DE102010039188A1 - Method for detecting component e.g. oxygen in exhaust gas of combustion engine, involves applying voltage nearer to Nernst voltage to pump cell, to determine storage capacity value that affects value of current flowing via pump cell - Google Patents

Abstract

The method involves measuring current flowing through pump cell of sensor element in measurement mode (156). The storage capacity of reference gas space is checked during diagnostic mode (158). The voltage nearer to Nernst voltage is applied to the pump cell, so as to determine storage capacity value that affects the measured value of current flowing through pump cell in measurement mode. An independent claim is included for device for detecting component of gas in gas measuring chamber.

Description

State of the art

A large number of sensor elements and methods for detecting at least one property of a gas in a measuring gas space are known from the prior art. In principle, these can be any physical and / or chemical properties of the gas, one or more properties being able to be detected. The invention is described below in particular with reference to a qualitative and / or quantitative detection of a gas component of the gas, in particular with reference to a detection of an oxygen content in the gas. 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 gas can be detected.

In particular, ceramic sensor elements are known from the prior art, which are based on the use of electrolytic properties of certain solids, ie ion-conducting properties of these solids. In particular, these solids can be ceramic solid electrolytes, such as, for example, zirconium dioxide, in particular yttrium-stabilized zirconium dioxide (YSZ) and / or scandium-doped zirconium dioxide (ScSZ). For example, such sensor elements may be configured as so-called lambda probes, as are known, for example, in Robert Bosch GmbH: Sensors in Motor Vehicles, Edition 2007, pages 154-159. In addition to so-called jump probes, lambda probes are also known which are based on the use of one or more pump cells. These pump cells can be used in a single-celled structure or as more complex multicellular structures. For example, in known lambda probes for use in diesel systems in lean operation, oxygen is pumped from the sample gas space, for example an exhaust tract of the internal combustion engine, from a first pumping electrode, for example an inner pumping electrode, into a reference gas space, for example an exhaust air duct. The exhaust duct is typically designed such that the delivery of oxygen to the ambient air through the exhaust duct is severely hampered. This means that in lean operation an oxygen overpressure builds up in the exhaust air duct and oxygen is stored. An example of such a sensor element, which is suitable for this purpose and which can also be used in the context of the present invention is in DE 10 2008 002 734 A1 described. In the exhaust air duct or generally in the reference gas channel, in particular a specifically formed oxygen storage can be provided. The oxygen, which is stored in this oxygen storage, can be used in short fat phases, as they occur, for example, in the regeneration of NOx storage catalysts, to oxidize the present in the sample gas at the inner pumping electrode fat gases. This makes a time-limited measurement of fat lambda values possible with the sensor element. In particular, the system can decide at any time via a model of the oxygen loading in the exhaust air duct that is running in the background whether sufficient oxygen is present in the exhaust air duct for the intended fat measurement.

In such sensor elements, in which the exhaust duct or a part of the same itself acts as an oxygen storage for a short-term rich gas operation, but in particular mechanical damage in use, such as cracks in the region of the exhaust duct, cause the properties of the oxygen storage change greatly. In this case, the loading model used to decide on the possibility of performing a short-term fat measurement may provide incorrect information about the amount of oxygen available for fat measurement. In extreme cases, no oxygen is available, and instead of the correct rich lambda value (λ <1), the sensor element gives a value of λ = 1. Since this possible malfunction occurs only with rich exhaust gas, this usually falls in the normal, lean lambda mode Diesel sensor elements not on. In some cases, malfunctions can be detected due to plausibility considerations of the supplied lambda values. In other cases, however, such recognition is not possible.

An example of a critical case is the regeneration of NOx storage catalysts (NSCs). During regeneration, GHGs are consumed in the NSC. A sensor element located downstream of the NSC receives a gas mixture with the air ratio λ = 1 during regeneration. However, once the stored NOx is removed, rich gas arrives at the sensor element located downstream of the NSC. The task of the sensor element is to detect this fat gas and measure it if necessary. If a regeneration strategy is chosen in which the regeneration is not completely carried out, then the sensor element located downstream of the NSC does not receive any rich gas during the regeneration. In case of malfunctions of the NSC, however, breaks down fat gas to the sensor element. A sensor element with a highly leaking exhaust duct would not recognize this breakthrough and thus the malfunction of the NPC. It would therefore be desirable to have a device and a method which enable a metrological diagnosis of malfunctions. In particular, a metrological possibility for the diagnosis of Leaks in the area of the exhaust duct of the sensor element, in particular a lambda probe suitable for diesel applications, are made available. As a result, in particular an on-board diagnosis of malfunctions should be made possible.

Disclosure of the invention

Accordingly, a method and a 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 devices. In particular, as described above, the at least one property of the gas, which may in principle be any physical and / or chemical property, may be a fraction of at least one gas component in the gas, for example a partial pressure and / or a percentage of gas component. The gas component may in particular be oxygen. However, other properties are basically detectable. 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 and, in particular, an exhaust gas in the case of the gas.

