WO2012097897A1

WO2012097897A1 - Method and device for capturing at least one parameter of a gas

Info

Publication number: WO2012097897A1
Application number: PCT/EP2011/070329
Authority: WO
Inventors: Jens Schneider; Helge Schichlein
Original assignee: Robert Bosch Gmbh
Priority date: 2011-01-19
Filing date: 2011-11-17
Publication date: 2012-07-26
Also published as: CN103314287B; DE102011002856A1; CN103314287A

Abstract

Proposed is a method and a corresponding device for capturing at least one parameter of a gas in a flow pipe (112), in particular for detecting at least one gas component in an exhaust gas in an exhaust-gas section. In the method, at least two gas sensors (122, 124, 126) arranged at different locations in the flow pipe (112) are used. The gas sensors (122, 124, 126) have in each case at least one Nernst cell, wherein in each case at least one Nernst voltage is captured across the Nernst cells. The gas sensors (122, 124, 126) are in each case regulated to at least one predetermined temperature. The method is carried out such that the at least one parameter is captured at at least two different predetermined temperatures.

Description

description

title

METHOD AND DEVICE FOR DETECTING AT LEAST ONE PARAMETER OF A GAS

PRIOR ART Numerous methods and devices for detecting at least one parameter of a gas are known from the prior art. At least one

Parameters can basically be any physical and / or chemical property of the gas. In particular, this at least one property may be a proportion of a gas component of the gas, that is, for example, a percentage and / or a partial pressure of the at least one gas component, in particular an oxygen content and / or a proportion

Nitrogen oxides and / or fatty gases, so for example hydrocarbons and / or H ₂ . Corresponding sensors may for example be based on the use of at least one solid electrolyte, for example zirconium dioxide, optionally doped or stabilized with yttrium (YSZ) and / or scandium (ScSZ), for example. such

Gas sensors, to which reference is made below in the description of the invention, without limitation of other possible embodiments, are described for example in Robert Bosch GmbH: Sensors in the motor vehicle, edition 2007, pages 154-159 using the example of so-called lambda sensors.

From the prior art is basically known that a temperature of the

Sensor elements can have a significant impact on the properties of solid electrolyte-based sensor elements. In DE 35 19 410 A1 a modulation of an operating temperature of a sensor is described with a predetermined frequency, wherein a resulting and fluctuating with the same frequency measurement signal is detected. In DE 10 2005 020 363 A1 it is described to first heat a measuring sensor to a temperature with a first heating voltage and then a second heating voltage. In DE 690 06 503 T2, a temperature gradient between two electrodes of a sensor element is used. In DE 10 2008 005 110, a method is described in which a heating element of a lambda probe is heated regulated by a heating element control. In general, lambda probes, in particular jump probes, without a

Temperature control can be operated, the lambda probes are operated, for example, in a timed start phase with reduced heating power. In this case, however, there is usually an uncontrolled and unknown temperature of the sensor element, depending usually on the cold start conditions of the engine, the

Engine load condition, an exhaust gas temperature or similar factors. A changed in this time control position behavior and / or dynamic behavior of the lambda probe is often accepted. Furthermore, lambda probes can generally also be operated with a temperature control, for example via a

Internal resistance measurement of the lambda probe. This temperature control can, for example, within a tolerance corridor to a target temperature of the

Sensor element, for example, to an internal resistance of 220 Ω, corresponding to an operating temperature of 780 ° C. In such a scheme, the lambda probe shows an exhaust gas temperature-independent, consistent

Functional characteristic with respect to a control position and dynamics.

Despite the numerous detailed improvements of the various known from the prior art designs and operations of sensor elements of the type mentioned, there is still a considerable potential for improvement,

in particular with regard to a measuring accuracy, a dynamics and a

Poisoning resistance of the described sensor elements. Thus, in some cases, conflicts of interest are to be determined in that in particular jump probes at lower

Temperatures have a higher accuracy, especially for deviations from an air ratio λ = 1. At the same time occurs at such lower temperatures, however, an increased risk of electrode poisoning, and the dynamics of

Sensor elements sinks. It would therefore be desirable to have an operating method in which improvements are achieved with regard to the properties described above and in which the described conflict of objectives is at least largely resolved.

Disclosure of the invention

Accordingly, a method for detecting at least one parameter of a gas in a flow tube and a device for detecting at least one parameter of a gas in a flow tube are proposed. As described above, the at least one parameter, which in the Method is qualitatively and / or quantitatively detected, in principle to act any physical and / or chemical parameters, preferably a proportion of a gas component of the gas and in particular by a proportion of a gas component selected from: oxygen, nitrogen oxides, fat gases. The gas can be

in particular, to act as an exhaust gas of an internal combustion engine, for example in a motor vehicle. For example, the gas may flow through the flow tube in a main flow direction, for example, in a main flow direction directed away from the internal combustion engine. The flow pipe can thus be in particular an exhaust gas line or an exhaust pipe. In principle, the flow tube can have any cross section, preferably a round or polygonal cross section. The method is thus particularly preferably used for detecting at least one gas component in an exhaust gas in an exhaust gas line, in particular for the qualitative and / or quantitative detection of oxygen and / or nitrogen oxides and / or fatty gas.

