JPH07333191A - Oxygen concentration detector - Google Patents

Abstract

PURPOSE:To provide an oxygen concn. detector which is excellent in durability and is capable of maintaining a stable sensor output over a long period of time by preventing the formation of an impermeable glasslike adhering film on the surface of the oxygen detecting element. CONSTITUTION:An oxygen concn. detector is provided with a cylindrical oxygen detecting element 91 with its one end closed that is provided with an electrode protective layer 2 consisting of an inside electrode 32 and an outside electrode 31 and an electrode protective layer 2 made of a ceramic porous body provided further on the outside of outside electrode 31, a heater 5 that is inserted inside the detecting element for heating the detecting element 91, an output taking-out means that has been electrically connected to the inside electrode 32 on the inside surface of the oxygen detecting element, and a housing for housing the oxygen detecting element 91. Further, the detector is provided with a trap layer 1 which is made of a ceramic porous body and whose surface roughness is 20 to 100mum by the designation of JIS 10-point average roughness (JIS B 0601-1982: R2), on the outside of the electrode protective layer 2.

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 (oxygen sensor, air-fuel ratio sensor, lean sensor, etc.) effectively used for combustion control in an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, ZrO _{2 has been used} as a gas detector for detecting the oxygen concentration in the exhaust gas of an automobile internal combustion engine.
For example, an oxygen concentration electromotive force type using a solid electrolyte is well known, and such a type has been widely put into practical use. As the electromotive force type gas detector, there is an oxygen concentration detector as disclosed in Japanese Patent Publication No. 2-15017.

The oxygen concentration detector is provided with an oxygen detecting element at the tip of the detector, and the oxygen detecting element has a structure in which an inner electrode, a solid electrolyte sintered body, an outer electrode and an electrode protective layer are formed in this order. It is a cylinder with a bottom. Further, a heater is inserted in the lumen of the oxygen detection element. The electrode protection layer is formed of a ceramic coating layer or a layer in which a γ-Al ₂ O ₃ layer is provided on the ceramic coating layer. The exhaust gas reaches the outer electrode through the ceramic coating layer or the γ-Al ₂ O ₃ layer to obtain a sensor output. But,
Under certain practical conditions, the surface of the outermost layer of the oxygen sensing element is coated with deposits derived from exhaust gas.
This deposit is an oil component such as P, Ca, Zn, Si,
And fine particles of a mixed gasoline component such as K, Na, and Pb, or a film-like vitreous material. The surface of the electrode protective layer is covered with the deposits to prevent the exhaust gas from diffusing to the outer electrode. Hinder. This causes quality deterioration such as a decrease in sensor output and a decrease in responsiveness. Therefore, when such an adhered substance adheres, there is a problem that the gas detector cannot obtain stable sensor characteristics for a long period of time.

Therefore, in order to solve the above problems, for example, a relatively porous sprayed film or γ-Al having a particle size of several μm is used.
An improvement plan has been proposed in which a poisoning substance trap layer made of ₂ O ₃ particles is provided on the electrode protection layer so that clogging does not occur. The first of the proposals is to coat the surface of the oxygen detection element on the side exposed to exhaust gas with an insulating film made of a metal oxide that is heat-resistant and porous and is permeable to the detection gas. An oxygen sensing element in which a coating carries a catalyst has been proposed (JP-A-52-73089). As the insulating coating, γ-Al ₂ O ₃ , ZrO ₂ , MgO or the like is used. As the catalyst, Pt, Pd, Rh or the like is adopted. The insulating coating prevents poisoning components from directly adhering to the oxygen detection element, so that the durability of the gas detector itself is improved.

The second of the above-mentioned proposals is the detection gas of the oxygen detection element.
A protective layer made of alumina spinel on the surface of the electrode
Γ-Al having a high adsorption ability on the outer surface of the protective layer.
₂O ₃There is an oxygen sensor provided with the outermost layer of poisonous substances
(JP-A 61-153561). The alumina spinel is
By controlling the flow rate of the discharged gas and improving the reactivity at the electrode
Both have the function of protecting the electrodes.

The above-mentioned proposed gas detector described above is particularly effective for detecting exhaust gas of an internal combustion engine, that is, it is very effective in capturing poisoning components such as Pb, P, S, Si and Zn. is doing. It also has the effect of preventing poisoning and deterioration of the internal catalyst components and greatly improving durability. However, in recent years, in response to global environmental policy, further improvement of fuel efficiency and performance improvement in internal combustion engines has been promoted,
The usage environment of gas detectors is becoming more severe.
That is, the operating temperature of the gas detector is increasing and the amount of poisoning component is increasing. Therefore, the captured poisoning components cause a chemical reaction with each other at high temperature, or cause melting, and after cooling, form a dense glass-like adhered film that does not have air permeability on the surface of the oxygen sensing element. However, there is a situation that causes clogging.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been earnestly studied in response to the above situation, and prevents formation of a dense glass-like adhered film having no air permeability on the surface of an oxygen sensing element,
An object of the present invention is to provide an oxygen concentration detector having excellent durability without causing clogging, that is, capable of maintaining a stable sensor output for a long period of time.

