JP2010203389A - Catalyst deterioration determination device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst deterioration determination device, highly accurately and simply determining deterioration of a catalyst, based on upstream and downstream air-fuel ratio parameters detected at optimal timing depending on actual states of exhaust gas flowing into the catalyst. <P>SOLUTION: The deterioration determination device 1 detects the air-fuel ratio parameters AFEX1, AFEX2 of upstream and downstream of the catalyst 7. When determining deterioration, air-fuel ratio deviation ΔAFEX12 is compared with a determination value DAF12 to determine the deterioration of the catalyst 7. The air-fuel ratio deviation ΔAFEX12 is a difference between the upstream air-fuel ratio parameter AFEX1 and the downstream air-fuel ratio parameter AFEX2, which are detected after the exhaust gas is switched from an oxydizing atmosphere to a reducing atmosphere and when the upstream air-fuel ratio parameter AFEX1 is within a predetermined range corresponding to the reducing atmosphere of the exhaust gas and variation in upstream air-fuel ratio parameter AFEX1 becomes a predetermined value ΔAFREF or smaller. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a catalyst deterioration determination device that is provided in an exhaust passage of an internal combustion engine and determines deterioration of a catalyst for purifying exhaust gas.

  As a conventional catalyst deterioration determination device, for example, one disclosed in Patent Document 1 is known. This deterioration determination device determines deterioration of a catalyst such as a NOx catalyst or a three-way catalyst having an oxygen storage capacity. An upstream air-fuel ratio sensor and a downstream air-fuel ratio sensor for detecting the air-fuel ratio of exhaust gas are provided on the upstream side and downstream side of the catalyst, respectively.

  When performing the deterioration determination, first, the oxygen trapped by the catalyst is released by switching the air-fuel ratio of the air-fuel mixture from a leaner state to a richer state than the stoichiometric air-fuel ratio. During the air-fuel ratio enrichment control, a number of upstream air-fuel ratios and downstream air-fuel ratios detected at predetermined intervals by the upstream air-fuel ratio sensor and the downstream air-fuel ratio sensor are used to determine a predetermined deterioration catalyst model. The model parameters are identified by the least square method. This deteriorated catalyst model is represented by Y = β · X, where X is an upstream air-fuel ratio, Y is a downstream air-fuel ratio, and β is a model parameter. When the identification parameter βmin obtained by identifying the model parameter β is smaller than the determination value, it is determined that the catalyst is deteriorated because the delay of the downstream air-fuel ratio with respect to the upstream air-fuel ratio is small. The

JP 2007-292014 A

  However, in the above-described conventional deterioration determination device, it is necessary to set a deterioration catalyst model, use a large number of detected upstream air-fuel ratios and downstream air-fuel ratios, and identify model parameters by the least square method. The calculation process is complicated and the calculation load increases. For this reason, it is not possible to easily determine the deterioration of the catalyst.

  In the above-described deterioration determination device, sampling of a large number of upstream air-fuel ratios and downstream air-fuel ratios is performed over the entire region after the upstream air-fuel ratio has changed to a richer side than the stoichiometric air-fuel ratio. For this reason, the sampled upstream air-fuel ratio and the downstream air-fuel ratio include those sampled in a state where the upstream air-fuel ratio has changed greatly. The delay of the downstream air-fuel ratio with respect to the above does not necessarily represent properly. As a result, accurate determination of catalyst deterioration cannot be performed, the accuracy of the catalyst may be reduced, and unnecessary catalyst replacement may be performed due to erroneous determination.

  The present invention has been made to solve such a problem, and is based on upstream and downstream air-fuel ratio parameters detected at an optimal timing according to the actual state of exhaust gas flowing into the catalyst. An object of the present invention is to provide a catalyst deterioration determination device capable of accurately and easily determining catalyst deterioration.

