JP2010151110A - Catalyst deterioration determination device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology discriminatedly determining deterioration of a catalyst and deterioration of dispersion of a reducing agent and accurately determining the deterioration of the catalyst, in a catalyst deterioration device for an internal combustion engine. <P>SOLUTION: The catalyst deterioration determination device for the internal combustion engine is provided with the SCR catalyst arranged in an exhaust passage of the internal combustion engine and cleaning NOx in the exhaust gas by feeding of urea; and a urea addition valve for adding the urea to the SCR catalyst. When the deterioration of the catalyst and the deterioration of dispersion of the urea are discriminatedly determined by comparing an air amount-a cleaning ratio reference characteristic with the present air amount-a cleaning ratio present characteristic, the air amount-a cleaning ratio reference characteristic is calculated when the optimum addition amount determined from the reducing agent amount-the cleaning ratio characteristic is more than a predetermined amount or the highest cleaning ratio is higher than the predetermined value and when the air amount-the cleaning ratio reference characteristic is not calculated at the past. <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

  However, the discrepancy between the estimated ammonia concentration downstream of the catalyst and the measured ammonia concentration is not only caused by catalyst deterioration, but also caused by abnormalities in the reducing agent addition valve to which the reducing agent is added or damage to the exhaust passage to which the reducing agent is added. It is also caused by the deterioration of agent dispersion. 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 dispersion is deteriorated, 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 dispersion deterioration in an internal combustion engine catalyst deterioration determination device. It is to provide technology to do.

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;
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 purification rate characteristic of the catalyst with respect to the amount of reducing agent added from the reducing agent adding means (reduction) Reducing agent amount-purification rate characteristic calculating means for calculating (agent amount-purification rate characteristic);
While adding the optimum addition amount calculated from the reducing agent amount-purification rate characteristic calculated by the reducing agent amount-purification rate characteristic calculating unit from the reducing agent adding unit, the amount of air flowing through the catalyst is changed. An air amount-purification rate characteristic calculating unit that detects a NOx concentration by a NOx concentration detecting unit and calculates a purification rate characteristic (air amount-purification rate characteristic) of the catalyst with respect to the amount of air flowing through the catalyst;
Comparison between the air amount-purification rate reference characteristic calculated by the air amount-purification rate characteristic calculating unit in the past and the current air amount-purification rate current characteristic calculated by the air amount-purification rate characteristic calculating unit. Determination means for distinguishing between catalyst deterioration and reducing agent dispersion deterioration,
With
The air amount-purification rate reference characteristic is obtained when the optimum addition amount obtained from the reducing agent amount-purification rate characteristic calculated by the reducing agent amount-purification rate characteristic calculating means is higher than a predetermined amount or when the maximum purification rate is a predetermined value. And when the air amount-purification rate reference characteristic has not been acquired in the past, the air amount-purification rate characteristic calculating unit calculates the catalyst deterioration determining device for an internal combustion engine. It is.

  In order to distinguish between the deterioration of the catalyst and the deterioration of the reducing agent dispersion, the air amount-purification rate reference characteristic is compared with the current air amount-purification rate characteristic calculation means calculated by the current air amount-purification rate characteristic calculating means. . Here, there are individual differences between the internal combustion engine and the catalyst mounted on the internal combustion engine. For this reason, when the air amount-purification rate reference characteristic is uniformly determined and the uniform air amount-purification rate reference characteristic is compared with the current air amount-purification rate current characteristic, uniform air has been introduced from the beginning of use of the device due to the influence of individual differences. There may be a discrepancy between the amount-purification rate reference characteristic and the air amount-purification rate current characteristic. Thereby, even if catalyst deterioration or reducing agent dispersion deterioration does not actually occur, it may be erroneously determined as catalyst deterioration or reducing agent dispersion deterioration.

  Therefore, in the present invention, the air amount-purification rate reference characteristic is determined when the optimum addition amount obtained from the reducing agent amount-purification rate characteristic calculated by the reducing agent amount-purification rate characteristic calculating means is greater than a predetermined amount or the highest. When the purification rate is higher than a predetermined value, and when the air amount-purification rate reference characteristic has not been acquired in the past, it is calculated by the air amount-purification rate characteristic calculating means.

