JPH02107956A - Internal construction of gas sensor - Google Patents

Abstract

PURPOSE:To enable prevention of a short circuiting between metals for terminals by covering the surfaces of a plurality of metals for terminals to connect a plurality of conducting contact parts at a detector section to a plurality of leads extending outward from inside a housing with an electrically insulating film. CONSTITUTION:Metals 18a-18d for terminals are mounted in a housing to connect internal, external electrode layers 22 and 24 of an oxygen detector 4 and an electrode 28 of a heater 6 to a lead 20. The metal 18a is provided to connect the electrode layer 24 to a lead 20a and an insulation layer 50 is provided on the surface of a pole body 42a thereof to cut current from the vicinity of the center thereof to near a lead gripping section 44a. The layer 50 is formed from a tube 52 made of polytetrafluoroethylene or teflon with a thickness of about 0.1-0.2mm. In other words, a compressed air is sent into a through hole of the tube 52 to expand and the tube 52 is placed at a specified position of the pole body 42a through the gripping section 44a. Thereafter, the tube 52 is heated to shrink and fastened on the surface of the pole body 42a. The same insulation layer is formed for the metals 18b-18d.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to the internal structure of a gas sensor, such as an oxygen sensor.

[Prior Art] Conventionally, for example, a ceramic detection element loaded in the housing of an oxygen sensor has been equipped with a conductive contact part for detection to extract the output of the sensor element and a conductive contact part for the heater to supply electric power to the heater. ing.

Further, a plurality of lead wires are attached to the oxygen sensor and are connected to each of the conductive contact portions and extend from inside the housing to the outside.

As shown in FIG. 5, a terminal fitting A4 is used to connect the conductive contact portion A2 of the detection element A1 and the lead wire A3.
is used. This terminal fitting A4 is formed from an elongated metal plate in the shape of an oval character, and one end of the rod body A5 in the center has a 6-inch connector attached to an electrode connecting portion that grips the conductive contact portion A2.
The other end is provided with a lead wire gripping part A7 for gripping the end of the lead wire.

[Problems to be Solved by the Invention] However, when a large number of terminal fittings are arranged in a narrow space in the housing as in this type of oxygen sensor, the terminal fittings may come into contact with each other due to photographing during use, etc. There were times when it would short out. Conventionally, countermeasures against short circuits include increasing the accuracy of each component, paying close attention to the assembly of terminal fittings, and also inspecting the assembly using transmitted X-rays.

However, even with such precautions, prevention of short circuits between terminal fittings was not always sufficient.

SUMMARY OF THE INVENTION An object of the present invention is to prevent short-circuits between a plurality of terminal fittings arranged in a housing of an oxygen sensor.

[Means for Solving the Problems] ]11] The present invention for solving the above problems includes a detection element part housed in a housing of a gas sensor, and a plurality of conductive elements exposed on the surface of the detection element part. An internal structure of a gas sensor comprising a contact portion, a plurality of lead wires extending outward from the inside of the housing, and a plurality of terminal fittings for connecting each of the conductive contact portions and the lead wires within the housing, The gist of the present invention is an internal structure of a gas sensor characterized in that the surface of the terminal fitting is covered with an electrically insulating film.

Here, the gas sensor is, for example, an oxygen sensor that detects the oxygen concentration of exhaust gas.

Further, the detection element section is composed of an oxygen detection element made of, for example, zirconia or titania, and a heater arranged near the oxygen detection element in order to improve the output characteristics of the oxygen detection element. Moreover, as another configuration of the detection element section, the above-mentioned heater may not be provided.

Furthermore, the plurality of conductive contact parts are, for example, terminals for extracting the output of the oxygen detection element and terminals for supplying power to the heater, and the number of the terminals may be 4 in total, 2 to 8, etc. terminals can be adopted.

As the above-mentioned terminal fitting, one can be used in which a rod body, which is an elongated member, is provided with lead wire gripping portions for fixing the lead wires at both ends thereof, and electrode connection portions in contact with the conductive contact portions. In order to prevent these terminal fittings from coming into contact with each other, they may be arranged concentrically within the housing, and polygons such as triangles or squares may be arranged to maximize the distance between the terminal fittings. It may be arranged so that it is located at the apex of.

In addition, an electrically insulating film is a film that covers the central part (rod body) of a terminal fitting and blocks the flow of electricity.
It can be formed by fixing a Teflon (registered trademark) tube to the rod body, or by coating Teflon or ceramics such as alumina.

[Function] The internal structure of the gas sensor of the present invention includes a plurality of exposed conductive contact portions formed on the surface of the detection element housed within the housing of the gas sensor, and a plurality of leads extending outward from the inside of the housing. line is attached. Terminal fittings each having an electrically insulating film formed on its surface connect these conductive contact portions and the lead wires.

Therefore, even if the terminal fittings come into contact with each other due to vibrations during use, the electrically insulating coating blocks the flow of electricity and prevents short-circuiting between the terminal fittings.

