KR20190070864A - Method for correcting modeled ammonia mass flow rate and modeled nitrogen oxide mass flow rate, and method for controlling scr-catalytic converter system - Google Patents

Abstract

The present invention relates to a method for correcting (78, 79) a modeled ammonia mass flow rate (q_NH3 modeling) and a modeled nitrogen oxide mass flow rate (q_NOx modeling) between two SCR-catalytic converters continuously arranged within an exhaust gas line in an SCR-catalytic converter system. The SCR-catalytic converter system includes only one reducing agent metering unit upstream of the two SCR-catalytic converters. A first sum value (S_1) is calculated through the sum (74) of the modeled ammonia mass flow rate (q_NH3 modeling) and the modeled nitrogen oxide mass flow rate (q_NOx modeling). A second sum (S_2) is calculated from a signal (q_NH3/NOx measurement) of a sensor arranged between the two SCR-catalytic converters and sensitive to ammonia and a nitrogen oxide. The ratio (V) of the two sum values (S_1, S_2) is calculated for the correction (78, 79). In a method for controlling (80) an SCR-catalytic converter system (20), the modeled ammonia mass flow rate (q_NH3 modeling) and the modeled nitrogen oxide mass flow rate (q_NOx modeling) between the two SCR-catalytic converters are corrected by the correction method.

Description

Technical Field [0001] The present invention relates to a method for correcting a modeled ammonia flow amount and a modeled nitrogen oxide flow amount, and a control method of an SCR catalytic converter system, and a method for controlling the SCR catalytic converter system,

The present invention relates to a method for correcting a modeled ammonia flow quantity and a modeled nitrogen oxide flow quantity between two SCR catalytic converters arranged in succession in an exhaust gas line. The present invention also relates to a control method of an SCR catalytic converter system. The invention also relates to a computer program for executing each step of one or more of the above methods and to a machine-readable storage medium storing such a computer program. Finally, the present invention relates to an electronic control device configured to execute one or more of the above methods.

A promising way to reduce nitrogen oxides in oxygen-rich exhaust gases is Selective Catalytic Reduction (SCR) using ammonia or ammonia decomposition reactants. The efficiency of an SCR catalytic converter depends on its temperature, the space velocity of the exhaust gas, and very critically, the level of charge of ammonia absorbed on its surface. In addition to the ammonia being directly metered for the reduction of nitrogen oxides, absorbed ammonia is also provided, so that the efficiency of the SCR catalytic converter rises compared to that of an empty catalytic converter. This storage characteristic depends on the operating temperature of each of the catalytic converters. The lower the temperature, the larger the storage capacity.

When the SCR catalytic converter fully charges its reservoir, ammonia slip may occur even when the ammonia or ammonia decomposition reactant is no longer metered into the exhaust line at the time of the load rise of the internal combustion engine where the exhaust gas is reduced by the SCR catalytic converter have. If the highest possible nitrogen oxide conversion is to be achieved, it is inevitable to operate the SCR system at high ammonia charge levels. When the temperature of the fully charged SCR catalytic converter rises due to the load increase of the internal combustion engine, the ammonia storage capacity is lowered, which causes ammonia slip.

This effect is particularly pronounced when the SCR catalytic converters are mounted close to the internal combustion engine such that the SCR catalytic converter quickly reaches its operating temperature after the cold start of the internal combustion engine. Thus, a second SCR catalytic converter downstream of the first SCR catalytic converter can be provided in the exhaust gas line to absorb ammonia from the ammonia slip of the first catalytic converter and subsequently perform the conversion. For cost reasons, only one metering valve is typically installed upstream of the first SCR catalytic converter for metering the ammonia decomposition reducing agent solution into the exhaust gas line. Thus, the ammonia charging of the second SCR catalytic converter is only carried out through the ammonia slip of the first SCR catalytic converter.

The guidelines for on-board diagnostics (OBD) require that two SCR catalytic converters be monitored. To this end, there is usually one nitrogen oxide sensor downstream of each of the two SCR catalytic converters.

