JP2017014905A - Catalyst deterioration determination device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst deterioration determination device which is reduced in a possibility of the erroneous determination that a catalyst is deteriorated when poisoning such as HC occurs at the catalyst.SOLUTION: A CPU performs active air-fuel ratio control for forcibly switching an air-fuel ratio of a gas which flows into a catalyst to a rich air-fuel ratio and a lean air-fuel ratio on the basis of an output of a downstream-side air-fuel ratio sensor, and calculates a maximum oxygen occlusion amount. The CPU integrates deviation between an output of a downstream-side exhaust gas sensor and a rich-side integrated reference value at times t1 to t2, acquires a determination integration value (an area of a region S1), and calculates a value proportional to the times t1 to t2 (the sum of an area of the region S1 and an area of a region S2). When a value (ratio) which is obtained by dividing the determination integration value with [the value proportional to the times t1 to t2] is not larger than a first determination prohibition threshold, the CPU determines that HC poisoning occurs, and does not use the maximum oxygen occlusion amount which is obtained at the determination to catalyst deterioration determination.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a catalyst deterioration determination device for determining whether or not a catalyst provided in an exhaust passage of an internal combustion engine has deteriorated.

  Patent Document 1 discloses a catalyst deterioration determination device (hereinafter referred to as “conventional device”) for determining whether or not a catalyst (three-way catalyst) provided in an exhaust passage of an internal combustion engine has deteriorated. Has been. This conventional apparatus includes a downstream exhaust gas sensor that is a sensor that outputs a value corresponding to the air-fuel ratio of the exhaust gas downstream of the catalyst (hereinafter referred to as “downstream air-fuel ratio”). Further, as shown in time t1 to time t4 in FIG. 11, the conventional apparatus downstream of the air-fuel ratio of the exhaust gas upstream of the catalyst (hereinafter referred to as “upstream air-fuel ratio” or “inflowing gas air-fuel ratio”). Based on the output of the side exhaust gas sensor, control is performed to switch between “rich air-fuel ratio and lean air-fuel ratio”. This control is also referred to as “active air-fuel ratio control”. In this specification, the rich air-fuel ratio is an air-fuel ratio that is smaller (ie, richer) than the stoichiometric air-fuel ratio, and the lean air-fuel ratio is an air-fuel ratio that is larger (ie, leaner) than the stoichiometric air-fuel ratio. .

  More specifically, in the conventional apparatus, as shown in FIG. 11, for example, at time t2, the output of the downstream side exhaust gas sensor changes from a value indicating a rich air-fuel ratio to a value indicating a lean air-fuel ratio. Along with this, the upstream air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio. As a result, the output value of the downstream side exhaust gas sensor switches from the value indicating the lean air-fuel ratio to the value indicating the rich air-fuel ratio at time t3 when the period Δt1 has elapsed from time t2. The conventional device switches the upstream air-fuel ratio from the rich air-fuel ratio to the lean air-fuel ratio at time t3. As a result, the output value of the downstream side exhaust gas sensor switches from the value indicating the rich air-fuel ratio to the value indicating the lean air-fuel ratio at time t4 when the period Δt2 has elapsed from time t3.

  In the period from time t2 to time t3, the conventional apparatus calculates the maximum oxygen storage amount Cmax1 (index value indicating the oxygen storage capacity of the catalyst) as follows.

The conventional apparatus calculates a change amount (decrease amount) ΔO2 per unit time of the oxygen storage amount of the catalyst during the period from time t2 to time t3, and uses the change amount ΔO2 at time t2. From time to time t3. Then, the conventional apparatus calculates the change amount ΔO2 at time t3 as the maximum oxygen storage amount Cmax1. That is, the conventional apparatus acquires the maximum oxygen storage amount Cmax1 using the following equation (2). In the following formula (1), the value “0.23” is the weight ratio of oxygen contained in the atmosphere. mrf is the weight per unit time of the fuel injected from the fuel injection valve provided in the internal combustion engine between time t2 and time t3. Furthermore, stoich is the stoichiometric air fuel ratio, and abyfs is the upstream air fuel ratio detected based on the output value of the upstream exhaust gas sensor.

ΔO2 = 0.23 ・ mrf ・ (stoich-abyfs) (1)

Cmax1 = ΣΔO2 (integration interval t = t2 to t3) (2)

Similarly, in the period from time t3 to time t4, the conventional apparatus calculates the maximum oxygen storage amount Cmax2 of the catalyst using the following formula (3) and the following formula (4).

ΔO2 = 0.23 ・ mrf ・ (abyfs-stoich) (3)

Cmax2 = ΣΔO2 (integration interval t = t3 to t4) (4)

  The sequential oxygen storage amount OSA of the catalyst in the period from time t2 to time t4 is as shown in FIG. The conventional apparatus compares the maximum oxygen storage amount (Cmax1, Cmax2 and / or average value thereof) of the catalyst calculated in this way with a predetermined threshold value, and when the maximum oxygen storage amount is equal to or lower than the predetermined threshold value, It is determined that the catalyst has deteriorated.

Japanese Patent Laid-Open No. 2004-28029

  By the way, the catalyst may be poisoned by HC (hydrocarbon) and / or S (sulfur). When HC poisoning or S poisoning occurs in the catalyst, the output waveform of the downstream exhaust gas sensor (for example, the downstream O2 sensor) changes as compared with the case where neither HC poisoning nor S poisoning occurs.

  More specifically, for example, as shown in FIG. 1, in the state where the catalyst is poisoned by HC (see FIG. 1B), the state where no HC poisoning has occurred. Compared with (see (A) of FIG. 1), the output value of the downstream side exhaust gas sensor becomes earlier after the upstream side air-fuel ratio (inflow gas air-fuel ratio) is switched from the lean air-fuel ratio to the rich air-fuel ratio. It starts to change toward a value indicating a rich air-fuel ratio.

  That is, when the upstream air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio at time t0, the output value of the downstream side exhaust gas sensor becomes rich air-fuel ratio after time t2 in a state where the catalyst is not HC poisoned. It starts to change rapidly toward the value indicating. In contrast, when the catalyst is poisoned by HC, the output value of the downstream side exhaust gas sensor changes relatively gently toward the value indicating the rich air-fuel ratio at time t1, which is a time earlier than time t2. start.

  Due to this phenomenon, in the HC poisoning state, there is a period from when the upstream air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio until the output value of the downstream exhaust gas sensor reaches a value indicating the rich air-fuel ratio. Shorter. For this reason, even if the oxygen storage capacity of the catalyst is the same, the calculated maximum oxygen storage amount may be smaller in the HC poisoning state than in the HC poisoning state. As a result, the conventional apparatus may erroneously determine that the catalyst has deteriorated because the maximum oxygen storage amount is not more than a predetermined threshold value even though the catalyst has not deteriorated.

  This phenomenon is presumed to occur when a part of the catalyst becomes difficult to release oxygen due to HC poisoning. That is, this phenomenon is caused by the fact that some of the unburned components that have flowed into the catalyst remain in the catalyst despite the fact that some of the oxygen stored in the catalyst is not released and this unreleased oxygen still remains in the catalyst. It is inferred to occur by passing through.

  Similarly, as shown in FIG. 2, when the upstream air-fuel ratio is switched from the rich air-fuel ratio to the lean air-fuel ratio, S poisoning occurs in a state where the catalyst is poisoned with sulfur (sulfur poisoning). Compared to the state where no air-conditioning occurs, after the upstream air-fuel ratio is switched from the rich air-fuel ratio to the lean air-fuel ratio, the output value of the downstream exhaust gas sensor changes toward the value indicating the lean air-fuel ratio earlier. start.

