DE102016202682A1 - Method for automating a resistance compensation on a feed pump of an SCR system and SCR system for using the method - Google Patents

Abstract

The present invention relates to a method of automating a resistance compensation on a feed pump (14) of an SCR system (10) by activating a resistance balance by interrogating conditions to enable resistance compensation, measuring a total resistance (RGT) at an adaptation temperature, determining a first virtual one Resistance value (R1) and determining a second virtual resistance value (R2) and storing the first and second resistance value (R1, R2) in a control unit (22) and an SCR system for carrying out such a method.

Description

The invention relates to a method for automating a resistance compensation on the feed pump of an SCR system.

The invention further relates to an SCR system for the application of such a method. Selective Catalytic Reduction (SCR) is a proven process for reducing nitrogen oxides in internal combustion engines (especially diesel engines). In this case, so-called SCR delivery systems are used, which usually comprise a reducing agent tank with removal tube, a pump module and an injection nozzle. For exhaust gas treatment, a reducing agent (urea water solution, for example AdBlue) is sprayed into an exhaust gas stream. The amount of reductant that is injected into the exhaust system determines either engine management (e.g., an engine control unit) or a separate SCR controller.

In modern SCR conveyor systems, a heatable SCR tank module with a feed pump is integrated directly into the tank. In addition to the actual feed pump (metering pump), such conveyor systems also include a tank heater, pressure and temperature sensors and sensors for determining the fill level and the quality of the reducing agent (for example: state of aggregation and / or concentration of the reducing agent). See, e.g. 10 2008 002 353 A1 or 10 2010 013 696 A1.

Such a highly integrated design also makes it possible to use certain components several times. In addition to the use of the pumped-around by reducing agent to promote the reducing agent whose coil (the motor winding) can be used as a heating coil to heat the reducing agent in the pump. Such an additional heating makes it possible to produce the metering readiness more quickly at low temperatures. By determining the electrical resistance of the coil, the temperature in the feed pump or that of the coil can also be determined.

For this purpose, a voltage drop in the circuit of the SCR delivery pump is measured in the engine control unit or its own SCR control unit and from this a total resistance is determined, which results from the partial resistances of the SCR delivery pump itself and the line resistance, the wiring and the necessary connections (connectors) includes these components.

With the help of this, the temperature-dependent electrical resistance determined by the voltage drop (composed of the line resistance and the resistance of the SCR feed pump) and by knowing the reference resistance of the SCR feed pump at a standard temperature (eg 20) and the material-dependent temperature coefficient can be the temperature of the SCR Determine delivery pump.

For this purpose required reference values are usually determined within the scope of the engine control unit application process and stored as fixed values in the engine control unit. However, the values may vary from vehicle model to vehicle model due to manufacturing tolerances in the SCR delivery pump itself and in the wiring of this component, and may even be vehicle-specific.

To rule this out, one could either use additional temperature sensors or accept inaccurate temperature readings, which could lead to malfunction. An incorrect determination of the pump temperature can lead to damage to this component and to incorrect entries.

Thus, there is a need for an improved method of resistance compensation that at least partially eliminates the above disadvantages. There remains a need for a correspondingly improved SCR delivery system.

• – Aktivieren eines Widerstandsabgleichs durch Abfragen von Bedingungen zur Freigabe eines Widerstandsabgleichs,
• – Messen eines Gesamtwiderstandes bei einer Adaptionstemperatur,
• – Bestimmen eines ersten virtuellen Widerstandswertes und Bestimmen eines zweiten virtuellen Widerstandswertes und
• – Speichern des ersten und zweiten virtuellen Widerstandswertes in einem Motorsteuergerät.

This object is achieved by the method according to claim 1 and the inventive SCR conveyor system according to claim 9. The inventive method for automating the resistance compensation on the feed pump of an SCR conveyor system comprises the steps:

• Activating a resistance match by querying conditions to enable a resistance match,
• Measuring a total resistance at an adaptation temperature,
• Determining a first virtual resistance value and determining a second virtual resistance value and
• Storing the first and second virtual resistance values in an engine control unit.

This basic method makes it possible to determine the first (temperature-independent) virtual resistance value (at a reference temperature, preferably 20 ° C.) during operation under suitable and determinable boundary conditions and a second virtual (temperature-dependent) resistance value and both values in an engine control unit to save and update. The point is then to divide the resistor into a "virtual" temperature-dependent and a "virtual" temperature-independent part and to determine these based on the measured total resistance. The resistance values determined in this way can be further used in the temperature model for determining the coil temperature of the feed pump, without the need for a complex application process in the development phase of the system. The necessary values are determined regularly during operation and, if necessary, readjusted and updated.

• – Abfragen eines Zündung-an-Zustands, und
• – Bewerten eines vorhandenen Anlern- oder Bewertungsfaktors.

There are methods in which querying conditions to release a resistance match comprises at least one of the following steps:

• - polling an ignition-on-state, and
• - Evaluate an existing learning or evaluation factor.

By interrogating these conditions, it is ensured that a meaningful resistance adjustment can take place regularly during operation. It is noted that the ignition is on, and a learning or weighting factor is taken into account to perform the resistance equalization under qualitatively at least equivalent conditions (or better) than a previously performed resistance calibration, the results of which are stored in the engine control unit.

There are also methods in which the release of the resistance compensation is optionally supplemented by one or more of the following steps:
Querying an ambient temperature. In this case, for example, conditions for a temperature range can be stored, in which such a comparison makes sense.

Querying a heating / operating status of the feed pump. Here it can be determined whether the feed pump has assumed an operating state (for example, heating or defrosting), which would possibly falsify a resistance balance.

Query a first coldstart status. Here it can be determined whether a cold start status exists, in which the resistance adjustment makes sense. This can be done, for example, by determining that the temperature of a coolant, the temperature in an exhaust stream downstream of a particulate filter, and the ambient temperature are within a narrow temperature window.

Querying a second cold start status. Here, for example, by considering an engine off time, it can be determined whether the engine and thus the SCR conveyor system have been shut down / shut down long enough to have cold start conditions.

The combination of the first and second cold start status inquiry allows a particularly fail-safe assessment.

Querying an error status. Here it is determined if there is another fault in the system which prevents a resistance adjustment.

Querying an SCR system state. Resistance compensation is only useful if the pump was not active before the resistance measurement, otherwise the measurement of the resistance value could possibly be falsified by the current supplied to the pump motor.

Querying a period of time after a coil measurement. This ensures that the resistance compensation is performed only after the end of a coil measurement and that at the same time the last measurement is not too long ago.

• – zum einen geprüft, ob eine noch zulässige Temperaturerhöhung der Spule vorliegt, die durch wiederholte initiale Spulentemperaturmessungen verursacht wurde (die Temperaturerhöhung darf nur sehr klein sein), und
• – zum anderen, ob eine genügend lange Steuergerät-aus-Zeit verstrichen ist, um ein notwendiges Abkühlen der Spule (Absinken der Spulentemperatur) sicherzustellen.

Polling a coil temperature condition. Here is

• On the one hand checked whether there is still a permissible increase in the temperature of the coil, which was caused by repeated initial coil temperature measurements (the temperature increase may only be very small), and
• - On the other hand, if a sufficiently long controller off-time has elapsed to ensure a necessary cooling of the coil (drop in coil temperature).

• – nämlich das Berechnen eines aktuellen Anlern-/Bewertungsfaktors aus mehreren Teilfaktoren mit
• – Bestimmen eines ersten Teilfaktors aus der Differenz einer Abgleichtemperatur mit einer Normtemperatur. Dieser Faktor hängt von der Differenz zwischen der Abgleichtemperatur, die der Reduktionsmitteltemperatur entspricht, und einer Referenztemperatur (z.B. 20°C). Der Faktor wird anhand einer Kennlinie bestimmt, die so ausgebildet ist, dass der bestmögliche Wert 1,0 dann erreicht wird, wenn die Differenz zwischen der Abgleichtemperatur und der Normtemperatur gleich Null ist. Der Faktor erhält den schlechtestmöglichen Wert von 0 in dem Fall, wenn die Differenz zwischen den beiden Temperaturwerten (Abgleichtemperatur minus Normtemperatur) einen bestimmten Grenzwert überschreitet (z.B. 10°C).
• – Bestimmen eines zweiten Teilfaktors aus der Differenz zwischen der Abgleichtemperatur und der Umgebungstemperatur. Auch hier wird anhand einer Kennlinie ein Faktor zwischen 0 und 1 bestimmt. In diesem Fall derart, dass der bestmögliche Wert 1 erhalten wird, wenn die Abgleichtemperatur (SCR-Tanktemperatur) gleich der Umgebungstemperatur ist. Der schlechtestmögliche Wert von 0 wird dann erreicht, wenn die Differenz größer einem zweiten Grenzwert ist, der beispielsweise 20°C betragen kann. Durch diese beiden temperaturbedingten Teilfaktoren wird sichergestellt, dass die Temperaturabweichungen der einzelnen relevanten Komponenten von der Umgebungstemperatur bzw. einer Referenztemperatur, möglichst in einem engen, vorgebbaren Rahmen liegen. So werden Zustände, bei denen die Temperaturen homogen sind, besonders gut bewertet.
• – Bestimmen eines dritten Teilfaktors aus der Abstellzeit des Systems. Auch hier wird eine Kennlinie genutzt, die so gestaltet/bedatet ist, dass der bestmögliche Wert von 1 erhalten wird, wenn die Abstellzeit größer gleich einer bestimmten Abstellzeit ist, beispielsweise acht Stunden. Der schlechtmöglichste Wert von 0 wird erreicht, wenn die Abstellzeit einen unteren Grenzwert unterschreitet, z.B. gleich 0 ist.

