JP2010048115A - Catalyst deterioration determination device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology distinguishing between deterioration of a catalyst and abnormality of reducer addition means and accurately determining the deterioration of the catalyst in a catalyst deterioration determination device for an internal combustion engine. <P>SOLUTION: This device includes an SCR catalyst disposed at an exhaust passage of the internal combustion engine and converting NOx in exhaust gas by supply of urea, and an urea addition valve adding urea to the SCR catalyst, calculates air quantity-conversion rate characteristics of the SCR catalyst, determines deterioration of SCR catalyst when inclination of the air quantity-conversion rate characteristics in relation to air quantity in a prescribed range is constant, and determines abnormality of the urea addition valve when inclination of the air quantity-conversion rate characteristics in relation to air quantity in the prescribed range is not constant. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

Conventionally, a catalyst that purifies NOx in exhaust gas by supplying ammonia or a reducing agent that is a precursor thereof is disposed in an exhaust passage of an internal combustion engine. A technique is disclosed in which the ammonia concentration downstream of the catalyst is estimated, the ammonia concentration downstream of the catalyst is actually measured, and the catalyst deterioration is determined based on the difference between the estimated ammonia concentration and the actually measured ammonia concentration (for example, Patent Documents). 1).
JP 2006-125323 A JP 2008-82201 A JP 2007-32472 A

  However, the discrepancy between the estimated ammonia concentration downstream of the catalyst and the measured ammonia concentration is caused not only by the catalyst deterioration but also by the abnormality of the reducing agent addition valve for adding the reducing agent. Therefore, in the technique of Patent Document 1, even if it is determined that the catalyst is deteriorated, there is a case where the catalyst is not deteriorated and the reducing agent addition valve is abnormal, and the catalyst deterioration cannot be accurately determined.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to accurately determine catalyst deterioration by distinguishing between catalyst deterioration and reducing agent addition means abnormality in an internal combustion engine catalyst deterioration determination device. It is to provide a technique for making a determination.

In the present invention, the following configuration is adopted. That is, the present invention
A catalyst that is disposed in an exhaust passage of the internal combustion engine and purifies NOx in the exhaust by being supplied with a reducing agent;
Reducing agent addition means for adding a reducing agent to the catalyst;
An air amount-purification rate characteristic calculating means for calculating a characteristic of the purification rate of the catalyst with respect to the amount of air flowing through the catalyst;
Determination that distinguishes between catalyst deterioration and abnormality of the reducing agent addition unit based on a change in the slope of the air amount-purification rate characteristic calculated by the air amount-purification rate characteristic calculation unit in an air amount within a predetermined range. Means,
An apparatus for determining deterioration of a catalyst for an internal combustion engine, comprising:

  Here, the amount of air in a predetermined range is a range in which the amount of air that is completely purified by the catalyst without passing through the catalyst by NOx is too small, and the amount of air by which almost all of the NOx in the exhaust passes through the catalyst. This is the amount of air between the excessive range. That is, in this predetermined amount of air, a part of the NOx in the exhaust gas is purified by the catalyst, and another part of the NOx in the exhaust gas passes through the catalyst.

Based on the inventors' diligent study, the catalyst deterioration rate and the reducing agent based on the characteristics of the purification rate of the catalyst with respect to the amount of air flowing through the catalyst in a predetermined range of air amount, that is, the slope of the air amount-purification rate characteristic. It has been found that it can be distinguished from abnormality of the adding means. Therefore, according to the present invention, it is possible to distinguish between catalyst deterioration and abnormality of the reducing agent addition means, and it is possible to accurately determine catalyst deterioration.

  As a result of intensive studies by the present inventors, when the variation of the inclination of the air purification rate characteristic of the catalyst with respect to the amount of air flowing through the catalyst within the predetermined amount of air, that is, the variation of the slope of the air amount-purification rate characteristic falls within the predetermined range, the catalyst deterioration occurs. I found out. Further, it has been found that when the fluctuation of the slope of the air amount-purification rate characteristic in a predetermined range of air amount exceeds a predetermined range, an abnormality of the reducing agent adding means occurs. As described above, when the catalyst is deteriorated and when the reducing agent addition unit is abnormal, the variation in the slope of the air amount-purification rate characteristic in the air amount within a predetermined range is bounded by the predetermined region. I found something different.

