DE102018211195A1 - Method for evaluating a reaction rate of a chemical reaction in an exhaust gas filter - Google Patents

Abstract

The invention describes a method for evaluating a conversion rate of a chemical reaction in an exhaust gas filter (25) - in particular a soot particle filter - of an internal combustion engine (10), an air / fuel mixture to an exhaust gas being provided in a combustion chamber (48) of the internal combustion engine (10) (50) is burned, which flows into an exhaust tract (53) with the exhaust gas filter (25) and a chemical composition of the exhaust gas (50) in the exhaust gas filter (25) changes with the conversion of oxygen and by a sensor (28) in front of the exhaust gas filter (25) and a sensor (29) after the exhaust gas filter (25) detects a change in a property of the exhaust gas (50) and that a critical rate of conversion in the exhaust gas filter (25) is based on an at least achieved difference in the concentration (DkO2) of the oxygen in the Detect exhaust gas (50) before and after the exhaust gas filter (25) as well as this at least reached duration (Dt) of this at least achieved difference t will.

Description

State of the art

From the publication of the German patent application DE 10 2013 218 900 A1 the construction of an exhaust line of an internal combustion engine is known, which has a so-called soot particle filter as an exhaust gas filter. Immediately before the particle filter, ie between the internal combustion engine and the particle filter, and immediately after the particle filter, ie between the particle filter and the exhaust pipe of the exhaust system, there is a so-called lambda probe. In the method disclosed there, a particle loading of the particle filter is determined. Depending on the determined particle loading, a modified lambda value is determined so that an uncontrolled regeneration of the particle filter is avoided.

From the DE 10 2013 220 881 A1 it is known that an excessively high temperature of the exhaust gas and / or an excessively long duration of the burning process of the particle filter will in practice result in the temperature of the particle filter increasing to an unacceptably high degree. To solve this problem, it is proposed there to make the material of the particle filter particularly temperature-resistant. It is also proposed there to keep the temperature below a temperature critical for the material of the particle filter during the regeneration of the particle filter and also not to allow the period of time required for the regeneration to last too long.

Embodiments of the invention

According to a first aspect of the invention, a method is proposed which carries out an evaluation of a reaction rate of a chemical reaction in an exhaust gas filter. Such an exhaust gas filter is in particular a soot particle filter of an internal combustion engine. For this purpose, the internal combustion engine can be designed as a so-called self-igniter (in particular a diesel type) or an external ignition (in particular an Otto type). In a combustion chamber of the internal combustion engine, an air-fuel mixture is burned to form an exhaust gas, which flows into an exhaust line with an exhaust gas filter. In the exhaust gas filter, a chemical composition of the exhaust gas changes with the conversion of oxygen. A change in a property of the exhaust gas is determined by a sensor in front of the exhaust gas filter and by a sensor after the exhaust gas filter. It is provided that one sensor is arranged in front of the exhaust gas filter directly in front of the exhaust gas filter and the other sensor is arranged immediately after the exhaust gas filter. Immediately here means preferably that there is not yet another device between a sensor and the exhaust gas filter, which in particular additionally causes a change in the property of the exhaust gas. Within the scope of the method, it is provided that a critical conversion speed in the exhaust gas filter is recognized by an at least achieved difference in the concentration of oxygen in the exhaust gas before and after the exhaust gas filter and additionally by an at least reached duration of this at least achieved difference in the concentration of oxygen. A critical conversion speed is a measure of the heat energy or quantity released by the reaction and thus also an indication of a thermal hazard to the exhaust gas filter. In particular, it can be provided that the at least achieved difference in the concentration DKO2 of the oxygen in the exhaust gas before and after the exhaust gas filter exceeds an applied or preset threshold, which is stored in particular in a control unit - which is used to carry out the method. The applied threshold of the concentration DKO2 of oxygen can, for example, be approximately or exactly 9% (volume concentration). The threshold can alternatively be approximately or exactly 6% or 11%, for example. Furthermore, it is provided that this difference in the concentration of oxygen lasts for a certain applied, preset minimum duration, which is stored in particular in the control unit - which is used to carry out the method.

This minimum duration depends on some system parameters. This includes, for example, the volume of the exhaust gas line between the two sensors and also the current volume flow of the exhaust gas.

According to a further aspect of the invention, it is provided that after the detection of a critical speed of reaction (reaction speed), an air-fuel mixture is generated which has a substoichiometric proportion of oxygen. This means that the lambda is reduced and the mixture changes in the "rich" direction. It follows from this that no further oxygen is available in the exhaust gas for a chemical reaction, in particular with the soot of the exhaust gas filter, in particular the soot particle filter, and the regeneration is interrupted in this way. Lambda indicates a mass ratio of air and fuel in a combustion process.

According to a further aspect of the invention, it is provided that a higher amount of fuel is metered, in particular injected. Such an increase in the amount of fuel can take place in the combustion chamber of the internal combustion engine (direct injection) or in an intake tract in front of the combustion chamber. In connection with the determination of the change in a property of the exhaust gas before and after the exhaust gas filter the exhaust gas filter by means of a sensor in each case it should be mentioned that for this purpose in particular the signal of an oxygen sensor, in particular a lambda probe, is determined and evaluated.

• 1 in abstrakter Weise eine Brennkraftmaschine mit einem Ansaugtrakt, einem Abgassammler, einem Auslassrohr, einem ersten Sensor, einem Abgasfilter, einem zweiten Sensor, einer Signalauswerteeinheit und einem Einspritzsteuergerät,
• 2 ein Diagramm, in dem
  • - eine Temperatur im Abgasfilter,
  • - ein gemessener bzw. errechneter Unterschied der Konzentration des Sauerstoffs vor und nach dem Abgasfilter sowie
  • - verschiedene beispielhafte Richtwerte von 6%, 9% und 11% Unterschied der Konzentration des Sauerstoffs über die Zeit dargestellt sind,
• 3 ein Diagramm, in dem
  • - ein Verlauf der Konzentration des Sauerstoffs im Abgas vor und nach dem Abgasfilter,
  • - ein gemessener bzw. errechneter Unterschied der Konzentration des Sauerstoffs vor und nach dem Abgasfilter sowie
  • - verschiedene beispielhafte Richtwerte von 6%, 9% und 11% Unterschied der Konzentration des Sauerstoffs über die Zeit dargestellt sind, sowie
  • - die Temperatur im Abgasfilter.

The invention is described in more detail with reference to the figures given below. Show it:

• 1 in an abstract manner an internal combustion engine with an intake tract, an exhaust manifold, an outlet pipe, a first sensor, an exhaust gas filter, a second sensor, a signal evaluation unit and an injection control unit,
• 2 a diagram in which
  • - a temperature in the exhaust filter,
  • - A measured or calculated difference in the concentration of oxygen before and after the exhaust filter and
  • various exemplary guide values of 6%, 9% and 11% difference in the concentration of oxygen over time are shown,
• 3 a diagram in which
  • a course of the concentration of oxygen in the exhaust gas before and after the exhaust gas filter,
  • - A measured or calculated difference in the concentration of oxygen before and after the exhaust filter and
  • - Various exemplary guide values of 6%, 9% and 11% difference in the concentration of oxygen over time are shown, as well
  • - The temperature in the exhaust filter.