  Here, the predetermined amount of the optimum addition amount is an amount by which it can be determined that if the amount of the reducing agent is larger than that, the catalyst has not deteriorated yet and the reducing agent dispersion has not deteriorated yet. Further, the predetermined value of the maximum purification rate is a value by which it can be determined that if the purification rate is higher than that, the catalyst has not deteriorated yet and the reducing agent dispersion has not deteriorated yet.

  When the optimum addition amount is higher than the predetermined amount or when the maximum purification rate is higher than the predetermined value, the catalyst has not deteriorated yet and the reducing agent dispersion has not deteriorated yet. Further, when the air amount-purification rate reference characteristic has not been acquired in the past, the internal combustion engine and the catalyst are in the initial stage of use of a new device or the like. Therefore, in such a case, by obtaining the air amount-purification rate reference characteristic, the air amount-purification rate reference characteristic specific to the device taking into account individual differences such as the internal combustion engine and the catalyst mounted on the internal combustion engine. Can be calculated. Therefore, by comparing the inherent air amount-purification rate reference characteristic with the current air amount-purification rate current characteristic changed from the inherent air amount-purification rate reference characteristic, catalyst deterioration and reducing agent dispersion deterioration And the catalyst deterioration can be accurately determined.

  When the operating state of the internal combustion engine remains in the low air amount region where the amount of air flowing through the catalyst is small, the determination means is the air amount-purification previously calculated by the air amount-purification rate characteristic calculating means. A low air amount region reference characteristic which is a characteristic of the range of the low air amount region in the rate reference characteristic, and an air amount−purification rate currently calculated only by the current air amount−purification rate characteristic calculating means. It is preferable to determine whether or not the reducing agent dispersion is deteriorated by comparing the current characteristics of the low air amount region, which is a property of the range of the low air amount region within the characteristics.

  When the operating state of the internal combustion engine remains in a low air amount region where the amount of air flowing through the catalyst is small, the amount of air flowing through the catalyst cannot be changed. For this reason, in this case, the air amount-purification rate current characteristic cannot be calculated by the air amount-purification rate characteristic calculating means. Therefore, it becomes impossible to distinguish between catalyst deterioration and reducing agent dispersion deterioration. However, in the range of the low air volume within the air volume-purification rate characteristics, the characteristics are similar when normal and when the catalyst is deteriorated. Is different. Therefore, in the present invention, when the operating state of the internal combustion engine remains in the low air amount region where the amount of air flowing through the catalyst is small, it is determined whether or not the reducing agent dispersion has deteriorated. According to the present invention, even when the operating state of the internal combustion engine remains in the low air amount region where the current characteristic of the air amount-purification rate cannot be calculated and the catalyst deterioration and the reducing agent dispersion deterioration cannot be distinguished and determined. Whether or not the reducing agent dispersion has deteriorated can be determined quickly.

  The determination means includes an air amount-purification rate reference characteristic previously calculated by the air amount-purification rate characteristic calculating means, and an air amount-purification rate current characteristic calculated by the current air amount-purification rate characteristic calculating means. And when it is determined that the catalyst is not deteriorated, based on a change in the reducing agent amount-purification rate characteristic calculated by the reducing agent amount-purification rate characteristic calculating means from the previous determination to the present. It is better to distinguish between catalyst deterioration and reducing agent dispersion deterioration.

  Even if it is possible to compare the air quantity-purification rate reference characteristic and the air quantity-purification rate current characteristic and determine that the reduction of the reducing agent dispersion is not the catalyst deterioration, the catalyst deterioration is actually not the deterioration of the reducing agent dispersion. It may be. Therefore, in the present invention, when the air amount-purification rate reference characteristic and the air amount-purification rate current characteristic are compared and it is determined that the catalyst is not deteriorated, the reducing agent amount-purification rate characteristic from the previous determination to the present is determined. Based on this change, the catalyst deterioration and the reducing agent dispersion deterioration are distinguished and judged. According to the present invention, catalyst deterioration and reducing agent dispersion deterioration can be distinguished and determined in more detail, and catalyst deterioration can be determined more accurately.

  According to the present invention, in a catalyst deterioration determination device for an internal combustion engine, catalyst deterioration and reducing agent dispersion deterioration can be distinguished and determined, and catalyst deterioration can be accurately determined.

