JP2015014233A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system for an internal combustion engine that enables an abnormality diagnosis of addition means of a reducing agent by using a simple configuration.SOLUTION: An exhaust emission control system 1 for an internal combustion engine includes: a reduction catalyst 3 for reducing NOx in exhaust gas of the internal combustion engine by using a reducing agent added into the exhaust gas; reducing agent addition means 4 for adding the reducing agent to the exhaust gas flowing into the reduction catalyst 3; a NOx sensor 7 installed downstream of the reducing agent addition means 4 and upstream of the reduction catalyst 3 and having sensitivity to the reducing agent; a theoretical measurement value calculation means that uses an operating state of the internal combustion engine and physical quantity related to an additive amount of the reducing agent as parameters and estimates a theoretical measurement value of NOx flowing into the reduction catalyst 3; and treatment means for performing an abnormality diagnosis of the reducing agent addition means 4 on the basis of a difference between an actual measurement value obtained by the NOx sensor 7 and the theoretical measurement value.

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine.

  As an exhaust purification system that purifies NOx discharged from an internal combustion engine, a reduction catalyst that selectively reduces and purifies NOx in the presence of a reducing agent is disposed in the exhaust passage, and the reducing agent is exhausted from upstream of the reducing catalyst. There is something to add to.

  In such an exhaust purification system, a technique for adjusting the amount of urea water added by arranging a NOx sensor for measuring NOx in exhaust gas flowing into the reduction catalyst between the urea water addition means and the reduction catalyst has been proposed. (See Patent Document 1). If the sensitivity to the urea water of the NOx sensor arranged before and after the urea water addition means is used, it can be diagnosed whether or not the urea water addition means is abnormal (see, for example, Patent Document 2). In addition, there are various techniques for diagnosing the exhaust purification system (see, for example, Patent Document 3-4).

JP 2011-94592 A JP 2010-163923 A Japanese Patent No. 4822772 Japanese Patent No. 4976694

  When the abnormality diagnosis of the adding means for adding the reducing agent to the exhaust gas sent to the reduction catalyst is performed based on, for example, the difference between the measured values of the NOx sensors arranged before and after the adding means, the cost associated with the increase in the number of NOx sensors Cost.

  Therefore, an object of the present invention is to provide an exhaust gas purification system for an internal combustion engine that can realize abnormality diagnosis of the reducing agent addition means with a simple configuration.

  In order to solve the above-mentioned problem, the present invention performs abnormality diagnosis of the reducing agent adding means based on the difference between the actual measured value and the theoretical measured value of the NOx sensor installed on the downstream side of the reducing agent adding means.

  Specifically, it is an exhaust gas purification system for an internal combustion engine, in which NOx in the exhaust gas of the internal combustion engine is reduced by a reducing agent added to the exhaust gas, and the reducing agent is added to the exhaust gas flowing into the reducing catalyst. A reducing agent adding means to be added; a NOx sensor having sensitivity to the reducing agent, disposed downstream of the reducing agent adding means and upstream of the reducing catalyst; an operating state of the internal combustion engine; and the reducing agent Based on the difference between the actual measured value of the NOx sensor and the theoretical measured value, the reducing agent based on the theoretical measured value calculating means for estimating the theoretical measured value of NOx flowing into the reduction catalyst using the physical quantity related to the addition amount as a parameter Processing means for performing abnormality diagnosis of the adding means.

In the exhaust purification system, a NOx sensor for measuring NOx in the exhaust gas flowing into the reduction catalyst exists on the downstream side of the reducing agent addition means, and the NOx sensor has sensitivity not only to NOx but also to the reducing agent. Therefore, in addition to the amount of NOx contained in the exhaust gas sent from the internal combustion engine, the actual measured value of the NOx sensor observed in the state where the reducing agent is added by the reducing agent addition means includes the addition of the reducing agent. The component added by is included. For example, when the NOx sensor is sensitive to NH ₃ , the reducing agent addition means adds NH ₃ to the exhaust as the reducing agent, so that the NOx sensor has sensitivity to not only NOx but also the reducing agent. Show.

