JP4415620B2 - Catalyst deterioration determination device for internal combustion engine - Google Patents

Description

  The present invention relates to a catalyst deterioration determination device for an internal combustion engine.

  By providing a catalyst having an oxidation function downstream of the NOx storage reduction catalyst (hereinafter referred to as NOx catalyst), when the reducing agent is supplied to the NOx catalyst, the reducing agent passes without reacting with the NOx catalyst. Can be purified with a catalyst having a downstream oxidation function.

  By the way, the NOx catalyst and the catalyst having an oxidation function provided downstream from the NOx catalyst are deteriorated by the heat of the high-temperature exhaust gas accompanying the regeneration process of the NOx catalyst. When the degree of deterioration increases, the amount of reducing agent that reacts with the catalyst having an oxidizing function decreases, and the exhaust purification rate decreases.

Further, during NOx purging or SOx purging of the NOx catalyst, a technique for judging deterioration of the NOx catalyst based on outputs of _two O ₂ sensors provided upstream and downstream of the catalyst having an oxidizing ability downstream of the NOx catalyst. (For example, refer to Patent Document 1).

JP 2001-289037 A JP 2003-97334 A Japanese Patent Laid-Open No. 11-107741

Incidentally, it is also important to determine the degree of deterioration of a catalyst having an oxidation function provided downstream of the NOx catalyst. Thus, if the deterioration of the catalyst having the oxidation function can be detected, the user or the like can be prompted to replace the catalyst having the oxidation function.

The present invention has been made in view of the above-described problems, and in a catalyst deterioration determination device for an internal combustion engine, accurately determines deterioration of a catalyst having an oxidation function provided downstream of a NOx catalyst. The purpose is to provide technology that can be used.

In order to achieve the above object, an internal combustion engine catalyst deterioration determination apparatus according to the present invention employs the following means. That is,
A NOx storage reduction catalyst provided in an exhaust passage of the internal combustion engine, a catalyst having an oxidation function provided downstream of the NOx storage reduction catalyst, and an air-fuel ratio of exhaust gas flowing into at least the NOx storage reduction catalyst Air-fuel ratio control means for eliminating sulfur poisoning of the NOx storage reduction catalyst by intermittently reducing the NOx storage reduction catalyst,
With
And a catalyst deterioration determining means for determining deterioration of the catalyst having the oxidation function when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is intermittently lowered by the air-fuel ratio control means. Features.

The most important feature of the present invention is that the deterioration determination of the catalyst having an oxidation function is accurately performed by utilizing the fluctuation of the exhaust air-fuel ratio that is performed a plurality of times when the sulfur poisoning of the NOx catalyst is eliminated.

That is, when the sulfur poisoning of the NOx catalyst is eliminated, the air-fuel ratio of the exhaust gas is intermittently lowered, so that the air-fuel ratio of the exhaust gas that circulates upstream and downstream of the catalyst having an oxidation function changes greatly. At this time, if the catalyst having the oxidation function is deteriorated, the air-fuel ratio of the exhaust downstream of the catalyst having the oxidation function becomes a value corresponding to the deterioration. That is, the greater the degree of deterioration of the catalyst having the oxidation function, the smaller the difference between the air-fuel ratio of the exhaust gas flowing into the oxidation function and the air-fuel ratio of the exhaust gas flowing out. This is because as the degree of deterioration of the catalyst having an oxidation function increases, the exhaust gas passing through the catalyst is less affected by the catalyst.

Then, by performing the deterioration determination at the time of eliminating SOx poisoning in which the air-fuel ratio of the exhaust gas is intermittently changed, the air-fuel ratio before and after the catalyst having the oxidation function can be compared continuously. Further, since the catalyst having an oxidation function is provided downstream of the NOx catalyst, when the low air-fuel ratio exhaust gas passes through the NOx catalyst, the low air-fuel ratio portion diffuses and spreads over a wide range. Thereby, since the change of the exhaust air-fuel ratio when the oxidation catalyst is deteriorated appears in a wider range, it becomes easy to perform the deterioration determination. In this way, it is possible to improve the accuracy of determining deterioration of a catalyst having an oxidation function.

In the present invention, first air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust downstream of the NOx storage reduction catalyst and upstream of the catalyst having the oxidation function;
Second air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust downstream of the catalyst having the oxidation function;
With
The catalyst deterioration determination means relates to the first air-fuel ratio detection means and the reference value when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is intermittently lowered by the air-fuel ratio control means. A first value and a second value related to the detection value of the second air-fuel ratio detection means and the reference value are calculated, and the first value is compared with the second value. Accordingly, it is possible to determine the deterioration of the catalyst having the oxidation function.

  As described above, when the catalyst having the oxidation function is deteriorated, the air-fuel ratio of the exhaust downstream of the catalyst having the oxidation function becomes a value corresponding to the degree of deterioration. The degree of deterioration can be obtained by comparing the first value and the second value.

  First, since the first value is a value related to the air-fuel ratio and the reference value detected upstream of the catalyst having an oxidation function, the first value is irrelevant to the degree of deterioration of the catalyst having the oxidation ability. Here, the reference value is, for example, an air-fuel ratio of exhaust that may be during sulfur poisoning elimination. The first value can be, for example, the time when the air-fuel ratio of the exhaust gas is lowered and the air-fuel ratio of the exhaust gas becomes the reference value, and the air-fuel ratio of the exhaust gas is less than the reference value. The integrated value of the difference between the reference value and the air-fuel ratio can be used.

  On the other hand, since the second value is a value related to the air-fuel ratio and the reference value detected downstream of the catalyst having the oxidation function, the second value is a value corresponding to the degree of deterioration of the catalyst having the oxidation ability. That is, when the catalyst having oxidation ability deteriorates, the oxygen storage ability of the catalyst having oxidation ability decreases. Therefore, even if the exhaust gas whose air-fuel ratio has been lowered passes through the catalyst having the oxidation ability, the amount of released oxygen is small and the oxygen concentration in the exhaust gas hardly changes. Therefore, the air-fuel ratio of the exhaust gas detected downstream of the catalyst having oxidation ability approaches the air-fuel ratio of the exhaust gas detected upstream of the catalyst having oxidation ability. On the contrary, the smaller the degree of deterioration of the catalyst having oxidation ability, the more oxygen is released from the catalyst having oxidation ability, and the oxygen concentration in the exhaust gas increases. For this reason, while the oxygen is released, the decrease in the air-fuel ratio of the exhaust gas becomes slow, the time until the air-fuel ratio of the exhaust gas reaches the reference value becomes longer, and further, the air-fuel ratio that finally reaches the air-fuel ratio becomes smaller. Get higher.

Therefore, for example, when the air-fuel ratio of the exhaust gas is lowered, the time when the air-fuel ratio detected by the first air-fuel ratio detecting means and the second air-fuel ratio detecting means becomes equal to the reference value is set to the first value. When compared as the second value, the difference between the second value and the first value decreases as the degree of deterioration increases. Further, for example, the integrated value of the difference between the reference value and the air-fuel ratio when the air-fuel ratio detected by the first air-fuel ratio detecting means and the second air-fuel ratio detecting means is equal to or less than the reference value is set to the first value, respectively. When compared as the value and the second value, the difference between the first value and the second value decreases as the degree of deterioration increases. In this way, the degree of deterioration can be determined.

In addition, a NOx catalyst is provided upstream of the catalyst having an oxidation function, and when the NOx catalyst is subjected to the deterioration determination when sulfur poisoning is eliminated, the reducing agent diffuses when passing through the NOx catalyst, and the air-fuel ratio is lowered. Exhaust range expands. That is, as compared with the case where the NOx catalyst is not provided, the time required for the fluctuation of the air-fuel ratio per time in the catalyst having the oxidation ability becomes longer. As a result, the time during which the air-fuel ratio detected by the first air-fuel ratio detecting means and the second air-fuel ratio detecting means is below the reference value is lengthened. Therefore, when comparing the integrated value of the difference between the reference value and the air-fuel ratio when the air-fuel ratio of the exhaust gas is less than or equal to the reference value, this comparison is facilitated and the accuracy of deterioration determination is improved. Can do.

Furthermore, in order to determine the deterioration of the catalyst having oxidation ability at the time of sulfur poisoning recovery of the NOx catalyst,
Since the comparison between the first value and the second value can be repeated, the catalyst is deteriorated when the difference between the first value and the second value happens to be small due to other factors. It is possible to suppress the determination and, conversely, when the difference happens to be large, it can be determined that the catalyst has not deteriorated despite the deterioration.

