JPS59148857A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To perform measurement nearly at a theoretical air-fuel ratio with good accuracy and to measure the concn. of O2 without influence of the temp. in the atmosphere to be measured by dividing the measuring electrode of a sensor to a measuring side current conducting electrode and a reference electrode, providing a diffusion layer on at least the current conducting electrode and enabling the drawing out of the potential between the reference electrode and a standard electrode. CONSTITUTION:An oxygen sensor 10 is constituted by forming successively a standard electrode 12, an oxygen ion conductive solid electrolyte 23 on a base plate 11 having a heating element 12, then dividing a measuring electrode to a measuring side current conducting electrode 24 and a reference electrode 25 and forming the same on the electrolyte 23. A diffusion layer 26 is then formed to cover only the electrode 24 or the reference electrode 25 as well and thereafter a protective layer 27 is provided. A power source conducts between the electrode 24 and a standard electrode 22, and a standard partial oxygen pressure is controlled to enable the drawing out of the potential between the electrode 25 and the electrode 22 to a differential amplifier 34. An oxygen sensor 10 which can detect an air-fuel ratio with good accuracy in a range of 450+ or -150 deg.C by decreasing the influence of the change in the temp. of the atmosphere to be measured at near around air-fuel ratio lambda=1.6 and can control the air-fuel ratio from the voltages of the electrode 25 and the electrode 22 at near lambda=1 by controlling the air-fuel ratio on the rich side at a high speed or accelerating is thus obtd. A considerable improvement in the fuel cost is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oxygen sensor suitable for detecting the oxygen concentration in an atmosphere to be measured, and in particular, the present invention relates to an oxygen sensor suitable for detecting the oxygen concentration in an atmosphere to be measured. This invention relates to an oxygen sensor suitable for controlling the air-fuel ratio.

Conventionally, this type of oxygen sensor has a structure shown in FIG. 1, for example. This oxygen sensor l has a heating element 2
A reference electrode 4, an oxygen ion conductive solid electrolyte 5. A measurement electrode 6° and a diffusion layer 7 are sequentially laminated. When detecting the oxygen concentration in the atmosphere to be measured using this oxygen sensor l, as shown in FIG. The oxygen partial pressure at the reference electrode 4 is controlled by causing the movement of oxygen ions, and the electromotive force (
The output voltage) was measured by the voltage measuring means 9 to detect the oxygen partial pressure at the measurement pole, that is, the oxygen concentration in the atmosphere to be measured. In this case, the pore volume of the diffusion layer 7 (cc/g
) is relatively large (for example, when it is 0.2 cc/g or more), oxygen molecules in the atmosphere to be measured easily reach the measurement electrode 6, so that the electromotive force (output voltage) is reduced to an air-fuel ratio of 14.
The pore volume of the diffusion layer 7 becomes smaller (for example, when the excess air ratio is around 1), it changes rapidly around 7 (i.e., when the excess air ratio is around 1).
．． 2 cc/g or less), the so-called diffusion limit behavior when oxygen molecules in the atmosphere to be measured reach the measurement electrode 6 increases, so the oxygen partial pressure at the measurement electrode becomes lower than the oxygen partial pressure in the atmosphere to be measured. and therefore the excess air side (λ
>1 side), the output voltage changes rapidly, and control on the lean burn side becomes possible.

However, in such a conventional oxygen sensor, the measurement electrode 6 has a structure that also serves as a current-carrying electrode, so there is a problem that the output fluctuates greatly due to temperature changes in the atmosphere to be measured, and the air-fuel ratio detection accuracy is poor. There was a point. To explain this more precisely, FIG. 3 shows the case where the excess air ratio is 1.
Layer 7 is placed in the expansion 11 so that the output voltage changes rapidly near 6.
FIG. 2 is a schematic diagram showing the output characteristics of an oxygen sensor in which the pore volume, sensor current, etc. of the oxygen sensor are determined, and the sensor output voltage differs depending on the gas temperature. In this case, when the air-fuel ratio control accuracy is set to 1.6±0.03, the exhaust gas VM degree must be within the range of 450'C±50°C. However, the exhaust gas temperature changes considerably depending on the startup or driving conditions, and it is desirable that the appropriate exhaust gas temperature be as wide as possible, but in the conventional case, as mentioned above, it is narrow, and the air-fuel ratio detection There was a problem that the accuracy was not good.

