Method for determining the state parameters of exhaust gas sensors

Abstract

The present invention relates to a method for determining state parameters of an exhaust gas sensor (10), the exhaust gas sensor having a sensor element (12) and a heating device (60) arranged in the sensor element (12) for heating the sensor element (12). The heating device (60) includes a heating section (62) arranged in the sensor element (12), the heating section being electrically connected via a first electrical line (64) and a second electrical line (66) to a control device for electrically operating the heating section (62). The heating device (60) further includes a measuring line (68) electrically connected between the control device and the first electrical line (64), by means of which the temperature-dependent resistance of the heating section (62) can be controlled. The method according to the invention includes determining a measuring voltage drop between the first electrical line (64) and the measuring line (68), determining a compensation voltage based on a predetermined reference voltage and the determined measuring voltage, and determining the state parameters of the exhaust gas sensor (10) by allocating the determined compensation voltage to the state parameters.

Description

Technical Field

[0001] The present invention relates to a method for determining state parameters of an exhaust gas sensor, such as a nitrogen oxide sensor, and more particularly to a method for determining a calibrated nitrogen oxide value and / or temperature of a nitrogen oxide sensor element. Background Technology

[0002] Exhaust gas sensors, such as nitrogen oxide sensors, lambda sensors, and oxygen sensors, can be based on the ammeter principle, that is, on electrochemical methods used to quantitatively determine chemical substances. Specifically, a current is set at the electrodes of the exhaust gas sensor to create a time-constant electrochemical potential. For example, a nitrogen oxide sensor allows the measurement of nitrogen oxide concentration in the exhaust gas of an internal combustion engine, such as a gasoline or diesel engine. This, for example, enables optimal adjustment and diagnostics of the nitrogen oxide catalytic converter via engine control devices.

[0003] This exhaust gas sensor has a body made of a solid electrolyte, within which a cavity with assigned electrodes is disposed. Furthermore, a heating device is arranged within the body, configured to heat the body to and maintain at a predetermined operating temperature, for example, at approximately 850°C. Due to additional external heating, such as exhaust gas circulating through the sensor, the electrodes may become hotter than initially, potentially leading to an increased signal from the sensor, such as excessively high nitrogen oxide values.

[0004] Other exhaust gas sensors are known from CN 102 798 654 B, US 2019 / 0078491 A1, US 7 462 266 B2, US 2005 / 0029250 A1 and US 6 939 037 B2. Summary of the Invention

[0005] The objective of this invention is to describe a method for determining the state parameters of an exhaust gas sensor, by means of which the accuracy of the exhaust gas sensor can be improved at least partially.

[0006] This task is solved using the method according to independent claim 1. Advantageous embodiments are described in the dependent claims.

[0007] The core idea of ​​this invention is to determine the voltage drop between the electrical leads of the heating element in the exhaust gas sensor and the measuring circuit connected to those leads, and to compare this determined voltage drop with a predetermined reference voltage to determine a compensation voltage. The determined compensation voltage can then be used to determine the state parameters of the exhaust gas sensor by allocating it to state parameters. For example, the state parameters could be a compensation nitrogen oxide (NOx) value, which can be used to correct for NOx values ​​determined by the exhaust gas sensor. Alternatively or additionally, the state parameters could indicate the average temperature of the sensor element in the region of the electrical leads of the heating element.

[0008] In particular, the determined compensation voltage can be used to indicate the average temperature of the sensor element in the region of the electrical leads of the heating device, and based on this average temperature, the housing temperature of the exhaust gas sensor can be determined. An increase in the average temperature of the sensor element in the region of the electrical leads of the heating device and / or an increase in the housing temperature can lead to distortion of the measurement accuracy of the exhaust gas sensor. Specifically, the increased temperature in the lead region may interfere with heat transfer from the heating section of the heating device to the tip of the sensor element where it is positioned. This can alter the temperature profile at the tip of the sensor element, which is very difficult to compensate for. However, this altered temperature profile may cause the pump electrode, positioned closer to the tip of the sensor element, to be colder than the measuring electrode. This can result in the aforementioned measurement error in the detected nitrogen oxide concentration.

