JPH0941954A - Deterioration detector for catalyst of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent misdetection of catalyst deterioration and to attain an accurate deterioration judgment by installing a deterioration detection prohibiting means to prohibit the detection of deterioration of a catalytic means at a time when the concentration of evaporated fuel to be discharged to an intake system by a purge means is dense enough. SOLUTION: A three-way catalyst 16 for purifying exhaust gas is installed in an exhaust pipe 12. An evaporation correction factor for compensating influence of evaporated fuel by a purge is set to 1.0 when it is not purged, but when being purged, it is set to a value between 0 and 1.0. It is shown that the smaller in the value of this evaporation correction, the larger in the purge influence. When the evaporation correction factor is 1.0 or less, this purge influence grows larger and thereby an accurate deterioration judgment cannot be done, so that deterioration monitoring is not performed. Accordingly, a misjudgment due to a fact that a downstream side oxygen sensor output is deviated to a rich side by the purge influence, and thereby an oxygen storage capacity of catalyst is not accurately judgeable is prevented.

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 catalyst deterioration detecting device for purifying exhaust gas of an internal combustion engine, an air-fuel ratio of an air-fuel mixture to be supplied to the engine is determined in accordance with an output of an oxygen concentration sensor provided downstream of the catalyst in an exhaust passage of the engine. The applicant of the present invention has already proposed a method of performing feedback control and detecting the oxygen storage capacity of the catalyst by using the reversal period of the oxygen concentration sensor output at that time as a catalyst deterioration determination parameter to determine the deterioration (Japanese Patent Laid-Open No. Hei 6 (1994) -6). −
212955, Japanese Patent Application No. 6-308229).

Further, a vaporized fuel discharge suppressing device for storing vaporized fuel generated in a fuel tank in a canister and appropriately discharging it to an intake system of an engine has been widely used.

[0004]

However, when the influence of the purge of the vaporized fuel on the intake system is large, the air-fuel ratio of the air-fuel mixture is biased to the rich side, so the oxygen concentration sensor provided downstream of the catalyst. There is a problem that it is difficult to accurately determine the oxygen storage capacity of the catalyst from the output inversion cycle, and it is not possible to accurately determine deterioration.

The present invention has been made paying attention to this point, and is based on the output of the oxygen concentration sensor, which is caused by the air-fuel ratio of the air-fuel mixture being biased to the rich side due to the influence of the evaporated fuel purged into the intake system. It is another object of the present invention to provide a catalyst deterioration detecting device capable of preventing an erroneous detection of catalyst deterioration due to the catalyst deterioration judgment parameter and making an accurate deterioration judgment.

[0006]

In order to achieve the above object, the present invention is provided in an exhaust system of an internal combustion engine provided with a purge means for discharging evaporated fuel generated from a fuel tank to an intake system, and purifies exhaust gas. A catalyst unit for performing the above, an oxygen concentration detecting unit provided downstream of the catalyst unit for detecting the oxygen concentration in the exhaust gas, and an air-fuel ratio for calculating an air-fuel ratio control amount according to the output of the oxygen concentration detecting unit. Control amount calculation means, air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture to be supplied to the engine based on the air-fuel ratio control amount, and oxygen concentration detection means when the air-fuel ratio is controlled by the air-fuel ratio control means In a 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 a catalyst deterioration determining parameter based on the output of When the concentration is higher than the reference level, to provide a catalyst deterioration detecting apparatus characterized by having a deterioration detection inhibiting means for inhibiting the deterioration detection of the catalyst device.

Further, an air-fuel ratio detecting means for detecting the air-fuel ratio of the air-fuel mixture supplied to the engine on the upstream side of the catalyst means, an air-fuel ratio correction coefficient calculating means based on the detected air-fuel ratio, and the air-fuel ratio correction coefficient calculating means. It is desirable to have a purge concentration calculating means for calculating the concentration of the evaporated fuel based on the fuel ratio correction coefficient.

According to the present invention, when the concentration of the evaporated fuel released to the intake system by the purge means is high, the deterioration detection of the catalyst means is prohibited.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an internal combustion engine (hereinafter referred to as "engine") incorporating a catalyst deterioration detecting device according to an embodiment of the present invention.
And a control device therefor. For example, a throttle valve 3 is arranged in the middle of an intake pipe 2 of a four-cylinder engine 1. A throttle valve opening (θTH) sensor 4 is connected to the throttle valve 3 and outputs an electric signal corresponding to the opening of the throttle valve 3 to output an electronic control unit for engine control (hereinafter referred to as “ECU”).
5

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.

An engine speed (NE) sensor 10 is provided around a camshaft or a crankshaft (not shown) of the engine 1.
And a cylinder discrimination (CYL) sensor 11. The engine speed sensor 10 outputs a TDC signal pulse at a crank angle position before a predetermined crank angle with respect to the top dead center (TDC) at the start of the intake stroke of each cylinder of the engine 1 (every 180 ° crank angle in a four-cylinder engine). The cylinder discriminating sensor 11 outputs a cylinder discriminating signal pulse at a predetermined crank angle position of a specific cylinder. These signal pulses are supplied to the ECU 5.

