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
  • G01N27/4078—Means for sealing the sensor element in a housing
• • 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

Definitions

• the invention relates to an electrochemical sensor for determining the oxygen content of gases, in particular for determining the oxygen content in exhaust gases from internal combustion engines according to the preamble of claim 1 and to a method for producing the meter according to the preamble of claim 9.
• Electrochemical sensors of the generic type are known. These are designed, for example, in a so-called finger design, in which a solid electrolyte body forms a sensor element which is tightly fixed as a closed tube in a metallic housing. With the finger probes, a distinction is made between potential-free and potential-bound sensors. In the case of the potential-bound sensors, a conductor track of an outer electrode of the sensor element is connected to the housing by means of an electrically conductive sealing ring contacted. In the case of the potential-free sensors, the electrode is connected directly to a control unit so that there is no electrical contact with the housing. A seal between the sensor element and the housing must be implemented in both cases.
• a sensor is known from US Pat. No. 5,228,975, in which a seal between the sensor element and the housing is achieved in that the sensor element is arranged in an additional inner tube and this is opposite the housing by means of a sealing ring and a inorganic sealing compound is sealed.
• the lead-through tube for the sensor element requires an additional seal by means of ceramic rings and an also inorganic sealing compound.
• the overall structure is very complicated.
• the sensor according to the invention with the features mentioned in claim 1 offers the advantage that a gas and heat permanent seal between a sensor element and a housing can be reached.
• the Di consists of a fine-grained or powdery material, preferably of coated graphite grains, the volume of which in the unloaded state is greater than a sealing gap between the sensor element and the housing, it is possible in a simple manner to attach this sealing element to ge ⁇ suitable place between the. Introduce sensor element and the housing, while the final formation of the sealing element only results during the joining of the housing with the sensor element. Due to the final formation of the sealing element only during the joining, the sealing element is optimally matched to the sealing surfaces of the housing or the sensor element.
• the sealing element forms an areal seal between the sensor element and the housing during the joining, so that a reliable gas- tight or temperature-tight seal takes place.
• the inventive Ver ⁇ in a simple manner the sensor including the sealing between the element and Sensor ⁇ ⁇ stellen the Gepatiu e in suitable for automated production manner forth * *.
• step of joining the housing with the sensor element can be used to form the sealing element. Since no prefabricated, tight and mechanically stable sealing elements are used, the tolerance of the sealing areas of the sensor element and / or the housing does not have to be extremely high, since the possible tolerance deviations from that which occurs only during the joining trained sealing element can be easily compensated.
• the sealing element is applied as a bed to at least one of the sealing areas of the sensor element or of the housing before the joining, here generally known and proven techniques, such as flame spraying, plasma spraying, are advantageously used as the application method.
• Roll-up or the like can be used.
• a pre-pressed sealing ring can also be used, which can be easily deformed during the joining process. Overall, this results in an easy-to-use, reliably sealing method.
• the formation of the sealing element means that there is no need for stocking with different sealing elements until during the joining with different sensors.
• the sealing elements according to the invention can thus, for example, use contaminated and potential-free sensors.
• Figure 1 shows schematically a sectional view through an electrochemical sensor
• Figure 2 schematically shows an enlarged view of a sealing zone of a floating sensor
• Figure 3 schematically shows an enlarged view of a sealing zone of a potential-free sensor.
• the sensor 10 has a metallic housing 12 which has a key hexagon 14 on its outside and a thread 16 for fastening in a measuring gas tube, not shown.
• the housing 12 is sleeve-shaped and has a through opening 18 Through opening 18 is designed as a stepped bore and forms a sealing seat 20.