[0008]

SUMMARY OF THE INVENTION Therefore, the present invention provides the electrode protection layer according to claim 1, that is, an inner electrode and an outer electrode on the inner and outer surfaces, respectively, and a ceramics porous body on the outer side of the outer electrode. At least an oxygen detection element having an output detection means electrically connected to the inner electrode on the inner surface of the oxygen detection element, and a housing for accommodating the oxygen detection element. A ceramic porous body is provided on the outer side of the protective layer, and has a surface roughness of JIS 10-point average roughness (JIS B 0
The problem is solved by adopting an oxygen concentration detector characterized in that a trap layer having a thickness of 60 to 1982: R _z ) and a thickness of 20 to 100 μm is provided.

In addition, claim 6, that is, spherical, lump-shaped, fiber-shaped, foam-shaped, column-shaped or needle-shaped α-Al ₂
O ₃ , γ-Al ₂ O ₃ , mullite, MgO · Al ₂ O ₃
A slurry in which one or more kinds of heat-resistant particles of spinel, an inorganic binder and a dispersant are dispersed in water is formed of an inner electrode and an outer electrode on the inner and outer sides, respectively, and a ceramic porous body on the outer side of the outer electrode. Forming a trap layer by depositing the slurry by dipping or spraying on the electrode protection layer of a cylindrical oxygen detection element with one end closed and having an electrode protection layer, and then baking at 500 to 900 ° C. The oxygen concentration detector of the present invention is provided by employing the method for manufacturing an oxygen concentration detector characterized by the above. .

[0010]

By making the surface of the trap layer uneven, even when a glass-like deposit adheres to the surface of the trap layer in a harsh environment of use, the deposit will not be present between the convex portion and the concave portion. It is not divided and does not cover the entire surface of the trap layer, and the opening portions of the pores near the surface are surely secured, and clogging does not occur.

That is, even if deposits derived from poisoning components adhere to the surface of the trap layer to form a dense glassy layer, many open holes are always maintained, and the gas to be detected reaches the electrode. It can be prevented from reaching. Further, it is possible to prevent the attached matter from reaching the electrode protective layer formed inside the trap layer. Thereby, the gas to be detected passes from the measurement atmosphere through the trap layer and the electrode protective layer,
The electrodes can be easily reached and a stable sensor output can be maintained for a long period of time.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is for explaining the structure of an oxygen concentration detector 90 of the present invention. In the figure, an oxygen concentration detector 90 is an oxygen sensing element 9 forming an electrochemical cell.
1 and a housing 92 that houses the oxygen detection element 91. The housing 92 has a body portion 93 provided with a flange 931 at a substantially central portion thereof, an exhaust cover 94 inserted into the exhaust passage below the body portion 93, and an upper portion above the body portion 93. It has an atmosphere cover 95 in contact with the atmosphere. The exhaust cover 94 has an inner cover 941 and an outer cover 942 made of stainless steel. The inner cover 941 and the outer cover 942 have exhaust ports 943, 94.
4 is provided.

On the other hand, the atmosphere cover 95 has the body portion 9
3 is provided with a main cover 951 and a sub cover 952 that covers a rear end portion of the main cover 951. The main cover 951 and the sub cover 95 are provided.
2 has an air intake port (not shown). The oxygen concentration detector 90 is sandwiched by the body 93 via an insulating member 932. Further, the internal electrode 911 and the external electrode 912 of the oxygen detection element 91 (the internal electrode 911 and the external electrode 912 are the following first to fourth electrodes, respectively).
In the embodiment, the internal electrode 911 is replaced by the internal electrode 3
2. The external electrodes 912 are indicated as the external electrodes 31 by reference numerals), and metal plate terminals 961 and 962 for sandwiching them so as to wrap them are connected. The plate-shaped terminals 961 and 962 are connected to the output lead wire 97.
1, 972 are connected. That is, the plate-shaped terminal 96
1, 962, strip-shaped terminal pieces 963, 964 are provided so as to project from the contact pieces 965, 966. The terminal pieces 963 and 964 have connectors 981 and 98 whose other ends 983 and 984 are connected to the lead wires 971 and 972.
2 is connected to one ends 985 and 986. The plate-shaped terminals 961 and 962 are formed by deforming an inverted T-shaped metal plate into a tubular shape and sandwiching the internal electrode 911 or the external electrode 912. An appropriate contact pressure is applied between the plate-shaped terminals 961 and 962, the internal electrode 911, and the external electrode 912 by the spring elastic force of the metal plate. On the other hand, a pulling force acting in the axial direction of the oxygen sensor 90 acts on the lead wires 971 and 972, so that the plate terminals 961 and 962 are pulled through the connectors 981 and 982 and slide in the axial direction. I have something to do. In order to prevent this, the oxygen sensor 90
A stopper 993 sandwiched between rubber bushes 991 and 992 is provided at the end of the. The stopper 993 is
The connector 981 and 982 are printed to prevent movement of the connectors 981 and 982, and are formed of a resin material for maintaining insulation between the lead wires 971 and 972. Incidentally, 973
Is a wire for a heater that heats the oxygen detection element 91. The oxygen sensor 90 has the exhaust cover 94 inserted into the exhaust passage and is fixed to the exhaust passage by the flange 931. The oxygen sensor 90 having the above structure is one in which an electrode is provided on both surfaces of a solid electrolyte that is an oxygen ion conductor to form an electrochemical cell, and exhaust gas is introduced into one of the electrodes and the other is introduced into the other. The atmosphere is introduced into the chamber and the air-fuel ratio is detected from the potential difference between the electrodes caused by the difference in oxygen concentration between the two.

