JP7288738B2 - Exhaust treatment system controller and exhaust treatment system - Google Patents

Description

The present invention relates to a control device for an exhaust treatment system having a NOx reduction catalyst, and an exhaust treatment system.

Conventionally, as an exhaust treatment system for an internal combustion engine, a NOx reduction catalyst (SCR catalyst) is arranged in an exhaust passage of the internal combustion engine, and an exhaust passage is arranged upstream of the NOx reduction catalyst. There is known an exhaust treatment system having a urea water supply valve that supplies urea water to the urea water supply valve and a control device that controls the urea water supply valve (see Patent Documents 1 and 2, for example). In such an exhaust treatment system, the urea water supplied from the urea water supply valve into the exhaust gas is hydrolyzed by the heat of the exhaust gas to produce ammonia (NH ₃ ). This ammonia reduces NOx in the exhaust under the catalytic action of the NOx reduction catalyst. In this manner, purification of NOx in the exhaust gas is achieved. Further, in the case of such an exhaust treatment system, a NOx sensor is generally arranged in the exhaust passage on the downstream side of the NOx reduction catalyst (for example, see Patent Documents 1 and 2).

Further, in recent years, ammonia storage control is generally performed in which ammonia is stored in the NOx reduction catalyst up to a predetermined target storage amount (see, for example, Patent Document 2).

JP 2010-77812 A Japanese Unexamined Patent Application Publication No. 2012-2063

The higher the temperature of the NOx reduction catalyst, the lower the amount of ammonia (storage capacity) that the NOx reduction catalyst can store. Therefore, when the temperature of the exhaust gas rises sharply, such as when the vehicle is suddenly accelerated or when PM regeneration processing for removing PM accumulated on the filter is executed, the temperature of the NOx reduction catalyst rises accordingly. As a result, the storage capacity of the NOx reduction catalyst may drop sharply and the stored ammonia may be released. In such a case, if urea water is normally supplied from the urea water supply valve, the amount of ammonia flowing downstream from the NOx reduction catalyst (that is, ammonia slip amount) may become excessive. .

The present invention has been made in view of the above, and an object thereof is to provide a control device for an exhaust treatment system and an exhaust treatment system capable of suppressing an excessive ammonia slip amount when the temperature of a NOx reduction catalyst rises sharply. It is to provide a system.

In order to achieve the above object, the control device for an exhaust treatment system according to the present invention includes a NOx reduction catalyst disposed in an exhaust passage of an internal combustion engine, and a NOx reduction catalyst disposed upstream of the NOx reduction catalyst in the exhaust passage. A control device applied to an exhaust treatment system having a urea water supply valve and a NOx sensor arranged in the exhaust passage downstream of the NOx reduction catalyst, the control device being applied to an exhaust treatment system upstream of the NOx reduction catalyst. An upstream NOx concentration acquisition unit that acquires an upstream NOx concentration, which is the NOx concentration in the exhaust, and a downstream NOx concentration acquisition unit that acquires a downstream NOx concentration, which is a detection value of the NOx sensor and is the sum of the NOx concentration and the ammonia concentration in the exhaust. and the downstream NOx concentration acquired by the downstream NOx concentration acquiring unit and the downstream NOx concentration acquired by the upstream NOx concentration acquiring unit after the rate of increase in the temperature of the NOx reduction catalyst has become greater than a preset reference value. stop the supply of the urea water from the urea water supply valve, or the amount of urea water supplied from the urea water supply valve when the difference from the upstream NOx concentration becomes larger than a preset threshold value and a control unit that starts executing a control process that reduces the threshold, wherein the threshold value is set to a value that starts execution of the control process after a time equal to or longer than the ammonia slip start response delay time has passed. do.

Further, in order to achieve the above object, an exhaust treatment system according to the present invention includes a NOx reduction catalyst arranged in an exhaust passage of an internal combustion engine, and urea water arranged in the exhaust passage on the upstream side of the NOx reduction catalyst. It is characterized by comprising a supply valve, a NOx sensor arranged in the exhaust passage on the downstream side of the NOx reduction catalyst, and the control device described above.

