JPH1061427A - Catalyst deterioration judging device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst deterioration judging device which has a comparatively simple structure and can judge deterioration of catalyst over a wide scope in a condition in which an internal combustion engine is operated accurately. SOLUTION: Air-fuel ratio feedback control is done in accordance with output SVO2 of an O2 sensor on the downstream side of catalyst, change cycle of output SVO2 is measured, and judgement time TCHK is calculated (S3, S5). By adding up a basic value TIM of an amount of fuel which is supplied to an internal combustion engine, a flow rate added up value GAIRSUM which corresponds to an added value of flow rate of exhaust gas is calculated, and judgement parameter OSCINDEX which indicates oxygen storage capacity of catalyst is calculated (S6) by multiplying the flow rate added up value GAIRSUM to the judgement time TCHK. When the judgement parameter OSCINDEX is smaller than a predetermined reference value LMTDC, it is judged that catalyst is deteriorated (S9, S10).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art As a method for determining the deterioration of a catalyst for purifying exhaust gas of an internal combustion engine, the following is conventionally known.

(1) The air-fuel ratio of the air-fuel mixture supplied to the engine is feedback-controlled in accordance with the output of an oxygen concentration sensor provided downstream of a catalyst mounted in the exhaust passage of the engine, and the output of the oxygen concentration sensor at that time is controlled. A method of determining the deterioration of the catalyst using the reversal cycle (for example, Japanese Patent Application Laid-Open No. 5-106494).

(2) A lambda sensor (excess air ratio sensor) and a flow rate sensor for detecting a gas weight flow rate flowing through the catalyst are provided upstream and downstream of the catalyst, and the detection value of the upstream lambda sensor and the gas weight flow rate are provided. And the time integral value of the product of the gas mass flow rate and the detection value of the downstream lambda sensor, and the deterioration (determination) of the catalyst is performed using the difference (or ratio) between the two time integral values. This makes it possible to reduce the influence of the engine operating condition on the deterioration judgment method (Japanese Patent Laid-Open No. 5-14 / 1993).
No. 9128).

[0005]

However, in the above method (1), there is a case where the accuracy of the deterioration determination is reduced due to a change in the engine operating state. In the above method (2), the influence of the engine operating state can be reduced. However, since the output of a sensor provided on the upstream side of the catalyst needs to be used, there is a problem that the arithmetic processing becomes complicated. Was.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and provides a catalyst deterioration judging device capable of performing accurate deterioration judgment over a wide range of engine operating conditions with a relatively simple configuration. With the goal.

[0007]

According to a first aspect of the present invention, there is provided a catalyst provided in an exhaust system of an internal combustion engine for purifying exhaust gas, and a catalyst provided downstream of the catalyst. Oxygen concentration detection means for detecting the oxygen concentration in the exhaust gas; air-fuel ratio control means for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the engine according to the output of the oxygen concentration detection means; A catalyst deterioration determination unit for determining deterioration of the catalyst unit based on an output of the oxygen concentration detection unit at the time of air-fuel ratio control by a fuel ratio control unit. Correction means for correcting a cycle parameter representing an output change cycle of the oxygen concentration detection means in accordance with a value of a flow parameter representing an exhaust gas flow rate of the engine. And performing the deterioration determination based on the period parameter after positive.

According to a second aspect of the present invention, in the catalyst deterioration judging apparatus according to the first aspect, the correction means uses a parameter representing a fuel amount supplied to the engine as the flow rate parameter. And

The invention described in claim 3 is the first or second invention.
In the catalyst deterioration determination device described above, the correction unit performs the correction by multiplying the periodic parameter by the flow parameter.

According to the present invention, the cycle parameter representing the output change cycle of the oxygen concentration detecting means is corrected according to the value of the flow parameter representing the exhaust gas flow rate of the engine.
The catalyst deterioration is determined based on the corrected cycle parameter.

[0011]

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

(First Embodiment) FIG. 1 is an overall configuration diagram of an internal combustion engine (hereinafter referred to as an "engine") and a control device thereof according to an embodiment of the present invention. A throttle valve 3 is disposed in the middle of the pipe 2. Throttle valve opening (θTH) for throttle valve 3
A sensor 4 is connected, outputs an electric signal corresponding to the opening degree of the throttle valve 3 and supplies the electric signal to an electronic control unit for engine control (hereinafter referred to as “ECU”) 5.

A fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of an intake valve (not shown) of the intake pipe 2, and each injection valve is connected to a fuel pump (not shown). The ECU 5 is electrically connected to the ECU 5 and controls a valve opening time of fuel injection based on a signal from 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 an 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 mounted downstream thereof, detects the intake air temperature TA, outputs a corresponding electric signal, and supplies the electric signal 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 camshaft (not shown) of the engine 1 or around a crankshaft.
The engine speed sensor 10 outputs a pulse (hereinafter referred to as a “TDC signal pulse”) at a predetermined crank angle position every time the crankshaft of the engine 1 rotates 180 degrees, and the CRK sensor 11 outputs a pulse at each predetermined crank angle, for example, 45 degrees. And outputs a signal pulse (hereinafter referred to as “CRK signal pulse”) at the crank angle position of
It is supplied to CU5.

