DE102008000608A1 - Exhaust gas after treatment system i.e. particle filter, regenerating method for internal-combustion engine in vehicle, involves detecting beginning and temporal progress of regeneration process by temporal progress of parameters - Google Patents

Abstract

The method involves detecting a parameter (dp) characterizing upstream pressure of an exhaust gas after treatment system i.e. particle filter, and a parameter (vA) characterizing flow rate of exhaust gas. Temporal progress of quotient of the parameters is detected. Beginning and the temporal progress of regeneration process is detected by the temporal progress of the parameters. Time derivatives of the parameter characterizing the upstream pressure and the temporary progress of the quotient of the parameters are stored. Independent claims are also included for the following: (1) a computer program comprising a set of instructions for performing a method for regenerating an exhaust gas after treatment system (2) a computer program product comprising program code for performing a method for regenerating an exhaust gas after treatment system.

Description

The Invention relates to a method for regenerating an exhaust aftertreatment system, in particular a particulate filter arranged in a vehicle Internal combustion engine according to the preamble of the independent Claim 1.

object The present invention also relates to a computer program a computer program product with a program code written on a Machine-readable carrier is stored for execution of the procedure.

State of the art

Such a method is for example from the DE 10 2004 005 072 A1 known.

at Reciprocating internal combustion engines that are electronically controlled by an engine control unit be controlled and regulated, arise in the implementation of the chemical bonded fuel energy into heat essentially pollutants in the form of nitrogen oxides and particles.

Around Filter out particles from the exhaust are in such internal combustion engines provided in the exhaust system particle filter in which the emitted Particles are stored. A large proportion of the particles is flammable, especially carbon-based particles. These are commonly referred to as soot. After a certain Operating time is a regeneration of the particulate filter neces- the embedded particles are oxidized. In this process will Heat released. The heat release during the regeneration phases must be controlled and controlled, otherwise there may be temperature peaks in the particle filter, the the durability and overall function of the particulate filter adversely affect or even destroy it. For this reason, care must be taken that a certain inlet temperature of the exhaust gas in the particulate filter is adjusted for the oxidation of the particles. For this are, for example, exhaust gas temperature-increasing measures provided, for example, a shift in the start of injection the main injection after late or additional Fuel injection in the same cycle after the main injection as so-called post-injection. The course of regeneration takes place Timed, partly based on a modeling in a control unit the internal combustion engine.

From the non-prepublished patent application DE 10 2006 055 237.7 the applicant is a method for assessing the completeness of a regeneration of a flowed through by the exhaust gas of the internal combustion engine particle filter emerges, wherein a pressure difference, which occurs at a flow through the particulate filter on the particulate filter, is detected and evaluated for the assessment. In this case, the time derivative of the detected differential pressure is formed and the assessment of the completeness of the regeneration is made as a function of the time derivative. In this case, the time derivative is formed after one end of a regeneration and compared with a predetermined threshold. The regeneration is judged successful if the time derivative is less than the predetermined threshold. This is based on the finding that the differential pressure in a fully regenerated particulate filter increases only slowly, whereas it rises comparatively quickly in the case of a particle filter that has not been completely regenerated, so that the time derivative of the differential pressure exceeds the threshold value. This method allows the assessment of a complete regeneration.

With However, it is not easily possible to use the method to determine the beginning and the course of the regeneration.

Of the The invention is therefore based on the object, a method for regenerating an exhaust aftertreatment system of the generic type in such a way that also the beginning and the course of the Regeneration can be assessed.

Disclosure of the invention

Advantages of the invention

These The object is achieved by a method for regenerating an exhaust aftertreatment system of Specially described with the features of the type described above Claim 1. By detecting a pressure upstream of the particle filter characterizing size and one characterizing the flow rate of the exhaust gas Size and recording of the time course the quotient of these sizes, it is possible to determine the time of the start of firing exactly. This is it is possible in a particularly advantageous manner, a regeneration to make with greater temporal precision and so measures to protect the filter substrate of the particulate filter to take. This allows, despite limited temperature in the particle filter achieved a higher soot turnover in the regeneration which results in a shorter regeneration period and a greater time interval to a following Generation. This in turn has a lower fuel consumption result.

By this method it is also possible to compensate for the failure or inaccuracies of the temperature sensor before the particulate filter. By an exact determination of the time of the Start of burning, the time interval can be minimized at the beginning of the controlled regeneration at a known temperature. The higher the controlled temperature in front of the filter, the faster it can be regenerated. In addition, with a suitable model, an auxiliary variable for a failed temperature sensor can be formed in front of the particle filter. This can reduce error messages, which in turn reduces complaint rates and warranty costs for a vehicle with a particulate filter.

