DE102015206867A1 - Method for operating a sensor for detecting at least one property of a measuring gas in a measuring gas space - Google Patents

Abstract

A method for operating a sensor (10) for detecting at least one property of a measurement gas in a measurement gas space, in particular for detecting a proportion of a gas component in the measurement gas or a temperature of the measurement gas, is proposed. The sensor (10) comprises a sensor element (12) for detecting the property of the measurement gas, wherein the sensor element (12) comprises a solid electrolyte (14), a first electrode (16), a second electrode (18), a third electrode (20). and a fixed electrode (22), wherein the first electrode (16) and the second electrode (18) are connected to the solid electrolyte (14) such that the first electrode (16), the second electrode (18) and the solid electrolyte ( 14) form a pumping cell (36), wherein the third electrode (20) and the fourth electrode (22) are connected to the solid electrolyte (14) such that the third electrode (20), the fourth electrode (22) and the solid electrolyte (14) form a Nernst cell (40). In the method, a Nernstspannung (UVS) of the Nernst cell (40) is regulated, wherein for controlling the Nernst voltage (UVS) at least one measured variable is detected, further a compensation variable is determined, wherein at least one corrected measured variable is determined from the measured variable and the compensation variable , wherein the property of the measurement gas in the measurement gas space is determined from the corrected measured variable, the compensation variable being at least partially dependent on a pumping current (IP) and a voltage (UP) applied to the pumping cell (36).

Description

State of the art

A large number of sensors and methods for detecting at least one property of a measurement gas in a measurement gas space are known from the prior art. In principle, these can be any physical and / or chemical properties of the measurement gas, one or more properties being able to be detected. The invention will be described below in particular with reference to a qualitative and / or quantitative detection of a proportion of a gas component of the measurement gas, in particular with reference to a detection of an oxygen content in the measurement gas part. The oxygen content can be detected, for example, in the form of a partial pressure and / or in the form of a percentage. Alternatively or additionally, however, other properties of the measuring gas are detectable, such as the temperature.

In particular ceramic sensors are known from the prior art which are based on the use of electrolytic properties of certain solids, that is, on the ion-conducting properties of these solids. In particular, these solids may be ceramic solid electrolytes, such as zirconia (ZrO ₂ ), in particular yttrium stabilized zirconia (YSZ) and scandium doped zirconia (ScSZ), the minor additions of alumina (Al ₂ O ₃ ) and / or silica (SiO ₂ ) ₂ ).

For example, such sensors may be configured as so-called lambda probes or as nitrogen oxide sensors, as they may for example K. Reif, Deitsche, KH. et al., Kraft Paperback, Springer Vieweg, Wiesbaden, 2014, pages 1338-1347 , are known. With broadband lambda probes, in particular with planar broadband lambda probes, it is possible, for example, to determine the oxygen concentration in the exhaust gas over a large range and thus to deduce the air-fuel ratio in the combustion chamber. The air ratio λ (lambda) describes this air-fuel ratio. Nitric oxide sensors determine both the nitrogen oxide and the oxygen concentration in the exhaust gas.

By combining a pump cell, the measuring cell, and an oxygen reference cell, the Nernst cell, a sensor can be set up to measure the oxygen content in an ambient gas. In a pump cell, which operates on the amperometric pumping principle, diffuse upon application of a voltage or a current to the pumping electrodes, which are located in different gas chambers, an oxygen ion current through a ceramic body (the oxygen-conducting solid electrolyte) which separates the gas chambers ("Pump "). If the pumping cell is used to keep the oxygen partial pressure constant in a cavity into which ambient gas can diffuse, then it is possible to deduce the transported amount of oxygen via the measurement of the electric current. This pumping current is, according to the law of diffusion, directly proportional to the partial pressure of oxygen in the ambient gas. With a Nernst cell, the ratio of the oxygen partial pressure in the cavity to the oxygen partial pressure in a further reference gas space can be determined via the Nernst voltage that is being formed

The electrochemical unit of such a sensor can be regarded as a controlled system in a control loop. The control variable of this control loop is the voltage at the pump electrode pair. The controlled variable is the Nernst voltage that is measured. The aim of the scheme is, despite changes in the oxygen content in the exhaust gas to keep the oxygen partial pressure in the cavity as close to a specified or predetermined value. For measuring the oxygen partial pressure in the cavity or the ratio of the oxygen partial pressure in the cavity to the partial pressure in the reference cell, the Nernst voltage is used. Via the applied voltage to the pump electrode pair, the oxygen partial pressure in the cavity can be controlled. The fact that the oxygen is transported into or removed from the cavity, which is also referred to as a pump, the gas concentration can be actively influenced by the applied pumping voltage. All electrodes in the cavity have a common return conductor. In order to be able to represent also negative voltages, this virtual mass lies on an increased potential for the electrical mass. This voltage is related to the Nernst voltage or the voltage at the outer pumping electrode.

Despite the advantages of the sensors known from the prior art and methods for operating the same, they still have room for improvement. Thus, in the case of broadband lambda probes and nitrogen oxide sensors, a pump current signal is evaluated which, in static operation, is linear to the present oxygen concentration. Fast fat-lean changes, such as those found in gasoline engines, or diesel applications with NSC catalysts require accurate oxygen signal evaluation. By electrochemical charge effects in the sensor element, the pumping current in the passage fat-lean or lean-fat can be falsified by a ripple in the signal, which is known as so-called lambda = 1 - ripple. For some sensor types, the lambda = 1 ripple is so strong that an evaluation the oxygen signal is not possible for the above-mentioned applications.

