JPH0763719A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To obtain an oxygen sensor which excels in anti-temperature characteristic and responsiveness with a simple structure by forming an oxygen concentration detecting section from a compound in which a specified perovskite type oxide is doped with alkaline earth metal. CONSTITUTION:An oxygen concentration detecting section (thin film) is formed on a substrate 10 by a laser abrasion method or the like. The detecting section 12 is formed from a compound in which a perovskite type oxide of an ABO3 type comprising ittrium or lanthanoid at an A site and chromium or manganese at a B site is doped with alkali earth metal. To measure electric conductivity of the thin film 12 by a DC 4 terminal method, an ammeter 18 is connected in series to a power source 16 through a terminal 14. A voltmeter 22 is connected through a terminal 20. As the electric conductivity of the thin film 12 varies with the concentration of oxygen in the atmosphere, the electric conductivity of the thin film 12 is measured in various atmospheres with the concentration of oxygen known is measured beforehand. This clarifies a correspoding relationship between the concentration of oxygen and the electric conductivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor for controlling combustion air ratio in an engine, for example.

[0002]

BACKGROUND OF THE INVENTION Controlling the air ratio in combustion (actual air quantity / theoretical air quantity required to completely oxidize fuel) is essential for proper combustion. Very important. Particularly, in the engine, in order to properly operate the three-way catalyst installed in the downstream (exhaust gas side) in order to reduce NO _x , the air ratio in combustion is set to a narrow range of about 1.0 (0.9 ~ 1.1,
It is necessary to control to preferably 0.95 to 1.05).

Conventionally, as an oxygen sensor for controlling such an air ratio, an electromotive force type oxygen sensor using stabilized zirconia as a solid electrolyte has been widely used. This electromotive force type oxygen sensor has the advantage of high reliability, but since it uses an air electrode as a reference electrode, it is necessary to introduce air to the counter electrode side with a solid electrolyte in between, and the structure is complicated and the manufacturing cost is high. It had the drawback of being expensive.

On the other hand, a semiconductor type oxygen sensor utilizing the property that the electric conductivity of a semiconductor based on TiO ₂ changes depending on the oxygen concentration of the atmosphere has been studied, but it has been studied that the oxygen sensor has temperature resistance and responsiveness. There is a problem and it has not been put to practical use.

That is, the conventional semiconductor oxygen sensor has the following drawbacks.

Poor temperature resistance. In the hole conduction type, when the temperature of the sensor becomes low, the electric resistance becomes high even in an oxidizing atmosphere, and it becomes indistinguishable from the reducing atmosphere. On the contrary, in the case of the electron conduction type, when the temperature of the sensor becomes low, the electric resistance becomes high even in the reducing atmosphere, so that it cannot be distinguished from the oxidizing atmosphere. As described above, it is difficult to set a reference with a constant electric conductivity because the electric conductivity changes remarkably with temperature.

Poor responsiveness. Since it is made of a sintered body and has a large thickness, it takes a long time to diffuse oxygen, and a change in oxygen concentration cannot be detected quickly.

An object of the present invention is to solve the above-mentioned drawbacks of the conventional oxygen sensor, to provide an oxygen sensor having a simple structure and excellent temperature characteristics and responsiveness.

[0009]

The oxygen sensor of the present invention comprises:
The oxygen concentration detecting section is composed of a compound obtained by doping an ABO ₃ type perovskite type oxide in which the A site is yttrium or lanthanoid and the B site is chromium or manganese with an alkaline earth metal, or a solid solution between these compounds. (Claim 1).

It is preferable that the oxygen concentration detecting section has metallic electric conductivity in an oxidizing atmosphere (claim 2).

Further, it is preferable that the oxygen concentration detecting section is made of a compound in which LaCrO ₃ or LaMnO ₃ is doped with strontium or calcium at 20 to 70% of the A site or a solid solution between these compounds (claim 3).

Furthermore, the oxygen concentration detector has a thickness of 0.
It is preferably a thin film of 01 to 5 μm (claim 4).

[0013]

According to the present invention, the oxygen concentration detection unit is LaM
Since it consists of a compound in which a perovskite type oxide such as nO ₃ or LaCrO ₃ is doped with an alkaline earth metal, or a solid solution between these compounds, it has an extremely excellent catalytic ability for oxygen dissociation as compared with TiO _2. And has excellent responsiveness to changes in oxygen concentration. That is, since the oxygen concentration detecting unit changes the electric conductivity according to the oxygen concentration of the atmosphere, the oxygen concentration can be quickly detected by providing the means for measuring the electric conductivity.

Further, in the oxygen concentration detecting portion, the electric conductivity is hardly affected by temperature, and the temperature resistance is excellent.

When a relatively large amount of alkaline earth metal is doped so that the oxygen concentration detecting portion has metallic electrical conductivity in an oxidizing atmosphere, the electric resistance in the oxidizing atmosphere serving as a reference is temperature-dependent. The temperature dependence is further improved, and the electric conductivity value, which is a reference value in controlling the air ratio, can be set more easily.

