WO2020260330A1

WO2020260330A1 - Method for the operation of an exhaust gas sensor for an internal combustion engine, and exhaust gas sensor for an internal combustion engine

Info

Publication number: WO2020260330A1
Application number: PCT/EP2020/067584
Authority: WO
Inventors: Sebastian Reiß
Original assignee: Vitesco Technologies GmbH
Priority date: 2019-06-28
Filing date: 2020-06-24
Publication date: 2020-12-30
Also published as: DE102019209456B3

Abstract

The present invention relates to a method for operating an exhaust gas sensor (100) for an internal combustion machine and an exhaust gas sensor for an internal combustion engine. The exhaust gas sensor (100) comprises a main body (112), a first pump cavity (120) arranged in the main body (112), in which first pump cavity there is arranged a first pump electrode (124), a second pump cavity (220) arranged in the main body (112), in which second pump cavity there is arranged a second pump electrode (224), and a reference cavity (50) arranged in the main body (112), in which reference cavity there is arranged a reference electrode (52). The method according to the invention comprises the steps of determining the oxygen content in the exhaust gas from the internal combustion engine, determining a target voltage value for the second electrode voltage (V3) that forms between the second pump electrode (224) and the reference electrode (52), and controlling the pump current (IP3) applied to the second pump electrode (224) in such a way that the second electrode voltage (V3) forms with the determined target voltage value between the second pump electrode (224) and the reference electrode (52).

Description

description

Method for operating an exhaust gas sensor for an internal combustion engine and an exhaust gas sensor for an internal combustion engine

The present invention relates to a method for operating an exhaust gas sensor for an internal combustion engine and an exhaust gas sensor for an internal combustion engine, in particular a method for determining a voltage setpoint for an electrode voltage of the exhaust gas sensor, in particular an exhaust gas sensor for detecting the nitrogen oxide and / or ammonia content in the exhaust gas

Internal combustion engine.

Exhaust sensors, such as B. nitrogen oxide sensors allow a measurement of the

Concentration of components in the exhaust gas of internal combustion engines,

for example gasoline or diesel engines. The components of the exhaust gas from the internal combustion engine include Ammonia (NH3) and nitrogen oxides (NOx), knowledge of the respective concentration for controlling the internal combustion engine, in particular the exhaust gas aftertreatment device, can be advantageous.

For this purpose, DE 10 2007 035 768 A1 discloses a method for diagnosing an engine that is arranged in an exhaust system of an internal combustion engine

Nitrogen oxide sensor, the at least one setting device for setting the oxygen content of exhaust gas that has entered the sensor by means of a

electrical variable and at least one measuring device outputting a measurement value characterizing the nitrogen oxide content of the exhaust gas.

Furthermore, DE 697 32 582 T2 discloses a method and a device for measuring the oxygen concentration and the nitrogen oxide concentration

Use of a nitrogen oxide sensor known.

In addition, DE 103 12 732 B4 discloses a method for operating a measuring probe for measuring a gas concentration in a measuring gas with a

Oxygen ion-conducting solid electrolyte, which has a measuring cavity for receiving the Has measuring gas, a measuring electrode and an outer electrode. A pump current flowing between the measuring electrode and the outer electrode is transported

Oxygen ions from the measuring electrode to the outer electrode. This is a check of the measuring electrode by a determination of the effective for the

Oxygen diffusion available electrode area or a value dependent thereon is carried out by setting a predetermined oxygen concentration in the measuring cavity, impressing a predetermined constant pump current between the measuring electrode and the outer electrode and measuring the resulting Nernst potential at the measuring electrode, the time until the measured Nernst potential is measured jumps from small to large values, the measured time period is compared with a predetermined threshold value and a defect in the measuring electrode is detected when the measured time period falls below the predetermined threshold value.

WO 2017/222001 A1, WO 2017/222002 A1 and WO 2017/222003 A1 each disclose nitrogen oxide sensors that are provided with a pre-cavity in which a pre-electrode is provided. By controlling the pump electrode and the pre-electrode, the ammonia content in the exhaust gas can be qualitatively determined

Internal combustion engine are determined.

DE 10 2009 036 060 A1 relates to a method for determining a

NOx raw emissions from an internal combustion engine that can be operated with exhaust gas recirculation.

DE 10 201 1 003 514 A1 relates to a method for monitoring a function of a chemoresistive field effect transistor, in which an optimal setting of its operating point is to be achieved

Changes in the concentration of the substance to be detected to obtain the greatest possible change in the current.

