JPH02212757A - Oxygen sensor for controlling air/fuel ratio with protective layer containing oxygen occluded material and making thereof - Google Patents

Abstract

PURPOSE:To prevent a deterioration in endurance on severe heat cycle conditions while achieving an accurate air/fuel ratio control by coupling a protective layer to a base part of a sensor element through a spherical protrusion while an oxygen occluded material is contained in the protective layer. CONSTITUTION:A protective layer 4 comprising a heat resistant metal oxide is provided on a side exposed to an exhaust gas of a sensor element through an electrode 3. A body 1 of the sensor element is made up of a base part 1a and a plurality of spherical protrusions 1b. The layer 4 contains an oxygen occluded material. According to an oxygen sensor thus arranged, the protrusion 1b functions as wedge to allow the coupling of the layer 4 to the body 1 firmly. As a result, there is no deterioration in endurance such as peeling even under severe heat cycle conditions. Thus, an action of a material 4a contained in the layer 4 can be delivered sufficiently for a long period of time, thereby achieving an accurate air/fuel control in accelerated and normal operations.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an oxygen sensor for air-fuel ratio control that is used in combination with a three-way catalyst in an exhaust gas purification system for automobiles and the like.

[Prior art and issues] Exhaust gas regulations for automobiles, etc. are becoming increasingly strict.

Many oxygen sensors have been developed. Under these circumstances, an oxygen sensor has been proposed that has a layer made of a combination of a catalyst and cerium oxide, etc., which exhibits oxygen storage and release properties (
Japanese Patent Publication No. 81-791.55. 62-245148).

However, oxygen sensors are usually used under severe thermal cycle conditions, and in all of the oxygen sensors proposed above, when used, the cerium oxide or other catalyst layer may peel off from the sensor element. Furthermore, since the coating is made by mixing cerium oxide or the like with a catalyst, both components exist in a single layer.

Therefore, due to the strong influence of the catalyst components, the occlusion and release of oxygen by cerium oxide, etc. is excessively increased, and the control frequency as a sensor decreases, causing it to fall out of the window of the three-way catalyst of the exhaust gas purification system. There is also.

[Means for solving problems, actions, and effects] Therefore, the oxygen sensor for air-fuel ratio control of the present invention is as follows.

A protective layer made of a heat-resistant metal oxide is provided on the side of the sensor element exposed to exhaust gas, covering at least the electrode, and the protective layer consists of a main body or base of the sensor element and a plurality of spherical protrusions, and the protective layer is spherical. Connected to the base via the protrusion.

Protection [Tower contains oxygen storage substances. It is characterized by

According to this oxygen sensor, one spherical protrusion functions as a wedge, so that the element body and the protective layer can be firmly connected. Therefore, 1. Even under normal severe thermal cycle conditions, the protective layer reliably protects the element body and electrodes from exhaust gas without causing durability deterioration such as peeling. Therefore, the action of the oxygen storage material (hereinafter referred to as rO3cJ) contained in the protective layer can be fully exerted over a long period of use. That is, the O20 contained in the 1-layer Jψ layer is I! J! When the A/F is richer than the theoretical value, there is almost no oxygen adsorption capacity, and it is very
The oxygen adsorption capacity increases when the temperature is A or F (Fig. 7). Therefore, when the amount of air increases rapidly (during lean A/F) such as during acceleration, the exhaust gas absorbs oxygen and reaches the sensor element with less oxygen than the actual exhaust gas.As a result, the sensor Delays the output timing of the single signal. Furthermore, when the engine finishes accelerating and returns to normal operation, it acts as a protective layer to protect the measurement electrodes, preventing the λ point from shifting and reducing the output.

Therefore, the deviation of the λ point due to a sudden increase in air volume (so-called rich excursion) is minimized by using an oxygen storage material. can be achieved.

In the oxygen sensor of the present invention, the protective layer protects the electrode, particularly the measurement electrode, from exhaust gas both initially and after durability. The protective layer is preferably composed of a refractory metal oxide, such as alumina spinel and magnenia, beryllia, zirconia, etc., or a mixture thereof.

Especially Mg0-A, f! A material mainly composed of spinel such as 203 is preferable. It supports O20 in a highly dispersed state and exhibits its oxygen storage function over a long period of use, and has excellent heat resistance. It may be formed by using a stoichiometric compound and a non-stoichiometric compound in combination. Its porosity is 5-20
%, preferably 7 to 20%, and the thickness is 30 to 200 μm, preferably 50 to 17 μm. The (measuring) electrode can be reliably protected without impeding exhaust gas permeability.

