JP2009036055A - Control device of exhaust gas treatment device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of an exhaust gas treatment device capable of suppressing consumption of a reducer, effectively reducing a specific component in exhaust gas, and purifying the exhaust gas even while having simple and inexpensive structure. <P>SOLUTION: Unlike the prior art of injecting and adding urea water addition amount suitable for a NOx discharge amount discharged from an internal combustion engine 1 upon starting urea water addition, urea water is injected and added by increasing its amount from a state of urea water adding amount =0 by a first prescribed amount at every predetermined time (S1-S3), a detection signal of an ammonia sensor 8 is observed, when NH<SB>3</SB>flows out to an exhaust gas downstream side of a urea SCR catalyst 5, the urea water addition amount is decreased at every predetermined time (S1, S2, S4, S5), and when NH<SB>3</SB>stops flowing out to the exhaust gas downstream side of the urea SCR catalyst 5, the urea water addition amount at that time is maintained (S5, S6). Therefore, compared to the prior art, NOx in exhaust gas can be reduced and exhaust gas can be purified while suppressing the consumption amount of urea water. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for an exhaust treatment device that processes a gas (exhaust gas) discharged from an internal combustion engine and containing various exhaust substances.

  Purifying the exhaust from the combustion device to suppress the spread of environmental pollution is an important issue. For example, in the case of a diesel combustion engine, PM (particulate matter: particulate matter = mainly black smoke) in the exhaust (Soot), to suppress the emission of unburned fuel called SOF, components of lubricating oil, components generated from sulfur in diesel fuel called sulfate, and other solid substances) to the atmosphere In addition, for example, a diesel particulate filter (CSF) or a CSF (catalyzed soot filter) is installed in the exhaust passage, and the exhaust gas is passed through the diesel particulate filter or CSF so that the PM in the exhaust gas is passed. While collecting, diesel particulate filter and CSF It has been made to be reproduced by the people of the way.

  Further, for example, in Patent Document 1, in order to realize simultaneous reduction of NOx and PM contained in exhaust gas, a diesel particulate filter and CSF are interposed in the exhaust passage, and at the downstream side, NOx reduction is performed. It has been proposed to interpose an effective urea SCR (Selective Catalytic Reduction). Urea SCR is a selective reduction-type NOx catalyst that has the property of selectively reacting NOx with a reducing agent even in the presence of oxygen. And NOx in the exhaust gas is reduced and purified on the selective reduction type NOx catalyst using the generated ammonia as a reducing agent.

More specifically, in the conventional exhaust treatment apparatus as described in Patent Document 1, for example, as shown in FIG. 6, the exhaust gas temperature on the most upstream side of the exhaust passage 2 of the internal combustion engine 1 such as a diesel combustion engine is used. The diesel particulate filter 3 with an oxidation catalyst is interposed at a relatively high position from the viewpoint of regeneration efficiency and the like, and the urea water addition device 4 and the urea SCR catalyst 5 are disposed downstream thereof, and from the urea SCR catalyst 5 An ammonia oxidation catalyst 6 for oxidizing excess ammonia (NH ₃ ) leaking was interposed.

  Further, in Patent Document 2 and Patent Document 3, as shown in FIG. 7, the amount of urea water supplied from the urea water adding device 4 to the urea SCR catalyst 5 is set to ammonia provided on the exhaust downstream side of the urea SCR catalyst 5. An apparatus is described in which feedback control is performed based on the detection result of the sensor (or NOx sensor) 8.

here,
When urea water is heated, CO (NH ₂ ) ₂ + H ₂ O → 2NH ₃ + CO ₂ is obtained, and NH ₃ (ammonia) is obtained.
NH ₃ and NOx react in the urea SCR catalyst 5,
NO + NH ₃ → N ₂ + H ₂ O + H
NO ₂ + NH ₃ → N ₂ + H ₂ O + OH
→ 2N ₂ + 3H ₂ O
By this reaction, NOx is reduced.

Therefore, it is necessary to add urea water so that the same number of N as N of NOx can be supplied. If the amount of urea water added is excessive, NH ₃ is discharged from the urea SCR catalyst 5 while the amount of addition is insufficient. If there is, NOx is discharged from the urea SCR catalyst 5.

