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

Definitions

• the invention is based on known sensor elements which are based on electrolytic properties of certain solids, ie the ability of these solids to conduct certain ions.
• Such sensor elements are used in particular in motor vehicles to measure air-fuel-gas mixture compositions.
• sensor elements of this type are used in so-called “lambda sensors” and play an essential role in the reduction of pollutants in exhaust gases, both in petrol engines and in diesel technology, as well as other types of sensor elements which comprise solid electrolytes of the type described.
• the invention is applicable, so in addition to jump probes and broadband probes, for example, on particle sensors or similar types of sensors with solid electrolyte, for example, for the measurement of CO, NO x or NH 3.
• the invention is based on the example of lambda probes
• sensor elements for example sensor elements for determining the concentration or molar fraction of other gas components, for example oxygen-containing gas components, can be produced.
• Lean gas mixtures ie gas mixtures with a fuel deficiency
• sensor elements are also used in other areas of technology (in particular combustion technology). set, for example in aviation technology or in the control of burners, eg in heating systems or power plants.
• Lambda sensors are known in various embodiments.
• a first embodiment is the so-called "jump probe” whose measuring principle is based on the measurement of an electrochemical potential difference between a reference gas and the gas mixture to be measured.
• zirconia eg yttrium-stabilized zirconia, YSZ
• pump cells are used, in which an electrical “pumping voltage” to two connected via the solid electrolyte electrodes is applied, wherein the “pumping current” is measured by the pumping cell.
• lambda probes in particular broadband lambda probes based on the double-cell principle, operate with an electrode cavity in which at least one of the electrodes is arranged.
• the oxygen partial pressure in this electrode cavity is kept constant over the measured Nernst voltage.
• a flow barrier which is frequently referred to in the literature as a diffusion barrier, diffuses a limited amount of gas from the exhaust gas into the electrode cavity. When pumping the oxygen or when pumping oxygen can be concluded from the pumping current to the respective oxygen excess or lack of oxygen.
• control of the internal resistance of the Nernst cell or, preferably, the internal resistance of a heating element is often kept constant.
• a lambda probe should normally only determine the proportion of a gas component, for example the mole fraction of oxygen and / or fat gases in the exhaust gas, in order to operate the internal combustion engine appropriately.
• the lambda probe in the Usually only measure this. Only at known total pressure can be converted from the partial pressure on the mole fraction.
• an external pressure sensor or model is required. However, this is in many cases subject to great errors because of the not exactly known mass flow and the geometry. The error of the total pressure is multiplied by the factor of the so-called static pressure dependence in the total error.
• a sensor element for determining at least one physical quantity of a measurement gas in a measurement gas space which at least largely avoids the disadvantages of known sensor elements.
• the sensor element can be used in particular for determining at least one proportion of at least one gas component in the gas, in particular an exhaust gas of an internal combustion engine, for example for determining a mole fraction of oxygen and / or of fatty gases in the exhaust gas.
• the invention is based on the consideration that the target conflict described above can be avoided by combining the known flow barrier with a corresponding diffusion channel.
• the flow barrier can be combined with an upstream and / or a subsequent diffusion channel such that results in a low static pressure dependence at the same time low dynamic pressure dependence.
• the flow barrier is designed by a large cross-section and a short length such that their limiting current in relation to the limiting current and volume of the diffusion channel, which preferably has the smallest possible cross-section and a long length, is very large.
• the ratio of the diffusion limiting currents of the two components that is to say the proportion of the flow barrier and the proportion of the diffusion channel, that is to say the components with high and low static pressure dependence, sets the entire static pressure dependence, since both diffusion resistors act as connected in series.
• D denotes the total diffusion coefficient.
• the smallest possible volume for the diffusion channel, in particular the section of the diffusion channel in the flow direction behind the flow barrier is advantageous.
• the sensor element with at least one first electrode, at least one second electrode and at least one solid electrolyte connecting the first electrode and the second electrode, wherein the second electrode is arranged in at least one electrode cavity.
• the first electrode, the solid electrolyte and the second electrode can thus together form a pumping cell and also be operated as such a pumping cell.
• the sensor element can be designed as a broadband lambda probe according to the double-cell principle, as is known, for example, from the prior art described at the beginning.
• the sensor element has at least one Gaszutrittsweg, via which the electrode cavity can be acted upon with gas from the sample gas space.
• This gas inlet path includes all elements, cavities, channels, porous elements and the like, which must penetrate or overcome the gas from the sample gas space in order to reach the electrode cavity.
• this gas access path may include a gas access hole, a flow barrier, or additional diffusion channels, and generally describes a void or path through which the gas can and must pass on its way to the electrode cavity to enter the electrode cavity and within which no electrodes are disposed.
