JPH05203618A - Air-fuel ratio sensor - Google Patents

Abstract

(57) [Summary] [Purpose] To accurately detect the air-fuel ratio even in the combustion state where the oxygen partial pressure is low near the theoretical air-fuel ratio. [Structure] The second oxygen ion conductor 8 is fired into a porous structure so as to form a small hole as an outflow passage that connects the measurement electrode 9 and the reference electrode 10. Then, the oxygen in the diffusion chamber 13 that is in contact with the measurement electrode 9 is
The electrons are given to be ionized by, and are sequentially transported to the reference electrode 10 side through the oxygen defects in the second oxygen ion conductor 8, and the electrons are deprived by the reference electrode 10 to become oxygen molecules. The oxygen ion conductor 8 is returned into the diffusion chamber 13 through the small holes. This ensures a higher oxygen partial pressure on the reference electrode 10 side than in the diffusion chamber 13, and
The oxygen partial pressure in the diffusion chamber 13 becomes substantially equal to the actual oxygen partial pressure of the exhaust gas G.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio sensor which is provided in, for example, an automobile engine and is suitable for detecting an air-fuel ratio in a fluid to be measured such as exhaust gas.

[0002]

2. Description of the Related Art Generally, an air-fuel ratio sensor for detecting an air-fuel ratio in a fluid to be measured such as exhaust gas detects an oxygen concentration in the exhaust gas and uses a zirconia-type oxygen sensor. There is known one using an electrochemical device as disclosed in Japanese Laid-Open Patent Publication No. 62-214347.

Among these types of air-fuel ratio sensors, the latter one disclosed in Japanese Patent Laid-Open No. 62-214347 discloses a first oxygen ion conductor formed in a plate shape from a solid electrolyte and the first oxygen ion conductor. One side electrode provided on one surface side of the oxygen ion conductor, another side electrode provided on the other surface side of the first oxygen ion conductor facing the one side electrode, and the other side electrode A second oxygen ion conductor which is provided facing each other and is formed in a plate shape from a solid electrolyte, a measurement electrode which is provided on one surface side of the second oxygen ion conductor, and which faces the measurement electrode. A reference electrode provided on the other surface side of the second oxygen ion conductor, and a reference electrode provided between the other side electrode and the measurement electrode, and diffuses the fluid to be measured that has flowed in from the outside through the flow hole. A diffusion chamber and a current is supplied from the reference electrode to the measurement electrode, A DC power supply for ionizing oxygen in the measurement fluid at the measurement electrode and transporting it to the reference electrode side was compared with the voltage generated between the measurement electrode and the reference electrode and the reference voltage, and the difference between them was determined. A comparison supply means for supplying a pump current to the one-side electrode or the other-side electrode and another surface side of the reference electrode for accommodating oxygen generated on the reference electrode side to secure a predetermined oxygen partial pressure. It consists of an oxygen storage unit.

In this type of air-fuel ratio sensor, oxygen in the fluid to be measured, which has flowed into the diffusion chamber, is ionized at the measuring electrode by the current from the DC power source, and then is standardized via the second oxygen ion conductor. The oxygen is transported to the electrode side, and electrons (oxygen molecules) are taken from the oxygen ions at the reference electrode to form oxygen (oxygen molecule). This oxygen is stored in the oxygen storage part, and the oxygen partial pressure (oxygen (Concentration) is secured. As a result, a voltage corresponding to the difference between the oxygen partial pressure in the diffusion chamber and the oxygen partial pressure in the oxygen storage portion is generated between the measurement electrode and the reference electrode, and the comparison supply unit generates the voltage and the reference voltage. Compare
A pump current according to the difference between the two is supplied from one electrode to the other electrode.

Oxygen in the fluid to be measured is ionized by the other side electrode by this pump current, and then is transported to the one side electrode through the first oxygen ion conductor, and electrons are transferred by the one side electrode. Are depleted and become oxygen molecules, which are discharged into the external fluid to be measured. When the pump current is negative, oxygen ionized at one electrode is transported to the other electrode and discharged from the other electrode into the diffusion chamber. Therefore,
By measuring the direction and magnitude of the pump current supplied from the comparison supply means, the oxygen concentration of the fluid to be measured can be detected and the air-fuel ratio can be known.

