DE102011000153A1 - Method for the diagnosis of exhaust gas aftertreatment - Google Patents

Abstract

Method for on-board diagnosis of an exhaust gas aftertreatment device 3 for an internal combustion engine 1, the exhaust gas aftertreatment device 3 having means for converting an exhaust gas component and sensor means 4 arranged downstream of the exhaust gas aftertreatment device 3, the exhaust gas component being detected by means of the sensor means 4 and based on the quantity of the detected exhaust gas component on the quality of the means for converting the exhaust gas component, wherein a signal from the sensor means 4 is forwarded to a system for on-board diagnosis.

Description

The invention relates to a method for on-board diagnosis of an exhaust aftertreatment device for an internal combustion engine, wherein the exhaust aftertreatment device comprises means for converting an exhaust gas component and downstream of the exhaust gas aftertreatment device sensor means are provided.

At present, the state of the art is that a soot particle filter stores soot in the so-called adsorption mode. Particulate filters are also referred to as diesel particulate filters (DPF). If the particulate filter can not absorb any more soot, it must be burned free by a regeneration. For this purpose, there are various measures, one of which is, for example, to heat the exhaust by appropriate measures in addition, so that the soot burns in the filter with oxygen contained in the lean exhaust gas. This soot combustion is usually incomplete, d. H. there are products of incomplete combustion, such as carbon monoxide. Furthermore, it is state of the art that the particulate filter is catalytically coated, whereby the carbon monoxide oxidizes to a very large extent to carbon dioxide, so that the carbon monoxide emission is very low during a regeneration phase of the particulate filter behind the filter. Problems now arise from the fact that this catalytic layer ages within the particulate filter, so that it is inactive and no longer ensures a conversion of the carbon monoxide resulting from the regeneration. This aging process of the catalytic coating and the concomitant increased carbon monoxide emission during the regeneration of the particulate filter is in practice a not immediately recognizable problem.

The DE 10 2007 009 873 A1 discloses a method for detecting the occurrence of cross sensitivities of an exhaust gas sensor. The method is used in diesel engines, which have in their exhaust line an oxidation catalyst, a particulate filter and a particle sensor. It is intended to close by operation-related or deliberately made variations in the concentration of a second exhaust gas component in front of the catalyst on a defect of the catalyst with respect to its conversion capability for this second exhaust gas component. It should be made possible to conclude the presence of the unconverted exhaust gas components in the region of the exhaust gas sensor and, if necessary, to carry out a corresponding correction of the sensor signal.

On this basis, it is an object of the present invention to diagnose the catalytic coating of particle filters in their effectiveness.

The object is achieved by a method for on-board diagnosis of an exhaust aftertreatment device for an internal combustion engine, wherein the exhaust aftertreatment device comprises means for converting an exhaust gas component and the exhaust aftertreatment device downstream sensor means are provided, wherein the exhaust gas component is detected by the sensor means and that on the basis of the quantity detected exhaust gas component is closed on the quality of the means for converting the exhaust gas component, wherein a signal of the sensor means is forwarded to an on-board diagnosis system. This advantageously provides a method in which the presence or absence of the exhaust gas component in question can be detected directly. Since, with functional exhaust aftertreatment device and correspondingly effective means for converting the exhaust gas component in question, this, if any, is present only in extremely low concentrations, it can be concluded from this that the means for converting this exhaust gas component work properly. On the other hand, if a significantly increased concentration of the exhaust gas component in question is measured by the sensor means, this is an indication that the means for converting the exhaust gas component are defective or defective. In this case, in particular, a comparison with a reference value, for example a functional exhaust aftertreatment device which is used as a reference, may be provided. If the value is greater than the reference value, it is possible to detect defective means for converting the exhaust gas component.

In a concrete embodiment it is provided that the exhaust aftertreatment device has at least one soot particle filter with a catalytic coating for the conversion of the exhaust gas component, wherein a regeneration of the exhaust gas aftertreatment device is carried out during which the exhaust gas component is formed. The advantage here is that the filter function and the conversion function is summarized in a component which is available in various configurations on the market. It is also favorable that the soot particle filter, which also contains the catalytic coating for converting the exhaust gas component, converts the exhaust gas component released during the regeneration phase.

