JPH0354448A - Sensor element of oxygen sensor - Google Patents

Abstract

PURPOSE:To enhance reliability by preventing the change of the effective area of one electrode cooperating with the other electrode in oxygen bombing action by forming the latter electrode to the entire single surface of a pellet. CONSTITUTION:One electrode 2c is formed to the entire single surface of a pellet 1 and the other electrode 2a is formed to the other surface of the pellet 1 so that the center thereof is almost matched with the center line of the pellet 1. Even when the electrode 2a is formed to the pellet 1 so as to be eccentric left and right from the center line of the pellet 1, the entire surface of the electrode 2a becomes an effective area functioning as oxygen bombing action in cooperation with one electrode 2c as it is. As a result, any change is not generated in the effective area of the electrode 2a and, since the considerable degree of freedom is permitted in centering in forming the electrode 2a, forming work becomes easy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sensor element of an oxygen sensor used for measuring oxygen concentration in various atmospheres.

[Conventional technology]

As shown in FIG. 4, a conventional sensor element has electrodes 2a and 2b formed on both sides of a pellet 1 of an ion-conducting solid electrolyte (for example, made of stabilized zirconia) (for example, by platinum screen printing). ), a capsule 5 in which a gas diffusion hole 3 is penetrated through one side (electrode 2a side) of the pellet 1 and a heater 4 is formed (for example, screen printed in a C shape) is used as a gas reaction chamber. It is sealed with a sealing material 7 (eg, glass) with a sealing member 6 interposed therebetween.

Then, the sensor element of the oxygen sensor installed in the gas component applies a voltage between the electrodes 2a and 2b and to the heater 4 (electrode 2a side is the cathode), and the electrode (2a , 2b) / Due to the oxygen bombing action of the pellet (1), a current using oxygen ions as carriers flows between the electrodes 2a and 2b, and the oxygen molecules that have diffused into the gas reaction chamber 6 through the gas diffusion hole 3 move the pellet 1. (arrows indicate transport of oxygen molecules).

At this time, since there is a flat region of the current that appears in a certain voltage region of the voltage-current characteristic, that is, there is a one-to-one relationship between the limiting current value and the oxygen concentration, the electrodes 2a, 2b and the heater 4 A constant voltage is applied to the sensor element, and the oxygen concentration is measured from the limiting current value of the sensor element at a predetermined temperature.

[Problem to be solved by the invention]

As described above, on both sides of the pellet 1 in the conventional sensor element, as shown in FIG. They are formed at the same and coincident position (because the gas diffusion holes 3 are on the center line of the pellet 1) by, for example, screen printing.

The reason for this is that the electrode 2
Although electrode 2b was formed at a predetermined position (centered on the center line of pellet 1), if electrode 2b was formed eccentrically from the center line of pellet 1 in the left, right, up, and down directions (Fig. 5 shows an example in which it is eccentric to the right). ), electrode 2 functioning for oxygen bombing action
This is to prevent the effective areas of both a and 2b from decreasing (becoming an overlapping portion S) and causing a change in the predetermined characteristics of the oxygen sensor.

Note that the same applies when the electrode 2a is eccentric.

Therefore, in the past, the process of forming the electrodes 2a and 2b was troublesome, hindering mass production, increasing costs, and lacking reliability.

The present invention has been made in view of the above points, and its purpose is to:
It is an object of the present invention to provide a reliable sensor element for an oxygen sensor in which the effective area of an electrode that functions for oxygen bombing does not change, the electrode can be easily formed, mass production is possible, and the sensor element is reliable.

[Means to solve the problem]

In order to achieve the above object, the present invention provides an oxygen sensor in which electrodes are formed on both sides of an ion-conducting solid electrolyte pellet, and a capsule equipped with a gas diffusion hole and a heater is sealed on one side of the pellet. The sensor element is characterized in that one of the electrodes is formed on the entire surface of one side of the pellet.

[Effect]

Since one of the electrodes is formed on the entire surface of one side of the pellet, even if the other electrode is formed with its center offset from the center line of the pellet, the entire surface of the other electrode will continue to absorb oxygen from the electrode/pellet. The effective area of the bombing action is (
(There is no change such as decrease in effective area), and reliable oxygen concentration measurement is possible.

〔Example〕

Embodiments of the present invention will be described with reference to the drawings.

Note that the parts are the same as the conventional example. are given the same symbol.

As shown in FIG. 1, a gas diffusion hole 3 is provided in the center, and a heater 4 is provided on the top surface (for example,
The capsule 5 (screen printed in a C-shape) is made of an ion-conducting solid electrolyte (for example, made of stabilized zirconia).
゜ on one side of Pele 7 and 1. - The reaction chamber 6 is sealed with a sealing material 7 (eg, glass).

The pellets 1 are disk-shaped, and the capsules 5 are circular in plane and U-shaped in longitudinal section.

Thus, one electrode 2c is formed on the entire surface of one side of the pellet 1, and the other electrode 2a is formed on the other side of the pellet 1.
is formed with its center substantially aligned with the center line of the pellet 1.

Note that since the oxygen concentration measurement is the same as in the conventional example, the transfer of oxygen molecules is indicated by an arrow and the explanation will be omitted.

Since each electrode is formed as described above, FIG.
) As shown in (B), even if the other electrode 2a is formed to be eccentric to the left and right from the center line of the pellet 1 (indicated by the dashed line), the entire surface of the electrode will continue to cooperate with the one electrode 2c to perform oxygen bombing. This is the effective area that functions.

Therefore, there is no change in the effective area of the electrode 2a,
Since a considerable degree of freedom is allowed for centering in forming the electrode 2a, the shaping process becomes extremely easy.

Further, the electrodes 2C are formed simultaneously by platinum screen printing on a large number of disc-shaped pellets 1 arranged in a bottomed frame 8, as shown in FIG.

Note that the electrode 2a is also formed into a circular shape by platinum screen printing.

In this embodiment, an example in which the other electrode 2a is eccentric to the left and right has been described, but the eccentricity in the vertical direction (viewed in a plane) is also the same, and since the capsule 5 is sealed, the electrode Although an example in which 2C is formed on the entire surface of the pellet 1 has been shown, the present invention is not necessarily limited to this.

〔Effect of the invention〕

The present invention has the following effects by forming one electrode on the entire surface of one side of the pellet.

(a) Since there is no change in the effective area of one electrode and the other electrode that cooperate with each other in the oxygen bombing action, a highly reliable oxygen sensor can be provided.

(b) Since there is a degree of freedom in centering the pellet when forming the other electrode, the electrode forming operation is extremely easy, mass production is possible, and costs are reduced.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional view of an embodiment of the sensor element according to the present invention, Fig. 2 (A) and (B) are explanatory longitudinal sectional views of electrode eccentricity, and Fig. 3 is a longitudinal sectional view of an embodiment of the sensor element according to the present invention. Explanatory diagram: Figure 4 is a vertical cross-sectional view of a conventional sensor element, Figure 5 is an explanatory diagram of electrode eccentricity, Figure (A) is a plan view, Figure (B) is an explanatory diagram.
is a vertical sectional view. 1... Pellet, 2a, 2c... Electrode, 3... Gas diffusion hole, 4... Heater, 5... Capsule.

Claims (1)

[Claims] It consists of an ion-conductive solid electrolyte pellet with electrodes formed on both sides, and a capsule sealed on one side of the pellet and equipped with a gas diffusion hole and a heater, with one of the electrodes formed on the entire surface of one side of the pellet. A sensor element for an oxygen sensor characterized by: