JP2002333422A - Oxygen concentration detector and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen concentration detector and its manufacturing method having the state wherein the porosity and the mean pore size of a protective layer are uniform and sufficient throttling effect and excellent poison- resistance can be acquired, having an excellent output characteristic, capable of utilizing raw material effectively in manufacturing, and manufacturing easily and inexpensively with simple manufacturing facilities. SOLUTION: In this oxygen concentration detector comprising a cup-shaped oxygen concentration detection element 1 and a housing for storing the element, a sprayed layer 14 is provided on the surface of an outside electrode 131, and the protective layer 11 is provided on the surface of the sprayed layer 14, and the value of the ratio (RB/RA) of the mean particle size RB of coarse particles to the mean particle size RA of fine particles in the protective layer 11 is thirty or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen concentration detector used for controlling combustion of an internal combustion engine and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as a gas detector for detecting the oxygen concentration in exhaust gas of an automobile internal combustion engine, for example, an oxygen concentration electromotive force type oxygen concentration detector using a ZrO ₂ solid electrolyte is well known. Has been widely used.

The oxygen concentration detector has an oxygen concentration detecting element inside. The oxygen concentration detecting element is made of, for example, a solid electrolyte made of an oxygen ion conductive metal oxide such as a solid solution of ZrO ₂ —Y ₂ O ₃ , and the solid electrolyte has an outer electrode on the outer surface facing the gas to be measured. And an inner electrode is provided on the inner surface facing the reference gas. The outer and inner electrodes are made of a catalytic metal such as Pt. In order to protect the outer electrode, a porous protective layer is provided on the surface of the outer electrode, through which the gas to be measured can flow. The protective layer is a coating of a heat-resistant metal oxide.

Meanwhile, the protective layer in the oxygen concentration detecting element is provided to prevent unburned substances in the exhaust gas, which is the gas to be measured, from adhering to the electrode, and to prevent the unburned substance from adhering to the electrode on the outer electrode. In order to promote the equilibrium reaction between carbon monoxide and hydrocarbons contained in the water and residual oxygen, etc., and to obtain a sufficient throttling effect to obtain sharp output characteristics (see FIG. 4), Must be configured. That is, it is necessary that the porosity and the average pore diameter of the protective layer are appropriately small.

Conventionally, as described in Japanese Patent Application Laid-Open No. S51-145390, the protective layer is formed by applying a powder of a heat-resistant metal oxide such as spinel at a high temperature to the outer electrode. It was constructed by spraying and adhering to the surface of.

[0006]

However, the above-mentioned conventional protective layer has the following problems. First, since the melting point of the heat-resistant metal oxide is high, it is difficult to sufficiently melt it in a plasma flame, and it is difficult to reduce the pore diameter. For this reason, there is a possibility that the diameter of the pores formed in the protective layer is large and a dense protective layer cannot be obtained. In such a protective layer, in order to obtain the above-described drawing effect, the thickness of the protective layer had to be sufficiently large.

[0007] In addition, the method called plasma spraying has a low material yield and requires a large amount of electric power, and thus cannot effectively utilize material resources. In addition, the equipment had the disadvantage that it was large and expensive.

Further, Japanese Patent Application Laid-Open No. 1-227955 discloses that a coarse particle layer having a high porosity obtained by thermal spraying is formed, and then the voids in the coarse particle layer are formed by vacuum impregnation or pressure impregnation. It has been proposed to form a protective layer with small porosity by filling with ultrafine particles.

[0009] However, in order to impregnate the voids of the coarse particle layer so as to be almost uniform, the average particle diameter of the ultrafine particles needs to be 0.01 to 0.5 µm. However, when the ultrafine particles having an average particle diameter of less than 0.1 μm are used, cracks may be generated in the obtained protective layer. Furthermore, in the vacuum impregnation and the pressure impregnation, special operations and equipment are required, and it is also difficult to stably and surely fill the voids of the sprayed layer with ultrafine particles, and it is also difficult to confirm the fact.

Further, since the coarse particle layer is formed by thermal spraying, the coarse particle layer is formed by fusion bonding of coarse particles. That is, the shape of the coarse particles becomes flat in the process of fusion bonding and acts as an aggregate of the protective layer. For this reason, in the protective layer, the mixing state of the coarse particles and the ultrafine particles varies from place to place, and there is a possibility that the protective layer becomes uneven as a whole. Therefore, in the protective layer according to the above-mentioned conventional method, the porosity varies, which causes unstable output characteristics.

[0011] In a conventional oxygen concentration detecting element using a plasma sprayed layer, P,
Oil components such as Ca, Zn, Si, K, Na, Pb
And other gasoline components (collectively referred to as poisoned components)
When the amount is large, these adhere to the surface of the oxygen concentration detecting element, causing clogging on the surface of the protective layer, thereby deteriorating the output characteristics of the oxygen concentration detecting element (poisoning deterioration).

Therefore, in order to prevent clogging due to this poisoning, as shown in JP-A-6-174683, a γ-
It has been proposed to provide a so-called trap layer made of a porous layer of a heat-resistant metal oxide such as Al ₂ O _{3 on} the surface of the protective layer. However, although the trap layer can prevent poisoning, it complicates the structure of the oxygen concentration detecting element, and an extra step is added to the manufacturing process. For this reason, there is a problem that the manufacturing cost increases.

In view of the above problems, the present invention is in a state where the porosity and the average pore diameter in the protective layer are uniform, and a sufficient drawing effect and excellent poisoning resistance can be obtained. Another object of the present invention is to provide an oxygen concentration detector capable of effectively utilizing raw materials in the production thereof, and having a simple, easy and inexpensive production facility, and a method of producing the same.

[0014]

According to a first aspect of the present invention, there is provided a cup type oxygen concentration detecting element having an inner electrode provided on an inner surface of a solid electrolyte and an outer electrode provided on an outer surface, and the cup type oxygen concentration detecting element. In an oxygen concentration detector comprising a housing, an exhaust cover provided on an exhaust passage side of the housing, and an air cover provided on an air side of the housing, a thermal spray layer is provided on a surface of the outer electrode. A protective layer comprising coarse particles and fine particles, and having a structure in which fine particles are filled in voids formed between the coarse particles, and an average particle diameter of the fine particles. The ratio of the average particle diameter RB of the coarse particles to RA (RB /
The value of RA) is 30 or more in the oxygen concentration detector.