The main part of the present invention will be described below. [First Example] In the first example, the surface of a poisoning substance trap layer (hereinafter referred to as a trap layer), which will be described in detail below, is intentionally made uneven so that a glassy deposit adheres to a convex portion and a concave portion. In doing so, it was found that the adhered matter was divided between the two and the whole surface layer was not covered, and the ventilation path of the exhaust gas was secured.

The oxygen concentration detector 90 of this embodiment is an oxygen concentration electromotive force type sensor and is shown in FIG. Oxygen sensing element 9
1 has a pair of outer electrode 31 and inner electrode 32, a porous electrode protective layer 2 that protects the outer electrode 31 and controls gas diffusion, and a trap layer 1 that covers the electrode protective layer 2. In addition, the trap layer 1 is composed of a porous body for capturing poisoning components. The electrode protection layer 2 is made of Mg
It is a porous protective layer formed by thermal spraying of O.Al ₂ O ₃ spinel or the like. The trap layer 1 is a porous body formed of a large number of particles as shown in FIG. The particles are thermally stable and continuously bond to form the trap layer 1.

The surface of the trap layer 1 has a structure having irregularities as shown in FIG. The trap layer 1
Even if lath-like deposits adhere to the surface of the trap layer 1 (described in FIG. 5) by making the surface of the surface uneven, the deposits are divided between the convex portions and the concave portions, and the entire surface layer Is not covered, thus ensuring a ventilation path for exhaust gas. The depth of the unevenness is 10-point average roughness (JIS B 0601-
1982: R _z ), the effect cannot be obtained unless it is 20 μm or more. The unevenness has a ten-point average roughness (R _z ) of 20 μm.
If it is less than 1, the amount of deposits is small when the use time is short, and the opening of the opening near the surface of the trap layer 1 is maintained. The adhered matter and the adhered matter in the recess are connected to each other, which may cause clogging.

The trap layer 1 is prepared by adding water and 3 to 20% by weight of the inorganic binder and dispersant to the particles forming the trap layer to prepare a slurry. It is attached by dipping or spraying and then baked at 500 to 900 ° C. By setting the particles used for preparing the slurry to have an average particle size of 20 μm or more and 10% or less of particles having a particle size of 10 μm or less, the ten-point average roughness (R _z ) of the surface of the trap layer 1 can be 20 μm or more. it can.

Even when the proportion of particles having a size of 10 μm or less is 10% or more, the ten-point average roughness (R _z ) can be made to be 20 μm or more by mixing coarse particles having a size of 50 μm or more. The ten-point average roughness (R _z ) can be adjusted by controlling the particle size distribution of particles forming the trap layer 1. The ten-point average roughness (R) can also be obtained by mixing an organic substance such as a resin agent, which is scattered by combustion at 500 to 900 ° C., into the slurry, adhering it to the surface of the oxygen detecting element 91 by a dipping method or the like, and then baking it. _z ) can be adjusted.

The trap layer 1 is composed of α-Al ₂ O ₃ , γ
It is preferable to be composed of one or more heat-resistant particles of —Al ₂ O ₃ , mullite, and MgO · Al ₂ O ₃ spinel. Also,
The particle shape can be selected from spherical shape, massive plate shape, fiber shape, foam shape, column shape, needle shape and the like. In addition, the trap layer 1 can also use secondary particles formed by a collection of dense primary particles of 1 μm or less. The average pore diameter d of the trap layer 1 is larger than the average pore diameter of the porous electrode protection layer. If the average pore size of the electrode protective layer is less than the average pore size, the deposits of poisoning components may clog the trap layer 1 to cover the surface and prevent exhaust gas from passing through.

The average pore diameter d of the trap layer 1 is 0.
It is preferably 5 μm or more. If it is less than 0.5 μm, the amount of deposits is small when the usage time is short, and the opening of the opening near the surface of the trap layer 1 is maintained,
The longer the use time is, the larger the amount of deposits is. Therefore, a continuous deposit layer may be formed near the surface of the trap layer 1 to cause clogging. On the other hand, if the average pore diameter is too large, conventional fine deposits may pass through the pores and reach the electrode protective layer, and the electrode protective layer may be clogged. Therefore, the average pore diameter d is preferably 0.5 to 50 μm.

It is obvious that the thickness T of the trap layer 1 is larger than the surface roughness R _z required to divide the deposit, and it is preferably 30 to 500 μm. Three
When the thickness is less than 0 μm, the thinnest part of the trap layer 1 is 1
The thickness is less than 0 μm, and there is a possibility that the effect as the trap layer 1 cannot be exhibited due to being too thin. Conversely, 5
If it is thicker than 00 μm, the trap layer 1 may be too thick, and the adhesion between the electrode protection layer and the trap layer 1 may be reduced. Further, the diffusion of the exhaust gas of the trap layer 1 itself may be hindered, and the initial characteristics of the sensor may be adversely affected. Furthermore, it is preferably 50 to 300 μm.

