JP2006009698A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for quickly determining deterioration of a catalyst, in an exhaust emission control device for an internal combustion engine. <P>SOLUTION: The exhaust emission control device comprises: an occlusion reduction type NO<SB>x</SB>catalyst occluding NO<SB>x</SB>when oxygen concentration in exhaust is high and reducing the occluded NO<SB>x</SB>when the oxygen concentration is decreased and a reducer exists; and a catalyst deterioration determination means determining deterioration of the occlusion reduction type NO<SB>x</SB>catalyst when oxidation capacity of the occlusion reduction NO<SB>x</SB>catalyst is more than predetermined capacity. At the initial stage wherein a NO<SB>x</SB>occlusion capacity of the occlusion reduction type NO<SB>x</SB>catalyst is lowered, the deterioration of the occlusion reduction NO<SB>x</SB>type catalyst is determined based on a fact that the oxidation capacity is increased while NO<SB>x</SB>occlusion capacity is deceased. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine, and more particularly to determination of catalyst deterioration.

The catalyst provided in the exhaust passage of the internal combustion engine deteriorates when exposed to high-temperature exhaust. When the catalyst performance decreases due to this deterioration, the purification rate of harmful components in the exhaust gas decreases. Therefore, a technique is known in which a reducing agent is added to a catalyst, and deterioration of the catalyst is determined from output values of air-fuel ratio sensors provided upstream and downstream of the catalyst at this time (see, for example, Patent Document 1). .).
JP-A-11-93742 JP 2002-309928 A JP-A-8-270438

  By the way, in the deterioration determination based on the output value of the air-fuel ratio sensor, it is necessary to reduce all NOx stored in the NOx storage reduction catalyst, and therefore it is necessary to add a reducing agent for a long period of time. For this reason, the consumption of the reducing agent is large, and when the fuel of the internal combustion engine is used as the reducing agent, the fuel consumption deteriorates. Further, if the addition of the reducing agent has to be performed for a long time, there is a high possibility that the operating state of the internal combustion engine becomes unsuitable for the addition of the reducing agent during the addition of the reducing agent. And the opportunity of deterioration determination will decrease because addition of a reducing agent is stopped.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of determining the deterioration of a catalyst more quickly in an exhaust gas purification apparatus for an internal combustion engine.

In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention employs the following means. That is,
A NOx storage reduction catalyst that stores NOx when the oxygen concentration in the exhaust gas is high, and reduces the NOx stored when the oxygen concentration decreases and a reducing agent is present;
Catalyst deterioration determination means for determining that the NOx storage reduction catalyst has deteriorated when the oxidation capacity of the NOx storage reduction catalyst is equal to or greater than a predetermined capacity;
It is characterized by comprising.

  The most important feature of the present invention is that the NOx storage capacity of the NOx storage reduction catalyst decreases while the oxidation capacity increases while the deterioration determination of the NOx storage reduction catalyst is performed.

  The NOx storage reduction catalyst has NOx storage capacity and oxidation capacity. The oxidation capacity of the NOx storage reduction catalyst is suppressed by the NOx storage capacity. That is, when the NOx storage ability is exhibited, the oxidation ability cannot exhibit its original ability. Here, the NOx storage capacity of the NOx storage reduction catalyst decreases faster than the oxidation capacity. Then, the NOx occlusion ability is lowered, so that the degree of suppression of the oxidation ability is lowered and the oxidation ability is raised. This increase in oxidation capacity exceeds the decrease in oxidation capacity due to deterioration at the initial stage where the NOx storage reduction catalyst deteriorates, and the overall oxidation capacity of the NOx storage reduction catalyst increases.

  Therefore, when the oxidation capacity of the NOx storage reduction catalyst increases, it can be determined that the NOx storage capacity of the NOx storage reduction catalyst has decreased, that is, the NOx storage reduction catalyst has deteriorated. . Since this determination can be made even before the reduction of NOx is completed, it can be made promptly.

  In the present invention, the catalyst deterioration determining means has a predetermined oxidation capacity of the NOx storage reduction catalyst when the oxidation capacity of the NOx storage reduction catalyst is equal to or higher than the oxidation capacity of the NOx storage reduction catalyst when it is new. It can be determined that the capacity is exceeded.

  That is, when the NOx storage capacity of the NOx storage reduction catalyst starts to decrease, the oxidation capacity of the NOx storage reduction catalyst becomes higher than when it is new. Therefore, when the oxidation capacity of the NOx storage reduction catalyst becomes higher than when it is new, it can be determined that the NOx storage reduction catalyst has deteriorated.

In the present invention, reducing agent addition means for adding a reducing agent from the upstream of the NOx storage reduction catalyst,
Catalyst temperature detecting means for detecting the temperature of the NOx storage reduction catalyst;
Further comprising
Whether the catalyst deterioration determining means has an oxidation capacity of the NOx storage reduction catalyst equal to or greater than a predetermined capacity based on a temperature change of the catalyst detected by the catalyst temperature detecting means when the reducing agent is added by the reducing agent adding means. By determining whether or not, it is possible to determine whether or not the NOx storage reduction catalyst has deteriorated.

  Here, when the oxidation ability of the NOx storage reduction catalyst increases, the temperature of the NOx storage reduction catalyst when the reducing agent is added tends to increase. Therefore, the degree of temperature increase of the NOx storage reduction catalyst after the reducing agent is added by the reducing agent addition means varies depending on the degree of deterioration of the NOx storage reduction catalyst. Accordingly, the oxidation capability of the NOx storage reduction catalyst can be detected from the temperature change of the catalyst detected by the catalyst temperature detection means when the reducing agent is added by the reducing agent addition means, and the NOx storage reduction catalyst can be detected. It is possible to perform the deterioration determination. Note that the “predetermined capacity” can be an oxidation capacity exhibited by the NOx storage reduction catalyst when it can be assumed that the NOx storage reduction catalyst is deteriorated.

  In the present invention, the catalyst deterioration determining means has a time from when the addition of the reducing agent by the reducing agent adding means is started until the temperature of the catalyst detected by the catalyst temperature detecting means starts to increase. When it is shorter than one predetermined time, it can be determined that the NOx storage reduction catalyst has deteriorated.

  That is, when the NOx storage reduction catalyst deteriorates, the oxidizing agent resulting from this deterioration increases, so that the reducing agent is quickly oxidized. Therefore, the temperature of the NOx storage reduction catalyst after the addition of the reducing agent is increased. Time to start climbing is shortened. Therefore, the time from when the reducing agent is added to the NOx storage reduction catalyst until the temperature of the catalyst rises is the minimum value of the time during which the catalyst can be regarded as not deteriorated (that is, the first predetermined value). If the time is shorter than (time), it can be determined that the catalyst has deteriorated.

  In the present invention, the catalyst deterioration determining means has a time from when the addition of the reducing agent by the reducing agent adding means is started until the temperature of the catalyst detected by the catalyst temperature detecting means reaches a maximum value. When the time is shorter than the second predetermined time, it can be determined that the NOx storage reduction catalyst has deteriorated.