  Therefore, the determination unit determines that the catalyst has deteriorated when the variation in the slope of the air amount-purification rate characteristic calculated by the air amount-purification rate characteristic calculation unit in a predetermined range of air amount falls within a predetermined range. When the variation in the slope of the air amount-purification rate characteristic calculated by the air amount-purification rate characteristic calculating unit in a range of air amounts exceeds a predetermined range, it may be determined that the reducing agent addition unit is abnormal.

  Here, the fluctuation in the inclination of the predetermined range is a threshold value that can be determined as catalyst deterioration when it falls within that range, and that it can be determined as an abnormality of the reducing agent addition means when exceeding that, and is obtained in advance through experiments and verifications. Can do.

  According to the present invention, it is possible to distinguish between the catalyst deterioration and the abnormality of the reducing agent addition means, and it is possible to accurately determine the catalyst deterioration.

NOx concentration detection means that is disposed in the exhaust passage downstream of the catalyst and detects the NOx concentration in the exhaust discharged from the catalyst;
The NOx concentration is detected by the NOx concentration detecting means while changing the amount of reducing agent added from the reducing agent adding means, and the characteristic of the purification rate of the catalyst with respect to the amount of reducing agent added from the reducing agent adding means is calculated. Reducing agent amount-purification rate characteristic calculating means,
With
The air amount-purification rate characteristic calculating means adds the optimum addition amount calculated from the reducing agent amount-purification rate characteristic calculated by the reducing agent amount-purification rate characteristic calculating means from the reducing agent addition means, The NOx concentration may be detected by the NOx concentration detecting means while changing the amount of air flowing through the catalyst, and the purification rate characteristic of the catalyst with respect to the amount of air flowing through the catalyst may be calculated.

  According to the present invention, the air amount-purification rate characteristic can be accurately calculated, and the catalyst deterioration determined based on the air amount-purification rate characteristic and the abnormality of the reducing agent addition means can be accurately distinguished.

  The air amount-purification rate characteristic calculating means is such that the optimum addition amount obtained from the reducing agent amount-reduction rate characteristic calculated by the reducing agent amount-purification rate characteristic calculating means is equal to or less than a predetermined amount, and the reducing agent amount- When the maximum purification rate obtained from the reducing agent amount-purification rate characteristic calculated by the purification rate characteristic calculating means is equal to or less than a predetermined value, the characteristic of the purification rate of the catalyst with respect to the amount of air flowing through the catalyst may be calculated.

  Here, the predetermined amount of the optimum addition amount is an amount that may cause another abnormality when the amount of the reducing agent is larger than that. Moreover, the predetermined value of the maximum purification rate is a value at which it can be determined that the catalyst has not yet deteriorated if the purification rate is higher than that.

According to the present invention, when the optimum addition amount is a predetermined amount or less and the maximum purification rate is a predetermined value or less,
Since the air amount-purification rate characteristic is calculated by the air amount-purification rate characteristic calculating means, it is possible to eliminate the case where another abnormality has occurred or the catalyst has not deteriorated. For this reason, the air amount-purification rate characteristic can be accurately calculated, and the catalyst deterioration determined based on the air amount-purification rate characteristic and the abnormality of the reducing agent addition means can be accurately distinguished.

  According to the present invention, in the catalyst deterioration determination device for an internal combustion engine, it is possible to distinguish between catalyst deterioration and abnormality of the reducing agent addition means, and it is possible to accurately determine catalyst deterioration.

  Specific examples of the present invention will be described below.

<Example 1>
FIG. 1 is a diagram illustrating a schematic configuration of an internal combustion engine to which the catalyst deterioration determination device for an internal combustion engine according to the present embodiment is applied and an exhaust system thereof. An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-stroke cycle diesel engine having four cylinders. The internal combustion engine 1 is mounted on a vehicle.

  An exhaust passage 2 is connected to the internal combustion engine 1. An SCR catalyst 3 is disposed in the exhaust passage 2. The SCR catalyst 3 purifies NOx in the exhaust gas flowing through the exhaust passage 2 by supplying urea as a reducing agent to the SCR catalyst 3. The SCR catalyst 3 of this example corresponds to the catalyst of the present invention. In this embodiment, urea is used as the reducing agent, but the reducing agent of the present invention is not limited to this.