A three-way catalyst (hereinafter referred to as a catalyst) 16 for purifying exhaust gas is provided in the exhaust pipe 12, and an upstream O 2 sensor 14 as an oxygen concentration detecting means is mounted at a position upstream of the catalyst 16. At the same time, a downstream O2 sensor 15 as an oxygen concentration detecting means is also mounted at a downstream position of the catalyst 16, each detects the oxygen concentration in the exhaust gas, and an electric signal (PVO2, SVO2) corresponding to the detected value is EC.
It is supplied to U5. 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 17 for detecting the speed V of a vehicle equipped with the engine 1 and an atmospheric pressure (PA) sensor 18, and detection signals of these sensors are supplied to the ECU 5. .

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 has a function of shaping input signal waveforms from various sensors, correcting a voltage level to a predetermined level, converting an analog signal value to a digital signal value, and the like, and a central processing circuit ( 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.

The CPU 5b, as will be described later, on the basis of the above-mentioned various engine parameter signals, a plurality of specific operation regions (hereinafter referred to as "open loop control regions") in which the air-fuel ratio feedback control region and the air-fuel ratio feedback control are not performed.
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 × KEVAP × 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, which is obtained in accordance with the oxygen concentration in the exhaust gas detected by the O2 sensors 14 and 15 during the air-fuel ratio feedback control. Is set to the value.

KEVAP is an evaporation correction coefficient for compensating the influence of the evaporated fuel due to the purge, and is set to 1.0 when the purge is not performed, and 0 to when the purge is performed.
Set to a value between 1.0. This evaporation correction coefficient KE
The smaller the value of VAP, the greater the effect of purging.

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 state. 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 also responds to the engine operating state. Purge control valve 2
0 opening / closing control is performed.

Next, deterioration detection of the catalyst 16 (deterioration monitor)
Will be described.

Feedback control for monitoring the deterioration of the catalyst 16 is performed by the output SVO of the downstream O 2 sensor 15.
2 based on In order to skip the correction coefficient KO2 from the rich side to the lean side with respect to the stoichiometric air-fuel ratio at a time point after a predetermined time TRD has elapsed from the time point when the output SVO2 is inverted from the lean side to the rich side with respect to the predetermined reference voltage SVREF. Lean side special P item PLS
P is generated, and the delay time TL from this time to the time when the output SVO2 is inverted from the rich side to the lean side is detected. In addition, the output SVO2 is inverted from the rich side to the lean side with respect to the reference value SVREF from the time point of the predetermined time TL
At the time point after the lapse of D, a rich side special P term PRSP for causing the correction coefficient KO2 to skip from the lean side to the rich side with respect to the stoichiometric air-fuel ratio is generated, and the output SVO2 is inverted from the lean side to the rich side from this time point. The delay time TR up to the point of time is detected. Then, these delay times TL and TR are used as deterioration determination parameters to make the catalyst 1
Degradation of 6 is determined.

Next, the overall structure of the catalyst deterioration monitoring process will be described with reference to the flowcharts of FIGS. This process uses a timer to perform C every predetermined time (for example, 10 msec)
It is executed by the PU 5b.

First, in step S1, it is determined whether or not the deterioration monitor permission flag FCATCHK, which is set in the processing of FIG. 4 and indicates the deterioration monitor permission by "1", is "1".
When CHK = 1, the change amount DPBA4 (= current value PBA (n) -previous value PBA of the intake pipe absolute pressure PBA
It is determined whether or not the absolute value of (n-1)) is smaller than the predetermined change amount DPBCATM (step S2), and | DPBA
4 | <DPBCATM and the fluctuation of the intake pipe absolute pressure PBA is small, the fuel supply amount TF per unit time
It is determined whether the average value TFAVE of is larger than the predetermined upper limit value TFMAX, that is, whether it is in the high rotation and high load operation state (step S3).

Here, the fuel supply amount TF per unit time
And its average value TFAVE is calculated by the following formula.

TF = TOUT × NE / A TFAVE (n) = α × TF + (1-α) × TFAVE
(N-1) A is a constant (for example, 2 to the 12th power), and α is a smoothing coefficient set to a value between 0 and 1.

The answer to step S1 or S2 is negative (NO).
Or when the answer to step S3 is affirmative (YES),
That is, the deterioration monitor is not executed when the deterioration monitor condition is not satisfied, when the fluctuation in the intake pipe absolute pressure PBA is large, or in the high rotation and high load operation state where the fuel supply amount per unit time is large. That is, the process proceeds to step S7, and the hold flag FSVO2HLD indicating "1" indicating that the change in the output SVO2 of the downstream O2 sensor 15 is small is set to "0".
, And forced purge cut (purge control valve 20
The purge cut flag FCATPG indicating "1" to be closed is set to "0" (step S9), a predetermined monitor start delay time TCATM is set to the down count timer tmCATM, and the timer is started (step S1).
2) Then, the monitor execution flag FCATM indicating "1" indicating that the deterioration monitor is being executed is set to "0" (FIG. 3, step S14), and this processing ends. The hold flag FSVO2HLD is set by the process of FIG. 6 described later.

In step S3, the deterioration monitor is not executed during the high rotation and high load operation state in which the fuel supply amount per unit time of the engine is large. This is because the oxygen storage time is shortened and the oxygen storage characteristics similar to those of the deteriorated catalyst are exhibited, so that it may be erroneously determined that the normal catalyst is deteriorated.

