EP0257842A2
Expired / Lapsed
EP
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Electrochemical NOx sensor
Assignee: NGK Insulators Ltd
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Filing: 1987-08-03
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Granted: —
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Expires: 2007-08-03
Abstract
Abstract An NOx sensor for determining the concentraiton of NOx in a measurement gas avoids inconsistency caused by varying oxygen partial pressure. The sensor has first and second electrochemical detecting elements each of which includes an oxygen pumping cell and an oxygen sensing cell. Each of the pumping and sensing cells of the first and second detecting elements consists of a solid electrolyte (l2) and a pair of electrodes (20,22;24,26;30,32;34,36). At least one (32) of the electrodes of the oxygen pumping and sensing cells of the second detecting element which are exposed to the introduced measurement gas, is a catalytic electrode which is provided with a catalyst for reducing the nitrogen oxides contained in the measurement gas. The second detecting element detects an oxygen partial pressure of the measurement gas while the nitrogen oxides are reduced by the catalyst of the catalytic electrode. The NOx concentration is determined, based on a difference between two outputs of the first and second detecting elements which represent the oxygen partial pressures of respective portions of the measurement gas detected by the first and second detecting elements.
Inventors
- 👤 Makoto Noda
- 👤 Nobuhide Kato
- 👤 Hiroshi Kurachi
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-03 08:34
CPC Classifications
G; G01; G01N; G01N27/00; G01N27/26; G01N27/403; G01N27/406; G01N27/407; G01N27/4073; G01N27/4074; G01N27/4071; G01N27/4072
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
445 words
An NOx sensor for determining the concentration of nitrogen oxides contained in a measurement gas in an external measurement-gas space, comprising: a first electrochemical oxygen partial pressure detecting element including (a) a first electrochemical oxygen pumping cell having an oxygen-ion conductive solid electrolyte body, and a pair of electrodes, (b) a first electrochemical oxygen sensing cell having an oxygen-ion conductive solid electrolyte body, and a pair of electrodes, (c) first diffusion-resistance means for introducing said measurement gas from said external measurement-gas space, with a first predetermined diffusion resistance, so that one of said pair of electrodes of said first oxygen pumping cell, and one of said pair of electrodes of said first oxygen sensing cell, are exposed to the introduced measurement gas, and (d) first reference-gas inlet means for exposing the other of said pair of electrodes of said first oxygen sensing cell to a reference gas; a second electrochemical oxygen partial pressure detecting element including (i) a second electrochemical oxygen pumping cell having an oxygen-ion conductive solid electrolyte body, and a pair of electrodes, (ii) a second electrochemical oxygen sensing cell having an oxygen-ion conductive solid electrolyte body, and a pair of electrodes, (iii) second diffusion-resistance means for introducing said measurement gas from said external measurement-gas space, with a second predetermined diffusion resistance substantially equal to said first predetermined diffusion resistance, so that one of said pair of electrodes of said second oxygen pumping cell, and one of said pair of electrodes of said second oxygen sensing cell, are exposed to the introduced measurement gas, and (iv) second reference-gas inlet means for exposing the other of said pair of electrodes of said second oxygen sensing cell to a reference atmosphere substantially the same as said reference gas; at least one catalytic electrode which consists of at least one of said one electrode of said second oxygen pumping cell and said one electrode of said second oxygen sensing cell, which are exposed to a portion of the measurement gas introduced through said second diffusion-resistance means, said at least one catalytic electrode being provided with a catalyst for reducing nitrogen oxides contained in the introduced measurement gas, so that said second electrochemical oxygen partial pressure detecting element detects an oxyen partial pressure of the portion of the measurement gas introduced through said second diffusion-resistance means, while said nitrogen oxides are reduced by said catalyst; and means for determining the concentration of said nitrogen oxides based on a difference between two outputs of said first and second electrochemical oxygen partial pressure detecting elements, said two outputs representing the oxygen partial pressures of the respective portions of the measurement gas introduced through said first and second diffusion-resistance means.