• any hollow space within which the second electrode and / or elements of this second electrode, for example partial electrodes of this second electrode are arranged, is arranged as the electrode cavity, wherein the kiterale extent of the second electrode and / or the components of the second electrode limits the electrode cavity by definition.
• the gas access path can also be seamlessly transitioned into this electrode cavity, wherein the boundary between gas inlet path and electrode cavity is to be set at the point at which the spatial extent of the second electrode begins.
• this Gaszulingersweg at least a first section and at least a second section. At least one flow barrier is arranged in the first section.
• this first section may correspond, for example, to the conventional flow barriers in broadband lambda probes.
• a flow barrier is to be understood as meaning a porous element which has a proportion of not more than 50% of open porosity, preferably of not more than 35% or even not more than 30%.
• the first section can preferably be completely filled by this flow barrier, or the flow barrier can also be designed in several parts.
• the second section preferably has at least one diffusion channel and / or is formed by this at least one diffusion channel.
• a diffusion channel is an element to understand, which has a relatively low flow resistance to the flow barrier, preferably a flow resistance, which is at least a factor of 2, preferably a factor of 10 or more, less than the flow resistance of the flow barrier.
• this is an open channel.
• a complete or partial filling of the diffusion channel with a porous, coarsely porous material, for example an aluminum oxide is in principle possible, this porous material preferably having an open porosity of more than 50%, in particular of at least 60%.
• the first section and the second section are connected in series one behind the other.
• the inflow of the gas from the sample gas space into the electrode cavity defines a respective flow direction in the gas inlet path, ie a direction in which the gas would flow mainly at the respective location.
• the sequence of the first section and the second section can basically be configured as desired, so that, for example, first the first section, followed by the second section, can be arranged.
• a reverse arrangement is also possible in principle.
• a subdivision of the sections into subsections is also possible, so that, for example, a first subsection of the second section can be arranged before the first section, and a second subsection of the second section can be arranged after the first section.
• the gas inlet path may initially comprise the gas inlet hole, which penetrates a possible layer structure of the sensor element in order to guide the gas from the sample gas space to a deeper layer plane, this gas inlet hole forming a first section of the second section.
• the flow barrier can join this first subsection, as the first section of the gas access path, followed by a narrow cross-section diffusion channel as the second subsection of the second section.
• the first section and the second section are each provided with a first or second diffusion resistance. These diffusion resistances can be comparatively easily influenced by a corresponding dimensioning of the cross sections of the individual sections as well as by a corresponding dimensioning of the porosity of the flow barrier. Examples of such an adjustment of the diffusion resistances of the sections are detailed below.
• the first diffusion resistance of the first section make up a proportion of between 20% and 80% of the total diffusion resistance of the gas access path, preferably a proportion of between 40% and 60% and particularly preferably a proportion of approximately 50%.
• the sensor element according to the invention thus has a low static pressure dependence and a low response time, at the same time lower dynamic pressure dependence and low mean value shift.
• the porous flow barrier preferably has an open porosity of not more than 30%.
• this porous flow barrier can be produced by using porous ceramic materials, for example by using aluminum oxides and / or zirconium oxides.
• the diffusion channel at least partially with the smallest possible volume.
• the partial section of the diffusion channel or of the second section, which is arranged downstream of the flow barrier in the flow direction, should be designed as small as possible. This can be done in particular via an adaptation of the cross section of the diffusion channel, which should be made technically as small as reproducible producible.
• the diffusion channel can be at least partially, in particular in a behind the Flussbarrie- Re arranged portion, be configured with a cross section perpendicular to the flow direction between 250 microns 2 and 40,000 microns 2 , preferably of about 2000 microns.
• the diffusion channel has a width perpendicular to the flow direction of 0.05 mm to 1 mm, preferably 0.2 mm, at least in a subsection, in particular in a subsection arranged behind the flow barrier in the flow direction Height perpendicular to the flow direction of 5 microns to 40 microns, preferably of 10 microns, having.
• a dimension can be regarded as the height perpendicular to the layer planes of a layer structure of the sensor element, as a width one dimension parallel to these layer planes.
• a low diffusion resistance in the form of a coarse-pore porous material of the flow barrier can be combined with a short diffusion channel with a narrow cross-section, since a coarse-pored material already has a low static pressure dependence which, to compensate for the dynamic pressure dependence, only combined with a short diffusion channel must be in order to achieve the described ratio of about 50%.
• a coarse-pore or open-pored material is to be understood as meaning a material having a pore size of at least 1.0 ⁇ m, in particular of at least 1.5 ⁇ m.
• the diffusion channel for example, a length between 0.5 and 1.5 mm, in particular of 1 mm, have, so be designed comparatively short.
• a finely porous material for the porous flow barrier that is to say a material having a pore size of, for example, 0.2 ⁇ m to 1.0 ⁇ m, in particular less than 0.5 ⁇ m, in combination with a long diffusion channel a diffusion channel which exceeds the length of the porous flow barrier along the flow direction of the gas.
• this length can be between 1 mm and 3 mm, preferably about 1.5 mm. For a smaller cross-section but shorter lengths can be used.
• the porous flow barrier at least partially has a larger cross section perpendicular to the flow direction of the gas than the diffusion channel, in particular as a partial section of the diffusion channel, which adjoins this flow barrier in the flow direction.
• the flow barrier can have a cross section of 40,000 ⁇ m 2 to 500,000 ⁇ m 2 , in particular a cross section of 180,000 ⁇ m.
• the flow barrier can, for example, have a width of 1 mm to 5 mm, in particular of 3 mm, and a height of 40 ⁇ m to 100 ⁇ m, preferably of 60 ⁇ m. This enlargement of the cross section of the Flow barrier relative to the diffusion channel can cause a volume difference between the flow barrier and the diffusion channel, which in turn can have a positive effect on the reduction of pressure dependencies.
• the cross section of the flow barrier can also be designed to vary.
• the porous flow barrier may have a different cross section perpendicular to the flow direction of the gas, at least in two subsections.
• the cross section in a downstream section, may be narrower than in an upstream section of the flow barrier, so that in the flow direction of the gas, the cross section of the flow barrier can decrease continuously or stepwise. It is particularly preferred if the cross section in the flow direction of the gas generally decreases, in particular at least partially continuously.
• the cross section of the flow barrier essentially corresponds to the cross section of the diffusion channel.
• Figure 1 shows a first embodiment of a sensor element according to the invention in a sectional detail view, wherein an open-pore flow barrier is used in combination with a short, low diffusion channel;
• Figure 2 shows a second embodiment of the sensor element with a fine-pored flow barrier and a long, low diffusion channel
• Figure 3 shows a third embodiment with a diffusion barrier with continuously in
• FIG. 1 shows a first exemplary embodiment of a sensor element 110 according to the invention.
• the illustration shows a section of the sensor element 110 in a sectional view perpendicular to a layer structure of the sensor element 110.
• the sensor element 110 is configured to measure an oxygen concentration in a gas in a measurement gas space 112.
• the sensor element 110 has a first electrode 114, which is exposed to the measuring gas chamber 112 directly or via a gas-permeable protective layer, via a solid electrolyte 116 and via a second electrode 118.
• This second electrode 118 is located in a lower layer plane of the Sensor element 110 is arranged and is optionally divided into two partial electrodes in the illustrated embodiment.
• the second electrode 118 is arranged in an electrode cavity 120, which is separated from the measurement gas space 112 by at least one layer of the layer structure of the sensor element 110, for example the solid electrolyte layer 116.
• the electrode cavity 120 can be acted upon with gas from the measurement gas space 112 via a gas inlet path 122.
• This gas inlet path 122 is shown only in a rudimentary manner in FIG. 1 and may, for example, also comprise a gas access hole running perpendicular to the layer structure of the sensor element 110, for example to the left of the section shown in FIG.
• the Gaszufrittsweg 122 is divided into two sections in the illustrated embodiment.
• a first section 124 with a length L 1 in this case comprises a flow barrier 126.
• the gas inlet path 122 further comprises a second section 130.
• This second section 130 is either formed as an open channel or is filled with a porous, but largely gas-permeable material, which comparatively low flow resistance opposes the flow of the gas.
• this porous material may be a material having an open porosity greater than 60%, such as a porous alumina, as opposed to the flow barrier 126, which preferably has an open porosity of about 30%.
• the second section 130 is subdivided into a first section 132 and a second section 134. While the first Subsection 132 of the flow barrier 126 is upstream in the flow direction 128 of the inflowing gas, the second section 134 is downstream in the illustrated embodiment of the flow barrier 126 in the flow direction 128 and disposed between the flow barrier 126 and the electrode cavity 120. While the first subsection 132 is provided with a comparatively large cross section, this second subsection 134, that is to say the subsection disposed between the flow barrier 126 and the electrode cavity 120, is preferably provided with the smallest possible cross section in order to keep the volume to be filled as small as possible. This second subsection 134 represents a diffusion channel 136.
• the ratio of the diffusion resistance of the flow barrier 126 to the total diffusion resistance of the gas access path 122 can be adjusted in particular via the porosity of the flow barrier 126 in relation to the length and the cross section of the diffusion channel 136.