  That is, when the upstream air-fuel ratio is switched from the rich air-fuel ratio to the lean air-fuel ratio at time t1, the output value of the downstream side exhaust gas sensor becomes the lean air-fuel ratio after time t4 when the catalyst is not poisoned with S. It starts to change rapidly toward the value indicating (see FIG. 2A). On the other hand, in the state where the catalyst is poisoned with sulfur, the output value of the downstream side exhaust gas sensor changes relatively gently toward the value indicating the lean air-fuel ratio at time t2, which is a time earlier than time t4. Start (see FIG. 2B).

  Due to this phenomenon, in the S poisoning state, there is a period from when the upstream air-fuel ratio is switched from the rich air-fuel ratio to the lean air-fuel ratio until the output value of the downstream exhaust gas sensor reaches a value indicating the lean air-fuel ratio. Shorter. For this reason, even if the oxygen storage capacity of the catalyst is the same, the calculated maximum oxygen storage amount may be smaller in the S-poisoned state than in the non-S-poisoned state. As a result, the conventional apparatus may erroneously determine that the catalyst has deteriorated because the maximum oxygen storage amount is not more than a predetermined threshold value even though the catalyst has not deteriorated.

  Note that this phenomenon is presumed to occur when a part of the catalyst becomes difficult to occlude oxygen due to S poisoning. In other words, this phenomenon makes it difficult for some of the catalyst to occlude oxygen, so that even if oxygen is not occluded without S poisoning, part of the oxygen that flows into the catalyst passes through the catalyst. It is presumed that this happens.

  The present invention has been made to solve the above-described problems. That is, an object of the present invention is to provide a catalyst deterioration determination device that reduces the possibility of erroneous determination that a catalyst has deteriorated when HC poisoning and / or S poisoning occurs in the catalyst. It is to provide.

  The catalyst deterioration determination device of the present invention (hereinafter referred to as “the device of the present invention”) is provided at a downstream position of the catalyst disposed in the exhaust passage of the internal combustion engine and corresponds to the air-fuel ratio of the exhaust gas flowing through the position. A downstream exhaust gas sensor that outputs a value, an upstream exhaust gas sensor that outputs a value corresponding to the air-fuel ratio of the exhaust gas that is provided at the upstream position of the catalyst in the exhaust passage, and that flows through the same position; an air-fuel ratio control unit; and an indicator A value calculating unit; and a deterioration determining unit.

The air-fuel ratio control unit performs active air-fuel ratio control described below.
That is, the air-fuel ratio control unit
The inflow gas air-fuel ratio, which is the air-fuel ratio of the exhaust gas flowing into the catalyst,
(1) When the output of the downstream side exhaust gas sensor passes through a predetermined lean determination threshold and changes to an output showing a lean air-fuel ratio compared to the stoichiometric air-fuel ratio, it is rich compared to the stoichiometric air-fuel ratio. Set to rich air-fuel ratio,
(2) When the output of the downstream side exhaust gas sensor passes through a predetermined rich determination threshold and changes to an output indicating a rich air-fuel ratio compared to the stoichiometric air-fuel ratio, it is lean compared to the stoichiometric air-fuel ratio. Set to lean air-fuel ratio.

The index value calculation unit
From the first time point when the inflow gas air-fuel ratio is switched from one of the rich air-fuel ratio and the lean air-fuel ratio during the active air-fuel ratio control to the other, the inflow gas air-fuel ratio is the rich air-fuel ratio and the rich air-fuel ratio. The oxygen storage capacity (for example, maximum oxygen storage) of the catalyst based on the output of the upstream side exhaust gas sensor during a period from the other of the lean air-fuel ratios to the second time point when the one is switched to the one (that is, the first period). An index value indicating (quantity) is calculated.

  The deterioration determination unit determines the deterioration of the catalyst based on a catalyst deterioration determination parameter that is a value corresponding to the calculated index value.

  Furthermore, the deterioration determination unit is configured to execute at least one of “first process and second process” described below.

The first process is a process performed when “the inflow gas air-fuel ratio in the first period is set to the rich air-fuel ratio”.
The first process corresponds to an air-fuel ratio that is richer than an air-fuel ratio at which the output of the downstream side exhaust gas sensor corresponds to the lean determination threshold value from the “first time point that is the start time point of the first period”. In the second period until the end point when the rich side integrated reference value is reached, the integrated value obtained by integrating the magnitude of the deviation between the output of the downstream side exhaust gas sensor and the rich side integrated reference value or the integrated value Obtain a value with a certain value added as the integrated value for judgment,
The index value calculated in the first period when the ratio of the acquired integrated value for determination to the value proportional to the length of the second period is equal to or less than a predetermined first determination prohibition threshold. Is a process that is not used for determining the deterioration of the catalyst.

The second process is a process performed when “the inflow gas air-fuel ratio in the first period is set to the lean air-fuel ratio”.
The second process corresponds to an air / fuel ratio that is leaner than an air / fuel ratio at which the output of the downstream side exhaust gas sensor corresponds to the rich determination threshold value from “the first time that is the start time of the first period”. In the third period up to the “end point at which the lean side integration reference value is reached”, the integrated value obtained by integrating the magnitude of the deviation between the output of the downstream side exhaust gas sensor and the lean side integration reference value or the integrated value Obtain a value with a certain value added as the integrated value for judgment,
The index value calculated in the first period when the ratio of the acquired integrated value for determination to a value proportional to the length of the third period is equal to or less than a predetermined second determination prohibition threshold. Is a process that is not used for determining the deterioration of the catalyst.

In the first process and the second process, “not using an index value for deterioration determination”
Invalidating (degradation determination of catalyst) made using the catalyst deterioration determination parameter obtained based on the index value (not regarded as a formal deterioration determination);
Not using the index value as the original data of the catalyst deterioration determination parameter; and
If the catalyst deterioration determination parameter is obtained based on the index value, do not use the catalyst deterioration determination parameter for the deterioration determination;
Etc.

  As described above, during the active air-fuel ratio control, when the upstream air-fuel ratio (the inflow gas air-fuel ratio that is the air-fuel ratio of the exhaust gas flowing into the catalyst) is a rich air-fuel ratio, the downstream when no HC poisoning occurs The output of the side exhaust gas sensor suddenly changes from a value indicating a lean air-fuel ratio to a value indicating a rich air-fuel ratio. Therefore, as shown in FIG. 5, “the integrated value for determination (for example, The ratio of “area S1 in FIG. 5)” is relatively large.

  On the other hand, when the upstream air-fuel ratio is the rich air-fuel ratio during the active air-fuel ratio control, the output of the downstream exhaust gas sensor when HC poisoning occurs gently changes the rich air-fuel ratio from the value indicating the lean air-fuel ratio. It changes to a value indicating the fuel ratio. Therefore, as shown in FIG. 6, “the integrated value for determination (for example, The ratio of “area S1 in FIG. 6)” is relatively small.

  Therefore, HC poisoning does not occur when the “ratio” is larger than the first determination prohibition threshold, but HC poisoning occurs when the “ratio” is equal to or less than the first determination prohibition threshold. Can be determined.

  Therefore, as described above, the deterioration determination unit has a ratio of “the acquired integrated value for determination” to “a value proportional to the length of the second period” equal to or less than a predetermined first determination prohibition threshold. At this time, the index value calculated in the first period (that is, the period including the second period in which the possibility of occurrence of HC poisoning is high) is not used for the deterioration determination of the catalyst.