As individual method steps can be provided that the exhaust gas component is detected over a period of time, which extends from a first time during the start phase of regeneration at least until a second time during regeneration, preferably at the end of the regeneration. It can be provided that the first time with the initiation of Regeneration coincides or is later than the initiation of regeneration. If the first time coincides with the initiation of regeneration, this has the advantage of a simple start condition. In general, the initiation of the regeneration by internal engine measures such as throttling, later injection timing, additional and / or later injection is performed. By this means, unburned fuel quantities intentionally enter the oxidation catalytic converter. Due to the forced thereby reactions in the oxidation catalyst in this the exhaust gas temperature rises to about 620 ° C to 630 ° C, but only with a certain time delay to the beginning of the internal engine measures. During this period, a breakthrough or slip of the non-converted by the oxidation catalyst exhaust gas component can take place. Only after the oxidation catalyst has heated to an exhaust gas temperature of about 620 ° C to 630 ° C, this exhaust gas component is converted. This can be referred to as the end of the starting phase. The heated exhaust then initiates the burn-off process of the soot in the particulate filter. In order not to detect this proportion of the unconverted exhaust gas component, the first time of the measurement by the sensor means arranged downstream of the particle filter may be later in time to initiate the regeneration. As a release condition for the timing of this time relative to the initiation of regeneration, for example, the temperature of the exhaust gas can be used for oxidation catalyst.

The fact that the first time is set before the beginning of the regeneration ensures that the exhaust gas component in question, if it has already been emitted by the internal combustion engine and has not been converted by an upstream oxidation catalyst, can already be detected in its concentration. This can be used later as a correction factor.

Specifically, it is provided that the exhaust gas component is carbon monoxide whose content is detected by means of a carbon monoxide sensor. As stated in the introduction, this is a product of the mostly incomplete soot combustion during the regeneration phase. When the catalytic filter of the particulate filter is functioning, carbon monoxide is oxidized to carbon dioxide. The carbon monoxide sensor can directly detect how high the concentration of the exhaust gas component is carbon monoxide during a regeneration phase of the particulate filter, that is, how much carbon monoxide has not been effectively converted to carbon dioxide.

It is preferably provided that when a threshold value of the quantity of the exhaust gas component is exceeded, a signal of the sensor means is forwarded to an on-board diagnostic (OBD) system. The signal of the sensor means, which are preferably designed as a carbon monoxide sensor, preferably represents the quantity, the concentration or the measure of the unconverted exhaust gas component in the entire exhaust gas flow after filter. As a result, it is ensured in an advantageous manner that in the operation then control light - malfunction indicator light MIL - can be activated and the causative malfunction can be logged.

Furthermore, the object is achieved by an apparatus for on-board diagnosis of an exhaust gas aftertreatment device for an internal combustion engine, wherein the exhaust aftertreatment device comprises means for converting an exhaust gas component and wherein sensor means are provided and the sensor means downstream of the exhaust aftertreatment device to a not complete conversion of the exhaust gas component Detecting the same, and wherein the sensor means are connected to an on-board diagnostic system.

It is preferably provided that the exhaust gas aftertreatment device has at least one soot particle filter with a catalytic coating for the conversion of the exhaust gas component. The advantage here is that the filter function and the conversion function is combined in one component.

In a preferred embodiment, it is provided that the sensor means comprise a carbon monoxide sensor. By the carbon monoxide sensor can be detected directly, how high the concentration of the exhaust gas component is carbon monoxide during a regeneration phase of the particulate filter, that is, how much carbon monoxide has not been effectively converted into carbon dioxide.

Alternatively, it can be provided that the sensor means for measuring carbon monoxide are adapted from a lambda sensor, a NOx sensor or an electrochemically operating sensor. This results in the advantage that these sensors are available in a variety of ways both on the market, and have already been implemented in an environment of an exhaust system.

As a further alternative it can be provided that the sensor means comprise a catalytic coating and a temperature sensor. In this embodiment, the detection of the exhaust gas component carbon monoxide, if this is not converted due to a defective catalytic coating within the particulate filter, characterized in that the carbon monoxide, which leaves the particle filter unconverted, then in the downstream catalytic coating of the sensor means is converted, thereby generating a temperature rise, which is detected by the temperature sensor.

For each of the embodiments, it can be provided that the sensor means are connected to a system for on-board diagnostics (OBD). As a result, it is ensured in an advantageous manner that in the operation then control light - malfunction indicator light MIL - can be activated and the causative malfunction can be logged.

In the following the method according to the invention and the device for diagnosing the ability to convert a soot particle filter by means of carbon monoxide measurement will be described with reference to figures. Herein show:

1 a schematic representation of an exhaust system;

2a Temperature profile of a soot particle filter with a phase of regeneration;

2 B Carbon monoxide emissions of a catalytic particulate particulate filter;

2c Carbon monoxide emissions of a soot particle filter without catalytic coating.

1 shows a schematic representation of a conventional exhaust system 6 with an internal combustion engine 1 , which operates on the diesel principle, for example, and downstream of the flow direction A, an oxidation catalyst 2 , a soot particle filter 3 and a carbon monoxide sensor 4 which is connected to a control unit 5 is connected to monitor the sensor signals. The internal combustion engine may also be a lean-burn gasoline engine. In unspecified but generally known manner, the controller is at least part of an on-board diagnostic (OBD) system. The soot particle filter 3 is provided with a catalytic coating in its interior, which due to the basic representation not closer in 1 is shown.

Furthermore, a possibility for temperature measurement after the oxidation catalyst 2 be provided. This allows a diagnosis of the oxidation catalyst 2 by evaluating a temperature profile behind the catalyst after emissions of unburned hydrocarbons or carbon monoxide have been fed before the catalyst.

In the 2 For example, over time different profiles of the temperature of a particulate filter and the emissions of carbon monoxide by filter are shown. In detail shows 2a a temperature profile of a soot particle filter over a period of time within which regeneration is initiated by conventional measures. One possible measure may be to additionally heat the exhaust gas by means of corresponding internal engine operating states, so that the soot in the filter burns with oxygen contained in the lean exhaust gas. This phase of regeneration R is in the course of the temperature 2a to recognize by the increase in temperature.

2 B Figure 12 shows the carbon monoxide emissions of a catalytic particulate particulate filter. Immediately after the beginning of the regeneration, the concentration of carbon monoxide K briefly increases until the catalytic coating has heated and the carbon monoxide oxidizes to carbon dioxide. In 2 B is still the integral I of carbon monoxide emissions drawn.

For comparison are in 2c the carbon monoxide emissions of a non-catalytically coated soot particle filter shown. In such a regeneration R is a significant increase in the concentration of carbon monoxide K recorded. Integral I indicates that a significantly larger total amount of carbon monoxide is compared with a catalytic coated particulate filter ( 2 B ) was emitted.

The basic idea of the method and the device according to the invention is based, on the one hand, on the fact that the carbon monoxide concentration in the exhaust stream can be measured by means of a carbon monoxide sensor and, on the other hand, that a catalytically coated soot particle filter whose coating has become inactive as a result of aging or other harmful influencing factors is, at least in principle in the 2c shown course of the concentration of carbon monoxide during regeneration R will have. In this case, therefore, an increased concentration of carbon monoxide is measured by the carbon monoxide sensor during regeneration. If now can continue to be ruled out that by other malfunctions in the exhaust system 6 in front of soot particle filter 3 an increased concentration of carbon monoxide is formed, it can be diagnosed that the catalytic coating of the particulate filter is defective, so that they can no longer convert the carbon monoxide formed during the regeneration R to carbon dioxide, but the carbon monoxide is emitted unconverted.

• – Einleiten der Regeneration durch herkömmliche Maßnahmen,
• – Messen der Kohlenmonoxidemissionen,
• – Integrieren der Kohlenmonoxidemissionen, vorzugsweise bis zum Ende der Regeneration,
• – Vergleich des Integrals der Kohlenmonoxidemissionen mit einem Referenzwert eines Referenzfilters, der vorzugsweise ein bezüglich der Konvertierung voll funktionstüchtiger Filter ist, beispielsweise mit einer Konvertierungsrate von 99%,
• – Einleitung von Maßnahmen in Abgängigkeit des Wertevergleich, wobei auf eine fehlerhafte Beschichtung erkannt wird, wenn der Messwert größer als der Referenzwert ist.

