DE102016210847A1 - Method for operating an SCR system - Google Patents

Abstract

The invention relates to a method for operating an SCR system with a metering module and a delivery module. In this case, a feed pump and a return pump of the delivery module are connected via a common electrical supply line to a control unit of the SCR system or an internal combustion engine. The temperature of the feed pump is derived from the current strength of a current applied to the feed pump. Based on the applied current, a resistance is determined and compared with a reference resistor stored in the control unit. In order to enable an improved calculation of the temperature at the feed pump, a voltage drop at the feed pump is taken into account when the return pump is operated simultaneously with the feed pump and this simultaneous operation leads to a voltage drop at the feed pump. In this case, a voltage offset caused by a voltage drop across the feed pump due to the electric current through the return pump and the line resistance calculated and the calculated temperature applied to the feed pump with a correction factor to allow an improved calculation of the temperature at the feed pump.

Description

The invention relates to a method for operating an SCR system with a delivery and a metering module for metering a reducing agent for exhaust aftertreatment in the exhaust passage of an internal combustion engine.

In order to reduce the consumption of internal combustion engines and the associated CO ₂ emissions, fuel-optimized combustion processes are being developed for internal combustion engines. In diesel engines, direct fuel injection and improved combustion processes have made it possible to achieve a significant increase in the efficiency of the internal combustion engine. One way to reduce the consumption of a gasoline engine is a lean burn process, ie a combustion process in which the internal combustion engine is operated as far as possible with a superstoichiometric combustion air ratio. Since NOx emissions can no longer be adequately reacted with a conventional three-way catalytic converter from the exhaust gas in a diesel engine or a lean-burn gasoline engine, additional catalysts such as catalysts for the selective, catalytic reduction of nitrogen oxides (SCR catalysts) are available. known, with which the nitrogen oxide emissions in the exhaust gas can be reduced.

As a reducing agent for such SCR catalysts aqueous urea solution is used, which has a freezing point of about -11 ° C at a urea mass fraction of 32.5%. In order to ensure the operational readiness of a selective catalytic reduction (SCR) system, even at low temperatures, it is necessary to heat parts of the system. Such an SCR system has a delivery module and a metering module and a delivery pump and a return pump, with which the reducing agent can be conveyed from a reservoir to the metering and back into the reservoir. In order to restore the operational readiness after a freezing of the reducing agent in the SCR system and maintain it during operation, it is possible to energize the electric coils of the feed pump and the return pump and thus to achieve a heating effect. In order to prevent thermal damage to the delivery module in this process, which comprises the delivery pump and the return pump, the temperature is determined and monitored by means of a temperature model. For this purpose, the current of the feed pump is measured in an engine control unit, converted into a resistor and compared with a stored in the engine control unit software reference resistance. In this case, the resistance in addition to the resistance of the coil in the feed pump also includes the electrical resistance of the supply line between the control unit and the feed pump and the electrical resistance of an output stage.

If the feed pump and the return pump are connected to the battery via a common electrical line, a control of the return pump can lead to a voltage drop across the feed pump, as a result of which the temperature at the feed pump can not yet be determined exactly. In the worst case, this can lead to a low heat output and as a result to an insufficient thawing of the reducing agent in the feed pump.

From the DE 10 2012 212 564 A1 For example, a method for operating a metering and delivery module is known in which a temperature of the delivery module is calculated, in which a return path of the reducing agent is cooled by the return pump to reduce the temperature influence of the hot components by the heated reducing agent.

From the DE 10 2012 212 570 A1 a method for operating a conveying and metering system is known, wherein at least one heater for heating the reducing agent is provided on the conveying and metering system, wherein during a heating of the conveying and metering system, in particular during a thawing of the reducing agent, a flushing operation is provided in which the reducing agent is conveyed with closed dosing unit by the feed pump from the reducing agent tank and by the return pump back into the reducing agent tank.

The invention is based on the object of proposing a method with which an improved modeling and calculation of the temperatures at the pumps of the delivery module is possible without additional lines being required.

