JP5240065B2 - Failure detection device for exhaust gas purification device - Google Patents

Description

  The present invention relates to a failure detection device for an exhaust gas purification device.

There is known a technique for determining that the NOx catalyst has deteriorated when the difference between the estimated value and the measured value of the ammonia concentration downstream of the selective reduction type NOx catalyst provided in the exhaust passage of the internal combustion engine is larger than a predetermined value. (For example, refer to Patent Document 1). However, it may be determined that the NOx catalyst has deteriorated even when there is an abnormality in the ammonia supply apparatus. In other words, even if the NOx catalyst deteriorates or there is an abnormality in the ammonia supply device, the NOx purification rate decreases,
It is necessary to determine which of the influences reduces the NOx purification rate.

JP 2006-125323 A JP 2006-207512 A JP 2002-250220 A

The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of determining an abnormality of a reducing agent supply device in distinction from deterioration of a selective reduction type NOx catalyst.

In order to achieve the above object, the failure detection device for an exhaust gas purification device according to the present invention employs the following means. That is, the failure detection device for the exhaust gas purification device according to the present invention is:
A selective reduction type NOx catalyst that is provided in an exhaust passage of the internal combustion engine and selectively reduces NOx by a reducing agent;
A reducing agent supply device for supplying a reducing agent into the exhaust gas upstream of the selective reduction type NOx catalyst;
Upstream detection means for detecting the NOx concentration upstream of the selective reduction type NOx catalyst;
Downstream detection means for detecting a NOx concentration downstream of the selective reduction type NOx catalyst;
In the failure detection device of the exhaust gas purification device provided with
Estimating means for estimating a ratio of NO ₂ in NOx flowing into the selective catalytic reduction NOx catalyst;
When the ratio of NO ₂ estimated by the estimation means is within a predetermined range, the NOx concentration detected by the upstream detection means and the downstream detection means when the reducing agent is supplied by the reducing agent supply device. Calculation means for calculating a NOx purification rate in the selective reduction type NOx catalyst based on:
Determination means for determining abnormality of the reducing agent supply device based on an average value and variation of the NOx purification rate calculated a plurality of times by the calculation means;
It is characterized by providing.

The selective reduction type NOx catalyst selectively reduces NOx using, for example, ammonia as a reducing agent. The reducing agent supply device may include an injection device that injects ammonia or urea water, for example. The upstream detection means may estimate the NOx concentration based on the operating state of the internal combustion engine, for example, or may measure it with a sensor. The downstream side detection means measures the NOx concentration after the NOx is purified by the selective reduction type NOx catalyst, for example, with a sensor. NOx
Includes NO and NO ₂ . The reducing agent supply device supplies, for example, a sufficient amount of reducing agent to reduce NOx flowing into the selective reduction type NOx catalyst.

The estimation means estimates the ratio of NO ₂ in NOx based on, for example, the operating state of the internal combustion engine. The ratio of NO ₂ in NOx may be detected using a sensor or the like.

Calculating means, the purification rate of NOx ratio of NO ₂ is calculated in the time within a predetermined range. The calculation of the NO ₂ ratio is performed a plurality of times. By calculating multiple times, the NOx purification rate when the ratio of NO ₂ is different is calculated. That is, it can be seen how the NOx purification rate changes with respect to the change in the NO ₂ ratio.

Here, the NOx purification rate in the selective reduction type NOx catalyst varies depending on the ratio of NO ₂ in NOx flowing into the selective reduction type NOx catalyst when the reducing agent is sufficiently supplied. That is, since NOx is reduced by the reaction formula of NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O, NO and NO ₂ are purified by substantially the same amount, so the ratio of NO ₂ is a specific value (for example, 50% NOx purification rate becomes maximum when When the selective reduction type NOx catalyst is deteriorated, although reduced overall is NOx purification rate, the ratio of NO ₂ is the NOx cleaning ratio is not changed to be greatest when a specific value.