There are methods in which the evaluation of the learning or weighting factor comprises several substeps,

• Namely, the calculation of a current learning / evaluation factor from several partial factors
• - Determining a first partial factor of the difference of an adjustment temperature with a standard temperature. This factor depends on the difference between the calibration temperature, which corresponds to the reducing agent temperature, and a reference temperature (eg 20 ° C). The factor is determined on the basis of a characteristic curve which is designed such that the best possible value 1.0 is reached when the difference between the calibration temperature and the standard temperature is equal to zero. The factor receives the worst possible value of 0 in the case when the difference between the two temperature values (calibration temperature minus standard temperature) exceeds a certain limit (eg 10 ° C).
• Determining a second sub-factor from the difference between the calibration temperature and the ambient temperature. Again, a factor between 0 and 1 is determined by means of a characteristic curve. In this case, such that the best possible value of 1 is obtained when the match temperature (SCR tank temperature) is equal to the ambient temperature. The worst possible value of 0 is reached when the difference is greater than a second limit, which may be 20 ° C, for example. These two temperature-related partial factors ensure that the temperature deviations of the individual relevant components are from the ambient temperature or a reference temperature, if possible within a narrow, specifiable framework. Thus, states in which the temperatures are homogeneous, evaluated particularly well.
• Determining a third partial factor from the shutdown time of the system. Again, a characteristic curve is used that is designed / supplied to give the best possible value of 1 when the shutdown time is greater than or equal to a particular shutdown time, for example eight hours. The worst possible value of 0 is reached when the stop time falls below a lower limit, eg equal to 0.

In a further step, the partial factors (first, second and third partial factors) are multiplied together, so that a learning factor is formed, which also assumes a value between 0 and 1.

In a further step, this calculated learning factor is then compared with the last available and stored learning factor. The newly calculated learning factor serves on the one hand to release the actual resistance compensation, in the case that this learning factor is greater than or equal to, that is, better or qualitatively at least equivalent to the previous learning factor. On the other hand, it serves as the new, improved and stored learning factor to provide the next reference value.

The method may further comprise steps in which, for the determination of a first and a second reference resistance value, the following is done modularly:
Determining a coil resistance of the feed pump coil (windings of the motor) at the match temperature. This can be calculated on the basis of the adjustment temperature via resistance characteristics of the feed pump. Such a characteristic curve is supplied with the temperature-dependent resistance coefficient of the coil material, for example with the values of copper.

In the same way, a standard coil resistance is determined, which applies to a selected reference temperature, for example, for 20 ° C.

Furthermore, a first resistance offset value is determined, which is formed from the difference between the coil resistance at the calibration temperature and the standard coil resistance:
Another second resistance offset value is determined from the standard coil resistance, the coil resistance, and the total resistance at the compensation temperature. It results from the difference between coil resistance at standard temperature and coil resistance at match temperature, which is divided by this coil resistance and then multiplied by the total resistance.

Finally, a standard total resistance is determined at a reference temperature (for example, 20 ° C.), which results once from the sum of the total resistance and the second resistance offset value, to which the following is added: The difference between the difference between the first resistance offset and the coil standard resistance and the sum of the total resistance and the second resistance offset, wherein the difference is multiplied by a weighting factor that weights the proportion of resistors outside the coil.

This weighting factor depends on the actual execution of the piping system and can take values between 0 and 1, between 0.25 and 0.75, between 0, 4 and 0.6 and a value of 0.5.

In a further embodiment of the method, the first and second reference resistance can now be determined from the variables determined above.

Accordingly, the first reference resistance, which designates a temperature-independent resistance at standard temperature, results from the difference between the standard total resistance and the standard coil resistance multiplied by the weighting factor.

The second reference resistance results from the difference between the standard total resistance and the first reference resistance.

The method uses valuation and / or weighting factors with amounts between 0 and 1. This allows a very simple scaling, which allows an evaluation or scaling of the affected size in a transparent and easily comprehensible manner.

The evaluation or scaling factors are stored either as fixed values, as scaled characteristic curves or characteristic maps in a suitable memory, or calculated for the application from other fixed values, characteristic curves, characteristic diagrams or other data that occur during operation.

The invention further relates to an SCR system having means adapted to carry out the method according to one of the preceding claims. In this way, an SCR system is available, in which a repeatable temperature determination of the SCR delivery pump can be carried out in operation with the aid of the automated resistance compensation, without the need for additional temperature sensors or a complex implementation process. The system is self-learning and self-correcting.

There are conveyor systems, in which the means comprise a separate control unit with a memory, a computer and data / signal interfaces, and this control unit controls the SCR feed pump and processes the sensor data required for carrying out the method. Thus, a largely self-sufficient SCR control system with its own intelligence is available.

In alternative embodiments, it is also possible that only the SCR delivery pump and the required sensors are arranged in such a module, while the steps required to carry out the method are carried out in a central external engine control unit, which also has a memory, a computer and corresponding data / signal interfaces. Such an embodiment simplifies the SCR system and utilizes existing structures that need only be appropriately sized and programmed to perform the method.

There are also methods in which the temperature adjustment can be based on the temperature of the reducing agent in the feed pump.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings. It shows:

1 a schematic representation of an embodiment of the method according to the invention;

2 a graph with different resistance components of the relevant current-carrying components, and

3 a schematic representation of an embodiment of an inventive SCR conveyor system.

This in 1 Scheme shows six functional blocks in which the main process steps are grouped and which are interconnected. Here, solid arrow lines represent input and output variables that are in the respective function blocks 1 - 6 processed or determined and output. Dotted arrow lines represent enable signals that indicate the processing in the respective function blocks 1 - 6 activate, trigger or release.

In the block 1 On the one hand, an enable _signal b _{Trig is} generated, which releases the execution of the resistance adaptation in the other blocks, and on the other hand determines a weighting or learning factor f _R , which designates the quality of the boundary conditions as a current calculation.

The main input variables in the function block 1 are:
an activation _signal b _Act , via which the function as a whole is activated, an activation _flag b _Upd , indicating that due to the standard activation of the SCR feed pump for an initial coil temperature measurement at KL-15 on (ignition on) new data of the current back measurement of the SCR Feed pump present.

• – Um die Freigabe der einzelnen Berechnungsfunktionen in den anderen Funktionsblöcken 2–6 über ein Signal b_Trig zu triggern, wird zunächst ein aktueller Anlernfaktor f_Ra bestimmt, der mit einem gespeicherten, vorhandenen Anlernfaktor f_Rv verglichen wird. Die Funktion wird nur ausgelöst, wenn der aktuelle Anlernfaktor f_Ra größer gleich dem vorhandenen Anlernfaktor f_Rv ist. Damit wird sichergestellt, dass die beim Abgleich berechneten Werte qualitativ mindestens gleichwertig zu den vorhandenen Werten sind, ist dies der Fall, wird eines von mehreren Freigabebits gesetzt.
• – Ein weiteres Freigabebit wird gesetzt, wenn das Aktivierungssignal b_Akt eingegeben wurde, das beispielsweise durch ein Aktivierungsflag b_Upd ausgelöst wird, welches anzeigt, dass neue Messwerte vorhanden sind.

Further input variables that are taken into account are the engine shutdown time Z _MA , the ambient temperature T _U and an adjustment temperature T _AG , which corresponds to the temperature of a reducing agent 15 in a reducing agent tank 11 corresponds (also SCR temperature). In the function block 1 This information is used to determine:

• - To release the individual calculation functions in the other function blocks 2 - 6 To trigger a signal b _Trig , a current learning factor f _Ra is first determined, which is compared with a stored existing learning factor f _Rv . The function is only triggered if the current learning factor f _{Ra is} greater than or equal to the existing learning factor f _Rv . This ensures that the values calculated during the adjustment are qualitatively at least equivalent to the existing values. If this is the case, one of several enable bits is set.
• A further enable bit is set when the activation _signal b _{Akt has been} input, which is triggered, for example, by an activation _flag b _Upd , which indicates that new measured values are present.

• – ein SCR-Fördersystemzustand, der anzeigt, dass die Pumpe nicht aktiv ist, um Reduktionsmittel zu fördern,
• – dass kein relevanter Fehler im Gesamtsystem vorliegt (dies kann die SCR-Anlage aber auch den Systemzustand des Motors bzw. des gesamten Fahrzeugs betreffen,
• – eine Bewertung des Zustands als Kaltstartbedingung, z.B. auf der Grundlage der Motorabstellzeit oder Motorauszeit Z_MA oder durch Abfrage einer Temperaturbedingung wie der, ob die Temperaturen von Kühlmittel, Abgas stromabwärts des Partikelfilters in der Abgasanlage und der Umgebungstemperatur T_U gleich sind,
• – einer Zustandsabfrage, ob die SCR-Dosierpumpe nach Einschalten der Zündung noch nicht geheizt oder defrostet hat,
• – einer Abfrage einer Umgebungstemperatur, die innerhalb eines zulässigen Bereichs liegen muss,
• – eine Abfrage, ob die Zündung eingeschaltet ist,
• – einer Abfrage, ob die Temperatur der Spule der SCR-Pumpe durch wiederholte Durchführung einer initialen Spulentemperaturmessung noch nicht so weit erhöht ist, dass eine Verfälschung beim Widerstandsabgleich auftreten könnte, und
• – die Abfrage einer Bedingung zur Betriebsunterbrechung, die beispielsweise eine Motorabstellzeit Z_MA oder eine Abstellzeit eines zugehörigen Steuergerätes berücksichtigt.

Further input variables, from which additional enable bits may need to be calculated, are indicated by the large dashed frame arrow. These can be, for example, the following:

• An SCR delivery system state indicating that the pump is not active to deliver reductant,
• - that there is no relevant error in the overall system (this may affect the SCR system but also the system state of the engine or the entire vehicle,
• An assessment of the condition as a cold start condition, eg based on the engine shutdown time or engine off time Z _MA or by interrogation of a temperature condition such as whether the temperatures of coolant, exhaust downstream of the particulate filter in the exhaust system and ambient temperature T _{U are the} same,
• - a status inquiry as to whether the SCR dosing pump has not yet heated or defrosted after switching on the ignition,
• A query of an ambient temperature which must be within a permissible range,
• A query whether the ignition is switched on,
• A query as to whether the temperature of the coil of the SCR pump has not yet been increased so much by repeated execution of an initial coil temperature measurement that a falsification of the resistance compensation could occur, and
• - The query of a condition for business interruption, which takes into account, for example, an engine shutdown time Z _MA or a shutdown time of an associated control unit.

The information of each individual bit is summarized in a "total byte". This is compared to a desired byte value. If the comparison result is positive, the method is activated and the quantities are determined as described below.

• – Ein Normabweichungsfaktor f_D20, der die Abweichung der Abgleichtemperatur T_AG von der Normtemperatur T₂₀ berücksichtigt. Die Normtemperatur T₂₀ ist beispielsweise 20°C. Beispielsweise wird der Faktor davon ausgehend so bestimmt, dass dieser bei einer betragsmäßigen Differenz von mehr als 10°C gleich 0 ist, dem schlechtestmöglichen Wert, oder bei einer Abweichung gleich 0, also wenn die Abgleichstemperatur T_AG gleich der Normtemperatur ist, gleich 1 ist (bestmöglicher Wert).
• – Der weitere Faktor f_DT, der als Messabweichungsfaktor bezeichnet wird, berücksichtigt in gleicher Weise die Abweichung der Abgleichtemperatur T_AG von der Umgebungstemperatur T_U. Er ergibt sich beispielsweise so, dass bei einer betragsmäßigen Differenz von ≥ 20°C der Faktor f_DT gleich 0 ist, und bei einer Abweichung von 0°C gleich 1.
• – Einen dritten Faktor bildet beispielsweise ein Abstellabweichungsfaktor f_DZ, der die Dauer der Motorabstellzeit Z_MA berücksichtigt. Hier wird beispielsweise ein bestmöglicher Wert 1 erhalten, wenn die Abstellzeit ≥ 8 Stunden ist, und ein schlechtestmöglicher Wert 0, wenn die Abstellzeit 0 Stunden beträgt.

