KR20140137498A - Reductant injection volume control device of a vehicle and method of controlling the same - Google Patents

Abstract

The present invention relates to an injection control device for a vehicle reductant to purify exhaust gas suitable to an operational condition by controlling the amount of aqueous solution injection of a reductant by applying a selective catalytic reduction (SCR) reaction model combined with a numerical analysis and a chemical kinetics. The injection control device for a vehicle reductant comprises: an engine; an SCR catalyst to purify NOx with the reduction reaction of NOx and NH3 included in an exhaust gas; first and second NOx sensors to detect the end-to-end NOx concentration of the SCR catalyst; a dosing module to inject the aqueous solution of a reductant on the front end of the SCR catalyst; a temperature sensor to detect the temperature of the SCR catalyst; and a control unit to determine the operational condition determined by analyzing the amount of air, the number of revolutions of an engine, and the temperature of the exhaust gas and is determined by analyzing the informaiton on the first and second NOx sensors and the information on the temperature sensor in regards to the purification efficiency of NOx of the SCR catalyst, and to determine the amount of the aqueous solution injection of a reductant by calculating the amount of NH3 required for the SCR catalyst through the SCR reaction model in accordance to the NOx purification efficiency of the SCR catalyst. According to the characteristics of the present invention, the method to control the injection of a reductant comprises the following steps of: detecting the operational condition, the temperature of the SCR catalyst, and the purification efficiency of NOx; calculating the adsorption amount of NH3 in accordance to the operational condition and the NOx purification efficiency by applying the SCR reaction model; and determining the amount of the aqueous solution injection of a reductant in accordance to the adsorption amount of NH3.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method and apparatus for controlling a reducing amount of a reducing agent in a vehicle,

The present invention relates to an apparatus and method for controlling the injection amount of a reducing agent in a vehicle, and more particularly, to an apparatus and method for controlling the injection amount of a reducing agent by controlling an SCR (Selective Catalytic Reduction) reaction model combining numerical analysis and reaction kinetics, And an apparatus and method for controlling a reducing agent injection amount of a vehicle for purifying an appropriate exhaust gas.

Generally, diesel engine vehicles are classified into hazardous substances such as NOx, CO, THC, soot, Particulate Matters, etc. contained in the exhaust gas according to North American diesel Tier 2 BIN5 regulation or Euro 6 exhaust gas regulations. And a post-treatment apparatus for removing the post-treatment apparatus.

A post-treatment device mounted on a diesel vehicle is a DOC (Diesel Oxidation Catalyst) which is disposed in the exhaust pipe in the closest proximity to the engine and performs the NMHC conversion function, a particulate filter (PM) disposed downstream of the DOC and collecting particulate matters CPF (Catalyzed Particulate Filter), an SCR catalyst disposed downstream of the CPF, consisting of V2O5 / TiO2, Pt / Al2O3 or Zeolite, and purifying NOx through a reduction action.

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

The reduction reaction of NOx and NH3 is as follows.

NOx + NH3? N2 + H2O

In order to maintain the NOx purifying performance of the SCR catalyst at a certain level or more, a reducing agent aqueous solution is injected into the dosing module, and NH3 generated by the evaporation and decomposition of the reducing agent aqueous solution is obtained, .

Generally, increasing the injection amount of the reducing agent aqueous solution increases the NOx purification rate. However, when the reducing agent aqueous solution is injected at a certain amount or more, excessive formation of NH3 causes severe environmental pollution and odor.

The background of the invention is disclosed in U.S. Patent No. 6,427,439, wherein the purification of the exhaust gas is carried out by catalytically reducing nitrogen oxides, NOx. The addition of the reducing agent is controlled by an electronic engine controller, EEC, and the controller determines the amount of reducing agent to be added proportionally to the NOx concentration when the NOx concentration exceeds the predetermined value. When the NOx concentration is low and the amount of ammonia absorbed is less than the ammonia capacity of the catalyst, the amount of reducing agent added is a predetermined value. EEC uses signals from measurements of NOx concentration, NH3 concentration, temperature, engine speed and engine load to calculate the amount of NH3 adsorbed on the catalyst surface and the amount of reducing agent addition during the calculation period. However, this means that different measurements and calculations are involved in the vehicle in which the load of the engine increases and decreases periodically and rapidly.

