KR100992816B1 - System for correction a stored ammonia quantity of emission reduce line on diesel vehicle and method thereof - Google Patents

Abstract

The present invention tracks the amount of ammonia stored in the SCR catalyst in the after-treatment system of a diesel vehicle to determine that an error occurs, thereby providing stable NOx purification by correcting and controlling the amount of ammonia stored.

The present invention is a process for estimating the amount of NOx generated by the SCR catalyst, measuring the amount of NOx generated in the SCR catalyst, and extracting and accumulating the difference with the predicted NOx amount, the difference between the accumulated amount of NOx over the reference value set If ammonia slip is detected in the state of determining ammonia storage tracking error, if the ammonia slip is detected, it is determined as ammonia storage under-prediction error, reducing ammonia production, NOx in determining ammonia storage tracking error. If excessive emissions are detected, ammonia storage overprediction errors are determined and the process includes increasing ammonia production.

SCR catalyst, urea, ammonia stock, trace error

Description

METHOD AND CORRECTION A STORED AMMONIA QUANTITY OF EMISSION REDUCE LINE ON DIESEL VEHICLE AND METHOD THEREOF}

The present invention relates to a post-treatment system of a diesel vehicle, and more particularly, to determine that an error occurs by tracking the amount of ammonia stored in the SCR (Selective Catalytic Reduction) catalyst and to stabilize the ammonia storage accordingly. An apparatus and method for compensating ammonia storage in a aftertreatment system in a diesel vehicle to provide NOx purification.

Vehicles with diesel engines are subject to hazardous substances such as NOx, CO, THC, soot and Particulate Matters (PM) contained in the exhaust gases in accordance with North American Diesel Tier 2 / BIN5 regulations or Euro 6 emission regulations. Equipped with various types of post-treatment systems to eliminate this.

Post-treatment systems include DOC (Diesel Oxidation Catalyst), which performs NMHC (Non-Methane HydroCarbons) conversion, Catalytic Particulate Filter (CPF), which collects particulate matter (PM), and SCR catalyst, which purifies NOx through reduction. Included.

SCR catalyst uses ammonia (NH3) produced from urea solution as a reducing agent to purify NOx, and has excellent selectivity to NOx and promotes reaction between NOx and ammonia even in the presence of oxygen. There is this.

In diesel vehicles, NOx can be purified without any delay by adsorbing and storing ammonia in SCR catalyst.In addition to controlling ammonia consumption in addition to ammonia consumption that reacts with NOx in order to maintain ammonia storage stably, a control amount to meet the ammonia storage target is provided. Consider.

In order to control the ammonia storage amount, as shown in FIG. 3, an appropriate amount of ammonia adsorption is set for each influence factor by identifying how the amount of ammonia adsorbed on the SCR catalyst changes according to various influence factors including temperature.

In addition, various SCR-related reactions are considered to determine the amount of adsorption to the catalyst without reacting in the ammonia generated from the urea injected through the dosing module disposed at the front end of the SCR catalyst.

However, even if ammonia adsorption amount and reaction amount are set through repeated experiments, the difference between the predicted value of the ammonia storage amount and the actual storage amount stored in the SCR catalyst occurs due to the accumulation of errors.

This difference is greater than a certain level and affects performance. The more accurate the SCR model is, the longer it will take, but ammonia stock tracking errors will always occur because 100% accurate modeling is not practical.

For example, if ammonia storage maintains the target storage volume or if the storage error is too low, the tracking control is executed in a direction to increase the ammonia storage, causing ammonia slip to cause secondary pollution. There is a problem.

In addition, when the ammonia storage amount is less than the target storage amount or the storage amount causes excessive tracking error, the storage amount control is executed in a direction for lowering the ammonia storage amount, thereby reducing the NOx purification rate.

The difference in the ammonia storage control logic's predicted accuracy depends on the time it takes for the ammonia stock tracking error to grow beyond a certain level, but after a certain amount of time it is necessary to calibrate it unless it has 100% accuracy.

