KR101180941B1 - System for control urea injection quantity of vehicle and method thereof - Google Patents

Abstract

The present invention is to provide a higher purification performance for the same level of ammonia storage by optimizing and controlling the distribution of ammonia stored in the SCR catalyst in a vehicle equipped with a SCR (Selective Catalytic Reduction) catalyst.

The present invention is to divide the SCR catalyst into N blocks to calculate the ammonia storage for each block having different temperature, ammonia storage amount, NOx purification rate, the process of calculating the utility index for each block, the target storage amount for each block The process includes applying the utility index to the ammonia storage amount and the target storage amount for each block, calculating the ammonia storage amount and the target storage amount of the entire block, and controlling the ammonia storage amount by controlling the urea injection amount according to the difference with the target storage amount.

SCR catalyst, ammonia, distribution, utility index, block

Description

Urea injection volume control device and method of vehicle {SYSTEM FOR CONTROL UREA INJECTION QUANTITY OF VEHICLE AND METHOD THEREOF}

The present invention relates to a vehicle equipped with a SCR (Selective Catalytic Reduction) catalyst, and more particularly, a vehicle that provides higher purification performance for ammonia storage by optimizing and controlling the distribution of ammonia stored in the SCR catalyst. It relates to a urea injection amount control apparatus and method.

Diesel-powered vehicles can be used in various forms to remove hazardous substances such as NOx, CO, THC, and Particulate Matters contained in the exhaust according to the North American diesel Tier 2 / BIN 5 regulation or the Euro 6 emission regulation. The aftertreatment device is mounted.

As a post-treatment device, the DOC (Diesel Oxidation Catalyst), which collects non-methane hydrocarbons (NMHC), and the Particulate Particulate Filter (DPF), which collect particulate matter (PM), which reduce NMHC, SCR catalyst is included to purify NOx.

The SCR catalyst uses ammonia (NH ₃ ) as a reducing agent for purifying NOx, and has an advantage in that the reaction between NOx and ammonia is promoted even in the presence of oxygen as well as excellent selectivity to NOx.

SCR catalyst sprays urea into a dosing module placed at the front end of the SCR catalyst to maintain NOx purification performance at a certain level or higher, and ammonia generated by evaporation and decomposition of the injected urea To maintain ammonia storage in the SCR catalyst.

A mixer is disposed between the dosing module and the SCR catalyst, which collides with the urea particles injected through the dosing module, thereby splitting the particles, and reflecting the urea particles so that well wetting does not occur. .

This improves the NOx purification efficiency by uniformly mixing the exhaust gas and the injected urea particles to improve the uniformity at the inlet end of the SCR catalyst and optimally mixing the NOx in the exhaust gas and the ammonia obtained from the injected urea.

The urea injection amount control method applied to the conventional vehicle calculates the required amount of ammonia according to the stoichiometric ratio (NH ₃ / NOx), which is the ratio of NOx generation amount and ammonia in the driving state, and calculates the urea amount according to the ammonia requirement. By operating the pump installed in the tank, the injector of the dosing module that takes a certain pressure, about 5 bar pressure is operated to inject the calculated amount of urea.

The other method is to calculate the ammonia requirement according to the ammonia storage amount in the SCR catalyst, calculate the urea amount according to the ammonia requirement, and then apply the pressure of the dosing module that takes a certain pressure, about 5 bar, by the operation of the pump installed in the urea tank. The injector is operated to inject the calculated amount of urea.

As described above, the amount of ammonia stored is controlled based on the amount of ammonia adsorbed on the entire SCR catalyst, thereby improving NOx purification performance and preventing ammonia slip.

However, the adsorbed ammonia does not have a uniform distribution on the SCR catalyst but has a non-uniform distribution according to the adsorption-desorption and reaction history, thereby affecting the NOx purification performance.

Adsorption of ammonia on the SCR catalyst depends on the temperature of the SCR catalyst, the ammonia supply amount, and the ammonia saturation on the SCR catalyst.

For example, as the temperature of the SCR catalyst increases, the ammonia adsorption amount decreases but the adsorption rate increases. As the ammonia supply amount increases or the ammonia saturation decreases, ammonia adsorption is advantageous.

As can be seen from the graph of the change in adsorption ammonia distribution with temperature shown in FIG. 3, the ammonia adsorption proceeds slowly at low temperatures and the adsorptive amount is large, so that the difference between the front and rear end adsorption amounts is large, and the ammonia adsorption at high temperatures is fast. Since the adsorbable amount is small and the amount of adsorption is small, the difference between the front and rear end adsorption amounts is small.