That is, when the NOx storage reduction catalyst is deteriorated, the reducing agent is rapidly oxidized due to the increase in oxidation ability due to the deterioration. The time to reach the maximum value is shortened. Therefore, the time from when the reducing agent is added to the NOx storage reduction catalyst until the temperature of the catalyst reaches the maximum value is the minimum value of time that the catalyst can be regarded as not deteriorated (that is, When the time is shorter than the second predetermined time, it can be determined that the catalyst has deteriorated.

  In the present invention, the catalyst deterioration determining means is when the rate of change of the temperature of the catalyst detected by the catalyst temperature detecting means when the reducing agent is added by the reducing agent adding means is greater than a first predetermined value. In addition, it can be determined that the NOx storage reduction catalyst has deteriorated.

  That is, when the NOx storage reduction catalyst is deteriorated, the reducing agent is rapidly oxidized due to the increase in the oxidation ability due to the deterioration, so the rate of increase in the temperature of the NOx storage reduction catalyst (per unit time). Temperature). That is, the rate of change in temperature increases. Therefore, the rate of change of the temperature of the catalyst when the reducing agent is added to the NOx storage reduction catalyst is larger than the rate of change (that is, the first predetermined value) that can be assumed that the catalyst has not deteriorated. When it becomes, it becomes possible to determine that the catalyst has deteriorated.

In the present invention, further comprising a catalyst reference temperature calculation means for calculating a reference temperature of the NOx storage reduction catalyst after the reducing agent is started by the reducing agent addition means,
The catalyst deterioration determination means obtains a change width of a difference between the temperature detected by the catalyst temperature detection means and the reference temperature, and when the change width becomes larger than a second predetermined value, the occlusion reduction It can be determined that the type NOx catalyst has deteriorated.

  The change width is a value obtained by subtracting the minimum value from the maximum value of the difference between the temperature detected by the catalyst temperature detecting means and the reference temperature.

  When the storage reduction type NOx catalyst deteriorates, the temperature of the storage reduction type NOx catalyst rapidly rises when a reducing agent is added. That is, immediately after the addition of the reducing agent, the rate of change in the temperature of the NOx storage reduction catalyst is large. On the other hand, since the reducing agent that is oxidized decreases with time after the addition of the reducing agent, the rate of change in temperature of the NOx storage reduction catalyst becomes small.

  Here, based on the temperature of the NOx storage reduction catalyst that can be regarded as not deteriorated, the temperature of the catalyst that has deteriorated is higher immediately after the addition of the reducing agent, and the deterioration occurs over time. The temperature of the catalyst that is not higher is higher. Therefore, when the catalyst is deteriorated, the difference between the actual catalyst temperature detected when the reducing agent is added and the reference catalyst temperature changes. In the initial stage where the NOx storage reduction catalyst deteriorates, the difference between the actual catalyst temperature and the reference catalyst temperature increases as the degree of deterioration increases. Therefore, the change width of the difference between the actual catalyst temperature when the reducing agent is added to the NOx storage reduction catalyst and the temperature of the reference catalyst is the change width that the catalyst is not degraded. When it becomes larger than (that is, the second predetermined value), it can be determined that the catalyst has deteriorated.

In the present invention, further comprising a catalyst reference temperature calculation means for calculating a reference temperature of the NOx storage reduction catalyst after the reducing agent is started by the reducing agent addition means,
The reducing agent addition means performs at least two kinds of reducing agent additions with different reducing agent addition amounts per time,
The catalyst deterioration determining means obtains a change width of a difference between the temperature detected by the catalyst temperature detecting means and the reference temperature in each case of at least two kinds of reducing agent addition, and the at least two kinds of reductions It can be determined that the NOx storage reduction catalyst has deteriorated when the difference in the amount of change in the addition of the agent is greater than a third predetermined value.

  That is, when the NOx storage reduction catalyst is not deteriorated, the temperature rise due to the addition of the reducing agent is slowed down, so that the variation in the temperature change rate of the catalyst becomes small. This becomes more prominent as the amount of reducing agent added per time decreases. Therefore, when the NOx storage reduction catalyst is not deteriorated, the change width of the difference between the reference temperature and the detected temperature increases as the amount of reducing agent added per time decreases. On the other hand, when the NOx storage agent is deteriorated, the temperature of the catalyst quickly rises when the reducing agent is added. In this case, there is little influence of the addition amount of the reducing agent per time. That is, when the NOx storage reduction catalyst is deteriorated, the change width of the difference between the reference temperature and the detected temperature becomes large regardless of the amount of reducing agent added per time.

  Therefore, when adding at least two types of reducing agents with different amounts of reducing agent added per time, the change width of the difference between each reference temperature and the detected temperature is obtained, which is small when the amount of reducing agent added is large. When the difference in change from the time is larger than the third predetermined value, it is possible to determine that the NOx storage reduction catalyst has deteriorated. The third predetermined value is the minimum value of the difference in change width that can be assumed that the NOx storage reduction catalyst is not deteriorated.

  Here, examples of the two types of reducing agent addition include reducing agent addition performed during NOx reduction and reducing agent addition performed during sulfur poisoning recovery. That is, as an example when the amount of reducing agent added per time is small, there can be mentioned reducing agent addition performed when NOx stored in the NOx storage reduction catalyst is reduced. Further, as an example when the amount of the reducing agent added per time is large, there can be mentioned the addition of the reducing agent that is performed when the sulfur poisoning of the NOx storage reduction catalyst is recovered.

  In the present invention, the catalyst deterioration determining means is configured to detect the NOx storage reduction catalyst when the temperature of the NOx storage reduction catalyst after the addition of the reducing agent by the reducing agent addition means is higher than a predetermined temperature. It can be determined that the oxidation capacity is greater than or equal to the predetermined capacity.

  In other words, the increase in oxidation ability makes it easier for the temperature of the NOx storage reduction catalyst to rise when the reducing agent is added, and the maximum temperature of the NOx storage reduction catalyst becomes higher. Therefore, if the maximum value of the temperature at which the NOx storage reduction catalyst can be regarded as not deteriorated is set in advance as the predetermined temperature, the temperature after adding the reducing agent to the NOx storage reduction catalyst is the predetermined temperature. It is possible to determine that the NOx storage reduction catalyst is deteriorated when the NOx catalyst is deteriorated.

  In the present invention, the NOx storage reduction catalyst that can be regarded as not deteriorated includes an NOx storage reduction catalyst in which the NOx storage capacity is reduced to the maximum extent within an allowable range.

  In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the deterioration of the catalyst can be determined more quickly based on the temperature change of the catalyst when the reducing agent is added.

  Hereinafter, specific embodiments of an exhaust emission control 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 an exhaust gas purification apparatus for an internal combustion engine according to this embodiment is applied and an exhaust system thereof.