Disclosure of the invention

A method is therefore proposed for operating a sensor for detecting at least one property of a measurement gas in a measurement gas space, which at least largely avoids the disadvantages of known methods for operating these sensors and in which the lambda = 1 ripple is removed, in particular by improved signal evaluation is significantly reduced, that the corrected signal corresponds approximately to the real oxygen content, in particular in the range around lambda = 1.

An inventive method for operating a sensor for detecting at least one property of a measurement gas in a measurement gas space, in particular for detecting a portion of a gas component in the measurement gas or a temperature of the measurement gas comprises a sensor element for detecting the property of the measurement gas, wherein the sensor element is a solid electrolyte, a first electrode, a second electrode, a third electrode and a fixed electrode, wherein the first electrode and the second electrode are connected to the solid electrolyte such that the first electrode, the second electrode and the solid electrolyte form a pumping cell, the third electrode and the fourth electrode are connected to the solid electrolyte in such a way that the third electrode, the fourth electrode and the solid electrolyte form a Nernst cell, wherein a Nernst voltage of the Nernst cell is regulated, wherein at least one measured variable is detected to regulate the Nernst voltage, wherein a compensation variable is further determined, wherein at least one corrected measured variable is determined from the measured variable and the compensation variable, the characteristic of the measuring gas in the measuring gas space being determined from the corrected measured variable, the compensation variable being at least partially dependent on a pumping current and on the Pump cell applied voltage.

The compensation quantity may be at least partially dependent on a temporal change of the pumping current and the voltage applied to the pumping cell. To determine the compensation quantity, a current equivalent of the voltage applied to the pumping cell can be formed. The current equivalent may be formed based on an impedance of the pump cell. The impedance of the pumping cell may be determined based on the voltage applied to the pumping cell and the pumping current. The impedance of the pumping cell can be determined by means of an adaptation algorithm. To determine the compensation variable, a time-varying proportion of the voltage applied to the pump cell and a time-varying proportion of the pump current can be determined. The time-varying proportion of the voltage applied to the pumping cell can be determined by means of high-pass filtering, in particular by means of time differentiation or another type of high-pass filtering, the current equivalent of the voltage applied to the pumping cell and the time-varying portion of the pumping current by means of high-pass filtering, in particular be determined by means of temporal differentiation or another type of high-pass filtering, the pump current. To determine the compensation variable, a difference signal between the time-varying proportion of the pumping current and the time-varying proportion of the voltage applied to the pumping cell can be formed. The compensation quantity may be determined based on a low-pass filtering of the difference signal. The corrected measured variable can be determined by subtracting the compensation variable from the measured variable. In other words, the corrected measured variable can be determined by subtracting the compensation variable from the measured variable.

In addition, a computer program is proposed which is set up to carry out each step of the method according to the invention.

Furthermore, an electronic storage medium is proposed, on which a computer program for carrying out the method according to the invention is stored.

The invention further comprises an electronic control unit which comprises the electronic storage medium according to the invention with the said Computer program for carrying out the method according to the invention comprises.

Finally, the invention also relates to a sensor for detecting at least one property of a measurement gas in a measurement gas space, in particular for detecting a proportion of a gas component in the measurement gas or a temperature of the measurement gas, comprising a sensor element for detecting the property of the measurement gas, wherein the sensor element is a solid electrolyte, a first electrode, a second electrode, a third electrode and a fixed electrode, wherein the first electrode and the second electrode are connected to the solid electrolyte such that the first electrode, the second electrode and the solid electrolyte form a pumping cell, the third electrode and the fourth electrode are connected to the solid electrolyte such that the third electrode, the fourth electrode and the solid electrolyte form a Nernst cell, wherein the sensor further comprises an electronic control unit with the computer program according to the invention for carrying out the invention en method.

In the context of the present invention, a solid electrolyte is to be understood as meaning a body or article having electrolytic properties, that is to say having ion-conducting properties. In particular, it may be a ceramic solid electrolyte. This also includes the raw material of a solid electrolyte and therefore the formation as a so-called green or brownling, which only becomes a solid electrolyte after sintering. In particular, the solid electrolyte may be formed as a solid electrolyte layer or from a plurality of solid electrolyte layers. In the context of the present invention, a layer is to be understood as a uniform mass in the areal extent of a certain height which lies above, below or between other elements.

An electrode in the context of the present invention is generally understood to mean an element which is capable of contacting the solid electrolyte in such a way that a current can be maintained by the solid electrolyte and the electrode. Accordingly, the electrode may comprise an element to which the ions can be incorporated in the solid electrolyte and / or removed from the solid electrolyte. Typically, the electrodes comprise a noble metal electrode which may, for example, be deposited on the solid electrolyte as a metal-ceramic electrode or otherwise be in communication with the solid electrolyte. Typical electrode materials are platinum cermet electrodes. However, other precious metals, such as gold or palladium, are in principle applicable.

In the context of the present invention, a heating element is to be understood as meaning an element which serves for heating the solid electrolyte and the electrodes to at least their functional temperature and preferably to their operating temperature. The functional temperature is the temperature at which the solid electrolyte becomes conductive to ions and which is approximately 350 ° C. Of this, the operating temperature is to be distinguished, which is the temperature at which the sensor element is usually operated and which is higher than the operating temperature. The operating temperature may be, for example, from 700 ° C to 950 ° C. The heating element may comprise a heating area and at least one feed track. In the context of the present invention, a heating region is to be understood as the region of the heating element which overlaps in the layer structure along an axis perpendicular to the surface of the sensor element with an electrode. Usually, during operation, the heating area heats up more than the supply track, so that they are distinguishable. The different heating can for example be realized in that the heating area has a higher electrical resistance than the supply track. The heating area and / or the supply line are formed for example as an electrical resistance path and heat up by applying an electrical voltage. The heating element may for example be made of a platinum cermet.

