DE102016216473B4 - Method for operating an exhaust gas recirculation device - Google Patents

Abstract

Method for operating an exhaust gas recirculation device (2) for an internal combustion engine (16) for a motor vehicle (1), the exhaust gas recirculation device (2) having at least one exhaust gas cooler (4) and a bypass line (5) and a bypass valve (7), the bypass valve (7) is set up to direct an exhaust gas flow at least partially through the exhaust gas cooler (4) or through the bypass line (5), and the method comprises at least the following steps: a) determining a current flow resistance of the exhaust gas cooler (4), b ) Determining a first quotient from the current flow resistance of the exhaust gas cooler (4) determined in step a) and a reference flow resistance of the exhaust gas cooler (4), c) determining a current flow resistance of the bypass line (5), d) determining a second quotient from that in step c) determined current flow resistance of the bypass line (5) and a reference flow resistance of the bypass line (5) , unde) triggering an error message when at least one of the following parameters reaches a limit: - the first quotient, - the second quotient, or - a parameter calculated from the first quotient and the second quotient.

Description

The invention relates to a method for operating an exhaust gas recirculation device for an internal combustion engine for a motor vehicle. The method is particularly suitable for diagnosis and correction of component sooting of the exhaust gas recirculation device.

It is known to recycle exhaust gas emitted by internal combustion engines to reduce nitrogen oxide emissions. This means that part of the exhaust gas is returned to the combustion chambers of the internal combustion engine via an exhaust gas recirculation device. It is also known to cool the recirculated exhaust gas. In particular, this enables the internal combustion engine to be loaded more densely and increases the power or reduces the power loss generated by the exhaust gas recirculation. For the purpose of cooling, cooling devices are usually integrated into the exhaust gas recirculation device. However, it regularly happens that the exhaust gas recirculation device, and in particular the cooling devices, soot therein. In this context, “to scrub” means that deposits are formed from the exhaust gas in the exhaust gas recirculation device or in the cooling device. This can even block the cooling device or the exhaust gas recirculation device. A resulting reduction in the cross-section can result in an unwanted and uncontrolled reduction in the mass flow of recirculated exhaust gas. This can reduce the effect of exhaust gas recirculation and / or lead to further losses in performance. The desired reduction in nitrogen oxide emissions also no longer takes place. In order to recognize such effects, a sooting of an exhaust gas recirculation device and in particular a sooting of cooling devices in exhaust gas recirculation devices should be recognized. A diagnosis of such a reduction in the returned mass flow is advantageous, in particular on the basis of legal requirements.

From the DE 10 2007 050 299 A1 A method for operating an exhaust gas recirculation device for an internal combustion engine for a motor vehicle is known, the exhaust gas recirculation device having at least one exhaust gas cooler and a bypass line and a bypass valve, and wherein the bypass valve is set up to at least partially block an exhaust gas flow through the exhaust gas cooler or through the bypass line to steer. A current flow resistance of the exhaust gas cooler and the bypass line can be determined and an error message can be triggered.

From the US 2009/0000367 A1 a method and a device for determining the mass flow of an exhaust gas recirculation are known. A quotient can be formed from a pressure difference and an amplitude of the pressure difference. The pressure difference is the difference between pressures measured at different positions.

From the DE 10 2007 007 945 A1 a method for setting an exhaust gas recirculation rate of an internal combustion engine is known.

From the US 2016/0069301 A1 a method and a system for diagnosing an exhaust gas recirculation system are known.

From the JP 2006-299 895 A1 an EGR device for an internal combustion engine is known.

Proceeding from this, it is an object of the present invention to solve or at least alleviate the technical problems described in connection with the prior art. In particular, a method for operating an exhaust gas recirculation device is to be presented, with which sooting within the exhaust gas recirculation device can be diagnosed and compensated for particularly well.

These objects are achieved with a method according to the features of claim 1. Further advantageous refinements of the method are specified in the dependent claims. The features listed individually in the patent claims can be combined with one another in any technologically meaningful manner and can be supplemented by explanatory facts from the description, further embodiment variants of the invention being shown.

1. a) Ermitteln eines aktuellen Strömungswiderstandes des Abgaskühlers,
2. b) Ermitteln eines ersten Quotienten aus dem in Schritt a) ermittelten aktuellen Strömungswiderstand des Abgaskühlers und einem Referenzströmungswiderstand des Abgaskühlers,
3. c) Ermitteln eines aktuellen Strömungswiderstandes der Bypassleitung,
4. d) Ermitteln eines zweiten Quotienten aus dem in Schritt c) ermittelten aktuellen Strömungswiderstand der Bypassleitung und einem Referenzströmungswiderstand der Bypassleitung, und
5. e) Auslösen einer Fehlermeldung, wenn mindestens einer der folgenden Parameter einen Grenzwert erreicht:
   • - der erste Quotient,
   • - der zweite Quotient, oder
   • - ein aus dem ersten Quotienten und dem zweiten Quotienten berechneter Parameter.

According to the invention, a method for operating an exhaust gas recirculation device for an internal combustion engine for a motor vehicle is presented, the exhaust gas recirculation device having at least one exhaust gas cooler and a bypass line and a bypass valve, the bypass valve being set up to at least partially direct an exhaust gas flow through the exhaust gas cooler or through the bypass line , and wherein the method comprises at least the following steps:

1. a) determining a current flow resistance of the exhaust gas cooler,
2. b) determining a first quotient from the current flow resistance of the exhaust gas cooler determined in step a) and a reference flow resistance of the exhaust gas cooler,
3. c) determining a current flow resistance of the bypass line,
4. d) determining a second quotient from the current flow resistance of the bypass line determined in step c) and a reference flow resistance of the bypass line, and
5. e) Triggering an error message if at least one of the following parameters reaches a limit:
   • - the first quotient,
   • - the second quotient, or
   • a parameter calculated from the first quotient and the second quotient.

The internal combustion engine can be particularly suitable for a motor vehicle. The internal combustion engine preferably has combustion chambers in which fuel can be burned with air. After combustion, exhaust gas can be discharged through an exhaust system. The exhaust system preferably has at least one exhaust treatment component, e.g. B. a catalyst and / or a particle filter for exhaust gas purification. The exhaust gas recirculation device connects an exhaust system of the internal combustion engine to an intake line of the internal combustion engine and is set up to return exhaust gas in a targeted manner to the intake line of the internal combustion engine

The exhaust gas treatment device preferably has an exhaust gas turbocharger. A turbocharger usually has a turbine that is driven with an exhaust gas flow in the exhaust gas treatment device. This turbine drives a compressor in the intake area. This turbine compresses the air supplied to the internal combustion engine. In this case, one can differentiate between high-pressure exhaust gas recirculation and low-pressure exhaust gas recirculation. In high-pressure exhaust gas recirculation, the exhaust gas is usually branched off upstream of the turbocharger and fed to the compressed air in the intake region downstream of the turbocharger. In the case of low-pressure exhaust gas recirculation, exhaust gas is branched off downstream of the turbocharger and is fed upstream of the turbocharger to the air which has not yet been compressed. Mixed forms and combinations of high-pressure exhaust gas recirculation and low-pressure exhaust gas recirculation are also known. In such mixed forms, the exhaust gas recirculation device is branched and can optionally be connected upstream and / or downstream of the turbocharger to the intake line or the exhaust gas treatment device. The method described here is preferably used for high-pressure exhaust gas recirculation, but it can also be used for low-pressure exhaust gas recirculation or a mixed form.

For particularly efficient loading of the internal combustion engine with air, the recirculated exhaust gas is preferably cooled via an exhaust gas cooler. A bypass line is preferably also available to regulate the extent to which cooling is carried out. The exhaust gas recirculated via the exhaust gas recirculation device can preferably flow through the exhaust gas cooler and in parallel through the bypass line, a cooling effect occurring only in the exhaust gas cooler and the recirculated exhaust gas passing through the bypass line uncooled. The distribution of the flow between the exhaust gas cooler and the bypass line can be regulated via the bypass valve. The bypass valve can preferably be adjusted continuously so that any distribution of the exhaust gas flow to the exhaust gas cooler and the bypass line is possible. Alternatively, it is preferred that the bypass valve has only exactly two positions: a first position in which the entire exhaust gas flow is directed through the exhaust gas cooler and a second position in which the entire exhaust gas flow is directed through the bypass line. The term “parallel flow” is to be understood here in particular in terms of time. The exhaust gas cooler and the bypass line can in particular be flowed through simultaneously.

Steps a) to e) are preferably, but not necessarily, carried out in the order given. In step a) the current flow resistance of the exhaust gas cooler is preferably determined by comparing measured values recorded at at least two different points of the exhaust gas cooler (preferably in particular at the beginning and at the end of the exhaust gas cooler). The measured values can be, for example, pressure measured values, mass flow measured values or similar measured values. From these measured values, a value for the current flow resistance is preferably calculated using a mathematical model. The same applies to step c) for the current flow resistance of the bypass line, which is preferably determined by comparing measured values recorded at at least two different points of the bypass line (preferably in particular one at the beginning and one at the end of the bypass line). The same type of measured value is preferably used for step a) and step c) (e.g. pressure measured values in both cases).

The measurement values required for steps a) and c) are preferably recorded using pressure measuring devices, for example pressure sensors, arranged at the respective points. For carrying out step a) (determining the flow resistance of the exhaust gas cooler), the entire exhaust gas flow preferably flows through the exhaust gas cooler. For this purpose, the bypass valve is set so that the entire exhaust gas flow flows through the exhaust gas cooler.

For the implementation of step c) (determination of the flow resistance of the bypass line), the entire exhaust gas flow preferably flows through the bypass line. For this purpose, the bypass valve is set so that the entire exhaust gas flow flows through the bypass line.

In step b) the first quotient (Q ₁ ) is formed from the current flow resistance of the exhaust gas cooler (resFlow _AGRK ) divided by the reference flow _{resistance of} the exhaust gas cooler (resFlow _{AGRK REF} ): $$Q_1=\frac{resFlO{w}_{AGRK}}{resFlO{w}_{AGRKREF}}.$$

In step d) the second quotient (Q ₂ ) is formed from the current flow resistance of the _bypass line (resFlow _Bypass ) divided by the reference flow resistance of the _bypass line (resFlow _{Bypass REF} ): $$Q_{\mathrm{2nd}}=\frac{resFlO{w}_{Bypass}}{resFlO{w}_{BypassREF}}.$$

The first quotient is a measure of the sooting of the exhaust gas cooler. The second quotient is a measure of the sooting of the bypass line.

If one or both of these variables change to such an extent that a previously determined maximum level of sooting is exceeded, this may be due to sooting of the corresponding component (exhaust gas cooler or bypass line). It is therefore advantageous if the error message is triggered in accordance with step e) as soon as either the first quotient and / or the second quotient reach a respectively set limit value. Depending on how the first quotient and the second quotient are formed, the term “reaching” can mean something different. The term “reaching” means, for example, that a quantity that is initially smaller than a limit value becomes so large that it matches or even exceeds the limit value. Reaching also means that a quantity that is initially larger than a limit value becomes so small that it matches or even falls below the limit value.

The error message can, for example, be an electronically coded message that can be transmitted via an electrical signal and that is suitable for enabling an interaction between an electronic system and a user of the same. For example, the error message can be displayed by a computer for a user in the form of an image and / or text. In particular, it is preferred that the error message is processed by a control unit of the motor vehicle and possibly saved for later analysis. In a workshop, for example, the error message can be read out by connecting an analysis device to the motor vehicle. A targeted repair can be made possible by the error message. B. that an excessively soaked component can be exchanged in a targeted manner.

For step e) there is preferably a continuous comparison of the first quotient or the second quotient with the corresponding limit value. This is preferably done using computer software, for example in a control unit of the motor vehicle. A function of a corresponding program preferably carries out the comparison using a mathematical model, in particular separately for the exhaust gas cooler and the bypass line.

A parameter calculated from the first quotient and the second quotient is proposed here as a further variable, which is compared with a limit value in step e). Such a parameter enables a comparison of the sooting of the exhaust gas cooler and the bypass line in particular. For the comparison of such a calculated parameter with a limit value and the criteria for when such a calculated parameter “reaches” a limit value, the explanations given above in connection with the first quotient and the second quotient apply.

wobei der erste Grenzwert mit GW₁ bezeichnet wurde. Der erste Quotient ist ein Maß für die Versottung des Abgaskühlers. Diese Formel wird als „erste Bedingung“ bezeichnet. Je kleiner der erste Quotient ist, umso kleiner ist die Versottung des Abgaskühlers. Vorzugsweise ist der erste Quotient an einem neuen Abgaskühler (d.h. bei einem Referenzabgaskühler) genau 1. Sobald eine Versottung des Abgaskühlers eintritt, ist mit einem Anstieg des ersten Quotienten zu rechnen. Wird ein Wert des ersten Quotienten erreicht, der einem nicht mehr akzeptablen Versottungsgrad des Abgaskühlers entspricht (dies ist vorzugsweise der erste Grenzwert), wird vorzugsweise die Fehlermeldung ausgegeben.In a preferred embodiment of the method, the error message is only triggered in step e) if the first quotient is greater than a first limit value: $$Q_1=\frac{resFlO{w}_{AGRK}}{resFlO{w}_{AGRKREF}}>G{W}_1,$$

where the first limit was designated GW ₁ . The first quotient is a measure of the sooting of the exhaust gas cooler. This formula is called the "first condition". The smaller the first quotient, the smaller the sooting of the exhaust gas cooler. The first quotient on a new exhaust gas cooler (ie in the case of a reference exhaust gas cooler) is preferably exactly 1. As soon as the exhaust gas cooler becomes soiled, an increase in the first quotient can be expected. If a value of the first quotient is reached which corresponds to an unacceptable degree of sooting of the exhaust gas cooler (this is preferably the first limit value), the error message is preferably output.

wobei der zweite Grenzwert mit GW₂ bezeichnet wurde. Der zweite Quotient ist ein Maß für die Versottung der Bypassleitung. Dies wird als „zweite Bedingung“ bezeichnet. Vorzugsweise ist der zweite Quotient bei einer neuen Bypassleitung (d.h. bei einer Referenzbypassleitung) genau 1. Konstruktionsbedingt kann die Versottung der Bypassleitung als sehr viel geringer als die Versottung des Abgaskühlers erwartet werden. Insbesondere wird vorzugsweise angenommen, dass die Bypassleitung nicht oder zumindest nicht messbar versottet. Die Bypassleitung weist kein Kühlrohr oder ähnliches auf, in dem über eine große Oberfläche ein Wärmeaustausch stattfinden soll, und das besonders anfällig für eine Versottung wäre. Weiterhin wird vorzugsweise angenommen, dass weitere Bauteile, insbesondere das Bypassventil, nicht versotten. Sollte der zweite Quotient dennoch signifikant ansteigen, ist es wahrscheinlich, dass ein anderer Fehler vorliegt als die Versottung der Bypassleitung. Durch entsprechende Wahl des zweiten Grenzwerts kann damit erreicht werden, dass die Fehlermeldung in Schritt e) nur ausgelöst wird, wenn die Bauteilversottung der Bypassleitung nicht in unrealistisch hohem Maße (d.h. insbesondere fälschlicherweise) diagnostiziert wird. Eine verlässliche Aussage über die Versottung des Abgaskühlers wird dann vorzugsweise als nicht möglich betrachtet. In a further preferred embodiment of the method, the error message is only triggered in step e) if the second quotient is less than a second limit value: $$Q_{\mathrm{2nd}}=\frac{resFlO{w}_{Bypass}}{resFlO{w}_{BypassREF}}<G{W}_{\mathrm{2nd}},$$

the second limit was designated GW ₂ . The second quotient is a measure of the sooting of the bypass line. This is called the "second condition". The second quotient in a new bypass line (ie in a reference bypass line) is preferably exactly 1. Due to the design, the sooting of the bypass line can be expected to be much less than the sooting of the exhaust gas cooler. In particular, it is preferably assumed that the bypass line is not, or at least not measurably, soiled. The bypass line has no cooling pipe or the like in which heat exchange is to take place over a large surface and which would be particularly susceptible to sooting. Furthermore, it is preferably assumed that other components, in particular the bypass valve, do not jam. Should the second quotient increase significantly, it is likely that there is a different error than the sooting of the bypass line. By selecting the second limit value accordingly, it can be achieved that the error message in step e) is only triggered if the component sooting of the bypass line is not diagnosed to an unrealistically high degree (ie in particular incorrectly). A reliable statement about the sooting of the exhaust gas cooler is then preferably not considered possible.

It is preferred that the error message in step e) is only triggered if both quotients (first quotient and second quotient) each reach the intended limit values (first limit value and second limit value). This combination can ensure that an error message is only triggered if both the sooting of the exhaust gas cooler is diagnosed as sufficiently strong, but at the same time the measured sooting of the bypass line is within a realistic range.

wobei der dritte Grenzwert als GW₃ bezeichnet wurde. Dies wird als „dritte Bedingung“ bezeichnet. Diese Differenz ist ein Beispiel für einen aus dem ersten Quotienten und dem zweiten Quotienten berechneten Parameter. Diese Differenz ist folglich ein Maß für die Versottung des Abgaskühlers im Vergleich zur Versottung der Bypassleitung. Der Vergleich der Differenz mit einem dritten Grenzwert kann dazu genutzt werden, dass keine ungerechtfertigte Fehlermeldung gemäß Schritt e) ausgegeben wird. Vorzugsweise wird die Fehlermeldung in Schritt e) nur ausgelöst, wenn die drei Bedingungen gleichzeitig erfüllt sind.In a further preferred embodiment of the method, the error message is only triggered in step e) if the difference between the first quotient and the second quotient is greater than a third limit value: $$Q_1-Q_{\mathrm{2nd}}>G{W}_{\mathrm{3rd}},$$

the third limit was designated as GW ₃ . This is called the "third condition". This difference is an example of a parameter calculated from the first quotient and the second quotient. This difference is therefore a measure of the sooting of the exhaust gas cooler compared to the sooting of the bypass line. The comparison of the difference with a third limit value can be used to ensure that no unjustified error message according to step e) is output. The error message in step e) is preferably only triggered if the three conditions are met at the same time.

It is also possible that the various conditions mentioned are viewed historically in order to decide whether an error message is output or not. For example, it is not necessary that all three of the conditions mentioned must be fulfilled at the same time in order for an error message to be output. It is possible that an error message is only output if the first condition and the third condition are fulfilled at the same time. It is also possible for a storage to be made as to whether the third condition was once met. If the first condition and the second condition are then met, an error message is output regardless of whether the third condition is currently met.

In a further preferred embodiment of the method, the current flow resistance of the exhaust gas cooler is determined in step a) from a pressure drop across the exhaust gas cooler and in step c) the flow resistance of the bypass line is determined from a pressure drop across the bypass line.

The pressure drop across the exhaust gas _cooler (ΔP _AGRK ) is preferably calculated from a first pressure measured at the beginning of the exhaust gas _cooler P ₁ and a second pressure measured at the end of the exhaust gas cooler P ₂ and a pressure drop ΔP _{EGR valve} over the exhaust gas recirculation valve: $$\Delta P_{AGRK}=P_1-P_{\mathrm{2nd}}-\Delta P_{AGRK-Ventil}.$$

