JP2012031826A - Failure detection system for exhaust emission control device - Google Patents

Abstract

An object of the present invention is to suppress an increase in exhaust emission when an abnormality detection process is performed in a system for detecting an abnormality of an exhaust purification device including a reducing agent supply device, a selective reduction catalyst, and an oxidation catalyst. This is the issue.
In order to solve the above-described problems, the present invention executes a reduction process for reducing the supply amount of the reducing agent when an abnormality occurs in the exhaust gas purification apparatus, and NO _X before and after the execution of the reduction process. By comparing the purification rates, it is determined whether the cause of the abnormality is in the selective reduction catalyst, the oxidation catalyst, or the supply device.
[Selection] Figure 5

Description

  The present invention relates to a technology for detecting an abnormality of an exhaust purification device provided in an exhaust passage of an internal combustion engine, and more particularly to a technology for detecting an abnormality of an exhaust purification device provided with a selective reduction catalyst.

  As an exhaust gas purification system for an internal combustion engine, a selective catalytic reduction catalyst and an oxidation catalyst are arranged along the flow direction of exhaust gas, and into an exhaust gas upstream of the selective catalytic reduction catalyst to an ammonia-derived reducing agent (for example, an aqueous urea solution). What is supplied is known.

As a technique for detecting an abnormality of such an exhaust gas purification system, the NO _X sensor arranged downstream of the oxidation catalyst, decreasing the supply amount of the output of the NO _X sensor when increasing the supply amount of the reducing agent reducing agent There has been proposed a technique for detecting an abnormality by comparing the output of the NO _X sensor when the sensor is operated (see, for example, Patent Document 1).

JP 2009-156159 A JP 2009-191756 A JP 2004-176719 A

  By the way, if the supply amount of the reducing agent is increased when an abnormality occurs in the oxidation catalyst, the exhaust emission may increase.

  The present invention has been made in view of the above-described circumstances, and its purpose is to provide a system for detecting an abnormality of an exhaust purification device including a reducing agent supply device, a selective reduction catalyst, and an oxidation catalyst. The object is to suppress an increase in exhaust emission when the abnormality detection process is performed.

In order to solve the above-described problems, the present invention reduces the amount of reducing agent supplied when an abnormality occurs in the exhaust gas purification apparatus, and causes the occurrence of the abnormality to be in the selective reduction catalyst and the oxidation catalyst. NO _X purification rate has focused on matters showing changes characteristic in each of the cases in some cases the feeder.

Therefore, the abnormality detection system for the exhaust gas purification apparatus according to the present invention is:
An exhaust purification device including a selective reduction catalyst, an oxidation catalyst disposed downstream of the selective reduction catalyst, and a supply device for supplying a reducing agent derived from ammonia into the exhaust upstream of the selective reduction catalyst;
An acquisition unit for acquiring the amount of NO _X flowing into the exhaust purification device;
A NO _X sensor that measures the amount of NO _X flowing out of the exhaust purification device;
A calculation unit that calculates the NO _X purification rate in the exhaust purification device using the NO _X amount acquired by the acquisition unit and the NO _X sensor as a parameter;
A weight reduction processing unit that executes a weight reduction process that is a process for controlling the supply device to reduce the supply amount of the reducing agent when the NO _X purification rate calculated by the calculation unit is lower than a threshold;
A determination unit that determines an abnormal portion of the exhaust purification device by comparing the NO _X purification rate calculated by the calculation unit before and after the execution of the weight reduction process;
I was prepared to.

The “NO _X purification rate” here indicates the ratio of the NO _X amount purified by the exhaust purification device to the NO _X amount flowing into the exhaust purification device. That is, acquisition value acquisition unit (NO _X flowing amount) from the NO _X sensor acquisition value (NO _X outflow) obtained by subtracting the value (= NO _X inflow -NO _X outflow), divided by the NO _X flow rate (= (NO _X inflow amount−NO _X outflow amount) / NO _X inflow amount). Further, the “threshold value” here is a value obtained by adding a predetermined margin to the NO _X purification rate at which the amount of NO _X that flows out without being purified in the exhaust purification device exceeds the allowable value or the regulation value.

