JPS6130758A - Air/fuel ratio sensor - Google Patents

Abstract

PURPOSE:To simplify the construction, by arranging an oxygen sensor comprising a reference side first electrode, a measuring side second electrode and an oxygen ion conductive solid electrolyte and first and second oxygen pumps for controlling the concentration of oxygen of the first and second electrodes. CONSTITUTION:An oxygen sensor 25 is provided having a reference side first electrode 22 and a measuring side second electrode 23 as opposed to each other on the surface and back of an oxygen ion conductive solid electrolyte 24 respectively. A first oxygen pump 29 in which third and fourth electrodes 26 and 27 are provided on the surface and back of an oxygen ion conductive solid electrolyte 28 as opposed to each other is provided and an oxygen gas exhaust port 31 is provided in a spaced 30 defined while fifth and sixth electrodes 32 and 33 are provided on the surface and back of an oxygen ion conductive solid electrolyte 34 as opposed to each other and a second oxygen pump 36 having a combustion exhaust gas introduction port 35 formed at the center thereof 32 and 33 is provided to define a space 37. Moreover, a voltage measuring means 41 is connected between the electrodes 22 and 23, a first oxygen pump current source 42 between the electrodes 26 and 27 and a second oxygen pump current source 43 between the electrodes 32 and 33 to construct an air/fuel sensor 21.

Description

[Detailed Description of the Invention] (& Field of Industrial Application) This invention relates to an air-fuel ratio sensor used to detect the ratio of air to fuel based on the oxygen concentration in combustion exhaust gas. .

(Prior Art) Conventionally, there have been air-fuel ratio sensors of this type, such as those shown in FIGS. 8 and 9, for example.

That is, the air-fuel ratio sensor 1 shown in FIG.
1-, a first electrode 3 serving as an oxygen sensor and an oxygen pump;
and an oxygen ion conductive solid electrolyte 4 are sequentially laminated, and on top of the solid electrolyte 4, a second electrode 5 for an oxygen sensor and a third electrode 6 for an oxygen pump are arranged with the second electrode 5 sandwiched therebetween. A gas diffusion control layer 7 is laminated on the second electrode 5 and the third electrode 6, and a voltage measuring means 8 is connected between the first electrode 3 and the second electrode 5. 1st
It has a configuration in which a pump current source is connected between the electrode 3 and the third electrode 6.

In the air-fuel ratio sensor 1 having such a configuration, when no current is applied from the pump current source 2, the oxygen concentration in the combustion exhaust gas that reaches the second electrode 5 via the gas diffusion R-control N7 is A characteristic in which the output changes rapidly at the stoichiometric air-fuel ratio is obtained by the voltage measuring means 8. On the other hand, when a pump current is supplied from the pump current source 2 from the first electrode 3 to the third electrode 6 within the oxygen ion conductive solid electrolyte 4, oxygen is consumed at the third electrode 6. Therefore, the oxygen concentration in the combustion exhaust gas that passes through the gas diffusion control layer 7 and reaches the second electrode 5 is lower than the oxygen concentration in the actual combustion exhaust gas, so it is on the lean (excess air) side than the stoichiometric air-fuel ratio. The voltage measuring means 8 obtains a characteristic in which the output changes rapidly at .

Further, the air-fuel ratio sensor 11 shown in FIG. 9 has a first electrode 13 for an oxygen sensor and a second electrode 14 for an oxygen pump sandwiching the first electrode 13 stacked side by side on a substrate 12.
An oxygen ion conductive solid electrolyte 15 is stacked on the first electrode 13 and the second electrode 14, and a third electrode 16 for an oxygen pump is sandwiched between the third electrode 16 and the third electrode 16 on top of the solid electrolyte 15. A fourth electrode 17 for an oxygen sensor is stacked side by side, and a gas diffusion control layer 1 is formed on the third electrode 16 and the fourth electrode 17.
A voltage measuring means 12 is connected between the oxygen sensor first electrode 13 and the fourth electrode 17, and a pump current is connected between the oxygen pump second electrode 14 and the third electrode 16. It has a configuration in which a power source 20 is connected (Japanese Patent Laid-Open No. 56-14.534-2).

Similarly to the air-fuel ratio sensor 1 described above, the air-fuel ratio sensor 11 having such a configuration also has the characteristic that the output changes rapidly at the stoichiometric air-fuel ratio when no pump current is applied. from the second electrode 14 to the third electrode 16
By flowing the pump current towards the lean side (excess air), a characteristic can be obtained in which the output changes rapidly on the lean (excess air) side.

