CA1072633A - Oxygen sensor - Google Patents
Oxygen sensorInfo
- Publication number
- CA1072633A CA1072633A CA264,894A CA264894A CA1072633A CA 1072633 A CA1072633 A CA 1072633A CA 264894 A CA264894 A CA 264894A CA 1072633 A CA1072633 A CA 1072633A
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- Canada
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- electrolyte
- oxygen sensor
- section
- elongated
- chamber
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- Measuring Oxygen Concentration In Cells (AREA)
Abstract
Abstract of the Disclosure An oxygen sensor comprises an electrolyte which is shaped into a conical tube having a closed end of small diameter and an open end of large diameter. The wall thickness of the electrolyte is gradually decreased toward the closed end from the open end and that of the closed end is 0.3 to 1.0 mm so as to provide a high sensitivity.
Description
~ 3 ~he present inven-tion relates in general to a sensor and more particularly to a measurlng cell for determining oxygen concentration in a gaS mixture flowing through a tube.
In connection with the problem of reducillg air pollu-tion resulting from the automobile internal combustion engine, it is well known that if the air to fuel ratio oE the intake charge to the engine is maintained at or near stoichiometric condition during most modes of operationr the exhaust gases will contain less harmful components, i.e. hydrocarbons (HC), carbon monoxide ~CO~ and nitrogen oxides (NOX). For controlling the air to fuel ratio of the intake char~e at the stoichiometric con-dition, a so-called closed loop system having an oxygen sensor placed in communication with the exhaust gases issued from the engine has been widely used. The oxygen sensor is constructed to generate an electrical signal responsive -to the oxygen content of the exhaust gases. The electrical signal in turn is received in a control means connected to the engine for regulating or varying the charactor~ of the intake air-~uel charge so as to maintain the charge at the stoichiometric condition.
Hitherto, stabilized zirconium oxide (ZrO2) has been widely employed as a main element of the oxygen sensor~ As is well known, the stabilized zirconium .
, :
~-
In connection with the problem of reducillg air pollu-tion resulting from the automobile internal combustion engine, it is well known that if the air to fuel ratio oE the intake charge to the engine is maintained at or near stoichiometric condition during most modes of operationr the exhaust gases will contain less harmful components, i.e. hydrocarbons (HC), carbon monoxide ~CO~ and nitrogen oxides (NOX). For controlling the air to fuel ratio of the intake char~e at the stoichiometric con-dition, a so-called closed loop system having an oxygen sensor placed in communication with the exhaust gases issued from the engine has been widely used. The oxygen sensor is constructed to generate an electrical signal responsive -to the oxygen content of the exhaust gases. The electrical signal in turn is received in a control means connected to the engine for regulating or varying the charactor~ of the intake air-~uel charge so as to maintain the charge at the stoichiometric condition.
Hitherto, stabilized zirconium oxide (ZrO2) has been widely employed as a main element of the oxygen sensor~ As is well known, the stabilized zirconium .
, :
~-
-2~
~ 33 oxide (ZrO2) exhibits conductivity by means of oxygen ions which transfer therethrough. In reality, if some gas mixture whose partial oxygen pressure or absolute oxygen pressure must be measured is present on one side S of a partition member made of the zirconium oxide, and simultaneously, a reference gas having a known partial oxygen pressure is present on the other side, a con-siderable voltage diference (E) is generated by the movement of the oxygen ions between the one and the other sides of the partition member. The magnitude of the voltage difference (E) is generally estimated by the next Nernst equation;
E - 4T ln pl .. ~................... ~. (1) -where: R ...... gas constant T ... absolute temperature F ... Faraday constant Pl... partial oxygen pressure of the reference gas: -P2.... partial oxygen pressure of the ..
unknown gas mixture .
With this equation, it will be appreciated that the partial oxygen pre~sure of the unknown gas mixture and accordingly the oxygen concentration of the same are ~:
calculated by measuring the voltage difference tE).
.: ~
_ 3 - ~
' ' ~
~0'~2~33 By the way, it was revealed that the oxygen concen~ration of the exhaust gases issued from the en~ine is critically dependent upon the air to fuel ratio of the intake charge to the engine.
Apart from this, it has been observed that the zirconium oxide oxygen sensor does not generate sufficient voltage difference at low temperature. In fact, a sufficient voltage difEerence for measuring the oxygen concentration can not be expected at a temperature below about 350C. Therefore, when equippecl in the exhaust tube of the engine, the zirconiumoxyqen sensor must be located in a position where a highest possible temperature of the exhaust gases from the engine exists.
The present invention will be illustrated by way of the accompanying drawings, in which:
Fig. 1 is a sectional view of a conventional oxygen sensor, the sensor being shown fixed to an exhaust tube of an engine system;
Fig. 2 is an illustration showing the distribution of temperature provided in the exhaust tube;
Fig. 3 is a sectional view of a further oxygen sensor;
Fig. 4A and 4B are sectional views of main parts of a preferred embodiment of the oxygen sensor according to the present invention;
Fig. 4C is an enlarged sectional view of a slightly modified electrically conducting means employable in the oxygen sensor of the present invention; and Fig. 5 is a sectional view of main parts of a still further oxygen sensor.
In particular Fig. 2 shows the distribution of tempera-ture in the exhaust tube in a case where the displacement of the associated engine is 2000 cc and the inside diameter of the exhaust tube is 45 mm. The curves a and b represent the respective temp- -erature distribution in two cases wherein the engine speeds are '' -~ .
~ 4-~ Z~3~ .
1200 rpm and 800 rpm, respectively. From this Fi~ure, it will be noted that in the exhaust tube ! a temperature difference ranging from about 150C to about 200C will appear in each engine operation mode. Furthermore, the temperature gradient is maximum in a region between the inner surface of the exhaust tube and a portion about 10 mm away from the inner surface of the tube. These phenomena similarly occur also in other cases wherei.n the displace-ment of the engine changes from about 1000 cc to about 4000 cc and the inside diameter of the exhaust tube changes ~rom about 40 mm to 60 mm. From this description, it will be appreciated that the zirconium oxide oxygen sensor should be arranged insuch a manner that the sensitive part thereof is located in a position at least 10 mm away from the inner surface of the exhaust tube.
Therefore, the present invention provides an improved oxygen sensor which has a very sensitive part located in a position where a highest possible temperature of the exhaust gases exists.
The present invention also provides an improved oxygen sensor :-which comprises a tubular electrolyte having one closedend projecting into the interior of the exhaust tube and the other open end mount- .
ed in a holder connected to the exhaust tube. .
The present invention further provides an improved .
oxygen sensor which compris0s a tubular electrolyte, of stabilized ~ .
zirconium oxide, ;
.
'"' .
~ -5- , ~ 33 having a closed end wall the thickness of which is about 0.3 to 1.0 mm, the closed end being projected into the interior of the exhaust tube.
The present invention also provides an improved oxygen sensor having an extending portion of at least 12 mm, the extending portion being projected into the interior of -the exhaust tube so as to be adequately exposed to the exhaust gases emitted from the engine.
The present invention still further provides an improved oxygen sensor comprising a tubular electrolyte ha~ing a closed end and an open end, the wall thickness of the electrolyte being gradually decreased toward the closed end from the open end.
The present invention also provides an improved oxygen sensor which comprises a tubular electrolyte having on its . .
surface smoothly rounded of~ sec~ions for facilitating the operation of the platinum coating on the surfaces of the electro~
lyte.
The present invention again provides an improved oxygen sensor which comprises a tubular eIectrolyte and terminal means, the terminal means being disposed in an open end of the electrolyte so as to provide an effective electrical connection between them.
According to the prese~t invention there is provided an .
oxygen sensor for determining oxygen concentration in a gas mixture, comprising: a solid-state axially elongated tubular electrolyte having an axial closed end and an axial open end; :.
first and second electrodes respectively co~ering the outer and inner surfaces of said electrolyte, said second electrode defining ..
.
a generally hollow chamber near said open end of said electrolyte; : .
an electrically conducting annular head member tightly disposed in the chamber of said second electrode an electrically conducting elongated member including an elongated section of a diameter smallerthan that :
- , ~, -, . ~ .
~ 7Z~3~
of said chamber, said elongated member bein~ inserted into sald chamber so that said elongated section is located between said annular head member and said raised section and said raised section is tightly engaged with said inner sur~ace of said tubular electro-lyte via said second electrode; and a corrugated, cylindrical metallic member coaxially disposed around said elongated section, the corrugations thereof beiny in contact with the outer surface of said elongated section and with the inner surface of said tubular electrolyte via said second electrode.
According to one embodiment of the present invention . .
there is provided an oxygen sensor for determining oxygen concentration in a gas mixture flowing through a tube, comprising:
a metallic holder defining two open ends and a hore, one of said . . .
ends being coupled in an aperture formed iTI a wall portion of the tube, with the other end being directed outwardly from the tube; .
a solid-state electrolyte shaped into a conical tube with a ~ ~.
closed end and an open end having a larger diameter than that of said closed end, the wall thickness of said electrolyte gradually ~ :
decreasingtoward the closed end from the oPen end, said ..
electrolyte being disposed in said metallic holder with the closed end thereof projecting into said tube, and the closed end having a wall thickness ranging from about 0.3 to 1.0 mm; first and second electrodes respectively covering the outer and inner surfaces of the conical shaped electrolyte, said first electrode being in contact with said metallic holder, and said second electrode defining a generally hollow chamber near said open end;
an electrically conducting elongated member tightly disposed in said chamber; an electrically conducting elongated member including an elongated section of a diameter smaller than that of said chamber and a radially outwardly raised section of a diameter equal to ~hat of said chamber, said elongated member being ~ . . :
. .
fi33 inserted into said chamber so that said elongated section is located between said annular head member and said raised section and said raised section is tightly engaged with the inner surface of said tubular electrolyte via said second electrode; and a corrugated cylindrical metallic member coaxially disposed around said elongated section, the co.rrugations thereo:E being in contact with an outer surface of said elongated section and with the inner surface of said tubular electrolyte via said second electrode.
Referring once more to the accompanying drawings in 10 order to clearly define the inventive steps of the present ~.
invention over the prior art, a detailed description of one of the conventional oxygen sensors will be given with the aid of .
Fig. 1.
In this Figure, the conventional oxygen scnsor is -7- .
generally designated by the numeral 10 and is shown accompanied with an exhaust tube 12 through which exhaust gases issued from an engine, i.e., an internal combustion engine, flow.
