JPH0436341B2 - - Google Patents

Description

Detailed Description of the Invention Technical Field The present invention relates to an air-fuel ratio detection device that detects the air-fuel ratio of an air-fuel mixture based on the oxygen concentration in exhaust gas resulting from combustion of an air-fuel mixture, and particularly relates to an air-fuel ratio detection device for detecting an air-fuel ratio of an air-fuel mixture based on oxygen concentration in exhaust gas resulting from combustion of an air-fuel mixture. The present invention relates to an air-fuel ratio detection device suitable for detecting the air-fuel ratio of air.

BACKGROUND ART 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 air-fuel ratio of the air-fuel mixture is detected by detecting the oxygen concentration in exhaust gas, which has a correlation with the air-fuel ratio. is detected to perform feedback control of the fuel supply amount.

Conventionally, as an oxygen sensor used in such an air-fuel ratio detection device, for example, Japanese Patent Application Laid-Open No. 57-76450
There is an oxygen sensor as described in Japanese Patent Publication No. 1, and such an oxygen sensor will be explained with reference to FIG.

This oxygen sensor 1 applies the principle of a kind of concentration battery that generates an electromotive force according to the oxygen concentration, and has a reference electrode 3 mainly composed of platinum on both sides of an oxygen ion conductive solid electrolyte 2. and an oxygen electrode 4 made of an alloy of gold and platinum are formed to face each other, and the reference electrode 3 is covered with a porous protective layer (coating layer) 5, and the oxygen electrode 4 is formed so as to prevent inflow and diffusion of oxygen. It is coated with a porous protective layer (coating layer) 6 that limits the

In this oxygen sensor 1, when a predetermined magnitude of current Is is supplied to the reference electrode 3 in a gas to be measured, for example, exhaust gas, oxygen ions O ^2- are produced in an amount corresponding to the magnitude of the current Is. moves through the solid electrolyte 2 in the opposite direction to the current Is, so a reference oxygen partial pressure Pa is generated at the reference electrode 3, and at this time, an oxygen partial pressure Pb is generated at the oxygen electrode 4 due to the oxygen partial pressure of the gas to be measured. are doing.

Accordingly, between the reference electrode 3 and the oxygen electrode 4, based on the oxygen partial pressures Pa and Pb, E=RT/4F・ln(Pa/Pb)... However, R: gas constant, T: Absolute temperature, F: Electromotive force E expressed by the Nernst equation, Faraday constant
is generated, and this electromotive force E changes depending on the oxygen concentration of the gas to be measured, so this is the output of the oxygen sensor 1.
It can be taken out to the outside as Vs.

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.
The oxygen concentration is shown in terms of the air-fuel ratio (equivalence ratio λ, where λ=current air-fuel ratio/stoichiometric air-fuel ratio) of the air-fuel mixture supplied to the internal combustion engine.

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

Therefore, the output Vs of this oxygen sensor 1 is set to the target voltage Va (for example, approximately the intermediate value between the upper and lower limits of the oxygen sensor output Vs that changes suddenly at the switching air-fuel ratio).
Set the oxygen sensor output Vs as this target value
When the sink current Is is supplied so that it becomes Va,
The value of this injected current Is continuously changes depending on 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 over a wide range.

However, in the case of such an air-fuel ratio detection device, as can be seen from Fig. 3, the value of the injected current Is is limited only when the value of the injected current Is shifts to the lean side with the stoichiometric air-fuel ratio (λ = 1) as the minimum value. It also increases when moving to the rich side.

This is because in the rich region, there is almost no oxygen in the exhaust gas, so the oxygen ions in the solid electrolyte do not reach an equilibrium state corresponding to the rich air-fuel ratio, but instead become oxygen molecules and unilaterally enter the exhaust gas. This is due to diffusion and outflow, and the more the exhaust gas moves to the rich side, the more oxygen ions move, and the value of the inflow current Is increases.

Therefore, near the stoichiometric air-fuel ratio, there are two values of air-fuel ratio for the same value of injected current Is, and it is not possible to calculate the air-fuel ratio in a wide range from rich to lean by simply looking at the value of injected current Is. There is a problem that the air-fuel ratio (oxygen concentration) cannot be detected over a wide range.

