JP5165500B2 - Selective catalytic reduction control system and method - Google Patents

Description

  The present invention relates to selective catalytic reduction (SCR) catalyst control and, more particularly, to control of a vehicle engine SCR catalyst.

  A selective catalytic reduction (SCR) catalyst removes the most abundant and polluting nitrogen oxides (NOx) of exhaust gases by a chemical reaction between the exhaust gas, the reducing agent and the catalyst.

Control of the selective catalytic reduction (SCR) catalyst is performed by injecting a predetermined amount of reducing agent, typically urea. Urea is also known as carbamide ((NH2) 2CO), which is water, oxygen, and decomposes into ammonia (NH ₃₎ and carbon dioxide in a state where heat is present. Ammonia then reacts with NOx gas to generate nitrogen and water. The amount of reductant injected needs to maximize the NOx conversion efficiency and at the same time keep excess NH ₃ , also known as NH ₃ slip, at a low value. SCR catalysts have been mainly introduced in heavy vehicles. In heavy vehicles, high levels of NOx exist and steady state is considered the main operating condition. In these states, the SCR control supplies NH ₃ at a predetermined ratio with respect to NOx. This is usually mapped as a function of speed and load.

When this type of control is applied to a passenger car that has a high frequency of transients, it usually requires a specific transient correction. Furthermore, in many cases, heavy vehicles use vanadium-based catalysts, and this technique uses the buffer effect (which temporarily stores NH ₃ ) in passenger car (light vehicle) applications. Lower than zeolite based catalysts (Fe, Cu).

Another possible way to control the SCR catalyst is to model the chemical behavior of the catalyst and run this model in an engine control unit (ECU). This method requires a large amount of calibration work to identify all parameters that need to be considered in the chemical model. Furthermore, the computational load required by this method is very high, as is required to calculate a number of complex chemical reactions that occur where the catalyst is sliced along its length. The chemical reaction at the catalyst is determined by the temperature of the catalyst and the concentration of various compounds. Catalyst temperatures and compound concentrations vary along the length of the catalyst, especially during transient conditions. Thus, to obtain an accurate model of all reactions at the catalyst, calculations are required to model several series of slices. Normally, closed loop control of such a system is performed by placing NOx sensors before and after the SCR catalyst. These sensors also respond to NH _3, therefore, generate difficulties additional to consider the closed-loop control.

German Patent DE102005012568 discloses a device and method for removing nitrogen oxides from the exhaust of an internal combustion engine. Agglomerates containing a reducing agent are added to the exhaust depending on variables such as engine load, air-fuel ratio, and engine speed.
German patent DE102005012568

  SUMMARY OF THE INVENTION The present invention relates to a selective catalytic reduction (SCR) catalyst control system and method, and more particularly to a vehicle emission SCR catalyst control system and method.

According to a first aspect of the present invention, there is provided a selective catalytic reduction (SCR) catalyst control system for an engine having an SCR catalyst, comprising:
Nitrogen oxide (NOx) engine emission determining means for determining the NOx engine emission value;
Urea control means capable of supplying a predetermined amount of urea to the SCR catalyst;
NOx efficiency target means for determining a target value of stored ammonia (NH ₃ ) in the SCR catalyst based on the required NOx efficiency and the SCR catalyst temperature determined by the SCR catalyst temperature determination means;
An SCR catalyst model that determines a stored NH ₃ value in the SCR catalyst based on a NOx engine emission value, an SCR catalyst temperature, an amount of urea supplied to the SCR catalyst, and a predetermined conversion efficiency of NOx gas;
Storage NH ₃ compares the storage NH ₃ value in the target value and the SCR catalyst further comprises a differential determination means for determining a storage NH ₃ differential,
The urea control means is provided with a system that determines the amount of urea that needs to be supplied to the SCR catalyst based on the stored NH ₃ differential.

  Preferably, the NOx ratio calculating means receives the first temperature value from the first temperature sensor and calculates the NOx ratio according to the first temperature value.

  Preferably, the first temperature sensor measures an oxidation catalyst temperature.

  In another aspect, the first temperature sensor measures the particulate filter temperature.

  In another aspect, the first temperature sensor measures a first temperature value between the particulate filter and the oxidation catalyst.

  Preferably, the NOx engine emission determining means is a model of NOx flowing out from the engine.

