Method for self-diagnosis of NOx sensor of internal combustion engine

Abstract

The invention relates to a method for the self-diagnosis of a NOx sensor of an internal combustion engine, in which the NOx sensor detects a first oxygen signal and a second oxygen signal, in which the first oxygen signal detects a positive oxygen concentration at an air-fuel ratio greater than 1 and a negative oxygen concentration at an air-fuel ratio less than 1, in which the first oxygen signal detects a positive oxygen concentration at an air-fuel ratio greater than 1 and the second oxygen signal detects a negative oxygen concentration at an air-fuel ratio less than 1. The second oxygen signal corresponds to a voltage applied between an exhaust gas electrode and a reference electrode of the NOx sensor, the measured voltage being less than 450 mV in the case of a positive oxygen concentration in the exhaust gas and greater than 450 mV in the case of a negative oxygen concentration in the exhaust gas, a characteristic curve dependent on the first oxygen signal and the second oxygen signal is stored in the controller, a correlation variable is determined on the basis of the second oxygen signal and the characteristic curve, a difference between the first oxygen signal and the correlation variable is determined, and a diagnosis / self-diagnosis for the NOx sensor is performed on the basis of the determined difference.

Description

Background Art

[0001] DE 10 2009 046 232 A1 relates to a method for diagnosing a NOx measuring value receiver for detecting the NOx concentration in the exhaust system of an internal combustion engine, comprising two measuring chambers (110, 120), wherein the exhaust gas to be measured is supplied to the first measuring chamber (110) and the oxygen concentration is set by means of a first oxygen ion pump current, and the second measuring chamber (120) is connected to the first measuring chamber (110), and wherein the two measuring chambers are arranged in a solid electrolyte, characterized by the following steps: - at a predeterminable operating point, the internal gas in the first measuring chamber (110) is reduced in such a way that the oxygen concentration is set in the first measuring chamber (120). The invention relates to a method for determining the oxygen content of the exhaust gas by adjusting the pump voltage at the pump electrode of the exhaust gas and at the oxygen measuring electrode (124) in the second measuring chamber (120) so that the oxygen content of the exhaust gas is set in the second measuring chamber (120) at the NOx measuring electrode (126) arranged therein; determining the oxygen content in the second measuring chamber (120); additionally determining the oxygen content by means of an independent device; comparing the two values ​​representing the oxygen concentration and inferring a defective sensor if the oxygen concentration value determined in the second measuring chamber (120) deviates from the oxygen concentration value determined by means of the independent sensor device by a predeterminable amount. Summary of the Invention

[0002] In a first aspect, the present invention relates to a method for self-diagnosis of a NOx sensor for an internal combustion engine, wherein the NOx sensor acquires a first oxygen signal and a second oxygen signal, wherein the first oxygen signal acquires a positive oxygen concentration at an air-fuel ratio λ greater than 1 and a negative oxygen concentration at an air-fuel ratio λ less than 1, wherein the second oxygen signal corresponds to a voltage applied between an exhaust gas electrode and a reference electrode of the NOx sensor, wherein the measured voltage is less than 450 mV in the case of a positive oxygen concentration in the exhaust gas and greater than 450 mV in the case of a negative oxygen concentration in the exhaust gas, wherein a characteristic curve dependent on the first oxygen signal and the second oxygen signal is stored in a controller, wherein a relevant variable is acquired based on the second oxygen signal and the characteristic curve, wherein a difference between the first oxygen signal and the relevant variable is acquired, and diagnosis / self-diagnosis of the NOx sensor is performed based on the acquired difference.

[0003] Advantageously, a method for self-diagnosis of a NOx sensor enables passive, emissions-neutral verification of the sensor's oxygen signal characteristics without requiring information from additional sensors in the exhaust system or active mixture adjustment based on λ≠1. By using two oxygen signals—a linear and a binary signal—and their correlation, a correlation variable can be obtained, which serves as a reference for the first oxygen signal. The difference between the first oxygen signal and the correlation variable forms the basis for verifying and diagnosing the oxygen signal characteristics. By using a characteristic curve that depends on the first and second oxygen signals, the method can be used even with different air-fuel ratios. Compared to the prior art, the method enables more accurate and reliable self-diagnosis of NOx sensors without requiring additional sensors or active mixture adjustment.

[0004] In a special embodiment, a defective NOx sensor is detected if the detected difference exceeds a predefinable upper threshold value or falls below a lower threshold value.

