JP2008157136A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine, determining NOx slip and ammonia slip in an SCR catalyst by simple structure and easy control using a NOx sensor. <P>SOLUTION: When a NOx concentration deviation Ne1 being a difference between an actual NOx concentration Na1 detected by the NOx sensor provided on the exhaust gas downstream side of the SCR catalyst (selective catalytic reduction catalyst) and a previously set appropriate NOx concentration Nr, is larger than a predetermined value α, a urea water adding amount is reduced by a predetermined amount, and it is determined as NOx slip or ammonia slip if a NOx concentration deviation Ne2 after reducing the urea water adding amount is larger or smaller than the NOx concentration deviation Ne1 before reduction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to a technology for determining NOx slip and ammonia slip in a selective reduction type NOx catalyst.

As one means for reducing nitrogen oxide (NOx) contained in exhaust gas of an internal combustion engine (hereinafter also referred to as engine), ammonia (NH) generated by hydrolysis by adding a reducing agent such as urea water to the exhaust gas. ₃ ), a NOx catalyst that selectively reduces NOx to nitrogen (N ₂ ) and water (H ₂ O), a so-called SCR catalyst is known.
The SCR catalyst has a NOx purification performance that varies depending on the amount of urea water added, and the urea water addition amount has an appropriate range in which sufficient NOx purification performance is exhibited depending on the operating state of the engine. For example, when the urea water addition amount is insufficient from the appropriate range, a so-called NOx slip occurs in which NOx cannot be completely purified by the SCR catalyst and NOx is discharged into the atmosphere. On the other hand, when the urea water addition amount is excessive from the appropriate range, so-called ammonia slip occurs in which excess ammonia is discharged into the atmosphere.

Here, a configuration in which NOx slip is mainly detected by providing a NOx sensor on the exhaust downstream side of the SCR catalyst is conceivable.
In general, a NOx sensor has a catalyst component (for example, zirconia) in its detection part. By the action of the catalyst component, first, an O ₂ component in exhaust gas is removed, and the remaining NO component is converted into N ₂ and O ₂ . The NOx concentration is detected by decomposing and measuring the amount of O ₂ . However, in the NOx sensor configured as described above, the ammonia component is oxidized in the detection unit (4NH ₃ + 5O ₂ → 4NO + 6H ₂ O), thereby generating the NO component, and the amount of O ₂ decomposed from the NO component Have the property of measuring. As described above, since the NOx sensor receives the interference of ammonia, it cannot be distinguished whether the NOx slip or the ammonia slip occurs when the urea water addition amount is out of the proper range.

Therefore, NOx sensors are provided on the exhaust upstream side and downstream side of the NOx catalyst, the actual NOx purification rate of the SCR catalyst is calculated based on the sensor outputs of the two NOx sensors, and the NOx purification rate is set in advance for the target NOx purification rate. A technique for controlling the amount of urea water added so as to achieve a rate has been developed (see Patent Document 1). According to Patent Document 1, when the actual NOx purification rate is smaller than the target NOx purification rate, the urea water addition amount is increased and corrected, and the NOx purification rate is not improved despite the increase correction. Is controlled to determine that ammonia slip has occurred.
JP 2003-293743 A

However, in the technique disclosed in Patent Document 1, it is necessary to provide NOx sensors at two locations on the exhaust upstream side and downstream side of the NOx catalyst, which leads to a complicated configuration and an increase in the number of parts and cost. There's a problem.
Moreover, in the said patent document 1, while performing NOx purification rate control of the said NOx catalyst, there exists a problem that determination of ammonia slip is performed and control becomes complicated.

  The present invention has been made to solve such problems, and the object of the present invention is to determine NOx slip and ammonia slip in the SCR catalyst with a simple configuration and easy control using a NOx sensor. An object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can perform the above-described operation.

  In order to achieve the above object, in the exhaust gas purification apparatus for an internal combustion engine according to claim 1, a reducing agent adding means provided in an exhaust passage of the internal combustion engine for adding urea water or ammonia into the exhaust gas as a reducing agent; Provided on the exhaust gas downstream side of the reducing agent adding means in the exhaust passage and selectively reducing NOx in the exhaust gas by the reducing agent added by the reducing agent adding means, and provided on the exhaust downstream side of the NOx catalyst. A NOx sensor that detects NOx in the exhaust gas, detects ammonia as well as the NOx, and outputs a value corresponding to the concentration of the NOx and ammonia, and the NOx catalyst according to the operating state of the internal combustion engine Appropriate NOx concentration setting means for setting an appropriate NOx concentration downstream of the exhaust gas, and reducing agent addition for controlling the amount of reducing agent added by the reducing agent addition means Calculated by the amount control means, the NOx concentration deviation calculating means for calculating the deviation between the appropriate NOx concentration set by the appropriate NOx concentration setting means and the value output by the NOx sensor, and the NOx concentration deviation calculating means. When the deviation becomes larger than a predetermined value, the reducing agent addition amount control means decreases the reducing agent addition amount, and the deviation calculated by the NOx concentration deviation detecting means after the reducing agent addition amount decreases is the reducing agent addition amount. Slip determination means is provided for determining NOx slip when the deviation before the addition amount is decreased, and for determining ammonia slip when the deviation is less than the deviation before the reducing agent addition amount is decreased. It is a feature.

  In the exhaust gas purification apparatus for an internal combustion engine according to claim 2, a reducing agent adding means provided in the exhaust passage of the internal combustion engine for adding urea water or ammonia into the exhaust gas as a reducing agent, and the reducing agent adding means in the exhaust passage. A NOx catalyst that is provided on the exhaust downstream side and selectively reduces NOx in the exhaust gas by the reducing agent added by the reducing agent addition means, and is provided on the exhaust downstream side of the NOx catalyst to detect NOx in the exhaust gas. At the same time, ammonia is detected in the same manner as the NOx, and a NOx sensor that outputs a value corresponding to the concentration of the NOx and ammonia, and an appropriate NOx concentration on the downstream side of the exhaust of the NOx catalyst according to the operating state of the internal combustion engine. An appropriate NOx concentration setting means for setting, a reducing agent addition amount control means for controlling the addition amount of the reducing agent added by the reducing agent addition means, and the appropriate NOx The NOx concentration deviation calculating means for calculating the deviation between the appropriate NOx concentration set by the degree setting means and the value output by the NOx sensor, and the deviation calculated by the NOx concentration deviation calculating means is larger than a predetermined value. When the reducing agent addition amount control means increases the reducing agent addition amount, the deviation calculated by the NOx concentration deviation detecting means after the reducing agent addition amount increase is greater than the deviation before the reducing agent addition amount increase. When it decreases, it is judged as NOx slip, and when the deviation calculated by the NOx concentration deviation detecting means after increasing the reducing agent addition amount is larger than the deviation before increasing the reducing agent addition amount, ammonia slip Is provided with a slip determination means.

According to a third aspect of the present invention, the reducing agent addition amount control means increases the reducing agent addition amount when the NOx slip is determined by the slip determination means. It is characterized by controlling as follows.
The exhaust gas purification apparatus for an internal combustion engine according to claim 4, wherein, in any one of claims 1 to 3, when the reducing agent addition amount control means determines that ammonia slip has occurred by the slip determination means, the reducing agent addition amount. It is characterized by controlling so as to decrease.

  In the exhaust gas purifying apparatus for an internal combustion engine according to claim 5, when the reducing agent addition amount control means is determined as NOx slip or ammonia slip by the slip determination means in claim 1 or 2, the proper NOx concentration setting is performed. The reducing agent addition amount is feedback-controlled so that the deviation between the appropriate NOx concentration set by the means and the value output by the NOx sensor decreases.

  In the exhaust gas purification apparatus for an internal combustion engine according to claim 1 of the present invention using the above-described means, ammonia is detected together with NOx on the exhaust downstream side of the NOx catalyst that selectively reduces NOx by the reducing agent added from the reducing agent addition means. In the configuration provided with the NOx sensor, when the deviation between the proper NOx concentration and the output value of the NOx sensor becomes larger than a predetermined value, the reducing agent addition amount is decreased, and the deviation increases due to the reduction of the reducing agent addition amount. If it is determined, it is determined that the reducing agent addition amount is insufficient (NOx slip). On the other hand, when the deviation decreases due to the decrease in the reducing agent addition amount, it is determined that the reducing agent addition amount is excessive (ammonia slip).

  Thus, the exhaust gas purification apparatus for an internal combustion engine according to claim 1 has a simple configuration in which only one NOx sensor is provided on the exhaust downstream side of the NOx catalyst, and the appropriate NOx concentration and the output value of the NOx sensor are NOx slip and ammonia slip can be determined by easy control of reducing the reducing agent addition amount when the deviation becomes larger than a predetermined value and seeing the change in deviation due to the reduction of the reducing agent addition amount.