In the method, at least two at different locations in the

Flow tube arranged gas sensors used. In particular, at least one first gas sensor upstream of at least one second gas sensor in the

Flow tube may be arranged, for example, at a distance of at least 50 mm, preferably at least 100 mm and more preferably of at least 200 mm, for example, along a main flow direction in the flow tube.

A gas sensor is generally understood to mean a sensor which can detect the at least one parameter qualitatively and / or quantitatively. The at least two gas sensors may preferably be of identical construction, as will be explained in greater detail below. The gas sensors each comprise at least one Nernst cell, preferably exactly one Nernst cell. Under a Nernst cell is one

to understand electrochemical cell, wherein at least two electrodes

are provided, which are connected to one another via at least one electrolyte, that is, via at least one ion-conductive material. The electrolyte may particularly preferably be a solid electrolyte, in particular a ceramic solid electrolyte, for example a zirconia-based ceramic solid electrolyte, preferably yttrium-stabilized zirconium dioxide and / or scandium-doped zirconium dioxide. Particularly preferably, the gas sensors or at least one of the gas sensors are configured such that at least one first electrode of the Nernst cell can be acted upon with gas from the flow tube, for example directly or after penetration of at least one porous element, for example a diffusion barrier, wherein at least one second electrode is provided, which is preferably not exposed to the gas from the flow tube. For example, the at least one second electrode can be arranged in a reference gas space in which there is at least one reference gas with a known property and can thus be designed, for example, as a reference electrode. For example, the reference gas space may comprise at least one reference gas channel, preferably at least one reference air channel and / or at least one exhaust air channel. Thus, for example, one or both of the gas sensors can be designed such that at least one first electrode can be acted upon by the gas and at least one second electrode with a reference gas, wherein the first electrode and the second electrode via the at least one electrolyte, preferably the at least one solid electrolyte and particularly preferably a ceramic solid electrolyte, are ionically conductively connected to each other. The reference gas space can be designed, for example, as a simple reference gas channel or for example as a pumped reference. Thus, for example, preferably by applying a voltage, in particular a constant voltage, to the Nernst cell, constant or at regular or irregular intervals a reference gas can be pumped to the second electrode, for example oxygen, so that for example by this pumped reference always a lean atmosphere the second electrode, which can act as a reference electrode, is present.

One or more of the gas sensors are thus preferably designed as a so-called jump probe, preferably as so-called two-point lambda probes, as described, for example, in Robert Bosch GmbH: Sensors in Motor Vehicles, pages 154-157. It should be noted, however, that the present invention is fundamentally also applicable to other configurations of gas sensors, for example to so-called broadband lambda probes, as described, for example, in Robert Bosch GmbH: Sensors in Motor Vehicles, Edition 2007, pages 158-159. Again alternatively or additionally, the invention is also applicable to gas sensors for

Detection of nitrogen oxides applicable, which are described for example in EP 0 769 693 A1. The invention will be described in the following with reference to a device having two gas sensors of the type of unicellular jumping probes, without limiting further possible embodiments. In the proposed method, in each case at least one Nernst voltage is detected at the Nernst cells. Thus, for example, a first Nernst voltage can be detected at a first of the gas sensors, and at least a second Nernst voltage at the second of the gas sensors. From the detected Nernst voltages can be concluded, for example, on the at least one parameter of the gas. For example, this can be done using a known relationship between the

Nernst voltage and an air ratio and / or an oxygen partial pressure. Such methods are known in principle to the person skilled in the art. In the method, the gas sensors are each controlled to at least one target temperature. In the context of the present invention, a regulation is understood to be a process in which at least one actual value is detected and, depending on its deviation from at least one nominal value, is corrected in the system, for example via at least one actuator. For example, an actual temperature can be detected directly or indirectly and / or an actual variable that correlates to this actual temperature. This can be compared with the at least one setpoint temperature and / or a setpoint value that correlates to this setpoint temperature and influence the temperature of the respective gas sensor according to this comparison, for example by means of at least one heating element. In general, it should be pointed out that in the context of the present invention, a temperature of the gas sensor is understood to mean a temperature which is present in a sensitive region of the respective sensor. For example, this may be an averaged temperature in the Nernst cell of the respective sensor. The method is further performed such that the at least one parameter is detected at at least two different setpoint temperatures. This can be done in different ways, which can also be combined with each other.

For example, the at least two different setpoint temperatures may be present simultaneously at at least two different locations, for example by controlling the first gas sensor to a first setpoint temperature, and the second gas sensor to a second setpoint temperature, wherein the at least one parameter is simultaneously and / or delayed by means of these gas sensors of the gas is detected.

Preferably, both capture in this or in other embodiments

Gas sensors the same parameter of the gas, for example one each

Oxygen content in the gas, but deviations may occur in the measured value. Alternatively, or in addition to the possibility that the at least two different setpoint temperatures are detected simultaneously at different locations, these at least two different setpoint temperatures can also detect at least two setpoint temperatures set at different times. These at least two setpoint temperatures set at different times can

for example, in one and the same gas sensor at different times, as will be explained in more detail below, and the at least one parameter can be detected by this gas sensor at the different times.