In general, the NOx sensor has the property of detecting not only the NOx concentration in the exhaust gas but also the ammonia concentration in the exhaust gas due to its concentration detection principle. Therefore, the downstream NOx concentration, which is the value detected by the NOx sensor, is the concentration (NOx concentration+ammonia concentration) containing not only pure NOx but also ammonia. Therefore, the downstream NOx concentration, which is the value detected by the NOx sensor, tends to increase as the amount of ammonia slip increases, and as a result, the difference between the downstream NOx concentration and the upstream NOx concentration tends to increase. Therefore, when the difference between the downstream NOx concentration and the upstream NOx concentration becomes larger than a preset threshold value, it can be determined that the ammonia slip amount has increased.

Then, according to the present invention, when the rate of increase in the temperature of the NOx reduction catalyst becomes larger than a preset reference value, the difference between the downstream NOx concentration and the upstream NOx concentration becomes larger than the preset threshold value. When the temperature of the NOx reduction catalyst suddenly rises and the amount of ammonia slip increases, the supply of urea water from the urea water supply valve is stopped, or the amount of urea water supplied from the urea water supply valve Since the execution of the control process for decreasing the NOx reduction catalyst is started, it is possible to suppress the ammonia slip amount from becoming excessively large when the temperature of the NOx reduction catalyst suddenly rises.

1 is a configuration diagram schematically showing the configuration of a portion of a vehicle according to an embodiment; FIG. It is an example of the flowchart for demonstrating ammonia slip suppression control processing.

(embodiment)
Hereinafter, an exhaust treatment system 10 according to an embodiment of the present invention and a control device 20 applied to this exhaust treatment system 10 will be described with reference to the drawings. FIG. 1 is a configuration diagram schematically showing a configuration of part of a vehicle 1 according to this embodiment. Although the type of the vehicle 1 is not particularly limited, in this embodiment, a large commercial vehicle such as a truck or a bus is used as an example of the vehicle 1 .

A vehicle 1 includes an internal combustion engine 2 , an exhaust passage 4 and an exhaust treatment system 10 . In this embodiment, as an example of the internal combustion engine 2, a diesel engine that uses light oil as fuel is used. The exhaust passage 4 is a passage through which the exhaust gas discharged from the cylinders 3 of the internal combustion engine 2 passes.

The exhaust treatment system 10 includes an oxidation catalyst 11 , a filter 12 , a urea water supply valve 13 , a NOx reduction catalyst 14 , an ammonia slip catalyst 15 , various sensors, and a control device 20 . Note that FIG. 1 illustrates an upstream NOx sensor 16, a downstream NOx sensor 17, and a temperature sensor 18 as sensors. The oxidation catalyst 11, the filter 12, the NOx reduction catalyst 14, and the ammonia slip catalyst 15 are arranged in the exhaust passage 4 in this order when viewed in the exhaust flow direction. The urea water supply valve 13 is arranged in the exhaust passage 4 upstream of the NOx reduction catalyst 14 and downstream of the filter 12 .

The filter 12 has a function of collecting PM (particulate matter) in the exhaust. The oxidation catalyst 11 has a structure in which a noble metal catalyst such as platinum (Pt) or palladium (Pd) is supported on a carrier through which exhaust gas can pass. The oxidation catalyst 11 accelerates an oxidation reaction that converts nitrogen monoxide (NO) in the exhaust gas into nitrogen dioxide (NO ₂ ) by the oxidation catalytic action of the noble metal catalyst. When the exhaust gas temperature reaches or exceeds the activation temperature of the oxidation catalyst 11, the nitrogen dioxide generated in the oxidation catalyst 11 burns the PM trapped in the filter 12 and discharges it as carbon dioxide (CO ₂ ). can be done.