Typically, the temperature, pressure, and concentration of the exhaust gas are used for the diagnosis of the aftertreatment system. In the case of the SCR catalyst, since the heat of reaction generated by the NOx purification reaction is small and the temperature difference is not severely generated, the signal of the NOx sensor is analyzed. Diagnosis

However, since NOx sensor measures not only NOx but also ammonia, it needs to be distinguished from this. Also, since NOx concentration measured by NOx sensor and actual NOx mass and flow rate are different, it is necessary to use NOx sensor under unstable conditions. There is a problem that the measured value cannot be used as it is.

In addition, the measurement limit of the NOx sensor can not measure more than a certain level of NOx, there is a problem that a large error occurs even if the NOx below a certain level can be measured.

Figure 4 shows the change in NOx purification rate according to the temperature of the SCR catalyst in a diesel vehicle, it can be seen that the temperature window is wider in the case of the unaging SCR catalyst, in the case of low temperature outside the temperature window in the figure It can be seen that the error can be large because the change in the NOx purification rate is large.

The present invention has been invented to solve the above problems, the object of which is to track the amount of ammonia stored in the SCR catalyst, and if a tracking error occurs, by performing correction control accordingly to maintain the optimal storage amount, NOx It is to ensure the purification performance and to prevent the slip of ammonia.

Features of the present invention for realizing the above object,

engine; SCR catalyst for purifying NOx by the reduction reaction of NOx and NH3 contained in the exhaust gas; First and second NOx sensors detecting NOx concentration between both ends of the SCR catalyst; It comprises a dosing module for injecting an aqueous urea solution to the front end of the SCR catalyst,

And a controller for determining an ammonia storage amount tracking error in the SCR catalyst and controlling the ammonia storage amount according to the determined storage under prediction error or over prediction error.

In addition, another feature of the present invention, the process of predicting the amount of NOx generation of the SCR catalyst;

Measuring the amount of NOx generated in the SCR catalyst and extracting and accumulating a difference from the predicted amount of NOx;

Determining an ammonia storage amount tracking error if the difference between the accumulated NOx amount is greater than or equal to the set reference value;

If ammonia slip is detected in the state of determining the ammonia storage amount tracking error, determining that the ammonia storage amount is underestimated error and reducing ammonia production;

If an excessive release of NOx is detected in the state where the ammonia storage amount tracking error is determined, it is determined as an ammonia storage amount excessive prediction error, and the process includes increasing ammonia production.

By the above configuration, the present invention accurately tracks the ammonia storage amount of the SCR catalyst and maintains a stable storage amount, thereby improving stable and fast response and NOx purification performance, and since ammonia slip is not generated, the purification performance is improved compared to the ammonia consumption. Is expected.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

Since the present invention can be implemented in various different forms, the present invention is not limited to the exemplary embodiments described herein, and parts not related to the description are omitted in the drawings in order to clearly describe the present invention.

1 is a view schematically showing an ammonia storage amount correction device of the after-treatment system in a diesel vehicle according to an embodiment of the present invention.

The present invention is an engine (2) as a power source, an exhaust pipe (6) for discharging exhaust gas combusted from the engine (2), an SCR catalyst (10), a first NOx sensor (12), a second NOx sensor (14), a temperature sensor 16, the control unit 18, the dosing module 20, the mixer 22, the urea tank 30, the pump 32, the urea supply line 34 and the pressure sensor 36.

The SCR catalyst 10 is made of V ₂ O ₅ / TiO ₂ or Pt / Al ₂ O ₃ or zeolite, and is disposed at a predetermined position of the exhaust pipe 6 connected to the engine 2 as a power source. The ammonia generated from the urea injected from the dosing module 20 is adsorbed and stored, and the ammonia and NOx are reduced to purify the NOx.

The first NOx sensor 12 is disposed at the inlet side of the SCR catalyst 10 to detect the amount of NOx contained in the exhaust gas flowing into the SCR catalyst 10 and provide information to the controller 18.

The second NOx sensor 14 is disposed at the outlet side of the SCR catalyst 10 to detect the amount of NOx contained in the exhaust gas purified through the reduction reaction of the SCR catalyst 10 and provide information to the controller 18 about the amount thereof. do.

The temperature sensor 16 detects the temperature of the SCR catalyst 10 activated by the temperature of the exhaust gas and provides information about the SCR catalyst 10 to the controller 18.

The controller 18 provides information such as operating conditions of the engine 2, exhaust gas flow rate, NOx concentration at the front end of the SCR catalyst 10 measured by the first NOx sensor 12, SCR catalyst 10 temperature, ammonia adsorption amount, and the like. It is applied to calculate the reaction rate of NOx in the SCR catalyst 10, by applying it to predict the amount of NOx generated in the rear end of the SCR catalyst (10).

In addition, the amount of NOx generated is measured through the second NOx sensor 14, and the cumulative difference is calculated by calculating the difference between the predicted amount of NOx and the measured amount of NOx generated. Is determined to have occurred.

If it is determined that an error has occurred in the tracking of the ammonia storage amount, it is determined whether the ammonia storage amount is under prediction error or excessive prediction error according to whether the ammonia slip or the NOx emission is excessive, and accordingly, the SCR catalyst 10 controls the ammonia storage amount. Allow the target stock of ammonia to be adsorbed and stored.

The control unit 18 lowers the ammonia production amount by controlling the urea injection amount when it is determined that the ammonia storage amount under prediction error is determined, and increases the ammonia production amount by controlling the urea injection amount when the ammonia storage amount over prediction error is determined.

The dosing module 20 operates the injector under the control of the controller 18 to inject the urea amount determined according to the determination of the ammonia storage amount prediction error.

The mixer 22 is disposed between the dosing module 20 and the SCR catalyst 10 to collide the liquid urea particles injected through the dosing module 20 to split the particles, thereby allowing the exhaust gas and the urea particles to split. Mix evenly to improve uniformity at the inlet of SCR catalyst 10.

The urea tank 30 accommodates the urea solution for spraying and forms an even pressure set in the urea supply line 34 by the driving of the pump 32 mounted therein so that the dosing module 20 is in accordance with the PWM signal. When activated, the high pressure injection of the liquid element is provided at the front end of the SCR catalyst 10.

The pressure sensor 36 detects the pressure formed in the urea supply line 34 and provides information about the pressure to the control unit 18 so that the set pressure can be maintained at all times while the engine 2 is kept starting. Make sure

The operation of compensating for the estimation error of the ammonia storage amount in the present invention including the function described above will be described in more detail as follows.

When the vehicle is running, the controller 18 controls the temperature of the SCR catalyst 10 measured through the temperature sensor 16, the flow rate of the exhaust gas, and the front end of the SCR catalyst 10 measured through the first NOx sensor 12. The NOx reaction rate is calculated by applying information such as NOx concentration, ammonia accumulated storage amount, NO ₂ / NOx, and aging degree, and the calculated NOx reaction rate is applied to predict the amount of NOx generated at the rear end of the SCR catalyst 10 (S101).

The NOx generation amount prediction at the rear end of the SCR catalyst 10 is calculated by the NOx mass flow rate x [1-NOx reaction rate] at the front end of the SCR catalyst 10.

When the amount of NOx generated at the rear end of the SCR catalyst 10 is predicted as described above, the amount of NOx generated at the rear end of the SCR catalyst 10 is measured through the second NOx sensor 14 (S102), and the amount of NOx is compared with the predicted amount of NOx generated. After extracting the difference, the extracted difference is accumulated (S103).

It is determined whether the difference between the accumulated NOx amount is greater than or equal to the set reference value (S104). If the difference between the accumulated NOx amount is less than or equal to the set reference value, it is returned. If it is greater than or equal to the reference value, it is determined that there is an error in tracking the ammonia storage amount (S105).

When the occurrence of the ammonia storage amount tracking error is determined as described above, it is determined whether the ammonia slip is detected in the SCR catalyst 10 (S106).