The evaluation factor or learning factor f _R also calculated for the release of the method is determined by calculating several deviation factors via characteristic curves or characteristic diagrams or other available data. This includes:

• - A standard deviation factor f _D20 , which takes into account the deviation of the balancing temperature T _AG of the standard temperature T ₂₀ . The standard temperature T ₂₀ is, for example, 20 ° C. For example, the factor thereof is determined so that it is equal to 0 at an absolute difference of more than 10 ° C, the worst possible value, or at a deviation equal to 0, ie when the adjustment temperature T _{AG is} equal to the standard temperature, equal to 1 (best possible value).
• The further factor f _DT , which is referred to as a measurement deviation factor, likewise takes into account the deviation of the calibration temperature T _AG from the ambient temperature T _U. It results for example in such a way that with an absolute difference of ≥ 20 ° C the factor f _{DT is} equal to 0, and with a deviation of 0 ° C it is equal to 1.
• - A third factor forms, for example, a Abstellabweichungsfaktor f _DZ , which takes into account the duration of the engine shutdown time Z _MA . Here, for example, a best possible value of 1 is obtained if the stop time is ≥ 8 hours, and a worst possible value of 0 if the stop time is 0 hours.

Multiplication of the factors f _D20 , f _DT and f _DZ results in a current learning factor f _RA . Formula 1 applies: f _Ra = f _D20 × f _DT × f _DZ (1)

This current learning factor f _RA is compared with the existing learning factor f _RV and replaces it in the case when the current learning factor f _{RA is} greater (and thus qualitatively "better") than the existing learning factor f _RV . At the same time, the corresponding enable bit is set in this case, which then leads to the release of the further method in conjunction with the other bits.

The factors are determined on the basis of characteristic curves or characteristic diagrams, by means of which the desired boundary conditions are mapped to the values between 0 and 1.

In the function block 2 Then a temperature-independent resistance _offset R _{O1 is} calculated. This results from the total resistance R _{GT of} the circuit, determined on the basis of a measured voltage drop U, during the energization of the SCR delivery pump (see later 3 ). This total resistance R _GT consists of the partial resistors for the wiring harness and the connection contacts (plug connections and other connections) as well as from the coil resistance of the motor winding of an SCR delivery pump 14 , From this total resistance R _GT , the coil resistance R _{SPT is} subtracted. The formula 2 applies: R _O1 = R _GT - R _SPT (2)

The considered coil resistance R _SPT is dependent on the adjustment temperature T _AG , which corresponds to the reducing agent temperature. In the present case, T _{SPT is determined} from a characteristic curve which takes into account the temperature dependence of the coil material resistance (for example copper) via a material coefficient. Output size of the function block 2 is the temperature-independent resistance _offset R _O1 , and the coil resistance R _SPT .

In the function block 3 a temperature-dependent resistance _offset R _{O2 is} calculated. It results from a coil resistance factor f _RT , which results from the difference between a coil standard resistance R _SP20 (calculated, for example, at standard temperature, for example at 20 ° C) and the coil resistance R _SPT at calibration temperature (both are determined by the characteristic curve) divided by the resistance R _SPT at the match temperature. The formula is:

This factor is multiplied by the total resistance R _GT . The formula is:

The factor f _R denotes a characteristic number which indicates the deviation of the coil resistance at the adjustment temperature from the coil resistance at standard temperature.

In the function block 4 Then, a standard total resistance is determined, which would be present if the adjustment temperature T _{AG would be} equal to the standard temperature T ₂₀ . The value is given by the following formula: R _G20 = (R + R _{GT O2)} + _((O1 + R R _SP20) - (R _GT + _O2 R)) * (1 - f _G) (5)

The value results from two summands. The first summand contains the sum of the total resistance R _GT and the temperature-dependent resistance _offset R _O2 . The second summand is formed from the difference between two summands, namely the difference between the temperature-independent resistance offset R _O1 and the coil normal resistance R _SP20 and the sum of the total resistance R _GT and the temperature-dependent resistance _offset R _O2 . This value is corrected with a selectable weighting factor f _G (by the difference 1-f _G ), which takes into account the non-coil resistance component of the total resistance.