The urea water supply valve 13 is connected to a urea water supply device (not shown) through a pipe (not shown), and is a valve body that supplies the urea water supplied from the urea water supply device to the exhaust gas. be. The NOx reduction catalyst 14 is a catalyst (that is, an SCR catalyst (selective reduction catalyst)) that selectively reduces NOx in exhaust gas using ammonia generated by hydrolysis of urea water. The specific type of the NOx reduction catalyst 14 is not particularly limited, and a known NOx reduction catalyst such as vanadium (V), molybdenum (Mo), tungsten (W), zeolite, etc. is used. be able to.

The urea water supply valve 13 receives an instruction from the control device 20 and supplies the urea water into the exhaust upstream of the NOx reduction catalyst 14 after the NOx reduction catalyst 14 reaches the activation temperature or higher. Urea in the urea water supplied into the exhaust is hydrolyzed by the heat of the exhaust, and as a result, ammonia (NH ₃ ) is produced. This ammonia reduces NOx under the catalytic action of the NOx reduction catalyst 14 . As a result, nitrogen and water are produced. In this way, purification (reduction) of NOx in the exhaust gas is achieved.

The ammonia slip catalyst 15 is an oxidation catalyst that oxidizes ammonia that has passed through the NOx reduction catalyst 14 . By including the ammonia slip catalyst 15 in the exhaust treatment system 10 as in the present embodiment, it is possible to effectively suppress the release of ammonia into the atmosphere. However, the ammonia slip catalyst 15 is not an essential component for this embodiment. Therefore, the exhaust treatment system 10 does not have to include the ammonia slip catalyst 15 .

The upstream NOx sensor 16 detects the NOx concentration in the exhaust upstream of the NOx reduction catalyst 14 (hereinafter referred to as “upstream NOx concentration”) and notifies the controller 20 of the detected value. As an example, the upstream NOx sensor 16 according to the present embodiment detects the NOx concentration in the exhaust upstream of the NOx reduction catalyst 14 and further upstream of the urea water supply valve 13 .

The downstream NOx sensor 17 is a NOx sensor arranged in the exhaust passage 4 on the downstream side of the NOx reduction catalyst 14 . The concentration as a value detected by the downstream NOx sensor 17 is called "downstream NOx concentration". Note that the downstream NOx sensor 17 according to the present embodiment is arranged further downstream than the ammonia slip catalyst 15, so the downstream NOx concentration according to the present embodiment is the same as that in the exhaust gas downstream of the ammonia slip catalyst 15. is the concentration value of Downstream NOx sensor 17 conveys the detected value to control device 20 .

Note that the downstream NOx sensor 17 is a NOx sensor (that is, an existing NOx sensor) arranged in a portion of the exhaust passage on the downstream side of the NOx reduction catalyst in a general exhaust treatment system. It is used.

A temperature sensor 18 detects the temperature of the NOx reduction catalyst 14 and notifies the controller 20 of the detected value.

The control device 20 includes a microcomputer, and the microcomputer includes a CPU 21 that executes various control processes, and a storage unit 22 that stores various information, programs, and the like used for the operation of the CPU 21. there is Note that, for example, a ROM, a RAM, or the like can be used as the storage unit 22 . The control device 20 controls the fuel injection timing, fuel injection amount, etc. of the internal combustion engine 2 . Further, the control device 20 controls the operation of the exhaust treatment system 10 by controlling the urea water supply timing of the urea water supply valve 13, the urea water supply amount, and the like. That is, in the present embodiment, the control device 20 that integrally controls the operation of the internal combustion engine 2 also functions as a control device that controls the urea water supply valve 13 . However, the configuration of the control system of the vehicle 1 is not limited to this. may be

Next, details of control of the urea water supply valve 13 by the control device 20 will be described. After the internal combustion engine 2 is started, the control device 20 performs a control process for supplying urea water to the urea water supply valve 13 when the NOx reduction catalyst 14 reaches the activation temperature or higher (hereinafter referred to as "normal control process"). ) is started.

