WO2010072490A1

WO2010072490A1 - Sensor array comprising a temperature probe

Info

Publication number: WO2010072490A1
Application number: PCT/EP2009/065635
Authority: WO
Inventors: Jens Schneider; Lothar Diehl
Original assignee: Robert Bosch Gmbh
Priority date: 2008-12-22
Filing date: 2009-11-23
Publication date: 2010-07-01
Also published as: CN102257383B; DE102008055108A1; CN102257383A

Abstract

The invention proposes a sensor array (112) for sensing at least one property of a gas in a test gas chamber (110), in particular for determining a concentration of a gas component in the gas. The sensor array (112) comprises at least one sensor element (116). The sensor element (116) has at least one Nernst cell (120) with at least one first electrode (122) to which the gas from the test gas chamber (110) can be applied, at least one second electrode (124) which is arranged in a reference gas chamber (126), and at least one solid electrolyte (128) which connects the first electrode (122) and the second electrode (124). The sensor array (112) has at least one temperature probe (138) for sensing a temperature of the gas in the test gas chamber (110). The sensor array (112) also comprises at least one controller (114) and is set up to detect a signal from the Nernst cell (120) and to evaluate said signal taking into account the temperature.

Description

description

title

Sensor arrangement with temperature sensor

State of the art

The invention is based on known ceramic sensor elements, in particular 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. An important example of ceramic sensor elements in motor vehicles are sensor elements for determining a composition of an air-fuel mixture, which are also referred to as "lambda sensors" and play a significant role in the reduction of pollutants in exhaust gases, both in gasoline engines and in However, the invention can also be applied to other types of ceramic sensor elements, for example particle sensors or similar types of solid electrolyte sensors, in particular in the exhaust gas sensor system Without limiting the scope of protection, the invention will be explained below using the example of lambda probes, Lambda probes are known in the prior art in numerous different embodiments can be modified according to the invention are in Robert Bosch GmbH: "Sensors in the motor vehicle", 2nd edition, April 2007, p.

154-159.

A technical challenge with known sensor elements is that the ability of solid electrolyte materials to conduct certain ions is highly dependent on the temperature of the solid electrolyte material. Many sensor elements therefore comprise at least one heating element, by means of which the temperature of the Solid electrolyte can be adjusted specifically to a specific value. In order to control the temperature, it is possible, for example, to use the internal resistance of a Nernst cell in double-cell and single-cell broadband probes. This is described for example in DE 101 01 351 A1. However, a disadvantage of such sensor arrangements is that they require a relatively complex control on the one hand. On the other hand, sensor elements used in sensor arrays of this type are comparatively complicated to produce since, on the one hand, the production of the heating elements requires a considerable additional technical outlay, and since the wiring of the heating element and the remaining components of the sensor element involves a plurality (usually

4 to 5) of connection contacts on the sensor element makes necessary. In particular, for low-cost applications, such as in the two-wheeler, but sensor arrays would be desirable, which are equipped with relatively simple sensor elements and still reliably allow detection of readings for the engine control.

Disclosure of the invention

Therefore, a sensor arrangement and a sensor element suitable for use in such a sensor arrangement are proposed. The sensor arrangement serves to detect at least one property of a gas in a measuring gas space, in particular a physical and / or chemical property. In particular, this at least one property may be a fraction of a gas component in the gas, for example, oxygen. For example, this percentage may be represented by a percentage or a

Partial pressure can be specified. In particular, the sensor arrangement can accordingly be designed to detect an oxygen content in an exhaust gas of an internal combustion engine. The invention will be described below essentially with reference to such a configuration as a lambda probe, but in principle also other embodiments are possible, for example embodiments for measuring another gas component, embodiments as particle sensors or the like.

A basic idea of the present invention is that an electronic circuit and / or a configuration of the sensor elements can be greatly simplified if the sensor arrangement is a combined measurement of a Nernstsignals and a temperature measurement allows. Such a sensor arrangement with a combined measurement function can very well fulfill the requirements for two-wheel applications, in particular. The use of a heating element can preferably be completely dispensed with, so that, for example, the temperature of the gas itself can be used, for example a hot exhaust gas, in order to bring the sensor element to a required operating temperature.

The sensor arrangement comprises at least two components, namely at least one controller and at least one sensor element. The controller may be wholly or partially integrated in the sensor element, but may also be wholly or partially configured as an external controller and serves to control and evaluation of the at least one sensor element. The control can also be fully or partially integrated with other components of a system, for example an engine control system of a motor vehicle.

The sensor element comprises at least one Nernst cell with at least one directly or indirectly acted upon by the gas from the measuring gas chamber first electrode. By way of example, this first electrode can be exposed directly to the measurement gas space and / or can be designed to be separated from this measurement gas space via a porous, gas-permeable protective layer. In particular, this first electrode can be configured as an outer electrode (APE), which is arranged on a surface of the sensor element facing the measurement gas space. Furthermore, the Nernst cell comprises at least one second electrode arranged in a reference gas space. This reference gas space should be at least largely separated from the measurement gas space, such that preferably a complete, gas-impermeable separation takes place. Alternatively or additionally, however, can also be a separation such that a gas exchange between the reference gas space and sample gas space is possible only on a time scale, which includes significantly longer times than the other, relevant for the operation of the sensor element times, for example, a transport of ions through the solid electrolyte , The reference gas space is accordingly designed as a room with a defined atmosphere, which can be realized in various ways. For example, the atmosphere in the reference gas space can be specifically adjusted by one or more pumping cells

