Method for operating a sensor element

Abstract

Method for operating a sensor element (112) for detecting at least one oxygen fraction of an exhaust gas (113) in an exhaust tract, wherein the sensor element (112) comprises at least one pump cell (114) with at least two pump electrodes (118) connected to each other by at least one solid electrolyte (116), wherein the pump electrodes (118) comprise a first pump electrode and a second pump electrode, wherein the first pump electrode is arranged as an inner pump electrode (124) in a cavity of the sensor element (112) and can be exposed to the exhaust gas (113) via a diffusion barrier (121), wherein the second pump electrode is an exhaust air electrode (119) which can be connected to ambient air (125) via an exhaust air duct (123), wherein at least one measured quantity is detected in the method, wherein the measured quantity is a pump current (Ip) between the first and the second electrode, which represents a limiting current, and wherein at least one compensation quantity is determinedwherein the compensation quantity is at least partially dependent on capacitive effects at at least one junction between at least one of the pump electrodes (118) and the solid electrolyte (116), namely a charging current (Δlp) between the first and the second electrode, which is determined by measuring at least one time course of at least one electrical voltage across at least one electrochemical double layer U, dl (t) is determined using the time course of the electrical voltage across the electrochemical double layer U dl (t) and at least one electrode capacitance C IPE using the formula Δ I p = ∂ Q ∂ t = CIPE ∂ U dl ∂ t ΔIp where at least one corrected measured quantity (Ip) is obtained from the measured quantity and the compensation quantity. korr ) is determined using the formula IP korr = Ip - ΔIp, where the corrected measured quantity (Ip) korr) the oxygen content in the exhaust gas (113) is determined.

Description

State of the art

[0001] Sensor elements and methods for operating these sensor elements for determining at least one fraction of a gas in a measuring gas chamber are known in the prior art. The invention is described below, without limiting further possible embodiments, essentially with reference to methods and devices that serve for the quantitative and / or qualitative detection of at least one concentration of at least one gas component in the gas, in particular a gas mixture. For example, the gas mixture could be exhaust gas from an internal combustion engine, particularly in the automotive sector. The measuring gas chamber could, for example, be an exhaust system. The sensor element could, for example, be a lambda sensor. Alternatively, the sensor element could also be a NO sensor. x-Sensor. Lambda sensors, for example, are described in REIF, Konrad (ed.): Sensors in Motor Vehicles. Wiesbaden: Springer, 2010 (Bosch Automotive Technical Information). pp. 160-165. ISBN 978-3-8348-1315-2. https: / / doi.org / 10.1007 / 978-3-8348-9718-3_3. In particular, the gas component can be oxygen and / or nitrogen and / or at least one nitrogen oxide and / or at least one hydrocarbon and / or another type of gas component. Sensor elements of the type mentioned can be based, in particular, on the use of one or more solid electrolytes, i.e., on the use of solids, especially ceramic solids, which have ion-conducting, especially oxygen-ion-conducting, properties. Examples of such solid electrolytes are zirconium dioxide-based solid electrolytes, such as yttrium-stabilized zirconium dioxide (YSZ) and / or scandium-stabilized zirconium dioxide (ScSZ).Lambda sensors typically operate on the principle of a pump cell. The gas component can preferably be an oxygen partial pressure and / or an oxygen fraction and / or an oxygen volume fraction. A measurement of the oxygen partial pressure in the exhaust gas can, for example, be performed based on the usually linear relationship between a limiting flow rate and an oxygen partial pressure.

[0002] In broadband lambda sensors, also known as wideband lambda probes, the amount of O2 or rich gas diffusing into a measuring cavity is measured either by means of a limiting current, preferably in single-cell systems, especially in the LSP (proportional lambda probe), or by means of a pumping current necessary to regulate a cavity concentration to lambda=1, which can then also correspond to a limiting current, for example in dual-cell systems, especially in the LSU (universal lambda probe). A flowing pumping current, especially as a measuring current, is usually proportional to the O2 content in the exhaust gas and / or to the rich gas content in the exhaust gas.

[0003] The pump voltage required for electrochemical reactions and ohmic losses in the solid electrolyte is typically provided in a two-cell system by a so-called Nernst control. In a single-cell system, the pump voltage is usually adjusted to the pump current using a linear ramp or multiple ramps, for example, with different slopes. This is referred to, for example, as pump voltage tracking.

[0004] The known methods and devices of the prior art have several disadvantages. For example, in pump voltage tracking for single-celled organisms, a double-layer capacitance of an inner pump electrode (IPE) is recharged. The resulting recharge currents are typically visible as overshoots and / or undershoots in a probe signal, such as the limiting current, when the proportion of gas in the measuring gas chamber changes, for example, when the exhaust gas composition changes, and can lead to signal errors. These signal errors can be particularly pronounced during rapid changes in the gas in the measuring gas chamber, such as during rapid gas exchanges, and can, for example, prevent the use of certain applications that require a highly dynamic probe signal.Therefore, a method and a device that at least partially mitigate the disadvantages known from the prior art would be desirable.

[0005] Furthermore, such procedures are known from DE 10 2010 042 695 A1, DE 10 2010 000 663 A1 and DE 10 2010 031 060 A1. Disclosure of the invention

[0006] Accordingly, a method and a device are proposed which largely avoid the disadvantages of known methods and devices. The device according to the invention comprises at least one sensor element for detecting at least a fraction of a gas in a measuring gas chamber. The sensor element can, in principle, be any device configured to detect the fraction of the gas in the measuring gas chamber. Preferably, the sensor element can be a lambda probe, for example, a single-cell and / or a two-cell probe. In principle, the sensor element can also be an NO sensor. xThe sensor element can be a broadband lambda sensor and / or a wideband lambda sensor. For example, the sensor element can be a lambda sensor, as described in Robert Bosch GmbH: Sensors in Motor Vehicles, 1st edition 2010, pages 160-165. The sensor element can preferably be a ceramic sensor element. The detection method can be quantitative and / or qualitative. The gas can be any gas. Particularly preferably, the gas can be exhaust gas from an internal combustion engine. The gas component can be, for example, a concentration and / or a percentage and / or a partial pressure and / or a volume fraction of at least one gas component. The gas component can be, for example, oxygen and / or NO. xand / or a nitrogen oxide and / or a hydrocarbon. The gas can comprise at least one gas component. The measuring gas chamber can, in principle, be any space designed to be exposed to the gas. Preferably, the measuring gas chamber can be an exhaust gas tract. For example, the measuring gas chamber can be a space containing the gas.

[0007] The sensor element comprises at least one pump cell with at least two pump electrodes connected to each other by at least one solid electrolyte. The pump cell can, in principle, be any electrochemical cell comprising at least two pump electrodes and the solid electrolyte. The cell can preferably be operated in pump mode. The solid electrolyte can, in particular, be a ceramic solid. The solid electrolyte can preferably have ion-conducting, especially oxygen-ion-conducting, properties. Examples of such solid electrolytes are zirconium dioxide-based solid electrolytes, such as yttrium-stabilized zirconium dioxide (YSZ) and / or scandium-stabilized zirconium dioxide (ScSZ). A pump cell can, in particular, be a cell through which an ion current can flow and / or through which an ion current can be driven.At the pump electrodes of the pump cell, conversions from an ion current to an electron current and / or vice versa can occur, for example, through oxidation and / or reduction. The pump electrodes can be at least partially constructed of at least one conductive material, for example, at least one metallic material. A conversion of an ion current to an electron current can take place on at least one surface of a pump electrode. Of the pump electrodes, a first pump electrode, for example, an outer pump electrode, can be exposed to the gas mixture. A second pump electrode can be arranged in a cavity, separated from the gas, for example, by at least one porous diffusion barrier and / or by the solid electrolyte. The cavity can preferably be connected to an exhaust duct.For example, the cavity can also be connected to another space, such as at least one reference gas space, via a further diffusion barrier and / or via the solid electrolyte. The second pump electrode can, for example, be at least one inner pump electrode.

