JPH0648219B2 - Temperature sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a temperature sensor that uses a thermistor as a temperature detecting element, and is particularly suitable for measuring the temperature of combustion exhaust gas discharged from an internal combustion engine or the like.

[Prior Art] As a method of measuring combustion exhaust gas temperature of an internal combustion engine or various combustion furnaces, a temperature sensor incorporating an oxygen ion conductive type or electronic conductive type thermistor as a temperature detecting element is used. Works as a kind of oxygen battery that uses oxygen ions as a conduction medium for electric charges, so stable and reliable measurement results must be obtained if there is not more than a certain concentration of oxygen (generally 5% or more) in the atmosphere with which the thermistor contacts. Can't get

The structure of the temperature sensor is roughly the same as that of the thermistor protective cover and sensor mounting metal fittings. The thermistor is housed at the sealed end inside a heat-resistant metal tube whose one end is sealed, and the lead wire for taking out its electrical output. Is connected to the wiring cord fitted to the open end of the tube.

[Problems to be Solved by the Invention] In the temperature sensor having the above-described structure, the inner wall surface of the metal tube is gradually oxidized by being combined with oxygen existing in the tube during use. The oxygen concentration in the atmosphere around the thermistor decreases with the passage of time, and the electrical output characteristics of the thermistor also fluctuate accordingly, and the reliability of the temperature sensor decreases over time.

As a countermeasure, it is necessary to make a large number of small holes on the sealed end side of the tube so that the space inside the tube communicates with the atmosphere, or to provide the wiring cord with a ventilation structure.

However, if the space inside the tube is not communicated with the outside air as described above, for example, the temperature of the combustion exhaust gas having an extremely low oxygen concentration cannot be accurately measured.

The present invention relates to a temperature sensor using a thermistor as a temperature detecting element, which is required to be used in an atmosphere in which the oxygen concentration is kept at a certain level or higher, and a hole for electrically connecting the inside of the protective casing to the outside air. An object of the present invention is to provide a temperature sensor that does not require troublesome processing and can be used with high reliability even in an atmosphere in which oxygen is not scarce or does not exist at all.

[Means for Solving the Problems] The present invention provides a space in which a gas containing oxygen is present and a part of a thermistor raw material for firing a thermistor in which oxygen ions are a conductive medium is present, and the thermistor. And a structure obtained by integrally firing a plurality of porcelain blanks for firing, including a surface having a pattern print of a conductive paste for forming the electrodes, and the space being an integral part of the porcelain blank. A temperature sensor including a gas containing oxygen existing in a closed space closed by firing, a thermistor fired in the closed space, and a thermistor electrode closed in the structure is adopted as technical means.

[Operation and Effect of the Invention] The temperature sensor of the present invention can be manufactured by firing once. Further, in the temperature sensor of the present invention, a thermistor as a temperature detecting element, which is required to be used in an atmosphere in which oxygen exists at a concentration of a certain level or higher, is formed of a heat resistant magnetic material and is housed in a closed space. Moreover, since a gas containing oxygen exists in this space, it is possible to perform a troublesome processing work such as drilling a large number of small holes for introducing the outside air into the casing of the sensor like the conventional temperature sensor using the same type of thermistor. Make it unnecessary.

Since the thermistor is made of a non-metallic material and is housed in a sealed space in which oxygen exists, the accuracy of measurement should change with time even for high-temperature gas containing almost no oxygen such as combustion exhaust gas. Can be performed with reliable temperature measurement.

[Examples] The configuration of the present invention will be specifically described below based on Examples shown in the accompanying drawings.

1 and 2 show an example of a thermistor sealing structure for sealing a negative temperature coefficient thermistor as a temperature detecting element incorporated in a temperature sensor according to the present invention in a space surrounded by a heat resistant insulating material. It is the sectional side view shown and explanatory drawing of the formation method of this closed structure.

The thermistor 1 as a temperature measuring element is made of zinc oxide to yttrium oxide of 20 mol%, and the unfired sheet-like bodies 3, 4 and 5 of alumina porcelain as a heat resistant insulating material are laminated and integrally fired. It is housed in the formed enclosed space 2.

