Search

DE-102023106186-B4 - On-board diagnostic procedure for a NOx sensor

DE102023106186B4DE 102023106186 B4DE102023106186 B4DE 102023106186B4DE-102023106186-B4

Abstract

On-board diagnostic procedure (1) for a NOx sensor (2) coupled to an engine control unit (5) of an internal combustion engine (4) for measuring nitrogen oxides and ammonia in the exhaust gas of the internal combustion engine (4), in particular of a motor vehicle (3), - wherein the NOX sensor (2) generates an electrical binary signal which is monitored with respect to a predetermined threshold in order to decide whether the readings from the NOX sensor represent nitrogen oxides when the binary signal is below the predetermined threshold, or represent ammonia when the binary signal is above the predetermined threshold, - in which the NOX sensor (2) is decoupled from the engine control (5), - in which, after or with the decoupling of the NOX sensor (2) from the engine control (5), the temperature of a ceramic element (12) of the NOX sensor (2) is reduced to a predetermined diagnostic temperature, - in which the electrical binary signal of the NOX sensor (2) is monitored, - where proper functioning of the NOX sensor (2) is established when the binary signal rises to a predetermined minimum value within a predetermined time period that is greater than the predetermined threshold, the predetermined time period being measured from the time at which the diagnostic temperature has been reached, - where a malfunction of the NOX sensor (2) is detected if the binary signal does not rise to the minimum value within the predetermined time period.

Inventors

  • Christian Feil
  • Roland Fechler

Assignees

  • DR. ING. H.C. F. PORSCHE AKTIENGESELLSCHAFT

Dates

Publication Date
20260513
Application Date
20230313

Claims (9)

  1. On-board diagnostic procedure (1) for an engine control unit (5) of an internal combustion engine a NOX sensor (2) coupled to the engine control unit (4) for measuring nitrogen oxides and ammonia in the exhaust gas of the internal combustion engine (4), in particular of a motor vehicle (3), - wherein the NOX sensor (2) generates an electrical binary signal which is monitored with respect to a predetermined threshold value in order to decide whether the measured values of the NOX sensor represent nitrogen oxides if the binary signal is below the predetermined threshold value, or represent ammonia if the binary signal is above the predetermined threshold value, - wherein the NOX sensor (2) is decoupled from the engine control unit (5), - wherein, after or during the decoupling of the NOX sensor (2) from the engine control unit (5), the temperature of a ceramic element (12) of the NOX sensor (2) is reduced to a predetermined diagnostic temperature, - wherein the electrical binary signal of the NOX sensor (2) is monitored, - wherein proper functioning of the NOX sensor (2) is verified, if the binary signal rises to a predetermined minimum value within a predetermined time period which is greater than the predetermined threshold, the predetermined time period being measured from the time at which the diagnostic temperature has been reached, - where a malfunction of the NOX sensor (2) is detected, if the binary signal does not rise to the minimum value within the predetermined time period.
  2. On-board diagnostic procedures (1) according to Claim 1 , characterized in that , in the event that the proper functioning of the NOX sensor (2) has been established, the ceramic element (12) is heated to a predetermined operating temperature.
  3. On-board diagnostic procedures (1) according to Claim 2 , characterized in that , with or after the heating of the ceramic element (12) to the operating temperature, the NOX sensor (2) is coupled to the motor control (5).
  4. On-board diagnostic procedures (1) according to one of the Claims 1 until 3 , characterized in that , in the event that the malfunction of the NOX sensor (2) has been detected, a corresponding error message is transmitted to the engine control unit (5).
  5. On-board diagnostic procedures (1) according to one of the Claims 1 until 4 , characterized in that - a reduction of the temperature is carried out passively by switching off or reducing a heater (13) of the NOX sensor (2), which serves to heat the ceramic element (12) to a predetermined operating temperature, or by controlling it to set the diagnostic temperature, and/or - a rise in the temperature is carried out actively by controlling a heater (13) of the NOX sensor (2), which serves to heat the ceramic element (12) to a predetermined operating temperature, to set the operating temperature.
  6. On-board diagnostic method (1) according to one of the preceding claims, characterized in that the NOX sensor (2) is positioned on an exhaust system (6) of the internal combustion engine (4) such that the NOX sensor (2) measures nitrogen oxides and ammonia in a composition of the exhaust gas with which the exhaust gas exits the exhaust system (6) into the environment (7).
  7. On-board diagnostic method (1) according to one of the preceding claims, characterized in that - the internal combustion engine (4) has an exhaust system (6) with several exhaust aftertreatment devices (8) through which the exhaust gas flows, - the NOX sensor (2) is arranged on the exhaust system (6) such that it measures nitrogen oxides and ammonia in the exhaust gas downstream of the last exhaust aftertreatment device (8) through which the exhaust gas flows.
  8. Diagnostic device (11) for a motor vehicle (3), - wherein the diagnostic device (11) can be coupled or is coupled to an engine control unit (5) for controlling an internal combustion engine (4) of the motor vehicle (3) and to a NOx sensor (2) for measuring nitrogen oxides and ammonia in the exhaust gas of the internal combustion engine (4), - wherein the diagnostic device (11) is configured to perform the on-board diagnostic procedure (1) according to one of the following during the operation of the internal combustion engine (4). Claims 1 until 7 carries out.
  9. Motor vehicle (3), in particular passenger car, - with an internal combustion engine (4), - with an engine control unit (5) for controlling the internal combustion engine (4), - with a NOx sensor (2) for measuring nitrogen oxides and ammonia in the exhaust gas of the internal combustion engine (4), - with a diagnostic device (11) according to Claim 8 .