  Therefore, in the exhaust gas purification system, the theoretical measurement value and the actual measurement value are estimated after estimating the theoretical measurement value of NOx flowing into the reduction catalyst using the operating state of the internal combustion engine and the physical quantity relating to the addition amount of the reducing agent as parameters. The abnormality diagnosis of the reducing agent adding means is performed on the basis of the difference. If there is an abnormality in the reducing agent addition means, the difference between the theoretical measurement value using the physical quantity related to the addition amount of the reducing agent as a parameter and the actual measurement value obtained from the NOx sensor having sensitivity to the reducing agent changes. Abnormality diagnosis is possible even if it is not arranged before or after the reducing agent addition means, and the configuration relating to the abnormality diagnosis of the reducing agent addition means can be simplified.

  By the way, the processing means learns an error between the actual measured value in a state where the addition of the reducing agent is stopped and the estimated value of NOx in the exhaust estimated from the operating state of the internal combustion engine. The abnormality diagnosis may be performed based on a difference between the actual measurement value and the theoretical measurement value obtained by adding the learning value of the error. Here, the estimated value of NOx is the amount of NOx in the exhaust estimated from the operating state of the internal combustion engine, and for example, a value estimated based on a measured value obtained from sensors other than the NOx sensor is applied. Can do. If the abnormality diagnosis is executed after learning the error between the actual measurement value and the estimated value, the accuracy of the diagnosis result is improved even if the accuracy of various sensors provided in the internal combustion engine or the exhaust purification system varies. be able to.

  The processing means diagnoses that the cartridge is abnormal when the reducing agent addition means diagnoses that the reducing agent addition means is abnormal within a predetermined period of time after the reducing agent cartridge is loaded in the reducing agent addition means. It may be what performs. This diagnosis is based on the idea that if it is diagnosed that the reducing agent addition means is abnormal soon after the cartridge is loaded, there is a high probability that the loaded reducing agent cartridge is abnormal. Therefore, it can be determined whether or not the abnormality of the reducing agent addition means is due to the abnormality of the reducing agent cartridge.

When the reducing agent is NH ₃ , the physical quantity related to the addition amount may be the NH ₃ addition amount or the added NH ₃ concentration. When the reducing agent is NH ₃ , if the NH ₃ addition amount or the added NH ₃ concentration is used as a parameter when estimating the theoretical measurement value, the apparent fluctuation added to the output of the NOx sensor by the addition of the reducing agent. The quantity can be included in the estimated theoretical measurement. Here, the added NH ₃ concentration can be estimated based on, for example, the exhaust gas amount of the internal combustion engine and the NH ₃ addition amount. Further, the amount of exhaust gas can be estimated by, for example, the amount of intake air of an internal combustion engine or various sensors.

  According to the present invention, the abnormality diagnosis of the reducing agent addition means can be realized with a simple configuration.

FIG. 1 is an example of a configuration diagram illustrating an exhaust gas purification system for an internal combustion engine according to an embodiment. FIG. 2 is an example of a flowchart of a diagnostic process of the NH ₃ addition system executed by the ECU. FIG. 3 is an example of a graph showing actual measured values, estimated values, and theoretical measured values of the NOx sensor. FIG. 4 is an example of a processing flow diagram obtained by modifying the processing content of step S105. FIG. 5 is an example of a diagram showing a modification of the exhaust purification system. FIG. 6 is an example of a diagram in which the processing flow executed by the ECU is modified. In the processing flow diagram shown in FIG. 2, processing further executed after step S106 is further added.

  Hereinafter, embodiments of the present invention will be described. Embodiment described below is one form for implementing this invention, and does not limit the technical scope of this invention.

  FIG. 1 is an example of a configuration diagram illustrating an exhaust gas purification system for an internal combustion engine according to an embodiment. The exhaust purification system 1 according to the embodiment is provided with an exhaust path 2 connected to an internal combustion engine.

The exhaust path 2 of the exhaust purification system 1 is provided with a reduction catalyst (for example, an SCR (Selective Catalytic Reduction) catalyst) 3 that selectively reduces and purifies NOx in exhaust using ammonia as a reducing agent. Further, the exhaust purification system 1, (which is an example of referred herein "reducing agent addition means") NH 3 in the exhaust passage 2 NH ₃ addition system for adding _(referred to herein is a an example of a "reducing agent") 4 is provided. The NH ₃ addition system 4 is disposed in an upstream portion of the reduction catalyst 3 in the exhaust path 2 and includes an addition valve 5 for adding NH ₃ gas into the exhaust. Further, the NH ₃ addition system 4 supplies NH ₃ gas into the addition valve 5 NH ₃ gas cartridge (referred to herein is an example of a "cartridge reducing agent") 6 is provided. NH ₃ added to the exhaust gas from the addition valve 5 functions as a reducing agent for reducing NOx in the reduction catalyst 3. The reduction catalyst 3 is not limited to the SCR catalyst, and may be, for example, SCRF in which the SCR catalyst is combined with a filter that captures PM (Particulate Matter). Further, the NH ₃ addition system 4, a temperature sensor for measuring the temperature of the NH ₃ gas cartridge 6, a heater for heating the NH ₃ gas cartridge 6 may be provided with a pressure sensor for measuring the pressure of the NH ₃ gas cartridge 6 .

