KR101048125B1 - Urea injection quantity control device and method of vehicle - Google Patents

Abstract

The present invention accurately predicts the total consumption of ammonia generated in an SCR catalyst in a vehicle equipped with an SCR (Selective Catalytic Reduction) catalyst, thereby controlling the ammonia responsiveness to rapid changes in operating conditions by controlling the amount of ammonia stored. To improve.

The present invention is a process for calculating the total consumption of ammonia generated in the SCR catalyst by applying ammonia consumption, ammonia storage amount, ammonia reaction rate, HC adsorption amount and aging degree according to NOx emissions; Calculating urea requirements by calculating ammonia requirements according to the calculated ammonia consumption; Detecting the temperature of the SCR catalyst and performing urea injection of the required amount if the injection temperature is possible.

SCR catalyst, urea, ammonia (NH3), consumption forecast, reaction amount, aging degree, adsorption amount

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, to accurately predict the total consumption of ammonia generated from the SCR catalyst, and to control the ammonia storage accordingly to quickly change the operating conditions. A urea injection amount control apparatus and method for a vehicle for improving the responsiveness of NOx purification.

Vehicles with diesel engines remove harmful substances such as NOx, CO, THC, soot, and particulate matter contained in exhaust gases in accordance with North American Diesel Tier 2 / BIN5 regulations or Euro 6 emission regulations. Various types of post-treatment devices are mounted.

The post-treatment unit is located close to the engine and performs DOC (Diesel Oxidation Catalyst), which collects Non-Methane HydroCarbons (NMHC), Catalytic Particulate Filter (CPF) to collect particulate matter (PM), and reduction. SCR catalyst is included to purify NOx.

The SCR catalyst uses ammonia (NH3) as a reducing agent for purifying NOx, and has an advantage that the reaction between NOx and ammonia is promoted even in the presence of oxygen as well as excellent selectivity to NOx.

In order to maintain the NOx purification performance of the SCR catalyst above a certain level, the urea is injected into a dosing module disposed at the front end of the SCR catalyst, 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 optimally mixing NOx in the exhaust gas and ammonia obtained from the injected urea by uniformly mixing the exhaust gas and the injected urea particles at the SCR catalyst inlet end.

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, which 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.

In the conventional urea injection amount control method, the former method has a disadvantage in that it is difficult to control a slow response and a low performance and slip amount compared to ammonia consumption.

In addition, the latter method may bring performance improvement compared to the former method, but may have a problem that may worsen the situation than the former method when the characteristics of the catalyst are not properly reflected.

In addition, the control based on the NOx purification rate according to the basic reaction is made, there is a problem that can not effectively cope with the case that the exhaust conditions are greatly changed because more precise control is not made.

The present invention has been invented to solve the above problems, and its purpose is to accurately calculate the consumption amount of ammonia consumed according to NOx emission amount and ammonia accumulation amount, adsorption and desorption of HC, oxidation reaction of ammonia, aging, etc. It is to improve the stable purification efficiency and purification performance by controlling the required ammonia storage amount by calculating.

A urea injection amount control apparatus for a vehicle according to a feature of the present invention for realizing the above object includes an 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; A dosing module for injecting an aqueous urea solution at the tip of the SCR catalyst; It includes a temperature sensor for detecting the temperature of the SCR catalyst,

It includes a control unit for estimating the total ammonia consumption generated in the SCR catalyst to calculate the ammonia requirement, and determine the injection amount of the urea according to the ammonia requirement.

In addition, the method of controlling the urea injection amount of the vehicle according to the characteristics of the present invention, the process of calculating the total ammonia consumption from the SCR catalyst by applying the ammonia consumption, ammonia storage amount, ammonia reaction rate, HC adsorption amount and aging degree according to the NOx emissions ; Calculating urea requirements by calculating ammonia requirements according to the calculated ammonia consumption; Detecting the temperature of the SCR catalyst and performing urea injection of the required amount if the injection temperature is possible.