In general, the at least two different setpoint temperatures can

for example, be selected from the group consisting of: at least two setpoint temperatures set at different times; at least two setpoint temperatures set at different locations, namely, for example, at the at least two different locations of the at least two gas sensors present different setpoint temperatures. Different configurations and

Combination possibilities of these different possibilities to detect the at least one parameter at at least two different setpoint temperatures are described in more detail below.

The at least two setpoint temperatures may in particular deviate from one another by an amount of at least 30 ° C., preferably at least 50 ° C., more preferably by at least 100 ° C., and particularly preferably by at least 150 ° C. or even at least 200 ° C. Examples of such deviations will be described in more detail below.

To control the respective setpoint temperature of at least one of the gas sensors, preferably both gas sensors or all gas sensors, in particular at least one internal resistance of the respective Nernst cell of the respective exhaust gas sensor can be detected as an actual value and compared with at least one desired value.

According to this comparison, for example, at least one heating power of at least one heating element of the gas sensor can be changed, for example as a manipulated variable.

The at least two gas sensors should be at different locations in the

Flow tube may be arranged. An arrangement in the flow tube is to be understood as meaning an arrangement in which the respective gas sensor can measure the at least one parameter at the respective location. For this purpose, the gas sensor should be acted upon with gas from the respective location of the flow tube. To this end the gas sensor does not necessarily have to be completely or partially in the

Flow tube may be arranged, but may also be arranged for example outside the flow tube and be acted upon with gas from the flow tube.

In the method, in particular at least one treatment device can be used for the treatment of the gas in the flow tube, in particular a particle filter and / or a catalyst. For example, this can

Processing device may be arranged directly in an exhaust line, such as an exhaust pipe, or via a bypass with the exhaust line and / or

Be connected exhaust pipe. The gas sensors are preferably each selected from the group consisting of: one in the flow tube upstream of the

Processing device arranged gas sensor, in particular one in the

Flow tube upstream of a catalyst arranged gas sensor; a arranged in the processing device gas sensor, in particular one in a

Catalyst arranged gas sensor; a gas sensor disposed in the flow tube downstream of the treatment device, in particular one in the

Flow tube downstream of a catalyst arranged gas sensor. Without

Limiting the possibility that instead of or in addition to a catalyst also at least one particulate filter, such as a soot filter can be used, the following possible embodiments are described with reference to a catalyst. For example, a first gas sensor upstream of the

Catalyst may be arranged, which is also referred to as Vorkat gas sensor (vK gas sensor). A second gas sensor may then be arranged, for example, in the catalytic converter (Midbrick gas sensor, MB gas sensor) and / or downstream of the catalytic converter

Catalyst (post-cat gas sensor, n K gas sensor). Alternatively or additionally, at least one gas sensor can be arranged downstream of the catalyst and at least one further gas sensor in the catalyst and / or upstream of the catalyst. With respect to the possible definitions of the terms "before", which is used here to mean "upstream", and "to", which is used here to mean "downstream", reference may be made to the above description. By capturing the at least one property

different locations in the flow tube can be, for example

Perform plausibility checks of the individual measurements and / or

Check functionalities of the measurements, since, for example, the different installation locations may be exposed to different loads. As described above, the gas sensors may be in particular identical gas sensors. Particularly preferably, the gas sensors comprise identical jump probes, preferably identical jump probes, each with exactly one Nernst cell. However, other embodiments are possible in principle.

Further possible embodiments of the method preferably relate to the times and / or locations to or at which the at least two different

Set temperatures are present and the parameter is detected. As described above, for example, one and the same gas sensor can be operated at different times regulated to different target temperatures. This embodiment can basically also be implemented in an arrangement in which only one gas sensor is present. However, an embodiment in which at least two gas sensors are present, as described above, is particularly preferred. Alternatively or additionally, however, the at least two setpoint temperatures can also be set at different locations, namely for example in different gas sensors.

In a preferred embodiment of the method, at least one of

Gas sensors controlled in at least a first operating phase to a first setpoint temperature and in at least a second operating phase to at least a second

Setpoint temperature, which preferably deviates from the first setpoint temperature by at least the above-mentioned amount. The first operating phase may preferably be prior to the second operating phase. However, other embodiments are possible, for example embodiments in which there are more than two operating phases and / or in which repeatedly between the first operating phase and the second

Operating phase is switched. The first set temperature may preferably be 400 ° C to 650 ° C, more preferably 550 ° C to 600 ° C, and most preferably 580 ° C. The second set temperature may preferably be 650 ° C to 1000 ° C, in particular 700 ° C to 850 ° C and more preferably 780 ° C.