However, when the supply amount of the reducing agent is insufficient, the influence on the NOx purification rate due to the short supply amount of the reducing agent is greater than the influence that the ratio of NO ₂ in NOx has on the NOx purification rate. That is, the NOx purification rate decreases regardless of the NO ₂ ratio. For this reason, NO ₂
Even when the ratio is the specific value, the NOx purification rate is low. That is, if the NOx purification rate decreases as a whole, it can be determined that there is an abnormality in the reducing agent supply device. The abnormality of the reducing agent supply device here refers to a case where the actual supply amount is smaller than the required amount of the reducing agent. If the average value of the NOx purification rate decreases, it can be determined that the NOx purification rate is overall reduced.

Further, if the supply amount of the reducing agent is insufficient, the average value of the NOx purification rate is lowered and the variation of the NOx purification rate is reduced. On the other hand, when the degree of deterioration of the selective reduction type NOx catalyst increases, the NOx purification rate significantly decreases. Thus, even when the selective reduction type NOx catalyst is deteriorated, the NOx purification rate changes according to the NO ₂ ratio, so that the variation in the NOx purification rate becomes large. That is, when the variation in the NOx purification rate is small, it can be determined that there is an abnormality in the reducing agent supply device.

Thus, when there is an abnormality in the reducing agent supply device, the average value of the NOx purification rate is reduced and the variation is reduced. Thereby, it is possible to distinguish between the deterioration of the selective reduction type NOx catalyst and the abnormality of the reducing agent supply device.

The predetermined range refers to a range of the NO ₂ ratio with a low NOx purification rate even when there is no abnormality in the reducing agent supply device. As described above, since NO and NO ₂ are purified by substantially the same amount, the NOx purification rate decreases as the ratio of NO ₂ increases from a specific value or decreases. When the NO ₂ ratio is near 0% or near 100%, the NOx purification rate becomes near 0%. In such a case, even if there is no abnormality in the reducing agent supply device, the average value of the NOx purification rate becomes low or the variation in the NOx purification rate becomes small. It becomes difficult to determine abnormality. That is, the predetermined range is set as a range in which the difference in the NOx purification rate depending on whether there is an abnormality in the reducing agent supply device can be determined.

Further, in the present invention, the abnormality of the reducing agent supply device is determined using the ratio of NO ₂ in NOx, but instead, the degree of deterioration can be determined using the ratio of NO in NOx. . That is, if NOx is made of NO and NO ₂ Prefecture, the larger the proportion of NO ₂ in NOx, the ratio of the amount NO is reduced. Using this relationship, the degree of deterioration can be determined using the ratio of NO in NOx.

In the present invention, the determination means determines that the reducing agent supply device is abnormal when the average value of the NOx purification rate is not more than a first predetermined value and the deviation is not more than a second predetermined value. Can do.

Here, when the average value of the NOx purification rate is small, in addition to the supply amount of the reducing agent being insufficient, the selective reduction type NOx catalyst is deteriorated or the upstream side detection means or the downstream side detection means is abnormal. Is also possible. On the other hand, when the deviation of the NOx purification rate is small, an abnormality in the upstream side detection means or the downstream side detection means may be considered in addition to the supply amount of the reducing agent being insufficient. However, when the average value of the NOx purification rate is small and the deviation of the NOx purification rate is small, only an abnormality of the reducing agent supply device can be considered. As such a determination criterion, a first predetermined value and a second predetermined value are set.

Thus, by comparing the average value of the NOx purification rate with the first predetermined value and comparing the deviation of the NOx purification rate with the second predetermined value, it is possible to easily determine the abnormality of the reducing agent supply device. . Note that the deviation is a difference from the average value, and a value representing variation in the NOx purification rate such as standard deviation or dispersion can be used instead.

Further, in the present invention, the determination unit is configured to supply the reducing agent supply device when an average value of the NOx purification rate calculated by the calculation unit is larger than a first predetermined value and a deviation is equal to or smaller than a second predetermined value. It can be determined that there is an abnormality in at least one of the upstream side detection means and the downstream side detection means.