  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 is supplied from the urea tank 5 to the urea addition valve 4. Urea added from the urea addition valve 4 flows through the exhaust passage 2 and 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.

  A dispersion plate 6 that disperses urea added from the urea addition valve 4 is disposed in the exhaust passage downstream of the urea addition valve 4 and upstream of the SCR catalyst 3. The exhaust passage 2 has a certain narrow passage area upstream from the dispersion plate 6 with the dispersion plate 6 as a boundary, and the passage area becomes wider as the downstream side approaches the SCR catalyst 3 than the dispersion plate 6.

  A NOx sensor 7 for detecting 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 7 of this embodiment corresponds to the NOx concentration detecting 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 8 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 8 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 7, the ECU 8 includes an accelerator opening sensor 9 that outputs an electric signal corresponding to the amount of depression of the accelerator pedal, and a crank position sensor 10 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 8.

  On the other hand, the urea addition valve 4 is connected to the ECU 8 via electric wiring, and the urea addition valve 4 is controlled by the ECU 8 to instruct the added urea amount, the addition timing, and the like.

  Conventionally, the NOx concentration is detected by the NOx sensor 7 while changing the urea amount added from the urea addition valve 4, and the purification rate of the SCR catalyst 3 with respect to the urea amount 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. The urea amount-purification rate characteristic corresponds to the reducing agent amount-purification rate characteristic in the present invention. Further, the NOx concentration upstream of the SCR catalyst 3 is estimated by the ECU 8.

  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 is concentrated in part due to abnormality of the urea addition valve 4, breakage of the exhaust passage 2 or the dispersion plate 6, etc., so that urea is dispersed in the SCR catalyst 3. May get worse. 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 urea dispersion deteriorates. It was not possible to accurately determine deterioration.

  By the way, the NOx concentration is detected by the NOx sensor 7 while changing the amount of air flowing through the SCR catalyst 3 while adding the optimum addition amount of urea obtained from the urea amount-purification rate characteristic, and the amount of air flowing through the SCR catalyst 3 It is also possible to calculate the characteristic of the purification rate of the SCR catalyst 3 (hereinafter referred to as the air amount-purification rate characteristic). In this embodiment, the amount of air flowing through the SCR catalyst 3 is changed by changing the operating state of the internal combustion engine 1. Further, the NOx concentration upstream of the SCR catalyst 3 is estimated by the ECU 8. As a result of intensive studies by the present inventors, it has been found that the air amount-purification rate characteristics are different when drawn in normal, when the catalyst is deteriorated, and when urea dispersion is deteriorated.

Specifically, in a normal time in which neither catalyst deterioration nor urea dispersion deterioration occurs, in a low air amount region where the amount of air flowing through the SCR catalyst 3 is small, as shown by the solid air amount-purification rate characteristic shown in FIG. It shows a high and constant purification rate, and the purification rate gradually decreases as the air amount increases from the low air amount region. In the middle of the reduction of the purification rate, there is a portion where the purification rate does not change temporarily even if the intake air amount changes. As the purification rate decreases, the gradient of the purification rate that gradually decreases as the air amount increases remains substantially constant.

  When the catalyst is deteriorated, as in the air amount-purification rate characteristic indicated by a thin broken line in FIG. 5, in the low air amount region where the amount of air flowing through the SCR catalyst 3 is small, the same high purification rate as in the normal state is shown. As the air amount increases from the low air amount region, the purification rate decreases more rapidly than normal. While the purification rate is decreasing, there is a portion where the purification rate does not change temporarily even if the intake air amount changes. That is, when the catalyst is deteriorated, the entire characteristic is shifted to the left as compared with the normal state, and the inclination of the purification rate that decreases as the air amount increases is steeper than the normal state. As the purification rate decreases, the gradient of the purification rate that rapidly decreases as the amount of air increases remains substantially constant.

  When the urea dispersion deteriorates, the low air amount region in which the amount of air flowing through the SCR catalyst 3 is small, as shown by the rough dashed air amount-purification rate characteristic shown in FIG. The purification rate is shown, and as the air amount increases from the low air amount region, the purification rate falls more slowly than normal. As the purification rate decreases, the slope of the purification rate that falls as the air amount increases varies finely.

  Reflecting the above characteristics and distinguishing between catalyst deterioration and urea dispersion deterioration, the normal air amount-air amount indicating the purification rate characteristic-purification rate reference characteristic and the current air amount of the SCR catalyst 3- It is conceivable to compare the air amount indicating the purification rate characteristic with the current characteristic of the purification rate. Accordingly, for example, when the air amount-purification rate current characteristic is substantially equal to the air amount-purification rate reference characteristic, it can be determined that the air is normal. For example, when the current characteristic of air amount-purification rate is shifted to the left as a whole, and the slope of the purification rate that decreases as the air amount increases becomes steep compared to the reference characteristic of air amount-purification rate Can be determined as catalyst degradation. For example, the current air amount-purification rate characteristic shows a lower constant purification rate in the low air amount region than the air amount-purification rate reference characteristic, and the purification rate increases as the air amount increases from the low air amount region. When the purification rate gradually decreases and the purification rate decreases, if the slope of the purification rate that decreases as the air amount increases finely, it can be determined that the urea dispersion has deteriorated.

  Here, there are individual differences between the internal combustion engine 1 and the SCR catalyst 3 mounted on the internal combustion engine 1. For this reason, the air amount-purification rate reference characteristic is uniformly determined in advance, and the uniform air amount-purification rate reference characteristic is compared with the current air amount-purification rate current characteristic. There may be a discrepancy between the air amount-purification rate reference characteristic and the air amount-purification rate current characteristic. Thereby, even if catalyst deterioration or urea dispersion deterioration does not actually occur, it may be erroneously determined as catalyst deterioration or urea dispersion deterioration.

  Therefore, in this embodiment, the air amount-purification rate reference characteristic is determined when the optimum addition amount obtained from the calculated urea amount-purification rate characteristic is larger than a predetermined amount or when the maximum purification rate is higher than a predetermined value. And when the said air quantity-purification rate reference | standard characteristic was not acquired in the past, it was made to calculate.

  Here, the predetermined amount of the optimum addition amount is an amount that can be determined that catalyst deterioration has not occurred yet and urea dispersion deterioration has not yet occurred if the amount of reducing agent is larger than that. The predetermined value of the maximum purification rate is a value at which it can be determined that if the purification rate is higher than that, catalyst deterioration has not yet occurred and urea dispersion deterioration has not yet occurred.

When the optimum addition amount is higher than the predetermined amount or when the maximum purification rate is higher than the predetermined value, catalyst deterioration has not yet occurred and urea dispersion deterioration has not yet occurred. Further, when the air amount-purification rate reference characteristic has not been acquired in the past, the internal combustion engine 1 and the SCR catalyst 3 are in the initial stage of use of a new device or the like. Therefore, in such a case, by acquiring the air amount-purification rate reference characteristic, the air amount inherent to the device in consideration of individual differences such as the internal combustion engine 1 and the SCR catalyst 3 mounted on the internal combustion engine 1- Purification rate reference characteristics can be acquired. Therefore, by comparing the inherent air amount-purification rate reference characteristic with the current air amount-purification rate current characteristic changed from this inherent air amount-purification rate reference characteristic, catalyst deterioration and urea dispersion deterioration Thus, it is possible to determine the catalyst deterioration accurately.

  Next, the catalyst deterioration determination control routine 1 according to this embodiment will be described. FIG. 6 is a flowchart showing a catalyst deterioration determination control routine 1 according to this embodiment. This routine is repeatedly executed by the ECU 8 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 7 while changing the amount of urea added from the urea addition valve 4 while the air amount is constant. The ECU 8 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 not more than the predetermined amount and the maximum purification rate is not more than the predetermined value, the process proceeds to step S106. As a result, the process proceeds to step S106 only in the case of catalyst deterioration in which the SCR catalyst 3 has deteriorated or in the case of urea dispersion deterioration in which the SCR catalyst 3 has not deteriorated. 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, the process proceeds to step S103.

  In step S103, it is determined whether or not the air amount-purification rate reference characteristic has been acquired. Since the air amount-purification rate reference characteristic is stored in the ECU 8 when acquired, it is determined that the air amount-purification rate reference characteristic has been acquired when the ECU 8 stores the air amount-purification rate reference characteristic. When the SCR catalyst 3 is replaced, the acquired air amount-purification rate reference characteristic may be deleted from the ECU 8 and reset to an unstored state.

