JP2012211561A - Degradation determination device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a degradation determination device for performing degradation determination of a catalyst converter and a rear air-fuel-ratio sensor with higher accuracy and preventing incorrect determination thereof from being performed.SOLUTION: The degradation determination device includes a degradation determination means which includes a fuel supply stop means including the catalyst converter for purifying exhaust gas from an internal combustion engine and the rear air-fuel-ratio sensor disposed on the downstream side of the catalyst converter, and stopping fuel supply to the internal combustion engine, a response time measurement means for measuring response time of the rear air-fuel-ratio sensor, and a response time tendency calculation means for checking response time tendency, and which determines a response time from a stop of fuel supply until the rear air-fuel-ration sensor outputs a predetermined output signal under different intake air amount conditions, determines a gradient amount as response time tendency of the rear air-fuel-ratio sensor from a plurality of determined response times, and determines degradation of the catalyst sensor if the determined gradient amount is smaller than a predetermined gradient amount.

Description

  The present invention relates to a deterioration determination device, and in particular, a deterioration determination device for an exhaust gas purification system including a catalytic converter that purifies harmful components of exhaust gas from an internal combustion engine, and a rear air-fuel ratio sensor disposed downstream of the catalytic converter. About.

Conventionally, a vehicle having an internal combustion engine is provided with an exhaust gas purification system for purifying exhaust gas. The exhaust gas purification system is provided with a catalytic converter with a built-in catalyst that purifies harmful components of exhaust gas, and in order to check the purification rate of harmful components in the exhaust gas of the catalytic converter, the front air-fuel ratio is upstream of the catalytic converter. A sensor is provided, and a rear air-fuel ratio sensor is provided downstream of the catalytic converter, and the purification efficiency of harmful components in the exhaust gas is increased from the detection results of the front air-fuel ratio sensor and the rear air-fuel ratio sensor.
A deterioration determination device that determines deterioration of the exhaust gas purification system detects an abnormality in response deterioration of the rear air-fuel ratio sensor by monitoring the response time of the rear air-fuel ratio sensor signal when the fuel supply is stopped (see FIG. 4). . As shown in FIG. 10, the response time of the rear air-fuel ratio sensor signal is obtained by measuring the time from the fuel supply stop time A to the time B when the voltage of the rear air-fuel ratio sensor signal drops to the predetermined determination voltage. .
The response time of the rear air-fuel ratio sensor and the deterioration state of the catalytic converter are closely related, and the response time of the rear air-fuel ratio sensor is absorbed by the catalytic converter when the catalytic converter is normal. (There is a large amount of oxygen adsorbed in the exhaust gas), the change in the air-fuel ratio appears later in the signal of the rear air-fuel ratio sensor (the response of the rear air-fuel ratio sensor is slow, that is, the response time is long). . When the catalytic converter deteriorates, the catalytic converter cannot absorb the change in the air-fuel ratio (the amount of adsorbing oxygen in the exhaust gas is small), and the change in the air-fuel ratio appears early in the signal of the rear air-ratio ratio sensor (the rear empty space). The response of the fuel ratio sensor becomes faster, that is, the response time becomes shorter.)

As described above, the response time of the rear air-fuel ratio sensor is affected by the state (deterioration degree) of the catalytic converter. As shown in FIG. 11, the signals of the rear air-fuel ratio sensor are (A). When the catalytic converter is normal and the rear air-fuel ratio sensor is normal, the amplitude is small, and (B). When the catalytic converter is deteriorated and the rear air-fuel ratio sensor is normal, the amplitude becomes large, and (C). When the catalytic converter is deteriorated and the rear air-fuel ratio sensor is deteriorated, the amplitude is small.
In other words, the rear air-fuel ratio sensor and the catalytic converter are deteriorated from each other (FIG. 11C), and the rear air-fuel ratio sensor and the catalytic converter are normal to each other (FIG. 11A). Since no significant change appears in the response time of the air-fuel ratio sensor, their deterioration cannot be detected. Therefore, in order to detect the response deterioration of the rear air-fuel ratio sensor without being affected by the degree of deterioration of the catalytic converter, the rear air-fuel ratio sensor is determined from the relationship of the response time of the rear air-fuel ratio sensor to the average intake air amount when the fuel supply is stopped. There is a method for detecting the deterioration of response.
FIG. 12A shows response times when the rear air-fuel ratio sensor is normal and deteriorated (response delay occurs) under the condition that the catalytic converter deteriorates, and FIG. 12B shows that the catalytic converter operates normally. Each response time when the air-fuel ratio sensor under normal conditions is normal and deteriorated (response delay occurs) is shown. FIG. 12 (C) shows a combination of FIGS. 12 (A) and 12 (B).
Conventionally, in order to determine that the rear air-fuel ratio sensor has deteriorated, the rear air-fuel ratio sensor response deterioration threshold is set to a relatively long response time as shown by the broken line in FIG. 12C, and is longer than this threshold. When the response time is reached, it is determined that the rear air-fuel ratio sensor has deteriorated. However, this method can determine that the rear air-fuel ratio sensor has deteriorated when the catalytic converter is operating normally. When the catalytic converter is deteriorated, the response time of the rear air-fuel ratio sensor is short. Therefore, even if the rear air-fuel ratio sensor is deteriorated, it is erroneously determined that the rear air-fuel ratio sensor is operating normally. There was a problem.
In addition, the rear air-fuel ratio sensor deteriorates and a response delay of the rear air-fuel ratio sensor occurs, which causes a problem that the deteriorated catalytic converter is determined to be operating normally (see FIG. 13).

  There exists patent document 1 (patent 2858406) as a prior art with respect to the said problem. In Patent Document 1, a technique using an oxygen sensor that calculates the air-fuel ratio by looking at the oxygen concentration in the exhaust gas is introduced in order to see the air-fuel ratio in the exhaust gas. Specifically, after the fuel supply to the internal combustion engine is stopped, the elapsed time from the time when the output signal from the rear oxygen sensor crosses the predetermined level from the rich side to the lean side is measured, and this elapsed time is set to the predetermined time. When the output value of the rear oxygen sensor at the time of reaching the richer side than the first judgment level set on the lean side, or when the time until reaching the first judgment level exceeds a predetermined time A technique for judging deterioration of a rear oxygen sensor is introduced. Thus, in Patent Document 1, the deterioration of the rear oxygen sensor can be detected without being affected by the degree of deterioration of the catalytic converter.

Patent No. 2858406

However, Patent Document 1 has the following problems.
When the amount of intake air is large, there is no possibility that a large difference appears in the response time of the rear oxygen sensor, and an erroneous deterioration determination of the rear oxygen sensor may be made.
As described above, the oxygen adsorption capacity of the plotter converter decreases as the deterioration progresses. When the amount of intake air to the internal combustion engine increases and a large amount of air flows into the deteriorated catalytic converter, most of the oxygen in the air flows into the rear oxygen sensor without being adsorbed by the catalytic converter. Then, there may be no difference in response time between the functioning rear oxygen sensor and the deteriorated rear oxygen sensor.
A similar problem occurs when the oxygen sensor is replaced with an air-fuel ratio sensor. As the air-fuel ratio sensor also deteriorates, the change in the output signal slows down, so that the deterioration determination of the air-fuel ratio sensor and the catalytic converter cannot be accurately performed.

  An object of the present invention is to provide a deterioration determination device that performs deterioration determination of a catalytic converter and a rear air-fuel ratio sensor with higher accuracy and suppresses erroneous determination of those.

  The present invention relates to a deterioration determination apparatus for determining deterioration of an exhaust gas purification system, wherein the exhaust gas purification system is disposed on the downstream side of the catalytic converter for purifying the exhaust gas of the internal combustion engine and in the exhaust gas. A fuel supply stop means for stopping the supply of fuel to the internal combustion engine, a response time measuring means for measuring a response time of the rear air fuel ratio sensor, Response time trend calculation means for determining response time trends from a plurality of response times, and the intake air amount conditions with different response times from when the fuel supply is stopped until the rear air-ratio ratio sensor outputs a predetermined output signal An inclination amount that is a response time tendency of the rear air-fuel ratio sensor is obtained from the obtained plurality of response times, and when the obtained inclination amount is smaller than a predetermined inclination amount, Converter is characterized in that it comprises determining degradation determination means to be deteriorated.

  The deterioration determination device according to the present invention can determine deterioration of a catalytic converter more accurately by observing the response time tendency of the rear air-fuel ratio sensor under a plurality of different operating conditions of the internal combustion engine.

FIG. 1 is a flowchart of determination by the deterioration determination apparatus. (Example) FIG. 2 is a schematic configuration diagram of the deterioration determination apparatus. (Example) FIG. 3 is a system configuration diagram of the deterioration determination apparatus. (Example) FIG. 4 is a diagram showing a delay in response time of the rear air-fuel ratio sensor. (Example) FIG. 5 is a diagram showing calculation of the amount of inclination from the response time of the rear air-fuel ratio sensor. (Example) FIG. 6 is a diagram illustrating calculation of the correction amount from the tilt amount. (Example) FIG. 7 shows each response time when the catalytic converter is deteriorated and the rear air-fuel ratio sensor is normal and deteriorated, each response time when the catalytic converter is normal and the air-fuel ratio sensor is normal and deteriorated, and for the deterioration determination after correction It is a figure which shows this threshold value. (Example) FIG. 8 is a diagram showing a deterioration determination region of the catalytic converter by threshold correction for deterioration determination of the rear air-fuel ratio sensor. (Example) FIG. 9 is a diagram showing a map of the response time of the rear air-fuel ratio sensor with respect to the intake air amount. (Example) FIG. 10 is a diagram showing response time measurement of the rear air-fuel ratio sensor. (Conventional example) FIG. 11 shows changes in the rear air-fuel ratio sensor signal, (A) shows the amplitude of the rear air-fuel ratio sensor signal when the catalytic converter is normal and the rear air-fuel ratio sensor is normal, and (B) shows deterioration of the catalytic converter. FIG. 8C is a diagram showing the amplitude of the rear air-fuel ratio sensor signal when the rear air-fuel ratio sensor is normal, and FIG. 10C is a diagram showing the amplitude of the rear air-fuel ratio sensor signal when the catalytic converter is degraded and the rear air-fuel ratio sensor is degraded. is there. (Conventional example) FIG. 12 shows the response time and threshold value of the rear air-fuel ratio sensor. FIG. 12A shows the response time when the catalytic converter is deteriorated and the rear air-fuel ratio sensor is normal and deteriorated. FIG. FIG. 8C is a diagram showing response times when the air-fuel ratio sensor is normal and deteriorated, and FIG. 8C is a response time and deterioration determination when the rear air-fuel ratio sensor combining the above-described (A) and (B) is normal and deteriorated. It is a figure which shows the threshold value for use. (Conventional example) FIG. 13 is a diagram showing the relationship between the deterioration judgment value of the catalytic converter and the response time delay of the rear air-fuel ratio sensor. (Conventional example)

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

1 to 9 show an embodiment of the present invention. In FIG. 2, 1 is an internal combustion engine, 2 is a cylinder block, 3 is a cylinder head, 4 is a cylinder head cover, 5 is a piston, 6 is a combustion chamber, 7 is an intake port, 8 is an exhaust port, 9 is an intake valve, An exhaust valve, 11 is an intake camshaft, and 12 is an exhaust camshaft.
The internal combustion engine 1 is provided with an intake passage 18 that communicates with an intake port 7 by sequentially connecting an air cleaner 13, an intake pipe 14, a throttle body 15, a surge tank 16, and an intake manifold 17 as an intake system. A throttle valve 19 is provided in the intake passage 18 of the throttle body 15. Further, the internal combustion engine 1 is provided with an exhaust passage 24 that sequentially connects an exhaust manifold 20, an upstream exhaust pipe 21, a catalytic converter 22, and a downstream exhaust pipe 23 as an exhaust system, and communicates with the exhaust port 8. . The catalytic converter 22 incorporates a catalyst 25.
The internal combustion engine 1 includes a fuel tank 26 as a fuel system, a fuel pump 27 that sucks and pumps fuel into the fuel tank 26, and a fuel filter 28 and a pressure regulator 29. A fuel supply pipe 30 to which one end side is connected is provided. A fuel return pipe 31 opened in the fuel tank 26 is connected to the pressure regulator 29. The other end side of the fuel supply pipe 30 is connected to a fuel distribution pipe 32. A fuel injection valve 33 for each cylinder attached to the intake manifold 17 is connected to the fuel distribution pipe 32.
One end of an evaporation pipe 35 is connected to the fuel tank 26 via a two-way check valve 34. The evaporation pipe 35 is connected to the canister 36 at the other end. One end of a purge pipe 37 is connected to the canister 36. The other end of the purge pipe 37 communicates with the intake passage 18 upstream of the throttle valve 19 provided in the throttle body 15.
The internal combustion engine 1 has an ignition coil 38 for each cylinder attached to a cylinder head cover 4 as an ignition system. The ignition coil 38 is ignited by a spark plug facing the combustion chamber 6 of each cylinder. The internal combustion engine 1 is provided with a tank side blow-by gas passage 40 that communicates with the intake passage 18 of the surge tank 16 through the PCV valve 39 in the cylinder head cover 4, and a cleaner side blow-by that communicates with the air cleaner 13 in the cylinder head cover 4. A gas passage 41 is provided. Further, the internal combustion engine 1 is provided with a bypass air passage 42 that bypasses the throttle valve 19 and communicates with the intake passage 18, and an idle air amount control valve 43 that adjusts the amount of idle air is provided in the middle of the bypass air passage 42. Yes.

The internal combustion engine 1 includes an electronic control unit 44. As shown in FIG. 3, the electronic control unit 44 is connected to the fuel pump 27 via the fuel pump relay 45, to the fuel injection valve 33, and to the ignition coil 38 via the igniter 46. A quantity control valve 43 is connected.
The electronic control unit 44 includes a throttle opening sensor 47 for detecting the throttle opening of the throttle valve 19, an intake pressure sensor 48 for detecting the intake pressure downstream of the throttle valve 19, and a crank for detecting the engine speed. A crank angle sensor 49 for detecting the angle, a water temperature sensor 50 for detecting the coolant temperature, a knocking sensor 51 for detecting knocking, and an upstream side of the catalytic converter 22 for detecting the air-fuel ratio in the exhaust gas. The front air-fuel ratio sensor 52 is connected to the rear air-fuel ratio sensor 53 that is disposed downstream of the catalytic converter 22 and detects the air-fuel ratio in the exhaust gas, and the battery 56 is connected via the main relay 54 and the fuse 55. (See FIG. 2).
In addition, a check engine lamp 57 is connected to the electronic control unit 44, a radiator cooling fan 59 is connected via a radiator fan relay 58, an A / C compressor clutch 60 of an air conditioner is connected, a tachometer 61 is connected, Connect A / T controller 62 of automatic transmission, and also send various signals such as battery voltage, ignition switch status signal, vehicle speed signal, brake switch signal, A / C signal of air conditioner, A / T signal of automatic transmission, etc. An input internal combustion engine signal unit 63 is connected.
The electronic control unit 44 detects the throttle opening from the throttle opening sensor 47, the intake pressure from the intake pressure sensor 48, the engine speed and cylinder discrimination from the crank angle sensor 49, the coolant temperature from the water temperature sensor 50, and the knock level from the knock sensor 51. Then, the detection signals of the air-fuel ratio of the exhaust gas upstream of the catalytic converter 22 and the air-fuel ratio of the exhaust gas downstream of the catalytic converter 22 are input from the front air-fuel ratio sensor 52. The electronic control unit 44 controls the operation of the fuel pump 27, the fuel injection valve 33, the ignition coil 38, the idle control valve 43, and the like based on these input detection signals, and controls the fuel injection amount, the ignition timing, the idle speed, and the like. To do. The intake air amount of the internal combustion engine 1 is obtained from the intake air pressure of the intake pressure sensor 48. The method of obtaining the intake air amount is an example, and an air flow sensor that can directly detect the intake air amount may be used instead of the intake pressure sensor 48.

As shown in FIG. 2, the internal combustion engine 1 includes a catalytic converter 22 that purifies exhaust gas, and a front air-fuel ratio sensor 52 that is disposed upstream of the catalytic converter 22 and detects an air-fuel ratio in the exhaust gas. And a rear air-fuel ratio sensor 53 that is disposed downstream of the catalytic converter 22 and detects an air-fuel ratio in the exhaust gas is provided. The exhaust gas purification system 64 controls the fuel supply amount from the detection results of the front air-fuel ratio sensor 52 and the rear air-fuel ratio sensor 53 by the electronic control unit 44, and is harmful in the exhaust gas by the catalyst 25 built in the catalytic converter 22. Increases purification efficiency of ingredients.
The internal combustion engine 1 is provided with a deterioration determination device 65 that determines deterioration of the exhaust gas purification system 64. As shown in FIG. 3, the deterioration determination device 65 is disposed on the downstream side of the catalytic converter 22 that purifies the exhaust gas of the exhaust gas purification system 64 and detects the air-fuel ratio in the exhaust gas. The rear air-fuel ratio sensor 53 is provided in the electronic control unit 44. The deterioration determination device 65 includes a fuel supply stop unit 66, a response time measurement unit 67, a response time tendency calculation unit 68, a correction value calculation unit 69, and a deterioration determination unit 70 in the electronic control unit 44.
The fuel supply stop means 66 stops the supply of fuel to the internal combustion engine 1 by the fuel injection valve 33. The response time measuring unit 67 measures the response time of the rear air-fuel ratio sensor 53. The response time tendency calculating means 68 looks at the response time tendency from the plurality of response times detected by the response time measuring means 67. The correction value calculating means 69 obtains a correction value for correcting the response time of the rear air-fuel ratio sensor 53 from the amount of inclination that is the response time tendency of the rear air-fuel ratio sensor 53.
The deterioration determining means 70 obtains the response time from when the fuel supply to the internal combustion engine 1 is stopped until the rear air-ratio sensor 53 outputs a predetermined output signal under different intake air amount conditions, Is obtained from the response time of the rear air-fuel ratio sensor 53, and it is determined that the catalyst 25 of the catalytic converter 22 is deteriorated when the obtained inclination amount is smaller than the predetermined inclination amount. Further, the deterioration determination means 70 determines that the rear air-fuel ratio sensor 53 has deteriorated when the response time of the rear air-fuel ratio sensor 53 corrected by the correction value is longer than a predetermined response time.

Next, the operation of the deterioration determination device 65 will be described.
As shown in FIG. 1, when the deterioration determination program starts (100), the deterioration determination device 65 detects the fuel supply state (101) and determines whether the fuel supply is stopped (102).
). If this determination (102) is NO, this determination is repeated. When this determination (102) is YES, in order to determine whether the catalytic converter 22 has deteriorated, the response time tr of the rear air-ratio ratio sensor 53 at a plurality of different average intake air amounts during the stop of fuel supply is measured. (103) The response time tendency (inclination amount g) of the rear air-fuel ratio sensor 53 with respect to the average intake air amount is obtained from these response times tr (104).
As shown in FIG. 10, the response time tr of the rear air-ratio ratio sensor 53 measures the time from the fuel supply stop time A to the time B when the voltage of the rear air-fuel ratio sensor signal 53 drops to a predetermined determination voltage. Get by. Further, as shown in the map of FIG. 9, the response time tr can be obtained more accurately as the number of collected measurement data of the response time tr with respect to the average intake air amount increases. Note that the number of collected measurement data of the response time tr may be changed as appropriate according to the situation.
It is determined whether the inclination amount g obtained in (105) is smaller than the predetermined inclination amount GD (inclination amount g <predetermined inclination amount GD) (105). As the catalytic converter 22 deteriorates, the oxygen adsorption capacity decreases. Therefore, the response time of the rear air ratio sensor 53 in the case of the catalytic converter 22 having deteriorated is the same as the response time regardless of the amount of intake air. (See FIG. 5). That is, when the inclination amount g is smaller than the predetermined inclination amount GD that can be determined that the catalytic converter 22 is deteriorated (105: YES), it is determined that the catalytic converter 22 is in a deteriorated state (106), and correction is performed. The process proceeds to calculation of value COV (108). On the other hand, when the amount of inclination g is larger than the predetermined amount of inclination GD (105: NO), it is determined that the catalytic converter 22 is normal (107), and the process proceeds to calculation of the correction value COV (108).
When measuring the response time of the rear air-fuel ratio sensor 53 for a plurality of different average intake air amounts, it is desirable to measure under the same conditions. This condition includes, for example, the cooling water temperature of the internal combustion engine 1, the engine speed, the state of the rear air-ratio ratio sensor 53 (the voltage and the active state of the rear air-fuel ratio sensor 53), and the like. Thus, the deterioration determination device 65 can perform the deterioration determination of the catalytic converter 22 with higher accuracy by looking at the response time tendency of the rear air-fuel ratio sensor 53 under a plurality of different operating conditions of the internal combustion engine 1.

After the catalytic converter 22 determines the deterioration state (106) and (107), the response time of the rear air-fuel ratio sensor 53 is corrected from the inclination amount g calculated in (104) as shown in FIG. A correction value COV for obtaining the value is obtained (108). The response time tr of the rear air-fuel ratio sensor 53 measured by the obtained correction value COV is corrected to be a correction response time Ctr (see FIG. 7). Whether the correction response time Ctr is longer than the predetermined response time Dtr (correction response time Ctr) > Predetermined response time Dtr) is determined (109).
When the corrected response time Ctr is longer than the predetermined response time Dtr (109: YES), it is determined that the rear air-fuel ratio sensor 53 is in a deteriorated state (110), and the program is ended (112). On the other hand, if the corrected response time Ctr is shorter than the predetermined response time Dtr (109: NO), it is determined that the rear air-fuel ratio sensor 53 is normal (111), and the program is ended (112).
The correction value COV of the response time tr is set smaller as the inclination amount g is smaller (see FIG. 6). This correction value COV reflects the oxygen adsorption capability of the catalytic converter 22. As described above, since the oxygen adsorption capacity of the catalytic converter 22 decreases as the deterioration progresses, it is necessary to decrease the correction value COV as the inclination amount g decreases. Thus, the correction response time Ctr of only the rear air-fuel ratio sensor 53 independent of the degree of deterioration of the catalytic converter 22 can be obtained, and the deterioration of the rear air-fuel ratio sensor 53 is determined without being affected by the degree of deterioration of the catalytic converter 22. it can.
Accordingly, the deterioration determination device 65 can obtain the response time of the rear air-fuel ratio sensor 53 excluding the deterioration state of the catalytic converter 22 from the response time tendency of the rear air-fuel ratio sensor 53, and the deterioration of the rear air-fuel ratio sensor 53 is determined. The determination can be made without being affected by the deterioration state of the catalytic converter 22. Further, the deterioration determination device 65 corrects the response time tr of the rear air-fuel ratio sensor 53 with the correction value COV obtained from the inclination amount g, thereby expanding the deterioration determination region based on the response time tr of the rear air-fuel ratio sensor 53. Thus, it is possible to eliminate a region where deterioration or abnormality of the rear air-fuel ratio sensor 53 cannot be detected (see FIG. 8).
In addition, when it is determined that the rear air-fuel ratio sensor 53 is deteriorated, it may be configured to prohibit the deterioration diagnosis of the catalytic converter 22 from being performed. In this case, the process proceeds to (108) after the process of (104). Using the detection result of the deteriorated rear air-fuel ratio sensor 53, an erroneous deterioration diagnosis of the catalytic converter 22 is prevented.

As described above, the deterioration determination device 65 uses the characteristic that the oxygen storage capacity of the catalyst 25 built in the catalytic converter 22 changes in accordance with the degree of deterioration of the catalytic converter 22, and deteriorates the catalytic converter 22 and the rear air-fuel ratio sensor 53. Is judged. The normal catalytic converter 22 has a large oxygen storage capacity, and there is a delay in the response time until the voltage of the signal of the rear air-ratio ratio sensor 53 drops from the fuel supply stop time to the specified determination voltage (see FIG. 4). .
On the other hand, in the deteriorated catalytic converter 22, the oxygen storage capacity is reduced, so that a response time is hardly delayed. The influence on the response time due to the degree of deterioration of the catalytic converter 22 increases as the average intake air amount during the stop of fuel supply decreases. That is, when the tendency of the response time is seen on the basis of the average intake air amount when the fuel supply is stopped, the inclination is different. As shown in FIG. 5, the inclination amount of the response time of the normal catalytic converter 22 is larger than the inclination amount of the response time of the deteriorated catalytic converter 22.
The deterioration determination device 65 uses this difference in response time tendency to estimate the oxygen storage capacity of the catalytic converter 22, determine the deterioration degree of the catalytic converter 22 from the amount of inclination, and obtain a correction value from the amount of inclination ( By correcting the response time of the rear air-fuel ratio sensor 53 (see FIG. 7), it becomes possible to accurately determine the deterioration of the rear air-fuel ratio sensor 53, and to determine the deterioration of the rear air-fuel ratio sensor 53. It is possible to eliminate the range where detection is impossible.
As a result, the deterioration determination device 65 can accurately determine the deterioration determination of the catalytic converter 22 and can accurately execute the response deterioration diagnosis of the rear air-fuel ratio sensor 53 without being affected by the deterioration degree of the catalytic converter 22. (See FIG. 8). When only the rear air-fuel ratio sensor 53 is deteriorated, the response time delay of the deteriorated rear air-fuel ratio sensor 53 is increased as compared with the response time of the rear air-fuel ratio sensor 53 without deterioration, but the fuel supply is stopped. There is no change in the slope of the response time based on the average intake air amount (see FIG. 2).

Although the correction value of the response time is calculated from the response time obtained under different intake air amount conditions in the above-described embodiment, the same effect can be obtained by changing to the following contents.
1. The response time of the rear air-fuel ratio sensor 53 is stored according to the set engine speed map, and a correction value is calculated from the read response time according to the engine speed. The smaller the engine speed, the smaller the intake air amount, and the response time in that case becomes longer.
2. The response time of the rear air-fuel ratio sensor 53 is stored according to the set intake air amount map, and a correction value is calculated from the inclination amount of the response time read out according to the intake air amount. The intake air amount is the intake air amount at the moment when a predetermined time has elapsed since the fuel supply was stopped. The intake air amount at a certain moment or during a predetermined period is measured, and the response time tendency of the rear oxygen sensor is obtained.

  The present invention can perform deterioration determination of a catalytic converter and a rear air-fuel ratio sensor with higher accuracy, and can be applied to vehicles, ships, and the like equipped with an internal combustion engine equipped with an exhaust gas purification system.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 20 Exhaust manifold 21 Upstream exhaust pipe 22 Catalytic converter 23 Downstream exhaust pipe 24 Exhaust passage 44 Electronic control part 52 Front air fuel ratio sensor 53 Rear air fuel ratio sensor 64 Exhaust gas purification system 65 Degradation judgment device 66 Fuel supply stop means 67 Response time measuring means 68 Response time tendency calculating means 69 Correction value calculating means 70 Degradation determining means

Claims (2)

  In the deterioration determination device for determining the deterioration of the exhaust gas purification system, the exhaust gas purification system includes a catalytic converter that purifies the exhaust gas of the internal combustion engine, and an air-fuel ratio in the exhaust gas that is disposed downstream of the catalytic converter. A fuel supply stop means for stopping the fuel supply to the internal combustion engine, a response time measurement means for measuring a response time of the rear air fuel ratio sensor, and a plurality of response times. Response time trend calculating means for determining the response time trend from the time when the fuel supply is stopped and the rear air-ratio sensor outputs a predetermined output signal under different intake air amount conditions, An inclination amount which is a response time tendency of the rear air-fuel ratio sensor is obtained from the obtained plural response times, and the catalytic converter is obtained when the obtained inclination amount is smaller than a predetermined inclination amount. Deterioration determination device, characterized in that it comprises determining degradation determination means to be deteriorated. Correction value calculating means for obtaining a correction value for correcting the response time of the rear air-fuel ratio sensor from the amount of inclination; and the deterioration determining means, the response time of the rear air-fuel ratio sensor corrected by the correction value is a predetermined response time. 2. The deterioration determination device according to claim 1, wherein the deterioration determination device determines that the rear air-fuel ratio sensor has deteriorated when the value is larger than the value.

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