Since RB / RA is 30 or more, fine particles can sufficiently fill gaps between coarse particles. Therefore, the porosity and the average pore diameter in the protective layer can be sufficiently reduced. The above RB /
When RA is less than 30, fine particles cannot sufficiently fill gaps between coarse particles, and therefore,
The porosity and the average pore diameter of the protective layer may increase.

The upper limit of the RB / RA is preferably 500 or less. As a result, a dense protective layer can be stably obtained, and as described above, a drawing effect can be obtained. When RB / RA is larger than 500, the adhesion of the protective layer decreases, Cracking or peeling may occur, and a dense protective layer may not be obtained, and the above-described drawing effect may not be obtained.

The operation of the present invention will be described below. The protective layer of the cup-type oxygen concentration detecting element according to the oxygen concentration detector of the present invention has a structure in which fine particles are filled in voids formed between coarse particles, and RB / RA is 30 or more ( (See FIG. 2). Thereby, the porosity and the average pore diameter in the protective layer are small and uniform.

Therefore, particularly when the exhaust gas discharged from the internal combustion engine is used as the gas to be measured, the protective layer serves as an equilibrium reaction between carbon monoxide and hydrocarbons contained in the gas to be measured and residual oxygen and the like. Can be exhibited on the outer electrode. Therefore,
The oxygen concentration detector according to the present invention is an excellent oxygen concentration detector having excellent output characteristics as shown by a solid line in FIG.

Further, the oxygen concentration detector according to the present invention has a sprayed layer on the surface of the outer electrode. Thereby, the sprayed layer and the outer electrode are strongly bonded. For this reason, when the oxygen concentration detector is used, particularly when the ambient temperature increases, the deterioration of the outer electrode due to thermal aggregation can be suppressed.

The thickness of the sprayed layer is 30-100 μm.
m is preferable. If the thickness is smaller than 30 μm, deterioration of the outer electrode due to thermal aggregation cannot be prevented, and the output characteristics may be deteriorated by using the oxygen concentration detector at a high temperature. On the other hand, 1
When the thickness is larger than 00 μm, there is a possibility that problems such as effective use of materials and manufacturing costs may occur due to poor material yield in the method of thermal spraying.

Next, the average particle diameter RA of the fine particles is set at 0.1.
It is preferably from 1 to 1 μm. RA above 0.1μ
If it is less than m, cracks are likely to occur in the protective layer in the drying step when forming the protective layer. Since the porosity and the average pore size of the cracked protective layer are increased, an excellent drawing effect may not be obtained. On the other hand, if the RA is larger than 1 μm, the fine particles may not be able to fill the voids between the coarse particles. Further, the porosity and the average pore diameter may be increased.

Further, the average particle size RB of the coarse particles is preferably larger than the average particle size RA and 3 to 50 μm or less. If the RB is less than 3 μm, the fine particles may not be able to fill gaps between the coarse particles. Further, the porosity and the average pore diameter of the protective layer may increase. On the other hand, the above RB is 50 μm.
If it is larger than m, the bonding force between the coarse particles may decrease when the protective layer is baked on the thermal sprayed layer. In this case, when the oxygen concentration detector is used, the protective layer may peel off from the sprayed layer.

The particle size distribution of the fine particles is as follows:
It is preferable that 80% of the particles be contained in the range of 0.5 RA to 3 RA with respect to the average particle diameter RA.
Similarly, with respect to the particle size distribution of the coarse particles, it is preferable that 80% of all particles are contained in the range of 0.5 RB to 3 RB with respect to the average particle size RB.

When the particle size distribution does not satisfy the above conditions and becomes broader, first, the size of the gaps formed between the coarse particles becomes noticeable. In addition, the size of the fine particles filling the gap also becomes noticeable. For this reason, the porosity and the average pore diameter of the protective layer may increase as a whole.

Next, as in the second aspect of the present invention, the ratio of the content WA of the fine particles to the total amount W (= WA + WB) of the content WA of the fine particles and the content WB of the coarse particles in the protective layer. The value of (WA / W) is preferably from 15 to 80%.

Thus, the gap between the coarse particles can be sufficiently filled with the fine particles, and the porosity and the average pore diameter of the protective layer can be reduced. The above WA / W is 15%
If the average particle diameter is smaller than the above range, the fine particles cannot sufficiently fill the gaps between the coarse particles, so that the porosity and the average pore diameter of the protective layer may increase.

When the ratio WA / W is larger than 80%, the volume of the entire fine particles is larger than the volume of the gap between the coarse particles, and there is almost no coarse particles, and only the fine particles are present. Is formed in the protective layer. In this case, the porosity and the average pore diameter of the protective layer become non-uniform, so that a sufficient drawing effect may not be obtained. The values of WA, WB and W are based on weight.

Next, as in the third aspect of the present invention, the coarse particles and the fine particles are made of Al ₂ O ₃ , ZrO ₂ , MgO.
It is preferable to use one or more heat-resistant particles selected from the group consisting of Al ₂ O ₃ spinel and mullite. The heat-resistant particles are thermally and chemically stable. For this reason, when the oxygen concentration detector is used, there is no risk of deterioration of the protective layer, and stable characteristics can be maintained. This effect is particularly remarkable when the atmosphere is at a high temperature.
The shape of the coarse and fine particles is, for example, spherical,
It can be selected from groups such as block, plate, column, and needle.

Next, the porosity ε of the protective layer is preferably 50% or less. As a result, a dense protective layer can be obtained, and the above-described drawing effect can be reliably obtained. If the porosity ε is larger than 50%, a dense protective layer cannot be obtained, and the above-described drawing effect may not be obtained.

