DE102010031655A1 - Method for operating pressure-regulated dosing system for selective catalytic reduction catalyzer, utilizing dosing system which comprises dosing valve and actuator, particularly pump motor for uptitration of fluid reducing agent solution - Google Patents

Abstract

The method involves utilizing a dosing system which comprises a dosing valve and an actuator, particularly a pump motor for uptitration of a fluid reducing agent solution in an exhaust strand of an internal-combustion engine upstream the selective catalytic reduction catalyzer. An adaptive servo control is used, which originates from a predetermined characteristic line or a predetermined characteristic field. Independent claims are also included for the following: (1) a computer program; and (2) a computer program product with program code.

Description

The present invention relates to a method for operating a pressure-controlled metering system for a precontrolled SCR catalytic converter.

State of the art

Methods and apparatuses for operating an internal combustion engine, in particular in motor vehicles, are known, in the exhaust gas region of which an SCR catalytic converter (selective catalytic reduction) is arranged, which reduces the nitrogen oxides (NOx) contained in the exhaust gas of the internal combustion engine to nitrogen in the presence of a reducing agent. As a result, the proportion of nitrogen oxides in the exhaust gas can be significantly reduced. For the course of the reaction ammonia (NH ₃ ) is required, which is admixed to the exhaust gas. As reactants or reducing agents therefore NH ₃ or NH _3- splitting reagents are used. As a rule, an aqueous urea solution is used for this purpose, which is metered into the exhaust gas line upstream of the SCR catalytic converter. From this solution forms NH ₃ , which acts as a reducing agent.

The urea solution is kept in a reducing agent tank, which is usually equipped with a suction line to suck the urea solution from the tank can. To promote the urea solution, a pump is provided, which promotes the solution through a line system, so that the urea solution can be injected via one or more metering valves, such as electromagnetic injectors, under pressure in the exhaust line.

The reducing agent solution must be injected very precisely and precisely as needed. Depending on the reducing agent pressure, a regulated control of the metering valve takes place. The metering system, which acts as a hydraulic system, is adjusted to a predefinable setpoint pressure, whereby the control of the pump motor or another actuator is used as a manipulated variable. To shorten the settling time, the pump motor can be pre-controlled by the dosing quantity. The input signal is the actuating signal for the metering valve, in particular its duty cycle. The pump motor control, in particular the Pumpenmotortastverhältnis, is set according to the current requirements for the opening period of the metering valve. The requirements for the actuation stored for the precontrol are usually stored in a table with constant values. By pre-control, the control performance of the pressure regulator can be improved with changes in the control of the metering valve and the Einregelzeit be shortened. However, the feedforward control is not optimal under all conditions. Due to the high dependence of the required control of the pump motor of various factors, such as the temperature of the reducing agent or the atmospheric pressure, it may come to long settling times, so that an optimal exhaust aftertreatment is not always secured.

The present invention is therefore based on the object to improve the method for operating a pressure-controlled metering system for an SCR catalyst. In particular, the control quality of the pressure regulator is to be optimized in order to avoid the high pressure overshoot and undershoot, which occurs, for example, in the case of large dosing quantity changes, as well as associated long settling times.

This object is achieved by a method for operating a pressure-controlled metering system, as it is the subject of claim 1. Preferred embodiments of this method emerge from the dependent claims.

Disclosure of the invention

Advantages of the invention

The core of the invention is that in the inventive method for operating a pressure-controlled metering system for an SCR catalyst, an adaptive feedforward control is used. By means of the adaptive or learning pilot control, the pump motor actuating signal can be taught in with different metering valve actuations and the necessary pump motor actuating signal can be determined on the basis of two or more taught-in points. In the following explanations, the pump motor is used as a manipulated variable for the pressure-controlled dosing system. However, other actuators of the dosing system can be used in a corresponding manner. By the method according to the invention can be reduced in a particularly advantageous manner Drucküber- or undershoots in their amplitude. Furthermore, as a result of this, the settling time can be considerably reduced, in particular with high dosing quantity changes or, in general, with changes in the control of the dosing valve.