(pumped reference). Alternatively or additionally, the reference gas space can but also be associated with at least one surrounding space, such as an engine compartment of a motor vehicle. Accordingly, the reference gas space, for example, wholly or partially be configured as a reference air duct and / or communicate with such a reference air duct. Various configurations are possible. Furthermore, the Nernst cell comprises at least one solid electrolyte connecting the first electrode and the second electrode. This solid electrolyte may include, for example, yttria-stabilized zirconia (YSZ). Alternatively or additionally, however, other solid electrolyte materials are also possible in principle, for example scandium-stabilized zirconium dioxide (ScSZ). Other materials are possible in principle. The Nernst cell supplies at least one signal from which the property of the gas can be deduced. For example, this can be an oxygen partial pressure in the measurement gas space, so that the Nernst cell can be designed, for example, as a simple jump probe.

Furthermore, the sensor arrangement comprises at least one temperature sensor for detecting at least one temperature of the gas in the measuring gas space. As will be described in more detail below, this temperature sensor may for example be wholly or partially integrated in the sensor element and / or may be wholly or partly designed as an external, separate from the sensor element and / or the Nernst cell temperature sensor. Various embodiments will be described in more detail below. The at least one temperature sensor can in principle fall back on known measuring principles for the detection of temperatures. For example, the temperature sensor can comprise at least one temperature resistor (thermistor), ie a resistor whose electrical properties, for example its specific resistance, depend on the temperature. Various such thermistors are known. For example, resistors with a negative temperature coefficient (NTC resistors) and / or resistors with a positive temperature coefficient (PTC resistors) can be used. Numerous such temperature sensors are known from the prior art and can in principle also be used in the context of the present invention. Such thermistors are characterized by high accuracy, high robustness and a high temperature measuring range. The sensor arrangement is set up to detect a signal of the Nernst cell, that is to say a signal from which basically the at least one property of the gas can be deduced. The sensor arrangement is set up in order to evaluate this signal, taking into account the temperature of the gas in the measuring gas space determined by the temperature sensor.

The term evaluation is to be understood broadly. For example, the evaluation may involve simply providing the Nernst cell signals, for example to a motor controller. For example, as will be explained below, only those signals of the Nernst cell of the

Selected and provided for which the measured temperature was above a threshold temperature. Alternatively or additionally, however, the evaluation may also comprise a complete or partial processing of the signals, for example filtering, otherwise complete or partial signal processing, derivation of further measured variables (for example a conversion into a lambda value and / or another quantification of the measurements to be measured Property of the gas) or the like.

Thus, not only can the temperature of the sensor element be actively adjusted and / or regulated, but in any case in many cases

High temperatures occurring around the sensor element can also be used to set a required operating temperature of, for example, at least 400 ^° C., in particular at least 500 ^° C. For example, as long as the required operating temperature is not reached, the sensor arrangement may be arranged to completely reject the Nernst cell signal. Alternatively or additionally, a correction of the signal of the Nernst cell with an analytical, empirical or semiempirical correction function, for example a continuous function and / or a jump function, can generally also be carried out.

In particular, for two-wheel applications, but also for other applications in which a low-cost sensor assembly is required, this may mean, for example, that when starting still no signal of a lambda probe is available. Only later, when an operating temperature is reached, signals of the lambda probe can be detected and evaluated, which detected by the inventive provision of at least one temperature sensor when this time of appropriate operating conditions has been reached. Accordingly, the sensor element can preferably be configured completely without an active heating element.

The evaluation of the signal of the Nernst cell can, as illustrated above, be carried out in various ways, for example using one or more correction functions. Alternatively or additionally, which can also be understood by the term of the correction function, however, threshold value methods can also be used. In this threshold value method, for example, at least one threshold temperature may be predetermined, which may be stored, for example, in a data memory of the controller. In this threshold value method, for example, the signal of the Nernst cell can only be evaluated if the temperature of the gas detected by the at least one temperature sensor is above at least one threshold temperature. However, as discussed above, more complex threshold methods are possible. Thus, for example, a plurality of temperature ranges can be predetermined by corresponding threshold temperatures, whereby a different evaluation takes place within these temperature ranges, for example taking into account the respective ionic conductivity of the solid electrolyte in the current range.

The temperature sensor and the Nernst cell may be at least partially identical. For example, the Nernst cell itself can be used as a thermistor. The controller may then be configured to time-separate the detection of the temperature and the detection of the Nernst cell signal. Thus, the signal of the Nernst cell is detected by detecting a voltage at the Nernst cell (Nernst voltage). The temperature can be detected, for example, by passing a current through the Nernst cell, wherein the resistance of the Nernst cell can be determined, it being possible to deduce the resistance of the Nernst cell to the temperature of the gas in the measurement gas space. Other embodiments are possible.

The time-separated detection can be done in various ways. For example, a time measurement scheme can be used in which the temperature is detected at predetermined intervals, whereas in the remaining time and / or in other intervals at least temporarily the signal is recorded. Nernst cell is detected. For example, a temporal measuring sequence can be used in which measuring phases for detecting the signal of the Nernst cell and temperature measuring phases alternate at predetermined time intervals. Alternatively, however, the measurement scheme can also be adapted to the requirements, for example by carrying out frequent measurements of the temperature when a drop in temperature is recorded. Various configurations are possible.