As a result of the inventor's earnest experiment and verification, when the supply amount of the reducing agent is reduced when an abnormality occurs in the exhaust gas purification apparatus, the selective reduction catalyst is abnormal and the oxidation catalyst is abnormal. NO _X purification rate in the cases when the supply device is abnormal is found to exhibit different behavior (change) phase.

For example, when an abnormality occurs in the selective catalytic reduction catalyst, the amount of NO _x purified by the selective catalytic reduction catalyst (hereinafter referred to as “maximum purification amount”) decreases. Along with this, the amount of reducing agent that reacts with NO _X in the selective reduction catalyst (hereinafter referred to as “reducing agent consumption”) also decreases. Therefore, the reducing agent supply amount becomes excessive with respect to the reducing agent consumption amount in a situation where the same amount of reducing agent is supplied as that of the selective catalytic reduction catalyst. Therefore, when the reduction processing is performed when an abnormality has occurred in the selective reduction catalyst, NO _X purification rate before and after the reduction process execution becomes substantially equal.

However, the maximum purification weight reducing agent consumption commensurate with (hereinafter, referred to as "minimum consumption") if the amount of the reducing agent supply than is less, NO _X purification rate is lowered. Therefore, it is desirable that the reducing agent supply amount after the weight reduction process is determined so as not to fall below the minimum consumption amount. By the way, since the minimum consumption varies depending on the degree of deterioration of the selective catalytic reduction catalyst, it is necessary to obtain the minimum consumption corresponding to each degree of deterioration, and the work becomes complicated. Therefore, minimal consumption when the degree of NO _X purification rate becomes equal to the threshold selective reduction catalyst has degraded (hereinafter, referred to as "minimum amount") previously obtained in advance, and the reducing agent supply amount after reduction process execution May be executed so that the value is equal to the lower limit amount.

Next, when an abnormality occurs in the oxidation catalyst, the amount of reducing agent that can be purified by the oxidation catalyst decreases. That is, among the reducing agents that have passed through the selective catalytic reduction catalyst, the amount of the reducing agent that is not purified by the oxidation catalyst increases. Here, when the reducing agent derived from ammonia comes into contact with the NO _X sensor, NO _X is generated. Therefore, when the amount of the reducing agent that is not purified by the oxidation catalyst increases, the NO _X amount measured by the NO _X sensor increases. In contrast, if the supply amount of the reducing agent is reduced, the reducing agent reaching the NO _X sensor decreases, NO _X amount measured by the NO _X sensor is reduced. As a result, NO _X purification rate calculated by the arithmetic unit increases. Therefore, if an abnormality occurs in the oxidation catalyst, it is NO _X purification rate after execution compared to the previous execution of the reduction process becomes high.

Further, when an abnormality in the supply system has occurred, it is NO _X purification rate after execution compared to the previous execution of the reduction process is low. It should be noted that the abnormality in the supply device referred to here indicates an abnormality in which the actual supply amount decreases with respect to the indicated value.

As described above, the behavior of the NO _X purification rate at the time of reduction processing execution differs in the case the supply device and the case when the oxidation catalyst selective reduction catalyst is abnormal is abnormal is abnormal. Thus, by comparing the NO _X purification rate calculating unit is calculated before and after the execution of the reduction process, it is possible to identify the abnormal point of the exhaust gas purification device (determination).

For example, when the NO _X purification rate calculated by the calculation unit after execution of the weight reduction process is higher than the NO _X purification rate calculated by the calculation unit before execution of the reduction process, the determination unit determines that the oxidation catalyst is abnormal. be able to.

