Classifications

• • 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
  • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
  • F02D41/1454—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an oxygen content or concentration or the air-fuel ratio
  • F02D41/1456—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an oxygen content or concentration or the air-fuel ratio with sensor output signal being linear or quasi-linear with the concentration of oxygen
• • 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
  • G01N27/4072—Cells and probes with solid electrolytes for investigating or analysing gases using sensor elements of laminated structure characterized by the diffusion barrier
• • 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

Definitions

• the invention relates to a gas sensor according to the preamble of claim 1.
• Oxygen sensor gas sensors in the form of lambda probes are used in large numbers in exhaust systems of internal combustion engines in motor vehicles in order to be able to provide signals for the engine control via the exhaust gas composition. In this way, the engine can be operated so that the exhaust gases have an optimum composition for the aftertreatment with today in the exhaust system usually present catalysts.
• Fig. 1 a known from the prior art gas sensor is shown.
• the sensor element 100 has a gas inlet hole 115 through which exhaust gas flows and passes through a diffusion barrier 120 into a measuring space 130.
• an inner pumping electrode 140 is arranged in the measuring space.
• An outer pumping electrode 150 is exposed on the outside of the solid electrolyte 110 and under a porous protective layer 155 to the exhaust gas of an internal combustion engine (not shown).
• a pumping voltage U pUm p is applied, so that a pumping current l pUm p flows.
• a heater 160 embedded in an insulating layer 162 is further arranged. By this heater 160, the sensor element on heats a temperature that allows optimal operation of the sensor element 100.
• This planar broadband lambda probe according to the limiting current principle is subjected to a fixed pumping voltage U pUm p.
• U pUm p With a lean exhaust gas, ie with an excess of exhaust gas, the fixed pumping voltage generates a positive pumping current I pUm p, which is clearly related to the oxygen content of the exhaust gas.
• a positive pumping current also occurs due to the decomposition of the water contained in the exhaust gas.
• the applied pumping voltage Up to p is well below the decomposition voltage of the water, but since hydrogen exists in the exhaust gas, the water decomposition is energetically possible, because at the outer pumping electrode 150, water is generated from the reaction of the hydrogen with the oxygen ions.
• the pumping current l pUm p is therefore limited by the hydrogen content in the case of rich exhaust gas. Since this pumping current Ipu m p in the rich exhaust gas has the same direction as the pumping current I pUm p with lean exhaust gas, it is no longer possible to deduce the exhaust gas composition from the pumping current I pum p.
• Object of the present invention is to develop a generic gas sensor such that both in the presence of a lean exhaust gas and in the presence of a rich exhaust gas can be clearly concluded on the exhaust gas composition.
• the basic idea of the invention is to enable a defined gas diffusion towards the outer exhaust gas electrode by arranging the outer pumping electrode in its own measuring volume and providing a second diffusion barrier with a diffusion coefficient which differs from that of the first diffusion barrier, thus unambiguously defining the pumping current depending on the exhaust gas composition and thus in turn Ström to close the exhaust gas composition.
• the electronic circuit that generates the pumping voltage and the pumping current must be designed so that a reversal of the pumping voltage is possible. By reversing the polarity of the pump voltage, the diffusion direction of the oxygen or of the hydrogen in the exhaust gas can be reversed, from which conclusions about the exhaust gas composition are possible in the manner described in more detail below.
• a particularly advantageous embodiment provides an electronic circuit in which a rectangular alternating pumping voltage is generated.
• the electronic circuit Preferably, the electronic circuit generates a rectangular alternating pumping voltage, preferably in the frequency range between 2 and 500 Hz, in particular between 20 and 50 Hz.
• a rectangular polarity reversal of the pumping voltage a corresponding inversion of the pumping direction, which provides qualitative information, whether fat or lean gas is present .
