DE102010040821A1 - Method for determining a property of a gas in a measuring gas space - Google Patents

Abstract

A method is proposed for determining at least one property of a gas in a measurement gas space (112), in particular for detecting at least one gas component in the gas. At least one sensor element (114) is used, wherein the sensor element (114) has at least one pump cell (125) with at least one first electrode (120), at least one second electrode (124) and at least one of the first electrode (120) and the second electrode (124) connecting solid electrolyte (123). From a pumping current through the pumping cell (125) is closed on the property. In at least one measuring step of the method, the pumping cell (125) is controlled or controlled using at least one reference variable (148). In at least one control step of the method, the reference variable (148) is changed and a change in the pumping current is detected.

Description

State of the art

Numerous different devices and methods for determining the properties of gases in a sample gas space are known from the prior art. In the following, the invention will be described essentially with reference to devices and methods which use at least one solid electrolyte material, that is to say a material which has ion-conducting properties, for example a ceramic solid electrolyte material. Examples of such ceramic solid electrolyte materials are yttrium-stabilized zirconia (YSZ) and / or scandium-doped zirconia (ScSZ). Examples of devices of the type mentioned are in Robert Bosch GmbH: Sensors in the motor vehicle, issue 2007, pages 154-159 described. The at least one property of the gas may in particular be a fraction of a gas component of the gas, which can be determined qualitatively and / or quantitatively. In particular, an oxygen content can be determined. The proportion can be given for example in the form of a percentage and / or in the form of a partial pressure. Alternatively or additionally, however, other properties of the gas can also be determined, for example physical and / or chemical properties.

In devices according to the above-described prior art, which are used to determine an oxygen content in a gas, which are also commonly referred to as lambda probes, in addition to so-called jump probes also so-called broadband lambda probes exist. Such broadband lambda probes exist in a single-cell configuration or in a multi-cell configuration. In the case of single-cell lambda probes, an amount of O ₂ and / or fat gas diffusing into a measuring cavity is generally determined on the basis of a limiting current which is established by the cell. In multicellular broadband lambda probes, such as in Robert Bosch GmbH: Sensors in the motor vehicle, issue 2007, pages 158-159 described, the oxygen content is measured using the necessary to control a cavity concentration on λ = 1 pumping current. The pumping current is at least approximately proportional to the O ₂ or fat gas content in the exhaust gas. The measurement of the cavity concentration is usually based on the determination of a Nernst voltage between a Nernst electrode in the cavity and an oxygen-purged reference electrode in a reference space. From the prior art, it is generally known to influence the target Nernst voltage, for example to lower permanently or to set a higher Nernst voltage. Out DE 10 2005 056 515 A1 furthermore, a method is known in which a gas composition or a gas type of a gas supplied to a lambda probe is detected by means of a modulated measurement gas change. In this case, the sensitivity of the probe for various gases is periodically changed by periodically adjusting the air ratio in the cavity of the lambda probe.

However, a technical challenge of known devices and methods basically consists in the fact that it can lead to a passivation of the inner pumping electrode arranged in the cavity. Such passivations may be caused, for example, by chromium deposition and / or by platinum segregation and / or by other processes which may reduce the activity and / or the number of three-phase sites on the electrode. In this case, at a certain pumping current I _p from the inner pumping electrode (IPE) to the outer pumping electrode (APE), a significant overvoltage at the interface between the electrode and the solid electrolyte is lost. As a result, the nominal Nernst voltage, which is typically set at 450 mV, can already be achieved with smaller currents than would be necessary for the adjustment of λ = 1 in the electrode cavity. The result is too small a pumping current, ie a drop in the characteristic I _p (λ).

Disclosure of the invention

Accordingly, a method and a sensor device for detecting at least one property of a gas in a measurement gas space are proposed, which at least largely avoid the disadvantages of known methods and sensor devices. The method and the sensor device can be used, in particular, to qualitatively and / or quantitatively detect a proportion of at least one gas component in the gas, for example a percentage and / or a partial pressure of the gas component, which in particular can be oxygen.

In the proposed method, at least one sensor element is used, wherein the sensor element comprises at least one pump cell with at least one first electrode, at least one second electrode and at least one solid electrolyte connecting the first electrode and the second electrode. The first electrode and / or the second electrode may, for example, be designed as cermet electrodes, for example as platinum cermet electrodes.

The solid electrolyte can basically be any body with ion-conducting properties. In particular, this may be a solid. In principle, however, as an alternative or in addition to a solid, but also Body in another state of aggregation conceivable, for example, liquid electrolytes. In particular, the solid electrolyte may be a ceramic solid electrolyte or may comprise a ceramic solid electrolyte. Alternatively or additionally, however, the solid electrolyte may also comprise one or more other materials having ion-conducting properties, for example one or more polymers. The solid electrolyte may be, for example, a zirconia-based solid electrolyte, for example YSZ and / or ScSZ.

