JPH0634004B2 - Oxygen concentration detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to an oxygen sensor for detecting an oxygen concentration in a gas to be measured, and more particularly to an oxygen sensor for detecting an oxygen concentration in exhaust gas of an internal combustion engine.

BACKGROUND ART Generally, in an internal combustion engine, in order to control the air-fuel ratio of the intake air-fuel mixture to a target value with high accuracy, the oxygen concentration in the exhaust gas that has a correlation with the air-fuel ratio is detected, and the detected oxygen concentration Accordingly, the fuel supply amount is feedback-controlled.

Conventionally, as an oxygen sensor used in such an air-fuel ratio detection device, there is one described in, for example, JP-A-57-76450. This oxygen sensor will be described with reference to FIG. To do.

This oxygen sensor 1 applies the principle of a kind of concentration battery that generates an electromotive force according to the oxygen concentration, and a reference electrode 3 containing platinum as a main component is formed on both surfaces of an oxygen ion conductive solid electrolyte 2. And an oxygen electrode 4 made of an alloy of gold and platinum so as to face each other, the reference electrode 3 is covered with a porous protective layer (coating layer) 5, and the oxygen electrode 4 inflows and diffuses oxygen. Is covered with a porous protective layer (coating layer) 6 for limiting the temperature.

In the oxygen sensor 1, when a flow-in current Is of a predetermined magnitude is supplied to the reference electrode 3 in a gas to be measured, for example, exhaust gas, the amount of oxygen ions O ²⁻ corresponding to the magnitude of the current Is is increased. Moves in the direction opposite to the current Is through the solid electrolyte 2, so that 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. is doing.

Therefore, 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) ... where R: gas constant, T: Absolute temperature F: Faraday constant An electromotive force E represented by the Nernst equation is generated, and this electromotive force E changes depending on the oxygen concentration of the gas to be measured. You can

FIG. 2 shows the change of the output Vs for each flowing current value. In this case, the exhaust gas of the internal combustion engine is used as the gas to be measured, and the oxygen concentration thereof is the air-fuel ratio (equivalent ratio λ, where λ = current air-fuel ratio / current air-fuel ratio) of the air-fuel mixture supplied to the internal combustion engine. ).

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

Therefore, the output Vs of the oxygen sensor 1 is set to the target voltage Va.
(It may be any value as long as it is a value corresponding to the output Vs, but for example, it is set as an intermediate value between the upper limit and the lower limit of the oxygen sensor output Vs which changes suddenly in the air-fuel ratio), and the oxygen sensor output Vs is set to this target. When the pouring current Is is supplied so as to have the value Va, the value of the pouring current Is becomes a value according to the current air-fuel ratio, as shown in FIG.

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

Thus, in the conventional oxygen sensor, the gas to be measured is passed through the porous layer that limits the diffusion of oxygen, and by detecting the oxygen passing through the porous layer as a current,
The oxygen concentration in the measured gas is detected.

Therefore, when the measured gas contains deposits such as carbon particles, the porous layer becomes clogged, the amount of oxygen molecules diffusing changes, the output characteristics change, and the oxygen concentration becomes accurate. May not be detected.

Aim The present invention has been made in view of the above points, and an object thereof is to make it possible to detect an oxygen concentration with high accuracy over a long period of time.

Structure Therefore, the oxygen concentration detection apparatus according to the present invention comprises electrodes provided on both surfaces of a closed chamber isolated from the gas to be measured and a member formed of the oxygen ion conductive first solid electrolyte. A first oxygen concentration battery and a first oxygen pump, one of which faces the interior of the closed chamber, and electrodes provided on both sides of a member formed of an oxygen ion conductive second solid electrolyte. A second oxygen concentration battery and a second oxygen pump in which one of the electrodes faces the inside of the sealed chamber; and the sealed chamber includes a first oxygen concentration battery and a first oxygen pump. A first compartment, a second oxygen concentration cell and a second
An oxygen sensor having a partition wall that divides into a second small chamber provided with the oxygen pump, and a small passage communicating between the small chambers, and the first oxygen pump based on the output of the first oxygen concentration battery. A pump current supplied to the second oxygen pump based on the output of the second oxygen concentration battery by maintaining the oxygen concentration in the first small chamber at a first predetermined value by increasing or decreasing the pump current supplied to the second oxygen pump. The oxygen concentration of the second small chamber is kept at a second predetermined value by increasing or decreasing the oxygen concentration, and the oxygen concentration of the measured gas is detected by detecting the value of the pump current supplied to at least one of the oxygen pumps. And a concentration detection circuit.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to FIG.