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

  Further, an exhaust passage 2 leading to the combustion chamber is connected to the internal combustion engine 1. This exhaust passage 2 communicates with the atmosphere downstream.

  In the middle of the exhaust passage 2, an upstream side catalyst 3 and a storage reduction type NOx catalyst 4 (hereinafter referred to as NOx catalyst 4) are provided in order from upstream.

  The upstream catalyst 3 is a catalyst having oxidation ability.

  The NOx catalyst 4 uses, for example, alumina as a carrier, and on the carrier, an alkali metal such as potassium (K), sodium (Na), lithium (Li), or cesium (Cs), barium (Ba) or calcium ( At least one selected from alkaline earths such as Ca), rare earths such as lanthanum (La) or yttrium (Y), and a noble metal such as platinum (Pt) are supported.

  This NOx catalyst 4 stores NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reduces the stored NOx when the oxygen concentration of the inflowing exhaust gas decreases and a reducing agent is present. Have

  A first air / fuel ratio sensor 5 for detecting the air / fuel ratio of the exhaust gas flowing through the exhaust passage 2 is attached to the exhaust passage 2 upstream of the NOx catalyst 4. Further, in the exhaust passage 2 downstream of the NOx catalyst 4, an exhaust temperature sensor 6 that detects the temperature of the exhaust gas that flows through the exhaust passage 2 and a second air that detects the air-fuel ratio of the exhaust gas that flows through the exhaust passage 2. A fuel ratio sensor 7 is attached.

  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 4 before the NOx stored in the NOx catalyst 4 is saturated.

  Therefore, in this embodiment, a reducing agent addition valve 9 (reducing agent adding means) for adding fuel (light oil) as a reducing agent into the exhaust gas flowing through the exhaust passage 2 upstream from the upstream catalyst 3 is provided. Here, the reducing agent addition valve 9 is opened by a signal from the ECU 10 described later to inject the reducing agent. The reducing agent injected into the exhaust passage 2 from the reducing agent addition valve 9 makes the air-fuel ratio of the exhaust flowing from the upstream of the exhaust passage 2 rich. During NOx reduction, so-called rich spike control is performed in which the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 4 is made rich in a spike (short time) in a relatively short cycle.

  On the other hand, the NOx catalyst 4 also stores sulfur oxide (SOx) generated by combustion of sulfur contained in the fuel by the same mechanism as NOx. The stored SOx is less likely to be released than NOx and is accumulated in the NOx catalyst 4. As the SOx is occluded, the amount of NOx that can be occluded decreases, and the NOx occlusion force of the NOx catalyst 4 decreases. This is called sulfur poisoning (SOx poisoning), and it is necessary to perform a poisoning recovery process for recovering from sulfur poisoning at an appropriate time. This poisoning recovery process is performed by circulating the exhaust gas in which the oxygen concentration is lowered by adding fuel from the reducing agent addition valve 9 while the NOx catalyst 4 is at a high temperature (for example, about 600 to 650 ° C.) to the NOx catalyst 4. Yes.

  Although the poisoning recovery process is also performed by the rich spike control, the opening time of the reducing agent addition valve 9 per rich spike performed in the poisoning recovery process is longer than that during NOx reduction. That is, the amount of reducing agent added per rich spike during the poisoning recovery process is larger than that during NOx reduction.

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

  The above-described sensor or the like is connected to the ECU 10 via an electrical wiring, and an output signal from the sensor or the like is input thereto.

  On the other hand, the reducing agent addition valve 9 is connected to the ECU 10 through electric wiring, and the ECU 10 controls the reducing agent addition valve 9.

  By the way, the NOx catalyst 4 may deteriorate due to secular change or heat, and the NOx occlusion ability may be lowered. When the NOx storage capacity decreases, the temperature change of the NOx catalyst 4 at the time of addition of the reducing agent remarkably appears.

  As described above, the NOx catalyst 4 includes the NOx storage agent potassium (K), sodium (Na), lithium (Li), cesium (Cs), barium (Ba) calcium (Ca), lanthanum (La), or At least one such as yttrium (Y) is supported. When these NOx storage agents exceed 700 ° C., for example, the deterioration is remarkably advanced and the NOx storage capacity is lowered. On the other hand, noble metals such as platinum (Pt) have an oxidizing function. However, when the temperature exceeds 800 ° C., for example, the deterioration proceeds remarkably and the oxidizing ability is lowered. Thus, since the NOx storage agent deteriorates at a lower temperature than the noble metal such as platinum (Pt), the NOx storage agent progresses faster than the noble metal such as platinum (Pt).

  Moreover, the oxidation function of noble metals such as platinum (Pt) is suppressed due to the presence of the NOx storage agent. And if the function of NOx storage agent falls by deterioration, the oxidation function of noble metals, such as platinum (Pt), will increase in connection with it. Therefore, as shown in FIG. 2, at the initial stage where the NOx catalyst 4 is deteriorated, the increase in the oxidation ability due to the decrease in the function of the NOx storage agent exceeds the decrease in the oxidation ability due to the deterioration of the noble metal such as platinum (Pt). Therefore, the oxidation capacity of the NOx catalyst 4 increases. That is, in the initial stage where the NOx catalyst is deteriorated, the oxidation ability is higher than that in the new state.

  Here, FIG. 2 is a time chart showing the transition of the NOx storage capacity and the oxidation capacity of the NOx catalyst. The vertical axis represents the high catalyst processing capacity of the NOx catalyst 4 as a whole.

  Thus, in the initial stage where the NOx storage capacity of the NOx catalyst 4 decreases, the oxidation capacity of the NOx catalyst 4 as a whole increases, so that the reducing agent is more easily oxidized in the NOx catalyst 4, and when the reducing agent is added. The temperature of the NOx catalyst 4 rises quickly.

  Here, FIG. 3 is a time chart showing the time transition of the temperature of the NOx catalyst 4 during the rich spike control for NOx reduction. The upper part shows the change in the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 4, and the lower part shows the bed temperature of the NOx catalyst 4 when the NOx catalyst 4 is new and deteriorated (deteriorated product).

  If the NOx catalyst 4 is deteriorated, the oxidizing agent of the NOx catalyst 4 is increased, so that the reducing agent is rapidly oxidized. Therefore, the temperature of the NOx catalyst 4 is rapidly increased. Since the reducing agent is almost oxidized before the next addition of the reducing agent, the temperature of the NOx catalyst 4 hardly increases immediately before the next reducing agent point. That is, the temperature rise of the NOx catalyst 4 is slow.

On the other hand, when the NOx catalyst 4 is new, that is, when no deterioration has occurred, the oxidation ability of the NOx catalyst 4 is suppressed, so that the oxidation of the reducing agent becomes slow. As a result, the temperature rise also slows and continues to rise until the next time the reducing agent is added.