The method is carried out such that from a pumping current through the pumping cell is closed to the property, for example, the oxygen content in the sample gas space. In particular, the sample gas space may be an exhaust tract of an internal combustion engine, and the gas may be an exhaust gas of the internal combustion engine. However, other embodiments and / or purposes are in principle possible.

In at least one measuring step of the method, the pumping cell is operated or controlled using at least one reference variable. In particular, as will be explained in more detail below, the second electrode may be arranged in an electrode cavity. For example, it is possible to detect a Nernst voltage between a measuring electrode which is likewise arranged in the electrode cavity and which may be configured as identical to the second electrode or which may be designed as a separate measuring electrode, and a reference electrode arranged in a reference gas space, for example a reference gas channel, and Actual value can be used. This actual value of the Nernst voltage can be compared with a predetermined nominal value of a Nernst voltage as a reference variable, and the pumping current through the pumping cell can be adjusted such that a control difference between the actual value and the reference variable disappears. For this process variant, for example, on Robert Bosch GmbH: Sensors in the motor vehicle, issue 2007, pages 158-159 and the regulation described there of a broadband lambda probe be referenced. Alternatively or additionally, however, the pumping cell can also be controlled and / or controlled using other controlled variables, control variables or reference variables. For example, a pumping current can be regulated by the pumping cell to a predetermined value.

In addition to the described measurement step, which can be carried out simply, repeatedly or even over a longer period of time, the method furthermore comprises at least one control step, which can likewise be carried out simply, repeatedly or even over a relatively long period of time. For example, at least one control step can be followed by at least one measuring step, after which a second measuring step can again follow. For example, measuring step and control step can be carried out alternately. However, other embodiments are possible in principle.

In the control step, the reference variable is changed. This change can take place, for example, by a predetermined amount, for example by a setpoint Nernst voltage U _{N, setpoint being changed} by, for example, a predetermined amount, in particular increased. Alternatively or additionally, a desired pumping voltage U _{P, desired} and / or a desired pumping current U _{P, desired} can also be changed, for example likewise increased by a predetermined amount, in particular.

The change in the reference variable can be done once or several times. In particular, the change can also be repeated, with the same change or an adapted change. In particular, the change in the reference variable can also be performed oscillating, for example periodically oscillating. The adaptation can then take place, for example, in such a way that the mean value of the oscillation of the reference variable is adjusted in such a way, for example by a regulating device, that the resulting change in the pumping current, for example the resulting pumping current amplitude or amplitude of the change in the pumping current, is a predetermined threshold value, for example 20 μA, does not exceed.

Furthermore, in the control step, a change of the pumping current I _p is detected by the pumping cell. In other words, the change of the pumping current can be detected in response to the change of the command variable. This change can be detected as an absolute change or in the form of a temporal evolution of the pumping current. Other ways of quantifying the change are possible, such as detecting a change over a period of time.

In particular, the method can be carried out in such a way that the reference variable in the measuring step is adapted, in particular increased, if the change in the pumping current in the control step no longer satisfies at least one threshold condition. For example, in this control step it can be queried whether the pumping current reaches, exceeds or falls below at least a predetermined threshold value. For example, it is possible to query whether the pumping current or a characteristic variable derived therefrom or the change in the pumping current or whose magnitude is less than a predetermined threshold, less than or equal to a predetermined threshold, or similar threshold conditions may be set. In particular, the threshold condition can be adapted in such a way that a variation of the pump current which is still tolerable within the scope of customary changes of the sensor element still fulfills the threshold condition, whereas changes which indicate strong electrode polarization and / or contamination of the electrodes and / or passivation of the electrodes , in particular the first electrode, which no longer fulfill at least one threshold condition.

In particular, the method may be performed such that on-board compensation of electrode polarization is performed, for example, in the multi-cell broadband lambda probes described above. The method can be carried out in particular such that a nominal Nernst voltage in the control step, which is also referred to as the test phase, by a defined amount, for example by 20 to 400 mV, in particular by 100 to 300 mV and more preferably by 200 mV, briefly is increased, for example, a period of 0.5 to 10 s, in particular a period of 0.8 to 2 s and more preferably for a period of 1 s. If the pump current I _P increases by at least one threshold value or by more than one threshold value, a new control setpoint value of the Nernst voltage U _{N, setpoint} can be stored in a control electronics. By way of example, the threshold value can be 50 μA to 400 μA, in particular 100 μA to 300 μA, and particularly preferably 200 μA. The control setpoint of the Nernst voltage can be raised, for example, by 20 mV to 400 mV, in particular by 100 mV to 300 mV and particularly preferably by 200 mV.