The exhaust pipe 12 is provided with a three-way catalyst (hereinafter simply referred to as "catalyst") 13 for purifying exhaust gas.
Reference numeral 3 includes a front catalyst 13a and a rear catalyst 13b. An upstream O2 sensor 14 as oxygen concentration detecting means is mounted at an upstream position of the catalyst 13, and a downstream O2 sensor 15 as oxygen concentration detecting means is provided between the front catalyst 13a and the rear catalyst 13b. The ECU 5 detects the oxygen concentration in the exhaust gas and supplies an electric signal (PVO2, SVO2) corresponding to the detected value to the ECU 5. Further, a catalyst temperature (TCAT) sensor 16 for detecting the temperature is mounted on the catalyst 13, and an electric signal corresponding to the detected catalyst temperature TCAT is supplied to the ECU.

The downstream O2 sensor 15 may be mounted downstream of the rear catalyst 13b.

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

The intake pipe 2 is connected to a canister (not shown) for adsorbing the evaporated fuel generated in the fuel tank through a passage 19, and a purge control valve 20 is provided in the passage 19 in the middle thereof. I have. The purge control valve 20 is provided by the ECU 5
And its opening and closing are controlled by the ECU 5. The purge control valve 20 is opened in a predetermined operation state of the engine 1, and supplies the fuel vapor stored in the canister to the intake pipe 2.

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

Based on the various engine parameter signals, the CPU 5b performs various engine operation states in an air-fuel ratio feedback control region or a plurality of specific operation regions where air-fuel ratio feedback control is not performed (hereinafter referred to as "open loop control region"). Is calculated, and a fuel injection time TOUT of the fuel injection valve 6 synchronized with the TDC signal pulse is calculated based on the following equation (1) in accordance with the determined engine operating state.

TOUT = TIM × KO2 × K1 + K2 (1) where TIM is a basic fuel amount, specifically, the fuel injection valve 5
The basic fuel injection time is determined by searching a TI map set according to the engine speed NE and the intake pipe absolute pressure PBA. The TI map indicates the engine speed NE.
In the operating state corresponding to the intake pipe absolute pressure PBA, the air-fuel ratio of the air-fuel mixture supplied to the engine is set to be substantially equal to the stoichiometric air-fuel ratio. That is, the basic fuel amount TIM has a value substantially proportional to the intake air amount (weight flow) of the engine.

KO2 is an air-fuel ratio correction coefficient (hereinafter, simply referred to as a "correction coefficient"), which is obtained according to the oxygen concentration in the exhaust gas detected by the O2 sensors 14 and 15 during the air-fuel ratio feedback control. In the open loop control region, the value is set to a value corresponding to each operation region.

K1 and K2 are other correction coefficients and correction 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 condition. Is determined to be 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 based on the fuel injection time TOUT obtained as described above, and responds to the engine operating state. Purge control valve 2
0 opening / closing control is performed.

Next, determination of deterioration of the catalyst 13 (deterioration monitor)
Will be described.

The feedback control for monitoring the deterioration of the catalyst 13 is based on the output SVO of the downstream O 2 sensor 15.
2 based on The time TL from the time when the output SVO2 is inverted from the lean side to the rich side with respect to the predetermined reference voltage SVREF to the time when the output SVO2 is inverted in the opposite direction, and the output SVO2 is set to the reference voltage RVRE
The time TR from the time when the output is inverted from the rich side to the lean side with respect to F to the time when the output SVO2 is inverted in the reverse direction is measured, and the deterioration of the catalyst 13 is determined based on these times TL and TR (FIG. 6).

FIG. 2 is a flowchart showing the overall configuration of the catalyst deterioration monitoring process. This process is executed by the CPU 5b at predetermined time intervals (for example, every 10 msec).

In step S1, a precondition flag FMCND indicating "1" that a precondition (hereinafter referred to as "precondition") for executing the deterioration monitor is satisfied is set to "1".
It is determined whether or not FMCND = 0, and this process ends immediately.

Referring now to FIG. 3, the precondition determination processing (processing for setting the precondition flag FMCND) will be described.

First, in a step S21, it is determined whether or not the monitor permission flag FGO67 is "1". The monitor permission flag FGO67 is set to "0" when an O2 sensor deterioration monitor other than the catalyst deterioration monitor, evaporative fuel emission suppression system failure monitor, fuel system abnormality monitor, etc. is being executed, and other monitors are being executed. This flag is set to "1" when there is no flag. When the monitor permission flag FGO67 is “0” and another monitor is being executed, the timer tCATM is set to a predetermined time TCATM and started, and the precondition is not satisfied (FMCND = 0).

When the monitor permission flag FGO67 is "1" and the catalyst deterioration monitoring is permitted, the flag is set to "1" when the operation state in which the purge of the fuel vapor from the canister to the intake pipe 2 should be cut off. Purge cut flag F
It is determined whether or not PGSCNT is "1" (step S2).
2) If FPGSCNT = 1 and the operating state requires purge cut, the process proceeds to steps S30 and S32, and the precondition is not satisfied. When FPGCNT = 0,
It is determined whether or not the limit flag FKO2LMT is “1”. The limit flag FKO2LMT is determined by the correction coefficient KO2
Is a flag that is set to “1” when it is stuck to a predetermined upper limit value or lower limit value for a predetermined time or longer (in a KO2 limit stuck state).

If FKO2LMT = 1 and the KO2 limit is stuck, the end flag FDONE indicating "1" indicating the end of the catalyst deterioration monitor is set to "1", and the routine proceeds to step S30.

When FKO2LMT = 0 and the KO2 limit is not stuck, the intake air temperature TA is further increased to a predetermined upper / lower limit value TACATCHKH (for example, 100 ° C.).
Whether the engine coolant temperature TW is within a range of CATCHKL (for example, -0.2 ° C.) is determined by a predetermined upper and lower limit value TWCATCH.
KH (for example, 100 ° C.), TWCATCHKL (for example, 80 ° C.), and whether the engine speed NE is higher or lower than a predetermined upper and lower limit value NECCATCHKH (for example, 3500 rpm)
m), whether it is within a range of NECCATCHKL (for example, 1000 rpm), whether the intake pipe absolute pressure PBA is a predetermined upper and lower limit value PBCATCHKH (for example, 510 mmHg), P
Whether the vehicle speed V is within a range of BCATCHKL (for example, 300 mmHg) is determined by a predetermined upper / lower limit value VCATCHKH.
(For example, 80 km / h), VCATCHKL (for example,
2 km / h) (step S25), and when all of these operating parameters are within the range of predetermined upper and lower limits, the temperature TC of the catalyst 13 is further increased.
It is determined whether the AT is within a predetermined range (for example, 350 ° C. to 800 ° C.) (step S26). This catalyst temperature T
As the CAT, a detected value of the sensor is used, but a temperature value estimated according to an engine operating state may be used.

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 made, for example, by determining whether or not the state where the fluctuation of the vehicle speed V is 0.8 km / sec or less has continued for a predetermined time (for example, 2 seconds). When the vehicle is in a cruise state, the intake pipe absolute pressure PB
A fluctuation amount ΔPB4 of A (for example, a change amount during 5 msec)
Is smaller than or equal to a predetermined value PBCAT (for example, 16 mmHg) (step S28). Here, the variation ΔPB4
Is smaller than or equal to the predetermined value PBCAT, it is determined whether or not the feedback control based on the upstream O2 sensor output PVO2 is being executed (step S29). If the answer to any of steps S25 to S29 is negative (NO), the process proceeds to step S30, while if all the answers are affirmative (YES), that is, if the driving state is a predetermined state, , The timer tCAT started in step S30
It is determined whether or not the count value of M is “0”. At first tC
Since ATM> 0, the precondition is not satisfied (step S3).
2), a predetermined time TC after the operating state has reached a predetermined state
When the ATM (e.g., 5 seconds) has elapsed, it is determined that the precondition is satisfied, the precondition flag FMCND is set to "1" (step S33), and the process ends.

Returning to FIG. 2, when FMCND = 1 and the precondition is satisfied, it is determined whether or not the end flag FDONE is "1". When FDONE = 1, the present process is immediately terminated. I do. When FDONE = 0,
An SVO2 cycle measurement process is executed (step S3).

FIG. 5 is a flowchart of the cycle measurement process. When FMCND = 1 and FDONE = 0, the air-fuel ratio correction coefficient KO2 is calculated according to the output SVO2 of the downstream O2 sensor 15, and the air-fuel ratio correction coefficient KO2 is calculated. Since the fuel ratio feedback control is executed, FIG. 4 is calculated first, and the KO2 calculation process will be described.

In step S41 of FIG. 4, the output SVO2
It is determined whether or not the magnitude relationship between the reference voltage SVREF and the reference voltage SVREF has been inverted.
It is determined whether it is lower than REF (step S42).
If SVO2 <SVREF, the rich special P term PRSP is added to the value immediately before the correction coefficient KO2, while if SVO2> SVREF, the lean special P term is subtracted from the value immediately before the correction coefficient KO2. (Steps S43 and S44).

If the answer in step S41 is negative (NO), it is determined whether or not the output SVO2 is lower than the reference voltage SVREF (step S45). If SVO2 <SVREF, the value is set to the value immediately before the correction coefficient KO2. If SVO2> SVREF while adding the special I term IRSP, the special I term ISP is calculated from the value immediately before the correction coefficient KO2.
Integral control for subtracting LSP is performed (steps S46 and S46).
47).

By the processing of FIG. 4, the downstream O2 sensor output SVO2 and the correction coefficient KO2 change periodically as shown in FIG. Hereinafter, the change cycle of the sensor output SVO2 is referred to as “S
VO2 cycle ".

Next, the SVO2 cycle measurement processing will be described with reference to FIG.

In a step S51, an initialization flag FCATMS indicating "0" indicating that the present process is the first execution.
It is determined whether or not T is "0". At first FCATMST =
Since it is 0, the process proceeds to step S52, where the flag FC
ATMST is set to "1", and then various parameters are initialized (step S53). That is, a counter nT that counts the number of times the cycle is measured, a measurement start flag FCATMON indicating that the cycle measurement has been started by “1”,
Integrated value TLSUM of time TL and integrated value TR of time TR
SUM is set to “0”. Subsequent step S5
4, the cycle measurement up-count timer tmSTRG
Is cleared (set to "0"), and the process proceeds to step S55.

At the time of the next or subsequent execution of this processing, the FCATM
Since ST = 1, the process immediately proceeds from step S51 to step S55.

In step S55, it is determined whether or not the magnitude relationship between the downstream O2 sensor output SVO2 and the reference voltage SVREF has been inverted. If not, the process is immediately terminated. When it is reversed, the measurement start flag FC
It is determined whether or not the ATMON is "1" (step S5).
6) Since FCATMON = 0 at first, this flag FCATMON is set to “1”, and the measurement management flag FCATMEAS is set to “0”, and the process proceeds to step S64. The measurement management flag FCATMEAS is
This flag is provided to execute an even number of measurements (that is, to perform the same number of calculations of the integrated value TRSUM and TLSUM) regardless of whether the measurement is started from either the time TL or the TR. In step S64, the timer tmSTRG is cleared, and the process ends.