Also, although many methods are known in the art for controlling the injection of reducing agent into the exhaust gas, it is still necessary to improve the NOx conversion by controlled injection of the reducing agent to prevent detrimental leaks of the reducing agent to the surrounding environment Do.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems and it is an object of the present invention to provide a reducing agent aqueous solution which is required to generate NH3 required for purifying NOx in an SCR catalyst by applying a numerical analysis and a reaction kinetics- The amount of the reducing agent to be injected is controlled so as to purify the exhaust gas suited to the operating conditions.

According to an aspect of the present invention, there is provided an apparatus for controlling a reducing agent injection amount of a vehicle, the apparatus comprising: an engine; An SCR catalyst for purifying NOx by a reduction reaction of NOx and NH3 contained in the exhaust gas; A first and second NOx sensor for detecting NOx concentrations between both ends of the SCR catalyst; A dosing module for spraying a reducing agent aqueous solution on the tip of the SCR catalyst; And a temperature sensor for detecting the temperature of the SCR catalyst, wherein the NOx purification efficiency of the SCR catalyst is determined by analyzing the information of the first and second NOx sensors and the temperature sensor information And a control unit for calculating an amount of NH 3 necessary for the SCR catalyst through the SCR reaction model according to the determined operating conditions and the NO x purification efficiency of the SCR catalyst to determine the amount of reducing agent aqueous solution injected.

The SCR reaction model is characterized in that numerical analysis and reaction kinetics are combined and set in a table according to the temperature condition of the SCR catalyst, the exhaust flow rate, the NOx concentration, and the NH3 concentration.

Also, a method of controlling a reducing agent injection amount of a vehicle according to an aspect of the present invention includes the steps of: detecting an operating condition, a temperature of an SCR catalyst, and a NOx purification efficiency; Calculating a NH3 adsorption amount according to the operating condition and the NOx purification efficiency by applying the SCR reaction model; And determining the amount of the reducing agent solution injected according to the adsorption amount of NH3.

And the reducing agent aqueous solution is any one of NH3 and Urea.

The NH3 adsorption amount is calculated by applying the NOx reduction characteristics according to the temperature of the SCR catalyst, the exhaust flow rate, the NOx concentration, and the NH3 concentration.

According to the apparatus and method for controlling the amount of reducing agent injected into a vehicle according to the present invention, an amount of the reducing agent aqueous solution required for generating NH 3 is determined and injected in the SCR catalyst, thereby maximizing the purification efficiency of NOx while minimizing the consumption of the reducing agent aqueous solution .

In addition, since the reducing agent aqueous solution is controlled at a realistic injection amount suitable for the engine conditions, there is an effect that the exhaust gas instability due to excessive or under-production of NH 3 is not generated.

1 is a schematic view of a reducing agent injection amount control apparatus for a vehicle according to an embodiment of the present invention,
FIG. 2 is a flowchart of a method for controlling a reducing agent injection amount in a vehicle according to an embodiment of the present invention;
FIG. 3 is a graph showing adsorption and desorption relations of NH 3 in an SCR catalyst of a vehicle according to an embodiment of the present invention;
4 is a graph showing the purifying performance of NOx by SCR catalyst temperature in a vehicle according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of an apparatus and method for controlling a reducing agent injection amount of a vehicle according to the present invention will be described in detail with reference to the accompanying drawings.

The embodiments of the present invention can be modified into various forms and the scope of the present invention should not be construed as being limited to the embodiments described in detail below.

In addition, the shape and the like of the elements in the drawings may be exaggerated in order to emphasize a clearer description, and detailed description of known functions and configurations that are considered to be unnecessarily obscured by the gist of the present invention will be omitted.

FIG. 1 is a schematic view of a reducing agent injection amount control apparatus for a vehicle according to an embodiment of the present invention, FIG. 2 is a flowchart for executing a reducing agent injection amount control in a vehicle according to an embodiment of the present invention, FIG. 4 is a graph showing the purifying performance of NOx by SCR catalyst temperature in a vehicle according to an embodiment of the present invention. FIG. 4 is a graph showing adsorption and desorption relations of NH3 in an SCR catalyst of a vehicle according to an embodiment.