A NOx sensor 7 that measures the amount of NOx in the exhaust gas flowing into the reduction catalyst 3 is provided between the addition valve 5 and the reduction catalyst 3 in the exhaust path 2. The NOx sensor 7 is a sensor having sensitivity not only to NOx but also to NH ₃ . For example, in the case of a NOx sensor incorporating a Pt group electrode, NH ₃ contained in the exhaust gas is oxidized at the Pt group electrode and changed to NO. In this case, the NOx sensor 7 outputs a measured value of an amount obtained by further adding the NO amount changed from NH ₃ to the NOx amount contained in the exhaust gas.

  The ECU (an example of “theoretical measurement value calculation means” and “processing means” in the present application) 8 is a computer that controls the internal combustion engine, and is input with detection values from various sensors including the NOx sensor 7. The ECU 8 acquires the operating state of the internal combustion engine and the driver's request based on detection values (parameters) input from various sensors, and controls the operation of various devices including the addition valve 5. Further, the ECU 8 estimates the amount of NOx in the exhaust discharged from the internal combustion engine by calculations based on various detection values and information input to the ECU 8.

FIG. 2 is an example of a flowchart of the diagnostic process of the NH ₃ addition system 4 executed by the ECU 8. ECU8 implement | achieves the following diagnostic processing, when an arithmetic unit accesses the computer program memorize | stored in the memory in ECU8. The flowchart of the diagnostic process shown in FIG. 2 is repeatedly executed during operation of the internal combustion engine.

In the process of step S101, ECU 8 is, NH ₃ addition system 4 determines whether or not is being added NH _3. Whether NH ₃ addition system 4 is being added NH _3, for example, it can be determined based on the open or closed state of the addition valve 5. ECU8, if NH ₃ addition system 4 is determined to be in addition to NH ₃ in the process in step S101, executes the process of step S102. If the ECU 8 determines in the process of step S101 that the NH ₃ addition system 4 is not adding NH ₃ , the ECU 8 executes the process of step S106.

  In the process of step S102, the ECU 8 determines whether or not learning of an error between the actual measured value of the NOx sensor 7 and the estimated value of NOx has been completed. Here, the actual measured value of the NOx sensor 7 is the amount of NOx in the exhaust gas observed by the NOx sensor 7. The estimated value of NOx is the amount of NOx in exhaust gas estimated from the operating state of the internal combustion engine, and is obtained from sensors other than the NOx sensor 7 (for example, a sensor that measures the operating state of the internal combustion engine). A value estimated based on the measured value can be applied. Whether or not the error learning is completed can be determined based on, for example, the state of a variable representing the error. When the ECU 8 determines that the error learning has been completed in the process of step S102, the ECU 8 executes the process of step S103. If the ECU 8 determines that the error learning has not been completed in the process of step S102, the process of steps S103 to S105 is skipped.

In the process of step S103, the ECU 8 determines whether or not the difference between the actual measurement value of the NOx sensor 7 and the theoretical measurement value is within a certain range. The theoretical measurement value is a theoretical measurement value of NOx flowing into the reduction catalyst 3 estimated by the ECU 8 using the operating state of the internal combustion engine and a physical quantity related to the amount of addition of the reducing agent as parameters. The physical quantity related to the amount of reducing agent added is a parameter that can derive the proportion of NH ₃ contained in exhaust gas (added NH ₃ concentration). By using this parameter when estimating the theoretical measurements of NOx by ECU 8, it included in the output of the NOx sensor 7 having a sensitivity to NH _3, plus the output of the NOx sensor 7 by addition of NH ₃ by NH ₃ addition system 4 The amount measured can be included in the theoretical measurement.