  A urea addition valve 4 that adds urea into the exhaust passage 2 is disposed in the exhaust passage 2 upstream of the SCR catalyst 3. Urea added from the urea addition valve 4 is supplied to the SCR catalyst 3. The urea addition valve 4 of this embodiment corresponds to the reducing agent addition means of the present invention.

  In the exhaust passage downstream of the urea addition valve 4 and upstream of the SCR catalyst 3, a dispersion plate 5 for dispersing urea added from the urea addition valve 4 is disposed. The exhaust passage 2 has a constant narrow passage area upstream from the dispersion plate 5 with the dispersion plate 5 as a boundary, and the passage area becomes wider as the downstream side approaches the SCR catalyst 3 than the dispersion plate 5.

  A NOx sensor 6 that detects the NOx concentration in the exhaust gas flowing out from the SCR catalyst 3 is disposed in the exhaust passage 2 immediately downstream of the SCR catalyst 3. The NOx sensor 6 of this embodiment corresponds to the NOx concentration detection means of the present invention. The exhaust passage 2 and the devices arranged in the exhaust passage 2 constitute an exhaust system of the internal combustion engine 1.

  The internal combustion engine 1 configured as described above is provided with an ECU 7 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 7 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.

  In addition to the NOx sensor 6, the ECU 7 includes an accelerator opening sensor 8 that outputs an electric signal corresponding to the amount of depression of the accelerator pedal, and a crank position sensor 9 that detects the engine speed of the internal combustion engine 1 via electric wiring. The output signals of these various sensors are input to the ECU 7.

  On the other hand, the urea addition valve 4 is connected to the ECU 7 through electric wiring, and the urea addition valve 4 is controlled by the ECU 7 to instruct the added urea amount, the addition timing, and the like.

Conventionally, the NOx concentration is detected by the NOx sensor 6 while changing the amount of urea added from the urea addition valve 4, and the purification rate of the SCR catalyst 3 with respect to the amount of urea added from the urea addition valve 4 shown in FIG. (Hereinafter, urea amount-purification rate characteristic) was calculated. Then, catalyst deterioration is determined from the difference in urea amount-purification rate characteristics.

  FIG. 3 shows three cases with different urea amount-purification rate characteristics. The urea amount-purification rate characteristic shown by the solid line in FIG. 3 is a characteristic when the SCR catalyst 3 is normal. The urea amount-purification rate characteristic indicated by the broken line in FIG. 3 is a characteristic when the SCR catalyst 3 deteriorates and the 50% purification rate deteriorates. The urea amount-purification rate characteristic of the alternate long and short dash line shown in FIG. 3 is a characteristic when the urea amount supplied to the SCR catalyst 3 is insufficient by 50% although urea is added from the urea addition valve 4. Conventionally, it has been determined that the SCR catalyst 3 has deteriorated due to the broken line characteristics shown in FIG.

  However, as shown in FIG. 4, urea added from the urea addition valve 4 concentrates on a part, and dispersion of urea in the SCR catalyst 3 may deteriorate. Also in this case, it has been found that the urea amount-purification rate characteristic indicated by the broken line in FIG. 3 is obtained. That is, even when the dispersion of urea from the urea addition valve 4 to the SCR catalyst 3 is deteriorated and the 50% purification rate is deteriorated, the urea amount-purification rate characteristic of the broken line shown in FIG. 3 is obtained.

That is, when the dispersion of urea in the SCR catalyst 3 is deteriorated, NH ₃ generated by the reaction of urea with a part of the SCR catalyst ₃ is concentrated. Therefore, the dispersion of the urea resulting in the addition of urea amount when normal, slipping from the portion where NH ₃ in the SCR catalyst 3 is concentrated in the NH ₃ occurs. Therefore, when the dispersion of urea in the SCR catalyst 3 deteriorates, the characteristic is calculated like the urea amount-purification rate characteristic of the broken line shown in FIG. 3 even though the SCR catalyst 3 is not deteriorated. End up.

  From the above, even if the deterioration of the SCR catalyst 3 is determined from the difference in the urea amount-purification rate characteristics, the deterioration of the SCR catalyst 3 does not occur and the abnormality of the urea addition valve 4 may occur. The deterioration of the catalyst 3 could not be accurately determined.