  In order to achieve the above object, the invention according to claim 1 is provided in an exhaust passage of the internal combustion engine 3 (the exhaust pipe 5 in the embodiment (hereinafter, the same applies in this section)), and the exhaust gas of the internal combustion engine 3 is in an oxidizing atmosphere. The deterioration determination device 1 of the catalyst 7 has an oxygen storage capacity for storing oxygen in the exhaust gas, and releases the stored oxygen when the exhaust gas is in a reducing atmosphere, and determines deterioration of the catalyst 7 that purifies the exhaust gas. An upstream air-fuel ratio parameter sensor (upstream LAF sensor 12) for detecting an upstream air-fuel ratio parameter (upstream exhaust gas air-fuel ratio AFEX1) representing the air-fuel ratio of exhaust gas upstream of the catalyst 7 in the exhaust passage; A downstream air-fuel ratio parameter set for detecting a downstream air-fuel ratio parameter (downstream exhaust gas air-fuel ratio AFEX2) representing the air-fuel ratio of the exhaust gas downstream of the catalyst 7 in the exhaust passage. Control means (ECU2) for controlling exhaust gas flowing into the catalyst 7 through the upstream (downstream LAF sensor 13) and upstream air-fuel ratio parameter sensor 12 between an oxidizing atmosphere and a reducing atmosphere, and a controlling means After the exhaust gas is switched from the oxidizing atmosphere to the reducing atmosphere, the detected upstream air-fuel ratio parameter is within a predetermined range corresponding to the reducing atmosphere of the exhaust gas, and the amount of change in the upstream air-fuel ratio parameter (upstream air A value (air-fuel ratio deviation DAFEX12) representing the degree of deviation between the upstream air-fuel ratio parameter and the downstream air-fuel ratio parameter detected when the fuel ratio change amount ΔAFEX1) is equal to or less than the predetermined value ΔAFREF is compared with the determination value DAF12. Thus, a deterioration determination means (ECU 2, steps 9 to 11) for determining deterioration of the catalyst 7 is provided.

  According to this catalyst deterioration determination device, the upstream air-fuel ratio parameter and the downstream air-fuel ratio parameter respectively representing the air-fuel ratio of the exhaust gas on the upstream side and downstream side of the catalyst in the exhaust passage are the upstream air-fuel ratio parameter sensor and Each is detected by a downstream air-fuel ratio parameter sensor. Further, a value representing the degree of divergence between the upstream air-fuel ratio parameter and the downstream air-fuel ratio parameter, which is detected after the exhaust gas flowing into the catalyst is switched from the oxidizing atmosphere to the reducing atmosphere by the control means, is a determination value. By comparing, the deterioration of the catalyst is determined.

  When the exhaust gas flowing into the catalyst is switched from the oxidizing atmosphere to the reducing atmosphere, the air-fuel ratio of the exhaust gas on the upstream side of the catalyst immediately changes to the rich side. On the other hand, the air-fuel ratio of the exhaust gas on the downstream side of the catalyst is rich immediately because oxygen stored when the exhaust gas is in an oxidizing atmosphere is released from the catalyst and consumed to oxidize the reducing agent in the exhaust gas. It changes with a delay with respect to the upstream air-fuel ratio. Further, when the catalyst is deteriorated, the oxygen storage capacity of the catalyst is reduced, and the amount of oxygen stored in the catalyst is accordingly reduced, so that the delay of the downstream air-fuel ratio with respect to the upstream air-fuel ratio becomes small. From the above, it is possible to determine the deterioration of the catalyst by comparing the value indicating the degree of divergence between the upstream air-fuel ratio parameter and the downstream air-fuel ratio parameter detected after switching to the reducing atmosphere of the exhaust gas with the determination value. it can.

  Further, according to the catalyst deterioration determination device, the upstream air-fuel ratio parameter is within a predetermined determination value range corresponding to the reducing atmosphere of the exhaust gas after the exhaust gas is switched from the oxidizing atmosphere to the reducing atmosphere, and the upstream side. The above determination is performed using the upstream air-fuel ratio parameter and the downstream air-fuel ratio parameter detected when the amount of change in the side air-fuel ratio parameter is equal to or less than a predetermined value. For this reason, the optimal timing is ensured that the exhaust gas flowing into the catalyst is switched to the reducing atmosphere, is sufficiently stable in that state, and the degree of deviation between the upstream air-fuel ratio parameter and the downstream air-fuel ratio parameter is relatively large. The deterioration of the catalyst can be accurately determined using the upstream and downstream air-fuel ratio parameters detected in step (1).

