and when CSTRG ≦ TSTRG is satisfied, it is determined whether the inversion flag FHANTEN is “1” (step S113). First is FHANTEN
= 0 (see FIG. 8, step S83) step S1
14, the upstream O2 sensor output FVO2 is higher than the upstream reference value FVREF (at the rich side) "1"
It is determined whether or not the upstream rich flag FAF1 set to No. 1 is the same as the upstream rich flag FAF1B last time. F
If AF1 = FAF1B and it is not inverted,
In step S119, it is further determined whether or not the first and second downstream rich flags FAFR1 and FAFR2 are equal. If they are not equal, the process is immediately terminated, while if they are equal, the one-shot OK determination counter is used. CSTR
Increment G by "1" (step S12
0), this processing is ended. By the execution of step S120, the value of the counter CSTRG increases as shown in FIG.

In step S114, FAF1 ≠ FAF1B
When the upstream rich flag FAF1 is inverted, the process proceeds to step S115, the counter CSTRG is reset, and the inversion flag FHANTEN is set to "1".
As a result, this processing is ended.

In step S115, the inversion flag FHANT
When EN is set to "1", the answer to step S113 is affirmative (YES), and the routine proceeds to step S116, where the upstream rich flag FAF1 is the upstream rich flag FAF last time.
It is determined whether or not it is the same as 1B. If FAF1 = FAF1B and it is not reversed, the upstream rich flag FAF1 and the second downstream rich flag F are determined in step S117.
It is determined whether AFR2 is equal. And FAF1 ≠
If FAFR2, the process proceeds from step S117 to S118, and the value of the counter CSTRG is the second predetermined value TSTR.
It is determined whether it is smaller than G2 (for example, set to a value corresponding to 0.3 seconds).

If the answer to step S117 or S118 is affirmative (YES), the process proceeds to step S119,
If the upstream rich flag FAF1 is inverted before the value of the counter CSTRG reaches the second predetermined value TSTRG2,
The answer to step S116 is negative (NO), and the counter CSTRG is reset at step S122.

Further, in step S118, the counter CST
When the value of RG reaches the second predetermined value TSTRG2, the process proceeds to step S121, it is determined that the system is normal, that is, the catalyst C is not deteriorated, and the normality determination flag FOK67 is set to "1" to indicate that. Then, this processing is finished.

In step S111, CSTRG> TS
When TRG is satisfied, the deterioration monitoring is stopped, the precondition determination timer tCATM is set to the predetermined time TCATM and started (step S112), and this processing is ended.

Next, the contents of the deterioration determination process A of FIG. 9 will be specifically described with reference to FIG.

At the time t0 when the monitoring is started, both the upstream and downstream O2 sensor outputs FVO2 and RVO2 are on the rich side, and the inversion flag FHANTEN is "0". At time t1, the upstream O2 sensor output FVO2 is inverted, and the inversion flag FHANTEN changes from "0" to "1". Thereafter, until time t5, the inversion flag FHANTEN remains “1”, and the counter CSTRG is reset each time the upstream O2 sensor output FVO2 is inverted (time t2, t3, t).
4).

At time t5, the downstream O2 sensor output RVO2 is inverted, and the inversion flag FHANTEN is "1".
From "0", the counter CSTRG is reset (FIG. 8, step S83). From time t5 to t6, since FAFR1 ≠ FAFR2, the counter CSTRG is not counted up (step S119).

At time t7, the upstream O2 sensor output FVO2
When is inverted, the inversion flag FHANTEN changes from "0" to "1". At this time, the upstream rich flag FAF
Since 1 and the second downstream rich flag FAFR2 are equal, the process proceeds from step S117 to step S119, and step S118 is not executed. Therefore, the counter CST
The RG is counted up unless its value exceeds the first predetermined value TSTRG. Then, at time t8, the upstream O2 sensor output FVO2 is inverted and the counter CS
TRG is reset. After time t8, FAF1 ≠
Since it becomes FAFR2, the processing is performed from steps S117 to S117.
At 118, the value of the counter CSTRG reaches the second predetermined value TSTRG2 at time t9, and the system normal (catalyst C
Is not deteriorated). This decision is OK
We call it judgment. When the normality determination flag FOK67 is set to "1", the answer to step S10 in Fig. 2 is affirmative (YES), and the deterioration monitoring is stopped.

