DE102014223069A1 - Method and device for detecting gas bubbles in a reducing agent conveyor - Google Patents

Abstract

The invention relates to a method for operating a conveyor for reducing agent for nitrogen oxide reduction of exhaust gas of an internal combustion engine with a first reciprocating pump with a delivery chamber and a first solenoid, wherein an energy demand per stroke of the first reciprocating pump and a system pressure on the pressure side of the conveyor are determined. The invention further relates to a device for carrying out the method. Method and apparatus allow earlier detection of sucked gas in the conveyor and a reduction of malfunction of the conveyor.

Description

State of the art

The invention relates to a method for operating a conveyor for reducing agent for nitrogen oxide reduction of exhaust gas of an internal combustion engine with a first reciprocating pump with a delivery chamber and a first solenoid, wherein an energy demand per stroke of the first reciprocating pump and a system pressure on the pressure side of the conveyor are determined.

The invention further relates to a control device for controlling a conveyor for reducing agent for nitrogen oxide reduction of exhaust gas of an internal combustion engine, wherein the conveyor has at least a first reciprocating pump with a delivery chamber, a first solenoid and a pressure sensor for determining a system pressure of the conveyor, wherein the control means associated with a processing device and wherein the processing means are supplied with values of an electric current through the first solenoid and the system pressure.

The nitrogen oxide emission of internal combustion engines can be reduced by exhaust aftertreatment by means of selective catalytic reduction (SCR). This can in particular also in diesel engines with temporally predominantly lean, i. nitrogen oxide rich exhaust gas can be used. In this case, a defined amount of a selectively acting reducing agent is added to the exhaust gas. For this example, ammonia can be used, which is added directly in gaseous form or is obtained from a precursor substance in the form of urea or from a urea-water solution (HWL).

In the DE 10139142 A1 is described an exhaust gas purification system of an internal combustion engine, in which an SCR catalyst is used to reduce the NO _x emission, which reduces the nitrogen oxides contained in the exhaust gas with the reagent ammonia to nitrogen. The ammonia is recovered from the HWL in a hydrolysis catalyst upstream of the SCR catalyst. The hydrolysis catalyst converts the urea contained in the HWL to ammonia and carbon dioxide. In a second step, the ammonia reduces the nitrogen oxides to nitrogen, with water being produced as a by-product. The exact procedure has been adequately described in the specialist literature (cf. WEISSWELLER in CIT (72), pages 441-449, 2000 ). The HWL is provided in a reagent tank and is known, for example, under the name AdBlue as a 32.5% solution.

The HWL is conveyed by a line from the tank to a metering valve and metered into the exhaust tract. In the DE 196 07 073 A1 a Flüssigkeitszudosiersystem, in particular for metering of liquids to a fuel or in combustion resulting exhaust gases, described which an electrically operable Dosierpumpeinrichtung for conveying the metered liquid from a Zudosierflüssigkeitstank to be mixed with Zudosierflüssigkeit medium, a detection arrangement for detecting a During operation of the metering pump device adjusting and characterizing this operating variable and an evaluation unit for comparing the operating variable with at least one reference value and for determining the operating state of the metering pump means based on the comparison result comprises. It is further provided that is detected as the operating variable flowing through the metering pumping pumping current. By evaluating the time course of the pumping current and comparison with reference curves and / or threshold values stored in a characteristic map, error states during the movement of the armature of the pumping device can be detected and, secondly, the accuracy of the metered addition can be increased, irrespective of, for example, the viscosity state of the metered-addition liquid.

In current metering systems, as are known by way of example under the name DENOXTRONIC 5.1 from Bosch, a reciprocating pump sucks the HWL from the reagent tank in a delivery module and compresses it to the system pressure of 4.5 to 8.5 bar required for atomization. A metering module measures the amount of HWL required for NO _x reduction and atomizes it into the exhaust gas stream upstream of the SCR catalyst. Control of the dosing and heating strategy as well as on-board diagnostics (OBD) can be performed by a higher-level engine control or by a dosing control unit. With the processing of the current engine operating data and all required sensor data, the amount of reducing agent is matched exactly to the engine operating point and to the catalyst-specific properties for maximum nitrogen oxide reduction.