In one embodiment of the method according to the invention, the adaptive precontrol can start from a characteristic curve which characterizes the relationship between the pump motor actuating signal or the activation of the pump motor or another actuator and the metering valve control. In a particularly preferred embodiment of the method according to the invention, the dosing system is based on a characteristic map which determines this relationship between the pump motor actuating signal and the dosing valve control for various types Indicates operating conditions. In this way, for example, different operating temperatures or different pressure conditions, for example due to the atmospheric pressure, can be taken into account in the method according to the invention. Starting from the predefinable characteristic curve or the predefinable characteristic map, according to the invention, an adapted characteristic curve or an adapted characteristic field is learned by starting various operating points.

The predefinable characteristic curve or the predeterminable characteristic map initially specifies the nominal values with which the pump motor is controlled. Deviations from the desired pressure, the z. B. caused by disturbances or other errors are corrected by the superordinated use of a controller. The observable after the successful control points of the characteristic curve or the characteristic map with respect to the pump motor control signal are used according to the invention for updating the characteristic curve or the map.

For learning an adapted characteristic curve or an adapted characteristic diagram, it is first possible to specify a characteristic curve or a typical characteristic diagram which is typical for the respective metering system. In another embodiment, the predeterminable characteristic curve or the predeterminable characteristic field may contain values of zero. In this case, the system is operated solely with the controller until the first adaptation of the pilot control on the underlying characteristic or the map. After specification of the characteristic curve or the characteristic map, the points of the characteristic curve or characteristic diagram which can be observed at various operating points are recorded. The observable points relate to the pump motor control which takes place during the regulation. From the updated points, an adapted characteristic curve or an adapted characteristic map is created. For this purpose, different approximations of the characteristic curve or the characteristic diagram can be used. In the simplest case, a straight line or another approximated curve between two determined points is used. Between several observed or determined points of a characteristic curve or a characteristic field, it is also possible partly to use a rectilinear and partially approximated course.

The various operating points for determining the updated points of the characteristic curve or the characteristic map can be specified or determined dynamically during operation. The various operating points can be approached directly, for example in a learning phase of the system, and the points observable thereby can be used to adapt the characteristic curve or the characteristic diagram. In another embodiment of the method according to the invention, the various operating points can be approached by the system during operation. In addition to a targeted control of the operating points and the approached from the operation out operating points can be used for the update. In this case, the observable points are then used for the update when the adjustment has taken place, d. H. when the pressure curve is sufficiently stable.

With the updated points of the characteristic curve or the map, an adapted characteristic curve or an adapted characteristic map is created. The predefinable characteristic curve or the predefinable characteristic map, which was the starting point in the learning phase, is replaced by the adapted characteristic curve or the adapted characteristic diagram. The changeover from the output characteristic curve or from the output characteristic field to the adapted characteristic curve or the adapted characteristic diagram can take place continuously, it being possible for the characteristic curve or the characteristic field to be adapted several times with regard to an optimum feedforward control during the learning phase. For example, the output characteristic curve can already be replaced by an adapted characteristic curve if only two operating points have been approached to produce the adapted characteristic curve. In the further course of the learning phase, when further operating points have been approached, the adapted characteristic curve (or the characteristic diagram) can be further optimized and replace the previously adapted characteristic curve. This procedure is particularly advantageous if the output characteristic curve or the output characteristic field contains values of zero. In this way, a first adapted characteristic curve or a first adapted characteristic diagram can be provided very quickly, which enables a significantly improved quality of control.

In another embodiment of the method according to the invention, the switching over from the output characteristic curve or the output characteristic field to the adapted characteristic curve or the adapted characteristic diagram can occur abruptly. For example, the changeover can take place when a predefinable number of operating points for the preparation of the updated characteristic curve or the updated map has been approached.