To this end, as in claim 3, LaC
A compound in which rO ₃ or LaMnO ₃ is doped with strontium or calcium so that they are 20 to 70% of the A site, or a solid solution between these compounds is preferable. The doping amount of strontium or calcium is more preferably 30 to 50%.

Further, it is preferable that the oxygen concentration detecting portion is a thin film having a thickness of 0.01 to 5 μm as described in claim 4 because the responsiveness to changes in oxygen concentration is further improved. As a method for obtaining such a thin film, a laser ablation method,
Screen printing method, spray pyrolysis method, calendar rolling method and the like.

[0018]

An embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, reference numeral 10 denotes a substrate, on which an oxygen concentration detecting portion, La _0.60 Sr having a thickness of 3 μm, is formed.
_{The 0.39} CrO ₃ thin film 12 is formed by the laser ablation method. In order to measure the electrical conductivity of the thin film 12 by the DC four-terminal method, a power source (constant current source) 16 and an ammeter 1 are provided at both ends of the upper surface of the thin film 12 via terminals 14.
8 are connected in series. A voltmeter 22 is connected to the middle of the upper surface of the thin film 12 via a terminal 20.

Since the electric conductivity of the thin film 12 changes depending on the oxygen concentration of the atmosphere, it is necessary to measure the electric conductivity of the thin film 12 by placing this device in various atmospheres in which the oxygen concentration is known in advance. , The correspondence between oxygen concentration and electrical conductivity is known. In order to obtain the oxygen concentration of the sample atmosphere, the electric conductivity of the thin film 12 in the atmosphere can be measured, and the oxygen concentration can be obtained based on the correspondence relationship before the measured value.

Using this apparatus, the electric conductivity of the thin film 12 was measured in an atmosphere of oxygen concentration equivalent to the exhaust gas of an engine burned at an air ratio of 1.1. 50 ± 10S ・ c in temperature range
It was in the range of m. The electric conductivity was measured while raising the temperature in an electric furnace. Next, when the electric conductivity in an atmosphere of oxygen concentration equivalent to the exhaust gas of the engine burned at an air ratio of 0.9 was measured, it was 5 S · cm or less in the temperature range of 700 to 1000 ° C. Than these things,
It was found to have a sufficient oxygen sensor function. Also,
For example, if the electric conductivity is set within the range of 5 to 40 S · cm and controlled, the air ratio of the engine can be controlled within the range of 0.9 to 1.1.

Further, the 90% responsiveness between the both atmospheres at 1000 ° C. (time until the electrical conductivity changes by 90% when the atmosphere is changed) of this apparatus is 1 minute or less, which is an excellent response. Showed sex.

In the above embodiments, the electric conductivity of the thin film 12 was measured by the DC four-terminal method, but the present invention is not limited to this, and may be measured by, for example, the DC two-terminal method (not shown). .

When the oxygen sensor of the present invention is incorporated in the air ratio control system of an engine, only the oxygen concentration detecting section is attached to the exhaust gas line and the oxygen is detected by a control unit (not shown) located at a distance. The electrical conductivity of the concentration detector may be detected.

[0025]

The oxygen sensor of the present invention has a simple structure,
It also has excellent temperature characteristics and responsiveness.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of the present invention.

[Explanation of symbols]

10 substrate 12 oxygen concentration detector (La _0.60 Sr _0.39 Cr
O ₃ thin film) 14 terminals 16 power supply 18 ammeter 20 terminals 22 voltmeter

Front page continuation (72) Minoru Suzuki Minoru 4-1-2, Hiranocho, Chuo-ku, Osaka City, Osaka Gas Co., Ltd. (72) Inventor Tadayuki Sogi 4-1-2, Hiranocho, Chuo-ku, Osaka In-house (72) Inventor Atsuko Kajimura 2-5-904 Kusatsu, Kusatsu City, Shiga Prefecture

Claims (4)

[Claims] 1. A compound obtained by doping an ABO ₃ -type perovskite-type oxide, in which the A site is made of yttrium or lanthanoid and the B site is made of chromium or manganese, with an alkaline earth metal, or between these compounds, in the oxygen concentration detector. Oxygen sensor consisting of a solid solution of. 2. The oxygen sensor according to claim 1, wherein the oxygen concentration detector has metallic electrical conductivity in an oxidizing atmosphere. 3. The oxygen concentration detector is made of a compound in which LaCrO ₃ or LaMnO ₃ is doped with strontium or calcium at 20 to 70% of the A site, or a solid solution between the compounds. The oxygen sensor described in 1. 4. The oxygen concentration detector has a thickness of 0.01 to 5 μm.
It is a thin film of m, The oxygen sensor of any one of Claims 1-3 characterized by the above-mentioned.