That is, when the average value of the NOx purification rate is larger than the first predetermined value, it can be considered that there is no abnormality anywhere, or the upstream detection means or the downstream detection means is abnormal. Further, when the deviation of the NOx purification rate is smaller than the second predetermined value, an abnormality of the upstream side detection means or the downstream side detection means may be considered in addition to the supply amount of the reducing agent being insufficient. However, when the average value of the NOx purification rate is larger than the first predetermined value and the deviation of the NOx purification rate is equal to or less than the second predetermined value, there is an abnormality in the reducing agent supply device and the upstream side detection means or the downstream side It is thought that there is an abnormality in the detection means. In this way, an abnormality other than the reducing agent supply device can be determined.

According to the present invention, it is possible to determine the abnormality of the reducing agent supply device in distinction from the deterioration of the selective reduction type NOx catalyst.

It is a figure which shows schematic structure of the internal combustion engine which concerns on an Example, and its exhaust system. It is the figure which showed the relationship between addition amount ratio and NOx purification rate. Is a diagram showing the relationship between the ratio and the NOx purification rate of NO ₂ in NOx. From the top, NO ₂ ratio in NOx, the NOx purification rate when the reducing agent addition amount is sufficient, the NOx purification rate when the amount of reducing agent added is insufficient, it showed a time chart of the deviation of the NOx purification rate FIG. 5 is a flowchart illustrating a flow of determining an abnormality of the reducing agent addition amount according to the first embodiment. It is the figure which showed the relationship between the average value of NOx purification rate, deviation, and an abnormal part. 10 is a flowchart for determining an abnormal part according to the second embodiment.

  Hereinafter, specific embodiments of a failure detection device for an exhaust gas purification device according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its exhaust system according to the present embodiment. An internal combustion engine 1 shown in FIG. 1 is a diesel engine having four cylinders. In this embodiment, a urea SCR system is employed.

  An exhaust passage 2 is connected to the internal combustion engine 1. In the middle of the exhaust passage 2, a selective reduction type NOx catalyst 4 (hereinafter referred to as NOx catalyst 4) is provided.

An injection valve 5 that injects urea water into the exhaust gas in the exhaust passage 2 upstream of the NOx catalyst 4.
Is attached. The injection valve 5 is opened by a signal from the ECU 10 described later and injects urea water into the exhaust gas. In this embodiment, the injection valve 5 corresponds to the reducing agent supply device in the present invention. Further, the reducing agent supply device can include a pump that discharges the reducing agent, a passage through which the reducing agent flows, and an ECU 10 that controls the injection valve 5.

The urea water injected from the injection valve 5 is hydrolyzed by the heat of the exhaust to become ammonia (NH ₃ ) and is adsorbed on the NOx catalyst 4. This NH ₃ reduces NOx.

A first NOx sensor 7 for measuring the NOx concentration in the exhaust is attached to the exhaust passage 2 upstream of the injection valve 5. Further, in the exhaust passage 2 downstream of the NOx catalyst 4, N in the exhaust gas is exhausted.
A second NOx sensor 8 for measuring the Ox concentration and a temperature sensor 9 for measuring the temperature of the exhaust are attached. In the present embodiment, the first NOx sensor 7 corresponds to the upstream side detection means in the present invention. In the present embodiment, the second NOx sensor 8 corresponds to the downstream side detection means in the present invention. Further, instead of measuring the NOx concentration by the first NOx sensor 7, the NOx concentration may be estimated based on the operating state of the internal combustion engine 1.

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

  In addition to the above sensors, the ECU 10 outputs an electric signal corresponding to the amount of depression of the accelerator pedal 11 by the driver to detect the engine load, and an accelerator position sensor 12 for detecting the engine speed. 13 are connected via electric wiring, and the output signals of these various sensors are input to the ECU 10.

  On the other hand, the injection valve 5 is connected to the ECU 10 via electric wiring, and the ECU 10 controls the opening and closing timing of the injection valve 5.

Here, the purification rate of NOx in the NOx catalyst 4 is changed according to the amount ratio of the ratio of NO ₂ in NOx reducing agent. The addition amount ratio is an actual reducing agent addition amount with respect to a reducing agent addition amount necessary for reducing all NOx flowing into the NOx catalyst 4.

