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
  • G01N27/4067—Means for heating or controlling the temperature of the solid electrolyte

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.
• sensor elements are used in particular in motor vehicles to measure Lxift fuel gas mixture compositions, in which case these sensor elements are also known as "lambda probe" and an essential role in the reduction of pollutants in exhaust gases, both in gasoline engines and in the Diesel technology, play.
• Such sensor elements are now known in numerous different embodiments.
• One embodiment is the so-called "jump probe” whose measuring principle is based on the measurement of an electrochemical potential difference between a reference electrode exposed to a reference gas and a measuring electrode exposed to the gas mixture to be measured conductive properties usually doped zirconia (eg yttrium-stabilized ZrO2) or similar ceramics can be used as a solid electrolyte.
• doped zirconia eg yttrium-stabilized ZrO2
• Various Ausflihrungsbeiitul such jump probes, which are also referred to as "Nernst cells” are described for example in Robert Bosch GmbH: Sensors in the motor vehicle, 1st edition 2001, pp. 112-115.
• so-called "pump cells” are used in which an electrical “pumping voltage” is applied to two electrodes connected via the solid electrolyte, whereby the “pumping current” is measured by the pump cell
• one of the two electrodes (usually via a permeable protective layer) is exposed directly to the gas mixture to be measured, however, the second of the two electrodes is designed such that the gas mixture does not flow directly towards it
• This electrode may pass, but must first penetrate a so-called “diffusion barrier” to get into a cavity adjacent to this second electrode.
• a porous ceramic structure with specifically adjustable pore radii is used as the diffusion barrier.
• the sensor elements are usually operated in the so-called limiting current operation, that is, in an operation in which the pumping voltage is selected such that the oxygen entering through the diffusion barrier is completely pumped to the counterelectrode.
• the pumping current is approximately proportional to the partial pressure of the oxygen in the exhaust gas mixture, so that such sensor elements are often referred to as proportional sensors.
• proportional sensors can be used as so-called broadband sensors over a comparatively wide range for the air number Lamb da.
• the sensor principles described above are also combined so that the sensor elements contain one or more sensors operating according to the jump sensor principle ("cells”) and one or more proportional sensors. widen the above-described principle of working according to the pumping cell principle "unicellular” by adding a snap cell (Nernst cell) to a "double cell” expand.
• a snap cell Nelnst cell
• DE 10 2005 003 813 A1 describes a sensor element in which the measurement of the Nernst voltage is carried out relative to a vehicle mass when the reference electrode is connected to the ground.
• the jump probe can be operated such that a heater supply is performed via the same cable as one of the two terminals of the Nernst cell, wherein the signal is evaluated clocked. This allows the operation of a heated jump probe with three cables or connections.
• the sensor element shown in DE 10 2005 003 813 A1 there is still a need for further savings in order to further reduce the costs of the sensor elements.
• a basic idea of the present invention is to operate the readout of the secondary voltage and the probe heating via the same, preferably single, inlet skable and to carry out the heating or reading relative to a mass, in particular a vehicle mass. Accordingly, the invention proposes a sensor element as well as a sensor arrangement comprising the sensor element which measures the number of sensor elements Contacts, by means of which the sensor element must be contacted, in particular the number of cables and / or leads, can be significantly reduced, to a single cable.
• the sensor element serves to determine at least one physical property of a gas in a measuring gas space.
• the sensor element can be designed to determine a concentration and / or a partial pressure of a gas component in a gas in the measurement gas space, in particular an oxygen concentration or an oxygen partial pressure.
• the sensor element can be used in the exhaust gas of an internal combustion engine.
• to be detected gas components and purposes are conceivable, for example, with reference to the above description of the prior art.
• the sensor element has at least one first electrode, at least one second electrode and at least one solid electrolyte connecting the first electrode and the second electrode.
• the solid electrolyte may, for example, be an oxygen ion-conducting solid electrolyte, for example yttrium-stabilized zirconium dioxide (YSZ). However, other solid electrolyte materials can be used.