In general, the adjustment of the reference variable can be simple or iterative. If an iterative adaptation, for example, the reference variable can be increased or decreased so many times by one or more predetermined amounts, which can be adapted to the number of steps and / or, for example, increasingly smaller, until the change in the pumping current in the Control step that meets at least one threshold condition.

If it is detected in the control step that the change in the pumping current in the control step no longer fulfills the at least one threshold condition, one or more further measures can be taken, alternatively or in addition to a change in the reference variable or an adjustment of the reference variable. In a preferred embodiment of the method, for example, if it is determined that the change in the pumping current no longer satisfies the at least one threshold condition, a regeneration step can be initiated. Such regeneration steps may include various measures that at least partially reverse the change in one or more of the electrodes. For example, a regeneration step may include a pump flow reversal by the pump cell. Such pumping current reversal can be initiated for example for a certain period of time. Alternatively or additionally, for example, temperature increases or other measures for the regeneration of one or more of the electrodes come into consideration, for example, by the sensor element is temporarily exposed to a rich exhaust gas.

The method can be carried out in particular such that the first electrode and / or the second electrode are acted upon with gas from the measurement gas space or can be acted upon. For example, the sensor element may be configured such that the first electrode and / or the second electrode are in communication with the measurement gas space directly or via a gas-permeable protective layer. Alternatively, however, the first electrode and / or the second electrode may also be connected to the measuring gas space by at least one diffusion barrier. Thus, the first electrode and / or the second electrode can be arranged, for example, on a surface of the sensor element or in an electrode cavity in the interior of the sensor element, which communicates with the measuring gas space via the at least one diffusion barrier. The at least one diffusion barrier can, for example, protect the first electrode and / or the second electrode from contamination and / or set a limiting current of the pump cell.

Alternatively or additionally, one or more of the electrodes may be in communication with a reference gas space. For example, the second electrode may be an electrode in communication with a reference gas space, while, for example, the first electrode may be supplied with gas from the measurement gas space. Accordingly, the second electrode can for example be arranged directly in the reference gas space or communicate with this reference gas space in another way. The reference gas space is a gas space in which a defined gas atmosphere can be established. For example, this can be a closed cavity, which can be acted upon by a pumping process with a defined atmosphere. Alternatively or additionally, however, the reference gas space may also comprise at least one reference gas channel, for example one Air reference channel, which may for example be connected to an environment of the sensor element, which may be formed separately from the sample gas space, for example. In this way, for example, a defined air atmosphere can be established in the reference gas space. The proposed embodiment, in which the second electrode communicates with at least one reference gas space, can be used in particular in the case of a single-cell sensor structure. However, other sensor structures are basically possible.

As an alternative or in addition to the arrangement in which the second electrode is arranged in a reference gas space, the second electrode or at least one of the second electrodes (if a plurality of second electrodes are provided) can also be arranged in an electrode cavity. This electrode cavity can be formed, for example, separated from the sample gas space by the solid electrolyte. For example, the electrode cavity may be configured as a cavity in which a defined gas atmosphere or gas composition is to be set by the control or regulating method described above, for example a defined lambda value. For this purpose, for example, at least one measuring electrode, for example at least one Nernst electrode, can furthermore be arranged in the electrode cavity. This at least one measuring electrode may be wholly or partly identical to the component with the second electrode or electrically connected to the second electrode, which is particularly preferred in the context of the present invention and as for example in Robert Bosch GmbH: Sensors in the motor vehicle, issue 2007, pages 158-159 is described. In the case of such second electrodes, which are used at the same time as a pumping electrode for a pumping cell and as a Nernst electrode for a Nernst voltage measurement, the avoidance according to the invention or the balancing of the electrode polarization according to the invention is particularly advantageously noticeable. Alternatively, however, the at least one measuring electrode in the electrode cavity may also be formed separately from the second electrode. Other embodiments are possible.

The pumping cell can be operated in the measuring step, in particular in a limiting current operation. Under a limiting current is to be understood as the saturation current at a certain composition of the gas, which sets in the pumping current-voltage characteristic. The pumping voltage can in particular be selected such that the pumping current is in the saturation region, as is common in many broadband probes.

The command variable can, as described above, be configured in various ways. In particular, the reference variable may comprise at least one desired value of a potential and / or a voltage at the second electrode. As described above, in particular a desired Nernst voltage can be specified as a reference variable, which is measured, for example, between the second electrode and a reference electrode, which can be arranged, for example, in a reference gas space in the manner described above.