4 and 5 are a cross-sectional view and an exploded perspective view of an embodiment of the oxygen sensor in the oxygen concentration detecting device of the present invention.

This oxygen sensor 11 includes a flat plate-shaped oxygen ion conductive first solid electrolyte 12, a partition plate 13 having a square through hole 13a, a flat plate partition plate 14, and a square through hole. A partition plate 15 having a hole 15a and a flat plate-shaped second solid electrolyte 16 are laminated to form a closed chamber 11C isolated from the gas to be measured.

On the other hand, the first solid electrolyte 12 has a first sensor electrode 20 and a first pump electrode 21 on the outer surface, and a first sensor electrode 20 and a first pump electrode 21 on the inner surface facing the first sensor electrode 20 and the first pump electrode 21.
Of the reference electrode 22 are provided, and these constitute the first oxygen concentration battery and the first oxygen pump (11A).

In addition, the second solid electrolyte 16 has a second sensor electrode 23 and a second pump electrode 24 on the outer surface, and a second sensor electrode 23 and a second pump electrode 24 on the inner surface facing the second sensor electrode 23 and the second pump electrode 24.
Of the reference electrode 25, and these constitute the second oxygen concentration battery and the second oxygen pump (11B).

The partition plate 14 serves as a partition that divides the closed chamber 11C into a first small chamber 17 and a second small chamber 18.

The first small chamber 17 includes a first oxygen concentration battery and a first oxygen pump (11A), and similarly, the second small chamber 18 includes a second oxygen concentration battery and a second oxygen pump (11B). I have it. The partition plate 14 has a small hole 19 as a small passage for communicating the first small chamber and the second small chamber,
This small hole 19 limits the diffusion of oxygen between the two small chambers.

In addition, the first and second solid electrolytes 12, 16 are formed around the through hole 13 a on the side surface of the first solid electrolytic chamber 12 of the partition plate 13.
In order to maintain the activity of the above, a heater 30 for heating these is formed by printing.

In addition, the first sensor electrode 20, the first pump electrode 21,
Lead wires 32 to 34 are connected to the first reference electrode 22, respectively.
Lead wires 35 to 37 are connected to the second sensor electrode 23, the second pump electrode 24, and the second reference electrode 25, respectively, and lead wires 38 and 39 are connected to the heater 30, respectively.

Further, as the first and second solid electrolytes 12 and 16,
For example, a sintered body in which C ₂ O, MgO, Y ₂ O ₂ , YB ₂ O ₃ or the like is solid-dissolved in an oxide such as ZrO ₂ , HrO ₂ , ThO ₂ , or Bi ₂ O ₃ is used. 25 has platinum or gold as a main component.

Furthermore, in this embodiment, the first and second small chambers 17,
All of the partition walls that isolate 18 from the gas to be measured are
The solid electrolytes 12 and 16 of
You may form only the part corresponding to 25 with a solid electrolyte.

FIG. 6 is a circuit diagram showing an example of an oxygen concentration (air-fuel ratio) detection circuit in the oxygen concentration detection device of the present invention.

Briefly described, this oxygen concentration detection circuit increases or decreases the oxygen concentration of the first small chamber 17 by increasing or decreasing the pump current supplied to the first oxygen pump based on the output of the first oxygen concentration battery. The oxygen concentration in the second small chamber 18 is maintained at the second predetermined value by maintaining the predetermined value and increasing or decreasing the pump current supplied to the second oxygen pump based on the output of the second oxygen concentration battery, and at least The oxygen concentration of the measured gas is detected by detecting the value of the pump current supplied to one of the oxygen pumps. Specifically, the first control circuit 41, the second control circuit 42, and And an averaging circuit 43.

The first control circuit 41 first sets the potential Vs ₁ between the first reference electrode 22 and the first sensor electrode 20 and the target voltage Va.
₁ (Va ₁ = 0) is detected by the differential amplifier 45,
The differential voltage ΔVs ₁ (Δ
Vs ₁ = Vs ₁ ) according to the first pump current supply circuit 4
6 is directed to the first pump electrode 21 in a direction in which oxygen ions move in the first solid electrolyte 12 from the first sensor electrode 20 and the first pump electrode 21 side toward the first reference electrode 22 side. The first pump current Ip ₁ is supplied.

That is, the first pump current supply circuit 46 increases the first pump current Ip ₁ if the difference voltage ΔVs ₁ from the differential amplifier 45 is positive, and increases the first pump current Ip ₁ if the difference voltage ΔVs ₁ is negative. Pump current Ip ₁ of Vs ₁
The first pump current Ip ₁ is controlled so that = Va ₁ = 0.