Next, the average pore diameter d of the protective layer is preferably in the range of 0.01 to 0.3 μm. Thereby, a dense protective layer can be obtained, and the above-described drawing effect can be stably obtained.
If the above d is less than 0.01 μm, cracks may occur during drying when forming the protective layer, the porosity and the pore diameter may be increased, and a sufficient drawing effect may not be obtained.
On the other hand, when d is larger than 0.3 μm, a dense protective layer cannot be obtained, and the above-described aperture effect may not be obtained.

Next, according to a sixth aspect of the present invention, there is provided a cup-type oxygen concentration detecting element in which an inner electrode is provided on the inner surface of the solid electrolyte and an outer electrode is provided on the outer surface, and the cup-type oxygen concentration detecting element is accommodated. In a method for manufacturing an oxygen concentration detector comprising a housing, an exhaust cover provided on an exhaust passage side of the housing, and an air cover provided on an air side of the housing, a heat-resistant metal oxide is sprayed on a surface of the outer electrode. Thus, a thermal spray layer is provided, and a protective layer having a structure in which coarse particles and fine particles are formed and fine particles are filled in voids formed between the coarse particles is provided on the surface of the thermal spray layer. First, the slurry obtained by dispersing coarse particles and fine particles composed of heat-resistant particles in a solvent is applied to the sprayed layer, and then heated and baked to form a protective layer. In the manufacturing method of the oxygen concentration detector, characterized by.

According to the above manufacturing method, the protective layer can be formed by a simple method of attaching the slurry to the thermal sprayed layer, heating and baking. In the above method, the material is hardly wasted, the material yield is excellent, and no large-scale equipment is required. That is, this is a method that can easily and inexpensively manufacture an oxygen concentration detector. In particular, conventionally, the protective layer was formed by thermal spraying or the like, but in comparison with this, the protective layer can be manufactured at a low cost.

Further, in the above method, coarse particles and fine particles can be uniformly mixed and dispersed in the slurry. Since such a slurry is used, the coarse particles and the fine particles can uniformly adhere to the sprayed layer. Therefore, a protective layer having a uniform porosity and an average pore diameter can be obtained by the above production method. Therefore, as in the case of the first aspect, it is possible to manufacture an oxygen concentration detector having a sufficient aperture effect and excellent output characteristics as shown by a solid line in FIG.

In the present invention, before forming the protective layer, a sprayed layer is provided by spraying a heat-resistant metal oxide on the surface of the outer electrode. Thus, when the oxygen concentration detector is used, it is possible to manufacture an excellent oxygen concentration detector that hardly deteriorates due to thermal aggregation of the outer electrode, particularly when the ambient temperature increases.

As described above, according to the present invention, the protective layer is in a state where the porosity and the average pore diameter are uniform and a sufficient drawing effect can be obtained, and the protective layer has excellent output characteristics. It is possible to provide a method of manufacturing an oxygen concentration detector that can effectively utilize raw materials in manufacturing, and whose manufacturing facilities are simple, easily and inexpensively manufactured.

Various methods such as dipping and spraying can be used as a method for applying the slurry. To obtain the slurry, it is preferable to add an inorganic binder in an amount of 1 to 10% based on the total weight of the coarse particles and the fine particles.

Next, as in the invention of claim 7, the ratio of the average particle diameter RB of the coarse particles to the average particle diameter RA of the fine particles (RB / RA) is preferably 30 or more. Thereby, the gap between the coarse particles can be sufficiently filled with the fine particles, and a protective layer having a sufficiently small porosity and average pore diameter can be manufactured. A detector can be manufactured.

Next, the value of the ratio (RB / RA) of the average particle diameter RB of the coarse particles to the average particle diameter RA of the fine particles is 10 or more, and the protective layer Is the porosity of ε (%), and the average pore diameter of the protective layer is d.
(Μm), when the thickness of the protective layer is L (μm),
The value of {(ε / 100) × d / L} is 2.0 × 10 ^{−5 to} 3
It is preferably in the range of 0 × 10 ⁻⁵ .

In the present invention, the RB / RA is 1
0 or more, and {(ε / 100) × d / L} is within the above range. Thus, similarly to the first aspect, the gap between the coarse particles is sufficiently filled with the fine particles, and a protective layer having sufficiently small porosity and average pore diameter can be obtained.

If the RB / RA is less than 10, the fine particles cannot sufficiently fill the gaps between the coarse particles and the porosity and average pore diameter of the protective layer increase. There is a risk. The upper limit of the RB / RA is preferably 500 or less. As a result, a dense protective layer can be stably obtained, and the above-described drawing effect can be obtained. When RB / RA is larger than 500, the adhesion of the protective layer is reduced, and cracks and Peeling may occur, a dense protective layer may not be obtained, and the above-described drawing effect may not be obtained.

When the above {(ε / 100) × d / L} is less than 2.0 × 10 ⁻⁵ , since the drawing effect is large, carbon monoxide and hydrocarbon, which contribute to the equilibrium reaction, Sharp output characteristics are obtained by equilibrating sufficiently on the outer electrode such as residual oxygen, but the diffusion of the above reaction gas is slow.
Response may be slow. On the other hand, if it is larger than 30 × 10 ^-5 , sharp output characteristics cannot be obtained because carbon monoxide, hydrocarbons, residual oxygen and the like are not sufficiently equilibrated on the outer electrode because the drawing effect is not sufficient. There is a risk.

Next, the ratio of the average particle diameter RB of the coarse particles to the average particle diameter RA of the fine particles (R
B / RA) is 10 or more, the porosity of the protective layer is ε (%), and the average pore diameter of the protective layer is d (μ).
m), when the thickness of the protective layer is L (μm),
The value of {(ε / 100) × d / L} is 30 × 10 ⁻⁵ or less, ε is 15 to 50%, and {(ε / 1
00) × d} is preferably 5.0 × 10 ⁻³ or more.

By the way, as described in the prior art, the protective layer in the cup-type oxygen concentration detecting element of the oxygen concentration detector is used to prevent unburned substances in the exhaust gas as the gas to be measured from adhering to the electrodes. Further, on the outer electrode, a sufficient throttling effect for promoting an equilibrium reaction between carbon monoxide and hydrocarbons contained in the exhaust gas and residual oxygen, etc. to obtain a sharp output characteristic (see FIG. 4). In order to obtain the protective layer, it is necessary that both the porosity and the average pore diameter of the protective layer are appropriately small.

