WO2008080735A1

WO2008080735A1 - Sensor element with additional fat gas regulation

Info

Publication number: WO2008080735A1
Application number: PCT/EP2007/063231
Authority: WO
Inventors: Henrico Runge; Holger Reinshagen
Original assignee: Robert Bosch Gmbh
Priority date: 2006-12-29
Filing date: 2007-12-04
Publication date: 2008-07-10
Also published as: CN101573613B; CN101573613A; DE102006061954A1

Abstract

The invention relates to a method for measuring a gas constituent of a gas mixture in a gas space (212), using a sensor element (210) comprising at least one first electrode (218), at least one second electrode (216), and at least one solid electrolyte (214) connecting the at least two electrodes (216, 218). The at least one second electrode (216) is shielded from the gas space (212) and connected to a reference gas space (242). The sensor element (210) also comprises a control device (510) comprising at least two operating states, first, a lean regulation state during which an air ratio λ is derived from a linear pump flow characteristic and a corresponding lean regulation can be carried out, and then, a fat regulation state in which a defined air ratio λ < 1 in the fat region (112) of the gas mixture can be adjusted by using a pump voltage which corresponds to the Nernst voltage occuring for said air ratio.

Description

description

title

Sensor element with additional grease gas control

State of the art

The invention is based on known sensor elements which are based on electrolytic properties of certain solids, ie the ability of these solids to conduct certain ions. Such sensor elements are used in particular in motor vehicles to measure air-fuel-gas mixture compositions. In particular, sensor elements of this type are used in so-called "lambda sensors" and play an essential role in the reduction of pollutants in exhaust gases, both in gasoline engines and in diesel technology.

With the so-called air ratio "lambda" (λ), the relationship between an air mass actually offered and a theoretically required (that is to say stoichiometric) air mass is generally referred to in combustion technology

Air ratio is measured by one or more sensor elements usually at one or more locations in the exhaust system of an internal combustion engine. Correspondingly, "rich" gas mixtures (i.e., gas mixtures with a fuel surplus) have an air ratio λ <1, whereas "lean" gas mixtures (i.e., gas mixtures with a fuel deficiency) have an air ratio λ> 1. In addition to automotive technology, such and similar

Sensor elements in other areas of technology (in particular combustion technology) used, for example in aeronautical engineering or in the control of burners, z. B. in heating systems or power plants. Numerous different embodiments of the sensor elements are known from the prior art and are described, for example, in Robert Bosch GmbH: "Sensors in Motor Vehicles", June 2001, pp. 112-117 or in T. Baunach et al: "Clean exhaust gas through ceramic sensors", Physik Journal 5 (2006) No. 5, pp. 33-38. One embodiment represents the so-called "jump probe" whose measuring principle is based on the measurement of an electrochemical potential difference between a reference electrode exposed to a reference gas and a measuring electrode exposed to the gas mixture to be measured. As a rule, the potential difference between the electrodes, especially at the transition between the rich gas mixture and the lean gas mixture, has a characteristic jump, which can be exploited in order to be able to use zirconium dioxide (eg yttrium-stabilized zirconium dioxide) or similar ceramics Various exemplary embodiments of such jump probes, which are also referred to as "Nernst cells", are described, for example, in DE 10 2004 035 826 A1, DE 199 38 416 A1 and DE 10 2005 027 225 A1.

Alternatively or in addition to jump probes, so-called "pump cells" are used in which an electrical "pumping voltage" is applied to two electrodes connected via the solid electrolyte, whereby the "pumping current" is measured by the pump cell In the case of pump cells, both electrodes are usually connected to the gas mixture to be measured, whereby one of the two electrodes (usually via a permeable protective layer) is exposed directly to the gas mixture to be measured, alternatively this electrode can also be exposed to an air reference The second of the two electrodes However, it is usually designed such that the gas mixture can not get directly to this electrode, but must first penetrate a so-called "diffusion barrier" to get into an adjacent to this second electrode cavity. The diffusion barrier used is usually a porous ceramic structure with specifically adjustable pore radii. If lean exhaust gas passes through this diffusion barrier into the cavity, oxygen molecules are electrochemically reduced to oxygen ions by means of the pumping voltage at the second, negative electrode, are transported through the solid electrolyte to the first, positive electrode and released there again as free oxygen. The sensor elements are usually operated in the so-called limiting current mode, that is to say in an operation in which the pump voltage is selected such that the oxygen entering through the diffusion barrier is completely pumped to the counter electrode. In this operation, the pumping current is approximately proportional to the partial pressure of the oxygen in the exhaust gas mixture, so that such sensors Sorelemente often be referred to as Proportionalsensoren. In contrast to jump sensors, pump cells can be used over a comparatively wide range for the air ratio lambda, which is why pump cells are used in particular in so-called broadband sensors in order to measure and / or control gas mixture compositions apart from λ = 1.

