DE102014223069B4 - Method and device for detecting gas bubbles in a conveyor system for reducing agents - Google Patents

Abstract

Method for operating a delivery device for reducing agents to reduce nitrogen oxides in the exhaust gas of an internal combustion engine with a first reciprocating pump (16) with a delivery chamber and a first magnetic coil (15), with an energy requirement per stroke with reducing medium of the first reciprocating pump (16) and a system pressure on the pressure side of the delivery device, characterized in that a comparative value for the energy requirement per stroke is determined as a function at least of the system pressure in a delivery chamber filled with reducing agent, and in that gas in the delivery chamber of the first reciprocating piston pump (16) is inferred if the energy requirement per stroke at a specified system pressure is below the comparison value by a specified amount.

Description

State of the art

The invention relates to a method for operating a delivery device for reducing agents to reduce nitrogen oxides in the exhaust gas of an internal combustion engine with a first reciprocating pump with a delivery chamber and a first magnetic coil, with an energy requirement per stroke of the first reciprocating pump and a system pressure on the pressure side of the delivery device being determined.

The invention also relates to a control device for activating a delivery device for reducing agents for reducing nitrogen oxides in the exhaust gas of an internal combustion engine, the delivery device having at least a first reciprocating piston pump with a delivery chamber, a first magnetic coil and a pressure sensor for determining a system pressure of the delivery device, with the control device being assigned a processing device and wherein values of an electrical current through the first solenoid and the system pressure are fed to the processing means.

Nitrogen oxide emissions from internal combustion engines can be reduced by exhaust gas aftertreatment using selective catalytic reduction (Selective Catalyst Reduction - SCR). This can also be used in particular in diesel engines with predominantly lean exhaust gas, i.e. exhaust gas rich in nitrogen oxides. Here, a defined quantity of a selectively acting reducing agent is added to the exhaust gas. Ammonia can be used for this purpose, for example, which is metered in 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 describes an exhaust gas cleaning system of an internal combustion engine in which an SCR catalytic converter is used to reduce NO _x emissions, which reduces the nitrogen oxides contained in the exhaust gas to nitrogen using the reagent ammonia. The ammonia is obtained from the HWL in a hydrolysis catalytic converter arranged upstream of the SCR catalytic converter. The hydrolysis catalytic converter converts the urea contained in the HWL into 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 through a line from the tank to a metering valve and metered into the exhaust tract. In the DE 196 07 073 A1 describes a liquid metering system, in particular for metering liquids into a fuel or into exhaust gases resulting from combustion, which has an electrically operable metering pump device for conveying the liquid to be metered from a metering liquid tank to the medium to be mixed with metering liquid, a detection arrangement for detecting a operating variable that occurs during operation of the metering pump device and characterizes it, 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 device based on the comparison result. It is also provided that the pump current flowing through the metering pump device is recorded as the operating variable. By evaluating the time curve of the pump current and comparing it with reference curves and/or threshold values stored in a characteristic map, error states during the movement of the armature of the pump device can be detected and the metering accuracy can be increased, independently of the viscosity state of the metered liquid, for example.

In current dosing systems, such as those known under the name DENOXTRONIC 5.1 from Bosch, a reciprocating pump sucks the HWL out of 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 dosing module meters the amount of HWL required for NO _x reduction and atomizes it into the exhaust gas flow upstream of the SCR catalytic converter. The control of the dosing and heating strategy as well as an on-board diagnosis (OBD) can be carried out 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 precisely matched 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. If gas gets into the reciprocating pump, its pumping capacity is greatly reduced due to its design, since its compression ratio is too low to pump sucked-in gas through a downstream non-return valve to the system pressure side. If such a condition is detected at an early stage, the gas can be flushed out via the return flow if gas was only sucked in for a short time.

The DE102012212560A1 describes a method for operating a pump system which is intended to deliver a liquid medium from a tank and to meter the medium via a pressure line by means of at least one metering unit, the pump system having at least one delivery pump and at least one device for returning the medium, in particular a return pump and/or a switching valve for a return, characterized in that, in order to eliminate gas volumes in the pump system, medium or a medium-gas mixture or gas is conveyed by activating the feed pump with the dosing unit closed and the device for returning the medium is activated becomes. In the DE102012212560A1 Examples are described of how 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 dry components of a delivery and dosing system which is provided for delivering a liquid medium from a tank and for dosing the medium via a pressure line by means of at least one dosing unit, the system having at least one delivery pump and at least one device for conveying the medium back into the tank, in particular a return pump and/or a switching valve for a return, characterized in that when the dosing unit is closed, medium is conveyed out of the tank by activating the conveying pump and by activating the device for conveying the medium back into the tank is running. The DE102012212558A1 describes a method for removing a volume of gas from the system, particularly when the system is restarted. However, early detection of a gas volume during operation is not described.