[0008] The pump electrodes can therefore, for example, comprise at least one first pump electrode and at least one second pump electrode. The first pump electrode and / or the second pump electrode can, in principle, be designed like a pump electrode as described above. The terms "first" and "second" are purely descriptive and do not, in particular, indicate any sequence or whether, for example, further pump electrodes are included, such as at least one third pump electrode. The device can, for example, comprise at least one further pump electrode and / or at least one further electrode, preferably at least one reference electrode. The reference electrode can, for example, be arranged at least partially in at least one reference gas channel.The term "exposed to the gas mixture" can be understood, for example, to mean that the first pump electrode can be exposed to the gas mixture, in particular directly, but also indirectly, preferably via at least one porous layer, for example, via at least one porous protective layer. The term "diffusion barrier" can be understood, for example, as a layer of material that suppresses the flow of the gas and / or a fluid and / or the gas mixture and / or the gas component, while the layer promotes the diffusion of the gas and / or the fluid and / or the gas mixture and / or the gas component and / or ions.The term "cavity" can be understood as a space within the sensor element that, while structurally separated from the measuring gas chamber, can nevertheless be exposed to the gas component and / or the gas mixture and / or the gas from the measuring gas chamber, for example, via at least one gas inlet path and / or via the diffusion barrier. For instance, the cavity can also be exposed to gas and / or the gas component only via the solid electrolyte. The exhaust duct can, for example, be a connection to the outside air, particularly to prevent overpressure in the cavity.

[0009] Alternatively, the first pump electrode can be an internal pump electrode and the second pump electrode an exhaust duct electrode. The internal pump electrode can be located within the cavity. The internal pump electrode can be exposed to gas via the diffusion barrier. The exhaust duct electrode can be at least partially connected to air, preferably ambient air, via the exhaust duct.

[0010] The device comprises at least one control unit. The control unit is configured to perform a method according to the invention for operating the sensor element, as described below. The control unit and / or the device may include at least one data processing device. For example, the data processing device may be integrated into the control unit. However, the data processing device may also be arranged, at least partially, separately from the control unit. The control unit and / or the data processing device may, for example, be connected to and / or connectable with the sensor element. The term "control unit" can be understood to mean a device configured to support and / or control at least one function of the device, in particular of the sensor element.The term "connectable" can be understood, for example, as a property that allows for or already exists the establishment of an electrical connection. The control circuitry can be designed to be wholly or partially separate from the sensor element, or it can be wholly or partially integrated into the sensor element, for example, into at least one connector of the sensor element and / or the device. The control circuitry can comprise at least one voltage measuring device and / or at least one current measuring device for detecting at least one pump current and / or at least one pump voltage and / or at least one limiting current and / or for controlling the pump voltage and / or for controlling the pump current. Particularly preferably, the control circuitry can at least partially comprise at least one pump voltage tracking device. The pump voltage tracking device can, for example, be configured to adjust the pump voltage to the pump current in a single-celled organism.Alternatively or additionally, the control unit and / or the sensor element and / or the device may include at least one supply device and / or at least one pump voltage control unit. The supply device may, in particular, comprise at least one voltage source and / or at least one current source. For example, the supply device may be configured to supply the sensor element with the pump current and / or the pump voltage and / or to implement the pump voltage control, at least partially.

[0011] In a further aspect of the present invention, a method for operating a sensor element for detecting at least a proportion of a gas in a measuring gas chamber is proposed.

[0012] According to the invention, a method for operating a sensor element for detecting at least one oxygen fraction of an exhaust gas in an exhaust tract is provided, wherein the sensor element has at least one pump cell with at least two pump electrodes connected to each other by at least one solid electrolyte, wherein the pump electrodes comprise a first pump electrode and a second pump electrode, wherein the first pump electrode is arranged as an inner pump electrode in a cavity of the sensor element and can be exposed to the exhaust gas via a diffusion barrier, wherein the second pump electrode is an exhaust air electrode that can be connected to ambient air via an exhaust air duct, wherein at least one measured variable is detected in the method, wherein the measured variable is a pump current between the first and the second electrode, which represents a limiting current, and wherein at least one compensation variable is further determined.wherein the compensation quantity is at least partially dependent on capacitive effects at at least one junction between at least one of the pump electrodes and the solid electrolyte, namely a charging current between the first and the second electrode, which is determined by determining at least one time course of at least one electrical voltage across at least one electrochemical double layer, using the time course of the electrical voltage across the electrochemical double layer and at least one electrode capacitance using the formula, ΔIp=∂Q∂t=CIPE∂Udl∂t, wherein at least one corrected measured quantity is determined from the measured quantity and the compensation quantity, using the formula Ip korr = Ip - ΔIp, where the oxygen content in the exhaust gas is determined from the corrected measured quantity.

[0013] The method can be carried out, at least partially, by at least one control unit, for example, by the control unit as described above. The control unit can, for example, comprise at least one ASIC (application-specific integrated circuit). The method can, for example, be carried out, at least partially, by the data processing device. The method can be carried out, for example, each time the proportion of gas in the measuring gas chamber is measured, but can also be repeated at least once at any desired time interval. For example, the compensation value can be stored, for example, in a memory, preferably in a memory of the control unit. The compensation value can, for example, be used several times when measuring the proportion of gas in the measuring gas chamber, for example, for several measured values, preferably measured at different times.

[0014] The pump cell can, for example, be operated in pulsed mode. The pump cell can be operated in pulsed mode, for example, by means of a control signal. Particularly preferably, the pump cell and / or the sensor element can be operated in pulsed mode by means of pulse width modulation. Preferably, pulse pauses can occur between voltage and / or current pulses. The pulse pause can, in particular, be a phase in the operation of the sensor element during which no electrical current is applied to the pump cell. The pump cell can, in particular, be operated in pulsed mode such that it is supplied with a square wave voltage and / or a square wave current. The time course of the electrical voltage across the electrochemical double layer U dl (t) can be determined by measurement at at least two different pulse intervals. Alternatively or additionally, the time course of the electrical voltage across the electrochemical double layer can be derived. ∂Udl∂t=Upj−UpiΔti,j The measurement can be taken at at least two different pulse intervals. The pulse interval can, in particular, be a pulse interval of a pulse-width modulation. During the measurement at least two different pulse intervals, an electrical voltage Up can be measured, and / or a quantity that depends on the electrical voltage, for example, an electrical current and / or an ohmic resistance. For example, at least an i-th and at least a j-th pulse interval can be measured at a time interval of Δt. i,j can be used. i and j can preferably be integers, where i ≠ j is preferred. For example, at least one pump voltage can be used during the i-th pulse pause Up. i and at least one pump voltage during the j-th pulse pause Up j be recorded. Using the formula ∂Udl∂t=Upj−UpiΔti,j For example, at least one derivative, preferably as defined above, of the time course of the electrical voltage across the electrochemical double layer can be used. ∂Udl∂t can be determined. The pulse intervals i and j can preferably be adjacent pulse intervals; in particular, j = n and i = n - 1.

[0015] Alternatively or additionally, at least one temporal change of at least one pump current can be implemented. ΔIpΔt can be recorded. For example, at least one change over time of at least one pump voltage can be recorded. ΔUpΔt The change in pump voltage over time can preferably be determined using the formula ΔUpΔt=ΔUpsoll⋅(1−exp(−Δt / τ))Δt be determined soll , preferred ΔUpsollΔt, This formula can preferably be calculated within the framework of a pump voltage control system, for example, by the control unit, particularly in the case of strong and / or rapid changes, such as nearly step-like changes, in the proportion of gas in the measuring gas chamber. This formula, especially its exponential part, specifically accounts for an attenuation of the pump voltage through the use of a low-pass filter. The low-pass filter can, for example, be included by the control unit and / or by the device, preferably to suppress oscillation behavior in the control system. Using the time-dependent change of the pump current... ΔIpΔt and the change in pump voltage over time ΔUpΔt and at least one ohmic resistance of at least a part of the solid electrolyte R ElektrolytFor example, at least one derivative, preferably as defined above, of the time course of the electrical voltage across the electrochemical double layer can be used. ∂Udl∂t can be calculated, in particular using the formula ∂Udl∂t=ΔUpΔt−RelectrolyteΔIpΔt⋅Δt Δt can, in principle, be freely chosen. Preferably, Δt can be chosen such that both the pump current Ip and the pump voltage Up change essentially linearly over this time interval Δt. The ohmic resistance of at least a portion of the solid electrolyte R Elektrolyt The voltage can be stored, for example, in the control circuitry and / or can be acquired in the process, for example, by applying a current and measuring the voltage and / or by applying a voltage and measuring the current. At least one derivative, preferably as defined above, of the time course of the electrical voltage across the electrochemical double layer. ∂Udl∂t can be calculated from the difference in the change in pump voltage ΔUpΔt in the pump voltage tracking taking into account the low-pass filter and the resistance of at least part of the solid electrolyte R across the ohmic resistance Elektrolyt decreasing electrical voltage.

[0016] In the process, at least one electrode capacitance C can be used. IPE can be recorded. In principle, the electrode capacitance C can be measured. IPE The electrode capacitance C is stored in the device, for example in a control unit memory. IPEFor example, it can be recorded each time the proportion of gas in the measuring gas space is measured, but it can also be recorded once and stored in such a way that the electrode capacity can be used multiple times, for example to measure the proportion of gas in the measuring gas space and / or to determine the compensation quantity.

[0017] For example, particularly for determining the electrode capacitance, at least one time-varying pump voltage can be applied to the pump cell. At least one time-dependent profile of at least one pump current can be recorded. From the time-dependent profile of the pump current, in particular by evaluating at least one area and / or at least one integral of the pump current, for example as a current response, the electrode capacitance C can be determined. IPE will be closed.

[0018] The method and device according to the invention can offer a multitude of advantages over known methods and devices. For example, software compensation of capacitive charging currents can be performed within the framework of the method and / or device according to the invention. For example, signal deviations during pump voltage tracking can be at least significantly reduced. This can, for example, ensure signal accuracy, particularly during rapid gas exchanges, and / or guarantee that dynamic system functions can also be applied, for example, when using the device and / or the method according to the invention in a vehicle.The inventive method and the inventive device can further compensate for signal delays caused by electrode recharging, which can occur, for example, even without pump voltage tracking. Brief description of the drawings

[0019] Exemplary embodiments of the invention are shown in the following figures and are explained in more detail in the following description.

[0020] They show: Fig. 1 an embodiment of a device according to the invention; Fig. 2 a diagram illustrating an embodiment of a method according to the invention; and Fig. 3 a diagram relating to a further embodiment of a method according to the invention. Embodiments of the invention

[0021] In Fig. Figure 1 shows an embodiment of a device 110 according to the invention. The device 110 comprises at least one sensor element 112 for detecting at least a fraction of a gas, for example, an exhaust gas 113, in a measuring gas chamber. The sensor element 112 comprises at least one pump cell 114 with at least two pump electrodes 118 connected to each other by at least one solid electrolyte 116. The device 110 comprises at least one control unit 120. The control unit 120 may include at least one data processing device 122. The control unit 120 is configured to carry out a method according to the invention. At least one of the pump electrodes 118 may, for example, be an internal pump electrode (IPE) 124. At least one of the pump electrodes 118 may, for example, be an exhaust duct electrode 119.The sensor element 112 can further comprise at least one diffusion barrier (DB) 121 and / or at least one exhaust air duct (AK) 123. The exhaust air duct electrode 119 can be at least partially in contact with air 125 via the exhaust air duct 123. For example, at least a portion of the exhaust gas 113 can reach the inner pump electrode 118 via the diffusion barrier 121. The inner pump electrode 118 and the exhaust air duct electrode can preferably be at least partially enclosed by the pump cell 114. The sensor element 112 can preferably be a broadband lambda probe, in particular a broadband lambda probe with a pump cell 114. The sensor element 112 can be at least partially connected to the control unit 120 and / or to the data processing device 122 via at least one interface 127.

[0022] In the Fig. 2 and Fig. Figure 3 shows diagrams illustrating two different embodiments of the method according to the invention. Pump currents Ip in mA and voltages in mV are shown against a time t in s. The method according to the invention is a method for operating a sensor element 112, for example as described above, for detecting at least a fraction of a gas in a measuring gas chamber. The sensor element 112 has at least one pump cell 114 with at least two pump electrodes 118 connected to each other by at least one solid electrolyte 116. In the method, at least one measured quantity is detected. The measured quantity can be, for example, the pump current Ip and / or the voltage U. Furthermore, at least one compensation quantity is determined. The compensation quantity can be, for example, a compensation current ΔIp.The compensation quantity is at least partially dependent on capacitive effects at at least one interface between at least one of the pump electrodes 118 and the solid electrolyte 116. At least one corrected measurement quantity is determined from the measured quantity and the compensation quantity. The proportion of gas in the measuring gas chamber is then determined from the corrected measurement quantity. For example, the proportion of gas in the measuring gas chamber can be determined from the corrected measurement quantity using at least one characteristic curve, such as a relationship between a pump current and the proportion of gas in the measuring gas chamber.

[0023] The measured quantity can include at least one pump current Ip. The compensation quantity can include at least one charging current ΔIp. The corrected measured quantity Ip korr can be calculated, for example, especially using the formula Ip korr= Ip - ΔIp. The method can be carried out, at least partially, by at least one controller, for example, a controller 120 as described above. Controller 120 can, for example, be an ASIC CJ135 or an ASIC CJ125. For example, controller 120 can include at least one ASIC CJ135 and / or at least one ASIC CJ125. In principle, the controller can be any controller. Preferably, the controller can include at least one ASIC, for example, at least one ASIC CJ125 and / or at least one ASIC CJ135 and / or at least one other ASIC.