wobei dVol_EGR den Volumenstrom des rückgeführten Abgases angibt. Vorzugsweise weist die Abgasrückführungseinrichtung ein Volumenstrommessgerät auf, mit dem der Volumenstrom des rückgeführten Abgases gemessen werden kann. Alternativ oder zusätzlich ist es bevorzugt, dass die Abgasrückführungseinrichtung ein Massenstrommessgerät aufweist, mit dem der Massenstrom des rückgeführten Abgases gemessen werden kann. Dieser kann als Alternative des Volumenstroms für die Bestimmung des Strömungswiderstandes verwendet werden. Es ist aber auch jede andere Ermittlung des Volumenstroms denkbar, beispielsweise eine Berechnung oder eine Schätzung basierend auf Betriebsdaten einer Verbrennungskraftmaschine.The pressure drop ΔP _{EGR valve} over the exhaust gas recirculation valve is preferably calculated using the throttle equation, which depends in particular on the mass flow through the exhaust gas recirculation valve and the setting of the valve opening. The flow resistance of the exhaust gas cooler is then defined as: $$resFlO{w}_{AGRK}=\frac{\Delta P_{AGRK}}{dVO{l}_{EGR}},$$

where dVol _EGR indicates the volume flow of the recirculated exhaust gas. The exhaust gas recirculation device preferably has a volume flow measuring device with which the volume flow of the recycled exhaust gas can be measured. Alternatively or additionally, it is preferred that the exhaust gas recirculation device has a mass flow measuring device with which the mass flow of the recirculated exhaust gas can be measured. This can be used as an alternative to the volume flow for determining the flow resistance. However, any other determination of the volume flow is also conceivable, for example a calculation or an estimate based on operating data of an internal combustion engine.

Analogously to the calculation of the flow resistance of the exhaust gas cooler, the following applies to the flow resistance of the _{bypass line} : This can be determined with the pressure drop across the bypass line (ΔP _bypass ): $$resFlO{w}_{Bypass}=\frac{\Delta P_{Bypass}}{dVO{l}_{EGR}}.$$

$$resFlo{w}_{BypassREF}=\frac{\Delta P_{BypassREF}}{dVo{l}_{EGR}}$$

wobei ΔP_{AGRK REF} der Druckabfall über dem Abgaskühler ohne Versottung und ΔP_{Bypass REF} der Druckabfall über der Bypassleitung ohne Versottung ist.The reference flow resistance of the exhaust gas cooler and the reference flow resistance of the bypass line are preferably determined experimentally with a non-soaked exhaust gas cooler or a non-soaked bypass line (for example, by means of series of measurements on an engine test bench). Alternatively or additionally, it is preferred that the reference flow resistances are calculated using a computer simulation. The following applies to the reference flow resistance in analogy to equations (7) and (8): $$resFlO{w}_{AGRKREF}=\frac{\Delta P_{AGRKREF}}{dVO{l}_{EGR}},$$

$$resFlO{w}_{BypassREF}=\frac{\Delta P_{BypassREF}}{dVO{l}_{EGR}}$$

where ΔP _{AGRK REF is} the pressure drop across the exhaust gas cooler without sooting and ΔP _{bypass REF is} the pressure drop across the bypass line without sooting.

In a further preferred embodiment of the method, the reference flow resistance of the exhaust gas cooler and the reference flow resistance of the bypass line are each defined as a characteristic map as a function of at least one operating point parameter of the internal combustion engine.

The reference flow resistance is a theoretical value that is suitable for carrying out the described method in the present context and may not match a physical flow resistance of the respective component. The reference flow resistance of both the exhaust gas cooler and the bypass line can depend on operating point parameters of the internal combustion engine, for example the speed, the power, the exhaust gas temperature, but also on the outside temperature or other factors. In order to be able to reasonably ascertain the sooting of components, as described, such dependencies are preferably taken into account. If, for example, the flow resistance is particularly high due to an operating state of the internal combustion engine, it is preferably not (incorrectly) concluded from this fact that the exhaust gas cooler, for example, is sooting.

The reference flow resistance of the exhaust gas cooler and the reference flow resistance of the bypass line are preferably stored in the form of the map in a memory and / or in a control unit of the motor vehicle. A map is understood to mean the specification of a parameter as a function of at least one operating point parameter.