  From the above, the deterioration determination of the NOx catalyst 4 can be performed based on the temperature transition of the NOx catalyst 4 during the rich spike control for NOx reduction. That is, the time from when the reducing agent is added at the start of rich spike control until the temperature of the NOx catalyst 4 starts to rise increases as the degree of deterioration of the NOx catalyst 4 increases. Then, the minimum time until the start of the temperature rise that can be assumed that the NOx catalyst 4 has not deteriorated is obtained in advance by an experiment or the like as a threshold, and the temperature rise starts after the reducing agent is added during the NOx reduction of the NOx catalyst 4 It can be determined that the NOx catalyst 4 has deteriorated when the actual time until becomes shorter than this threshold. Further, when the time from when the reducing agent is added during NOx reduction of the NOx catalyst 4 to when the temperature rise starts is shorter than the time from when the reducing agent is added to the new NOx catalyst 4 to when the temperature rise starts, the NOx is reduced. It may be determined that the catalyst 4 has deteriorated.

  Next, a flow for determining the deterioration of the NOx catalyst 4 according to this embodiment will be described.

  FIG. 4 and FIG. 5 are flowcharts showing a flow for determining deterioration of the NOx catalyst 4 according to this embodiment. This flow is for determining the deterioration of the NOx catalyst 4 based on the time from the start of the rich spike to the start of the temperature rise of the NOx catalyst 4. The rich spike performed in this routine is a rich spike for reducing the NOx stored in the NOx catalyst 4.

  In step S101, the ECU 10 determines whether or not the catalyst deterioration determination request flag is ON. This catalyst deterioration determination request flag is a flag that is turned ON when it is necessary to determine the deterioration of the NOx catalyst 4, and is turned ON every predetermined period.

  If an affirmative determination is made in step S101, the process proceeds to step S102, whereas if a negative determination is made, the process proceeds to step S103.

  In step S102, the ECU 10 determines whether or not the floor temperature stabilization flag is ON. If the temperature of the NOx catalyst 4 obtained by the exhaust gas temperature sensor 6 is within a predetermined range that may be constant, the floor temperature stabilization flag is turned on because the temperature of the NOx catalyst 4 is stable. Flag.

  If an affirmative determination is made in step S102, the process proceeds to step S108, whereas if a negative determination is made, the process proceeds to step S104.

  In step S103, the ECU 10 turns off the bed temperature stabilization flag. After the processing of step S103 is completed, the ECU 10 once ends this routine.

  In step S104, the ECU 10 prohibits the rich spike for a certain period. That is, the bed temperature of the NOx catalyst 4 is stabilized by prohibiting the rich spike for a certain period.

  In step S105, the ECU 10 determines whether or not the bed temperature of the NOx catalyst 4 is stable. If the temperature of the NOx catalyst 4 obtained by the exhaust temperature sensor 6 is within a predetermined range that is constant, the bed temperature of the NOx catalyst 4 is considered to be stable.

  If an affirmative determination is made in step S105, the process proceeds to step S106. On the other hand, if a negative determination is made, this routine is temporarily terminated.

  In step S106, the ECU 10 turns on the bed temperature stabilization flag.

  In step S107, the ECU 10 resets a counter indicating the elapsed time from the start of the rich spike to 0.

  In step S108, the ECU 10 starts rich spike control. The rich spike control at this time is rich spike control for reducing NOx stored in the NOx catalyst 4 as described above.

  In step S109, the ECU 10 advances the value of the counter.

  In step S110, the ECU 10 estimates the temperature of the exhaust gas obtained by the exhaust gas temperature sensor 6 when a reducing agent is added to a catalyst in a state serving as a reference in the deterioration determination of the NOx catalyst 4 (hereinafter referred to as a reference product). . This reference product may be a NOx catalyst in a state where it can be assumed that it has not deteriorated. Further, the estimated value is previously mapped by experiments or the like using the intake air amount of the internal combustion engine 1 and the temperature of the exhaust gas discharged from the internal combustion engine 1 (outgas temperature) as parameters. For example, since the temperature of the NOx catalyst 4 changes with the exhaust temperature, the temperature of the reference product is estimated to be higher as the exhaust temperature is higher. Further, as the amount of exhaust increases, the amount of heat taken away from the NOx catalyst 4 by the exhaust increases, so the temperature of the reference product is estimated to be low. The estimated value of the exhaust temperature thus obtained is hereinafter referred to as an estimated exhaust temperature.

  In step S111, the ECU 10 calculates the difference between the actual exhaust temperature obtained by the exhaust temperature sensor 6 (hereinafter referred to as the actual exhaust temperature) and the estimated exhaust temperature. This actual exhaust temperature is substantially equal to the bed temperature of the NOx catalyst 4.

  In step S112, the ECU 10 determines whether or not the temperature difference calculated in step S111 is larger than the deterioration determination temperature difference. This deterioration judgment temperature difference is a temperature difference that can be assumed that the temperature of the NOx catalyst 4 has risen above the estimated exhaust temperature due to the rich spike.

  If an affirmative determination is made in step S112, the process proceeds to step S113, whereas if a negative determination is made, the process proceeds to step S115.

  In step S113, the ECU 10 determines whether or not the counter value is smaller than the first determination time. The first determination time is the minimum value of the counter when it can be assumed that the NOx catalyst 4 has not deteriorated, and is obtained in advance by experiments or the like. When the value of the counter is smaller than the first determination time, it is determined that the NOx catalyst 4 has deteriorated.

  If an affirmative determination is made in step S113, the process proceeds to step S116, whereas if a negative determination is made, the process proceeds to step S114.

  In step S114, the ECU 10 turns off the catalyst deterioration determination flag. This catalyst deterioration determination flag is a flag that is turned ON when it is determined that the NOx catalyst 4 is deteriorated. After the process of step S114 is completed, ECU10 once complete | finishes this routine.

In step S115, the ECU 10 determines whether or not the counter value is greater than the second determination time. Here, when the deterioration of the NOx catalyst 4 progresses, the reduction of the oxidation ability of the NOx catalyst 4 becomes large, so that the reducing agent becomes difficult to react. For this reason, it is difficult to increase the temperature of the NOx catalyst 4 due to the addition of the reducing agent. Therefore, if the temperature of the NOx catalyst 4 does not rise above the deterioration determination temperature difference even when the rich spike control is performed for a long time, it is determined that the deterioration of the NOx catalyst 4 is proceeding. Here, the second determination time is the maximum value of the counter value that can be assumed that the NOx catalyst 4 has not deteriorated, and is obtained in advance by experiments or the like.

  If an affirmative determination is made in step S115, the process proceeds to step S116. On the other hand, if a negative determination is made, this routine is temporarily terminated.

  In step S116, the ECU 10 turns on the catalyst deterioration determination flag. After the processing of step S116 is completed, the ECU 10 once ends this routine.

  In this way, it is possible to determine the deterioration of the NOx catalyst 4 based on the time from the start of the rich spike until the temperature of the NOx catalyst 4 rises.

