JPH04295756A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To make it possible to detect the concentration of oxygen adequately regardless of the temperature of measuring atmosphere even when a heater is not used by forming the shape of each electrode which is formed on the surface of a solid electrolyte layer as the shape which is expanded to the approxiamtely equal distance from a through hole. CONSTITUTION:The surface of a hollow tubular body 2 is covered with a solid electrolyte layer 3. First-third reference electrodes 4a-4c are provided on the inner-surafce side of the electrolyte layer 3, and first-third measuring electrodes 5a-5c are provided on the outer surface side. First-third through holes 6a-6c are further formed so as to penetrate the tubular body 2 from the inner surface side to the outer surface side. The circular electrodes 4a-4c are provided at the inner surface side so as to hold the electrolyte layer 3 in such a way that the through holes 6a-6c are the centers of the circles. The circular electrodes 5a-5c are provided on the outer surface side of the electrode layer by the same way. The inner surface side of the electrode layers 3 is in contact with reference gas, and the outer surface side is in contact with gas to be measured. The current flowing across the electrodes provided on both surfaces is measured, and the partial pressure of oxygen in the gas to be measured is obtained.

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 oxygen concentration in exhaust gas from, for example, internal combustion engines and 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 has been measured, and air-fuel ratio feedback control of the internal combustion engine has been performed based on the measured value. Such measurement of the oxygen partial pressure in exhaust gas is performed, for example, by an oxygen sensor equipped with a detection element made of a solid electrolyte layer that conducts oxygen ions, such as a zirconia-yttria solid solution.

As the above-mentioned oxygen sensor, for example, one has been proposed that measures oxygen partial pressure by forming a measuring electrode on the surface of a flat detection element (Japanese Patent Application Laid-Open No. 12544/1983).
(See Publication No. 8 or Japanese Unexamined Patent Publication No. 60-36949, etc.). In addition, in order to improve the directionality of the flat detection element,
A sensor in which a plurality of rectangular electrodes are arranged around a cylindrical detection element has also been proposed (see Japanese Patent Laid-Open No. 1-43753).

0004

However, such an oxygen sensor has a problem in that the effective electrode area is small, so the internal resistance is high, and therefore a heater is required for normal measurements.

In other words, in the absence of heating of the detection element by a heater, if the temperature of the measurement atmosphere drops below a certain level, a stable and sufficient sensor output cannot be obtained due to the high internal resistance, and therefore, this oxygen sensor However, there is a problem in that the air-fuel ratio, etc., cannot be properly controlled based on the output.

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

[0007]

[Means for Solving the Problems] The invention of claim 1 to achieve the above object provides a hollow cylindrical body having an open end and a closed wall on the other end, and an inner surface of the hollow cylindrical body. An oxygen sensor comprising a plurality of through holes that communicate between the side and the outer surface side, and an oxygen ion conductive solid electrolyte layer that covers the through holes and wraps the hollow cylindrical body, the oxygen sensor having a plurality of through holes that correspond to the through holes. The object of the present invention is to provide an oxygen sensor characterized in that electrodes are formed on the inner and outer surfaces of the solid electrolyte layer, respectively, and the shape of the electrodes is expanded to approximately the same distance from the through hole.

The oxygen sensor according to claim 2 is the oxygen sensor according to claim 1, wherein at least two of the electrodes are integrally connected to each other on each of the inner and outer surfaces. This article focuses on an oxygen sensor characterized by:

[0009] Here, the solid electrolyte is one having oxygen ion conductivity, such as ZrO2-Y2O3, Z
rO2-CaO etc. are used. The electrodes can be made of, for example, noble metals such as platinum or gas-permeable materials mixed with ceramic powder.

[0010] For example, a green sheet of solid electrolyte on which electrodes are thickly printed is wrapped around a hollow cylindrical body, but when the winding is done, the inner surface of the electrode and the through-hole of the hollow cylindrical body are connected to each other. is placed in the corresponding position. Then, after winding it around a hollow cylindrical body, it is fixed in a cylindrical shape using a jig, and is baked and integrated to form an oxygen sensor.

[0011] Furthermore, it is preferable that the plurality of through holes formed in the hollow cylindrical body are arranged at intervals of the same center angle with the axis of the hollow cylindrical body as the center, since this reduces directivity. The shape of the electrodes formed on the inner and outer surfaces of the solid electrolyte is preferably circular, but polygonal electrodes with a large number of sides (for example, 6 or more sides) may also be used. It is possible.