As an alternative to the embodiment in which the temperature sensor and the Nernst- cell are at least partially identical, the temperature sensor and the

Nernst cell also be at least partially separated. The controller may then be configured to separately detect the temperature of the gas and the signal of the Nernst cell. This separate detection can be done in several ways. It is particularly preferred in general if a wiring is used which requires only two connection contacts.

This is also a particular advantage of the arrangement in which the temperature sensor and the Nernst cell are at least partially identical, since in this case offers a common contact.

Even in the case in which the Nernst cell and the temperature sensor are at least partially formed separately, however, a preferred summary of connection contacts is possible, so that generally preferably the sensor element is designed as a sensor element with only two connection contacts. For example, this can be done such that the Nernst cell is arranged in at least a first branch of a circuit of the sensor arrangement and that the temperature sensor is arranged in at least a second branch of the circuit. The first branch and the second branch can then preferably be connected in parallel, so that both branches can be contacted by two common connection contacts. In this parallel circuit, the separation of the signals of the Nernst cell and the signals of the

Temperature sensor carried out in various ways known to those skilled in the art. For example, a frequency-selective evaluation can take place. For example, this can be done by the temperature measurement at frequencies above 100 Hz, preferably above 1 kHz, whereas the detection of the signal of the Nernst cell only at frequencies zen below 100 Hz, for example, only at frequencies up to 10 Hz occurs. This allows the different information to be separated.

This separation can be favored, for example, by additionally accommodating at least one capacitive element in the second branch, that is to say in the branch in which the temperature sensor is arranged. For example, this at least one capacitive element in series with the temperature sensor, such as the thermistor, are switched. For example, this capacitive element may comprise at least one capacitor, for example a printed capacitor. With this configuration, with the at least one capacitive element in the second branch, the second branch blocks at low frequencies, so that the signals at low frequencies can be largely unambiguously assigned to the first branch, that is to say the branch comprising the Nernst cell. Advantageously, it is noticeable that the reference of the Nernst cell is not emptied or to a much lesser extent due to the capacitor. Accordingly, higher-frequency signals can be largely unambiguously assigned to the second branch, ie identified as temperature signals. In order to further favor the separation, at least one inductive element may additionally be accommodated in the first branch. This inductive element may for example comprise a coil. The inductive element can in particular be connected in series with the Nernst cell. Thus, the resistance of the Nernst cell connected in parallel does not affect the measuring accuracy of the resistance of the temperature sensor, for example of the thermistor, so that the full accuracy of the resistance of the thermistor can be used.

The temperature sensor can in principle be completely or partially integrated in the sensor element itself, for example in one or more of the ways described above. Alternatively or additionally, however, it is also possible in principle to form the temperature sensor completely or partially separate from the sensor element. For example, the temperature sensor may have a separate, for example commercially available, component as a separable unit, which is connected to the sensor element, for example connected to the sensor element. This can be done, for example, via a clamping or soldering of the supply cable or via a composite material.

Various configurations are possible. As described above, in addition to the sensor arrangement, a sensor element is furthermore proposed, which is set up for use in a sensor arrangement according to the invention in accordance with one or more of the embodiments described above. Accordingly, the above-described sensor arrangement can be further developed by using one or more of the sensor elements described below in one or more of the described embodiments. Alternatively or additionally, however, the use of other types of sensor elements is possible in principle, for example, as described above, the use of sensor elements without their own temperature sensor, wherein the sensor arrangement additionally comprises such an external temperature sensor. The sensor element is preferably designed as a two-contact sensor element, thus preferably has only two connection contacts. Basically, however, sensor elements are also possible with a higher number of connection contacts.

In the proposed sensor element of the temperature sensor is preferably at least partially designed as a thermistor. This means that the temperature sensor comprises at least one thermistor. In addition, the temperature sensor may optionally include other types of temperature sensor. Of the

Temperature sensor, in particular the thermistor, comprises at least one electrically connected to the second electrode inner electrode, that is, an electrode which is also arranged in the reference gas space. This at least one inner electrode may be formed separately from the second electrode and be electrically connected only to the second electrode. Preferably, however, the inner electrode is at least partially identical to the second electrode. For example, one and the same electrode can be used for the inner electrode and the second electrode. Furthermore, the temperature sensor comprises at least one outer electrode which is at least partially different from the first electrode. This outer electrode can, for example, in turn be arranged on a surface of a layer structure of the sensor element facing the measurement gas space and can be connected to the measurement gas space or be formed separately therefrom. However, it is preferred if this outer electrode is exposed to the gas in the measuring gas space directly or indirectly, for example via a porous protective layer. In this case, the inner electrode and the outer electrode are preferably connected by at least one resistance material which is at least partially different from the solid electrolyte. This resistance material can be, for example, a negative temperature coefficient resistor material or comprise a material of this type. Here, different resistance materials are used. In particular, it is possible to use metal-oxide materials which are known to have a resistor with a negative temperature coefficient. For example, ytterbium-terbium-X mixed oxides can be used, wherein X may comprise, for example, samarium and / or gadolinium. Such resistance materials are known, for example, from EP 0 810 611 A1. The resistor materials described there can also be used in the context of the present invention, for example.