• the electrodes may comprise, for example, cermet electrodes, for example platinum cermet electrodes.
• the at least two electrodes and the solid electrolyte can form a Nernst cell.
• the sensor element has at least one heating element.
• This heating element may comprise, for example, a meandering path of heating resistors.
• the heating element can in particular be configured to heat the sensing element to an optimal operating temperature, for example, a temperature between 500 0 C and 800 0 C.
• the heating element has at least two heater contacts on. At least one first heating contact of these heating contacts and the first electrode can be contacted via a common connection line.
• This common connection line is preferably integrated in a ceramic layer structure of the sensor element, so that it can be contacted by means of a single external connection. At least a second heating contact of the heating contacts and the second electrode are connected to a common ground line.
• This common ground line can for example be completely integrated into the ceramic layer structure and can be contacted, for example, with a housing of the sensor element, such as a metallic housing, so that an external Maisie tion of this mass Ie tion by a contact or a cable is not required.
• a housing of the sensor element such as a metallic housing
• the heating element in particular one or more heating meanders of the heating element, is preferably connected in parallel to the nominal cell. In this way, leads can be saved, so that the sensor element can finally be operated with only one supply line.
• the first electrode is preferably in communication with the measurement gas space, for example directly or via a gas-permeable protective layer, for example porous aluminum oxide.
• the second electrode is preferably in communication with a reference gas space separated from the measurement gas space.
• the first electrode and the second electrode, together with the solid electrolyte form a Nernst cell in which the potential of the first electrode is compared with the potential of the second electrode in the reference gas space.
• the reference gas may comprise a reference gas channel connected to a working environment.
• the work environment may include an engine compartment in which air is under normal conditions.
• other embodiments of the reference gas space are possible.
• a closed reference gas space can be used, that is to say a reference gas which is not or not significantly charged with gas from the measuring gas space and / or a working environment.
• a reference atmosphere within the closed reference gas space can be maintained or brought about by spatially operating this reference gas as a "pumped reference”, as is known, for example, from the prior art described at the outset
• At least one series resistor for example an ohmic series resistor, is provided between the first electrode and the common connection line.
• This series resistor can be completely integrated in the ceramic sensor element, for example in a layer structure of this sensor element. Alternatively or additionally, however, an embodiment of the series resistor outside the layer structure is also conceivable in principle. - -
• the heating element to the Nernst cell and the series resistor is connected in parallel.
• the series resistor serves to prevent damage to the Nernst cell in this parallel circuit, in particular in the case of clocked operation of the sensor element, as described in more detail below.
• the Nernst cell which comprises the first electrode, the solid electrolyte and the second electrode, preferably has a Nernst cell resistance.
• the series resistor is preferably selected in this case such that during operation of the sensor element, that is to say, for example, see operating temperatures of the sensor element, it has 2 to 10 times the magnitude, preferably approximately 6 times, the Nernst cell resistance.
• the additional series resistor can be completely dispensed with the additional series resistor, especially if the ohmic resistance of the Nernst cell itself is designed to be sufficiently large. This can be achieved for example via a sufficient thickness of the solid electrolyte, for example of the ZrCV material, and / or by its composition.
• the resistance should be chosen to be at least so great that, in particular after reaching the operating temperature, a sufficiently large proportion of the heating voltage across the solid electrolyte, for example the ZrCV ceramic, drops and only so little at the interface between the solid electrolyte and the electrode or electrodes Damage occurs.
• a sensor arrangement for determining at least one physical property of a gas in a measurement gas space which comprises at least one sensor element according to one or more of the embodiments described above.
• the sensor arrangement comprises at least one control which, for example, can be completely or partially integrated in an engine control unit of a motor vehicle.
• the controller can be set up to carry out the method described below for operating the sensor element, so that, in addition to the described controller and the sensor arrangement, such an operating method for operating the sensor element is proposed according to the invention.
