JPS60177258A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To detect oxygen concn. with high accuracy by uniting the reference space sides of the 1st pump element and the 2nd pump element to one body via a means for controlling oxygen diffusion and preventing said lumiting means from contacting with the gas to be measured. CONSTITUTION:The 1st reference space 17 isolated from the gas to be measured is formed of the 1st solid electrolyte 12 and partition plates 13, 14 and the 2nd reference space 18 isolated from the gas to be measured is formed of the partition plates 14, 15 and the 2nd solid electrolyte 16. A small hole 19 which limits diffusion of oxygen between the 1st space 17 and the 2nd space 18 is punched to the plate 14. Pump current is supplied to a pump electrode 21 to maintain the potential between a reference electrode 22 and sensor electrode 20 provided to the electrolyte 12 at target potential. The pump current is similarly supplied to the electrolyte 16 as well and these currents are converted to voltages and averaged to determine oxygen concn. If the sensor is constituted in the above-mentioned way, the plate 14 for limiting oxygen diffusion does not contact the gas to be measured and therefore the oxygen concn. is detected with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oxygen sensor that detects the oxygen concentration in an aliquot, and more particularly to an oxygen sensor that detects the oxygen concentration in the exhaust gas of an internal combustion engine.

In general, in internal combustion engines, in order to control the air-fuel ratio of the intake air-fuel mixture to a target value with high precision, the oxygen concentration in the exhaust gas, which has a correlation with the air-fuel ratio, is detected. The fuel supply amount is feedback-controlled in accordance with the oxygen concentration.

An example of an oxygen sensor conventionally used in such an air-fuel ratio detection device is the one described in Japanese Patent Application Laid-Open No. 57-76450. This oxygen sensor will be explained with reference to FIG. do.

This oxygen sensor 1 applies the principle of a kind of a-cell battery that generates an electromotive force in response to an oxygen concentration of 1.
A reference electrode B mainly composed of platinum and an oxygen electrode 4 made of an alloy of gold and platinum are formed on both sides of an oxygen ion conductive solid electrolyte 2, and the reference electrode 3 is made of a porous material. The layer 4 is coated with a porous protective layer (coating layer) 6 that restricts the diffusion of ink.

In this oxygen sensor 1, when an injected current Is of a predetermined magnitude is supplied to the reference electrode 3 in a gas to be measured, for example, an exhaust gas, an amount of oxygen ions corresponding to the magnitude of the current IS is generated. is the solid electrolyte 2 in the opposite direction to the current Is.
Because it moves through the reference voltage 4Ji! 71 based on 3! !
An oxygen partial pressure Pa is generated, and at this time, an oxygen partial pressure Pk) is generated at the oxygen electrode 4 due to the oxygen partial pressure of the scum to be measured.

Thereby, between the group (f+ electrode B and oxygen 'fM, pole 4, based on the oxygen partial pressures Pa and Pb, I':=RT
/4+"・ρr+(Pa/Pb)--(i) However, the electromotive force E expressed by the Nernst equation where ri: gas constant, T: absolute temperature and de: Faraday constant is generated, and this electromotive force E is Since it changes depending on the oxygen concentration of the gas to be measured, this can be taken out as the output Vs of the oxygen sensor 1.

FIG. 2 shows the change in the output Vs for each injected current value. In this case, the exhaust gas of the internal combustion engine is used as the gas to be measured, and the oxygen concentration is determined by the air-fuel ratio (equivalence ratio λ, where λ = current air-fuel ratio/stoichiometric air-fuel ratio) of the mixture supplied to the internal combustion engine. The figure is converted to .

However, since the output Vs of the oxygen sensor 1 is small in the air-fuel ratio range in which the output Vs changes when the inflow current Is is fixed, it is difficult to detect the air-fuel ratio over a wide range.

Therefore, the output Vs of this oxygen sensor 1 is set to the target voltage Va(
Any value may be used as long as it corresponds to the output Vs, but it is set as 1 (approximately the intermediate value between the upper and lower limits of the oxygen sensor output Vs, which changes suddenly at switching air-fuel ratio), and the oxygen sensor output Vs is set to this target value. When the inflow current Is is supplied so that Va becomes equal to Va, the value of this inflow current Is becomes a value corresponding to the current air-fuel ratio as shown in FIG.

Therefore, by detecting the value of the current Is flowing into the oxygen sensor 1, the actual air-fuel ratio can be detected.