  Preferably, the engine spill NOx model calculates a NOx engine emission value based on the amount of fuel injected into the engine, engine load, exhaust gas recirculation (EGR) rate, and ambient temperature.

  In another aspect, the NOx engine emission determination means is a NOx sensor positioned upstream of the SCR force and provides a NOx engine emission value.

Preferably, the NOx efficiency target means further includes a sensor that measures one or more parameters of parameters such as engine speed, engine load, air temperature, coolant temperature, or diesel particulate filter (DPF) regeneration mode. Is used to determine the target value of stored ammonia (NH ₃ ) for the SCR catalyst.

Preferably, the SCR model calculates the amount of SCR catalyst based on the physical properties of the SCR catalyst and the SCR catalyst temperature, and takes into account the value of the stored NH ₃ of the SCR catalyst, so that the amount of NH ₃ leaving the SCR catalyst. The NH ₃ slip value representing is determined.

Preferably, including NH ₃ slip control means and NOx engine emission increasing means,
If NH ₃ slip value may be is determined higher than a predetermined value or NH ₃ slip value is expected to rise above a predetermined value, the NOx engine emissions increasing means, in a direction to increase the NOx engine emissions Operates, thereby reducing NH ₃ slip.

  Preferably, the NOx engine emission increasing means is exhaust gas recirculation (EGR) means and increases NOx engine emission by reducing or stopping the amount of EGR to the engine.

  Preferably, the system includes SCR model changing means.

Preferably, the SCR model changing means includes an NH ₃ sensor capable of measuring an actual NH ₃ slip from the SCR catalyst, means for averaging the actual NH ₃ slip, means for averaging the NH ₃ slip value of the SCR model, A comparison means for comparing the outputs from the NH ₃ slip average means and the SCR model NH ₃ slip value average means to determine an NH ₃ slip approximate value error, and the NH ₃ slip approximate value by the SCR model changing means. Change according to the error.

Preferably, the SCR model changing unit can change the SCR model by changing a predetermined conversion efficiency of NOx gas based on an NH ₃ slip approximate value error.

In another aspect, the SCR model changing means can change the SCR model by changing the SCR catalyst capacity based on the NH ₃ slip estimate error.

Preferably, the SCR model changing means changes the SCR model by changing the SCR catalyst capacity when the SCR catalyst is filled with a predetermined minimum amount of NH ₃ for a predetermined time.

According to a second aspect of the invention, in a method for selective catalytic reduction (SCR) control of an engine having an SCR catalyst,
(I) determining a nitrogen oxide (NOx) engine emission value;
(Ii) controlling the amount of urea supplied to the SCR catalyst;
(Iii) measuring the SCR catalyst temperature from the SCR catalyst;
(Iv) determining the stored ammonia (NH ₃ ) target value of the SCR catalyst based on the target NOx conversion efficiency and the SCR catalyst temperature;
(V) calculating a NOx ratio which is a ratio of nitrogen dioxide in the NOx engine emission value;
(Vi) Using the SCR catalyst model, calculate the stored NH ₃ value of the SCR catalyst based on the NOx engine emission value, the SCR catalyst temperature, the urea supply amount to the SCR catalyst, the NOx ratio, and the predetermined conversion efficiency of the NOx gas. And a process of
(Vii) comparing the value of the storage NH ₃ target value and the SCR catalyst storage NH _3, and the step of determining a storage NH ₃ differential,
Step (ii) provides a method in which the required urea feed to the SCR catalyst is controlled based on the stored NH ₃ differential.

  Preferably, the step of calculating the NOx ratio includes a step of measuring the first temperature value from the first temperature sensor and a step of calculating the NOx ratio according to the first temperature value.

  Preferably, the first temperature value is an oxidation catalyst temperature value.

  In another aspect, the first temperature value is a particulate filter temperature.

  In yet another aspect, the first temperature value is measured between the particulate filter and the oxidation catalyst.

  Preferably, step (i) includes calculating (NOx) engine emission values based on an engine spill NOx model.

  Preferably, the step of calculating the (NOx) engine emission value is an engine effluent NOx model, taking into account the injected fuel flow to the engine, the engine load, the exhaust gas recirculation (EGR) rate, and the ambient temperature.

  In another aspect, step (i) includes measuring a NOx engine emission value from a NOx sensor positioned upstream of the SCR catalyst.