A possible offense in carrying out the method according to the invention may consist in the steps:

• Initiation of regeneration by conventional measures,
• - measuring carbon monoxide emissions,
• Integrating carbon monoxide emissions, preferably until the end of regeneration,
• Comparison of the integral of the carbon monoxide emissions with a reference value of a reference filter, which is preferably a converter fully functional with regard to the conversion, for example with a conversion rate of 99%,
• - Initiation of measures in the course of the comparison of values, whereby a faulty coating is detected if the measured value is greater than the reference value.

As a measure to be initiated, the illumination of a warning light (malfunction indicator lamp MIL) can be made initially for information. As further measures emergency operation of the internal combustion engine are conceivable.

By the method described, it is possible to detect an aging of the catalytic coating of the particulate filter. In turn, once the catalytic coating has aged, it can be concluded that the conversion of carbon monoxide (CO) and unburned hydrocarbons (HC) at cold temperatures, such as after a cold engine start, will also be reduced. Because of this relationship, it is indirectly possible by the method according to the invention also the CO and HC conversion ability in normal operation, including a cold start counts, to diagnose.

LIST OF REFERENCE NUMBERS

1

Internal combustion engine

2

oxidation catalyst

3

Rußpartikelfilter

4

Carbon monoxide sensor

5

control unit

6

exhaust gas line

R

regeneration

K

concentration

I

integral

A

flow direction

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely 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.

Cited patent literature

• DE 102007009873 A1 [0003]

Claims (11)

Method for on-board diagnosis of an exhaust aftertreatment device ( 3 ) for an internal combustion engine ( 1 ), wherein the exhaust aftertreatment device ( 3 ) Comprises means for converting an exhaust gas component and the exhaust aftertreatment device ( 3 ) downstream sensor means ( 4 ) are provided, characterized in that the exhaust gas component by means of the sensor means ( 4 ) and that the quality of the means for converting the exhaust gas component is determined on the basis of the quantity of the detected exhaust gas component, wherein a signal of the sensor means ( 4 ) is forwarded to a system for on-board diagnostics. A method according to claim 1, characterized in that the exhaust gas aftertreatment device at least one soot particle filter ( 3 ) having a catalytic coating for the conversion of the exhaust gas component, wherein a regeneration of the particulate filter ( 3 ) is carried out while the exhaust component is formed. Method according to one of claims 1 or 2, characterized in that the exhaust gas component is detected over a period of time which extends from a first time during the start phase of the regeneration at least until a second time during the regeneration, preferably at the end of the regeneration. A method according to claim 3, characterized in that the first time coincides with the initiation of the regeneration or is later in time to initiate the regeneration. Method according to one of claims 1 to 4, characterized in that it is the carbon monoxide in the exhaust gas component, the content of which by means of a carbon monoxide sensor ( 4 ) is detected. Method according to one of claims 1 to 5, characterized in that when exceeding a threshold value of the quantity of the exhaust gas component, a signal of the sensor means ( 4 ) is forwarded to the system for on-board diagnostics. Device for on-board diagnosis of an exhaust aftertreatment device ( 3 ) for an internal combustion engine ( 1 ), wherein the exhaust aftertreatment device ( 3 ) Comprises means for converting an exhaust gas component and wherein sensor means ( 4 ), characterized in that the sensor means ( 4 ) of the exhaust aftertreatment device ( 3 ) in order to detect a non-complete conversion of the exhaust gas component by detecting the same, and that the sensor means ( 4 ) are connected to a system for on-board diagnostics. Apparatus according to claim 7, characterized in that the exhaust gas aftertreatment device at least one soot particle filter ( 3 ) having a catalytic coating for the conversion of the exhaust gas component. Device according to one of claims 7 or 8, characterized in that the sensor means ( 4 ) comprise a carbon monoxide sensor. Device according to one of claims 7 to 9, characterized in that the sensor means ( 4 ) are adapted for measuring carbon monoxide from a lambda sensor, a NOx sensor or an electrochemical sensor. Device according to one of claims 7 to 10, characterized in that the sensor means ( 4 ) comprise a catalytic coating and a temperature sensor.

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