Based on this, then in the function block 5 the desired temperature-independent resistance R _{1 is} calculated at standard temperature (here 20 ° C), which results according to the formula 6. R ₁ = (R _G20 - R _SP20 ) · f _G (6)

It is composed of the total resistance at standard temperature (here 20 ° C) R _G20 , from which the coil standard resistor R _{SP20 is subtracted} with the weighting factor. And in the function block 6 then the temperature-dependent resistance at 20 ° R _{1 is} calculated, which results according to formula 7. R ₂ = R _G20 - R ₁ (7)

2 shows several temperature-dependent resistance curves (the resistance W is plotted here over the temperature T). The dot-dash line indicates the resistance curve of the coil (without wiring and terminations), the dotted line corrects the resistance of the coil by the temperature-independent offset (wiring and connections are temperature-independent) and the dotted line corrects the resistance of the coil by the temperature-dependent offset (wiring and Connections behave in a temperature-dependent way like the coil). By an appropriate choice of the weighting factor f _R results in the solid line, which reflects the resistance of the coil with weighted influence of the wiring and the connections, ie a close to reality course. This resistance profile can then be used to determine the coil temperature and thus also the temperature of the SCR delivery pump, for example, by a voltage measurement in the system described below.

3 shows the simplified structure of an SCR system 10 with a reducing agent tank 11 that with an SCR conveyor module 12 is provided, which via one or more sensors 13 which measure, for example, the reducing agent temperature, the reducing agent quality and / or the level. Furthermore, the SCR delivery module 12 with a feed pump 14 provided, which in the reducing agent tank 11 reducing agent present 15 over a line 16 and an injection nozzle 17 in an exhaust duct 18 metered in, where it reacts in the desired manner with nitrogen oxide-containing exhaust gases.

The pump 14 is from the reducing agent 15 lingers and therefore has about the temperature of the reducing agent 15 , To drive the pump 14 will the winding 19 via a power source 20 energized, via the wires of the wiring harness 21 , via several (not shown) contacts, connectors or the like with the power source or the winding 19 is coupled. The winding 19 , which is formed as a copper wire coil, and the wiring harness 21 each form partial resistors R _KB and R _SP .

By means of a voltage drop U measured in the cable harness, it is possible to determine the total resistance of the system, which results from the sum of the resistances R _KB and R _SP . The coil resistance varies with temperature according to a known temperature-dependent resistance coefficient.

Now, if the voltage U and the harness resistance R _{KB are} known, the coil resistance R _SP can be determined in conclusion and it can be determined by means of the resistance coefficient, the temperature T _SP and thus the temperature of the pump 14 , This replaces an additional temperature sensor with a voltage measurement in existing components.

The method described above is used to tune the resistors R _SP and R _{KB of} the system in order to obtain the most exact and repeatable temperature determination of the coil / winding 19 and thus the pump 14 (and ultimately also the reducing agent in the pump).

This tuning is performed regularly during operation (at least until a later no longer exceeded quality of the Anlernfaktors was achieved), for example, to be able to correct changes in the resistance R _KB .

The necessary calculations and evaluations are made via a control unit 22 that with a storage area 23 and a computing unit 24 is provided. The control unit 22 exchanges data and signals (dashed arrow 25 ) with the SCR system 10 off and also (shown by the dotted arrow 26 ) with a drive motor or and with other vehicle components. The control unit 22 can either be designed as a stand-alone "SCR control unit" and part of the SCR conveyor module 12 However, it can also be designed as a central engine control (ECU), in which the control of the SCR system 10 is performed.

Further variations and embodiments of the invention will become apparent to those skilled in the scope of the claims.

LIST OF REFERENCE NUMBERS

b _Act

 activation signal

b _Upd

 Activation flag, new readings available

b _Trig

 release trigger

b _SCR

 Enable SCR operation

f _R

 Factor / Anlernfaktor

f _Ra

 current learning factor

f _Rv

 existing learning factor

f _D20

 Standard deviation factor (deviation from standard temperature)

f _DT

 Deviation factor (deviation from the match temperature / SCR temperature)

f _DZ

 Abstellabweichungsfaktor (duration of the engine shutdown time)

_RT

 Coil resistance factor

R _GT

 Total resistance measured during calibration (at calibration / SCR temperature)

R _G20

 Norm total resistance

R _SPT

 Coil resistance calculated at calibration temperature (with temperature coefficients)

R _SP20

 Coil standard resistance calculated (with temperature coefficients)

R _O1

 temperature-independent resistance offset

R _O2

 temperature-dependent resistance offset

f _G

 Weighting factor (weights the "non-coil resistance")

R ₁

 virtual temperature-independent resistance (at standard temperature)

R ₂

 virtual temperature-dependent resistance (at standard temperature)