In the context of the present invention, a closed loop is to be understood as a self-contained course of action for influencing a physical quantity in a technical process. Essential here is the feedback of the current value, which is also referred to as the actual value, to the control device, which counteracts a deviation from the target value continuously. The control loop consists of the controlled system, the controller and a negative feedback of the actual value as a controlled variable. The controlled variable is compared with the setpoint value as a reference variable. The control deviation between the actual value and the desired value is supplied to the control unit, which forms a control variable for the controlled system in accordance with the desired dynamics of the control loop. In the context of the present invention, the controlled system is that part of the control loop which contains the control variable to which the control device is to act via the control or manipulated variable. In the context of the present invention, the electrochemical unit of the sensor is the controlled system.

In the context of the present invention, a measurand is in principle any physical and / or chemical quantity and a signal which indicates this variable (s) equivalently, ie. H. an equivalent signal, to understand. The measured variable is preferably at least one measuring signal of the sensor element. The measured variable may preferably be at least one pumping current, for example a limiting current. By way of example, the measured variable may be a variable dependent on the pumping current. By way of example, the measured variable may be a pump voltage and / or a converted charge. In the context of the present invention, the expression "to be detected" in this context means that the measured variable is output, for example, as a measuring signal from the sensor element and / or the measured variable is processed and / or evaluated and / or stored by a control device.

In the context of the present invention, a compensation variable is to be understood to mean in principle any chemical and / or physical variable and a signal which indicates this variable (s) equivalently, ie an equivalent signal. Preferably, the compensation quantity can same physical and / or chemical size include as the measured variable. Preferably, the compensation variable may be a pump current deviation. By way of example, the compensation variable may be at least one recharging current and / or at least one electrode charge. The compensation quantity is at least partially dependent on a pumping current and a voltage applied to the pumping cell. In particular, the compensation quantity is at least partially dependent on a temporal change of the pumping current and the voltage applied to the pumping cell. By way of example, the compensation variable may be a criterion for a falsification of the measured variable due to electrochemical charge transfer effects in the case of a lambda = 1 passage at the electrodes of the pump cell.

At least one corrected measured variable is determined from the measured variable and the compensation variable. In principle, the corrected measured variable may be any chemical and / or physical quantity and a signal which indicates this variable (s) equivalently, ie. H. an equivalent signal, act. The corrected measured variable may preferably be the same physical and / or chemical variable and / or the compensation variable. The corrected measured variable may be, in particular, a variable which has been corrected for parasitic effects. The proportion of the gas in the measuring gas space can preferably be determined more accurately from the corrected measured variable than from the measured variable. The determination of the corrected measured variable from the measured variable and the compensation variable can be, for example, a calculation and / or an assignment. Accordingly, the proportion of the measurement gas in the measurement gas space can be determined from the corrected measured variable, for example by calculation and / or by association. For example, at least one characteristic can be used in the determination of the proportion of the measurement gas in the measurement gas space from the corrected measured variable. The characteristic can be, for example, an assignment of the corrected measured variable to a proportion of the measuring gas. For example, the characteristic may be an association between a corrected pumping current and a proportion of oxygen in the measuring gas, for example an oxygen partial pressure.

The measured variable may include at least one pumping current. For example, the pumping current may be the total charge transferred through the pumping cell per time. For example, the measured variable may be the pumping current directly or a signal indicating the pumping current. For example, the pumping current may also be a measured variable which depends on the pumping current. By way of example, the measured variable may be a quantity dependent on the pumping current. For example, the measured variable may comprise at least the pumping current. The compensation variable may include at least one charge transfer current. The charge-reversal current can be currents which can occur through charging processes and / or discharge processes, for example when the proportion of the measurement gas in the measurement gas space changes. The charge-reversal current can be currents which can occur with a lambda = 1 passage. The amount of charge generated by recharge then usually does not form in the voltage of the regulator, because the source is the alternating Nernst voltage at the electrodes of the pump cell in the sensor element. The output voltage of the controller is not disturbed in the case of a lambda = 1 - passage, since this time runs after the lambda = 1 - passage.

The measured variable, compensation variable and corrected measured variable do not have to be present as absolute values according to the previous statements. The present invention explicitly allows, alternatively or additionally, a correction of the measured variable or compensation of the transhipment at the level of the signal processing, so that the measured variable, compensation variable and corrected measured variable can correspond to these characterizing signals.