  Further, since it is only necessary to use the upstream and downstream air-fuel ratio parameters detected at one timing as described above, it is possible to easily determine the deterioration of the catalyst without performing a complicated calculation process as in the prior art. be able to.

  According to a second aspect of the present invention, there is provided a sulfur poisoning amount calculating means (ECU 2, step 6) for calculating the sulfur poisoning amount QS of the catalyst 7 in the deterioration determination device 1 for the catalyst 7 according to the first aspect, and a determination value. The DAF 12 further includes determination value setting means (ECU 2, step 7, FIG. 4) for setting a larger value as the calculated sulfur poisoning amount QS is larger.

  In general, the fuel of an internal combustion engine contains a sulfur content, and when the catalyst is exposed to exhaust gas containing the sulfur content, the sulfur content adheres to the catalyst. As will be described later, it has been confirmed that the greater the amount of sulfur adhering (hereinafter referred to as “sulfur poisoning amount”), the higher the oxygen storage capacity of the catalyst. From such a viewpoint, according to the above configuration, the determination value used for the deterioration determination is set to a larger value as the sulfur poisoning amount of the catalyst calculated by the sulfur poisoning amount calculating unit is larger. As a result, an appropriate determination value according to the oxygen storage capacity that changes according to the sulfur poisoning amount is set, so that erroneous determination due to adhesion of sulfur content is avoided, and the accuracy of catalyst deterioration determination is further improved. Can do.

It is a figure which shows roughly the deterioration determination apparatus of the catalyst by this embodiment with the internal combustion engine to which this is applied. It is a flowchart which shows a deterioration determination process. It is a table for calculating the sulfur poisoning amount. It is a table for setting the determination value for deterioration determination. It is a timing chart which shows the operation example obtained by a degradation determination process.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a catalyst deterioration determination device 1 according to this embodiment and an internal combustion engine 3 to which the catalyst deterioration determination device 1 is applied. The internal combustion engine (hereinafter referred to as “engine”) 3 is a diesel engine mounted on a vehicle (not shown).

  An intake pipe 4 and an exhaust pipe 5 are connected to the cylinder head 3a of the engine 3, and a fuel injection valve (hereinafter referred to as "injector") 6 is attached so as to face the combustion chamber 3b. The injector 6 is disposed at the center of the top wall of the combustion chamber 3b, and injects fuel from a fuel tank (not shown) into the combustion chamber 3b. The fuel injection amount QINJ injected from the injector 6 is set by the ECU 2 described later, and is controlled by controlling the valve opening time of the injector 6 by a drive signal from the ECU 2.

  The exhaust pipe 5 is provided with a catalyst 7 composed of a NOx catalyst. The catalyst 7 has an oxygen storage capacity for capturing NOx in the exhaust gas and storing oxygen in the exhaust gas when the inflowing exhaust gas is in an oxidizing atmosphere having a high oxygen concentration. Further, when exhaust gas in a reducing atmosphere flows in, the catalyst 7 purifies the exhaust gas by releasing stored oxygen and reducing captured NOx.

  The exhaust pipe 5 is provided with an upstream LAF sensor 12 and a downstream LAF sensor 13 on the upstream side and downstream side of the catalyst 7, respectively. These LAF sensors 12 and 13 are composed of zirconia or the like, and linearly detect the oxygen concentration of the exhaust gas in a wide range where the air-fuel ratio of the air-fuel mixture supplied to the engine 3 ranges from a rich region to a lean region. . The upstream LAF sensor 12 detects the oxygen concentration of the exhaust gas on the upstream side of the catalyst 7, and the downstream LAF sensor 13 detects the oxygen concentration of the exhaust gas on the downstream side of the catalyst 7, and outputs these detection signals to the ECU 2. To do.