[0006]

By the way, in the air-fuel ratio sensor according to the above-mentioned prior art, oxygen in the fluid to be measured, which has flowed into the diffusion chamber, is transported from the measurement electrode to the reference electrode by the oxygen pump action, and the oxygen containing portion is supplied. The oxygen partial pressure is higher on the reference electrode side than on the measurement electrode side. However, in the combustion state near the stoichiometric air-fuel ratio, the oxygen partial pressure in the measured fluid is inherently low.Therefore, oxygen transport from the measurement electrode to the reference electrode causes the oxygen partial pressure in the diffusion chamber to decrease in the actual measured fluid. Will be lower than the oxygen partial pressure of.

Therefore, in the above-mentioned prior art, in the combustion state near the stoichiometric air-fuel ratio, an error occurs in the voltage generated between the measurement electrode and the reference electrode, so that the oxygen concentration detected by the comparison supply means is detected. The pump current as a signal also fluctuates in the vicinity of the theoretical air-fuel ratio, as shown by the chain double-dashed line in FIG. 6, and the air-fuel ratio cannot be accurately detected, resulting in a significant decrease in reliability. is there.

The present invention has been made in view of the above-mentioned problems of the prior art, and has made it possible to accurately detect the air-fuel ratio of a fluid to be measured even in a combustion state near a stoichiometric air-fuel ratio where the oxygen partial pressure is low. An object is to provide an air-fuel ratio sensor.

[0009]

In order to solve the above-mentioned problems, the structure adopted by the present invention is a first oxygen ion conductor formed in a plate shape from a solid electrolyte, and the first oxygen ion conduction member. One side electrode provided on one side of the body, another side electrode provided on the other side of the first oxygen ion conductor facing the one side electrode, and facing the other side electrode Is provided,
A second oxygen ion conductor formed in a plate shape from a solid electrolyte, a measurement electrode provided on one surface side of the second oxygen ion conductor, and the second oxygen ion facing the measurement electrode. A reference electrode provided on the other surface side of the conductor, a diffusion chamber provided between the other-side electrode and the measurement electrode, for diffusing a fluid to be measured that has flowed in from the outside through a flow hole, and the reference A current is supplied from an electrode to the measurement electrode, and a DC power supply that ionizes oxygen in the fluid to be measured at the measurement electrode and transports it to the reference electrode side is generated between the measurement electrode and the reference electrode. It comprises a comparison supply means for comparing the voltage with the reference voltage and supplying a pump current according to the difference between the voltage and the reference voltage to the one side electrode or the other side electrode.

The feature of the constitution adopted by the present invention to solve the problem is that the second oxygen ion conductor is
An outflow passage is formed to allow oxygen generated on the reference electrode side to flow out into the diffusion chamber.

[0011]

The oxygen ions in the fluid to be measured transported from the measurement electrode to the reference electrode via the second oxygen ion conductor are deprived of electrons by the reference electrode to become oxygen molecules, and then pass through the outflow passage. Flows out into the diffusion chamber and is returned to the fluid to be measured.
This makes it possible to prevent the oxygen partial pressure in the fluid to be measured from decreasing while ensuring a higher oxygen partial pressure on the reference electrode side than on the measuring electrode side.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 5 by taking as an example the case where it is used for detecting an air-fuel ratio of an automobile engine.

First, FIGS. 1 to 3 show a first embodiment of the present invention.

In the figure, reference numeral 1 denotes a sensor main body which is provided in the middle of an exhaust pipe (not shown) and constitutes an air-fuel ratio sensor together with an electric circuit composed of a differential amplifier 23 and the like, which will be described later. The oxygen pump section 2, the sensor section 7, which will be described later,
It is composed of a heater section 16.