• a sensor element 22 is guided in the through opening 18 of the housing 12.
• the sensor element 22 has a bead-shaped head 24, which forms an annular shoulder 26.
• a sealing element 30 is arranged between the sealing seat 20 and the annular shoulder 26 within the sealing zone 28.
• the specific configuration of the sealing zone 28 is explained in more detail with reference to FIGS. 2 and 3.
• the general structure of the measuring sensor 10 is further explained with reference to FIG. 1.
• the sensor 10 shown in FIG. 1 has a potential-free sensor element 22, the basic structure also applies to a sensor element 22 with potential.
• the differences between the sensor elements 22 which are arranged in a floating or potential-free manner are explained with reference to FIGS. 2 and 3, so that the general structure applies to both design variants.
• the sensor element 22 is an oxygen probe which is known per se and which is preferably used for measuring the oxygen partial pressure in exhaust gases, preferably in motor vehicles.
• the sensor element 22 has a tubular solid electrolyte body 32 whose end section on the measuring gas side is closed by means of a base 34.
• a layer-shaped, gas-permeable measuring electrode 36 is arranged on the outside of the solid electrolyte body 32 exposed to the measurement gas .
• a reference electrode 38 On the inside of the solid electrolyte body 32 facing away from the outside there is a reference electrode 38 which is exposed to a reference gas, for example air, and which is gas-permeable and likewise in the form of a layer.
• the measuring electrode 36 is connected to a first electrode contact 42 via a conductor track 40.
• a porous protective layer 44 is placed over the measuring electrode 36 and partly over the conductor track 40.
• the reference electrode 38 is connected to a second electrode contact 48 via a second conductor track 46.
• the electrode contacts 42 and 48 are each located on an end face 50 formed by the open end of the solid electrolyte body 32.
• the conductor tracks 40 and 46 are advantageously constructed as cermet layers and co-sintered with the sensor element 22.
• the sensor element 22 protruding from the passage opening 18 of the housing 12 on the measuring gas side is surrounded at a distance by a protective tube 52 which has openings 54 for the entry or exit of a measuring gas.
• the protective tube 52 is held at the measuring gas end of the housing 12, for example fitted into a groove 56.
• An interior space 58 of the sensor element 22 is filled, for example, by an i-shaped heating element 60.
• the heating element 60 is connected to connections (not shown) with a heating voltage source and is locked away from the measuring gas.
• a first contact part 62 rests on the first electrode contact 48 and a second contact part 64 rests on the second electrode contact 42.
• the Contact parts 62 and 64 are shaped such that they abut the tubular heating element 60 and are contacted with a measuring electrode connection 66 and a reference electrode connection 68.
• the connections 66 and 68 are contacted with connection cables, not shown, and led to the outside to a measuring or control device.
• an insulating sleeve 70 is also introduced, which is preferably made of a ceramic material. With the help of a mechanical means, not shown, the insulating sleeve 70 is pressed onto the contact parts 62 and 64, whereby an electrical connection to the electrode contacts 42 and 48 is realized.
• the annular shoulder 26 of the sensor element 22 is pressed against the sealing seat 20 of the housing 12.
• the sealing element 30 arranged between the sealing seat 20 and the annular shoulder 26 is also subjected to the press-in force 72 and, in a manner still to be explained, forms a gas, water and fuel impermeable seal.
• the sealing zone 28 of the sensor 10 is shown with a sensor element 14 which is arranged with a potential
• the sealing zone 28 is shown with a sensor element 14 which is arranged in a floating manner.
• the sensor element 22 is shown in the area of the ring shoulder 26.
• the conductor track 40 Arranged on the sensor element 22 is the conductor track 40, which connects the measuring electrode 36 to the electrode contact 42.
• the conductor track 14 bears against the inner wall of the through opening 18, so that an electrically conductive connection is created between the conductor track 40 and the housing 12.
• a sealing gap 74 is provided between the housing 12 and the sensor element 22 in the area of the sealing seat 20 and the annular shoulder 26 and has an axial extent in the direction of the through opening 18.
