JPH0731163Y2 - Electrode extraction part of limiting current type oxygen sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a limiting current type oxygen sensor in which a zirconia solid electrolyte plate or the like is used as a sensor element plate and the solid electrolyte plate is heated when the sensor element plate is driven. It is about improvement.

<Prior Art> An example of a conventional oxygen sensor of this kind is shown in FIGS. 7 to 8.

This oxygen sensor is a limiting current type sensor using a zirconia solid electrolyte plate as the sensor element plate 1, and sensor electrodes made of porous platinum or the like are provided on both sides of the sensor element plate 1.
A few are formed. Then, in the figure, the upper sensor electrode (cathode electrode) 2 portion is covered with a cap 4 that forms the sensor material R, and the lead portion of this cathode electrode 2 is covered.
2a is drawn out as shown in FIG. On the other hand, in the lower sensor electrode (anode electrode) 3 portion, a heater 6 is formed on the surface by a heater 6 by screen printing or the like.
Is installed via a breathable adhesive or the like. Further, electrode lead wires 7, 7, 8 and 8 are connected to the sensor electrodes 2 and 3 and the heater 6, respectively.

In the case of this oxygen sensor, when it is not driven, the air and gas in the installation environment are permeable to the air-permeable adhesive and the sensor element plate 1.
It is guided into the sensor chamber R through a diffusion hole (small hole) 9 in the center, and at the time of measurement, oxygen in the sensor chamber R is ionized and discharged by the pumping action of the sensor element plate 1 by the heating of the heater 6. The oxygen concentration is obtained from the limiting current value.

Although the heating of the sensor element plate 1 is performed by this heater, since a fairly high temperature (for example, about 400 ° C.) is required at present, the heater forming region (range) of the heating unit 5 is wide (sensor electrodes 2, 3). It is desired that the area be sufficiently covered), and in an actual case, it is slightly smaller than the size of the sensor element plate 1. For this reason, the temperature distribution in the sensor element plate 1 is shown in FIG. 9, and it can be seen that the edge portion 10 of the sensor element plate 1 is considerably hot.

<Problems to be Solved by the Invention> In such a limiting current type oxygen sensor, the lead portion 2a of the cathode electrode 2 which is a portion in contact with the sensor installation environment, for example, the outside air such as the atmosphere or the measurement gas has a high temperature. When,
Even in the sensor element plate 1 in this portion, oxygen ions are taken in and a pumping action is performed, so that the sensor performance is adversely affected.

In other words, unlike the inside of the sensor chamber R, even if oxygen is pumped, new oxygen is replenished from the surroundings in the portion that comes into contact with the outside air. Therefore, as shown in FIG. When the limit current region is reached, a flat limit current value I _L (A in the figure, the value of the graph shown by the dotted line) should be obtained, but the current value ( In the figure, the phenomenon that B, the value of the graph indicated by the solid line) increases occurs. With such an increase in the current value, for example, when the measurement voltage V ₁ is applied, the current value I _L ′ is detected as the limiting current value, so that the oxygen concentration is measured higher than it actually is.

Therefore, conventionally, as shown in FIG. 11, the entire lead portion 2a of the cathode electrode 2 is covered with a coating material 11 such as glass or ceramics.
However, there is a problem that cracks and the like are likely to occur in the coating portion, which is not preferable.

The present invention has been made in view of such a conventional situation.

<Means for Solving the Problem> The feature of the present invention is that the sensor electrode is provided on the sensor element plate of the solid electrolyte, and the sensor element plate is heated by the heater of the heating unit and driven. In the limiting current type oxygen sensor as described above, a low temperature portion is provided in at least a part of the sensor element plate, and at least one lead portion of the sensor electrode exposed to the outside air is drawn into the low temperature portion, and an electrode lead is provided in this portion. It is in the electrode extraction part of the limiting current type oxygen sensor that connects the wires.

<Operation> Since the lead portion of the sensor electrode is pulled out to the low temperature portion of the sensor element plate in this manner, the oxygen ion pumping action hardly occurs in this portion, and the deterioration of the sensor performance can be minimized.

<Embodiment> FIGS. 1 and 2 show an embodiment of an electrode extracting portion of a limiting current type oxygen sensor according to the present invention.

This oxygen sensor also basically has the same structure as the conventional sensor shown in FIG. 7 described above, but as is clear from FIG. 2, a part of the sensor element plate 1 of the solid electrolyte is made to project, and this projection is made. The portion 12 is a low temperature portion, the lead portion 2a of the sensor electrode (cathode electrode) 2 is drawn out to this portion, and the external electrode lead wire 7 is connected to this portion to form an electrode lead-out portion.

As shown in FIG. 1, the protruding portion 12 extends largely outward from the heating heater region of the heating portion 5, so that the heating effect of the heating heater 6 is hardly exerted and the protruding portion 12 is maintained at a low temperature. To be done. The temperature of the protrusion 12 is shown in FIG. 3, for example.

