Note: Descriptions are shown in the official language in which they were submitted.
~ 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
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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).
.: ~
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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
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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, ;
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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
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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
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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
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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
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.. . .
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
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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
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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
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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 -
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~ 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 ~ ~ ~
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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
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'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.
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