Note that it is considered that the following reaction mainly occurs in the NOx catalyst 4.
NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O Formula (1)
This reaction purifies NO and NO ₂ by an equal amount. That is, in this reaction, the ratio of NO to NO ₂ becomes purification rate of NOx greatest when one-to-one.

Here, the ratio of NO ₂ in NOx flowing into the NOx catalyst 4 is assumed to be equal to the ratio of NO ₂ in NOx discharged from the internal combustion engine 1. The ratio of NO ₂ in NOx discharged from the internal combustion engine 1 can be estimated based on the engine speed, fuel amount (may be engine load), combustion temperature, and the like. Since a well-known technique can be used for this estimation, description is abbreviate | omitted. Further, these relationships may be obtained in advance by experiments or the like and mapped and stored in the ECU 10.

FIG. 2 is a graph showing the relationship between the addition amount ratio and the NOx purification rate. A rhombus indicates a case where the ratio of NO ₂ in NOx is relatively high, and a triangle indicates a case where the ratio of NO ₂ in NOx is relatively low.

If the addition amount ratio is less than A, the difference in the NOx purification rate due to the difference in the ratio of NO ₂ in NOx is little. That is, the lack of the amount of addition of the reducing agent, when the required amount of half (amount ratio of 50%) was less than the no little influence of the ratio of NO ₂ in NOx for NOx purification rate.

Next, FIG. 3 is a diagram showing the relationship between the ratio of NO ₂ in NOx and the NOx purification rate. The solid line indicates that the amount of reducing agent added is sufficient (when the amount of reducing agent added is normal), and the one-dot chain line indicates that the amount of reducing agent added is insufficient (the amount of reducing agent added is half that of normal). Case). The case where the amount of reducing agent added is normal may be the case where the amount of reducing agent necessary for reducing the total amount of NOx flowing into the NOx catalyst 4 is added.

When the addition amount of the reducing agent is sufficient, NO and NO ₂ are purified by an equal amount by the reaction of the formula (1), so that the NOx purification rate becomes maximum when the NO ₂ ratio is approximately 50%. . On the other hand, when the amount of reducing agent added is insufficient, the overall NOx purification rate is low. That is, when the addition amount of the reducing agent is insufficient, there is almost no influence of the NO ₂ ratio on the NOx purification rate. This is because if the amount of NH ₃ is reduced, since the reaction rate of the formula (1) in NH ₃ than NO ₂ ratio is determined, is because the influence of NO ₂ ratio on the reduction reaction rate decreases. Furthermore, compared with the case where the amount of addition of the reducing agent is sufficient, when the amount of addition of the reducing agent is insufficient, the NOx purification rate becomes considerably low, so that both can be distinguished.

Further, when the amount of reducing agent added is sufficient, the variation in the NOx purification rate is relatively large compared to the case where the amount of reducing agent added is insufficient. This is because even if the NOx catalyst 4 deteriorates, the NOx purification rate varies depending on the NO ₂ ratio. That is, it can be determined whether or not the amount of the reducing agent added is sufficient based on the variation in the NOx purification rate.

Therefore, in this embodiment, it is determined whether or not the addition amount of the reducing agent is sufficient based on the average value and variation of the NOx purification rate. That is, the abnormality of the reducing agent supply device is determined.

Incidentally, NO less than the ratio of _2, for example, 30% of the NOx, or becomes 70% or more, by the NOx purification ratio is lowered in both cases insufficient and if the addition amount of the reducing agent is sufficient,
The difference between the two is reduced. If it is determined that the addition amount of the reducing agent is insufficient using the NOx purification rate in such a range, there is a risk of erroneous determination. Therefore, in this embodiment, the ratio of NO ₂ in NOx is 30%.
Based on the NOx purification rate when the amount is less than 70%, the reducing agent addition amount is determined to be insufficient.