In addition, since ammonia has an irritating odor, emission to the atmosphere should be avoided as much as possible. According to claim 1, slip determination is performed by reducing the amount of reducing agent added. The slip determination can be performed while suppressing the discharge of ammonia.
According to the exhaust gas purification apparatus for an internal combustion engine of claim 2, the NOx sensor for detecting ammonia as well as NOx is provided on the exhaust downstream side of the NOx catalyst that selectively reduces NOx by the reducing agent added from the reducing agent adding means. In the above configuration, when the deviation between the appropriate NOx concentration and the output value of the NOx sensor exceeds a predetermined value, the reducing agent addition amount is increased, and when the deviation decreases due to the increase in the reducing agent addition amount, the reduction is performed. It is determined that the additive amount is insufficient (NOx slip). On the other hand, if the deviation increases due to an increase in the reducing agent addition amount, it is determined that the reducing agent addition amount is excessive (ammonia slip).

  Thus, the exhaust gas purification apparatus for an internal combustion engine according to claim 2 has a simple configuration in which only one NOx sensor is provided on the exhaust downstream side of the NOx catalyst, and the deviation between the proper NOx concentration and the output value of the NOx sensor. NOx slip and ammonia slip can be determined by easy control of increasing the amount of reducing agent added when the value becomes larger than a predetermined value and seeing a change in deviation due to the increase in the amount of reducing agent added.

According to the exhaust gas purification apparatus for an internal combustion engine according to the third aspect, when the NOx slip is determined, the NOx slip can be easily eliminated.
According to the exhaust gas purification apparatus for an internal combustion engine according to the fourth aspect, when the ammonia slip is determined, the ammonia slip can be easily eliminated.
According to the exhaust gas purification apparatus for an internal combustion engine of claim 5, it is possible to reliably eliminate NOx slip and ammonia slip.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Referring to FIG. 1, there is shown a schematic configuration diagram of an engine provided with an exhaust purification device according to the present invention. Hereinafter, a description will be given based on FIG.
The engine 1 (internal combustion engine) is a diesel engine equipped with a common rail type fuel injection device, and supplies high pressure fuel accumulated in the common rail 2 to the fuel injection valve 5 of each cylinder 4 to inject fuel at an arbitrary injection timing and injection amount. The valve 5 is configured to be able to inject into the cylinder of each cylinder 4.

An intake manifold 6 is connected to the intake side of the engine 1, and an intake pipe 8 extends from the intake manifold 6. An air cleaner 10 is provided at the intake upstream end of the intake pipe 8, a compressor 12a of the turbocharger 12 is provided in the middle of the intake pipe 8, and an intercooler 14 is provided downstream of the compressor 12a. It has been.
On the other hand, an exhaust manifold 16 is connected to the exhaust side of the engine 1, and an exhaust pipe 18 extends from the exhaust manifold 16. An EGR passage 20 is connected to the exhaust manifold 16 and the intake manifold 6, and an EGR cooler 22 that cools the EGR gas and an EGR valve 24 that adjusts the recirculation amount of the EGR gas are provided in the EGR passage 20.

A turbine 12b that is coaxially connected to the compressor 12a is provided in the middle of the exhaust pipe 18.
Further, an SCR catalyst 30 (NOx catalyst) is provided on the exhaust downstream side of the exhaust pipe 18.
The SCR catalyst 30 is configured by, for example, supporting a catalytic metal such as vanadium oxide (V ₂ O ₅ ) on a ceramic catalyst carrier having a honeycomb structure, and the NOx in the exhaust gas is converted into nitrogen by ammonia (NH ₃ ). It is a NOx catalyst that selectively reduces to (N ₂ ) and water (H ₂ O).

An addition nozzle 32 (reducing agent addition means) capable of injecting urea water to the exhaust downstream side in the exhaust pipe 18 is provided on the exhaust upstream side of the SCR catalyst 30. The urea water sprayed from the addition nozzle 32 generates ammonia by hydrolysis.
The addition nozzle 32 is connected to a urea water supply device 34 (reducing agent addition means) mounted on the vehicle, and urea water is supplied to the urea water supply device 34 from a urea water tank 36 in which urea water is stored. Is done.