Further, with respect to NO _X purification rate by the calculation unit has calculated before reduction process execution, if NO _X purification rate calculation unit has calculated after reduction process execution are substantially equal, the determination unit, the selective catalytic reduction catalyst is abnormal It can be determined that

Further, when the NO _X purification rate calculated by the calculation unit after execution of the weight reduction process is lower than the NO _X purification rate calculated by the calculation unit before execution of the weight reduction process, the determination unit determines that the supply device is abnormal. be able to.

Incidentally, the abnormality detection system of the exhaust purification device according to the present invention, with respect to NO _X purification rate by the calculation unit has calculated before reduction process execution, whether NO _X purification rate by the calculation unit has calculated after reduction process execution is high Can be regarded as a system for determining whether or not the oxidation catalyst is abnormal.

  Since the abnormality detection process at that time is realized by reducing the amount of the reducing agent, even if the oxidation catalyst is abnormal, the reducing agent that is not purified by the oxidation catalyst does not increase. Therefore, it is possible to detect an abnormality in the oxidation catalyst while suppressing an increase in exhaust emission due to the execution of the abnormality detection process.

By the way, when the NO _X sensor is abnormal, the NO _X purification rate is reduced by the execution of the weight reduction process, as in the case where the supply device is abnormal. However, when the NO _X sensor is abnormal, the rate of decrease in the NO _X purification rate is higher than when the supply device is abnormal. Thus, the supply device equal to or less than the reference value decrease rate of the NO _X purification rate at the time of reduction processing execution is abnormal, the NO _X sensor if reduction rate of the NO _X purification rate at the time of reduction processing execution is greater than the reference value It can be determined that there is an abnormality. The reference value in this case corresponds to the maximum value that the NO _X purification rate can be reduced when the supply device is abnormal, or the minimum value that the NO _X purification rate can be reduced when the NO _X sensor is abnormal. It is assumed that it is obtained experimentally in advance.

  According to the present invention, in a system for detecting an abnormality of an exhaust emission control device including a reducing agent supply device, a selective reduction catalyst, and an oxidation catalyst, an increase in exhaust emission when performing abnormality detection processing is suppressed. Can do.

1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. It is a diagram showing a relationship between the reducing agent addition amount and the NO _X purification rate when the selective reduction catalyst is abnormal. Ammonia oxidation catalyst is a diagram showing the relationship between the reducing agent addition amount and the NO _X purification rate when it is abnormal. It is a diagram showing a relationship between the reducing agent addition amount and the NO _X purification rate when the urea addition valve has abnormality. It is a flowchart which shows the abnormality detection process routine in a 1st Example. NO _x sensor is a diagram showing a relationship between the reducing agent addition amount and _the NO _x purification rate in the case is abnormal.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

<Example 1>
First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. The internal combustion engine 1 shown in FIG. 1 is a compression ignition internal combustion engine (diesel engine), but may be a spark ignition internal combustion engine (gasoline engine).

  In FIG. 1, an exhaust passage 2 is connected to the internal combustion engine 1. A pre-stage catalyst 3 is disposed in the exhaust passage 2. The pre-stage catalyst 3 is a catalyst having a function of oxidizing hydrocarbons (HC), carbon monoxide (CO) and the like contained in the exhaust gas. A particulate filter 4 is disposed in the exhaust passage 2 immediately downstream of the front catalyst 3.

A selective catalytic reduction catalyst 5 is disposed in the exhaust passage 2 downstream from the particulate filter 4. Selective reduction catalyst 5 is selectively adsorbs polar molecules of ammonia (NH ₃₎ or the like, a catalyst for reducing and purifying NO _X in the exhaust gas adsorbed ammonia (NH ₃₎ as the reducing agent. An ammonia oxidation catalyst 6 for oxidizing ammonia (NH ₃ ) is disposed in the exhaust passage 2 immediately downstream of the selective catalytic reduction catalyst 5. The ammonia oxidation catalyst 6 corresponds to the oxidation catalyst according to the present invention.