Preferably, step (iv) further determines engine speed, engine load, air temperature, coolant temperature, or diesel particulate filter (DPF) regeneration to determine the target value of stored ammonia (NH ₃ ) on the SCR catalyst. Measuring one or more parameters such as mode.

Preferably, step (vi) further calculates the SCR catalyst capacity in the SCR model based on the physical properties of the SCR catalyst and the SCR catalyst temperature, and takes into account the value of stored NH ₃ in the SCR catalyst. Determining a NH ₃ slip value representative of the amount of NH ₃ exiting the SCR catalyst.

Preferably, the method includes the steps of controlling NH ₃ slip and increasing NOx engine emissions,
If the NH ₃ slip value is expected to be higher than or higher than the predetermined value, NOx engine emissions are increased, thereby reducing the NH ₃ slip.

  Preferably, increasing NOx engine emissions includes reducing or stopping the amount of exhaust gas recirculation (EGR) to the engine.

  Preferably, the method includes a step of changing the SCR model used in step (vi).

Preferably, the step of changing the SCR model includes measuring an actual NH ₃ slip using an NH ₃ sensor from the SCR catalyst, calculating an SCR model NH ₃ slip from the SCR model, and an actual NH ₃ A step of averaging the slip over a predetermined time, a step of averaging the SCR model NH ₃ slip over the same predetermined time, a step of comparing the averaged actual NH ₃ slip with the averaged SCR model NH ₃ slip When, and a step of determining the NH ₃ slip approximation errors, greatly modify the SCR model according NH ₃ slip estimate errors.

Preferably, the step of changing the SCR model changes the SCR model by changing a predetermined conversion efficiency of NOx gas based on an NH ₃ slip approximate value error.

In another aspect, the step of changing the SCR model changes the SCR model by changing the SCR catalyst capacity based on an NH ₃ slip estimate error.

Preferably, the step of changing the SCR model changes the SCR model by changing the SCR catalyst capacity when the SCR catalyst is filled with a predetermined minimum amount of NH ₃ for a predetermined time.

  According to a third aspect of the invention, there is provided a diesel engine incorporating a selective catalytic reduction (SCR) catalyst control system according to the first aspect of the invention.

  Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings.

As explained above, in order to inject an accurate amount of urea, it is necessary to know the NOx flow flowing out of the engine. When urea is too low can reduce efficiency, NH ₃ slip occurs if too large. Prior art systems use a NOx sensor located upstream of the SCR catalyst.

The present invention calculates the NOx conversion efficiency of the SCR catalyst using a simplified model and determines the amount of urea injection required to maintain this efficiency at a predetermined level. This model can take into account several important parameters listed below. These parameters include
Total NOx flow rate and NO2 / NOx ratio entering the SCR catalyst;
SCR catalyst temperature; and SCR catalyst storage NH ₃ .

  The total NOx flow rate can be measured by a NOx sensor disposed in front of the SCR.

  In another aspect, a NOx model can be used in place of the NOx sensor, as used in the preferred embodiment of the present invention. The NOx flow is modeled as a fraction of the injected fuel flow. This quantity is mapped as a function of engine load (IMEP (indicated mean effective pressure)) corrected for inert EGR (exhaust gas recirculation) rate and ambient temperature. FIG. 1 shows a comparison between modeled NOx and measured NOx using a passenger car US city cycle called FTP75 or EPAIII.

Referring now to FIG. 2, open-loop model for the selective catalytic reduction control device 10 of the engine exhaust system includes an engine outlet NOx model 12, the NO2 / NOx ratio model 14, storage and NOx conversion efficiency of NH ₃ SCR model 16 that models the NOx, NOx efficiency target model 18, and urea injection control device 20.

  As described above, the engine outflow NOx model 12 uses the injected fuel flow and calculates the NOx emission in consideration of the engine load, the EGR rate, and the ambient temperature.

  The NO2 / NOx ratio model 14 calculates the NO2 / NOx ratio based on the measured value of the temperature from the oxidation catalyst of the exhaust system. However, the measured value of temperature may be a value measured at another location in the exhaust system. Specifically, the temperature may be measured between the oxidation catalyst and the particulate filter, and in some cases may be measured behind the particulate filter. Further, the particulate filter affects the NO2 / NOx ratio and can therefore be taken into account in the NO2 / NOx ratio model 14.

