JPH05119017A - Gas sensor - Google Patents

Abstract

PURPOSE:To enable concentration of oxygen and that of carbon dioxide gas to be detected simultaneously and achieve compactness and energy saving by placing an oxygen detection element and a carbon dioxide gas detection element in lamination on a substrate with a heater. CONSTITUTION:An electrode 21, a solid electrolyte layer 22, and an electrode 23 are laminated on an upper surface of a substrate 11, thus enabling an oxygen detection element 2 to be constituted. Also, a reference electrode 32, an ion conductor layer 33, and a detection electrode 34 are provided on a substrate 31, which is coated with a detection material layer 35 and is sealed by a sealing material 36 for constituting a carbon dioxide gas detection element 3. Then, the element 3 is bonded to the element 2 through an inorganic film material 13. When a heater 12 conducts, the element 2 is heated first and further a temperature of the element 3 also increases due to thermal conductivity but a thickness of the substrate 31 and the film material 13 is adjusted so that a temperature of the element 3 reaches 400-600 deg.C when that of the element 2 reaches 500-700 deg.C, thus obtaining a compact and energy-saving type gas sensor which can detects concentration of oxygen and that of carbon dioxide gas simultaneously.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor for simultaneously measuring oxygen concentration and carbon dioxide concentration in atmospheric gas, and more particularly to a small gas sensor capable of simultaneously detecting oxygen and carbon dioxide contained in combustion gas. ..

[0002]

2. Description of the Related Art An oxygen sensor using zirconia as a solid electrolyte is known as a sensor for detecting the concentration of oxygen contained in the exhaust gas of an internal combustion engine. As such a zirconia sensor, one surface of a zirconia solid electrolyte is kept in an atmosphere containing a reference concentration of oxygen and the other surface is exposed to a gas to be detected, and the difference in electromotive force generated between electrodes provided on both surfaces is measured. There is a concentration cell type oxygen sensor that detects the oxygen concentration in the gas to be detected.

Further, as shown in FIGS. 4 (a) and 4 (b), for example, gas permeable platinum electrodes 21 and 23 are provided on both sides of the zirconia solid electrolyte layer 22, and one of the electrodes 23 is provided. The cover 24 having a small hole 25 that serves as a gas diffusion resistance, the porous plate 26, and the like are heated and heated by the heater 27, and the limiting current value when a constant voltage is applied from the outside is displayed. A so-called limiting current type oxygen sensor that detects the oxygen concentration in the atmosphere by measuring is also generally used.

On the other hand, as a sensor for detecting the concentration of carbon dioxide gas in a gas, a concentration battery type carbon dioxide gas sensor using an alkali metal ion conductor as a solid electrolyte is known. For example, as shown in FIG. 5, such a carbon dioxide sensor includes β-alumina and NASICON (general formula Na _1-x Zr ₂ P
_3-x Si _x O ₁₂ ) or another alkali metal ion conductor layer 33 is sandwiched between the electrodes, and gold or platinum electrodes are provided on both sides, and one of them is covered with a detection material layer 35 made of an alkali metal carbonate to form the detection electrode 3
4 and the other side is covered with the substrate 31 provided with the heater 37 to form the reference electrode 32, and the portion other than the detection material layer 35 is covered with the gas impermeable sealing material layer 36.

Each of these gas sensors has an optimum temperature condition for the solid electrolyte to function. For example, a zirconia oxygen sensor has a temperature of 600 to 700 ° C.
In the case of the CON carbon dioxide gas sensor, the temperature is 400 to 600 ° C., so that in each case, the sensor element is heated by the heater to maintain the operating state.

[0006]

When the conventional gas sensors are combined to detect the concentrations of oxygen and carbon dioxide in the gas to be detected at the same time, two types of sensors must be installed individually. However, there is a problem that not only the detection device becomes large but also the electric power for heating the element becomes large. Therefore, the present invention is to provide a small-sized and energy-saving integrated gas sensor capable of simultaneously detecting the oxygen concentration and the carbon dioxide concentration.

[0007]

In order to achieve the above object, the present invention provides a substrate provided with a heater for a solid electrolyte type oxygen sensing element operating at high temperature and a solid electrolyte type carbon dioxide sensing element operating at high temperature. A gas sensor was formed by stacking the layers on top of each other.

When stacking the oxygen sensing element and the carbon dioxide sensing element in the gas sensor of the present invention, for example, the oxygen sensing element and the carbon dioxide sensing element are sequentially stacked on one surface of the substrate, or both sides of the substrate are stacked. It is possible to adopt a method such as laminating oppositely on one surface, or laminating in parallel on one surface of the substrate.

The oxygen sensing element used in the gas sensor of the present invention is preferably a limiting current type zirconia sensor element, and the carbon dioxide sensing element is preferably a concentration cell type sensor element. The oxygen detection element and the carbon dioxide gas detection element are not particularly limited in shape, structure, characteristics, etc., and conventionally used ones can be used.

[0010]

In the gas sensor of the present invention, it is possible to simultaneously measure the gas concentrations of oxygen and carbon dioxide gas, since each gas detection element can be brought to a temperature suitable for operation with a heater that consumes less power.

[0011]

【Example】

(First Embodiment) A first embodiment of the gas sensor of the present invention is shown in FIG.
Shown in. In the figure, reference numeral 11 is a porous alumina ceramic substrate having a thickness of 0.3 mm, which is permeable to gas, and a heater 12 made of a platinum film formed by sputtering is provided on the lower surface thereof.

