DE102020202134A1 - Method of operating a dosing agent system - Google Patents

Abstract

The invention relates to a method for operating a metering agent system (100) with at least two metering modules (130, 131), by means of which each metering agent (121) is converted into a target system (170) with at least two transfer devices (each assigned to the metering modules (130, 131)). 140, 141), in which the dosing agent (121) is converted, wherein, in a measuring mode (210), the at least two dosing modules (130, 131) are controlled in such a way that at least temporarily an at least predominant proportion of a total of of the dosing agent system, the amount of dosing agent to be introduced is always only introduced into the target system (170) by means of exactly one selected metering module of the dosing modules (130, 131), and wherein, in the measuring mode (210), at least one characterizing the introduction of the dosing agent into the target system Property of the selected metering module (130, 131) is determined.

Description

The present invention relates to a method for operating a dosing agent system with at least two dosing modules as well as a computing unit and a computer program for its implementation.

State of the art

Dosing systems or dosing agent systems are used to introduce defined amounts of a dosing agent into a target system, e.g. a reducing agent or a reducing agent solution on catalysts in so-called SCR systems.

For this purpose, the so-called SCR process (Selective Catalytic Reduction) can be used for aftertreatment of exhaust gases in motor vehicles, in particular for the reduction of nitrogen oxides (NO _x). In particular, a urea-water solution is introduced into the typically oxygen-rich exhaust gas as a reducing agent solution.

For this purpose, a metering module or metering valve can be used which comprises a nozzle in order to spray or introduce the urea-water solution into the exhaust gas flow. Upstream of an SCR catalytic converter, the urea-water solution reacts to form ammonia, which then combines with the nitrogen oxides on the SCR catalytic converter, from which water and nitrogen are produced.

The metering module is typically connected to a pump or feed pump that delivers the urea-water solution from a reducing agent tank to the metering module.

Disclosure of the invention

According to the invention, a method for operating a dosing agent system as well as a computing unit and a computer program for its implementation with the features of the independent patent claims are proposed. Advantageous refinements are the subject matter of the subclaims and the description below.

The invention is concerned with the operation of a dosing agent system with at least two dosing modules, by means of which dosing agent is introduced into a target system with at least two transfer devices, each assigned to the dosing module, in which the dosing agent is converted. Although such systems with two dosing modules and correspondingly two transfer devices are common, the method can also be carried out for e.g. three or four dosing modules and transfer devices.

The dosing agent system can in particular be an SCR system for which a reducing agent or a reducing agent solution is used as the dosing agent, and at least two SCR catalysts are used as conversion devices in the target system. Even if such an SCR system with, in particular, two metering modules is used here and below to explain the invention, the invention can also be used for other metering systems.

The conversion devices or catalytic converters are usually arranged at different positions in an exhaust system of an internal combustion engine, e.g. one behind the other, which means that the at least two conversion devices are active one after the other, but in a close temporal relationship, ie dosing agent is converted there, or no longer phases occur in which metering is only carried out in a conversion device, which is the prerequisite for the most unambiguous possible identification of a system property.

The amounts of dosing agent to be dosed or introduced are generally specified in the context of a dosing strategy in such a way that the loading of the conversion devices or catalysts with the dosing agent is in an optimal state. This results in a metering strategy which typically reacts directly to raw emissions of the internal combustion engine that cannot be influenced by the metering system and thus generally leads to joint or mixed metering in the two or more metering modules.

Within the scope of such a regular operating strategy or in a regular operating mode, the metering modules are preferably each controlled in such a way that the metering agent is tracked according to an amount of metering agent converted in the respective associated conversion device. It goes without saying that there will be a certain time delay from the beginning of the conversion to the onset of the tracking and until the conversion device is reached. Nonetheless, the amount of dosing agent that has been converted can essentially be compensated for, possibly beyond the time of the conversion - in accordance with the previously mentioned delay. In this way, a level of loading of the respective relocating devices with dosing agent can be kept approximately constant overall.