In this way, in conventional oxygen sensors, the scum to be measured passes through a porous layer that restricts oxygen diffusion, and the oxygen passing through the porous layer is detected as an electric current.
The oxygen concentration in the waste to be measured is detected.

Therefore, if there are deposits such as carbon particles in the fixed waste, the porous layer will become clogged, and the amount of oxygen molecules diffusing will change, which will change the output characteristics and accurately It may become impossible to detect the concentration.

1. This invention has been made in view of the points mentioned in . . . and has an object of [1] to enable oxygen concentration to be detected with high precision over a long period of time.

Purchase--1 Therefore, the oxygen sensor according to the present invention has a first oxygen sensor isolated from the waste to be measured. A second space is formed, and a first space such as this is formed. Providing means for restricting the diffusion of oxygen between the second space and the first space; By forming part or all of each partition wall that isolates the second space from the waste to be measured from a solid electrolyte that conducts oxygen ions, and providing carved electrodes on both sides of each solid electrolyte, oxygen can be removed. This means that the means for restricting diffusion does not come into contact with the scum to be measured.

Embodiments of the present invention will now be described with reference to FIG. 4 and subsequent figures of the accompanying drawings.

4 and 5 are a cross-sectional view and an exploded perspective view of an oxygen sensor embodying the present invention.

This oxygen sensor 11 includes a flat oxygen ion conductive first solid electrolyte 12, a partition plate 1 having a square through hole 13a, a flat partition plate 14, and a square through hole 13a. It is constructed by stacking a partition plate 15 with holes 15a and a flat second solid electrolyte 16.

In this oxygen sensor 11, the J-th solid electrolyte 12
A first space 17 isolated from the waste to be covered 41 is formed by the partition plates 13, 14, and the partition plates 14.
15 and the second solid electrolyte 16 form a second space 18 isolated from the waste to be measured.

And the first of these. The partition plate 14 defining the second space 17,18 includes a first space 17, which is a means for restricting the diffusion of oxygen between the first space 17 and the second space. A small hole 19 communicating with the second space 17, 18 is provided.

On the other hand, the first solid electrolyte 12 has a first sensor electrode 20 and a first pump 'flt!' on its outer surface. 1ii21, a first reference electrode 22 facing the first sensor electrode 20 and the first pump electrode 21 is provided on the inner surface.

The second solid electrolyte 16 also has a second sensor electrode 23 and a second pump electrode 24 on its outer surface, and a second sensor electrode 23 and a second pump electrode 24 on its inner surface, which are opposed to each other.
A base electrode 25 is provided.

Note that the first solid electrolyte 12 of the partition plate 16 is surrounded by the through hole 13a on the side surface of the first solid electrolyte 12. Second solid electrolyte 12.16
In order to maintain the activity of these components, a heater 30 for heating them is formed by printing.

Moreover, the first sensor electrode 20. First pump electrode 21.
Lead wires 62 to 34 are connected to the first reference electrode 22, respectively.
Second sensor electrode 23. Second pump electrode 24. Lead wires 65 to 67 are connected to the second group 7 (+! electrode 25, respectively).
To the heater filter O, wires 21 to 38 and 39 are connected.

Furthermore, the first. Second solid electrolyte 12. As IEi, for example, ZrO2, Hr02, Tlx02 +Bi2
C20, MgO, Y2O2+YB20 in oxides such as O3
Using a sintered body melted with 3 etc. (!I), each electrode 20-25
The main component is platinum or gold.

Furthermore, in this embodiment, the first. Second space 17.
18 from the waste to be measured. Second
Although the solid electrolyte 12.16 is formed from the electrode 20~
Only the portion corresponding to 25 may be formed of solid electrolyte.

FIG. 6 is a circuit diagram showing an example of an oxygen concentration (air-fuel ratio) detection circuit using the oxygen sensor of this embodiment.

This oxygen concentration detection circuit includes a first control circuit 41 and a second control circuit 41.
It consists of a control circuit 42 and an averaging circuit 43.

The first control circuit 41 first controls the first i18 quasi Y6.
The difference between the potential V SH between the pole 22 and the first sensor electrode 20 and the target voltage V a l (V a 1 'L:0) is detected by the differential amplifier 45 , and the difference is detected from the differential amplifier 45 . The first pump current supply circuit 46 supplies voltage to the first pump electrode 21 from the first sensor electrode 20 and first pump electrode 21 side to the first pump current according to the output differential voltage ΔVsI (ΔVsI=Vsl). i<(!The first pump current IP+ is supplied in the direction in which oxygen ions move within the first solid electrolyte 12 toward the electrode 22 side.