  In the present invention, the reference value may be a stoichiometric air-fuel ratio.

  By setting the stoichiometric air-fuel ratio, for example, an oxygen concentration sensor whose output characteristics greatly change with the stoichiometric air-fuel ratio as a boundary can be used as the air-fuel ratio detecting means.

  With the catalyst deterioration determination device for an internal combustion engine according to the present invention, more opportunities for deterioration determination can be obtained, and more accurate deterioration determination can be performed.

  Hereinafter, a specific embodiment of a catalyst deterioration determination device for an internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 to which the internal combustion engine catalyst deterioration determination apparatus according to this embodiment is applied and its exhaust system.

  The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine.

  An exhaust passage 2 communicating with the combustion chamber is connected to the internal combustion engine 1. This exhaust passage 2 communicates with the atmosphere downstream.

  An occlusion reduction type NOx catalyst 3 (hereinafter referred to as NOx catalyst 3) is provided in the exhaust passage 2.

The NOx catalyst 3 has a function of storing NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reducing the stored NOx when the oxygen concentration of the inflowing exhaust gas is reduced and a reducing agent is present. Have.

  An oxidation catalyst 4 is provided in the exhaust passage 2 downstream of the NOx catalyst 3.

Further, in the exhaust passage 2 downstream of the NOx catalyst 3 and upstream of the oxidation catalyst, a first exhaust temperature sensor 5 for detecting the temperature of the exhaust gas flowing through the exhaust passage 2 and a first exhaust gas air-fuel ratio for detecting the air-fuel ratio of the exhaust gas. One air-fuel ratio sensor 6 is attached. A second exhaust temperature sensor 7 for detecting the temperature of the exhaust gas flowing through the exhaust passage 2 and a second air-fuel ratio sensor 8 for detecting the air-fuel ratio of the exhaust are attached to the exhaust passage downstream of the oxidation catalyst 4. ing.

  By the way, when the internal combustion engine 1 is operated in lean combustion, it is necessary to reduce the NOx stored in the NOx catalyst 3 before the NOx storage capability of the NOx catalyst 3 is saturated.

Therefore, in this embodiment, a reducing agent addition valve 9 for adding fuel (light oil) as a reducing agent to the exhaust gas flowing through the exhaust passage 2 upstream from the NOx catalyst 3 is provided. Here, the reducing agent addition valve 9 is opened by a signal from the ECU 10 described later to inject fuel. The fuel injected from the reducing agent addition valve 9 into the exhaust passage 2 reduces the oxygen concentration of the exhaust flowing from the upstream of the exhaust passage 2 and reduces NOx stored in the NOx catalyst 3.

The fuel is also used to raise the temperature of the NOx catalyst 3 when SOx poisoning for releasing the SOx stored in the NOx catalyst 3 is eliminated. That is, the fuel reacts with the NOx catalyst 3, and heat is generated at this time, and the temperature of the NOx catalyst 3 is increased by this heat.
As described above, when the temperature of the NOx catalyst 3 is increased and thereafter the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 3 is intermittently decreased, the SOx poisoning of the NOx catalyst 3 in the presence of the reducing agent (fuel). Is resolved.

Here, FIG. 2 is a time chart showing the waveform of the command signal of the ECU 10 sent to the reducing agent addition valve 9 and the change of the air-fuel ratio corresponding to the waveform on the same time axis. The reducing agent addition valve 9 is opened when the command signal shown in FIG. 2A is on (“ON”) and injects fuel. By performing the fuel addition, the fuel concentration in the exhaust gas flowing into the NOx catalyst 3 becomes higher (a rich spike is formed). Here, the longer the addition period (see FIG. 2 (a)), the greater the change in fuel concentration (see FIG. 2 (b)), and the longer the total addition period (see FIG. 2 (a)). The rich spike formation period (see FIG. 2B) becomes longer as the number of additions is increased (as the number of times of addition is increased). Further, as the addition interval (see FIG. 2A) is shortened, the fuel concentration in the exhaust gas becomes higher and the amount of increase in the temperature of the NOx catalyst 3 becomes larger. On the other hand, the length of the fuel addition suspension period (see FIG. 2A) is the period during which the oxidizing atmosphere continues (see FIG. 2B) between the continuously formed rich spikes, that is, the fuel concentration. Corresponds to the length of the period during which. The bed temperature of the NOx catalyst 3 can be adjusted according to the length of the pause period. That is, the longer the pause period, the lower the temperature of the NOx catalyst 3.