  As a result, it is possible to reduce the possibility of erroneous determination that a catalyst that has not deteriorated is deteriorated due to the occurrence of HC poisoning in the catalyst.

  Similarly, when the upstream air-fuel ratio (inflow gas air-fuel ratio) is the lean air-fuel ratio during the active air-fuel ratio control, the output of the downstream exhaust gas sensor when the S poisoning is not occurring rapidly increases the rich air-fuel ratio. It changes from the value shown to the value showing the lean air-fuel ratio. Accordingly, as shown in FIG. 8, “the integrated value for determination (for example, the value proportional to the length of the third period (for example, the sum of the area of the region S3 and the area of the region S4 in FIG. 8)”). The ratio of the area of the region S4 in FIG. 8) ”is relatively large.

  On the other hand, when the upstream air-fuel ratio is the lean air-fuel ratio during the active air-fuel ratio control, the output of the downstream exhaust gas sensor when the S poisoning occurs is gently reduced from the value indicating the rich air-fuel ratio. It changes to a value indicating the fuel ratio. Accordingly, as shown in FIG. 9, “the integrated value for determination (for example, , The area of the area S4 in FIG. 9) ”is relatively small.

  Accordingly, S poisoning does not occur when the “ratio” is larger than the second determination prohibition threshold, but S poisoning occurs when the “ratio” is equal to or less than the second determination prohibition threshold. Can be determined.

  Therefore, as described above, the deterioration determination unit has a ratio of “the acquired integrated value for determination” to “a value proportional to the length of the third period” equal to or less than a predetermined second determination prohibition threshold. At this time, the index value calculated in the first period (that is, the period including the third period in which the possibility of occurrence of S poisoning is high) is not used for determining the deterioration of the catalyst.

  As a result, it is possible to reduce the possibility of erroneously determining that an undegraded catalyst has deteriorated due to the occurrence of S poisoning in the catalyst.

  Other objects, other features and attendant advantages of the present invention will be readily understood from the description of the embodiments of the present invention described with reference to the following drawings.

It is a figure which shows the output waveform of the downstream exhaust gas sensor in the state where the catalyst is not HC poisoned and the state where HC is poisoned. It is a figure which shows the output waveform of the downstream exhaust gas sensor in the state which the catalyst is not sulfur poisoning, and the state which is sulfur poisoning. 1 is a schematic view of a catalyst deterioration determination device according to an embodiment of the present invention and an internal combustion engine to which the device is applied. FIG. 4 is a time chart showing a target air-fuel ratio, downstream exhaust gas sensor output, and oxygen storage / release amount when calculating the oxygen storage capacity of the catalyst shown in FIG. 3. FIG. 6 is a time chart showing an output of a downstream side exhaust gas sensor and a target air-fuel ratio when HC poisoning has not occurred. 6 is a time chart showing an output of a downstream side exhaust gas sensor and a target air-fuel ratio when HC poisoning occurs. It is the flowchart which showed the routine which CPU of ECU shown in FIG. 3 performs. It is the time chart which showed the output and the target air fuel ratio of the downstream exhaust gas sensor when S poisoning has not occurred. It is the time chart which showed the output and the target air fuel ratio of the downstream side exhaust gas sensor when S poisoning has occurred. It is the flowchart which showed the routine which CPU of ECU shown in FIG. 3 performs. It is the time chart which showed the change in the upstream air-fuel ratio, the downstream exhaust gas sensor output, and the oxygen storage amount of a catalyst in the conventional catalyst deterioration determination apparatus.

  Hereinafter, a catalyst deterioration determination device according to an embodiment of the present invention (hereinafter simply referred to as “the determination device”) will be described.

(Constitution)
This determination apparatus is applied to the internal combustion engine (hereinafter referred to as “engine”) 10 shown in FIG. The engine 10 is a well-known engine of inline 4-cylinder, spark ignition type, and gasoline injection type. The engine 10 includes a main body 20. Connected to the main body 20 are an intake system 30 for supplying a gasoline mixture to a cylinder formed in the main body 20 and an exhaust system 40 for releasing exhaust gas from the cylinder to the outside.

  The intake system 30 includes an intake passage portion 31 including an intake pipe and an intake manifold. The intake passage portion 31 includes a throttle valve 32 that can change the passage cross-sectional area of the intake pipe, and a throttle valve actuator 33 that rotationally drives the throttle valve 32. Further, the intake system 30 includes an injector 34 that injects fuel into the intake manifold of the intake passage portion 31.

  The exhaust system 40 includes an exhaust manifold and an exhaust pipe, and includes an exhaust passage portion 41 that constitutes an exhaust passage. A catalyst (a three-way catalyst having an oxygen storage function) 42 is disposed in the exhaust manifold or at an exhaust passage downstream of the exhaust manifold.

  The determination apparatus includes an electric control device (hereinafter referred to as “ECU”) 50. The ECU 50 is an electronic circuit device including a microcomputer that includes a CPU, a ROM, a RAM, and the like. The ECU 50 is connected to a throttle valve actuator 33, a plurality of injectors 34, an upstream side exhaust gas sensor 51, a downstream side exhaust gas sensor 52, a plurality of sensors (not shown), a plurality of actuators (not shown), and the like.

  An upstream exhaust gas sensor (upstream air-fuel ratio sensor) 51 is disposed in the exhaust passage portion 41. More specifically, the upstream side exhaust gas sensor 51 is provided at the exhaust manifold assembly part or at a downstream position from the assembly part and at an upstream position of the catalyst 42, and according to the air-fuel ratio of the exhaust gas flowing through the installation position. A value is output. The upstream side exhaust gas sensor 51 is a limiting current type air-fuel ratio sensor, and outputs a larger value as the air-fuel ratio of the exhaust gas is larger (lean).

  A downstream exhaust gas sensor (downstream air-fuel ratio sensor) 52 is disposed in the exhaust passage portion 41. More specifically, the downstream side exhaust gas sensor 52 is provided at a downstream position of the catalyst 42 and outputs a value corresponding to the air-fuel ratio of the exhaust gas flowing through the arrangement position. The downstream exhaust gas sensor 52 is a concentration cell type oxygen concentration sensor (O2 sensor). When the air-fuel ratio of the exhaust gas is a rich air-fuel ratio, it is about 0.9 (V), and the air-fuel ratio of the exhaust gas is a lean air-fuel ratio. When the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio, a voltage (value) of about 0.5 (V) is output. As is well known, the output of the downstream side exhaust gas sensor 52 rapidly decreases when the air-fuel ratio of the exhaust gas flowing through the position where the downstream side exhaust gas sensor 52 is disposed changes from the rich air-fuel ratio to the lean air-fuel ratio. When the air-fuel ratio of the exhaust gas flowing through the sensor 52 changes from the lean air-fuel ratio to the rich air-fuel ratio, it rapidly increases.

  The ECU 50 can send drive signals to the throttle valve actuator 33, the injector 34, and the like. Further, the ECU 50 can receive the output of the upstream side exhaust gas sensor 51, the output of the downstream side exhaust gas sensor 52, and the output from other sensors.

(Outline of catalyst deterioration judgment)
Hereinafter, the catalyst deterioration determination method executed by the determination apparatus will be described with reference to FIG. This determination device calculates the maximum oxygen storage amount of the catalyst 42 as “an index value indicating the oxygen storage capacity of the catalyst 42” in order to determine whether or not the catalyst 42 has deteriorated.