In other words, the first pump current supply circuit 46 increases the first pump current 1p+ when the differential voltage ΔV s H from the differential amplifier 45 is positive, and the differential voltage ΔV s 1
If is negative, the first pump current 11' + is decreased so that Vsl = Val = O.
The pump current 11”+ is controlled.

The first pump current 1p+ is supplied from the first pump current supply circuit 46 to the first pump electrode 21.
is converted into a voltage by a resistor 47 inserted in the power supply path, and the potential difference between both ends of this resistor 47 is detected by a differential amplifier 48 and outputted to the averaging circuit 43 as a voltage V1 (V+"Ip+).

The second control circuit 42 first detects the difference between the potential Vs2 between the second reference electrode 25 and the first sensor electrode 2 and the target voltage V a 2 from the power source 50 using the differential amplifier 51. Then, the differential voltage ΔVs2 output from this differential amplifier 51
(ΔVs2 = Vs2 Va 2 ), the second pump current supply circuit 52 supplies the second pump electrode 24 with the second sensor electrode 23 from the second base 1'# electrode 25 side.
and oxygen ions toward the second pump electrode 24 side.
A second pump current IP2 is supplied in the direction of movement within the solid electrolyte 16.

In other words, the second pump current supply circuit 52 reduces the second pump current IPz if the differential voltage ΔVS2 from the differential amplifier 51 is positive, and decreases the second pump current IPz if the differential voltage ΔVS2 is negative. The pump voltage d also increases IP2 and V
The second pump current 1p2 is controlled so that the second pump current 1p2 becomes S2''V a 2.

A second pump current rII2 is supplied from the second pump current supply circuit 52 to the second pump electrode 24.
is converted into a voltage by a resistor 53 inserted in the power supply path, and the ↑h voltage between both ends of this resistor 52 is detected by a differential amplifier 54 and sent to the averaging circuit 46 as a voltage ■, (■2=IP2). Output.

The average circuit 43 consists of a resistor 55 and a resistor 56 having the same resistance value, and has an average value (V, 10 V, . . .
)/2 is output as the average voltage VN.

Next, we will explain the operation of this embodiment configured in this way.
) 2.

First, the II standard pressure V a H in the first control circuit 41 of the oxygen level detection circuit is V a I=OlnV, and the II standard voltage V a 2 in the second control circuit 42 is V a I=OlnV.
When setting a2=500+nV, the first pump current supply circuit 4B has a voltage 'J s 1 or V s 1=
The first pump current II)+ such that V a ) = 0
is supplied to the first pump' city pole 21, and the second pump current supply circuit 52 has a voltage vS2 of V s 2 =V a 2
= 500mVIC, the second pump current IP2 is
is supplied to the pump electrode 24 of.

At this time, the oxygen partial pressure in the first space 17 is PL + the oxygen partial pressure in the second space 18 is P2 + the oxygen partial pressure in the gas to be measured is P
Assuming x, when the temperature is 1000 K, p(=Px,
P2ΣP x X 1. O-”=O.

Once, the 0 diffusion through the small holes of the partition plate 14
The quantity Q of 2 is Q”D (P+~
P2)...f3) = D (Px-0)...1 odor).

This amount Q of 02 is constantly determined by the first pump current IP
+ and second pump current TII;! Since the first pump current 1p+ and the second pump current 11'2 are proportional to IP! ""IP2"Kl 'Q=+ ・D−Px2 2・I"x・−・ku〈1). However, K, , , are constants.

In this equation -4), the first pump current ■1]1 and the second pump'l'II flow +112 are proportional to the oxygen content 11:i-''x in the gas to be measured. I understand.

That is, the first pump main flow IIM and the second pump current b
The value of ffi + P 2 represents the oxygen partial pressure (concentration) in the dregs to be measured.

Therefore, the control circuit 4 of the acid-Mj agricultural detection circuit 1
1 and 2nd control circuit 42 or I') Output electric current IIE
V+# and 2 correspond to the oxygen concentration in the sludge, respectively, and the average circuit 43 or +5 has a voltage V1,
■2-level averaging [Also, the average voltage according to the oxygen concentration\711
The output of J is 1゜ This is J, and the oxygen C agricultural detection circuit is outputted from the acid;
There is a small C in the diagram.