• the amount of current in one of the two pumping directions allows a quantitative concentration determination.
• the diffusion coefficient of the second diffusion barrier differs from that of the first diffusion barrier.
• An embodiment provides that the diffusion coefficient of the second diffusion barrier is smaller than the diffusion coefficient of the first diffusion barrier. In this case, a smaller current is produced with a lean exhaust gas than with a richer exhaust gas. The current is in a sense proportional to whether there is a lean or rich exhaust.
• the second diffusion barrier can be made more open-pored than the first diffusion barrier.
• Another embodiment provides that the second diffusion barrier in the flow direction of the exhaust gas has a shorter length than the first diffusion barrier.
• Fig. 2 shows an embodiment of a gas sensor according to the invention
• Fig. 3 shows another embodiment of a gas sensor according to the invention.
• a gas sensor known from the prior art has a sensor element 100, which is formed by a solid electrolyte 110.
• a measuring chamber 130 is formed, in which an inner pumping electrode 140 is arranged.
• the exhaust gas of an internal combustion engine flows through a gas inlet hole 115 via a diffusion barrier 120 in the measuring volume 130.
• an outer pumping electrode 150 is arranged, which is covered by an open-pored protective layer 155.
• a constant pumping voltage U pUm p is generated between the outer pumping electrode 150 and the inner pumping electrode 140 arranged in the measuring volume 130.
• the invention provides that the outer pumping electrode 150 is arranged in a further own measuring volume 230 into which exhaust gas flows through the gas inlet hole 115 via a second diffusion barrier 220.
• the second diffusion barrier 220 has a different diffusion coefficient than the first diffusion barrier 120. It is, for example, thinner and more open-pored than the first diffusion barrier 120.
• the idea of this arrangement is the following.
• the current l pUm p is limited by the diffusion of oxygen to the inner pumping electrode 140 (cathode).
• the pumping current I pUm p is limited by the diffusion of the hydrogen to the outer pumping electrode 150 (anode).
• the pumping current l pUm p becomes larger, since now the hydrogen diffusion limitation passes from the outer pumping electrode 150 (anode) to the inner pumping electrode 140 (cathode), which is easier to reach for inflowing gas.
• a higher H 2 concentration is available at the electrode at which the rate-determining reaction step, namely the H 2 oxidation to H 2 O takes place, than before the polarity reversal and as a result the current increases.
• the electronic circuit 190 performs such a current comparison in the case of a rectangular, high-frequency reversal of the polarity of the pump current U pUm inversion of the pumping direction. By this comparison, qualitative information can be obtained as to whether fat or lean gas is present. Due to the magnitude of the current I pUm p in one of the two pumping directions, a quantitative concentration determination can be made.
• This inversion pulse then provides information as to whether one is in the rich or lean load of the characteristic until the next zero crossing of the current.
• the inner pumping electrode 140 ie the cathode
• the potential of the anode ie the outer pumping electrode 150
• U pUm p the amount of the pumping voltage U pUm p.
• the frequency at which the pumping direction is reversed must be higher than the heater timing in order to avoid interference.
• the advantage of this embodiment is that a connecting cable is eliminated.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
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• Engineering & Computer Science (AREA)
• Biochemistry (AREA)
• Immunology (AREA)
• Physics & Mathematics (AREA)
• Analytical Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Electrochemistry (AREA)
• Pathology (AREA)
• Molecular Biology (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Measuring Oxygen Concentration In Cells (AREA)

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• 2005
  • 2005-11-14 DE DE200510054144 patent/DE102005054144A1/de not_active Withdrawn
• 2006
  • 2006-10-16 WO PCT/EP2006/067432 patent/WO2007054421A1/de active Application Filing
  • 2006-10-16 EP EP06807290A patent/EP1952136A1/de not_active Withdrawn
  • 2006-10-16 US US12/093,681 patent/US8828205B2/en not_active Expired - Fee Related
  • 2006-10-16 JP JP2008539383A patent/JP4709905B2/ja not_active Expired - Fee Related

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