Then, the first pump current Ip supplied from the first pump current supply circuit 46 to the first pump current 21.
₁ is converted into a voltage by a resistor 47 inserted in the feeding line,
The potential difference between both ends of the resistor 47 is detected by the differential amplifier 48 and output to the averaging circuit 43 as the voltage V ₁ (V ₁ ∝Ip ₁ ).

The second control circuit 42 first detects the difference between the potential Vs ₂ between the second reference electrode 25 and the first sensor electrode 23 and the target voltage Va ₂ from the power source 50 with the differential amplifier 51. hand,
The differential voltage ΔVs ₂ (ΔV
s ₂ = Vs ₂ −Va ₂ ), the second pump current supply circuit 52 supplies the second pump electrode 24 with the second sensor electrode 23 and the second pump electrode 24 from the second reference electrode 25 side. The second pump current Ip ₂ is supplied in the direction in which oxygen ions move toward the side in the second solid electrolyte 16.

That is, the second pump current supply circuit 52 decreases the second pump current Ip ₂ if the difference voltage ΔVs ₂ from the differential amplifier 51 is positive, and the second pump current Ip ₂ if the difference voltage ΔVs ₂ is negative. Pump current Ip ₂ of Vs ₂ =
The second pump current Ip ₂ is controlled so as to become Va ₂ .

Then, the second pump current Ip supplied from the second pump current supply circuit 52 to the second pump electrode 24.
₂ is converted into a voltage by a resistor 53 inserted in the power supply line,
The voltage across the resistor 52 is detected by the differential amplifier 54 and output to the averaging circuit 43 as the voltage V ₂ (V ₂ ∝Ip ₂ ).

The averaging circuit 43 is composed of a resistor 55 and a resistor 56 having the same resistance value, and the average value (V ₁ + V ₂ ) of the voltage V ₁ from the first control circuit 41 and the voltage V ₂ from the second control circuit 42. /
2 is output as the average voltage VN.

Next, the operation of this embodiment thus configured will be described.

First, the target voltage Va ₁ in the first control circuit 41 of the oxygen concentration detection circuit is set to Va ₁ = 0 mV, and the second control circuit 42
When the target voltage Va ₂ in the above is set to Va ₂ = 500 mV, the first pump current supply circuit 46 determines that the voltage Vs ₁ is V
The first pump current Ip ₁ that makes s ₁ = Va ₁ = 0
The second pump current supply circuit 52 supplies the voltage Vs ₂ to Vs ₂ = Va ₂ = 500 mV.
Of the pump current Ip ₂ is supplied to the second pump electrode 24.

At this time, the oxygen partial pressure of the first small chamber 17 is P ₁ , the oxygen partial pressure of the second small chamber 18 is P ₂ , and the oxygen partial pressure of the measured gas is P ₂ .
x, when the temperature is 1000 K, as is clear from the Nernst equation described above, P ₁ Px, P ₂
It becomes Px × 10 ⁻¹⁰ 0.

Therefore, O that diffuses through the small holes 19 of the partition plate 14
The quantity Q of ₂ is Q = D (P ₁ −P ₂ ) ... = D (Px−0).

The amount Q of O ₂ is normally the first pump current Ip.
_{Since the first} pump current Ip ₁ and the second pump current Ip ₂ are proportional to the _first and second pump currents Ip ₂ , Ip ₁ = Ip ₂ = K ₁ · Q = K ₁ · D · Px = K a ₂ · Px ....... However, K ₁ and K ₂ are constants.

From this equation, it can be seen that the first pump current Ip ₁ and the second pump current Ip ₂ are proportional to the oxygen partial pressure Px in the measured gas.

That is, the values of the first pump current Ip ₁ and the second pump current Ip ₂ both represent the oxygen partial pressure (concentration) in the measured gas.

Therefore, the voltages V ₁ and V ₂ output from the first control circuit 41 and the second control circuit 42 of the oxygen concentration detection circuit, respectively.
Are values corresponding to the oxygen concentration in the gas to be measured, and the averaging circuit 43 outputs the average voltage VN corresponding to the oxygen concentration obtained by averaging the voltages V ₁ and V ₂ .

FIG. 7 shows the characteristic of the average voltage VN with respect to the oxygen concentration output from the oxygen concentration detection circuit in this way.

By the way, in the oxygen sensor 11, the small holes 19 of the partition plate 14 which are means for limiting the diffusion of oxygen do not come into contact with the gas to be measured.