The method uses at least one sensor element with at least one cell. A cell is to be understood in particular as a ceramic element having at least two electrodes and at least one solid electrolyte according to the type described above, in particular a ceramic solid electrolyte. The cell accordingly comprises 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 sensor element can be constructed unicellularly and comprise no further cells and / or further electrodes in addition to the said cell. Alternatively, however, the sensor element may also have a more complex structure and be configured as a multicell sensor element.

The first electrode can be acted upon by the gas from the sample gas space. This application can be effected, for example, directly, for example by arranging the first electrode on an upper side of a layer structure of the sensor element and exposing it directly to the gas of the measuring gas space and / or by applying a gas-permeable protective layer to the gas. Alternatively, however, the first electrode can also be arranged in the interior of a layer structure of the sensor element and can be acted upon by gas from the measurement gas space via one or more gas inlet paths. For example, the first electrode can be designed as an inner pumping electrode and can be acted upon with gas via at least one gas inlet hole and preferably via at least one diffusion barrier which limits an inflow and / or outflow of gas to the first electrode. Embodiments will be described in more detail below.

The second electrode is in communication with at least one reference gas space. This can be done in such a way that the second electrode is arranged directly in the reference gas space or is connected to the reference gas space via at least one connection. A reference gas space is to be understood as a space within the sensor element which is formed separately from the measurement gas space, so that no compensation of gases between the reference gas space and the sample gas space can take place or only a greatly slowed gas balance, for example on a time scale of several minutes, preferably several hours or even several days. In particular, the reference gas space may comprise at least one reference gas channel. The reference gas channel may in particular be in communication with an environment, for example ambient air. The reference gas space should be set up to store a supply of a gas component of the gas, for example oxygen. In this case, storage may in particular be understood to mean a process in which the reference gas space holds the supply of the gas component on a time scale of at least a few minutes before this supply is optionally released to the ambient air and / or other spaces. In particular, the reference gas space for this purpose may include at least one memory in which the supply of the gas component can be stored. By way of example, this can be an oxygen reservoir which has been deliberately formed from a reference gas channel, as in FIG DE 10 2008 002 734 A1 is described. Accordingly, the sensor element set forth in this publication can also be used in the context of the present invention. The reference gas space and / or the memory within the reference gas space can be designed to be open. Alternatively or additionally, the reference gas space, in particular the memory, may also be completely or partially filled with at least one porous, gas-permeable material, for example a porous ceramic material.

To solve the problem described above, it is proposed that the proposed method comprises at least two operating modes. These operating modes can each be carried out simply or repeatedly. The operating modes may in particular be carried out at different times, for example in such a way that the Operating modes do not overlap in time. In addition to the operating modes mentioned below, one or more further operating modes can also be carried out, for example method steps which are not mentioned below. One or more of the following modes of operation may also be performed one at a time or several times.

Thus, the proposed method comprises at least one measurement mode. In this measurement mode, the cell is operated as a pump cell, i. H. it is subjected to at least one pumping voltage and / or at least one pumping current. By means of the at least one pumping current through the pumping cell is thereby closed to the at least one property to be detected. In this case, the pumping current can be detected directly and / or at least one variable correlating to the pumping current can be detected, for example at least one pumping voltage required to achieve at least one predetermined pumping current. Various embodiments are possible and generally known to the person skilled in the art, as can be concluded from the pumping current or, which is synonymous, at least one variable correlating to the pumping current to the at least one characteristic.

Furthermore, the method comprises at least one diagnostic mode. In the diagnostic mode, a storage capacity of the reference gas space is checked. A check of the storage capacity of the reference gas space can be understood in particular as to whether the reference gas space and / or a part thereof, for example a store arranged within the reference gas space for the at least one gas component, meets certain requirements. In particular, the storage capability may include a statement as to whether the reference gas space and / or a part thereof, for example the storage tank, have a predetermined minimum density. For example, the storage capability can include a statement as to whether the reference gas space and / or the store can hold the supply of the gas component for a predefined minimum time before the supply of the gas component in the reference gas space and / or the store has fallen below a predetermined value. The storage capacity can be specified in the form of a digital statement, for example in the form of a statement that the storage capacity of a minimum requirement is sufficient or not sufficient, or can also be specified quantitatively, for example by storage times before the supply within the reference gas space and / or Memory has dropped below a predetermined value. Alternatively or additionally, other information and / or measured variables can be used to qualify and / or quantify the storage capability.

In the diagnostic mode at least one measured variable is detected, which is influenced by a voltage applied to the cell Nernst voltage. The Nernst voltage applied between the second electrode and the first electrode is calculated according to the Nernst equation from the different partial pressures of the gas component at the first and the second electrode, for example by the different oxygen partial pressures at these electrodes. The measured variable influenced by this Nernst voltage may, for example, be a voltage and / or a current which are influenced by the Nernst voltage between the first electrode and the second electrode. For example, the Nernst voltage applied to the cell counteracts voltages impressed on the outside of the cell and thus influences an effective voltage at the Nernst cell, which in turn is the driving force for a current through the cell. Thus, the Nernst voltage can affect various measured variables which can be detected at the sensor element and / or a control of the sensor element. From this measurand can then be concluded on the storage capacity. Thus, for example, at least one absolute value of the measured variable and / or at least one time profile of the measured variable can be detected and from this the storage capability can be deduced. Various examples for performing such a diagnostic mode will be explained in more detail below.