1, the reducing agent injection amount control apparatus for a vehicle according to the present invention includes an engine 100 as a power source, an exhaust pipe 110 for exhausting burnt exhaust gas, an SCR catalyst 120, a first NOx sensor 130 A second NOx sensor 140, a temperature sensor 150, a controller 160, a dosing module 200, a reducing agent tank 300, and a pump 310.

The SCR catalyst 120 is disposed at a predetermined position of the exhaust pipe 110 connected to the engine 100 and is made of V2O5 / TiO2 or Pt / Al2O3 or Zeolite, and is made of NH3 (ammonia), Urea (urea, ) ≪ 2 >), the NOx is purified by the reduction reaction of NH3 and NOx, which is produced by the decomposition of the aqueous solution of the reducing agent.

The first NOx sensor 130 is disposed at an inlet side of the SCR catalyst 120 to detect the amount of NOx contained in the exhaust gas flowing into the SCR catalyst 120 and provides information on the detected NOx amount to the controller 160.

The second NOx sensor 140 is disposed at the outlet side of the SCR catalyst 120 to detect the amount of NOx contained in the exhaust gas purified by the reduction reaction of the SCR catalyst 120, to provide.

The temperature sensor 150 detects the temperature of the SCR catalyst 120 activated by the temperature of the exhaust gas and provides information on the detected temperature to the control unit 160.

The control unit 160 analyzes the information on the amount of air, the number of revolutions of the engine, and the exhaust gas temperature to analyze the operation conditions of the engine. The controller 160 controls the information of the first and second NOx sensors 130 and 140 and the information of the temperature sensor 150 The NOx purification efficiency of the SCR catalyst 120 according to the temperature is analyzed and the required NH3 amount of the SCR catalyst 120 is calculated by applying a SCR reaction model combining the numerical analysis and the reaction kinetics according to the operating conditions and the NOx purification efficiency .

Then, the injection amount of the reducing agent aqueous solution required is determined according to the amount of NH 3 necessary, and the injection of the reducing agent aqueous solution is controlled through the dosing module 200.

The control unit 160 controls the injection of the reducing agent aqueous solution by operating the dosing module 200 by outputting a PWM (Pulse Width Modulation) signal.

The reducing agent tank 300 accommodates a reducing agent aqueous solution for spraying on the tip of the SCR catalyst 120 according to the operating conditions and the pump 310 supplies the reducing agent aqueous solution supplied from the reducing agent tank 300 to the dosing module 200 So that a high pressure injection is provided when the dosing module 200 is operated according to the PWM signal.

The operation of controlling the injection amount of the reducing agent aqueous solution in the vehicle according to the present invention including the above-described functions will be described.

When the engine 100 of the vehicle is turned on, the controller 160 controls the operation of the engine 100 by integrating the information such as the amount of air, the number of revolutions of the engine, and the load (S10) The temperature of the SCR catalyst 120 is detected to determine whether the SCR catalyst 120 is activated (S20).

When the SCR catalyst 120 is activated, NOx concentrations at the upstream and downstream sides of the SCR catalyst 120 are detected (S30).

That is, the NOx purification efficiency of the SCR catalyst 120 is determined by analyzing the information of the first NOx sensor 130 disposed at the inlet side of the SCR catalyst 120 and the second NOx sensor 140 disposed at the outlet side.

The reaction modeling of the SCR catalyst 120 is as follows.

Adsorption of NH3 due to decomposition of the aqueous solution of the reducing agent is carried out as shown in Chemical Formula (1).

[Chemical Formula 1]

NH3 + S _ACID ? S _ACID NH3

The reaction between NH3 and NOx is represented by the general formula (2).

(2)

NO + NO ₂ + 2S _ACID NH ₃ → 2N ₂ + 3H ₂ O

4NO + O _{2 + 4S ACID NH 3 → 4N 2} + 6H 2 O

6NO ₂ + 8S _ACID NH ₃ → 7N ₂ +12 H ₂ O

Also, desorption of NH3 in the SCR catalyst 120 is performed as shown in Formula (3).