1. 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;
2. b) eine Meßeinrichtung (20) mißt, ob die Pumpe (11) leer läuft oder Leckage-Öl (3) fördert;
3. c) falls die Pumpe (11) leer läuft, wird die Taktfrequenz verringert bis zu einem vorgebbaren Mindestwert;
4. 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 determining, monitoring and adapted recirculation of the quantities of leakage oil (3) escaping from the components of a closed hydraulic system containing a tank (4) and collecting in the lower area of a housing (1) surrounding the hydraulic system through the following features:

1. a) a pump (11) intermittently conveys any leakage oil (3) that may be present from the lower region of the housing (1) back into the tank (4) of the hydraulic system at a predeterminable clock frequency;
2. b) a measuring device (20) measures whether the pump (11) is running empty or whether it is pumping leaked oil (3);
3. c) if the pump (11) runs empty, the clock frequency is reduced down to a predefinable minimum value;
4. d) if the pump (11) delivers leakage oil (3), the clock frequency is increased continuously or in stages up to a maximum delivery.

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

The DE 10 2013 200 570 A1 relates to a method for monitoring the system pressure in a delivery and dosing system with a delivery pump (10), a pressure line (14), at least one volume-taking element (18) and a dosing unit (15). According to the invention, a relationship between volume intake and pressure in the system is evaluated, with it being checked whether the relationship to be expected occurs in the current system pressure detection.

The DE 10 2013 200 541 A1 relates to a method for pressure indication in a dosing system, which has at least one diaphragm pump as a delivery pump for a liquid, which is driven by a magnetic coil, with an armature moving a diaphragm and thus with each stroke a defined quantity of liquid is delivered, with a release time of the armature using evaluation a current flowing through the magnetic coil and its derivatives over time are determined and pressure is indicated using table values or characteristic curves as a function of at least one on-board voltage Ubord, a temperature and a pressure with the determined start time. The invention also relates to a device, in particular a dosing control unit, for carrying out the method. According to the invention, a pressure indexing function is derived to determine the release time from the current curve I(t) over time and its time derivative ΔI/Δt, the time profile of which is used to determine the release time of the armature. The method and device enable an increase in the detection accuracy of the start of a stroke of the actuator or the armature of the diaphragm pump and thus an improvement in the accuracy of pressure detection. With the use of the method, a separate pressure sensor in the dosing system can be dispensed with.

The DE 10 2013 006 153 A1 relates to a method for operating an exhaust gas cleaning system of a motor vehicle internal combustion engine that has an SCR catalytic converter for the selective catalytic reduction of nitrogen oxides, in which a reducing agent containing ammonia is added to the exhaust gas at a predeterminable metering rate (D) that results from a base value and an adaptation factor that corrects the base value is added. From time to time, a test procedure is carried out to check and, if necessary, adjust the adaptation factor. According to the invention, a first nitrogen oxide value of the exhaust gas is compared with a second nitrogen oxide value of the exhaust gas during the test procedure, with the first nitrogen oxide value and the second nitrogen oxide value being determined with one and the same nitrogen oxide sensor (8) arranged downstream of the SCR catalytic converter (4). . The first nitrogen oxide value is determined when the metering of the reducing agent is switched off and the second nitrogen oxide value is determined when the reducing agent is metered at a predeterminable test metering rate (DP).

The DE 10 2012 213 525 A1 discloses a method for monitoring a delivery and metering system, in particular a delivery and metering system for an SCR catalytic converter. The conveying and dosing system is intended for conveying a liquid medium from a tank (110) and for dosing the medium via a pressure line (116) and a first dosing module (119). The delivery and dosing system comprises a delivery module, wherein the delivery module has a delivery path with a delivery pump (111) and a return path, preferably with a return pump (122). A further internal dosing module 123 is preferably provided. The monitoring method is characterized in that a comparison measurement is carried out with an internal reference to monitor the function of the first dosing module (119), the return pump (122) or the internal further dosing module (123), if present, being used as the internal reference.

