JPH10221304A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor which is highly durable to the poisoning of phosphorus, etc. SOLUTION: An oxygen sensor comprises an oxygen concentration cell 3 that porous electrodes 3b and 3c are formed on both sides of a solid electrolyte substrate 3a, an oxygen pumping element 5 that porous electrodes 5b and 5c are formed on both sides of the solid electrolyte substrate 5a as well, and a spacer 9 laminated between both these elements 3 and 5 to form a gas measuring chamber 7. This spacer 9 is provided with a pair of communication holes 19a on the right and left sides for the communication between the gas measuring chamber 7 and the outside, and dispersion velocity regulating layers 21a in which porous material is filled are formed in each of the communication holes 19a. These dispersion velocity regulating layers 21 regulate the velocity of a gas to be detected flowing into the gas measuring chamber 7. The whole of the dispersion velocity regulating layers 21 are especially formed of zirconium with a large number of gas permeating pores.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor having gas-permeable pores such as an oxygen sensor for measuring the concentration of oxygen in exhaust gas of an automobile or the like.

[0002]

2. Description of the Related Art Conventionally, an oxygen sensor has been arranged in an exhaust system to reduce, for example, CO, NOx, and HC in exhaust gas of an automobile, and a fuel mixture supplied to an engine based on an output of the oxygen sensor. The air-fuel ratio of the air is controlled.

As an oxygen sensor used for such air-fuel ratio control, for example, a full-range air-fuel ratio sensor provided with a measurement gas chamber and a diffusion-controlling layer between an oxygen concentration cell element and an oxygen pump element is known. ing. The diffusion-controlling layer is a porous layer having a large number of gas-permeable pores, for example, for controlling the diffusion of a detection gas (exhaust gas) introduced from outside into the measurement gas chamber.

[0004]

Generally, fuels and engine oils used in internal combustion engines such as automobile engines include those containing phosphorus (P). Is used, gaseous fine particles of P are discharged together with the exhaust gas. However, when these P fine particles (scattering components) adhere to the surface of the diffusion-controlling layer, there is a problem that the gas-permeable pores are clogged.

That is, since the temperature of the exhaust gas to which the oxygen sensor is applied is usually quite high, if P adheres to the diffusion-controlling layer during use of the oxygen sensor, the P reacts with the material of the diffusion-controlling layer to form a liquid phase. Is generated, whereby the glassy substance reacted with P accumulates on the surface of the diffusion-controlling layer, and the gas-permeable pores are clogged. When this clogging occurs, the diffusion resistance of the gas changes, so that the air-fuel ratio cannot be accurately detected.

In order to solve the problem of clogging, measures have been taken to adjust the porosity and pore diameter of the porous material, but they are not always sufficient. Particularly in recent years, with the increase in exhaust gas regulations, more precise air-fuel ratio control has been required, and long-term reliability has also been required. It is rare.

The present invention has been made to solve the above-mentioned problems, and has as its object to provide a gas sensor having high durability against poisoning of phosphorus or the like.

[0008]

According to the first aspect of the present invention, a gas sensor has a gas permeable pore through which a detection gas can be introduced into a detection section, and the gas permeable pore is formed in a gas sensor for detecting an air-fuel ratio in an entire region. A part or the whole of the structure is made of zirconia.

The present invention relates to a so-called full-range air-fuel ratio sensor. In this gas sensor, zirconia has poor reactivity with phosphorus (P), which is a scattered component in a detection gas, and therefore, the structure has Even if P adheres, it remains simply adhered and does not change into a glassy state by reacting as in the prior art. Therefore, when the present invention is applied to, for example, an oxygen sensor that detects the oxygen concentration in exhaust gas, clogging of the gas permeable pores of the structure is unlikely to occur, and durability is improved.

The entire structure may be made of zirconia, or the structure may contain zirconia at a predetermined ratio, or a part of the structure may be made of zirconia. . Examples of the detection unit of the sensor include a gas detection element in which a pair of electrodes (for example, a reference electrode and a measurement electrode) are provided on a substrate made of a ceramic gas-sensitive material. Examples include a solid electrolyte (e.g., zirconia) whose electromotive force changes according to the oxygen concentration in the gas, and a resistance change type material (e.g., titania) whose internal resistance changes according to the oxygen concentration in the detection gas.