[0024] The method allows for at least one temporal profile of at least one electrical voltage across at least one electrochemical double layer U. dl(t) can be determined. Preferably, at least one derivative of the time course of the electrical voltage across the electrochemical double layer can be determined in the method. ∂Udl∂t can be determined. For example, the electrical voltage across the electrochemical double layer U can be determined. dl(t), in particular a voltage across the electrochemical double layer capacitance, can be measured during operation, for example during pulsed operation, especially in pulsed operation as when using an ASIC CJ135. For example, the voltage across the electrochemical double layer can also be determined and / or calculated alternatively, for example using a pump voltage tracker. When using an ASIC CJ125, for example, the use of a pump voltage tracker may be indicated, since the voltage, in particular the electrical voltage across the electrochemical double layer, cannot usually be measured. In principle, the voltage across the electrochemical double layer and / or the time course of the voltage across the electrochemical double layer and / or the derivative of the time course of the electrical voltage across the electrochemical double layer can be determined. ∂Udl∂t Alternatively or additionally, the process can be determined by alternative methods. In the method, at least one, preferably capacitive, charging current ΔIp can be used as a compensation parameter, preferably the derivative of the time course of the electrical voltage across the electrochemical double layer. ∂Udl∂t, and at least one electrode capacitance C IPE to be determined, in particular using the formula ΔIp=∂Q∂t=CIPE∂Udl∂t. Software compensation within the scope of the present invention can, in particular, be based on correcting the measured quantity, for example the probe signal Ip, by a capacitive charging current ΔIp as a compensation parameter. At the voltage U dlFor example, it could be a voltage across an electrochemical double layer of at least one of the pump electrodes 118, for example at least one inner pump electrode 124, as for example in Fig. 1 shown, act.

[0025] In the Fig. 2 and Fig. 3. In particular, exemplary measured variables, especially pump currents Ip, are shown as lines 126 and 128. Lines 126 and 128 indicate in the Fig. 2 and Fig. Three overshoots of 130 each occur. These overshoots can, for example, be pump currents that are higher than a constant pump current that establishes itself, such as after a change in the proportion of gas in the measuring gas chamber. The area under the overshoots, particularly between the overshoots and a constant pump current that establishes itself after approximately 0.9 seconds, can represent a charge flow. The area under the overshoots can, for example, be proportional to an electrode capacitance and a change in voltage: ΔQ = C IPE · ΔU.

[0026] In the Fig. In the embodiment of the method according to the invention described in section 2, the pump cell 114 can, for example, be operated in pulsed mode. Pulse pauses can occur between voltage and / or current pulses. The temporal profile of the electrical voltage across the electrochemical double layer U dl(t) can be determined by measurement at at least two different pulse intervals. Preferably, the time course of the electrical voltage across the electrochemical double layer can be derived. ∂Udl∂t by measurements at least two different pulse intervals. For example, at least an i-th and at least a j-th pulse interval can be recorded at a time interval of Δt. i,j can be used. At least one pump voltage during the i-th pulse pause Up i and at least one pump voltage during the j-th pulse pause Up j can be recorded. Using the formula ∂Udl∂t=Upj−UpiΔti,j can be at least one derivative, preferably as defined above, of the time course of the electrical voltage across the electrochemical double layer ∂Udl∂t This embodiment can be determined, for example, using a digital ASIC CJ135 as the control input 120. With the digital ASIC CJ135, the compensation parameter ΔIp can be determined, for example, given a known capacitance C. IPE It can be calculated directly, since the voltage across the electrochemical double layer preferably corresponds to the voltage during the pulse interval: Udl(t) = Up(pulse interval). The voltage during the pulse interval, Up(pulse interval), and thus the voltage Udl(t), can be measured, for example, in the pulse intervals of each clock cycle. A change in the voltage, preferably for calculating the compensation quantity, can be calculated, for example, using the formula ∂Udl∂t≈(Up(pulse pause n)−Up(pulse pause n−1)) cycle time. The clock time can be, for example, Δt. n,n-1This involves, in particular, the time interval between the nth pulse pause and the n-1th pulse pause. In this embodiment, a correction can be made, in particular, by detecting the change. ΔUp(Pulse Pause)Δt The current is detected, preferably by at least one CJ135 as a control element 120. In this embodiment of the method according to the invention, a current required for recharging a double-layer capacitor can be corrected, preferably directly, by the compensation variable. This can, for example, have the positive side effect that at least one signal delay due to electrode recharging, which can occur even without pump voltage tracking, can be compensated, so that the corrected measured variable, for example as a signal, with up tracking, also called pump voltage tracking, can be even more dynamic than without up tracking. Fig. Figure 2 shows in particular a schematic representation of an embodiment of the method according to the invention, specifically without the pulsed operation of the CJ135 as the control 120 and without the signal ripple resulting from a step-like pump voltage tracking, although this should not change the fundamental behavior. With this embodiment of the method according to the invention, the overshoot 130 can be at least partially, preferably completely, compensated, provided, for example, that the electrode capacitance C IPE and / or the voltage curve U dl (t) are known and / or can be recorded as accurately as possible.