  In step S103, when an affirmative determination is made that the air amount-purification rate reference characteristic has been acquired, this routine is temporarily terminated. If it is determined in step S103 that the air amount-purification rate reference characteristic has not been acquired, the process proceeds to step S104. Accordingly, when the process proceeds to step S104, the optimum addition amount is greater than the predetermined amount or the maximum purification rate is higher than the predetermined value, and the air amount-purification rate reference characteristic has not been calculated in the past. Limited to.

  In step S104, it is determined that the SCR catalyst 3 is normal. Then, the process proceeds to step S105.

In step S105, the air amount-purification rate reference characteristic of the SCR catalyst 3 is calculated and acquired. The air amount-purification rate reference 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. The sensor 7 detects and calculates the NOx concentration. The ECU 8 that executes this step corresponds to the air amount-purification rate characteristic calculating means of the present invention. Here, since this step is when the SCR catalyst 3 is normal, the air amount-purification rate reference characteristic of the SCR catalyst 3 is calculated as shown by the solid line in FIG. The air amount-purification rate reference characteristic of the SCR catalyst 3 is stored in the ECU 8. After the processing of this step, this routine is once ended.

  On the other hand, in step S106, the air amount-purification rate current characteristic of the SCR catalyst 3 is calculated. The air amount-purification rate current 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. The sensor 7 detects and calculates the NOx concentration. The ECU 8 that executes this step corresponds to the air amount-purification rate characteristic calculating means of the present invention. Here, since it is the case of catalyst deterioration or urea dispersion deterioration that shifts to this step, the air amount-purification rate current characteristic of the SCR catalyst 3 is calculated as shown by a thin broken line or a rough broken line in FIG. .

  In step S107, it is determined whether or not a catalyst deterioration criterion is satisfied. The ECU 8 that executes this step corresponds to the determination means of the present invention. When the current characteristic of the air quantity-purification rate is shifted to the left as compared with the air quantity-purification rate reference characteristic, and the slope of the purification rate that decreases as the air quantity increases becomes steep. It is determined that the catalyst deterioration standard is satisfied, and otherwise, it is determined that the catalyst deterioration standard is not satisfied. In addition to the above-mentioned criteria, the air amount-purification rate current characteristic shows a constant purification rate lower in the low air amount region than the air amount-purification rate reference property, and the air amount from the low air amount region When the purification rate gradually decreases as the air flow increases and the purification rate decreases, if the slope of the purification rate that decreases as the air volume increases varies finely, it is determined that the catalyst deterioration criterion is not satisfied. May be. In addition to these standards, the current amount-purification rate characteristics and the air amount-purification rate reference characteristics are compared, and the same number of parts where the purification rate becomes flat when the air amount is changed. If present, it may be determined that the catalyst deterioration criterion is satisfied. In addition to these criteria, if the current characteristic of the air amount-purification rate is constant at a plurality of points with the slope of the purification rate decreasing as the air amount increases, it is determined that the catalyst deterioration criterion is satisfied. May be.

  If it is determined in step S107 that the air amount-purification rate current characteristic is the characteristic shown by the thin broken line in FIG. 5 and the catalyst deterioration criterion is satisfied, the process proceeds to step S108. If it is determined in step S107 that the air amount-purification rate current characteristic is a characteristic as shown by a rough broken line in FIG. 5 and the catalyst deterioration criterion is not satisfied, the process proceeds to step S109.

  In step S108, it is determined that the SCR catalyst 3 is deteriorated. Then, this routine is temporarily terminated.

  In step S109, it is determined that urea dispersion has deteriorated due to abnormality of the urea addition valve 4 or damage to the exhaust passage 2 or the dispersion plate 6. Then, this routine is temporarily terminated.

  According to this routine described above, the unique air amount-purification rate reference characteristic can be acquired, and the unique air amount-purification rate reference characteristic is compared with the current air amount-purification rate current characteristic. Thus, it is possible to distinguish and determine catalyst deterioration and urea dispersion deterioration.

<Example 2>
In the present embodiment, only the characteristic part will be described, and the same components as those in the above embodiment will be denoted by the same reference numerals and description thereof will be omitted.

