CA1088626A - Resistance-type ceramic sensor element and sensor for combustion gas sensing device - Google Patents
Resistance-type ceramic sensor element and sensor for combustion gas sensing deviceInfo
- Publication number
- CA1088626A CA1088626A CA300,135A CA300135A CA1088626A CA 1088626 A CA1088626 A CA 1088626A CA 300135 A CA300135 A CA 300135A CA 1088626 A CA1088626 A CA 1088626A
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- CA
- Canada
- Prior art keywords
- sensor
- oxygen
- combustion gas
- type
- sensor element
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- 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
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
Abstract
Abstract A resistance-type sensor for sensing the partial pressure of oxygen in a combustion gas mixture, and a method of its manufacture, which has a sensing element of a resistance ceramic material, such as titanium dioxide, the surface of the element for exposure to the combustion gases having thereon a nonconductive layer of a catalyst, which catalyst has a higher catalytic activity than the material of the sensor element for oxidation of carbon monoxide and hydrocarbons in the combustion gas to provide for lower temperature activation of the sensor than normally is achieved. The sensor comprises a sensor element of resistive-type ceramic material, having a noncon-ductive layer of catalyst thereon, supported by a ceramic insulator with conductive leads leading from the sensor to terminals for recording resistance changes, a ceramic housing about the ceramic insulator and a metallic housing containing the ceramic housing for placement of the sensor in a conduit for combustion gases to measure the oxygen partial pressure within such gases.
Description
-\ 1088~Z6 This invention relates to resistance-type oxygen sensors. Gas sensors are used in internal combustion exhaust systems for determining and controlling the air/fuel ratio of the engine system.
Generally, such sensors are of two types, a solid electrolyte type, such as zirconium dioxide, where a solid electrolyte is used to generate a voltage and a resistance type, such as titanium dioxide, where a change in ohmic resistance is monitored.
Prior Art In zirconium dioxide type gas sensors, a solid electrolyte is used in which the sensor operates ; on the principle of an oxygen concentration cell with ionic conductivity effected through the solid electrolyte with conductors on both sides of the cell used to measure cell voltage which is related to the partial pressure of the oxygen and thus determine the oxygen content of exhaust gas as : :
compared to a reference gas, such as the atmosphere.
i 20 Various conductors have been proposed for use on .
both sides of the solid electrolyte, with platinum one of the preferred conductors. When platinum is used as a conductor on the exhaust gas side of a solid electrolyte, it has been found to exhibit catalytic activity to effect oxidation of carbon monoxide and residual hydrocarbons in the exhaust gas, as well as act as a conductor. Illustrative of such zirconium dioxide sensors and the use of platinum as a conductive means on the external surface of the sensor are the sensors described in the following U.S. Patents:
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' --U.S. Patent No. _ssue Date Patentee 3,645,875 February 29, 1972 Record et al.
3,978,006 August 31j 1976 Robert Bosch G.m.b.H.
3,99~,375 December 21, 1976 Rudd.
These sensors teach the need for a conductive coating or film of platinum on the external surface of the sensor and various means of forming such coatings and protecting the coatings from the harsh environment to which they are subjected so as to ensure the conductive nature of the coating. Without such conductivity, the sensor would be inoperative. The teachings of U.S. Patent No. 3,941,673, issued March 2, 1976 to Nissan Motor Co., also relate to zirconium type oxygen sensors where a conductive layer or second electrode is used with a noncatalytic material used for the electrode such as gold, silver or a platinum electrode containing a substance such as lead, sulfur, phosphorous, arsenic or their compounds which function as a catalyst poison. In such a system, the layer serves as a conductor only, without evidencing catalytic activity.
In titanium oxide type sensors the sensor , .
exhibits an electrical resistance which, at elevated temperatures, varies as a function of the partial pressure of oxygen in the exhaust. Such titanium dioxide sensors often use heating elements either integral with the sensor or associated therewith in order to heat the sensor to an operating temperature where the resistance can be readily monitored. -Generally, such titanium oxide type sensors must be heated to a temperature of about 400-450 C before . .