Further, a NOx sensor 38 capable of detecting the NOx concentration in the exhaust gas that has passed through the SCR catalyst 30 is provided on the exhaust gas downstream side of the SCR catalyst 30.
The NOx sensor 38 has a catalyst component (for example, zirconia) in the detection unit, and by the action of the catalyst component, first, the O ₂ component in the exhaust gas is removed, and the remaining NO component is converted into N ₂ and O ₂ . The NOx concentration is detected by decomposing and measuring the amount of O ₂ .

On the other hand, with this configuration, in the NOx sensor 38, when ammonia is present, the ammonia component is oxidized in the detection unit as described above to generate a NO component (4NH ₃ + 5O ₂ → 4NO + 6H ₂ O). The sensor 38 has a property of measuring the amount of O ₂ decomposed from the NO component. That is, the NOx sensor 38 has a characteristic of detecting ammonia in the exhaust gas similarly to NOx.

Therefore, the output value of the NOx sensor 38 increases as the concentration of NOx and ammonia in the exhaust gas passing through the NOx sensor 38 increases.
Further, the vehicle is provided with an ECU (Electronic Control Unit) 40, and the ECU 40 has a function of performing various controls based on information from various sensors. The ECU 40 controls the operation of the engine 1 and, for example, sets the urea water addition amount and controls the urea water supply device 34 to add urea water from the addition nozzle 32 at a predetermined time (reducing agent addition). Quantity control means). Further, NOx slip and ammonia slip are determined from the output value of the NOx sensor 38 (slip determination means).

Hereinafter, the slip determination control and the urea water addition amount control in the exhaust gas purification apparatus for an internal combustion engine according to the present invention configured as described above will be described in detail.
Referring to FIG. 2, there is shown a flowchart of a slip determination control and urea water addition amount control routine executed by the ECU 40 of the exhaust gas purification apparatus for an internal combustion engine according to the present invention. Referring to FIG. A relationship map between the urea water addition amount and the NOx sensor output value is shown. Hereinafter, description will be made along the flowchart of FIG. 2 with reference to FIG.

First, in step S1, the output value of the NOx sensor 38 is acquired as the actual NOx concentration Na1.
In step S2, a NOx concentration deviation Ne1 that is a deviation between the actual NOx concentration Na1 acquired in step S1 and a preset appropriate NOx concentration Nr is calculated (NOx concentration deviation calculating means). The appropriate NOx concentration Nr is determined from a relationship map between the urea water addition amount and the output value of the NOx sensor 38 as shown in FIG. 3 created for each engine speed, fuel injection amount, or NOx catalyst temperature. The Specifically, as shown in FIG. 3, the output value of the NOx sensor 38 when the urea water addition amount is in the appropriate range, that is, the bottom value of the NOx sensor output in the map is set as the appropriate NOx concentration Nr (appropriate NOx concentration setting means). ).

  In step S3, it is determined whether or not the NOx concentration deviation Ne1, that is, the deviation between the actual NOx concentration Na1 and the appropriate NOx concentration Nr is larger than a predetermined value α set in advance. When the determination result is false (No), that is, when the actual NOx concentration Na1 is lower than the appropriate NOx concentration Nr, or when the difference between the actual NOx concentration Na1 and the appropriate NOx concentration Nr is relatively small below a predetermined value α. In this case, it is determined that the urea water addition amount is within an appropriate range, and the routine returns.

On the other hand, when the NOx concentration deviation Ne1 is larger than the predetermined value α, that is, when the urea water addition amount is outside the appropriate range, it is determined that NOx slip or ammonia slip has occurred, and the above determination result is true (Yes). Then, the process proceeds to the next step S4.
In step S4, the urea water supply device 34 is controlled so as to decrease the urea water addition amount by a predetermined amount. The predetermined amount may be, for example, about 10% of the urea water addition amount at this time, or the NOx sensor output value may be reduced to a predetermined range.

Subsequently, in step S5, the output value of the NOx sensor 38 after decreasing the urea water addition amount is acquired as the actual NOx concentration Na2, and in the next step S6, the deviation between the actual NOx concentration Na2 and the appropriate NOx concentration Nr. The NOx concentration deviation Ne2 is calculated.
In step S7, the difference between the NOx concentration deviation Ne1 before the urea water addition amount calculated in step S2 and the NOx concentration deviation Ne2 after the urea water addition amount calculated in step S6 is calculated as the NOx concentration change amount Nd. To do.

In step S8, it is determined whether or not the NOx concentration deviation change amount Nd is greater than 0, that is, the urea water addition amount is decreased, so that the NOx concentration deviation Ne2 becomes the NOx concentration deviation Ne1 before the urea water addition amount decreases. It is determined whether or not the number has increased.
If the determination result is true (Yes), that is, if the NOx concentration deviation Ne2 is increased by decreasing the urea water addition amount, the process proceeds to step S9.