  Here, FIG. 3 is a diagram showing the relationship between the total addition period and the rest period and the temperature of the oxidation catalyst 4.

  When the oxidation catalyst 4 is lower than 300 ° C., for example, the total addition period is 7 seconds and the rest period is 5 seconds. By making the total addition period longer than the rest period, the temperature of the oxidation catalyst 4 can be quickly raised.

  When the oxidation catalyst 4 is, for example, 300 ° C. or more and less than 400 ° C., the total addition period is 5 seconds and the rest period is 7 seconds. Furthermore, when the temperature of the oxidation catalyst 4 rises and is, for example, 400 ° C. or higher and lower than 500 ° C., the total addition period is 5 seconds and the rest period is 10 seconds. As described above, it is possible to suppress deterioration of the oxidation catalyst 4 due to heat by extending the pause period as the temperature of the oxidation catalyst 4 increases.

The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 10 for controlling the internal combustion engine 1. This ECU 10
Is a unit that controls the operating state of the internal combustion engine 1 in accordance with the operating conditions of the internal combustion engine 1 and the requirements of the driver.

  Various sensors and the like are connected to the ECU 10 via electric wiring, and output signals from the sensors and the like are input.

  On the other hand, the reducing agent addition valve 9 and the like are connected to the ECU 10 through electric wiring so that the above-described units can be controlled by the ECU 10.

By the way, if the oxidation catalyst 4 is deteriorated and the oxidation ability of the fuel is lowered, the fuel that reacts with the oxidation catalyst 4 decreases. When such deterioration occurs, the ability to purify the fuel that has passed without reacting with the NOx catalyst 3 is reduced.

  In this respect, in the present embodiment, it is possible to determine the deterioration of the oxidation catalyst 4 based on the output signals of the first air-fuel ratio sensor 6 and the second air-fuel ratio sensor 8 when the NOx catalyst 3 is eliminated from SOx poisoning. When the degree of deterioration of the oxidation catalyst 4 is large, a warning is issued to the user, the oxidation catalyst 4 can be replaced, and the reducing agent supply method can be changed according to the degree of deterioration.

  FIG. 4 is a time chart showing the air-fuel ratio of the exhaust gas obtained from the output signals of the first air-fuel ratio sensor 6 and the second air-fuel ratio sensor 8 at the time of fuel supply. 4A shows a case where the degree of deterioration of the oxidation catalyst 4 is large, and FIG. 4B shows a case where the degree of deterioration of the oxidation catalyst 4 is small. The horizontal axis represents time, and the vertical axis represents the exhaust air-fuel ratio.

  The solid line shows the detection value of the first air-fuel ratio sensor 6, and the broken line shows the detection value of the second air-fuel ratio sensor 8. Furthermore, an area surrounded by a line indicating the stoichiometric air-fuel ratio and a line indicating the detection value of the first air-fuel ratio sensor 6 that is equal to or lower than the stoichiometric air-fuel ratio is indicated by hatching and is defined as area a. Similarly, an area surrounded by a line indicating the stoichiometric air-fuel ratio and a line indicating the detection value of the second air-fuel ratio sensor 8 that is equal to or lower than the stoichiometric air-fuel ratio is indicated by hatching and is defined as area b. The area a and the area b are areas per rich spike and are calculated for each rich spike. The area a can also be an integrated value of the difference between the stoichiometric air-fuel ratio and the detected air-fuel ratio when the air-fuel ratio of the exhaust detected by the first air-fuel ratio sensor 6 is equal to or lower than the stoichiometric air-fuel ratio. Similarly, the area b can be an integrated value of the difference between the stoichiometric air-fuel ratio and the detected air-fuel ratio when the air-fuel ratio of the exhaust detected by the second air-fuel ratio sensor 8 is equal to or lower than the stoichiometric air-fuel ratio. .

  Further, the time when the detected value of the first air-fuel ratio sensor 6 becomes the stoichiometric air-fuel ratio when shifting from the lean air-fuel ratio to the rich air-fuel ratio is set to δ1, and the detected value of the second air-fuel ratio sensor 8 is changed from the lean air-fuel ratio. The time when the stoichiometric air-fuel ratio is reached when shifting to the rich air-fuel ratio is defined as δ2.

