Search

DE-102014226404-B4 - Method for removing at least a partial blockage of a metering valve of a reagent metering device due to crystal formation, device for carrying out the method, computer program and computer program product

DE102014226404B4DE 102014226404 B4DE102014226404 B4DE 102014226404B4DE-102014226404-B4

Abstract

A method for removing reagent (14) or a precursor of a reagent that has crystallized on a metering valve (24), wherein the metering valve (24) is included in a reagent metering system (10) which meters the reagent (14) into the exhaust gas channel (16) of an internal combustion engine (18), and wherein the removal of the crystals is carried out taking into account the temperature (t) of the metering valve (24), characterized in that, following a metering operation, when the temperature (t) of the metering valve (24) falls below a temperature threshold (tSW), at least one further cleaning metering process of the metering valve (24) is initiated in order to clean the metering valve (24) of any crystals that may be present.

Inventors

  • Marc RINGEISEN
  • Alexander Bräuer
  • Rajasekharan Ajeesh

Assignees

  • ROBERT BOSCH GMBH

Dates

Publication Date
20260513
Application Date
20141218

Claims (9)

  1. Method for removing reagent (14) or a precursor of a reagent that has crystallized on a metering valve (24), wherein the metering valve (24) is included in a reagent metering system (10) which meters the reagent (14) into the exhaust gas channel (16) of an internal combustion engine (18) and wherein the removal of the crystals is carried out taking into account the temperature (t) of the metering valve (24), characterized in that, following a metering operation, when the temperature (t) of the metering valve (24) falls below a temperature threshold (tSW), at least one further cleaning metering process of the metering valve (24) is initiated in order to clean the metering valve (24) of any crystals that may be present.
  2. Procedure according to Claim 1 characterized in that a minimal amount of the reagent (14) is dosed during at least one cleaning dosing process.
  3. Procedure according to Claim 1 , characterized in that the temperature threshold (tSW) is a maximum of 100 degrees Celsius.
  4. Procedure according to Claim 1 , characterized in that the temperature (t) of the metering valve (24) is calculated using a temperature model (44).
  5. Procedure according to Claim 1 , characterized in that a determination of at least partial blockage of the metering valve (24) due to crystallized reagent (14) is provided.
  6. Procedure according to Claim 5 , characterized in that , in order to determine the at least partial blockage of the metering valve (24) by crystals, the reagent metering system (10) is switched off, that after switching off the reagent metering system (10) a recirculation of the reagent (14) at least from the metering valve (24) is provided, that the pressure (p) of the reagent (14) is measured at least at one point in time during the recirculation, that the pressure (p) is compared with a vacuum threshold (pSW) and that, if the pressure (p) falls below the vacuum threshold (pSW), an at least partial blockage of the metering valve (24) by crystals is detected.
  7. Device for operating a reagent dosing device, characterized in that at least one for carrying out the method according to one of the Claims 1 - 6 A specially prepared control unit (26) is provided.
  8. Computer program that performs all steps of a procedure according to one of the Claims 1 - 6 executes when it runs on a computer.
  9. Computer program product with program code stored on a machine-readable medium for carrying out the procedure according to one of the Claims 1 - 6 , when the program is run on a computer.

Description

State of the art The invention relates to a method for removing at least a partial blockage of a metering valve of a reagent metering device due to crystal formation, which meters a reagent into an exhaust gas channel of an internal combustion engine, according to the preamble of the independent method claim. The invention further relates to a device for carrying out the method. The subject of this application also includes a computer program and a computer program product. Selective catalytic reduction (SCR) can be used for exhaust gas aftertreatment. In this process, a defined quantity of a selectively acting reagent is added to the exhaust gas. The reagent can be, for example, ammonia, which is obtained from a precursor in the form of a urea-water solution in the exhaust duct through hydrolysis. A suitable dosing device is, for example, made from the DE 196 07 073 A1 The urea-water solution is conveyed through a line from a tank to a metering valve and metered into an exhaust gas channel of an internal combustion engine upstream of an SCR catalyst in order to reduce the nitrogen oxide concentration. In current dosing systems, such as those known under the name DENOXTRONIC, a pump in a delivery module draws the urea-water solution from a reagent tank and compresses it to the system pressure intended for atomization, for example, 3 to 9 bar. Taking into account, for example, current combustion engine data and sensor data, the dosing rate is adjusted to achieve the maximum possible nitrogen oxide reduction. In the disclosure document DE 10 2006 044 080 A1 This document describes a procedure designed to prevent crystallization of a urea-water solution metered into the exhaust manifold of an internal combustion engine. The known method aims to achieve the most precise dosing possible, particularly at small quantities or rates. The metering valve, implemented as a solenoid valve actuated by an electromagnet interacting with an armature rigidly connected to a valve needle, is supplied with a pulse-width modulated (PWM) metering signal that determines the dispensed amount of urea-water solution. The valve's opening time is limited to a minimum duration that ensures the valve is fully open and is precisely calibrated to produce a correct spray pattern during dosing. This prevents crystallization of the urea-water solution, which could clog the metering valve. In the disclosure document DE 10 2012 200 917 A1 This document describes a method for detecting an existing blockage by crystallizing a urea-water solution, used as a precursor to a reagent, in one or more injection ports of a metering valve of a reagent metering system. The method includes closing the metering valve, determining an initial pressure profile in the reagent metering system, and then first determining the stiffness of the hydraulic system from this initial pressure profile. Subsequently, the metering valve is opened, a second pressure profile in the hydraulic system is determined, and a blockage of one or more injection ports of the metering valve is identified based on the stiffness and the second pressure profile. The second pressure profile can be determined by stopping the drive motor of a feed pump in the reagent dosing system after the metering valve has opened. Alternatively, it is suggested that a sudden change in the speed of the feed pump's drive motor be introduced after the metering valve has opened. The known method enables the detection of a blockage in a metering valve without requiring a mass flow sensor in the hydraulic system. One described method for determining stiffness involves stopping the drive motor of the feed pump before opening the metering valve and determining the stiffness from the initial pressure curve in the hydraulic system. Alternatively, it is also possible to trigger a speed change in the drive motor of the feed pump before opening the metering valve and then determine the stiffness from the initial pressure curve in the hydraulic system. By determining the second pressure curve in the hydraulic system after opening the metering valve in conjunction with the stiffness of the hydraulic system, a conclusion can be drawn about the transverse The cross-sectional area of the metering valve can be measured. By comparing the cross-sectional area determined in this way with the cross-sectional area of an unblocked metering valve, it can be concluded whether one or more of the metering valve's injection ports are blocked. The DE 10 2011 056 755 A1 This document discloses a method for preventing clogging of a urea injection nozzle during post-run operation. During post-run operation, the system pressure is monitored. If a blockage is detected based on the pressure or the pressure rise rate, the injection nozzle is repeatedly opened and closed to clear the blockage. However, the document does not describe triggering a cleaning process based on the metering valve temperature falling below a certain threshold after a me