[0012] The hollow cylindrical body constitutes a reference gas introduction path that passes through the cylinder from one open end side and reaches the through hole to introduce atmospheric air as a reference oxygen source. This hollow cylindrical body can be processed, for example, by die pressing or extrusion molding. As this material, for example, ceramics or metals having a coefficient of thermal expansion close to that of the solid electrolyte are used in order to prevent damage caused by differences in coefficient of thermal expansion. If it is exhaust gas from an engine, the temperature will be over 600℃, so
It is preferable to use ceramics. For example, when a metal such as a stainless steel alloy is used, the inner peripheral surface of the solid electrolyte layer and the electrodes are insulated.

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-temperature measurement environment.

[0014]

[Operation] In the oxygen sensor of the present invention, a reference gas introduction path is formed from one open end of the hollow cylindrical body to the electrode on the inner surface of the solid electrolyte layer via a plurality of through holes. Therefore, since the inner surface of the solid electrolyte layer is in contact with the reference gas and the outer surface is in contact with the measurement gas, the oxygen partial pressure in the measurement gas can be determined by measuring the current flowing between the electrodes provided on both sides. be able to.

[0015] Since the electrodes are formed so as to spread approximately equidistantly from the center of the through hole, the effective electrode area is extremely large. Therefore, since oxygen is efficiently transferred from the through-hole, internal resistance is low. As a result, even when the temperature of the measurement environment is low, the measurement can be performed without using a heater.
It becomes possible to accurately detect oxygen concentration.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. Incidentally, for the sake of explanation, the scale of each part in each figure is different.

As shown in FIG. 1 and FIG. 2 which is an A-A end view of FIG. 1, the oxygen sensor 1 of the first embodiment has a hollow cylindrical body 2
The surface of the solid electrolyte layer 3 is coated with a solid electrolyte layer 3. On the inner surface side of this solid electrolyte layer 3 are first to third reference electrodes 4a.
- 4c are provided, and on the other hand, first to third measurement electrodes 5a to 5c are provided on the outer surface side. Holes 6a to 6c are formed.

In other words, the first to third through holes 6a to 6c are as follows:
They are formed at intervals of 120 degrees around the central axis of the hollow cylindrical body 2, and the inner surface side with the solid electrolyte layer 3 in between is formed so that the first to third through holes 6a to 6c are the centers of the circle. Circular first to third reference electrodes 4a to 4c are provided on the outer surface thereof, and similarly circular first to third measurement electrodes 5a to 5c are respectively provided on the outer surface thereof.

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

Next, each component and manufacturing method of the oxygen sensor 1 will be explained based on FIGS. 3 to 5. 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.
It is a hollow cylinder of mm in diameter, and has 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 6 each having a diameter of 1 mm are provided.
A to 6c are drilled at every 120 degrees of central angle. Therefore, a reference gas introduction path is formed from the opening 18 to the first to third through holes 6a to 6c via the hollow part 20. Such a hollow cylindrical body 2 can be easily processed by die pressing or extrusion molding.

As shown in FIG. 4, the solid electrolyte layer 3 has the following structure:
The green sheet 3a is obtained by mixing a commonly used binder with a raw material powder of ZrO2-Y2O3 solid solution. At the corners of the green sheet 3a are first to third reference electrodes 4.
Through holes 7 are provided for connecting a to 4c to the reference electrode terminal 14.

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

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

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

[0025] Zirconia paste is applied to the back side of the thick-film printed green sheet 3a in this way, and the above-mentioned first to
The center of the third reference electrodes 4a to 4c is located at the first point of the hollow cylindrical body 2.
- Cover the outer periphery of the hollow cylindrical body 2 with the green sheet 3a so as to correspond to the third through holes 6a to 6c, respectively. Furthermore, a green sheet 3a is wrapped and crimped and fixed by performing a rubber press while vacuuming, and then the oxygen sensor 1 shown in FIG. 1 is obtained by firing at atmospheric pressure.