By the above-described configuration, the present invention accurately predicts ammonia consumption generated in the SCR catalyst and controls the storage amount of ammonia based on the predicted value, thereby improving the purification performance of NOx and improving the responsiveness to the rapid change of operating conditions. The effect of providing emission stabilization 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 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 NOx is purified by a reduction reaction of ammonia and NOx obtained from the urea injected from the dosing module 20.

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 by 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 calculates the ammonia requirements by estimating the total ammonia consumption in the exhaust system analyzed from the operating conditions of the engine 2, the exhaust gas temperature, and the information of the first and second NOx sensors 12 and 14, The injection amount of the urea is determined according to the required amount, and the urea injection is controlled through the dosing module 20.

The control unit 18 predicts ammonia consumption by applying ammonia consumption according to NOx emissions, ammonia storage amount, ammonia reaction amount, HC adsorption amount and high temperature exposure, and ammonia through urea injection according to the predicted value. Control the amount of storage.

Ammonia consumption according to the NOx emission amount is calculated from "NOx emission × stoichiometric ratio (NH ₃ / NOx) × ammonia reaction rate", and the ammonia storage amount is the consumption amount (reaction amount + desorption amount) at the value added with the current storage amount and the new inflow amount. Is subtracted and calculated.

The reaction amount of ammonia is divided into the reaction amount with NOx and oxygen, and the reaction amount with NOx is calculated by applying the NOx purification rate and stoichiometric ratio reflecting the change of the specific gravity of the reaction path according to the change of exhaust conditions.

The HC adsorption amount is calculated by subtracting the desorption amount and the reaction amount from the currently accumulated adsorption amount and the newly adsorbed amount.

The dosing module 20 operates the injector under the control of the controller 18 to execute the injection of the urea amount determined by the temperature condition.

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 the uniformity at the inlet end of the SCR catalyst 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 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

First, the characteristics of the SCR catalyst will be described.

2 is a view showing urea injection and purification characteristics of a catalyst immediately after starting an engine.

As shown, when a certain amount, for example, 200 g / h of the urea is injected immediately after starting the engine for a certain time, as shown in the "A" area after injection, the NOx emission is steadily decreased for a certain time.

This phenomenon can be seen that more than a certain level of ammonia is adsorbed in the SCR catalyst 10 for the reaction of NOx, the time required for stabilization takes longer at low temperatures with a large amount of adsorption of ammonia, on the contrary Since the amount of ammonia adsorption is small, the stabilization time is shortened.

Therefore, in a vehicle in which the driving conditions are changed irregularly, responsiveness to the purification of NOx can be accelerated when ammonia or more is adsorbed in advance.

3 is a graph showing the relationship between the temperature of the SCR catalyst and the ammonia storage amount.

As can be seen from the graph, the storage capacity of the ammonia adsorption decreases rapidly with increasing temperature of the SCR catalyst 10, but it can be seen that the constant temperature is maintained at a constant temperature of 260 ° C. or higher.

However, when the temperature condition of the SCR catalyst 10 suddenly changes to 260 ° C. or more in a state where the ammonia is pre-adsorbed at a maximum in a low temperature at which the temperature of the SCR catalyst 10 is maintained at 220 ° C. or less, SCR occurs. The phenomenon exceeding the ammonia storage capacity of the catalyst 10 occurs, whereby ammonia is desorbed to generate ammonia slip.

This phenomenon can be seen that even if ammonia is adsorbed in advance, it is necessary to reduce the maximum adsorption possible amount in consideration of the possible change in conditions. It is necessary to know the quantity exactly.

Table 1 below lists various reactions that may occur on the SCR catalyst 10, and it can be seen that the consumption path of ammonia (NH 3) exists in addition to the reaction of NOx, and in particular, ammonia oxidation may be actively performed at high temperature. This is an item that should be considered when calculating the ammonia requirements for the reaction.