The DE 10 2012 201 595 A1 relates to a method for load diagnosis of a filter, which is part of a metering system for reducing agents for NOx reduction of an exhaust gas of an internal combustion engine, the reducing agent being conveyed from a tank by means of a feed pump through the filter to a metering valve, with the metering valve being metered into an exhaust gas duct of the internal combustion engine and the feed pump and the dosing valve are controlled by a control unit of the dosing system. According to the invention it is provided that a pressure drop across the filter is inferred by means of a current measurement of a pump current of the feed pump and a diagnosis of the loading state of the filter is carried out using a differential pressure which is dependent on the pumped volume flow. The device for carrying out the method provides a corresponding diagnostic unit. With the method and the device for carrying out the method, the structure of such dosing systems can be simplified and costs can therefore be saved. There is no need for an additional pressure sensor. The process can also be transferred to returnless dosing systems.

The DE 10 2011 003 499 A1 relates to a method for monitoring a metering system, in particular for an SCR catalytic converter (12), with a tank (14) for a liquid medium, a pressure-controlled feed pump (16) and at least one metering valve (13), the control value of the feed pump (16) compared with predeterminable reference values and if the reference values are exceeded and/or not reached, a fault in the dosing system is concluded.

It is therefore the object of the invention to provide a method with which it is possible to determine as early as possible that a gas volume has been sucked into a delivery device for a reducing agent in order to avoid malfunctions in the system.

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

Disclosure of Invention

The object of the invention relating to the method is achieved in that a comparative value for the energy requirement per stroke is determined as a function at least of the system pressure in a delivery chamber filled with reducing agent and that gas in the delivery chamber of the first reciprocating pump is inferred if the energy demand per stroke at a specified system pressure is below the comparison value by a specified amount. The term conveying space is to be understood here as meaning 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 pumping capacity of the first reciprocating pump drops sharply at a high system pressure, which is in the range of 4.5 to 8.5 bar as intended. If a dosing process is carried out under such conditions, the system pressure drops impermissibly and it is assumed that the system is malfunctioning. If, according to the invention, gas is detected in the pumping chamber, no dosing process is triggered and countermeasures can be initiated the; a malfunction of the conveyor can be avoided.

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

In an advantageous development of the method, it is provided that the comparison value is stored in a characteristic map or a functional relationship as a function at least of the system pressure and/or a supply voltage of the first magnet coil and/or a temperature of the first magnet coil and for comparison with the energy requirement for the stroke to be checked is removed.

In one embodiment of the method, it is provided that the energy requirement is determined from a value for the electrical current through the first magnet coil at a stroke end and a stroke duration of the first reciprocating piston pump. In this embodiment, only two values need to be determined with the duration up to the end of the stroke and the current through the magnetic coil at this end of the stroke in order to determine the energy requirement, or at least a 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 infer gas in the pumping chamber of the first reciprocating pump if the energy requirement per stroke at a specified system pressure by one predeterminable amount is below the comparison value. With the addition of the processing device according to the invention, a partial volume of gas in the pumping chamber that leads to a reduced pumping capacity of the reciprocating pump can be detected early and countermeasures can be initiated before a pressure drop during operation of the pumping device leads to a malfunction.

• 1 eine Fördereinrichtung für Reduktionsmittel,
• 2 ein Diagramm zur Hubenergie einer ersten Hubkolbenpumpe.

The invention is explained in more detail below with reference to an exemplary embodiment illustrated in the figures. Show it:

• 1 a conveyor for reducing agents,
• 2 a diagram of the lifting energy of a first reciprocating pump.

1 shows a delivery device for a reducing agent 12 for nitrogen oxide reduction of exhaust gas of an internal combustion engine. The reducing agent 12 is removed from a reservoir 11 via an extraction line 13 by being sucked in by a first reciprocating piston pump 16 via a first check valve 14 . The first reciprocating piston pump 16 is driven by a first magnetic coil 15 which is controlled by a control device 10 . The first reciprocating pump 16 delivers the reducing agent 12 via a second check valve 17 to a metering unit 20, which meters the reducing agent 12 into an exhaust gas duct of the internal combustion engine upstream of a catalytic converter for selective catalytic reduction. The area between the first non-return valve 14 and the second non-return valve 17 is understood as a conveying chamber of the first reciprocating piston pump 16 . A pulse damper 18 and a pressure sensor 19 are connected to a pressure line between the second check valve 17 and the dosing unit 20 , the output signal of which is a system pressure which is supplied to the control device 10 . The pressure line between the second check valve 17 and the metering unit 20 is connected via a fourth check valve 25 to a second reciprocating pump 24 which is used to return reducing agent 12 to the reservoir 11 . The second reciprocating piston pump 24 is driven by a second magnetic coil 23, which is controlled by the control device 10 and, if required, delivers the reducing agent 12 or a mixture of gas and reducing agent 12 via a third check valve 22 and a return line 21 into the reservoir 11.

The reciprocating piston pump 16 has a low delivery rate at high system pressure with a gas volume in the delivery chamber, which can lead to an undesirable drop in pressure when the metering unit 20 carries out a metering process. When starting up with a system that is not yet filled with reducing agent 12 or if gas bubbles are pumped by the first reciprocating pump 16, a circulation of reducing agent 12 can be generated when the dosing unit 20 is closed by simultaneously actuating the first and second reciprocating pumps 16, 24 without any significant pressure build-up. which flushes out gas bubbles. Then, in normal operation, the first reciprocating pump 16 the system pressure of typically 4.5 to 8.5 bar can be built up.

2 shows in a diagram 30 along a stroke duration axis 32 and a current axis 31 lines of equal stroke energy with reducing medium for the first magnetic coil 15 of the first reciprocating pump 16. The stroke duration axis 32 shows the duration of a stroke of the first reciprocating pump 16 plotted under the current operating conditions with regard to supply voltage and temperature of the magnet coil. The current through the first magnetic coil 15 at the end of the stroke is plotted on the current axis 31 . Values of the same stroke energy lie, for example, on a first stroke energy line 33, a second stroke energy line 34 or a third stroke energy line 35. The same stroke energy with different stroke durations and different currents occurs with a constant system pressure and a variation in the boundary conditions such as a different supply voltage or temperature of the first Magnetic coil 15 on. A lifting energy reduced from a third lifting energy 35 to a second lifting energy 34 or a first lifting energy 33 occurs when the system pressure is reduced. This reduced system pressure is also detected by the pressure sensor 19. If the system pressure remains essentially the same, but the lifting energy nevertheless decreases in the direction of a lifting energy change 36, a gas volume in the delivery chamber of the first reciprocating piston pump 16 is inferred and countermeasures can be initiated before the delivery device malfunctions .

Claims (5)

Method for operating a delivery device for reducing agents to reduce nitrogen oxides in the exhaust gas of an internal combustion engine with a first reciprocating pump (16) with a delivery chamber and a first magnetic coil (15), with an energy requirement per stroke with reducing medium of the first reciprocating pump (16) and a system pressure on the pressure side of the delivery device, characterized in that a comparative value for the energy requirement per stroke is determined as a function at least of the system pressure in a delivery chamber filled with reducing agent and that gas in the delivery chamber of the first reciprocating piston pump (16) is inferred if the energy requirement per stroke at a specified system pressure is below the comparison value by a specified amount. procedure after claim 1 , characterized in that the comparison value is equated to the energy requirement for the stroke preceding a stroke or to an average value or a weighted average of the energy requirement for a predefinable number of preceding strokes. procedure after claim 1 or 2 , characterized in that the comparison value is stored in a characteristic map or a functional relationship as a function at least of the system pressure and/or a supply voltage of the first magnet coil (15) and/or a temperature of the first magnet coil (15) and for comparison with the energy requirement for removed from the stroke to be checked. Procedure according to one of Claims 1 until 3 , characterized in that the energy requirement is determined from a value for the electrical current through the first magnetic coil (15) at a stroke end and a stroke duration of the first reciprocating piston pump (16). Control device (10) for controlling a delivery device for reducing agents to reduce nitrogen oxides in the exhaust gas of an internal combustion engine, the delivery device having at least a first reciprocating piston pump (16) with a delivery chamber, a first magnetic coil (15) and a pressure sensor (19) for determining a system pressure of the delivery device , wherein a processing device is assigned to the control device (10) and wherein the processing device is supplied with values of an electrical current through the first magnetic coil (15) and the system pressure, characterized in that the processing device is designed to set an energy requirement per stroke with a default value compare and close to gas in the pumping chamber of the first reciprocating pump (15) when the energy requirement per stroke at a predetermined system pressure is a predetermined amount below the comparison value.

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