JP2514664B2 - Oxygen sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to an oxygen sensor for measuring the oxygen concentration in the exhaust gas of, for example, an internal combustion engine or various combustion equipment.

[Prior Art] Conventionally, for the purpose of preventing pollution and improving fuel efficiency, oxygen partial pressure in exhaust gas of an internal combustion engine is measured, and air-fuel ratio feedback control of the internal combustion engine is performed based on the measured value. Such measurement of the oxygen partial pressure in the exhaust gas can be performed by, for example,
It is performed by an oxygen sensor provided with a detection element composed of a solid electrolyte layer having oxygen ion conductivity such as a zirconia-yttria solid solution. Examples of the oxygen sensor include those disclosed in
55-125448 or JP-A-60-36949 has been proposed. That is, the measuring electrode is formed on the surface of the flat plate-shaped detecting element to measure the oxygen partial pressure.

[Problems to be Solved by the Invention] However, in such an oxygen sensor, since the measurement electrode is formed on the surface of the flat plate-shaped detection element, there is directionality with respect to the flow of the measurement gas. However, there is a problem in that the output of the oxygen sensor varies depending on the flowing direction of the measurement gas and the mounting position of the oxygen sensor, and the air-fuel ratio control or the like depending on the output cannot be appropriately performed.
In order to solve such a problem, an oxygen sensor using a cylindrical detection element has been proposed, as described in Japanese Patent Application No. 61-66663 (Japanese Patent Application Laid-Open No. 62-222159).

The present application improves the directionality of the sensor by using a tubular detection element and adding another configuration.

[Means for Solving the Problems] According to the configuration of the present invention for solving the above problems, a plurality of penetrating holes that communicate between the inner surface side and the outer surface side are provided while one end side is opened and the other end side is provided with a closing wall. A hollow cylindrical body having a hole; and an oxygen ion conductive solid electrolyte layer which encloses the hollow cylindrical body and has at least two pairs of electrodes on the inner and outer surfaces, and further, on the inner surface side of the solid electrolyte layer. An oxygen sensor in which electrodes are arranged at positions corresponding to the through-holes of the hollow cylindrical body, where N is the number of electrode pairs, the electrode pairs are solid electrolyte layers with the center of each electrode as a reference. On the circumference of the center angle
The gist of the oxygen sensor is that it is arranged at intervals of 360 ° / N-30 ° or more and 360 ° / N + 30 ° or less. That is, the gap between the electrode pairs is
Within 30 °, the oxygen partial pressure can be accurately measured regardless of the flow direction of the measurement gas. For example,
It is desirable to arrange the electrode pairs at an interval of 180 ° when there are two pairs and at an interval of 120 ° when there are three pairs in order to reduce the directivity.

Further, it is desirable from the viewpoint of heating efficiency of the heating element to form a heating element near the electrode on the inner surface or the outer surface of the solid electrolyte layer, thereby easily making the temperature in the vicinity of the electrode a suitable temperature for measurement. be able to.

The hollow cylindrical body constitutes a reference gas introduction path that passes through the inside of the cylinder from the opened one end side to reach the through hole and introduces the atmosphere as the reference oxygen source. This hollow cylindrical body
For example, it can be processed by a die press or extrusion molding. As the material, for example, ceramics or metal having a value close to the coefficient of thermal expansion of the solid electrolyte layer is used in order to prevent damage caused by a difference in coefficient of thermal expansion. In the case of exhaust gas from an engine, a high temperature of 600 ° C. or higher is used, so it is preferable to use ceramics. Further, for example, when a metal such as a stainless alloy is used, the inner peripheral surface of the solid electrolyte layer is insulated from the electrode.

The solid electrolyte layer has oxygen ion conductivity,
For example, ZrO ₂ —Y ₂ O ₃ , ZrO ₂ —CaO or the like is used.

The electrodes can be realized by, for example, a noble metal such as platinum or a gas permeable material in which ceramic powder is mixed with these.