The sensor principles of jump cells and pump cells described above can advantageously also be used in combination, in so-called "multicellulars." For example, the sensor elements may contain one or more cells operating according to the jump sensor principle and one or more pump cells is described in EP 0 678 740 B1. In this case, by means of a Nernst cell, the oxygen partial pressure in the above-described cavity of a pump cell adjoining the second electrode is measured and the pumping voltage is adjusted by regulation so that the condition λ = 1 always prevails in the cavity. Various modifications of this multicellular construction are known.

However, the known from the prior art sensor elements show in many cases only in the lean exhaust gas a unique characteristic. However, in the slightly lean region, ie when λ approaches 1, in many cases a deviation of the pumping current characteristic from the theoretical curve can be observed. Instead of sinking the pumping current with decreasing lambda values towards the value λ = 1, an increase of the

To observe pumping current. This deviation causes the pumping current characteristic no longer has a clear course, from which it can be concluded that the air ratio. This is for example in lambda probes for use in diesel vehicles, which is usually worked in the slightly lean area, negatively noticeable.

A further problem of known sensor elements is that different operating states exist, which require different control points, that is to say in particular the setting of specific air numbers, which lie in different ranges. For example, cost-effective limiting-current lean-load sensors in the form of single-cell pump cells can be used, in particular for the operation of diesel vehicles, since diesel vehicles are usually controlled to a lean air ratio. Nevertheless, especially in diesel vehicles with catalytic converters, there are operating states in which one another Air ratio, in particular to an air ratio in the slightly rich range (eg λ = 0.9) is controlled. In particular, these are operating states in which the catalyst (for example a NOx storage catalytic converter, NSC) and / or a filter, for example a particle filter, is regenerated. However, since conventional limiting current Magersonden provide in this area, ideally, no current signal in this area, such a change of operating condition with conventional sensor elements is not possible or difficult.

Disclosure of the invention

Accordingly, a method is proposed for measuring a gas component in a gas mixture which avoids the disadvantages of the sensor elements known from the prior art. In particular, the sensor element can be used in a lambda probe or as a lambda probe, preferably as a marginal flow lean-load sensor, preferably in the field of diesel technology. Alternatively or additionally, however, the method can also be used in the rich air range or for other types of control. The sensor element used by the method has at least one first electrode, at least one second electrode and at least one solid electrolyte connecting the at least one first electrode and the at least one second electrode.

A basic idea of the present invention is that the above-described non-uniqueness of the pumping current characteristic can be attributed to the reactions taking place at the anode in the case of simple pumping-current sensor elements (for example limit-current leaner probes) in the region of slightly lean exhaust gases and also in the area of rich gas mixtures , In this case, both electrodes are exposed to the exhaust gas. The reactions cause a current signal as in lean operation, resulting in a characteristic that is unique only in measurements in the lean exhaust gas. Even small amounts of fuel gas (especially H ₂ ) affect the measurement signal, so that the uniqueness of characteristics of the boundary-stream Magersonden even in non-equilibrium exhaust gas, as used for example in diesel technology, already close to λ = l, 0 is no longer given. Accordingly, according to the invention, the reactions taking place in the fatty gas at the pump anode, such as, for example, the reactions, are proposed

CO + O ² -> CO ₂ + 2e H ₂ + O ² -> H ₂ O + 2e,

to prevent the at least one second electrode (which is usually switched at least temporarily as a pump anode) is shielded from the gas space, so that in the vicinity of this at least one second electrode no or only slightly reducing gas components such For example, H ₂ or CO, are located.

According to the invention, this shielding is to take place in that, while the at least one first electrode can be acted upon by the gas mixture from the at least one gas space, the at least one second electrode is connected to at least one reference gas space separated from the gas space. For example, this may be an engine compartment of the internal combustion engine or else a separate reference gas chamber with an at least approximately known and constant gas mixture composition.