  Here, when the degree of deterioration of the oxidation catalyst 4 increases, the oxygen storage capacity of the oxidation catalyst 4 decreases. For this reason, when the air-fuel ratio is lowered, the amount of released oxygen decreases in the oxidation catalyst 4, and the time for the rich air-fuel ratio becomes longer downstream from the oxidation catalyst 4. That is, when the degree of deterioration of the oxidation catalyst 4 is large, the difference between the area a and the area b is reduced as shown in FIG. On the other hand, if the degree of deterioration is small, a large amount of oxygen is released from the oxidation catalyst 4 as the exhaust air-fuel ratio decreases, so that the air-fuel ratio does not readily decrease downstream of the oxidation catalyst 4, and further decreases. However, the finally reached air-fuel ratio becomes higher. That is, when the degree of deterioration of the oxidation catalyst 4 is small, the difference between the area a and the area b increases as shown in FIG.

  Further, when the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst 4 is reduced, the exhaust gas downstream of the oxidation catalyst 4 becomes smaller as the oxygen stored in the oxidation catalyst 4 decreases, that is, the degree of deterioration of the oxidation catalyst 4 increases. The air-fuel ratio of the engine will fall faster. That is, when the degree of deterioration of the oxidation catalyst 4 is small, a large amount of oxygen is released, so that the decrease in the air-fuel ratio of the exhaust downstream from the oxidation catalyst 4 is slow, but when the degree of deterioration is large, the oxygen Since the released amount is reduced, the air-fuel ratio of the exhaust downstream of the oxidation catalyst 4 is lowered more quickly.

  Therefore, as the degree of deterioration of the oxidation catalyst 4 increases, the time from time δ1 to time δ2, that is, the difference between time δ2 and time δ1 decreases. Conversely, as the degree of deterioration of the oxidation catalyst 4 decreases, the difference between the time δ2 and the time δ1 increases.

  As described above, it is possible to determine the deterioration of the oxidation catalyst 4 based on the difference between the area a and the area b or the difference between the time δ2 and the time δ1.

  5 and 6 are flowcharts showing a flow for determining the deterioration of the oxidation catalyst 4 according to this embodiment. This flow is executed at the time of temperature increase control accompanying the SOx poisoning elimination of the NOx catalyst 3. The reason for determining the deterioration of the oxidation catalyst 4 during the temperature rise control accompanying the SOx poisoning elimination of the NOx catalyst 3 is as follows. That is, since the air-fuel ratio is continuously fluctuated during the temperature rise control, the difference between the area a and the area b and the difference between the time δ2 and the time δ1 can be calculated continuously. This is because it is possible to determine deterioration by obtaining many samples in time. This makes it possible to suppress erroneous determination that may occur when deterioration determination is performed with a small number of samples.

  In step S101, the exhaust temperature TA detected by the first exhaust temperature sensor 5 and the exhaust temperature TB detected by the second exhaust temperature sensor 7 are read.

In step S102, it is determined whether the internal combustion engine 1 is in a steady state. The steady state refers to a case where the rotation speed and load of the internal combustion engine 1 are constant or within a specified range. When the internal combustion engine 1 is not in a steady state, the air-fuel ratio of the exhaust fluctuates and the NOx catalyst 3 may be overheated, so the temperature rise control is stopped.

  If an affirmative determination is made in step S102, the process proceeds to step S103, whereas if a negative determination is made, the process proceeds to step S105.

In step S103, it is determined whether or not the exhaust gas temperature TA read in step S101 is larger than a prescribed value α1 and smaller than a prescribed value α2. Here, the specified value α1 is NOx.
The activation temperature of the catalyst 3, and the specified value α2 is a temperature at which the NOx catalyst 3 is not likely to overheat. That is, when the exhaust gas temperature TA is equal to or less than the specified value α1, the NOx catalyst 3 is not activated and fuel cannot be added. When the specified value α2 or more, the NOx catalyst 3 may be thermally deteriorated, so that fuel cannot be added. That is, in step S103, it is determined whether or not the temperature increase control of the NOx catalyst 3 is possible.

  If an affirmative determination is made in step S103, the process proceeds to step S104. On the other hand, if a negative determination is made, the process proceeds to step S105.

  In step S104, fuel is added, and temperature increase control of the NOx catalyst 3 is started.

