JP7356388B2 - 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 other side and the gas to be measured on the other side, 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.

Japanese Patent Application Publication No. 57-40644

When measuring the electromotive force between the electrodes provided on both sides of the solid electrolyte body, it is necessary to supply electricity to both electrodes and the voltmeter that measures the electromotive force (voltage), and each electrode is connected with a lead wire. .

Each electrode and lead wire are bonded by baking a conductive paste, and although they are electrically and mechanically bonded, the mechanical strength is not sufficient and the wires may break due to tension.

The present invention has been made in view of the above-mentioned problems, and is intended to prevent the electrodes provided on the solid electrolyte from becoming disconnected from the lead wires in a gas sensor using a solid electrolyte, thereby increasing the reliability of the gas sensor. .

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. a reference electrode in contact with a reference gas, a sensor holder supporting and fixing the sensor tube using a sealing glass, and a measurement electrode connected to the measurement electrode and passing through the sensor holder while being fixed by the sealing glass. The gas sensor includes an electrode lead and a reference electrode lead that is connected to the reference electrode and fixed with the sealing glass while being folded back through the sensor holder.

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

According to the present invention, in a solid electrolyte type gas sensor, it is possible to prevent disconnection between an electrode provided on a solid electrolyte and a lead wire, thereby improving reliability.

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 structure of an electrode provided in a sensor tube of a gas sensor according to an embodiment of the present invention, and FIG. 2A and 2B are diagrams illustrating a lead wire connected to an electrode of a gas sensor according to an embodiment of the present invention; FIG. The gas sensor according to the embodiment of the present invention is explained, and FIG. 3A is a diagram showing the necessity of a resin coating part, and FIG. 3B is a diagram showing a form in which the reference electrode lead is folded back.

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.

The sensor tube 2 and the heater 5 are supported and fixed by glass at 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.

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

First, FIG. 2 explains the electrodes provided in the sensor tube 2. FIG. 2(a) is an external view seen from the side, and FIG. 2(b) is 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. 2(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.

After forming the measurement electrode 3 and the reference electrode 4 as shown in FIG. 2, it is necessary to provide a lead wire for the purpose of measuring the electromotive force between the two electrodes. An example of this is shown in FIG. 3A, in which a measurement electrode lead 31 is connected to the measurement electrode 3, and a reference electrode lead 41 is connected to the reference electrode 4. Excellent electrical connections can be ensured by baking a dense platinum paste between the measurement electrode 3 and the measurement electrode lead 31 and between the reference electrode 4 and the reference electrode lead 41. Note that it is preferable to use platinum wires made of the same material as the electrodes as the measurement electrode lead 31 and the reference electrode lead 41, and in consideration of strength, conductivity, cost, etc., the diameter is preferably in the range of 0.2 mm to 0.4 mm. It is.

Baking with a dense platinum paste intervening ensures mechanical connection, but this is not necessarily sufficient for the reference electrode lead 41. That is, since the measurement electrode lead 31 passes through the sensor holder 8 on the way to the reference gas (atmosphere) side, it is fixed by the glass sealing part 80, so the measurement electrode lead 31 is pulled from the reference gas side. Even if such a situation occurs, it will not affect the joint with the measurement electrode 3, but in the form of FIG. It may come off.

Therefore, in this embodiment, as shown in FIG. 3(b), after the reference electrode lead 41 connected to the reference electrode 4 is led to the measuring electrode 3 side and after passing through the glass sealing part 80 (or after passing through the glass sealing part 80) 80) and is guided to the reference gas side. With this configuration, even if the reference electrode lead 41 is pulled from the reference gas side, the influence on the joint with the reference electrode 4 can be eliminated.

Note that FIG. 4B shows an example of how the reference electrode lead 41 is folded back at the sensor holder 8, which was explained using FIG. It shows the state where it is stopped and fixed. In FIG. 4B, the reference electrode lead 41 is folded back after passing through the glass sealing part 80, but the reference electrode lead 41 is not limited to this, and may be folded back within the glass sealing part 80.

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 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 part 31 Measuring electrode lead 41 Reference electrode lead 60 Hole 61 Heat insulating material 80 Glass sealing part

Claims (2)

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;
a sensor holder that supports and fixes the sensor tube using sealing glass;
a measurement electrode lead connected to the measurement electrode and passing through the sensor holder while being fixed by the sealing glass;
A gas sensor comprising: a reference electrode lead connected to the reference electrode and fixed by the sealing glass in a folded state through the inside of the sensor holder. The gas sensor according to claim 1, wherein the component concentration is oxygen concentration.