  Based on the detection signal of the upstream LAF sensor 12, the ECU 2 detects the air-fuel ratio (hereinafter referred to as “upstream exhaust gas air-fuel ratio”) AFEX 1 upstream of the catalyst 7. Here, the “air-fuel ratio of exhaust gas” refers to the weight ratio of air and combustible gas in the exhaust gas. For this reason, the air-fuel ratio of the exhaust gas increases when the exhaust gas is in an oxidizing atmosphere and decreases when it is in a reducing atmosphere. Similarly, the ECU 2 detects an air-fuel ratio (hereinafter referred to as “downstream exhaust gas air-fuel ratio”) AFEX2 on the downstream side of the catalyst 7 based on a detection signal from the downstream LAF sensor 13.

  The ECU 2 is composed of a microcomputer (all not shown) including a CPU, a RAM, a ROM, an I / O interface, and the like. The detection signals from the various sensors 12 and 13 described above are input to the CPU after A / D conversion and shaping by the I / O interface. Further, the ECU 2 determines the operating state of the engine 3 according to the control program recorded in the ROM in accordance with these input signals, and controls the fuel injection amount QINJ of the injector 6 according to the determined operating state. Then, a deterioration determination process for determining deterioration of the catalyst 7 is executed.

  Further, the ECU 2 calculates the sulfur poisoning amount QS of the catalyst 7 as described later, and removes the sulfur content from the catalyst 7 when the calculated sulfur poisoning amount QS reaches a predetermined amount. Perform sulfur removal treatment. In the present embodiment, the ECU 2 corresponds to a control unit, a deterioration determination unit, a sulfur poisoning amount calculation unit, and a determination value setting unit.

  FIG. 2 is a flowchart showing the deterioration determination process for the catalyst 7 described above. This process is executed every predetermined time. Further, when executing the deterioration determination process, the air-fuel ratio control of the air-fuel mixture of the engine 3 is performed as follows. That is, in the engine 3, the air-fuel ratio of the air-fuel mixture is normally controlled to be leaner than the stoichiometric air-fuel ratio by controlling the fuel injection amount by the ECU 2, thereby controlling the exhaust gas in an oxidizing atmosphere. When executing the deterioration determination process, the exhaust gas is switched to the reducing atmosphere from this state by controlling the air-fuel ratio of the air-fuel mixture to be richer than the stoichiometric air-fuel ratio. Hereinafter, such control for switching the exhaust gas to the reducing atmosphere for the deterioration determination process is referred to as “exhaust gas reduction control”. The deterioration determination process is executed on condition that the engine 3 is in a stable predetermined operating state and the ECU 2 and the various sensors 12 and 13 are normal.

  First, in step 1 of FIG. 2 (illustrated as “S1”, the same applies hereinafter), it is determined whether or not the reduction control flag F_JUD is “1”. The reduction control flag F_JUD is set to “1” during the exhaust gas reduction control. If the answer to step 1 is NO, and the exhaust gas reduction control is not being performed, the fuel consumption integrated value SQF is calculated (step 2), and this process ends. The fuel consumption integrated value SQF is calculated as a value equal to the fuel injection integrated value obtained by integrating the fuel injection amount QINJ. Note that, when the above-described sulfur removal processing of the catalyst 7 is executed, the fuel consumption integrated value SQF is reset to “0”.

  If the answer to step 1 is YES and the exhaust gas reduction control is being performed, it is determined whether or not the upstream exhaust gas air-fuel ratio AFEX1 is smaller than a predetermined value AFREF (step 3). The predetermined value AFREF is set to a richer side than the air-fuel ratio of the exhaust gas corresponding to the stoichiometric air-fuel ratio of the air-fuel mixture, that is, a value corresponding to the reducing atmosphere. When the answer to step 3 is NO and AFEX1 ≧ AFREF, it is determined that the exhaust gas flowing into the catalyst 7 has not surely switched to the reducing atmosphere, and the deterioration determination of the catalyst 7 is not performed. This process ends.

  If the answer to step 3 is YES and the upstream side exhaust gas air-fuel ratio AFEX1 is smaller than the predetermined value AFREF, the difference (AFEX1 (n) between the previous value AFEX1 (n−1) and the current value AFEX1 (n) of the upstream side exhaust gas air / fuel ratio n-1) -AFEX1 (n)) is calculated as the upstream air-fuel ratio change amount ΔAFEX1 (step 4).

  Next, it is determined whether or not the upstream air-fuel ratio change amount ΔAFEX1 calculated in step 4 is equal to or less than a predetermined value ΔAFREF (step 5). If the answer to step 5 is NO and ΔAFEX1> ΔAFREF, the air-fuel ratio of the exhaust gas flowing into the catalyst 7 is not sufficiently stable, and thus the deterioration determination of the catalyst 7 is not performed. This process ends.

  When the answer to step 5 is YES and the upstream air-fuel ratio change amount ΔAFEX1 is equal to or less than the predetermined value ΔAFREF, the table shown in FIG. 3 is searched according to the fuel consumption integrated value SQF calculated in the step 2. The sulfur poisoning amount QS of the catalyst 7 is calculated (step 6). In this table, the sulfur poisoning amount QS is set to be proportional to the fuel consumption integrated value SQF.

  Next, a determination value DAF 12 for determining deterioration of the catalyst 7 is set by searching the table shown in FIG. 4 according to the sulfur poisoning amount QS calculated in step 6 (step 7). In this table, the determination value DAF12 is linearly set so as to increase as the sulfur poisoning amount QS of the catalyst 7 increases. This is because it is confirmed that the oxygen storage capacity of the catalyst 7 increases as the sulfur poisoning amount QS increases, so that the determination value DAF12 corresponding thereto is appropriately set. In addition, the larger the sulfur poisoning amount QS, the higher the oxygen storage capacity of the catalyst 7 is because the sulfur content is chemically adsorbed on the surface of the catalyst 7 in the form of sulfate radicals. It is presumed that the chemical state is easy to enter and exit.

  In the next step 8, the difference (AFEX2-AFEX1) between the downstream exhaust gas air-fuel ratio AFEX2 and the upstream exhaust gas air-fuel ratio AFEX1 is calculated as the air-fuel ratio deviation DAFEX12. Next, it is determined whether or not the air-fuel ratio deviation DAFEX12 is larger than the determination value DAF12 set in step 7 (step 9).

  When this answer is YES and DAFEX12> DAF12, it is estimated that the amount of oxygen stored in the catalyst 7 is sufficiently large, so that it is determined that the catalyst 7 is not deteriorated and this is expressed. Then, the catalyst deterioration flag F_CATNG is set to “0” (step 10), and this process is terminated. On the other hand, if the answer to step 9 is NO and DAFEX12 ≦ DAF12, it is estimated that the amount of oxygen stored in the catalyst 7 is small. In order to express this, the catalyst deterioration flag F_CATNG is set to “1” (step 11), and this process is terminated.

  FIG. 5 shows an operation example obtained by the deterioration determination process for the catalyst 7 described so far. The solid line and the alternate long and short dash line in FIG. 6 indicate the transitions of the upstream and downstream exhaust gas air-fuel ratios AFEX1 and AFEX2, respectively, when exhaust gas reduction control is performed. As shown in the figure, before the time point t1, since the condition for determining the deterioration of the catalyst 7 is not satisfied, the lean operation for controlling the air-fuel ratio of the air-fuel mixture to be leaner than the stoichiometric air-fuel ratio is performed. Yes. For this reason, the exhaust gas is controlled in an oxidizing atmosphere, and the upstream and downstream exhaust gas air-fuel ratios AFEX1 and AFEX2 have large values corresponding to the air-fuel ratio of the air-fuel mixture.

  Thereafter, when the condition for determining the deterioration of the catalyst 7 is satisfied (time t1), the reduction control flag F_JUD is set to “1”, and exhaust gas reduction control is started to control the air-fuel ratio of the air-fuel mixture to be richer than the theoretical air-fuel ratio Is done. Thereby, the exhaust gas is switched from the oxidizing atmosphere to the reducing atmosphere. Accordingly, the upstream side exhaust gas air-fuel ratio AFEX1 starts to decrease with a delay until the exhaust gas reaches the upstream side LAF sensor 12 (time point t2).