The SCR model 16 calculates the NOx conversion efficiency of the SCR in the exhaust system based on a function of the stored SCR NH ₃ , the urea injection amount from the urea injection control device 20, and the temperature. This efficiency is then corrected for the NO2 / NOx ratio obtained from the NOx ratio model 14. When the NOx conversion efficiency is known, the amount of NH ₃ used for NOx reduction can be calculated based on the predetermined NH ₃ amount required for the reduction of a predetermined amount of NOx. In this way, the amount of stored NH ₃ is calculated and the output of extra NH ₃ (NH ₃ slip) or NOx gas is calculated. Since the storage capacity of the SCR catalyst decreases with temperature, a predetermined amount of stored NH ₃ is released if the temperature rise of the SCR is too fast. The maximum storage capacity of NH ₃ of the SCR catalyst is calculated as a function of the SCR temperature. Thus, NH ₃ leaving the SCR (NH ₃ slip) is also the output of the SCR model 16. This provides a means for comparing the SCR model 16 with an NH ₃ sensor located downstream of the SCR catalyst (discussed in more detail below for closed loop control).

The NOx efficiency target model 18 generates a target value for stored NH ₃ . The NOx conversion efficiency is determined by the storage NH ₃ in the SCR catalyst based on the required NOx efficiency and the SCR temperature. If appropriate for the system, the target NOx efficiency is then corrected for other conditions including engine speed, engine load, air temperature, coolant temperature, and diesel particulate filter (DPF) regeneration mode. An example of NOx efficiency for stored NH ₃ is shown in FIG.

Then, the target storage NH ₃ value from the NOx efficiency target model 18, as compared to the calculated stored NH ₃ value, to generate the stored NH ₃ differential (storedNH ₃ differential) 22. This is the difference between the current storage NH ₃ and the demand NH ₃ (target storage NH ₃ ).

The urea injection control device 20 has as its input an exhaust gas temperature value measured directly from the stored NH ₃ differential 22 and the exhaust gas. Based on the NH ₃ differential 22, a proportional gain control device is used to calculate the urea injection amount, and the calculated stored NH ₃ value becomes the target stored NH ₃ value. Considering the oxidation of NH ₃ at high temperature and / or the fact that urea at low temperature does not hydrolyze, the urea injection amount is changed as a map function of the exhaust gas temperature.

When NH ₃ slip occurs, the amount of NH ₃ leaving the SCR can be reduced by increasing the NH ₃ consumption rate in the SCR. To do this, the SCR NOx flow needs to be increased. This is because NH ₃ reacts with NOx. In this example, and as shown in FIG. 4, the increase in NOx flow is accomplished by quenching the EGR. The SCR temperature 30 is shown to increase from about 200 ° C to about 300 ° C. If no action is taken, that is, if the EGR remains in the normal state, the NOx emission flowing out of the engine remains at about 40 ppm (parts per million), but the NH ₃ slip 34 is dramatically increased to over 100 ppm. To rise. This saturates the sensor used. Conversely, when the EGR is extinguished, the NOx emission 36 from the engine increases to about 100 ppm, but the NH ₃ slip 38 peaks at 70 ppm and then decreases. It should be noted that NOx emissions 32 and 36 are emissions from the engine and not from the exhaust. NH ₃ slip is generated by excessing NH ₃ with respect to NOx with the SCR catalyst, and therefore the NOx conversion efficiency is as high as possible.

Furthermore, urea injection can be shut off to reduce the amount of NH _{3 in} the SCR catalyst. These actions are performed when the NH ₃ slip determined by either the calculation by the SCR model 16 or the measurement by the NH ₃ sensor exceeds a predetermined threshold value.

As mentioned above, an important factor of the SCR model 16 is the stored NH ₃ mass. This calculation of the amount of stored NH ₃ is inaccurate or particularly inaccurate for a number of reasons running in a real system. For example, an SCR catalyst will degrade in capacity and efficiency over time due to aging, resulting in an error in the approximate value of stored NH ₃ . In addition, if the engine produces different levels of NOx than modeled due to engine-to-engine variation or engine aging, or if the urea flow is different than expected, an estimate of stored NH ₃ To bring an error.

Accurate physical modeling of the catalyst NH ₃ slip is too complicated to perform and calibrate in an ECU (Engine Control Unit). This is because a complicated chemical model is included. The SCR model 16 is an average NH ₃ slip estimator. The transient behavior of the SCR model 16 is not accurate. This is because the capacity of the SCR catalyst for storing NH ₃ is directly related to the temperature considered to be constant over the length of the SCR catalyst. However, the average NH ₃ mass predicted by the SCR model 16 can be compared to the average NH ₃ mass confirmed by the NH ₃ sensor downstream of the SCR catalyst in the exhaust system.

Accordingly, referring to FIG. 5, NH ₃ slip model 40 and NH ₃ slip sensor 42 compare NH ₃ slips from the model and the sensor, respectively. Next, an NH ₃ slip error 44 is generated before the capacity error 46 means and the efficiency error means 48.

Model is known to have the best accuracy, the sufficiently high specific state in the DOC temperature and SCR temperature is a predetermined range, NH ₃ flow of NH ₃ slip and the NH ₃ sensor exits the SCR model 16 is confirmed Is monitored over a predetermined time. Once time has passed, both values must be equal if the SCR model 16 is accurate.

Referring to FIG. 6, the SCR inlet temperature 50 increases from about 200 ° C. to 350 ° C. during a transient change in temperature. As a result, NH ₃ slip both of the NH ₃ slip model values 52 and NH ₃ slip sensor value 54 is increased, a time lag exists in connection with NH ₃ slip sensor value 54.

If the modeling period is long enough, the transient error can be ignored, and after a certain time, if the error remains between the modeled NH ₃ slip and the sensed NH ₃ slip, the SCR model 16 is You can change it accordingly.

According to various factors associated with the SCR model 16, the capacity of the SCR catalyst must be corrected and the NOx conversion efficiency changed. If the SCR catalyst is filled with NH ₃ by a predetermined minimum amount over a predetermined time, the capacity is corrected. Otherwise, change is made in accordance with the NOx conversion efficiency. If this input parameter is incorrect due to a change in accordance with the NOx conversion efficiency, the engine outflow NOx model can be corrected. A change in accordance with a predetermined NOx conversion efficiency acts as a comprehensive change factor. This is to correct for SCR efficiency, injector error, NOx flow model error, and urea quality. Since the target capacity of the SCR catalyst is set to a very low value in order to prevent NH ₃ slip from occurring during normal operation, there will never be a condition that requires correcting the capacity. Thus, it is advantageous to increase the NH ₃ storage target (fill the SCR catalyst to its maximum capacity) so that capacity correction can be made. Changes in efficiency are made relatively frequently. This is because, as mentioned above, a specific condition is required for correcting the capacity.

  Other changes and modifications can be made without departing from the scope of the invention.

FIG. 1 is a graph of measured NOx emissions and modeled NOx emissions. FIG. 2 is a flow diagram of an open loop control structure for selective catalytic reduction (SCR) catalyst. FIG. 3 is a graph of NOx efficiency versus stored NH ₃ . FIG. 4 is a graph showing changes in NH ₃ slip due to control of NOx emission. FIG. 5 is a flow diagram of an open loop control structure for a selective catalytic reduction catalyst with an additional closed loop control section. FIG. 6 is a graph of temperature change showing model NH ₃ outflow from the catalyst, measured NH ₃ concentration from the sensor, and gas temperature at the SCR inlet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Selective catalytic reduction control device 12 Engine outflow NOx model 14 NO2 / NOx ratio model 16 SCR model 18 NOx efficiency target model 20 Urea injection control device 22 Storage NH ₃ differential

Claims (35)