Examples of the O20 contained in the protective layer include non-stoichiometric compounds such as oxides of rare earth elements. Particularly preferred are cerium oxide and vanadium oxide. It has a strong ability to absorb and release oxygen, and to achieve the same effect with another substance, you need to increase its amount.

It needs to be thicker and therefore more prone to clogging.

O20 is present in an amount of 02 to 3 wt% (in terms of O5C metal element) based on the heat-resistant metal oxide constituting the protective layer. If it is less than 0.2 wt%, a large amount of excess oxygen cannot be stored, especially during transient response. on the other hand.

If it exceeds 30 νt%, the absorption and desorption effects will be too large even in a steady state, and the response frequency characteristics will become too gradual. However, in order to improve the durability of the O8C-containing layer as a protective layer as described below, when the protective layer is immersed in an O20 metal salt solution after forming the protective layer, 02 to 8 νt% is added to prevent clogging of the protective layer. , preferably 0.8 to 3 νt%.

Below the de limit, the effect of O20 becomes slightly worse. still.

The O8C content is the weight difference before and after providing the protective layer [X]
It was calculated from the weight increase [Y'l] and the weight increase after the inclusion of OSC as shown in the following formula.

(Here, A: atomic weight of the metal element O3C.

M: Molecular weight of O20 1 Area ratio: Area of the part immersed in O5C metal salt solution or coated with O20 slurry / Total surface area of protective layer) 08C is preferably contained in 1/2 or more of the total surface area of the protective layer. . If it is less than 1/2, a large amount of exhaust gas passes through areas other than the O8C existing area and reaches the (measurement) electrode, and output fluctuations in that area become dominant. Preferably it is 7710 or more.

The main body of the sensor element includes a base and a plurality of spherical protrusions, and a protective layer is coupled to the base via the spherical protrusions. Conventionally, the interface between the element body and the protective layer has been a flat surface, and the interface between the element body and the protective layer has been bonded only by thermal adhesive force during the formation of the protective layer. However, an electrode exists at such an interface, and the noble metal such as PT as the electrode material differs from the heat-resistant metal oxide that constitutes the element body material and the protective layer in various properties such as the coefficient of thermal expansion. Therefore, among the interface parts between the element body and the protective layer, the most important part for the detection characteristics where the (measuring) electrode is present sometimes suffers from durability deterioration such as sharpness and peeling due to use. However, as in the present invention, by providing a spherical protrusion made of the element body material at the interface between the element body and the protective layer, particularly in correspondence with the location of the (measuring) electrode, this spherical protrusion can be used as a so-called wedge. , the element body and the protective layer can be physically bonded more firmly. Therefore, even when used under severe thermal cycle conditions, the (measuring) electrode can be stably protected by the protective layer over a long period of time, and the action of the O8C contained in the protective layer can be exerted. Moreover, by making the (measuring) electrode uneven due to the presence of this spherical protrusion, its surface area can be increased and high λ detectability can be maintained in a narrow area.

The spherical protrusion is made of the element body material, that is, the solid electrolyte.

(such as ZrO), semiconductor materials (Tie, C.

0, etc.). in particular.

When the element body material is made of an oxygen ion conductive solid electrolyte 1 For example, element base ZrO-Y203 system 1 spherical protrusion Z
In addition to r OY 203 series, Zr02 (Ca O
It may also be a 1M g O) system. or.

The same composition may contain different amounts of stabilizer.

Note that the first spherical protrusion is inside the measurement electrode (closer to the element).

It may be provided either on the outside (closer to the protective layer).

The spherical protrusion consists of an aggregate of granulated particles.

It may be present in a single layer or in multiple layers. The particle size of the granulated particles is 4
The amount may be 0 to 100 μl, preferably 50 to 80 μl. If the thickness is less than 40 μm, it cannot function as a wedge sufficiently, and if it exceeds 1oon, the adhesion between the element body (base) or the protective layer and the spherical protrusion may become weak. It is preferable that the spherical protrusions are distributed such that there are recesses between each spherical protrusion.

It can further enhance the bonding force with the protective layer and expand the electrode surface area.

The oxygen sensor of the present invention further allows the following configuration, for example.