(3)

S _ACID NH3? NH3 + S _ACID

Then, the SCR reaction model combining the numerical analysis and the reaction kinetics is applied (S40), and the adsorption amount of NH3 is predicted according to the NOx purification efficiency of the SCR catalyst 120 determined in the current operating condition (S50).

The NH3 adsorption amount prediction is determined according to the temperatures of the SCR catalyst 120, the exhaust flow rate, the NOx concentration, and the NH3 concentration. The NH3 adsorption and desorption relations of the SCR catalyst 120 are shown in FIG. Respectively.

If the actual NH3 adsorption amount of the SCR catalyst 120 according to the current operating condition is predicted in S50, the amount of the reducing agent aqueous solution to be injected is determined in operation S60.

The amount of the reducing agent aqueous solution injected to the tip of the SCR catalyst 120 is such that the amount of NH 3 adsorbed by the S 50 is followed by applying a constant such that the aqueous solution of the reducing agent can be converted into NH 3.

The control unit 160 operates the dosing module 200 as a PWM signal so that the reducing agent aqueous solution is supplied to the tip of the SCR catalyst 120 To purify the exhaust gas suitable for the operating conditions.

Therefore, the SCR catalyst 120 enhances the purifying efficiency of NOx by reducing reaction with NOx under the condition that there is no slip or lack of NH3, and enhances the commerciality of the vehicle by eliminating the secondary pollution caused by the slip of NH3 .

FIG. 3 is a graph showing a comparison result of NOx purification performance predicted values and experimental values when the conditions of the SCR catalyst 120, the exhaust flow rate, the NOx concentration, and the NH3 concentration are set as shown in the following table.

SCR catalyst temperature (캜) Exhaust flow rate (kg / h) Shear NOx (ppm) NH3 / NOx 250 156 347 1.18 1.50 300 164 448 1.12 1.50 400 199 756 1.10

As shown in FIG. 4, it can be confirmed that the NOx purifying efficiency of the SCR catalyst 120 according to the injection of the reducing agent aqueous solution determined through the above procedure shows the same or similar characteristics as the predicted value and the experimental value.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be construed as limited to the particular details of the embodiments set forth herein. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.

100: engine 110: exhaust pipe
120: SCR catalyst 130: first NOx sensor
140: second NOx sensor 150: temperature sensor
160: control unit 200: dosing module
300: reducing agent tank 310: pump

Claims (5)

An engine 100;
An SCR catalyst 120 for purifying NOx by the reduction reaction of NOx and NH3 contained in the exhaust gas;
A first and second NOx sensor (130) (140) for detecting the concentration of NOx between both ends of the SCR catalyst (120);
An injection module (200) for injecting a reducing agent aqueous solution at the tip of the SCR catalyst (120);
And a temperature sensor (150) for detecting the temperature of the SCR catalyst (120)
The NOx purifying efficiency of the SCR catalyst 120 is determined by analyzing the information of the first and second NOx sensors 130 and 140 and the information of the temperature sensor 150 Further comprising a controller (160) for calculating an amount of NH3 necessary for the SCR catalyst (120) through the operating conditions and the SCR reaction model to determine the amount of the reducing agent solution injected. The method according to claim 1,
The SCR reaction model is set in a table according to the temperature condition, the exhaust flow rate, the NOx concentration, and the NH3 concentration of the SCR catalyst 120 by combining the numerical analysis and the reaction kinetics according to the NOx purification efficiency of the SCR catalyst 120 The amount of reducing agent injected into the vehicle. The NOx purifying efficiency of the SCR catalyst 120 is determined by analyzing the information of the first and second NOx sensors 130 and 140 and the information of the temperature sensor 150 Detecting the operating conditions, the temperature of the SCR catalyst 120, and the NOx purifying efficiency;
Calculating an NH3 adsorption amount according to an operating condition and an NOx purification efficiency by applying an SCR reaction model;
Determining an injection amount of the reducing agent aqueous solution according to the adsorption amount of NH3;
Wherein the reducing agent injection amount control method comprises the steps of: The method of claim 3,
Wherein the reducing agent aqueous solution is one of NH3 and Urea. The method of claim 3,
Wherein the NH3 adsorption amount is calculated by applying a NOx reduction characteristic according to a temperature, an exhaust flow rate, an NOx concentration, and an NH3 concentration of the SCR catalyst (120).

Images