DE102006033567B4 - Method for determining the triggering point in time for triggering the regeneration process for regenerating a particle filter - Google Patents

Abstract

Method for determining the triggering time of a regeneration process for regenerating a particle filter switched on in the exhaust system of an internal combustion engine with the following steps: - determining the current soot loading condition of the particle filter, - comparing the determined loading condition with a map, constructed from data which, in different operating states of the internal combustion engine, represent a regeneration process with sufficient regeneration success, necessary soot loading, - setting a flag "loading condition OK" if the currently determined soot loading is greater than or equal to the minimum soot loading required by the map and - if the flag "loading condition OK" is set, determining the probable regeneration success, if at the time of this determination, depending on the current operating state of the internal combustion engine, the regeneration process would be triggered, and setting a "Regeneration Start" flag, if the probable regeneration success is sufficient.

Description

The invention relates to a method for determining the triggering point in time of the regeneration process for regenerating a particle filter connected to the exhaust line of an internal combustion engine.

In order to reduce particle emissions, particularly soot emissions, particle filters are installed in the exhaust system of diesel engines. When the diesel engine is in operation, soot particles gradually accumulate on the filter surface of the particle filter. In order to regenerate such a particle filter, it is known to eliminate the soot by burning off the soot and thus by oxidation. Such a soot burn-off occurs automatically when the exhaust gas temperature flowing onto the particle filter is higher than the ignition temperature of the soot. Fuel additives are used to lower the soot ignition temperature. The exhaust gas temperature usually exceeds the soot ignition temperature when the diesel engine is operated under a certain load for a certain period of time, for example when driving at high speed. Active regeneration processes are used to enable regeneration of the particulate filter even in those operating states in which the exhaust gas temperature is lower than the soot ignition temperature. This is done by supplying thermal energy, for example via thermoelectric heating elements or by injecting fuel into the exhaust gas flow. In order for the particle filter to be regenerated as intended by burning off soot, it is necessary for the particle filter to have a specific soot load. If the amount of soot accumulated on the particulate filter is too small, this can lead to incomplete, uneven soot burn-off.

Out of DE 199 45 372 A1 a method for controlling a regeneration of a particle filter is known. In this method, the particle filter is regenerated if a condition indicator describing a need for regeneration is exceeded and lies between two limit values.

DE 198 38 032 B4 relates to a method for regenerating a particle filter, in which method the regeneration is carried out as a function of the loading state of the particle filter and is carried out until the normalized exhaust gas back pressure is less than the limit value of the normalized exhaust gas back pressure.

Based on the discussed prior art, the invention is therefore based on the object of further developing the method mentioned in such a way that the above DE 199 45 372 A1 identified disadvantages are avoided, thus is taken care of a uniform regeneration of the particle filter over the cross-sectional area.

• - Bestimmen des aktuellen Rußbeladungszustandes des Partikelfilters,
• - Vergleichen des ermittelten Beladungszustandes mit einem Kennfeld, aufgebaut aus Daten, die bei unterschiedlichen Betriebszuständen der Brennkraftmaschine die für ein Regenerationsprozess mit hinreichendem Regenerationserfolg notwendige Rußbeladung darstellen,
• - Setzen eines Flag „Beladungszustand OK“, wenn die aktuell ermittelte Rußbeladung größer oder gleich der durch das Kennfeld geforderten Mindestrußbeladung ist und
• - wenn das Flag „Beladungszustand OK“ gesetzt ist, Bestimmen des voraussichtlichen Regenerationserfolges, wenn im Zeitpunkt dieser Bestimmung in Abhängigkeit von dem aktuellen Betriebszustand der Brennkraftmaschine der Regenerationsprozess ausgelöst werden würde, und Setzen eines Flag „Regeneration Start“, wenn der voraussichtliche Regenerationserfolg hinreichend ist.