In this normal time control process, the control device 20 executes a storage control process for causing the NOx reduction catalyst 14 to store ammonia up to a predetermined target storage amount (target storage amount) set in advance. Then, the control device 20 calculates the amount of ammonia that can reduce the amount of NOx discharged from the internal combustion engine 2, taking into account the amount of ammonia occluded in the NOx reduction catalyst 14. Calculate the amount of urea water that can generate The control device 20 controls the urea water supply valve 13 so that the calculated urea water amount is periodically supplied during exhaustion. It should be noted that this normal time control process is generally performed in a vehicle equipped with an exhaust treatment system, and is within the category of known technology, so further detailed description will be omitted.

On the other hand, when the rate of increase in the temperature of the NOx reduction catalyst 14 exceeds a preset reference value (that is, when the temperature of the NOx reduction catalyst 14 rises sharply), the controller 20 controls the downstream NOx concentration and the upstream NOx concentration becomes larger than a preset threshold value, the control process ( Execution of the "ammonia slip suppression control process" hereinafter) is started. This ammonia slip suppression control process will be described below using a flowchart.

FIG. 2 is an example of a flowchart for explaining the ammonia slip suppression control process. It is assumed that the normal time control process has already been executed at the time of the first start in FIG. Each step in FIG. 2 is executed by the CPU 21 of the control device 20 .

In step S10, the control device 20 determines whether or not the temperature increase rate of the NOx reduction catalyst 14 (hereinafter referred to as "catalyst temperature increase rate") has exceeded a preset reference value. The details of this step S10 are as follows.

First, as the reference value in step S10, for example, when the rate of catalyst temperature rise exceeds this reference value (that is, when the temperature of the NOx reduction catalyst 14 rapidly rises), the storage capacity of the NOx reduction catalyst 14 suddenly increases. It is possible to use a value that is considered to decrease and cause the NOx reduction catalyst 14 to release a larger amount of ammonia than the predetermined value. An appropriate value for this reference value is obtained in advance by performing experiments, numerical simulations, or the like, and is stored in the storage unit 22 (that is, set in advance).

In the present embodiment, at least when the vehicle 1 is suddenly accelerated (when the accelerator pedal is suddenly depressed), or when PM regeneration processing (forcibly increasing the exhaust gas temperature upstream of the filter 12) The reference value in step S10 is set in advance so that a YES determination is made in step S10 when the control process for removing PM deposited on the filter 12 in step S10 is executed. That is, in the case of the present embodiment, YES is determined in step S10 at least when the vehicle 1 is rapidly accelerated or when the PM regeneration process is executed.

Also, the control device 20 according to the present embodiment acquires the rate of increase in catalyst temperature in step S10 based on the detection result of the temperature sensor 18 . Then, the control device 20 executes step S10 by determining whether or not the catalyst temperature increase rate acquired in this manner is greater than the reference value of the storage section 22 .

However, the specific execution method of step S10 is not limited to the above method. For example, when acquiring the catalyst temperature increase rate in step S10, the control device 20 determines the catalyst temperature A rate of climb may be estimated.

When determined as YES in step S10, the control device 20 determines whether or not the difference between the downstream NOx concentration and the upstream NOx concentration is greater than a preset threshold (step S20). Specifically, the controller 20 acquires the NOx concentration detected by the downstream NOx sensor 17 as the "downstream NOx concentration" in step S20. Further, the control device 20 acquires the NOx concentration detected by the upstream NOx sensor 16 as the "upstream NOx concentration" in step S20. Then, the control device 20 calculates the difference between the downstream NOx concentration and the upstream NOx concentration thus obtained, and determines whether or not the value of this difference is greater than the threshold value stored in the storage unit 22. Thus, step S20 is executed.

Here, in general, the NOx sensor has the property of detecting not only the NOx concentration in the exhaust gas but also the ammonia concentration in the exhaust gas due to its concentration detection principle. Therefore, the "downstream NOx concentration", which is the value detected by the downstream NOx sensor 17, is a concentration (NOx concentration+ammonia concentration) containing not only pure NOx but also ammonia. Therefore, as the amount of ammonia slip increases, the downstream NOx concentration detected by the downstream NOx sensor 17 tends to increase, and as a result, the difference between the downstream NOx concentration and the upstream NOx concentration tends to increase. Therefore, when the difference between the downstream NOx concentration and the upstream NOx concentration becomes larger than the threshold value, it can be determined that the ammonia slip amount has increased.