  In this determination apparatus, the output of the downstream side exhaust gas sensor is between the rich determination voltage (0.5 (V) corresponding to the theoretical air-fuel ratio and 0.9 (V) corresponding to the maximum voltage of the downstream side exhaust gas sensor. When the voltage increases from less than (the voltage set to 1) to the rich determination voltage or more, it is determined that the output of the downstream exhaust gas sensor has changed to a value indicating the rich air-fuel ratio. The rich determination voltage is also referred to as a “rich determination threshold”.

  Further, the determination apparatus is configured such that the output of the downstream side exhaust gas sensor is between the lean determination voltage (0.5 (V) corresponding to the theoretical air-fuel ratio and 0.1 (V) corresponding to the minimum voltage of the downstream side exhaust gas sensor. When the output voltage of the downstream side exhaust gas sensor has decreased to a value indicative of a lean air-fuel ratio, the value decreases to a value equal to or less than the lean determination voltage. The lean determination voltage is also referred to as a “lean determination threshold”.

  In order to calculate the maximum oxygen storage amount, this determination apparatus performs “active air-fuel ratio control” described in Patent Document 1, and the air-fuel ratio of the exhaust gas flowing into the catalyst 42 (that is, the inflowing gas air-fuel ratio) is set to the rich air. Alternately switch between fuel ratio and lean air-fuel ratio. The switching of the inflow gas air-fuel ratio is achieved by switching the target air-fuel ratio (upstream target air-fuel ratio, that is, the target value of the air-fuel ratio of the air-fuel mixture supplied to the engine).

  When the active air-fuel ratio control is started at time t1 in FIG. 4 and the target air-fuel ratio is switched from the lean air-fuel ratio (target lean air-fuel ratio) to the rich air-fuel ratio (target rich air-fuel ratio) as shown at time t2. Since the unburned components flowing into the catalyst 42 are purified (oxidized) by oxygen released from the catalyst, the unburned components do not flow out downstream of the catalyst 42. Therefore, the output of the downstream side exhaust gas sensor 52 maintains a value indicating the lean air-fuel ratio for a while. Thereafter, when most of the oxygen stored in the catalyst 42 is consumed for the oxidation of the unburned component flowing into the catalyst 42, the exhaust gas containing the unburned component (rich air-fuel ratio exhaust gas) is downstream of the catalyst 42. leak. As a result, the output of the downstream side exhaust gas sensor 52 changes to a value indicating a rich air-fuel ratio (a value equal to or higher than the rich determination voltage) at time t3.

  Furthermore, the target air-fuel ratio is switched from the rich air-fuel ratio to the lean air-fuel ratio (target lean air-fuel ratio) as the output of the downstream side exhaust gas sensor 52 changes to a value indicating the rich air-fuel ratio at time t3. The oxygen flowing into the catalyst 42 is occluded by the catalyst. For this reason, oxygen does not flow downstream of the catalyst 42. Therefore, the output of the downstream side exhaust gas sensor 52 maintains a value indicating the rich air-fuel ratio for a while. Thereafter, when the oxygen storage amount of the catalyst 42 reaches the maximum oxygen storage amount and the catalyst 42 cannot store the oxygen, exhaust gas containing oxygen (exhaust gas with a lean air-fuel ratio) flows out downstream of the catalyst 42. As a result, the output of the downstream side exhaust gas sensor 52 changes to a value indicating a lean air-fuel ratio (a value equal to or less than the lean determination voltage) at time t4.

This determination device calculates the total amount of oxygen released by the catalyst 42 during the period (first period) Δth in which the target air-fuel ratio is set to the rich air-fuel ratio during execution of the active air-fuel ratio control. More specifically, the determination apparatus calculates a change amount (oxygen release change amount) ΔO2 per unit time of the oxygen storage amount according to the following equation (5) that is the same as the equation (1) in the period Δth. . Furthermore, this determination apparatus calculates the integrated value by accumulating the change amount ΔO2 according to the following equation (6) that is the same as the equation (2) in the period Δth. Then, the determination apparatus calculates the integrated value at the end point of the first period (that is, time t3) as “an index value indicating the oxygen storage capacity, that is, the maximum oxygen storage amount Cmaxh”.

ΔO2 = 0.23 ・ mrf ・ (stoich-abyfs) (5)

Cmaxh = ΣΔO2 (integration interval t = t2 to t3) (6)

Further, the present determination device calculates the total amount of oxygen stored in the catalyst 42 during the period (first period) Δtk in which the target air-fuel ratio is set to the lean air-fuel ratio during execution of the active air-fuel ratio control. More specifically, the determination apparatus calculates a change amount (oxygen storage change amount) ΔO2 per unit time of the oxygen storage amount according to the following equation (7) in the period Δtk. Further, this determination apparatus calculates an integrated value by accumulating the change amount ΔO2 according to the following equation (8) in the period Δtk. Then, the determination device calculates the integrated value at the end of the period Δtk (that is, time t4) as “an index value indicating the oxygen storage capacity, that is, the maximum oxygen storage amount Cmaxk”.

ΔO2 = 0.23 ・ mrf ・ (abyfs-stoich) (7)

Cmaxk = ΣΔO2 (integration interval t = t3 to t4) (8)

  This determination apparatus acquires a plurality of maximum oxygen storage amounts Cmaxh and maximum oxygen storage amounts Cmaxk (for example, 6 each), and calculates an average value thereof as “a value corresponding to an index value indicating oxygen storage capacity (ie, catalyst Deterioration determination parameter) ”. The determination apparatus determines that the catalyst 42 has deteriorated when the catalyst deterioration determination parameter is equal to or less than a predetermined threshold (a value corresponding to the maximum oxygen storage amount of the deteriorated catalyst).

(HC poisoning judgment method)
When it is determined that “catalyst HC poisoning” has occurred, this determination device discards the maximum oxygen storage amount Cmaxh acquired at that time (not used as original data for the catalyst deterioration determination parameter). . Hereinafter, this point will be described.

  As described with reference to FIG. 1, when the upstream air-fuel ratio (inflow gas air-fuel ratio) is a rich air-fuel ratio during active air-fuel ratio control, depending on whether HC poisoning has occurred in the catalyst. The output waveform of the downstream side exhaust gas sensor 52 is greatly different.

  More specifically, FIG. 5 shows an output waveform of the downstream side exhaust gas sensor 52 when HC poisoning does not occur, and FIG. 6 shows the downstream side exhaust gas sensor 52 when HC poisoning occurs. The output waveform is shown.

  In order to distinguish these waveform differences, the determination apparatus calculates “ratio = X / Y” described below. The numerator X of this ratio indicates the difference between the rich side integrated reference value and the output of the downstream side exhaust gas sensor 52, and the output of the downstream side exhaust gas sensor 52 is rich from the "lean / rich switching time t1" during active air-fuel ratio control. This is an integrated value obtained by integrating the magnitude of the deviation between the output of the downstream side exhaust gas sensor 52 and the rich-side integrated reference value in a period (second period Δt2) until the end point t2 when the side integrated reference value is reached. Note that the lean / rich switching time is the time when the inflow gas air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio during the active air-fuel ratio control, and is also referred to as the first time point. That is, the molecule X is the area of the region S1 surrounded by the line connecting the points A-B-P in FIGS. The rich side integration reference value is “a voltage corresponding to the output of the downstream side exhaust gas sensor 52” corresponding to “an air / fuel ratio richer than an air / fuel ratio corresponding to a lean determination threshold”. In this example, the rich side integration reference value is set to the same value as the rich determination threshold value (rich determination voltage).