The fuel gas concentrations in the non-equilibrium exhaust gas (e.g.

Non-equilibrium exhaust gas close to λ = l) and the excess fuel gases in the rich exhaust gas can then no longer influence the signal of the sensor element, since no fuel gas conversion can take place at the pump anode. Accordingly, the at least one reference gas space should be realized in such a way that it ensures a removal of the gas, in particular of the oxygen, which is formed at the at least one second electrode. The result of this sensor element arrangement is an unambiguous characteristic curve in the range of air> λ> 1, so that this simple sensor element, for example as a single cell, can be used cost-effectively for use in diesel vehicles for measurement in the air> λ> 1 range.

Investigations have shown that in the construction of the sensor element with the shielded at least one second electrode can actually achieve a unique pumping current characteristic, since in the lean exhaust gas, a pumping current is measured according to the oxygen partial pressure. In contrast, no pumping current is measured in the rich exhaust gas, since there is no free oxygen and since during operation the pumping voltage (typically between 100 mV and 1.0 V, preferably between 300 mV and 800 mV and particularly preferably between 600 mV and 700 mV) below the Decomposition voltage of water is. Thus, no fuel gas oxidations at the at least one second electrode, which is now shielded and "fuel gas blind", run off. D-

The sensor element can thus be used as a limit current lean-burn sensor because of the unique characteristic in the lean range. For this purpose, for example, an electronic control device may be provided, which may initially (optionally) comprise at least one operating state, which is designed as a lean control state. This lean control state can be used in the lean range of the gas mixture, i. in a range in which there is a stoichiometric excess of the gas component to be detected (for example oxygen). In this lean control state, the control device is set up to charge the at least two electrodes with a (for example constant) pumping voltage, which is preferably selected such that it ensures a limiting current operation (ie an operation in the saturation region of the pumping current). In this case, at least one pump current signal is measured between the at least one first electrode and the at least one second electrode. Due to the now given uniqueness of the pumping current characteristic, this current signal can for example be assigned a lambda value.

The above-described measures alone, however, do not yet make it possible to control certain operating states in the range λ <1.0, for example in diesel applications. For the regeneration of certain filters (for example, diesel particulate filters) and / or catalysts in the diesel exhaust line, however, a control of operating states is also to be ensured in the range between λ = 0.9 and λ = 0.95, ie in the rich region. The term "catalyst" is to be understood broadly and generally includes exhaust aftertreatment systems, such as NSC systems (NSC: NOx storage catalyst, NOx storage catalysts).

In addition to the above-described advantage of a clear characteristic in the lean region, combined with a corresponding lean control state, the proposed method thus still offers the advantage of at least one second operating state, namely at least one rich state. For example, the above-described lean-control state can be used in normal operation, whereas the at least one rich-control state is used in a regeneration operation of the at least one catalyst and / or filter. Alternatively, however, the method can also be used only with the at least one grease control state. In the at least one grease control stand the sensor element is operated in a rich area of the gas mixture, ie in a region in which there is a stoichiometric deficit of the gas component to be detected. Here, a control point of the gas mixture is set (for example, one or more predetermined lambda values, for example in the range described above between 0.9 and 0.95). The gas component to be detected is present at the control point in a predetermined concentration, which corresponds to a control Nernst voltage between the at least one first electrode, which is exposed to the gas mixture, and the at least one second electrode, which is exposed to the reference atmosphere in the reference gas space , The control device is set up to apply a regulating pumping voltage to the at least one first electrode and the at least one second electrode, which is directed counter to the normal Nernst voltage, so that the two voltages are just compensated at the control point. In this case, a current signal between the at least one first electrode and the at least one second electrode is measured. If this at least one current signal is different from zero, this indicates a deviation from the at least one control point, which in turn can be used, for example, to generate a control signal for changing the gas mixture composition in the gas space, for example in the form of an effect on an air mass feed to one combustion process.