• the control can, for example, be wholly or partly by means of a data processing device can be carried out and can include corresponding program-technical steps, which are implemented for example by means of a suitable computer program.
• the controller is set up to connect the connecting cable optionally to an electrical energy source or a measuring device.
• an electrical energy source may include, for example, a voltage and / or current source.
• the controller may be configured to connect the connection line to an electrical positive pole of the electrical energy source.
• the measuring device may in particular comprise an electrical measuring device, in particular a voltage measuring device and / or a pulse measuring device.
• the control is preferably configured separately from this layer structure.
• the controller may be connected to the sensor element, for example, via one or more connection lines or cables.
• connection lines or cables As described above, preferably only a single cable is used to connect the controller to the connecting line, whereas the ground line is connected to a ground of the sensor element.
• This mass which may comprise, for example, a sensor housing may be connected, for example, with an engine block or the mass of a motor vehicle.
• the controller is set up such that in at least one heating phase the connecting line is connected to the electrical energy source and in at least one measuring phase with the measuring device.
• the controller can be set up to close at least one signal of the measuring device on the physical property of the gas, in particular on an oxygen concentration or an oxygen partial pressure.
• This evaluation process can be performed absolutely by correlating the absolute signal of the measuring device, for example analytically, empirically or semiempirically, with the physical property, for example via corresponding evaluation functions, tables, correlation curves or the like.
• the evaluation is thus a digital evaluation which, instead of an absolute measured value, only supplies a fat / mag er information.
• the sensor element is operated in a clocked manner.
• the reading of the Nernst voltage is preferably carried out in a time between two heating cycles. Accordingly, it is possible to alternately switch back and forth between heating phases and measuring phases. In this case, for example, the heating phases can be made longer than the measuring phases. Variable temporal lengths of the phases are conceivable, for example in the context of pulse width modulation.
• the controller can be set up to operate the heating element with alternating electrical polarity in successive heating phases.
• a sensor element and a sensor arrangement can be produced which are extremely simple in construction and which at the same time nevertheless provide a reliable and controllable reference for a measurement of the Nernst potential.
• FIG. 1 shows an embodiment of a sensor arrangement according to the invention with a single supply line and a reference air channel.
• 1 shows an exemplary embodiment of a sensor arrangement 110 according to the invention.
• the sensor arrangement 110 comprises a sensor element 112 and a controller 114, which are connected to one another via a single feed line 116.
• the sensor element 112 comprises a housing 118 indicated symbolically in FIG. 1, which may be connected, for example, to a mass 120 of a motor vehicle.
• the actual active sensor element is integrated as a ceramic layer structure 122.
• Robert Bosch GmbH "Sensors in the Motor Vehicle", 1st edition, 2001, pages 112 to 115.
• the sensor element 112 or the ceramic layer structure 122 comprise a first electrode 124, a solid electrolyte 126 and a second electrode 128. While the first electrode 124 is in communication with a measurement gas space 130, for example an exhaust tract of an internal combustion engine, in which an oxygen concentration or an oxygen partial pressure is to be determined, the second electrode 128 is arranged in a reference gas space 132.
• a measurement gas space 130 for example an exhaust tract of an internal combustion engine, in which an oxygen concentration or an oxygen partial pressure is to be determined
• the second electrode 128 is arranged in a reference gas space 132.
• this reference gas chamber 132 is part of a reference air channel 134, via which the reference gas 132 is in communication, for example, with an engine compartment which is separate from the sample gas chamber 130.
• the reference air channel 134 may, for example, be designed as an open channel or as a reference air channel filled with a gas-permeable, porous medium (for example an open-pored aluminum oxide).
• a gas-permeable, porous medium for example an open-pored aluminum oxide
• the sensor element 112 comprises a heating element 136 in the exemplary embodiment shown in FIG. 1.
• This heating element 136 serves to regulate the sensor element 112 to an optimum operating temperature, for example to set an oxygen ion conductivity of the solid electrolyte 126 and to ensure sufficient robustness against pollutants from the exhaust gas sure.