[Example code] Next, embodiments of the present invention will be described based on the drawings.

FIG. 1 shows a partially cutaway internal structure of an oxygen sensor 2 according to a first embodiment.

In the figure, a detection element section 8 composed of an oxygen detection element 4 and a heater 6 is connected to a metal shell 10. It is housed in a housing 16 consisting of an inner tube 12 and a protective outer tube 14, and lead wires 20 are connected to the upper ends of four terminal fittings extending from the detection element section 8, respectively.

The oxygen detection element 4 is made of a solid electrolyte such as zirconia that is formed into a cylinder shape with one end closed, and an inner electrode layer 22 of platinum deposited by vapor deposition or the like is formed on the inner surface of the oxygen detection element 4. Furthermore, an inner electrode layer 22 is also formed on the outer surface.
Similarly, an outer electrode layer 24 coated with platinum is formed.

Further, the heater 6 is a rod-shaped ceramic heater that heats the oxygen detection element 4 and is arranged in the inner hole 26 of the oxygen detection element 4. The heater 6 is made by wrapping an alumina sheet with a tungsten heater pattern printed on the inside around an elongated tubular alumina core, and both ends of the heater pattern are connected through through holes. , is connected to an electrode 28 on the outer surface made of nickel-plated tungsten.

Furthermore, a caulking part 30 is formed at the upper part ζ of the metal shell 10 of the housing 16, and when the caulking part 30 is tightened, the ceramic sleeve 32 disposed on the inner periphery of the metal shell 10 is filled. talcum powder 33
．． The oxygen detection element 4 is fixed within the housing 16 via the insulating ceramic spacer 34 and the insulating ceramic spacer 34 . On the other hand, a protector 36 for protecting the oxygen detection element 4 is attached to the lower part of the metal shell 10.

Further, an inner cylinder 12 that protects the internal structure of the oxygen sensor 2 extends upward from the crimped portion 30 of the metal shell 10, and a protective outer cylinder 14 is fitted into the upper part of the inner cylinder 12. A spacer 38 and a sealing material 40 are loaded inside the protective outer cylinder 14 in order to insulate and hold the lead wire 20 and the like and maintain airtightness.

Further, inside the housing 16, as shown in FIG.
first to fourth terminal fittings 1 for connecting with the electrodes 28 of
The sun is attached.

Among these, the first terminal fitting 18a is the outer electrode of the lead wire 20a and the oxygen detection element 4! 24, and a lead wire gripping part 44a and an electrode connecting part 46b are provided at both ends of the central rod body 42a. The second terminal fitting 18b connects the lead wire 20b and the inner electrode layer 22 of the oxygen detection element 4, and is slightly different from the first terminal fitting 18a. The wire gripping part 44b and the electrode connection part 4 are press-fitted into the inner hole 26 of the oxygen detection element 4 while gripping the heater 6.
6b. In addition, the third and fourth terminal fittings 1
8c and 18d are for connecting the lead wires 20c and 20d to the electrode 28 of the heater 6, respectively, and hold the lead wires 20c and 20d at one end and connect the electrode 28 of the heater 6 with the other end by brazing. It is joined.

Next, the first terminal fitting 18a and the second terminal fitting 18b, which are the main parts according to this embodiment, will be explained.
b has almost the same configuration, so the second terminal fitting 18bj
A detailed explanation of this problem will be omitted.

As shown in FIG. 3(a), the first terminal fitting 18a is made of stainless steel strip 5US631-C9P (JIS-・G4313), which is, for example, precipitation hardening stainless steel.
) etc.

The lead wire gripping portion 44a provided at one end of the rod body 42a includes left and right small wing portions 44aa and 44ab that crimp and grip the lead wire 20a (FIG. 1).
The electrode connecting portion 46a at the other end of the rod body 42a is left and right large wing portions 46aa that grip the oxygen detection element 4 from the outside and contact the outer electrode layer 24.

Equipped with 46ab. These large wing parts 46aa, 46ab
A plurality of claws 50 are formed at the tip of the oxygen detection element 4 to prevent it from shifting or loosening when the oxygen detection element 4 is gripped.

Further, on the surface of the rod body 42a, there is an insulating layer 5 for blocking current from the vicinity of the center to the vicinity of the lead wire gripping part 44a.
0 is provided, and this insulating layer 50 is shown in FIG. 3(b).
Polytetrafluoroethylene (PTFE) or Teflon (
(registered trademark) tube 52.

The method for forming the insulating layer 50 made of the tube 52 is as follows: First, a Teflon tube 52 with a small inner diameter that tightly adheres to the rod body 42a is manufactured, and then compressed air is fed into the through hole 54 of the tube 52 at room temperature. And the lead wire grip part 4
The through hole 54 is widened to the extent that it can pass through the through hole 54.

