Method for determining a leakage in the exhaust system of an internal combustion engine

Abstract

The invention relates to a method for determining a leakage in the exhaust system of an internal combustion engine, wherein the internal combustion engine comprises an engine block with a flowable intake system and the flowable exhaust system, comprising a cleaning system, and wherein a first measuring unit of the exhaust system is used to determine an air-fuel ratio value in the exhaust system, and a second measuring unit of the exhaust system is used to determine a current NOₓ value. x -emission value in the exhaust system, and wherein the internal combustion engine includes a control and regulating unit for operating the internal combustion engine. According to the invention, - in a first step, the internal combustion engine is operated substoichiometrically at an operating point at which an inflow of air through a suction effect into the exhaust system is possible in the event of a leak in the exhaust system, - in a second step, a current NO x -Emission value measured using the second measuring unit, - in a third step, a theoretical NO assigned to the operating point x -Emission value determined, - in a fourth step, a comparison of the current NO x -emission value and the theoretical NO x -emission value was measured, and - in a fifth step, the leakage of the exhaust system is determined based on the comparison.

Description

[0001] Die Erfindung betrifft ein Verfahren zur Bestimmung einer Leckage eines Abgassystems einer Verbrennungskraftmaschine, insbesondere eines Kraftfahrzeugs, gemäß dem Oberbegriff des Patentanspruchs 1.

[0002] Zur Reduzierung von Emissionen der Verbrennungskraftmaschine sind in einem Abgassystem der Verbrennungskraftmaschine unterschiedliche Abgasreinigungseinheiten stromab eines Auslassventils der Verbrennungskraftmaschine angeordnet, insbesondere ein Katalysator und dazugehörend eine NO x -Sensor technology, including at least one NO x -Sensor whose task is to continuously detect nitrogen oxide emissions from the internal combustion engine.

[0003] Sofern das Abgassystem undicht ist, somit das Abgassystem eine Leckage aufweist, besteht die Gefahr, dass insbesondere in bestimmten Betriebspunkten der Verbrennungskraftmaschine Luft in das Abgassystem eintritt und somit die NO x-The sensor delivers an erroneous measurement result. Further complicating matters is the fact that the NO x -Sensor hinter einem, betrachtet in serieller Anordnung im Abgassystem ausgehend von der Verbrennungskraftmaschine, letzten abgasbeeinflussenden Bauteil des Abgassystems liegen muss. Somit ist es durchaus möglich, dass sich das Abgassystem, ausgehend von der Verbrennungskraftmaschine bis zum NO x The sensor extends over a length of two meters. This means that mounting options, for example in the form of screw-in fittings and flanges for mounting the NO, are required. x -Sensors must be designed which carry a potential for leaks.

[0004] Patent EP 1 227 234 B1 describes a method for operating a NOₓ device arranged in the exhaust system of an internal combustion engine. x -Sensors known, wherein an operating state of the internal combustion engine with known NO x- content in the exhaust gas is adjusted, a with a NO x -Sensor measured signal value with a known NO x -Content corresponding signal value at the respective known NO x -Content is adjusted, a correction value is determined from a difference between the measured and known signal value and the NO level. x The sensor's measured signal value is corrected by the correction value.

[0005] According to patent application US 2015 / 082771A1, a system for detecting a leak in the intake manifold of an internal combustion engine is described, in which the fresh air flowing into the internal combustion engine is measured, the amount of injected fuel is recorded, and the air-fuel ratio is determined based on this measurement. The determined air-fuel ratio is then compared with an air-fuel ratio determined based on the exhaust gas, and a leak in the intake manifold is detected based on this comparison.

[0006] Patent EP 3 227 544 B1 discloses a leak detection system for a low-pressure EGR circuit of an internal combustion engine, wherein an air-fuel ratio, which is determined based on a measured or estimated quantity of fresh air in an intake system of the internal combustion engine and a measured or estimated quantity of fuel injection, is combined with a further air-fuel ratio, which is determined by measuring or estimating the further air-fuel ratio and / or NO. x Emissions in the exhaust pipe are determined, compared, and based on this, a leak in the low-pressure EGR circuit is concluded.

[0007] Patent DE 10 2017 218 327 B4 discloses a method for operating an internal combustion engine with a three-way catalyst, in which a detected NO x -value with a predefined NO x The value is compared.