The trap layer 1 has a porosity of 40-80.
% Is preferable. If it is less than 40%, the trap layer 1 is too dense and may cause clogging. Therefore, by increasing the surface roughness to, for example, 50 μm or more, an exhaust gas ventilation path is secured. If it exceeds 80%, the strength of the trap layer 1 may decrease.

As described in this embodiment, by making the surface of the trap layer 1 uneven, when the glassy deposit adheres to the surface of the trap layer 1 in the harsh environment of use. In addition, the adhered matter is not divided between the convex portion and the concave portion to cover the entire surface of the trap layer 1, the open portion of the pores near the surface is surely secured, and clogging does not occur. .

That is, even if a deposit derived from a poisoning component adheres to the surface of the trap layer 1 to form a dense glassy layer, many open holes are always maintained, and the gas to be detected is the electrode. It does not prevent you from reaching. Further, the attached matter is
It does not reach the electrode protection layer formed inside the trap layer 1. As a result, the gas to be detected can easily reach the electrode from the measurement atmosphere through the trap layer 1 and the electrode protective layer, and a stable sensor output can be maintained for a long period of time.

The surface roughness R _z (μm), thickness T (μm), average pore diameter d (μm), and porosity (%) of the trap layer 1 were variously changed by the manufacturing method described above. Sensors were manufactured and measured for poisoning durability and initial response. The surface roughness R _z of the trap layer 1 is 5 to 10
0 μm, thickness T is 20 to 300 μm, average pore diameter d
Was 2 to 50 μm, and the porosity was changed in the range of 20 to 80%. Poisoning durability was determined by the rate of change in sensor responsiveness before and after the accelerated poisoning durability test. When the rate of change was less than 5%, it was evaluated as ⊚ when it was 5% or more and less than 10%, as Δ when it was 10% or more and less than 20%, and as X when it was 20% or more. Initial response is ◎, 100 when less than 100 ms
○ for ms and less than 150 ms, 150 ms or more 2
When it was less than 00 ms, it was determined as Δ, and when it was 200 ms or more, it was determined as x.

The test conditions in the durability test were continuously repeated under the condition that a 2000 cc in-line 4-cylinder engine with a fuel injection device was rotated for 30 minutes at an engine speed of 4000 rpm after 30 minutes of idling. The endurance temperature is
It is 500-700 degreeC. The gasoline used was unleaded gasoline with 5 wt% of engine oil and detergent added. The durability time is 100 hours.

The measurement of the responsiveness shows that when the gas response time, that is, when switching from λ0.9 to λ1.0, the output is 0.
The measurement is for the time to change from 6V to 0.3V. The measurement was carried out on a 2000cc inline 6-cylinder engine with a fuel injection system, using unleaded gasoline, and a rotation speed of 1100 rpm.
I was driven by. The measurement is performed before and after the durability test.

From the results of this experiment, the surface roughness R _z of the trap layer 1 is 20 to 100 μm and the thickness T is 50 to 3
In the case of 00 μm, average pore diameter d of 0.5 to 50 μm, and porosity of 40 to 80%, good poisoning durability was obtained without deterioration of initial responsiveness. Table 1 shows an example of the result of this experiment.

[0029]

[Table 1]

Second Embodiment In this embodiment, in the oxygen concentration detector 90 shown in FIG. 4, the second trap layer 12 having a structure in which the surface of the trap layer 1 is made uneven, and the trap layer Compared with No. 12, the two-layer structure provided with the first trap layer 11 which is denser than that of No. 12 improves the poisoning durability, and the details will be described below.

As shown in FIG. 6, the oxygen detecting element 91 is
A pair of outer electrode 31 and inner electrode 32 and the outer electrode 3
Porous electrode protective layer 2 for protecting 1 and controlling gas diffusion
And the first trap layer 11 covering the electrode protection layer 2 and more porous than the electrode protection layer 2 and the first trap layer 11
And a second trap layer 12 that covers the above and is more porous than the first trap layer 1 and has rough pores. The first trap layer 11 and the second trap layer 12 of the first trap layer 11 are formed of a porous body for capturing poisoning components. The electrode protective layer 2 is a porous protective layer formed by thermal spraying of MgO.Al ₂ O ₃ spinel or the like. The first trap layer 1
1 and the second trap layer 12 are porous bodies formed of a large number of particles as shown in FIG. The particles are
It is thermally stable and is continuously bonded to form the first trap layer 11 and the second trap layer 12.
The trap layer 1 composed of such two layers is, for example,
It is formed as follows. First, γ with an average particle size of 4 μm
-Al ₂ O ₃ as an inorganic binder, 3 to 20 wt% of alumina sol, a dispersant, and water were added to the particles to prepare a slurry, and this slurry was applied to the surface of the oxygen detection element by dipping or spraying. The first trap layer 11 is formed by depositing and baking at 500 to 900 ° C. Then, similarly, the average particle size is 20 μm.
As an inorganic binder, 3 to 20 wt% of alumina sol, dispersant, and water are added to m of γ-Al ₂ O ₃ to prepare a slurry, and the slurry is prepared by using the slurry of the first trap layer. The surface of 11 is attached by dipping or spraying, and further baked at 500 to 900 ° C. to form the second trap layer 12.

The surface of the second trap layer 12 has an uneven structure as in the first embodiment.
The ten-point average roughness (R _z ) has a depth of 20 μm or more. Average pore diameter d of the second trap layer 12
Is 0.5 to 50 μm. Second trap layer 1
The thickness T of 2 is 30 to 300 μm. The porosity of the second trap layer 12 is 40 to 80%.