  As described above, the temperature of the NOx catalyst 4 is not calculated by using the difference between the actual exhaust temperature and the estimated exhaust temperature but using the difference between the actual exhaust temperature and the temperature of the NOx catalyst 4 at the start of reducing agent addition. It is also possible to determine whether or not has started to rise. However, according to the present embodiment, which can take into account fluctuations in the exhaust temperature due to changes in the operating state of the internal combustion engine 1, it is possible to detect the temperature increase of the NOx catalyst 4 due to the addition of the reducing agent with higher accuracy.

  As described above, according to the present embodiment, the time from the start of addition of the reducing agent for reducing the NOx stored in the NOx catalyst 4 until the temperature of the NOx catalyst 4 rises is the first determination time. Shorter than that, it can be determined that the NOx catalyst 4 has deteriorated. In addition, since the deterioration determination of the NOx catalyst 4 can be performed before all the NOx stored in the NOx catalyst 4 is reduced, it is possible to quickly determine the deterioration. Furthermore, since it is not necessary to add a reducing agent only for determining the deterioration of the NOx catalyst 4, deterioration of fuel consumption can be suppressed.

  Next, another embodiment of the exhaust gas purification apparatus for an internal combustion engine will be described. Since the hardware is the same as that of the first embodiment, the description thereof is omitted. The rich spike in the present embodiment is a rich spike for NOx reduction.

  Here, when the NOx catalyst 4 is deteriorated, the temperature change rate of the NOx catalyst 4, that is, the temperature change amount per unit time varies. That is, immediately after the addition of the reducing agent, the amount of oxidation of the reducing agent is large and the temperature of the NOx catalyst 4 rapidly rises, so that the rate of change in temperature is large. The rise in temperature becomes slow and the rate of change in temperature becomes small. Thus, the rate of change of the temperature of the NOx catalyst 4 is large immediately after the addition of the reducing agent, but decreases immediately thereafter. On the other hand, if the NOx catalyst 4 is not deteriorated, the rate of temperature increase immediately after addition of the reducing agent is small as compared to when it is deteriorated. And since the quantity of unreacted reducing agent also reduces gradually, the change of a temperature change rate also becomes small.

  Therefore, it can be said that the degree of deterioration of the NOx catalyst 4 increases as the change in the temperature change rate of the NOx catalyst 4 increases. That is, it can be said that the degree of deterioration of the NOx catalyst 4 increases as the difference between the maximum value and the minimum value of the temperature change rate of the NOx catalyst 4 increases. For example, the difference between the maximum value and the minimum value of the rate of change, which can be determined as a threshold value that can be regarded as not deteriorating the NOx catalyst 4, is obtained in advance through experiments or the like, and the NOx catalyst 4 during rich spike control. It can be assumed that the NOx catalyst 4 is deteriorated when the difference between the maximum value and the minimum value of the change rate of the temperature becomes larger than this threshold value.

Further, the maximum value of the rate of change of the temperature of the NOx catalyst 4 increases as the degree of deterioration of the NOx catalyst 4 increases. Therefore, if the maximum value of the temperature change rate of the NOx catalyst 4 is larger than a threshold value that can be regarded as indicating that the NOx catalyst 4 has not deteriorated, it can be determined that the NOx catalyst 4 has deteriorated.

  Further, it may be determined that the NOx catalyst 4 is deteriorated when the temperature change rate of the NOx catalyst 4 immediately after the addition of the reducing agent is larger than a threshold value that can be regarded as the NOx catalyst 4 is not deteriorated.

  Further, it may be determined that the NOx catalyst 4 is deteriorated when the maximum temperature of the NOx catalyst 4 that is reached after the addition of the reducing agent is higher than a threshold value that the NOx catalyst 4 can be assumed not to be deteriorated. When the temperature of the NOx catalyst 4 reaches a temperature higher than a threshold that can be regarded as indicating that the NOx catalyst 4 has not deteriorated after addition of the reducing agent, it may be determined that the NOx catalyst 4 has deteriorated.

  As described above, according to the present embodiment, the deterioration determination of the NOx catalyst 4 can be performed before all of the NOx stored in the NOx catalyst 4 is reduced. is there.

  Next, another embodiment of the exhaust gas purification apparatus for an internal combustion engine will be described. Since the hardware is the same as that of the first embodiment, the description thereof is omitted.

  In this embodiment, the temperature when the NOx catalyst 4 is not deteriorated when the reducing agent is added to the NOx catalyst 4 is set as the reference temperature, and the difference between the actually detected temperature and the reference temperature is changed. When the width is larger than a value that can be assumed that the NOx catalyst 4 has not deteriorated, it is determined that the NOx catalyst 4 has deteriorated.

  Here, FIG. 6 is a time chart showing the time transition of the catalyst bed temperature (actual exhaust temperature) during NOx reduction in the deteriorated NOx catalyst. The reference temperature in FIG. 6 is discharged from the reducing agent addition amount, the intake air amount of the internal combustion engine 1 and the internal combustion engine 1 when the reducing agent is added to the NOx catalyst that can be assumed not to be deteriorated. The exhaust temperature (outgas temperature) is obtained as a parameter. This reference temperature may be obtained in advance through experiments or the like and mapped. Since the temperature of the NOx catalyst 4 varies with the exhaust temperature, the higher the exhaust temperature, the higher the reference temperature. Further, as the amount of exhaust increases, the amount of heat taken away from the NOx catalyst 4 by the exhaust increases, so the reference temperature is lowered. The reference temperature is the temperature of the NOx catalyst when a reducing agent is added to the reference product, as in the above embodiment.

  When the reducing agent is added to the deteriorated NOx catalyst 4, immediately after the reducing agent is added, the actual exhaust temperature first becomes higher than the reference temperature, and a maximum temperature difference of Δt1 occurs. On the other hand, as time elapses, the actual exhaust temperature becomes lower than the reference temperature, and a maximum temperature difference of Δt2 occurs. Here, Δt1 and Δt2 are values obtained by subtracting the reference temperature from the actual exhaust temperature. That is, in the case of FIG. 6, Δt2 is a negative value. In this embodiment, the difference between the maximum value and the minimum value of the difference between the actual exhaust temperature and the reference temperature, that is, Δt1−Δt2 is referred to as “temperature change width”.

  In this embodiment, the temperature change range from the start of addition of the reducing agent until a predetermined time has elapsed is obtained. This predetermined time is the time required to detect the temperature that has risen due to one or two rich spikes, and the time until the temperature rise due to the second or third rich spike begins. can do.

Here, the greater the temperature change width, the greater the variation in the temperature change rate of the NOx catalyst 4, and the greater the degree of deterioration of the NOx catalyst 4. Therefore, the maximum value of the temperature change width that can be assumed that the NOx catalyst 4 is not deteriorated is obtained in advance by experiments or the like as a threshold value, and the NOx catalyst is obtained when the actually obtained temperature change width becomes larger than the threshold value. 4 can be determined to have deteriorated.

  Next, another aspect of determining the deterioration of the NOx catalyst 4 will be described.