(a) A second protective layer may be further provided by covering the protective layer (hereinafter also referred to as "first protective layer j").The heat resistance is further improved, and the above-mentioned O20 This second protective layer can be made of the same heat-resistant metal oxide as the first protective layer.Also, the first protective layer can be made of a stoichiometric compound, and the second protective layer can be made of a non-stoichiometric compound. logical compounds such as TiO(x-0,02-0.03), Ni
It may be composed of -x such as O. Note that the porosity of the second protective layer is 1.5 times or more greater than that of the first protective layer (for example, 8 to 35%).

The thickness should be small (for example, 10 to 50μ0+).

While effectively exhibiting the oxygen storage effect of O20 in the first protective layer, deterioration of exhaust gas permeability and sensor responsiveness can be prevented.

Further, it is preferable that this second protective layer supports a noble metal. Precious metals act as catalysts to bring unburned components in exhaust gas into equilibrium. Therefore, deviation of λ toward the lean side due to unburned components can be prevented as much as possible. For example, PT is the main precious metal (80v
t% or more).

Among unburnt components, the oxidation reaction of Co and HC can be particularly promoted. In addition, if Rh and Pd are the main components, NO
can promote the reduction reaction of The supported amount is 0.01 to 5vt% with respect to the heat-resistant metal oxide constituting the second protective layer.
It is recommended to set it within the range of . If it is less than 0.01wt%, there is no effect, and if it exceeds 5vt%, clogging may occur.

However, under conditions of exposure to rich exhaust gas, approximately I
It is preferably Vt%. If it exceeds 3wt%,
There is a risk that unburned components present in large quantities may adsorb or react with the precious metal catalyst, causing the protective layer to crack.

(b) A heater may be anchored near the sensor element. Even at low temperatures, the OSC of the protective layer can stably exhibit its oxygen storage and release effects.

(c) In the protective layer, non-oxides of group IIa components Ca and Mg, such as CaC0, CaCjl! 2. Mg(NO3)2
may be included. Poisoning by Si in oil can be prevented.

Next, the method for manufacturing the oxygen sensor for air-fuel ratio control of the present invention is as follows:
About the treatment of the side exposed to the exhaust gas of the sensor
1. A culm in which a number of spherical substances made of the main body material of the element are arranged at least in correspondence with the positions of the electrodes.

After the heat-resistant metal oxide is deposited, it is immersed in a metal salt solution of an oxygen storage substance.

It is characterized by including.

This manufacturing method makes it possible to mass-produce the aforementioned oxygen sensor, that is, an oxygen sensor that can reliably protect the element body and electrodes from deterioration due to exhaust gas even under normal severe thermal cycle conditions, and stably exhibit the OSC function. Can be manufactured well.

The base of the element body is formed after mixing and calcining base material powders such as solid electrolyte or conductor.

It is preferable to form secondary particles (20-1,5011 m, preferably 70111 A or higher) by pulverization (2.5 μl+ or less) and then spray drying, and mold them into a predetermined shape.

The formation of spherical protrusions is achieved by forming an average particle size of 4 on the surface of the base material of the element body.
It is preferable to attach spherical particles of 0 to I OQ Itll and then bake. Even after the electrode deposition treatment of the rear culm, sufficient unevenness as a wedge remains, making it possible to obtain a strong bond with the protective layer. That is, if the spherical particles after firing are less than 401 m long, they will form a wedge. 1100f.
When it exceeds 1, the adhesion to the base material becomes weak. More preferably, the thickness is 50 to 80 μm. Fine grains of 10 μm or less may be mixed to further improve the strength.

It is preferable that the base material of the element body and the spherical particles be fired simultaneously. The adhesion strength of both can be increased. The firing temperature is 14
It is preferable to set the temperature to 00 to 1500°C. Alternatively, one spherical particle may be formed after the electrode folding treatment. Particularly when one spherical particle is formed first (=J), it is effective when it is not possible to form an electrode (Δ1).In other words, the electrode is formed on the raw material by screen printing, etc., and then the powdered particles are formed. This is effective when simultaneously firing after adhering.

The formation of the electrodes is not particularly limited either, and in addition to conventional plating processes such as i-plating and chemical plating, it may also be performed by a conventional vapor phase + I-i deposition method such as sputtering, vapor deposition, or screen printing.