In view of the prior art, it is an object of the present invention to provide a method for operating an in an exhaust line of a

Internal combustion engine arranged exhaust gas sensor to provide with which the Detection of the relevant exhaust gas parameters, in particular the nitrogen oxide and / or ammonia content, can be detected as precisely as possible.

This object is with a method according to claim 1 and a

Exhaust gas sensor according to claim 10 solved. Further advantageous refinements are given in the subclaims.

The present invention is essentially based on the idea of dynamically adapting the voltage setpoint for an electrode voltage of an exhaust gas sensor as a function of the prevailing oxygen content and / or water content in the exhaust gas of the internal combustion engine. In particular, the

Voltage setpoint of that electrode voltage dynamically adjusted, which is achieved by applying a pump current to pump out ionized oxygen from the exhaust gas sensor at the corresponding pump electrode and a

Reference electrode, which is in contact with the ambient air, forms. Thus, the entire operation of the exhaust gas sensor can be optimized, above all

with regard to the measurement accuracy of the exhaust gas parameters, such as the nitrogen oxide content and / or the ammonia content in the exhaust gas

Internal combustion engine.

Consequently, according to a first aspect of the present invention, a method for operating an exhaust gas sensor, which has a main body and is arranged in an exhaust system of an internal combustion engine, is disclosed, which has a first pump cavity arranged in the main body and connected to the exhaust gas, in which a first pump electrode is arranged, an im A second pump cavity arranged in the main body and connected to the exhaust gas, in which a second pump electrode is arranged, and a reference cavity arranged in the main body and connected to the ambient air, in which a reference electrode is arranged. The method according to the invention comprises determining the oxygen content in the exhaust gas of the internal combustion engine, determining a voltage setpoint value for the second that is formed between the second pump electrode and the reference electrode on the basis of a pump current applied to the second pump electrode

Electrode voltage as a function of the determined oxygen content and / or Water content and controlling the pump current applied to the second pump electrode in such a way that the second electrode voltage is determined between the second pump electrode and the reference electrode

Voltage setpoint forms.

Because the voltage setpoint for the second electrode voltage is dynamically adapted as a function of the determined oxygen content and / or water content during operation of the internal combustion engine

For example, the ammonia content and / or nitrogen oxide content in the exhaust gas can be determined even more precisely. By suitably adapting the voltage setpoint for the second electrode voltage, the

Internal combustion engine and thus different exhaust gas compositions an optimal separability between the nitrogen oxide and ammonia content can be guaranteed.

The oxygen content in the exhaust gas of the internal combustion engine is preferably determined based on a first pump current applied to the first pump electrode to keep a first electrode voltage constant between the first pump electrode and the reference electrode. Alternatively, the oxygen content in the exhaust gas of the internal combustion engine is determined based on the oxygen signal of a separate lambda probe arranged in the exhaust gas line of the internal combustion engine. As an even further alternative, the oxygen content in the exhaust gas of the internal combustion engine is determined based on the signal from a separate exhaust gas sensor arranged in the exhaust gas line of the internal combustion engine.

In a further preferred embodiment of the method according to the invention, the nominal voltage value for the second electrode voltage increases with increasing oxygen content. The desired chemical reactions at the electrode essentially take place at low oxygen partial pressures. In order to ensure sufficient dwell time at the electrode under favorable conditions when the oxygen content is high when the gas enters, it is advantageous to control or regulate to a higher average electrode voltage at the second pump electrode. In a further preferred embodiment, the inventive

The method further comprises determining the water content in the exhaust gas

Internal combustion engine, wherein the determination of the first voltage setpoint is carried out at least partially based on the determined water concentration in the exhaust gas. The water content can preferably be determined by comparing the two pump currents at the first and second electrodes. Depending on the water content in the exhaust gas, the ratio of the pump currents changes due to the water breakdown at the electrodes.

By taking into account the water content in the exhaust gas, the measurement accuracy of the exhaust gas sensor can be further improved, since the water content in the exhaust gas also influences the chemical reaction equilibrium of the ammonia reactions.

As with the oxygen-dependent readjustment of the target voltage, the differentiation between nitrogen oxide and ammonia effects is improved and the sensitivity increased.

In a further preferred embodiment of the method according to the invention, the exhaust gas sensor furthermore has a first measuring cavity, arranged in the main body and connected to the first pump cavity, in which a first measuring electrode is arranged, and one arranged in the main body and with the second

Pump cavity connected to the second measuring cavity, in which a second measuring electrode is arranged. In this preferred embodiment, the method according to the invention further comprises controlling a pump current applied to the first pump electrode in such a way that a first electrode voltage that forms between the first pump electrode and the reference electrode is reduced to a

predetermined further voltage setpoint value is kept constant, and determining a first nitrogen oxide value based on one of the first

First measuring current applied to the measuring electrode, a control of the second pump current applied to the second pump electrode in such a way that the second pump current which is formed between the second pump electrode and the reference electrode

Electrode voltage is kept constant at the determined voltage setpoint, and determining a second nitrogen oxide value based on one of the second measuring current applied to the second measuring electrode, and determining the ammonia content in the exhaust gas of the internal combustion engine based on the determined first nitrogen oxide value and the determined second nitrogen oxide value.

In a further alternative preferred embodiment of the method according to the invention, the exhaust gas sensor furthermore has a measuring cavity which is arranged in the main body and connected to the first and second pump cavities and in which a measuring electrode is arranged. In such an alternative preferred

In an embodiment, the method according to the invention also includes controlling a first pump current applied to the first pump electrode in such a way that a first electrode voltage that forms between the first pump electrode and the reference electrode is kept constant at a predetermined further voltage setpoint value, and a first nitrogen oxide value is determined based on a the first measuring current applied to the measuring electrode, controlling the second pump current applied to the second pump electrode in such a way that the second electrode voltage that forms between the second pump electrode and the reference electrode is kept constant at the determined voltage setpoint, and determining a second nitrogen oxide value based on one at the measuring electrode applied second measurement current, and determining the

Ammonia content in the exhaust gas of the internal combustion engine based on the determined first nitrogen oxide value and the determined second nitrogen oxide value.

According to a further aspect of the present invention, an exhaust gas sensor to be arranged in the exhaust system of an internal combustion engine is disclosed. The exhaust gas sensor has a main body, a first pump electrode which is assigned to a first pump cavity connected to the exhaust gas and provided in the main body, a second pump electrode which is assigned to a pump cavity connected to the exhaust gas and provided in the main body, and a control unit which is connected to the first pump electrode and the second pump electrode is connected and configured to carry out a method according to the present disclosure. Other features and objects of the invention will become apparent to those skilled in the art by practicing the present teachings and reviewing the accompanying drawings, in which:

1 shows a schematic sectional view through an exhaust gas sensor according to an exemplary first embodiment,

2 shows a schematic sectional view through an exhaust gas sensor according to an exemplary second embodiment,

Fig. 3 shows a diagram in which curves are entered which the

Electrode voltage versus the pump currents of the exhaust gas sensor for a predetermined nitrogen oxide content and a predetermined one

Represent ammonia content with a low oxygen content in the exhaust gas,

Fig. 4 shows a diagram in which curves are plotted that the

Represent ammonia content with an oxygen content in the exhaust gas that is higher than that in FIG. 3, and

5 shows an exemplary flow chart of a method according to the invention for operating an exhaust gas sensor.

Elements of the same construction or function are provided with the same reference symbols in all the figures.

In the context of the present disclosure, the term “control” includes the control-related terms “control” and “regulate”. The person skilled in the art will recognize when a technical control control and when a

regulatory rules are to be applied. With reference to FIG. 1, a schematic sectional view through an exhaust gas sensor 100 according to an exemplary first embodiment is shown, which is designed to be arranged in an exhaust line of an internal combustion engine (not shown) and to contain nitrogen oxide, ammonia and / or

Detect oxygen content in the exhaust gas of the internal combustion engine.

The exhaust gas sensor 100 has a main body 112 made of a solid electrolyte, which is preferably formed from a mixed crystal of zirconium oxide and yttrium oxide and / or by a mixed crystal of zirconium oxide and calcium oxide. In addition, a mixed crystal made from hafnium oxide, a mixed crystal made from

Perovskite-based oxides or a mixed crystal of trivalent metal oxide can be used.

