KR100993364B1 - System for control urea injection quantity of vehicle and method thereof - Google Patents

Abstract

According to the present invention, a vehicle equipped with a Selective Catalytic Reduction (SCR) catalyst controls the amount of ammonia stored in advance by predicting a change in catalyst operating conditions, thereby providing a preliminary response to changes in exhaust conditions to provide an improvement in performance of the SCR catalyst. will be.

The present invention is a process for determining the control condition by calculating the ammonia storage control temperature, the process of determining the target ammonia storage amount according to the control conditions, extract the difference value between the target storage amount and the current accumulated storage amount and exhaust gas temperature, flow rate and catalyst temperature The process of determining the ammonia storage control value by applying the conditions of the.

SCR catalyst, urea, ammonia (NH3), dosing module, injection rate control, preliminary prediction

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 an SCR (Selective Catalytic Reduction) catalyst. More particularly, the present invention relates to an SCR catalyst by providing a preliminary response to changes in exhaust conditions by controlling the amount of ammonia stored in advance by predicting changes in catalyst operating conditions. An apparatus and method for controlling urea injection amount of a vehicle that provides an improvement in performance.

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.

Reduction of ammonia (NH ₃ ) NO x is the same as in formula (1).

2NH ₃ + 2O ₂ → N ₂ O + 3H ₂ O

4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O

4NH ₃ + 5O ₂ → 4NO + 6H ₂ O

In order to maintain the NOx purification performance of the SCR catalyst to a certain level or more, 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 is injected. And maintain the storage amount of ammonia inside 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 generation amount of NOx and the ratio of ammonia (NH ₃ ) / NOx in the running state, calculates the amount of urea according to the required amount of ammonia, and then The injector of the dosing module, which takes a constant pressure and a pressure of about 5 bar, is operated by the operation of the pump installed therein to inject the calculated amount of urea.

Another method is to calculate the required amount of ammonia according to the storage amount of ammonia in the SCR catalyst, calculate the amount of urea according to the required amount of ammonia, and then apply a constant pressure, about 5 bar, by the operation of a pump installed in the urea tank. The injector of the module 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, by using a fixed target storage amount, it does not effectively cope with the case that the exhaust conditions are greatly changed, and thus there is a disadvantage that the optimum control for the production and utilization of ammonia is not achieved.

The present invention has been made to solve the above problems, and its object is to provide a preliminary response to changes in exhaust conditions by controlling the amount of ammonia stored in advance by predicting changes in operating conditions of the SCR catalyst.

In addition, by separately calculating the temperature for controlling the storage amount in addition to the temperature of the SCR catalyst, to control the ammonia storage amount according to the storage amount temperature to improve the low temperature performance and the suppression of the high temperature slip amount.

Device for controlling the urea injection amount of a vehicle according to a feature of the present invention for achieving the above object, the 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 controlling the urea injection amount through the dosing module by calculating the storage amount control temperature for predicting the change in the catalyst operating conditions in addition to the catalyst temperature.

In addition, the method for controlling the amount of urea injection of a vehicle according to an aspect of the present invention includes the steps of: calculating ammonia requirement according to ammonia consumption in the SCR catalyst, and estimating the urea requirement accordingly; If the temperature of the SCR catalyst is a sprayable temperature and the calculated urea requirement is less than the set maximum sprayable amount, providing injection of the urea required amount; If the temperature of the SCR catalyst is below the sprayable temperature or the required amount of urea is below the set minimum sprayable amount, the urea spraying step is not performed.

In addition, the method of controlling the urea injection amount of a vehicle according to an aspect of the present invention, the process of determining the control condition by calculating the ammonia storage amount control temperature; Determining an ammonia target storage amount according to the control condition; Extracting a difference value between the target storage amount and the current accumulated storage amount, and determining the ammonia storage amount control value by applying the conditions of the exhaust gas temperature, the flow rate, and the catalyst temperature.

By the above-described configuration, the present invention improves the NOx purification performance at low temperature conditions by controlling the storage amount of ammonia by predicting the operating conditions of the SCR catalyst in advance, and providing the emission stabilization by suppressing the slip amount of ammonia at high temperature conditions. The effect is expected.

In addition, it improves the responsiveness to rapid changes in exhaust conditions, provides an improvement in performance against consumption of ammonia, and cost reduction is expected due to the volume reduction due to the increased utilization of the SCR catalyst.