  FIGS. 4 and 7 are flowcharts showing another deterioration determination flow of the NOx catalyst 4 according to this embodiment. This flow is for determining the deterioration of the NOx catalyst 4 based on the temperature change width of the NOx catalyst 4 during the rich spike. The rich spike performed in this routine is a rich spike for reducing the NOx stored in the NOx catalyst 4.

  Here, since FIG. 4 was already demonstrated, description is abbreviate | omitted. Further, in FIG. 7, steps in which processing similar to that in the above-described flow is performed are denoted by the same numbers and description thereof is omitted.

  In step S201, the ECU 10 calculates a temperature change width. This temperature change width is a value obtained by subtracting the minimum value from the maximum value of the temperature difference calculated in step S111, and corresponds to Δt1−Δt2.

  In step S202, the ECU 10 determines whether or not the temperature change width is larger than a determination value. This determination value is the maximum value of the temperature change width that can be assumed that the NOx catalyst 4 has not deteriorated, and is obtained in advance through experiments or the like.

  If an affirmative determination is made in step S202, the process proceeds to step S116, whereas if a negative determination is made, the process proceeds to step S114.

  In this way, it is possible to determine the deterioration of the NOx catalyst 4 based on the temperature change width of the NOx catalyst 4 during the rich spike.

  Next, another embodiment of the exhaust gas purification apparatus for an internal combustion engine will be described. Since the hardware is the same as that of the first embodiment, the description thereof is omitted.

  Here, in this embodiment, the deterioration determination of the NOx catalyst 4 is performed based on the temperature change of the NOx catalyst 4 when the reducing agent is added to recover the sulfur poisoning of the NOx catalyst 4.

  FIG. 8 is a time chart showing the time transition of the temperature of the NOx catalyst 4 during rich spike control for recovering sulfur poisoning. The upper part shows the change in the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 4, and the lower part shows the bed temperature of the NOx catalyst 4 when the NOx catalyst 4 is new and deteriorated (deteriorated product). At the time of sulfur poisoning recovery, the amount of reducing agent added per rich spike is larger than that during NOx reduction. Therefore, the temperature rise of the NOx catalyst 4 per rich spike is large.

  Here, if the NOx catalyst 4 is deteriorated, the reducing agent is rapidly oxidized due to the high oxidizing ability of the NOx catalyst 4, so that the temperature of the NOx catalyst 4 rapidly increases. Since the temperature rise of the NOx catalyst 4 per rich spike is large, the temperature of the NOx catalyst 4 reaches the maximum temperature in the first rich spike, and then the temperature decreases. Then, the temperature is raised again by the next rich spike. By repeating this, the temperature of the NOx catalyst 4 varies.

On the other hand, if the NOx catalyst 4 is not deteriorated, the oxidation ability of the NOx catalyst 4 is suppressed, so that the oxidation of the reducing agent becomes slow. As a result, the temperature rise is slow, but the temperature rise of the NOx catalyst 4 per rich spike is large, so the temperature of the NOx catalyst 4 reaches the maximum temperature in one rich spike. Then, the temperature is raised again by the next rich spike. By repeating this, the temperature of the NOx catalyst 4 varies.

  From the above, the deterioration determination of the NOx catalyst 4 can be performed based on the temperature transition of the NOx catalyst 4 during the rich spike control for sulfur poisoning recovery. That is, the time from the addition of the reducing agent at the start of the rich spike control until the temperature of the NOx catalyst 4 reaches the maximum temperature becomes faster as the degree of deterioration of the NOx catalyst 4 increases. Then, the minimum time to reach the maximum temperature at which the NOx catalyst 4 can be assumed not to have deteriorated is obtained in advance by experiments or the like as a threshold, and the time to reach the maximum temperature during the poisoning recovery processing of the NOx catalyst 4 When it becomes smaller than this threshold, it can be determined that the NOx catalyst 4 has deteriorated.

  Here, the “maximum temperature” may be a temperature when the temperature of the NOx catalyst 4 reaches a maximum value, or may be a temperature immediately before the temperature of the NOx catalyst 4 starts to decrease.

  Next, a flow for determining the deterioration of the NOx catalyst 4 according to this embodiment will be described.

  FIGS. 4 and 9 are flowcharts showing another deterioration determination flow of the NOx catalyst 4 according to this embodiment. This flow is for determining the deterioration of the NOx catalyst 4 based on the time from the start of the rich spike until the temperature of the NOx catalyst 4 reaches the maximum temperature. The rich spike performed in this routine is a rich spike for recovering the sulfur poisoning of the NOx catalyst 4.

  Here, since FIG. 4 was already demonstrated, description is abbreviate | omitted. Also, in FIG. 9, steps in which processing similar to that in the flow shown in FIG. 5 is performed are assigned the same numbers and description thereof is omitted.

  In step S301, the ECU 10 starts rich spike control. The rich spike control at this time is rich spike control for recovering sulfur poisoning of the NOx catalyst 4.

  In step S302, the ECU 10 determines whether or not the temperature difference calculated in step S111 is greater than or equal to the peak threshold value. The peak threshold is a temperature difference that allows the temperature of the NOx catalyst 4 to be close to the maximum value due to the addition of the reducing agent, and is obtained in advance through experiments or the like.

  If an affirmative determination is made in step S302, the process proceeds to step S303, whereas if a negative determination is made, the process proceeds to step S304.

  In step S303, the ECU 10 determines whether or not the counter value is smaller than the third determination time. This third determination time is the minimum value of the counter when it can be assumed that the NOx catalyst 4 has not deteriorated, and is obtained in advance by experiments or the like. When the value of the counter is smaller than the third determination time, it is determined that the NOx catalyst 4 has deteriorated.

  If an affirmative determination is made in step S303, the process proceeds to step S116, whereas if a negative determination is made, the process proceeds to step S114.

In step S304, the ECU 10 determines whether or not the counter value is greater than the fourth determination time. Here, when the deterioration of the NOx catalyst 4 progresses, the reducing agent does not react due to a decrease in the oxidation ability of the NOx catalyst 4. Therefore, even if the reducing agent is added, the temperature of the NOx catalyst 4 does not rise or becomes slow even if it rises. Therefore, if the temperature of the NOx catalyst 4 does not rise or continues to rise slowly even if the rich spike control is performed for a long time, it is determined that the deterioration of the NOx catalyst 4 is proceeding. Here, the fourth determination time is the maximum value of the counter value that can be assumed that the NOx catalyst 4 has not deteriorated, and is obtained in advance through experiments or the like.

  If an affirmative determination is made in step S304, the process proceeds to step S116. On the other hand, if a negative determination is made, this routine is temporarily terminated.

  In this way, the deterioration determination of the NOx catalyst 4 is performed based on the time taken from the start of the rich spike for recovery of sulfur poisoning of the NOx catalyst 4 until the temperature of the NOx catalyst 4 reaches the maximum value. It can be carried out.

  In this flow, the deterioration determination of the NOx catalyst 4 is performed based on the time from the start of addition of the reducing agent until the temperature difference becomes equal to or greater than the peak threshold value. The deterioration determination of the NOx catalyst 4 may be performed based on the time until the exhaust gas temperature obtained by the sensor 6 reaches the maximum value.