T _AG

 Temp / SCR temperature

T _U

 ambient temperature

T ₂₀

 standard temperature

Z _MA

 Motorabstellzeit

1 to 6

 function blocks

10

 SCR system

11

 Reductant tank

12

 SCR-delivery module

13

 sensors

14

 pump

15

 reducing agent

16

 management

17

 injection

18

 exhaust duct

19

 Winding / coil

20

 power source

21

 harness

22

 control unit

23

 Storage

24

 computer unit

25

 Arrow (data exchange SCR system)

29

 Arrow (data exchange engine / vehicle)

formulas:

• f _Ra = f _D20 × f _DT × f _DZ (1)
• R _O1 = R _GT - R _SPT (2)
  
• R _G20 = (R + R _{GT O2)} + _((O1 + R R _SP20) - (R _GT + _O2 R)) * (1 - f _G) (5)
• R ₁ = (R _G20 - R _SP20 ) · f _G (6)
• R ₂ = R _G20 - R ₁ (7)

Claims (10)

Method for automating a resistance compensation on a feed pump ( 14 ) of an SCR system ( 10 ): activating a resistance balance by interrogating conditions for enabling a resistance balance measuring a total resistance (R _GT ) at an adaptation temperature determining a first virtual resistance value (R ₁ ) and determining a second virtual resistance value (R ₂ ) and storing the first and second resistance values (R ₁ , R ₂ ) in a control unit ( 22 ). The method of claim 1, wherein querying resistance cancellation enabling conditions includes at least one of the steps of: - polling an ignition - polling an ambient temperature - polling a heater status - polling a first coldstart status - polling a second coldstart status - polling an error status - polling a Pressure state in the SCR system (pump not active) - polling a period after a coil measurement - evaluating an existing learning / evaluation factor (f _Rv ) - polling an activation switch position - querying a coil temperature condition - interrogating an operation interruption The method of claim 2, wherein the evaluating the existing training / evaluation factor (f _Rv ) comprises: calculating a current training / evaluation factor (fRa) determining a first partial factor (f _D20 ) from the difference of an adjustment temperature (T _AG ) and a standard temperature (T ₂₀ ) determining a second partial factor (f _DT ) from the difference between the calibration temperature (T _AG ) and the ambient temperature (T _U ) determining a third partial factor (f _DZ ) from a stop time of the system (Z _M ) multiplying the partial factors to Teach-in factor (f _Ra ) Compare the calculated teach-in / weighting factor (f _Ra ) with the available teach-in / weighting factor (f _Rv ). The method of claim 1, 2 or 3, wherein determining the first and second resistance values (R ₁ ; R ₂ ) comprises: determining a coil resistance (R _SPT ) of the SCR pump coil at the match temperature (T _AG ), determining a standard coil resistance ( R _SP20 ) of the SCR pump coil at the standard temperature (T ₂₀ ) Determining a first resistance _offset value (R _O1 ) from the total resistance (R _GT ) and the coil resistance (R _SPT ) Determining a second resistance _offset value (R _O2 ) from the standard coil resistance (R _SP20 ), the coil resistance (R _SPT ) and the total resistance (R _GT ) determining a standard total resistance (R _G20 ) from the total resistance (R _GT ), the first and second resistance _offset values (R _O1 , R _O2 ), the standard coil resistance (R _SP20 ), and a weighting factor (f _G ). Method according to claim 4, wherein the first resistance value (R ₁ ) results from the difference between the standard total resistance (R _G20 ) and the standard coil resistance (R _SP20 ) multiplied by the weighting factor (f _G ). Method according to claim 4 or 5, wherein the second resistance value (R ₂ ) results from the difference between the standard total resistance (R _G20 ) and the first reference resistance (R ₁ ). Method according to one of the preceding claims, wherein the evaluation and / or weighting factors between 0 and 1 amount. Method according to claim 7, wherein the evaluation and / or weighting factors consist of in a memory ( 23 ) stored data, characteristic, maps and / or determined from the operation of data, characteristics, maps are determined. SCR system ( 10 ) with a reducing agent delivery pump ( 14 ) and funds ( 12 ; 13 ; 16 ; 17 ; 22 ), which are adapted to carry out the method according to one of the preceding claims. SCR system ( 10 ) according to claim 9, wherein the means is a control unit ( 22 ) with a memory ( 23 ), a computer ( 24 ) and data / signal interfaces ( 25 . 26 ), wherein the control unit ( 22 ), the reducing agent delivery pump ( 14 ) and the sensors required to carry out the process ( 13 ) together in an SCR funding module ( 12 ) are arranged.

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