The first trap layer 11 is mainly for trapping fine deposits from the prior art, and the average pore diameter d thereof is the average fineness of the electrode protective layer which is a porous body. It is preferably larger than the pore size, and preferably 0.1 to 0.5 μm. When the average pore size is less than 0.1 μm, the deposits composed of poisonous components are trapped in the trap layer 1.
There is a risk of clogging in 1 and blocking the exhaust gas. In consideration of capturing fine poisonous substances, the average pore diameter is preferably less than 0.5 μm. The porosity of the first trap layer 11 is preferably 15 to 50% or more. If it is less than 15%, the first trap layer 11
Is too dense and may be clogged with poisonous components. Moreover, in order to reliably capture fine poisonous substances, the porosity is preferably less than 50%. The thickness T of the first trap layer 11 is preferably 5 to 100 μm. 5μ
If it is less than m, it may be too thin to exert the effect as the trap layer 1. If it is thicker than 100 μm, the initial characteristics of the sensor may be adversely affected.
The first trap layer 11 and the second trap layer 12
Is α-Al ₂ O ₃ , γ-Al ₂ O ₃ mullite, MgO
-It is preferable to be composed of one or more heat-resistant particles of Al ₂ O ₃ spinel and TiO ₂ . Further, the particle shape can be selected from a spherical shape, a lump shape, a plate shape, a fiber shape, a foam shape, a columnar needle shape and the like.

As described above, by providing the trap layer 1 having a two-layer structure, even if a glassy poisonous substance adheres and deposits (see FIG. 8) under practical use, the surface with the uneven surface is formed. The second trap layer 12 prevents the adhered matter from being divided between the convex portion and the concave portion, so that the entire surface of the trap layer 1 is prevented from being covered and a ventilation path for exhaust gas is secured. Further, since the second trap layer 12 is very porous, fine poisonous substances may pass through the second trap layer 12 and may clog the relatively dense electrode protective layer. Since it is captured by the first trap layer 11, there is no problem.

Further, since the first trap layer 11 has a denser structure than the second trap layer 12, it is possible to efficiently trap fine poisonous substances from the prior art. The thickness of the entire trap layer 1 can be reduced as compared with the structure. That is, when the trap layer 1 has a two-layer structure, a further poisoning substance trapping effect can be expected, and stable sensor characteristics can be maintained for a long period of time. By the manufacturing method described above, the average pore diameter d (μm), porosity (%), and thickness T (μm) of the first trap layer 11 and the second trap layer 12 are obtained.
Average pore diameter d (μm), porosity (%), and thickness T of
(Μm) and various oxygen concentration detectors as shown in Table 2 were manufactured, and the durability against poisoning and the initial response were measured. As a result, the average pore diameter d of the first trap layer 11 is 0.1 to 0.5 μm, and the porosity is 15 to 50.
%, The thickness T is in the range of 10 to 50 μm, the surface roughness R _z of the second trap layer 12 is 20 to 100 μm, the average pore diameter d is 3 to 50 μm, and the porosity is 50 to 80%.
Good results were obtained when the thickness T was in the range of 50 to 300 μm. Table 2 shows an example of the test results.

The poisoning durability was judged by the rate of change in sensor responsiveness before and after the accelerated poisoning durability test. A rate of change of less than 5% was rated as ⊚, a rate of 5% or more and less than 10% was rated as ◯, a rate of 10% or more and less than 20% was rated as Δ, and a rate of 20% or more was rated as x. Initial response is ◎, 100 when less than 100 ms
○ for ms and less than 150 ms, 150 ms or more 2
When it was less than 00 ms, it was determined as Δ, and when it was 200 ms or more, it was determined as x. The durability test conditions and the responsiveness were measured by the same method as in Example 1.

[0037]

[Table 2]

[Third Embodiment] In this embodiment, in the oxygen concentration detector shown in FIG. 4, the trap layer 1 has an inclined structure whose porosity continuously increases from the electrode protective layer 2 toward the surface. By doing so, it is possible to dramatically improve the durability by capturing the poisonous substances step by step. The details will be described below.

As shown in FIG. 9, the oxygen detecting element 91 is
A pair of outer electrode 31 and inner electrode 32 and the outer electrode 3
Porous electrode protective layer 2 for protecting 1 and controlling gas diffusion
And a trap layer 1 covering the electrode protection layer 2, the trap layer 1 being composed of a porous body for trapping poisoning components as shown in FIG. Reference numeral 2 is a porous protective layer formed by thermal spraying of MgO.Al ₂ O ₃ spinel or the like. The trap layer 1 is a porous body formed of a large number of particles as shown in FIG. The particles are thermally stable and continuously bond to form the trap layer 1.