In the context of the present invention, an impedance of the pumping cell does not mean the ohmic resistance of the pumping cell, but rather a sensor-element-specific relationship between pumping voltage and a current equivalent of the pumping voltage, which is, inter alia, frequency-dependent. Under certain operating conditions, the current equivalent of the pumping voltage is equal to the pumping voltage (eg, with little change in the O2 concentration in the exhaust gas over time). In the DC case considered here (limiting current operation), the impedance value depends on the oxygen concentration in the exhaust gas but also on further exhaust gas conditions, such as, for example, the gas velocity. In the context of the present invention, the impedance describes in particular the ratio of current equivalent of the pump voltage and pump voltage. The impedance of the pumping cell can generally be defined as a complex numerical value. The impedance of the pumping cell can thus also be frequency-dependent. In the context of the present invention, the impedance of the pumping cell can be determined by means of an adaptation algorithm from the combinations of the voltage at the pumping cell and the pumping current. The impedance of the pumping cell can be determined as a function of the voltage applied to the pumping cell (or alternatively as a function of the pumping current). In a further step of the method according to the invention is generates a signal that reflects the changing portion of the voltages and currents applied to the pump cell. This can be done for example by a time differentiation or another type of high-pass filtering. Generally, high-pass filtering is performed here. In the context of the present invention, a high pass is to be understood as meaning a filter which transmits high-frequency signal components above its cut-off frequency, while low-frequency signal components are attenuated. Constant or slow changing signal components can be removed. Filtering can also change the phase of the signal. For example, a differentiator has a phase of 90 ° (linear phase). High-pass filters can be realized within the scope of the present invention as recursive filters or non-recursive filters. You can have a finite or infinite impulse response.

With a lambda-1 ripple, the pump current signal and the voltage on the pump cell show a different course. The information about divergence of the voltages and currents applied to the pumping cell is in the difference of the voltage and current change signals applied to the pumping cell. This difference signal is also a measure of the shift of charges during the transfer of the electrochemical cells. Recharging the electrochemical cell causes a change in the current without a change in the voltage applied to the pumping cell. By changing the Nernst voltage at the electrodes of the pumping cell, a charge-reversal current is generated. This recharge current is superimposed on the actual signal from the limiting current operation. In the difference signal then only the change of the charge current is mapped.

The difference signal of the current changes is summed over a time interval, while this sum signal is gradually reduced again. This results in a charge equivalent to the Umladungssstrom signal, the charge-reversal compensation signal. For this purpose, the difference signal can be filtered with a low-pass filter. In the context of the present invention, a low-pass filter is to be understood as meaning a filter which transmits low-frequency signal components below its cut-off frequency, while high-frequency signal components are attenuated. The task of the low-pass filter is to sum the course of the signal of the difference signal over the time interval of the disturbance. If the difference signal is small, the compensation current signal will go to zero. A simple Tierfpass implementation can be achieved, for example, with a leaky integrator. In an alternative implementation, the characteristics of the low-pass filter may be changed depending on the size of the input signal.

In a final step, the charge-transfer compensation signal is subtracted from the measured pump current signal. From the corrected pumping current signal, a signal representing the concentrations and changes over time of the oxygen content of the ambient gas can now be derived. In subsequent steps, a calibrated oxygen signal can be derived from the corrected pump current signal with the aid of characteristic maps.

A basic idea of the present invention is to remove or greatly reduce the lambda = 1 ripple by an improved signal evaluation. The electrochemical cause of the signal disturbance, a recharge of the active electrodes, is at least approximately corrected by additional evaluation of electrical quantities.

The Lambda 1 ripple in the lean / rich (rich / lean) gas exchange can be approximately compensated in a processing step in the microcontroller with the aid of the measured signals of the pumping current and the pumping voltage. In the event of a gas exchange, voltages and currents occur at the electrodes which lead to a charge shift. A change in the Nernst voltage, ie the controlled variable occurs delayed. The associated current flow appears as lambda 1 ripple in the oxygen signal.

In the post-processing step in the microcontroller, a signal corresponding to the charge shift can be determined from the time change of the pump voltage and pump current signals. Hereby, the disturbance, ie the lambda 1 ripple, can be compensated. About the characteristic resistance of the pump cell or its impedance, a relationship between the voltage at the pumping cell and pumping current can be determined. This impedance may be a function of the voltage applied to the pumping cell or the pumping current. This characteristic resistance can be determined for the fat and lean mode with fixed values or by adaptively learned values specific to the probe.

In the context of the present invention, U _VS denotes a reference cell voltage, which is the Nernst voltage that forms between the reference electrode in the first gas cavity and the reference electrode. In the control loop, U _VS serves as a controlled variable. U _P is the voltage applied to the pumping cell. U _IP is the voltage drop at the measuring resistor R _{Shunt of} the pump cell (U _IP = R _Shunt * I _P I _P is the pump current which determines the amount of oxygen ions pumped

The voltage applied to the pumping cell is called the voltage difference between the outer Pump electrode and the reference voltage measured at the common return conductor. The voltage drop across the measuring resistor of the pumping cell is measured as a voltage difference between the output of the voltage controlled by the O2 regulator or alternatively by the O2 regulator controlled current source and the voltage at the outer pumping electrode. The voltage drop U _IP at the measuring resistor is determined by the pumping current I _P. In the static case, this pumping current is again proportional to the oxygen concentration to be measured in the ambient gas. The manipulated variable of the controlled system can be a voltage or a current at the pump cell. Here, alternative structures are possible, but where in each case pumping current I _P and pumping voltage U _P can be measured. In the case of a voltage-controlled control on the outer pumping electrode, the manipulated variable is either the voltage at the outer pumping electrode U _P or the voltage U _RS at the measuring resistor U _RS = U _P + R _shunt * I _P , where R _{shunt is} the ohmic resistance of the measuring resistor. In a current-controlled control at the outer pumping electrode, the manipulated variable is the current at the outer pumping electrode. In an alternative voltage-controlled regulation, the voltage at the inner pumping electrode is kept at a common reference voltage by regulating the voltage U _P at the outer pumping electrode. A voltage driver at a measuring resistor R _shunt to the inner pumping electrode is regulated by the Vs regulator. Alternatively, the current driver is controlled at the measuring resistor to the inner pumping electrode. The controlled variable is the Nernst voltage U _VS , which is measured between the reference electrode and the reference voltage at the common return conductor.

• 1. Normierung der Pumpspannung auf Pumpstrom mit einem Verhältnis I_P(U_P)/U_P;
• 2. zeitliche Änderung von I_{P_aus_UP} und I_P, die aus einer Differenzierung bzw. einer Hochpassfilterung erfolgt;
• 3. Differenz von d/dt (I_{P_aus_UP}) und d/dt (I_P)
• 4. Tiefpassfilterung von (d/dt(I_P) – d/dt(I_{P_aus_UP})), die einen Korrekturterm ergibt;
• 5. Kompensation des Fehlers im Messgassignal.

In the signal post-processing in the context of the present invention, the following steps are basically carried out:

• 1. Normalization of the pumping voltage to pumping current with a ratio I _P (U _P ) / U _P ;
• 2. temporal change of I _{P_out_UP} and I _P , which takes place from a differentiation or a high-pass _filtering ;
• 3. Difference of d / dt (I _{P_out_UP} ) and d / dt (I _P )
• 4. low-pass filtering of (d / dt (I _P ) _-d / dt (I _{P_out_UP} )) _yielding a correction term;
• 5. Compensation of the error in the measured gas signal.

Brief description of the drawings

Further optional details and features of the invention will become apparent from the following description of preferred embodiments, which are shown schematically in the figures.

Show it:

1 a basic structure of a sensor according to the invention,

2 a block diagram of the signal evaluation with Umladekorrektur at the sensor,

3 a block diagram of a signal processing in the Umladekorrektur,

4 a time course of a pump current signal, a corrected pump current signal and a fault signal,

5 a waveform of the sensor with interference and compensated interference and

6 a temporal waveform at the sensor.

Embodiments of the invention

1 shows a basic structure of a sensor according to the invention 10 , The in 1 illustrated sensor 10 can be used to detect physical and / or chemical properties of a sample gas, wherein one or more properties can be detected. The invention will be described below in particular with reference to a qualitative and / or quantitative detection of a gas component of the measurement gas, in particular with reference to a detection of an oxygen content in the measurement gas. The oxygen content can be detected, for example, in the form of a partial pressure and / or in the form of a percentage. In principle, however, other types of gas components are detectable, such as nitrogen oxides, hydrocarbons and / or hydrogen. Alternatively or additionally, however, other properties of the measuring gas can also be detected. The invention can be used in particular in the field of motor vehicle technology, so that the measuring gas chamber can be, in particular, an exhaust gas tract of an internal combustion engine, with the measuring gas in particular being an exhaust gas.

The sensor 10 has a sensor element 12 on. The sensor element 12 may be formed as a ceramic layer structure, as described in more detail below. The sensor element 12 has a solid electrolyte 14 , a first electrode 16 , a second electrode 18 , a third electrode 20 and a fourth electrode 22 on. The solid electrolyte 14 may be composed of a plurality of ceramic layers in the form of solid electrolyte layers or may comprise a plurality of solid electrolyte layers. For example, the solid electrolyte includes 14 a pumping film or pumping layer, an intermediate film or intermediate layer and a heating foil or heating layer, which are arranged one above the other or one below the other. The name of the electrodes 16 . 18 . 20 . 22 should not indicate a weighting of their meaning, but only allow them to be differentiated conceptually.

The sensor element 12 also has a gas access path 24 on. The gas access route 24 has a gas entry hole 26 up, extending from a surface 28 of the solid electrolyte 14 inside the layer structure of the sensor element 12 extends. In the solid electrolyte 14 is an electrode cavity 30 provided that the gas access hole 26 surrounds, for example, annular or rectangular. The electrode cavity 30 is part of the gas access route 24 and can stand over the gas entry hole 26 in communication with the sample gas chamber. For example, the gas access hole extends 26 as a cylindrical blind hole perpendicular to the surface 28 of the solid electrolyte 14 in the interior of the layer structure of the sensor element 12 , In particular, the electrode cavity 30 formed substantially annular or rectangular and when viewed in a cross-sectional view of three sides of the solid electrolyte 14 limited. Between the gas access hole 26 and the electrode cavity 30 is a channel 32 arranged, which is also part of the Gaszutrittswegs 24 is. In this channel 32 is a diffusion barrier 34 arranged, which a subsequent flow of gas from the sample gas space into the electrode cavity 30 diminished or even prevented and only allows diffusion.

The first electrode 16 is on the surface 28 of the solid electrolyte 14 arranged. The first 16 electrode may be the gas access hole 26 surrounded annular and separated from the sample gas space, for example, by a gas-permeable protective layer not shown in detail. The second electrode 18 second electrode 18 is in the electrode cavity 30 arranged. The second electrode 18 can also be designed annular and rotationally symmetrical about the gas inlet hole 26 be arranged. For example, the first electrode 16 and the second electrode 18 coaxial with the gas inlet hole 26 arranged. The first electrode 16 and the second electrode 18 are so with the solid electrolyte 14 and in particular the pumping layer connected, in particular electrically connected, that the first electrode 16 , the second electrode 18 and the solid electrolyte 14 a pump cell 36 form. About the diffusion barrier 34 can be a limiting current of the pumping cell 36 to adjust. The limiting current thus provides a current flow between the first electrode 16 and the second electrode 18 over the solid electrolyte 14 represents.

