JPH0629737Y2 - Oxygen sensor element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to improvement of the inner surface shape of an internal void of an oxygen sensor element formed in a long flat plate shape.

(Prior Art) In recent years, from the viewpoint of ease of manufacturing, compactness, etc., oxygen using an oxygen sensor element formed in a long flat plate shape has been used instead of the existing low and low cylindrical oxygen sensor. Sensors have been proposed.

FIG. 5 is an exploded view of an example of a conventional structure of such a long flat plate-shaped oxygen sensor element.

The oxygen sensor element 10 is an oxygen sensor element with a heater, and is roughly composed of a sensor section 20 and a heater section 30.

The sensor unit 20 is a long flat solid electrolyte plate 21 made of an oxygen ion conductive solid electrolyte containing zirconia as a main component.
And a solid electrolyte plate 26 made of the same material as this and having a void 27 from one end to the vicinity of the other end are stacked to form an outer shell.

Then, at one end of the surface of the flat solid electrolyte plate 21,
A porous measuring electrode 22 made of platinum or the like is applied by printing, and the measuring electrode is sandwiched by the solid electrolyte plate 21 on the back surface.
A reference electrode 25 made of the same material is applied so as to face 22.

Further, on both surfaces of the solid electrolyte plate 21, leads 28, 29 made of the same material as the electrodes 22, 25 are coated in a strip shape from both electrodes 22, 25 to the other end of the solid electrolyte 21, The ends are the reference electrode terminal 23 and the measurement electrode terminal 24.

The reference electrode 25 has a front surface exposed in the void 27 and is exposed to the outside air flowing from the open end of the void 27.

The heater portion 30 is composed of two long flat plate-shaped insulating ceramic layers.
31 and 32 are overlapped, and the resistance heating element 35 is sandwiched between the one ends of the resistance heating element 35. Two conductive strips running from both poles of the resistance heating element 35 to the other ends of the insulating ceramic layers 31 and 32 are formed in a strip shape. Leads 36 and 37 are similarly sandwiched between the insulating ceramic layers 31 and 32.

(Problems to be Solved by the Invention) However, in the above-described conventional oxygen sensor element 10, since the shape of the void 27 for introducing the reference gas is a rectangular parallelepiped shape, the following inconvenience may occur. .

That is, when the members developed and shown in FIG. 5 are assembled, the tip of the oxygen sensor element 10 has a structure as shown in FIG.

As can be seen from the figure, the closed end of the void 27 is
Has sides 27a and 27b that are perpendicular to the plane of the plane, and the planes that sandwich these sides 27a and 27b intersect at a right angle.

Since the tip of the oxygen sensor element 10 is placed in a high temperature atmosphere such as in a furnace or an exhaust pipe of an automobile, thermal stress is applied to the oxygen sensor element 10.

This thermal stress acts largely in the width direction of the oxygen sensor element 10 (indicated by the arrow W in FIG. 6). The reason is that the thermal stress generated in the thickness direction of the oxygen sensor element 10 (indicated by the arrow D in FIG. 6) is small because the oxygen sensor element 10 is extremely thin and the temperature distribution difference in the element is small. Therefore, since the difference in thermal expansion is also small, it is relatively small. On the other hand, a difference in temperature distribution occurs in the width direction of the oxygen sensor element 10, and thermal stress increases.

The generated thermal stress is generated on both sides of the tip of the void 27.
There is a risk of concentrating on 27a and 27b and causing cracks at these positions.

Further, in the case of the oxygen sensor element 10 having the heater portion 30, the difference in the temperature distribution is likely to be large immediately after the heater is energized, which is a factor for increasing the crack occurrence rate as described above.

(Means for Solving the Problems) In order to solve the above problems, the present invention is formed in a long flat plate shape mainly with an oxygen ion conductive solid electrolyte and has a tubular void inside the longitudinal direction. The oxygen sensor element has a feature that at least a part of the inner surface of the closed end of the tubular void is a curved surface having a curvature radius of 50 μm or more.

(Operation) As described above, according to the present invention, by forming at least a part of the inner surface of the void into a curved surface, it is possible to reduce or eliminate the above-mentioned portion where the thermal stress is concentrated and prevent the occurrence of cracks.

(Example) An example of the present invention will be described.

FIG. 1 is a diagram showing the structure of the tip portion of the oxygen sensor element 40 of the present embodiment, which has the same configuration as the conventional example shown in FIGS. 5 and 6 except for the shape of the void 27. Therefore,
The same components are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 1, a portion 27 corresponding to the sides 27a and 27b in the conventional example of the closed end of the void 27 in this example.
a ′ and 27b ′ are curved surfaces.

This structure is obtained by changing the shape of the solid electrolyte plate 26 shown in FIG. 5 to the shape shown in FIG.
That is, if both sides 27a 'and 27b' of the tip of the void 27 formed in the solid electrolyte plate 26 are curved in advance and other members are laminated and fired, the structure shown in FIG. 1 is obtained. . The curved surfaces 27a 'and 27b' may be formed by punching with a mold when forming the solid electrolyte plate 26.

With the above configuration, the oxygen sensor element 40 of the present embodiment, thermal stress generated in the width direction of the element, even if applied to both corners of the tip portion of the void 27, because these portions have a curved shape, It has resistance to thermal stress and can prevent cracks from occurring.

Experimental results are shown to more specifically show this effect. In this experiment, an organic resin binder, a plasticizer, and a solvent were added to ZrO ₂ powder to which 8% Y ₂ O ₃ was added to form a green body sheet of the solid electrolyte plates 21 and 26, and a heater part 30 was used. Is used after being laminated and fired.

Then, the thickness and width of the void 27, and the above-mentioned both corners 27a ′, 2
Five pieces of which the radius of curvature of 7b 'was changed little by little were created, and when a voltage of 14 V was applied to the resistance heating element 35 to generate heat (when the heater was energized), 300 ° C, 8
In a case where a thermal cycle test was performed in which the substrate was alternately exposed to an atmosphere of 00 ° C. for 5 minutes each, it was examined how many of the 5 cracks were generated. The results are shown in Table 1.

As can be seen from Table 1, the size of the void 27 has little relation, and the crack generation rate is related to the size of the radius of curvature of both corners 27a 'and 27b'.

And if the radius of curvature is less than 50 μm (this is
It is hard to say that it is a curved surface, and cracks cannot be completely prevented on the sides 27a, 27b shown in FIG. 5), but if the radius of curvature is 50 μm or more, cracks can be almost completely prevented. .

The present invention is characterized in that the portion in the void 27 where cracks may occur is a curved surface, and is not limited to the above embodiment.

However, since the cracking rate is high at the tip of the element where the thermal change is large, it is desirable to form a curved surface at the closed end of the void 27 as in the above embodiment. In this case, the shape is not limited to that of the above-described embodiment, and for example, as shown in FIG. 3, the closed end portion 27c of the void 27 may be formed into a semicircular shape, or may be formed into a circular shape as shown in FIG. Target.

The radius of curvature of the curved surface is preferably 50 μm or more as described above.

Furthermore, the present invention is not limited to the oxygen sensor element 40 with a heater as in the above embodiment, but can be applied to any oxygen sensor element in the form of a long flat plate having a structure having a void 27.

(Advantages of the Invention) The present invention is an oxygen sensor which is formed in the shape of a long flat plate and has a tubular void inside the longitudinal direction thereof. By forming at least a part of the inner surface of the tubular void into a curved surface,
It is possible to reduce or eliminate the portion where the thermal stress is concentrated, and prevent the occurrence of cracks due to the thermal stress. This makes it possible to provide an oxygen sensor element that is resistant to thermal shock.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a tip portion of an oxygen sensor element according to an embodiment of the present invention, FIG. 2 is a perspective view showing a shape of a solid electrolyte plate which is one of the constituent members of the embodiment, and FIG. 4 and 5 are plan views of the solid electrolyte plate 26 showing another shape of the tip of the void 27, FIG. 5 is an exploded perspective view showing the structure of a conventional oxygen sensor element, and FIG. 6 is a conventional oxygen sensor. It is a perspective view which shows the structure of the front-end | tip part of an element. 21,26 …… Solid electrolyte plate 22 …… Measurement electrode, 25 …… Reference electrode 27 …… Void, 30 …… Heater part 27a ′, 27b ′, 27c… Curved part

Claims (1)

[Scope of utility model registration request] 1. An oxygen sensor element having a long flat plate shape mainly composed of an oxygen ion conductive solid electrolyte and having a tubular void inside the longitudinal direction thereof, wherein at least one inner surface of a closed end of the tubular void is formed. An oxygen sensor element, wherein the part is a curved surface having a radius of curvature of 50 μm or more.