1 shows a basic structure of an internal combustion engine 10 with an intake tract 13 , in the by means of an injector 16 Fuel is or can be injected into the intake tract. To the internal combustion engine 10 is a "flue gas collector" 19 attached, in this case in an exhaust pipe 22 (Exhaust) passes. In the exhaust pipe 22 there is an exhaust filter 25 , In front of the exhaust filter 25 there is a first sensor 28 and after the exhaust filter 25 a second sensor 29 , These two sensors 28 . 29 are over signal lines 30 with a signal evaluation unit 33 connected. The injector 16 - For example, one or more injection nozzles - is via a signal line 30 with an injection control unit 36 connected. The injection control unit 36 and the signal evaluation unit 33 are also via a signal line 30 connected. The injection control unit and the signal evaluation unit can also be integrated in an engine control unit, as is the case with most modern systems. The exhaust filter 25 is a particulate filter in particular. So it is with the internal combustion engine 10 is a machine in which an air-fuel mixture ignites automatically after sufficient compression (self-igniter, e.g. diesel principle), this can be, for example, a particle or soot particle or diesel particle filter. So it is with the internal combustion engine 10 is a machine whose mixture burned there burns by so-called spark ignition (e.g. gasoline principle), the exhaust gas filter is a particle or soot particle or gasoline particle filter.

Generally it works too 1 described device such that through an opening 39 Air in the intake tract 13 flows in, for example by self-priming of the internal combustion engine 10 or by pushing it in using an exhaust gas turbocharger. Into this air 42 is by means of the injector 16 (e.g. injector) fuel 45 (e.g. gasoline or diesel) injected. That air 42 and this fuel 45 form a so-called air-fuel mixture. This type of mixture formation is representative of a general mixture formation in internal combustion engines 10 , A general distinction is made, for example, between outer and inner mixture formation. External mixture formation takes place, for example, through intake pipe injection (petrol). Internal mixture formation takes place, for example, through direct injection into the combustion chamber 48 (Diesel, petrol) instead.

In the example, the internal combustion engine shown there 10 four combustion chambers 48 , After burning in the combustion chamber 48 becomes from the combustion chamber 48 an exhaust gas 50 in the exhaust system 53 omitted. The exhaust gas flows in the process 50 first through the exhaust manifold 19 and from there typically into a single exhaust pipe 22 , The exhaust gas 50 passes the first sensor 28 , By means of this sensor 28 becomes a state of the exhaust gas 50 determined. In particular, with the help of this sensor 28 a change in a property of the exhaust gas 50 determined. This sensor 28 is designed in particular as an oxygen sensor, in particular as a lambda probe. A signal from the sensor 28 is on the signal line 30 to the signal evaluation unit 33 transmitted. The exhaust gas flowing on 50 flows into the exhaust filter 25 , In this exhaust filter 25 is, in particular, a substance on its surface as a constituent from exhaust gas which has previously flowed through it 50 deposited (particles). This substance (soot, soot particles) becomes present at the required reaction temperature together with components of the exhaust gas 50 implemented. In particular, soot is present in the exhaust gas 50 located oxygen, e.g. B. to CO2, implemented. This changes the chemical composition of the exhaust gas 50 with passing the exhaust filter 25 so the exhaust 50 if it is the second sensor 29 happens to have a different composition than when passing the first sensor 28 , The oxygen mentioned here is oxygen that is generated during combustion in the combustion chamber 48 as part of the air 42 not burned - e.g. B. during a so-called overrun phase, in which the injection is stopped - but was transported through the combustion chamber. As is known, the chemical composition of the exhaust gas changes 50 in the exhaust filter 25 under sales of oxygen. This conversion or conversion reaction results in the amount of oxygen involved and in the exhaust gas filter 25 deposited material or soot 56 more or less thermal energy (exothermic reaction). This amount released here is problematic if it leads to the exhaust filter 25 Is heated "supercritically". This means that a supercritical amount of heat causes the exhaust filter 25 is damaged or destroyed at least in places. To determine such a critical situation or critical implementation speed or thermal energy generated in the exhaust gas filter 25 becomes a difference in concentration DKO2 of oxygen in the exhaust gas 50 before and after the exhaust filter 25 determined. Both sensors are used for this 28 . 29 and their to the signal evaluation unit 33 transmitted signals.

