EP3290681B1 - Method for operating an exhaust gas recycle system - Google Patents

Description

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

It is known to recycle exhaust gas emitted by internal combustion engines for the reduction of nitrogen oxide emissions. This means that a portion of the exhaust gas is supplied via an exhaust gas recirculation device again to the combustion chambers of the internal combustion engine. It is also known to cool the recirculated exhaust gas. This allows in particular a denser loading of the internal combustion engine 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 happens regularly that the exhaust gas recirculation device and in particular the cooling devices mop up therein. In this case, it is said that deposits are formed from the exhaust gas in the exhaust gas recirculation device or in the cooling device. The cooling device or the exhaust gas recirculation device can thereby even clog. By a resulting reduction of the cross section, a mass flow of recirculated exhaust gas can be reduced unintentionally and uncontrollably. This can reduce the effect of exhaust gas recirculation and / or lead to further power losses. The desired reduction of nitrogen oxide emissions also no longer takes place. In order to detect 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 detected. In particular, due to legal requirements, a diagnosis of such a reduction of the recirculated mass flow is advantageous.

From the DE 10 2007 050 299 A1 a method for operating an internal combustion engine is known in which a fluid in a first position of a bypass valve is passed through a first fluid line and in a second position of the bypass valve through a second fluid line.

From the EP 2 009 267 A2 For example, a method and an apparatus for determining the mass flow of an exhaust gas recirculation are known. From the DE 10 2008 041 804 A1 For example, a method for diagnosing an exhaust gas recirculation arrangement of an internal combustion engine is known. From the DE 10 2014 222 529 A1 For example, a method and system for determining fouling of the exhaust gas recirculation cooler is known.

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

These objects are achieved by a method according to the features of claim 1. Further advantageous embodiments of the method are given in the dependent formulated claims. The features listed individually in the claims can be combined with each other in any technologically meaningful manner and can be supplemented by explanatory facts from the description, with further embodiments 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, wobei der erste Quotient ein Maß für die Versottung des Abgaskühlers ist,
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, wobei der zweite Quotient ein Maß für die Versottung der Bypassleitung ist,
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; und
6. 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.

According to the invention, a method is provided for diagnosing and correcting a component scavenging of an exhaust gas recirculation device for an internal combustion engine for a motor vehicle, wherein the exhaust gas recirculation device has at least one exhaust gas cooler and a bypass line and a bypass valve, wherein the bypass valve is adapted to at least partially exhaust gas flow through the exhaust gas cooler or through to direct 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 of the current flow resistance of the exhaust gas cooler determined in step a) and a reference flow resistance of the exhaust gas cooler, wherein the first quotient is a measure for the sooting of the exhaust gas cooler,
3. c) determining a current flow resistance of the bypass line,
4. d) determining a second quotient of the current flow resistance of the bypass line determined in step c) and a reference flow resistance of the bypass line, wherein the second quotient is a measure for the sooting of the bypass line,
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; and
6. f) changing an adjustment of an exhaust gas recirculation valve taking into account at least the first quotient, so that a change of a mass flow of recirculated exhaust gas is compensated due to an increase of the flow resistance of the exhaust gas cooler.

The internal combustion engine may be suitable in particular 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 removed via an exhaust system. The exhaust system preferably has at least one exhaust gas treatment component, for. B. a catalyst and / or a particulate filter for emission control. 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 configured to recirculate 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 treatment device. With this turbine, a compressor is driven in the intake area. This turbine compresses the air supplied to the internal combustion engine. In that case, one can distinguish 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 low-pressure exhaust gas recirculation, exhaust gas is branched off downstream of the turbocharger and supplied to the not yet compressed air upstream of the turbocharger. 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 to the intake line or the exhaust gas treatment device optionally upstream and / or downstream of the turbocharger. The method described here is preferably used in 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. To regulate the extent to which it is cooled, there is also preferably one Bypass line. Preferably, the exhaust gas recirculated via the exhaust gas recirculation device can flow through the exhaust gas cooler and parallel to the bypass line, wherein a cooling effect occurs only in the exhaust gas cooler and the recirculated exhaust gas passes through the bypass line without cooling. The distribution of the flow to the exhaust gas cooler and the bypass line can be controlled via the bypass valve. In this case, 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 only has exactly two positions: a first position, in which the entire exhaust gas flow is passed through the exhaust gas cooler and a second position, in which the entire exhaust gas flow is passed through the bypass line. The term "parallel flow" is to be understood here in particular temporally. The exhaust gas cooler and the bypass line can be flowed through in particular at the same time.

The steps a) to e) are preferably, but not necessarily, run through 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 one at the beginning and one at the end of the exhaust gas cooler). The measured values can be, for example, pressure readings, mass flow readings or similar measured values. From these measured values, a value for the current flow resistance is preferably calculated via a mathematical model. For step c), the same applies to 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). Preferably, the same type of measurement is used for step a) and step c) (e.g., pressure measurements in both cases).

The recording of the measured values required for steps a) and c) is preferably carried out via pressure measuring devices arranged at the respective points, for example pressure sensors. For carrying out step a) (determination of the flow resistance of the exhaust gas cooler), preferably the entire exhaust gas flow flows through the exhaust gas cooler. For this purpose, the bypass valve is adjusted so that the entire exhaust gas flow flows through the exhaust gas cooler.

For carrying out step c) (determination of the flow resistance of the bypass line), preferably the entire exhaust gas flow flows through the bypass line. For this purpose, the bypass valve is adjusted 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} ): $${\mathrm{<figure-callout\; id="1"\; label="Q"\; filenames="imgf0001.png"\; state="\{\{state\}\}">Q</figure-callout>}}_1=\frac{\mathit{resFlo}{w}_{\mathit{AGRK}}}{\mathit{resFlo}{w}_{\mathit{AGRK}\mathit{REF}}},$$

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} ): $${\mathrm{<figure-callout\; id="2"\; label="Q"\; filenames="imgf0001.png"\; state="\{\{state\}\}">Q</figure-callout>}}_2=\frac{\mathit{resFlo}{w}_{\mathit{bypass}}}{\mathit{resFlo}{w}_{\mathit{bypass}\mathit{REF}}},$$

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 amount of sooting is exceeded, this may be due to a sooting of the corresponding component (exhaust gas cooler or bypass line). Therefore, it is advantageous if, according to step e), the error message is triggered 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, something different can be understood by the term "reaching". By way of example, the term "reaching" means that a quantity which is initially smaller than a limit value becomes larger in such a way that it matches or even exceeds the limit value. Achieving also means that a size that is initially greater than a threshold will become smaller enough to match or even exceed the threshold.

The error message may, for example, be an electronically coded message which can be transmitted via an electrical signal and which is suitable for allowing interaction between an electronic system and a user thereof. For example, the error message from a computer for a user in the form of an image and / or text can be displayed. In particular, it is preferable for the error message to be processed by a control unit of the motor vehicle and possibly stored for later analysis. In a workshop, for example, by connecting an analyzer to the motor vehicle, the error message can be read. The error message can be a targeted repair allows, ie z. B. that a too Versottetes component can be exchanged targeted.

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

As a further variable, which is compared with a limit value in the context of step e), a parameter calculated from the first quotient and the second quotient is proposed here. Such a parameter allows in particular a comparison of the sooting of the exhaust gas cooler and the bypass line to one another. For the comparison of such a calculated parameter with a limit value and the criteria 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 GW ₁ 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: $${\mathrm{<figure-callout\; id="1"\; label="Q"\; filenames="imgf0001.png"\; state="\{\{state\}\}">Q</figure-callout>}}_1=\frac{\mathit{resFlo}{w}_{\mathit{AGRK}}}{\mathit{resFlo}{w}_{\mathit{AGRK}\mathit{REF}}}>{\mathit{<figure-callout\; id="1"\; label="GW"\; filenames="imgf0001.png"\; state="\{\{state\}\}">GW</figure-callout>}}_1.$$

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. Preferably, the first quotient of a new exhaust gas cooler (ie, a reference exhaust gas cooler) is exactly 1. As soon as a sooting of the exhaust gas cooler occurs, an increase of the first quotient is to be expected. If a value of the first quotient is reached which corresponds to an unacceptable degree of mucking of the exhaust gas cooler (this is preferably the first limit value), the error message is preferably output.

wobei der zweite Grenzwert mit GW ₂ 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: $${\mathrm{<figure-callout\; id="2"\; label="Q"\; filenames="imgf0001.png"\; state="\{\{state\}\}">Q</figure-callout>}}_2=\frac{\mathit{resFlo}{w}_{\mathit{bypass}}}{\mathit{resFlo}{w}_{\mathit{bypass}\mathit{REF}}}<{\mathit{<figure-callout\; id="2"\; label="GW"\; filenames="imgf0001.png"\; state="\{\{state\}\}">GW</figure-callout>}}_2.$$

the second limit being designated GW ₂ . The second quotient is a measure of the sooting of the bypass line. This is called a "second condition". Preferably, the second quotient for a new bypass line (ie for a reference bypass line) is exactly 1. Due to the design, the sooting of the bypass line can be expected to be much lower than the sooting of the exhaust gas cooler. In particular, it is preferably assumed that the bypass line does not mess up or at least not measurably. The bypass line does not have a cooling tube or the like in which a 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 spoil. Should the second quotient nevertheless increase significantly, it is probable that there is a different error than the sooting of the bypass line. By appropriate selection of the second limit value, it can thus be achieved that the error message in step e) is triggered only if the component scorching of the bypass line is not diagnosed in an unrealistically high degree (ie, in particular erroneously). A reliable statement about the sooting of the exhaust gas cooler is then preferably considered not possible.

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

wobei der dritte Grenzwert als GW ₃ 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: $$Q_1-{\mathrm{<figure-callout\; id="2"\; label="Q"\; filenames="imgf0001.png"\; state="\{\{state\}\}">Q</figure-callout>}}_2>{\mathit{<figure-callout\; id="3"\; label="GW"\; filenames="imgf0001.png"\; state="\{\{state\}\}">GW</figure-callout>}}_3.$$

the third limit being referred to as GW ₃ . This is called a "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 sooting of the bypass line. The comparison of the difference with a third limit value can be used so that no unjustified error message according to step e) is output. Preferably, the error message in step e) is triggered only if the three conditions are met simultaneously.

It is also possible that the various conditions mentioned are considered historically in order to decide whether an error message is issued or not. It is not necessary, for example, that all three conditions mentioned must be fulfilled simultaneously, so that an error message is issued. It is possible that an error message will only be issued if the first condition and the third condition are fulfilled at the same time. It is also possible that is stored in a memory, if the third condition was met once. If the first condition and the second condition are then fulfilled, an error message is output regardless of whether the third condition is currently fulfilled.

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

The pressure drop across the exhaust gas _cooler ( ΔP _AGRK ) is preferably calculated from a measured at the beginning of the exhaust gas _cooler first pressure P ₁ and a measured at the end of the exhaust gas cooler second pressure P ₂ and a pressure drop ΔP _{EGR valve} on the exhaust gas recirculation valve: $${\mathit{.DELTA.P}}_{\mathit{AGRK}}=P_1-P_2-{\mathit{.DELTA.P}}_{\mathit{AGR}-\mathit{Valve}},$$

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} above the exhaust gas recirculation valve is preferably calculated via the throttle equation, which depends in particular on the mass flow through the exhaust gas recirculation valve and the adjustment of the valve opening. The flow resistance of the exhaust gas cooler is then defined as: $$\mathit{resFlo}{w}_{\mathit{AGRK}}=\frac{{\mathit{.DELTA.P}}_{\mathit{AGRK}}}{\mathit{dVo}{l}_{\mathit{EGR}}}.$$

where dVol _EGR indicates the volume flow of recirculated exhaust gas. Preferably, the exhaust gas recirculation device has a volumetric flow meter with which the volume flow of the recirculated exhaust gas can be measured. Alternatively or additionally, it is preferred that the exhaust gas recirculation device has a mass flow meter 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 the determination of the flow resistance. However, any other determination of the volume flow is conceivable, for example a calculation or an estimate based on operating data of an internal combustion engine.

Analogously for the calculation of the flow resistance of the exhaust gas cooler, for the flow resistance of the _{bypass line} , it can be determined with the pressure drop across the bypass line ( ΔP _bypass ): $$\mathit{resFlo}{w}_{\mathit{bypass}}=\frac{{\mathit{.DELTA.P}}_{\mathit{bypass}}}{\mathit{dVo}{l}_{\mathit{EGR}}},$$

$$\mathit{resFlo}{w}_{\mathit{Bypass}\mathit{REF}}=\frac{{\mathit{\Delta P}}_{\mathit{Bypass}\mathit{REF}}}{\mathit{dVo}{l}_{\mathit{EGR}}}$$