  In the first embodiment, the air amount-purification rate current characteristic is calculated, and the inherent air amount-purification rate reference characteristic is compared with the current air amount-purification rate current characteristic. Judgment is made with distinction. However, when the operating state of the internal combustion engine 1 remains in the low air amount region where the amount of air flowing through the SCR catalyst 3 is small, the amount of air flowing through the SCR catalyst 3 cannot be changed. For this reason, in this case, the air amount-purification rate current characteristic cannot be calculated as in step S106 of FIG. Therefore, it becomes impossible to distinguish between catalyst deterioration and urea dispersion deterioration.

  However, in the range of the low air amount region within the air amount-purification rate characteristic, although the characteristics are similar at normal time and when the catalyst is deteriorated as shown by the solid line and the thin broken line in FIG. 5, the rough broken line shown in FIG. As described above, when the urea dispersion is deteriorated, the characteristics are clearly different from those at the normal time and when the catalyst is deteriorated. In other words, the purification rate is clearly lower when urea dispersion is worse than when it is normal and when the catalyst is deteriorated.

  Therefore, in the present embodiment, when the operating state of the internal combustion engine 1 remains in the low air amount region where the amount of air flowing through the SCR catalyst 3 is small, the low air within the air amount-purification rate reference characteristics calculated in the past. Low air volume area reference characteristics that are characteristics of the volume area range, and low air volume area current characteristics that are the characteristics of the low air volume area within the current air volume-purification rate current characteristics that are calculated only for the current low air volume area By comparing the characteristics, it was determined whether or not the urea dispersion was deteriorated.

  According to the present embodiment, even if the operating state of the internal combustion engine 1 remains in the low air amount region, the current characteristic of the air amount-purification rate cannot be calculated and the catalyst deterioration and the urea dispersion deterioration cannot be distinguished and determined. Whether or not the urea dispersion is deteriorated can be quickly determined.

  Next, the catalyst deterioration determination control routine 2 according to this embodiment will be described. FIG. 7 is a flowchart showing a catalyst deterioration determination control routine 2 according to this embodiment. This routine is repeatedly executed by the ECU 8 every predetermined time. Note that description of the same processing as the routine shown in FIG. 6 is omitted.

  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 S201. As a result, the process proceeds to step S201 only in the case of catalyst deterioration in which the SCR catalyst 3 has deteriorated or in the case of urea dispersion deterioration in which the SCR catalyst 3 has not deteriorated.

  In step S201, it is determined whether or not the operating state of the internal combustion engine 1 remains in the low air amount region for a predetermined time or more. If the predetermined time is longer than that, the current amount-purification rate current characteristic cannot be calculated, and the catalyst deterioration and the urea dispersion deterioration cannot be distinguished and determined. For example, when the idling operation is continued for a long time, it is determined that the operation state of the internal combustion engine 1 remains in the low air amount region for a predetermined time or more.

  If it is determined in step S201 that the operating state of the internal combustion engine 1 remains in the low air amount region for a predetermined time or longer, the process proceeds to step S202. If it is determined in step S201 that the operating state of the internal combustion engine 1 does not remain in the low air amount region for a predetermined time or longer, the process proceeds to step S106.

In step S202, the low air amount region current characteristics of the SCR catalyst 3 are calculated. The current characteristic of the low air amount region is that the amount of air flowing through the SCR catalyst 3 is added only to the low air amount region while the optimum addition amount obtained from the urea amount-purification rate characteristic calculated in step S101 is added from the urea addition valve 4. The NOx concentration is detected and calculated by the NOx sensor 7 while being changed. For this reason, the current characteristic of the low air amount region is a property in the range of the low air amount region within the current amount of air amount-purification rate. The ECU 8 that executes this step corresponds to the air amount-purification rate characteristic calculating means of the present invention. Here, since this step is a case of catalyst deterioration or urea dispersion deterioration, the SCR catalyst 3 having a substantially constant purification rate as shown by a thin broken line or a rough broken line in the low air amount region of FIG. The current characteristic of the low air amount region is calculated.