- mb/t~ - 2 -., ~
-`"` 10886216 they begin to function and, unless heating is provided, such as by a heating element, the sensor would not be operative in an exhaust gas system until the exhaust gases are at or above that elevated temperature to heat the sensor. Warm up time is then needed before readings can accurately be made of the composition of the exhaust gas. The titanium oxide type sensors are exemplified by the disclosures of the following U.S. Patents all issued to the Ford Motor Co.: U.S.
Patent No. 3,886,785, issued June 3, 1975, which teaches a sintered ceramic body of such material, U.S. Patent No. 3,868,846, issued March 4, 1975, which uses a sensor in connection with a heating element to heat the sensor to a most efficient operating tempe,rature of about 600 to 900 C, U.S. Patent No.
~; 3,936,794, issued February 3, 1976, which employs a -heater wire in association with the sensor in a probe , design, and U.S. Patent No. 3,933,028, issued January 20, 1976, which teaches a cobalt monoxide ceramic resistance material in connection with a Z heating coil to raise the temperature of the sensor to operating temperature.
As discussed in the article entitled "TiO2 as an Air-to-Fuel Ratio Sensor for Automobile Exhausts"
by T. Y. Tien, H. L. Stadler, E. F. Gibbons and P. J.
Zacmanidis, Ceramic Bulletin 54(3), p. 280 (1975) at page 281 thereof, the titanium dioxide, itself, when used in an oxygen sensor, acts as a catalyst to ; catalyze the reaction between carbon monoxide and oxygen at the solid-gas interface thereof. ~ith such -: catalysis effected by titanium dioxide, there is no need for platinum or other catalysis for such a purpose.
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We have found, however, that by applying a nonconductive catalyst layer, such as platinum, on the titanium dioxide sensor, the temperature range of operation of such a sensor is extended and that the sensor will begin operation at temperatures as low as 30QC, as compared with normal temperatures of 400-450 C for such sensors, and that the heating elements generally associated with such sensors can be eliminated.
Summary of the Invention The present invention provides a resistive-type oxygen sensing element and a sensor for determining the partial pressure of oxygen within a combustion gas mixture that is operative at temperatures below that normally required for resistive-type sensors and does not require a heating element as is normally found with such sensors, and a method of forming - such sensors.
In accordance with the invention there is provided a sensor element for use in an oxygen sensor of the resistive-type for measuring the partial pressure of oxygen gas in combustion gas mixture comprising a body of resistance-type ceramic sensor material having conductive leads therein, a surface ; of the body having thereon a nonconductive layer of a catalyst, the catalyst having a higher catalytic activity than the resistance-type ceramic sensor material for oxidation of carbon monoxide and hydro-carbons in a combustion gas.
The invention also relates to an improvement in a method for forming oxygen sensors of the mb/Jo . -resistive-type for sensing the partial pressure of oxygen gas in a combustion gas mixture wherein a sensor element is supported by a ceramic insulator and conductive leads provided from the sensor element to means for recording resistance changes in said sensor element upon contact of a combustion gas mixture with a surface of said element. The --invention comprises applying a nonconductive layer of a catalyst to the sensor element surface, the catalyst having a hlgher catalytic activity than the sensor element for oxidation of carbon monoxide and hydrocarbons in a combustion gas.
Brief Description of the Drawings - Figure 1 is a cross-sectional view of an oxygen sensor of the resistive-~ype of the present invention and Figure 2 is a graph illustrating the lower temperature activation of sensors of the present invention as compared with titanium dioxide sensor ~ 20 elements not having a catalyst layer thereon, both ; in the lean and rich air-to-fuel regions.
~; Detailed Description of the Preferred Embodiment Referring to the drawing, an oxygen sensor 1 of the resistive-type for sensing the partial pressure of oxygen in a combustion gas mixture is illustrated.
The sensor 1 comprises a resistance-type sensor element 3 which is preferably a titanium dioxide element . but which may also be composed of other resistive-... .
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type ceramic material, such as cobalt monoxide, which resistive-type ceramic materials are known in the art.