In step S105, fuel addition is not performed, and the temperature raising control of the NOx catalyst 3 is not performed.
Thereafter, this routine is terminated.

  In step S106, it is determined whether or not the exhaust temperature TB read in step S101 is larger than a specified value α3. Here, the specified value α3 is the activation temperature of the oxidation catalyst 4. That is, when the exhaust temperature TB is equal to or less than the specified value α3, the oxidation catalyst 4 is not activated, and the deterioration determination of the oxidation catalyst 4 cannot be performed. In this case, as shown in FIG. 3, the temperature of the oxidation catalyst 4 is increased quickly by making the total addition period longer than the suspension period. Thus, in this embodiment, the deterioration determination of the oxidation catalyst 4 is performed only when the oxidation catalyst 4 is activated.

  If an affirmative determination is made in step S106, the process proceeds to step S107. On the other hand, if a negative determination is made, this routine is terminated.

  In step S107, catalyst deterioration determination control is started.

  In step S108, the difference between the area a and the area b described in FIG. 2 is obtained by n rich spikes, and the average value of n times is obtained. Alternatively, the difference between the time δ2 and the time δ1 described in FIG. 2 is obtained for every n rich spikes, and the average value of the n times is obtained. Here, the reason for obtaining the average value of n times is to improve the accuracy of the deterioration determination.

  In step S109, whether or not the average value of the difference between the area a and the area b obtained in step S108 is smaller than the specified value σ, or the average value of the difference between the time δ2 and the time δ1 is larger than the specified value θ. Judge whether it is small.

  The specified value σ and the specified value θ are values indicating that the degree of deterioration of the oxidation catalyst 4 has become larger than the allowable range, and are obtained in advance through experiments or the like.

  If an affirmative determination is made in step S109, the process proceeds to step S110. On the other hand, if a negative determination is made, this routine is terminated.

  In step S110, it is determined that the degree of deterioration of the oxidation catalyst 4 is large.

  In step S111, the catalyst deterioration determination control is terminated.

  In this way, the deterioration of the oxidation catalyst 4 can be determined.

  In this embodiment, in order to further improve the accuracy of the deterioration determination of the oxidation catalyst 4, whether or not the average value of the difference between the area a and the area b is smaller than the specified value σ in step S109, and The deterioration may be determined based on both whether or not the average value of the difference between the time δ2 and the time δ1 is smaller than the specified value θ.

  FIG. 7 is a flowchart showing another deterioration determination flow of the oxidation catalyst 4 according to this embodiment. The first half of the flow is the same as in FIG. Moreover, the same step number is attached | subjected to the process similar to FIG. 6, This description is abbreviate | omitted.

  In step S112, the difference between the area a and the area b described in FIG. 2 is obtained by n rich spikes, and the average value of n times is obtained. Further, the difference between the time δ2 and the time δ1 described in FIG. 2 is obtained by n rich spikes, and the average value of the n times is obtained. Here, the reason for obtaining the average value of n times is to further increase the accuracy of determining the catalyst deterioration.

  In step S113, it is determined whether or not the average value of the difference between the area a and the area b is smaller than the specified value σ and the average value of the difference between the time δ2 and the time δ1 is smaller than the specified value θ.

  If an affirmative determination is made in step S113, the process proceeds to step S114. On the other hand, if a negative determination is made, this routine is terminated.

  In step S114, a temporary flag indicating whether or not the degree of deterioration of the oxidation catalyst 4 is large is set to ON. The temporary flag being ON indicates that the degree of deterioration of the catalyst is large.

  In step S115, it is determined whether or not the temporary flag is ON continuously N times or more. Here, N times is the number of times set in order to increase the accuracy in the deterioration determination, and the value of N differs depending on how much accuracy is required. N times, the higher the number, the higher the accuracy. That is, the temporary flag may be turned ON for some reason other than the deterioration of the oxidation catalyst 4. Even in such a case, it is not immediately determined that the degree of catalyst deterioration is large. Thereby, erroneous determination is suppressed.

  If an affirmative determination is made in step S115, the process proceeds to step S110. On the other hand, if a negative determination is made, this routine is terminated.

  In this way, the deterioration determination of the oxidation catalyst 4 can be performed with higher accuracy.