Claim 2
Dependent Claim
445 words
An NOx sensor for determining the concentration of nitrogen oxides contained in a measurement gas in an external measurement-gas space, comprising: a first electrochemical oxygen partial pressure detecting element including (a) a first electrochemical oxygen pumping cell having an oxygen-ion conductive solid electrolyte body, and a pair of electrodes, (b) a first electrochemical oxygen sensing cell having an oxygen-ion conductive solid electrolyte body, and a pair of electrodes, (c) first diffusion-resistance means for introducing said measurement gas from said external measurement-gas space, with a first predetermined diffusion resistance, so that one of said pair of electrodes of said first oxygen pumping cell, and one of said pair of electrodes of said first oxygen sensing cell, are exposed to the introduced measurement gas, and (d) first reference-gas inlet means for exposing the other of said pair of electrodes of said first oxygen sensing cell to a reference gas; a second electrochemical oxygen partial pressure detecting element including (i) a second electrochemical oxygen pumping cell having an oxygen-ion conductive solid electrolyte body, and a pair of electrodes, (ii) a second electrochemical oxygen sensing cell having an oxygen-ion conductive solid electrolyte body, and a pair of electrodes, (iii) second diffusion-resistance means for introducing said measurement gas from said external measurement-gas space, with a second predetermined diffusion resistance substantially equal to said first predetermined diffusion resistance, so that one of said pair of electrodes of said second oxygen pumping cell, and one of said pair of electrodes of said second oxygen sensing cell, are exposed to the introduced measurement gas, and (iv) second reference-gas inlet means for exposing the other of said pair of electrodes of said second oxygen sensing cell to a reference atmosphere substantially the same as said reference gas; at least one catalytic electrode which consists of at least one of said one electrode of said second oxygen pumping cell and said one electrode of said second oxygen sensing cell, which are exposed to a portion of the measurement gas introduced through said second diffusion-resistance means, said at least one catalytic electrode being provided with a catalyst for reducing nitrogen oxides contained in the introduced measurement gas, so that said second electrochemical oxygen partial pressure detecting element detects an oxyen partial pressure of the portion of the measurement gas introduced through said second diffusion-resistance means, while said nitrogen oxides are reduced by said catalyst; and means for determining the concentration of said nitrogen oxides based on a difference between two outputs of said first and second electrochemical oxygen partial pressure detecting elements, said two outputs representing the oxygen partial pressures of the respective portions of the measurement gas introduced through said first and second diffusion-resistance means.
Claim 3
Dependent Claim
33 words
An NOx sensor according to claim l, wherein said catalyst consists of at least one material selected from the group consisting of rhodium, cobalt oxide, nickel oxide, palladium, cerium oxide and lanthanum oxide.
Claim 4
Dependent Claim
35 words
An NOx sensor according to claim l or claim 2, wherein said catalyst is applied to said at least one catalytic electrode such that said at least one catalytic electrode is impregnated with said catalyst.
Claim 5
Dependent Claim
38 words
An NOx sensor according to claim l or claim 2, wherein said catalyst is applied to said at least one catalytic electrode such that said at least one catalytic electrode is coated with a layer of said catalyst.
Claim 6
Dependent Claim
47 words
An NOx sensor according to claim l or claim 2, wherein said catalyst is applied to said at least one catalytic electrode such that said at least one catalytic electrode is coated with a ceramic overcoat, and a layer of said catalyst formed on said ceramic overcoat.
Claim 7
Dependent Claim
41 words
An NOx sensor according to claim l or claim 2 wherein said catalyst is applied to said at least one catalytic electrode such that said least one catalytic electrode is coated with a ceramic overcoat which is impregnated with said catalyst.
Claim 8
Dependent Claim
30 words
An NOx sensor according to any one of claims l to 6, wherein said first and second electrochemical oxygen partial pressure detecting elements consist of an integrally formed one-piece structure.
Claim 9
Dependent Claim
26 words
An NOx sensor according to claim 7, wherein said first and second diffusion-resistance means are defined by an integral portion of said integrally formed one-piece structure.
Claim 10
Dependent Claim
27 words
An NOx sensor according to claim 7, wherein said first and second reference-gas inlet means are defined by an integral portion of said integrally formed one-piece structure.
Claim 11
Dependent Claim
46 words
l0. An NOx sensor according to any one of claims 7 to 9, wherein at least one of said pair of electrodes of said first oxygen pumping cell is commonly used as at least one of said pair of electrodes of said first oxygen sensing cell.
Claim 12
Dependent Claim
45 words
An NOx sensor according to any one of claims 7 to l0, wherein at least one of said pair of electrodes of said second oxygen pumping cell is commonly used as at least one of said pair of electrodes of said second oxygen sensing cell.
Claim 13
Dependent Claim
40 words
An NOx sensor according to any one of claims l to ll, further comprising integrally formed heating means for heating said first and second oxygen pumping and sensing cells of said first and second electrochemical oxygen partial pressure detecting elements.
References Cited (Backward Citations)
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