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-quenched exhaust gas cooler or a non-tripped bypass line (eg by series of measurements on an engine test bench). Alternatively or additionally, it is preferred that the reference flow resistances be calculated with a computer simulation. The reference flow resistance is analogous to equations (7) and (8): $$\mathit{resFlo}{w}_{\mathit{AGRK}\mathit{REF}}=\frac{{\mathit{.DELTA.P}}_{\mathit{AGRK}\mathit{REF}}}{\mathit{dVo}{l}_{\mathit{EGR}}}.$$

$$\mathit{resFlo}{w}_{\mathit{bypass}\mathit{REF}}=\frac{{\mathit{.DELTA.P}}_{\mathit{bypass}\mathit{REF}}}{\mathit{dVo}{l}_{\mathit{EGR}}}$$

where ΔP _{AGRK REF is} the pressure drop across the _uncooled exhaust gas _cooler 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 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 may depend on operating point parameters of the internal combustion engine such as the speed, the power, the exhaust gas temperature, but also on the outside temperature or other factors. In order to make sense, as described, to be able to conclude the sooting of components, such dependencies are preferably taken into account. If, for example, the flow resistance due to an operating state of the internal combustion engine is particularly high, it is preferably not (inaccurately) concluded from this fact that the soot, for example, of the exhaust gas cooler is closed.

Preferably, the reference flow resistance of the exhaust gas cooler and the reference flow resistance of the bypass line are stored in the form of the characteristic 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.

The method further includes the following step:
f) changing an adjustment of an exhaust gas recirculation valve taking into account at least the first quotient, so that a change of a mass flow of recirculated exhaust gas is compensated due to an increase of the flow resistance of the exhaust gas cooler.

The exhaust gas recirculation valve (often referred to as an EGR valve) is preferably configured to adjust 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 the exhaust gas recirculation can be achieved independently of the sooting of components. The compensation preferably takes place in such a way that the specific value for the first quotient (preferably continuously) is passed to a control unit of the motor vehicle in which the compensating adjustment of the exhaust gas recirculation valve can be initiated by appropriate processing.

Also to be described here is an exhaust gas recirculation device for an internal combustion engine for a motor vehicle, wherein the exhaust gas recirculation device has at least one exhaust gas cooler and a bypass line and a bypass valve, wherein the bypass valve is adapted 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 arranged to operate in accordance with a method as described.

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

Preferably, the motor vehicle further comprises an engine control unit, in which program routines are deposited for carrying out the method. The engine control unit is connected to perform the method 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 gauges for monitoring the flow resistance.

The particular advantages and design features of the method described above are applicable to the described exhaust gas recirculation device and the motor vehicle described and transferable.

Fig. 1:

eine schematische Darstellung eines Kraftfahrzeugs mit einer Abgasrückführungseinrichtung,

Fig. 2:

einen Verlauf des Drucks entlang der Abgasrückführungseinrichtung aus Fig. 1.

The invention and the technical environment will be explained in more detail with reference to FIGS. The figures show particularly preferred embodiments, to which the invention is not limited. In particular, it should be noted that the figures and in particular the illustrated proportions are only schematic. Show it:

Fig. 1:

a schematic representation of a motor vehicle with an exhaust gas recirculation device,

Fig. 2:

a curve of the pressure along the exhaust gas recirculation device Fig. 1 ,

Fig. 1 shows a motor vehicle 1 of an internal combustion engine 16 having an intake passage 17 for the intake of air and an exhaust system 18 with at least one exhaust gas treatment component 3. The motor vehicle further comprises an exhaust gas recirculation device 2. In the exhaust gas recirculation device 2, an exhaust gas cooler 4 is integrated. In parallel, a bypass line 5 is arranged. Via a bypass valve 7, the distribution of an exhaust gas flow through the exhaust gas cooler 4 and the bypass line 5 can be adjusted. For determining flow resistances, a first pressure gauge 8 is arranged in front of the exhaust gas cooler 4 and a second pressure gauge 9 behind it. These two pressure measuring devices 8, 9 are shown here only as an example. If necessary, the determination of flow resistances can also take place with pressure gauges arranged at other locations or with the aid of models, calculations, etc. Also shown are an exhaust gas recirculation valve 6 and a volumetric flow meter 10. In particular, the volumetric flow meter 10 may also be omitted. A volumetric flow determination can take place, for example, via a model suitable for this purpose, calculations from operating parameters or in a similar way. For better representability, the connecting lines between the components of the exhaust gas recirculation device 2 and the bypass line 5 are each shown only as dashes. The exhaust gas cooler 4, however, is shown expanded so that it can be seen how a deposit 11 caused by sooting narrows the cross-section of the exhaust gas cooler 4.

