CN107542562B

CN107542562B - Fault detection in an SCR system by means of efficiency

Info

Publication number: CN107542562B
Application number: CN201710500623.9A
Authority: CN
Inventors: F.米科利斯; A.沃洛诺; M.通多
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2016-06-28
Filing date: 2017-06-27
Publication date: 2021-12-21
Anticipated expiration: 2037-06-27
Also published as: KR20180002058A; CN107542562A; DE102016211572A1

Abstract

The invention relates to a method for fault detection in an SCR system of an internal combustion engine in a motor vehicle, comprising two SCR catalysts and two nitrogen oxide sensors. One nitrogen oxide sensor is arranged upstream of the two SCR catalysts and one nitrogen oxide sensor is arranged downstream of the two SCR catalysts. The method comprises the following steps: adjusting a prescribed ammonia fill level in a first SCR catalyst, wherein the ammonia fill level is below a maximum ammonia fill level for the SCR catalyst; measuring a nitrogen oxide concentration upstream of the SCR catalyst and a nitrogen oxide concentration downstream of the SCR catalyst; during the evaluation phase, a comparison of the actual efficiency of the first SCR catalyst with the expected efficiency of the first SCR catalyst is derived therefrom; a fault in at least one of the two SCR catalysts is identified based on a comparison of the actual efficiency to the expected efficiency.

Description

Fault detection in an SCR system by means of efficiency

Technical Field

The invention relates to a method for fault detection in an SCR system having two SCR catalysts by means of efficiency. Furthermore, the invention relates to a computer program which executes each step of the method when the computer program runs on a computer, and to a machine-readable storage medium which stores the computer program. Finally, the invention relates to an electronic control unit which is set up to carry out the method.

Background

Selective Catalytic Reduction (SCR) is a widely spread technology for reducing nitrogen oxides (NOx) in the exhaust gases of combustion motors in motor vehicles. In an SCR system, it will be commercially also referred to as AdBlue^®The urea-water solution, which is known per se, is injected into the exhaust system upstream of the at least one SCR catalytic converter by means of an injection module. The ammonia separated from the urea-water-solution reacts with the nitrogen oxides at the SCR catalyst for selective catalytic reduction to form elemental nitrogen.

Due to the introduction of more stringent emission regulations, a plurality of SCR catalysts are used, which act on the same exhaust gas. In the event of an insufficient efficiency of the SCR catalytic converter for reducing the nitrogen oxide emissions in the exhaust system, provision is made for a fault detection to be carried out by the vehicle's own detection method (which is usually implemented in an electronic control unit). For this reason, continuous monitoring is carried out during normal operation of the vehicle. For a common detection method, at least one nitrogen sensor arranged upstream of the SCR catalyst and at least one nitrogen sensor arranged downstream of the SCR catalyst are used. For a single SCR catalyst, two nox sensors are sufficient for calculating the efficiency of the SCR system and for monitoring the nox emissions at the same time.

The extension of the SCR system to a plurality of (n) SCR catalysts in the same exhaust system is conventionally based on an n +1 nox sensor for detecting at least one SCR catalyst which is not or poorly functioning by means of a pin-point strategy. Accordingly, a non-or poorly functioning SCR catalyst can be repaired or replaced in a targeted manner, while the better functioning SCR catalyst or the SCR system remains unaffected. However, the use of the needle-point strategy is not necessary during normal operation of the vehicle, since it is sufficient here to monitor the efficiency only. In the case of a non-or poorly functioning SCR catalyst, the driver can be alerted, for example, by a signal light on the dashboard, whereupon he drives the vehicle, for example, to a service point. During the repair-point repair, the needle-point-type strategy mentioned is used in the detection method for detecting the non-or poorly functioning SCR catalyst.

Disclosure of Invention

The method relates to an SCR system of a combustion motor in a motor vehicle. In this case, the SCR system has two SCR catalytic converters arranged one behind the other in a common exhaust system. The exhaust gas first passes through the first SCR catalyst and is subsequently conducted on to the second SCR catalyst, so that both SCR catalysts act on the exhaust gas. Furthermore, the SCR system has two nox sensors, which are likewise arranged in this exhaust system. A first nitrogen oxide sensor is arranged upstream of the two SCR catalysts and is able to measure there the nitrogen oxide concentration before the exhaust gas treatment by the SCR catalysts. The second nitrogen oxide sensor is arranged downstream of the two SCR catalysts and is able to measure the nitrogen oxide concentration there after exhaust gas aftertreatment by the SCR catalysts.

The method comprises the following steps. The ammonia filling level specified in the first SCR catalyst (Ammoniak-F will) is first set. The prescribed ammonia fill level is below a maximum ammonia fill level that can be stored in the SCR catalyst. As a result, the amount of ammonia separated from the urea-water solution injected into the exhaust system is completely stored in the first SCR catalyst. Accordingly, there is no ammonia available for the second SCR catalyst to reduce, and thus the second SCR catalyst does not contribute to the reduction of the nitrogen oxides.

The nitrogen oxide concentration is subsequently measured both upstream and downstream of the SCR catalyst. The actual efficiency of the first SCR catalyst can preferably be derived from the ratio of these two nitrogen concentrations. As described above, the actual efficiency obtained relates only to the first SCR catalyst, although the exhaust gas passes through both SCR catalysts, since no reduction takes place at the second SCR catalyst due to the lack of ammonia. According to a further aspect, it can be provided that the expected efficiency of the first SCR catalyst is determined for the first SCR catalyst from a characteristic curve which indicates a correlation between efficiency and ammonia filling level.

In a further process, during an evaluation phase, a comparison of the actual efficiency of the first SCR catalyst with an expected efficiency is carried out. Finally, a fault in at least one of the two SCR catalysts is identified on the basis of the comparison. It is particularly preferred here to identify a fault in the first SCR catalyst if the actual efficiency of the first SCR catalyst differs from the expected efficiency.

Alternatively, the measurement of the nitrogen oxide concentration upstream of the SCR catalyst and the measurement of the nitrogen oxide concentration downstream of the two SCR catalysts can be carried out at the beginning of the method. In this case, the two SCR catalytic converters are operated in normal operation. A malfunction in the SCR system is identified if the NOx concentration downstream of the two SCR catalysts does not match the expected NOx concentration. It is particularly preferred here to identify a fault in the second SCR catalyst if a fault in the SCR system is identified as described and additionally the actual efficiency of the first SCR catalyst corresponds to the expected efficiency.

According to a further aspect, it can be provided that, after the defective catalytic converter has been repaired or replaced on the basis of the method, the motor vehicle travels the specified distance and/or time and then the method is carried out again. This also takes into account the rare case of two SCR catalysts having a malfunction at the same time. Optionally, the evaluation phase can also be changed when the method is re-implemented, so that a larger fault spectrum (Fehlerspektrum) can be covered.

The computer program is set up for: in particular, each step of the method is carried out when it is implemented on a computer or a controller. The computer program enables the method to be implemented in a conventional electronic controller without structural modifications thereto. To this end, the computer program is stored on the machine-readable storage medium.

The electronic control unit is obtained by loading the computer program onto a conventional electronic control unit, which is set up to carry out fault detection in the SCR system. In this case, the electronic control unit can be both the control unit of the vehicle itself and an external control unit, such as a diagnostic unit, which is connected to the SCR system during fault detection and controls the method.

Drawings

Embodiments of the invention are illustrated in the drawings and are explained in detail in the following description. In the drawings:

fig. 1 schematically shows an SCR system which comprises two SCR catalysts and three nitrogen oxide sensors and which enables fault detection by means of conventional methods;

fig. 2 shows schematically an SCR system which comprises two SCR catalysts and two nitrogen oxide sensors and which can carry out fault detection by means of the method according to the invention;

FIG. 3 shows a flow chart of an exemplary embodiment of the method according to the present invention; and is

Fig. 4 shows a diagram of a characteristic curve of the efficiency of the SCR catalyst as a function of the ammonia filling level, which can be used in one exemplary embodiment of the method according to the invention.

Detailed Description

Fig. 1 shows a generic SCR system 100 of a combustion motor, not shown, in a motor vehicle, having a first SCR catalyst 101 and a second SCR catalyst 102, for which a fault can be identified in a conventional manner. The two

SCR catalysts

101 and 102 are arranged one behind the other in the exhaust system 120, wherein the first SCR catalyst 101 is arranged closer to an injection module 130, which injects a urea/water solution into the exhaust system 120 upstream of the two

SCR catalysts

101 and 102. Furthermore, the SCR system 100 comprises a first nitrogen oxide sensor 110, which is arranged between the injection module 130 and the first SCR catalyst 101 and is able to measure there the nitrogen oxide concentration NOx of the exhaust gas before the exhaust gas is post-treated by the

SCR catalysts

101 and 102 _{Before processing}. Furthermore, the SCR system 100 comprises a second NOx sensor 111, which is arranged downstream of the second SCR catalyst 102 and is able to measure there the nitrogen concentration NOx of the exhaust gas after-treatment of the exhaust gas by the two

SCR catalysts

101 and 102_{After processing}. The SCR system alsoA third nitrogen oxide sensor 112 is additionally included, which is arranged between the first SCR catalyst 101 and the second SCR catalyst 102 and is able to measure there the nitrogen oxide concentration of the exhaust gas after the exhaust gas aftertreatment by the first SCR catalyst 101. The three

nox sensors

110, 111 and 112 and the injection module 130 are connected to and controlled by an electronic controller 140.

In a conventional method for fault detection, the actual difference between the nox concentration at the first nox sensor 110 and the third nox sensor 112 or the actual difference between the nox concentration at the third nox sensor 112 and the second nox sensor 111 is detected and compared with the expected difference. If at least one of the actual differences does not correspond to the respective expected difference, a fault in the

SCR catalyst

101 or 102 lying between them is concluded.

Fig. 2 shows an SCR system 200 of a combustion motor, not shown, in a motor vehicle, which likewise comprises a first SCR catalyst 201 and a second SCR catalyst 202, for which a fault can be identified by means of an embodiment of the method according to the invention. The two

SCR catalysts

201 and 202 are respectively arranged one behind the other in the exhaust system 220, wherein the first SCR catalyst 201 is arranged closer to the injection module 230 as described above. However, the SCR system 200 shown here only comprises a first nitrogen oxide sensor 210 arranged between the injection module 230 and the first SCR catalyst 201 and a second nitrogen oxide sensor 211 arranged downstream of the second SCR catalyst 202. The two SCR

catalytic converters

210 and 211 and the injection module 230 are connected to an electronic control unit and are controlled by the latter at least during the fault detection. In another embodiment, the electronic control unit can be an external device which is connected to the SCR system 200 during the fault detection.

Said first nitrogen oxide is transferred toThe sensor 210 measures the nitrogen oxide concentration NOx of the exhaust gas before the exhaust gas is post-treated by the

SCR catalysts

101 and 102 _{Before processing}And the second nitrogen oxide sensor 211 measures the nitrogen concentration NOx of the exhaust gas after exhaust gas aftertreatment by the two

SCR catalysts

101 and 102_{After processing}. The SCR system 200 of fig. 2 therefore differs from the SCR system of fig. 1 only in that the third nitrogen oxide sensor 112 is not required.

An exemplary embodiment of a method according to the present invention for fault detection in the SCR system 200 described above is illustrated in fig. 3 as a flow chart. In a first step, the nitrogen oxide concentration NOx at the first nitrogen oxide sensor 210 is determined_{Before processing}And the nitrogen oxide concentration NOx at the second nitrogen oxide sensor 211_{After processing} A measurement 300 is performed. If the nitrogen oxide concentration NOx after exhaust gas aftertreatment by means of the two

SCR catalysts

201 and 202 is present_{After processing}And from the nitrogen oxide concentration NOx_{Before processing}And the expected values obtained in the conversion of the two SCR catalysts, a fault in the SCR system 200 is identified 301. That is to say that at least one of the two

SCR catalysts

201 or 202, and in rare cases also both SCR catalysts, has a malfunction and/or at least one reduced conversion rate. If no fault in the SCR system 200 is identified 301, the method is ended 302.

Otherwise, in a further step, the combustion motor of the stopped motor vehicle is switched 303 to idle and then operated 304 at the specified operating point. Then waits until the NOx concentration NOx at the first NOx sensor 210_{Before processing}And the nitrogen oxide concentration NOx at the second nitrogen oxide sensor 211_{After processing}The same, and the urea-water-solution is then injected 306 into the exhaust train 220. Thus, the ammonia filling level NH in the first SCR catalyst 201_{3_ fill level}Up to a prescribed value below the maximum ammonia fill level of the first SCR catalyst. MakingAs a result, ammonia is no longer supplied to the second SCR catalyst and therefore the second SCR catalyst does not contribute to the reduction of nitrogen oxides in the exhaust gas. NH if the specified ammonia fill level is reached_{3_ fill level}Then, on the one hand, the NOx concentration NOx at the first NOx sensor 210 is renewed_{Before processing}And the nitrogen oxide concentration NOx at the second nitrogen oxide sensor 211_{After processing} A measurement 308 is carried out and the actual efficiency η of the first SCR catalyst 201 is derived from the measurement 308 _{' actual}. On the other hand, from a defined ammonia filling level NH in the first SCR catalyst 201_{3_ fill level}To obtain the expected efficiency η of the first SCR catalyst 201_Expected. For this purpose, the characteristic curve 400 of the first SCR catalyst shown in fig. 4 is used.

In comparison 311, during an evaluation phase, the actual efficiency η is compared_{' actual}With expected efficiency eta_ExpectedAnd (6) comparison. If the actual efficiency η_{' actual}With expected efficiency eta_ExpectedIn contrast, a malfunction in the first SCR catalyst 201 is identified 320, since only the first SCR catalyst contributes to the reduction of nitrogen oxides in the exhaust gas. As a further step 321, the faulty first SCR catalyst 201 is repaired or replaced. If the actual efficiency η_{' actual}With expected efficiency eta_ExpectedIn agreement, a fault at the first SCR catalyst 201 cannot be determined. However, since a fault in the SCR system 200 is identified in the measurement 300, it can be assumed that the second SCR catalyst 202 is faulty. Accordingly, a fault in the second SCR catalyst 202 is identified 330 in this case. Here, too, the faulty second SCR catalyst 202 is repaired or replaced as a further step 331.

In order to rule out the rare case that both

SCR catalysts

201 and 202 are defective, the motor vehicle is first driven 340 for a defined time and/or distance when a defect in the first SCR catalyst 201 is detected 320. The method is then repeated from the beginning. In a further embodiment, it is provided that the evaluation phase is changed during the repetition of the method.

FIG. 4 shows, as mentioned, that the efficiency η depends on the ammonia fill level NH_{3_ fill level}Characteristic curve 400. At point 401, the specified ammonia fill level NH from step 307 is recorded_{3_ fill level}. Furthermore, the point 402 shows the actual efficiency η_{' actual}And the expected efficiency η that can be read from the characteristic 400 with respect to the point 401_ExpectedThe consistency of (c). While the point 403 shows the actual efficiency η_{' actual}This actual efficiency does not correspond to the characteristic curve 400 and therefore also to the expected efficiency η_ExpectedAnd are inconsistent.

Claims

1. Method for fault detection in an SCR system (200) of an internal combustion engine in a motor vehicle, having two SCR catalysts (201; 202) and two nitrogen oxide sensors (210; 211), comprising a first nitrogen oxide sensor and a second nitrogen oxide sensor, wherein the first nitrogen oxide sensor (210) is arranged upstream of the two SCR catalysts (201; 202) and the second nitrogen oxide sensor (211) is arranged downstream of the two SCR catalysts, comprising a first SCR catalyst and a second SCR catalyst, through which exhaust gas first passes and then is conducted further to the second SCR catalyst, comprising the following steps:

Switching a combustion motor of a stationary motor vehicle to idle and subsequently operating the combustion motor at a defined operating point, and subsequently waiting until the concentration of nitrogen oxides at the first nitrogen oxide sensor is the same as the concentration of nitrogen oxides at the second nitrogen oxide sensor, and subsequently injecting a urea-water solution into the exhaust system,

-setting (307) a defined ammonia filling level (NH) in the first SCR catalyst (201)_{3_ fill level}) Wherein the ammonia fill level (NH)_{3_ fill level}) Below a maximum ammonia fill level for the first SCR catalyst (201);

-measuring (308) the nitrogen oxide concentration (NOx) upstream of the two SCR catalysts (201; 202)_{Before processing}) And the two SCR catalysts (201; 202) downstream of nitrogen oxide concentration (NOx)_{After processing}）；

-during an evaluation phase, comparing the actual efficiency (η) of the first SCR catalyst (201)_{' actual}) With an expected efficiency (η) of the first SCR catalyst (201)_Expected) Performing a comparison (311);

-according to said actual efficiency (η)_{' actual}) And expected efficiency (eta) _Expected) To identify (320; 330) the two SCR catalysts (201; 202) if the actual efficiency (η) of the first SCR catalyst (201)_{' actual}) And expected efficiency (eta)_Expected) If not, a fault in the first SCR catalyst (201) is identified (320).

2. Method according to claim 1, characterized in that the nitrogen oxide concentration (NOx) is initially upstream of the two SCR catalysts_{Before processing}) And the two SCR catalysts (201; 202) downstream of nitrogen oxide concentration (NOx)_{After processing}) A measurement (300) is carried out, wherein two SCR catalysts (201; 202) is operated in normal operation and if the two SCR catalysts (201; 202) downstream of nitrogen oxide concentration (NOx)_{After processing}) A fault in the SCR system (200) is identified (301) if the expected nox concentration does not match.

3. The method according to claim 2, characterized in that if a fault in the SCR system (200) is identified (301) and the actual efficiency (η) of the first SCR catalyst (201) is reached _{' actual}) And expected efficiency (eta)_Expected) Are consistent with each other(311) A fault in the second SCR catalyst (202) is identified (330).

4. The method according to any one of the preceding claims, characterized in that after repair or replacement (321; 331) of a defective SCR catalyst, the motor vehicle is driven (340) for a defined distance and/or time and each step of the method is subsequently repeated.

5. Method according to any of claims 1 to 3, characterized in that the nitrogen oxide concentration (NOx) upstream from the two SCR catalysts (201; 202)_{Before processing}) And downstream nitrogen oxide concentration (NOx)_{After processing}) Obtaining (309) an actual efficiency (η) of the first SCR catalyst (201)_{' actual}）。

6. Method according to any one of claims 1 to 3, characterized in that the expected efficiency (η) of the first SCR catalyst (201) is determined (310) from a characteristic curve (400) for the first SCR catalyst (201)_Expected）。

7. A machine-readable storage medium, on which a computer program is stored, which computer program is set up for: carrying out each step of the method according to any one of claims 1 to 6.

8. An electronic controller configured to: fault detection is carried out in the SCR system by means of the method according to any one of claims 1 to 6.