The sensor element 12 also has a reference gas space 38 on. The reference gas space 38 may be perpendicular to a direction of extension of the gas inlet hole 26 into the interior of the solid electrolyte 14 extend. As mentioned above, the gas entry hole is 26 cylindrically shaped, so that the extension direction of the gas inlet hole 26 parallel to a cylinder axis of the gas inlet hole 26 runs. In this case, the reference gas space extends 38 perpendicular to the cylinder axis of the gas inlet hole 26 , It is expressly mentioned that the reference gas space 38 also in an imaginary extension of the gas access hole 26 and thus further inside the solid electrolyte 14 can be arranged. The reference gas space 38 does not have to be designed as a macroscopic reference gas space. For example, the reference gas space 38 be executed as a so-called pumped reference, that is, as an artificial reference.

(Lambda) = 1 oder eine andere bekannte Zusammensetzung herrscht. Diese Zusammensetzung wird wiederum von der Nernstzelle 40 erfasst, indem eine Nernstspannung U_VS zwischen der dritten Elektrode 20 und der vierten Elektrode 22 gemessen wird. Da in dem Referenzgasraum 38 eine bekannte Gaszusammensetzung vorliegt bzw. diese einem Sauerstoffüberschuss ausgesetzt ist, kann anhand der gemessenen Spannung auf die Zusammensetzung in dem Elektrodenhohlraum 30 geschlossen werden.The third electrode 20 is also in the electrode cavity 30 arranged. For example, the third electrode is located 20 the second electrode 18 across from. The fourth electrode 22 is in the reference gas space 38 arranged. The third electrode 20 and the fourth electrode 22 are so with solid electrolytes 14 connected to that third electrode 20 , the fourth electrode 22 and that part of the solid electrolyte 14 between the third electrode 22 and the fourth electrode 22 a Nernst cell 40 form. By means of the pumping cell 36 For example, a pumping current through the pumping cell 36 be adjusted so that in the electrode cavity 30 the condition

(Lambda) = 1 or another known composition prevails. This composition in turn is from the Nernst cell 40 detected by a Nernst voltage U _VS between the third electrode 20 and the fourth electrode 22 is measured. As in the reference gas space 38 a known gas composition is or is exposed to an excess of oxygen, based on the measured voltage on the composition in the electrode cavity 30 getting closed.

In the extension of the extension direction of the gas access hole 26 is a heating element 42 in the layer structure of the sensor element 12 arranged. The heating element 42 has a heating area 44 and electrical supply tracks 46 on. The heating area 44 For example, it is meandering. The heating element 42 is in the solid electrolyte 14 disposed between the intermediate layer and the heating layer. It is expressly mentioned that the heating element 42 is surrounded on both sides by a thin layer of an electrically insulating material, such as alumina, even if this is not shown in detail in the figures. In other words, between the intermediate layer and the heating element 42 and between the heating element 42 and the heating layer arranges the thin layer of the electrically insulating material. Since such a layer is known for example from the above-mentioned prior art, this will not be described in detail. For Further details regarding the layer of the electrically insulating material are therefore referred to the above-mentioned prior art, the contents of which relating to the layer of the electrical material is incorporated herein by reference.

2 shows a block diagram of the signal evaluation with Umladekorrektur at the sensor 10 , As in 2 is shown, the sensor points 10 an electronic control unit 48 on. The electronic control unit 48 has a controller 50 for controlling a Nernst voltage U _{VS of} the Nernst cell 40 on. Between the controller 50 and the first electrode 16 is a measuring resistor 52 arranged. Furthermore, an RC bridge is optional 54 (Series connection of resistor and capacitor) between the first electrode 16 and the third electrode 20 arranged. Furthermore, the electronic control unit 48 a signal post-processing unit 56 and a data interface 58 on. As in 2 shown and recognizable by the signal waveforms shown schematically, is a manipulated variable of the electronic control unit 48 one of the pumping cell 36 supplied voltage U _RS . The controlled variable is the Nernst voltage U _VS. Based on the pump cell 36 supplied voltage U _Rs and one to the pumping cell 36 applied voltage U _P is a voltage drop U _IP on the Messwidertand 52 from the control device 50 determined. So the voltage drop is U _IP over the measuring resistor 52 the difference between the manipulated variable U _RS and the voltage applied to the pumping cell U _P. In this way, in addition, the dependent of the oxygen concentration current I _O2 , in the pumping cell 36 flows in or out of this, from the voltage drop U _IP via the measuring resistor 52 be determined because the measuring resistance 52 between an output of the controller 50 and the first electrode 16 is arranged. On the basis of the waveforms, the peculiarity of the present invention can be seen. So not only the voltage drop U _IP over the measuring resistor 52 the signal post-processing unit 56 fed, but also to the pumping cell 36 applied voltage U _P. On the basis of the pump cell 36 applied voltage U _P and the signal from the post-processing unit 56 becomes the data interface 58 supplied a signal indicating the oxygen content.

3 schematically shows a signal processing of the Umladungskorrektur in the signal post-processing unit 56 , The signal post-processing unit 56 a first input signal in the form of the voltage drop U _IP at the measuring resistor 52 , which is dependent on the pumping current I _P , and a second input signal in the form of the pump cell 36 applied voltage U _P. In addition, a voltage between the outer pumping electrode and the inner pumping electrode can be used as the input signal.