• – Ermittlung des Widerstands der gemeinsamen elektrischen Zuleitung zur Förderpumpe und Rückförderpumpe,
• – Ermittlung der elektrischen Stromstärke, welche durch die Rückförderpumpe fließt,
• – Berechnung eines Spannungsoffsets verursacht durch einen Spannungsabfall an der Förderpumpe aufgrund der elektrischen Stromstärke durch die Rückförderpumpe sowie des Leitungswiderstandes,
• – Berechnung einer Temperatur an der Förderpumpe aus der elektrischen Stromstärke durch die Förderpumpe, wobei
• – die Temperatur aus dem Spulenwiderstand der Spule der Förderpumpe ermittelt wird, und wobei
• – eine durch den Spannungsoffset verursachten Spannungsabfall an der Förderpumpe beim Betrieb der Rückförderpumpe hervorgerufene Widerstandserhöhung zur Bildung eines Korrekturfaktors für die Berechnung der Temperatur genutzt wird.

The object is achieved by a method for operating an SCR system with a delivery and a metering module for metering a reducing agent into an exhaust passage of an internal combustion engine, wherein the delivery module comprises a delivery pump and a return pump, comprising the following steps:

• Determination of the resistance of the common electrical supply line to the feed pump and return pump,
• Determination of the electric current flowing through the return pump,
• - Calculation of a voltage offset caused by a voltage drop at the feed pump due to the electric current through the return pump and the line resistance,
• - Calculating a temperature at the feed pump from the electric current through the feed pump, wherein
• - The temperature is determined from the coil resistance of the coil of the feed pump, and wherein
• - A caused by the voltage offset voltage drop at the pump during operation of the return pump caused increase in resistance to form a correction factor is used for the calculation of the temperature.

Since the voltage at the feed pump in an SCR system with a common electrical supply line for feed pump and return pump can not be measured directly on the feed pump, but is determined indirectly via a voltage at the main relay, can in known from the prior art SCR systems a voltage drop due to the simultaneous operation of feed pump and return pump are not taken into account. This leads to a deviation in the temperature model. The inventive method is also in SCR systems with a common electrical supply line for the feed pump and the return pump a significantly improved determination of the temperature at the pump possible. With the help of the proposed method, a compensation of the influence of the return pump on the temperature model of the feed pump is possible, so that the risk of damage to the feed pump due to insufficient thawed reducing agent by a too low heating power to the coil of the feed pump greatly reduced.

Advantageous improvements and further developments of the method proposed in the independent claim for operating an SCR system are possible by the measures listed in the dependent claims.

In a preferred embodiment of the invention it is provided that the correction factor for the temperature is determined by dividing the increase in resistance by a reference resistor and the temperature coefficient of the conductor material of the electrical supply line. The resistance of the common electrical supply line of feed pump and return pump can be calculated by knowing the length of the supply line, the cross-section of the supply line and the material of the supply line or metrologically determine in the course of the application and deposit as parameters in the software of a control unit, in particular the engine control unit , Thus, a further improvement of the method is possible.

In a further preferred embodiment of the invention it is provided that for determining the voltage drop across the feed pump, the following input variables are determined: a virtual, temperature-independent reference resistance of the feed pump, a virtual, temperature-dependent reference resistance of the feed pump, the electric current of a current through the return pump, and the ambient temperature , As a result, a voltage drop across the feed pump can be determined even more precisely by triggering the return pump, which contributes to a further improvement of the method according to the invention.

According to a further improvement of the method, it is provided that the resistance of the common electrical supply line from the feed pump and the return pump is subjected to a correction factor as a function of the ambient temperature. Since the resistance of the conductor material is temperature-dependent, a correction factor can be used to achieve a further improvement of the modeled temperature at the delivery pump.

It is particularly advantageous if, in the calculation of the correction factor, first the resistance of the wiring harness of the entire electrical wiring from a battery of the internal combustion engine via the delivery module to the control unit is calculated. Thereby, the resistance in the wire harness can be estimated, which contributes to an increase in the accuracy of the model.

According to an advantageous embodiment, it is provided that the calculation of the resistance of the wiring harness by a subtraction of the coil resistance at 20 ° C from the virtual, temperature-dependent resistor and a subsequent addition of the virtual, temperature-independent reference resistance of the feed pump. It is particularly advantageous if the resistance of the wiring harness is subjected to a correction factor in order to take into account a deviation of the resistance of the wiring harness from a resistance of the wiring harness at a reference temperature of 20 ° C. As a result, an additional temperature compensation of the resistance in the wiring harness as a function of the ambient temperature is possible, which contributes to a further improvement of the calculation model for the temperature at the feed pump.

According to a further improvement of the method, it is provided that the calculation of the resistance of the supply line from the resistance of the wiring harness minus the output stage resistance of the control unit is divided by an applicable factor. Thus, the calculation model can be further improved, which contributes to a more accurate determination of the temperature at the feed pump and thus to a further improvement of the result.

According to the invention, a control device for an internal combustion engine is provided, wherein the control device has a computer-readable program algorithm for controlling a method for operating an SCR system. By a stored in the control unit program code is a simple implementation of the method of the invention underlying calculation of the temperature at the feed pump possible.

In the context of the invention is also an SCR system for metering a reducing agent for selective catalytic reduction in an exhaust passage of an internal combustion engine, comprising a metering module and a delivery module and a reservoir for storing the reducing agent, and a control unit, wherein the control device is set to a Perform a method with features or feature combinations according to this representation.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with each other.

The invention will be explained below in embodiments with reference to the accompanying drawings. Show it:

1 an SCR system for carrying out a method according to the invention on an exhaust gas passage of an internal combustion engine,

2 an electrical circuit diagram for an SCR system for carrying out a method according to the invention,

3 a calculation scheme for temperature correction according to the invention of the determined temperature at a feed pump of an SCR system.

1 shows an embodiment of an SCR system 10 on an exhaust duct 24 an internal combustion engine 22 , The internal combustion engine 22 is preferably designed as a diesel engine, but may alternatively be designed as a gasoline engine. The SCR system 10 includes a conveyor module 12 , a dosing module 14 and a reservoir 16 for storing a reducing agent, in particular aqueous urea solution. The storage tank 16 can have a heater 38 have, with which a freezing of the reducing agent can be prevented or frozen reducing agent for commissioning of the SCR system 10 can be thawed. The conveyor module 12 , the dosing module 14 as well as the heating 38 are via signal lines 36 with a control unit 34 of the internal combustion engine 22 connected. The conveyor module 12 has a dosing line 40 on which the conveyor module 12 with the dosing module 14 combines. The dosing module 14 has a filter 42 and a metering valve 44 on. The conveyor module 12 has a feed pump 18 and a return pump 20 on, with the reservoir 16 via a first connection line 46 with the feed pump 18 of the conveyor module 12 and via a second connection line 48 with the return pump 20 the delivery module is fluidly connected. The pump 18 points upstream of a pump element of the feed pump 18 a first check valve 50 and a second check valve downstream of the pump element 52 on to prevent a reducing agent flow contrary to the intended flow direction. The return pump 20 has upstream of a pump element of the return pump 20 a first check valve 54 and a second check valve downstream of the pump element 56 on to prevent a flow of the reducing agent against the intended flow direction. The pump 18 also has a coil 26 for controlling the feed pump 18 on, which in addition to heating the feed pump 18 can be used. The metering valve 44 , the heating system 38 as well as the pumps 18 . 20 of the conveyor module are via signal lines 36 or via joint leadership 28 with the control unit 34 connected to the internal combustion engine. Here are the feed pump 18 and the return pump 20 via a common electrical line 28 connected to the battery, which in each case separate lines for the feed pump and the return pump can be saved.

In 2 is an electrical schematic for the SCR system 10 shown. A battery 30 of the internal combustion engine 22 is with her minus pole to ground 60 connected. The battery 30 is with its positive pole with a main relay 58 connected. The SRC system 10 is via an SCR relay 62 switchable, which via the common electrical supply line 28 with the conveyor module 12 connected is. The common electrical supply line 28 is preferably made of copper and has a conductor cross section of about 0.5mm ² . The conveyor module 12 has the feed pump 18 and the return pump 20 on, which via the common electrical supply line 28 can be controlled.

In operation of the internal combustion engine 22 The aqueous urea solution is in the exhaust channel 24 of the internal combustion engine 22 dosed to the nitrogen oxide emission of the internal combustion engine 22 to minimize. Since aqueous urea solution has a freezing point of about -11 ° C and the operational readiness of the SCR system 10 even at low Temperatures must be ensured, it is necessary that parts of the SCR system, such as the reservoir 16 and the delivery pump 18 as well as the return pump 20 can be heated. For this purpose it is possible to use the copper coils 26 the feed pumps 18 . 20 to energize and achieve in this way a heating effect. So that this process does not damage the conveyor module 12 due to overheating, the temperature of the feed pump 18 and the return pump 20 determined and monitored by means of a temperature model. This is done in the control unit 34 the flow of the feed pump 18 measured, converted into a resistor and this resistance with one in the software of the controller 34 deposited reference resistance. The resistance includes besides the resistance of the copper coil 26 the feed pump 18 also the electrical resistance of the common electrical supply line 28 between the controller 34 and the feed pump and the resistance of the final stage of the controller 34 ,

Because the feed pump 18 and the return pump 20 via a common electrical supply line 28 with the SCR relay 62 or with the battery 30 connected, leads a simultaneous control of the two pumps 18 . 20 to a voltage drop at the feed pump 18 , This situation lies in the operation of the SCR system 10 especially at low ambient temperatures often before, as well as the return pump 20 is controlled in heating mode. Because the voltage on the feed pump 18 However, not directly measured, but for the calculation of the voltage at the feed pump 18 the voltage at the main relay 58 is used, the voltage drop in known from the prior art temperature models is not taken into account and leads to a deviation in the temperature model.

• 1. Der Leitungswiderstand R_L der gemeinsamen elektrischen Zuleitung 28 von Förderpumpe 18 und Rückförderpumpe,
• 2. Die Stromstärke des Stroms I_RP des elektrischen Stroms, der durch die Rückförderpumpe 20 fließt.

Using the method proposed here, the influence of the return pump 20 on the temperature model of the feed pump 18 be compensated. The following quantities must be known:

• 1. The line resistance R _{L of} the common electrical supply line 28 from pump 18 and return pump,
• 2. The current flow I _{RP of} the electric current passing through the return pump 20 flows.

The line resistance R _L can be determined metrologically by knowledge of length, cross section and material or mathematically in the course of the application process and as parameters in the software of the control unit 34 deposit. Alternatively, the line resistance R _{L can be determined} from values measured in the control unit.

The current I _{RP of} the return pump is in the control unit 34 already calculated for other purposes and can be used for this task. In a defrost operation of the SCR system 10 flows through the return pump 20 for example, a current of about 1.7 A.

Using the current I _{RP of} the current through the return pump 20 and the line resistance R _{L of} the common electrical supply line 28 can be a voltage drop ΔU at the feed pump 18 calculate as follows: ΔU = R _L * I _RP

In the temperature model of the feed pump 18 the calculation of the temperature T is carried out by a read back of the pump flow through the feed pump 18 , By the coil resistance R _{SPFP of} the coil 26 the feed pump 18 , which can be calculated from it, finally their temperature is modeled. However, the effective voltage deviates from the feed pump 18 by a voltage drop .DELTA.U, this leads to an apparent increase in the resistance .DELTA.R and thus to an error in the temperature model. ΔR = ΔU / (I _FP )

From this increase in resistance ΔR, the deviation of the temperature model ΔT can be calculated: ΔT = ΔR / (α _L × R _REF )

The proposed method can compensate for this deviation and thus achieve a higher accuracy in the temperature modeling.