Therefore, in the protruding portion 12, even when the sensor is driven, the pumping action of oxygen ions that occurs in a high temperature state hardly occurs, and the deterioration of the sensor performance due to the removal of the cathode electrode 2 can be minimized. This relationship is illustrated in FIG. 4, and the limiting current value I _L (A in the figure, the value of the graph indicated by the solid line) is obtained, which is a clean flat region. Note that, in the figure, the graph portion indicated by B and the dotted line shows the case where a pumping action occurs in the electrode extraction portion and the current increases (corresponding to the conventional example in FIG. 10).

FIG. 5 shows another embodiment of the electrode extraction portion of the limiting current type oxygen sensor according to the present invention.

The oxygen sensor in this case also has basically the same structure as the conventional sensor shown in FIG. 7 described above, but in this oxygen sensor, the large (outer diameter) of the solid electrolyte sensor element plate 1 is
The heating portion 5 is made considerably larger than the heating portion 5, and the enlarged edge portion 13 is used as a low temperature portion, and the lead portion 2a of the sensor electrode (cathode electrode) 2 is pulled out to a part thereof, and an external electrode lead is provided to this. The wire 7 is connected to form an electrode extraction portion.

Therefore, similar to the sensor of FIGS. 1 and 2, the expanded edge portion is used.
The temperature of 13 is maintained at a low temperature, for example, as shown in FIG. 6, the oxygen ion pumping action hardly occurs, and the deterioration of the sensor performance due to the removal of the cathode electrode 2 can be minimized.

In each of the above-mentioned embodiments, the low temperature portion for taking out the sensor electrode 2 is constituted by the protruding portion 12 and the enlarged-diameter edge portion 13 of the sensor element plate 1, but the present invention is not limited to this, in short, the sensor element Other structures may be used as long as the low temperature part is formed in a part of the sensor element plate 1 in consideration of the size and shape of the plate 1 and the heater formation region (range) of the heating part 5.

<Effects of Device> As is apparent from the above description, the electrode extraction portion of the limiting current type oxygen sensor according to the present invention has the following excellent effects.

(1) First, since the lead portion of the cathode electrode, which is at least the side exposed to the outside air, is drawn out to the low temperature portion formed in a part of the solid electrolyte sensor element plate, deterioration of the sensor performance can be minimized. You can

(2) In addition, since the electrodes exposed to the outside air can be taken out, there are advantages that the degree of freedom in design is increased, the sensor is easily manufactured, and the sensor is highly reliable.

[Brief description of drawings]

FIG. 1 is a partially exploded sectional view showing an embodiment of an electrode lead-out portion of a limiting current type oxygen sensor according to the present invention, FIG. 2 is a plan view of FIG. 1, and FIG. 3 is a limiting current of FIG. 4 is a graph showing the temperature distribution of the sensor element plate in the oxygen sensor, FIG. 4 is a graph showing the limiting current characteristics of the limiting current type oxygen sensor of FIG. 1, and FIG. 5 is a limiting current type oxygen sensor according to the present invention. 6 is a partially exploded cross-sectional view showing another embodiment of the electrode extraction portion of FIG.
5 is a graph showing the temperature distribution of the sensor element plate in the limiting current type oxygen sensor of FIG. 5, FIG. 7 is a partially exploded sectional view showing a conventional oxygen sensor, FIG. 8 is a plan view of FIG.
9 is a graph showing the temperature distribution of the sensor element plate in the oxygen sensor of FIG. 7, FIG. 10 is a graph showing the limiting current characteristics of the oxygen sensor of FIG. 7, and FIG. 11 is another conventional oxygen. It is a partially exploded sectional view showing a sensor. In the figure, 1 ... Sensor element plate, 2,3 ... Sensor electrode, 2a ... Lead part, 4 ... Cap, 5 ... Heating part, 6 ... Heating heater, 7,8 ... Electrode lead wire, 9 ... Diffusion hole, 12 ... Projection part (low temperature part), 13 ... Edge part (low temperature part), R ... Sensor chamber,

Claims (3)

[Scope of utility model registration request] 1. A limiting current type oxygen sensor in which a sensor electrode is provided on a solid electrolyte sensor element plate, and the sensor element plate is heated and driven by a heater of a heating unit. A low temperature part is provided in a part, and the sensor electrode is drawn out to the low temperature part.
An electrode lead-out portion of a limiting current type oxygen sensor characterized in that an electrode lead wire is connected to this portion. 2. The electrode lead-out portion of a limiting current type oxygen sensor according to claim 1, wherein a part of the sensor element plate is projected, and the projected portion is a low temperature portion. 3. The electrode lead-out portion of the limiting current type oxygen sensor according to claim 1, wherein the sensor element plate is formed larger than the heating portion, and an edge portion thereof is a low temperature portion.