R_Shunt [Ω] der Widerstand des Messwiderstands 52 an der ersten Elektrode 16 oder der zweiten Elektrode 18 ist. Der Spannungsabfall U_IP ist proportional zum Pumpstrom I_P. Zur Bestimmung der Kompensationsgröße wird ein Strom-Äquivalent I_UP der an die Pumpzelle 36 angelegten Spannung U_P gebildet. Das Strom-Äquivalent I_UP wird basierend auf einer Impedanz Z_P der Pumpzelle 36 gebildet. Die Impedanz Z_P der Pumpzelle 36 wird basierend auf der an die Pumpzelle 36 angelegten Spannung U_P und dem Pumpstrom I_P bestimmt, beispielsweise in der Form:

The pumping current I _P can be expressed:

R _shunt [Ω] is the resistance of the measuring resistor 52 at the first electrode 16 or the second electrode 18 is. The voltage drop U _IP is proportional to the pump current I _P. To determine the compensation quantity, a current equivalent I _{UP is applied} to the pump cell 36 applied voltage U _P formed. The current equivalent I _UP is based on an impedance Z _{P of} the pump cell 36 educated. The impedance Z _{P of} the pump cell 36 is based on the pump cell 36 applied voltage U _P and the pump current I _P determined, for example in the form:

The impedance Z _{P of} the pump cell 36 describes the ratio of current equivalent of pump voltage and pump voltage in the form:

The impedance Z _{P of} the pump cell 36 can generally be defined as a complex number. The impedance Z _{P of} the pump cell 36 can thus also be frequency-dependent. The impedance Z _{P of} the pump cell 36 is determined by means of an adaptation algorithm.

The signal thus converted from U _IP becomes a high-pass filter 60 and the signal converted from U _P becomes a high-pass filter 62 fed. A time-varying proportion dU _P of the pump cell 36 applied voltage U _P and a time-varying portion dI _{P of} the pump current I _P are in the high-pass filters 60 . 62 determined. The time-varying proportion dU _P of the pump cell 36 applied voltage U _P can by means of temporal differentiation or another type of high-pass filtering of the current equivalent I _UP to the pumping cell 36 applied voltage U _{P are} determined and the time-varying portion dI _{P of} the pump current I _P can be determined by means of temporal differentiation or another type of high-pass filtering of the pump current I _P.

Subsequently, a difference signal DI _O2 between the time-varying portion dI _{P of} the pump current I _P and the time-varying proportion dU _P of the pump cell 36 applied voltage U _{P is} formed, for example in the form: DI _O2 = dI _P1 - dI _UP1

This difference signal DI _O2 is also a measure of the shift of charges during the transfer of the electrochemical cells. A recharge of the electrochemical cell causes a change in the current, without a change in the pump cell 36 applied voltage U _P. By changing the Nernst voltage at the electrodes 16 . 18 The pumping cell is a Umladungsstrom generated. This recharge current is superimposed on the actual signal from the limiting current operation. In the difference signal DI _O2 then only the change of the charge current is mapped.

The compensation variable is determined by means of a low-pass filtering of the difference signal DI _O2 . For this purpose, the difference signal DI _O2 with a low-pass filter 64 be filtered. The low pass filter 64 represents a component that sums up the input signals but gradually reduces the signal contained in its internal states over time. At the output of the low-pass filter 64 is the charge-transfer compensation _{current signal} I _Komp . Task of the low-pass filter 64 is to sum the course of the difference signal DI _O2 over the time interval of the disturbance. If the difference signal DI _{O2 is} small, the compensation _{current signal} I _Komp becomes zero.

The corrected measured variable is finally determined by subtracting the compensation variable from the measured variable. Thus, in particular, the charge-transfer compensation signal I _{comp is} subtracted from the measured pump current signal I _P , for example in the form: I _PO2 = I _P - I _comp .

From the corrected pump current signal I _PO2 , a signal can now be derived which represents the concentrations and changes with time of the oxygen content of the measurement gas. Below, with the help of at least one map 65 From the corrected pump current signal I _PO2 a calibrated oxygen signal can be derived as a corrected measurement quantity.

In the method described above, in principle, the pumping current of the pumping cell and the voltage applied to the pumping cell must be related to one another. The further computation steps do not necessarily have to take place in equivalent streams. The division of the voltages by the impedances can be avoided. Alternatively, they can be multiplied by their reciprocals or other equivalent factors.

4 shows time courses of a pump current _{signal of} a corrected pump current _signal I _PO2 and the disturbance Q. This disturbance Q should be approximated by the compensation _signal I _comp as possible). On the X-axes 66 each time is plotted. In the upper illustration is on the Y-axis 68 the pumping current I _P or the corrected _pumping current I _{P_korr is plotted} as a corrected measured variable. In the lower illustration is on the Y-axis 68 the disturbance Q is applied. The curve 70 indicates the pumping current signal without reloading correction. As can be seen, this has at least one clearly recognizable peak in the case of a lambda = 1 passage 72 on. A curve 74 g indicates the corrected pump current signal. There is no peak 72 more available.

The curve 76 indicates the fault Q Evident is the peak determined in this way 72 , which is subtracted from the pump current signal I _P for correction. The curve results accordingly 74 because of the peak 72 is subtracted. The charge current is correspondingly the change of the disturbance Q with time, ie Q / dt.

5 shows waveforms at the sensor 10 , On the X axis 78 the time is up. On the left Y-axis 80 the pumping current I _{P is} plotted. On the right Y-axis 82 the pumping voltage U _{P is} plotted. The curve 84 indicates an ideal course of the pump current signal I _P. The curve 86 indicates the pump current signal I _P without correction and similarly has a clearly recognizable peak as described above 72 on. The curve 88 indicates the time course of the pumping voltage U _P. The curve 90 indicates the corrected pump current _signal I _{P_korr} . It can be seen that the curve 90 , the curve 84 due to the correction or the compensation of the disturbance Q is approximated.