At least one switching time between the first operating phase and the second operating phase, that is, a time of a transition from the first operating phase to the second operating phase or vice versa, can be configured and / or triggered in various ways. For example, this switching can take place at least one predetermined time. For example, switching from the first operating phase to the second operating phase at a time between 5 Seconds and 5 minutes after a start of an internal combustion engine, preferably at a time between 10 seconds and 3 minutes and

especially between 30 seconds and 5 minutes. Alternatively or additionally, switching between the first operating phase and the second operating phase can also be made dependent on the presence of one or more boundary conditions which are detected. Particularly preferably, switching between the first operating phase and the second operating phase can take place in accordance with a detected temperature of the gas. For example, at least one temperature of the gas can be detected in at least one location, and this at least one temperature can be compared with at least one condition, for example with at least one threshold. For example, according to the fulfillment or non-fulfillment of this at least one condition, the switching can be triggered. For example, the gas may be an exhaust gas in the exhaust gas of an internal combustion engine, wherein the first operating phase at least part of a starting phase of the

Internal combustion engine, wherein it is detected whether a temperature of the

Exhaust gas is below a dew point temperature of the exhaust gas. According to this detection, a switchover between the first operating phase and the second operating phase can take place. A dew-point temperature can be understood to mean the temperature at which the so-called dew-point end is reached, that is, there is no longer any liquid water in the exhaust-gas line upstream of one or more of the gas sensors. In this regard, reference may be made, for example, to DE 102 51 364 A1. In this way, for example, at least one of the gas sensors in a starting phase of the internal combustion engine in which there is an increased danger of water hammer, at a lower temperature, for example, the first target temperature described above, operated, whereas at a later date, for example, switching to a higher, second

Set temperature can be done.

The method can furthermore be carried out such that at least one of the gas sensors is operated such that a repeated change between the first setpoint temperature and the second setpoint temperature and / or between the second setpoint temperature

Set temperature and the first setpoint temperature takes place. For example, a

regular or irregular switching between the set temperatures occur, for example, at regular or irregular intervals and / or periodically. The method can furthermore be carried out in such a way that at least one of the gas sensors is operated at a setpoint temperature of at most 650 ° C., more preferably of at most 600 ° C. and in particular of not more than 500 ° C., if an air ratio λ of the gas is more than 0.003 of λ = 1, preferably by more than 0.002 and more preferably by more than 0.001 or even more than 0.0007 or more than 0.0005. Preferably, otherwise, so outside of said

Temperature range, the at least one gas sensor at a setpoint temperature of more than 650 ° C, preferably more than 700 ° C and in particular more than 750 ° C and more preferably at least 780 ° C are operated. This embodiment of the invention has the particular background that at lower set temperatures and thus lower operating temperatures of the gas sensors, as will be described below, a larger measurement signal between the Nernst voltage at λ = 1 and the Nernst voltage in the rich or lean exhaust gas is present, so that within a larger range around λ = 1 can be detected with greater accuracy a Nernst voltage.

In a further possible embodiment of the method, the gas sensors can be operated in a controlled manner to different setpoint temperatures in at least one operating phase. This can be done in particular such that at least one of the first gas sensors is controlled to at least one target temperature for this gas sensor, and at least a second of the gas sensors to at least one deviating therefrom target temperature.

In a further possible embodiment of the method is at least one

Control step performed. In this control step, a comparison of the parameters detected at the at least two different setpoint temperatures can be performed. For example, in this comparison, the parameters and / or at least one of these parameters, for example a difference value, can be compared with at least one condition, for example by comparison with at least one threshold value. In particular, at least one detection of an influence on at least one electrode of at least one of the gas sensors may take place in the control step, in particular an electrode poisoning and / or an influence of one or more of the electrodes by fat gases. The latter is referred to, for example, as a continuous shift down, CSD, and is described for example in DE 10 2006 060 633 A1. This embodiment of the method is associated with the fact that gas sensors arranged at different locations in the flow tube typically differ Loads, for example, by electrode poisons and / or fat gases are exposed, so that, for example, a strong deviation of the parameters detected by the respective gas sensors can infer from one another poisoning and / or a CSD of one or both of the gas sensors. Alternatively or additionally, at least one plausibility check of the parameter can also be carried out in the control step

be performed. For example, deviations of the respectively detected parameters of the gas sensors can be detected, for example by comparison with at least one threshold value. The checking step can also be carried out in such a way that a result of this at least one checking step is brought to the attention of a user and / or another device, for example in the form of a warning signal and / or error signal and / or in the form of a correction signal.

In another aspect of the present invention, as described above, an apparatus for detecting at least one parameter of a gas in one

Flow tube proposed. The apparatus includes at least two gas sensors for use in the gas at different locations in the flow tube. The

Apparatus may further comprise the flow tube itself or a part thereof. The gas sensors each have at least one Nernst cell. The apparatus further comprises at least one driver, wherein the apparatus is set up to carry out a method according to one or more of the embodiments described above and / or one or more of the exemplary embodiments described below. Accordingly, for possible

Embodiments of the devices, the gas, the parameter, the flow tube, the gas sensors and the Nernst cells as well as possible procedural aspects, for example, to the above description. The control may comprise, for example, at least one microcomputer, wherein the microcomputer may be configured to effect, for example, a switching between the described operating phases and / or setpoint temperatures. In particular, the

Device be set up such that a common temperature control is provided for the gas sensors. The drive can furthermore have one or more electronic components, for example one or more

Temperature controls, preferably a common temperature control for the exhaust gas sensors or at least two of the exhaust gas sensors. The drive may comprise at least one data processing device, for example, as stated above, at least one microcomputer. By way of example, the data processing device can be set up in terms of programming in order to implement the above steps or parts to do the same. Furthermore, the drive may, alternatively or additionally, also comprise at least one application-specific integrated circuit (ASIC). Various configurations are possible. The method and apparatus have been described above such that at least two gas sensors are provided. However, the principle according to the invention of detecting the at least one parameter at at least two different setpoint temperatures can in principle also be transferred to a device with only one gas sensor, including the optional features described above, according to which one and the same exhaust gas sensor at different times, for example in different Operating phases, operated at different setpoint temperatures regulated.

The proposed method and apparatus have numerous advantages over known methods and apparatus. In particular, can be by a temporary or permanent operation of at least two

temperature-controlled gas sensors, preferably lambda probes and particularly preferably jump probes, to at least two different, but preferably precisely known setpoint temperatures and thus temperature levels, in particular

Temperature levels Ti and T ₂ with preferably Ti «T ₂ , achieve numerous advantages. In particular, a robustness increase can be achieved, as well as a

Water hammer protection of the exhaust gas sensors, at the same time earlier

Operational readiness, especially in low-temperature operation of a

Internal combustion engine. Furthermore, an adjusted control position for a starting phase and for a continuous operation can be achieved, for example, a greasy rule position at an engine start. In addition, new reconciliation procedures and new

Implement plausibility functions, for example in the form of a

Poisoning detection. As described above, this can be done, for example, by comparing signals from gas sensors in different installation positions, for example in the Vorkat position (vK) and / or Midbrick position (MB) and / or in the Nachkat position (nK).

As another possible advantage, the conflict of objectives described above can be resolved. In particular, a greater measuring sensitivity of a gas sensor,

preferably a jump probe, outside of λ = 1 at low setpoint temperature and thus realize at low operating temperature by a larger measurement signal. Furthermore, can be realized by means of the proposed method and the proposed device, a variety of embodiments in which the previously

described positive properties and advantages of the invention are particularly beneficial.

Thus, for example, in a realizable embodiment, a first gas sensor, for example a vK jump probe, can be used with a temporary operation on one

lowered first set temperature ΤΊ in a start phase (also referred to as warm-up phase) operate, followed by a change to a second setpoint temperature T ₂ in at least a second operating phase, for example, after a start phase of the internal combustion engine. A second gas sensor, for example an nK-jump probe, can constantly run at its own, independent desired temperature, for example, also constantly at the second setpoint temperature T ₂ .

In a further feasible embodiment, both gas sensors, for example a vK and an nK-jump probe, can be operated in a temporary operation at a first set temperature, for example a lowered temperature Ti, for example in a start phase, followed by a common change to a second Target temperature, for example, a higher target temperature T ₂ .

In a further realizable embodiment, which can be realized in particular for operation of the internal combustion engine at λ << 1 (for example with a deviation of 1 by not more than 0.1), at least two gas sensors can be operated in permanent operation at different setpoint temperatures.

For example, a vK lambda probe can be operated in a permanent mode at a first operating temperature Ti, and a second gas sensor, for example an nK lambda probe, with permanent operation at a second set temperature, for example T ₂ . Such operation of gas sensors at different temperature levels may contribute to optimizing the control attitude and optimizing the life of the gas sensors.

In a further realizable embodiment, which is suitable in particular for operation of an internal combustion engine at λ> 1, 0, preferably λ> 1, 1, the method can basically be carried out according to the embodiment described above. Here, an increased accuracy of the gas sensors at lowered Operating temperature, preferably at the first setpoint temperature, are used. As a result, for a larger number of vehicle systems, it is possible, instead of, for example, to use a broadband probe as a control probe, in particular as a control probe vK.

A further realizable embodiment may also basically correspond to the two embodiments described above, but preferably operating the internal combustion engine at λ <1, 0, preferably λ <1, 1, takes place. These

Embodiment may include, for example, a so-called component protection and / or be realized in the context of a component protection. This refinement can thus comprise a rich operation of an internal combustion engine controlled by jump probes, in particular of a motor controlled with jump probes, in the component protection. In component protection, an engine is intentionally operated in rich fat when components on the engine and in the exhaust system reach their temperature limits. The excess fuel can thus not be burned, but evaporates and absorbs heat. The advantage of the method is that the driver does not notice this "deterrent." Disadvantages are the resulting HC emissions, because the component protection, however, in the

Driving cycles for measuring emissions does not occur (maximum speed about 120 km / h in each cycle), he is usually not relevant to emissions, i. Vehicles with component protection can still be approved to EU or US standards. In this case, for example, by an enrichment of the gas, for example enrichment of the mixture, a temperature of the gas and / or an engine temperature can be lowered, for example by condensation of unburned fuel. In this case, for example, an increased accuracy of the gas sensors when lowered

Operating temperature can be used. This can be used for a larger number of

Vehicle systems to realize the possibility instead of a broadband probe to use a jump probe as a control probe vK.