In this way, inexpensive, simply constructed sensor elements can be produced which can be used, for example, both as a limiting current lean-burn sensor and for the described regeneration operation. In addition to the described design features of the shielding of the at least one second electrode, this requires only a small amount of equipment, since essentially a corresponding control device (for example, with one or more microcomputers, hardware components and software components) must be provided to the Inventive embodiment of the sensor element to achieve. -O-

Brief description of the drawings

Exemplary embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. Show it:

Figure 1 is a pumping current characteristic;

FIG. 2 shows a layer structure of a sensor element configured as a single cell with an inner pumping cathode and inner pump anode and superimposed supply lines; 3 shows a sensor element according to Figure 3, but with adjacent leads;

FIG. 4 shows a sensor element with an external pump cathode and an inner pump anode;

Figure 5 is a schematic representation of a system with a sensor element and a control device; and

Figure 6 shows an example of a pumping current control with a control point in the rich area.

Embodiments of the invention

FIG. 1 schematically shows a profile of a pumping current I _p as a function of the air ratio λ of a gas mixture. This is the expected course of the characteristic curve for a design according to the invention of a sensor element with a second electrode, which is completely shielded from the gas mixture (fuel gas). Here, as in the following, it is assumed as an example that this at least one second electrode is operated as a pump anode. However, other types of wiring are conceivable, for example, sonication with alternating polarity. In FIG. 1, the vertical dashed line 110 denotes the value λ = 1, which separates the rich region 112 from the lean region 114. It can be seen that the expected characteristic increases linearly in the range λ> 1 and assumes the value 0 in the rich range, ie for λ <1.

If the second pumping electrode (pumping anode) were not shielded from the fuel gas, as the invention suggests, then in particular in the rich region 112, a non-disappearance would occur. dender pumping current to be observed, which is due to the above-described fatty gas reactions at the pump anode. Even in the slightly lean region, ie in the region 114 close to λ = 1, a deviation from the linear course of the characteristic would be observed.

2 shows a first exemplary embodiment of a sensor element 210 in a perspective representation of the layer structure, which can be used for the method according to the invention. In this sensor element 210 is a protozoa, which is comparatively easy and inexpensive to implement. The described sensor element 210 can be used, for example, as a limit current lean-burn probe in order to analyze gas mixture in a gas space 212.

The sensor element 210 has, on the side facing the gas space 212, a first solid electrolyte 214, for example an yttrium-stabilized zirconium dioxide electrolyte. In a layer plane on the side of the solid electrolyte 214 facing away from the gas space 212, the solid electrolyte 214 is contacted by a pump anode 216 (for example a platinum electrode and / or an oxide electrode) and a pump cathode 218, wherein pump anode 216 and pump cathode 218 are arranged next to one another. The pumping cathode 218 functions as the above-described first electrode, and the pumping anode 216 constitutes the second electrode.

Below pump anode 216 and pump cathode 218, a second solid electrolyte 220 is arranged so that pump anode 216 and pump cathode 218 are embedded between the two solid electrolytes 214, 220. While the pump anode 216 is merely formed as a single electrode, the pump cathode 218 has a first partial cathode 222 and a second partial cathode 224, the first partial cathode 222 contacting the uppermost solid electrolyte 214, and the second partial cathode 224 contacting the lower, second solid electrolyte 220. However, the two partial cathodes 222, 224 are electrically conductively connected so that they act as a single pumping cathode 218, but with an enlarged surface area. As a result, the internal resistance of the sensor element 210 can be reduced.

Between the two partial cathodes 222, 224, a cathode cavity 226 is provided. Via a gas inlet hole 228 in the overhead solid electrolyte 214, gas mixture from the gas space 212 can penetrate into the cathode cavity 226. In doing so, a distinction is hole 228 and cathode cavity 226 a diffusion barrier 230 is provided, which has a porous, dense ceramic material and which limits the limiting current of the pumping cathode 218. The pump cathode 218 is electrically contacted by a cathode lead 232 disposed on the lower solid electrolyte 220. Via a cathode connection 234 on the upper side of the solid electrolyte 214 and an electrical through-connection 236, the pump cathode 218 can be connected to a corresponding electronic circuit (see FIG. 5) and, for example, supplied with a voltage.