On the upper surface of the substrate 11, a gas-permeable electrode 21 made of a platinum film having a thickness of 0.7 μm formed by sputtering and a stabilized zirconia having a thickness of 8.0 μm also formed by sputtering. The solid electrolyte layer 22 and a gas-permeable electrode 23 made of a platinum film formed in the same manner are sequentially laminated to form the oxygen detection element 2.

Reference numeral 31 is a gas-impermeable alumina ceramic substrate having a thickness of 0.5 mm, reference numeral 32 is a reference electrode made of a platinum film formed by sputtering, and an ion conductor layer 33 is formed thereon. Has been formed. Further, a detection electrode 34 similar to the reference electrode is provided on the ion conductor layer 33, and an alkali metal carbonate detection material layer 35 is provided.
Is covered with. The periphery of these is sealed with a gas impermeable sealing material 36 except the upper surface, and constitutes the carbon dioxide detection element 3.

The carbon dioxide gas detecting element 3 is adhered so that the lower surface of the ceramic substrate 31 is laminated on the oxygen detecting element 2 with a gas-permeable inorganic coating material 13 interposed between the oxygen detecting element 2 and the oxygen detecting element 2. The surroundings of the carbon dioxide detecting element 3 as well as the surroundings are integrally covered with the inorganic coating material 13,
As a whole, a combined gas sensor is configured.

In the gas sensor having such a structure, when the heater 12 is energized, the oxygen detecting element 2 provided in contact with the substrate 11 is first heated, and the temperature of the carbon dioxide detecting element 3 is also increased by heat conduction. Since the heat is dissipated from the surface of the gas sensor, the temperature of the carbon dioxide sensing element 3 becomes lower than the temperature of the oxygen sensing element 2, but the temperature of the oxygen sensing element 2 is 500 to 700 ° C, preferably 600 to 700 ° C.
The temperature of the carbon dioxide sensing element 3 is 400 to 60
It is desirable to adjust the thickness of the substrate 31 and the inorganic coating material 13 so as to be 0 ° C.

(Second Embodiment) Second embodiment of the gas sensor of the present invention
An example is shown in FIG. In this example, the oxygen sensing element 2 is provided on the substrate 11 provided with the heater 12, as in the first embodiment, but the carbon dioxide sensing element 3 is provided on the heater 12 side of the substrate 11. This is different from the first embodiment. In this case, the ceramic substrate 31 covering the reference electrode 32 of the carbon dioxide detection element 3 is made thick to suppress heat conduction so that the temperature becomes lower than that of the oxygen detection element 2. However, other configurations are It is almost the same as the first embodiment.

(Third Embodiment) Third embodiment of the gas sensor of the present invention
An example is shown in FIG. This example is different from the previous example in that the oxygen detecting element 2 and the carbon dioxide detecting element 3 are provided side by side on one side of the substrate 11 provided with the heater 12. That is, the ceramic substrate for preventing the solid electrolyte layer 22 in the oxygen sensing element 2 from spreading so as to cover the mounting position of the carbon dioxide sensing element 3 and directly transferring the heat of the substrate 11 to the carbon dioxide sensing element 3. Instead of 31. However, the other structure is almost the same as that of the second embodiment.

[0018]

In the gas sensor of the present invention, the oxygen detecting element is laminated on the substrate provided with the heater and the carbon dioxide detecting element is also laminated, so that not only the heater capacity is small but also the size is further reduced. Thus, a gas sensor is obtained that is not restricted by the installation position when simultaneously measuring oxygen and carbon dioxide.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of a gas sensor of the present invention.

FIG. 2 is a diagram showing the configuration of a second embodiment of the gas sensor of the present invention.

FIG. 3 is a diagram showing the configuration of a third embodiment of the gas sensor of the present invention.

FIG. 4 is a diagram showing a configuration of an example of a conventional oxygen sensor.

FIG. 5 is a diagram showing a configuration of an example of a conventional carbon dioxide sensor.

[Explanation of symbols]

 2 Oxygen detecting element 3 Carbon dioxide detecting element 11 Substrate 12 Heater 13 Inorganic coating 21 Electrode 22 Solid electrolyte layer 23 Electrode 24 Cover 25 Small hole 26 Porous plate 27 Heater 31 Substrate 32 Reference electrode 33 Ion conductor layer 34 Detection electrode 35 Detection Material Layer 36 Encapsulation Material Layer 37 Heater

Claims (6)

[Claims] 1. A gas sensor comprising a solid electrolyte type oxygen sensing element operating at high temperature and a solid electrolyte type carbon dioxide sensing element operating at high temperature, which are laminated on a substrate provided with a heater. 2. The gas sensor according to claim 1, wherein the oxygen detecting element and the carbon dioxide detecting element are sequentially laminated on one surface of the substrate. 3. The gas sensor according to claim 1, wherein the oxygen sensing element and the carbon dioxide sensing element are laminated on both side surfaces of the substrate so as to face each other. 4. The gas sensor according to claim 1, wherein the oxygen detecting element and the carbon dioxide detecting element are laminated in parallel on one surface of the substrate. 5. The gas sensor according to claim 1, wherein the oxygen detection element is a limiting current type zirconia sensor element. 6. The gas sensor according to claim 1, wherein the carbon dioxide detection element is a concentration cell type sensor element.