Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/403—Cells and electrode assemblies
  • G01N27/406—Cells and probes with solid electrolytes
  • G01N27/407—Cells and probes with solid electrolytes for investigating or analysing gases
  • G01N27/4071—Cells and probes with solid electrolytes for investigating or analysing gases using sensor elements of laminated structure
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/416—Systems
  • G01N27/417—Systems using cells, i.e. more than one cell and probes with solid electrolytes

Definitions

• the invention relates to a lean-back probe for the determination of the oxygen concentration in exhaust gases, in particular the exhaust gases of internal combustion engines according to the preamble of the main claim.
• measuring sensors or so-called ⁇ probes with at least one measuring cell with an electrode exposed to the exhaust gas and an electrode normally exposed to air, the so-called reference electrode, and a solid electrolyte between the two electrodes.
• Known sensors of this type are based on the principle of the oxygen concentration chain with ion-conducting solid electrolytes. They exist e.g. B. from a tube closed on one side made of stabilized zirconium dioxide, on the outer surface facing the exhaust gas there is a porous platinum layer which forms the electrode and at the same time catalyzes the greatest possible adjustment of the thermodynamic equilibrium. The one The electrode exposed to reference gas is inside the tube. Such sensors or ⁇ probes the so-called.
• Finger versions are e.g. B. from DE-PS 28 52 647 and
• both electrodes of the oxygen concentration cell are arranged one behind the other on a massive, electrically insulating carrier body, with an upper surface area of the solid electrolyte between the electrodes.
• DE-PS 27 18 907 it is also known to produce sensors with a plurality of measuring cells connected in series, the individual measuring cells alternately having successive electrode and solid electrolyte regions and being combined to form a rod-shaped measuring cell arrangement. With this configuration, the sensor not only reaches its working temperature very quickly, but also provides an increased output voltage through the series connection of several measuring cells, which is easier to evaluate than the output voltage of a single measuring cell, and with which a drop in the output voltage due to aging processes can be better controlled.
• planar exhaust gas probes to determine the ⁇ value of gas mixtures, which can be produced in a particularly cost-effective manner using ceramic film and screen printing technology.
• ZrO 2 , CeO 2 , HfO 2 and ThO 2 moldings can be used as solid electrolytes is due to the presence of oxygen ion vacancies as
• Oxygen content in gases, especially in the exhaust gases of internal combustion engines, consists in the solid electrolyte substrates being subject to electrolytic decomposition as a result of an excessive current load or short circuits or
• Solid electrolyte applies a suspension or paste with a compound with one or more 5- or higher-valent cations and allows the 5- or higher-valent cations to diffuse into the solid electrolyte by heating.
• a disadvantage of the known lean-back or ⁇ probes of the prior art is that the output signal is comparatively low.
• Another disadvantage of the known lean-back probes of the finger version is that the heating power is relatively large.
• a lean-back probe according to the invention with the features of the main claim has significant advantages over a single lean-back probe. For example, it initially has a much higher output signal than a single lean-to-notch probe. It has been found that, if several ⁇ probes are connected in series according to the invention, the output signals of the individual probes add up. For example, with six individual probes connected in series, you can achieve practically 6 times the output voltage of a simple Nernst cell. Since each ⁇ probe delivers a defined output signal with a close tolerance, the reproducibility of the output signal becomes significantly better than that of previously known limit current probes. The signal can be evaluated in a customary and known manner. Since the
• a probe delivers a voltage signal
• direct evaluation with microprocessors is possible.
• the response time corresponds to that of the known ⁇ probes and is therefore significantly faster than that of previously known limit current probes, in which diffusion processes determine the speed.
• the heating power is considerably reduced by the direct contact of the heating layer with the ceramic.
• precise temperature control is possible via a heating resistor or via the internal resistance of the nerast cells.
• the lean-toe probe consists of at least two, preferably four and in particular four to six Nernst cells or individual probes connected in series, which are gas-tight
• Layers e.g. B. Al 2 O 3 layers, or by diffusing z. B. Nb 5+ or Ta 5+ created in the solid electrolyte to suppress an O 2- ion line, as is known for example from DE-OS 37 26 479.
• the individual Nernst cells are arranged in a so-called "Janus shape".