These are, for example, a solid electrolyte green sheet on which an electrode is printed as a thick film is wound around a hollow cylindrical body, and at the time of winding, the electrode on the inner surface side and the through hole of the hollow cylindrical body correspond to each other. Place in position. Then, after being wound around the hollow cylindrical body, it is fixed in a cylindrical shape by a jig and integrated by firing to obtain an oxygen sensor.

[Operation] In the oxygen sensor of the present invention, the reference gas introduction path extending from at least one open end of the hollow cylindrical body to at least two or more electrodes on the inner surface side of the solid electrolyte layer through the plurality of through holes. It is formed. Therefore, since the inner surface side of the solid electrolyte layer is in contact with the reference gas and the outer surface side is in contact with the measurement gas, the oxygen partial pressure in the measurement gas is obtained by measuring the current flowing between the electrodes provided on both surfaces. be able to. When the number of the electrode pairs is N, the electrode pairs are centered on the circumference of the solid electrolyte layer with reference to the center of each electrode.
Since they are arranged at intervals of 360 ° / N-30 ° or more and 360 ° / N + 30 ° or less, the oxygen concentration can be accurately detected regardless of the flow direction of the measuring gas and the mounting position of the oxygen sensor.

[Embodiment] A first embodiment of the present invention will be described below with reference to Figs. For the sake of explanation, the scale of each part is different in each drawing.

As shown in FIG. 1, the oxygen sensor 1 of the first embodiment is
The surface of the hollow cylindrical body 2 is coated with the solid electrolyte layer 3. A first reference electrode 4 and a second reference electrode 5 are provided on the inner surface side of the solid electrolyte layer 3, and a first measurement electrode 6, a second measurement electrode 7 and a heating element 8 are provided on the outer surface side thereof.
First to fourth through holes 9 that connect the inner surface side and the outer surface side to each other
12 are formed.

The first to fourth through holes 9 to 12 include a pair of first and second through holes 9 and 10 and another pair of third and fourth through holes 11 and 1.
2 and 2 are arranged to face each other. And II-II in Fig. 1
As shown in FIG. 2 which is an end view, the first reference electrode 4 is provided on the inner peripheral surface of the solid electrolyte layer 3 in contact with the hollow cylindrical body 2, and the first measurement electrode 6 is provided on the outer peripheral surface thereof. It is provided at a position corresponding to the first through hole 9. Similarly, the third through hole 11
The second reference electrode 5 and the second measurement electrode 7 are provided at positions corresponding to. Further, the heating element 8 is provided on the outer peripheral surface of the solid electrolyte layer 3.

The first and second reference electrodes 4 and 5 are connected to the reference electrode terminal 14 shown in FIG. 1 via through holes provided in the solid electrolyte layer 3. Also, the first and second measuring electrodes 6,7
Is connected to the measuring electrode terminal 15 and the heating element 8 is connected to the heating element terminals 16 and 17, respectively.

Next, each member and manufacturing method of the oxygen sensor 1 will be described.
First, the hollow cylindrical body 2 shown in FIG. 3 has an outer diameter of 3.2 mm and an inner diameter.
It is a 1.5 mm hollow cylinder having an opening 18 at one end and a closing wall 19 at the other end. Side wall 2a near the closing wall 19
The above-mentioned two pairs of the first to fourth through holes 9 to 12 having a diameter of 1 mm are formed facing each other. Therefore, the first to fourth through holes 9 to 12 are formed from the opening 18 through the hollow portion 20.
A reference gas introduction path leading to is formed. Such a hollow cylindrical body 2 can be easily processed by die pressing or extrusion molding.

The solid electrolyte layer 3, as shown in FIG. 4, ZrO ₂ -
The raw material powder Y ₂ O ₃ solid solution, obtained from the green sheet 3a mixed with binders commonly used. Through holes 21 for connecting the first and second reference electrodes 4 and 5 to the reference electrode terminals 14 are formed in the corners of the green sheet 3a.