The oxygen sensor 10 comprises an outer cylindrical holder 14 of metal having an externally threaded portion 16 terminating in a radial shoulder portion 18 and a relatively thin plate tube portion 20 extending outwardly from the radial shoulder portion 18. The radial shoulder portion 18 is used for facilitating acceptance and seating of the outer cylindrical holder 18 in a threaded bore 22 formed in an annular connector 24 which has been firmly connected to the exhaust tube 12 by welding~
Disposed in the outer cylindrical holder 14 while projecting at its leading portion into the interior of the exhaust tube 12 is a solid state oxygen sensitive electrolyte 26 which is formed into a generally cylindrical structure having a closed end 28, an open end 30 and having at its generally middle portion a radially outwardly raised portion 31. As shown, the closed end 28 is located in or projected into the interior of the exhaust tube 12. The electrolyte 26 comprises zirconium ~ioxide (ZrO2) and and stabilizer, such as calcium oxide (CaO). Now, it should be noted that the wall thickness of this conven- -tional e~ectrolyte 28 is generally uniform in the section .
.. . .
between the closed end 28 and the raised portion 31, as shown. The outer and inner surfaces of the cylin-drical electrolyte 26 are covered or coated with first and second platinum electrodes 32 and 34 which are electrically insulated from each other. The electrolyte 26 with the firs~ and second platinum electrodes 32 and 34 is disposed in the outer cylindrical holder 14 in such a manner that the radially outwardly raised position 31 thereof is snugly fitted in an enlarged bore 36 formed in the holder 14. Thus, th~ axial movement of the electrolyte 26 toward the inside of the exhaust tube 12 relative to the holder 14 is prevented and simultane-ously, the elec~rical connection between the holder 14 and the first platinum electrode 32 is provided. A
space (no numeral) defined between the holder 14 and the first platinum electrode 32 and extending from the raised portion 31 to the open end 30 of the electrolyte 26 is filled or packed with an electrically conductive powder 38 such as Copp~ Aluminum and/or Graphite powder, so that the electrical connection between the outer holder 14 and the first platinum electrode 32 is effectively made. Within the space for the powder 38 are tightly disposed spaced first and second conductive rings 40 and 42 which can more effectively provide the -electrical connection between the holder 14 and the ' "
.:
.. . . . .
:~0~ 33 first platinum electrode 32 while steadily supporting the electrolyte 26 in the holder 14. A connecting rod 44 is secured at its enlarged head portion 46 to the second platinum electrode 34 located on a stepped portion 48 formed at the inner surface of the electxolyte 26 near the open end 30. The connecting rod 44 is formed with an axially extending passage 50 for providing a fluid communication between the interior of the electrolyte 26 and the atmosphere. A space (no.numeral) defined between the second platinum electrode 34 and the con-necting rod 44 and extending from the enlarged head portion 46 to the open end of the electrolyte 26 is also filled or packed with the above-mentioned electrically conductive powder. A third conductive ring 52 is tightly disposed in this space for achieving effective electrical connection between the second platinum electrode 34 and the connecting rod 44.
By the way, in such a conventional oxyyen sensor, it has been usually observed that the length (L) of a portion defined between the tip of the electrolyte 26 and the leading edge of the raised portion 31 is deter-mined about 25 to 30 mm, and the wall thickness of the '3 portion is about 2 to 3 mm~ With this construction, - ~:
~ s~
however, the following several problems ha~e ~cc~ s~.
(1) When such conventional oxygen sensor is '- ' :.:
`
~ .... . .
~ 3 subjected to a so-called therlnal shock cyclin~ test in which (800C x 3 minutes - 25~C x 1 minute) composes one cycle, a lot of hair-shaped cracks appear on the cl.osed end of the electrolyte 26 and on the leading edge o~ the raised portion 31 before the test proceeds to five cycles Thts means that the thermal shock resistance of this conventional electrolyte is very poor.
~2~ Because the closed end and its neiyhbourhood of the electrolyte 26 are constructed to have the large wall thick-ness throughout thereof, the inner impedance of the electrolyte 26 is undesirably increased. Usually, several MQ resistance i5 `:
provided to the electrolyte 26 at about 400C. Furthermore, because o~ its large wall thickness of the electrolyte, it takes a relatively long time to warm up the electrolyte. Consequently, both the sensitivity of the oxygen sensor 10 and the lasting quality of the same are unwantedly decreased.
Therefore, as mentioned before, the present invention is proposed to pro~ide an improved oxygen sensor which can ~ :
eliminate such drawbacks and disadvantages encountered in th~
convent;onal oxygen sensor. :
Referring to Fig. 3 of the drawings, the oxygen sensor 10' comprises generally the same parts or elements as in the `'~ `' - 1 1- `
- - - ~ ~ . .. .. ... .
~ 3 case of the above-mentioned conventional one (Fig . 1 ) .
As shown in this drawing, the electrolyte 26' is formed into a generally conical tube with a closed end 2B' of small diameter and an open end 30' of large diametex.
