JP3003957B2 - Oxygen sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor for measuring the concentration of oxygen in exhaust gas of, for example, an internal combustion engine or various combustion equipment.

[0002]

2. Description of the Related Art Conventionally, for the purpose of preventing pollution and improving fuel efficiency, the partial pressure of oxygen in the exhaust gas of an internal combustion engine is measured, and the air-fuel ratio feedback control of the internal combustion engine is performed based on the measured value. Such measurement of the partial pressure of oxygen in the exhaust gas is performed, for example, by an oxygen sensor provided with a detection element composed of an oxygen ion conductive solid electrolyte layer such as a zirconia-yttria solid solution.

As the oxygen sensor, there has been proposed, for example, a sensor in which a measurement electrode is formed on the surface of a detection element having a flat plate shape to measure the oxygen partial pressure (Japanese Patent Laid-Open No. 55-12544).
8 or JP-A-60-36949).
In addition, in order to improve the directionality of the flat detection element,
A device in which a plurality of rectangular electrodes are arranged around a cylindrical detection element has also been proposed (see Japanese Patent Application Laid-Open No. 1-43753).

[0004]

However, such an oxygen sensor has a problem that the effective electrode area is small and the internal resistance is high, so that a normal measurement requires a heater.

In other words, if the temperature of the measurement atmosphere drops below a certain level when the detection element is not heated by the heater, a stable and sufficient sensor output cannot be obtained due to the high internal resistance. However, there has been a problem that the control of the air-fuel ratio or the like performed based on the output cannot be suitably performed.

It is an object of the present invention to provide an oxygen sensor that can appropriately detect an oxygen concentration regardless of the temperature of a measurement atmosphere even when a heater is not used.

[0007]

According to a first aspect of the present invention, there is provided a hollow cylindrical body having an opening at one end and a closed wall at the other end, and an inner surface of the hollow cylindrical body. A plurality of through-holes communicating the side and the outer surface side, and an oxygen ion-conductive solid electrolyte layer covering the hollow cylindrical body covering the through-holes, an oxygen sensor comprising: Thus, an oxygen sensor is characterized in that electrodes are formed on the inner surface and the outer surface of the solid electrolyte layer, respectively, and the shape of the electrodes is expanded to be substantially equidistant from the through hole.

According to a second aspect of the present invention, in the oxygen sensor of the first aspect, at least two of the electrodes are connected to each other on an inner surface and an outer surface to be integrated. The gist is an oxygen sensor characterized by the above.

Here, the solid electrolyte has oxygen ion conductivity, for example, ZrO ₂ —Y ₂ O ₃ , Zr
O ₂ -CaO or the like is used. The electrode can be realized by, for example, a noble metal such as platinum or a gas permeable material obtained by mixing these with a ceramic powder.

In these, for example, a green sheet of a solid electrolyte on which an electrode is printed in a thick film is wound around a hollow cylindrical body. At the time of winding, the electrode on the inner side and the through-hole of the hollow cylindrical body are formed. Is placed at the corresponding position. Then, after being wound around the hollow cylindrical body, it is fixed in a cylindrical shape by a jig, and is fired and integrated to form an oxygen sensor.

Further, it is preferable that the plurality of through holes formed in the hollow cylindrical body are arranged at the same center angle interval about the axis of the hollow cylindrical body, so that the directionality is small. The shape of the electrodes formed on the inner surface and the outer surface of the solid electrolyte is preferably circular, but in addition, a polygonal electrode having a large number of sides (for example, having six or more sides) is also employed. It is possible.

The hollow cylindrical body constitutes a reference gas introduction path for introducing air as a reference oxygen source from the open one end through the inside of the cylinder to the through hole. This hollow cylindrical body can be processed by, for example, die pressing or extrusion molding. As this material, for example, a ceramic or a metal having a value close to the coefficient of thermal expansion of the solid electrolyte is used to prevent breakage 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 more is used, and therefore, it is preferable to use ceramics. When a metal such as a stainless alloy is used, for example, the inner peripheral surface of the solid electrolyte layer is insulated from the electrode.

Although the oxygen sensor of the present invention operates satisfactorily even without a heater, a heater may be provided in order to function more accurately even in a low measurement environment.

[0014]

In the oxygen sensor of the present invention, a reference gas introduction passage is formed from one open end of the hollow cylindrical body to the electrode on the inner surface side of the solid electrolyte layer through a plurality of through holes. Accordingly, since the solid electrolyte layer contacts the reference gas on the inner surface side and the measurement gas on the outer surface side, the oxygen partial pressure in the measurement gas is determined by measuring the current flowing between the electrodes provided on both surfaces. be able to.

Since the electrodes are formed so as to extend substantially equidistantly about the through hole, the effective electrode area is extremely large. Therefore, the transfer of oxygen from the through hole is efficiently performed, and the internal resistance is small. As a result, even when the temperature of the measurement environment is low, without using a heater,
It is possible to accurately detect the oxygen concentration.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. In the description, each figure is different in scale from part to part.