On the back surface of the green sheet 8a, which is the inner peripheral surface of the solid electrolyte layer 3, a thickness of platinum containing zirconia 10
The μm first and second reference electrodes 4, 5 are thick film printed.

On the other hand, the surface of the green sheet 3a, which is the outer peripheral surface of the solid electrolyte layer 3, has a thickness of platinum containing zirconia.
10 μm reference electrode terminal 14, measuring electrodes 6, 7 and measuring electrode terminal
15 is first thick film printed. Next, 20 μm thick protective layers 22 and 23 made of alumina containing platinum are thick-film printed on the surfaces of the measurement electrodes 6 and 7, respectively. Next, the first insulating layer 24 made of alumina and having a thickness of 30 μm is formed on the reference electrode terminal described above.
14 and the upper surface 25 of the measuring electrode terminal 14 and the window 2 of the measuring electrodes 6 and 7.
A thick film is printed on the surface of the green sheet 3a except for 6,27. Furthermore, the thickness of platinum containing alumina is 10 μm.
Of the heating element 8 and the heating element electrodes 16 and 17 of the first and second
The first insulating layer 2 is formed in a U shape around the measuring electrodes 6 and 7, respectively.
Thick film printed on the surface of 4. Finally, the second insulating layer 28 made of alumina containing silica and having a thickness of 20 μm is the first insulating layer except the upper surface 29 of the heating element electrodes 16 and 17 and the window portions 30 and 31 of the measuring electrodes 6 and 7. Thick film printing on 24 surfaces.

In this way, the zirconia paste is applied to the back surface of the thick film printed green sheet 3a, and the first and second reference electrodes 4 and 5 are formed into two pairs of the first to fourth through holes 9 of the hollow cylindrical body 2.
The outer periphery of the hollow cylindrical body 2 is covered with the green sheet 3a so as to be located at positions corresponding to .about. Further, by performing rubber pressing while evacuating, the green sheet 3a is wound and pressure-fixed, and then fired at atmospheric pressure to obtain the oxygen sensor 1 shown in FIG.

As shown in FIG. 5, the oxygen sensor 1 obtained as described above is fixed to a holder 32 by a filling powder 33 such as carbon graphite or talc, a packing 34 and a caulking ring 35. Further, the crimp terminal fittings 36 are attached to the above-mentioned terminals, and the lead wires 37 are further crimped. Then, the metal shell 38, the protective outer cylinder 39, the grommet 40, and the protector 41 are attached to form the oxygen detection probe 42.

With the oxygen sensor 1 thus configured, the following effects can be obtained.

First, since the electrode pair composed of the first reference electrode 4 and the first measurement electrode 6 and the electrode pair composed of the second reference electrode 5 and the second measurement electrode 7 are formed to face each other, the measurement gas It is possible to reduce the influence on the output of the oxygen sensor 1 due to the flow direction of the oxygen sensor 1, and it is possible to maintain high accuracy even when the mounting position of the oxygen sensor 1 is deviated.

In the first embodiment described above, two pairs of electrodes are arranged facing each other at an interval of 180 °. With this arrangement, even if the flow direction of the measurement gas is not perpendicular to the electrode surface, the oxygen partial pressure can be accurately measured, as will be apparent from an experimental example described later. In addition, the electrode pair,
It is preferable to arrange them at equal intervals, such as 120 ° intervals in the case of 3 sets and 90 ° intervals in the case of 4 sets, since the directionality of the oxygen sensor is small.

Even if the distance between the arranged electrode pairs is deviated from the equal distance, if the deviation is within 30 °, the oxygen sensor has little directionality. That is, assuming that the number of electrode pairs is N, the electrode pair is centered on the circumference of the solid electrolyte layer with the center angle of 360 ° / N-30 ° or more and 360 ° / N + 30 ° or less with reference to the center of each electrode. By arranging at an interval of, it is possible to realize an acid side sensor with little directivity.

