JP3067445B2 - Catalyst deterioration determination device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for determining catalyst deterioration of an internal combustion engine, and more particularly to an apparatus for determining the deterioration of a catalyst body due to production variation and use deterioration of a first exhaust sensor provided in an exhaust passage upstream of the catalyst body. The present invention relates to a catalyst deterioration determination device for an internal combustion engine that can prevent an increase in variation and can improve the accuracy of determination of catalyst deterioration.

[0002]

2. Description of the Related Art In an internal combustion engine mounted on a vehicle, a catalyst is provided in an exhaust passage, and a first O2 sensor and a second O2 sensor serving as exhaust sensors are respectively provided in upper and lower exhaust passages of the catalyst.
In some cases, two sensors are provided and control means for performing feedback control so that the air-fuel ratio becomes a target value based on the first detection signal and the second detection signal output from the first O2 sensor and the second O2 sensor. As a result, in the internal combustion engine, the exhaust gas purification efficiency of the catalyst body is improved, and the exhaust emission harmful component value is reduced.

[0003] Japanese Patent Application Laid-Open No. Hei 4-10904 discloses a technique for reducing the value of harmful exhaust components emitted from an internal combustion engine.
No. 5 and Japanese Patent Application Laid-Open No. 4-116239.

[0004] Japanese Patent Application Laid-Open No. 4-10945 discloses a first O2 sensor and a second O2 sensor located upstream and downstream of exhaust gas purifying means provided in an exhaust passage of an internal combustion engine.
An O2 sensor is provided to feedback-control the air-fuel ratio to a target value based on the first detection signal output from the first O2 sensor.
2 By the change of the response of the second detection signal output from the sensor,
The deterioration of the purifying means is monitored.

Japanese Unexamined Patent Publication No. 4-116239 discloses a first O2 sensor and a second O2 sensor located upstream and downstream of exhaust gas purifying means provided in an exhaust passage of an internal combustion engine.
An apparatus in which an O2 sensor is provided and the air-fuel ratio is feedback-controlled to a target value based on a first detection signal output from the first O2 sensor, wherein the output of the first O2 sensor and the output of the second O2 sensor are compared during feedback control. A deterioration determining means for determining deterioration of the catalyst body is provided, and a determination prohibiting means for prohibiting the deterioration determination by the deterioration determining means when the number of updates of the feedback control learning value is equal to or less than a predetermined number is provided.

[0006]

Incidentally, the catalyst provided in the exhaust passage of the internal combustion engine does not cause a significant reduction in its purifying function under a normal operating condition.

However, the catalyst body is made of lead when the leaded gasoline is supplied to an internal combustion engine that uses unleaded gasoline as a fuel, or when the engine is operated with the ignition plug high tension cord disconnected for some reason. Poisoning or damage due to raw gas may occur.

Such poisoning or breakage of the catalyst body degrades the catalyst body, significantly lowers the purification function, and lowers the exhaust gas purification efficiency. As a result, the deterioration of the catalyst body has a disadvantage in that a large amount of unpurified exhaust gas is discharged into the atmosphere, thereby causing environmental destruction.

Therefore, in an internal combustion engine, it is desired to be able to accurately measure the state of deterioration of the catalyst body and to accurately determine the state of deterioration. When the accuracy of the determination of the deterioration state of the catalyst body is low, the abnormality of the catalyst body is notified even though the function of the catalyst body is normal, which causes inconvenience and inconvenience and lowers the reliability. .

[0010] Such a catalyst deterioration judging device for judging the deterioration state of the catalyst body includes a start and a decrease of the first feedback control correction amount due to rich inversion and lean inversion of the first detection signal output from the first O2 sensor. Second from start
A deterioration judgment value is calculated based on a lean response delay time and a rich response delay time until a lean inversion and a rich inversion of the second detection signal of the O2 sensor, and the deterioration judgment value is compared with a deterioration set value. In some cases, the state of deterioration of the catalyst body is determined.

[0011]

SUMMARY OF THE INVENTION In order to eliminate the above-mentioned disadvantages, the present invention provides first exhaust passages respectively upstream and downstream of a catalyst provided in an exhaust passage of an internal combustion engine. An internal combustion engine having a sensor and a second exhaust sensor, and control means for performing feedback control so that the air-fuel ratio becomes a target value based on the first detection signal and the second detection signal output from the first exhaust sensor and the second exhaust sensor. In the engine, a lean response delay time and a rich response from the time when the first feedback control correction amount is reduced and increased by the rich inversion and the lean inversion of the first detection signal to the lean inversion and the rich inversion of the second detection signal. A rich / lean inversion time is calculated based on the delay time, and a first feedback is performed from the time of the rich inversion of the first detection signal and the time of the lean inversion. A correction determination delay time is calculated from the rich determination delay time and the lean determination delay time until the start and decrease of the correction amount and the cycle of the first feedback control correction amount, and the rich / lean inversion time and the correction delay time are calculated. A deterioration determination comparison value for a target feedback cycle is determined based on the determination delay time, and a determination function for comparing the deterioration determination comparison value with a predetermined deterioration determination value to determine a deterioration state of the catalyst body is added to the control means. It is characterized by being provided.

[0012]

According to the configuration of the present invention, the lean from the start of the decrease and the increase of the first feedback control correction amount due to the rich inversion and the lean inversion of the first detection signal to the lean inversion and the rich inversion of the second detection signal. A rich / lean inversion time is calculated based on the response delay time and the rich response delay time, and a rich determination delay time from the time of rich inversion of the first detection signal and the time of start of reduction and increase of the first feedback control correction amount from the time of rich inversion. A correction determination delay time is calculated based on the lean determination delay time and the cycle of the first feedback control correction amount, and a deterioration determination comparison value with respect to the target feedback cycle is calculated based on the rich / lean inversion time and the correction determination delay time. The deterioration state of the catalyst body is determined by comparing the deterioration determination comparison value with a preset deterioration determination value. , Even if there are variations in the output characteristics due to production and degradation of the first exhaust sensor, it is possible to reliably perform the deterioration determination of the catalyst body, it is possible to improve the accuracy of the deterioration determination of the catalyst body.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

FIGS. 1 to 11 show an embodiment of a catalyst deterioration judging device according to the present invention. In FIG. 2, 2
Denotes an internal combustion engine, 4 denotes an intake passage, and 6 denotes an exhaust passage. The intake passage 4 of the internal combustion engine 2 is formed by an air cleaner 8, an air flow meter 10, a throttle body 12, and an intake manifold 14 which are sequentially connected from the upstream side. The intake passage 4 in the throttle body 12 is provided with an intake throttle valve 16. The intake passage 4 is communicated with a combustion chamber 18 of the internal combustion engine 2.

The exhaust passage 6 communicating with the combustion chamber 18 of the internal combustion engine 2 includes an exhaust manifold 20, an upstream exhaust pipe 22, a catalytic converter 24, and a downstream exhaust pipe 26 which are sequentially connected from the upstream side. It is formed. A catalyst body 28 is provided in the exhaust passage 6 in the catalytic converter 24.

The internal combustion engine 2 is provided with a fuel injection valve 30 directed toward the combustion chamber 18. The fuel injection valve 30
The fuel supply passage 34 communicates with the fuel tank 36 via the fuel distribution passage 32. The fuel in the fuel tank 36 is pumped by a fuel pump 38 and a fuel filter 40
Then, the dust is removed, and the dust is supplied to the fuel distribution passage 32 by the fuel supply passage 34 and distributed to the fuel injection valve 30.

The fuel distribution passage 32 is provided with a fuel pressure adjusting section 42 for adjusting the fuel pressure. The fuel pressure adjusting unit 42 adjusts the fuel pressure to a constant value by the intake pressure introduced from the pressure guiding passage 44 communicating with the intake passage 4, and returns excess fuel to the fuel tank 36 through the fuel return passage 46.

The fuel tank 36 is provided with a passage 4 for the evaporated fuel.
8, a two-way valve 50 and a canister 52 are provided in communication with the intake passage 4 of the throttle body 12 in the middle of the evaporative fuel passage 48. The throttle body 12 is provided with a bypass passage 54 that bypasses the intake throttle valve 16, and an idle air amount control valve 56 is provided in the middle of the bypass passage 54. Reference numeral 58 denotes an air regulator, reference numeral 60 denotes a power steering switch, reference numeral 62 denotes an air amount control valve for power steering,
4 is a blow-by gas passage, and 66 is a PCV valve.

The air flow meter 10 and the fuel injection valve 3
The idle air amount control valve 56 and the power steering air amount control valve 62 are connected to a control unit 68 as control means. The control unit 68 includes a crank angle sensor 70,
The distributor 72, the opening degree sensor 74 of the intake throttle valve 16, the knock sensor 76, the water temperature sensor 78, and the vehicle speed sensor 80 are connected to each other. Note that reference numeral 8
Reference numeral 2 denotes an ignition coil, and reference numeral 84 denotes an ignition power unit.

In the internal combustion engine 2, a first O 2 sensor 8, which is an exhaust sensor for detecting an oxygen concentration as an exhaust component value, is provided in the exhaust passage 6 on the upstream side and the downstream side of the catalyst body 28, respectively.
6 and a second O2 sensor 88 are provided. These first O
The 2 sensor 86 and the second O2 sensor 88 are provided so as to be connected to the control section 68.

As shown in FIG. 3, the controller 68 controls the first O2
The operation of the fuel injection valve 30 is feedback-controlled based on the first detection signal and the second detection signal output from the sensor 86 and the second O2 sensor 88 so that the air-fuel ratio becomes a target value. Thereby, the exhaust gas purification efficiency by the catalyst body 28 is improved, and the emission harmful component value is reduced.

Reference numeral 90 denotes a dash pot, and reference numeral 9
2 is a thermofuse, 94 is an alarm relay, 96 is a warning light, 98 is a diagnosis switch,
100 is a TS switch, 102 is a diagnosis lamp, 104 is a main switch, 106
Is a battery.

The cycle of the first detection signal output from the first O 2 sensor 86 changes depending on the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 2. On the other hand, the second O2
The period of the second detection signal output by the sensor 88 is
8, the change is shorter at the time of the low purification rate in which the catalyst body 28 is deteriorated than at the time of the high purification rate of 8.

Therefore, it is desired to realize a catalyst deterioration determining apparatus which can accurately measure the deterioration state of the catalyst body 28 and accurately determines the deterioration state. Incidentally, the applicant of the present invention uses a period ratio (period ratio = TFR ÷ TRE) of the period TFR of the first detection signal and the period TRE of the second detection signal as one of the first detection signals as the catalyst deterioration determination device. A deterioration determination value is calculated based on an area ratio of the area SFR surrounded by the locus of the cycle TFR and the area SRE surrounded by the locus of one cycle TRE of the second detection signal (area ratio = SRE ÷ SFR). An application for judging the deterioration state of the catalyst body 28 has already been filed.

In the internal combustion engine 2 described above, the control section 68 is provided with a determination section 108 for calculating to determine the state of deterioration of the catalyst body 28.

The determination unit 108 performs a lean response from the time when the first feedback control correction amount FAF starts decreasing and increasing due to the rich inversion and the lean inversion of the first detection signal until the lean inversion and the rich inversion of the second detection signal. The rich time is determined by the delay time TRL and the rich response delay time TLR.
The lean inversion time TDLY is calculated, and the rich determination delay time DLR and the lean determination delay time DR from the rich inversion of the first detection signal and from the time of the lean inversion to the start of the decrease and the increase of the first feedback control correction amount FAF.
L and the period TFB of the first feedback control correction amount FAF
To calculate the correction determination delay time TFBa, and calculate the rich / lean inversion time TDLY and the correction determination delay time TFB.
The deterioration determination comparison value REKCAT with respect to the target feedback cycle TFBo is obtained from the value a, and the deterioration determination comparison value REKCAT is compared with a deterioration determination value REK that is a preset deterioration determination value to determine the deterioration state of the catalyst body 28. Things.

Next, the judgment by the catalyst deterioration judging device will be described with reference to FIG.

The internal combustion engine 2 is started to make a determination (step 20).
When 0) starts, a predetermined catalyst deterioration determination condition is read (step 202), and it is determined whether the catalyst deterioration determination condition is satisfied (step 204).

As shown in FIG. 4, the catalyst deterioration determination condition is that the condition is within a catalyst deterioration determination region set by the engine load Ec and the engine speed Ne, and that the internal combustion engine 2 has been completely warmed up. The intake air temperature is equal to or higher than a set value (intake air temperature ≧ set value), the first feedback control is being performed by the first O2 sensor 86, and at a constant speed (intake air amount, throttle valve opening, fuel injection amount) , The amount of change in the engine load Ec such as the intake pressure is equal to or less than a set value).

In the above judgment (step 204), if either one is not satisfied and the judgment is NO, the process returns to the reading of the catalyst deterioration judgment condition (step 202). In the above judgment (step 204), if all are satisfied and YE
In the case of S, the first feedback control correction amount FAF is increased for catalyst deterioration determination (step 206).

The first feedback control correction amount FAF for determining catalyst deterioration is set to a value corresponding to the state of deterioration of the catalyst body 28 at this time or a value set in the control unit 68 in advance. This is because, as shown in FIG. 6, by increasing the value of the first feedback control correction amount FAF, which is the air-fuel ratio feedback (F / B) correction amount at the time of catalyst deterioration determination, the measurement variation of the rich / lean inversion time TDLY described later is performed. This is because (ΔTDLYAV) can be reduced, and the accuracy of the determination can be improved.

Next, as shown in FIG. 5, the period TFB of the first feedback control correction amount FAF, and the start and decrease of the first feedback control correction amount FAF due to rich inversion and lean inversion of the first detection signal. And the rich / lean inversion time TDLY, which is the average of the lean response delay time TRL and the rich response delay time TLR from the time when the second detection signal reaches the lean inversion and the rich inversion, and the air amount GA
Is measured (step 208), and the difference ΔTF
B (TFB-TFBNEW) is obtained (step 210),
Rich / lean inversion time TD when period TFB is constant
To measure LY, ΔTFB is equal to the ΔTFB determination value (TF
K) to determine whether they are less than (Step 21)
2) Do it. The ΔTFB determination value (TFK) is determined by the controller 6
8 is set.

In the cycle TFB, the first cycle TFB is set to TFB = TFB1, and the second and subsequent cycles TFB are set to TF
As B = (previous TFB + TFBn) ÷ 2, a final cycle TFB is obtained.

The rich / lean inversion time TDL
As shown in FIG. 5, Y is obtained by calculating the lean response delay time TRL and the rich response delay time TLR of the second O2 sensor 88 by the equation of TDLY = (TRL + TLR) / 2.

In the determination (step 212), Δ
If the TFB is equal to or larger than the TFB (ΔTFB ≧ TFK) and is NO, the N-time measurement counter is cleared to 0, and the process returns to the reading of the catalyst deterioration determination condition (step 202). In step (212), if ΔTFB is less than TTK (ΔTFB <TFK) and the result is YES, it is determined whether or not the measurement has been completed N times (step 214).

In the determination (step 214), N
In the case of O, the catalyst deterioration determination condition is read (step 20).
Return to 2). In the above (Step 214), in the case of YES, the average of the final cycle TFB and the rich / lean inversion time TDLY / air amount GA measured N times is calculated to obtain TDLYAV / GAAV (Step 216).

Then, the first feedback control correction amount F
The first feedback control correction amount FAF from the time of rich inversion of the first detection signal and the time of lean inversion from the AF cycle TFB.
Judgment delay time DL until the start of the decrease and the start of the increase
R and the lean determination delay time DRL are subtracted to obtain a correction determination delay time TFBa. As shown in FIG. 7, the target feedback cycle (deterioration) is determined by the relationship between the average TDLYAV of the rich / lean inversion time TDLY and the correction determination delay time TFBa. Determination) A correction coefficient FBK for TFBo is obtained. The correction determination delay time TFBa is calculated using this correction coefficient FB.
Correction is performed by K, and a deterioration determination comparison value REKCAT is calculated. That is, the average TDLYAV of the rich / lean inversion time TDLY is calculated as REKCAT = TDLYAV +
Correction is made by the formula of (TFBo-TFB) × FBK to obtain a deterioration determination comparison value REKCAT (step 218).
At this time, the air amount GA and the target feedback cycle TFBo in the equation have a relationship as shown in FIG.