[0005] Advantageously, the claimed features enable a faulty NOx sensor to be identified if the detected difference exceeds a predeterminable upper threshold value or falls below a lower threshold value. This ensures verification and diagnosis of the oxygen signal characteristic of the NOx sensor to ensure that the NOx sensor complies with legal requirements for on-board monitoring. Compared to the prior art, which does not specify specific requirements for NOx sensors for stoichiometrically operated gasoline-powered vehicles, the method provides a passive, emissions-neutral verification of the sensor's oxygen signal characteristic. This verification does not require information from additional sensors in the exhaust system and does not require active mixture adjustments based on λ≠1, which could potentially lead to emissions.

[0006] In an advantageous embodiment, a properly functioning NOx sensor is detected if the determined difference falls below a predefinable upper threshold value or exceeds a lower threshold value.

[0007] Advantageously, the claimed features enable a properly functioning NOx sensor to be identified if the determined difference falls below a predetermined upper threshold or exceeds a lower threshold. This ensures verification and diagnosis of the NOx sensor's oxygen signal characteristics to ensure adherence to required OBM tolerances. In particular, NOx sensors can comply with regulatory requirements for onboard monitoring. Compared to existing technologies that require active mixture control based on λ≠1, the method is emission-neutral and does not require information from additional sensors in the exhaust system. Furthermore, the method enables filtering of the calculated oxygen concentration difference to suppress short-term signal disturbances and averaging of multiple values.

[0008] In a further refinement, activation of the self-diagnosis is permitted if an operating state of the internal combustion engine with an air-fuel ratio close to the value 1 exists, in particular a steady-state or quasi-steady-state state of the internal combustion engine exists.

[0009] Advantageously, the claimed features enable more precise verification and diagnosis of the oxygen signal characteristic of a NOx sensor by executing the method in operating conditions of an internal combustion engine with an air-fuel ratio close to 1. Limiting the method to steady-state or quasi-steady-state conditions ensures that the NOx sensor signal lies within a specified range of exhaust gas oxygen concentrations, or exhaust gas lambda. This increases the accuracy of the conversion of the O2bin signal to positive or negative oxygen concentrations, thereby improving verification and diagnosis of the oxygen signal characteristic. Compared to the prior art, which is not restricted to specific operating conditions, the claimed features result in higher accuracy and reliability of the diagnostic results.

[0010] In a further aspect, the invention relates to a device, in particular a control unit, and a computer program, which are designed, in particular programmed, to carry out one of the methods. In a still further aspect, the invention relates to a machine-readable storage medium, on which the computer program is stored. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention will be explained in more detail below based on the embodiments shown in the accompanying drawings, in which:

[0012] Figure 1 A schematic diagram shows an internal combustion engine with a three-way catalytic converter.

[0013] Figure 2 The first oxygen concentration and the second oxygen concentration O2 are shown. lin ;O2 bin An exemplary correlation between

[0014] Figure 3 A schematic flow chart for self-diagnosis of a NOx sensor is shown. DETAILED DESCRIPTION

[0015] The present invention is described below using an engine system with a three-way catalytic converter as an example. However, the present invention is also applicable to other catalyst types, such as a combination of a three-way catalytic converter and an NH3 storage catalyst, such as an SCR catalyst (SCR) and / or an ammonia slip catalyst (ASC). For simplicity, the following description uses an exhaust system with a three-way catalytic converter as a starting point. The present invention is also applicable to exhaust systems with multiple catalysts.

[0016] Figure 1The vehicle's internal combustion engine 10 is shown in detail. The vehicle has an air supply system 12, an exhaust system 14, and a control unit 16. Air flow meter 18 and a throttle plate of a throttle plate unit 19, located downstream of air flow meter 18, are located in the air supply system 12. Air flowing into the internal combustion engine 10 via the air supply system 12 mixes in the combustion chamber 20 of the internal combustion engine 10 with gasoline injected directly into the combustion chamber 20 via an injection valve 22. The resulting combustion chamber charge is ignited and combusted by an ignition device 24, such as a spark plug. A rotational angle sensor 25 detects the rotational angle of the shaft of the internal combustion engine 10 and, therefore, allows the control unit 16 to trigger and detect ignition in a predetermined angular position of the shaft. Exhaust gases resulting from the combustion are discharged through the exhaust system 14.