In addition, a conventional oxygen concentration detector having a cup-type oxygen concentration detecting element having a protective layer using plasma spraying can detect a cup-type oxygen concentration when the poisoning component is large. It adheres to the surface of the element, causes clogging on the surface of the protective layer, and causes a problem (poisoning deterioration) that deteriorates the output characteristics of the oxygen concentration detector.

Therefore, in the present invention, the RB /
RA is 10 or more, {(ε / 100) × d / L} is 30 ×
10 ⁻⁵ or less, ε is 15 to 50%, and ｛(ε / 10
0) × d｝ is 5.0 × 10 ⁻³ or more, so that the protective layer can obtain a sufficient drawing effect, does not cause clogging on its surface, and obtains excellent poisoning resistance. Can be. Preferred upper limits of the RB / RA and the like are the same as those of the first aspect. In addition, the above ｛(ε / 100) × d /
Preferred lower limits of L｝ are the same as in claim 8.

When ε is less than 15%, a sufficient throttling effect can be obtained. However, since the protective layer is dense, the poisoning components contained in the exhaust gas are not deposited on the surface of the protective layer. There is a possibility that clogging may easily occur due to adhesion. on the other hand,
If the above ε is more than 50%, a dense protective layer cannot be obtained, and the above-described drawing effect may not be obtained.

Further, when the value of {(ε / 100) × d} is less than 5 × 10 ⁻³ , a sufficient drawing effect can be obtained, but since the protective layer is dense, the exhaust gas Poisoning components contained therein may adhere to the surface of the protective layer and clogging may easily occur. On the other hand, the above ｛(ε / 100)
The upper limit of the value of × d｝ is preferably 40 × 10 ⁻³ or less, and when the value of {(ε / 100) × d} exceeds 40 × 10 ⁻³ , the value of ｛(ε / 100) There is a possibility that the value of × d / L｝ cannot be set within a practical range of the film thickness.

Next, as in the tenth aspect of the present invention, the ratio of the content WA of the fine particles to the total amount W (= WA + WB) of the content WA of the fine particles and the content WB of the coarse particles in the protective layer. (WA / W value) is preferably from 15 to 80%. Thereby, the gap between the coarse particles can be sufficiently filled with the fine particles, and a protective layer having a sufficiently small porosity and average pore diameter can be manufactured. A detector can be manufactured.

Next, the heating at the time of forming the protective layer is performed at a baking temperature of 500 to 1000 ° C.
It is preferable to carry out in an atmosphere of the following temperature. Thereby, a protective layer having a strong adhesive force can be obtained. If the heating and baking temperature is less than 500 ° C,
The effect of the inorganic binder may not be exhibited. On the other hand, when the temperature is higher than 1000 ° C., the sintering shrinkage of the coarse particles and the fine particles may occur, whereby cracks may easily occur in the protective layer.

[0050]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference Example 1 An oxygen concentration detecting element according to a reference example will be described with reference to FIGS. Note that the oxygen concentration detecting element of this example is an element of the oxygen concentration electromotive force type. As shown in FIG. 1, the oxygen concentration detecting element 1 of the present embodiment has an inner electrode 132 on the inner surface of the solid electrolyte 12 and an outer electrode 131 on the outer surface.

Then, on the surface of the outer electrode 131,
As shown in FIG. 2, the protective layer 11 includes coarse particles 112 and fine particles 111 and has a structure in which fine particles 111 are filled in gaps formed between the coarse particles 112.
Is provided. In the figure, reference numeral 4 denotes a heater for heating the oxygen concentration detecting element 1 to the element activation temperature, and 129 denotes an atmosphere chamber into which the atmosphere serving as a reference gas is introduced.

Next, a method for manufacturing the oxygen concentration detecting element 1 will be described in detail. First, a cup-shaped solid electrolyte 12 having one end closed and the other end opened is formed. In the above molding, 95 mol% of ZrO ₂ and 5 mol% of Y ₂ O
₃ is mixed, pulverized, granulated using a spray drier,
Make raw material particles.

Next, the raw material particles are formed into a desired shape, and then ground to form a formed body. Next, the compact is fired at 1600 ° C. for 2 hours. Thus, the solid electrolyte 12 is obtained. Next, the inner surface and the outer surface of the solid electrolyte 12 are made uneven by etching or the like, and the inner electrode 132 and the outer electrode 131 are formed by chemical plating.

Next, the protective layer 11 is provided on the surface of the outer electrode 131. In forming the protective layer 11, first,
Coarse particles 112 and fine particles 111 made of Al ₂ O ₃ are prepared as heat-resistant particles. The average particle diameters RA, RB, WA / W, etc. of the fine particles 111 and the coarse particles 112 are the same as those of the sample 9 shown in Table 1 described later.

Next, the coarse particles 112 and the fine particles 111
And to form a mixture. 20 parts by weight of water and 2 parts by weight of an inorganic binder are added to 100 parts by weight of the mixture to form a slurry. The inorganic binder is Al
(OH) ₃ .

Next, the slurry was applied to the outer electrode 1.
31 is applied by dipping. Thereafter, the solid electrolyte 12 coated with the slurry is dried, and then heated and baked at a temperature of 700 ° C. to form the protective layer 11 having a porosity and an average pore diameter shown in Table 1.
Thus, the oxygen concentration detecting element 1 is obtained.

FIG. 3 shows an oxygen concentration detector 90 provided with the oxygen concentration detection element 1 described above. The above oxygen concentration detector 9
0 is installed in the exhaust passage of the vehicle engine for combustion control in the vehicle engine. The oxygen concentration detector 90 has the oxygen concentration detection element 1 and a housing 92 that houses the oxygen concentration detection element 1. The housing 92 has a body portion 93 provided with a flange 931 at a substantially central portion. An exhaust cover 94 inserted into an exhaust passage is provided below the body portion 93, while an exhaust cover 94 is provided above the body portion 93. Is provided with an atmosphere cover 95 that is in contact with the atmosphere.

The exhaust cover 94 has an inner cover 941 and an outer cover 942 made of stainless steel, and the inner cover 941 and the outer cover 942 are provided with exhaust gas inlets 944 and 943, respectively. The inner cover 94
The space defined by 1 is a measured gas chamber in the oxygen concentration detector 90.

On the other hand, the air cover 95 includes a main cover 951 attached to the body 93 and a sub cover 952 covering an upper part of the main cover 951. The main cover 951 and the sub cover 95
An air intake port (not shown) is provided in 2. The air introduced from the air intake is the above air cover 9
5, the oxygen gas is introduced into the atmosphere chamber 129 (see FIG. 1) of the oxygen concentration detecting element 1 described above.

The oxygen concentration detecting element 1 includes an insulating member 93
2, it is sandwiched between the inside of the body 93. The outer electrode 131 and the inner electrode 132 of the oxygen concentration detecting element 1 are connected to metal plate terminals 961 and 962 sandwiching the outer electrode 131 and the inner electrode 132.

The output terminals 971 and 972 are connected to the plate terminals 961 and 962, respectively. That is, the plate-shaped terminals 961 and 962 are provided with strip-shaped terminal pieces 963 and 964, respectively. The other ends of the terminal pieces 963 and 964 are connected to the lead wires 971 and 9
One end 985 of connectors 981, 982 connected to
986.

The plate-like terminals 961 and 962 are formed by deforming an inverted T-shaped metal plate into a cylindrical shape, and hold the inner electrode 132 and the outer electrode 131 therebetween. Then, the plate-like terminals 961 and 962 and the inner electrode 1 are formed by the spring elastic force of the metal plate.
An appropriate contact pressure is applied between the outer electrode 32 and the outer electrode 131.

On the other hand, the lead wires 971 and 972
Since a tensile force acts in the axial direction of the oxygen concentration detector 90, the connector 981, 982
The plate terminals 961 and 962 may be pulled and slide in the axial direction. In order to prevent this, rubber bushings 991, 9 are provided at the end of the oxygen concentration detector 90.
A stopper 993 sandwiched between the holes 92 is provided. The stopper 993 suppresses movement of the connectors 981 and 982, and is formed of a resin material for maintaining insulation between the lead wires 971 and 972.

In the drawing, reference numeral 973 denotes a heater 4 provided for heating the oxygen concentration detecting element 1.
(See FIG. 1). The oxygen concentration detector 90 has the exhaust cover 94 inserted into the exhaust passage, and is fixed to the exhaust passage by the flange 931.

Next, the operation and effect of this embodiment will be described. The protective layer 11 of the oxygen concentration detecting element 1 of this embodiment
It has a structure in which the fine particles 111 are filled in the gaps formed between them (see FIG. 2). Thereby, the porosity and the average pore diameter in the protective layer 11 are small and uniform.

For this reason, particularly when the exhaust gas discharged from the automobile engine is used as the gas to be measured, the equilibrium reaction between carbon monoxide and hydrocarbons contained in the gas to be measured and the residual oxygen is measured on the outer electrode 131. The protective layer 11 can have a sufficient squeezing effect to promote it. Therefore, the oxygen concentration detecting element 1 can have excellent output characteristics as shown by a solid line in FIG.

Further, according to the manufacturing method of this embodiment, the protective layer 11 can be formed by a simple method of attaching the slurry to the outer electrode 131, heating and baking. The above method is excellent in material yield and inexpensive in equipment costs. Therefore, the oxygen concentration detecting element 1 can be manufactured at low cost. Further, coarse particles 112 and fine particles 111
Can be uniformly mixed in the slurry, so that the protective layer 11 having uniform porosity and average pore diameter can be obtained.

Next, the performance of the oxygen concentration detecting element according to the present embodiment will be described with reference to FIG. First, the oxygen concentration detecting elements of Samples 1 to 18 were prepared by the above-described manufacturing method. Each of the above samples has a particle size RA and RB of fine particles and coarse particles, and a ratio RB /
RA, the content ratio WA / W, and the thickness of the protective layer were made different as shown in Table 1. For reference, an oxygen concentration detecting element provided with a protective layer formed by plasma spraying was also prepared. This is Sample 19.

Next, the performance evaluation of the samples 1 to 19 will be described. The oxygen concentration detecting element according to each of the above samples was installed in the oxygen concentration detector shown in FIG. Here, as shown in FIG. 4, the relationship shown by the solid line in FIG. 4 is obtained between the excess air ratio λ and the output voltage in the oxygen concentration detecting element having the excellent throttling effect. That is, λ
= 1, which is a step-like relationship that changes abruptly, with a large difference between the rich-side output voltage and the lean-side output voltage.

On the other hand, the relationship in the oxygen concentration detecting element having a poor throttling effect is as shown by a broken line in FIG. That is, the output voltage changes slowly around λ = 1, and the difference between the rich and lean output voltages is small.

Therefore, the oxygen concentration detector provided with each of the samples 1 to 19 is attached to the exhaust pipe of the engine, and the excess air ratio is gradually changed, and the output of the oxygen concentration detector at that time is measured. That is, the output voltage of the oxygen concentration detecting element from λ = 0.9 to λ = 1.1 was measured, and the sample whose output voltage difference was 0.6 V or more at ◎, 0.5 to
The results were evaluated as ○ when the voltage was less than 0.6 V and X when the voltage was less than 0.5 V.

According to the table, samples 3 to 5 and 8 to 18
It was found that the drawing effect was equal to or higher than that of the sample 19 having the protective layer provided by plasma spraying as in the related art. In particular, it was found that Samples 9 to 15 all have particularly low porosity and average pore diameter, and have a sufficient drawing effect even when the protective layer is thin. On the other hand, in samples 1, 2, 6, and 7, it was found that the drawing effect was poor.