Further, as compared with the plate-shaped oxygen sensor, the thin hollow cylindrical body 2 having a hollow in the center can be used, so that the heat capacity of the oxygen sensor 1 is small and the heat efficiency of the heating element 8 is improved. As a result, power consumption can be reduced, and since the heating element 8 is thick-film printed on the surface of the green sheet 3a, it is extremely easy to manufacture.

Next, an example of an experiment conducted to confirm the effect of this example will be described.

Experimental Example The experimental apparatus uses an automobile engine of 2.0 and uses the output of the oxygen sensor to feedback the air-fuel ratio so that gasoline and air are mixed and burned at a theoretical air-fuel ratio (excess air ratio λ = 1). Take control. In this experiment,
As shown in the figure, in addition to using the oxygen sensor A in which the electrode A2 is provided so as to face the surface of the cylinder A1 similar to the first embodiment, as Comparative Example 1, the electrode is formed on the surface of the conventional plate-shaped substrate B1. As the oxygen sensor B provided with B2, as the comparative example 2, the oxygen sensor C in which the electrode C2 is arranged only in one direction of the cylinder C1 was used. Then, the positions of the electrodes of the oxygen sensors A, B, and C were changed every 30 degrees with respect to the flow direction of the measurement gas, and the air-fuel ratio characteristics at that time were examined.

The results of this experiment are shown in FIG. 7. As is clear from the figure, in the plate-shaped comparative example 1, the variation in the air-fuel ratio of the exhaust gas was remarkable, but in the first example, the directionality was Almost none, which is preferable. It should be noted that the cylindrical comparative example 2 is superior in its directionality and superior to the comparative example 1, but the oxygen sensor 1 of the present embodiment is preferable because it has less directionality.

Next, a second embodiment of the present invention will be described with reference to FIG. The feature of the second embodiment is that the heating element is provided on the outer peripheral surface of the solid electrolyte layer in contrast to the heating element provided on the inner peripheral surface of the first embodiment.

As shown in FIG. 8, on the back surface of the green sheet 101a, which is the inner peripheral surface of the solid electrolyte layer, a pair of reference electrodes 102, 103,
The first insulating layer 104, the heating element 106, and the second insulating layer 107 are thick-film printed in this order. On the other hand, on the surface of the green sheet 101a which is the outer peripheral surface of the solid electrolyte layer, a pair of measuring electrodes 108, 109,
A pair of protective layers 110, 111, a third insulating layer 112, a reference electrode terminal 113,
The measurement electrode terminal 114 and the heating element terminals 115 and 116 are thick-film printed in this order. The reference electrodes 102, 10 thus thick-film printed
The hollow cylindrical body 117 is attached to the green sheet 1 so that the positions 3 correspond to the two pairs of through holes 118 to 121 of the hollow cylindrical body 117.
An oxygen sensor is formed by coating with 01a and firing in the same manner as in the first embodiment described above. The component of each member is the first
It is similar to the embodiment.

In the second embodiment, the heating element 106 is printed on the same side as the reference electrodes 102, 103 on the green sheet 103a, so that the thermal efficiency in heating to a temperature suitable for measurement is extremely high. This is particularly effective because it is difficult to cool the measuring part even when measuring the oxygen partial pressure of the low temperature measurement gas. Therefore, for example, when it is used for measuring exhaust gas of an automobile or the like, the measurement can be started promptly after the engine is started.

Next, a third embodiment of the present invention will be described with reference to FIG. The third embodiment is the hollow cylindrical body 2 described in the first embodiment.
Is applied to an air-fuel ratio sensor equipped with an oxygen pump element.