The protective layer is preferably formed after the element body λ (material and spherical 13+) are fired to form the base and spherical protrusions of the element body (however, as described later, the protective layer material may also be formed at the same time). Firing [, may be used].As a method for forming the protective layer material, there are various methods such as applying a solution or powder of the protective layer material with a brush, dipping and spraying, and then firing, but thermal spraying, particularly plasma spraying, is preferable.゜The adhesion strength between the thermal spray powders is strong, and by appropriately changing the conditions, it is possible to achieve any porosity and pores iY.
After printing electrodes with precious metal paste on a green sheet made of a solid electrolyte (rO solid electrolyte, TiO, CoO + conductor, etc.), a protective layer material and [2 Af! 203 etc. may be printed on the surface and C may be printed at the same time and fired at the same time. In addition to metal oxides, the protective layer material may be a compound capable of forming a metal oxide by thermal decomposition, such as a hydroxide or a salt. The powder particle size is preferably 2 μm or less.

Supporting the OSC of the protective layer/＼ means that at least the protective layer is
It is preferable to immerse it in a metal salt solution of C, then dry and bake it. After the protective layer is tightly encased in the element body, a metal salt solution of OSC is soaked into the protective layer (porous), which allows OSC to be highly dispersed and prevents it from scattering during use. can. Therefore, the effect of OSC can be maintained stably for a long period of time.

Examples of metal salts of OSC include nitrates and acetates. In the case of Ce salt 1, for example, cerium nitrate may be used. p
l+ should be 5 or more. The metal salt solution penetrates deeply into the protective layer, increasing the strength of the 08CO attached 11, and has very high dispersibility. More preferably, the pH is set to 3 or less. Since it penetrates into the protective layer, Ce can be reliably dispersed in the exhaust gas flow path within the protective layer. Immersion is 300+n+
It is preferable to carry out under vacuum or reduced pressure or under pressure of not more than nHg, especially not more than 200+n+++Hg. The solubility of the metal salt can be increased and it can be highly dispersed deeply and efficiently within the protective layer.

If it exceeds 300 g or 11 g, a long immersion treatment time or recovery will be required, and there is a risk that the protective layer will be clogged because more of it will adhere to the surface rather than the inside of the protective layer. The immersion is preferably carried out at room temperature or higher, more preferably at 20'C or higher.

In the immersion treatment, the protective layer is formed in advance by thermal spraying or the like, and is firmly bonded to the element body by the spherical protrusions. Therefore.

Even if the protective layer is impregnated with the metal salt solution of OSC by the dipping treatment, the bonding between the element body and the protective layer is not inhibited. Moreover, since the protective layer is formed porous (with continuous pores) and is subsequently subjected to a dipping treatment, it can be highly dispersed and supported in a portion of the porous ventilation pores. Therefore, the element body and electrodes can be reliably protected by the protective layer under severe thermal cycle conditions, and the OSC function can be exhibited extremely efficiently even after durability.

Further, the second protective layer is immersed with the sensor detection part positioned downward, and in this case, it is preferable to immerse up to 95% of the lower end of the protective layer.

If it exceeds 95%, OSC is applied to the element flange that should become a conductive part.
There is a risk that the metal salt solution may adhere to the product and impede its conductivity during use. The protective layer may be immersed in the metal salt solution containing a heat-resistant metal oxide such as alumina or spinel.

However, in this case, there is a risk that durability may be reduced.

Further, the amount of O8C supported by impregnation is preferably 0.2 to 8 vt% (in terms of OSC metal element) based on the heat-resistant metal oxide. More preferably 0.8 to 3 vt%. The upper limit is set to prevent clogging of the protective layer and also to prevent the protective layer from coming loose when the sensor is used. Below the lower limit, the OSC effect will be slightly worse.

After impregnation with O8C metal salt solution by dipping treatment.

Heat treatment is preferably carried out in an oxidizing atmosphere at a temperature of 300°C to 850°C. It can be converted into OSC by thermally decomposing the metal salt of OSC and volatilizing the water. If the temperature is lower than 300°C, this effect may be insufficient, whereas if the temperature exceeds 850°C, 02 may be adsorbed to the electrodes, etc., and the OSC may temporarily store a large amount of oxygen, causing the release of this oxygen during use. There is a risk that it will become difficult. Preferably it is 800°C or less.

Furthermore, if this heat treatment is performed in a reducing atmosphere, toxic No. 1, for example, is generated in the case of nitrates, making handling complicated.

The present invention provides two different types of oxygen sensors for air-fuel ratio control, namely stoichiometric air-fuel ratio control, lean air-fuel ratio control; solid electrolyte type (Z
, rO), semiconducting type (T iO2.