[0073]

[Table 1]

Embodiment 1 In this embodiment, as shown in FIG. 5, an oxygen concentration detecting element 1 in which a sprayed layer 14 is provided on the surface of an outer electrode 131 will be described. In the oxygen concentration detecting element 1 of the present embodiment, the outer electrode 13
1 is provided with a thermal spray layer 14 formed by thermal spraying a heat-resistant metal oxide. The thermal spray layer 14 has coarse particles 112 and fine particles 111 on the surface thereof. Fine particles 1 are placed in the voids formed between the particles 112.
A protective layer 11 (see FIG. 2) having a structure filled with 11 is provided. Others are the same as in Reference Example 1.

In manufacturing the oxygen concentration detecting element 1 of this embodiment, first, the solid electrolyte 12 is formed, and the inner electrode 132 is provided on the inner surface of the solid electrolyte 12, and the outer electrode 131 is provided on the outer surface. Next, the outer electrode 131
The thermal spray layer 14 is provided on the surface of the substrate by plasma spraying MgO.Al ₂ O ₃ spinel. Then, Reference Example 1
In the same manner as described above, the protective layer 11 is provided on the surface of the thermal spray layer 14 to obtain the oxygen concentration detecting element 1.

Next, the performance of the oxygen concentration detecting element according to this example will be described with reference to Table 2 together with comparative samples. First, oxygen concentration detecting elements of samples 20 to 30 were prepared by the above-described manufacturing method. Each of the above-mentioned samples includes the thickness of the sprayed layer, the porosity, the average pore diameter, and the particle diameters RA and RB of the fine particles and coarse particles constituting the protective layer, their ratio RB / RA,
Further, the content ratio WA / W and the thickness of the protective layer were made different as shown in Table 2 to prepare. For comparison, the above sample 2
Nos. 0 and 30 did not have a thermal spray layer. Samples 28 to 3
In No. 0, no protective layer was provided.

Next, the performance evaluation of the samples 20 to 30 will be described. First, the squeezing effect was evaluated by the same method as in Reference Example 1, and the results of ◎, ，, and × are shown in Table 2. The heat resistance was evaluated by the following test. That is, an acceleration durability test was performed by placing the oxygen concentration detecting element according to each sample in an electric furnace and heating at 1000 ° C. for 100 hours. As a result of the above accelerated durability test,
Table 2 shows the case where the area of the hole of the outer electrode caused by aggregation was 30% or more of the entire area of the outer electrode, ×, when it was less than 10 to 30%, and ◎ when it was less than 10%.
It was noted in.

According to the table, it was found that Samples 22 to 27 provided with the sprayed layer according to the present example had excellent heat resistance as well as excellent drawing effect. Further, it was found from the samples 20 and 21 that when the thermal sprayed layer was not provided or only the thin thermal sprayed layer was provided, the heat resistance was slightly inferior to the samples 22 to 27.

Further, when the thermal spray layer is sufficiently thicker than the samples 28 and 29, the thermal spray layer plays the same role as the protective layer, and it is possible to obtain a certain drawing effect and excellent heat resistance. Do you get it. However, as described above, a layer formed by plasma spraying cannot make effective use of resources due to a lower material yield as compared with a case where a thick layer is formed. In addition, there is a problem that it is difficult to obtain stable performance. Furthermore, sample 30 has neither a thermal spray layer nor a protective layer. Therefore, both the drawing effect and the heat resistance were poor.

As described above, by providing both the thermal spray layer according to the present example (there is no need to increase the thickness as in the prior art) and the protective layer, it is possible to obtain an oxygen concentration detecting element having an excellent drawing effect and an excellent heat resistance. I found that I could do it.

[0081]

[Table 2]

Embodiment 2 In this embodiment, as shown in FIGS. 6 and 7, an oxygen concentration detecting element 1 in which a trap layer 15 is provided on the surface of a protective layer 11 will be described. The oxygen concentration detecting element 1 shown in FIG. 6 has an inner electrode 132 on the inner surface of the solid electrolyte 12, and an outer electrode 131 on the outer surface.
1 is provided with a trap layer 15 on the surface of the protective layer 11. The trap layer 15 is a porous layer made of γ-Al ₂ O ₃ . Others are the same as in Reference Example 1.

Next, the oxygen concentration detecting element 1 shown in FIG.
An inner electrode 132 is provided on the inner surface of the solid electrolyte 12, and an outer electrode 131 is provided on the outer surface. The sprayed layer 14 is provided on the surface of the outer electrode 131, and the protective layer 11 is provided on the surface of the sprayed layer 14.
However, on the surface of the protective layer 11, a trap layer 15 similar to the oxygen concentration detecting element 1 shown in FIG.
Others are the same as in Reference Example 1.

In the oxygen concentration detecting element 1 of this embodiment, poisoning substances such as oil components such as P, Ca, Zn, and Si and gasoline components such as K, Na, and Pb contained in the gas to be measured are described. The protective layer 11 adheres to the surface of the oxygen concentration detecting element 1 and
Has a trap layer 15 provided on the surface of the protective layer 11 to prevent clogging and deteriorate output characteristics, that is, to prevent so-called poisoning.

That is, the poisoning substance is trapped in the trap layer 15. Therefore, the protective layer 1
1 does not cause clogging, so that the oxygen concentration detecting element 1 can maintain stable output characteristics for a long period of time.

Reference Example 2 As shown in FIG. 8, the oxygen concentration detecting element 2 of this embodiment is a stacked oxygen concentration detecting element in which an outer electrode 231 and an inner electrode 232 are provided on a plate-like solid electrolyte 22. . The oxygen concentration detecting element 2 shown in FIG.
An outer electrode 231 is provided on the outer surface facing the gas chamber to be measured (see FIG. 3), and a protective layer 21 is provided on the surface of the outer electrode 231.

On the other hand, a heater 41 made of Al ₂ O ₃ having a heater heating element 42 inside is provided on the inner surface opposite to the outer surface. The heater 41 has a duct 26, and an inner electrode 232 is provided so as to face the duct 26. The duct 26 is an atmosphere chamber. Others are the same as in Reference Example 1. Further, the oxygen concentration detecting element 2 of the present example has the same operation and effect as the reference example 1.