In the case of such ammonia distribution, since both ammonia and NOx are higher in the front of the SCR catalyst, the reaction proceeds more smoothly than the latter, but the NOx purification by the shear ammonia greatly decreases the amount of shear ammonia, which can be smaller than the latter. have.

As described above, the conventional ammonia storage amount control is controlled based on the total amount of ammonia stored in the SCR catalyst, and thus the performance difference according to the distribution of ammonia stored in the SCR catalyst is not properly reflected, thereby reducing the NOx purification efficiency.

The present invention has been invented to solve the above problems, and its object is to perform ammonia storage amount control in consideration of performance difference according to ammonia distribution in SCR catalyst, thereby providing higher NOx purification performance for the same level of ammonia storage amount. To make it possible.

The urea injection amount control apparatus for a vehicle according to a feature of the present invention for achieving the above object,

An SCR catalyst for purifying exhaust gas by reacting ammonia and NOx;

A dosing module for injecting urea in front of the SCR catalyst;

By dividing the SCR catalyst into N blocks, the temperature, ammonia storage amount, utility index, and target storage amount for each block are calculated, and the ammonia storage amount and target storage amount for each block are calculated by applying the utility index to the ammonia storage amount and target storage amount for each block. And a control unit configured to execute ammonia storage amount control by controlling the urea injection amount according to a difference from the target storage amount.

In addition, the method for controlling the urea injection amount of a vehicle according to a feature of the present invention,

Dividing the SCR catalyst into N blocks and calculating ammonia storage amount for each block having different temperature, ammonia storage amount, and NOx purification rate for each block;

Calculating a utility index for each block;

Calculating a target storage amount according to the catalyst temperature for each block;

The method includes calculating the ammonia storage amount and the target storage amount of the entire block by applying the utility index to the ammonia storage amount and the target storage amount of each block, and controlling the ammonia storage amount by controlling the urea injection amount according to the difference with the target storage amount.

According to the above-described configuration, the present invention improves the response of NOx purification to rapid change of exhaust conditions, improves the prediction accuracy of ammonia consumption on the SCR catalyst, and improves the control performance of the ammonia storage amount and NOx purification in preparation for ammonia consumption. The effect of improving performance can be 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 illustrating an apparatus for controlling urea injection amount of a vehicle according to an exemplary 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 and NOx, which are obtained from the urea injected from the dosing module 20, are reduced by reaction 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 the 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 SCR catalyst 10 and provide the information to the controller 18.

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

In order to control the storage amount in consideration of the ammonia distribution of the SCR catalyst 10, the controller 18 determines the temperature for each block by dividing the SCR catalyst 10 into N blocks, and determines the ammonia storage amount for each block according to the temperature for each block. Calculate the target storage capacity according to the block-by-block temperature.
The temperature for each block may be determined by linear interpolation based on the front and rear temperature.

Subsequently, the target storage amount and ammonia storage amount of the entire block are calculated by applying the utility index for each block, and based on the calculated ammonia amount, the ammonia storage control is performed by controlling the injection amount of urea.

The controller 180 calculates the ammonia storage amount for each block is calculated by applying the adsorption amount, desorption amount, and reaction amount calculated by the relationship between the block temperature and the saturation and inflow amount of the SCR catalyst.

The dosing module 20 is operated by the injector under the control of the control unit 18 to perform the injection of the element.

Mixer 22 is disposed between the dosing module 20 and the SCR catalyst 10 to collide the liquid element particles injected through the dosing module 20 to split the particles, thereby the exhaust gas and the injected elements The particles are evenly mixed to improve uniformity at the inlet end of the SCR catalyst 10 so as to optimally mix NOx in the exhaust gas and ammonia obtained from urea.

The urea tank 30 accommodates the urea solution for spraying, and forms a uniform pressure set in the urea supply line 34 by driving the pump 32 mounted therein, so that the dosing module 20 is driven according to 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

In the present invention including the functions described above, the operation of the ammonia storage control to optimize the ammonia distribution on the SCR catalyst is as follows.

When the engine is turned on, the controller 18 divides the SCR catalyst 10 into N blocks (S101), and then each block having a difference in NOx purification rate according to the temperature of each block, the ammonia storage amount according to the ammonia storage amount, and the ammonia storage amount. Calculate the starch ammonia storage (S102).

The amount of ammonia stored as a function of temperature decreases as the temperature is higher, and the amount of ammonia adsorption is proportional to the amount of ammonia injected, but becomes larger as (1-saturation) = {(Storage-Storage) / Storage}. The bigger it gets.

