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
  • G01N27/416—Systems
  • G01N27/417—Systems using cells, i.e. more than one cell and probes with solid electrolytes
  • G01N27/419—Measuring voltages or currents with a combination of oxygen pumping cells and oxygen concentration cells
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/02—Circuit arrangements for generating control signals
  • F02D41/14—Introducing closed-loop corrections
  • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
  • F02D41/1493—Details
  • F02D41/1496—Measurement of the conductivity of a sensor
• • 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
  • G01N27/4073—Composition or fabrication of the solid electrolyte

Definitions

• the invention relates to a method for operating a sensor element for determining the concentration of gas components in the exhaust gas of internal combustion engines and a sensor element for determining the concentration of gas components in the exhaust gas of internal combustion engines, which can be used in such a method.
• the subject matter of the present invention is also a computer program and a computer program product which are suitable for carrying out the method.
• Such sensors are also referred to as lambda probes and are described, for example, in the book publication "Bosch Kraftfahrtechnisches Taschenbuch” 25th edition, pages 133 ff.,
• a sensor for determining gas components and / or the concentration of gas constituents in gas mixtures, in particular in exhaust gases of internal combustion engines With a reference electrode, which is acted upon via a reference gas channel with a reference gas, in particular air or an oxygen-containing gas, is also known from DE 100 43 089 C2.
• Sensor elements for lambda probes which are usually constructed in a planar manner, have a reference gas channel in which a reference electrode is arranged. These sensors are used for example as jump probes.
• these sensors are also pumped with a so-called
• Reference electrode or in an adjacent reference gas volume unburned hydrocarbons occur, for example, come from contaminated and / or overheated components or a leaky package of the probe.
• these unburned hydrocarbons By means of these unburned hydrocarbons, a non-negligible part of the oxygen supplied to the reference electrode is consumed, so that the oxygen concentration at the reference electrode is reduced and thus the probe function is disturbed. This phenomenon is known as CSD behavior ("characteristic shift-down")
• the unburned hydrocarbons are preferably present on the hot, catalytically active surfaces, ie in particular on the reference electrode in the hot region the probe ("hot spot area") are oxidized.
• the unburned hydrocarbons diffuse into the reference gas channel usually slower than oxygen, but a single hydrocarbon molecule usually converts more than a single oxygen molecule, so that the effective oxygen consumption rate by diffused unburned
• Hydrocarbons is greater than the diffusion of oxygen. This results in a relative enrichment of unburned hydrocarbons or a relative lack of oxygen at the reference electrode. Finally, due to the explained mechanisms, the risk of CSD behavior in the reference gas channel is significantly greater than in the inner volume in the probe housing, which is in communication with the reference gas channel.
• the CSD behavior can now be counteracted by applying an electron current through the sensor element, which thereby drives an oxygen flow.
• the oxygen flow starts from the reference electrode and leads via the reference channel into the outer region of the sensor element. there for example, sufficient oxygen partial pressure is generated to oxidize or carry away fatty gas components, actively eliminating CSD behavior.
• the internal resistance of such lambda probes is also temperature-dependent. If such probes are operated with a pumping current, a pumping current leads to a voltage drop at the internal resistance and thus to a displacement of the measuring signal. With constant supply voltage and constant internal resistance (which is caused by a constant temperature), the voltage drop is constant and can thus be considered in advance in the control unit. For unheated sensors, however, the internal resistance depends on the exhaust gas temperature. This can lead to a temperature-dependent voltage drop across the internal resistance, which corresponds to a signal delay. This is proportional to the pumping current.
• Lambda sensors known from the prior art are usually operated without pumping current. On the one hand, due to the proportionality to the internal resistance, this leads to a disappearance of the temperature-dependent signal delay. On the other hand, in this way no pumping action to eliminate the CSD behavior by flushing the reference channel can be achieved.
• the object of the invention is to provide a method for operating an unheated sensor element, in particular a lambda probe, and such a lambda probe, in which the CSD behavior is eliminated.
• the basic idea of the invention is to thereby minimize the CSD behavior in the case of unheated lambda probes, that is to say a signal delay in these probes, that the control point is adapted to the respective internal resistance conditions.
• the internal resistance of the sensor element can be measured directly.
• the internal resistance over the temperature of the sensor element based on the operating parameters of the internal combustion engine is calculated or taken from a map.
• the exhaust-gas temperature and / or the exhaust-gas ratio and / or the exhaust-gas mass flow are determined, and from these conclusions are drawn about the temperature and thus the internal resistance of the sensor element.
• a threshold for the resistance value for example, a resistance value between 500 and 3500 ⁇ , in particular 1, 5 k ⁇ can be selected.
• Gas components in the exhaust gas of internal combustion engines is characterized in that the printed electrolyte layer consists of scandium-stabilized zirconium oxide.
• a printed electrolyte can be produced substantially thinner compared to an electrolyte produced by means of a green phosphor, which considerably reduces the internal resistance.
• scandium-stabilized zirconium oxide instead of yttrium-stabilized zirconium oxide, especially in the low-temperature range, achieves a lower internal resistance value for the same layer thickness.