The first electrode can in particular be charged with gas from the measuring gas space, as stated above. The sensor element can furthermore comprise at least one reference electrode in at least one reference gas space, wherein a Nernst voltage U _N between the second electrode and the reference electrode can be detected. In the measuring step, as stated above, in particular the pumping current through the pumping cell can be regulated by using a nominal Nernst voltage U _{N, nominal} as a reference variable. In the control step can, as stated above, in particular the target Nernst voltage U _{N, target} by a value .DELTA.U _{N, to be} changed, in particular be increased, wherein the change .DELTA.I _{P of} the pump current is detected and compared with at least one threshold. The nominal Nernststpannung can for example be changed, in particular be increased when the change .DELTA.I _P reaches or exceeds the threshold. For example, the desired Nernst voltage U _{N, Soll} by one or more predetermined amounts are changed, the amounts can be fixed or can for example be adapted to the iteration of the process, for example, iteratively smaller can be selected when the change .DELTA.I _{P of} the pump current approaches the threshold.

Alternatively or additionally, the reference variable may also include a pump voltage U _P , for example a desired pump voltage. In the control step, this pumping voltage can be changed by a value ΔU _P , wherein the change ΔI _P of the pumping current can be detected in response to this change in the pumping voltage and compared with at least one threshold value. In the measuring step, the pumping voltage can then be changed, in particular increased, if the change ΔI _P at least reaches or exceeds the threshold value. In this way, for example, unicellular sensor elements can be operated with the proposed method.

Alternatively or additionally, the reference variable may also include a pumping current I _p . In the control step, the pumping current can be changed by a value ΔI _p . This can be a Change .DELTA.U _{p of} a pump voltage and / or a change .DELTA.U _{N of} a Nernst voltage detected and compared with at least one threshold. For an intact sensor element, for example, it may be required that the resulting ΔU _p or ΔU _N exceeds or does not fall below the threshold value. For example, in the measuring step, the pumping current can be changed, in particular increased, if the changes ΔU _p or ΔU _N exceed or do not fall below the threshold value.

In a further aspect of the present invention, a sensor device is proposed for detecting at least one property of a gas in a measurement gas space, which in particular can be set up to carry out a method according to one or more of the embodiments described above. Accordingly, for possible embodiments of the sensor device, reference may be made to the above description of the proposed method. The sensor device may include corresponding devices to perform one, several or all of the substeps of the method described above. The sensor device comprises at least one sensor element, in particular at least one ceramic sensor element. The sensor element comprises at least one pump cell having at least one first electrode, at least one second electrode and at least one solid electrolyte connecting the first electrode and the second electrode. For further possible embodiments of the sensor element, reference may be made to the above description. The sensor device further comprises at least one controller connected to the sensor element or at least connectable. The controller can be set up centrally or else decentrally and can include, for example, one or more data processing devices. The control can also be completely or partially integrated in a central motor control or also be integrated in whole or in part in the sensor element and / or a plug.

The controller is arranged to close the property from pumping current through the pumping cell. For example, the controller may for this purpose comprise at least one application device, for example at least one voltage source and / or current source, in order to apply at least one pumping voltage and / or at least one pumping current to the pumping cell. For example, from the pumping current to the gas composition, for example, the proportion of the gas of the gas component in the measuring gas space, be closed, for example, an oxygen content. For this purpose, the controller may, for example, further comprise at least one measuring device, for example at least one current measuring device and / or a voltage measuring device, for example in order to measure the pumping current through the pumping cell. The controller is furthermore set up to operate or control the pumping cell in at least one measuring step using at least one reference variable. For this purpose, the controller may comprise, for example, at least one voltage regulation and / or at least one current regulation and / or at least one voltage control and / or at least one current control, which may be connected to the pump cell, for example. The controller is further configured to change the reference variable in at least one control step and to detect a change in the pumping current. For this purpose, for example, the controller can be set up in terms of programming in order to carry out the checking step and to carry out the corresponding changes or measurements. To carry out the measurements, the controller can, for example, comprise at least one measuring device, as stated above.

The proposed method and the proposed sensor device have numerous advantages over known methods and devices. Thus, these can be used in particular for reliable on-board compensation of a change in one or more of the electrodes of the sensor element. In this way it is possible to reliably prevent or at least reduce a change in the measured value and / or a signal distortion which can occur as a result of aging.

Brief description of the drawings

Exemplary embodiments of the invention, which are illustrated by way of example in the figures, are explained below. The invention is not limited to the embodiments.

In detail show:

1 an embodiment of a sensor device according to the invention;

2 Pump current-pump voltage characteristics and Nernstspannungs-pump voltage characteristics for various sensor elements; and

3 Pump current setpoint Nernst voltage characteristic curves for proper sensor elements and for sensor elements with electrode polarization.