2 shows a diagram with a time course of different sizes. So the diagram shows z. B. by means of the solid straight lines the previously mentioned fictitious, constant difference in concentration DKO2 of oxygen in the exhaust gas 50 before and after the exhaust filter 25 for different differences in concentration DKO2 of oxygen. In this case, the diagram shows the differences in concentration as an example DKO2 of oxygen of 6%, 9% and 11% (volume concentration). For different procedures, these measures are therefore a type of measurement or calculation value for the change in a proportionate amount of oxygen in the exhaust gas 50 before passing the exhaust filter 25 and approximately the proportionate amount of oxygen in the exhaust gas 50 after passing the exhaust filter 25 , I.e. this change in the concentration of oxygen in the exhaust gas 50 means the percentage of oxygen in the exhaust gas 50 after the exhaust filter 25 is no longer carried, around which the exhaust gas 50 is reduced to reduce the amount of particles (especially soot) in the exhaust gas filter 25 has led. The difference between the two concentrations or oxygen proportions provides information about the strength of the regeneration taking place in the exhaust gas filter 25 , This consists of a current particle load, in particular soot load, and the temperature in the exhaust filter 25 together. There may be situations in which all of the incoming oxygen or exhaust gas 50 in the exhaust filter 25 carried oxygen is implemented. This would result in a high oxygen concentration before passing through the exhaust filter 25 and a high particle load or quantity as well as a sufficient reaction temperature a very strong regeneration of the exhaust gas filter 25 and accordingly a high temperature or rising temperature of the exhaust gas filter 25 mean. If only part of the oxygen was converted, this would mean either a low temperature in the course of the exothermic reaction or only a small particle load or soot load on the exhaust gas filter 25 ,

The particle load or soot in an exhaust gas filter 25 or in particular a gasoline particle filter burns with oxygen z. B. to CO2. This results in an internal combustion engine 10 with spark ignition (e.g. gasoline engine), which is operated primarily when lambda = one, the regeneration of the exhaust gas filter 25 passively takes place only in overrun mode. In overrun mode, for example, no combustion takes place in the internal combustion engine, so that a particularly large amount of oxygen is drawn into the exhaust gas tract by the intake but not burned air 53 is left out. In 2 are corresponding curves of the temperatures in the exhaust gas filter 25 shown. This exhaust filter 25 is close to the internal combustion engine 10 built-in. Several overrun phases are shown here. For the consideration, the process begins with a particle loading or soot loading in the area of the maximum permissible loading of the exhaust gas filter used here 25 of approx. 2 grams (0.002 kg) at the beginning of a first relapse phase 61 , The one in overrun mode with an outlet temperature of approx. 700 ° C to 770 ° C in the exhaust filter 25 entering oxygen as part of the exhaust gas 50 leads to an exothermic combustion or implementation in the exhaust filter 25 accumulated particle load or soot 56 , The in 2 The course of the measurements shown initially begins with a loaded exhaust gas filter 25 with the approx. 2 grams of soot just mentioned 56 , During the first overrun phase 61 is in the course of the temperature curve T due to the curve shown, a clear exotherm or heat development in the exhaust gas filter 25 to recognize. The temperature T increases from a starting temperature T61 to a maximum value T61max of this overrun phase. This first push phase 61 and the associated conversion of part of the particle load (soot burn-off) is also based on the difference signal or the determined concentration difference of the oxygen ( DKO2 , Difference in concentration KO2 of oxygen in the exhaust gas 50 before and after the exhaust filter 25 ) clearly visible. For a period Dt61 The value for the difference in the concentration of the oxygen increases by approximately 12 seconds DKO2 for more than three seconds as an example of a minimum duration Dt above the threshold of 9% concentration difference DKO2 , This means that a lot of the exhaust gas 50 entered oxygen in the exhaust filter 25 is implemented. One starts after about 76 seconds second overrun phase 62 , How well it can be recognized is at the beginning of the second relapse phase 62 a start temperature T62 regeneration significantly lower (approx. -65 ° C). During this second overrun phase 62 the or part of the particle loading is implemented much more slowly. Thus, the heat development or exothermic is less strong than in the first overrun phase 61 pronounced. Basically, only the falling trend of temperature T between the two overrun phases 61 . 62 somewhat delayed or delayed. Because of the significantly lower converted particle load and therefore less oxygen used from the exhaust gas 50 is the difference between the concentrations DKO2 of oxygen in the exhaust gas 50 before and after the exhaust filter 25 clearly lower. This is especially true for the second concentration maximum 622 , which is compared to the first concentration maximum 621 is not even half as high.

As for the third push phase 63 The temperature can be easily recognized T63 at the beginning of this third relapse phase 63 again significantly higher and is approx. 660 ° C. After passing through a minimum temperature Tm, this is caused, for example, by a short phase in which the internal combustion engine 10 was operated at an operating point with a higher load and / or speed. This leads to a higher temperature level of the exhaust gas 50 , With the beginning of the subsequent third push phase 63 and strong oxygen flow through the exhaust system 53 because of the initially high reaction temperature, the reactivity of the particle loading increases. However, because of the overrun phases that had just ended 61 . 62 not too much particle load or particle mass in the exhaust filter 25 is present, only a little particle mass is converted, so that the temperature T increases, but only by approx. 20 ° C. This is compared to the temperature increase during the first overrun phase 61 of about 130 ° C relatively little. Accordingly, there is also the third overrun phase 63 no risk of damage or destruction of the exhaust gas filter 25 , The time or duration Dt61 . DT62 , Dt631, Dt632, during which the course of the difference in concentrations of oxygen DKO2 in the exhaust gas 50 Remaining above the 9% concentration difference threshold are different. The length of time Dt61 is approximately 12 seconds, the duration DT62 approx. 1.8 seconds, the duration Dt631 approx. 2.7 seconds and the duration Dt632 approx. 7.2 seconds. These time periods are another important measure when evaluating the thermal energy introduced into the exhaust gas filter 25 , A major challenge here is the time offset between the first sensor 28 and the second sensor 29 not recognizable as a critical burn. This offset largely depends on the volume between the two sensors 28 . 29 , as well as the current exhaust gas volume flow of the internal combustion engine 10 from.

The times or periods mentioned above Dt61 . DT62 , Dt631, Dt632 are for a difference in concentration of oxygen DKO2 in the exhaust gas 50 stated above the threshold of 9%. As with the determined curve for the difference in concentration of oxygen DKO2 in the exhaust gas 50 is clear, the times for a lower approved threshold of 6% are inevitably longer, since signal edges for the difference in concentration of oxygen DKO2 in the exhaust gas 50 not with an infinitely large incline or slope, but with a finite incline or slope. That is, with a low threshold value, the at least reached duration Dt of the at least achieved difference for the concentration of oxygen tends to occur DKO2 is longer. Conversely, the difference in the concentration of oxygen applies DKO2 in the exhaust gas 50 for a higher approved threshold - for example 11% - that the times are necessarily shorter. That is, with a higher threshold value, the at least reached duration Dt of the at least achieved difference for the concentration of oxygen tends to occur DKO2 is shorter.

In 3 is shown as the course of the various concentrations of oxygen KO228 . KO229 in the exhaust system 53 , ie here at the position of the first sensor 28 and at the position of the second sensor 29 , comes about. The course of the curve KO228 shows the course of the concentration of oxygen by the sensor 28 before passing the exhaust filter 25 is determined. The dashed course shows the course of the concentration KO229 of the oxygen which is sent through the second sensor 29 after passing the exhaust filter 25 is determined. The dotted line shows the difference between the two signals, DKO2 , This makes it clear how a signal, in particular maximum in the difference, arises from the time offset of the two lambda probe signals.

• - es soll ein Unterschied der Konzentration des Sauerstoffs DKO2 im Abgas 50 vor und nach dem Abgasfilter 25 - ermittelt unter Zuhilfenahme von Sensoren 28, 29 (insbesondere Lambdasensoren bzw. Lambdasonden) - größer einer voreingestellten Schwelle vorliegen, die insbesondere in einem Steuergerät - welches zur Durchführung des Verfahrens verwendet wird - gespeichert ist. Diese Schwelle ist während einer sogenannten Applikationsphase an das jeweilige System, in dem sich die Brennkraftmaschine 10 befindet, anzupassen.
• - das zeitliche Andauern des Unterschieds der Konzentration des Sauerstoffs im Abgas 50 vor und nach dem Abgasfilter 25 oberhalb der voreingestellten Schwelle, d. h. des mindestens erreichten Unterschieds der Konzentration DKO2 des Sauerstoffs im Abgas 50, soll während einer mindestens erreichten Dauer Dt erreicht worden sein. Diese Dauer Dt ist abhängig vom Abgasvolumenstrom und ist daher in der Applikationsphase anzupassen und zu gewichten. Die Dauer Dt ist zudem ebenfalls vom Volumen zwischen den beiden Sensoren 28, 29 abhängig.

To protect the exhaust filter 25 In particular, it is provided that overrun phases must be ended under certain conditions (overrun cutoff):

• - there is supposed to be a difference in the concentration of oxygen DKO2 in the exhaust gas 50 before and after the exhaust filter 25 - determined with the help of sensors 28 . 29 (in particular lambda sensors or lambda probes) - greater than a preset threshold, which is stored in particular in a control unit - which is used to carry out the method. This threshold is during a so-called application phase to the respective system in which the internal combustion engine is located 10 located to adjust.
• - the time duration of the difference in the concentration of oxygen in the exhaust gas 50 before and after the exhaust filter 25 above the preset threshold, ie the at least achieved difference in concentration DKO2 of oxygen in the exhaust gas 50 , Dt is said to have been reached for a minimum duration. This duration Dt depends on the exhaust gas volume flow and must therefore be adjusted and weighted in the application phase. The duration Dt is also the volume between the two sensors 28 . 29 dependent.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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 102013218900 A1 [0001]
• DE 102013220881 A1 [0002]

Claims (6)

Method for evaluating a conversion rate of a chemical reaction in an exhaust gas filter (25) - in particular a soot particle filter - of an internal combustion engine (10), an air / fuel mixture being burned into an exhaust gas (50) in a combustion chamber (48) of the internal combustion engine (10) is, which flows into an exhaust tract (53) with the exhaust gas filter (25) and a chemical composition of the exhaust gas (50) in the exhaust gas filter (25) changes with the conversion of oxygen and by a sensor (28) in front of the exhaust gas filter (25) and a change in a property of the exhaust gas (50) is determined by a sensor (29) after the exhaust gas filter (25) and that a critical conversion speed in the exhaust gas filter (25) is based on an at least achieved difference in the concentration (DKO2) of the oxygen in the exhaust gas (50) before and after the exhaust gas filter (25) and additionally by an at least reached duration (Dt) of this at least achieved difference. Procedure according to Claim 1 , characterized in that the difference in the concentration (DKO2) of the oxygen in the exhaust gas (50) before and after the exhaust gas filter (25) exceeds a preset threshold. Procedure according to Claim 1 or 2 , characterized in that the at least reached duration (Dt) of this at least achieved difference lasts a preset minimum duration. Method according to one of the preceding claims, characterized in that after the detection of a critical implementation speed, an air-fuel mixture is generated which has a lower oxygen content. Procedure according to Claim 4 , characterized in that for this purpose a higher amount of fuel is metered, in particular injected, and this is metered into the combustion chamber (48) or the intake tract (13). Method according to one of the preceding claims, characterized in that a signal from an oxygen sensor, in particular a lambda probe, is evaluated.

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