[0008] The object of the present invention is to provide an improved method for determining a leakage in the exhaust system of an internal combustion engine.

[0009] The problem is solved according to the invention by a method for determining a leakage in the exhaust system of an internal combustion engine with the features of claim 1. Advantageous embodiments with expedient and non-trivial further developments of the invention are specified in the respective dependent claims.

[0010] A method according to the invention for determining a leakage of an exhaust system of an internal combustion engine, in particular of a motor vehicle, wherein the internal combustion engine has an engine block with a flowable intake system and the flowable exhaust system comprising a cleaning system, and wherein a first measuring unit of the exhaust system for determining a combustion air ratio value in the exhaust system and a second measuring unit of the exhaust system for determining a current NO x -emission value in the exhaust system, and wherein the internal combustion engine comprises a control and regulating unit for operating the internal combustion engine, is characterized according to the invention in that - in a first step, the internal combustion engine is operated substoichiometrically at an operating point where an inflow of air through a suction effect into the exhaust system is possible in the event of a leak in the exhaust system, - in a second step, a current NO x -Emission value is measured using the second measuring unit, - in a third step, a theoretical NO assigned to the operating point x -emission value is determined - in a fourth step, a comparison of the current NO x -emission value and the theoretical NO x -emission value is measured, and - in a fifth step, the leakage of the exhaust system is determined based on the comparison.

[0011] The advantage of the method according to the invention lies in the fact that the method for checking the tightness of the exhaust system can be easily carried out as part of a basic vehicle diagnostic check after the vehicle has been produced. For example, no additional measuring devices need to be used for the test, since all systems and measuring units are already present in the produced vehicle. Likewise, the method can also be easily carried out during a workshop visit of the vehicle, ensuring a high degree of NO detection accuracy. x -Sensors, and also the second measuring unit, are correct and the vehicle can be handed over to its owner with a correctly installed exhaust system.

[0012] The single figure shows a schematic representation of an internal combustion engine for a motor vehicle, in which a method according to the invention is used.

[0013] The figure illustrates an internal combustion engine 1, in particular an internal combustion engine 1 in the form of a spark-ignition engine, which has an engine block 6 with an intake system 7 and an exhaust system 2, wherein the engine block 6 is connected to the intake system 7 and the exhaust system 2 in a flow-through manner. The exhaust system 2 has a cleaning system 8 for cleaning the exhaust gas of the internal combustion engine 1. Furthermore, the internal combustion engine 1 has a control unit 5, which is designed for operating the internal combustion engine 1. The control unit 5 has characteristic maps and / or characteristic curves and / or routines by which, for example, a fuel quantity is determined to achieve a requested operating point at a specific load requirement.

[0014] The cleaning system 8 may have a catalyst and / or a particulate filter. It could also include a so-called DeNOx system. x -catalyst, or the cleaning system 8 could also be equipped with a urea container for supplying urea to the exhaust gas for NO reduction x -Emission reduction must be implemented. Numerous possible implementations of cleaning system 8 are conceivable.

[0015] To determine the current air-fuel ratio of the internal combustion engine 1, a so-called lambda sensor 9 of a first measuring unit 3 of the internal combustion engine 1 is integrated into the exhaust system 2, wherein the first measuring unit 3 is designed to determine the current air-fuel ratio. Furthermore, the internal combustion engine 1 includes a device for determining the current NO x -Emission value in the exhaust system 2 a NO x-Sensor 10, wherein a second measuring unit 4 of the internal combustion engine 1 is configured to determine a current NOx emission value. It should be mentioned here that the first measuring unit 3 and the second measuring unit 4 are configured to communicate with the control unit 5.

[0016] In principle, and particularly in accordance with future emission regulations, it is necessary to be able to accurately record current emission values ​​of the internal combustion engine 1 so that effective cleaning with the help of the cleaning system 8 is possible. Thus, to accurately record NO x -Emission value requires that the exhaust system 2 be sealed, i.e., leak-free, since at certain operating points of the internal combustion engine 1, a distorted NO value can occur due to possible air ingress into the exhaust system 2 via the leakage point of the exhaust system 2. x -Emission value can be determined.