Embodiments of the invention

In 1 is an example of an embodiment of a sensor device according to the invention 110 for detecting at least one property of a gas in a sample gas space 112 shown. In particular, an oxygen content in the sample gas space 112 be determined. The sensor device 110 includes a sensor element 114 and one with the sensor element 114 via an interface and / or another connection 116 connected control 118 ,

The sensor element 114 includes in the illustrated embodiment, a first electrode 120 , which is also referred to below as APE (outer pumping electrode) and which may be arranged on an outer side of the sensor element. The first electrode 120 For example, by a gas-permeable protective layer 122 from the sample gas space 112 be separated. Furthermore, the sensor element comprises 114 a second electrode 124 , which in the illustrated embodiment in an electrode cavity 126 is arranged and which accordingly can also be referred to as inner pumping electrode (IPE). The electrode cavity 126 is over a gas access hole 128 and a diffusion barrier 130 , which limits a Nachdiffusion of oxygen and / or gas, with the sample gas space 112 in conjunction and is thus acted upon with gas from the sample gas space. The second electrode 124 is with the first electrode 120 over a solid electrolyte 123 connected. The first electrode 120 , the solid electrolyte 123 and the second electrode 124 together form a pump cell 125 , Furthermore, the sensor element comprises 114 in the illustrated embodiment, a third electrode 132 , which is also referred to as a reference electrode (RE) and which in a reference gas space 134 is arranged. The reference gas space 134 , which may be open or which may be wholly or partially, as in 1 represented with a gas-permeable, porous material 136 can be filled, for example, as a reference gas channel 138 be configured, for example, as an air reference channel. The second electrode 124 , the solid electrolyte 123 and the third electrode 132 together form a Nernst cell 139 ,

the interface 116 preferably includes electrode leads 140 . 142 and 144 to the first electrode 120 , to the second electrode 124 and to the third electrode 132 , The control 118 includes in the illustrated embodiment, a control device 146 , About the control device 146 can be a Nernst voltage between the IPE 124 and the RE 132 to a target Nernst voltage U _{N, target} as a reference variable 148 be set or adjusted. For example, the controller 118 for this purpose an adjustable voltage source 150 to specify the target Nernstspannung. For example, one end of the voltage source 150 and the electrode lead 142 the second electrode 124 on electrical ground 152 be switched so that the via the electrode lead 144 the third electrode 132 provided Nernst voltage U _N (actual value) and the target Nernst voltage U _{N, target} (setpoint) in a comparison device 154 (For example, a comparator) can be compared with each other to a control difference from a control variable and / or manipulated variable 156 in the form of a pump voltage U _P and / or a pump current I _P to generate, with which in turn the APE 120 is applied to one of the reference variable 148 corresponding atmosphere in the electrode cavity 126 adjust.

The specification of the reference variable 148 For example, by a data processing device 158 in the controller 118 done, which, for example, the adjustable voltage source 150 influenced and / or may include them in whole or in part. Furthermore, the controller 118 one or more measuring devices 160 include, for example, the pumping current I _P and / or the pumping voltage U _{P can} detect. The measured values of this measuring device 160 For example, to the data processing device 158 to be provided. Alternatively or additionally, the measuring device 160 also completely or partially in the data processing device 158 be integrated. The data processing device 158 For example, it may be program-technically configured to perform a method according to one or more of the method variants described above. The data processing device 158 For example, it may include a microcontroller. Alternatively or additionally, the controller 118 also be designed in whole or in part as an application-specific integrated circuit (ASIC). Various other configurations are possible.

Based on 2 and 3 should the problem of conventional devices 110 and methods are explained. In conventional sensor devices 110 Of the described type, which are not set up to perform a method according to the invention, the control setpoint of the Nernst voltage U _{N, target is} usually fixed. This serves to provide a void concentration of λ = 1 in the electrode cavity 126 adjust or regulate. For typical sensor devices, the control setpoint is over the life of the sensor device 110 typically 450 mV. However, this leads, as based on the 2 should be described, especially in sensor elements 114 in which the second electrode 124 used simultaneously for a pump current measurement and for a Nernst voltage measurement, to aging effects, which affect the measurement. So it can over the lifetime lead to a passivation of the electrode cavity 126 arranged inner pumping electrode 124 For example, by chromium deposition or by platinum segregation or by other processes, the activity and / or the number of three-phase sites the electrode 124 can reduce. In this case IP falls from the IPE at a given pumping current 124 to the outer pumping electrode 120 a significant overvoltage at the interface IPE 124 / Solid electrolyte 123 from. As a result, the setpoint Nernst voltage U _{N, setpoint} of, for example, 450 mV can already be achieved with smaller currents than for the regulation of λ = 1 in the electrode cavity 126 would be necessary. The result is too small a pumping current I _P , ie a drop in the characteristic I _P (λ).