As a result, however, there are predominantly operating states in which all the dosing modules involved in the system are active at the same time, ie they introduce dosing agents into the target system, or no longer phases occur in which only is metered into a transfer device, whereby a defined identification of the influence of an individual metering module is extremely difficult. The latter, however, is desirable, for example, to increase the system performance and a monitoring accuracy of the system, also in the light of strict emissions requirements.

In the context of the invention, it is now proposed that the at least two metering modules are controlled in a measuring mode in such a way that at least temporarily an at least predominant proportion of the total amount of metering agent to be introduced into the target system by means of the metering agent system is only ever introduced by means of precisely one selected metering module of the metering modules . Although it is particularly preferred that this proportion is 100%, ie that dosing agent is always introduced into the target system by means of exactly one, namely the selected dosing module, it can also be provided that this proportion is, for example, at least 70% or at least 85%, etc. . amounts to.

In this way, an at least extensive or even complete decoupling of the times in which the metering modules are active is achieved. In this way, due to the simplified conditions, at least one property of the selected dosing module that characterizes the introduction of dosing agent into the target system (which is then largely or completely the only active dosing module) can be determined in the measurement mode.

A metering agent flow and / or a tolerance of the metering agent flow are particularly suitable as such a property of the selected metering module. Such properties can then be determined, for example, in a manner known for systems with only one metering module. For example, refer to the DE 10 2016 220 795 A1 referenced procedure described.

With increased accuracy of the knowledge of this tolerance, on the one hand, for example, the legal requirement for monitoring the dosing quantity ("Consumption Deviation Monitoring" in SCR systems) can be met with greater reliability. On the other hand, for example, knowledge of the tolerance can be used to improve the dosing quantity accuracy of the respective dosing module.

At this point it should also be mentioned that a significantly better determination of such properties is already possible if at least the majority of the total amount of dosing agent to be introduced is introduced by means of only one dosing module. In contrast, such a total amount of dosing agent in the regular operating mode is often the same or approximately the same distributed over all the dosing modules.

The measurement mode can be used as required and / or other specifications, i.e. it can be changed from the regular operating mode that is otherwise used, after the end of the determination of the desired properties, it can then be changed back to the regular operating mode. In other words, the dosing strategy will only be changed temporarily.

The desired property can be determined for all dosing modules in a (continuous) measuring mode, i.e. the individual dosing modules can alternately form the selected dosing module.

By decoupling the times in which the metering modules are active, there are deviations in the loading of the conversion devices with the metering agent, since the conversion of metering agents in the conversion devices or catalysts does not change as a result of the decoupling. In order to compensate for this despite the decoupling, two different options are preferred.

In this case, the at least two metering modules can be controlled in the measuring mode in such a way that an amount of metering agent is increased in one of the conversion devices before a conversion (of the metering agent) and a follow-up of metering agent is delayed during conversion. In this way, the loading of the relocating device is increased as far as possible (i.e., as long as a storage capacity is available or sufficient), then the loading is reduced by conversion and before the loading becomes too low, dosing means can be added again. In the period in between, however, the dosing module in question is not used; instead, one of the other dosing modules can then be active. In the case of the respectively active dosing module, the desired property can then be determined - in the sense of a selected dosing module.

In the case of more than two dosing modules, these can also be controlled in such a way that in all conversion devices except for one a quantity of dosing agent is increased before a conversion (of the dosing agent) and replenishment of dosing agent is delayed during the conversion. The dosing module corresponding to this one conversion device can then be active in the period in between.

Likewise, in the measuring mode, the at least two metering modules can be controlled in such a way that metering agent is tracked in one of the conversion devices during conversion is delayed in time, with the follow-up at least temporarily a higher amount of metering agent being added than is or has been reacted in the reaction. This can compensate for the delayed tracking. Due to the delayed start of the tracking in the case of one dosing module, one of the other dosing modules can therefore be active on its own.