This object is achieved by a generic method mentioned at the beginning with the following steps:

• - Determination of the current soot loading status of the particle filter,
• - Comparing the determined loading condition with a map, built up from data that represent the soot loading necessary for a regeneration process with sufficient regeneration success in different operating states of the internal combustion engine,
• - Setting a flag "loading status OK" if the currently determined soot load is greater than or equal to the minimum soot load required by the map and
• - if the flag "loading condition OK" is set, determining the expected regeneration success if the regeneration process would be triggered at the time of this determination depending on the current operating state of the internal combustion engine, and setting a flag "regeneration start" if the expected regeneration success is sufficient .

In the context of these statements, the term “flag” is to be understood as meaning a status indicator or any element which is equivalent thereto and which has at least two states. The states can be called up from the flag.

In this method, the soot loading condition of the particle filter is determined in a first step and a flag "Loading status OK" is set if the currently determined soot loading is greater than or equal to a predefined minimum soot loading. In principle, it is irrelevant for the method in which way the soot load condition is determined. A method is preferred in which the soot load condition is determined as a function of the speed, the torque of the internal combustion engine, for example the diesel engine, and the exhaust gas back pressure, and the variable determined is compared with a characteristic map constructed from this data. The variable that represents a minimum load is shown in the characteristic diagram as a function of different operating states of the internal combustion engine. A determination of the soot loading of the particle filter according to this method can be carried out in any operating state of the diesel engine. Advantageously, the dynamic variables are only evaluated for determining the loading state if these have not changed within a specified time interval or have only changed within specified limits. In this method, the soot load is determined when the internal combustion engine is operated in a quasi-stationary manner within the specified limits. The necessary data for the construction of the characteristics map have also been determined in quasi-stationary states of the internal combustion engine.

If the “loading state OK” flag was set as part of the step of determining the loading state, the probable success of regeneration is determined in a second step as a function of the current operating state of the internal combustion engine. To ensure that soot is burned off sufficiently completely, the current operating state of the internal combustion engine is taken into account, specifically advantageously evaluated with regard to exhaust-gas-related characteristic values. According to a preferred embodiment, variables reflecting the operating state of the internal combustion engine are evaluated with regard to the oxygen content in the exhaust gas flow and the temperature of the exhaust gas flow. These two variables are preferably weighted in relation to one another, with the oxygen content in the exhaust gas flow being rated more highly than the temperature of the exhaust gas flow. Nevertheless, the temperature of the exhaust gas flow should not remain completely unconsidered. The "Regeneration Start" flag is set when suitable soot burn-off conditions (oxygen content, temperature) prevail based on the current operating status, represented for example by the speed and the torque depending on the soot load determined in the exhaust gas flow. The "Regeneration Start" flag is thus set when the current operating conditions of the diesel engine are suitable for sufficiently successful soot burn-off. In combination with the aforementioned characteristic values obtained from the exhaust gas mass flow or also independently thereof, characteristic values serving the same purpose can also be taken from the air mass flow supplied to the internal combustion engine. If the “Regeneration Start” flag is also set in addition to the “Load status OK” flag, the regeneration process can be triggered, for example by energizing a thermoelectric heating element assigned to the particulate filter.

A triggering of the regeneration process can be linked to the setting of one or more other flags, such as a flag that is set to "Regeneration Start" if, based on the operating profile of the internal combustion engine, a triggered regeneration process can be carried out completely with a sufficiently high probability. This additional flag is intended to ensure that a triggered regeneration process can also be carried out completely with regard to its duration and that the internal combustion engine will not be switched off with some probability within the period required for regeneration.

• 1: ein Kennfeld darstellend eine für das Auslösen einer Regeneration notwendige Mindestbeladung eines Partikelfilters in Abhängigkeit unterschiedlicher Betriebszustände eines Dieselmotors,
• 2: das Diagramm der 1 mit einem weiteren, die Maximalbeladung des Partikelfilters darstellenden Kennfeld und
• 3 : der zum Bestimmen des voraussichtlichen Regenerationserfolges in Abhängigkeit von dem aktuellen Betriebszustand des Dieselmotors betrachtete Ausschnitt des Motorkennfeldes mit beispielhaft darin eingetragenen relativen Beladungszustandsgrößen.