However, if we focus only on the lean region, for example, in this case, the value of the injected current and the air-fuel ratio will uniquely correspond, so the range from the stoichiometric air-fuel ratio (λ = 1) to the lean region will be It can be used for wide range detection purposes.

By the way, for automobile internal combustion engines that are operated at air-fuel ratios over a wide range of air-fuel ratios, including lean ranges or even rich ranges, it is necessary to particularly increase the exhaust purification rate in specific operating ranges such as city driving. be.

Therefore, in internal combustion engines that use a three-way catalyst to purify exhaust gas, it is necessary to control the air-fuel ratio to the stoichiometric air-fuel ratio in order to increase the purification efficiency of the three-way catalyst. When operating the vehicle, it is especially desirable to detect the point of λ=1 with high accuracy.

However, in the case of the above air-fuel ratio detection device,
Although it is possible to continuously detect the air-fuel ratio (oxygen concentration) over a wide range from the value of the injected current,
The detection accuracy of individual air-fuel ratios is rather lower than the method shown in Figure 2, which fixes the injected current and detects the air-fuel ratio from changes in the output voltage Vs. There is a risk that the air-fuel ratio detection result will be affected by the zero point offset, etc., resulting in an error.

Therefore, if this air-fuel ratio detection device is also used for stoichiometric air-fuel ratio control using a three-way catalyst, λ
There is a possibility that the necessary detection accuracy may not be obtained for the point where =1.

In addition, in this air-fuel ratio detection device, oxygen passing through a porous layer that restricts oxygen diffusion is injected to obtain the current value, so the response is somewhat slow, and as a result, the stoichiometric air-fuel ratio (λ = 1) There is a risk that the purification rate of the three-way catalyst will decrease if the

Purpose This invention has been made in view of the above-mentioned points, and it is possible to detect a wide range of air-fuel ratios with high precision, and also to detect the stoichiometric air-fuel ratio with higher precision and better responsiveness than other air-fuel ratios. The purpose is to

Configuration Therefore, the air-fuel ratio detection device according to the present invention has the following features:
Exhaust gas from the combustion of a mixture of air and fuel is
A gas introduction section introduced through a means for restricting gas diffusion, and an electrode exposed to the gas of the gas introduction section and the gas at a predetermined oxygen concentration, which face each other with an oxygen ion conductive solid electrolyte in between, It has an oxygen partial pressure ratio detection section that outputs a voltage according to the oxygen partial pressure ratio between both electrodes, and electrodes facing each other with an oxygen ion conductive solid electrolyte in between, and the oxygen partial pressure ratio detecting section outputs a voltage according to the oxygen partial pressure ratio between the two electrodes. An oxygen sensor configured with an oxygen partial pressure control section that controls the oxygen partial pressure of the gas introduction section is used, and the oxygen is adjusted such that the output of the oxygen partial pressure ratio detection section of the oxygen sensor matches a predetermined target value. A current is supplied to the partial pressure control section, and the voltage between both electrodes of the oxygen partial pressure control section is taken out as a detection output indicating the air-fuel ratio of the air-fuel mixture.

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

4 and 5 are a longitudinal sectional view and an exploded perspective view showing an example of an oxygen sensor constituting an air-fuel ratio detection device embodying the present invention.

This oxygen sensor 11 has an air introduction plate 13 with grooves 13a formed on a substrate 12 made of alumina, and a flat oxygen ion conductive first solid electrolyte 14 on this air introduction plate 13. do,
These grooves 13a of the air introduction plate 13 and the first solid electrolyte 14 form an air introduction section 15 into which air, which is a gas having a predetermined oxygen concentration, is introduced.

Then, on the first solid electrolyte 14, a spacer plate 16 with a thickness of L (L=about 0.1 mm) is laminated,
A flat second solid electrolyte 17 is stacked on this spacer plate 16, and these first solid electrolytes 1
4. A gas introduction section 1 which is a gap with a width L that also serves as a means for restricting the diffusion of gas into which exhaust gas is introduced by the spacer plate 16 and the second solid electrolyte 17.
8 is formed.