  The denominator Y of the ratio (= X / Y) is a value corresponding to “the sum of the area of the region S1 and the area of the region S2” in FIGS. That is, the denominator Y is an area of a rectangular region (S1 + S2) surrounded by a line connecting the points A-B-C-D. In this case, the line segment CD is set to “0 (V) which is a lean-side ideal value”. In other words, the denominator Y is a value proportional to the length Δt2 of the period from the first time point t1 to the end time point t2.

  As is clear from FIGS. 5 and 6, this ratio (= X / Y) is relatively large (close to “1” in this example) when HC poisoning is not generated in the catalyst 42. When the HC poisoning occurs in the catalyst 42, the value is relatively small (in this example, a small value deviating from “1”). Therefore, when the ratio (= X / Y) is larger than the first determination prohibition threshold R1th, the determination apparatus determines that HC poisoning has not occurred in the catalyst 42, and the ratio (= X / Y) is When it is less than or equal to the first determination prohibition threshold R1th, it is determined that HC poisoning has occurred in the catalyst 42.

  Furthermore, when this determination apparatus determines that HC poisoning is occurring in the catalyst 42, the first period (from the first time point t1) including the second period in which the ratio (= X / Y) is obtained. The maximum oxygen storage amount Cmaxh acquired during the period until time t2 when the output of the downstream side exhaust gas sensor 52 crosses the rich determination voltage is not used for catalyst deterioration determination. Thereby, this determination apparatus can reduce the possibility of erroneously determining that the catalyst 42 has deteriorated even though it has not deteriorated.

(Actual operation 1)
Next, actual processing that is performed when the ECU 50 of the determination apparatus performs catalyst deterioration determination will be described.

  The CPU of the ECU 50 executes the routine shown by the flowchart of FIG. 7 every elapse of a predetermined time. Therefore, the CPU starts the process from step 700 at a predetermined timing, proceeds to step 705, and determines whether “active air-fuel ratio control is being executed”. In the active air-fuel ratio control, for example, after the engine 10 is started, the catalyst deterioration determination is not made once, the engine 10 is warmed up, and the load of the engine 10 (for example, in one intake stroke) This is executed when the amount of air taken into one cylinder) is substantially constant over a predetermined time. If the active air-fuel ratio control is not being executed, the CPU makes a “No” determination at step 705 to directly proceed to step 795 to end the present routine tentatively.

  On the other hand, if active air-fuel ratio control is being executed, the CPU makes a “Yes” determination at step 705 to proceed to step 710, where the target air-fuel ratio currently set is the rich air-fuel ratio (target rich air-fuel ratio). It is determined whether or not. If the target air-fuel ratio is not a rich air-fuel ratio, the CPU makes a “No” determination at step 710 to directly proceed to step 795 to end the present routine tentatively.

  On the other hand, if the target air-fuel ratio is a rich air-fuel ratio, the CPU makes a “Yes” determination at step 710 to proceed to step 715, where the deviation D between the rich side integrated reference value A and the downstream side exhaust gas sensor output Voxs. (= A−Voxs) is integrated to update the actual integrated value SA. More specifically, the CPU calculates a value obtained by adding the deviation D to the actual integrated value SA immediately before proceeding to step 715 as a new actual integrated value SA. The actual integrated value SA is initialized to “0” when the target air-fuel ratio is changed from the lean air-fuel ratio to the rich air-fuel ratio.

  Next, the CPU proceeds to step 720 to update a value proportional to the time from when the target air-fuel ratio is set to the rich air-fuel ratio (that is, the first proportional value). More specifically, the CPU adds the rich side integration reference value A (deviation between the rich side integration reference value A and the lean side ideal value 0 (V)) to the first proportional value SB immediately before proceeding to step 720. And a coefficient k (in this example, k = 1) plus a product k · A is calculated as a new first proportional value SB. The value of the first proportional value SB is also initialized to “0” when the target air-fuel ratio is changed from the lean air-fuel ratio to the rich air-fuel ratio.

  Next, the CPU proceeds to step 725 to calculate a change amount (oxygen release change amount) ΔO2 of the oxygen storage amount per unit time according to the above-described equation (5), and to calculate this change amount ΔO2 according to the above-described equation (6). Integration is performed to update the release amount integrated value (oxygen release amount) OSCh. Note that the release amount integrated value OSCh is also initialized to “0” when the target air-fuel ratio is changed from the lean air-fuel ratio to the rich air-fuel ratio.

  Next, the CPU proceeds to step 730 to determine whether or not the output Voxs of the downstream side exhaust gas sensor 52 has increased from a value smaller than the rich determination voltage to a value larger than the rich determination voltage. That is, the CPU determines whether or not the output Voxs of the downstream side exhaust gas sensor 52 has changed to an output that shows a rich air-fuel ratio compared to the stoichiometric air-fuel ratio through a predetermined rich determination threshold. If the downstream side exhaust gas sensor output Voxs has not increased from a value smaller than the rich determination voltage to a value larger than the rich determination voltage, the CPU makes a “No” determination at step 730 to directly proceed to step 795 to perform this routine. Is temporarily terminated.

  On the other hand, when the downstream side exhaust gas sensor output Voxs increases from a value smaller than the rich determination voltage to a value larger than the rich determination voltage, the CPU determines “Yes” in step 730 and proceeds to step 735. The numerator X (that is, the area of the region S1 = the integrated value for determination) of the ratio (R = X / Y) is acquired, and the denominator Y (that is, the area of the region S1 + the area of the region S2 = first proportional value). To get. More specifically, the CPU takes in the actual integrated value SA at that time as the value X, and takes in the first proportional value SB at that time as the value Y.

  Next, the CPU proceeds to step 740 and calculates the ratio (area ratio) R by dividing the value X by the value Y. Then, the CPU proceeds to step 745 to determine whether or not the ratio (area ratio) R is equal to or less than “first determination prohibition threshold R1th for determining whether HC poisoning has occurred”.

  When the ratio (area ratio) R is equal to or less than the first determination prohibition threshold R1th, it can be determined that HC poisoning has occurred in the catalyst 42. Therefore, in this case, the CPU makes a “Yes” determination at step 745 to proceed to step 750 to discard the release amount integrated value OSCh integrated by the processing at step 725. Thereafter, the CPU proceeds to step 795 to end the present routine tentatively.

  On the other hand, when the ratio (area ratio) R is larger than the first determination prohibition threshold R1th, it can be determined that HC poisoning has not occurred in the catalyst 42. Accordingly, in this case, the CPU makes a “No” determination at step 745 to proceed to step 755, and stores the released amount integrated value OSCh integrated by the processing at step 725 as the maximum oxygen storage amount Cmaxh. Thereafter, the CPU proceeds to step 795 to end the present routine tentatively.

  Further, the CPU repeatedly executes the routine of FIG. 7 until the process of step 740 is executed a predetermined number of times to obtain one or a plurality of maximum oxygen storage amounts Cmaxh. The CPU stores the maximum oxygen storage amount Cmaxh obtained by the process of step 740 in a RAM (not shown) of the ECU 50.

(S poisoning determination method)
The determination device further calculates the maximum oxygen storage amount Cmaxk during the period (first period) in which the target air-fuel ratio is set to the lean air-fuel ratio during execution of the active air-fuel ratio control. Then, it is determined whether or not S poisoning has occurred as described below, and the maximum oxygen storage amount Cmaxk obtained when S poisoning of the catalyst has occurred is discarded (for catalyst deterioration determination). Not used as parameter source data.) Hereinafter, this point will be described.

  As described with reference to FIG. 2, when the upstream air-fuel ratio (inflow gas air-fuel ratio) is the lean air-fuel ratio during the active air-fuel ratio control, depending on whether or not S poisoning occurs in the catalyst. The output waveform of the downstream side exhaust gas sensor 52 is greatly different.