Here, as the physical quantity related to the addition amount of the reducing agent, for example, the influence of NH _{3 on} the observed value of the NOx sensor 7 such as the concentration of NH ₃ to be added, the addition amount, the pressure, the opening degree of the addition valve 5 and the like is large. Various physical quantity parameters proportional to the height can be applied. Further, the added NH ₃ concentration can be estimated based on, for example, the exhaust gas amount and the NH ₃ addition amount. Further, the amount of exhaust gas can be estimated by, for example, the amount of intake air of an internal combustion engine or various sensors. Further, the certain range is a range of a difference between the actual measurement value and the theoretical measurement value when the NH ₃ addition system 4 is recognized to be operating normally. For example, the accuracy of the NOx sensor 7 and the added NH ₃ A predetermined range appropriately determined according to the accuracy of the concentration, the addition amount, the pressure, the opening degree of the addition valve 5 or the like, or a range specified by the ECU 8 learning various state quantities by itself can be applied.

  If the ECU 8 determines that the difference between the actual measurement value and the theoretical measurement value is within a certain range in the process of step S103, the ECU 8 executes the process of step S104. If the ECU 8 determines that the difference between the actual measurement value and the theoretical measurement value is outside the predetermined range in the process of step S103, the ECU 8 executes the process of step S105.

In the process of step S104, the ECU 8 gives a diagnosis result that the NH ₃ addition system 4 is normal. The ECU 8 may store the diagnosis result in a memory or display it on a display device after giving a diagnosis result that the NH ₃ addition system 4 is normal.

In the process of step S105, the ECU 8 gives a diagnosis result that the NH ₃ addition system 4 is abnormal. The ECU 8 may store the diagnosis result in a memory or display it on a display device after giving a diagnosis result that the NH ₃ addition system 4 is abnormal.

In the process of step S106, the ECU 8 learns an error between the actual measured value of the NOx sensor 7 and the estimated value of NOx. ECU8 by executing the learning of the error in a state in which NH ₃ is not added, to identify the error without the effect of addition of NH _3. For example, the ECU 8 calculates the estimated value of the NOx amount in the exhaust gas estimated from the operating state of the internal combustion engine, and then calculates the difference between the actual measured value of the NOx sensor 7 and the estimated value as the error learning value.

FIG. 3 is an example of a graph showing actual measured values, estimated values, and theoretical measured values of the NOx sensor 7. For example, when the internal combustion engine is started, the exhaust gas containing NOx begins to flow through the exhaust path 2, so that the actual measured value of the NOx sensor 7 gradually increases. The error between the actual measured value and the estimated value of the NOx sensor 7 is due to the accuracy of various sensors provided in the internal combustion engine and the exhaust purification system 1, for example. Therefore, the error between the actual measured value and the estimated value of the NOx sensor 7 observed during the period after the start of the internal combustion engine and before the start of the addition of NH ₃ is substantially constant as shown in the graph of FIG. It is. When the addition of NH ₃ is started, the NOx sensor 7 outputs not only the NOx in the exhaust sent from the internal combustion engine but also a value obtained by adding the added amount of NH ₃ , as shown in the graph of FIG. , the actual measurement value of the NOx sensor 7 which is observed after addition start of NH ₃ becomes larger than before the start of addition of NH _3.

When the actual measured value and the estimated value of the NOx sensor 7 exhibit the above behavior after the internal combustion engine is started, the series of processing flows are executed after the internal combustion engine is started and before the addition of NH ₃ is started. Then, the ECU 8 makes a negative determination in step S101, and executes the error learning process in step S106. Then, the ECU 8 calculates the difference between the actual measured value and the estimated value of the NOx sensor 7 indicated as “error” in the graph of FIG. 3 as the error learned value.

Further, after the error learning process in step S106 is performed and the addition of NH ₃ is started, when the series of process flows is performed, the ECU 8 makes an affirmative determination in steps S101 and S102, The determination process in step S103 is executed. If the NH ₃ addition system 4 is normal, the ECU 8 determines that the difference between the actual measurement value and the theoretical measurement value is within a certain range in the process of step S103, and executes the process of step S104. become. If there is an abnormality in the NH ₃ addition system 4, the ECU 8 determines that the difference between the actual measurement value and the theoretical measurement value is outside a certain range in the process of step S 103, and executes the process of step S 105. become.

