JP7399770B2 - gas sensor - Google Patents

Description

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

BACKGROUND ART There is a method using a solid electrolyte such as zirconia as a gas sensor used to measure the concentration of a specific gas component such as oxygen in exhaust gas from an automobile engine or the like or in a container used in various manufacturing processes. A gas sensor using a solid electrolyte has electrodes such as platinum on both sides of a solid electrolyte body of a predetermined shape that is ionically conductive to a specific gas at high temperatures, and the concentration of the specific gas is maintained at a constant level on one side of the electrode. By contacting the reference gas on the one side and the gas to be measured on the other electrode, the electromotive force between the two electrodes is measured based on the difference in the specific gas concentration. It measures the concentration of a specific gas in the measurement gas.

Unexamined Japanese Patent Publication No. 2016-1106

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

When the solid electrolyte is formed into a cantilevered shape of a capillary in this manner, stress tends to be concentrated in the portion where the capillary is held. For this reason, the gas sensor may be damaged by shock during the process of assembling it as a gas sensor or by vibrations received from the surrounding environment while it is installed as a gas sensor.

The present invention has been made in view of the above problems, and is intended to improve the durability against mechanical shock in a gas sensor formed by holding a solid electrolyte in the form of a thin tube in a cantilevered state.

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

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

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

According to the present invention, durability against mechanical shock is improved in a gas sensor formed by holding a solid electrolyte in the form of a capillary in a cantilevered state.

1A is an external view showing a schematic structure of a gas sensor according to an embodiment of the present invention, and FIG. 1B is a sectional view showing an internal mechanical structure. 2A and 2B are diagrams illustrating the effects of the resin coating section according to the embodiment of the present invention, and FIG. 3A is a diagram showing the position of the resin coating section, and FIG. 2A and 2B are diagrams illustrating the structure of an electrode provided in a sensor tube of a gas sensor according to an embodiment of the present invention, and FIG.

Embodiments of the present invention will be described using the drawings. FIG. 1 is a diagram showing a schematic structure of a gas sensor 1 according to an embodiment of the present invention. FIG. 1(a) is an external view of the gas sensor 1 seen from the side, and FIG. It shows the mechanical configuration. Note that the description of the embodiment below is limited to an example in which the specific gas component whose concentration is to be measured is oxygen, but if the gas sensor uses a solid electrolyte with the same configuration as this embodiment, the specific gas component is limited to oxygen. However, the present invention is applicable to a gas sensor that measures the concentration of at least one component in a gas to be measured.

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

As shown in FIG. 2, the sensor tube 2 and the heater 5 are supported and fixed by glass in a glass sealing part 80 in the through hole of the sensor holder 8. Note that the glass of the glass sealing part 80 is melted at a high temperature with the sensor tube 2 and heater 5 arranged, and then cooled and solidified.

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

By the way, in the gas sensor of this embodiment in which the gas component to be measured is oxygen, porous electrodes are provided on both sides of the partition wall of the solid electrolyte that exhibits oxygen ion conductivity, so that the gas sensor that is the gas component to be measured in concentration is provided with porous electrodes on both sides of the partition wall of the solid electrolyte that exhibits oxygen ion conductivity. Electric power is measured to determine the oxygen partial pressure (concentration) on one side (the oxygen partial pressure on the opposite side is known), but the solid electrolyte partition wall does not conduct oxygen ions unless the temperature is over 400°C. Does not show gender. Additionally, the higher the solid electrolyte partition wall temperature, the greater the electromotive force, so the partition wall temperature is usually heated to around 700°C, but unless the temperature is raised quickly and maintained at a high temperature, accurate oxygen concentration cannot be determined. .

Therefore, the sensor tube 2 has a small diameter cylindrical shape so as to have a small heat capacity, 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 some parts during handling, and even if stabilized zirconia, which has relatively toughness, is used as the solid electrolyte, damage may occur at locations where stress is concentrated, and the heater 5 may break. 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. 2(b), the sensor tube 2 and the heater 5 may break at the holding end PS. Ta.

On the other hand, by applying resin to cover the (left) holding end of the glass sealing part 80 and providing a resin coating part 81 as shown in FIG. 2(a), both the sensor tube 2 and the heater 5 can be bent. I found that it became difficult. Although the mechanism by which the sensor tube 2 and the heater 5 become difficult to break due to the resin coating part 81 has not yet been elucidated, by applying the epoxy adhesive to a thickness of 1 mm, it is possible to Impact resistance has been improved by 20 times.

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

FIG. 3 explains the electrodes provided in the sensor tube 2, with FIG. 3(a) being an external view seen from the side, and FIG. 3(b) showing a cross-sectional view. In this 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) with an inner diameter of 0.7 mm and a partition wall thickness of 0.3 mm.

As shown in FIG. 3(b), the left end of the sensor tube 2 is closed with a glass sealing part 21, but the right end is open, and the outside of the side marked as gas to be measured in FIG. It is a gas atmosphere, and the outside and inside of the side marked as reference gas is a 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. Note that the reference gas is a gas whose oxygen partial pressure is known, and the atmosphere is usually used in oxygen concentration measurement.

The measuring electrode 3 and the reference electrode 4 are formed by applying and baking platinum paste, but the portions of the measuring electrode 3 and the reference electrode 4 that are inside the sensor tube 2 are porous to allow oxygen to pass through. However, it is desirable that the outer part of the sensor tube 2 at the reference electrode 4 be formed densely from the viewpoint of ensuring conductivity. Note that the thickness of the measurement electrode 3 and the reference electrode 4 after baking is 50 μm in this embodiment, but is not limited to this.

By the way, although there is a measurement electrode 3 on the tip side of the sensor tube 2, an electrode protection film 32 is usually provided on the surface of the measurement electrode 3. Therefore, the weight of the side far from the glass sealing part 80 is increased. Because of this configuration, it is clear that the stress applied to the sensor tube 2 on the right end side of the glass sealing part 80 is further increased compared to FIG. 2. For this reason as well, the need for the resin coating section 81 is increasing.

As described above, in this embodiment, the gas sensor in which the specific gas to be measured is oxygen has been described as an example, but 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 measured. It may be other than oxygen. That is, even if the solid electrolyte is not zirconia, the same effects can be expected by providing the same structural requirements as the present invention.

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 section 31 Measuring electrode lead 60 Hole 61 Heat insulating material 80 Glass sealing section 81 Resin coating section 82 Gasket

Claims (3)

A gas sensor for measuring the concentration of at least one component in a gas to be measured,
A sensor tube made of an ion-conductive solid electrolyte formed into a thin tube 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 a reference gas;
and a sensor holder that supports and fixes the sensor tube using sealing glass,
A gas sensor comprising a resin applied to an end surface of the sealing glass on the measurement electrode side. The gas sensor according to claim 1, wherein the resin is an epoxy resin. The gas sensor according to claim 1 or 2, wherein the component concentration is an oxygen concentration.