• a gas-permeable protective layer for example, an open-pore alumina layer, which is not shown in Figure 1
• the Nernst cell 138 thus has a first Nernst cell Feed line 140, which is arranged for example as a conductor on the upper side of the ceramic layer structure 122 and which contacts the first electrode 124, and a second Nernstzellen supply line 142, which is arranged for example in the reference air channel 134 and which contacts the second electrode 128.
• the heating element 136 which is designed for example as Bankzeander or, for example, at least one Walkermäander comprehensive stas, via a first heating contact 144 and a second heating contact 146.
• the heating contacts 144, 146 and the Nernstzellen supply lines 140, 142 may, for example, as a printed conductive Webs be implemented in the layer structure 122 and may include additional, not shown in Figure 1 insulation layers.
• the second Nernst cell feed line which contacts the second electrode 128 functioning as a reference electrode, and the second heating contact 146 are connected to a common ground line 148.
• This combination of the lines 142 and 146 can still take place within the layer structure 122 or can also take place outside of this layer structure, but within the housing 118.
• a summary within the layer structure is possible, for example, by using corresponding plated-through holes.
• a summary of the common mass Ie tion 148 outside the ceramic layer structure 122 is indicated symbolically in FIG.
• the ground line 148 may be connected, for example, to the ground 120, which in turn may in turn be connected to the housing 118, for example.
• a series resistor 150 is integrated in the first Nernstzellen supply line 140.
• This series resistor 150 may for example be part of the ceramic layer structure 122 or, alternatively or additionally and as shown in FIG. 1, may also be realized outside of the ceramic layer structure 122.
• Ohmic resistances can be produced, for example, by appropriate printed layers, for example by ceramic printed layers or similar materials.
• a distribution of the series resistor 150 to a plurality of partial resistors, which may be connected in series, for example, is also conceivable.
• the resistance of the Nernst cell 138 can be selected to be sufficiently large, for example by selecting a suitable geometry and / or by selecting a suitable material composition and / or by a suitable operating temperature.
• the first Nernst cell feed line 140 and the first heating contact 144 are connected to a common connecting line 152.
• This connection of the lines 140, 144 to the common connection line 152 can, for example, again take place within the ceramic layer structure 122, for example, again by using corresponding plated-through holes.
• the series resistor 150 is preferably part of the ceramic layer structure 122.
• the connection to the common connection line 152 can also take place outside of the ceramic layer structure 122, as indicated in FIG.
• the sensor element 112 thus has in the embodiment shown in Figure 1 only a single terminal contact, which is symbolically denoted by the reference numeral 154 and which is connected to the connecting line 152.
• the connection contact 154 may in turn be connected to the supply line 116, which connects the sensor element 112 to the controller 114.
• a switch 156 is provided, via which the common connection line 152 can be connected optionally to an electrical energy source 158 or to a measuring device 160.
• the switch 156 may be, for example, a switch controlled by an electronic control device, such as a microcontroller.
• the electric power source 158 may include, for example, a voltage source, for example, a voltage source with a constant voltage of about 11 V, via the switch 156, the connecting line 152, for example, with a positive pole of this Sp annungs source is connectable.
• the measuring device 160 may include, for example, a voltage measuring device, which is symbolically indicated in FIG. For example, the voltage across a Me ss resistance (not shown in Figure 1) can be measured.
• the measuring device 160 may, for example, be connected to a mass 120 on its side opposite the switch 156.
• the reference electrode lies on zirconium oxide and is located in the reference air channel 134 or is pumped as te reference operated.
• the heating element 136 has two separate connections. Overall, the sensor element must therefore be contacted with four contacts or connections.
• the sensor element 112 according to the invention in FIG. 1 is designed in such a way that it can be contacted exclusively with the single supply line 116.
• the heater circuit of the heating element 136 has only a single connecting cable, and the current flows from the positive pole of the power source 158 via the heating element 136 to the vehicle mass 120.