In the case of more than two dosing modules, these can also be controlled in such a way that, in all conversion devices, except for one, replenishment of dosing agent is delayed during implementation, with the replenishment at least temporarily adding a higher amount of dosing agent than is implemented during the implementation or has been. The metering module corresponding to this one conversion device can then be active accordingly.

Furthermore, it is expedient if the at least two metering modules are controlled in such a way that the loads of the respective transfer devices do not exceed a maximum load and do not fall below a minimum load.

In this way, a dosing strategy is implemented which ensures that the loading of the conversion devices or catalysts with dosing or reducing agent can always represent the required conversion.

The dosing agent is preferably fed to the at least two dosing modules by means of a common pump. In such a system, the proposed procedure is particularly effective because, due to the common pump, the amount of dosing agent delivered by this cannot be assigned to one of the dosing modules.

A computing unit according to the invention, e.g. a control unit of a motor vehicle such as an engine control unit or a separate exhaust gas aftertreatment control unit, is set up, in particular in terms of programming, to carry out a method according to the invention.

The implementation of a method according to the invention in the form of a computer program or computer program product with program code for performing all method steps is advantageous, since this causes particularly low costs, especially if an executing control device is used for other tasks and is therefore available anyway. Suitable data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard drives, flash memories, EEPROMs, DVDs, etc. A program can also be downloaded via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention emerge from the description and the accompanying drawing.

The invention is shown schematically in the drawing using an exemplary embodiment and is described below with reference to the drawing.

Figure list

• 1 shows schematically a dosing agent system with which a method according to the invention can be carried out.
• 2 shows schematically a sequence of a method according to the invention in a preferred embodiment.

Embodiment (s) of the invention

In 1 is a schematic and exemplary embodiment of a dosing system designed as an SCR system 100 shown, with which a method according to the invention can be carried out. The SCR system 100 includes a pump 110 , with the reducing agent 121 (or a reducing agent solution) as a dosing agent from a reducing agent tank 120 to a dosing module 130 as well as a dosing module 131 can be promoted.

There is the reducing agent 121 then in a target system designed as an exhaust system of an internal combustion engine 170 introduced or sprayed. In the exhaust line there are one to the metering module 130 associated conversion device, designed for example as an SCR catalytic converter 140 and one to the dosing module 131 associated conversion device, designed for example as an SCR catalytic converter 141 provided, the relocating device 141 downstream of the converting device 140 in the exhaust gas flow 171 is arranged.

In addition, there is a computing unit designed as an exhaust gas aftertreatment control device 180 provided with the pump 110 and the dosing modules 130 , 131 can be controlled.

At this point it should be mentioned that the dosing system is shown here purely by way of example and in a simplified manner. It goes without saying that other components or possibly also a return line can also be provided, which, however, are no longer relevant for the present invention.

In 2 a sequence of a method according to the invention is now shown schematically in a preferred embodiment, as it is, for example, with the in 1 SCR system shown can be used. For this purpose, in the diagrams in the top row there is a load B of the SCR catalytic converters with minimum load Bmin and maximum load Bmax, in the middle row a mass flow or an amount per time M _in a metering agent introduced by means of a metering module, and in the lower row _{Series shows an amount M u} converted per time in an SCR catalytic converter, in each case shown over time t.

The curves for the SCR catalytic converter are shown with dashed lines or V ₁ 130 (or a first SCR catalytic converter) and with solid lines or V ₂ the curves for the SCR catalytic converter 131 (or a second SCR catalyst) shown. In addition, the diagrams on the left show a regular operating mode 200 , the right diagrams show a measurement mode 210 .

In the regular operating mode 200 it can be seen that as soon as the reducing agent is converted in the SCR catalytic converter, a short time later dosing agent is introduced by means of the corresponding metering module, with the same amount per time as it is converted in the SCR catalytic converter. The loading of the SCR catalytic converter thus initially drops, then remains constant after the update, ie as soon as the reducing agent has reached the SCR catalytic converter, and is brought back to the previous level of loading after the end of the conversion.

This means that the loading condition for both SCR catalytic converters can be kept relatively constant, but most of the time both metering modules are active, which makes it virtually impossible to determine the desired properties. The short times in which there is no overlap are usually not sufficient.