If FCATMON = 1 in step S56, it is determined whether or not the output SVO2 is higher than the reference voltage SVREF (step S58), and SVO2> SVR
If it is EF, the value of the timer tmSTRG is added to the value immediately before the integrated value TRSUM to obtain the integrated value TRSU.
M is calculated (step S59), and SVO2 <SVREF
, The timer tm is added to the value immediately before the integrated value TLSUM.
An integrated value TLSUM is calculated by adding the values of STRG (step S60), and the process proceeds to step S61.
The value of the timer tmSTRG immediately after the inversion of the output SVO2 is
As shown in FIG. 6, since it corresponds to time TL or TR,
(TRSUM + TLSUM) is an integrated value of two SVO cycles (reversal cycle of sensor output).

In step S61, the measurement management flag FC
It is determined whether ATMEAS is "1". First FCA
Since TMEAS = 0, this flag FCATMEA
S is set to "1" (step S63), and the process proceeds to step S64. When FCATMEAS = 1 and the current measurement is an even number, the counter nT is incremented by “1” and the flag FCATMEAS is incremented.
Is returned to "0" (step S62), and step S62 is performed.
Proceed to 64.

Returning to FIG. 2, in step S4, the counter n
The value of T, that is, the number of times of measurement of the cycle is a predetermined value NTLMT
It is determined whether or not (for example, 3) or more, and this process is immediately terminated while nT <NTLMT. Thus, S
The VO2 cycle measurement process is repeatedly executed, and nT = NTL
When it reaches MT, the process proceeds to step S5.

In step S5, the following equation (2) is used.
The determination time TCHK is calculated as an average value of two SVO2 cycles measured NTLMT times. Note that the predetermined value NTLMT may be “1”, in which case the determination time TCHK is the measured value itself.

In the present embodiment, the determination time TCHK is used as a parameter representing the output change cycle of the oxygen concentration detecting means.

TCHK = (TLSUM + TRSUM) / nT (2) In the following step S6, the catalyst 13 is calculated by the following equation (3).
Determination parameter OSCIN representing the oxygen storage capacity of
Calculated DEX and backed up by battery (storage contents are not erased even if ignition switch is turned off)
Store in the ring buffer.

OSINDEX = TCHK × GAIRSUM (3) Here, GAIRSUM is an integrated value (hereinafter, referred to as “flow integrated value”) of a parameter representative of the exhaust gas flow rate during the SVO2 cycle measurement period. It is calculated by processing. The process of FIG. 7 is executed every time a TDC signal pulse is generated.

In step S71 of FIG.
It is determined whether or not DONE is “1”. If FDONE = 0, it is determined whether or not the measurement start flag FCATMON is “1” (step S72). And FDONE
= 1 and the catalyst deterioration monitoring is completed or F
If CATMON = 0 and the measurement of the SVO2 cycle has not been started, the flow rate integrated value GAIRSUM is set to “0” (step S73), and this processing ends.

On the other hand, FDONE = 0 and FCATMON =
When it is 1, the flow rate integrated value G is calculated by the following equation (4).
AIRSUM is calculated (step S74).

GAIRSUM = GAIRSUM + TIM (4) Here, GAIRSUM on the right side is a previously calculated value, and TIM is a basic fuel amount of the above-described formula (1). Basic fuel amount TIM
Has a value proportional to the amount of intake air as described above, and since the amount of intake air is substantially equal to the flow rate of exhaust gas, it is used as a parameter representative of the flow rate of exhaust gas. This allows
A parameter corresponding to the integrated value of the exhaust gas flow rate can be obtained without providing an intake air amount sensor or an exhaust gas flow rate sensor.

The flow rate integrated value GAI thus calculated
The determination parameter OSCINDEX is calculated by multiplying the determination time TCHK by RSUM, and the catalyst deterioration determination is performed using the determination parameter OSCINDEX. Therefore, the influence of the engine operation state is reduced, and the accuracy is improved over a wide range of the engine operation state. This makes it possible to make an appropriate deterioration determination. That is, even if the oxygen storage capacity of the catalyst is the same, the larger the exhaust gas flow rate is, the shorter the determination time TCHK tends to be. In the conventional method, the determination time TCHK is compared with a predetermined reference value.
Since the deterioration of the catalyst was determined, it was necessary to limit the engine operating state for performing the deterioration determination to a relatively narrow range.However, according to the present embodiment, the determination was made in consideration of the change in the exhaust gas flow rate. Therefore, the above effects can be obtained.

Here, the determination parameter OSCINDEX
The reason why the oxygen storage capacity of the catalyst 13, that is, the maximum oxygen storage amount can be accurately grasped by the above will be described below.

In FIG. 6, a period (TL) in which the sensor output SVO2 is higher than the reference voltage SVREF is a period in which oxygen is accumulated in the catalyst. At this time, the correction coefficient KO2 decreases linearly with time. Is controlled by
The excess air ratio λ in the exhaust gas is considered to increase almost linearly with time. Accordingly, the determination parameter OSCINDEX calculated by multiplying the integrated flow rate value GAIRSUM corresponding to the integrated value of the exhaust gas flow rate by the determination time TCHK is proportional to the amount of oxygen accumulated in the catalyst 13 during the determination time TCHK. Parameters. Strictly speaking, about の of the determination time TCHK is a period in which oxygen is accumulated, and the remaining １ ／ is a period in which oxygen is released, but the determination parameter OSCINDEX is
It is almost the same as the oxygen storage capacity of the catalyst 13.