As shown in FIG. 9, on the back surface of the green sheet 201a which is the inner peripheral surface of the solid electrolyte layer, the second pump electrodes 202, 203,
Diffusion rate controlling layer 204, measuring electrode 205, 206, solid electrolyte layer 207, 208
And the reference electrodes 209 and 210 are sequentially thick film printed. On the other hand, on the surface of the green sheet 201a which is the outer peripheral surface of the solid electrolyte layer, the first pump electrodes 211, 213, the first insulating layer 213, and the heating element 214 are formed.
And the second insulating layer 215 is sequentially thick-film printed. The green sheet 201a thus thick-film printed is used as a hollow cylindrical body 22 in which two pairs of through holes 216 to 219 are formed, as in the first embodiment.
After being wound around 0, the air-fuel ratio sensor is formed by firing in the atmosphere.

The third embodiment having the above-described structure is extremely easy to manufacture as an air-fuel ratio sensor including an oxygen pump element, as compared with a structure in which each element and the like are laminated in a plate shape, and with such a simple structure. The air-fuel ratio signal can be detected from the pump current by combining the oxygen concentration cell element and the oxygen pump element. Further, since it is composed of the hollow cylindrical body 220 and the one-layer green sheet 201a, the heat capacity is small, the power consumption of the heating element 214 can be reduced, and the durability thereof can be improved.

Although the embodiments of the present invention have been described above, the present invention is not limited to such embodiments, and it is needless to say that the present invention can be implemented in various modes without departing from the scope of the invention. .

[Effects of the Invention] As described above, according to the present invention, in the oxygen sensor, when the number of electrode pairs is N, the electrode pairs are arranged around the circumference of the solid electrolyte layer with the center of each electrode as a reference. Above, central angle 360
Since they are arranged at intervals of ゜ / N-30 ゜ or more and 360 ゜ / N + 30 ゜ or less, the acid velocity concentration can be detected accurately regardless of the flow direction of the measuring gas and the mounting position of the oxygen sensor. Further, since the hollow cylindrical body is used, the heat capacity becomes small, the power consumption of the heating element is small, and the durability can be improved.

[Brief description of drawings]

1 is a partially cutaway perspective view of the oxygen sensor of the first embodiment, FIG. 2 is an end view of II-II, FIG. 3 is a partially cutaway view of a hollow cylindrical body, and FIG. 1 is an exploded view showing an embodiment, FIG. 5 is a partially cutaway view of an oxygen detection probe, FIG. 6 is an illustration showing the direction of electrodes of an oxygen sensor, FIG. 7 is a graph showing the effect of the embodiment, FIG. 8 is an explanatory diagram of the second embodiment, and FIG. 9 is an explanatory diagram of the third embodiment. 1 …… Oxygen sensor 2,117,220 …… Hollow cylinder detection element 4,5,102,104,209,210 …… Reference electrode 6,7,108,109,205,206 …… Measuring electrode 9,10,11,12,118,119,120,121,216,217,218,219 …… Through hole

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ken Minowa 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Japan Special Ceramics Co., Ltd. (56) Reference JP-A-61-272649 (JP, A)

Claims (3)

(57) [Claims] 1. A hollow cylindrical body having an opening on one end side and a closing wall on the other end side, and having a plurality of through holes communicating between the inner surface side and the outer surface side, and the hollow cylindrical body wrapping the inner and outer surfaces. And an oxygen ion conductive solid electrolyte layer having at least two pairs of electrodes, and the electrode on the inner surface side of the intrinsic electrolyte layer is disposed at a position corresponding to the through hole of the hollow cylindrical body. In the sensor, assuming that the number of the electrode pairs is N, the electrode pairs are arranged on the circumference of the solid electrolyte layer with a central angle of 36 mm with respect to the center of each electrode.
An oxygen sensor characterized by being arranged at intervals of 0 ° / N-30 ° or more and 360 ° / N + 30 ° or less. 2. The oxygen sensor according to claim 1, wherein the solid electrolyte layer has a heating element on its inner surface. 3. The oxygen sensor according to claim 1, wherein the solid electrolyte layer has a heating element on its outer surface.