If a resistor material formed separately from the solid electrolyte is used for the thermistor, there are various possibilities for this

Insert resistance material in the sensor element. In particular, the resistance material can be embedded in a carrier material, for example a carrier layer. This can be done, for example, by the carrier material, for example the carrier layer, having a corresponding opening into which the resistance material is introduced. This introduction can take place, for example, by introducing a prefabricated piece of a layer of the resistance material into the opening of the carrier material. Alternatively or additionally, however, it is also possible to use paste techniques, for example printing techniques, doctoring techniques or the like, in which the resistance material is introduced into the opening in the layer of the carrier material. The carrier material may be, for example, the solid electrolyte itself. Thus, for example, a corresponding opening, which is to receive the resistance material, are punched into a foil of the solid electrolyte and / or cut. The solid electrolyte and the resistance material can be optimized separately. Alternatively or additionally, however, the carrier material may also comprise another material which differs from the solid electrolyte. For example, the carrier material may be an insulating material, for example Al ₂ O ₃ and / or another type of insulating material. In this case, for example, the solid electrolyte may also be completely or partially embedded in the carrier material, for example, in turn, by one or more of the embedding techniques described above. The sensor element is preferably designed as a two-contact sensor element. Accordingly, in the present invention, it is particularly preferable that the Nernst cell and the thermistor are electrically connected in parallel. This parallel connection is preferably carried out directly on the sensor element, as can be saved in this way connection contacts. This can be realized, for example, in that the sensor element comprises a first connection contact, which is electrically connected to the first electrode and the outer electrode, and also a second connection contact, which is electrically connected to the second electrode and the inner electrode. In this case, the above subdivision of a circuit can be carried out in the two branches, wherein in the first branch, the Nernst cell is arranged, and in the second branch of the temperature sensor or the thermistor.

Also the one described above, with the temperature sensor, in particular the

Thermistor, connected in series, optional capacitive element and / or the at least one optional inductive element connected in series with the Nernst cell may be integrated wholly or partly directly in the sensor element. Thus, the sensor element can comprise such a capacitive element connected in series with the thermistor and / or an inductive element connected in series with the Nernst cell. The capacitive element and / or the inductive element can be designed, for example, wholly or partially as printed elements, for example as a printed capacitor and / or as a printed coil. Since printed coils generally have very small inductances, such printed coils can be used in particular for measurements with a high measuring frequency, in particular for the measurement of the temperature signals. Alternatively or additionally, the capacitive element and / or the inductive element can also be configured by means of separate components. Overall, in this way, as described above, the frequency-selective separation between the signals of the Nernst cell and the temperature signals can be easily accomplished.

The proposed sensor arrangement and the proposed sensor element have a number of advantages over known sensor arrangements and known sensor elements. Thus, in particular, the sensor element can be realized with a small space, in particular when integrating the Temperature sensor in the sensor element. In comparison to two separate exhaust gas probes, compact and inexpensive sensor elements can be realized in this way. This can be of decisive advantage, in particular in two-wheel applications, in which such sensor elements have to be mounted, for example, in a manifold and / or a cylinder head of small engines. Since it is preferable to completely dispense with a heating element in the sensor element, for example in the form of an unheated lambda probe, the sensor element and the sensor arrangement are characterized by a low energy requirement. This low energy requirement, for example in the form of a low power consumption, is limited in particular in applications

Capacity of the power supply, such as limited battery capacity, in turn, of vital importance. In this respect, too, the sensor arrangement and the sensor element are characterized in particular for use in two-wheeled applications.

A further advantage is that in particular two-pole sensor elements can be realized by means of the concepts proposed above, that is to say sensor elements which have only two connection contacts. This results in a simpler wiring, and there may be cost advantages in the component design and in the control unit. Further advantages are that connection contacts are usually technically very complex to produce. In particular, in layer structures deeper layers must be electrically connected by plated-through holes. However, such through-contacts can represent sources of error and can increase the reject in the production of the sensor elements. In this respect, the proposed concepts of the sensor elements can simplify manufacturing processes and it is possible to produce more cost-effective and robust sensor elements.

A further advantage of the proposed sensor elements and sensor arrangements is that two relevant measured variables for the engine control, namely the temperature and the signal of the Nernst cell (for example the lambda value) can be detected by means of one and the same sensor element. This integration can thus also achieve cost advantages. On the other hand, the signal of the Nernst cell detected in this way, for example the lambda signal, can be evaluated in a simple yet reliable manner. That's how it works For example, simply evaluate the validity of the measured lambda signal, for example, by only above a certain threshold temperature, the measured value is recognized as reliably evaluated.

The changed compared to conventional sensor elements and sensor arrangements and optionally increased requirements for the evaluation can be easily realized, for example, by appropriate design of the controller, such as a programmatic design of a control device. Thus, for example, an interval operation described above of signal processing, in which a change takes place between a temperature measurement and a Nernst measurement (for example, a lambda reading), can be implemented easily. Also, a change between a control and a control, for example by characteristics and / or maps, can be implemented easily and inexpensively, without an additional sensor for temperature detection would be required.

Brief description of the drawings

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description.