As described above, in addition to the at least two modes of operation, further method steps may be performed. For example, at least one regeneration phase can be carried out between the at least one measurement mode and the at least one diagnostic mode. Thus, many sensor elements, as known from the prior art, used in so-called limit current operation. In the limiting current operation, for example, all oxygen molecules arriving at the first electrode, for example all oxygen molecules penetrating a diffusion barrier upstream of the first electrode, are pumped to the second electrode so that the oxygen partial pressure at the first electrode is practically zero and not the oxygen partial pressure in the sample gas chamber. The regeneration phase can be used, for example, to at least largely match the partial pressure of the gas component, in particular the oxygen partial pressure, to the partial pressure of the gas component in the measurement gas space, for example up to at least 90%, preferably up to at least 95% or even up to at least 99 %. In particular, for this purpose in conventional Diffusion barriers a regeneration phase are performed with a period of 10 ms to 2 s, preferably a regeneration phase of 50 ms to 1.5 s and more preferably a regeneration phase of 100 ms to 1 s. For example, regeneration phases of 200 ms to 800 ms can be used. If several measurement modes and several diagnostic modes are performed, for example alternating, then several regeneration phases can also be carried out.

As described above, in particular, loading models exist which at least approximately describe the supply of the gas component of the gas in the reference gas space, for example at a specific time of operation of the sensor element, for example at a specific time during the method. These loading models can be carried out, for example, by means of at least one data processing device, for example by means of at least one microcomputer set up in the program. These loading models may include, for example, simple rate equations or differential equations that take into account the known accesses and outlets of the gas component in the reference gas space, in particular in a memory. For example, access or exit of gas molecules of the gas component may be through a pumping process through the cell, for example, this access may be quantified by known currents through the cell. Furthermore, in particular with a reference gas channel, an outflow of molecules of the gas component can be quantified by known diffusion properties and / or flow properties of the reference gas channel. Thus, for example, diffusion properties and / or flow properties of the reference gas channel can be determined analytically, empirically or semiempirically, for example in the form of one or more diffusion coefficients. In this way, for example, an expected outflow and / or expected Abdiffusion be quantified from the memory through the reference gas channel. In this way, loading models can be set up, which in known sensor elements, such as the in DE 10 2008 002 734 A1 described sensor element, are already used and which, for example, have an expected time course of the gas component (for example, a partial pressure and / or a percentage of the gas component) at the second electrode to the result. From this loading model can thus be concluded that an expected partial pressure of the gas component in the reference gas space and / or at the second electrode. From the expected partial pressure can be concluded that an expected Nernst voltage of the cell. For example, the expected Nernst voltage can be calculated from the Nernst equation using the expected partial pressure at the second electrode and a partial pressure at the first electrode (calculated, for example, based on the last known lambda value). From the expected Nernst voltage can in turn be concluded on an expected measure. This expected measured variable may be, for example, the Nernst voltage itself or, as stated above, at least one measured quantity influenced by the expected Nernst voltage. The measured variable actually measured can then be compared with the expected measured variable and concluded from this comparison on the storage capacity. This comparison can be done, for example, again by means of one or more thresholds. Thus, for example, a difference between the measured variable and the expected measured variable or an amount of this difference can be formed and this difference can be compared with at least one threshold value. For example, if the actually measured variable deviates from the expected measured variable by at least or more than a predetermined threshold value, it can be concluded that the storage capability of the reference gas space and / or a part thereof, for example the memory, has an abnormality. For example, such an abnormal storage capability may indicate a leakage of the reference gas space, such as the presence of one or more cracks and / or other irregularities.

In general, in the proposed method, the measured variable itself or at least one value derived from the measured variable, for example a difference between the measured variable and the expected measured variable, can be compared with at least one threshold value and concluded from the comparison of the storage capability. In particular, this at least one threshold value can be at least one predefined threshold value. Alternatively or additionally, however, the at least one threshold value may also include at least one threshold value calculated according to a loading model of the reference gas space, for example as described above. The threshold value can be fixed in time or, in turn, can in both cases also be a function of the time, for example a function of the time after the start of the diagnostic mode and / or after the end of the measurement mode.

As described above, the measured variable is basically any variable detectable within or outside the sensor element, for example a current and / or a voltage which is influenced by the Nernst voltage applied to the cell. In particular, the Measure the Nernst voltage U _N to the cell itself or include the Nernstspannung UN. Alternatively or additionally, the measured variable may also be a time profile of the Nernst voltage UN (t) at the cell and / or comprise this time profile. Again alternatively or additionally, the measured variable may also be or include a time change of the Nernst voltage UN at the cell, for example a time change ΔU _N over a predetermined period of time or a time derivative of the Nernst voltage. Again alternatively or additionally, the measured variable may also include a period of time until the Nernst voltage UN reaches at the cell at least a predetermined threshold value, for example a period of time from a predetermined start time, for example a start time at which the diagnostic mode is started.

