JP2021156732A - Gas sensor - Google Patents

Abstract

To improve durability to mechanical shock, in a gas sensor holding a thin pipe-shaped solid electrolyte in a cantilever state.SOLUTION: A gas sensor for measuring the concentration of at least one ingredient in measured gas, includes a sensor pipe made of an ion conductive solid electrolyte formed in a thin pipe shape blocked at a tip end, a measuring electrode that is formed on the outer side on the tip end side of the sensor pipe and contacted with the measured gas, a reference electrode that is formed inside the sensor pipe, and is contacted with reference gas, and a sensor holder that supports and fixes the sensor pipe using a sealing glass. Resin is applied on the measuring electrode side of the sealing glass.SELECTED DRAWING: Figure 2

Description

The present invention relates to a gas sensor that measures the concentration of at least one component in a gas to be measured.

As a gas sensor used to measure the concentration of a specific gas component such as oxygen in the exhaust gas of an automobile engine or the like or in a container used in various manufacturing processes, there is a method using a solid electrolyte such as zirconia. A gas sensor using a solid electrolyte is provided with electrodes such as platinum on both sides of a solid electrolyte having a predetermined shape, which has ionic conductivity to a specific gas at a high temperature, and the concentration of the specific gas is constant on one of the electrodes. By contacting the reference gas of No. 1 and contacting the electrode to be measured with the electrode on the other side and measuring the electromotive force between the two electrodes based on the difference in the specific gas concentration, the electrode under test is used using Nerunst's theoretical formula. It measures the concentration of a specific gas in the measurement gas.

Japanese Unexamined Patent Publication No. 2016-1106

In a gas sensor using a solid electrolyte, it is necessary to stably heat it to a high temperature of a predetermined shape in order to exhibit ionic conductivity. Therefore, the predetermined shape is often a cantilever shape as a thin tube shape in order to suppress the heat capacity as much as possible (Patent Document 1).

When the solid electrolyte has a cantilever shape in the shape of a thin tube in this way, stress tends to be concentrated on the portion where the thin tube is held. For this reason, the gas sensor may be damaged due to an impact in the process of assembling the gas sensor or a vibration received from the surrounding environment while the gas sensor is installed.

The present invention has been made in view of the above problems, and is intended to improve the durability against mechanical impact in a gas sensor in which a thin tube-shaped solid electrolyte is held in a cantilever state.

In order to solve the above problems, the invention according to claim 1 is
A gas sensor for measuring the concentration of at least one component in the gas to be measured.
A sensor tube made of an ion-conducting solid electrolyte formed in a thin tubular shape with a closed tip, a measurement electrode formed on the outside of the tip side of the sensor tube and in contact with the gas to be measured, and an inside of the sensor tube. A reference electrode that is in contact with the reference gas and a sensor holder that supports and fixes the sensor tube using a sealing glass are provided.
The gas sensor is characterized in that a resin is applied to the measurement electrode side of the sealing glass.

The invention according to claim 2 is the gas sensor according to claim 1.
This is a gas sensor that uses an epoxy resin as the resin.

The invention according to claim 3 is the gas sensor according to claim 1 or 2.
A gas sensor in which the component concentration is an oxygen concentration.

According to the present invention, the durability against mechanical impact is improved in a gas sensor in which a thin tube-shaped solid electrolyte is held in a cantilever state.

It shows the schematic structure of the gas sensor which concerns on embodiment of this invention, is (a) external view, and (b) is the cross-sectional view which shows the mechanical structure inside. It is a figure explaining the effect of the resin coating part which concerns on embodiment of this invention, (a) figure which shows the position of the resin coating part, (b) figure which shows the example which there is no resin coating part. The configuration of the electrode provided in the sensor tube of the gas sensor according to the embodiment of the present invention is described, and is (a) an external view and (b) a cross-sectional view showing a state inside the sensor tube.

Embodiments of the present invention will be described with reference to the drawings. 1A and 1B are views showing a schematic structure of a gas sensor 1 according to an embodiment of the present invention, FIG. 1A is an external view of the gas sensor 1 as viewed from the side, and FIG. 1B is a cross-sectional view of the inside. It shows the mechanical configuration. In the following embodiment, the specific gas component to be measured for concentration is limited to oxygen, but if the gas sensor uses a solid electrolyte having the same configuration as that of the present embodiment, the specific gas component is limited to oxygen. The present invention is applicable to a gas sensor that measures the concentration of at least one component in the gas to be measured.

In the gas sensor 1, as shown in FIG. 1B, the sensor tube 2 and the heater 5 are covered with a sensor cover 6 having a hole 60 and fixed to the housing 7 while being held by the sensor holder 8. ing.

As shown in FIG. 2, the sensor tube 2 and the heater 5 are supported and fixed by glass at a glass sealing portion 80 in the through hole of the sensor holder 8. The glass of the glass sealing portion 80 is formed by melting at a high temperature and then cooling and solidifying in a state where the sensor tube 2 and the heater 5 are arranged.

The sensor holder 8 holding the sensor tube 2 and the heater 5 is fixed to the housing 7 via the gasket 82. Therefore, when the housing 8 is fixed to the outside of the closed container in which the gas to be measured is present and the sensor cover 6 side is inserted into the container, the gas to be measured can be shut off on the right side of the sensor holder 8.