Description

The present invention relates to an on-board diagnostic method for a NOx sensor integrated into the engine control unit of an internal combustion engine for measuring nitrogen oxides and ammonia in the exhaust gas of the internal combustion engine, in particular of a motor vehicle. The invention also relates to a diagnostic device for carrying out this on-board diagnostic method and to a motor vehicle equipped with such a diagnostic device. To comply with increasingly stringent environmental regulations, it is necessary to monitor the levels of nitrogen oxides (NOx, NOₓ , NO₂ , N₂O₃ , and N₂O₄ ) and ammonia ( NH₃ ) in the exhaust gases emitted by combustion engines. NOx sensors are used for this purpose, as their cross-sensitivity allows them to measure both nitrogen oxides and ammonia. To ensure the proper functioning of the NOx sensor can be verified during operation of the combustion engine or the vehicle equipped with it, on-board diagnostics of the NOx sensor are desirable. Such on-board diagnostics can be performed relatively easily, for example, by deliberately operating the combustion engine in a manner that increases the amount of nitrogen oxides in the exhaust gas, thus verifying the functionality of the NOx sensor with regard to nitrogen oxide measurement. Similarly, the combustion engine can be deliberately operated in a manner that increases the amount of ammonia in the exhaust gas, to verify the functionality of the NOx sensor with regard to ammonia measurement. However, such diagnostic procedures, in which the emissions to be avoided are deliberately generated, are undesirable if the pollutants are checked at the end of the exhaust system, as this would allow the pollutants to escape unhindered into the environment. From the DE 10 2011 077 246 B3 A filtering method is known for a NOx sensor in an exhaust system that includes an SCR catalyst. In this method, NOx concentrations upstream and downstream of the SCR catalyst are determined, and based on these measurements, NOx conversion and NH3 slip behavior are modeled. By calculating errors in the model, it can be determined whether the currently measured data from the NOx sensor represent NH3 values or NOx values. From the DE 10 2011 077 251 B3 A diagnostic procedure for a filter of a NOx sensor of an exhaust system with an SCR catalyst is known. This diagnostic procedure includes operating the filter, including calculating a NOx estimate downstream of the SCR catalyst, modeling a linear NOx model based on the NOx estimate, performing a comparison by means of an error calculation between the calculated NOx estimate and a modeled NOx estimate, and deactivating the filter if the error determined thereby is below a threshold value. From the US 2019 / 0 136 785 A1 is an on-board diagnostic procedure for a NOX sensor coupled to an engine control unit of an internal combustion engine for measuring nitrogen oxides and ammonia in the exhaust gas of the internal combustion engine, in which the temperature of a measuring cell is lowered and its voltage is observed for diagnostic purposes. From the DE 10 2019 208 254 A1 A method for determining the nitrogen oxide and/or ammonia content in the exhaust gas of an internal combustion engine is known, in which an exhaust gas sensor generates a main signal indicating the nitrogen oxide and/or ammonia content and a binary or linear lambda signal. If the lambda signal is greater than a lambda threshold, the main signal indicates the nitrogen oxide content. If, on the other hand, the lambda signal is less than the lambda threshold, the main signal indicates the ammonia content. Further methods and/or sensors are available from the DE 198 52 244 C1 , DE 10 2015 117 530 A1 , DE 10 2016 110 167 A1 and DE 100 49 685 A1 known. The present invention addresses the problem of providing an improved or at least a different embodiment for the diagnosis of a NOX sensor during the operation of the internal combustion engine, which is characterized by high environmental compatibility with a comparatively simple feasibility. This problem is solved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims. The invention is based on the general concept of decoupling the NOx sensor for on-board diagnostics from the engine control unit and setting the temperature of a ceramic element of the NOx sensor to a predetermined diagnostic temperature, which is below the operating temperature of the NOx sensor. An electrical signal from the NOx sensor is monitored with respect to voltage and/or current. Proper functioning of the NOx sensor is then confirmed when the signal at the diagnostic temperature is within the specified range. The voltage and/or current rises to a predetermined minimum value. A malfunction of the NOx sensor is assumed if the signal does not rise at the diagnostic temperature or does not rise to the minimum value. The invention utilizes the fact that, in a f