• the diffusion channel 136 has a longitudinal extent L 2 in the flow direction 128 and a height H 2 perpendicular to the flow direction 128 and a width (not shown in FIG. 1, again perpendicular to the plane of the drawing) B 2 .
• the product of height and width, as with the flow barrier 126, determines the cross section of the diffusion channel 136.
• a concept for achieving a proportion of approximately 50% of the diffusion resistance of the flow barrier 126 is realized on the total diffusion resistance of the gas access path 122 which is formed on an open-pore flow barrier 126, in combination with a short diffusion channel 136 is based.
• the flow barrier 126 is typically made to be similarly thick and similar in width to the adjoining electrode cavity 120, in the illustrated embodiment, the flow barrier 126 is made wider and higher than the diffusion channel 136 and the electrode cavity 120.
• widths B 1 of 1 to 5 mm are preferred, in particular a width of about 3 mm.
• a height H 1 is a height of 40 .mu.m to 100 .mu.m, in particular from about 50 to 60 microns, preferably.
• lengths between 1 and 3 mm can be used as the length Li of the flow barrier 126, for example lengths of 1.4 mm.
• the flow barrier 126 is designed to be open-pored. For example, it can use a pore size of at least 1.0 ⁇ m, in particular more than 1.5 ⁇ m. Because of this open porosity, this flow barrier 126 has a comparatively low static pressure dependence.
• the subsequent diffusion channel 136 can therefore be made comparatively short. Widths B 2 of 0.05 to 1 mm, preferably 0.2 m, heights H 2 between 5 and 40 ⁇ m, preferably 10 ⁇ m and lengths L 2 in the range from 0.5 to 1.5 mm, in particular approx . 1 mm. Further elements of the sensor element 110 are not shown in FIG.
• additional electrodes such as a reference electrode, additional cavities, such as at least one reference cavity and / or a Referenzka- channel, heating elements, electrode leads or the like are not shown in Figure 1.
• reference may be made, for example, to the prior art described at the beginning, for example the relevant publications on broadband lambda probes according to the double-cell principle.
• FIG. 2 shows a second exemplary embodiment of the sensor element 110 according to the invention.
• the structure essentially corresponds to the exemplary embodiment according to FIG. 1, the first electrode 114 and the solid electrolyte 116 not being shown in FIG. These are to be supplemented analogously to FIG. Shown is only the Gaszufrittsweg 122 and the electrode cavity 120 and the second electrode 118th
• the second section 130 of the gas access path 122 is again subdivided into a first section 132 and a second section 134.
• a fine-pore flow barrier 126 is used, for example a flow barrier 126 having an average pore size of not more than 1.0 ⁇ m.
• the porosity can be adjusted to the starting materials of the flow barrier 126 by adding suitable pore formers.
• a long diffusion channel 136 should be inserted between the flow barrier 126 and the electrode cavity 120 to produce the described inventive ratio of the diffusion resistance of the first section 124 to the total diffusion resistance of the gas access path 122.
• diffusion channels 136 having a length L 2 have, for example, between 1 and 3 mm , In particular, 1, 5 mm, proved suitable.
• FIG. 1 for the widths and heights of the flow barrier 126 or of the diffusion channel 136.
• the cross sections described there can also be used analogously in the exemplary embodiment according to FIG.
• FIG. 3 shows a third exemplary embodiment of the sensor element 110 according to the invention, in a representation similar to that in FIG. 2. Again, reference can be made to FIG. 1 and the associated description for further detail of the sensor element.
• a flow barrier 126 is realized which has a cross section which varies in the flow direction 128.
• the flow barrier 126 may be constructed analogously to the exemplary embodiment illustrated in FIG. 2, that is to say in turn be composed of the fine-pored material described therein.
• the flow barrier 126 is adjoined in turn by a long diffusion channel 136 having, for example, the dimensions described in FIG. 1 with regard to the cross section and the length.
• the flow barrier 126 has a continuously decreasing cross-section in the illustrated embodiment.
• the flow barrier 126 starting from the first subsection 132, is continuously reduced in the flow direction 128 towards the diffusion channel 136, so that this overall represents a smaller volume in comparison to the exemplary embodiment according to FIG.
• embodiments are also conceivable which, for example, have a discontinuous course of the cross section, for example a stepped course of the cross section.

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• 2008
  • 2008-07-04 DE DE200810040175 patent/DE102008040175A1/de not_active Withdrawn
• 2009
  • 2009-05-29 EP EP09772250A patent/EP2300811A1/de not_active Withdrawn
  • 2009-05-29 CN CN200980125684.5A patent/CN102084242B/zh not_active Expired - Fee Related
  • 2009-05-29 WO PCT/EP2009/056623 patent/WO2010000550A1/de active Application Filing

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