Returning to FIG. 2, in step S7, a counter ndetect for counting the number of times the determination parameter OSCINDEX is calculated is incremented by "1".
This count value ndetect is determined by the determination parameter OS
Like CINDEX, it is stored in memory backed up by a battery.

In the following step S9, it is determined whether or not the first determination parameter OSCINDEX calculated in step S6 is equal to or greater than a first determination reference value LMTDC.
If DEX ≧ LMTDC, immediately step S1
Proceed to 1. When OSCINDEX <LMTDC, it is determined that the catalyst 13 has deteriorated, and the first OK flag FOKDC is set to "0" to indicate that the catalyst 13 has deteriorated in the first determination (step S9). At the same time, the first deterioration flag FNGDC is set to "1" (step S10), and the process proceeds to step S11.

In step S11, the count value ndet
is determined to be equal to or greater than a predetermined value nDC (for example, 6). Immediately when ndetect <nDC, and when ndetect ≧ nDC, ndetect =
The process proceeds to step S13 as nDC (step S12).

In step S13, the moving average value OSCMA of the first judgment parameter OSCINDEX is calculated by the following equation (5), and this moving average value OSCMA is used as the second judgment parameter.

OSCMA = {OSCINDEX (n) + OSCINDEX (n-1) + ... + OSCINDEX (n-ndetect + 1)} / ndetect ... (5) Here, (n) indicates the present value, and (n-1) indicates the last time. value,
(N-ndetect + 1) is (ndetect-
1) Indicates the calculated value before the time. Note that the first determination parameter OSCINDEX is sequentially stored in the ring buffer backed up by the battery as described above. The ring buffer of OSCINDEX is initially initialized to “0”, and once the calculated value is stored, the calculated value in the past is held unless the battery is removed or the like.

In the following step S14, the count value nd
The LMTMA table shown in FIG. 8 is searched according to the “select” to obtain a second determination reference value LMTMA. LMTMA
The table is set so as to decrease as the ndetect value increases (in a direction in which it is difficult to determine deterioration). Note that the first determination reference value LMTDC is nd
Second determination reference value LMTMA when select = 1
The value is set to a value smaller than the second determination reference value LMTMA (a reference value that is most easily determined to be deteriorated) (a value that is less likely to be determined to be deteriorated).

Next, the second determination parameter OSCMA calculated in step S13 is equal to the second determination reference value LMTMA.
It is determined whether or not this is the case (step S15), and OSCMA ≧
If it is LMTMA, it is determined to be normal and the second OK
The flag FOKMA is set to "1" (step S1).
6) Go to step S18. OSCMA <LMT
When it is MA, it is determined that the catalyst 13 has deteriorated,
The second OK flag FOKMA is set to "0" and the second deterioration flag FNGMA is set to "1" (step S17), and the process proceeds to step S18. Step S1
8, an end flag FDO is provided to indicate the end of the deterioration monitor.
NE = 1 is set, and this process ends.

The process of FIG. 2 is executed at predetermined time intervals when the ignition switch is turned on. However, when the engine is started and the processes of steps S5 to S18 are performed once, the processes of steps S5 to S18 are performed thereafter. Is not executed. Thereafter, when the engine is stopped and restarted, the determination processing of steps S5 to S18 is performed once. That is, assuming that the period from when the ignition switch is turned on to when the engine is started and stopped is one operation period, the deterioration determination is performed once during one operation period. In the present embodiment, by a process not shown,
When the first deterioration flag FNGDC becomes "1" twice consecutively, or when the second deterioration flag FNGMA becomes "1" twice consecutively, the deterioration judgment is determined and the driver is notified. A lamp that warns of catalyst deterioration is turned on. Otherwise, the warning lamp is not turned on.

As described above, in the present embodiment, the first determination parameter OSCINDEX is calculated once during one operation period, and the moving average value OSCMA of the calculated value is used as the second determination parameter as the second determination criterion. Since the deterioration determination is performed in comparison with the value LMTMA, the accuracy of the deterioration determination can be improved. It is proven by general statistical theory that the larger the number of samples for which a moving average is taken, the higher the accuracy of determination.

The first determination parameter OSCIND
When the number of times of calculation of EX (the number of times of measurement of TCHK) is small, the second determination reference value LMTMA is set according to the number of times of calculation ndetect. Therefore, even when the data to be averaged is small, the deterioration can be reliably reduced. Can be determined.

Further, in step S9, by performing the deterioration judgment based on the presently calculated value of the first judgment parameter OSCINDEX, sudden deterioration which may not be detected immediately by the judgment based on the second judgment parameter OSCMA (for example, due to misfire). (E.g., deterioration due to abnormal combustion, deterioration due to poisoning due to poor quality fuel, etc.) can also be detected quickly. That is, since the second determination parameter OSCMA is a moving average value, when the past value of the first determination parameter OSCINDEX is normal and decreases to a value indicating deterioration only this time, the OSCMA value does not decrease so much. Therefore, the sudden deterioration may not be detected unless the number of samples is increased. However, such a deterioration can be detected immediately by the determination in step S9.