In step S9, for example, as shown in part A of FIG. 3, the fact that the NOx concentration deviation Ne2 has increased by decreasing the urea water addition amount means that the urea water addition amount is insufficient and the purification performance of the SCR catalyst 30 decreases. This means that the amount of NOx emissions has increased, and it is determined that NOx slip has occurred.
In the subsequent step S10, the urea water addition amount is controlled to increase in order to eliminate the NOx slip, and the routine returns.

On the other hand, if the determination result in step S8 is false (No), that is, if the NOx concentration deviation Ne2 is decreased by decreasing the urea water addition amount, the process proceeds to step S11.
In step S11, for example, as shown in part B of FIG. 3, the fact that the NOx concentration deviation Ne2 has decreased by decreasing the urea water addition amount has decreased the ammonia that has been exhausted to the exhaust downstream side. Therefore, it is determined that ammonia slip has occurred.

In the subsequent step S12, the urea water addition amount is controlled to be reduced so as to reduce the excess ammonia in order to eliminate the ammonia slip, and the routine is returned.
As described above, in the configuration in which the NOx sensor 38 is provided on the exhaust downstream side of the SCR catalyst 30, the slip determination control is performed by setting the output value of the NOx sensor 38, that is, the actual NOx concentration Na1 and the appropriate NOx concentration set in advance. When the NOx concentration deviation Ne1, which is a deviation from Nr, becomes larger than the predetermined value α, the urea water addition amount is decreased, and when the NOx concentration deviation Ne2 increases due to the decrease in the urea water addition amount, the urea water It is determined that the addition amount is insufficient, that is, NOx slip. On the other hand, when the NOx concentration deviation Ne2 decreases due to the decrease in the urea water addition amount, it is determined that the urea water addition amount is excessive, that is, ammonia slip.

  Therefore, the exhaust gas purification apparatus for an internal combustion engine according to the present invention has a simple configuration in which only one NOx sensor 38 is provided on the exhaust downstream side of the SCR catalyst 30, and the output value of the NOx sensor 38 and the appropriate NOx concentration Nr. NOx slip and ammonia slip are judged by easy control of reducing the urea water addition amount when the deviation from the above becomes greater than a predetermined value α and seeing the change in the NOx concentration deviation due to the decrease in the urea water addition amount. It can be carried out.

Then, when the NOx slip is determined by the determination, the urea water addition amount is increased, and when the ammonia slip is determined, the NOx slip and the ammonia slip are reduced by easy control to decrease the urea water addition amount. It can be eliminated.
Moreover, since slip determination is performed by reducing the addition amount of urea water, the slip determination can be performed while suppressing discharge of ammonia having an irritating odor.

Although the description of the embodiment of the exhaust gas purification apparatus for an internal combustion engine according to the present invention is finished above, the embodiment is not limited to the above embodiment.
For example, in the above embodiment, the engine 1 is a diesel engine, but the engine is not limited to this, and may be, for example, a gasoline engine.
In the above embodiment, when the NOx concentration deviation Ne1 is larger than the predetermined value α, the slip determination is performed by decreasing the urine water addition amount by a predetermined amount. For example, the NOx concentration deviation Ne1 is larger than the predetermined value α. When the NOx concentration deviation after the increase in the urea water addition amount is decreased and the NOx concentration deviation after the urea water addition amount is increased, it is determined as NOx slip, and when the NOx concentration deviation is increased, it is determined as ammonia slip. The slip determination control may be performed.

Moreover, in the said embodiment, although it is the structure provided with only the SCR catalyst 30 as an exhaust gas purification apparatus, it is good also as a structure which provided other catalysts, such as an oxidation catalyst, a particulate filter, etc. in the exhaust path, for example.
In the above embodiment, control is performed to increase the urea water addition amount when it is determined as NOx slip, and to decrease the urea water addition amount when it is determined as ammonia slip. The urine water addition amount may be controlled by feedback control in a direction in which the deviation decreases. Thus, NOx slip and ammonia slip can be reliably eliminated by feedback control of the urea water addition amount.

  Further, in the above embodiment, NOx is selectively reduced by the SCR catalyst 30 by adding and hydrolyzing urea water from the addition nozzle 32, but, for example, a configuration in which ammonia is directly added from the addition nozzle may be employed.