A sensor anode 20, which is an electrode exposed to the atmosphere, which is a predetermined gas in the atmosphere introduction part 15, and a gas introduction part 18 are placed on both sides of the first solid electrolyte 14.
Sensor cathodes 21, which are electrodes exposed to exhaust gas, are provided facing each other, and these sensor anodes 2
0 and the sensor cathode 21, that is, the oxygen partial pressure ratio between the atmosphere introduction part 15 and the gas introduction part 18 (hereinafter referred to as "sensor cell SC"). ).

Further, on both surfaces of the second solid electrolyte 17, a pump cathode 22, which is an electrode exposed to the exhaust gas from the gas introduction part 18, and a pump anode 23, which is an electrode directly exposed to the exhaust gas, are provided to face each other. It constitutes an oxygen partial pressure control section (hereinafter referred to as "pump cell PC") that controls the oxygen partial pressure of the gas introduction section 18 according to the amount of current supplied between the pump cathode 22 and the pump anode 23.

In addition, on the surface of the substrate 12 on the side of the atmosphere introduction part 13,
First solid electrolyte 14 and second solid electrolyte 17
Heater 2 heats these in order to maintain their activity.
5 is printed and formed.

In addition, a sensor anode 20, a sensor cathode 2
Lead wires 26 and 27 are connected to the pump cathode 22 and pump anode 23, respectively.
8, 29, and lead wires 30, 31 to the heater 25.
is connected.

Further, as the first and second solid electrolytes 14 and 17, for example, oxides such as ZrO ₂ , HrO ₂ , ThO ₂ , Bi ₂ O ₃ , C ₂ O, MgO, Y ₂ O ₂ , YB ₂ O ₃ etc. Each electrode 20 to 24 has platinum or gold as a main component.

Furthermore, in this embodiment, the atmosphere introduction section 15
The entire partition between the gas inlet 18 and the gas inlet 18 is covered with the first solid electrolyte 14, and the entire partition between the gas inlet 18 and the exhaust gas atmosphere is covered with the second solid electrolyte 1.
7, however, only the portions corresponding to the electrodes 20 to 24 may be formed of a solid electrolyte.

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

In this air-fuel ratio detection circuit, the differential amplifier 33
is the potential of the sensor anode 20 with respect to the sensor cathode 21 of the sensor cell SC of the oxygen sensor 11
The difference (Va - Vs) between Vs and the target voltage (target value) Va from the power supply 34 is detected, and the difference voltage ΔV is output.

The pump current supply circuit 35 is a current supply means, and includes a negative coefficient integration circuit 36 that integrates the differential voltage ΔV from the differential amplifier 33, and this negative coefficient integration circuit 36.
The pump anode 23 of the pump cell PC of the oxygen sensor 11 converts the integral output Vb from the differential amplifier 33 into a current, and converts the pump current Ip in the magnitude and direction according to the differential voltage ΔV from the differential amplifier 33 to the pump anode 23 of the pump cell PC of the oxygen sensor 11. and controls the differential voltage ΔV from the differential amplifier 33 to be ΔV=0 (Vs=Va).

The negative coefficient integration circuit 36 consists of a resistor 38, a capacitor 39, and an operational amplifier 40, and inputs the differential voltage ΔV from the differential amplifier 33, and integrates this differential voltage ΔV to output an integral output Vb (Vb=-K∫ΔVdt ，
K: positive constant) is output.

Further, the V-I conversion circuit 37 includes an operational amplifier 4
1. The output of the differential amplifier 43, which is composed of a resistor 41 and a differential amplifier 43, and detects the voltage across the resistor 41 according to the integral output Vb from the negative coefficient integration circuit 36 and the pump current Ip supplied to the pump anode 23. Accordingly, the operational amplifier 41 supplies a pump current Ip corresponding to the integral output Vb.

And the pump cathode 22 of the oxygen sensor 11
The potential Vp of the pump anode 23 relative to the pump anode 23 is outputted as an air-fuel ratio (oxygen concentration) detection output Vp via a buffer amplifier 44.

That is, in this air-fuel ratio detection circuit, the lead wire 28 for grounding the pump cathode 22
The pump cathode of the pump sensor PC, which is the oxygen partial pressure control section of the oxygen sensor 11, is connected by the lead wire 29 for connecting the pump anode 23 to the buffer amplifier 44 and the signal line for taking out the buffer amplifier 44 and its output. 22 and the pump anode 23 as a detection output indicating the air-fuel ratio of the air-fuel mixture.