Show it

1 shows a first embodiment of a sensor arrangement according to the invention;

Figure 2 shows a second embodiment of a sensor arrangement according to the invention with a first embodiment of a sensor element according to the invention;

FIG. 3 shows a third exemplary embodiment of a sensor arrangement according to the invention with a second exemplary embodiment of a sensor element according to the invention;

FIG. 4 shows an equivalent circuit diagram for the sensor arrangements in FIGS. 1 to 3 and in FIG. 6; Figure 5 is a plan view of a surface of a possible embodiment of a sensor element in Figures 2 and 3; and

6 shows a fourth embodiment of a sensor arrangement according to the invention.

embodiments

The invention will be described in the following, without limitation of other possible embodiments, with reference to lambda probes, by means of which an oxygen content in a measuring gas chamber 1 10 is to be determined. According to the invention, sensor arrangements 12 are proposed, which comprise at least one controller 114 and at least one sensor element 16, which communicate with each other via an interface 118 indicated only symbolically in the figures. The controller 1 14 is indicated only symbolically in Figures 1, 2, 3 and 6. This controller 114 may comprise, for example, one or more voltage measuring devices for detecting a Nernst voltage and / or one or more current sources and / or voltage measuring devices for detecting a resistance of a thermistor and / or other measuring devices and / or current and / or voltage sources. The electrical structure of such a controller 114 is basically known to the person skilled in the art or can easily be deduced by the person skilled in the art from the following description. Furthermore, the controller 1 14 may include a corresponding evaluation, which, as described below, may perform a signal evaluation. For this purpose, the controller 1 14 may include, for example, one or more data processing devices and / or data storage, wherein the data processing device may be set up, for example, programmatically to perform the described evaluation. The data processing device and / or the data memory may, for example, be wholly or partially components of a motor control device.

The sensor arrangement 1 12 can fall back on basically known sensor elements and use these according to the invention. For example, the sensor elements 116 in the embodiments of Figure 1 and Figure 6 be configured according to the prior art. Alternatively or additionally, however, sensor elements 116 according to the invention can also be used in the context of sensor arrangement 12, that is to say sensor elements 116 which are particularly modified and particularly suitable for the implementation of the inventive concept. Such embodiments of sensor elements 116 according to the invention are shown in FIGS. 2, 3 and 5.

The sensor elements 16 in the exemplary embodiments illustrated comprise a Nernst cell 120. This Nernst cell 120 comprises a first electrode 122 exposed to the sample gas chamber 110 directly or via a gas-permeable protective layer (not shown in the figures), which in the illustrated exemplary embodiments is designated AE (outer electrode). is designated. Furthermore, the Nernst cell 120 comprises a second electrode 124. In the exemplary embodiments illustrated, this second electrode 124 is arranged in a reference gas space 126 which is arranged separately from the sample gas chamber 110 in the interior of the sensor element 16. This reference gas space 126 is designed, for example, as an air reference, for example as a reference channel, which is connected to an engine compartment of a motor vehicle or another external space.

Furthermore, the Nernst cell 120 comprises a solid electrolyte 128 connecting the first electrode 122 and the second electrode 124. This solid electrolyte 128 may, for example, comprise YSZ and / or ScSZ and / or ZrO ₂ doped with other metal oxides as shown above. However, other materials and / or material combinations are basically possible. As a rule, the electrolytic conductivity of the solid electrolyte 128 with increasing

Temperature increases, the solid electrolyte 128 is in some ways a material with a negative temperature coefficient of electrical resistance (NTC material). The solid electrolyte 128 is accordingly designated NTCi in the figures. In the exemplary embodiments illustrated, the first electrode 122 and the second electrode 124 are connected to the interface 118 via connection lines 130, 132 and via connection contacts 134, 136 arranged on the sensor element 116.

Furthermore, the sensor arrangement 112 comprises at least one temperature sensor 138. This temperature sensor 138 is exemplary in all examples

Thermistor 140 configured, so as a resistor whose resistance value of the temperature of the gas in the measuring gas chamber 1 10 depends. The exemplary embodiments of the sensor arrangement 1 12 and of the sensor elements 116, as shown in FIGS. 1 to 6, differ with respect to the arrangement and configuration of this temperature sensor 138. FIGS. 1 to 3 and 6 show four different embodiments of sensor arrangements

In each case, thermistors 140 are used, which comprise a resistance material 142 having, for example, a negative temperature coefficient (NTC). In contrast to the solid electrolyte 128, this resistance material 142 is designated NTC ₂ in the figures.

The four embodiments of the sensor arrangement 112 will be briefly described below.

FIG. 1 shows a first exemplary embodiment of a sensor arrangement 112, in which the solid electrolyte 128 may comprise, for example, yttrium-stabilized zirconium dioxide. Here as well as in the other exemplary embodiments, the electrodes 122, 124 may be designed, for example, as cermet electrodes, for example as platinum cermet electrodes. The Nernst cell 120, which includes the first electrode 122 (outer electrode, AE), the solid electrolyte 128 and the second electrode 124 (inner electrode, IE), is also referred to as

Temperature sensor 138 is inserted and thus forms a temperature-dependent resistance element (thermistor 140), which is used as a resistive temperature sensor. For example, the controller 114 may be configured to alternately detect at intervals the Nernst voltage at the Nernst cell 120 (DC voltage) and, alternately, the temperature in the sample gas space

1 10, expressed by the resistance of the thermistor 140. The controller 1 14, as described above, for example, be set up so that only lambda signals of the Nernst cell 120 are evaluated, which are above a predetermined threshold temperature. Other evaluation methods taking into account the temperature in the sample gas chamber 1 10 are possible.