[0017] In a special embodiment, the exhaust system can also have a high-pressure exhaust gas recirculation and / or a low-pressure exhaust gas recirculation, by which the exhaust gas can be guided back into the combustion chamber via the air supply system. The controller 16 can thereby determine the high-pressure side exhaust gas recirculation rate r exh,HD and the exhaust gas recirculation rate r on the low-pressure side exh,HD .

[0018] The exhaust system 14 has at least one three-way catalytic converter 26. The three-way catalytic converter 26 converts three exhaust gas components, namely nitrogen oxides, hydrocarbons, and carbon monoxide, and also has an oxygen storage effect.

[0019] Upstream of the at least one three-way catalytic converter 26, a front exhaust gas sensor 32 that is exposed to the exhaust gas 28 is arranged immediately in front of the three-way catalytic converter 26. Downstream of the three-way catalytic converter 26, a rear exhaust gas sensor 34 that is also exposed to the exhaust gas 28 is arranged immediately behind the three-way catalytic converter 26. The first exhaust gas sensor 32 is preferably a wideband lambda probe 32 that allows the measurement of a first air-fuel ratio lambda over a wide range of air coefficients. 1,sens .

[0020] The first exhaust gas sensor 32 is arranged downstream of the internal combustion engine 10 and upstream of the three-way catalytic converter 26 .

[0021] The second exhaust gas sensor 34 (ie, located downstream of the three-way catalyst 26) is preferably a NOx sensor 34, which obtains the NOx concentration downstream of the three-way catalyst 26 and the second air-fuel ratio λ ds .

[0022] The NOx sensor 34 is arranged at the end of the exhaust gas aftertreatment system. "End of the exhaust system" can be understood to mean, in particular, that the NOx sensor 34 is arranged as the last component downstream of the three-way catalytic converter 26. The NOx sensor 34 is preferably arranged near the outlet of the three-way catalytic converter 34.

[0023] The NOx sensor 34 used consists of multiple cells. In a first cell, which is exposed to the exhaust gas 28 via a diffusion barrier, a constant, stoichiometric mixture is set using an electrically driven oxygen pump current. The air-fuel ratio in the exhaust gas 28 can be inferred from the pump current required for this purpose. Nitrogen oxides (NOx) are not reduced by a suitable design of the internal electrodes in the first pump cell, but are transferred from the first cell to the second cell via a second diffusion barrier and measured there as a second pump current. Optionally, the NOx sensor can have its own controller to perform signal and calculation operations. Signals for the exhaust gas lambda and NOx concentration are transmitted by the NOx sensor 34 to the engine controller 16.

[0024] In the exemplary embodiment shown, a step detector 36 which is exposed to the exhaust gas 28 may be arranged.

[0025] Control unit 16 processes the signals of air mass flow meter 18 , rotational angle sensor 25 , first exhaust gas sensor 32 , second exhaust gas sensor 34 , and an optional temperature sensor.

[0026] Furthermore, the control unit 16 stores the regulation for the fuel injection or the mixture treatment as well as the control for the cylinder shutoff.

[0027] exist Figure 2 An exemplary dependency for a characteristic map K stored in control unit 16 is shown in FIG.

[0028] The diagram shows a characteristic diagram K, wherein the second oxygen concentration O2, in particular binary, is plotted on the abscissa. bin , and the ordinate shows a particularly linear first oxygen concentration O2 lin The first oxygen concentration O2 lin It is expressed as a percentage and can have both positive and negative values. In contrast, the second oxygen concentration O2 bin It is shown in volts and ranges from 0 to 1.

[0029] The first oxygen signal O2 of the NOx sensor 34 lin At an air-fuel ratio greater than 1, a measured value for a positive oxygen concentration in the exhaust gas is provided, and at an air-fuel ratio less than 1, a theoretical negative oxygen concentration is provided.

[0030] Second oxygen signal O2 bin A voltage signal corresponding to the Nernst voltage applied between the exhaust gas electrode and the reference electrode of the NOx sensor 34, which Nernst voltage is significantly greater than 450 mV at a positive oxygen concentration and significantly less than 450 mV at a negative oxygen concentration. This can be used to determine the second oxygen signal O2 of the NOx sensor 34.bin With the first oxygen signal O2 lin The correlation between the second oxygen signal O2 is, for example, in the form of a characteristic curve K shown as an example, which is used to convert the second oxygen signal O2 bin Convert to positive or negative oxygen concentration.

[0031] In this case, the characteristic curve K is preferably acquired during the application phase for the NOx sensor and stored in the control unit 16 .