The trap layer 1 has its outermost surface composed of coarse particles, and has a surface roughness of 10-point average roughness (R _z ) of 20.
It is more than or equal to μm, and it becomes dense with many fine particles toward the inside, and has a structure having a porosity larger than that of the electrode protective layer even at the innermost side. Such a trap layer 1
Is formed as follows, for example. First, six types of particles having different average particle sizes of 4 μm to 30 μm and having different particle sizes are prepared so as to be evenly spaced. An inorganic binder, a dispersant, and water of 3 to 20% by weight based on the weight of the particles are added to each of the 6 types of particles having different particle sizes to prepare slurries having different average particle sizes. Then, the trap layer 1 is attached in order from the slurry having a small average particle diameter to the slurry having a large average particle diameter by dipping or spraying, and further baked at 500 to 900 ° C. to form the trap layer 1. Alternatively, a slurry is prepared by adding 3 to 20% by weight of the inorganic binder, dispersant, and water to the mixture of particles having different particle sizes used in the above method. The slurry is attached to the surface of the sensor element by dipping to form the trap layer 1. At this time, when the slurry is stirred with a stirrer or the like, particles having a large particle size are collected on the outer peripheral portion of the container by centrifugal force, Particles having a small particle size are gathered in the central part of the rotation, and a particle size distribution occurs in which the particle size increases in order from the central part to the outer peripheral part in the container. The trap layer 1 is attached by putting a sensor element in the central part of the slurry having a small particle size, moving it toward the outer peripheral direction having the largest particle size, and pulling up the sensor element at the outermost peripheral part having the largest particle size. The trap layer 1 thus attached is further baked at 500 to 900 ° C. to form the trap layer 1.

The distribution of the porosity and the surface roughness R _z of the trap layer 1 can be adjusted by the particles used for preparing the slurry, the mixing method, the stirring speed and the dipping position. The thickness T of the trap layer 1
Requires 10 μm or more in the thinnest part in order to exert the function of the trap layer 1, and in order to prevent clogging of exhaust gas even if glassy poisoning deposits are deposited,
Since the surface roughness of the ten-point average roughness (R _z ) is required to be 20 μm or more, 30 μm or more is preferable, and the initial response of the sensor and the adhesive force between the trap layer 1 and the electrode protective layer are 500 μm or less. Is preferred.

The trap layer 1 is formed of α-Al ₂ O ₃ ,
It is preferable to be composed of one or more heat-resistant particles of γ-Al ₂ O ₃ , mullite, MgO.Al ₂ O ₃ spinel, and TiO ₂ . The particle shape can be selected from spherical, lump, plate, fiber, foam, column, needle and the like. With the above structure, even if a poisonous substance adheres and accumulates under practical use, the glass-like adhered substance is divided between the convex portion and the concave portion due to the unevenness of the outermost surface, and the entire surface of the trap layer 1 is Since the opening is maintained without continuous coating, deterioration of the sensor output does not occur. Further, since minute poisonous substances are also captured inside the trap layer 1, it is possible to prevent the poisoning substances from reaching the electrode protection layer and causing clogging. Further, since fine poisonous substances are trapped stepwise inside the trap layer 1 having different pore states, it is necessary to make the entire trap layer 1 thinner than the structure of the first embodiment or the structure of the second embodiment. You can From the above, Example 1 and Example 2
It is possible to maintain stable sensor characteristics for a longer period of time.

The oxygen detecting element 91 of the present invention having the trap layer 1 formed was manufactured by the manufacturing method described above. FIG. 10 shows the result of measuring the change in responsiveness of the oxygen concentration detector 90 of the present invention equipped with the oxygen detecting element 91, which was poisoned and durable. The durability test conditions and the responsiveness were measured by the same method as in Example 1. The trap layer 1
Has a thickness T of 100 μm and a surface roughness R _z of 50 μm. Using six slurries having different average particle sizes, the trap layer 1 is formed by dipping in order from a slurry having a small average particle size to a slurry having a large average particle size. Attach 50
The trap layer 1 was formed by baking at 0 to 900 ° C. Table 3 shows the results of measuring the average pore diameter d and the porosity of each layer.

[0044]

[Table 3]

[Fourth Embodiment] This embodiment is based on the first to third embodiments.
In the oxygen concentration detector 90 shown in FIG. 5, a method for ensuring the binding force between particles forming the trap layer 1 and achieving both poisoning resistance and durability is found. Details. As shown in FIG. 12, the oxygen detection element 91 includes a pair of outer electrodes 31 and inner electrodes 32, a porous electrode protection layer 2 that protects the outer electrodes 31, and the trap layer 1 that covers the electrode protection layer 2. The trap layer 1 is composed of a porous body for capturing poisoning components as shown in FIG. The electrode protection layer 2 is made of MgO.
It is a porous protective layer formed by thermal spraying of Al ₂ O ₃ spinel or the like. The trap layer 1 is a porous body formed of a large number of particles as shown in FIG. The particles are thermally stable and continuously bond to form the trap layer 1. The outermost surface of the trap layer 1 is composed of coarse particles, and the surface roughness is 20 μm or more in ten-point average roughness (R _z ).

The above-mentioned trap layer 1 is, for example,
It is formed as follows. First, the average particle size is 20 μm
An inorganic binder, a dispersant, and water are added to the γ-Al ₂ O ₃ particles to prepare a slurry. This slurry is attached to the surface of the sensor element by dipping,
The trap layer 1 is formed by baking at 0 to 900 ° C. The particles forming the trap layer 1 obtain a bonding force between particles by baking at the temperature, but it is essential that the particles and the inorganic binder are of the same kind. That is, the baking of the trap layer 1 must be performed in the temperature range as described above, but the adhesion force between particles becomes weak in such a temperature range. Therefore, by using an inorganic binder of the same quality as the particles, the inorganic binder is homogenized with the particles in the baking process, and a cross-linking structure is formed between the particles to obtain a bonding force between the particles. .