In the present embodiment, the first air-fuel ratio sensor 6 and the second air-fuel ratio sensor 8 detect the air-fuel ratio of the exhaust gas. Instead, is the air-fuel ratio of the exhaust gas lean? only is rich or may comprise a detectable O ₂ sensor. According to this O ₂ sensor, the time δ1 and the time δ2 can be detected. Alternatively, the time δ1 and the time δ2 may be detected using either the first air-fuel ratio sensor 6 or the second air-fuel ratio sensor as an O ₂ sensor.

  In this embodiment, the areas a and b and the times δ1 and 2 are obtained using the theoretical air-fuel ratio as a reference value, but the areas a and b and the times δ1 and 2 are set using other air-fuel ratios as reference values. May be requested.

It is a figure which shows schematic structure of the internal combustion engine which applies the catalyst degradation determination apparatus of the internal combustion engine which concerns on an Example, and its exhaust system. It is a time chart which shows the waveform of the command signal of ECU sent to a reducing agent addition valve, and the change of the air fuel ratio corresponding to the waveform on the same time axis. It is the figure which showed the relationship between the total addition period, a rest period, and the temperature of an oxidation catalyst. It is a time chart showing the air-fuel ratio of exhaust gas obtained from the output signals of the first air-fuel ratio sensor and the second air-fuel ratio sensor when fuel is supplied. FIG. 4A shows a case where the degree of deterioration of the oxidation catalyst is large, and FIG. 4B shows a case where the degree of deterioration of the oxidation catalyst is small. It is the flowchart figure which showed the first half of the deterioration determination flow of the oxidation catalyst by an Example. It is the flowchart figure which showed the second half of the deterioration determination flow of the oxidation catalyst by the Example. It is the flowchart figure which showed the other deterioration determination flow of the oxidation catalyst by an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Exhaust passage 3 NOx catalyst 4 Oxidation catalyst 5 1st exhaust temperature sensor 6 1st air fuel ratio sensor 7 2nd exhaust gas temperature sensor 8 2nd air fuel ratio sensor 9 Reductant addition valve 10 ECU

Claims (3)

A NOx storage reduction catalyst provided in an exhaust passage of the internal combustion engine, a catalyst having an oxidation function provided downstream of the NOx storage reduction catalyst, and an air-fuel ratio of exhaust gas flowing into at least the NOx storage reduction catalyst Air-fuel ratio control means for eliminating sulfur poisoning of the NOx storage reduction catalyst by intermittently reducing the NOx storage reduction catalyst,
With
Further, catalyst deterioration determination means for determining deterioration of the catalyst having the oxidation function when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is intermittently lowered by the air-fuel ratio control means ;
Emissions downstream of the NOx storage reduction catalyst and upstream of the catalyst having the oxidation function
First air-fuel ratio detecting means for detecting the air-fuel ratio of the air;
Second air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust downstream of the catalyst having the oxidation function;
With
The catalyst deterioration determination means flows into the NOx storage reduction catalyst by the air-fuel ratio control means.
The time until the air-fuel ratio of the exhaust gas detected by the second air-fuel ratio detection means reaches a reference value when the air-fuel ratio of the exhaust gas to be reduced is detected by the first air-fuel ratio detection means A catalyst deterioration determination device for an internal combustion engine , wherein the catalyst having an oxidation function is determined to be deteriorated when a difference between the time until the air-fuel ratio of the exhaust gas reaches a reference value and a predetermined value is less than a specified value . The catalyst deterioration determination means flows into the NOx storage reduction catalyst by the air-fuel ratio control means.
When the air-fuel ratio of the exhaust gas
A time until the air-fuel ratio of the exhaust detected by the second air-fuel ratio detection means becomes a reference value; a time until the air-fuel ratio of the exhaust detected by the first air-fuel ratio detection means becomes a reference value; When the difference is less than the specified value,
In addition, the integrated value of the difference between the reference value and the air-fuel ratio when the air-fuel ratio of the exhaust gas detected by the second air-fuel ratio detection means is below the reference value and the first air-fuel ratio detection means are detected. When the difference between the reference value when the air-fuel ratio of the exhaust gas is less than the reference value and the integrated value of the difference between the air-fuel ratio is less than the specified value, it is determined that the catalyst having the oxidation function has deteriorated catalyst deterioration determination device for an internal combustion engine according to claim 1, characterized in that.   The catalyst deterioration determination device for an internal combustion engine according to claim 1 or 2, wherein the reference value is a stoichiometric air-fuel ratio.

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