By the way, in this oxygen sensor 11, the small hole 19 of the partition plate 15, which is a step for restricting the diffusion of acid, does not come into contact with the scum 41.

Therefore, even if particles 1- such as carbon particles are included in the measurement waste, the particles 1- will not adhere to the small pores 1S, and the amount of diffused V elementary molecules will not change. , the oxygen concentration can be detected with high precision over a long period of time.

In the above embodiment, the oxygen partial pressure in the first space 17 is kept the same as the oxygen partial pressure in the scum to be measured, and the oxygen partial pressure in the second space 17 is
Approximately 1 / of the oxygen partial pressure of i1'l constant
Although the magnification was kept at IO'', it may be kept at other magnifications.

For example, the oxygen partial pressure in the first space 17 is maintained at twice the oxygen partial pressure of the gas to be measured, and the oxygen partial pressure in the second space 18 is maintained at 1/2 times the oxygen partial pressure of the gas to be measured. The oxygen concentration in the waste to be measured can be detected.

In other words, a current is supplied to the first solid electrolyte 12 to move oxygen ions, the oxygen concentration in the first space 17 is maintained at the first predetermined interval of the oxygen concentration of the waste to be measured, and the second solid electrolyte is 16 to move oxygen ions, keep the oxygen concentration in the second space 18 at a second predetermined times the oxygen concentration of the gas to be measured, and By detecting at least one of the currents supplied to d1, it is possible to detect the oxygen concentration of the scum to be subjected to d1.

FIG. 8 is a cross-sectional view showing another example of an oxygen sensor embodying the present invention.

This oxygen sensor 61 is constructed by laminating a partition plate 62 with one through hole 62a formed therein, and a first solid electrolyte 12 and a second solid electrolyte 16 sandwiching this partition plate 62, and is isolated from the surrounding waste. 1st. A common space 63 is formed in common with the second space, and this common space 63 is filled with a porous material 64 that restricts the diffusion of oxygen.

In this case, 1. Since the second space is a common space, there are no clear boundaries between the two, but in reality, the first
A portion of the porous body 64 near the reference electrode 22 forms a first space, a portion of the porous body 64 near the second reference electrode 25 forms a second space, and the porous body 64 in the vicinity of the second reference electrode 25 forms a second space. substance 6
4 forms a means for restricting oxygen diffusion.

The configuration of an oxygen detection circuit using this oxygen sensor 61 is as follows:
Since this embodiment is similar to the embodiment described above, the explanation will be omitted.

FIGS. 9 and 10 are cross-sectional views showing still other different examples of oxygen sensors embodying the present invention.

The oxygen sensor 71 shown in FIG.
A partition plate 16, a third solid electrolyte 72 having small holes 19 for restricting oxygen diffusion, a partition plate 15, and a second solid electrolyte 16 are laminated.

A first sensor electrode 20, a first pump electrode 21, and a first reference electrode 22 are provided on both sides of the first solid electrolyte 12, and a second sensor electrode 20, a first pump electrode 21, and a first reference electrode 22 are provided on both sides of the second solid electrolyte 16.
A pump electrode 24 is provided with a second reference electrode 25, and a third reference electrode 25 is provided.
A second sensor electrode 73 and a third reference electrode 74 are provided on both sides of the solid electrolyte 72 .

In this oxygen sensor 71, the difference between the oxygen partial pressure in the first space 17 and the oxygen partial pressure in the second space 18 is detected by the second sensor? ! ! The electrode 73 and the third group 7 (+8 electric current (CEF 4) are detected, and the second pump current flowing between the second pump electrode 24 and the second reference electrode 25 is controlled according to the detection result. to maintain the oxygen partial pressure in the second space 18 at a predetermined value.
Control of the oxygen partial pressure in the first space 17 is the same as in the above embodiment.

Next, the oxygen sensor 81 shown in FIG. 82. And t% to form a popular introduction space 8 to introduce the atmosphere! !
The solid electrolyte partition plate 82 formed with 82 b and the second solid type g! It is laminated with E91F+.

And the first solid electrolyte? (The first sensor electrode 20 and the first pump electrode 21 and the first base (1!
", lj pole 22 is provided, a second pump electrode 24 and a second base@pole 25 are provided on both sides of the second solid electrolyte τ16, and a second space 18 and an atmosphere introduction space 83 are provided. A second sensor electrode 84 and a third reference electrode 85 are provided on both sides of the partition wall of the partition plate 82 between the two.