Reference Example 3 Next, the performance of the oxygen concentration detecting element according to this example will be described with reference to Tables 3 to 8. First, the oxygen concentration detecting elements according to the samples 31 to 56 were prepared by the manufacturing method shown in the above-mentioned Reference Example 1. Each of the above samples has a particle diameter RA and RB of fine particles and coarse particles, a ratio RB / RA thereof, a content ratio WA / W, a porosity ε of the protective layer, an average pore diameter d, and a thickness L. Table 3, Table 4, Table 6, Table 7 were made differently as shown in Table 7. For reference, an oxygen concentration detecting element provided with a protective layer formed by a plasma sprayed layer was also prepared. This is the sample 57.

Next, the performance evaluation of Samples 31 to 57 was performed in the same manner as in Reference Example 1, and the results are shown in Tables 5 and 8. According to the table, {(ε / 100) × d / L} is 2.0 × 1
Samples 31 to 33, 38 to 4 at 0 ^-5 to 30 × 10 ^-5
8, 51, 52, and 54 to 56 were found to have a drawing effect equal to or higher than that of the sample 57 having the protective layer provided by plasma spraying as in the related art. In particular, it was found that in Samples 39 to 41 and 44 to 46, the porosity and the average pore diameter were particularly low, and that even if the thickness of the protective layer was small, a sufficient drawing effect was obtained.

On the other hand, samples 34 and 3 having a large average pore diameter
5, 49, 50, and sample 53 with a large porosity,
It was found that by increasing the thickness of the protective layer, the same drawing effect as that of the sample 57 having the protective layer provided by plasma spraying can be obtained as in the related art. However, the sample 36 having a large porosity and a large average pore diameter,
In No. 37, it was found that even if the thickness of the protective layer was increased, it was not possible to obtain the same drawing effect as the conventional plasma sprayed layer.

[0091]

[Table 3]

[0092]

[Table 4]

[0093]

[Table 5]

[0094]

[Table 6]

[0095]

[Table 7]

[0096]

[Table 8]

Embodiment 3 Next, the performance of an oxygen concentration detecting element having a sprayed layer on the surface of the outer electrode will be described with reference to Tables 9 to 11. First, the sample 6 was manufactured by the manufacturing method described in the first embodiment.
Oxygen concentration detecting elements ranging from 0 to 68 were prepared. In addition,
As shown in Tables 9 and 10, each of the above-mentioned samples has a particle diameter RA and RB of fine particles and coarse particles, a ratio RB / RA thereof, a content ratio WA / W, a porosity ε of the protective layer, and an average fine particle. It was created with different hole diameter d and thickness L. As a comparative sample,
Samples 59 and 71 having no thermal spray layer were prepared.
Similarly, samples 69 to 71 having no protective layer were prepared.

Next, the performance evaluation of Samples 59 to 71 was performed in the same manner as in Reference Example 1, and the results are shown in Table 11. Also,
The heat resistance was evaluated by the following test. That is,
An accelerated endurance test was performed by placing the oxygen concentration detecting element according to each of the above samples in an electric furnace and heating at 1000 ° C. for 100 hours. As a result of the above accelerated durability test,
When the area of the hole of the outer electrode caused by the aggregation was 30% or more of the entire area of the outer electrode, it was evaluated as ×, when 10 to 30% was Δ, and when less than 10%.

According to the table, it was found that Samples 61 to 68 provided with the sprayed layer according to the present example have an excellent drawing effect and an excellent heat resistance. Sample 59,
60, it was found that when the thermal sprayed layer was not provided or only the thin thermal sprayed layer was provided, the heat resistance was slightly inferior to the samples 61 to 68.

Further, from the samples 69 and 70, it was found that when the sprayed layer is sufficiently thick, the sprayed layer plays a role similar to that of the protective layer, and a certain degree of drawing effect and excellent heat resistance can be obtained. . However, as mentioned above,
As for the layer formed by plasma spraying, the resources cannot be effectively used because the material yield is lower than when a thick layer is formed. In addition, there is a problem that it is difficult to obtain stable performance. Furthermore, sample 71 has neither a thermal spray layer nor a protective layer.
Therefore, it was found that both the drawing effect and the heat resistance were poor.

As described above, by providing both the thermal sprayed layer according to the present example (there is no need to increase the thickness as in the prior art) and the protective layer, an oxygen concentration detecting element having excellent heat-resistance and excellent drawing effect can be obtained. I found that I could do it.

[0102]

[Table 9]

[0103]

[Table 10]

[0104]

[Table 11]

Reference Example 4 In this example, a trap layer was provided for each of the samples prepared in Reference Example 3, and their poisoning resistance was examined.

The above trap layer is formed by mixing heat stable ceramic particles such as α-alumina, mullite, γ-Al ₂ O ₃ , MgO.Al ₂ O ₃ spinel, an inorganic binder alumina sol, and water. A slurry was prepared, and then the slurry was adhered to the surface of the protective layer by dipping or spraying, followed by heat treatment.

The resistance to poisoning of the samples 31 to 71 provided with the trap layers was measured in the following manner. However, in each of the above samples, the protective layer having a thickness of 200 μm was provided with a trap layer and the poisoning resistance was measured. Also, sample 57 has only a protective layer formed by plasma spraying, samples 69 and 70 do not have a protective layer, and the sprayed layer provided on the outer electrode surface has a trap layer, and sample 71 has a protective layer. However, the trap layer is provided directly on the surface of the outer electrode.

The poisoning durability was determined based on the rate of change in sensor response before and after the accelerated poisoning durability test. That is, the rate of change of the responsiveness after endurance with respect to the initial responsiveness T0 (T-T0)
/ T0 is calculated. When this value is less than 0.5, the result is indicated by ○, and when the value is 0.5 or more, the result is indicated by ×.

According to the table, when ε is 15% or more and ({(ε / 100) × d}) is 5.0 × 10 ⁻³ or more, a trap layer is provided on the conventional protective layer. It was found that the sample was excellent without significant difference from the sample 58 having the specified specifications.
On the other hand, ε is less than 15% or (｛(ε / 100) ×
Samples 45, 54, 57, d５７) of less than 5.0 × 10 ⁻³
63 and 64 showed a high rate of change and poor poisoning resistance.