1 is a schematic configuration diagram of an engine provided with an exhaust purification device according to the present invention. 3 is a flowchart showing a slip determination control and urea water addition amount control routine executed by the ECU of the exhaust gas purification apparatus for an internal combustion engine according to the present invention. It is a relationship map of the urea water addition amount at the time of a predetermined driving | running state, and a NOx sensor output value.

Explanation of symbols

1 engine (internal combustion engine)
18 Exhaust pipe (exhaust passage)
30 SCR catalyst (NOx catalyst)
32 Addition nozzle (reducing agent addition means)
34 Urea water supply device 36 Urea water tank 38 NOx sensor 40 ECU (reducing agent addition amount setting means, slip determination means)

Claims (5)

A reducing agent adding means provided in the exhaust passage of the internal combustion engine and adding urea water or ammonia as a reducing agent into the exhaust gas;
A NOx catalyst provided on the exhaust gas downstream side of the reducing agent adding means in the exhaust passage and selectively reducing NOx in exhaust gas by the reducing agent added by the reducing agent adding means;
A NOx sensor that is provided on the exhaust downstream side of the NOx catalyst, detects NOx in the exhaust gas, detects ammonia as well as the NOx, and outputs a value corresponding to the concentration of the NOx and ammonia;
An appropriate NOx concentration setting means for setting an appropriate NOx concentration on the exhaust downstream side of the NOx catalyst according to the operating state of the internal combustion engine;
Reducing agent addition amount control means for controlling the addition amount of the reducing agent added by the reducing agent addition means;
NOx concentration deviation calculating means for calculating a deviation between the appropriate NOx concentration set by the appropriate NOx concentration setting means and the value output by the NOx sensor;
When the deviation calculated by the NOx concentration deviation calculating means becomes larger than a predetermined value, the reducing agent addition amount control means decreases the reducing agent addition amount, and after the reducing agent addition amount decreases, the NOx concentration deviation detecting means. Is determined to be NOx slip when it is greater than the deviation before the reducing agent addition amount is decreased, and ammonia slip is determined when the deviation is less than the deviation before the reducing agent addition amount is decreased. An exhaust emission control device for an internal combustion engine, comprising slip determination means for determining. A reducing agent adding means provided in the exhaust passage of the internal combustion engine and adding urea water or ammonia as a reducing agent into the exhaust gas;
A NOx catalyst provided on the exhaust gas downstream side of the reducing agent adding means in the exhaust passage and selectively reducing NOx in exhaust gas by the reducing agent added by the reducing agent adding means;
A NOx sensor that is provided on the exhaust downstream side of the NOx catalyst, detects NOx in the exhaust gas, detects ammonia as well as the NOx, and outputs a value corresponding to the concentration of the NOx and ammonia;
An appropriate NOx concentration setting means for setting an appropriate NOx concentration on the exhaust downstream side of the NOx catalyst according to the operating state of the internal combustion engine;
Reducing agent addition amount control means for controlling the addition amount of the reducing agent added by the reducing agent addition means;
NOx concentration deviation calculating means for calculating a deviation between an appropriate NOx concentration set by the appropriate NOx concentration setting means and a value output by the NOx sensor;
When the deviation calculated by the NOx concentration deviation calculating means becomes larger than a predetermined value, the reducing agent addition amount control means increases the reducing agent addition amount, and after the reducing agent addition amount increases, the NOx concentration deviation detecting means. Is determined to be NOx slip when the deviation before the reducing agent addition amount is increased, the deviation calculated by the NOx concentration deviation detecting means after the reducing agent addition amount is increased, An exhaust gas purifying apparatus for an internal combustion engine, comprising slip determining means for determining that the slip is an ammonia slip when the deviation before the reducing agent addition amount increases.   The exhaust gas of an internal combustion engine according to claim 1 or 2, wherein the reducing agent addition amount control means controls to increase the reducing agent addition amount when the slip determination means determines NOx slip. Purification equipment.   4. The internal combustion engine according to claim 1, wherein the reducing agent addition amount control means controls to reduce the reducing agent addition amount when the slip determination means determines that the ammonia slip has occurred. Exhaust purification equipment.   The reducing agent addition amount control means is a deviation between the proper NOx concentration set by the proper NOx concentration setting means and the value output by the NOx sensor when the slip judgment means judges NOx slip or ammonia slip. The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the amount of addition of the reducing agent is feedback controlled in a direction in which the amount of reducing agent decreases.

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