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

As the ratio of NO ₂ / NOx is lower, the purification rate also increases rapidly as the temperature of the SCR catalyst 10 increases, but when the ratio of NO ₂ / NOx is high, the purification rate at low temperature increases rapidly and is constant. When the temperature reaches 200 ° C, the maximum purification rate is kept stable.

This phenomenon can be seen that the ratio of NO ₂ / NOx and temperature are important factors of stoichiometry, reaction rate, and purification rate, and when HC is adsorbed on SCR catalyst 10, it hinders the purification reaction of NOx. Adsorption and desorption and oxidation should also be considered.

In addition, it is obvious that performance changes due to flow rate (space velocity) and catalyst aging should also be considered.

Summarizing the above characteristics, the following conclusion can be obtained.

It is necessary to study the rapid response at low temperature by adsorbing ammonia to the SCR catalyst 10 in advance, and in order to control the amount of ammonia adsorption, it is necessary to know the reaction amount correctly. Adsorption and desorption and oxidation reactions should also be considered.

In addition, the flow rate (space velocity) and the degree of catalyst aging must also be considered, and the NO ₂ / NO x ratio, stoichiometric ratio, and reaction rate are also important factors that determine the purification rate of NO x.

According to the characteristics of the SCR catalyst described above, the operation of accurately calculating the consumption amount of ammonia under various conditions and controlling the ammonia storage amount accordingly will be described in more detail as follows.

When the vehicle is running, the controller 18 detects general driving information including the temperature of the SCR catalyst 10, the flow rate of the exhaust gas, the concentration of NOx, the cumulative amount of ammonia, NO ₂ / NOx, and the aging degree. Next, the mass flow rate of NOx and the stoichiometric ratio (NH ₃ / NO x) are multiplied to calculate the ammonia stoichiometric ratio equivalent (S101).

The stoichiometric ratio (NH ₃ / NO x) is determined as a function of catalyst temperature, NO ₂ / NO x ratio, and aging degree.

  When the ammonia stoichiometric ratio equivalent is calculated as described above, the ammonia consumption is calculated by multiplying the ammonia equivalent calculated in S101 and the ammonia reaction rate (S102).

In addition, ammonia consumption is calculated by adding the ammonia storage amount controlled to the ammonia consumption calculated in S102 (S103), multiplying the ammonia required calculated in S103 by the molecular weight ratio (urea / NH ₃ ), and then calculating the result. The required amount of urea is calculated by dividing by the urea mass fraction in the urea water (S104).

According to the above procedure, if the required amount of the elements required to secure ammonia is calculated, the temperature of the SCR catalyst 10 measured by the temperature sensor 14 is detected (S105), and the temperature of the SCR catalyst 10 is the sprayable temperature, For example, it is determined whether the temperature of 200 ° C. or more, which is the lowest temperature at which NOx purification can be performed, is maintained (S106).

If it is not the condition of the sprayable temperature in the determination of S106, the control unit 18 is turned off by the injector operation of the dosing module 20 to maintain the state of the spray stop without the injection of the element (S111), If it is a condition, it is determined whether the required amount of urea has a value larger than the minimum sprayable amount (S107).

In the judgment of S107, if the amount of urea required is less than the minimum sprayable amount, the controller 18 stops urea injection (S111). If the amount of urea has a value greater than the minimum sprayable amount, the required amount of urea can be injected. It is determined whether the value is smaller than the maximum amount (S108).

If it is determined in S108 that the required amount of urea has a value smaller than the maximum sprayable amount, the controller 18 controls the injector of the dosing module 20 to inject the required amount of urea calculated in S104 (S109).

However, if it is determined in S108 that the required amount of urea has a value larger than the maximum sprayable amount, the controller 18 controls the injector of the dosing module 20 to execute the spraying of the urea at the maximum sprayable amount set (S110).

The maximum amount that can be sprayed is set as a limit value according to the hardware, the exhaust temperature and the flow rate of the dosing module 20, the temperature conditions of the catalyst, the value is changed according to the deviation.