As shown in FIG. 1 and FIG. 2 which is an AA end view of FIG. 1, the oxygen sensor 1 of the first embodiment has a hollow cylindrical body 2.
Is coated with a solid electrolyte layer 3. First to third reference electrodes 4a are provided on the inner surface side of the solid electrolyte layer 3.
4c, on the other hand, first to third measurement electrodes 5a to 5c are provided on the outer surface side, and further, the first to third penetrations are made by communicating the inner surface side and the outer surface side of the hollow cylindrical body 2 with each other. Holes 6a to 6c are formed.

That is, the first to third through holes 6a to 6c are
It is formed every 120 degrees about the center axis of the hollow cylindrical body 2, and the inner surface side of the solid electrolyte layer 3 is sandwiched between the first to third through holes 6 a to 6 c so as to be the center of the circle. Are provided with circular first to third reference electrodes 4a to 4c, and circular first to third measurement electrodes 5a to 5c are also provided on the outer surface side.

The first to third reference electrodes 4a to 4c are integrally connected by an electrode wire 7, and are connected to a reference electrode terminal 1 through a through hole 7 (FIG. 4) provided in the solid electrolyte layer 3.
4 is connected. On the other hand, the first to third measurement electrodes 5a to 5a
5c is integrally connected by the electrode wire 8 and is connected to the measurement electrode terminal 15.

Next, each member and manufacturing method of the oxygen sensor 1 will be described with reference to FIGS. First, as shown in FIG. 3, the hollow cylindrical body 2 has an outer diameter of 3.2 mm and an inner diameter of 1.6.
mm hollow cylinder having an opening 18 at one end and a closing wall 19 at the other end. In the side wall 2a near the closing wall 19, the first to third through holes 6a to 1 mm having a diameter of 1 mm described above are provided.
6c are formed every 120 degrees of the central angle. Therefore,
A reference gas introduction passage extending from the opening 18 to the first to third through holes 6a to 6c via the hollow portion 20 is formed. Such a hollow cylindrical body 2 can be easily processed by die pressing or extrusion molding.

The solid electrolyte layer 3 is formed as shown in FIG.
The green sheet 3a is obtained by mixing a raw material powder of a ZrO ₂ —Y ₂ O ₃ solid solution with a commonly used binder.
The first to third reference electrodes 4 are provided at the corners of the green sheet 3a.
A through hole 7 for connecting a to 4c to the reference electrode terminal 14 is provided.

On the back surface of the green sheet 3a serving as the inner peripheral surface of the solid electrolyte layer 3, first to third reference electrodes 4a to 4c having a thickness of 10 μm and made of platinum containing zirconia are provided.
And the electrode wire 7 is printed in a thick film.

On the other hand, a 10 μm-thick reference electrode terminal 14 made of platinum containing zirconia is provided on the surface of the green sheet 3 a which is the outer peripheral surface of the solid electrolyte layer 3.
Measurement electrodes 5a to 5c, electrode wire 8, and measurement electrode terminal 15
Is printed in a thick film. Next, protective layers 22a to 22c made of alumina containing platinum and having a thickness of 20 μm are formed on the first to third layers.
A thick film is printed on the surfaces of the measurement electrodes 5a to 5c.

Next, the insulating layer 24 made of alumina and having a thickness of 30 μm is formed on the upper surface 25 of the reference electrode terminal 14 and the measurement electrode terminal 14 and the windows 26a to 26c of the first to third measurement electrodes 5a to 5c. Except for the above, a thick film is printed on the surface of the green sheet 3a.

As described above, the zirconia paste is applied to the back surface of the green sheet 3a on which the thick film is printed, and
The center of the third reference electrodes 4a to 4c is
The green sheet 3a is coated on the outer periphery of the hollow cylindrical body 2 so as to correspond to the third through holes 6a to 6c, respectively. Further, the oxygen sensor 1 shown in FIG. 1 is obtained by performing a rubber press while evacuating, winding and fixing the green sheet 3a by pressure, and then firing at atmospheric pressure.

The oxygen sensor 1 obtained as described above is
As shown in FIG. 5, the holder 32 is fixed by a filling powder 33 such as carbon graphite or talc, a packing 34 and a caulking ring 35. In addition, each of the terminals 14, 1 already described
5 is soldered with a crimp terminal fitting 36,
Crimp. Thereafter, the oxygen detection probe 42 is formed by attaching the metal shell 38, the protective outer cylinder 39, the grommet 40, and the protector 41.

The following effects can be obtained by the oxygen sensor 1 configured as described above. First, since the first to third reference electrodes 4a to 4c and the first to third measurement electrodes 5a to 5c are circular, the effective electrode area is the largest, and the loss caused by the potential difference between the electrodes is proportional to the electrode area. As the current decreases, the transfer efficiency of oxygen increases, and the internal resistance decreases. Therefore, even when the temperature of the measurement environment is low, there is a feature that the oxygen concentration can be accurately detected without heating by the heater.