In 2 is the pump voltage U _P on the horizontal axis on the pumping cell 125 applied. On the left vertical axis of the pumping current I _{P is} plotted. The curve 162 , which is assigned to this left vertical axis, denotes a pumping current-pumping voltage characteristic of an intact sensor element 114 in which there is still no electrode polarization at the second electrode 124 occured. The dashed curve 164 on the other hand, denotes a pumping current of a polarizing sensor element 114 , So a sensor element 114 in which at the second electrode 124 the polarization effects described above have occurred. It can be seen that this curve is considerably flatter and later approaches the saturation pump current I _S.

gilt für ein polarisierendes Sensorelement 114 mit den Kurven 164, 168:

In anderen Worten hängt bei einem intakten Sensorelement 114 der sich einstellende Pumpstrom I_P kaum von der Führungsgröße U_N,Soll ab, während bei polarisierenden Sensorelementen 114 ein starker Anstieg des Pumpstroms I_P mit der Führungsgröße U_N,Soll zu verzeichnen ist. Dies ist in 3 gezeigt. Hier bezeichnet die Kurve 170 den Pumpstrom I_P eines intakten Sensorelements als Funktion der Führungsgröße U_N,Soll, wohingegen die Kurve 172 den Pumpstrom eines polarisierenden Sensorelements 114 bezeichnet.Furthermore, in 2 on the right vertical axis, the Nernst voltages U _N plotted as a function of the pumping voltage U _P. Again, the solid curve indicates 166 a Nernst voltage of an intact sensor element 114 whereas the dashed curve shows 168 a Nernst voltage of a polarizing sensor element 114 denotes, that is, a sensor element 114 in which the second electrode 124 having the polarization effects described above. Starting from these curves 166 . 168 can describe the effect outlined above. Typically, in sensor devices 110 the in 1 described type the Nernst voltage to a value U _{N, set} by 450 mV, which is an intact sensor element 114 the pump voltage U _{P, 1} corresponds. How out 2 recognizable, is the pumping current characteristic 162 such an intact sensor element 114 at this pumping voltage U _{P, 1} already in the saturation region and has at least approximately the value I _S on. In a polarizing sensor element 114 on the other hand, it falls on the polarizing second electrode 124 , which both as an electrode for the pumping current measurement by the pumping cell 125 as well as Nernst electrode for the Nernst cell 139 is used, a high voltage at the passage resistance, which adds to the Nernst voltage. As a result, the effectively measured voltage U _{N reaches} the electrode lead 144 in 1 even at smaller pump currents I _P the value U _{N, target} of 450 mV. In 2 this is illustrated by the fact that the Nernst voltage curve 168 of the polarizing sensor element 114 rises significantly earlier than the Nernst voltage curve 166 of the intact sensor element 114 , Accordingly, the curve reaches 168 even at a considerably smaller pumping voltage U _{P, 2} the value of 450 mV. At this pumping voltage U _{P, 2} is the pumping current characteristic 164 of the polarizing sensor element 114 but not yet in saturation, but at a value I _P * at which the pumping current characteristic still rises sharply. While for an intact sensor element 114 thus essentially:

applies to a polarizing sensor element 114 with the curves 164 . 168 :

In other words, with an intact sensor element, it hangs 114 the self-adjusting pump current I _P hardly from the reference variable U _{N, Soll} from, while in polarizing sensor elements 114 a sharp increase in the pump current I _P with the reference variable U _{N, target} is recorded. This is in 3 shown. Here is the curve 170 the pump current I _{P of} an intact sensor element as a function of the reference variable U _{N, Soll} , whereas the curve 172 the pumping current of a polarizing sensor element 114 designated.

However, precisely this relationship is preferably used in a method according to the invention. In such a method, the pump cell is in at least one measuring step 125 using the reference variable U _N, controlled or controlled operated and pumped from the flow on the property of the gas in the sample gas space 112 , For example, the oxygen partial pressure, closed. In contrast, in at least one control step of the method, the reference variable U _{N, target is} changed, for example by a predetermined amount ΔU _{N, Soll} . In this case, the change in the pumping current ΔI _{P is} detected. In the curve 170 in 3 this change is almost 0 or very small. In a non-intact sensor element 114 with the curve 172 on the other hand is a very steep increase of the reference variable I _P D _{L, Soll,} recorded at least at the operating point of 450 mV. In other words, ΔI _{P is} divided by ΔU _{N, target is} greater than 0. This ΔI _P (or, which means ΔI _P divided by ΔU _{N, Soll} or, which is also equivalent, I ' _P ) can be at least one threshold be compared. If this at least one threshold is at least reached or exceeded, then it can be concluded that the sensor element 114 is no longer intact. In this case can For example, a warning can be issued or the reference variable U _{N, target} can be adjusted. For example, the reference variable I _{N, Soll can be} increased, for example, by a predetermined amount. Thereafter, a further control step can be run through and, if appropriate, the setpoint Nernst voltage can be further increased, provided that the above-described threshold condition is still not met and the change ΔI _{P is} still too large. In this way it can be achieved that U _N in 2 is increased so that U _{P, 2} so far to the right in 2 shifts that the pumping current I _P * approaches the saturation pumping current I _S.

The method can for example be carried out such that at fixed time intervals, for example every 5 hours and / or preferably in a lean exhaust gas state, preferably - but not necessary - in overrun, the change of the pump current I _P with an increase of U _{N, target} detected and then optionally the target Nernst voltage U _{N, Soll is} increased. Then another test cycle, ie a further control step, can be run through and, if appropriate, the setpoint Nernst voltage U _{N, setpoint can be} further increased. Optionally, further control steps may follow. Preferably, the change .DELTA.I _{P is} measured at a U _{N, target increase} and subsequent reduction to produce a redundancy of the data. Alternatively or additionally, the target Nernst voltage U _{N, set} in this or in other embodiments of the inventive method, as well as one or more other control variables, permanent oscillate, for example with an amplitude of 10 mV, and for example with a frequency of 100 Hz. The mean value of this oscillation can be regulated by a control device to a minimum value such that a resulting pump current amplitude does not exceed a specific threshold value, for example 20 μA.

The inventive method was above the example of a multi-cell sensor element 114 described. Alternatively or additionally, however, the method described above can also be applied to a single-cell lambda probe, for example to a sensor element 114 which is just the pump cell 125 having. In this case, for example, the desired Nernst voltage U _{N, target can be} replaced by a desired pump voltage U _{P, Soll} . Because the curve 164 in 2 significantly later saturation I _S reaches than the intact curve 162 can also be detected by a threshold method in the control step when the pump cell 125 no longer running in limit current mode. In this case, for example, the desired pumping voltage U _{P, Soll can be} increased, which in turn can also take place in one or more steps, optionally also iteratively and / or oscillatingly.

By the method described above and the sensor device described above 110 a high robustness against an electrode polarization can be achieved. In addition, the method described above allows a continuous operation of the sensor element 114 at a lowered temperature, which for example by means of a in 1 not shown heating element can be adjusted. For example, with the proposed method in one or more of the variants presented above, a temperature of the pumping cell 125 be set to a value of 500 to 800 ° C, in particular to a value of 600 to 700 ° C. Due to this lowered temperature of the sensor element 114 and in particular the pumping cell 125 a heating power requirement can be significantly reduced. Furthermore, the amount of catalytically active noble metal in one or more of the electrodes can also be determined with the proposed method and the resulting robustness with respect to electrode polarization 120 . 124 and 132 especially in the IPE 124 , significantly reduce. Furthermore, the detection of an electrode polarization in the at least one control step, for example by varying the command variable and in particular the target Nernst voltage, in one or more of the methods described above as a trigger for a regeneration process, for example by means of a temporary pumping current reversal and / or a temporary or permanent increase in temperature and / or a temporary application of grease gas can be used. Such measures generally have a regenerating effect.

The change in the reference variable can be carried out in any method according to the invention both in the positive and in the negative direction. Thus, substantially increases in the reference variable have been described above. As in 2 can be seen, but in principle also decreases in the reference variable are possible, for example by not only increasing a nominal Nernst voltage, but, alternatively or additionally, also lowered to detect a polarization.

The method described above and the sensor device described above 110 were using the example of sensor devices 110 for the detection of oxygen in the sample gas space 112 shown. Also for other applications are the proposed method and the proposed sensor device 110 but basically suitable. For example, the proposed method can in principle also be applied to NOx sensors, so that the sensor device 110 for example, for detecting a NOx content in the Measuring gas chamber 112 can be used. Such sensor elements are basically also known from the prior art.

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 patent literature

• DE 102005056515 A1 [0002]

Cited non-patent literature

• Robert Bosch GmbH: Sensors in the motor vehicle, edition 2007, pages 154-159 [0001]
• Robert Bosch GmbH: Sensors in the motor vehicle, edition 2007, pages 158-159 [0002]
• Robert Bosch GmbH: Sensors in the motor vehicle, edition 2007, pages 158-159 [0008]
• Robert Bosch GmbH: Sensors in motor vehicles, Edition 2007, pages 158-159 [0019]

Claims (12)

Method for determining at least one property of a gas in a measuring gas space ( 112 ), in particular for detecting at least one gas component in the gas, wherein at least one sensor element ( 114 ) is used, wherein the sensor element ( 114 ) at least one pump cell ( 125 ) with at least one first electrode ( 120 ), at least one second electrode ( 124 ) and at least one the first electrode ( 120 ) and the second electrode ( 124 ) connecting solid electrolyte ( 123 ), wherein from a pumping current through the pumping cell ( 125 ) is closed to the property, wherein in at least one measuring step of the method, the pumping cell ( 125 ) using at least one reference variable ( 148 ) is controlled or controlled, wherein in at least one control step of the method, the reference variable ( 148 ) is changed and a change in the pumping current is detected. Method according to the preceding claim, wherein the reference variable ( 148 ) is adjusted in the measuring step, in particular is increased if the change in the pumping current in the control step no longer meets at least one threshold condition. Method according to the preceding claim, wherein the adaptation of the reference variable ( 148 ) iteratively until the change in pumping current in the control step satisfies the at least one threshold condition. Method according to one of the preceding claims, wherein at least one regeneration step is initiated if it is determined in the control step that the change in the pumping current no longer fulfills the at least one threshold condition, in particular a regeneration step with at least one pumping current reversal in the pump cell ( 125 ) and / or a temporary or permanent increase in temperature and / or with a temporary application of grease gas. Method according to one of the preceding claims, wherein the second electrode ( 124 ) is selected from: one with at least one reference gas space ( 134 ) associated electrode ( 124 ), in particular one with at least one reference gas channel ( 138 ) associated electrode ( 124 ); one in an electrode cavity ( 126 ) arranged electrode ( 124 ). Method according to one of the preceding claims, wherein the pump cell ( 125 ) is operated in the measuring step in a limit current operation. Method according to one of the preceding claims, wherein the reference variable ( 148 ) at least one desired value of a potential and / or a voltage at the second electrode ( 124 ). Method according to the preceding claim, wherein the second electrode ( 124 ) with gas from the sample gas space ( 112 ) is applied, wherein the sensor element ( 114 ) further at least one reference electrode ( 132 ) in at least one reference gas space ( 134 ), wherein a Nernst voltage U _N between the second electrode ( 124 ) and the reference electrode ( 132 ), wherein in the measuring step the pumping current through the pumping cell ( 125 ) using a desired Nernst voltage U _{N, setpoint} as a reference variable ( 148 ) is regulated. Method according to the preceding claim, wherein in the control step, the setpoint Nernst voltage U _{N, setpoint is changed} by a value ΔU _{N, Soll} , wherein the change ΔI _{p of} the pumping current is detected and compared with at least one threshold value, wherein the setpoint Nernst voltage changes is increased, in particular, when the change .DELTA.I _p reaches or exceeds the threshold. Method according to one of the preceding claims, wherein the reference variable ( 148 ) Comprises a pump voltage U _p, wherein the pump voltage and the change is detected .DELTA.I _p of the pump current and compared with at least one threshold value is changed by a value .DELTA.U _p in the control step, wherein the pumping voltage is changed in the measuring step, in particular increased, when the change ΔI _p reaches or exceeds the threshold value. Method according to one of the preceding claims, wherein the reference variable ( 148 ) comprises a pumping current I _p , wherein in the control step the pumping current is changed by a value ΔI _p , wherein a change ΔU _{p of} a pumping voltage and / or a change ΔU _{N of} a Nernst voltage are detected and compared with at least one threshold value, wherein in the measuring step the pumping current is changed, in particular is increased, when the changes .DELTA.U _p or .DELTA.U _N exceed the threshold or not fall below. Sensor device ( 110 ) for detecting at least one property of a gas in a sample gas space ( 112 ), in particular using a method according to one of the preceding claims, comprising at least one sensor element ( 114 ), wherein the sensor element ( 114 ) at least one pump cell ( 125 ) with at least one first electrode ( 120 ), at least one second electrode ( 124 ) and at least one the first electrode ( 120 ) and the second electrode ( 124 ) connecting solid electrolyte ( 123 ), wherein the Sensor device ( 110 ) at least one with the sensor element ( 114 ) connected control ( 118 ), wherein the controller ( 118 ) is adapted to be pumped by the pumping cell ( 125 ) to close the property, the controller ( 118 ) is further set up in at least one measuring step, the pump cell ( 125 ) using at least one reference variable ( 148 ) controlled or controlled, the controller ( 118 ) is further set up in at least one control step, the reference variable ( 148 ) and detect a change in pumping current.

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