CN115244283A

CN115244283A - Catalyst deterioration diagnosis device

Info

Publication number: CN115244283A
Application number: CN202080097947.2A
Authority: CN
Inventors: 藤田晋二
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 2020-03-05
Filing date: 2020-03-05
Publication date: 2022-10-25
Anticipated expiration: 2040-03-05
Also published as: JP7372440B2; WO2021176671A1; CN115244283B; JPWO2021176671A1; BR112022017146A2

Abstract

Provided is a catalyst degradation diagnosis device capable of detecting the degree of degradation of a catalyst device by 1 oxygen concentration sensor. The catalyst degradation diagnosis device includes: an oxygen concentration sensor (90) provided on the downstream side of a catalyst (C) provided in an exhaust pipe (19) of an engine (E); and a control unit (100) that diagnoses the degree of degradation of the catalyst (C) based on the output signal of the oxygen concentration sensor (90), wherein the catalyst degradation diagnosis device is provided with a perturbation mechanism (105), and the perturbation mechanism (105) performs a perturbation process of alternately shifting the air-fuel ratio of the air-fuel mixture supplied to the engine (E) to a target air-fuel ratio that is set to the rich side and the lean side of the stoichiometric air-fuel ratio. A control unit (100) estimates and detects the air-fuel ratio upstream of the catalyst (C) based on the target air-fuel ratio and the output signal of the oxygen concentration sensor (90) during the perturbation process.

Description

Catalyst deterioration diagnosis device

Technical Field

The present invention relates to a catalyst deterioration diagnosis device, and more particularly, to a catalyst deterioration diagnosis device that detects a degree of deterioration of a catalyst device provided in an exhaust pipe of an engine.

Background

A catalyst deterioration diagnosis device that detects a degree of deterioration of a catalyst device provided in an exhaust pipe of an engine is known in the related art.

Patent document 1 discloses the following configuration: an oxygen concentration sensor is disposed on the upstream side and the downstream side of the catalyst device, and the degree of degradation of the catalyst device is detected based on a change in the output signal of the oxygen concentration sensor when the air-fuel ratio is switched between the rich side and the lean side.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2007-285288

Disclosure of Invention

Problems to be solved by the invention

However, in the configuration of patent document 1, since 2 oxygen concentration sensors are required and the cost is high, a configuration in which the catalyst degradation degree is executed by 1 oxygen concentration sensor is sought.

The present invention has an object to solve the above problems of the prior art and to provide a catalyst degradation diagnosis device capable of detecting the degree of degradation of a catalyst device with 1 oxygen concentration sensor.

Means for solving the problems

In order to achieve the above object, a 1 st aspect of the present invention is a catalyst deterioration diagnosis device including: an oxygen concentration sensor (90) provided on the downstream side of a catalyst (C) provided in an exhaust pipe (19) of an engine (E); and a control unit (100) that diagnoses a degree of deterioration of the catalyst (C) based on an output signal of the oxygen concentration sensor (90), wherein the catalyst deterioration diagnosis device is characterized by comprising a perturbation mechanism (105), the perturbation mechanism (105) performing a perturbation process of alternately shifting an air-fuel ratio of a mixture gas supplied to the engine (E) to a target air-fuel ratio, the target air-fuel ratio being set to a rich side and a lean side of a theoretical air-fuel ratio, and the control unit (100) estimating and detecting an air-fuel ratio on an upstream side of the catalyst (C) based on the target air-fuel ratio and the output signal of the oxygen concentration sensor (90) during the perturbation process.

In addition, in the case of the 2 nd aspect, when the theoretical air-fuel ratio is 14.5, the coefficient indicating the degree of transition to the rich side or the lean side in the perturbation process for detecting the degree of degradation is K, and the correction coefficient determined from the target air-fuel ratio and the output signal of the oxygen concentration sensor (90) is H, AFR, which is the air-fuel ratio on the upstream side of the catalyst (C), is obtained by the following equation: AFR =14.5 ÷ K × H.

In addition, in the 3 rd aspect, the correction coefficient is calculated by performing PID control for a deviation of the target air-fuel ratio from the output signal of the oxygen concentration sensor (90).

In the case of claim 4, where the amount of air per 1 cycle is GAIR, O2, which is the amount of oxygen flowing into the catalyst (C) upstream of the catalyst, is obtained by the following equation: o2= GAIR × (1-14.5 ÷ AFR).

Further, in the 5 th aspect, the control portion (100) calculates the oxygen adsorption capacity of the catalyst (C) by accumulating the amount of inflow oxygen, and diagnoses the state of degradation of the catalyst (C).

ADVANTAGEOUS EFFECTS OF INVENTION

According to the 1 st aspect, the catalyst deterioration diagnosis device has: an oxygen concentration sensor (90) provided on the downstream side of a catalyst (C) provided in an exhaust pipe (19) of an engine (E); and a control unit (100) that diagnoses the degree of deterioration of the catalyst (C) based on an output signal of the oxygen concentration sensor (90), wherein the catalyst deterioration diagnosis device is characterized by being provided with a perturbation mechanism (105), the perturbation mechanism (105) performing perturbation processing for alternately shifting the air-fuel ratio of a mixture gas supplied to the engine (E) to a target air-fuel ratio, wherein the target air-fuel ratio is set to a rich side and a lean side of a theoretical air-fuel ratio, and the control unit (100) can detect the degree of deterioration of the catalyst by only 1 oxygen concentration sensor provided on the downstream side of the catalyst by estimating and detecting the air-fuel ratio on the upstream side of the catalyst (C) based on the target air-fuel ratio and the output signal of the oxygen concentration sensor (90) during the perturbation processing.

According to the second aspect of the present invention, when the stoichiometric air-fuel ratio is 14.5, the coefficient indicating the degree of transition to the rich side or the lean side in the perturbation process for detecting the degree of degradation is K, and the correction coefficient determined from the target air-fuel ratio and the output signal of the oxygen concentration sensor (90) is H, AFR, which is the air-fuel ratio on the upstream side of the catalyst (C), is obtained by the following equation: AFR =14.5 ÷ K × H, the air-fuel ratio on the catalyst upstream side can be calculated by a simple equation.

According to claim 3, the correction coefficient is calculated by PID control of the deviation between the target air-fuel ratio and the output signal of the oxygen concentration sensor (90), and thus the correction coefficient can be calculated using a normal feedback process.

According to the 4 th aspect, when the amount of air per 1 cycle is GAIR, O2, which is the amount of oxygen flowing into the upstream side of the catalyst (C), is obtained by the following equation: o2= GAIR × (1-14.5 ÷ AFR), whereby the amount of oxygen flowing into the upstream side of the catalyst can be calculated by a simple calculation formula.

According to the 5 th aspect, the control portion (100) calculates the oxygen adsorption capacity of the catalyst (C) by accumulating the amount of inflow oxygen, and diagnoses the degradation state of the catalyst (C), whereby the degree of degradation of the catalyst can be detected only by 1 oxygen concentration sensor provided on the downstream side of the catalyst.

Drawings

Fig. 1 is a left side view of a motorcycle as a saddle-ride type vehicle according to an embodiment of the present invention.

Fig. 2 is a sectional view of an enlarged diameter portion provided midway in the exhaust pipe.

Fig. 3 is a schematic diagram showing the relationship of the engine and the oxygen concentration sensor.

Fig. 4 is a block diagram showing a configuration of a control unit that performs degradation diagnosis of the catalyst device.

Fig. 5 is a diagram illustrating the responsiveness before and after deterioration of the catalyst device.

Fig. 6 is a timing chart when the deterioration diagnosis is performed on the deteriorated catalyst device.

Fig. 7 is a timing chart when the deterioration diagnosis is performed on the catalyst device before deterioration.

Detailed Description

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Fig. 1 is a left side view of a motorcycle 1 as a saddle-ride type vehicle according to an embodiment of the present invention. A head pipe 12 that rotatably supports a steering system 10 is attached to a front end of a body frame 2 of a motorcycle 1 as a saddle-ride type vehicle. A steering handle 6 is attached to an upper end of the steering system 10 via a roof rail, not shown. A top beam that rotates integrally with the steering system 10 supports a pair of left and right front forks 16 together with a bottom beam, not shown, that is fixed to the steering system 10 at a lower portion of the head pipe 12. The front wheel WF having the brake disk 35 is rotatably supported by the lower end of the front fork 16.

A parallel two-cylinder engine E in which the lower portion of a cylinder head 18 is supported by a hanger 17 extending downward from the rear of the head pipe 12 is disposed at the lower portion of the vehicle body frame 2. A generator cover Ea and a drive sprocket cover Eb are attached to the left side of the engine E in the vehicle width direction. A radiator 15 for engine cooling water is disposed in front of hanger 17.

The vehicle body frame 2 supports the engine E at an upper portion and a rear portion of the engine E, and pivotally supports a swing arm 24 by a pivot shaft 21 so as to be swingable. Pedals 23 for the driver are provided in pairs on the left and right sides below a pivot plate 21a that pivotally supports the pivot shaft 21, and foldable rider pedals 21b are arranged on a pedal bracket 21c on the rear and upper side thereof. Further, a main stand 22 for allowing the rear wheel WR of the motorcycle 1 to freely stand in an air-floating manner during parking and a side stand 140 for allowing the vehicle body to freely stand with inclination to the left are attached below the step plate 23. The main stand 22 and the side stand 140 are in the stored state by being swung substantially 90 degrees to the vehicle body rear side.

An exhaust device 20 for purifying and silencing exhaust gas from the engine E and discharging the exhaust gas rearward is attached to a lower portion of the motorcycle 1. The exhaust device 20 includes an exhaust pipe 19 connected to an exhaust port of the cylinder block and guiding exhaust gas rearward, and a muffler 26 connected to a rear end of the exhaust pipe 19. An exhaust pipe cover 5a for covering the front and side of the exhaust pipe 19 is disposed in front of and below the cylinder head 18. The swing arm 24 pivotally supported by the pivot shaft 21 is suspended from the vehicle body frame 2 by a rear cushion portion not shown. The driving force of the engine E is transmitted to a rear wheel WR rotatably supported at the rear end of the swing arm 24 via a drive chain 25.

A storage box 4 that protrudes from the large opening/closing cover 3 is provided above the engine E and at a position covered with a side cowl 5 as an exterior member. A headlight 13 is disposed in front of the side cowl 5, and a pair of left and right flashers 11 and a windshield 9 are disposed above the headlight 13. A joint cover 8 and a mirror 7 are attached to the left and right steering grips 6. A pair of left and right fog lamps 14 are attached to the lower portion of the side cowl 15 and at positions outside the front fork 16 in the vehicle width direction, and a front fender 36 for preventing splash or the like of the vehicle body is attached above the front wheel WF.

A rear frame 29 that supports a fuel tank 28 and the like is attached to the rear of the vehicle body frame 2. The rear frame 29 is covered on the left and right sides with seat covers 31, and a driver seat 27 and a passenger seat 30 are disposed on the upper portion thereof. A tail lamp device 32 is attached to the rear end of the seat cover 31, and a rear flasher 33 is supported by a rear fender 34 extending rearward and downward from the seat cover 31.

Fig. 2 is a sectional view of the enlarged diameter portion 61 provided in the middle of the exhaust pipe 19. The catalyst device C is housed in the diameter-enlarged portion 61, and the air-fuel ratio sensor 80 is disposed behind the catalyst device C. The diameter-enlarged portion 61 is configured to hold the catalyst C inside the front outer cylinder 76 via a spacer 75, and to weld and fix the catalyst C and the rear end portion of the front outer cylinder 76 to the outer peripheral surface of the funnel-shaped rear outer cylinder 78 by a weld B. The air-fuel ratio sensor 90 is screwed and held to a pedestal 86 as a mount base, and the pedestal 86 is welded and fixed to the rear outer tube 78.

The air-fuel ratio sensor 90 can employ a LAF sensor capable of linearly detecting a change in oxygen concentration or an O2 sensor that detects only a case at the stoichiometric air-fuel ratio by reversing an output value bounded by the stoichiometric air-fuel ratio. The oxygen concentration sensor 90 may be a sensor with a heater that achieves optimal temperature management by the heater controlled by the control unit 100.

Fig. 3 is a schematic diagram showing the relationship of the engine E and the oxygen concentration sensor 90. The exhaust device 20 has an oxygen concentration sensor 90 located on the downstream side of the catalyst device C. An injector 57 as a fuel injection device is provided in an intake pipe 56 of the engine E, and an intake air amount sensor 55 is disposed upstream thereof. The sensor signal of the intake air amount sensor 55 is input to the air amount detection portion 58. The injector control section 59 controls the injector 57 based on signals from the air amount detection section 58 and the control section 100 in addition to information on the throttle operation and the engine speed, and performs combustion at an appropriate air-fuel ratio.

In general, the deterioration diagnosis of the catalyst device C is performed by 2 sensors, that is, an oxygen concentration sensor disposed on the upstream side of the catalyst device C and an oxygen concentration sensor disposed on the downstream side of the catalyst device C. Specifically, the change accompanying the deterioration of the catalyst device C is detected by focusing attention on the relationship between the sensor output of the upstream oxygen concentration sensor and the sensor output of the downstream oxygen concentration sensor. For example, in a method focusing on a decrease in the adsorption rate of oxygen associated with deterioration of the catalyst device C, when the air-fuel ratio is feedback-controlled based on the output of the downstream oxygen concentration sensor, the response time until the oxygen concentration in the exhaust gas changes due to the feedback control changes under the influence of the deterioration, and therefore the deterioration state of the catalyst can be determined by determining whether or not the change cycle of the output of the downstream oxygen concentration sensor corresponds to a predetermined catalyst deterioration condition. Specifically, a counting method of counting the number of times the downstream oxygen concentration sensor changes a predetermined amount within a predetermined time can be used.

Such degradation diagnosis processing involves performing perturbation processing for alternately shifting the air-fuel ratio of the internal combustion engine to the rich side and the lean side. Specifically, deterioration of the catalyst device C is detected by repeating the following operations: during the period from when the air-fuel ratio is switched to the lean side until the value of the downstream-side oxygen concentration sensor reaches a predetermined value, whether or not the accumulated oxygen amount exceeds a threshold value is observed using the upstream-side oxygen concentration sensor, and then during the period from when the air-fuel ratio is switched to the rich side until the value of the downstream-side oxygen concentration sensor reaches the predetermined value, whether or not the accumulated oxygen amount exceeds the threshold value is observed using the upstream-side oxygen concentration sensor. In the case of performing such perturbation processing, although accumulation is possible in the normal catalyst device C, the lean operation is performed so as to supply oxygen in an amount that cannot be accumulated in the degraded catalyst device C, and then the rich operation is performed by switching to the rich operation so as to release substantially all of the accumulated oxygen. As described above, although the output of the oxygen concentration sensor 90 is not substantially changed if the catalyst device C is not deteriorated, the output of the oxygen concentration sensor 90 is increased when the catalyst device C is deteriorated, and deterioration diagnosis can be performed.

In the present embodiment, since there is no oxygen concentration sensor on the upstream side of the catalyst device C, the oxygen concentration on the upstream side of the catalyst device C is estimated and detected based on the output of the downstream oxygen concentration sensor, and the deterioration diagnosis of the catalyst device C is performed based on the estimated and detected value.

Fig. 4 is a block diagram showing the configuration of the control unit 100 that performs degradation diagnosis of the catalyst device C. The control unit 100 includes a perturbation mechanism 105, a pre-catalyst air-fuel ratio calculation unit 101, a pre-catalyst oxygen amount calculation unit, a pre-catalyst oxygen amount accumulation unit 103, and a catalyst diagnosis unit 104. The output signal of the oxygen concentration sensor 90 is input to the pre-catalyst air-fuel ratio calculation portion 101. Further, the output signal of the air quantity sensor 58 is input to the pre-catalyst oxygen quantity calculation portion 102. The catalyst diagnosis unit 104 is configured to notify the occupant of the deterioration of the catalyst device C by using the indicator 74 provided in the instrument device or the like.

The perturbation mechanism 105 executes perturbation processing for shifting the air-fuel ratio of the internal combustion engine to the rich side and the lean side. The pre-catalyst air-fuel ratio calculation unit 101 obtains AFR, which is an air-fuel ratio on the upstream side of the catalyst device C, by an equation of AFR =14.5 ÷ K × H.

Fig. 5 is a diagram illustrating the responsiveness of the catalyst device C before and after degradation. The catalyst device C after deterioration has a lower purification rate and a lower oxygen storage capacity than the catalyst device C before deterioration, and thus the response of the oxygen concentration sensor 90 disposed downstream of the catalyst becomes faster. As described above, the perturbation process repeats the following operations: if the catalyst device C is normal, accumulation is possible, and if the catalyst device C is degraded, the lean operation is performed so that oxygen is supplied in an amount that the accumulation is not possible, and then the operation is switched to the rich operation, and the rich operation is performed so that substantially all of the accumulated oxygen is released. If the perturbation process is executed, the following difference occurs: the output of the oxygen concentration sensor 90 is substantially unchanged before the catalyst device C is degraded, and the output of the oxygen concentration sensor 90 is increased after the degradation.

Fig. 6 is a timing chart when the deterioration diagnosis is performed on the deteriorated catalyst device C. Fig. 7 is a timing chart when the deterioration diagnosis is performed on the catalyst device C before deterioration. In the two time charts, the estimated air-fuel ratio on the upstream side of the catalyst device C (solid line), the target air-fuel ratio (solid line), the air-fuel ratio on the downstream side of the catalyst based on the oxygen concentration sensor 90 (two-dot chain line), a coefficient indicating the degree of transition to the rich side or the lean side in the perturbation process for detecting the degree of degradation (solid line), a correction coefficient H (broken line) determined from the target air-fuel ratio and the output signal of the oxygen concentration sensor 90, the oxygen storage capacity at the time of rich indication (OSR), the oxygen storage capacity at the time of rich indication (OSL) (solid line), and the amount of O2 (one-dot chain line) as the amount of inflow oxygen on the upstream side of the catalyst device C are shown from top to bottom. In the present embodiment, the deviation between the target air-fuel ratio and the air-fuel ratio on the downstream side of the catalyst obtained by the oxygen concentration sensor 90, and the 3 elements of the integral and the derivative thereof are used. Since the air-fuel ratio on the downstream side of the catalyst obtained by the oxygen concentration sensor 90 before degradation greatly deviates from the target air-fuel ratio, if the correction coefficient H is increased to adjust the deviation, the air-fuel ratio on the downstream side of the catalyst obtained by the oxygen concentration sensor 90 overshoots. The NG catalyst after degradation follows the air-fuel ratio on the downstream side of the catalyst obtained by the oxygen concentration sensor 90 to the target air-fuel ratio faster than the new catalyst before degradation and does not overshoot.

The AFR, which is the air-fuel ratio on the upstream side of the catalyst device C, is obtained by an equation of AFR =14.5 ÷ K × H. At this time, 14.5: theoretical air-fuel ratio, K: coefficient indicating the degree of transition to the rich side or the lean side in the perturbation process for detecting the degree of degradation, H: a correction coefficient determined by the output signal of the target air-fuel and oxygen concentration sensor 90.

Specifically, at t = a in fig. 6, K =1.025, H =0.99, when indicated as 2.5% rich in perturbation processing. The correction coefficient H is calculated by PID control for deviation from the target air-fuel ratio. This enables the correction coefficient to be calculated using normal feedback processing.

Thus, AFR =14.5 ÷ 1.025 × 0.99=14.005.

On the other hand, at time B of fig. 6, when the 2.5% lean of the perturbation process indicates, K =0.975, H =1.01. Thus, AFR =14.5 ÷ 0.975 × 1.01=15.02. Thus, the air-fuel ratio on the upstream side of the catalyst device C is calculated by the equation AFR =14.5 ÷ K × H.

Next, the pre-catalyst oxygen amount calculation unit 102 obtains O2 as the inflow oxygen amount on the upstream side of the catalyst device C by an equation of O2= GAIR × (1-14.5 ÷ AFR). At this time, GAIR: air amount per 1 cycle.

Specifically, at time a of fig. 6, at AGAIR:1mg and 2.5% rich in perturbation treatment, at AFR:14.005, O2=1 × (1-14.5 ÷ 14.005) = -0.0353mg (negative for reduction in oil-rich).

On the other hand, at time B of fig. 6, at the time of 2.5% lean indication of perturbation processing and AFR:15.02, O2=1 × (1-14.5 ÷ 15.02) =0.0346mg. Thus, the amount of oxygen flowing into the upstream side of the catalyst device C was calculated by the formula O2= GAIR × (1-14.5 ÷ AFR).

The pre-catalyst oxygen amount accumulation unit 103 accumulates the calculated amount of the inflow oxygen to determine the oxygen storage capacity (OSR) at the time of the rich instruction and the oxygen storage capacity (OSL) at the time of the rich instruction, and diagnoses the deterioration of the catalyst device C.

As described above, the catalyst degradation diagnosis device according to the present invention includes: an oxygen concentration sensor 90 provided on the downstream side of a catalyst device C provided in an exhaust pipe 19 of the engine E; and a control unit 100 that diagnoses a degree of deterioration of the catalyst device C based on an output signal of the oxygen concentration sensor 90, the catalyst deterioration diagnosis device including a perturbation mechanism 105, the perturbation mechanism 105 performing a perturbation process of alternately shifting an air-fuel ratio of a mixture gas supplied to the engine E to a target air-fuel ratio set to a rich side and a lean side of a stoichiometric air-fuel ratio, the control unit 100 estimating and detecting the air-fuel ratio on an upstream side of the catalyst device C based on the target air-fuel ratio and the output signal of the oxygen concentration sensor 90 during the perturbation process, and thus being capable of detecting the degree of deterioration of the catalyst device C using only 1 oxygen concentration sensor 90 provided on a downstream side of the catalyst device.

The form of the motorcycle, the shape and structure of the catalyst device and the oxygen concentration sensor, the configuration of the control unit, the transition concentration in the perturbation process, and the like are not limited to the above-described embodiments, and various modifications are possible. The catalyst deterioration diagnosis device of the present invention can be applied to various internal combustion engines having a catalyst device and an oxygen concentration sensor.

Description of the reference numerals

1 … motorcycle, 19 … exhaust pipe, 74 … indicator, 90 … oxygen concentration sensor, 100 … control unit, 101 … pre-catalyst air-fuel ratio calculation unit, 102 … pre-catalyst oxygen amount calculation unit, 103 … pre-catalyst oxygen amount accumulation unit, 104 … catalyst diagnosis unit, 32105 zxft 3272 perturbation mechanism, E … engine, C … catalyst device, air-fuel ratio on the rich side of AFR … catalyst device, coefficient for shifting degree to the rich side or lean side in perturbation processing, H …, correction coefficient determined by output signals of target air-fuel ratio and oxygen concentration sensor, O2 zxft 6223 exhaust pipe, and air amount per cycle of flow rate per gaxft of ir 621 cycle of air flowing into the catalyst.

Claims

1. A catalyst degradation diagnosis device includes:

an oxygen concentration sensor (90) provided on the downstream side of a catalyst (C) provided in an exhaust pipe (19) of an engine (E); and a control unit (100) that diagnoses a degree of deterioration of the catalyst (C) based on an output signal of the oxygen concentration sensor (90), the catalyst deterioration diagnosis device being characterized in that,

a perturbation means (105) for performing perturbation processing for alternately shifting the air-fuel ratio of the mixture gas supplied to the engine (E) to a target air-fuel ratio set to the rich side and the lean side of the theoretical air-fuel ratio,

the control unit (100) estimates and detects the air-fuel ratio upstream of the catalyst (C) based on the target air-fuel ratio and the output signal of the oxygen concentration sensor (90) during the perturbation process.

2. The catalyst degradation diagnostic device according to claim 1,

when a theoretical air-fuel ratio is 14.5, a coefficient indicating a degree of transition to a rich side or a lean side in a perturbation process for detecting a degree of degradation is K, and a correction coefficient determined from the target air-fuel ratio and an output signal of the oxygen concentration sensor (90) is H, AFR, which is an air-fuel ratio on the upstream side of the catalyst (C), is obtained by the following equation:

AFR＝14.5÷K×H。

3. the catalyst degradation diagnosis device according to claim 2,

the correction coefficient is calculated by performing PID control for a deviation of the target air-fuel ratio from the output signal of the oxygen concentration sensor (90).

4. The catalyst degradation diagnosis device according to claim 2 or 3,

when the amount of air per 1 cycle is GAIR, O2, which is the amount of oxygen flowing into the upstream side of the catalyst (C), is obtained by the following equation:

O2＝GAIR×(1-14.5÷AFR)。

5. the catalyst degradation diagnostic device according to claim 4,

the control portion (100) calculates the oxygen adsorption capacity of the catalyst (C) by accumulating the amount of inflow oxygen, and diagnoses the state of degradation of the catalyst (C).