A selective catalytic reduction (SCR) catalyst control system (10) for an engine with an SCR catalyst, comprising:
A nitrogen oxide (NOx) engine emission determining means (12) for determining a NOx engine emission value;
Urea control means (20) capable of supplying a predetermined amount of urea to the SCR catalyst;
NOx efficiency target means (18) for determining the storage ammonia (NH ₃ ) target value in the SCR catalyst based on the target value of NOx conversion efficiency and the SCR catalyst temperature determined by the SCR catalyst temperature determination means;
A SCR catalyst model (16) for determining a storage NH ₃ value in the SCR catalyst based on a NOx engine emission value, the SCR catalyst temperature, an amount of urea supplied to the SCR catalyst, and a NOx gas conversion efficiency; In a system (10) including:
Includes a NOx ratio calculating means (14) for determining the NOx ratio is the ratio of nitrogen dioxide in the NOx engine emission value, the SCR catalyst model (16), when determining the storage NH ₃ value, considering the NOx ratio And
Further comprising a differential determination means for said storage NH ₃ by comparing the storage NH ₃ value of the target value in the SCR catalyst to determine a stored NH ₃ differential,
The system (10) characterized in that the urea control means determines the amount of urea that needs to be supplied to the SCR catalyst based on the stored NH ₃ differential. The system (10) according to claim 1, wherein
The NOx ratio calculating means (14) receives a first temperature value from a first temperature sensor and calculates the NOx ratio according to the first temperature value. The system (10) according to claim 2, wherein
The first temperature sensor is a system (10) for measuring an oxidation catalyst temperature. The system (10) according to claim 2, wherein
The first temperature sensor measures a particulate filter temperature (10). The system (10) according to claim 2, wherein
The first temperature sensor is a system (10) for measuring a first temperature value between the particulate filter and the oxidation catalyst. In the system (10) according to any one of claims 1 to 5,
The NOx engine emission determining means (12) is a system (10) which is a model of NOx flowing out from the engine. The system (10) according to claim 6, wherein:
Model of NOx flowing out of the engine, calculates the NOx engine emission value based the amount of fuel injected into the engine, engine load, exhaust gas recirculation (EGR) rate, and ambient temperature, the system (10 ). In the system (10) according to any one of claims 1 to 5,
The NOx engine emission determining means (12) is a NOx sensor positioned upstream of the SCR catalyst and provides a NOx engine emission value. In a system (10) according to any one of the preceding claims,
The NOx efficiency target means (18) further measures the engine speed, engine load, air temperature, coolant temperature, or one or more parameters of the diesel particulates filter (DPF) regeneration mode parameters A system (10) that uses the value from the sensor to determine the target value of stored ammonia (NH ₃ ) for the SCR catalyst. The system according to any one of claims 1 to 9,
The SCR model (16) exits the SCR catalyst by calculating the SCR catalyst capacity based on the physical characteristics of the SCR catalyst and the SCR catalyst temperature and taking into account the value of the stored NH ₃ of the SCR catalyst. determining the NH ₃ slip value representing the amount of NH _3, system. The system according to any one of claims 1 to 10, further comprising:
NH ₃ slip control means and NOx engine emission increasing means,
If NH ₃ slip value may be is determined higher than a predetermined value or NH ₃ slip value is expected to rise above a predetermined value, the NOx engine emissions increasing means, in a direction to increase the NOx engine emissions A system that operates and thereby reduces NH ₃ slip. The system of claim 11, wherein
The NOx engine emission increasing means is exhaust gas recirculation (EGR) means and increases NOx engine emissions by reducing or stopping the amount of EGR to the engine. The system according to any one of claims 1 to 12, further comprising:
The system includes a SCR model changing means (40, 42, 46, 48). The system of claim 13, wherein
The SCR model changing means includes an NH ₃ sensor (42) capable of measuring an actual NH ₃ slip from the SCR catalyst, means for averaging the actual NH ₃ slip, means for averaging the NH ₃ slip value of the SCR model, Comparing the output from the actual NH ₃ slip average means and the output from the SCR model NH ₃ slip value average means to determine an NH ₃ slip approximate value error, the SCR model comprising: The system is changed according to the NH ₃ slip approximate value error by the SCR model changing means. 15. The system according to claim 13 or 14,
The SCR model changing means can change the SCR model by changing the conversion efficiency of NOx gas based on the NH ₃ slip approximate value error (46, 48). 16. A system according to claim 13, 14, or 15,
The SCR model changing means can change the SCR model by changing the SCR catalyst capacity (46) based on the NH ₃ slip approximate value error. The system of claim 16, wherein