(Second Embodiment) In the first embodiment,
The output SVO2 of the downstream O2 sensor 15 by the processing of FIG.
Of the SVO2 cycle in the process of FIG. 5, that is, the calculation of the integrated values TRSUM and TLSUM in order to calculate the determination time TCHK as a cycle parameter representing the output change cycle of the oxygen concentration detecting means. Although the calculation is performed, in the present embodiment, the correction coefficient KO2 and the integrated values TRSUM and TLSUM are calculated by the processing of FIGS. 9 and 10 instead of these processings. The rest is the same as the first embodiment. In the present embodiment, during the catalyst deterioration monitoring, the feedback control is performed by using CATKO2 calculated by the process of FIG. 9 as KO2 of the above equation (1).

FIG. 9 is a flowchart of the CATKO2 calculation process. FIG. 11 shows the downstream O2 sensor output S.
It is a figure which shows transition of VO2, various flags, etc., and this figure is also referred to together.

First, in step S141, it is determined whether or not the downstream O2 sensor output SVO2 is lower than the reference value SVREF. If SVO2 <SVREF, the first rich flag FAFR1 is set to "0", and SVO2≥SVR.
If it is EF, the flag FAFR1 is set to "1" (steps S142 and S143). Subsequent step S
In 144, it is determined whether or not the first rich flag FAFR1 has been inverted.
When the process proceeds to step 48, the first rich flag F
It is determined whether or not AFR1 is “0” (step S14)
5). When FAFR1 = 0 and the downstream-side O2 sensor output SVO2 is inverted from the rich side to the lean side (at times t1, t5, and t9 in FIG. 11), a predetermined lean-side time TLD is set in the down count delay timer TDLYR. And start (step S146), and conversely, F
When AFR1 = 1 and inversion from the lean side to the rich side (t3, t7, t11 in FIG. 11), the rich side predetermined time TRD is set and started (step S14).
7), proceed to step S148.

In step S148, the measurement start flag F
It is determined whether or not CATMON is “1”. Since FCATMON = 0 at the beginning of execution of the monitor, step S1 is executed.
Proceeding to 49, initialization of various timers, counters, flags and the like is performed. That is, the delay timer TDLYR, the delay time TL, the up-count timer TSTR for measuring TR
G, counters NTL and NTR for counting the number of times the delay times TL and TR are measured, and an integrated value TLSU of the delay times
M and TRSUM are all set to “0”, the second rich flag FAFR2 is set to be the same as the first rich flag FAFR1, and the deterioration monitoring air-fuel ratio correction coefficient CATKO2 is set to the air-fuel ratio correction coefficient KO2 (KO2 value immediately before the start of deterioration monitoring). ), And sets the measurement start flag FCATMON to “1”.

In a succeeding step S158, it is determined whether or not the second rich flag FAFR2 is "1".
When it is 0 (FIG. 11, t2 to t4, t6 to t8),
The special I term ILS is added to the value immediately before the correction coefficient CATKO2.
Integral control for adding P is performed (step S159), and F
When AFR2 = 1 (FIG. 11, t4 to t6, t8
To t10), integration control for subtracting the special I term ILSP from the value immediately before the correction coefficient CATKO2 is performed (step S160), and this processing ends.

At the next execution of this process, when the process reaches step S148, since FCATMON = 1 was set at the previous step S149, the process proceeds to step S150 to determine whether the first rich flag FAFR1 is equal to the second rich flag FAFR2. Is determined. And FAFR1 = FAFR
2 (FIG. 11, t2 to t3, t4 to t5, t
6 to t7, t8 to t9, t10 to t11), the process proceeds to step S158, and when FAFR1 ≠ FAFR2 (FIG. 11, t1 to t2, t3 to t4, t5 to t6, t
7 to t8, t9 to t10), first rich flag FAFR
It is determined whether 1 is “1” (step S15)
1).

If FAFR1 = 0 in step S151 (see FIG. 11, t1 to t2, t5 to t6, t9 to t1).
0), it is determined whether or not the value of the delay timer TDLYR is “0” (step S152). If TDLYR> 0, the process proceeds to step S158. And TDLYR
= 0 (t2, t6, t10 in FIG. 11), the second rich flag FAFR2 is made equal to the first rich flag FAFR1 (step S154), and the correction coefficient CATKO2 is set.
The special P-term PRSP is added to the value immediately before (step S155), and this processing ends.

If FAFR1 = 1 in step S151 (FIG. 11, t3 to t4, t7 to t8), it is determined whether or not the value of the delay timer TDLYR is "0" (step S153). If there is, the process proceeds to step S158. When TDLYR = 0 (t4, t8 in FIG. 11), the second rich flag FAFR2
Equal to the first rich flag FAFR1 (step S
156), the special P-term PRSP is subtracted from the value immediately before the correction coefficient CATKO2 (step S157), and this processing ends.

As described above, according to the processing of FIG. 9, the inversion point (t1, t3, t3) of the downstream O2 sensor output SVO2 is obtained.
5, t7, t9), the proportional control is executed with a delay of a predetermined time (TRD or TLD) (t2, t4, t6, t8,
t10) During the period in which the second rich flag FAFR2 = 0, the integral control in the increasing direction of the CATKO2 value is executed, and
During the period of FR2 = 1, the integral control in the decreasing direction of the CATKO2 value is executed.

FIG. 10 is a flowchart of the TL and TR calculation process. FIG. 11 is also referred to.