• Lean-rest probes, in which the individual Nernst cells are arranged in a "Janus-like" manner, are those that are the same or practically the same on both sides
• Opposing Nernst cells can be connected through an insulation layer system of the heater corresponding layer system can be largely galvanically decoupled if the heater is not used.
• the position of the probe in the exhaust gas flow is of little influence.
• the heating power can easily be concentrated on the electrode area.
• a double air reference arrangement is also advantageously possible with a Janus arrangement of the Nernst cells. In this case, plated-through holes in the area of the sensor cells can be dispensed with.
• Comparatively thin ceramic foils based on are suitable for the production of lean-back probes according to the invention
• Oxides of tetravalent metals such as in particular ZrO 2 , CeO 2 , HfO 2 and ThO 2 , with a certain content of divalent alkaline earth metal oxides and / or preferably trivalent oxides of rare earths or yttrium oxide with a strength of preferably 0.1 to 0.6 mm, in particular 0.25 to
• the reference channel z. B. can be produced in a known manner by punching or by printing a layer which can be evaporated or burned out during the sintering process.
• customary known cavity formers can be used, for. B. organic compounds, for example based on polyurethane, or theobromine, salts, such as. B. ammonium carbonate or thermal carbon black powder.
• Via holes can be created by simply punching them out.
• the isolation of the via holes can, for. B. by means of an insulating Al 2 O 3 layer or by means of a suspension or paste, as is used to form the conductor tracks, but one or more connections with a 5- upper waswer term cation is added, which is found in the
• Laminating process subsequent sintering process at temperatures up to 1600 ° C, preferably 1350 to 1500 ° C can diffuse into the solid electrolyte substrate.
• pastes based on noble metal are preferably used in thick-film technology.
• Such pastes can be produced in a known manner using organic binders and / or adhesion promoters, plasticizers and organic solvents.
• the electrodes and associated ones are identical to the electrodes and associated ones.
• Conductor tracks made from a mixture of 60 vol.% Pt and 40
• the insulation of the conductor tracks or electrode feeds, the electrical connection between the individual electrodes including the plated-through holes and, if present, the heating layer is expediently carried out using a Pt-Nb 2 O 5 mixture, such as that obtained from the
• the films required for the production of a lean-back probe according to the invention can be advantageously used with interlaminar binders, e.g. B. laminate together on a YSZ basis.
• the laminate dressing is then sintered, e.g. B. by heating for 1 to 10 hours at temperatures of 1350 to 1500 ° C. After, but possibly also before The sintering process can be printed with electrical contact areas in the area of the via holes.
• Fig. 1 a lean notch probe according to the invention with simpler
• FIG. 2 shows the lean-to-notch probe according to FIG. 1 in plan view
• FIGS. 1 and 2 shows the layout of a lean-to-notch probe according to the invention of the type shown in FIGS. 1 and 2;
• Fig. 4 shows a lean-break probe according to the invention with "Janus arrangement" of the Nernst cells in section;
• FIG. 5 shows the layout of a lean-to-notch probe according to the invention of the type shown in FIG. 4;
• Fig. 6 shows a further advantageous embodiment of a
• Lean-break probe according to the invention with a "Janus arrangement" of the Nernst cells without through-contacts on average;
• Fig. 7 is a perspective view of part of a
• Fig. 8 shows a further advantageous embodiment of a
• Lean-break probe according to the invention without through-contacts with lateral channels for supplying part of the electrodes with air and exhaust gas.
• 1 and 2 is a probe made of foils 1, 2, 3 and 4 with six series-connected Nernst cells with the external electrodes exposed to the exhaust gas E 1 to E 6 and the Reference electrodes E 7 to E 12 arranged in reference channel 5.
• the individual electrodes are printed on the solid electrolyte film 2 and compared to this by first applied insulating layers, for. B. based on Al 2 O 3 , electrically isolated.
• the film 2 has plated-through holes 6 with electrical insulation, which create a galvanic connection of the electrodes E 1 -E 8 , E 2 -E 9 , E 3 -E 10 , E 4 -E 11 and E 5 -E 12 .
• the outer electrode E 6 is on the conductor track 7 and
• Reference electrode E 7 is connected to the conductor track 8.
• the heater 9 with the Heier connection 10 is printed on the film 4.
• the outer electrodes E 1 to E 6 are covered with a porous cover 11, e.g. B. based on Al 2 O 3 or Mg spinel.
• the conductor tracks 7 and 8 are surrounded by insulating regions, as is indicated in FIG. 2 by the dashed lines.