Below the pump anode 216, an anode cavity 238 is provided which is connected via an exhaust air channel 240 with a separate from the gas chamber 212 reference gas space 242. Anodenhohlraum 238 and / or exhaust duct 240 are filled with an oxygen-permeable porous filling element 244 on Al ₂ θ ₃ basis or filled with another porous material or unfilled executed. The exhaust air duct 240 preferably has at least one of the following properties: the at least one exhaust air duct 240 has a rectangular cross-sectional area; the at least one exhaust duct 240 has a length in the range of 1 mm to 50 mm, preferably in the range of 10 mm to 30 mm; the at least one exhaust duct 240 has a cross-sectional area in the range of 0.001 mm ² to 1 mm ² , preferably from 0.01 to 0.1 mm ² ; - The at least one exhaust duct 240 has a cross-sectional area, wherein the

Ratio of the cross-sectional area to the surface of the at least one pump anode 216 in the range between 2 and 0.01, preferably in the range between 0.3 and 0.05, is located. In this way, on the one hand optimal removal of oxygen from the pump anode 216 is ensured, and on the other hand diffusion of impurities to the pump station 216 through the exhaust air duct 240 is largely prevented.

The pump anode 216 is electrically contacted via an anode feed line 246 and connected via a further electrical through-connection 248 in the solid electrolyte 214 to an anode connection 250 arranged on the upper side of the solid electrolyte 214. Via this anode terminal 250, the pump anode 216 can be connected, for example, to the electronic device described above, so that, for example, a voltage can be applied between pump anode 216 and pump cathode 218 and / or a pump current can be measured. Anode lead 246 and cathode lead 232 are in the Exemplary embodiment according to Figure 2 arranged one above the other. An electrical insulation of pump anode 216 or anode feed line 246 relative to the cathode feed line 232 takes place through the porous filling element 244, which has electrically non-conductive properties.

Below the second solid electrolyte 220, a heating element 252 is arranged, which comprises a heating resistor element 256 embedded between two insulator foils 254. The heating resistance element 256 can be electrically contacted via through-connections 258 in a carrier substrate 260 (for example, again a solid electrolyte) via heating connections 262 on the side of the carrier substrate 260 facing away from the gas space 212 and supplied with a heating current. For example, this heating current can be regulated with a regulation which, for example, sets a constant internal resistance of the sensor element 210.

By means of the exemplary embodiment of a sensor element 210 described in FIG. 2, the pumping current characteristic shown in FIG. 1 can essentially be realized. When used as a lambda probe, a pumping current corresponding to the oxygen partial pressure is measured in the lean region 114 (linearly increasing characteristic curve), no current in the rich region 112, since there is no free oxygen and the selected pumping voltage is advantageously below the decomposition voltage of the water. Thus, no fuel gas oxidation can occur on the internal, shielded fuel gas-blind pump anode 216. This makes it possible to realize a cost-effective sensor element 210 constructed as a single cell, which is also suitable for use in diesel vehicles.

FIG. 3 shows a perspective view of a second exemplary embodiment of a sensor element 210 which can be used for the proposed method, again not showing electronic circuit components. The structure corresponds largely to the embodiment of Figure 2, so that reference can be made to this embodiment with respect to the individual elements. In contrast to the exemplary embodiment according to FIG. 2, in the exemplary embodiment according to FIG. 3 not only the pump cathode 218 has two partial cathodes 222, 224, but also the pump anode 216 is formed in two parts, with an upper partial anode 310 which contacts the upper solid electrolyte 214, and a lower second partial anode 312, which contacts the underlying solid electrolyte 220. The partial anodes 310, 312 are in turn, in analogy to the partial cathodes 222, 224, electrically connected to each other. The advantage of this arrangement, as stated above, in a reduction of the internal resistance of the sensor element 210, since now pumping currents can be effectively passed through the upper solid electrolyte 214 and the lower solid electrolyte 220.

The two partial anodes 310, 312 are separated from each other by the anode cavity 238, which in turn, in analogy to FIG. 3, is filled with the porous filling element 244. Analogously to FIG. 2, the anode cavity 238 is also connected to the reference gas space 242 via the exhaust air duct 240, which is likewise filled with the porous filling element 244, in the exemplary embodiment according to FIG.

Also in contrast to the exemplary embodiment according to FIG. 2, in the exemplary embodiment of the sensor element 210 according to FIG. 3 there is no arrangement of the electrode feed lines 232, 246 arranged one above the other, by means of which the pump cathode 218 and the pump anode 216 are contacted. The anode feed line 246 and the cathode feed line 232 are arranged next to one another on the lower solid electrolyte 220, wherein the exhaust air channel 240 extends centrally between the two electrode feed lines 232, 246 and parallel to them. The contacting of the electrode leads 232, 246 takes place analogously to the exemplary embodiment in FIG. 2 via the electrode terminals 234, 250. For the other components and the mode of operation, reference is made to the above description. The sensor element 210 according to FIG. 3 thus again has a "fuel gas-blind" pump anode 216, so that in turn the characteristic shown in FIG. 1 can be achieved.