In FIG. 10, first, at step S171, it is determined whether or not the first rich flag FAFR1 (FIG. 11 (b)) has been inverted. When the first rich flag FAFR1 has been inverted, it is determined that the delay time measurement period is "1". Invert timer flag FTS
It is determined whether or not TRG (FIG. 11E) is “1” (step S172). Then, step S171 or S17
If the answer to 2 is negative (NO), that is, if the first rich flag FAFR1 is not inverted or if the inverted timer flag FTSTRG is "0", step S18.
Proceed to 6 and delay timer TDLYR (FIG. 11 (c))
Is determined to be 0 or not, and if TDLYR> 0, a delay time measurement up-count timer TSTRG is determined.
(FIG. 11 (f)) is set to "0" (step S18).
7), an output range flag FSVO2C indicating "1" that the change of the downstream O2 sensor output SVO2 is equal to or greater than a predetermined value.
AT is set to “0” (step S188), and the process proceeds to step S192.

If TDLYR = 0 at step S186, the process proceeds to step S189, where the downstream O2 sensor output S
VO2 is at a predetermined upper level SVO2CATH (for example, 0.
586 V) is determined, and SVO2 <SVO2 is determined.
If it is 2CATH, it is further determined whether the SVO2 value is higher than a predetermined lower level SVO2CATL (for example, 0.430 V) (step S190). as a result,
Immediately when SVO2CATL <SVO2 <SVO2CATH, and SVO2 ≧ SVO2CATH or SVO2CATL <SVO2CATH
If VO2 ≦ SVO2CATL, the output range flag FSVO2CAT is set to “1” (step S1).
91), and proceed to step S192. That is, the output range flag FSVO2CAT is set to the first rich flag FAFR.
After a lapse of a predetermined time (TLD or TRD) from the inversion of 1 (downstream O2 sensor output SVO2), the SVO2 value is maintained at "0" when the SVO2 value is near the reference value SVREF, and the change in the downstream O2 sensor output SVO2 is small. Indicates that

In step S192, it is determined whether or not the second rich flag FAFR2 (FIG. 11D) has been inverted. If the second rich flag FAFR2 has not been inverted, immediately, and if it has been inverted, the inverted timer flag FTSTRG is set to "1". After setting (step S193), this process ends.

On the other hand, the answers of steps S171 and S172 are both affirmative (YES), that is, the first rich flag FAFR
1 is inverted and the inverted timer flag FTSTRG is “1”
, The process proceeds to step S173, where the inversion timer flag FTSTRG is returned to “0”, and the output range flag FS
It is determined whether VO2CAT is "1" (step S1).
74). When FSVO2CAT = 0 and the change in the downstream O2 sensor output SVO2 is small, the hold flag FSVO2HLD is set to “1” (step S175). When FSVO2CAT = 1,
The flag FSVO2CAT is returned to "0" (step S176), and the process proceeds to step S177.

In step S177, it is determined whether or not the first rich flag FAFR1 is "1". If FAFR1 = 0, and the downstream O2 sensor output SVO2 is equal to the reference value SVRE.
When F is on the lean side (FIG. 11, t1, t
5, t9), and calculates the lean integrated value TLSUM by the following equation (step S178). The value of the timer TSTRG added here corresponds to the delay time TL in FIG.

TLSUM = TLSUM + TSSTRG Next, the lean counter NTL is incremented by "1" (step S179), and the up-count timer T
Return the value of STRG to “0” (step S180),
Proceed to step S192.

In step S177, if FAFR1 = 1 and the downstream O2 sensor output SVO2 is on the rich side with respect to the reference value SVREF (FIG. 11, t3, t7, t
11), the rich-side integrated value TRSUM is calculated by the following equation (FIG. 1).
1 (g)) is calculated (step S181). The value of the timer TSTRG added here is the delay time T in FIG.
It corresponds to R.

TRSUM = TRSUM + TSTRG Next, the rich counter NTR (FIG. 11 (h)) is incremented by "1" (step S182), the value of the up-count timer TSTRG is returned to "0" (step S183), and the lean side is set. It is determined whether the value of the counter NTL is “0” (step S184). Then, immediately when NTL> 0, and when NTL = 0 and immediately after the start of deterioration monitoring, the rich-side integrated value TRSUM and the rich-side counter NTR are returned to “0” (step S185), and Proceed to S192.

Steps S184 and S185 are steps for returning the rich integrated value TRSUM and the counter NTR to "0" when TR is measured for the first time since the measurement of the delay time starts from TL. It is provided.

As described above, according to the processing of FIG. 10, every time the downstream O2 sensor output SVO2 is inverted, the delay time TL
Alternatively, TR is integrated, and integrated values TLSUM and TRSUM are calculated. In FIG. 11, the lean integrated value TLSU is shown.
Although the transitions of M and the lean counter NTL are not shown, the rich-side integrated value TR at times t1, t5 and t9 is not shown.
It is incremented similarly to the SUM and the rich counter NTR.

The integrated value TRSU calculated as described above
M and TLSUM are applied to the equation (2), and the count value of the rich counter NTR is applied to nT in the equation (2) to calculate the determination time TCHK.

As described above, the determination time TCHK is set to the downstream O
Not limited to the change cycle of the two-sensor output SVO2, a parameter correlated with the change cycle may be used.

(Other Embodiments) The present invention is not limited to the above-described first and second embodiments, and various modifications are possible.

In the above-described embodiment, the first determination parameter OSCINDEX is calculated by equation (3), and the moving average value is used as the second determination parameter OSCMA.
The determination in step S15 in FIG. 2 is performed, but the moving average values TCHKAVE and GAIRSUMAVE of the determination time TCHK and the flow rate integrated value GAIRSUM, respectively.
Is calculated by the following equations (6) and (7), and TCHKAV is calculated.
The determination in step S15 in FIG. 2 may be performed with E × GAIRSUMAVE = OSCMA.