  Incidentally, the NOx concentration is detected by the NOx sensor 6 while changing the amount of air flowing through the SCR catalyst 3, and the characteristic of the purification rate of the SCR catalyst 3 with respect to the amount of air flowing through the SCR catalyst 3 (hereinafter referred to as air amount-purification rate characteristic). Can also be calculated. As a result of diligent studies by the present inventors, it has been found that the SCR catalyst 3 is deteriorated when the air amount-purification rate characteristic has a constant air amount within a certain range. Further, it has been found that the urea addition valve 4 is abnormal if the air amount is not constant within a certain range of the air amount-purification rate characteristics. Thus, it has been found that the slope of the air amount-purification rate characteristic differs between the deterioration of the SCR catalyst 3 and the abnormality of the urea addition valve 4.

  Here, the constant slope of the air amount-purification rate characteristic means that the fluctuation of the slope of the air amount-purification rate characteristic is within a predetermined range, and the slope of the air amount-purification rate characteristic is not constant. This refers to a case where the fluctuation of the slope of the amount-purification rate characteristic exceeds a predetermined range. In addition, the fluctuation in the inclination of the predetermined range is a threshold value that can be determined as catalyst deterioration when it falls within the predetermined range, and can be determined as an abnormality of the reducing agent addition means when exceeding that, and is determined in advance through experiments and verifications. be able to.

First, a case where the SCR catalyst 3 is deteriorated will be described. When the degradation of the SCR catalyst 3 occurs, medium NH ₃ is distributed and adsorbed throughout the SCR catalyst 3 as shown in FIG. Then, when the air amount-purification rate characteristic of the SCR catalyst 3 is calculated, it is as shown in FIG. In FIG. 6, in the range of the “a” air amount where the air amount is small, the air amount is excessively small, and NOx does not slip through the SCR catalyst 3 and is completely purified in the SCR catalyst 3. In the range of medium air volume “I”, the air volume is large, and some NOx cannot be sufficiently reduced in the SCR catalyst 3, and some NOx becomes SCR catalyst 3. Slip through. In the range of the air amount “I”, as the air amount increases, the amount of NOx passing through the SCR catalyst 3 increases, and the purification rate decreases. In the range of the air amount of “U” where the air amount is excessively large, the air amount is excessively large and almost all NOx passes through the SCR catalyst 3.

  Here, when the air amount is in the range of “I”, the slope of the air amount-purification rate characteristic when the SCR catalyst 3 is deteriorated is constant. From this fact, the present inventors have found that the SCR catalyst 3 is deteriorated when the slope of the air amount-purification rate characteristic in the range of “i” is constant.

On the other hand, the case where abnormality of the urea addition valve 4 occurs will be described. Here, a case where urea is concentrated in the vicinity of the center portion of the SCR catalyst 3 and urea dispersion is deteriorated will be exemplified. When abnormality of the urea addition valve 4 occurs, as shown in FIG. 7, a large amount of NH ₃ is distributed and adsorbed in the central portion of the SCR catalyst 3 extending from upstream to downstream in the exhaust flow direction. In addition, a small amount of NH ₃ is distributed and adsorbed on the edge around the center of the SCR catalyst 3. Then, when the air amount-purification rate characteristic of the SCR catalyst 3 is calculated, it is as shown in FIG. In FIG. 8, in the range of the “ka” air amount with the smallest air amount, the air amount is excessively small, and NOx is purified without slipping through both the center portion and the edge portion in the SCR catalyst 3. In the “ki” air amount range in which the air amount is slightly small, the air amount is slightly increased, and NOx is purified without slipping through the central portion in the SCR catalyst 3. On the other hand, a part of NOx cannot perform a sufficient reduction reaction at the edge in the SCR catalyst 3, and a part of NOx slips through the edge in the SCR catalyst 3. In the air volume range where the air volume is medium, the air volume increases, and NOx is purified without passing through the center of the SCR catalyst 3. On the other hand, almost all NOx passes through the edge in the SCR catalyst 3 at the edge in the SCR catalyst 3. In the range of the air amount of “ke” where the air amount is larger, the air amount is further increased, and some of the NOx cannot perform a sufficient reduction reaction in the center of the SCR catalyst 3, and some of the NOx. Slips through the center of the SCR catalyst 3. On the other hand, almost all NOx passes through the edge in the SCR catalyst 3 at the edge in the SCR catalyst 3. In the range of the “ko” air amount in which the air amount is excessively large, the air amount is excessively large, and almost all NOx slips through both the central portion and the edge portion in the SCR catalyst 3.