Further, even if N from the urea water adheres to a certain point on the catalyst of the urea SCR catalyst 5, NOx does not always arrive at the certain point, so that N from the urea water can meet NOx with a high probability. In order to achieve this, the urea water is dispersed throughout the exhaust gas, and the urea water addition amount (supply) is supplied from the urea water adding device 4 so that the ratio of N between NOx and urea water (that is, NH ₃ ) is 1 or more. In order to increase the probability of encountering NOx, a large amount is set.

For this reason, conventionally, for example, as shown in step 200 (S200) of the flowchart of FIG. 8, the amount of NOx discharged from the internal combustion engine 1 is calculated from the operating state (rotational speed, load, etc.) of the internal combustion engine. Alternatively, it is obtained based on the detection signal of the NOx sensor 7 provided in the exhaust passage 2, while the NOx emission amount can be reliably reduced, that is, the ratio of N of urea water (NH ₃ ) to N of NOx. Is increased and supplied to the exhaust gas from the urea water adding device 4 (for example, the urea water amount obtained by multiplying the NOx emission amount by the correction coefficient α (a value of 1 or more)). It was like that.

Furthermore, conventionally, using a control method as described in Patent Documents 2 and 3, for example, as shown in the flowchart of FIG. 8, changes in the operating state of the internal combustion engine 1, individual differences, Based on the detection result of the NOx sensor (or ammonia sensor) 8 provided on the exhaust downstream side of the urea SCR catalyst 5 in order to follow the disturbance or the like and use the urea water for the NOx reduction action without excess or deficiency, the urea water addition device 4 The feedback control is performed to correct the increase / decrease in the amount of urea water supplied from the control unit.
JP 2007-2697 A Japanese Patent Laid-Open No. 2001-234736 JP 05-33948 A

  Here, the cost of the urea water is high, and there is a desire to reduce the capacity of the urea water tank that stores the urea water and to lengthen its replenishment cycle, and it is desired to reduce the consumption of urea water.

  In addition, conventionally, knowledge about the characteristic peculiar to the selective reduction type NOx catalyst in which a reducing agent is added and supplied to exhaust gas is insufficient. For this reason, it is the same as the conventional exhaust control in an oxidation catalyst or a three-way catalyst. By a method based on the concept, for example, as shown in the flowchart of FIG. 8, the NOx emission amount discharged from the internal combustion engine 1 is calculated from the operating state of the internal combustion engine or the like or from the NOx sensor 7 provided in the exhaust passage 2, Based on this, the amount of urea water as a reducing agent to be added and supplied from the urea water addition device 4 is obtained and added to the exhaust gas (see S200), and the ammonia sensor 8 provided downstream of the urea SCR catalyst 5 in the exhaust gas. Based on the detection signal, the amount of urea water supplied from the urea water adding device 4 is corrected to increase or decrease (see S300 to 700). Was not a control method was sufficiently considered unique properties as described above for reduction type NOx catalyst.

  The present invention has been made in view of such circumstances, and effectively reduces and purifies a specific component (for example, NOx) in exhaust gas while suppressing consumption of a reducing agent while having a simple and inexpensive configuration. An object of the present invention is to provide a control device for an exhaust treatment device having a selective reduction catalyst capable of performing

For this reason, the control device of the exhaust treatment device according to the present invention is:
A control device for an exhaust treatment device that selectively reduces a specific component in the exhaust by a selective reduction catalyst by adding a reducing agent to the exhaust discharged from the internal combustion engine via a reducing agent adding means,
A reducing agent component detecting means disposed on the exhaust downstream side of the selective catalytic reduction catalyst for detecting a predetermined component caused by the reducing agent;
From the start of the addition of the reducing agent to the exhaust gas via the reducing agent adding means, the amount of reducing agent added from the reducing agent adding means until the predetermined component is detected by the reducing agent component detecting means. A gradually increasing reducing agent addition amount control means;
The reducing agent addition amount is gradually reduced when the predetermined component is detected by the reducing agent component detection means while the reducing agent addition amount is gradually increased by the reducing agent addition amount gradually increasing control means. Control means;
A reducing agent that maintains a predetermined amount of reducing agent when the predetermined component is no longer detected by the reducing agent component detecting means while the reducing agent addition amount is gradually decreasing by the reducing agent addition amount gradually decreasing control means. Addition amount maintaining means,
It is characterized by including.

  Here, the present invention is a selective reduction type NOx catalyst in which the selective reduction catalyst selectively reduces NOx, and the added reducing agent is a reducing agent capable of supplying ammonia to the selective reduction type NOx catalyst. It can be characterized by being.