Then, the lead wire gripping portion 44a is passed through the through hole 54 of the expanded tube 52, and the tube 52 is placed at a predetermined position on the rod body 42a. Thereafter, by heating at approximately 360° C. for 60 minutes, the tube 52 is shrunk and the rod body 42 is heated.
Fix it to the surface of a.

The first terminal fitting 18a manufactured in this manner has the advantage that the insulating layer 50 can be formed extremely easily, and furthermore, it has an extremely excellent electrical insulation property.

An experiment conducted to confirm the electrical insulation properties of the first terminal fitting 18a will be described below.

First, in order to examine the room temperature insulation, a voltage of 500 V was applied between the Teflon insulation layer 50 and the electrode connection part 46a of the rod body 42a, and the Teflon insulation layer 50 and the electrode connection part 46a were
The resistance value between a and a was measured. As a result, the resistance value is 10
It was found that the resistance was 0 MΩ or more, indicating excellent electrical insulation properties at room temperature.

Further, in order to examine high-temperature insulation, the oxygen sensor 2 was heated with a propane burner, and the resistance value between the Teflon insulating layer 50 and the lead wire gripping portion 44a was measured. the result,
The tip of the oxygen detection element 4 of the oxygen sensor 2 is 700 to 950
℃, the temperature of the main metal fitting 10 is 450 to 650 degrees Celsius, and the temperature of the rod body 42a of the first terminal fitting 18a is 150 to 300 degrees Celsius,
The above resistance value was 100 MΩ or more. Therefore, it was found that it has extremely high electrical insulation properties even at high temperatures as well as at room temperatures.

Next, the first terminal fitting 18a (not shown) of the second embodiment will be explained.

In this second embodiment, instead of using the Teflon tube 52 as in the first embodiment, a paste-like Teflon is applied directly to the surface of the rod body 42a, so that the thickness is 30 mm.
An insulating layer of ~50 μm is formed. That is,
To form this Teflon insulating layer, first, water and Triton X (registered trademark) as a dispersion medium are added to Teflon powder to form a paste with a concentration of 700 to 800 g/Q. Next, the paste is applied to the rod body 42a using compressed gas.
The insulating layer of Teflon is sprayed onto the area where the insulating layer will be formed, and then heat treated at approximately 370°C for 5 minutes to complete the process.

Next, the first terminal fitting 18a of the third embodiment will be explained.

In this embodiment, as shown in FIG. 4, the surface of the rod body 42a is coated with ceramics instead of Teflon. As the ceramic, alumina, silica, magnesia, etc. can be used, and the thickness of the ceramic insulating layer 56 to be formed is preferably 30 to 150 LLm because it has excellent electrical insulation.

Among these ceramics, for example, the method of coating alumina is to first add water or water glass to alumina powder with an average particle size of 40 to 60 LLm to form a paste, apply the alumina paste to the rod body 42a, and then apply it to a temperature of about 150°C. about 1
Bake for 20 minutes to complete.

And the first in the second and third embodiments as described above.
The terminal fitting 18a also has good electrical insulation properties as in the first embodiment.

In addition, in the above description, the rod body 42 of the first terminal fitting 18a
An insulating layer 5 is formed on the surface of a using Teflon or ceramics.
Although the example in which 0.56 is formed has been described in detail, the same applies to the second terminal fitting 18b.

Further, in order to further improve the electrical insulation inside the housing 16 of the oxygen sensor 1, similar insulating layers 50 and 56 may be formed on the third and fourth terminal fittings 18c and 18d.

[Effects of the Invention] The present invention connects the plurality of conductive contact portions of the detection element portion and the plurality of lead wires extending outward from the inside of the housing with a terminal fitting, and coats the surface of the terminal fitting with an electrically insulating coating. covered. Therefore, even if the terminal fittings come into contact with each other due to vibration or the like during use, there will be no electrical short circuit. Furthermore, even if the precision of each component is reduced and the spacing between the terminals becomes uneven, there will be no electrical short circuit because the electrically insulating coating is formed.

[Brief explanation of drawings]

Figure 1 is a partially cutaway pressure surface view of the oxygen sensor, Figure 2 is a perspective view showing the arrangement of terminal fittings, Figure 3(a) is a perspective view of terminal fittings, and Figure 3(b) is a Teflon tube. FIG. 4 is a perspective view of another terminal fitting, and FIG. 5 is an explanatory diagram of the prior art. 2...Oxygen sensor 4...Oxygen detection element 6...Heater 16...Housing 1 day...Terminal fitting 20...Lead wire 22...Inner electrode layer 24...Outer electrode Layer 50.56...Insulating layer

Claims (1)

[Claims] a detection element part housed in a housing of the gas sensor; a plurality of conductive contact parts exposed on the surface of the detection element part;
a plurality of lead wires extending from inside the housing to the outside;
An internal structure of a gas sensor comprising a plurality of terminal fittings for connecting each of the conductive contact parts and the lead wires in the housing, characterized in that the surface of the terminal fittings is covered with an electrically insulating film. The internal structure of the gas sensor.