The pressure and the flow rate must be maintained and monitored during operation. Device gas in the reciprocating pump whose capacity decreases by design very strong because their compression ratio is too low to promote sucked gas through a downstream check valve to the system pressure side. If such a condition is detected early, the gas can be flushed out via the return if gas has been sucked in for only a short time.

The DE102012212560A1 describes a method for operating a pump system which is provided for conveying a liquid medium from a tank and for metering the medium via a pressure line by means of at least one metering unit, wherein the pump system at least one feed pump and at least one means for the return of the medium, in particular a return pump and / or a switching valve for a return, characterized in that for the elimination of gas volumes in the pump system medium or a medium-gas mixture or gas is promoted via activation of the feed pump with the metering unit closed and the means for returning the medium activated becomes. In the DE102012212560A1 Examples are described, whereby gas volumes can occur in the system and what disadvantages this can entail. However, it is not described how early such a gas volume can be detected.

The DE102012212558A1 describes a method for filling and venting of dry components of a delivery and metering system, which is provided for conveying a liquid medium from a tank and for metering the medium via a pressure line by means of at least one metering unit, the system at least one feed pump and at least one device for the return conveyance of the medium into the tank, in particular a return pump and / or a switching valve for a return, comprises, characterized in that medium is pumped from the tank by activating the feed pump and by activating the means for returning the medium back into the tank is running. The DE102012212558A1 describes a method for removing a volume of gas from the system, especially when the system is restarted. However, it does not describe an early detection of a gas volume during operation.

• a) eine Pumpe (11) fördert diskontinuierlich mit einer vorgebbaren Taktfrequenz periodisch gegebenenfalls vorhandenes Leckage-Öl (3) aus dem unteren Bereich des Gehäuses (1) zurück in den Tank (4) des Hydrauliksystems;
• b) eine Meßeinrichtung (20) mißt, ob die Pumpe (11) leer läuft oder Leckage-Öl (3) fördert;
• c) falls die Pumpe (11) leer läuft, wird die Taktfrequenz verringert bis zu einem vorgebbaren Mindestwert;
• d) falls die Pumpe (11) Leckage-Öl (3) fördert, wird die Taktfrequenz stetig oder stufig erhöht, bis zu einer maximalen Förderung.

The DE3834073A1 Describes a method for detecting, monitoring and adapted return of the components of a closed, a tank ( 4 ) containing hydraulic system escaping amounts of leakage oil ( 3 ) located in the lower area of a housing surrounding the hydraulic system ( 1 ), characterized by the following features:

• a) a pump ( 11 ) conveys intermittently with a predetermined clock frequency periodically possibly existing leakage oil ( 3 ) from the bottom of the housing ( 1 ) back to the tank ( 4 ) of the hydraulic system;
• b) a measuring device ( 20 ) measures whether the pump ( 11 ) runs empty or leakage oil ( 3 ) promotes;
• c) if the pump ( 11 ) is idle, the clock frequency is reduced to a predetermined minimum value;
• d) if the pump ( 11 ) Leakage oil ( 3 ), the clock frequency is increased steadily or in stages, up to a maximum promotion.

In the DE3834073A1 a method is specified, with which an idling a reciprocating pump can be determined. Here, the duration of a stroke of the pump is determined, which is shorter when idling than a stroke with promotion of liquid.

It is therefore an object of the invention to provide a method with which it is possible, as early as possible to detect a suction of a gas volume in a conveyor for a reducing agent to avoid malfunction of the system.

It is a further object of the invention to provide a device for carrying out the method.

Disclosure of the invention

The object of the invention relating to the method is achieved in that a comparison value for the energy requirement per stroke is determined as a function of at least the system pressure in a delivery chamber filled with reducing agent and that gas in the delivery chamber of the first reciprocating pump is closed when the energy requirement per stroke at a given system pressure is a predetermined level below the comparison value. The term delivery chamber here is to be understood as the volume between the first check valve and the second check valve. If there is a gaseous partial volume in this volume or if the volume is completely filled with a gaseous substance, the delivery capacity of the first reciprocating pump drops sharply at a high system pressure, which is intended to be in the range of 4.5 to 8.5 bar. If a dosing process is carried out under such conditions, the system pressure decreases inappropriately and a malfunction of the system is assumed. If according to the invention gas is detected in the delivery chamber, no dosing process is triggered and countermeasures can be initiated; a malfunction of the conveyor can be avoided.

In a particularly simple and cost-effective method variant, the comparison value is equated to the energy requirement for the stroke preceding a stroke or an average or a weighted average of the energy requirement for a predefinable number of preceding strokes. In this variant, the comparison value determined during operation with completely filled with reducing agent pumping space and a first suction of gas volume, for example, in an emptying reservoir or briefly in the intake low fluid level found. A low intake fluid level in the intake area may occur during slosh events due to high vehicle accelerations.

In an advantageous continuation of the method is provided that the comparison value stored in a map or a functional context as a function of at least the system pressure and / or a supply voltage of the first solenoid and / or a temperature of the first solenoid and for comparison with the energy requirements for the is removed to be checked.

In one embodiment of the method, it is provided that the energy requirement is determined from a value for the electric current through the first magnetic coil at a stroke end and a stroke duration of the first reciprocating piston pump. In this embodiment, only two values have to be determined with the duration up to the stroke end and the current through the magnetic coil at this stroke end in order to determine the energy requirement, or at least one value characterizing this. This variant of the method is therefore particularly easy to implement.

The object of the invention relating to the device is achieved in that the processing device is designed to compare an energy requirement per stroke with a default value and to close gas in the delivery chamber of the first reciprocating pump when the energy demand per stroke at a given system pressure by one is below the reference value. With the addition of the processing device according to the invention, a partial volume of gas leading to a reduced capacity of the reciprocating pump can be detected early in the delivery space and countermeasures can be initiated before a pressure drop during operation of the delivery device leads to a malfunction.

The invention will be explained in more detail below with reference to an embodiment shown in FIGS. Show it:

1 a conveyor for reducing agents,

2 a diagram for Hubenergie a first reciprocating pump.

1 shows a conveyor for a reducing agent 12 for nitrogen oxide reduction of exhaust gas of an internal combustion engine. The reducing agent 12 gets out of a reservoir 11 via a sampling line 13 taken from it by a first reciprocating pump 16 via a first check valve 14 is sucked. The first reciprocating pump 16 is from a first solenoid 15 powered by a control device 10 is controlled. The first reciprocating pump 16 promotes the reducing agent 12 via a second check valve 17 to a dosing unit 20 which the reducing agent 12 metered into an exhaust passage of the internal combustion engine before a catalyst for selective catalytic reduction. As a delivery chamber of the first reciprocating pump 16 this is the area between the first check valve 14 and the second check valve 17 construed. At a pressure line between the second check valve 17 and the dosing unit 20 are a pulse damper 18 and a pressure sensor 19 connected, whose output signal is a system pressure, the control device 10 is supplied. The pressure line between the second check valve 17 and the dosing unit 20 is over a fourth check valve 25 with a second reciprocating pump 24 connected to the recycling of reducing agent 12 in the reservoir 11 serves. The second reciprocating pump 24 is from a second solenoid 23 powered by the control device 10 is controlled and promotes the reducing agent as needed 12 or a mixture of gas and reducing agent 12 via a third check valve 22 and a return line 21 in the reservoir 11 ,

The reciprocating pump 16 , has at high system pressure with gas volume in the delivery chamber, a low flow rate, which can lead to an undesirable pressure drop when the dosing unit 20 performs a dosing. When commissioning with a not yet with reducing agent 12 filled system or if from the first reciprocating pump 16 Gas bubbles can be promoted, with closed dosing unit 20 by simultaneous control of the first and second reciprocating pump 16 . 24 without significant pressure build-up a circulation of reducing agent 12 be generated, which rinses out gas bubbles. Subsequently, in a normal operation of the first reciprocating pump 16 the system pressure of typically 4.5 to 8.5 bar are built.