  A urea addition valve 7 for adding a urea aqueous solution as a reducing agent into the exhaust is attached to the exhaust passage 2 located between the particulate filter 4 and the selective catalytic reduction catalyst 5. A tank 8 for storing an aqueous urea solution is connected to the urea addition valve 7. The urea addition valve 7 and the tank 8 are an embodiment of the supply device according to the present invention.

The urea addition valve 7 adds an aqueous urea solution stored in the tank 8 into the exhaust when the selective catalytic reduction catalyst 5 is in an active state. The urea aqueous solution added to the exhaust gas is thermally decomposed and hydrolyzed in the exhaust gas or in the selective reduction catalyst 5 to generate ammonia (NH ₃ ). Ammonia (NH ₃ ) is adsorbed by the selective catalytic reduction catalyst 5 and reduces NO _X in the exhaust.

The exhaust purification system configured in this manner is provided with an ECU 9. The ECU 9 is an electronic control unit that includes a CPU, a ROM, a RAM, a backup RAM, and the like. The ECU 9 is supplied with output signals from various sensors such as a NO _X sensor 10, an accelerator position sensor 11, and a crank position sensor 12.

The NO _X sensor 10 is a sensor that is disposed in the exhaust passage 2 downstream of the ammonia oxidation catalyst 6 and outputs an electrical signal correlated with the amount (concentration) of nitrogen oxide (NO _X ) contained in the exhaust. The accelerator position sensor 11 is a sensor that outputs an electrical signal correlated with the amount of operation of the accelerator pedal (accelerator opening). The crank position sensor 12 is a sensor that outputs an electrical signal correlated with the rotational position of the crankshaft.

  The ECU 9 controls the operation state of the urea addition valve 7 and the internal combustion engine 1 based on the output signals of the various sensors described above. For example, the ECU 9 executes an abnormality detection process for the ammonia oxidation catalyst 6 in addition to known controls such as fuel injection control and urea addition control. Hereinafter, the abnormality detection process of the ammonia oxidation catalyst 6 will be described.

In the abnormality detection process in this embodiment, ECU 9, first calculates the NO _X purification rate of the exhaust gas purification device. The “exhaust gas purification device” here is a selective reduction catalyst 5, an ammonia oxidation catalyst 6,
And the urea addition valve 7 is a general term. Further, where the term "NO _X purification rate", to _the amount of NO _X flowing into the exhaust purification device (NO _X inflow amount), the ratio of the amount of NO _X to be purified by the exhaust purification apparatus.

Since the NO _X inflow amount corresponds to the NO _X amount discharged from the internal combustion engine 1, the operating conditions (engine speed, accelerator opening, fuel injection amount, etc.) of the internal combustion engine 1 can be calculated as parameters. Note that a NO _X sensor may be attached between the particulate filter 4 and the selective catalytic reduction catalyst 5, and the output signal of the NO _X sensor may be the NO _X inflow amount. Thus ECU9 that by obtaining the NO _X flow rate, acquisition unit according to the present invention is implemented.

The ECU 9 calculates the NO _X purification rate Enox using the NO _X inflow amount, the output signal of the NO _X sensor 10 (NO _X outflow amount), and the following equation. In the following formula, ANO _X in is the NO _X inflow amount, and ANO _X out is the NO _X outflow amount.

Enox = (ANO _X in-ANO _X out) / ANO _X in

ECU9 is, NO _X purification rate Enox it is determined whether or not the threshold Enox0 more. Here, the “threshold Enox0” is a value obtained by adding a predetermined margin to the NO _X purification rate at which the amount of NO _X flowing out without being purified in the exhaust purification device exceeds the allowable value or the regulation value. This threshold value Enox0 is obtained in advance by an adaptation operation using an experiment or the like.