Further, the present invention can be characterized in that the predetermined component resulting from the reducing agent is ammonia.
In the present invention, when the purification catalyst for purifying the predetermined component is disposed on the exhaust downstream side of the selective reduction catalyst, the reducing agent component detection means is disposed on the exhaust upstream side of the purification catalyst. It can be characterized by that.

  According to the present invention, there is provided a selective catalytic reduction catalyst capable of effectively reducing and purifying a specific component (for example, NOx) in exhaust gas while suppressing consumption of a reducing agent while having a simple and inexpensive configuration. It is an object of the present invention to provide a control device for an exhaust treatment device.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the accompanying drawings. The present invention is not limited to the embodiments described below.

A schematic overall configuration of an exhaust treatment apparatus having a selective reduction catalyst according to an embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 1, an exhaust treatment apparatus according to an embodiment of the present invention has a regeneration efficiency or the like at a relatively high exhaust temperature position on the most upstream side of an exhaust passage 2 of an internal combustion engine 1 such as a diesel combustion engine. In view of the above, a diesel particulate filter 3 with an oxidation catalyst is interposed, a urea water addition device 4 and a urea SCR catalyst 5 which is a selective reduction catalyst are interposed downstream thereof, and leakage from the urea SCR catalyst 5 occurs. An ammonia oxidation catalyst 6 for oxidizing the surplus ammonia (NH ₃ ) is interposed. The ammonia oxidation catalyst 6 constitutes an example of a purification catalyst according to the present invention.

  The urea water adding device 4 corresponds to a reducing agent adding means according to the present invention, and is used as a reducing agent for exhaust gas based on a control signal from an engine control unit (ECU: engine control unit) (not shown). A urea water injection nozzle 4A that supplies and adds (adds) urea water while metering it in a predetermined amount, a urea water tank 4B that stores urea water, and urea water stored in the urea water tank 4B with respect to exhaust gas A supply pump 4C that supplies and supplies the urea water injection nozzle 4A with a predetermined pressure.

  Further, in the present embodiment, an ammonia sensor 8 including a sensor element that selectively detects a predetermined component (here, ammonia) is provided on the exhaust downstream side of the urea SCR catalyst 5. The ammonia sensor 8 corresponds to the reducing agent component detecting means according to the present invention.

Such a sensor element is preferably, for example, a sensor element that can selectively detect ammonia even in the presence of NOx, or a sensor element that is hardly affected by NOx. The ammonia sensor 8 provided with such a sensor element includes a reference electrode on one surface of a solid electrolyte body having a known oxygen ion conductivity such as a zirconia-based sintered body and a LaGaO ₃ -based sintered body, and two or more layers on the other surface. Further, it can be obtained by using an element provided with a heater element for heating and holding the solid electrolyte body so that the internal resistance value of the solid electrolyte body becomes constant or as a separate body.

  The detection signal of the ammonia sensor 8 is sent to the engine control unit and used for supply control (addition control) of a reducing agent to be described later.

  Here, the denitration characteristic (NOx reduction characteristic) in the urea SCR catalyst 5 will be described with reference to FIG.

When urea water is used as the reducing agent, latent heat of vaporization is necessary to evaporate the water of the urea water. In addition, the reaction for generating NH ₃ from urea water is an endothermic reaction and also requires latent heat of evaporation for evaporating the generated H ₂ O.
Therefore, the reaction for producing NH ₃ from the urea water tends to have a slow reaction rate.

  For this reason, as shown in FIG. 2, even when the addition of urea water is started in a state where NOx is supplied to the urea SCR catalyst 5 (catalyst bed temperature 230 ° C. or higher), the urea is delayed with a predetermined period of time. Ammonia is produced from water, and the ammonia produced with a delay of this predetermined period is used for the NOx reduction reaction. Therefore, until a predetermined degree of NOx reduction is obtained, a considerable period (for example, 10 seconds).