The wall thickness of the electrolyte 26' is gradually decreased toward the closed end 28' from the radially outwardly raised portion 32' snugly coupled in the bore 36 formed in the outer cylindrical holder 14~ Now, it should be noted that the wall thickness of the closed end 28' is determined about 0.3 to 1.0 mm, and the wall thickness of a portion, indicated by the letter c, adjacent the left leading edge of the raised portion
~ 33 oxide (ZrO2) exhibits conductivity by means of oxygen ions which transfer therethrough. In reality, if some gas mixture whose partial oxygen pressure or absolute oxygen pressure must be measured is present on one side S of a partition member made of the zirconium oxide, and simultaneously, a reference gas having a known partial oxygen pressure is present on the other side, a con-siderable voltage diference (E) is generated by the movement of the oxygen ions between the one and the other sides of the partition member. The magnitude of the voltage difference (E) is generally estimated by the next Nernst equation;
E - 4T ln pl .. ~................... ~. (1) -where: R ...... gas constant T ... absolute temperature F ... Faraday constant Pl... partial oxygen pressure of the reference gas: -P2.... partial oxygen pressure of the ..
unknown gas mixture .
With this equation, it will be appreciated that the partial oxygen pre~sure of the unknown gas mixture and accordingly the oxygen concentration of the same are ~:
calculated by measuring the voltage difference tE).
.: ~
_ 3 - ~
' ' ~
~0'~2~33 By the way, it was revealed that the oxygen concen~ration of the exhaust gases issued from the en~ine is critically dependent upon the air to fuel ratio of the intake charge to the engine.
Apart from this, it has been observed that the zirconium oxide oxygen sensor does not generate sufficient voltage difference at low temperature. In fact, a sufficient voltage difEerence for measuring the oxygen concentration can not be expected at a temperature below about 350C. Therefore, when equippecl in the exhaust tube of the engine, the zirconiumoxyqen sensor must be located in a position where a highest possible temperature of the exhaust gases from the engine exists.
The present invention will be illustrated by way of the accompanying drawings, in which:
Fig. 1 is a sectional view of a conventional oxygen sensor, the sensor being shown fixed to an exhaust tube of an engine system;
Fig. 2 is an illustration showing the distribution of temperature provided in the exhaust tube;
Fig. 3 is a sectional view of a further oxygen sensor;
Fig. 4A and 4B are sectional views of main parts of a preferred embodiment of the oxygen sensor according to the present invention;
Fig. 4C is an enlarged sectional view of a slightly modified electrically conducting means employable in the oxygen sensor of the present invention; and Fig. 5 is a sectional view of main parts of a still further oxygen sensor.
In particular Fig. 2 shows the distribution of tempera-ture in the exhaust tube in a case where the displacement of the associated engine is 2000 cc and the inside diameter of the exhaust tube is 45 mm. The curves a and b represent the respective temp- -erature distribution in two cases wherein the engine speeds are '' -~ .
~ 4-~ Z~3~ .
1200 rpm and 800 rpm, respectively. From this Fi~ure, it will be noted that in the exhaust tube ! a temperature difference ranging from about 150C to about 200C will appear in each engine operation mode. Furthermore, the temperature gradient is maximum in a region between the inner surface of the exhaust tube and a portion about 10 mm away from the inner surface of the tube. These phenomena similarly occur also in other cases wherei.n the displace-ment of the engine changes from about 1000 cc to about 4000 cc and the inside diameter of the exhaust tube changes ~rom about 40 mm to 60 mm. From this description, it will be appreciated that the zirconium oxide oxygen sensor should be arranged insuch a manner that the sensitive part thereof is located in a position at least 10 mm away from the inner surface of the exhaust tube.
Therefore, the present invention provides an improved oxygen sensor which has a very sensitive part located in a position where a highest possible temperature of the exhaust gases exists.
The present invention also provides an improved oxygen sensor :-which comprises a tubular electrolyte having one closedend projecting into the interior of the exhaust tube and the other open end mount- .
ed in a holder connected to the exhaust tube. .
The present invention further provides an improved .
oxygen sensor which compris0s a tubular electrolyte, of stabilized ~ .
zirconium oxide, ;
.
'"' .
~ -5- , ~ 33 having a closed end wall the thickness of which is about 0.3 to 1.0 mm, the closed end being projected into the interior of the exhaust tube.
The present invention also provides an improved oxygen sensor having an extending portion of at least 12 mm, the extending portion being projected into the interior of -the exhaust tube so as to be adequately exposed to the exhaust gases emitted from the engine.
The present invention still further provides an improved oxygen sensor comprising a tubular electrolyte ha~ing a closed end and an open end, the wall thickness of the electrolyte being gradually decreased toward the closed end from the open end.
The present invention also provides an improved oxygen sensor which comprises a tubular electrolyte having on its . .
surface smoothly rounded of~ sec~ions for facilitating the operation of the platinum coating on the surfaces of the electro~
lyte.
The present invention again provides an improved oxygen sensor which comprises a tubular eIectrolyte and terminal means, the terminal means being disposed in an open end of the electrolyte so as to provide an effective electrical connection between them.
According to the prese~t invention there is provided an .
oxygen sensor for determining oxygen concentration in a gas mixture, comprising: a solid-state axially elongated tubular electrolyte having an axial closed end and an axial open end; :.
first and second electrodes respectively co~ering the outer and inner surfaces of said electrolyte, said second electrode defining ..
.
a generally hollow chamber near said open end of said electrolyte; : .
an electrically conducting annular head member tightly disposed in the chamber of said second electrode an electrically conducting elongated member including an elongated section of a diameter smallerthan that :
- , ~, -, . ~ .