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 analyzes the operating conditions of the engine 2 and the exhaust gas temperature, the information of the first and second NOx sensors 12 and 14, and the information of the temperature sensor 16 to analyze the ammonia of the SCR catalyst 10. Calculate the consumption amount to calculate the required amount of ammonia, and determine the injection amount of the urea according to the required amount of ammonia to control the injection of the urea through the dosing module 20.

The controller 18 controls the urea injection amount through the dosing module 20 by calculating a storage control temperature for predicting the change of the catalyst operating condition in advance in addition to the current catalyst temperature in order to consider the change of the catalyst operating condition.

The calculation of the temperature for controlling the ammonia storage amount predicts the temperature of the SCR catalyst 10, calculates the temperature change rate from the difference between the predicted temperature and the actual temperature of the catalyst, calculates the amplification rate according to the magnitude and continuity of the temperature change, The temperature for controlling the storage volume is determined from the predicted catalyst temperature and the temperature change amplification rate.

The control unit 18 actively controls the storage amount of ammonia in accordance with the conditions of the temperature, increases the storage amount of ammonia under conditions favorable for the generation / storage of ammonia when the possibility of temperature drop is high to improve the low temperature performance, The amount of ammonia is reduced beforehand when the possibility of temperature increase is large for slip amount control.

The controller 18 predicts the temperature of the SCR catalyst 10 from the temperature change rate, calculates an amplification rate according to the magnitude and continuity of the temperature change, and calculates a storage volume control temperature from the predicted catalyst temperature and the temperature change amplification rate. .

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, thus optimally mixing 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.

FIG. 6 is a diagram illustrating the injection reaction characteristics of urea and catalyst purification immediately after starting an engine in a vehicle.

As shown, when a certain amount, for example, 200 g / h of urea is injected immediately after starting the engine, does not represent the final NOx emission immediately after the injection, and as shown in the "A" area, the NOx emission is continuously maintained for a certain time. It shows a decreasing pattern.

This phenomenon can be seen that a certain amount of ammonia should be adsorbed for the reaction of NOx inside the SCR catalyst 10, the time required for stabilization takes longer at low temperatures with a large amount of ammonia adsorption, on the contrary Because the adsorption amount of ammonia 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.

FIG. 7 is a view illustrating the injection of urea in a vehicle and the change of NOx emissions before and after the SCR.

In the drawing, section (a) shows the change of NOx emissions before and after the SCR catalyst 10 when the urea is injected. When the temperature of the SCR catalyst 10 is lower than 200 ° C., the NOx is reduced despite the urea injection. Although not properly purified, it can be seen that NOx begins to be purified at a temperature of about 200 ° C.

And, in the section (b), the injection of urea was not carried out, but in the section (a), it can be seen that NOx is purified by the ammonia stored on the SCR catalyst 10, and the SCR catalyst ( It can be seen that the difference between the front and rear NOx amounts in 10) decreases and finally becomes the same as the section (c).

Therefore, when a predetermined amount of ammonia is adsorbed to the SCR catalyst 10, it can be confirmed that NOx can be purified without a delay time.

FIG. 8 is a diagram illustrating the change of urea injection in the cold start condition of the vehicle and the NOx emission before and after the SCR. Even if the urea is pre-injected at a temperature of 200 ° C. or less immediately after the cold start, the purification performance can be seen. none.

FIG. 9 is a view showing the change of NOx emission before and after the SCR in the hot start state after the adsorption of ammonia in the late stage of cold start of the vehicle, and it can be seen that the purification of NOx occurs even below 200 ° C. .

These results indicate that the formation of ammonia and the catalytic reaction activity increase with increasing temperature. Adsorption of ammonia on the SCR catalyst 10 in advance, but pre-adsorption of ammonia at a high temperature of 200 ° C. or higher, purifies the NOx. In particular, it can bring about improved performance at low temperatures.

FIG. 10 is a diagram illustrating slip of ammonia in a hot start condition of a vehicle, in which ammonia is pre-adsorbed to provide a performance improvement for NOx purification of the SCR catalyst 10 immediately after engine start, but the temperature is increased. As a result, a large amount of ammonia slip was generated as shown in the "B" region.

This is because the storage capacity of ammonia decreases as the temperature of the SCR catalyst 10 increases.