• the air reference channel 5 can have a porous filling.
• Such porous fillings e.g. B. based on Al 2 O 3 or ZrO 2 are known.
• an opening 12 is provided in the film 1 for producing the cover 11.
• the cover is designed so that it protects the electrodes E 13 to E 18 , but the
• the film 1 in the embodiment shown in FIG. 3 also has an opening 13 to the reference channel 5 in order to reduce the diffusion resistance.
• a corresponding opening 13 ′ is also located in the film 2, from which a through hole 14 for the electrical connection of the conductor track 15 to the connection 16 is also punched out.
• the electrode E 13 is connected via the conductor track 17 to the connection 16 'and the
• the film 3 has a punched-out reference channel 5.
• the channel can also be produced by printing on a cavity former of the type already mentioned and decomposing or burning the same during the sintering process to be carried out later.
• the probe also has a heater element consisting of the film 4 with a printed heater 9, through holes 19 and connections 20 and 20 '.
• the individual foils are connected to one another by laroining by means of layers 21, 21 'and 21 "of interlaminar binder, as is usually used for the production of planar probes based on solid electrolytes.
• films based on zirconium dioxide stabilized with Y 2 O 3 so-called YSZ films with z. B. 4 mol%
• the cover of the outer electrodes can e.g. B. by inserting a porous sintering ZrO 2 film or by impressing an Al 2 O 3 -containing porous engobe layer in the intended
• Outer electrodes and reference electrodes can have the usual composition for known planar probes and thus consist for example of noble metal cermet electrodes, e.g. B. Platinum cermet electrodes, at for example with 60 vol% Pt and 40 vol% YSZ (with 4 mol% Y 2 O 3 ).
• the insulation of the electrodes from the film substrates and the creation of insulating areas between the individual Nernst cells can advantageously be carried out according to the method known from DE-OS 37 26 479, after which a suspension or paste with at least one is applied to the areas of the solid electrolyte substrate to be electrically isolated Connection with one or different 5- or
• 22 22 'and 22 "Nb 2 O 5 suspensions with 5 mol% ZrO 2 can be used to form the insulations.
• the electrical insulation of the conductor tracks from the solid electrolyte films can also be carried out according to the method known from DE-OS 37 26 479 by adding one or more compounds with one or different 5- or higher-valued compounds to the materials used to print the conductor tracks or connections or the via-compound materials Add cations of the type mentioned.
• the layers of interlaminar binder that are used to laminate the individual films together have the usual known composition, ie they can consist, for example, of a YSZ composition with 4 mol% of Y 2 O 3 .
• Foils are also made in a manner known for the production of planar probes, e.g. B. by heating for 0.5 to 3 hours to a temperature of 1200 to 1400 ° C.
• the lean-rest probe shown in section in FIG. 4 according to the invention in Janus form has four Nernst cells.
• Invention lean-throated probes in "Janus shape" can, however, also be constructed from just as much individual Nernst cells as the embodiment shown in FIGS. 1-3 of a lean-throated probe according to the invention with a simple series connection of the Nernst cells.
• a lean-back probe according to the invention in Janus form can also be constructed, for example, from six or eight or even more individual Nernst cells.
• FIG. 4 consists of the solid electrolyte foils 1 ', 2', 3 'and 4' with the E 25 -E 26 electrodes; E 27 -E 28 , E 29 -E 30 and
• E 31 -E 32 formed Nernst cells. Between the Nernst cells E 25 -E 26 and E 27 -E 28 on the one hand and the Nernst cells E 29 -E 30 and E 31 - ⁇ 32 on the other hand there is the air reference channel 5 via which the reference electrodes are supplied with air and via the sealing frame 40 is sealed. In the air reference channel 5 is in a porous insulating material, for. B. porous Al 2 O 3 embedded heater 9. The electrode E 25 is with the electrode E 28 on the
• Vias 24 and electrode E 29 are electrically connected to electrode E 32 via vias 25.
• the electrode E 26 is galvanically connected to the electrode E 30 via the plated-through hole 26.
• the exposed to the exhaust gas outer electrodes E 25 and E 27 and E 30 and E 32 have like the outer electrodes of the embodiment shown in FIGS. 1 to 3 form porous covers 11.