Therefore, even if the gas to be measured contains deposits such as carbon particles, the deposits do not adhere to the small holes 19 and the amount of oxygen molecules diffused does not change.

As a result, the oxygen concentration can be detected with high accuracy over a long period of time.

In the above embodiment, the oxygen partial pressure of the first small chamber 17 is kept the same as the oxygen partial pressure of the gas to be measured, and the second small chamber 1
The oxygen partial pressure of 8 was maintained at about 1/10 ¹⁰ of the oxygen partial pressure of the gas to be measured, but it may be maintained at another ratio.

For example, even if the oxygen partial pressure of the first small chamber 17 is kept at twice the oxygen partial pressure of the measured gas, and the oxygen partial pressure of the second small chamber 18 is kept at 1/2 the oxygen partial pressure of the measured gas. The oxygen concentration in the measured gas can be detected.

That is, a current is supplied to the first solid electrolyte 12 to move oxygen ions, the oxygen concentration in the first small chamber 17 is kept at a first predetermined multiple of the oxygen concentration of the gas to be measured, and the second solid electrolyte 16 is kept. Current is supplied to move the oxygen ions to keep the oxygen concentration in the second small chamber 18 at the second predetermined multiple of the oxygen concentration of the gas to be measured, and to the first solid electrolyte 12 and the second solid electrolyte 16. The oxygen concentration of the gas to be measured can be detected by detecting at least one of the supplied currents. That is, in this oxygen sensor, the closed chamber 11C isolated from the gas to be measured is divided into two small chambers 17 and 18, and both small chambers 1
7 and 18 are connected by a small hole 19,
Although diffusion of oxygen to some extent is secured, this diffusion is limited, and it becomes possible to maintain the oxygen concentration in each of the small chambers 17 and 18 at different concentrations. Therefore, the first
The first small chamber 1 by increasing or decreasing the pump current supplied to the first oxygen pump based on the output of the oxygen concentration battery of
The oxygen concentration in the second small chamber 18 is set to the second predetermined value by increasing or decreasing the pump current supplied to the second oxygen pump based on the output of the second oxygen concentration battery while maintaining the oxygen concentration in the second small chamber 18 at the first predetermined value. It is possible to detect the oxygen concentration of the gas to be measured by keeping the predetermined value of and detecting the magnitude of the supply current at this time.

8 and 9 are transverse cross-sectional views showing still another different example of the oxygen sensor embodying the present invention.

The oxygen sensor 71 shown in FIG.
The partition plate 13, the third solid electrolyte 72 having the oxygen diffusion limiting small holes 19 formed therein, the partition plate 15, and the second solid electrolyte 16 are laminated.

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

In the oxygen sensor 71, the difference between the oxygen partial pressure of the first small chamber 17 and the oxygen partial pressure of the second small chamber 18 is detected by the second sensor electrode 73 and the third reference electrode 74. The second pump current flowing between the second pump electrode 24 and the second reference electrode 25 is controlled according to the detection result to maintain the oxygen partial pressure of the second small chamber 18 at a predetermined value. The first small chamber 1
The control of the oxygen partial pressure of No. 7 is the same as that of the above embodiment.

Next, the oxygen sensor 81 shown in FIG. 9 has a first solid electrolyte 12, a partition plate 13, and a partition plate 1 having small holes 19 formed therein.
4, a partition plate 82 of a solid electrolyte having a through hole 82a forming the second small chamber 18 and a groove 82b forming an atmosphere introducing space 83 for introducing the atmosphere, and the second solid electrolyte 16
And are stacked.

Then, the first sensor electrode 20, the first pump electrode 21 and the first reference electrode 22 are formed on both surfaces of the first solid electrolyte 12.
And the second pump electrode 24 and the second reference electrode 25 are provided on both surfaces of the second solid electrolyte 16, and
The second sensor electrode 84 and the third reference electrode 85 are formed on both sides of the partition wall of the partition plate 82 between the small chamber 18 and the air introduction space 83.
And are provided.

In this oxygen sensor 81, the oxygen partial pressure of the atmosphere and the second
The difference between the oxygen partial pressure of the small chamber 18 and the oxygen partial pressure of the second chamber is detected by the second sensor electrode 84 and the third reference electrode 85, and the second pump electrode 24 and the second reference electrode 25 are detected according to the detection result. By controlling the second pump current flowing between them, the oxygen partial pressure in the second small chamber 18 is kept at a predetermined value higher than atmospheric pressure. The first small chamber 17
The control of the oxygen partial pressure is the same as in the above embodiment.