6 shows time courses of the signals at the sensor 10 , On the X axis 92 the time is plotted and on the y-axis 94 is the oxygen content percentage signal. The curve 96 returns the ideal signal again. The curve 98 again indicates the signal determined from the pumping current I _P and indicating the oxygen content without correction, which has a clearly recognizable peak 100 having. The curve 102 indicates the oxygen content indicating signal with a charge compensation. Clearly recognizable is an approximation of the curve 102 to the curve 96 , Further, the charge-reversal compensation can be optimized with an adaptation of the characteristic impedance Z _{P of} the pumping cell 36 in the manner described above. This is based on the curve 104 shown almost with the curve 96 coincides.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• K. Reif, Deitsche, KH. et al., Automotive Handbook, Springer Vieweg, Wiesbaden, 2014, pp. 1338-1347 [0003]

Claims (15)

Method for operating a sensor ( 10 ) for detecting at least one property of a measurement gas in a measurement gas space, in particular for detecting a portion of a gas component in the measurement gas or a temperature of the measurement gas, comprising a sensor element ( 12 ) for detecting the property of the measuring gas, wherein the sensor element ( 12 ) a solid electrolyte ( 14 ), a first electrode ( 16 ), a second electrode ( 18 ), a third electrode ( 20 ) and a solid electrode ( 22 ), wherein the first electrode ( 16 ) and the second electrode ( 18 ) in such a way with the solid electrolyte ( 14 ), that the first electrode ( 16 ), the second electrode ( 18 ) and the solid electrolyte ( 14 ) a pump cell ( 36 ), the third electrode ( 20 ) and the fourth electrode ( 22 ) in such a way with the solid electrolyte ( 14 ), that the third electrode ( 20 ), the fourth electrode ( 22 ) and the solid electrolyte ( 14 ) a Nernst cell ( 40 ), wherein a Nernst voltage (U _VS ) of the Nernst cell ( 40 ), wherein for controlling the Nernst voltage (U _VS ) at least one measured variable is detected, wherein furthermore a compensation variable is determined, wherein at least one corrected measured variable is determined from the measured variable and the compensation variable, the characteristic of the measured gas being determined from the corrected measured variable the compensation gas quantity is at least partially dependent on a pumping current (I _P ) and on the pumping cell ( 36 ) applied voltage (U _P ). Method according to the preceding claim, wherein the compensation quantity is at least partially dependent on a temporal change of the pumping current (I _P ) and that on the pumping cell ( 36 ) applied voltage (U _P ). Method according to one of the preceding claims, wherein for determining the compensation quantity, a current equivalent (I _UP ) of the pump cell ( 36 ) applied voltage (U _P ) is formed. Method according to the preceding claim, wherein the current equivalent (I _UP ) is based on an impedance (Z _P ) of the pump cell ( 36 ) is formed. Method according to the preceding claim, wherein the impedance (Z _P ) of the pump cell ( 36 ) based on the pump cell ( 36 ) applied voltage (U _P ) and the pumping current (I _P ) is determined. Method according to the preceding claim, wherein the impedance (Z _P ) is determined by means of an adaptation algorithm. Method according to one of the four preceding claims, wherein a time-varying proportion (dU _P ) of the pump cell ( 36 ) applied voltage (U _P ) and a time-varying proportion (dI _P ) of the pumping current (I _P ) is determined. Method according to the preceding claim, wherein the time-varying proportion (dU _P ) of the pump cell ( 36 ) applied voltage (U _P ) by means of high-pass filtering of the current equivalent (I _UP ) of the pump cell ( 36 ) applied voltage (U _P ) is determined and the time-varying proportion (dI _P ) of the pumping current (I _P ) by means of high-pass filtering of the pumping current (I _P ) is determined. Method according to one of the two preceding claims, wherein a difference signal (DI _O2 ) between the time-varying portion (dI _P ) of the pumping current (I _P ) and the time-varying portion (dU _P ) of the pumping cell ( 36 ) applied voltage (U _P ) is formed. Method according to the preceding claim, wherein the compensation quantity low-pass filtering of the difference signal (DI _O2 ) is determined. Method according to the preceding claim, wherein the corrected measured variable is determined by subtracting the compensation quantity from the measured variable. Computer program which is set up to perform each step of the method according to one of the three preceding claims. An electronic storage medium on which a computer program according to the preceding claim is stored. Electronic control unit ( 48 ) comprising an electronic storage medium according to the preceding claim. Sensor ( 10 ) for detecting at least one property of a measurement gas in a measurement gas space, in particular for detecting a portion of a gas component in the measurement gas or a temperature of the measurement gas, comprising a sensor element ( 12 ) for detecting the property of the measuring gas, wherein the sensor element ( 12 ) a solid electrolyte ( 14 ), a first electrode ( 16 ), a second electrode ( 18 ), a third electrode ( 20 ) and a solid electrode ( 22 ), wherein the first electrode ( 16 ) and the second electrode ( 18 ) in such a way with the solid electrolyte ( 14 ), that the first electrode ( 16 ), the second electrode ( 18 ) and the solid electrolyte ( 14 ) a pump cell ( 36 ), the third electrode ( 20 ) and the fourth electrode ( 22 ) in such a way with the solid electrolyte ( 14 ), that the third electrode ( 20 ), the fourth electrode ( 22 ) and the solid electrolyte ( 14 ) a Nernst cell ( 40 ) form, wherein the Sensor continues to be an electronic control unit ( 48 ) according to the preceding claim.

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