• Such a sensor element can be used particularly preferably for carrying out the method according to the invention.
• the sensor element is advantageously operated via a voltage divider which has variable divider resistors. As a result, a pump voltage can be switched on in a technically simple manner and thus the sensor element can be operated with a pumped reference.
• Such a lambda probe can also with a very small
• Pumping current can be operated, which leads to the lowest possible voltage distortion and still ensures a CSD and shunt resistance.
• the pump currents are advantageously in the range between 0 .mu.A and 10 .mu.A, preferably between 2 .mu.A and 5 .mu.A.
• Fig. 1 shows a sensor element according to the invention schematically in section;
• Fig. 2 shows a circuit arrangement for operating a sensor element.
• Embodiments of the invention 1 shows schematically a sensor element which is formed by an electrolyte 100 made of scandium-stabilized zirconium oxide, which can be applied to a carrier 105, for example by screen printing.
• the electrolyte has a thickness of about 500 ⁇ m.
• the printing technique for producing the electrolyte in the region 101 under the outer electrode 110 is used to obtain a small layer thickness of scandium-stabilized zirconia, thereby minimizing the internal resistance due to the ion incorporation reaction.
• the lambda probe has a reference electrode 1 10 exposed to the exhaust gas (not shown), which is connected to a control unit SG via an electrical line 1 1 1 shown only schematically in FIG. 1 and a reference electrode 120 arranged in a reference gas volume 130, which likewise is connected via a line 140 to the control unit SG.
• the electrode surface of the electrode 1 10 exposed to the exhaust gas is chosen to be as large as possible, ideally selected to be maximum, taking into account the structural conditions.
• the reference electrode 120 is positioned as close as possible to the outer surface of the probe exposed to the exhaust gas in order to couple the electrolyte arranged therebetween as well as possible to the hot exhaust gas.
• the probe can be operated with a pump current that is chosen to be as small as possible in order to cause a small voltage delay and still ensure the CSD and shunt capability.
• the pump currents are in the range between 0 ⁇ A and 10 ⁇ A, in particular and preferably in the range between 2 ⁇ A and 5 ⁇ A.
• An outlet 132 of the pumping gas is dimensioned small in order to prevent a penetration of grease gas to the reference electrode 120 as possible. However, it must be chosen so large that a pressure equalization with the environment is guaranteed. In this case, porous layers with high flow resistance must be avoided. To prefer is an open channel with correspondingly small
• the reference channel can be realized by a simple printing layer with a sacrificial layer of thickness 20 to 30 microns and a channel width between 0.5 and 1 mm (not shown). In principle, it is also possible to use a not quite tight printed electrode lead as a reference channel (not shown). In addition, it can be provided with a porous
• Pressure layer 133 in the input region of the reference channel a further Eindrin- gene of fat gas components in the reference gas channel 130 to suppress and simultaneously adjust the flow resistance and thus the pressure build-up in the reference range.
• FIG. 2 schematically shows a voltage divider consisting of the resistors Ri and R 2 which, via a series resistor Rv, is a probe voltage
• the voltage U 0 is divided by the voltage divider, wherein a divider voltage UT via the series resistor Rv as the probe voltage Us applied to the probe, which is shown in Fig. 2 schematically by an internal resistance Ri and a voltage source in the form of Nernstschreib UN.
• a lambda probe i. a lambda probe
• hybrid model the operation of the probe with air reference or with a pumped reference, depending on the temperature-related internal resistance of the probe.
• the probe In the area of high internal resistance and low temperatures, the probe is conventionally operated with air reference. If the resistance falls below a specifiable threshold value, which, as mentioned above, can be 1 or 1.5 k ⁇ , then the temperature has risen far enough, a pump voltage is switched on.
• the internal resistance can be measured directly or be determined by a resistance model, in which case the exhaust gas temperature, the exhaust gas mass flow and other operating variables of the internal combustion engine can be used as input variables. These variables can be carried out, for example, by means of other sensors or based on the knowledge of a characteristic field stored in the control unit SG with respect to speed and load.
• the above-described hybrid model can be used without compensation of the control point by switching a pump voltage from 500 ° C of the sensor element temperature. If the internal resistance of the sensor element is further reduced on the sensor element by further measures, the temperature range in which largely distortion-free pumping is possible is correspondingly increased.
• the method described above can be implemented, for example, as a computer program in the control unit of the internal combustion engine and run there.
• the program code can be stored on a machine-readable carrier which the control unit SG can read.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Biochemistry (AREA)
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• General Physics & Mathematics (AREA)
• General Health & Medical Sciences (AREA)
• Combustion & Propulsion (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Measuring Oxygen Concentration In Cells (AREA)
• Combined Controls Of Internal Combustion Engines (AREA)

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• 2009
  • 2009-03-25 DE DE200910001843 patent/DE102009001843A1/de not_active Withdrawn
• 2010
  • 2010-02-19 RU RU2011142615/28A patent/RU2011142615A/ru unknown
  • 2010-02-19 EP EP10707488A patent/EP2411796A1/de not_active Withdrawn
  • 2010-02-19 CN CN2010800133592A patent/CN102362176A/zh active Pending
  • 2010-02-19 WO PCT/EP2010/052143 patent/WO2010108735A1/de active Application Filing

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