Further, in consideration of errors such as disturbances, the NOx purification rate is detected a plurality of times, and the average value is used to determine whether or not the reducing agent addition amount is normal. For example, there is a possibility that the amount of reducing agent added is insufficient when the average value of the NOx purification rate is equal to or less than the first predetermined value. Similarly, when the deviation of the NOx purification rate is less than or equal to the second predetermined value, the amount of reducing agent added may be insufficient. Then, for example, when the average value of the NOx purification rate is equal to or less than the first predetermined value and the deviation of the NOx purification rate is equal to or less than the second predetermined value, it is determined that the amount of addition of the reducing agent is insufficient.

FIG. 4 shows, in order from the top, the NO ₂ ratio in NOx, the NOx purification rate when the reducing agent addition amount is sufficient, the NOx purification rate when the reducing agent addition amount is insufficient, and the deviation time of the NOx purification rate. It is the figure which showed the chart.

The NO ₂ ratio in NOx varies depending on the operating state of the internal combustion engine 1. When the reducing agent addition amount is sufficient, the NOx purification rate changes according to the NO ₂ ratio in NOx as shown by the solid line in FIG. This average value is relatively high. On the other hand, when the amount of reducing agent added is insufficient, NOx purification rate is hardly influenced by the ratio of NO ₂ in NOx. This average value is relatively low.

In the deviation of the NOx purification rate, the solid line shows the case where the reducing agent addition amount is insufficient, and the broken line shows the case where the reducing agent addition amount is sufficient. Thus, there is a difference in the deviation of the NOx purification rate, and the deviation is smaller when the reducing agent addition amount is insufficient.

  Next, FIG. 5 is a flowchart showing a flow of determining an abnormality of the reducing agent addition amount according to the present embodiment. This routine is repeatedly executed every predetermined time by the ECU 10 during the period in which the reducing agent is added.

  In step S101, it is determined whether or not there is an abnormality determination request for the reducing agent addition amount. For example, it is assumed that there is an abnormality determination request when the vehicle travels a specified distance or when a predetermined driving state is performed for a predetermined time. For example, it is assumed that there is an abnormality determination request when the injection valve 5 becomes clogged. If an affirmative determination is made in step S101, the process proceeds to step S102. If a negative determination is made, it is not necessary to determine whether the reducing agent addition amount is abnormal, and thus this routine is terminated.

In step S102, 0 is substituted into the counter TC. This counter TC is NOx
This is used to count the number of times the NOx amount is stored when obtaining the average value of the purification rate. 0 is substituted as an initial value.

In step S103, the ratio of NO ₂ in NOx flowing into the NOx catalyst 4 is determined whether it is within a predetermined range. As shown in FIG. 3, for example, when the NO ₂ ratio is 30% or more and less than 70%, it is set within the predetermined range. This range is a range of the NO ₂ ratio in which the abnormality determination can be accurately performed. The ratio of NO ₂ in NOx flowing into the NOx catalyst 4 is, changes according to the operating state of the internal combustion engine 1, to obtain the ratio of NO _2, for example, by substituting the operating state of the internal combustion engine 1 on the map. If an affirmative determination is made in step S103, the process proceeds to step S104. If a negative determination is made, the routine is terminated because accurate abnormality determination is difficult. In this embodiment, the ECU 10 that estimates the NO ₂ ratio in step S103 corresponds to the estimation means in the present invention.

In step S104, the input NOx amount is acquired. The amount of input NOx is the amount of NOx flowing into the NOx catalyst 4 per unit time. The input NOx amount is calculated based on the NOx concentration obtained by the first NOx sensor 7 and the engine operating state (intake air amount, fuel injection amount). Then, it is stored in the ECU 10 in association with the counter TC.

In step S105, the output NOx amount is acquired. The output NOx amount is the NOx amount flowing out from the NOx catalyst 4 per unit time. The output NOx amount is calculated based on the NOx concentration obtained by the second NOx sensor 8 and the engine operating state (intake air amount, fuel injection amount). Then, it is stored in the ECU 10 in association with the counter TC.

  In step S106, 1 is added to the counter TC.