Two measurement paths 110, 210 are provided within the main body 112, which are essentially independent of one another and which are each connected to the exhaust gas. The first measuring path 110 has a first cavity 130, a first pump cavity 120 and a first measuring cavity 140. The first cavity 130 is connected to the exterior of the main body 112 via a first connecting path 115. In particular, exhaust gas can enter the first cavity 130 through the first connecting path 115. The first pump cavity 120 is connected to the first cavity 130 via a first diffusion path 125. The first diffusion path 125 is provided, for example, in the form of a very thin slit through which the gas mixture can pass at a predetermined rate. Alternatively, the first diffusion path 125 may be filled with a porous filler to form a

Diffusion rate regulation layer be filled or padded.

The first measuring cavity 140 is connected to the first pump cavity 120 via a second diffusion path 135. The second diffusion path 135 is provided, for example, in the form of a very thin slit through which the gas mixture can pass at a predetermined rate. Alternatively, the second diffusion path 135 may be filled with a porous filler to form a

Diffusion rate regulation layer be filled or padded. The Diffusion rate layers can alternatively be referred to as diffusion barriers.

The first diffusion path 125 and the second diffusion path 135 are designed such that the gas mixture can only partially pass through them. By knowing the cross sections of the first and second diffusion path 125, 135 and / or by knowing the respective porous filler, the

Diffusion rate through the first and second diffusion path 125, 135 can be determined and established.

In an alternative embodiment of the exhaust gas sensor 100, the first

Measurement path 110 only has the first pump cavity 120 and the first measurement cavity 140, which is connected to the first pump cavity 120 via the second diffusion path 135. In such an alternative embodiment of the exhaust gas sensor 100, the first pump cavity 120 is then connected to the exhaust gas via a connection path which corresponds to the path through the first connection path 115, the first cavity 130 and the first diffusion path 125 of the exhaust gas sensor 100 of FIG. 1. In such an alternative embodiment of the exhaust gas sensor 100, the exhaust gas from the exhaust line can enter the first pump cavity 120 directly through this connecting path.

The second measuring path 210 has a second pump cavity 220, a second cavity 230 and a second measuring cavity 240. The second pump cavity 220 is connected to the exterior of the main body 112 via a second connection path 215. In particular, exhaust gas can enter the second pump cavity 220 through the second connection path 215. The second cavity 230 is connected to the second pump cavity 220 via a third diffusion path 225. The third diffusion path 225 is provided, for example, in the form of a very thin slit through which the gas mixture can pass at a predetermined rate. Alternatively, the third diffusion path 225 may be filled with a porous filler to form a

Diffusion rate regulation layer be filled or padded. The second measuring cavity 240 is connected to the second cavity 230 via a fourth diffusion path 235. The fourth diffusion path 235 is provided, for example, in the form of a very thin slit through which the gas mixture can pass at a predetermined rate. Alternatively, the fourth diffusion path 235 may be filled with a porous filler to form a

Diffusion rate regulation layer be filled or padded. The

Diffusion rate layers can alternatively be referred to as diffusion barriers.

The third diffusion path 225 and the fourth diffusion path 235 are designed such that the gas mixture can only partially pass through them. By knowing the cross sections of the third and fourth diffusion paths 225, 235 and / or by knowing the respective porous filler, the

Diffusion rate through the third and fourth diffusion path 225, 235 can be determined and set.

In an alternative embodiment of the exhaust gas sensor 100, the second

Measurement path 210 only has the second pump cavity 220 and the second measurement cavity 240, which is connected to the second pump cavity 220 via a diffusion path which corresponds to the path through the third diffusion path 225, the second cavity 230 and the fourth diffusion path 235 of the exhaust gas sensor 100 of FIG. 1 corresponds. In such an alternative embodiment of the exhaust gas sensor 100, the exhaust gas can flow from the second pump cavity 220 through this diffusion path directly into the second

Enter measurement cavity 240.

In addition, a reference cavity 50 is formed in the flake body 112, which is directly connected to the exterior of the flake body 12. Within the

A reference electrode 52 is arranged in the reference cavity 50. In particular, the reference cavity 50 is in contact with the ambient air, i.e. H. does not come into contact with the exhaust gas and is designed to provide an oxygen reference for the im

To form the main body 1 12 of the exhaust gas sensor 100 arranged different electrodes. An exhaust gas electrode (also called “P +” electrode) 22 that is in contact with the exhaust gas is arranged on an outside of the main body 112.

In particular, during a measuring operation of the exhaust gas sensor 100 by applying a reference current to the exhaust gas electrode 22, the oxygen in the exhaust gas can be ionized or converted and diffuse through the main body 112 as oxygen ions to the reference electrode 52 and there again

Oxygen molecules are converted to form an oxygen reference.