It should be noted that the threshold in step S20 corresponds to "the value of the difference between the downstream NOx concentration and the upstream NOx concentration" for determining whether or not to execute step S30, which will be described later. Although the specific value of this threshold is not particularly limited as long as it is a value greater than zero, it is preferable to set it based on, for example, the following points of view.

First, the smaller the threshold in step S20 is, the more likely it is that step S20 will be determined to be YES, and as a result, step S30, which will be described later, tends to be executed more easily (that is, step S30 tends to be executed more frequently). . Therefore, by appropriately setting the threshold value of step S20, the execution frequency of step S30 can be adjusted. Therefore, it is preferable to set the threshold so that the execution frequency of step S30 becomes an appropriate value.

In addition, the smaller the threshold in step S20, the shorter the elapsed time from the determination of YES in step S10 to the execution of step S30. That is, it is also possible to adjust the elapsed time from when YES is determined in step S10 to when step S30 is executed, depending on the magnitude of the threshold in step S20. Therefore, it is preferable to set the threshold value so that the elapsed time from the determination of YES in step S10 to the execution of step S30 has an appropriate value.

Specifically, the release of ammonia (ammonia slip) from the NOx reduction catalyst 14 tends to start with a slight delay after the temperature of the NOx reduction catalyst 14 rises sharply. That is, the ammonia slip from the NOx reduction catalyst 14 is started after a predetermined time (this is referred to as "ammonia slip start response delay time") has passed after the determination of YES in step S10. Therefore, the magnitude of the threshold in step S20 is set so that a YES determination is made in step S20 and step S30 is executed after a period of time equal to or longer than the ammonia slip start response delay time has elapsed since the determination was YES in step S10. preferably.

As a specific numerical example of the threshold value of step S20, for example, if a value within the range of 50 ppm to 150 ppm is used, the execution frequency of step S30 is appropriate, and step S30 is executed after it is determined YES in step S10. It is thought that the elapsed time until the ammonia slip start response delay time can be made longer. Therefore, in the present embodiment, a value (specifically, 100 ppm) selected from this numerical range is used as an example of the threshold in step S20. However, this numerical value is merely an example, and is not limited to this.

If it is determined YES in step S20, the control device 20 starts executing the ammonia slip suppression control process (step S30). Specifically, the control device 20 stops the supply of the urea water from the urea water supply valve 13, or changes the supply amount (mm ³ /s) of the urea water from the urea water supply valve 13 to YES in step S20. The amount of urea water supplied at the time of determination (this is the amount of urea water supplied during normal control processing) is decreased.

As a specific example of step S30, the control device 20 according to the present embodiment stops the supply of urea water.

The ammonia slip suppression control process in step S30 is continuously executed until NO is determined in step S20. That is, the ammonia slip suppression control process according to the present embodiment is continuously executed until the difference between the downstream NOx concentration and the upstream NOx concentration becomes equal to or greater than the threshold.

If NO is determined in step S10, or if NO is determined in step S20, the control device 20 executes normal control processing (step S40). Specifically, when the normal-time control process has already been executed before step S40 is executed, the control device 20 continues executing the normal-time control process in step S40. When the control process is not being executed (when the ammonia slip suppression control process is being executed), the execution of the ammonia slip suppression control process is ended in step S40, and the execution of the normal time control process is started. After step S40, the control device 20 executes the flowchart again from the start (return).

In step S20, the CPU 21 of the control device 20 that acquires the upstream NOx concentration and the CPU 21 of the control device 20 that acquires the downstream NOx concentration act as an "upstream NOx concentration acquisition unit" and a "downstream NOx concentration acquisition unit", respectively. is an example of a member having the function of The CPU 21 of the control device 20 that executes step S30 stops the supply of urea water from the urea water supply valve 13 or reduces the amount of urea water supplied from the urea water supply valve 13 (ammonia slip suppression). It is an example of a member having a function as a “control unit” that starts execution of control processing).