[0027] In Fig. Figure 2 shows in particular an embodiment of the method according to the invention by means of a correction via Up (pulse pause), for example with a CJ135 as control 120. Line 132 shows in particular an exemplary course of the corrected measured quantity, for example of Ip. korr Line 134 shows the pump current Ip without Up tracking. Line 136 shows an example of the pump voltage during the pulse pauses Up(pulse pause) = U(IPE). Fig. In Figure 2, the described overshoot 130 is clearly visible below line 126. The areas between line 126 and line 134, particularly the pump currents Ip with and without up-tracking, correspond to the charge required for electrode recharging. The lines mentioned in Fig. 2 are, for example, generated by a simulation, for example, when the proportion of the gas changes, in particular a gas exchange, for example from 6% to 21% oxygen (O2).

[0028] In which Fig. In the further embodiment of the method according to the invention belonging to 3, at least one temporal change of at least one pump current can be achieved. ΔIpΔt can be recorded. For example, at least one change over time of at least one pump voltage can be recorded. ΔUpΔt can be determined using the time-dependent change in the pump flow. ΔIpΔt and the change in pump voltage over time ΔUpΔt and at least one ohmic resistance of at least one part of the solid electrolyte 116 R Elektrolyt For example, at least one derivative, preferably as defined above, of the time course of the electrical voltage across the electrochemical double layer can be used. ∂Udl∂t can be calculated, in particular using the formula ∂Udl∂t=ΔUpΔt−RelectrolyteΔIpΔt. In this further embodiment, an ASIC CJ125 can be used as the control input 120, for example. When using the ASIC CJ125, a change in the voltage drop across the electrode double-layer capacitance can typically be achieved. ∂Udl∂t The voltage drop across the electrode double-layer capacitance can not be measured directly. However, it can at least be estimated from a change in the pump voltage, which can be calculated for tracking, especially for up tracking, in the control unit 120, particularly in the control unit ASIC CJ125. For this purpose, the total change in the pump voltage ΔUp can preferably be reduced by the component that drops as ohmic loss across the solid electrolyte 116. The change in the pump voltage ΔUp can be obtained, for example, by calculating a change in Upset, for example ΔUpset, which can be calculated, for example, from a ramp for the pump voltage tracking, taking into account a low-pass filter, for example a PT-1 filter, as expressed in the following formula: ΔUp = ΔUpset · (1 - e (-Δt÷τ)). is detected. In this further embodiment of the method according to the invention, this can in particular involve a correction via the change of the predetermined pump voltage, preferably using at least one CJ125 as a control 120. As in Fig. As can be seen in Figure 3, overshoots 130, especially signal overshoots, can also be significantly reduced if the change in the electrode double-layer capacitance, for example the electrode voltage, is estimated from the up tracking. Fig. Figure 2 shows in particular that the overshoot 130 can also be significantly reduced by correcting the applied pump voltage, either alternatively or additionally, as illustrated in line 138. Line 138 shows in particular the corrected measured quantity, for example, Ip. korr Line 140 shows the pump current Ip without tracking. Line 142 shows the pump voltage Up.