In the diagnostic phase, in particular, at least one predetermined pumping current I _{p can be set} by the cell. This pumping current can be 0 or can also assume a value other than 0. As stated above, the pumping current I _{p is driven} by an effective pumping voltage on the cell resulting from a superposition of the externally applied pumping voltage U _p and the Nernst voltage across the cell. In particular, a pump current 0 ≤ | I _p | ≤ 0.1 mA can be set. The pumping current is preferably 0 ≦ | I _p | ≦ 0.7 mA, and more preferably 0 ≦ | I _p | ≤ 0.5 mA. For example, as stated above, a pump current I _p of 0 mA can be set. However, deviating from 0 pumping currents are basically adjustable. If at least one predetermined pumping current I _{p is} set, which can be predetermined in terms of time or variable in time, then the measured variable can be selected in particular from: a pumping voltage U _p required for setting the pumping current; a change over time of the pumping voltage U _p required for setting the pumping current; a time profile of the pump voltage required for the adjustment of the pumping current U _p ; a period of time until the pumping voltage U _p required for setting the pumping current reaches at least a predetermined threshold value. Combinations of the mentioned measured variables and / or other measured variables can also be used. Since, as described above, the pumping current is caused by the effective voltage at the cell, for example, the pumping voltage U _p required for the setting of the predetermined pumping current is a measured quantity which depends on the current Nernst voltage and / or the course of the Nernst voltage, as well as the others mentioned measurands.

As an alternative or in addition to the abovementioned possibilities, the cell can also be subjected to at least one predetermined pumping voltage in at least one diagnostic phase. In particular, this may be a pump voltage U _p , which is opposite to the pump voltage U _p used during the measurement mode. In other words, during the diagnostic phase, for example, the pumping direction through the cell may be reversed. However, other embodiments are possible in principle. If the cell is acted on in the diagnostic phase by the at least one predetermined pump voltage U _p , then the at least one measured variable can be selected in particular from: a pumping current I _p through the cell; a change over time of the pumping current I _p (ie in turn, for example, a change ΔI _p during a predetermined period of time and / or a derivative of the pumping current I _p ); a time profile of the pump current I _p , that is, for example, a function I _p (t); a period of time until the pump current I _{p reaches} at least a predetermined threshold, which in turn may be fixed or variable. Combinations of the aforementioned and / or other embodiments of the measured variable are possible.

In particular, in the method in which a pumping voltage U _{p is} predetermined and the at least one measured variable is at least partially derived from a pumping current I _p in this diagnostic phase, in particular a loading model can again be used. Thus, for example, from a loading model of the reference gas space to at least one expected partial pressure of the gas component, for example, an oxygen partial pressure, in the reference gas space and / or a part thereof, for example, a memory closed. From the expected partial pressure, in particular at the second electrode, it is again possible to deduce an expected Nernst voltage of the cell, for example by predetermining and / or assuming a partial pressure of the gas component at the first electrode, for example again based on the last measured lambda value , From the pumping voltage U _p during the diagnosis phase and the expected Nernst voltage, as stated above, an expected effective voltage at the cell can be concluded, since the pump voltage U _p and the Nernst voltage U _N are superimposed on the cell. From the expected effective voltage can then in turn be concluded on an expected measurand. This expected measurand can be compared with the actual measured variable and concluded from this comparison on the storage capacity. For example, it can be concluded from the expected effective voltage to an expected measurand, which is selected from: an expected pumping current; an expected change over time of the pumping current; one too expected time course of the pumping current; an expected period of time until the pumping current reaches at least a predetermined threshold. The comparison of the expected measured variable and the actual measured variable can, for example, in turn be carried out by means of at least one threshold value method in order, for example, to obtain a qualitative and / or quantitative statement about the storage capacity by means of this threshold value method.

If it is determined in the diagnostic mode that the storage capability, for example, qualitatively does not meet one or more minimum requirements, then at least one warning may be output to a user and / or to a control unit, for example. Other measures are possible in principle. For example, countermeasures can be taken to compensate, for example, the deteriorated storage capacity completely or partially electronically.

In addition to the method described above in one or more of the embodiments described above, a device for detecting at least one property of a gas in a measuring gas space is also proposed, in particular for detecting a gas component of the gas. The device comprises at least one sensor element and at least one controller connected to the sensor element. With respect to the possible embodiments of the sensor element can be made to the above description. The controller may be configured centrally or decentrally and may be completely or partially connected to the sensor element via at least one interface or may also be completely or partially integrated into the sensor element. It is particularly preferred if the control is completely or partially integrated in a central engine control and / or is in communication with a central engine control. The controller may in particular comprise at least one electronic component, preferably at least one program-technically configured data processing device. The sensor element has, as described above, at least one cell, which in turn comprises 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 can be acted upon with gas from the measurement gas space, and the second electrode is in communication with at least one reference gas space. The reference gas space is set up to store a supply of the gas component. The controller is configured to perform a method according to one or more of the embodiments described above. For example, the controller can be set up for this purpose programmatically, for example to perform a predetermined sequence with the at least two operating modes, ie at least one measuring mode and at least one diagnostic mode. For carrying out the measuring mode, the controller may, for example, comprise at least one loading device in order to apply at least one pumping current and / or at least one pumping voltage to the cell, and at least one measuring device to measure at least one pumping current and / or at least one pumping voltage at the cell. Other embodiments are possible. To carry out the diagnostic mode, the controller may, for example, also comprise at least one application device for charging the cell with at least one pumping current and / or at least one pumping voltage, for example a current regulator and / or a voltage regulator. Furthermore, the controller for carrying out the diagnostic mode may comprise at least one measuring device, for example a voltage measuring device and / or a current measuring device. Various other configurations are possible.