In this oxygen sensor 81, the atmospheric oxygen partial pressure and the second
The difference between the oxygen partial pressure in the space 18 and the oxygen partial pressure in the space 18 is detected by the second sensor electrode 84 and the third reference electrode 85, and the difference between the second pump electrode 24 and the second reference @ pole 25 is detected according to the detection result. The oxygen partial pressure in the second space 18 is maintained at a predetermined times that of the atmosphere by controlling the second pump current flowing through the air. Note that the first space 17
The control of the oxygen partial pressure is the same as in the above embodiment.

In these oxygen sensors 71 and 81, the small hole 19, which is a means of restricting the diffusion of RF and elements, does not touch the 41! Can be detected.

In each of the embodiments described above, the positional relationship between the sensor electrode, the pump electrode, and the reference electrode may be reversed, or the sensor electrode and the reference electrode facing the pumps 7' and 474 may be separate.

In addition, by using the pump electrode and the sensor electrode in common, the electrode that supplies the pump current and the electric current Jf generated by the oxygen partial pressure ratio.
It can also be used as an electrode for detecting.

However, in this case, the voltage between the electrodes includes not only the voltage generated by the oxygen partial pressure ratio but also the voltage drop due to the internal resistance of the sensor, so the oxygen content between both sides of the solid electrolyte PAj is reduced. In order to accurately set the 1" standard voltage to keep the pressure ratio constant, is it necessary to compensate for the voltage drop due to this internal resistance?
As seen in Japanese Patent No. 92850, an alternating current is superimposed on the current flowing between the electrodes of the oxygen sensor, and the resistor 4 shown in FIG.
The DC component of the signal detected from both ends of 7゜53 is used as the IP detection signal, and the internal resistance is calculated from the AC component, and the voltage drop due to the internal resistance of the oxygen sensor is calculated by multiplying by l p detected by the DC component. , by adding this to obtain the target voltage, it is possible to continuously detect the air-fuel ratio with high precision as in the above-described embodiment.

As described above, according to the present invention, since the means for restricting the diffusion of scum in the oxygen sensor does not come into contact with the i(+1 constant gas), the oxygen concentration can be detected with high precision over a long period of time.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an example of a conventional oxygen sensor;
6 and 6 are diagrams showing the oxygen sensor output-air-fuel ratio characteristic and the injected current-air-fuel ratio characteristic for explaining the operation of FIG. 1. FIG. 4 and FIG. 5 show an embodiment of the present invention. A cross-sectional view and an exploded perspective view of the oxygen sensor; Fig. 6 is a circuit diagram showing an example of an oxygen concentration detection circuit using the oxygen sensor; Fig. 7 shows the output-oxygen concentration and air-fuel ratio characteristics. FIG. 8 is a cross-sectional view of an oxygen sensor showing another embodiment of the present invention; FIGS. 9 and 10 are cross-sectional views of an oxygen sensor showing still other different embodiments of the present invention. It is a diagram. 11.61, 71.81...Oxygen sensor 12...1st
solid? l! M quality 13.14, 15.62.72.82...Partition plate 16
-Second solid electrolyte 1-7...First space 18...Second space 1st...Small hole 20...First sensor electrode 21...First pump electrode 22...First 1 base $dent! i23...Second sensor electrode 24...Second pump electrode 25...Second reference electrode 66...Porous body first prisoner Figure 2 Air-fuel ratio (equivalence ratio λ) Figure 4 Figure 5 Figure 6 Figure 7 Air-fuel ratio (A/F) Figure 8 Figure 10

Claims (1)

[Claims] 1. If! The first one isolated from the constant dregs. forming a second space; means for restricting the diffusion of oxygen between the second spaces; A part or all of each of the partition walls separating the second space from the fixed dregs 41 is formed by dissolving an oxygen ion conductive solid 71, and opposing electrodes are provided on both sides of each solid electrolyte. An oxygen sensor characterized by: 2. The means for restricting oxygen diffusion is provided in the above-mentioned 1. The oxygen sensor according to claim 1, which is a small hole communicating with the second space. 3 1st. 2. The RJ61 elementary sensor according to claim 1, wherein the second space is a common space, and the means for restricting oxygen diffusion is a porous body filled in the common space.