[0029] In one embodiment of the method according to the invention, for example in one of the embodiments described above, at least one electrode capacitance C can be added, for example IPE The process can be recorded. For example, at least one time-varying pump voltage can be applied to the pump cell 114. At least one time-dependent profile of at least one pump current can be recorded. From the time-dependent profile of the pump current, the electrode capacitance C can be determined. IPE to be closed. A prerequisite for an embodiment of the method according to the invention may be, in particular for determining the compensation quantity, for example a compensation function, that the electrode capacitance C IPEThe electrode capacitance is known or can be determined. Since the value of the electrode capacitance can change significantly, for example due to aging, it can be advantageous to measure the electrode capacitance during operation, for example when carrying out the method according to the invention. This can be done, for example, by applying a voltage current to the sensor element 112, in particular to a probe, preferably in limiting current operation, and evaluating an area under a current response.

Claims

[1] Method for operating a sensor element (112) for detecting at least one oxygen fraction of an exhaust gas (113) in an exhaust tract, wherein the sensor element (112) has at least one pump cell (114) with at least two pump electrodes (118) connected to each other by at least one solid electrolyte (116), wherein the pump electrodes (118) comprise a first pump electrode and a second pump electrode, wherein the first pump electrode is arranged as an inner pump electrode (124) in a cavity of the sensor element (112) and can be exposed to the exhaust gas (113) via a diffusion barrier (121), wherein the second pump electrode is an exhaust air electrode (119) which can be connected to ambient air (125) via an exhaust air duct (123), wherein at least one measured quantity is detected in the method, wherein the measured quantity is a pump current (Ip) between the first and the second electrode, which represents a limiting current,furthermore, at least one compensation parameter is determined, wherein the compensation parameter is at least partially dependent on capacitive effects at at least one transition between at least one of the pump electrodes (118) and the solid electrolyte (116), namely a charging current (Δlp) between the first and the second electrode, which is determined by measuring at least one time course of at least one electrical voltage across at least one electrochemical double layer U. dl (t) is determined using the time course of the electrical voltage across the electrochemical double layer U dl (t) and at least one electrode capacitance C IPE using the formula ΔIp=∂Q∂t=CIPE∂Udl∂t ΔIp where at least one corrected measured quantity (Ip) is obtained from the measured quantity and the compensation quantity. korr ) is determined using the formula IP korr= Ip - ΔIp, where the corrected measured quantity (Ip) korr ) the oxygen content in the exhaust gas (113) is determined. [2] Method according to any of the preceding claims, wherein the method is carried out at least partially by at least one control (120). [3] Method according to the preceding claim, wherein the pump cell (114) is operated in pulsed mode, wherein pulse pauses occur between voltage and / or current pulses, wherein the time course of the electrical voltage over the electrochemical double layer U dl (t) is recorded by measurement during at least two different pulse pauses. [4] Method according to the preceding claim, wherein at least one i-th and at least one j-th pulse pause occurs at a time interval of Δt i,j is used, with at least one pump voltage being applied during the i-th pulse pause. i and at least one pump voltage during the j-th pulse pause Up jto be recorded, using the formula ∂Udl∂t=Upj−UpiΔti,j at least one derivative of the time course of the electrical voltage across the electrochemical double layer ∂Udl∂t is determined. [5] Method according to one of the three preceding claims, wherein at least one time change of at least one pump current ΔIpΔt is recorded, whereby at least one temporal change of at least one pump voltage is detected. ΔUpΔt is determined by using the time-dependent change of the pump current. ΔIpΔt and the change in pump voltage over time ΔUpΔt and at least one ohmic resistance of at least one part of the solid electrolyte R Elektrolyt at least one derivative of the time course of the electrical voltage across the electrochemical double layer ∂Udl∂t is calculated, in particular using the formula ∂Udl∂t=ΔUpΔt−RelectrolyteΔIpΔt. [6] Method according to any one of the preceding claims, wherein the electrode capacitance C IPE is recorded. [7] Method according to the preceding claim, wherein at least one time-varying pump voltage is applied to the pump cell (114), wherein at least one time profile of at least one pump current is recorded, wherein the electrode capacitance C can be determined from the time profile of the pump current. IPE will be closed. [8] Device (110) comprising at least one sensor element (112) for detecting at least one fraction of a gas in a measuring gas chamber, wherein the sensor element (112) has at least one pump cell (114) with at least two pump electrodes (118) connected to each other by at least one solid electrolyte (116), wherein the device (110) comprises at least one control unit (120), wherein the control unit (120) is configured to carry out a method for operating the sensor element (112) according to one of the preceding claims.

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