Fig. 2 shows the pressure P within the exhaust gas recirculation device 2 Fig. 1 represented in arbitrary units (this is the abbreviation au) as a function along the direction x, which corresponds to the flow direction of the exhaust gas through the exhaust gas recirculation device, also shown in arbitrary units. Beginning on the left side of the diagram, the pressure initially has the value P ₁ measured by the first pressure measuring device 8. Proceeding further to the right, the pressure drops due to a pressure drop across the exhaust gas recirculation valve 6, then remains constant, then to the level of measured by the second pressure gauge 9 value P ₂ due to a pressure drop across the exhaust gas cooler 4 and over the bypass line fall. As can be seen, the pressure between the two pressure drops differs as follows: while the pressure in the exhaust gas cooler without sooting 12 is the lowest, the pressure in the gasifier 13 with sooting 13 is greatest. In the bypass line 5, the sooting plays a minor role. Therefore, the pressure in the by-pass bypass pipe 14 is only slightly less than the pressure in the soot-by-15 bypass pipe.

LIST OF REFERENCE NUMBERS

1. 1 motor vehicle
2. 2 exhaust gas recirculation device
3. 3 exhaust treatment component
4. 4 exhaust gas cooler
5. 5 bypass line
6. 6 exhaust gas recirculation valve
7. 7 bypass valve
8. 8 first pressure gauge
9. 9 second pressure gauge
10. 10 volumetric flow meter
11. 11 deposit
12. 12 Pressure in the exhaust gas cooler without sooting
13. 13 Pressure in the exhaust gas cooler with sooting
14. 14 Pressure in the bypass line without sooting
15. 15 Pressure in the bypass line with sooting
16. 16 internal combustion engine
17. 17 intake pipe
18. 18 exhaust system

Claims (8)

1. A method for diagnosis and correction of sooting of components of an exhaust-gas recirculation means (2) for an internal combustion engine (16) for a motor vehicle (1), wherein the exhaust-gas recirculation means (2) has at least an EGR cooler (4) and a bypass line (5) and also a bypass valve (7), wherein the bypass valve (7) is set up to guide an exhaust-gas flow at least partially through the EGR cooler (4) or through the bypass line (5), and wherein the method comprises at least the following steps:

   a) ascertaining a current flow resistance of the EGR cooler (4),

   b) ascertaining a first quotient from the current flow resistance of the EGR cooler (4) ascertained in step a) and a reference flow resistance of the EGR cooler (4), wherein the first quotient is a measurement of the sooting of the EGR cooler (4),

   c) ascertaining a current flow resistance of the bypass line (5),

   d) ascertaining a second quotient from the current flow resistance of the bypass line (5) ascertained in step c) and a reference flow resistance of the bypass line (5), wherein the second quotient is a measurement of the sooting of the bypass line (5),

   e) triggering a fault indication if at least one of the following parameters reaches a limit value:

   - the first quotient,

   - the second quotient, or

   - a parameter calculated from the first quotient and the second quotient; and

   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 because of an increase in the flow resistance of the EGR cooler (4) is compensated.
2. A method according to Claim 1, wherein in step e) the fault indication is only triggered if the first quotient is greater than a first limit value.
3. A method according to one of the preceding claims, wherein in step e) the fault indication is only triggered if the second quotient is less than a second limit value.
4. A method according to one of the preceding claims, wherein in step e) the fault indication is only triggered if the difference between the first quotient and the second quotient is greater than a third limit value.
5. A method according to one of the preceding claims, wherein in step a) the current flow resistance of the EGR cooler (4) is ascertained from a pressure drop over the EGR cooler (4), and wherein in step c) the current flow resistance of the bypass line (5) is ascertained from a pressure drop over the bypass line (5).
6. A method according to Claim 4, wherein the reference flow resistance of the EGR cooler (4) and the reference flow resistance of the bypass line (5) are defined in each case as a characteristic map dependent on at least one operating-point parameter of the internal combustion engine (16).
7. An exhaust-gas recirculation means (2) for an internal combustion engine (16) for a motor vehicle (1), wherein the exhaust-gas recirculation means (2) has at least an EGR cooler (4) and a bypass line (5) and also a bypass valve (7), wherein the bypass valve (7) is set up to guide a settable part of an exhaust-gas flow through the bypass line (5) instead of through the EGR cooler (4), and wherein the exhaust-gas recirculation means (2) contains a control unit which carries out all the steps according to a method according to one of the preceding claims.
8. A motor vehicle (1) comprising at least one exhaust-gas recirculation means (2) according to Claim 7.

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