Method and Device for Diagnosing a Coated Particulate Filter Arranged in an Exhaust-Gas Duct of a Motor Vehicle

Abstract

Various embodiments include a method for regenerating a coated particulate filter arranged in an exhaust-gas duct of a motor vehicle. The method may include: detecting a need for particulate filter regeneration; determining a first diagnosis value before initiating particulate filter regeneration; after determining the first diagnosis value, carrying out particulate filter regeneration; determining a second diagnosis value after particulate filter regeneration; determining a difference between the first determined diagnosis value and the second determined diagnosis value; comparing the determined difference with a threshold value; and identifying a particulate filter defect if the determined difference exceeds the threshold value.

Claims

1. A method for regenerating a coated particulate filter arranged in an exhaust-gas duct of a motor vehicle, the method comprising: detecting a need for particulate filter regeneration; determining a first diagnosis value before initiating particulate filter regeneration; after determining the first diagnosis value, carrying out particulate filter regeneration; determining a second diagnosis value after particulate filter regeneration; determining a difference between the first determined diagnosis value and the second determined diagnosis value; comparing the determined difference with a threshold value; and identifying a particulate filter defect if the determined difference exceeds the threshold value.

2. The method as claimed in claim 1, wherein the threshold value comprises a specified constant value.

3. The method as claimed in claim 1, wherein the particulate filter defect occurred during regeneration.

4. The method as claimed in claim 3, wherein the particulate filter defect comprises a crack in the particulate filter.

5. The method as claimed in claim 1, further comprising using the determined difference for correcting a particulate filter regeneration strategy for subsequent particulate filter regeneration.

6. The method as claimed in claim 5, wherein the corrected strategy includes lowering the temperature for the subsequent particulate filter regeneration.

7. The method as claimed in claim 5, wherein the corrected strategy includes lowering a threshold value for the particulate filter loading at which particulate filter regeneration is considered necessary.

8. The method as claimed in claim 1, wherein determining the diagnosis values includes using output signals from two sensors, wherein the first sensor is arranged upstream of the particulate filter and the second sensor is arranged downstream of the particulate filter.

9. The method as claimed in claim 8, wherein at least one of the two sensors comprises a NOx sensor.

10. The method as claimed in claim 8, wherein the diagnosis values comprises gradient values.

11. The method as claimed in claim 10, wherein determining a gradient value includes evaluating an output signal of the second sensor after a jump occurs in an ammonia value measured upstream of the particulate filter.

12. The method as claimed in claim 1, wherein the method is performed by a control unit.

13. The method as claimed in claim 12, further comprising putting out control signals required for diagnosis on the basis of a stored work program and stored data.

14. A device for diagnosing a coated particulate filter arranged in an exhaust-gas duct of a motor vehicle, the device comprising a control unit programmed to: detect a need for particulate filter regeneration; determine a first diagnosis value before initiating particulate filter regeneration; after determining the first diagnosis value, carrying out particulate filter regeneration; determine a second diagnosis value after particulate filter regeneration; determine a difference between the first determined diagnosis value and the second determined diagnosis value; compare the determined difference with a threshold value; and identify a particulate filter defect if the determined difference exceeds the threshold value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Further properties of the teachings herein are addressed in the following explanation of FIG. 1. The figure shows an exemplary embodiment of a device for diagnosing a coated particulate filter arranged in an exhaust-gas duct of a motor vehicle.

DETAILED DESCRIPTION

[0022] The teachings of the present disclosure may include a method for diagnosing a coated particulate filter arranged in an exhaust-gas duct of a motor vehicle, the following steps are carried out: recognizing the need for particulate filter regeneration, determining a first diagnosis value after recognizing the need for particulate filter regeneration and before initiating the particulate filter regeneration, after determining the first diagnosis value, carrying out the particulate filter regeneration, determining a second diagnosis value after particulate filter regeneration has been carried out, determining a difference between the two determined diagnosis values, comparing the determined difference with a threshold value, and detecting a particulate filter defect if the determined difference exceeds the threshold value.

[0023] The teachings of the present disclosure allow a detected particulate filter defect to be assigned to a cause of the particulate filter defect. In particular, the methods allow the detected particulate filter defect to be assigned to particulate filter regeneration that has been carried out. For instance, if an excessive temperature occurs during particulate filter regeneration, it may happen that the material of the particulate filter partially melts and cracks occur in the material, as a result of which the filtering efficiency is reduced in subsequent operation of the particulate filter and for example falls below specified limit values for on-board diagnosis. A use of the methods described herein may involve such particulate filter defects being detected and assigned to the particulate filter regeneration process.

[0024] In some embodiments, the difference between the two diagnosis values that indicates the particulate filter defect can be used for correcting the particulate filter regeneration strategy for subsequent particulate filter regeneration. For example, the temperature for subsequent particulate filter regeneration may be lowered. In some embodiments, a threshold for the particulate filter loading at which particulate filter regeneration is considered necessary may be lowered.

[0025] FIG. 1 shows an example embodiment wherein a coated diesel particulate filter 2 is arranged in the exhaust-gas duct 1 of a motor vehicle. This coated diesel particulate filter is intended to filter out pollutant particles from the exhaust gas emitted by the engine of the motor vehicle, which flows through the coated diesel particulate filter 2 in the exhaust-gas flow direction 6, so that the exhaust gas emitted by the particulate filter 2 has a reduced pollutant content.

[0026] In the course of the operating life of the motor vehicle, filtered out pollutant particles, in particular soot particles, are deposited on the inner walls of the particulate filter, so that the particulate filter loading of the particulate filter becomes increasingly greater. To avoid clogging of the particulate filter caused by this increasing particulate filter load, particulate filter regeneration is required. For this particulate filter regeneration, the temperature of the exhaust gas flowing through the particulate filter is increased to about 600° C. At this high temperature, the pollutant particles deposited on the inner walls of the particulate filter burn, so that the walls of the particulate filter are freed from pollutant particles.

[0027] To recognize the need for particulate filter regeneration, the output signals 3a of a sensor 3 and the output signals 4a of a further sensor 4 are fed to a control unit 5. This evaluates the output signals of the sensors on the basis of a stored work program and stored data, recognizes the need to carry out particulate filter regeneration and provides control signals 5a that are required for carrying out the method according to the invention.

[0028] The stored data include, inter alia, an empirically determined threshold value for the particulate filter loading, which, if exceeded, causes the control unit 5 to recognize the need for particulate filter regeneration. The particulate filter loading of the particulate filter 2 is determined using the output signals of the sensors 3 and 4, which in the exemplary embodiment shown are NOx sensors. These NOx sensors are used for example to measure the NOx content of the exhaust gas fed to the particulate filter and the NOx content of the exhaust gas discharged from the particulate filter, and the need for particulate filter regeneration is recognized from the measured values by the control unit 5 using a difference calculation.

[0029] After the need for a particulate filter regeneration has been recognized and before this particulate filter regeneration is initiated, a first diagnosis value is determined. After this first diagnosis value has been determined, the particulate filter regeneration is carried out, in which the exhaust gas flowing through the particulate filter is brought to a high temperature, of for example 600° C., in order to burn off the pollutant particles deposited on the walls of the particulate filter.

[0030] After the particulate filter regeneration has been carried out, a second diagnosis value is determined. The difference between the two diagnosis values is then determined. The difference determined is then compared with a specified threshold value. This threshold value was empirically determined in advance and stored together with other data in a memory to which the control unit 5 has access. This threshold value is a specified constant value.

[0031] If the determined difference exceeds the specified threshold value, then it is recognized that there is a particulate filter defect. This particulate filter defect is a particulate filter defect that occurred during the particulate filter regeneration, in particular a crack in the housing of the particulate filter caused by an excessive temperature during the particulate filter regeneration. This particulate filter defect can be reliably identified and assigned to the particulate filter regeneration by means of the method described. Without carrying out the methods described herein, the cause of a great reduction in the efficiency of the particulate filter determined as part of an on-board diagnosis of the particulate filter could only be identified by a complex complete check of the entire exhaust system of the motor vehicle.

[0032] If the presence of a particulate filter defect that can be attributed to an excessive temperature during the particulate filter regeneration is detected on the basis of the determined difference, then the determined difference can be used for correcting the previously used particulate filter regeneration strategy. For example, the temperature used for subsequent particulate filter regeneration may be reduced. In some embodiments, the threshold value for the particulate filter loading, which when exceeded is used to recognize the need for particulate filter regeneration, may be reduced. Both of the aforementioned measures lead to the avoidance of an excessive temperature occurring in future particulate filter regenerations.

[0033] The aforementioned diagnosis values are also values that are determined using the output signals of the sensors 3 and 4. The diagnosis values are preferably gradient values. For example, a gradient value may be determined by evaluating the output signal of an NOx sensor arranged downstream of the particulate filter after the occurrence of a jump in an ammonia value measured upstream of the particulate filter.

[0034] It can be checked whether the difference in the diagnosis values, for example gradients of the NOx sensor output signal downstream of the particulate filter after an NH3 jump upstream of the particulate filter after the particulate filter regeneration and before the particulate filter regeneration, exceeds a specified threshold value, for example 20 ppm within 4 seconds, or whether this is not the case. If this is the case, then the presence of a filter crack is detected. This measure makes diagnosis of the particulate filter more robust and improves fault assignment.