• the solid electrolyte films 1 'and 4' have openings 12 for covers 11, as in the case of the embodiment shown in FIGS. 1-3, which have the outer electrodes E 25 and E 27 and E, respectively Cover 30 and E 32 , but allow the exhaust gas to enter the electrodes.
• the film 2 ' has plated-through holes 6 and is on one side with the electrodes E 25 and E 27 , the conductor track 27 and the connections 16 and 16' and on the other side with the electrodes E 26 and E 28 and the connection 16 "
• the electrodes are insulated from the film substrate, as in the case of the embodiment shown in FIGS. 1-3, by means of insulations 22 and 22 'produced by the screen printing process. In the case of the embodiment shown in FIGS the the the
• Electrodes E 26 and E 28 facing side of the solid electrolyte film 2- a layer 30 of an interlaminar binder with cutouts 31 and 32 are printed. However, this layer can optionally also be omitted.
• the film 3 ' is printed in the same way as the film 1' on one side with the electrodes E 29 and E 31 and the conductor track 28 and on the other side with the electrodes E 30 and E 32 and the connections 34 and 35.
• the plated-through holes 6 and 6 ' serve to produce plated-through holes 25 and 26, respectively.
• the plated-through holes produced with the aid of the plated-through holes 6 "and 6"' establish the electrical contact with the connections 34 and 35.
• a layer 36 of interlaminar binder is introduced between the film 3 'and the film 4'.
• Two porous sintering Al 2 O 3 insulation layers 38 and 39 with printed, hermetically sealing frames 40 and 41 based on ZrO 2 stabilized with Y 2 O 3 are used to produce the heater and the air reference channel.
• the heater 9 can are printed on the insulation layer 39 using thick-film technology. Pastes suitable for printing are e.g. B.
• the air reference channel 5 can be protruded from the layer 39 or can be generated by means of a cavity former of the type already mentioned by printing on an appropriate paste and decomposing or burning the cavity former during the sintering process.
• the lamination and sintering together is again carried out in the manner known and customary for the production of planar probes.
• the electrodes E 33 and E 36 forming the Nernst cell or ⁇ probe 1
• the electrodes E 34 and E 35 forming the Nernst cell or ⁇ probe 2
• the Nernst cell or ⁇ probe 3 forming electrodes E 35 and E 38 and the heater 23, which is electrically insulated from the solid electrolyte foils 2 and 3, as indicated by 43.
• the electrodes E 33 and E 35 are connected to an upper and the electrode E 37 to a lower air reference channel and covered with a gas-tight cover 51.
• the electrodes E 34 , E 36 and E 38 are on the exhaust gas.
• the latter preferably have a porous cover 11.
• the electrodes E 33 and E 38 are connected to the conductor tracks 44 and 45, respectively.
• Electrodes E 36 and E 37 are galvanically connected.
• FIG. 7 illustrates the course of the air reference channels via which the reference electrodes E 33 , E 35 and E 37 are supplied with air.
• the heater has been omitted for the sake of clarity.
• the insulated heater in contrast to the embodiment shown in FIGS. 6 and 7, is not arranged centrally between the electrodes, but below the electrodes. At this
• the lean-break probe essentially consists of the solid electrolyte foils 1, 2 and 3 and the foils 4 and 4 'forming the heater unit, which form the first Nernst cell or ⁇ probe
• Electrodes E 39 and E 44 have electrical connections 49 and 50, respectively.
• the electrodes E 42 and E 44 are supplied with exhaust gas via the lateral channels 46 and 47, which have a porous filling, and the reference electrode E 43 is supplied with air via the lateral channel 48.
• These lateral channels can, for example, be analogous to the reference channel 5 the embodiment shown in Fig. 3 are made.
• the lean-back detectors according to the invention can be used, for example, in housings of the type known from DE-OS 32 06 903 and 35 37 051 and can be used to determine the oxygen concentration of the exhaust gases from motor vehicles.

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• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Health & Medical Sciences (AREA)
• Physics & Mathematics (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Molecular Biology (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Measuring Oxygen Concentration In Cells (AREA)

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• 1988
  • 1988-10-01 DE DE3833541A patent/DE3833541C1/de not_active Expired - Lifetime
• 1989
  • 1989-09-29 KR KR1019900701028A patent/KR900702363A/ko not_active Withdrawn
  • 1989-09-29 WO PCT/DE1989/000613 patent/WO1990003570A1/de unknown

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