~ 7Z~3~
of said chamber, said elongated member bein~ inserted into sald chamber so that said elongated section is located between said annular head member and said raised section and said raised section is tightly engaged with said inner sur~ace of said tubular electro-lyte via said second electrode; and a corrugated, cylindrical metallic member coaxially disposed around said elongated section, the corrugations thereof beiny in contact with the outer surface of said elongated section and with the inner surface of said tubular electrolyte via said second electrode.
According to one embodiment of the present invention . .
there is provided an oxygen sensor for determining oxygen concentration in a gas mixture flowing through a tube, comprising:
a metallic holder defining two open ends and a hore, one of said . . .
ends being coupled in an aperture formed iTI a wall portion of the tube, with the other end being directed outwardly from the tube; .
a solid-state electrolyte shaped into a conical tube with a ~ ~.
closed end and an open end having a larger diameter than that of said closed end, the wall thickness of said electrolyte gradually ~ :
decreasingtoward the closed end from the oPen end, said ..
electrolyte being disposed in said metallic holder with the closed end thereof projecting into said tube, and the closed end having a wall thickness ranging from about 0.3 to 1.0 mm; first and second electrodes respectively covering the outer and inner surfaces of the conical shaped electrolyte, said first electrode being in contact with said metallic holder, and said second electrode defining a generally hollow chamber near said open end;
an electrically conducting elongated member tightly disposed in said chamber; an electrically conducting elongated member including an elongated section of a diameter smaller than that of said chamber and a radially outwardly raised section of a diameter equal to ~hat of said chamber, said elongated member being ~ . . :
. .
fi33 inserted into said chamber so that said elongated section is located between said annular head member and said raised section and said raised section is tightly engaged with the inner surface of said tubular electrolyte via said second electrode; and a corrugated cylindrical metallic member coaxially disposed around said elongated section, the co.rrugations thereo:E being in contact with an outer surface of said elongated section and with the inner surface of said tubular electrolyte via said second electrode.
Referring once more to the accompanying drawings in 10 order to clearly define the inventive steps of the present ~.
invention over the prior art, a detailed description of one of the conventional oxygen sensors will be given with the aid of .
Fig. 1.
In this Figure, the conventional oxygen scnsor is -7- .
generally designated by the numeral 10 and is shown accompanied with an exhaust tube 12 through which exhaust gases issued from an engine, i.e., an internal combustion engine, flow.
The oxygen sensor 10 comprises an outer cylindrical holder 14 of metal having an externally threaded portion 16 terminating in a radial shoulder portion 18 and a relatively thin plate tube portion 20 extending outwardly from the radial shoulder portion 18. The radial shoulder portion 18 is used for facilitating acceptance and seating of the outer cylindrical holder 18 in a threaded bore 22 formed in an annular connector 24 which has been firmly connected to the exhaust tube 12 by welding~
Disposed in the outer cylindrical holder 14 while projecting at its leading portion into the interior of the exhaust tube 12 is a solid state oxygen sensitive electrolyte 26 which is formed into a generally cylindrical structure having a closed end 28, an open end 30 and having at its generally middle portion a radially outwardly raised portion 31. As shown, the closed end 28 is located in or projected into the interior of the exhaust tube 12. The electrolyte 26 comprises zirconium ~ioxide (ZrO2) and and stabilizer, such as calcium oxide (CaO). Now, it should be noted that the wall thickness of this conven- -tional e~ectrolyte 28 is generally uniform in the section .
.. . .
between the closed end 28 and the raised portion 31, as shown. The outer and inner surfaces of the cylin-drical electrolyte 26 are covered or coated with first and second platinum electrodes 32 and 34 which are electrically insulated from each other. The electrolyte 26 with the firs~ and second platinum electrodes 32 and 34 is disposed in the outer cylindrical holder 14 in such a manner that the radially outwardly raised position 31 thereof is snugly fitted in an enlarged bore 36 formed in the holder 14. Thus, th~ axial movement of the electrolyte 26 toward the inside of the exhaust tube 12 relative to the holder 14 is prevented and simultane-ously, the elec~rical connection between the holder 14 and the first platinum electrode 32 is provided. A
space (no numeral) defined between the holder 14 and the first platinum electrode 32 and extending from the raised portion 31 to the open end 30 of the electrolyte 26 is filled or packed with an electrically conductive powder 38 such as Copp~ Aluminum and/or Graphite powder, so that the electrical connection between the outer holder 14 and the first platinum electrode 32 is effectively made. Within the space for the powder 38 are tightly disposed spaced first and second conductive rings 40 and 42 which can more effectively provide the -electrical connection between the holder 14 and the ' "
.:
.. . . . .
:~0~ 33 first platinum electrode 32 while steadily supporting the electrolyte 26 in the holder 14. A connecting rod 44 is secured at its enlarged head portion 46 to the second platinum electrode 34 located on a stepped portion 48 formed at the inner surface of the electxolyte 26 near the open end 30. The connecting rod 44 is formed with an axially extending passage 50 for providing a fluid communication between the interior of the electrolyte 26 and the atmosphere. A space (no.numeral) defined between the second platinum electrode 34 and the con-necting rod 44 and extending from the enlarged head portion 46 to the open end of the electrolyte 26 is also filled or packed with the above-mentioned electrically conductive powder. A third conductive ring 52 is tightly disposed in this space for achieving effective electrical connection between the second platinum electrode 34 and the connecting rod 44.