However, when an organic binder is used, it scatters due to combustion or the like during the baking process, cannot contribute to the bonding between particles, and the bonding force is weak, so that the trap layer 1 is Peel it off. Even if peeling does not occur in the step of forming the trap layer 1, the peeling may occur due to vibration or thermal stress during use. In the case of γ-Al ₂ O ₃ used in this example, the particles and the inorganic binder have the same quality in the baking at 500 to 900 ° C. after the alumina sol, which is the same type as the particles, is applied by dipping. To obtain a strong bonding force (described in FIG. 13).

The amount of the inorganic binder used is preferably 3 to 20% based on the weight of the particles. That is, if the amount of the binder is too small, the amount of the binder existing between the particles is very small, and the binding force for connecting the particles cannot be obtained. On the contrary, when the amount of the binder is too large, the binding force between the particles can be obtained, but the excess binder not involved in the binding of the particles is accumulated in the pores of the trap layer 1 to block the pores or cover the particles. And
The ability to trap poisonous substances may be impaired. By adjusting the type and amount of the inorganic binder, the average pore diameter of the trap layer 1 is 0.5 μm or more, and the porosity is 40 to 90.
%, And the film thickness is 30 to 500 μm, the trap layer 1 can be formed with good resistance to poisoning. The trap layer 1 is formed of α-Al ₂ O ₃ , γ-Al.
₂ O ₃ , mullite, MgO / Al ₂ O ₃ spinel, Ti
It is preferably composed of one or more heat-resistant particles of O ₂ .

Further, the particle shape may be spherical, lump, plate, fiber, foam, column, needle or the like. Also in the above-mentioned materials and particle shapes, the same kind of inorganic binder as the particles is used, and the amount thereof is adjusted in the range of 3 to 20% with respect to the weight of the particles, whereby the poisoning resistance and the durability are combined. The trap layer 1 can be formed, and stable oxygen concentration detection characteristics can be maintained for a long period of time.

The oxygen detection element 91 of the present invention was manufactured by forming the trap layer 1 by the manufacturing method described above.
Γ-Al ₂ O ₃ was used as the particles of the trap layer 1 and alumina sol, which is the same type as the particles, was used as the inorganic binder, and the amount of the inorganic binder was varied between 1 and 30%. From the results of this experiment, the same kind of inorganic binder as the particles constituting the trap layer 1 was used in an amount of 3 to 2 times the weight of the particles.
It was found that when 0% was added, the bond strength between the particles was secured, the initial characteristics were not deteriorated, and good poisoning durability was obtained. Table 4 shows an example of the result of this experiment.

The durability test conditions and the response were measured in the same manner as in Example 1. The criteria for determining the initial responsiveness and poisoning durability are the same as in Example 1. The adhesive force was evaluated by taping, and the case where the trap layer 1 was peeled off was determined as x, and the case where the trap layer 1 was not peeled off was determined as o.

The trap layer 1 in the above first to fourth embodiments is not limited to the cup-type oxygen detecting element of the present embodiment, and the same effect can be obtained even if it is a laminated oxygen detecting element. Needless to say. Further, not only the oxygen concentration electromotive force type sensor, but also the oxide semiconductor type oxygen concentration detection detector, further, the lean sensor is a limiting current type oxygen concentration detector, and the air-fuel ratio sensor air-fuel ratio sensor and the like. It goes without saying that the same effect can be obtained by doing so.

[0053]

[Table 4]

[0054]

As described above, it is possible to prevent the formation of a dense glass-like adhered film having no air permeability on the surface of the oxygen sensing element and to prevent clogging and to have excellent durability, that is, stable for a long period of time. It is possible to provide an oxygen concentration detector that can maintain the above sensor output.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross-sectional view of an oxygen concentration detector of the present invention.

FIG. 2 is a view showing a cross-sectional view of an oxygen detection element which is a part of the oxygen concentration detector of the first embodiment of the present invention.

FIG. 3 is an enlarged view of a cross section of an oxygen detection element which is a part of the oxygen concentration detector of the first embodiment of the present invention.

FIG. 4 is an enlarged view of a cross section of a trap layer of an oxygen detection element, which is a part of an oxygen concentration detector according to a first embodiment of the present invention, showing a concept of a concavo-convex state on a surface.

FIG. 5 is a cross-sectional view showing a state in which deposits adhere to the oxygen detection element that is a part of the oxygen concentration detector of the first embodiment of the present invention.

FIG. 6 is a view showing a cross-sectional view of an oxygen detection element which is a part of the oxygen concentration detector of the second embodiment of the present invention.

FIG. 7 is an enlarged view of a cross section of an oxygen detection element which is a part of an oxygen concentration detector according to a second embodiment of the present invention.

FIG. 8 is a cross-sectional view showing a state in which deposits are attached to an oxygen detection element that is a part of the oxygen concentration detector of the second embodiment of the present invention.

FIG. 9 is a diagram showing an enlarged view of a cross section of an oxygen detection element which is a part of an oxygen concentration detector according to a third embodiment of the present invention.

