KR102664097B1 - System and method for controlling ammonia occlusion amount of selective catalytic reduction system - Google Patents

Abstract

The present invention relates to a system and method for controlling the storage amount of a reducing agent such as ammonia in an SCR post-treatment system, which allows controlling the storage amount of a reducing agent such as ammonia depending on the degree of activation of the SCR catalyst.
For this purpose, the present invention determines the degree of activation of the catalyst by calculating the frequency of exposure to a certain temperature or higher based on the average temperature of the SCR catalyst, and then determines the storage amount of a reducing agent such as ammonia based on this. Provides a system and method for controlling the amount of reducing agent stored in an SCR post-treatment system to improve control accuracy.

Description

System and method for controlling the amount of reducing agent stored in the SCR post-treatment system {SYSTEM AND METHOD FOR CONTROLLING AMMONIA OCCLUSION AMOUNT OF SELECTIVE CATALYTIC REDUCTION SYSTEM}

The present invention relates to a system and method for controlling the storage amount of reducing agent in an SCR post-treatment system. More specifically, the control of the storage amount of reducing agent in an SCR post-treatment system allows the storage amount of a reducing agent, such as ammonia, to be adjusted depending on the degree of activation of the SCR catalyst. It relates to systems and methods.

As a type of exhaust gas purification system for diesel engine vehicles, a reducing agent for removing nitrogen oxides, such as ammonia (NH ₃ ) or urea containing ammonia as the main ingredient, is sprayed into the exhaust pipe so that the SCR catalyst can effectively purify nitrogen oxides. It is equipped with an SCR (Selective Catalytic Reduction) post-processing system.

The SCR catalyst is called a selective reduction catalyst in the sense that it allows a reducing agent such as ammonia to react better with nitrogen oxides among oxygen and nitrogen oxides.

The SCR post-treatment system includes a reducing agent tank, an SCR catalyst mounted at a predetermined position in the exhaust pipe, and a dosing module that injects the reducing agent in the reducing agent tank into the exhaust pipe in front of the SCR.

Therefore, when a reducing agent such as ammonia is injected from the injection module into the exhaust gas passing through the exhaust pipe, the injected reducing agent is stored in the SCR catalyst and undergoes a reaction to purify nitrogen oxides contained in the exhaust gas.

At this time, the amount of reducing agent stored in the SCR catalyst is closely related to the degree of aging of the SCR catalyst, and the reason is that more reducing agent than the amount that can be stored at the current degree of aging of the SCR catalyst is stored in the SCR catalyst. This is because part of the reducing agent slips from the SCR catalyst and cannot be stored.

Accordingly, the storage amount of a reducing agent such as ammonia in the SCR catalyst is controlled differently depending on the degree of SCR catalyst aging.

Here, the method for controlling the amount of reducing agent stored in a conventional SCR post-treatment system is as follows with reference to FIG. 1 attached thereto.

As shown in FIG. 1, the conventional reducing agent storage amount control system includes a control unit 10 that calculates the reducing agent storage amount differently depending on the degree of deterioration of the SCR catalyst and outputs it to the injection module, and this control unit 10 controls the SCR catalyst temperature. It is composed of an SCR temperature sensor 20 that detects and inputs , and an odometer 30 that inputs mileage information to the control unit 10.

The control unit 10 includes an aging factor calculation unit 12 that calculates an aging factor based on the SCR catalyst temperature input from the SCR temperature sensor 20 and the mileage information input from the odometer 30. It is composed of an storage amount determination unit 14 that determines the storage amount of the reducing agent based on map data according to the aging factor.

For reference, the map data includes a map representing the maximum storage amount and a map representing the minimum storage amount according to the airing factor, and using this map data, the storage amount determination unit 14 determines the storage amount maximum value and The range value between the minimum storage amount is determined as the reducing agent storage amount.

Therefore, the aeration factor calculation unit 12 of the control unit 10 calculates the aging factor, which is a value between 0 and 1, based on the SCR catalyst temperature and mileage information, and sends it to the storage amount determination unit 14. When output, the storage amount determination unit 14 determines the final reducing agent storage amount in the range between the maximum storage amount and the minimum storage amount based on the map data and outputs it to the injection module, thereby determining the injection amount of the reducing agent in the injection module and the SCR catalyst. The amount of reducing agent stored can be adjusted.

However, conventionally, the aging factor is simply determined by estimating the degree of deterioration of the SCR catalyst based on the SCR catalyst temperature and mileage. Regardless of the degree of deterioration of the SCR catalyst, how much the SCR catalyst is exposed to above a certain temperature is determined. As the fact that the degree of activation of the catalyst varies depending on the temperature is not taken into consideration, there is a problem in that the control accuracy of the amount of reducing agent stored is low.

For example, in the case of an under-floor-type SCR system, the degree of activation may be low even when the catalyst is deteriorated significantly as the catalyst is located relatively far from the engine, while in the case of a close-coupled (CC) system, the degree of activation may be low In the case of -type SCR systems, the catalyst is exposed to relatively high temperatures as the catalyst is located close to the engine, so the degree of activation can be high even when deterioration is less advanced.

Accordingly, because the degree of activation of the SCR catalyst affects the NOx purification efficiency of the SCR catalyst, it is necessary to control the storage amount of a reducing agent such as ammonia differently depending on the degree of activation.

The present invention was developed to solve the above-described conventional problems. Based on the average temperature of the SCR catalyst, the frequency of exposure to a certain temperature or higher is calculated to determine the degree of activation of the catalyst, and based on this, a reducing agent such as ammonia is used. The purpose is to provide a system and method for controlling the storage amount of reducing agent in an SCR post-treatment system that improves the control accuracy of the storage amount of reducing agent by allowing the storage amount to be determined.

One embodiment of the present invention for achieving the above object includes: an aging factor calculation unit that calculates an aging factor based on the SCR catalyst temperature input from the SCR temperature sensor and the mileage information input from the odometer; A catalyst activity calculation unit that calculates the degree of activation of the SCR catalyst and outputs an activation factor; and a storage amount determination unit that determines a different storage amount of reducing agent based on map data according to the aging factor and activation factor. It provides a reducing agent storage amount control system for an SCR post-treatment system, characterized in that it includes.

Another embodiment of the present invention for achieving the above object is: comparing the SCR catalyst temperature and the SCR activation reference temperature; When the SCR catalyst temperature is greater than the SCR activation reference temperature, a timer is activated to accumulate the time when the SCR catalyst temperature is greater than the SCR activation reference temperature; Dividing the accumulated time from the timer by the full activation reference time and outputting an activation factor value between 0 and 1; Determining the final reducing agent storage amount using the activation factor value in the storage amount determination unit; It provides a method for controlling the storage amount of reducing agent in an SCR post-treatment system, comprising:

Through the means for solving the above problems, the present invention provides the following effects.

First, the control accuracy of the reducing agent storage amount can be improved by controlling the ammonia storage amount according to the degree of activation of the catalyst in addition to the degree of deterioration of the SCR catalyst.

Second, as the SCR catalyst lasts, the storage capacity of reducing agents such as ammonia decreases, but as activation progresses, the NOx purification efficiency improves, so the ammonia storage amount can be controlled to reduce the ammonia storage amount.

In other words, if the SCR catalyst is activated, the storage amount of the reducing agent, such as ammonia, can be reduced by controlling the reduction of the storage amount of the reducing agent even if the degree of deterioration is low, thereby securing the same NOx purification efficiency at a faster time than before.

Third, the amount of urea water injection used to store a reducing agent such as ammonia in the SCR catalyst can be reduced, ultimately reducing the ammonia consumption rate.

Fourth, it is possible to prevent excessive ammonia from being stored in the SCR catalyst, and also prevent the phenomenon of excessively stored ammonia slipping away from the SCR catalyst and being released into the atmosphere.

Figure 1 is a configuration diagram showing the reducing agent storage amount control system of a conventional SCR post-treatment system;
Figure 2 is a configuration diagram showing the reducing agent storage amount control system of the SCR post-treatment system according to the present invention;
Figure 3 is a flowchart showing a method for controlling the storage amount of reducing agent in the SCR post-treatment system according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Typically, the SCR catalyst deteriorates as it receives heat load, and the degree of heat load is proportional to the rate of decrease in the storage amount of ammonia (NH ₃ ), a reducing agent of the SCR catalyst.

However, the catalyst aged at 680 ℃ for 10 hours and the catalyst aged at 550 ℃ for 96 hours have the same ammonia storage amount, so it can be judged that the degree of deterioration of the two catalysts is the same. However, as a result of the experiment, the NOx purification efficiency is 10 hours at 680 ℃. The aged catalyst was found to be superior.

The reason why the NOx purification efficiency of the above two catalysts is different is due to the effect of catalyst activation (for example, Cu-activation of Cu-Zeolite type SCR catalyst), and Cu-activation of this catalyst is independent of heat load. This is because it varies depending on how much higher temperature it is exposed to.

Accordingly, the present invention determines how much the catalyst has deteriorated due to heat load and calculates the existing aging factor to determine the ammonia storage amount of the SCR catalyst. The main point is to determine the extent of exposure and determine the amount of reducing agent stored using the activation factor.

The attached Figure 2 is a configuration diagram showing the reducing agent storage amount control system of the SCR post-treatment system according to the present invention.

As shown in FIG. 2, the reducing agent storage amount control system according to the present invention includes a control unit 10 that calculates the reducing agent storage amount differently depending on the degree of deterioration of the SCR catalyst and outputs it to the injection module, and an SCR control system to this control unit 10. It includes an SCR temperature sensor 20 that detects and inputs the catalyst temperature, and an odometer 30 that inputs mileage information to the control unit 10.

In particular, the control unit 10 includes an aging factor calculation unit that calculates an aging factor based on the SCR catalyst temperature input from the SCR temperature sensor 20 and the mileage information input from the odometer 30. 12) and a catalyst activity calculation unit 16 that calculates the degree of activation of the SCR catalyst and outputs an activation factor, and determines the amount of reducing agent stored differently based on map data preset according to the aging factor and/or activation factor. It is configured to include a storage amount determining unit 14.

More specifically, the catalyst activity calculation unit 16 includes a comparator 16-1 that compares the SCR catalyst temperature input from the SCR temperature sensor 20 and the SCR activation reference temperature, and the SCR catalyst temperature. A timer (16-2) that accumulates the time when the SCR activation temperature is greater than the standard temperature, and an activation that divides the accumulated time by the full activation standard time and outputs an activation factor value between 0 and 1. It consists of a factor calculation unit 16-3.

In addition, the control unit 10 multiplies the aging factor calculated by the aeration factor calculation unit 12 and the activation factor output from the catalyst activity calculation unit 16 and outputs the product to the storage amount determination unit 14. 18) is further included.

Here, the method for controlling the storage amount of reducing agent of the present invention based on the above-described configuration is as follows.

The attached Figure 3 is a flowchart showing a method for controlling the storage amount of reducing agent in the SCR post-treatment system according to the present invention.

First, when SCR temperature information is input from the SCR temperature sensor 20 to the catalyst activity calculation unit 16, it is compared with the SCR activation reference temperature previously stored in the catalyst activity calculation unit 16 (S101).

That is, the comparator 16-1 of the catalyst activity calculation unit 16 compares the SCR catalyst temperature and the SCR activation reference temperature.

As a result of comparison, if the SCR catalyst temperature is greater than the SCR activation reference temperature, the timer 16-2 is turned on (S102).

Accordingly, the timer 16-2 accumulates the time when the SCR catalyst temperature is greater than the SCR activation reference temperature (S103).

Subsequently, when the time accumulated by the timer is divided by the pre-stored full activation reference time in the activation factor calculation unit 16-3, an activation factor value between 0 and 1 is output (S104 ).

At this time, the SCR activation reference temperature and full activation reference time are constant values set according to the characteristics of the catalyst, and are stored in advance in the catalyst activation calculation unit 16.

Preferably, when the catalyst is exposed to the SCR activation reference temperature or higher for a very long time, the accumulated time may become very large and may be greater than the full activation reference time, taking into account that the activation factor may be greater than 1. The maximum value of the activation factor is limited to 1.

Accordingly, when the activation factor calculation unit 16-3 outputs the activation factor value to the storage amount determination unit 14, after checking whether the activation factor value is a value between 0 and 1 (S105), the activation factor If the value is between 0 and 1, it is output as is. Otherwise, the activation factor value is output as the maximum value of 1.

Next, the storage amount determination unit 14 determines the final reducing agent storage amount in the range between the maximum storage amount and the minimum storage amount based on the map data according to the activation factor value and outputs it to the injection module, so that the reducing agent of the injection module The injection amount and the amount of reducing agent stored in the SCR catalyst can be adjusted.

More specifically, the map data includes a map representing the maximum storage amount and a map representing the minimum storage amount according to the airing factor. Using this map data, the storage amount determination unit 14 determines the activation factor. Depending on the value, the map representing the maximum storage amount and the map representing the minimum storage amount are internally divided, and a specific value in the range between the maximum storage amount and the minimum storage amount is determined as the final reducing agent storage amount.

Subsequently, the final reducing agent storage amount determined in the storage amount determination unit 14 is output to the injection module, so that the injection module injects the reducing agent according to the final reducing agent injection amount, so that the storage amount of the reducing agent for the SCR catalyst can be appropriately adjusted.

Meanwhile, the aging factor calculation unit 12 outputs an aging factor, which is a value between 0 and 1, based on the SCR catalyst temperature and mileage information, and this aging factor value and the activation factor calculation unit 16 The activation factor value output in -3) can be multiplied by the multiplier 18 and output to the storage amount determination unit 14. Accordingly, the storage amount determination unit 14 makes the final decision based on the aging factor value and the activation factor value. The amount of reducing agent stored can be determined.

In this way, regardless of the durability of the SCR catalyst, the time of exposure to high temperatures above a certain temperature is determined to calculate the activation factor value that determines the degree to which the SCR catalyst is activated, and this is used to more efficiently control the ammonia storage amount. can do.

In addition, by determining the degree to which the SCR catalyst is activated, the amount of ammonia stored can be lowered when the activation degree is high. Therefore, the amount of urea water injection and the ammonia consumption rate used to store a reducing agent such as ammonia in the SCR catalyst can be reduced, and the existing It is also possible to prevent ammonia excessively stored in the SCR catalyst from slipping off and being released into the atmosphere and being consumed.

10: control unit
12: Aging factor calculation unit
14: storage amount determination unit
16: Catalyst activity calculation unit
16-1: Comparator
16-2: Timer
16-3: Activation factor calculation unit
20: SCR temperature sensor
30: Odometer

Claims (7)

An aging factor calculation unit that calculates an aging factor based on the SCR catalyst temperature input from the SCR temperature sensor and the mileage information input from the odometer;
A catalyst activity calculation unit that calculates the degree of activation of the SCR catalyst and outputs an activation factor; and
a storage amount determination unit that determines a different storage amount of reducing agent based on map data according to the aging factor and the activation factor;
A reducing agent storage amount control system for an SCR post-treatment system comprising:
In claim 1,
The catalyst activity calculation unit:
A comparator that compares the SCR catalyst temperature input from the SCR temperature sensor and the SCR activation reference temperature;
A timer that accumulates the time when the SCR catalyst temperature is greater than the SCR activation reference temperature; and
An activation factor calculation unit that divides the accumulated time by the full activation reference time and outputs an activation factor value between 0 and 1;
A reducing agent storage amount control system for an SCR post-treatment system, characterized in that it consists of.
In claim 1,
A reducing agent storage amount control system for an SCR post-treatment system, further comprising a multiplier that multiplies the aging factor and the activation factor and outputs the product to a storage amount determination unit.
Comparing the SCR catalyst temperature and the SCR activation reference temperature;
When the SCR catalyst temperature is greater than the SCR activation reference temperature, a timer is activated to accumulate the time when the SCR catalyst temperature is greater than the SCR activation reference temperature;
Dividing the time accumulated by the timer by the full activation reference time and outputting an activation factor value between 0 and 1;
Determining the final reducing agent storage amount using the activation factor value in the storage amount determination unit;
A method for controlling the storage amount of reducing agent in an SCR post-treatment system, comprising:
In claim 4,
When outputting the activation factor value, the maximum value of the activation factor value is limited to 1. A method for controlling the storage amount of reducing agent in an SCR post-treatment system.
In claim 4,
A method for controlling the storage amount of reducing agent in an SCR post-treatment system, characterized in that the storage amount determination unit determines the final storage amount of reducing agent in the range between the maximum storage amount and the minimum storage amount based on map data according to the activation factor value.
In claim 4,
The activation factor value is multiplied by the aging factor calculated in the aeration factor calculation unit and output to the storage amount determination unit.

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