A method of forming the closed space 2 will be described with reference to FIG. 2. First, three alumina porcelain material plates 3, 4 and 5 which are formed into unfired extremely thin sheet strips are prepared. These three porcelain material plates have the same width, and the length is set such that the lowermost porcelain material plate 3 is somewhat longer.
Although these three porcelain material plates are stacked and sintered to be integrated, the porcelain material plate 4 serving as the intermediate layer of the laminated structure has one end in the longitudinal direction before firing. Square, circular or any other suitable hollow hole
4a is provided, and the electrodes 6 and 7 for extracting the output of the thermistor 1 are provided on the upper surface of the slightly longer porcelain material plate 3 which is the lowermost layer.
The conductive paste composition is formed by the printing method. One ends of the two electrodes 6 and 7 formed by the printing method are positioned so as to face each other in the hollow hole 4a.

After that, when the middle layer porcelain material plate 4 is overlaid on the bottom layer porcelain material plate 3 on which a pair of electrodes are printed, the hollowed-out hole 4a part becomes a recess, so the thermistor as a semiconductor porcelain is located in this recess. Fill 1 amount of unfired material into the depressions in an amount that is insufficient to completely fill the depressions. Finally, the uppermost porcelain material plates 5 are piled up, placed in a firing furnace and heated by a conventional method, so that the three layers of porcelain material plates 3, 4 and 5 are fired and combined into an integrated structure, and the hollow hole 4a is formed. The part creates a closed space 2 which is isolated from the outside world, as can be seen in FIG. 1 as a side sectional view of the thermistor closed structure.

In the firing process of the porcelain material plate, the unfired material of the thermistor 1 which is enclosed in the closed space 2 formed as described above in an amount that is insufficient to completely fill this space is also fired at the same time. Will be done. Since the electrodes 6 and 7 for taking out the output of the thermistor 1 are printed in advance on the bottom surface of the closed space 2, the lead wire is joined to the thermistor 1 at the same time in the firing process. 20 indicates a container made of thermistor material.

Since air trapped in the voids during the firing process exists in the upper layer portion of the airtight void 2 of the thermistor hermetically sealed structure formed in this way, an oxygen ion conducting type or electron conducting type as a temperature detecting element is used. The requirement for using the thermistor is that it must be placed in an atmosphere in which a certain concentration of oxygen (generally 5% or more) is present.

Since the porcelain material plates 3 to 5 and the thermistor material 1 use pure aluminum oxide and zinc oxide to yttrium oxide respectively, impure gas as a reaction product in the closed void 2 in the firing process. There is no inconvenience to occupy.

Moreover, since the constituent material of the hermetically sealed air gap 2 that encloses the thermistor 1 under the condition that the thermistor 1 is completely shielded from the outside air is pure alumina porcelain, the temperature sensor can reach 1000 ° C or more for a long time Even if it is used for a long time, the alumina porcelain does not react with oxygen existing in the closed void to reduce the oxygen content in the void.

FIG. 3 shows an example of the structure of a temperature sensor for measuring combustion exhaust gas temperature of an internal combustion engine, which is an axial sectional view, in which the thermistor closed structure shown in the above-mentioned embodiment is incorporated.

The thermistor closed structure A is supported and fixed by a heat resistant adhesive 12 to the shaft core in a heat resistant and corrosion resistant metal tube 10 whose one end is sealed. The thermistor 1 is arranged in contact with the sealed end side of the tube 10. A hollow bolt-shaped temperature sensor mounting bracket 11 is externally fitted to the metal tube 10 that serves as a thermistor protection cover.
A joint pipe 14 for attaching a wiring cord 15 is fitted on the open end side of 10.

Lead wires 8 are soldered to the output extraction electrodes 6 and 7 of the thermistor 1 which are formed on the lower porcelain material plate 3 by a printing method, and one of the electrodes is soldered to a core wire 9 of a wiring cord 15. The other electrode is attached to the mounting bracket 11 of the temperature sensor. b is the soldering point, 14a is the caulking point of the joint pipe 14, 1
7 is a wiring connector.