The answer to step S3 is affirmative (YES),
That is, when TFAVE <TFMAX and the high rotation / high load operation state is not set, the monitor execution flag FCATM is executed.
It is determined whether is "1" (step S4). Since FCATM = 0 at first, the process immediately proceeds to step S6, and when FCATM = 1 is set in step S16 described later, the maximum value P of the absolute intake pipe absolute pressure PBA during the monitoring is performed.
The difference between BCTMAX and the minimum value PBCTMIN is the predetermined value D
It is determined whether it is smaller than PBCATG (step S
5), PBCTMAX-PBCTMIN <DPBCAT
If it is G, the process proceeds to step S6.

The maximum value PBCMAX and the minimum value PB
CMIN is initialized to 00 (hexadecimal) and FF (hexadecimal), respectively, when the deterioration monitor is not executed (FIG. 5, step S49), and executed every time a TDC signal pulse is generated. In the process, while the deterioration monitor is being executed (when FCATM = 1), the detected absolute pressure P in the intake pipe is detected.
When BA is higher than the maximum value PBCMAX, the maximum value PBCMAX is updated by the PBA value at that time, while when the detected intake pipe absolute pressure PBA is lower than the minimum value PBCMIN, the minimum value PBCMIN is set by the PBA value at that time. Calculated by updating.

Since the deterioration monitor is not executed when the fluctuation of the intake pipe absolute pressure PBA during the deterioration monitor is large in steps S4 and S5, the reversal cycle of the downstream O2 sensor output SVO2 is changed when the load fluctuation is large. It is possible to prevent erroneous determination due to instability.

In step S6, the hold flag FSV
It is determined whether O2HLD is "0". First is FSVO
Since 2HLD = 0, the process proceeds to step S8, and when FSVO2HLD = 1 in the process of step S17 described later, that is, when it is determined that the change in the downstream O2 sensor output SVO2 is small, the process proceeds to step S7. , Deterioration monitor is not executed.

In step S6, when the change in the downstream O2 sensor output SVO2 is small, the deterioration monitor is not executed. Therefore, especially when the catalyst is new, the output S2 is reduced.
It is possible to prevent erroneous determination due to the fact that VO2 is stagnant in the vicinity of the reference value SVREF and accurate oxygen storage time cannot be detected.

In step S8, it is determined whether or not the feedback control flag FO2FB, which indicates "1" indicating that it is in the air-fuel ratio feedback control region, is "1", and FO2FB is determined.
When = 0, the process proceeds to step S9, and FO2F
When B = 1, the purge cut flag FCATFG
Is set to "1" for forced purge cut (step S10). Next, the evaporation correction coefficient KEVAP is 1.0.
Is determined (step S11), and KEVAP
When it is <1.0, the influence of the purge is great and the deterioration cannot be accurately determined. Therefore, the process proceeds to step S12, and the deterioration monitoring is not performed.

As a result, the downstream side O
It is possible to prevent erroneous determination due to the fact that the 2-sensor output SVO2 is biased to the rich side and the oxygen storage capacity of the catalyst cannot be accurately determined.

On the other hand, when KEVAP = 1.0,
Timer tmCATM started in step S12
It is determined whether the value of is 0 or not. Since tmCATM> 0 at first, the process proceeds to step S14, and the predetermined delay time T
When CATM elapses and tmCATM = 0, deterioration determination is performed in steps S15 and below in FIG.

First, in step S15, a calculation process (details are shown in FIG. 5) of the air-fuel ratio correction coefficient CATKO2 during deterioration monitoring based on the downstream O2 sensor output SVO2 is executed. This correction coefficient CATKO2 is KO of the above equation (1).
Instead of 2, it is used to calculate the fuel injection time TOUT.

Then, the monitor execution flag FCATM is set to "1" (step S16), and the delay times TL and T are set.
The rich side TR counter NT indicating the number of times the delay time TR is calculated by executing the R calculation process (FIG. 6) (step S17).
It is determined whether the value of R is smaller than the predetermined value NTRC (step S18). Since initially NTR <NTRC, the deterioration determination process A (FIG. 8) of step S19 is executed, and then the normality determination flag FOK67 indicating "1" that the determination that the catalyst 16 is normal is confirmed is " It is determined whether it is "1" (step S20). And F
If OK67 = 0 and the normal determination has not been confirmed, this processing is immediately terminated, and if FOK67 = 1 and the normal determination has been determined, the deterioration monitor flag FCATM.
Is set to "0" (step S22), and this processing ends.

When NTR = NTRC in step S18, the routine proceeds to step S21, where the deterioration determination process B (FIG. 9) is executed, and the routine proceeds to step S22.

FIG. 4 shows the deterioration monitor permission flag FCATCH.
It is a flowchart of the setting process of K, and this process is executed in the background where other processes with high priority are not executed.

First, in step S31, the intake air temperature TA is a predetermined upper and lower limit value TACATH (for example, 100 ° C.), TACA
Whether the engine water temperature TW is within a range of TL (for example, −0.2 ° C.) is a predetermined upper and lower limit value TWCATH (for example, 10).
0 ° C.), TWCATL (for example, 80 ° C.), whether or not the vehicle speed V is a predetermined upper and lower limit value VCATH (for example, 80
km / h), VCATL (for example, 32 km / h), whether the engine speed NE is a predetermined upper / lower limit value N or not.
ECATH (eg 3200 rpm), NECCATL
(For example, 2800 rpm) and whether or not the intake pipe absolute pressure PBA is a predetermined upper and lower limit value PBCATH (for example, 510 mmHg) and PBCATL (for example, 410 m).
mHg) within the range, and if any of these operating parameters is outside the predetermined upper and lower limits,
The deterioration monitor execution permission flag FCATCHK is set to "0" (step S37), and the deterioration monitor execution is disabled.

On the other hand, when all the determined operation parameters are within the predetermined upper and lower limit values, it is indicated by "1" that the temperature TCAT of the catalyst 16 is further within the predetermined range (for example, 350 ° C to 800 ° C). It is determined whether the catalyst temperature flag FTCAT is "1" (step S32). This flag FTCAT is set by the detection value T of the catalyst temperature sensor 13.
Although the CAT is used, a temperature value estimated according to the engine operating state may be used. When FTCAT = 0 and the catalyst temperature TCAT is out of the predetermined range, the process proceeds to step S37, and the deterioration monitor cannot be executed. As a result, it is possible to prevent erroneous determination that the oxygen storage capacity is lowered and the normal catalyst is deteriorated due to the low catalyst temperature.

When FTCAT = 1 in step S32 and the catalyst temperature TCAT is within the predetermined range, it is determined whether the learning value KEVAPREF of the evaporation correction coefficient KEVAP is larger than the predetermined value KEVAPCAT (for example, 0.781). Yes (step S33).

The learning value KEVAPREF is the idle learning value KE calculated when the engine is in the idle state.
There are VAPREF1 and an off-idle learning value KEVAPREF0 calculated when the vehicle is not in the idle state,
These learned values are
It is calculated by the following formula (2).

KEVAPREFi (n) = CEVREFi × KEVAP / B + (B-CEVREFi) × KEVAPREFi (n−1) (2) Here, i = 0 or 1, and B is set to 2 to the 16th power, for example. The constant CEVREFi is a smoothing coefficient set to a value between 1 and B.

In step S33, KEVAPREF ≦ KE
When VAPCAT is established and the influence of the purge is large, the process proceeds to step S37, and deterioration monitoring cannot be executed. As a result, it is possible to prevent erroneous determination due to the fact that the downstream O2 sensor output SVO2 is biased to the rich side due to the effect of purging and the oxygen storage capacity of the catalyst cannot be accurately determined.

In step S33, KEVAPREF> KE
When VAPCAT is established and the effect of purging is small,
It is determined whether or not the cruise flag FCRS, which indicates "1" that the vehicle is in the cruise state, is "1" (step S34). The cruise flag FCRS is, for example, the vehicle speed V.
Is set to "1" when the state of fluctuation of 0.8 km / sec or less continues for a predetermined time (for example, 2 seconds).

When the vehicle is not in the cruise state in step S34, the process proceeds to step S37 and the deterioration monitor cannot be executed. As a result, it is possible to prevent erroneous determination due to instability of the downstream O2 sensor output SVO2 due to a large load change.

The answer in step S34 is affirmative (YE
S), that is, when the vehicle is in a cruise state, the air-fuel ratio correction coefficient KO2 is stuck to the predetermined upper limit value or the lower limit value for a predetermined time or more (the KO2 limit is stuck state).
The sticking flag FKO2LMT indicating "1" is "0"
It is determined whether or not (step S35), FKO2LMT =
If it is 1 and the KO2 limit is stuck, the process proceeds to step S37, and the deterioration monitor cannot be executed.

When all the answers in steps S31 to S35 are affirmative (YES), the deterioration monitor execution permission flag FCATCHK is set to "1" (step S3).
6) Then, this process ends.

FIG. 5 shows C in step S15 of FIG.
It is a flow chart of ATKO2 calculation processing. Further, FIG. 7 is a diagram showing transitions of the downstream O2 sensor output SVO2, various flags and the like, and this figure will also be referred to.

First, in step S41, it is determined whether or not the downstream O2 sensor output SVO2 is lower than the reference value SVREF. When SVO2 <SVREF, the first rich flag FAFR1 is set to "0", and SVO2≥SVRE.
When it is F, the flag FAFR1 is set to "1" (steps S42 and S43). In a succeeding step S44, it is determined whether or not the first rich flag FAFR1 is inverted. If it is not inverted, the process immediately proceeds to step S48, while if it is inverted, it is determined whether or not the first rich flag FAFR1 is "0". It is determined (step S45). And
FAFR1 = 0 and downstream O2 sensor output SVO2
Is inverted from the rich side to the lean side (FIG. 7, time t1, t5, t9), the down count delay timer T
When the lean side predetermined time TLD is set in DLYR to start (step S46), conversely when FAFR1 = 1 and the lean side is reversed to the rich side (FIG. 7, t).
3, t7, t11), a predetermined rich side time TRD is set and started (step S47), and step S48
Proceed to.

In step S48, the monitor execution flag F
It is determined whether CATM is "1". At the beginning of monitor execution, FCATM = 0 (since FCATM is set to “1” after the CATKO2 calculation process is executed),
In step S49, various timers, counters, flags, etc. are initialized (step S49). That is, the delay timer TDLYR, the delay times TL and TR, the up-count timer TSTRG for measuring, and the delay times TL and TR.
The counters NTL and NTR for counting the number of times of measurement of the above, and the integrated values TLSUM and TRSUM of the delay time are all set to "0", the second rich flag FAFR2 is made the same as the first rich flag FAFR1, and the deterioration monitoring air-fuel ratio is set. The correction coefficient CATKO2 is set to the air-fuel ratio correction coefficient KO2, and the maximum value PBCTMAX of the intake pipe absolute pressure PBA is set to 0.
0 (hexadecimal) and the minimum value PBCTMIN to FF (1
Hexadecimal).

In a succeeding step S58, it is determined whether or not the second rich flag FAFR2 is "1", and FAFR2 = 0.
(FIG. 7, t2 to t4, t6 to t8), integration control is performed to add the special I term ILSP to the value immediately before the correction coefficient CATKO2 (step S59), and FAFR2
= 1 (FIG. 7, t4 to t6, t8 to t1
0), from the value immediately before the correction coefficient CATKO2 to the special I
Integral control for subtracting the term ILSP is performed (step S6
0), this process ends.

When step S48 is reached at the next execution of this processing, since FCATM = 1 is set in step S16 of FIG. 3, step S50 follows and the first rich flag F is set.
It is determined whether AFR1 and the second rich flag FAFR2 are equal. When FAFR1 = FAFR2 (FIG. 7, t2 to t3, t4 to t5, t6 to t7,
t8 to t9, t10 to t11), the process proceeds to step S58, and when FAFR1 ≠ FAFR2 (FIG. 7, t).
1-t2, t3-t4, t5-t6, t7-t8, t9
~ T10), it is determined whether or not the first rich flag FAFR1 is "1" (step S51).

When FAFR1 = 0 in step S51 (FIG. 7, 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 S52). When TDLYR> 0, the process proceeds to step S58. And TDLYR = 0
Then (FIG. 7, t2, t6, t10), the second rich flag FAFR2 is made equal to the first rich flag FAFR1 (step S54), and the special P term PRSP is added to the value immediately before the correction coefficient CATKO2 (step S5).
5), end this processing.

When FAFR1 = 1 in step S51 (FIG. 7, t3 to t4, t7 to t8), it is judged whether the value of the delay timer TDLYR is "0" (step S51).
56), if TDLYR> 0, then step S5
Proceed to 8. Then, when TDLYR = 0 (FIG. 7, t
4, t8), the second rich flag FAFR2 is made equal to the first rich flag FAFR1 (step S56), and the special P term PRSP is calculated from the value immediately before the correction coefficient CATKO2.
Is subtracted (step S57), and this processing ends.

As described above, according to the processing shown in FIG. 5, the time point (t1, t3, t) at which the downstream O2 sensor output SVO2 is reversed.
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 of the second rich flag FAFR2 = 0, integration control in the increasing direction of the CATKO2 value is executed, and FA
During the period of FR2 = 1, integral control in the decreasing direction of the CATKO2 value is executed.

FIG. 6 shows T in step S17 of FIG.
It is a flow chart of L and TR calculation processing. Note that FIG.
See also.

In FIG. 6, first, in step S71, it is determined whether or not the first rich flag FAFR1 (FIG. 7 (b)) is inverted, and when it is inverted, it is "1" that it is the delay time measurement period. Inversion timer flag FTSTRG
It is determined whether or not (Fig. 7 (e)) is "1" (step S
72). When the answer to step S71 or S72 is negative (NO), that is, the first rich flag FAFR1.
Is not inverted or the inversion timer flag FTSTR
When G is “0”, the process proceeds to step S86, and it is determined whether the value of the delay timer TDLYR (FIG. 7 (c)) is 0. When TDLYR> 0, the delay time counting up count is performed. The timer TSTRG (FIG. 7 (f)) is set to "0" (step S87), and the output range flag FSVO2CAT is set to "0", which indicates "1" that the change in the downstream O2 sensor output SVO2 is equal to or more than a predetermined value. After setting (step S88), the process proceeds to step S92.

When TDLYR = 0 in step S86, the process proceeds to step S89, and the downstream O2 sensor output SVO
2 is a predetermined upper level SVO2CATH (for example, 0.58
6V), SVO2 <SVO2C
If it is ATH, it is further determined whether or not the SVO2 value is higher than a predetermined lower level SVO2CATL (for example, 0.430V) (step S90). As a result, SVO
Immediately when 2CATL <SVO2 <SVO2CATH, and SVO2 ≧ SVO2CATH or SVO2
When ≦ SVO2CATL, the output range flag FS
Set VO2CAT to "1" (step S91),
It proceeds to step S92. That is, the output range flag FS
VO2CAT is a predetermined time (TLD) from the reversal of the first rich flag FAFR1 (downstream O2 sensor output SVO2).
Or TRD), the SVO2 value is the reference value SV.
When it is near REF, it is maintained at "0", indicating that the change in the downstream O2 sensor output SVO2 is small.

In step S92, the second rich flag F
It is determined whether AFR2 (FIG. 7 (d)) has been inverted, and if it is not inverted, immediately, and if it is inverted, the inversion timer flag FTSTRG is set to "1" (step S
93), and this processing ends.

On the other hand, when the answers to steps S71 and S72 are both affirmative (YES), that is, when the first rich flag FAFR1 is inverted and the inversion timer flag FTSTRG is "1", the process proceeds to step S73 and the inversion timer flag F
Return TSTRG to "0" and set the output range flag FSVO2
It is determined whether CAT is "1" (step S74).
When FSVO2CAT = 0 and the change in the downstream O2 sensor output SVO2 is small, the hold flag FSVO2HLD is set to "1" (step S7).
5) Also, when FSVO2CAT = 1, the flag FSVO2CAT is returned to "0" (step S7).
6) and proceeds to step S77. This hold flag FS
The VO2HLD is referred to in step S6 of FIG. 2 as described above.

In step S77, the first rich flag F
It is determined whether AFR1 is “1”, FAFR1 = 0 and the downstream O2 sensor output SVO2 is the reference value SVREF.
When it is on the lean side with respect to (Fig. 7, t1, t5, t
9), the lean side integrated value TLSUM is calculated by the following formula (step S78). Timer TST added here
The value of RG corresponds to the delay time TL in FIG. 7.

TLSUM = TLSUM + TSTRG Then, the lean side counter NTL is incremented by "1" (step S79), and the up count timer TS is increased.
The value of TRG is returned to "0" (step S80), and the process proceeds to step S92.

When FAFR1 = 1 in step S77 and the downstream O2 sensor output SVO2 is on the rich side with respect to the reference value SVREF (FIG. 7, t3, t7, t1).
1), the rich side integrated value TRSUM (Fig. 7)
(G)) is calculated (step S81). The value of the timer TSTRG added here corresponds to the delay time TR in FIG. 7.

TRSUM = TRSUM + TSTRG Next, the rich side counter NTR (FIG. 7 (h)) is set to "1".
Only (step S82), the value of the up-count timer TSTRG is returned to "0" (step S83), and it is determined whether the value of the lean side counter NTL is "0" (step S84). Then, when NTL> 0, immediately, 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 S8).
5) Then, the process proceeds to step S92.

In steps S84 and S85, since the delay time starts to be measured from TL, when the TR is first measured, the rich side integrated value TRSUM and the counter NTR are reset to "0". It is provided.

As described above, according to the processing of FIG. 6, the delay time TL or TR is integrated every time the downstream O2 sensor output SVO2 is inverted, and the integrated values TLSUM, TRSUM are calculated. Note that FIG. 7 does not show changes in the lean-side integrated value TLSUM and the lean-side counter NTL,
At times t1, t5, t9, the rich side integrated value TRSU
It is incremented similarly to M and the rich side counter NTR.

FIG. 8 is a flowchart of the deterioration determination process A in step S19 of FIG. 3, in which the value of the up-count timer TSTRG is a predetermined normality determination reference value TSTRG.
It is determined whether or not it is larger than OK (step S101),
If TSTRG ≦ TSTRGOK, immediately, and if TSTRG> TSTRGOK, the catalyst 16 is determined to be normal, the normality determination flag FOK67 is set to “1” (step S102), and this processing is ended.

By this processing, when the delay time is very long, it is immediately determined to be normal, and the time required for the determination can be shortened.

FIG. 9 is a flowchart of the deterioration determination process B in step S21 of FIG.

First, in step S111, the determination time TCHK is calculated by the following equation. As is clear from the equation below, the determination time TCHK is an average value of the delay times TL and TR.

[0078]

[Equation 1] Next, the determination time TCHK is the deterioration determination threshold value TCHKLM.
It is determined whether it is larger than T (step S112).
Here, the deterioration determination threshold value TCHKLMT is determined according to the average value TFAVE of the fuel injection amount TF per unit time.
The TCHKLMT table shown in FIG. 10 is searched and determined. The TCHKLMT table is set so that the deterioration determination threshold value TCHKMLT decreases as the average value TFAVE increases.

If the answer to step S112 is affirmative (YES), the normality determination flag FOK67 is set to "1" (step S113), and if negative (NO), it is set to "0" (step S114). , This process ends.

FIG. 11 is a flow chart of the main routine of the evaporation correction coefficient KEVAP calculation process, and this process is executed in synchronization with each generation of the TDC signal pulse.

First, in step S121, it is determined whether or not the engine 1 is in the starting mode. In the starting mode, the value of the evaporation correction coefficient KEVAP is set to 1.0 (step S122), and the learning value of the evaporation correction coefficient is set. KEVAPR
The EF is set to 1.0 (step S123), and this processing ends.

When not in the start mode, the purge permission flag FFR indicating "1" indicating that purging is possible is "1".
It is determined whether or not (step S124), and when FFR = 1, the purge control valve 2 calculated in the process not shown.
The purge duty amount DFR of 0 (the larger this value,
The purge amount increases) is greater than the predetermined amount DFREV (step S125), and DFR> DFRE
When it is V, it is further determined whether or not the engine speed NE is lower than a predetermined speed NHOP (step S12).
6). When the answer to any of steps S124 to S126 is negative (NO), that is, when purging is not permitted, when the purge duty amount DFR is less than or equal to a predetermined value, or when the engine speed NE is more than or equal to a predetermined value, In step S132, both flags FKO2EVH and FKO2EVL used in the process of FIG. 12 described later are set to “0”.
And

Next, the purge-on transition timer tmEVDE
A predetermined time (for example, 0.5 seconds) is set in C and started (step S133), and it is determined whether or not the value of the purge-off transition timer tmEVADD is 0 (step S134). Immediately after the transition to purge off (purge cut), tmEVADD> 0, so step S136.
Then, the processing is terminated with the evaporation correction coefficient KEVAP held at the previous value, and after a predetermined time, tmEVADD = 0
Then, the previous value KEVA of the evaporation correction coefficient KEVAP
Add a predetermined addition term DKEVADD to P (n-1),
The current value KEVAP (n) is calculated (step S13
5), end this processing.

In step S135, the evaporation correction coefficient KEVAP gradually increases from a small value during execution of purge toward 1.0.

The answer to step S126 is affirmative (YE
If S), the process proceeds to step S127, and it is determined whether the evaporation correction coefficient KEVAP is smaller than the predetermined value KEVADD. As a result, KEVAP <KEVADD, and when the amount of evaporated fuel to be purged is large and the influence of purging is large, the process proceeds to step S129, and a purge off transition timer tmEVADD is set to a predetermined time (for example, 1.0 second) and set. Start and proceed to step S130. If KEVAP ≧ KEVADD and the influence of the purge is small, the process proceeds to step S128, the timer tmEVADD is set to 0, and the process proceeds to step S130. Therefore, when the influence of the purge is small, the above-mentioned step S13 is performed.
Step S135 will be executed immediately without going through 6.

In step S130, as shown in FIG.
The KEVAP calculation process of No. 13 is executed, the learning value KEVAPREF of the evaporation correction coefficient KEVAP is further calculated (step S131), and this process is ended. The learning value K
The calculation of EVAPREF is performed by the above equation (2).

12 and 13 show step S of FIG.
6 is a flowchart of KEVAP calculation processing in 130.

First, in step S141, the air-fuel ratio correction coefficient KO2 set in accordance with the oxygen concentration in the exhaust gas,
The upper threshold value KO2EVH and the lower threshold value KO2EVL in consideration of the influence of the purge are calculated by the following equations.

KO2EVH = KREF + DKO2EVH KO2EVL = KREF-DKO2EVL where KREF is a learning value of the air-fuel ratio correction coefficient KO2, D
KO2EVH is a predetermined addition term, and DKO2EVL is a predetermined subtraction term. The learning value KREF is calculated based on the value of the air-fuel ratio correction coefficient KO2 during the air-fuel ratio feedback control, and has various values according to the operating state. However, the evaporation correction coefficient KEVAP is the predetermined value K.
When it is smaller than EVAPLL, it is determined that the influence of the purge is large, and the learning value KREF is prohibited from being calculated.

In the following step S142, the air-fuel ratio correction coefficient K
It is determined whether the value of O2 is larger than the learning value KREF,
When KO2> KREF, the air-fuel ratio correction coefficient K
It is determined whether or not the value of O2 is smaller than the upper threshold value KO2EVH (step S143). As a result, when the value of the air-fuel ratio correction coefficient KO2 is greater than or equal to the upper threshold value KO2EVH, the upper flag FKO2EVH is set to "1" and the lower flag FKO2EVL is set to "0", and step S1 is performed.
Go to 48. Further, the air-fuel ratio correction coefficient KO2 is the upper threshold K
When it is smaller than O2EVH, the upper flag FKO2FH
Also, the lower flag FKO2FL is set to "0" (step S146), and the process proceeds to step S148.

If the value of the air-fuel ratio correction coefficient KO2 is less than or equal to the learning value KREF in step S142, the process proceeds to step S144, and it is further determined whether or not it is larger than the lower threshold value KO2EVL. When the air-fuel ratio correction coefficient KO2 is less than or equal to the lower threshold value KO2EVL, the upper flag FKO2EV
H is set to "0", the lower flag FKO2EVL is set to "1" (step S147), and the process proceeds to step S148, where the value of the air-fuel ratio correction coefficient KO2 is the lower threshold KO2EV.
If larger than L, the process proceeds to step S146.

At step S148, the lower flag FKO is set.
It is determined whether 2EVL is "1", and FKO2EVL = 0
If it is, it is determined whether or not the upper flag FKO2EVH is "1" (step S149). When both the lower flag FKO2EVL and the upper flag FKO2EVH are "0", the process proceeds to step S163 (FIG. 13), the evaporation correction coefficient KEVAP is held at the previous value, and the process ends. That is, the value of the air-fuel ratio correction coefficient KO2 is
If it is within the upper and lower thresholds, the evaporation correction coefficient KEVAP
The value of (n) is fixed to the previous value.

When FKO2EVL = 0, FKO2EV
When H = 1, the routine proceeds to step S162, where the current value KO2 (n) of the air-fuel ratio correction coefficient KO2 is the previous value KO2.
It is determined whether or not it is larger than (n-1), and KO2 (n)>
If KO2 (n-1) and the value of the air-fuel ratio correction coefficient KO2 increases and changes in the direction away from the learning value KREF, the process proceeds to step S164 (FIG. 13) and the previous value K
The addition term DKEVAPP is added to EVAP (n-1) to obtain the current value KEVAP (n). On the other hand, KO2 (n) ≦
If KO2 (n-1) and the air-fuel ratio correction coefficient KO2 is decreasing, the process proceeds to step S163 and the evaporation correction coefficient KEVAP is held at the previous value.

Further, in step S148, FKO2EVL
= 1, the change amount D of the throttle valve opening θTH
It is determined whether or not TH (= θTH (n) -θTH (n-1)) is larger than a negative predetermined value DTHKEV (step S
150), DTH> DTHKEV, and when the engine is accelerating or decelerating and the deceleration is small, the current value KO2 (n) of the air-fuel ratio correction coefficient KO2 is the previous value KO2.
It is determined whether it is smaller than (n-1) (step S1).
51). As a result, when DTH ≦ DTHKEV and the deceleration is large, or when KO2 (n) ≧ KO2 (n−1) and the air-fuel ratio correction coefficient KO2 is increasing, the routine proceeds to step S163, and the previous value is calculated. Retain.