In measurement mode 210 on the other hand, the loading of the first SCR catalytic converter is now increased to the maximum loading by introducing reducing agent, to be precise before a conversion begins. By knowing the current operating position of the internal combustion engine, it is possible to determine those situations in which no implementation takes place or is about to be implemented.

The conversion then takes place in the first SCR catalytic converter (the conversions are the same as in the regular operating mode), but no reducing agent is added with the associated metering module. Rather, this tracking is delayed in time, in this case until - with even a further conversion - a minimal load of the SCR catalytic converter is reached. The tracking then takes place with an increased amount (per time).

In this way, the first metering module is not active during conversion in the second SCR catalytic converter, but the second metering module can replenish metering agent. Here it is even conceivable that, possibly only temporarily, more dosing agent is added or introduced than is implemented in order to increase the loading of the second SCR catalytic converter up to the maximum loading. This means that during the time in which the first metering module is active, it is not necessary to introduce it by means of the first metering module. Rather, this can take place after the end of the tracking or introduction of reducing agent by the first metering module.

This means that the two dosing modules are only active separately and desired properties such as the steady flow of the respective - then selected - dosing module can be determined for each of these times.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was 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.

Patent literature cited

• DE 102016220795 A1 [0015]

Claims (11)

Method for operating a dosing agent system (100) with at least two dosing modules (130, 131), by means of which each dosing agent (121) is converted into a target system (170) with at least two transfer devices (140, 141) assigned to each of the dosing modules (130, 131) , in which the dosing agent (121) is reacted, is introduced wherein, in a measuring mode (210), the at least two metering modules (130, 131) are controlled in such a way that at least temporarily an at least predominant proportion of the total amount of metering agent to be introduced into the target system (170) by means of the metering agent system is always only using exactly one selected Dosing module of the dosing modules (130, 131) is introduced, and wherein, in the measuring mode (210), at least one property of the selected dosing module (130, 131) characterizing the introduction of dosing agent into the target system is determined. Procedure according to Claim 1 wherein the at least one property of the selected dosing module (130, 131) comprises a dosing agent flow and / or a tolerance of the dosing agent flow. Procedure according to Claim 1 or 2 , in which, in a regular operating mode (200), the metering modules (130, 131) are each controlled in such a way that the metering agent (121) is tracked according to an amount of metering agent converted in the respective associated conversion device (140, 141). Method according to one of the preceding claims, wherein, in the measuring mode (210), the at least two metering modules (130, 131) are controlled in such a way that in one of the conversion devices (140, 141) an amount of metering agent is increased before a conversion, and a Tracking of dosing agent is delayed in implementation. Method according to one of the preceding claims, wherein, in the measuring mode (210), the at least two metering modules (130, 131) are controlled such that in one of the conversion devices (140, 141) tracking of metering agent is delayed during conversion, with during the follow-up, a higher amount of metering agent is added at least at times than is or has been reacted during the reaction. Method according to one of the preceding claims, wherein, in the measuring mode (210), the at least two dosing modules (130, 131) are controlled in such a way that at least temporarily at least 70%, preferably at least 85%, more preferably 100%, a total of by means of the Dosing agent system to be introduced amount of dosing agent is only ever introduced into the target system by means of the selected dosing module. Method according to one of the preceding claims, in which the dosing agent is fed to the at least two dosing modules by means of a common pump (110). Method according to one of the preceding claims, in which the dosing agent system (100) comprises an SCR system and a reducing agent or a reducing agent solution is used as the dosing agent (121), and in which in the target system (170) at least two SCR catalysts are used as conversion devices ( 140, 141) can be used. Computing unit (180) which is set up to carry out all method steps of a method according to one of the preceding claims. Computer program that causes a computing unit (180) to perform all method steps of a method according to one of the Claims 1 until 8th perform when it is executed on the computing unit (180). Machine-readable storage medium with a computer program stored thereon Claim 10 .

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