Since the exhaust gas purification system 1 according to the above embodiment performs abnormality diagnosis based on the difference between the actual measurement value and the theoretical measurement value, the abnormality diagnosis can be performed without arranging the NOx sensor before and after the NH ₃ addition system 4. Thus, the configuration related to abnormality diagnosis can be simplified. Further, since the exhaust gas purification system 1 according to the above embodiment employs a system configuration in which NH ₃ is added into the exhaust gas instead of urea water, the sensitivity of the NOx sensor 7 to NH _{3 is used} for diagnosis of the NH ₃ addition system 4. Is available. Therefore, in the exhaust purification system 1 according to the above embodiment, the addition of the reducing agent is compared with the diagnosis of the urea water addition means in the exhaust purification system in which urea water is added to the exhaust gas and NOx is reduced and purified by the reduction catalyst. The diagnostic accuracy of the means is improved.

Incidentally, if the learning of the error is completed between the estimated value and actual measured values, for example, by executing the processes of steps S103~S105 in a state of addition of NH ₃ by NH ₃ addition system 4 is not running if, for example, NH ₃ addition system 4 is open the addition valve 5 despite stops addition of NH _3, it is also possible to detect an abnormal condition that the NH ₃ is added erroneously is there.

<Modification 1>
In the process of step S105, the ECU 8 may execute the following process. FIG. 4 is an example of a processing flow diagram obtained by modifying the processing content of step S105. When the ECU 8 determines that the difference between the actual measurement value and the theoretical measurement value is outside a certain range in the process of step S103, the ECU 8 executes the processes of steps S105-1 to S105-3.

In the process of step S105-1, the ECU 8 determines whether or not the elapsed period from when the NH ₃ gas cartridge 6 is loaded in the NH ₃ addition system 4 to the present is within a predetermined period. The elapsed time from when the NH ₃ gas cartridge 6 is loaded to the NH ₃ addition system 4 to the present time is, for example, the elapsed time from the loading of the NH ₃ gas cartridge 6 to the present time, the cumulative NH ₃ injection time, NH ₃ number of injections, NH ₃ injection amount, NH ₃ remaining in the gas cartridge 6, the pressure of the NH ₃ gas cartridge 6 can be determined based on any element related to the remaining amount of the other NH ₃ gas. The predetermined period is a period during which the NH ₃ gas cartridge 6 is recognized as having an initial failure, and is a period defined in advance according to the quality standards of the NH ₃ gas cartridge 6, for example. When the ECU 8 determines that the elapsed time from when the NH ₃ gas cartridge 6 is loaded in the NH ₃ addition system 4 to the present time is within the predetermined period in the process of step S105-1, the process of step S105-2 is executed. To do. If the ECU 8 determines that the elapsed time from when the NH ₃ gas cartridge 6 is loaded into the NH ₃ addition system 4 to the present time is not within the predetermined period in the process of step S105-1, the process of step S105-3 is executed. To do.

In the processing of step S105-2, the ECU 8 gives a diagnosis result that the NH ₃ gas cartridge 6 is abnormal. The ECU 8 may store the diagnosis result in a memory or display it on a display device after giving a diagnosis result that the NH ₃ gas cartridge 6 is abnormal.

In the process of step S105-3, the ECU 8 gives a diagnosis result that the NH ₃ gas cartridge 6 is normal. The ECU 8 gives a diagnosis result that the NH ₃ addition system 4 is abnormal. The ECU 8 may store the diagnosis result in a memory or display it on a display device after giving a diagnosis result that the NH ₃ addition system 4 is abnormal.

If the process of step S105 is modified in this way, it can be determined whether the abnormality of the NH ₃ addition system 4 is due to the initial failure of the NH ₃ gas cartridge 6 or not.

<Modification 2>
FIG. 5 is an example of a diagram showing a modification of the exhaust purification system 1. In the exhaust purification system 1, for example, a plurality of systems of the exhaust path 2 provided with the reduction catalyst 3 can be combined with one NH ₃ gas cartridge 6. For example, as shown in FIG. 5, when two exhaust paths 2 are combined for one NH ₃ gas cartridge 6, the ECU 8 determines that the abnormality of the NH ₃ addition system 4 is due to the abnormality of the NH ₃ gas cartridge 6. Whether it is a thing or not can also be determined as follows.

For example, as shown in FIG. 5, when two exhaust paths 2 are combined with respect to one NH ₃ gas cartridge 6, in the process of step S 105-1, the ECU 8 makes a determination based on the elapsed period. Instead, or in combination with the determination based on the elapsed time, determine whether the difference between the actual measurement value and the theoretical measurement value is outside a certain range is common to all systems, or is limited to a specific system You may make it do. When the ECU 8 determines that the difference between the actual measurement value and the theoretical measurement value is out of a certain range for all the systems, the ECU 8 executes the process of step S105-2. If the ECU 8 determines that the difference between the actual measurement value and the theoretical measurement value is outside a certain range is only a specific system, the ECU 8 executes the process of step S105-3.