The sensor element 3 is supported by a ceramic insulator S which is formed of an insulating ceramic material, such as mullite, a spinel, or preferably alumina, A1203. The sensor element has on the surface 7 thereof, which is to be in contact with the combustion gas, a nonconductive catalytic layer 9. The catalytic layer is preferably platinum but may be of other catalytic ; 10 composition which is known to have a higher catalytic activity than the resistance type ceramic sensor material to effect oxidation of carbon monoxide and residual hydrocarbons in combustion gases, such as a palladium catalyst or the like.
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Conductive leads 11, such as thin platinum wires, are disposed in the sensor element 3 which pass through the ceramic insulator 5 and are conductively coupled to terminals 13 through a conductive seal 15, such as a ,, .
conductive glass seal, for example, the type of borosili-cate glass seal described in U. S. Patents 3,959,765, :. ~"~ -and~4,001,758, issued May 25, 1976 and January 4, 1977 to the Ford Motor Co., which is provided to seal the ceramic insulator 5 and the ceramic housing 17, which ceramic housing is of the same or similar insulative ceramic as the ceramic insulator 5. The ceramic housing has a center bore 27 and an enlarged bore 29 in which the ceramic insulator 5 is situated. Terminals 13 are then, as is conventional, electrically coupled to a resistance monitoring device (not shown) to record - 30 resistance changes in the sensor element 3 and thus monitor the partial pressure of oxygen in the combustion gas to which the surface 7 of the sensor element is exposed.
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1~8862G -To complete the sensor unit a metal housing 19 is provided to encase a portion of the ceramlc housing 17, with a hot press section 21 and a gasket seal 23 provided, which sealing means are known in the art for encasing such ceramic sections in metallic housings. A threaded portion 25 is pro-vided for securing the sensor into the wall of a combustion gas conduit, As illustrated in Figure 2, sensor elements composed - of titanium dioxide were compared with sensor elementsof the present invention wherein a titanium dioxide sensor has a non-conductive catalyst layer thereon. The sensor elements were composed of titanium dioxide, unlayered sensors designated as "L" and "R" and sensors with a nonconductive platinum catalyst ; layer thereon designated as "L-P" and "R-P." As illustrated, both in the lean range, i.e a combustion gas composition having a fuel lean value with respect to stoichiometry, and in the rich range, i.e. a combustion gas composition having a fuel rich value with respect to stoichiometry, the unlayered sensors "L" and "R" did not exhibit resistance readings until the tem-perature was in the range of about 400C. In the sensors of the present invention, however, as illustrated, resistance readings were exhibited at temperatures below 300C, indicating the effect of the catalytic layer upon the sensor activity.
In a method for forming a resistive-type oxygen sensor for sensing the partial pressure of oxygen in a combustion gas ., .
, ,' :
--~.
,', '~
' ' ' `- ^ 1088~26 mixture, a prefired ceramic insulator 5 containing platinum lead wires 11 is fabricated and the combination is refired into a ceramic housing 17 to form a ceramic subassembly.
The housing 17 is formed with a center bore 27 through which the ceramic insulator passes, with a portion there~f extending from the insulator, the bore having an enlarged section 29 for insertion of terminals as hereinafter described. When the ceramic subassembly has been refired, a conductive sealant such as a conductive glass seal 15 is provided and the sealant is heat softened while terminals 13 are pressed therein to provide a conductive coupling for the platinum wires 11 and terminals 13 as well as a seal between the ceramic insulator 5 and .
the ceramic housing 17. To the end of the ceramic insulator S there is then provided the sensing element 3.
~i~ ( The sensing element 3 of a resistive-type compound, . such as titanium dioxide, may be affixed to the ceramic insulator 5 such as by plasma or flame spraying or other deposition methods. Or, preformed resistive-type ceramic sensors can be used, such as those described in the . Ford Motor Co. U.S. Patents Nos. 3,932,246 and 3,893,230, i issued January 13, 1976 and July 8, 1975, respectively, wherein the platinum wires 11 would be sandwiched between titanium dioxide tapes and the sensor fired into a chip or wafer which would then be affixed to the ceramic .: insulator.
` The sensor element 3 has applied to the surface 7 .; .
thereof, which is the surface that is to be in contact with the combustion gas mixture, a nonconductive layer 9 of a catalyst mb/J~ - 8 -'"
.~
10886Z6 ::
which has a higher catalytic activity than the resistance-type ceramic sensor material to catalyze the oxidation of carbon monoxide and hydrocarbons in the combustion gas mixture. Such catalysts are well known, such as platinum or palladium, with platinum being preferred. The nonconductive catalyst layer can be applied to the sensor chip by various known methods for applying such catalysts, such as by vacuum deposition, by painting with a platinum paste, or by depositing a chloro-platinic acid solution on the sensor surface and heating the surface to affix the platinum catalyst thereto. Where a pre-formed chip or wafer of resistive-type ceramic material is used as a sensor element, the platinum catalyst may be applied prior to or after affixing of the chip to the ceramic insulator.
The ceramic subassembly, with the ~ensor affixed and the catalyst layer applied thereto, is then secured within a metal housing 19 by hot pressing section 21 and the unit sealed by placement of gaskets 23 therebetween. The completed unit is easily placed into a threaded orifice in a combustion gas conduit wall by use of threaded section 25, while the terminals 13 are easily electrically coupled to a monitoring device for determination of the oxygen content of combustion gases.
,~_ ~ .
Generally, such sensors are of two types, a solid electrolyte type, such as zirconium dioxide, where a solid electrolyte is used to generate a voltage and a resistance type, such as titanium dioxide, where a change in ohmic resistance is monitored.
Prior Art In zirconium dioxide type gas sensors, a solid electrolyte is used in which the sensor operates ; on the principle of an oxygen concentration cell with ionic conductivity effected through the solid electrolyte with conductors on both sides of the cell used to measure cell voltage which is related to the partial pressure of the oxygen and thus determine the oxygen content of exhaust gas as : :
compared to a reference gas, such as the atmosphere.
i 20 Various conductors have been proposed for use on .
both sides of the solid electrolyte, with platinum one of the preferred conductors. When platinum is used as a conductor on the exhaust gas side of a solid electrolyte, it has been found to exhibit catalytic activity to effect oxidation of carbon monoxide and residual hydrocarbons in the exhaust gas, as well as act as a conductor. Illustrative of such zirconium dioxide sensors and the use of platinum as a conductive means on the external surface of the sensor are the sensors described in the following U.S. Patents:
~- mb/~
' --U.S. Patent No. _ssue Date Patentee 3,645,875 February 29, 1972 Record et al.
3,978,006 August 31j 1976 Robert Bosch G.m.b.H.
3,99~,375 December 21, 1976 Rudd.
These sensors teach the need for a conductive coating or film of platinum on the external surface of the sensor and various means of forming such coatings and protecting the coatings from the harsh environment to which they are subjected so as to ensure the conductive nature of the coating. Without such conductivity, the sensor would be inoperative. The teachings of U.S. Patent No. 3,941,673, issued March 2, 1976 to Nissan Motor Co., also relate to zirconium type oxygen sensors where a conductive layer or second electrode is used with a noncatalytic material used for the electrode such as gold, silver or a platinum electrode containing a substance such as lead, sulfur, phosphorous, arsenic or their compounds which function as a catalyst poison. In such a system, the layer serves as a conductor only, without evidencing catalytic activity.
In titanium oxide type sensors the sensor , .
exhibits an electrical resistance which, at elevated temperatures, varies as a function of the partial pressure of oxygen in the exhaust. Such titanium dioxide sensors often use heating elements either integral with the sensor or associated therewith in order to heat the sensor to an operating temperature where the resistance can be readily monitored. -Generally, such titanium oxide type sensors must be heated to a temperature of about 400-450 C before . .
- mb/t~ - 2 -., ~
-`"` 10886216 they begin to function and, unless heating is provided, such as by a heating element, the sensor would not be operative in an exhaust gas system until the exhaust gases are at or above that elevated temperature to heat the sensor. Warm up time is then needed before readings can accurately be made of the composition of the exhaust gas. The titanium oxide type sensors are exemplified by the disclosures of the following U.S. Patents all issued to the Ford Motor Co.: U.S.