On the other hand, the answer in step S151 is affirmative (YE
S), that is, KO2 (n) <KO2 (n-1) and the air-fuel ratio correction coefficient KO2 is decreasing, an initial flag FFRA indicating that the initial purge state is indicated by "1".
It is determined whether or not DD is "1" (step S152). Since FFRADDD = 1 at the beginning of the purge, the process proceeds to step S153 to measure the time after the end of the initial purge state (refer to step S154 described later). The delay timer tmDRKDEC is set to a predetermined time and started, and it is determined whether or not the value of the purge-on transition timer tmEVDEC started in step S133 of FIG. 11 is "0" (step S155).

Since tmEVDEC> 0 at first, the process proceeds to step S156, the evaporation correction coefficient KEVAP is held at the previous value, and when tmEVDEC = 0, the first subtraction term DKEVDEC from the previous value KEVAP (n-1) at step S157. By subtracting the current value KEVAP
After calculating (n), the process proceeds to step S158.

At step S158, the learning value KEVAP
The lower limit reference value KEVLMREF is calculated by subtracting the predetermined value DKEVLMRF from REF, and then the evaporation correction coefficient K
The current value KEVAP (n) of EVAP is the lower limit reference value K
It is determined whether or not it is larger than EVLMREF (step S
159) and KEVAP (n) ≦ KEVLMREF, the current value KEVAP (n) is set to the lower limit reference value KEV.
While setting to LMREF (step S160) and ending this processing, when KEVAP (n)> KEVLLMREF, this processing is immediately ended.

After that, when the initial flag FFRADD becomes "0", the process proceeds from step S152 to S154, and it is determined whether or not the value of the delay timer tmDRKDEC is "0".
Since tmDRKDEC> 0 at first, the process proceeds to step S155, and when tmDRKDEC = 0, the second subtraction term DKEVAPM from the previous value KEVAP (n-1).
Is subtracted to calculate the current value KEVAP (n) (step S161), and this processing ends.

As described above, according to the processing of FIGS. 12 and 13, the evaporation correction coefficient KEVAP is set in accordance with the air-fuel ratio correction coefficient KO2 so as to supplement the correction by the correction coefficient KO2.

In the above-described embodiment, the delay times TL and TR are used as the catalyst deterioration determination parameter, but instead of this, the reference value SVRE of the downstream O2 sensor output SVO2 is used.
Inversion time with respect to F ((TLD + TR), (TR
D + TL) may be used.

[0101]

As described above in detail, according to the present invention, when the concentration of the vaporized fuel discharged to the intake system by the purge means is high, the deterioration detection of the catalyst means is prohibited, so that the intake system is purged. It is possible to prevent erroneous detection of catalyst deterioration by the catalyst deterioration determination parameter based on the oxygen concentration sensor output, which is caused by the air-fuel ratio of the air-fuel mixture being biased to the rich side due to the influence of the evaporated fuel, and to make an accurate deterioration determination. it can.

[Brief description of 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 showing an overall configuration of catalyst deterioration determination processing.

FIG. 3 is a flowchart showing the overall configuration of catalyst deterioration determination processing.

FIG. 4 is a flowchart of a process of setting a deterioration monitor permission flag (FCATCHK).

FIG. 5 is an air-fuel ratio correction coefficient (CATKO during execution of deterioration determination).
It is a flowchart of the process which calculates 2).

FIG. 6 is a flowchart of a process of calculating a reversal time during execution of deterioration determination.

FIG. 7 is a diagram for explaining the processing content of FIGS. 5 and 6;

8 is a flowchart of a deterioration determination process B of FIG.

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

FIG. 10 is a diagram showing a table used in the processing of FIG. 9;

FIG. 11 is a flowchart of a main routine of an evaporation correction coefficient (KEVAP) calculation process.

FIG. 12 is a flowchart of an evaporation correction coefficient (KEVAP) calculation process.

FIG. 13 is a flowchart of an evaporation correction coefficient (KEVAP) calculation process.

[Explanation of symbols]

 1 Internal Combustion Engine 5 Electronic Control Unit 7 Intake Pipe Absolute Pressure Sensor 15 Downstream O2 Sensor 16 Three-Way Catalyst 20 Purge Control Valve

Claims (2)

[Claims] 1. A catalyst means for purifying exhaust gas, which is provided in an exhaust system of an internal combustion engine equipped with a purge means for discharging evaporated fuel generated from a fuel tank to an intake system, and a catalyst means provided downstream of the catalyst means. The oxygen concentration detecting means for detecting the oxygen concentration in the exhaust gas, the air-fuel ratio control amount calculating means for calculating the air-fuel ratio control amount according to the output of the oxygen concentration detecting means, and based on the air-fuel ratio control amount An air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine, and a catalyst deterioration determination parameter based on the output of the oxygen concentration detection means when controlling the air-fuel ratio by the air-fuel ratio control means In a catalyst deterioration detecting device for an internal combustion engine, comprising catalyst deterioration detecting means for detecting deterioration, when the concentration of evaporated fuel discharged to the intake system by the purging means is high, the deterioration detection of the catalyst means is prohibited. Catalyst deterioration detecting device for an internal combustion engine and having a degradation detection inhibiting means for. 2. An air-fuel ratio detecting means for detecting an air-fuel ratio of an air-fuel mixture supplied to the engine on an upstream side of the catalyst means, and an air-fuel ratio correction coefficient calculating means based on the detected air-fuel ratio,
2. The catalyst deterioration detecting device for an internal combustion engine according to claim 1, further comprising purge concentration calculating means for calculating a concentration of the evaporated fuel based on the air-fuel ratio correction coefficient.