In a further possible embodiment, which can be realized advantageously, at least one control function and / or at least one control step can be realized as described above. For example, in this embodiment, a

Plausibilisierung and / or balancing function are used, for example, a plausibility or balancing function of a MB lambda probe and a nk lambda probe by a temporary, for example, interval, change of both gas sensors between at least two different set temperatures,

for example, between Ti and T ₂ . This may, for example, the possibility a direct comparison of a rule situation and / or dynamics of the two

Gas sensors come in different mounting positions. This can

For example, carried out a diagnosis of a catalyst. Alternatively or additionally, for example, a probe poisoning can be detected, since typically a characteristic curve of gas sensors with a poisoning changes.

The embodiments described above can be carried out, for example, with setpoint temperatures ΤΊ = 580 ° C. and T ₂ = 780 ° C., for example for the sensor element of a jump probe. However, other temperatures can also be used in principle, for example the above-mentioned ranges for the first or second setpoint temperature. The proposed method is basically in particular for gas sensors with

at least one integrated heating element and / or with at least one separately provided heating element suitable. For example, the method can be designed particularly favorable for jump probes with integrated and / or separately provided heating element, for example a rod heater. Alternatively or additionally, however, the method can also be applied to the operation of other types of gas sensors, for example other types of exhaust gas sensors, for example oxygen wideband probes and / or nitrogen oxide sensors. Brief description of the drawings

Further optional details and features will become apparent from the following description of preferred embodiments. Show it:

Figure 1 shows an embodiment of a device for detection

at least one parameter of a gas in a flow tube;

Figure 2 shows a temperature dependence of functional characteristics more typical

Jump sensors;

Figures 3A and 3B dependence of sensor signals non-temperature controlled

Jump probes (FIG. 3A) and temperature-controlled jump probes (FIG. 3B) of an exhaust gas temperature; and FIG. 4 shows exemplary characteristics of poisoned jump probes.

EMBODIMENTS OF THE INVENTION FIG. 1 shows an exemplary embodiment of a device 110 for detecting at least one parameter of a gas in a flow tube 112. The device is used in this example, for example, to detect an oxygen content in an exhaust gas of an internal combustion engine 1 14, so that it can be exemplified by the flow tube 1 12 an exhaust pipe 1 16 an exhaust tract, which is traversed in a main flow 1 18. By way of example, a catalyst 120 is used in the flow tube 112 as an example of a treatment device and / or an exhaust aftertreatment device. Alternatively or additionally, other types of such devices may be used. The apparatus 110 includes in the illustrated embodiment, at least two gas sensors, here three gas sensors 122, 124 and 126. According to the arrangement in front of the catalyst 120, within the catalyst 120 or after the catalyst 120, these gas sensors 122 - 126 as vK (Vorkat ), MB (Midbrick) and nK (Nachkat). All the gas sensors 122-126 are, for example, jump probes 128 which have at least one Nernst cell, for example a Nernst cell, in which at least one electrode is exposed to the exhaust gas in the exhaust pipe 16 and at least one second electrode

(Reference electrode) a reference gas space, preferably a reference air channel or reference gas channel, preferably with a pumped reference as described above. All jump probes 128 are temperature controlled jump probes. It should be noted that the device 110 could in principle also be designed with a single jump probe 128 or with only two or more than three jump probes, for example only one of the gas sensor pairs 122, 124, 122, 126 and 124, 126 Structure of the gas sensors described 122 - 126 can be exemplified by Robert Bosch GmbH, sensors in

Motor vehicle, edition 2007, pages 154-157 are referenced, but in addition a temperature control 130 is present, preferably a common

Temperature control 130 in a drive 132 of the device. These

Temperature control 130 may be configured to, for example

Internal resistance of Nernstzellen the jump probes 128 to measure and by means of a Set the heating element to a certain value, which is a predetermined

Set temperature for the respective gas sensor 122, 124, 126 corresponds.

FIG. 2 shows typical Nernst voltages U _N and correlating oxygen partial pressures of jump probes 128 of the type described for different temperatures of the Nernst cell. It follows that in particular in the rich exhaust gas (λ <1), a temperature dependence exists, and the Nernst voltage U _N decreases with increasing temperature, whereas the oxygen partial pressure p ₀ 2 with increasing

Temperature rises. In this area dominates the temperature dependence of the equilibrium reactions, such as a decomposition of C0 ₂ in carbon monoxide and oxygen and / or a decomposition of water into hydrogen and oxygen. In the lean region, however, (λ> 1), the temperature dependence of the

Nernst voltage, which results from the Nernst equation:

^N 4F P (0 ₂ ")

Here, R denotes the general gas constant, F the Faraday constant, T the temperature of the Nernst cell, and P (0 ₂ ') and P (0 ₂ ") the oxygen partial pressures at the electrodes of the Nernst cell.