  On the other hand, the downstream exhaust gas air-fuel ratio AFEX2 decreases with a delay corresponding to the amount of stored oxygen, that is, the oxygen storage capacity of the catalyst 7, because the oxygen stored by the catalyst 7 during the lean operation is released.

  Further, the upstream side exhaust gas air-fuel ratio AFEX1 crosses the predetermined value AFREF (time point t3) and becomes lower (step 3: YES). Thereafter, the upstream air-fuel ratio change amount ΔAFEX1 gradually decreases. At time t4, when the upstream air-fuel ratio change amount ΔAFEX1 becomes equal to or smaller than the predetermined value ΔAFREF (step 5: YES), the difference between the downstream exhaust gas air-fuel ratio AFEX2 and the upstream exhaust gas air-fuel ratio AFEX1 detected at that time The deterioration determination of the catalyst 7 is performed by comparing a certain air-fuel ratio deviation DAFEX12 with the determination value DAF12 (steps 9 to 11). Thereafter, the upstream exhaust gas air-fuel ratio AFEX1 further decreases and converges to a value corresponding to the air-fuel ratio of the air-fuel mixture during exhaust gas reduction control, and the downstream exhaust gas air-fuel ratio AFEX2 converges similarly thereafter.

  As described above, according to the present embodiment, the air-fuel ratio deviation DAFEX12 that is the difference between the downstream exhaust gas air-fuel ratio AFEX2 and the upstream exhaust gas air-fuel ratio AFEX1 detected during the exhaust gas reduction control is compared with the determination value DAF12. Thus, the deterioration of the catalyst 7 is determined. When the catalyst 7 deteriorates, its oxygen storage capacity decreases, and accordingly, the amount of oxygen stored in the catalyst 7 decreases. Therefore, the delay of the downstream exhaust gas air-fuel ratio AFEX2 with respect to the upstream exhaust gas air-fuel ratio AFEX1 becomes small. Therefore, the deterioration of the catalyst 7 can be determined by comparing the air-fuel ratio deviation DAFEX12 calculated as described above with the determination value DAF12.

  Further, as the upstream and downstream exhaust gas air-fuel ratios AFEX1 and AFEX2 when calculating the air-fuel ratio deviation DAFEX12, the upstream exhaust gas air-fuel ratio AFEX1 is less than a predetermined value AFREF, and the upstream air-fuel ratio change amount ΔAFEX1 is not more than a predetermined value ΔAFREF. Use the one detected when. As a result, the exhaust gas air-fuel ratio AFEX1 and AFEX2 upstream and downstream, where the exhaust gas is reliably switched to the reducing atmosphere and sufficiently stable in that state, and the air-fuel ratio deviation DAFEX12 is detected at a relatively large optimum timing, can be obtained. By using this, it is possible to accurately determine the deterioration of the catalyst 7.

  Further, since it is only necessary to use the upstream and downstream exhaust gas air-fuel ratios AFEX1 and AFEX2 detected at one timing described above, the deterioration determination of the catalyst 7 can be performed without performing complicated arithmetic processing as in the prior art. Can be performed easily.

  Further, as the sulfur poisoning amount QS of the catalyst 7 is larger, the determination value DAF12 compared with the air-fuel ratio deviation DAFEX12 is set to a larger value. As a result, an appropriate determination value DAF12 corresponding to the oxygen storage capacity that changes in accordance with the sulfur poisoning amount QS is set, so that erroneous determination due to adhesion of sulfur content is avoided, and the accuracy of deterioration determination of the catalyst 7 is further increased. Can be improved.

  In addition, this invention can be implemented in various aspects, without being limited to the described embodiment. For example, in the embodiment, the upstream and downstream exhaust gas air-fuel ratios AFEX1 and AFEX2 are used as the air-fuel ratio parameter, but any other parameter representing the air-fuel ratio of the exhaust gas may be used. For example, the oxygen concentration or the concentration of the reducing agent in the exhaust gas may be used, or the equivalent ratio that is the ratio of the air-fuel ratio of the exhaust gas corresponding to the stoichiometric air-fuel mixture to the actual air-fuel ratio is used. Also good.

  In the present embodiment, the difference between the downstream exhaust gas air-fuel ratio AFEX2 and the upstream exhaust gas air-fuel ratio AFEX1 is used as a value representing the degree of divergence between the upstream air-fuel ratio parameter and the downstream air-fuel ratio parameter. However, the ratio of both AFEX1 and AFEX2 may be used.

  Alternatively, the embodiment is an example in which the catalyst 7 is a single NOx catalyst. However, if the catalyst 7 has an oxygen storage capacity, the type, arrangement, and number thereof can be arbitrarily changed. Of course, for example, a three-way catalyst may be used.

  Furthermore, although embodiment is an example which applied this invention to the diesel engine mounted in the vehicle, this invention is not restricted to this, You may apply to various engines, such as gasoline engines other than a diesel engine. Also, the present invention can be applied to engines other than those for vehicles, for example, engines for marine propulsion devices such as outboard motors having a crankshaft arranged vertically. In addition, it is possible to appropriately change the detailed configuration within the scope of the gist of the present invention.

1 Degradation judgment device
2 ECU (control means, deterioration determination means, sulfur poisoning amount calculation means, determination value setting means)
3 Engine (Internal combustion engine)
5 Exhaust pipe (exhaust passage)
7 Catalyst
12 Upstream LAF sensor (upstream air-fuel ratio parameter sensor)
13 Downstream LAF sensor (downstream air-fuel ratio parameter sensor)
AFEX1 upstream exhaust air-fuel ratio (upstream air-fuel ratio parameter)
AFEX2 Downstream exhaust air-fuel ratio (downstream air-fuel ratio parameter)
ΔAFEX1 upstream air-fuel ratio change (upstream air-fuel ratio parameter change)
ΔAFREF predetermined value
QS sulfur poisoning amount DAFEX12 air-fuel ratio deviation (value indicating the degree of deviation between upstream air-fuel ratio parameter and downstream air-fuel ratio parameter)
DAF12 judgment value

Claims (2)

Provided in the exhaust passage of the internal combustion engine, having an oxygen storage capacity for storing oxygen in the exhaust gas when the exhaust gas of the internal combustion engine is in an oxidizing atmosphere, and releasing the stored oxygen when the exhaust gas is in a reducing atmosphere; A catalyst deterioration determination device for determining deterioration of a catalyst for purifying exhaust gas,
An upstream air-fuel ratio parameter sensor for detecting an upstream air-fuel ratio parameter representing an air-fuel ratio of exhaust gas upstream of the catalyst in the exhaust passage;
A downstream air-fuel ratio parameter sensor for detecting a downstream air-fuel ratio parameter representing an air-fuel ratio of exhaust gas downstream of the catalyst in the exhaust passage;
Control means for switching and controlling the exhaust gas flowing into the catalyst through the upstream air-fuel ratio parameter sensor between the oxidizing atmosphere and the reducing atmosphere;
After the exhaust gas is switched from the oxidizing atmosphere to the reducing atmosphere by the control means, the detected upstream air-fuel ratio parameter is within a predetermined range corresponding to the reducing atmosphere of the exhaust gas, and the upstream side By comparing a value indicating a degree of deviation between the upstream air-fuel ratio parameter and the downstream air-fuel ratio parameter detected when the amount of change in the air-fuel ratio parameter becomes a predetermined value or less with a determination value, the catalyst Degradation determination means for determining degradation of
An apparatus for determining deterioration of a catalyst, comprising: A sulfur poisoning amount calculating means for calculating the sulfur poisoning amount of the catalyst;
Determination value setting means for setting the determination value to a larger value as the calculated sulfur poisoning amount is larger;
The catalyst deterioration determination device according to claim 1, further comprising:

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