Thus, in the processing of FIG. 9, the upstream side O2
After the sensor output FVO2 is inverted, the second predetermined value TS
When the downstream O2 sensor output RVO2 does not reverse within a predetermined time corresponding to TRG2, that is, when the phase difference between the upstream O2 sensor output FVO2 and the downstream O2 sensor output RVO2 is a predetermined value or more, the oxygen storage capacity of the catalyst C is It is judged to be large, the system is judged to be normal, and the deterioration monitor is ended. As a result, the catalyst OK can be quickly determined. Further, for example, when the fuel vapor is purged from the canister during deceleration of the engine and the air-fuel ratio continues to be rich, the upstream O2 sensor output F
Since the VO2 also continues to be in the rich state (state higher than the reference values FVREF and RVREF) similarly to the downstream O2 sensor output RVO2, it is possible to prevent erroneous OK determination in such a case.

When the upstream O2 sensor output FVO2 is reversed in a relatively short cycle (FIG. 10, t0 to t).
7) Since the counter CSTRG is reset even if the downstream O2 sensor output RVO2 is not reversed, the one-shot OK determination is not made.

FIG. 11 is a flowchart of the deterioration determination process B executed in step S9 of FIG.

First, in step S131, the determination time TCHK is calculated by the following equation (6).

[0080]

[Equation 1] Here, KO2SUM / (IRSP × nTR) on the right side
Is a correction term according to the variation amount of the correction coefficient KO2, and by performing the correction by this, it is possible to perform accurate deterioration determination even when the air-fuel ratio changes. The reason will be described later.

In the following step S132, the deterioration determination threshold value TCHKMLT is calculated by searching the TCHKLMT table shown in FIG. In FIG. 12, TF on the horizontal axis
AVE is the intake air amount T per unit time of the engine 1.
It is the average value of F. The intake air amount TF is proportional to the product of the basic fuel injection time Ti and the engine speed NE.
× NE or a value obtained by multiplying this by a constant, and using the average value T
FAVE is calculated by a calculation formula using a known smoothing coefficient. Of course, the intake air amount itself may be detected by a sensor. Further, TCHKLMTL is a lower limit value of deterioration determination and is set to, for example, 200 msec.

Next, it is judged whether or not the judgment time TCHK is smaller than the deterioration judgment threshold value TCHKLMT (step S133). When TCHK ≧ TCHKLMT is established, it is judged that the catalyst C is not deteriorated, and the normal condition is satisfied. Set the determination flag FOK67 to "1" (step S135),
This process ends.

On the other hand, when TCHK <TCHKLMT is satisfied, the determination time TCHK is further decreased by the deterioration determination lower limit value T.
It is determined whether or not it is larger than CHKLMTL (step S134). When TCHK> TCHKLMTL is established, it is determined that the catalyst C is deteriorated, and the abnormality determination flag FFSD67 is set to "1" (step S
136), and this processing ends. Also, TCHK ≤ TCH
If KLMTL is established, the accuracy of the TCHK value itself is doubtful, and therefore the determination is suspended and this processing is immediately terminated.

Next, the correction term KO2SUM / (IRSP × nTR) of the equation (6) will be described with reference to FIG.

In the figure, the solid line corresponds to the steady running state in which the air-fuel ratio does not fluctuate, and the broken line corresponds to the running state in which the air-fuel ratio fluctuates. In the following description, the value of the correction coefficient KO2 at each of the points A to D and B'to D'shown in FIG.
2 (A), KO2 (B), ... KO2 (D ′).