  Here, when the abnormality of the urea addition valve 4 occurs, the range of the air amount corresponding to the range of the air amount of “yes” when the deterioration of the SCR catalyst 3 occurs is “ki”, “ku”, It is the range of air volume of “ke”. In these “ki”, “ku”, and “ke” air quantity ranges, the slope of the air quantity-purification rate characteristic when the SCR catalyst 3 deteriorates is “ki”, “ku”, “ke”. ”Differs in the range of air volume. Therefore, the slope of the air amount-purification rate characteristic in these ranges is not constant, and has a plurality of different slopes. Therefore, the inventors of the present invention have a non-constant slope of the air amount-purification rate characteristic in the air amount range of “ki”, “ku”, and “ke” corresponding to the air amount range of “i”. And found that an abnormality of the urea addition valve 4 occurred.

  As described above, the present inventors have found that the slope of the air amount-purification rate characteristic differs between the deterioration of the SCR catalyst 3 and the abnormality of the urea addition valve 4.

  Therefore, in this embodiment, the deterioration of the SCR catalyst 3 and the abnormality of the urea addition valve 4 are distinguished from each other based on the change in the slope of the air amount-purification rate characteristic in the air amount within a predetermined range. That is, it is determined that the SCR catalyst 3 has deteriorated when the slope of the air amount-purification rate characteristic in the air amount in the predetermined range is constant, and when the slope of the air amount-purification rate characteristic in the air amount in the predetermined range is not constant. It was determined that the urea addition valve 4 was abnormal.

Here, the air amount in the predetermined range is a range in which the amount of air that is completely purified by the SCR catalyst 3 without passing through the SCR catalyst 3 without passing through the SCR catalyst 3, and almost all the NOx in the exhaust passes through the SCR catalyst 3. This is the amount of air between the range where too much air passes through. That is, with this amount of air, when no abnormality has occurred in the urea addition valve 4, a part of the NOx in the exhaust is purified by the SCR catalyst 3, and another part of the NOx in the exhaust is removed. This is a range that passes through the SCR catalyst 3. In the present embodiment, the range that substantially includes the range of “い” shown in FIG. 6 is defined as the predetermined range. The predetermined range of the air amount can be obtained in advance by experiment, verification, or the like.

  According to the present embodiment, the deterioration of the SCR catalyst 3 and the abnormality of the urea addition valve 4 can be distinguished and determined, and the deterioration of the SCR catalyst 3 can be accurately determined.

  Here, calculating the air amount-purification rate characteristic means that the NOx is obtained while changing the amount of air flowing through the SCR catalyst 3 while adding the optimum addition amount obtained from the urea amount-purification rate characteristic from the urea addition valve 4. The sensor 6 detects and obtains the NOx concentration.

  According to this embodiment, the air amount-purification rate characteristic can be accurately calculated, and the deterioration of the SCE catalyst 3 determined based on the air amount-purification rate characteristic and the abnormality of the urea addition valve 4 are accurately distinguished. be able to.

  In addition, calculating the air amount-purification rate characteristic is that the optimum addition amount obtained from the urea amount-purification rate characteristic is not more than a predetermined amount and the maximum purification rate obtained from the urea amount-purification rate characteristic is not more than a predetermined value. In case you asked.

  Here, the predetermined amount of the optimum addition amount is an amount that may cause another abnormality when the urea amount is larger than that. Moreover, the predetermined value of the maximum purification rate is a value at which it can be determined that the SCR catalyst 3 has not yet deteriorated if the purification rate is higher than that.

  According to the present embodiment, the air amount-purification rate characteristic is calculated when the optimum addition amount is equal to or less than the predetermined amount and the maximum purification rate is equal to or less than the predetermined value. The case where is not deteriorated can be excluded. Therefore, the air amount-purification rate characteristic can be accurately calculated, and the deterioration of the SCR catalyst 3 determined based on the air amount-purification rate characteristic and the abnormality of the urea addition valve 4 can be accurately distinguished. .