The invention is described below using an exemplary embodiment with reference to the accompanying figures. Show it:

• 1 : a map showing a minimum load of a particle filter required for triggering regeneration depending on different operating states of a diesel engine,
• 2 : the diagram of 1 with a further map showing the maximum load of the particle filter and
• 3 : the section of the engine map considered to determine the probable success of regeneration as a function of the current operating state of the diesel engine, with relative load state variables entered therein as examples.

To determine the triggering point in time for triggering regeneration of a particle filter connected to the exhaust system of a diesel engine, the soot loading condition of the particle filter is determined at time intervals during operation of the diesel engine. This variable “soot loading status” is used to determine the expediency and necessity of triggering a regeneration process to regenerate the particulate filter. In this exemplary embodiment, the soot loading state of the particle filter is determined using a load variable, the speed and the exhaust gas back pressure in the inflow-side section of the exhaust line in front of the particle filter. The torque or the exhaust gas temperature, for example, can be used as a load-dependent variable. In the following, the torque is used as a load-dependent variable. The determined values are then included in the evaluation if they have not changed within a specified time interval or have only changed within specified limits. This measure is intended to prevent the aforementioned variables from being evaluated in connection with a determination of the soot loading state when the diesel engine is operated too dynamically. Rather, provision is made for a measurement result to be evaluated when at least approximately stationary measurement conditions are given. If the measured values recorded in a predetermined time interval meet the requirements made for the changes, the torque, the exhaust gas back pressure and the speed are recorded or the values recorded continuously in this regard are included in the evaluation. evaluated the quantities determined are determined by comparing them with a map. The characteristic map shows the minimum charge level of the particle filter in different operating states. Such a map of a specific particulate filter connected to the exhaust system of a diesel engine is in 1 shown. The map is made up of the same variables that are used to determine the current soot load status of the particle filter. in the in 1 The map shown shows the torque (y-axis) and the speed of the diesel engine (x-axis) on the xy plane. The exhaust back pressure is plotted on the z-axis as a measure of the soot loading of the particle filter. The data required to set up the characteristics map have been determined during steady-state or quasi-steady-state operation of the diesel engine and are stored in a memory in the control unit for carrying out the method. The map varies with respect to its z-values under different operating conditions of the diesel engine.

The currently recorded operating variables (torque, speed, exhaust back pressure) are compared with the in 1 map shown. If the currently determined loading condition of the particle filter is on the map or above it, the particle filter is sufficiently loaded with soot to be able to successfully carry out a regeneration process based on the loading condition. A first flag is set on the system side, namely the “load status OK” flag.

In order to reduce erroneous determinations, it can be provided that the “loading status OK” flag is only set when two or more consecutive current loading status determinations have led to the same result.

The "Loading status OK" flag is deleted again when the loading status has reached a level at which soot burn-off should no longer be actively triggered. 2 shows a above the map of 1 with the minimum load a map with the maximum load of the particle filter.

However, the regeneration process is not triggered solely on the basis of the "load status OK" flag that has been set. The regeneration process is triggered depending on the result of the determination of the probable success of regeneration, namely depending on the current operating status of the diesel engine. This is to ensure that the soot burn-off carried out for the regeneration of the particle filter is carried out with sufficient success. The determined current operating state variables of the diesel engine - torque and speed - are also evaluated for the probable regeneration success if this would be triggered at the time of the determination, if the flag "loading state OK" is set. This evaluation is based on a map, in which a section of the engine map is considered. The map is determined by those operating state variables of the diesel engine that allow conclusions to be drawn about the success of the regeneration. In the exemplary embodiment described, the oxygen content in the exhaust gas flow and the temperature of the exhaust gas flow are used for this purpose, these two variables being weighted in relation to one another. These two parameters are weighted in favor of the oxygen content. 3 shows such a map. The characteristic values - oxygen content, temperature - are weighted in favor of the oxygen content. Isolines are plotted in the characteristic map, which represent a regeneration enable at a specific soot loading of the particulate filter. The regeneration success that is likely to occur parallel or approximately parallel to the isolines. This is best on the right-hand edge of the map - i.e. at higher speeds and medium load - and most unfavorable at low speeds and low load.

The additional “Regeneration Start” flag is set if, after the “Loading state OK” flag was previously set, the current engine speed and the torque are in such a relationship to one another that the determined value is to the right of the isoline reflecting the previously determined loading state. It is then assumed that the conditions necessary for the desired regeneration success prevail in the exhaust system.

This in 3 The map shown clarifies the further strategy pursued by this method. With increasing soot loading, the "Regeneration Start" flag is also set if only moderate regeneration success is to be expected. This is done against the background that soot burn-off is to be avoided if the particle filter has a high or excessively high loading state, in which soot burn-off could lead to overheating of the particle filter. The method will therefore be operated in such a way that the "Regeneration Start" flag is set as early as possible in relation to the loading status of the particle filter.

The variables included in the evaluation depend on the diesel engine and the particle filter used. Dependence on the particle filter does not only include its material dependency but also its size. In the method described by way of example, the flag “loading status OK” is set when the particle filter has reached a soot loading status of 75% in relation to the soot loading status permitted for carrying out a regeneration. This flag is deleted when the load exceeds 100%.

If the “Regeneration Start” flag is set, the regeneration process of the particulate filter can be triggered by supplying thermal energy, which in the exemplary embodiment described takes place by means of a thermoelectric heating element. Equally, such a regeneration process can also be triggered, for example, by injecting fuel into the exhaust line if an oxidation catalytic converter is connected upstream of the particle filter.

• - Auswerten der nach einem Motorstopp zurückliegenden Motorbetriebszeit in Bezug auf Zeitpunkte oder -intervalle, in denen der Prozess hätte ausgelöst werden können und/oder in denen der Prozess nicht hätte ausgelöst werden sollen,
• - Speichern des Auswerteergebnisses,
• - Addieren des Auswerteergebnisses des nächsten Motorbetriebzeitintervalls zu dem gespeicherten Auswerteergebnis und Speichern desselben als kumuliertes Auswerteergebnis, wobei unter Verwendung des kumulierten Auswerteergebnisses als Summand dieser Schritt für alle weiteren Motorbetriebszeitintervallauswertungen durchgeführt wird und
• - Setzen eines Flag „Prozessstart“ oder „Prozesssperre“ während einer laufenden Motorbetriebszeit in Abhängigkeit von dem aktuellen Zeitpunkt innerhalb der laufenden Betriebszeit und der diesem Zeitpunkt entsprechenden Information aus dem kumulierten Auswerteergebnis.

In a further development of the method, it is provided that after setting the "Regeneration Start" flag, which requires that the "Loading State OK" flag has been set beforehand, the actual start of regeneration depends on one or more other flags indicating the start of the release the regeneration process. According to a preferred embodiment, the regeneration does not start until after setting the “Regeneration Start” flag due to the operating profile of the internal combustion engine with a sufficiently high probability that a triggered regeneration process can also be completed in terms of its timing. Such a driving profile can be created in a particularly simple manner with the following steps:

• - Evaluation of the engine operating time after an engine stop in relation to points in time or intervals in which the process could have been triggered and/or in which the process should not have been triggered,
• - save the evaluation result,
• - Adding the evaluation result of the next engine operating time interval to the stored evaluation result and storing the same as a cumulative evaluation result, this step being carried out for all further engine operating time interval evaluations using the cumulative evaluation result as a summand and
• - Setting a "process start" or "process lock" flag during an ongoing engine operating time depending on the current point in time within the current operating time and the information from the cumulative evaluation result corresponding to this point in time.

In this method, the engine operating times after an engine stop (engine off) are evaluated retrospectively to determine at which points in time the desired process could have been triggered, taking into account its process duration, and at which times it could not. By summing up the results assigned to the individual points in time or periods of time over the past engine operating times, a driving profile is obtained in which those points in time or periods of time are defined depending on the driving behavior of the driver and the required process duration in which the process would have started and was complete can be carried out. In principle, the entire engine operating time preceding an engine stop is considered in the evaluation. As a rule, an evaluation is carried out in such a way that, starting from the respective engine stop, those points in time are evaluated negatively at which a start of regeneration and a sequence of the process would no longer have been possible. The remaining points in time or time segments of the preceding engine operating time receive a positive value. If the process had been started in the times with a positive value, the process would have been run through completely. By adding the evaluation results of the individual engine operating times that take place one after the other, an evaluation result is obtained that is cumulated over the individual engine operating times. Based on the values of the positive and negative counters assigned to each time segment, this represents a value for the probability that the process triggered in this time segment can be carried out completely or not. This evaluation is typically based on a specified threshold value, which must be present so that the flag can be set to "process start". Otherwise, this flag assumes the value "process lock". The threshold value is usually defined by the difference between the positive counter and the negative counter at a point in time or within a time interval. In this way, driving patterns can be generated and evaluated in a simple manner.

In an extension of this method step, an evaluation is carried out as a function of the exhaust gas temperature. For example, if the exhaust gas temperature is relatively low, a longer time is required for burning off the soot than with a higher exhaust gas temperature. An evaluation at a lower exhaust gas temperature of the engine operating time after an engine stop is carried out with the proviso that a longer period of time reaching back from the engine stop will be assessed negatively, whereas at a higher exhaust gas temperature the past starting from the engine stop, time to be evaluated negatively or observed time intervals is lower.

Claims (10)

Method for determining the triggering point in time of a regeneration process for regenerating a particle filter connected to the exhaust system of an internal combustion engine, with the following steps: - Determination of the current soot loading status of the particle filter, - Comparing the determined loading condition with a map, built up from data that represent the soot loading necessary for a regeneration process with sufficient regeneration success in different operating states of the internal combustion engine, - Setting a flag "loading status OK" if the currently determined soot load is greater than or equal to the minimum soot load required by the map and - if the flag "loading condition OK" is set, determining the expected regeneration success if the regeneration process would be triggered at the time of this determination depending on the current operating state of the internal combustion engine, and setting a flag "regeneration start" if the expected regeneration success is sufficient . procedure after claim 1 , characterized in that the soot loading is detected using one or more load-dependent variables of the internal combustion engine. procedure after claim 2 , characterized in that a soot loading detection is only carried out if the at least one load-dependent variable has not changed within a predetermined time interval or has only changed within predefined limits. procedure after claim 2 or 3 , characterized in that the torque and/or the exhaust gas temperature, the exhaust gas back pressure prevailing on the inflow side in front of the particle filter are evaluated together with the speed of the internal combustion engine as a load-dependent variable. Procedure according to one of Claims 1 until 4 , characterized in that the probable regeneration success is determined on the basis of characteristic values obtained from the air mass flow supplied to the internal combustion engine and/or the exhaust gas mass flow. procedure after claim 5 , characterized in that the acid content in the exhaust gas flow and the temperature of the exhaust gas flow are used as characteristic values. procedure after claim 6 , characterized in that the characteristic values are weighted relative to one another. Procedure according to one of Claims 1 until 7 , characterized in that the flag "load status OK" is deleted when the currently determined soot load is greater than a predetermined threshold. Procedure according to one of Claims 1 until 8th , characterized in that after setting the flag "Regeneration Start" triggering the regeneration process is dependent on the state of one or more other flags. procedure after claim 9 , characterized in that the further flag is set to "process start" when, based on the operating profile of the internal combustion engine, a triggered regeneration process can be carried out completely with a sufficiently high probability.

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