• the sealing element 30 is introduced into this sealing gap 74.
• the sealing element 30 is introduced here before the sensor element 22 is joined to the housing 12 by means of the press-in force 72.
• the sealing element 30 consists here, for example, of a bed 76 of individual graphite grains 78 provided with a nickel coating. These are only indicated as indicated.
• the bed 76 is applied, for example, to the sensor element 22 in the region of the annular shoulder 26 by means of a generally known method, for example flame spraying, plasma spraying, rolling up, brushing or the like.
• a layer thickness of the bed 76 applied is greater than the later axial extent of the annular gap 74.
• the bed 76 By introducing the sensor element 22 into the housing 12 while simultaneously applying the press-in force 72, the bed 76 is pressed against the sealing seat 20 of the housing 12, so that the bed 76 is compressed or compressed.
• the nickel-coated graphite grains 78 form a composite of this type which is gas, vapor and / or liquid-tight and temperature-resistant.
• this composite is impermeable to the hot gases entering the protective tube 52 through the openings 54, which can also contain fuel mixtures, so that the sensor element 22 is completely sealed between the exhaust gas side and the side remote from the exhaust gas.
• any unevenness on the sealing seat 20 or the annular shoulder 26, optionally the conductor track 40 applied there, is compensated for, so that even micro-roughness and / or corrugation can be compensated for.
• the sealing element 30 resulting from the compacted bed 76 thus adapts to the predetermined contour without problems.
• an areal sealing element 30 is created, since by adapting to any contour, the surface relief of the contours, here the sealing seat 20 and the ring shoulder 26, is shaped by the sealing element 30 during pressing.
• the bed 76 can already be pre-pressed before the sensor element 22 is introduced, which can be done, for example, during the application of the bed 76, so that a Adhesive strength to the sensor element 22 is improved.
• An axial extent of the pre-pressed sealing ring is also greater than the later axial extent of the annular shoulder 26.
• FIG. 3 shows the sealing zone 28 in the case of a sensor element 22 which is arranged in a potential-free manner, the section shown here being associated with the sensor 10 shown in FIG.
• an insulating layer 80 is provided here between the conductor track 40 and the housing 12.
• the insulating layer 80 ensures electrical insulation between the conductor track 40 and thus the sensor element 22 and the housing 12, so that it is arranged in a potential-free manner.
• the insulating layer 80 can be provided over the entire length of the sensor element 22 with which it comes to lie within the housing 12. According to FIG. 3, however, the insulating layer 80 can also only extend over the sealing zone 28.
• the protective layer 80 can consist, for example, of plasma-sprayed magnesium spinel or a glaze, which can also be co-sintered.
• the material of the insulating layer 80 is selected in particular so that it withstands the press-in forces 72 when the sensor element 22 is joined to the housing 12 and supports the compression of the bed 76 to the sealing element 30, already mentioned.
• any sensor element 22 can be arranged in a housing 12 with potential as well as potential-free, with an absolute gas and heat-resistant seal between the Sensor element 22 and the housing 12 takes place. Provision of appropriately designed sealing rings and the like for special designs of sensors 10 is therefore not necessary.
• the methods for applying the bed 76 are compatible with the methods for producing the sensor element 22 and can therefore be easily integrated into a production process.

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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)

Applications Claiming Priority (3)

Publications (1)

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• 1994
  • 1994-10-07 DE DE4435885A patent/DE4435885A1/de not_active Ceased
• 1995
  • 1995-09-14 JP JP8512242A patent/JPH09506977A/ja active Pending
  • 1995-09-14 EP EP95931132A patent/EP0733202A1/de not_active Withdrawn
  • 1995-09-14 WO PCT/DE1995/001256 patent/WO1996011393A1/de not_active Application Discontinuation
  • 1995-09-14 KR KR1019960702728A patent/KR960706071A/ko not_active Application Discontinuation
  • 1995-09-14 CN CN95191010A patent/CN1136846A/zh active Pending

Non-Patent Citations (1)

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