  Next, the catalyst deterioration determination control routine according to this embodiment will be described. FIG. 9 is a flowchart showing a catalyst deterioration determination control routine according to this embodiment. This routine is repeatedly executed by the ECU 7 every predetermined time.

  In step S101, the urea amount-purification rate characteristic of the SCR catalyst 3 is calculated. The urea amount-purification rate characteristic is calculated by detecting the NOx concentration by the NOx sensor 6 while changing the amount of urea added from the urea addition valve 4 while the air amount is constant. The ECU 7 that executes this step corresponds to the reducing agent amount-purification rate characteristic calculating means of the present invention.

  In step S102, it is determined whether the optimum addition amount obtained from the urea amount-purification rate characteristic calculated in step S101 is equal to or less than a predetermined amount, and whether the maximum purification rate obtained from the urea amount-purification rate characteristic is equal to or less than a predetermined value. Determine. The optimum addition amount is the urea amount when the purification rate becomes the highest among the urea amount-purification rate characteristics shown in FIG. The maximum purification rate is the purification rate when the optimum addition amount is added among the urea amount-purification rate characteristics shown in FIG.

If it is determined in step S102 that the optimum addition amount is equal to or less than the predetermined amount and the maximum purification rate is equal to or less than the predetermined value, the process proceeds to step S103. As a result, the process proceeds to step S103 only when the SCR catalyst 3 has deteriorated and when the SCR catalyst 3 has not deteriorated and the urea addition valve 4 has malfunctioned. If it is determined in step S102 that the optimum addition amount is greater than the predetermined amount or the maximum purification rate is higher than the predetermined value, this routine is temporarily terminated.

  In step S103, the air amount-purification rate characteristic of the SCR catalyst 3 is calculated. The air amount-purification rate characteristic is obtained by adding the optimum addition amount obtained from the urea amount-purification rate characteristic calculated in step S101 from the urea addition valve 4 while changing the amount of air flowing through the SCR catalyst 3, and the NOx sensor. 6, the NOx concentration is detected and calculated. The ECU 7 that executes this step corresponds to the air amount-purification rate characteristic calculating means of the present invention. Thereby, as shown in FIG. 10, the air amount-purification rate characteristic of the SCR catalyst 3 is calculated. Here, the solid line shown in FIG. 10 is a characteristic when the SCR catalyst 3 is deteriorated, and the broken line is a characteristic when the urea addition valve 4 is abnormal.

  In step S104, it is determined whether or not the slope of the air amount-purification rate characteristic calculated in step S103 for a predetermined range of air amount is constant. The ECU 7 that executes this step corresponds to the determination means of the present invention.

  If it is determined in step S104 that the slope of the air amount-purification rate characteristic in the air amount in the predetermined range is constant as indicated by the solid line in FIG. 10, the process proceeds to step S105. If it is determined in step S104 that the slope of the air amount-purification rate characteristic in the air amount in the predetermined range is not constant as indicated by the broken line in FIG. 10, the process proceeds to step S106.

  In step S105, it is determined that the SCR catalyst 3 has deteriorated. Then, this routine is temporarily terminated.

  In step S106, it is determined that the urea addition valve 4 is abnormal. In step S107 following step S106, the injection pressure of the urea addition valve 4 is increased to promote atomization of urea added to the exhaust gas, thereby improving the dispersibility of urea. Then, this routine is temporarily terminated. Note that the processing in step S107 is not limited to the above-described increase in the injection pressure, and urea atomization may be promoted by, for example, turning on the urea line heater.

  According to this routine described above, it is possible to determine that the SCR catalyst 3 has deteriorated when the slope of the air amount-purification rate characteristic in a predetermined range of air amount is constant, and the air amount in the predetermined range of air amount− When the slope of the purification rate characteristic is not constant, it can be determined that the urea addition valve 4 is abnormal.

  In this embodiment, when the variation in the slope of the air amount-purification rate characteristic falls within a predetermined range, the slope of the air amount-purification rate characteristic is constant, and when the slope is constant, it is determined that the SCR catalyst 3 has deteriorated. Then, it has been described that it is determined that the urea addition valve 4 is abnormal when the inclination is not constant. However, the present invention is not limited to this. Any method may be adopted as long as it is possible to distinguish the deterioration of the SCR catalyst 3 from the abnormality of the urea addition valve 4 based on the fluctuation of the slope of the air amount-purification rate characteristic in the air amount within a predetermined range.