FIGS. 3A and 3B show the manner in which the temperature of the exhaust gas in the exhaust pipe 16 takes an influence on the signals U _{N of} the jump probes 128. Accordingly, signals of non-temperature controlled jump probes 128 are shown in FIG. 3A. As shown in FIG. 2, the exhaust gas temperature has a considerable influence on the functional behavior of the jump probes, and the

Exhaust gas temperature has a significant influence on the functional characteristics. In contrast, FIG. 3B shows a characteristic curve of a temperature-controlled jump probe 128, as used in the context of the device 110. The exhaust gas temperature T _g and their

Changes here are compensated by the temperature control 130, which influences, for example, a heat output of one or more heating elements of the gas sensors 122, 124, 126, wherein these heating elements may comprise integrated heating elements and / or external heating elements.

According to the invention, it is provided that the gas sensors 122 - 126 are respectively controlled to at least one setpoint temperature, wherein at least one parameter of the Gas, for example, in Figure 1, an oxygen partial pressure is detected at at least two different target temperatures. This can be done in various ways, which are explained in the following embodiments. Embodiment 1

The gas sensors 122 (vK) and 126 (nK) are used. In a first

Operating phase, which also as a start phase or warm-up phase of

Internal combustion engine 1 14 may be configured, the vK gas sensor 122 is operated at a lowered temperature Ti. After the start phase, a change then takes place to T ₂ > Ti, preferably T ₂ »Ti. The nK gas sensor 126 preferably runs at a constant high temperature T» Ti, preferably also at T ₂ . The starting phase may be, for example, a phase which extends to a dew point end, that is to say to a temperature of the exhaust gas in which no liquid constituents, in particular no liquid water, are present in the exhaust gas. This phase can be, for example, 30 seconds to 2 minutes, depending on the application. The temperature Ti may for example be 400 to 650 ° C, in particular 550 ° C to 600 ° C and more preferably 580 ° C, and the second set temperature typically 650 ° C to 1000 ° C, especially 700 ° C to 850 ° C and especially preferably 780 ° C.

Embodiment 2: vK gas sensor 122 and nK gas sensor 126 are both operated with temporary operation in a start / warm-up phase according to Embodiment 1 at a lowered temperature Ti. In this case, the temperature Ti may preferably be in the range described above, preferably at 580 ° C. The lowered temperature Ti may be identical for both gas sensors 122, 126, but may in principle also deviate slightly, preferably not more than 50 °, preferably not more than 20 °. Subsequently, preferably at the same time or with a time offset of preferably not more than 20 seconds, in particular not more than 10 seconds and more preferably not more than 5 seconds, a change to an elevated temperature T _{2 takes} place, for example in the above-indicated temperature range , However, the temperature T ₂ may not be identical for both exhaust gas sensors 122, 126, but may in principle be slightly different, preferably not more than 50 °, in particular not more than 20 ° and more preferably not more than 10 °. Embodiment 3

This embodiment is particularly suitable for engine operation at λ = 1, for example, an engine operation in which the air ratio λ by not more than 0, 1 deviates from λ = 1, preferably by not more than 0.05. Again, the gas sensors 122 and 126 are used, as well as in the embodiments 1 and 2. The vK gas sensor 122 is operated in the permanent mode at a lowered temperature Ti, for example, the lowered temperature Ti in the temperature range indicated in Example 1. The nK gas sensor 126 is operated in the permanent mode at elevated temperature T ₂ , for example in the above-indicated preferred temperature range. The operation of the gas sensors 122, 126 on different

Temperature levels may be used to optimize a control location and lifetime of the device 110 and / or the jump probes 128.

Embodiment 4

This embodiment can in particular for an operation of the

Internal combustion engine 1 14 at λ> 1, ie in the lean area, are used. Basically, this embodiment corresponds to the embodiment 3, but for the lean operation of a controlled with jump probes 128 engine one

Internal combustion engine 1 14. Here, the precisely increased accuracy of the jump probes 128 is used at a lowered operating temperature, which results for example in FIG. This creates for a larger number of

Vehicle systems, the possibility to use one or more jump probes 128 as a control probe vK before the catalyst 120 instead of a broadband probe.

Embodiment 5: This embodiment again corresponds to the embodiment 3, wherein, however, an operation in the rich gas range λ <1 takes place. This embodiment is particularly suitable for the fat operation of a controlled with jump probes engine in the so-called component protection. In this case, an engine temperature of the internal combustion engine 1 14 is lowered by enrichment of the mixture of the internal combustion engine 1 14, in particular by condensation of unburned fuel. In this case, the increased accuracy of the jump probes 128 is lowered Operating temperature Ti used. This creates for a larger number of

Vehicle systems the ability to use a jump probe 128 as a control probe vk instead of a broadband probe. Embodiment 6:

In this embodiment are preferably, in contrast to the

Embodiments 1 to 5, the MB gas sensor 124 and the nK gas sensor 126 used. Both gas sensors are repeated between a low one

Setpoint temperature ΤΊ and a high setpoint temperature T ₂ , for example, in the above-mentioned temperature ranges, switched. For example, a temporary, in particular intervals, change of the two gas sensors 124, 126 between ΤΊ and T ₂ take place. For example, a first operating phase, in which a