The SCR model changing means changes the SCR model by changing the SCR catalyst capacity when the SCR catalyst is filled with a predetermined minimum amount of NH ₃ for a predetermined time. In a method for controlling selective catalytic reduction (SCR) of an engine having an SCR catalyst,
(I) determining a nitrogen oxide (NOx) engine emission value;
(Ii) controlling the amount of urea supplied to the SCR catalyst;
(Iii) measuring the SCR catalyst temperature from the SCR catalyst;
(Iv) determining a stored ammonia (NH ₃ ) target value of the SCR catalyst based on a target value of NOx conversion efficiency and the SCR catalyst temperature;
(V) calculating a NOx ratio which is a ratio of nitrogen dioxide in the NOx engine emission value;
(Vi) Using the SCR catalyst model, based on the NOx engine emission value, the SCR catalyst temperature, the urea supply amount to the SCR catalyst, the NOx ratio, and the NOx gas conversion efficiency, the stored NH ₃ value of the SCR catalyst A process of calculating
(Vii) comparing the target value of the storage NH ₃ and the value of the storage NH ₃ in the SCR catalyst, and the step of determining a storage NH ₃ differential,
The step (ii) is a method in which a required supply amount of urea to the SCR catalyst is controlled based on the stored NH ₃ differential. The method of claim 18, wherein
The method of calculating the NOx ratio includes measuring a first temperature value from a first temperature sensor and calculating the NOx ratio according to the first temperature value. The method of claim 19, wherein
The method wherein the first temperature value is an oxidation catalyst temperature value. The method of claim 19, wherein
The method wherein the first temperature value is a particulate filter temperature. The method of claim 19, wherein
The method wherein the first temperature value is measured between a particulate filter and an oxidation catalyst. 23. A method as claimed in any one of claims 18 to 22,
The step (i) includes calculating the (NOx) engine emission value based on an engine effluent NOx model. 24. The method of claim 23, wherein
The method of calculating the (NOx) engine emission value, wherein the engine outflow NOx model takes into account injected fuel flow to the engine, engine load, exhaust gas recirculation (EGR) rate, and ambient temperature. 23. A method as claimed in any one of claims 18 to 22,
The step (i) includes a step of measuring a NOx engine emission value from a NOx sensor positioned upstream of the SCR catalyst. 26. The method according to any one of claims 18 to 25, wherein:
The step (iv) further includes engine speed, engine load, air temperature, coolant temperature, or diesel particulate filter (DPF) regeneration mode to determine a target value of stored ammonia (NH ₃ ) at the SCR catalyst. Measuring one or more of the parameters of the command. 27. A method according to any one of claims 18 to 26,
The step (v) further calculates the SCR catalyst capacity in the SCR model based on the physical characteristics of the SCR catalyst and the SCR catalyst temperature, and takes into account the value of stored NH _{3 in} the SCR catalyst. Determining a NH ₃ slip value representative of the amount of NH ₃ exiting the SCR catalyst. 28. A method according to any one of claims 18 to 27, further comprising:
Controlling NH ₃ slip and increasing NOx engine emissions,
When said NH ₃ slip value is expected to be higher than the high or predetermined value than a predetermined value, to increase the NOx engine emissions, thereby reducing NH ₃ slip method. The method of claim 28, wherein
The method of increasing the NOx engine emissions includes decreasing or stopping an amount of exhaust gas recirculation (EGR) to the engine. 30. The method according to any one of claims 18 to 29, further comprising:
Changing the SCR model used in step (vi). The method of claim 30, wherein
The step of changing the SCR model includes measuring an actual NH ₃ slip from the SCR catalyst using an NH ₃ sensor;
Calculating the SCR model NH ₃ slip from the SCR model;
Averaging the actual NH ₃ slip over a predetermined time;
Averaging the SCR model NH ₃ slips over the same predetermined time;
Comparing the averaged actual NH ₃ slip with the averaged SCR model NH ₃ slip;
Determining an NH ₃ slip estimate error,
A method of significantly changing the SCR model according to the NH ₃ slip estimate error. 32. The method of claim 31, wherein
The method of changing the SCR model includes changing the SCR model by changing the conversion efficiency of NOx gas based on an NH ₃ slip estimate error. 32. A method according to claim 30 or 31,
The method of changing the SCR model comprises changing the SCR model by changing the SCR catalyst capacity based on an NH ₃ slip estimate error. 34. The method of claim 33, wherein
The step of changing the SCR model is to change the SCR model by changing the SCR catalyst capacity when the SCR catalyst is filled with a predetermined minimum amount of NH ₃ for a predetermined time. Method.   A diesel engine comprising the selective catalytic reduction (SCR) catalyst control system according to claim 1.

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