By the way, in such a conventional oxyyen sensor, it has been usually observed that the length (L) of a portion defined between the tip of the electrolyte 26 and the leading edge of the raised portion 31 is deter-mined about 25 to 30 mm, and the wall thickness of the '3 portion is about 2 to 3 mm~ With this construction, - ~:
~ s~
however, the following several problems ha~e ~cc~ s~.
(1) When such conventional oxygen sensor is '- ' :.:
`
~ .... . .
~ 3 subjected to a so-called therlnal shock cyclin~ test in which (800C x 3 minutes - 25~C x 1 minute) composes one cycle, a lot of hair-shaped cracks appear on the cl.osed end of the electrolyte 26 and on the leading edge o~ the raised portion 31 before the test proceeds to five cycles Thts means that the thermal shock resistance of this conventional electrolyte is very poor.
~2~ Because the closed end and its neiyhbourhood of the electrolyte 26 are constructed to have the large wall thick-ness throughout thereof, the inner impedance of the electrolyte 26 is undesirably increased. Usually, several MQ resistance i5 `:
provided to the electrolyte 26 at about 400C. Furthermore, because o~ its large wall thickness of the electrolyte, it takes a relatively long time to warm up the electrolyte. Consequently, both the sensitivity of the oxygen sensor 10 and the lasting quality of the same are unwantedly decreased.
Therefore, as mentioned before, the present invention is proposed to pro~ide an improved oxygen sensor which can ~ :
eliminate such drawbacks and disadvantages encountered in th~
convent;onal oxygen sensor. :
Referring to Fig. 3 of the drawings, the oxygen sensor 10' comprises generally the same parts or elements as in the `'~ `' - 1 1- `
- - - ~ ~ . .. .. ... .
~ 3 case of the above-mentioned conventional one (Fig . 1 ) .
As shown in this drawing, the electrolyte 26' is formed into a generally conical tube with a closed end 2B' of small diameter and an open end 30' of large diametex.
The wall thickness of the electrolyte 26' is gradually decreased toward the closed end 28' from the radially outwardly raised portion 32' snugly coupled in the bore 36 formed in the outer cylindrical holder 14~ Now, it should be noted that the wall thickness of the closed end 28' is determined about 0.3 to 1.0 mm, and the wall thickness of a portion, indicated by the letter c, adjacent the left leading edge of the raised portion
3~' is determined about 2 to 5 mm. In addition, the unlt consisting of the electrolyte 26' and the first and second platinum electrodes 32 and 34 is so con-structed to have an exhaust gas exposed portion which ha~ at least 12 mm axial length (~) so that the thin closed end 28' can be located in the hot zone in the exhaust tube 12.
With this construction, the oxygen sensor 10' can operate optimally with increase of the sensitivity and the lasting quality thereof.
Several experiments have revealed that the thermal shock resistance of the subject electrolyte 26' is remarkably increased. More specifically~ under the ~ 12 -, , ,!
- . : .: ~ :
~ 2~3 before-mentioned the.r~al shock cycling test, no cracks appear on the electrolyte 26~ even when the test proceeds to twenty cycles. Furthermore, the inner impedance of the subject electrolyte 26' is pre~erably reduced to about lO to 25~ the impedance of the conventional one shown in Fig. l. In addition, the warming up time of the oxygen sensor lO' is reduced to abou-t 60 to 70% the time of the conventional sensor.
Re:Eerring to ~igs. 4A and 4B, there is shown an electrolyte, having similar construction to the electrolyte 26' of Fig. 3, to which an improved connecting means 54 is engaged.
The connecting means 54 comprises an enlarged annular head rnember 56 having a through hole 58 and a female portion 60. As shown, .
the annual head member 56 is snugly engaged to the stepped portion 48 formed in the electrolyte 26' so that the female portion 60 faces the open end 30' of the electrolyte 26' An elongate member 62 having a circular cross section and having at its generally middle portion a radially outwardly raised portion 64 is snugly engaged at one end or male portion thereof with the female portion 60 of the head member 56 while tiyhtly contacting at the raised port;on 64 wi~h the second platinum electrode 34 at the open end thereof. A space 66 defined between the second platinum electrode 34 '~
and the elongate member 62 and extending from the head member 56 to the outwardly raised portion 64 contains therein a corrugated cylindrical member 68 made of Copper, or the like. The corrugated cylindrical member 68 is arranged in such a manner that when the elongate member 62 is moved toward the enlarged head member 56 to be secured to each other, the corrugated cylindrical member 68 is compressed ur~ing the corrugations into electrical contact with the outer surface of the elongate member 62 and the inner surface of khe second platinum electrode 34. The elongate member 62 has an axially extending through hole 70 which is to be connected with the above-mentioned through hole 58 of the head member 56 when the elongate member 62 is secured to the head :
member 56. Fig. 4B shows a state wherein the elongate ~-~
member 62 is about to engage with the head member 56.
b~i~
It should be noted that before~compressed in th~ space .
66, the corrugated cylindrical member 68 has maximum outside diameter slightly smaller than the inside diameter of the open end portion of the electrolyte 26', and mini-mum inside diameter slightly larger than the outside :
diameter of the elongate member 62.: With this, the insertion of the corrugated cylindrical member 68 into the space 66 is facilitated.