3 is a flowchart illustrating a procedure for calculating an ammonia reaction rate.

The ammonia reaction rate applied to calculate the ammonia consumption in S102 of FIG. 2 is calculated as follows.

The reaction rate of ammonia and NOx is calculated from a function of catalyst temperature and exhaust gas flow rate, NOx concentration, ammonia cumulative storage amount, NO2 / NOx, high temperature exposure, HC adsorption amount (S201), catalyst temperature and exhaust gas flow rate, The reaction rate of ammonia and oxygen is calculated from a function of cumulative ammonia storage amount, NO2 / NOx, aging according to high temperature exposure, and HC adsorption amount (S202).

The reaction rate of ammonia and NOx calculated in S201 and the reaction rate of ammonia and oxygen calculated in S202 are calculated to calculate ammonia reaction rate (S203).

7 is a flowchart illustrating a procedure for determining an ammonia storage amount control value.

The ammonia storage control value applied to calculate the ammonia requirement in step S103 of FIG. 2 is calculated as follows.

The ammonia target storage amount is calculated from the function of the catalyst temperature, the exhaust velocity, the aging degree, and the HC adsorption amount (S301), and the difference value of the ammonia storage amount is calculated by differentially calculating the current accumulated storage amount from the calculated ammonia target storage amount (S302). ).

Thereafter, the ammonia storage amount control value is calculated from a function of the difference value of the ammonia storage amount calculated in S302 and the exhaust gas temperature, the flow rate of the exhaust gas, and the catalyst temperature (S303).

8 is a flowchart illustrating a procedure for calculating an ammonia storage amount.

The ammonia storage amount accumulated in the SCR catalyst 10 is calculated according to the current operating conditions (S401).

That is, the reaction amount of ammonia is calculated by applying the ammonia consumption according to the emission of NOx and the reaction rate of ammonia and oxygen.

The cumulative storage amount is calculated by calculating the difference in the ammonia reaction amount calculated in S401 from the cumulative storage amount to calculate the cumulative storage amount currently stored in the SCR catalyst 10 (S402).

Then, the new inflow amount generated by the injection of the element through the dosing module 20 is calculated (S403).

The new inflow amount is determined as a result calculated by dividing the result value calculated by multiplying the urea injection amount by the urea mass fraction.

Thereafter, the maximum storage amount that the SCR catalyst 10 can store is calculated as a function of the catalyst temperature, the exhaust gas flow rate, and the aging degree (S404), and the current saturation degree of the SCR catalyst 10 is calculated as the cumulative storage amount / maximum storage amount ( S405).

Then, the ammonia desorption amount is calculated in the SCR catalyst 10 (S406), and then the actual storage amount is calculated (S407).

The actual storage amount calculated in S407 is calculated as the difference of the desorption amount calculated in S406 from the result of adding the new storage amount calculated in S403 to the cumulative storage amount calculated in S402.

If the actual storage amount exceeds "0" (S408), if it is less than "0", it returns to the process of S401 and repeats the above-described operation, and the calculated value when the calculated actual storage amount exceeds "0" Is applied as a storage amount of ammonia (S409).

9 is a diagram illustrating a procedure for calculating the HC adsorption amount.

The reaction amount of HC is calculated by applying a function including the catalyst temperature, the exhaust gas temperature, and the aging degree to the adsorption amount of HC accumulated in the SCR catalyst 10 (S501), and the amount of HC accumulated in the SCR catalyst 10 is calculated. The cumulative amount of adsorption, which is a substantial amount of HC adsorption adsorbed on the SCR catalyst 10, is calculated by calculating the amount of reaction calculated in S501 from the amount of adsorption (S502).