• Parallel to the heating meander of the heating element 136, the Nernst cell 138 and connected in series with the series resistor 150 is connected.
• the heating meander of the heating element 136 is designed as high as possible, for example, with a heating resistor of 30 ohms.
• a heating power of approximately 3.8 W can be fed into the heating element 136, of which the highest possible through low-resistance design of the supply line (that is, the lines 144, 146, 148 and 116) Share on the meander, so the actual heating resistor, the heating element 136 should drop.
• the Nernst cell 138 has a Nernst cell resistance and the heating element 136 has a heater resistance.
• Heater resistance and Nernst cell resistance are selected such that at least approximately (i.e., with a deviation of not more than 20%) at the operating temperature, the heater resistance is one fifth of the Nernst cell resistance, plus the resistance of the optional series resistor 150.
• the activation of the sensor arrangement 110 should take place in clocked fashion by means of the control 114.
• the switch 156 clocked back and forth, so that, for example, in each heating phase, the switch 156 is in the position shown in Figure 1, whereas in measuring phases, the switch 156 is connected such that the supply line. 1 16 is connected to the measuring device 160.
• the heating and measuring phases can be designed to be the same or the same length.
• a variable embodiment is also possible, for example in the form of a merely on-demand interposition of one or more measuring phases between one or more longer heating phases.
• a high duty cycle ie a high ratio between the heating phases and the measuring phases, is preferably selected for a clocked circuit.
• duty cycles between 20% and 50% can be selected.
• the housing 118 may be configured as a protective tube, which may be made closed.
• the Nernst cell 138 should have the lowest possible DC resistance when using the series resistor 150, for example, a maximum of 20 ohms.
• the series resistor 150 of the Nernst cell 138 should be about six times as large as the Nernst cell resistance of the Nernst cell 138, that is, for example, 120 ohms.
• approximately 11 V thus drops over the heating meander of the heating element 136. Due to the parallel connection according to the invention, the same voltage drops across the Nernst cell 138 and the series resistor 150.
• this reference air channel 134 should be equipped with a high storage volume and / or a high limit current Alternatively or additionally, in a further embodiment
• the heating element 136 can be operated by appropriate design of the electrical energy source 158 and / or by an additional polarity reversal switch in the controller 114 such that the heating element 136 is acted upon by an alternating polarity
• the positive polarity is applied to the heating element 136 for a longer period of time to slightly “inflate" the reference gas 132, that is, to pressurize it with an increased oxygen partial pressure.
• the interference voltages possibly applied to the vehicle mass 120 are typically up to approximately 50 mV. Application-specific, this value must be secured. If this value of the interference voltages comes within the range of the voltages to be measured by means of the device 160, the resistance values described above, in particular the value of the series resistor 150, must be dimensioned differently.
• the internal resistance of the Nernst cell 138 is 140 ⁇ . Then arise at least approximately the same voltages as in the embodiment described above with series resistor 150th
• the sensor element 112 is designed as a sensor element with reference air channel 134.
• a pumped reference may be used.
• the polarity of the Nernst cell 138 may be such that the reference gas space 132 is inflated with oxygen during the heating phases in which, for example, 1.5 V can be applied to the Nernst cell 138.
• the first electrode 124 or an additional pumping electrode, which is used for filling the reference gas space 132 should be operated as an anode, ie should be connected to a negative pole of a pumping voltage source.

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• Chemical & Material Sciences (AREA)
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• Physics & Mathematics (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
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• Pathology (AREA)
• Measuring Oxygen Concentration In Cells (AREA)
• Combined Controls Of Internal Combustion Engines (AREA)

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• 2008
  • 2008-04-17 DE DE102008001223A patent/DE102008001223A1/de not_active Withdrawn
• 2009
  • 2009-03-06 EP EP09731958A patent/EP2269047A1/de not_active Withdrawn
  • 2009-03-06 US US12/736,516 patent/US20110108419A1/en not_active Abandoned
  • 2009-03-06 CN CN2009801133169A patent/CN102007399A/zh active Pending
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