As shown in FIG. 9, the determination of the deterioration state of the catalyst body 28 is made based on the deterioration determination comparison value REKCAT at the time of the target feedback cycle (for deterioration determination) TFBo according to the air amount GA (GAAV). The deterioration determination comparison value REKCAT is compared with a deterioration determination value (set value) REK preset in the control unit 68 to perform the determination (step 220), and the deterioration determination comparison value REKCAT is determined.
Is less than or equal to the set value REK (step 22).
2) Do it.

In this determination (step 222), the deterioration determination comparison value REKCAT exceeds the set value REK (REK
If CAT> REK) is NO, the engine is not deteriorated, and the determination of the deteriorated state is prohibited until the internal combustion engine 2 is stopped (step 226), and the operation ends (step 228).

In the above determination (step 222), the deterioration determination comparison value REKCAT is equal to or less than the set value REK (REK).
When CAT ≦ REK) is YES, the catalyst is deteriorated, so it is determined that the catalyst body 28 is deteriorated, and a warning means (not shown) such as a warning lamp is activated to issue a warning (step 224). Thereafter, the determination of the deterioration state is prohibited until the internal combustion engine 2 is stopped (step 226), and the process ends (step 228).

In addition, when the first O2 sensor 86 is in rich inversion and lean inversion, the first feedback control correction amount F
It changes according to the change in the air-fuel ratio due to the increase and decrease of AF.

Therefore, the rich inversion delay time and the lean inversion delay time from the rich inversion and lean inversion of the first O2 sensor 86 to the rich inversion and lean inversion of the second O2 sensor 88 include the production variation of the first O2 sensor 86 and the lean inversion delay time. A change in output characteristics due to use deterioration, particularly a change in response time, will be included. Therefore, the first O2
Since the variation in the output characteristics of the sensor 86 falls within the measurement time of the rich / lean inversion time TDLY,
There is a disadvantage that the rich / lean inversion time TDLY varies.

Therefore, the rich / lean inversion time TDLY
Is the lean inversion of the second detection signal output from the second O2 sensor 88 from the time when the first feedback control correction amount FAF starts decreasing and increasing due to the rich inversion and lean inversion of the first detection signal output from the first O2 sensor 86. By setting the lean response delay time TRL and the rich response delay time TLR until the rich inversion, the first O2 sensor 86
Of output characteristics of the device is rich / lean inversion time TDL
The measurement time of Y does not enter.

However, if the rich / lean inversion time TDLY is obtained based only on the lean response delay time TRL and the rich response delay time TLR of the second O2 sensor 88, the first detection signal is obtained from the rich inversion and the lean inversion from the lean inversion. There is a disadvantage that the rich / lean inversion time TDLY varies due to the rich determination delay time DLR and the lean determination delay time DRL until the start and decrease of the one feedback control correction amount FAF.

For this reason, the first feedback control correction amount FAF due to the rich inversion and the lean inversion of the first detection signal.
The rich / lean inversion time TDLY is calculated from the lean response delay time TRL and the rich response delay time TLR from the start of the decrease and the start of the increase to the lean inversion and rich inversion of the second detection signal, and the richness of the first detection signal is calculated. Correction determination delay based on the rich determination delay time DLR and lean determination delay time DRL from the time of inversion and lean inversion to the start and decrease of the first feedback control correction amount FAF, and the period TFB of the first feedback control correction amount FAF. A time TFBa is calculated, and a deterioration determination comparison value REKCAT with respect to the target feedback cycle TFBo is obtained from the rich / lean inversion time TDLY and the correction determination delay time TFBa.
T and a deterioration determination value REK which is a predetermined deterioration determination value
To determine the state of deterioration of the catalyst body 28, the first O 2 provided in the exhaust passage 6 on the upstream side of the catalyst body 28.
The catalyst body 28 due to production variation and use deterioration of the sensor 86
The influence on the determination of the deterioration state of
The rich / lean inversion time TDLY can be correlated with the period TFB of the feedback control correction amount FAF.

Thus, the correction determination delay time TFBa
Is not affected by the first O2 sensor 86 at all, it is possible to prevent the variation in the accuracy of the determination of the deterioration state of the catalyst body 28 from increasing, and to improve the accuracy of the determination of the deterioration state. The problem of not being able to report abnormalities even though the function is normal, avoiding the inconvenience of inconvenient confusion, and improving reliability, as well as the inconvenience of discharging large quantities of unpurified exhaust gas to the atmosphere can be avoided. Can be avoided.