  More specifically, FIG. 8 shows an output waveform of the downstream side exhaust gas sensor 52 when S poisoning does not occur, and FIG. 9 shows the downstream side exhaust gas sensor 52 when S poisoning occurs. The output waveform is shown.

  In order to distinguish these waveform differences, the determination apparatus calculates “ratio = Z / W” described below. The numerator Z of this ratio is the difference between the lean side accumulated reference value and the output of the downstream side exhaust gas sensor 52, and the output of the downstream side exhaust gas sensor 52 becomes leaner from the "rich / lean switching time t3" during the active air-fuel ratio control. This is an integrated value obtained by integrating the magnitude of the deviation between the output of the downstream side exhaust gas sensor 52 and the lean-side integrated reference value in the period (second period Δt2) until the end point t4 when the side-side integrated reference value is reached. The rich / lean switching time is a time when the inflow gas air-fuel ratio is switched from the rich air-fuel ratio to the lean air-fuel ratio during the active air-fuel ratio control, and is also referred to as a first time point. That is, the molecule Z is the area of the region S4 surrounded by the line connecting the points HGQ in FIGS. The lean side integration reference value is “a voltage corresponding to the output of the downstream side exhaust gas sensor 52” corresponding to “an air / fuel ratio leaner than an air / fuel ratio corresponding to a rich determination threshold”. In this example, the lean side integration reference value is set to the same value as the lean determination threshold value (lean determination voltage).

  The denominator W of the ratio (= Z / W) is a value corresponding to “the sum of the area of the region S1 and the area of the region S2” in FIGS. That is, the denominator W is an area of a rectangular region (S3 + S4) surrounded by a line connecting the points E-F-G-H. In this case, the line segment EF is set to “1 (V), which is the ideal value on the rich side”. In other words, the denominator W is a value proportional to the length Δt2 of the period from the first time point t3 to the end time point t4.

  As is clear from FIGS. 8 and 9, this ratio (= Z / W) is relatively large (close to “1” in this example) when S poisoning is not generated in the catalyst 42. And a relatively small value (in this example, a small value deviating from “1”) when S poisoning occurs in the catalyst 42. Therefore, when the ratio (= Z / W) is larger than the second determination prohibition threshold R2th, this determination apparatus determines that S poisoning has not occurred in the catalyst 42, and the ratio (= Z / W) is If it is equal to or less than the second determination prohibition threshold R2th, it is determined that S poisoning has occurred in the catalyst 42.

  Furthermore, when this determination apparatus determines that S poisoning is occurring in the catalyst 42, the first period (from the first time point t3) including the third period in which the ratio (= Z / W) is obtained. The maximum oxygen storage amount Cmaxk acquired in the period until time t4 when the output of the downstream side exhaust gas sensor 52 crosses the lean determination voltage is not used for catalyst deterioration determination. Thereby, this determination apparatus can reduce the possibility of erroneously determining that the catalyst 42 has deteriorated even though it has not deteriorated.

(Actual operation 2)
The CPU of the ECU 50 executes the routine shown by the flowchart of FIG. 10 in addition to FIG. 7 every elapse of a predetermined time. Therefore, the CPU starts the process from step 1000 at a predetermined timing, and proceeds to step 1005 to determine whether “active air-fuel ratio control is being executed”. This step is the same as step 705 in FIG. If the active air-fuel ratio control is not being executed, the CPU makes a “No” determination at step 1005 to directly proceed to step 1095 to end the present routine tentatively.

  On the other hand, if the active air-fuel ratio control is being executed, the CPU makes a “Yes” determination at step 1005 to proceed to step 1010, where the target air-fuel ratio currently set is the lean air-fuel ratio (target lean air-fuel ratio). It is determined whether or not. If the target air-fuel ratio is not a lean air-fuel ratio, the CPU makes a “No” determination at step 1010 to directly proceed to step 1095 to end the present routine tentatively.

  On the other hand, when the target air-fuel ratio is the lean air-fuel ratio, the CPU makes a “Yes” determination at step 1010 to proceed to step 1015, where the deviation between the lean side integrated reference value B and the downstream side exhaust gas sensor 52 output Voxs is determined. E (= Voxs−B) is integrated to update the actual integrated value SC. More specifically, the CPU calculates a value obtained by adding the deviation E to the actual integrated value SC immediately before proceeding to Step 1015 as a new actual integrated value SC. The actual integrated value SC is initialized to “0” when the target air-fuel ratio is changed from the rich air-fuel ratio to the lean air-fuel ratio.

  Next, the CPU proceeds to step 1020 to update a value proportional to the time from when the target air-fuel ratio is set to the lean air-fuel ratio (that is, the second proportional value). More specifically, the CPU adds the difference C between the rich ideal value (1 (V) in this example) and the lean integrated reference value B to the second proportional value SD immediately before proceeding to Step 1020 and the coefficient k. A value obtained by adding a product k · C with (k = 1 in this example) is calculated as a new second proportional value SD. The value of the second proportional value SD is also initialized to “0” when the target air-fuel ratio is changed from the rich air-fuel ratio to the lean air-fuel ratio.

  Next, the CPU proceeds to step 1025 to calculate a change amount (oxygen storage change amount) ΔO2 of the oxygen storage amount per unit time according to the above-described equation (7), and to calculate this change amount ΔO2 according to the above-described equation (8). Integration is performed to update the storage amount integrated value (oxygen storage amount) OSCk. The stored amount integrated value OSCk is also initialized to “0” when the target air-fuel ratio is changed from the rich air-fuel ratio to the lean air-fuel ratio.

  Next, the CPU proceeds to step 1030 to determine whether or not the output Voxs of the downstream side exhaust gas sensor 52 has decreased from a value larger than the lean determination voltage to a value smaller than the lean determination voltage. In other words, the CPU determines whether or not the output Voxs of the downstream side exhaust gas sensor 52 has passed a predetermined lean determination threshold value and has changed to an output indicating a lean air-fuel ratio as compared with the stoichiometric air-fuel ratio. If the downstream side exhaust gas sensor output Voxs has not decreased from a value larger than the lean determination voltage to a value smaller than the lean determination voltage, the CPU makes a “No” determination at step 1030 to directly proceed to step 1095 to execute this routine. Is temporarily terminated.

  On the other hand, when the downstream side exhaust gas sensor output Voxs decreases from a value larger than the lean determination voltage to a value smaller than the lean determination voltage, the CPU determines “Yes” in step 1030 and proceeds to step 1035. The numerator Z (that is, the area of the region S4 = the integrated value for determination) of the ratio (R = Z / W) is acquired, and the denominator Y (that is, the area of the region S3 + the area of the region S4 = second proportional value). To get. More specifically, the CPU takes in the actual integrated value SC at that time as the value Z, and takes in the second proportional value SD at that time as the value W.

  Next, the CPU proceeds to step 1040 to calculate the ratio (area ratio) R by dividing the value Z by the value W. Then, the CPU proceeds to step 1045 to determine whether the ratio (area ratio) R is equal to or less than “second determination prohibition threshold R2th for determining whether or not S poisoning has occurred”.

  When the ratio (area ratio) R is equal to or less than the second determination prohibition threshold R2th, it can be determined that S poisoning has occurred in the catalyst 42. Therefore, in this case, the CPU makes a “Yes” determination at step 1045 to proceed to step 1050 to discard the accumulated amount integrated value OSCk accumulated by the processing at step 1025. Thereafter, the CPU proceeds to step 1095 to end the present routine tentatively.