By the inventive method for detecting the Burning and the course of regeneration can also Disturbances are taken into account, which can not be measured directly by other means. For example, the amount and type of deposited on the soot Hydrocarbons by the engine operation or the engine wear significantly vary. This also changes the time and the temperature level of the start of burning.

advantageous Embodiments and other advantages of the method are the subject each dependent on the independent claim 1 dependent Dependent claims.

So are advantageously both the pressure characterizing signal as well as the flow velocity of the exhaust gas characterizing Signal over time or over the speed of the Internal combustion engine filtered.

Prefers The first and second time derivatives of the filtered signals are transmitted over the time captured and saved.

• – das Erreichen des Wertes null der ersten Ableitung bei negativem Wert der zweiten Ableitung als Identifikation eines Maximums;
• – das Überschreiten eines Schwellenwertes des Absinkens des Signals, das die Strömungsgeschwindigkeit des Abgases charakterisiert, über der Zeit. Dies entspricht dem Überschreiten des Schwellenwerts der ersten Ableitung;
• – ein vorgebbarer Schwellenwert der zweiten Zeitableitung des die Strömungsgeschwindigkeit des Abgases charakterisierenden Signals über der Zeit wird als Maß für den Zeitpunkt des Überschreitens einer Änderung der Strömungsgeschwindigkeit herangezogen;
• – ein Extremwert der zweiten Ableitung des die Strömungsgeschwindigkeit charakterisierenden Signals über der Zeit wird als Maß für den Zeitpunkt der größten Änderungsgeschwindigkeit herangezogen;
• – arithmetische Kombination der vorgenannten Größen, auch unter Einbeziehung ihres zeitlichen Verlaufs.

From the filtered pressure signal and the filtered signal of the flow velocity of the exhaust gas, the start and the course of Rußabbrandes the regeneration is determined. The following criteria can alternatively be used:

• - reaching the value zero of the first derivative with a negative value of the second derivative as identification of a maximum;
• - Overshooting a threshold value of the falling of the signal, which characterizes the flow velocity of the exhaust gas, over time. This corresponds to exceeding the threshold of the first derivative;
• A prescribable threshold value of the second time derivative of the signal characterizing the flow velocity of the exhaust gas over time is used as a measure for the time of exceeding a change in the flow velocity;
• - An extreme value of the second derivative of the flow rate characterizing signal over time is used as a measure of the time of the greatest rate of change;
• - arithmetic combination of the aforementioned quantities, including their time course.

Prefers becomes the determined burning start of the regeneration and the course Rußabbrandes for precise timing of measures for Slowing down or accelerating Rußabbrandes used. Regeneration processes are delayed, brought forward and / or shortened or canceled.

According to one advantageous embodiment is provided, the method according to a Use feedforward control in the time window in which the regeneration control of the engine control unit expects to start burning. this makes possible the limitation to a narrower time window after the precontrol and thus saves on computer and storage resources in the control unit of the combustion device.

After all The method can also be used to model the temperature before Particle filter are used.

Brief description of the drawings

embodiments The invention is illustrated in the drawings and in the following Description explained in more detail.

It demonstrate:

1 schematically an internal combustion engine having a particulate filter in the exhaust system and

2 An embodiment of a method according to the invention in the form of a flow chart.

embodiments the invention

1 schematically shows an internal combustion engine 12 with a particle filter 10 from the left to the right of the exhaust of the internal combustion engine 12 is flowed through. The particle filter 10 has a porous filter structure 14 on, which is permeable to the exhaust gas, but in the exhaust gas contained soot particles only a small part. The porous filter structure 14 has in the embodiment of 1 Mutually closed left or right channels 16 . 18 on, passing through porous walls 20 are separated from each other. To the particle filter 10 To pass, the exhaust must pass the porous walls 20 flow through. In the process, soot particles contained in the exhaust gas are deposited in pores of the walls 20 what are these gradually clogged and the flow resistance of the particulate filter 10 elevated.

The flow resistance leads to the flow through the particle filter 10 to a pressure drop, for example, from a differential pressure sensor 22 detected as differential pressure dp and to a control unit 24 is handed over. Instead of the differential pressure sensor and a pressure sensor upstream of the particulate filter may be provided (not shown). Like the differential pressure sensor, it measures the pressure upstream of the particle filter, because the pressure downstream of the particle filter essentially corresponds to the atmospheric pressure. Hereinafter, both the differential pressure and the pressure signal will be denoted by the same reference numeral dp. This pressure signal corresponds - as mentioned - substantially the pressure upstream of the particulate filter. The control unit 24 forms a measure of the loading of the particulate filter 10 with soot in dependence on the pressure signal dp. Depending on the configuration, the pressure signal dp can also be used directly as a measure of the load, since the differential pressure dp above the particle filter 10 monotonous with the loading of the particulate filter 10 increases with soot. Through another sensor 29 In addition, the Strömungsge speed of the exhaust gas vA before the particulate filter 10 measured. This signal is also sent to the controller 24 fed.

At the control unit 24 it is preferably a control unit, the manipulated variables S_L and S_K for the operation of the internal combustion engine 12 depending on the signal dp of the pressure sensor 22 as well as the signal vA of the sensor 29 and the signals BP, T other sensors 26 . 28 forms. In the signals BP of the sensors 26 form operating parameters of the internal combustion engine 12 As speed, intake air mass, boost pressure, driver's request, combustion chamber pressure, combustion noise, etc., this list is not exhaustive and the control unit 24 also does not have to process signals for all mentioned operating parameters. The sensor 28 detects a temperature T in front of the particle filter 10 , This temperature T can be used as an actual value for a temperature control, with which the particle filter temperature during a regeneration of the particulate filter 10 held above the ignition temperature of the soot serve. With the manipulated variables S_L, the control unit engages 24 on an air system 30 , For example, to a throttle valve or an exhaust gas recirculation valve, and with the control variables S_K on a fuel system 32 , For example, to an injector, the internal combustion engine 12 one.

Incidentally, the controller 24 to set up, in particular programmed to control a flow of the inventive method or a flow of one or more of its embodiments.

2 shows an embodiment of the method according to the invention in the form of a flow chart. It represents step 210 a main program for controlling the internal combustion engine 12 that in the control unit 24 is processed. In the main program of the step 210 becomes the internal combustion engine 12 operated in a normal mode NB. The term normal operation is used to distinguish from the concept of regeneration operation and therefore includes all modes BA, in which no regeneration of the particulate filter 10 takes place. In the main program of the step 210 Therefore, the selected operating mode BA is the normal operation NB (BA = NB).

To check the loading of the particulate filter 10 with soot the main program branches out of step 210 repeated in one step 220 , in which the differential pressure dp above the particulate filter 10 as he from the differential pressure sensor 22 is provided is detected. Alternatively or additionally, moreover, by means of the sensor 29 the flow velocity of the exhaust gas are detected. This is followed by a step 230 in which the value of the detected pressure difference dp is compared with a threshold value S1. As long as dp does not exceed the threshold S1, the program branches back to the step 210 in which the internal combustion engine 212 continues to operate in normal operation NB. Accordingly, the flow rate of the exhaust gas vA can be compared with a threshold value, and when this threshold value is exceeded, step 210 branched.

If, however, the threshold value is exceeded, that is, the differential pressure dp exceeds the threshold value S1 and / or the flow rate of the exhaust gas vA exceeds a corresponding threshold value, the step follows 230 a step 240 in which the operating mode BA of the internal combustion engine 12 is switched from normal operation NB in a regeneration mode RB or reversed. In this regeneration mode RB controls the controller 24 the internal combustion engine 12 so that the temperature of its exhaust gases is increased so that the ignition temperature of the soot in the particulate filter is reached or exceeded. This is preferably done by changing the manipulated variables S_L for the air system 32 and / or S_K for the fuel system 30 ,

In order to increase the exhaust gas temperature, early, burning or accumulated post-injections, a retardation of the main injection and an intake air throttling or an increase in the exhaust gas recirculation rate come into question. Combinations of these measures are also possible. As an alternative or in addition, late postinjections come into question which, due to the oxidation of the fuel which is no longer burned in the combustion chamber, can be combined in one Oxidizing catalyst lead to a further increase in exhaust gas temperature.

To ensure reliable regeneration of the particulate filter even in unfavorable environmental conditions 10 to ensure the exhaust gas temperature is preferably controlled during regeneration. The temperature signal of the temperature sensor serves as an input variable for the regulation of the exhaust gas temperature 28 , in front of the particle filter 10 or in the particle filter 10 arranged itself. As an alternative or in addition to detecting an actual temperature of the particulate filter or of the exhaust gas, such an actual temperature can also be determined from operating parameters of the internal combustion engine 12 , such as B. sucked amount of air and injected fuel amount in the control unit 24 be calculated by a realized as a software module exhaust temperature model.

In order to determine the exact start of combustion of Rußabbrandes and the course of Rußabbrandes is provided according to the inventive method, in step 242 the differential pressure and in step 244 to detect the flow velocity of the exhaust gas vA. From these two quantities is determined by quotient formation in step 246 a size RESFLOW formed. All sizes will be in step 250 filtered over time or over the speed of the internal combustion engine. Then in step 260 formed the first time derivative and the second time derivative Z1, Z2 either the pressure signal dp or the ratio RESFLOW over time and recorded in a time window. In this context, "written in a time window" means that these variables are stored within a predefinable time interval, which is determined by incrementing a variable characterizing the time and comparing this variable with a threshold value.