2 shows in a diagram 30 along a stroke-duration axis 32 and a current axis 31 Lines of the same Hubenergie with reduction medium for the first solenoid 15 the first reciprocating pump 16 , On the stroke-duration axis 32 is the duration of a stroke of the first reciprocating pump 16 applied at the current operating conditions with respect to supply voltage and temperature of the solenoid coil. On the current axis 31 is the electricity through the first solenoid 15 applied at stroke end. Values of the same Hubenergie are exemplary on a line of first Hubenergie 33 , a line of second Hubenergie 34 or a line of third Hubenergie 35 , A same Hubenergie with different stroke duration and different current occurs at a constant system pressure and a variation of the boundary conditions such as different supply voltage or temperature of the first solenoid 15 on. One of a third Hubenergie 35 on a second Hubenergie 34 or a first Hubenergie 33 reduced Hubenergie occurs at a reduction of the system pressure. This reduced system pressure is also from the pressure sensor 19 detected. If the system pressure remains substantially the same, however, the lifting energy nevertheless decreases in the direction of a change in the hive energy 36 , is based on a gas volume in the delivery chamber of the first reciprocating pump 16 closed and countermeasures can be initiated before it comes to a malfunction of the conveyor.

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 10139142 A1 [0004]
• DE 19607073 A1 [0005]
• DE 102012212560 A1 [0008, 0008]
• DE 102012212558 A1 [0009, 0009]
• DE 3834073 A1 [0010, 0011]

Cited non-patent literature

• WEISSWELLER in CIT (72), pages 441-449, 2000 [0004]

Claims (5)

Method for operating a delivery device for reducing agent for nitrogen oxide reduction of exhaust gas of an internal combustion engine with a first reciprocating piston pump ( 16 ) with a delivery chamber and a first magnetic coil ( 15 ), wherein an energy requirement per stroke with reduction medium of the first reciprocating pump ( 16 ) and a system pressure on the pressure side of the conveyor are determined, characterized in that a comparison value for the energy requirement per stroke as a function of at least the system pressure at a filled with reducing agent delivery chamber is determined and that on gas in the delivery chamber of the first reciprocating pump ( 16 ) is closed when the energy requirement per stroke at a given system pressure is a pre-limit below the comparison value. Method according to Claim 1, characterized in that the comparison value is equated with the energy requirement for the stroke preceding a stroke or an average or a weighted average of the energy requirement for a predefinable number of preceding strokes. A method according to claim 1 or 2, characterized in that the comparison value in a characteristic field or a functional relationship as a function of at least the system pressure and / or a supply voltage of the first magnetic coil ( 15 ) and / or a temperature of the first magnetic coil ( 15 ) and taken for comparison with the energy requirement for the hub to be tested. Method according to one of claims 1 to 3, characterized in that the energy demand from a value for the electric current through the first magnetic coil ( 15 ) at a stroke end and a stroke duration of the first reciprocating pump ( 16 ) is determined. Control device ( 10 ) for controlling a conveyor for reducing agent for nitrogen oxide reduction of exhaust gas of an internal combustion engine, wherein the conveyor at least a first reciprocating pump ( 16 ) with a delivery chamber, a first magnetic coil ( 15 ) and a pressure sensor ( 19 ) for determining a system pressure of the conveyor, wherein the control device ( 10 ) is assigned to a processing device and wherein the processing device values of an electrical current through the first magnetic coil ( 15 ) and the system pressure are supplied, characterized in that the processing device is designed to compare an energy requirement per stroke with a default value and to gas in the delivery chamber of the first reciprocating pump ( 15 ) when the energy demand per stroke at a given system pressure is a pre-limit below the comparison value.

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