ECU9 determines that NO _X purification rate Enox is equal threshold Enox0 above, is normal exhaust emission control device. On the other hand, when the NO _X purification rate Enox is below the threshold Enox0, ECU 9 determines that an abnormality has occurred in the exhaust purification apparatus. By the way, as the abnormality of the exhaust purification device, the abnormality (deterioration) of the selective catalytic reduction catalyst 5, the abnormality (deterioration) of the ammonia oxidation catalyst 6, and the abnormality of the urea addition valve 7 are considered. Therefore, it is necessary to factor in NO _X purification rate Enox falls below the threshold Enox0 it is determined whether the abnormality (deterioration) of the ammonia oxidation catalyst 6.

On the other hand, as a result of intensive experiments and verifications by the present inventor, if the amount of urea aqueous solution added is reduced when an abnormality occurs in the exhaust gas purification apparatus, the selective catalytic reduction catalyst 5 is abnormal (deteriorated). If the ammonia oxidation catalyst 6 is abnormality (deterioration) when the urea addition valve 7 is has been found to exhibit abnormal NO _X purification rate Enox in the case of the (degraded) is different behavior.

Figure 2 is a diagram showing the relationship between the added amount and the NO _X purification rate of the urea aqueous solution in the case where the abnormality in the selective reduction catalyst 5 has occurred. One-dot chain line in FIG. 2 shows the NO _X purification rate at the time of the normal of the selective reduction catalyst 5, the two-dot chain line in FIG. 2 shows the NO _X purification rate when the selective reduction catalyst 5 deteriorates. Further, “Aur0” in FIG. 2 indicates an addition amount of the selective catalytic reduction catalyst 5 in a normal state (hereinafter referred to as “basic addition amount”). Base supply quantity Aur0 is the addition amount of the minimum in the range of NO _X purification rate is maximized (= Enoxmax) during normal selective reduction catalyst 5.

When the selective catalytic reduction catalyst 5 deteriorates, the NO _X amount (maximum purification amount) purified by the selective catalytic reduction catalyst 5 decreases, and the consumption amount (reducing agent consumption amount) of ammonia (NH ₃ ) also decreases accordingly. Decrease. As a result, the basic addition amount Aur0 is excessive with respect to the reducing agent consumption. Therefore, even if reduction treatment amount is performed, NO _X purification rate becomes substantially constant.

However, the addition amount than the reducing agent consumption commensurate with the maximum purification amount (minimum consumption) is reduced, NO _X purification rate is lowered. Therefore, it is desirable that the addition amount after the weight reduction process is determined so as not to be less than the minimum consumption amount. Therefore, the reduction process of the present embodiment is performed so that the addition amount after the reduction process is performed becomes the lower limit amount Aur1. The lower limit amount Aur1 corresponds to a minimum consumption in case of a degree that NO _X purification rate becomes equal to the threshold Enox0 selective reduction catalyst 5 was deteriorated (see solid line in FIG. 2) was determined experimentally in advance Value.

When reduction processing by such procedure is performed, reduction process execution before (quantity of urea solution = base supply quantity Aur0) and reduction process after execution of the NO _X purification rate (quantity of urea solution = lower limit amount AUR1) It becomes equivalent to the value (= Enox1) the NO _X purification rate of.

Next, FIG. 3 is a diagram showing the relationship between the added amount and the NO _X purification rate of the urea aqueous solution in the case where abnormality in the ammonia oxidation catalyst 6 occurs. One-dot chain line in FIG. 3 shows the NO _X purification rate at the time of normal ammonia oxidation catalyst 6, a two-dot chain line in FIG. 3 shows the NO _X purification rate when the ammonia oxidation catalyst 6 is deteriorated. Also, “Aur0” and “Aur1” in FIG. 3 are the same values as in FIG.