It can be widely applied as an oxygen sensor such as Cod).

〔Example〕

U-shaped tube type oxygen sensors (Sample Nos. 1-4, Comparisons I-■) as shown in FIGS. 1-3 were obtained through the following steps. The specific composition of each sample is shown in Table 1.

Step 1: Z r O2 with a purity of 99% or more and Y2 with a purity of 99.9%
After adding 5 mo1% of O3 and mixing, 1800'
Bake for 2 hours at c.

Step 2: Add water and wet process in a ball mill until 80% of the particles are 2.
Grind until the particle size is less than 5 mm.

Step 3: Add a water-soluble binder and spray dry to obtain spherical granulated particles with an average particle size of 70 mm.

Step 4: The powder obtained in Step 3 is rubber pressed to form a desired tubular shape (U-shaped tubular shape), dried, and then ground into a predetermined shape using a grindstone.

Step 5: A slurry prepared by adding a water-soluble binder cellulose sodium glycolate and one portion of a solvent to the granulated particles obtained in Step 3 is attached to the outer surface.

Step 6: After drying, it is fired at 1500°C for 2 hours. For the part corresponding to the detection part, the axial length was 25 mm, the outer diameter was approximately 5 Illlφ, and the inner diameter was 3 U+φ. Step 7: A PTT constant electrode layer was applied to the outer surface by electroless plating to a thickness of 0.
．． Fold into 9 μl and then bake at 1000°C (=7).

Step 8: Mg0-Af! 203 (spinel) powder is plasma sprayed to form a protective layer with a thickness of about 150 JIll.

- "Step 9:" In the same manner as Step 7, a PT-based electrode layer was formed on the inner surface.

Step 10+ Cerium nitrate was dissolved in a solution of nitric acid diluted with water to prepare two different concentrations of cerium nitrate solution i11.

Step 11: ] The protective layer of the element obtained in Steps 1 to 9 is immersed in the solution obtained in Step 10, and 50 to 250+! The protective layer was left under a pressure of +mHg for about 10 minutes to impregnate cerium nitrate into the protective layer. Thereafter, the protective layer was treated in the atmosphere at 600° C. to support cerium oxide.

Step 12 After inserting the element 'T-1 into the housing 7, a caulking ring 8 and a filler material 9 such as talc are inserted to fix the element B inside the housing 7.

Step 13: Leads are connected to the electrode parts 2 and 3 via terminals.

Step 14: Place the protective layer 10 covering the tip of the element B and attach the housing 7.
Weld the tip and the rear end of the protective tube lO.

Step 15: Cover with the outer cylinder to obtain the oxygen sensor.

1 to 5, A is an oxygen sensor, B is an oxygen sensor element, 1 is an element body (oxygen ion conductive solid electrolyte body or semiconductor), 1a is a base, lb is a spherical protrusion, 2 is a reference electrode 23 A measuring electrode, 4 a protective layer, 4a O3C, 6 a heater, 7 a t\Using, 8 a caulking ring, 9 a filler, and 10 a protective tube, respectively.

[Tests] Each sample thus obtained was subjected to a test such as -FallL.

(B) Each sample was tested in an actual vehicle for 500 hours under a temperature cycle of 2 degrees Celsius or lower (20 minutes) and 900 degrees Celsius or higher (30 minutes). After that, it was dropped from the 50ew+J: direction onto the concrete under the floor five times. After letting it fall, the appearance was evaluated.The judgment was as follows.

No peeling, etc. 〇 Partial peeling △ All peeling × U After the test described in ■, each sample was attached to a professional cleaning device, the burner was fired, and the atmosphere was temporarily changed from λζ098 to 1 as shown in Figure 7. .1 and moved it to the lean side, and investigated the force situation of the sensor at that time. The verdict is as follows.

Almost no output change Approximately 100 mV change 200W or more -1-change × The results are shown in the table below.