As described above, when a plurality of systems of the exhaust path 2 provided with the reduction catalyst 3 are combined with one NH ₃ gas cartridge 6, the ECU 8 determines that the difference between the actual measurement value and the theoretical measurement value is in all the systems. Whether the abnormality of the NH ₃ addition system 4 is due to the abnormality of the NH ₃ gas cartridge 6 can be determined depending on whether it is outside the certain range or only a specific system is outside the certain range.

<Modification 3>
In addition, after performing said step S106, ECU8 may further perform the following processes. FIG. 6 is an example of a diagram in which the processing flow executed by the ECU 8 is modified. The processing flow diagram shown in FIG. 2 further includes processing to be executed after step S106. The ECU 8 learns an error between the actual measured value and the estimated value of the NOx sensor 7 in the process of step S106, and then further executes the processes of steps S106-1 to S106-3.

  In the process of step S106-1, the ECU 8 determines whether or not an error between the actual measured value and the estimated value of the learned NOx sensor 7 is equal to or less than a certain value. The term “constant” as used herein refers to the magnitude of a difference that can appear due to an error in the actual measurement value of the NOx sensor 7 or the estimated value of NOx. It is possible to apply a maximum value of a difference that can be generated due to an error in the estimated value of the NOx amount in the exhaust gas estimated from the state. When the ECU 8 determines that the error between the actual measured value and the estimated value of the NOx sensor 7 learned in the process of step S106-1 is not more than a certain value, the ECU 8 executes the process of step S106-2. If the ECU 8 determines that the error between the actual measured value and the estimated value of the NOx sensor 7 learned in the process of step S106-1 is not below a certain level, the ECU 8 executes the process of step S106-3.

  In the process of step S106-2, the ECU 8 gives a result that the error learning in step S106 is normal, and maintains the difference calculated in the process of step S106.

  In the process of step S106-3, the ECU 8 gives a result that the error learning in step S106 is abnormal, and gives a diagnosis result that the NOx sensor 7 or NOx estimation is abnormal.

After the process in step S106, since if performs step S106-1～S106-3, be used learning result of incorrect error diagnosis of NH ₃ addition system 4 disappears, for example, NH ₃ added Although the system 4 is normal and the NOx sensor 7 or the NOx estimation is abnormal, it is possible to reduce the possibility of giving an erroneous diagnosis result that the NH ₃ addition system 4 is abnormal.

1 exhaust gas purification system 2 exhaust path 3 reduction catalyst 4 NH ₃ addition system 5 addition valve 6 NH ₃ gas cartridge 7 NOx sensor 8 ECU

Claims (5)

A reduction catalyst for reducing NOx in the exhaust of the internal combustion engine with a reducing agent added to the exhaust;
Reducing agent addition means for adding the reducing agent to the exhaust gas flowing into the reduction catalyst;
A NOx sensor having sensitivity to the reducing agent, installed downstream of the reducing agent addition means and upstream of the reduction catalyst;
A theoretical measurement value calculation means for estimating a theoretical measurement value of NOx flowing into the reduction catalyst, using the operating state of the internal combustion engine and a physical quantity related to the amount of addition of the reducing agent as parameters;
Processing means for diagnosing abnormality of the reducing agent addition means based on the difference between the actual measurement value of the NOx sensor and the theoretical measurement value;
An exhaust purification system for an internal combustion engine. The processing means learns an error between the actual measurement value in a state where the addition of the reducing agent is stopped and the estimated value of NOx in the exhaust estimated from the operating state of the internal combustion engine, Performing the abnormality diagnosis based on the difference between the actual measurement value and the theoretical measurement value obtained by adding the learning value of the error;
The exhaust gas purification system for an internal combustion engine according to claim 1. The processing unit diagnoses that the cartridge is abnormal when the reducing agent addition unit diagnoses that the reducing agent addition unit is abnormal within a predetermined period of time after the reducing agent cartridge is loaded in the reducing agent addition unit. ,
The exhaust gas purification system for an internal combustion engine according to claim 1 or 2. The reducing agent adding means adds NH ₃ to the exhaust as the reducing agent.
The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 3. The physical quantity related to the addition amount is NH ₃ addition amount or addition NH ₃ concentration.
The exhaust gas purification system for an internal combustion engine according to claim 4.

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