TCHKAVE = {TCHK (n) + TCHK (n-1) +... + TCHK (n-ndetect + 1)} / ndetect ... (6) GAIRSUMAVE = {GAIRSUM (n) + GAIRSUM (n-1) + ... + GAIRSUM (n-) (ndetect + 1)｝ / ndetect (7) Further, instead of the determination in step S15 of FIG. 2, the following may be performed. That is, a determination map as shown in FIG. 12 is set in advance in accordance with the moving average values TCHKAVE and GAIRSUMAVE, and the calculated TCHKAVE
It may be determined whether the value and the GAIRSUMAVE value are in a deteriorated area or a normal area on this map.

In the above-described embodiment, the second determination parameter OSCMA is calculated by averaging the first determination parameter OSCINDEX.
The average of CHK is used as a second determination parameter OSC.
MA may be used.

In the above-described embodiment, the moving average value is calculated. However, the averaging may be performed using a so-called smoothing equation such as the following equation (8). “Averaging” in this specification includes such arithmetic processing.

OSCMA (n) = C × OSCINDEX (n) + (1−C) × OSCMA (n−1) (8) where C is a positive constant smaller than 1.

In the above embodiment, the basic fuel amount T
By integrating IM, the flow rate integrated value GAIRSUM
Is calculated, the intake air amount or the exhaust gas flow rate may be actually detected by a sensor.
A map in which the exhaust gas flow rate is set in advance in accordance with E and the intake pipe absolute pressure PBA is provided, and the detected NE value and P
The map is searched according to the BA value, the flow rate of the exhaust gas is obtained, and the flow rate is integrated to obtain a flow rate integrated value GAIR.
SUM may be calculated.

In the above-described embodiment, the deterioration monitor is performed once in one operation period as the diagnosis period.
It may be performed twice or more.

In the above-described embodiment, the warning lamp is turned on when the deterioration is determined twice consecutively. However, for example, the deterioration is monitored three times, and the deterioration is determined twice. It may be turned on when it is turned on. That is, when the frequency of determining deterioration is equal to or higher than a predetermined frequency, it is desirable to determine the deterioration and turn on the warning lamp.

[0100]

As described above in detail, according to the deterioration judging device of the first aspect, the cycle parameter representing the output change cycle of the oxygen concentration detecting means is the flow parameter representing the exhaust gas flow rate of the engine. Since the correction is made according to the value and the deterioration of the catalyst is determined based on the corrected cycle parameter, the deterioration can be accurately determined over a wide range of the engine operating state with a relatively simple configuration. .

According to the deterioration judging device of the second aspect,
Since a parameter representative of the amount of fuel supplied to the engine is used as the flow parameter, there is no need to provide a sensor for actually detecting the exhaust gas flow rate, and the configuration of the apparatus can be simplified.

[Brief description of the drawings]

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

FIG. 2 is a flowchart of a process for determining deterioration of a catalyst.

FIG. 3 is a flowchart of a process of determining a prerequisite for performing a catalyst deterioration determination.

FIG. 4 is a flowchart of a process for calculating an air-fuel ratio correction coefficient (KO2) during a catalyst deterioration determination process.

FIG. 5 is a flowchart of a process for measuring a change cycle of an output of an O2 sensor downstream of a catalyst.

FIG. 6 is a diagram showing changes in an air-fuel ratio correction coefficient and an output of an O2 sensor.

FIG. 7 is a flowchart of a process for calculating an integrated value (GAIRSUM) of a parameter representing an exhaust gas flow rate.

FIG. 8 is a diagram showing a table used in the processing of FIG. 2;

FIG. 9 is a flowchart of a process for calculating an air-fuel ratio correction coefficient (CATKO2) during a catalyst deterioration determination process.

FIG. 10 is a flowchart of a process for calculating a parameter representing a change cycle of the output of the O2 sensor on the downstream side of the catalyst.

FIG. 11 is a diagram for explaining the processing in FIGS. 9 and 10;

FIG. 12 is a diagram showing a map for determining catalyst deterioration.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 5 Electronic control unit (ECU) 6 Fuel injection valve 12 Exhaust pipe 13 Three-way catalyst 15 Downstream oxygen concentration sensor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yukito Fujimoto 1-4-1 Chuo, Wako-shi, Saitama

Claims (3)

[Claims] A catalyst means provided in an exhaust system of the internal combustion engine for purifying exhaust gas; an oxygen concentration detection means provided downstream of the catalyst means for detecting an oxygen concentration in the exhaust gas; Air-fuel ratio control means for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the engine according to the output of the oxygen concentration detection means, and based on the output of the oxygen concentration detection means at the time of air-fuel ratio control by the air-fuel ratio control means A catalyst deterioration determination device for an internal combustion engine, comprising: a catalyst deterioration determination unit that determines deterioration of the catalyst unit. The catalyst deterioration determination unit sets a cycle parameter representing an output change period of the oxygen concentration detection unit to the engine parameter. Correction means for correcting according to the value of the flow parameter representing the exhaust gas flow rate of the exhaust gas, and performing the deterioration determination based on the periodic parameter corrected by the correction means. Catalyst deterioration determination device for an internal combustion engine to be. 2. The apparatus according to claim 1, wherein the correction unit uses a parameter representing a fuel amount supplied to the engine as the flow parameter. 3. The apparatus according to claim 1, wherein the correction unit performs the correction by multiplying the cycle parameter by the flow rate parameter.