A first pump electrode (also called “P -” electrode) 124 is arranged within first pump cavity 120. In particular, during the

Measurement operation of the exhaust gas sensor 100 by applying a first pump current IR0 to the first pump electrode 124, the oxygen in the exhaust gas can be converted or ionized within the first pump cavity 120 and through the

Main body 1 12 migrate or arrive or diffuse as oxygen ions. Because of the oxygen ions discharged from the first pump cavity 120, a first electrode voltage or first Nernst voltage V0 is indirectly formed between the first pump electrode 124 and the reference electrode 52. More precisely, the first electrode voltage or the first Nernst voltage V0 is formed directly from the residual oxygen still present in the immediate vicinity of the first pump electrode 124.

An oxygen concentration in the pump cavity 120 can be set with IR0; depending on the level of the set oxygen concentration, the nitrogen oxides can be reduced or the ammonia oxidized.

A first measuring electrode (also called first “M2” electrode) 144 is arranged within the first measuring cavity 140, which is designed to detect the oxygen and / or oxygen present within the first measuring cavity 140 when a first measuring current IP21 is applied during the measuring operation of the nitrogen oxide sensor 100 To ionize or convert nitrogen oxides so that the oxygen ions can migrate or get through the main body 112. Due to the oxygen ions discharged or pumped out of the first measuring cavity 140, a first one forms between the first measuring electrode 144 and the reference electrode 52 Measurement electrode voltage or first measurement Nernst voltage V21, which is kept at a constant value by applying the first measurement current IP21 to the first measurement electrode 144. More precisely, the first is formed

Measurement electrode voltage or the first measurement Nernst voltage V21 directly from the residual oxygen still present in the immediate vicinity of the first measurement electrode 144. The first measurement current IP21 applied is then an indication of the nitrogen oxide content within the exhaust gas.

The first pump current IPO applied to the first pump electrode 124 is controlled in such a way that preferably only the oxygen is ionized or converted, but not the nitrogen oxides. For this purpose it is provided to control the first pump current IPO in such a way that the first electrode voltage or first Nernst voltage V0 is kept constant at a first voltage setpoint value, for example 220 mV. In particular, the first pump electrode 124 is designed to pump almost all of the oxygen from the exhaust gas during normal operation of the nitrogen oxide sensor 100, so that almost only nitrogen oxides are still present in the first measuring cavity 140. The first measuring electrode 144 is designed to the

To ionize or convert nitrogen oxides, the first measurement current IP21 applied to the first measurement electrode 144 being a measure of the nitrogen oxide content in the exhaust gas.

A second pump electrode (also called “M0” electrode) 224 is arranged within the second pump cavity 220. Here, during the measuring operation of the exhaust gas sensor 100, by applying a second pump current IP3 to the second pump electrode 224, the oxygen in the gas mixture can be ionized or converted within the second pump cavity 220 and through the

Main body 1 12 migrate or arrive or diffuse as oxygen ions. Due to the oxygen ions discharged from the second pump cavity 220, a second electrode voltage or second Nernst voltage V3 is indirectly formed between the second pump electrode 224 and the reference electrode 52. More precisely, the second electrode voltage or the second is formed

Nernst voltage V3 directly from the residual oxygen still present in the immediate vicinity of the second pump electrode 224. A second measuring electrode (also called a second “M2” electrode) 244 is arranged within the second measuring cavity 240, which is designed to detect the oxygen and / or oxygen present within the second measuring cavity 240 when a second measuring current IP22 is applied during the measuring operation of the nitrogen oxide sensor 100 To ionize or convert nitrogen oxides so that the oxygen ions can migrate or get through the main body 112. Due to the oxygen ions discharged or pumped out of the second measuring cavity 240, a second measuring electrode voltage or first measuring Nernst voltage V22 is formed between the second measuring electrode 244 and the reference electrode 52, which is generated by applying the second measuring current IP22 to the second measuring electrode 244 is kept constant. More precisely, the second is formed