• f) Verändern einer Einstellung eines Abgasrückführungsventils unter Berücksichtigung zumindest des ersten Quotienten, so dass eine Veränderung eines Massenstroms von rückgeführtem Abgas aufgrund einer Erhöhung des Strömungswiderstandes des Abgaskühlers ausgeglichen wird.

In a further preferred embodiment, the method further comprises the following step:

• f) changing a setting of an exhaust gas recirculation valve, taking into account at least the first quotient, so that a change in a mass flow of recirculated exhaust gas is compensated for due to an increase in the flow resistance of the exhaust gas cooler.

The exhaust gas recirculation valve (often also referred to as an EGR valve) is preferably set up to set the amount of recirculated exhaust gas. Through step f), the amount of recirculated exhaust gas can be kept constant despite sooting. As a result, the advantageous effect of exhaust gas recirculation can be achieved independently of the sooting of components. The compensation preferably takes place in such a way that the determined value for the first quotient (preferably continuously) is passed to a control unit of the motor vehicle, in which the compensating setting of the exhaust gas recirculation valve can be initiated by appropriate processing.

An exhaust gas recirculation device for an internal combustion engine for a motor vehicle is also to be described here, the exhaust gas recirculation device having at least one exhaust gas cooler and a bypass line and a bypass valve, the bypass valve being designed to direct an adjustable part of an exhaust gas flow through the bypass line instead of through the exhaust gas cooler, and wherein the exhaust gas recirculation device is set up to operate according to a method as described.

Another aspect of the invention relates to a motor vehicle comprising at least one exhaust gas recirculation device as described.

The motor vehicle preferably further comprises an engine control unit in which program routines for carrying out the method are stored. To carry out the method, the engine control unit is connected to components of the exhaust gas recirculation device, in particular to a bypass valve and an exhaust gas recirculation valve and preferably also to pressure measuring devices for monitoring the flow resistance.

The particular advantages and features of the method described above can be applied and transferred to the exhaust gas recirculation device and the motor vehicle described.

• 1: eine schematische Darstellung eines Kraftfahrzeugs mit einer Abgasrückführungseinrichtung,
• 2: einen Verlauf des Drucks entlang der Abgasrückführungseinrichtung aus 1.

The invention and the technical environment are explained in more detail below with reference to the figures. The figures show particularly preferred exemplary embodiments, to which the invention is, however, not limited. In particular, it should be pointed out that the figures and in particular the proportions shown are only schematic. Show it:

• 1 : a schematic representation of a motor vehicle with an exhaust gas recirculation device,
• 2nd : a course of the pressure along the exhaust gas recirculation device 1 .

1 shows a motor vehicle 1 an internal combustion engine 16 having an intake pipe 17th for sucking in air and an exhaust system 18th with at least one exhaust gas treatment component 3rd . The motor vehicle also has an exhaust gas recirculation device 2nd on. In the exhaust gas recirculation device 2nd is an exhaust gas cooler 4th integrated. In parallel there is a bypass line 5 arranged. Via a bypass valve 7 can be the distribution of an exhaust gas flow through the exhaust gas cooler 4th and the bypass line 5 can be set. A first pressure measuring device is used to determine flow resistances 8th in front of the exhaust gas cooler 4th and a second pressure gauge 9 arranged behind. These two pressure gauges 8th , 9 are only shown here as examples. Flow resistances can also be determined using pressure measuring devices located at other locations or using models, calculations, etc. An exhaust gas recirculation valve is also shown 6 and a volume flow meter 10th . In particular the volume flow meter 10th can also be omitted. Volume flow can be determined, for example, using a suitable model, calculations from operating parameters or in a similar way. The connecting lines between the components of the exhaust gas recirculation device are for better illustration 2nd and the bypass line 5 each shown only as lines. The exhaust gas cooler 4th on the other hand is shown extensively, so that it can be seen how a deposit formed by sooting 11 the cross section of the exhaust gas cooler 4th narrowed.

2nd shows the pressure P inside the exhaust gas recirculation device 2nd out 1 represented in arbitrary units (the abbreviation stands for au) as a function along the direction x , which corresponds to the flow direction of the exhaust gas through the exhaust gas recirculation device, is also shown in any units. Starting on the left side of the diagram, the pressure initially shows that of the first pressure measuring device 8th measured value P ₁ on. Proceeding further to the right, the pressure drops due to a pressure drop across the exhaust gas recirculation valve 6 , then remains constant in order to subsequently due to a pressure drop across the exhaust gas cooler 4th or above the bypass line 5 to the level of that of the second pressure gauge 9 measured value P ₂ to fall. As can be seen, the pressure between the two pressure drops differs as follows: while the pressure in the exhaust gas cooler is without sooting 12 the lowest is the pressure in the exhaust gas cooler with sooting 13 the biggest. At the bypass line 5 sooting plays a minor role. Therefore the pressure in the bypass line is without sooting 14 only slightly less than the pressure in the bypass line with sooting 15 .

Reference symbol list

1

Motor vehicle

2nd

Exhaust gas recirculation device

3rd

Exhaust treatment component

4th

Exhaust gas cooler

5

Bypass line

6

Exhaust gas recirculation valve

7

Bypass valve

8th

first pressure measuring device

9

second pressure gauge

10th

Volume flow meter

11

deposit

12

Pressure in the exhaust gas cooler without sooting

13

Pressure in the exhaust gas cooler with sooting

14

Pressure in the bypass line without sooting

15

Pressure in the bypass line with sooting

16

Internal combustion engine

17th

Suction pipe

18th

Exhaust system

Claims (9)

Method for operating an exhaust gas recirculation device (2) for an internal combustion engine (16) for a motor vehicle (1), the exhaust gas recirculation device (2) having at least one exhaust gas cooler (4) and a bypass line (5) and a bypass valve (7), the bypass valve (7) is set up to direct an exhaust gas flow at least partially through the exhaust gas cooler (4) or through the bypass line (5), and the method comprises at least the following steps: a) determining a current flow resistance of the exhaust gas cooler (4), b) determining a first quotient from the current flow resistance of the exhaust gas cooler (4) determined in step a) and a reference flow resistance of the exhaust gas cooler (4), c) determining a current flow resistance of the bypass line (5), d) determining a second quotient from the current flow resistance of the bypass line (5) determined in step c) and a reference flow resistance of the bypass line (5), and e) Triggering an error message if at least one of the following parameters reaches a limit: - the first quotient, - the second quotient, or a parameter calculated from the first quotient and the second quotient. Procedure according to Claim 1 , the error message being triggered in step e) only if the first quotient is greater than a first limit value. Method according to one of the preceding claims, wherein in step e) the error message is only triggered if the second quotient is less than a second limit value. Method according to one of the preceding claims, wherein in step e) the error message is only triggered if the difference between the first quotient and the second quotient is greater than a third limit value. Method according to one of the preceding claims, wherein in step a) the current flow resistance of the exhaust gas cooler (4) is determined from a pressure drop across the exhaust gas cooler (4), and wherein in step c) the current flow resistance of the bypass line (5) from a pressure drop the bypass line (5) is determined. Procedure according to Claim 4 , wherein the reference flow resistance of the exhaust gas cooler (4) and the reference flow resistance of the bypass line (5) are each defined as a map depending on at least one operating point parameter of the internal combustion engine (16). Method according to one of the preceding claims, further comprising the following step: f) changing a setting of an exhaust gas recirculation valve (6) taking into account at least the first quotient, so that a change in a mass flow of recirculated exhaust gas due to an increase in the flow resistance of the exhaust gas cooler (4) is compensated. Exhaust gas recirculation device (2) for an internal combustion engine (16) for a motor vehicle (1), the exhaust gas recirculation device (2) having at least one exhaust gas cooler (4) and a bypass line (5) and a bypass valve (7), the bypass valve (7) for this purpose is set up to direct an adjustable part of an exhaust gas flow instead of through the exhaust gas cooler (4) through the bypass line (5), and the exhaust gas recirculation device (2) is set up for operation according to a method according to one of the preceding claims. Motor vehicle (1) comprising at least one exhaust gas recirculation device (2) Claim 8 .

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