In a further embodiment of the method according to the invention, provision may be made for switching between a pure control without pilot control and a control with pilot control, in particular with an adaptive pilot control. For example, it is possible to dispense with the precontrol if the metering quantity change, that is to say the changes in the control of the metering valve, do not exceed a specifiable level. As soon as a higher dosing quantity change is requested, the pre-control is activated. For this purpose, for example, a threshold value for the difference of the drive signals of the Metering valve can be specified. If the difference of the control signals during operation, ie the Dosiermengenänderung, above the threshold, the feedforward is active or is activated, the difference of the control signals is below the threshold, the feedforward is not active or is inactivated.

The invention further includes a computer program that performs all the steps of the described method when executed on a computing device or controller. Finally, the invention comprises a computer program product with program code, which is stored on a machine-readable carrier, for carrying out the method according to the invention when the program is executed on a computing device or a control device. The control unit may be, for example, the control unit of the internal combustion engine or a control unit of the metering device for the SCR catalytic converter. The embodiment of the method according to the invention as a computer program or as a computer program product has the advantage that with the aid of this program, the method according to the invention can also be implemented, for example, in existing motor vehicles without having to install further components. In this way, the control quality of the dosage of the reducing agent for an SCR catalyst system can be greatly improved without great effort even in existing vehicles, so as to ensure optimal exhaust aftertreatment.

The training phase for the adaptation of the precontrol can be carried out, for example, at a predefinable time, for example at the beginning of a driving cycle. During this time-limited phase, the various required operating points will be approached and the updating of the characteristic curve or characteristic map will be carried out. Furthermore, the learning phase can also be distributed over the entire driving cycle by using the various operating points, which are already approached during ongoing operation, for updating the points of the characteristic curve or the characteristic diagram. The training phase can be repeated at different predeterminable times. In other embodiments, it may also be provided to adapt the characteristic curve or the characteristic map constantly during ongoing operation.

Further advantages and features of the invention will become apparent from the following description of embodiments in conjunction with the drawings. In this case, the individual features can be implemented individually or in combination with each other.

Brief description of the drawings

In the drawings show:

1 a schematic representation of the components of a metering device of an SCR catalyst system (prior art) and

2 a schematic flow diagram of the method according to the invention.

Description of exemplary embodiments

1 shows in a schematic way the known components of a metering device of an SCR catalyst system. In the exhaust system 10 an internal combustion engine 11 is an SCR catalyst 12 arranged, which selectively reduces nitrogen oxides in the exhaust gas by a selective catalytic reduction (SCR). For this reaction, ammonia (NH ₃ ) is used as a reducing agent. Since ammonia is a toxic substance, this substance is derived from the non-toxic carrier substance urea. The urea is used as a liquid urea water solution via a metering valve 13 in the exhaust system 10 upstream of the SCR catalyst 12 injected. The aqueous urea solution is placed in a reducing agent tank 14 stored. To remove the urea solution is a suction line 15 intended. The reducing agent is via a feed pump 16 from the reducing agent tank 14 conveyed and under pressure in the pressure line 17 to the metering valve 13 directed. The urea solution is tailored and precisely in the exhaust system 10 injected. In this case, the pressure of the reducing agent in the pressure line plays 17 a significant role. This reducing agent pressure is adjusted to a predefinable target pressure. For detecting the actual pressure in the pressure line 17 is a pressure sensor 18 provided, the detected pressure signals to a control unit 19 forwards. The pump 16 is used as an actuator via a signaling device of the control unit 19 controlled, so that a predetermined target pressure can be adjusted. The activation of the metering valve 13 is also required depending on a signaling of the controller 19 ,

To improve the control quality of the dosing system, it is provided according to the invention, an adaptive pilot control for the metering of the urea solution in the exhaust system 10 use. Here, the actuating signal for the metering valve forms 13 the input quantity. Depending on the current requirement for the opening duration of the dosing valve 13 becomes the control of the feed pump 16 adjusted accordingly. In a learning phase, the pump motor control signal is taught at different Dosierventilansteuerungen and based on two or more learned points a characteristic curve or a map is created, which is used to adapt the pilot control. This can be reduced in a particularly advantageous manner, over or undershoot the pressure curve. The settling time until the stable setting of the predefinable pressure can be considerably reduced. These advantages of the method according to the invention come in particular at high Dosiermengenänderungen, ie for changes in the control of the metering to bear.