With this construction, the following merits and . ~ 14 ~ ~ ~
-~t~tZfi33 advantages will arise. First, the radially outward and radially inward movements of the corrugations on corrugated cylindrical member 68 due to the compression thereof produce not only tight connection between the electrolyte 26' and the connecting means 54 but also reliable electrical contact between the second platinum electrode 34 and the connecting means 54. Second, since the radially outward and r~dially inward movements of :~
the corrugations on the corrugated cylindrical member 68 can be controlled ~y the urging forc~ applied thereto by the inward movement of the elongate member 62, the small variations in diameter of two portions between which the corrugated cylindrical member 68 is dispos~d are easily compensated.
If desired, as shown in Fig. 4C, each of the corrugations on the corrugated cylindrical member 68 may be formed so ~hat the cross section of ~he corrugations has a generally saw-tooth section, the combination of er~d~
the perpendicular and slanted portions 72 and 74 e~i~r the corrugated cylindrical member 68 with improved mechanical connection between the electrolyte 26' and ~ :
the connecting means 54. ~:
Referring now to Fig. 5 of the drawings, there is shown an electrolyte 26" which i~ slightly modified in .:
shape. As shown, each of curved portions formed on ~he ,:
, ...~.' ., 'Z633 outer and inner surfaces of the electroly-te 26" is smoo-thly rounded off. Preferably, the radius of curvature of the each curved portion is not less than 2 mm.
With this construction of the electrolyte 26", unwant-ed phenomenon in which the platinum electrodes 32 and 34 covering the curved portions come off during the coating process thereof does not occur. This is because the thickness of each platinum electrode on the electrolyte 26" can be uniform throughout to prevent the occurrence of the stress concentration in the platinum electrode at the each curved portion o~ the electrolyte during the platinum coating process.
With this construction, the oxygen sensor 10' can operate optimally with increase of the sensitivity and the lasting quality thereof.
Several experiments have revealed that the thermal shock resistance of the subject electrolyte 26' is remarkably increased. More specifically~ under the ~ 12 -, , ,!
- . : .: ~ :
~ 2~3 before-mentioned the.r~al shock cycling test, no cracks appear on the electrolyte 26~ even when the test proceeds to twenty cycles. Furthermore, the inner impedance of the subject electrolyte 26' is pre~erably reduced to about lO to 25~ the impedance of the conventional one shown in Fig. l. In addition, the warming up time of the oxygen sensor lO' is reduced to abou-t 60 to 70% the time of the conventional sensor.
Re:Eerring to ~igs. 4A and 4B, there is shown an electrolyte, having similar construction to the electrolyte 26' of Fig. 3, to which an improved connecting means 54 is engaged.
The connecting means 54 comprises an enlarged annular head rnember 56 having a through hole 58 and a female portion 60. As shown, .
the annual head member 56 is snugly engaged to the stepped portion 48 formed in the electrolyte 26' so that the female portion 60 faces the open end 30' of the electrolyte 26' An elongate member 62 having a circular cross section and having at its generally middle portion a radially outwardly raised portion 64 is snugly engaged at one end or male portion thereof with the female portion 60 of the head member 56 while tiyhtly contacting at the raised port;on 64 wi~h the second platinum electrode 34 at the open end thereof. A space 66 defined between the second platinum electrode 34 '~
and the elongate member 62 and extending from the head member 56 to the outwardly raised portion 64 contains therein a corrugated cylindrical member 68 made of Copper, or the like. The corrugated cylindrical member 68 is arranged in such a manner that when the elongate member 62 is moved toward the enlarged head member 56 to be secured to each other, the corrugated cylindrical member 68 is compressed ur~ing the corrugations into electrical contact with the outer surface of the elongate member 62 and the inner surface of khe second platinum electrode 34. The elongate member 62 has an axially extending through hole 70 which is to be connected with the above-mentioned through hole 58 of the head member 56 when the elongate member 62 is secured to the head :
member 56. Fig. 4B shows a state wherein the elongate ~-~
member 62 is about to engage with the head member 56.
b~i~
It should be noted that before~compressed in th~ space .
66, the corrugated cylindrical member 68 has maximum outside diameter slightly smaller than the inside diameter of the open end portion of the electrolyte 26', and mini-mum inside diameter slightly larger than the outside :
diameter of the elongate member 62.: With this, the insertion of the corrugated cylindrical member 68 into the space 66 is facilitated.
With this construction, the following merits and . ~ 14 ~ ~ ~
-~t~tZfi33 advantages will arise. First, the radially outward and radially inward movements of the corrugations on corrugated cylindrical member 68 due to the compression thereof produce not only tight connection between the electrolyte 26' and the connecting means 54 but also reliable electrical contact between the second platinum electrode 34 and the connecting means 54. Second, since the radially outward and r~dially inward movements of :~
the corrugations on the corrugated cylindrical member 68 can be controlled ~y the urging forc~ applied thereto by the inward movement of the elongate member 62, the small variations in diameter of two portions between which the corrugated cylindrical member 68 is dispos~d are easily compensated.