As described above, the denitration characteristic of the urea SCR catalyst 5 has a characteristic that the reaction delay is relatively large, and the engine control unit allows the operation state (rotation speed, load (intake air flow rate) of the internal combustion engine 1 as in the past. , Etc.) or the detection signal of the NOx sensor 7, the amount of NOx discharged from the internal combustion engine 1 is obtained, and the amount of urea water necessary to reduce the obtained NOx emission amount Even if (ie, the amount of NH ₃ ) is added to the exhaust gas, NH ₃ may be discharged from the urea SCR catalyst 5 without contributing to the reduction of NOx. Particularly in a transient operation state, the amount of NOx emission increases as the load increases. Even if the amount of urea water is increased to match this, NH ₃ is discharged from the urea SCR catalyst 5 without contributing to the reduction of NOx. There is a fear.

Therefore, if NH ₃ discharged without contributing to such reduction of NOx can be reduced, the consumption of urea water can be reduced.

  In the present embodiment, focusing on this point, supply (addition) control of the reducing agent (urea water) as shown in FIG. 3 is executed. As will be described below, the supply (addition) of the reducing agent (urea water) is controlled by the reducing agent addition amount gradual increase control means, the reducing agent addition amount gradual decrease control means, and the reducing agent addition amount maintenance means according to the present invention. Will function as.

As shown in the flowchart of FIG.
In S (step in the figure, the same applies hereinafter) 1, it is determined whether or not a condition for adding and supplying urea water to the exhaust gas is satisfied by the urea water adding device 4. Whether or not the condition is satisfied can be determined based on, for example, the operating state of the internal combustion engine 1 (NOx emission state), the exhaust temperature, the catalyst bed temperature of the urea SCR catalyst 5, and the like.
If YES, from the urea water injection nozzle 4A constituting the urea water addition device 4, the first predetermined amount (addition amount less than the urea water addition amount commensurate with the NOx discharge amount discharged from the internal combustion engine 1 (supply amount) )), The injection of urea water into the exhaust gas is executed (started), and the process proceeds to S2. If NO, this flow ends and the next routine is prepared for execution.

In S2, based on the detection signal (sensor output B) of the ammonia sensor 8, it is determined whether NH ₃ has flowed out to the exhaust downstream side of the urea SCR catalyst 5 (whether B> 0).
If NO, the process proceeds to S3, the amount of urea water added is increased by the first predetermined amount, and the process returns to S1. That is, in this embodiment, instead of injecting and adding the urea water amount commensurate with the NOx emission amount discharged from the internal combustion engine 1 as in the prior art, by repeating S1 to S3 until YES is determined in S2, The urea water is injected and added from the state where the urea water addition amount = 0 in increments of the first predetermined amount every predetermined time (see FIGS. 2 and 4).

That is, after the start of the urea water injection addition, if NO in S2, the reaction for generating NH ₃ from the urea water has not started, or even if it has started, all of the generated NH ₃ is reduced to NOx. S1 to S3 are repeated until YES is determined in S2 so that the amount of urea water added is increased by a predetermined amount.

On the other hand, if YES is determined in S2, it is determined that the reaction for generating NH ₃ from the urea water is started and surplus NH ₃ has started to flow out to the exhaust downstream side of the urea SCR catalyst 5, and the process proceeds to S4. .

In S4, since it is determined that surplus NH ₃ has started to flow out downstream of the urea SCR catalyst 5, the amount of urea water added from the urea water injection nozzle 4A to the exhaust gas is reduced by a predetermined amount.

In S5, based on the detection signal B of the ammonia sensor 8, it is determined whether NH ₃ no longer flows out to the exhaust downstream side of the urea SCR catalyst 5 (whether B = 0).
In the case of YES, NH ₃ does not flow out to the exhaust downstream side of the urea SCR catalyst 5, and the urea water addition amount (that is, NH ₃ amount) necessary for reducing the NOx emission amount from the internal combustion engine 1 is exhausted. It is determined that the injection has been added, the current addition amount is maintained, the urea water injection is continued, the present flow is terminated, and the next routine is prepared.
In the case of NO, the process returns to S1 and repeats steps S2 to S5, and the amount of urea water added is reduced by a predetermined amount every time S4 is passed (that is, a second time every predetermined time) until YES is determined in S5. The urea water is injected and added while the amount is decreased by a predetermined amount (see FIG. 4 and the like).

As described above, according to the present embodiment, when the urea water addition is started, the urea water addition amount corresponding to the NOx emission amount discharged from the internal combustion engine 1 is not injected and added as in the prior art. The urea water addition amount is injected and added in increments of a first predetermined amount (a smaller amount than the urea water addition amount commensurate with the NOx emission amount discharged from the internal combustion engine 1) every predetermined time from the state of urea water addition = 0. At the same time, the detection signal of the ammonia sensor 8 is observed, and when NH ₃ flows out to the exhaust gas downstream side of the urea SCR catalyst 5, the urea water addition amount is reduced every predetermined time, and the urea SCR catalyst 5 is exhausted downstream of the exhaust gas. When NH ₃ stops flowing out, the urea water addition amount at that time is maintained, so that the exhaust amount of urea water is suppressed as compared with the conventional method (see the hatched portions in FIGS. 2 and 4). NOx inside is reduced and exhausted It will be able to process of.

  Note that, using the output B of the ammonia sensor 8 detected in S2, the output B is compared with the system failure determination reference value F in S7 (for example, whether BF> 0), and the output B Is larger than the system failure determination reference value F, it is determined that there is some abnormality in the system (urea water adding device 4, urea SCR catalyst 5, etc.), and the system failure is determined in S8. Can be stored, and the supply control (addition control) of urea water can be stopped, or a driver can be notified that a system failure has occurred.

  Here, in the present embodiment, as illustrated in FIG. 1, the configuration has been described in which the ammonia sensor 8 is interposed between the urea SCR catalyst 5 and the ammonia oxidation catalyst 6. As described above, the ammonia sensor 8 may be arranged on the exhaust downstream side of the ammonia oxidation catalyst 6.

  However, as shown in FIG. 1, when the ammonia sensor 8 is disposed between the urea SCR catalyst 5 and the ammonia oxidation catalyst 6, the urea SCR catalyst is compared with the configuration example shown in FIG. Since ammonia flowing out from the tank 5 can be detected directly with good responsiveness and high accuracy, the urea water addition control can be executed with high responsiveness and high accuracy. It can be effectively suppressed.

  Further, as shown in FIG. 1, when the ammonia sensor 8 is disposed between the urea SCR catalyst 5 and the ammonia oxidation catalyst 6, urea water is added compared to the configuration example shown in FIG. Since the (supply) control can be executed with high responsiveness and high accuracy, the amount of excess ammonia flowing out from the urea SCR catalyst 5 can be suppressed to a small level, so that the capacity of the ammonia oxidation catalyst 6 can be reduced or omitted. It becomes possible to do.

Here, in the present embodiment, the internal combustion engine 1 is based on the operating state (rotational speed, load (intake air flow rate, fuel injection amount, etc.)) of the internal combustion engine 1 or the like, or based on the detection signal of the NOx sensor 7. NOx sensor 7 can be omitted because the NOx emission amount from 1 is obtained and the urea water addition amount (that is, NH ₃ amount) necessary to reduce the obtained NOx emission amount is not added to the exhaust gas. However, it is also possible to provide the NOx sensor 7 and variably set the first predetermined amount and the second predetermined amount according to the output of the NOx sensor 7.

  For example, when the output of the NOx sensor 7 is large and the NOx emission amount is large, the first predetermined amount or the second predetermined amount is set to a relatively large value, and the output of the NOx sensor 7 is small and the NOx emission amount is small. When the amount is small, the first predetermined amount or the second predetermined amount is set to a relatively small value so that the occurrence of overshoot or the like is suppressed, and urea can be responsive to a sudden change in the NOx emission amount. Water addition control can be followed.

Note that the first predetermined amount and the second predetermined amount to be added every predetermined time can be made variable according to a predetermined pattern at each addition without depending on the output of the NOx sensor 7.
Further, the addition of urea water is not limited to the case of linearly increasing or decreasing the amount of time (elapsed time). For example, as shown in FIG. ) Can be increased or decreased in a curved manner.

  Further, the present invention is not limited to the case where the reducing agent (urea water) is constantly increased in S3 of FIG. 3 (by repeating S1 to S3), and is shown as an example in FIG. 4B. As described above, during the period from the start of the addition of the reducing agent to the exhaust through the reducing agent addition means until the predetermined component is detected by the reducing agent component detection means, the addition amount of the reducing agent may be gradually increased. It is. That is, as illustrated in FIG. 4B as an example, even if the amount is not increased or decreased in a certain part of the period, the reducing agent may be gradually increased as the entire period.