Therefore, in order to prevent ammonia slip due to the temperature increase, it is necessary to appropriately limit the ammonia storage amount, which is not only the temperature increase due to the driver's intention, but also when the engine control means artificially raises the temperature for regeneration of the DPF in the DPF + SCR system. It also corresponds to

As described above, the characteristics of the SCR catalyst can be summarized. In the case of adsorbing ammonia in advance, responsiveness to NOx purification can be accelerated, and the low temperature performance can be improved by adsorbing ammonia at a high temperature in advance.

In addition, ammonia generation proceeds at a high temperature as much as possible, and in particular, it is not to be carried out at an operating temperature of 200 ° C. or lower, and the amount of ammonia adsorption decreases at higher temperatures, so that the amount of storage at elevated temperature is reduced to prevent ammonia slip problems.

The operation of controlling the storage amount of ammonia by predicting a change in operating conditions of the catalyst according to the basic characteristics of the SCR catalyst as described above 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. (S101).

Thereafter, the mass flow rate of NOx, the NOx purification rate, and the stoichiometric ratio are multiplied to calculate the consumption amount of ammonia (NH ₃ ) (S102), and the required amount of ammonia consumption and the ammonia storage amount are calculated to calculate the required amount of ammonia (S103). .

The purification rate of NOx is estimated from f {catalyst temperature, exhaust gas flow rate, NOx concentration, ammonia cumulative storage amount, NO ₂ / NOx, aging degree}, and stoichiometric ratio (NH ₃ / NOx ratio) is f {catalyst temperature , NO2 / NOx, aging degree}.

The calculated amount of ammonia is multiplied by the molecular weight ratio {urea / NH ₃ }, and then the required amount of urea is calculated by dividing the result by the urea mass fraction in urea (S104).

When the required amount of the elements necessary to secure ammonia is calculated as described above, the temperature of the SCR catalyst 10 measured by the temperature sensor 14 is higher than the sprayable temperature, for example, 200 ° C. or more, which is the minimum temperature at which the purification of NOx can be performed. It is determined whether to maintain the temperature (S105).

If it is not the condition of the sprayable temperature in the determination of S105, 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 (S110), If the condition, it is determined whether the required amount of the element has a value larger than the minimum sprayable amount (S106).

If it is determined in S106 that the amount of urea required is smaller than the minimum sprayable amount, the control unit 18 stops urea injection (S110). If the amount of urea required is higher than the minimum sprayable amount, the urea required amount can be injected. It is determined whether the value is smaller than the maximum amount (S107).

If it is determined in S107 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 (S108).

However, if it is determined in S107 that the required amount of urea has a value greater 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 (S109).

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.

In addition, the operation of calculating the ammonia storage amount control value will be described with reference to FIG. 3.

The control unit 18 calculates the temperature for controlling the ammonia storage amount (S201) and determines whether the active control temperature condition (S202).

The calculation of the temperature for controlling the ammonia storage amount predicts the temperature of the SCR catalyst 10, calculates the temperature change rate from the difference between the predicted temperature and the actual temperature of the catalyst, calculates the amplification rate according to the magnitude and continuity of the temperature change, The temperature for the stock control is determined from the predicted catalyst temperature and the rate of change in temperature change.

In the determination of S202, if the active control temperature condition, the ammonia storage amount is determined as the active control target storage amount (S203), and if the active control temperature condition is not determined, the ammonia storage amount is determined as the passive control target storage amount (S204).

The ammonia target storage amount is determined as a function of f {temperature for storage control, exhaust gas flow rate, aging degree}.

When the control condition for ammonia storage is determined according to the temperature of the SCR catalyst 10 as described above, the difference value of the storage amount is calculated by calculating the difference of the accumulated storage amount from the target value of the storage amount (S205), and then controlling the difference value of the ammonia storage amount. Determined by the value (S206).

In the process of determining the control value of the ammonia storage amount, the conditions of the exhaust gas temperature, the exhaust flow rate, and the catalyst temperature may be further included.

Referring to Figure 4 describes the procedure for calculating the ammonia storage amount as follows.

Calculate the actual storage amount by calculating the consumption amount of ammonia consumed according to the current operating conditions from the ammonia storage amount accumulated in the SCR catalyst 10 (S301), and the new generated by the injection of urea through the dosing module 20 Calculate the flow rate into (S302).

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.