In addition, the HC adsorption amount newly adsorbed to the SCR catalyst 10 is calculated by applying a function including the catalyst temperature, the exhaust gas flow rate, and the saturation rate to the HC inflow amount (S503), and the catalyst temperature, the exhaust gas flow rate, and the aging degree are calculated. A maximum HC adsorption amount that can be adsorbed to the SCR catalyst 10 is calculated by applying a function including the SCR (S504).

Thereafter, HC saturation in the SCR catalyst 10 is calculated from the relationship between the cumulative adsorption amount calculated in S502 and the maximum adsorption amount calculated in S504 (S505), and the catalyst temperature, The desorption amount of HC in the SCR catalyst 10 is calculated by applying a function including exhaust gas temperature and saturation (S506).

The actual HC adsorption amount is calculated by calculating the difference between the HC desorption amount calculated in S506 from the value obtained by adding the accumulated HC adsorption amount calculated in S502 and the new HC adsorption amount calculated in S503 (S507).

It is determined whether the actual HC adsorption amount calculated in step S507 exceeds "0" (S508). If the amount does not exceed "0", the process returns to step S501 and repeats the above-described step. HC adsorption amount calculated in the above is applied to determine the ammonia control amount control value (S509).

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.

FIG. 2 shows the injection of urea and the purification of catalyst immediately after engine start in a vehicle.

3 is a graph showing the relationship between the SCR catalyst temperature and the ammonia storage amount in a vehicle.

4 is a graph showing the NOx purification rate with temperature in a vehicle.

5 is a flowchart for performing urea injection amount control in a vehicle according to an embodiment of the present invention.

6 is a flowchart for performing ammonia reaction rate calculation in a vehicle according to an embodiment of the present invention.

7 is a flowchart for performing ammonia storage value control value calculation in a vehicle according to an embodiment of the present invention.

8 is a flowchart for performing ammonia storage amount calculation in a vehicle according to an embodiment of the present invention.

9 is a flowchart for performing HC adsorption amount calculation in a vehicle according to an embodiment of the present invention.

<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 (8)

delete 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; A dosing module for injecting an aqueous urea solution at the tip of the SCR catalyst; A temperature sensor detecting a temperature of the SCR catalyst; In the urea injection amount control apparatus of a vehicle comprising a control unit for determining the urea injection amount by predicting the ammonia consumption of the SCR catalyst, The control unit predicts ammonia consumption by applying ammonia consumption according to NOx emissions, ammonia storage amount, ammonia reaction rate, HC adsorption amount and high temperature exposure, and controls urea injection amount of a vehicle controlling ammonia storage amount according to the predicted value. Device. The method of claim 2, The control unit is a urea injection amount control device for calculating ammonia consumption according to the NOx emissions by applying the "NOx emissions × stoichiometric ratio (NH ₃ / NOx) × ammonia reaction rate". The method of claim 2, The control unit is a urea injection amount control device for calculating the ammonia storage amount by applying the "current storage amount" + "new inflow amount"-"consumption amount (reaction amount + desorption amount)". The method of claim 2, The control unit divides the reaction amount of ammonia into the reaction amount with NOx and the reaction amount with oxygen, and the reaction amount with NOx is calculated by applying the NOx purification rate and stoichiometric ratio reflecting the change of the specific gravity of the reaction path according to the change of exhaust conditions. Urea injection rate control device. Calculating the total ammonia consumption from the SCR catalyst by applying ammonia consumption, ammonia storage amount, ammonia reaction rate, HC adsorption amount and aging degree according to NOx emission; Calculating urea requirements by calculating ammonia requirements according to the calculated ammonia consumption; In the method for controlling the urea injection amount of a vehicle comprising detecting the temperature of the SCR catalyst and performing the urea injection of the required amount if the injection possible temperature, The ammonia reaction rate includes a reaction rate with NOx and a reaction rate with oxygen, The ammonia storage amount is calculated as "cumulative storage amount stored in the SCR catalyst" + "new inflow amount extracted from urea"-"ammonia consumption amount applied to the reaction amount and desorption amount". delete delete

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