[0017] This means that, in order to ensure that the exhaust gas flowing from the internal combustion engine 1 completely passes through the cleaning system 8 and can thus exit the exhaust system 2 in a cleaned state, it is necessary that the exhaust system 2 is sealed, or in other words, leak-free, over its entire length up to the last component of the cleaning system 8.

[0018] Typically, the last component of the cleaning system is the NO. x -Sensor 10, which is used to measure the NO x -Emission of the internal combustion engine 1 is formed.

[0019] To test for a leak in the exhaust system 2, or in other words to test for a leakage in the exhaust system 2, a method according to the invention is designed, wherein - in a first step the internal combustion engine 1 is operated substoichiometrically at an operating point at which an inflow of air through a suction effect into the exhaust system 2 is possible in the event of a leak in the exhaust system 2, - in a second step, a current NO x -Emission value is measured using the second measuring unit 4, - in a third step, a theoretical NO assigned to the operating point x -emission value is determined - in a fourth step, a comparison of the current NO x -emission value and the theoretical NO x -emission value is measured, and - in a fifth step, the leakage of the exhaust system 2 is determined based on the comparison.

[0020] The substoichiometric operation of the internal combustion engine 1 is set using the first measuring unit 3, whereby the current air-fuel ratio is determined using the lambda sensor 9. Substoichiometric operation results in an air-fuel ratio of less than 1. Therefore, the air-fuel ratio must be set to a value of less than 1, in particular 0.9, in the procedure. In other words, the air-fuel ratio must be set so that the current air-fuel ratio measured using the lambda sensor 9 is less than 1, in particular 0.9.

[0021] Operating points of the internal combustion engine 1 which tend to cause a suction effect in the exhaust system 3 in the event of a leak are, in particular, an idle speed of the internal combustion engine 1 or an increased idle speed. Therefore, an operating point, in particular an idle speed or an increased idle speed, that is, an idle speed with an increased rotational speed, must be set.

[0022] Using the second measuring unit 4 and the NO x -Sensor will measure the current NO x -Emission value with a theoretical NO x -Emission value, which for example is a characteristic map of the control unit 5, which theoretically represents NO x The emission values ​​at corresponding operating points can be obtained and compared. That is, the current NO is compared. x -emission value and the theoretical NO x -Emission value carried out.

[0023] Provided the current NO x-Emission value is greater than the theoretical NO x Based on the emission value, exhaust system 2 can be considered sufficiently sealed. However, if the current NO x -Emission value lower than the theoretical NO x The emission value indicates that exhaust system 2 is leaking because the exhaust gas is "diluted" due to air being drawn into exhaust system 2. This mixing of the exhaust gas with the air reduces the concentration of NOx emissions in the exhaust gas. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] EP 1 227 234 B1

[0004] US 2015 / 082 771 A1

[0005] EP 3 227 544 B1

[0006] DE 10 2017 218 327 B4

[0007]

Claims

[1] Method for determining a leakage of an exhaust system (2) of an internal combustion engine (1), wherein the internal combustion engine (1) comprises an engine block (6) with a flowable intake system (7) and the flowable exhaust system (2), comprising a cleaning system (8), and wherein a first measuring unit (3) of the exhaust system (2) for determining a combustion air ratio value in the exhaust system (2) and a second measuring unit (4) of the exhaust system (2) for determining a current NO x -emission value in the exhaust system (2), and wherein the internal combustion engine (1) comprises a control and regulating unit (5) for operating the internal combustion engine (1) characterized by , that - in a first step the internal combustion engine (1) is operated substoichiometrically at an operating point at which an inflow of air through a suction effect into the exhaust system (2) is possible in the event of a leak in the exhaust system (2), - in a second step, a current NO x -Emission value is measured using the second measuring unit (4), - in a third step, a theoretical NO assigned to the operating point x -emission value is determined - in a fourth step, a comparison of the current NO x -emission value and the theoretical NO x -emission value is measured, and - in a fifth step the leakage of the exhaust system (2) is determined based on the comparison. [2] Method according to claim 1, characterized by , that the substoichiometric operation is set using the first measuring unit (3). [3] Method according to claim 1 or 2, characterized by , that the internal combustion engine (1) is designed in the form of a gasoline engine. [4] Method according to any one of the preceding claims, characterized by that the operating point is an idle or an increased idle.

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