[0009] Therefore, the average temperature of the sensor element in the region of the electrical leads of the heating device can be determined using the determined compensation voltage, thereby compensating for the distorted measurement value of the exhaust gas sensor. Therefore, according to a first aspect of the invention, a method for determining the state parameters of an exhaust gas sensor is disclosed, the exhaust gas sensor having a sensor element and a heating device arranged in the sensor element for heating the sensor element. The heating device includes a heating section arranged in the sensor element, the heating section being electrically connected via a first electrical line and a second electrical line to a control device for electrically controlling the heating section. The heating device further includes a measuring line electrically connected between the control device and the first electrical line, by means of which the temperature-dependent resistance of the heating section can be controlled. The method according to the invention includes determining a measured voltage drop between the first electrical line and the measuring line, determining a compensation voltage based on a predetermined reference voltage and the determined measured voltage, and determining the state parameters of the exhaust gas sensor by allocating the determined compensation voltage to the state parameters.

[0010] Preferably, the determined compensation voltage is assigned to the state parameters using an allocation table and / or allocation criteria, such as mathematical mapping. It may be advantageous that the allocation table has predetermined empirical values ​​under predetermined conditions, which assign the corresponding state parameters to the determined compensation voltage.

[0011] Advantageously, determining the compensation voltage involves determining the difference between a predetermined reference voltage and a determined measured voltage. Here, the predetermined reference voltage preferably corresponds to the measured voltage that drops between the first circuit and the measuring circuit at a predetermined temperature of the sensor element and during the thermally stable operation of the exhaust gas sensor. The predetermined temperature is preferably room temperature of about 20°C.

[0012] In a particularly preferred embodiment of the method according to the invention, the state parameter is a compensated nitrogen oxide (NOx) value. Preferably, the method further includes determining a corrected NOx value while taking into account the compensated NOx value. Preferably, determining the corrected NOx value includes determining the NOx value using an exhaust gas sensor and determining the corrected NOx value by subtracting the compensated NOx value from the determined NOx value. In particular, this can at least partially compensate for any deviation in the NOx value.

[0013] Alternatively, the state parameter can be the average temperature of the section of the sensor element surrounding the first circuit, the second circuit, and the measuring circuit.

[0014] The exhaust gas sensor further includes a housing in which the sensor element, along with a heating device, is arranged. Preferably, the method according to the invention further includes determining the temperature of the housing based at least in part on the average temperature of the section of the sensor element surrounding the first electrical line, the second electrical line, and the measuring line.

[0015] Based on the determined temperature of the housing, it is preferable to determine the state of the exhaust gas sensor, in which it may be advantageous to shut it off to protect the housing components from overheating. For example, an increased temperature of the housing may cause a possible seal at the electrical connection plug to no longer seal as intended. Instead of shutting off the exhaust gas sensor, it may be advantageous to output a warning signal indicating a faulty exhaust gas sensor with an insufficiently accurate exhaust gas signal. Attached Figure Description

[0016] Other features and objectives of the invention will become clear to those skilled in the art by practicing these teachings and considering the accompanying drawings, wherein:

[0017] Figure 1A schematic cross-sectional view is shown through an exhaust gas sensor for an internal combustion engine in a vehicle, exemplarily shown in the form of a nitrogen oxide sensor.

[0018] Figure 2 Showing the passage along line II-II Figure 1 A schematic cross-sectional view of the exhaust gas sensor, and

[0019] Figure 3 An exemplary flowchart of a method for determining a corrected nitrogen oxide value according to the present invention is shown. Detailed Implementation

[0020] Within the scope of this disclosure, sensors operating in an ammeter-like manner, such as nitrogen oxide sensors, lambdasonde probes, and oxygen sensors, are characterized in that their measurement principle is based on current analysis, i.e., on electrochemical methods for quantitatively determining chemical substances. In particular, a current is set at the working electrode such that a time-constant electrochemical potential is achieved.

[0021] Furthermore, within the scope of this disclosure, the term "control" includes both the terms "control" and "regulation" related to regulatory control techniques. Those skilled in the art will recognize, respectively, when control using regulatory control techniques can be applied and when regulation using regulatory control techniques can be applied.

[0022] Figure 1 An exemplary nitrogen oxide sensor 10 is shown, which exemplarily represents an exhaust gas sensor. Therefore, the invention is also contemplated for use in all sensors for internal combustion engines in vehicles, such as λ probes and oxygen sensors, which have heating devices. In particular, the invention can be applied to exhaust gas sensors comprising a ceramic substrate having electrode pairs mounted thereon.

[0023] refer to Figure 1 The diagram shows a schematic cross-sectional view of an exemplary nitrogen oxide sensor 10, which is configured to be arranged in the exhaust manifold of an internal combustion engine (not shown) and to quantitatively detect the nitrogen oxide content or oxygen content in the exhaust gas of the internal combustion engine.