The new SCR catalytic converter model is a balanced model of two SCR catalytic converters, which can calculate the ammonia slip and nitrogen oxide slip between two SCR catalytic converters to some degree. From DE 10 2016 201 602 A1 it is known how to make it possible to detect the ammonia slip between the SCR catalytic converters based on the evaluation of nitrogen oxide sensors upstream and downstream of the second or downstream SCR catalytic converter. The NOx flow rate between the two SCR catalytic converters is calculated through a model of the first or upstream SCR catalytic converter. Even a very small model error, after only a few hours of operation, causes a large deviation between the expected ammonia charge level and the actual ammonia charge level in the second SCR catalytic converter. If the nitrogen oxide flow between two SCR catalytic converters is underestimated, the physical ammonia charge level in the second SCR catalytic converter is lowered. If the physical ammonia charge level is too low, the nitrogen oxide conversion of these SCR catalytic converters will be reduced, which may result in an over-legal threshold. Although the rapid adaptation method can again correct the nitrogen oxide setpoint on the downstream side of the second SCR catalytic converter, it is difficult to eliminate the cause of the error because in this adaptation method, the cause of the error can be detected by the SCR catalytic converter of any of the SCR catalytic converters Because they do not know if they can be found in the domain.

The method is used to calibrate the modeled ammonia flow volume and the modeled nitrogen oxide flow volume between two SCR catalytic converters. These two SCR catalytic converters are arranged in series in the exhaust gas line to form one SCR catalytic converter system. This SCR catalytic converter system includes only one reducing agent metering unit upstream of the two SCR catalytic converters. The first total value is calculated through the sum of the modeled ammonia flow rate and the modeled nitrogen oxide flow rate. The second summation value is calculated from the signals of the sensors arranged between the two SCR catalytic converters. These sensors are sensitive to ammonia and nitrogen oxides, and can be conventional nitrogen oxide sensors. The ratio of the two summation values is calculated for correction.

This method is based on the knowledge that when the ammonia flow rate and the nitrogen oxide flow rate are modeled very accurately in the model of the first SCR catalytic converter, the sum of the modeled flow quantities must correspond to the sum signal of the sensors. The larger the deviation of the two summation values, the greater the modeling error to be corrected.

Preferably, for the calculation of the first total value, after the modeled ammonia flow rate or the modeled nitrogen oxide flow rate is first provided in parts per million (ppm), especially in the milligrams per second (mg / s) / RTI > Then, such nitrogen oxides and the like are added together. As a result, a weight based on the amount of exhaust gas flow can be obtained.

Since the calibration is based on the information of all previous monitoring, the sum of the measured flow quantities as well as the modeled flow quantities is preferably filtered. To this end, the flows are integrated in one embodiment of the method and multiplied by a factor of less than 1 and greater than zero when the application threshold is reached. In an alternative embodiment, a Kalman filter is used.

The correction is preferably performed by multiplying the modeled ammonia flow rate and the modeled nitrogen oxide flow rate with a correction factor calculated from the ratio, respectively. In this simple manner, only one correction factor can be applied to the two flow quantities modeled.

In this case, particularly preferably, the correction coefficient is calculated by forming and / or limiting the ratio through the characteristic curve. As a result, the calculated or empirically calculated data can be included in the calculation of the correction coefficient.

In a method for controlling an SCR catalytic converter system, a modeled ammonia flow rate and a modeled nitrogen oxide flow rate between two SCR catalytic converters are corrected by a correction method of the flow quantities.

If the nitrogen oxide sensor used in this control is located downstream of the second SCR catalytic converter, the threshold for control should no longer be calculated based on the modeled NOx flow rate downstream of the second SCR catalytic converter. Instead, the value measured by this nitrogen oxide sensor is controlled to a setpoint, which is calculated from the total efficiency of the NOx sensor and the SCR catalytic converter system arranged upstream of the SCR catalytic converters. The overall efficiency consists of the individual efficiencies of the two SCR catalytic converters. These individual efficiencies are the activation energy of the SCR reaction; The temperature of each SCR catalytic converter; The normalized area coefficient of each SCR catalytic converter; Frequency coefficient of SCR response; The set charge level, maximum ammonia storage capacity and residence time of each SCR catalytic converter.