When the ammonia slip is detected in the determination of S106, it is determined that the ammonia storage amount is under prediction error (S107) and the urea injection amount is controlled through the dosing module 20 to lower the ammonia production amount (S108).

That is, since the ammonia more than the target storage amount is adsorbed and stored in the SCR catalyst 10 to generate ammonia slip, the ammonia stored in the SCR catalyst 10 is maintained at the target storage amount by lowering the ammonia production amount, thereby reducing the slip of ammonia. Do not occur.

However, if the ammonia slip is not detected in S106, it is determined whether excessive discharge of NOx is generated (S109).

If the excessive discharge of NOx does not occur in the determination of S109, the process returns to the process of S106. If the excessive discharge of NOx occurs, it is determined that the ammonia storage excess prediction error (S110) and the urea injection amount through the dosing module 20. Controlling to increase the ammonia production (S111).

That is, ammonia that does not reach the target storage amount is adsorbed and stored in the SCR catalyst 10, and NOx is excessively discharged by the control of lowering the ammonia production amount. Therefore, ammonia of the target storage amount is adsorbed to the SCR catalyst 10 by increasing the ammonia production amount. To be stored, thereby ensuring a stable NOx purification performance.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It is included in the scope of rights.

1 is a view schematically showing an ammonia storage amount correction device of the after-treatment system in a diesel vehicle according to an embodiment of the present invention.

2 is a flowchart schematically illustrating a procedure for correcting ammonia storage amount in a aftertreatment system in a diesel vehicle according to an exemplary embodiment of the present invention.

3 is a graph showing the relationship between the outlet temperature of the SCR catalyst and the ammonia storage in a typical diesel vehicle.

4 is a graph showing the NOx purification rate according to the temperature of the SCR catalyst in a typical diesel vehicle.

<Explanation of symbols for the main parts of the drawings>

 2: engine 6: exhaust pipe

10: SCR catalyst 12: 1st NOx sensor

14 second NOx sensor 16 temperature sensor

18: control unit 20: dosing module

22: mixer 30: urea tank

32: pump 34: urea supply line

Claims (6)

engine; SCR catalyst for purifying NOx by the reduction reaction of NOx and NH3 contained in the exhaust gas; First and second NOx sensors detecting NOx concentration between both ends of the SCR catalyst; It comprises a dosing module for injecting an aqueous urea solution to the front end of the SCR catalyst, And a control unit for determining an ammonia storage amount tracking error in the SCR catalyst and controlling the ammonia storage amount according to the determined storage under-prediction error or over-prediction error. The method of claim 1, The control unit extracts and accumulates the difference between the amount of NOx by comparing the estimated amount of NOx and the measured amount of NOx under the current operating conditions. Ammonia Stock Correction System. The method of claim 1, The control unit is ammonia storage amount correction device of the after-treatment system in a diesel vehicle to reduce the ammonia production by determining that the ammonia storage amount under prediction error is detected when ammonia slip is detected in the state of determining the ammonia storage amount tracking error. The method of claim 1, The control unit is ammonia storage amount correction device of the after-treatment system in the diesel vehicle to increase the ammonia production by determining that the ammonia storage excess prediction error is detected in the state of determining the ammonia storage amount tracking error. Predicting NOx generation amount of SCR catalyst; Measuring the amount of NOx generated in the SCR catalyst and extracting and accumulating a difference from the predicted amount of NOx; Determining an ammonia storage amount tracking error if the difference between the accumulated amount of NOx is greater than or equal to the set reference value; If ammonia slip is detected in the state of determining the ammonia storage amount tracking error, determining that the ammonia storage amount is underestimated error and reducing ammonia production; If an excessive discharge of NOx is detected in the state where the ammonia storage amount tracking error is determined, determining that the ammonia storage amount is excessive prediction error and increasing ammonia production; Ammonia storage correction method of the after-treatment system in a diesel vehicle comprising a. The method of claim 5, The amount of NOx generated by the SCR catalyst is ammonia storage amount correction method for the aftertreatment system in a diesel vehicle predicted by the NOx mass flow rate x [1-NOx reaction rate] of the SCR front end.

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