It should be noted that the present invention is not limited to the above-described embodiment, and various application modifications are possible.

For example, in the embodiment of the present invention, control is performed to calculate the correction determination delay time using the cycle of the first feedback control correction amount. It is also possible to calculate the correction determination delay time by using this.

[0049]

As described above in detail, according to the present invention, the lean inversion of the second detection signal is started from the start of the decrease and the increase of the first feedback control correction amount due to the rich inversion and the lean inversion of the first detection signal. And the rich / lean inversion time is calculated from the lean response delay time up to the rich inversion and the rich response delay time, and the decrease and start of the first feedback control correction amount from the rich inversion of the first detection signal and from the lean inversion. The correction judgment delay time is calculated based on the rich judgment delay time and the lean judgment delay time up to and the cycle of the first feedback control correction amount, and the deterioration judgment for the target feedback cycle is calculated based on the rich / lean inversion time and the correction judgment delay time. A comparison value is obtained, and this deterioration determination comparison value is compared with a preset deterioration determination value to determine By providing a judgment function for judging the deterioration state in addition to the control means, even if the output characteristics of the first exhaust sensor vary due to production and deterioration, it is possible to reliably judge the deterioration of the catalyst body. In addition, the accuracy of the catalyst body deterioration determination can be improved, which is practically advantageous.

[Brief description of the drawings]

FIG. 1 is a flowchart of a determination by a catalyst deterioration determination device for an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a catalyst deterioration determination device.

FIG. 3 is a block diagram of a catalyst deterioration determination device.

FIG. 4 is an explanatory diagram of a catalyst deterioration determination region.

FIG. 5 is a diagram showing an output waveform of a first O2 sensor, a waveform of a first feedback control correction amount, and an output waveform of a second O2 sensor.

FIG. 6 is a diagram illustrating a relationship between a first feedback control correction amount and a deterioration determination value.

FIG. 7 is a diagram showing a relationship between a cycle of a first feedback control correction amount and a correction determination delay time.

FIG. 8 is a diagram illustrating a relationship between a target feedback cycle for deterioration determination and an air amount.

FIG. 9 is a diagram illustrating a relationship between a deterioration determination comparison value and an air amount.

FIG. 10 is a diagram illustrating a relationship between a physical delay time due to an exhaust system and an air amount.

FIG. 11 is a diagram showing a relationship between a delay time due to a catalyst and an air amount.

[Explanation of symbols]

 2 Internal combustion engine 4 Intake passage 6 Exhaust passage 24 Catalytic converter 28 Catalyst 30 Fuel injection valve 68 Control unit 86 First O2 sensor 88 Second O2 sensor 108 Judgment unit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-212955 (JP, A) JP-A-6-129294 (JP, A) JP-A-6-129285 (JP, A) JP-A-6-129285 81632 (JP, A) JP-A-6-81633 (JP, A) JP-A-6-146865 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 3/20 F02D 41 / 14 F02D 45/00

Claims (1)

(57) [Claims] A first exhaust sensor and a second exhaust sensor are provided in an exhaust passage upstream and downstream of a catalyst body provided in an exhaust passage of an internal combustion engine, respectively, and the first exhaust sensor and the second exhaust sensor are provided. The internal combustion engine provided with control means for performing feedback control so that the air-fuel ratio becomes a target value based on the first detection signal and the second detection signal output from the first and second detection signals.
The rich response is determined by the lean response delay time and the rich response delay time from the start of the decrease and the increase of the first feedback control correction amount due to the rich inversion and lean inversion of the detection signal to the lean inversion and rich inversion of the second detection signal.
A lean inversion time is calculated , and a rich determination delay time and a lean determination delay time from a rich inversion of the first detection signal and a lean inversion to a start of decrease and an increase of the first feedback control correction amount and the first feedback. The correction determination delay time is calculated based on the cycle of the control correction amount, and the deterioration determination ratio with respect to the target feedback cycle is calculated based on the rich / lean inversion time and the correction determination delay time.
Seeking較値, internal combustion engine, characterized in that a determination function state of deterioration of comparing the degradation determination value previously set as the deterioration judgment comparison value the catalyst is provided in addition to the control means Device for determining catalyst deterioration.