• – R_FIX: ein virtueller, temperaturunabhängiger Referenzwiderstand der Förderpumpe 18
• – R_coil: ein virtueller, temperaturabhängiger Referenzwiderstand der Förderpumpe 18
• – I_RP: die Stromstärke eines Stroms durch die Rückförderpumpe 20
• – T_UmG: die Umgebungstemperatur

The following input variables are calculated in the control unit to calculate the voltage drop ΔU 34 processed and calculated according to the procedure described above.

• - R _FIX : a virtual, temperature-independent reference resistance of the feed pump 18
• - R _coil : a virtual, temperature-dependent reference resistance of the feed pump 18
• - I _RP : the current of a current through the return pump 20
• - T _UmG : the ambient temperature

From this, the output voltage is the voltage drop .DELTA.U at the feed pump 18 by controlling the return pump 20 determined.

Also calculated in the function is the resistance R _{L of} the common electrical supply line 28 , For this purpose, first the resistance R _{KB of} the wiring harness of the entire wiring of the battery 30 via the conveyor module 12 to the control unit 34 calculated. This is done according to the formula: R _KB = (R _coil - R _{coil20 °} ) + R _Fix

The values for the virtual, temperature-independent reference resistance of the feed pump 18 R _Fix and the virtual, temperature-dependent reference _resistor R _coil are thereby removed from the control unit 34 The value R _{coil20 °} corresponds to the coil resistance of the coil 26 the feed pump 18 at 20 ° C and is used as an applicable value already in other functions.

The resistance of the common electrical supply line 28 R _L is then calculated from the resistance of the cable harness R _KB minus the output stage resistors R _{End of} the control unit 34 divided by an applicable factor K: R _L = (R _KB - R _End ) / K

The values for the resistance of the final stage R _{End of} the control unit 34 need from the datasheet of the controller 34 be taken over. With the applicable factor K, it is possible, the aspect ratio of supply and control line to the engine control unit 34 adapt.

Since the calculated values all refer to a temperature of 20 ° C, the resistance is converted to the current harness temperature with a function to obtain a resistance value of the supply line corrected to the ambient temperature. The voltage drop is then calculated from the determined quantities using Ohm's law: ΔU = R _L * I _RP

The voltage drop ΔU calculated in the new model is used in the existing function for correction of the rms voltage, which is the rms value of that at the feed pump 18 expressing applied voltage. With the help of this voltage, the resistance of the circuit is calculated and thus the temperature at the feed pump 18 modeled. In this way, the influence of the return pump 20 considered in the temperature model.

The inventive method is in 3 shown graphically.

LIST OF REFERENCE NUMBERS

10

SCR system

12

delivery module

14

dosing

16

reservoir

18

feed pump

20

Return pump

22

internal combustion engine

24

exhaust duct

26

Coil of the feed pump

28

(common) electrical supply line

30

battery

32

harness

34

control unit

36

signal line

38

heater

40

connecting line

42

filter

44

metering valve

46

connecting line

48

connecting line

50

check valve

52

check valve

54

check valve

56

check valve

58

main relay

60

Dimensions

62

SCR relay

I _FP

Amperage of a current through the feed pump

I _RP

Amperage of a current through the return pump

K _T

Correction factor for the temperature

R _coil

virtual temperature-dependent reference resistance of the feed pump

R _End

Resistance of the power amplifier

R _fix

virtual, temperature-independent reference resistance of the feed pump

R _KB

Resistance harness

R _L

Resistance of the common supply line

R _REF

reference resistor

R _SpFp

Coil resistance of the feed pump

T

temperature

T _UMG

ambient temperature

.DELTA.R

resistance change

.DELTA.T

Correction factor temperature

.DELTA.U

voltage drop

α _L

temperature coefficient

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102012212564 A1 [0005]
• DE 102012212570 A1 [0006]