△ ○ (blank space below) Table 1 1) This amount is OSC/metal oxide, converted to O3C metal element (Ce) 2) Spinel: Mg O-A, in e2'03 test (f), comparative sample (1) An oxygen sensor manufactured in substantially the same manner as the embodiment disclosed in JP-A-81791-55, in which CeO2 is not immersed in a solution of Ce salt, but
The layer formed by coating a mixed powder slurry of Al2O3 and CeO2, with a thickness of 20 to 30μ+i) is a layer of Al2O3 and CeO2 formed on a spinel protective layer.
The layer consisting of peeled off from the spinel protective layer. Therefore,
It is inferior to chopsticks in terms of durability under heat cycle conditions. In addition, the comparative sample tooth, ■ (which has a protective layer of the same composition formed by being immersed in a Ce salt solution under the same vacuum conditions as Example sample No. 2, but does not have one spherical protrusion) is , part of the protective layer peeled off. Furthermore, comparative sample No. I (Ce
Regarding the method in which O2 was formed by applying a CeO2 powder slurry alone, rather than by immersion in a Ce salt solution,
Most of the Ce O2 was formed as a layer on the surface of the spinel layer, and peeling was observed in a part of the Ce O2. In contrast, Example Sample Nos. 1 to 4. For Comparative Sample (3), such peeling was not observed at all, and the protective layer carrying CeO2 was stably fixed to the element body and protected the element body and electrodes. Therefore, it has been found that it has extremely excellent durability under thermal cycling conditions, and exhibits excellent λ detection characteristics and responsiveness even when used for a long period of time under severe thermal cycling conditions.

In test (b), as is clear from Figure 7.

Comparative sample I (already mentioned) after durability test, comparative sample No. I
V (already mentioned), comparative sample No., and II [(oxygen sensor with only a spinel protective layer), the A/F is approximately the theoretical value (λ = 0
．． 98) to the lean side (λ-1, 1), even if the A/F returns to approximately the theoretical value (λ = 0.98), the A/F curve becomes rich due to the response delay. This results in a large excursion to the side (rich excursion). On the other hand, Example samples Nos. 072 to 4 temporarily store oxygen when the air amount increases due to the presence of O20, thereby delaying the timing of outputting the lean signal and, as a result, shortening the period during which the lean signal is output. . Therefore, the rich excursion phenomenon described above does not occur.

After the air increase is completed, the A/F quickly returns to near the theoretical value. Moreover, almost the same effect was observed for Example Samples No. 1 and Comparative Sample H.

Therefore, Example sample Nos. 1 to 4. In particular, samples 2 to 4 exhibit excellent λ-1 detection characteristics and sufficient responsiveness even after durability. Therefore, it is extremely useful particularly in air-fuel ratio control systems where the gas flow rate in the exhaust system is high. In addition, accurate air-fuel ratio control is possible without causing a λ point shift even when the amount of air increases sharply during acceleration or the like. In this way, even if used for a long time under severe thermal cycle conditions, it will not come off the window of the three-way catalyst of the exhaust purification system, and its harmful substance purification properties can be maintained at a high level.

[Brief explanation of the drawing]

FIG. 1 is a half-sectional view showing an example of a U-tube type oxygen sensor according to the present invention. Figure 2 is a schematic diagram of an enlarged section of Figure 1. Figure 3 is a schematic diagram of an enlarged section of Figure 2. FIG. 4 is a perspective view showing another example of the oxygen sensor according to the present invention, in which FIG. 4(a) shows an example of a plate-shaped oxygen sensor, and FIG. 4(b) shows a cylindrical type oxygen sensor. An example of an oxygen sensor. FIG. 5 is a partially enlarged sectional view of the plate-shaped oxygen sensor shown in FIG. 4(a). Figure 6 shows the immersion process in O8C metal salt solution (Example process 11).
) Fig. 7 is a graph showing the relationship between O20 oxygen storage and λ, and Fig. 8 is a graph showing the results of the test (b). Shows the relationship between time and sensor output. respectively. A... Oxygen sensor element body 1b... Spherical protrusion 4... Protective layer 4a... Oxygen storage material B... Oxygen sensor element 1a... Base 3... Measuring electrode (O20)

Claims (2)

[Claims] (1) A protective layer made of a heat-resistant metal oxide is provided on the side of the sensor element exposed to exhaust gas, covering at least the electrode, and the main body of the sensor element is composed of a base and a plurality of spherical protrusions. An oxygen sensor for air-fuel ratio control, characterized in that the layer is bonded to a base via a spherical protrusion, and the protective layer contains an oxygen storage substance. (2) Regarding the treatment of the side of the sensor element exposed to exhaust gas, the step of attaching a spherical substance made of the main body material of the element, at least corresponding to the position of the electrode, and the step of attaching a heat-resistant metal oxide A method for manufacturing an oxygen sensor for controlling an air-fuel ratio, the method comprising: immersing the sensor in a metal salt solution of an oxygen storage substance.