FIG. 4 shows the temperature measurement side end of the temperature sensor as the second embodiment. The difference from the first embodiment is that a group of communication holes 10a with the outside air is provided at the temperature measurement side end of the protective metal tube 10 of the thermistor 1.

As described at the beginning, the temperature sensor according to the present invention has one feature in that it does not require a troublesome drilling process for providing an oxygen supply communication hole to the thermistor in the protection tube of the thermistor as a temperature detecting element. There is. However, by sealing the thermistor inside the metal tube, direct contact between the temperature-measured gas and the thermistor is blocked, so it may take some time before the accurate temperature measurement result is displayed. It will be. Therefore, when responsiveness to the temperature change of the gas to be measured and quick measurement are particularly required, it is desirable to provide the thermistor protection metal tube 10 with the communication hole 10a with the outside air.

When the gas to be measured is, for example, combustion exhaust gas of various combustion furnaces or internal combustion engines, the sensor function is lost because the oxygen concentration is too low with the conventional temperature sensor of the same type, but in the sensor of this embodiment, the thermistor is used. 1 is completely covered by a cover body made of alumina porcelain and is placed under the condition that oxygen of a required concentration coexists, so that it plays its role without any trouble. It is also possible to prevent the thermistor 1 from being adversely affected by the exhaust gas having strong chemical activity.

FIG. 5 shows a conventional type temperature sensor in which the temperature sensor of the present invention having the structure shown in FIG. 4 and a conventional thermistor having no hermetic structure instead of the thermistor hermetically sealed structure A of the temperature sensor are incorporated. The data of the experiment comparing the respective output characteristics of the sensor and the sensor are shown in the form of a graph.
The experiment shows that the oxygen concentration in the area where the temperature sensor is placed is 5
The oxygen concentration was changed in a so-called oxidizing atmosphere of 5% or more and in a reducing atmosphere of 5% or less.

When the graph of the electric resistance value (log R) vs. ambient temperature of both sensors was obtained, the graph of the same shape was drawn for the sensor of the present invention regardless of whether it was an oxidizing atmosphere or a reducing atmosphere. In contrast, the conventional sensor showed the same curve as the graph (a) in the oxidizing atmosphere, but a completely different graph (b) in the reducing atmosphere.

That is, as a result of the experiment, it was confirmed that the measured value of the conventional temperature sensor fluctuates remarkably depending on the concentration of oxygen existing in the temperature measuring range, whereas that of the present invention does not show oxygen concentration dependency at all. It was.

[Brief description of drawings]

FIG. 1 is a side sectional view of a thermistor mounting structure incorporated in a sensor of the present invention, FIG. 2 is an explanatory view of the manufacturing process of this mounting structure, and FIG. 3 is a thermistor mounting structure of FIG. FIG. 4 is a partial sectional view of the temperature sensor as the second embodiment, and FIG. 5 is a comparative data graph of the output characteristics of the sensor of the present invention and the conventional sensor. In the figure A ... Thermistor mounting structure, 1 ... Thermistor, 2 ... Oxygen-sealed space, 3, 4, 5 ... Heat-resistant insulating material, 6, 7 ... Thermistor electrode, 10 ... Thermistor Protective tube for mounting structure, 11 …… Temperature sensor mounting bracket, 15 …… Wiring cord

Claims (1)

[Claims] 1. A space in which a gas containing oxygen is present, a part of a thermistor raw material for firing a thermistor using oxygen ions as a charge-conducting medium, and a conductivity for forming an electrode of the thermistor. A structure obtained by integrally firing a plurality of porcelain material plates for firing that wrap around a surface having a pattern print of the paste, and the space is present in a closed space that is closed by the integral firing of the porcelain material plate. A temperature sensor including a gas containing oxygen, a thermistor baked in the closed space, and a thermistor electrode closed in the structure.