In step S107, it is determined whether the counter TC is greater than or equal to a specified value. This specified value is a value necessary for the influence of the shortage of the reducing agent addition amount to appear on the average value of the NOx purification rate.
If an affirmative determination is made in step S107, the process proceeds to step S108. If a negative determination is made, the process returns to step S103, and the input NOx amount and the output NOx amount are continuously calculated.

In step S108, the NOx purification rate average value NOx_ave is calculated. The NOx purification rate is the ratio of the NOx amount purified by the NOx catalyst 4 to the input NOx amount, and is obtained by the following equation.
NOx purification rate = (input NOx amount-output NOx amount) / (input NOx amount)
In this embodiment, the ECU 10 that calculates the NOx purification rate corresponds to the calculating means in the present invention. The NOx purification rate average value NOx_ave is this average value.

In step S109, the NOx purification rate deviation NOx_dev is calculated. This is calculated based on the input NOx amount and the output NOx amount stored in the ECU 10. This deviation is NOx
It may be the difference between the maximum value and the minimum value of the purification rate.

  In step S110, it is determined whether the NOx purification rate average value NOx_ave is equal to or smaller than a first predetermined value and the NOx purification rate deviation NOx_dev is equal to or smaller than a second predetermined value. The first predetermined value and the second predetermined value are obtained in advance by experiments or the like as the maximum values when the reducing agent addition amount is abnormal and stored in the ECU 10. If an affirmative determination is made in step S110, the process proceeds to step S111, and if a negative determination is made, the process proceeds to step S112. In this embodiment, the ECU 10 that processes step S110 corresponds to the determination unit in the present invention.

  In step S111, the abnormality flag is turned ON. The abnormality flag is a flag that is turned off when the amount of addition of the reducing agent is normal and is turned on when it is abnormal. When the abnormality flag is ON, the driver or the like may be warned that there is an abnormality in the reducing agent supply device or the exhaust gas purification device.

  In step S112, the abnormality flag is turned OFF, and then this routine is terminated.

As described above, according to the present embodiment, since it is possible to determine the shortage of the reducing agent addition amount from the average value and variation of the NOx purification rate, it is determined whether there is an abnormality in the reducing agent supply device. Can do. When this determination is made, it can be distinguished from the deterioration of the NOx catalyst 4.
That is, when the reducing agent addition amount is insufficient, since the influence of the NO ₂ ratio on the NOx purification rate is small, an abnormality of the reducing agent supply device can be distinguished from the deterioration of the NOx catalyst 4. Here, when the exhaust gas purification device is normal, the NOx purification rate varies depending on the NO ₂ ratio in NOx, but it may be difficult to accurately obtain this NO ₂ ratio. For example, since the NO ₂ ratio varies depending on the degree of deterioration of the NOx catalyst 4 and the catalyst provided upstream thereof, it is difficult to accurately obtain the NO ₂ ratio without accurately obtaining the degree of deterioration of these catalysts. Thus, even if an accurate estimate of the NO ₂ ratio is difficult, it is possible to determine an abnormality of the reducing agent addition system knowing the approximate NO ₂ ratio.

In this embodiment, abnormalities other than the reducing agent addition amount are also determined based on the average value and deviation of the NOx purification rate of the NOx catalyst 4. Since other devices are the same as those in the first embodiment, description thereof is omitted. In this embodiment, in addition to the abnormality in the reducing agent addition amount, the NOx catalyst 4 is deteriorated or the first NOx sensor 7
Alternatively, the abnormality of the second NOx sensor 8 can be determined.

FIG. 6 is a diagram showing the relationship between the average value of NOx purification rate, the deviation, and the location where an abnormality has occurred. The average value and deviation of the NOx purification rate are obtained in the same manner as in Example 1.

When the average value of the NOx purification rate is high and the deviation is large, the exhaust purification device is normal.
That is, the NOx purification rate changes according to the NO ₂ ratio, and the NOx purification rate is high.

When the average value of the NOx purification rate is high and the deviation is small, it is considered that the reducing agent addition amount is reduced because the deviation is small. However, when the average value of the NOx purification rate is high, the amount of reducing agent added is considered normal. In such a case, it is determined that the reducing agent addition amount is abnormal and the first NOx sensor 7 or the second NOx sensor 8 is abnormal.