2 illustrates in a schematic way essential points in the course of the method according to the invention. After starting the system (step 20 ), the learning of the characteristic (step 30 ). Subsequently, the operation of the system with the adapted pilot control in step 40 be made. During operation, the characteristic can be further updated (step 50 ), so that during operation (step 40 ) a continuous adaptation of the feedforward takes place.

In a particularly preferred embodiment of the method according to the invention, instead of the characteristic curve, a characteristic field is used which, in addition to the relationship between the actuating signal of the metering valve and the activation of the pump motor, takes into account further variables, for example the ambient temperature and / or the temperature of the reducing agent used, which has an influence exercise the precision of the dosage. Another example of another size is the atmospheric pressure, which also affects the precision of the metering of the reducing agent. The map can be adapted continuously during operation of the internal combustion engine by taking into account the corresponding information. For example, the ambient temperature may be detected by a corresponding temperature sensor or by inference from other data or values. The update of the pump motor drive at certain operating points is used in this embodiment, depending on, for example, the respective ambient temperature for the adaptation of the map. In this way, the dependence of the dosing of such further conditions for the precontrol can be considered and their influence can be minimized. This further optimizes the overall control quality of the dosing system.

In addition to improving the control quality of the system compared to conventional methods, the method according to the invention has the further advantage that a calibration of the dosing system can be operated with less effort, for example after the completion of the motor vehicle, since the calibration is essentially performed by the adaptive feedforward control according to the invention during the ongoing operation of the motor vehicle can take place.

Claims (12)

Method for operating a pressure-controlled metering system for an SCR catalytic converter ( 12 ), wherein the dosing system at least one metering valve ( 13 ) and an actor ( 16 ), in particular a pump motor, for metering a liquid reducing agent solution into the exhaust gas line (US Pat. 10 ) an internal combustion engine ( 11 ) upstream of the SCR catalyst ( 12 ), characterized in that an adaptive feedforward control is used. A method according to claim 1, characterized in that the adaptive feedforward control of a predefinable characteristic curve or a predeterminable characteristic field, the or a relationship between the control of the at least one metering valve ( 13 ) and the activation of the actuator ( 16 ), and a learning of an adapted characteristic curve or an adapted characteristic field takes place by approaching different operating points. A method according to claim 2, characterized in that the predetermined characteristic curve or the predeterminable characteristic diagram is a typical characteristic curve or a typical characteristic diagram. A method according to claim 2, characterized in that the predeterminable characteristic curve or the predeterminable characteristic field contains values of zero. Method according to one of claims 2 to 4, characterized in that the various operating points can be predetermined and / or dynamically determined during operation. Method according to one of Claims 2 to 5, characterized in that the various operating points are approached in a targeted manner and the points of the characteristic line or the characteristic field which can be observed thereby are updated. Method according to one of claims 2 to 5, characterized in that the various operating points are approached during operation of the system and the thereby observable points of the characteristic curve or the map are updated. A method according to claim 6 or claim 7, characterized in that the updated points are used to create an adapted characteristic curve or an adapted characteristic field. Method according to one of claims 2 to 8, characterized in that a change of the predetermined characteristic curve or the predeterminable characteristic map on the adapted characteristic curve or the adapted characteristic map continuously takes place. Method according to one of claims 2 to 8, characterized in that a change from the predeterminable characteristic curve or the predeterminable characteristic field to the adapted characteristic curve or the adapted characteristic field occurs abruptly. A computer program executing all the steps of a method according to any one of claims 1 to 10 when mounted on a computing device or controller ( 19 ) is performed. Computer program product with program code, which is stored on a machine-readable carrier, for performing a method according to one of claims 1 to 10, when the program is stored on a computing device or a control device ( 19 ) is performed.

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