The present invention has been made by focusing on the conventional problems noted in L. It is an object of the present invention to provide an oxygen sensor that is less affected by output changes due to temperature changes in the atmosphere to be measured and that can accurately detect the air-fuel ratio. It is an object.

In this invention, a substrate, a reference electrode, an oxygen ion conductive solid electrolyte, and a measurement electrode are laminated, and current is passed between the reference electrode and measurement electrode to cause movement of oxygen ions within the solid electrolyte. In an oxygen sensor that controls partial pressure, the measuring electrode is divided into a measuring side advancing electrode and an A11l constant side reference electrode, and at least the measuring side advancing electrode has a diffusion layer that causes diffusion limit behavior of oxygen molecules in the atmosphere to be measured. and control the reference electrode oxygen partial pressure by supplying current between the reference electrode and the measurement side forwarding electrode, making it possible to take out the potential between the measurement side current electrode, the measurement side reference electrode, and the reference electrode. It is characterized by what it did.

Hereinafter, embodiments of the present invention will be described in more detail based on the drawings.

FIG. 4 and FIG. 5 are a schematic cross-sectional view and a manufacturing process explanatory diagram, respectively, of an oxygen sensor 10 in an embodiment of the present invention. To explain according to the diagram, one of the substrate materials 11a (for example, 8X10X0
．． 7t+nl11), a heating element 12 is printed and laminated in the shape shown by the dotted line in FIG.
5. Arrange 16. Next, four through holes (diameter 0.6 mm) 17, 18, 19. ．． 20 (for example, 8×10×0.7
'tmm) are laminated under pressure, and the through holes 17 and 18 are laminated under pressure.
, 19.20 and put platinum paste into the through holes 17, 18.1'-9, 20 and the single lead wires 13, 14, 1.
5.16 to enable electrical connection between (after firing)
(See FIG. 5(a)) The substrate 11 is manufactured. Note that both ends of the heating element 12 are connected to lead wires 13 at both ends.
16 can be connected. ζHere, the substrate 11
Although alumina green sheets are used as the IT materials 11a and 11b, other materials may be used as long as they are heat resistant and insulating, such as forsterite, steatite, mullite, spinel, etc. . Furthermore, in forming the heating element 12, a platinum paste made by kneading platinum powder and lacquer is used to laminate the heat generating element by printing, but other material having electronic conductivity such as platinum wire may also be embedded. You can. Furthermore, although platinum is used here as the material for the heating element 12, other materials may be used as long as they have electronic conductivity. Furthermore, the lead wire 13
, 14, 15, and 16 are made of corrosion-resistant platinum wire, but other materials may be used as long as they have electron conductivity. Next, if necessary, add 5 mol% Y2O3-95 mol% ZrO2 to the state shown in FIG. 5(a).
An intermediate layer is laminated by printing using a ceramic paste coated with lacquer and lacquer (not shown). This intermediate layer ensures adhesion strength between the substrate 11 and the reference electrode 22, which will be described later, and oxygen ions that are forcibly sent to the reference electrode 22 side become oxygen molecules at the base 1μ electrode 22, and some of these This is to prevent the solid electrolyte 23 (described later) from being destroyed by the pressure of the oxygen molecules accumulated in the reference electrode 22 by the oxygen molecules diffusing through the pores in the intermediate layer and escaping to the outside. Hoga Y203, ZrO2 stabilized with MgO, C, aO, etc., A text, 03. A ceramic paste obtained by kneading a lacquer with ceramics such as Mg0-A or OA can be used. Next, the reference electrode 22 is laminated on the top of the substrate 11 or on the middle layer by printing using a platinum paste made by kneading Pt powder and lacquer (fifth layer).
(See figure (b)). Note that at this time, a part of the reference electrode 22 is connected to the lead wire 14 via the through hole 18.

Further, as the material for the reference electrode 22, any material having electron conductivity may be used. In particular, platinum or an alloy containing platinum, which has a catalytic action and is corrosion resistant, may be used.

preferable. Furthermore, in order to increase the bonding strength between the substrate 11 or the intermediate layer and the solid electrolyte 23 (described later) and the reference electrode 22, it is also preferable to use cermet, which is a mixture of ceramics and metal, as the material for the reference electrode 22. . At this time, the metal is preferably the aforementioned platinum or an alloy containing platinum, and the ceramic is Z stabilized with Y203, Cao, MgO, etc., which is the same material as the solid electrolyte 23.
Suitable materials include rO2, alumina, mullite, and spinel. Next, 5 mol% Y2O3 was added to the state shown in Figure 5(b).
A solid electrolyte 23 is laminated by printing using a solid electrolyte/Ilf material paste in which 41 wires of -95 mol % ZrO2 holes and anchors are formed (see FIG. 5 (Q)). Here, as the material for the solid electrolyte 23, in addition to those mentioned above, a conventionally known solid electrolyte having oxygen ion conductivity may be used. Next, the measuring side reverse electrode 24 and the measuring side reference electrode 25 are laminated on the state shown in FIG. 5(C) by printing using the same platinum paste as the reference electrode material (see FIG. 5(d)).
. At this time, the - section of the measurement side reverse electrode 24 is connected to the lead wire 16 via the through hole 20, and the measurement side reference electrode 25 is connected to the lead wire 16 through the through hole 20.
A part of the lead wire 15 can be connected to the lead wire 15 via a through hole 19. Although the distance between the measurement side reverse electrode 24 and the measurement side reference electrode 25 cannot be determined clearly, for example,
It is preferable to set it to 0.2 to 1 mmW degrees. In this way, measurement electrodes up to 24.25 were stacked on substrate 1 (5th
(see Figure (d)) is fired at 1500° C. for 2 hours in an air atmosphere. Next, it is also desirable to ultrasonically wash the fired element in an organic solvent, dry it, and then form a second measurement electrode (not shown) on at least the measurement side advancing electrode 24 by PVD. By providing this second measurement electrode, the surface area of the electrode that comes into contact with the gas to be measured increases, and the three-phase interface where the gas to be measured, the electrode, and the solid electrolyte come into contact increases, so the response speed of the sensor element becomes faster.

Next, in the state shown in Fig. 5(d), an average particle size of 10 g was added.
c7) Using spinel (MgO-Al20s), a diffusion layer 26 is provided by plasma spraying. At this time, a diffusion layer is created using the plasma spraying method. In establishing 6,
Spraying distance: 10-15cm, spraying power: 12-50KW
Ar and He were used as the plasma generating gas, an internal powder supply device was used, and the number of rotations of the jig was 50-10 Or, p, m for picking up the element.

Under these conditions, the pore volume of the diffusion layer 26 is 0.2 cc/g or less, and the thickness of the diffusion layer 16 is 10 to 300 cc/g.
It is more desirable to make it so that it becomes gm. Here, it is preferable to use Mg0-AJ1203 spinel as the thermal spraying material, but other conventionally known ceramic materials may also be used. Further, when the diffusion layer 26 is provided under the above solvent conditions,
It has been confirmed that the durability against the gas to be measured, especially the exhaust gas from automobile internal combustion engines, is good, but thermal spraying is required to make the pore volume of the diffusion layer 26 0.01 to 0.2 cc/g under the above conditions. The average particle size of the material is lo~4゜7zm
It was found that it is best to use a powder that is In this embodiment, a plasma spraying method was used to provide the diffusion layer 26, but other methods such as a dipping method or a screen printing method may also be used. Finally, one side of the element is coated with spinel (M g O-A
The protective layer 27 was formed by thermal spraying 1 203 ).

Note that in the oxygen sensor 10 described in ]2, the substrate 11 is the structural base, but other structural bases may be used.
Further, a porous structural base made of the same material as the solid electrolyte 23 may be used, and appropriate modifications are possible.

Next, install the oxygen sensor 10 in Figure 6 and screen 7.
Using the connections shown in the figure, changes in output due to changes in air-fuel ratio were investigated. In addition, in FIG. 6 and FIG. 7, 31 is an external power supply for energizing, and 33 and 34 are differential amplifiers.

Among these, as shown in FIG. The output VR-E from the dynamic amplifier 33 corresponds to the curve VR-H in FIG.
become that way. Further, as shown in FIG. 7, the reference electrode 22
An external power supply 31 is connected between the current-carrying rod 24 and the reference electrode 2.
2 and the reference pole 25 are connected to the differential amplifier 34, the output VR-3 from the differential amplifier 34 becomes like the curve VR-3 in FIG.

Here, the reason why the curve VR-E shown in FIG. 8 is obtained is as follows.
Since the change in oxygen partial pressure Po2 on the lean side (in> l side) is small, the potential of the i-opening 25 hardly changes. Reference electrode 25 due to concentration depletion
The potential of the current-carrying rod 24 is as shown in FIG. 8. In this case, it should be noted that the curves vs-E and -[
When comparing the curve VRE shown in FIG. 2, only the output level differs in the region of input>1, and the abrupt turning point of the output hardly changes.

Moreover, the reason why the curve VR-5 shown in FIG. 8 is obtained is that the reference electrode oxygen partial pressure is kept constant by energization from the external power supply 31, but the oxygen partial pressure of the reference electrode 25 is lower than the stoichiometric air-fuel ratio. Since the potential of the reference electrode 22 with respect to the reference electrode 25 is taken as shown in FIG. 8, it changes rapidly at the boundary.

- On the other hand, when we investigated the influence of temperature changes on the output shown in the above curve, we found that curve Vpt-E is small and curve 1 is V R-H.
As shown in FIG.
．． In order to set the temperature to 03, the exhaust gas temperature must be 450℃±150℃.
It was confirmed that the virus spread to a range of ℃. Therefore, it is possible to accurately detect the oxygen concentration in a lean atmosphere over a wider temperature range than in the past.

Furthermore, in the oxygen sensor of the above embodiment, the curve VR-s may be used to detect the air-fuel ratio in the vicinity of ON=1. At this time, it is considered possible to use the curve VR-1: from Fig. 8, but ■Special measures are required to distinguish it from the sudden change in output at a lean air-fuel ratio, ■Response speed is the curve V R
- Since it is slightly slower than the case of S, the curve VR near input = 1
It is not a good idea to use -s for some reasons.

Next, the oxygen sensor O according to this embodiment is 7/<-
An example of a basic circuit when used in an air-fuel ratio detection system for combustion control of an engine is shown in Fig. 1θ. In the figure,
10 is an oxygen sensor, 31 is an external power supply, 32 is a Zener diode for voltage stabilization, 33.34 is a differential amplifier, 35 is an output selection circuit, 3G is an output selection Comparison of the output V from the I835 in Figure 1 and the reference voltage v5 and control signal output V. It is a comparator that generates In such a circuit, 1. During lean combustion control, the output of the differential amplifier 33 is used for control, and when engine output is required at high speed or acceleration, the air-fuel ratio moves to the rich side, and when the input value approaches 1, the output of the differential amplifier 34 increases. Since the signal becomes larger than a certain level, the output selection circuit 35 selects the output of the differential amplifier 34, which becomes the input of the comparator 36. therefore,
In such an air-fuel ratio detection system, an arbitrary lean combustion state (on>1) can be controlled by the sensor current, and the air-fuel ratio in the vicinity of on=1 can be controlled, so that fuel efficiency improves dramatically.

Figure f511 and Figure 12 are diagrams showing other embodiments of the present invention, and the oxygen sensor lO shown in Figure 11 has a measurement side reverse electrode 24 and a measurement side reference electrode 25 on a solid electrolyte 23.
The figure shows a case in which the diffusion layer 26 is provided only on the surface of the measurement side reverse electrode 24. In this case, since the measurement-side reference electrode 25 is not covered with the diffusion layer 26, there is an advantage that the potential change of the reference electrode 25 in response to an atmosphere change near input=1 can be made faster. ing. Further, the oxygen sensor 10 shown in FIG. 12 shows a case where an iU contact reference electrode 25 is formed on the substrate 11, and in this case as well, the potential change of the reference electrode 25 with respect to changes in the atmosphere can be made faster.

As explained above, according to the present invention, the substrate, the reference electrode, the oxygen ion conductive solid rut solute, and the measurement electrode are laminated, and current is passed between the reference electrode and the measurement electrode to generate the electrolyte in the solid electrolyte. The measurement electrode is divided into a measurement side counter electrode and a measurement side reference electrode by causing movement of oxygen ions, and at least the measurement side counter electrode is provided with a diffusion layer that causes diffusion limit behavior of oxygen molecules in the atmosphere to be measured. At the same time, current is applied between the reference electrode and the counter electrode on the measurement side to control the reference electrode oxygen partial pressure, and it is possible to take out the potential between the reference electrode on the measurement side and the reference electrode. It has many excellent effects, such as being less affected by changes in output due to temperature changes, being able to accurately detect the oxygen concentration in the atmosphere to be measured, and having a simple and robust structure.

[Brief explanation of the drawing]

ff11 is a schematic cross-sectional view of a conventional oxygen sensor, FIG. 2 is a wiring diagram of the oxygen sensor in FIG. 1, and FIG. 3 is a graph showing changes in output voltage characteristics due to changes in ambient temperature of the oxygen sensor in FIG. 1. FIG. 4 is a schematic cross-sectional view of an oxygen sensor according to an embodiment of the present invention, FIGS. Figure 7 is the wiring diagram for the oxygen sensor in Figure 5! Figure 88 is the first
Figure 9 is a graph showing the output voltage characteristics of the oxygen sensor shown in Figure 4, and Figure 9 is a graph showing changes in the output voltage characteristics due to atmospheric temperature changes at
Figure 0 is a wiring diagram showing a basic circuit example when the oxygen sensor in Figure 4 is used in an air-fuel ratio detection system, Figure 11 and Figure 1
2 are schematic cross-sectional views of oxygen sensors according to other embodiments of the present invention. DESCRIPTION OF SYMBOLS 10... Oxygen sensor, 11... Substrate, 22... Reference electrode, 23... Oxygen ion conductive solid electrolyte, 24...
... Measuring side reverse electrode, 25... Measuring side lock 1jlJ, pole,
'26... Diffusion layer, 31... External power supply. Fig. 1 Fig. 2 Air-to-air ratio (A/F) Fig. 4 2 Fig. 5 (a) (b) ((j' (-d) Fig. 6 Fig. 7/8 im Air overflow ratio ( χ) Figure 9 □" 5 4 "Sho 1)), 2 1 Figure 127 2

Claims (1)

[Claims] (1) A substrate, a reference electrode, an oxygen ion conductive solid electrolyte, and a measurement electrode are laminated, and electricity is applied between the reference electrode and measurement electrode to cause movement of oxygen ions within the solid electrolyte, and the oxygen ions are separated from the reference electrode. In an oxygen sensor that controls pressure, the measuring electrode is divided into a measuring electrode and a measuring side reference electrode, and at least the measuring electrode is provided with a diffusion layer that causes diffusion-limited behavior of oxygen molecules in the atmosphere to be measured. In addition, the oxygen sensor is characterized in that current is applied between the reference electrode and the measuring electrode to control the reference electrode oxygen partial pressure, thereby making it possible to take out the potential between the measuring side reference electrode and the reference electrode. .