  On the other hand, when the ratio (area ratio) R is larger than the second determination prohibition threshold R2th, it can be determined that S poisoning has not occurred in the catalyst 42. Therefore, in this case, the CPU makes a “No” determination at step 1045 to proceed to step 1055, and stores the stored amount integrated value OSCk integrated by the processing at step 1025 as the maximum oxygen stored amount Cmaxk. Thereafter, the CPU proceeds to step 1095 to end the present routine tentatively.

  Further, the CPU repeatedly executes the routine of FIG. 10 until the process of step 1040 is executed a predetermined number of times, and acquires one or a plurality of maximum oxygen storage amounts Cmaxk. The CPU stores the maximum oxygen storage amount Cmaxk obtained by the process of step 740 in a RAM (not shown) of the ECU 50.

  The CPU executes the routine of FIG. 7 and the routine of FIG. 10 to execute a catalyst deterioration determination process by executing a deterioration determination routine (not shown) when the processes of step 755 and step 1055 are respectively performed a predetermined number of times.

  In this deterioration determination routine, the CPU obtains “average value of the single or plural maximum oxygen storage amounts Cmaxh” obtained by the process of step 755 and stored in the RAM as the catalyst deterioration determination parameter P1, and the catalyst deterioration determination parameter. It is determined whether P1 is equal to or greater than the catalyst deterioration determination threshold value P1th. Then, the CPU determines that the catalyst 42 has deteriorated when the catalyst deterioration determination parameter P1 is less than the catalyst deterioration determination threshold value P1th. Thus, the CPU does not use the OSCh discarded in step 750 as the original data when obtaining the catalyst deterioration determination parameter P1.

  Further, in this deterioration determination routine, the CPU obtains the “average value of the single or plural maximum oxygen storage amounts Cmaxk” obtained by the processing of step 1055 and stored in the RAM as the catalyst deterioration determination parameter P2, and the catalyst deterioration. It is determined whether or not the determination parameter P2 is equal to or greater than the catalyst deterioration determination threshold value P2th. Then, the CPU determines that the catalyst 42 has deteriorated when the catalyst deterioration determination parameter P2 is less than the catalyst deterioration determination threshold value P2th. Thus, the CPU does not use the OSCk discarded in step 1050 as original data when obtaining the catalyst deterioration determination parameter P2.

As described above, this determination apparatus is
The inflow gas air-fuel ratio, which is the air-fuel ratio of the exhaust gas flowing into the catalyst 42, is
(1) When the output of the downstream side exhaust gas sensor 52 passes through a predetermined lean determination threshold (lean determination voltage) and changes to an output showing a lean air-fuel ratio compared to the stoichiometric air-fuel ratio, the stoichiometric air-fuel ratio is reached. A rich air-fuel ratio that is richer than that is set (see time t2 to time t3 in FIG. 4).
(2) When the output of the downstream side exhaust gas sensor 52 passes through a predetermined rich determination threshold (rich determination voltage) and changes to an output indicating a rich air-fuel ratio compared to the theoretical air-fuel ratio, the stoichiometric air-fuel ratio is set. In comparison, the lean air-fuel ratio is set to be lean (see time t3 to time t4 in FIG. 4).
An “air-fuel ratio control unit (part of the function of the ECU 50)” that performs active air-fuel ratio control is included.

Furthermore, this determination device
From the first time point (for example, time t2 or time t3 in FIG. 4) when the inflow gas air-fuel ratio is switched from one of the rich air-fuel ratio and the lean air-fuel ratio to the other during the active air-fuel ratio control. A period (that is, a first period) until a second time point (for example, time t3 or time 4 in FIG. 4) when the inflowing gas air-fuel ratio is switched from the other of the rich air-fuel ratio and the lean air-fuel ratio to the one. An index value indicating the oxygen storage capacity of the catalyst 42 based on the output of the upstream side exhaust gas sensor 51 in Δt1, for example, the period Δth from time t2 to t3 in FIG. 4 and the period Δtk from time t3 to t4 in FIG. , Maximum oxygen storage amount) (step 725, step 730 and step 755 in FIG. 7, and step 1025, step 1030 and step 10 in FIG. 10). 5).

  In addition, the determination apparatus includes a deterioration determination unit that determines the deterioration of the catalyst based on a catalyst deterioration determination parameter (P1, P2, P, etc.) that is a value corresponding to the calculated index value.

The deterioration determination unit
When the inflow gas air-fuel ratio in the first period is set to the rich air-fuel ratio, the output of the downstream side exhaust gas sensor is determined to be the lean determination from the first time point that is the start time point of the first period. Deviation between the output of the downstream side exhaust gas sensor and the rich-side integrated reference value in the second period until the end of reaching the rich-side integrated reference value corresponding to the air-fuel ratio richer than the air-fuel ratio corresponding to the threshold value for use An integrated value SA obtained by integrating the magnitudes of D (or a value obtained by adding a constant value to the integrated value) is acquired as an integrated value for determination X, and the acquired determination for a value Y proportional to the length of the second period. When the ratio of integrated values (= X / Y) is equal to or less than a predetermined first determination prohibition threshold R1th, a first process (FIG. 5) in which the index value calculated in the first period is not used for deterioration determination of the catalyst. Step 71 of 7 Through S 750), and,
When the inflow gas air-fuel ratio in the first period is set to the lean air-fuel ratio, the output of the downstream side exhaust gas sensor is determined to be the rich determination from the first time point that is the start time point of the first period. Deviation between the output of the downstream side exhaust gas sensor and the lean side integrated reference value in the third period until the end point of reaching the lean side integrated reference value corresponding to the air / fuel ratio leaner than the air / fuel ratio corresponding to the threshold value An integrated value SC obtained by integrating the magnitude of E (or a value obtained by adding a constant value to the integrated value) is acquired as an integrated value for determination Z, and the acquired determination is made for a value W proportional to the length of the third period. When the ratio of integrated values (= Z / W) is equal to or less than a predetermined second determination prohibition threshold R2th, a second process (FIG. 5) that does not use the index value calculated in the first period for determining deterioration of the catalyst. 10 steps 1 10 to step 1050),
Execute.

  Therefore, this determination apparatus can reduce the possibility of erroneously determining that the catalyst 42 has deteriorated due to occurrence of HC poisoning and / or S poisoning in the catalyst 42.

  The present invention is not limited to the above embodiment, and various modifications can be employed within the scope of the present invention. For example, the determination apparatus may perform only one of the first process and the second process. Furthermore, this determination apparatus may use only one of the catalyst deterioration determination parameters P1 and P2 for the catalyst deterioration determination.

  Furthermore, in the above-described embodiment, the rich side integration reference value A is set to the same value as the rich determination threshold value (rich determination voltage), but they may be different from each other. In this case, the rich side integration reference value A needs to be a value larger than the lean determination threshold (lean determination voltage). Further, it is desirable that the rich side integrated reference value A is larger than the output value (0.5 (V)) of the downstream side exhaust gas sensor 52 corresponding to the theoretical air-fuel ratio. Further, it is desirable that the rich side integration reference value A is a value equal to or less than the rich determination voltage.

  In the above embodiment, since the rich side integration reference value A is set to the rich determination voltage, “the time when the target air-fuel ratio in the active air-fuel ratio control is changed from the rich air-fuel ratio to the lean air-fuel ratio” , “The end point at which the output of the downstream side exhaust gas sensor 52 reaches the rich side integrated reference value A” coincided with this. However, when the rich-side integration reference value A and the rich determination voltage are different from each other, the two time points do not coincide with each other, and the rich-side integration reference value A is a value less than the rich determination voltage (see A1 in FIG. 5). In some cases, the end time point when the output of the downstream side exhaust gas sensor 52 reaches the rich-side integrated reference value A = A1 (see the point C1 in FIG. 5) is “the target air-fuel ratio in the active air-fuel ratio control is the rich air-fuel ratio. Before the point of time when the air-fuel ratio is changed to the lean air-fuel ratio (see point B in FIG. 5).