By the way, in the gas sensor of the present embodiment in which the gas component to be measured for concentration is oxygen, porous electrodes are provided on both sides of a partition wall of a solid electrolyte exhibiting oxygen ion conductivity, and the gas sensor is generated according to the partial pressure of oxygen on both sides. The oxygen partial pressure (concentration) on one side (the oxygen partial pressure on the other side is known) is obtained by measuring the electric power, but the partition wall of the solid electrolyte conducts oxygen ions unless it has a high temperature of 400 ° C. or higher. Does not show sex. Further, since the electromotive force increases as the partition temperature of the solid electrolyte increases, the partition temperature is usually heated to about 700 ° C., but the accurate oxygen concentration cannot be known unless the temperature is raised rapidly and the high temperature state is maintained. ..

Therefore, the sensor tube 2 has a small-diameter cylindrical thin tube so that the heat capacity becomes small, and the heater 5 also has an elongated shape. Specifically, in the sensor tube 2, the inner diameter is about 0.5 mm to 1 mm, the partition wall thickness is about 0.3 mm to 1 mm, and the tube length is about 30 to 100 mm. For this reason, stress may be applied to a part of the solid electrolyte during handling, and even when stabilized zirconia having relatively toughness is used as the solid electrolyte, it may be damaged at the place where the stress is concentrated, and the heater 5 is broken. Sometimes.

Therefore, when holding the sensor tube 2 and the heater 5 in the sensor holder 8, if the sensor tube 2 and the heater 5 are sealed only with glass as shown in FIG. 2B, the sensor tube 2 and the heater 5 may break at the holding end PS. rice field.

On the other hand, as shown in FIG. 2A, by applying resin so as to cover the (left side) holding end of the glass sealing portion 80 and providing the resin coating portion 81, both the sensor tube 2 and the heater 5 are broken. I found it difficult. Although the mechanism by which the resin coating portion 81 makes it difficult for the sensor tube 2 and the heater 5 to break has not been clarified, when vibration is applied to the left end of the sensor tube 2 by applying an epoxy adhesive with a thickness of 1 mm. Impact resistance is improved 20 times.

Although the main structural parts of the gas sensor 1 have been described above in FIGS. 1 and 2, FIG. 3 shows a part related to the sensor function.

FIG. 3 describes an electrode provided on the sensor tube 2, FIG. 3A is an external view seen from the side, and FIG. 3B is a cross-sectional view. In the present embodiment, the sensor tube 2 is made of zirconia ceramics which is an oxygen ion conductive electrolyte, and has a hollow cylindrical shape (outer diameter is 1.3 mm) having an inner diameter of 0.7 mm and a partition wall thickness of 0.3 mm.

As shown in FIG. 3B, the left end of the sensor tube 2 is closed by the glass sealing portion 21, but the right end is open, and the outside of the side marked as the gas to be measured in FIG. 3 is to be measured. It is a gas atmosphere, and the outside and the inside of the side marked as the reference gas are the reference gas atmosphere. Therefore, the measurement electrode 3 is in contact with the gas to be measured, and the reference electrode 4 is in contact with the reference gas. The reference gas is a gas having a known oxygen partial pressure, and the atmosphere is usually used for measuring the oxygen concentration.

The measurement electrode 3 and the reference electrode 4 are formed by applying platinum paste and then baking, but the portion inside the sensor tube 2 of the measurement electrode 3 and the reference electrode 4 is porous to allow oxygen to permeate. Although it is formed as a quality, it is desirable that the outer portion of the sensor tube 2 of the reference electrode 4 is precisely formed from the viewpoint of ensuring conductivity. The thickness of the measurement electrode 3 and the reference electrode 4 after baking is 50 μm in the present embodiment, but the thickness is not limited to this.

By the way, although the measuring electrode 3 is located on the tip end side of the sensor tube 2, usually, an electrode protective film 32 is provided on the surface of the measuring electrode 3. Therefore, the weight on the side far from the glass sealing portion 80 is increased. From such a form, it is clear that the stress applied to the sensor tube 2 on the right end side of the glass sealing portion 80 is further increased as compared with FIG. For this reason as well, the need for the resin coating portion 81 is increasing.

In the present embodiment, the gas sensor in which the specific gas to be measured is oxygen has been described as an example. However, if the solid electrolyte type gas sensor measures the concentration of at least one component in the gas to be measured, the specific gas can be used. It may be other than oxygen. That is, even if the solid electrolyte is not zirconia, the same effect can be expected by having the same constituent requirements as this.

1 Gas sensor 2 Sensor tube 3 Measuring electrode 4 Reference electrode 5 Heater 6 Sensor cover 7 Housing 8 Sensor holder 21 Tip sealing part 31 Measuring electrode lead 60 holes 61 Insulation material 80 Glass sealing part 81 Resin coating part 82 Gasket

Claims (3)

A gas sensor for measuring the concentration of at least one component in the gas to be measured.
A sensor tube made of an ion-conducting solid electrolyte formed in a thin tubular shape with a closed tip,
A measurement electrode formed on the outside of the tip side of the sensor tube and in contact with the gas to be measured,
A reference electrode formed inside the sensor tube and in contact with the reference gas,
A sensor holder for supporting and fixing the sensor tube using sealing glass is provided.
A gas sensor characterized in that a resin is applied to the measurement electrode side of the sealing glass. The gas sensor according to claim 1, wherein an epoxy resin is used as the resin. The gas sensor according to claim 1 or 2, wherein the component concentration is an oxygen concentration.

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