If desired, as shown in Fig. 4C, each of the corrugations on the corrugated cylindrical member 68 may be formed so ~hat the cross section of ~he corrugations has a generally saw-tooth section, the combination of er~d~
the perpendicular and slanted portions 72 and 74 e~i~r the corrugated cylindrical member 68 with improved mechanical connection between the electrolyte 26' and ~ :
the connecting means 54. ~:
Referring now to Fig. 5 of the drawings, there is shown an electrolyte 26" which i~ slightly modified in .:
shape. As shown, each of curved portions formed on ~he ,:
, ...~.' ., 'Z633 outer and inner surfaces of the electroly-te 26" is smoo-thly rounded off. Preferably, the radius of curvature of the each curved portion is not less than 2 mm.
With this construction of the electrolyte 26", unwant-ed phenomenon in which the platinum electrodes 32 and 34 covering the curved portions come off during the coating process thereof does not occur. This is because the thickness of each platinum electrode on the electrolyte 26" can be uniform throughout to prevent the occurrence of the stress concentration in the platinum electrode at the each curved portion o~ the electrolyte during the platinum coating process.
Claims (11)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An oxygen sensor for determining oxygen concentra-tion in a gas mixture, comprising: a solid-state axially elongated tubular electrolyte having an axial closed end and an axial open end; first and second electrodes respectively covering the outer and inner surfaces of said electrolyte, said second electrode defining a generally hollow chamber near said open end of said electrolyte; an electrically conducting annular head member tightly disposed in the chamber of said second electrode; an electrically conducting elongated member including an elongated section of a diameter smaller than that of said chamber and a radially outwardly raised section of a diameter equal to that of said chamber, said elongated member being inserted into said chamber so that said elongated section is located between said annular head member and said raised section and said raised section is tightly engaged with said inner surface of said tubular electrolyte via said second electrode; and a corrugated, cylindrical metallic member coaxially disposed around said elon-gated section, the corrugations thereof being in contact with the outer surface of said elongated section and with the inner surface of said tubular electrolyte via said second electrode.
2. An oxygen sensor as claimed in Claim 1, wherein said annular head member and said elongated member are respectively formed with through passages which are aligned with each other to provide a fluid communication between said chamber and the atmosphere.
3. An oxygen sensor as claimed in Claim 2, wherein said annular head member is formed with a female portion into which a male portion formed on an end of said elongated section is tightly disposed.
4. An oxygen sensor as claimed in Claim 1, wherein the cross-section of each corrugation of said corrugated cylindrical member comprises perpendicular and slanted portions with respect to the axis of said corrugated cylindrical member, whereby a saw-tooth configuration is defined.
5. An oxygen sensor as claimed in Claim 1, wherein said closed end of said electrolyte has a wall thickness ranging from about 0.3 to 1.0 mm.
6. An oxygen sensor as claimed in Claim 5, wherein the wall thickness of said electrolyte gradually decreases in the direction toward said closed end from said open end.
7. An oxygen sensor as claimed in Claim 6, wherein each curved portion formed on said outer and inner surface of said electrolyte is smoothly rounded off.
8. An oxygen sensor as claimed in Claim 7, wherein the radius of curvature of each curved portion is at least about 2 mm.
9. An oxygen sensor for determining oxygen concentration in a gas mixture flowing through a tube, comprising: a metallic holder defining two open ends and a bore, one of said ends being coupled in an aperture formed in a wall portion of the tube, with the other end being directed outwardly from the tube; a solid-state electrolyte shaped into a conical tube with a closed and and an open end having a larger diameter than that of said closed end, the wall thickness of said electrolyte gradually decreasing toward the closed end from the open end, said electrolyte being disposed in said metallic holder with the closed end thereof projecting into said tube, and the closed end having a wall thick-ness ranging from about 0.3 to 1.0 mm; first and second electrodes respectively covering the outer and inner surfaces of the conical-shaped electrolyte, said first electrode being in contact with said metallic holder, and said second electrode defining a generally hollow chamber near said open end; an electrically conducting elongated member tightly disposed in said chamber; an electrically conducting elongated member including an elongated section of a diameter smaller than that of said chamber and a radially outward-ly raised section of a diameter equal to that of said chamber, said elongated member being inserted into said chamber so that said elongated section is located between said annular head member and said raised section and said raised section is tightly engaged with the inner surface of said tubular electrolyte via said second electrode; and a corrugated cylindrical metallic member coaxially disposed around said elongated section, the corrugations thereof being in contact with an outer surface of said elongated section and with the inner surface of said tubular electrolyte via said second electrode.
10. An oxygen sensor as claimed in Claim 9, wherein said electrolyte and said first and second electrodes comprise a portion which projects into said tube to be exposed to said gas mixture, the axial length of said portion being at least about 12 mm.
11. An oxygen sensor as claimed in Claim 10, wherein the cross-section of each corrugation of said corrugated cylindrical member comprises perpendicular and slanted portions with respect to the axis of said corrugated cylindrical member, whereby a saw-tooth configuration is defined.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA264,894A CA1072633A (en) | 1976-11-04 | 1976-11-04 | Oxygen sensor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA264,894A CA1072633A (en) | 1976-11-04 | 1976-11-04 | Oxygen sensor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1072633A true CA1072633A (en) | 1980-02-26 |
Family
ID=4107200
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA264,894A Expired CA1072633A (en) | 1976-11-04 | 1976-11-04 | Oxygen sensor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1072633A (en) |
-
1976
- 1976-11-04 CA CA264,894A patent/CA1072633A/en not_active Expired
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| MKEX | Expiry |