• – das Erreichen des Wertes null der ersten Ableitung Z1 dieser Größen bei negativen Wert der zweiten Ableitung Z2 als Identifikation eines Maximums;
• – das Überschreiten eines Schwellenwerts des Absinkens dieser Größen über der Zeit als Identifikation eines Schwellenwerts der ersten Ableitung Z1;
• – das Erreichen eines Schwellenwerts der zweiten Zeitableitung Z2 dieser Größen über der Zeit als Maß für den Zeitpunkt des Überschreitens einer zeitlichen Änderung dieser Größen;
• – ein Extremwert der zweiten Ableitung Z2 dieser Größen über der Zeit als Maß für den Zeitpunkt der größten zeitlichen Änderung und
• – arithmetische Kombination aus den oben genannten Größen auch unter Einbeziehung ihres zeitlichen Verlaufs.

In step 270 is then determined from a reduction of the filtered differential pressure value dp or the filtered signal RESFLOW the start and the course of Rußabbrands. In this case, the criterion can alternatively be used:

• - reaching the value zero of the first derivative Z1 of these quantities at negative value of the second derivative Z2 as an identification of a maximum;
• The exceeding of a threshold value of the decrease of these quantities over time as identification of a threshold of the first derivative Z1;
• - reaching a threshold of the second time derivative Z2 of these quantities over time as a measure of the time of exceeding a temporal change of these quantities;
• - An extreme value of the second derivative Z2 of these variables over time as a measure of the time of the largest temporal change and
• - Arithmetic combination of the above variables including their time course.

In step 280 The so determined exact start of combustion and the course of Rußabbrands is used at the exact time in the control of measures to slow down or accelerate Rußabbrandes, for example, for delay, for shortening and the like. In this case, the manipulated variables S_L for the air system 32 and / or S_K for the fuel system 30 changed accordingly.

The Method can optionally be used after a pilot control, in the time window in which a regeneration control of the engine control unit expected to start burning. The limitation to a narrower time window after pre-control, the saving of computer and memory resources in the engine control unit.

In addition, the start of combustion and the course of Rußabbrandes can be used to a failure of the temperature sensor 28 in front of the particle filter 10 to compensate. In this case, the temperature is determined by a suitable model. This model can also be used to monitor a malfunctioning temperature sensor and to make its output values plausible.

The method described above can be used, for example, as a computer program on a computing device, in particular the control device 24 be implemented the internal combustion engine and run there. The program code may be stored on a machine-readable medium that the controller 24 can read.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• DE 102004005072 A1 [0003]
• - DE 102006055237 [0006]

Claims (9)

Method for regenerating an exhaust aftertreatment system, in particular a particle filter ( 10 ), an engine disposed on a vehicle ( 12 ), by a control device ( 24 ) controlled regeneration cycles, characterized in that a pressure upstream of the exhaust aftertreatment system characterizing size (dp) and a flow rate of the exhaust gas characterizing variable (vA) are detected and from the time course of the quotient (RESFLOW) of these sizes and / or at the temporal Course of these variables on the beginning and the time course of the regeneration process is concluded. Method according to claim 1, characterized in that that the quotient and / or the size above the Time or filtered over the speed of the internal combustion engine become. A method according to claim 1 or 2, characterized in that the first and second time derivative (Z2) of the pressure (dp) upstream of the particulate filter (Z) 10 ) characterizing size and / or the quotient (RESFLOW) are formed and their temporal courses are stored. Method according to Claim 3, characterized in that threshold values of the first and second time derivatives (Z1, Z2) are formed and from this a reduction of the variable (dp) characterizing the pressure upstream in the exhaust aftertreatment system and / or the variable characterizing the flow rate of the exhaust gas ( vA) is determined and from this on the start and the course of a regeneration process, in particular of Rußabbrandes in a particle filter ( 10 ) is closed. Method according to claim 4, characterized in that that starting from the determined start of Rußabbrandes and the course of the regeneration process measures to Delay, acceleration or termination of a regeneration process be made. Method according to one of the preceding claims, characterized in that on the basis of the quotient (RESFLOW) and / or the pressure (dp) or the flow velocity of the exhaust gas (vA) before the particle filter characterizing quantities and / or their time derivatives (Z1, Z2) to the temperature before the exhaust aftertreatment system, in particular before the particulate filter ( 10 ), is closed. Method according to one of the preceding claims, characterized in that it within a predetermined time window is used after a pilot control. Computer program that shows all the steps of a procedure according to one of claims 1 to 7 executes when it runs on a computing device. Computer program product with program code, which is stored on a machine-readable carrier, for carrying out the method according to one of claims 1 to 7, when the program is stored on a computer or a control unit ( 24 ) an internal combustion engine ( 12 ) expires.