  By the way, also at the time of sulfur poisoning recovery, the time from the start of addition of the reducing agent until the temperature of the NOx catalyst 4 starts to rise increases as the degree of deterioration of the NOx catalyst 4 increases as in the case of NOx reduction. Therefore, the deterioration determination of the NOx catalyst 4 can be performed based on the time from the start of addition of the reducing agent until the temperature of the NOx catalyst 4 starts to rise in the same way as during NOx reduction and during the recovery of sulfur poisoning.

  Further, the maximum value of the rate of change of the temperature of the NOx catalyst 4 increases as the degree of deterioration of the NOx catalyst 4 increases. Therefore, if the maximum value of the temperature change rate of the NOx catalyst 4 is larger than a threshold value that can be regarded as indicating that the NOx catalyst 4 has not deteriorated, it can be determined that the NOx catalyst 4 has deteriorated.

  Further, it may be determined that the NOx catalyst 4 is deteriorated when the temperature change rate of the NOx catalyst 4 immediately after the addition of the reducing agent is larger than a threshold value that can be regarded as the NOx catalyst 4 is not deteriorated.

  Further, it may be determined that the NOx catalyst 4 is deteriorated when the maximum temperature of the NOx catalyst 4 that is reached after the addition of the reducing agent is higher than a threshold value that the NOx catalyst 4 can be assumed not to be deteriorated. When the temperature of the NOx catalyst 4 reaches a temperature higher than a threshold that can be regarded as indicating that the NOx catalyst 4 has not deteriorated after addition of the reducing agent, it may be determined that the NOx catalyst 4 has deteriorated.

  As described above, according to the present embodiment, the deterioration determination of the NOx catalyst 4 can be performed with one rich spike at the time of sulfur poisoning recovery, and therefore, it is possible to quickly determine the deterioration.

  Next, another embodiment of the exhaust gas purification apparatus for an internal combustion engine will be described. Since the hardware is the same as that of the first embodiment, the description thereof is omitted.

In this embodiment, the NOx catalyst 4 is judged for deterioration by comparing the temperature transition during NOx reduction of the NOx catalyst 4 with the temperature transition during recovery from sulfur poisoning. Here, when the NOx catalyst 4 is deteriorated, the temperature change rate of the NOx catalyst 4 varies greatly during NOx reduction and during sulfur poisoning recovery. On the other hand, when the NOx catalyst 4 is not deteriorated, the change in the temperature change rate of the NOx catalyst 4 during NOx reduction is small, but the change in the change rate during recovery from sulfur poisoning is large. From the above, it can be said that the NOx catalyst 4 has deteriorated if the change in the temperature change rate of the NOx catalyst 4 does not change greatly between NOx reduction and sulfur poisoning recovery.

  In this embodiment, the temperature change widths are obtained during NOx reduction and during sulfur poisoning recovery. Here, the temperature change width at the time of NOx reduction is the same as that described in the above embodiment. Moreover, the temperature change width at the time of sulfur poisoning recovery is obtained as follows.

  FIG. 10 is a graph showing the temperature transition of the NOx catalyst 4 and the reference temperature during the recovery from sulfur poisoning. The reference temperature at the time of sulfur poisoning recovery is a line indicating the center of the temperature fluctuation of the reference product, and the amount of reducing agent, the intake air amount of the internal combustion engine 1 and the internal combustion engine 1 when the reducing agent is added to the reference product. As a parameter, the temperature of the exhaust gas discharged from the exhaust gas (outgas temperature) is obtained. This reference temperature may be obtained in advance through experiments or the like and mapped. In addition, since the temperature of the NOx catalyst 4 changes with the change of the exhaust gas temperature, the reference temperature is raised as the exhaust gas temperature is higher. Further, as the amount of exhaust increases, the amount of heat taken away from the NOx catalyst 4 by the exhaust increases, so the reference temperature is lowered.

  After the reducing agent is added, first, the actual exhaust temperature becomes higher than the reference temperature, and a maximum temperature difference of Δt1 occurs. On the other hand, as time elapses, the actual exhaust temperature becomes lower than the reference temperature, and a maximum temperature difference of Δt2 occurs. Here, Δt1 and Δt2 are values obtained by subtracting the reference temperature from the actual exhaust temperature. That is, in the case of FIG. 10, Δt2 is a negative value. Also in this embodiment, the difference between the maximum value and the minimum value of the difference between the actual exhaust temperature and the reference temperature, that is, Δt1−Δt2 is referred to as “temperature change width”. The temperature change width may be obtained as a difference between the maximum temperature after adding the reducing agent to the NOx catalyst 4 and the minimum temperature thereafter.

  Then, when the difference between the temperature change width at the time of sulfur poisoning recovery and the temperature change width at the time of NOx reduction is smaller than the threshold value, it can be determined that the NOx catalyst 4 has deteriorated. The threshold here is a minimum value that can be assumed that the NOx catalyst 4 is not deteriorated, and is obtained in advance by experiments or the like.

  Next, another aspect of determining the deterioration of the NOx catalyst 4 will be described.

  FIGS. 11, 12 and 13 are flowcharts showing another deterioration determination flow of the NOx catalyst 4 according to this embodiment. This flow is for determining the deterioration of the NOx catalyst 4 based on the difference between the temperature change width at the time of sulfur poisoning recovery and the temperature change width at the time of NOx reduction.

  Here, in FIG. 11, FIG. 12, and FIG. 13, the steps in which the same processing as that of the above-described flow is performed are assigned the same numbers and the description thereof is omitted.

  In step S401, the ECU 10 determines whether or not the short time rich spike is ON. The short-time rich spike refers to a rich spike that is performed to reduce NOx stored in the NOx catalyst 4. The short time rich spike end flag is a flag that is turned ON when the short time rich spike ends.

  If an affirmative determination is made in step S401, the process proceeds to step S402. On the other hand, if a negative determination is made, the process proceeds to step S403.

In step S402, the ECU 10 performs long-time rich spike control. This long-time rich spike control refers to a rich spike that is performed to recover sulfur poisoning of the NOx catalyst 4. At the same time, ON when rich spike ends for a long time.
The long-time rich spike end flag is turned ON.

  In step S403, the ECU 10 performs short-time rich spike control. Due to the short-time rich spike control being performed, the short-time rich spike end flag is turned ON.

  In step S404, the ECU 10 determines whether or not the short time rich spike end flag is ON.

  If an affirmative determination is made in step S404, the process proceeds to step S405. On the other hand, if a negative determination is made, this routine is temporarily terminated.

  In step S405, the ECU 10 determines whether or not the long-time rich spike end flag is ON.

  If an affirmative determination is made in step S405, the process proceeds to step S406. On the other hand, if a negative determination is made, the process proceeds to step S408.