  In step S203, the low air amount region current characteristic and the low air amount region reference characteristic are compared, and it is determined whether or not the difference in the purification rate in the low air amount region is greater than or equal to a reference value. The ECU 8 that executes this step corresponds to the determination means of the present invention. The low air amount region reference characteristic is a characteristic in the range of the low air amount region within the air amount-purification rate reference characteristic calculated in the past. Here, the air amount-purification rate reference characteristic stored in the ECU 8 is called, and only the characteristic in the range of the low air amount region is captured. Therefore, the low air amount region reference characteristic of the SCR catalyst 3 having a substantially constant purification rate is calculated as shown by the solid line in the low air amount region of FIG. Then, the current characteristic of the low air amount region and the reference characteristic of the low air amount region are compared to determine the difference in the purification rate. If the difference in the purification rates is greater than or equal to the reference value, it can be determined that urea dispersion has deteriorated. Note that the reference value for the difference in purification rate is a threshold value that can be determined as deterioration of urea dispersion when the value is larger than that, and is obtained in advance through experiments or the like.

  If it is determined in step S203 that the purification rate difference is greater than or equal to the reference value, the process proceeds to step S109. If it is determined in step S203 that the difference in the purification rates does not exceed the reference value, this routine is temporarily terminated. In step S203, if it is determined that the difference in the purification rates does not exceed the reference value, it may be determined that the catalyst has deteriorated. This is because, in step S102, it is determined that the catalyst has deteriorated or urea dispersion has deteriorated, and if a negative determination is made in step S203, it can be determined that the catalyst has deteriorated and is eliminated.

  According to this routine described above, even if the operation state of the internal combustion engine 1 remains in the low air amount region, it can be quickly determined only whether the urea dispersion has deteriorated.

<Example 3>
In the present embodiment, only the characteristic part will be described, and the same components as those in the above embodiment will be denoted by the same reference numerals and description thereof will be omitted.

  In the first embodiment, the air amount-purification rate current characteristic is calculated, and the inherent air amount-purification rate reference characteristic is compared with the current air amount-purification rate current characteristic. Judgment is made with distinction. However, even if it is possible to determine that the urea dispersion deterioration has been made by comparing the inherent air amount-purification rate reference characteristic and the current air amount-purification rate current characteristic, the catalyst degradation actually does not deteriorate the urea dispersion. It may be.

  Therefore, in this embodiment, the air amount-purification rate reference characteristic and the air amount-purification rate current characteristic are compared, and when it is determined that the catalyst is not deteriorated, the urea amount-purification rate characteristic from the previous determination to the present is determined. Based on this change, the catalyst deterioration and the urea dispersion deterioration were distinguished and judged in more detail.

  According to this embodiment, the catalyst deterioration and the urea dispersion deterioration can be distinguished and determined in more detail, and the catalyst deterioration can be determined more accurately.

  Next, the catalyst deterioration determination control routine 3 according to this embodiment will be described. FIG. 8 is a flowchart showing the catalyst deterioration determination control routine 3 according to this embodiment. This routine is repeatedly executed by the ECU 8 every predetermined time. Note that description of the same processing as the routine shown in FIG. 6 is omitted.

In step S301, the urea amount-purification rate characteristic of the SCR catalyst 3 is calculated as in step S101 of the above embodiment. At the same time, the calculated urea amount-purification rate characteristic is stored in the ECU 8.

  If it is determined in step S107 that the current air amount-purification rate current characteristic is a characteristic as shown by a rough broken line in FIG. 5 and the catalyst deterioration standard is not satisfied, the process proceeds to step S302.

  In step S302, it is determined whether or not the thermal deterioration criterion is satisfied. The ECU 8 that executes this step corresponds to the determination means of the present invention. The thermal deterioration criterion is a criterion for determining whether the urea amount-purification rate characteristic is gradually deteriorated (thermal deterioration) or whether the urea amount-purification rate characteristic is abruptly deteriorated. When the change in the urea amount-purification rate characteristic calculated in the current step S301 from the previous determination gradually deteriorates, it is determined that the heat deterioration criterion is satisfied, and when the change rapidly deteriorates, the heat It is determined that the deterioration standard is not satisfied. For example, when the difference between the maximum purification rate of the urea amount-purification rate characteristic at the previous determination and the current urea amount-purification rate characteristic divided by the energy flowing into the SCR catalyst 3 is a predetermined value or less, It is determined that the heat deterioration standard is satisfied. As shown in FIG. 9, the urea amount-purification rate characteristic gradually deteriorates from the characteristic of (c) to the characteristic of (d) according to the amount of heat energy when the catalyst is deteriorated, whereas when the urea dispersion deteriorates. Then, since the characteristic of (a) rapidly deteriorates to the characteristic of (d) due to abnormality of the urea addition valve 4 or damage of the exhaust passage 2 or the dispersion plate 6, it can be used as a criterion for discrimination.