According to the second aspect of the present invention, the structure is composed of a plurality of porous layers, and the outer layer is made of zirconia. That is, by forming the layer made of zirconia on the outside, it effectively acts on the scattered P and can effectively prevent clogging. That is, clogging hardly occurs in the outer layer to which a large amount of P adheres.

When the structure is, for example, a diffusion-controlling layer, the roles can be divided so that the inner layer is mainly used for controlling diffusion and the outer layer is mainly used for preventing clogging. In addition, a configuration that can maximize each function can be obtained. According to the third aspect of the present invention, the structure includes a porous diffusion-controlling layer.

When the diffusion-controlling layer is clogged, the degree of diffusion-controlling changes, which adversely affects the output of the gas sensor. In the present invention, however, the gas-permeable pores of the diffusion-controlling layer are clogged. , It is possible to accurately detect, for example, the oxygen concentration in the exhaust gas over a long period of time.

According to the fourth aspect of the present invention, the diffusion resistance of the diffusion-controlling layer is set to be large at the inside portion and small at the outside portion. In other words, P, which is a poisoning substance, naturally adheres to the diffusion-controlling layer on the side where the detection gas is introduced (outside portion).
In the present invention, since the diffusion resistance of the outer part is set to be small (for example, the outer part is coarse), even if P slightly adheres to the outer part and the diffusion resistance partially increases, even if the diffusion resistance is increased. The influence on the overall diffusion resistance is reduced, and a good gas sensor output is obtained.

According to the fifth aspect of the present invention, the temperature range of the gas-permeable pores when the gas sensor is used is 500 ° C. or more. In other words, in this temperature range, clogging is likely to occur if, for example, P adheres to, for example, the diffusion-controlling layer of the oxygen sensor. Precise measurements can be made over time. In the case of 700 ° C. or higher,
Clogging is more likely to occur, but even under such severe conditions,
The gas sensor having the configuration of the present invention can be applied.

According to the sixth aspect of the present invention, M
g and / or Ca components are coated. In addition, the surface of this structure means the surface of the wall surface (for example, the inner peripheral surface of the hole) constituting the gas permeable pores. Mg or Ca
Has a high P-capturing ability and becomes a solid phase instead of a liquid phase even when it reacts with P, so that it is possible to prevent the occurrence of glassy clogging as in the prior art.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, examples (embodiments) of a gas sensor according to the present invention will be described. (Embodiment 1) The gas sensor of this embodiment is an oxygen sensor which is attached to, for example, an exhaust system of an automobile and measures an oxygen concentration (air-fuel ratio) in a detection gas (exhaust gas). This is a so-called all-area air-fuel ratio sensor that can be detected over a range.

A) The oxygen sensor of this embodiment has a plate-like sensor element mainly made of ceramics disposed in a metal cylindrical container (not shown). As shown in FIGS. 1 and 2, the sensor element portion 1 has an oxygen concentration cell element 3 having porous electrodes 3b and 3c formed on both sides of a solid electrolyte substrate 3a, and a porous element An oxygen pump element 5 having electrodes 5b and 5c formed thereon,
A detection member 6 comprising a spacer 9 laminated between these two elements 3 and 5 to form a measurement gas chamber 7 is provided. Further, a spacer 11 is provided outside the detection member 6 on the oxygen pump element 5 side. A heater 13 for heating both elements 3 and 5 is provided at a predetermined interval.

Here, the two elements 3 and 5 are provided with rectangular porous electrodes 3b, 3c, 5b and 5 on both sides of solid electrolyte substrates 3a and 5a made of a yttria-zirconia solid solution.
c, and the porous electrodes 3b, 3c,
5b and 5c are formed from a yttria-zirconia solid solution and the balance platinum as a co-base. The solid electrolyte substrates 3a and 5a may be made of a solid solution of yttria-zirconia, a solid solution of calcia-zirconia, a solid solution of cerium dioxide, thorium dioxide, hafnium dioxide or the like, a perovskite-type solid solution, or a trivalent metal oxide solid solution. Etc. can be used.

The outside of the oxygen pump element 3 is covered with an insulating layer 15 made of alumina having a hollow portion 15a corresponding to the porous electrode 3c. In the hollow portion 15a, a porous electrode protection layer 17 mainly made of alumina is formed to cover and protect the porous electrode 3c from the outside.

The measurement gas chamber 7 contains the oxygen concentration cell element 3
A measuring gas chamber formed by joining a spacer 9 mainly composed of alumina having a hollow portion 9a corresponding to the porous electrodes 3c and 5b between the oxygen gas pumping device 5 and the oxygen pump element 5; 7, the two porous electrodes 3c and 5b are exposed.

The spacer 9 has a pair of left and right communication holes 19a, 19b for communicating the measurement gas chamber 7 with the outside.
b, and each of the communication holes 19a, 19b has a diffusion-controlling layer 21a, 21b (2) filled with a porous material.
1 is formed, and the diffusion control layer 21 controls the flow rate of the detection gas such as flowing into the measurement gas chamber 7. In particular, in this embodiment, the entire diffusion-controlling layer 21 is made of zirconia having a large number of gas-permeable pores.

A shield 23 made of a solid electrolyte is attached to the outside of the oxygen concentration cell element 3 so as to cover the porous electrode 3b. From the porous electrode 3b side
When a small current iCP flows to the c side, the porous electrode 3b
The oxygen pumped to the side is not discharged as it is. Further, the oxygen concentration cell element 3 is provided with a leak resistance portion 3d (see FIG. 3) for leaking a part of the oxygen pumped to the porous electrode 3b side into the measurement gas chamber 7. I have.

A heating pattern 27 is provided on one side of the heater 13, that is, on the side of the oxygen pump element 5, and a well-known migration prevention pattern 29 is formed on the other side. b) Next, the electrical configuration of the oxygen sensor and its control will be described with reference to FIG.

As shown in FIG. 3, the porous electrode 3 in contact with the measurement gas chamber 7 of the oxygen concentration cell element 3 and the oxygen pump element 5
c and 5b are grounded via a resistor R2, and the other porous electrodes 3b and 5c are connected to a detection circuit 25, respectively. In the detection circuit 25, the porous electrode 3b on the shield 23 side of the oxygen concentration cell element 3 is connected to a resistor R1 to which the other end is applied with a constant voltage VCP. The resistor R1 is connected to the oxygen concentration cell element 3 with a substantially constant minute current iCP.
And the resistance of the resistor R
The value is sufficiently larger than the internal resistances of the element 2 and the oxygen concentration cell element 3.

The porous electrode 3b connected to the resistor R1 is connected to the negative input terminal of the differential amplifier AMP. Since the reference voltage VCO is input to the + input terminal of the differential amplifier AMP, the reference voltage VCO and the porous electrode 3 of the oxygen concentration cell element 3 are supplied from the differential amplifier AMP.
A voltage corresponding to the difference from the b-side voltage is output. The output of the differential amplifier AMP is connected to a porous electrode 5c on the heater 13 side of the oxygen pump element 5 via a resistor R3. As a result, the pump current ip flows in the oxygen pump element 5 in both directions according to the output of the differential amplifier AMP. That is, the detection circuit 25 applies a minute current iCP to the oxygen concentration cell element 3 to
By pumping oxygen into the cell, the porous electrode 3b functions as an internal oxygen reference source to generate a voltage at both ends of the oxygen concentration cell element 3 according to the oxygen concentration in the measurement gas chamber 7,
Further, the pump current ip is supplied from the differential amplifier AMP to the oxygen pump element 5 so that the voltage (including the voltage between both ends of the resistor R2) becomes the reference voltage VCO. It is configured to control to keep the oxygen concentration constant.

Since the pump current ip generated by this control corresponds to the oxygen concentration in the surrounding measurement gas atmosphere, the pump current ip is converted into a voltage signal by the resistor R3, and the voltage signal is converted into the oxygen signal in the exhaust gas. An electronic control circuit (hereinafter referred to as an ECU) comprising a microcomputer or the like for controlling the internal combustion engine as a detection signal representing the concentration, and hence the air-fuel ratio.
).

A heater voltage VH is applied to the heat generation pattern 27 of the heater 13 via a voltage switching circuit 33. The voltage switching circuit 33 is configured to output, for example, a battery voltage VB and a changed value thereof as the heater voltage VH applied to the heater 13, respectively.
Any of them is applied to the heating pattern 27 as the heater voltage VH in accordance with the voltage switching command output from.

B) Next, a method of manufacturing the sensor element portion 1 of the oxygen sensor having the above-described configuration will be briefly described. First, using a PVB-based binder and an organic solvent for the yttria-zirconia-based powder, a green sheet that becomes the (solid electrolyte substrates 3a, 5a of the oxygen concentration cell element 3 and the oxygen pump element 5) is formed by a well-known doctor blade method. To manufacture.

Next, a paste made of a material composed of platinum and a yttria-zirconia-based co-base using a PVB-based binder and an organic solvent is printed on a green sheet by a screen to form a paste (solid electrolyte substrate 3a). , 5a
The electrode pattern which becomes the porous electrode 3b, 3c, 5b, 5c) is formed.

Next, the green sheet formed in this manner and the insulating layer 1 made of alumina formed in the same manner.
5. The green sheets such as the shielding plate 23 and the spacer 9 are laminated and pressed. Here, in particular, the green sheet serving as the spacer 9 is provided with a space serving as the hollow portion 9a and the communication holes 19a and 19b. In the present embodiment, the green sheet for the spacer 9 is replaced with another green sheet. After being press-bonded to the sheet, a paste to be the diffusion-controlling layer 21 is printed in the spaces to be the communication holes 19a and 19b.

This paste is produced as follows. Based on zirconia powder (average particle diameter: 20 to 40 μm), Ethocel is added at a solid content ratio of 12% by weight, butyl carbitol is added at a solid content ratio of 50% by weight, and a sublimable filler for forming pores is added at a solid content ratio of 10% by weight. The resulting mixture is kneaded in a mortar to form a paste.

That is, this paste is a paste obtained by using a zirconia-based material and a PVB-based binder and an organic solvent, and when fired, becomes a porous layer of zirconia having a large number of gas-permeable pores. . And
After laminating and pressing the green sheets and the like, for example, 15
By performing baking at a temperature of 00 ° C. for one hour, a plate-shaped detection member 6 is obtained.

On the other hand, the heater 13 is formed by printing a paste for forming the heat generation pattern 27 on a green sheet of alumina in the same manner, laminating another green sheet on the paste, and firing similarly. The fired detection member 6 and the heater 13 are bonded to each other with a heat-resistant inorganic adhesive to form the sensor element portion 1. Separately, a green sheet or the like serving as the detection member 6 and the heater 13 are formed. A green sheet or the like may be laminated and fired at the same time to form the sensor element portion 1.

In the oxygen sensor of this embodiment manufactured as described above, since the entire diffusion-controlling layer 21 is made of zirconia having low reactivity with P, as will be apparent from an experimental example described later, Even when P in the exhaust gas adheres to the diffusion-controlling layer 21, the component of the diffusion-controlling layer (alumina) as in the prior art
Does not react with P to form a liquid phase, but simply remains attached.

That is, in this embodiment, since the P compound does not become glassy and clogging of the gas permeable pores unlike the conventional case, the diffusion resistance hardly changes even after long-term use, and the durability is high. It has the advantage of being rich. (Embodiment 2) Next, Embodiment 2 will be described. However, this embodiment is different from Embodiment 1 only in the diffusion-controlling layer, and the other parts are the same. Therefore, only different points will be described.

The diffusion-controlling layer in this embodiment is a layer in which Ca is coated on the surface of a substrate made of zirconia. Next, a method of manufacturing the sensor element portion having the diffusion-controlling layer will be briefly described. First, as in the first embodiment,
Using a PVB-based binder and an organic solvent for the yttria-zirconia-based powder, a green sheet serving as a (solid electrolyte substrate) is manufactured by a well-known doctor blade method.