Also in these oxygen sensors 71 and 81, the oxygen concentrations of the small chambers 17 and 18 can be maintained at different concentrations, and the small holes 19 that are means for limiting the diffusion of oxygen are added to the gas to be measured. Since it is not touched, the oxygen concentration can be detected with high accuracy over a long period of time.

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

Further, the pump electrode and the sensor electrode may be commonly used, and the electrode for supplying the pump current and the electrode for detecting the voltage generated by the oxygen partial pressure ratio may be used in common.

However, in this case, the voltage between the electrodes includes not only the voltage generated by the oxygen partial pressure ratio but also the voltage drop due to the internal resistance of the sensor, so that the oxygen partial pressure ratio between the two surfaces of the solid electrolyte is constant. In order to accurately set the target voltage for maintaining the voltage, it is necessary to compensate for the voltage drop due to this internal resistance. For example, Japanese Patent Laid-Open No. 57-1928.
As seen in Japanese Patent Laid-Open No. 50, the alternating current is superposed on the current flowing between the electrodes of the oxygen sensor, and the resistors 47 and 53 shown in FIG.
The DC component of the signal detected from both ends of is the detection signal of Ip, the internal resistance is calculated from the AC component, and Ip detected by the DC component is multiplied to obtain the voltage drop due to the internal resistance of the oxygen sensor. If the target voltage is set by adding the above, it is possible to continuously and accurately detect the air-fuel ratio as in the above-described embodiment.

Effect As described above, according to the present invention, the closed chamber isolated from the gas to be measured is divided into two small chambers, and both small chambers are connected by the small passage. It is possible to maintain different concentrations, and it is possible to prevent the small passages that restrict oxygen and diffusion from coming into contact with the gas to be measured, so that the oxygen concentration can be detected with high accuracy over a long period of time.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a conventional oxygen sensor, and FIGS. 2 and 3 are lines showing oxygen sensor output-air-fuel ratio characteristics and flow-in current-air-fuel ratio characteristics, which are used to explain the operation of FIG. FIG. 4, FIG. 4 and FIG. 5 are cross-sectional views and exploded perspective views of an oxygen sensor showing an embodiment of the present invention, and FIG. 6 is a circuit diagram showing an example of an oxygen concentration detection circuit using the oxygen sensor. FIG. 7 is a diagram similarly showing the output-oxygen concentration and air-fuel ratio characteristics, and FIGS. 8 and 9 are transverse sectional views of an oxygen sensor showing another different embodiment of the present invention. 11, 71, 81 ... Oxygen sensor, 11A ... First oxygen concentration battery and first oxygen pump, 11B ... Second oxygen concentration battery and second oxygen pump, 11C ... Closed chamber,
12 ... First solid electrolyte, 14, 72 ... Partition plate (partition wall dividing the first and second small chambers), 16 ... Second solid electrolyte, 17 ... First small chamber, 18 ... Second chamber, 1
9 ... Small hole (small passage), 20 ... First sensor electrode, 2
1 ... 1st pump electrode, 22 ... 1st reference electrode, 2
3 ... second sensor electrode, 24 ... second pump electrode,
25 ... Second reference electrode

Claims (1)

[Claims] 1. A closed chamber isolated from a gas to be measured, and electrodes provided on both surfaces of a member formed of an oxygen ion conductive first solid electrolyte, one of the electrodes being the closed chamber. Electrodes are provided on both surfaces of a first oxygen concentration battery and a first oxygen pump facing inside, and a member formed of a second solid electrolyte having oxygen ion conductivity, and one of the electrodes is provided. A second oxygen concentration battery and a second oxygen pump facing the inside of the sealed chamber; a closed chamber, a first small chamber provided with the first oxygen concentration battery and the first oxygen pump; Oxygen concentration cell and second
An oxygen sensor having a partition wall that divides into a second small chamber provided with the oxygen pump, and a small passage communicating between the small chambers, and the first oxygen pump based on the output of the first oxygen concentration battery. A pump current supplied to the second oxygen pump based on the output of the second oxygen concentration battery by maintaining the oxygen concentration in the first small chamber at a first predetermined value by increasing or decreasing the pump current supplied to the second oxygen pump. The oxygen concentration of the second small chamber is kept at a second predetermined value by increasing or decreasing the oxygen concentration, and the oxygen concentration of the measured gas is detected by detecting the value of the pump current supplied to at least one of the oxygen pumps. An oxygen concentration detecting device comprising: a concentration detecting circuit;