When an abnormality occurs in the ammonia oxidation catalyst 6, the amount of ammonia (NH ₃ ) that can be purified by the ammonia oxidation catalyst 6 decreases. That is, the amount of ammonia (NH ₃ ) that is not purified by the ammonia oxidation catalyst 6 among the ammonia (NH ₃ ) that has passed through the selective catalytic reduction catalyst 5 increases.

Here, when ammonia (NH ₃ ) comes into contact with the NO _X sensor 10, NO _X is generated. Therefore, when ammonia (NH ₃ ) that is not purified by the ammonia oxidation catalyst 6 increases, the amount of NO _X measured by the NO _X sensor 10 increases. On the other hand, when the amount reduction process is performed, ammonia (NH ₃ ) reaching the NO _X sensor 10 decreases, and therefore the NO _X amount measured by the NO _X sensor 10 decreases. As a result, (the addition amount of the aqueous urea solution = base supply quantity Aur0) reduction process execution previously for NO _X purification rate Enox2 in, (quantity of urea solution = lower limit amount AUR1) after reduction process execution in NO _X purification rate Enox0 Is higher.

4 is a diagram showing the relationship between the added amount of the aqueous urea solution when the abnormality in the urea addition valve 7 occurs (indicated value to be output to the urea addition valve 7 from ECU 9) and NO _X purification rate. Dashed line in Figure 4 shows the NO _X purification rate at the time of normal urea addition valve 7, the two-dot chain line in Figure 4 shows the NO _X purification rate when the urea addition valve 7 is degraded. Also, “Aur0” and “Aur1” in FIG. 4 are the same values as in FIG.

When an abnormality occurs in the urea addition valve 7, the amount of urea aqueous solution actually added from the urea addition valve 7 becomes smaller than the indicated value. Therefore, even indicated value A equal to the basic amount Aur0, NO _X purification rate is lower than the NO _X purification rate Enoxmax of normal. This tendency is the same when the indicated value is reduced. That, NO _X purification rate when the indicated value is reduced is reduced at a reduced degree substantially equal to the degree indicated value. As a result, (the addition amount of the aqueous urea solution = base supply quantity Aur0) reduction process execution previously for NO _X purification rate Enox3 in, (quantity of urea solution = lower limit amount AUR1) after reduction process execution in NO _X purification rate Enox4 Becomes lower.

Above As mentioned, the reduction process is carried out when the NO _X purification rate Enox is below the threshold Enox0, selective reduction catalyst 5 is abnormal (deteriorated) at a case the ammonia oxidation catalyst 6 is abnormality (deterioration) It shows the NO _X purification rate Enox different behavior in the case when the urea addition valve 7 is is abnormal (deteriorated).

Therefore, the ECU 9 determines the NOx purification rate before execution of the weight reduction process and the N _X after execution of the weight reduction process.
By comparing the O _X purification rate can be selective reduction catalyst 5 or is abnormal, or ammonia oxidation catalyst 6 is abnormal, or urea addition valve 7 is determined whether the abnormality.

For example, if it is within tolerance difference was determined in advance and the reduction process execution before of the NO _X purification rate reduction processing after execution of the NO _X purification rate, the ammonia oxidation catalyst 6 is normal, selective reduction catalyst 5 Can be determined to be abnormal.

Further, the difference between the NO _X purification rate before reduction processing execution and reduction process after execution of the NO _X purification rate is greater than the allowable value, and NO _X purification rate after reduction process execution than NO _X purification rate before reduction process execution Is low, it can be determined that the ammonia oxidation catalyst 6 is normal and the urea addition valve 7 is abnormal.

Moreover, the difference between the NO _X purification rate before reduction processing execution and reduction process after execution of the NO _X purification rate is greater than the allowable value, and NO _X purification rate after reduction process execution than NO _X purification rate before reduction process execution Is high, it can be determined that the ammonia oxidation catalyst 6 is abnormal.

  Hereinafter, the execution procedure of the abnormality detection process in the present embodiment will be described with reference to FIG. FIG. 5 is a flowchart showing an abnormality detection processing routine. This routine is stored in advance in the ROM of the ECU 9 and is periodically executed by the ECU 9.

  In the routine of FIG. 5, the ECU 9 first determines whether or not an abnormality detection condition is satisfied in S101. As the abnormality detection condition, for example, a condition such that the internal combustion engine 1 is in a warm-up completion state or the internal combustion engine 1 is in a steady operation state can be used. If a negative determination is made in S101, the ECU 9 once ends the execution of this routine. On the other hand, if an affirmative determination is made in S101, the ECU 9 proceeds to S102.

In S102, ECU 9 calculates the NO _X purification rate Enoxbef. Subsequently, ECU 9 proceeds to S103, the NO _X purification rate Enoxbef calculated in S102 it is determined whether the threshold Enox0 or less. If a negative determination is made in S103 (Enoxbef ≧ Enox0), the ECU 9 proceeds to S111 and determines that the exhaust purification device (the selective reduction catalyst 5, the ammonia oxidation catalyst 6, and the urea addition valve 7) is normal.

  If an affirmative determination is made in S103 (Enoxbef <Enox0), the ECU 9 proceeds to S104 and executes a reduction process. Specifically, the ECU 9 changes the target addition amount of the urea addition valve 7 from the basic addition amount Aur0 to the lower limit amount Aur1. In this way, the ECU 9 executes the process of S104, thereby realizing the weight reduction processing unit according to the present invention.

In S105, ECU 9 calculates the NO _X purification rate Enoxaft after reduction process execution. The ECU 9 executes the processes of S102 and S105, thereby realizing the arithmetic unit according to the present invention.

In S106, the ECU 9 determines whether or not the difference (= | Enoxaft−Enoxbef |) between the NO _X purification rate Enoxbef calculated in S102 and the NO _X purification rate Enoxaft calculated in S105 is an allowable value α or less. Is determined. Incidentally, Enoxbef as used herein corresponds to the NO _X purification rate before reduction process execution.

  If an affirmative determination is made in S106 (| Enoxaf−Enoxbef | ≦ α), the ECU 9 proceeds to S107. In S107, the ECU 9 determines that the ammonia oxidation catalyst 6 is normal and the selective catalytic reduction catalyst 5 is abnormal.

On the other hand, if a negative determination is made in S106 (| Enoxaft-Enoxbef |> α), the ECU 9 proceeds to S108. In S108, ECU 9 is, NO _X purification rate Enoxaft calculated in the S105, it is determined whether or not greater than NO _X purification rate Enoxbef calculated in the S102.

  If an affirmative determination is made in S108 (Enoxaft> Enoxbef), the ECU 9 proceeds to S109. In S109, the ECU 9 determines that the ammonia oxidation catalyst 6 is abnormal (the selective reduction catalyst 5 and the urea addition valve 7 are normal).

  On the other hand, if a negative determination is made in S108 (Enoxaft <Enoxbef), the ECU 9 proceeds to S110. In S110, the ECU 9 determines that the ammonia oxidation catalyst 6 is normal and the urea addition valve 7 is abnormal.

  In addition, the determination part concerning this invention is implement | achieved when ECU9 performs the process of S106 thru | or S110.

  As described above, the ECU 9 can detect the abnormality of the ammonia oxidation catalyst 6 as well as the abnormality of the selective reduction catalyst 5 and the abnormality of the urea addition valve 7 by executing the routine of FIG. it can. Furthermore, since the abnormality detection processing according to the present invention is realized by reducing the amount of the reducing agent (urea aqueous solution) added, abnormality detection is performed even when an abnormality has occurred in the selective catalytic reduction catalyst 5. An increase in exhaust emission due to the execution of the process can be suppressed.

<Example 2>
Next, a second embodiment of the present invention will be described with reference to FIG. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.

  The difference between the first embodiment and the present embodiment is that the abnormality of the NOx sensor 10 is detected in addition to the abnormality of the exhaust purification device. When an abnormality occurs in the NOx sensor 10, the NOx purification rate Enoxaft after the reduction process is executed becomes lower than the NOx purification rate Enoxbef before the reduction process is executed. That is, when an abnormality occurs in the NOx sensor 10, the magnitude relationship between the NOx purification rate Enoxbef before execution of the reduction process and the NOx purification rate Enoxaft after execution of the reduction process is the same as when the abnormality occurs in the urea addition valve 7. Become.

  However, as shown in FIG. 6, when an abnormality occurs in the urea addition valve 7, the decrease degree of the urea aqueous solution addition amount and the NOx purification rate decrease degree are substantially equal (see the solid line in FIG. 6). ). On the other hand, when an abnormality occurs in the NOx sensor 10, the degree of decrease in the NOx purification rate is greater than the degree of decrease in the amount of urea aqueous solution added (see the two-dot chain line in FIG. 6).

  Therefore, if the degree of decrease (slope) from the NOx purification rate Enoxbef before execution of the weight reduction process to the NOx purification rate Enoxaft after execution of the weight reduction processing is equal to or greater than a certain amount, the NOx sensor 10 is abnormal, and NOx purification before the reduction processing is executed. If the degree of decrease (slope) from the rate Enoxbef to the NOx purification rate Enoxaft after the reduction processing is less than a certain amount, it can be determined that the urea addition valve 7 is abnormal.

  According to the embodiment described above, it is possible to distinguish between abnormality of the selective reduction catalyst 5, abnormality of the ammonia oxidation catalyst 6, abnormality of the urea addition valve 7, and abnormality of the NOx sensor 10.

1 Internal combustion engine 2 Exhaust passage 3 Pre-stage catalyst 4 Particulate filter 5 Selective reduction catalyst 6 Ammonia oxidation catalyst 7 Urea addition valve 8 Tank 9 ECU
10 NO _x sensor

Claims (4)

An exhaust purification device including a selective reduction catalyst, an oxidation catalyst disposed downstream of the selective reduction catalyst, and a supply device for supplying a reducing agent derived from ammonia into the exhaust upstream of the selective reduction catalyst;
An acquisition unit for acquiring the amount of NO _X flowing into the exhaust purification device;
A NO _X sensor that measures the amount of NO _X flowing out of the exhaust purification device;
A calculation unit that calculates the NO _X purification rate in the exhaust purification device using the NO _X amount acquired by the acquisition unit and the NO _X sensor as a parameter;
A weight reduction processing unit that executes a weight reduction process that is a process for controlling the supply device to reduce the supply amount of the reducing agent when the NO _X purification rate calculated by the calculation unit is lower than a threshold;
A determination unit that determines an abnormal portion of the exhaust purification device by comparing the NO _X purification rate calculated by the calculation unit before and after the execution of the weight reduction process;
An abnormality detection system for an exhaust purification device comprising: The determination unit according to claim 1, wherein the NO _X purification rate calculated by the calculation unit after execution of the weight reduction process is higher than the NO _X purification rate calculated by the calculation unit before execution of the reduction process. An abnormality detection system for an exhaust gas purification apparatus that determines that the oxidation catalyst is abnormal. Equivalent in claim 1 or 2, wherein the determination unit is configured to weight loss NO _X purification rate the calculation unit is calculated before executing the process, NO _X purification rate the calculation unit is calculated after the execution of the reduction process is If this is the case, an abnormality detection system for the exhaust gas purification apparatus that determines that the selective catalytic reduction catalyst is abnormal. 4. The determination unit according to claim 1, wherein the determination unit calculates the NO _X calculated by the calculation unit after execution of the weight reduction process with respect to the NO _X purification rate calculated by the calculation unit before execution of the weight reduction process. An abnormality detection system for an exhaust gas purification device that determines that the supply device is abnormal when the _X purification rate is low.

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