Note that the buffer amplifier 44 can be omitted, and in this case, the signal line connected to the pump cathode 22 and pump anode 23 of the oxygen sensor 11 constitutes means for extracting this voltage.

Next, the operation of this embodiment configured as described above will be explained.

First, pump current supply circuit 3 of the air-fuel ratio detection circuit
5 is connected to the sensor anode 20 and sensor cathode 2 of the sensor cell SC so that the oxygen concentration (oxygen partial pressure) in the gas introduction part 18 becomes a predetermined oxygen concentration.
A pump current Ip is supplied to the pump anode 23 of the pump cell PC so that the potential Vs between the voltage and the target voltage Va matches the target voltage Va.

In other words, when the oxygen concentration in the gas introduction section 18 is lower than the predetermined oxygen concentration, as shown in FIG.
Supplying a pump current Ip flowing from the pump cathode 22 of the pump cell PC toward the pump anode 23 (in the direction of arrow IR) to move oxygen ions from the pump anode 23 to the pump cathode 22,
The oxygen concentration in the gas introduction section 18 is controlled to a predetermined oxygen concentration.

Further, when the oxygen concentration in the gas introduction part 18 is higher than the predetermined oxygen concentration, as shown in FIG. 4, the pump current Ip flows from the pump anode 23 of the pump cell PC toward the pump cathode 22 (in the direction of the arrow IL). is supplied to move oxygen ions from the pump cathode 22 to the pump anode 23 to control the oxygen concentration in the gas introduction section 18 to a predetermined oxygen concentration.

In this case, the target voltage Va is the sensor anode 2
Any value may be used as long as it corresponds to the potential Vs that occurs at zero, but in order to accurately maintain the potential Vs at the target value, it is preferable to adjust the potential to a change in the oxygen concentration in the gas introduction section 18. It is preferable to set it at a point where the slope of the change in Vs is the largest, that is, at a value midway between the upper and lower limits of the voltage value at which the potential Vs suddenly changes in response to a change in oxygen concentration.

Therefore, if the target voltage Va is set to Va = 500 mV, for example, the pump current supply circuit 35 applies the voltage to the pump anode electrode 23 so that the potential Vs between the sensor anode 20 and the sensor cathode 21 becomes Vs = 500 mV. Supply pump current Ip.

Therefore, the oxygen partial pressure in the atmosphere introduction part 15 is PC,
If the oxygen partial pressure in the gas introduction part 18 is PB, then the oxygen partial pressure ratio PB/PC is, when the temperature is 1000K, from the Nernst equation (formula) mentioned above, PB/PC=10 ^-10 , and PC≒0.206. Since it is atm, PB≒0.206×10 ^-10 atm.

Here, if PA is the partial pressure of oxygen in the gas to be measured, for example, exhaust gas, the gas enters the gas introduction section 18, which is a gap that also serves as a means to restrict gas diffusion.
The amount Q of O ₂ is Q=D(PA-PB), where D is the diffusion coefficient, and since PB≈0, Q≈D·PA.

An amount of O ₂ equivalent to this amount Q of O ₂ is pumped at
Moving the second solid electrolyte 17 by Ip,
Since the oxygen concentration in the gas introduction section 18 is maintained at a predetermined oxygen concentration, Ip∝Q Ip∝K ₁ ·PA . . . However, K ₁ is a constant.

In other words, the value of the pump current Ip is proportional to the oxygen partial pressure in the gas to be measured.

In this case, on the lean (λ>1) side of the air-fuel ratio (A/F), oxygen molecules are pumped into the exhaust gas from the gas introduction part 18, so
The above formula is valid as is.

On the other hand, when the air-fuel ratio is rich (λ<1), the amount of oxygen molecules in the exhaust gas is extremely small.
The oxygen partial pressure PA is about 10 ^-2 ₀ to 10 ^-25 (equilibrium oxygen partial pressure).

At this time, there are many carbon dioxide molecules CO ₂ in the exhaust gas.

And the oxygen partial pressure in this exhaust gas is 10 ^-20 ~
At 10 ^-25 , set the oxygen partial pressure in the gas introduction part 18.
In order to maintain the oxygen concentration at 0.206×10 ^-10 , a pump current Ip is supplied to the gas introduction section 18 from the exhaust gas atmosphere, that is, in a direction to move oxygen molecules from the pump anode 23 to the pump cathode 22.

Therefore, especially on the surface of the pump anode 23, a reaction of CO ₂ + 2e ^- → CO + C ^2- occurs, and the O ^2- is transferred to the second solid electrolyte 17.
The gas is moved inside and transferred to the gas introduction section 18.

As a result, a reaction of 2CO + O ₂ → 2CO ₂ occurs, especially on the surface of the pump cathode 22, and the
_O2 is consumed.

In other words, on the rich side, the amount of O ₂ consumed by the above reaction is measured by the pump current.

The above reaction is proportional to the amount of CO that diffuses into the gas introduction section 18. That is, in the gas introduction section 18, CO is also consumed by the above reaction, and the CO partial pressure becomes approximately zero, so the amount of CO entering the gas introduction section 18, Qco, is equal to the amount of CO in the exhaust gas. If the CO partial pressure is Pco and the diffusion coefficient is D', then Qco=D'(Pco-0) = D'・Pco.

Therefore, the amount of O ₂ required to maintain the oxygen partial pressure in the gas inlet 18 at 0.206×10 ^-10 on the rich side, that is, the amount of O ₂ pumped from the exhaust gas atmosphere by the pump current. is CO in exhaust gas
The value is proportional to the concentration of

On the rich side, the concentration of CO (or CO + HC) has a good correlation with the air-fuel ratio, so the pump current Ip changes continuously with the air-fuel ratio even on the rich side.

Now, considering the pump cell PC consisting of the second solid electrolyte 17, pump cathode 22, and pump anode 23, this pump cell PC
As shown in Figure 7, the equivalent circuit of is self-electromotive force
It can be divided into Ep and internal resistance Rp.

Therefore, pump cathode 2 of pump cell C
The potential (air-fuel ratio detection output) Vp of the pump anode 23 with respect to 2 is as follows: Vp=Ep+Ip·Rp...

By the way, as mentioned above, this self-electromotive force Ep is calculated by changing the partial pressure of oxygen in the exhaust gas to PA, the gas introduction part 1
If the oxygen partial pressure in 8 is PB, it is expressed as Ep=RT/4F・ln(PA/PB)... from the Nurnst equation mentioned above.

When the target voltage Va is set to 500 mV, the oxygen partial pressure PB of the gas introduction section 18 is maintained at approximately 10 ^-10 as described above. (PB=
^10-10 ).

On the other hand, oxygen partial pressure in exhaust gas (equilibrium oxygen partial pressure)
PA is approximately 10 ^-20 atm on the rich side and approximately 10 ^-2 atm on the lean side, with the stoichiometric air-fuel ratio (λ = 1) as the boundary.

As a result, the self-electromotive force Ep changes with respect to the air-fuel ratio (equivalent ratio λ) as shown in FIG. 8, as can be seen from the above-mentioned equation.

On the other hand, if the temperature is constant, the internal resistance Rp is approximately constant on both the rich side and the lean side, and the pump current Ip is a value proportional to the air-fuel ratio from the rich side to the lean side, as described above. , Ip and Rp in the above-mentioned equation change as shown in FIG. 9 with respect to the air-fuel ratio (equivalence ratio λ).

Therefore, the air-fuel ratio detection output Vp, which is the potential between the pump cathode 22 and the pump anode 23 of the pump cell PC, is determined by the voltage drop of the internal resistance Rp due to the self-electromotive force Ep and the pump current Ip ( Ip・Rp), so
It changes as shown in FIG. 10 with respect to the air-fuel ratio (equivalence ratio λ).

In this way, the air-fuel ratio detection output from the pump cell
The potential Vp between both electrodes of PC is the stoichiometric air-fuel ratio (λ=1)
It changes suddenly on and off at , and changes continuously at other air-fuel ratios.

That is, the air-fuel ratio detection output Vp is dominated by the self-electromotive force Ep near the stoichiometric air-fuel ratio (λ=1), and is dominated by the pump current Ip at other air-fuel ratios.

Therefore, the response around the stoichiometric air-fuel ratio (λ=1) is determined by the response of the self-electromotive force Ep,
As can be seen from the above equation, this self-electromotive force Ep is determined by the oxygen partial pressure PA in the exhaust gas, so it follows extremely quickly changes in the air-fuel ratio in the exhaust gas.

Therefore, the responsiveness of the air-fuel ratio detection output Vp near the stoichiometric air-fuel ratio (λ=1) is extremely fast.

In this way, in this air-fuel ratio detection device,
Air-fuel ratios can be detected over a wide range from rich to lean regions, and the stoichiometric air-fuel ratio (λ=1) can be detected with higher precision and better responsiveness than other air-fuel ratios.

Therefore, by using this air-fuel ratio detection device in combination with a three-way catalyst, the purification rate of exhaust gas can be increased.

FIG. 11 is a longitudinal sectional view showing an example of an oxygen sensor used in the present invention.

This oxygen sensor 51 includes a first solid electrolyte 14
and the second solid electrolyte 17 with a spacer plate 52 having a through hole 52 a interposed therebetween to form a gas introduction section 18 and to form a gas introduction section 1 .
8, the second solid electrolyte 17 and the bomb cathode 2
The exhaust gas is introduced through a small hole 53, which is a means for restricting the diffusion of gas, provided in the pump anode 2 and the pump anode 23. Note that the other configurations are the same as those in the previous embodiment.

Even when this oxygen sensor 51 is used, by using an air-fuel ratio detection circuit similar to that of the previous embodiment, an air-fuel ratio detection output as shown in FIG.
You can get VP.

FIGS. 12 and 13 are a cross-sectional view and an exploded perspective view showing still another embodiment of the oxygen sensor used in the present invention.

This oxygen sensor 61 is constructed by stacking an oxygen ion conductive solid electrolyte 62 on an atmosphere introduction plate 13, and an atmosphere introduction part 15 into which the atmosphere, which is a predetermined gas, is introduced.
A spacer plate 63 having a rectangular through hole 63a is formed on the solid electrolyte 62, and a partition plate 64 is laminated on this spacer plate 63 to form the gas introduction part 18. The gas to be measured is introduced into the section 18 through a small hole 65 formed in the partition plate 64 and serving as a means for restricting the diffusion of the gas.

A common electrode 66 exposed to the atmosphere in the atmosphere introduction part 15 and a sensor electrode 67 and a pump electrode 68 exposed to the gas to be measured in the gas introduction part 18 are provided on both sides of the solid electrolyte 62. 66 and the sensor electrode 67 constitute an oxygen partial pressure ratio detection section (sensor cell SC), and the solid electrolyte 62, the common electrode 66, and the pump electrode 68 constitute an oxygen partial pressure control section (pump cell PC). There is.

Note that these common electrodes 66 and sensor electrodes 6
7. The pump electrode 68 has lead wires 70 and 7, respectively.
1 and 72 are connected.

Even when this oxygen sensor 61 is used, a detection output Vp as shown in FIG. 10 can be obtained, for example, by using the air-fuel ratio detection circuit of the embodiment described above.

In this oxygen sensor 61, the common electrode 66, the sensor electrode 67, and the pump electrode 68 may be provided oppositely, or the common electrode 66 may be provided as two electrodes facing the sensor electrode 67 and the pump electrode 68, respectively. May be divided.

This oxygen sensor 61 has improved durability compared to the oxygen sensor 11 shown in FIGS. 4 and 5.

That is, in the oxygen sensor 11 described above, in order to move oxygen ions from the exhaust gas with a low oxygen concentration to the gas introduction part 18 when the air-fuel ratio is on the rich side, oxygen molecules in the second solid electrolyte 17 itself A phenomenon occurs in which the solid electrolyte 17 is slightly decomposed and transferred to the gas introduction part 18, and if the rich side is used for an extremely long period of time, there is a risk that the first solid electrolyte 17 will deteriorate.

On the other hand, in the case of the oxygen sensor 61 of this embodiment, since the oxygen molecules from the atmosphere introduction section 15 are transferred to the gas introduction section 18, there is no possibility that the oxygen molecules of the solid electrolyte 62 itself will be decomposed on the rich side. Since there are no scratches, durability is significantly improved.

In the above embodiments, an oxygen sensor that uses the atmosphere as a gas with a predetermined oxygen concentration is described, but this is not limiting. May be used.

Furthermore, as an oxygen sensor, instead of forming the means for restricting gas diffusion as gaps or small holes as in the above embodiment, other porous bodies etc. can be used. For example, as in the above embodiment, The gas introduction section may be filled with a porous material.

Furthermore, the air-fuel ratio detection device according to the present invention can also be used to detect the air-fuel ratio of various internal combustion engines for vehicles, fixed plants, industries, ships, etc., or to detect the air-fuel ratio of combustion gas in blast furnaces, etc. can.

Effects As explained above, the air-fuel ratio detection device according to the present invention supplies current to the solid electrolyte in order to control the oxygen partial pressure of the gas introduction part where the exhaust gas of the oxygen sensor is introduced with diffusion restricted. Since the voltage between the electrodes is extracted and this voltage is used as the air-fuel ratio detection output, the air-fuel ratio can be detected over a wide range, and moreover, it can detect the air-fuel ratio near the stoichiometric air-fuel ratio with higher precision and better response than other air-fuel ratios. Since it can be detected, the exhaust purification rate is improved when combined with a three-way catalyst.

[Brief explanation of drawings]

Fig. 1 is a schematic cross-sectional view showing an example of a conventional oxygen sensor, Fig. 2 is a diagram showing the relationship between the sensor output and the air-fuel ratio, and Fig. 3 is a diagram showing the relationship between the sensor output and the air-fuel ratio. 4 and 5 are a longitudinal sectional view and an exploded perspective view showing an example of an oxygen sensor according to an embodiment of the present invention, and FIG.
Figure 7 is a circuit diagram showing an example of the air-fuel ratio detection circuit, Figure 7 is a circuit diagram showing an equivalent circuit of the pump cell of the oxygen sensor, and Figure 8 is the relationship between the self-electromotive force of the pump cell and the air-fuel ratio. Figure 9 is a diagram showing the relationship between the voltage due to the internal resistance of the pump cell and the air-fuel ratio, and Figure 10 is a diagram showing the relationship between the voltage between the electrodes of the pump cell (air-fuel ratio detection output) and the air-fuel ratio. A diagram showing the relationship, FIG. 11 is a longitudinal sectional view showing another example of the oxygen sensor used in the present invention, and FIGS. 12 and 13 are diagrams showing still other examples of the oxygen sensor used in the present invention. FIG. 2 is a cross-sectional view and an exploded perspective view. DESCRIPTION OF SYMBOLS 11, 51, 61...Oxygen sensor, 14...First solid electrolyte, 15...Air introduction part, 17...Second solid electrolyte, 18...Gas introduction part, 20...Sensor anode, 21...Sensor cathode, 22...Pump Cathode, 23...Pump anode, SC...Sensor cell (oxygen partial pressure ratio detection section), PC...Pump cell (oxygen partial pressure control section), 33...Differential amplifier, 34...Power supply, 3
5...Pump current supply circuit, 43...Buffer amplifier, 53, 65...Small hole, 62...Solid electrolyte, 66
...Common electrode, 67...Sensor electrode, 68...Pump electrode.

Claims (1)

[Scope of Claims] 1. A gas introduction part into which exhaust gas from combustion of a mixture of air and fuel is introduced via a means for restricting gas diffusion, and a gas introduction part that faces across an oxygen ion conductive solid electrolyte. an oxygen partial pressure ratio detection section that has an electrode exposed to the gas of the gas introduction section and a gas of a predetermined oxygen concentration, and outputs a voltage according to the oxygen partial pressure ratio between the two electrodes; and an oxygen ion conductive solid electrolyte. an oxygen sensor comprising electrodes facing each other and an oxygen partial pressure control section that controls the oxygen partial pressure of the gas introduction section according to the amount of current supplied between the two electrodes; current supply means for supplying current to the oxygen partial pressure control section so that the output voltage of the pressure ratio detection section matches a preset target value; 1. An air-fuel ratio detection device comprising: means for extracting a detection output indicating an air-fuel ratio of an air-fuel mixture.