[0024] The nitrogen oxide sensor 10 has a body 12 made of a solid electrolyte, which is preferably composed of a mixed crystal made of zirconium oxide and yttrium oxide and / or a mixed crystal made of zirconium oxide and calcium oxide. Alternatively, a mixed crystal made of hafnium oxide, a mixed crystal made of perovskite-based oxides, or a mixed crystal made of trivalent metal oxides, such as aluminum oxide (Al₂O₃), can be used. The body 12 constitutes the sensor element of the exhaust gas sensor 10. Therefore, the body 12 is also referred to below as sensor element 12.

[0025] The exemplary nitrogen oxide sensor 10 has a first pump chamber 20, a second pump chamber 30, and a measuring chamber 40 disposed within its body 12. The first pump chamber 20 is connected to the outside of the body 12 via a connection path 15. In particular, exhaust gas can flow into the first pump chamber 20 through the connection path 15. The second pump chamber 30 is connected to the first pump chamber 20 via a first diffusion path 25.

[0026] The measuring chamber 40 is connected to the second pump chamber 30 via the second diffusion path 35.

[0027] A reference cavity 50 is further formed within the main body 12, which is directly connected to the outside of the main body 12. A reference electrode 52 is arranged within the reference cavity 50. In particular, the reference cavity 50 is connected to the outside air, i.e., not to exhaust gas, and is configured to provide an oxygen reference for the various electrodes arranged in the nitrogen oxide sensor 10.

[0028] The exhaust gas electrode 22 is disposed on the outside of the body 12. In particular, during the measurement operation of the nitrogen oxide sensor 10, by applying a reference current to the exhaust gas electrode 22, oxygen in the exhaust gas can be ionized and diffused through the body 12 as oxygen ions to the reference electrode 52, where it is converted back into oxygen molecules to construct an oxygen reference.

[0029] The first pump electrode 24 is disposed within the first pump chamber 20. Specifically, during the measurement operation of the nitrogen oxide sensor 10, by applying a first pump current IP0 at the first pump electrode 24, oxygen in the exhaust gas can be ionized within the first pump chamber 20 and migrate or pass through the body 12 as oxygen ions. Due to the oxygen ions emitted from the first pump chamber 20, a first electrode voltage or first Nernst voltage V0 is indirectly formed between the first pump electrode 24 and the reference electrode 52. More precisely, the first electrode voltage or first Nernst voltage V0 is directly constituted by the residual oxygen still present in the first pump chamber 20.

[0030] The second pump electrode 34 is disposed within the second pump chamber 30. Here, during the measurement operation of the nitrogen oxide sensor 10, by applying a second pump current IP1 at the second pump electrode 34, oxygen in the gas mixture can be ionized within the second pump chamber 30 and migrate or pass through the body 12 as oxygen ions. Due to the oxygen ions emitted from the second pump chamber 30, a second electrode voltage or second Nernst voltage V1 is indirectly formed between the second pump electrode 34 and the reference electrode 52. More precisely, the second electrode voltage or second Nernst voltage V1 is directly constituted by the residual oxygen still present in the second pump chamber 30.

[0031] A measuring electrode 44 is arranged within a measuring chamber 40. This measuring electrode is configured to ionize oxygen and / or nitrogen oxides present in the measuring chamber 40 during the measurement operation of the nitrogen oxide sensor 10, when a measuring current IP2 is applied, allowing oxygen ions to migrate or pass through the body 12. Due to the oxygen ions emitted or pumped from the measuring chamber 40, a third electrode voltage or third Nernst voltage V2 is formed between the measuring electrode 44 and the reference electrode 52. This third electrode voltage or third Nernst voltage is maintained at a constant value by applying the measuring current IP2 at the measuring electrode 44. More precisely, the third electrode voltage or third Nernst voltage V2 is directly constituted by the residual oxygen still present in the measuring chamber 40. The applied measuring current IP2 then serves as an indicator of the nitrogen oxide content in the exhaust gas.

[0032] Therefore, an exemplary representation of a sensor based on the ammeter measurement principle is shown in... Figure 1 The nitrogen oxide sensor 10 shown has three associated electrode pairs: a first electrode pair consisting of a first pump electrode 24 and an exhaust gas electrode 22, a second electrode pair consisting of a second pump electrode 34 and an exhaust gas electrode 22, and a third electrode pair consisting of a measuring electrode 44 and an exhaust gas electrode 22.