  Further, in step 735, the CPU obtains a value obtained by adding the constant value CC to the actual integrated value SA as a value X (= determined integrated value), and obtains a value obtained by adding the constant value CC to the first proportional value SB. The value Y may be acquired.

  Similarly, in the above embodiment, the lean-side integration reference value B is set to the same value as the lean determination threshold (lean determination voltage), but they may be different from each other. In this case, the lean-side integration reference value B needs to be a value smaller than the rich determination threshold value (rich determination voltage). Further, it is desirable that the lean side integrated reference value B is smaller than the output value (0.5 (V)) of the downstream side exhaust gas sensor 52 corresponding to the theoretical air-fuel ratio. Further, it is desirable that the lean side integration reference value B is a value equal to or higher than the lean determination voltage.

  In the above embodiment, the lean side integration reference value B is set to the lean determination voltage, so that “the time when the target air-fuel ratio in the active air-fuel ratio control is changed from the lean air-fuel ratio to the rich air-fuel ratio” , “The end point at which the output of the downstream side exhaust gas sensor 52 reaches the lean side accumulated reference value B” coincided with this. However, when the lean side integration reference value B and the lean determination voltage are different from each other, the above two time points do not coincide with each other, and when the lean side integration reference value B is larger than the lean determination voltage, the downstream side exhaust gas sensor 52. The “end point when the output reaches the lean-side integrated reference value B” comes earlier than “the point when the target air-fuel ratio in the active air-fuel ratio control is changed from the lean air-fuel ratio to the rich air-fuel ratio”.

  Further, in step 1035, the CPU acquires a value obtained by adding the constant value DD to the actual integrated value SC as a value Z (= determined integrated value), and obtains a value obtained by adding the constant value DD to the second proportional value SD. It may be acquired as a value W.

  Further, the first determination prohibition threshold value R1th and the second determination prohibition threshold value R2th may be the same value or different from each other.

  Furthermore, in the above embodiment, the release amount integrated value OSCh is discarded in step 750. However, in step 750, the release amount integrated value OSCh is not discarded, and the data including the release amount integrated value OSCh is included. Based on this, the catalyst deterioration determination parameter P1 may be obtained, and such catalyst deterioration determination parameter P1 may not be used for catalyst deterioration determination. Furthermore, such a catalyst deterioration determination may be invalid after such a catalyst deterioration determination parameter P1 is used for the catalyst deterioration determination. In other words, in the present invention, the index value (maximum oxygen storage amount) acquired when HC poisoning has occurred should not be substantially used for the catalyst deterioration determination.

  Similarly, in the above embodiment, the occlusion amount integrated value OSCk is discarded in step 1050. However, the data including the occlusion amount integrated value OSCk is not discarded in step 1050. The catalyst deterioration determination parameter P2 may be obtained based on the above, and the catalyst deterioration determination parameter P2 may not be used for the catalyst deterioration determination. Furthermore, such a catalyst deterioration determination may be invalid after such catalyst deterioration determination parameter P2 is used for catalyst deterioration determination. That is, in the present invention, the index value (maximum oxygen storage amount) acquired when S poisoning is occurring may not be substantially used for the catalyst deterioration determination.

  In addition, one or both of the lean determination voltage and the rich determination voltage may be a value (for example, 0.5 (V)) that the downstream air-fuel ratio sensor 52 outputs to the exhaust gas having the stoichiometric air-fuel ratio.

  DESCRIPTION OF SYMBOLS 10 ... Engine, 20 ... Main-body part, 30 ... Intake system, 34 ... Injector, 40 ... Exhaust system, 41 ... Exhaust passage part, 42 ... Catalyst, 51 ... Upstream exhaust gas sensor, 52 ... Downstream exhaust gas sensor.

Claims (1)

A downstream exhaust gas sensor that outputs a value corresponding to the air-fuel ratio of the exhaust gas that is provided at a downstream position of the catalyst disposed in the exhaust passage of the internal combustion engine and flows through the same position;
An upstream exhaust gas sensor that outputs a value corresponding to an air-fuel ratio of exhaust gas that is provided at an upstream position of the catalyst in the exhaust passage and flows through the same position;
The inflow gas air-fuel ratio, which is the air-fuel ratio of the exhaust gas flowing into the catalyst, is changed to an output in which the output of the downstream exhaust gas sensor passes a predetermined lean determination threshold value and shows a lean air-fuel ratio compared to the theoretical air-fuel ratio. Is set to a rich air-fuel ratio that is rich compared to the stoichiometric air-fuel ratio, and the output of the downstream exhaust gas sensor passes a predetermined rich determination threshold value and is richer than the stoichiometric air-fuel ratio. An air-fuel ratio control unit that performs active air-fuel ratio control, which is control for setting a lean air-fuel ratio that is lean compared to the stoichiometric air-fuel ratio when the output changes to
From the first time point when the inflow gas air-fuel ratio is switched from one of the rich air-fuel ratio and the lean air-fuel ratio during the active air-fuel ratio control to the other, the inflow gas air-fuel ratio is the rich air-fuel ratio and the rich air-fuel ratio. An index for calculating an index value indicating the oxygen storage capacity of the catalyst based on the output of the upstream side exhaust gas sensor in a first period that is a period from the other of the lean air-fuel ratios to a second time point when the other is switched to the one. A value calculator,
A deterioration determination unit that performs deterioration determination of the catalyst based on a catalyst deterioration determination parameter that is a value according to the calculated index value;
In the catalyst deterioration determination device provided with
The deterioration determination unit
When the inflow gas air-fuel ratio in the first period is set to the rich air-fuel ratio, the output of the downstream side exhaust gas sensor is determined to be the lean determination from the first time point that is the start time point of the first period. Deviation between the output of the downstream side exhaust gas sensor and the rich-side integrated reference value in the second period until the end of reaching the rich-side integrated reference value corresponding to the air-fuel ratio richer than the air-fuel ratio corresponding to the threshold value for use An integrated value obtained by integrating the magnitudes of the values or a value obtained by adding a constant value to the integrated value is acquired as an integrated value for determination, and a ratio of the acquired integrated value for determination to a value proportional to the length of the second period is A first process that does not use the index value calculated in the first period for deterioration determination of the catalyst, when the threshold value is equal to or less than a predetermined first determination prohibition threshold; and
When the inflow gas air-fuel ratio in the first period is set to the lean air-fuel ratio, the output of the downstream side exhaust gas sensor is determined to be the rich determination from the first time point that is the start time point of the first period. Deviation between the output of the downstream side exhaust gas sensor and the lean side integrated reference value in the third period until the end point of reaching the lean side integrated reference value corresponding to the air / fuel ratio leaner than the air / fuel ratio corresponding to the threshold value An integrated value obtained by integrating the magnitudes of the values or a value obtained by adding a constant value to the integrated value is acquired as an integrated value for determination, and a ratio of the acquired integrated value for determination to a value proportional to the length of the third period is A second process that does not use the index value calculated in the first period for deterioration determination of the catalyst when the threshold value is equal to or less than a predetermined second determination prohibition threshold;
Configured to perform at least one of the processes,
Catalyst deterioration judgment device.

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