FIG. 4 shows an alternative embodiment of a sensor element 210 to FIGS. 2 and 3, in which, in contrast to the exemplary embodiments in FIGS. 2 and 3, only the anode 216 is arranged in the sensor element interior, whereas the pump cathode 218 is arranged on the outer, the gas space 212 facing surface of the solid electrolyte 214 is arranged.

The pump anode 216 is formed integrally in this case and arranged directly above the upper insulator film 254 of the heating element 252. Via the anode lead 246, which is also arranged on the upper insulator film 254, the anode via 248 in the upper solid electrolyte 214 and the anode terminal 250, the pump anode 216 may be supplied with a potential or connected to a corresponding electronic circuit (see below Figure 5). Again, the anode 216 communicates with the reference gas space 242 via the exhaust air duct 240, which in turn is filled with the porous element 244. Exhaust duct 240 and porous element 244 isolate the A- nodenzuleitung 246 relative to the upper solid electrolyte 214. Furthermore, in this embodiment, again, an (not shown here) anode cavity may be provided, which in turn may be configured hollow or with a porous filling element.

The pump cathode 218 is disposed on top of the solid electrolyte 214 and may be electrically contacted by a cathode lead 232 and a cathode terminal 234, which are also disposed on the surface of the solid electrolyte 214. The cathode feed line 232 is electrically separated from the solid electrolyte 214 by an insulation element 410.

The pump cathode 218 is shielded with a gas-impermeable cover layer 412 opposite the gas space 212. On an end face on which the covering layer 412 leaves open a gap to the solid electrolyte 214, the diffusion barrier 230 is provided, the function of which has already been described above and which limits the limiting current of the pumping cathode 218. Gas mixture from the gas space 212 must penetrate the diffusion barrier 230 in order to reach the pumping cathode 218. Again, a cathode cavity may also be provided here, which in turn is filled or hollowed out with a porous filling element and which is not shown in FIG.

The mode of operation of the sensor element 210 essentially corresponds to the mode of operation of the sensor elements according to FIGS. 2 and 3, so that reference can be made to the above description with regard to the further components. By means of the sensor element 210 shown in FIG. 4, the characteristic shown in FIG. 1 can be realized on the basis of the pump anode 216 which is shielded with respect to the gas space 212.

As described above, the sensor elements 210 according to the invention can thus be used as lean-burn lean-load sensors due to their construction with the "fuel gas-blind" pump anode 216. At the same time, however, a targeted control of rich operating be possible, for example, for a time-limited regeneration of a catalyst. Accordingly, the system according to the invention has an electronic control device 510, the mode of operation of which is to be explained with reference to FIGS. 5 and 6. Here, FIG. 5 shows a sensor element 210 according to the invention and a control device 510, wherein a sensor element structure is used which substantially corresponds to the exemplary embodiment according to FIG. Accordingly, with respect to this structure, reference may be made to the above description. However, other types of sensor elements 210 with "fuel gas-blind" pump anode 216 can also be used according to the invention. <br/> FIG. 6 shows a pump current characteristic which is used for targeted control.

The control device 510 according to FIG. 5 is initially designed in order to utilize the linear pump current characteristic for a broadband control in a lean control state in the lean region 114. In this case, a pump voltage source 512 is used to apply a pumping voltage between pump anode 216 and pump cathode 218. In this case, the "pump anode" 216 actually functions as an anode during the pumping process, so is applied with a positive pump voltage U _p. By means of a pump current-measuring device 514, the pump current I _p is measured, which is indicated by the pump anode 216, pump cathode 218 and solid electrolyte 214 6 can clearly be deduced from the unambiguous and linear characteristic curve in the lean region 114. For example, the control device 510 may comprise an electronic control unit 518 comprising the pumping voltage source 512 and the pumping current measuring device This control electronics 518 can, for example, generate a control signal 520 which corresponds to the air ratio and forward it to other components of the internal combustion engine, for example a motor control. Conversely, the control electronics 518 can be activated via corresponding control signals 522, for example is to switch between the different operating states.