  In step S406, the ECU 10 calculates a temperature change width difference that is a difference between the temperature change width calculated in step S201 and a short-time temperature change width described later. The temperature change width calculated in step S201 here is due to a long-time rich spike. In this step, the temperature change width difference is calculated by subtracting the temperature change width caused by the short time rich spike from the temperature change width caused by the long time rich spike.

  In step S407, the ECU 10 determines whether or not the temperature change width difference calculated in step S406 is larger than a threshold value. This threshold value is an upper limit value of the temperature change width difference that can be regarded as the deterioration of the NOx catalyst 4. If the temperature change width difference is larger than this threshold value, it is determined that the NOx catalyst 4 has not deteriorated.

  If an affirmative determination is made in step S407, the process proceeds to step S114. On the other hand, if a negative determination is made, the process proceeds to step S116.

  In step S408, the ECU 10 inputs the temperature change width at the time of the short time rich spike control as the short time temperature change width.

  In step S409, the ECU 10 turns off the short time rich spike flag and turns off the long time rich spike flag. After the processing of step S409 is completed, the ECU 10 once ends this routine.

  In this way, it is possible to determine the deterioration of the NOx catalyst 4 based on the difference in temperature change width between the long time rich spike and the short time rich spike.

It is a figure which shows schematic structure of the internal combustion engine which applies the exhaust gas purification apparatus of the internal combustion engine which concerns on an Example, and its exhaust system. FIG. 6 is a time chart showing the transition of NOx storage capacity and oxidation capacity of the NOx catalyst. FIG. 6 is a time chart showing the time transition of the temperature of the NOx catalyst during rich spike control for NOx reduction. FIG. 3 is a flowchart showing a flow of NOx catalyst deterioration determination according to Examples 1, 3 and 4. FIG. 3 is a flowchart showing a flow for determining deterioration of a NOx catalyst according to the first embodiment. FIG. 6 is a time chart showing the time transition of the catalyst bed temperature (actual exhaust temperature) during NOx reduction in a deteriorated NOx catalyst. FIG. 12 is a flowchart showing another deterioration determination flow of the NOx catalyst according to the third embodiment. FIG. 5 is a time chart showing the time transition of the temperature of the NOx catalyst during rich spike control for recovering sulfur poisoning. FIG. 12 is a flowchart showing another deterioration determination flow of the NOx catalyst according to the fourth embodiment. It is the figure which showed the temperature transition of the NOx catalyst at the time of sulfur poisoning recovery | restoration, and its reference temperature. FIG. 12 is a first flowchart showing another deterioration determination flow of the NOx catalyst according to the fifth embodiment. FIG. 10 is a second flowchart showing a flow of other deterioration determination of the NOx catalyst according to Embodiment 5. FIG. 10 is a third flowchart showing a flow of other deterioration determination of the NOx catalyst according to Embodiment 5.

Explanation of symbols

Reference Signs List 1 internal combustion engine 2 exhaust passage 3 upstream catalyst 4 NOx storage reduction catalyst 5 first air-fuel ratio sensor 6 exhaust temperature sensor 7 second air-fuel ratio sensor 9 reducing agent addition valve 10 ECU

Claims (10)

A NOx storage reduction catalyst that stores NOx when the oxygen concentration in the exhaust gas is high and reduces NOx that is stored when the oxygen concentration is low and a reducing agent is present;
Catalyst deterioration determination means for determining that the NOx storage reduction catalyst has deteriorated when the oxidation capacity of the NOx storage reduction catalyst is equal to or greater than a predetermined capacity;
An exhaust emission control device for an internal combustion engine, comprising:   The catalyst deterioration determining means is configured such that when the oxidation capacity of the NOx storage reduction catalyst is greater than or equal to the oxidation capacity of the NOx storage reduction catalyst when it is new, the oxidation capacity of the NOx storage reduction catalyst is greater than or equal to a predetermined capacity. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the determination is made. Reducing agent addition means for adding a reducing agent from upstream of the NOx storage reduction catalyst;
Catalyst temperature detecting means for detecting the temperature of the NOx storage reduction catalyst;
Further comprising
Whether the catalyst deterioration determining means has an oxidation capacity of the NOx storage reduction catalyst equal to or greater than a predetermined capacity based on a temperature change of the catalyst detected by the catalyst temperature detecting means when the reducing agent is added by the reducing agent adding means. 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein it is determined whether or not the NOx storage reduction catalyst is deteriorated by determining whether or not the NOx storage reduction catalyst is deteriorated.   The catalyst deterioration determination means has a time from when the addition of the reducing agent by the reducing agent addition means is started until the temperature of the catalyst detected by the catalyst temperature detection means starts to rise higher than a first predetermined time. 4. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein it is determined that the NOx storage reduction catalyst has deteriorated when the time is short.   The catalyst deterioration determining means has a time from when the addition of the reducing agent by the reducing agent adding means is started until the temperature of the catalyst detected by the catalyst temperature detecting means reaches a maximum value from a second predetermined time. 4. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein it is determined that the NOx storage reduction catalyst has deteriorated when the time is shorter.   The catalyst deterioration determining means is configured to store the storage reduction type when the rate of change of the temperature of the catalyst detected by the catalyst temperature detecting means when the reducing agent is added by the reducing agent adding means is greater than a first predetermined value. 4. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein it is determined that the NOx catalyst has deteriorated. Further comprising a catalyst reference temperature calculation means for calculating a reference temperature of the NOx storage reduction catalyst after the addition of the reducing agent by the reducing agent addition means,
The catalyst deterioration determination means obtains a change width of a difference between the temperature detected by the catalyst temperature detection means and the reference temperature, and when the change width becomes larger than a second predetermined value, the occlusion reduction 4. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein it is determined that the type NOx catalyst has deteriorated. Further comprising a catalyst reference temperature calculation means for calculating a reference temperature of the NOx storage reduction catalyst after the addition of the reducing agent by the reducing agent addition means,
The reducing agent addition means performs at least two kinds of reducing agent additions with different reducing agent addition amounts per time,
The catalyst deterioration determining means obtains a change width of a difference between the temperature detected by the catalyst temperature detecting means and the reference temperature in each case of at least two kinds of reducing agent addition, and the at least two kinds of reductions 4. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the storage reduction type NOx catalyst is determined to have deteriorated when the difference in the change width of the additive addition is larger than a third predetermined value.   The addition of the at least two kinds of reducing agents includes the addition of a reducing agent for reducing NOx stored in the NOx storage reduction catalyst and the recovery of sulfur poisoning in which the amount of addition of the reducing agent is larger than that. The exhaust gas purification apparatus for an internal combustion engine according to claim 8, wherein the reducing agent is added to perform the operation.   When the temperature of the NOx storage reduction catalyst after the addition of the reducing agent by the reducing agent addition means is higher than a predetermined temperature, the oxidation reduction ability of the NOx storage reduction catalyst has a predetermined capacity. The exhaust emission control device for an internal combustion engine according to claim 3, wherein the exhaust gas purification device is determined as above.

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