The method and apparatus described above in one or more of the described embodiments have a number of advantages over prior art devices and methods. In particular, it is possible to conclude a storage capability of the reference gas space in a metrologically simple manner by means of one or more of the above-described embodiments of the at least one diagnostic mode. In this way, for example, can easily achieve leaks in the region of an exhaust duct of a lambda probe, especially for diesel applications. For example, simple on-board diagnostics of malfunctions can be performed.

The invention may in particular be based on the fact that the changeover from the measuring mode into the diagnostic mode takes place in a known lambda point, for example in the case of a lean air ratio, for example during idling. In this phase, for example, the partial pressure of oxygen or the partial pressure of the gas component in the reference gas space, in particular in the exhaust duct, and the temporal change of the same can be followed and thus leaks can be detected. The advantages of the invention are, in particular, the costs for implementing the proposed method. In the implementation of the method described above, it may preferably be exclusively software diagnosis functions that can be implemented with the aid of, for example, an already existing hardware of the controller, which is already used today for example in single-cell lambda sensors for diesel operation.

Brief description of the drawings

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

Show it:

1 an embodiment of a device according to the invention;

2A and 2 B a first embodiment of a method according to the invention, wherein in the diagnostic mode as a measured variable, a voltage at the cell of the sensor element according to 1 is recorded;

3A and 3B a second embodiment of the method according to the invention, wherein in the diagnostic mode, a pumping current is reversed compared to the measuring mode and adjusted to a predetermined value, wherein the required pumping voltage is detected as a measured variable; and

4A and 4B a modification of the embodiment according to the 3A and 3B , in which the diagnostic mode is carried out over a longer period.

Embodiments of the invention

In 1 is an embodiment of a device according to the invention 110 for detecting at least one gas in a sample gas space 112 shown. The device 110 can be used in particular as a lambda probe for diesel applications in lean operation. Accordingly, it may be in the sample gas space 112 for example, an exhaust tract of an internal combustion engine act, for example, an exhaust passage of a diesel engine. The device 110 includes a controller 114 which have at least one interface 116 with at least one sensor element 118 connected is. This sensor element 118 For example, analogous to the in DE 10 2008 002 734 A1 be configured described sensor element. However, other embodiments of the sensor element are in principle possible.

The sensor element 118 For example, in the illustrated embodiment, it may comprise a layer structure and comprises a first electrode 120 , what a 1 also referred to as IPE (inner pumping electrode), and a second electrode 122 , what a 1 Also referred to as ALE (exhaust air electrode), and at least one of the electrodes 120 . 122 connecting solid electrolyte 124 , While the IPE 120 the exhaust air to the sample gas space 112 exposed directly or indirectly, for example via a gas access hole 126 and / or a diffusion barrier limiting the after-flow of gas 128 where, for example, the IPE 120 in an electrode cavity 130 is located, the ALE is in a reference gas space 132 arranged. This reference gas space 132 can, for example, as a reference gas channel 134 be configured, in particular as a reference air duct 136 , The reference gas space 132 is arranged to supply at least one gas component of the gas in the sample gas space 112 to store, in particular a gas component, for the ions of the solid electrolyte 124 has a conductivity, for example for oxygen. For this purpose, the reference gas space 132 in whole or in part as storage 138 be designed. For example, the reference gas channel 134 in an environment 140 open, for example in air. The reference gas channel 134 can be completely or partially with an in 1 be filled porous gas-permeable medium not shown. In this case, the reference gas channel 134 For example, be wholly or partially designed as memory, for example by, as in DE 10 2008 002 734 A1 described in the reference gas channel 134 a targeted formed oxygen storage is provided. The sensor element 118 In addition, further, in 1 not shown elements include, for example, at least one heating element.

The control 114 is in 1 illustrated by way of example and schematically in a possible embodiment. However, other embodiments are possible. So can the controller 114 for example, two terminals 142 . 144 comprising, for example, in 1 not shown supply lines and / or the interface 116 with the electrodes 120 . 122 are connectable. Furthermore, the controller 114 one or more measuring devices 146 . 148 include, for example, as in 1 shown, a measuring device 146 for detecting a voltage between the terminals 142 . 144 and / or a measuring device 148 for detecting a current, for example a pump current. Furthermore, the controller 114 at least one loading device 150 include one through the electrodes 120 . 122 and the solid electrolyte 124 formed cell 152 to apply a voltage and / or a current. For example, this loading device may be 150 to act a voltage source and / or a power source. The loading device 150 In particular, it can be designed to be adjustable and / or regulatable, for example by comprising a controllable voltage source and / or a controllable current source. Furthermore, the controller 114 at least one data processing device 154 exhibit. This data processing device 154 For example, it may be program-programmable to perform an above described one To perform method or a method described below in one or more of the illustrated embodiments. Furthermore, the data processing device 154 also be set up, for example, by means of a loading model of the reference gas space 132 to a current partial pressure of the gas component, for example, a current oxygen partial pressure and / or a profile of the oxygen partial pressure in the reference gas space 132 close and generate in this way an expected partial pressure of the gas component. Such loading models are basically known from the prior art.

For example, by means of in 1 A method can be carried out, which will be described below in various embodiments. These embodiments can also be combined with one another as desired. As indicated above, the method includes at least one measurement mode and at least one diagnostic mode. These modes are explained below using the example of a lambda probe for diesel applications. In measuring mode, for example, components of the exhaust gas pass out of the measuring gas space 112 over the diffusion barrier 128 to the IPE 120 , In the lean exhaust gas is oxygen at the IPE 120 converted to oxygen ions (O ^2- ). These are over the solid electrolyte 124 to the ALE 122 transported there and converted back to gaseous oxygen (O ₂ ) and into the reference air channel 136 , which is also referred to below as the exhaust duct, delivered. The driving force behind this process is that between the electrodes 120 . 122 applied pumping voltage U _p .

As described above, the method further includes at least one diagnostic mode. In this diagnostic mode is based on a storage capacity of the memory 138 closed, for example, malfunctions of the memory 138 to detect. For this purpose, as stated above, at least one by one on the cell 152 measured Nernst voltage influenced measured variable and concluded from this measure on the storage capacity. For detecting this at least one measured variable, whereby several measured variables can also be detected, there are several possibilities, which can also be combined.

Diagnostic option 1:

During lean operation it builds up when the sensor element functions correctly 118 an oxygen overpressure in the reference gas space 132 at the ALE 122 on. The diagnostic option 1 is based on it, as a measure of the Nernst voltage to the cell 152 or to detect a measured variable derived from the Nernst voltage. For example, the partial pressure of oxygen at the ALE 122 about the operation of the sensor element 118 be determined as oxygen concentration cell, analogous to the measuring principle of a jump probe. During this diagnosis, the most constant, lean air ratio λ should be in the sample gas chamber 112 available. The oxygen partial pressure at the ALE 122 then results from the Nernst equation to:

Here R denotes the general gas constant, T the temperature in K, F the Faraday constant, U _N the Nernst voltage at the cell 152 , P _O₂ (ALE) the oxygen partial pressure at the ALE 122 , and P _O₂ (IPE) the partial pressure of oxygen at the IPE 120 , The oxygen partial pressure P _O₂ (IPE) is basically known, for example, from the measuring mode when in the electrode cavity 130 the same gas mixture composition is present as in the sample gas space 112 , When switching from the at least one measurement mode in the at least one diagnostic mode can be waited accordingly for a certain time, which can also be referred to as regeneration phase, as in the measurement mode in the rule (especially during operation of the sensor element 118 in limit current operation during the measurement mode) the electrode cavity 130 the IPE 120 is almost free of oxygen by the measuring operation. After switching, therefore, it should be waited until the gas composition in the electrode cavity via the diffusion processes 130 the IPE 120 at least approximately that of the exhaust gas in the sample gas space 112 equivalent. Typical times are between 200 ms and 800 ms. The oxygen content in the exhaust gas is known in principle via the measurement signal immediately before switching over, for example via the last measurement signal in the measurement mode, so that the oxygen pressure at the ALE is determined via the Nernst equation 122 can be determined. In case of malfunctions of the reference gas space 132 does not build enough pressure on the ALE 122 to, and the Nernst voltage U _N according to equation (1) is too low.

An example of a measurement according to this diagnostic option 1 is in the 2A and 2 B shown. It shows 2A the pump current I _p during the measurement mode 156 and during the diagnostic mode 158 (a regeneration phase between these modes 156 . 158 is in the 2A and 2 B not shown), and 2 B shows a voltage U at the cell 152 during the two modes of operation 156 . 158 , The current and the voltage are each shown as a function of time t. For example, the voltage U in 2 B the by means of the measuring device 146 in 1 be recorded tension. The total time for diagnosis in the diagnostic mode is usually in one range from 0.5 s to 2 s. However, other times are possible in principle.

The actual diagnosis can be done in several ways. For example, a general minimum pressure can be specified as a diagnostic threshold. With the known partial pressure of oxygen at the IPE 120 this results in a threshold value for the detected voltage U according to 2 B which must not be fallen short of. As a further condition for this diagnosis, it should be ensured that the vehicle was operated for a sufficiently long time in the lean exhaust gas before the diagnostic operation, for example for one or more seconds at λ> 1.2.

A further, alternative or additional usable possibility of diagnosis according to diagnostic option 1 is the oxygen partial pressure in the reference gas space 132 via a moving load model, for example a in the data processing device 154 calculated loading model, to simulate. In this way, an expected Nernst voltage U _N can be calculated. By comparing measured and expected Nernst voltage, a respective diagnostic threshold can then be applied in order to carry out the diagnosis and to conclude the storage capability in this way.

The implementation in the control 114 can be done in several ways, which are also combinable. For example, in the diagnostic mode 158 the loading device 150 , For example, a pumping current regulator, are turned off, and it can, for example via the measuring device 146 , a resulting voltage U according to 2 B which in this case are in the diagnostic mode 158 essentially corresponds to the Nernst voltage U _N.

A second, alternatively or additionally implementable possibility is the loading device 150 , For example, the pump current controller is not completely off but, for example to regulate to a known pump current, such as a pump current I _p of 0 or close to 0. For example, = 0 effected a regulation to a resulting pumping current of I _p U _p as a reference variable. Without significant changes in the meaningfulness, low pump currents in the range 0 ≤ | I _p | ≤ 0.1 mA or similar pumping currents. In this case, the pumping voltage acts on the cell 152 the Nernst voltage on the cell 152 opposite. When the pumping voltage U _p and the Nernst voltage U _N cancel each other out, the pumping current I _p disappears. At the same time, these methods require correct contacting.

A third possibility, which can also be implemented alternatively or additionally, of implementing the diagnostic option 1 is, in turn, to deduce an expected Nernst voltage U _N from a loading model and then to select the pump voltage U _{p in} such a way that it precisely compensates for the expected Nernst voltage U _N should. In turn, the pump current I _p , for example detected by the measuring device, can then be used as the measured variable 148 , be used and / or its temporal change and / or its deviation from the expected pumping current I _p , which is 0.

Diagnostic option 2:

In a second, alternatively or in addition to the diagnostic option 1 feasible diagnostic option 2 can be assumed in principle the same starting conditions for the start of the diagnostic mode as in the diagnostic option 1. In contrast to the diagnostic option 1 but now with a predetermined pumping current I _p , for example, with a predetermined constant pumping current, oxygen from the reference gas space 132 from the ALE 122 to the IPE 120 be pumped, so with a relation to the measuring mode opposite pumping direction. The _p for achieving this pumping current I required pump voltage U _p to the change and / or the time course is recognized as a measure and / or. As indicated above, the driving force for the pumping current I _{p is} the effective voltage U _eff , which results from a superposition of the voltage externally by the controller 114 impressed pump voltage U _p and the Nernst voltage U _N in the cell 152 results. Thus, for example, at least one absolute value of the required pump voltage U _p and / or a time profile of the pump voltage U _p or a temporal change of the pump voltage, for example a derivative, can be detected. This is exemplary in the 3A and 3B shown. Again, the reference number 156 doing the measuring mode, and the reference number 158 denotes a diagnostic mode. An optional regeneration phase is again not shown. In the diagnostic mode, in this case, the pumping voltage U _p , for example, measured by the measuring device 146 , recorded as a measured variable as a time course. By means of this time course can on the temporal change of the oxygen partial pressure in the reference gas space 132 getting closed. Malfunction of the reference gas space 132 , For example, the exhaust duct, express themselves in a rule in a strong change over time of the pumping voltage U _p . 3B schematically shows the time course of U _p , while 3A shows the course of I _p . The one for the diagnosis in the diagnostic mode 158 used currents are preferably in a range of -0.15 mA to -0.7 mA. A statement about the Storage capacity of the reference gas space 132 , For example, via a leaktightness or leakage of the exhaust duct, can be taken for example by means of at least one threshold value. Thus, one or more threshold values can be preset, for example, both for the absolute value of U _p and, alternatively or additionally, for the time change ΔU _p in the time interval Δt. Other types of evaluations are possible. The time interval .DELTA.t is preferably selected in the range between 0.5 s and 8 s, preferably from 1.5 s to 4 s. The total time of diagnosis is preferably from 1 second to 10 seconds, preferably from 2 seconds to 6 seconds.

Diagnostic option 3:

The diagnostic options 1 and 2 can, as described above, also be combined, resulting in a diagnostic option 3. For example, the diagnostic option 3 can begin with the diagnostic option 1. At the end, however, it is not possible to enter the measuring mode, for example 156 but another diagnostic mode 158 in particular according to the diagnostic option 2. The combined information increases the reliability of the diagnosis. Other combinations are possible in principle.

Diagnostic option 4:

Another diagnostic option (diagnostic option 4) is in the 4A and 4B shown. This diagnostic option 4 is based in principle on verifying which amount of oxygen is actually available for a quantity of fat gas. This method usually requires a much longer time than the diagnostic options 1 to 3 above and accordingly places higher demands on the operating points at which the diagnosis can be performed. The diagnostic option 4 is based, for example, on the method according to the diagnostic option 2. This means that in the diagnostic mode 158 with a predetermined pumping current I _p , which may be constant or non-constant, oxygen from the reference gas space 132 , For example, the exhaust duct, for IPE 120 is pumped. However, in this diagnostic option 4, the effect is exploited that with an empty reference gas space 132 U _p , which in turn, for example, by the measuring device 146 is detectable, falls extremely sharply. This is in the 4A and 4B recognizable, wherein 4A turn the pumping current I _p and 4B the pump voltage U _p , each as a function of time t, shows. The currents used for this diagnostic option 4 are typically in the range of -0.3 mA and -1 mA. However, other streams are basically used.

For the actual diagnosis according to the diagnostic option 4, in particular the methods described below can be used, which, however, can also be combined.

In a first method, the time to reach a predetermined pumping voltage U _p can be determined, for example, a predetermined pumping voltage, in the region of the steeply sloping curve at the right end of 2 B lies. This can be compared with given values and / or compared with the time calculated via a loading model. Advantage of this method is that the value obtained can be used for example as a calibration size for the loading model. However, a disadvantage of this method is that as a rule the time required for the diagnosis is unknown. Accordingly, it is usually not known after which time, for example, it is possible to switch back to a measuring mode.

According to a second method according to the diagnostic option 4, the pumping voltage U _p can be determined after a predetermined time. If the pumping voltage U _{p is} still above at least one diagnostic threshold after a fixed time, the storage capacity is still in order. This method can be carried out in particular such that a lower limit value for U _{p is} specified as an additional termination condition.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102008002734 A1 [0002, 0008, 0014, 0030, 0031]

Claims (10)

Method for detecting at least one property of a gas in a measuring gas space ( 112 ), in particular for detecting a gas component of the gas, wherein at least one sensor element ( 118 ) with at least one cell ( 152 ) is used, the cell ( 152 ) at least one first electrode ( 120 ), at least one second electrode ( 122 ) and at least one the first electrode ( 120 ) and the second electrode ( 122 ) connecting solid electrolyte ( 124 ), wherein the first electrode ( 120 ) with gas from the sample gas space ( 112 ) is acted upon, wherein the second electrode ( 122 ) with at least one reference gas space ( 132 ), the reference gas space ( 132 ) is arranged to store a supply of a gas component of the gas, the method comprising at least two operating modes: - at least one measuring mode ( 156 ), wherein in the measuring mode the cell ( 152 ) is operated as a pump cell and is closed from at least one pumping current through the pump cell to the property, and - at least one diagnostic mode ( 158 ), in the diagnostic mode ( 158 ) a storage capacity of the reference gas space ( 132 ), at least one of which is attached to the cell ( 152 ) Nesselstspannung affected measured variable is detected and is concluded from the measured variable on the storage capacity. Method according to the preceding claim, wherein between the measuring mode ( 156 ) and the diagnostic mode ( 158 ) at least one regeneration phase is carried out, in particular a regeneration phase of 10 ms to 2 s. Method according to one of the preceding claims, wherein from a loading model of the reference gas space ( 132 ) to an expected partial pressure of the gas component in the reference gas space ( 132 ), wherein from the expected partial pressure to an expected Nernst voltage of the cell ( 152 ) is closed, which is concluded from the expected Nernst voltage to an expected measurand, the measured variable is compared with the expected measure and is concluded from this comparison on the storage capacity. Method according to one of the preceding claims, wherein the measured variable is compared with at least one threshold value, wherein from the comparison on the storage capability is concluded. Method according to the preceding claim, wherein the threshold value is selected from: at least one fixed predetermined threshold value; at least one according to a loading model of the reference gas space ( 132 ) calculated threshold. Method according to one of the preceding claims, wherein the measured variable is selected from: the Nernst voltage at the cell ( 152 ); a time course of the Nernst voltage at the cell ( 152 ); a temporal change of the Nernst voltage at the cell ( 152 ); a period of time until the Nernst voltage on the cell ( 152 ) reaches at least a predetermined threshold. Method according to one of the preceding claims, wherein in the diagnostic phase at least one predetermined pumping current through the cell ( 152 ) is set, in particular adjusted, wherein the measured variable is selected from: a pump voltage required for the adjustment of the pumping current; a change over time of the pumping voltage required for the adjustment of the pumping current; a time course of the pump voltage required for the adjustment of the pumping current; a period of time until the pumping voltage required for setting the pumping current reaches at least a predetermined threshold value. Method according to one of the preceding claims, wherein in the diagnostic mode ( 158 ) the cell ( 152 ) is applied with at least one predetermined pumping voltage, wherein the measured variable is selected from: a pumping current; a temporal change of the pumping current; a time course of the pumping current; a period of time until the pumping current reaches at least a predetermined threshold value. Method according to the preceding claim, wherein from a loading model of the reference gas space ( 132 ) to an expected partial pressure of the gas component in the reference gas space ( 132 ), wherein from the expected partial pressure to an expected Nernst voltage of the cell ( 152 ), wherein from the pumping voltage and the expected Nernst voltage to an expected effective voltage at the cell ( 152 ) is closed, being closed from the expected effective voltage to an expected measurand, the measured variable is compared with the expected measure and is concluded from this comparison on the storage capacity. Contraption ( 110 ) for detecting at least one property of a gas in a sample gas space ( 112 ), in particular for detecting a gas component of the gas, wherein the device comprises at least one sensor element ( 118 ) and at least one with the sensor element ( 118 ) connected control ( 114 ), wherein the sensor element ( 118 ) at least one cell ( 152 ), wherein the cell ( 152 ) at least one first electrode ( 120 ), at least one second electrode ( 122 ) and at least one the first electrode ( 120 ) and the second Electrode ( 122 ) connecting solid electrolyte ( 124 ), wherein the first electrode ( 120 ) with gas from the sample gas space ( 112 ) is acted upon, wherein the second electrode ( 122 ) with at least one reference gas space ( 132 ), the reference gas space ( 132 ) is arranged to store a supply of the gas component, the controller ( 114 ) is arranged to perform a method according to any one of the preceding claims.

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