The oxygen concentration detecting elements shown in the first to third embodiments are λ sensors for detecting the stoichiometric air-fuel ratio in an automobile internal combustion engine. However, for example, also in a limiting current type oxygen concentration detecting element, that is, a lean sensor or a full range air-fuel ratio sensor, the protective layer according to the present invention can be used as a diffusion resistance layer.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view of an oxygen concentration detecting element in Reference Example 1.

FIG. 2 is an explanatory cross-sectional view of a main part of an oxygen concentration detecting element in Reference Example 1.

FIG. 3 is an explanatory cross-sectional view of an oxygen concentration detector in Reference Example 1.

FIG. 4 is a diagram showing a relationship between an air surplus ratio and an output voltage in Reference Example 1.

FIG. 5 is an explanatory sectional view of an oxygen concentration detecting element having a sprayed layer according to the first embodiment.

FIG. 6 is an explanatory sectional view of an oxygen concentration detecting element having a trap layer according to a second embodiment.

FIG. 7 is an explanatory cross-sectional view of an oxygen concentration detection element having a thermal spray layer and a trap layer according to a second embodiment.

FIG. 8 is an explanatory sectional view of a stacked oxygen concentration detecting element in Reference Example 2.

[Explanation of symbols]

 1,2. . . Oxygen concentration detecting element, 11, 21. . . Protective layer, 111. . . Fine particles, 112. . . Coarse particles, 12,22. . . Solid electrolyte, 131, 231. . . Outer electrode, 132,232. . . 13. inner electrode; . . Sprayed layer,

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yasumichi Hotta 1-1-1, Showa-cho, Kariya-shi, Aichi Pref. (72) Inventor Motoaki Sato 1-1-1 Showa-cho, Kariya-shi, Aichi F-term in DENSO Corporation (reference) 2G004 BB01 BC02 BF03 BF04 BF05 BF08 BF09 BJ02 BM07

Claims (11)

[Claims] 1. A cup-shaped oxygen concentration detecting element having an inner electrode provided on an inner surface and an outer electrode provided on an outer surface of a solid electrolyte, a housing accommodating the cup-shaped oxygen concentration detecting element, and an exhaust passage of the housing. In an oxygen concentration detector comprising an exhaust cover provided on the side and an air cover provided on the atmosphere side of the housing, a sprayed layer is provided on the surface of the outer electrode, and coarse particles and fine particles are formed on the surface of the sprayed layer. And a protective layer having a structure in which fine particles are filled in gaps formed between the coarse particles, and a mean particle diameter of the coarse particles with respect to the average particle diameter RA of the fine particles is provided. An oxygen concentration detector, wherein the value of the ratio of RB (RB / RA) is 30 or more. 2. The ratio (WA / W) of the fine particle content WA to the total amount W (= WA + WB) of the fine particle content WA and the coarse particle content WB in the protective layer. Is between 15% and 80%. 3. The method according to claim 1, wherein the coarse particles and the fine particles are made of Al ₂ O ₃ , ZrO ₂ , MgO.A.
An oxygen concentration detector comprising one or more heat-resistant particles selected from the group consisting of l ₂ O ₃ spinel and mullite. 4. The method according to claim 1, wherein:
An oxygen concentration detector, wherein the porosity ε of the protective layer is 50% or less. 5. The method according to claim 1, wherein:
An oxygen concentration detector, wherein the average pore diameter d of the protective layer is in the range of 0.01 to 0.3 μm. 6. A cup-shaped oxygen concentration detecting element provided with an inner electrode on an inner surface and an outer electrode on an outer surface of a solid electrolyte, a housing for accommodating the cup-shaped oxygen concentration detecting element, and an exhaust passage of the housing. In a method for manufacturing an oxygen concentration detector comprising an exhaust cover provided on the side of the housing and an air cover provided on the atmosphere side of the housing, a sprayed layer is provided by spraying a heat-resistant metal oxide on the surface of the outer electrode. In order to provide a protective layer having a structure in which coarse particles and fine particles are formed on the surface of the sprayed layer and fine particles are filled in the gaps formed between the coarse particles, first, heat-resistant particles are formed. An acid characterized in that a slurry obtained by dispersing coarse particles and fine particles in a solvent is adhered to the sprayed layer, and then heated and baked to form a protective layer. Manufacturing method of elemental concentration detector. 7. The method according to claim 6, wherein the ratio of the average particle diameter RB of the coarse particles to the average particle diameter RA of the fine particles (RB / RB)
An oxygen concentration detector wherein the value of RA) is 30 or more. 8. The method according to claim 6, wherein the ratio of the average particle diameter RB of the coarse particles to the average particle diameter RA of the fine particles (RB /
RA) is 10 or more, and the porosity of the protective layer is ε (%), the average pore diameter of the protective layer is d (μm), and the thickness of the protective layer is L (μm). , ｛(Ε / 10
0) The method of manufacturing an oxygen concentration detector, wherein the value of xd / L｝ is in the range of 2.0 × 10 ⁻⁵ to 30 × 10 ⁻⁵ . 9. The method according to claim 6, wherein the ratio of the average particle diameter RB of the coarse particles to the average particle diameter RA of the fine particles (RB / RB)
RA) is 10 or more, and the porosity of the protective layer is ε (%), the average pore diameter of the protective layer is d (μm), and the thickness of the protective layer is L (μm). , ｛(Ε / 10
0) × d / L} is 30 × 10 ⁻⁵ or less and ε
Is 15 to 50% and {(ε / 100) × d}
Is a value of 5.0 × 10 ⁻³ or more. 10. The fine particle content WA based on the total amount W (= WA + WB) of the fine particle content WA and the coarse particle content WB in the protective layer according to any one of claims 6 to 9, Ratio (value of WA / W) is 15 to 8
A method for manufacturing an oxygen concentration detector, wherein the oxygen concentration is 0%. 11. The heating and baking temperature according to claim 6, wherein the temperature of heating and baking at the time of forming the protective layer is 50.
A method for producing an oxygen concentration detector, wherein the method is performed in a temperature atmosphere of 0 to 1000 ° C.