Then, the maximum storage amount that the SCR catalyst 10 can store is calculated as a function of catalyst temperature, exhaust gas flow rate, and aging degree (S303), and the current saturation degree of the SCR catalyst 10 is calculated as cumulative storage amount / maximum storage amount ( S304).

Then, the ammonia desorption amount is calculated in the SCR catalyst 10 (S305), and the current cumulative storage amount is calculated (S306).

The cumulative storage amount is calculated as a result of the difference calculation of the desorption amount calculated in S305 from the result of adding the new inflow amount calculated in S302 to the actual storage amount calculated in S301 (S306).

Then, it is determined whether the cumulative storage amount is "0" or less (S307). If it is "0" or less, it is determined that ammonia is not currently stored in the SCR catalyst 10 (S308).

However, if the calculated cumulative storage amount has a value larger than the maximum value that the SCR catalyst 10 can store, it is determined that the storage amount of ammonia maintains the maximum value (S309) (S310).

Referring to FIG. 5 with respect to the above operation is as follows.

The ammonia storage target is not zero in the non-injection section (1) in which the temperature of the SCR catalyst 10 is maintained at 200 ° C or lower, which is the activation reference temperature, because the ammonia is stored by spraying urea in advance.

Therefore, by setting the storage amount target to a desired amount using a combination of the actual temperature and the temperature for the storage amount control, a preliminary response to changes in the exhaust gas is provided.

As the storage control temperature is lower, the injection volume is further increased, and as the temperature is increased, the injection volume is reduced.

Accordingly, the ammonia generation performance and the performance of the SCR are improved at higher temperatures, and the ammonia storage capacity is deteriorated at higher temperatures.

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

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

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

5 is a diagram illustrating a storage amount control step for each temperature region in a vehicle according to an exemplary embodiment of the present invention.

FIG. 6 is a diagram illustrating the injection reaction characteristics of urea and catalyst purification immediately after starting an engine in a vehicle.

FIG. 7 is a view illustrating the injection of urea in a vehicle and the change of NOx emissions before and after the SCR.

FIG. 8 is a diagram illustrating changes of urea injection and NOx emissions before and after SCR in a cold start condition of a vehicle.

FIG. 9 is a diagram illustrating changes of urea injection and NOx emissions before and after SCR in a hot start condition of a vehicle.

<Explanation of symbols for 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; 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, A control unit for controlling the urea injection amount through the dosing module by calculating a storage control temperature for predicting a change in the catalyst operating condition in addition to the catalyst temperature; Urea injection amount control device of a vehicle comprising a. The method of claim 1, The controller predicts the temperature of the SCR catalyst, calculates the temperature change rate from the difference with the actual temperature of the catalyst, calculates the amplification rate according to the magnitude and continuity of the temperature change, and controls the storage amount from the predicted catalyst temperature and the temperature change amplification rate. Urea injection amount control device for calculating the temperature. The method of claim 1, The control unit is a urea injection amount control device of the vehicle for controlling the slip amount by increasing the storage amount of ammonia in the temperature lowering conditions, and reduces the storage amount of ammonia at high temperature. Calculating ammonia requirements according to ammonia consumption in the SCR catalyst and estimating urea requirements accordingly; Determining whether the temperature of the SCR catalyst is a sprayable temperature; Providing urea injection if the temperature of the SCR catalyst is injectable and the calculated urea requirement is less than the set maximum injection possible; Urea injection is not performed if the temperature of the SCR catalyst is below the sprayable temperature or the required amount of urea is less than the set minimum sprayable amount; Urea injection amount control method of a vehicle comprising a. Determining a control condition by calculating an ammonia storage control temperature; Determining an ammonia target storage amount according to the control condition; Determining ammonia storage control value by extracting a difference value between a target storage quantity and a current accumulated storage quantity and applying conditions of an exhaust gas temperature, a flow rate, and a catalyst temperature; Urea injection amount control method of a vehicle comprising a. The method of claim 5, The ammonia target storage amount is, Calculating a cumulative storage amount stored in the SCR catalyst, calculating a new inflow amount extracted from the urea, and calculating a maximum storage amount of the SCR catalyst; Calculating the saturation of the SCR catalyst, calculating the desorption amount of ammonia, calculating the actual cumulative storage amount, and then determining the target ammonia storage amount; Urea injection quantity control method of a vehicle.

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