In addition, the ammonia desorption amount increases as the temperature and saturation degree increase.

When ammonia is injected into an arbitrary block, the amount of adsorption determined by conditions of inflow and catalyst temperature and saturation is subtracted, and the amount of desorption determined by storage and catalyst temperature and saturation is added to the next block. It continues continuously up to the last block determined on the outlet side of catalyst 10.

As described above, when the ammonia storage amount is calculated for each block, the NOx purification rate for each block is determined according to the catalyst temperature, the exhaust flow rate, the NOx amount, the ammonia storage amount, and the NO ₂ / NOx ratio. It is determined by finding the amount of NOx to be purified and then finding the equivalent amount of ammonia.

At this time, it may be determined whether ammonia slip occurs in the last block, and control according to ammonia slip may be performed.

Then, the efficiency index for each block is calculated (S103), and the block ammonia target storage amount according to the temperature of each block is calculated for controlling the storage amount of ammonia on the SCR catalyst 10 (S104).
The temperature for each block may be determined by linear interpolation based on the front and rear temperature.

Here, since the availability of the ammonia storage amount differs for each block, the ammonia storage amount and the target storage amount of all blocks are calculated by applying the storage amount utility index to the ammonia storage amount and the target storage amount for each block (S105).

The block-efficiency index (weighting value) for each block is determined through the following process.

Combining the blocks pre-adsorbed ammonia by the desired amount to form the SCR catalyst, and then the reaction gas flow to measure the change of NOx purification rate according to the distribution of ammonia, and from the first block on the inlet side of the SCR catalyst to know the contribution of each block The evaluation is carried out one by one to calculate the utility index from the difference in NOx purification according to the ammonia distribution.

When the ammonia storage amount and the target storage amount of the entire block are calculated in S105, the ammonia storage amount control amount is calculated (S106). In step S108, ammonia storage amount control is provided, which provides a uniform distribution.

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 illustrating an apparatus for controlling urea injection amount of a vehicle according to an exemplary embodiment of the present invention.

2 is a flowchart illustrating a urea injection amount control procedure for a vehicle according to an exemplary embodiment of the present invention.

Figure 3 is a graph showing the change in adsorption ammonia distribution with the temperature of a typical SCR catalyst.

<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

Claims (7)

An SCR catalyst for purifying exhaust gas by reacting ammonia and NOx; A dosing module for injecting urea in front of the SCR catalyst; / RTI &gt; The SCR catalyst is divided into N blocks to calculate the temperature for each block, the ammonia storage amount and the target storage amount for each block, and the ammonia storage amount and the target storage amount for the entire block are calculated by applying the efficiency index for each block, and the difference between the target storage amount A control unit for performing urea injection amount control by controlling ammonia storage amount accordingly; Urea injection amount control device of a vehicle comprising a. The method of claim 1, The control unit is a urea injection amount control device for a vehicle characterized in that for calculating the NOx purification rate for each block by applying the temperature, exhaust flow rate, NOx amount, ammonia storage amount, NO ₂ / NOx ratio of the SCR catalyst. The method of claim 1, The control unit calculates the amount of NOx to be purified by multiplying the amount of NOx and the NOx purification rate, and then calculates the amount of ammonia corresponding to the amount of ammonia reaction amount of the vehicle, characterized in that for calculating the amount of ammonia reaction. Calculating the ammonia storage amount of each block having different temperature and NOx purification rate by dividing the SCR catalyst into N blocks; Calculating a utility index for each block; Calculating a target storage amount according to the temperature of each block; Calculating ammonia storage amount of all blocks by applying a utility index to the ammonia storage amount of each block; Calculating a target storage amount of all blocks by applying a utility index to the target storage amount for each block; Controlling the urea injection amount by controlling the ammonia storage amount according to the difference between the ammonia storage amount and the target storage amount of the entire block; Urea injection amount control method of a vehicle comprising a. 5. The method of claim 4, The ammonia storage amount calculation for each block is calculated by applying the adsorption amount, desorption amount and reaction amount of the urea injection amount control method of the vehicle. 5. The method of claim 4, The ammonia storage amount control method is a urea injection amount control method of the vehicle is carried out by applying the conditions of the target storage amount, storage amount, exhaust temperature, exhaust flow rate, catalyst temperature. 5. The method of claim 4, The ammonia reaction amount for each block is calculated by calculating the amount of NOx purified by multiplying the NOx amount and the NOx purification rate, and then calculating the amount of ammonia corresponding thereto.

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