Where ammonia sensors are arranged between SCR catalytic converters, preferably the values measured by the ammonia sensor are considered in the modeling of the NOx flow rate at the time of control. This further improves the accuracy of the modeled nitrogen oxide flow rate between the two SCR catalytic converters. At this time, this nitrogen oxide flow rate may even be calculated simply from the deviation between the signal of the nitrogen oxide sensor arranged between the two SCR catalytic converters and the signal of the ammonia sensor.

The computer program of the present application is configured to execute each step of the method, particularly when executed in a computing device or an electronic control device. This makes it possible to implement different embodiments of the method within the electronic control unit without having to perform structural changes. To this end, the computer program is stored in a machine-readable storage medium. An electronic control unit configured to correct the modeled ammonia flow rate and the modeled nitrogen oxide flow rate by the correction method and / or to control the SCR catalytic converter system by the control method by installing the computer program in a conventional electronic control unit Is obtained.

Embodiments of the present invention are illustrated in the drawings and are described in further detail in the following description.
1 is a schematic diagram of a SCR catalytic converter system that may be controlled by a method in accordance with an embodiment of the present invention.
2 is a flow diagram of a method in accordance with an embodiment of the present invention.

The internal combustion engine 10 includes, within its own exhaust line 11, the SCR catalytic converter system 20 shown in Fig. This system includes a reducing agent metering unit 50 that allows the urea aqueous solution to be injected into the exhaust gas line 11. [ From these units ammonia is generated at high exhaust gas temperatures. A first SCR catalytic converter (21) and a second SCR catalytic converter (22) are arranged downstream of the reducing agent metering unit (50). The catalytic material of the first SCR catalytic converter is arranged on the particle filter (SCR on filter; SCRF). The first NOx sensor 31 is arranged upstream of the reducing agent metering unit 50 in the exhaust gas line 11. A second NOx sensor 32 is arranged between the two SCR catalytic converters 21,22. And the third NOx sensor is arranged downstream of the second SCR catalytic converter 22. [ Further, an ammonia sensor 40 is arranged between the second NOx sensor 32 and the second SCR catalytic converter 22. All of the NOx sensors 31, 32, and 33 and the ammonia sensor 40 transmit their signals to the electronic control unit 60. [ Since the NOx sensors 31, 32, and 33 respond to ammonia in a cross-sensitized manner, the signals of these sensors are the sum signal for nitrogen oxides and ammonia. However, since the first NOx sensor is arranged upstream of the reducing agent metering unit 50, such a sensor reliably measures the amount of nitrogen oxides in the exhaust gas. If the SCR catalytic converter system 20 is operated such that ammonia slip does not occur in the second SCR catalytic converter 22, it can be assumed that the signal of the third NOx sensor is based solely on nitrogen oxides. Because the ammonia slip is provided in the first SCR catalytic converter 21 to provide ammonia to the second SCR catalytic converter 22, the second NOx sensor 32 also provides a sum signal of ammonia and nitrogen oxides. The reducing agent metering unit 50 also reports the amount of ammonia metered into the exhaust gas line 11 to the controller 60 as well.

In an embodiment of the method according to the invention schematically shown in Figure 2, through the model of the first SCR catalytic converter 21, the modeled ammonia flow volume in ppm between the two SCR catalytic converters 21, (q _NH3 modeling) is provided (70). This modeled ammonia flow (q _NH3 modeling) is converted to an equivalent amount of nitrogen oxides (q _NH3 equivalent) in mg / s (71). In addition, the model of the first SCR catalytic converter 21 provides a modeled _NOx flow rate (q _NOx modeling) between the two SCR catalytic converters 21, 22 (72). This is similarly converted to an equivalent amount of nitrogen oxides (q _NOx equivalent) (73). The two flow quantities (q _NH3 equivalent, q _NOx equivalent) that are converted to an amount such as nitrogen oxide are summed to obtain the first total value (S ₁ ) (74). The second NOx sensor 32 performs a measurement 75 of the sum signal (q _{NH3 / NOx} measurement) of the ammonia flow volume and the nitrogen oxide flow volume between the two SCR catalytic converters 21, This sum signal (q _{NH3 / NOx} measurement) is used as a second sum value (S _2). The two summation values (S ₁ , S ₂ ) are divided 76 to obtain their ratio (V). Which is formed and limited through the characteristic curve 77. [ In this manner, the correction coefficient f is obtained. By multiplying 78 by the modeled ammonia flow (q _NH3 modeling) and the correction factor (f), a corrected ammonia flow (q _NH3 correction) is obtained. (79), a corrected nitrogen oxide flow rate (q _NOx correction) is obtained by multiplying the modeled _NOx flow rate (q _NOx modeling) by the correction factor (f). The corrected flow quantities (q _NH3 correction, q _NOx correction) are supplied to the control unit 80 of the SCR catalytic converter system 20 in the electronic control unit 60.