However, such conventional air-fuel ratio sensor 1.11
So, is the problem that the oxygen concentration of the oxygen sensor reference electrode 3°13 is difficult to increase because the oxygen sensor electrode 5, 13.17 and the oxygen pump electrode 6, 14.16 are too close? there were. Further, the second electrode 5 and the fourth electrode 17, which are measurement electrodes for the oxygen sensor, cause the generation of Co and H2 near the oxygen pump electrodes 6 and 16, and the first electrode 3. There was also the problem that sufficient output characteristics could not be obtained when affected by 02 flare-up occurring in the oxygen pump mold electrode 14.

(Object of the Invention) The present invention was made by focusing on the above-mentioned problems of the conventional art. By doing so, it is possible to always maintain a stable and high oxygen concentration at the reference electrode, and there is no need to introduce atmospheric air from the outside, so the structure can be simplified, and the generation of C0IH2 at the measurement electrode is possible. Yao2
The purpose is to obtain stable mm force characteristics without being affected by flailing, etc.

(Structure of the Invention) The air-fuel ratio sensor according to the present invention includes an oxygen sensor including a pair of a first electrode on the reference side, a second electrode on the measurement side, and an oxygen ion conductive solid electrolyte, and an oxygen concentration sensor in the first electrode on the reference side. a first oxygen pump consisting of a pair of third and fourth electrodes that control the oxygen ion conductive solid electrolyte; a pair of fifth and sixth electrodes that control the oxygen concentration of the second electrode on the measurement side; In the air-fuel ratio sensor according to the present invention, the material and forming method of the electrodes constituting the oxygen sensor and the oxygen pump are not particularly limited. First, it is possible to select from conventional electrode materials 4 and forming means. Further, the oxygen ion conductive solid electrolyte constituting the oxygen sensor and the oxygen pump can be constructed as an integral structure or as separate structures. Furthermore, the material and formation method of this oxygen ion conductive solid electrolyte are not particularly limited. Furthermore, this oxygen ion conductive solid electrolyte may be used as a structural base, or a separate structural base may be provided. Furthermore, it is also desirable to provide a heating element if necessary.

(Embodiment) FIG. 1 is a schematic cross-sectional view of an air-fuel ratio sensor according to an embodiment of the present invention. A pair of third electrodes 26 and A first oxygen pump 22 is provided in which a fourth electrode 27 is formed I7 facing the front and back surfaces of an oxygen ion conductive solid electrolyte 28, and a space 30 is formed between the oxygen sensor 25 and the first oxygen pump 22. , an oxygen gas discharge 1'' 31 is formed in a part of this space 30, and a pair of fifth electrodes 3 are arranged at a distance on the measuring side second electrode 23 side of the oxygen sensor 25.
28, the sixth electrode 33 is an oxygen ion conductive solid electrolyte 3
Between the oxygen sensor 25 and the second oxygen pump 36, a second oxygen pump 36 is provided opposite to each other on the front and back surfaces of the oxygen sensor 25 and has a combustion exhaust gas introduction port 35 formed in the center of the electrode 32, 33. A space 37 is formed in the oxygen sensor 2.
At the same time, the voltage measuring means 41 is connected between the first electrode 22 and the second electrode 23 of the first oxygen pump 22, and the first oxygen pump is connected between the third electrode 26 of the first butyric pump 22 and the fourth electrode 8i27. The second oxygen pump current source 4z is connected between the fifth electrode 32 and the sixth electrode 33 of the second oxygen pump 36.

FIG. 2 is an exploded explanatory diagram showing the manufacturing procedure of the air-fuel ratio sensor 21 shown in FIG.
Ceramic grease consisting of O3-95 mol% ZrO2
Cut out from the sheet and prepare. This solid electrolyte 28
A rectangular groove-shaped space 30 is formed therein, and a groove-shaped butylene gas (discharge I) 31 is also formed.

Then, on the back surface of the solid electrolyte 28, a third electrode 26 for an oxygen pump is laminated using, for example, platinum paste and dried.
Similarly, a fourth electrode 27 for an oxygen pump is laminated on the bottom surface of the substrate 0 using platinum paste and dried. At this time, one-year lead portions 26a and 27a are formed on both electrodes 26 and 27.

Further, the oxygen ion conductive solid electrolyte 24 constituting the oxygen sensor 25 may be made of, for example, 5 mol% y2o3-95 mol% Zr.
Cut from 1 rune sheet of ceramic gel made of O2 (1
Remove and prepare. This solid electrolyte 24 has a rectangular spiral space 37 formed therein. Then, the solid electrolyte 2
The first electrode 22 for the oxygen sensor is laminated on the back side of the solid electrolyte 2 using, for example, platinum paste and dried.
The second electrode 23 for the oxygen sensor is laminated on the upper surface of the electrode 4 and the bottom surface of the space 37 using platinum paste, and then dried. At this time, the lead portion 22 is attached to both electrodes 22 and 23.
a, 23a is formed in advance. Then, the solid electrolyte 2 for the oxygen sensor is overlapped on a part of the solid electrolyte 28 for the oxygen pump. At this time, the ends of the lead wires 52, 57 connected to the respective lead parts 22a, 27a are inserted between the two Ryogoku body electric cables M 24, 28. In addition, the reed part 26
The tip of the lead wire 56 is attached to a.

Further, an oxygen ion conductive solid electrolyte 34 constituting the second oxygen pump 36 is prepared by cutting out a ceramic green sheet made of, for example, 5 mol % Y and 03-95 mol % ZrO. This solid electrolyte 34 is provided with a small hole 35b for forming an exhaust gas introduction hole 35. Then, on the back side of the solid electrolyte 34, for example, using platinum paste, the fifth electrode 32 for the oxygen pump is laminated and dried, and on the top side of the solid electrolyte 34, platinum paste is also used to layer the fifth electrode 32 for oxygen pumping. The sixth pump electrode 33 is stacked and dried. At this time, small holes 35a and 35C for forming the exhaust gas introduction hole 35 are provided in both electrodes 32 and 33 at the same position as the small hole 35b, and lead portions 32a and 3
Form 3a. Then, the solid electrolyte 34 for the oxygen pump is placed on top of the solid electrolyte 24 for the oxygen sensor.

At this time, between the Ryogokutai electrolytes 24 and 34, the lead wires 53 and 62 connected to the respective reed parts 23a and 32a are connected.
Insert the tip of the saw. Furthermore, the tip of the lead wire 63 is attached to the lead portion 33a.

Thereafter, the laminate is fired under appropriate hot air conditions. Note that a porous protective layer may be provided if necessary.

FIG. 3 is a diagram showing an example of wiring in the air-fuel ratio sensor 21 shown in FIG.
Lead wires 56 and 57 are connected between the fourth electrode and 27, respectively.
A constant current source 42 for the first oxygen pump is connected through the oxygen sensor 25, and a voltage measuring means 41 is connected between the first electrode 22 and the second electrode 23 of the oxygen sensor 25 through lead wires 52 and 53, respectively. , a second oxygen pump variable current source 43 and a resistor 44 are connected between the fifth electrode 32 and the sixth electrode 33 of the second oxygen pump 36 via lead wires 62 and 63, respectively.

When detecting the air-fuel ratio based on the oxygen concentration in the combustion exhaust gas using the air-fuel ratio sensor 21 having such a configuration, a current is supplied from the first oxygen pump constant current source 42 to the oxygen ion conductive solid. A constant current is passed from the fourth electrode 27 to the third electrode 26 within the electrolyte 28 . Therefore, oxygen ions move from the third electrode ai2.6 toward the fourth electrode 27, and oxygen is generated at the fourth electrode 27, resulting in a high oxygen concentration state in the space 30, and excess oxygen gas is exhausted. Exit 31
Therefore, the oxygen concentration in the space 30 is maintained almost constant at a high level, and the first electrode 22 of the oxygen sensor 25
The oxygen concentration is also maintained at a high level. On the other hand, the second electrode 23 of the oxygen sensor 25 comes into contact with the combustion gas that has flowed into the space 37 through the combustion gas inlet 35, and corresponds to the difference between the oxygen concentration in the combustion exhaust gas and the oxygen concentration at the first electrode 22. The resulting output is measured by the voltage measuring means 41.

On the other hand, when changing the current value from the second oxygen pump variable current source 43 so that the output of the oxygen sensor 25 measured by the voltage measuring means 41 is constant, for example, In a lean atmosphere with a high butyric concentration, more current flows from the sixth electrode 33 to the fifth electrode 32 in the solid electrolyte 34 in the second oxygen pump 36 in order to keep the output of the oxygen sensor 25 constant. On the other hand, in a rich atmosphere where the oxygen concentration in the combustion exhaust gas is low, in order to keep the output of the oxygen sensor 25 constant, the fifth electrode 32 to the sixth electrode are It is necessary to send more current toward 33. In this way, the current of the second oxygen pump variable current source 3 that is supplied to the second oxygen pump 36 changes linearly in accordance with the change in the equivalence ratio of the combustion exhaust gas, and therefore, as shown in FIG. The potential voltage (2) at both ends of the resistor 44 also changes linearly, resulting in the characteristics shown in FIG.

A specific circuit for obtaining the characteristics shown in Figure 4 is shown in Figure 5.
As shown in the figure. That is, as shown in FIG. 5, the first electrode 22 constituting the oxygen sensor 25 is input to one end of the differential amplifier 46 via the resistor R1, and the second electrode 23 is grounded. Further, a reference voltage from a reference voltage generator 47 is inputted to the other end of the differential amplifier 46, and the output side of the differential amplifier 46 is connected to the sixth electrode 63 constituting the second oxygen pump 36 via a resistor R2. The fifth electrode 32 is connected to a terminal IP connected to pump current detection means (not shown) and grounded via a resistor R3.

In such a circuit configuration, for example, when the gas to be measured is in a lean state (excess air), the oxygen sensor 25
Since the output from the differential amplifier 46 becomes smaller than the reference voltage, the output of the differential amplifier 46 becomes large on the positive side, and the voltage from the sixth electrode 33 to the fifth electrode becomes smaller than the reference voltage.
The pump current flowing to the electrode 32 increases. Conversely,
When the measured gas is rich (excess fuel),
Since the output of the oxygen sensor 25 becomes larger than the reference voltage, the output of the differential amplifier 46 increases to the negative side, and the pump current flowing from the fifth electrode 32 to the sixth electrode 33 increases, as shown in FIG. The pump current characteristics will be as shown. Accordingly, this determines how rich, stoichiometric, or lean the atmosphere to be measured is, and controls, for example, the amount of fuel injected from the fuel injection valve.

FIG. 6 is a schematic cross-sectional view of an air-fuel ratio sensor according to another embodiment of the present invention, in which a pair of reference-side first electrode 22 and measurement-side second electrode 23 are connected to oxygen ions. An oxygen sensor 25 is provided to face the front and back surfaces of the conductive solid electrolyte 24, and a pair of third electrodes 26 are provided at a distance from each other on the reference side first electrode 22 side of the oxygen sensor 25.
and the fourth electrode 27 is an oxygen ion conductive solid electrolyte 28.
A first oxygen pump 29 is provided to face the front and back surfaces of the oxygen sensor 25 and the first oxygen pump 22, and a 1'FIII 30 is formed between the oxygen sensor 25 and the first oxygen pump 22, and a part of this space 30 is filled with oxygen gas exhaust. A porous gas diffusion layer 77 that forms the outlet 31 and also forms a microspace 37 is laminated on two sides of the measurement side second electrode 23 of the oxygen sensor 25, and on the second side of this gas diffusion layer 77, A pair of fifth electrode 32 and sixth electrode 3
A second oxygen pump 36 is provided, and a voltage measuring means 41 is provided between the first electrode 22 and the second electrode 23 of the oxygen sensor 25. At the same time, a current source 42 for the first butyric pump is connected between the third electrode 26 and the fourth electrode 27 of the first oxygen pump 22 , and the fifth electrode 32 of the second oxygen pump 36 is connected.
and the sixth electrode 33, a second butyric pump current s, 43
It has a configuration in which the two are connected.

In this way, even when the space 37 is formed from a microspace made of the porous gas diffusion layer 77, characteristics similar to those of the air-fuel ratio sensor 21 shown in FIG. 1 can be obtained.

FIG. 7 is a schematic cross-sectional view of an air-fuel ratio sensor according to still another embodiment of the present invention. 24, a reference side $1 electrode 22 is formed on the solid electrolyte 24 facing one space 30, and
A measurement-side second electrode 23 is formed on the solid electrolyte 24 facing the other space 37, and the first electrode 22, the second electrode 23, and the solid electrolyte 24 constitute the oxygen sensor 25, and the oxygen sensor 25 is formed in the solid electrolyte 24 facing the other space 37. A fourth electrode 27 for the first oxygen pump is formed on the solid electrolyte 24 facing the solid electrolyte 30, and a third electrode 26 is formed on the opposite side of the solid electrolyte 24 facing the fourth electrode 27. The first oxygen pump 22 is composed of the third electrode 26, the fourth electrode 27, and the solid electrolyte 24, and the solid electrolyte 24 is formed with an oxygen scum discharge port 31 for discharging the oxygen gas in the space 30. A fifth electrode 32 for the second oxygen pump is formed on the solid electrolyte 24 facing the space 37, and a sixth electrode 33 is formed on the opposite side of the solid electrolyte 24, facing the fifth electrode 32. A second oxygen pump 36 is formed by the fifth electrode 32, the solid electrolyte 24, and the sixth electrode 33.
A voltage measuring means 41 is connected between the first electrode 22 and the second electrode 23 of the oxygen sensor 25, and a voltage measuring means 41 is connected between the third electrode 26 and the fourth electrode 27 of the first oxygen pump 29. A current source 42 for the first oxygen pump is connected, and a current source 43 for the second oxygen pump is connected between the fifth electrode 32 and the sixth electrode 33 of the second oxygen pump 36.

In the air-fuel ratio sensor 81 having such a configuration as well, the first oxygen pump 29 operates in the space 30, that is, the oxygen sensor 2
The oxygen concentration of the reference side first electrode 22 of the oxygen sensor 25 is controlled to be constant, and the measurement side second electrode of the oxygen sensor 25 is controlled by the second oxygen pump 36.
If the pump current is controlled so that the oxygen concentration of the electrode 23 is constant, the pump current of the second oxygen pump 36 changes almost linearly with respect to the change in the equivalence ratio of the combustion exhaust gas, as in the previous embodiment, The air-fuel ratio can be detected by this pump current.

(Effects of the Invention) As described above, according to the present invention, there is provided an oxygen sensor including a pair of reference-side first electrodes, a measurement-side t52 electrode, and an oxygen ion-conducting solid electrolyte;
A first oxygen pump comprising a pair of third and fourth electrodes that control the oxygen concentration of the electrodes and an oxygen ion conductive solid electrolyte, a pair of fifth electrodes that control the oxygen concentration of the measurement side second electrode, and Since the configuration includes the sixth electrode and the second oxygen pump consisting of the oxygen ion conductive solid electrolyte, the first oxygen pump is used to connect the first oxygen sensor to the reference side.
! It is possible to control the oxygen concentration of the electrode, and at the same time, it is possible to control the oxygen concentration of the second electrode on the measurement side of the oxygen sensor with the second oxygen pump, and the oxygen concentration of the first electrode on the reference side of the oxygen sensor. Since it is not necessary to control the oxygen concentration to a constant level by introducing atmospheric air, the configuration including the sensor holder etc. can be made extremely simple. By detecting the pump current from the second oxygen pump, it is possible to detect a wide range of air-fuel ratios from the rich side with excess fuel to the lean side with excess air, and the flow mechanism of oxygen ions and oxygen gas can be detected. Because it is simple, sensor design is easy, and the measuring electrode that makes up the oxygen sensor is made of Co,
Since it is not affected by the occurrence of H2 or the flare-up of 02, it has the advantage of being able to obtain excellent output characteristics.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an air-fuel ratio sensor according to an embodiment of the present invention, FIG. 2 is an exploded perspective view showing the procedure for manufacturing the air-fuel ratio sensor of FIG. 1, and FIG. Fig. 4 is an explanatory diagram showing an example of the connection of the air-fuel ratio sensor shown in Fig. 4. Fig. 4 is an explanatory diagram showing the output change with respect to the equivalence ratio change obtained by the wiring diagram in Fig. 3. Fig. 5 is a specific circuit diagram of the wiring diagram in Fig. 3. FIG. 6 and FIG. 7 are both schematic cross-sectional diagrams of an air-fuel ratio sensor according to another embodiment of the present invention, and FIGS. 8 and 9 are each a model of a conventional air-fuel ratio sensor. FIG. 21.71.81...Air-fuel ratio sensor, 22...First
Electrode, 23... Second electrode, 24... Oxygen ion conductive solid electrolyte, 25... Oxygen sensor, 26... Third electrode, 27... Fourth electrode, 28... Oxygen ion Conductive solid electrolyte, 22... First oxygen pump, 30.37... Space, 32... Fifth electrode, 33... Sixth electrode, 34... Oxygen ion conductive solid electrolyte, 36 ...Second oxygen pump, 41...Voltage measuring means, 42...Current source for first oxygen pump, 43...Current source for second oxygen pump, 77...Porous gas diffusion layer. Figure 1 King Figure 2 Italy Figure 8 Figure 9

Claims (1)

[Claims] (1) An oxygen sensor consisting of a pair of reference-side first electrodes, a measurement-side second electrode, and an oxygen ion-conducting solid electrolyte, and a pair of third and fourth electrodes that control the oxygen concentration of the reference-side first electrodes. a first oxygen pump consisting of an electrode and an oxygen ion conductive solid electrolyte; and a second oxygen pump consisting of a pair of fifth and sixth electrodes that control the oxygen concentration of the measurement side second electrode and an oxygen ion conductive solid electrolyte. An air-fuel ratio sensor characterized by comprising an oxygen pump.