Patent No. 3,886,785, issued June 3, 1975, which teaches a sintered ceramic body of such material, U.S. Patent No. 3,868,846, issued March 4, 1975, which uses a sensor in connection with a heating element to heat the sensor to a most efficient operating tempe,rature of about 600 to 900 C, U.S. Patent No.
~; 3,936,794, issued February 3, 1976, which employs a -heater wire in association with the sensor in a probe , design, and U.S. Patent No. 3,933,028, issued January 20, 1976, which teaches a cobalt monoxide ceramic resistance material in connection with a Z heating coil to raise the temperature of the sensor to operating temperature.
As discussed in the article entitled "TiO2 as an Air-to-Fuel Ratio Sensor for Automobile Exhausts"
by T. Y. Tien, H. L. Stadler, E. F. Gibbons and P. J.
Zacmanidis, Ceramic Bulletin 54(3), p. 280 (1975) at page 281 thereof, the titanium dioxide, itself, when used in an oxygen sensor, acts as a catalyst to ; catalyze the reaction between carbon monoxide and oxygen at the solid-gas interface thereof. ~ith such -: catalysis effected by titanium dioxide, there is no need for platinum or other catalysis for such a purpose.
.
mbt~ ~ 3 ~
~ .
We have found, however, that by applying a nonconductive catalyst layer, such as platinum, on the titanium dioxide sensor, the temperature range of operation of such a sensor is extended and that the sensor will begin operation at temperatures as low as 30QC, as compared with normal temperatures of 400-450 C for such sensors, and that the heating elements generally associated with such sensors can be eliminated.
Summary of the Invention The present invention provides a resistive-type oxygen sensing element and a sensor for determining the partial pressure of oxygen within a combustion gas mixture that is operative at temperatures below that normally required for resistive-type sensors and does not require a heating element as is normally found with such sensors, and a method of forming - such sensors.
In accordance with the invention there is provided a sensor element for use in an oxygen sensor of the resistive-type for measuring the partial pressure of oxygen gas in combustion gas mixture comprising a body of resistance-type ceramic sensor material having conductive leads therein, a surface ; of the body having thereon a nonconductive layer of a catalyst, the catalyst having a higher catalytic activity than the resistance-type ceramic sensor material for oxidation of carbon monoxide and hydro-carbons in a combustion gas.
The invention also relates to an improvement in a method for forming oxygen sensors of the mb/Jo . -resistive-type for sensing the partial pressure of oxygen gas in a combustion gas mixture wherein a sensor element is supported by a ceramic insulator and conductive leads provided from the sensor element to means for recording resistance changes in said sensor element upon contact of a combustion gas mixture with a surface of said element. The --invention comprises applying a nonconductive layer of a catalyst to the sensor element surface, the catalyst having a hlgher catalytic activity than the sensor element for oxidation of carbon monoxide and hydrocarbons in a combustion gas.
Brief Description of the Drawings - Figure 1 is a cross-sectional view of an oxygen sensor of the resistive-~ype of the present invention and Figure 2 is a graph illustrating the lower temperature activation of sensors of the present invention as compared with titanium dioxide sensor ~ 20 elements not having a catalyst layer thereon, both ; in the lean and rich air-to-fuel regions.
~; Detailed Description of the Preferred Embodiment Referring to the drawing, an oxygen sensor 1 of the resistive-type for sensing the partial pressure of oxygen in a combustion gas mixture is illustrated.
The sensor 1 comprises a resistance-type sensor element 3 which is preferably a titanium dioxide element . but which may also be composed of other resistive-... .
.~. .
. . ~, ~, . . .
. :.
' mb/J~ 5 ;" ' :
\
type ceramic material, such as cobalt monoxide, which resistive-type ceramic materials are known in the art.
The sensor element 3 is supported by a ceramic insulator S which is formed of an insulating ceramic material, such as mullite, a spinel, or preferably alumina, A1203. The sensor element has on the surface 7 thereof, which is to be in contact with the combustion gas, a nonconductive catalytic layer 9. The catalytic layer is preferably platinum but may be of other catalytic ; 10 composition which is known to have a higher catalytic activity than the resistance type ceramic sensor material to effect oxidation of carbon monoxide and residual hydrocarbons in combustion gases, such as a palladium catalyst or the like.
. ~ .
Conductive leads 11, such as thin platinum wires, are disposed in the sensor element 3 which pass through the ceramic insulator 5 and are conductively coupled to terminals 13 through a conductive seal 15, such as a ,, .
conductive glass seal, for example, the type of borosili-cate glass seal described in U. S. Patents 3,959,765, :. ~"~ -and~4,001,758, issued May 25, 1976 and January 4, 1977 to the Ford Motor Co., which is provided to seal the ceramic insulator 5 and the ceramic housing 17, which ceramic housing is of the same or similar insulative ceramic as the ceramic insulator 5. The ceramic housing has a center bore 27 and an enlarged bore 29 in which the ceramic insulator 5 is situated. Terminals 13 are then, as is conventional, electrically coupled to a resistance monitoring device (not shown) to record - 30 resistance changes in the sensor element 3 and thus monitor the partial pressure of oxygen in the combustion gas to which the surface 7 of the sensor element is exposed.
., mb/~ - 6 -:. .
\
1~8862G -To complete the sensor unit a metal housing 19 is provided to encase a portion of the ceramlc housing 17, with a hot press section 21 and a gasket seal 23 provided, which sealing means are known in the art for encasing such ceramic sections in metallic housings. A threaded portion 25 is pro-vided for securing the sensor into the wall of a combustion gas conduit, As illustrated in Figure 2, sensor elements composed - of titanium dioxide were compared with sensor elementsof the present invention wherein a titanium dioxide sensor has a non-conductive catalyst layer thereon. The sensor elements were composed of titanium dioxide, unlayered sensors designated as "L" and "R" and sensors with a nonconductive platinum catalyst ; layer thereon designated as "L-P" and "R-P." As illustrated, both in the lean range, i.e a combustion gas composition having a fuel lean value with respect to stoichiometry, and in the rich range, i.e. a combustion gas composition having a fuel rich value with respect to stoichiometry, the unlayered sensors "L" and "R" did not exhibit resistance readings until the tem-perature was in the range of about 400C. In the sensors of the present invention, however, as illustrated, resistance readings were exhibited at temperatures below 300C, indicating the effect of the catalytic layer upon the sensor activity.
In a method for forming a resistive-type oxygen sensor for sensing the partial pressure of oxygen in a combustion gas ., .
, ,' :
--~.
,', '~
' ' ' `- ^ 1088~26 mixture, a prefired ceramic insulator 5 containing platinum lead wires 11 is fabricated and the combination is refired into a ceramic housing 17 to form a ceramic subassembly.
The housing 17 is formed with a center bore 27 through which the ceramic insulator passes, with a portion there~f extending from the insulator, the bore having an enlarged section 29 for insertion of terminals as hereinafter described. When the ceramic subassembly has been refired, a conductive sealant such as a conductive glass seal 15 is provided and the sealant is heat softened while terminals 13 are pressed therein to provide a conductive coupling for the platinum wires 11 and terminals 13 as well as a seal between the ceramic insulator 5 and .
the ceramic housing 17. To the end of the ceramic insulator S there is then provided the sensing element 3.
~i~ ( The sensing element 3 of a resistive-type compound, . such as titanium dioxide, may be affixed to the ceramic insulator 5 such as by plasma or flame spraying or other deposition methods. Or, preformed resistive-type ceramic sensors can be used, such as those described in the . Ford Motor Co. U.S. Patents Nos. 3,932,246 and 3,893,230, i issued January 13, 1976 and July 8, 1975, respectively, wherein the platinum wires 11 would be sandwiched between titanium dioxide tapes and the sensor fired into a chip or wafer which would then be affixed to the ceramic .: insulator.