In the embodiment according to FIG. 1, therefore, the material of the solid electrolyte 128 is simultaneously used as resistance material 142 of the thermistor 140. This makes it possible to realize a very simple construction of the sensor element 116. Through the temporal sequence of temperature measurements and

Nernst voltage measurements can be a mutual interference of Messun- avoid it. A disadvantage of the sensor arrangement 112 according to FIG. 1, however, may be that in this case a simultaneous optimization of the material properties of the solid electrolyte 128 must take place in order to serve both as a carrier material and as an oxygen ion conductor as well as a resistance material 128. This may possibly result in lower accuracy and sensor dynamics.

In Figure 2, therefore, an embodiment of a sensor arrangement 112 is shown, which overcomes this disadvantage. In principle, the sensor element 116 used here largely corresponds to the sensor element 16 according to FIG. 1. In contrast to the construction shown there, however, the temperature sensor 138 and the Nernst cell 120 are configured separately. The temperature sensor 138 comprises an inner electrode 144 in the reference gas space 126 which is identical or combined with the second electrode 124 in this exemplary embodiment, but has an outer electrode 146 which is separated from the first electrode 122 and exposed to the reference gas space 110. Furthermore, the temperature sensor 138 comprises a Resistor material 142, which connects the inner electrode 144 and the outer electrode 146 with each other. This resistance material 142 is separated from the material of the solid electrolyte 128 in this embodiment. The solid electrolyte 128 acts as a carrier material 148, in particular as a carrier layer into which the resistance material 142 is inserted. For example, the solid electrolyte 128 may be configured as a ceramic foil, and the resistance material 142 may be embedded as a thermistor material in this carrier material 148. The resistance material 142 may accordingly be optimized to optimize the temperature in the relevant exhaust gas temperature range, for example between 300 ^° C. and 1000 ^° C. The resistance material 142 is accordingly designated NTC _{2 in} FIG. Such optimized resistance materials 142 are already known from the prior art as materials in individual temperature sensors. Particularly suitable for the embodiment according to FIG. 2 are, for example, Y-Tb-X mixed oxides, where X may be, for example, samarium and / or gadolinium. Such materials can be used at temperatures above 1 100 ⁰ C as thermistors. An advantage of such materials is that they undergo no phase transformation, that they are compatible with the typical ceramics of the solid electrolyte 128 and, in particular, can also be produced simultaneously with these, for example by so-called co-firing. The resistance material 142 may be in the support material 148, for example, in the YSZ Tarrägerfolie, in particular by means of one or more of the following ceramic manufacturing processes are embedded: embedding as inlay or stamped into the substrate 148 (so-called green film technology) and / or as a paste or extruder mass for filling this provided recesses. The inserted resistance material 142, for example the NTC ₂ -lnlay, can additionally be sealed off from the carrier material 148 by further measures. For example, a seal can optionally be made by glazing.

The contacting of the thermistor 140 or of its electrodes 144, 146 can take place via the same connection lines 130, 132, which are also used for contacting the first electrode 122 and the second electrode 124. An embodiment of a corresponding electronic circuit is explained below with reference to Figures 4 and 5.

The embodiment of the sensor arrangement 112 shown in FIG. 2 has the advantage over the exemplary embodiment in FIG. 1 that the resistance material 142 can be selected specifically for the temperature measurement and thus can be optimized separately from the solid electrolyte 128. The dimensioning of the resistance material 142 should be designed so high impedance that the limiting current of optionally configured as a reference air duct reference gas space 126 is not exceeded by a short-circuit current of the Nernst cell. In this way, an occurrence of CSD (characteristic shift down, for example, loading of the second electrode 124 by fat gases) can be effectively avoided. Overall, the separate optimization of the

Resistance material 142, regardless of the solid electrolyte 128, a higher accuracy for the temperature measurement and thus for the entire measurement of the sensor assembly 1 12 achieve.

In the exemplary embodiment of the sensor arrangement 1 12 and of the sensor element 1 16 according to FIG. 2, the solid electrolyte 128 itself serves as carrier material 148 into which the resistance material 142 is inserted, for example as an inlay. As a result, however, the solid electrolyte 128 generally has to be optimized simultaneously for two requirements, namely the carrier function and the solid electrolyte function. However, there is often a conflict of objectives here, which The reason is that an increasing ionic conductivity in many cases has to be paid for with a reduced mechanical strength.

In contrast, FIG. 3 shows an exemplary embodiment of a sensor arrangement 1 12 and of a sensor element 1 16 according to the invention, in which also the

Solid electrolyte 128 is embedded in a separately formed from the solid electrolyte 128 carrier material 148. Otherwise, the exemplary embodiment largely corresponds to the exemplary embodiment according to FIG. 2, so that reference can largely be made to the description of this figure. As carrier material 148, for example, an electrically insulating ceramic carrier, for example

AI ₂ O ₃ , are used. Then, the solid electrolyte 128 and the resistive material 142 may be separately optimized, where the solid electrolyte 128 may be optimized for ion conduction, such as oxygen ion conduction, and / or lambda determination, and the resistive material 142 for temperature measurement. The solid electrolyte 128 and the resistance material 142 may, for example, in turn be inserted separately into the carrier material 148, for example into a carrier foil. For the insertion techniques, reference may be made to the above description of the insertion of the resistance material 142 according to FIG. In this way, functional advantages can be achieved by selectively selected materials both for the lambda measurement by means of the Nernst cell 120, in particular with regard to the accuracy, dynamics and low-temperature behavior, as well as for the temperature measurement by means of the thermistor 140, in particular with regard to the accuracy over one large measuring range. At the same time, the carrier material 148 can be improved to an optimum strength and optionally to further properties, for example with regard to an insulating property.

In the exemplary embodiments in FIGS. 2 and 3, in particular the Nernst cell 120 and the thermistor 140 can be connected in parallel. This can be done, for example, according to the embodiments shown in FIGS. 4 and 5. FIG. 4 shows an equivalent circuit diagram of the parallel circuit comprising Nernst cell 120 and thermistor 140, and FIG. 5 shows a plan view of a surface of a possible modification of the sample gas chamber 110 of a possible modification of the exemplary embodiments of a sensor element 116 shown in FIGS. 2 and 3. Here, the Nernst cell 120 and the temperature sensor 138 in one

Circuit of the sensor assembly 1 12 interconnected in such a way that this are accommodated in differently arranged branches 150, 152. In a first branch 150 of the circuit while the Nernstzelle 120 is received, whereas in a second branch 152, which is connected in parallel to the first branch 150, the thermistor 140 is received. Furthermore, a capacitive element 154 in the form of, for example, a printed capacitor, which is connected in series with the thermistor 140, is optionally accommodated in the second branch 152. The thermistor 140 is thus connected in parallel in this embodiment via a capacitor in series with the Nernst cell 120. For example, capacitances of 100 pF to 1 μF, preferably of about 1 nF, are suitable for the capacitive element 154. For this preferred choice of capacitances, the DC evaluation of the Nernst cell 120 is maintained because at low frequencies the second branch 152 blocks. A short circuit of the Nernst cell 120 via the second branch 152 is avoided. The temperature measurement can then take place at frequencies, for example above 1 kHz, whereas the lambda measurement is evaluated only up to 10 Hz. This allows the information to be separated.

Furthermore, an inductive element 156 may also be accommodated in the first branch 150, in which the Nernst cell 120 is accommodated, which is shown symbolically in FIG. 4 and, for example, also in the exemplary embodiment according to FIG. 5 and / or in the exemplary embodiments according to FIGS and 3 can be realized. In the equivalent circuit diagram shown in FIG. 4, the Nernst cell 120 is symbolically symbolized by a Nernst voltage source 158 (denoted by U _N ) and the solid electrolyte 128 connected in series to this Nernst voltage source 158. By inserting the inductive element 156 into the first branch 150 of the circuit, the resistance of the solid electrolyte 128 with respect to the resistance of the resistance material 142 of the thermistor 140 in the measurement accuracy of the thermistor 140 is not or only insignificantly, and the full measurement accuracy of the thermistor 140 can be used.

In the embodiments according to FIGS. 4 and 5, the circuit via which the Nernst cell 120 and the temperature sensor 138 are connected in parallel to one another is completely accommodated in or on the sensor element 116. For example, this can be achieved by corresponding printed connection lines 130,

132 done. Furthermore, the temperature sensor 138 is completely in the sensor integrated into element 1 16. However, a different design is also possible in principle. An example of such a deviating embodiment is shown in FIG. 6, which in turn shows a sensor arrangement 112 with a sensor element 16. In this case, the sensor element 1 16 in the illustrated exemplary embodiment largely corresponds to the sensor element, for example

1 16 according to FIG. 1. In this respect, reference may be made, for example, to the above description. In contrast to the exemplary embodiment according to FIG. 1, however, in the exemplary embodiment illustrated in FIG. 6, the Nernst cell 120 is not simultaneously used as a temperature sensor 138 as well. Also not, as in Figures 2 and 3, in the sensor element 1 16 integrated temperature sensor

138, but a temperature sensor 138, such as a thermistor 140, which is designed as a separate, non-integrated component. For example, as a temperature sensor 138, a separate and commercially available component can be used. The temperature sensor 138 may, for example, be connected to the sensor element 116 as a detachable unit. This can be done for example by clamping or soldering the supply cable, and / or via a composite material, for example, with a printed lead 130, 132 for the Nernstzelle 120 on the ceramic substrate.

Analogous to the exemplary embodiments in FIGS. 4 and 5, for example, a parallel connection of the temperature sensor 138 and the Nernst cell 120 can take place, with two branches 150, 152 connected in parallel, as shown in FIG. Again, optionally, a capacitive element 154 in the second branch 152 and / or an inductive element 156 (not shown in FIG. 6) may be provided in the first branch 150, which in turn may be connected in series with the temperature sensor 138 or the Nernst cell 120 can be switched.

An advantage of the embodiment shown in FIG. 6 is that the ceramic processes which are required for the production of the sensor element 16 can be greatly simplified. In particular, the resistance material 142 and / or the capacitive element 154 and / or the inductive element 156 need not necessarily be sintered in the manufacture of the sensor element 16. Furthermore, the sealing problem described above, which typically results in the integration of the resistor material 142 into a layer structure of a Nernst cell 120 or of a sensor element 116, can be avoided. In the exemplary embodiments in FIGS. 4, 5 and 6, the capacitive element 154 and / or the inductive element 156 can be embodied, for example, as printed elements. Thus, for example, a capacitor may advantageously be constructed as a thick-film element directly on the sensor element 16, for example by means of superimposed and / or printed layers arranged in a plane. In this case, for example, an Al ₂ O ₃ layer and / or a layer of another insulator material, in particular a material having high relative permittivity ε _r , can be printed on a first electrode surface, for example a platinum surface. Subsequently, a second electrode surface, for example a second platinum surface, can be printed over this structure, so that a sandwich structure is created, which acts as a capacitive element 154. The inductive element 156 can be similarly produced by a printing technique.

The sensor elements 1 16 in the illustrated embodiments according to the figures 1 to 6 can be integrated in a conventional manner, for example in a (not shown in the figures) probe housing. For example, probe housings with a thread of 12 mm or 18 mm can be used, for example customary thread sizes for exhaust gas probes. The sensor elements 1 16 can in particular be configured as two-pole sensor elements 116, that is to say as sensor elements 1 16 with only two connection contacts 134, 136, so that, for example, two-pole probe housings can be used. In this way, small-volume, inexpensive and simple and robust to produce sensor elements 116 can be realized, which, together with the controller 1 14, can be used as a sensor assembly 1 12, for example in two-wheel applications.

Claims

claims

1. Sensor arrangement (112) for detecting at least one property of a gas in a measuring gas space (110), in particular for determining a portion of a gas component, wherein the sensor arrangement (112) comprises at least one sensor element (16), wherein the sensor element ( 1 16) at least one Nernst cell (120) having at least one first electrode (122) to be acted upon by the gas from the measurement gas space (110), at least one second electrode (124) arranged in a reference gas space (126) and at least one first electrode ( 122) and the second electrode (124) connecting solid electrolyte (128), wherein the sensor arrangement (1 12) at least one temperature sensor (138) for detecting a temperature of the gas in the sample gas space (1 10), wherein the sensor arrangement ( 112) comprises at least one controller (114) and is arranged to detect a signal of the Nernst cell (120) and evaluate it taking into account the temperature.

2. Sensor arrangement (1 12) according to the preceding claim, wherein the evaluation of the signal of the Nernst cell (120) takes place according to a threshold value method, in particular a threshold value method, in which the signal of the Nernst cell (120) is only evaluated when the temperature above at least one threshold temperature.

3. Sensor arrangement (112) according to one of the preceding claims, wherein the temperature sensor (138) and the Nernst cell (120) are at least partially identical, wherein the controller (1 14) is adapted to the detection of the temperature and the detection of the Signal of the Nernst cell (120) carried out separately in time.

4. Sensor arrangement (112) according to one of claims 1 to 3, wherein the temperature sensor (138) and the Nernst cell (120) are formed at least partially separated.

5. Sensor arrangement (112) according to the preceding claim, wherein the Nernst cell (120) in at least a first branch (150) of a circuit of the sensor arrangement (1 12) is arranged, wherein the temperature sensor (138) in at least one second branch (152). the circuit is arranged, wherein the first branch (150) and the second branch (152) are connected in parallel.

6. Sensor arrangement (112) according to the preceding claim, wherein the controller (114) is adapted to the signal of Nernstzelle (120) and a

Separate signal from temperature sensor (138) by frequency-selective evaluation.

7. Sensor arrangement (112) according to one of the two preceding claims, wherein in the second branch (152) in addition at least one capacitive element (154) is received.

8. Sensor arrangement (112) according to one of the three preceding claims, wherein in the first branch (150) in addition at least one inductive element EI (156) is received.

9. sensor element (1 16) for detecting at least one property of a gas in a measuring gas space (1 10), in particular for determining a proportion of a gas component, wherein the sensor element (1 16) at least one Nernstzelle (120) with at least one with the Gas from the measuring gas chamber (1 10) acted upon first electrode (122), with at least one in a reference gas chamber (126) arranged second electrode (124) and at least one of the first electrode (122) and the second electrode (124) connecting solid electrolyte ( 128), wherein the sensor element (1 16) has an at least partially designed as a thermistor (140)

Temperature sensor (138) and having at least one inner electrode (144) electrically connected to the second electrode (124) and at least one outer electrode (146) different from the first electrode (122), the inner electrode (144) and the outer electrode (146) by at least one of the solid electrolyte (128) at least partially different

Resistor material (142) are connected.

10. Sensor element according to the preceding claim, characterized in that the second electrode (124) with the inner electrode (144) is at least partially identical.

1 1. Sensor element (116) according to any one of claims 9 or 10, characterized in that the outer electrode (146) the gas in the measuring gas space (110) can be exposed.

12. Sensor element (1 16) according to any one of claims 9 to 1 1, wherein the resistance material (142) is embedded in a carrier material (148).

13. Sensor element (116) according to the preceding claim, wherein the carrier material (148) is the solid electrolyte (128).

14. Sensor element (116) according to claim 12, wherein the carrier material (148) is an insulating material, in particular Al ₂ O ₃ , wherein the solid electrolyte (128) is likewise embedded in the carrier material (148).

15. The sensor element according to claim 9, comprising a first connection contact, wherein the first connection contact is electrically connected to the first electrode and to the outer electrode, further comprising one second terminal (136), wherein the second terminal (136) is electrically connected to the second electrode (124) and the inner electrode (144).

16. Sensor element (116) according to any one of claims 9 to 15, further comprising at least one with the thermistor (140) connected in series capacitive element (154), in particular a printed capacitor.

17. Sensor element (116) according to one of claims 9 to 16, further comprising at least one inductive element (156) connected in series with the Nernst cell (120).