Measuring electrode voltage or the second measuring Nernst voltage V22 directly from the residual oxygen still present in the immediate vicinity of the second measuring electrode 244. The first measurement current IP21 applied is then an indication of the nitrogen oxide content within the exhaust gas. The proportion of ammonia in the exhaust gas can then be determined from the applied second measurement current IP22 and the applied first measurement current IP21, in particular since the ammonia in the exhaust gas is present in the two measurement paths 110, 210

different points is oxidized and thus in each case before and after

Oxidation covers different diffusion distances

The second pump current IP3 applied to the second pump electrode 224 is set in such a way that preferably only the ammonia and oxygen present in the exhaust gas are ionized or converted. For this purpose, it is provided to control the second pump current IP3 in such a way that the second electrode voltage or second Nernst voltage V3 is kept constant at a second voltage setpoint value, for example 550 mV. In particular, the second pump electrode 224 is designed to pump almost all of the oxygen from the exhaust gas during normal operation of the nitrogen oxide sensor 100, so that in the second

Measurement cavity 240 is almost exclusively nitrogen oxides. The second measuring electrode 244 is designed to ionize or convert the nitrogen oxides, the second measuring current IP22 applied to the second measuring electrode 244 being a measure of the nitrogen oxide content in the exhaust gas. The different diffusion capacities of ammonia (NH3) and nitrogen oxide (NO) result from those based on the molar masses

Diffusion coefficients of ammonia and nitrogen. Since ammonia molecules are lighter than nitric oxide molecules, ammonia can get through better

Main body 1 12, d. H. through the diffusion paths 115, 125, 215, 225, diffuse as nitrogen oxide. The diffusion of ammonia and nitrogen oxide takes place in particular due to the concentration gradient between the several cavities.

Consequently, the ammonia present in the exhaust gas can in each case get better from the first cavity 130 into the first pump cavity 120 or from the second pump cavity 120 into the second cavity 230 than the nitrogen oxide present in the exhaust gas.

The exhaust gas sensor 100 according to the invention also has a control unit (not explicitly shown) which is connected to the first pump electrode 124, the exhaust gas electrode 22, the second pump electrode 224, the first measuring electrode 144, the second measuring electrode 244 and the reference electrode 52 and is designed to these electrodes each with the currents IR0, IP3, IP21 and IP22

apply and record the respective Nernst voltages V0, V3, V21 and V22. The control unit is thus designed to control the operation of the exhaust gas sensor 100. In addition, the control unit is designed to

To store voltage setpoints for the respective Nernst voltages V0, V3, V21 and V22 and to adapt them according to the present invention.

In further alternative configurations of the exhaust gas sensor 100, it can be advantageous to provide a further pump cavity between the first pump cavity 120 and the first measurement cavity 140, in which a further pump electrode is arranged, with which a further pump electrode may possibly come out of the first pump cavity 120

Oxygen can now be completely pumped out of the gas mixture. In a similar manner, it can be advantageous to provide a further pump cavity between the second cavity 230 and the second measuring cavity 240, in which a further pump electrode is arranged, with which any oxygen that may still come from the second pump cavity 220 is now completely removed from the

Gas mixture can be pumped out. Within the main body 1 12, a heating device 60 is also arranged, which is designed to the main body 1 12 to a predetermined

To heat the operating temperature and to keep it at this, for example at approx. 850 ° C. The heating device 60 can also be controlled and operated by the control unit.

FIG. 2 shows a schematic sectional view through an exhaust gas sensor 200 according to an exemplary second embodiment, which extends from

Exhaust gas sensor 100 of FIG. 1 differs in that only one measurement path 110 is present, which is from the second pump cavity 220 in which the second

Pump electrode 224 is arranged, the first pump cavity 120, in which the first pump electrode 124 is arranged, and the (first) measuring cavity 140, in which the (first) measuring electrode 144 is arranged, is formed. In the embodiment of the exhaust gas sensor according to FIG. 2, the two measuring paths 110, 210 are implemented in that the two pump electrodes 124, 224 are operated selectively and alternately. This means that in a first operating mode the first pump current IR0 is applied to the first pump electrode 124, the second pump electrode 224 being deactivated and the second pump cavity 220 thus representing the first cavity 130, and in a second operating mode the second pump current IP3 to the second pump electrode 224 is applied, the first

Pump electrode 124 is deactivated and thus first pump cavity 120 represents second cavity 230. The first measurement current IP21 is applied to the measurement electrode 144 in the first operating mode, the second measurement current IP22 being applied to the measurement electrode 144 in the second operating mode.