The first to third reference electrodes 4a to 4c
Since the first to third measurement electrodes 5a to 5c are arranged at intervals of 120 degrees, the oxygen partial pressure can be accurately measured even when the flow direction of the measurement gas is not perpendicular to the electrode surface. In addition, there is an advantage that the directionality of the oxygen sensor 1 is small.

Next, an experimental example performed to confirm the effect of the present embodiment will be described. (Experimental example) The experimental apparatus uses a 2000 cc automobile engine, mixes gasoline and air at a stoichiometric air-fuel ratio (excess air ratio λ = 1), that is, an air-fuel ratio (A / F) = 14.4 and burns. The air-fuel ratio feedback control was performed using the output of the oxygen sensor. Then, using the oxygen sensor of this embodiment and the oxygen sensor of the comparative example, a change in the control air-fuel ratio when the exhaust gas temperature was changed was observed.

FIG. 6 shows the results of this experiment. As is clear from the figure, in this embodiment, even when the exhaust gas temperature is low,
Although the deviation of the control air-fuel ratio from the stoichiometric air-fuel ratio was small and suitable, in the comparative example, when the exhaust gas temperature was low, the deviation of the control air-fuel ratio was large and was unsuitable.

Next, a second embodiment will be described with reference to FIGS. The second embodiment is characterized in that the number of through holes formed is larger than that of the first embodiment, and that the electrodes are not separated but are in contact with each other and are integrated.

As shown in FIG. 7, a petal reference electrode 5 is provided on the back surface of the green sheet 50a to be the solid electrolyte layer 50.
The reference electrode 52 having a shape in which the ends of two, that is, five circles overlap each other, is printed in a thick film. On the other hand, on the surface of the solid electrolyte layer 50, a measurement electrode 54 having the same shape as the reference electrode 52 is printed in a thick film, and on the surface of the measurement electrode 54, a protection layer 56 having a similar petal shape and a window portion are formed. Insulating layer 60 with 58
Are printed in this order in thick film.

When covering the hollow cylindrical body 62 with the green sheet 52a, the centers of the five circles of the reference electrode 52 correspond to the five through holes 64 of the hollow cylindrical body 62, respectively. And fired in the same manner as in the first embodiment to form an oxygen sensor. The components of each member are the same as in the first embodiment.

The second embodiment has the same effects as the first embodiment, and since the five circles are integrally formed, the internal resistance is small and a sufficient sensor output can be obtained even at a low temperature. Advantageously, since the structure is simple, a failure such as disconnection hardly occurs.

The embodiments of the present invention have been described above.
The present invention is not limited to such an embodiment at all, and it goes without saying that the present invention can be implemented in various modes without departing from the scope of the present invention.

For example, the shape of the electrodes to be combined may be a polygonal shape close to a circle other than a circle. Also,
The number of electrodes to be combined and the number of through holes to be formed are not particularly limited. Further, a heater may be attached to the configuration of the above embodiment.

[0037]

As described above, in the present invention, the shape of the electrode formed on the surface of the solid electrolyte layer is a shape that is extended to substantially the same distance from the through hole, or a combination thereof. Accordingly, since the effective electrode area is large, the internal resistance is small, and thus, there is an effect that the oxygen concentration can be detected accurately and stably even when the measurement environment is at a low temperature.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an oxygen sensor according to a first embodiment of the present invention, partially cut away.

FIG. 2 is an AA end view of the oxygen sensor of the first embodiment.

FIG. 3 is a partially cutaway view of a hollow cylindrical body.

FIG. 4 is an explanatory view showing an exploded view of the first embodiment.

FIG. 5 is a partial cutaway view of the oxygen detection probe.

FIG. 6 is a graph showing the effect of the oxygen sensor of the first embodiment.

FIG. 7 is an explanatory diagram showing an exploded view of the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Oxygen sensor 2, 62 ... Hollow cylindrical body 3, 50 ... Solid electrolyte layer 4a, 4b, 4c, 52 ... Reference electrode 5a, 5b, 5c, 54 ... Measurement electrode 6a, 6b, 6c, 64 ... Through-hole

Claims (2)

(57) [Claims] 1. A hollow cylindrical body having an open end at one end and a closed wall provided at the other end, a plurality of through-holes communicating an inner surface and an outer surface of the hollow cylindrical body, An oxygen ion-conductive solid electrolyte layer covering the hollow cylindrical body, and forming an electrode on the inner surface and the outer surface of the solid electrolyte layer corresponding to the through hole, respectively. An oxygen sensor, wherein the shape of the electrode is widened to substantially the same distance from the through hole. 2. The oxygen sensor according to claim 1, wherein at least two of the electrodes are connected to each other on an inner surface and an outer surface to be integrated. .