In addition to the described lean control state there exists at least one further operating state, namely a rich control state, in which a specific λ value <1 is to be regulated. At λ values <1, ie at an oxygen deficit in comparison to the stoichiometric (ie λ = 1 mixture), a Nernst voltage arises between the pump anode in pump cell 516 due to the oxygen concentration gradient between anode cavity 238 and cathode cavity 226 216 and pump cathode 218, which is the one described above. written pumping voltage is set opposite. The "pump cell" 516 in this case forms a Nernst cell in which the "pump cathode" 218 now acts as a Nernst anode and the "pump anode" 216 as a Nernst cathode Value calculate this Nernst voltage or determine it experimentally.

If a specific λ value <1 (control point) is set, a voltage is now applied by the control device 510 by means of the pump voltage source 512 between pump cathode 218 and pump anode 216, which corresponds in magnitude to the Nernst voltage which corresponds to the desired λ Value, which is, however, directed just opposite to the Nernst voltage. The pumping voltage U _p thus compensates for the Nernst voltage U _N at the control point. Exactly at the control point, therefore, no current flows between the two electrodes 216, 218. The control point is then identified by zero (no current flow) and minus (low pumping current in the opposite direction to the "lean pumping current".) Between the pumping electrodes 216, 218 an effective pump voltage U _eff , which results from the difference between the applied pump voltage U _p and the Nernst voltage U _N :

By means of this "zero-minus switch", for example, a required λ-value in the range between 1.0>λ> 0.9 for a regeneration of a catalyst and / or filter in an internal combustion engine, in particular in a diesel motor vehicle For example, a control point 610 is selected at λ = 0.9 in Figure 6. Accordingly, a pump voltage U _{p is} set, which corresponds to the Nernst voltage U _N for the control point λ = 0.9 solid graph 612 shows the theoretical pump current characteristic at high voltage U _p , at pump voltages which are far above the Nernst voltage U _N. Graph 614 shown in dashed lines, on the other hand, shows the pump current characteristic at a pump voltage U _p , which is precisely the Nernst voltage. voltage U _N for λ = 0.9 corresponds. drops from λ from the lean region 114 starting at λ = 1, then no pumping current is first measured, since the effective pump voltage U _e s still positive and, as described above, at the pump anode 216 no fuel gas reactions can take place. From λ = 0.9, as the λ values become smaller, the effective pumping - - Voltage U _eff negative, since the Nernst voltage U _N overcompensates the pump voltage U _p . Consequently, a current is measured according to the direction of the electric potential determined by the Nernst voltage, which is perceptible by the pump current measuring device. This current is opposite to the current direction in lean operation and is therefore recorded as a negative pumping current. Alternatively or additionally, the mode of operation can also be modified in such a way that voltage changes on the electrodes are detected instead of the current.

By way of example, the control device 510 can be configured such that it can be switched over between the two operating states by means of a drive signal 522. Also, for example, in an electronic data memory 524, various control points 610 may be predetermined, for example in the form of pump voltages which correspond to particular λ values. For example, this can be done in the form of an electronic table.

Claims

claims

1. A method for measuring a gas component of a gas mixture in at least one gas space (212) by means of a sensor element (210), which at least one first electrode (218), at least one second electrode (216) and at least one at least one first electrode (218) and the at least one second electrode (216) connecting solid electrolyte (214), wherein the at least one first electrode (218) is acted upon by the gas mixture from the at least one gas space (212) and wherein the at least one second electrode (216) with at least a reference gas space (242) separated from the gas space (212), characterized in that in at least one rich control state the sensor element (210) is operated in a rich region (112) of the gas mixture, the gas component in the rich region (112) being in is a stoichiometric deficit, wherein a control point (610) of the

Gas mixture is adjusted, wherein the gas component to be detected in the control point (610) is present in a predetermined concentration, the control state corresponds to a control Nernst voltage between the at least one first electrode (218) and the at least one second electrode (216) and the at least one first electrode (218) and the at least one second electrode (216) are supplied with a control pump voltage which is opposite to the control Nernst voltage, at least one pump current signal being connected between the at least one first electrode (218). and the at least one second electrode (216) is measured.