According to the present embodiment as described above, when the rate of increase in the temperature of the NOx reduction catalyst 14 exceeds the preset reference value, the difference between the downstream NOx concentration and the upstream NOx concentration is set in advance. When the threshold value is exceeded, that is, when the temperature of the NOx reduction catalyst 14 rapidly rises and the amount of ammonia slip increases, the urea water supply from the urea water supply valve 13 is stopped or the urea water supply is stopped. The amount of urea water supplied from the valve 13 can be reduced. As a result, it is possible to prevent the ammonia slip amount from becoming excessively large when the temperature of the NOx reduction catalyst 14 suddenly rises.

Further, according to the present embodiment, the detection value of the downstream NOx sensor 17 (that is, the existing NOx sensor) on the downstream side of the NOx reduction catalyst 14 is used to execute the ammonia slip suppression control process. It is not necessary to separately arrange an ammonia sensor downstream of the NOx reduction catalyst 14 in order to detect the increase in the amount. In this respect, an increase in cost is suppressed. That is, according to the present embodiment, it is possible to prevent the ammonia slip amount from becoming excessively large when the temperature of the NOx reduction catalyst 14 suddenly rises, while suppressing an increase in cost as much as possible.

(Modification 1 of Embodiment)
Next, Modification 1 of the above embodiment will be described. In acquiring the upstream NOx concentration in step S20, the control device 20 according to this modification estimates the upstream NOx concentration based on the operating state of the internal combustion engine 2 instead of acquiring the detection value of the upstream NOx sensor 16 .

Specifically, in this modified example, the rotational speed and load of the internal combustion engine 2 are used as an example of parameters indicating the operating state of the internal combustion engine 2 . The control device 20 estimates the upstream NOx concentration based on the rotational speed and load of the internal combustion engine 2, and obtains the estimated upstream NOx concentration as the "upstream NOx concentration" in step S20.

More specifically, in the storage unit 22 of the control device 20 according to the present modification, a storage unit for calculating the upstream NOx concentration based on the rotation speed (rpm) and the load (fuel injection amount as an example) of the internal combustion engine 2 is stored. A map is pre-stored. The control device 20 acquires the rotational speed and load of the internal combustion engine 2 in step S20, and calculates the upstream NOx concentration using the acquired rotational speed and load of the internal combustion engine 2 and the map of the storage unit 22 (that is, estimated), and this calculated upstream NOx concentration is obtained as the upstream NOx concentration in step S20.

Note that the control device 20 may use the NOx concentration calculated from the map as the upstream NOx concentration in step S20, which is further corrected based on the cooling water temperature. Further, when the operating state of the internal combustion engine 2 is in a transitional state, the control device 20 may acquire, as the upstream NOx concentration related to step S20, the upstream NOx concentration estimated by the above-described method and further corrected. .

Also in this modified example, it is possible to obtain the same effects as those of the above-described embodiment. In addition, according to this modified example, the manufacturing cost of the exhaust treatment system 10 can be reduced compared to the above-described embodiment in that the upstream NOx sensor 16 is not required.

(Modification 2 of Embodiment)
Next, Modification 2 of the above embodiment will be described. The exhaust treatment system 10 according to this modification is characterized in that the upstream NOx sensor 16 is arranged in a portion of the exhaust passage 4 upstream of the NOx reduction catalyst 14 and downstream of the urea water supply valve 13. , differs from the previous embodiment. Also in this modified example, it is possible to obtain the same effects as those of the above-described embodiment.

However, when the upstream NOx sensor 16 is arranged downstream of the urea water supply valve 13 as in this modification, the upstream NOx sensor 16 detects not only the NOx concentration in the exhaust gas but also the urea water supply valve The concentration of ammonia generated by hydrolysis of the urea water supplied from 13 into the exhaust is also detected as the upstream NOx concentration. Therefore, in step S20, the control device 20 of this modification estimates the concentration of ammonia produced by hydrolysis of the urea water supplied from the urea water supply valve 13, and subtracts this ammonia concentration from the detected value of the upstream NOx sensor 16. It is preferable to correct and obtain this corrected value as the "upstream NOx concentration". As a result, the NOx concentration on the upstream side of the NOx reduction catalyst 14 can be obtained with high accuracy.

In estimating the concentration of ammonia generated by hydrolysis of the urea water supplied from the urea water supply valve 13, the control device 20 uses preset map data (for example, the amount of urea water supplied and the exhaust gas temperature to determine the ammonia concentration This ammonia concentration can be estimated using map data for estimating .

Alternatively, instead of correcting the detection value of the upstream NOx sensor 16 as described above, the "threshold" in step S20 may be changed. Specifically, the detected value of the upstream NOx sensor 16 arranged on the downstream side of the urea water supply valve 13 is higher than the detected value of the upstream NOx sensor 16 arranged on the upstream side of the urea water supply valve 13. The value tends to be large because it includes the concentration of ammonia generated by hydrolysis of urea water. Therefore, when the upstream NOx sensor 16 is arranged on the downstream side of the urea water supply valve 13, compared to the case where the upstream NOx sensor 16 is arranged on the upstream side of the urea water supply valve 13, A smaller value is preferably used as the "threshold" in step S20. It should be noted that this threshold should be set to an appropriate value that can cancel the influence of the ammonia concentration through experiments, numerical simulations, or the like.

Further, since the upstream NOx concentration estimated by the "method for estimating the upstream NOx concentration" according to Modification 1 described above is the NOx concentration that does not include the ammonia concentration (that is, the pure NOx concentration), the urea water supply valve The detected value of the upstream NOx sensor 16 (which includes the concentration of ammonia) located downstream of the NOx sensor 13 tends to be larger than the estimated value of the upstream NOx concentration according to the first modification. Therefore, when the upstream NOx sensor 16 is arranged downstream of the urea water supply valve 13, the "threshold" in step S20 is set to , it is preferable to use a smaller value.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. is possible.

1 vehicle 2 internal combustion engine 4 exhaust passage 10 exhaust treatment system 11 oxidation catalyst 12 filter 13 urea water supply valve 14 NOx reduction catalyst 15 ammonia slip catalyst 16 upstream NOx sensor 17 downstream NOx sensor 18 temperature sensor 20 control device 21 CPU (upstream NOx concentration acquisition unit, downstream NOx concentration acquisition unit, control unit)

Claims (2)

A NOx reduction catalyst arranged in an exhaust passage of an internal combustion engine, a urea water supply valve arranged in the exhaust passage upstream of the NOx reduction catalyst, and arranged in the exhaust passage downstream of the NOx reduction catalyst. A control device applied to an exhaust treatment system having a NOx sensor,
an upstream NOx concentration acquiring unit that acquires an upstream NOx concentration, which is the NOx concentration in the exhaust upstream of the NOx reduction catalyst;
a downstream NOx concentration acquisition unit that acquires a downstream NOx concentration that is a detected value of the NOx sensor and that is the sum of the NOx concentration and the ammonia concentration in exhaust gas;
After the rate of increase in the temperature of the NOx reduction catalyst becomes greater than a preset reference value, the downstream NOx concentration acquired by the downstream NOx concentration acquiring unit and the upstream NOx concentration acquired by the upstream NOx concentration acquiring unit When the difference from the NOx concentration becomes greater than a preset threshold value, the urea water supply from the urea water supply valve is stopped, or the urea water supply amount from the urea water supply valve is reduced. A control unit that starts executing the control process ,
A control device for an exhaust gas treatment system, wherein the threshold value is set to a value at which execution of the control process is started after a time equal to or longer than an ammonia slip start response delay time has elapsed. a NOx reduction catalyst disposed in an exhaust passage of an internal combustion engine;
a urea water supply valve arranged in the exhaust passage on the upstream side of the NOx reduction catalyst;
a NOx sensor disposed in the exhaust passage downstream of the NOx reduction catalyst;
An exhaust treatment system comprising: the control device according to claim 1 .

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