  Similarly, the present invention is not limited to the case where the reducing agent (urea water) is constantly reduced in S4 of FIG. 3 (by repeating S1, S2, S4, and S5), and the reducing agent addition amount is gradually increased. During the period from when the predetermined component is detected by the reducing agent component detecting means during the gradual increase of the reducing agent by the control means, until the predetermined component is no longer detected by the reducing agent component detecting means, the reducing agent addition amount is gradually increased. It is a good thing to do. That is, even if the amount is not decreased or increased in a certain part of the period, the reducing agent may be gradually decreased as the entire period.

By the way, in this Embodiment, although the case where urea water was used as a reducing agent of the urea SCR catalyst 5 which is an example of a selective reduction type NOx catalyst was demonstrated as an example, this invention is not limited to this, urea Other than water, for example, deoxyme (denoxium “trade name”, manufactured by Kerima, Finland, reference URL http: containing formic acid and ammonia water as components and having a low freezing point and improved freezing so as not to freeze even at −30 ° C. //www.kemira.com/NR/rdonlyres/D96C8072-48F9-46E5-A6AF-F1A995ECD4A6/0/Denoxium_brochure.pdf#search='denoxium ') can also be used as the reducing agent of the present invention.
In the present embodiment, the internal combustion engine 1 can be, for example, a diesel engine that performs diesel combustion, but is not limited thereto, and may be an internal combustion engine that uses gasoline or other substances as fuel. Furthermore, it can be a mobile / stationary internal combustion engine.

  The embodiment described above is merely an example for explaining the present invention, and various modifications can be made without departing from the gist of the present invention.

1 is a diagram schematically showing an overall configuration example of an exhaust treatment apparatus according to an embodiment of the present invention. It is a figure for demonstrating the denitration characteristic of a selective reduction type NOx catalyst (urea SCR catalyst). It is a flowchart for demonstrating the reducing agent addition control performed in embodiment same as the above. It is a timing chart for demonstrating the aspect of the reducing agent addition performed in embodiment same as the above. It is a figure which shows roughly another example of the exhaust-gas treatment apparatus which concerns on embodiment same as the above. It is a schematic whole block diagram which shows an example of the conventional exhaust-air-treatment apparatus. It is a schematic whole block diagram which shows another example of the conventional exhaust processing apparatus. It is a flowchart which shows an example of the control method of the conventional exhaust processing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Exhaust passage 4 Urea water addition apparatus (equivalent to reducing agent addition means)
4A Urea water injection nozzle 4B Urea water tank 4C Supply pump 5 Urea SCR catalyst (equivalent to selective reduction catalyst)
6 Ammonia oxidation catalyst (equivalent to purification catalyst)
7 NOx sensor 8 Ammonia sensor (equivalent to reducing agent component detection means)

Claims (4)

A control device for an exhaust treatment device that selectively reduces a specific component in the exhaust by a selective reduction catalyst by adding a reducing agent to the exhaust discharged from the internal combustion engine via a reducing agent adding means,
A reducing agent component detecting means disposed on the exhaust downstream side of the selective catalytic reduction catalyst for detecting a predetermined component caused by the reducing agent;
From the start of the addition of the reducing agent to the exhaust gas via the reducing agent adding means, the amount of reducing agent added from the reducing agent adding means until the predetermined component is detected by the reducing agent component detecting means. A gradually increasing reducing agent addition amount control means;
The reducing agent addition amount is gradually reduced when the predetermined component is detected by the reducing agent component detection means while the reducing agent addition amount is gradually increased by the reducing agent addition amount gradually increasing control means. Control means;
A reducing agent that maintains a predetermined amount of reducing agent when the predetermined component is no longer detected by the reducing agent component detecting means while the reducing agent addition amount is gradually decreasing by the reducing agent addition amount gradually decreasing control means. Addition amount maintaining means,
A control device for an exhaust treatment device, comprising:   The selective reduction type catalyst is a selective reduction type NOx catalyst that selectively reduces NOx, and the added reducing agent is a reducing agent that can supply ammonia to the selective reduction type NOx catalyst. Item 2. A control device for an exhaust treatment device according to Item 1.   The exhaust gas treatment device control device according to claim 1 or 2, wherein the predetermined component resulting from the reducing agent is ammonia. When the purification catalyst for purifying the predetermined component is disposed on the exhaust downstream side of the selective reduction catalyst, the reducing agent component detection means is disposed on the exhaust upstream side of the purification catalyst. The control device of the exhaust treatment device according to any one of claims 1 to 3.