METHOD AND EXHAUST SYSTEM FOR CHECKING A LOADING STATE OF A PARTICLE FILTER

Abstract

A method for checking a load condition of a particulate filter in an exhaust line of an internal combustion engine, wherein the exhaust line comprises at least the particulate filter, a first lambda sensor that is arranged upstream from the particulate filter, and a second lambda sensor that is arranged downstream from the particulate filter, includes at least the following steps: introducing an exhaust gas with an excess of oxygen into the exhaust line upstream from the first lambda sensor, there being a temperature of at least 500 C. in the particulate filter; detecting the excess of oxygen by the first lambda sensor at a first time; detecting the excess of oxygen by the second lambda sensor at a second time; and determining a load condition of the particulate filter from a time difference between the first time and the second time. The invention further relates to an exhaust system of a motor vehicle.

Claims

1. A method for checking a load condition of a particulate filter in an exhaust line of an internal combustion engine, wherein the exhaust line comprises at least the particulate filter, a first lambda sensor that is arranged upstream from the particulate filter, and a second lambda sensor that is arranged downstream from the particulate filter, the method comprising at least the following steps: a) introducing an exhaust gas with an excess of oxygen into the exhaust line upstream from the first lambda sensor, there being a temperature of at least 500 C. in the particulate filter; b) detecting the excess of oxygen by the first lambda sensor at a first time; c) detecting the excess of oxygen by the second lambda sensor at a second time; and d) determining a load condition of the particulate filter from a time difference between the first time and the second time.

2. The method as set forth in claim 1, wherein, at least during the execution of steps a), b), and c), the operation of the internal combustion engine is controlled by a natural frequency control of the lambda sensors through switching between operation with an excess of oxygen and operation with oxygen deficiency based on the identification of the changing composition of the exhaust gas by the second lambda sensor.

3. The method as set forth in claim 2, wherein the oxygen content in the exhaust gas during natural frequency control is set to a lambda value of from 0.960 to 0.985 for a rich mixture and to a lambda value of from 1.005 to 1.020 for a lean mixture.

4. The method as set forth in claim 3, wherein a difference between the maximum value and the minimum value of the respective lambda values is at least 0.02.

5. The method as set forth in claim 1, wherein at least an oxygen storage capacity of the particulate filter and a transit time of the exhaust gas from the first lambda sensor to the second lambda sensor are taken into account in step d).

6. The method as set forth in claim 1, wherein a first lambda sensor of a broadband lambda sensor type is used in step b), and a second lambda sensor of a two-point lambda sensor type is preferably used in step c).

7. An exhaust system of an internal combustion engine of a motor vehicle, comprising at least: one exhaust line, one particulate filter arranged in the exhaust line, one first lambda sensor arranged upstream from the particulate filter, one second lambda sensor arranged downstream from the particulate filter, and a control unit for detecting measurement signals of the first lambda sensor and of the second lambda sensor, the control unit (15) being configured to detect and evaluate a time difference between a first measurement signal of the first lambda sensor and a second measurement signal of the second lambda sensor.

8. The exhaust system as set forth in claim 7, wherein the first lambda sensor is a broadband lambda sensor and the second lambda sensor is a two-point lambda sensor.

9. The exhaust system as set forth in claim 7, wherein the particulate filter has no catalytically active coating.

10. The exhaust system as set forth in claim 7, wherein the particulate filter is arranged at a distance of no more than 80 centimeters from a combustion chamber of the internal combustion engine along a flow line through the exhaust line.

Description

[0044] The invention and the technical environment will be explained in greater detail with reference to the figures. It should be noted that the invention is not intended to be limited by the embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the features explained in the figures and to combine them with other components and insights from the present description and/or figures. In particular, it should be pointed out that the figures and, in particular, the illustrated proportions are only schematic. Same reference symbols designate same objects, so that explanations of other figures can be consulted where necessary. In the drawing:

[0045] FIG. 1 shows a motor vehicle;

[0046] FIG. 2 shows a lambda value/time diagram; and

[0047] FIG. 3 shows the procedure of the method in a lambda value/time diagram.

[0048] FIG. 1 shows a motor vehicle 14 is that comprises an internal combustion engine 3 with an exhaust system 13, the exhaust system 13 having at least one exhaust line 2, one particulate filter 1 arranged in the exhaust line 13, one first lambda sensor 4 arranged upstream from the particulate filter 1 (in the exhaust line 2) and one second lambda sensor 5 arranged downstream from the particulate filter 1 (in the exhaust line 2), as well as a control unit 15 for detecting measurement signals 16 of the first lambda sensor 4 and of the second lambda sensor 5. A time difference 9 between a first measurement signal 16 of the first lambda sensor 4 and a second measurement signal 17 of the second lambda sensor 5 can be detected and evaluated by a control unit 15. For instance, an excess of oxygen of an exhaust gas 6 that is introduced into the exhaust line 2 can be detected by the first lambda sensor 4 at a first time 7 and by the second lambda sensor 5 at a second time 8.

[0049] The particulate filter 1 (or its upstream end side) is arranged at a distance 10 along an (idealized) flow line 11 through the exhaust line 2 from (an outlet of) a combustion chamber 12 of the internal combustion engine 3. The flow line 11 extends along a center line of the exhaust gas line 2 (and thus runs through the area centers of the cross sections of the exhaust gas line 2).

[0050] FIG. 2 shows a lambda value/time diagram. The lambda value 18 is plotted on the vertical axis, with the lambda value of 1.00 being clarified by the horizontal dotted line. Superstoichiometric lambda values 20 lie above this line, and substoichiometric lambda values 21 lie below this line. The time 19 is plotted on the horizontal axis.

[0051] The different controls for the switching of the operation of the internal combustion engine 3 are illustrated here. The dashed line represents the progression of the second measurement signals 17 of the second lambda sensor 5. During the execution of steps a), b), and c), the operation of the internal combustion engine 3 is controlled by a natural frequency control 23 of the lambda sensors 4, 5 through switching between operation with an excess of oxygen (superstoichiometric lambda value 20) and operation with oxygen deficiency (substoichiometric lambda value 21) based on the identification of the changing composition of the exhaust gas 6 by the second lambda sensor 5.

[0052] During natural frequency control 23, the switching of the operation of the internal combustion engine 3 is specified by the lambda sensors 4, 5. In contrast, in the case of a so-called balanced lambda control 22, which is represented here by the solid line, the switching takes place at a fixed and constant frequency.

[0053] Only slight adaptation of the oxygen content in the exhaust gas 6 is performed during balanced lambda control 22. A substantially more pronounced adjustment of the oxygen content in the exhaust gas 6 is performed during natural frequency control 23.

[0054] FIG. 3 shows the procedure of the method in a lambda value/time diagram. The lambda value 18 is plotted on the vertical axis, with the lambda value of 1.00 being clarified by the horizontal dotted line. Superstoichiometric lambda values 20 lie above this line, and substoichiometric lambda values 21 lie below this line. The time 19 is plotted on the horizontal axis. The upper diagram shows the progression of the first measurement signals 16 of the first lambda sensor 4. The lower diagram shows the progression of the second measurement signals 17 of the second lambda sensor 5.

[0055] The method starts by switching from the balanced lambda control 22 to the natural frequency control 23. At first, a rich mixture (substoichiometric lambda value 21) is introduced as exhaust gas 6 into the exhaust gas line 2. After the switch to a lean mixture (superstoichiometric lambda value 20), the first lambda sensor 4 registers the exhaust gas 6 with the excess of oxygen at the first time 7. In step a), an exhaust gas with an excess of oxygen is thus introduced into the exhaust line 2 upstream from the first lambda sensor 4, there being a temperature of at least 500 C. in the particulate filter 1. In step b), the excess of oxygen in the exhaust gas 6 is detected by the first lambda sensor 4 at a first time 7. In step c), the excess of oxygen is detected by the second lambda sensor at a second time 8. In step d), the load condition of the particulate filter 1 is calculated from a time difference 9 between the first time 7 and the second time 8.

[0056] In the lower diagram, the dashed line of the natural frequency control 23 shows the progression of the second measurement signals 17 of the second lambda sensor 5 when the particulate filter 1 has only a low particulate load. The continuous line of the natural frequency control 23 shows the progression of the second measurement signals 17 of the second lambda sensor 5 when the particulate filter 1 has a high particulate load. It can be seen here that, when the particulate filter 1 has a low particulate load, the time difference 9 is small, and when the particulate filter 1 has a high particulate load, the time difference 9 is large.

[0057] The exhaust gas 6 with the excess of oxygen enters the particulate filter 1 downstream from the first lambda sensor 4, with an oxidative conversion of the embedded particulates taking place within the particulate filter 1. As a result of the oxidative conversion, the amount of excess oxygen contained in the exhaust gas 6 is reduced. Exhaust gas 6 with an excess of oxygen will also occur downstream from the particulate filter 1 only once the particulates that are embedded in the particulate filter 1 have been converted by oxidation. Only then is the oxygen excess set in the exhaust gas 6 detected by the second lambda sensor 5 (step c)).

[0058] Therefore, the exhaust gas 6 that is introduced into the exhaust line 2 with the excess of oxygen downstream from the particulate filter 1 will appear only with a time delay. The delay depends on the amount of the oxygen excess flowing into the particulate filter 1 on the one hand and on the load condition of the particulate filter 1 on the other hand. The set excess of oxygen is known (e.g., from the control unit 15, via which the mixture of fuel and air to be supplied to the combustion chambers 12 of the internal combustion engine 3 is set), so that it is possible to calculate the load condition of the particulate filter 1 from the delay of the occurrence of exhaust gas 6 with an excess of oxygen at the second lambda sensor 5.

[0059] The oxygen storage capacity of the particulate filter 1 and the transit time of the exhaust gas 6 from the first lambda sensor 4 to the second lambda sensor 5 are additionally taken into account in step d). If the particulate filter 1 has only a low particulate load, the exhaust gas 6 with the excess of oxygen will flow through the particulate filter 1 without substantial conversion of oxygen contained in the exhaust gas 6. The time difference 9 between the first time 7 and the second time 8 then depends essentially only on the flow rate of the exhaust gas 6 (depending on the operating point of the internal combustion engine 3). The time difference 9 can also be influenced by the oxygen storage capacity of the particulate filter 1.

LIST OF REFERENCE SYMBOLS

[0060] 1 particulate filter [0061] 2 exhaust line [0062] 3 internal combustion engine [0063] 4 first lambda sensor [0064] 5 second lambda sensor [0065] 6 exhaust gas [0066] 7 first time [0067] 8 second time [0068] 9 time difference [0069] 10 distance [0070] 11 flow line [0071] 12 combustion chamber [0072] 13 exhaust system [0073] 14 motor vehicle [0074] 15 control unit [0075] 16 first measurement signal [0076] 17 second measurement signal [0077] 18 lambda value [0078] 19 time [0079] 20 superstoichiometric lambda value (lambda value >1; exhaust gas with oxygen excess) [0080] 21 substoichiometric lambda value (lambda value <1; exhaust gas with oxygen deficiency) [0081] 22 balanced lambda control [0082] 23 natural frequency control