Reference numeral 2 denotes an oxygen pump portion. The oxygen pump portion 2 comprises a first oxygen ion conductor 3 formed from a solid electrolyte such as zirconia in the form of a long flat plate, and the first oxygen ion conductor 3. One side electrode 4 provided on one surface side (upper side in the figure) of the body 3 and provided on the other surface side of the first oxygen ion conductor 3 facing the one side electrode 4 and the one side electrode 4. , The other side electrode 5 formed of platinum or the like, and one surface side of the one side electrode 4 is covered with a protective layer 6 made of a ceramic material such as alumina, so that the exhaust gas G as a fluid to be measured is covered. It is not exposed directly. The one side electrode 4 and the other side electrode 5 are connected to a differential amplifier 23 and the like. Then, the oxygen pump unit 2 includes a differential amplifier 2
When the pump current Ip from 3 is supplied from the one-side electrode 4 to the other-side electrode 5, the exhaust gas G contacting the other-side electrode 5
After giving an electron to the oxygen in it to ionize it, the oxygen ion (adsorbed oxygen ion) is transported to the one-side electrode 4 via the oxygen defect in the first oxygen ion conductor 3, whereby the one-side electrode 4 is transported. At the electrode 4, the electrons of oxygen ions are deprived to oxygen molecules,
It is released into the exhaust pipe. When the pump current Ip is supplied from the other side electrode 5 to the one side electrode 4, the oxygen pump section 2 transports oxygen ionized in the one side electrode 4 to the other side electrode 5 side. ..

Reference numeral 7 denotes a sensor portion provided so as to face the oxygen pump portion 2, and the sensor portion 7 includes a second oxygen ion conductor 8 formed in a disk shape from a solid electrolyte such as zirconia. A measurement electrode 9 provided on one surface side of the second oxygen ion conductor 8 and made of platinum or the like, and the measurement electrode 9
Is provided on the other surface side of the second oxygen ion conductor 8 so as to face with the reference electrode 10 made of platinum or the like. The electrodes 9 and 10 are connected to a differential amplifier 23, a DC power supply 21 described later, and the like. Here, the second oxygen ion conductor 8 is formed into a porous body by firing zirconia having a large particle size, and as a result, the second oxygen ion conductor 8 serves as a large number of outflow paths communicating between the measurement electrode 9 and the reference electrode 10. Of small holes (not shown) are formed. Then, the sensor unit 7 is operated by the current from the DC power source 21 to measure the measuring electrode 9
Oxygen ions are transported to the reference electrode 10 from the reference electrode 10, and a voltage signal corresponding to the difference between the oxygen partial pressure in the diffusion chamber 13 and the oxygen partial pressure on the reference electrode 10 side, which will be described later, is generated on the reference electrode 10 side. The signal is output to the differential amplifier 23.

Reference numeral 11 denotes a spacer (only shown in FIG. 1) provided between the oxygen pump portion 2 and the sensor portion 7, and an insulating film 12 is provided on one surface side of the spacer 11. 1
Reference numeral 3 denotes a circular diffusion chamber formed in the spacer 11, and the diffusion chamber 13 has an organic film 14 made of, for example, carbon or phenol resin as shown in FIG.
It is formed by stacking between the measurement electrode 9 and the measurement electrode 9 and then burning out when firing the element. Further, the diffusion chamber 13 communicates with the inside of the exhaust pipe through a circulation hole 15 penetrating from the oxygen pump portion 2 to the heater portion 16 via the sensor portion 7, and the circulation hole 15
The exhaust gas G flowing in from is diffused and brought into contact with the other electrode 5 and the measurement electrode 9.

Reference numeral 16 denotes a heater portion provided on the other surface side of the sensor portion 7. The heater portion 16 is a one-side heater substrate 17 formed in a flat plate shape from a solid electrolyte such as zirconia.
The other side heater substrate 18 and a heater wire 20 provided between the heater substrates 17 and 18 and covered with insulating films 19 and 19 are formed. Then, the heater section 16
Is for heating the sensor unit 7 to, for example, about 700 to 800 ° C. when a current is supplied from a heater power source (not shown).

Reference numeral 21 denotes a DC power source provided outside the sensor unit 7. The DC power source 21 has its positive side connected to the reference electrode 10 and the differential amplifier 23 via a voltage dividing resistor 22, and at the same time. The minus side is connected to the measurement electrode 9 and a reference power supply 24 described later. Then, the DC power supply 21 causes the oxygen in the exhaust gas G ionized at the measurement electrode 9 to be transported to the reference electrode 10 side by passing a current from the reference electrode 10 toward the measurement electrode 9.

Reference numeral 23 denotes a differential amplifier as comparison and supply means. The differential amplifier 23 has a negative side input terminal to which the DC power source 21 and the reference electrode 10 are connected, and a positive side input terminal side to which a reference power source 24 is connected. In addition to being connected, the output side is connected to the one-side electrode 4 via the voltage detecting resistor 25. Then, the differential amplifier 23 compares the voltage generated between the measurement electrode 9 and the reference electrode 10 with the reference voltage of the reference power source 24, and thereby the pump current Ip (oxygen concentration detection) according to the difference between the two. Signal) is supplied from the one-side electrode 4 to the other-side electrode 5.

The air-fuel ratio sensor according to this embodiment has the above-mentioned structure. Next, a method for manufacturing the sensor body 1 will be described with reference to FIG.

First, the electrodes 4 and 5 are formed on one surface side and the other surface side of the first oxygen ion conductor 3 by means of printing or the like to form the oxygen pump section 2. Further, the insulating film 12 is provided on the outer peripheral side of the other side electrode 5, and the organic film 14 is provided on the other surface side of the other side electrode 5, and these are integrated with the oxygen ion conductor 3. Then, one surface of the porous second oxygen ion conductor 8 located on the one side heater substrate 17,
The measurement electrode 9 and the reference electrode 10 are provided on the other surface side, and the sensor unit 7
Make up. In addition, the insulating film 1 is formed on the other side heater substrate 18.
The heater wire 20 sandwiched by 9 is printed and laminated, and the one side heater substrate 17 is provided to form the heater portion 16.

Next, the oxygen pump portion 2, the sensor portion 7, the heater portion 16 and the like thus constructed are laminated, the one side electrode 4 is covered with the protective layer 6, and then along the axis O--O '. To form the flow hole 15. Then, the entire sensor body 1 is gradually heated to burn away the organic film 14 to form the diffusion chamber 13, and the entire body is further heated to, for example, about 1400 ° C. to perform main firing, and as shown in FIG. The sensor body 1 of the fuel ratio sensor is completed.

Next, the sensor body 1 manufactured in this manner is mounted so as to project into the exhaust pipe, and a part of the exhaust gas G flowing in the exhaust pipe is passed through the flow hole 15 to the diffusion chamber 1.
Inflow into 3. Then, the sensor unit 7 is heated by the heater unit 16 and the electrodes 9, 1
Supply current to zero. As a result, on the measurement electrode 9 side,
As shown in Chemical Formula 1 below, electrons are added to oxygen in the exhaust gas G that is in contact with the measurement electrode 9 and the second oxygen ion conductor 8 to generate oxygen ions.

[0025]

[Chemical formula 1] O ₂ + 4e → 2O ^{2 −} However, O ₂ : oxygen molecule e: electron O ^2- : oxygen ion

Then, the oxygen ions are sequentially transported to the reference electrode 10 side via the oxygen defects in the second oxygen ion conductor 8, and the reference electrode 10 deprives the electron thereof as shown in the following chemical formula 2. And become oxygen molecules. As a result, the reference electrode 1
On the 0 side, an oxygen partial pressure higher than the oxygen partial pressure in the diffusion chamber 13, such as about 1 atm, is always ensured.

[0027]

[Chemical formula ² ] 2O ^2- → O ₂ + 4e

Since the oxygen generated on the reference electrode 10 side is electrically neutral, it is returned to the diffusion chamber 13 through a large number of small holes in the second oxygen ion conductor 8. This prevents the partial pressure of oxygen in the diffusion chamber 13 from decreasing.

On the other hand, a diffusion chamber 13 is provided between the electrodes 9 and 10.
A voltage signal corresponding to the difference between the oxygen partial pressure inside and the oxygen partial pressure on the reference electrode 10 side is generated, and this voltage signal is input to the differential amplifier 23. Then, the differential amplifier 23 includes the electrodes 9 and 1
The voltage signal between 0 and the reference voltage of the reference power supply 24 are compared, and the pump current corresponding to the difference between the two is supplied to the one-side electrode 4.

Here, when the exhaust gas G is in a so-called lean state where the air is excessive, the oxygen partial pressure in the exhaust gas G is relatively large, and the difference in oxygen partial pressure between the diffusion chamber 13 and the reference electrode 10 is small. A small voltage signal corresponding to the oxygen partial pressure difference is generated at the reference electrode 10, and this voltage signal is input to the differential amplifier 23. Then, the differential amplifier 23 compares this voltage signal with the reference voltage of the reference power supply 24, and outputs a pump current corresponding to the voltage difference between the two in the direction of arrow A in FIG. As a result, a part of the oxygen in the diffusion chamber 13 is ionized by the other side electrode 5 and transported to the one side electrode 4, and is converted into molecules at the one side electrode 4 and discharged into the exhaust pipe.

Further, when the exhaust gas G is in a so-called rich state where the amount of fuel is excessive, the oxygen partial pressure in the exhaust gas G is extremely low, and the difference between the oxygen partial pressures of the diffusion chamber 13 and the reference electrode 10 is large. A relatively large voltage corresponding to the oxygen partial pressure is generated in the reference electrode 10, and this voltage signal is input to the differential amplifier 23. Then, this voltage signal becomes larger than the reference voltage of the reference power supply 24, and the difference between the two becomes negative, so that the differential amplifier 23 outputs the pump current Ip in the direction of arrow B. As a result, oxygen in the exhaust pipe is ionized by the one-side electrode 4 and then transported to the other-side electrode 5, and discharged from the other-side electrode 5 into the diffusion chamber 13.

By measuring the direction and magnitude of the pump current Ip from the differential amplifier 23 via the voltage detecting resistor 25, the oxygen concentration of the exhaust gas G, as shown by the solid line in FIG. That is, the air-fuel ratio of the engine can be detected.

Thus, according to this embodiment, the reference electrode 1
Since the second oxygen ion conductor 8 is formed so as to be porous so that an outflow passage communicating between the 0 side and the diffusion chamber 13 is formed, oxygen generated on the reference electrode 10 side is discharged through the outflow passage. Can be effectively discharged into the diffusion chamber 13 through a large number of small holes. As a result, it is possible to prevent a decrease in the oxygen partial pressure in the diffusion chamber 13 while securing a predetermined oxygen partial pressure on the reference electrode 10 side by the DC power supply 21. As a result, even in a combustion state near the stoichiometric air-fuel ratio, oxygen is transported from the measurement electrode 9 to the reference electrode 10 to cause diffusion chamber 13
It is possible to effectively prevent the oxygen partial pressure in the inside from becoming lower than the actual oxygen partial pressure of the exhaust gas G, and to prevent an error from occurring in the voltage signal generated on the reference electrode 10 side depending on the oxygen partial pressure difference. The air-fuel ratio can be measured with high accuracy over a wide range and accurate air-fuel ratio control can be performed, and the reliability and the like can be significantly improved.

Further, since a predetermined oxygen partial pressure can be secured on the reference electrode 10 side without providing the oxygen containing portion described in the prior art, the entire size can be surely reduced by the amount corresponding to the oxygen containing portion, and the sensor can be mounted. The degree of freedom in time can be improved, and the number of parts can be reduced for efficient manufacturing. Further, when the sensor body 1 is arranged in the exhaust pipe, the flow of the exhaust gas G is not adversely affected, and the reliability can be improved.

Next, FIGS. 4 and 5 show a second embodiment of the present invention, which is characterized in that the second oxygen ion conductor 32 is provided with communication holes 35, 35 ,. Has been drilled. In the present embodiment, the above-mentioned first
The same components as those of the embodiment are given the same reference numerals and the description thereof will be omitted.

In the figure, reference numeral 31 denotes a sensor portion according to this embodiment, which is substantially the same as the sensor portion 7 described in the first embodiment and is made of a solid electrolyte such as zirconia and has a long flat plate shape. A second oxygen ion conductor 32 formed in
From the measurement electrode 33 provided on one surface side of the second oxygen ion conductor 32, and the reference electrode 34 provided on the other surface side of the second oxygen ion conductor 32 facing the measurement electrode 33. It is configured. However, in the second oxygen ion conductor 32, oxygen generated on the side of the reference electrode 34 is supplied to the diffusion chamber 1.
In order to return to the inside of 3, the communication holes 3 as a large number of small-diameter outflow passages
5, 35, ... Are drilled. Then, the sensor unit 3
As shown in FIG. 5, 1 is laminated in a state of being sandwiched between the oxygen pump section 2 and the heater section 16 as in the first embodiment described above.

Thus, in this embodiment having such a structure, it is possible to obtain substantially the same operational effects as those of the first embodiment described above.

In the first embodiment, it is described that the second oxygen ion conductor 8 is made porous and zirconia having a large particle size is used in order to obtain small pores as an outflow passage. , In place of this, the second oxygen ion conductor 8
A small hole as an outflow passage may be secured by reducing the thickness dimension of.

In each of the above embodiments, the case where the air-fuel ratio of the automobile engine is detected has been described as an example. However, the present invention is not limited to this, and the air-fuel ratio detection of another combustion engine such as a boiler is performed. Can also be applied to.

[0040]

As described above, according to the present invention, the second
In the oxygen ion conductor of, the outflow passage for letting out the oxygen generated on the reference electrode side into the diffusion chamber is formed,
Oxygen, which has been transported from the measurement electrode to the reference electrode via the second oxygen ion conductor, has been deprived of electrons by the reference electrode to become molecules, flows out into the diffusion chamber through the outflow passage and is returned to the fluid to be measured. Be done. As a result, while maintaining a higher oxygen partial pressure on the reference electrode side than that on the measurement electrode side, it is possible to prevent the oxygen partial pressure in the measured fluid from decreasing, and in the combustion state near the theoretical air-fuel ratio, diffusion It is possible to effectively prevent the oxygen partial pressure in the chamber from becoming lower than the actual oxygen partial pressure of the fluid to be measured. As a result, it is possible to prevent an error in the voltage signal generated on the reference electrode side depending on the oxygen partial pressure difference, measure the air-fuel ratio with high accuracy over a wide range, and perform accurate air-fuel ratio control. It is possible to improve the sex.

Further, since the oxygen storage portion described in the prior art is not required, the overall size can be reduced, the mounting flexibility at the time of mounting the sensor can be improved, and the change given to the flow of the fluid to be measured can be reduced. ..

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an air-fuel ratio sensor according to a first embodiment of the present invention.

FIG. 2 is an exploded perspective view showing an assembled state of the sensor body in FIG.

FIG. 3 is a perspective view showing a completed state of the sensor body.

FIG. 4 is a vertical sectional view showing an air-fuel ratio sensor according to a second embodiment of the present invention.

5 is an exploded perspective view showing an assembled state of the sensor body in FIG. 4. FIG.

FIG. 6 is a characteristic diagram showing characteristics of pump current of an air-fuel ratio sensor according to a conventional technique.

[Explanation of symbols]

 3 First Oxygen Ion Conductor 4 One Side Electrode 5 Other Side Electrode 8,32 Second Oxygen Ion Conductor 9,33 Measurement Electrode 10,34 Reference Electrode 13 Diffusion Chamber 21 DC Power Supply 23 Differential Amplifier (Comparative Supply Means ) 35 communication hole (outflow path)

Claims (1)

[Claims] 1. A first oxygen ion conductor formed in a plate shape from a solid electrolyte, one side electrode provided on one surface side of the first oxygen ion conductor, and facing the one side electrode. A second electrode provided on the other surface of the first oxygen ion conductor, and a second oxygen ion conductor provided in a plate shape from the solid electrolyte, the second oxygen ion conductor provided to face the other electrode. A measurement electrode provided on one surface side of the second oxygen ion conductor, a reference electrode provided on the other surface side of the second oxygen ion conductor facing the measurement electrode, and the other side A diffusion chamber provided between the electrode and the measurement electrode, for diffusing the fluid to be measured that has flowed in from the outside through the flow hole, and supplying a current from the reference electrode to the measurement electrode, the fluid to be measured. A direct current power source for ionizing oxygen in the measurement electrode and transporting it to the reference electrode side; In the air-fuel ratio sensor consisting of a comparison supply means for comparing the voltage generated between the measurement electrode and the reference electrode with the reference voltage, and supplying a pump current according to the difference between them to the one side electrode or the other side electrode. The air-fuel ratio sensor is characterized in that the second oxygen ion conductor is provided with an outflow passage through which oxygen generated on the reference electrode side flows out into the diffusion chamber.