Set temperature ΤΊ is set, and a second operating phase, in which a

Set temperature T _{2 is} set, alternate. For example, the first

Operating phase have a duration of 5 minutes, and the second phase of operation each have a duration of 1 min. Preferably, the temperatures Ti for both gas sensors 124, 126 are substantially the same, for example, with a deviation of less than 10 ° C and more preferably less than 5 ° C, and also the elevated

Temperatures T ₂ are preferably the same for both gas sensors 124, 126,

preferably again with a deviation of not more than 10 °, in particular not more than 5 °. This results in the possibility of a direct comparison of

Sensor signals of the gas sensors 124, 126 and thus the possibility of a direct comparison of a control position and / or dynamics of the two gas sensors 124, 126 in different mounting positions. In this way, a diagnosis of the catalyst 120 and / or an influence of electrodes of one or more of the

Exhaust gas sensors 124, 126. This is explained using the example of FIG.

FIG. 4 shows probe signals U _s , for example Nernst voltages U _N , of

Jump probes 128 whose electrodes are influenced in various ways. The curve denoted by N denotes the new state. The location of the jump point at new probes is usually due to the diffusion properties of the

Electrode protective layer conditioned. In = 1 gas in the engine H2 and 02 are next to each other. H2 diffuses much faster than 02 because of the smaller molecular diameter. If access to the outer electrode of the jump probe is hindered by a protective layer, H2 preferably reaches the outer electrode. Even with slightly lean gas then the jump probe shows fat gas. About the nature of

Protective layer, the position of the jump point can be adjusted. The curve Si denotes a curve in which a sensor electrode was poisoned with silicon, and the curve designated Pb a curve in which a sensor electrode was poisoned with lead. The curve labeled CSD represents a curve at which a reference electrode of the jump probe 128 was affected, for example, by gasses of fats. This effect is referred to as Continuous Shift Down, CSD. By comparing the sensor signals of the gas sensors 124, 126 and / or other gas sensors, for example, a plausibility check and / or a detection of probe poisonings can thus be carried out.

It should be noted that the embodiments 1 to 5 can preferably be carried out with the temperatures ΤΊ and T ₂ described above. The

Method is for jump probes 128 with integrated or separately provided

Heating element, such as a rod heater, can be used, but can also on the operation of other sensor elements, such as other types of

Exhaust gas sensors are adapted, in particular on oxygen broadband probes and / or nitric oxide probes.

Claims

Claims 1. Method for detecting at least one parameter of a gas in one

Flow tube (1 12), in particular for the detection of at least one

Gas component in an exhaust gas in an exhaust line, wherein at least two at different locations in the flow tube (1 12) arranged gas sensors (122, 124, 126) are used, wherein the gas sensors (122, 124, 126) each have at least one Nernst cell, wherein at least one each

Nernst voltage is detected at the Nernstzellen, wherein the gas sensors (122, 124, 126) are each controlled to at least one target temperature, wherein the

Method is performed such that the at least one parameter is detected at at least two different target temperatures.

2. Method according to the preceding claim, wherein the at least two

different setpoint temperatures are selected from the group consisting of: at least two setpoint temperatures set at different times; at least two setpoint temperatures set at different locations.

3. The method according to any one of the preceding claims, wherein the at least two set temperatures differ by at least 30 ° C, preferably by at least 50 ° C, in particular by at least 100 ° C and more preferably by at least 150 ° C or at least 200 ° C.

4. The method according to any one of the preceding claims, wherein at least one of the gas sensors (122, 124, 126) is regulated in at least a first operating phase to a first setpoint temperature and is controlled in at least a second operating phase to at least a second setpoint temperature.

5. The method according to the preceding claim, wherein the first set temperature

400 ° C to 650 ° C, preferably 550 ° C to 600 ° C and more preferably 580 ° C, and wherein the second set temperature is 650 ° C to 1000 ° C, in particular 700 ° C to 850 ° C and more preferably 780 ° C.

6. The method according to one of the two preceding claims, wherein at least one switching between the first operating phase and the second operating phase takes place in accordance with a detected temperature of the gas.

7. The method according to any one of the preceding claims, wherein the gas sensors (122, 124, 126) are operated simultaneously regulated in at least one operating phase to different target temperatures.

8. The method according to any one of the preceding claims, wherein at least one

Control step is performed, wherein in the control step, a comparison of the detected at the at least two different target temperatures parameters is performed.

A method according to the preceding claim, wherein in the control step

at least one plausibility check of the parameter is performed.

10. The method according to one of the two preceding claims, wherein in the

Control step at least one detection of an influence of at least one electrode of at least one of the gas sensors (122, 124, 126) takes place, in particular an electrode poisoning and / or an influence of the electrode by fat gases.

1 1. Device (1 10) for detecting at least one parameter of a gas in a flow tube (1 12), wherein the device at least two gas sensors (122, 124, 126) for use in the gas at different locations in the flow tube (112) comprising, wherein the gas sensors (122, 124, 126) each at least one

Nernst cell, wherein the device further comprises at least one drive, wherein the device is arranged to perform a method according to any one of the preceding claims.