` The sensor element 3 has applied to the surface 7 .; .
thereof, which is the surface that is to be in contact with the combustion gas mixture, a nonconductive layer 9 of a catalyst mb/J~ - 8 -'"
.~
10886Z6 ::
which has a higher catalytic activity than the resistance-type ceramic sensor material to catalyze the oxidation of carbon monoxide and hydrocarbons in the combustion gas mixture. Such catalysts are well known, such as platinum or palladium, with platinum being preferred. The nonconductive catalyst layer can be applied to the sensor chip by various known methods for applying such catalysts, such as by vacuum deposition, by painting with a platinum paste, or by depositing a chloro-platinic acid solution on the sensor surface and heating the surface to affix the platinum catalyst thereto. Where a pre-formed chip or wafer of resistive-type ceramic material is used as a sensor element, the platinum catalyst may be applied prior to or after affixing of the chip to the ceramic insulator.
The ceramic subassembly, with the ~ensor affixed and the catalyst layer applied thereto, is then secured within a metal housing 19 by hot pressing section 21 and the unit sealed by placement of gaskets 23 therebetween. The completed unit is easily placed into a threaded orifice in a combustion gas conduit wall by use of threaded section 25, while the terminals 13 are easily electrically coupled to a monitoring device for determination of the oxygen content of combustion gases.
,~_ ~ .
Claims (14)
1. In an oxygen sensor of the resistive-type for sensing the partial pressure of oxygen gas in a combustion gas mixture, wherein a sensor element of resistive-type ceramic sensor material is supported by a ceramic insulator with conductive leads provided from the sensor element to means for recording resistance changes in said sensor element upon contact of a combustion gas mixture with a surface of said element, the improvement comprising a nonconductive catalyst layer on said surface of the sensor element, said catalyst having a higher catalytic activity than the sensor element for oxidation of carbon monoxide and hydrocarbons in a combustion gas.
2. In an oxygen sensor of the resistive-type for sensing the partial pressure of oxygen gas in a combustion gas mixture as defined in claim 1, the improvement wherein said nonconductive catalyst layer is platinum.
3. In an oxygen sensor of the resistive-type for sensing the partial pressure of oxygen gas in a combustion gas mixture as defined in claim 1, the improvement wherein said sensor element comprises titanium dioxide.
4. In an oxygen sensor of the resistive-type for sensing the partial pressure of oxygen gas in a combustion gas mixture as defined in claim 1, the improvement wherein said sensor element comprises cobalt monoxide.
5. In an oxygen sensor of the resistive-type for sensing the partial pressure of oxygen gas in a combustion gas mixture as defined in claim 1, the improvement wherein a por-tion of the ceramic insulator is positioned within a ceramic housing, with terminals situated within the housing and conductively coupled with said conductive leads.
6. In an oxygen sensor of the resistive-type for sensing the partial pressure of oxygen gas in a combustion gas mixture as defined in claim 5, the improvement comprising a conductive glass seal conductively coupling said terminals and conductive leads.
7. In a method for forming an oxygen sensor of the resistive-type for sensing the partial pressure of oxygen gas in a combustion gas mixture wherein a sensor element is sup-ported by a ceramic insulator and conductive leads provided from the sensor element to means for recording resistance changes in said sensor element upon contact of a combustion gas mixture with a surface of said element, the improvement comprising applying a nonconductive layer of a catalyst to said sensor element surface, said catalyst having a higher catalytic activity than the sensor element for oxidation of carbon monoxide and hydrocarbons in a combustion gas.
8. In a method for forming an oxygen sensor of the resistive-type for sensing the partial pressure of oxygen gas in a combustion gas mixture as defined in claim 7, the improve-ment comprising applying said nonconductive layer of catalyst to said sensor element after said element is affixed to the ceramic insulator.
9. In a method for forming an oxygen sensor of the resistive-type for sensing the partial pressure of oxygen gas in a combustion gas mixture as defined in claim 7, the improve-ment comprising applying said nonconductive layer of catalyst to said sensor element prior to affixing the sensor element to the ceramic insulator.
10. In a method for forming an oxygen sensor of the resistive-type for sensing the partial pressure of oxygen gas in a combustion gas mixture as defined in claim 7, the improve-ment comprising positioning the ceramic insulator within a ceramic housing having an enlarged bore, with conductive leads extending from one end of said insulator to the enlarged bore, applying a sensor element to said one end of the ceramic insulator, firing the same to form a ceramic subassembly, and applying the nonconductive catalyst layer to the sensor element supported by the ceramic subassembly.