FIG. 10 is a cross-sectional view showing a state in which deposits adhere to the oxygen detection element that is a part of the oxygen concentration detector of the third embodiment of the present invention.

FIG. 11 is a graph showing a sensor responsiveness change rate with the endurance time of the oxygen concentration detector of the third embodiment of the present invention.

FIG. 12 is a diagram showing an enlarged view of a cross section of an oxygen detection element which is a part of an oxygen concentration detector of a fourth embodiment of the present invention.

FIG. 13 is a diagram showing an example of a joined state of heat-resistant particles in the trap layer of the oxygen concentration detector of the fourth example of the present invention.

[Explanation of symbols]

1 Trap Layer 11 1st Trap Layer 12 2nd Trap Layer 2 Electrode Protection Layer 3 Electrode 31 Outer Electrode 32 Inner Electrode 4 Solid Electrolyte Sintered Body 5 Heater 7 Glassy Adhesive (Glassy Poisonous Substance) 90 Oxygen Concentration Detection Element 91 Oxygen detection element 92 Housing 93 Output extraction means (96 terminals, 97 leads,
98 connector) 96 terminal 961 plate terminal 962 plate terminal 97 lead 971 output lead wire 972 output lead wire 98 connector 981 connector 982 connector

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiromi Sano, 1-1, Showa-cho, Kariya city, Aichi prefecture, Nihon Denso Co., Ltd. (72) Masahiro Shibata, 1-1, Showa-cho, Kariya city, Aichi prefecture, Nihon Denso Co., Ltd. Within the corporation

Claims (11)

[Claims] 1. An oxygen sensing element having an inner electrode and an outer electrode on an inner side surface and an outer side surface respectively, and an electrode protective layer made of a ceramic ceramic on the outer side of the outer electrode, and an oxygen sensing element on the inner side surface of the oxygen sensing element. At least an output take-out means electrically connected to the inner electrode and a housing for accommodating the oxygen detection element are provided. Moreover, a ceramic ceramic porous body is further provided outside the electrode protection layer, and has a surface roughness. Is JIS ten-point average roughness (JI
S B 0601-1982: R _z ) display 20 to 1
An oxygen concentration detector comprising a trap layer having a thickness of 00 μm. 2. The electrode protection layer is a thermal sprayed ceramic coating layer porous body, and the trap layer is spherical, lumpy, fiber-like, foam-like, columnar or needle-like α.
-Al ₂ O ₃ , γ-Al ₂ O ₃ , mullite, MgO · A
_2. The oxygen concentration detector according to claim 1, which is a ceramics porous body which is one or more heat-resistant particles of l ₂ O ₃ spinel. 3. The trap layer has a thickness of 50 to 300 μm.
The oxygen concentration detector according to claim 1, wherein 4. The trap layer has an average pore size of 0.5 to 5
The oxygen concentration detector according to claim 1, wherein the oxygen concentration detector has a diameter of 0 μm. 5. The oxygen concentration detector according to claim 1, wherein the trap layer has a porosity of 40 to 80%. 6. A spherical, lump, fiber, foam, column, or needle-shaped α-Al ₂ O ₃ , γ-Al ₂ O
₃ , a slurry in which one or more heat-resistant particles of mullite, MgO · Al ₂ O ₃ spinel, an inorganic binder, and a dispersant are dispersed in water, and an inner electrode, an outer electrode, and an outer electrode are provided on the inner surface and the outer surface, respectively. Of the cylindrical oxygen sensing element having one end closed and provided with an electrode protective layer made of a ceramic ceramic on the outer side of the electrode protective layer, the slurry is attached by dipping or spraying, and then at 500 to 900 ° C. A method for manufacturing an oxygen concentration detector, which comprises forming a trap layer by baking at. 7. A heat-resistant particle having an average particle diameter of several kinds and having a surface roughness of JIS ten-point average roughness (JIS B).
0601-1982: R _z ) display 20 to 100 μ
7. The method for manufacturing an oxygen concentration detector according to claim 6, wherein a trap layer having m is formed. 8. The trap layer comprises a first trap layer and a second trap layer, the first trap layer is formed on an electrode protection layer, and the second trap layer is the first trap layer. A layer formed on the layer, and the first trap layer is more porous than the electrode protection layer and denser than the second trap layer.
The oxygen concentration detector described. 9. The layer structure according to claim 1, wherein a porosity of the trap layer increases from an electrode protective layer side of the trap layer toward an outer surface side of the trap layer. Oxygen concentration detector. 10. Slurries of heat-resistant particles having different average particle sizes are prepared, and in order from the slurry having the smallest average particle size, an inner electrode and an outer electrode are respectively formed on the inner side surface and the outer surface, and a ceramics is further provided outside the outer electrode. On the electrode protective layer of the cylindrical oxygen sensing element having one end closed with the electrode protective layer made of a porous body, the slurry is repeatedly attached by dipping or spraying to form a trap layer having a layer structure. The method for manufacturing an oxygen concentration detector according to claim 6, wherein the oxygen concentration detector is formed. 11. Oxygen concentration detection, wherein the same kind of inorganic binder as the kind of the heat resistant particles is used, and the amount of the inorganic binder is 3 to 20% by weight based on 100% by weight of the heat resistant particles. The method for manufacturing an oxygen concentration detector according to claim 6,