Next, a material composed of platinum and a yttria-zirconia based material is pasted using a PVB-based binder and an organic solvent, and printed on a green sheet by a screen to form a (porous electrode). An electrode pattern is formed. Next, the green sheet thus formed and an insulating layer made of alumina formed in the same manner,
A green sheet such as a shielding plate and a spacer is laminated and pressure-bonded. In this case, after a green sheet serving as a spacer for forming a measurement gas chamber and a communication hole is pressure-bonded to another green sheet, a space serving as a communication hole is formed. Then, a paste containing zirconia as a main component to be a diffusion-controlling layer is printed. still,
This paste is the same as in the first embodiment.

After the green sheets and the like are laminated and pressed, the plate is fired at a temperature of, for example, 1500 ° C. for 1 hour to obtain a plate-shaped detection member. In particular, in this embodiment, after firing of the detection member, C
a. In this case, for example, a concentration of 24
A weight% aqueous solution of calcium acetate is dropped, for example, about 0.1 μl from the outside of the diffusion-controlling layer, and firing is performed at 1250 ° C. for 60 minutes.

As a result, Ca is coated on the surface of zirconia constituting the diffusion-controlling layer (that is, the surface of the gas-permeable pores). That is, since the aqueous calcium acetate solution penetrates into the inside of the diffusion-controlling layer while wetting the inner peripheral surface of the gas-permeable pores, the Ca coat layer is formed over the entire diffusion-controlling layer.

Since the diffusion-controlling layer of the oxygen sensor of this embodiment manufactured in this manner has a Ca coating layer formed over the entire surface of the substrate made of zirconia,
As is clear from an experimental example described later, when P in the exhaust gas adheres to the diffusion-controlling layer, first, Ca and P react to generate solid-phase calcium phosphate, which is diffused in a conventional manner. The component (alumina) of the rate controlling layer does not react with P to form a liquid phase. That is, clogging is prevented by this Ca.

Further, in the present embodiment, since zirconia is used as the base material of the diffusion-controlling layer, it is assumed that the coating layer Ca is peeled off and the zirconia is exposed at a portion where the zirconia is exposed.
No liquid phase is generated even if adheres. Therefore, also from this point, a remarkable effect that clogging hardly occurs is exhibited.

In place of Ca (or over Ca),
When coating with Mg, an aqueous solution of magnesium acetate is used in the same manner. However, when P is adhered to the surface of the diffusion-controlling layer, the coating with Mg does not become a liquid phase, but becomes a solid phosphorus. This is preferable because it becomes magnesium acid and does not cause clogging of gas-permeable pores. (Embodiment 3) Next, Embodiment 3 will be described. However, the present embodiment and Embodiment 1 are mainly different from each other in the diffusion control layer, and the other parts are the same. Therefore, only different points will be described.

As shown in FIG. 4, the diffusion-controlling layer 3 of this embodiment is
Reference numeral 1 denotes a two-layer structure including an outer layer 35 and an inner layer 37 provided side by side in the communication hole 33. Among them, the inner layer 35 is a layer made of the same alumina as in the prior art and mainly performing diffusion restriction (high diffusion resistance). On the other hand, the outer layer 37 is a layer (small diffusion resistance) for mainly depositing P or the like, and is made of the same zirconia as in the first embodiment.

When the diffusion-controlling layer 31 having the two-layer structure as described above is formed, after the green sheet of the spacer 39 having the space for the communication hole 33 is laminated, alumina as the inner layer 35 is mainly used. A paste and a paste mainly composed of zirconia to be the outer layer 37 are applied to the corresponding positions by printing, and then, another green sheet or the like is laminated and fired.

As described above, in this embodiment, the diffusion-controlling layer 31
Is an outer layer 37 made of zirconia for removing deposits such as P and the like.
Since it has a two-layer structure consisting of the following, a configuration that makes full use of each function can be obtained. That is, as the inner layer 35, for example, alumina or the like having excellent workability and strength can be used to reliably form gas-permeable pores necessary for restricting diffusion. Therefore, zirconia having a preferable porosity for adhering P can be used without being restricted by the porosity, so that each excellent function can be exhibited. (Embodiment 4) Next, Embodiment 4 will be described. The present embodiment and Embodiment 1 are mainly different from each other in the diffusion-controlling layer, and the other parts are the same. Therefore, only different points will be described.

As shown in FIG. 5, the diffusion-controlling layer 4 of this embodiment is
1 is an inner layer 45 provided in the communication hole 43 and the communication hole 4
3 has a two-layer structure including an outer layer 47 covering the outer opening 43a (on the side surface of the detection member). Of these, the inner layer 4
Numeral 5 is a layer made of alumina for limiting diffusion, as in the third embodiment. On the other hand, the outer layer 47 is a layer for depositing P or the like, and is made of the same zirconia as in the first embodiment.

When the diffusion-controlling layer 41 having the two-layer structure as described above is formed, after the green sheet of the spacer 49 having the space for the communication hole 43 is laminated, the inner layer 45 is mainly composed of alumina. Apply the paste by printing,
After that, another green sheet or the like is laminated. Further, a paste containing zirconia as a main component to be the outer layer 47 is printed and baked so as to cover the outer side of the inner layer 45 (the outer opening 43a side).

As described above, in the present embodiment, similarly to the third embodiment, the diffusion-controlling layer 41 is made of the inner layer 45 for substantially limiting diffusion and zirconia for removing deposits such as P. Since it has a two-layer structure including the outer layer 47, it is possible to make a configuration that makes full use of each function.

Particularly, in this embodiment, since the outer layer 47 is formed on the side surface of the detecting member, there is an advantage that the effective surface area for removing the deposit can be increased.
In the present embodiment, the inner layer 45 and the outer layer 47 are fired simultaneously. However, for example, the inner layer 45 is fired once together with the green sheet, and then, for the fired inner layer 45, the diffusion control is adjusted. After that, the paste to be the outer layer 47 may be applied to the side surface of the detection member and then fired.

(Experimental Examples) Next, experimental examples using the oxygen sensor of each of the above embodiments will be described. This experiment is a P poisoning durability test, in which a change in diffusion resistance caused by clogging caused by P adhesion is examined.

More specifically, the oxygen sensor of each of the above embodiments and the conventional oxygen sensor of the comparative example were attached to the exhaust pipe of the engine, and the rate of change of the ip current (Δip) was determined from the change over time. The state of deterioration (ie, the state of clogging) was examined. The results are shown in Tables 1 and 2 below and FIG.

(Experimental conditions) Engine: 2000cc in-line 4-cylinder, gasoline engine, NA ・ Set air-fuel ratio; theoretical air-fuel ratio λ = 1 ・ Operating condition: No load, 3000rpm steady operation ・ Fuel: Regular gasoline + Zn-DBP (addition (Amount 50cc / 20L)

[0054]

[Table 1]

[0055]

[Table 2]

As is clear from Tables 1 and 2 and FIG.
The oxygen sensor of each of the above embodiments is suitable because it has excellent durability because the change in ip current is small even after a long period of time and clogging hardly occurs. On the other hand, in the case of the comparative example, since the ip current changes greatly in a short period of time, clogging is likely to occur and the durability is poor, which is not preferable.

It should be noted that the present invention is not limited to the above-described embodiment at all, and it is needless to say that the present invention can be implemented in various modes without departing from the gist of the present invention. (1) For example, in each of the above embodiments, as the oxygen sensor,
Although the full range air-fuel ratio sensor has been described as an example, the present invention may be applied to a λ sensor. For example, the protective layer covering the detection gas side of the λ sensor may be made of a material that suppresses the generation of the liquid phase described above.

(2) In each of the above embodiments, the diffusion-controlling layer is configured to prevent clogging. However, when a protective layer is provided on the surface of the electrode (measurement electrode) on the side where the detection gas reaches,
The protective layer may be configured to prevent clogging similarly to the diffusion-controlling layer. (3) In the case where a material that suppresses the generation of a liquid phase when P adheres to a substrate made of zirconia (or contains zirconia) is supported as a single body to form a structure, the element to be supported is The base is immersed in a solution (for example, an aqueous solution) in which a salt (a salt that decomposes at a low temperature) is dissolved, or the solution is brush-coated on the base to attach the salt, and then heat-treated to form a simple substance As an element.

(4) Further, when a material that suppresses the formation of a liquid phase when P adheres to a substrate made of zirconia (or contains zirconia) as a compound to form a structure, The compound can be supported by immersing the base material in a solution (for example, an aqueous solution) in which the compound is dissolved, or by brushing the base material with the solution and then performing a heat treatment. In addition, as a compound, calcium phosphate and magnesium phosphate are preferable because they are excellent in the ability to capture P and hardly become a liquid phase even after the capture.

[0060]

As described above in detail, according to the first aspect of the present invention, in the full-range air-fuel ratio sensor, zirconia contained in the structure has a poor reactivity with P which is a scattered component in the detection gas. Therefore, even if P adheres to the structure, it remains simply adhered and does not change to a glassy state by reacting as in the prior art. Therefore, clogging is unlikely to occur in the gas permeable pores of the structure, and the durability of the gas sensor is improved.

According to the second aspect of the present invention, by forming a layer made of zirconia on the outer side, it effectively acts on the scattered P and can effectively prevent clogging. Also,
Roles can be shared such that the inner layer is mainly a layer that controls diffusion and the outer layer is mainly a layer for preventing clogging, so that the structure of each layer can be maximized.

According to the third aspect of the present invention, the gas-permeable pores of the diffusion-controlling layer are unlikely to be clogged, so that, for example, the oxygen concentration in the exhaust gas can be accurately detected over a long period of time. According to the fourth aspect of the present invention, since the diffusion resistance of the outer portion is set to be small, even if P slightly adheres to the outer portion and the diffusion resistance partially increases, the influence on the diffusion resistance of the entire diffusion-controlling layer is exerted. And a good output of the gas sensor is obtained.

According to the fifth aspect of the present invention, even if the temperature at which P is attached to the diffusion-controlling layer becomes a temperature at which a liquid phase is likely to be generated, clogging hardly occurs because P remains attached to the surface.
Precise measurement can be performed over a long period. In the invention of claim 6, since the surface of the structure is coated with a component of Mg and / or Ca, even if it reacts with P, it becomes a solid phase instead of a liquid phase, and the glassy clogging as in the prior art is prevented. Can be prevented.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a sensor element portion of an oxygen sensor according to a first embodiment with a part thereof cut away.

FIG. 2 is an explanatory diagram illustrating a diffusion-controlling layer of a sensor element portion of the oxygen sensor according to the first embodiment.

FIG. 3 is an explanatory diagram illustrating an electrical configuration of the oxygen sensor according to the first embodiment.

FIG. 4 is an explanatory diagram showing a sensor element portion of an oxygen sensor according to a third embodiment in a cutaway manner.

FIG. 5 is an explanatory view showing a sensor element portion of an oxygen sensor according to a fourth embodiment in a cutaway manner.

FIG. 6 is a graph showing experimental results.

[Explanation of symbols]

 1: Sensor element part 3: Oxygen concentration cell element 3a, 5a: Solid electrolyte substrate 3b. 3c, 5b, 5c: Porous electrode 5: Oxygen pump element 6: Detection member 7: Measurement gas chamber 9, 11: Spacer 13: Heater 21, 21a, 21b, 31, 41: Diffusion controlling layer

Claims (6)

[Claims] 1. A gas sensor having gas-permeable pores capable of introducing a detection gas into a detection portion of a sensor and detecting an air-fuel ratio in an entire region, wherein a part or the whole of a structure forming the gas-permeable pores is:
A gas sensor comprising zirconia. 2. The structure comprises a plurality of porous layers,
2. The gas sensor according to claim 1, wherein the outer layer is made of zirconia. 3. The gas sensor according to claim 1, wherein the structure is a porous diffusion-controlling layer. 4. The gas sensor according to claim 3, wherein the diffusion resistance of the diffusion-controlling layer is set to be larger at the inner portion and smaller at the outer portion. 5. The gas sensor according to claim 1, wherein a temperature range of the gas permeable pores when the gas sensor is used is 500 ° C. or more. 6. The method according to claim 6, wherein the surface of the structure is made of Mg and / or C.
The component (a) is coated with the component (a).
6. The gas sensor according to any one of 5.