[0026] The oxygen sensor 1 obtained as described above is
As shown in FIG. 5, it is fixed to the holder 32 with a filling powder 33 such as carbon graphite or talcum, a packing 34, and a caulking ring 35. In addition, each terminal 14, 1 described above
5, the crimp terminal fitting 36 is brazed to the lead wire 37.
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 oxygen sensor 1 constructed in this manner provides the following effects. 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 maximum, and the loss caused by the potential difference between the electrodes is proportional to the electrode area. As the current becomes smaller, the oxygen transfer efficiency becomes higher and the internal resistance becomes smaller. Therefore, even when the temperature of the measurement environment is low, the oxygen concentration can be detected with high accuracy without heating with a heater.

[0028] Furthermore, 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, oxygen partial pressure can be measured with high accuracy even when the flow direction of the measurement gas is not perpendicular to the electrode surface. Moreover, there is an advantage that the oxygen sensor 1 has less directionality.

Next, an experimental example conducted to confirm the effects of this embodiment will be explained. (Experiment example) The experimental device uses a 2000cc automobile engine to mix and combust gasoline and air at a stoichiometric air-fuel ratio (excess air ratio λ = 1), that is, air-fuel ratio (A/F) = 14.4. Air-fuel ratio feedback control was performed using the output of the oxygen sensor so as to Then, using the oxygen sensor of this example and the oxygen sensor of the comparative example, changes in the controlled air-fuel ratio were observed when the exhaust gas temperature was changed.

The results of this experiment are shown in FIG. As is clear from the figure, in this example, even when the exhaust gas temperature is low,
Although the deviation of the controlled air-fuel ratio from the stoichiometric air-fuel ratio was small and suitable, in the comparative example, the deviation of the controlled air-fuel ratio increased as the exhaust gas temperature became lower, which was unsuitable.

Next, a second embodiment will be explained with reference to FIG. 7 along with its manufacturing procedure. The second embodiment is characterized in that a larger number of through holes are formed than in the first embodiment, and that the electrodes are not separate but in contact with each other and are integrated.

As shown in FIG. 7, a petal-shaped reference electrode 5 is provided on the back side of the green sheet 50a which becomes the solid electrolyte layer 50.
A reference electrode 52 having a shape in which the ends of two or five circles overlap each other is printed as a thick film. On the other hand, on the surface of the solid electrolyte layer 50, a measuring electrode 54 having the same shape as the reference electrode 52 is printed as a thick film, and on the surface of the measuring electrode 54, a protective layer 56 having a similar petal shape and a window portion are formed. Insulating layer 60 with 58
are printed in this order.

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. The oxygen sensor is formed by arranging the oxygen sensor so that Note that the components of each member are the same as in the first embodiment.

This second embodiment has the same effects as the first embodiment, and since the five circles are integrally formed, the internal resistance is small and sufficient sensor output can be obtained even at low temperatures. It is suitable and has the advantage that failures such as disconnection are less likely to occur because the structure is simple.

Although the embodiments of the present invention have been described above,
It goes without saying that the present invention is not limited to these embodiments in any way, and can be implemented in various forms without departing from the scope of the invention.

For example, the shape of the electrodes to be combined may be a polygonal shape close to a circle instead of a circle. Also,
There are no particular limitations on the number of electrodes to be combined or the number of through holes to be formed. Furthermore, a heater may be attached to the configuration of the above embodiment.

[0037]

As explained above, in the present invention, the shape of the electrode formed on the surface of the solid electrolyte layer is expanded to approximately the same distance from the through hole, or a combination thereof. Therefore, since the effective electrode area is large, the internal resistance is small, so that even if the measurement environment is low temperature, the oxygen concentration can be detected accurately and stably.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view of an oxygen sensor according to a first embodiment of the present invention.

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 diagram showing an exploded view of the first embodiment.

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

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

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

[Explanation 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...Measuring electrodes 6a, 6b, 6c, 64...through hole

Claims (2)

[Claims] Claim 1: A hollow cylindrical body having one end open and a closed wall provided on the other end, a plurality of through holes communicating the inner and outer sides of the hollow cylindrical body, and a plurality of through holes. an oxygen ion conductive solid electrolyte layer that covers and envelops the hollow cylindrical body, and electrodes are formed on the inner and outer surfaces of the solid electrolyte layer corresponding to the through holes, and . An oxygen sensor characterized in that the shape of the electrode is expanded to approximately the same distance from the through hole. 2. The oxygen sensor according to claim 1, comprising:
An oxygen sensor characterized in that at least two of the electrodes are integrally connected to each other on each of the inner and outer surfaces.