Usually, the value of the nitrogen oxide flow rate downstream of the two SCR catalytic converters 21, 22, as measured by the third nitrogen oxide sensor 33, is controlled to a set value. These set values include the amount of nitrogen oxides leaving the internal combustion engine 10, as measured by the first nitrogen oxide sensor 31; SCR < / RTI > catalytic converter system 20. The overall efficiency consists of the individual efficiencies of the two SCR catalytic converters 21,22. In the control unit 80, the amount of nitrogen oxide flow between the two SCR catalytic converters 21, 22 can be calculated by subtracting the sensor signal of the ammonia sensor 40 from the sensor signal of the second nitrogen oxide sensor 32.

Claims (10)

In the SCR catalytic converter system 20 comprising only one reducing agent metering unit 50 upstream of the two SCR catalytic converters 21 and 22 two SCR catalytic converters A method for correcting (78, 79) a modeled ammonia flow (q _NH3 modeling) and a modeled nitrogen oxide flow (q _NOx modeling) between a catalytic converter (21, 22)
A first total value S ₁ is calculated through a sum 74 of the modeled ammonia flow (q _{NH 3} modeling) and the modeled nitrogen oxide flow (q _{NO x} modeling); A second sum value S ₂ is calculated from the signal (q _{NH 3 / NO x} measurement) of the sensor 32, which is sensitive to ammonia and nitrogen oxides, arranged between the two SCR catalytic converters 21 and 22; The ratio V of the two summation values (S ₁ , S ₂ ) is calculated for the corrections 78, 79; And the flow rate correction method. The method of claim 1, wherein the first sum value for the calculation of (S _1), the modeled ammonia flow rate (q _NH3 modeling) and the modeled NOx flow rate (q _NOx modeling) is approximately NOx, etc. (q _NH3 equivalent, q _NOx , And is summed and summed. 3. The method according to claim 1 or 2, characterized in that the corrections (78,79) are performed such that the modeled ammonia flow (q _NH3 modeling) and the modeled nitrogen oxide flow (q _NOx modeling) (f), respectively. < / RTI > The flow rate correction method according to claim 3, characterized in that the correction coefficient (f) is calculated (77) by forming and / or limiting the ratio (V) through a characteristic curve. A method for controlling (80) an SCR catalytic converter system (20) comprising two SCR catalytic converters (21, 22) arranged in series in an exhaust line (11)
The modeled ammonia flow rate (q _NH3 modeling) and the modeled nitrogen oxide flow volume (q _NOx modeling) between the two SCR catalytic converters 21, 22 are corrected by the method according to any one of claims 1 to 4 Gt; SCR < / RTI > catalytic converter system. 6. A method according to claim 5, wherein the values measured by the nitrogen oxide sensor (33) arranged downstream of the SCR catalytic converters (21, 22) are controlled to a set value, Is calculated from the total efficiency of the NOx sensor (31) arranged upstream and the SCR catalytic converter system (20). 7. Method according to claim 5 or 6, characterized in that during the modeling of the nitrogen oxide flow rate, the values measured by the ammonia sensor (40) arranged between the SCR catalytic converters (21, 22) Control method of converter system. A computer program configured to execute each step of the method according to any one of claims 1 to 7. 9. A machine-readable storage medium having stored thereon a computer program according to claim 8. A method according to any one of claims 1 to 4, characterized by correcting the modeled ammonia flow rate (q _NH3 modeling) and the modeled nitrogen oxide flow rate (q _NOx modeling) and / An electronic control device (60) configured to control an SCR catalytic converter system (20) by a method according to any one of the preceding claims.

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