[0032] exist Figure 3 An exemplary sequence of a method for self-diagnosis of a NOx sensor 34 of an internal combustion engine 10 is shown in FIG. 1 using a flowchart.

[0033] The following examples are limited to the NOx sensor 34 .

[0034] The method begins in step 200 , wherein the current air-fuel ratio λ is acquired by the controller 16 . ist The air-fuel ratio λ is preferably obtained by a λ probe arranged in the exhaust system. ist The lambda probe is preferably arranged downstream of the internal combustion engine 10 and upstream of the catalytic converter 22 .

[0035] The controller 16 monitors the current air-fuel ratio λ ist .

[0036] In a preferred design, if the current air-fuel ratio λ is set near the stoichiometric air-fuel ratio of 1, ist , the activation of the method can then be authorized by the controller 16 with the aid of a predefinable debounce.

[0037] In a special embodiment, control unit 16 queries further evaluation criteria, for example whether a current steady-state or quasi-steady-state state exists for internal combustion engine 10 .

[0038] If such a state exists, the activation is permitted and the method continues in step 210 .

[0039] In step 210, the controller 16 and the NOx sensor 34 continuously obtain the first oxygen signal and the second oxygen signal O2 lin ;O2 bin .

[0040] In addition, according to the second oxygen signal O2 bin Obtain the relevant parameter O2 from the characteristic curve K stored in the controller 16 kor .

[0041] The method then continues in step 220 .

[0042] In step 220, a first oxygen signal O2 is obtained. lin Related parameters O2 kor The difference D between them.

[0043] The method then continues in step 230 .

[0044] In step 230 , the control unit 16 checks whether the detected difference value D lies within a predefinable threshold value range.

[0045] The predefinable threshold value range is here in particular composed of a predefinable upper threshold value S o and a predeterminable lower threshold S u constitute.

[0046] If the difference D obtained is lower than the upper threshold S o And the difference D obtained is lower than the lower threshold S u , the NOx sensor 34 is identified as fully functional and this information is stored in the controller 16 .

[0047] If the difference D obtained exceeds the upper threshold S o Or the difference D obtained is lower than the lower threshold S u , the NOx sensor 34 is identified as faulty and this information is stored in the controller 16 .

[0048] In a special embodiment, the exceeding or falling below of an upper or lower threshold value by the difference value can be performed by means of debouncing.

[0049] The method can then be ended or restarted in step 200 .

Claims

1. A method for self-diagnosis of a NOx sensor (34) for an internal combustion engine (10), in, The NOx sensor (34) acquires a first oxygen signal and a second oxygen signal, Wherein, the first oxygen signal (O2 lin ) obtains a positive oxygen concentration (O2 lin ) and a negative oxygen concentration (O2 lin ), Wherein, the second oxygen signal (O2 bin ) corresponds to the voltage applied between the exhaust gas electrode and the reference electrode of the NOx sensor (34), wherein the measured voltage is less than 450 mV at a positive oxygen concentration in the exhaust gas and greater than 450 mV at a negative oxygen concentration in the exhaust gas, The controller (16) stores the information dependent on the first oxygen signal and the second oxygen signal (O2 lin ;O2 bin ) characteristic curve (K), Characterized in that, according to the second oxygen signal (O2 bin ) and the characteristic curve (K) to obtain the relevant parameters (O2 kor ), Wherein, the first oxygen signal and the related parameters (O2 kor ), and performing diagnosis / self-diagnosis on the NOx sensor (34) based on the acquired difference (D).

2. The method according to claim 1, characterized in that If the difference value (D) obtained exceeds a predeterminable upper threshold value (S o ) or below the lower threshold (S u ), a faulty NOx sensor (34) is identified.

3. The method according to claim 1, characterized in that If the difference value (D) obtained is below a predeterminable upper threshold value (S o ) or exceeds the lower threshold (S u ), then a NOx sensor (34) that can operate normally is identified.

4. The method according to claim 1, wherein The activation of the self-diagnosis is permitted if an operating state for the internal combustion engine with an air-fuel ratio (λ) close to the value 1 exists, in particular a steady-state or quasi-steady-state state for the internal combustion engine (10). 5 . Computer program designed to carry out the method according to claim 1 .

6. Electronic storage medium having a computer program according to claim 5.

7. A device, in particular a control unit (16), which is configured to carry out the method according to claim 1.

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