  If it is determined in step S301 that the heat deterioration criterion is satisfied, the process proceeds to step S108. If it is determined in step S301 that the heat deterioration criterion is not satisfied, the process proceeds to step S109.

  According to the routine described above, the catalyst deterioration and the urea dispersion deterioration can be distinguished and determined in more detail by the thermal deterioration reference in addition to the catalyst deterioration reference. An erroneous determination can be avoided.

  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 of urea dispersion | distribution deterioration in which urea is concentrated and added to a part of SCR catalyst which concerns on Example 1. FIG. The figure which shows the air quantity-purification rate characteristic at the time of normal time, catalyst deterioration, and urea dispersion deterioration which concern on Example 1. FIG. 3 is a flowchart showing a catalyst deterioration determination control routine 1 according to the first embodiment. 7 is a flowchart showing a catalyst deterioration determination control routine 2 according to the second embodiment. 10 is a flowchart showing a catalyst deterioration determination control routine 3 according to the third embodiment. The figure which shows the case where the urea amount-purification rate characteristic changes by catalyst deterioration or the urea dispersion | distribution deterioration which concerns on Example 3. FIG.

Explanation of symbols

1 Internal combustion engine 2 Exhaust passage 3 SCR catalyst 4 Urea addition valve 5 Urea tank 6 Dispersion plate 7 NOx sensor 8 ECU
9 Accelerator opening sensor 10 Crank position sensor

Claims (3)

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;
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 (reduction) Reducing agent amount-purification rate characteristic calculating means for calculating (agent amount-purification rate characteristic);
While adding the optimum addition amount calculated from the reducing agent amount-purification rate characteristic calculated by the reducing agent amount-purification rate characteristic calculating unit from the reducing agent adding unit, the amount of air flowing through the catalyst is changed. An air amount-purification rate characteristic calculating unit that detects a NOx concentration by a NOx concentration detecting unit and calculates a purification rate characteristic (air amount-purification rate characteristic) of the catalyst with respect to the amount of air flowing through the catalyst;
Comparison between the air amount-purification rate reference characteristic calculated by the air amount-purification rate characteristic calculating unit in the past and the current air amount-purification rate current characteristic calculated by the air amount-purification rate characteristic calculating unit. Determination means for distinguishing between catalyst deterioration and reducing agent dispersion deterioration,
With
The air amount-purification rate reference characteristic is obtained when the optimum addition amount obtained from the reducing agent amount-purification rate characteristic calculated by the reducing agent amount-purification rate characteristic calculating means is larger than a predetermined amount or when the maximum purification rate is a predetermined value. And when the air amount-purification rate reference characteristic has not been acquired in the past, the air amount-purification rate characteristic calculating means calculates the catalyst deterioration determining device for an internal combustion engine. .   When the operating state of the internal combustion engine remains in the low air amount region where the amount of air flowing through the catalyst is small, the determination means is the air amount-purification previously calculated by the air amount-purification rate characteristic calculating means. A low air amount region reference characteristic which is a characteristic of the range of the low air amount region in the rate reference characteristic, and an air amount−purification rate currently calculated only by the current air amount−purification rate characteristic calculating means. 2. The internal combustion engine according to claim 1, wherein whether or not the reducing agent dispersion is deteriorated is determined by comparing a current characteristic of the low air amount region that is a property of the range of the low air amount region within the characteristic. Engine catalyst deterioration judgment device.   The determination means includes an air amount-purification rate reference characteristic previously calculated by the air amount-purification rate characteristic calculating means, and an air amount-purification rate current characteristic calculated by the current air amount-purification rate characteristic calculating means. And when it is determined that the catalyst is not deteriorated, based on a change in the reducing agent amount-purification rate characteristic calculated by the reducing agent amount-purification rate characteristic calculating means from the previous determination to the present. 2. The catalyst deterioration determination device for an internal combustion engine according to claim 1, wherein the determination is made by distinguishing between catalyst deterioration and reducing agent dispersion deterioration.

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