  The catalyst deterioration determination device for an internal combustion engine according to the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the scope of the present invention.

1 is a diagram illustrating a schematic configuration of an internal combustion engine and an exhaust system thereof according to Embodiment 1. FIG. FIG. 3 is a diagram illustrating urea amount-purification rate characteristics according to the first embodiment. The figure which shows three cases from which the urea amount-purification rate characteristic which concerns on Example 1 differs. The figure which shows the case where urea concentrates and is added to a part of SCR catalyst by abnormality of the urea addition valve which concerns on Example 1. FIG. It shows a catalyst in the NH ₃ distribution when the SCR catalyst according to Example 1 is deteriorated. The figure which shows the air quantity-purification rate characteristic when the SCR catalyst which concerns on Example 1 deteriorates. It shows a catalyst in the NH ₃ distribution when urea dispersion according to Example 1 was concentrated in the catalyst center. The figure which shows the air quantity-purification rate characteristic when urea dispersion | distribution which concerns on Example 1 concentrates on the catalyst center part. 3 is a flowchart showing a catalyst deterioration determination control routine according to the first embodiment. The figure which shows the air quantity-purification rate characteristic in case the inclination in the air amount of the predetermined range which concerns on Example 1 is constant, and when inclination is not constant.

Explanation of symbols

1 Internal combustion engine 2 Exhaust passage 3 SCR catalyst 4 Urea addition valve 5 Dispersion plate 6 NOx sensor 7 ECU
8 Accelerator opening sensor 9 Crank position sensor

Claims (4)

A catalyst that is disposed in an exhaust passage of the internal combustion engine and purifies NOx in the exhaust by being supplied with a reducing agent;
Reducing agent addition means for adding a reducing agent to the catalyst;
An air amount-purification rate characteristic calculating means for calculating a characteristic of the purification rate of the catalyst with respect to the amount of air flowing through the catalyst;
Determination that distinguishes between catalyst deterioration and abnormality of the reducing agent addition unit based on a change in the slope of the air amount-purification rate characteristic calculated by the air amount-purification rate characteristic calculation unit in an air amount within a predetermined range. Means,
An apparatus for determining catalyst deterioration of an internal combustion engine, comprising:   The determination unit determines that the catalyst has deteriorated when a change in the slope of the air amount-purification rate characteristic calculated by the air amount-purification rate characteristic calculation unit within a predetermined range falls within a predetermined range. The abnormality of the reducing agent addition unit is determined when a variation in the slope of the air amount-purification rate characteristic calculated by the air amount-purification rate characteristic calculation unit in an air amount exceeds a predetermined range. The catalyst deterioration determination device for an internal combustion engine according to claim 1. NOx concentration detection means that is disposed in the exhaust passage downstream of the catalyst and detects the NOx concentration in the exhaust discharged from the catalyst;
The NOx concentration is detected by the NOx concentration detecting means while changing the amount of reducing agent added from the reducing agent adding means, and the characteristic of the purification rate of the catalyst with respect to the amount of reducing agent added from the reducing agent adding means is calculated. Reducing agent amount-purification rate characteristic calculating means,
With
The air amount-purification rate characteristic calculating means adds the optimum addition amount calculated from the reducing agent amount-purification rate characteristic calculated by the reducing agent amount-purification rate characteristic calculating means from the reducing agent addition means, 3. The characteristic of the purification rate of the catalyst with respect to the amount of air flowing through the catalyst is calculated by detecting the NOx concentration by the NOx concentration detecting means while changing the amount of air flowing through the catalyst. The catalyst deterioration determination device for an internal combustion engine according to claim 1.   The air amount-purification rate characteristic calculating means is such that the optimum addition amount obtained from the reducing agent amount-reduction rate characteristic calculated by the reducing agent amount-purification rate characteristic calculating means is equal to or less than a predetermined amount, and the reducing agent amount- Calculating the characteristic of the purification rate of the catalyst with respect to the amount of air flowing through the catalyst when the maximum purification rate obtained from the reducing agent amount-purification rate characteristic calculated by the purification rate characteristic calculating means is equal to or less than a predetermined value; The catalyst deterioration determination device for an internal combustion engine according to claim 3,

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