First, when there is no correction term, the determination time TCHK during steady running is calculated by the following equation (7), for example.

TCHK = ((TL1 + TR1) / 2 + (TL2 + TR2) / 2 + (TL3 + TR3) / 2) / 3 (7) On the other hand, when there is no correction term, the determination time TCHK 'is calculated by the following equation. It is calculated by (8) and (9).

TCHK ′ = ((TL1 ′ + TR1) / 2 + (TL2 + TR2) / 2 + (TL3 + TR3 ′) / 2) / 3 (8) TL1 ′ = TL1 + TD1, TR3 ′ = TR3 + TD2 (9) Therefore, the air-fuel ratio TD1, in equation (9), caused by the fluctuation
The determination time TCHK can be corrected by obtaining TD2.

Here, paying attention to the value of the correction coefficient KO2 during the feedback control based on the downstream O2 sensor output RVO2, the amount chasing in the rich direction and the amount chasing in the lean direction are steadily equal. K if not equal
This is because the O2 value diverges. Therefore, KO immediately after being subtracted by the lean side special P term PLSP
The two values are all the same during steady running, and KO2 (A) = K
O2 (B) = KO2 (C) = KO2 (D).

On the other hand, when the air-fuel ratio changes, in the illustrated example, KO2 (A) ≠ KO2 (B ') = KO2 (C') ≠
It is KO2 (D '). Where KO2 (B ') and K
O2 (D ') is represented by the following formulas (10) and (11).

KO2 (B ′) = KO2 (A) − (TL1 ′ + TLD) × I + PRSP + (TR1 + TRD) × I-PLSP (10) KO2 (D ′) = KO2 (C ′) − (TL3 ′ + TLD) × I + PRSP + (TR3 + TRD) × I-PLSP (11) However, IRSP = ILSP = I.

Further, KO2 (B) and KO2 during steady running
(D) is represented by the following equations (12) and (13).

KO2 (B) = KO2 (A) − (TL1 + TLD) × I + PRSP + (TR1 + TRD) × I-PLSP (12) KO2 (D) = KO2 (C) − (TL3 + TLD) × I + PRSP + (TR3 + TRD) × I-PLSP (13) Therefore, (KO2 (B ')-KO2 (A)) is calculated as follows.

KO2 (B ′) − KO2 (A) = KO2 (B ′) − KO2 (B) (∵KO2 (A) = KO2 (B)) = (TL1-TL1 ′) × I (∵Equation (10 ) −Equation (12)) = −TD1 × I (14) (∵Equation (9)) Further, from Equation (11) -Equation (13), KO2 (D ′) − KO2 (D) = KO2 (C) ') -KO2 (C) + (TR3'-TR3) * I Therefore, KO2 (D')-KO2 (C ') = KO2 (D) -KO2 (C) + (TR3'-TR3) * I = ( TR3′−TR3) × I (∵KO2 (D) = KO2 (C)) = TD2 × I (15) (∵Equation (9)) Therefore, from Equations (14) and (15), TD1 and TD2 are It becomes as follows.

TD1 = | KO2 (B ′) − KO2 (A) | / I (16) TD2 = | KO2 (D ′) − KO2 (C ′) | / I (17) Equations (16) and (16) From 17), the correction term for the air-fuel ratio fluctuation is obtained by dividing the change amount | KO2AF-KO2BF | of the KO2 value immediately after the occurrence of the lean side special P term PLSP by the I term, that is, dividing the change amount integrated value KO2SUM by IRSP × nTR. It can be seen that Therefore, according to the equation (6), it is possible to obtain the determination time TCHK in which the influence of the air-fuel ratio fluctuation is eliminated.

As described above, according to the present embodiment, even if the air-fuel ratio changes during the catalyst deterioration determination, the determination time T
By correcting CHK according to the change amount integrated value KO2SUM, it is possible to eliminate the influence of the change and perform accurate deterioration determination.

Further, in step S4 of FIG. 2, when the change amount integrated value KO2SUM is larger than a predetermined value, the deterioration monitor is prohibited, so that an inaccurate determination is made when the air-fuel ratio fluctuation amount is large. Can be prevented.

In the above embodiment, the inversion time T
L and TR are the times from when the proportional control is executed until the downstream O2 sensor output RVO2 is inverted (FIG. 7, T3, T
5, T9), but the invention is not limited to this, and the reversal time of the downstream O2 sensor output RVO2 (FIG. 7, T2 + T).
3, T4 + T5, T8 + T9).

[0099]

As described in detail above, according to the present invention, when the phase difference between the outputs of the upstream side oxygen concentration detecting means and the downstream side oxygen concentration detecting means is equal to or more than a predetermined value (TSTRG2), the catalyst means deteriorates. Therefore, even if the output of the downstream oxygen concentration detection means does not reverse due to the effect of purge fuel for a relatively long time, it is possible to erroneously determine that the deteriorated catalyst means is normal. Can be prevented.

When the change in the output of the downstream oxygen concentration detecting means is detected for a predetermined period and the phase difference is equal to or more than the predetermined value, the catalyst means is determined to be normal. Can be determined quickly.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an internal combustion engine and a control system therefor according to an embodiment of the present invention.

FIG. 2 is a flowchart showing an overall configuration of a process for determining deterioration of a catalyst.

FIG. 3 is a flowchart of a process of determining a precondition.

FIG. 4 is a flowchart of a process of calculating an air-fuel ratio correction coefficient.

FIG. 5 is a flowchart of a process of calculating an air-fuel ratio correction coefficient.

FIG. 6 is a flowchart of a process of initializing a counter and a flag.

FIG. 7 is a diagram for explaining an air-fuel ratio correction coefficient calculation method.

FIG. 8 shows reversal time (TR, TL) and change amount integrated value (K
It is a flowchart of the process which calculates O2SUM).

9 is a flowchart of deterioration determination processing A. FIG.

FIG. 10 is a diagram for explaining the contents of deterioration determination processing A.

FIG. 11 is a flowchart of deterioration determination processing B.

FIG. 12 is a diagram showing a table for calculating a deterioration determination threshold value.

FIG. 13 is a diagram for explaining correction of the determination time (TCHK) when the air-fuel ratio changes.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 5 Electronic control unit (air-fuel ratio control means, catalyst deterioration detection means, determination means) 6 Fuel injection valve 12 Exhaust pipe C Three-way catalyst FS Upstream O2 sensor RS Downstream O2 sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area F02D 41/22 305 K

Claims (2)

[Claims] 1. A catalyst means provided in an exhaust system of an internal combustion engine for purifying exhaust gas, and an upstream oxygen concentration detection means provided upstream of the catalyst means for detecting oxygen concentration in exhaust gas. A downstream oxygen concentration detecting means provided downstream of the catalyst means for detecting the oxygen concentration in the exhaust gas, and a mixture supplied to the engine using at least one of the upstream side and downstream oxygen concentration detecting means Air-fuel ratio control means for controlling the air-fuel ratio of air, and catalyst deterioration detection means for detecting deterioration of the catalyst means based on the output of the downstream side oxygen concentration detection means at the time of controlling the air-fuel ratio by the air-fuel ratio control means In the catalyst deterioration detecting device for an internal combustion engine comprising, the catalyst deterioration detecting means, when the phase difference between the output of the upstream oxygen concentration detecting means and the downstream oxygen concentration detecting means is a predetermined value or more, Deterioration inspection Catalyst deterioration detecting device for an internal combustion engine, characterized in that to stop. 2. The catalyst deterioration detecting means detects a change in the output of the downstream oxygen concentration detecting means over a predetermined period, and when the phase difference is equal to or more than the predetermined value, the catalyst means is normal. The catalyst deterioration detection device for an internal combustion engine according to claim 1, further comprising a determination unit that determines that