3 and 4 show diagrams in which two curves 302, 304, 402, 404 are entered, each showing the second electrode voltage V3 versus the first measurement current IP2 or IP21 / lp22 of the exhaust gas sensor 100 for a respectively predetermined nitrogen oxide content (curves 302, 402) and a respectively predetermined ammonia content (curves 304, 404) with a low oxygen content (FIG. 3) and a comparatively higher oxygen content (FIG. 4) in the exhaust gas. In particular, the diagrams of FIGS. 3 and 4 show characteristics of the

Exhaust gas sensor 100 and not just from one of the electrodes.

The curves 302, 304 of FIG. 3 were determined for an exemplary oxygen content of approximately 1% in the exhaust gas. The curve 302 shows the course of the first measurement current IP2 versus the second electrode voltage V3 in the presence of nitrogen oxide (for example approximately 250 ppm nitrogen oxide in the exhaust gas) and the simultaneous absence of ammonia (ie 0 ppm ammonia in the exhaust gas) and the curve 304 shows that Course of the second pump current IP3 compared to the second

Electrode voltage V3 in the absence of nitrogen oxide (i.e. 0 ppm nitrogen oxide in the exhaust gas) and the simultaneous presence of ammonia (e.g. approximately 250 ppm ammonia in the exhaust gas). The curves 402, 404 of FIG. 4 were each determined with the same nitrogen oxide or ammonia conditions in the exhaust gas, the

Oxygen content in the exhaust gas was greater than in FIG. 3, namely approximately 10%. The respective useful signal to differentiate between nitrogen oxide content and

The ammonia content in the exhaust gas is indicated in FIGS. 3 and 4 by the arrows 306, 406.

It can be seen from the diagrams in FIGS. 3 and 4 that the useful signal 406 of FIG. 4 has its maximum at a higher second electrode voltage V3 than in FIG. 3. Thus, the predefined second voltage setpoint for the second electrode voltage V3 is at the by creating the first

Measurement current IP21 at the first measurement electrode 144 is to be controlled or regulated, depending on the oxygen content present in the exhaust gas. The present invention makes use of this knowledge in that the second voltage setpoint value is dynamically adapted as a function of the currently present oxygen content in the exhaust gas so that the nitrogen oxide content and ammonia content in the exhaust gas can be determined even more precisely. For example, the second voltage setpoint is approximately 500 mV with an oxygen content of approximately 3% (see FIG. 3) and approximately 550 mV with an oxygen content of approximately 10% (see FIG. 4). As a result, the voltage setpoint for the second rises

Electrode voltage V3 increases with increasing oxygen content. FIG. 5 shows an exemplary flow chart of a method according to the invention for operating the exhaust gas sensor 100 of FIG. 1. The method starts at step 500 and then proceeds to step 502, where the current

Oxygen content in the exhaust gas is determined. The oxygen content in the exhaust gas can, for example, based on the first pump current IR0 applied to the first pump electrode 124, for constant fluxing between the first

Pump electrode 124 and the reference electrode 52 forming the first

Electrode voltage V0 can be determined. Alternatively, the oxygen content can be determined based on the oxygen signal of a separate lambda probe arranged in the exhaust system of the internal combustion engine. In addition, the oxygen content in the exhaust gas of the internal combustion engine can alternatively be based on the signal of a separate one arranged in the exhaust gas line of the internal combustion engine

Exhaust gas sensor, for example by means of a corresponding IPO signal from a separate nitrogen oxide sensor, are determined.

In a subsequent step 504, depending on the oxygen content in the exhaust gas determined in the previous step 502, the second voltage setpoint for the second electrode voltage V3 is dynamically adjusted and in a further step 506 the second pump current IP3 applied to the second pump electrode 224 is controlled or regulated in such a way that The second electrode voltage V3 with the determined second voltage setpoint value is formed between the second pump electrode 224 and the reference electrode 52. For example, a

Assignment of the determined oxygen content in the exhaust gas to an associated voltage setpoint of the second electrode voltage V3 take place by means of a table stored in the control unit. Alternatively, this assignment can take place by means of a mathematical mapping that establishes the relationship between the oxygen content and the voltage setpoint for the second electrode voltage V3. The method of FIG. 5 then ends at step 508.

Claims

1 . Method for operating an exhaust gas sensor (100) which has a main body (1 12) and is arranged in an exhaust line of an internal combustion engine, which has a first pump cavity (120) arranged in the main body (1 12) and connected to the exhaust gas, in which a first pump electrode (124 ) is arranged, a second pump cavity (220) arranged in the main body (1 12) and connected to the exhaust gas, in which a second pump electrode (224) is arranged, and one arranged in the main body (1 12) and connected to the

Has ambient air connected reference cavity (50) in which a

Reference electrode (52) is arranged, the method comprising:

Determining the oxygen content and / or water content in the exhaust gas of the internal combustion engine,

Determination of a voltage setpoint for the second electrode voltage (V3) that is formed between the second pump electrode (224) and the reference electrode (52) on the basis of a pump current (IP3) applied to the second pump electrode (224) as a function of the determined

Oxygen content and / or water content, and

Controlling the pump current (IP3) applied to the second pump electrode (224) in such a way that the second electrode voltage (V3) with the determined voltage setpoint is formed between the second pump electrode (224) and the reference electrode (52).

2. The method according to claim 1, wherein the oxygen content in the exhaust gas of the internal combustion engine is based on a first pump current (IR0) applied to the first pump electrode (124) to keep a constant one between the first pump electrode (124) and the reference electrode (52) forming Electrode voltage (V0) is determined.

3. The method according to claim 1, wherein the oxygen content in the exhaust gas of the internal combustion engine is determined based on the oxygen signal of a lambda probe arranged in the exhaust system of the internal combustion engine.

4. The method according to claim 1, wherein the oxygen content in the exhaust gas of the internal combustion engine is determined based on the signal of a separate exhaust gas sensor arranged in the exhaust gas line of the internal combustion engine.

5. The method according to any one of the preceding claims, wherein the voltage setpoint for the second electrode voltage (V3) with increasing

Oxygen content increases.

6. The method according to any one of the preceding claims, further comprising:

Determination of the water content in the exhaust gas of the internal combustion engine, wherein the determination of the voltage setpoint also takes place at least partially based on the determined water concentration in the exhaust gas.

7. The method according to claim 6, wherein the water concentration is determined by comparing the pump currents (IPO, IP3) of the first and second pump electrodes (124, 224).

8. The method according to any one of the preceding claims, wherein the exhaust gas sensor (100) furthermore a first measuring cavity (140) arranged in the main body (1 12) and connected to the first pump cavity (120), in which a first measuring electrode (144) is arranged, and a second measuring cavity (240) arranged in the main body (112) and connected to the second pump cavity (220), in which a second measuring electrode (244) is arranged, further comprising:

Controlling a first pump current (IPO) applied to the first pump electrode (124) in such a way that a first electrode voltage (V0) forming between the first pump electrode (124) and the reference electrode (52) is kept constant at a predetermined further voltage setpoint, and determining a first nitric oxide value based on one of the first

Measuring electrode (144) applied first measuring current (IP21),

Controlling the second pump current (IP3) applied to the second pump electrode (224) in such a way that the between the second

Pump electrode (224) and the reference electrode (52) forming the second

Electrode voltage (V3) constant at the determined first voltage setpoint is held, and determining a second nitrogen oxide value based on a second measurement current (IP22) applied to the second measurement electrode (244), and

Determining the ammonia content in the exhaust gas of the internal combustion engine based on the determined first nitrogen oxide value and the determined second nitrogen oxide value.

9. The method according to any one of claims 1 to 7, wherein the

Exhaust gas sensor (100) further comprises a measuring cavity (140) which is arranged in the main body (112) and is connected to the first and second pump cavities (120, 220) and in which a measuring electrode (144) is arranged, further comprising:

Controlling a first pump current (IR0) applied to the first pump electrode (124) in such a way that a first electrode voltage (V0) formed between the first pump electrode (124) and the reference electrode (52) is kept constant at a predetermined further voltage setpoint, and determining a first nitrogen oxide value based on a first measurement current (IP21) applied to the measurement electrode (144),

Pump electrode (224) and the reference electrode (52) forming the second

Electrode voltage (V3) is kept constant at the determined voltage setpoint value, and determining a second nitrogen oxide value based on a second measurement current (IP22) applied to the measurement electrode (144), and

10. Exhaust gas sensor (100) to be arranged in the exhaust line of a

Internal combustion engine, the exhaust gas sensor (100) having:

a main body (1 12),

a first pump electrode (124) which is assigned to a first pump cavity (120) connected to the exhaust gas and provided in the main body (112), a second pump electrode (224) which is assigned to a pump cavity (220) connected to the exhaust gas and provided in the main body (112), and

a control unit which is connected to the first pump electrode (124) and the second pump electrode (224) and is designed to carry out a method according to one of the preceding claims.