A method according to the preceding claim, characterized by additionally a lean control state in which the sensor element (210) is operated in a lean region (114) of the gas mixture, wherein the gas component in the lean region (114) is in a stoichiometric excess, the at least two electrodes (216, 218) are subjected to a pumping voltage and wherein at least one pumping current signal is measured between the at least one first electrode (218) and the at least one second electrode (216). - o-

3. The method according to one of the two preceding claims, characterized in that the sensor element (210) is operated in the limiting current operation.

4. Method according to claim 1, characterized in that at least one control signal (520) is generated for changing the mixed gas composition in the gas space (212), wherein in the at least one rich control state the control signal (520) is designed to increase the gas flow rate Concentration of the detected gas component in the gas mixture to cause when the at least one pumping current signal is different from zero, and to cause no change in the concentration of the gas component to be detected in the gas mixture, when the at least one pumping current signal is zero.

5. The method according to any one of the preceding claims, characterized in that the at least one control pump voltage in at least one table, in particular an electronic table, is stored retrievable.

6. Method (210) according to one of the preceding claims, characterized in that the at least one second electrode (216) is connected to the at least one reference gas space (242) via at least one exhaust air duct (240).

7. Method (210) according to the preceding claim, characterized in that the at least one exhaust duct (240) has at least one porous filling element (244), in particular at least one porous filling element (244) based on Al ₂ O 3.

8. The method (210) according to one of the two preceding claims, characterized in that the at least one exhaust duct (240) has at least one of the following properties: the at least one exhaust duct (240) has a rectangular cross-sectional area; the at least one exhaust duct (240) has a length in the range of 1 mm to 50 mm, preferably in the range of 10 mm to 30 mm; the at least one exhaust duct (240) has a cross-sectional area in the range from 0.001 mm ² to 1 mm ² , preferably from 0.01 to 0.1 mm ² ; the at least one exhaust air duct (240) has a cross-sectional area, the ratio of the cross-sectional area to the area of the at least one first electrode (216) being in the range between 2 and 0.01, preferably in the range between 0.3 and 0.05.

9. Method (210) according to one of the preceding claims, characterized in that the at least one second electrode (216) is arranged in the interior of the sensor element (210) and is separated from the gas space (212) by at least one gas-impermeable layer (214) ,

10. The method (210) according to the preceding claim, characterized in that in addition the at least one first electrode (218) in the interior of the sensor element (210) is arranged and with the gas space (212) via at least one gas inlet hole (228) is connected ,

11. The method (210) according to claim 1, wherein the at least two electrodes (216, 218) have at least one of the following configurations: the at least one first electrode (218) has at least one first electrode cavity (226) which communicates with the at least one first electrode (218); the at least one second electrode (216) has at least one second electrode cavity (238) in communication with the at least one second electrode (216); - The at least one first electrode (216) is separated from the gas space (212) by at least one diffusion barrier (230); at least one of the at least one first electrode (218) and the at least one second electrode (216) is formed in several parts with at least one first partial electrode (222, 224; 310, 312) and at least one second partial electrode (222, 224; 310, 312) wherein the at least one first sub-electrode (222, 224; 310, 312) contacts at least a first sub-layer of the at least one solid electrolyte (214) and wherein the at least one second sub-electrode (222, 224; 310, 312) comprises at least a second sub-layer of the at least contacted a solid electrolyte (214).

12. Use of a method according to any one of claims 2-11 for controlling an internal combustion engine of a motor vehicle, in particular a diesel engine, wherein the motor vehicle has at least one catalyst and / or filter for reducing the pollutant emissions, wherein in normal operation of the motor vehicle of the

The lean control state is used and wherein in at least one regeneration operation of the at least one catalyst and / or filter, the at least one rich state is used.

13. An electronic control device (510) for measuring a gas component of a gas mixture in at least one gas space (212), wherein the electronic control device (510) comprises means for performing a method according to one of claims 1-11.

14. System for measuring a gas component of a gas mixture in at least one gas space (212), comprising at least one sensor element (210), which has at least one first electrode (218), at least one second electrode (216) and at least one at least one first electrode ( 218) and the at least one second electrode (216) connecting solid electrolyte (214), wherein the at least one first electrode (218) is acted upon by the gas mixture from the at least one gas space (212) and wherein the at least one second electrode (216) is connected to at least one reference gas space (242) separate from the gas space (212); and at least one electronic control device (510) according to the preceding claim.