[0033] The pump currents IP0 and IP1 applied to the first and second pump electrodes 24 and 34 are configured such that preferably only oxygen is ionized, while nitrogen oxides are not ionized. Specifically, the first pump electrode 24 is configured to pump almost all oxygen from the exhaust gas during normal operation of the nitrogen oxide sensor 10, or to allow a predetermined oxygen flow from the first pump chamber 20 to the second pump chamber 30. The second pump electrode 34 is configured to ionize and expel oxygen not yet pumped from the first pump chamber 20, such that almost only nitrogen oxides are present in the measuring chamber 40. The measuring electrode 44 is configured to ionize nitrogen oxides, wherein the measuring current IP2 applied at the measuring electrode 44 is a measure of the nitrogen oxide content in the exhaust gas.

[0034] In addition, a heating device 60 is arranged inside the main body 12, which is configured to heat the main body 12 to a predetermined operating temperature and maintain it at that operating temperature, for example, at about 850°C.

[0035] The operating method for determining the nitrogen oxide content in the exhaust gas of an internal combustion engine using the disclosed nitrogen oxide sensor 10 is known from the prior art, and reference is made to that prior art. That is... Figure 1 The control principle of the regulation and control technology of the nitrogen oxide sensor 10 is characterized by maintaining the corresponding electrode voltages or Nernst voltages V0, V1, V2 at a constant level by applying and adapting pump currents IP0, IP1 and measuring current IP2.

[0036] Figure 2 Showing the passage along line II-II Figure 1 A cross-sectional view of the exhaust gas sensor 10. Figure 2 As can be seen, the heating device 60 is fully embedded in and arranged within the sensor element 12 and has a heating section 62 configured to heat the sensor element 12. This heating section 62 is electrically connected via a first electrical line 64 and a second electrical line 66 to a control device (not explicitly shown) for electrically operating the heating section 62. Figure 2 In the diagram, the heating section 62 is shown separated from the first electrical line 64 and the second electrical line 66 by a dashed line. Specifically, the heating section 62 is a heating spiral filament configured to heat the sensor element 12 to an operating temperature of approximately 850°C, particularly in the vicinity of the first pump chamber 20, the second pump chamber 30, and the second measuring chamber 40. Therefore, electrodes 24, 34, and 44 (see...) Figure 1 Thus, it is also heated accordingly.

[0037] Additionally, the heating device 60 has an electrical measuring line 68 electrically connected between the control device and the first electrical line 64. The measuring line 68 is particularly a high-resistance line (approximately 6 ohms) relative to the first line (approximately 0.4 ohms) and the second line (approximately 0.4 ohms), bridging the heating section 62 and configured to control the resistance or operating temperature of the sensor element 12 in the region of the heating section 62. Specifically, the resistance of the heating section 62 can be determined by resistance measurement between the first line 64 and the measuring line 68, or by resistance measurement between the second line 66 and the measuring line 68, so as to control the heating energy electrically supplied to the heating section 62 for heating the sensor element 12 to a predetermined rated temperature. The heating section 62 is particularly arranged in the end region 13 of the sensor element.

[0038] In additional reference Figure 3 In such cases, an exemplary method for determining the corrected nitrogen oxide value according to the present invention is described below.

[0039] Figure 3The method begins at step 100 and then proceeds to step 110, where the measured voltage drop between the first line 64 and the measuring line 68 is determined. In the subsequent step 120, a compensation voltage is determined based on a predetermined reference voltage and the determined measured voltage. The predetermined reference voltage is, for example, the measured voltage drop between the first line 64 and the measuring line 68, which drops between the two lines 64, 68 at a predetermined (known) temperature of the sensor element 12 (such as room temperature at approximately 20°C). In particular, at step 120, the compensation voltage is determined by constituting the difference between the predetermined reference voltage and the determined measured voltage.

[0040] In another step 130, the compensation nitrogen oxide value is determined by assigning the determined compensation voltage to the compensation nitrogen oxide value. This can be done, for example, according to an allocation table that assigns the determined compensation voltage to the corresponding compensation nitrogen oxide value. Alternatively, the allocation can be performed using a mathematical mapping.

[0041] In another step 140, the nitrogen oxide value detected by the exhaust gas sensor 10 as the measuring current IP2 is then corrected to a corrected nitrogen oxide value, taking into account the determined compensated nitrogen oxide value. Here, in particular, the determined compensated nitrogen oxide value, indicated by the measuring current IP2, is subtracted from the nitrogen oxide value detected by the exhaust gas sensor 10.

[0042] According to another method according to the invention, replacing or adding to Figure 3 Step 130 involves performing a method step in which the corresponding sensor element temperature value for the region surrounding the circuit lines 64, 66, 68 of the sensor element 12 is assigned to the determined compensation voltage. In another step, the temperature of the (not explicitly shown) housing of the exhaust gas sensor 10 can be estimated from the thus determined sensor element temperature value. The determined nitrogen oxide value of the exhaust gas sensor 10 can then be compensated based on the determined average temperature of the region surrounding the circuit lines 64, 66, 68 of the sensor element 12 and / or based on the determined housing temperature.

[0043] Therefore, the nitrogen oxide offset, which may be due to increased temperature in the regions of the circuits 64, 66, 68 of the sensor element 12, can be at least partially compensated by the method according to the invention. In particular, the exhaust gas from the circulating exhaust gas sensor 10 may cause an increase in temperature in the aforementioned regions of the sensor element 12. The hot exhaust gas can increase the temperature of the housing of the exhaust gas sensor 10, which in turn may cause the regions of the sensor element 12 surrounding the circuits 64, 66, 68 to heat up via convection and conduction. Furthermore, heated exhaust pipes and other external heat sources, such as turbochargers and exhaust manifolds, may cause an increase in the temperature of the housing of the exhaust gas sensor 10, which may in turn affect the measurement accuracy of the exhaust gas sensor (see above). Due to the increased temperature of the sensor element 12 of the exhaust gas sensor 10, less temperature may be dissipated from the measurement area in front of the sensor element 12 compared to normal operation or a new state of the exhaust gas sensor 10, which may cause a shift in the temperature profile of the electrodes of the exhaust gas sensor 10. Due to the increased temperature of measuring electrode 44, the measuring current IP2 may become larger, and therefore the NOx signal may be larger than it actually is.

Claims

1. A method for determining state parameters of an exhaust gas sensor (10), the exhaust gas sensor having a sensor element (12) and a heating device (60) disposed in the sensor element (12) for heating the sensor element (12), wherein the heating device (60) has a heating section (62) disposed in the sensor element (12), the heating section being electrically connected via a first electrical line (64) and a second electrical line (66) to a control device for electrically controlling the heating section (62), wherein the heating device (60) further has a measuring line (68) electrically connected between the control device and the first electrical line (64), by means of which the temperature-dependent resistance of the heating section (62) can be controlled, wherein the method comprises: - Determine the measured voltage that drops between the first circuit (64) and the measuring circuit (68). - The compensation voltage is determined based on a predetermined reference voltage and a determined measurement voltage, and - The state parameters of the exhaust gas sensor (10) are determined by assigning a determined compensation voltage to the state parameters, wherein the state parameters can be the compensation nitrogen oxide value or the average temperature of the sensor element in the region of the electrical leads of the heating device.

2. The method of claim 1, wherein the determined compensation voltage is assigned to the state parameters by means of an allocation table and / or allocation criteria.

3. The method according to claim 1 or 2, wherein determining the compensation voltage comprises: - Determine the difference between the predetermined reference voltage and the determined measurement voltage.

4. The method according to claim 1 or 2, wherein the predetermined reference voltage corresponds to the measurement voltage that drops between the first electrical line (64) and the measurement line (68) at a predetermined temperature of the sensor element (12).

5. The method according to claim 4, wherein the predetermined temperature corresponds to room temperature of about 20°C.

6. The method according to claim 1 or 2, wherein the state parameter is a compensated nitrogen oxide value, and wherein the method further comprises: - Determine the corrected nitrogen oxide value while taking into account the compensated nitrogen oxide value.

7. The method of claim 6, wherein determining the corrected nitrogen oxide value comprises: - The nitrogen oxide value is determined by means of the exhaust gas sensor (10), and - The corrected nitrogen oxide value is determined by subtracting the compensated nitrogen oxide value from the determined nitrogen oxide value.

8. The method according to claim 1 or 2, wherein the state parameter is the average temperature of the section of the sensor element (12) surrounding the first electrical line (64), the second electrical line (66) and the measuring line (68).

9. The method according to claim 8, wherein the exhaust gas sensor (10) further has a housing, the sensor element (12) together with the heating device (60) is arranged in the housing, and the method further comprises: The temperature of the housing is determined at least in part based on the average temperature of the section of the sensor element (12) surrounding the first electrical line (64), the second electrical line (66), and the measuring line (68).

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