  When the average value of the NOx purification rate is low and the deviation is large, it is determined that the NOx catalyst 4 is deteriorated or the first NOx sensor 7 or the second NOx sensor 8 is abnormal. That is, there is no abnormality in the amount of reducing agent added.

When the average value of the NOx purification rate is low and the deviation is small, as described in Example 1,
Abnormal amount of reducing agent added.

  FIG. 7 is a flowchart for determining an abnormal part according to the present embodiment. This routine differs from the flow shown in FIG. 5 in the processing after step S109.

  In step S201, it is determined whether the NOx purification rate average value NOx_ave is equal to or less than a first predetermined value. The first predetermined value is obtained in advance by experiments or the like as a maximum value when the amount of addition of the reducing agent is abnormal, and is stored in the ECU 10. If an affirmative determination is made in step S201, the process proceeds to step S202, and if a negative determination is made, the process proceeds to step S205.

  In step S202, it is determined whether or not the NOx purification rate deviation NOx_dev is equal to or less than a second predetermined value. The second predetermined value is obtained in advance by experiments or the like as the maximum value when the amount of addition of the reducing agent is abnormal, and is stored in the ECU 10. When an affirmative determination is made in step S202, the process proceeds to step S203, and when a negative determination is made, the process proceeds to step S204.

  In step S203, it is determined that the reducing agent addition amount is abnormal.

  In step S203, it is determined that the NOx catalyst 4 has deteriorated or the first NOx sensor 7 or the second NOx sensor 8 is abnormal.

  In step S205, the same processing as in step S202 is performed. If an affirmative determination is made in step S205, the process proceeds to step S206, and if a negative determination is made, the process proceeds to step S207.

In step S206, it is determined that the reducing agent addition amount is abnormal or that the first NOx sensor 7 or the second NOx sensor 8 is abnormal.

  In step S207, it is determined that the exhaust purification device is normal.

  Thus, according to this embodiment, it is possible to determine an abnormality other than the reducing agent addition amount.

1 Internal combustion engine 2 Exhaust passage 4 Selective reduction type NOx catalyst 5 Injection valve 7 First NOx sensor 8 Second NOx sensor 9 Temperature sensor 10 ECU
11 Accelerator pedal 12 Accelerator opening sensor 13 Crank position sensor

Claims (3)

A selective reduction type NOx catalyst that is provided in an exhaust passage of the internal combustion engine and selectively reduces NOx by a reducing agent;
A reducing agent supply device for supplying a reducing agent into the exhaust gas upstream of the selective reduction type NOx catalyst;
Upstream detection means for detecting the NOx concentration upstream of the selective reduction type NOx catalyst;
Downstream detection means for detecting a NOx concentration downstream of the selective reduction type NOx catalyst;
In the failure detection device of the exhaust gas purification device provided with
Estimating means for estimating a ratio of NO ₂ in NOx flowing into the selective catalytic reduction NOx catalyst;
When the ratio of NO ₂ estimated by the estimation means is within a predetermined range, the NOx concentration detected by the upstream detection means and the downstream detection means when the reducing agent is supplied by the reducing agent supply device. Calculation means for calculating a NOx purification rate in the selective reduction type NOx catalyst based on:
Determination means for determining abnormality of the reducing agent supply device based on an average value and variation of the NOx purification rate calculated a plurality of times by the calculation means;
A failure detection device for an exhaust gas purification device. The determination means determines that there is an abnormality in the reducing agent supply device when an average value of the NOx purification rate is not more than a first predetermined value and a deviation is not more than a second predetermined value. The failure detection device for the exhaust gas purification device according to 1. When the average value of the NOx purification rate calculated by the calculating means is larger than the first predetermined value and the deviation is equal to or smaller than the second predetermined value, the determining means is abnormal in the reducing agent supply device and the upstream The failure detection apparatus for an exhaust gas purification apparatus according to claim 1, wherein it is determined that at least one of the side detection means or the downstream detection means is abnormal.

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