Claims (10)

Method for operating an SCR system ( 10 ) with a delivery module ( 12 ) and a dosing module ( 14 ) for dosing a reducing agent in an exhaust gas channel ( 24 ) of an internal combustion engine ( 22 ), whereby the delivery module ( 12 ) a feed pump ( 18 ) and a return pump ( 20 ), comprising the following steps: - determination of the resistance (R _L ) of a common electrical supply line ( 28 ) to the feed pump ( 18 ) and return pump ( 20 ), - determination of the electric current (I _RP ) of a current, which by the return pump ( 20 ), - calculation of the voltage drop (ΔU) at the feed pump ( 18 ) due to the electric current (I _RP ) through the return pump ( 20 ) as well as the line resistance (R _L ), - calculation of a temperature (T) on the feed pump ( 18 ) from the electric current (I _FP ) by the feed pump ( 18 ), wherein - the temperature (T) from the coil resistance (R _SPFP ) of the coil ( 26 ) of the feed pump ( 18 ) is determined, characterized in that - a voltage drop caused by a voltage offset (.DELTA.U) on the feed pump ( 18 ) during operation of the return pump ( 20 ) is used to form a correction factor (ΔT) for calculating the temperature (T). Method according to Claim 1, characterized in that the correction factor (ΔT) is obtained by dividing the resistance increase (ΔR) by a reference resistance (R _REF ) and the temperature coefficient (α _L ) of the conductor material of the electrical supply line (ΔT). 28 ) is determined. A method according to claim 1 or 2, characterized in that for determining the voltage drop (ΔU) on the feed pump ( 18 ), the following input variables are determined: a virtual, temperature-independent reference resistor (R _fix ) of the feed pump ( 18 ), - a virtual, temperature-dependent reference resistance (R _coil ) of the feed pump ( 18 ), - the electrical current (I _RP ) of a current through the return pump ( 20 ), - the ambient temperature (T _UMG ), and therefrom a voltage drop (ΔU) on the feed pump ( 18 ) by controlling the return pump ( 20 ) is determined. Method according to one of claims 1 to 3, characterized in that the resistance of the electrical supply line ( 28 ) As a function of the ambient temperature (T _amb) with a correction factor (K _T) is applied. Method according to Claim 4, characterized in that the correction factor (K _T ) is calculated by first determining the resistance (R _KB ) of a cable harness ( 32 ) of the entire electrical wiring of a battery ( 30 ) of the internal combustion engine ( 22 ) via the conveyor module ( 12 ) to the control unit ( 34 ) is calculated. A method according to claim 5, characterized in that the calculation of the resistance of the wiring harness (R _KB ) by a subtraction of the coil resistance (R _coil20 ) at 20 ° C of the virtual temperature-dependent resistor (R _coil ) and a subsequent addition of the virtual temperature-independent reference resistor ( R _fix ) of the pump ( 18 ) he follows. A method according to claim 6, characterized in that the calculation of the resistance of the supply line (R _L ) from the resistor (R _KB ) of the wiring harness ( 32 ) minus the output stage resistances (R _End ) of the control unit ( 34 ) divided by an applicable factor. A method according to claim 7, characterized in that the resistance of the wiring harness (R _KB ) is subjected to a correction factor to a deviation of the resistance of the wiring harness (R _KB ) of a resistance of the wiring harness (R _KB20 ) at a reference _temperature of 20 ° C. to take into account. Control unit ( 34 ) for an internal combustion engine, wherein the control device has a computer-readable program algorithm for controlling a method according to one of claims 1 to 8. SCR system ( 10 ) for dosing a reducing agent for selective catalytic reduction into an exhaust gas duct ( 24 ) of an internal combustion engine ( 22 ) comprising a dosing module ( 14 ) and a conveyor module ( 12 ) and a storage container ( 16 ) for storing the reducing agent, and a control unit ( 34 ), whereby the control unit ( 34 ) is arranged to perform a method according to any one of claims 1 to 8.

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