11. In a method for forming an oxygen sensor of the resistive-type for sensing the partial pressure of oxygen gas in a combustion gas mixture as defined in claim 10, the improve-ment comprising inserting terminals into said enlarged bore and conductively coupling said conductive leads and said terminals by means of a conductive glass seal.
12. A sensor element for use in an oxygen sensor of the resistive-type for measuring the partial pressure of oxygen gas in a combustion gas mixture comprising a body of resistance-type ceramic sensor material having conductive leads therein, a surface of said body having thereon a nonconductive layer of a catalyst, said catalyst having a higher catalytic activity than the resistance-type ceramic sensor material for oxidation of carbon monoxide and hydrocarbons in a combustion gas.
13. A sensor element for use in an oxygen sensor of the resistive-type for measuring the partial pressure of oxygen gas in a combustion gas mixture as defined in claim 12 wherein said resistance-type ceramic sensor material is titanium dioxide.
14. A sensor element for use in an oxygen sensor of the resistive-type for measuring the partial pressure of oxygen gas in a combustion gas mixture as defined in claim 13 wherein said catalyst is platinum.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US83203777A | 1977-09-12 | 1977-09-12 | |
| US832,037 | 1977-09-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1088626A true CA1088626A (en) | 1980-10-28 |
Family
ID=25260497
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA300,135A Expired CA1088626A (en) | 1977-09-12 | 1978-03-31 | Resistance-type ceramic sensor element and sensor for combustion gas sensing device |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5451597A (en) |
| AU (1) | AU3833578A (en) |
| CA (1) | CA1088626A (en) |
| DE (1) | DE2833993A1 (en) |
| FR (1) | FR2402869A1 (en) |
| GB (1) | GB2004068A (en) |
| IT (1) | IT1099041B (en) |
| SE (1) | SE7809439L (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2142147A (en) * | 1983-06-24 | 1985-01-09 | Standard Telephones Cables Ltd | Gas sensor |
| DE4022546A1 (en) * | 1990-07-16 | 1992-01-23 | Emitec Emissionstechnologie | Sensor device for monitoring vehicle exhaust systems - uses two temp.-sensors, one of which is coated with catalyst to promote oxidn. of hydrocarbon(s) and carbon mon:oxide |
| DE4243732A1 (en) * | 1992-12-23 | 1994-06-30 | Bosch Gmbh Robert | Sensor arrangement for determining gas components and / or gas concentrations of gas mixtures |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4066413A (en) * | 1975-03-03 | 1978-01-03 | Nippon Soken, Inc. | Gas component detection apparatus |
| JPS5276991A (en) * | 1975-12-23 | 1977-06-28 | Nippon Soken | Detector for gas composition |
| US4012709A (en) * | 1976-01-12 | 1977-03-15 | Ford Motor Company | Cobalt-magnesium monoxide alloy ceramic partial pressure of oxygen sensor |
-
1978
- 1978-03-31 CA CA300,135A patent/CA1088626A/en not_active Expired
- 1978-07-12 FR FR7820815A patent/FR2402869A1/en not_active Withdrawn
- 1978-07-20 GB GB7830457A patent/GB2004068A/en not_active Withdrawn
- 1978-07-25 AU AU38335/78A patent/AU3833578A/en active Pending
- 1978-08-03 DE DE19782833993 patent/DE2833993A1/en not_active Withdrawn
- 1978-09-06 JP JP10870278A patent/JPS5451597A/en active Pending
- 1978-09-07 SE SE7809439A patent/SE7809439L/en unknown
- 1978-09-11 IT IT27505/78A patent/IT1099041B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5451597A (en) | 1979-04-23 |
| SE7809439L (en) | 1979-03-13 |
| GB2004068A (en) | 1979-03-21 |
| AU3833578A (en) | 1980-01-31 |
| IT1099041B (en) | 1985-09-18 |
| IT7827505A0 (en) | 1978-09-11 |
| DE2833993A1 (en) | 1979-03-22 |
| FR2402869A1 (en) | 1979-04-06 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |